239 10 13229 https://digitalcollections.lakeheadu.ca/files/original/120e905556b72cb3b85c97724adc63b1.pdf f816fd7a26d0eab0f8140bc1a62bda1b PDF Text Text A BSTRACTS a PROCEEDINGS Twenty Seventh Annual Meeting INSTITUTE ON LAKE SUPERIOR GEOLOGY HELD AT THE KELLOGG CENTER MICHIGAN STATE UNIVERSITY EAST LANSING MICHIGAN MAY 14-15, 1981 �Award Guidelines SAM GOLDICH MEDAL Preamble The Institute on Lake Superior Geology was born on or around 1955, as documented by the fact that the 27th annual meeting will be held in 1981. The Institutes are exemplory in their continuing objectives of dealing with those aspects of geology that are related geographically to Lake Superioq of encouraging the discussion of subjects and sponsoring field trips which will bring together geologists from the academia, government surveys, and industry; and of maintaining an exceedingly informal but highly effective mode of operation. During the course of its existence the membership of the Institute (that is, those geologists who indicate an interest in the objectives of the LL.S.G. by attending) has become aware of the fact that certain of their colleagues have made particularly noteworthy and meritorious contributions to the improvement of understanding of "Lake Superior" geology and its mineral deposits. The exemplory award was made by LL.S.G. to Sam Goldich in 1979 for his many contributions to the geology of the region extending over about 50 years. Award Guidelines I) The medal shall be awarded annually by the Board of Directors, I.L.S.G., to a geologist whose name is associated with a substantial sustained interest in, or a major contribution to, the geology of the Lake Superior Region. 2) The Board of Directors, LL.S.G. shall appoint the Nominating Committee. Their annual nominee will be voted on at the annual business meeting. The initial appointment will be of three members, one to serve for three years, one for two, and one for one year, the member with the briefest incumbency to be chairman. After the first year the Board of Directors shall appoint at each spring meeting one new member who will serve for three years. In the third year this member shall be the chairman. The Committee membership should reflect the main fields of interest and geographic distribution of l.L.S.G. membership. 3) The Goldich Medal Nominating Committee shall select the medalist and will make its recommendation to the Board of Directors by November 1 of that year. 4) The Board of Directors normally will accept the nominee of the Comittee, will inform the medalist immediately, and will have one medal engraved appropriately for presentation at the May meeting. 5) It is recommended that the Institute set aside annually from whatever sources, such funds as will be required to support the continuing costs of this award. April 4, 1981 J. Kalliokoski, Chairman Bill Cannon Fred Kehlenbeck Glenn Morey Greg Mursky �ABSTRACTS and PROCEEDINGS Twenty Seventh Annual Meeting INSTITUTE ON LAKE SUPERIOR GEOLOGY I-bid at The Kellogg Center Michigan State Lhiversity East Lansing, Michigan May 14- 15, 1981 Sponsored by DEPARTMENT OF GEOLOGY, MICHIGAN STATE UNIVERSITY East Lansing, Michigan and MICHIGAN DEPARTMENT OF NATURAL RESOURCES, GEOLOGICAL SURVEY Lansing, Michigan F. W. Cambray, B. K. Parker, R. C. Reed, 3. W. Trow, T. A. Vogel 3. T. Wilband and S. E. Wilson Editors Gerraid Bennett Field Trip Coordinator and Director MINISTRY OF NATURAL RESOURCES, SAULTE STE. MARIE MINING DIVISION Saulte Ste. Marie, Ontario ��Thursday May 14, 1981 Session Chairpersons S. S. Goldrich and C. Laberge 1:30 to 1:50 1:50 to 2:10 2:10 to 2:30 A GEOCHEMICAL RECONNAISSANCE STUDY OF GROUNDWATER FROM AN EIGHTEEN COUNTY AREA OF NORTHWESTERN OHIO Mohr, Eileen T., Deering, Mark F., and Carlson, Ernest H. THE DISTRIBUTION OF LITHIUM, RUBIDIUM AND CESIUM IN LAKE MUDS NORTH OF LAKE SUPERIOR M. A. Vos and R. 3. Stevenato THE SIGNIFICANCE OF THE DISTRIBUTION OF CLASTIC LENSES WITHIN THE NEGAUNEE IRON FORMATION AT THE EASTERN END OF THE 2:30 to 3:00 3:00 to 3:20 3:20 to 3:40 PALMER BASIN, MARQUETTE SYNCLINORIUM, NORTHERN MICHIGAN *Mark S. Breithart and F. William Cambray Coffee Break PRELIMINARY ASSESSMENT OF RARE EARTH ELEMENT GEOCHEMISTRY OF VARIOUS IRON FORMATIONS OF THE LAKE SUPERIOR DISTRICT Elaine L. Slaughter, Susan E. Tituskiri, and John T. Wilband LITHOLOGIC AND SEDIMENTOLOCIC CHARACTERISTICS OF THE COPPER HARBOR CONGLOMERATE, NONESUCH SHALE AND FREDA SANOSTONE FORMATIONS OF NORTHERN MICHIGAN AND WISCONSIN Paul A. Daniels, Jr. 3:40 to 4:00 THE ROLE OF HYDROTHERMAL ALTERATION AND TECTONISM IN 4:00 to 4:20 WISCONSIN MOLYBDENITE OCCURRENCES 3. K. Greenberg RETROGRADE PREHNITE-PUMPELLYITE FACIES METAMORPHISM IN THE SOUTHERN VERMILION GRANITIC COMPLEX, NORTHERN MINNESOTA Robert L. Bauer 6:00 pm 7d30 pm Cash Bar Banquet Big TenRoorn Big Ten Room POST PRANDIAL Presentation of the Sam Goldich Medal by Dr. Samuel S. Goldich to Dr. Carl E. Ijutton ADDRESS by F. B. Van 1-buten entitled PHANEROZOIC OOLITIC IRONSTONE - A FACES MODEL (See abstract by F.B. Van Houten and D. Bhattacharyya) �Friday May 15, 198! Session Chairpersons 3. 1. Wilband and C. Anderson Coffee will be available from 8J0 a.m. 8:20 to 9:20 9:20 to 9:30 9:30 to 9:50 9:50 to 10:10 10:10 to 10:30 10:30 to 11:00 11:00 to 11:20 Decade of North American Geology - Open Discussion break WISCONSIN GRAVITY BASE STATION NET WORK--! 980 C. Patrick Ervin PALEOMAGNETISM OF THE MEMESAGEMASING AND CARIBOU LAKES NORITES, GRENVILLE PROVINCE, ONTARIO * S. Dey, D. T. A. Symons, and M. Stupavsky GEOPHYSICAL INVESTIGATIONS OF THE SLATE iSLANDS CRYPTOEXPLOSION STRUCTURE M. E. Bengtson, and R. P. Meyer, H. C. Halls, and 3. I-I. Karl, and D. Dushek Coffee Break JOINT ORIENTATION ANALYSIS IN THE NORTHERN MICI-{ICAN BASIN Timothy B. 1—blst 11:20 to 11:40 I 1:40 to 12:00 IMPACT AS A POSSIBLE ORIGIN FOR SUBSIDED BASINS Jack B. Hartung PRELIMINARY RESULTS OFA GRAVITY SURVEY IN THE EASTERN HALF OF THE IRON RIVER-CRYSTAL FALLS DISTRICT, IRON COUNTY, MICHIGAN * D. R. Paddock, K. Fujita, F. W. Cambray, and H. F. Bennett 12:00 Lunch 5ession Chairpersons Friday afternoon 3. W. Trow and 3. 3. Mancuso 1:30 to 1:50 SUBAQUEOUS PYROCLASTIC FLOW DEPOSITS IN THE VICINITY OF THE HELEN MINE, WAWA, ONTARIO Mark Osterberg and R. L. Morton 1:50 to 2:10 PRE- AND POST-DORE SEQUENCES IN THE WAWA VOLCANIC BELT, ONTARIO 2:10 to 2:30 2:30 to 3:00 3:00 to 3:20 3:20 to 3:40 K. Attoh PETROGENETIC MODELS OF KEWEENAWAN BASALTIC ROCKS, UPPER MICHIGAN John T. Wilband and Pipob Wasuwanich Coffee Break PETROCHEMISTRY AND STRUCTURE OF THE MIDDLE PROTEROZOIC SUCCESSION, HURLEY-TO-MINONG, KEWEENAWAN VOLCANIC WISCONSIN * Hassan Au and Campbell Craddock EARLY PROTEROZOIC GABBROIC, DIORITIC, AND QUARTZ MONZONITIC INTRUSIONS IN THE MINNESOTA RIVER VALLEY: PETROLOGY AND SIGNIFICANCE 3:40 to 4:00 M. Dewitt Daggett THE PETROLOGY AND PETROGENESIS OF THE GAMITAGAMA IGNEOUS COMPLEX, WAWA, NORTHERN ONTARIO * Abdul Choudhry and T. E. Smith �27th Annual INSTITUTE ON LAKE SUPERIOR GEOLOGY Annual Banquet PHANEROZOIC OOLITIC IRONSTONE - A FACIES MODEL Address by delivered by F. B. Van 1—buten (Abstract by Van Houten & D. Bhattacharyya follows) �PHANEROZOIC OOLITIC IRONSTONE - A FADES MODEL F. B. Van Houten and D. Bhattacharyya Department of Geological and Geophysical Sciences, Princeton University Princeton, New Jersey 08544 Almost all of the Phanerozoic ferric oxide-chamosite oolitic ironstones are associated with detrital aeposits that accumulated in low energy, nearshore marine environments, commonly along a broadly embayed coastline. Processes and products were like those on the chenier coast of southwestern Louisiana and the front of the low-energy, wave-dominated Rhone Delta. There were no well-developed tidal features or large, well-winnowed shoreface sandbodies. A subdued, deeply weathered source supplied mature fine-grained sediment composed mostly of quartz, kaolinite, and iron and aluminum oxide. The detrital deposits are arranged in a of asymmetrical, upwardshoaling sequences produced by small- scale Ferruginous ooids formed on detritus-starved mudflats that supported abundant micro-organisms and burrowers. These sites were either mudflats along microtidal coasts protected by breaker bars remote from a prograding delta, or on delta-front and interd istributary coastal flats following delta abandonment. Most of the plastic ooids were carried from their place of origin by coastal currents, and in aecreting, cross-bedded Repeated interruptions in concentrated bars. accumulation of ooids permitted increased burrowing that commonly destroyed the bedding fabric, as well as precipitation of ferric oxide cement. Locally, lapses in bar building led marine mud. to deposition of laminated succession regressions. Each sequence commenced with muddy open shelf deposits locally associated with bioclastic debris, and culminated in either a prograding front of a small delta or a shoreline complex of bars anc lagoons. Waning of cietrital influx was accompanied by development of abundant Commonly ooid bars graded laterally or were succeeded by a thin ferruginous phosphatic intraclast lag deposit developed when waves ana currents of renewed transgression encroached on the detritus-starved mudflats and crests of ooid bars. Each mound of ooids and associated lag deposit was then buried by marine mud into, ooids. that accumulated during an early stage of rapid transgression and renewed supply of Specific control of the prograding sequences has not been established in many sediment. Some may reflect diversion of a major river to a more distant part of the cases. coastal plain while the abandoned muddy shelf continued to subside and was inundated by renewed transgression. Other sequences may reflect more regional control such as tectonic pulses of subsidence or repeated eustatic rise of sealevel. This facies model emphasizes the role of repeated upward-shaling sequences, of abrupt waning of sediment supply, and of renewed rapid rise of sea level as the local framework of accumulation of most oolitic ironstones. A similar sequence of fades dominated the less common development of oolitic ironstone along carbonate coasts. Within this framework both the iron-rich oolites and associated phosphatic intraclast lenses developed at or near the lithofacies discordance between successive sequences. �INSTITUTE ON LAKE SUPERIOR GEOLOGY Annual Goldich Medal Award for 1981 Will be presented to Carl E. Dutton at the Banquet Thursday evening Dr. Carl E. Dutton was born in Dunkirk, Ohio on January 24th 1904. He receivea his B.A. from DePauw University in 1926, his M.A. from the University of Illinois in 1928 and his Ph.D. from the University of Minnesota in 1931. He was a teaching assistant at the University of illinois, an Instructor at Minnesota and an Assistant Professor at Wayne State University and The University of Michigan. He jointed the U.S. Geological Survey in 1943, becoming regional geologist in 1948 and Research Geologist in 1962 and has been based in Madison, Wisconsin where he participated in the Mineral Resources Cooperative Program of the Wisconsin Geological and Natural History Survey and the USGS in addition to teaching some classes at the University. Carl Dutton has had a lifelong interest in the geology of the Precambrian, and particularly in the Great Lakes area. He is widely regarded as an authority on iron formations, he has served on the United Nations Committee on Iron Resources in Geneva in 1953-54 and studied iron ore deposits in Yugoslovia with the AID program in 1961. He is perhaps best known to us for his work in the Menominee District of Michigan and Wisconsin (USGS Prof. Paper 573 and Map 1-466, the Cuycera District, Minnesota (USGS Maps MF-99 & ME 181 the Iron River, Crystal Falls District, Michigan) (USGS Prof. Paper 570 & Map MF-225 and for his series of lithologic, geophysical and mineral commodity maps of the Precambrian Rocks of Wisconsin (USGS Map 1-631). He has written many other papers and particularly field guide books which have opened an understanding of the region for those of us who now try to follow in his footsteps. The members of the Institute are proud to recognize the achievements of one of their distinguished colleagues in the awarding of the 1981 Sam Goldich Medal to Dr. Carl E. Dutton. ��PRE- AND POST-DORE SEQUENCES IN THE WAWA VOLCANIC BELT, ONTARIO K. Attoh Hope College I-blland, Michigan 49423 An unconformity at the base of Dor Fm and equivalent sedimentary rocks marks a significant stratigraphic break on the basis of which the volcanic-sedimentary succession in the Wawa greenstone belt can be subdivided into pre- and post-Dor Sequences. The pre-Dor Sequence includes at least two cycles of mafic-felsic containing iron volcanism, each an formation unit, but only the lower mafic-felsic volcanic cycle which is terminated by an extersive siderite deposit completely preserved. Two post-Dore' Sequences have been identifiea; an older Sequence represented by a mafic flow unit, which directly overlies sedimen tary rocks equivalent to the Doré and a younger Sequence, which is structurally discordant with the underlying rnafic fLOW, is characterized by a distinct b reccia unit interpreted as a debris flaw. Post-Dora' Sequences do not contain iron formation is units. �RETROGRADE PRLHNITE-PUMPELLYITE FACIES METAMORPHISM IN THE SOUTHERN VERMILION GRANITIC COMPLEX, NORTHERN MINNESOTA Robert L. Bauer Department of Geology, Macalester College, and Minnesota Geological Survey St. Paub Minnesota 55105 Regional prehnite-pumpellyite metamorphism (M2) overprinted fades middle Most previous studies describing prehnite in biotite do not ascribe this lenses amphibolite facies (Ml) assemblages in the rocks of the southern Vermilion Granitic occurrence to reactions involving biotite, Complex, but pta-dated dynamic metamorphism associated with (M3) strike-slip displacement on the Vermilion prehnite components along biotite cleavage fault. The M2 event is defined on the basis of the occurrence of various combinations the prehnite, of Ca-Al silicates, pumpellyite, epidote, and grandite garnet along with chlorite, adularia, albite, sericite, sphene, i. calcite in the biotite schists, lamprophryes, and granitic rocks exposed in the area. The M2 phases may pervade a given sample, but are more commonly concentrated adjacent to thin quartz or adularia veins or fractures in the but rather to the introduction of all the traces. Observations made during the present study, including the albitization of plagioclase and the occurrence of prehnite, adularia, and sphene within a single chlorite pseudomorph after biotite, are consistent with following prehnite-forming the reaction: anorthite (component) + biotite + H20 = prehnite + chlorite + adularia + sphene sericite aligned parallel to the cleavage traces in The other Ca-At silicates occuring as lenses in biotite or chlorite may also have formed by similar reactions involving the breakdown of biotite. has a similar mode of occurrence, but also occurs in thin veins ± prehnite. M2 epidote and rare pumpellyite may occur as lenses in biotite or chlorite, but are more commonly associated with sericite or rare calcite as alteration products of plagioclase. M2 stability of the Ca-Al silicates indicate a rocks. The prehnite and grandite occur most commonly as lenses or barrel-shaped grains biotite or chlorite after biotite. Adularia No regional variations in the observed assemblages have been found which might indicate systematic spatial variations in the conditions of M2 metamorphism. Comparison of the coexisting mineral assemblages with experimental data on the occurs as fine-grained granular clusters in chlorite after biotite and is pseudomorphic after rutile needles in probable range of conditions for the metamorphism of 250 to 350 degrees chlorite in some of the lamprophyres. P(H20) = P(total). sphene centigrade and 2 to 4 kilobars at P(fluid) = �GEOPHYSICAL INVESTIGATIONS OF THE SLATE ISLANDS CRYPTOEXPLOSION STRUCTURE M. E. Bengtson, and R. P. Meyer Geophysical and Polar Research Center, Department of Geology and Geophysics University of Wisconsin, Madison, Wisconsin 53706 H. C Halls Department of Geology, Erindale College, University of Toronto Mississauga, Ontario, Canada L5L 1C6 3. H. Karl, and D. Dushek Department of Physics and Astronomy, University of Wisconsin Oshkosh, Wisconsin 54901 A survey of the underwater crater area (defined by an irregular arcuate bathymetric rise) surrounding the Slate Islands of northern Lake Superior is now nearly complete. A close order aeromagnetic survey (l000yd spacing, 425m above lake level) and a set of marine magnetic and high resolution 3.5kc bottom and subbottom profiles taken under flight lines has been acquired. These have revealed several short wavelength anomalies on the east side of the islands. The sources of these anomalies appear to be 1/2 km to 1 km below lake level and none seem to have any bathymetric expression. To the west a longer wavelength anomaly trending NW-SE This feature correlates predicted contact. The islands about a roughly defined arcuate magnetic high. Short wavelength has been delineated. with a igneous-sedimentary seem to be centered well previously anomalies have been found over the islands. A set of marine refraction and reflection records was also obtained. Data was recorded digtally. Large thicknessess (Up to I km) of a '-'3.5km/sec layer underlaid by a —5.5km/sec refractor have been detected exterior to the crater. Inside the crater rim, the 3.5km/sec layer is absent. Here, only a 4.8km/sec refractor, lying directly beneath recent sediments, has been detected. All layers appear to have a gentle southerly dip. �THE SIGNIFICANCE OF THE DISTRIBUTION OF CLASTIC LENSES WITHIN THE NEGAUNEE IRON FORMATION AT THE EASTERN END OF THE PALMER BASIN, MARQUETTE SYNCLINORIUM, NORTHERN MICHIGAN * Mark S. Breithart and F. William Cambray Department of Geology, 206 Natural Science, Michigan State University East Lansing, Michigan 48824 The vertical and horizontal distribution of clastics found within the Negaunee Iron Formation in the eastern end of the Palmer Basin, T47N-R26W sections 26, 27, and 28, was studied to determine the geometry of the region at the time of deposition of the sediments. Previous work by Gair (1975), Davis (1965) and Mengel (1956) has suggested that a relict sedimentary Their conclusions were based upon and textural qualitative sedimentars' descriptions. This study has attempted to test this concept with a quantitative approach based upon the vertical and the Palmer Basin is basin. horizontal variation in amount, type, and grain size of clastics observed in the subsurface. The data indicates that the earlier models are correct and that the Palmer Basin is a relict sedimentary basin. The Palmer Basin is located on the south limit of the Marquette synclinorium in the Upper Peninsula of Michigan. It contains over 2,000 feet of middle Proterozoic age sediments and has been down-faulted along the E-W trending Palmer Fauilt relative to the main synclinorium. This study utilized 84,000 feet of core made available by the Cleveland-Cliffs Iron Company. two main The clastics were divided into matrix composition (chloritic vs. iron oxide). The size distribution was divided into coarse (1.05 ± .l5), medium (1.82 + .28) and fine (2.80 + types based upon .46 ':0. From petrographic analysis of over IOU thin sections of the clastics could best be * Presentation eligible Award for the Student classified as immature sediments of the lithic-quartz wacke clan. The quartz is subangular and is supported by a variable matrix of chlorite and iron oxides with minor cryptocrystalline quartz (chert) and carbonate. The majority of lithic fragments were either rounded chert or chloritic clasts. Feldspar was rarely noted. Most bedding contacts between clastics and iron formation are sharp. The vertical and horizontal variation indicates that: 1) the south margin of the Palmer Basin has a consistently higher percentage of coarse clastics with a chioritic type matrix dominating, 2) depositional centers of clastics varied with vertical position throughout the basin, and 3) the source areas for the clastics is indicated to be to the SW, S or SE. All of this supports the idea of the Palmer Basin being a relict sedimentary basin. The best model for the deposition of the sediments is one involving mass flows and/or submarine fans with migrating feeder channels and depositional centers. This would account for the high percentage of matrix, the immaturity of grains, the wide horizontal and vertical distribution and the sharp bedding contacts. A source area for the clastics low in feldspar is also inferred. The pattern is consistent with the concept of a basin which was progressively subsiding during deposition. The periodic supply of clastics by mass flow being controlled disturbances by perhaps associated with fault movements controlling the subsidence. �MIDDLE PROTEKOZOIC DEFORMATION IN NORTHERN AND CENTRAL WISCONSIN B. A. Brown and .1 K. Greenberg Wisconsin Geological and Natural History Survey, 1815 University Avenue Madison, Wisconsin 53706 Recent mapping and compilation by the Wisconsin Geological Survey has pointed out the compelling need for reinterpretation of the Proterozoic tectonic history of northern and central Wisconsin. Tectonic structures observed in this region were predominantly formed during the Penokean deformationM event, and have been modified locally and possibly on a regional scale by later events. In central Wisconsin, the Wolf River granitic complex of 1500 m.y. age represents a major plutonic event, covering over 3600 km2. A plutonic event of this magnitude would be expected to produce at least locally intense deformation as well as thermal metamorphism. Mapping in the Wisconsin Northeast sheet (Greenberg and Brown, revealed has 1980) metamorphic and deformational various features associated with the Wolf River complex, including: amphibolite-grade (I) metamorphism and intense folding near the northern margin of the Wolf River complex Langlade in and Lincoln Counties; (2) recrystallization and refoliation of the 1850 granitic complex Athelstane in southwestern Marinette County; (3) thermal metamorphism in the Mountain (Lahr, 1972) m.y. and Thunder Mountain areas; (4) crenulation and chevron folding of metavolcanic rocks in the Mountain area where earlier fabrics impinge at high angles to the granite's contact; tectonic reorientation in (5) Marathon and Portage Counties, as shown by (6) intense aeromagnetic trends; deformation observed in metavolcanic units caught between the Wolf River complex and major Penokean pluton in Marathon County (LaBerye, 1980). a eastern Deformation related to the emplacement of the Wolf River complex is restricted to the rocks south of the major structural boundary proposed by Brown and Greenberg (1980) and Greenberg and Brown (1980). Structures to the north of this boundary trend to the northeast in Lincoln County, gradually arching eastward until trends are east-west to slightly southeast in central Marinette County. In south-central Wisconsin, broad, open folding is preserved in widely scattered exposures of quartzite and underlying 1760 m.y. old rhyolites. If the interpretation of Dott and DaIziel (1972) is correct, and the quartzites are correlative over a wide area, considerable strain has been superimposed on the basement rocks of central Wisconsin the 1760 m.y. plutonic-volcanic episode, and the intrusion of the 1500 m.y. anorogenic Wolf River complex. Deformation appears to increase in intensity between from west to east. This is exhibited in contrasting modification minor the of the Sioux structural and Barron quartzites (west) with the obvious folding and metamorphism evident in McCaslin, Thunder Mountain, Baraboo, and Waterloo quartzites (east). The deformation is closely related in time to the resetting of Rb-Sr ages (1600 n.y.) observed widely in northcentral Wisconsin (Van Schmus, 1980; Sims and Peterman, 1980). The 1500 m.y. intrusive episode itself may be envisioned as a result of the 1600 m.y. event, just prior to (and during?) intrusion. Confirmed Archean rocks are known only in northernmost Wisconsin and as limitea exposures Proterozoic surrounded rocks in intruded by and Central Wisconsin. Current data indicate no Archean rocks exposed in the main part of the Proterozoic belt. volcanic The complexity of deformation observed in this belt is probably due to multiple deformation and intrusion during the Penokean event, with local, and possibly widespread overprinting by younger events at 1600 m.y. and associated with the 1500 m.y. Wolf River complex. The apparent absence of Archean ages in the volcanic belt of northeastern Wisconsin better supports this interpretation than alternatic'e interpretations which appeal to Penokean deformation overprinting Archean structures in this region. �THE PETROLOGY AND PETROGENESIS OF THE GAMITAGAMA IGNEOUS COMPLEX, WAWA, NORTHERN ONTARIO * Abdul Choudhry and T. E. Smith Department of Geology Windsor, Ontario, Canada, N9B 3P4 The Gamitagama Lake Complex is a plug-shaped, elliptical gabbroic complex of orthopyroxene Archean the respective parent magmas, at pressures less than 5 Kb, to give calc-alkalic differentiation trends within each series. age (Rb/Sr 2642 Ma), approximately 7 x 10 km in dimensions. It outcrops in the metasedimentarymetavolcanic rocks of the Shebandowan Greenstone Belt of the Superior Province, clinopyroxene + + titaniferous magnetite, crystallized out of Many of the rocks of the complex are cumulative in origin, and their major and approximately 40 km south of Wawa. trace Five intrusive phases are recognized in the complex, four of which are subalkaline. They include an olivine- bearing representative of the liquid line of descent. However, their incompatible element contents may be compared to those of other complexes considered to be cumulate rocks produced during calc-alkaline fractionation. The most basic rocks of each discrete, intrusive event are successively less basic in composition indicating that fractionation inner gabbroic series, partly surrounded by a middle zone of less basic, gabbroic rocks, and an outer group of dioritic rocks. The dioritic group includes hornblende- gabbro, diorite, quartzdiorite, quartzmonzodi orite, and tonalite. Arcuate outcrops of leucocratic granodiorite and granite occur within the diorite zone. The granites and diorites are cut by a large dyke- like body of quartz- monzonite which has alkaline affinities. In the olivine- bearing inner gabbroic series, olivine gabbronorite and gabbronorite dominate, and troctolite, norite, and andesine anorthosite are subordinate. In the middle zone of gabbroic rocks, gabbronorite and amphibole gabbronorite occur with lesser amounts of narita and pyroxene diorite. Late dykes of fine- grained gabbroic rocks with porphyritic amphibole and phlogopite intrude the inner and outer gabbroic series. the inner qabbroic series olivine + + titaniferous magnetite + clinopyroxene + orthopyroxene, and in the In plagioclase eligible for the chemistry Student is not occurring in the source magma chamber, at deeper levels. The late fine-grained gabbroic intrusions in the was complex contain amphibole and phlogopite phenocrysts. This suggests that the differentiation was controlled by the separation of amphibole and phiogopite at more than 10Kb pressure ("-'35 km depth). The complex is compared to several well described hornblende-beari ng gabbroic plutons occurring in the Cordilleran batholiths of North and South America. It is concluded that the Gamitagama Complex is most similar to the Guadalupe Complex in California. Within the Gamitagama Complex there is a complete range of rock types from troctolites, through amphibole gabbros and diorites, to quartz-diorites and granitoid rocks. It is considered to represent an excellent illustration of the fractionation of gabbroic ultimately yield granitoid rocks. middle gabbroic series plagioclase + * Presentation Award element melts to �EARLY PROTEROZOIC GAbI3ROIC, DIORITIC, AND QUARTZ MONZONITIC INTRUSIONS IN THE MINNESOTA RIVER VALLEY: PETROLOGY AND SIGNIFICANCE M. DeWitt Daggett Minnesota Geological Survey, University of Minnesota, St. Paul, MN 55108 present address, Noranda Exploration, Inc., Cobalt, ID 83229 Three, small, early Proterozoic plutons intrude the Archean gneiss terrane of the Minnesota River Valley south of Franklin, Redwood County, Minnesota. The largest is the Cedar Mountain Complex, a composite intrusion consisting of a chilled margin of diabase and microgabbro, a main body of flow-layered hornblende diorite, and a quartz monzonite core. This complex is 600 meters in diameter. Two smaller plugs consisting of 1) diabase and gabbro, and 2) granodiorite, crop out five kilometers east of Cedar Mountain. Cross cutting and orthoclase in diabase indicate that the parent melt was potassic. Assimilation of sialic crust during magma intrusion affected the final mineralogies chemistries of and the Franklin-area plugs. Xenoliths of Archean yneiss occur throughout the Cedar Mountain diorite and the gabbro plug to the east; emplacement of the plugs to a fairly shallow depth proceeded in part by stoping of the country rock. from these rocks suggest that the dioritic, These early Proterozoic intrusives may a part of a limited but widespread shallow level igneous event which occurred in the southern Lake Superior region about 1,760 m.y. ago. The Minnesota River Valley plugs are lithologically somewhat similar to the Fox River rhyolites and related granites of south-central Wisconsin, and to the granodioritic, and differentiated from monzonitic melts common gabbroic Amberg quartz monzonite and related intrusions of northeast Wisconsin. These parent magma by fractional crystallization rocks all occur as small, isolated, epizonal clinopyroxene, of olivine, and calcic plagioclase. Feldspar compositions range continuously from An80 in diabase and gabbro to An2 in quartz monzonite. Olivine in the diabase is Fo53 to Fo6. Clinopyroxene from diabase, gabbro, and intrusions or extrusive flows; they all possess a calc-alkaline chemical character. The presence of rare rhyolite clasts in conglomerate units of the middle-Proterozoic Sioux quartzite indicates the former existence of additional similar rocks in Minnesota. relationships between rock types identify three distinct stages of intrusion: l)gabbro, 2)diorite and granodiorite, and 3) quartz rnonzonite. Petrographic and mineral chemistry data a hornblende diorite is diopside or diopsidic The restricted range of augite. clinopyroxene compositions and the lack of iron enrichment trend for an overall clinopyroxene phenocrysts are evidence for melt with calc-alkaline original an affinities. High modal abundances of biotite be This 1,760 m.y. old igneous event followed the Penokean orogeny but preceded the more voluminous igneous activity which accompanied crustal extension in middleand late-Proterozoic time. �LITHOLOGIC AND SEDIMENTOLOGIC CHARACTERISTICS OF THE COPPER HARBOR CONGLOMERATE, NONESUCH SHALE AND FREDA SANDSTONE FORMATIONS OF NORTHERN MICHIGAN AND WISCONSIN Paul A. Daniels, 3r., Hunt Energy Corporation, Lansing, Michigan The Keweenawan Age Copper Harbor Interfingering with the Copper Harbor Conglomerate, Nonesuch (Shale) Formation, Conglomerate is the Nonesuch (Shale) Formation, an unoxidized sequence of gray-black siltstone, shale, and sandstone and Freda Sandstone formations comprise the Oronto Group and are found in outcrop over some 200 kilometers in northern western Upper Michigan. These formations are part of a volcanic-elastic sequence created in response to the formation of the Midcontinent Rift System. Although intercalated volcanics are found in the lower one-third of this group, the sedimentary depositional regime was dominant. Along the Keweenaw Peninsula three paleocurrent indicators for all formations show that the predominant paleoflow directions were generally in northerly directions. In contrast, sedimentary structures in the Copper Wisconsin and Harbor Conglomerate on the opposite side of the rift (i.e., Isle Royale) indicate stream flow was to the south and east. Harbor Depositionally, the Copper Conglomerate is a basinward-thickening of volcanogenic clastics wedge and subordinate volcanics that decreases in average grain-size upsection. Various facies comprise the Copper Harbor and these have interpreted collectively been as representing a prograding alluvial fan complex. Maximum thickness is on the with a maximum thickness of 215 meters. The Nonesuch contrasts with the redbed sequences, both above and below, by: 1) having been deposited in a reducing environment, 2) increased textural maturity, and 3) hydrocarbon, sulfide and chlorite content. The Nonesuch is interpreted as having been deposited in a rift-flanking lacustrine environment of varying depth. Initiation of lacustrine conditions probably occurred through disruption of existing drainages by alluvial, volcanic, and/or tectonic processes. As with the underlying Copper Harbor, a gradational contact exists with the overlying Freda Sandstone. The Freda Sandstone is a ferruginous, lithic sequence of cyclic sandstone and exceeding 3660 meters in maximum thickness. Although similar in appearance to some sandstones of the mudstone Copper Harbor Conglomerate, the Freda, overall, is of greater compositional maturity conglomerate facies are uncommon. The Freda is dominantly fluvial in origin and appears to have "overridden" the Nonesuch and environments. clast-supported and comprised of volcanic clasts with an overall compositional ratio of mafic to silicic plus intermediate clasts of about 2:1. The heavy-mineral suite for the Copper Harbor (as well as for the Nonesuch and Freda) mainly consists of ilmenite plus Although complex in detail, the overall depositional model for the three formations is one of siomple transgressive-regressive relationships between alluvial fan/ lacustrine/ fluvial environments (Elmore and Daniel; 1980b). Important aspects of such a model are that: I) all the formations are genetically related with no major unconformities between them, and 2) the intervening Nonesuch Formation is, at least in part, equivalent in age to the upper similar opaque minerals, and epidote. Copper Harbor and the lower Freda. order of 1830 meters. Principal lithologies are red-brown, oxidized, lithic graywacke volcanogenic conglomerates. The conglomeratic facies are predominantly and �I PALEOMAGNETISM OF THE MEMESAGEMASING AND CARIBOU LAKES NORITES, GRENVILLE PROVINCE, ONTARIO * S. Dey, D. 1. A. Symons, and M. Stupavsky Department of Geology, University of Windsor Windsor, Ontario, Canada N9B 3P4 The Memesagemasing and Caribou Lake 20 km2 stocks intruding the high rank granitic gneisses in the Crenville Province about 60 km S of the Grenville Front. Five cores yielding 10 specimens were drilled in the stocks at Sch of 24 and 26 sites respectively. Low-field magnetic susceptibility measurements show that both layered norites outcrop as oval, stocks have a central phase with magnetite content. a high their airborne magnetic anomaly pattern rather than invoking a funnel-shape. Anisotropy of magnetic susceptibility measurements show This explains that the norites are strongly layered even though most outcrops appear unbanded, and that the plutons have not been structurally compressed or tilted as previously suggested. AF, thermal, and chemical step demagnetization and general AF cleaning all isolate a stable remanence component with 95 percent confidence of r-.'3l0°, 5l in the Memesagemasing stock using conventional tiered statistical analysis. This component * Presentation eligible Award for the Student resides in titanomagnetite with numerous exsolution lamellae. The same component is isolated in the Caribou Lake stock by point density stereonet contouring only after AF cleaning. Its less stable remanence resides in coarser unexsolved t itanomagetite grains. Eight baked contact tests using more than 100 additional specimens and including 2 profiles show that: I) the norite remanence predates emplacement of the crossing cutting -.s 1250 Ma Sudbury olivine diabase dikes and — 1100 Ma granite pegmatite dikes, and 2) the norite was 2000 when the dikes were cooled to emplaced. The norite pole lies on the -'l760 Ma position of the North American APW path implying: 1) emplacement during the terminal stages of the Hudsonian Orogeny dated by Rb-Sr at r 1800 + 100 Ma ago; 2) possibly comagmatic emplacement with the Sudbury Irruptive which is —90 km NW in the Southern Province; ano 3) the juxtaposition of the Grenville and Southern Provinces as far back as 1760 Ma. �WISCONSIN GRAVITY BASE STATION NETWORK--1980 C. Patrick Ervin Department of Geology, Northern illinois Lkiiversity DeKaIb, Illinois 60115 The Wisconsin Geological and Natural History Survey has embarked regional gravity surveying upon a program. Mapping is being done on a one mile grid insofar as the road system and elevation control permit. The Northeast Wisconsin Sheet is "in press" and was presented at this meeting last year. The rest of the state will be covered in the coming years. A successful field program is dependent on the existence of a high precision, internally consistent base station network. To facilitate field operations, a base station should be readily accessible by auto, no more than 25-30 feet from a road or drive, to locate, permanent, relatively isolated from foot and vehicular traffic, and easy have a stable base on which to set the meter. Additionally, no point in the state should be more than about a 45 minute drive from a base station. A statewide base station network, consisting of 30 stations, was established in 1980 the summer of LaCoste-Romberg model C using two gravimeters. Use of two gravimeters doubles the number of ties between stations and facilitates error detection. The network was designed to include several extant oase stations and is in good agreement with the earlier measurements. �THE PENOKEAN OROGENY Samuel S. Goldich Department of Geology, Colorado School of Mines Golden, Colorado 804131 The Penokean orogeny, which occurred in the Lake Superior district approximately 1800 m.y. ago, was a complex event that involved more than mountain building by uplift followed by erosion. As in the development of the more recent mountain chains, igneous and metamorphic activity on a grand scale characterized the Penokean orogeny. Graywacke-argillite sequences with intercalated volcanic rocks were folded, metamorphosed, and intruded by a variety of igneous rocks ranging from gabbroic to granitic in composition. Published U-Pb zircon ages from Wisconsin and Michigan indicate two pulses of igneous activity. The older, 1835 ± 15 The data available at this time indicate more or less continuous igneous activity in the Lake Superior region between 1850 and 1750 m.y. ago. The 2600-m.y. old McGrath Gneiss of eastern Minnesota was strongly deformed during the Penokean orogeny. The U-Pb ages on zircons from the gneiss are strongly discordant and reflect the 1800-m.y. deformation. Similarly, old rocks in Wisconsin and in Michigan were severely affected by the Penokean orogeny, and the earlier geologic history, as a result, is difficult to decipher. The similarity in lithologic types and structural style of the rocks involved in the m.y. ago, involved a variety of rock types, 1800-m.y., whereas the younger pulse, 1760 ± ID m.y. ago, appears to have been restricted to granite and rhyolite. Unpublished U-Pb analyses of zircon concentrates from a large number of samples representing tonalitic to granitic rocks in east-central Minnesota are closely related in time, 1804÷ 24 m.y. Rb-Sr isochron ages for the rocks of east-central Minnesota range from 1700 m.y. to 1750 m.y. and are distinctly younger orogenic events in the Lake Superior region is striking. In each case metasedimentaryvolcanic accumulations, a variety of igneous intrusive rocks, and migmatitic development were involved. Regional folaing gave way to higher grades of metamorphism accompanying igneous activity, and late shearing with recrystallization are characteristic. Emplacement of pegmatite and aplite dikes followed each major than the corresponding U-Pb zircon ages. the orogenic event. 2600-m.y., and in older �THE ROLE OF HYDROTHERMAL ALTERATION AND TECTONISM IN WISCONSIN MOLYBDENITE OCCURRENCES .1. K. Greenberg Wisconsin Geological Survey Madison, Wisconsin 53706 Molybdenite is known to occur in three places in northeastern Wisconsin. These appear to be situated along a north-south region restricted near 88°W Molybdenum mineralization in longitude. Michigan's Upper Peninsula is also concentrated near the same longitude. In all Wisconsin cases, Penokean-age granite plutons are directly with the mineralization. The best known occurrence, near Middle Inlet in Marinette County, is in quartz veins within the Mount Tom granite body. The other two associated occurrences, near Amberg in Marinette County and in southeast Florence County, are pegmatite mineralizations. Chemically, the granite host rocks are calcalkaline to alkaline, with no "unusual" trace element characteristics. }—bwever, near the site of mineralization in veins or pegmatites, the host rocks show the effects of hydrothermal alteration, especially alkali Dramatic examples of metasomatism. potassium metasomatism are apparent at Middle Inlet and southeastern Florence County. The granite at Middle Inlet has also been albitized and silicified proximal to quartz veins. These alteration effects should be considered as essential guides in exploring for molybdenum in Wisconsin. Wisconsin occurrences of molybdenum are similar to those in older Precambrian terranes of the world, such as in Ontario and Western Australia. However, these cannot be equated with the extensive ore resources porphyry-type deposits represented by typical of younger plate tectonic environments. �IMPACT AS A POSSIBLE ORIGIN FOR SUBSIDED BASINS Jack B. l-brtung NationaL Research Council Senior Post-doctoral Research Associate Code SN6-NASA Johnson Space Center, F-kiuston, Texas 77058 Subsidence of basins, Michigan must basin, circular roughly intracontinental such have mechanism or energy source. as a the driving Mechanisms directly related to plate tectonics do not operate slowly enough to explain a record of almost continuous subsidence of the Michigan basin throughout the Paleozoic Era. Thermal contraction of the lithosphere underlying the basin is another mechanism, but even proponents of this idea recognize "little direct evidence that an initial heating actually occurred in the Michigan basin immediately before the start of subsidence." Another energy source which could lead to a subsiding basin is the impact event of an asteroid or comet roughly ID km in diameter. During such an impact material is excavated from depths of a few tens of km and deposited on the surrounding area. The is filled temporary cavity produced immediately by material that was originally below the cavity. The resulting structure, similar to those observed on the Moon and Mars, is a broad topographic low surrounded by higher rocks capped by ejecta deposits. Of particular importance is the likelihood that a state of isostatic equilibrium will be established or closely approached after motions directly related to the impact have The mass deficiency associated with the topographic low may be expected to be compensated for by excess mass related to more dense rocks centrally uplifted below the basin. Basin evolution ceased. with erosion of surrounding highlands and deposition within the basin. If proceeds it is required that isostatic equilibrium is maintained, the to the basin will subside in and the surrounding highlands will be uplifted. This response sediment load process will continue until the more dense material underlying the basin is returned approximately to its original level or until no topographic difference exists between the basin center and the surrounding area. A significant characteristic of this process is that the rate of subsidence is controlled entirely by the rate of sedimentation, which may be extremely slow or even nonexistent at times. On the Earth an evolved impact basin may take the appearance of a subsided sedimentary basin, something like the Michigan basin. �EVIDENCE FOR MULTIPLE DEFORMATION IN THE MIDDLE PRECAMBRiAN THOMSON FORMATION Timothy B. Hoist Department of Geology, University of Minnesota, Duluth Duluth, Minnesota 55812 The Thomson Formation of East-Central exhibits numerous structural features which have been interpreted to have formed during the Penokean Orogeny. In the Thomson-Cariton-Cloquet area there are open folds on a scale from centimeters to kilometers. The folds are upright, and Minnesota fold axes trend about east-west and are horizontal to gently plunging either east or west. An axial-planar cleavage, vertical or nearly vertical, is present. To the south there is a pervasive bedding-parallel foliation which has previously been interpreted as having formed in a metamorphic event which predated deformation. Evidence of the amount of compressional strain associated with foliation (Wood, 1974) as well as abundant extensional features (boudinage) within the foliation plane in this region suggest that the bedding-parallel foliation is associated with a deformation. Folds are with southern area, present in the geometries and attitudes similar to those in the north. A vertical crenulation cleavage, axial-planar to these folds where both are observable, is also present. The crenulation cleavage can be found even where folds are not found, in the area from Denham to Atkinson. The deformation which caused the bedding-parallel foliation must then pre-d ate that which caused the open, upright, sub-horizontal folds. Isoclinal, recumbant folds, to which the earlier foliation is axial-planar, have been found in several localities. These folds vary in scale from centimeters to meters. Fold hinges are fairly rare because of the isoclinal nature of the folds. The pervasive nature of this earlier foliation suggests that isoclinal, recumbent folds of a large scale also may be present. The deformation history involves an early stage of indicated isoclinal, recumbant folding, with the development of an axial planar foliation. A latter stage of deformation involved the development of open, upright folds, with an axial-planar foliation also, which is a crenulation cleavage where the earlier foliation is present, and a slaty cleavage where the earlier foliation is not present. Evidence for the earlier deformation has been found from Denham to just northeast of Atkinson, whereas evidence for the second deformation can be found in the entire region of Thomson Formation exposure. �JOINT ORIENTATION ANALYSIS IN THE NORTHERN MICHIGAN BASIN Timothy B. 1-blst Department of Geology, University of Minnesota, Duluth Duluth, Minnesota 55812 The orientations of 14,687 joints were measured at 142 locations in the Paleozoic rocks of the Michigan Basin. The data were for each of the four sets. The local variation could not be correlated with taken which ranged from Manitoulin Island on the east, the south Joint set orientation is independent of regional strike around the Michigan Basin Door Peninsula on the west and the northern which varies from about 020 degrees (N200E) to about 115 degrees (N65°W) in an area shore of Lake Superior on the north, the portion of the lower peninsula of Michigan on the south. The rocks at the sample localities range in age from Cambrian to Devonian. Most of the localities are in carbonate rocks, but data were taken from outcrops of sandstone and shale also. Almost all (over 98%) of the joints are vertical or nearly vertical. Four main joints sets are present in the northern Michigan Basin. The largest peak in the data is a joint set with a strike of about 054 degrees (N54°E). The second-largest peak in the data is a set with a strike of about 133 degrees (N47°W). Two peaks of about the same height are joint sets striking 002 degrees (N02°E) and 092 degrees (N88°W). Local mean orientation of any of the sets does vary from location to location, but is relatively consistent over the entire area lithogy, age of rock, or geographic location. across the study area. Possible structural trends in the Precambrian rocks below the Devonian rocks in the area, postulated from geophysical data, do not correlate with any of the joint sets. Trends of axes of folds present in the Paleozoic strata of the lower peninsula average about 135 degrees (N45°W). This suggests that the joint set of nearly the same strike direction may be related to these folds (the b-c joints of Price, 1966). In-situ stress measurements in the Paleozoic rocks of the mid-continent region (summarized in Haimson, 1978) show the maximum principal compressive stress in the horizontal plane to be quite consistent in orientation, averaging 053 degrees (N53°E). This suggests that the joint set with a nearly-idential strike may be extensional, and fairly recent in age. �A GEOCHEMICAL RECONNAISSANCE STUDY OF GROUNDWATER FROM AN EIGHTEEN COUNTY AREA OF NORTHWESTERN OHIO Mohr, Eileen T., Deering, Mark F., and Carison, Ernest H. Department of Geolgy, Kent State Lkiiversity Kent, Ohio 44242 A reconnaissance study of groundwater techniques showed sulfate and silica to be quality in Northwestern Ohio was undertaken in which 100 samples from actively pumping wells were collected. The major supply of groundwater for this area is from carbonate aquifers which locally evaporites contain and epigenetic present in concentrations of 4-1500 ppm and 7.2-29.0 respectively. ppm Fe, also determined spectrophotometri c by a mineralization that may be the source of natural trace element pollution. Major industrial centers and agricultural areas may also be a prime source of pollution. technique, ranged from 0.0 ppm to 11.2 ppm. The concentrations of K (1.0-34.4 ppm), Zn ( less than 40 ppb-l.7 ppm), Co less than 300 ppb), ana Na (5.5-150.6 ppm) were determined by atomic absorption techniques. Other trace elements including As, Cd, On site measurements of static water Cu, Be, Pb and Sr will be measured by level, temperature, (6.85-8.5 5), pH conductivity (100-2500 micromhos), alkalinity (83-580 ppm), F (0.2-2.8 ppm) and Cl (3-230 ppm) were made. Digital graphite furnace techniques, while Hg concentrations will be determined by a flameless AA method. It will be determined titration analyses performed on filtered, acidified samples indicated Ca to be present in concentrations from 27-560 ppm and Mg from 14-192 ppm, while spectrophotometric if any of the trace elements present a health hazard and should, therefore, limit water utilization or require special treatment of water supplies. �RB-SR DATING OF PRECAMBRIAN BASEMENT FROM ILLINOIS DEEP HOLE PROJECT CORE UPH-3 Carla W. Montgomery Department of Geology, Northern Illinois University DeKaib, Illinois 60115 Eble UPH-3 Deep core 840 m approximately of Precambrian granitic basement. Whole-rock samples taken over the full length of the Precambrian portion of the core fit a single Rb-Sr isochron with slope age of 1479 + 10 m.y. and initial 87Sr/86Sr of o.71i12 + .0025 (Iderrors). Mineral isochrons frorii measurements, indicating that these rocks have not been affected by any significant thermal event since that time. The initial strontium isotope ratio reflects some contribution of radiogenic Sr from older crust. The l479-m.y. age is similar to ages several core samples yield essentially the same age within the precision of the region, illinois penetrated reported for granitic rocks in Wisconsin, Missouri, and elsewhere in the mideontinent suggesting widespread activity at about that time. igneous ��PRELIMINARY RESULTS OFA GRAVITY SURVEY IN THE EASTERN HALF OF THE IRON RIVER-CRYSTAL FALLS DISTRICT, IRON COUNTY, MICHIGAN * D. R. Paddock, K. Fujita, F. W. Cambray, and H. F. Bennett Department of Geology, 206 Natural Science, Michigan State University East Lansing, Michigan 48824 A gravity survey was conducted in the eastern portion of the Iron River-Crystal Falls district of Iron County, northern Michigan. Measurements were taken on five profiles, three east-west profiles to the south of Crystal Falls and two north-south profiles to the west of Crystal Falls. The stations along each profile were separated by an average of 750 meters. Altitude control was maintained by an altirrter and 1:24,000 topographic maps. Accuracy of the data after reduction to bouguer anomalies is about plus or minus 1.4 milligals. A maximum amplitude of 34 milligals is observed over the Iron-River Crystal Falls district. Our observed data are in agreement with those obtained by Bacon and Wyble (1952). The anomaly is centered to the south and west of the iron formation The shape of the anomaly indicates that the source is at depth. exposures. Several crustal models were developed to interpret the data. If the stratigraphic section reported in the literature is used, only a 9 milligal anomaly is obtained. * Student Presentation eligible Student Award Linear stretching of the stratigraphic succession requires a sedimentary thickness of greater than 40 km to fit the amplitude of the anomaly. With no stretching of the column, and an iron formation density of gm/cc, an increase of the iron formation thickness from 200 to 1200 meters is required. An increase in the 3.21 density of the Riverton Iron Formation to 3.56 gm/cc would reduce the total sedimentary thickness to the reported 12 km with an iron formation thickness of 600 These iron formation thicknesses greatly in excess of the reported average thickness of 200 meters. An alternative possibility is that the Paint River group and Badwater Greenstone are directly underlain by basalt. This model postulates a sedimentary thickness of 2800 meters (of which 200 is iron formation) and 1800 meters of greenstone. To fit the observed anomaly, an underlying basaltic meters. are layer of between 3200 ana 3900 meters is required. This could be caused by the sub-aqueous emplacement of basalts in a rift basin which has subsequently filled with sediments. for the ��PRELIMINARY ASSESSMENT OF RARE EARTH ELEMENT GEOCHEMISTRY OF VARIOUS IRON FORMATIONS OF THE LAKE SUPERIOR DISTRICT * Elaine L. Slaughter, Susan E. Tituskin, and John 1. Wilband Department of Geology, 206 Natural Science, Michigan State University East Lansing, Michigan 48824 Several samples of banded ironformation (6W) from the Wawa district and the Gunflint, Vulcan, and Negaunee Iron Formations have been analyzed for their patterns to the carbonate samples. investigation to determine the use of REE as indicators of depositional environments and to investigate their mobility during intermediate to these groups. rare earth elements (REE) as part of an metramorphism, oxidation, and leaching. Our preliminary results cannot be interpreted too literally in terms of genetic modeling because the experimental base, such as exists for magmatic rock—forming minerals, is very weak for BIF sedimentary systems. The carbonate rich sediments of the Negaunee I.F. at the Empire Mine show relatively strong fractionation of the light REE (La/SM 3-5x chondrite) and have surprisingly uniform total abundances with respect to depth. The clastic lenses are in total considerably more enriched abundances yet show similar distribution * Student Presentation Student Award eligible for the The "jaspilite" and "hard ores" (Cliffs Shaft) of the Michigan formations are most REE enriched, Vulcan samples the least, and Tilden and Empire Mine oxide ores are We suggest the REE enrichment in the to be a response to solutions migrating through the formations (e.g. oxides Cannon, 1975 - hard ores) or depletions in response to increase in metamorphic grade (Vulcan). In the Empire and Tilden environments where carbonate to oxide reactions are obvious or implied, preliminary data indicate that the abundance of REE in the oxides are similar to that of the carbonates. Cherts, carbonates and oxides do not exhibit a Ce depletion. The Gunflint and Negaunee cherts have "terrestrial" REE patterns similar to other "land exposed" cherts. �THE DISTRIBUTION OF LITHIUM, RUBIDIUM AND CESIUM IN LAKE MUDS NORTH OF LAKE SUPERIOR M. A. yes and R. 3. Stevenato Ontario Geological Survey Oronto, Ontario A study of the distribution of Li, Rb and Cs in lake muds north of Lake Superior is funded by the Ministry of Northern Affairs under the Northern Industrial Mineral Study program, and is supervised by staff of Mineral Deposits Geological Survey. Ontario Section, Centre-lake samples covering an area of 27,700 sq. km. (NTS 42D, 1/2 of 42E, 52A, 1/2 of 52H), originally the Federal-Provincial collected for Uranium Reconnaissance Program of 1977, The primary were used in this study. purpose is to evaluate the geochemical response of lithium and related trace elemental concentrations in lake sediments and determine its potential as a tool for lithium exploration. The lake sediment samples were collected at an average ciensity of sample per 13 sq. km. A total of 1782 samples were 1 analyzed for Li, Rb and Cs by Barringer Ltd. not including randomly control reference and blind duplicate samples. Two hundred and four samples were analyzed for tin and tantalum. Lithium, rubidium and cesium were Magenta inserted analyzed by flame atomic absorption upon reverse HF/HCIO4/HNO3 The detection limits were 1 digestion. ppm, 10 ppm ppm respectively. Tantalum was analyzed by plasma emission upon reverse and a HF/HCIO4/HNO3 digestion The redissolution in 0.5 N HCI/HF. Tin was detection limit was 5 ppm. analyzed colourimetrically upon fusion with ammonium iodide; the detection limit being and 1 I ppm. Control reference, blind duplicate and field duplicate samples were utilized to determine the precision and accuracy of the data. Precision of the four different control samples ranged from 8% to 18% for lithium Blind and from 6% to 10% rubidium. duplicate accuracy was 16% and 20% for lithium and rubidium respectively, while field duplicate accuracy was 7% for Li and 12% for Rb. Cesium was not considered since most concentrations recorded were below the detection limit of the lab equipment. high lithium While generally coincide with concentrations high rubidium concentrations, no large anomalous regions were detected in a preliminary visual examination except in the area southwest of Progress of a detailed Thunder Bay. computer analysis amalgamating the data with major element and base metal values of the lake muds is discussed. �PETROGENETIC MODELS OF KEWEENAWAN BASALTIC ROCKS, UPPER MICHIGAN John T. Wilband and Pipob Wasuwanich Department of Geology, 206 Natural Science, Michigan State University East Lansing, Michigan 48824 Lower Keweenawan diabase dikes from Marquette-Baraga Counties, and middle Keweenawan Portage Lake Lavas from upper Michigan, can each be subdivided into two chemically distinct groups: a low Tb2- P205 group characterized by higher AI2O3 content, higher Mg ratio, and lower total Fe end REE abundances than a high Ti02-P2O5 group. Both groups, which are indistinguishable in the field, are enriched in the LREE relative to the HREE, and have similar normalized REE abundance patterns. respective type. The wide gap between the TiO2-P205 contents of each group cannot be resolved by a simple fractionation or mixing model, especially because the Ti02/P205 ratio remains remarkably constant within each group. We conclude that two sources perhaps from different depths or with separate REE signatures, are required to produce the two groups and suggest each linear trend is indicative of liquids derived by varying degrees of partial melting of these sources. Similar chemical the dikes have been trends within but nonparallel for each subgroup of the interpreted to mean that the magmatic processes must have This correlation can be interpreted to mean that the rocks, regardless of mode of formation, are coeval within their early opening stages of the Keweenawan rift in Michigan. Plots of La/Sm vs. La and Yb are linear basalt. same been operative during their emplacement in the �AUTHOR H. All and C. Craddock K. Attoh R. L. Bauer M. E. Bengtson, R. P. Meyer, I-I. C. Halls, 3. H. Karl, and D. Dushek M. S. Breithart and F. W. Cambray B. A. Brown and 3. K. Greenberg A. Choudhry and T. E. Smith M. D. Daggett P. A. Daniels, Jr. S. Day, D. T. A. Symons, and M. Stupavsky C. P. Ervin H. P. Gilbert S. S. Goldich 3. K. Greenberg 3. 8. Hartung 1. 6. F-blst 1. 8. HoIst E. T. Mohr, M. F. Deering, and F. H. Carlson C. W. Montgomery M. Osterberg and R. L. Morton D. S. Paddock, K. Fujit F. W. Cambray, and H. F. Bennett P. K. Sims and Z. E. Peterman F. L. Slaughter, S. E. Tituskin, and 3. T. Wilband F. B. Van 1-buten and D. Bhattacharyya M. A. Vos and 5. 3. Stevenato 3. T. Wilband and P. Wasuwanich TIME 3:00 to 3:20 Friday 1:50 to 2:10 Friday 4:00 to 4:20 Thursday LOflOto 10:30 Friday 2:10 to 2:30 Thursday 11:00 to 1 iao Thursday 3:40 to 4:00 Friday 3:20 to 340 Friday 3:20 to 3:40 Thursday 9:50 to 10:10 Friday 9ö0 to 9:50 Friday 9•30 to 9:50 Thursday lOdOto 10:30 Thursday 3:40 to 400 Thursday 11:20 to 11:40 Friday 1 h20 to 1 h40 Thursday 11:00 to 11:20 Friday h30 to 1:50 Thursday 11:40 to 12:00 Thursday 1:30 to 1:50 Friday 11:40 to 12:00 Friday 9:50 to 10:10 Thursday 300 to 3:20 Thursday Thursday evening 1:50 to 2:10 Thursday 2:10 to 2:30 Friday � https://digitalcollections.lakeheadu.ca/files/original/e0aa4ed07dd4add1745e0969cdcbfe3d.pdf edcf69eb414fe00bfd52b2bc8c45457a PDF Text Text Twenty Seventh Annual Meeting Institute a Lake Lansing, Michigan Stperior Geology May 11—12, 1981 The Huronian Between Sault Ste. Marie and Thessalon �I I THE HURONIAN ROCKS BETWEEN SAULT STE. MARIE AND THESSALON DISTRICT OF ALGOMA ONTARIO MAY 11-12, 1981 FIELD EXCURSION GUIDE Prepared By Gerald Bennett, Ontario Ministry of Natural Resources �I THE HURONIAN SUPERGROUP OF THE SAULT STE. MARIE AND THESSALON AREAS, ONTARIO I Introduction: Previous Work: The Huronian Supergroup is probably the most studied sequence of rocks in Canada with published observations going back to 1821. Knight (1915) investigated part of the areas and recognized volcanic rocks in the Thessalon area. Collins (1925) memoir included the first accurate geological map of the North Shore of Lake Huron and his stratigraphic subdivision of the Huronian has only recently been supplanted. McConnell (1927) described the rocks of the Sault Ste. Marie area and placed the Huronian rocks in their correct stratigraphic position. Chandler (1973, 1976) did detailed mapping for the Ontario Division of Mines in the area west of Wakomata Lake. Frarey (1977) culminated several seasons of mapping for the Geological Survey of Canada with the publication of a memoir on the geology between Sault Ste. Marie and Blind River. Frarey revised the stratigraphic scheme for the Sault Ste. Marie area and recognized additional Huronian volcanic rocks in the Aberdeen Lake area. The writer carried out ¾ mile to the inch mapping for the Ontario Geological Survey between Sault Ste. Marie and the Aberdeen Lake ares between 1974 and 1977. A study of the stratigraphic relationships of the Huronian volcanic rocks was begun in 1978 (Bennett in preparation). In addition to the above studies there are many studies of specific problems relating to the Huronian geology. Most of the significant theses and publications are given in the references accompanying this field guide. General Geology: The Lower Proterozoic (Aphebian) Huronian Supergroup forms part of the Southern Province of the Canadian Shield. These predominantly clastic sedimentary rocks form an eastwest trending belt about 35 miles (56 km) wide extending along the north shore of Lake Huron as far east as the Quebec border, a distance of approximately 200 miles (320 km). The total stratigraphic thickness of Huronian rocks is about 40,000 feet (12,000 m). �I -2An absolute age for the Huronian rocks has not yet been firmly established. The basal Huronian rocks lie unconformably upon Archean granitic rocks of the Superior Province which give K-Ar ages of 2,500 m.y. Nipissing diabase which intrudes the Huronian sequence has been dated by Sr-Rb methods at 2,150 m.y. (Van Schmus, 1965). The Huronian rocks along the north shore of Lake Huron are part of the Penokean Fold Belt and have undergone varying degrees of deformation and metamorphism. Radiometric dating of metamorphic rocks generally gives ages between 1,600 and 1,800 m.y. In the area between Sault Ste. Marie and the east end of Quirke Lake Syncline Huronian rocks are metamorphosed to lower greenschist facies and strata are deformed into open folds or a south to southwest dipping homocline. Normal fault sets strike northeast and northwest. Most movement occurred along northwest trending thrust faults (Frarey, 1977). East of the Quirke Lake Syncline the metamorphism and deformation is more intense. In the Sudbury-Espanola area dips are generally steep, folds are locally tight and the metamorphic grade is almandine-amphibolite facies (Card et al 1972). Elliot Lake Group: In the Sault Ste. Marie and Thessalon areas the Elliot Lake Group is represented by the Livingstone Creek, Thessalon, and Matinenda Formations. The McKim Formation, a very thick sequence of mudstones, siltstone and turbidites present in the eastern half of the Huronian belt has; not been recognized in the area between Sault Ste. Marie and Thessalon (Frarey, 1977) The Livingstone Creek Formation; The Livingstone Creek Formation is a clastic sedimentary sequence which overlies the Archean basement rocks and which is, in turn, overlain by the Thessalon Formation volcanics. In the Quirke Lake Syncline the Livingstone Creek Formation is missing and the Thessalon volcanics lie directly on the basement. In the Sault Ste. Marie area the Livingstone Creek Formation can be subdivided into a conglomerate member, a sandstone member, and a quartz-arenite member. The conglomerate member of variable thickness is locally present at the base of the formation, although in Morin Township, about 25 miles (40 km) north of the Thessalon area, the conglomerate member occurs at least one hundred feet (33 m) above the base. �I -3— TABLE OF FORMATIONS FOR THE SAULT STE. MARIE AND THESSALON AREAS I PHANEROZOIC (max. thickness in feet) CENOZOIC Pleistocene and Recent Gravel, sand, silt, clay and organic deposits Unconformity Paleozoic Ordovician Limestone, shale, sandstone Unconformity — PRECAMBRIAN LATE PRECAMBRIAN (PROTEROZOIC) Jacobsville Formation (+ 700) Sandstone, shale, conglomerate Unconformity KEWEENAWAN GROUP Mamainse Point Formation Basalt, rhyolite, conglomerate, diabase, felsite dikes Unconformity Olivine diabase dikes, lamprophyre dikes Intrusive Contact MIDDLE PRECAMBRIAN (PROTEROZOIC) Nipissing Diabase Gabbro, diabase, granophyre HURONIAN SUPERGROUP COBALT GROUP Bar River Formation (1000) Quartz arenite Gordon Lake Formation (1000) Siltstone, chert Lorrain Formation (8000) Arkose, quartz arenite, pebble conglomerate, siltstone, mudstone Gowganda Formation (3500) Matrix supported and clast supported conglomerates, siltstone, mudstone, wacke, arkose �-4Dis conformity QUIRKE LAKE GROUP Serpent Formation (800) Subarkose, conglomerate Espanola Formation (650) Grey limestone, siltstone, dolomite Bruce Formation (300) Matrix supported conglomerate Local Disconformity ROUGH LAKE GROUP Mississagi Formation (5000?) Subarkose, pebble conglomerate, arkose Aweres Formation Subarkose, arkose, clast and matrix supported conglomerate, siltstone Pecors Formation (Not recognized in Sault Ste. Marie area) Muds tone Ramsay Lake Formation Matrix supported conglomerate Local Disconformity ELLIOT. LAKE GROUP McKim Formation (Not recognized in Sault Ste. Marie area) Mudstone, siltstone, wacke Matinenda Formation Arkose, subarkose, quartz wacke, uraniferous quartz pebble conglomerate Disconformity Thessalon Formation (3500) Basalt, andesite, rhyolite, basaltic andesite, minor arkose, pebble conglomerate Dis conformity Livingstone Creek Formation (+ 1000) Subarkose, clast supported conglomerate, quartz arenite Unconformity EARLY PRECAMBRIAN (ARCHEAN) Late Intrusive Diabase, Rocks gabbro dikes Intrusive Contact U �-5-Plutonic Rocks Porphyritic quartz monzonite, granitic gneiss, migma t it e Intrusive Contact Metavolcanic-metasedimentary belts Mafic to felsic metavolcanics, metasedirnents, gabbro and porphyry intrusions Sources of Information: Frarey, 1977. Robertson et al, 1969. Bennett et al, 1975. U �1 1 — J LEGEND FOR FIGURE 1 Formation LAKE GROUP — ————— EARLY PRECAMBRIAN BASEMENT Livings tone Creek Formation Thessalon Formation ELLIOT LAKE GROUP Matinenda Formation HOUGH QUIRKE LAKE GROUP Gowganda Formation Lorrain Gordon Lake and Bar River Formations COBALT GROUP DIABASE LATE PRECAMBRIAN AND PALEOZOIC E'H NIPISSING I ____ I 4. Highway — — with number I II a__I h Thrust fault (Hanging wall) Fault Symbols �M. S S Superior Lake - ,' -s-- ...4. .It. Figure I j((tS of jrJortfl2tth &ibI'n pE,L&hy,J.,ord kobertsJA., 919. FrneyMJ-, I?fl s S Jonj. IkIwl.J G3I Field Iip 51095 Souls Ste. MorirthessolOfi Area Geotogy and Field Slops t (if �I —7— The conglomerate member consists of clast supported cobble to boulder conglomerate with coarse sandstone interbeds. The granitic megaclasts are typically pale grey in contrast to the pink to reddish granitic rocks which make up much of the basement. Clasts of diorite, gabbro, quartz and mafic volcanics are subordinate to the granitic component. granite The sandstone member forms the bulk of the Livingstone Creek Formation. This unit consists predominantly of fine to medium-grained, grey subarkose and arkose displaying planar and trough cross-beds. Interbeds of siltstone, mudstone or pebble conglomerate are rare within the sandstone member. The member is locally calcareous. An upper quartzarenite member of the Livingstone Creek Formation, up to 10 meters (30 feet) thick, has been recognized only in the Sault Ste. Marie area where it directly underlies the Thessalon flows. It is a pale grey to white, or yellowish grey, fine-grained, silicious subarkose and quartzarenite. The quartzarenite member is generally well sorted and finer grained than the subarkose member. The Livingstone Creek Formation is up to at least 1,200 feet (350 m) thick in the Sault Ste. Marie area. Frarey (1977) gives the thickness of the Livingstone Creek Formation in the Thessalon area as up to 300 feet (100 m). The Thessalon Formation: The Thessalon Formation (Frarey, 1967) is a predominantly volcanic sequence near or at the base of the Huronian Supergroup west of the nose of the Quirke Lake Syncline. The distribution of the Thessalon Formation is shown in Figure 2. The Thessalon Formation is underlain by the Livingstone Creek Formation as far east as the Crazy Lake area. In the Dollyberry Lake and Pecors Lake areas the Thessalon Formation lies directly on the Early Precambrian basement. Drill logs indicate that the Livingstone Creek Formation is missing throughout the Quirke Lake Syncline. In the Sault Ste. Marie and Aberdeen Townships areas the Thessalon Formation is up to at least 3,500 feet (1000 m) thick. In the Thessalon area the Huronian volcanics are about 1,500 feet (450 m) thick, but may be thicker under Lake Huron. In the Quirke Lake Syncline drill hole data indicates thickness from 0 to about 500 feet (150 m) of Thessalon Formation is present. b �cx 48' I I FEB Ii Paleozoic Rocks Grenville Province Rocks Sudbury Irrupttve Whitewater Group Rocks 10 kitom.tert LN Hutonian Superyroup -1 ftjj Archean Cc,. 0 0 8: Copper (]iIf Fo,r,iolion FEB Huronian Vokonic Rocks El Slobie Formation the Spiogge 111 Solinay I.ole Fotmotion (including and Runt Volcancs) El [Isle Mountain Formal,on Thesso$on Formation FIGURE 2 Presence confirmed by drilling Subsurface EnSenf [I Thenolon [ Dollyberry tale Area Presence assumed [.j Duncan iwp Area [ Aberdeen Twp Area [1 Crazy tale Arm NI Priors Fake Area H Cooper Lake Area Gabbro Anorthosile Rocks ni. 8 a 48 N.' —' lot �I -9Thin lenses of coarse, poorly-sorted arkose and quartz pebble conglomerate are locally present at the base, or intercalated with the lowermost few flows, of the Thessalon Formation. These clastic units are in places pyritic and radioactive. These radioactive quartz pebble conglomerates are not correlated with the uranium bearing Matinenda Formation of the Elliot Lake area because thin elastic units, lithologically identical to these at the base of the Thessalon Formation in the Sault Ste. Marie-Thessalon area, occur at the base of the Thessalon Formation in the Dollyberry Lake and Crazy Lake areas (Figure 2). At the latter location the Matinenda Formation overlies the volcanic rocks and there is evidence of disconformity between them. The available whole rocks chemical analyses suggest that the volcanic rocks of the Thessalon Formation can be subdivided into two groups or members, an (upper) tholeiitic basalt member, and a (lower) mixed member. There is some interfingering of these members, and in the Sault Ste. Marie area the mixed member is locally missing or very thin so that the basaltic member rests on the Livingstone Creek Formation. The mixed member varies in content from area to area. In the Sault Ste. Marie and Aberdeen Lake areas the mixed member is predominantly basaltic andesite with minor hawaiite. In the Thessalon area icelandite, rhyolite, tholeiitic andesite, high-magnesium tholeiitic basalt and mugearite are present. In the Dollyberry Lake area mugearite, hawaiite rhyolite, volcanic breccia and high-magnesium tholeiitic basalt, tholeiitic basalt and andesite have been identified. The (upper) tholeiitic basalt member is prominent in the Sault Ste. Marie and Aberdeen Lake areas where it is about 1,500 feet (500 meters) thick. The basalt member is thinner in much of the Thessalon area and apparently missing in the Dollyberry Lake and Pecors Lake areas of the Quirke Lake Syncline. The Thessalon Formation typically exhibits a greenschist mineralogy. The basalts are made up of albite, clinozoisite epidote, actinolite, chlorite and oxides. Primary clinopyroxene is locally preserved in basalts of the Sault Ste. Marie area. The icelandites and basaltic andesites generally contain biotite and stilpnomelane in addition to albite, chlorite actinolite epidote and quartz. Many, if not all of the volcanic rocks of the Thessalon Formation have undergone varying degrees of metasomatic alteration involving mainly addition of Na20, grain or loss of K)0, and loss of calcium. Spilitization is especially pron&inced in some parts of the Sault Ste. Marie area where metabasalts have soda contents of over 5 percent. �I - 10 Explanation - of Table 2: 1. Average analysis of tholeiitic basalt, Thessalon Formation, Thessalon area. 2. Average analysis of icelandite. Lower mixed member, Thessalon Formation, Thessalon area. 3. Average analysis of high magnesium basalt. Mixed member, Thessalon Formation, Thessalon area. 4. Average analysis of basaltic andesite. Mixed member, Thessalon Formation, Duncan Township area. 5. Average Hawaiite-mugearite. Mixed member, Thessalon Formation, Dollyberry Lake area. 6. Rhyolite. Mixed member, Thessalon Formation, Dollyberry Lake area. �j 1 59.03 50.65 14.26 2.43 S102 A1203 Fe203 1.304 0.174 1.31 0.28 0.02 0.14 0.78 0.89 0.28 7.78 3.31 0.58 1.02 0.13 0.023 0.21 0.20 2.12 0.28 99.32 12 103 81 Na20 K2O Ti02 S MnO CO2 1120+ H20- Total n Cr Ni 5 5 12 99.23 3.01 4.07 3.61 341 885 5 99.28 0.44 1.606 0.38 0.19 0.021 0.78 2.28 9.99 9.38 CaO 1.92 6.01 10.41 Mg0 7.41 10.32 1.94 9.89 50.46 3 FeO 2.47 14.04 2 1 Analysis No. Major Components in Weight Percent Trace Elements in Parts per Million CHEMICAL ANALYSES OF HURONIAN VOLCANIC ROCKS - 42 22 11 99.99 0.43 2.16 0.62 0.19 0.06 0.38 1.99 1.27 4.71 5.54 4.21 9.64 2.69 14.3 51.8 4 TABLE 2 6 5 51 — 8 1 99.8 0.38 0.51 0.09 0.04 0.03 0.23 0.75 4.07 3.66 0.94 0.62 2.23 1.08 14.5 70.5 43 9 100.21 0.41 1.80 0.19 0.17 0.07 0.42 2.27 0.95 5.90 4.65 2.73 9.51 4.15 15.3 51.69 5 �I - 12 - Rock names assigned using the Irvine and Baragar (1969) procedure were scrutinized by examination of immobile elements such as Ti, P, Al, Cr, Ni. A triangular diagram of TiO/P9Oç/ AlO proved useful in grouping the volcanic rocks. th Jener cation plot (Jensen, 1976) aided the classification of subalkaline rocks. The Matinenda Formation: The Matinenda Formation is the host of the major uranium deposits of the Elliot Lake area, and is by far the most commercially significant formation of the Huronian Supergroup. The Elliot Lake deposits and enclosing rocks are described by Robertson (1968, 1976), Roscoe (1969), Piennar (1963), Theis (1973), and others. In the Quirke Lake Syncline the Natinenda Formation overlies the volcanic rocks of the Thessalon Formation or, where the Thessalon Formation is absent, it lies on the Early Precambrian basement (Bennett, 1979a). The writer knows of no specific locality, either in outcrop, in mine workings, (personal communication with mine geologists) or from diamond drilling (Leahy, 1973) where rocks of the Matinenda Formation interfinger with the Thessalon volcanics. In at least two localities a regolith is preserved at the top of the Thessalon Formation in the Quirke Lake Syncline. It is the conclusion of the writer that a significant disconformity exists between the Thessalon and overlying Matinenda Formation. This is in contrast to the view held by Bottrill (1971) that the Matinenda Formation and the Huronian volcanics are essentially coeval. A unit of pale grey to yellowish subarkose overlying the Thessalon Formation in the Thessalon area and at one locality in the Sault Ste. Marie area is assigned to the Matinenda Formation by the writer (Bennett, l977a, l977b) In these areas the nature of the contact with the Thessalon Formation could not be determined. The Aweres Formation: A thick sequence of conglomerates and sandstones which overlie the Thessalon Formation in the Sault Ste. Marie area was termed the Aweres Formation by McConnell (1926) The lowermost member of the Aweres Formation is a discontinuous unit of clast-supported, metabasalt conglomerate up to 300 feet (100 meters) thick. Megaclasts �U - 13 - in the metabasalt conglomerate are more than 807 mafic metavolcanics of the Thessalon Formation with scattered megaclasts of grey sandstone from the underlying Livingstone Creek Formation. With increasing stratigraphic height the granitic clasts become more abundant in the conglomerates and the proportion of arkose matrix generally increases. This polymictic conglomerate member passes upward into a mixed conglomerate-sandstone member and finally into a member comprised mainly of arkose, subarkose with some wacke and siltstone as well as subordinate matrix-supported and clast-supported conglomerates. The total thickness of the Aweres Formation may be as much as 6,000 feet (2,000 meters), but this may be an exaggeration since there may have been a considerable primary dip. The correlation of the Aweres Formation has been a problem for some time. McConnell (1927) placed the Aweres Formation at the top of his "Soo Series" which included the Duncan (Thessalon Formation) and the Driving Creek (Livingstone Creek) Formation. The Soo Series was placed by McConnell directly below the Bruce Group (the present Bruce Formation). Hay (1964) considered the Aweres Formation equivalent to the Serpent Formation; and Roscoe (1967) correlated the Aweres Formation in the Mississagi Formation of the Hough Lake Group, and noted the presence of conglomerates resembling the Ramsay Lake Formation. Frarey (1977) tentatively correlated the lower, conglomeratic part of the Aweres Formation with the Ramsay Lake Formation and the sandstone-rich upper part with the Mississagi Formation. In 1977 the writer found, in the Sault Ste. Marie area, conglomerate resembling those of the Aweres Formation overlying yellowish, sericitic sandstone which he correlated with the Matinenda Formation (Bennett, 1976, l977b) The writer favours correlating the Aweres Formation with the Mississagi Formation and the Ramsay Lake Formation. The Aweres Formation appears to represent an alluvial fan complex formed as a clastic wedge at the base of a prominent fault scarp. The coarse, proximal deposits of the Aweres Formation may pass laterally and vertically into the Mississagi Formation. �U -14- I The Hough Lake, Quirke Lake, and Cobalt Groups: Each of these groups contains a repeated litho— logical assemblage which begins with matrix-supported conglomerate followed by mudstone, siltstone or limestone, and completed with the deposition of a thick sandstone sequence (Table 1) (Roscoe, 1967) The conglomeratic sequences (Ramsay Lake, Bruce, and parts of the Gowganda Formation) contain much matrix— supported conglomerate generally held to be glaciogenic. The only limestone in the Huronian is found in the Espanola Formation which is probably of shallow marine origin (Young, 1973) and represents the earliest record of platform sedimentation (Frarey and Roscoe, 1970). The thick cross-bedded arenite sequences (the Mississagi, Serpent and Lorrain Formations) had sources areas on the Archean craton to the north, northwest, and west (McDowell, 1957, Long, 1978, Hadley, 1968) For the most part these formations are fluvial (braided stream) deposits laid down on a great outwash plain (Frarey and Roscoe, 1970, Long, . 1978) A shallow marine or beach environment of deposition has been advocated for parts of the Lorrain Formation (Hadley, 1968, Pettijohn, 1970). It has been pointed out (Piennar, 1963; Roscoe, 1968; Frarey and Roscoe, 1970) that regoliths developed below the Matinenda Formation are depleted in iron, in contrast to more recent soils. Also, rocks of the lower three groups of the Huronian are drab coloured while those of the Cobalt Group, in particular the Lorrain and Gordon Lake Formations, contain reddish and maroon coloured hematite-bearing beds. Pyrite, apparently of detrital origin, is abundant in parts of the Matinenda Formation and is common in the Mississagi Formation but generally lacking in rocks of the Cobalt Group. These features have been interpreted as evidence for a change from essentially reducing atmosphere to an atmosphere containing free oxygen (Frarey and Roscoe, 1970). The large uranium deposits of the Elliot Lake area are considered by most recent workers to be of a placer or modified placer origin. The transportation of uraninite by surface streams is believed to be possible only under reducing atmospheric conditions (Roscoe, 1968). �U -15II A RIFT MODEL FOR HURONIAN SEDIMENTATION By G. Bennett and D. G. Innes The concept of a rift through Lake Huron is not entirely new. Kumarapeli and Saul (1966) postulated a westward extension of the St. Lawrence Valley rift passing along the north shore of Lake Huron to join the Lake Superior rift. Innes (1977) completed a detailed study of the Huronian volcanics in the Sudbury area and proposed that the volcanics were fissure eruptions associated with cratonic rifting. He noted the significance of the alkalic volcanics in the Dollyberry Lake area. The following is a scenario in an attempt to interpret the features of the Elliot Lake Group in an intracratonic rift environment. Early Rifting Stage: The Livingstone Creek Formation is interpreted as being deposited in a graben or graben complex with a conglomeratic sequence along fault scarps and a more distal sandstone facies. A period of relative crustal stability permitted the weathering and reworking of the Livings tone Creek sands to produce an upper quartzarenite member. a. Tectonic uplift, somewhere east of the present Elliot Lake area, bevelled the Livingstone Creek Formation. The upper quartz arenite member was removed east of the Sault Ste. Marie area and the entire sequence was eroded away in the Quirke Lake Syncline. b. Main Rifting Stage: Volcanism begins initially from central vents to provide the icelandite, rhyolite, tholeiitic and mildly alkalic rocks of the lower part of the Thessalon Formation. c. Rifting and volcanism continues with voluminous eruption of subaerial tholeiitic basalt which forms the upper member of the Thessalon Formation. d. A return of uplift east of the present Elliot Lake area causes a bevelling of the Thessalon Formation. The upper tholeiitic volcanic sequence is removed in the Quirke Lake Syncline and the entire formation is eroded further e. east. �U - 16 - f. Thermotectonic subsidence following the cessation of Thessalon volcanic activity results in an influx of sands and quartz and pyrite-rich gravels of the Matinenda Formation in the Elliot Lake area. In the Massey-Sudbury area volcanism is renewed with the extrusion of thick sequences of tholeiitic basalts of the Elsie Mountain and Stobie Formations, and finally the eruption of rhyolites of the Copper Cliff Formation. g. The gabbro-anorthosite complex (Agnew Lake Formation) between Massey and Sudbury were probably emplaced during one of the volcanic episodes. An earlier statement that the intrusive complex was equivalent to the Thessalon Formation and unconformably overlain by the volcanics of the Sudbury area (Bennett and Innes, 1979) did not stand up under further field investigations (our own) (Bennett, 1979) Late Rifting Stage: The end of Huronian volcanic activity is followed by a period of thermotectonic collapse. Some of the subsidence took place along one of the rift boundary faults which was later reactivated as the Murray Fault. The slowly subsiding basin is filled by fine clastic detritius of the McKim Formation. h. i. This elongate zone of subsidence and structurally weakened crust provides the initial trough for sedimentation from the craton. The basin expands laterally under the continuing load of Huronian sediments now represented by the Hough Lake, Quirke Lake, and Cobalt Groups. Perhaps other equally detailed scenarios may be constructed to account for the observed features of the Huronian Supergroup. However, the writers feel that any scheme to explain the origin of the Huronian basin must place emphasis on the rocks of the Elliot Lake Group, since these are the oldest preserved Huronian rocks. The Elliot Lake Group is atypical of Huronian sequences, since the former contains the only volcanic rocks of the Huronian succession. The volcanic suite contains tholeiitic and alkalic rocks typical of rift environments and large gabbro-anorthosite intrusions (or intrusion) with a stratigraphic position similar to that of the Duluth Complex of the Lake Superior Rift System. The Elliot Lake Group does not contain the conglomeratemudstone-arenite cycle of the overlying grQups. There is evidence of significant erosion intervals within the Elliot �I - 17 - Lake Group, and formations of the oldest Huronian group tend to be discontinuous or more variable in lithology and thickness along strike than formations of the overlying groups. Given a Huronian rifting event it is tempting to look upon the Penokean tectonism and magmatic events as the closing stage of a Wilson Cycle. Unfortunately the area south of the Huronian belt is covered by Phanerozoic rocks and it is not possible to choose between an intracratonic and continental marine environment for the bulk of the Huronian Supergroup. �____ U -17a—I LEGEND FOR FIGURE 3 I MIDDLE PRECAMBRIAN L+1 Nipissing Diabase Gabbro, diabase, granophyre HURONIAN SUPERGROUP Hough Lake Group Mississagi Formation E:::::] Subarkose, arkose, pebble conglomerate Elliot Lake Group Matinenda Formation Su1arkose, grit, conglomerate Thessalon Formation Mafic to intermediate metavolcanics Felsic Metavolcanics Livings tone Creek Formation Subarkose, granite-cobble conglomerate EARLY PRECAMBRIAN kU Felsic plutonic rocks S ymb — 01 S Fault (inferred) Strike and dip of bed or flow Anticlinal axis 0:7 Highway with number Secondary road �— (FJ Field Trip Slops Figure 3 + 4. + • + + + o I. - M11c3 J kdonifre Geology and Field Stops Thessalon Area LAKE HLIRON L----- -. • t I __________ C I. I. I. I. I. I_I. L LA- L LILLLL LL I. I. I. I. I. I. LI. LI. I. I. I. I. I. LI. I LI. I. I. I. I. I. I. LLLLLLLLLL I. I. L L I. L LLL I. I. I. I. L LLLL LLI. L L L L LI. LLLL I. LLLL I. I.I.I.LI.LLLLLLLLLL LLI.LLLLLLLLLI I. C - I. - I. I. I. - I. I. I. L I. I. I. I. I. I. I. I. I. I. I. I. I. I. I. ennefl in prepQrcxhorl Irorey1 1977. L, L, LLL lnformgtIL V'-. I. L L Source5 of 'L.) I. I. I. I. I. LC LI.L LLLLLI.LL LI. LI.LI. I. LI. I. I. LLLLLLI.LLLLLLLLLL LI. LI. I. LLLLI.LLI. I. LLLLLLLI.LI.L LI. LL LI. LI. LI LI. I.LLLI.I.I.LLLLI.LL ILL LI. LLL_r.,CI.LLLLLLI.I. I I. i-LI. .1 I. I LI. LI.I.LI.LLLLI.LLLLLI.LCLLL LLI.LI. LI.LLLCLI.LLLLLI.I.I.LLI L C L C L C C I.I. I.LI.LLI.LLLLLLLLI.LL L L L I. I. L = I. C L I. I. I. LI.LLI.I.I.I.I.L I.LLLI.I.LI.LLI.L LLLLLLI.LLLLLLLI- LI LLLLLLLLLL LI.LI. LLLLLLLL LLLLLLI LI.LL LLI.L LLLLLLLI.LI.LLLLLL LI. LI. i-LI. I. CCLI. LI. I. CLI. LLLI. I. I. LI. LI. CLI LI. I. LI.I.I.LL I. LI.LL I. LLL I. LI- I. I. LI. LI.I I.LLLI.LI.LLLLLLI.LI.LL I. L LI. I. LI. LI. LII. I. I. LI. I. LI. LI. I. I. I. I. LLLLLI. LI. LL L LI. I. LILLL-LLLLI.LLL LLI.LLLLI.I. I. LLLLL LI. LI. LI. LLLLI. LI. I. CLI. LLLL LI. CLLI. LLI.LI.I. - LLI.LI.LI.I. LLLLCLI.I.L LLLLL _LLLLL I.LLL - LI. LI. I. LI. LLLLLL LI. L LI. LI. I-I. LI. LI. I. LI. I. LI. LII. I. LL L LLLLLL L I. LLI. LLLL LLLLI.LI.ILL I. I. LI.:ILLCl LLI./LLLLLLLI.LL LLLLLLLI-LI. I. I- LI. I.LI. LLLLL LI. I. I. LI. LI. _I. LLLLLLLLLI.LI I. L C LL LLLL I. L LL I. LI. LLLLLLLLLL LI. LI. LI. LI. LLI. LI. LL I. LI. LI. LI.L LL I. ri-LI. LCI.LCI.LLLLLLL LI. LI. ILL LI. LI. L ti-I. LLI. I. ILL LI.I LI. L!LI. I. I. LI. LI.LLL LI. I.I. LI.LLLI. I. I. L I. I. I. LI. I. C LI. II.L LLL ILL LLLL I.LLLI.LLA L Kirkwood 1 �I - 18 - Description of Stops and Roadlog for the Huronian Supergroup in the Sault Ste. Marie •and Thessalon Areas Time constraints are uncertain. To allow for flexibility some optional stops have been included. Also included are some locations and very brief descriptions for those following the guide at their leisure. DAY 1: HURONIAN STRATIGRAPHY IN THE THESSALON AREA (Figure 3) The mileage count begins at the intersection of Highway 17 and Highway 129 at the town of Thessalon about 80 km (50 miles.) east of Sault Ste. Marie. KM MILES 00 00 Intersection of Highway 129 and Highway 17. at Thessalon. Continue east on Highway 17. Count begins at 0 km. 6.0 3.7 Pine Ridge Road and Highway17 east. right (south) on to Pine Ridge Road. 8.5 1.6 At Lake Huron.Cross causeway on foot to small, rocky island with boat house. This is private property. You should contact Guaranty Trust Realtor, Sault Ste. Marie, Ontario, for permission to enter. Stop 1 - Livingstone Creek Formation. STOP 1 Turn LIVINGSTONE CREEK FORMATION CONGL0RATE The clast-supported conglomerate is pale-grey to white weathering with megaclasts mainly of grey equigranular and porphyritic granitic rocks and subordinate mafic rocks. The maximum clast size is about 70 cm with most in the 5-25 cm range. The sparse matrix is poorly sorted grey a.rkose. A few arkose lenses are crudely cross-bedded. The gradational contact with the basement Early Precambrian granitic rocks is exposed on one of the small islands about .250 m (800 feet) east of here. At that location massive granite gives way to angular blocks of grey granite separated by sandstone. Over a few meters this regolith zone grades into clasts.upported conglomerate (See Robertson and Card, 1972, p.10). Return to vehicle at northwest end of causeway. �U - 19 KM MILES 00 00 STOP 2 - Outcrop west of road - Stop 2. LOWER (MIXED MEMBER) OF THESSALON FORMATION South end of Pine Ridge Road - Rocks here are dark grey-green, fine-grained tholeiitic andesite with areas of epidote alteration up to a meter across. A chemical analysis from near the shore of Lake Huron, about 100 m (300 feet) west of here, indicates the volcanics are tholeiitic andesite with a low TiO content (O.777). Similar volcanics have been ound near the base of the volcanic sequence in the Dollyberry Lake area. • Proceed north on Pine Ridge Road. .8 .5 Pink to redgranite along the road. Note contrast with colour of conglomerate clasts at Stop 1. 1.1 .7 Partly leichen covered outcrop east of road - Stop 3. REGOLITH BELOW LIVINGSTONE CREEK FORMATION STOP 3 The regolith here is a breccia comprised of blocks of grey granite and gneiss separated by fine-grained grey sandstone. The breccia probably formed as sand sifting down through a coarse rubble or talus. The blocks represent bleached equivalent of red and pink granite and gneiss found nearby. The bleaching is generally considered to be due to reduction of ferric iron under the influence of a reducing atmosphere. 1.7 STOP 4 1.1 Low outcrops along road - Stop 4. THESSALON ARKOSE Along east side of road are low outcrops of grey, coarse, poorly sorted arkose of the Thessalon Formation. Similar sandstones are found in the Sault Ste. Marie, Aberdeen Lake, and Dollyberry Lake areas. The Thessalon sandstones are found as thin discontinuous units between the Livingstone Creek Formation and the volcanics, or intercalated with the lowermost flows. �I - 20 KM - MILES The fine—grained volcanics in the area are icelandite in composition. They can usually be recognized by their very dark colour and faint bluish to purplish tint as a result of abundant, very fine biotite. 2.3 1.4 Highway 17 East. Continue north on Pine Ridge Road. 00 00 2.3 1.4 STOP 5 Weir's Farm. Private land. Inquire at farmhouse before continuing - Stop 5. Continue on foot through farm yard to long outcrop ridges in field to the east. Note: if access to farm is not possible the high magnesium tholeiite described below can be seen on the east side of the road about 300 m (1000 feet) south of farm gate. HIGH MAGNESIUM THOLEIITE OF THE THESSALON FM. An average analysis of this flow is given in Table 2. The high magnesium tholeiite is a relatively pale green colour in spite of its basic composition. The mineralogy is predominantly actinolite with subordinate albite. The normative composition suggests it was originally a clinopyroxene-rich basalt. The high magnesium tholeiite contains many irregular coarse-grained areas (pegmatoid patches). A chemical analysis of one of these patches indicates composition similar to a tholeiitic basalt. High magnesium tholeiite (with pegmatoid patches) have been identified in the Dollyberry Lake and Pecors Lake areas; providing evidence for stratigraphic equivalence with the Thessalon Formation (Bennett, in preparation). Continuing eastward to the furthest outcrop ridge. These are icelandites near the base of the Thessalon Formation. See Table 2 for composition. These flows are similar to those of Stop 4. Continuing southeast along farmers trail. �I - 21 MILES - Low outcrops of Livingstone Creek subarkose. The fine-grained, grey, cross-bedded subarkose is typical of the bulk of the Livingstone Creek Formation. South of the stockyard near Thessalon Station the upper part of the Livingstone Creek sandstone is very pale-grey and yellowish grey. Chemical analysis reveals a composition typical of a Huronian regolith (Bennett in preparation). Return to Pine Ridge Road. Outcrop of radioactive Thessalon Formation pyritic conglomerate in a field west of Pine Private land; obtain permission Ridge Road. at house. Here pale-pink and rusty, pyritiferous quartz-feldspar grit and conglomerate is This unit is at or exposed in a low outcrop. near the base of the Thessalon Formation. Note fresh appearance of pink feldspar ?Iphenocrysts?v as clasts in grit and conglomerate. -Assay indicates the radioactivity is due mainly to Very similar thorium (50 ppm, 0.1 lb./ton). radioactive conglomerate occurs at the base of the Thessalon Formation in the Crazy Lake area. Return to Highway 17 via Pine Ridge Road. Proceed west on Highway 17. 00 00 Highway 17 and Pine Ridge Road. 3.19 2.0 Turn off on to road to south. Field with old barn due south of turn-off. This is private Permission to enter may be obtained property. from owner who resides on north side of road just east of turn-off. Low outcrops in field Stop 6. near barn are rhyolite. STOP 6 RHYOLITE OF THESSALON FORMATION This is pink to grey, fine-grained rhyolite with large flattened amygdules filled with quartz and biotite or stilpnomelane. Dark staining is due to local concentration of The rhyolite consists mainly of a pyrite. fine-grained mosaic of albite, k-feldspar and quartz with very minor green pleochroic biotite. h �U - 22 KM - MILES Since this area is located near the crest of an anticlinal structure we are near the base of the Thessalon Formation. A felsic volcanic center was located in this area or perhaps under Lake Huron to the south. 00 00 Return, to Highway 17. 2.6 1.6 Intersection of Highway 129 and Highway 17. Outcrops of tholeiitic basalt are located just north of Highway 17 on Highway 129. Stop 7. STOP 7 Proceed west. THOLEIITIC BASALT OF THESSALON FORMATION The dark green amygdaloidal metabasalt consists mainly of fine albite, chlorite, epidoteclinozoisite, leucoxene, and minor quartz and oxides. The larger amygdules are generally concentrically zoned with quartz-calcite-epidote being a common sequence. Small amygdules are chlorite, quartz, calcite or epidote. This outcrop is located near the top of the Thessalon Formation. 00 .5 00 .3 Continue north on Highway 129. Low outcrop of very pale sandstone on east side of Highway 129 is Matinenda Formation. Stop 8. STOP 8 MATINENDA FORMATION SANDSTONE Fine-grained,pale pink to pale yellowish sandstone displays well developed trough crossbedding and yellow (sericitic) partings between beds. The trough cross-beds and sericite are typical of the Matinenda Formation but the fine-grain size is not. This rock type occurs as a unit up to a few hundred feet thick directly overlying the volcanics. The contact between the two was not observed in this area. Return to junction of Highway 129 and Highway 17. 00 00 Proceed west (turn right) on Highway 17. Outcrops found along the highway for the next five kilometers, with few exceptions, are Nipissing gabbro and part of a large sill which extends as far west as Bruce Mines-. �U -23MILE S 15.6 9.7 Waltonen Road. Continue on Highway 17. Oi.tcrops of Mississagi Formation on both sides of highway. Stop 9. MISSISSAGI FORNATION STOP 9 This is grey to pinkish-grey cross-bedded subarkose of the Mississagi Formation. Pebbly layers are mainly quartz, black chert and very sparse jasper. Very fine pyrite is concentrated in thin, continuous layers along fore-set beds and in the narrow pebble conglomerate layers. With a hand lens it can be seen that the pyrite is largely crystalline in outline while the distribution strongly suggests a detrital origin. Recently Innes and Colvine (1979) have suggested that the Huronian Supergroup is a potential host of base metal and gold deposits of sedimentary origin. Continue west on Highway 17. Town of Bruce Mines. 20 11.4 Junction of Route 561 and Highway 17. Town of Bruce Mines. Bruce Mines is the location of the first known copper deposits in the north shore region. Development work began on the veins in 1846 and production took place intermittently until 1921. Production statistics are incomplete but the grade appears to have been between 3 and 47 copper over five feet. Some orebodies were continuous for a length of over 1800 feet (550 m) The deposits are fissure veins of quartz, carbonate, chalcopyrite and bornite in Nipissing diabase and related granophyre (Frarey, 1977, Knight, 1915) Mineralized quartz vein in diabase outcrop on north side of Highway in Bruce Mines. Stop 10. STOP 10 MINERALIZED QUARTZ VEIN The vein is about 2 m (6 feet) wide but appears to pinch toward the northwest. It may be divided into three zones which are, from east to west, disseminated bornite and chalcopyrite in quartz, chalcopyrite, bornite, chalcocite and quartz: quartz-diabase breccia. The host �U - 24 - rock is Nipissing gabbro and granophyre. Some of the old workings can be seen just north of the highway. Thanks to the efficiency of the Cornish miners who first worked these veins, there is very little high-grade material left at the surface. YOU ARE THEREFORE ASKED NOT TO TAKE SAMPLES OF THIS VEIN. This is the last stop of Day 1 - Continue west on Highway 17 to Sault Ste. Marie. �____ U - 24a - LEGEND FOR FIGURE 4 —I LATE PRECAMBRIAN I I Jacobsville Formation Sandstone, siltstoné, conglomerate MIDDLE PRECAMBRIAN Nipissing Diabase Gabbro, diabase, granophyre r+ HURONIAN SUPERGROUP COBALT GROUP Lorrain Formation Quartzarenite, quartz-pebble conglomerate, arkose Gowganda Formation Paraconglomerate, siltstone, mudstone, arkose HOUGH LAKE GROUP E: Aweres Formation Arkose, subarkose, paraconglomerate, basalt cobble conglomerate, orthoconglomerate ELLIOT LAKE GROUP kI Thessalon Formation Tholeiitic basalt, basaltic andesite, spilite, arkos Li Livings tone Creek Formation Subarkose, granite cobble conglomerate, quartzarenit EARLY PRECAMBRIAN LLL1 Felsic Plutonic Rocks Quartz monzonite, gneissic granite, rnigrnatite ij1I1th Metavolcanic Rocks Mafic metavolcanics, amphibolite SYMBOLS 'w-' — jiuiu.. 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NJ �U - 24c - ISLAND LAKE AREA (FIGURE 4) DAY 2: The mileage log begins at the junction of Highway 556 and Highway 17 in the village of Heyden, about 15 km (10 miles) north of Sault Ste. Marie on Highway 17. KM MILES 00 00 Turn right (east) on Highway 556. 7.4 4.6 Abandoned section of Highway 556 branches off to the right. Turn off onto abandoned The abandoned section is highway and park. washed out about 100 m (100 yards) ahead. Vehicles with very low ground clearance may park a few hundred feet ahead on the right Walk north along old side of the road. highway to washout and from there walk about 500 feet (200 m) through the bush in an easterly to east-southeasterly direction as Ear as theAlgoma Central Railway track. Proceed northeast along the track to outcrops of dark green metabasalts of the Thessalon Stop llA. Formation. STOP hA SPILITES OF THE THESSALON FORMATION Dark green, massive and amygdaloidal spihite of the tholeiitic basalt member is exposed along both sides of the track. Amygdules up to 3 cm across contain quartz, epidote, pink Black chlorite amygdules albite, and calcite. a few millimeters across are characteristic of the mafic rocks of the Thessalon Formation. Amygdaloidal flow tops and flow breccia are found near the southwest end of the outcrop. Thin seams of chalcopyrite occur along fractures and veins of epidote, pink albite, and calcite are common. Primary clinopyroxene are generally presented in the basalts of this area. The soda content is from 3 to over 5 percent. Proceed southwest on the track across a gully which marks a fault between the volcanics and Stop llB. the overlying Aweres Formation. �U - 25 STOP 11B - AWERES FORMATION Clast-supported and matrix-supported conglomerates of the Aweres Formation are exposed in rock-cuts and outcrops along the tracks. The predominant megaclasts are mafic volcanics and granitic rocks with minor subarkose and dark chert in a matrix of coarse, poorly sorted subarkose and subwacke. Bedding planes are poorly defined. Continuing up-section the matrix becomes more abundant and contains many angular, shard-shaped fragments a few centimeters or less in size. A few pyrite nodules up to 12 cm across occur in the upper part of this section. The coarse arkose which makes up much of the upper part of the Aweres Formation is not exposed along the railway track section. A few kilometers south of here in Jarvis and Aweres Townships the conglomerates are found intercalated with coarse, poorly sorted arkose. The writer believes that the Aweres Formation represents a thick clastic wedge deposited along prominent fault scarps. KM MILES Return to Highway 556 either by continuing along the track or proceeding to the right through the bush for a few hundred feet (100 m). Continue east on Highway 556. 9.6 STOP 12 6.0 Rock-cut on the right. Stop 12. GOWGANDA MIXITE AND THESSALON SPILITE This is a good example of matrix-supported conglomerate (mixite) of the Gowganda Formation in fault contact with glomeroporphyritic spilite of the (upper) tholeiite basalt member of the Thessalon Formation. The conglomerate consists of clasts of pink granitic rocks, dark green volcanics and some quartz pebbles in an abundant dark green wacke This type of conglomerate is generally matrix. considered a tillite. �I - 26 - Using Irvine and BaragarTs (1971) procedure, the glomerophyritic volcanic would be classified as hawaiite, as would many of the upper tholeiitic basalts. The low Ti02 (0.7), low P205 content (0.077), and cromium content (110 ppm) shows that it is not. It is a spilite with over 4.87 total alkalis. The mineralogy is clinopyroxene, albite, chlorite, actinolite, epidote, and leucoxene. Turn round and proceed west for about 5 km (3 miles) on Highway 556 to the junction with Highway 552. Park near railway track on Highway 552 and locate a bush road on west side of Highway 552 near railway track. Continue on the bush road or trail which continues west and then turns north, up the A few hill for about 500 m (1500 feet) outcrops of brecciated granitic rocks and a small, low outcrop of fine-grained, red Keweenawan felsite dike is exposed on the One of the mineralized exploration trail. trenches of the Nystedt copper prospect is found near the trail near the crest of the . hill. Stop 13. NYSTEDT COPPER PROSPECT STOP 13 - Chalcopyrite occurs as seams, disseminated grains and massive patches in pink quartz syenite and breccia. Veinlets and disseminated grains of specular hematite are common in the surrounding rocks. This is one of four known major surface showings in the immediate area; a fifth occurs just east of Highway 552. Kennco Explorations (Canada) Ltd. optioned the property in 1965-66, and carried out a diamond drilling program. Assays from one diamond drill hole returned 0.78 copper over 95.3 feet. The copper deposits are set in pink syenite and chloritic granite-breccia consisting of fragments of gneissic and massive granite in a matrix of quartz, chlorite and feldspar. The granite breccia extends to the east of Highway 552 and there is well exposed in rock-cuts along the highway. Return to Sault Ste. Marie. �U - 27 - HURONIAN STRATIGRAPHY EAST OF SAULT STE. MARIE DAY 2 (Figure 1) Proceed east from Sault Ste. Marie on Highway 17 to the town of Echo Bay, a distance of about 25 km (15 miles). Turn left on Highway 638 in Echo Bay. 00 00 Town of Echo Bay. 1.1 1.3 Highway 638 East to Leeburn - 6.5 4.2 Outcrop on south side of highway. One to twofoot (.5 m) quartz-specular hematite vein in white, pale yellow medium-grained quartzarenite of the Lorrain Formation. 10.9 6.8 McCarroll Lake Road - Continue on Highway 638. 11.8 7.4 High rock-cut along both sides of road. turn left. Stop 14. GORDON LAKE FORNATION STOP 14 The rocks here are from the transition zone between the Gordon Lake Formation and the underlying Lorrain Formation. Rocks are pink to white fine-grained, well sorted silicious subarkose to quartzarenite with well developed cross-beds.. Ripple marks and slickensides are found on some partings. Sandstone sequence contains a narrow unit of laminated ferruginous siltstone with green (sericitic) partings. An east-west trending, 1 to 2-foot wide (30-60 cm) hematitic shear zone with wide flanking bleached zones is located near the east end of outcrop. 7.2 10.7 Gordon Lake Road - Continue on 638, left turn. 23.6 14.7 Bass Lake Road - Continue on 638. 24.4 15.1 Village of Leeburn.. 49.7 30.9 Center Line Road - Continue on 638, turn left. 31.8 19.8 Poplar Dale Road - 32.4 20.1 Route 638 - Continue on 638, turn left. MacKay Road - turn turn right on 638. left onto MacKay Road. �I - 28 ai MILES 34.3 21.3 STOP 15 - Proceed about 100 yards (100 m) north on MacKay Road to abandoned farm house on the Harnden farm. This is private property. Obtain permission to enter from resident of house east of Harnden farm. Proceed northwest on foot to pale grey outcrops on hill west of farm house. The outcrops on the north slope of the hill are outcrops of Mississagi Formation. Stop 15. MISSISSAGI, BRUCE, ESPANOLA, AND SERPENT FORMATIONS Pale grey subarkose of the Mississagi Formation display well developed cross-bedding with cosets about a meter thick. These exposures are typical of the upper half of the Mississagi Formation. The lower half of the formation is generally finer-grained, darker grey and approaches a subwacke in composition. A few hundred feet (less than 100 m) to the south is grey weathering, matrix-supported conglomerate of the Bruce Formation. The predominant clasts are granite, mafic metavolcanics, and quartz in an abundant, dark, quartz wacke matrix. This is the second of the extensive mixite units in the Huronian and like the Ramsay Lake and Gowganda mixites is generally considered to be a tillite. Further to the southwest the Espanola Formation is exposed. The Espanola Formation consists of three members: The Bruce limestone, the Espanola siltstone member, and the Espanola dolomite member. Only the Bruce limestone member is exposed here. The Bruce limestone member consists of alternating thin layers of pale grey, white or pink limestone and dark grey argillite and siltstone. The Bruce lime-. stone is generally highly deformed. Some discussion has arisen over whether or not the tight folding is tectonic or syndepositional (Young, 1973a, Frarey, 1977) The distinctive appearance and composition of the Espanola Formation along with its widespread distribution makes the Espanola Formation the most useful stratigraphic marker in the Huronian Supergroup. The Espanola Formation is overlain by the Serpent Formation, the lowermost part of which is exposed on a south-facing steep slope just �I - 29 KM - MILES south of the Espanola Formation outcrops. In this area the lowermost part of the Serpent Formation consists of a thin unit of tightly packed polymictic conglomerate with well rounded cobbles of granite, maic igneous rocks and small fragments of Bruce limestone (Frarey, 1977). Continuing to the south one, comes upon exposures of pale pink, mediurn-grained, well sorted, massive subarkose, which makes up most of the Frarey (1977) gives the Serpent Formation. composition of the subarkose at this location asquartz (807), plagioclase (20%) with traces of chlorite, zircon, tourmaline or hornblende and opaques. 000 000 Return to intersection of Highway 638 and 561. Turn left (south) on 561. 1.1 0.7 Polymictic matrix-supported conglomerate of the Gowganda Formation is exposed on both sides of road. 2.0 STOP 16 1.2 Large outcrop ridge west of road. Stop 16. GOWGANDA FORMATION Near the road thin beds of fine-grained, pink weathering sandstone are interbedded with dark green mudstone and siltstone. The sandstone beds have undergone considerable deformation and disruption which appears to have been the result of syndepositional slumping. A mixite0unit striking about 150° and dipping The about 45 south overlies the mudstone. mixite consists of rounded to angular clasts of granitic rocks up to over a meter (3 feet) long in an abundant dark green, wacke matrix. Just above the mixite unit, mudstone and siltstone contains large, well rounded balls of pink weathering sandstone producing an ttintraformational mixite". A 10-meter 30 feet) wide Nipissing type diabase strikes 140 near the crest of the outcrop. The features and relationships displayed in this exposure are typical of much of the middle part of the Gowganda Formation in the Sault Ste. Marie area. �U - 30 KM MILES Continue south on Highway 561. 7.4 4.6 The rocky, hill ½ to 1 mile to the west of the road reveal four of the six members of The most distant hill the Lorrain Formation. consists of the upper white quartzite member, the pinkish summit of the nearest hill is part of the upper red quartzite member; this is underlain by the jasper conglomerate member (white from a distance) which is in turn underlain by the, mostly tree covered, lower red quartzite member. The remaining purple siltstone and basal arkose members are further to the north but cannot be distinguished from this point. Mount Zion Road - Cotinue on Route 561. 8.1 5.0 Outcrops of jasper conglomerate. Stop 17. JASPER CONGLOMERATE OF THE LORRAIN FORMATION STOP 17 The jasper conglomerate (known locally as "puddingstone") is probably the most distinctive and attractive rock in the north shore area. It consists of rounded to angular pebbles up to 7 cm (3 inches) of quartz and abundant vancoloured Jasper. The jasper conglomerate and intercalated white quartzarenite units make up the jasper conglomerate member of the Lorrain This member is up to 200 m (600 feet) Formation. thick (Frarey, 1977). 8.5 5.3 Large, high outcrop area to the right (west) of Stop 18. Upper red quartzite. the road. UPPER RED QUARTZITE OF THE LORRAIN FORMATION STOP 18 The outcrop consists mainly of well cross-bedded, poorly sorted, reddish quartzarenite, with thin pebble conglomerate interbeds. The red colouring Thin seams of detnital is due to fine hematite. grey hematite can be seen along fore-set beds and within continuous layers of quartz and jasper The upper red quartzite pebble conglomerate. member varies from 260 m (850 feet) to as much as 20 m (1700 feet) (Frarey, 1977) Continue south on Highway 561. 9.5 5.9 Outcrop of white quartzite Ledyit Line Road. on west side of road. Stop 19. �I - 31 KM - I MILES STOP 19 UPPER WHITE QUARTZITE MEMBER OF LORRAIN FORMATION The outcrop consists mainly of white, to pink, medium-to-coarse-grained quartzarenite with scattered pebble layers. This is the uppermost and thickest member of the Lorrain Formation. It is the thickest member, about 740 m (2400 feet) (Frarey, 1977). — 12.8 7.8 Village of Rydal Bank. 00 00 Highway 561 turns left. Plurnmer road straight ahead. Proceed on Plunimer Road. 3.8 2.4 Plummer Road and West Road. Outcrops of Gordon Lake Formation on west side of West Road about 100 m (100 yards) north of junction. Stop 20. STOP 20 GORDON LAKE FORMATION Thinly bedded and laminated, fine-grained sandstone, siltstone, mudstone and chert are exposed here. Frarey (1977) suggests that some chert may be the result of the diagenetic replacement of siltstone. Curving, and branching mud cracks in mudstone beds are filled with fine sandstone. The Gordon Lake Formation contains sedimentary structures indicative of a stable, low energy environment, probably nearshore marine to littoral or in part lagoonal (Frarey, 1977). See Wood (1973) for a discussion of the depositional environment of the Gordon Lake Formation. Proceed northwest on Plummer Road. 7.2 4.5 Center Line Road. 8.3 5.2 Outcrops of white quartzite to the right (north). Continue to top of hill and park. Stop 21. Continue on Plununer Road. BAR RIVER FORMATION STOP 21 Almost all of the Bar River Formation consists of thick bedded, white quartzarenite similar in most aspects to the upper white quartzite of the Lorrain Formation. The rocks here are white to pale yellow quartzarenite with little visible structure. 00 00 Return to Center Line Road via Plunimer Road. Turn right (south on Center Line Road). �• U-s 3 t —— I * I 500 2000 Alteration feet (000 metres 3000 — a rknse • bjacke — GOUCAIIDA FOR1IAT!ON I is tone, conglomerate. EIIT1 titnia tutu' • ci Arkose, quartzite, conglomerate IIURONIA'4 SUPERGLOUP JORRA III FOROATION breccia LEGEND McGreQ 561 /'Highway 4 Radicactive occurrence NIFISSIN(; F ROTE ROZO IC JJj Gahbro, granophyre; diabase dikes 1000 4 't%%, >'—i N p Pyrite occurrence —Geological Sketch Map ol (lie McGregor Road Breccia Zone. FIGURE 5 //// I Fault (defined, inferred) SYMBOLS ::::::::::::::::.,j,,a!I ::::::::::::::::::::::::::::::::::::::: •.::c•:•:': aaaa r1 p fl �I - 32 KM - MILES Turn left (east) on Government 5.4 3.4 Government Road. 00 00 Road. 1.7 00 1.1 00 Caribou Road. 3.7 2.3 Outcrop on left (east side of road is sulfide stained outcrop of McGregor Road breccia. Fragments of Lorrain Formation arkose and quartzarenite are set in a quartz and pyrite Sulfide-rich samples gave values of matrix. 0.20 and 0.34 ounces of silver /ton). 3.8 2.4 This is private Tractor road to the right (west). Inquire at farmhouse directly east of here land. Outcrop area is located for permission to enter. about 100 m (100 yards) west of Caribou Road. (Stop 22, McGregor Road Breccia). STOP 22 Turn right (south) on Caribou Road. McGREGOR ROAD BRECCIA The McGregor Road breccia (Figure 5) is emplaced along the south side of a down-dropped fault block of basal arkose of the Lorrain Formation. The surrounding rocks are part of the Gowganda The breccia consists mainly of Formation. angular to rounded fragments of Gowgands siltstone and mudstone, and arkose, quartzarenite and jaspe.r conglomerate of overlying members of the Lorrain Formation. Fragments of jasper conglomerate are about 1000 m (3000 feet) below their stratiAlthough in places the breccia graphic position. is polymictic, there are localities where the predominant clast lithology varies (from south to north) in a manner corresponding to their original position in the Huronian stratigraphy. Near the west end of the breccia fractured Gowganda argillite is altered to a locally pyritic, hard, pink rock approaching pure albite Small radioactive occurrences in composition. (up to 10 times background) occur in the breccia. The breccia may be a fissure diatreme formed as a result of explosive degassing of magma along Alternatively, the breccia may be the a fault. result of fracturing and spalling along a dilatent zone formed along the down dropped fault block. �I - 33 KM MILES - Just north of the tractor road a Nipissing type diabase dike intrudes breccia consisting of arkose and quartzarenite of the Lorrain Formation along with brown weathering, dark green fragments of diabase. Continuing north the breccia is comprised mainly of fragments, blocks and fractured slabs of Lorrain quartzite. Continuing for about 200-300 m (yards) north and west are outcrops of pink, locally pyritic albitized, laminated mudstone of the Gowganda Formation. Continue south on Caribou Road to the Town of Bruce Mines. Turn right (west) on Highway 17. 00 00 Bruce Nines. 12.3 7.6 Village of Desbarats - Large pink outcrops of basal arkose of the Lorrain Formation just east Stop 23. of the village. BASAL ARKOSE MEMBER OF THE LORRAIN FOPNATION STOP 23 The basal arkose member is up to 500 m (1700) feet thick (Frarey, 1977). In Desbarats well sorted pink arkose of this member are exposed The dark spots in rock-cuts along Highway 17. commonly found in this member are due to fine hematite. Disseminated chalcopyrite and pyrite mineralization occurs in this member about 3 km (2 miles) northThe mineralization may be west of Desbarats. syngenetic but Pearson (1979) suggests a diagenetic origin. 13.3 STOP 24 8.6 Dark red to maroon outcrops of the purple siltstone member of the Lorrain Formation are exposed along the highway. Stop 24. PURPLE SILTSTONE MEMBER OF THE LORRAIN FORMATION This unit is a thick bedded, massive, fine-grained arkose and, silts tone with a hematitic matrix. It appears to be a relatively local, true red bed, and is evidence for an oxygen bearing (The unit is atmosphere during its deposition. about 30 m (100 feet) thick (Frarey, 1977). �U - 34 KM MILES 15.3 9.5 - I "Ripple Rock". Thinly bedded arkosic sandstone of the Lorrain Formation displays excellent examples of asymmetrical ripple marks. This outcrop is a designated historical site and should not be defaced. End of Field Trip - Return to Sault Ste. Marie. i �I - 35 - SELECTED BIBLIOGRAPHY OF THE HURONIAN ROCKS OF THE SAULT STE. MARIE AREA Bennett, G. 1977a: Huronian Volcanism, District of Algoma and Sudbury; pp. 102-103, in Summary of Fieldwork, 1977, by the Geological Branch, edited by V.G. Milne, 0. L. White, R. B. Barlow, and J. A. Robertson; Ontario Geological Survey Misc. Paper 75, 208p. *Bennett, G. 1978: Huronian Volcanism, Districts of Algoma and Sudbury, pp. 105-111, in Summary of Fieldwork, 1978, by the Ontario Geological Survey, edited by V. G. Milne, 0. L. White, R. B. Barlow, and J. A. Robertson; Ontario Geological Survey Misc. Paper 82, 235p. Bennett, G. l979a: Huronian Volcanism, Districts of Algoma and Sudbury; pp. 84-85, in Summary of Fieldwork, 1979, by the Ontario GeologicalSurvey, edited by V. G. Milne, 0. L. White, R. B. Barlow, and C. R. Kustra; Ontario Geological Survey Misc. Paper 90, 245p. Bennett, G. 1979b: The McGregor Road Breccia Zone, District of Algoma; pp.82-83, in Summary of Fieldwork, 1979, by the Ontario Geological Survey, edited by V. C. Mime, 0. L. White, R. B. Barlow, and C. R. Kustra; Ontario Geological Survey Misc. Paper 90, 245p. Bennett, G. 1979c: Geology of the Two horse Lake Area, District of Algoma; Ontario Geological Survey Open File Report 5277, 99p. with uncoloured geological map at 1 inch to ¼ mile. Bennett, G., Hillier, R.D., Nentwich, F., Dupuis, C,P.. and Pucovsky, M. 1975: Jarvis Lake—Garden River Area, District of Algoma; Ontario Div. Mines, Prelim. Map. Pp. 1064, Geol. Ser., scale 1 inch to ¼ mile or 1:15,840. *Bennett, G., Sawitsky, E., and Whittaker, P. 1976: Jarvis Lake-Duncan Township Area, District of Algoma; Ontario Div. Mines, Prelim. Map P1190, Geol. Ser., scale 1:15,840. Bennett, G., and Sawiuk, M. 1979: Jarvis Lake-Garden River Area, Southern Part, District of Algoma; Ontario Geological Survey, Prelim. Map P2241, Geol. Ser., scale 1:15,840. *See Addenda, page 42. �U - 36 - Bottrill, T.J. 1970: Geology and genesis of uranium deposits in the Huronian and associated geology, Blind River, Sudbury, and Gowganda areas, Ontario, (41 I, J, 0, F); in Report of Activities, Part A: April to October, 1969, pp. 57, 58; Geol. Surv. Can., Paper 70—i, pt. A, 25lp. Bottrill, T.J. 1971: Uraniferous conglomerates of the Canadian Shield; PP. 77-83,. in Report of Activities, Part A, Geol. Surv. Canada Paper 71-7; (R.G. Blackadar, editor), 259p. Card, K.D., Church, W.R., Franklin, J.M., Robertson, J.A., West, G.F., and Young, G.M. 1972: The Southern Province; PP. 336-379, in Variation in Tectonic Styles in Canada; edited by R. A. Price and J. W. Douglas, G.A.C. Special Paper No. 11, 688p. Card, K.D., and Pattison, E.F. 1973: Nipissing Diabase of the Southern Province, Ontario; in Huronian Stratigraphy and Sedimentation, pp. 7-37, edited by G. I. Young; Geol. Assoc. Canada Special Paper No. 12, 27 lp. Casshyap, S.M. 1969: Petrology of the Bruce and Cowganda Formations and its Bearing on the Evolution of Huronian Sedimentation in the Espanola-Willisville Area, Ontario (Canada); Palaeography, Palaeoclimatology, Palaeoecology, 6 (1969), PP. 5-36. Casshyap, S.M. 1971: Petrology and Sedimentation of Huronian Arenites, south of Espanola, Ontario; Can. J. Earth Sci., V. 8, pp. 20-49. Chandler, F.W. 1973: Geology of McMahon and Morin Townships, District of Algoma, Ontario Div. Mines CR112, 77p; accompanied by Map 2272, scale 1 inch to ½ mile. Chandler, F.W. 1976: Geology of the Saunders Lake Area, District of Algoma; Ontario Div. Mines CR155, 46p.; accompanied by Map 2331, scale 1 inch to ½ mile (1:31,680). Chandler, F.W., Young, G.M., and Wood, J. 1969: Diaspore in Early Proterozoic Quartzites (Lorrain Formation) of Ontario; Can. J. Earth Sci., v; 6, pp. 337-340. Church, W.R. 1971: The Nature and Evolution of Proterozoic and Phanerozoic Orogenic Belts; Abstract, Geol. Assoc. Canada, Mineral Assoc. Canada, Abstracts and Program, Sudbury, pp. 14-15. �I - 37 - Collins, W.H. 1925: North Shore of Lake Huron; Geol. Surv. Canada Mem. 143, l86p. Douglas, R.J.W. 1980: Proposals for Time Classification and Correlation of Precambrian Rocks and Events in Canada and Adjacent Areas of the Canadian Shield. Part 2: A Provisional Standard for Correlating Precambrian Rocks; Geol. Surv. Canada, Paper 80-24, l9p. Frarey, M.J. 1967: Three New Huronian Formational Names; Geol. Surv. Canada Paper 67-6, 3p. Frarey, M.J. 1977: Geology of the Huronian Belt Between Sault Ste. Marie and Blind River, Ontario; Geol. Surv. Canada Memoir 383, 87p., with four geological maps at a scale of 1:50,000. Frarey, M.J., and Roscoe, S.M. 1970: The Huronian Supergroup North of Lake Huron; in Synposium on Basin and Geosynclines of the Canadian Shield; A. J. Baer, ed., Geol. Surv. Can. Paper 70-40, pp. 143-158. Gay, A.L., and Grandstaff, D.F. 1980: Chemistry and Mineralogy of Precambrian Paleosols at Elliot Lake, Ontario, Canada; Precambrian Research, Vol. 12, No. 1-4, pp. 349-373. Giblin, P.E., Leahy, E.J., and Robertson, J.A. 1979: Sault Ste. Marie-Elliot Lake Sheet, Algoma, Manitoulin and Sudbury Districts; Ont. Dept. Mines Compilation Series, Map 2419, scale 1 inch to 4 miles (1:253,440). Original compilation by Compilation 1974-76. P. E. Giblin and E. J. Leahy, 1964, Map 2108, 1967. Grandstaff, D.E. 1980: Origin of Uraniferous Conglomerates at Elliot Lake, Canada, and Witwatersrand, South Implications for Oxygen in the Precambrian Africa: Atmosphere; Precambrian Research, Vol. 13, No. 1, pp. 1-26. Sedimentology of the Huronian Lorrain Hadley, D.G. 1968: Formation, Ontario and Quebec, Canada; Unpub. Ph.D. Thesis, Johns Hopkins University, Baltimore, Maryland, 3Olp. Sault Ste. Marie, Dist. of Algoma; Geol. Hay, R.E. 1961: Surv. Can., Map 26-l96l,scale 1 inch to 1 mile. The Geology of the Sault Ste. Marie Map Hay, R.E. 1963: Area; unpublished Ph.D. Thesis, McGill University, 325p. �I - 38 - Hughes, C.J. 1972: Spilites, Keratophyres and the Igneous Spectrum; Geol. Mag. Vol. 199, PP. 513-527. Innes, D.G. l972 Proterozoic Volcanism and Associated Suiphide Bearing Metasediments in the Sudbury Area, Ontario; unpublished B.Sc. Thesis, Laurentian University, 65p. Innes, D.G. 1977: Proterozoic Volcanism in the Southern Province of the Canadian Shield; unpublished M.Sc. Thesis, School of Graduate Studies, Laurentian University (Sudbury, Ontario), l5Op. Irvine, T.N., and Baragar, W.R.A. 1971: A Guide to the Chemical Classification of Common Volcanic Rocks; Canadian Jour. Earth Sci. Vol. 27, pp. 179-203. Jensen, L.S. 1976: A New Cation Plot for Classifying Subalkaline Volcanic Rocks; Ont. Div. Mines, Misc. Paper 66, 22p. Kimberly, M.M., Tanaka, R.T., and Farr, M.R. 1980: Composition of Middle Precambrian Uraniferous Conglomerates in the Elliot Lake-Agnew Lake Area of Canada; Precambrian Research, Vol. 12, No. 1-4, pp. 375-392. Knight, C.J. 1966: A Study of Rb-Sr Whole-Rock Ages of Volcanics on the North Shore of Lake Huron, Ontario, Canada; M.I.T.-138l-l4, Fourteenth Ann. Rep. (1966), U.S. At. Energy Comm. Contract AT (3O-l)-l38l, pp. 129-139. Knight, C.W. 1915: The North Shore of Lake Huron; Ont. Bur. of Mines Ann. Rept., Vol. 24, Pt. 1, 1915, pp. 216-241. Kumarapeli, P.S., and Saul, V.A. 1966: The St. Lawrence Rift Valley System: A North American Equivalent of the East African Rift Valley System; Can. Jour. Earth Sci., Vol. 3, pp. 639-658. Leahy, E.J. 1973: Diamond Drilling in the Huronian Supergroup, Sault Ste. Marie-Elliot Lake Area; Ont. Div. Mines, Geol. Br. Open File Report 5093. Lindsay, D.A. 1967: The Sedimentology of the Huronian Gowganda Formation, Ontario, Canada (With Special Reference to the Whitefish Falls Area); unpub. Ph.D. Thesis, The Johns Hopkins University, Baltimore, Maryland, 295p. �U - 39 - Lindsay, D.A. 1969: Glacial Sedimentology of the Precambrian Gowganda Formation, Ontario, Canada; Geol. Soc. America Bull., Vol. 80, PP. 1625-1702. Long, D.G.F. 1976: The Stratigraphy and Sedimentology of the Huronian (Lower Aphebian) Mississagi and Serpent Formations; unpublished Ph.D. Thesis, University of Western Ontario, 29lp. Long, D.G.F. 1978: Deposition Environments of a Thick Proterozoic Sandstone: The (Huronian) Mississagi Formation of Ontario, Canada; Canadian Jour. Earth Sci., Vol. 15, No. 2, pp. 190-206. McConnell, R.G. 1926: Sault Ste. Marie Area, District of Algoma; Ont. Dept. Mines, Vol. 35, Pt. 2, pp. 1-52 (Published 1927). Accompanied by Map 35a, scale 1 inch to 2 miles. McDowell, J.P. 1957: The Sedimentary Petrology of the Mississagi Quartzite in the Blind River Area. Ont. Dept. Nines, Geol. Circ. No. 6, 3lp. McLennan, S.M., Fryer, B.J., and Young, G.M. 1979: The Geochemistry of the Carbonate-Rich Espanola Formation (Huronian) with Emphasis of the Rare Earth Elements; Canadian Jour. Earth Sci., Vol. 16, No. 2, pp. 230-239. Moore, E.S. 1929: Ore Deposits near the North Shore of Lake Huron; Ont. Dept. of Mines, Vol. 38, Pt. 7, (published in 1930). Ovenshine, A.T. 1964: Glacial Interpretation of the Precambrian Gowganda Formation, North Shore of Lake Huron, Canada; Geol. Soc. Am., Abstr. (ann. mtg.), pp. 146. - Palonen, P.A. 1973: Paleogeography of the Mississagi Formation and Lower Huronian Cyclicity; in Huronian Stratigraphy and Sedimentation, ed. G. M. Young; Geol. Assoc. Canada, Spec. Paper 12, Pp. 157-168. Parviainen, E.A.U. 1973: The Sedimentology of the Huronian Ramsay Lake and Bruce Formations, North Shore of Lake Huron; unpublished Ph.D. Thesis, University of Western Ontario, London, Ontario. Pearson, W.N. 1978: Copper Netallogeny, Lake Huron, Ontario; Current Research, Part A, Geol. Surv. Canada, Paper 78-lA, pp. 263-268. �U - 40 - Pearson, W.N. 1979: Copper Metallogeny, North Shore Lake Huron, Ontario; Geol. Surv. Canada, Paper 79-lA, Current Research, pp. 289-304. of Pettijohn, F.J. 1957a: Paleocurrents of Lake Superior Precambrian Quartzites; Geol. Soc. Am., Bull., v. 68, pp. 469-480. Pettijohn, F.J. 1970: The Canadian Shield: A Status Report, 1970 (and discussion); in Symposium on Basins and Geosynclines of the Canadian Shield, ed. A. J. Baer, pp. 239-255, 262-265; Geol. Surv. Can., Paper 70-40, 265p. Pienaar, P.J. 1963: Stratigraphy, Petrography and Genesis of the Elliot Group, Blind River, Ontario, including the Uraniferous Conglomerate; Geol. Surv. Can., Bull. 83, l4Op. Robertson, J.A. 1963: Geology of the Iron Bridge Area; District of Algoma; Ont. Dept. Mines Geol. Rept. No. 17, 69p. Robertson, J.A. 1968: Geology of Township 149 and Township 150, District of Algoma; Ont. Dept. Mines Geol. Rept. 57, l62p. Accompanied by Maps 2113 and 2114, at a scale of 1 inch to mile. Robertson, J.A. 1976: The Blind River Uranium Deposits: The Ores and their Setting; Ontario Div. Mines, M.P. 65, 4Sp. Robertson, J.A., Frarey, M.J., and Card, K.D. 1969: The Federal-Provincial Committee on Huronian Stratigraphy: Progress Report; Ontario Dept. Mines and Northern Affairs, MP31, 26p. Robertson, J.A., and Card, lCD. 1972: Geology and Scenery, North Shore of Lake Huron; Ont. Mm. Nat. Resour., Geol. Guidebook No. 4, 224p. Roscoe, S.M. 1969: Huronian Rocks and Uraniferous Conglomerates; Geol. Surv. Can., Paper 68-40, 205p. Rupert, R.J., Leahy, E.J., and Mirza, 5. 1972: Subsurface Stratigraphy, Blind River-Elliot Lake Sheet, Dist. of Algoma; Ont. Div. Mines, Geol. Compil. Ser., Prelim. Map 753. Sims, P.1K., Card, K.D., Morey, G.B., and Peterman, Z.E. 1980: The Great Lakes Tectonic Zone: A Major Crustal Structure in Central North America; Geol. Soc. Am. Bull., Pt. 1, Vol. 91, pp. 690-698. h �U - 41 Syrnons, D.T.A., Wander and Volcanics; No. 7, pp. - and OtLeary, R.J. 1978: Huronian Paleomagnetism of the Thessalon Canadian Journal Earth Sci., Vol. 15, 1141-1150. Van Schmus, W.R. 1965: The Geochronology of the Blind River-Bruce Mines Area, Ontario; J. Geol., v. 73, pp. 755-780. Van Schmus, W.R. 1976: Early and Middle Proterozoic History of the Great Lakes Area, North America; Royal Soc. London, Phil. Trans., Ser. A., v. 280, pp. 605-628. Wood, J. 1970: Evidence for a Tropical Climate and Oxygenic Atmosphere in Upper Huronian Rocks of the Rawhide Lake-Flack Lake Area, Ontario (abstr.); in 16th ann. mtg. Inst. on Lake Superior Geol. program (Thunder Bay, Ont.), pp. 45, 46. Wood, J. 1973: Stratigraphy and Depositional Environments of Upper Huronian Rocks of the Rawhide Lake-Flack Lake Area, Ontario; Geol. Assoc. Canada Spec. Paper No. 12, pp. 73-95, edited by G.M. Young. Young, G.M. 1969: Geochemistry of Early Proterozoic Tillites and Argillites of the Gowganda Formation, Ontario, Canada; Geochim. Cosmochim. Acta, v. 33, pp. 483-492. Young, G.M. 1971: Stratigraphic and Sedimentological Framework of the Huronian Rocks of the Southern Province of the Canadian Shield; Abstract, Geol. Assoc. Canada, Mineral Assoc. Canada, Abstracts and Program, Sudbury, 1971, pp. 75-76. Young, G.M. l973a: Origin of Carbonate-Rich Early Proterozoic Espanola Formation, Ontario, Canada; Geol. Soc. Am., Bull., v. 84, pp. 135-160. Young, G.M., and Chandler, F.W. 1968: Possible Glacial Origin for Three Precambrian (Huronian) Conglomerates, North Shore of Lake Huron (abstr.); in 14th ann. mtg. Inst. on Lake Superior Geol. programSuperior, Wis.), pp. 42, 43. �U - 42 - ADDENDA: Bennett, C. 1977b: Garden River Indian Reserve Area, District of Algoma; pp. 104-106, in Summary of Fieldwork, 1977, by the Geological Branch, edited by V.G. Mime, O.L. White, R.B. Barlow, and J.A. Robertson, Ontario Geological Survey Misc. Paper 75, 208p. Bennett, C., and Innes, D.C. 1979: Huronian Volcanic Rocks, North Shore of Lake Huron, Ontario; 25th Annual Institute on Lake Superior Geology, Duluth, Minnesota, pp. 8. Bennett, C., and Innes, D.G. (in preparation): Huronian Volcanism, Ontario Geological Survey, Geological Report. � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1981 Description An account of the resource Institute on Lake Superior Geology. Michigan State University, East Lansing, Michigan. May 14-15, 1981. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1981 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English Contributor An entity responsible for making contributions to the resource H. All K. Attoh R. L. Bauer H. F. Bennett M. E. Bengtson D. Bhattacharyya M. S. Breithart B. A. Brown F. W. Cambray F. H. Carlson A. Choudhry C. Craddock M. D. Daggett P. A. Daniels, Jr. S. Day M. F. Deering D. Dushek C. P. Ervin K. Fujita H. P. Gilbert S. S. Goldich J. K. Greenberg H. C. Halls J. B. Hartung T.B. HoIst J. H. Karl R. P. Meyer E. T. Mohr C. W. Montgomery R. L. Morton M. Osterberg D. S. Paddock Z. E. Peterman P. K. Sims T. E. Smith F. L. Slaughter R.J. Stevenato M. Stupavsky D. T. A. Symons, S. E. Tituskin F. B. Van Houten M. A. Vos P. Wasuwanich J. T. Wilband https://digitalcollections.lakeheadu.ca/files/original/f1d5e221c5cffdc5a211c58e555219cd.pdf b5e94ac35469c5f8f9aa1d6ea0771619 PDF Text Text rn V I CD -I Twenty- Eighth I r C') C a) Annual C) CD -' C a) 0 CD IC —U , I Cl) Institute , on Lake Superior 1< 03 ts) (0 -S 03 (31 a I (a CD 0 0 Geology w 0 Cl) CD -< -' Survey C ano- a I''I CD S. Sponsored by Minnesota Geological CD 5 a I = CD 5- a) May 5 - 8 , 1982 International Falls, Minnesota �PROCEEDINGS PROCEEDINGS S ANNUAL TWENTY - E I G H T H ANNUAL TWENTY-EIGHTH INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIOR INSTITUTE GEOLOGY GEOLOGY S held held at at HOLIDAY INN INN NOLIDAY Highways Highways 11 1 1 and and 71 71 International Falls, Falls, Minnesota Minnesota 56649 56649 International I May May 5—8, 5-8, 1982 1982 under under the the sponsorship sponsorshipof of I Minnesota Minnesota Geological Geological Survey Survey University of of Minnesota Minnesota University 1633 1633 Eustis Eustis Street Street St. St. Paul, Paul, Minnesota Minnesota 55108 55108 G.B. G.B. Morey Morey and and John John Splettstoesser Splettstoesser I General General Editors Editors I �I TABLE TABLE OF OFCONTENTS CONTENTS p v V GENERAL GENERAL INFORMATION INFORMATION vv INSTITUTE INSTITUTEBOARD BOARD OF OFDIRECTORS DIRECTORS LOCAL LOCALCOMMITTEE COMMITTEE VI VI GOLDICH GOLDICHMEDAL MEDALCOMMITTEE COMMITTEE VI VI SESSION SESSIONCHAIRMEN CHAIRMEN VII VII ANNUAL BANQUET BANQUET SPEAKER SPEAKER ANNUAL VII VI I GOLDICH GOLDICH MEDAL MEDAL RECIPIENT RECIPIENT VII VII ACKNOWLEDGMENTS ACKNOWLEDGMENTS VII VII IX CALENDAR CALENDAR OF OF EVENTS EVENTSM4D ANDPROGRAM PROGRAM p 1 ABSTRACTS ABSTRACTS 53 FIELD FIELD TRIPS TRIPS 1) 1.• 1 MINERAL MINERAL DEPOSITS DEPOSITS OF OFTHE THEFORT FORTFRANCES-MINE FRANCES-MINECENTRE CENTRE 55 ONTARIO AREA, ONTARIO 22.• ARCHEAN GEOLOGY GEOLOGY OF THE THEINTERNATIONAL INTERNATIONALFALLS-KABETOGAMA FALLS-KABETOGaMA ARCHEM4 AREA, MINNESOTA MINNESOTA AREA, I I I III 89 �GENERAL GENERAL INFORMATION INFORMATION 28th 28th Annual Annual INSTITUTE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY INSTITUTEON ONLAKE Holiday Holiday Inn Inn International International Falls, Falls, Minnesota Minnesota May May 5—8, 5-8, 1982 1982 Sponsored Sponsored by by Minnesota Minnesota Geological Geological Survey Survey University University of of Minnesota Minnesota 1633 1633 Eustis Eustis Street Street St. Paul, Paul, Minnesota Minnesota 55108 55108 INSTITUTE OF DIRECTORS DIRECTORS INSTITUTE HOARD BOARD OF State University, W.C. W.C. Cambray, Cambray, Department Department of of Geology, Geology, Michigan Michigan State University, East East Lansing, Lansing, Michigan Michigan (1981) (1981) M.F. M.F. Kehlenbeck, Kehlenbeck, Department Department of of Geology, Geology, Lakehead Lakehead University, University,Thunder ThunderBay, Bay, Ontario Ontario (1977) (1977) G. G. Mursky, Mursky, Department Department of of Geological Geological Sciences, Sciences, University university of of Wisconsin, Wisconsin, Milwaukee, Milwaukee, Wisconsin Wisconsin (1978) (1978) P.E. P.E. Myers, Department Department of of Geology, University University of of Wisconsin, Eau Eau Claire, Claire, Wisconsin Wisconsin (1980) (1980) R.W. R.W. Ojakangas, Ojakangas, Department Department of of Geology, Geology, University University of of Minnesota, Duluth, Duluth, Minnesota Minnesota (1979) (1979) R.C. R.C. Reed, Division, Department of Natural Reed, Geological Geological Survey Survey Division, Department of ~aturalSciences, Sciences, Lansing, Lansing, Michigan Michigan (secretary—treasurer) (secretary-treasurer) D.L. D.L. Southwick, Southwick, Minnesota Minnesota Geological Geological Survey, Survey, St. St. Paul, Paul, Minnesota Minnesota (1982) (1982) V �I LOCAL LOCAL COMMITTEE COMMITTEE Conference Conference Chairman Chairman D.L. D.L. Southwick, Southwick, Minnesota Minnesota Geological Geological Survey, Survey, University University of of Minnesota, Minnesota, 1633 1633Eustis EustisStreet, Street,St. St. Paul, Paul,Minnesota Minnesota55108. 55108. Conference Conference Treasurer Treasurer G.E. G.B. Morey, Morey, Minnesota MinnesotaGeological GeologicalSurvey, Survey,University UniversityofofMinnesota, Minnesota, 1633 St. Paul, Paul, Minnesota Minnesota 55108. 55108. 1633 Eustis Eustis Street, Street, St. Field Field Trips Trips K. K. Howard Howard Poulsen, Poulsen, Queen's Queen's University, University, Kingston, Kingston, Ontario, Ontario, K7L X7L 3N6 3N6 Warren Warren C. C. Day, Day, Minnesota MinnesotaGeological GeologicalSurvey, Survey,University UniversityofofMinnesota, Minnesota, St. St. Paul, Paul, Minnesota Minnesota55108 55108 R.W. R.W. Ojakangas, Ojakangas, Department Departmentof of Geology, Geology, University UniversityofofMinnesota, Minnesota, Duluth, Duluth, Minnesota Minnesota 55812 55812 D.L. D.L. Southwick, Southwick, Minnesota MinnesotaGeological GeologicalSurvey, Survey,1633 1633Eustis EustisSt., St., St. St. Paul, Paul, Minnesota Minnesota 55108 55108 Physical Physical Arrangements Arrangements Douglas Douglas Bergstrom, Bergstrom, Minnesota Minnesota Geological Geological Survey, Survey, University University of of Minnesota, Minnesota, St. St. Paul, Paul, Minnesota Minnesota 55108 55108 Mark Mark Jirsa, Jirsa, Minnesota Minnesota Geological Geological Survey, Survey,University Universityof ofMinnesota, Minnesota,St. St. Paul, Paul, Minnesota Minnesota 55108 55108 Best Best Student Student Paper Paper Committee Committee W.F. W.F. Cannon, Cannon, U.S. U.S. Geological Geological Survey, Survey, Reston, Reston, Virginia Virginia 22092 22092 F.J. F.J. Sawkins, Sawkins, Department Department of of Geology Geology and and Geophysics, Geophysics, University University of of Minnesota, Minnesota, Minneapolis, Minneapolis, Minnesota Minnesota 55455 55455 W.R. W.R. Zwickey, Zwickey, Kimberly—Clark Kimberly-Clark Corporation, Corporation, Neenah, Neenah, Wisconsin Wisconsin 54956 54956 MEDAL COMMITTEE COMMITTEE GOLDICH MEDAL GOLDICH C.L. c.L. Iverson, Iverson, U.S. U.S. Steel Steel Corporation, Corporation, Virginia, Virginia, Minnesota Minnesota 55792 55792 G.L. G.L. LaBerge, LaBerge, Geology Geology Department, Department, University University of WisconsinOshkOsh, Wisconsin-Oshkosh, Oshkosh, Wisconsin Wisconsin 54901 54901 Oshkosh, M.E. M.E. Ostrom, Ostrom, Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, University of of Wisconsin Wisconsin — Extension, Extension, Madison, Madison, Wisconsin Wisconsin 53706 53706 University - VI �SESSION SESSIONCHAIRMEN CHAIRMEN I p R.L. R.L. Bauer, Bauer, Department Departmentof of Geology, Geology, Macalester Macalester College, College, St. St. Paul, Paul, Minnesota Minnesota55105 55105 V.W. V.W. Chandler, Chandler, Minnesota MinnesotaGeological GeologicalSurvey, Survey, St. St. Paul, Paul, Minnesota Minnesota55108 55108 J.C. J . C . Green, Green, Department Departmentof of Geology, Geology, University University of of Minnesota, Minnesota, Duluth, Duluth, Duluth, 55812 Duluth, Minnesota Minnesota55812 P.L. P.L. McSwiggen, McSwiggen, Minnesota Minnesota Geological GeologicalSurvey, Survey, St. St. Paul, Paul, Minnesota Minnesota 55108 55108 D.G. Meineke, Meriden Engineering, Hibbing, Minnesota 55746 D.G. Meineke, Meriden Engineering, Hibbing, Minnesota 55746 M.G. M.G. Mudrey MudreyJr., Jr., Wisconsin WisconsinGeological Geologicaland andNatural Natural History HistorySurvey, Survey, Madison, 53706 Madison, Wisconsin Wisconsin 53706 K.J. K.J. Schulz, Schulz, Department Department of of Earth Earth and and Planetary Planetary Sciences, Sciences, Washington Washington University, St. Louis, Louis, Missouri Missouri63130 63130 University, St. P.W. P.W. Weiblen, Weiblen, Department Department of of Geology Geologyand and Geophysics, Geophysics, University University of of Minnesota, Minneapolis, Minnesota 55455 Minnesota, Minneapolis, Minnesota 55455 I ANNUAL BANQUET BANQUET GUEST GUESTSPEAKER SPEAKER ANNUAL fice of of Marine Randolph RandolphA. A. Koski, Koski, Of Office Marine Geology, U.S. U.S. Geological Geological Survey, Survey, Menlo 94025 Men10 Park, Park, California California 94025 I GOLDICH GOLDICH MEDAL MEDAL RECIPIENT RECIPIENT Ralph W. Ralph W. of of Marsden, Marsden, Professor Professor&rieritus EmeritusDeparment Deparmentof ofGeology, Geology, University University Minnesota, 55812 Minnesota, Duluth, Duluth, Duluth, Duluth, Minnesota Minnesota 55812 'I ACKNOWLEDGMENTS ACKNOWLEDGMENTS I The The organizing organizing committee committee of of 1982 1982 Institute I n s t i t u t e on on Lake Lake Superior Superior Geology Geology gratefully acknowledge the work of Mrs. Jeanne Perrin and Mrs. Linda Linda g r a t e f u l l y acknowledge t h e work of Mrs. Jeanne P e r r i n and Mrs. the Proceedings. Proceedings. McDonald in i n typing typing the the final f i n a l manuscript manuscript for f o r the McDonald VII VII �a a a a (I) —1 C) > -1 CI) 03 ABSTRACTS S — a �MAGNETIC INVESTIGATIONS INVESTIGATIONS OF OFTHE THEBARAGA BARAGACOUNTY COUNTY DIABASE DIABASE MAGNETIC BARAGA BARAGA COUNTY, COUNTY, MICHIGAN MICHIGAN T.D. p,nderson, Anderson, Union Oil Oil of of California, California, P.O. P.O. Box Box 76, 76, Brea, Brea, California California T.D. 92621; J.F. J.F. Diehi, Diehl, Michigan Michigan Technological Technological University, University, Houghton, Houghton, Michigan Michigan 92621; 4993 1 49931 ABSTRACT ABSTRACT Aeromagnetic data from parts of Aeromagnetic data from parts ofBaraga Baraga and andMarquette Marquette Counties, Counties,Michigan Michigan are are dominated dominated by by linear, linear,east—west east-west trending trendingmagnetic magnetic lows lows associated associated with with reversely • Close reverselymagnetized magnetized diabase diabasedikes dikes. Close examination examination of ofground groundmagnetommagnetom- eter profiles profiles shows shows that that prominent prominent dike dike intrusions intrusionssometimes sometimes occur occur as as eter groups of small, interrelated interrelated dikes. dikes. In In one one case case these thesedikes dikeswere were groups of 22 to to 44 small, found to thicken at 22 to km intervals intervals along along strike strikecausing causing found to thicken or or converge converge at to 33 km p in aeromagnetic • periodic maxima maxima in aeromagnetic anomalies anomalies. periodic The The ground ground magnetometer magnetometer propro- files normally exist filesalso alsoprovide provideevidence evidencethat that normallymagnetized magnetized diabase diabase dikes dikes may may exist sites in in more reversed dikes dikes at at 22 sites in in close closeassociation associationwith withthe the morecommon common reversed Baraqa County. Baraga County. The The magnetic magnetic anomalies anomalies of of Baraga Baraga County County Diabase Diabase intrusions intrusions diminish diminish in in magnitude under the the Baraga Baraga Plains Plains where where the the dikes dikes are are covered covered by by glacial glacial deposits deposits and and possibly possibly by by Jacobsville Jacobsville Sandstone. Sandstone. It was was found found that that estiestimates mates of of depth depth to to the the diabase diabase dikes dikes in In the the Baraga Baraga Plains Plains area area could could be be used used The to to interpret interpret basin basin structure structure on on the the surface surface of of the the Middle Middle Precambrian. Precambrian. The results showed evidence evidence of of aa possible possible valley or or ledge ledge in in the Middle Middle results ofof Keweenaw to the the Keweenaw Bay Bay to Precambrian representing representing aapossible possibleburied buriedextension extension Precambrian southwest from from L'Anse, LIAnse, Michigan. Michigan. southwest Several have reported Several investigators investigators have reported cells cells of of anomalous anomalous remanence remanence in in The Baraga Baraqa County County Diabase Diabase outcrops. outcrops. The variable variable intensity intensity and and small—scale small-scale in these these cells complexity of complexity of magnetization magnetization in cellsargue argue against against explaining explaining these these cells cellsasaslightning—induced lightning-induced magnetization. magnetization. Detailed Detailed paleomagnetic paleomagnetic sampling sampling of two of of these these cells cells suggests suggests that that the the observed observed patterns patterns result result from from of lightning—induced magnetization magnetization superimposed superimposed on dramatic lightning-induced dramatic susceptibility susceptibility It was variations in in the the diabase. diabase. was possible possible to to map map the the probable probable path path of of flow in in both both cases. cases. current flow It S 3 �FOLDING THE WESTERN Fl REcjjENT RECUMBENT FOLDINGININ THE WESTERN VEI4ILtON VERMILION F1 GREENSTONE-GRANITE NEMINNESOTA MINNESOTA GREENSTONE-GRANITE TERRANE, TERRANE, NE R.L. Bauer, Bauer, Department Department of of Geology, Geology, Macalester Macalester College, College, St. St. Paul, Paul, Minnesota Minnesota R.L. P.J. Hudleston, Hudleston, Department Department of of Geology Geology and and Geophysics, Geophysics, University University of of 55105; P.J. 55105; a Minnesota, Minnesota, Minneapolis, Minneapolis, Minnesota Minnesota 55455 55455 ABSTRACT ABSTRACT granite-migmatite terrane terrane The Vermilion Vermilion Granitic Granitic Complex, Complex, aa granite—migmatite The recrystallized recrystallized in in the the amphibolite amphibolite facies, facies, is is in in fault fault contact contact along along its its southern southern boundary boundary with with the the Vermilion Vermilion district, district, aa greenstone—granite greenstone-granite Analysis terrane terrane in in the thegreenschist greenschist facies. facies. Analysis of of structural structural facing facing in in folded folded Archean Archean strata strata in in the the southern southern Vermilion Vermilion Granitic Granitic Complex Complex and and western western Vermilion Vermilion district district indicates indicates that that the the sedimentary sedimentary sequence sequence underunderwent Fl folding folding prior prior to to the the development development of of the the dominant dominant went recumbent recumbent F1 beF2 folds. folds. AA major major F2 F2 antiform antiform mappable mappable across across the the faulted faulted boundary boundary beF2 tween tween the the two two terranes, terranes, displays displays downward downward structural structural facing facing indicating indicating the the inversion of of this this portion portion of of the the sedimentary sedimentary sequence prior prior to to the the inversion To the southeast, in the Vermilion district, upward strucfolding. To the southeast, in the Vermilion district, upward strucF2 folding. F2 tural tural facing facing is is observed observed in in F2 F2folded foldedstrata. strata. The The regional regional change change in in structural structural facing facing to to the the southeast southeast is is attributed attributed to to crossing crossing of of the theaxial axial surface surface of of aa major major F1 Fl nappe. nappea Finite Finite strain strain data data determined determined from from clasts clasts in in the the greenschist greenschist facies facies sedimentary/volcaniclastic sedimentary/volcaniclastic units in the the Vermilion Vermilion greenstone greenstone terrane terrane can can be completely accounted for in terms of the deformation producing the be completely accounted for in terms of the deformation producing the to downslope downslope .F2 folds. Locally Locally intense intense F1 Fl folding folding is is therefore therefore attributed attributed to F2 folds. amphibolite facies soft sediment. However, slump slump movement movement of of soft sediment. However, amphibolite facies biotite biotite schists, making up part of the same F1 schists, making up part of the same Fl structure structure in in the the Vermilion Vermilion Granitic Granitic Complex, display display aa pronounced pronounced SSlfoliation foliationthat thatdeveloped developed parallel parallel to to Complex, We suggest that metabedding during the early stages of metamorphism. bedding during the early stages of metamorphism. We suggest that metamorphic occurring in in the lower to the the morphic dehydration dehydration reactions reactions occurring lower strata strata led led to development of high pore pressures in the upper portion of the sedimentary development of high pore pressures in the upper portion of the sedimentary ofhigh highpore porepressures pressuresand andgravitational gravitational instabilThe combination combination of instabilpile. pile. The ity during the F1 folding resulted in soft sediment slumping in the upper ity during the Fl folding resulted in soft sediment slumping in theupper strata while while the the lower lower strata strata underwent underwent strain strain and and metamorphic metamorphic strata Soft—sediment i folding recrystallization recrystallization during during F1 Fl folding. folding. Soft-sediment Fl folding in in the the Vermilion district could have led to a rather complex distribution Vermilion district led to a rather complex distribution of of Ely F l structures, Structures, because the the more competent volcanic flows, such as the Ely F1 greenstone, may may have have undergone undergone aa much much different different response response to to the the greenstone, folding. F l folding. F1 I I 4 4 �RB-SR RB-SRAND ANDSM-ND SM-ND ISOTOPIC ISOTOPIC STUDIES STUDIES OF OF PROTEROZOIC PROTEROZOICMAFIC MAFIC DIKES DIKES NORTHEASTERN MINNESOTA IN IN NORTHEASTERN MINNESOTA Warren V. Rama Kama Murthy, Murthy, Department Department of of Geology Geology and andGeophysics, Geophysics, Warren Beck Beck and and V. University of Minnesota, Minneapolis, MN 55455 University of Minnesota, Minneapolis, MN 55455 ABSTRACT ABSTRACT AA major major northwest—trending northwest-trending mafic mafic dike dike swarm swarm of of Proterozoic Proterozoic age age intrudes intrudes the 2.7 b.y.—old greenstone—granite terrane of northeastern Minnesota the 2.7 b.y.-old greenstone-granite terrane of northeastern Minnesotaand and adjacent adjacent southern southern Ontario. Ontario. Of Of these, these, two two large largevertical vertical composite composite dikes dikes a combined isotopic study. have have been been selected selectedfor for a combinedRb-Sr, Rb-Sr,Sm-Nd Sm-Nd isotopic study. These These dikes dikes intrude Complex Lake in in northeastnortheastKabetogama Lake intrudethe theVermilion VermilionGranitic Granitic Complexwest westof ofKabetogama This research was undertaken to complement petrologic ern ernMinnesota. Minnesota. This research was undertaken to complement petrologicand and paleomagnetic paleomagnetic studies studies which which are are being being done done by by David David Southwick Southwickof of the theMinneMinneHalls of sota sota Geological Geological Survey Survey and and by by Henry Henry Halls of the theUniversity Universityof ofToronto. Toronto. The dikes analyzed analyzedin in this this study colinear.Although Although The composite composite dikes study are arenearly nearlycolinear. they be followed followed continuously continuouslyon on the the aeromagnetic aeromagneticmaps, maps, we we infer inferfrom from they cannot cannot be structural, structural, petrologic petrologic and and geochemical geochemical characteristics characteristics that that they they are are probprobably ably parts parts of of aasingle singleintrusive intrusivebody. body. The The sites sites sampled sampled are are separated separated along along strike strike by by about about 2.5 2.5 km. km. An An earlier earlier reconnaissance reconnaissance of of this this dike dike swarm swarm yielded yielded K—Ar K-Ar ages ages ranging ranging from The eight eight samples samples analyzed analyzed for for the the present present study study plot plot b.y. The from 1.6 1.6 to to 2.2 2.2 b.y. The on on aa single single Rb—Sr Rb-Sr isochron isochron and and define define an an age age of of 2120 2120 t 67 67 m.y. m.y. The relarelatively ratio tively high high initial initial 87srfi6sr ^sr/^sr ratio of of 0.70449 0.70449 implies impliesthat thatthe thecrust crustwas was involved magmagenesis genesisororthat thatthe themagma magmawas wascontain— contaminvolved in in the theprocess processof ofdike dikemagma mated inatedduring duringemplacement emplacementinto intogranitic granitic rocks. rocks. The The fact fact that that samples samples from from plot on the same inner inner and and outer outer dikes dikes of of both both composite composite dikes dikes plot on the sane isochron isochron is is thethe dikes originated froom same suggestive suggestive that thatall all dikes originated froomthe the samesource. source. + The Assumin that that The Sm—Nd Sm-Nd data data from from these these dikes dikes do do not not form form an an isochron. isochron. Assuming the the emplacement emplacement age age is is 2120 2120 m.y., my., then then aa calculation calculationof of the theinitial initial '43Nd/ ^%id/ 144Nd ld4Nd isotopic isotopic ratios ratios for for these these samples samples reveals reveals that that the the source source region region for for the LREEdepleted. depleted. The The combined combined Sr Sr and and Nd Nd characteristics characteristics of of these these the magma magma is is LREE dikes (1) the the source source region region for for these these dikes dikes appears appears dikes suggest suggest 22 conclusions: conclusions: (1) to to be be in in the the mantle mantle and and not not in in the the crust, crust, and and (2) (2)the the dike dike magma magma was was subsesubsequently quently contaminated contaminated by by crustal crustal material material during during passage passage through through the the crust crust or or during during intrusion. intrusion. In In both both composite composite dikes dikes the the outer outer dike dike is is enriched enriched in in Rb Rb and and Rb/Sr Rb/Sr ratio to the the inner innerdike. dike. This This suggests suggests that that the the inner inner dikes dikes may may ratio relative relative to represent represent aa reinjection reinjection of of aa cumulate cumulate after after the themain mainpulse pulseof ofdike dikeinjecinjection. tion. 5 �STRATIFIED STRATIFIED OCEANS OCEANS AND AND THE ORIGIN ORIGIN OF OFIRON-FORMATION IRON-FORMATION William 22092 William F. F. Cannon, U.S. U.S. Geological Geological Survey, Survey, Reston, Reston, Virginia Virginia 22092 ABSTRACT ABSTRACT The great by those of great Proterozoic Proterozoic XX banded banded iron—formations, iron-formations, typified by the Lake Superior region, have long presented a geochemical enigma. Lake Superior region, have long presented a geochemical enigma. Vast quantities of iron iron must must have have been been dissolved dissolved in in and and precipitated precipitated from from seaseawater to deposits, form these yet iron is virtually insoluble water to these deposits, iron is virtually insoluble in in even even slightly oxygenated Thus, oxygenated water. water. Thus, many many investigators investigators have have concluded concluded that that anoxic water, in anoxic in which which iron iron is is more more soluble, soluble, must have have dominated dominated the the Proter— Proterozoic oceans and and that that iron—formations iron-formations were were deposited deposited as as that that water water was was ozoic XX oceans oxygenated. Most have assumed that this oxygenation of the oceans oxygenated. have assumed that this oxygenation the oceans was was aa unique event event in in the the evolution evolution of of the the atmosphere atmosphere and and hydrosphere hydrosphere caused caused by by the first appearance, roughly 2 billion years ago, of photosynthetic organthe first appearance, roughly 2 billion years ago, of photosynthetic organisms and and hence hence the the permanent permanent shift shift from from an an oxygen—free oxygen-free to to an an oxygen—rich oxygen-rich atmosphere. atmosphere. jn In contrast, contrast, research, research, largely largely in in the the petroleum petroleum industry, industry, in in the the past past few years years has has shown shown that that major major parts parts of of the the world's world's oceans oceans repeatedly repeatedly bebecame strongly strongly stratified stratified and and were were anoxic anoxic below below the the depth depth of of surface surface turbuturbulence lence for for substantial substantial periods periods of of Phanerozoic Phanerozoic time. time. These These so—called so-called ocean ocean anoxic anoxic events events took took place place during during periods periods of of major major marine marine transgression transgression and and warm Decreased oceanic warm climate. climate. oceanic circulation circulation resulted resulted from from warm warm climate, climate, and and increased increased oceanic oceanic productivity productivity resulted resulted from from equable equable climate climate and and exexpanded to create create an an panded highly highly productive productive shelf shelf seas. seas. These These conditions conditions combined combined to excess excess of of organic organic matter matter over over available available oxygen oxygen in in deep deep oceans oceans which led led to to anoxic anoxic conditions. conditions. The recurrence recurrence of ocean ocean anoxic anoxic events events throughout throughout Phan— Phanerozoic erozoic time time periodically periodically resulted resulted in in large large quantities quantities of of anoxic anoxic ocean ocean water water having relatively Mn, and PP and and probably probably relatively high high contents contents of of dissolved dissolved Fe, Fe, Mn, controlled controlled the the temporal temporal distribution distribution of of deposits deposits of of these these elements elements in in PhanPhanerozoic erozoic rocks. rocks. Such Such ocean ocean anoxic anoxic events events might might also also have have taken taken place place during during the the Precam— Precambrian, and brian, and they, they, in in addition addition to to one—time one-time only only oxidation oxidation related related to to permapermanent changes time, may changes in in the the atmosphere atmosphere and and oceans oceans during during Proterozoic Proterozoic XK time, have resulted resulted in in deposition deposition of of iron—formation. iron-formation. Thus, the the major major distinction distinction from from past past theories theories is is the the idea idea that that after after an an early early oxygen—free oxygen-free atmosphere atmosphere and ocean time, younger younger ocean may may have have been been oxidized oxidized initially initially in in Proterozoic Proterozoic KX time, oceans oceans were were probably probably capable capable of of returning returning to to anoxic anoxic conditions conditions and and depositdepositing ing iron—formations iron-formations even even in in the the presence presence of of an an oxygen—rich oxygen-rich atmosphere. atmosphere. - The Proterozoic Proterozoic KX banded banded iron—formations iron-formations of of the the Lake Lake Superior Superior region region seem by an an ocean—anoxic—event ocean-anoxic-event model model in in which which oceans oceans were were oxygenoxygenseem explainable explainable by ated both During periods iron-formation deposition. deposition. periods of of h t h before before and and after iron—formation ocean ocean anoxia, anoxia, the the deep deep oceans oceans acted acted as as geochemical geochemical sinks sinks for for iron, iron, and and the the anoxic anoxic waters waters were were enriched enriched in in dissolved dissolved iron. iron. Iron Iron was was then then precipitated precipitated in iron—formations iron-formations either either by by upwelling upwelling and and consequent consequent oxidation oxidation during during the the anoxic anoxic event event or or by by aa more more widespread widespread oxygenation oxygenation of of the the ocean ocean as as the the anoxic event event waned. waned. Iron—formations Iron-formations commonly occur occur at at several several stratigraphic stratigraphic horizons horizons in in iron—bearing iron-bearing regions (for (for instance, instance, at least least five five horizons horizons are are present present in in These repeated the of Michigan). Michigan). repeated cycles cycles of of deposition deposition seem seem the Proterozoic Proterozoic KX of more more consistent consistent with aa model model involving involving repeated repeated ocean ocean anoxia anoxia than than with with models models involving involving only only one one oxygenation oxygenation event. event. 6 �S STUDIES OF OF TUE MAGNETIC ANOMALY ANOMALY STUDIES THE NORTHERN NOBTHERN ANIMIKIE BASIN BASIN MAGNETIC • S Val W. W. Chandler, Chandler, Minnesota Minnesota Geological GeologicalSurvey, Survey,University UniversityofofMinnesota, Minnesota,St. St. Val Paul, Minnesota, Minnesota, 55108; 55108; Arthur Arthur B. B. Watts, Watts, Arco Arco Petroleum, Petroleum, Dallas, Dallas, Texas, Texas, Paul, 75221; L. Gulbranson, Gulbranson, Minnesota Minnesota Geological Geological Survey, Survey, University University of of 75221; and and Brian Brian L. Minnesota, St. St. Paul, Paul, Minnesota Minnesota 55108 55108 Minnesota, ABSTRACT ABSTRACT Mesahi Iron Iron Range, Range, exposures exposures of of the the lower lower Except along along the the Mesabi Except Proterozoic Proterozoic Aniinikie Animikie Group Group are are widely widely scattered scattered and and wells wells penetrating penetrating to to As aa consequence, consequence, little little can can be be Archean basement basement are are nonexistent. nonexistent. As Archean • inferred inferred about about the the structure structure of of the the Animikie Animikie basin basin without without the the aid aid of of Detailed aeromagnetic data data recently recently acquired acquired by by the the geophysical data. data. Detailed aeromagnetic geophysical Minnesota Minnesota Geological Geological Survey Survey have have been been used used to to elucidate elucidate the the structure structure of of the the northern northern flank flank of of the the basin basin in in an an area area of of about about3500 3500 km2 km2 in in St. St. Louis Louis and Itasca Itasca Counties, Counties, Minnesota. Minnesota. and The The northern northern edge edge of of the the basin basin is ischaracterized characterized by by aa complex complex and and • • • (>SO0 gammas) ganmas) anomaly anomaly expression expression caused caused by by the the typically high—amplitude high-amplitude (>500 typically Biwabik Iron Iron Formation. Formation. AA broad broad zone zone with with smoother smoother anomaly anomaly expression expression and and Biwabik moderate moderate amplitudes amplitudes (100—SOD (100-500 gammas) gammas) extends extends about about 20 20 km km southward southward into into the the basin basin and and reflects reflects the the southward southward thickening thickening of of the the essentially essentially non— nonmagnetic magnetic slate slate and and graywacke graywacke of of the the Virginia Virginia Formation Formation that that overlie overlie the the iron-formation. The The anomalies anomalies within within this this zone zone are are thus thus assumed assumed to to arise arise iron—formation. , from from structures structures within within the the buried buried iron—formation iron-formation or or from from sources sources within within the the underlying underlying Archean Archean basement. basement. Beyond Beyond 20 20 km km into into the the basin basin the the magnetic magnetic anomaly character character becomes becomes extremely extremely subdued, subdued, reflecting reflecting deeply deeply buried buried anomaly anomaly anomaly sources sourcesbeneath beneath non—magnetic non-magnetic slate slateand andgraywacke. graywacke. Because the the overlying overlying slate slate and and graywacke graywacke are are essentially essentially Because non-magnetic, non-magnetic, magnetic magnetic depth depth estimates estimates will will indicate indicate source source tops tops either either in in the Archean basebase the Biwabik Biwabik Iron Iron Formation Formation or or in in the the immediately immediately underlying underlying Archean ment. Therefore Therefore these these depth depth estimates estimates should should delineate delineate the the general general shape shape ment. and and deep deep structure structure of of the the Animikie Animikie basin. basin. Depth Depth estimates estimates were were obtained obtained graphically from from maps maps and and by by computer—based computer-based estimates estimates along along flight flight graphically km profiles. The The results results reveal reveal aa gently gently dipping dipping shelf shelf out out to to about about 20 20 km profiles. south south of of the the edge edge of of the the basin, basin, where where depths depthsof of around around1 1 km kmare areindicated. indicated. AA structural structural relief relief of of aa few few hundred hundred meters meters is is inferred inferred to to be be superimposed superimposed upon this this shelf shelf along along the the southwest southwest extension extension of of the the Virginia Virginia horn. horn. upon Southward to steepen steepen abruptly abruptly to to depths depths Southward from from this this shelf shelf the the basin basin appears appears to in excess excess of of 22 1cm. km. South South of of 47N 47-Nthe thedepth depthestimates estimateson on aabroad broad east— eastin trending trending maximum maximum indicate indicate depths depths in in excess excessof of 33km. km. • The encouraging encouraging results results of of this this preliminary preliminary study study suggest suggest that that The further further geophysical geophysical work, work, including including similar similar studies studies over over the the remainder remainder of of the the basin basin and and also also seismic seismic investigations, investigations, would would be be fruitful. fruitful. The The implied implied thickening 20 km km into into the the basin basin may may reflect reflect aa transition transition thickening of of the the sequence sequence 20 from from aa stable stable shelf shelf to to the the more more mobile mobile environment environment characteristic characteristic of of the the Great Lakes Lakes tectonic tectonic zone. zone. Great S 7 �GRANITIC PHASES GRANITIC PHASES IN INTHE THENORTHERN NORTHERNBORDER BORDER ZONE ZONE THE VERMILION 0? THE VERMILION GRANITIC GRANITICCOMPLEX COMPLEX OF Warren C. Warren C . Day, Day, Minnesota Geological Geological Survey, 1633 1633 Eustis Street, St. Paul, Paul Weiblen, Weiblen, Department of Geology and Minnesota 55108; 55108; Paul and Geophysics, Geophysics, 108 108 Pillsbury Hall, 310 Pillsbury Pillsbury Pillsbury Drive SE, Minneapolis, Minnesota 55455 Vermilion Granitic an Archean granite—migmatite Granitic Complex Complex is is an Archean granite-miqmatite The Vermilion terrane which by the the extensive earlytonalite tonalite terrane which has has formed formed by extensive emplacement emplacement ofofearly to post—tectonic and syn— into supracrustal syn- to post-tectonic granite granite into supracrustal metamorphic metamorphic rocks rocks and (chiefly biotite biotite schist Two main main types of granite (chiefly schist in in the thestudy study area). area). Two granite occur along along the the northern biotite granite granite 1) aa grayish—pink occur northern border border zone: zone: 1) grayish-pink biotite and 2) Croix Granite), biotite—muscovite leucogranite. leucogranite. (Lac La Croix 2) a biotite-muscovite (Lac Granite), and Geochemical Geochemical and mineral studies studies have been been undertaken undertaken to to distinguish distinguish the the similarities and and differences two granite and to similarities differences between between these these two granite types, types, and to investigate the the origin Theresults results are are relevant investigate origin of of the theleucogranite. leucoqranite. The relevant to to the general of the the origin origin of batholithic granites granites in in the general problem problem of of late—stage late-stage batholithic greenstone—graniteterranes. terranes. greenstone-granite The Lac La Croix Granite, a major component of the Complex, occurs as batholithic phase phase and and as as the neosome portion portion of of the late—stage late-stage intrusive batholithic granite—rich migmatite. on the other hand hand occurs occurs only as as granite-rich migmatite. The leucogranite on small bodies bodies within within the neosome portions of the the schist—rich schist-rich migmatite and small the biotite biotite schist. granites are Qtz—Or—Ab abundances. However, The two two granites are similar in their Qtz-Or-Ab However, distinctive differences are seen seen in in accessory accessory phases and and in in major major element element Garnet is restricted to the and trace trace element element chemistry. chemistry. Garnet the leucogranite, leucogranite, magnetite is is common theLac LacLaLaCroix CroixGranite Granitebut butrare rare in in the whereas magnetite ,whereas common ininthe the leucogranite. The leucogranite lower in MgO, MgO, FeOt and and leucogranite. leucogranite is significantly significantly lower content in the leuco— Ti02 compared La Croix Croix Granite. Granite. The LaN Compared to to the the Lac La Lan content leucogranite ranges granite ranges from from 95 95 to to 140 140 xx chondrite. chondrite. garnet are locally developed Sillinanite, staurolite, muscovite, Sillimanite, staurolite, muscovite, and garnet within the the biotite biotite schist. schist. Thin veins of fine—grained fine-grained leucocratic leucocratic grano— granothick) and and pods podsof of pegmatite pegmatiteare are isoclinally isoclinally diorite and diorite and granite granite (few (few mm mu thick) folded and withinthe the host host biotite andandcommonly folded and boudinaged boudinaged within biotite schist, schist, commonly are are bordered by biotite selvage bordered selvage zones. zones. These veins coalesce into larger larger len— lenAs the As the ratio ratio of of leucogranite leucogranite to to biotite biotite ticular leucogranite leucogranite bodies. bodies. tends to crosscut schist increases, increases, the leucogranite leucogranite tends crosscut earlier earlier tectonic tectonic fabric. fabric. These relationships are compatible with an anatectic origin for the MgO, FeOt FeO and and TiO2 Ti02 content content of of the the leucogranite leucogranite may leucogranite. The low MgO, digestion of mafic minerals be attributed be attributed to low low degrees degrees of of (1) minerals (e.g. (e.g. (1) digestion The data biotite, amphibole, garnet, etc.) biotite, etc.) in the the source source during during melting. melting. The obtained thus far far suggest suggest therefore therefore that that the the leucogranite leucogranite is is an an anatectic anatectic supracrustal sedimentary sedimentary rocks, rocks, and and that that it it has melt produced produced from from (2) (2) supracrustal metasedimentary syntectonically into into higher portions of of moved syntectonically the metasedimentary Trace element analyses sequence. analyses are presently underway to to help help model the sequence. Trace origin of the the leucogranite. leucogranite. 8 �S HANSON GEOLOGY GEOLOGYOF OFTHE THECYPRESS, CYPRESS, HANSONANt) ANDSOUTH SOUTHARM ARM OF OF IQ4IFE KNIFELAKE LAKEAREA AREA NORTHEAST B.W.C.A., B.W.C.A., NORTHEASTMINNESOTA MINNESOTA TimothyFlood, Flood, Department Department ofofGeology, Geology, University University of ofMinnesota, Minnesota,Morris, Morris, Timothy Minnesota 56267 Minnesota 56267 ABSTRACT ABSTRACT Archean Archean volcanic volcanic and andvolcanogenic volcanogenic sedimentary sedimentary rocks rocks of of the theCypress, Cypress, Hanson and South Arm of Knife Lake area are located within the eastern Hanson and South Arm of Knife Lake area are located within the eastern vermilion vermiliondistrict districtand andlie lieininthree threeof ofGruner's Gruner's (1941) (1941)structural structuralsegments. segments. • The TheSpoon SpoonLake Lakesegment segmentisiscomposed composeddominantly dominantlyofofdacite daciteporphyry, porphyry,dac— dacThe graywacke is porphyry conglomerate and graywacke—argillite. ite porphyry conglomerate and graywacke-argillite. The graywacke isofof ite both both the thefeldspathic feldspathicand andlithic lithictype, type, and andis isinterbedded interbeddedwith with conglomerate. conglomerate. Two Twosmall smallfault faultslices slicesofofgreenstone greenstoneare arepresent presentwithin withinthe the segment segmentas asare are igneous and the sedimentary the Keweenawan diabasic dikes which intrude both Keweenawan diabasic dikes which intrude both the igneous and the sedimentary to500E 500Eand anddips dipssteeply steeplytotothe the Bedding strikes strikes predominantly predominantly 40° 400 to rocks. rocks. Bedding The Knife Lake synclinorium segment is composed southeast and northwest. southeast and northwest. The Knife Lake synclinorium segment is composed of tuff-maficconglomerate—mixed conglomerate-mixed conglomerate conglomerate unit, unit, and and aa of two twounits: units: aa tuff—mafic These two units are interbedded and gradational graywacke unit. younger younger graywacke unit. These two units are interbedded and gradational diabasicdike dikeisis present present ininthe into intoone oneanother. another. One One Keweenawan Keweenawan diabasic thesegment. segment. to near—vertical and dips Bedding strikes predominantly northeast Bedding strikes predominantly northeast and dips near-vertical tothe thenorthnorthwest. west. Significant Significant conclusions conclusions drawn drawn from from this this study study and and based based on on petrographic petrographic analysis and measurement, and interpretation of lineations, foliations analysis and measurement, and interpretation of lineations, foliationsand and primary primary sedimentary sedimentarystructures structuresinclude: include: 1) 1) The The granite granite pebble pebble conglomerate conglomerate of of the theKnife KnifeLake Lakegreenstone greenstoneunit unit (Gruner, 1941) is actually a greenstone pebble conglomerate. (Gruner, 1941) is actually a greenstone pebble conglomerate. 2) 2) source Source areas areas for for the the metasediments metasediments are are exclusively exclusively volcanic volcanic in in origin. origin. No No plutonic plutonicrock rockfragments fragmentswere wereobserved. observed. 3) 3) No No potassium potassium feldspar feldspar grains grains were were found foundeither either microscopically microscopically or or staining with sodium—cobaltinitrate, and no rock fragmentshave have by staining with sodium-cobaltinitrate, and no rockfragments by aa composition composition more more felsic felsicthan thandacite. dacite. 4) 4) No No Saganaga Saganaga detritus detritus was was deposited deposited within within the the sediments sediments and and hence hence and no no supporting supporting evidence evidence for for penecontemporaneous peneconteinporaneousvolcanism volcanism and unroof— unroofing of of the the Saganaga Saganaga batholith, batholith, as as suggested suggested by by previous previous investigainvestigaing tion, tion, was wasfound. found. 5) 5) Turbidite Turbidite sequences sequences in in all all segments segments are arecharacteristic characteristicturbidites turbidites corresponding to the theinner inneror or middle middlelobe lobeof ofa asubmarine submarinefan. fan. correspondingto 6) 6) The Knife Lake be acacThe structure structure of ofthe the Knife Lakesynclinorium synclinoriun segment segment can can be counted for in counted for in terms terms of of three three tectonic tectonic deformations. deformations. The The first first producedisoclinal isoclinal folds, deformation produced folds, the theaxes axesofofwhich which period of of deformation period to 50°E and plunge 30° to the northeast. The second second trend NN 40° 40 to 5 0  ° and plunge 300 to the northeast. The trend • • period to 60° 60- WW cleavage. cleavage. period of of deformation deformation produced produced aa pervasive pervasive NN 54° 54" to The regional scale scale and and The third third period period of of deformation deformation occurred occurred on on aa regional 9 S �produced major longitudinal faults, which have divided the present produced major longitudinal faults, which have divided the present area of study into petrographically distinct structural blocks. area of study into petrographical].y distinct structural blocks. 1 REFERENCE REFERENCE Gruner, J.W., 1941, Structural geology of the Knife Lake area of northeastStructural geology of the Knife Lake area of northeastGeological Society of America Bulletin, v. 52, p. 1577- Gruner, 1941, ern LW., Minnesota: ern Minnesota: 1642 1642. Geological Society of America Bulletin, v. 52, p. 1577— 10 �IRON-ENRICHED IRON-ENRICHED BASALTIC BASALTICFRAGMENTAL FRAGMENTAL ROCKS BOCKS ERUPTED ERUPTED IN INA ASHALLOW SHALLOWSUBAQUEOUS SUBAQUEOUS ENVIRONMENT, THE HEMLOCK FORMATION, FORMATION, AMASA AMASA QUADRANGLE, QUADRANGLE, MICHIGAN MICHIGAN ENVIRONMENT, THE HEMLOCK Charles Charles W. Geology and Graft, Department Department of of Geology and Geological Geological Engineering, Engineering, Graft, Michigan Michigan Technological Technological University, University, Houghton, Michigan Michigan 49931 49931 ABSTRACT ABSTRACT The Hemlock Formation Precambrian subaqueous The Hemlock Formation is is aa Precambrian subaqueous metavolcanic metavolcanic complex within the Oval in in Iron It isisoverlain complex within the Ainasa Amasa Oval IronCounty, County, Michigan. Michigan. It overlain by by whichoutlines outlinesthe the oval oval as the the Amasa Amasa Formation, Formation, a a banded banded iron—formation iron-formation which as The formation formation is is underlain well thethe Hemlock. well as as the theupper upper limits limitsofof Hemlock. The underlain by by the and the the Goodrich Quartzitewhich whichininturn turn rest rest on the Randville Randville Dolomite Dolomite and Goodrich Quartzite on the the Archean Archean basement of Bell Bell Creek Creek Granite Granite Gneiss. Gneiss. This study deals with formation in in thethe Amasa the the upper upper third thirdofofthe the formation Amasa7—1/2 7-1/2 minute minute quadrangle quadrangle just just east east of ofthe thetown townofofAmasa. Amasa. Approximately 5 square Approximately 5 square miles miles were mapped mapped for for correlation correlation with with the the previously mapped areas areas to the north and east in Kelso previously mapped in the the Ned Ned Lake Lake and and Kelso Thirty—five samples were analyzed Junction Junction Quadrangles Quadrangles respectively. respectively. Thirty-five analyzed for for Ten of geochemical correlation with pre—existing the Hemlock. from the Hemlock. Ten of pre-existing data data from Jesse D. these these were re—analyses re-analyses of samples taken by D . Jay Johnson (1975) (1975) and Jesse C. C . Dann Dann (1978). (1978). p lithologic variation variation occurs occurs within the the Significant chemical Significant chemical and and lithologic lithologies consist Main consist of massive Hemlock Formation. Formation. Main lithologies massive and and pillowed pillowed lavas, lavas, pillow pillow breccias, breccias, broken broken pillow pillow breccias breccias and and hyaloclastites. hyaloclastites. The first first basalts basalts of of the the Hemlock Hemlock chemically chemically resemble resemble oceanic tholeiites; later rocks rocks are are compositionally compositionally closer closer to to continental continental tholeiites. tholeiites. Minor amounts amounts The formation of rhyolite to have have been been erupted erupted in in 33 rhyolite also also occur. occur. formation appears to main cycles cycles of of volcanism volcanism with with increasing increasing iron iron enrichment enrichment (up (up to 24% FeO Iron—formations occur stratigraphically (total)). Iron-formations occur stratigraphically above above the iron—rich iron-rich (total)). these enriched enriched (icelandites). There may be a correlation between these basalts (icelandites). basalts and the basalts the deposition deposition of the the overlying overlying iron—formations. iron-formations. in shallow shallow water Hemlock was erupted in of the the Hemlock I infer that most most of I infer that because: because: a) a) there there is is aa high high percentage percentage of of interbedded interbedded volcaniclastic sedisedi- • b) the massive massive lava lava flows, flows, pillows pillows and and pillow pillow fragments fragments are ments and b) ments and vesicular. This implies implies subsidence of the the basement basement during during the the generally vesicular. emplacement of the the volcanics. volcanics. The Hemlock Formation reaches its maximum thickness of 7500 7500 m on on the the southwest southwest side side of of the the oval oval and and thins thins to to about about Johnson (1975) 750 mm to (1975) has shown shown that that this this increase increase is is to the the northeast. northeast. due to to actual actual stratigraphic stratigraphic thickening thickening and and is is not not structurally structurally related. related. Some time time after after volcanism volcanism the the rocks rocks underwent underwent low—grade low-grade regional regional metametamorphism (chlorite which was was followed by (chlorite grade in the Amasa Amasa Quadrangle), Quadrangle), which followed by the the Amasa structural structural uplift, uplift, producing producing the the oval. oval. REFERENCES igneous the Emperor igneous Major—element variation within the J .C., 1978, 1978, Major-element J.C., M.S. volcanic formations: M and Badwater Badwater volcanic complex the Hemlock and complex and the .S. Thesis, Michigan Michigan Technological Technological University. University. Dann, Dann, Johnson, D.J., D.J., 1975, 1975, Petrology of a portion of the Hemlock Formation, Formation, Iron County, Michigan: M.S. Thesis, Michigan Technological Michigan: M.S. Thesis, Michigan Technological University, University, 26 26 p.* P 11 11 �STRATIGRAPHY O' THE STRATIGRAPHY AND AND LITHOLOGY LITHOLOGY OF THEGLACIOGENIC GLACIOGENICSEDIMENTS SEDIMENT$ OF THE TWO HARBORS AREA, NORTHEASTERN THE TWO HARBORS NORTHEASTERN MINNESOTA MINNESOTA Laura Laura B. Gross, University University of of Minnesota, Minnesota, Duluth, mluth, Minnesota Minnesota 55812 55812 ABSTRACT ABSTRACT Several Several distinct distinct episodes episodes of of the the Late Late Wisconsin Wisconsin glaciation glaciation are are recorded recorded in the Quaternary deposits of the Two Harbors and. Whyte quadrangles the Quaternary deposits of the Two Harbors and Whyte quadrangles in in northeastern Ortho-tills northeastern Minnesota. Minnesota. Ortho-tills and a variety variety of of glacially glacially derived derived sediments, the Rainy Bainy and and sediments, including a clayey clayey diamicton, diamicton, are attributed attributed to the Superior lobe advances during the St. Croix and Automba phases advances during the St. Croix and Automba phases that that ococcurred The curred after after 16,000 16,000 years years B.P. B.P. The lithologic lithologic characteristics characteristics and and strati— stratigraphic distribution graphic distribution of of this this glacial glacial sedimentary sedimentary pile, along along with the origin of of the the red red clay clay are are elucidated elucidated in in this thisstudy. study. The The oldest oldest glaciation, glaciation, associated associated with the the St. St. Croix Croix phase, phase, is is reprerepresented in the northwestern part of the Whyte quadrangle by a distinctive in the northwestern part of the Whyte quadrangle by a distinctive topography topography of of the the southwest-oriented southwest-oriented drumlins drumlins (the (the Toimi Toimi drumlin drumlin field) field) and and abandoned subglacial subglacial streams. streams. These These features features are are attributed attributed to to the the Rainy Rainy lobe advance tunnel valley, valley, partially partially occupied occupied by by advance from from the the northeast. northeast. A tunnel Sullivan Lake, and small askers along Sullivan Creek were formed during ice ice Sullivan Lake, and small eskers along Sullivan Creek were formed during stagnation, when the the high high velocity velocity stream stream in in this this subglacial subglacial tunnel tunnel changed changed stagnation, when its habit from erosional to depositional. The drumlins consist its habit from erosional to depositional. The drumlins consist of of lodgelodgement till till with with aa strong strong northeast—trending northeast-trending fabric. fabric. Near Sullivan Sullivan Lake Lake glaglacial sediment thick. The drift drift is is grey grey to to brown brown (1OYR (10YR sediment is is more more than than 55 ina thick. 4/3), Large Large clasts clasts sandy to to stony, stony, with with aa sand:silt:clay sand:siltsclay ratio ratio of of 74:22:04. 74:22:04. 4/3), sandy are mainly lithic fragments of granite, granophyre, are mainly lithic fragments of granite, granophyre, greenstone, greenstone, and and gabbro. gabbro. The The glacial glacial sedimentation sedimentation associated associated with with the the Automba Automba phase phase of of the the SuSuperior lobe is recorded in a complex of deposits contained mainly lobe is recorded in a complex of deposits contained mainly in in the the Highland The sediments Highland Moraine. Moraine. sediments range range from from non—sorted, non-sorted, non—bedded non-bedded lodgelodgement ment till, till, to to supraglacially supraglacially derived derived debris, debris, including including gravity gravity flow flow deposdeposits and and well—sorted well-sorted fluvial fluvial and and lacustrine lacustrine sediments. sediments. The The lodgement lodgement till till of the brown (5YR (Sm 3/4), the Superior Superior lobe lobe is is reddish reddish brown 3/4), sandy sandy to to clayey, clayey, with a sand:silt:clay The clasts sandssi1t:clay ratio ratio of of 60:31:09. 60:31:09. clasts are are predominantly predominantly from from the the North Shore Shore Volcanics Volcanics (amygdaloidal (amygdaloidal basalt basalt and and rhyolite), rhyolite), granophyre granophyre and and red red sandstone sandstone of of Keweenawan Keweenawan age. age. The The Highland Highland Moraine Moraine is is aa hummocky hummocky kettle kettle and and kame kame topography topography in in the the northwestern northwestern part of of the the Two Two Harbors Harbors quadrangle quadrangle and and the the southeastern southeastern part part of by aa string string of of of the the whyte Whyte quadrangle. quadrangle. It It is is bordered on on its its western western edge edge by small Southeast of of small lakes, lakes, marking marking the the lateral lateral extent extent of of the the Superior Superior lobe. lobe. Southeast the abthe Highland Highland Moraine, Moraine, concentrated concentrated flows flows and and outwash outwash streams streams from from the the ablating lating Superior Superior lobe lobe deposited deposited aa variety variety of of slumped slumped glacial glacial sediments sediments and and gravel gravel lag lag debris. debris. Sediment Sediment supplied supplied from from stagnant stagnant ice ice sources sources and and melt— meltwater from from the the retreating retreating Superior Superior lobe lobe formed formed large large deltaic deltaic deposits deposits of of cross—bedded cross-bedded sands sands and and gravel, gravel, interfingered interfingered with with thin thin lenses lenses of of clay—rich clay-rich diamictons, by flow flow tills. tills. These These sediments sediments mark mark the the 348-366 348-366 mm and overlain overlain by diamictons, and strandline strandline of of Glacial Glacial Lake Lake Duluth, Duluth, aa proglacial proglacial lake lake which which formed formed along along the the margin of of the the retreating retreating Superior Superior lobe. lobe. Lacustrine Lacustrine clays, clays, deposited deposited concontemporaneously temporaneously with the the deltas, deltas, cover cover much much of of the the southern southern part part of of the the quadrangle (5YR 4/4), 4/4), with with aa quadrangle below below this this strandline. strandline. The The clay clay is is red/brown red/brown (5Th 12 �sand:silt:clay sand:silt:clay ratio r a t i oofof15:18:67, 15:18:67, and andranges rangesfrom frommassive, massive,highly highlyjointed, jointed, to finely laminated with pockets with with pebbly pebbly"lag "lagdeposits," deposits," t o f i n e l y laminated with pockets ofof "sand "sand nests," nests," to t overy veryplastic p l a s t i cand andstony. stony. It It is isexposed exposed extensively extensively along along the the lakeshore, streamvalleys, v a l l e y s , and andasa sthe t h esurficial s u r f i c i a ldeposit depositofof much much of of the the lakeshore, in i nstream North LakeSuperior. Superior. NorthShore ShoreofofLake Distinguishing till and and lake lake clay clayini nthe theLake LakeSuperior Superior Distinguishing between between clayey clayey till the south Though the red clay of region problematical. Though t h e red c l a y of t h e southshore, shore, the the region isisproblematical. "Douglas ''Douglas Till," T i l l , " isisattributed a t t r i b u t e dtot osubglacial subglacialprocesses processes(Johnson, (Johnson, 1980), l98O), my my investigation i n v e s t i g a t i o nconfirms confirmsthe t h einterpretation i n t e r p r e t a t i o nof of aalacustrine l a c u s t r i n eorigin o r i g i nof of the t h ered red clay c l a yalong alongthe t h enorth northshore shore(Moss, (Moss,1977), 1977). Restricted Restricted occurrence occurrencebelow belowhigh high association level strandlines, stacked lake terraces within the region, of l e v e l s t r a n d l i n e s , stacked lake t e r r a c e s within t h e region, association of "lag " l a g deposits," deposits," and andfine f i n elaminations laminationsindicate i n d i c a t e aa glacial g l a c i a l lacustrine l a c u s t r i n e rather rather than than subglacial subglacial origin o r i g i n for f o r the t h eclay—rich clay-rich diamicton diamicton of of the the North North Shore Shore of of Lake LakeSuperior. Superior. REFERENCES REFERENCES 1980, The The origin o r i g i n of of the the Lake Lake Superior Superior red red clay c l a y along alongWisconWisconM., 1980, Johnson, M., Johnson, sin's the Bayfield Bayfield peninsula: Peninsula: UnpubUnpubs i n ' s Lake Lake Superior Superior shoreline shoreline west west of of the lished M.S. thesis, University of Wisconsin, Madison, 90 p. l i s h e d M.S. t h e s i s , University of Wisconsin. Madison, 90 p. Moss, C.M., C.M., 1977, The The surf s u r f icial i c i a l and and environmental environmental geology geology of of the t h e French French 1977, Moss, Unpublished M.S. River quadrangle, St. Louis County, Minnesota: thesis, River quadrangle, St. Louis County, Minnesota: Unpublished M. S' thesis, University Universityof of Minnesota, Minnesota, Duluth. Duluth. I I p I I 13 �PRECAMBRIAN PRECAMBRIAN DIKE DIKESWARMS: SWARMS: PATTERNS PATTERNSAND AND PROBLEMS PROBLEMS H.C. H.C. Halls, Halls, Erindale Erindale Campus, campus, University University of of Toronto, Toronto, Mississauga, Mississauga, Ontario Ontario LSL L5L 1C6 1C6 ABSTRACT Precambrian Precambrian dikes dikes criss—cross criss-cross all all the the world's world's Precambrian Precambrianshields; shields; swarms swarms extend extend for for many many hundreds hundreds ofofkilometers, kilometers, and andobviously obviouslyrepresent represent Dikes Dikes are arecommonly commonly thought thought to to develop environment; develop in in aarift rift environment;preserved preservedswarms swarms along along the themargins margins of of the the Atlantic ~tlanticfor for example example represent represent the the earliest earliest rift rift stages stages in in the the formation formation of of this this ocean ocean during duringJurassic—Triassic Jurassic-Triassictimes. times. However However despite despite considerable considerable work work on on models models of ofrifting riftingand andsea—floor sea-floor spreading, spreading, little little work work has has been been done done on on dike dike swarms, swarms, particularly particularly the the enormous enormous Precambrian Precambrian ones ones that that are are not major question question about about not so so obviously obviouslyrelated relatedto tocontinental continentalseparation. separation. AA major these these and and younger younger swarms swarmsconcerns concernstheir theirmode modeofofemplacement. emplacement. What what is is the the form of of magma form and and location location magma chambers chambers that that fed fed these these swarms, swarms, how how has has the the magma of of dike swarm? magma flowed, flowed, and and what what controls controlsthe theorientation orientation dike swarm? major events in in Earth major magmatic magmatic events Earth history. history. Possible tothese these questions questions are are discussed discussed using using examples examples of of Possible solutions solutions to dike dike swarms swarms from from the the Canadian, Canadian, African, African, kustralian Australian and and Indian Indian 2+ 2+ Ga ca Shields. and geochemical Shields. tn In particular particular paleomagnetic, paleomagnetic, structural structural and geochemical results results will from thethe Matachewan—Hearst Kenora—Kabetogama will be begiven given from Matachewan-Hearstand and Kenora-Kabetogama swarms swarms that that have and direction of magma have bearing bearing on on regional regionalstructure structure andthe the direction of magmaflow. flow. By By analogy analogy with with more more recent recentdike dikeswarms, swarms, aaworking working hypothesis hypothesis that that shows magma dominantly sub—horizontal swarms shows promise promise is isthat that magmaflow flowisis dominantly sub-horizontalalong along swarms and changes petrology, and that thatlateral lateral changesinin petrology,geochemistry geochemistry and and fabric fabric may may help help to to locate ofof considerable importance locatemagma magma sources. sources. This This aspect aspectisis considerable importanceininmost most Precambrian Precambrian (and (andyounger) younger) dike dikeswarms swarms for forwhich which evolutionary evolutionarymodels modelshave have ' yet developed. yettotobebedeveloped. 14 �MICHIGAN'SS ENERGY ENERGY RESOURCES: RESOURCES: AAGEOLOGICAL GEOLOGICALPERSPECTIVE PERSPECTIVE MICHIGAN' Kalliokoski, Department Department of of Geology Geology and and Geological GeologicalEngineering, Engineering,Michigan Michigan JJ•. Kalliokoski, Technological Houghton, Michigan 49931 TechnologicalUniversity, University, Houghton, Michigan 49931 ABSTRACT ABSTRACT Michigan energy energy supply supply and and demand demand patterns patterns of of the the study study year year 1972 1972 Michigan (Fig. 1) 1) indicate indicate in in aa general general manner manner the thesituation situationas asititexists existsinin1982. 1982. (Fig. Line thicknesses thicknesses represent represent quantities quantities of of energy energy in in terms terms of of their their heat heat Line The wiggly wiggly line line at at top topisishydroelectric hydroelectricpower, power, the thesatellite satellite content. The content. symbol symbol is is nuclear nuclear power, power, and and blank blank box box above above "Transp." "Transp." represents represents the the use use of of oil oil by by the themanufacturing manufacturingindustry industryasasraw rawfeed feedfor forplastics. plastics. In In 1982 1982 coal coal consumption consumption is is down down by by about about one one third third and and oil oil is is up up by by aa like like amount, amount, some some of of the theshift shiftto toalleviate alleviateair airpollution. pollution. About About as as much much heat heat energy energy ultimately ultimately is is lost lost as as is isused, used, because becauseofofinefficiencies inefficiencies of of all all kinds kinds in in the the conversion conversionof of heat heat to touseful usefulenergy. energy. Michigan Michigan obtains obtains about about 1/5 1/5 of of its its gas gas and and oil oil from front in—state in-state sources. sources. Based on on aa review review of of the the occurrence occurrence and and possible possible quantities quantitiesof ofgeogeoBased logicaland and non—geological non-geological types types of of fuels fuels in in Michigan, Michigan, the the writer writer concludes concludes logical that that the the state state has has aafew fewenergy energyoptions optionsfor forthe thefuture future(Fig. (Fig.2). 2). On On the the right, right, for for purposes purposes of of comparison, comparison, are are shown shown the the fuel fuel requirements requirements for for On the the left left are are the the in—state in-state reserves reserves utilized utilized in in 1981, 1981, with with an an 1972. On 1972. estimate estimate of of the the years years that thatthey theywill willlast. last. In In the the center center are are listed listed the the resources resources to to which which Michigan Michigan might might turn turn as as the thepresent present reserves reserves become become continued energy self—sufficiency be level of exhausted, should some level of continued energy self-sufficiency be should some exhausted, deemed to to have have economic economic value. value. Coal Coal and and peat peat may may be be less less important important than than deemed In the the northern northern part part of of the the bitumen— bitumen- and and kerogen—containing kerogen-containing Antrim Antrim Shale. Shale. In the the lower lower peninsula peninsula several several hundred hundred square square miles miles are are underlain underlain by by this this shale that that contain contain between between 10 10 and and 15 15 gallons gallons per ton ton of of Fisher Fisher assay assay shale extractable oil oil across across30 30 feet. feet. extractable Production State Resources TODAY TODAY HYORO FUTURE FUTURE NNucl. 77 GAS 30 yr8 Antrim Sh. 50-100 yrs 10 yrs Figure Figure 22 Figure 11 Figure 15 LTt'J LtJ WOOD OIL - 1972 1972Rem. Reg. YARD YARD STICK STICK ILj hid....rnuj �THE VOLCANIC VOLCANIC ROCKS ROCKS OF OF THE THE UNNAMED UNNAMED FORMATION, FORMATION, THE PORCUPINE MOUNTAINS MOUNTAINS REGION, REGION, PORCUPINE MICHIGAN MICHIGAN - AA MIDDLE MIDDLE KEWEENAWAN ICEWEENAWAN ERUPTIVE CENTER ERUP2IVE CENTER - Paul J. J.Kopydlowski, Kopydlowski,Department Department of OfGeology Geology and and Geological Geological Engineering, Engineering,MichMichPaul igan Technological Technological University, University, Houghton, Houghton, Michigan Michigan 49931 49931 igan ABSTRACT ABSTRACT The unnamed unnamed formation formation is isa aMiddle MiddleICeweenawan Kewenawan central central shield shield volcano volcano The (White, (White, 1972) 1972) which which crops crops out out in in the the vicinity vicinity of of the the Porcupine Porcupine Mountains Mountains in in the the Upper U p p r Peninsula Peninsulaof of Michigan. Michigan. Maximum Maximum surface surface thickness thickness of of this this lensoid— lensoidshaped formation formation is is about about 8,000 8,000 ft. in in the the Bergland Bergland and and Thomaston Thoroaston quadranquadranshaped gles. gles. The The volcanic volcanic pile pile gradually gradually narrows, narrows, eventually eventually wedging wedging out out in in the the Greenland quadrangle to to the the east east and and in in the the Little Little Girls Girls Point Point quadrangle quadrangle Greenland quadrangle to to the the west. west. The The formation formation is is conformable conformable on on and and is is aa continuation continuation of of the the underlying underlying Portage Portage take Lake Volcanics. Volcanics. Previously grouped with the Portage Previously grouped with the Portage ft. Lake Lake Volcanics, Volcanics, the the unnamed unnamed formation formation was was first first recognized recognized as as aa separate separate unit unit by by Johnson Johnsonand and White White (1969). (1969). The The distinction distinction between between the the two two units units is is that the the unnamed unnamed formation formation contains contains aa greater greater percentage percentage of of relatively relatively acidacidthat ic ic volcanic volcanic rocks. rocks. Overlying overlying and and locally locally interfingering interfingering with with the the unnamed unnamed formation is is the the Copper Copper Harbor Harbor Conglomerate. Conglomerate. formation Spatial relationships relationships between between the the various various rock rock types types within within the the unnamed unnamed Spatial formation formation were were observed observed in in the the field. field. Samples Samples were were collected collected perpendicular perpendicular to to strike striketo to obtain obtain representative representativevertical verticalsections sectionsof ofthe theformation. formation. ForForty—seven ty-seven samples samples were were analyzed analyzed for for major major and and minor minor elements. elements. Compositions Compositions of baof the the lava lava flows flows within within the the unnamed unnamed formation formation range range from from rhyolite rhyolite to to basalt. salt. Mdesite Andesiteisisthe themost mostcommon commonrock rocktype. type. Twenty—five Twenty-five samples samples from from six six distinct topdistinct felsite felsite bodies bodies were were analyzed. analyzed. These These include: include: 1) 1) the the felsite felsite topping ping Copper Copper Peak Peak (Chippewa (ChippewaHill), Hill), 2) 2) the the felsite felsite that that makes makes up up the the highhighlands lands of of the the Porcupine Porcupine Mountains Mountains Wilderness Wilderness State State Park, Park, 3) 3) the the Chippewa Chippewa 2felsite elsite located between between White White Pine Pine and and Bergland, Bergland, 4) 4) two two quartz quartz latite latite flows flows within the the Porcupine Porcupine Mountains Mountains Wilderness Wilderness State State Park, Park, 5) 5)the the quartz quartz porphyporphywithin ry located located north north of of Bergland Bergland and and 6) 6 )an anash—flow ash-flowtuff tufflocated locatedaobut aobut77miles miles ry southeast southeast of of White White Pine. Pine. Emphasized Emphasized to to aa lesser lesser extent extent in in the the study study are are the the analyses analyses of of 15 15 basic basic and and intermediate intermediateflows. flows. Finally, Finally, 44 intrusions intrusions were were chemically chemically analyzed. analyzed. They They includes include: 1) 1) two two basaltic basaltic sills sills from from within within the 2 ) aa diorite diorite dike dike which which intrudes intrudesthe the felsite felsite of of the the the quartz quartz porphyry, porphyry, 2) Porcupine Porcupine Mountains Mountains and and 3) 3 ) aa diabase diabase granophyre yranophyre complex complex positioned positioned at at the the base base of of the the unnamed unnamed formation formationnear nearthe the western edge of the Matchwood quadwestern edge of the Matchwood quad— rangle. rangle. Evaluation Evaluation of of the thechemical chemical variance variance between between and indiand within within the the indi- vidual flows flows and and intrusions intrusions is is incomplete incomplete at the time time of of this thiswriting. writing. vidual at the Lavas of ofthe theunnamed unnamed formation formation may may have in an anenvironment environment simisimiLavas have erupted erupted in lar lar to to that that of of the the Tertiary Tertiary of of eastern eastern Iceland Iceland (Green, (Green,1977). 1977). Flood basalt basalt Flood flows interfingflows from from fissures fissures within within the the Midcontinent Midcontinent Rift Rift overlapped overlapped and and interfing— ered with with relatively relatively acidic acidic flows flows from from the the central central shield shield volcano. volcano. At At the the ered sane time, time, emplacement emplacement of of shallow shallow intrusions intrusions occurred occurred at at vent vent areas areas and and hyhysame drothermal drothermal activity activity took tookplace place locally. locally. The The central central shield shield volcano volcano of of the the unnamed formation formationdiffers differsfrom fromcentral central volcanoes volcanoesof of the theTertiary Tertiaryof of eastern eastern unnamed Iceland in in that that the theformer formeris ismuch muchlarger largerin insize sizeand andcontains containsa agreater greater Iceland percentage percentage of of andesite andesite than thanthe thelatter. latter. Dike Dike swarms swarms which which are are common common in in 16 4 � central centralvolcanoes volcanoesofofthe theTertiary Tertiaryof ofeastern easternIceland Icelandare arelacking lackingininthe theununAfter volcanism, the volcanic rocks of the unnamed named namedformation. formation. After volcanism, the volcanic rocks of the unnamedforformation mation were wereregionally regionallymetamorphosed metamorphosedtotothe thechlorite chloritefacies. facies. Subsidence Subsidence within the Lake Superior Syncline tilted the unnamed formation within the Lake Superior Syncline tilted the unnamed formationnorthward northward exposing exposinga across—sectional cross-sectionalview viewofofthe thecentral centralvolcano. volcano. Further Furtherfolding foldinginin the the vicinity vicinity of ofthe thePorcupine PorcupineMountains Mountainsresulted resultedininthe theformation formationofofthe the At its center, the unnamed formation Porcupine PorcupineMountain Mountainanticline. anticline. At its center, the unnamed formationisisexexposed posedforming formingthe thehighlands highlandswithin withinthe thePorcupine PorcupineMountains MountainsWilderness WildernessState State Park. Park. REFERENCES REFERENCES Green, J.c., J.C., Green, 1977, 1977, Keweenawan Keweenawanplateau plateauvolcanism volcanismininthe theLake LakeSuperior SuperiorRegion, Region, 16, p. 407—422. Geol. Geol. Association Associationof ofCanada, Canada,Special SpecialPaper Paperno. no. 16, p. 407-422.  Johnson, Johnson,R.F. R.F. and andWhite, White,W.S., W.S., 1969, 1969,Preliminary Preliminaryreport reporton onthe thebedrock bedrockgeolgeolMatchwood quadrangle, Ontonagon ogy ogy and andcopper copperdeposits depositsof of the the Matchwood quadrangle, OntonagonCounty, County, Michigan, Michigan, U.S. u.S. Geol. Geol. Survey, Survey,Open-file open-file Report. Report. White, White, W.S., W.S., 1972, 1972, Keweenawan Keweenawan flood floodbasalts basalts and and continental continentalrifting, rifting,Geol. Geol. Soc. no. 7,7,p.p. 732—734. 732-734. Soc. America, America, Abs. Abs. with withPrograms, Programs,v. v. 4,4,no. I I I S 17 S �HYDROTHERMAL PROCESSESAND M'IDMASSIVE MASSIVESULFIDE SULFIDE DEPOSITS HYDROTHERMAL PROCESSES DEPOSITS AT OCEANIC OCEANIC SPREADING SPREADING CENTERS CENTERS Randolph Randolph A. A. Icoski, Koski, U.S. U.S. Geological Geological Survey, Survey, 345 345 Middlefield MiddlefieldRoad, Road, Menlo-park, Menlo-Park, California 94025 California 94025 ABSTRACT ABSTRACT Active hydrothermal hydrothermal vents vents and and metal metal sulfide sulfide deposits deposits have have been been located located and and sampled sampled along along Pacific Pacific Ocean Ocean spreading spreading centers, centers, including including the the East East PacifPacific Rise, fica Ridge Ridge (Fig. (Fig. Rise, the the Galapagos Galapagos spreading spreading center, center, and and the the Juan Juan de de Fuca 1). These discoveries discoveries have have confirmed confirmed predictions, predictions, based based on on studies studiesof of heat— heat1 ) . These flow flow patterns, the the widely widely distributed distributed basal metalliferous metalliferous sedimentary sedimentary layer layer overlying overlying oceanic oceanic crust, crust, basalt/seawater—interaction basalt/seawater-interactionphenomena, phenomena, and and volcano— volcanogenic sulfide sulfide deposits deposits in in ophiolite ophiolite complexes, complexes, that fluids fluids circulating circulating through formedlithosphere lithosphereatat oceanic oceanic spreading spreadingcenters centers can can effective effectivethrough newly newly formed ly mineraldeposits deposits on onthe the sea sea floor. ly mobilize mobilize metals metals and and form form mineral floor. A for the A genetic genetic model model for the deposition deposition of of polymetallic sulfides sulfides at at medium— mediumto from aa magma magma to fast-rate spreading centers proposes that the heat flux from fast—rate spreading centers proposes that the heat flux chamber at aashallow level (1—3 1cm) the sea chamber emplaced emplaced at shallow level (1-3 km) below below the sea floor floorinduces induces convective recharge of of seawater lithoconvective flow flow and and continuous continuous recharge seawater through through permeable permeable litho- sphere along the flankstoward towardthe theheat heat source source (Fig. sphere from from along the oceanic—ridge oceanic-ridge flanks (Fig. 2). 2). 4 The The cycle cycle continues continues with with deep deep penetration penetration along along cracking cracking fronts fronts through through the the lava flows flows and and dike dike complex complex of of oceanic oceanic layer layer 22 to to levels levels near near the the magma magma chamber, chamber, and is is followed followed by by upwelling upwelling of of the the buoyant buoyant hydrothermal hydrothermal fluid fluid along fractures At high fractures and and faults faults to to the the sea sea floor. floor. high temperatures temperatures and and water/rock water/rock ratios, ratios, hydrolytic hydrolytic and and oxidative oxidative reactions reactions with with mafic mafic wallrock wallrock generate aa low—pH low-pH low—Eh low-Eh solution solution capable capable of of leaching leaching and and transporting transporting transition transition metals metals and and sulfur. sulfur. Cooling of of the the upwelling upwelling fluid fluid during during adiaadiabatic batic expansion expansion and and then then its its further further cooling cooling and and neutralization neutralization upon subsubsurface mixing mixing with with ambient ambient seawater seawater cause cause deposition deposition of of sulfide sulfide minerals minerals along rapid fluid fluid flow flow results results in in the the discharge discharge of of along subsurface subsurface channelways; channelways; rapid reduced fluid and seafloor/seaand the the deposition deposition of of massive massive sulfide sulfide at at the the seafloor/seawater water interface. interface. Oxidizing Oxidizing conditions on the the sea sea floor floor promote promote the the devel— development Un from from optnent of of distal distal silicate silicateand and oxide oxide facies facies and the the fractionation fractionation of Mn Fe. Fe. 0 Preliminary Preliminary investigations investigations of of sulfide sulfide deposits deposits along along the the Pacific Pacific Ocean Ocean ridge ridge system system reveal reveal considerable considerable diversity. diversity. For For example, example, on on the the East East PacifPacific ic Rise Rise at at lat. lat. 21°N, 21aN, composite composite mound—chimney mound-chimney edifices edifices composed composed of of Zn, Zn, Fe, Fe, and and Cu Cu sulfides, sulfides, Ca Ca and and Ba Ba sulfates, sulfates, and and silica silica overlie overlie basalt basalt in in aa horst— horstand—graben and-graben terrain terrain near near the the volcanically volcanically active active ridge ridge axis. axis. Active Active vents vents are in parparare vigorously vigorously discharging discharging high—temperature high-temperature (350°—400°C) (350°-40O0C fluid fluid rich rich in ticulate sulfide sulfide (black (black smokers) smokers) and silica silica (white (white smokers); smokers); the the latter latter host host exotic exotic communities communities of of worms, worms, crabs, crabs, and and clams. clams. In In the the southern southern trough trough of of the the Guaymas Guaymas Basin Basin in in the the Gulf Gulf of of California, California, hot hot springs springsare are depositing depositing mounds mounds of of Fe Fe and and Zn Zn sulfides sulfides (the (the unusual unusual assemblage assemblage pyrrhotite + + sphaler— sphaler- and talc on and ledges ledges of of Fe—rich Fe-rich talc on rapidly rapidlyaccumulating accumulating ponds ponds of of unconsolunconsolidated idated ooze ooze and and mud. mud. In addition, addition, hydrothermal hydrothermal activity generated generated by the its) ite) intrusion into water—saturated intrusion of of diabase diabase sills sills into water-saturated sediment sediment rich rich in inorganic organic material into gasoline—range material has hastransformed transformed the theorganic organicmaterial material into gasoline-rangehydrocarhydrocarbons. S 18 �170°W 90° 120° 150° 60° 70°N 600 30° mineral deposits Guaymas Basin DSDP 471\ East Pacific Riselat 21° East Pacific lat 13ON 0° East Pacific Rise lat 20's I I 25° S Figure Figure 19 1 1 ! �AXIS OF SPREADING . -IMASSIVE SULFIDE OXIDE & SILICATE HEAT SOURCE Figure Figure2 2 20 �On On the theGalapagos GalapagosRift Rift at atlong. long. 86°w, 86OW, hydrothermal hydrothermaldeposits depositsoccur occuralong along the the base base ofofnormal—fault normal-faultscarps scarpsbounding boundinga ahorstlike horstlikecentral centralridge. ridge. AA large(1,000 (1,000 mm long, long, 150 150 mm wide, wide, 35 35 mm thick) thick)prism prismofofCu—rich Cu-richand andZn—poor Zn-poor large massive massive sulfide sulfide with with numerous numerous large large inactive inactive chimneys chimneys has has formed formedalong along aa On the the southern southern Juan Juan de de Fuca Fuca Ridge, Ridge, encrustations encrustations south-facingescarpment. escarpment. On south—facing of of Zn—rich zn-rich and andCu—poor Cu-poormassive massivesulfide sulfideand andassociated associatedbenthic benthic organisms organisms mark nark aa series series of ofhydrothermal hydrothermal vents vents and andvent vent fields fieldsin ina aregion regionunderlain underlain sheetflows. The deposits deposits are arespatially spatiallyassoassolargelyby by glassy glassyferrobasalt ferrobasalt largely sheetf lows. The ciated ciated with with aa shallow shallowcleft cleftininthe theaxial—valley axial-valleyfloor. floor. Continued Continued research research on on hydrothermal hydrothermal systems systemsand andpolymetallic polymetallic sulfide sulfide deposits deposits on on the themidoceanic—ridge midoceanic-ridge system systemwill willstimulate stimulateand andimprove improvecurrent current concepts concepts in in such such diverse diverse fields fieldsas as ore ore genesis, genesis, mineral mineral exploration, exploration, evoluevolutionary tionarybiology, biology, and anddeep—seabed deep-seabedmining. mining. I I I 21 �A A GEOCHEMICAL GEOCHENICM. CORRELATION, CORRELATION, WITH WITH CORRELATIVE CORRELATIVE INFERENCES INFERENCESFROM FROM PETROGRAPHIC PETROGRAPHICAND AND PALEOMAGNETIC PALEOMAGNETIC DATA, DATA, OF OFTHE THEGREENSTONE G R E E N S W E FLOW, FLOW, KEWEENAW PENINSULA AND ROYALE, MICHIGAN KEWEENAW PENINSULA AND ISLE ISLE ROYALE, MICHIGAN I A.A. A.A. Longo, Longo, Department Department of ofGeology Geology and and Geological Geological Engineering, Engineering, Michigan Michigan TechTechnological nological University, University, Houghton, Houghton, Michigan Michigan 49931 49931 ABSTRACT ABSTRACT correlation correlation across across the the Lake Lake Superior Superior syncline syncline between between Isle IsleRoyale Royale and Peninsulaof of Michigan Michiganwas wasfirst first proposed and the theKeweenaw Keweenaw Peninsula proposed by by Lane Lane (1899). (1898). AA The The key key to to this this correlation correlation was was the thepresence presence of ofone oneimmense, immense,continuous continuous Middle Middle Ketqeenawan Keweenawan tholeiitic tholeiitic flow known known as as the the Greenstone Greenstone Flow Flow (GSF). (GSF). Thickness Thickness data data for for the the GSF GSF on on Isle Isle Royale Royale (Lane, (Lane, 1898 1898;1911) 191 1)and andthe theKewee— Keweenaw naw Peninsula Peninsula (Cornwall, (Cornwall, 1951) 1951) imply imply aa total total volume volume for for the the GSF GSF of of 1,000 1,000 km3, km3, which which has has been been viewed viewed as as "a "a conservative conservative estimate" estimate* (White, (White, 1960). 1960). Ru— Huher her (1973) (1973) confined confirmedthe thesimilarities similaritiesofofthe theGSF GSFononIsle IsleRoyale Royaleand andthe theICe— Keweenaw weenaw Peninsula, Peninsula, and and he he supported supported the the correlation. correlation. AA single single lava lava flow flow of of such such great great magnitude magnitude would would possibly possibly be be the the world's world's largest. largest. However, However, evievidence dence for for this this correlation correlation was was based based solely solely on on field fieldcriteria. criteria. This This paper paper is is the the first first quantitative quantitative study study to to test test the the validity validity of of the the proposed proposed corre— correlation. lation. AA total (34of ofwhich whichwere wereoriented) oriented)were were used used in in this this total of of 57 57 samples samples(34 The The samples samples were were collected collected in in stratigraphic stratigraphic sequence sequence across across the the GSF GSF at at Blake Blake Point, Point, Isle Isle Royale, Royale, Michigan, Michigan, and and at at Cliff Cliff Drive Drive and and Phoenix, Phoenix, Michigan Other Michigan on on the theKeweenaw KeweenawPeninsula. Peninsula. Other samples samples were were collected collected from from directly directly above above and and below below the the CS? GSF from from the the latter latterthree threesites, sites,from fromthe theGB? GSF in in the the MTh MTU experimental experimental mine, mine, and and from from aa drill drill core core through through the the GB? GSF in in SenSeneca, eca, Michigan. Michigan. The The latter latter two two sites sites were were places places where where oriented oriented sampling sampling was was not not possible, possible, and and the the GB? GSF was was the the thinnest thinnest (45—15 (45-75 m). m). study. study. I I II All All rocks rockswere wereanalyzed analyzedby byXR? XRFfor forboth bothmajor majorand andtrace traceelements. elements. Only Only specimens specimens least least affected affected by by migrating migrating hydrothermal hydrothermal fluids fluids were were chosen chosen for for chemical chemical evaluation. evaluation. These These sample sample sites sites were were ophitic ophitic zones zonesin inthe theflow, flow, which zones of of lowest lowest permeability permeability and and least least alteration. alteration. which are are the the zones Thin Thin sections sectionswere were studied studied to to observe observe changes changes in in mineralogy, mineralogy, mode, node, textexture and plagioclase composition. For samples with >35% plagioclase ture and plagioclase composition. For samples with >35% plagioclase an an XRD XRD method method for for plagioclase plagioclase determination determination was was utilized utilized (Smith (Smithand and Gay, Gay, 1958). 1958). Type Type and and degree degree of of alteration alterationwere were evaluated evaluatedto toassist assistininthe theselection selectionof of samples for geochemical analysis, and to aid in the interpretation of samples for geochemical analysis, and to aid in the interpretation of samples samples with with radically radicallydifferent differentgeochemistry. geochemistry. Core Core specimens specimens were were taken taken from from the the oriented oriented samples samples for for paleomagnetic palmagnetic evaluation. Statistical results of the remanent magnetism evaluation. Statistical results of the remanent magnetism on on Isle IsleRoyale Royale were compared to present (this paper) and previous work on Keweenaw were compared to present (this paper) and previous work on Keweenaw(Books, (Books, 1972). 1972). The The results results were were used used as as aa correlation correlationtool. tool. The The CS?, GSF, an an olivine olivinetholeiite, tholeiite, is is the the thickest thickest flow flow in in the the Portage Portage Lake Lake Volcanic Sequence of Michigan's Copper Country. Volcanic Sequence of Michigan's Copper Country. Thicknesses Thicknessesrange rangefrom from 30 30 to to 245 245 mm on on Isle Isle Royale Royale (Huber, (Huber, 1973) 1973)and and from from 45 45 to to 427 427 mm on on the the Keweenaw Keweenaw Peninsula (Cornwall, 1951). 22 �- The The flow flow is is stratified stratified due due to to differentiation differentiation into into chemically chemically distinct distinct fractions, fractions, which which are are the the pegmatitic pegmatitic lenses lenses with with associated associated granophyric granophyric dikes dikes Most differentiated differentiatedare are the the peg— pegand and sills sills (pegmatoids), (pegmatoids),and and ophitic ophitic zones. zones. Most matoids matoids whose whose frequency frequency varies varies proportionally proportionally with with total total flow flowthickness. thickness. These These coarse—grained coarse-grained fractions fractions vary vary in in thickness thickness and and shape, shape, usually usually occur occur as stratiform stratiform features, features, but but were were also also noted noted to to occur occur as as auto—intrusions auto-intrusions in in as the the columnar—jointed columnar-jointed melaphyre melaphyre on on Isle IsleRoyale. Royale. Pegmatoids Pegmatoids are are permeable permeable channelways channelways for for the the deuteric deuteric and andlater laterhydrothermal hydrothermal fluids. fluids. Therefore, Therefore, these for chemical chemical correlation correlation in in flood flood basalt basalt ter— terthese zones zones are are poor poor sites sites for ranes. ranes. ophitic Ophitic areas, areas, the the major major flow flow units, units, presumably presumably occurred occurred as as continuous continuous In thicker thicker portions portions of of layers layers in in the the upper upper and and lower lower sections sections of of the the GSF. GSF. In lenses with intermingling pegmatoids are subophitic to ophitic the GSF subophitic to ophitic lenses with intermingling pegmatoids are the GSF sandwiched sandwiched between between the the upper upper (UO) (UO) and and lower lower (LO) (LO) ophitic ophitic zones zones and and are are prepresumed stratigraphically discontinuous. sumed stratigraphically discontinuous. In In summary, summary, the the UO UO and and LO LO are are presumed presumed continuous continuous throughout throughout the the flow flow and and are are low low in in permeability; permeability; thus thus they they were were least least affected affected by by migrating migrating hydrothermal LO were were chosen chosen as as ideal ideal sites sites hydrothermal fluids. fluids. Therefore, Therefore, the the UO UO and and LU for chemical correlations within the Portage Lake Volcanics. for chemical correlations within the Portage Lake Volcanics. An An average average OS? GSF composition composition as as calculated calculated from from this this study study was: was: Trace Trace Elements Elements (ppm) (pp) Major Elements Elements (wt.%) (wt.%) Major CaC Si02 == 46.7 46.7 CaO Si02 == 15.1 Na20 Al^ 1 5 . 1 Na20 A1203 FeO ~ 112.8 2.8 K20 FeO* K20 = MgO MgO = 7.8 7.8 TiO, Ti02 p205 == 0.14 0.14 p205 == 9.9 9.9 = 2.1 = 2.1 = 0.4 0.4 =" Ba = 103.5 213.4 Cr Cu = 66.4 La = 10.9 Mn 1675.4 1.2 1.2 Ni = Pb = Rb S Sc Sn Sr = 258.7 V 194.7 186.2 Y <2 Zn Zr 7.8 <50 27.9 5.9 13.5 84.4 91.8 The The data data have have revealed revealed the the following followingfacts: facts: 1 • can be be demonstrated demonstrated within within ophitic remarkable chemical chemical homogeneity homogeneity can ophitic remarkable sections of of the the OS?. GSF. sections A A 2. Similar geochemistry geochemistry existed in all all sites sites analyzed analyzed with with the the exception exception the GB? from altered GSF from the MTU chlorite-prehnite-punpellyite altered MTU experiexperiof the the chlorite—prehnite—pumpellyite of mental mine. mine. mental 3. Most flows flows directly directly beneath beneath the the GSF GSF are are chemically chemically similar similar to to the the GB?, GSF, and believed believed to to be be part part of of aa magmatic magmatic cycle cycle which which terminated terminated with with the the extrusion extrusion of of the the GB?. GSF. 4. similar Similar petrology is found found in in all all OS? GSF sample sample sites sites except except the the altered altered OS? HTU mine. mine. GSF from from the the MTU 5. Flows Flows directly directly above above the the GB? GSF display display different different chemistry chemistry and and petrology petrology in most most sample sample sites. sites. in Petrology Petrology of of flows flows directly directlybeneath beneaththe theGB? GSF are are similar to tothe theGB?. GSF. similar 23 �- ' - . à 6. 6. statistically similar similar directions directions of of remanent magnetization Statistically magnetization are found found for the GSF on Isle Royale and the Iceweenaw Peninsula. the on Isle Boyale and the Keweenaw Peninsula. 7. 7 . statistically similar directions of remanent Statistically remanent magnetization magnetization direction direction are found for flows directly beneath the GSF on Kewee— found for flows directly the on Isle Isle Royale Royale and Keweenaw Peninsula (Books, 1972) which tend to diverge away from the diverge away from the mean mean Peninsula (Books, 1972) which remanent magnetization direction of the G5F. However, limited data direction of the GSF. However, exist. In light light of of all all the the data data collected collected for for this this study, study, no no inconsistencies inconsistencies were found to occur through the entire GSF. Since a possibility exists were found to occur through the entire GSF. that the GSF on Isle Royale and the GSF on the Keweenaw Peninsula are two on Isle Boyale and the GSF on the Keweenaw Peninsula separate flows from the same magmatic cycle, cycle, a positive correlation correlation cannot cannot be be proved. proved. ii I I I I 4I 1I 24 24 1 �URANIUM URANIUM IN IN LOWER LOWER PROTEROZOIC PROTEROZOICPHOSPHATE-RICH PHOSPHATE-RICHMETASEDIMENTARY METASEDIMENTARYROCKS BOCKS OF EAST-CENTRAL MINNESOTA EAST-CENTRAL MINNESOTA Peter Peter L. L. McSwiggen, McSwiggen, Minnesota Minnesota Geological Geological Survey, Survey, University University of of Minnesota, Minnesota, St. Paul, Paul, Minnesota Minnesota 55108 55108 ABSTRACT ABSTRACT Exploration for uranium uranium deposits deposits related related to to the the unconformity unconformity between between the lower Proterozoic Thomson Formation and the middle the lower Proterozoic Thomson Formation and the middle Proterozoic Proterozoic Fond Fond du du Lac Lac Formation Formation in in east—central east-central Minnesota Minnesota has has defined defined several several very very low low grade grade uranium uranium occurrences. occurrences. Most Most of of these these occurrences occurrences are are associated associated with with phosphosin the Thomson Formation, which consists dominantly phate—rich units phate-rich units the Thomson Formation, which consists dominantly of of interlayered interlayered feldspathic feldspathic graywacke, graywacke, siltstone, siltstone, and mudstone mudstone and and lesser lesser amounts of of carbonaceous carbonaceous mudstone, mudstone, dolomite, dolomite, quartzite quartzite and and volcanic volcanic rocks. rocks. The formation was deformed and metamorphosed under lower The formation was deformed and metamorphosed under lower greenschist greenschist to to middle middle amphibolite amphibolite facies facies conditions conditions during during the the Penokean Penokean orogeny orogeny approxiapproximately m.y. ago. ago. mately 1,870 1,870 m.y. Samples of the the phosphate phosphate units units from from two two localities localities were were studied studied to to characterize characterize the the uranium uranium occurrences. occurrences. The The Thomson Thomson Formation Formation at at these these lolocalities occurs at chlorite grade, and the uranium in the samples calities occurs at chlorite grade, and the uranium in the samples averages averages at ppm. The The phosphate phosphate units units are are relatively relatively thin, thin, having having aa maximaxiat least least 400 400 ppm. mum thickness of about 30 cm (Ulimer, 1981), and are intercalated mum thickness of about 30 cm (Ullmer, 19811, and are intercalated with with beds beds of black black to to gray gray recrystallized recrystallized chert, chert, and and lesser lesser amounts amounts of of carbonaceous carbonaceous slate slate and and siliceous siliceous carbonates. carbonates. The The units units consist consist of of both both conglomeratic conglomeratic The conglomerate is characterized and and thinly thinly laminated laminated rock. rock. The conglomerate is characterized by by angular angular to to subrounded pebbles of cryptocrystalline apatite and recrystallized of cryptocrystalline apatite and recrystallized chert chert set in in aa matrix matrix of of apatite, apatite, quartz, quartz, and and lesser lesser amounts amounts of of argillaceous argillaceous Both the pebbles and groundmass contain variable material. amounts of of carcarmaterial. Both the pebbles and groundmass contain variable amounts The thinly laminated rock consists of interlayered bonaceous bonaceous material. material. The thinly laminated rock consists of interlayered apatite, apatite, quartz, quartz, and and lesser lesser amounts amounts of of argillaceous argillaceous and carbonaceous carbonaceous material. material. textural textural arrangement arrangement of of the the uranium uranium in in these these phosphate—rich phosphate-rich samples indicates that samples indicates thatthe theuranium uranium has has had had aacomplex complex paragenetic paragenetic history. history. within the Much Much of of the the uranium uranium occurs occurs evenly evenly disseminated disseminated within the phosphatic phosphatic pebpebbles implying that that it it was was precipitated precipitated syngenetically syngenetically with with the the bles and layers, layers, implying The The phosphatic material, material, or or was was fixed fixed out out of of the the Thomson Thomson sea sea by by the the phosphatic phosphatic Concentrations sediments sediments on the the sea sea floor. floor. Concentrations of somewhat somewhat younger younger uranium uranium along planes recrysplanes that that parallel parallel the the tectonic tectonic foliation foliation imply imply secondary secondary recrysAdditional tallization, probably probably during during the the metamorphism. metamorphism. Additional concentrations concentrations of uranium uranium along along joint joint or or fracture fracture planes planes at at an an angle angle to to the the foliation foliation indicate indicate aa postmetamorphic postmetamorphic mobilization mobilization of of the the uranium. uranium. Uranium as overgrowths overgrowths around around pyrite pyrite grains grains and and as as individindividUranium also also occurs occurs as ual mineral mineral grains. grains. Nearly Nearly all all of of the the pyrite pyrite grains grains in in the the samples samples studied studied ual are are surrounded surrounded by by some some uranium uranium mineralization, mineralization, and and many many show show aa multi—stage multi-stage history of of replacement replacement of of the the pyrite pyrite by by aa uranium uranium phase. phase. The The individual individual uranium mineral grains grains commonly commonly contain contain other other phases, phases, such such as as pyrite pyrite and and possibly possibly barite. barite. These These mineral mineral grains grains are are typically typically subrounded subrounded to to rounded, rounded, Associated and contain contain 55—75 55-75 percent percent UO2. UO;. Associated with with the the uranium uranium in in these these grains grains are Pb, Pb, P, P, Ca, Ca, Fe, Fe, Ba, Ba, 5, S, Ti, Ti, Cu Cu and and Zn. Zn. are E., 1981, 1981, A mid—Proterozoic mid-Proterozoic phosphate phosphate occurrence occurrence in in east—central east-central Ullmer, E., Minnesota: Newsletter Newsletter IGCP IGCP Project Project 156, 156, no. no. 8, 8, p. p. 22—25. 22-25. 25 �MINERALOGIC AND OF ANORTHOSITES DULUTH MINERALCGIC AND TEXTURAL TEXTURAL VARIATIONS VARIATIONS OF ANORTHOSITES IN INTHE THE DULUTHCOMPLEX, COMPLEX, FOREST CENTER W QUADRANGLE, MINNESOTA FOREST CENTER NW I). James Miller, Jr. GeoJames D . Miller, Jr. and and Paul Paul W. W. Weiblen, Weiblen, Department Department of Geology Geology and and Geophysics, physics, University University of ofMinnesota, Minnesota, Minneapolis, Minnesota Minnesota 55455 55455 ABSTRACT ABSTRACT Although anorthositic rocks occur over over 60 60 percent of of the the exposure exposure area area of of the the Duluth Duluth Complex, Complex, they they are are inadequately inadequately studied studied and and poorly poorly understood. understood. The anorthosites anorthosites are to be gabbroic older gabbroicsequence sequence The are considered considered to be part partofofananolder was intruded by troctolite and gabbro, that that was intruded by troctolite and gabbro, but this this interpretation interpretation is is not not definitive. This report definitive. This report on on the the preliminary preliminary results results of of field field and and petrograph— petrographic ic studies studies is is part part of of aa broader broader study study to to acquire acquire new new data data that that bear bear on on the the origin of the anorthositic rocks. Detailed lakeshore mapping of the origin of the anorthositic rocks. Detailed the study study area I), which was previously mapped at reconnaissance scale in in 1968 1968 area (Fig. (Fig. 1), by Phinney, was was conducted conducted in in the the summer summer of of 1981. 1981. NW quadrangle quadrangle appear appear to to The anorthositic anorthositic rocks in in the the Forest Forest Center Center NW form aa cap over over troctolitic troctolitic rocks, rocks, which which are are exposed exposed in in three three separate separate Exposed contacts areas. areas. contacts between between troctolite troctolite and and anorthosite anorthosite are are commonly commonly broad, complex complex zones zones of of mixed rock rock types. types. The anorthositic anorthositic rocks rocks are are extremely extremely variable variable in inmineralogy, mineralogy, texture, texture, Igneous lamination laminationisis erratic erratic and structure structure over and over most most of of their theirexposure. exposure. Igneous over small contrasting rock over small distances distances and and contacts contacts between between contrasting rock types types can can genergenerThus stratigraphic ally be i~ ally be traced only on on an an outcrop outcrop scale. scale. stratigraphic control control is generally relationships generally nonexistent. nonexistent. Nevertheless, Nevertheless, three three consistent consistent contact contact relationshipâ have been been found: have found: outcrops, plagioclase plagioclase lamination in one rock type type is is par1) In 1) In some some outcrops, lamination in one rock parallel contact with a contrasting rock type having discordant alleltotothe the contact with a contrasting rock type having discordantpla— plagioclase lamination. lamination. This Thisis is taken taken to to imply implyintrusion intrusionofof the the first first rock qioclase rock type into type into the thesecond. second. 2) 2) similarly, a contrasting Similarly, where where plagioclase plagioclase lamination lamination wraps wraps around around a contrasting rock type, the the latter tobe bean aninclusion. inclusion. rock type, latterisisinterpeted interpetedto In other with concordant 3) other exposures, exposures, contrasting contrastingrock rocktypes types with concordantplagio— plagio3) In clase lamination each other across centimeter— to to meter—wide clase laminationgrade gradeinto into each other across centimetermeter-wide types displaying displaying gradational gradational contacts contacts are zones. Rock zones. Bock types are considered considered to to be be cogenetic. cogenetic. Based on these these relationships, Based on relationships,which which are are consistent consistentbetween between particular rock rock three stages emplacement been distinguished distinguished in types, types, three stagesof ofanorthosite anorthosite emplacement have have been in petrographic the as early, late. A the study study area area and and are are denoted denoted as early, main, main, and and late. A petrographic summary therock rocktypes typesofofeach eachstage stage is is given 1. summary ofofthe given in in Table Table 1. Five anorthosite have have been beenidentified identified (Table Five types types of ofmain—stage main-stage anorthosite (Table 1). 1). Over 80 percent Over 80 percent of the the total total anorthosite anorthosite exposure exposure consists of main—stage main-stage in large—spotted anorthosite and anorthosite (LSA) troctolitic (TAM) (LSA) in troctolitic anorthosite anorthosite (TAM) and large-spotted roughly difference between between these these two two types types is is roughly equal equal proportions. proportions. The major difference texture of olivine which in TAM and ophitic the the texture of olivine which is interstitial interstitial in ophitic in in LSA. LSA. 26 �à "in s s a I 6-10 I (Rio) 2) (E)uhedral, (S)ubhedral, - 8 % liii, plagioclase; Apt Medium = 16 - 22 Rio, 1—4 (I)nterstitiai, (S)ubophitic, (O)phitic, (R)ims on (O1)ivine, (V)ariable. - 22 liii, Apt I I - 40 mm 2 Rio, - % zoning with no. of cycles, V — variable. 8 mm. 6—8 Rio, lib <5—20mm 5-0 In t I S-0 <l-Smm S 10 mm S - 0 Trace-St S 0 5 2 mm S nsa ma, Coarse = 4-8 mm, I'egioatite 19 Rio, 10 Trace - R (01) — 3 5-0 5) Range represents uncertainty of rock type designation due to a lack of contact relatLonships. 4) 3) MS — normal sector t I C520ma % S <5—20mm 5 S ma R (01) — 1-5% 40 mm S-U - 5 ma S - 0• 6 cm 5-0 I 5 - <I - 3% R (01) S (A)nhedral, (V)nrinhlc. zoning, PS - patchy sector zoning, Osc(P) — oscillatory 1) Grain size measured normal to (010) in cumulus Modes are visual approximations TOTAL SECTIONS5 OIlIER MINERALS I mm <5mm S I I 1 Trace , '' (fib) cSmm % OikiocrystSize I i-S S Texture/Habit4 IRON OXIDE Oikiocryst Size a! % S* - -s " R (01) s Texture/habit4 5 — 40 mm <S mm - 20 - 2-10% 2 5-18% am, sIt 10 1, Anhedral 2 ma — 52 cm I I, Anhedral Oikiocryst Size I ORTHOPYROXENE S 0-2% 5-0 nsa V - S—0 2—lOt S E 80—95% Peux + Cpx Osc(I,5-2) A Peox + Cpx - S- Poor - Good 2-7% s2% S Excellent 90-97% - edium-Pegmati 0 Peox + Cpx NS ,oocl Medium Gabbroic Anorthosite 2—15% S_0 CT,IMOPYROXF.NE 01 MAIN STAGE Snail Spotted Anorthosite ________ ______ 5-15% : 0—5% I None • w Texture/Habit4 2 mm 1, Fqtuant 8-15% Peox Feox + Cpx flsc(2-3) 01 Cpx V - V MS V MS 80—95% Poor — Good V Good Medium — Coarse 80-90% - Poor Coarse Anorthosite __________ Large Spotted S - Medium Anorthosite Troctolitic 95-98% Excellent S PrfH1OGRAPHIC DESCRIPTIONS OP ANORTIIOSITES 0 S Excellent Mc,! I um Anorthosite ______ TABLE I V 85—95% Good - Medium Anorthosite STAGE S w —4 EARLY Troctolitic V N I'-, Texture/Habit4 Grain Size OI,IVINE Inclusions Zoning3 Habit2 PLAGI1LASE lamination Grain Size1 w " te Pair PS A S 1 3 (Rio) 55mm 1-5 5 % to mou None - S 1-3% None Fcox + Cpx MS - S 95-98% Poor - Medium - Coars1 Anorthosite a - V 0 - CI - 3 % ulmu 5—12 (Rio) 5-0 2—Smm 5 5 R (01) S 30 mm sum <I - 2% 10 - 0-5% 0.5 - 8 1, Equant 8-20% Feox + Cpx 75-85% S Tr. Coarse Poor - Pair Medium Anorthositic Troctolitic Au,.- I S �The other other three three main—stage main-stage rock rock types types occur occur in in gradational gradational contact contact only only with LSA. both TAM TAM and The early troctolitic troctolitic anorthosite occurs as inclusions in both occurrences of the early—stage LSA. Only two occurrences early-stage anorthosite were found as inclusions in clusions in LSA. LSA. Late—stage troctolitic anorthosite (TAL) Late-stage (TALI intrudes intrudes all all main-stage main-stage rock rock types. TAN and and TAL are petrographically types. TAM petrographically very similar similar (Table (Table 11)) and are distinguishable distinguishable in in the the field field only only where contact contact relationships relationships are are observed. observed. Major and minor element and microprobe microprobe analyses analyses of the the anorthosites anorthosites are are planned in in order order to to test test and and refine refine these these field field and and petrographic petrographic observa— observations tions. Figure 11 Figure - of the the Duluth Duluth Complex General geology aecLogy of Complex in in the th NE Minnesota. Forest Center NW quadrangle, HE EI!L*NA? InN £.r I, Pnt..*rl.. traltic •tflS1.at. In In...tsnt •1 in. P.. idIl P,.ca.n.. wiIC1Iø 28 �PROGRESS REPORT ON THE THE BEDROCK GEOLOGY GEOLOGY OF THE REPORT ON OF THE NORTHWEST MAP WISCONSIN MAP SHEET, SHEET, WISCONSIN M.G. M.G. Mudrey, Mudrey, Jr., Jr., Wisconsin Wisconsin Geological and Natural History History Survey, Survey, UniverUniversity Wisconsin—Extension, sityofof Wisconsin-Extension, 1815 University University Avenue, Avenue, Madison, Madison, Wisconsin Wisconsin 53706; G.L. G.L. LaBerge, LaBerge, Geology Geology Department, Department, University University of of Wisconsin, Wisconsin, Oshkosh, oshkosh, Wisconsin Wisconsin 54901; 54901; P.E. P.E. Myers, Myers, Department Department of of Geology, University University of of Wisconsin, Eau Eau Claire, Claire, Wisconsin Wisconsin 54701; 54701; and and W.S. W.S. Cordua, Cordua, Department Department of of Plant Plant and and Earth Earth Science, Science, University University of of Wisconsin, Wisconsin, River River Falls, Falls, Wisconsin Wisconsin 54022 54022 p ABSTRACT ABSTRACT Precambrian Precambrian rocks rocks have have been been the the focus focus of ofgeologic geologicmapping mapping in in the theNorthNorthThe area area is is bounded bounded on on the the north north and and The south 46O and and 45° 45O latitudes, latitudes, respectively; respectively; on on the the east east by by 900 90 longilongisouth by by the the 46° tude; tude; and and on on the the west west by by the the Wisconsin—Minnesota Wisconsin-Minnesota state state boundary. boundary. Bedrock Bedrock exposures to river river exposures in in the the east east half half of of the the map map sheet sheet are are generally generally limited limited to valleys; valleys; in in the the west west the the outcrops outcrops are are extremely extremely sparse, sparse, and and have have no no obvious obvious pattern. pattern. As As aa result, result, extensive extensive use use has has been been made made of of aeromagnetic aeromagnetic data data and and available available drill drill core core and and cuttings. cuttings. Gravity Gravity data data are are too too sparse sparse in in the the map map area area to to be be of of much much value. value. west west map map sheet, sheet, Wisconsin Wisconsin since since 1976. 1976. Archean Archean gneisses gneisses are are inferred inferred from from two two outcrops outcrops and and the the related related domal domal aeromagnetic aeromagnetic patterns near Fifield Fifield and and on on the the Chippewa Chippewa River River in in T.39N., T.39N., R.6W. Relations to other other units units are are not not known. known. R.6W. Relations of of these these rocks rocks to tower Lower Proterozoic Proterozoic units units include include aa dominantly dominantly metasedimentary metasedimentary sequence sequence trending centered near near Park Park Falls. Falls. Numerous electromagnetic trending east—northeast east-northeast centered Numerous electromagnetic anomalies this unit of Sternberg anomalies are areknown known from from this unit(Flambeau (FlambeauAnomaly Anomaly of Sternberg and and Clay, Clay, 1977), 1977), and and those those that that have have been been drilled drilled consist consist almost almost exclusively exclusively of of gargar- net—bearing net-bearing graphite graphite schists schists with with trace trace amounts amounts of of sulfide. sulfide. Typical Typical Pro— Proterozoic terozoic iron iron formations formations and and associated associated carbonate carbonate rocks rocks are are known known from from this this unit. to metavolcanic metavolcanic units units to to the the south south are are not not unit. Relations Relations of of this this unit unit to known known because because of of aa major major fault. fault. Although Although exposure exposure is is poor, poor, this this metavol— metavolcanic canic terrane terrane apparently apparently extends extends from from the the central central part part of of Price Price County County to to the Aeromagnetic expression expression and and available available the southern southern part part of of Taylor Taylor County. County. Aeromagnetic outcrops outcrops suggest suggest that that the the metavolcanic metavolcanic rocks rocks north north of of the the Jump Jump River River Fault Fault are are dominantly dominantly amphibolite amphibolite facies, facies, whereas whereas those south of the the fault fault are are greenschist greenschist facies facies and and more more felsic. felsic. Although Although not not seen seen in in this this map map area, area, relations by Myers Myers along along the the North North Fork Fork of of the the Eau Eau Claire Claire River River relations described described by suggest suggest that that the the greenschist—facies greenschist-facies rocks rocks unconformably unconformably overlie overlie the the amphib— amphibolite—facies olite-facies rocks. rocks. These These stratiform stratiform rocks rocks were were intruded intruded by by granitic granitic rocks rocks around 1,880 million years ago, and by granite near Radisson about 1,760 around 1,880 million years ago, and by granite near Badisson about 1,760 million million years years ago. ago. Two Two volcanogenic volcanogenic massive massive sulfide sulfide occurrences occurrences are are known known in in these these meta— metavolcanic rocks. In the late 1960's the Flambeau and Thornapple volcanic rocks. In the late 1960's the Flambeau and Thornapple deposits deposits were were discovered discovered by by aa subsidiary subsidiary of of Kennecott Kennecott Copper, Copper, and and 44 to to 66 million million tons of 4 percent copper ore were identified. tons of 4 percent copper ore were identified. Exploration Exploration has has continued continued in in the the area area but but no nodetails detailsare areavailable. available. Mineral Mineral potential potential is is considered considered good, good, particularly particularly in in the the greenschist greenschist felsic felsic rocks. rocks. After After deformation deformation of of the the Lower Lower Proterozoic Proterozoic rocks, rocks, aa Middle Middle Proterozoic Proterozoic conglomerate and quartzite sequence was deposited. conglomerate and quartzite sequence was deposited. The The principal principal unit unit is is 29 �I the Barron Quartzite of the Barron Quartzite of western western Rusk Rusk and and adjoining adjoining counties. counties. Present Present work restricts the the age m.y. restricts age of of the the quartzite quartzite sequence sequence between between 1,700 1,700 m .y. and 1,100 1,100 m.y. The Keweenawan diabase m.y. The younger younger is is controlled controlled by by presumed presumed Keweenawan diabase dikes dikes in in the the quartzite. Recently, U U.S. Department of of Energy .S. Department Energy National National Uranium Uranium Resource Resource quartzite. Recently, Evaluation work work suggested suggested some somepotential potential for Evaluation forunconformity unconformity related relateduranium uranium occurrences in occurrences in northern northernRusk RuskCounty, County, although althoughno nouranium uraniumanomalies anomalies were were Field work identified. Field suggested that identified. work by by DOE DOE contractors contractors suggested thata aweakly weaklymetamormetamorphosed regolith quartzite. phosed regolith is is unconformably unconformably overlain overlain by by the the quartzite. Iceweenawan volcanic rocks rocks on on the the western western edge edge of of the the map map sheet sheet adjacent adjacent Keweenawan volcanic to Minnesota, These Chenqwatana Volcanic Volcanic Group. Group. These to Minnesota, are are correlated correlated with with the the Chengwatana volcanic rocks are volcanic are poorly poorly exposed, exposed, but but where where studied, studied, tend tend to to consist consist of of thick basalt basalt flows thick flows that that have have been been metamorphosed metamorphosed to to grades grades ranging ranging from from zeo— zeolite Cordua and others (1979) lite to to lower lower greenschist. greenschist. Cordua and others (1979) have have previously previously reportreported the copper copper mineralization mineralization in in both the ed ott on the the Keweenawan Keweenawan volcanic volcanic rocks rocks and and the overlying overlying Upper Upper Cambrian Cambrian sandstones. sandstones. Mineral potential is is not not considconsidered significant. significant. I Faults are Faults are generally generally recognized recognized from from aeromagnetic aeromagnetic signatures. signatures. The The domdminant structure structure in in the the western part of the the map sheet is the St. St. Croix horst and its its bounding bounding faults faults including including the the Lake Lake Owen, Owen, Cottage Cottage Grove Grove and and Pine Pine Faults. Aeromagnetic lineament analysis and sparse sparse outcrop control control in in the the east half of the the map sheet, sheet, suggest suggest that that the northeast—trending northeast-trending faults were active during the active the Keweenawan inasmuch inasmuch as the the Barron Quartzite is cut by the faults. faults. We believe believe that that at at least least some some of of the the activity activity along along these these faults, faults, particularly Riverand andMonico Monico faults,isis early early Proterozoic particularly the the Jump Jump River faults, Proterozoic in in age, age, with reactivation • The The with reactivationduring during the theMiddle Middle and andpossibly possiblyLate LateProterozoic Proterozoic. principal fault,the the Hawkins Hawkinsfault, fault,is is defined defined entirely entirely principal northwest—trending northwest-trending fault, from aeromagnetic from aeromagnetic lineament lineament analysis. analysis. Mudrey's efforts have focused Mudrey's focused in the the northeastern northeastern part of the the map; La Berge in in the the southeast southeast corner; corners Myers Myers in in the the south—central, south-central, and and Cordua Cordua in in early version version of of the the east part of this the western parts. Pin An early this map was was pubwork in to lished by Sims, Cannon Cannon and and Mudrey Mudrey (1978). (1978). Work in future future years years relating relating to the Precambrian Precambrian rocks will be directed directed to to improved improved petrographic petrographic and and strucstrucdata. tural descriptions, and refined analysis of geophysical data. REFERENCES REFERENCES Cordua, W.S., W.S., Bauer, Bauer, D.P., D.P., Gilbertson, Gilbertson, J.P., J.P., Icoskelin, Koskelin, K.M., K.M., and and Oberli, Oberli, 1979, Geologic Geologic setting setting of copper J.W., 1979, copper mineralization mineralization in in Precambrian Precambrian J.W., (Iceweenawan) basaltic basaltic volcanics volcanics and and Upper Upper Cambrian Cambrian sediments sedinents in (Keweenawan) in the the St. St. Geological Labs.]: Geological Society Society Croix Falls Falls area, area, Wisconsin Wisconsin and and Minnesota Minnesota labs.]: of Mterica America Abstracts Abstracts with with Programs, Programs, v. 11, no. 5, 5, p. p. 227. 227. v. 11, P.K., W.F., M.G., Jr., Sims, P .K., Cannon, W .F., and Mudrey, M .G., Jr., 1978, 1978, Preliminary Preliminary geologic U.S. map of of Precambrian Precambrian rocks rocks in in part part of of northern northern Wisconsin: Wisconsin: U .S. Geological 78-318. al Survey Survey Open—File Open-File Report Report 78—318. Sternberg, B.IC. and Clay, C.S., anomaly; aa high-conductivity high—conductivity Sternberg, B.K. and C.S., 1977, 1977, Flaxttheau Flambeau anomaly; anomaly in &Heacocic, Heacock, in the the southern southern extension extension of of the theCanadian CanadianShield, Shield,in and physical its nature The Earth's crust; J.G., al., The Earth's crust; its nature physical J.G., et eds., al., properties: properties: American Geophysical Geophysical Union Union Monograph Monograph 20, 20, p. p. 501—530. 501-530. e., 30 �STRUCTURAL PIBALYSIS OF THE DULUTH COMPLEX FOREST CENTER NW QUADRANGLE, MINNESOTA Eugene E. Mullenmeister and James D. Miller, Jr., Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota 55455 ABSTRACT We report here the results of a structural analysis of the joint, dike, and lineament orientations in a portion of the Duluth Complex. The study was initiated to document the brittle structures in the Complex and to integrate them into its structural history. Joint and dike orientations were measured in the field within a 26 km2 area. Lineament azimuths and lengths were measured from a high—altitude aerial photo (scale 1:39,000) that covers approximately 1,200 km2 and includes the smaller area studied on the ground. The dominant rock types of the Duluth Complex in this area are trocto— lite and anorthosite (see Miller and Weiblen, this volume, Fig. 1). These rocks intrude Archean metasedimentary rocks, greenstone, and granite of the eastern Vermilion district. Plagioclase lamination and modal layering in the troctolite generally are parallel to the basal contact which trends N70°E to N50°E. The dominant structural fabric of the metamorphic country rock trends NW to E-W. A total of 4,435 joint orientations were recorded and plotted on rose diagrams in 5° intervals. Only azimuths were recorded as most of the joints are near vertical. Three types of joints were recognized: unmin— eralized joints, joints filled with green chlorite (408 total), and joints filled with white sericite (169 total). The green chlorite—filled joints occur predominantly in the troctolite; 287 (94%) occur within 2 km of the contact. White sericite—filled joints are generally confined to the anorthosite. The major differences in fracture trend are related to rock type. Figures la and b summarize the azimuths of all joints measured in the trocto.-. lite and anorthosite, respectively. The troctolite contains predominant joint sets at N25°—45°W, N10°—20°E and N85°W—N85°E with lesser peaks at N65°-75°W and N50°—55°E. Total joints in the anorthosite define a prominent, broad peak at N50°—85°W. Considering only the mineralized joints (Figs. ic and d), the troctolite data retain only the N25°—45°W and N10°20°E sets. The mineralized joints in anorthosites show considerable scatter with 4 significant and 3 to 4 lesser peaks. Stereo plots were made of 33 diabase dikes (Fig. 2) and 34 granitic veins and dikes. Although considerable scatter is present, the mean dia— base dike strikes N51°E ± 26° and dips 51° ± 22° SE (1 std. dev.). The granitic dikes, which occur only in the anorthosite, show greater variation in orientation than do the diabase dikes but generally trend NNE to E-W. The azimuth and length of 437 aerial photo lineaments are plotted in Figure le. The total lineament data show a strong peak at N30°-45°E and lesser peaks at N10°—20°E and N5°—20°W. 31 �I The jointing jointing in in the the study study area area may may be be attributed attributed to to several several causes: The causes: ( 1 ) contraction during cooling of the contact-area rocks (we suggest that (1) contraction during cooling of the contact—area rocks (we suggest that most mineralized mineralized joints jointsmay may have haveformed formedininthis thismanner); manner); (2) upward propamost (2) upward propagation of of basement basement structure; structure; (3) ( 3 ) response response to to regional regional stresses; stresses; and and (4) (4) gation isostatic rebound due to erosion and glacial unloading. Diabase and granisostatic rebound due to erosion and glacial unloading. Diabase and granite dike dike orientations orientations indicate indicate tensional tensional stresses stresses oriented oriented NW-SE, normal ite NW—SE, normal to the Duluth Complex contact, during the later stages Keweenawan igneigneto the Duluth Complex contact, during the later stages ofofICeweenawan N to HE lineament orientaous activity in the area. The predominance of ous activity in the area. The predominance of N to NE lineatnent orientations probably probably is is biased biased by by glacial glacial scour, scour, but, but, nevertheless, most lineations nevertheless, most lineament trends may be related to joint and dike orientations. Definitive ment trends may be related to joint and dike orientations. Definitive evidence of faulting was found at only one location where a fault is oriorievidence of faulting was found at only one location where a fault is ented N20°E The extent of faulting in the area is difficult to assess ented N20°E. The extent of faulting in the area is difficult to assess and complex complex intrusive intrusiverelationships relationships. due to to poor poor exposure exposure and due Figure 1 Figure 1 I I Rose diagrams diagrams of of brittle brittle structures structures in in the the Duluth Complex. Rose Duluth Complex. I A) E) ram , TOTIL LIRNT CAm -t — VEIN .E FTIJI 'u_oil T0T TN POINTS S 2251 — 333 WA POINTS È - .E FTØI 5 W. m POINTS 432 CATA 107*. am 4fl = POINTS 9.S m POINTS 8.5 3 I CATA POINTS 4 B) Wa! Figure 2 /I1(N VEIN FACICA Figure 2 '0.033 Diabaae Dikes Dikes 2171 IOTA.. WA POINTS 37.5 oarn POINTS Diabase M I a- a. •4 .- '-.;z,,S .. C) I 1*XTt.L SOLE FACt : T0T ITA P011415 S 0 •1S. 410 —' 10.8 TR POINTS — w%as D) 'ElM %.E F7 i O.3 T0T TA POINTS * 160 3.3 CAIn POINTS 32 S �STRATIGRAPHY STRATIGRAPHYMID ANDDEPOSITIONAL DEPOSITIONALENVIRONMENT ENVIRONMENTOFOFARCHEAN ARCHEAN FELSIC VOLCANICS, WAWA, FELSIC VOLCANICS, WAWA,ONTARIO ONTARIO pp marK L.L. Nebel, Nebel, Department Department ofof Geology, Geology, University University ofofMinnesota—Duluth, Minnesota-Duluth, Mark Duluth, Minnesota 55812 Duluth, Minnesota 55812 ABSTRACT ABSTRACT Archean Archean volcanic volcanic rocks rocksof ofthe theWawa Wawaarea, area,ininthe theMichipicoten Michipicoten district district of northern Ontario, form part of the Wawa greenstone of northern Ontario, form part of the Wawa greenstone belt. belt. The Therocks rocks studied studiedare aresituated situatednortheast northeastofofthe thecity cityofofWawa, Wawa,and andcomprise comprisethe theupper upper portion portion of ofa amafic—to—felsic mafic-to-felsic volcanic volcaniccycle cyclewhich which includes includesthe theHelen HelenIron Iron deposit. Formation, a volcanogenic massive sulfide—type Formation, a volcanogenic massive sulfide-type deposit. On Onthe thebasis basisofofpreserved preservedprimary primarytextures texturesand andstructures, structures, the therocks rocks spherulitic, flow—laminated, can be be divided divided into: into: 1)1) massive, massive, flow-laminated, spherulitic, and and can lithophysae-bearing massive toto well-bedded well-bedded lithophysae-bearing lava lava domes domes and and flows, flows, 2)2 ) massive pyroclastic 3 )volcanogenic volcanogenicsedimentary sedimentaryrocks. rocks. pyroclasticrocks, rocks,and and3) One One series series of of pyroclastic pyroclastic rocks rocks exhibits exhibits aa marked marked lateral lateral facies facies of the change, change, with with coarse, coarse, massive massivebeds bedsininthe thecentral centralportion portion of thestudy studyarea area grading gradinglaterally laterallyeastward eastwardinto intothin thinand andgraded gradedbeds. beds. The Thechanges changesiningrain grain size and and bedding bedding characteristics characteristics indicate indicate a a westerly westerly source source for for the the size deposition. materials, materials,while whilethin thinand andgraded gradedbeds bedssuggest suggestsubaqueous subaqueous deposition. Volcanogenic Volcanogenic sedimentary sedimentary rocks rocks at at the the top topof ofthe thefelsic felsicvolcanic volcanic sucsuccontain Formation) cession cession (directly (directly underlying underlying the the Helen Helen Iron Iron Formation) contain numerous numerous sedimentary sedimentary structures structures indicative indicative of of shallow shallow water water deposition. deposition. paleocurrent analysis of cross—bed dip directions indicates Paleocurrent analysis of cross-bed dip directions indicatesaasource sourceto to the the west. west. vesiculated Vesiculated pillow—basalts pillow-basalts overlie overlie the the Helen Helen Iron Iron Formation Formation and and are are indicative indicativeof ofaashallow shallowsubaqueous subaqueousenvironment. environment, p The as having having been been deposited deposited in in The felsic felsic volcanic volcanic rocks rocks are are envisioned envisioned as Volcanic center(s) both both aa subaerial subaerialand and shallow shallowsubaqueous subaqueousenvironment. environment. Volcanic center(s)to to the the west west were were topographically topographically high high areas areas that that were were periodically periodically or or concontinuously tinuouslyexposed exposedabove abovethe thewater water surface, surface,whereas whereasthe theflanks flanks of of the thevolca— volcain a shallow basin. nos were were periodically periodically or or continuously continuouslysubmersed submersed in a shallow basin. nos S 33 �TIDAL BASIN OF OF THE TIDAL DEPOSITS DEPOSITS IN INTHE THEEARLY EARLY PROTEROZOIC PROTEROZOIC BASIN THE LaKE LAKE SUPERIOR SUPERIOR REGION-REGION-POKEGAJ4A FORMATION: FORMATION: EVIDENCE EVIDENCE FOR FOR SUBTIDAL-SHELF THE PALMS PALMS AND AND POKEGAMA SUBTIDAL-SHELF DEPOSITION DEPOSITION OF OF SUPERIOR—TYPE SUPERIOR-TYPE BANDED BANDEDIRON—FORMATION IRON-FORMATION Richard of Geology, University of DuRichard W. W. Ojakangas, Ojakangas, Department Department of Geology, University of Minnesota, Minnesota, Du- luth, luth, Minnesota Minnesota 55812. 55812. ABSTRACT ABSTRACT The Palms Palms Formation in Wisconsin Wisconsin and and Michigan Michigan and and the the correlative correlative PokegPokegThe Formation in ama Quartzite in Minnesota are interpreted interpreted as tidal deposits formed along the margins margins of of the the early early Proterozoic Proterozoic Animikie Animikie basin. basin. The well—exposed which extends extends for for 85 km along well-exposed Palms Formation, Formation, which along the the Gogebic Gogebic range, range, is 150 m thick and can be divided divided into into three units on the basis thin lower basis of of rock rock types types and and bedding bedding styles. styles. (1) AA thin lower unit consists consists of of unconformably overlies overli.es aa low-relief low—relief surthin—bedded argillaceous surthin-bedded argillaceous rocks rocks and unconformably Archeangranite granite and face of of Archean and greenstone greenstone and and older older Proterozoic Proterozoic sedimentary sedimentary thick middle unit consists consists of units. A thick middle unit of thin thinalternating alternatingbeds bedsof ofargil— argilunits. (2) (2) A lite, siltstone andand sandstone vary considerably texture and compolite, siltstone sandstonethat that vary considerablyinin texture and composition. sition. Bedding types types include include parallel, wavy, cross cross and and flaser flaser lamination, lamination, An upper unit and aa variety variety of of sedimentary sedimentary structures structures are are present. present. (3) An consists of thicker consists thicker beds of parallel and cross—bedded cross-bedded sandstone. other measurements and and 52 A total total of of 199 cjross—bedded cross-bedded measurements 52 measurements measurements of of other paleo—current indicators paleo-current indicators from the the Palms Palms Formation Formation yields yields aa crude crude bimodal— bimodalbipolar distribution, distribution, with a broad broad primary primary mode mode to to the the west west and and aa weaker weaker sandstones are are mineralogically mode to to the the east. east. The The sandstones mineralogically mature; most of the the grains are quartz grains. The sandstones sandstones of of the framework grains framework are rounded rounded quartz grains. The the middle middle whereas those are unit have sericitic matrix, those of the the upper upper unit unit are unit have an an abundant abundant, sericitic matrix, whereas texturally more texturally more mature. mature. The pokegama The Pokegama Quartzite Quartzite is is exposed exposed at at only only aa few few places places along along the the 130 130 km km long Mesabi range range on on what what was was about about the the northwest northwest margin margin of of the the Animikie Animikie However, basin. However, the the entire entire formation formation can can be be viewed viewed in in two two drill drill cores cores in in Sedimentary sequences sequences and the mineralogiwhich it thick. Sedimentary which it is is5050inm and and 26 26in m thick. paleocurrent plot plot (Nm38) (N38) is cal attributes are are similar similar to to the the Palms. Palms. The paleocurrent is north and bimodal—bipolar with primary modes to crudely bimodal-bipolar to the the north and south. south. By utilization utilization of of Waither's Walther's Law Law of of facies facies relationships relationships and and comparisons comparisons with modern environments, environments, it can can be be postulated postulated that that both both formations formations were were deposited under transgressive transgressive tidal tidal conditions. conditions. In this model, model, the the lower lower (shaly) facies (shaly) facies was was deposited deposited in in aa low—energy low-energy domain domain of of the the upper upper (shoreward) (shoreward) tidal tidal flat, flat, the the middle middle facies facies (shale—siltstone—sandstone) (shale-siltstone-sandstone) was was deposited deposited on on a middle middle tidal tidal flat flat under under alternating alternating low low and and high high energy energy conditions, conditions, and and the upper subtidal upper facies facies (sandstone) (sandstone) was was deposited deposited in in lower lower tidal tidal flat flat or or subtidal high—energy high-energy development. development. The Palms Palms and and Pokegama Pokegama formations formations pass upward upward into into the the Ironwood Ironwood and and Biwabik Iron Iron Formations, Formations, respectively. respectively. Again using Walther's Walther's Law, it it can can be postulated were deposited deposited on on a shelf located postulated that the the iron—formations iron-formations were seaward from subtidal sandstone sandstone facies. The The "cherty" "cherty" (coarser (coarser grained, grained, seaward from the the subtidal thicker bedded iron iron oxide—chert) oxide-chert) facies facies was was deposited deposited in in shallower shallower water water 34 �than than was was the the "slaty" "slaty" (finer (finer grained, grained, thinner thinner bedded, bedded, iron iron silicate—iron silicate-iron carbonate) carbonate) facies. facies. The The tidal—subtidal tidal-subtidal facies facies model model developed developed here here provides provides an an independent independent approach in evaluation of the environment of deposition of one approach in evaluation of the environment of deposition of one kind kind of of Lake Lake The model is primarily based upon Superior-type banded iron—formation. Superior-type banded iron-formation. The model is primarily based upon the the siliciclastic siliciclastic lithologies lithologies associated associated with with iron-formation iron-formation rather rather than than upon upon the the iron—formation iron-formationitself. itself. 35 �I SEDIMENTATION AND MID PETROLOGY OF ARCHEAN FELDSPATHIC FELDSPATHIC QUARTZITE SEDIMENTATION QUARTZITE AND CONGLOMERATE MINNESOTA CONGLOMERATE (SEINE (SEINE SERIES SERIES EQUIVALENT), EQUIVALENT), RAINY RAINY LAKE, MINNESOTA R.W. Ojakangas, Department Department of Geology, R.W. Ojakangas, Geology, University University of of Minnesota, Minnesota, Duluth, Duluth, Minnesota 55812; and Jean New Jean M. M. Olson, Olson, Chevron, Chevron, Inc., Inc., 935 935 Gravier Street, New Orleans, Orleans, Louisiana Louisiana 70112 70112 I ABSTRACT ABSTRACT The greenstone belt which into the The greenstone belt which extends extends westward westward into the Rainy Rainy Lake Lake area area of of Minnesotafrom fromOntario Ontarioincludes includesaa clastic clastic succession succession of of feldspathic—lithic feldspathic-lithic Minnesota quartzite The quartzite quartzite forms an easterly easterly trending quartziteand andconglomerate. conglomerate. The forms an trending unit unit about 16 long and forms aa lens about 16 km km long and about about 0.8 0.8 km km wide, wide, and and the the conglomerate conglomerate forms lens of long and and 180 180m mthick thickatatthe thetop top of of the the unit. unit. The rocks are of 33 kin km long The rocks are about about vertical and and top The vertical top to to the the south south as as determined determined by by abundant abundant cross—bedding. cross-bedding. The quartzite—conglomerate unit unit of of the the Seine Series of Ontario quartzite-conglomerate Ontario occupies occupies the same stratigraphic position position 26 26 km to the the east, east, and and continues continues eastward eastward for another 40 km. another 40 km. contact of the contact The of the the feldspathic—lithic feldspathic-lithic quartzite quartzite with with the theunderlying underlying volcanic exposed Minnesota, quartzite—conglomerate volcanic rocks rocks isisnot not exposedinin Minnesota,and andthe the quartzite-conglomerate unit appears to be interbedded with greenschist. Thus it it has interunit appears to be interbedded with greenschist. Thus has been been interpreted as an essentially conformable contact (Ojakangas, 1972), but struc(Ojakangas, 1972), strucpreted tural complications complications and an unconformity unconformity may well be obscured obscured by the the lack lack of outcrop. To the east in Ontario near Mine Centre, an unconformable the east in Ontario near Mine Centre, an unconformable basal basal outcrop. contact has been been described described by by Lawson Lawson (1913) (1913) and Wood Hood (1980), (19801, and and Lawson Lawson also interpreted the contact in Minnesota as an unconformity. interpreted the contact in Minnesota as an unconformity. Paleocurrent Paleocurrent analysis analysis of of the the cross—bedding, cross-bedding, which which is is dominantly doninantly of of the the trough type, shows a strong mode to the southwest after a two—tilt correctrough type, shows to the southwest after a two-tilt correction, and and the the variance variance is is aa low low 4051. 4051. The cross—bedding cross-bedding style, the the lack lack of original shale, the abundance of original sandstone, the abundance of original shale, the abundance of original sandstone, the abundance of clay— clayey matrix in in the the sandstone, sandstone, and and the the variance variance are are all all suggestive suggestiveof of deposideposition in in aa braided braided stream stream environment. environment. The associated associated conglomerate, conglomerate, which is largely clasts as is largely clast clastsupported supported with with rounded rounded clasts as large largeasas25 25cm, cm,contains contains clasts of "granite," feldspar porphyry, quartz—feldspar porphyry, clasts of "granite," feldspar porphyry, quartz-feldspar porphyry, quartzite, quartzite, chert, and biotite schist. The conglomerate conglomeratecan can be be interpreted pro— chert, and biotite schist. The interpretedas asa a prograding alluvial fan deposit. Wood (1980) arrived at a similar interpretagrading alluvial fan deposit. Wood (1980) arrived similar interpretation for Lawson (1913) (1913) interpreted the the for the the equivalent equivalent Seine Seine Series, Series, and and Lawson sequence as fanglomerates and fluvial deposits. sequence fanglanerates fluvial The sources sources of the the detritus detritus in in the the quartzite quartzite and and conglomerate conglomerate are are ininterpreted to have been nearby volcanic rocks and coeval plutons intrusive been nearby volcanic rocks and coeval plutons intrusive The unconformity, into the the volcanic volcanic pile. pile. unconformity, if present all along the the belt, probably is a minor erosional surface within the volcanic—sedimentary probably is a minor erosional surface within the volcanic-sedimentary sesequence, similar to quence, similar tothat thatbetween between the theSaganaga Saganaga batholith batholith and and the theKnife KnifeLake Lake It in the Group Group in the eastern eastern Vermilion Vermilion district district of of northeastern northeastern Minnesota. Minnesota. It seems likely that that at at least least moderate moderate relief relief was was present present in in the the source source area, area, perhaps along the the southern southern edge edge of of aa long long fault fault block, block, with with alluvial alluvial fans fans adjacent to the the source source rapidly rapidly grading grading southward southward into into aa braided braided alluvial alluvial plain. Renewed upliftinin the the source source area area caused progradation of of the Renewed uplift caused aa progradation the fans fans over the alluvial Goldich and and over alluvial plain, at least least in in the the Minnesota Minnesota sequence. sequence. Goldich (1961), suggested suggested that that the tonalite on Grassy others km others (19611, Grassy Island, Island, just just 1.3 1.3 km north of the the conglomerate, conglomerate, was was aa possible possible source source of of some some clasts. clasts. 36 I �Wood Wood(1980) (1980)suggested suggestedthat thatthe theturbidites turbiditesofofthe theQuetico Queticometasedimenmetasedimentary taryunit unitwhich whichborders bordersthe thequartzite-conglomerate quartzite-conglomerateon onthe thesouth, south,may maybebethe the deep—water deep-water equivalent equivalent of ofthe theterrestrial terrestrialSeine SeineSeries. Series. The Themetamorphic metamorphic recrystallization theequivalent equivalentbiotite biotite metasedimentsand andof ofthe recrystallizationofofthe theQuetico Queticometasediments schistsjust justto tothe thesouth southofofthe theRainy RainyLake—Seine Lake-SeineRiver RiverFault FaultininMinnesota Minnesota schists mineralogic comparisons components makes detailed detailedoriginal original mineralogic comparisonsofoforiginal original componentsofof makes the biotite biotite schist schistwith withthose thoseofofthe thelower lowergrade gradequartzite quartziteimpossible. impossible. AA the limited limited study study of of zircon zircongrains grainsshows showsthat thatthere thereare aredifferences differencesin inthe the varieties varietiesof ofzircons zirconsininthe thetwo twounits, units,and andthis thiscan canbebeinterpreted interpretedasasevievidence dence of ofdifferent differentsource sourceareas. areas. However, However, horizontal horizontal movement movement along alongthe the Rainy Rainy Lake—Seine Lake-SeineRiver RiverFault Faultcould couldhave haveplaced placedwidely widelyspaced spacedsedimentary sedimentary georockunits unitswhich whichwere were derived derived from from different differentsources sourcesbecause because of oftheir their georock graphical graphicalpositions, positions, into intojuxtaposition. juxtaposition. Thus, Thus,original originallateral lateralfacies facies relationships relationships in in the theRainy Rainy Lake Lakevicinity vicinity cannot cannotbe beproven provenuntil untilmovement movement along alongthe thefault faultisisbetter betterunderstood. understood. REFERENCES REFERENCES Goldich,5.5., S.S., Nier, Nier,4.0., A.O., Baadsgaard, Baadsgaard,H., H., Hoffman, Hoffman,J.H. J.H. and andKrueger, Krueger,H.W., H.W., Goldich, 1961, 1961, The The Precambrian Precambriangeology geologyand andgeochronology geochronology of ofMinnesota: Minnesota: 193 p. sota Geol. Surv. Bull. 41, sota Geol. Surv. Bull. 41, 193 p. MinneMinne- Lawson,A.C., A.c., 1913, 1913, The The Archean Archeangeology geologyof ofRainy RainyLake Lakerestudied: restudied: Canada Canada Lawson, Geol. Survey Mem. 40, 115 p. Geol. Survey Mem. 40, 115 p. R.W., 1972, 1972, Rainy Rainy Lake Lakearea: area: in 2 Sims, Sims,P.K. P.K. and andMorey, Morey,G.B., G.B., Ojakangas,R.W., ojakangas, A centennial Volume, Minnesota Geol. A Centennial Volume, Minnesota Geol.Surv., Surv., Eds., Geology of Minnesota: Eds., Geology of Minnesota: 163-171. .p. 163—171. Wood, John, John, 1980, 1980, Epiclastic Epiclastic sedimentation sedimentation and and stratigraphy stratigraphy in inthe theNorth North Wood, Spirit Lake Spirit Lakeand andRainy RainyLake Lake areas: areas: aacomparison: comparison: Precambrian PrecambrianResearch, Research, V. v. 12, 12,p.p.227—255. 227-255. I p I 37 S �MINERALOGY OF GRANITIC GRANITIC ROCKS, MINERALOGY OF ROCKS, WISCONSIN WISCONSIN W.L. Geophysics, University W.L. Petro, Department Department of of Geology Geology & & Geophysics, University of of Madison, Madison, 53706 Madison, Wisconsin Wisconsin 53706 WisconsinWisconsin— ABSTRACT ABSTRACT Crystallization histories have have been Crystallization histories been determined determined for for several several Penokean Penokean plutons in in northern northern Wisconsin, Wisconsin, with with emphasis emphasis on on the the extent extent and and nature nature of of mineral equilibria equilibria developed developed during during magmatic magmatic as well asassubsequent subsequent subas well sub— solidus solidus conditions. conditions. Detailed Detailed electron electron microprobe microprobe analyses analyses of minerals minerals show show that most of the variation is equilibration to incomplete incomplete equilibration that most of the compositional compositional variation is due due to during during various various stages stages of of crystallization. crystallization. This is preserved preserved in in some some cases cases This is as zoned mineral grains, as zoned mineral grains, especially especially plagioclase. plagioclase. Systematic Systematic element element parpartitioning proximity titioning indicates indicates that that only only grains grains in incontact contactororclose close proximityhave have approached approached chemical chemical equilibrium. equilibrium. Comparison Comparison of of partitioning partitioning with with published published experimental experimental and and empirical empirical studies studies allows allows some some mineral mineral pairs pairs to to be be used used to to estimate estimate intensive intensive parameters parameters obtained obtained during during crystallization crystallization (e.g., (e.g., plagioclase alkali feldspar). feldspar). These These relations relations are are often often complicated complicated by by plagioclase — alkali more more than than one one superimposed superimposed event. event. flthough Although most most of of the the data data presented presented are are from from the the Penokean Penokean batholith batholith in in northern northern Wisconsin, Wisconsin, comparisons comparisons with with published published data data from from the the Wolf Wolf River River and and Wrntello Montello batholiths batholiths allow allow definition definition of of some some spatial spatial and and temporal temporal patterns patterns in in granitic granitic plutonism. plutonism. All All three three batholithic batholithic suites suites have have peraluminous peralminous and and metaluminous metalminous rocks, rocks, with with peralkaline Some mineralogical peralkaline rocks rocks absent. absent. mineralogical differences differences between between the the orogenic orogenic Penokean Penokean batholith batholith and and anorogenic anoroqenic Wolf Wolf River River and and Montello Montello batholiths batholiths are are similar similar to to differences differences between between Mesozoic—cenozoic Mesozoic-Cenozoic granitic granitic rocks rocks of of contrasted contrasted tectonic tectonicsetting. setting. - I I I '1 I 38 �MINERALOGY ANDMETAMORPHISM METANORPHISM PELITIC ROCKS, MINERALOGY AND OFOFPELITIC ROCKS, WISCONSIN WISCONSIN 0 Geophysics, University University of of W.L. Petro, Department Department of of Geology Geology && Geophysics, W.L. Petro, C.A. Geiger, Department of Wisconsin—Madison, Wisconsin-Madison, Madison, Madison, Wisconsin Wisconsin 53706; 53706; C.A. Geiger, Department of Geophysical Geophysical Sciences, Sciences, University University of of Chicago, Chicago, Chicago, Chicago, Illinois Illinois 60637; 60637; C.V. C.V. Department of Geological Sciences, University of Maine—Orono, Guidotti, Department of Geological Sciences, University of Maine-Orono, Guidotti, Orono, Maine Maine 04469 04469 ABSTRACT ABSTRACT I Pelites Pelites from from several several locations locations in in Wisconsin Wisconsin have have been been sampled sampled for for Pelitic compositions are sensitive to grade of metamorphism so that Politic compositions are sensitive to grade of metamorphism so that petrographic petrographic analysis analysis to to determine determine metamorphic metamorphic assemblages assemblages can can define define relarelaIn addition, electron microprobe tive pressure and temperature conditions. tive pressure and temperature conditions. addition, electron microprobe study. study. 0 analyses analyses of selected selected mineral mineral pairs pairs allow allow estimates estimates of of pressure pressure and and tem— temperature based on comparisons with published experimental and empirical perature based on comparisons with published experimental and empirical studies studies (e.g., (e.g., garnet—biotite garnet-biotite Fe—Mg Fe-Mg exchange exchange equilibria). equilibria). Comparisons Comparisons with with published and unpublished literature allow spatial and temporal published and unpublished literature allow spatial and temporal patterns patterns of of Two major metamorphism to to be be determined. determined. major periods periods of of Proterozoic Proterozoic metametamorphism are politic rocks rocks of of Wisconsin, Wisconsin, and and each each period period are recorded recorded in in the the pelitic may may be be subdivided subdivided into into several several events. events. The The older older period period occurred occurred 1800—2000 1800-2000 Mya, and reached reached a peak peak of of amphibolite amphibolite grade grade in in parts parts of of northern northern and and Mya, This central Wisconsin. Wisconsin. This metamorphism metamorphism was was predominantly predominantly low low pressure pressure type type central (andalusite ± sillimanite) sillimanite) with one one important important exception exception being the the Powell Powell (andalusite kyanite kyanite locality locality where where medium medium pressure pressure was was obtained. obtained. High High pressure pressure metametaeclogite morphism morphism (i.e., (i.e., eclogite or or blueschist) blueschist) has has not not been recognized recognized in in Wisconsin, Wisconsin, which which is is an important important constraint constraint on on Penokean Penokean tectonic tectonic models. models. The The younger younger period period occurred occurred 1600—1700 1600-1700 Mya, and and was was low low grade grade over over much much of of northern reaching aa peak of amphibolite northern and central central Wisconsin, Wisconsin, reaching amphibolite grade grade at Waterloo. Waterloo. +  I I 39 �MINERAL UNERAI, DEPOSITS DEPOSITS OF OF THE THE FORT FORT FRANCES-MINE FRANCES-MINE CENTRE CENTRE AREA AREA K. K. Howard Howard poulsen, poulsen, Queen's Queen's University*, University*, Kingston, Kingston, Ontario, Ontario, X7L K7L 3N6 3N6 ABSTRACT ABSTRACT The Centrearea areaisis part part of The Fort Fort Frances—Mine Frances-Mine Centre of the theRainy Rainy Lake Lake region, region, an an area has played played aa significant area which which has significant role role in inthe theevolution evolutionof ofideas ideasabout about the the Archean Archean geology geology of of the the Canadian Canadian Shield. Shield. Since Since representatives representatives of of all all major rock types of Archean terranes (mafic to felsic metavolcanics, wackes major rock types of Archean terranes (mafic to felsic metavolcanics, wackes and and mudstones, mudstones, conglomerates conglomerates and and arenites, arenites, layered layered gabbroic gabbroic intrusions, intrusions, tonalitic intrusions and granodiorite—quartz monzonite tonalitic intrusions and granodiorite-quartz monzonite plutons) juxplutons) are are juxtaposed In taposed here, here, it it was was once once considered considered aa type type area. area. In addition addition to to the the lithological lithological diversity, diversity, aa wide wide variety variety of of mineral mineral deposit deposit types types is is present. present. Stratiform Stratiform volcanic—hosted volcanic-hosted mineralization mineralization consists consists of of ironstones, ironstones, base base metal suif ides and intercalations of the two. Four metal sulfides and intercalations of the two. Four sub—types sub-types are are recognized. ides (Gagne recognized. First, First, narrow narrow lenses lenses of of Zn—Pb Zn-Pb sulf sulfides (Gagne Lake Lake type) type) are are overlain overlain by by chert chert and andunderlain underlain by by sulfide—bearing, sulfide-bearing, altered altered lapilli lapilli tuff tuff which locally consists of a chlorite—cordierite—anthophyllite assemblage. which locally consists of a chlorite-cordierite-anthophyllite assemblage. mineralization (Port Second, Second, wide wide zones zonesofoflow—grade low-grade Zn—Cu Zn-Cu mineralization (PortArthur ArthurCopper Copper type) consist of 1— seams of to20—centimeter—wide 20-centimeter-wide seams of massive massive sphalerite— sphaleritetype) consist of 1- to chalcopyrite—pyrite chalcopyrite-pyrite which are are intercalated intercalated with with similar similar widths widths of of barren barren chlorite niafic conunonlya abrecciated brecciatedamygdaloidal amygdaloidal mafic chlorite schist. schist. The The host host rock rock is iscommonly metavolcanic, metavolcanic, but but felsic felsic volcanics volcanics occur occur both both above above and and below below the the mineramineralized lized zone. zone. Third, Third, Zn—Cu Zn-Cu mineralization mineralization (Pocket (PocketPond Pondtype) type) is is found found in in black black pyritic pyritic shale shale and and in inmassive massive pyrite—pyrrhotite pyrite-pyrrhotite lenses lenseswhich whichare areconconformable to 22 percent percent Zn Zn occur occur formable with with chert—magnetite chert-magnetite ironstones: ironstones: grades grades of of 1 1 to over over five—meter five-meter widths. widths. Fourth, Fourth, ironstones ironstones composed composed of ofchert—magnetite, chert-magnetite, massive ides and massive suif sulfides and minor minor skarn skarn commonly commonly contain contain only only traces traces of of chalcopyrite. chalcopyrite. Of Of the the above above four four types types of of mineralization, mineralization, the the first first two two represent represent low—grade low-grade volcanogenic volcanogenic sulfides sulfides localized localized at at particular particular strat— stratigraphic volcaniclastics. The The last last igraphic horizons horizons in in areas areas of ofabundant abundantfelsic felsicvolcaniclastics. two two types types are are analogous analogous to to Phanerozoic Phanerozoic Besshi—type Besshi-type mineralization mineralization and and are are found found in in volcanic volcanic sequences sequences dominated dominated by by mafic mafic metavolcanics, metavolcanics, gabbros gabbros and and metamorphosed metamorphosed wackes. wackes. Layered Layered gabbro—anorthosite gabbro-anorthosite sills sills contain contain both both sulfide sulfide and and oxide oxide mineralization. Chalcopyrite—pyrrhotite mineralization. Chalcopyrite-pyrrhotite lenses lenses containing containing minor minor pentpentlandite, landite, molybdenite, molybdenite, apatite apatite and and ilmenite ilmenite are are distributed distributed along along the the base base of of the the Grassy Grassy Portage Portageintrusion, intrusion, the thebest bestconcentrations concentrations comprising comprising the the Northrock 1.89 percent percent Cu. Cu. This This type type of of Northrock deposits deposits of of 300,000 300,000 tons tons grading grading 1.89 mineralization netand anddroplet droplettextures textures as as well mineralization displays displays magmatic magmatic net well as as local local zones ides and zones of of remobilized remobilized suit sulfides and hydrothermal hydrothermal alteration. alteration. At At aahigher higher stratigraphic stratigraphic level level in in the theintrusion, intrusion, lower lower grade grade Cu Cu mineralization mineralization is is found found within within aa siliceous siliceoushost host which which may may represent represent assimilated assimilated country country rock. rock. Fe-Ti Fe-Ti oxide oxide mineralization mineralization also also occurs occurs in in the the upper upper part part of ofthe theintrusion intrusion as as lenses lenses of ofdisseminated disseminatedtotomassive massivemagnetite—ilmenite magnetite-ilmenite and andasasirregular irregular masses rutile-apatite rock. rock. Oxide Oxide mineralization mineralization is is also also masses of of nelsonite, nelsonite, aa rutile—apatite well well developed developed in in the theSeine SeineBay Bay anorthositic anorthositicsill. sill. I Quartz Quartz vein vein mineralization mineralization is is of of two two types. types. Molybdenite, Molybdenite, with with pyrite pyrite and and local local chalcopyrite, chalcopyrite, occurs occurs in in quartz quartzstockworks stockworks and and extensional extensional veins veins 40 �with metasedimentary within within granodioritic granodioritic intrusions intrusionsnear nearcontacts contacts with metasedimentarycountry country gold, along with carbonates and ides, contrast In rocks. rocks. In contrast gold, along with carbonates and base base metal metal sulf sulfides, occurs occurs in in lenticular lenticular quartz quartz veins veins associated associated with with shear shear zones zones and and saddle saddle Gold—bearing reefs. reefs. Gold-bearing veins veins occur occur in in aa variety variety of of rock rock types types and and are are They greenschist—facies metamorphism. zones of to restricted be restricted to zones of greenschist-facies metamorphism. They can can be related related to to shear sheardisplacements displacementsononregional regionaltranscurrent transcurrentfaults faultsand andtheretherefore represent a late stage of mineralization. fore represent a late stage of mineralization. * AA distinctive distinctive clastic clastic ultramafic ultramafic unit unit is is exposed exposed within within the themafic mafic porporIt is likely of epiclastic origin tion tion of of the the volcanic volcanic succession. succession. It is likely of epiclastic originand andis is compositionally compositionally magnesian maqnesian (21 (21percent percent MgO). MgO). Local Local zones zonesof of foliated foliatedultra— ultramafic mafic rock rock contain contain disseminated disseminated Ni—Cu Ni-Cu sulfides sulfideswhich which may may result resultfrom frommetametamorphic morphic remobilization. remobilization. The The various various types types of of mineralization mineralization at at Rainy Rainy Lake Lake can can be be related related to to the the •8 •Â  geological geological evolution evolution of of the the rocks rocks of of the the region. region. Early Early volcanism volcanism and and iron and generated stratiforra systems related related hydrothermal hydrothermal systems generated stratiform iron and base base metal metal mineralization. mineralization. Coeval Coeval subvolcanic subvolcanic sills, sills, which which possibly possibly drove drove these these conconand yield magmatic sulfide to differentiated vective vective systems, systems, differentiated to yield magmatic sulfide and oxide oxide concentrations. concentrations. Granodiorite Granodiorite intruded intruded the the supracrustal supracrustal sequence sequence after after iniinitial tial folding folding and and local local stockworks stockworks developed developed near near pluton pluton contacts. contacts. Con— Continued tinned folding folding and and metamorphism metamorphism took took place place within within aatectonic tectonicwrench wrenchzone, zone, generating gold—bearing veins in dilational structures while remobilization generating gold-bearing veins in dilational structures while remobilization of of existing existing mineralization mineralization took tookplace. place. In In aa metallogenic metallogenic sense, sense, copper copper is is the only commodity which is common to all environments of mineralization: the only commodity which is common to all environments of mineralization: this this may may reflect reflect the the importance importance of of rifts rifts in in the the early early history history of of the the region. region. * Study Study supported supported by by Mineral Mineral Deposits Deposits Section, Section, Ontario Ontario Geological Geological Survey Survey * p I 41 p �GOLD GOLD MINERALIZATION MINERALIZATION MID AND OCCURRENCES OCCURRENCES IN IN THE THE ATIKOKAN AREA ATIXOXAN AREA B.R. B.R. $chnieders, Schnieders, Resource Resource Geologist, Ministry of Natural Resources, Thunder Natural Resources, Bay, Ontario Ontario ABSTRACT ABSTRACT Atikokan is is situated situated 200 200 3cm km west Bay and and earned earned its its mining mining west of Thunder Bay fame from the the discovery discovery of of the the Steep Steep Rock Bock Iron Iron Range Range in in the the late late 1930's. 1930's. Gold, however, however, was was discovered discovered in in the the Atikokan Atikokan and and Mine Mine Centre Centre areas areas in in the the late 1800's 1800's and and eventually eventually led led to to one one of of Ontario's Ontario's first first gold gold camps. camps. The general general geology geology of of the the area area consists consists of of early early Precambrian Precambrian rocks rocks of of the Wabigoon and and Quetico Quetico subprovinces, subprovinces, separated separated by by the the east—west east-west Quetico Quetico fault. The Wabigoon fault. Wabigoon subprovince, subprovince, to to the the north, north, consists consists of of metavolcanics, metavolcanics, minor metasediments metasediments and and granitic granitic batholiths. batholiths. The The Quetico Quetico subprovince subprovince consists of metasediments sists metasediments and and granitoids. granitoids. ultramafic plutons plutons occur occur Small ultramafic throughout throughout the the metasediments. metasediments. Within radius of of Atikokan, Atikokan, more than 50-km radius than 50 50 gold gold occurrences, occurrences, prosprosWithin aa 50—1cm pects and and past producers producers have have been been discovered discovered since since the the 1600's. 1800's. The ~tikoThe Atilco— kan kan gold study study performed performed by by the the Ontario Ontario Geological Geological Survey survey (Wilkinson, (Wilkinson, 1982) 1982) area; the MarmHarm— defined three three types types of of gold gold mineralization mineralization in in the the Atilcokan Atikokan area; ion Lake Batholith ion Lake Batholith type, type, the the contact contact zone zone type, type, and and the the metavolcanic—hosted, metavolcanic-hosted, Twenty—oneproperties properties in stratabound type. type. stratabound Twenty-one in the the area areawere were geologically geologically sampled, researched, mapped and mapped and sampled, researched, and petrographically petrographically and and geochemically geochemically studied. Geological observations studied. Geological observations and and data data from front the the Atikokan Atikokan Economic Economic GeolGeolwill also be presented in discussing discussing the the types types of of gold gold mineralmineralogy Program Program will also be ization, ization, genetic genetic models models and and exploration exploration targets targets and and techniques. REFERENCE deposits of Wilkinson, S.J., 1982, Gold deposits of the Atikokan Atikokan area: Wilkinson, $.J., 1982, Geological Geological Survey, Survey, Mineral Mineral Deposits Deposits Circular Circular 24, 24, 54 54 p. 42 Ontario Ontario �NATURE SEDIMENTARY ROCKS NATURE AND SIGNIFICANCE OF SHALLOW SHALLOW WATER WATER SEDIMENTARY ROCKS IN NORTHEASTERN IN NORTHEASTERN WISCONSIN WISCONSIN Klaus JJ.. Schulz, Schulz, Department of Earth Earth and and Planetary Planetary Sciences, Sciences, Washington Washington Klaus Ho. 63130 63130 and and U.S. U.S. Geological Geological Survey; Survey; Paul Paul K. K. Sims, University, St. St. Louis, Mo. U.S. Geological U.S. Geological Survey, Survey, Denver, Denver, Colorado Colorado 80225 80225 Recent reconnaissance reconnaissance mapping in northern northern Wisconsin Wisconsin has resulted resulted in in the recognition of a shallow water, sedimentary sequence underlying the recognition of shallow water, sedimentary sequence underlying the Quinnesec Formation (HoskinLake Lake Granite) Granite) Formation and and overlying overlying the the Bush Bush Lake Lake lobe lobe (Hoskin of the These sediments the Dunbar Dunbar gneiss gneiss dome dome in in Florence Florence County. County. sediments were in in part recognized by Dutton (U.S.G.S. P.P. 1971) but were considered recognized by Dutton (U.S.G.S. P.P. 633, but considered 633, local deposits deposits within within the the metavolcanic metavolcanic Quinnesec Quinnesec Formation. Formation. The present present mapping, in conjunction mapping, conjunction with drill drill hole hole and and geophysical geophysical data, data, show show that that these sediments form an outward—facing, steeply—diping (70—80°) continuous these sediments form an outward-facing, steeply-diping (70-80"') continuous sequence along the western, western, northern and eastern eastern portions portions of of the the Dunbar Dunbar All dome. All the the rocks rocks in in this this area area lie lie within within the the garnet garnet zone zone of of the the Florence metamorphic node. Florence metamorphic node. poorly known but but The stratigraphy stratigraphy of the the sedimentary sedimentary succession succession is poorly consists of biotite schist, quartzite, marble, calc—silicate rock, meta— biotite schist, quartzite, marble, calc-silicate rock, metaGarnet and are present present in some arkose and some and graphite graphite schist. schist. and anda.lusite andalusite are the layers. The gross gross aspects aspects of some some of of these these rocks rocks resemble resemble those in the lower part of the the Marquette Marquette Range Range Supergroup Supergroup in in the the Menominee Menominee district district to to Marble and associated calc—silicate rocks exposed northwest the north. the north. and associated calc-silicate rocks exposed northwest of possible cryptalgal cryptalgal structures West Bass Lake contain contain siliceous, Bass Lake structures and siliceous, possible resemble parts of the Randville Dolomite, and a thick quartzite the Randville Dolomite, and a thick quartzite section section exposed along the Popple exposed along the Popple River, Diver, about about 33 km to to the the northwest, northwest, resembles resembles the the A h meta—arkose meta-arkose unit, unit, about about 100 100 mm thick, thick, is exposed exposed Sturgeon Quartzite. Quartzite. locally near the base of the sequence arkose and arkosic sequence and is not unlike arkose conglomerate conglomerate of of the the Fern Fern Creek Creek Formation. Formation. Although differences differences do schist—pelitic schist-politic compositions), exist exist (e.g. (e.9. greater abundance of greater of biotite biotite the metasedimentary rocks rocks exposed around the western margin margin of the western the Dunbar Dunbar dome dome have have affinities affinities with with those those characcharacteristic of the the basal basal Chocolay Chocolay Group Group of of the the Marquette Marquette Range Range Supergroup, Supergroup, is tentatively proposed. This correlation and a general correlation is and general correlation proposed. correlation suggests: suggests: 1) The rocks rocks of of the the Dunbar Dunbar dome dome represent represent pre—Chocolay pre-Chocolay basement basement in in 1) northeastern northeastern Wisconsin. Wisconsin. 2) 2) The Quinnesec Formation Formation is definitely Proterozoic in age and may be time time correlative correlative with the the Hemlock Hemlock Formation Formation of of Upper Michigan. Michigan. 3) 3) The Niagara Fault recently proposed recently proposed does not represent represent a crustal crustal suture suture zone zone as was by some authors. by some authors. 43 �I DUNBAR GNEISS GNEISS DOME DUNBAR DOME AND AND IMPLICATIONS IMPLICATIONS FOR FOR THE THE PROTEROZOIC STRATIGRAPHY STRATIGRAPHY OF OF NORTHERN NORTHERN WISCONSIN WISCONSIN P.K. Sims, UU.S. Geological Survey, P.K. .S. Geological Survey, Denver, Colorado Colorado 80225; 80225; Zell Zell E. E. Peterman, Peterman, U.S. Denver, Colorado 80225; Klaus J J. U.S. Geological Survey, Denver, . Schulz, WashingSt. Louis, Missouri 63130 ton University, St. ABSTRACT The The Dunbar Dunbar gneiss gneiss dome dome is is aa newly newly recognized recognized feature feature of of the the Proterozoic Proterozoic crystalline terrane crystalline terrane of of northeastern northeastern Wisconsin. Wisconsin. The dome is 20 km by 30 30 km across, trends northwest, km. across, northwest, and has aa structural structural relief relief greater greater than 11 km. The core core of of the the dome dome is is composed composed of of complexly complexly deformed deformed and and metamorphosed metamorphosed varied biotite gneisses, varied gneisses, foliated foliated megacrystic megacrystic granite, granite, and and foliated foliated gray gray tonalite. tonalite. It is unconformably mantled by less deformed metavolcanic rocks of the the Quinnesec Quinnesec Formation, Formation, and and locally locally by by quartzite, quartzite, marble, marble, meta—arkose, meta-arkose, These rocks dip steeply and biotite biotite schist. schist. These steeply and and face face stratigraphically stratigraphically as indicated by pillow pillow structures structures in in the The boundary beoutward, as indicated by the lavas. lavas. The outward, mantle is a zone about 500 500 mm wide wide characterized by by a a tween tween the the core and the mantle steeply plunging lineation, many cataclastic foliation, foliation, steeply plunging lineation, many small small bodies bodies of of compositionally diverse, diverse, syntectonic syntectonic granitoid granitoid rocks rocks that that are are confined confined to to compositionally Metathe mantle, mantle, and small small bodies bodies of of posttectonic posttectonic granite granite and and tonalite. tonalite. Metaamphibolite facies in most of the core and morphic zoning zoning is is concentric: concentric: amphibolite in the inner inner part part of of the the mantle mantle and and greenschist greenschist facies facies in in the the outer outer part. part. boundary was a zone The boundary zone of high high strain strain and and metamorphic metamorphic intensity intensity and and assoassoThe ciated anatexis that accompanied diapiric rise of the dome. The core is accompanied diapiric rise of the dome. The interpreted as a window exposing part of an extensive terrane terrane that suffered during diapirism dynamothermal prior to dynamothermal metamorphism metamorphism prior to diapirism; diapirism; during diapirism intense intense cataclasis in the boundary zone accompanied folding in the mantle. cataclasis zone mantle. Despite contrasting histories, rocks rocks of of the the core core and and the mantle mantle have have Despite contrasting histories, yielded nearly identical m.y. by the the U—Pb U-Pb zir1,860 m.y. yielded identical isotopic isotopic ages ages of about about 1,860 con method (Banks and Cain, 1969; Banks and Rebello, 1969), recalculated (Banks and Cain, 1969; Rebello, 1969), using new using new constants. constants. This apparent early Proterozoic age for both rock assemblages though simisimisemblages contrasts contrasts with the the domes domes in in northern northern Michigan Michigan which, though lar to the Dunbar dome in many ways, have cores of Archean basement to the Dunbar dome in many ways, have cores of Archean basement gneiss gneiss rocks and and granitoid granitoid rocks and mantles mantles of of early earlyProterozoic Proterozoicmetasedimentary metasedimentary and and Tentatively, from reconnaissance mapping metavolcanic rocks. metavolcanic rocks. Tentatively, from reconnaissance mapping the theDunbar Dunbar dome appearstoto be be just just one one of of the theseveral severaldomes domes in innorthern northernWisconsin Wisconsin havhavdome appears Where dated, these basement ing cores of Proterozoic rocks. cores of Proterozoic rocks. Where dated, basement rocks give ages of about about 1,850 1,850 n.y. m.y. (W.R. (W.R. Van Schmus, Schmus, oral oral comm., corn., 1981). 1981). We suggest that the norththe supracrustal supracrustal rocks that mantle the domes of northern Wisconsin are underlain by an extensive early Proterozoic amphibolite— underlain extensive amphiboliteThe supra— facies terrane facies terrane evidently evidently not not represented represented in in northern northern Michigan. Michigan. supracrustal rocks of northern Wisconsin, however, probably are coextensive crustal rocks northern are coextensive with the Marquette Range Range Supergroup Supergroup of of Michigan. REFERENCES Zircon ages ages of Precambrian Banks, .O., and Cain, Cain, J .A., 1969, Precambrian granitic granitic .Y.A., 1969, Zircon Banks, PP.O., Journal of Geology, v. 77, rocks, northeastern northeastern Wisconsin: Wisconsin: Journal 77, p. p. 208—220. 208-220. Banks, and Rebello, 1969, Banks, P.O., P.O., Rebello, D.P., D.P., 1969, Zircon Zircon age age of of Precambrian Precambrian rhyolite, rhyolite, Geological Society northeastern Wisconsin: northeastern Wisconsin: Geological Society of of America America Bulletin, Bulletin, v. v. 80, 80, p. 907—910. p. 907-910. 44 4 �PRELIMINARY PROGRAM PRELIMINARY RESULTS RESULTS OF OFAADRILLING DRILLING PROGRAMACROSS ACROSS THE THE GREAT GREAT LAKES LAKES TECTONIC TECTONICZONE, ZONE,CENTRAL CENTRALMINNESOTA MINNESOTA David David L. L. Southwick, Southwick, Minnesota Minnesota Geological Geological Survey, Survey, 1633 1633 Eustis Eustis Street, Street, St. St. Paul, Minnesota Minnesota55108 55108 Paul, ABSTRACT ABSTRACT The The Great Great Lakes Lakes tectonic tectonic zone zone (GLTZ), (GLTZ), aa complex complex intracratonic intracratonic deformed deformed belt Archean greenstone—granite greenstone-granite terrane terrane on on the the north north belt separating separating long—stable long-stable Jrchean from from multiply—reactivated multiply-reactivated Archean—Proterozoic Archean-Proterozoic gneiss gneiss terrane terrane on on the the south, south, has has been been defined defined in ineast—central east-central Minnesota, Minnesota, northern northern Wisconsin, Wisconsin, and and upper upper Michigan Michigan by by careful careful mapping mapping of of the the exposed exposed geology, geology, together together with with critical critical geochronologic geochronologic and and geophysical geophysical studies studies (Morey (Morey and and Sims, Sims, 1976; 1976; Sims Sims and and others, 1980). 1980). However, However, in in west—central west-central Minnesota, Minnesota, where where Precambrian Precambrian basebaseothers, ment ment is is concealed concealed by by thick thick glacial glacial drift, drift, the the trend trend and and extent extent of of the the GLTZ GLTZ have have been been inferred inferred largely largely from from regional regional gravity gravity and and aeromagnetic aeromagnetic patterns. patterns. During During the the past past two two years, years, aa traverse traverse across across the the GLTZ GLTZ approximately approximately at at longitude longitude 95°W 95OW in in central central Minnesota Minnesota has has been been investigated investigated by by COCORP COCORP seismic seismic reflection reflection profiling profiling and and also also by by detailed detailed gravity gravity and and aeromagnetic aeromagnetic surveys. surveys. Ten Ten holes holes over over aa distance distance of of 60 60km km have havebeen been drilled drilled into intobasement basement along along this this traverse traverse to to provide provide direct direct lithologic lithologic data data for for use use in ingeophysical geophysical modeling modeling (still (stillin in progress). progress). At At two two sites sites just just north north of of the theGLTZ, GLTZ,within withinthe thegreenstone—granite greenstone-granite block, the the drill drill encountered encountered massive, massive, coarse—grained coarse-grained amphibolite amphibolite derived derived block, from from gabbro gabbro and and aa closely closely allied allied quartz—poor quartz-poor hornblende hornblende quartz quartz diorite. diorite. At At aa site site just just south south of of the the GLTZ, GLTZ, within within the the gneiss gneiss block, block, the the drill drill encounencountered tered gneiss gneiss composed composed of of tonalitic tonalitic and and granitic granitic layers, layers, grossly grossly similar similar to the the Morton Morton Gneiss Gneiss of of the the Minnesota Minnesota River River Valley. Valley. Three drilled into into the the northern northern part part of of the the GLTZ GLTZ penetrated penetrated lowlow Three holes holes drilled grade grade metavolcanic metavolcanic and and volcaniclastic volcaniclastic rocks rocks of of intermediate intermediate composition. composition. Strong Strong cataclasis cataclasis is is evident evident in in two two cores cores drilled drilled close close to to the the inferred inferred north boundary. boundary. Two Two holes holes drilled drilled into into the the southern southern part part of of the the GLTZ GLTZ penepenenorth trated trated well—cleaved, well-cleaved, thin—bedded thin-bedded to to laminated, laminated, dark dark gray gray to to black black slate slate and and This metasiltstone. This slate slate is is lithologically lithologically akin akin to to various various Proterozoic Proterozoic metasiltstone. slates MilleLacs Lacsand andAnimikie AnimikieGroups Groups(although (althoughits itsage age is is not not known) known) slates in in the the Mule and and thus thus opens opens the the possibility possibility that that Proterozoic Proterozoic supracrustal supracrustal rocks may occur cur within within and and near near the the GLTZ GLTZ for for some some distance distance west west of of the the presently presently mapped mapped margin of of the the Animikie Animikie basin. basin. margin Biotite—hornblende high near near the the center center Biotite-hornblende diorite from from an an oval oval magnetic magnetic high the GLTZ has a panhedral or "lamprophyric" texture and is inferred to be of the GLTZ has a panhedral or "lamprophyric" texture and is inferred to be of Migmatized Miginatized biotite biotite paragneiss paragneiss from from the the flank km north north of of the the inferred inferred south south margin margin of of flank of of aa magnetic magnetic high high about about 22 km the the zone zone is is tentatively tentatively viewed viewed as as belonging belonging to to the the gneiss gneiss terrane. terrane. posttectonic, high—level high-level pluton. pluton. aa posttectonic, The GLTZ GLTZ in in central central Minnesota Minnesota is is occupied occupied largely largely by by low-grade low-grade meta— metavolcanic volcanic and and metasedimentary metasedimentary rocks rocks and and appears appears to to be be bounded bounded on on the the north north by aa major major steeply steeply dipping dipping fault fault zone. zone. No direct direct evidence evidence has has been been found found by 45 �ffor o r major faulting f a u l t i n g along along the t h e south south boundary, boundary, which instead may be an unconunconformable along part i t s length length with with Archean Archean and and possible possible formable contact contact along p a r t of of its Proterozoic Proterozoic supracrustal supracrustal rocks rocks resting r e s t i n g on on older older Archean Archean gneiss. gneiss. The ages ages of the GLTZ, GLTZ, and and their t h e i r structural s t r u c t u r a l relationship r e l a t i o n s h i p to to of the t h e supracrustal supracrustal rocks rocks in i n the granitoid g r a n i t o i d rocks, rocks, remain remain to t o be be demonstrated. demonstrated. REFERENCES REFERENCES Morey, G.E., G.B., Morey, and Sims, Sims, P.K., P.K., 1976, 1976, Boundary Boundary between between two two Precambrian Precambrian WW ter— tergeologic significance: Geological Society geologic significance: Geological Society of Nnerica America Bulletin, Bulletin, v. v. 87, 87, p. p. 141—152. 141-152. ranes and iits ranes in i n Minnesota Minnesota and ts S i m s , P.R., P.K., Card, Card, lcD., K . D . , Morey, Morey, G.E., G.B., and andPeterutan, Peterman, Z.E., Z.E., 1980, The The Great Great 1980, Sims, Lakes Lakes tectonic t e c t o n i c zone——a wneÑ major major crustal c r u s t a l structure s t r u c t u r e in i n central c e n t r a l North North Mteri— America: ca: Geological Geological Society Society of of America America Bulletin, Bulletin, Part P a r t I, I, v. v. 91, 91, p. p. 690—698. 690-698. 46 �WEATHERING AS RELATED WEATHERING OF ARCHEAN ARCHEAN ROCKS ROCKS AS BELATED TO TO IRON-FORMATIONS IRON-FORMATIONS G.M. Spencer, Jr., National Bank, Duluth, MNMN55812 G.H. Spencer, Jr., 619 619First First National Bank, Duluth, 55812 ABSTRACT ABSTRACT The The Archean Archean volcanic volcanic and and sedimentary sedimentary belts belts of of northern northern Minnesota Minnesota and and northwestern northwestern Ontario Ontario contain contain many many thin thin belts belts of of iron—formation. iron-formation. The The sedisedimentary mentary rocks rocks are are largely largely conglomerate, conglomerate, graywacke, graywacke, and and slate slate with with variable variable The amounts amounts of of volcanic volcanic material. material. The composition composition of of the the sedimentary sedimentary rocks rocks indicates indicates rapid rapid disintegration, disintegration, erosion, erosion, and and deposition deposition with with little little attenattendant dant oxidation oxidation and and leaching. leaching. In H20, C02, CO,, and and In the the earliest earliest period, period, the the atmosphere atmosphere was was accumulating accumulating H20, Basin waters were probably acidic as metals due to frequent vulcanism. Basin waters were probably acidic as metals N, due to frequent vulcanism. N2 were were dissolved dissolved out out of of the the volcanic volcanic rocks rocksat atthe thesame samerate rateasasthe thealkalis. alkalis. Within Within aa few few million million years years aa basin basin could could be be neutralized neutralized and and iron iron deposited deposited as as carbonate carbonate or or oxides, oxides, with with residual residual silica silica deposited deposited in in alternate alternate bands bands Clay was not flocculated as close because of seasonal flocculation. because of seasonal flocculation. Clay was not flocculated as close to to shore as was iron—formation which varied to deep deep water water fades facies shore as was iron-formation which varied from from shallow shallow to (Goodwin,1973). 1973). (Goodwin, Three Three types types of of iron—formation iron-formation are are present: present: a) a) the the Keewatin; Keewatin; the Lake Superior—Labrador Timiskaming or graywacke; and c) Timiskaming or graywacke; and c) the Lake Superior-Labrador Basin. Basin. the the In the In the b) b) Keewatin Keewatin type, type, iron iron occurs occurs with with chert chert as as siderite siderite or or iron iron oxides; oxides; these these components were derived from acid decomposition of pyroclastics components were derived from acid decomposition of pyroclastics with with some some The contribution contribution from from volcanic volcanic gases. gases. The volcanic volcanic gas gas quickly quickly decomposed decomposed under under acidic acidic conditions conditions and and alumina, alumina, alkalis, alkalis, and and silica silica formed formed clays clays in in It is believed the iron oxides and chert flocculated deeper deeper waters. waters. It is believed the iron oxides and chert flocculated and and precipitated precipitated closer closer to to the the sources sources of of the the decomposing decomposing volcanics, volcanics, while while some some soluble silica and alumina, being lighter and slower to flocculate, soluble silica and alumina, being lighter and slower to flocculate, were were removed. removed. The The Timiskaming Timiskaming or or graywacke graywacke type type of of iron—formation iron-formation is is associated associated with with These occur as thin beds and lenses chert chert and and slate slate beds. beds. These occur as thin beds and lenses of of iron iron oxides oxides deposited deposited during during quiet quiet periods periods of of turbidity turbidity flows, flows, and and are are related related to to rapid rapid There is sedimentation sedimentation in in troughs troughs adjacent adjacent to to steep steep mountain mountain chains. chains. There is little little indication decompsiindication of of active active vulcanism, vulcanism, but but bacterial bacterial action action in in mineral mineral decomposition tion may may have have occurred. occurred. Decomposition Decomposition of of the the pyroxenes pyroxenes and and amphibole amphibole minminerals erals in in graywacke graywacke resulted resulted in in aa pH pH of of more more than than9. 9. If If calcium, calcium, magnesium, magnesium, and and alumina alumina were were removed, removed, the the remaining remaining iron iron and and silica silica particles particles caused caused mutual mutual precipitation. precipitation. The Lake Lake Superior—Labrador Superior-Labrador Basin Basin type type of of iron—formation iron-formation occurs occurs on on the the flanks flanks or or shelves shelves of of the the Archean Archean masses. masses. These These deposits deposits may may be be 100 100 to to 300 300 meters meters thick thick and and 100 100 or or 200 200 kilometers kilometers in in strike strike length. length. Thin Thin beds beds of of carcarbonate, iron oxides, oxides, and and chert chert alternate, alternate, and and are are typified typified by by granular granular bonate, oolitic oolitic textures. textures. The The iron—formations iron-formations are are part part of of aa sedimentary sedimentary series series of of quartzite, quartzite, iron—formation, iron-formation, dolomite, dolomite, and and shale shale or or graywacke graywacke lying lying on on aa peneplained peneplained Archean Archean surface. surface. The sedimentary sedimentary sequence sequence is the result result of of transgressive seas seas spreading spreading over over aa peneplained peneplained and and glaciated glaciated surface surface and and sorting sorting the the pre—existing pre-existing sediments sediments into into sand, sand, silt, silt, and and clay clay fractions. fractions. 47 �Fine—grained Fine-grained materials such such as as volcanic volcanic ash ash or or clays clays were were susceptible susceptible to to rapid rapid chemical chemical decomposition decomposition in in both both acid acid and and alkaline alkaline conditions. conditions. The separation begun very early under under separation into oxides, oxides, clays clays and and solutes solutes may have have begun both both volcanic volcanic acid acid or or organic organic acid acid attack. attack. Silica Silica is is present present as as quartz, quartz, microcrystalline, microcrystalline, cristobalite, cristobalite, amorphous amorphous or opaline silica, and silica in solution. solution. The The two two intermediate intermediate forms forms may may alter alter to to quartz quartz grains, grains, chert, chert, clay, clay, or tests. be present present in in diatom diatom tests. or be Iron have formed formedhydroxides, hydroxides,oxides, oxides, carbonate carbonate sulfide sulfide or Iron materials materials may may have or migrated in solution. migrated in solution. Alumina mayhave havebeen beenremoved removed either acid acid or Alumina may in ineither or alkaline alkalineconditions conditionsororformed formedclays claysunder undernormal normal pH pH conditions. conditions. The The various various weathering possibilities depended on temperature, temperature, moisture, moisture, and and the the organic organic weathering possibilities depended on and mayhave havebeen beenaaparticular particular form and chemical chemical environment. environment. Iron—formations Iron-formations may form of of residual residual weathering weathering with with aa substantial substantial contribution contribution of of soluble soluble and and colloidal colloidaliron ironleached leachedfrom from nearby nearby soils soils or or sediments. sediments. REFERENCE REFERENCE Goodwin, 1973, Goodwin, A.M., A.M., 1973, Archean Archean iron—formations iron-formations and tectonic basins of the the Canadian Canadian Shield: Shield: Economic Economic Geology, Geology, v. v. 68, 68, p. p. 915—933. 915-933. 48 �SEASONAL SEASONAL THERMAL THERMAL ENERGY ENERGY STORAGE STORAGE (STES) (STES) SYSTEMS SYSTEMS IN IN MINNESOTA MINNESOTA Matt Matt Walton, Walton, Minnesota Minnesota Geological Geological Survey, Survey, 1633 Eustis Street, Street, St. St. Paul, Paul, Minnesota Minnesota 55108 55108 ABSTRACT ABSTRACT energy andand man—made "waste"heat heat provide provide alSeasonal Seasonal fluxes fluxes of ofsolar solar energy man-made "waste" al- ternatives ternatives to to fossil and and nuclear nuclear fuels fuels for for low—grade low-grade heat. heat. The key key is is Large be developed developed at at very very low—unit low-unit cost cost Large thermal thermal storage storage masses masses must must be because Geologic because of the the low low energy energy density density of of stored stored heat. heat. Geologic formations, formations, structures and and materials materials with with appropriate appropriate boundary boundary conditions conditions can can provide provide this this capacity. capacity. AA fluid fluid heat heat exchange exchange medium medium (air (air or or water) water) is is circulated circulated through through aa geologic geologic body body by by exploiting exploiting natural natural hydrogeologic hydrogeologic characteristics characteristics or or by by constructing constructing aa circulation circulation system. system. Diffusion and and dispersion dispersion of of heat are limited limited by by suitable suitable hydraulic hydraulic and and thermal thermal boundary boundary conditions. conditions. STES. STES. AA powerful powerful Aquifer Aquifer Thermal Thermal Energy Energy Storage Storage (ATES) (ATES)test test facility facility has has been been built on the St. Paul campus of the University of Minnesota to investigate on the St. Paul campus of the University of Minnesota to investigate storage storage of of superheated superheated water water in in aa deep, deep, confined confined lower lower Paleozoic Paleozoicaquifer. aquifer. Water from the Franconia—Ironton—Galesville aquifer is drawn from a supply from the Franconia-Ironton-Galesville well, well, heated heated in in aa heat heat exchanger exchanger and and injected injected in in aa heat heat storage storage well well in in the the Heat is extracted by reversing the cycle and injecting same aquifer. same aquifer. is extracted by reversing the cycle and injecting the the The spent spent water water back back in in the the supply supply well well with with no no net net loss loss of of water. water. The heat heat storage storage capacity capacity and and hydraulics hydraulics of of the the water—filled, water-filled, underground underground iron iron mines mines at Ely, Minnesota, are being investigated as the heat source for a at Ely, Minnesota, are being investigated as the heat source for acoinmun— community ity district district heating heating system. system. Heat extracted extracted by heat pumps pumps from from mine mine water water at ambient underground temperature during the winter can be replenished ambient underground temperature winter can be replenished during during the thesummer summer by exchanging exchanging chilled chilled mine mine water water for for sun—warmed sun-warmed surface surface In water from an open pit above the underground workings. front an open pit above the underground workings. In Blue Blue Earth, Earth, Minnesota, Minnesota, air is is drawn drawn through through aa grid grid of of drain drain tiles tiles buried buried in in glacial glacial the ground in the the winter, till, extracting extracting heat heat from from the ground in winter, returning returning heat heat to to the the till, ground in the and providing providing tempered temperedair air worth worth thousands thousands of of dollars ground in thesummer summer and dollars conditioning cost savings. air per per year year in inheating heating and and air conditioning cost savings- STES systemsinin deep deep and and shallow shallow aquifers, aquifers, soils, STES systems soils,massive massiveimpervious impervious rocks, rocks, processed processed rock rock materials, surface surface water water bodies bodies and and mined mined caverns caverns are are High temperature heat being investigated investigated in in aa number number of of countries. countries. High temperature heat sources sources include include cogenerated cogenerated or or rejected rejected heat heat from from energy energy conversion conversion and and industrial industrial standby heating capacity and processes, waste processes, waste incineration, incineration, heating capacity and intensified intensified solar solar radiation. radiation. Low temperature temperature sources sources include include seasonal seasonal temperature temperature regimes regimes in in air, air, soil soil and and rock, rock, surface surface water, water, ice ice and and ground ground water. water. Heat Heat pumps are are commonly commonly used used to to interface interface with with low low temperature temperature sources. sources. Heat Heat reservoirs reservoirs can can be be used used as as sinks sinks for for cooling cooling as as well well as as sources sources for for heating. heating. heating and summer cooling are major sinks for conventional Winter Winter heating and summer cooling are major sinks for conventional energy energy resources, resources, especially especially in ina amidcontinent midcontinent climate climate such as as Minnesota's, Minnesota's, but but the same same seasonal seasonal AAT be converted converted to toa amajor majorsource sourceofofnon—polluting non-polluting the T can can be thermal thermal energy energy where where suitable suitable geologic geologic formations formationsand and boundary boundary conditions conditions can can be be found found for forSTES. STES. 49 �- - - I - SIMILARITIES ININTHE REGIONAL THE KEWEENAWAN SIMITARITIES THE REGIONALGEOLOGY GEOLOGY OF OFINTRUSIVE INTRUSIVEROCKS ROCKSININ THE KEWEENAWAN MIDCONTINENTRIFT, RIFT, THE MIDCONTINENT THE PERMIAN PERMIAN OSLO OSLO RIFT, RIFT,AND ANDTHE THETERTIARY TERTIARYGEOLOGY GEOLOGY OF OF THE THE NORTH ATLANTIC NORTH ATLANTIC Paul W. Miller, Jr., Paul W. Weiblen Weiblen and and James James D. D. Miller, Jr.,Department DepartmentofofGeology Geologyand andGeoGeophysics, physics, University UniversityofofMinnesota, Minnesota,Minneapolis, Minneapolis,Minnesota Minnesota55455 55455 ABSTRACT the Oslo Oslo Rift and the TerIntrusive rocks in in the the Midcontinent Midcontinent Rift, Rift, the tiary tiary of of East East Greenland, Iceland, Iceland, and and the the Faeroe Faeroe Islands, Islands, exhibit exhibit similarisimilariof intrusive types types and and magma magma ties in the temporal temporal and spatial distribution of Burke and Dewey (1973) compositions. Burke (1973) related related all three three areas to triple triple rifting, and Green (1977) between the junction rifting, (1977) has noted the similarities similarities between extrusive rocks rocks of the the Lake Superior Superior region region and Iceland. Iceland. The intrusive intrusive rocks rocks in the the Midcontinent Rift can be divided into three Nephelinitic—carbonatitic and and alkaline plutonic rocks i) Nephelinitic-carbonatitic rocks reprerepregroups: i) km) complexes at the southern southern end of the ( < 10 km) the Kapuska— Kapuskasented by the small small (< 1). sing Structural Structural Zone and and the the Coldwell Coldwell Province, Province, respectively respectively (Fig. (Fig. 1). ii) Diabasic dikes and sills sills which which occur occur as as quartz quartz tholeiite tholeiite and and olivine olivine tholeiite The plutonic plutonic gabbrogabbro— tholeiite swarms swarms flanking flanking Lake Lake Superior Superior (Fig. (Fig. 1). 1). iii) The ic and associated differentiates differentiates represented represented by the the Crystal Crystal Lake Lake Gabbro Gabbro in in Ontario, the the Duluth Duluth Complex Complex in in Minnesota, and and the the Mellen Mellen Complex Complex in in Wisconsin 1). sin (Fig. (Fig. 1). The spatial of the intrusive units units referred referred to to above above is spatial distribution distribution of consistent with a triple junction tectonic setting in the take Superior consistent with triple junction setting Lake Superior region (Fig. 1). Analogoustectonic tectonic settings settings have for the 1). Analogous have been been proposed proposed for the region (Fig. Oslo Rift (Fig. Oslo (Fig. Similarities in Similarities in a) a) 2) 2 ) and the Tertiary geology geology of the geology of the three the geology the three areas areas the may nay North Atlantic (Fig. (Fig. 3). 3). be summarized as summarized as follows follows: The alkaline intrusion in in East East Greenland, Greenland, the Larvik Larvik alkaline lcangerdlugssuaq Kangerdlugssuaq intrusion Ring Complex in the Oslo Rift, and the Coldwell Complex in Ontario all all in the the occupy similar positions the rifting rifting directions directions in each each occupy positions relative relative to the juncto define define a failed failed arm arm of a triple junccase and all all may be construed construed to tion (Figs. 1—3). tion (Figs. 1-3). The extensive area of East Greenland b) extensive dike dike swarm swarm in in the the Icangerdlugssuaq Kangerdlugssuaq area Greenland b) shows six crosscutting intrusive relationships. However, the major six crosscutting intrusive relationships. However, sequences are an sequences an early early high—Ti high-Ti quartz quartz tholeiite tholeiite followed followed by by olivine olivine tholeiite of MORB affinity. The high—Ti quartz tholeiite is similar in tholeiite of MORE affinity. high-Ti composition to plateau basalts basalts of East Greenland and the Faeroe Island compositions are analogous to the the early early high-Ti high—Ti quartz quartz basalts. The two compositions tholeiite diabases and the second generation olivine tholeiite diabases tholeiite diabases and the second generation olivine tholeiite diabases in the In the the Oslo Oslo Rift, Rift, quartz quartz tholeiite compocompothe Lake Lake Superior Superior region. region. In sition is represented by fine—grained gabbroic intrusions and minor lava sition is represented fine-grained intrusions olivine tholeiite has been reported. flows. However, no no olivine tholeiite reported. In the the Oslo Oslo Rift, Rift, the the parent parent magma magma of of coarse-grained coarse—grained gabbroic gabbroic intrusions intrusions c) c) These intrusions may be less fracmay be related to quartz tholeiite. intrusions related to quartz tholeiite. tionated equivalents of the early magma (Anorthositic) series in (Anorthositic) series in the tionated equivalents of early The presumed parent magma for Duluth Complex. ~ u l u t hComplex. for the the Skaergaard Skaergaard intru— intru- 50 50 �sion, sion, formed formed during during the the Tertiary Tertiary rifting rifting in in the the North North Atlantic, Atlantic, is is comcomto the proposed parent magma composition for the troctolitic— parable parable to the proposed parent magma composition for the troctolitic- gabbroic intrusions gabbroic Keweenawan Keweenawan intrusions. These These rift rift systems systems exhibit exhibit an an expected expected progression progression of of magma magma types types of of Taken carbonatitic, alkaline, quartz tholeiite, and olivine tholeiite. carbonatitic, alkaline, quartz tholeiite, and olivine tholeiite. Taken totogether, The rel1) The relgether, the the intrusive intrusive rocks rocks in in these these rift rift systems systems suggest suggest that: that: 1) ative volume of magma produced during rifting increases through the ative volume of magma produced during rifting increases through the above above succession succession and and is is correlated correlated with with the the extent extent of of rifting: rifting: Oslo Oslo Rift Rift (minor), (minor), Keweenawan Keweenawan Rift Rift (intermediate), (intermediate), North North Atlantic Atlantic (extensive). (extensive). 2) 2) Quartz Quartz thotholeiite is is an an important important transitional transitional magma magma type type between between early early volatile—rich volatile-rich The Keeweenawan and and later later volatile—poor volatile-poor magmas. mamas. 3) 3) The Keeweenawan intrusive intrusive igneous igneous rocks rocks provide nq rifting riftinathan than herehereprovide aa more more complete complete record record of magma evolution during tofore tofore recognized recognized. - - REFERENCES REFERENCES C.K., 1973, 1973, Rifting and doming doming in in southern southern East East Greenland: Greenland: Brooks, C.K., Phys. Phys. Science, Science, v. v. 244, 244, p. p. 23—25 23-25. Nat. Nat. triple junctions: Burke, K., K., and and Dewey, Dewey, .3.F., J.F., 1973, 1973, Plume—generated Plume-generated triple junctions: key key indicators indicators in in applying applying plate plate tectonics tectonics to toold oldrocks: rocks: J. J. Geol., Geol., v. v. 81, 81, p. p.406—433 406-433. Green, J.C., J.C., 1977 1977 Keweenawan Keweenawan plateau plateau volcanism volcanism in in the the Lake Lake Superior Superiorarea, area, in Baragar, Coleman, Baragar, W.R.A., W.R.A., Coleman, L.C., L.C., and Hall, Hall, J.M., J.M., eds., eds., Volcanic Volcanic reregimes gimes of of Canada: Canada: Geol. Assoc. Canada Canada Spec. Spec. Paper Paper 16, 16, p. p. 407—422. 407-422. - FIGURES FIGURES I 1A c.YSUL I, 4r PvOSWA CO* PU X / ulOSON sflRI LLECOMftEP RRAA SIAA -t Fig. Fig. 1 1 Fig. Fig. 1 1 Fig. Fig. 2 2 Fig. 22 Fig. Pig. 33 Distribution of Keweenawan -- Distribution Keweenawan intrusive intrusive rocks rocks in in the the Lake Lake Superior Superior region region. -— Schematic Schematic map of of the the breakup breakup of of the the North North Atlantic, Atlantic, after after Brooks Brooks (1973). (1973) Fig. 33 — The The Jutland triple triple junction junction rift, rift, after after Burke Burke and and Dewey Dewey (1973). (1973). A, B, Rifting developed basins (double (double line) line) but but no no magmatism. magmatism. A, B, and C define define the the expected expected locus locus of of dominant dominant alkaline, alkaline, quartz quartz tholelite, tholeiite, and and olivine 1-3. olivine tholeiite tholeiite magnatism, magmatism, respectively, respectively, in in Figures Figures 1—3. - 51 �GEOLOGY GEOLOGY OF THE THEFRIDAY FRIDAYBAY BAYQUADRM4GLE, QUADRANGLE,MINNESOTA MINNESOTA K. K. Wirth, Wirth, G. G. Crouse Grouseand andU.N. H.H. Woodard, Woodard, R.D. R.D. Salisbury SalisburyDepartment Department of ofGeology, Geology, Be].oit Beloit College, College, Beloit, Beloit, Wisconsin Wisconsin 53511 53511 ABSTRACT ABSTRACT Detailed Detailed geologic geologic mapping mapping in in the the United United States States portion portion of of the the Friday Friday Bay quadrangle, Minnesota, was carried out during the 1981 field Bay quadrangle, Minnesota, was carried out during the 1981 fieldseason. season. The The quadrangle quadrangle is is situated situated in in the the southeast southeast contact contactzone zoneof ofthe theVermilion Vermilion Granitic Complex. The rocks of the Friday Bay quadrangle, and Granitic Complex. The rocks of the Friday Bay quadrangle, and adjacent adjacent areas, areas, comprise comprise aa typical typical granite—migmatite granite-migmatite terrane. terrane. The The oldest oldest rocks rocks in in the the Friday Friday Bay Bay quadrangle quadrangle are are high—grade high-grade metamormetamorphic biotite schists and amphibolites. phic biotite schists and amphibolites. These These rocks rocks were were probably probably originaloriginally ly deposited deposited as as intermediate intermediateto to mafic mafic composition compositionvolcaniclastic volcaniclasticsediments. sediments. AA general general north—south north-south compression compression system system folded folded the themetasedimentary metasedimentary sesequence into a large east—west trending synform. quence into a large east-west trending synform. The The axes axes of of small small folds folds closely closely parallel parallel the the orientation orientation of of the the axis axis of of the the large large synform synform suggestsuggesting that folding was due primarily to a single deformation event. A n early early ing that folding was due primarily to a single deformation event. An episode episode of of anatexis anatexis produced produced the thefirst firstneosome. neosome. Folding by the the emplacement emplacement of of aa large large leuco— leucoanatexis were were followed followed by Folding and and anatexis cratic cratic biotite biotite adamellite adarnellite mass to to the the north north and and west west of of the the Friday Friday Bay Bay quadrangle. quadrangle. Pressure—temperature Pressure-temperature data data from from feldspar feldspar composition composition pairs pairs in in pegmatites pegmatites indicate 600-680° ±+ indicate aa temperature temperature and and pressure pressure of of formation formation of of 600—680°C 50°C 5O0C at at 2—4 2-4 kilobars kilobarspressure. pressure. tate—stage late-stage cross—cutting cross-cutting dikes dikes of of pegma— tite and comprise thethe second neosome tite andaplite aplite comprise second neosomeand andinvaded invadedboth both the thecountry country rocks micro— rocks and and the the leucocratic leucocratic biotite biotiteadamellite. adamellite. Coarse Coarse phenoblasts phenoblastsofof micro- dine in aa late—stage late-stage cline were were formed formed in in the the contact contact zone zone of of the the batholith batholith in feldspathization feldspathizationevent. event. Retrograde Retrograde chlorite—facies chlorite-fades metamorphism, metamorphism, faulting faulting and and hydrothermal hydrothermal alalteration, teration, and and fracturing fracturing are are the the last last events events recorded recorded in in the the Precambrian Precambrian rocks rocks of of the the Friday Friday Bay Bay quadrangle. quadrangle. Joint Joint sets sets show show aa strong strong bimodal bimodal oriorientation. entation. The The strike strike and and dip dip of of the the country country rock rock layering layering and and foliation foliation and and late—stage late-stage faulting faulting appear appear to to be be the the major major factors factors controlling controlling the the distribution distribution and and orientation orientation of of the the two twojoint joint sets. sets. Future Future mapping mapping will will extend extend to to the the east, east, southeast southeast and and west west in in adjacent adjacent quadrangles. quadrangles. 52 �S V S -1 m ra -n FIELD C,) -D I, TRIPS W S �FIELDTRIP TRIPI I FIELD FRANCES - MINE CENTRE AREA, ONTARIO MINERAL DEPOSITS OF THE FORT by KingstOflt Ontario IC7L 3N6 K . H . Poulsen, Poulsen, Queen's Queen'sUniversitY, University, Kingston, mtar-lo K ~ T ,3 ~ 6 X.H. 55 �Paper Paper I1 - MINERAL DEPOSITS OF OF THE THE FORT FORT FRM4CES FRANCES - MINE MINE CENTRE CENTRE AREA, AREA, ONTARIO ONTARIO MINEM LL DEPOSITS by by K.H. K.H. Paulsen, Poulsen, Queens Queen's University, University, Kingston, Kingston, Ontario Ontario K7L K7L 3N6 3N6 TABLE TABLE OF OF CONTENTS CONTENTS INTRODUCTION INTRODUCTION REGIONAL REGIONAL SETTING SETTING Wabigoon Wabigoon Subprovince Subprovince Quetico Subprovince Quetico Subprovince Regional Regional Distribution Distribution of of Mineralization Mineralization GENERAL GENERAL GEOLOGY GEOLOGY Stratigraphy Stratigraphy Structure Structure Metamorphism MINERAL MINERAL DEPOSITS DEPOSITS Classification Classification Type Type Type Type Type Type Type Type 1: 1: 2: 2: 3: 3: 4: 4: Metavolcanic—hOsted Metavolcanic-hosted mineralization fflinera~~zai;i.on Gabbro—hosted Gabbro-hosted mineralization mineralization Vein mineralization mineralization Ultramaf ic—hosted mineralization mineralization Ultramafic-hosted REFERENCES REFERENCES CITED CITED FIELD FIELD TRIP TRIP II Introduction Introduction Stop Fe formation, formation, Nickel Nickel Lake Lake Stop 11 — Fe Stop Stop 22 — Zn, Zn, Cu, Fe Fe mineralization, mineralization, Pocket Pocket Pond Pond prospect prospect Stop Ni, Cu mineralization, mineralization, Belacoma Belacoma property property Stop 33 — Ni, Stop Stop 44 — Cu, Cu, Ni mineralization, mineralization, Northrock Northrock Mine Mine Stop Stop 55 — Ti, Ti, Fe Fe mineralization, mineralization, Traverse Traverse Bay Bay Stop Cu mineralization, mineralization, Mironski Mironski showing showing Stop 66 — Cu Stop Stop 77 — No Mo mineralization, mineralization, Bear Bear Pass Pass showing showing mineralization, Stellar Mine Stop 8 — Au mineralization, Stellar Mine , Stop 8 Cu mineralization, mineralization, Port Stop Stop 9 9 - Zn, Zn, Cu Port Arthur Arthur Copper copper Mine Mine Stop Stop 10 10 — Zn, Zn, Pb mineralization, mineralization, Pidgeon Pidgeon showing showing - -- 57 �INTRODUCTION INTRODUCTION The Archean The Archean rocks rocks of of the the Wabigoon Wabigoon subprovince subprovince of of northwestern northwestern Ontario Ontario host several several producing producing and and past—producing past-producing deposits deposits of of iron, iron, base base metals metals and and gold. gold. Most production production has has come come from from deposits deposits near near the the subprovince subprovince margins and and the the following following pages pages describe describe the the nature nature and and distribution distribution of of margins mineralization mineralization along along the the southwest southwest margin margin at at Rainy Rainy Lake. Lake. Studies of Rainy Lake mineralization have been supported supported by the the Mineral Mineral Deposits Deposits Section Section of of the the Ontario Ontario Geological Geological Survey. Survey. Discussions Discussions in in the field field with A.C. A.C. Colvine Colvine and and 3. Wood Wood of of the the OGS OGS have have been been valuable valuable in in clarifying clarifying the the data data presented. presented. Some Some of the the following following material has been adapted from from OGS summary summary of field field work reports reports prepared prepared by by the the auther. auther. S.T. Spivak S.T. Spivak drafted drafted the the figures. figures. Typing Typing and and drafting drafting services services for for this this manuscript manuscript were funded funded in in part part by by proceeds proceeds from from the the 1977 1977 LSI LSI meeting meeting at Thunder Thunder Bay. Bay. REGIONAL SETTING SETTING The Archean Archean rocks rocks of of the the Mine Centre—Fort Centre-Fort Frances Frances area area lie lie within within aa boundary zone zone between between the the Wabigoon Wabigoon and and Quetico Quetico subprovinces subprovinces of of the the Superior Superior structural structural province. province. In the Rainy River District of Ontario and adjacent parts by aa system system of of parts of of Minnesota, this this boundary boundary is is defined defined by steeply-dipping steeply-dipping dextral dextral wrench wrench faults, faults, the the largest largest of of which which are are the the ). These major wrench Quetico and Seine Seine River-Rainy River-Rainy Lake Lake faults faults (Fig. (Fig. 11). faults faults bound aa "wedge" "wedge" of of crust crust which which is is structurally structurally discordant discordant from from both both subprovinces subprovinces but, because because of of gross gross lithological lithological similarity, similarity, is is generally generally considered considered part of of the the Wabigoon Wabigoon subprovince. subprovince. Wabigoon Wabigwn Subprovince Subprovince The structure structure of of the the Wabigoon Wabigoon granite—greenstone granite-greenstone terrane terrane is is dominated dominated by domal domal features features of of variable variable size. size. The largest largest of these, such such as the the Rainy Lake Lake complex complex and and Irene—Eltrut Irene-Eltrut Lakes Lakes complex, complex, are are greater greater than than 50 50 km km in diameter diameter and and are are composed composed of of smaller smaller gneissic gneissic domes, domes, central central batholiths batholiths and marginal crescent—shaped crescent-shaped granitoid granitoid intrusions. intrusions. The larger larger complexes complexes and small small gneissic gneissic domes domes have have been been interpreted interpreted as as first first and and second second order order gneiss diapirs diapirs which are are the the product product of of gravitational, gravitational, solid solid state state remobiremobilization lization of tabular tabular batholiths batholiths beneath beneath aa supracrustal supracrustal sequence sequence (Schwerdtner al., 1979). 1979). Supracrustal Supracrustal metavolcanic metavolcanic and metasedimen— metasedimen(Schwerdtner et al., tary rocks rocks now now occupy the the margins margins of of the the gneissic gneissic domes domes with with the the largest largest stratigraphic stratigraphic thicknesses thicknesses preserved preserved between between first—order first-order structures, structures. Metavolcanic lithologies Metavolcanic lithologies dominate dominate and and comprise comprise metabasalt metabasalt flows flows with with local local accumulations of accumulations of flows, flows, and and pyroclastic pyroclastic and and epiclastic epiclastic rocks rocks of of interintermediate mediate to to felsic felsic composition. composition. as conglomerate, conglomerate, wacke, wacke, mudstone mudstone and and iron— ironMetasedimentary rocks rocks such such as formation commonly formation commonly form form units units within within the the volcanic volcanic sequences. sequences. A dolomite dolomite unit with with algal algal stromatolite stromatolite mounds mounds occurs occurs within within the the supracrustal supracrustal rocks rocks at Steeprock Steeprock Lake. Lake. Numerous stocks, stocks, commonly commonly of of quartz quartz monzonite, monzonite, intrude intrude Wabigoon subprovince the Wabigwn subprovince supracrustal supracrustal rocks rocks the supracrustal supracrustal rocks rocks (Fig. (Fig. 1). 1). 58 �0 01 . Figure 1: Figure 1: Regional Geology Geology (RED: (RBD: Rice Rice Bay Bay Dome, Dome, BP: BP: Bean Bean Pass Pass pluton, pluton, GP: GP: Grassy Grassy Portage Portage intrusion, i n t r u s i o n , RI: RI: Rest R e s t Island Island granite, g r a n i t e , OTL: OTL: ML: Mud Otter Tail T a i l Lake pluton, pluton, ML: Mud Lake pluton, pluton, SB: SB: Seine Bay By: Bad Vermilion Vermilion tonalite, iintrusion, n t r u s i o n , BV: t o n a l i t e , SG: SG: Seine Seine Group, Group, VG: VG: Vermilion Vermilion Granite). Granite). �are are metamorphosed metamorphosed to to assemblages assemblagescharacteristic characteristicof of the thegreenschist greenschistand and Patterns of metamorphism amphibolite amphibolitefacies facies(Ayres, (Ayres,1978). 1978). Patterns of metamorphism are are closely closely related relatedto tothose thoseof of the thegneissic gneissicdomes domessuch suchthat thathighest highestmetamorphic metamorphic grades grades are are indicated indicatedadjacent adjacentto tothe thefirst—order first-order structures. structures. With With the the exception exceptionof of aa few fewnorthwesterly—striking northwesterly-striking Proterozoic Proterozoicdiabase diabasedikes, dikes,most most of of the the Wabigoon Wabigoon subprovince subprovincerocks rocksin inthe theRainy Rainy River Kiver District Districtare areof of Archean Archeanage. age. Although Although there there is is discrepancy discrepancy among among ages ages derived derived by by difdifferent ferent geochronological geochronologicalmethods, methods, it it is isclear clearthat thatthe therocks rocksof of the thearea area were Ma. The The oldest oldest ages ages were thermally thermallyactive activein inthe theinterval interval2700 2700to to2400 2400Ma. reflect reflect widespread widespread igneous igneousactivity activitywhereas whereas successively successivelyyounger youngerages agesare are likely likely the the result result of of metamorphism, metamorphism, metasomatism, metasomatism, and and crustal crustal uplift. uplift. p e t i c o Subprovince Subprovince Quetico contrasts with with that that of The structure structureof ofthe theQuetico Quetico subprovince subprovince contrasts of the the The Wabigoon. Wabigoon. ItItisischaracterized bybya aconsistent strike of of metasedimentary characterized consistent strike metasedimentary units Seine River—Rainy fault. Near Near the the unitssub—parallel sub-parallelwith withthe the Seine River-Rainy Lake Lake fault. northern Quetico subprov— northernboundary, boundary,low—grade low-grade metasedimentary metasedimentary rocks rocksof ofthe the Quetico subprov- ince sets; an ince dip dip steeply steeply and and display display three three discrete discrete cleavage cleavage sets; an early early set set isis subparallel subparallel with with east—trending east-trending bedding bedding but but has has aa more more northerly northerly strike, strike, whereas whereas aa second secondset setwith with an aneven evenmore morenortheasterly northeasterlystrike strikemakes makesaa moderate moderate angle anglewith withbedding. bedding. AA late late set set includes includes crenulation crenulation cleavage cleavage and and kink kink bands bands which which strike strikenorthwesterly northwesterlyand anddeflect deflectthe theother othercleavages cleavagesas as well well as as bedding. bedding. The The metasedimentary metasedimentary strata stratacommonly commonly display displaygood goodgraded graded bedding youngingdirections directions that that despite bedding and and younging despite some some reversals, reversals,are aredomidominantly nantlynorthward northward (Hawley, (Hawley, 1930; 1930; Merritt, Merritt, 1934; 1934; Ojakangas, Ojakanqas, 1972; 1972; Harris, Harris, 1974; 1974; wood Wood et et al., al., 1980; 1980;this thisstudy). study). Southward, Southward, the the metasedimentary metasedimentary rocks rocks become become migmatitic migmatitic and and primary primary structures structuresand and cleavage cleavageare areobscured. obscured. Schist—rich miqmatitespossess possessbedding—parallel bedding-parallel Schist-rich and and granite—rich granite-rich jaigmatites foliations foliationswhich which are are folded folded into intolarge, large,open, open, shallow shallow plunging plunging structures structures which which trend trendeast—west east-west (Southwick, (Southwick,1972; 1972; Southwick Southwick and and Sims, Sims, 1980). 1980). Major Major antiforms coredbybymassive massivegranitoid granitoidbodies bodiesof of irreqular irregular antifoms are arecommonly commonly cored migmatitic terrane, terrane, the the These granites granites occur occur within within aa migmatitic shapes shapes (Fig. (Fig. 1). 1). These whichoccupies occupiesthe thecentral central part part of Vermilion Granitic GraniticComplex, Complex, which of the theQuetico Quetico Vermilion biotite schists areare metamorphosed The metasedimentary metasedimentary biotite schists metamorphosed to to subprovince. subprovince. The assemblages grade (Pine assemblages indicative indicative of ofaasouthward southward increase increasein inmetamorphic metamorphic grade (Pirie assemblages and Mackasey, Mackasey, 1978). 1978). pelitic Peliticrocks rockswith withgreenschist greenschistfacies facies assemblages and (chlorite-sericite; chlonite—biotite) chlorite-biotite) are are found found just just to to the the south south of of the the (chiorite—sericite; subprovince (biotitesubprovince boundary boundary whereas whereas amphibolite amphibolite facies facies assemblages assemblages (biotite— cordierite—staurolite—garnet-sillimanite; cordierite-staurolite-garnet-sillimanite; biotite—garnet—andalusite— biotite-garnet-andalusitestaurolite; staurolite; and and biotite—garnet-sillimanite) biotite-garnet-sillimanite) have have been been observed observed in in the the central central part part of of the the subprovince subprovince (Southwick, (Southwick, 1976; 1976; Pine Pirieand andMackasey, Mackasey, The observed observed sequence sequence of of assemblages assemblages is is consistent consistent with with moderate moderate 1978). The 1978). as metamorphic metamorphic pressures pressures of of 22to to44kb kband andtemperatures temperatures ranging ranging as as high high.as 600°C 600°C. Geochronological data from fromthis this part part of Geochronological data ofthe theQuetico Queticosubprovince subprovince show show that thatmost mostigneous igneousand andmetamorphic metamorphic events eventswere werebroadly broadlycontemporaneous contemporaneous subprovince. with those in the Wabigoon with those in the Wabiqoon subprovince. Regional Regional Distribution Distribution of of Mineralization Mineralization The The Rainy Rainy River River district district of of Ontario Ontario and and adjacent adjacent parts parts of of Minnesota Minnesota 1890's. Gold proprowere the site of intensive prospecting for gold in the were the site of intensive prospecting for gold in the 1890's. Gold duction duction from from small small mines mines in in the the interval interval 1893—1902 1893-1902 came came principally from 60 �Figure 2: Regional distribution of mineralization. Lo&. - Distribution of Mineralization • Rainy River 0 Zinc — Copper - Iron rormoton occurrence 20KM I I0-IOOoz. '0° - '000 oz '.000 - 10.000 oz- • 10,000-100,000 oz • S • • District, Ontario and adjacent Parts of S , — Minnesota. — H t0 �I two twoareas, areas, Mine MineCentre Centreand andAtikokan: Atikokan: these thesewere wereknown knownas as the theLower LowerSeine Seine and andUpper UpperSeine Seinegold goldregions, regions,respectively. respectively. Total Totalproduction productionat atthat thattime time and andduring duringsubsequent subsequentactivity activityreached reached25,000 25,000 oz. oz. Au Auand and3,000 3,000oz. oz. Ag. Ag. The Thedeposits depositsare areconcentrated concentratedalong alongthe thesubprovince subprovinceboundaries boundariesand andare are related In the the relatedspatially spatiallyto tothe themajor majorfaults faultsand andtheir theirsplays splays(Fig. (Fig.2). 2). In early earlypart part of ofthe the20th 20thcentury, century,some someexploration explorationfor foriron ironin inthis thisregion region resulted Sapawe, resultedin inlimited limitedproduction productionfrom fromthe theAtikokan AtikokanIron IronMine, Mine, near nearSapawe, between between1907 1907and and1911. 1911. The Themajor majoriron ironore oredeposits depositsat atSteeprock SteeprockLake Lakewere were developed developed during duringWorld World War War II I1and andproduction productionbegan beganin in1945, 1945,continuing continuing until until1979. 1979. Low Lowgrade gradeiron—formations iron-formations also alsoare arecommon commonin inthe theregion regionand and i— tend tendto tobe be concentrated concentratednear nearthe thesubprovince subprovinceboundaries. boundaries. Several Severalsignif signifiTwo cant cantprospects prospectscontaining containingbase basemetals metalsalso alsohave havebeen beendiscovered. discovered. Two broad broad types typesare arepresent: present: zinc—copper zinc-coppermineralization mineralizationoccurs occursat atspecific specific horizons horizonswithin within the themetavolcanic metavolcanicsuccession successionand andcopper—nickel copper-nickelmineralizamineralization tionis isassociated associatedwith withmafic maficand andultramafic ultramaficrocks, rocks,particularly particularlyintruintrusions sions(Fig. (Fig.2). 2). Although Although some someof of these these prospects prospects have have been been extensively extensively developed, developed,very very limited limitedbase—metal base-metal production productionhas hasbeen beenreported reportedfrom fromthis this Clearly there thereis is aa strong strongspatial spatialcorrelation correlationbetween betweenknown known region. Clearly region. In particular, particular, mineralizamineralizamineralization mineralizationand andthe thesubprovince subprovinceboundary. boundary. In tion tionrepresenting representingall allof ofthe theabove abovetypes typesisisconcentrated concentratedwithin withinthe thebounboundary theRainy RainyLake Lakearea. area. dary zone zonein inthe a a GENERAL GENERAL GEOLOGY GEOLOGY Stratigraphy Stratigraphy The The stratigraphy stratigraphyofofArchean Archeanrocks rocksatatRainy RainyLake Lakehas haslong long proved proved aa of A.C. (1913) established established aa source source of ofcontroversy. controversy. The The mapping mapping of A.C. Lawson Lawson (1913) stratigraphic stratigraphicnomenclature nomenclature which which included included the the dominantly dominantly metavolcanic metavolcanic a Keewatin Keewatin Group, Group, metasedimentary metasedimentary biotite biotiteschists schistsof of the theCoutchiching CoutchichingGroup, Group, and Using the the principles principles of of strucstrucand the the conglomerate—bearing conglomerate-bearingSeine SeineGroup. Group. Using tural Lawson interpreted interpretedthe theCoutchiching CoutchichingGroup Groupto tobe be the the tural superposition, superposition,Lawson oldest, With oldest, followed followed in inturn turnby by the theKeewatin KeewatinGroup Groupand andthe theSeine SeineGroup. Group. With the by Grout Grout and and his his coworkers coworkers(Grout (Groutet et al., al., the exception exception of of disagreement disagreement by 1951), 19511, this this stratigraphic stratigraphic interpretation interpretation has has prevailed prevailed until until recently recently (Poulsen, 1980a; 1980s; Wood Wood et et al., al., 1980). 1980). Unfortunately, Unfortunately, previous previous interpretainterpreta(Poulsen, tions be tions were were based based on on observations observations around around the the Rice Rice Bay Bay dome dome where where it it can can be As shown shown that that structural structural superposition superposition is is not not aa valid valid stratigraphic stratigraphic tool. tool. As revised stratigraphic stratigraphic column column(Table (Table1) 1)is is based based upon upon data data aa result, result, aa revised obtained obtained from from recent recent mapping mapping by by the the Ontario Ontario Geological GeologicalSurvey Survey (Wood (Woodet et al., al., The spatial distribu1980; Harris, 1974; Poulsen, 1980b; Poulsen, 1981). The spatial distribu1980; Harris, 1974; Poulsen, 198Db; Poulsen, 1981). tion 1. tion of of the the units units is is shown shownin in Figure Figure 1. structure Structure a In In the the fault zone which north, the Quetico Fault is represented by a 700 m—wide north, the Quetico Fault is represented by a 700 nt-wide fault zone which includes includes mylonite, mylonite, blastomylonite blastomylonite and, and, locally, locally, ultramylonite ultramylonite and and The mylonitic fabric strikes east and parallels parallels the the pseudotachylite. The nylonitic fabric strikes east and pseudotachylite. The mylonitic mylonitic rocks rocks are are commonly commonly offset offset by by small small dextral dextral fault zone. zone. The fault faults faults and, and, locally, locally, small small folds folds are are superimposed superimposed on on the the mylonite. mylonite. Rocks Bocks of the Wabigoon subprovince are exposed north of the fault. of the Wabiqoon subprovince are exposed north of the fault. TWO regional regional faults faults are are exposed exposed within within the the map map area area (Fig. (Fig. 3). 3). Two 62 �TABLE TABLE 11.• TABLE OF LITHOLOGIC TABLE OF LITHOLOGIC UNITS OMITSFOR FORTHE THEMINE MINECENTRE-FORT CENTRE-FORTFRANCES FRANCESAREA AREA LITHOLOGIC UNIT LITHOLOGIC Fault rocks rocks (12) Fault (12) DESCRIPTION DESCRIPTION Schists, Schists, mylonites, mylonites, cataclastites cataclastitesdeveloped developed on on heterogeneous lithologies heterogeneous lithologies Dyke Dyke rocks rocks (11) (11 ) Unmetamorphosed Unmetamorphosed granitoid granitoid rocks rocks (10) (10) Metamorphosed Metamorphosed conglomerate conglomerate and (9) and sandstone sandstone (9) Fault Fault Contact Contact Diabase, gabbrc', lamprophyre, quartz-feldspar quartz—feldspar Diabase, gabbro, lamprophyre, porphyry porphyry Intrusive intrusive Contact Contact Granite, Granite, granodiorite, granodiorite, monzonite, monwnite, monzo— monzodiorite, quartz quartz mon— quartz raonzonite, monwnite, quartz monzodiorite zodiorite Intrusive intrusive Contact Contact Conglomerate, Conglomerate, arkose, arkose, subarkose, subarkose, lithic lithic arenite, lithic lithic arkose arkose Angular Angular Unconformity Unconformity Metamorphosed ~etamorphosed granitoid (8) granitoid rocks rocks (8) Tonalite, Tonalite, trondhjemite, trondhjemite, granite granite gneiss, gneiss, Metamorphosed Metamorphosed gabbroic (7) gabbroic rocks rocks (7) Gabbro, melagabbro, leucogabbro, anortho— anorthosite, quartz quartz gabbro, gabbro, quartz quartz diorite, diorite, meta— meta- Metamorphosed Metamorphosed wackes wackes and (6) and mudstones mudstones (6) Metamorphosed Metamorphosed chemical chemical strata strata and and related related clastic (5) clastic rocks* rocks* (5) Ultramaf Ic metavolcanic metavolcanic Ultramafic rocks* rocks* (4) (4) Felsic Felsic metavolcanic metavolcanic rocks rocks (3) (3) Intermediate Intermediate metavolcanjc metavolcanic rocks (2) rocks (2) Mafic Mafic metavolcanic metavolcanic rocks (1 ) rocks (1) quartzofeldspathic quartzofeldspathicgneiss*** gneiss*** Intrusive Intrusive Contact Contact diabase**, , azuphibolite amphibolite diabase Intrusive Intrusive Contact Contact Biotite schist, schist, biotitic biotitic siltstone, siltstone, slate, slate, Biotite wacke, mudstone, mudstone, migmatite migmatite (biotitic (biotitic wacke, paleosome) paleosome) Chert, Chert, chert-magnetite, chert-magnetite, pyrite—pyrrhotite, pyrite-pyrrhotite, pyritic slates, slates, slate, slate, siltstone, siltstone, wacke wacke pyritic Metamorphosed Metamorphosed lapilli—tuff, lapilli-tuff, tuff, tuff, magnetic magnetic chlorite chlorite schist schist Metamorphosed Metamorphosed rhyolite rhyolite and and rhyodacite rhyodacite flows, flows, amygdaloidal flows, amygdaloidal flows, tuffs, tuffs, lapilli—tuffs, lapilli-tuffs, lapillistone, lapillistone, agglomerate agglomerate and and quartz quartz sericite sericite schist schist Metamorphosed andesite to to dacite dacite flows, flows, pilpu— lowed lowed and amygdaloidal amygdaloidal flows, flows, chioritic chloritic tuffs, tuffs, lapilli—tuff, lapilli-tuff, agglomerate, agglomerate, breccia breccia and and quartz—chlorite quartz-chlorite schist schist Metamorphosed Metamorphosed basaltic basaltic flows, flows, mafic mafic tuffs, tuffs, amphibolite, amphibolite, chlorite chlorite schist, schist, migmatite migmatite (axnphibolitic paleosome) ( amphibolitic paleosome) NOTES NOTES * Although Although the the table table represents represents the the broad stratigraphic stratigraphic order order among among these these rock rock types, types, local local intercalation intercalation of of lithologies lithologies is is common. common. this this type type are are common common throughout throughout the the volcanic volcanic succession succession and and consticonstitute tute aa substantial substantial fraction fraction of of the the total total thickness thickness of of metavolcanic metavolcanic rock. rock. Not Not necessarily necessarily orthogneiss. orthogneiss. ** Sills Sills of of ** *** 63 �a C' Figure 3: SEQUENCE VOLCANO-SEDIMENTARY : : B 3A Ao.S A Mo,S £ 2A • Ce.Ni B 0 Cu C • Ft,Ti : Port Arthur Copper Mine Pocket Pond Prospect Belacoma Property 5 6 4 Gagne Lake Occurrence Wind Bay Deposit Lochart Lake Farrington Boundary Occurrence Lithology and mineral deposits, Fort Frances—Mine Centre area. • Northrock Deposit Mironski Property Olive Mine Golden Star Mine Foley Mine Nickel Lake Iron Formation McTavish Prospect �In Inthe thesouth, south,the theSeine SeineRiver-Rainy Fliver-MinyLake LakeFault Faultisisexpressed expressedas asphyl— phyllitic liticshear shearzone w n ewhich whichstrikes strikeseasterly. easterly. The Therocks rocksto tothe thesouth southof of this this fault Quetico faultare arelargely largelymetasedimentary metasedimentarybiotite biotiteschists schistsof ofthe theQuetico subprovince. subprovince. At ~tleast leastthree threefold foldsets setsmay maybe berecognized recognizedininthe thearea areabetween betweenthe the The youngest youngestof of these theseconsists consistsof of small m a l l folds, folds,F3, ,F which which have have faults. faults. The northwesterly—striking northwesterly-strikingaxial axialsurfaces. surfaces. These Thesefolds foldsare arecommonly comonlymetre— metresized sizedand andpossess possessan anaxial axialplanar planarcrenulation crenulationcleavage. cleavage. Kink Kink bands bands also also are arecommon commonininthis thisfold foldset. set. Ductile Ductile shear shearzones, zones,particularly particularlywell well developed developed in incoarse—grained coarse-grainedrocks, rocks, also alsotend tendto tostrike strikenorthwesterly northwesterlyand and may theF3 F3fold foldset. set. may be begenetically geneticallyrelated relatedtotothe F3 colds foldsmay may be be observed observedsuperimposed superimposedon onthe thecleavage cleavageand andminor minorfolds folds F3 of F2folds foldsplunge plunge northeasterly northeasterlyand andsouthwesterly southwesterly ofananolder olderset. set. These TheseF2 and and vary vary in inwavelength wavelengthfrom fromaafew fewcentimeters centimetersto toaafew fewkilometers. kilometers. Axial Axial surfaces surfacesdip dipsteeply steeplyand andare arecommonly commonlycoplanar coplanarwith with aastrong strongpenetrative penetrative cleavage. F2 folds foldsand and cleavage cleavage are are dominant dominant in in defining defining the the strucstruccleavage. The The F2 tural astributionof of turalgrain grainof of the theregion regionand andstrongly stronglyinfluence influencethe thedistribution lithologic units. units. lithologic F2 folds folds in in the the Rice Rice Bay—Bear Bay-Bear Pass Pass Of importance importance is is the the fact fact that that F2 Of area areaface facedownward. downward. Observations Observations of of stratigraphic stratigraphictops, tops, based based on on graded graded beds antiformal bedsand andpillow pillowlavas, lavas,contradict contradictthe thestructural structuralorder ordersosothat thatantifortual features featuressuch suchas asthe theRice RiceBay Bay dome domeare arestratigraphic stratigraphicsynclines. synclines. degrees have been observed. beds with dips as low as 45 The Overturned beds with dips as low as 45 degrees have been observed. The Overturned entire significance significance of of the the downward downward facing facing is is undetermined, undetermined, but but it it is is entire clear must have have taken takenplace place in in order order to to invert invert clear that that an an earlier earlier deformation deformationmust the 1980). Large, Large, recumbent recumbent the stratigraphic stratigraphicsequence sequence(Poulsen (Poulsenet et al., al., 1980). F, folds folds are are inportant important to to an an understanding understanding of of the the distribution distribution of of litho— lithoF1 logic Eastward in in the the Mine Mine logic units units in in the theRice Rice Bay Bay Dome h m earea area(Fig. (Fig.4). 4). Eastward Centre Centre area, area, the thestructure structureappears appearsto tobe be aa simple simple northward—facing northward-facing limb limb of o The transition transition from from ductile ductile to to brittle brittle aa large largeupright uprightfold fold(Fig. (Fig.5). 5). The deformation deformation is is evidenced evidenced by by the the pervasive pervasive development development of of mesoscopic—scale mesoscopic-scale shear zones. zones. Two Two fundamental fundamental shear—zone shear-zone orientations orientations exist: exist: one one set set with with shear right—hand right-hand sense sense of of displacement displacement parallels parallels the the major major faults faults and and strikes strikes approximately approximately east east and and the the other other conjugate conjugate left—hand left-hand set set strikes strikes to to the the north-northwest. north—northwest. These These systematic systematic orientations orientations and and senses senses of of displacement displacement are are equally equally well well developed developed on on northward— northward- and and southward—facing southward-facing sequences, sequences, and and involve involve The shear shear zones zones are are interpreted interpreted to to broadly broadly postdate pestdate all rock rock types. types. The all folding. These These zones zones are are consistent consistent with with the the interpretation interpretation that that the the folding. thethe area is aisright—hand wrench 3ominant structure structureinin area a right-hand wrenchzone zoneof ofwhich which the the dominant boundary faults are merely the most obvious manifestation. two boundary faults are merely the most obvious manifestation. two Metamorphism Metamorphism The rocks rocks exposed exposed between between the the two two boundary boundary faults faults have have been been metametaThe morphosed to assemblages characteristic of the greenschist and morphosed to assemblages characteristic of the greenschist and amphibo— mphiboto amphibolite mphibolite facies facies The transition transition from from greenschist greenschist to lite facies. facies. The lite indicates a northwestward increase in grade and involves both indicates a northwestward increase in grade and involves both regional regional and an 65 �C' C.' —— . Figure 4: dome. 7a — overturned anticline (with plunge Antiform (with plunge) RICE BAY DOME AREA lOa —- Portog e 70 - over x Zn,Cu Geology of the Rice Bay Dome area. Rock types are keyed to Table 1. Note the recumbent antjcljne which IS refolded pillow lava, top shown overturned graded beds — Lithological contact Lithotype (see table I) Fault .7 Mineral occurrence Field Trip Stop �-J 0" F - --- / - Sb 8b ——— , Figure 5: Figure 5: Geology of of the the Mine Mine Centre centre area. area. Rock to Table Table m c k types types are are keyed keyed to 1. 1. Note that that younging information infornation obtained from from southwest southwest of area suggests that the the sequence sequence northwest northwest of of Bad m d the map area Vermilion Vermilion Lake Lake faces faces northwestward. northwestward. - p® x~ ....# anticline anticline (volcanics) (volcanics ) with with plunge plunge pi1lawlava7 lava top top 7' pillow syncline (canglornerates, (conglomerates, arenites arenites)) reclined syncline reclined ,/ 5< attitude attitudeand andfacing focingofofcross— crossfault bedding xAu x Au mineral occurrence occurrence bedding orenites arenites lithologic contact contact Field trip stop 0 @ Field stop 5 mi. I lithotype ((see see table I ) n n krn " I —- • Mine Centre Ic / 8c MINE CENTRE AREA 3b Turtle I �contact contact metamorphism metamorphism (Fig. (Fig. 3). 3). In In the the greenschist greenschist facies, facies, chlorite chlorite schists are common and chioritoid with chlorite and white mica schists are common and chloritoid with chlorite and white mica are are present present in the Shoal Lake area. Staurolite, andalusite, sillimanite, garnet, in the Shoal Lake area. Staurolite, andalusite, sillimanite, garnet,Mg— Mgchlorite chlorite and and biotite biotiteform forman anunaltered unalteredprograde progradeassemblage assemblage in inthe theBear Bear Passage Passage area, area,and and diopside—bearing diopside-bearing araphibolites amphibolites occur occur along along the the northeast northeast M,undant evidence of retrogressive metamargin of the Rice Bay Dome. Abundant evidence of retrogressive metamargin of the Rice m y Dome. The northwestward increase in throughout the area. morphism exists The northwestward increase in grade grade morphism exists throughout the area. a similar southward increase contrasts with within the boundary zone within the boundary zone contrasts with a similar southward increase in in the Quetico subprovince. subprovince. the Quetico MINERAL MINEPAL DEPOSITS DEPOSITS Classification Classification The Lakearea area has has aa long Rainy Lake long history history of ofmineral mineralexploration explorationand and The Rainy exploitation since the discovery of gold at Mine Centre in 1893. At At that that exploitation since the discovery of gold at Mine Centre in1893. time, three three deposits, deposits, the the Olive, Olive, Golden Golden Star, Star, and and Foley, Foley, were were worked, worked, and and tine, coupled coupled with with renewed renewed activity activity during during the the 1930's, 1930's, aa total total production production of of approximately 485 kg of Au and 20 kg of Ag was realized (Beard approximately 485 kg of Au and 20 kg of Ag was realized (Beardand and Garratt, 1976). 1976 ) Garratt, . The The noted noted similarity similarity of of iron—formations iron-formations at at Nickel Nickel Lake Lake with with those those at at Diamond— Michipicoten led to exploration around the turn of the century. Michipicoten led to exploration around the turn of the century. Diamonddrill minimum of of 22 million million tonnes tonne6 of of drill programs programs in in 1920 1920 and and 1955 1955 defined defined aa minimum magnetite—ilmenite mineralization hosted by anorthosite and gabbro magnetite-ilmenite mineralization hosted by anorthosite and gabbronorth north of 1969). of Seine Seine Bay Bay (Rose, (Rose,1969). since since the the mid mid 1950s, 1950s, exploration exploration in in the the region region has has been been focused focused The discovery of largely copper in in gabbro gabbro largely on on the the search search for for base base metals. metals. The discovery of copper at Grassy Portage Bay in 1958 led to the development of a 70 m two— at Grassy Portage Bay in 1958 led to the development of a 70 m twocompartment compartment shaft shaft and and aa 200 200 in m drift through through the the mineralization mineralization by by Recent exploration exploration programs programs have have Northrock Northrock Mines Mines Limited Limited in in1973. 1973. Recent investigated investigated zinc—copper zinc-copper mineralization mineralization hosted hosted by by metavolcanic metavolcanic rocks. rocks. Numerous occurrences have been evaluated by diamond—drilling and geophysigeophysiNumerous occurrences have h e n evaluated by diamond-drilling and cal to date, date, no no economically economically viable viable deposits deposits have have been been cal methods methods but, but, to outlined. outlined. rn In total, total, over over 75 75 individual individual mineral mineral properties properties have have been been developed developed Recent mapping by the Ontario Geological Survey to to various various degrees. degrees. Recent mapping by the Ontario Geological Survey (Poulsen, (Poulsen, 198Db; 1980b; Poulsen, mulsen, 1981) 1981) was was initiated initiated to to identify identify the the geological geological settings settings of of the the different different mineralization mineralization types types with with an an objective objective of of establishing All significant significant establishing exploration exploration criteria criteriafor forthis thisarea. area. All occurrences in terms terms of of strati— straticonsidered in of mineralization mineralization have have been been considered occurrences of These characteristics characteristics graphic graphic setting, setting, mineralogy mineralogy and and deposit depositmorphology. morphology. These scattered form form the the basis basis of of the the deposit depositclassification classificationshown shownininTable Table2.2. Scattered development, on which which there therehas hasbeen been no no development, have have been been noted noted minor occurrences, occurrences, on minor spatial distribution The spatial distribution of of selected selected but are are not not included included in in the the table. table. The but deposits deposits is is shown shown in in Figure Figure 3. 3. Descriptive Descriptive aspects aspects for for each each deposit deposit type type may may be be illustrated illustrated by by data data from particular^ emphasis emphasis on on the the largest largest from all all occurrences occurrences of of that that class class with with particular and and most most completely completely developed developed properties. properties. 68 �TABLE TABLE 2. 2. MINERAL DEPOSIT CLASSIFICATION MINERAL DEPOSIT CLaSSIFICATIONFOR FORFRANCES-MINE FRANCES-MINECENTRE CENTREAREA ARBA NUMBER NUMBER OP OF PROPERTIES EXAMPLES PROPERTIES EXAMPLES TYPE TYPE 1 1 FIELD FIELD TRIP TRIP STOP STOP NO. NO- - Stratabound Stratabound mineralization mineralization hosted hosted by by felsic to mafic metavolcanics — felsic to mafic metavolcanics A: A: Sphalerite—galena—chalcopyrite Sphalerite-galena-chalcopyrite associated associated with with siliceous siliceous volcanic volcanic rocks rocks 22 Gagne G a p e Lake Lake Pidgeon Pidgeon B: B: Sphalerite—chalcopyrite Sphalerite-chalcopyrite associated associated Sc amygdaloidal amygdaloidal with with intermediate intermediate to to maf mafic volcanic flows, tuffs and breccias volcanic flows, tuffs and breccias 99 Wind Wind Bay, Bay, Port Port Arthur Arthur Copper copper - 9 C: C: Sphalerite—chalcopyrite Sphalerite-chalcopyrite associated associated with with iron iron formation formation 4 4 McTavish, McTavish, Pocket Pocket Pond 2 - D: Lean Lean iron iron formation formation — mainly mainly chert— chertmagnetite and massive pyrite—pyrrhotite, magnetite and massive pyrite-pyrrhotite, minor chalcopyrite chalcopyrite common common 13 Reef Reef Point, mint, Nickel Lake, L Nickel ,& Shoal Shoal Lake Lake 10 1 - 22 — Mineralization Mineralization hosted hosted by by layered layered gabbroic gahbroic intrusions intrusions A: A: Chalcopyrite Chalcopyrite associated associated with with gabbro gabbro and and leucogabbro leucogabbro near near the the base of sills sills B: B: Disseminated Disseminated chalcopyrite chalcopyrite associated associated with with siliceous siliceous phases phases of of the the intrusions intrusions C: Ilmenite-magnetite-apatite-rutile lenses lenses C: Ilmenite—magnetite—apatite—rutile in in the the upper upper portions portions of of the the intrusions intrusions Northrock Northrock Island Island Bay Bay 4 1 Mironski Mironski 6 4 4 Traverse Traverse Bay Bay Seine Seine Bay Bay 5 26 26 Foley, Foley, Stell Golden Golden Star Star 77 1 - Vein Vein mineralization mineralization 33 — g A: Quartz—gold Quartz-gold sulfide sulfide veins veins in in shear shear zones wnes B: Quartz—molybdenite—pyrite wartz-molybdenite-pyrite veins veins in in unmetamorphosed unmetamorphosed granitoid granitoid rocks rocks 66 S Bear Bear Pass pass 7 Belacoma 3 - mineralization hosted by ultramafic 44 - Disseminated Disseminated chalcopyrite—pyrrhotite chalcopyrite-pyrrhotite mineralization hosted by ultramafic metavolcanics metavolcanics I 69 �Type Type 1: 1: Metavolcanic—hosted Metavolcanic-hosted mineralization mineralization Zinc—copper mineralization Zinc-copper mineralization at Painy Rainy Lake Lake occurs in in a number of specific volcanic volcanic environments. The mineralization at Gagne Lake (Type environments. The (Type 1A) 1A) consists of lenses of massive sphalerite and galena, as wide as 20 cm, lenses sphalerite as which parallel which parallel similar similar overlying overlying pyritic pyritic layers. layers. Rocks of the footwall footwall to to the south of the mineralized zone consist dominantly of rhyolitic south the zone consist dominantly rhyolitic lalapillistone which locally pillistone locally contains contains aa distinctive distinctive spotted spotted alteration alteration of of chlorite and centimeter—sized porphyroblasts of pinitized chlorite centimeter-sized porphyroblasts pinitized cordierite. The hanging—wall The hanging-wall rocks rocks consist consist of of fine—grained fine-grained siltstone siltstone and and chert chert which which locally form a coarse breccia having clasts as much as 50 cm in form coarse breccia clasts as as 50 in diameter. diameter. On strike strike with with the the mineralization, mineralization, the the breccia breccia contains contains clasts clasts of of massive massive pyrite. Although drilling to date by Armstrong—Hupchuk has shown the pyrite. Although drilling to date by Armstrong-Hupchuk has shown the mineralization mineralization to to be be very very thin, thin, the the geologic geologic setting setting and and alteration alteration show show aa resemblance to many volcanogenic massive sulfide deposits (Sangster, volcanogenic massive sulfide deposits (Sangster, resemblance 1972). Mineralization at the the Pidgeon Pidgeon property occupies occupies aa similar similar setting. setting. sphalerite-galena-chalcopyrite with with iron iron carcarHere en echelon echelon lenses lenses of sphalerite—galena—chalcopyrite bonates are are conformable conformable with with siliceous siliceous metavolcanic metavolcanic rocks. rocks. A diamond diamond yielded assays per tonne tonne have have felsic lapilli felsic lapilli more laterally more drill (7 ft) ft) true true width width drill intersection intersection of approximately approximately 22 m (7 of 0.53% 0.53% Zn, 1.76% 1.76% Pb. Low Ag values values as as high high as as 0.3 0.3 03. oz. Pyritic blebs in been been reported reported from from sulfide—rich sulfide-rich material. material. Pyritic tuff tuff typify typify the the zones zones of of footwall footwall alteration alteration which which are are extensive than individual individual sulfide sulfide lenses. lenses. Although the the Type Type lB 1B occurrences occurrences are are similar similar in in mineralogy mineralogy to to the the massive sulfide sulfide deposits deposits (sphalerite, (sphalerite, pyrite, pyrite, pyrthotite, pyrrhotite, chalcopyrite, chalcopyrite, minor galena), they they possess possess aa number number of of distinctive distinctive characteristics. characteristics. The host rock rock is is commonly commonly an an amygdaloidal, amygdaloidal, brecciated, brecciated, intermediate intermediate to to mafic mafic to 20 20 cm cm metavolcanic metavolcanic rock. rock. The mineralization occurs occurs as discrete discrete seams seams 11 to wide to 20 cm) of of barren barren wide which are are separated separated by substantial substantial widths (1 to chloritic host chloritic host rock. rock. At the the Wind Bay property, aa typical typical drill drill section section through through 50 50 mm of of tuffaceous chlorite and 8.6 8.6 mm in in schist yielded yielded two two mineralized mineralized zones, zones, 77 mm and tuffaceous chlorite schist 1.5% Zn Zn and and 0.2% 0.2% Cu Cu and and 1.1% 1.1% Zn Zn and and 0.09% 0.09% Cu, Cu, true width, which averaged averaged 1.5% Where the respectively (George 1980). Where respectively (George Armstrong, Armstrong, personal communication, communication, 1980). quartz—chlorite schist quartz-chlorite schist is is only only weakly weakly deformed, deformed, primary primary features features such such as as angular fragments and amygdules are recognizable, suggesting suggesting aa derivation derivation The distinctive distinctive chlorite schist unit is from volcanic flows flows and and tuffs. tuffs. The underlain to by rhyolite rhyolite lapillistone lapillistone and and tuff tuff which, which, near near the the underlain to the the south south by of abundant abundant pyrite pyrite and. and mutual contact, contains contains alteration consisting of chlorite schists schists are pyrrhotite blebs pyrrhotite blebs with minor minor chalcopyrite. chalcopyrite. The chlorite The stratistrati— rhyolite tuffs. The overlain by relatively unaltered quartz—eye quartz-eye rhyolite succession and locally graphic succession locally the the mineralized mineralized zones, are are dissected dissected by three laterally laterally extensive extensive mafic sills sills which are are slightly slightly discordant discordant to to the the strike of metavolcanic rocks. strike rocks. At the Port Arthur Copper Mine, the the stratigraphic stratigraphic setting setting of of the the mineralization is Here, the mineralization is virtually identical identical to to that that at at Wind Bay. Bay. Here, amygdaloidal and brecciated nature of of the the chloritic chloritic host host rock rock is is clearly clearly anygdaloidal 70 �evident. evident. Diamond Diamond drilling drilling by by Stratmat Stratmat Limited Limited revealed revealed aa zonal zonal arrangearrangement ment of of copper copper and and zinc zinc within within the the host host (Fig. (Fig. 6). 6). zinc—rich Zinc-rich zones zones are are underlain by copper—rich copper-rich mineralization. mineralization. The underlain to to the the south south by The latter latter was was mined in in 1916 1916 and and aa few few carloads carloads of of material material grading grading approximately approximately 3% 3% Cu Cu were were shipped shipped to to British British Columbia. Columbia. The by aa The mineralized mineralized horizon horizon is is succeeded succeeded abruptly abruptly to to the the north north by cherty cherty horizon horizon approximately approximately 11 mm wide wide which which in in turn turn is is overlain overlain by by felsic felsic quartz—eye quartz-eye tuffs tuffs which which forms forms aa thick thick hanging—wall hanging-wall sequence. sequence. Nine Nine occurrences occurrences of of the the Wind Wind Bay—Port Bay-Port Arthur Arthur Copper Copper type type occupy occupy aa single single stratigraphic stratigraphic horizon horizon which which is is exposed exposed over over aa strike strike length length exceeding These are are thought thought to to represent represent poorly poorly focused focused discharge discharge km. These exceeding 25 25 km. of Although these these deposits deposits collectively collectively reprerepreof metals metals over over aa large large area. area. Although sent no single single prospect prospect has has sent aa substantial substantial accumulation accumulation of of base base metals, metals, no been been shown shown to to have have sufficient sufficient metal metal content content or or tonnage tonnage to to be be economically economically viable viable at at this this time. time. Likewise, Likewise, mineralization mineralization of of Type Type IC 1C represents represents substantial substantial dispersion dispersion of of metal metal with with resulting resulting low low grade. grade. At At Pocket Pocket Pond Pond (Figure (Figure 1) 1) significant significant quantities quantities of of sphalerite sphalerite and and chalcopyrite chalcopyrite are are associated associated with with iron—formation iron-formation which which is is dominantly dominantly comcomposed The base base metals metals posed of of chert—magnetite chert-magnetite and and sulfide—bearing sulfide-bearing carbonates. carbonates. The are are hosted hosted by by aa unit unit of of pyritic, pyritic, black black shale shale and and siltstone siltstone which which is is immeimmediately single drill drill intersection intersection through through diately beneath beneath the the iron—formation. iron-formation. A single this this mineralization mineralization yielded yielded assays assays averaging averaging 1.73% 1.73% Zn Zn and and 0.09% 0.09% Cu over over aa true communication, 1980). 1980). Chip true width width of of 10 10 m (George (George Armstrong, Armstrong, personal personal communication, sampling McTavish Option, Option, sampling across across aa similar similar zone zone by by Noranda Noranda Mines Mines at at the the Mctavish Nickel Nickel Lake, Lake, yielded yielded average average assays assays of of 0.3% 0.3% Zn Zn and and 0.1% 0.1% Cu Cu (Resident (Resident Geologist's Geologist's Files, Files, Ontario Ontario Ministry Ministry of of Natural Natural Resources, Resources, Kenora). Kenora). AA second second type type of of mineralization, mineralization, more more massive massive than than this, this, occurs occurs at at the the main main showing showing at at Pocket Pocket Pond Pond where where aa small small lens lens of of massive massive pyrrhotite—sphalerite pyrrhotite-sphalerite less less than than 0.5 0.5 mm wide wide occurs occurs in in aa laterally laterally extensive extensive lenticular lenticular zone zone of of stratigraphiThe sulfides sulfides are are here here overlain overlain stratigraphi— massive massive pyrrhotite—pyrite. pyrrhotite-pyrite. The cally cally by by aa 0.3 0.3 mm layer layer of of chert—magnetite. chert-magnetite. The The host host rocks rocks for for all all of of the the type type 1C 1C mineralization mineralization are are quite quite mafic mafic and and consist consist of of basaltic basaltic flows flows and and coarse—grained coarse-grained amphibolites amphibolites which which likely likely clastic rocks rocks and and turbidite—type turbidite-type represent represent metadiabase metadiabase sills. sills. Ultramafic clastic Iron— metasedimentary metasedimentary rocks rocks occur occur at at higher higher stratigraphic stratigraphic levels. levels. Ironformation formation (Type (Type 1D) ID) is is aa common common constituent constituent of of the the predominantly predominantly mafic mafic volcanic volcanic terrane terrane in in the the western western part part of of the the study study area area at at localities localities such such as chertas Nickel Nickel Lake Lake and and Reef Reef Point. Point. There There is is aa common common association association of chert— magnetite magnetite beds beds immediately immediately adjacent adjacent to to aa massive massive pyrite—pyrrhotite pyrite-pyrrhotite zone, zone, which which at at some some localities localities contains contains minor minor chalcopyrite. chalcopyrite. Total Total thicknesses thicknesses of of aa few few metres metres are are rarely rarely exceeded exceeded and and whereas whereas the the immediate immediate host host is is comcommonly monly aa biotitic biotitic metasedimentary metasedimentary rock, rock, the the iron—formations iron-formations are are broadly broadly associated associated with with sections sections in in which which metabasalt metabasalt is is abundant. abundant. 7]. �PORT ARTHUR COPPER DEPOSIT ASSAY PLAN ;.,< quartz diorite - Shallow Drill Hole Projections > 2 % comb. Zn>Cu a >.2% comb. Zn>Cu >2% -- -" comb. Cu > Z n . 50 FT. 1 >.2% comb. Cu > Z n lithobgial contact fault Figure 6: Figure 6: 0 I Assay plan of the Port Arthur Copper deposit. DATA FROM: STRATMAT LTD Drill ~ l a n s Values shown are Assay plan of the Port Arthur the vertical projections of shallow diamond drill intersections Copper deposit. Values shown are the vertical projections approximateand nominally represent of theshallow distribution metals diamondofdrill intersections and represent the distribution of metals approximately nominally 75 feet below surface. ly 75 feet below surface. 72 I �Type Type 2: 2: Gabbro—hosted Gabbro-hosted mineralization mineralization Two Two large, large, steeply steeply dipping, dipping, layered layered gabbroic gabbroic sills, sills, the the Grassy Grassy Portage Portage and and Seine Seine Bay—Bad Bay-Bad Vermilion Vermilion intrusions, intrusions, are are exposed exposed in in the the study study area. area. Layering Layering is is expressed expressed by by modal modal variations variations in in mineralogy, mineralogy, chemical chemical variations variations across across strike, strike, and and rhythmic rhythmic mineral mineral layering, layering, which which is is well well exposed exposed in in the 1dgut Bedgut Bay Bay area. area. Rock Rock compositions compositions range range from from melagabbro melaqabbro to to anorthosite, anorthosite, and and internal internal layering layering suggests suggests that that Grassy Grassy Portage Portage intruintrusion sion faces faces southward, southward, whereas whereas the the Seine Seine Bay—Bad Bay-Bad Vermilion Vermilion intrusion intrusion faces faces northward. northward. The The basal basal part part of of the the latter latter intrusion intrusion is is truncated truncated by by the the Seine Seine River—Rainy River-Rainy Lake Lake Fault. Fault. Mineralization Mineralization occurs occurs at at three three specific specific horizons chalcopyritehorizons in in the the intrusions. intrusions. Basal Basal segregations segregations of of chalcopyrite— pyrrhotite—pentlandite pyrrhotite-pentlandite (Type (Type 2A) 2A) form form important important occurrences occurrences along along the the northern northern margin margin of of the the Grassy Grassy Portage Portage intrusion. intrusion. The The best best example example of of this this type type occurs occurs at at the the Northrock Northrock deposit, deposit, where where 300,000 300,000 tonnes tonnes of of material material The grading grading 1.89% 1.89% Cu Cu have have been been outlined. outlined. The mineralization mineralization is is hosted hosted by by gabbro, gabbro, metagabbro metagabbro and and leucogabbro leucogabbro near near the the base base of of the the Grassy Grassy Portage Portage intrusion intrusion at at the the contact contact with with pillow pillow lava lava and and pillow pillow breccia. breccia. MineralizaMineralization tion consists consists of of heavy heavy disseminations disseminations of of chalcopyrite chalcopyrite and and pyrrhotite pyrrhotite with with minor minor pentlandite pentlandite and and pyrite. pyrite. Ilmenite, Ilmenite, apatite apatite and and molybdenite molybdenite are are prespresent ent locally. locally. The The sulfide sulfide minerals minerals show show textures textures which which suggest suggest aa magmatic magmatic origin, origin, whereas whereas sulfide sulfide veins veins and and local local hydrothermal hydrothermal alteration alteration show show evievidence dence of of deuteric deuteric or or metamorphic metamorphic remobilization. remobilization. The The deposit deposit consists consists of of long and and 10 m wide. three three en en echelon echelon lenses, lenses, each each approximately approximately 50 50 in m long Several Several other other occurrences occurrences of of similar similar type type are are exposed exposed along along strike strike from from the the deposit deposit for for 88 km km to to the the northeast. northeast. Near pyrrhotiteNear the the top top of of the the Grassy Grassy Portage Portage Intrusion, Intrusion, disseminated disseminated pyrrhotite— chalcopyrite to siliceous siliceous zones zones within within the the chalcopyrite mineralization mineralization is is related related to intrusion intrusion (Type (Type 2B). 2B). Known Known as as the the Mironski MironSki showing, showing, this this occurrence occurrence was was drilled drilled by by Phelps Phelps Dodge Dodge Corporation Corporation of of Canada Canada Limited Limited in in 1966 1966 and and again again by by Belacoma Belacoma Mines Mines Limited Limited in in 1978. 1978. Approximately Approximately 300,000 300,000 tonnes tonnes of of material material Although these these zones zones grading (Harris,1974). 1974). Although Cu are are present present (Harris, grading 0.8 0.8 percent percent Cu may may represent represent granophyric granophyric differentiates, differentiates, their their sharp sharp contacts contacts and and generally generally blocky blocky nature nature suggest suggest that that they they are are assimilated assimilated blocks blocks of of country country rock rock near near the the roof roof of of the the intrusion. intrusion. In In the the central central to to upper upper levels levels of of both both intrusions, intrusions, substantial substantial accuaccumulations 2 0 occur occur as as lenticular lenticular mulations of of iron—titanium iron-titanium mineralization mineralization (Type (Type 2C) zones to massive massive magnetite magnetite ++ ilmenite ilmenite with with local local zones of of disseminated disseminated to apatite—rutile. apatite-rutile. Type 3: 3: Vein vein mineralization mineralization Type Although most most are are Quartz Quartz veins veins are are common common throughout throughout the the study study area. area. Although unmineralized, unmineralized, two two particular particular types types host host gold gold and and molybdenite molybdenite mineralizamineralization. Gold—bearing Gold-bearing veins veins (Type (Type 3A) 3A) in in the the area area have have been developed developed and tion. be the veins veins may may be exploited exploited intermittently intermittently since since the the 1890s. 1890s. In most cases, the related shear zones zones and and commonly commonly occupy occupy aa central central first—order first-order related to to discrete discrete shear 7c). Second—order Second-order veins are foliation—normal, foliation-normal, but third— thirdfissure (Figure (Figure 7c). fissure order sets sets are are foliation—parallel. foliation-parallel. order The The principal principal veins veins range range in in width width from from 10 10 cm cm to to 22 mm and and are are composed composed primarily primarily of of quartz quartz with with minor minor carbonate carbonate and and local local tourmaline. tourmaline. Visible 73 �5' C Aprox. aETI® FAULT Figure Figure7:7: Gold Golddeposits depositsofofthe theRainy BainyLake Lakearea. area. a) a)Metamorphic Metamorphiccontrols controlsonongold goldmineralization. mineralization. b) b)Rose Rosediagram diagramdepicting depictingthe theorientation orientationand anddisplacement displacement sensenses sesofofmesoscopic mesoscopicductile ductileshear shearzones. zones. c) c)Schematic Schematicdiagram diagramillustrating illustratingthe therelationship relationshipofofgold— goldbearing ductileshear shear bearingquartz quartzveins veins(principal (principalveins) veins)totoductile zones. zones. Such Suchzones zonesare arewell welldeveloped developedinincoarse—grained coarse-grainedplu— plutonic tonicrocks. rocks. I 74 a �gold and electrum were identified identified in a few few veins and sulfide sulfide minerals are Pyrite, sphalerite, present in substantial quantities. in substantial sphalerite, galena, galena, Scheelite has been chalcopyrite, arsenopyrite and argentite are common. common. Scheelite reported from gabbro—hosted gabbro-hosted quartz veins near Swell Swell Bay (Harris, (Harris, 1974). 1974). Gold content Gold content of of veins veins is is variable, variable, but but aa study study of of available available assay assay ppm Au may be realistically realistically sought data suggest that grade as high as 15 15 ppm m. over widths of approximately approximately 11 m . This represents represents the the approximate approximate average average grade of the two most successful successful past producers, the Olive and Golden Star Mines (Beard (Beard and and Garratt, Garratt, 1976). 1976). The shear zones The zones are systematically systematically oriented and show show senses senses of 7a,b). The displacement consistent with a right—hand right-hand wrench zone zone (Figures (Figures 7a,b). shear zones and their gold—bearing veins are found in most lithologies zones their gold-bearing in lithologies in the area (Table (Table 3), but there is a clear clear affinity affinity for for a coarse—grained coarse-grained trondhjemite suite. felsic plutonic host of the suite. felsic the earlier earlier tonalite tonalite — trondhjemite Although shear zones are present throughout the study area, only those ~lthough zones throughout the those which occur in rocks metamorphosed to to the the greenschist greenschist facies facies contain contain gold— gold, suggest late— bearing vein systems (Figure 7a). The above relationships a late systems (Figure 7a). tectonic emplacement of the veins in rocks which readily formed dilatant tectonic emplacement the in rocks readily formed zones zones at metamorphic grades grades suitable suitable for for precipitation precipitation of gold. gold. - TABLE 3. TABLE 3. LITHOLOGIC CONTROLS ON GOLD-BEARING GOLD-BEARING QUARTZ VEINS, MINE CENTRE-FORT FRANCES FRANCES AREA AREA Numberof of Veins Veins Number Host Rock Rock Type Host Type trondhjemite Tonalite, Tonalite, trondhjemite intermediate metavolcanic rocks Felsic, rocks Felsic, Metadiabase, amphibolite amphibolite Metabasalt, chlorite chlorite schist schist Gabbro, anorthosite anorthosite Conglomerate Conglomerate Quartz monzonite—granodiorite Quartz monzonite-granodiorite 46 16 9 5 4 1 0 TOTAL NUMBER TOTAL SOMBER OF VEINS 81 TOTAL NUMBER OF PROPERTIES TOTAL PROPERTIES 26 26 The molybdenite-bearing molybdenite—bearing veins (Type The (Type 3B) in the the Bear Pass—Rice Pass-Rice Bay These generally show area show no evidence of shear zone development. area show no evidence of shear zone development. These generally show sharp contacts with undeformed granodiorite or quartz monzonite and granodiorite quartz and are are The best with contacts with biotite schist. spatially associated associated . spatially contacts biotite schist. The is located at Bear locatedon onHighway Highway 11 1 1 at Bear Pass, Pass,where where molybdenite molybdenite and and occurrence is occurrence are abundant in tensional tensional quartz veins in the Bear Pass pluton pyrite are pyrite strike northerly and and westerly westerly and and the the best mineral(Figure 4). (Figure 4). The veins strike A number ization is is located located in in veins near near the the pluton margins. margins. A number of other quartz—pyrite—molybdenite occurrences to dikes dikes and and sills sills of of quartz-pyrite-molybdenite occurrences are are related related to The majority majority of molybmolyb— plutons. The granodiorite well removed from the main plutons. denite occurrences occurrences are are restricted restricted to to areas areas of of amphibolite amphibolite facies facies metamorphism. 75 �4I Type 4: mineralization Type 4: Ultramafic—hosted Ultramafic-hosted mineralization The magnetic, clastic unit in the RiceRice Bay—Redgut The magnetic, elasticultramafic ultramafic unit in the Bay-RedgutBay Bay area area hosts low—grade hostsa anumber numberofofshowings showingsofof low-gradecopper—nickel copper-nickel mineralization, mineralization, referred referred to to as as the the Belacoma Belacoma property. property. Disseminated Disseminated pyrrhotite pyrrhotite with some some chalcopyrite chalcopyrite occurs occurs as as blebs blebs and and stringers stringers in in narrow narrow zones zones of foliated foliated ultramafic ultramafic metavolcanic metavolcanic rocks. rocks. Reported grades are variable with best grab grab samples samples assaying assaying as as much much as as 0.29 0.29 percent percent Cu, Cu, 1.23 1.23 percent percent Ni, 0.17 0.17 percent Cu and and percent Co, Co, and and best best diamond—drill diamond-drill intersections intersections of of 0.45 0.45 percent percent Cu 0.12 0.12 percent Ni Ni over over 0.55 0.55 mm (Resident (Resident Geologist's Geologist's Files, Files, Ontario Ontario Ministry Ministry of of Natural Natural Resources, Resources, Kenora). Kenora). Away from from the the mineralized areas, the the ultramafic ultramafic metavolcanic metavolcanic rocks rocks contain contain approximately approximately 1150 1150 ppm ppm Ni Ni (average (average of 44 samples) samples) indicating indicating that that metamorphic metamorphic remobilization remobilization may have produced the the low—grade low-grade sulfide sulfide zones. zones. 4 REFERENCES REFERENCES CITED CITED Ayres, 1978, L.D., 1978, Metamorphism in in the the Superior Superior province province of of Northwestern Northwestern Ayres, L.D., Ontario to crustal crustal development, in Metamorphism Ontario and and its its relationship relationship to in in the the Canadian Canadian Shield, Shield, eds. eds. J.A. J.A. Fraser FraSer and and W.W. W.W. Heywood; ~eywood;Geol. Geol. Surv. Surv. Can., Can., Paper Paper 78—10, 78-10, p. p. 25—36. 25-36. Beard, R.C., and and Garratt, Garratt, G.L., G.L., 1976, 1976, Gold Gold deposits deposits of of the the Kenora—Fort Kenora-Fort Beard, R.C., I Frances Frances area, area, Districts Districts of of Kenora Kenora and and Rainy Rainy River; River; Ontario Ontario Div. Div. Mines, Mineral Mineral Deposits Deposits Circ. Circ. 16, 16, 46 46 p. p. Grout, F.F., F.F., Gruner, Gruner, LW., J.W., Schwartz, Schwartz, G.M., G.M., and and Thiel, Thiel, G.A., G.A., 1951, 1951. Grout, Precambrian Precambrian stratigraphy stratigraphy of of Minnesota; Minnesota; Geol. Geol. Soc. Soc. Am. Am. Bull., Bull., v. v. 62, 62, p. p. 1017—1078. 1017-1078. 4 Harris, Harris, F.R., F.R., 1974, 1974, Geology Geology of of the the Rainy Rainy Lake Lake area, area, District District of of Rainy Rainy River; Ontario Div. Mines, GR 115, 94 p. Accompanied by maps 2278 and and River; Ontario Div. Mines, GR 115, 94 p. Accompanied by maps 2278 1 inch to 1,' mile. 2279, scale 2279, scale 1 inch to 1h mile. Hawley, Hawley, J.E., J . E . , 1930, 1930, "Seine" "Seine" or or "Coutchiching"; "Coutchiching"; J. J. Geol., Geol., v. v. 38, 38, p. p. 52 1—547. 521-547. I Lawson, A.C., A.C., 1913, 1913, The The Archean Archean geology geology of of Rainy Rainy Lake Lake re—studied; re-studied; Can., Can., Lawson, Geol. 1 1 1 p. Geol. Sun., Sum., Mem. Mem. 40, 40, 111 I Merritt, Merritt, Am. Bull., ~ull., v. v. P.L., 1934, 1934, Seine—Coutchiching Seine-Coutchiching problem; problem; Geol. Geol. Soc. Soc. Am. P.L., 45, 45, p. p. 333—374. 333-374. Ojakangas, R.W., 1972, ojakangas, R.W., 1972, Rainy Rainy Lake Lake area, area, in & I Geology Geology of of Minnesota: Minnesota: aa centencentennial Sims and and G.B. G.B. Morey; Morey; Minn. Minn. Geol. Surv., nial volume, volume, eds. eds. P.IC. P.K. Sims Sum., p. p. 163—171. 163-171. Pirie,J., J., and andMackasey, Mackasey, W.O., W.O., 1978, 1978, Preliminary Preliminary examination examination of of regional regional Pine, metamorphism metamorphism in in parts parts of of Quetico Quetico metasedimentary belt, Superior province, &I Metamorphism Metamorphism in in the the Canadian Canadian Shield, Shield, eds. eds. J.A. J.A. province, Ontario; Ontario; in Fraser Fraser and and W.W. W.W. Heywood; Heywood; Geol. Geol. Surv., Surv., Can., Can., Paper Paper 78—10, 78-10, p. p. 37—48. 37-48. Poulsen, Poulsen, K.H. K.H. 1980a, 1980a, The The stratigraphy, stratigraphy, structure structure and and metamorphism metamorphism of of Archean unpubl. M.S. Archean rocks rocks at at Rainy Rainy Lake, Lake, Ontario; Ontario; unpubl. M.S. thesis, Lakehead University, University, 99 99 p. p. 76 76 I �Poulsen, K.H., K.H., 198Db, of mineralization in Poulsen, 1980b, The geological setting s e t t i n g of i n tthe h e Mine Centre—Fort Frances area, District of Rainy River; p. 162—168, District Rainy River; p. 162-168, in Centre-Fort Summary of Field Work, 1990, by the Ont. Geol. Sum., Surv., G. ed. V.G. V.G. Milne, Mime, Summary of F i e l d Work, 1980, by t h e Ont. Geol. O.L. White, R.B. Barlow, J.A. Robertston and A.C. A.C. Colvine; Ont. 0.L. R.B. Barlow, J.A. and Geol. Surv., p. Geol. Surv., Misc. Misc. Paper 96, 96, 201 201 p. Poulsen, K.H., 1981, K.H., 1981, The The geological geological setting s e t t i n g of mineralization in i n the Mine Mine Poulsen, Centre—Fort Frances area, p. 190—195 River; p. 190-195 in in Centre-Fort area, District of Rainy River; Summary of of F Field Work, 1981 1981 by by tthe Ont. Geol. Geol. Surv., Sun., ed. .7..wood, Wood, ed. J. Summary i e l d Work, h e Ont. O.L. White, R.B. O.L. R.B. Barlow and A.C. A.C. Colvine; Ont. O n t . Geol. Geol. Surv., Surv., Misc. Misc. Paper 100, 100, 255 255 p. p. Poulsen, K.H., Borradaile, and Kehlenbeck, Kehlenbeck, M.M., M.M., 1980, 1980, An An inverted K.H., Borradaile, G.J.. G.J. and Poulsen, .7. Earth Sci., Sci., v. . Earth v. 17, Archean succession succession at a t Rainy Rainy Lake, Lake, Ontario; Ontario; Can. Can. J 17, p. 1358—1369. p. 1358-1369. Rose, E.R., 1969, E.R., 1969, Geology Geology of titanium titanium and and titaniferous t i t a n i f e r o u s deposits deposits of of Canada; Rose, Geol. Surv. Geol. Surv. Can., Can., Econ. Econ. Geol. Geol. No. No. 25, 25, 171 171 p. p. Sangster, I).?., 1972, Precambrian Precambrian volcanogenic volcanogenic massive massive sulphide suiphide deposits deposits Sangster, D.F., 1972, Canada: a review; Geol. Sum. Surv. Can. Can. Paper 72-22, 72—22, 44 p. p. iin n Canada: review; Geol. Schwerdtner, Stone, D., Osadetz, K., K., Morgan, J., and Stott, S t o t t , G.M., G.M., Schwerdtner, W.M., W.M., Stone, D., Osadetz, Morgan, 3., 1979, Granitoid Granitoid complexes complexes and tthe Archean ttectonic 1979, h e Archean e c t o n i c record iin n the part Ontario; Can. Can. 3. v. 16, 16, p. p. southern p a r t of of northwestern Ontario; J. Earth Sci., Sci., v. 1965—197 7. 1965-1977. Southwick, D.L., D.L., 1972, p. 108—119 in 1972, Vermilion granite—migmatite granite-migmatite massif; massif; p. 108-119 & I Southwick, Geology of Minnesota: Minnesota: aa centennial centennial volume, volume, eds. eds. P.K. P.K. Sims Sins and and G.B. G.B. Morey; Minn. Morey; Minn. Geol. Geol. Surv., Surv., 623 623 p. p. Southwick, D.L., D.L., 1976, High—grade metamorphism metamorphism associated with the Southwick, 1976, High-grade Ontario; aabstracts Vermilion batholith, b a t h o l i t h , Minnesota — Ontario; b s t r a c t s Institute I n s t i t u t e on Lake Geology, 22nd Annual Meeting, Meeting, St. p. 61. St. Paul, Paul, Minn., Minn., p. 61. Superior Geology, - Southwick, D.L., D.L., and Sims, Granitic Southwick, Sins, P.K., P.K., 1980, 1980, The Vermilion G r a n i t i c Complex——a Complex--a new new name name for f o r old o l d rocks rocks in i n northern northern Minnesota: Minnesota: U.S. U.S. Geological Geological Survey Survey Professional Professional Paper Paper 1124, 1124, p. p. Al—All. At-All. Wood, J., Dekker, Dekker, J., J., Jensen, Jensen, J.G., J.G., Keay, J.P., J.P., and and Panagapko, Panagapko, D., D., 1980, 1980, Wood, 3., Keay, Geol. Surv. Surv. Prelim. Prelim. Ont. Geol. Mine Centre Centre area, area, District D i s t r i c t of of Rainy Rainy River; River; Grit. inch to maps P2201 P2201 and and P2202; Geological Geological Series, S e r i e s , scale s c a l e 1:15,840 1:15,840 or o r 11 inch 1/4 mile. Geology Geology 1976, 1976, 1977. 1 /4 mile. 1977. I: DESCRIPTIONS DESCRIPTIONS OF OF FIELD STOPS, K.H. K.H. Poulsen, Poulsen, leader leader FIELD TRIP I: The The field f i e l d trip t r i p is i s designed designed as a s aa one one day day excursion excursion illustrating i l l u s t r a t i n g the the It begins from Fort types and setting s e t t i n g of mineralization at a t Rainy Lake. Lake. It the size s i z e of of the the Frances and involves as a s many as a s 10 10 stops, s t o p s , depending depending upon upon the Many of of lookout at a t Bear Pass is is a suitable s u i t a b l e lunch lunch stop. stop. Many group. The scenic lookout properties and aare intermittthe he p r o p e r t i e s visited v i s i t e are d a rPRIVATE e PRIVATE and r e under under development development intermitProceed USE DISCRETION in gaining accessand andi nin sampling. sampling. Proceed PLEASE US E DISCRETION i n gaining access ttently. e n t l y . PLEASE o tthe h e Windy Point Bridge eastward 11 tto eastward from Fort Frances on Highway 11 77 �Lake NICKEL LAKE IRON IRON FORMATIONS FORMATIONS NICKEL iron formation, ironstone e iron formation, ironstone 30 minor folds with Su Su Ox Ox CB CB Figure Figure 8: 8: sulfide rich rich chert— chert- magnetite magnetite carbonates carbonates 30 d Field F i e l d trip t r i p stop stop no. no. 1. 1. 78 minor folds with plunge plunge 1/4 mi. 1/4 mi. �approximately approximately1313miles miles(21 (21kin) km) from from downtown downtown Fort Fort Frances. Frances. SET SETMILEAGE. MILEAGE. Proceed Proceed eastward eastward for for 4.4 4.4 miles miles (7 (7km) km) to to aa side side road road to to the the right right immeimmediately diately opposite opposite the the Ministry Ministry of of Transportation Transportation garage garage and and sand sand dome. dome. Park Park and and walk walk southward southward for for approximately approximately 1000 1000 feet feet (300 (300 m) m) along along the the priprivate 8 )to to an an outcrop outcrop 50 50 feet feet (1.5 (1.5 m) m) south south of of the the main main gate. gate. vate road road (Fig. (Fig. 8) - STOP STOP 11 — Nickel Nickel Lake Lake Iron Iron Formation Formation The The chert—magnetite chert-magnetite iron—formation iron-formation exposed exposed here here is is typical typicalof of many many At Nickel Lake, the iron—formation is hosted occurrences in the area. occurrences in the area. At Nickel Lake, the iron-formation is hosted by by amphibolites amphibolites and and defines defines aa major major synformal synformalfold fold which which mimics mimics the the shape shape of of the the lake lake (Fig. (Fig. 8). 8). The The minor minor folds folds which which are are prominent prominent in in this this outcrop outcrop are are coaxial coaxial with with the the major major structure structure and and are are of of tectonic tectonic origin origin as as evievidenced by axial planar cleavage exposed in a small glaciated outcrop denced by axial planar cleavage exposed in a small glaciated outcrop approximately approximately 100 100 feet feet (30 (30m) m) further further south. south. The The iron—formation iron-formation is is too too lean to be of economic significance but a shaft on the south side lean to be of economic significance but a shaft on the south side of of the the lake lake investigated investigated the the possibility possibility of of base base metals metals associated associated with with aa massive massive pyritic chert-magnetite-grunerite pyritic horizon horizon immediately immediately adjacent adjacent to to the the chert—magnetite—grunerite iron—formation. iron-formation. At At Reef Beef Point, Point, 6.2 6.2 miles miles (10 (10 km) km) west west of of here, here, metametamorphic morphic segregation segregation of of magnetite magnetite produced produced aa somewhat somewhat enriched enriched material material which which was was mined mined in in from from aa small smallopen open pit pit in in the the mid—1950's. mid-1950's. Return 11, proceed proceed approximately approximately 2.5 2.5 mi. mi. (4 ( 4km) km) eastward eastward Return to to Highway Highway 11, Turn left and proceed 1.6 miles (2.6 3cm) northward to to Highway Highway 502. 502. Turn left and proceed 1.6 miles (2.6 km) northward to to aa Turn right and drive approximately 400 dirt feet dirt road road just just past past aa creek. creek. Turn right and drive approximately 400 feet Walk to each each of of the the localities localitiesshown shownin inFigure Figure9. 9. m) and and park. park. Walk to (120 m) (120 - STOP STOP 22 — Pocket Pocket Pond Pond Zn—Cu—Fe Zn-Cu-Fe occurrences occurrences At At this this prospect, prospect, zinc zinc and and copper copper have have been been located located at at two two horizons horizons The selected localities shown on within within aa mafic mafic succession. succession. The selected localities shown on Figure Figure 99 illustrate illustrate the the nature nature of of the the mineralization mineralization as as well well as as the the host host rocks. rocks. Locality Locality 2a: 2a: metasedimentary metasedimentary rocks rocks Structurally, Structurally, these these outcrops outcrops of of biotite biotite schist schist are are located located on on the the northeast northeast margin margin of of the the Rice Rice Bay Bay Dome Dome as as confirmed confirmed by by the the bedding bedding orienorientation The rocks rocks are are part part of of the the historic historic tation observed observed at at this this locality. locality. The Coutchiching to Coutchiching Group Group of of Lawson Lawson (1913) (1913)and and were were once once thought thought to to be be basal basal to The "knotty" "knotty" beds beds here here the the volcanic volcanic sequence sequence exposed exposed to to the the northeast. northeast. The consist consist of of the the mineral mineral assemblage assemblage garnet—biotite—muscovite garnet-biotite-muscovite and and sillimanite. sillimanite. Locality Locality 2b: 2b: magnetic magnetic ultramafic ultramafic rock rock This This small small outcrop outcrop is is composed composed of of the the magnetic ultrabasic unit which It is is cut cut here here by by an an amphibolitic amphibolitic dike. dike. is is better better exposed exposed at at Stop Stop 3. 3. It Locality 2c: metabasalt metabasalt Locality 2c: This facing pillowed Pillowed metabasalts metabasalts here here face face southwestward. southwestward. This facing direction direction can can be be confirmed confirmed at at three three other other localities localities on on this this prospect prospect and and coupled coupled with with the the northeasterly northeasterly dip, dip, indicates indicates that that the the succession succession here here is is strucstrucThe amphibolite amphibolite facies facies metamorphic metamorphic assemblage assemblage in in these these turally turally inverted. inverted. The 79 �a a I a 4 wz 008 a I a a 2. a 0 Ñ- a -Z no. stop trip Field U3UaJ1 l ~ 'SI!DJ+ p dip PUD w k c f ' ONOd 13YOOd S ~ D O Jl Buippaq P S3ON3WnOOO ad - W - u Z 9: a M'JIlld Figure SMDI a (Sa x ^JiaaSt- d w piau SUOZ!JO~ e u o ~ s u o ~ ~ dOlS a 0 �rocks contains diopside; this is is consistent consistent with the the appearance appearance of silli— sillimanite at Locality 2a. at Locality 2a. Locality 2d: ides Locality 2d: lean lean massive massivesuif sulfides This This pit exposes exposes aa lens lens of of massive massive pyrite—pyrrhotite pyrite-pyrrhotite with with minor minor chalcopyrite. A narrow chert—magnetite unit stratigraphically chalcopyrite. chert-magnetite stratigraphically overlies overlies the the massive sulfides. The generally mafic nature of the host rocks massive sulfides. the rocks adjacent adjacent to to the the pit pit can can be be noted. noted. Locality 2e: 2e: main pit CAUTION: DEEP HOLE MOLE CAUTION: In this pit, the extension extension of the the zone zone exposed exposed at the the previous locallocality has been excavated. A A narrow zone of massive pyrrhotite-sphalerite pyrrhotite—sphalerite grading to as much as 14% 14% Zn was discovered discovered here and a few few loose loose pieces of similar material may be found on the dump. Diamond drilling showed that found the this zone had limited depth extent and that grades, averaged over zone that averaged over 10—foot 10-foot widths, were only of the order of 1 to 2% Zn. only of the order of 1 to 2% Locality 2f: Oxide Oxide facies facies iron—formation iron-formation This small outcrop thinly bedded This unit unit This small outcrop exposes exposes thinly bedded chert—magnetite. chert-magnetite. This immediatelyoverlain overlain to to has been traced across across the is immediately has been traced the entire entireproperty property and and is the skarn. the southwest southwestby bya anarrow narrowgarnet—pyroxene—epidote garnet-pyroxene-epidote skarn. Locality 2g: 2g: pyritic pyritic black Locality black shale shale stratigraphically underlies underlies the In addistratigraphically theiron—formation. iron-formation. In addito pyrite, the shale shale contains contains finely finely disseminated disseminated sphalerite: sphalerite: aa diamond drill intersection intersection yielded 1.73% 1.73% Zn over over 32.5 32.5 feet. feet. AA similar unit in in the the Nickel Nickel Lake Lake area area also also contains contains low low copper copper and and zinc zinc values. values. tion tion This This unit unit Return 1 1 and and turn turn left, left, Return to to Highway Highway 502, 502, return return southward southward to to Highway Highway 11 Walk eastward. Proceed east for and stop stop at right. Walk eastward. Proceed for 1.1 1.1 miles miles (1.8 (1.8 kin) km) and through the bush 600 feet feet (180 through (180 m) northward northward to to outcrops outcrops at south south side side of aa pond (Fig. (Fig. 10). 10). ic—hosted Cu-Ni Cu—Ni STOP 3: Ultramaf Ultramafic-hosted Locality 3a: These Locality These small small outcrops outcrops expose expose aa clastic clastic rock rock composed composed domidominantly of of fine—grained fine-grained ultramafic ultramafic material. material. The rock is magnesian rich (21% MgO) MgO) and both both clasts and matrix contain finely disseminated disseminated (21% small percentage of amphibolitic amphibolitic clasts clasts also also are are present. magnetite. A small The origin origin of of this this unit unit is is unknown unknown but but possibilities possibilities include include an an ultramafic ultramafic pyroclastic, an an epiclastic epiclastic rock rock derived derived from from ultramafic ultramafic flows, flows, or or aa prodprodIt is of of interest that that this unit is is idenidenuct of of magnesian magnesian metasomatism. metasomatism. It and texturally texturally totothe Steeprock is tical tical chemically and the Steeprock"ash—rock" "ash-rock" which which is conformable with the km) to to conformable the hematitic hematitic iron iron ore ore at Atikokan, 62 62 miles miles (100 (100 km) the the east. east. the south south side Proceed approximately 700 feet (210 (210 m) eastward around the the pond to small pits beside of the pond to small pits beside the thebush bush road. road. 81 �I v b Field Trip Stop gabbro; leucogabbro; garnetiferous N i c u } mineral occurrences quartz gabbro @ mt metosedimentary biotite schist facing of units ; pi1low lavas ; magnetic graded beds (overturned 1 I km ultromafic schist metobasalt ; pillowed I 1/2 mi. >^, ^S I I 6.. Figure 10: 10: Field F i e l d trip trip stops stops no. no. 3, 3, 4, 5, 5, and and 6 Figure 82 I �I Locality Locality 3b: 3b: These Thesepits pits have have been been developed developedon onfoliated foliatedmineralized mineralizedequivalents equivalentsof of the the ultramafic ultramaficunit. unit. Finely Finely disseminated disseminated chalcopyrite chalcopyriteand and pyrrhotite pyrrhotite are are present present and and assays assaysof of grab grabsamples samplesaverage averageapproximately approximately0.3% 0.3% Cu, Cu, 0.1% 0.1% Ni, Ni, 0.03% 0.03% Co. Co. Return 1 1 and and proceed proceed 1.6 1.6 miles miles (2.6 (2.6 km) km) southward; southward; turn turn Return to to Highway Highway 11 right THIS ROAD ROAD IS IS VERY VERY ROUGH ROUGH M4D AND NOT NOT SUITABLE SUITABLE right on on aa dirt dirt road. road. CAUTION CAUTION - THIS FOR FOR LOW—RIDING LOW-RIDING VEHICLES. VEHICLES. Proceed Proceedto tothe theend endof ofthe theroad road(it (itmay may be be necessary necessaryto towalk walk part part way). way). Note Note that that alternate alternate Stop Stop4A, 4A, north north of of the the railway 11, serves serves to to illustrate illustratesome someof of the thefeatures features railway overpass overpass on on Highway Highway 11, - mineralizationinin aa trench trench aa few feet from of Northrock—type Northrock-type mineralization few hundred hundred feet from the the of highway 10). highway (Fig. (Fig.10). STOP 4: The STOP 4: The Northrock Northrock Deposit Deposit This This deposit deposit was was discovered discovered in in 1959 1959 by by Noranda Noranda propsectors. propsectors. Subsequent Seemarand andNorthrock Northrock Mines, Mines, Subsequent development, development, followed followedby by options optionsto toSeemar led led to to the the sinking sinking of of aa 200-foot-deep 200-foot-deep two—compartment two-compartment shaft shaft in in 1973; 1973; aa 600—foot 600-foot drift drift was was driven driven eastward eastwardon on the the125—foot 125-foot level. level. The The drift drift cut cut through throughthe the three three lenticular lenticularore ore zones zonesand and sulfide—rich sulfide-rich material material was was stockpiled. Walk to to outcrops outcrops at at the the northwest northwest corner corner of of the the hoist hoist stockpiled. Walk building. building. Locality The footwallrocks rocks to to the the Grassy Grassy Portage PortageSill. Sill. The Locality 4a: 4a: These These are are the the footwall pillowed pillowed metabasalts metabasalts here here extend extend southwestward southwestwardfrom fromthe thevicinity vicinityof ofthe the previous previous stop stopand and throughout throughoutthis thisdistance distanceindicate indicatesouthward southwardyounging. younging. Walk Walk directly directly south south past past the the west west side side of of the the building building across acrossthe the Walk towards towards the the dump dump and and stop stop at at an an outcrop outcrop contact contact with with the the metagabbro. metagabbro. Walk to to the the right right of of the thecleared clearedarea. area. • Locality Locality4b: 4b: This This is is aa typical typical exposure exposure of of metagabbro metagabbro in in the the Grassy Grassy Portage The plagioclase: plagioclase: mafic mafic mineral mineral ratio ratio is is variable variable locally locally Portage Sill. Sill. The The and to leucogabbro. leucogabbro. The roelagabbroto and in in the the area area of of the the deposit deposit ranges ranges from from melagabbro sill sill consists consists of of uralitized uralitized pyroxene pyroxene and and altered altered plagioclase plagioclase (AnSO). (An50). Locality Locality 4c: 4c: • The The dump dump material material is is divided divided into into waste waste (east (eastside) side) and and ore ore (west (west In the dump, representative specimens of mineralized material can side). In the dump, representative specimens of mineralized material can side). Particular types types include: include: bleached bleached chalcopyrite—rich chalcopyrite-rich ore; ore; be be obtained. obtained. Particular net ides in dark gabbro; "spotted" net and and droplet—textured droplet-textured sulf sulfides "spotted" ilmenite—rich ilmenite-rich material with with biotite biotiterims rimson onilmenite ilmenitecores; cores;apatite—bearing apatite-bearing ores; ores;and and material molybdenite—bearing ore (rare). (rare). molybdenite-bearing ore Return 11; Stop Stop 0.9 0.9 mile mile (1.5 Return towards towards Highway Highway 11; (1.5 km) km) from from the the highway highway at to the at aa small small clearing clearing to the left left (Fig. (Fig.10). 10). STOP 5: ~Fe—Ti oxide mineralization STOP 5: e - ~oxide i mineralization in aa A A small small outcrop outcrop in in the theclearing clearingexposes exposesdisseminated disseminated magnetite magnetite in fine—grained fine-grained matrix matrix composed composed of of chlorite chlorite and and actinolite. actinolite. apatite apatite can can be be observed observed in in thin thin section. section. 83 Fine—grained Fine-grained �walk Walk northward northward along along an an abandoned abandoned drill drill road road for for approximately approximately 300 300 feet (100 (100 m) to to an an outcrop outcrop at at trail trail side. side. Here green apatite and reddish reddish brown rutile rutile crystals crystals comprise comprise an an irregular irregular mass of of "nelsonite". "nelsoniten. Such Such rocks are well known associates associates of anorthosites anorthosites and are are thought thought to to result result from Fe-Ti-P enriched enriched melt. melt. At this from liquid liquid immiscibility immiscibility in in an an Fe—Ti—p this locality locality quartz so so that that Ti02 nO2 grades the rutile poikilitically encloses abundant quartz grades do do not exceed exceed aa few few percent. percent. Return 11, turn turn left left and and proceed proceed back back northward northward approxiapproxiReturn to to Highway Highway 11, mately 0.3 0.3 mile (0.5 (0.5 km) km) to to aa road road leading leading to to the the right. right. Stop here and 1 1 to to the the north north side side of of the the walk northward northward along along the the east east side side of of Highway Highway 11 outcrop (Fig. outcrop (Fig. 10). 10). STOP occurrence STOP 6: 6: Disseminated Disseminated Cu, Cu, Mironsici Mironski occurrence The The light-coloured light-coloured siliceous siliceous rock rock exposed exposed here here contains contains fine fine dissemidissemimineralization was discovered discovered in in nated chalcopyrite chalcopyrite and and pyrrhotite. pyrrhotite. The mineralization 1966 as a result of highway construction, construction, and subsequent subsequent drilling drilling by Phelps—Dodge Ltd., Belacoma Mines, Mines, has has outlined outlined approximately approximately Phelps-Dodge Ltd., and and later later by by Belacoma 300,000 tonnes tonnes grading grading 0.8% 0.8% Cu. Cu. The siliceous siliceous host rock rock consists consists of of quartz—plagioclase—biotite and quartz-plagioclase-biotite and may may represent represent either either aa siliceous siliceous differendifferentiate of the tiate the gabbroic gabbroic intrusion intrusion or or an an assimilated assimilated country country rock. rock. The this outcrop outcrop is is near the the top top of the the latter appears to to be more likely as this intrusion where blocks of metavolcanic metavolcanic rock rock also also are are present. A trail, beginning on on the the opposite opposite side side of of the the highway, highway, leads leads westwesttrail, beginning ward to to aa number number of of small small exposures exposures and and pits pits which which illustrate illustrate the the nature nature Magnetite—ilmenite mineralization, which of the the mineralization. Magnetite-ilmenite which is is likely likely continuous with that exposed at Stop continuous Stop 5, was intersected intersected in in drill drill holes just to the north of these these exposures. exposures. 7: Mo Mineralization, Bear Pass STOP 7: Pass These These outcrops outcrops of of granodiorite granodiorite of of the the Bear Bear Pass Pass pluton pluton contain contain aa set set of northwesterly northwesterly striking striking quartz quartz veins veins which which contain contain pyrite pyrite or or pyrite pyrite ++ molybdenite. molybdenite. Veins range range in in width from from 0.5 0.5 cm cm to to 30 30 cm cm and and are are spaced spaced approximately Quartz-pyrite-molybdenite occur occur nearest nearest to to the the approximately 0.5 0.5 mm apart. apart. Quartz—pyrite—molybdenite bridge, whereas whereas to to the the west, quartz—pyrite quartz-pyrite veins veins give give way way to to sulfide—free sulfide-free veins. To To the the northeast, northeast, across across Bear Bear Pass, Pass, the the International International Nickel Nickel Company drilled Company drilled 55 holes holes in in 1966 1966 to to evaluate evaluate aa similar similar vein vein set. set. Assays up to to 0.65% 0.65% MoS2 MoS2 0ver Over 1.5 1.5 mm were were reported reported but but values values are are erratically erratically distributed. distributed. Traces molybdenite mineralimineraliTraces of of copper copper were were also also reported. reported. In total, molybdenite The zation is distributed over an area approximately 700 x 150 m. quartz distributed area approximately 700 x 150 m. The quartz veins in to be be extensional extensional in in nature, nature, have have in the the Bear Bear Pass Pass pluton pluton appear appear to sharp contacts with the the granodiorite, granodiorite, and and locally locally possess possess bleached bleached alteraalteraSome molybdenite occurs as dissem— tion selvages at the wallrock contact. selvages the contact. molybdenite occurs as disseniinations in inations in the the wallrock. wallrock. Reset Reset mileage mileage and and continue continue eastward eastward along along Highway Highway 11; 11; mileage mileage 12.2 12.2 (19.5 1cm) Turtle River Road; mileage 13.8 (22.2 km) turn right (19.5 km) Turtle River Road; mileage 13.8 (22.2 km) turn right on on aa priprivate dirt the road, road, turn turn around around and return back in'the dirt road, road, continue continue to to fork fork in' 84 �BAD VERMILION LAKE AREA xznscu OSSff Trondhjemite leucogabbro ;metadiabase felsic t u f f , lapilli tuff intermediate metavolcanic flows ;tuff mofic metavolcanics 0 0 Figure 11: 11: Field Field trip trip stops stops no. no. 88 and and 9. 9. 85 } mineral occurrence shaft I krn 1/2 mi. �I along along the the road road for for approximately approximately 1/8 1/8 mile mile (0.2 (0.2 km). km). AA trail trail leads leads westwestward ward through through the the bush, bush, across across aa marsh marsh to to aa series series of of outcrops. outcrops. AA shaft shaft and and dump dump may may be be found found approximately approximately 200 200 feet feet (60 (60 m) m) due due west west of of the the marsh marsh (Fig. (Fig. 11). 11). STOP STOP 8: 8: Au Au mineralization, mineralization, Stellar Stellar Mine Mine This This three—compartment three-compartment shaft, shaft, approximately approximately 50 50 feet feet deep, deep, was was sunk sunk in in 1934 1934 on on the the Rainbow Rainbow vein vein of of the the Stellar Stellar Mining Mining Property. Property. The The vein vein is is len— lenticular m) halfway halfway down down to as as much much as as 3.8 3.8 feet feet (1.2 (1.2 m) in shape shape and and widens widens to ticular in the the shaft. shaft. The The host host rock rock is is aa carbonate—rich carbonate-rich chlorite—sericite chlorite-sericite schist schist which which forms forms aa dextral dextral shear shear zone zone cutting cuttingequigranular equigranular trondhjemite. trondhjemite. Note Note the shear zone development the oblique oblique foliation foliationininthe the shear zoneand andthe thelocal local development of of third-order veins 7c). The The vein vein material material consists consists of of laminated laminated third—order veins (see (see Fig. Fig. 7c). quartz quartz and and ankerite ankerite with with local local siderite, siderite, pyrite, pyrite, pyrrhotite, pyrrhotite, chalcopyrite, chalcopyrite, sphalerite, Gold values values reported reported during during the the sphalerite, galena galena and and rare rare visible visible gold. gold. Gold shaft oz. per per tonne tonne shaft sinking sinking were were erratic erraticbut butaveraged averagedapproximately approximately 11 oz. along strike strike from across Surface sampling sampling along from across the the vein vein to to aa depth depth of of 24 24 feet. feet. Surface the the shaft shaft yielded yielded much much lower oz. per per tonne tonne approximately 0.2 0.2 oz. lower values, values, approximately across across 3—foot 3-foot widths. widths. At At the the time time of of development, development, the the vein vein was was traced traced on on surface surface for for 150 150 feet feet (45 (45 m) m) to to the the northeast northeast and and 60 60 feet feet (18 (18 m) m) to to the the southwest. southwest. In In addition addition to to the the shear shear zone—hosted zone-hosted quartz quartz veins, veins, the the outcrops outcrops near near the the shaft shaft provide provide aa good good opportunity opportunity to to examine examine the the equigranular equigranular trond— trondhjemite The trondhjemite, trondhjemite, along along with the the hjemite of of the the Mud Mud Lake Lake intrusion. intrusion. The gabbro—anorthosite gabbro-anorthosite to to the the south, south, forms forms aa concordant, concordant, possibly possibly subvolcanic, subvolcanic, intrusive intrusive complex complex which which has has been been mapped mapped for for aa length length of of 19 19 miles miles (30 (30 km). km). This This intrusive intrusive complex complex resembles resembles the the Bell Bell River River Complex Complex at at Mattagami, Mattagami, LakeComplex ComplexatatSturgeon Sturgeon Lake, Lake, Ontario Ontario Quebec and and the theBeidelman Beidelman Bay—Pike Bay-Pike Lake Quebec where the intrusions intrusions are where the are thought thought to to relate relatetotomassive massive sulfide sulfidemineralizamineralization in in tion overlying overlying volcanic volcanic strata. strata. A similar similar relationship relationship may exist exist bebestop. tween tween this this intrusion intrusion and and the the base base metal metal mineralization mineralization at at the the next next stop. Return Return to to Highway Highway 11; 11; turn turn right right and and proceed proceed eastward eastward for for 11 mile mile (1.5 (1.5 km), km), pull pull to to the the right right of of the the highway highway opposite opposite aa trail trail leading leading northward northward Walk along along the the trail trail to to the the cleared cleared area area into the the bush bush (Figure (Figure11). 11). walk into beside 6). beside aa water—filled water-filled pit pit (Figure (Figure 6). - CAUTION CAUTION - DEEP DEEP PIT PIT AND AND OPEN OPEN SHAFT. SHAFT. STOP STOP 9: 9: Zn, Zn, Cu Cu Mineralization, Mineralization, Port Port Arthur Arthur Copper Copper Mine Mine The The open open cut cut of of the the Port Port Arthur Arthur Copper Copper mine mine was was developed developed during during the the winter winter 1916—1917. 1916-1917. Later Later in in 1917 1917 aa 100—foot—deep 100-foot-deep shaft shaft with with aa first—level first-level "several" carloads carloads of of ore ore drift drift 200 200 feet feet long long were were developed. developed. In total, "several" The property was was grading 33 to to 3.5% 3.5% Cu Cu were were shipped shippedto toTrail, Trail,B.C. B.C.. • The grading further further developed developed by by aa 5,000—foot 5,000-foot drill drill program program in in 1956 1956 by by Stratmat Stratmat Limited. AA mineralized mineralized zone zone over over 600 600 feet feet (180 (180 m) m) long long and and 75 75 feet feet (23 (23 m) m) Limited. wide was was outlined. outlined. Mineralization Mineralization consists consists of seams seams and and stringers stringers of of wide pyrite, pyrite, sphalerite sphalerite and and chalcopyrite chalcopyrite in in aa host host composed composed of of amygdaloidal amygdaloidal chlorite schist. schist. The The mineralization mineralization is is crudely crudely zoned zoned (Fig. (Fig. 6) 6) with with aa chlorite zinc—rich toward the the stratigraphic stratigraphic top, top, and and aa copper—rich copper-rich zinc-rich north north zone, zone, toward 86 �-4 I 2 9 3 Figure 12: Field trip stop no. 10. 00 x Zn, Pb PIGEON Pb - e felsic motavolcanics intermediate metavolcanics mafic metavolcanics conglomerate , arenite — ——— 2.-' ——7 —— Pb 1/2 mi. pillow facing in bosalts mineral occurrences OCCURRENCE —— C--, . — — #0 �south zone. samples of mineralization may be found The south zone. Good samples found in the dump. dump. The distribution appearance of distribution of of mineralization mineralization can can be be noted noted by by the the "rusty11 "rusty" appearance unmineralized amygdaloidal metameta— the outcrop outcrop surface. surface. Good exposures of mineralized volcanic rock rock can can be noted just just east east of of the the open open cut. cut. AA siliceous, "cherty" unit unit which caps the mineralization is exposed in the northwestern "cherty" northwestern of the Smalloutcrops outcropsininthe the clearing clearing north part of the main main outcrop. outcrop. Small north of of here here expose unmineralized, dacitic tuff. These These give way way expose unmineralized,carbonate—bearing, carbonate-bearing, dacitic to quartz—eye tuff. The The footwall footwall rocks rocks to to the zone northward to quartz-eye tuff. the mineralized mineralized zone are not not exposed here and andaa gabbro-diorite gabbro—dioritesill sill separates separates the the mineralizaare exposed here mineralization from south which the south whichare arecomposed composed of of tion from the the nearest nearestvolcanic volcanicrocks rockstotothe chloritic felsic felsic tuff. chloritic tuff. Return 11, and proceed east for approximately 6.4 6.4 miles Return to Highway 11, (10.3 km). (10.3 Stop just before a point where the power line crosses crosses the road (Figure 12) and walk through through a "cut—over" (Figure "cut-over" area to a series of pits located located the ridge. Alternatively, roadside along the eastern margin of the ridge. Alternatively, roadsideexposures exposures and pits pits northeast of Highway 11 1 1 may be examined to illustrate illustrate the setting setting and of mineralization. STOP 10: Zn, Pb Pb mineralization, mineralization, Pidgeon Pidgeon Property Property The pits and outcrops outcrops here here expose expose stratabound stratabound sphalerite—galena sphalerite-galena This mineralmineral— mineralization associated associated with felsic felsic volcaniclastic volcaniclastic rocks. rocks. This ization was tested short diamond diamond drill drill holes holes in in 1969 1969 by by Kerr Kerr Addisson Addisson ization tested by short The mineralization mineralization Mines and and by by aa longer longer hole hole in in 1978 1978 by by Hanna Hanna Mines. Mines. The consists of lenticular consists lenticular masses of sphalerite—galena—ankerite sphalerite-galena-ankerite with with minor minor pyrite and Quartz veins are and chalcopyrite chalcopyrite in in aa siliceous, siliceous, sericitic sericitic host. host. Quartz during present and suggest suggest some some remobilization of mineralization during metamorphism. Spotted pyritic alteration is ubiquitous ubiquitous in the felsic felsic lapilli tuffs to the the northwest northwest (footwall?) (footwall?) of of the the mineralization: the the lapilli tuffs to Hanging wall Hanna program indicated Harma indicated low low zinc zinc values values within within this this zone. zone. Hanging core logs logs as as "andesite". "andesite". rocks are not exposed exposed here but are are described described in in core A roadside roadside outcrop outcrop to to the the northeast northeast contains contains minor minor magnetite magnetite iron— ironformation overlain southward-facing pillow pillow lavas lavas (Fig. (Fig. 12). 12). formation overlain by southward—facing TRIP. RETURN TO FORT FRANCES FRANCES MU) AND INTERNATIONAL INTERNATIONAL FALLS. FALLS. END OF TRIP. 88 �FIELD TRIP TRIP II: 11: FIELD ARCHEAN OF ARCHEAN GEOLOGY GEOLOGY O F THE THEINTERNATIONAL INTERNATIONAL FAILSflBETOGANA PALLS-KABETOGAMA AREA, MINNESOTA MINNESOTA AREA, by R.W. Ojakangas, Ojakangas, University University of of Minnesota, Minnesota, Duluth, Duluth, 55812 55812 R.W. W.C. W.C. Day, Minnesota Minnesota Geological Geological Survey, Survey, Day, St. S t . Paul, Paul, 55108 55108 and and D.L. Southwick, Southwick, Minnesota Minnesota Geological Geological Survey, Survey, St. S t . Paul, Paul, 55108 55108 D.L. �Paper Paper 11 GENERALIZED GEOLOGY OF THE GEOLOGY OF THE RAINY RAINYLAKE LAKE AREA, MINNESOTA MINNESOTA by Richard W. Ojakangas Ojakangas Richard W. Minnesota, Minnesota, Duluth Duluth Duluth, Minnesota 55812 Ouluth, Minnesota 55812 University University of of INTRODUCTION INTRODUCTION The The Rainy Rainy Lake Lake area area is is in in the the western western part part of of an an east—northeast—trendeast-northeast-trending ing metavolcanic—metasedimentary metavolcanic-metasedimentary sequence sequence more more than than 300 300 km km long long and and 10 10 to to 30 km wide that lies adjacent to and astride the International Boundary. It that lies adjacent to and astride the International It is is bounded bounded on on the the south south by the the Vermilion Vermilion Granitic Granitic Complex Complex (Southwick, (Southwick, 1972; 1972; Southwick Southwick and and Sims, Sims, 1980) 1980) and and on on the the north north in in Ontario Ontario by by another another maszif massif of of Primary zircon ages and whole—rock granitic rocks of probable similar age. granitic rocks of probable similar age. Primary zircon ages and whole-rock Rb—Sr from the the Rainy Rainy Lake Lake area area suggest suggest that that all all of of the the rock—forming rock-forming Rb-Sr ages ages from events, except for the mafic dikes, occurred between 2700 m y . ago ago events, except for the mafic dikes, occurred between 2700 and and 2750 2750 m.y. (Peterman (Peterman and and others, others, 1972). 1972). Reconnaissance mapping Reconnaissance mapping was undertaken undertaken in in the the late late 1960's; 1960's; this this has has been published as the International Falls 1:250,000 sheet (Southwick and Ojakanpublished as the International Falls 1:250,000 sheet (Southwick and Ojakan— gas, 1979a). details on on the the geology geology can can be found found in in aa report report on on the the 1979a). More details then—proposed then-proposed Voyageurs National National Park Park (Minnesota (Minnesota Geological Geological Survey, Survey, 1969) 1969) and in in Ojakangas Ojakangas (1972). (1972). The The supracrustal supracrustal rocks rocks in in the the Rainy Rainy Lake Lake area area north north of of the the Rainy Rainy Lake— LakeSeine Seine River fault fault (Figure (Figure 1) 1) are are part part of of the the larger larger Wabigoon Wabigoon metavolcanic— metavolcanicmetasedimentary metasedimentary belt. belt. They They are are aa diverse diverse assemblage assemblage of of sedimentary, sedimentary, extruextrusive, and intrusive greenintrusive rock rock types, types, generally generally metamorphosed metamorphosed to to the the upper upper green— schist schist facies, facies, and (Ojakanand have have an an estimated estimated aggregate aggregate thickness thickness of of 2400 2400 mm (Ojakan— gas, 1972). 1972). In contrast, the biotite schist schist to to the the south south of the the Rainy Lake— LakeSeine Seine River River Fault Fault has has aa metamorphic metamorphic mineral mineral assemblage assemblage characteristic characteristic of of the facies. However, However, the the change change in in metamorphic metamorphic grade grade across across the amphibolite amphibolite facies. the The schist schist south south of of the fault fault is is somewhat somewhat transitional transitional rather rather than than sharp. sharp. The the the fault fault has has aa minimum thickness thickness of of 3600 3600 m. m. For to consider consider the the geology geology of of the the For descriptive descriptive purposes purposes it it is is useful useful to Rainy The central central belt Rainy Lake Lake area area as as consisting consisting of of three three lithologic lithologic belts. belts. The consists ic to to intermediate intermediate metavolcanic and consists of of aa complex complex assortment assortment of of mat mafic hypabyssal rocks hypabyssal rocks and and is is referred referred to to in in general general terms terms as as the the greenstone greenstone belt. belt. The on the the north north by by aa belt belt of of metagraywacke metagraywacke The greenstone greenstone belt belt is is flanked flanked on (passing I1 field field guide guide in (passing through Ranier; see stops 1 and 9 of the Trip II this this volume), volume), and and on on the the south south by by another another belt belt of of metagraywacke metagraywacke that that may may or or may not be correlative correlative with with the the metagraywacke metagraywacke to to the the north. north. The The south south belt belt of is broken by the the Rainy Riverfault fault (see (see stop of metagraywacke metagraywacke is broken by Rainy Lake—Seine Lake-Seine River stop 11 11 of of the field field guide). guide). A fourth fourth important important lithostratigraphic lithostratigraphic unit in in the the area This clas— clasarea consists consists of of feldspathic—lithic feldspathic-lithic quartzite quartzite and and conglomerate. conglomerate. This tic tic succession succession occurs occurs within within the the central central greenstone greenstone belt belt (see (see stops stops 22 and and 88 of the the field field guide). guide). 91 �0 0-J u-s a- u-s C 0 aD aC a- o Sc —Jo z'a Ilmm - Biotite schist schist a Metasedimentary unit unit Metasedimenmry (feldspathic quartzite (feldspathic quartzite and andconglomerate) conglomerate1 EEI tuffaceous biotite—chtorite tuffoceous biotite-chlorite schist, schist, chlorite schist, — actinohte schist, schist, chlorite chlorite-actinolite piltowed greenstone, fetsic tuff, pillowed greenstone, felsic tuff, metaplutonic rocks including felsite, and and metoplutonic including feisite, intermediate, mcfic mafic ond and ultramafic types intermediote, types Ililut' II I II Metavalcanic Metavolcon>c— metaplutonic rnetaplutonic unit unit: A .. Inclined bed, bed, overturned overturned I t EXPLANATION and bedding Vertical foliation Vertical foliation and bedding Y Inclined foliotion foliation and and bedding bedding Inclined + lncined lineation lineation Inclined Vertical foliation Vertical .2t *a Inclined Inclined foliation - -5' eo lop at Top of bedCin beds'in direction direction of arrow arrow -7 not determined Vertical bed, Vertical bed, top top direction direction not determined in direction direction of of dot Vertical bed, bed, top Vertical top in dot - 3t- Inclined bed. bed, top top direction direction not determined Inclined determined 2:c:;-5 e—7ç of the western part of the Figure 1. Figure 1. Geologic map of the Rainy Rainy Lake Lake area, area, Minnesota. From Ojakangas Ojakangas (1972). (1972). to 4) a 4, - a) 14 rn in in belt belt of ofg-reenstone greenstone feldspathic Metasedirnentary unit Metcsedimentory unit: feldspothic quartzite and and conglomerate conglomerate Racks Rocks racks, undivided Granitic rocks, undivided Hornblendegobbro gabbro and and diorite Hornblende diorite I'' m 4 M pie 40 -' Inclined bed, right right side side up up Inclined bed, 3" -- ... Contact Contact Short dash dash where whereinferred inferred or or gradational; gradational; Short dotted where dotted where concealed concealed by water water ....... Inferred fault fault Inferred Dotted where where concealed concealed by by water water Dotted --- islands Seven Sister �I p The The stratigraphic stratigraphic and and structural structural relationships relationships among among the the greenstone, greenstone, the the two two belts belts of of metagraywacke, metagrayuacke, and and the the feldspathic feldspathic quartzite—conglomerate quartzite-conglomerate sequence sequence have have been been debated debated for for decades. decades. The The problems problems are are discussed discussed briefly briefly in in later later sections. sections. Most ~ o s tvolcanic—sedimentary volcanic-sedimentary rock rock types types in in the the Rainy Kainy Lake Lake area area are are schis— schistose i— tose and and many many are are sheared, sheared, making makingrecognition recognitionof ofprimary primaryrock rocktypes typesdiff difficult. cult. Small Small bodies bodies and and dikes dikes of of granitic granitic rocks rocks intrude intrude the the metamorphic metamorphic rocks. rocks. Some Some of of these these previously previously have have been been called called Laurentian Laurentian granites granites (Law(Lawson, son, 1913; 1913; Hart Hart and and Davis, Davis, 1969; 1969;Peterman Petermanan.d aqd Goldich, Goldich, 1970). 1970). Late Late mafic mafic dikes dikes (2100—2200 (2100-2200 m.y.) my.) cut cut all all rocks rocks in in the the region region (Hanson (Hansonand and Malhotra, Malhotra, 1971). 1971). Exposures Exposures are are generally generally limited limited to to the the lake lake shores shores and and islands, islands, and and to to inland to the the For several several kilometers kilometers to inland knobs knobs of of the the Kabetogama Kabetogama Peninsula. Peninsula. For south, south, large large muskeg muskeg swamps swamps obscure obscure the the geology. geology. Metagraywacke Metagraywacke bothsides sidesofofthe thebelt belt of of greenstone is characterThe The metagraywacke metagraywacke onon both greenstone is character- ized dark—gray beds thatare aregenerally generally from from 55 to to 35 cm thick thick ized by by medium— medium- orordark-gray beds that 35 cm An excellent foliation, generally are as much as 1.2 m thick. but but are as much as 1.2 m thick. excellent foliation, generally parallel parallel to Original grain grain shapes shapes and and to bedding, bedding, is is given given by by well—aligned well-aligned biotite. biotite. Original Most samples are comsizes have been obliterated by recrystallization. samples are comsizes have been obliterated by recrystallization. posed 20-40 percent percent quartz, quartz, and and 10—15 10-15 percent percent posed of of 50—60 50-60 percent percent plagioclase, plagioclase, 20—40 Minor minerals include chlorite, muscovite, garnet, sillimanite, biotite. biotite. minerals include chlorite, garnet, sillimanite, staurolite, staurolite, hornblende, tourmaline, tourmaline, epidote, epidote, apatite, apatite, and and pyrite. South— Southwick (1972) described related biotite schists farther to wick (1972) described related biotite schists farther to the the south south in in greater greater detail. detail. • The The original original succession succession probably probably consisted consisted of of alternating alternating beds beds of of graded graywacke sandstones and generally thinner mudstones, the graded graywacke sandstones and generally thinner mudstones, the latter latter now now constituting Original bedding bedding survived survived the the constituting the the more more biotite—rich biotite-rich beds. beds. Original metamorphism. Graded beds beds have have been been obscured obscured by by metamorphism metamorphism at at most most locallocalmetamorphism. Graded ities, but can be detected even in some highly recrystallized schists. ities, can be detected even in some highly recrystallized schists. Other Other sedimentary sedimentary features, features, including including concretions, concretions, flame flame structures, structures, and and Turbidity load casts on the bottoms of a few beds, are rare. load casts on the bottoms of a few beds, are rare. Turbidity current current depodeposition sition on on submarine submarine fans fans provides provides aa likely likely model model for for sedimentation. sedimentation. Quartzite—Conglomerate Quartzite-Conglomerate Unit Unit in in the the Greenstone Greenstone Belt Belt Feldspathic—lithic Feldspathic-lithic quartzite quartzite and and conglomerate conglomerate constitute constitute aa clastic clastic sucsuccession within the predominant volcanogenic rocks of the greenstone cession within the predominant volcanogenic rocks of the greenstone belt. belt. This (19721, in in the the abstract abstract by by Oja— OjaThis succession succession is is described described in in Ojankangas Ojankangas (1972), 2 and 8 of the field guide kangas kangas and and Olson Olson in in this this volume, volume, and and in in stops stops 2 and 8 of the field guide in in fluvial-alluvial fan fan this volume. volume. It has been interpreted as a braided fluvial—alluvial association. association. this Metavolcanic Metavolcanic Rocks Bocks in in the the Greenstone Greenstone Belt Belt S A A complex complex volcanogenic volcanogenic association association that that includes includes tuffaceous tuffaceous schist, schist, felsic felsic tuff, felsite, felsite, greenschist, greenschist, pillowed pillowed greenstone, greenstone, iron—formation, iron-formation, 93 �felsic hypabyssal hypabyssal rocks, metadiorite, metagabbro, peridotite, and and anorthosite, makes up most of the the greenstone greenstone belt and is is intercalated intercalated with quartzite—conglomerate unit Shearing is pervasive in the quartzite-conglomerate unit described described above. above. Shearing in all the rocks, and positive identification identification of rock rock types types generally generally requires requires microscopic microscopic study. study. Chlorite, amphibole, amphibole, and and epidote epidote impart impart aa green green color to the the rocks. rocks. Tuffaceous schist, consisting Tuffaceous consisting of interstratified interstratified thin thin fine—grained fine-grained beds and of biotite-rich, biotite-rich, chlorite-rich, chlorite—rich, and and laiuinae laminae of and sericite—rich sericite-rich composition, composition, occurs occurs in in aa zone zone near near the the southern southern edge edge of of the the greenstone greenstone belt belt adjacent adjacent to to the ish Bay 8ay to the viviJackfish the southern southern metagraywacke metagraywacke belt, belt, and and extends extends from from Jack! Jackfish and Red Bed Sucker cinity of Cranberry Cranberry Island. Island. Another major body is is on Jackfish Is lands at at the the northern northern edge of the These rocks Islands the belt. These rocks are are interpreted interpreted to to be tuffaceous tuffaceous because because they they are are associated associated with with coarser coarser felsic felsic tuffs, tuffs, and and because because they they contain contain scattered scattered felsic felsic volcanic volcanic rock rock fragments fragments and and large large plagioclase grains in aa recrystallized recrystallized matrix matrix of of fine fine quartz quartz plagioclase grains (volcanic?) (volcanic?) in plagioclase, which up about about two thirds thirds of the and plagioclase, which malces makes up the rock. rock. Minor felsic felsic tuff tuff is is interbedded interbedded with with greenschist greenschist at at several several localilocalities. Exposures at the the eastern eastern end of Dryweed Island Island appear appear to to consist consist of lapilli tuff. lapilli tuff. Felsic flows Felsic flows occur occur in in aa few few small small exposures. exposures. Fine—grained, Fine-grained, dense dense meta— metaandesite commonly with with deformed deformed pillows, pillows, constitutes a andesite or or nietabasalt, metabasalt, commonly poorly poorly exposed exposed 360—meter-wide 360-meter-wide unit unit along along the the shoreline shoreline east east of of Birch Birch Point, Point, near the Rainy Lake. Lake. Other Other much much smaller smaller exposures exposures are are prespresthe western western end end of of Rainy ent ent on on islands. islands. fine-grained Rocks mapped as greenschist greenschist consist consist of thinly thinly bedded, fine—grained chlorite schist, chlorite—actinolite chlorite-actinolite schist, and actinolite actinolite schist. This This rock type is common throughout the belt of greenstone; it occurs both north occurs north common throughout the and south 1). south of the the quartzitrconglomerate quartzite-conglomerate unit unit (Fig. (Fig. 1). Sheared and altered altered metaplutonic rocks rocks of variable composition composition constiwnstitute the the bedrock of several several small small islands, especially especially in in the the eastern eastern part of of the the belt. belt. A small small island island just just off the the northeast northeast corner corner of Grindstone Grindstone island is Anorthosite comcomIsland is composed composed entirely entirely of of serpentinized serpentinized peridotite. peridotite. Anorthosite prises the the one one small small island island of of the the Seven Seven Sister Sister Islands Islands that that is is on on the the United States States side side of of the the International International Boundary. Boundary. Northern Zone Northern Zone of Granitic Granitic Rocks Rocks granitic rocks in the the western part of Medium-grained granitic rocksare arecommon common in western part ofRainy Rainy Lake, especially on the Ontario mainland and islands, and constitute the especially on the Ontario mainland and islands, and constitute the Lake, of aa large southern edge rocks that that lies lies to to the the north north of of southern edge of large area area of granitic rocks the Minnesota Minnesotaside side of of the Rainy Lake Lake volcanic—sedimentary the Bainy On the the volcanic-sedimentary sequence. sequence. On the International Boundary, gray,biotitic biotitic granitic International Boundary, gray, graniticrocks rocksoccur occur on on several several of of granitic rocks composition gran— the small granthe small islands. islands. The The granitic rockshave havethe thegeneral general compositionofof Grassy Island A large body of gray, sheared tonalite occurs on odiorite. odiorite. large sheared tonalite occurs on Grassy Island and is is intrusive green— and on the the adjacent and on adjacent islands islandsand and mainland, intrusiveinto into greenmainland, and schists. schists. 94 �I Late LateMafic MaficDikes Dikes Two Twowell—exposed well-exposedmafic maficdikes, dikes,from from4545toto7575meters meterswide, wide,which whichare arethe the youngest rocks in the area, are present on the islands in the western youngest rocks in the area, are present on the islands in the westernpart part of of Rainy RainyLake Lakeand andseveral severaladditional additionaldikes dikesare areexposed exposedsporadically sporadicallyininthe the These dikes strike N. 30—40° vicinity of International Falls. vicinity of International Falls. These dikes strike N. 30-400 W. W. and andare are vertical. Theyappear appearto tobe bealigned alignedwith withsimilar similardikes dikesininCanada Canadaand andsouthsouthvertical. They in Minnesota, and are part of a major dike swarm in the western part ward ward in Minnesota, and are part of a major dike swarm in the western part ofofthe theCanadian CanadianShield Shield(Southwick (Southwickand andDay, Day,1981). 1981). p STRUCTURAL STRUCTURALINTERPRETATION INTERPRETATION The Themajor major structural structuralgrain grainof ofthe theregion regionisiseast—northeast, east-northeast,and andisis given by major fold axes, faults, shear zones, bedding, and foliation. given by major fold axes, faults, shear zones, bedding, and foliation. Most Most ofof the the,bedded bedded rocks rocksare areinclined inclinedsteeply; steeply;the theonly onlyexception exceptionis isin inthe the Brule SaginawBay Bayarea areato tothe theeast, east,where wheregentle gentleopen openfolds foldsare are BruleNarrows NarrowstotoSaginaw elongated minerals, present. present. LineatiOn5mainly Lineations--mainly elongated minerals,schistosity—bedding schistosity-beddinginterintersections, plunge Both ENE. Both sections, and and minor minor fold foldaxes——generally axes~generally plunge30°—50° 30"-50a ENE. northwest— northwest- and and northeast—trending northeast-trendinglineaments, lineaments, some someof of which whichrepresent represent minor minor can be seen on aerial photographs. faults, can be seen on aerial photographs. faults, Lawson Lawson (1913) (1913)interpreted interpretedthe thebelt belt of ofgreenstone greenstoneand andassociated associated rocks rocks to be synclinal, with the quartzite unit (which he called to be synclinal, with the quartzite unit (which he calledHuronian) Huronian) in in the the core coreand and conglomerate conglomerate(also (alsocalled calledHuronian), Huronian), greenstone greenstone(called (calledCeewatin), Keewatin), and and biotite biotite schist schist(called (calledCoutchiching) Coutchiching)forming formingsuccessively successivelyolder older units units Grout (1925a), both north and south of the quartzite (Fig. 2A). noting both north and south of the quartzite (Fig. 2 A ) . Grout (1925a), noting that that all all the the cross crossbeds beds in inthe thequartzite quartzite face facesouthward, southward, interpreted interpreted the the major major structure to be anticlinal, and interpreted quartzite to lens out structure to be anticlinal, and interpreted quartzite to lens out near the be absent absent on on the thenorth northflank flank near the eroded eroded crest crest of of the theanticline anticlineand andto tobe • — (Fig. It is is noteworthy, noteworthy,however, however, that that the the northern northernconglomerate conglomerateunit unit 2B). It (Fig. 2B). mapped by both Lawson and Grout appears to consist of a few mapped by both Lawson and Grout appears to consist of a fewminor minorlenses lenses at at best, be assumed assumed to tobe be the thesame sameunit unit that that is is present present to to the the best, and and should shouldnot not be south southon onNeil NeilPoint. Point. Furthermore, Furthermore, greenschist greenschist occurs occurs both both stratigraphistratigraphibelow and above the feldspathic—lithic guartzite cally cally below and above the feldspathic-lithic quartzite and and conglomerate; conglomerate; these latter rock types are interbedded with greenschist. P Lawson thus, these latter rock types are interbedded with greenschist. Lawson thus, Such (1913)said said these these sediments sedimentswere weredeposited depositedupon upona amajor majorunconformity. unconformity. Such (1913) an an unconformity unconformity is isindeed indeed exposed exposedto tothe theeast east in in Ontario Ontario (Lawson, (Lawson,1913; 1913; Wood, If so, so, Wood, 1980) 1980)and and could couldbe be present, present, but but hidden, hidden, in in Minnesota Minnesota as as well. well. If (See the abstract by Ojakangas and Olson it it may may be be aa minor minor unconformity. unconformity. (See the abstract by Ojakangas and Olson in in this this volume.) volume.) Data Data obtained obtained during during my my study study permit permit aa different different structural structural interpretainterpretaNearly tion all strati— strati2 0 . Nearly all tion involving involvingboth both folding foldingand and faulting faulting(Fig. (Fig. 2C). graphic graphic tops tops in in the the belt belt of of greenstone greenstoneon on Rainy Rainy Lake Lake face facesouthward, southward, indicating The metagray— metagrayindicating aa lack lack of of major major folding folding within within the the belt belt itself. itself. the wacke wacke (biotite (biotiteschist) schist)that that lies liessouth southof of the the greenstone greenstoneunit unit faces faces northward, in an an area area several several p. 356) 356) in northward, as as previously previously noted noted by by Merritt Merritt (1934, (1934, p. kilometers Also, most most kilometers to to the the east, east, but but at at the the same same stratigraphic stratigraphicposition. psition. Also, metagraywacke Folding alone alone metagraywacke just just north north of of the the greenstone greenstone faces faces northward. northward. Folding for these cannot account account for these relationships; relationships: aa major major longitudinal longitudinal fault fault along along cannot to the the strike strike of of the the rock rock the southern southern boundary boundary of of the the belt, belt, parallel parallel to the units, units, seems seems necessary, necessary, and and aa fault fault along along the the northern northern boundary boundary of of the the greenstone greenstone belt belt apparently apparentlyalso alsois isrequired. required. 95 S �NNW NNW ssE SSE / / x A x (After Lawson, 1913 a) //__-__ — I (After Grout, 1925a) B i (Ojakan gas1 C NNW *4040* this report) 0 0 0 0 OSSE Generalized diagrammatic interpretation of this report D EXPLANATION I'' C m -Jo 02 Hornblende gabbro and and diorite Hornblende gabbro a- Granitic rocks, rocks, undivided undivided Rocks in in belt Rocks belt of of greentone greenstone a Melasedimentary unit: unit: te[dspathic Melasedimentary feldsoothic quartzite and quartzite and conglomerate conglome&e 'C 0 a, 'C U a, 0 a- U 3 0 -J "-I IIIIIIIIII{I - Metavolcanic metaplutonic unit: Metovolcanic —metaplutonic unit: tuttaceous tuffoceous biotite—chtorite biotite-chlorite schist, schist, chlorite schist, schist, chiorile-actinolite chlorite-actinolite schist, schist, chlorite pillowed greenstone, felsic tuft, tuff, greenstone, felsic telsite, fetsite, and and metaplutonic metaplutonic rocks rocks including including intermediate, matic and ultramafic types intermediate. mafic tvoes . . EEi Metosedimentary unit unit Metasedimentary (feldspathic (feldspathic quartzite quartzite and andconglomerate) conglomerate) 0 Biotite Biotite schist schist 4 Direction toward toward which Direction which stratigraphic stratigraphic top indicators indicators face face Figure Figure 2. 2. Diagrammatic Diagrammatic geologic geologic sections sections showing showing structural structural interpretainterpreta— of Lawson Lawson (1913), (19131, Grout Grout (1925a), (1925a), and and this t h i s report. report. Arrows tions of Arrows indimdi— cate directions directions of of stratigraphic stratigraphic tops. tops. Line of section X-X' shown shown on on section X—X' Figure Figure 1. 1 . From From Ojakangas Ojakangas (1972). (1972). 96 �Evidence of aa major of the the bbelt Evidence of major ffault a u l t along along the t h e southern southern boundary boundary of e l t inin- a   cludes cludes widespread widespread crinkling, crinkling, abundant abundant quartz quartz veins veins and and pods, pods, silicifica— silicificattion, i o n , slickensides, slickensides, and and cliffs c l i f f s (fault ( f a u l t scarpsfl. scarps?). Canadian Canadian geologic geologic maps maps show show aa major major fault f a u l t on on line l i n e with with this this fault f a u l t and and extending extending more more than than 200 200 km km Hawley (1930) and Merritt (1934), both of whom studied this t o the e a s t . Hawley (1930) and Herritt (19341, both of whom studied t h is to the east. fault it is is aa right r i g h t lateral l a t e r a l fault. f a u l t . The concluded it The f a u l t zone zone east e a s t of of Rainy Rainy Lake, Lake, concluded metamorphic the southern southern block block of of biotite b i o t i t e schist s c h i s t and and lower lower metamorphic grade grade (higher (higher in i n the in the northern greenstone block) indicates that the southern block i n t h e northern greenstone block) i n d i c a t e s t h a t t h e southern block also also to the t h e greenstone greenstone block. block. This This fault f a u l t is is now now called called moved upward upward relative r e l a t i v e to moved t h e Rainy Rainy Lake—Seine Lake-Seine River River fault f a u l t in i n Minnesota Minnesota (Southwick (Southwick and and Ojakangas, Ojakangas, the 197gb). Additional structural s t r u c t u r a l data data and and interpretations i n t e r p r e t a t i o n s can can be be found found in in 1979b). Additional Oj akangas. 0j akanqas . of of structural s t r u c t u r a l significance significance to to the t h e Rainy Rainy Lake Lake area area is is recent recent work work by by Poulsen has mapped Poulsen Poulsen (1980) (1980) and and Poulsen Poulsen and and others o t h e r s (1980). (1980). Poulsen has mapped nappe nappe structures s t r u c t u r e s in i n Ontario Ontario just j u s t 15 15 km km to to the t h e north north of of the t h e area a r e a under under discussion discussion The possibility of such structures being present in Minnesota must The p o s s i b i l i t y of such s t r u c t u r e s being present i n Minnesota must here. here. This is of relevance to the This is of relevance t o the be be considered considered in i n any any future f u t u r e detailed d e t a i l e d mapping. mapping. the metagraywacke 'Coutchiching problem,' the stratigraphic positioning of "Coutchiching problem," t h e s t r a t i g r a p h i c positioning of the metagraywacke u n i t s (biotite ( b i o t i t e schist) s c h i s t ) relative r e l a t i v e to to the t h e greenstones. greenstones. The The problem problem was was units discussed at a t some some length length by by Ojakangas Ojakangas (1972). (1972). discussed 97 �Paper 22 Paper GEOLOGY AND GEOCHEMISTRY GEOCHEMISTRY OF THE GEOLOGY AND THE VERMILION GRANIPIC GRANITICCOMPLEX COMPLEX Warren Warren C. C. Day, Minnesota Geological Geological Survey, 1633 1633 Eustis Eustis Street, St. St. Paul, Minnesota 55108 Minnesota 55108 INTRODUCTION INTRODUCTION Archean Archean granite granite and and migmatite migmatite of of the the Vermilion Vermilion Granitic Granitic Complex Complex form form the the southwestern southwestern portion portion of of the the Quetico Quetico subprovince, subprovince, aa major major petrotectonic petrotectonic division of the the Superior Superior Province Province of of the the Canadian Canadian Shield Shield that that extends extends eastward eastward from from northern northern Minnesota Minnesota into into Ontario. Ontario. The The northern northern margin margin of of the the Vermilion Vermilion Granitic Granitic Complex Complex grades grades into into aa broad broad belt belt of of biotite biotite schist schist which River fault fault by the the Rainy Rainy Lake—Seine Lake-Seine River which is is truncated truncated on on the the north north by (Southwick and Ojakangas, 1979a); (Southwick 1979a); the the fault fault marks the the north north boundary of the Quetico the Quetico subprovince subprovince in in Minnesota. Minnesota. Metavolcanic and metasedimentary metasedimentary rocks of the the Rainy Rainy Lake Lake area, area, part of of the the Wabigoon Wabigoon subprovince, subprovince, abut abut the the biotite The southern contact of the (Figure 1). 1). The southern contact the biotite schist schist across across the the fault fault (Figure Vermilion Vermilion Granitic Granitic Complex Complex is is defined defined by by the the Vermilion Vermilion fault, fault, south south of of which which are are the the metavolcanic metavolcanic and and metasedimentary metasedimentary rocks rocks of of the the Vermilion Vermilion Vermilion Granitic district. The western western end end of of the the Vermilion Granitic Complex Complex is is defined defined by by the Vermilion Vermilion Biver fault fault and and the the convergence convergence of the the Rainy Rainy Lake—Seine Lake-Seine River fault. Bedrock exposureisisquite quiteextensive extensiveininthe the eastern eastern portion portion of of the Bedrock exposure the complex, quality and as the complex, but the the quality and quantity quantity of ofoutcrop outcropdiminish diminishwestward westward as the thickness of glacial cover thickness cover increases. increases. History of Investigations Investigations During During the the summer summer of of 1887 1887 H.V. H.V. Winchell, Winchell, H.W. H.W. Fairbanks, Fairbanks, W.F. W.F. Trussel Trussel and and two two "Indian "Indian canoe—men" canoe-men" set set out out in in two two birchbark birchbark canoes canoes from from Tower, Minnesota to conduct conduct aa geologic geologic expedition expedition in in northern northern Minnesota, Minnesota, Minnesota to journeying through Lake region. region. They They went went journeying through the theRainy RainyLake Lake and andKabetogama Kabetogama Lake from Vermilion Lake from Vermilion Lake north north up up the the Little Little Fork Fork River River to to the the international international boundary, and and then then eastward eastward along along Rainy Rainy Lake Lake River River (as (as the the Rainy Rainy River River was was then known)toto "Chadierre "Chadierre Falls" Falls" and Fromthere there they they prothen known) and Fort Fort Frances. Frances. From pro- ceeded along the the south take, south ceeded along south shore shore of of Rainy Rainy Lake, south into intoBlack BlackBay, Bay, portaged portaged into Lake, and peninsula by intoKabetogama Kabetogama Lake, and circumnavigated circumnavigated the theKabetogama Kabetogama peninsula by traveling Namakan travelingeastward eastwardthrough through Namakan and and Sand Sand Point PointLakes Lakes and and then thencoming coming back westward back westward through through Rainy Rainy Lake. Lake. During this this first first expedition expedition Winchell Winchell and his colleagues colleagues described described the the rocks rocks and and presented presented the the earliest earliest ideas ideas for for their their origin. origin. Grout (1923, Grout (1923, 1925b, 1925b, 1926) 1926) presented presented detailed detailed lithologic lithologic descriptions, descriptions, geochemical analyses, and geologic map of Vermilion Granite, the and aa geologic of the Vermilion the to the the terrane terrane now now called called the the Vermilion Vermilion Granitic Granitic name applied by Grout Grout to Geochronological work on rocks Complex. Geochronological rocks from from the the area area was initiated initiated by Goldich and others (1961) who determined a K—Ar age for the main (1961) who determined a K-Ar age for the main batho— bathoGoldich and others lithic phase of La Croix of the the Vermilion Vermilion Granite Granite (now (now termed termed the the Lac Lac La 98 �S 0 '0 S S I Generalized geologic map of the Vermilion Granitic Complex. The large—scale, east—west trending folds in the migatatite are clearly indicated by the map pattern between Pelican and Namakan Modified after Southwick and Sims (1980). Lakes. Figure 1. 0 0 �'reported Granite) Granite) of of about about 2,550 2,550 m.y. m. y. Peterman Petermanand andothers others(1972) (1972) 'reportedaa Pb—Sr Rb-Sr initial whole whole rock—isochron rock-isochron age age of of 2,680 2,680 12 95 m.y., my., with with an an 87sr/86sr ^sr/%r initial ratio ratio of of 0.7005 0.7005 ± 0.0012. 0.0012. Jahn Jahn and and Murthy Murthy (1975) (1975)determined determined aa more more refined refined Rb-Sr Rb-Sr whole whole rock—isochron rock-isochronage ageof of 2,700 2,700 ± 50 50 m.y., my., with with an an 7sr/86sr 87sr/86sr initial initial ratio ratioofof0.7004 0.7004 ±+ 0.0003. 0.0003. + + Recent Recent reconnaissance reconnaissancegeologic geologic mapping mapping of of the the Vermilion Vermilion Granitic Granitic Complex begun in in1968 1968 Complex and and the theMinnesota Minnesota portion portion of of the theRainy Rainy Lake Lakearea areawas wasbegun by by D.L. D.L. Southwick Southwickand and R.W. R.W. Ojakangas Ojakangasof of the theMinnesota Minnesota Geological GeologicalSurvey. Survey. Ojakangas Ojakangas published published aa description descriptionof of the thegeology geology in in the theRainy Rainy Lake Lake greenstone greenstone belt belt in in 1972, 1972, and and the the same same year year Southwick Southwick described describedthe thegranit— granitic Kabetogama, which which he he termed termed collectively collectively the the ic rocks rocks south south of of Lake Lake Icabetogama, Vermilion Vermilion granite—migmatite granite-migmatitemassif. massif. In In 1980 1980 Southwick Southwick and and Sims Sins replaced replaced the the informal informalterm termVermilion Vermiliongranite—migmatite granite-migmatite macsiC massif with with the theformal formalname name Vermilion the Vermilion Vermilion Granitic GraniticComplex, Complex, and and renamed renamed the Vermilion Granite Granite of ofGrout Grout (1925b) La Croix Croix Granite. Granite. The The most most recent recent geologic geologic map, map, at at (1925b) as as the the Lac Lac La scale scale 1:250,000, 1:250,000, was was published published by by Southwick Southwick and and Ojakangas Ojakangas(1979a). (1979a). 0 Lithologic Lithologic Units Units Lithologic be that that established establishedby by the the Lithologic nomenclature nomenclatureused used here here will will be IUGS Subcommission on the systematics of igneous rocks (Streckeisen, (Streckeisen, IUGS Suhcomission on the systematics of igneous rocks The three three most moat important important rock rock units units in in the the Vermilion Vermilion Granitic Granitic 1973). The 1973). Complex are migmatite, granite, and early plutonic rocks (Figure The 2). The Complex are migmatite, granite, and early plutonic rocks (Figure2). migmatite migmatite has has been been divided divided by by Southwick Southwick (1972) (1972)into into schist—rich schist-rich and and granite—rich The paleo— paleogranite-rich types typesdepending dependingon onthe theneosome/paleosome neosome/paleosomeratio. ratio. The somes of the migmatite are biotite schist, amphibolite, early migmatite, somes of the migmatite are biotite schist, amphibolite, early migmatite, and and early early plutonic plutonic rocks, rocks, and and the the neosomes neosomes are are two—mica two-mica leucogranite leucogranite and and The latter is similar to and grayish—pink biotite granite. presumably grayish-pink biotite granite. The latter is similar to and presumably cogenetic cogenetic with with the the Lac Lac La La Croix Croix Granite, Granite, the the dominant dominant batholithic batholithic phase phase of of The leucogranite neosome is present Vermilion Granitic Complex. the in the Vermilion Granitic Complex. The leucogranite neosome is present in small north thethecomplex small quantities quantities within within the the biotite biotiteschist schist northofof complex and and is isthe the Pink granite is the dominant dominant neosome in schist—rich migmatite. dominant neosome in schist-rich migmatite. Pink granite is the dominant neosome in rnigmatite classed as The early early plutonic plutonicrocks rocks neosome in migmatite classed as granite—rich. granite-rich. The within the complex range from granodiorite through tonalite/trondhjemite within the complex range from granodiorite through tonalite/trondhjenite These rocks rocks to and toquartz quartzdiorite diorite andform form small, small, generally generally irregular irregularmasses. masses. These the first igneous activity in the area, having been invaded represent on represent the first igneous activity in the area, having been invaded on all all scales scales by by the the 2,700 2,700 m.y.—old my.-old Lac Lac La La Croix Croix Granite. Granite. The The radiometric radiometric age age of of the the early early plutonic plutonic rocks rocks is is as as yet yet undetermined. undetermined. 4 VERMILION COMPLEX DESCRIPTIONS DESCRIPTIONS OF OF UNITS UNITSININTHE THE VERMILIONGRANITIC GRANITIC COMPLEX Biotite BiotiteSchist Schist I Biotite Biotite schist schist is is widely widely distributed distributed within within the the complex complex and and also also occurs occurs as as aa separate separate mappable mappable unit unit that that flanks flanks the the complex complex on on the the north north and west. west. Within Within the the complex complex the the biotite biotite schist schist occurs occurs as as more more or or less less and intact intact blocks blocks surrounded surrounded by by granite granite and and also also as as an an important important component component of of anan eguigranular, medium— equigranular, medium- to to Itisis the the paleosome paleosome of of migmatitic migmatitic rocks. rocks. It fine-grained schist schist composed composed dominantly dominantly of of quartz, quartz, plagioclase, plaqioclase, and and fine—grained 100 �I-. 0 F.' ~ o r l ymigmatite ,, I AMPHIBOLITE wvam wvom Amphiboiite migmotite CUTS 1 Burntside Gneiss WVb jrrelationships among lithologic ~ ~ i h & t o lower grade suprdcrustal rocks of the flanking greenstone belts BIOTITE SCHIST Wvbs I SCHIST -RICH MIGMATITE related to Lac La Cmix Granite Wvgm GRANITE-RICH MiGMATITE to Lac La Crolx Granite wvgm 1 CUT Late-stage, straight, sharpl i e d pegmatite dikes I complex. complex. Schematicdiagram diagramof ofthe the interrelationships among lithologic Figure2.2. schematic Figure Intrusiveunits unitsare are subdivisionsof of the thevermilion Vermilion GranitiC GraniticComplex. Complex. Intrusive subdivisions Names spelled arrangedwith withthe theyoungest youngestat at the thetop topof ofthe thediagram. diagram. Names spelled arranged outin inthe thecapital capitalletters letters are are the themore moreabundant abundantcomponents componentsof ofthe the out diorite and diorite ark gray hornblende quartz VERMILION GRANITIC COMPLEX I gobbm younger than and ... to IM vermilion Granitic Complex - 1 I �t biotite. biotite. Bedding Beddingand andgraded gradedbedding bedding are arewidely widelypreserved. preserved. Oriented Oriented biotite defines the strong schistosity, which is regionally biotite defines the strong schistosity, which is regionallyparallel parallelto to schist, Isoclinal folding is common in the with quartz quartz bedding. bedding. Isoclinal folding is common in the biotite schist, with stringers being and and feldspar feldspar"sweat—out" "sweat-out" pods pods and and stringers beingfolded foldedcongruently. congruently. biotite S of the thethe Vermilion The mineralogy mineralogy of the biotite biotiteschist schistnorth northofof VermilionGranitic Granitic The Complex is fairly constant, reflecting the chemical homogeneity Complex is fairly constant, reflecting the chemical homogeneity of of the the graywacke protolith. However, graywacke protolith. However, there there are are local local variations variations among among bedding bedding within the schist, as on the south shore of Kabetogama Lake horizons horizons within the schist, as on the south shore of Kabetogama Lakeby by Chippewa N., Chippewa Lodge Lodge CT. (T. 69 69N., R. R. 22 22W.), W.), where wheregarnet, garnet, staurolite, staurolite,and andsillisilli- land Sugarbush manite manite occur occur ininaluminous aluminous beds, beds, and andon on the thesouth southshore shoreofof SugarbushIsIsland ininKabetogama Lake,where wherefelsic felsic horizons horizons with with poikioblastic poikioblastic plagioclase Kabetogama Lake, plagioclase occur. occur. Migmatite migmatite The structure within within the the dominantly dominantly migmatitic migmatitic terrane terranein in The broad—scale broad-scale structure the thewest west part partof ofthe thecomplex complex is is delineated delineated by by foliation foliationwithin within the the Large folds foldswithin withinthe themigmatite migmatite trend trend roughly roughlyeast—west, east-west, paleosome. Large paleosome. flanking parallel to tothe themajor major structural structuralfabric fabricininthe the flankinggreenstone greenstone belts belts parallel (Southwick, 1979a). The The fold fold patterns patterns (Southwick,1972; 1972;Southwick Southwick and and Ojakangas, Ojakangas, 1979a). outlined outlinedby byschistose schistosepaleosomes paleosomes are arepreserved preserved even even into intothe thegranite—rich granite-rich 1978)states states "the consistency of migma— Southwick C (1978) "thestructural structural consistency of migmaportions. portions. Southwick tite paleosomes tite paleosomes in in the the western western portion portion of of the the Vermilion Vermilion Granitic GraniticComplex, Complex, even in in rocks rocks that that are are chiefly chiefly granite, granite, indicates indicates that thatthe thegranite granite even fraction, origin, was emplaced fraction,whatever whatever its its origin, was emplaced in ina amanner manner that that did did not not completely inin pre—existing The granite granite completely disrupt disrupt structural structuraltrends trends pre-existing rocks." rocks." The seems seems to to have have been been passively passively injected, injected,with withsome some flattening flatteningand andbroadening broadening of the thepre—existing pre-existing folds folds within within the thecountry country rocks. rocks. of The thethe complex predominantly The eastern easternportion portionofof complexisis predominantlymassive massiveLac LacLa La The perperCroix percent xenoliths. xenoliths. The Croix Granite, Granite, which which incorporates incorporates less lessthan than55 percent centage centage of of supracrustal supracrustal inclusions inclusions increases increases to to the thewest, west, with with the theli— lithology thology grading gradingregionally regionallyfrom frommassive massive granite granitethrough throughgranite—rich granite-rich In aa general general sense, sense, the the migmatite migmatite to toschist—rich schist-rich migmatite migmatite (Figure (Figure 1). 1). In Lac La La Croix Croix component component within within the the neosome neosome also also decreases decreases westward. westward. Lac Southwick Southwick (1972) (1972)argued argued that that the the schist—rich schist-rich migmatite migmatite of of the the western western porportion tion of of the thecomplex complexrepresents representsthe theinjected injectedand and remobilized remobilizedroof roofof ofaa batholith cored cored by by massive massive granite. granite. The The inferred inferred depth depth of of emplacement emplacement was was batholith on km (pressure (pressureof of 3-4 3-4 kb). kb). on the the order order of of 9—12 9-12 km The The structure structure and and fabric fabricof of the the migmatite migmatite vary vary on on the the outcrop outcrop scale, scale, depending depending on on the the amount amount of of neosome neosome present present and and the the manner manner of of its its In the the schist—rich schist-rich migmatite migmatite the the neosome neosome is is commonly commonly emplacement. In emplacement. interlayered interlayered with with the the paleosome, paleosome, producing producing aa stromatic stromatic structure structure (Mehnert, (Mehnert, commonly are small granitic stringers within the paleosome blocks Small granitic stringers within the paleosome blocks commonly are 1968). 1968). These leucocratic leucocratic boudinaged boudinaged and and thrown thrown into into small—scale small-scale isoclinal isoclinal folds. folds. These stringers stringers which which are are as as narrow narrow as as aa few few millimeters millimeters in in width, width, typically typically are are bordered by by aa biotite biotite selvage selvage zone. zone. bordered migmatitepresents presents several several fabric The granite—rich granite-rich migmatite fabric styles stylesdepending depending The emplacement. the degree of paleosome assimilation and manner of granite on the degree of paleosome assimilation and manner of granite emplacement. on 102 I �• Where Where the the granitic granitic neosome neosome is is dominant, dominant, paleosome paleosome blocks blocks (up (upto toten tenmeters meters Some paleosome blocks are sharp in size) are rafted in neosome. in size) are rafted in neosome. Some paleosome blocks are sharp and and distinct, distinct, typical typical of of an an agmatic agmatic migmatite, migmatite, many many have have the the pronounced pronounced flow flow fabric of a schlieren migmatite, and many are the ghostly, fabric of a schlieren migmatite, and many are the ghostly, digested digested remreuinants nants characteristic characteristicof of nebulitic nebulitic migmatite miqmatite (Mehnert, (Mehnert,1968). 1968). The The contacts contacts are contained are especially diffuse around tonalite blocks that are especially diffuse around tonalite blocks that are contained in in Lac lac The feldspar "halo" surrounding such inclusions is La Croix Granite. La Croix Granite. The feldspar "halo" surrounding such inclusions is interpreted interpreted as as representing representing alkali alkali metasomatism, metasomatism, with with the the introduction introduction of of potassium into the tonalite, and of calcium and sodium into potassium into the tonalite, and of calcium and sodium intothe thegranite. granite. The The neosome neosome of of the theschist—rich schist-richmigmatite miqmatite is iswhite white to tolight lightpink pink This is a coarse—grained to pegmatitic material leucogranite. leucogranite. This is a coarse-grained to pegmatitic material composed composed dominantly Muscovite, biotite biotite and and dominantly of of quartz, quartz, microcline microcline and and plagioclase. plagioclase. Muscovite, Garnet, epidote and zircon chlorite are common minor minerals. chlorite are common minor minerals. Garnet, epidote and zircon occur occur as as accessory accessory minerals. minerals. I • As As discussed discussed earlier, earlier, the the leucogranite leucogranite in in the the schist—rich schist-rich migmatite migmatite is intimately enfolded and boudinaged with the paleosome. is intimately enfolded and boudinaged with the paleosome. Poikioblastic Poikioblastic microcline microcline and and plagioclase plagioclase are are developed developed in in thin thin stringers stringers within within biotite biotite schist schist without without disruption disruption of of biotite biotite foliation foliation in in the the surrounding surrounding paleosome. paleosome. Southwick Southwick (1972) (1972)suggested suggested that that this this texture texture indicates indicates aa replacement origin or metasomatic growth of feldspar during metamorphism. replacement origin or metasomatic growth of feldspar during metamorphism. This be seen seen especially especially well well on on the the south south end end of of the the roadcut roadcut This texture texture can can be 6.6 6.6 miles miles north north of of Cusson, Cusson, Minnesota Minnesota along along U.S. U.S. Highway Highway 53. 53. The The neosome neosome of of the the granite—rich granite-rich migmatite migmatite is is predominantly predominantly grayishgrayishThe local mineralogy and chemical composition composition pink pink Lac Lac La La Croix CroixGranite. Granite. The local mineralogy and chemical of The neosome neosome of the the granite granite vary vary with with the the degree degree of of paleosome paleosome digestion. digestion. The also leucogranite and and Lac Lac La La also varies varies with with the the amount amount of of mixing mixing between between the the leucogranite Croix This is is seen seen along along the the Crane Crane Lake Lake Road, mad, north north of of Croix granitic granitic phases. phases. This the the junction junction with with the the Echo Echo Trail. Trail. Early Early Plutonic Plutonic Rocks Bocks Granodiorite, Granodiorite, trondhjemite, trondhjenite, tonalite, tonalite, and and quartz quartz diorite diorite represent represent the Although the earliest earliest igneous igneous activity activity in in the the Vermilion Vermilion Granitic Granitic Complex. Complex. Although these these rocks rocks occur occur as as relatively relatively minor minor intrusive intrusive bodies, bodies, they they hold hold aa key key to to understanding understanding the the early early geologic geologic and and geochemical geochemical evolution evolution of of the the region. region. In In most most cases cases crosscutting crosscutting relationships relationships easily easily establish establish relative relative ages, ages, but but radiometric radiometric dating dating has has not not been been conducted conducted on on these these earliest earliest phases phases to to determine determine their their absolute absolute ages. ages. P • Two to show show on on the the 1:250,000 1:250,000 Two early early plutonic plutonic units units are are large large enough enough to One is is an an east— eastscale scale geologic geologic map map by by Southwick Southwick and and Ojakangas Ojakangas (1979a). (1979a). One west trending trending body body of of biotite—hornblende biotite-hornblende quartz quartz diorite diorite which which crops crops out out west Sullivan BayBay of of Icabetogama tansouth southofof Sullivan KabetogamaLake Lake along the theAsh Ash River River Trail Trail3 3km along This rock rock has has aa massive, massive, mediwn—grained medium-grained hypidiomorphic hypidiomorphic (Figure 1). 1). This (Figure Modal proportions proportions of of the the leucocratic leucocratic minerals minerals are are plotted plotted in in texture. Modal texture. The melanocratic melanocratic minerals minerals hornblende hornblende and and biotite biotite comprise comprise up up Figure Figure 3a. 3a. The This biotite—hornblende biotite-hornblende quartz quartz diorite diorite is is to to 35 35 percent percent of of the the unit. unit. This crosscut crosscut by by numerous numerous dikes dikes and and irregular irregular masses masses of of biotite biotite granite granite and and The amphibole amphibole and and oxide oxide phases phases display display interesting interesting textural textural granodiorite. granodiorite. The 103 �a. QTZ rocks P LAG OR K QTZ QTZ /LOC Granite La Croix Granite 34.1 35.9 OR OR PLAG P LAG 33 N=45 v ~ = 4 5 \ FPLAG LAG OR QTZ C. "Ne N -9 .'— x Leucogranite /////////T Leucogranite OR Figure 3. Figure 3. vV ol 4) 29.6 4.4 44 QTZ 29.6 QTZ 5.6 OR 31.3 5.6 OR 34.3 7.3 PLAG 39.4 PLAG 39.4 73 N = 23 N=23 PL AG PLAG Modal abundances Data taken taken from Modal abundancesofofOr—Qtz—Pl. Or-Qtz-Pl. Data from Southwick Southwick (1972), Rye and Boy Roy (1978), (1978), and and unpublished unpublished data data on file at at Minnesota Minnesota (1972), Eye and on file Geological Survey. Geological Survey. a) Early Plutonic a) Plutonic Phases: o—granodiorite o-granodiorite along along Ash River; River; x— xgranodiorite on on west west side side of of Pelican Pelican La Lake; —small granodiorite ke;. -small bodies and neosomes of neosomes of early early migiuatites. migmatites. b) Lac La Croix Croix Granite Granite c)) Leucogranite Leucogranite c 104 �relationships relationships in in this this quartz quartz diorite, diorite, with with magnetite/hematite magnetite/hematite intergrowths intergrowths forming fine exsolution laaellae along cleavage forming fine exsolution lamellae along cleavage traces traces within within the the central central portion (ferrohastingsite). portion of of the the amphibole amphibole(ferrohastingsite). The The other other early early plutonic plutonic phase phase which whichhas hassignificant significantarea). areal exposure exposure is a weakly foliated, coarse—grained, biotite—hornblende granodiorite is a weakly foliated, coarse-grained, biotite-hornblende granodiorite that that occurs Modal proportions proportions are are 1 ) . Modal occurs at at the the west west end end of of Pelican Pelican Lake Lake (Figure (Figure1). plotted plotted in in Figure Figure3a. 3a. The The granodiorite granodiorite occupies occupies the the nose nose of of aa broad broad westwestplunging fold, with the east—west-trending limbs extending ward plunging fold, with the east-west-trending limbs extending into into ward to poor Due to poor exposure, exposure, the thestrat— stratgranite—rich granite-rich and and schist—rich schist-rich migmatite. migmatite. Due igraphic is uncertain, considered igraphic position position of of this this body body is uncertain, but but it itisis consideredto tobe be an early early plutonic plutonic phase. phase. an The The biotite biotite tonalite tonalite and and trondhjemite trondhjemitewithin within the theVermilion VermilionGranitic Granitic Complex Complex occur occur as as dikes dikes and and small small irregular irregular bodies bodies intruding intruding metamorphic metamorphic Locally these these create create an an early early migmatite migmatite which which is is crosscut crosscut country rock. rock. Locally country The tonalite and trondhjemby Lac Lac La La Croix Croix Granite Granite and and by by leucogranite. leucogranite. The tonalite and trondhjemby ite ite are are light light gray, gray, weakly weakly foliated, foliated, medium— medium- to to coarse—grained, coarse-grained, and and They intrude the country rockalong alongfoliation, foliation, hypidiomorphic hypidiomorphic in in texture. texture. They intrude the country rock and in in places places are are folded folded syntectonically syntectonically with with it. it. and Granite Granite Lac La La Croix Croix Granite Granite Lac This very very mass mass of of granite granite is is fairly fairly homogeneous homogeneous in in composition, composition, is is This r medium— medium- to to coarse—grained, coarse-grained, and and has has hypidiomorphic hypidiomorphic granular granular texture. texture. Floating Floating blocks blocks of of partly partly digested digested biotite biotite schist schist and and amphibolite amphibolite make make up up no no more more than than 55 percent percent of of the the rock rock within within the the area area mapped mapped (Southwick (Southwickand and to Ojakangas, 1979a). 1979a). Isolated Isolated megacrysts megacrysts of of microcline, microcline, ranging ranging from from 11 to Ojakangas, Pegmatitic and aplitic dikes cut the cm in in length, length, are are widespread. widespread. Pegmatitic and aplitic dikes cut the 15 cm 15 granite granite along along parallel parallel fractures, fractures, suggesting suggesting that that solidification solidification of of the the late—stage batholith batholith was was followed followed closely closely by by fracturing fracturing and and injection injectionof of late-stage Figure 3b 3b shows shows the the modal modal range range of ofthe thedominant dominant granitic material. material. Figure granitic medium-grained granite granite of of the the Lac Lac La La Croix. Croix. medium—grained Granite Graniteof ofthe theLac LacLa LaCroix Croixtype typeforms formsthe theneosome neosome of of migmatite migmatite that that. migmatite The color color of of the thegranite graniteininthe the migmatitediverges diverges flanks the the intrusion. intrusion. The flanks from grayish—pink from the the characteristic characteristic grayish-pink of ofthe themassive massive interior interior to to aa lighter lighter granite in is better better foliated The granite in the the migmatite migmatite is foliated pink or orpinkish—white. pinkish-white. The pink sub— suband it it also alsotends tendstoward towarda acoarser, coarser, than in inthe themassive massive interior; interior; and than accessory mineral mineral in in the Magnetite is isa acommon common accessory the pegmatitic texture. texture. Magnetite pegmatitic massive interior interiorofofthe the LacLa LaCroix, Croix,generally generallyforming forming medium-grained medium-grained massive Lac In the the border border neosome neosome and and late—stage late-stage pegmatites pegmatites the the subhedral crystals. crystals. In subhedral Grout (1923, (1923, en)euhedral euhedralcrystals. crystals. Grout magnetite occurs occurs as as large large (0.5 (0.5 to to 22 cm) magnetite 1926) 1926) first first noted noted this this occurrence occurrence and and surveyed surveyed these these magnetite magnetitepegznatites pegmatites for possible economic exploitation. for possible economic exploitation. Leucogranite U co g r a n it e Le • p The maincategory categoryof of granite granite in The second second main inthe theVermilion Vermilion Granitic GraniticComplex Complex The leucogranite is restricted The leucogranite is restricted is a gray to white two-mica leucogranite. is a gray to white two—mica leucogranite. 105 �13.2 16.9 16.8 54.5 69.0 70.4 64.7 65.2 7)) Amphibolite Amphibolite 7 8) 8 ) Trondhjemite Trondhjemite 9) 9 ) Granodiorite Granodiorite 10) Tonalite Tonalite 10) Tonalite 11) Tonalite * 14.1 47.5 6) 6 ) Amphibolite Amphibolite 1.78 1.90 0.74 0.75 0.73 6.73 9.03 6.58 9.10 ±0.06 0.13 ±0.08 3.16 33.00 1.79 1.84 11.68 13.05 8.21 11.40 ±0.22 0.57 +.29 1.42 ±0.27 t42 0.35 5.79 FeO(t) 2.40 MgO 0.50 0.30 0.23 1.00 0.74 1.11 1.50 ±0.07 0.10 ±0.05 0.19 0.53 +O.iO Ti02 5.29 5.29 4.21 4 .21 2.73 2 .73 3.50 3 .50 7.80 7 .80 11.48 7.63 7 .63 11.78 1 1.78 - 0.90 0.90 +O. 35 - 0.88 +0.19 ±0.19 - 2.72 2.72 +0.39 ±0.39 cao 4.06 3.564 5.62 6.30 3.28 2.88 3.74 1.56 ±0.87 2.60 ±0.87 2.64 ±0.71 3.66 Na20 1.61 2.19 1.26 0.93 0.94 0.92 1.82 1.05 ±1.05 5.65 ±0.49 5.81 ±0.27 2.93 1(20 H20 not determined determined H20 sample. Analyses done using atomic absorption with at least ten determinations on each element per sample. 17.5 19.90 15.9 53.4 5)) I'unphibolite 5 Amphibolite 14.1 ±1.01 49.1 15.3 +0.65 ±0.48 73.7 14.7 73.4 ±1.14 ±1.06 ±1.32 16.1 63.8 4) 4 ) Mtphibolite Amphibolite 3) 3 ) Leucogranite Leucogranite ave. ave . 2) 2) Lac Lac La La Croix Croix ave. ave. 1) Biotite Schist 1) Biotite Schist ave. ave. Al203 Major—element Major-element Composition of rocks in the Vermilion Granitic Complex 8i02 TABLE 1. TABLE 1. 0.06 0.05 0.02 0.03 0.19 0.22 0.12 0.19 0.02 +0.01 ±0.01 0.02 ±0.01 0.10 MnO No. NO. 10 5 7 99.52 99.87 99.67 99.46 99.27 99.92 98.96 99.78 98.97 99.41 98.13 Samples Total* Samples Total* �a NOTES FOR FOR TABLE TABLE NOTES 1) 1) • 1 1 Biotite schist schist (average (averageof of 77 rock rockanalyses), analyses),Kabetogaina Xabetogama Lake Lake area. area. Biotite 2 ) tac Lac La La Croix Croix Granite Granite (average (average of of 55 rock rock analyses), analyses), interior interior of of 2) batholith, 11 km km spacing spacing along alongEcho Echo Trail, Trail, east east of of Little LittleSioux SiouxIndian Indian batholith, River, Shell Shell Lake Lake quad. quad. River, Leucogranite Leucoqranite (average (average of of 10 10 rock rock analyses), analyses), small small bodies bodies in in biotite biotite schists and and schist—rich schist-rich miginatite, migmatite,Kabetogama Kabetogama Lake Lake area. area. schists 3) 3) 4 ) Medium—grained Medium-grained clinopyroxene—hornblende clinopyroxene-hornblende amphibolite amphibolite paleosome, paleosome, 0.8 0.8 km km 4) (0.5 (0.5 ml) mi) west of of Crane Crane Lake Lake Road Faad on on U.S. U.S. Forest Forest Service Service Vermilion Vermilion Falls Falls 17 W., Echo Lake quad. (8—1l—VGM—14). 35, T. 67 N., R. T . 67 N . , R . 17 W . , Echo Lake quad. (8-11-VGM-14). Road, SW~/.MW~/~, sec. 35, sec. Road, SWI/4NW1/4, Foliated Foliated coarse—grained coarse-grained biotite—hornblende biotite-hornblende amphibolite amphibolite paleosome, paleosome, 3.0 3.0 sec. km Road, NE1/4SE1/4, km (1.9 (1.9 mi) mi) south southof ofCrane CraneLake LakeononCrane CraneLake Lake Road, NE~/'sE~/~, sec. 35, 35, T. T. W., Echo Echo Lake Lake quad. quad. (8—10-VGM—1OA). (8-10-VGM-10A). 67 N., N., R. R. 17 17 q•, 67 5) 5) • 6) Foliated Foliated medium—grained medium-grained clinopyroxene—hornblende clinopyroxene-hornblende amphibolite amphibolite 6) paleosome, paleosome, 4.6 4.6 km km (2.9 (2.9 ml) mi) west west of of Elephant Elephant Lake Lake on on U.S. U.S. Forest Forest Service Service 18 W., Elephant Lake 19, T. 66 N., R. quad. Cusson Road, Road, NE1/4NW1/4, N E ~ / ~ N w sec. ~ , 66 N., R. 18 W., Elephant lake quad. Cusson sec. (8-12-VSM-4). (8—12—VSM—4). Coarsegrained paleosome, NW1/4SEI/4, Coarse-grainedamphibolite amphibolite paleosome, NW~/~SE~/', sec. sec. 22, 22, t. T. 65 65 N., N., R. R. W., Picket Picket Lake Lake quad. quad. (8—9—VAN—3). (8-9-VAM-3). W., 7) 7) 8) 8) Light—gray Light-gray biotite biotite trondhjemite, trondhjemite, same same location location as as 66 (8-12—VSM—1). (8-12-VSM-1). 9 ) Biotite Biotite granodiorite, granodiorite, same samelocation locationasas6 6(8—12-VSt4—3). (8-12-VSM-3). 9) 10) Light-gray hornblende biotite biotite tonalite, tonalite, same same locations locations as as 44 10) Light—gray hornblende (8-11-VGM-15). (8—11—VGt4—15). • 1 1 ) Foliated Foliated light—gray light-gray hornblende—biotite hornblende-biotite tonalite, tonalite, U.S. U.S. Highway Highway 53, 53, 2.9 2.9 11) km km (1.8 (1.8 mi) mi) west west of of St. St. Louis Louis Co. Co. Road Road 122 122 (8-14—VGM—A). (8-14-VGM-A). p I 107 16 16 �BIOTITE SCHIST BIOTITE SCHIST 10.00 oa: 6.00 cc 4.0 ci 2.00—— 0 10.00 6.00 U. —— — 1.00 2.00 1.00 .20—— — .20 .10 .10 .06 .06 : .01— — I I MG FE TI MN SI AL CA NA : .01 K METRGRRYMRCKE ME TA G 19 A I WA CKE 10.00 o 6.00 C 10.00 L U. 4.00 2 6.00 4.00 — 0 200 .40-— —— .40 LjJ ._j a- U, .20—— .20 .10 .10 .06 .06 .04— — .04 .02—— — .02 — .01 .01— I I I I I I MCFETI MNSI ALCANA K Figure 4. Major-element data normalized against average biotite schist Figure 4. Major—element data normalized against average biotite schist from Kabetogama Lake area. from Kabetogama Lake area. a) Biotite schist at Lake Kabetogama. Note narrow range in a) Biotite schist at Lake Kabetogama. Note narrow range in composition. composition. b) Metagraywacke from neighboring greenstone belts. b) Metagraywacke from neighboring greenstone belts. 108 I �to to small tothe theneosome neosome of of schist—rich schist-rich migmatite migmatite and and to small bodies bodies within within biotite biotite The leucogranite varies along the northern border of the complex. schist schist along the northern border of the complex. The leucogranite varies greatly greatly in in mineralogy, mineralogy, texture, texture, and and geochemistry. geochemistry. S * Figure Figure 3c 3c shows shows the the modal modal variability variability of of the theleucogranite. leucogranite. The The leucogrartite contains small but persistent amounts of primary muscovite leucogranite contains small but persistent muscovite and and garnet. garnet. Garnet Garnet typically typically makes makes up up aa few few percent percent of of the the leucogranite leucogranite whereas whereas it it is is totally totally absent absent from from the the Lac Lac La La Croix Croix Granite. Granite. Magnetite, Magnetite, on on the the other other hand, hand, is is aa common commonaccessory accessoryin inthe thet.ac Lac La Croix Croix but but is is rare rare in in the the leucogranite. leucogranite. The The texture texture of of the the leucogranite leucogranite varies varies locally locally from from medium—grained medium-grained hypidiomorphic Different textural textural hypidiomorphic granular granular to to coarse—grained coarse-grained pegmatitic. pegmatitic. Different subunits leucogranite commonly commonly cut cut across across one one another another (as (asat at Wooden Wooden subunits of of the the leucogranite Frog Frog Campground; Campground) Stop Stop 13, 13, field field trip trip II, 11, this this volume). volume). These These textural textural subunits subunits are are thought thought to to be be cogenetic wgenetic and and virtually virtually coeval. coeval. Possibly Possibly the the most most significant significant feature feature of of the the leucogranite leucogranite is is its its relation Along the the relation to to the the deformation deformation history history of of the the biotite biotite schist. schist. Along south south shore shore of of Kabetogama Kabetogama Lake Lake the the leucogranite leucogranite is is isoclinally isoclinally folded folded with with biotite biotite schist; schist; the the leucogranite leucogranite has has been been boudinaged boudinaged along along isoclinal isoclinal fold fold limbs, limbs, and and thickened thickened within within hinges. hinges. Physically Physically indistinguishable indistinguishable leucogranite The seemingly seemingly leucogranite also also cuts cuts discordantly discordantly across across these these folds. folds. The incongruent incongruent timing timing of of leucogranite leucogranite emplacement emplacement is is best best explained explained by by concontinual tinual mobilization mobilization of of granitic granitic material material during during deformation deformation of of the the biotite biotite schist. schist.  I GEOCHEMISTRY GEOCHEMISTRY Biotite Biotite Schist Schist 8 P 8 0 Major— Major- and and trace—element trace-element analyses analyses were were made made to to determine determine the the geochemgeochemical nature nature of of the the biotite biotite schist schist in in the the Kabetogama Kabetogama Lake Lake region. region. To To ical obtain obtain representative representative chemical chemical analyses, analyses, rock rock samples samples were were selected selected from from average of of seven the the least—weathered least-weathered massive massive beds beds of of schist. schist. Pat An average seven separate separate analyses Figure 4a 4a displays displays the the range range of of major major eleele1. Figure analyses is is listed listed in in Table Table 1. ments Although ments for for the the specimens, specimens, normalized normalized against against the the average average schist. schist. Although beds beds with with aluminous aluminous and and quartzofeldspathic quartzofeldspathic compositions compositions do do occur occur locally, locally, This conconthe typical typical biotite biotite schist schist has has fairly fairly constant constant modal modal mineralogy. mineralogy. This the sistency sistency is is reflected reflected in in limited limited variation variation in in major major element element abundances. abundances. Figure Figure 4b 4b shows shows the the major major element element composition composition of of volcanogenic volcanogenic graywacke graywacke from from neighboring neighboring terranes terranes normalized normalized against against the the average average comcomposition of of the the biotite biotite schist. schist. Two Two new new analyses analyses of of metagraywacke metagraywacke from from position the the Rainy Bainy Lake Lake greenstone greenstone belt belt are are displayed, displayed, along along with with published published values values for for the the Knife Knife Lake Lake Formation Formation (Arth (Arth and and Hanson, Hanson, 1975), 1975), aa metasedimentary metasedimentary rock rock from from Wabigoon Wabigoon subprovince subprovince (Williams, (Williams, 1978) 1978) and and aa sample sample of of Coutchiching Coutchiching metagraywacke metagraywacke (Goldich (Goldich and and Peterman, Peterman, 1978). 1978). The The only only signisignificant MgO content content of of the the neighboring neighboring ficant variation variation is is the the higher higher MgO The observed observed higher higher MgO MgO content content could could reflect reflect aa more more metagraywackes. The mafic mafic original original composition composition within within the the metagraywackes, metagraywackes, or or it it could could reflect reflect case, the the major element element chemical chemical adjustments adjustments during during metamorphism. metamorphism. In any case, 109 �compositionof of the the biotite from Icabetogaina Lakeregion region is is very composition biotiteschist schist fromthe the Kabetogama Lake very similar ofof neighboring volcanogenic similar to tothat that neighboring volcanogenicmetasedimentary metasedimentary rocks. rocks. In 5 the contentofofaabiotite biotite schist the rare rare earth earthelement element (REE) In Figure Figure 5 (REE) content schist from the the Icabetogama Lakearea area is is compared with that metagraywacke from Kabetogama Lake compared with thatof ofa a metagraywacke from the the Rainy Lake greenstone greenstonebelt belt at from Rainy Lake at Ranier, Ranter, Minnesota. Minnesota. Also Also depicted depicted are the KEE content content of ofmetasedimentary metasedimentary rocks rocksfrom from the theKnife KnifeLake LakeFormation Formation are theBEE (Arth and Hanson, 1975) 1975)and andfrom fromthe theCrystal Crystal Lake Lake area area of of Ontario (Arth and Hanson, Ontario The REE content of the biotite schist (Williams, BEE content schist from from the the (Williams, 1978). The Kabetogama Lake Kabetogama Lake area area is is clearly clearly within within the the range range of of volcanogenic volcanogenic metagraywacke metagraywacke from from neighboring neighboring terranes. terranes. From the From the earliest earliest observations observations there there has has been been general general agreement agreement that that the protolith for the biotite schist was bedded graywacke. the protolith for the biotite schist was bedded graywacke. Alexander in the of the Winchell, the 16th 16thAnnual Annual Report Report of the Geological Geological and and Natural Natural History History Winchell, in Survey of Minnesota Survey Minnesota (1888, "the crystalline crystalline schists schistsappear appear (1888,p.p. 367) 367)states, states, "the to to me to to have have been been original original sediments sediments which which have have been been partly partly decomposed decomposed and fixed fixed in in new new combinations combinations while while in in aa semi-plastic semi-plastic state state occasioned occasioned by by heat and alkaline waters." heat and alkaline waters." Even though though our methods of investigation investigation are are more sophisticated, sophisticated, nearly nearly one one century century later later the the same same view view is is held. held. I Amphibolite Amphibolite Four samples samples from from amphibolite amphibolite inclusions inclusions within within Lac Lac La La Croix Croix Granite Granite analyzed for for major abundance(Table (Table1); 1); trace trace element element content content were analyzed major element element abundance was determined determinedfor for one one of of these In Figure was these samples samples (Table (Table 22). ). In Figure 6a 6a the themajor major elements are normalized against a low—Ti elements low-Ti basalt from the the upper member of the (Schultz, 1980). 1980). This This stanstanthe Ely Greenstone Greenstone in in the the Vermilion Vermilion district district (Schultz, dard to dard was chosen chosen because because basalts basalts like like those those in in the the Vermilion Vermilion district district to the south Outlined the south are are likely likely protoliths protoliths for for the the amphibolite amphibolite xenoliths. xenoliths. Outlined in Figure 6b Schulz (1980) (1980) 6b are are the the ranges ranges for for Ely Ely basalt basalt reported reported by Schulz and Arth and Hanson Hanson (1975), (19751, and and for for Newton Newton Lake Lake basalt basalt (Schulz, (Schulz, 1980). 1980). This plot gives gives aa feel feel for for the the normal normal range range of of major elements elements in in neigh— neighboring basalts. basalts. Although there is distinct diversity in the the geochemistry do of the the individual individual amphibolite amphibolite xenoliths, xenoliths, their their major major element element data data do display basaltic content in significantly higher higher 1(20 K20 content is aa significantly display basaltic affinity. affinity. There is amphibolite xenoliths, which the amphibolite which could could be aa result result of of metasomatism metasomatism by the the enclosing granite. enclosing granite. content of xenolith is is chondrite-normalized PEE REE content of one one axnphibolite amphibolite xenolith The chondrite—normalized plotted ininFigure sample from thethe Newton plotted Figure7,7,along alongwith witha a sampleofofbasalt basalt from Newton Lake Lake REE contents contents (Arth and and Hanson, Hanson, 1975). 1975). Williams Williams (1978) (1978) reported reportedPEE Formation (Arth for two amphibolite inclusions for inclusions within early tonalite tonalite from the the Crystal crystal Lake area, Ontario, and BEE patterns patterns were were flat flat and noted noted that that the the normalized normalized REE (approximately 1 1 x chondrites), very similar similar to to the the Newton Newton Lake Lake basalt. basalt. (approximately 11 The REE content content of of the the analyzed analyzed amphibolite amphibolite inclusion inclusion is is less less than than The overall overall PEE that that of of these these other other metabasalts metabasalts (7—9 (7-9 xx chondrites). chondrites). In addition, the the inclusion has a depleted = similar to inclusion depleted light light PEE KEE profile (La/Smn (La/% = 0.75), 0.75), similar to Type II ocean basalts identified identified by by Bryan and others Type ocean floor floor tho].eiitic tholeiitic basalts (1976). (1976). There are There are two two viable viable hypotheses hypotheses for for the the origin origin of of the the amphibolite amphibolite xenoliths. One possibility is is that that they they are are cognate cognate inclusions, inclusions, repre— repre- 110 S S �U I- C z 0 3: 0 LU -J 0 4 (I) La Ce Nd Sm Eu Gd Tb Dy Er Yb Lu REE plot p l o tof:• o f :—biotite  ¥ - b i o t i schist t s c h i s(Kabetogama t (Kabetogama Lake); Lake); Figure 55. • REE Figure A —metagraywacke, Crystal Lake, Lake, Ontario 0 —metagraywacke -metagraywacke (Ranier, (Ranier,Mn) Mn);A-metagraywacke, Crystal Ontario Cl ; (Williams,1978); 1978); O-metagraywacke, Knife Knife Lake Lake Group Group (l¼rth (Arth and and (Williams, O—metagraywacke, (Haskin and and others, others, Normalized against against chondrites chondrites (Haskin Hanson, 1975). 1975). Normalized Hanson, 1968). 1968). Ui Ill �S TABLE TABLE 2.2. Trace in rocks Trace element element abundances abundance8 in rocks of of the theVermilion Vermilion Granitic Granitic Complex, Complex, in in ppm ppm Uu Th Th Ta Ta 1 2 — 2.5 0.20 0.092 7.8 0.56 3 2.8 10.4 0.45 4 5 1.7 1.8 6.2 24.9 0.33 0.48 4.23 3.40 3.5 U Sc sc 37.3 Cr cr Ni Ni 151 79 19.1 117 82 Co CO 51.0 25.5 Rb Rb Sr sr 12 141 142 113 Ba Ba Cs cs 87 559 La La Ce ce 2.39 6.7 Nd Nd Sm sm Fu FU Tb Tb .27 — 10.9 109 28 16.5 12.1 — 6.3 1.47 296 12.3 355 803 3.30 126 6.0 126 130 542 1.51 23.09 46.6 31.83 58.9 26.83 48.8 43.80 84.0 74 84 17 24 17 31 3.94 0.95 0.47 4.38 Yb Yb Lu LU 1.73 0.63 0.36 1.52 0.23 0.25 1.02 0.35 1.15 0.21 2.92 0.65 0.16 0.30 0.061 6.01 0.57 0.47 0.66 0.11 Hf Hf 1.24 3.53 3.99 3.49 5.33 Zr zr 1.52 134 145 133 148 NOTES: NOTES : 1) 1) Foliated Foliated paleosome paleosome composed composed of of medium—grained medium-grained clinopyroxene clinopyroxene hornblende hornblende amphibolite. km (2.9 (2.9 mi) mi) west west of of Elephant Elephant Lake Lake on on U.S. U.S. Forest Forest Service Service amphibolite. 4.6 4.6 km T. 66 66 N., N., R. R. 18 18 W., w., Elephant Elephant Lake Lakequad. quad. cussonRoad, Road,NE1/4, NE1/4, NW1/4, NW1/4, sec. sec. 19, 19, T. Cusson (8-12-VSM-4) (8-12-VSM—4). 2) 2) Biotite Biotiteschist, schist,Rocky RockyPoint PointResort, Resort,SW1/4SE1/4, SW~/'SE~/~, sec. sec. 6, 6, T. T. 69 69N., N., Kabetogama Kabetogama quad. quad. (8—15—MS—5). (8-15-MS-5). R. 21 21 W., w., ft. 3) Metagraywacke, Metagraywacke, Ranier, Banier, MN MN (8-19-7). (8-19-7). 3) 4) 4 ) Early Early tonalite, tonalite, 4.3 4.3 km km (2.7 (2.7 mi) mi) west west of of Crane Crane Lake Lake Road Road on on U.S. U.S. Forest Forest Service Vermilion Vermilion Falls Falls Road, Road, NWI/45E%, NWl/isEl/4, sec. sec. 33, 33, T. T. 6767N., N., R.R. 17 17 W., W., Service Kabustasa Lake quad. (8—11—VGM—19). (8-11-VGM-19). Icabustasa 5) La Croix Croix Granite Granite 2.4 2.4 km km (1.5 (1.5 mi) mi) east east of of Little little Sioux Sioux Indian Indian River River 5 ) Lac Lac La on sec. SE~/~NW~/', sec. 1,1, T. T. 65 65 N., N., R. R. 15 15 W., W., Shell Shell Lake Lakequad. quad. on Echo Echo Trail1 Trail, SE¼NW1/4, (VLG-4B 1. (VLG—4B). Neutron Neutron activation; activation; analyses analyses done done by by Klaus Klaus Schultz Schultz at at Washington Washington University, Mo. University, St. St. Louis, Louis, Mo. 112 �XENOLITHS RMPH IBOLI TEXENOLITHS AMPHIBOLITE 10.00 y 10.00 10.00 6.00 6.00 4.00 C a: cc C z 4.00 2.00 2.00 1 1.00 (I-) .40 .40 — -j a. .20 — — .10 — — .10 .06 .04 — — .06 — — .04 .20 ra: 0- U) I- 00 .60 .60 Lii • 02 .02 .01 .01 MG FE TI MN Si AL CA NA K VERMILION DISTRICT DISTRICTBASALTS BRSRLTS VERMILION 10.00 10.00 6.00 0 cc cc 4.00 — 6.00 4.00 cc 2.00— 2.00 1.00 1.00 0 I.- (F) I— -j 0- LU ra: U, I- .60 .40 .60 .40 — .20 — b. — .20 .10 .10 .06 .04 — .06 .04 .02 — .02 .01 .01 SI AL CA NA K Major-element data data normalized normalized against againstlow—Ti low-Ti basalt basaltfrom fromupper upper Figure6.6. Major—element Figure member of Ely Greenatone (Schulz, 1980). Greenstofle (Schulz, 1980). of Ely member ~mnhibolifce xenolithswithin withinvermilion VermilionGranitic GraniticComplex. COBplex. -.Amphibolite xenoliths a)a\ MG FE TI tIN ~~~ b)Ely ~ land and y Newton NewtonLake Lake basalts. basalts. b) 113 �uJ F- Ix zC I 0 0 uJ -J 0- C (I) 200 •1 4La Ce Nd Sm Eu Gd REE Tb Dy Ho Er REE plot of amphibolite xenolith and basalt from Newton Lake Normalized against chondrites (Haskin and others, 1968). Formation. Figure 7. Yb Lu �senting sentingunmelted m e l t e d residuum residuumfrom fromthe thesource sourceregion, region, that thatwere were brought brought up up The residual phase from partial within withinthe therising risinggranitic graniticdiapir. diapir. The residual phase from partial melting light BEE content content of of 15 15 to to 20 20 xx melting of of aa graywacke grakacke should shouldhave haveaalight . BEE and chondrites, chondrites, and and aaheavy heavy BEE REE content contentof of 3—5 3-5 xxchondrites chondrites(Arth (Arth and Hanson, Hanson, 1975). This This character character is is not not displayed displayed in in the the analyzed analyzed amphtholite amphibolite 1975). xenolith. xenolith. The The second second hypothesis hypothesisis is that thatthe theamphibolite amphibolitexenoliths xenolithswere were simply simply country rock which was intruded by and entrained within the rising country rock which was intruded by and entrained within the rising granit— granitic ic melt. melt. This This is is supported supportedby by the thebasaltic basalticatajor major element element affinities affinities and and trace traceelement element abundances abundancesin inthe theanalyzed analyzedsamples. samples. This This does does not not mean mean to to imply imply that that all all of of the the amphibolite amphibolite xenoliths xenoliths within within the the complex complex have have this this origin, origin, but but the the analyzed analyzed samples samples seem seem to to have have been been country country rock rockthat that was was incorporated by the encroaching granite. incorporated by the encroaching granite. Early Early Plutonic Plutonic Rocks Bocks Major Major element element abundances abundances were were determined determinedfor for four four samples samplesof of the the The trace element content trondhjemite—granodiorite trondhjemite-granodiorite suite suite (Table (Table1). 1). The trace element content for for one ~ 1 is is~ For each each of of these these rocks rocks the the A1203 one sample sample was was determined determined (Table (Table2). 2). For greater greater than than 15 15 wt%, wt%, placing placing them them in in the the high—Al203 high-A1203 trondhjemite trondhjemitegroup group of of Barker Barker and and others others (1976). (1976). Major Major element element analyses analyses for for three three trondhjemite trondhjemite samples (1980)are are plotted plotted in in samples previously previously obtained obtained by by Southwick Southwick and and Sims Sims(1980) Figure An average average of of these these seven seven was was Figure Ba 8a along along with with the the four four new new analyses. analyses. An used used for for normalization normalization in in Figures Figures 8a 8a and and Sb. 8b. AA wide wide composition composition spread spread within within this this class class of of rocks rocks is is seen seenin in Figure as separate separate small small 8a. This This is is not not surprising surprising since since the the rocks rocks occur occur as Figure Ba. bodies Factors such such as as difdifbodies throughout throughout an an area area of of more more than than 1000 1000 km2. km2. Factors ferences ferences in in source source rock rock composition, composition, mineral mineral fractionation fractionationduring during transport transport and and emplacement emplacement of of the the melt, melt, and and subsequent subsequent metamorphic metamorphic overoverprinting printing would would contribute contribute to to the the chemical chemical variations variations observed. observed. Figure Figure 8b 8b shows shows major major element element compositions compositions for for the theSaganaga Saganaga Tonalite Tonalite and FeO and and Systematic variations variationscan canbe beseen seenininFeO and Northern Northern Light Light Oneiss. Gneiss. Systematic Ti02, in constant TiO2, which which remain remain in constant ratio ratioeven even though though their theirabsolute absoluteabundances abundances mineralsuch suchasasilmenite ilmenitein in the the source A Fe—Ti Fe-Ti mineral source basalt basaltcould couldhave have vary. A vary. buffered and Ti02 Ti02during duringmelting, melting, resulting resulting in buffered the theFeO FeO and in the thesystematic systematic behavior behavior seen seen in in the the derived derived tonalites. tonalites. The trondhjemite-granodiorite The major major element element composition composition of of the the early early trondhjemite—granodiorite suite suite of of the the complex complex is is very very similar similar to to those those of of the the Saganaga Saganaga Tonalite Tonalite and and The only only discrepancy discrepancy is is in in the the Ti02 Ti02 content, content, the the Northern Northern Light Light Gneiss. Gneiss. The Ti02 More data data which could could reflect reflectrelative relative TiO,abundance abundance in in the thesource source rock. rock. More which are needed needed in in order order to to delineate delineate this thisdifference. difference. The The chondrite— chondriteare for one one sample sampleare are plotted plotted in Also SEE abundances abundances for in Figure Figure 9. 9. Also normalized PEE normalized depicted are are the the ranges ranges for for the the Saganaga Saganaga Tonalite Tonalite and and the the Northern Northern Light Light depicted Gneiss (Arth (Arth and and Hanson, Hanson, 1975). 1975). The The trondhjemite trondhjemite has has aa steep steep negative negative Gneiss The Light—REE Light-REE content content is is pattern (La/Lun 45), and and no no Eu Eu anomaly. anomaly. The (La/Lun == 45), pattern approximately approximately 33 times times greater greater than than that that of of the the Saganaga Saganaga tonalite, tonalite, while while The overall overall PEE BEE content content is is the heavy heavy PEE BEE abundances abundances are are quite quite comparable. comparable. The the very very similar similar to to the the Northern Northern Light Light Gneiss. Gneiss. 115 0 ~ �TRONDHJEMITE-GRRNODIORITE TRONDHJEM I TE—GARNOD IOn I IF SUITE SUITE 10.00 10.00 C cc cc C 6.00 4.00 — 4.00 cc 2.00 — 2.00 1.00 — 1.00 — .60 .40 I— 8.00 U, I- .60 .40 — — Lu -J a- .20 cc U, .10 — .10 Os — I- .04 — — .06 .04 .02— — — .02 .01 — — .01 : 10.00 a. — MG FE TI (IN SI AL CR NA — .20 K SRGRNRGR TONAL TONRLITE SAGANAGA ITE 10. 00 10.00 C 0 6.00 6.00 cc a 4.00 4.00 ci: ec C z cc ^p NORTHERN LIGHT GNEISS NORTHERN LIGHT GNEISS — — 2.00 — I— 6.00 4.00 2.00 (I) 1.00 eQ S uJ -J aci: (1) 1.00 .60 40 .20 — — — — .20 b. .10 .10 .06 I— .60 .40 .08 .04 — .04 .02 — .02 .0! .0! MG FE TI MN SI AL CR NA Figure Figure8.8. K Major—element Major-element data datanormalized normalizedagainst againstaverage averageof of seven sevenearly early plutonic emite—granodiorite samples. plutonictrondhj trondhjemite-granodiorite samples. a ) Trondhjemite—granodiorite Trondhjemite-granodioritesuite, suite,Vermilion VermilionGranitic Granitic Complex. Complex. a) b) b)Saganaga SaganagaTonalite Tonaliteand andNorthern NorthernLight LightGneiss. Gneiss. 116 �I I I I I I I I ARCHEAN I I I I I I I TONALITE -- U - F— C z 0 I0 U -j --- Vermilion Granitic Complex a- - C - - (I) en 4 --- I La La I Ce Ce 1 I Pr Pr Nd Nd I Pm Pm I Sm Sm I I I I Eu Eu Gd Gd Tb Dy Dy I Ho Ho I Er Er I Tm Tm I Yb Yb I Lu LU plot of early Archean tonalites tonalites from from northern northern Minnesota. Minnesota. PEE plot Figure Figure 9. 9. BEE •—early tonalite, Vermilion Granitic Complex; fl—Northern >-early tonalite, Vermilion Granitic Complex; S-Northern Light Gneiss; Saganaga Tonalite. Tonalite. Normalized Normalized against against Gneiss; shaded shaded area area is is Saganaga chondrites chondrites (Haskin 1968). (Haskin and and others, others, 1968) 117 �^ 10.00 l0.00 C a 6.00 — 4.00 — 4.00 cE 2.00 U-) cc 0 C 10.00 LRCLA LRCROIX CROIXGRANITE GRRNITE LAC — — a. a. — 6.00 4.00 — 2.00 1.00— — 1.00 .60 — — .40 — — .60 .40 -J 0 .20 — — — .20 cc .10 — — — .10 06 — .04 — — — — — .06 .04 — — — .02 .01 — — — .0! : — 10.00 I- F— = Li-i U) F-- OZ MG FE TI MN SI AL CA NA 10.00 lO00: Cec ccU C0 zcc LRCLA LR CROIX CROIXNEOSOME NEOSOME LAC &00 — 4.00— 400 2.00 F— K — - — 6.00 4.00 2 00 U) LOU— 1.00 .60 — I— .40 — - .60 .40 - .20 Li-i a- -J .20 — cc .10 — - .10 06— : .04 — - .06 .04 U) I— = b. .02— — - .02 .01 — — — 01 MG FE TI MN SI AL CA NA LEUCOGRRNITES LEUCOGRANITES 1000: 0 6.006.00 C a:!$ cca C a a: I— (I-) I— li-i 4.00 2.00 2.00— — 2.00 L00 • element chemistry. b) Lac La Croix Granite b) Lac La Croix Granite which comprises granitic which comprises granitic neosome in granite-rich neosome in granite—rich migmatite. migmatite. c ) Leucogranite from the c) Leucogranite northern border from zonethe of the northern border zone of the Vermilion Granitic Complex. Vermilion Granitic Complex. Note average of MgO, FeO(t) Note average of MgO, FeO(t) and TiOg are significantly and Ti02 are of significantly below those the massive below those of massive Croix. interior Lac Lathe interior t.ac La Croix. 00 .60 40 — .40 .10 u) I .60 — a: massive interior of Lac ~a massive interior of Lac La Croix Granite. Croix Granite. a) Massive interior of Lac a) interior of Lac LaMassive Croix Granite. Note La Croix Granite. Note limited range in major limited in major elementrange chemistry. 6MG — .20 normalized against average 20.00 4.00— 4.00 -J 0S K Figure 10. Major-element data Figure 10. Major—element data normalized against average — .20 C — .10 .06 — .06 .04 — .04 .02 — .02 .01 0I MG FE TI MN SI AL CA NA I K 118 I �Hanson Hanson and and Goldich Goldich (1972) (1972)and and Arth Arth and and Hanson Hanson (1972, (1972, 1975) 1975) advanced advanced aa partial melting model for the origin of the Saganaga Tonalite and partial melting model for the origin of the Saganaga Tonalite and Northern Northern Light Archean tholeiitic tholeiitic material material was was metametaLight Gneiss. Gneiss. They They argued argued that that Archean morphosed morphosed to to amphibolite amphibolite or or eclogite eclogite grade, grade, and and upon upon 20% 20% partial partial melting melting would would produce produce the the REE REE content content observed. observed. This This model model is is consistent consistent with with the the In order for this model to produce REE experimental work of Green (1973). experimental work of Green (1973). In order for this model to produce BEE abundances abundances found found in in the the trondhjemite trondhjemite of of the the Vermilion Vermilion Granitic Granitic Complex, Complex, the degree of partial melting would have been less (<5%) and/or the degree of partial melting would have been less (<5%) and/or the the source source basalt was slightly enriched in light REE. basalt was slightly enriched in light REE. Granite Granite Lac Lac La La Croix Croix Granite Granite Five Five rock rock samples samples spaced spaced approximately approximately 11 km km apart apart within within the the massive massive interior of the batholith were analyzed to establish a representative interior of the batholith were analyzed to establish a representative average average composition composition for for the the Lac Lac La La Croix Croix Granite. Granite. This This average average for for the the major elements is listed in Table 1, and is used for normalizing granite major elements is listed in Table 1, and is used for normalizing granite compositions Figure lOa 10a displays displays the the narrow narrow range range in in compositions in in Figures Figures ba—c. 10a-c. Figure The individual major element composition for the massive Mc La Croix. major element composition for the massive Lac La Croix. The individual compositions compositions of of five five Lac Lac La La Croix Croix neosome neosome portions portions from from granite—rich granite-rich As can be seen, migmatite are plotted in Figure tUb. there is is aa greater greater migmatite are plotted in Figure lob. As can be seen, there diversity in neosome compositions relative to the massive interior. diversity in neosome compositions relative to the massive interior. This This probably probably reflects reflects country country rock rock assimilation assimilation which which has has contaminated contaminated these these granite granite neosomes. neosomes. plotted is aa new new REE BEE analysis analysis from from the the massive massive interior interior 1 1 is plotted in in Figure Figure 11 of of the the Lac Lac La La Croix Croix Granite, Granite, compared compared with with the the field field for for Giants Giants Range Range granites granites (Arth (Arth and and Hanson, Hanson, 1975). 1975). Both Both the the Mc Lacl.a La Croix Croix and and Giants Giants Range Range granites Ce content content (between (between granites have have steep steep negative negative chondritic chondritic patterns, patterns, high high Ce 100—45 100-45 xx chondrites), aa negative negative Eu Eu anomaly, anomaly, and and low low Lu Lu content content (3.5—2.5 (3.5-2.5 xx chondrites). Arth Arth and and Hanson Hanson (1975) (1975) proposed proposed that that the the batholithic batholithic gran— granchondrites). ites ites were were derived derived from from 20-50% 20-50% partial partial melting melting of of aa short—lived short-lived (<50 (<50m.y.) my.) graywacke graywacke source source at at crustal crustal depths. depths. Sims Sins (1976) (1976) proposed proposed that that this this depth depth was kbars). was between between 99 and and 12 12 kilometers kilometers (2—3 (2-3 kbars). initial The 8sr/86sr initial ratio The low low ^sr/^sr ratio (0.7004) (0.7004) indicates indicates that that the the source source for for the This dicdicthe Lac Lac La La Croix Croix was was relatively relatively young young at at the the time time of of melting. melting. This tates tates that that the the batholithic batholithic granite granite did did not not melt melt from from early early or or middle middle Archean Archean sialic sialic crustal crustal material. material. However, tonalitic tonalitic to to granodioritic granodioritic plutonism plutonism did Therefore, it it is is did occur occur early early during during the the evolution evolution of of the thecomplex. complex. Therefore, feasible feasible that that the the batholithic batholithic granite granite may may have have melted melted from from slightly slightly older older tonalite tonalite and and granodiorite, granodiorite, or or from from short—lived short-lived graywacke, graywacke, as as Arth Arth and and Hanson (1975)originally originally suggested. suggested. Hanson (1975) Rye Rye and and Roy Roy (1978) (1978)investigated investigated the the Th—U—K Th-U-K systematics systematics of of the the Vermilion Vermilion Granitic Granitic Complex, Complex, trying trying to to delineate delineate the the origin origin of of granite granite within within the them.igmatite. migmatite. If If the the mtgmatite m b t i t e formed formed by by in in situ sit" partial partial melting melting in in a a closed closed system, system, the thesum sum of of the the thorium thorium and and uranium uranium in in the the paleosome paleosome should equal plus neosome neosome should equal the the original original starting starting protolith protolith composition. composition. plus foundthat that the Rye Rye and and Roy Roy found the radioelement radioelement content content within within the themigmatite migmatite exceeded by 22 to to 33 times starting exceeded by timesthe thepresumed presumed Knife Knife Lake—like Lake-like starting 119 �LU I- 0 z 0 0 I U -J 0 C (J) La Figure 1 1 . Ce Nd Sm Eu Gd Tb Dy Er Yb Lu REE plot of Lac La Croix Granite and range of Giants Range Figure Granite. 11. REE Normalized plot of Lac against La Croixchondrites Granite and (Haskin others, 1968). range and of Giants Range Granite. Normalized against chondrites (Haskin and others, 1968). 120 �0 composition. composition. They They concluded concluded that that the the additional additional thorium thorium and and uranium uranium were were introduced introduced into into the the migmatite migmatite system system by by the the granitic granitic leucosome leucosome component, component, possibly possibly having having been been transported transportedin in the the volatile volatile phase phase derived derived from from the the intruding intruding granitic granitic batholith. batholith. Leucogranite Leucogranite • were determined determined on on 10 10 leucogranite leucogranite samples Major Major element element abundances abundances were samples from from the the northern northern border borderzone zoneof ofthe theVermilion VermilionGranitic GraniticComplex. Complex. An An individual analyses average for these these is is listed average for listedin inTable Table 1. 1. The The individual analyses are are plotted plottedininFigure FigurelOc, lOc,normalized normalizedagainst againstthe theaverage averageLac LacLa La Croix Croix granite. Clearly there there is is aa wide wide range range in in major major element element composition composition granite. Clearly within within the the leucogranite, leucogranite, and and some some overlap overlap with with the the Lac Lac La La Croix Croix comcomposition The distinguishing distinguishing feature feature between between the the two two granite granite types types position field. field. The is is that that the the MgO, MgO, total total FeO, FeO, and and Ti02 Ti02 abundances abundances in in the the average average leucogranite leucogranite are are well well below below the the observed observed values values for for the the Lac Lac La La Croix. Croix. This This may may be be attributable attributable in in part part to to higher higher modal modal abundances abundances of of magnetite magnetite and and biotite biotite in La Croix Croix (Tables (Tables 111—22 111-22 and and 111—24; 111-24; Southwick, Southwick, 1972). 1972). in the the Lac Lac La The The origin origin of of the the leucogranite leucogranite is is ambiguous ambiguous and and complex, complex, with with field field The granite melt may have evidence allowing two end member hypotheses. The granite melt may have evidence allowing two end member hypotheses. been been generated generated from from biotite biotite schist schist during during ultrametamorphism ultrametamorphism as as an an in in situ situ melt phase, or it may have been produced within a separate source region melt phase, or it may have been produced within a separate source region and localThe best evidence evidence for for the the local— and injected injected into into the the biotite biotite schist. schist. The hypothesis is found in the biotite schist along the northern source source hypothesis is found in the biotite schist along the northernborder border There, one one can canobserve observenarrow narrowpegmatitic pegmatitic"sweat—out" "sweat-out" zone zone of of the thecomplex. complex. There, • • pods and thin thin granitic pods and granitic and and granodioritic granodioriticstringers stringerswhich which are arebordered bordered by by a a biotite These thin thin biotite selvage selvage zone zone depleted depleted in in leucocratic leucocratic minerals. minerals. These are syntectonically deformed with the biotite schist, stringers stringers are syntectonically deformed with the biotite schist, and and for the the Evidence for coalesce coalesce into into larger larger veins veins and and small, small, irregular irregular bodies. bodies. Evidence injection hyothesis is best seen within the schist—rich m.igmatite. injection hyothesis is best seen within the schist-rich migmatite. Paleosomes Paleosomes of of biotite biotite schist schist are are rafted rafted within within leucogranite, leucogranite, the theborders borders which are sharp and distinct, without obvious mineral depletion of of which are sharp and distinct, without obvious mineral depletion zones zones or or mafic mafic selvages. selvages. A plausible plausible explanation explanation for for the the origin origin of of the the leucogranite leucogranite is is aa comcomIn this scenario, anatectic bination of both end—member hypotheses. bination of both end-member hypotheses. anatectic melt was was generated generated within within aa volcanogenic volcanogenic metasedimentary metasedimentary pile pile at at crustal crustal levels levels This melt phase was during regional metamorphism and deformation. This melt phase was con— conduring regional metamorphism and deformation. tinually tinually being being formed formed and and remobilized remobilized syntectonically syntectonically within within the the metasedi— metasedimentary rocks, infiltrating into the structurally higher portion mentary rocks, infiltrating into the structurally higher portion of of the the The initiation of the early anatectic melt may have been triggered pile. pile. The initiation of the early anatectic melt may have been triggered by heat heat and and volatiles volatiles derived derived from from the the rising rising mass mass of of Lac Lac La La Croix Croix Granite Granite. I for the the Origin of the Summary Summary Model Model for Origin of the Vermilion Granitic GraniticComplex Complex A frameworkfor forthe the petrogenesis petrogenesis of of the A framework the Vermilion Vermilion Granitic Granitic Complex is Complex is is an iterated iterated version version of the the history history proposed proposed by outlined outlined below. below. This is This model model is is founded founded on on the the geologic geologic mapping mapping and and Southwick (1978). (1978). This Southwick structural structural studies studies of of Southwick Southwick (1972), (1972). Southwick Southwick and and Ojakangas Ojakangas (1979a) (1979al 121 �and Southwjck Southwick and and Sims Sins (1980). (1980). The geochemical geochemical guidelines for this this model are the the major and trace trace element element arguments arguments presented above, and and those those by by Goldich and others Goldich others (1972), (19721, Arth and and Hanson Hanson (1975), (19751, Barker Barker and and Arth (1976), (1976), and Rye Bye and and Roy Boy (1978). (1978). Trondhjemitic—granodiorite Trondhjemitic-granodiorite magmas were melted from from amphibolite/ amphibolite/ 11)) eclogite at mantle km) leaving leaving aa residue residue of of garnet, garnet, eclogite mantle depths depths (10 (10 kb; 30 30 km) pyroxene and/or hornblende. This early magma rose to the surface surface and vented, providing volcanogenic Small vented, volcanogenic detritus detritus for for the the graywacke graywacke sequence. sequence. Small of cosanguinous trondhjemite—granodioriteliquids liquids penetrated penetrated those cosanguinous trondhjemite-granodiorite those bodies of sedimentaryrocks, rocks, creating creating the Basaltic volcanism sedimentary the early earlymigmatite. migmatite. Basaltic volcanism added added a mafic to the the supracrustal supracrustal sedimentary a mafic component component to sedimentary sequence. supracrustal rocks metamorphosed, 2) 2) The The supracrustal rocks were were buried, buried,regionally regionally metamorphosed, and and tectonized. Incipient Incipient anatexis liquid of of the tectonized. anatexis occurred, occurred, producing producing liquid the leucogranite suite. suite. This leucogranite Thisleucogranite leucogranitewas wascontinuously continuouslyformed formed and and underunderwent went syntectonic syntectonic mobilization into higher portions of the supracrustal supracrustal pile. magma of of the the Lac Lac La Croix crustal levels (9—12 Croix Granite Granite krn) magma 33)) At At deeper deeper crustal (9-12 kin) plu— was generated from more complete partial melting of graywacke graywacke and/or and/or plutonic rock tonic rock of of the the tonalite—granodiorite tonalite-granodiorite suite. This episode of melting biotite. left a residue of plagioclase, amphibole, garnet, and pyroxene or biotite. ratio The low low intial intial $7Sr/86sr ^sr/^sr ratio suggests suggests that that the the source source for for the the Lac Lac La La Granite was younger Croix Granite younger than than 50 50 m.y. m.y. at at the the time time of of melting. melting. The Lac La Croix magma rose diapirically diapirically into the supracrustal supracrustal rocks rocks 4) 4) early migmatite. This rising heat source risingdiapir diapirmay may have have been been the heat source and early migrnatite. This that initiated and/or metasedimentary that initiated and/orperpetuated perpetuatedmelting meltingwithin withinthe the metasedimentary rocks. rocks. The granitic granitic diapir struc5) 5) The diapir passively passively intruded intrudedalong along the thepre—existing pre-existing structural grain, tural grain,assimilating assimilatingand and entraining entraining portions portions of of the thecountry country rock. rock. Granite—rich and and schist-rich schist—rich migmatites migmatites were were formed, formed, depending depending on on the the Granite-rich amountofofgranite granite intruded intruded into into the Volatile—rich fluids fluids amount the country country rock. rock. Volatile-rich accompaniedthe the granite accompanied graniteneosome, neosome, concentrating radioelements in the roof and border border zones zonesof of the the diapir. diapir. and structural effect granite emplacement tobroaden broaden and The structural effectofofthe the granite emplacementwas was to 6)) The 6 earlier regional flatten earlier flatten regional folds. The western portion of the Vermilion Granitic Complex was near the the roof roof of of the the granite granite diapir. diapir. 122 �. FIELD FIELD TRIP TRIP II: 11: THE INTERNATIONAL INTERNATIONALFALLS-ICABETOGANA FALLS-KABETOGAMA ARCHEAN GEOLOGY GEOLOGY OF THE ARCHEAN AREA, MINNESOTA MINNESOTA AREA, R.W. W.C. Day, Day, and and D.L. D.L. Southwick Southwick R.W. Ojakangas, Ojakangas, W.C. Objectives Objectives and and Regional Regional Relationships Relationships The objective objective of of this this field field excursion excursion is is to to illustrate illustratethe thegeology geology of of the two Archean Archean terranes in northern northern Minnesota. Minnesota. The The first first part part of of the the trip, trip, two terranes in 1—10, will focus on the metavolcanic and metasedimentary rocks stops 1-10, will focus on the metavolcanic and metasedimentary rocks of of stops the (Ojakangas, 1972), 1972), which which are are at at the the south south edge edge of of the the the Rainy Rainy Lake Lake area area (Ojakangas, wabigoon Wabigoon subprovince subprovince of of the the Superior Superior province province of of the the Canadian Canadian Shield Shield (see (see ~ i g s .I1 and and 2, 2, map map A). A). The The second second part, part, stops stops 11—18, 11-18, will will focus focus on on the the Figs. transition transition southward southward from from metagraywacke metagraywacke (biotite (biotiteschist) schist) into into the the Vermilion Granitic Granitic Complex Complex (see [see Figs. Figs. I1 and and 3, 3, map map B). B). The The rocks rocks at at stops stops Vermilion 11-18 are are all all in in the the Quetico Quetico subprovince. subprovince. 11—18 • The The trip trip starts starts in in the the metavolcanic—metasedimentary metavolcanic-metasedimentary terrane terrane of of the the Rainy Rainy Lake Lake area area east east of of International International Falls, Falls,Minnesota. Minnesota. Metagraywacke, Metagraywacke, greenstone, tuffaceous tuffaceous biotite—chiorite biotite-chlorite schist, schist, felsic felsic tuft, tuff, feldspathic feldspathic greenstone, quartzite, The Rainy Rainy Lake—Seine Lake-Seine River River be examined. examined. The quartzite, and and conglomerate conglomerate will will be fault fault (unexposed (unexposed in in Minnesota) Minnesota) marks marks the the boundary boundary between between greenschist greenschist facies facies metamorphic metamorphic lithologies lithologies to to the the north north and and somewhat somewhat higher—grade higher-grade metagraywacke bemetagraywacke (biotite (biotiteschist) schist) to to the the south, south, and and also also is is the the boundary boundary be— The broad broad belt belt of of biotite biotite tween the the Wabigoon Wabiqoon and and Quetico Quetico subprovinces. subprovinces. The tween schist schist south south of of the the fault fault originally originally was was included included in in the the Coutchiching Coutchiching Series of of Lawson Lawson (1913). (1913). The The equivocal equivocal relationship relationship of of these these metasedimen— metasedimenSeries tary on the the north north was was central central to to the the classic classic tary rocks rocks to to metavolcanic metavolcanic rocks rocks on debate debate about about the the stratigraphy stratigraphy and and structure structure of of the the Rainy Rainy Lake Lake area area (Adams (Adams and and others, others, 1905; 1905; Lawson, Lawson, 1913), 1913), and and still still has has not not been been firmly firmly resolved. resolved. In to the the proper proper stratigraphic stratigraphic posiposiIn view view of of the the continuing continuing uncertainty uncertainty as as to tion tion of of these these rocks, rocks, they they are are now now mapped mapped in in Minnesota Minnesota simply simply as as unnamed unnamed biotite schist. schist. Similar Similar rocks rocks directly directly along along strike strike in in Canada Canada have have biotite recently recently been been termed termed the the Quetico Quetico metasediments metasediments by by wood Wood (1980), (1980), who who proproposed posed that that the the name name be be used used informally. informally. Two—mica Two-mica leucogranite leucogranite of of proposed proposed anatectic anatectic origin origin has has been been emplaced emplaced The relative relative abundance abundance of of the the leucogranite leucogranite into into the the biotite biotite schist. schist. The increases southward toward toward the the Vermilion Vermilion Granitic Granitic Complex; Complex; the the north north conconincreases southward tact tact of of the the complex complex with with biotite biotite schist schist is is gradational gradational and and is is mapped mapped arbitrarily subequal to to biotite biotite arbitrarily at at the the horizon horizon where where leucogranite leucogranitebecomes becomessubequa]. Within the the contact contact zone zone the the biotite biotite schist schist is is also also intruded intruded by by schist. schist. within tonalite by grayish—pink grayish-pink tonalite and and granodiorite, granodiorite, which which in in turn turn are are cut cut across across by granite granite equivalent equivalent to to the the Lac Lac La La Croix Croix Granite, Granite, the the major major intrusive intrusive phase phase The nature nature of of of of Vermilion Vermilion Granitic Granitic Complex Complex (Southwick (Southwick and and Sims, Sims, 1980). 1980). The these these intrusive intrusive events events and and the the textures textures of of the the migmatites migmatites produced produced will will be be examined examined at at several several stops. stops. The road log log for for this this trip trip includes includes more more stops stops than than can can be be visited visited on on The The leaders leaders will will select select among among the the stops, stops, taking taking into into aa one—day one-day excursion. excursion. The account time of of day, day, and and group group desires. desires. account road road conditions, conditions, time 123 �to '-a 'a 9 3° 30' 0- I 0 48°30' , I I 5 10 Miles MAP ® Figure 1. General location map showing the areas covered by detailed maps A and B. -— in- 9245' �S ROAD LOG LOG ROAD • This road This road log l o g starts s t a r t s at a t the t h e intersection i n t e r s e c t i o n of of U.S. U.S. Highway Highway 53 53 and and Minnesota Highway 11 near the center of International Falls, Minnesota Highway 11 near the center of I n t e r n a t i o n a l F a l l s , Minnesota (3rd Ave. Ave. and 4 4th Part of the ttrip t h St.) St.) and terminates terminates at a t Ash Ash River. River. P a r t of rip duplicates stops in an earlier guidebook by Southwick and Ojakangas d u p l i c a t e s stops i n an e a r l i e r guidebook by Southwick and Ojakangas (1979b); tthe regional geology geology of of tthe area tto be covered is is shown aatt sscale cale (1979b); h e regional h e area o be 1:250,000 on the geologic map of Minnesota, International Falls sheet 1:250,000 on t h e geologic map of Minnesota, I n t e r n a t i o n a l F a l l s sheet Stops 1 1 tto plotted (Southwick and Ojakangas, Ojakangas, 1979a). 1979a). Stops o 11 aare re p l o t t e d on Fig. Fig. 2, 2, map A; stops 12-18 are on Fig. 3, map B. A; s t o p s 12-18 on Fig. 3, map B. Approximate Approximate Mileage [accumulated i n brackets] brackets1 Mileage [accumulated mileage mileage in S 0.0 0.0 [0.01 r0.01 Junction with with U.S. U.S. 53 and Minnesota Minnesota Highway Highway 11. Proceed east Junction 53 and 11. Proceed e a s t on on Highway 11. Highway 11. 1.4 1.4 [1.4] r1.41 Bridge. Bridge. 1.2 [2.6] [2-61 Junction with with Koochiching Koochiching County County Highway Highway 20; Junction 20; tturn u r n left l e f t (north) (north) tto o Ranier. Banter. 0.35 0.35 [2.951 [2.95] Metasedimentary rocks which Lawson STOP 1. STOP 1. Metasedimentary rocks which Lawson (1913) (1913) called c a l l e d the the Coutchiching in the Rainy Lake area are present near Coutchiching i n the Rainy Lake area a r e present near both both Fort Fort This exposure of Frances and IInternational n t e r n a t i o n a l Falls. Falls. This of metagraywacke (fine—grained biotite i s representative (fine-grained b i o t i t e schist) s c h i s t ) is The b best expoof tthe e s t expoof h e least l e a s t metamorphosed metamorphosed parts p a r t s of of this t h i s unit. unit. The ssure u r e has been a small knob just j u s t south of of the t h e municipal liquor growth, sodding and concrete have in in eestablishement, s t a b l i s h m e n t , but lichen growth, recent years p partially a r t i a l l y obscured the t h e original o r i g i n a l sedimentary N. 45° E./80° NW. NW. and sstructures. t r u c t u r e s . The beds have an attitude a t t i t u d e of of N. 45O E./80 display d i s p l a y excellent e x c e l l e n t grading with tops to t o the t h e northwest. northwest. Lineations plunge to the north—northeast SmallSmallnorth-northeast at a t 45—50°. 45-5O0. Lineations scale cross—bedding occurs locally in interbedded silty s c a l e cross-bedding locally i n s i l t y laminae visible places. and flame structures s t r u c t u r e s are v i s i b l e in i n a few places. o and Although aa few few llarge a r g e detrital d e t r i t a lgrains grainsofofquartz quartz andpla— plathese exposures consist dominantly of gioclase are present, present, these consist of g i o c l a s e are recrystallized plagioclase, with lesser amounts of ffinely i n e l y r e c r y s t a l l i z e d plagioclase, with lesser amounts of general the the rocks biotite; i s rare. rare. IIn n general qquartz u a r t z and b i o t i t e ; garnet garnet is resemble coarser grained garnet— garnet- and staurolite—bearing staurolite-bearing biotite biotite of the greenstone belt, b e l t , some some of sschists c h i s t s that t h a t crop out south of w i l l be be seen seen in i n the the last l a s t several several stops stops on on this this field field which will ttrip. rip. some route route to to Highway Highway 11. 11. Return over some 0.35 0.35 [3.31 (3.31 Junction with Highway 11; 11; tturn u r n left l e f t (east). (east). 2.5 2.5 [5.8] t5.81 Junction with with Koochiching Koochiching County Junction County Highways Highways 20 20 and and 109. 109. rright i g h t (south) (south) and and follow follow Highway Highway 109. 109. 125 Turn Turn �0\ t.J I-. 930 rns3, ms2, metasedimentary rocks, undivided; chiefly metagraywacke mniv, mixed volcanic and volcaniclastic rocks (chiefly mafic) fqc, feldspothic quartzite and conglomerate c Irnmv BEDDED ROCKS 1 Figure 2. Simplified geology map of the Rainy Lake area showing locations of stops through 11 dikes of Proterozoic age. Dl ABASE I\dl INTRUSIVE ROCKS �I 1.2 1 .2 [7.0] [7.01 P This exposure exposure of feldspathic—lithic feldspathic-lithic guartzite quartzite is is one one of a number that form a discontinuous easterly—trending belt 16 discontinuous easterly-trending 16 km long east—northeast, are long and and 0.8 0.8 km km wide. wide. The beds strike strike east-northeast, axe vertical to the the east east at at vertical to to slightly slightly overturned, overturned, and and plunge plunge to 3°55°. cross—beds indicate that the unit 3°-550 Abundant Abundant cross-beds indicate that the unit dips dips to to the the south. south. The The cross—bedding cross-bedding (trough—type) (trough-type) is is partially partially obscured obscured by shearing; shearing; it it is is best best seen seen on on the the south south side side of of the the exposure exposure about original clastic texture about 30 30 mm east east of of the the road. road. The is The original clastic texture is commonly commonly well well preserved preserved in in spite spite of of pervasive pervasive shearing. shearing. Quartz Quartz comprises comprises 50 50 percent of of the the rock; rock; other other grains grains in in the the abundant abundant sericitic sericitic matrix matrix include include felsic felsic to to intermediate intermediate volcanic volcanic rock rock fragments, plagioclase, plagioclase, K—feldspar, K-feldspar, felsic felsic plutonic plutonic rock rock fragments, fragments, carbonate carbonate and and pyrite. pyrite. This quartzite quartzite and and the the conglomerate are equivalent equivalent to to the the Seine Seine Series Series conglomerate of of stop stop 88 are (Seine (Seine Conglomerate) Conglomerate) to to the the east—northeast east-northeast in in Ontario Ontario in in the the same same greenstone greenstone belt. belt. Lawson Lawson (1913) (1913) called called these these units units Huronian, noted noted that that they they clearly clearly overlie overlie an an unconformity unconformity in in Huronian, Ontario, and and placed them them at at the the core core of of aa syncline. syncline. Grout Grout (1925a) (1925a) said said the the structure structure was was an an anticline. anticline. Ojakangas Ojakangas (1972), (19721, partly partly on on the the basis basis of of the the consistent consistent southerly southerly topping topping direcdirection of of the the cross—beds, cross-beds, interpreted tion interpreted them them to to be be part part of of aa southward-facing fault block. accompanying text southward-facing fault block. (See (See accompanying text in in this this volume.) The The quartzites quartzites are are interpreted interpreted as as braided braided stream stream volume.) deposits abstract by deposits with with the the source source to to the the north. north. (See (See abstract by Ojakangas and Olson, this volume.) Ojakangas and Olson, this volume.) STOP STOP 2. 2. Turn Turn around around and and return return to to Highway Highway 11. 11. [8.2] [8.21 Turn Turn right right (east) (east) and and proceed proceed to to low low rock rock outcrop outcrop on on left left (north) side of highway just west of Bohman Airways. (north) side highway just west of Bohman Airways. 0.9 STOP STOP 3. 3. 1.2 1.2 (9.1] [9.11 This This outcrop outcrop consists consists of two two lithologies: lithologies: (1) (1) aa mixed schist schist (thin (thin alternating alternating laminae laminae of of chloritic chloritic and and biotitic biotitic fine—grained fine-grained schist) schist) which which is is in in part part ankeritic ankeritic or or sideritic sideritic and ic hypabyssal (B) massive massive greenstone greenstone (metamorphosed (metamorphosedmat mafic hypabyssal and (B) intrusive intrusive rocks) rocks) on on the the northwest northwest part part of of the the outcrop. outcrop. Eastward Eastward along along strike strike are are greenschists. greenschists. The The mixed schist schist is is interpreted interpreted as as aa sheared sheared tuffaceous tuffaceousrock. rock. (This (This locality locality is is about north of Riverfault.) fault.) km north of the theRainy RainyLake—Seine Lake-Seine River about 2.5 2.5 km 0.1 0.1 [9.21 19-21 Continue across bridge bridge over Continue east east on on Highway Highway 111 1 across over Jackfish JackfishCreek. Creek. 0.2 0.2 Turn on on Koochiching County Turn left left(north (north Koochiching CountyHighway Highway 103. 103. (9.4] 19.41 0.4 0.4 STOP STOP 4. 4. (9.81 L9.81 Some Some traces traces of of sheared sheared pillows pillows may may be be present. present. About About 10 10 mm west west of of driveways driveways in in woods woods is is aa very very coarse—grained, coarse-grained, massive massive Greenschist .1—10, Greenschistoutcrops outcropsbybydriveways driveways J-10,.1—11 J-11and and.1—12. J-12. greenstone containing crystals with greenstone containing long long pyroxene pyroxene crystals with aa"branching" "branching" habit spihabit (quench (quench textures, rapid crystallization?) crystallization?) resembling resembling spi— nifex nifex texture. texture. 127 �S Proceed Proceed eastward. eastward. 0.8 0.8 (1.2 (1.2 mi mi in in from from Hwy Hwy 11) 11) 0.2 0.2 [10.81 [10.8] (1.4 (1.4 mi mi in in from from Hwy Hwy Greenschist Greenschist with with granitic granitic stringers stringers from from the the west west end end of of Grassy Grassy Island Island "tonalite", "tonalite", aa 44 km km long long by by 0.3 0.3 km km wide wide intrusion. intrusion. To To the the south south of of the the road road and and to to the the north north on on the the lakeshore NNW and and diabase dike dike which which trends trends NNW lakeshore is is aa 30 30 meter—wide meter-wide diabase has has been been dated dated at at about about 2200 2200 m.y. m.y. by by Hanson Hanson and and Maihotra Malhotra (1971). This This dike dike is is the the western western dike dike of of aa closely closely spaced spaced pair pair (1971). of of dikes dikes which which lines lines up up with with dike dikeexposures exposuresnear nearIcabetogama Kabetoqama Lake km to to the the south south and and with with other other dike dike exposures exposures as as far far as as Lake 22 22 km 40 40 km km to to the the southeast southeast and and as as far far as as 25 25 km km to to the the northwest northwest near near the the Quetico Quetico Fault. Fault. STOP STOP 5. 5. [10.61 (10.6] 11) 11) 0.4 greenschist and STOP STOP 6. 6. Large Large roadcut roadcut on on hilltop hilltop of of greenschist and "mixed "mixed schist" Disseminated boudinaged quartz quartz and and granite. granite. Disseminated schist" with with minor minor boudinaged pyrite pyrite and and minor minor chalcopyrite chalcopyrite are are present present in in this this cut. cut. I S Continue Continue south south past past other other outcrops outcrops of of biotite biotite schist schist and and seri— sericite cite schist schist (metamorphosed (metamorphosedfelsic felsic tuffs tuffs and and metasediments?). metasediments?). Junction 11. Junction with with Highway Highway 11. Turn Turn left left (east). (east). [11.2] Turn Turn 1.6 [12.8] Junction Junction Highway Highway 11 1 1 and and Koochiching Koochiching County County Highway Highway 138. 138. left left (north). (north). 0.3 [13.1] Crossing Crossing topographic topographic low low along along Rainy Rainy Lake—Seine Lake-Seine River River Fault. Fault. 0.45 [13.55] STOP 7. Gravel Gravel pit pit in in wood wood just just to to the the left left (west) (west) of of highway highway STOP 7. near near top top of of hill. hill. Sheared greenschist greenschist in the the Rainy Lake—Seine Lake-Seine Quartz and rusty River River Fault Fault zone zone is is visible visible here. here. Quartz rusty carbonate carbonate pods pods are are abundant abundant in in phyllitic phyllitic greenschist. greenschist. The The only only productive productive gold gold mine mine in in Minnesota Minnesota was was located located on on Little The km east east of of this this point. point. The Little America America Island Island just just 2.5 2.5 km Little Little America America mine, mine, in in aa 22 meter—wide meter-wide composite composite quartz quartz vein vein with with intermixed intermixed schist, schist, produced produced $4600 $4600 worth worth of of gold gold in in Several other other prospects prospects were were located located farther farther east. east. 1894—1895. 1894-1895. several On km to to the the east, east, aa prominent prominent gossan gossan is is On Bushyhead Bushyhead Island Island 66 km exposed exposed in in an an old old adit. adit. Continue Continue north. north. 0.1 - at next junction Fork and at junction as as well. well. Fork in in road road — bear right here and [13.65] 0.55 [14.2] S "Neil Point conglomerate" conglomerate" by garage and by house This unit, aa large large lens lens 180 180 m thick thick overlooking overlooking fault fault zone. zone. This and at least 4.5 km long, overlies the feldspathic—lithic and at least 4.5 km long, overlies the feldspathic-lithic quartzite clastquartzite of of stop stop 2. 2. The The massive massive conglomerate, conglomerate, largely largely clast— supported supported with aa biotitic biotitic and and feldspathic feldspathic sandy sandy matrix, matrix, concontains tains well—rounded well-rounded clasts clasts of of "granite," "granite," volcanic volcanic rocks, rocks, chert, chert, STOP STOP 8. 8. 128 �white quartzite white q u a r t z i t e and and biotite b i o t i t e schist. s c h i s t . Clasts 25 C l a s t s are a r e as a s large l a r g e as a s 25 cm. The conglomerate cm. The conglomerate is is interpreted i n t e r p r e t e d as a s an an alluvial a l l u v i a l fan fan deposit deposit which the sandstones sandstones (guartzite) ( q u a r t z i t e ) of of related related which prograded prograded over over the braided (See aabstract by Ojakanqas Ojakangas and braided streams. streams. (See b s t r a c t by and Olson, Olson, this this volume.)) volume. yollow ~ o l l o wroad road (which (which is is one—way) one-way) around around loop loop on on Neil Neil Point, Point, past past sstop t o p 77 to t o Highway Highway 11. 11. 0.0 Reset Mileage; Mileage; tturn Reset u r n right r i g h t (west) (west) on on Highway Highway 11 11 and and drive drive toward toward 3. IInternational n t e r n a t i o n a l Falls, F a l l s , past p a s t stop s t o p 3. 4.6 Junction Junction with with Koochiching Koochiching County County Highway Highway 332 332 (truck ( t r u c k by—pass by-pass Turn left around around International I n t e r n a t i o n a l Falls). F a l l s ) . Turn l e f t and and follow follow Highway Highway 332 332 (4.61 south. south. 0.6 [5.2] 0.3 [5.5] 0.4 Stop sign; junction with with 13th Street; S t r e e t ; tturn u r n left l e f t (east) ( e a s t ) con— conStop sign; junction ttinuing i n u i n g on on Highway Highway 332. 332. 9. Metaqraywacke Metagraywacke outcrops. STOP 9. STOP outcrops. These These are a r e located located on on aa 1.2 1.2 km wide metagraywacke metagraywacke belt, b e l t , within within the the broader broader greenstone greenstone belt, belt, that t h a t extends extends another another 40 4 0 km km to t o the the northeast northeast to t o Swell Swell Bay Bay of of Rainy Graded beds beds to to the t h e northeast northeast of of this this Rainy Lake Lake in i n Ontario. Ontario. Graded outcrop face face both both northwest northwest and and southeast, southeast, indicating indicating the the presence of of isoclinal i s o c l i n a l folds. folds. Additional outcrops 9. Additional outcrops of of metagraywacke metagraywacke as a s at a t stop s t o p 9. [5.9] 0.1 Right angle angle bend iin n road road to t o south. south. [6.0] 0.8 [6.8] 0.3 Large STOP Large STOP 10. 10. and amphibole. roadcut both chlorite roadcut of of ggreenschist r e e n s c h i s t containing containing both chlorite Minor magnetic iron—formation is also Minor magnetic iron-formation is a l s o present. present. This outcrop outcrop exhibits e x h i b i t s considerable considerable shearing, shearing, for f o r the t h e Rainy Rainy Lake—Seine River fault zone is just 0.3 mi to the south. Lake-Seine Elver f a u l t zone is j u s t 0.3 mi to the south. zone. Broad topographic Lake-Seine River Broad topographic low low is is the t h e Rainy Rainy Lake-Seine River ffault a u l t zone. [7.1] [7.8) Junction of Junction of Highway Highway 332 332 with with Koochiching Koochiching County County Highway Highway 24. 24. Turn right r i g h t (west). (west). 0.8 Junction 24 with with U.S. U.S. Highway Highway 53. 53. Junction of of Highway Highway 24 [8.6] (south). 1.1 STOP STOP 11. 11. 0.7 [9.7] Turn left left on both both sides Low outcrops outcrops on Low s i d e s of of U. U. S. S. Highway Highway 53. 53. TRAFFIC ISISHEAVY—-BE CAREFULI HEAVY--BE CAREFUL! Thebbiotite thisl locality is The i o t i t e schist s c h i s t (metagraywacke) (metagraywacke) a tatthis o c a l i t y is Rainy Lake—Seine River Lake-Seine River and therefore therefore is is within fault f a u l t and within the t h e Quetico superbelt. superbelt. approximately onemile mile south south of of the approximately one the 129 �Petrographically Petrographically the rock is quartwfeldspathic quartzofeldspathic biotite schist. It has equigranular texture texture with foliation has aa firie—grained, fine-grained, equigranular foliation biotite and and muscovite muscovite and and contains contains accessory accessory amounts amounts defined by biotite of fine—grained fine-grained poikiloblastic poikiloblastic garnet. garnet. Dikes Dikes of porphyritic porphyritic felsite lamprophyre cut across across schistosity felsite and and dark dark green, green lamprophyre schistosity and and bedding (strike (strike about about N90°E), N900E), and and are are parallel parallel to to aa second second cleavage (strike N70°E); N70-El; the the second second cleavage cleavage are axe the dikes and the cleavage (strike best seen seen on on top top of of the the east east outcrop. outcrop. These dikes may be related to the the volcanism volcanism within the the Rainy Lake greenstone greenstone belt related to to the to the north. north. I 0.0 RESET MILEAGE MILEAGEand and continue continue south U.S. 53. 53. BESET south on on U.S. 6.1 village of Village of Ericsburg; Ericsburg; continue continue south south on on U.S. U.S. 53. 53. [6.1] 5.9 Department of iatura1 Natural Resources Resources fire fire tower tower on on right right Minnesota Department [11.9] (west). (west). 0.7 Railroad overpass. Railroad overpass. [12.6] 1.6 [14.2) 7.1 121.3] village of Ray; sharp Village sharp corner corner at junction junction with Koochiching Koochiching U . S . 53. 53. County Highway Highway 217; 217; continue continue east east on on U.S. "Gateway Store" and junction junction with with St. St. Louis Louis County County Highway Highway 122. 122. Typical Typical northern northern Minnesota Minnesota walleye walleye on on left. left. Turn left (north) (north) Turn left and follow follow Highway Highway 122 122 toward toward Kabetogama Kabetogama Lake. Lake. [23.6] Junction with St. Louis Junction Louis County 123 123 (straight (straight ahead): turn turn left (west) and stay on Highway Highway 122. 122. (west) 3.3 [26.9) "Y" in in road at junction "Yn junction with St. Louis Louis County County Highway Highway 902; 902; con— continue tinue straight straight ahead ahead on on Highway Highway 902. 902. 0.3 [27.2] Paved road road ends; ends; continue continue on on gravel gravel road. road. 0.3 [27.5) St. Louis County Highways 673 Highway 902 ends at junction with St. to Rocky Point and 675; turn right and follow follow Highway 675 675 to Resort. 0.3 (27.8] Follow driveway on Obtain per— to Rocky Bocky Point Point Resort. Resort. Obtain perFollow on left left to mission mission from from resort resort owners owners before before examining examining outcrops. outcrops. 2.3 STOP STOP 12. 12. This outcrop on the the south south shore shore of Kabetogama Lake is transition zone between the relatively in the transition relatively granite—free granite-free to the the north, and and schist—rich schist-rich migmatite migmatite mapped mapped biotite schist schist to to the the south. with the the vermilion Vermilion Granitic Granitic Complex Complex to south. The amount amount of within the the biotite of leucogranite leucogranite within biotite schist schistincreases increasesfrom from north north Metamorphic recrystallizato in this zone. to south south in this transition transition zone. Metamorphic recrystallization tion has has obscured obscured original original textures textures here, but across across the the lake lake to north the the graded graded bedding bedding indicates indicates northward northward strati— stratito the the north graphic younging. graphic younging. 130 �H (A H Ia Int'l Falls vig vsm I — Ysm, schist—rich migmatite vhqd, hornblende quartz diorite PEN INSULA vlg, Lac LoCroix Granite vgm, granite—rich migmatite simplified geologic map of the Lake Kabetogama Kabetogama area showing Figure Figure 3. 3. Simplified locations locations of of stops stops 12 12 through through 18. 18. KABETOGAMA vgm vhqd VERMILION GRANITIC COMPLEX dikes of Proterozoic age. Chiefly metagraywacke; contains numerous small bodies of Ieucogranite near contact with vsm. METASEDIMENTARY ROCKS, UNDIVIDED ms2 DIABASE I\dI EXPLANATION �a The biotite biotite schist ofofthethe Icabetogama region has has aa The schist Kabetogama Lake Lake region fine—to to medium—grained, equigranularschistose schistosetexture. texture. Local finemedium-grained, equigranular Local a luminousbeds bedswithin withinthe theschist schist contain aluminous contain porphyroblasts porphyroblasts of of Schistosity, which is sillimanite, and staurolite. staurolite. Schistosity, is sillimanite, garnet, and parallel to,bedding, tobedding, is is isoclinally isoclinally folded. folded. generally parallel Pegmatite and coarse—grained coarse-grained leucogranite leucogranite are are enfolded enfolded and boudinaged concordantly concordantly within the the host biotite biotite schist. Dikes of granite granite that are physically indistinguishable indistinguishable from from the the folded leucogranite folded leucogranite cut cut across across the the schistosity schistosity and and isoclinal isoclinal folds. folds. I Return over Return over routes routes 675 675 and and 902 902 to to junction junction with with Highway Highway 122. 122. 0.0 0.0 RESET MILEAGE. MILEAGE. Turn Turn left left (east) (east) onto onto 122 122 and and proceed toward toward Chief Wooden Frog Frog Campground. Chief Wooden Campground. 0.4 0.4 "Y" in Highway 122, 'Y" 122, stay stay to to right. right. (0.4] [0.41 0.4 0.4 my,, "Y" in Highway in Highway 122; 122; stay stay to to left left on on 122. 122. [0.8) [0.81 0.5 [1.3]1 Chief Wooden Frog Frog Campground. Campground. Proceed Proceed to to camping camping area area B—3 B-3 (outcrop (outcrop description applies to any of the numerous low lying granitic outcrops granitic outcrops in in this this area). area). STOP STOP 13. 13. This This area area is is transitional transitional between between the the metasedimentary metasedimentary rocks to the south, with rocks to to the the north north and and schist—rich schist-rich migmatite to the leucogranite here greater than the amount amount of of leucogranite than at at Stop Stop 12. 12. Leucogranite thin veins that are syntectonically Leucogranite forms forms thin syntectonically enfolded enfolded and and boudinaged boudinaged with with the the schist, schist, and and also also forms forms lenticular lenticular bodies up to to aa few few hundred hundred feet feet long long which invade invade and and cut cut across across the the folds. folds. The leucogranite pegmaleucogranite has aa coarse—grained coarse-grained gneissic gneissic to to pegma— The mineralogy is is dominated dominated by quartz, microcline microcline and sodic sodic plagioclase, with accessory accessory garnet. garnet. The gneissic texture by biotite biotite and and primary primary muscovite. muscovite. texture is is defined defined by titic texture. titic texture. a Separate Separate textural textural subunits subunits of the the leucogranite leucogranite suite suite can can be be delineated delineated (pegmatitic, (pegmatitic, medium-grained medium-grained hypidiomorphic, hypidiomorphic, coarse—grained coarse-grained gneissic, gneissic, etc.), etc.), which which can can be be seen seen crosscutting crosscutting and and grading grading into into each each other. other. Although Although these these subunits subunits have have aa wide wide range range in in major major element element abundances, abundances, they they are thought thought to to be cogenetic. cogenetic. I Return Return over over same same route. route. 0.5 0.5 "Y" "Y" in in Highway Highway 122; 122; stay stay to to right right heading heading west. west. [1.8] [1.81 0.4 0.4 "Y" "Y" in in Highway Highway 122; 122; stay stay to to left left heading heading west. west. [2.2] E2.21 132 �0.4 [2.6] 3.3 [5.9] Stop sign, sign, junction Highway Highway 122 122 with with Highway Highway 902. 902. 122. (south) and continue on on Highway Highway 122. mm left Turn left Att Stop sign, sign, turn t u r n right r i g h t (south) (south) and and continue continue on on Highway Highway 122. 122. A top of hill south of junction is an excellent outcrop of a comt o p of h i l l of junction is of composite to aa swarm swarm of of p o s i t e diabase diabase dike. dike. Phis ^Phis dike dike belongs belongs to b.y.) that t h a t extends extends from from the the Proterozoic dikes (age (age about 2 b.y.) Mesabi Range, Minnesota to the vicinity of Kenora, Ontario; Range, Minnesota t o the v i c i n i t y of Kenora, Ontario; swan was another dike in i n tthe h e swarm was seen seen at a t stop s t o p 5. 5. (7.0] Junction Junction with with Highway Highway 123. 123. on 122. on 122. 0.4 Barney and Oscar's Oscar's Bar on left, l e f t , continue continue south, south, slow slow down. down. 1.1 Kay's Bar on left; Kay's l e f t ; continue south [7.4] 0.2 [7.6] Outcrops Outcrops on on both both sides s i d e s of of Highway Highway 122. 122. shoulder of of road. road. Pull P u l l vehicle onto outcrops on both sides STOP STOP 14. 14. Outcrops sides rich migmatite. Regionally this rich of of the t h e road are a r e of granite— graniterock type has 5 tto percent o 25 percent inclusions in a granitic neosome; the inclusions are biotite g r a n i t i c neosome; t h e are biotite inclusions i n Att this sschist, c h i s t , amphibolite, amphibolite, trondhjemite, trondhjemite, and and granodiorite. granodiorite. A locality most of the inclusions are trondhjemite. l o c a l i t y most of the inclusions a r e trondhjemite. On is aa glacially g l a c i a l l y polished polished On the the west west side s i d e of of the t h e road road is outcrop of migmatite with vague grayish grayish inclusions inclusions that t h a t are are partially p a r t i a l l y digested digested by by the t h e enclosing enclosing granite g r a n i t e neosome. neosome. Ductile and probably probably was the inclusions inclusions is is evident evident and was Ductile shearing shearing of of the associated with the emplacement emplacement of the granitic g r a n i t i c core of the complex complex to t o the the south. south. Plagioclase diffusion "halos" "halos" can be seen surrounding inclusions on the seen surrounding trondhjeiaitic trondhjemitic inclusions t h e ffresh r e s h roadcut on on the t h e east e a s t side s i d e of of the the road. road. Continue 122. Continue south south on on 122. 0.7 [8.31 1.5 [9.8] Stop sign, sign, junction junction with with U.S. U.S. 53. 53. proceed proceed west. west. mm Turnright r i g h tonto ontoU.S. U.S. 53 53 and and Pull Large roadcuts on on both both sides s i d e s of of U.S. U.S. 53. 53. P u l l off off highway onto onto shoulder. TRAFFIC IS IS HEAVY—PLEASE HEAVY-PLEASE BE BE CAREFUL. CAREFUL. STOP STOP 15. 15. These roadcuts encapsulate the structural s t r u c t u r a l and intruintruhistory ssive ive h i s t o r y of of the t h egranite—rich granite-rich migmatite migmatite in i n the t h eVermilion Vermilion Granitic The neosome neosomei sisl ilight gray tto g h t gray o pink pink granite granite G r a n i t i cComplex. Complex. The with aa coarse—grained, weaklygneissic gneissic texture. texture. Blocks with coarse-grained, weakly Blocks of of amphibolite, ttonalite, early migmatite a are biotite b i o t i t e sschist, c h i s t , amphibolite, o n a l i t e , and e a r l y migmatite re within the of asrafted r a f t e d within the granite g r a n i t e and and display display varying varying degrees degrees of asssimilation i m i l a t i o n and and deformation. deformation. Faint F a i n t outlines o u t l i n e s of of digested digested country country rock inclusions rock inclusions are a r e abundant. abundant. The included included blocks blocks of The of early e a r l ymigmatite migmatite have have paleosomes paleosomes of of amphibolite and and bbiotite amphibolite i o t i t e sschist, c h i s t , or amphibolite amphibolite alone, alone, and and 133 �neosomes of gray tonalite Much of tonalite or granodiorite. granodiorite. Much of the the ant— amphibolite phibolite is is coarse coarse grained grained and and foliated, foliated, with with aa "spotted" "spotted" appearance caused appearance caused by clusters clusters of biotite. Early migmatite paleosome and and blocks that that consist consist dominantly dominantly of of axnphibolite amphibolite paleosome tonalite neosome tonalite neosome typically typically show show agmatic agmatic structure, wherein wherein the amphibolite has been split amphibolite split into into distinct distinct pieces that that could could be fit £i back together together like like aa jigsaw jigsaw puzzle. puzzle. These east—trending east-trending cuts cuts are oriented oriented nearly parallel to to the planar fabric fabric of the the migmatite, and therefore therefore the the faces faces of the cuts appear to to contain contain a larger larger fraction fraction of inclusions inclusions than than is really really the the case case for for the the rock rock as as aa whole. whole. AA closer estimate of the the inclusion—to—granite inclusion-to-granite ratio ratio can can be made from from the the natural natural subhorizontal top of the the north north cut. cut. subhorizontal surface surface on the the top 0.0 MILEAGE. Turn RESET MILEAGE. Turn around around and and proceed proceed back back east east on on U.s. U.S. 53. 53. 1.5 Junction Junction with Highway Highway 122; 122; continue continue southeast southeast on on U.s. U.S. 53. 53. [1.5] 2.9 [4.4] 0.8 (5.2] Junction Junction with with St. St. Louis Louis County County Highway Highway 765 765 (Ash (AshRiver River Trail); Trail); turn turn left left (east). (east). Granite—rich migmatite, consisting of 5 to 10 percent percent STOP 16. STOP 16. Granite-rich inclusions in modally uniform, faintly gneissic granite, crops Numerous indefinitely River Trail. Numerous out just just north of the the Ash River lenses and layers of here, and bounded lenses and layers of pegmatite pegmatite occur occur here, and are are typical ofofgranite—rich in the typical granite-rich migmatite migmatite in theVermilion Vermilion Granitic Granitic Complex. Complex. Continue east Continue east on on Highway Highway 765. 765. 0.8 Cross over Daley Brook Brook in in marshy marshy area. area. [6.0) 3.7 right (south). (south). Outcrop on right (9.7) 17. This outcrop is dominantly a gray biotite-hornblende biotite—hornblende STOP 1 7. This quartz diorite, an early plutonic body within the quartz the Vermilion It is cut cut across by by numerous numerous veins veins of of Granitic Complex. It Granitic and pegmatite pegmatite believed believed to to be be related related to to the theLac Mc biotite granite and quartz diorite is massive with a uniform La Croix Croix Granite. The quartz mineralogic composition, mineralogic composition, and and has aa medium— medium- to to coarse—grained coarse-grained In thin thin section one one sees that hypidiomorphic granular hypidiomorphic granular texture. texture. In oxides are are exsolved fromthe the interior interior of iron oxides iron exsolved from ofthe theamphibole amphibole along cleavage traces. along cleavage traces. Continue eastward eastward toward towardthe the village village of Continue of Ash Ash River. River. 0.2 Sharp turn Sharp turn to to the the left left (north); (north); continue continue on on Highway Highway 765. 765. [9.9] 134 �0.6 Paved road road starts. starts. [10.5] 3.4 113.93 Ash Trail Trail Lodge. Park Park and and walk along along indistinct indistinct trail trail (starting by north side of green cabin) to top of hill bill at base (starting by of microwave—radio—relay. microwave-radio-relay. Obtain permission from cabin owners if cabin cabin is is occupied. occupied. STOP 18. STOP 18. This This large large knob knob of Lac Lac La Croix Croix Granite Granite (Vermilion (Vermilion Granite Granite of of Grout, Grout, 1923) 1923) is is part part of of aa crescent-shaped crescent-shaped body body that that occupies the occupies the hinge area of a large, east—plunging east-plunging fold. fold. It It contains no more than contains than 5 percent inclusions, several several of which microwave tower, are well displayed displayed near the the microwave tower, and and also also has has pegnatitic lenses. pegmatitic lenses. This This is is about as homogeneous homogeneous as the the Lac La Croix Croix Granite Granite gets gets in in the the northwest northwest part part of of the the Vermilion Vermilion Granitic Complex. Granitic Complex. Almost perfectly uniform granite granite crops crops out out some 50 km to some to the the southeast, southeast, well well beyond the the itinerary itinerary of this this field trip. field trip. The hilly vista to to the the southeast southeast is is typical typical of of terrain underlain terrain underlain by by the the Vermilion Vermilion Granitic Granitic Complex. Complex. Turn U.S. 53. 53. Turn around around and and return return over over Ash Ash River River Trail Trail to to U.S. 9.3 Junction with U.S. 53. 53. Junction with U.s. [23.2] END OF FIELD FIELD TRIP TRIP II. 11. FAILS. RETURN TO INTERNATIONAL INTERNATIONAL FALLS. 135 �I REFERENCES REFERENCES CITED, CITED, PAPERS PAPERS 11 and and 22 and and FIELD FIELD TRIP TRIP II I1 Adams, Adams, F.D., F.D., Bell, Bell, R., R., Lane, Lane, A.C., A.C., Leith, Leith,C.IC., C.K., Miller, W.G., W.G., and and Van Van Hise, Use, C.R., 1905, Report Report of of the the special special committee committee for for the the Lake Lake Superior Superior c.R., 1905, region: region: Journal Journalof of Geology, Geology, v. v. 13, 13, p. p. 89—104. 89-104. Arth, Arth, J.G., J.G., and and Hanson, Hanson, G.N., G.N., 1972, 1972, Quartz Quartz diorites diorites derived derived by by partial partial melting melting of of eclogite eclogite or or amphibolite amphibolite at at mantle mantle depths: depths: Contributions Contributions to to Mineralogy Mineralogy and and Petrology, Petrology, v. v. 37, 37, p. p. 161—174. 161-174. Arth, Arth, J.G., J.G., and and Hanson, Hanson, G.N., G.N., 1975, 1975, Geochemistry Geochemistry and and origin origin of of the the early early Precambrian Precambrian crust crust of of northeastern northeastern Minnesota: Minnesota: Geochimica Geochimica et et Cosmochimica v. 39, 39, p. p. 325—362. 325-362. Cosmochimica Acta, Acta, v. Barker, Barker, F., F., and and Arth, Arth, J.G., J.G., 1976, 1976, Generation Generation of of trondhjemite trondhjemite tonalitic tonalitic bimodal trondhjemite-basalt trondhjemite—basalt suites: suites: Geology, liquids Archean bimodal Geology, v. v. liquids and and Archean p. 596—600. 596-600. 4, p. 4, Barker, F., F., Arth, Arth, J.G., J.G., Peterman, Peterman, Z.E., Z.E., and and Friedman, Friedman, I., I., 1976, 1976, The The 1.71.7- to to Barker, 1.8— b.y. old old trondhjemites trondhjemites of of southwestern southwestern Colorado Colorado and and northern northern New New 1.8- b.y. Mexico: Mexico: Geochemistry Geochemistry and and depths depths of of genesis: genesis: Geological Geological Society Society of of America America Bulletin, Bulletin, v. v. 87, 87, p. p. 189—198. 189-198. I Bryan W.B., W.B., Thompson, Thompson, G., G., Frey, Frey, T.A., T.A., and and Dickey, Dickey, J.S., J.S., 1976, 1976, Inferred Inferred setsetBryan tings tings and and differentiation differentiation in in basalts basalts from from the the Deep Deep Sea Sea Drilling Drilling Project: Project: Journal Journal of of Geophysical Geophysical Research, Research, v. v. 81, 81, p. p. 4285—4304. 4285-4304. S.S., Hanson, Hanson, G.N., G.N., Hallford, Hallford, C.R., C.R., and and Mudrey, Mudrey, M.G., M.G., Jr., Jr., 1972, 1972, Goldich, 3.5., Goldich, Saganaga Lake—Northern Early Early Precambrian Precambrian rocks rocks in inthe the Saganaqa Lake-Northern Light Light Lake Lake area,Minnesota—Ontario, Minnesota-Ontario, Part Part I, I, Petrology Petrology and and structure, structure, in &I Doe, Doe, area, B.R., B.R., and and Smith, Smith, D.K., D.K., eds., &.,Studies Studiesininmineralogy mineralogy and and Precambrian Precambrian America geology: geology: Geological GeologicalSociety Societyofof AmericaMemoir Memoir135, 135,p.p.151—177. 151-177. Goldich, 5.5., S.S., Nier, Nier, A.O., A.O., Baadsgaard, Baadsgaard, H., H., Hoffman, Hoffman, J.H., J.H., and and Krueger, Krueger, Goldich, H.W., H.W., 1961, 1961, The The Precambrian Precambrian geology geology and and geochronology qeochronology of of Minnesota: Minnesota: Minnesota Minnesota Geological Geological Survey Survey Bulletin Bulletin 41, 41, 193 193 p. p. 1978, Geology and geochemistry geochemistry of of the the Goldich, 5.5., S.S., and and Peterman, Peterman, Z.E., Z.E., 1978, Goldich, Rainy Rainy Lake Lake area, area, in &I Smith, Smith, I.E.M. I.E.M. and and Williams, Williams, J.G., J.G., eds., Proceedings Proceedings of of the the 1978 1978 Archean Archean Geochemistry Geochemistry Conference, Conference, p. p. 209—234. 209-234. &., Green, Green, D.H., D.H., 1973, 1973, Experimental Experimental melting melting studies studies on on aa model model upper upper mantle mantle composition at high pressure under water—saturated and water— composition at high pressure under water-saturated and waterundersaturated Earth and and Planetary Planetary Science Science Letters, Letters, v. v. undersaturated conditions: conditions: Earth 15, p. p. 37—53. 37-53. 15, Grout, rout, F.F., F.F., 1923, 1923, The The magnetite magnetite pegmatites pegmatite8 of of northern northern Minnesota: Minnesota: Economic Geology, v. 18, p. 253—269. Economic Geology, V. p. 253-269. 1925a, The The Coutchiching Coutchichinq problem: problem: Geological Geological Society Society of of Grout, F.F., F.F., 1925a, Grout, America America Bulletin, Bulletin, v. v. 36, 36, p. p. 351—364. 351-364. The Vermilion Vermilion batholith batholith of of Minnesota: Journal Journal of of 1925b, The Grout, Grout, F.F., F.F., 1925b, Geology, Geology, v. v. 33, 33, p. p. 467—487. 467-487. 136 I �Grout, F.F., F.F., 1926, 1926, The The geology and magnetite deposits deposits of northern northern St. Louis 770 Louis County, County, Minnesota: Minnesota: Minnesota Minnesota Geological Geological Survey Survey Bulletin Bulletin 21, 220 p. P- Hanson, Hanson, G .N., and Goldich, 8.5., S.S., 1972, 1972, Early Precambrian Precambrian rocks rocks in the G.N., Saganaga 11, Saganaga Lake—Northern Lake-Northern Light Light Lake Lake area, area, Minnesota—Ontario, Minnesota-Ontario, Part Part II, Petrogenesis, & inI Doe, B.R., B.R., and and Smith, Smith, DO.K., .K., eds., eds., Studies in minerminer— - a logy and and Precambrian Precambrian geology: America alogy geology: Geological GeologicalSociety Societyofof AmericaMemoir Memoir 135, 135, p. 179—192. 179-192. Hanson, G.N., G.N., and and Malhotra, Malhotra, R., R., 1971, 1971, K—Ar K-Ar ages ages of of mafic mafic dikes dikes and and evieviHanson, dence dence for for low—grade low-grade metamorphism metamorphism in in northeastern northeastern Minnesota: Geological v. 82, 82, p. p. 1107—1114. 1107-1114. Geological Society Society of of America America Bulletin, Bulletin, v. Hart, S.R., S.R., and and Davis, Davis, G.L., G.L., 1969, 1969, Zircon Hart, Zircon U—Pb U-Pb and and whole whole rock rock Rb-Sr Rb-Sr ages ages and early early crustal crustaldevelopment development near near Rainy Painy Lake, Lake, Ontario: Ontario: Geological Geological Society Society of of America America Bulletin, Bulletin, v. v. 80, 80, p. p. 595-614. 595—614. LA., Haskin, Haskin, M.A., M.A., F.A., and andWildeman, Wildeman, TP.R., .R., 1968, 1968, Relative Relative Haskin, L.A., Frey, F.A., and absolute terrestrial terrestrial abundances of the the rare rare earths, earths, in inL.H. L.H. and absolute abundances of Anrens, ed., Origin distribution of Origin and and distribution theelements; elements;Pergamon Pergamon Press, Anrens, g., of the Press, New York, York, p. New p.889—912. 889-912. Hawley, J.E., Journal of Hawley, J. E., 1930, 1930, "Seine" "Seinen or or "Coutchiching": "Coutchiching": Journal of Geology, v. v. 38, 38, p. p . 521—547. 521-547. Jahn, Jahn, Bor-ming, and and Murthy, Murthy, V.R., V.R., 1975, 1975, Rb—Sr Rb-Sr isotopic isotopic studies studies of of the the Bor—ming, Vermilion Vermilion greenstone northeasternMinnesota: Minnesota: Geological Geological Society Society greenstone belt, belt, northeastern of p. 611. of America America Abstracts Abstracts with with Programs, Programs, v. v. 3, p . 611. 3, Lawson, A.C., A.C., 1913, 1913, The The Archean Archean geology geology of of Rainy Rainy Lake Lake restudied: restudied: Lawson, Geological Survey Geological Survey of of Canada Canada Memoir 40, 115 115 p. p. Mehnert, Mehnert, K.R., K.R., 1968, 1968, Migmatites Migmatites and and the the origin origin of of granitic granitic rocks; rocks; Elsevier Elsevier Publishing Company, Amsterdam, 393 p. Publishing 393 p . Merritt, P.L., P.L., Merritt, 1934,Seine—Coutchiching Seine-Coutchiching problem: 1934, problem: Geological Geological Society Society of America Bulletin, 45,p.p. 333-374. America Bulletin, v.v.45, 333—374. - Minnesota Minnesota Geological Geological Survey, Survey, 1969, 1969, The The proposed proposed Voyageurs Voyageurs National National Park Park — Its Its geology geology and and mineral mineral potential; potential: 16 16 p. p. ++ map. map. in Geology of Minnesota: centennial volume: &., Geology of Minnesota: A A centennial volume: Minnesota Minnesota Geological Geological Survey, Survey,p.p.162—171. 162-171. Ojakangas, R.W., R.W., 1972, Ojakangas, 1972, Rainy Rainy Lake Lake area, area, in Sims, Sims, P.K., P.K., and and Morey, Morey, G.E., G.B., eds., Peterman, Z.E., Z.E., and Goldich, 5.5., S.S., 1970, 1970, Early Precambrian Precambrian geology of the the Peterman, Rainy Eabs.1: Institute Institute on on Lake Lake Superior Superior Geology, Geology, 16th 16th Rainy Lake Lake district district [abs.]: Annual Annual Meeting, Meeting, Thunder Thunder Bay, Bay, Ontario Ontario [Proceedings], [Proceedings], p. p. 34. 34. Peterman, Z.E., Z.E., Goldich, Goldich, S.S., S.S., Hedge, Hedge, C.F., C.F., and and Yardley, D.H., D.H., 1972, 1972, Geochronology Geochronology of of the the Rainy Rainy Lake Lake region, region, Minnesota—Ontario, Minnesota-Ontario, in &I Doe, Doe, Studies in mineralogy and Precambrian B . R . , and Sims, P . K . , B.R., and Sims, P.R., eds., Studies in mineralogy and Precambrian geology: Geological Geological Society Society of of America America Memoir Memoir 135, 135, p. p. 193—215. 193-215. e., 137 �I I I Poulsen, K Poulsen, .H., K.H., 1980, The stratigraphy, structure and metamorphism of Archean rocks thesis, Lakehead Lakehead Archean rocks at at Rainy Rainy Lake, Lake, Ontario: Ontario: Unpub. Unpub. 14.5. M.S. thesis, p. University, Thunder Thunder Bay, Bay, Ontario, 99 99 p. K.H., Borradaile, J., and .M., 1980, Poulsen, Poulsen, K.!!., Borradaile, G. G.J., and Kehlenbeck, Kehlenbeck, MM.M., 1980, An An inverted inverted succession succession at Rainy Rainy Lake, Ontario: Canadian Canadian Journal Journal of Earth 17, p. p. 1358—1369. Sciences, v. Sciences, v. 17, 1358-1369. Rye, D.M., D.M., and Roy, Roy, R.F., R.F., 1978, 1978, The distribution distribution of thorium, uranium, and potassium Archean granites granites from from northeastern northeastern Minnesota: Minnesota: American American potassium in in Archean Journal of Journal of Science, Science, v. v. 278, 278, p. p. 354—378. 354-378. Schulz, K.J., K.J., 1980, 1980, The magmatic evolution evolution of the the Vermilion greenstone greenstone v. belt, NE Minnesota: Minnesota: Precambrian Precambrian Research, v . 11, 11, p. p. 215-245. 215—245. Sims, P .K., 1976, 1976, Early Precambrian Precambrian tectonic-igneous evolution evolution in the P.K., Vermilion district, Vermilion district, northeastern northeastern Minnesota: Geological Geological Society Society of of America Bulletin, America Bulletin, v. v. 87, 87, p. p. 379—389. 379-389. Southwick, D .L., 1972, Vermilion granite—migmatite granite-migmatite massif, in Sims, P .K., D.L., P.K., Morey, G G.E., eds., Geology of Minnesota: A centennial centennzl volume: and Wrey, .B., Minnesota Minnesota Geological Geological Survey, Survey, p. p. 108—119. 108-119. *., D.L., 1978, The Vermilion Granitic Complex, northern Minnesota, Southwick, D .L., and Williams, J J.G., eds., Proceedings Proceedings of the 1978 in Smith, I.E.M. I.E.M. .G., eds., Archean Geochemistry Archean Geochemistry Conference, p. p. 265—276. 265-276. - - Southwick, D.L., and D.L., and Day, W.C., W.C., 1981, 1981, Geology Geology and and petrology of Proterozoic Proterozoic mafic dikes, dikes, north—central north-central Minnesota Minnesota [abs.]: Labs.]: American Geophysical Union, Program Program for for 1981 1981 Midwest Meeting, Minneapolis. Minneapolis. of Minnesota, D.L., and Ojakangas, R.W., R.W., 1979a, 1979a, Geologic map of Southwick, D.L., International International Falls Falls Sheet: Sheet: Minnesota Geological Survey, scale 1:250,000. 1:250,000. Southwick, D.L., D.L., and Ojakangas, R.W., R.W., 1979b, Field trip trip guidebook guidebook for the the 1979b, western western Vermilion Vermilion district, district, northeastern northeastern Minnesota: Minnesota Minnesota 65 p. p. Geological Survey, Guidebook series series 10, 10, 65 - Southwick, D.L., D.L., P.K., 1980, 1980, The Vermilion Granitic Complex — AA and Sims, P.K., U.S. Geological Survey new name for old rocks in northern Minnesota: Minnesota: U .S. Geological Professional Professional Paper Paper 1124A, 1124A, p. p. Al—All. A1-All. Streckeisen, A .L., 1973, Plutonic rocks: rocks: Classification and A.L., chairman, 1973, nomenclature recommended nomenclature recommended by the IUGS IUGS Subcommission Subcommission on the Systematics Systematics of Igneous Igneous Rocks: cks: Geotimes, v. 18, p. 26—30. Geotimes, v. 18, p. 26-30. Williams, J.G., J.G., 1978, 1978, Geology of of the the Crystal Crystal Lake Lake area, area, Quetico Quetico in Smith, I.E.M. and Williams, J.G., Proceedings I.E.M. J.G., eds., Proceedings Subprovince, & p. 193—207. of the 1978 1978 Archean Geochemistry Conference, p. 193-207. *., Winchell, N.H., N.H., Geological Geological 1888, 1888, Sixteenth Sixteenth annual annual report report for for the the year 1887: 1887: Minnesota Minnesota and Natural History Survey, 504 p. and Natural History Survey, 504 p. 138 I �- a -- -_________ -4.- Wood, J., J., 1980, 1980, Epiclastic sedimentation Wood, sedimentation and and stratigraphy stratigraphy in in the the North Spirit Lake and and Rainy Rainy Lake comparison: Precambrian Precambrian Research, Research, Lake areas: areas: A comparison: V. 12, 12, p. p. 227—255. v. 227-255. 139 � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1982 Description An account of the resource Institute on Lake Superior Geology. International Falls, Minnesota. May 5-8, 1982. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1982 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/a589506b71d64a5c9fb6d07486e47152.pdf b9d36aa3afb42bdaafbeb6c04ecddc0e PDF Text Text �PROCEED PROCEEDIINGS NGS TWENTY-NINTH ANNUAL TWENTY-NINTH ANNUAL INSTITUTE INSTITUTE ON ON LAKE LAKESUPERIOR SUPERIOR GEO LOGY GEOLOGY held h e l d at at Michigan Technological University University lioughton, Michigan Houghton, Michigan 49931 49931 11—14, 1983 1983 May 11-14, Organized by the the Department of of Geology and Geological G e o l o g i c a l Engineering Engineering with iin n ccooperation ooperation w ith Division of Education and Public The D i v i s i o n of P u b l i c Services Services Michigan Technological University University Houghton, Michigan Houghton, 49931 49931 J . Bornhorst and J. J . F. F. Diehl Diehl T. T. J. Editors Editors �TABLE OF OFCONTENTS CONTENTS Volume II Volume GENERAL INFORMATION INFORMATION j i PURCHASE INFORMATION INFORMATION FOR FOR PROCEEDINGS PROCEEDINGSVOLUME VOLUME PURCHASE ji INSTITUTE INSTITUTEBOARD BOARD OF DIRECTORS i LOCAL COMMITTEE COMMITTEE ii GOLDICH MEDAL COMMITTEE COMMITTEE GOLD ICR MEDAL ii SESSION SESSION CHAIRMEN CHAIRMEN ii ANNUAL BANQUET SPEAKER iii GOLDICH GOLDICH MEDAL RECIPIENT iii ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS iii iii REPORT 2 8 t h I.L.S.G. I.L.S.G. REPORT OF OF THE CHAIRMAN CHAIRMAN —- 28th iiv v vii vii CALENDAR OF EVENTS AND PROGRAM PROGRAM 1 1 ABSTRACTS ABSTRACTS TRIP 1 4 , 1983 1983 FIELD T R I P ON MAY 14, ROPES GOLD MINE AND THE MICHIGAN GOLD MINE 43 Volume II I1 FIELD TRIP ON MAY 11, 11, 1983 1983 FIELD GUIDE TO THE GEOLOGY OF THE KEWEENAW PENINSULA FIELD 1-116 �GENERAL INFOR11ATION GENERAL INFORMATION 29th Annual INSTITUTE ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY University Michigan Technological University Houghton, Houghton, Michigan Michigan May 11—14, 11-14, 1983 1983 PROCEEDINGS VOLUME VOLUME PURCHASE INFORMATION FOR PROCEEDINGS Volume II && II I1 together t o g e t h e r for f o r sale s a l e at: at: The D i v i s i o n of Division of Education and Public P u b l i c Services Services University Michigan Technological University Volume II I1 only for f o r sale s a l e at: at: E. Bookstore E. R. R. Lauren Bookstore University Michigan Technological University OF DIRECTORS DIRECTORS INSTITUTE BOARD OF T.J. T . J . Bornhorst, Bornhorst, Department of of Geology and Geological Engineering, Engineering, Michigan Michigan Technological University, U n i v e r s i t y , Houghton, Houghton, Michigan (Chairman, (Chairman, 1983) 1983) D.L. Southwick, Minnesota Geological Survey, Survey, St. S t . Paul, P a u l , Minnesota (1982) (1982) D.L. Southwick, W.C. Cambray, W.C. Cambray, Department of of Geology, Geology, Michigan State S t a t e University, U n i v e r s i t y , East East Lansing, Lansing, Michigan (1981) (1981) Michigan P.E. Myers, Myers, Department P.E. Department of of (1980) Geology, University U n i v e r s i t y of of Wisconsin, C l a i r e , Wisconsin Wisconsin Geology, Wisconsin, Eau Claire, R.C. i v i s i o n , Department of Natural N a t u r a l Resources, Resources, Lansing, Lansing, R.C. Reed, Reed, Geological Survey D Division, Department of Michigan Michigan (Secretary—Treasurer) (Secretary-Treasurer) 1 �LOCAL COMMITTEE COMMITTEE LOCAL Conference Chairman Chairman Conference T.J. T . J . Bornhorst, Bornhorst, Department Department of of Geology Geology and and Geological Geological Engineering, Engineering, Michigan Michigan Technological University, U n i v e r s i t y , Houghton, Houghton, Michigan Michigan 49931. 49931. Technological F i e l d Trips Trips Field T.J. T.J. Bornhorst Bornhorst J . Kalliokoski Kalliokoski J. J . B . Paces Paces J.B. W . I . Rose, Rose, Jr. Jr. W.I. D.M. Rossell Rossell D.M. All A l l at a t the t h e Department Department of of Geology Geology and and Geological Geological Engineering, Engineering, Michigan Michigan Technological Technological University, U n i v e r s i t y , Houghton, Houghton, Michigan Michigan 49931. 49931. P h v s i c a l Arrangements Arrangements Physical J a n e Berner, Berner, Coordinator Coordinator Jane Jean Joffee, J o f f e e , Secretary Secretary Jean D i v i s i o n of of Education Education and and Public P u b l i c Services Services Division Michigan Michigan Technological Technological University, U n i v e r s i t y , Houghton, Houghton, Michigan Michigan 49931. 49931. Best Student Student Paper Paper Committee Committee Best 53706. M.G. M.G. Mudrey, Mudrey, Jr., J r . , Wisconsin Wisconsin Geological Geological Survey, Survey, Madison, Madison, Wisconsin Wisconsin 53706. S.C. S.C. Nordeng, Nordeng, Department Department of of Geology Geology and and Geological Geological Engineering, Engineering, Michigan Michigan Technological Technological University, U n i v e r s i t y , Houghton, Houghton, Michigan Michigan 49931. 49931. R. Rowe, Rowe, Exxon Exxon Minerals Minerals Company, Company, Rhinelander, Rhinelander, Wisconsin Wisconsin 54501. 54501. R. GOLDICH EDAL COMMITTEE COMMITTEE GOLD ICH M MEDAL G.L. G.L. LaBerge, LaBerge, Department Department of of Geology, Geology, University U n i v e r s i t y of of Wisconsin—Oshkosh, Wisconsin-Oshkosh, Oshkosh, Wisconsin Wisconsin 54901 54901 (Chairman). (Chairman) Oshkosh, R.L. R.L. Buchheit, Buchheit, Meridian Meridian Land Land and and Mineral Mineral Company, Company, Billings, B i l l i n g s , Montana Montana 59103. 59103. W.F. Cannon, Cannon, U.S. U.S. Geological Geological Survey, Survey, Reston, Reston, Virginia V i r g i n i a 22092. 22092. W.F. . CHAIRMAN SESSION CHAIRMAN SESSION W.S. Cordua, Cordua, Department Department of of Plant P l a n t and and Earth E a r t h Sciences, Sciences, University U n i v e r s i t y of of W.S. Wisconsin—River Wisconsin- River Falls, F a l l s , River River Falls, F a l l s , Wisconsin Wisconsin 54022. 54022. T.B. T.B. Holst, H o i s t , Department Department of of Geology, Geology, University U n i v e r s i t y of of Minnesota—Duluth, Minnesota-Duluth, Duluth, Duluth, Minnesota 55812. 55812. Minnesota A.M. Johnson, IInstitute A.M. Johnson, n s t i t u t eofofMineral MineralResearch, Research,Michigan MichiganTechnological Technological U n i v e r s i t y ,Houghton, Houghton, Michigan Michigan 49931. 49931. University, J . S . Klasner, Klasner, Department Department of of Geology, Geology, Western Western Illinois I l l i n o i s University, U n i v e r s i t y , Macomb, Macomb, J.S. I l l i n o i s 61455. 61455. Illinois Departmentofof Geology Geology and and Geological Geological Engineering, S.D. McDowell, McDowell, Department Engineering, Michigan Michigan S.D. Technological Technological University, U n i v e r s i t y ,Houghton, Houghton, Michigan Michigan 49931. 49931. :ii �N. Scofield, S c o f i e l d , Department of of Geology Geology and and Geological G e o l o g i c a l Engineering, Engineering, South South Dakota Dakota N. of Mines & Technology, Technology, Rapid City, School of C i t y , South Dakota 57701. 57701. D.L. Southwick, S t . Paul, P a u l , Minnesota 55108. D.L. Southwick, Minnesota Geological G e o l o g i c a l Survey, Survey, St. C.T. C T Young, Young, Department of of Geology and and Geological G e o l o g i c a l Engineering, Engineering, Michigan Michigan Technological U University, Houghton, Michigan 49931. Technological n i v e r s i t y , Houghton, 49931. .. ANNUAL ANNUAL BANQUET GUEST SPEAKER SPEAKER E. K Kesler, Department of of Geology, Geology, U University Michigan, Ann Arbor, Stephen E. e s l e r , Department n i v e r s i t y of of Michigan, Arbor, Michigan 48109. MEDAL GOLDICH M EDAL RECIPIENT Burton H. H. Boyum, Boyum, 1740 1740 Glendura Lane, Lane, Ishpeming, Ishpeming, Michigan 49849. ACKNOWLEDGEMENT S ACKNOWLEDGEMENTS The Organizing Organizing Committee of of the t h e 1983 1983 Institute I n s t i t u t e on Lake Superior S u p e r i o r Geology gratefully acknowledge the g r a t e f u l l y acknowledge t h e work of of JJulene u l e n e E. E. Erickson in i n typing t y p i n g drafts d r a f t s and final final manuscript for manuscript f o r the t h e Proceedings Proceedings Volumes. Volumes. 111 iii �REPORT REPORT OF THE THE CHAIRMAN 28th INSTITUTE ON LAKE SUPERIOR GEOLOGY 1982 The 28th Institute I n s t i t u t e on on Lake Superior Geology was hheld e l d May n May 5-8, 5—8, 1982 iin I n t e r n a t i o n a l Falls, F a l l s , Minnesota under the t h e sponsorship of International of the the Minnesota Minnesota Geological Survey. rofessional Survey. R e g i s t r a n t s numbered 147, 147, including i n c l u d i n g 121 p Registrants professional geologists g e o l o g i s t s and and 26 26 students. s t u d e n t s . The program included aa pre-meeting pre—meeting one-day one—day f i e l d trip t r i p to t o examine mineral occurrences iin n the o r t Frances-Mine entre field the F Fort Frances—Mine C Centre area, an overview overview of of a r e a , Ontario, Ontario, a post—meeting post-meeting one—day one-day field f i e l d ttrip r i p tto o pprovide r o v i d e an Falls Kabetogama, Minnesota, Minnesota, and tthe h e Archean geology near International International F a l l s and Kabetogama, four f o u r half—day half-day sessions s e s s i o n s of of technical t e c h n i c a l papers. papers. e r s o n s partic— particSeventy seven p persons pated p a t e d in i n the t h e pre—meeting pre-meeting trip, t r i p , 51 51 participated p a r t i c i p a t e d in i n the t h e post—meeting post-meeting trip, trip, oral presentation a p e r s were accepted for for o ral p r e s e n t a t i o n aatt tthe h e ttechnical echnical and 31 ppapers sessions. s e s s i o n s . Background papers for f o r the field f i e l d trips, t r i p s , ffield i e l d ttrip r i p road o g s , and road llogs, accepted w e r e published published in i n the the Proceedings Proceedinqs volume. volume. a c c e p t e d abstracts a b s t r a c t s were Att the A t h e Annual Dinner on on May 6, 6 , 1982 1982 Ralph Marsden was awarded the Institute's of his many ccontributions I n s t i t u t e ' s Goldich Medal in i n recognition r e c o g n i t i o n of o n t r i b u t i o n s tto o the the Institute I n s t i t u t e and and to t o the t h e geology geology of of the t h e Lake Lake Superior Superior region. region. The banquet address Koski of the U.S. U.S. Geological Survey, Survey, who a d d r e s s was given given by Dr. D r . Randolph Koskiaof described metal—precipitating d e s c r i b e d recent r e c e n t Oceanographic oceanographic research r e s e a r c h on m e t a l - p r e c i p i t a t i n g hhot o t ssprings prings along Pacific, a l o n g spreading s p r e a d i n g ridges r i d g e s in i n the t h e eastern eastern P a c i f i c , and sspeculated p e c u l a t e d on tthe h e rrole ole such hydrothermal systems production of of volcanicvolcanic— systems may have played in i n the production hosted h o s t e d sulfide s u l f i d e deposits d e p o s i t s in i n Archean Archean greenstone greenstone belts. belts. K. University, K. Howard Howard Poulsen, Poulsen, graduate graduate student s t u d e n t at a t Queen's Queen's U n i v e r s i t y , received received a cash award award for f o r presenting p r e s e n t i n g the the best b e s t paper paper by by aa student. s t u d e n t . His H i s paper was was entitled the Fort F o r t Frances—Mine Frances-Mine Centre Centre area." area." e n t i t l e d "Mineral "Mineral deposits d e p o s i t s of of the An open open discussion d i s c u s s i o n on on the the organization o r g a n i z a t i o n of of the t h e Institute I n s t i t u t e was held h e l d on the t h e evening evening of of May May 5, 5, 1982 1982 with w i t h J. J. Kalliokoski K a l l i o k o s k i acting a c t i n g as a s moderator. moderator. About and discussed a range of issues concerning the objec20 people attended a t t e n d e d and discussed of i s s u e s objectives pros the Institute, I n s t i t u t e the , the p r oand s andcons consof offormalization, f o r m a l i z a t i o n , and and tthe h e manner t i v e s of of the I n s t i t u t e now now manages manages or o r should should manage manage its its financial f i n a n c i a l affairs. affairs. iin n which the Institute Several w e r e passed passed arid and ttransmitted r a n s m i t t e d tto o the Board of of S e v e r a l informal informal motions motions were D i r e c t o r s for f o r consideration c o n s i d e r a t i o n at a t their t h e i r annual annual meeting. meeting. Many of of those those Directors attending a t t e n d i n g the t h e discussion d i s c u s s i o n were surprised s u r p r i s e d to t o learn l e a r n that t h a t the t h e IInstitute n s t i t u t e indeed of by-laws, by—laws, and aalso l s o hhas a s an does have a formal constitution c o n s t i t u t i o n and a set s e t of I.R.S. number as tax-exempt, non—profit non-profit organization. o r g a n i z a t i o n . The constitution constitution I.R.S. a s aa tax—exempt, and by—laws by-laws are a r e appended appended to t o this t h i s report. report. met 6, 1982 and took e t on May 6, The Board of of Directors D i r e c t o r s of of the t h e Institute Institute m the t h e following f o l l o w i n g action: action: 1. 1. Accepted with Geological the offer o f f e r of of the t h e Minnesota G e o l o g i c a l Survey to to with thanks thanks the maintain the mailing m a i l i n g list l i s t of of the t h e I.L.S.G. I.L.S.G. The list is i s now stored s t o r e d on a m a i n t a i n the floppy be amended amended easily e a s i l y on on the the Survey's Survey's word word processor. processor. f l o p p y disk d i s k and and can can be The Survey will update the list as instructed by each General Chairman Survey w i l l update t h e l i s t a s i n s t r u c t e d will mailing host i l l supply print—outs p r i n t - o u t s of of the t h e list l i s t and m a i l i n g llabels a b e l s tto o each h ost and w organizing o r g a n i z i n g committee. committee. iv �2. Agreed funds presently Agreed to t o leave l e a v e in i n Canada Canada those t h o s e I.L.S.G. I.L.S.G. funds that that p r e s e n t l y are a r e in in Canada, M.M. Kehienbeck, Kehlenbeck, Lakehead Lakehead University, U n i v e r s i t y , Thunder Thunder Canada, and and to t o appoint a p p o i n t M.M. Bay, Bay, Ontario, O n t a r i o , as a s custodian custodian of of the t h e Canadian Canadian account. account. The The Canadian Canadian monies obligations monies are a r e to t o be be used used against a g a i n s t I.L.S.G. I.L.S.G. o b l i g a t i o n s in i n Canada Canada to t o avoid avoid losses l o s s e s on on currency currency exchange. exchange. AA statement statement of of the the Canadian Canadian account account is is appended appended to t o this t h i s report. report. 3. Formally moved moved that t h a t henceforth henceforth one one dollar d o l l a r of of each each registration r e g i s t r a t i o n fee fee Formally w i l l be be set s e t aside a s i d e into i n t o aa special s p e c i a l fund fund to t o sustain s u s t a i n the the costs c o s t s of of striking striking will Goldich Goldich medals. medals. The w i l l be be kept kept separate s e p a r a t e from from The Goldich Goldich medal medal fund fund will I.L.S.G. operating o p e r a t i n g monies monies and and will w i l l be be maintained maintained in i n aa separate s e p a r a t e bank bank I.L.S.G. account. account. Under Under this t h i s plan p l a n enough enough money money will w i l l have have accumulated accumulated in i n 77 years y e a r s to t o strike s t r i k e aa batch batch of of 10 10 medals, medals, replacing r e p l a c i n g the the supply s u p p l y currently currently on hand. on hand. The The Board Board also a l s o noted noted for f o r the t h e record r e c o r d that t h a t the t h e first f i r s t Goldich Goldich S.S. Goldich, Goldich, the t h e second second to t o Carl C a r l Dutton, Dutton, and and the the medal was was awarded awarded to t o S.S. medal third t h i r d to t o Ralph Ralph Marsden, Marsden, leaving l e a v i n g 77 for f o r subsequent subsequent years y e a r s from from the the first first striking s t r i k i n g of of 10. 10. The The remaining remaining medals medals are a r e in i n the t h e custody custody of of G.B. G.B. Morey, Minnesota Minnesota Geological Geological Survey, Survey, and and are a r e stored s t o r e d in i n aa bank bank safety safety Morey, deposit d e p o s i t box box in i n Minneapolis. Minneapolis. 4. Instructed I n s t r u c t e d the t h e Secretary S e c r e t a r y — Treasurer T r e a s u r e r to t o move move I.L.S.G. I.L.S.G. funds from from the the funds present pays the the maximaxip r e s e n t non—interest—bearing non-interest-bearing account account to t o an an account account that t h a t pays mum mum rate r a t e obtainable o b t a i n a b l e while while maintaining maintaining liquidity. liquidity. 5. Noted Noted the t h e desire d e s i r e of of Robert Robert C. C. Reed, Reed, Secretary S e c r e t a r y — Treasurer, T r e a s u r e r , to t o retire retire from from his h i s position p o s i t i o n as a s of of the t h e next next Board Board meeting meeting in i n Houghton Houghton in i n May May 1983. 1983. AA new new Secretary S e c r e t a r y - Treasurer T r e a s u r e r will w i l 1 ,be b e elected e l e c t e d at a t the t h e Houghton Houghton Meeting. Meeting. - - - 6. Accepted ~ c c e p t e with dwith thanks thanks the t h e offer o f f e r of of the t h e Geology Geology Department Department of of the the University U n i v e r s i t y of of Wisconsin Wisconsin at a t Oshkosh Oshkosh to t o host h o s t the t h e 30th 30th I.L.S.G. I.L.S.G. at at Wausau, Wausau, Wisconsin Wisconsin in i n 1984. 1984. 7. Noted Noted with with anticipation a n t i c i p a t i o n the the informal informal offer o f f e r of of Charles Charles Blackburn, Blackburn, Ontario 1985 Institute Institute O n t a r i o Geological Geological Survey, Survey, Kenora Kenora Office, O f f i c e , to t o host h o s t the t h e 1985 in i n Kenora. Kenora. This T h i s offer o f f e r is i s understood understood to t o be be tentative, t e n t a t i v e , pending pending final final confirmation M r . Blackburn. Blackburn. c o n f i r m a t i o n from from Mr. 8. Moved be included i n c l u d e d each each year y e a r in in Moved that t h a t the t h e summary summary report r e p o r t of of the t h e Chairman Chairman be the c u r r e n t and and t h e next—following next-following Proceedings Proceedings volume volume so s o as a s to t o maintain maintain aa current public p u b l i c account account of of the theInstitute's I n s t i t u t e ' s affairs. affairs. 9. Appointed Appointed the t h e following following persons persons to t o serve s e r v e on on the t h e selection s e l e c t i o n committee committee for f o r recipients r e c i p i e n t s of of the t h e Goldich Goldich medal: medal: Gene y e a r term, term, Chairman Chairman (representing ( r e p r e s e n t i n g academia) academia) LaBerge, 11 year GeneLaBerge, Richard y e a r term, term, (representing ( r e p r e s e n t i n gindustry) industry) Richard Bucheit, Bucheit, 22 year William William Cannon, Cannon, 33 year y e a r term term (representing ( r e p r e s e n t i n g government) government) The The Board Board further f u r t h e r stipulated s t i p u l a t e dthat t h a t subsequent subsequent appointments appointments to t o fill fill vacancies on the committee should maintain the equal representation v a c a n c i e s on t h e committee should maintain t h e equal r e p r e s e n t a t i o n of of academia, academia, industry, i n d u s t r y , and andgovernment. government. V �11G. C. Moved that that the the committee committee to to select select the the best student student paper be appointed appointed the host host organizing organizing committee. committee. The The committee committee appointed appointed each year year by the should consist should consist of representatives representatives from academia, industry, and government. government . Financially the Financially the 28th 28th I.L.S.G. I.L.S.G. concluded concluded with with aa net net profit profit of of $2,210.64, and thus pumped some badly needed funds into the general general $2,210.64, and thus pumped some funds treasury recent deficit meetings meetings and treasury which which had had been been depleted depleted severely severely by recent In my opinion the the start—up start-up costs costs for for the the Goldich Goldich medal medal program. program. In opinion the the Institute is intellectually, and and it is Institute is in good shape both financially and intellectually, with a responsibility for with a sense sense of of satisfaction satisfaction and and relief relief that that I I turn over responsibility operations to Ted Bornhorst Bornhorst of 1983 operations of Michigan Michigan Tech. L. David L . Southwick Southwick David General General Chairman Chairman 28th 1.L-S.G. I.L.S.G. 28th July 30, 1982 1982 July 30, vi �CALENDER CALENDER OF EVENTS EVENTS AND AND PROGRAM PROGRAM TUESDAY, MAY 10, TUESDAY, 10, 1983 1983 7:00 p.m. —- 9:00 9:00 p.m. EARLY REGISTRATION REGISTRATION FOR FOR PARTICIPANTS PARTICIPANTS IN IN FIELD FIELD TRIP TRIP 1. 1. WEDNESDAY, WEDNESDAY, MAY MAY 11, 11, 1983 1983 8:00 8:00 a.m. a.m. —- 6:00 6:00 p.m. FIELD TRIP FIELD TRIP 1. 1. GEOLOGY THE KEWEENAW KEWEENAW PENINSULA, PENINSULA, GEOLOGY OF THE Rose and and J.B. J.B. Paces, Paces, MICHIGAN —- T.J. T.J. Bornhorst, Bornhorst, W.I. Rose leaders. leaders. 4:00 p.m. -- 10:00 p.m. 10:OO p.m. REGISTRATION —- MEMORIAL UNION BUILDING BUILDING 10:00 p.m. p.m. 7:00 p.m. —- 10:OO SMOKER AND CASH BAR 12, 1983 THURSDAY, 1983 THURSDAY, MAY MAY 12, 7:30 a.m. — - 4:30 4:30 p.m. p.m. REGISTRATION — MEMORIAL UNION BUILDING REGISTRATION - MEMORIAL BUILDING 8:20 a.m. — 8:20 - 8:25 a.m. 8:25 a.m. Dr. E.H.T. Whitten, Vice WELCOME TO MICHIGAN TECH, TECH, Dr. E.H.T. Whitten, Vice President Affairs, Michigan Technological President for for Academic Affairs, Technological University. University. 8:25 a.m. — 8:30 a.m. WELCOME TO WELCOME TO 29TH 29TH I.L.S.G., I.L.S.G., T.J. T.J. Bornhorst, Bornhorst, Chairman. Chairman. 8:30 a.m. — 12:00 p.m. TECHNICAL W.S. Cordua Cordua and and S.D. SD. McDowell, TECHNICAL SESSION I, W.S. McDowell, Co—Chairmen. Co-Chairmen. 8:30 a.m. John John C. C. Green Green —— -- COMPOSITION, COMPOSITION, ORIGIN ORIGIN AND AND EVOLUTION OF KEWEENAWAN MAGMAS REVIEW (invited (invited paper). paper). KEWEENAWAN MAGMAS - A REVIEW 9:00 a.m. Klaus J. -- GEOCHEMISTRY GEOCHEMISTRY OF THE THE VOLCANIC VOLCANIC ROCKS ROCKS Klaus J. Schulz Schulz —— OF OF NORTHEASTERN NORTHEASTERN WISCONSIN. WISCONSIN. 9:20 a.m. 9:40 a.m. 10:00 a.m. 10:20 a.m. *James D. Miller, Jr. Jr. -- MAJOR ELEMENT CHEMISTRY OF OF ELEMENT CHEMISTRY ANORTHOSITES ANORTHOSITES IN THE DULUTH COMPLEX, COMPLEX, SNOWBANK SNOWBANK LAKE LAKE THE DULUTH MINNESOTA. QUADRANGLE, MINNESOTA. A.P. Ruotsala, Paul Paul N. M. Stadnik Stadnik and T.J. Bornhorst Bornhorst —— -A.P. Ruotsala, COBALT, NICKEL AND COBALT, NICKEL AND VANADIUM CONTENTS OF PYRITE FROM VANADIUM CONTENTS PYRITE FROM MICHIGAMME SLATE, SLATE, MICHIGAN. MICHIGAN. MICHIGANME COFFEE COFFEE *Abelmonem A. Eldougdoug GEOLOGICAL AND GEOCHEMICAL -- GEOLOGICAL GEOCHEMICAL Eldougdoug —— CHARACTERISTICS GLEN CHARACTERISTICS OF THE VOLCANO-SEDIMENTARY GLEN TOWNSHIP FORMATION, TOWNSHIP FORMATION, EAST-CENTRAL EAST-CENTRAL MINNESOTA. MINNESOTA. vii vii �10:40 a.m. 11:00 a.m. M.L. M.L. Nebel Nebel and R.L. Morton Morton --- HYDROTHERMAL HYDROTHERMAL ALTERATION AT AT THE THE HELEN HELEN MINE, MINE, WAWA, WAWA, ONTARIO. ONTARIO. *Sarah *Sarah J. J. —— THE THE RELATIONSHIP Mills RELATIONSHIP BETWEEN THE BASAL Mills -- AND CLOUD ZONE CU-NI CU—NI SULFIDES, MINNAMAX MINNAMAX ZONE AND DEPOSIT, DEPOSIT, DULUTH DULUTH COMPLEX, COMPLEX, MINNESOTA. MINNESOTA. 11:20 a.m. *Warren ULTRAMETANORPHISM AND MIGMATITE MIGMATITE GENER— *Warren C. Day Day --- ULTRAMETAMORPHISM GENERIN THE ATION IN THEVERMILION VERMILIONGRANITE GRANITECOMPLEX, COMPLEX,NORTHERN NORTHERN MICHIGAN. MICHIGAN. 11:40 a.m. 11:40 a.m. *W.I. Petro —— IGNEOUS ROCKS ROCKS OF OF THE DISTRICT, -- IGNEOUS THE BARABOO BAMBOO DISTRICT, Petro WISCONSIN. WISCONSIN. 12:15 p.m. —- 1:45 p.m. 1:45 p.m. GROUP LUNCHEON, LUNCHEON, Dr. E.H.T. Whitten, Whitten, Vice President President for for Academic Academic Affairs, Affairs, Michigan Michigan Technological Technological University, University, Guest Guest Speaker. Speaker. ANNUAL ANNUAL MEETING, MEETING, I.L.S.G. I.L.S.G. BOARD 2:00 p.m. —- 5:00 p.m. 5:00 p.m. 2:00 p.m. p.m. TECHNICAL SESSION TECHNICAL SESSION II, 11, J.S. J.S. Kiasner Klasner and and C.T. C.T. Young, Young, Co—Chairmen. Co-Chairmen. *M.A. THREE-DIMENSIONAL STRUCTURE *M.A. Feighner Feighner --- THREE-DIMENSIONAL STRUCTURE OF OF THE THE CRUST AND UPPER MANTLE BENEATH LAKE SUPERIOR CRUST BENEATH THE THE LAKE SUPERIOR REGION. REGION. 2:20 2:20 p.m. p.m. C. Patrick LONG-WAVELENGTH GRAVITY Patrick Ervin Ervin --- LONG-WAVELENGTH GRAVITY ANOMALIES ANOMALIES GREAT LAKES IN THE GREAT LAKES REGION. REGION. 2:40 p.m. p.m. Robert J. Robert J. Ferderer, Ferderer, Val W. Chandler Chandler and Judson Judson Mead —— -GRAVITY MAGNETIC MODEL STUDIES GRAVITY AND MAGNETIC STUDIES OF OF THE THE SOUTHERN SOUTHERN DULUTH COMPLEX, NORTHEASTERN DULUTH NORTHEASTERN MINNESOTA. MINNESOTA. 3:00 p.m. Val —— Val W. W. Chandler Chandler -- PALEOMAGNETIC PALEOMAGNETIC AND AND MAGNETIC MAGNETIC ANOMALY ANOMALY STUDIES OF THE STUDIES THENORTHWESTERN NORTHWESTERN DULUTH DULUTH COMPLEX, LAKE LAKE COUNTY, MINNESOTA. MINNESOTA. 3:20 p.m. COFFEE COFFEE 3:40 p.m. STRUCTURE N.E. —— M.E. Bengtson, Bengtson,R.P. R.P.Meyer Meyerand andH.C. H.C.Halls Halls -- THE THE STRUCTURE OF THE SLATE SLATE ISLANDS ISLANDS AREA AREA OF OF LAKE LAKE SUPERIOR. SUPERIOR. 4:00 p.m. ORDOVICIAN CRYPTOEXPLOSION William William S. S. Cordua Cordua —— -- AN ORDOVICIAN CRYPTOEXPLOSION STRUCSTRUCTURE FROM TURE FROM NEAR ROCK ROCK ELM, ELM, PIERCE PIERCE COUNTY, COUNTY, WISCONSIN. WISCONSIN. 4:20 p.m. U.O. Atuanya, Atuanya, D.T.A. Symons —— PALEO— U.O. Symons and and N. M. Stupavsky PALEOStupavsky -MAGNETISM OF THE THE GUNFLINT GUNFLINT IRON IRON FORMATION FORMATION OF OF NORTH— NORTHWESTERN ONTARIO. WESTERN ONTARIO. 4:40 p.m. Kidjopa Attoh, Marc Vander Meulen and Daniel Daniel Brandsma Brandsma —— -MODELS FOR MODELS FOR THE THE COOLING COOLING OF OF THE THE PEAVY PEAVY POND POND COMPLEX: COMPLEX: IMPLICATIONS FOR THE METAMORPHIC METAMORPHIC EFFECT IN SURROUNDING IMPLICATIONS SURROUNDING ROCKS. ROCKS. viii viii �6:00 6:00 p.m. p.m. -- 77:30 : 3 0 p.m. p.m. COCKTAIL PARTY —- CASH CASH BAR 77:30 : 3 0 p.m. p.m. -- 9:30 p.m. 9:30 p.m. ANNUAL BANQUET Master of M a s t e r of Ceremonies C eremonies — - Dr. D r . Albert A l b e r t P. P . Ruotsala, R u o t s a l a , Michigan Michigan Technological T e c h n o l o g i c a l University. University. Guest - Dr. D r . Stephen S t e p h e n E. E . Kesler, K e s l e r , University U n i v e r s i t y of of G u e s t Speaker Speaker — Michigan, M i c h i g a n , "Precious " P r e c i o u s Metal M e t a l Deposits D e p o s i t s and and Metamorphic Metamorphic Processes". Processes". FRIDAY, MAY 13, FRIDAY, 13, 1983 1983 77:30 : 3 0 aa.m. .m. - 12:00 12:OO pp.m. .m. REGISTRATION -- MEMORIAL UNION BUILDING 8:30 12:00 pp.m. 8:30 a.m. a.m. —- 12:OO .m. TECI-INICALS ESESSION T.B. HHoist A.M. Johnson, TECHNICAL S S I O N 1III, 11, T.B. o i s t aand n d A.M. Co—Chairmen. Co-Chairmen. 8:30 a.m. J.K. J . K . Greenburg G r e e n b u r g —— -- RELATIVE AGE AGE AND AND TECTONIC TECTONIC SIGNIFICANCE SIGNIFICANCE OF PROTEROZOIC METASEDIMENTARY ROCKS IN I N THE THE UPPER MIDWEST. 8:50 a.m. REANY CREEK Mattson F.W. Cambray C a m b r a y —-- THE REANY CREEK FORMAFORMAa t t s o n and F.W. SS.R. .R. M MENOMINEE TION: T I O N : A MASS—FLOW MASS-FLOW DEPOSIT D E P O S I T OF OF POSSIBLE P O S S I B L EPOST POST MENOMINEE AGE. 9:10 a.m. AND STRUCTURAL *Fred S. S . Pulka —— -- DEPOSITIONAL DEPOSITIONAL AND STRUCTURAL FEATURE FEATURE OF OF THE UPPER FREDA FREDA SANDSTONE. SANDSTONE. - 9:30 -- EVIDENCE FOR FOR GLACIAL GLACIAL MARINE MARINE SEDIMENSEDIMEN**Lawrence L a w r e n c e C. C . Rosen R o s e n —— TATION IN I N THE EARLY PROTEROZOIC PROTEROZOIC GOWGANDA GOWGANDA FORMATION, FORMATION, ONTARIO, CANADA. NORTHEASTERN ONTARIO, CANADA. a.m. 9:50 a.m. COFFEE 10:20 a.m. Kehlenbach -- SUPERIMPOSED FOLDING AND AND ITS I T S IMPLICAIMPLICAM.M. e h l e n b a c h -— M.M. K TION T I O N ON ON THE THESHEBANDOWAN-QUETICO SHEBANDOWAN-QUETICO SUBPROVINCE SUBPROVINCE BOUNDARY, BOUNDARY, THUNDER BAY, ONTARIO. THUNDER BAY, ONTARIO. 10:40 a.m. FOR NAPPE T.B. H o i s—— t -- EVIDENCE EVIDENCE FOR NAPPE DEVELOPMENT DEVELOPMENT DURING DURING THE THE T . B . Hoist PENOKEAN OROGENYFROM FROM THE THE EARLY PENOKEAN OROGENY EARLY PROTEROZOIC PROTEROZOIC THOMSON THOMSON FORMATION, FORMATION, MINNESOTA. MINNESOTA. J.P. H.H. Woodard J . P . Kaszuba, K a s z u b a ,P.A. P.A.Schwarzweiier S c h w a r z w e l l and e r and H.H. W o o d a r—— d -- 11:00 a.m. FOLDED FOLDED ROCKS ROCKS IIN N THE THE EASTERN EASTERN CONTACT CONTACT ZONE ZONE OF OF THE THE . BATHOLITH. VERMILION BATHOLITH DOMES AND B.A. B.A. Brown B r o w n and J.G. J . G . Greenberg G r e e n b e r g —— -- GNEISS G N E I S S DOMES AND NOT— NOTSO-GNEISS DOMES IN I N THE PENOKEAN PENOKEAN TERRANES TERRANES OF O F NORTHERN NORTHERN S0-GNEISS WISCONSIN. 11:20 a.m. 12:15 p.m. — 1:15 p.m. GROUP LUNCHEON GROUP LUNCHEON - — REPORT ix FROM THE CHAIRMAN. CHAIRMAN. �1:30 p.m. — 4:30 p.m. 1:30 p.m. 1:50 p.m. TECHNICAL TECHNICAL SESSION S E S S I O N IV, I V Y D.L. D . L . Southwick S o u t h w i c k and and N. N. Scofield, Scofield, Co—Chairmen. Co-Chairmen. Gene -- LASALLE LASALLE FALLS F A L L S -- AN AN EXPOSED EXPOSED MASSIVE MASSIVE G e n e L. L . LaBerge L a B e r g e —— SULFIDE S U L F I D E DEPOSIT D E P O S I T IN I N FLORENCE FLORENCE COUNTY, COUNTY, WISCONSIN. WISCONSIN. *David * D a v i d A. A . Groves G r o v e s —— -- STRATIGRAPHY STRATIGRAPHY OF O F THE THE FOOTWALL FOOTWALL VOLCANIC VOLCANIC ROCKS ROCKS BENEATH BENEATH THE THE MATTABI MATTABI MASSIVE MASSIVE SULFIDE S U L F I D E DEPOSIT, DEPOSIT, STURGEON STURGEON LAKE, LAKE, ONTARIO. ONTARIO. 2:10 p.m. John John C. C . Green G r e e n --- PHYSICAL PHYSICAL VOLCANOLOGY VOLCANOLOGY OF O F THE THE KEWEENAWAN KEWEENAWAN NORTH NORTH SHORE SHORE VOLCANICS. VOLCANICS. 2:30 p.m. COFFEE COFFEE 3:00 p.m. Ted J . Smith, S m i t h , Paul P a u l L. L . Cloke C l o k e and and Stephen Stephen J. J. Kesler K e s l e r —— -T e d J. GEOCHEMISTRY GEOCHEMISTRY OF O F FLUID F L U I D INCLUSIONS I N C L U S I O N S FROM FROM ARCHEAN ARCHEAN AND AND PHANEROZOIC PHANEROZOIC GOLD GOLD DEPOSITS. DEPOSITS. 3:20 p.m. W.A. W.A. Bodwell, B o d w e l l , J.D. J . D . Strapko S t r a p k o and and G.J. G . J . Tonkin T o n k i n —— -- HISTORY, HISTORY, GEOLOGY, GEOLOGY, AND AND RECENT RECENT EXPLORATION EXPLORATION OF O F THE THE ROPES ROPES GOLD GOLD MINE, ( i n v i t e d paper). paper). MINE, MARQUETTE MARQUETTE COUNTY, COUNTY, MICHIGAN MICHIGAN (invited 4:10 p.m. *Dean * D e a n Rossell R o s s e l l —— -- ALTERATION ALTERATION OF O F THE THE DEER DEER LAKE LAKE PERIDOTITE PERIDOTITE IN I N THE VICINITY V I C I N I T Y OF O F THE THE ROPES GOLD GOLD MINE, MINE, MARQUETTE COUNTY, MICHIGAN. COUNTY , MICHIGAN. 4:30 4:30 p.m. p.m. ANNOUNCEMENT -- BEST B E S T STUDENT STUDENT PAPER PAPER AWARD AWARD ANNOUNCEMENT -- 1 4 , 1983 1983 SATURDAY, MAY MAY 14, SATURDAY, 8:00 a.m. a . m . —8:00 1. 1. 2. 2. 6:00 p.m. p.m. FIELD F I E L D TRIP T R I P II. 11. THE THE ROPES GOLD GOLD MINE MINE AND AND ITS I T S GEOLOGICAL GEOLOGICAT. SETTING S E T T I N G —- D. D. Rossell R o s s e l l and and J. J . Kalliokoski, K a l l i o k o s k i , leaders. leaders. U n d e r l i n e denotes d e n o t e s speaker speaker Underline *student * s t u d e n t paper paper x �ABSTRACTS 4BSTRACTS �2 of the t h e Gunflint G u n f l i n t Iron I r o n Formation of of Northwestern Ontario Ontario Paleomagnetism of U. U. 0. 0. ATUANYA, ATUANYA, D.T.A. D.T.A. SYMONS, SYMONS, and N. M. STUPAVSKY STUPAVSKY (Department (Department of of Geology, Geology, University U n i v e r s i t y of of Windsor, Windsor, Windsor, Windsor, Ontario, O n t a r i o , Canada Canada N9B 3P4) 3P4) Formation ooutcrops Bay, Ontario, The Gunf G u n f llint i n t I Iron r o n Formation u t c r o p s nnear e a r Thunder Bay, O n t a r i o , as as the unit t h e bbasal asal u n i t of of the t h e Animikie Series S e r i e s in i n the t h e Southern Province of of the the Canadian Precambrian Shield. S h i e l d . Paleomagnetic studies s t u d i e s on samples from 47 ssites i t e s employing alternating a l t e r n a t i n g field, f i e l d , thermal t h e r m a l and chemical demagnetdemagneti z a t i o n techniques t e c h n i q u e s lead l e a d to t o the t h e isolation i s o l a t i o n of of two major m agnetization ization magnetization components. The A component yields pole position component y ields a p ole p o s i t i o n of of l24°W, 124OW, 64°N 64ON (Sp = 100) to bbe primary oordiagenetic g o , 5m (Sm = 10') which is i s interpreted i n t e r p r e t e d 'to e aa primary r diagenetic (tjp == 90 component 23OO Ma. component aacquired c q u i r e d aat t -2300 Ma. A positive p o s i t i v e conglomerate conglomerate test t e s t supports supports this pole component gives gives a p o l e position p o s i t i o n of of 40°W, 40°W 7°S 7's t h i s conclusion. c o n c l u s i o n . The B component 130) (Sp which indicates the presence of a Hudsonian (tip == 8°, 8O, tjm = 13') i n d i c a t e s t h e presence of a Hudsonian 'm = orogenic metamorphic metamorphic ooverprint l72O Ma. Taken together orogenic v e r p r i n t aacquired c q u i r e d aat t -1720 Ma. Taken together "Penokean" orogeny orogeny of of tthe tthe h e rresults e s u l t s iindicate n d i c a t e tthat h a t tthe h e "Penokean" h e Southern Province iin United S States Province n tthe h e nnorthcentral o r t h c e n t r a l United t a t e s iis s eequivalent q u i v a l e n t to t o the the Hudsonian orogeny s l i g h t l y younger -l65O -1650 Ma Ma metamorphic orogeny in i n Canada. Canada. A slightly componetlt i is componetit s rrestricted e s t r i c t e d tto o aa few ssites i t e s in i n the t h e Gunflint. G u n f l i n t . Contact ttests ests w i t h a Keweenawan Logan Sill S i l l and and aa lava l a v a flow flow are a r e positive. positive. with �3 Models for forthe the Cooling Cooling of ofthe the Peavy PeavyPond Pond Complex: Complex:Implications Implications Models for the the Metamorphic Metamorphic Effect Effect in inSurrounding SurroundingRocks Rocks for ATTOH, KODJOPA KODJOPA (Department (Departmentof ofGeology, Geology,Hope HopeCollege, College,Holland, Holland,MIMI49423) 49423) ATTOH, VANDER MEULEN, MEULEN,MARC MARC (Department (Department of of Geology, Geology,Hope Hope College, College,Holland, Holland, VANDER MI 49423) 49423) MI BRANDSMA, BRANDSMA, DANIEL DANIEL (Department (Departmentof of Geological Geological Sciences, Sciences,University University of of Southern SouthernCalifornia, California,Los LosAngeles, Angeles,CACA90089) 90089) The Peavy Peavy Pond Pond Complex Complex(PVC), (PVC), located located'^ 12km 12km NW NW from from Iron Iron Mountain Mountain The in in northern northern Michigan, Michigan, is is comprised comprised predominantly predominantly of of gabbroic gabbroic and and dioritic dioritic intrusive intrusiverocks rocksexposed exposedin inan anarea area14km2. 14km2 It It is is interpreted interpreted as as aa sill-like sill-likebody body which which is is intrusive intrusive into into the the base base of of the the Michigamme Michigamme Fm Fm and and whose whose base base is is crudely crudely conformable conformable with with the the top top of of the the underunderlying Hemlock HemlockFm. Fm. lying . We We have have calculated calculated the the solidification solidificationpositions positions inside, inside,and and tempertemperature ature outside outside the the pluton pluton assuming assuming the the temperature temperatureof of emplacement emplacement of of the the magma magma is is % 1000°C 1000OC and and aa latent latent heat heat of of solidification solidification (AH) (AHs)asas % 100 100cal/gm. cal/gm. For For aa one-dimensional one-dimensional model, model, in in which which aa 3.2km 3.2km thick thick pluton pluton extending extending infinitely infinitelydownwards downwards cools cools by by conduction: conduction:the the 800°C 800° solidification 10 xx 10 103yrs yrs solidification position position is is .34km .34km from from the the contact contact after after % 10 during during which which time time the the maximum maximum temperature temperature reached reached at at the the contact contact is is In In this this model, model, the the PVC PVC is is completely completely solidified solidified 231 231 xx 103 103 yrs yrs 678'~. 678°C. after intrusion. intrusion. If If convection convection occurs occurs during during cooling, cooling, the the maximum maximum after temperature temperature at at the the contact contact is is 888°C 888% and and convection convection persists persists for for two-dimensional model model for for aa rectangular rectangular pluton pluton 157-x lo3 years. years. AA two-dimensional l57x (3.2 4.4km) produces produces maximum maximum contact contact temperatures temperaturesof ofonly only4970C. 497OC. (3.2 xx 4.4km) Temperatures Temperatures at at positions positions outside outside the the pluton, pluton, in in the the Michigamme Michigamme Fm, Fm, were calculated calculated from fromthe theone-dimensional one-dimensionalmodels. models. At At 2.6km 2.6km from from the the were contact, contact, aa position position corresponding corresponding to to the the mapped mapped staurolite staurolite isograd, isograd, the i3 yrs yrs is is 302°C, 302OC, during during the maximum maximum temperature temperature reached after 486 xx 103 cooling by by conduction. conduction. The The 5000C 5000C isotherm isotherm advances advances to to aa maximum maximum cooling distance of of % .78km .78km from from the the contact, contact, reaching reaching that that position position distance lo3years. years. During During cooling cooling involving involving convection, convection, the the after 76 76 xx iü after l.lkm from from the the contact, contact, maximum advance advance of of the the 500°C 500OC isotherm isotherm is is % 1.1km maximum lo3 yrs yrs after after intrusion, intrusion, and and the the maximum maximum temperature temperature arriving 100 100 xx i03 arriving reached at at the the staurolite stauroliteisograd isograd is is349°C. 349OC. reached The The calculated calculated temperatures temperatures (T) (T) outside outside the the pluton pluton are are much much lower lower than the the T-conditions T-conditions of of the the observed observed metamorphic metamorphiczones. zones. For For example, example, than the the temperature temperature for for the the staurolite staurolite isograd isograd is is estimated estimated from from the the garnet-biotite geothermometer geothermometer to to be be 540°C. 540°C Moreover, Moreover, the the T-gradient T-gradient garnet-biotite due to to thermal thermal effect effect of of PVC PVC is is % 80°C/km 80°C/k whereas whereas the the T-gradient T-gradient due 370C/km. inferred from from the the spacing spacing of of metamorphic metamorphic isograds isograds is is % 370C/km. inferred �4 The The Structure S t r u c t u r e of of the t h e Slate S l a t e Islands I s l a n d s Area Area of of Lake Lake Superior Superior M. E. E. Bengtson Bengtson and and R. R. P. P. Meyer Meyer (Geophysical (Geophysical and and Polar P o l a r Research Research M. Center, Department of of Geology Geology and and Geophysics, Geophysics, University U n i v e r s i t y of of C e n t e r , Department Wisconsin—Madison, Wisconsin-Madison, Madison, Madison, WI W I 53706) 53706) H. H. C. C. Halls H a l l s (Erindale ( E r i n d a l e College, College, Mississauga, Mississauga, Ontario, O n t a r i o , Canada, Canada, and and Canada) Department Department of of Geology, Geology, University U n i v e r s i t y of of Toronto, Toronto, Canada) The The origin o r i g i n of of the t h e Slate S l a t e Islands I s l a n d s structure s t r u c t u r e of of northern n o r t h e r n Lake Lake Some propose the islands S u p e r i o r is i s the t h e subject s u b j e c t of of debate. d e b a t e . Some propose t h e i s l a n d s are are Superior the t h e result r e s u l t of of meteoritic m e t e o r i t i c impact impact while w h i l e others o t h e r s advocate a d v o c a t e an an endogenous endogenous marine magnetic magnetic and and seismic s e i s m i c survey survey was was undertaken undertaken to to o r i g i n . AA marine origin. examine this t h i s question. question. examine Over Over 1,500 1,500 km km of of magnetic magnetic and and 3.5—kHz 3.5-kHz sonic s o n i c profiles p r o f i l e s were were taken. taken. The The sonic s o n i c data d a t a have have been been used used to t o construct c o n s t r u c t aa bedrock bedrock bathymetry bathymetry map, i s similar s i m i l a r to t o aa bottom bottom bathymetry bathymetry map map constructed c o n s t r u c t e d from from map, which which is Both show show aa d a t a taken t a k e n by by the t h e Canadian Canadian research r e s e a r c h vessel v e s s e lBayfield. B a y f i e l d . Both data concentric c o n c e n t r i c pattern p a t t e r n centered c e n t e r e d on on the t h e islands. i s l a n d s . However, However, the t h e bedrock bedrock The sonic data topography topography exhibits e x h i b i t s almost almost 50% 50%greater g r e a t e r relief. r e l i e f . The s o n i c data also a l s o indicate i n d i c a t e that t h a t the t h e bedrock bedrock is i s more more chaotic c h a o t i c inside i n s i d e the t h e bathybathym e t r i c high h i g h that t h a t surrounds s u r r o u n d sthe t h eislands. islands. metric curvilinear AA magnetic magnetic contour c o n t o u r map map has h a s also a l s o been been constructed. c o n s t r u c t e d . AA curvilinear north—south n o r t h - s o u t h trending t r e n d i n g magnetic magnetic gradient g r a d i e n t east e a s t of of the t h e islands i s l a n d s marks marks the t h e boundary boundary between between the t h e Port P o r t Coldwell Coldwell complex complex and and Archean Archean basement basement It appears a p p e a r s that t h a t the t h e Port P o r t Coidwell Coldwell complex complex extends e x t e n d s at a t least least r o c k s . It rocks. km iinto n t o the t h e lake. l a k e . Short—wavelength Short-wavelength anomalies anomalies on on the t h e east e a s t side side 25 kin 25 of of the t h e islands i s l a n d s have have half—widths h a l f - w i d t h s that t h a t indicate i n d i c a t e source s o u r c e depths d e p t h s 1/2 112 to to These may may well w e l l be b e feeders f e e d e r s for f o r the the km below below the t h e lake l a k e surface. s u r f a c e . These 11 km P o r t Coidwell Coldwell complex. complex. Port West West of of the t h e islands, i s l a n d s , aa northwest—trending n o r t h w e s t - t r e n d i n g linear l i n e a r anomaly anomaly has h a s been been This T h i s is i s most most likely l i k e l y due due to t o aa basin—bounding basin-bounding fault, f a u l t , with with it. Keweenawan volcanics v o l c a n i c s lying l y i n g only o n l y south s o u t h of of it. Keweenawan identified. identified. This Finally, F i n a l l y , the t h e islands i s l a n d s seem seem to t o be b e surrounded surrounded by by aa magnetic magnetic low. low. This is i s consistent c o n s i s t e n t with w i t h an an arcuate a r c u a t e increase i n c r e a s e in i n depth d e p t h to t o aa coherent c o h e r e n t magmagn e t i c basement basement centered c e n t e r e d on on the t h e islands. islands. netic Over Over 250 250 km km of of explosion e x p l o s i o n seismic s e i s m i c reflection r e f l e c t i o n and and refraction r e f r a c t i o n lines lines of aa Twenty-five km km east e a s t of of the t h e islands, i s l a n d s , over over 700 700 mm of were taken. taken. Twenty—five were 3.5—km/s 3.5-km/s material m a t e r i a l overlies o v e r l i e s about about 500 500 mm of of aa 4.5—km/s 4.5-km/s material. material. These These velocities v e l o c i t i e s have have been been correlated c o r r e l a t e d with w i t h the t h e Bayfield—Jacobsville Bayfield-Jacobsville s a n d s t o n e s and and the t h e Oronto Oronto Group, Group, respectively. r e s p e c t i v e l y . These These sediments sediments sandstones overlie o v e r l i e aa 5.8—km/s 5.8-km/s refractor, r e f r a c t o r , which which is i s the t h e Port P o r t Coldwell Coldwell complex. complex. Twelve Twelve km km west west of of the t h e islands, i s l a n d s , the t h e sediments sediments thin t h i n to t o aa total total t h i c k n e s s of of less l e s s than t h a n 500 500 m. m. Here Here they t h e y overlie o v e r l i e aa 6.1—km/s 6.1-km/s refractor, refractor, thickness which is i s probably probably the t h e Archean Archean basement. basement. This T h i s thinning t h i n n i n g suggests s u g g e s t s that that which the Archean basement basement rocks. rocks. t h e islands i s l a n d s lie l i e onapre—Keweenawan onapre-Keweenawan ridge r i d g e of of Archean All A l l refractors r e f r a c t o r s outside o u t s i d e the t h e peripheral p e r i p h e r a l trough t r o u g h have have aa southerly s o u t h e r l y dip. dip. �5 The The Structure S t r u c t u r e of of the t h e Slate S l a t e Islands I s l a n d s Area Area of of Lake Lake Superior S u p e r i o r (continued) (continued) In Here I n the t h e trough, t r o u g h , there t h e r e is i s some some evidence e v i d e n c e of of minor minor faulting. f a u l t i n g . Here only o n l y small s m a l l amounts amounts of of Bayfield—Jacobsville B a y f i e l d - J a c o b s v i l l e sandstones s a n d s t o n e s remain. remain. However, However, up up to t o 11 km km of of aa material m a t e r i a l with w i t h apparent a p p a r e n t velocities v e l o c i t i e s of of 4.2 4.2 t o 4.5 4.5 km/s exists. e x i s t s . This T h i s represents r e p r e s e n t s either e i t h e r Oronto Oronto Group Group material material to Below this t h i s material m a t e r i a l is i s aa refractor refractor or o r some some type t y p e of of crater c r a t e r breccia. b r e c c i a . Below T h i s is i s probably probably with w i t h apparent a p p a r e n t velocities v e l o c i t i e s of of about about 5.5 5.5 km/s. km/s. This fractured f r a c t u r e d Archean Archean basement. basement. Minor Minor faulting f a u l t i n g southwest southwest of of the t h e islands i s l a n d s has h a s also a l s o been been observed. observed. The sense s e n s e of of motion is i s consistent c o n s i s t e n t with w i t h the t h e interpretation i n t e r p r e t a t i o n of of aa basin—bounding basin-bounding fault f a u l t with w i t h the t h e basin b a s i n to t o the t h e south. south. In I n summary, summary, the t h e magnetic and seismic s e i s m i c data d a t a indicate i n d i c a t e aa morphology that t h a t supports s u p p o r t s the t h e impact impact origin o r i g i n hypothesis, h y p o t h e s i s , although a l t h o u g h an a n endogenous endogenous origin o r i g i n cannot cannot be b e completely completely ruled r u l e d Out. out. �6 Gneiss Domes and Not—5o—Gneiss Not-So-Gneiss domes in i n the the Penokean Terranes T e r r a n e s of of Northern Wisconsin BROWN, BROWN, B.A. B.A. (Wisconsin (Wisconsin Geological G e o l o g i c a l and and Natural N a t u r a l History H i s t o r y Survey, Survey, 1815 W I 53705—4096) 53705-4096) 1815 University U n i v e r s i t y Ave., Ave., Madison, Madison, WI GREENBERG, J.G. J . G . (Wisconsin (Wisconsin Geological G e o l o g i c a l and Natural N a t u r a l History H i s t o r y Survey, Survey, 1815 1815 University U n i v e r s i t y Ave., Ave., Madison, Madison, WI W I 53705—4096) 53705-4096) The Northern Penokean terrane t e r r a n e (NPT) (NPT) and and the t h e Penokean Penokean volcanic volcanic belt b e l t (PVB) (PVB) of of northern n o r t h e r n Wisconsin Wisconsin are a r e each each characterized c h a r a c t e r i z e d by by aa distinct d i s t i n c t type type of major major gneissic g n e i s s i c pluton. p l u t o n . The The Northern Northern Penokean Penokean terrane t e r r a n e is i s intruded i n t r u d e d by by aa series s e r i e s of of mantled mantled gneiss g n e i s s domes. domes. These These bodies b o d i e s are a r e gneiss g n e i s s domes domes in i n the t h e true t r u e sense, s e n s e , consisting c o n s i s t i n g of of Archean Archean (up b.y. old) (up to t o 3.5 3.5 b.y. o l d ) granitic g r a n i t i c rocks r o c k s which were remobilized and ememplaced p l a c e d at a t their t h e i r present p r e s e n t crustal c r u s t a l level l e v e l during d u r i n g the t h e Penokean Penokean Orogeny Orogeny (1850 The domes domes are a r e mantled by metasedimentary rocks r o c k s of of (1850 m.y. m.y. ago). ago). The the t h e Marquette Range Range Supergroup, Supergroup, and and their t h e i r outlines o u t l i n e s are a r e clearly c l e a r l y dedelineated l i n e a t e d by by the t h e magnetic magnetic expression e x p r e s s i o n of of the t h e iron i r o n formations. formations. The The Penokean Penokean volcanic v o l c a n i c belt b e l t contains c o n t a i n s large l a r g e foliated f o l i a t e d granitic g r a n i t i c bodies bodies of of aa distinctly d i s t i n c t l y different d i f f e r e n t character. c h a r a c t e r . The The gneisses g n e i s s e s and and granites granites themselves themselves are a r e superficially s u p e r f i c i a l l y similar s i m i l a r to t o those t h o s e in i n the t h e NPT, NPT, but b u t isoisotopic m.y. Also, Also, t o p i c evidence evidence suggests s u g g e s t s ages ages ranging r a n g i n g from from 1760 1760 to t o 2000 2000 m.y. these t h e s e rocks rocks are a r e intrusive i n t r u s i v e into i n t o greenschist g r e e n s c h i s t facies f a c i e s metavolcanic rocks. r o c k s . The The domes domes in i n the t h e NPT were formed formed in i n aa region r e g i o n of of amphibolite amphibolite faèies f a c i e s metamorphism. metamorphism. The The gneissic g n e i s s i c rocks rocks of of the t h e PVB PVB are a r e complex, complex, multiphase m u l t i p h a s e plutonic p l u t o n i c bodies, b o d i e s , probably probably representing r e p r e s e n t i n g magma magma emplaced emplaced at at aa deep deep crustal c r u s t a l level, l e v e l , which which rose r o s e diapirically d i a p i r i c a l l y to t o form form large l a r g e concorconcordant I t has h a s been been suggested suggested by by other o t h e r authors a u t h o r s that t h a t gneisses gneisses d a n t plutons. p l u t o n s . It in i n the t h e PVB PVB represent r e p r e s e n t basement basement to t o the t h e volcanic v o l c a n i c sequence. sequence. If I f this t h i s is is the t h e case, c a s e , they they must be b e only only slightly s l i g h t l y older o l d e r or o r their t h e i r isotopic i s o t o p i c syssystems tems must have have been been thoroughly thoroughly homogenized during d u r i n g the t h e Penokean Penokean to to account account for f o r the t h e apparent a p p a r e n t lack l a c k of of Archean ages ages so s o common common in i n the t h e NPT NPT gneisses. gneisses . We We suggest s u g g e s t that t h a t the t h e gneissic g n e i s s i c plutons p l u t o n s of of the t h e PVB PVB are a r e comparable comparable in in overall o v e r a l l aspect a s p e c t to t o the t h e large l a r g e composite composite batholiths b a t h o l i t h s typical t y p i c a l of of Archean Archean Greenstone Greenstone belts b e l t s of of the t h e Superior S u p e r i o r Province. Province. The The nature n a t u r e of of the t h e plu— plutons, t o n s , when when considered c o n s i d e r e d with w i t h the t h e localized l o c a l i z e d nature n a t u r e of of the t h e metamorphism metamorphism and and the t h e chemical chemical character c h a r a c t e r of of the t h e metavolcanic rocks r o c k s argues a r g u e s for for comparison comparison of of the t h e PVB PVB with w i t h greenstone g r e e n s t o n e belts b e l t s of of known known Proterozoic Proterozoic age, a g e , such such as a s Flin F l i n Flon Flon and and Lynn Lynn Lake Lake in i n Canada. Canada. The The contrast c o n t r a s t in i n the t h e character c h a r a c t e r of of plutonism plutonism further f u r t h e r underscores underscores the imt h e differences d i f f e r e n c e s between between the t h e NPT NPT and and the t h e PVB, PVB, and and emphasizes emphasizes the t h e importance p o r t a n c e of of the t h e Niagara Niagara tectonic t e c t o n i c zone zone as a s aa fundamental fundamental boundary boundary separating s e p a r a t i n g these t h e s e terranes. terranes. �7 Paleomagnetic Paleomagnetic and and Magnetic Magnetic Anomaly Anomaly Studies Studies of of the the Northwestern Northwestern Duluth Duluth Complex, Lake Lake County, County, Minnesota Minnesota Complex, VAL W. CHANDLER CHANDLER (Minnesota (Minnesota Geological Geological Survey, Survey, 1633 1633 Eustis Eustis Street, Street, St. St. VAL W. Paul, MN MN 55108) 55108) Paul, The The effect effect of of remanent remanent magnetization magnetization on on magTletic magnetic anomaly expression expression was was investigated investigated for for the the Bald Bald Eagle Eagle intrusion, intrusion, aa composite composite body body in in the the northwestern northwestern Duluth Duluth Complex. Complex. Unlike Unlike most most of of the the Duluth Duluth Complex, Complex, this this (30 1cm2) intrusion intrusion is is well well exposed exposed and and is is known known to consist (30 km2) consist of of an an outer outer (11 by 4 km) ring of of troctolitic troctolitic rocks rocks surrounding surrounding aa gabbroic gabbroic core. core. (11 km) ring The The magnetic magnetic anomaly anomaly expression expression in in the the area area does does not not correspond correspond to to either either the the Bald Bald Eagle Eagle intrusion intrusion or or surrounding surrounding features features in in that that indiindividual vidual anomalies anomalies appear appear to to be be shifted shifted eastward eastward from from their their probable probable sources. Broad, Broad, large—amplitude large-amplitude (>2000 02000 gammas) gammas) minima minima occur occur over over sources. parts impling that that reversely reversely polarized polarized parts of of the the Bald Bald Eagle Eagle intrusion intrusion impling rocks may may be be present. present. However, However, measured remanent remanent magnetizations magnetizations for for rocks oriented samples from five sites in the troctolitic oriented samples from five sites in the troctolitic rocks rocks and and two two sites sites in in the the gabbroic gabbroic rocks rocks indicate indicate that that the the Bald Bald Eagle Eagle intrusion intrusion actually has a remanent magnetization directed essentially actually has a remanent magnetization directed essentially along along the the average = 290°, 290° inclination inclination = 40°) 40° for for average normal normal direction direction (declination (declination = Keweenawan rocks rocks in in Minnesota. Minnesota. Thus, Thus, the the large large magnetic magnetic minima minima must must Keweenawan represent represent either either aa deep—seated deep-seated or or aa regional—scale regional-scale anomaly anomaly effect. effect. Remanent Remanent magnetization magnetization was was observed observed to to be be generally generally much much stronger stronger values in excess of 5 were than induced induced magnetization magnetization and and QQ values in excess of 5 were common. common. than To To correct correct for for the the anomaly anomaly effect effect of of the the strong strong remanent remanent magnetizamagnetization, reduction—to—pole filtering was done on a detailed tion, reduction-to-pole filtering was done on a detailed grid grid of of aeroaeromagnetic magnetic data data over over the the intrusion. intrusion. It It was was assumed assumed that that remanence remanence was was everywhere everywhere much stronger stronger than than induced induced magnetization magnetization and and total total polaripolarization 290 and and inclinainclinazation was was therefore therefore directed directed along along aa declination declination of of 290° tion of of 40°. 40° The The data data reduced reduced to to the the pole pole showed showed aa much much improved improved tion correspondence correspondence to to the the mapped mapped contacts contacts of of the the Bald Bald Eagle Eagle intrusion, intrusion, as as well as as to to contacts contacts of of several several surrounding surrounding features. features. Further Further proprowell cessing cessing of of the the reduced reduced data data by by high—pass high-pass filtering filtering revealed revealed intricate intricate structures structures within within individual individual rock rock units, units, and and appears appears to to have have isolated isolated a a previously previously unreported unreported fault fault intersecting intersecting the the Bald Bald Eagle Eagle intrusion intrusion and and extending extending northwestward northwestward at at least least as as far far as as the the basal basal contact contact zone zone of of the the Duluth Duluth Complex. Complex. The The results results of of this this study study demonstrate demonstrate the the power power of of reduction reduction to to the the pole pole in in accounting accounting for for complications complications arising arising i— from from strong strong remanent remanent magnetization. magnetization. The The procedure procedure should shouldsignif significantly cantly enhance enhance magnetic magnetic interpretations interpretations over over large, large, poorly poorly exposed exposed parts of of the the Duluth Duluth Complex. Complex. parts Alternating Alternating field field demagnetization demagnetization in in aa few few samples samples implies implies several several secondary secondary components, components, including including one one that that appears appears to to be be directed directed westwestward ward at at aa shallow shallow inclination. inclination. This This component component is is similar similar in in direction direction to to an an overprint overprint reported reported in in Michigan Michigan for for the the Copper Copper Harbor Harbor Conglomerate Conglomerate and and further further investigation investigationis is warranted. warranted. �8 An Ordovician O r d o v i c i a n Cryptoexplosion c r y p t o e x p l o s i o n Structure Structure An From Near Near Rock Rock Elm, Elm, Pierce P i e r c e County, County, Wisconsin Wisconsin From WILLIAM S. S . CORDUA, CORDUA, (Department (Department of o f Plant P l a n t and a n d Earth E a r t h Science, S c i e n c e , University university WILLIAM W I 54022) 54022) o f Wisconsin—River W i s c o n s i n - R i v e r Falls, F a l l s , River R i v e r Falls, F a l l s , WI of An An apparent a p p a r e n t cryptoexplosion c r y p t o e x p l o s i o n structure s t r u c t u r e centered c e n t e r e dnear n e a rRock RockElm, Elm, Pierce i s nearly n e a r l y circular c i r c u l a r with w i t h aa diameter d i a m e t e r of o f 6.5 6.5 P i e r c e County, County, Wisconsin W i s c o n s i n is k i l o m e t e r s and a n d an a n area a r e a of o f about a b o u t 33 33 km2. km 2 . The The structure s t r u c t u r e coincides coincides kilometers with pronounced reqional r e g i o n a l negative n e g a t i v e gravity g r a v i t y anomaly. anomaly. It I t is i s surrounded surrounded w i t h aa pronounced by by Prairie P r a i r i e du d u Chien Chien Group Group dolomites d o l o m i t e s which which are a r e folded, f o l d e d , faulted, f a u l t e d , and and brecciated b r e c c i a t e d within w i t h i n aa few few hundred h u n d r e d meters m e t e r s of o f the t h e edge e d g e of o f the t h e structure. structure. This i s particularly p a r t i c u l a r l y intense i n t e n s e within w i t h i n aa large, l a r g e , arcuate, arcuate, T h i s deformation d e f o r m a t i o n is fault-bounded f a u l t - b o u n d e d block b l o c k along a l o n g the t h e southern s o u t h e r n edge e d g e of o f the t h e structure. s t r u c t u r e . The The rocks r o c k s within w i t h i n the t h e structure s t r u c t u r e consist c o n s i s t of o f an a n unusual u n u s u a l sedimentary s e d i m e n t a r ysection. section. The exposed e x p o s e d base b a s e of o f the t h e section s e c t i o n is i s aa conglomeratic c o n g l o m e r a t i c quartz q u a r t z arenite arenite The containing c o n t a i n i n g chert, c h e r t , dolomite, d o l o m i t e rrhyolite, h y o l i t e , granite g r a n i t e and a n d quartzite q u a r t z i t e clasts. clasts. This T h i s unit u n i t forms forms aa domal domal uplift u p l i f t in i n the t h e middle m i d d l e of o f the t h e cryptoexplosion cryptoexplosion i s apparently a p p a r e n t l y overlain o v e r l a i n by by over over s t r u c t u r e . The The conglomeratic c o n g l o m e r a t i c sandstone s a n d s t o n e is structure. 30 meters m e t e r s of o f interbedded i n t e r b e d d e d grey g r e y pyritiferous p y r i t i f e r o u s shale s h a l e and and bioturbated bioturbated 30 T h i s in i n turn t u r n is i s overlain o v e r l a i n by by 77 meters m e t e r s of of f i n e - g r a i n e d quartz q u a r t z arenite. a r e n i t e . This fine—grained medium—bedded m e t e r s of o f massive, massive, medium-bedded fine—grained f i n e - g r a i n e d quartz q u a r t z arenite, a r e n i t e , 55meters friable a t least l e a s t 22 meters m e t e r s of o f ferruginous, f e r r u g i n o u s , medium— mediumf r i a b l e quartz q u a r t z arenite, a r e n i t e , and a n d at g r a i n e d quartz q u a r t z arenite. a r e n i t e . Lower Lower to t o middle m i d d l e Ordovician O r d o v i c i a n gastropods g a s t r o p o d s have have grained reportedly r e p o r t e d l y been b e e n found f o u n d in i n concretions c o n c r e t i o n s in i n the t h e shale, s h a l e , suggesting s u g g e s t i n g that that it i t is i s an a n anomalously a n o m a l o u s l y thick t h i c k section s e c t i o n of o f the t h e Readstown Readstown Member Member of o f the the S t . Peter P e t e r Formation. F o r m a t i o n . The The overlying o v e r l y i n g sands s a n d s could c o u l d thus t h u s correlate c o r r e l a t e with with St. T o n t i Member Member of o f the t h e St. S t . Peter P e t e r Formation, F o r m a t i o n , aa conclusion c o n c l u s i o n supported supported t h e Tonti the The shales s h a l e s and a n d other other by grain g r a i n size s i z e analysis a n a l y s i s and and heavy h e a v y mineral m i n e r a l studies. s t u d i e s . The by rocks r o c k s within w i t h i n the t h e cryptoexplosion c r y p t o e x p l o s i o n structure s t r u c t u r e have h a v e not n o t been been deformed deformed to to the Chien Formation F o r m a t i o n and and the t h e con— cont h e extent e x t e n t of o f the t h e surrounding s u r r o u n d i n g Prairie P r a i r i e du du Chien g l o m e r a t i c sandstones s a n d s t o n e s of o f the t h e central c e n t r a l dome. dome. glomeratic Diamonds Diamonds and and gold g o l d were reportedly r e p o r t e d l y found f o u n d in i n the t h e 1880's 1 8 8 0 ' s in i n the t h e gravels gravels from f r o m sixeams streams ddraining r a i n i n g tthe h e sstructure, t r u c t u r e , suggesting s u g g e s t i n g possible p o s s i b l e erosion e r o s i o n of of m i n e r a l i z e d bedrock. b e d r o c k . AA reconnaissance r e c o n n a i s s a n c e ground g r o u n d magnetic m a g n e t i c study s t u d y has has mineralized d e l i n e a t e d aa positive p o s i t i v e magnetic m a g n e t i c anomaly anomaly associated a s s o c i a t e d with w i t h the t h e northnorthdelineated w e s t e r n edge edge of o f the t h e structure, s t r u c t u r e , upstream u p s t r e a m from from the t h e former f o r m e r placer placer western I t is i s possible, p o s s i b l e , however, however, that t h a t the t h e minerals m i n e r a l s were w e r e eroding eroding o p e r a t i o n s . It operations. f r o m aa red r e d drift d r i f t cap c a p that t h a t partially p a r t i a l l y covers c o v e r s the t h e structure. s t r u c t u r e . So So far, far, from heavy heavy mineral m i n e r a l studies s t u d i e s of o f the t h e stream s t r e a m sediments s e d i m e n t s have h a v e yet y e t to t o turn t u r n up up any anomalies a n o m a l i e s that t h a t could c o u l d be b e related r e l a t e d to t o the t h e erosion e r o s i o n of o f mineralized mineralized any b e d r o c k or o r poorly p o o r l y exposed e x p o s e d plutons. plutons. bedrock i n c l u d e the the I m p o r t a n t constraints c o n s t r a i n t s on on the t h e structure's s t r u c t u r e ' s origin o r i g i n include Important circular c i r c u l a r shape, s h a p e , the t h e otherwise o t h e r w i s e undeformed nature n a t u r e of o f the t h e Paleozoic Paleozoic bedrock b e d r o c k in i n the t h e region, r e g i o n , and and the t h e post-Shakopee, p o s t - S h a k o p e e , pre-Readstown pre-Readstown timing timing o f the t h e intense i n t e n s e deformation. d e f o r m a t i o n . This T h i s Ordovician o r d o v i c i a n deformation d e f o r m a t i o n and a n d subsubof sequent s e q u e n t erosion e r o s i o n produced p r o d u c e d aa deep d e e p circular c i r c u l a r lowland l o w l a n d that t h a t progressively progressively filled f i l l e d with w i t h clay, c l a y , silt, s i l t , and and sand s a n d during d u r i n g St. S t . Peter P e t e r time. t i m e . The The strucstructure t u r e could c o u l d represent r e p r e s e n t an a n isolated i s o l a t e d explosive e x p l o s i v e volcanic v o l c a n i c feature, f e a t u r e , however, however, �9 of volcanic material does not tthe h e lack lack o f v olcanic m a t e r i a l anywhere in i n tthe h e region region d oes n o t ssupport upport tthis h i s interpretation. interpretation. A l t e r n a t i v e l y , the t h e structure s t r u c t u r e could c o u l d be b e an a n OrdoOrdoAlternatively, vician with Wells i t h sediment, s e d i m e n t , similar s i m i l a r to t o tthe he W ells v i c i a n astrobleme a s t r o b l e m e tthat h a t later l a t e r filled filled w Creek C r e e k and a n d Flynn F l y n n Creek structures s t r u c t u r e s in i n Tennessee. Tennessee. IIf f pplutonism l u t o n i s m and mineralization occurred have m ineralization o c c u r r e d in i n the t h e rregion, e g i o n , tthe h e pplutonism l u t o n i s m could could h a v e bbeen een triggered t r i g g e r e d by the t h e impact. i m p a c t . Alternatively, A l t e r n a t i v e l y , later l a t e r plutonism p l u t o n i s m and and mineralimineraliby ddeep—seated zzation a t i o n ccould o u l d hhave a v e bbeen e e n ccontrolled o n t r o l l e d by e e p - s e a t e d ffractures r a c t u r e s pproduced roduced So far, by the t h e impact. impact. f a r , however, however, no n o plutonic p l u t o n i c rocks r o c k s or o r features features characteristic of origin, orr characteristic o f iimpact mpact o r i g i n , such s u c h as a s shattercones, s h a t t e r c o n e s , ssuevites, uevites, o have been E l m structure. structure. A eejecta j e c t a bblankets lankets h ave b e e n found in i n or o r near n e a r the t h e Rock Rock Elm t h i r d alternative a l t e r n a t i v e is i s that t h a t the t h e structure s t r u c t u r e is i s related r e l a t e d to t o uplift u p l i f t and third differential d i f f e r e n t i a l weathering w e a t h e r i n g around a r o u n d aa large l a r g e unexposed unexposed pre—Readstown pre-Readstown pluton. pluton. Further F u r t h e r geologic g e o l o g i c studies, s t u d i e s , including i n c l u d i n g drilling, d r i l l i n g , heavy heavy mineral m i n e r a l analyses, analyses, seismic needed tto s e i s m i c arid and oother t h e r ggeophysical e o p h y s i c a l sstudies t u d i e s aare r e needed o further f u r t h e r elucidate elucidate the i n t e r e s t i n g structure. structure. t h e origin o r i g i n and and nature n a t u r e of o f this t h i s interesting �10 ULTRAMETAMORPHISM ULTRAMETAMORPHISM AND AND MIGMATITE THE MIGMATITE GENERATION GENERATION IN IN THE VERMILION GRANITE GRANITE COMPLEX, NORTHERN MINNESOTA VERMILION Warren C. (Minnesota Geological Geological Survey, Survey, 1633 1633 Eustis Eustis Street, Street, St. St. C- Day Day (Minnesota Minnesota 55108) 55108) Paul, Minnesota Paul, ABSTRACT ABSTRACT The 2,700—m.y.—old The 2,700-m.y.-old Vermilion Vermilion Granitic Granitic Complex Complex (VGC) (VGC)is is aa granite—migma-qranite-migmatite terrane tite terrane consisting consisting of aa supracrustal supracrustal sequence sequence of biotite biotite schist, schist, tonalite, and The granite garnet—bearing tonalite, and granite. granite. The granite is is of of two two types: types: garnet-bearing two—mica leucogranite two-mica leucogranite (LEUG) (LEUG) and and the the biotite-bearing biotite-bearing Lac Lac La La Croix Croix Granite Granite (LLCG). The The syntectonic syntectonic LEUG LEUG occurs occurs as as stringers stringers and and small small bodies bodies within within (LLCG). the biotite the biotite schist, schist, forming forming the the neosome neosomeof ofschist-rich schist-richmiginatite. migmatite. The The LLCG LLCG supracrustal country rocks, forming neosome of granite— graniteintrudes the supracrustal forming the neosome rich rich migmatite migmatite and and the the batholithic batholithic part part of of the the VGC. VGC. Metamorphic Metamorphic and and geochemical studies elucidate the petrogenesis of these geochemical studies were undertaken to elucidate granite granite neosomes neosomes along along the the northern northern border of the the VGC in in the the Kabetogama Kabetogama Lake area. Lake area. Three MI was was the the main main Three phases phases of of metamorphism metamorphism affected affected the the area. area. Ml regional was a a post—tectonic post-tectonic event event produced produced by by prograde event, event, and and M2 was regional prograde was a late—stage deuteric late-stage deuteric alteration. alteration. M3 was a metamorphic metamorphic recrystallization recrystallization event event along along the the major major bounding bounding faults. faults. The The regional regional Ml M1 metamorphic metamorphic conconditions ditions were were estimated estimated from from the the mineral mineral assemblages assemblages in in the the biotite biotite schist. schist. Petrographic Petrographic evidence evidence indicates indicates that that Ml MI exceeded exceeded the the breakdown breakdown reaction reaction + H20 + QTZ = H2O and the STAR transformaSTAR ++ MUSCO MUSCO + = SIL BIO ++ GAR + the AND = = SIL SIL ++ BIO SIL transformaQTZ tion. tion. However, there is no evidence for the breakdown reaction reaction MUSCO + QTZ = H20. The The data data indicate indicate that that peak peak regional regional Ml MI conditions conditions = SIL SIL ++ K-SPAR ++ H2O. ranged from to 55 kbar. kbar. These These conditions conditions Overlap overlap miniminiranged from 650°C 650° to to 700°C 700° and and 44 to conditions (Ptotal (total = schist, implying an mum melting conditions - PHlo) of the biotite schist, implying H2o) anatectic anatectic origin origin for for the the LEUG. LEUG. The objective The objective of of the the geochemical geochemical studies studies was was to to determine determine if if any any comcompositional gradients attributed to to anatexis. anatexis. positional gradients in in the the migmatite migmatite can can be attributed Millimeter—scale samples Millimeter-scale samples were taken taken normal normal to to foliation foliation across across two two hypothesis that schist/restite/leucosome transitions transitions to test the hypothesis that the LEUG melted from from the the biotite biotite schist, schist, leaving leaving the the restite restite margin margin as as aa residual residual wisp of of LEUG LEUG neosome, neosome, and another phase. One One traverse traverse crossed crossed an an8—trim—wide 8-mm-wide wisp another transected transected the the interface interface between between aa larger larger vein vein of of LEUG LEUG neosome neosome and and biotite biotite Small cores were drilled schist. (6 mm, 2 g) were drilled and analyzed analyzed for for major and schist. Small cores (6 Corresponding modes (obtained trace trace elements. elements. Corresponding (obtained using plane polarized light light and indicate that that quartz quartz and and feldspar feldspar dominate the and cathodoluininescence) cathodoluminescence) indicate leucosome, leucosome, whereas biotite, apatite, apatite, and oxides oxides are concentrated concentrated in in the the restite margin. restite margin. Of these these minerals minerals only only apatite apatite would would concentrate concentrate the the rare— rareearth (REE) earth elements elements (PEE). . �11 The results results of of the the chemical chemical analyses analyses indicate: indicate: The 1 ) As expected, expected, the the major and and minor element element content content reflect reflect modal 1) variations across both both traverses. traverses. Therefore variations across MgO, FeOt, FeOt, 1(20, K20, Ti02, Zr, Co, Co, Therefore MgO, Ti02, Zr, Ni, Sc Na20 and Ni, Sc are are concentrated concentrated in in the the biotite-rich biotite-rich margin, whereas whereas NanO and Si02 SiOy are concentrated in in the the quartz quartz and and feldspar feldspar neosome. neosome. In both traverses, traverses, are concentrated the total REE abundances abundances are are greater greater in in the the schist schist and and restite restite margin than than the total in in the the neosome. neosome. The two 2) The two traverses traverses show show significant significant differences differences in in PEE REE profiles. profiles. These These 2) differences differences reflect reflect the the dynamic dynamic behavior behavior of of the the migmatite migmatite generation. generation. a) a) The narrow The narrow 8-mm 8-mm LEUG LEUG wisp wisp formed formed as as aa closed closed system. system. This is indiindiThis is cated cated by comparatively comparatively enriched enriched PEE REE abundances abundances in in the the apatite—rich apatite-rich restite restite margin. margin. b) b) The 5-cm LEUG LEUG vein vein formed formed as as an an open open system. system. The The expected expected The larger larger 5—cm REE enrichment REE enrichment in in the the apatite—rich apatite-rich restite restite margin was not not observed. Although both vein vein types types appear appear mineralogically similar, similar, they they formed formed under considerably considerably different different petrogenetic petrogenetic conditions. conditions. �12 Geological Characteristics of of the the Volcano—Sedimentary Volcano-Sedimentary Geological and Geochemical Geochemical Characteristics Glen Glen Township Township Formation, Formation, East—Central East-Central Minnesota Minnesota ABDELMONEM A. ELDOUGDOUG ELDOUGDOUG (Department (Department of of Geology Geology and and Geophysics, Geophysics, ABDELMONEM University University of of Minnesota, Minnesota, Minneapolis, Minneapolis,Minnesota Minnesota551155) 55455) Petrographic Petrographic study study of of twelve twelve drill drill cores cores reveals reveals that that the the Township Formation Glen Township Formation consists consists of of the the following: following: 1) slate, quartzites, 1) Pelitic slate, quartzites, and and metaconglomerates. metaconglomerates. 2) 2) Oolitic Oolitic jaspilite. jaspilite. magnetite—silicate—(minor carbonate carbonate and quartz) 3) Cherty and slaty magnetite-silicate-(minor facies Iron Iron Formation Formation (I.F.). facies (I.F.). 14)Pyrite, Pyrite, pyrite-pyrrohotite, pyrite—pyrrohotite, and and pyrrohotite pyrrohotite bearing graphitic 4) graphitic argillite—sulphide I.F. argillite-sulphide facies facies I.F. siderite—(minor silicate, silicate, magnetite, magnetite, and quartz) 5) Massive and banded siderite-(minor fades I.F. — carbonate carbonate facies I.F. 6) Ankerite bearing 6) Ankerite bearing feldspathic feldspathic metagreywacke. metagreywacke. 7) Metavolcanics (metaandesites, (metaandesites, metadiorites, crystal tuff). tuff). 7) metadiorites, and crystal - The The sequence sequence has has been assigned assigned to to the the lower lower part of of the the Mille Mille Lacs Lacs Group Group and was metamorphosed and deformed during during the the Penokean Penokean Orogeny Orogeny (,'1,900 to 1,850 (&1,900 1,850 m.y. m.y. ago). ago). Massive Massive quartz quartz veinlets veinlets containing containing pyrite, pyrite, siderite siderite and and minor minor chal— chalcopyrite are lower part of of the the copyrite are present present throughout throughout the the sequence. sequence. The lower pyrite or or pyrrhotite pyrrhotite mesobands graphitic argillite contains pyrite mesobands (up (up to to upper part of of this this argillite argillite 10 mm thick) and is 1 0 nun is highly highly folded. folded. The upper This horizon contains pyrite-pyrrhotite horizon. This horizon contains contains contains aa massive pyrite—pyrrhotite angular argillite and in angular fragments fragments of of graphitic argillite in some some places places appears appears to to indibe cemented by siderite, chlorite and quartz. Textural evidence indialteration cates that this horizon represents a site of hydrothermal alteration and and fracturing. fracturing. The in the the The occurrence occurrence of of sulphides sulphides as as highly folded folded mesobands mesobands in argillite indicates indicates that they are of syngenetic graphitic argillite syngenetic origin. (1968) and This is is in in accord with the conclusion reached by Han (1968) contrasts epigenetic origin originproposed proposed by by Theil Theil(19214) (1924) and and contrasts with with the the epigenetic Schwartz (1951). Schwartz (1951). Data on Au, Ag, Zn, Data Zn, Co, Co, Ni, Cu, Cu, and As in in the the different different iron iron forformation facies, facies, pyrite—siderite—quartz pyrite-siderite-quartz veinlets, veinlets, and associated associated rocks rocks The results results and preliminary preliminary models models of of are are presently presently being being collected. collected. The the distribution, distribution, and mobility of precious metals in this type of of geologic terrane will be discussed along with their implications implications for exploration. exploration. References References Han, Tsu-ming Tsu—ming (1968): ( 1968): Ore mineral relations in in the the Cuyuna Cuyuna sulphide sulphide Han, deposits, Minnesota. Mineraliuni Deposita (Berlin), v. 3, deposits, Minnesota. Mineralium Deposita (Berlin), v. 3,p. p. 109—1314. 109-134. Schwartz, Schwartz, G.M. G.M. (1951): (1951): Minnesota iron iron suiphide: sulphide: in in Mining Symposium, Symposium, Geology of of the the Cuyuna Cuyuna Range, Range, Univ. Minn. General General Ext. Div., Div., April April 1951, p. 1411—115. 1951, p. 44-45. Theil, Iron sulphides suiphides in magnetite magnetite belts Theil, G.A. G.A. (19211): (1924): Iron belts near near the the Cuyuna Cuyuna Range, Econ. Range, Econ. Geol., Geol., v.v.19, 19,p.p.1466—1472. 466-472. �13 Long-Wavelengt h G r a v i t y Anomalies in i n the t h e Great Great Lakes Region Long—Wavelength Gravity C. PATRICK PATRICK ERVIN (Dept. C. (Dept. of of Geology, Geology, Northern Northern Illinois I l l i n o i s University, University, DeKaib, DeKalb, IL 60115) 60115) To examine possible p o s s i b l e relationships r e l a t i o n s h i p s between the t h e sources s o u r c e s of of major gravitational g r a v i t a t i o n a l anomalies in i n central c e n t r a l North America, America, the t h e gravity g r a v i t y field field was digitized d i g i t i z e d at a t aa 40 40 km km interval i n t e r v a l to t o produce aa 60 60 x 40 40 grid. g r i d . Using tthe h e two-dimensional, a s a guide, g u i d e , these t h e s e data d a t a were then then two—dimensional, power spectrum as wavelength—filtered possible w a v e l e n g t h - f i l t e r e d to t o enhance p o s s i b l e continuities c o n t i n u i t i e s between the the regional r e g i o n a l anomalies. anomalies. The analysis a n a l y s i s reaffirms r e a f f i r m s the t h e lack l a c k of of any direct direct relationship r e l a t i o n s h i p between the t h e Kapuskasing Anomaly and the t h e anomalies to t o the the south. s o u t h . A deep—seated deep-seated continuity c o n t i n u i t y of of the t h e Midcontinent Gravity G r a v i t y High Basins tthrough h r o u g h tthe h e Michigan and Illinois Illinois B a s i n s and into i n t o the t h e Mississippi Mississippi i s implied i m p l i e d by by the t h e long—wavelength long-wavelength field. f i e l d . Inclusion I n c l u s i o n of of Embayment is wavelengths degrades degrades tthis but iintermediate n t e r m e d i a t e wavelengths h i s ccontinuity, ontinuity, b u t suggests s u g g e s t s tthe he presence of of a regional, r e g i o n a l , northwest—trending n o r t h w e s t - t r e n d i n g fracture f r a c t u r e system. system. �14 Three—dimensional Three-dimensional structure structure of of the the crust crust and and upper upper mantle mantle beneath beneath the the Lake Lake Superior Superior region region M.A. M.A. FEIGI4ER* FEIGHNER* (Dept. (Dept. of of Geology Geology and and Geological Geological Engrg., Engrg., Michigan Michigan Tech. University, University, Houghton, Houghton, MI MI 49931) 49931) Tech. The The structure structure of of the the crust crust and and upper upper mantle mantle was was investigated investigated by by the the use wave arrival arrival times times recorded by the Michigan— use of of tele.seismic teleseismic PP wave the Upper MichiganNorthern Northern Wisconsin Wisconsin (UNNW) (UMNW) Seismic Seismic Network. Network. Four Four methods methods were were used used to to decipher decipher the the structure structure of of the the crust crust beneath beneath the the region. region. They They were: were: travel travel time time residuals, residuals, apparent apparent velocity velocity (reciprocal (reciprocal of of slowness) slowness) and and azimuth azimuth values values calculated calculated for for events, events, ray ray tracing, tracing, and and three—dimensional three-dimensional inversion of of residuals. residuals. The The inversion inversion method method allowed allowed determination determination of of inversion velocity velocity variations variations in in the the mantle mantle to to depths depths of of 500 500 km. km. Results Results show show that that the the Mohorovcic Mohorovcic Discontinuity Discontinuity beneath beneath the the UMNW UMNW Network Network to to be be aa north—south north-south trending trending antiform, antiform, plunging plunging to to the the north north totowards the the axis axis of of the the Lake Lake Superior Superior syncline. syncline. Seismic Seismic station station MEW MEW (Mel— (Melwards len, len, Wisconsin), Wisconsin), located located on on the the eastern eastern flank flank of of the the Midcontinent Midcontinent GravGravity had events events that that arrived arrived 0.7 0.7 to 1.0 1.0 second earlier ity High High (MCII), (MGH), had earlier than than at at other other stations stations in in the the network. network. Inversion Inversion studies studies indicate indicate that that the the crust crust beneath beneath NEW MEW has has aa six six percent percent higher higher velocity velocity than than at at the the other other stations. From From ray ray tracing, tracing, the the crust crust was was also also found found to to be be thin thin near near stations. this station. station. Therefore, Therefore, aa high high velocity velocity material material underlying underlying the the MGH MGH Is is this suggested suggested with thinning thinning of the the crust crust of of about about 55 km. km. The The nature nature of of the the mantle mantle beneath beneath the the region region as as determined determined by by three— threedimensional dimensional seismic seismic inversion inversion indicate indicate that: that: (1) The upper upper mantle mantle beneath beneath portions portions of of the the MGH MGH may may be be denser denser (1) The than surrounding surrounding areas. areas. This This is is indicated indicated by by aa zone zone of of velocities velocities fastfastthan er than than the the layer layer average average in in the the40 40toto200 200kin km depth depth range. range. The The anomaly anomaly is is present in in the the gneiss gneiss terrane terrane in in northwestern northwestern Wisconsin Wisconsin but but disapdisapThis suggests suggests that that the the pears northward into into the the greenstone greenstone terrane. terrane. This velocity velocity structure structure in in the the upper upper mantle mantle beneath beneath the the MGH MGH is is dependent dependent upon upon basement basement terrane. terrane. (2) An An east—west east-west velocity velocity boundary boundary in in northern northern Wisconsin Wisconsin is is pres(2) ent ent in in the the 200 200 to to 350 350 km km depth depth range range of of the the mantle. mantle. The The boundary boundary has has aa lateral lateral extent extent of some some 300 300 km km and and could could represent represent an an ancient ancient suture suture rerelated lated to to the the collision collision of of plates plates during during the the Penokean Penokean orogeny. orogeny. This This also also suggests suggests that continental continental plates plates have have structures structures that that extend extend to to depths depths of of 350 350 km km and and are are stable stable for for periods periods of of time time of of 1.8 1.8 bIllIon billion years. years. (3) Shorter Shorter wavelength wavelength velocity velocity anomalies anomalies are are present present in in the the 350 350 (3) to 500 km depth 500 km depth range range and suggest suggest that that heterogeneities heterogeneities exist exist at at these these depths depths in in the the mantle. mantle. *Now at Chevron Chevron Geosciences, Geosciences, Houston, Houston, TX. TX. �15 Duluth Complex, Gravity and Magnetic Model Studies Studies of the Southern Southern Duluth Northeastern Minnesota Northeastern ROBERT J. FERDERER (Minnesota (Minnesota Geological 1633 Eustis Street, Street, Geological Survey, Survey, 1633 St. Paul, Paul, MN MN 55108) 55108) VAL VAL W. W. CHANDLER CHANDLER (Minnesota (Minnesota Geological Geological Survey, Survey, 1633 1633 Eustis Eustis Street, Street, St. St. Paul, MN 55108) 55108) Paul, MN JUDSON JUDSON MEAD MEAD (Dept. (Dept. of of Geology, Geology, Indiana Indiana University, University, Bloomington, Bloominqton, IN IN 47401) 47401) Large—amplitude gravity Large-amplitude gravity and magnetic anomalies anomalies are are associated associated with the dominantly mafic igneous middle Proterozoic Proterozoic the igneous rocks of the the middle Two—dimensional gravity (Keweenawan Supergroup) Supergroup) Duluth (Keweenawan Duluth Complex. Two-dimensional gravity and magnetic magnetic model model studies studies along along three three profiles profiles extending extending across across the the southern half of the Duluth Complex Complex were performed performed in southern the Duluth in order to investigate the Duluth Complex investigate the structure structure of the the Duluth Complex at at depth and and the the locations of The three tions of near—surface near-surface rock—magnetization rock-magnetization contrasts. contrasts. The three profiles intersect Duluth Complex files intersect the the basal contact contact of the the Duluth Complex near near 47°27' N., N., 92O07' 92°07' W.; W.; 47°12' N., 92O12' 92°l2' W.; W.; and 46°57' N., 92°16' W. 47O12' N., 46O57' N., 92O16' W. 47O27' The The northernmost northernmost profile profile trends trends N. 900 90 E., E., and and the the two two southern southern proprofiles trend Density, magnetic magnetic susceptibility files trend N. N. 105° 105O E. E. Density, susceptibility and and remanent remanent magnetization magnetization data data were were measured measured from from rocks rocks throughout throughout the the southern southern Duluth Duluth Complex. Complex. Gravity model studies studies were constrained constrained by densities densities determined determined from from seismic refraction seismic refraction data data and and field field samples. samples. Seismically Seismically determined determined densities and densities and gravity gravity models models are are mutually supportive supportive for for Duluth Duluth Complex/country rock density contrasts which extend to density contrasts extend to aa depth depth of 20 20 Gravity models further imply that the basal contact of km. km. further imply that the contact of the the Duluth Complex dips E. near near the the northernmost northernmost profile profile and and 60° 60 E. and and 550 5S0 Complex dips 25° 2S0 E. E. near near the the two two southern southern profiles. profiles. Model Model studies studies utilizing utilizing aeromagnetic aeromagnetic data data upward upward continued continued to to aa level imply that that most of the the magnetic anomaly anomaly expression expression of of level of 11 km imply the southern Duluth Complex the southern Duluth Complex can can be accounted accounted for for by eastward-dipping eastward-dipping sources located within the km of crust, 6 km crust, polarized polarized near near or or sources located within the upper 6 along the Keweenawan normal direction along the average average Keweenawan direction (inclination (inclination = 40°, 40° = 290°) direction of polarization polarization is is consistent consistent declination = declination 290°). This direction Magnetic with rock rock magnetization magnetization data data which which imply imply an an average average QQ of of 3. Magnetic 3. models datafurther furtherimply implythat that an an increase increase in models and and rock—magnetization rock-magnetization data in rock—magnetizationoccurs occurs eastward eastward across across the rock-magnetization thesouthern southernDuluth DuluthComplex. Complex. The The increase increase in in magnetization, together together with its its low-dipping low-dipping normal normal direction, direction, can can account account for for the the regional regional magnetic magnetic low low which which occurs occurs over over the western portion of the complex. the western portion of the complex. Several large-amplitude large—amplitude magnetic anomalies (<3500 (c3500 gammas) occur Several The westernmost along the along the northern northern profile. profile. The westernmost of of these, these, whose whose maximum maximum occurs at N., 91°42' W., is caused by oxide-rich oxide-rich occurs at 47°27' 47O27' N., 91°42 W., is thought thought to to be caused troctolitic rocks troctolitic rocks which have have been been observed observed in in drill drill core core from from this this area. area. It It is is probable probable that that highly magnetized magnetized sources, sources, used used to to model model aa N., 91°24' broader anomaly anomaly with aa maximum located located at at 47°27' 47O27' N., 91024' W., W., are are related related to to similar similar troctolitic troctolitic rocks, rocks, although although there there are are no no outcrop outcrop or or drill drill core core data data to to verify verify this this possibility. possibility. Both ~ o t hof of these these large large The pres— presmagnetic magnetic anomalies anomalies are are bounded bounded to to the the east east by by felsic felsic rocks. rocks. The �16 ence ence of of eastward-dipping eastward-dipping contacts contacts in in the the magnetic magnetic models models implies implies that that the the felsic felsic rocks rocks lie lie stratigraphically stratigraphically above above the the inferred inferred troctolitic troctolitic masses. It It follows follows that that the the troctolitic troctolitic and and felsic felsic rocks rocks may may be be genegenemasses. tically be several several troctolite-felsic troctolite-felsic intruintrutically related related and and that that there there may may be sions sions along along the the profile. profile. �17 Composition, Composition, Origin O r i g i n and and Evolution E v o l u t i o n of of Keweenawan Keweenawan Magmas Review Magmas —- aa Review JOHN JOHN C. C. GREEN GREEN (Dept. (Dept. of of Geology, Geology, University U n i v e r s i t y of of Minnesota—Duluth, Minnesota-Duluth, Duluth, MN 55812) 55812) Duluth, MN masKeweenawan magma magma compositions compositions are a r e best b e s t approximated approximated by by the t h e masKeweenawan s i v e , least—altered l e a s t - a l t e r e d parts p a r t s of of the t h e abundant abundant aphyric a p h y r i c lavas l a v a s and and dikes. dikes. sive, Much more more study s t u d y is i s necessary n e c e s s a r y to t o be b e able a b l e to t o infer i n f e r with w i t h any any precision precision Much the t h e parent p a r e n t magmas magmas of of the t h e major major layered l a y e r e d intrusive i n t r u s i v e complexes. complexes. Lava analyses a n a l y s e s show show that t h a t the t h e most most primitive p r i m i t i v e liquids l i q u i d s were were high—Al high-Al Lava olivine ~ e + ~ =) 0.65—0.68, )0.65-0.68, rich rich o l i v i n e tholeiites t h o l e i i t e s with w i t h Mg Mg' (atomic (=atomicMg/(Mg Mg/ (Mg + Fe+2)) i n Ni N i and and Cr C r and and low low in i n the t h e incompatible i n c o m p a t i b l e elements elements such such as a s K, K, Ti, T i , P, P, in and and rare r a r e earths. e a r t h s . Olivine O l i v i n e tholeiites t h o l e i i t e s showing showing aa strong s t r o n g Fe Fe —- enrichment enrichment trend t r e n d to t o Mg MgO—0.45 -0.45 constitute c o n s t i t u t e the t h e most most abundant abundant lava l a v a type. t y p e . Also Also very very abundant are a r e "transitional" " t r a n s i t i o n a l " basalts b a s a l t s which which also a l s o tend tend to t o be b e Fe—rich Fe-rich but but abundant with w i t h increasing i n c r e a s i n g amounts amounts of of alkalies a l k a l i e s and and other o t h e r incompatibles. i n c o m p a t i b l e s . With With ininc r e a s i n g Si02 S i 0 2 and and alkalies a l k a l i e s these t h e s e merge merge into i n t o the t h e considerably c o n s i d e r a b l y less less creasing abundant abundant basaltic b a s a l t i c andesites a n d e s i t e s and and andesites a n d e s i t e s and and eventually e v e n t u a l l y icelandites. icelandites. R h y o l i t e s form form aa secondary secondary though though low low peak peak of of abundance. abundance. Minor Rhyolites Minor vavarieties r i e t i e s such s u c h as a s mugearite, mugearite, tholeiitic t h o l e i i t i c hawaiites, h a w a i i t e s , and and ferroandesite ferroandesite a r e locally l o c a l l y found found in i n the t h e North North Shore Shore Volcanic Volcanic Group Group (NSVG). (NSVG). are + -The most pprimitive The most r i m i t i v e oolivine l i v i n e ttholeiites h o l e i i t e s were probably derived d e r i v e d from from an undepleted u n d e p l e t e d spinel s p i n e l lherzolite l h e r z o l i t e mantle m a n t l e at a t moderate moderate 25—30% 25-30% melting m e l t i n g of of an d e p t h s (35—55 (35-55 1cm), km), w i t h perhaps n l y aa small s m a l l amount of olivine o l i v i n e fracfracdepths with perhaps oonly tionated t i o n a t e d out o u t in i n transit t r a n s i t to t o the t h e surface. s u r f a c e . The The origin o r i g i n of of the t h e Fe—enrichFe-enrichment trend t r e n d between between these t h e s e and and the t h e transitional t r a n s i t i o n a l basalts b a s a l t s is i s uncertain uncertain ment and and controversial. c o n t r o v e r s i a l . Were Were they t h e y derived d e r i v e d by by partial p a r t i a l melting m e l t i n g of of more more Fe— Fer i c h mantle m a n t l e than t h a n appears a p p e a r s in i n typical t y p i c a l peridotite p e r i d o t i t e xenoliths x e n o l i t h s in i n other other rich terranes? t e r r a n e s ? If I f so, s o , they t h e y must must have have resulted r e s u l t e d from from smaller s m a l l e r degrees d e g r e e s of of melting p r i m i t i v e tholeiites. t h o l e i i t e s . Are A r e they t h e y the t h e result r e s u l t of of fracfracm e l t i n g than t h a n the t h e primitive tional t i o n a l crystallization c r y s t a l l i z a t i o n of of the t h e primitive p r i m i t i v e composition? composition? Detailed D e t a i l e d modelmodeling i n g by by Brannon Brannon with w i t h major major and and trace t r a c e elements elements suggests s u g g e s t s not. n o t . Did Did primprimitive i t i v e basalt b a s a l t assimilate a s s i m i l a t e ancient a n c i e n t sialic s i a l i c crust? c r u s t ? Sr S r and and Nd Nd isotopes i s o t o p e s say say no. no. Did Did the t h e magmas magmas tend tend to t o equilibrate e q u i l i b r a t e with w i t h earlier e a r l i e r Keweenawan Keweenawan wall wall rocks r o c k s to t o produce produce this t h i s trend? t r e n d ? (Brannon (Brannon et e t al, a l , 1981.) 1981.) Could Could mixing mixing of of two end—members end-members (transitional ( t r a n s i t i o n a l basalt, b a s a l t , primitive p r i m i t i v e olivine o l i v i n e tholeiite) t h o l e i i t e ) be be two involved? involved ? The The origin o r i g i n of of the t h e compositional compositional trend t r e n d between between basaltic b a s a l t i c andesites andesites and and rhyolites r h y o l i t e s is i s almost almost as a s uncertain. u n c e r t a i n . Although Although mantle m a n t l e melting m e l t i n g can can be be ruled r u l e d out, o u t , various v a r i o u s combinations combinations of of fractional f r a c t i o n a l crystallization, c r y s t a l l i z a t i o n , crustal crustal m e l t i n g , wallrock w a l l r o c k reaction, r e a c t i o n , and and magma magma mixing mixing can c a n be b e entertained. entertained. melting, B a s i c chemical chemical data d a t a are a r e accumulating accumulating and and detailed d e t a i l e d modeling modeling necessary necessary Basic to narrow the possibilities is in progress. t o narrow t h e p o s s i b i l i t i e s i s i n p r o g r e s s . Reference Reference Brannon, J . C . , Haskin, Haskin, L.A. L.A. and and Green, Green, J.C., J . C . , 1981, 1981, Fractional F r a c t i o n a l crystal— crystalBrannon, J.C., lization l i z a t i o n in i n NSVG? NSVG? (abs.): ( a b s . ) : Geol. Geol. Soc. Soc. Amer. Amer. Abst. Abst. with w i t h Prog., Prog., v. v . 13, 13, p . 271. 271. p. �18 PHYSICAL VOLCANOLOGY VOLCANOLOGY OF OF THE KEWEENAWAN KEWEENAWAN NORTH NORTH SHORE SHORE VOLCANICS JOHN C. C. GREEN (Geology (Geology Department, University U n i v e r s i t y of of Minnesota, Minnesota, Duluth, Duluth, Duluth, Duluth, tIinnesota Minnesota 55812) 55812) Although their t h e i r individual i n d i v i d u a l extents e x t e n t s are a r e not n o t so s o well w e l l controlled c o n t r o l l e d by drilldrillLake vvolcanics White, 1960), 1960), the of the iing n g aas s tthe h e PPortage o r t a g e Lake o l c a n i c s (e.g. (e.g. White, t h e llavas a v a s of the well North Shore Volcanic Group (NSVG) (NSVG) are are w e l l exposed and many of of their t h e i r original original volcanic v o l c a n i c features f e a t u r e s are a r e observable. o b s e r v a b l e . IIn n aa study s t u d y correlating c o r r e l a t i n g field f i e l d observations observations and physical with p h y s i c a l characteristics characteristics w i t h chemical type t y p e of of 198 198 flows, f l o w s , the t h e following following generalizations g e n e r a l i z a t i o n s have have emerged. emerged. very ((a) a ) Explosive activity a c t i v i t y was v e r y rare r a r e except except in i n some some icelandite i c e l a n d i t e and and rrhyolite h y o l i t e ash a s h flows. flows. Even in i n interflow i n t e r f l o w sediments, s e d i m e n t s , vesicular v e s i c u l a r ash, a s h , scoria, s c o r i a , and sshards h a r d s are a r e rare. rare. Many textures (b) (b) t e x t u r e s as a s well w e l l as a s structures s t r u c t u r e s point p o i n t to t o the t h e low low viscosity v i s c o s i t y of of these t h e s e lavas l a v a s on eruption. eruption. 60% of of the non—porphyritic and thus ( c ) 60% t h e fflows l o w s aare re n o n - p o r p h y r i t i c and t h u s were erupted e r u p t e d at at (c) temperatures l i q u i d u s temperatures, t e m p e r a t u r e s , thus t h u s contribcontribt e m p e r a t u r e s aatt lleast e a s t aass hhigh i g h aass their t h e i r liquidus uting u t i n g to t o their t h e i r high h i g h fluidity. fluidity. (d) (d) The tops t o p s of of some some transitional t r a n s i t i o n a l basalts, b a s a l t s , quartz q u a r t z tholeiites, t h o l e i i t e s , basaltic basaltic andesites but a n d e s i t e s and more ffelsic e l s i c flows are a r e rrubbly, ubbly, b u t the t h e surfaces s u r f a c e s of of all a l l of of the the olivine and many of of the o l i v i n e tholeiites t h o l e i i t e s and t h e more evolved flows are a r e smooth or o r ropy at at various v a r i o u s scales. scales. bases of p practically unlike (e) ( e ) The b a s e s of r a c t i c a l l y aall l l flows were liquid, liquid, u n l i k e the t h e basal basal rubble r u b b l e zone of of typical t y p i c a l Hawaiian Hawaiian aa a a flows. flows. Pipe vesicle (f) i p e amygdules and v e s i c l e cylinders c y l i n d e r s are a r e common in i n olivine o l i v i n e tholeiite tholeiite (f) P flows but b u t are a r e absent a b s e n t in i n more more evolved evolved compositions. compositions. parts (g) (g) Amygdules in i n the t h e upper p a r t s of of flows are a r e round or o r amoeboid in i n the the basalts b a s a l t s but b u t are a r e commonly elongate, e l o n g a t e , indicating i n d i c a t i n g greater g r e a t e r viscosity, v i s c o s i t y , in i n andesites, andesites, iicelandites c e l a n d i t e s and rhyolites. rhyolites. Columnar (h) (h) Columnar jjointing o i n t i n g may occur in i n all a l l compositions from olivine o l i v i n e tholeiite tholeiite to it. t o rhyolite, r h y o l i t e , but b u t many many exposures exposures are a r e not n o t good good for f o r recognizing r e c o g n i z i n g it. Eruptive I c e l a n d (fissure—fed ( f i s s u r e - f e d flood flood E r u p t i v e style s t y l e was much more like l i k e that t h a t of of Iceland basalts with b a s a l t s intercalated intercalated w i t h more evolved evolved central c e n t r a l volcanoes) volcanoes) than t h a n Hawaii ((all a l l shields). shields). Reference White, W.S., W.S., 1960, 1960, The The Keweenaw Keweenaw lavas l a v a s of of Lake Lake Superior, S u p e r i o r , An example of of flood flood White, An example b a s a l t s : Amer. J o u r . S c i . , v . 258-A, p. 367-374. basalts: Amer. Jour. Sd., v. 258—A, p. 367—374. �19 Relative Relative Age Age and Tectonic Tectonic Significance Significance of of Proterozoic Proterozoic Metasedimentary Metasedimentary Rocks Rocks in in the the Upper Upper Midwest Midwest Geological and Natural GREENBERG, J.K. GREENBERG, J.K. (Wisconsin (Wisconsin Geological Natural History History Survey, Survey, 1815 1815 University University Ave., Madison, Madison, WI WI 53705—4096) 53705-4096) rocks are Four groups of Proterozoic sedimentary sedimentary rocks are recognized recognized in in Precambrian of the These are the Precambrian the upper upper Midwest. These are rocks rocks of the the northern Penokean Penokean terrane Penokean volcanic volcanic belt (PVB), northern terrane (NPT), (NPT), the the Penokean (PVB), Each of interval (BI), the Baraboo interval (BI), and the the Keweenawan Keweenawan basins basins (K). (K). Each of the four groups is characteristic of different tectonic conditions prevailing during the Proterozoic evolution margin the Proterozoic evolution of the the southern southern margin of the the Superior Superior Craton. Craton. The oldest group occurs occurs as as sequences sequences within within the the northern northern Penokean Penokean The oldestgroup which developed immediately upon Archean basement about terrane, which include the Marquette Marquette Range Supergroup 1900 m.y. m.y. ago. ago. These These units units include Supergroup 1900 Wisconsin and and northern northern Michigan Michigan and and the theMille Mule Lacs Group in in Wisconsin were originally Minnesota. They Minnesota. They were originally deposited deposited on on aa stable stable continental continental which gave way with with time to deeper water environments environments indicative indicative shelf which of subsidence. subsidence. The The uppermost uppermost units units in in the the succession, succession, which which correcorrelate Paint River Groups, Groups, are predominantly the Baraga and Paint late with the These were deposited in turbidites turbidites and tholeiitic tholeiitic volcanic volcanic rocks. rocks. These in a series series of of rift rift basins. basins. At about about the the same same time time or or later later than than deposition deposition in in the the northern northern Penokean terrane, Penokean volcanic belt was Penokean terrane, sedimentation sedimentation in in the the Penokean was taking place to the the south south in in environments environments similar similar to to island island arc, arc, back arc, arc, and interarc interarc basin basin complexes. complexes. Metasedimentary Metasedimentary rocks rocks are are in this this predominantly predominantly volcanic now poorly preserved and/or exposed in which extends much of terrane which extends over over much of northern northern Wisconsin. Wisconsin. The The sedimensedimenunits which which were were preserved seem to be relatively thin and quite tary units variable. Outcrops Outcrops and drill—core variable. drill-core data data suggest suggest that that turbidites, turbidites, graphitic carbonate iron graphitic shales, shales, sulfidic sulfidic and carbonate iron formation, formation, silty silty dolomite, various types volcanogenic sediments were deposited dolomite, and various types of volcanogenic sediments were deposited around centers centers of of calc—alkaline calc-alkaline volcanism. volcanism. The The observed contrast contrast in in lithologies and depositional settings make make it unreasonable unreasonable to correlithologies correlate units units between the late the two two Penokean Penokean terranes. terranes. Both terranes terranes were were apparently apparently deformed deformed together together during during the the Penokean Penokean orogeny, orogeny, about about 1850 m.y. m.y. ago. ago. At this this time, time, the the simatic simatic arcs arcs and and basins basins (PVB) (PVB) were were 1850 ted sial sial (NPT) (NPT) along along the craton margin margin to accreted to to the the rif rifted to the the north. north. major depositional depositional period, the Baraboo Baraboo interval The third major interval is is interinterresult of subsidence on relatively immature preted as a result subsidence on immature continental continental post—orogenic felsic crust. felsic crust. This sedimentation sedimentation immediately immediately followed followed post-orogenic magmatism m.y. ago to rifting rifting and and atypiatypimagmatism 1760 1760 m.y. ago and and was was both both unrelated unrelated to cal modern passive margins. Analogues cal of modern passive margins. Analogues of of the the Baraboo Baraboo interval interval Arabian Shield, in the the Lower Lower probably occur in in the the Eocambrian of the the Arabian Shield, in Proterozoic adjacent Guiana Shield, Proterozoic adjacent to the the Guiana Shield, and possibly in in the the Lower Lower Proterozoic Proterozoic of of the the Athabasca Athabasca Basin. Basin. �20 Other than the well known known red Baraboo, Baraboo, Barron, the well Barren, and Sioux Sioux Quartz— Quartzites, rock units in ites, in the the Baraboo Baraboo interval interval include include five five other other facies: facies: micaceous micaceous quartzite, quartzite, conglomerate, conglomerate, argillite, argillite, chert, chert, and and iron—rich iron-rich chemical sediments chemical sediments (including (including rare rare dolomite). dolomite). These sediments sediments may have been deformed about 1630 m.y. ago, as some evidence about 1630 m.y. ago, as some evidence suggests; suggests; metamorphosed during however they were definitely deformed and metamorphosed during the the intrusion intrusion of of alkalic alkalic plutons plutons 1500 1500 m.y. m.y. ago. ago. Rift—related Keweenawan sedimentary Rift-related Keweenawan sedimentary units units were deposited deposited in in aa stable stable continental continental environment environment at least least 300 300 m.y. after after the the Baraboo Baraboo The mostly quartzitic interval. interval. quartzitic Keweenewan Keweenewan rocks rocks are are exposed exposed along along both shores shores of Lake Superior Superior and include include both pre— pre- and post—volcanic post-volcanic sequences. sequences. Keweenawan Keweenawan units units were only only mildly or or locally locally affected affected by by the heat of of rift rift magmatism. magmatism. They were not not significantly significantly deformed. deformed. The The association association of of depositional depositional and tectonic tectonic environments environments reprerepresented by each each of of the the four four sedimentary sedimentary groups groups is is as as follows: follows: DEPOSITIONAL ENVIRONMENT ENVIRONMENT DEPOSITIONAL TECTONIC TECTONIC ENVIRONMENT ENVIRONMENT GROUP GROUP TINE TIME NPT NPT Continental about Continental shelf, shelf, rift rift about basins 1900 1900 basins m.y. ago ago Development of Atlantic— Development Atlanticcontinental margin type continental PVB PVB about about Small ocean, arc arc basins basins 1900— 19001850 1850 m.y. ago ago Early stages stages of conti— continent—volcanic nent-volcanic arc arc orogeny orogeny BI BI Epicontinental basin basin about Epicontinental about 1760 1760 m.y. ago ago Metastable continental Metastable continental crust, crust, subsidence subsidence due due to to thin thin sial sial after after cratoni— cratoniz at ion zation K Intracontinental about about Intracontinental rift rift basins 1300— 1300basins 900 900 m.y. ago ago Tensional reactivation reactivation of tectonic tectonic weaknesses weaknesses in mature continental continental crust crust �21 S t r a t i g r a p h y of h e Footwall he Stratigraphy of tthe Footwall Volcanic Volcanic Rocks Rocks Beneath tthe M a t t a b i Massive Sulfide S u l f i d e Deposit, D e p o s i t , Sturgeon Lake, Lake, Ontario Ontario Mattabi (Dept. of of Geology, Geology, University U n i v e r s i t y of of Minnesota—Duluth, Minnesota-Duluth, DAVID A. A. GROVES (Dept. Duluth, 55812) Duluth, MN 55812) The M Mattabi a t t a b i massive sulfide s u l f i d e deposit, d e p o s i t , situated s i t u a t e d in i n the t h e Wabigoon greenstone underlain is u n d e r l a i n by approximately a p p r o x i m a t e l y 22 km km of of predominantly g r e e n s t o n e belt, b e l t , is r o c k s in i n the t h e study s t u d y area a r e a are are m a f i c subaqueous subaqueous volcanic v o l c a n i c rocks. r o c k s . The rocks mafic trondhtterminated e r m i n a t e d by the t h e Beidelman Bay intrusion, i n t r u s i o n , a dioritic d i o r i t i c to t o trondh— jjemitic e m i t i c subvolcanic s u b v o l c a n i c sill. sill. D e t a i l e d geologic g e o l o g i c mapping and petrographic petrographic Detailed studies s t u d i e s have shown that t h a t this t h i s previously p r e v i o u s l y undifferentiated u n d i f f e r e n t i a t e d footwall footwall u n i t can be b e divided d i v i d e d into i n t o several s e v e r a l distinct d i s t i n c t volcanic v o l c a n i c deposit d e p o s i t types t y p e s on unit basis of p preserved primary ttextures, fragment type, mineralogy. tthe he b a s i s of r e s e r v e d primary e x t u r e s , fragment t y p e , and mineralogy. At A t the t h e base b a s e of of the t h e succession, s u c c e s s i o n , mafic m a f i c porphyritic p o r p h y r i t i c flows f l o w s and and flow flow breccias b r e c c i a s are a r e intruded i n t r u d e d by an a n altered a l t e r e d dioritic d i o r i t i c border b o r d e r phase of of the the mafic with Beidelman Bay intrusion. intrusion. The m a f i c fflows l o w s aare r e intercalated intercalated w i t h and overlain o v e r l a i n by thin t h i n felsic f e l s i c lavas l a v a s and hyaloclastites h y a l o c l a s t i t e s that t h a t grade g r a d e laterally laterally heterolithic iinto nto h e t e r o l i t h i c debris d e b r i s flows. flows. This T h i s felsic f e l s i c horizon h o r i z o n thickens t h i c k e n s on on both both western tthe he w e s t e r n and eastern e a s t e r n extremities e x t r e m i t i e s of of the t h e study s t u d y area a r e a and, and, locally, locally, Poorly bedded and graded m mafic iincludes n c l u d e s coarse c o a r s e block b l o c k and ash a s h layers. layers. P o o r l y bedded afic debris d e b r i s flows f l o w s overlying o v e r l y i n g this t h i s felsic f e l s i c horizon h o r i z o n are a r e composed largely l a r g e l y of of aphyric mafic w e s t of of Mattabi. Mattabi. aphyric m a f i c fragments and scoria s c o r i a and are a r e most common common west These deposits with d e p o s i t s interfinger i n t e r f i n g e r and mix w i t h felsic f e l s i c lavas l a v a s and flow f l o w breccias breccias east of of the t h e ore o r e deposit. d e p o s i t . The mine footwall f o o t w a l l horizon, h o r i z o n , approximately approximately m tthick, comprised of of ffelsic pyroclastic deposits h i c k , iis s comprised elsic p y r o c l a s t i c fflow low d e p o s i t s composed 200 m of poorly of coarse, coarse, p o o r l y graded tuff t u f f breccias b r e c c i a s and intercalated i n t e r c a l a t e d ash a s h beds. beds. The graded, immediate ffootwall o o t w a l l rrock o c k iis s aa ppoorly oorly g r a d e d , llapilli—rich a p i l l i - r i c h pyroclastic pyroclastic flow. of lower felsic w e s t and and east e a s t of of the the Thickening of f e l s i c flow f l o w horizons h o r i z o n s to t o the t h e west ore Comparisons of o r e deposit d e p o s i t suggest s u g g e s t at a t least l e a s t two felsic f e l s i c edifices. edifices. of felsic pyroclastic units felsic p yroclastic u n i t s immediately beneath b e n e a t h the t h e Mattabi M a t t a b i horizon h o r i z o n also also iindicate: ndicate: 1. 1. west An early e a r l y edifice e d i f i c e slightly slightly w e s t of of the t h e ore o r e deposit d e p o s i t produced beds and o overlying ccoarse o a r s e bbasal a s a l ppyroclastic y r o c l a s t i c beds v e r l y i n g aash s h beds that that ttruncate r u n c a t e mafic debris d e b r i s flow flow deposits. deposits. 2. 2. Later L a t e r volcanism east e a s t of of the t h e ore o r e deposit d e p o s i t produced subaqueous subaqueous pyroclastic grade westward into p y r o c l a s t i c fflows l o w s tthat hat g r a d e westward i n t o thinly t h i n l y bedded ash ash units. units. These flows f l o w s form form the t h e immediate immediate footwall f o o t w a l l at a t Mattabi. Mattabi. �22 Evidence Evidence for f o r nappe nappe development development during d u r i n g the t h e Penokean Penokean Orogeny Orogeny from from the the Early E a r l y Proterozoic P r o t e r o z o i c Thomson Thomson Formation, Formation, Minnesota Minnesota HOLST, HOLST, T.B., T.B., Department Department of of Geology, Geology, University U n i v e r s i t y of of Minnesota Minnesota Duluth, Duluth, Duluth, Duluth, Minnesota Minnesota 55812 55812 The The Penokean Penokean orogeny orogeny (1,900—1,800 (1,900-1,800 m.y.) m.y.) was was aa major major tectonic tectonic event e v e n t in i n the t h e Great Great Lakes Lakes region r e g i o n of of North North America America involving i n v o l v i n g deformadeformation, t i o n , metamorphism metamorphism and and igneous igneous activity. a c t i v i t y . In I n Minnesota, the t h e effects effects of of Penokean Penokean deformation deformation are are most most clearly c l e a r l y seen s e e n in i n the t h e Thomson Thomson FormaFormaTwo major major phases phases of of Penokean Penokean defordefortion t i o n of of east—central e a s t - c e n t r a l Minnesota. Minnesota. Two F i folds f o l d s are are mation mation are a r e now now recognized recognized in i n the t h e Thomson Thomson Formation. Formation. F1 isoclinal well-developed S1 S l axial—planar a x i a l - p l a n a r foliafoliai s o c l i n a l and and recumbent recumbent with w i t h aa well—developed A s hinge h i n g e regions r e g i o n s of of F1 F l folds f o l d s are a r e rare, r a r e , the t h e S1 S l foliation f o l i a t i o n is is tion. t i o n . As usually u s u a l l y observed observed to t o be b e very v e r y nearly n e a r l y bedding bedding —- parallel p a r a l l e l in i n outcrop. outcrop. F2 F2 folds f o l d s are a r e open, open, upright u p r i g h t to t o steeply s t e e p l y inclined, i n c l i n e d , and and subhorizontal. subhorizontal. This There i s aa foliation f o l i a t i o n that t h a t is i s axial—planar a x i a l - p l a n a r to t o the t h e F2 F2 folds. f o l d s . This There is foliation i s aa crenulation c r e n u l a t i o n cleavage c l e a v a g e where where the t h e S1 S i foliation f o l i a t i o n is i s present present f o l i a t i o n is The and and aa slaty s l a t y cleavage c l e a v a g e where where the t h e S1 Sl foliation f o l i a t i o n does does not n o t exist. e x i s t . The second second deformation d e f o r m a t i o n affected a f f e c t e d the t h e entire e n t i r e region r e g i o n of of Thomson Thomson Formation Formation outcrop, o u t c r o p , while w h i l e the t h e effects e f f e c t s of of the t h e first f i r s t deformation deformation are a r e found found only only in i n the t h e southern s o u t h e r n two—thirds two-thirds of of Thomson Thomson Formation Formation outcrop. outcrop. Several S e v e r a l lines l i n e s of of evidence e v i d e n c e indicate i n d i c a t e that t h a t northward—directed northward-directed This nappes nappes developed developed during d u r i n g the t h e Penokean Penokean deformation d e f o r m a t i o n in i n Minnesota. Minnesota. This evidence e v i d e n c e includes i n c l u d e s petrologic p e t r o l o g i c differences d i f f e r e n c e s between between the t h e areas a r e a s of of one one and S1 foliation f o l i a t i o n in i n the the and two two deformations, d e f o r m a t i o n s , the t h e pervasive p e r v a s i v e nature n a t u r e of of the t h e S1 area f a c i n g direction d i r e c t i o n of of F2 F2 folds, f o l d s , and and the t h e rerea r e a in i n which which it i t is i s found, found, facing fraction f r a c t i o n pattern p a t t e r n of of the the l Sl foliation f o l i a t i o n in i ngraded graded greywacke—slate greywacke-slate sesequences, showing that an area of up to several hundred quences, showing t h a t a n area of up t o s e v e r a l hundred square s q u a r e km km is is on on the t h e upper upper limb limb or o r limbs limbs of of large l a r g e northward—directed n o r t h w a r d - d i r e c t e d recumbent recumbent folds f o l d s (nappes) (nappes) of of the t h e early e a r l y phase phase of of deformation. deformation. Recent Recent tectonic t e c t o n i c models models of of the t h e Penokean Penokean orogeny orogeny in i n Minnesota Minnesota have have suggested that i t was w a s an a n intracratonic i n t r a c r a t o n i c event e v e n t with w i t h local l o c a l compression compression t h a t it and metamorphism metamorphism caused caused by by vertical v e r t i c a l ttremobi1izationt " r e m o b i l i z a t i o n " of of basement basement r o c k s . The The existence e x i s t e n c e of of nappes nappes and and later l a t e r upright u p r i g h t folds f o l d s with w i t h axial— axialrocks. planar p l a n a r foliation f o l i a t i o n suggests s u g g e s t s a significant s i g n i f i c a n t amount amount of of horizontal h o r i z o n t a l shortenshortening. i n g . These These features f e a t u r e s are a r e quite q u i t e compatible compatible with w i t h the t h e suggestions s u g g e s t i o n s that that Penokean Penokean deformation deformation took t o o k place p l a c e in i n aa plate p l a t e boundary boundary collision c o l l i s i o n environenvironment. ment. �23 Folded Rocks Rocks in i n the t h e Eastern E a s t e r n Contact Contact Zone Zone of of the t h e Vermilion Vermilion Batholith Batholith Folded 53511) J . P . KASZUBA KASZUBA (Department (Department of of Geology, Geology, Beloit B e l o i tCollege, College, Beloit, B e l o i t , WIW I53511) J.P. P.A. SCHWARZWELLER SCHWARZWELLER(Department (Department of of Geology, Geology, Beloit B e l o i tCollege, College, Beloit, Beloit, P.A. W I 53511) 53511) WI H.H. WOODARD WOODARD (Department (Department of of Geology, Geology, Beloit B e l o i t College, College, Beloit, B e l o i t , WI W I 53511) 53511) H.H. Detailed D e t a i l e d geologic g e o l o g i c and and structural s t r u c t u r a l mapping mapping was was carried c a r r i e d out o u t in i n aa portion portion (7% minute) minute) quadrangle, quadrangle, Minnesota—Ontario Minnesota-Ontario during during of the t h e Jackfish J a c k f i s h Lake Lake (7½ of T h i s mapping mapping has h a s demonstrated demonstrated the t h e existence e x i s t e n c eof of t h e 1982 1982 field f i e l d season. season. This the This aa major major fold f o l d sequence, sequence, here h e r e named named the t h e Crooked CrookedLake LakeFold FoldSequence. Sequence. This sequence sequence lies l i e s within w i t h i n the t h e southeastern s o u t h e a s t e r n contact c o n t a c t zone zone of of the t h e Vermilion Vermilion B a t h o l i t h , north n o r t h of of the t h e Vermilion Vermilion fault f a u l t zone. zone. Batholith, The The oldest o l d e s t rocks r o c k s in i n the t h e quadrangle quadrangle are a r ebiotite b i o t i t eschists, s c h i s t s , amphibolites, amphibolites, and and metabreccias m e t a b r e c c i a s associated a s s o c i a t e d with w i t h younger younger leucocratic l e u c o c r a t i c biotite b i o t i t e adamellite adamellite and and migmatites. migmatites. The Theoldest o l d e s t rocks r o c k s were were graywackes graywackes and and shales, s h a l e s , basalts basalts and andesites, a n d e s i t e s , and and mafic mafic volcaniclastic v o l c a n i c l a s t i c sediments. sediments. Mafic Mafic breccias b r e c c i a s sugsugand g e s t nearby nearby sources s o u r c e s of of mafic mafic volcanics. volcanics. gest After A f t e r deposition d e p o s i t i o n of of the t h e sediments, sediments, aa major major period p e r i o d of of deformation deformation T h i s sequence sequence concono c c u r r e d to t o produce produce the t h e Crooked Crooked Lake Lake Fold Fold Sequence. Sequence. This occurred s e r i e s of of often o f t e n overturned o v e r t u r n e d synclines s y n c l i n e s and and anticlines a n t i c l i n e s that that sists s i s t s of of aa series wide range r a n g e of of orientations orientations plunge gently g e n t l y to t o the t h e east e a s t and and northeast. n o r t h e a s t . AA wide plunge of of major major fold f o l d axes a x e s and and axial a x i a l planes p l a n e s suggests s u g g e s t s that t h a t the t h e deformational deformational event was was characterized c h a r a c t e r i z e d by by complex complex disharmonic disharmonic folding. f o l d i n g . The The changing changing event The fold f o l d sequence sequence i s illustrated i l l u s t r a t e d in i n Fig. F i g . 1. 1. The shape of of one one of of the t h e folds f o l d s is shape (7%minute) minute) quadquadextends e x t e n d s westward westward across a c r o s s strike s t r i k e through through the t h e Friday F r i d a y Bay Bay (7½ rangle 10 kilometers k i l o m e t e r s and and may may extend extend even even farther, f a r t h e r , into into r a n g l e for f o r approximately approximately 10 t h e Iron I r o n Lake Lake (7½ (7%minute) minute) quadrangle quadrangle and and the t h e Vermilion Vermilion Batholith. B a t h o l i t h . SouthSouththe east e a s t of of the t h e Jackfish J a c k f i s h Lake Lake quadrangle quadrangle the t h e Crooked Crooked Lake Lake Folds F o l d s can can be be followed ( 7 % minute) minute) quadrangle quadrangle followed across a c r o s s strike s t r i k e into i n t o the t h e Basswood Basswood Lake Lake West West (7½ where where they they may may be be terminated t e r m i n a t e d against a g a i n s t aa splay s p l a y of of the t h e younger younger Vermilion Vermilion f a u l t zone. zone. The The minimum minimum total t o t a l across—strike a c r o s s - s t r i k e distance d i s t a n c e of of the t h e fold fold fault When followed followed along a l o n g strike s t r i k e to to i s approximately approximately 23 23 kilometers. k i l o m e t e r s . When sequence is sequence the t h e northeast n o r t h e a s t into i n t o Canada, Canada, individual i n d i v i d u a l folds f o l d s pass p a s s into i n t o leucocratic l e u c o c r a t i c biotite biotite a d a m e l l i t e of of the t h e Vermilion Vermilion Batholith. B a t h o l i t h . Their T h e i r position p o s i t i o n within w i t h i n the t h e batho— bathoadamellite l i t h can can be be recognized recognized by by systematic s y s t e m a t i c changes changes in i n foliation f o l i a t i o norientations. orientations. lith After A f t e r the t h e major major deformational d e f o r m a t i o n a l period, p e r i o d , the t h e sediments sediments were were metamorphosed metamorphosed Migmatization and and formation formation of of leucocratic t o amphibolite a m p h i b o l i t e grade. grade. Migmatization l e u c o c r a t i c bio— bioto tite t i t e adamellite a d a m e l l i t e occurred o c c u r r e d after a f t e r amphibolite a m p h i b o l i t e grade grade metamorphism. metamorphism. Regional Regional structural s t r u c t u r a l continuity c o n t i n u i t y between between the t h e older o l d e r biotite b i o t i t e schists s c h i s t s and and the t h e adamel— adamellite l i t e suggests s u g g e s t s that t h a t the t h e migmatization migmatization which which produced produced the t h e adamellite adamellite probably i n aa younger younger pile p i l e of of felsic f e l s i c volcanics v o l c a n i c s which which were were overoverprobably occurred o c c u r r e d in The formation formation of of the t h e migmatites migmatites may may be be l y i n g the t h e more more mafic mafic schists. s c h i s t s . The lying t h e result r e s u l t of of aa combination combination of of several s e v e r a l mechanisms: mechanisms: anatexis, a n a t e x i s , metasoma— metasomathe t i s m , and and subsequent subsequent intrusion. intrusion. tism, Several S e v e r a l episodes e p i s o d e s of of faulting f a u l t i n g and and fracturing f r a c t u r i n g have have taken t a k e n place. p l a c e . These These events e v e n t s produced produced narrow narrow zones zones of of cataclasis, c a t a c l a s i s , brecciation, b r e c c i a t i o n , and and hydrohydrothermal alteration. a l t e r a t i o n . As A s the t h e Vermilion Vermilion Batholith B a t h o l i t h is i s approached, approached, the the thermal �24 number of of faults f a u l t s increases i n c r e a s e s significantly. s i g n i f i c a n t l y . Apparent Apparent displacement displacement on on number t h e s e faults f a u l t s dies d i e s out o u t as a s the t h e faults f a u l t s pass p a s s northward northward into i n t o the t h e more more these massive rock rock of of the t h e Vermilion Vermilion Batholith. B a t h o l i t h . Most Most faults f a u l t s when when traced t r a c e d over over massive long long distances d i s t a n c e s are a r e deflected d e f l e c t e d to t o the t h e north n o r t h and and west west as a s if i f they they were were being being c o n t r o l l e d by by the t h e southeastern s o u t h e a s t e r n margin margin of of the t h e batholith. batholith. controlled The The formation formation of of strong s t r o n g joint j o i n t sets s e t s accompanied accompanied the t h e faulting f a u l t i n g events. events. Many of of these t h e s e joint j o i n t sets s e t s show show aa strong s t r o n g bimodal bimodal distribution d i s t r i b u t i o n which which corcorMany responds responds to t o the t h e primary primary layering l a y e r i n g directions d i r e c t i o n s in i n the t h e opposing opposing limbs limbs of of leucot h e Crooked Crooked Lake Lake Folds. F o l d s . These These joints j o i n t s seem seem to t o persist p e r s i s t into i n t o the t h e leuco— the cratic c r a t i c biotite b i o t i t e adamellite a d a m e l l i t e of of the t h e Vermillion V e r m i l l i o n Batholith B a t h o l i t h and and may may represent represent o r i g i n a l planes p l a n e s of of weakness weakness in i n the t h e pre—batholith p r e - b a t h o l i t h pile p i l e of of felsic f e l s i c extruextruoriginal s i v e rocks. rocks. sive 0 I TT 1/2. t(ILOMETER F i g u r e 1. 1. Changing Changing shape shape of of one one of of the t h e anticlines a n t i c l i n e s in i n the t h e Crooked Crooked Lake Lake Figure These sections s e c t i o n s are a r e drawn drawn perpendicular p e r p e n d i c u l a r to to Fold Sequence. Sequence. These Fold the t h e strike s t r i k e of of aa 1.5 1 . 5 kilometer k i l o m e t e r segment segment of of the t h e axial a x i a l plane p l a n e of of t h e fold. f o l d . Vertical V e r t i c a l scale s c a l e equals e q u a l s horizontal h o r i z o n t a l scale. scale. the �25 ANDITS ITS IMPLICATION SUPERIMPOSED SUPERIMPOSED FOLDING FOLDING AND IMPLICATION ON ON THE THE SHEBAN])JWAN-QUETICO SUBPROVINCE BOUNDARY, THUNDER BAY, ONTARIO. SHEBANDOWAN-QUETICO SUBPROVINCE BOUNDARY, THUNDER BAY, ONTARIO. of Geology, Geology, Lakehead Lakehead University, M.M. M.M. KEHLENBECK KEHLENBECK (Department (Department of University, Thunder Thunder P7B 5E1) Bay, 5E1) Bay, Ontario Ontario Detailed structural studies Detailed structural studies were were carried carried out out over over a a distance distance of of +O 40 km km along an an east-west east-west trending trending zone zone which which is is characterized characterized by aa lithological lithological transition transition from from aa dominantly dominantly metavolcanic metavolcanic terrain terrain south south of of the metasedimentary rocks rocks exposed exposed north north of of the the the zone zone to to well well stratified stratified metasedimentary zone. zone. This This lithologic lithologic change change from from basic basic flows flows and and intermediate intermediate to to felsic felsic volcanoclastic rocks to a a sequence of of greywackes, greyackes, slates, slates, and and turbidites turbidites has boundary has been been defined defined on on published published geological geological survey survey maps maps as as the the boundary between the Shebandowan andQuetico Queticosubprovinces subprovincesininthe the area area north between the Shebandowan and north and and northwest northwest of ofThunder ThunderBay. Bay. The The metavolcanic metavolcanic and and metasedimentary metasedimentary rocks rocks have have been been subjected subjected to to regional regional greenschist greenschist facies facies metamorphism metamorphism and and possess possess aa single single well well defined bedding planes lanes (s0) are defined schistosity schistosity or or cleavage cleavage (51). Primary Primary bedding are well well preserved preserved in in the the metasedimentary metasedimentary rocks rocks as as are are primary primary structures structures such such as as graded graded bedding bedding and and cross cross bedding. bedding. Pillow Pillow structures, structures, although although not not uncommon, uncommon, are are often often too too deformed deformed to to permit permit determination determination of of local local tops tops or or of of primary primary bedding bedding surfaces surfacesin inthe theinetavolcanic metavolcanic succession. succession. (s~). (so) Based relationships, the the asymmetry asymmetry of of minor minor Based on on cleavage-bedding cleavage-bedding relationships, folds, local younging youngingderived derivedfrom fromprimary primary structures,aaset set of of folds folds, •and and local structures, folds has Field observations observations has been been delineated delineated in in the the metasedimentary metasedimentary sequence. sequence. Field in in aa number nuder of of fold fold hinge hinge zones zones have have clearly clearly shown shown that that the the subvertical, subvertical, northeast cleavageparallels parallelsthe the axial axial surfaces surfaces of of these these folds. folds. northeast striking striking SSlcleavage Observed intersection lineations lineations generally generally p1inge plunge steeply steeply to to the the Observed So/Si intersection northeast northeast and and are are coaxial coaxial with with the the axes axes of of these these folds. folds. Because Because of of their their steep steep plunge, plunge, the the structural structural facing facing of of the the folds folds is is primarily primarily sideways, sideways, and antiforms. These and hence hence they they cannot cannot be "beclassified classified as as synforms synformsor or antiforms. These folds folds therefore therefore form form aa set set of of vertically vertically plunging, plunging, sideways—closing sideways-closing folds. folds. so/sl When tracing tracing one one of of these these folds folds in in the the field field parallel parallel to to the the trace trace When of of the the axial axial surface, surface, aa number number of of reversals reversals in in the the structural structural facing facing direction direction of of the the fold fold occur. occur. In In some some portions portions the the structural structural facing facing direction direction is is to to the the northeast, northeast, elsewhere elsewhere to to the the southwest. southwest. ctending Extending such such observations observations over over the the entire entire area area reveals reveals the the existence existence of of distinctive distinctive regions regions in in which which the stratigraphy as a whole becomes younger toward the northeast, while the stratigraphy as a whole becomes younger toward the northeast, while other other parts parts indicate indicate an an overall overall stratigraphic stratigraphic younging younging to to the the southwest. southwest. The places where the reversals in the structural facing direction, The places where the reversals in the structural facing direction, and and mark the the position position of of the the therefore in in the the stratigraphic stratigraphic younging younging occur, occur, mark therefore trace trace of of the the axial axial surfaces surfaces of of an an earlier earlier set set of of folds. folds. Based on on the the structural structural data data from from this this area, area, it Based it is is suggested suggested that that the strata strata were folded folded about about gently gently plunging axes axes resulting in aa set set of of the resulting in IQfolds folds in in which which at at least least some some limbs limbs were were overturned. overturned. AA later isoclinal Fl isoclinal later refolding produced produced F2 Fz folds folds about about nearly nearly vertical vertical axes axes and and axial axial surfaces. surfaces. refolding The F2 F2 folding folding was was accompanied accompanied by by the the development development of of aa pervasive pervasive axial axial The planar schistosity schistosity or or cleavage. cleavage. planar Superimposed folding folding has has been been documented documented in in the the metasedimentary metasedimentary Superimposed rocks on on both both sides sides of of the the proposed proposed boundary boundary between between the the Shebandowan Shebandowan and and rocks Quetico Quetico subprovinces. subprovinces. No evidence evidence has has been been found found to to exclude exclude the the metavolcanic metavolcanic rocks from from the the folding folding demonstrated demonstratedin inthe themetasedinientary metasedimentary succession. succession. rocks �26 LaSalle Falls F a l l s -- An An Exposed Exposed Massive Massive Sulfide S u l f i d e Deposit Deposit LaSalle i n Florence Florence County, County, Wisconsin Wisconsin in GENE L. L. LA LA BERGE BERGE (Department (Department of o f Geology, Geology, University U n i v e r s i t y of of GENE Wisconsin-Oshkosh, Oshkosh, Oshkosh, WI W I 54901) 54901) Wisconsin-Oshkosh, La La Salle S a l l e Falls F a l l s (Pine (Pine Rapids) Rapids) on on the t h e Pine Pine River River in i n Florence Florence County, County, Wisconsin Wisconsin occurs o c c u r s at a t the t h e contact c o n t a c t between between felsic f e l s i c and and mafic mafic volcanic volcanic the rocks of o f the t h e early e a r l y Proterozoic P r o t e r o z o i c Quinnesec Quinnesec Formation. Formation. Along Along the rocks s o u t h side s i d eof o fthe t h ePine PineRiver Riverthe t hexposed e exposedrocks rocksare a r mainly e mainlymassive massive south and pillowed p i l l o w e d(?) ( ? ) greenstones greenstones with w i t hnumerous numerous massive massive and and layered layered and gabbroic dikes. d i k e s . Most Most exposures exposures have have aa prominent prominent foliation f o l i a t i o n and and gabbroic mineral mineral associations a s s o c i a t i o n s suggest s u g g e s t metamorphism metamorphism to t o lower lower amphibolite amphibolite f a c i e s . At A t LaSalle LaSalle Falls F a l l s and and on on the t h e north n o r t h side s i d e of of the t h e Pine Pine River River facies. the the dominant dominant lithology l i t h o l o g y of of the t h e Quinnesec Quinnesec Formation Formation is i s felsic f e l s i c volvolc a n i c rocks rocks that t h a t appear appear to t o be be coarsely c o a r s e l y fragmental. fragmental. Significant Significant canic pyrite, p y r i t e , pyrrhotite p y r r h o t i t e and and chalcopyrite c h a l c o p y r i t e are a r e disseminated disseminated in i n the t h e felsic felsic To the north the Quinnesec is in fault rocks a t LaSalle F a l l s . To t h e n o r t h t h e Quinnesec i s i n f a ult rocks at LaSalle Falls. contact c o n t a c t with w i t h the t h e Michigamme Michigamme Formation Formation along a l o n g the t h e Niagara Niagara Fault. Fault. To To the t h e south s o u t h the t h e volcanics v o l c a n i c s are a r e in i ncontact c o n t a c twith, w i t h ,and andintruded i n t r u d e d by, by, g r a n i t i c rocks rocks of o fthe t h eDunbar Dunbargneiss g n e i s sdome. dome. granitic sulfide deposit, a graphitic, fifty feet thick, occurs at the contact between the mafic The s u l f i d e d e p o s i t , a g r a p h i t i c , sulfide—rich s u l f i d e - r i c h sediment sediment zone zone The about f i f t y f e e t t h i c k , o c c u r s a t t h e c o n t a c t between t h e mafic about and felsic f e l s i c rocks. r o c k s . The The sedimentary sedimentary unit u n i t is i s mainly mainly aa finely f i n e l ylamlamand i n a t e d chloritic c h l o r i t i cand and sericitic s e r i c i t i cslate s l a twith e w i t discontinuous h discontinuous pyrite pyrite inated nun thick. t h i c k . Cherty Cherty layers l a y e r s are a r erelatively r e l a t i v e lcommon y common within within l e n s e s1 1 lenses —- 22 mm of the t h e zone. zone. Garnets Garnets are a r e abundant abundant in i n some some of t h e pelitic p o l i t i crocks. rocks. the Although only iiron Although only r o n sulfides s u l f i d e swere were observed observed in i n the t h esediments, sediments, drilling d r i l l i n gby bymining miningcompanies companies indicate i n d i c a t e the t h e presence presence of o fbase basemetal metal mainssulfide deposit underlies s u l f i d e s . The The main ulfide d e p o s i t apparently apparently u n d e r l i e s the the river river sulfides. channel removed channel below below tthe h e falls f a l l sand andhas h a sbeen beenlargely largely removed by by erosion. erosion. thisoccurrence occurrence along along the t h e Pine Pine River, River, aa base base metal metal I n addition a d d i t i o n to t o this In s u l f i d e d e p o s i t i n f e l s i c t u f f s h a s been d r i l l e d approximately approximately one one sulfide Massive sulfide deposits have also been reported m i l e t o t h e s o u t h . Massive s u l f i d e d e p o s i t s have a l s o been r e p orted mile to the south. the Quinnesec Formation in Marinette County. The i n t h e Quinnesec Formation i n M a r i n e t t e County. in The exposure exposure would would make make an an excellent e x c e l l e n t field f i e l d trip t r i p stop. stop. deposit in felsic tuffs has been drilled �27 The Reany Reany Creek Creek Formation: Formation: aaMass-Flow Mass-Flow Deposit Deposit of Possible of Possible Post Post Menominee Menominee Age Age S. R. of Geology, R. MATTSON MATTSON ((Department ~ e p a r t m e n t of Geology, Michigan Michigan SState t a t e University, University, East East Lansing, MI MI 48824-1115) 48824-1 115) F. W. (Departmentofof Geology, Geology, Michigan Michigan SState W. CAMBRAY CAMBRAY (Department t a t e University, University, East East Lansing, MI MI 48824-1115) 48824- 11 15) The Creek Formation crops out out in a narrow narrow east-west trending trending Reany Creek Formation (RCF) (RCF) crops The Reany belt to t o the t h e north north of of the t h eDead Dead River River storage storagebasin basin in in Marquette MarquetteCounty, County, Michigan. Michigan. Lithologiesofof tthe Lithologies h e formation are a r e meta-mudstones meta-mudstones with with both both round round and and angular, angular, matrix clasts (some matrix supported supported clasts (some up up to t o 33m m inindiameter); diameter);meta-arkosic-wackes; meta-arkosic-wackes; meta-feldspathic meta-feldspathic wackes; wackes; and and minor minor lithic greywackes greywackes which which also also have matrix matrix supported interpreted as being being of glacial glacial supported clasts. The The RCF R C F has has been been previously previously interpreted origin and stratigraphically origin and stratigraphically the t h e lowest lowest formation formation in in the t h eMarquette MarquetteSupergroup Supergroup This interpretation has (Puffet, 1969; 1969; Ojakangas, Ojakangas, 1982). 1982). This has largely largely been been supported supported by the by t h e presence presence of of matrix matrix supported supported clasts clasts which which were were interpreted interpreted as as glacial glacial drop stones. In this this report drop stones. In report the t h e RCF R C F isis interpreted interpreted asasa aproximal proximalmass-flow mass-flow The deposit. The RCF R C F has has similar lithologies and structural trends to t o the the Michigamme Michigamme slate. In sets of of mafic mafic dikes dikes occur occur in in the t h e Marquette Marquette area; area;Keweenawan Keweenawan In general, two t w o sets dikes and older older ssets of dikes dikes which whichaare Pre-Baraga inin age. age. The dikes and e t s of r e Pre-Baraga The base base of of the t h e RCF RCF lies unconformably tones. In In places unconformably on Archean Archean age a g egreens greenstones. places this this contact contact is is Keweenawan aage obscured by by the obscured t h e intrusion intrusion of of Keweenawan Keweenawan dikes. dikes. Keweenawan g e dikes also also No dikes of of an No dikes a n older older age age appear appear to t o cut c u t the t h e RCF. RCF. Regional mapping mapping(Puffet, (Puff et,1974) 1974)indicates indicatest hthat allolder older dikes dikes aare a t all r e truncated by by Regional the no aactual of t h e RCF. RCF. Detailed Detailedmapping mapping of of the t h e RCF R C F (this (this study) study) has has found found no c t u a l case of this truncation; truncation; however, however, many many dikes dikes have have been been observed observed to t o intrude intrude the the Menominee Group, Group, but but not not tthe Menominee h e RCF. RCF. occur occur within within the t h e RCF. RCF. Bedding-cleavage intersectionsand andminor minorfolds foldsaxes axes appear appear tto Bedding-cleavage intersections o indicate indicate aa shallow, doubly doublyplunging plungingsynform synformwith withananaxial axialplane plane dipping dippingslightly slightlytto shallow, o the the southwest. The The presence presence of of kink-bands kink-bands in cleavage indicates indicates aa F2 F2 deformation. deformation. southwest. Beddin& strikest otothe thenorthwest northwest and anddips dipstto Beddin t typically ically strikes o tthe h e southwest or northeast northeast Cleavage strikes strikes northwest (40-803.). ypCleavage northwest and and dips dips to t o the t h esouthwest southwest(55-80°). (55-80 1. (40-80 Measurementson on flow flow directional directional indicators indicators (e.g., (e.g., flute flute casts, Measurements casts, scour scour channels, channels, and tool marks) marks) suggest suggest north-south north-south transport directions directions (mean (mean NI7E N l 7 E or or SI7W, S17W, and N == 24) 24) and and aare r e similar to t o the t h e current current directions directions found found in in the t h e Michigamme Michigamme slate slate (Trow, personal communication). (Trow, All of of the structures of of the massAll t h e sedimentary sedimentary structures t h e RCF R C F can can be be explained explained by by aa massflow mechanism. Depositional models models which which involve involveaa glacial glacial environment flow mechanism. Depositional environment or or glacial marine marine environment environment are a r e unsupported unsupported by by any direct direct evidence evidence (e.g., (e.g., glacial glacial striations depositionala gage fortthe striations on on clasts). clasts). A A Post-Menominee Post-Menominee depositional e for h e RCF R C F is is supported by by tthe dikes and and tthe h e absence absence of of Menominee Menominee aage g e dikes h e apparent truncation truncation of of these dikes by by tthe RCF. Correlation h e RCF. Correlation of of the t h eHuronian Huronian tillites tillitesand and the t h eRCF R C Fwould would thus seem unjustified. �28 Major Element Anorthosites Duluth Complex Element Chemistry of of A n o r t h o s i t e s from the t h e Duluth Quadrangle, Minnesota Snowbank Lake Quadrangle, JANES D D. MILLER, JJR. . MILLER, R . (Dept. (Dept. of of Geology and and Geophysics, Geophysics, University U n i v e r s i t y of of JAMES Minnesota, 55455) MN 55455) Minnesota, Minneapolis, Minneapolis, MN Field petrographic F i e l d and p e t r o g r a p h i c studies s t u d i e s (1) (1) indicate i n d i c a t e that t h a t at a t least l e a s t three t h r e e stages stages main and and llate) of aanorthosite emplacement may may b be distinguished ((early, e a r l y , main a t e ) of n o r t h o s i t e emplacement e d istinguished in i n the t h e Duluth Complex in i n the t h e Snowbank Snowbank Lake quadrangle. quadrangle. P reliminary Preliminary e v a l u a t i o n of new microprobe d a t a on 18 a n o r t h o s i t i c gabbro and 22 evaluation of data on 18 anorthositic gabbro and samples from the ttroctolite r o c t o l i t e samples t h e study s t u d y aarea r e a defines d e f i n e s a number of of distinct distinct elationships w i t h i n and between the t h e anorthositic a n o r t h o s i t i c gabbro gabbro series series chemical rrelationships within and the t h e younger troctolitic t r o c t o l i t i c series. s e r i e s . Major and and minor element element abundances abundances olivine iin n pplagioclase l a g i o c l a s e (P1), (PI), o l i v i n e (01), ( 0 1 ) , clinopyroxene c l i n o p y r o x e n e (Cpx), (Cpx), orthopyroxene orthopyroxene (Opx), and and ooxide minerals Wee report (Opx), xide m i n e r a l s (Ox) (Ox) were analyzed. analyzed. W r e p o r t here h e r e the t h e gengeneral e r a l ccharacteristics h a r a c t e r i s t i c s of of the t h e major element element data. data. 1) Ass aa group, group, the t h e anorthositic a n o r t h o s i t i c suite s u i t e has h a s aa broad broad but b u t constant c o n s t a n t range r a n g e in in 1) A P1I composition (Fig. P (Fig. 1). 1 ) . When compared to t o the t h e troctolites t r o c t o l i t e s from the the study s t u d y aarea r e a and the t h e nearby South South Kawishiwi Kawishiwi Intrusion I n t r u s i o n (SKI—Fig. (SKI-Fig. 1, 1, 2), 2). higher tthe h e aanorthositic n o r t h o s i t i k rrocks o c k s aare re h i g h e r in i n An (Ca/Ca+Na+K) (Ca/ca+~a+K) over o v e r the t h e same same range mole%). This r a n g e of of Fo (Mg/Mg+Fe (Mg/Mg+Fe = = mg, mole%). T h i s relationship r e l a t i o n s h i p is i s also a l s o found found between gabbroic g a b b r o i c and anorthositic a n o r t h o s i t i c rocks r o c k s of of the t h e Stiliwater S t i l l w a t e r Complex Complex (3). (3). The m mg 2) 2) g ratio r a t i o of of the t h e mafic m a f i c phases p h a s e s in i n the t h e troctolitic t r o c t o l i t i c anorthosites a n o r t h o s i t e s of of all TAN, RAL) RAL) is main sstage olivine i s hhigher i g h e r tthan h a n in i n the t h e main tage o livine a l l stages s t a g e s (TAE, (TAE, TAM, ophitic (ANM) (Figs. (Figs. o p h i t i c aanorthosites n o r t h o s i t e s (LSA) (LSA) and the t h e main stage s t a g e anorthosite a n o r t h o s i t e (ANN) 1—4, Table mg 1-4, T a b l e 1). 1 ) . Gabbroic aanorthosite n o r t h o s i t e (CAM) (GAM) Cpx hhas a s intermediate intermediate m g rratios a t i o s (Table 1). 1). 3) The m mg mafic 3) g rratios a t i o s of of the the m a f i c phases p h a s e s indicate i n d i c a t e varying v a r y i n g degrees d e g r e e s of of equi— equimg llibrium i b r i u m over o v e r a cm scale. s c a l e . —— -- The m g relationship r e l a t i o n s h i p of of Opx rims r i m s on 01 0 1 in i n all all aanorthosites, n o r t h o s i t e s , indicates i n d i c a t e s that t h a t the t h e two two phases are a r e in i n disequilibrium d i s e q u i l i b r i u m (Fig. (Fig. 2); mineral 2 ) ; aadjacent djacent m i n e r a l pairs p a i r s plot p l o t below the t h e Fo—En Fo-En equilibrium e q u i l i b r i u m partitioning partitioning Ol—Opx p pairs ccurve u r v e (4). ( 4 ) . 01-Opx a i r s in i n troctolite t r o c t o l i t e are a r e near n e a r equilibrium. e q u i l i b r i u m . Over the mg the m g rrange a n g e cconsidered, o n s i d e r e d , the t h e equilibrium e q u i l i b r i u m curve c u r v e may may be be considered c o n s i d e r e d linear linear r i m s are a r e composition— compositionand simplified s i m p l i f i e d to: t o : Fo == -18.9 1.187 EnOpx. Enopx. Opx rims 18.9 + 1.187 aally l l y similar s i m i l a r to t o that t h a t in i n Opx—Ox Opx-Ox symplectites s y m p l e c t i t e s which which partially p a r t i a l l y replace r e p l a c e 01 01 in i s rare r a r e in i n the t h e troctolites. troctolites. i n aall l l anorthosites a n o r t h o s i t e s investigated, i n v e s t i g a t e d , but b u t is These symplectites s y m p l e c t i t e s are a r e thought thought to t o form form by low low temperature t e m p e r a t u r e (600—700°C), (600-700'~) , late l a t e magmatic to t o subsolidus s u b s o l i d u s oxidation o x i d a t i o n reactions, r e a c t i o n s , possibly p o s s i b l y involving involving mg some mass transfer t r a n s f e r (5). ( 5 ) . The result r e s u l t is i s an m g enrichment of of the t h e Opx r i m Opx Opx could c o u l d have have above that t h a t in i n equilibrium e q u i l i b r i u m with w i t h the t h e core c o r e 01. 01. The rim before formed b e f o r e or o r contemporaneously with w i t h the t h e symplectite. s y m p l e c t i t e . If I f before, b e f o r e , it it Textural rreequilibrated e e q u i l i b r a t e d during d u r i n g symplectite s y m p l e c t i t e formation. formation. T e x t u r a l evidence e v i d e n c e supports supports of Opx-Cpx Opx—Cpx intergrown mineral this -- The The En rratios a t i o s of intergrown m ineral t h i s interpretation. i n t e r p r e t a t i o n . —— pairs P), and of of Opx eexsolution 3, P ) , commonly aas s 001 1 rrims, i m s , and x s o l u t i o n lamellae lamellae p a i r s (Fig. ( F i g . 3, in a Cpx host (E) define a linear trend: + 1.2 EnCpx. l9.5 1 . 2 Encpx. in h o s t (El d e f i n e a l i n e a r t r e n d : Enop Enopx == -19.5 The m mg r i m Opx, Opx, g relationship r e l a t i o n s h i p of of intercumulus i n t e r c u m u l u s Cpx, Cpx, commonly commonly ophitic, o p h i t i c , and and rim which are mm scale, s c a l e , plot p l o t above the the a r e separated s e p a r a t e d by plagioclase p l a g i o c l a s e over a nun llinear i n e a r aarray r r a y (S) (S) indicating i n d i c a t i n g that t h a t most Cpx Cpx formed formed before b e f o r e the t h e Opx Opx or or before during —— The Fo—Encp i t reequilibrated reequilibrated d u r i n g symplectite s y m p l e c t i t e formation. f o r m a t i o n . -Fo-Enc b e f o r e it p compositions units broad p positive compositions of of the t h e vvarious arious u n i t s (Fig. ( F i g . 44) ) show aa single, s i n g l e , broad ositive trend. above, aan Fo—EnCpx t r e n d . From the t h e equilibrium e q u i l i b r i u m equations e q u a t i o n s dderived e r i v e d above, n Fo-Encpx + + x �29 hypothetical h y p o t h e t i c a l equilibrium e q u i l i b r i u m equation e q u a t i o n was was independently i n d e p e n d e n t l y calculated: calculated: Fo -42.1 ++1.425 1 . 4 2Encpx. 5 Encpx. Agreement Agreement of of this t h i s calculated c a l c u l a t e d curve c u r v e and and the the Fo == —42.1 data i s very v e r y good. good. d a t a is 4) 4) Cpx Cpx in i n inclusions i n c l u s i o n s in i n plagioclase p l a g i o c l a s e have h a v e lower lower En ratios r a t i o s than t h a n nearby nearby intercumulus 4, I). I ) . The The form form and and composition c o m p o s i t i o n of of these t h e s e inini n t e r c u m u l u s Cpx Cpx (Fig. ( F i g . 4, clusions, and o often c l u s i o n s , which which also a l s o contain c o n t a i n ilinenite i l m e n i t e and f t e n sodic s o d i c plagioclase, plagioclase, suggests m e l t inclusions. inclusions. s u g g e s t s that t h a t they t h e y represent r e p r e s e n t crystallized c r y s t a l l i z e d melt References: R e f e r e n c e s : 1) 1 ) Miller, Miller, J.D. J . D . and and Weiblen, Weiblen, P.W., P.W., 1982, 1982, Proceedings, P r o c e e d i n g s , 28th 28th ILSG, 26—28. P.W., 1982, 1982, Geol. Geol. Soc. Soc. Am. Am. Mem. Mem. 156, 1 5 6 , 57—82. 57-82. ILSG, 26-28. 2) Weiblen, Weiblen, P.W., 2) 3) I . S . , 1980, 1980, Geochini. Geochim. Cosinochim. Cosmochim. Acta, Acta, 3) Raedke, Raedke, L.D. L.D. and andMcCalluxn, McCallum, I.S., Suppi. Suppl. 12, 1 2 , 133—153. 133-153. 4) 4 ) Medaris, Medaris, L.G., L.G., 1969, 1969, Am. Am. J. J. Sd. S c i . 255, 255, 241—253. 241-253. a l . , 1982, 1982, Lithos L i t h o s 15, 1 5 , 173—182. 173-182. 55)) Zeck, Zeck, H.P., H.P., et e t al., Table T a b l e 1: 1: Compositional C o m p o s i t i o n a l range r a n g e of of mineral m i n e r a l phases phases Stage Rock An Fo An Fo Enoox Stage Rock Type(1) Type(1) Eflopx Early Early TAE TAE 59—70 54—60 54-60 67—70 LSA LSA 38—59 38-59 56—66 57—67 49—60 49-60 64—72 65—71 57—60 65—74 1 ANN ANM TAN TAM 55—72 60—66 54—64 52—66 57—66 TAL TAL 50—70 54—59 54-59 63—69 69—75 5 55—63 54—65 54-65 70—72 69—75 2 SSSA SA CAM GAM Ma Main in Late Late Troctolite Troctolite 65 1) 1) ' j FFo 0 EncDX_ ## samples samples Encpx , .- TAN TAM ± 60 TAE TAL x— x - Troct. Troct. 0- *- I 4 1 1 4 Olivine /Orthopyroxene lorthopyroxene Olivine 0 - LSA LSA o- Otivine Olivine /IPlagioclase Plagioclase 2 2) SKI 55. Troctolites 50 45. An 50 60 55 65 40 70 Enoøx Orthopyroxene Orthopyroxene/ ICilnopyroxene Clinopyroxene 80 55 Efloox 60 65 70 75 Olivine 1 Clinopyroxene 3) 4) 75 6 5 Fo ~ 60 - 70 *' 0$ 65 011* 01 60 : 55 55 60 65 70 75 55 60 65 70 75 �30 The Relationship R e l a t i o n s h i p Between the t h e Basal Zone and Cloud Zone Cu—Ni Cu-Ni Suif ides, Minnamax Deposit, Deposit, Duluth Duluth Complex, Complex, Minnesota Minnesota Sulfid e s , Minnamax (Dept. of of Geology, Geology, University U n i v e r s i t y of of Minnesota—Duluth, Minnesota-Duluth, SARAH J. J. MILLS (Dept. Duluth, Duluth, Minnesota, 55812) 55812) The copper—nickel of tthe Minnamax d deposit, copper-nickel sulf s u l f iides d e s of h e Minnamax e p o s i t , Babbitt, Babbitt, Minnesota, are Minnesota, a r e located l o c a t e d within w i t h i n two zones of of the t h e Duluth Complex; Complex; these these basal Sulfide minerals aare r e the the b a s a l and cloud zones. zones. Sulfide m i n e r a l s in i n each each consist c o n s i s t of of cchalcopyrite, h a l c o p y r i t e , cubanite, c u b a n i t e , pentlandite, p e n t l a n d i t e , and and pyrrhotite. pyrrhotite. Rock units u n i t s identified i d e n t i f i e d in i n drill d r i l l core c o r e include i n c l u d e a thick t h i c k (—150 ( ~ 1 5 0meters) meters) both overlain underssulfide—poor u l f i d e - p o o r aanorthositic n o r t h o s i t i c troctolite t r o c t o l i t e which is is b oth o v e r l a i n and underu n i t s are are llain a i n by irregularly i r r e g u l a r l y mineralized m i n e r a l i z e d mixed mixed zones. zones. These mixed units composed of of v varying proportions of aanorthosite, composed arying p r o p o r t i o n s of n o r t h o s i t e , troctolite, t r o c t o l i t e , and picrite, with ranging from from ffine (l5mm). p icrite, w i t h ggrain r a i n ssize i z e ranging i n e tto o ppegmatitic e g m a t i t i c (~151n.m). A highly h i g h l y mixed unit u n i t lies l i e s at a t the t h e base b a s e (lower (lower 50 50 meters) m e t e r s ) of of the t h e Duluth Duluth greatest number of mafic pegmatites, Complex and exhibits e x h i b i t s the the g r e a t e s t number of m afic p e g m a t i t e s , rock rock iinclusions, n c l u s i o n s , and the t h e highest h i g h e s t abundance abundance of of Cu—Ni Cu-Ni sulf s u l f ides i d e s ("basal ("basal zone" zone" ssulf u l f iides). des) . Sulfide mineralization most abundant abundant in i n the t h e highly h i g h l y mixed basal basal Sulfide m i n e r a l i z a t i o n is i s most Smaller intervals mineralization unit u n i t of of each each core. core. i n t e r v a l s of of m i n e r a l i z a t i o n also a l s o occur o c c u r in in the unit hundred m meters t h e mixed u n i t several s e v e r a l hundred e t e r s above the t h e base b a s e in i n what have Characteristics been termed "cloud "cloud zones." zones." C h a r a c t e r i s t i c s common to t o both b o t h the t h e basal basal occur iin mixed or zone and and cloud cloud zone zone sulf s u l f ides i d e s are: a r e : 1) 1 ) sulf s u l f i ides d e s occur n tthe h e mixed or highly units, h i g h l y mixed u n i t s , but b u t are a r e absent a b s e n t from the t h e large, l a r g e , consistent c o n s i s t e n t anor— anorthositic ) ssulfide u l f i d e abundances change aabruptly bruptly t h o s i t i c troctolitic t r o c t o l i t i c units, u n i t s , 22) and aare r e generally g e n e r a l l y accompanied by a corresponding change in i n rock r o c k type, type, 3) the most abundant sulfides are associated with mafic pegmatites 3) t h e most abundant s u l f i d e s a r e a s s o c i a t e d w i t h m a f i c p e g m a t i t e s in in both ) tthe h e Cu/Cu+Ni rratios a t i o s aare re b o t h the t h e cloud and basal b a s a l zones, zones, and 44) approximately approximately 0.8 0.8 in i n each. each. This T h i s study s t u d y suggests s u g g e s t s that t h a t there t h e r e is i s a strong s t r o n g correlation c o r r e l a t i o n between mafic mafic pegmatites p e g m a t i t e s and sulfide s u l f i d e occurrence o c c u r r e n c e in i n both b o t h the t h e basal b a s a l and cloud cloud zones. zones. The sulf ides (and ppegmatites) which occur occur iin mixed uunits cone g m a t i t e s ) which n tthe h e mixed n i t s aare r e consulfid e s (and and tto discontinuous ssidered i d e r e d in i n this t h i s study s t u d y to t o be b e inagmatic magmatic and o form d i s c o n t i n u o u s pods pods of of relatively r e l a t i v e l y small s m a l l dimension. dimension. �31 Hydrothermal Alteration A l t e r a t i o n at a t the t h e Helen Helen Mine, Mine, Wawa, Ontario Wawa, Ontario M.L. NEBEL (Dept. M.L. (Dept. of of Geology, Geology, University U n i v e r s i t y of of Minnesota, Minnesota, Duluth, MN 55812) Duluth, MN 55812) R.L. M MORTON R.L. ORTON (Dept. (Dept. of of Geology, University U n i v e r s i t y of of Minnesota, Minnesota, Duluth, MN 55812) Duluth, MN 55812) Felsic FormaF e l s i c vvolcanic o l c a n i c rrocks o c k s uunderlying n d e r l y i n g tthe h e Archean Helen Iron I r o n Formation include lava flows and domes, massive and bedded pyroclastic t i o n include l a v a flows domes, bedded p y r o c l a s t i c They have been v variably rocks, r o c k s , block b l o c k and ash a s h flows, flows, and and hyalotuffs. hyalotuffs. ariably altered hydrothermal solutions mineral— a l t e r e d by hydrothermal s o l u t i o n s to t o five f i v e chemically aand/or n d / o r mineralogically o g i c a l l y distinct d i s t i n c t alteration a l t e r a t i o n facies: f a c i e s : 1) 1 ) least l e a s t altered, a l t e r e d , 2) 2) sericite, sericite, 3) 4 ) chloritoid, c h l o r i t o i d , and and 5) 5 ) ankerite. ankerite. 3) chlorite, c h l o r i t e , 4) Least L e a s t aaltered l t e r e d rrocks o c k s have perhaps undergone spilitization, s p i l i t i z a t i o n , but but metamorhave been affected a f f e c t e d primarily p r i m a r i l y by regional r e g i o n a l greenschist g r e e n s c h i s t facies f a c i e s metamorphism, phism, and are are the t h e freshest f r e s h e s t rocks r o c k s to t o be b e found found in i n the t h e study s t u d y area. a r e a . The other named ffor dominant aalteration mineral o t h e r aalteration l t e r a t i o n ffacies a c i e s aare r e named o r tthe h e dominant lteration m ineral ppresent. resent. Sericite widespread (6x2 (6x2kin) km) semi—consemi-conS e r i c i t e facies f a c i e s alteration a l t e r a t i o n forms forms aa widespread formable zone beneath the t h e iron i r o n formation. formation. A less l e s s extensive e x t e n s i v e(2xl (2x1kin) km) pipe—like body, cconsisting of cchlorite, p i p e - l i k e body, o n s i s t i n g of h l o r i t e , cchioritoid, h l o r i t o i d , and aankerite nkerite facies alteration facie's a l t e r a t i o n zones, zones, cross—cuts c r o s s - c u t s the t h e sericite s e r i c i t e zone. zone. Based on mineralogy mineralogy and and cchemistry of the Based h e m i s t r y of t h e aalteration, l t e r a t i o n , and on the the of tthe zones, tthe geometry of h e aalteration l t e r a t i o n zones, h e ffollowing o l l o w i n g sequence of of events events Shallow for i s proposed. proposed. Shallow circulatcirculatf o r the t h e development of of the t h e alteration a l t e r a t i o n is ing heated by by aa ssubvolcanic w a t e r (1—3 (1-3 kin), km), heated u b v o l c a n i c intrusion i n t r u s i o n (possibly (possibly i n g sea water the of felsic within t h e JJubilee u b i l e e Stock), S t o c k ) , encountered rrocks o c k s of f e l s i c composition w ithin water—rock reactions the volcanic the v o l c a n i c succession. s u c c e s s i o n . Sea water-rock r e a c t i o n s evolved evolved an a n acidic, acidic, K—rich solution migrated upward, upward, rreacting with K-rich s o l u t i o n that t h a t migrated eacting w i t h overlying o v e r l y i n g felsic felsic plagioclase rrocks, o c k s , converting converting p l a g i o c l a s e to t o sericite s e r i c i t e and quartz q u a r t z by the t h e addition addition porosity of K and the t h e removal of of Na. N a . The p o r o s i t y in i n the t h e altered a l t e r e d rocks r o c k s was of decreased, widespread, relatively r e l a t i v e l y impermeable, impermeable, semi—conformsemi-conformd e c r e a s e d , forming a widespread, able hydrothermal system. a b l e sericitic s e r i c i t i c alteration a l t e r a t i o n zone over the t h e hydrothermal Deeper—circulating D e e p e r - c i r c u l a t i n g sea s e a water w a t e r reacted r e a c t e d with w i t h basaltic b a s a l t i c rock r o c k at a t depths depths greater Mg, Mn, Mn, and Ca relative e n r i c h e d in i n Fe, Fe, Mg, relative g r e a t e r than t h a n 3 km and became enriched This tto o tthe h e felsic f e l s i c rocks. rocks. T h i s second hydrothermal solution s o l u t i o n moved upward i t encountered the t h e previously p r e v i o u s l y altered, a l t e r e d , relatively r e l a t i v e l y impermeable impermeable where it Fracture cap rock. rock. F r a c t u r e and fault f a u l t systems were developed or o r reactivated reactivated l l o w i n g rreaction e a c t i o n of h i s ssolution olution w i t h sericite sericite rock, aallowing of tthis with iin n the the cap rock, This Mn and the the ffacies a c i e s rocks. rocks. T h i s involved the t h e addition a d d i t i o n of of Fe, Fe, Mg, and Mn att the t o form chlorite chlorite pyrophyllite a t h e expense of of K to removal of ± pyrophyllite ssericite. ericite. + �32 During During greenschist g r e e n s c h i s t facies f a c i e s metamorphism, metamorphism, the t h e assemblage assemblage chlorite chlorite + pyrophyllite p y r o p h y l l i t e was w a s converted c o n v e r t e d to t o chioritoid c h l o r i t o i d ++ quartz, q u a r t z , whereas whereas chlorite chlorite in i n the t h e absence absence of of an a n aluminum aluminum silicate s i l i c a t e phase phase remained remained stable. stable. + Near Near the t h e sea s e a floor, f l o o r , aa sudden sudden release r e l e a s e of of pressure p r e s s u r e on on the t h e solution, solution, coupled coupled with w i t h mixing of of cool c o o l sea s e a water, w a t e r , rapidly r a p i d l y decreased d e c r e a s e d carbon carbon dioxdioxide m a s s precipitation p r e c i p i t a t i o n of of iron i r o n carbonate c a r b o n a t eand andf f or— ori d e solubility, s o l u b i l i t y , causing c a u s i n g mass mation mation of of the t h e ankerite a n k e r i t e fades f a c i e s assemblage. assemblage. Precipitation P r e c i p i t a t i o n of of siderite siderite occurred sea floor. floor. o c c u r r e d on on the t h e sea The The absence absence of of base b a s e metals m e t a l s and and sulfur s u l f u r in i n the t h e Helen Helen deposit d e p o s i t sug— suggests h i g h water/rock w a t e r / r o c k ratio r a t i o for f o r the t h e hydro— hydrog e s t s aa low low temperature t e m p e r a t u r e and and aa high thermal thermal system. system. n Li H I Sericite SericiteAlteration Alteration I Chlorite Chlorite±iAl-Silicate AI-SilicateAlteration Alteration a ... :;::.. .... .p ::.+ :.:.::: Ankerite : AnkeriteAlteration Alteration .......... ......... Figure F i g u r e 1. 1. Alteration A l t e r a t i o n Model Model �33 IIgneous g n e o u s Rocks Rocks of of the t h e Baraboo Baraboo District, D i s t r i c t , Wisconsin Wisconsin W.L. W.L. PETRO PETRO (Dept. (Dept. of of Geology Geology and and Geophysics, Geophysics, University University of of Wisconsin, Wisconsin, Madison, Madison, WI W I 53706) 53706) Volcanic Volcanic rocks, r o c k s , granitic g r a n i t i c rocks r o c k s and and mafic mafic dikes d i k e s occur occur in i n the t h e Baraboo Baraboo district d i s t r i c t of of south—central s o u t h - c e n t r a l Wisconsin. Wisconsin. Recent Recent field f i e l d work work has h a s established e s t a b l i s h e d the t h e age age relations relations among these igneous rocks and the associated among t h e s e igneous r o c k s and t h e a s s o c i a t e d Baraboo Baraboo q u a r t z i t e , yielding y i e l d i n g important important information i n f o r m a t i o n on on the t h e geolgeolquartzite, ogic o g i c evolution e v o l u t i o n of of this t h i s part p a r t of of the t h e southern s o u t h e r n Lake Lake Superior Superior region. region. The The volcanic v o l c a n i c rocks r o c k s are a r e exposed exposed along a l o n g the t h e outer o u t e r margins margins of the quartzite ridges that outline the Baraboo synclinof t h e q u a r t z i t e r i d g e s t h a t o u t l i n e t h e Baraboo synclin— orium, orium, and and are a r e probably probably the t h e basement basement upon upon which which the t h e meta— metasedimentary sedimentary sequence sequence was was deposited. d e p o s i t e d . These These rocks r o c k s consist consist of of porphyritic p o r p h y r i t i c rhyolite r h y o l i t e flows, flows, tuffs t u f f s and and agglomerates. agglomerates. The The BaxterHollow B a x t e r H o l l o wgranite g r a n i t e contains c o n t a i n s sparse s p a r s e xenoliths x e n o l i t h s of of volcanic Where exposed exposed v o l c a n i c rocks r o c k sand andbanded b a n d e diron i r o n formation. formation. Where at a t the t h e base b a s e of of the t h e quartzite, q u a r t z i t e , the t h e chilled c h i l l e d margin margin has h a s been been dtsrupted disrupted by by granitic g r a n i t i c dikes. d i k e s . Mafic Mafic dikes d i k e s also a l s o intrude intrude the t h e Baxter Baxter Hollow Hollow granite. g r a n i t e . All A l l these t h e s e rocks r o c k s have have been been metamorphosed metamorphosed to t o low—grade low-grade assemblages. assemblages. The The relationship r e l a t i o n s h i p between between the t h e quartzite q u a r t z i t e and and granite g r a n i t e has has long From this t h i s new new informinformlong been been aa point p o i n t of of controversy. c o n t r o v e r s y . From ation, a t i o n , it i t is i s concluded concluded that t h a t the t h e quartzite q u a r t z i t e was was deposited deposited upon upon the t h e volcanic v o l c a n i c rocks, r o c k s , and and intruded i n t r u d e d by by the t h e Baxter Baxter Hollow Hollow granite. granite. �34 Depositional D e p o s i t i o n a l and and Structural S t r u c t u r a l Feature F e a t u r e of of the t h e Upper Freda Sandstone Sandstone Fred PULKA (Dept. (Dept. of of Geol. Geol. && Geol. Geol. Engrg., Engrg., Michigan Michigan Technological Technological Fred S. S. PULKA University, U n i v e r s i t y , Houghton, Houghton, MI M I 49931) 49931) The i s part p a r t of of the t h e Upper Upper Keweenawan Keweenawan Oronto Oronto Group. Group. The The The Freda Freda Sandstone Sandstone is upper upper beds beds of of the t h e Freda Freda exposed exposed at a t the t h e type t y p e locality l o c a l i t y at a t Freda, Freda, NI M I are are mostly mostly thin, t h i n , red, r e d , alternating a l t e r n a t i n g planar p l a n a r laminated laminated and and microtrough microtrough cross— crosslaminated laminated beds. beds. The The planar p l a n a r laminated laminated beds are a r e claystone c l a y s t o n e or o r very v e r y fine— fineto t o medium—grained medium-grained sandstone. sandstone. The The claystone c l a y s t o n e and and sandstone s a n d s t o n e are a r e distinct distinct The and non—gradational. non-gradational. The planar p l a n a r laminated laminated sandstones s a n d s t o n e s have have mica mica flakes flakes parallel p a r a l l e l to t o the t h e bedding and and often o f t e n have have parting p a r t i n g lineation l i n e a t i o n on on bedding bedding planes. p l a n e s . They They occasionally o c c a s i o n a l l y have have small s m a l l scale s c a l e straight s t r a i g h t to t o sinuous s i n u o u s current current ripple r i p p l e marks on the t h e bedding surface s u r f a c e causing c a u s i n g an undulating u n d u l a t i n g lamination lamination within w i t h i n the t h e horizontally h o r i z o n t a l l y laminated laminated beds beds due due to t o ripple r i p p l e migration. migration. The The microtrough microtrough cross—laminated cross-laminated beds beds usually u s u a l l y have have small s m a l l lunate l u n a t e ripple ripple Migration of of the t h e lunate l u n a t e ripples r i p p l e s probably probably marks marks on on the t h e bedding bedding planes. p l a n e s . Migration caused the t h e microtrough microtrough cross—lamination. c r o s s - l a m i n a t i o n . Raindrop Raindrop imprints i m p r i n t s can can be b e seen seen on some some lunate l u n a t e ripples r i p p l e s in i n close c l o s e association a s s o c i a t i o n with w i t h dessication d e s s i c a t i o n features. features. The claystone c l a y s t o n e planar p l a n a r laminated laminated beds are a r e alternating a l t e r n a t i n g greenish g r e e n i s h and and red r e d in in c o l o r . They commonly commonly have have distorted d i s t o r t e d or o r convolute c o n v o l u t e bedding. bedding. One One individual individual color. bed, bed, eight e i g h t inches i n c h e s thick t h i c k was was traced t r a c e d over over half h a l f aa mile. mile. The two two distinct d i s t i n c t grain g r a i n size s i z e facies f a c i e s and and the t h e bedding succession s u c c e s s i o n imply imply aa transitional f l u v i a l and and lacustrine l a c u s t r i n e condicondit r a n s i t i o n a l environment, environment, possibly p o s s i b l y between fluvial tions. t i o n s . The sandstone s a n d s t o n e mineralogy suggests s u g g e s t s aa mixed silicic s i l i c i c and and mafic volcanic volcanic source s o u r c e area. a r e a . The silicic s i l i c i c fraction f r a c t i o n has h a s aa high h i g h proportion p r o p o r t i o n of of strained s t r a i n e d quartz quartz suggesting s u g g e s t i n g aa subsidiary s u b s i d i a r y metamorphic metamorphic source. source. The Freda Sandstone Sandstone in i n this t h i s area a r e a has h a s aa well w e l l developed developed extensional e x t e n s i o n a l joint joint system striking N50E. The Freda is i s cut c u t by numerous normal s t r i k i n g approximately approximately N5OE. faults f a u l t s either e i t h e r perpendicular p e r p e n d i c u l a r to t o or o r parallel p a r a l l e l to t o the t h e joint j o i n t system. system. The The faults 30 feet. f e e t . Normal Normal faults faults f a u l t s have have vertical v e r t i c a l displacements d i s p l a c e m e n t s of of from from one one to t o 30 They parallel p a r a l l e l to t o the t h e master m a s t e r joint j o i n t system system occasionally o c c a s i o n a l l y have drag d r a g folds. f o l d s . They are i s lacking l a c k i n g along a l o n g the t h e faults. faults. a r e downthrown to t o the t h e west and mineralization m i n e r a l i z a t i o n is The faults t o the t h e master joint j o i n t system system are a r e the t h e most f a u l t s nearly n e a r l y at a t right r i g h t angles a n g l e s to The faulting f a u l t i n g and and abundant abundant and and are a r e frequently f r e q u e n t l y mineralized m i n e r a l i z e d with w i t h calcite. c a l c i t e . The folding developed late history f o l d i n g probably developed l a t e in i n the t h e subsidence h i s t o r y of of the t h e Lake S u p e r i o r Syncline. Syncline. Superior �35 Evidence for f o r Glacial G l a c i a l Marine Marine Sedimentation Sedimentation in i n the t h e Early E a r l y Proterozoic Proterozoic Evidence Gowganda Gowganda Formation, Formation, Northeastern N o r t h e a s t e r n Ontario, O n t a r i o , Canada Canada LAWRENCE C. C . ROSEN ROSEN (Dept. (Dept. of LAWRENCE of Geology, Geology, University U n i v e r s i t y of of Minnesota—Duluth, Minnesota-Duluth, Duluth, MN 55812) 55812) Uuluth, MN f o r glacial g l a c i a l marine sedimentation s e d i m e n t a t i o n in i n the t h e Gowganda Gowganda Formation Formation Evidence for (Huronian Gowganda—Elk Lake area (Huronian Supergroup) Supergroup) in i n the t h e Gowganda-Elk a r e a of of northeastern northeastern Ontario O n t a r i o changes changes the t h e previously p r e v i o u s l y known known regional r e g i o n a l distribution d i s t r i b u t i o n of of conticontinental n e n t a l glacial g l a c i a l and and glacial g l a c i a l marine marine sedimentary sedimentary facies. f a c i e s . Lindsey Lindsey (1969) (1969) interpreted i n t e r p r e t e d the t h e Gowganda Gowganda to t o be be aa marine marine deposit d e p o s i t in i n the t h e south s o u t h (Espanola— (EspanolaWhitefish Whitefish Falls) F a l l s ) and and aa continental c o n t i n e n t a l deposit d e p o s i t in i n the t h e north n o r t h (Cobalt (Cobalt area) area) which which includes i n c l u d e s the t h e area a r e a under under discussion d i s c u s s i o n here. here. In I n the t h e study s t u d y area, a r e a , the t h e Gowganda Gowganda rests r e s t s unconformably upon upon the t h e Archean Archean basement. i s from from 00 to t o >1700 >I700 mm thick thick basement. The The subhorizontal s u b h o r i z o n t a l formation formation is (based (based on drill d r i l l hole h o l e data) d a t a ) and and no no complete complete sections s e c t i o n s are a r e present. p r e s e n t . It It is i s a heterogeneous assemblage assemblage of of diamictites, d i a m i c t i t e s , orthoconglomerates, orthoconglomerates, gray— graywackes,arkoses, wackes,arkoses, siltstones, s i l t s t o n e s , argillites, a r g i l l i t e s , pebbly pebbly argillites, a r g i l l i t e s , and and breccias. b r e c c i a s . Lateral L a t e r a l and and vertical v e r t i c a l facies f a c i e s changes changes can can be b e rapid, r a p i d , however however the t h e graywacke—argillite g r a y w a c k e - a r g i l l i t e association a s s o c i a t i o n is i s abundant, abundant, widespread, widespread, and and conconstitutes dominant s t i t u t e s the thed o m i n a n tfacies. f a c i e s . Orthoconglomerates Orthoconglomerates and and massive massive to t o thick thick bedded bedded arkoses, a r k o s e s , occassionally o c c a s s i o n a l l y cross—bedded, cross-bedded, are a r e most most common common at a t the the base i s aa prominent prominent base of of the t h e section s e c t i o n and and again a g a i n near n e a r the t h e top. t o p . Diamictite D i a m i c t i t e is lithology l i t h o l o g y and and varies v a r i e s from from massive massive to t o weakly stratified s t r a t i f i e d with w i t h clasts c l a s t s up up to t o 1.2 1.2 m in i n apparent a p p a r e n t diameter; d i a m e t e r ; units u n i t s vary v a r y from from aa decimeter d e c i m e t e r to t o as a s much much as i n thickness. t h i c k n e s s . Wisps Wisps and and deformed deformed pieces p i e c e s of of sandy sandy material m a t e r i a l are are a s 20 20 mm in often o f t e n present p r e s e n t within w i t h i n the t h e diamictites. d i a m i c t i t e s . Contacts C o n t a c t s with w i t h other o t h e r units u n i t s can can be be sharp, s h a r p , irregular, i r r e g u l a r , or o r transitional. t r a n s i t i o n a l . The The diamictite d i a m i c t i t e is i s restricted r e s t r i c t e d to to the t h e lower lower two—thirds t w o - t h i r d s of of the t h e formation. formation. Interbedded Interbedded graywackes, graywackes, siltstones, s i l t s t o n e s , and and argillites a r g i l l i t e s commonly commonly conconstitute to 4 m thick s t i t u t e fining—upward fining-upward sequences sequences from from 22 cm cm t o 4 m t h i c k in i n the t h e lower lower portion p o r t i o n of of the t h e section s e c t i o n and and both both fining—upward fining-upward and and coarsening—upward coarsening-upward sequences in the upper part of the section. Internal sequences i n t h e upper p a r t of t h e s e c t i o n . I n t e r n a l stratification stratification includes i n c l u d e s graded beds, beds, ripple r i p p l e marks, marks, laminations, l a m i n a t i o n s , and and convolute c o n v o l u t e bedding. bedding. In I n addition, a d d i t i o n , features f e a t u r e s such such as a s ripped—up ripped-up clasts, c l a s t s , flame flame structures, s t r u c t u r e s , and and other o t h e r loading l o a d i n g phenomena phenomena are a r e present. p r e s e n t . Thinly Thinly laminated laminated siltstone s i l t s t o n e and and argillite 30 cm cm are a r e present present l a r g e as a s 30 a r g i l l i t e sequences sequences with w i t h lonestones l o n e s t o n e s as a s large thoughout thoughout the t h e lower lower two—thirds t w o - t h i r d s of of the t h e section. s e c t i o n . They They are a r e more more common common in the central and western portions i n t h e c e n t r a l and w e s t e r n p o r t i o n s of of the t h e study s t u d y area. a r e a . Lonestone Lonestone sequences t h i c k , while w h i l e individual i n d i v i d u a l units u n i t s vary v a r y from from 40 mm thick, sequences are a r e as a s much much as a s 40 11to 5 m thick. t o 5 m t h i c k . Breccias B r e c c i a s and and units u n i t s with w i t h soft s o f t sediment sediment deformation deformation structures s t r u c t u r e s are a r e fairly f a i r l y widespread widespread but b u t constitute c o n s t i t u t e aa minor minor part p a r t of of the the section; .5 to t o approximately approximately 44 mm thick. thick. s e c t i o n ; units u n i t s vary v a r y from from .5 The t h e Gowganda Gowganda in i n this t h i s area a r e a is is The following f o l l o w i n g depositional d e p o s i t i o n a l history h i s t o r y of of the Paleovalleys, P a l e o v a l l e y s , probably probably largely l a r g e l y tectonic t e c t o n i c in i n origin o r i g i n with with perhaps 1000 mm relief, r e l i e f , were were partially p a r t i a l l y filled f i l l e d by by fluvial fluvial perhaps as a s much much as a s 1000 processes p r o c e s s e s which which deposited d e p o s i t e d the t h e orthoconglomerates orthoconglomerates and and arkoses a r k o s e s prior p r i o r to to the t h e arrival a r r i v a l of of glacial g l a c i a l ice i c e in i n the t h e vicinity. v i c i n i t y . The The lonestones l o n e s t o n e s in i n the the laminated laminated units u n i t s are a r e interpreted i n t e r p r e t e d to t o be b e dropstones d r o p s t o n e s released r e l e a s e d from from meltmelting i n g icebergs i c e b e r g s or o r aa floating f l o a t i n g ice i c e shelf. s h e l f . The The paucity p a u c i t y of of unequivocable unequivocable indicated. indicated. �36 varved varved bedding bedding and and the t h e widespread widespread occurrence o c c u r r e n c e of of dropstone—bearing dropstone-bearing sequences sequences is i s suggestive s u g g e s t i v e of of aa glacial g l a c i a l marine marine rather r a t h e r than t h a n aa glacial glacial lacustrine l a c u s t r i n e environment. environment. The The weakly weakly stratified s t r a t i f i e d diamictites, d i a m i c t i t e s , in i n view view of of their t h e i r distribution d i s t r i b u t i o n and and transitional t r a n s i t i o n a l contacts c o n t a c t s with w i t h dropstone d r o p s t o n e units, units, are a r e interpreted i n t e r p r e t e d to t o be be the t h e products p r o d u c t s of of rapid r a p i d fallout f a l l o u t of of abundant abundant debris debris released r e l e a s e d beneath beneath an an ice i c e shelf. s h e l f . The The generally g e n e r a l l y thinner, t h i n n e r , massive massive diamic— diamictites t i t e s are a r e attributed a t t r i b u t e d to t o submarine submarine gravity g r a v i t y flow flow mechanisms mechanisms beneath beneath an an ice i c e shelf s h e l f or o r near n e a r the t h e margin margin of of aa melting m e l t i n g land—based land-based glacier. g l a c i e r . The The fining—upward fining-upward and and coarsening—upward coarsening-upward sequences sequences reflect r e f l e c t the t h e changing changing conditions c o n d i t i o n s within w i t h i n the t h e basin b a s i n as a s increases i n c r e a s e s and and decreases d e c r e a s e s in i n both b o t h energy energy and outwash. The The and sediment sediment supply supply occurred o c c u r r e d and and may may represent r e p r e s e n t submarine submarine outwash. graywackes graywackes resulted r e s u l t e d from from the t h e interaction i n t e r a c t i o n of of various v a r i o u s types t y p e s of of sediment sediment gravity dominantly turbidity t u r b i d i t y currents c u r r e n t s with w i t h subordinate subordinate g r a v i t y flows, f l o w s , dominantly fluidized/liquidized The more more well well f l u i d i z e d / l i q u i d i z e d flows flows and and possibly p o s s i b l y grain g r a i n flows. f l o w s . The sorted s i l t s t o n e s , and and argillites a r g i l l i t e s may may reres o r t e d and and laminated laminated sandstones, s a n d s t o n e s , siltstones, present p r e s e n t more more normal normal marine marine sedimentation. sedimentation. The The breccias b r e c c i a s and and deformed deformed units e i t h e r resedimentation r e s e d i m e n t a t i o n from from unstable u n s t a b l e depositional depositional u n i t s represent r e p r e s e n t either sites or minor tectonic instability. s i t e s o r minor t e c t o n i c i n s t a b i l i t y . The The distribution d i s t r i b u t i o n of of the t h e rock rock types t y p e s within w i t h i n the t h e thick t h i c k stratigraphic s t r a t i g r a p h i c column column suggests s u g g e s t s changing changing condiconditions t i o n s probably probably associated a s s o c i a t e d with w i t h advances advances and and retreats r e t r e a t s of of glaciers glaciers located Basin subsidence s u b s i d e n c e continued continued throughout throughout Gowganda Gowganda l o c a t e d to t o the t h e north. n o r t h . Basin time, allowing the great thickness of sediments to accumulate time, a l l o w i n g t h e g r e a t t h i c k n e s s of sediments t o accumulate and and be be preserved. preserved. In I n late l a t e Gowganda Gowganda time, time, amelioration a m e l i o r a t i o n of of the t h e climate c l i m a t e occuroccurred, r e d , indicated i n d i c a t e d by by the t h e lack l a c k of of glacial g l a c i a l features f e a t u r e s in i n the t h e deposits. deposits. Sedimentation Sedimentation appears a p p e a r s to t o have have been been largely l a r g e l y fluvial—deltaic, f l u v i a l - d e l t a i c , as a s also also evidenced in the overlying Lorrain Formation. e v i d e n c e d i n t h e o v e r l y i n g L o r r a i n Formation. �37 A l t e r a t i o n of of the t h e Deer Deer Lake Lake Peridotite P e r i d o t i t e in i n the t h e Vicinity Vicinity Alteration of the t h e Ropes Ropes Gold Gold Mine, Mine, Marquette Marquette County, County, Michigan Michigan of Geol. Engrg., Engrg., Michigan Michigan Technological Technological Dean Rossell R o s s e l l (Dept. (Dept. of of Geol. Geol. && Geol. Dean U n i v e r s i t y , Houghton, Houghton, MI M I 49931) 49931) University, Gold Gold mineralization m i n e r a l i z a t i o n at a t the t h e Ropes Ropes Mine Mine is i s contained c o n t a i n e d entirely e n t i r e l y in i n an an east— eastwest west striking s t r i k i n g septum septum of of highly h i g h l y altered a l t e r e d felsic f e l s i c rock r o c k within w i t h i n the t h e serpentin— serpentini z e d Deer Deer Lake Lake Peridotite. P e r i d o t i t e . Near Near the t h e Ropes Ropes Mine Mine the t h e serpentinite s e r p e n t i n i t e consist consist ized of two two principal p r i n c i p a l textural t e x t u r a l varieties: v a r i e t i e s : Type of A, with w i t h well w e l l preserved p r e s e r v e d relict relict Type A, B, showing showing recrystallized r e c r y s t a l l i z e d and and foliated f o l i a t e d textures, textures, igneous textures, t e x t u r e s , and and Type Type B, igneous probably produced produced by by shearing. s h e a r i n g . AA prominent prominent zone zone of of Type Type BB serpentinite serpentinite probably a l o n g the t h e north n o r t h shore s h o r e of of Deer Deer Lake Lake may may represent r e p r e s e n t an an extension e x t e n s i o n of of aa shear shear along zone along a l o n g the t h e felsic f e l s i c septum. septum. zone Compositionally, Compositionally, the t h e serpentinites s e r p e n t i n i t e s represent r e p r e s e n t altered a l t e r e d harzburgite h a r z b u r g i t e and and l h e r z o l i t e (Rossell ( R o s s e l l and and Kalliokoski, K a l l i o k o s k i , this t h i s volume). volume). An An original o r i g i n a l composicomposilherzolite t i o n a l zoning zoning or o r layering l a y e r i n g may may be b e reflected r e f l e c t e d by by wide wide variations v a r i a t i o n s in i n the t h e olivine olivine tional to t o pyroxene pyroxene ratios r a t i o s determined determined from from calculated c a l c u l a t e d mineral m i n e r a l modes, modes, but b u t the t h e scale scale of these t h e s e variations v a r i a t i o n s has h a s not n o t been been established. established. of + Serpentinite dolomite ±t magnesite magnesite S e r p e n t i n i t e has h a s been been extensively e x t e n s i v e l y altered a l t e r e d to t o aa talc t a l c + dolomite Major and and ±Â chlorite c h l o r i t e assemblage assemblage in i n aa zone zone adjacent a d j a c e n t to t o the t h e Ropes Ropes ore o r e body. body. Major trace t r a c e element element compositions, compositions, including i n c l u d i n g gold, gold, were were determined determined for f o r aa suite s u i t e of of talc—carbonate t a l c - c a r b o n a t e rocks r o c k s from from the t h e northern n o r t h e r n alteration a l t e r a t i o nzone. zone. From From this t h i s data d a t a relarelat i v e additions a d d i t i o n s and and losses l o s s e s of of chemical chemical components components were were computed computed by by two two methods: methods: tive f i r s t , a sassuming s u m i n g tthat h a t aalteration l t e r a t i o n ooccurred c c u r r e d at a t constant c o n s t a n t volume, volume, and and the the The first, The A 1 and and Sc Sc are a r e immobile immobile during d u r i n g alteration a l t e r a t i o n while w h i l e volume volume second assuming assuming that t h a t Al second i s allowed allowed to t o change. change. Changes Changes calculated c a l c u l a t e d using u s i n g the t h e first f i r s t method method appear appear to to is be b e more more consistent c o n s i s t e n t with w i t h observed observed mineralogical m i n e r a l o g i c a l changes changes than t h a n those t h o s e calculated calculated by the t h e latter l a t t e r method. method. by Talc—carbonate Talc-carbonate alteration a l t e r a t i o n at a t the t h e Ropes Ropes Mine Mine appears a p p e a r s to t o have have resulted r e s u l t e d in i n the the addition A l , and and the t h e removal removal of of H20 Hz0 and and Mg Mg from from the t h e serpentin— serpentinCO2, Ca Ca and and Al, a d d i t i o n of of CO2. i t e . Au Au abundance abundance in i n the t h e serpentinite s e r p e n t i n i t e samples samples analyzed analyzed were were found found to t o be b e near near ite. c r u s t a l averages. averages. Talc—carbonate Talc-carbonate samples samples showed showed greater g r e a t e r variation, v a r i a t i o n , but b u t gengencrustal erally e r a l l y had had Au Au concentrations c o n c e n t r a t i o n s equal e q u a l to t o or o r greater g r e a t e r than t h a n those t h o s e found found in i n serpen— serpent i n iites. tes. tin Gold may may have have been been transported t r a n s p o r t e d as a s aa carbonyl c a r b o n y l or o r carbonate c a r b o n a t e complex complex in i n aa Gold CO2 rich r i c h fluid f l u i d from from some some outside o u t s i d e source s o u r c e to t o the t h e ore o r e host h o s t rock. r o c k . Subsequent Subsequent CO2 c a r b o n a t e forming forming reactions r e a c t i o n s in i n the t h e ultramafic u l t r a m a f i c rock r o c k surrounding s u r r o u n d i n g the t h e ore o r e host host carbonate rock CO2 and/or r o c k sufficiently s u f f i c i e n t l y lowered lowered the t h e Pcoi a n d / o r decreased d e c r e a s e d the t h e acidity a c i d i t y to t o allow a l l o w for for structures d e p o s i t i o n of of gold gold in i n suitable suitable s t r u c t u r e s in i n the t h e ore o r e host h o s t rock. rock. deposition �38 C o b a l t , Nickel, Cobalt, Nickel, and Vanadium Contents of of P y r i t e from Michigamme Michigamme Slate, S l a t e , Michigan Michigan Pyrite A. P. P. Ruotsala, R u o t s a l a , Paul P a u l M. M. Stadnik, S t a d n i k , T. T. J. J . Bornhorst (Dept. (Dept. of of Geol. Geol. A. Geol. Engrg., Engrg., Michigan Michigan Tech. Tech. Univ., Univ., Houghton, Houghton, MI M I 49931) 49931) & Geol. i s an organic—rich o r g a n i c - r i c h metasedimentary rock r o c k in in S l a t e is The Michigamme Slate central Upper Peninsula of Michigan. central P e n i n s u l a of Michigan. The Michigan Geological G e o l o g i c a l Survey, Survey, with w i t h funding funding from from the t h e Department of Energy tested t e s t e d the t h e uranium uranium potenpotenof tthe Michigamme iin Marquette, Baraga Baraga and and IIron Counties w with ttial i a l of h e Michigamme n Marquette, r o n Counties ith drill ssix i x diamond d r i l l holes h o l e s (Trow, (Trow, 1979). 1979). IIn n tthis h i s study, s t u d y , pyrites p y r i t e s were separated material nickel, s e p a r a t e d from core core m a t e r i a l and analyzed for f o r cobalt, cobalt, n i c k e l , and vanadium with w i t h the t h e objective o b j e c t i v e of of determining d e t e r m i n i n g its i t s mode mode of of origin. origin. Most pyrites p y r i t e s fall f a l l into i n t o the t h e syngenetic s y n g e n e t i c field f i e l d of of Price P r i c e (1972), (1972), in in terms of of Co/Ni Co/Ni rratios; however, aa number number of of hhigh Co/Ni rratios were terms a t i o s ; however, i g h Co/Ni a t i o s were which fall found which f a l l into i n t o the t h e volcanic—exhalative v o l c a n i c - e x h a l a t i v e massive massive sulfide s u l f i d e field. field. References Trow, Trow, J., J . , 1979, 1979, Final F i n a l report r e p o r t diamond—drilling diamond-drilling for f o r geologic g e o l o g i c informainformaMiddle Precambrian Precambrian bbasins western portion of ttion i o n iin n tthe h e Middle a s i n s in i n tthe he w estern p o r t i o n of northern n o r t h e r n Michigan: Michigan: Geol. Geol. Surv. Surv. Div., Div., Michigan Dept. Dept. Nat. Nat. Re— ReOFR GJBX-162(79), CJBX—162(79), 44 UDOE OFR 44 p. p. ssources, o u r c e s , Lansing, Lansing, Open—File Open-File Report Report TJDOE Price, P r i c e , B.G., B.G., 1972, Minor elements elements in i n pyrites p y r i t e s from from the t h e Smithers Smithers map B.C. and eexploration of minor element studies x p l o r a t i o n aapplications p p l i c a t i o n s of studies aarea, r e a , B.C. (M.S. Thesis): T h e s i s ) : Univ. Univ. of of British B r i t i s h Columbia, Columbia, Vancouver, Vancouver, 270 270 p. p. (M.S. �39 Geochemistry of the the Volcanic Rocks of Northeastern Northeastern Wisconsin KLAUS Reston, Virginia Virginia J. SCHULZ SCHULZ (U.S. (U.S. Geological Geological Survey, Survey, Reston, KLAUS J. 22092) 22092) The The early early Proterozoic Proterozoic volcanic—plutonic volcanic-plutonic belt of north—central north-central Wisconsin Wisconsin is is well well exposed exposed in in the the northern northern half half of of Marinette Marinette County. County. In In this this area, area, the the volcanic volcanic sequence sequence has has been been informally informally divided divided into four formations Formation, the formations (Jenkins, (Jenkins, 1973): 1973): the Quinnesec Formation, McAllister McAllister Formation, Formation, the the Beecher Beecher Formation, Formation, and the the Pemene Pemene FormaFormaAlthough tion. Although stratigraphic stratigraphic relationships relationships between between these these are are still still tion. not fully fully resolved, resolved, it it appears appears that the overall section section represents represents a progression progression from from mafic mafic through through felsic felsic volcanics. volcanics. Although calc-alkaline affinity affinity has has been been recognized recognized Although aa general general caic—alkaline for the more felsic section, uncertainty uncertainty felsic portions of this volcanic section, still still remains as as to the the geochemical geochemical affinities of the basaltic rocks and their possible petrologic relationship relationship to the more felsic felsic volcanics. the present study, study, a suite suite of samples samples was collected volcanics. For the analysis (major for analysis (major elements, elements, rare rare earth, earth, and and other other trace trace elements) elements) with emphasis emphasis on on the the mafic mafic Quinnesec Quinnesec Formation. Formation. The diabases range The Quinnesec Quinnesec pillowed flows flows and associated diabases range from from basalt through through andesite andesite and show show little little evidence evidence of a trend in in iron iron high, A1203 and have variable, variable, though though generally high, enrichment. enrichment. They have elements (REE) (WE) show show aa wide wide range range Ti02 contents. contents. The rare earth elements low Ti02 in both total abundance abundance and and chondrite chondrite normalized normalized slopes. slopes. Most .14—.38 basalts show depletion with with [La/Smjn [LaISm] == .14-.38 show extreme light (L)REE (L)REE depletion (total range .14-.76). Two gabbro samples samples from from the the Sturgeon Sturgeon Falls Falls range .14—.76). sill, one of several large gabbroic sills within within the Quinnesec Forsill, mation, also show mation, show significant significant LREE LREE depletion depletion suggesting suggesting possible possible consanguinity with LREE The andesites andesites have enriched LREE consanguinity with the the basalts. basalts. The but relatively = ]1.23—1.47), 1.23-1.47), relatively low low total total REE REE abundances. abundances. ( [ ~ a / ~ =m ~ ([La/Sm]n whereas those Samples from the Beecher Formation are andesitic whereas Pemene Formation from the Pemene Formation are are rhyolitic. rhyolitic. The rhyolites rhyolites have higher REE REE abundances abundances and larger larger negative negative Eu anomalies anomalies than than the the andesites, andesites, show similar similar shaped, but show shaped, LREE—enriched LREE-enriched patterns. patterns. The The rhyolites rhyolites ppm) and higher Rb/Sr ratios than the also have lower Sr (55—133 (55-133 ppm) andesites S r ~ 3 6ppm). 0ppm). andesites ((Sr360 The The data data suggest suggest the the following following conclusions: conclusions: 11.. Quinnesec Formation basalts and related diabases are The Quinnesec compositionally Proterozoic compositionally distinct from the other early Proterozoic (i.e. Hemlock, Hemlock, Badwater, Badwater, etc.) etc.) basalts in in upper upper Michigan Michigan (i.e. which was was highly depleted and were derived from mantle which in large in large ion ion lithophile lithophile elements. elements. 2. 2. andesites of northeastern northeastern Wisconsin are not The basalts and andesites seperate related by crystal crystal fractionation fractionation but represent seperate melts melts from from compositionally compositionally distinct distinct sources. sources. 3. 3. The overall chemical characteristics characteristics of the Quinnesec Quinnesec basalts basalts �40 suggest affinities suggest affinities with with basalts basalts in in recent recent island—arcs island-arcs back—arc basins rather than those of the ocean and back-arc floor or floor or continental continental regions. regions. The The appearance appearance of of andesites and more andesites more felsic felsic units units with with these these basalts basalts supports such an island-arc island—arc to back-arc back—arc basin also supports environment. environment. Reference Reference Jenkins, A., 1973, 1973, Institute Institute on on Lake Lake Superior Superior Geology, Geology, Jenkins, R. R. A., 19th, 19th, p. p. 15—16. 15-16. �41 Geochemistry of of Fluid F l u i d Inclusions I n c l u s i o n s from from Archean Archean and and Phanerozoic Phanerozoic Gold Gold Deposits Deposits TED J. J. SMITH, SMITH, PAUL PAUL L. L. CLOKE, CLOKE, and and STEPHEN STEPHEN E. E. KESLER KESLER (Department (Department of of TED G e o l o g i c a l Sciences, S c i e n c e s , The The University U n i v e r s i t y of of Michigan, Michigan, Ann Ann Arbor, Arbor, MI MI Geological 48109) 48109) Fluid F l u i d inclusions i n c l u s i o n s from from various v a r i o u s Archean and and Phanerozoic Phanerozoic gold gold deposits deposits in i n metamorphic terrains t e r r a i n s were examined examined using u s i n g aa specially s p e c i a l l y designed designed gas gas chromatographic chromatographic analytical a n a l y t i c a l system system and and conventional c o n v e n t i o n a l heating/freezing heatinglfreezing techniques. techniques. The The inclusion i n c l u s i o n analyses a n a l y s e s indicate i n d i c a t e that, t h a t , in i n most most cases, c a s e s , the the fluids H20—C02 or H20—CH4—C02 m mixtures, with CO o r H20-CH4-C02 ixtures, w i t h trace t r a c e amounts amounts of of CO f l u i d s are a r e H20-C02 and and N2. No. Heating and and freezing f r e e z i n g measurements indicate i n d i c a t e the t h e presence p r e s e n c e of of low low salinity wt%NaCl), H20—C02 s a l i n i t y (<2 (<2 equiv. equiv. wtu%NaCl), H20-C02 and H20—CH4—C02 H20-CH4-CO2 fluid f l u i d inclusions, inclusions, confirming our o u r analyses. analyses. confirming Homogenization Homogenization of of the t h e inclusions i n c l u s i o n s occurred o c c u r r e d at at t e m p e r a t u r e s of of 220°C 220° to t o 380°C. 380°C Temperature and and f02 f o determinations determinations temperatures 2 diagrams were made made by plotting p l o t t i n g reaction r e a c t i o n lines l i n e s on on a02—temperature a 0 t e m p e r a t u r e diagrams 2utilizing u t i l i z i n g aa recently r e c e n t l y developed developed equation e q u a t i o n of of state s t a t e for f o r supercritical supercritical H20C02CH4 H20-Coy-CH4 fluids. fluids. Our Our results r e s u l t s indicate i n d i c a t e that t h a t the t h e fluids f l u i d s obtained obtained equilibrium n e a r the t h e QFM QFM e q u i l i b r i u m at a t temperatures t e m p e r a t u r e s of of 340°C 340° to t o 500°C 500° and and f02ts f ' s near 02. buffer. buffer. Isochores, I s o c h o r e s , also a l s o calculated c a l c u l a t e d from from the t h e equation e q u a t i o n of of state, s t a t e , indicate indicate high h i g h pressures p r e s s u r e s of of 2000 2000 to t o 4000 4000 bars. bars. �42 Jacobsville J a c o b s v i l l e Sandstone Sandstone Ridge Ridge in i n Keweenaw Keweenaw Bay Bay R. L. Wunderman Wunderman and and M. M. Rausch Rausch R. L. There There is i s aa north—northeast n o r t h - n o r t h e a s t trending t r e n d i n g lake l a k e bottom bottom ridge r i d g e of of Jacobs— Jacobsyule Sandstone in Keweenaw Bay (Fig. 1). A recent scuba dive v i l l e Sandstone i n Keweenaw Bay (Fig. 1 ) . A r e c e n t scuba d i v e conconfirms f i r m s the t h e presence p r e s e n c e of of subhorizontal s u b h o r i z o n t a l Jacobsville J a c o b s v i l l e Sandstone Sandstone 20 20 mm under under water w a t e r at a t aa point p o i n t 77 Km Km southeast s o u t h e a s t of of Portage P o r t a g e Entry Entry (88°22'W, (88¡22'W 46°56'N) 46'56'N) cropping cropping out o u t as a s aa detritus—free d e t r i t u s - f r e e north—west north-west facing f a c i n g scarp. s c a r p . At A t this this locality, l o c a l i t y , the t h e Jacobsville J a c o b s v i l l e Sandstone Sandstone is i s lithologically l i t h o l o g i c a l l y similar s i m i l a r to to s h o r e exposures. exposures. Warren Warren (1981, (1981, Figs. F i g s . 46 46 and and 47) 47) shows shows that that nearby shore this t h i s ridge r i d g e forms forms the t h e southeastern s o u t h e a s t e r n margin of of aa steep—sided s t e e p - s i d e d valley valley so s o that t h a t similar s i m i l a r excellent e x c e l l e n t exposures exposures of of bedrock are a r e likely l i k e l y to t o be b e found found Being sheltered s h e l t e r e d from from the t h e lake, lake, on the t h e northwest n o r t h w e s t ridge r i d g e face f a c e as a s well. w e l l . Being the t h e ridge r i d g e face f a c e more probably is i s related r e l a t e d to t o the t h e formation f o r m a t i o n of of the t h e steep— steepsided s i d e d valley v a l l e y than t h a n being b e i n g the t h e result r e s u l t of of wave erosion e r o s i o n on on aa lake l a k e cliff. cliff. Reference Reference Warren, Warren, E.J., E.J., 1981, 1981, The bedrock topography of the t h e Keweenaw Keweenaw Penninsula, Penninsula, dissertation), Michigan (Ph.D. (Ph.D. d i s s e r t a t i o n ) , Michigan Technological T e c h n o l o g i c a l University, University, Michigan Houghton, Houghton, 169 169 p. p. Figure F i g u r e 1: 1: Location L o c a t i o n Nap. Map. �43 ROPES ROPES GOLD GOLD MINE MINE AND AND ITS ITS GEOLOGICAL GEOLOGICAL SETTING SETTING Dean Dean Rossell Rossell and and 3. J. Kalliokoski Kalliokoski �44 THE ROPES GOLD GOLD MINE AND ITS ITS GEOLOGICAL GEOLOGICAL SETTING SETTING Dean Dean Rossell R o s s e l l and and J. J . Kalliokoski Kalliokoski INTRODUCTION INTRODUCTION Location Location The The Ropes Ropes Gold Gold Mine Mine is i s located l o c a t e d in i n Section S e c t i o n 29, 29, T48N—R27W, T48N-R27W, Marquette Marquette County, County, Michigan, Michigan, about three miles Ishpeming and and aa quarter q u a r t e r mile m i l e west of of Deer Deer Lake Lake (Figs. three m i l e s north n o r t h of of Ishpeming 1, ( F i g s . 1, 2). gold prosprosi s the t h e most most extensively e x t e n s i v e l y developed developed of of the t h e 20 20 or o r more more gold The Ropes Ropes Mine Mine is 2 ) . The pects p e c t s and and mines mines that t h a t comprise comprise the t h e Michigan Michigan gold gold belt. belt. His H i s tory tory Most of i s summarized summarized from from Broderick Broderick (1945). (1945). The Ropes ore ore of the t h e following f o l l o w i n g history h i s t o r y is body body was was discovered d i s c o v e r e d in i n 1880 1880 by by Julius J u l i u s Ropes Ropes while w h i l e he h e was was prospecting p r o s p e c t i n g for f o r asbestos asbestos among among the t h e outcrops o u t c r o p s of of the t h e Deer Deer Lake Lake Peridotite. P e r i d o t i t e . Mining Mining operations o p e r a t i o n s at a t the t h e Ropes Ropes began began in i n 1882 1882 and and continued c o n t i n u e d until u n t i l 1897 1897 when when the t h e mine mine was was closed c l o s e d by by creditors. c r e d i t o r s . At At the t h e time time of of closing, c l o s i n g , 15 1 5 levels l e v e l s had been developed developed to t o the t h e east e a s t and and west west of of the t h e Curry Curry shaft, s h a f t , that t h a t reached reached aa depth d e p t h of of 244 244 meters. meters. During During the t h e 15 1 5 years y e a r s that t h a t the t h e mine mine was was in i t produced 1250 1250 kg kg of of gold gold and and 6200 6200 kg kg of of silver s i l v e r from from 145,000 145,000 tons t o n s of of i n operation o p e r a t i o n it ore, o r e , averaging a v e r a g i n g 5.96 5.96 g/ton g / t o n gold gold and and 28.05 28.05 g/ton g / t o n silver s i l v e r (Morgan (Morgan and and DeCristoforo, D e C r i s t o f o r o , 1980). 1980). Around Around 1901 1901 some some 30,000 30,000 tons t o n s of of tailings t a i l i n g s were were cyanided. cyanided. In I n 1933 1933 the t h e Ropes property p r o p e r t y was acquired a c q u i r e d by the t h e Ishpeming Ishpeming Mining Mining Co., Co., which which continued continued surface s u r f a c e exploration e x p l o r a t i o n in i n the t h e area. a r e a . Calumet Calumet and and Hecla Hecla Mining Mining Co. Co. bought bought aa majority majority interest i n t e r e s t in i n the t h e Ishpeming Ishpeming Mining Mining Co. Co. in i n 1934. 1934. From From 1934 1934 to t o 1942 1942 they t h e y conducted conducted an an extensive e x t e n s i v e exploration e x p l o r a t i o n program program of of diamond diamond drilling, d r i l l i n g , drifting d r i f t i n g on on the t h e 15th 1 5 t h level, l e v e l , and and resampling resampling of of the t h e old o l d workings workings in i n an a n attempt a t t e m p t to t o find f i n d an an extension e x t e n s i o n of of the t h e Ropes Ropes ore ore body it body (Fig. (Fig. 3). 3 ) . Although Although this t h i s work work found found no no major major extensions e x t e n s i o n s of of the t h e ore o r e body, body, it did d i d disclose d i s c l o s e over over aa million m i l l i o n tons t o n s of of lower lower grade grade ore o r e in i n the t h e ore o r e host h o s t rock r o c k surrounding surrounding the 1st and and 15th 1 5 t h levels, l e v e l s , average average t h e old o l d workings. workings. These These zones, zones, located l o c a t e d between between the t h e 1st 0.13 0.13 oz/ton o z / t o n gold gold and and 0.7 0.7 oz/ton o z / t o n silver. s i l v e r . In time restrictions r e s t r i c t i o n s on on precious precious I n 1942 1942 war war time metal m e t a l mining mining stopped stopped operations o p e r a t i o n s at a t the t h e mine, mine, preventing p r e v e n t i n g further f u r t h e r exploration e x p l o r a t i o n below below the t h e 15th 1 5 t h level. level. In t h e Ropes Ropes Mine, Mine, began began aa new new expor— export h e present p r e s e n t owner owner of of the I n 1974 1974 Callahan Callahan Mining Mining Corp., Corp., the ation a t i o n program program to t o confirm c o n f i r m and and try t r y to t o expand expand the t h e low low grade g r a d e ore o r e reserves r e s e r v e s established e s t a b l i s h e d by by the t h e Calumet Calumet and and Hecla Hecla Mining Mining Co. Co. To To date d a t e this t h i s work work has h a s included i n c l u d e d rehabilitation r e h a b i l i t a t i o n of of the t h e old o l d mine mine workings, workings, an an extensive e x t e n s i v e surface s u r f a c e and and underground underground diamond diamond drilling d r i l l i n g camcampaign, worke x t r a c t i o n of of bulk b u l k samples samples for f o r metallurgical m e t a l l u r g i c a l tests, t e s t s , resampling resampling of of old o l d workp a i g n , extraction ings, remapping of of tthe i n g s , aand n d remapping h e surface s u r f a c e and underground underground geology geology (Skillings, ( S k i l l i n g s , 1981). 1981). Previous P r e v i o u s Geological G e o l o g i c a l Studies Studies The The only o n l y detailed d e t a i l e d geological g e o l o g i c a l work work on on the t h e Ropes Ropes Mine Mine is i s by by Broderick, Broderick, who who was was the the mine mine geologist g e o l o g i s t for f o r Calumet Calumet and and Hecla Hecla Mining Mining Co. Co. In I n 1945 1945 Broderick B r o d e r i c k published p u b l i s h e d aa detailed d e t a i l e d description d e s c r i p t i o n of of the t h e Ropes Ropes ore o r e body body and and the t h e surrounding s u r r o u n d i n g peridotite. p e r i d o t i t e . SubSubsequent sequent published p u b l i s h e d work work on on the t h e geology geology of of the t h e surrounding surrounding area a r e a has h a s been been by by Boyum Boyum (1964, Puffett l974),Clark 1975), P u f f e t t (1966, (1966, 1 9 7 4 ) , - C l a r k and and others o t h e r s (1975), (1975), Cannon Cannon and and (1964, 1970, 1970, 1975), Klasner Klasner (1975), (1975), and and Morgan Morgan and and DeCristoforo D e C r i s t o f o r o (1980). (1980). The The latter l a t t e r provide p r o v i d e the t h e most most Information recent r e c e n t data d a t a on on the t h e overall o v e r a l l geology geology of of the t h e Ishpeming Ishpeming greenstone g r e e n s t o n e belt. b e l t . Information on on the t h e ore o r e host h o s t rock r o c k comes comes from from an an unpublished unpublished mine mine report r e p o r t by by Creasy Creasy (1981). (1981). �_______ 45 LEGEND PALEOZOIC 1 UPPER P R E C A M B R I A N 1 UPPER PRECAMBRIAN s.*imen*ory LOWER F i g u r e 1. Figure 1. Racks 1 PRECAMBRIAN L o c a t i o n o f t h e Ropes Gold Mine. Location of the Ropes Gold Mine. — ç.J , L. F' 7 LN'\ igan Mine — • \•_j 0 Feet 4000 (Cannon and Kiasner, 1975; Clark and others.1075) Proterozoic Proterozoje Marquette Range SuperOrOUP Marquette Range SupergrOUp Archean Archean Granite Granite 1-1 (Cannon and Klasner, 1975; Clark and others.1975) ]-k .... ,,\; \>,iDeer Deer Lake Peridotite K Lake Peridotite Age relations uncertain Age relations uncertain Kitchi Schist [ Kitchi Schist ]Agglomerate Agglomerate interned. to fels. volcs. r -5 5 F i l d trip stops Field trip stops GEOLOGY OF THE AREA AROUND GEOLOGY OF THE AREA AROUND THE ROPES AND MICHIGAN GOLD MINES Intermed. to fels. voics. d Amphibolite '.,.J Amphibolite F i g u r e 2.2. Figure Regional geology of t h e Ropes Mine and Michigan Mine a r e a . Regional geology of the Ropes Mine and Michigan Mine area. �46 PLAN, 15 LEVEL LEGEND . Figure 3a. 3a. Figure .. Geologic p l a n of t h e e a s t h a l f of t h e 1 5 t h l e v e l . Geologic plan of the east half of the 15th level. 4 + OOE c r o s s - s e c t i o n through t h e Ropes o r e body. Dar- 3b. F i g u r e3b. Figure 4 + OOE cross—section through the Ropes Dark e r l i n e s i n 3a and 3b r e p r e s e n t r e v e r s e f a u l t s d i p p iore n g body. 30' t o 40 ker lines in 3a and 3b represent reverse faults dipping 300 to 400 3b modified from unpublished maps and ( F i g u r e s 3a and t o the t h e south. south. to (Figures 3a and 3b modified from unpublished maps and c r o s s - s e c t i o n s p r e p a r e d f o r Callahan Mfning Corp. by Resource Excross—sections prepared for Callahan Mining Corp. by Resource Exp l o r a t i o n Inc., I n c . , 1982). 1982). ploration �47 part A large large p a r t of of the t h e report r e p o r t that t h a t follows f o l l o w s is i s taken t a k e n from from an M.S. M.S. thesis t h e s i s under under prepprepa r a t i o n by the t h e senior s e n i o r author, a u t h o r y on the t h e alteration a l t e r a t i o n of of the t h e Deer Lake Peridotite P e r i d o t i t e in in aration the vicinity the v i c i n i t y of the t h e Ropes Ropes Gold Gold Mine. Mine. Regional Geology within The Ropes Gold Mine is i s situated situated w i t h i n the t h e Ishpeming greenstone g r e e n s t o n e belt, b e l t y part p a r t of of which which is This Archean iin i s shown in i n Figure F i g u r e 2. 2. T h i s bbelt e l t iis s Archean n aage, g e y and geologically g e o l o g i c a l l y similar s i m i l a r to t o the the other belts o t h e r greenstone greenstone b e l t s that t h a t occur o c c u r in i n the t h e main part p a r t of of the t h e Superior S u p e r i o r Geological G e o l o g i c a l Pro— Province, part v i n c e > north n o r t h of of Lake Lake Superior. S u p e r i o r . It rrepresents e p r e s e n t s the t h e easternmost easternmost p a r t of of the t h e granite— granitegreenstone g r e e n s t o n e terrane t e r r a n e in i n Michigan Michigan (Sims, (Simsy 1976). 1976). On the west, the w e s t , the t h e greenstone g r e e n s t o n e belt b e l t is i s cut c u t by younger granites, g r a n i t e s y and and on on the t h e east e a s t it i t is is covered by Lake Superior S u p e r i o r and probably the t h e Jacobsville J a c o b s v i l l e Sandstone. Sandstone. On the t h e north n o r t h and south s o u t h the t h e Archean rocks r o c k s form the t h e basement for f o r the t h e mildly m i l d l y metamorphosed sedimentary sedimentary rocks r o c k s of of the t h e Marquette Range Supergroup that t h a t oucrop in i n the t h e Dead River R i v e r Basin Basin and and are are with Kitchi River i t c h i schists s c h i s t s aalong l o n g the t h e Carp R i v e r Falls F a l l s shear, s h e a r y possibly possibly iin n ffault a u l t ccontact ontact w i t h tthe he K a reactivated r e a c t i v a t e d Archean fault f a u l t (Sims (Sims and and others, o t h e r s , 1980). 1980). The greenstone g r e e n s t o n e belt b e l t consists c o n s i s t s of of several s e v e r a l thousand thousand feet f e e t of of felsic f e l s i c to t o mafic m a f i c volcanic volcanic rocks, with i t h an abundant pyroclastic p y r o c l a s t i c component, componenty that t h a t are a r e intruded i n t r u d e d by by Archean Archean perido— peridorocksy w of Deer Lake Lake aa gray gray granite g r a n i t e in in ttites i t e s and granitic g r a n i t i c plutons p l u t o n s (Table (Table 1). 1 ) . Northwest of Kitchi Schist Rb/Sr of 2490 m.y. m.y. (Van itchi S c h i s t gave a ~ b / S rage of (Van Schmus, Schmusy 1974, 1974> in in aamphibolite mphibolite K and Morgan and DeCristoforo, onr rand D e C r i s t o f o r o y 1980). 1980). The vvolcanic o l c a n i c rocks r o c k s are a r e assigned a s s i g n e d to t o the t h e Mona Kitchi K i t c h i Schist S c h i s t formation f o r m a t i o n (Van (Van Hise H i s e and Bayley, Bayley* 1895), 1 8 9 5 ) > and and Morgan Morgan and and DeCristoforo DeCristoforo (1980) with y c l e s y bbeginning eginning w i t h mafic o t e tthat h a t bboth o t h fformations o r m a t i o n s rrepresent e p r e s e n t vvolcanic o l c a n i c ccycles, (1980) nnote with and ending w i t h more felsic f e l s i c volcanic v o l c a n i c units. units. The K Kitchi i t c h i Schist S c h i s t is i s the t h e host h o s t for f o r the t h e Deer Lake Lake Peridotite P e r i d o t i t e (also ( a l s o referred r e f e r r e d to t o as a s DLP). DLP). of Deer Lakey Lake, the Kitchi the K i t c h i Schist S c h i s t consists c o n s i s t s of of a lower lower mafic member that that IIn n tthe h e vvicinity i c i n i t y of is of bbasaltic diabases, i s composed of a s a l t i c flows, flows, d i a b a s e s y and gabbros, gabbrosy all a l l of which generally g e n e r a l l y are a r e metametamorphosed to t o the t h e amphibolite a m p h i b o l i t e grade. grade. The upper part p a r t contains c o n t a i n s andesite a n d e s i t e flows, f l o w s y coarse coarse grained units, breccias, g r a i n e d ddacitic a c i t i c ppyroclastic yroclastic u n i t s * flow top top b r e c c i a s > and fine f i n e grained g r a i n e d pyroclastic pyroclastic or o r crystal c r y s t a l tuffs t u f f s (Morgan (Morgan and DeCristoforo, D e C r i s t o f o r o y 1980). 1980). Overlying the K i t c h i Schist S c h i s t is t h e Kitchi i s the t h e Mona Schist, S c h i s t y consisting c o n s i s t i n g of of pillow p i l l o w basalts b a s a l t s and and of of pyroclastic Puffett ffelsic elsic p y r o c l a s t i c rocks, r o c k s y some some now now schistose. schistose. P u f f e t t described d e s c r i b e d the t h e contact c o n t a c t between the Kitchi t h e Mona and K i t c h i Schists S c h i s t s as a s conformable (Puffett, ( P u f f e t t y 1974) 1974) whereas Morgan and and De— DeCristoforo on C r i s t o f o r o interpret i n t e r p r e t it i t to t o be b e an an unconformity, u n c ~ n f o r m i t ybased ~ on the t h e higher h i g h e r metamorphic metamorphic grade grade of of some units u n i t s in i n the t h e Kitchi K i t c h i Schist S c h i s t near n e a r the t h e contact c o n t a c t (Morgan (Morgan and and DeCristoforo, D e C r i s t o f o r o y 1980). 1980). The Mona Schist S c h i s t has h a s been dated d a t e d as a s at a t least l e a s t 2750 2750 m.y. may. old o l d (Van (Van Schmus, Schmusy 1974, 1974y in in Morgan and DeCristoforo, D e C r i s t o f o r o y 1980). 1980). The Kitchi by aa nnortheast—trending body of of serpentinized K i t c h i Schist S c h i s t iis s t transected r a n s e c t e d by o r t h e a s t - t r e n d i n g body s e r p e n t i n i z e d ultra— ultramafic referred Km from from r e f e r r e d to t o as a s the t h e Deer Lake Peridotite. P e r i d o t i t e . The peridotite p e r i d o t i t e stretches s t r e t c h e s 6.5 6.5 Km River D e e r Lake. Lake. The DL? DLP is i s discordatit discordafit tto o most ontacts w ithin tthe h e Carp R i v e r Falls F a l l s Shear Shear to t o Deer most ccontacts within the Kitchi Schist, the K itchi S c h i s t , and for i s thought to t o be b e younger. younger. f o r this t h i s reason r e a s o n is Other ultramafic u l t r a m a f i c bodies b o d i e s in i n the t h e region r e g i o n are a r e the t h e Presque Presque Isle I s l e Peridotite, P e r i d o t i t e y northwest n o r t h w e s t of of of Marquette (Lewan, Puffett, (Lewany 1972; 1972; P u f f e t t > 1974) and the t h e Yellow Dog Dog Peridotite P e r i d o t i t e of of tthe h e ccity i t y of a g e y situated s i t u a t e d about about 20 20 miles m i l e s north—northwest north-northwest of of the t h e Ropes Ropes Gold Gold Mine Mine Lower Keweenawan age, (Klasner and o t h e r s y 1977; Morris and and Wilband, Wilbandy 1977). 1977). (Klasner others, �48 Table of of Formations Formations Ishpeming Greenstone Belt Belt PROTEROZOIC PROTEROZOIC Keweenawan Diabase dikes, d i k e s , Yellow Dog Peridotite Peridotite ?•arquette Marquette Range Range Supergroup Supergroup Q u a r t z i t e , dolomite, d o l o m i t e , slate, s l a t e ,conglomerant conglomerant Quartzite, banded banded iiron r o n formation, formation, and minor meta— metavolcanic v o l c a n i c rocks rocks -Unconformity ARCHEAN ARCHEAN River Dead R i v e r Pluton P l u t o n and Compeau Creek Gneiss Massive and foliated, f o l i a t e d , medium medium and coarse coarse g r a i n e d , intermediate i n t e r m e d i a t e to t o felsic f e l s i c plutonic plutonic grained, rocks rocks Intrusive Mona Mona SSchist chist Volcanic—plutonic baV o l c a n i c - p l u t o n i c ccycle y c l e of of pillowed p i l l o w e dba— ssalts, a l t s , ssericitic—chioritic e r i c i t i c - c h l o r i t i c sschist, c h i s t , rhy— rhyolite o l i t e tuff, t u f f , interlayered i n t e r l a y e r e d amphibolite a m p h i b o l i t e and eexhalites. xhalites. - ----------- Contact R e l a t i o n s h i p Uncertain Uncertain Contact Relationship Deer Lake Peridotite Peridotite Presque Isle I s l e Peridotite Peridotite ----------- --------------- S e r p e n t i n i z e d hharzburgite a r z b u r g i t e and lherzolite lherzolite Serpentinized Contact R elationship U ncertain Contact Relationship Uncertain Kitchi K i t c h i Schist Schist --------------- Volcanic-plutonic c y c l e of of gabbro, gabbro, dia— diaVolcanic—plutonic cycle bases b a s e s and basalts b a s a l t s (all ( a l l now now generally generally amphibolites), a m p h i b o l i t e s ) , intermediate i n t e r m e d i a t e and elsic and ffelsic agglomerates, ttuffs agglomerates, u f f s and flows flows ??? Basement Unknown Unknown Contact �49 ORE ORE HOST ROCK Occurrence Occurrence Ore grade grade mineralization m i n e r a l i z a t i o n at a t the t h e Ropes Ropes Mine Mine is i s confined c o n f i n e d entirely e n t i r e l y within w i t h i n aa narrow narrow body of w i l l be b e referred r e f e r r e d to t o as a s the t h e ore o r e host h o s t rock r o c k or o r the t h e OHR. OHR. The OHR OHR of rock r o c k that t h a t will tabular body of silicic rock that strikes N70°E along its is of s i l i c i c r o c k t h a t s t r i k e s N70° a l o n g i t s i s a nearvertical, nearvertical* tabular s o u t h by talc—carbonate talc-carbonate surface i s bounded on the t h e north n o r t h and and south s u r f a c e exposure. exposure. The OHR is rock which grades laterally into the serpentinite of the Deer Lake Peridotite. t h e s e r p e n t i n i t e t h e Lake Peridotite. rock grades l a t e r a l l y i n t o The OHR is about 16 meters wide at the surface, near the Curry shaft, is 16 m e t e r s a t t h e s u r f a c e * n e a r t h e Curry s h a f t * and and gradgradually increases in width to over 30 meters along the 15th level (Fig. 3). Latu a l l y increases i n width t o 30 m e t e r s a l o n g t h e 1 5 t h l e v e l ( F i g . 3 ) . Laterally, e r a l l y * the t h e OHR OHR extends e x t e n d s over 1400 1400 feet f e e t to t o the t h e east e a s t of of the t h e Curry Curry shaft, s h a f t * pinching pinching Out o u t before b e f o r e it i t reaches r e a c h e s the t h e shore s h o r e of of Deer Lake Lake (Fig. (Fig. 4). 4). The origin OHR and and its i t s relationship r e l a t i o n s h i p to t o the t h e surrounding s u r r o u n d i n g serpentinite s e r p e n t i n i t e and and talc— talco r i g i n of of the t h e OHR The early miners e a r l y miners carbonate rocks of the Deer Lake Peridotite remains problematic. c a r b o n a t e r o c k s of t h e P e r i d o t i t e remains p r o b l e m a t i c . referred r e f e r r e d to t o the t h e OHR OHR as a s the t h e mineral m i n e r a l dike. d i k e . Broderick B r o d e r i c k described d e s c r i b e d the t h e OHR OHR as a s aa segment segment of Keewatin basic lavas and fragmentals, equivalent to the volcanic rocks of the the of b a s i c l a v a s and f r a g m e n t a l s * e q u i v a l e n t t o t h e v o l c a n i c r o c k s of Kitchi K i t c h i Schist S c h i s t to t o the t h e immediate immediate west, w e s t * and and proposed proposed that t h a t faulting f a u l t i n g probably probably played played aa 1945). major role OHR within w i t h i n the t h e peridotite p e r i d o t i t e (Broderick, (Broderick* 1945). r o l e in i n emplacing emplacing the t h e OHR Recent Recent workers workers generally g e n e r a l l y support s u p p o r t Broderick's B r o d e r i c k ' s contention c o n t e n t i o n that t h a t the t h e OHR OHR is i s principally principally Morgan and and volcanic, but disagree on its mode of emplacement within the peridotite. v o l c a n i c s b u t d i s a g r e e on i t s mode of emplacement w i t h i n t h e p e r i d o t i t e . Morgan DeCristoforo suggest that the Deer Lake Peridotite may represent at least in part D e C r i s t o f o r o s u g g e s t t h a t t h e Deer Lake P e r i d o t i t e may r e p r e s e n t a t l e a s t i n p a r t aa series DeCristoforo, s e r i e s of of koinatiitic k o m a t i i t i c l lava a v a fflows l o w s oor r ssubvolcanic u b v o l c a n i c iintrusions n t r u s i o n s (Morgan and D eCri~toforo~ If this were the case, the OHR could represent a conformable sequence of t h e c a s e * t h e OHR could r e p r e s e n t a conformable sequence of 1980). I f t h i s 1980). Neverthemore more felsic f e l s i c volcanics, v 0 1 c a n i c s ~extruded e x t r u d e d during d u r i n g aa hiatus h i a t u s in i n komatiitic k o m a t i i t i c volcanism. volcanism. Nevertheless, OHR* Morgan and and DeCristoforo D e C r i s t o f o r o (1980) (1980) conconl e s s * emphasizing emphasizing the t h e sheared s h e a r e d nature n a t u r e of the t h e OHR, sider s i d e r the t h e OHR OHR a faulted—in f a u l t e d - i n portion p o r t i o n of of the t h e older o l d e r Kitchi K i t c h i Schist. Schist. Creasy (1981) (1981) also a l s o supports s u p p o r t s aa volcanic v o l c a n i c origin o r i g i n for f o r the t h e OHR OHR and and suggests s u g g e s t s that t h a t the the Creasy OHR and and peridotite p e r i d o t i t e is i s the t h e result r e s u l t of of magmatic magmatic intrusion i n t r u s i o n of of the the j u x t a p o s i t i o n of of the t h e OUR juxtaposition Deer (Greasy* 1981). 1981). Evidence collected Deer Lake Lake Peridotite P e r i d o t i t e around around the t h e OHR OHR (Creasy, c o l l e c t e d by the the s e n i o r author a u t h o r from from the t h e serpentinite s e r p e n t i n i t e and talc—carbonate t a l c - c a r b o n a t e rocks r o c k s surrounding s u r r o u n d i n g the t h e OUR, OHR* senior l e a d s him to t o favor f a v o r the t h e view that t h a t the t h e juxtaposition j u x t a p o s i t i o n of of the t h e contrasting c o n t r a s t i n g rock r o c k types types leads i s largely l a r g e l y the t h e result r e s u l t of of tectonism. t e c t o n i s m . Figure is F i g u r e 55 shows shows aa possible p o s s i b l e analog a n a l o g where where aa s l i v e r of of metasedimentary rock, r o c k * similar s i m i l a r in i n dimensions to t o the t h e OUR, OHR* has h a s been been sheared sheared sliver Townshipy Vermont Vermont (Gregg, (Gregg* 1975). 1975). i n t o an Alpine-type u l t r a m a f i c body in i n Ludlow Township, into Alpine—type ultramafic These These points p o i n t s will w i l l be b e addressed a d d r e s s e d further f u r t h e r in i n later l a t e r sections. sections. of the t h e OUR OHR Petrography of Based on on examination examinationof o r e * tthin h i n ssection e c t i o n work* a n a l y s i s of of selected selected Based of ccore, work, and chemical analysis t h e OUR, OHR* Creasy interprets rock from the the OUR to be i n t e r p r e t s t h e OHR t o b e aa sequence sequence of of intermediate i n t e r m e d i a t e to to f e l s i c fragmental f r a g m e n t a l rock r o c k of of varying v a r y i n g particle p a r t i c l e size s i z e and and composition, composition3 minor minor intermediate intermediate felsic f l o w s and possibly p o s s i b l y volcanically v o l c a n i c a l l y derived d e r i v e d sediments sediments and and exhalites e x h a l i t e s (Creasy, (Greasy* 1981). 1981). He He flows a l s o has h a s found found aa preservation p r e s e r v a t i o n of of relict r e l i c t volcanic v o l c a n i c textures, t e x t u r e s * primarily p r i m a r i l y in i n thin t h i n section, section* also i n spite s p i t e of of the t h e intense, i n t e n s e * pervasive in OHR. Relict p e r v a s i v e alteration a l t e r a t i o n throughout throughout the t h e OUR. R e l i c t textures textures recognized by by Creasy Creasy include i n c l u d e pseudomorphs pseudomorphs of of pyroxenes, pyroxenes9 amphiboles amphiboles and and feldspars, feldspars, recognized h y d r a t i o n fractures f r a c t u r e s of of originally o r i g i n a l l y glassy g l a s s y rocks, r o c k s * and and aa general g e n e r a l fragmental f r a g m e n t a l aspect a s p e c t of of hydration many many of of the t h e rocks r o c k s (Creasy, (Creasy 1981). 1981) �Inc., 1982). Map of the surface geology in the vicinity of the Ropes Figure 4. Surface projection of the east end of the 15th level denoted Mine. (Map compiled using information from unpublished company by (o). maps prepared for Callahan Mining Corp. by Resource Exploration, 0 �H- 0 H- CDGQ P1 CD P1 U' CDCD(D rPP1 CD (DCD CD H- Cl) • C) H- CD rr c'—' 0 H- f:-4 CD Cl) H- I CI P1 0 Hi H- 0 '—' P1 H-CD Hi' ci- CD-DQ o 0 • CD Hi •HiI-' 0•. ri-CD CD ECD () ,—.. 0 rf CDP1 Or-PCDHi CD rP CD H- 0 Hi C ci- Hi Hi (DO 0 U' H- B '--'0 CD Hi(D C)QCD Hi C) P1 0 ci—I CD B H- Hi 0QCD-O 01) P1 P1 0 H- CDrfC) (DP1 P10 CD CDHiCDCD- CD CD P1o HiD) I-hB CD P1 '—' Hi -< DCDCD 0 P1 CD C) H- CD H-'--' CD P1 HiO o D)CD . CD 0 B C) CD-B CD CDD) C)Hi 'c'-HCD CD o HiCD rrHi II H- r C)rrH-H- P1 ii- H- CD C)CD CD• rtfi o Orr CD P1 o Figure 5. Surface map (upper) and cross-section (lower) of an alpine type serpentinite body from southeastern Ludlow Township, Vermont. The serpentinite is crossed by a sliver of Cram Hill Phyllite (thought to be tectonically emplaced) similar in dimensions to the Ropes Gold Mine ore host rock (Modified from Gregg, 1975). •0 -. CD -' 44Lt 3 0) __.. _ _ 0) --_ ,— V-' CD CI) i—c. C) -' 0 LiY —I/ :\J'ç-. / :__ I _ I :_. I —._! __I __, CD CD I— I I r -n ::::::::::::::::::::::::::::::::::::::::::::::::::L'j - _—--_—_-- rn 0 Z m U U' Hi �52 At A t the t h e discovery d i s c o v e r y pit p i t (Fig. (Fig. 1, 1, Stop Stop 1) 1 ) the t h e rock r o c k is i s aa quartz—chlorite—sericite quartz-chlorite-sericite schist schist with mm grains g r a i n s of of quartz. q u a r t z . To the t h e nnorth, o r t h , six s i x feet f e e t south s o u t h of of the the w i t h abundant abundant 0.1 0 . 1 to t o 0.3 0.3 nun contact with contact w i t h the t h e talc—carbonate—altered t a l c - c a r b o n a t e - a l t e r e d peridotite, p e r i d o t i t e , the t h e rock r o c k displays d i s p l a y s in i n thin t h i n secsecmicro—breccia ttexture ttion i o n aa micro-breccia e x t u r e consisting c o n s i s t i n g of of angular a n g u l a r fragments of of darker d a r k e r quartz— quartzmaterial 0.5 cchlorite hlorite m a t e r i a l (0.2 (0.2 to to 0 . 5 mm in i n maximum dimension) in i n a lighter l i g h t e r colored c o l o r e d quartz— quartzssericite e r i c i t e matrix. m a t r i x . There are a r e also a l s o a few few 11 mm mm quartz q u a r t z grains. grains. A t h e talc—carbonate talc-carbonate Att the highly i s aa fine—grained, fine-grained, h i g h l y fractured, f r a c t u r e d , quartz—sericite quartz-sericite ccontact o n t a c t tthe h e oore r e hhost o s t rrock o c k is by ccoarser sschist, c h i s t , sporadically s p o r a d i c a l l y rreplaced e p l a c e d by o a r s e r grained g r a i n e d sericite s e r i c i t e and by younger veinlets veinlets of c chlorite of h l o r i t e and and carbonate. carbonate. Broderick describes d e s c r i b e s four f o u r types t y p e s of alteration a l t e r a t i o n from from the t h e OHR OHR within w i t h i n the t h e mine: mine: seri— seripyritization, notes ccitization, i t i z a t i o n , cchloritization, h l o r i t i z a t i o n , silicification, s i l i c i f i c a t i o n , and p y r i t i z a t i o n , and n o t e s that that sericitization i s more prevalent p r e v a l e n t than t h a n chioritization c h l o r i t i z a t i o n (Broderick, (Broderick, 1945). 1945). s e r i c i t i z a t i o n is Carbonatization, C a r b o n a t i z a t i o n , generally g e n e r a l l y cconsidered o n s i d e r e d to t o bbe e confined c o n f i n e d to t o the t h e talc—carbonate t a l c - c a r b o n a t e rocks rocks OHR, h has noted by the OHR. ssurrounding u r r o u n d i n g tthe h e OHR, a s been noted t h e senior s e n i o r author a u t h o r to t o overlap o v e r l a p into i n t o the t h e OHR. Although carbonatization c a r b o n a t i z a t i o n is i s not n o t pervasive p e r v a s i v e throughout throughout the t h e OHR, OHR, it i t is i s intensely intensely matrix, veinlets, developed locally, l o c a l l y , rreplacing eplacing m a t r i x , forming small small v e i n l e t s , and rimming quartz quartz i s most prevalent p r e v a l e n t along along and sericitic s e r i c i t i c fragments. fragments. Carbonate aalteration l t e r a t i o n of of the t h e OHR is the t h e south s o u t h ccontact o n t a c t and hhas a s produced aa zone of of carbonate—quartz—chlorite c a r b o n a t e - q u a r t z - c h l o r i t e rock r o c k that that will w i l l be b e described d e s c r i b e d further f u r t h e r in i n the t h e section s e c t i o n on on talc—carbonate t a l c - c a r b o n a t e alteration. alteration. of the Chemistry of t h e Ore Host Rock of v various Chemical analyses a n a l y s e s of a r i o u s rock r o c k types t y p e s from the t h e OHR OHR are a r e listed l i s t e d in i n Table T a b l e 2. 2. Analyses 1, 1, 2, 2, 3 and 4 aare r e from Creasy (1981); (1981); analyses a n a l y s e s 5, 5, 6 and 77 are a r e new new analyses, a n a l y s e s , from from aa series of samples collected s e r i e s of c o l l e c t e d from the t h e chloritic c h l o r i t i c OHR OHR along a l o n g the t h e north n o r t h edge edge of of the t h e disdiscovery ppit i t (Fig. (Fig. 4), 4 ) , and analysed a n a l y s e d for f o r this t h i s paper by Drs. D r s . T. T. Bornhorst and and W.I. W . I . Rose, Rose, Jr. by X-ray X—ray 'fluorescence Jr f l u o r e s c e n c e analysis. analysis. . with Creasy (1981) (1981) nnotes o t e s that t h a t based on comparison w i t h less l e s s altered a l t e r e d rocks r o c k s of of similar s i m i l a r silica silica content, c o n t e n t , the t h e Ropes Mine rocks r o c k s are a r e characterized c h a r a c t e r i z e d at a t a given given silica s i l i c a content c o n t e n t by by greater greater than of MgO, MgO, v very t h a n aaverage v e r a g e vvalues a l u e s of e r y low CaO, CaO, low to t o very v e r y low low Na20, Na20, and and K20 K2O in i n two two ranges, ranges, vvery e r y low or o r moderately high. h i g h . Creasy attributes a t t r i b u t e s these t h e s e variations v a r i a t i o n sto t o the t h e pervasive p e r v a s i v e alteralteration has OHR, and concludes c o n c l u d e s that t h a t on both b o t h chemical chemical and and textural textural a t i o n that that h a s affected a f f e c t e d the t h e OHR, grounds, portions grounds, p o r t i o n s of of the t h e OHR resemble lithologies l i t h o l o g i e s found found in i n the t h e Kitchi K i t c h i and and Mona Mona Schists Schists (Creasy, (Creasy, 1981). 1981). major oxides, MgO 7, T Table The lighter l i g h t e r major oxides, M gO and Si02, SiO2, in i n the t h e new analyses a n a l y s e s (5, (5, 6, 6, 7, a b l e 2) 2) may be b e significantly s i g n i f i c a n t l y in i n error e r r o r due due to t o matrix m a t r i x effects e f f e c t s resulting r e s u l t i n g from from aa suspected s u s p e c t e d high h i g h volavolatile t i l e content. c o n t e n t . Nevertheless, N e v e r t h e l e s s , the t h e values v a l u e s of of the t h e heavier h e a v i e r minor minor and and trace t r a c e elements, elements, Ti02 and and Zr2O3, Zr203, which which aare llike i k e Ti02 r e uunlikely n l i k e l y to t o bbe e significantly s i g n i f i c a n t l y in i n error, e r r o r , suggest suggest a pparent a r e n t composition of of an intermediate i n t e r m e d i a t e igneous igneous rock, rock, possibly p o s s i b l y an a n andesite, a n d e s i t e , of of alkaline alkaline aaffinity. ffinity . Mineralization Mineralization mineralization The gold m i n e r a l i z a t i o n of of the t h e Ropes ore o r e body (Figs. ( F i g s . 3, 3, 4) 4) can can be b e subdivided subdivided into into two types mineralization t y p e s following f o l l o w i n g the t h e work work of of Broderick Broderick (1945): (1945): 1) 1 ) hhigher i g h e r grade grade m ineralization associated with associated w i t h quartz—tetrahedrite q u a r t z - t e t r a h e d r i t e veins; v e i n s ; and 2) 2) lower lower grade, grade, disseminated d i s s e m i n a t e d minermineraalization l i z a t i o n that t h a t surrounds surrounds the t h e quartz—tetrahedrite q u a r t z - t e t r a h e d r i t e veins. veins. �53 ANALYSES RNflLYSES OF OFORE OREHOST HOSTROCK ROCKSAMPLES SRMPLES 5102 S102 AL203 RL203 FE203 FE203 FED FED MGO MGO cflo CR0 NR2O NR20 K20 K2 0 1102 TI02 P205 P2 05 MNO MNO C02 C02 1 2 3 4 5 6 7 37.70 55.40 72.00 48.39 50.05 23 .80 12 .80 61.30 16.30 13 .20 15 .07 15.68 11.20 1 .'40 .64 3.10 10.28 .00 5.50 17.50 4.60 6.10 .24 .00 8 .27 .00 49.57 17.85 7.67 1.90 16.57 .60 .18 .64 .18 .11 .05 .26 .07 '4.20 .48 .02 .01 .20 96.30 95.68 10 .60 .40 .52 5.70 1.10 .29 .03 ----------. TOTAL TOTRL Table Table 2. 2. 91.34 .60 .02 .01 .59 .1? .03 .50 94.52 .38 4.70 1 .30 14.33 1.23 .00 11.67 .19 .35 .20 3.55 4.54 .08 .05 .98 .07 .05 .77 .1? .03 95.24 94.40 92.82 3.01 1.01 Selected S e l e c t e d analyses a n a l y s e s of of ore o r e host h o s t rocks. rocks. Samples Samples 1—4 1-4 taken taken from from Creasy, Creasy, 1981. 1981. Samples Samples 5—7 5-7 are a r e new new analyses a n a l y s e s for f o r this this paper. w t . percent. percent. No. 5, 5, contact c o n t a c t with w i t h talc— talcpaper. Analyses Analyses in i n wt. No. carbonate b, 66 feet f e e t south s o u t h of of contact; c o n t a c t ; 7, 7, discovery d i s c o v e r y pit. pit. c a r b o n a t e rock; rock; b, �54 The The quartz—tetrahedrite q u a r t z - t e t r a h e d r i t e veins v e i n s still s t i l l remaining remaining in i n the t h e old o l d workings workings range r a n g e in i n thickthickness n e s s from from several s e v e r a l inches i n c h e s to t o several s e v e r a l feet, f e e t , and and Broderick Broderick reports r e p o r t s thicknesses t h i c k n e s s e s of of up up t o 38 38 feet f e e t for f o r veins v e i n s that t h a t had had already a l r e a d y been been mined. mined. Ore Ore veins v e i n s typically t y p i c a l l y strike s t r i k e northnorthto east, e a s t , oblique o b l i q u e to t o the t h e general g e n e r a l strike s t r i k e of of the t h e OUR, OHR, and and have have aa near—vertical n e a r - v e r t i c a l dip. d i p . Eight Eight major major veins v e i n s or o r vein v e i n systems systems were were exploited e x p l o i t e d during d u r i n g the t h e early e a r l y mining mining operations, o p e r a t i o n s , all all of which which pinched pinched out o u t along a l o n g strike s t r i k e and and with w i t hdepth. d e p t h . None None of of the t h e quartz—tetrahedrite quartz-tetrahedrite of v e i n s cross c r o s s the t h e OUR OHR contact c o n t a c t into i n t o the t h e surrounding s u r r o u n d i n g talc—carbonate t a l c - c a r b o n a t e rocks. r o c k s . These These veins veins veins are a r e composed composed mainly mainly of of white, w h i t e , splintery s p l i n t e r y quartz q u a r t z with w i t h minor minor tetrahedrite, t e t r a h e d r i t e , chalcopyrite, chalcopyrite, B r o d e r i c k (1945) (1945) also a l s o mentions mentions the t h e presence presence g a l e n a , pyrite p y r i t e and and rare r a r e native n a t i v e gold. gold. Broderick galena, One small s m a l l vein vein of sphalerite, s p h a l e r i t e , native n a t i v e silver, s i l v e r , aand n d rare r a r e molybdenite molybdenite and and tourmaline. t o u r m a l i n e . One of n e a r the t h e 1070 1070 cross—cut c r o s s - c u t on on the t h e 15th 1 5 t h level l e v e l consists c o n s i s t s primarily p r i m a r i l y of of massive massive chalcopyrite, chalcopyrite, near with w i t h galena, g a l e n a , tetrahedrite, t e t r a h e d r i t e , pyrite, p y r i t e , quartz q u a r t z and and possible p o s s i b l e ruby ruby silver s i l v e r widely widely scattered scattered S e v e r a l other o t h e r large l a r g e quartz q u a r t z veins veins along a l o n g thin t h i n carbonate—filled c a r b o n a t e - f i l l e d fractures f r a c t u r e s ini nthe t h evein. v e i n . Several within c o n t a i n large l a r g e pods pods of of pyrite p y r i t e but b u t no no signisigniw i t h i n the t h e OHR OHR with w i t h similar s i m i l a r orientation, o r i e n t a t i o n , contain f i c a n t gold. gold. ficant i s confined c o n f i n e d to t o the t h e hydrothermally hydrothermally altered altered The lower lower grade grade disseminated d i s s e m i n a t e d ore o r e generally g e n e r a l l y is The and pyritized p y r i t i z e d rock r o c k surrounding s u r r o u n d i n g the t h e quartz—tetrahedrite q u a r t z - t e t r a h e d r i t e veins. v e i n s . No No free f r e e gold gold has h a s been been and r e p o r t e d from from these t h e s e zones, zones, and and apparently a p p a r e n t l y most most of of the t h e gold gold and and silver s i l v e r is i s contained contained reported w i t h i n the t h e abundant abundant pyrite. p y r i t e . However, However, Broderick Broderick (1945) (1945) has h a s noted n o t e d that t h a t abundant abundant pyrite pyrite within i n the t h e OHR OHR does does not n o t necessarily n e c e s s a r i l y indicate i n d i c a t e ore o r e grade grade material, m a t e r i a l , in i n that t h a t some some pyritic pyritic in zones have have very v e r y low low gold gold values. values. zones i s not n o t evenly evenly distributed d i s t r i b u t e d throughout throughout the t h e OHR. OHR. The The Gold and and silver s i l v e r mineralization m i n e r a l i z a t i o n is Gold c l u s t e r i n g of of old o l d stopes s t o p e s shows shows that t h a t the t h e majority m a j o r i t y of of the t h e higher h i g h e r grade grade ore o r e was was found found clustering Smaller discontinuous d i s c o n t i n u o u s lenses l e n s e s of of ore ore along a l o n g the t h e south s o u t h contact c o n t a c t of of the t h e OUR OHR (Fig. ( F i g . 3). 3 ) . Smaller occur occur sporadically s p o r a d i c a l l y along a l o n g the t h e north n o r t h contact, c o n t a c t , but b u t generally g e n e r a l l y do do not n o t extend extend across a c r o s s to to OHR with w i t h very v e r y low low grades. grades. t h e south s o u t h contact, c o n t a c t , leaving l e a v i n g an an interior i n t e r i o r zone zone of of the t h e OHR the Skillings S k i l l i n g s (1981) (1981) reports r e p o r t s grades g r a d e s of of 0.15 0.15 oz/ton o z / t o n for f o r portions p o r t i o n s of of the t h e Ropes Ropes ore o r e body. body. Veins and and Evidence Evidence for f o r Faulting F a u l t i n g in i n the t h e OUR OHR Veins The OHR OHR has h a s undergone undergone obvious obvious deformation deformation shown shown locally l o c a l l y by by pronounced pronounced foliations, foliations, The i n t e n s e fracturing f r a c t u r i n g and vein v e i n development, development, boudinaged boudinaged quartz q u a r t z veins, v e i n s , and and faults. faults. intense H o w e v e r ,the t h e oore r e hhost o s t rrock o c k shows a r i e t y of However, shows aa wide wide vvariety of secondary alteration a l t e r a t i o n effects effects so s o pervasive p e r v a s i v e that, t h a t , in i n most cases, c a s e s , it i t has h a s not n o t been been possible p o s s i b l e to t o establish e s t a b l i s h suffisufficiently c i e n t l y distinctive d i s t i n c t i v e and and persistent p e r s i s t e n t map map units u n i t s to t o work work out o u t structural s t r u c t u r a l relationships. relationships. �55 Similarly, veins S i m i l a r l y , a number of of v e i n s are a r e exposed exposed within w i t h i n the t h e mine, mine, but b u t only o n l y aa few, few, none none of them m i n e r a l i z e d , show cross c r o s s cutting c u t t i n g relationships r e l a t i o n s h i p s to t o provide p r o v i d e data d a t a on on relative relative of mineralized, ages. a g e s . Thus, Thus, although a l t h o u g h the t h e available a v a i l a b l e data d a t a is i s insufficient i n s u f f i c i e n t for f o r determining d e t e r m i n i n g the t h e comcomplete vein p l e t e structural s t r u c t u r a l and v e i n emplacement emplacement history, h i s t o r y , several s e v e r a l features f e a t u r e s concerning concerning vein vein relationshipshavebeennoted. r e l a t i o n s h i p s h a v e b e e n n o t e d . For example, example, many small s m a l l quartz q u a r t z veins v e i n s scattered s c a t t e r e d throughthroughout o u t the t h e OHR show show cross—cutting c r o s s - c u t t i n g relationships, r e l a t i o n s h i p s , demonstrating d e m o n s t r a t i n g multiple m u l t i p l e periods p e r i o d s of of quartz q u a r t z vein v e i n formations. formations. Veins of banded carbonate c a r b o n a t e which which have have aa sporadic s p o r a d i c distribudistribut i o n throughout the t h e OHR, OHR, are a r e everywhere everywhere younger than t h a n quartz q u a r t z veins, v e i n s , where where crosscrosstion cutting c u t t i n g relationships r e l a t i o n s h i p s can c a n be b e observed. observed. The The entire e n t i r e sequence sequence of of ore o r e host h o s t rocks r o c k s and and the t h e surrounding s u r r o u n d i n g peridotite p e r i d o t i t e are a r e offset o f f s e t by by several s e v e r a l large l a r g e reverse r e v e r s e faults, f a u l t s , which strike s t r i k e to t o the t h e northeast n o r t h e a s t and and dip d i p between between 25° 25' and and 350 35' to t o the t h e south s o u t h (Fig. (Fig. 3; 3 ; 44 ++ 00 00 EE cross c r o s s cut). c u t ) . The The lower lower blocks b l o c k s are a r e rotated r o t a t e d clockclocka l o n g these t h e s e faults, f a u l t s , changing changing the t h e strike s t r i k e from from N70°E N70° at a t the t h e surface s u r f a c e to t o N80°E N80° at at wise along the t h e 15th 1 5 t h level. l e v e l . The larger l a r g e r reverse r e v e r s e faults f a u l t s are a r e commonly commonly marked by by one one to t o two two feet feet of breccia, but of b reccia, b u t the t h e smaller s m a l l e r ones ones commonly commonly contain c o n t a i n prismatic, p r i s m a t i c , terminated t e r m i n a t e d dolomite dolomite crystals, c r y s t a l s , with w i t h minor chalcopyrite c h a l c o p y r i t e and and pyrite. p y r i t e . Sprays of millerite of m i l l e r i t e are a r e also a l s o common common where reverse r e v e r s e faults f a u l t s cut c u t the t h e surrounding s u r r o u n d i n g talc—carbonate t a l c - c a r b o n a t e and and serpentinite. serpentinite. A A number of of older, o l d e r , high h i g h angle a n g l e faults f a u l t s are a r e also a l s o seen seen in i n the t h e mine mine workings, workings, but b u t most most appear to t o have have had had only o n l y limited l i m i t e d movement movement along a l o n g them. them. AA larger, l a r g e r , apparently a p p a r e n t l y high high angle, a n g l e , north—striking n o r t h - s t r i k i n g fault f a u l t offsets o f f s e t s the t h e OHR OHR to t o the t h e west of of the t h e Curry Curry shaft s h a f t (Fig. (Fig. 2). 2). DEER DEER LAKE LAKE PERIDOTITE PERIDOTITE Occurrence Occurrence The The Deer Lake Lake Peridotite P e r i d o t i t e is i s aa linear, l i n e a r , near—vertical n e a r - v e r t i c a l (Morgan (Morgan and and DeCristoforo, D e C r i s t o f o r o , 1980), 1980); tabular t a b u l a r ultramafic u l t r a m a f i c body, body, now predominantly composed composed of of serpentinite. s e r p e n t i n i t e . The serpen— serpentinites t i n i t e s form form prominent ridges r i d g e s in i n the t h e area, a r e a , providing p r o v i d i n g good good exposures. exposures. Good outcrops outcrops are a r e also a l s o found found along a l o n g the t h e north n o r t h shore s h o r e of of Deer Deer Lake. Lake. In I n general, g e n e r a l , the t h e contacts c o n t a c t s between the t h e Deer Lake Lake Peridotite P e r i d o t i t e and and the t h e surrounding s u r r o u n d i n g Kitchi Kitchi Schist S c h i s t are a r e very v e r y poorly p o o r l y exposed, exposed, typically t y p i c a l l y denoted denoted by by narrow narrow depressions. d e p r e s s i o n s . This T h i s concontact t a c t does outcrop o u t c r o p at a t two two locations l o c a t i o n s west of the t h e spillway s p i l l w a y on on the t h e north n o r t h side s i d e of of Deer Deer Lake. There There the t h e contact c o n t a c t is i s marked marked by by aa 33 to t o 66 foot f o o t wide wide zone zone of of soft s o f t actinolite— actinolitechlorite c h l o r i t e schist, s c h i s t , possibly p o s s i b l y similar s i m i l a r to t o the t h e tremolite—chlorite t r e m o l i t e - c h l o r i t e zones zones described d e s c r i b e d by by Chidester C h i d e s t e r and and others o t h e r s (1978) (1978) at a t the t h e contacts c o n t a c t s of of the t h e Belvidere B e l v i d e r eultramaf u l t r a m a fIc i c body body in in Vermont. Vermont. Serpentinite S e r p e n t i n i t e near n e a r the t h e actinolite—chlorite a c t i n o l i t e - c h l o r i t e schist s c h i s t contains c o n t a i n s abundant abundant carcarbonate b o n a t e and and talc, t a l c , which which diminish d i m i n i s h abruptly a b r u p t l y away away from from the t h e contact. c o n t a c t . The Kitchi K i t c h i Schist Schist near n e a r this t h i s contact c o n t a c t is i s strongly s t r o n g l y chioritized c h l o r i t i z e d and and contains c o n t a i n s numerous numerous quartz q u a r t z veins. veins. The i s still s t i l l unclear. u n c l e a r . Broderick B r o d e r i c k (1945), (1945), Clark Clark The origin o r i g i n of of the t h e Deer Lake Lake Peridotite P e r i d o t i t e is and others o t h e r s (1975), (1975), and and most recently r e c e n t l y Creasy Creasy (1981) (1981) suggest, s u g g e s t , based based largely l a r g e l y on on the the and discordant Kitchi Schist, and locally well preserved d i s c o r d a n t nature n a t u r e with w i t h the t h e surrounding s u r r o u n d i n g K i t c h i S c h i s t , and l o c a l l y w e l l p r e s e r v e d cumulate cumulate olivine o l i v i n e textures, t e x t u r e s , that t h a t the t h e Deer Deer Lake Lake Peridotite P e r i d o t i t e is i s aa magmatic magmatic intrusion. intrusion. On On the t h e basis b a s i s of of chemical chemical similarities s i m i l a r i t i e s and and pillow—like p i l l o w - l i k e structures s t r u c t u r e s found found near n e a r Deer Deer Lake, Morgan and and DeCristoforo D e C r i s t o f o r o (1980) (1980) propose propose that t h a t all, a l l , or o r part, p a r t , of of the t h e Deer Deer Lake Lake Lake, Peridotite P e r i d o t i t e may may be b e komatiitIc k o m a t i i t i c flows. flows. As A s previously p r e v i o u s l y mentioned, mentioned, the t h e present p r e s e n t authors authors have noted noted structural s t r u c t u r a l and and textural t e x t u r a l similarities s i m i l a r i t i e s between between the t h e Deer Deer Lake Lake Peridotite Peridotite have and and Alpine type t y p e ultramafics, u l t r a m a f i c s , and and thus t h u s there t h e r e is i s the t h e added added possibility p o s s i b i l i t y that t h a t the t h e Deer Deer Lake Lake Peridotite P e r i d o t i t e may may have have crystallized c r y s t a l l i z e d elsewhere elsewhere and and subsequently s u b s e q u e n t l y was was emplaced emplaced as a s aa solid or semi—solid body, in a manner similar to that proposed for alpine—type s o l i d o r semi-solid body, i n a s i m i l a r t o t h a t proposed f o r a l p i n e - t y p e ultramafic u l t r a m a f i c bodies. bodies. �56 Petrography of of Serpentinites Serpentinites Petrography A, Two distinct d i s t i n c t types t y p e s of of serpentinites s e r p e n t i n i t e s are a r e seen seen in i n the t h e Deer Deer Lake Lake Peridotite. P e r i d o t i t e . Type Type A, Two t h e most most common common variety v a r i e t y in i n surface s u r f a c e exposures, exposures, is i s dark d a r k gray gray on on fresh f r e s h surfaces, s u r f a c e s , with with the f i n e to t o medium medium grained g r a i n e d serpentine, s e r p e n t i n e , giving g i v i n g the t h e rock r o c k aa slightly s l i g h t l y greasy g r e a s y luster. l u s t e r . These These fine s e r p e n t i n i t e s generally g e n e r a l l y have have no no obvious obvious foliation, f o l i a t i o n , and and commonly commonly have have readily r e a d i l y idenidenserpentinites mm serpentine s e r p e n t i n e pseudomorphs pseudomorphs after a f t e r olivine o l i v i n e or o r pyroxene pyroxene outlined o u t l i n e d by by thin thin t i f i a b l e 1—5 1-5 mm tifiable s e l v a g e s of of white w h i t e carbonate c a r b o n a t e and and talc. t a l c . No No spinifex s p i n i f e x olivine o l i v i n e or o r pyroxene, pyroxene, considered considered selvages i n d i c a t i v e of of komatiitic k o m a t i i t i c flows, flows, were were recognized recognized anywhere. anywhere. indicative I n thin t h i n section, s e c t i o n , Type Type AA serpentinite s e r p e n t i n i t e frequently f r e q u e n t l y shows shows well w e l l developed developed serpentine serpentine In pseudomorphs after a f t e r olivine o l i v i n e and and pyroxene. pyroxene. The The pseudomorphed pseudomorphed olivine o l i v i n e commonly commonly shows shows pseudomorphs serpentine (1977), s e r p e n t i n e mesh mesh textures, t e x t u r e s , similar s i m i l a r to t o those t h o s e described d e s c r i b e d by by Wicks Wicks and and Whittaker Whittaker (1977), with w i t h subparallel, s u b p a r a l l e l , length—slow, length-slow, serpentine s e r p e n t i n e fibers f i b e r s growing growing toward toward the t h e grain g r a i n centers centers from original o r i g i n a l olivine o l i v i n e grain g r a i n boundaries b o u n d a r i e s and and fractures. f r a c t u r e s . In from I n some some sections s e c t i o n s accumulate accumulate textures r i m s of of dusty d u s t y magnetite, m a g n e t i t e , carbonate carbonate t e x t u r e s are a r e well w e l l preserved, p r e s e r v e d , outlined o u t l i n e d by by thin t h i n rims and talc t a l c (Fig. (Fig. 6). 6 ) . The The central c e n t r a l portions p o r t i o n s of of the t h e above above pseudomorphed pseudomorphed olivine o l i v i n e are are and replaced r e p l a c e d by by carbonate c a r b o n a t e and and talc, t a l c , which which are a r e generally g e n e r a l l y minor minor but b u t ubiquitous, u b i q u i t o u s , mineral mineral phases. phases. Serpentine S e r p e n t i n e pseudomorphs pseudomorphs after a f t e r pyroxene, pyroxene, called c a l l e d bastite b a s t i t e (Wicks (Wicks and and Whittaker Whittaker 1977) 1977) appear nun patches p a t c h e s of of parallel p a r a l l e l serpentine s e r p e n t i n e fibers f i b e r s which which mimic mimic one one of o f the the appear as a s 1—3 1-3 mm second relict r e l i c t cleavage c l e a v a g e is i s commonly commonly outlined o u t l i n e d by by sub— subpyroxene cleavage c l e a v a g e directions. d i r e c t i o n s . AA second pyroxene parallel p e r p e n d i c u l a r to t o the t h e serpentine s e r p e n t i n e orienta— orientap a r a l l e l lines l i n e s of of fine—grained f i n e - g r a i n e d magnetite, m a g n e t i t e , perpendicular t i o n . Bastite—rich mm wispy wispy flakes f l a k e s of of pleochroic pleochroic B a s t i t e - r i c h samples samples also a l s o contain c o n t a i n scattered s c a t t e r e d 1—3 1-3 mm .tion. c h l o r i t e with w i t h anomalous anomalous "Berlin " B e r l i n Blue" ~ l u e "birefringence, b i r e f r i n g e n c e , thought thought to t o be b e penninite. p e n n i n i t e . The The chlorite Type Type AA serpentinite s e r p e n t i n i t e textures t e x t u r e s correspond correspond to t o the t h e "Type "Type 3" 3" serpentine s e r p e n t i n e textures t e x t u r e s of of Wicks Wicks and Whittaker Whittaker (1977). (1977). and Type (1977) 'Type "Type 8" 8" Type BB serpentinite, s e r p e n t i n i t e , which which corresponds corresponds to t o Wicks Wicks and and Whittaker's W h i t t a k e r ' s (1977) serpentine s e r p e n t i n e texture, t e x t u r e , outcrops o u t c r o p s rarely r a r e l y but b u t is i s common common as a s 10—40 10-40 foot f o o t layers l a y e r s in i n drill drill The best b e s t surface s u r f a c e exposures exposures core c o r e from from the t h e serpentinites s e r p e n t i n i t e s south s o u t h of of the t h e Ropes Ropes ore o r e body. body. The Type BB serpeninite s e r p e n i n i t e ranges r a n g e s in i n color c o l o r from from 4 ) . Type a r e along a l o n g the t h e shore s h o r e of of Deer Deer Lake Lake (Fig. (Fig. 4). are pale i s extremely extremely fine f i n e grained, g r a i n e d , and and has has p a l e green green to t o yellowish y e l l o w i s h white w h i t e on on fresh f r e s h surface, s u r f a c e , is Commonly these t h e s e serpentinites s e r p e n t i n i t e s have have aa strong, strong, no recognizable r e c o g n i z a b l e relict r e l i c t igneous igneous textures. t e x t u r e s . Commonly no often o f t e n contorted c o n t o r t e d foliation, f o l i a t i o n , best b e s t seen seen on on weathered weathered surfaces. s u r f a c e s . Coarse Coarse grained g r a i n e d magnetite magnetite forms serv e i n l e t s and and streaks s t r e a k s along a l o n g foliations f o l i a t i o n s in i n most most Type Type BB ser— i r r e g u l a r veinlets forms prominent, prominent, irregular pentinites. pentiniteS. In I n thin t h i n section, s e c t i o n , Type BB serpentinite s e r p e n t i n i t e differs d i f f e r s from from Type Type AA in i n that t h a t no no pseudomorphic pseudomorphic t e x t u r e s are a r e preserved. p r e s e r v e d . Instead, I n s t e a d , serpentine s e r p e n t i n e occurs o c c u r s either e i t h e r as a s aa uniform, uniform, interintertextures locking 6c) or o r as a s strongly s t r o n g l y foliated f o l i a t e d (Fig. ( F i g . 6d). 6 d ) . Nearly Nearly white, white, l o c k i n g felted f e l t e d texture t e x t u r e (Fig. ( F i g . 6c) Type Type BB serpentinite s e r p e n t i n i t e from from drill d r i l l core, c o r e , contains c o n t a i n s abundant, abundant, very v e r y fined f i n e d grained, grained, secondary secondary dolomite. dolomite. Wicks Wicks and and Whittaker Whittaker (1977) (1977) have have correlated c o r r e l a t e d non—pseudomorphic non-pseudomorphic serpentine s e r p e n t i n e textures t e x t u r e s similar s i m i l a r to t o those t h o s e in i n Type Type BB serpentinites s e r p e n t i n i t e s with w i t h shearing s h e a r i n g proproc e s s e s and and prograde prograde metamorphic metamorphic environments. environments. cesses Whole—rock and Type Type BB Whole-rock X—ray X-ray diffraction d i f f r a c t i o n patterns p a t t e r n s of of aa number number of of samples samples of of Type Type AA and serpentinites s e r p e n t i n i t e s suggest s u g g e s t a difference d i f f e r e n c e in i n the t h e prevalent p r e v a l e n t serpentine s e r p e n t i n e structural s t r u c t u r a l variety variety i n the t h e two two types. t y p e s . Generally G e n e r a l l y Type Type AA serpentinite s e r p e n t i n i t e contains c o n t a i n s aa mixture m i x t u r e of of crystotile crystotile in and/or a n d / o r lizardite l i z a r d i t e with w i t h lesser l e s s e r amounts amounts of of antigorite. a n t i g o r i t e . Type Type BB serpentinite s e r p e n t i n i t e contains contains substantially s u b s t a n t i a l l y more more antigorite. a n t i g o r i t e . The presence p r e s e n c e of antigorite a n t i g o r i t e rather r a t h e r than t h a n crystotile crystotile or o r lizardite l i z a r d i t e is i s thought thought to t o be b e indicative i n d i c a t i v e of of prograde p r o g r a d e metamorphism, metamorphism, or o r serpentiniza— serpentinizat i o n in i n a higher h i g h e r pressure—temperature p r e s s u r e - t e m p e r a t u r e regime regime (Moody, (Moody, 1976). 1976). tion �57 6a 6b 6c 6d 6d t e x t u r e s from from the t h e Deer Deer Lake Lake Peridotite: Peridotite: Photomicrographs Photomicrographs of of serpentine s e r p e n t i n e textures a) a ) Type Type A A serpentinite, s e r p e n t i n i t e , serpentine s e r p e n t i n e pseudomorphs after a f t e r olivine; o l i v i n e ; b) b) Type A serpen— serpentinites, serpentinite, t i n i t e s , serpentine s e r p e n t i n e pseudomorph after a f t e r pyroxene pyroxene (bastite); ( b a s t i t e ) ; c) c ) Type Type BB serpentinite, recrystallized r e c r y s t a l l i z e d felted f e l t e d texture; t e x t u r e ; d) d ) Type Type BB serpentinite, s e r p e n t i n i t e , foliated f o l i a t e d texture. t e x t u r e . All All S c a l e on on all a l l photos, photos, 11 cm cm == 0.66 0.66 mm. mm. c r o s s e d polars. p o l a r s . Scale crossed F i g u r e 6; 6; Figure �37 A l t e r a t i o n of of the t h e Deer Deer Lake Lake Peridotite P e r i d o t i t e in i n the t h e Vicinity Vicinity Alteration of t h e Ropes Gold Mine, Marquette County, Michigan of the Ropes Gold Mine, Marquette County, Michigan Dean Dean Rossell R o s s e l l (Dept. (Dept. of of Geol. Geol. && Geol. Geol. Engrg., Engrg., Michigan Michigan Technological Technological M I 49931) 49931) University, Houghton, Houghton, MI University, i s contained contained entirely e n t i r e l y in i n an an east— eastGold mineralization m i n e r a l i z a t i o n at a t the t h e Ropes Ropes Mine Mine is Gold west w e s t striking s t r i k i n g septum septum of of highly h i g h l y altered a l t e r e d felsic f e l s i c rock rock within w i t h i n the t h e serpentin— serpentini z e d Deer Deer Lake Lake Peridotite. P e r i d o t i t e . Near Near the t h e Ropes Ropes Mine Mine the t h e serpentinite s e r p e n t i n i t e consist consist ized of two two principal p r i n c i p a l textural t e x t u r a l varieties: v a r i e t i e s : Type of Type A, A, with w i t h well w e l l preserved preserved relict relict igneous B, showing showing recrystallized r e c r y s t a l l i z e d and and foliated f o l i a t e d textures, textures, igneous textures, t e x t u r e s , and and Type Type B, probably produced produced by by shearing. shearing. AA prominent prominent zone zone of of Type Type BB serpentinite serpentinite probably along the t h e north n o r t h shore shore of of Deer Deer Lake Lake may may represent r e p r e s e n t an an extension extension of of aa shear shear along zone along along the t h e felsic f e l s i c septum. septum. zone Compositionally, Compositionally, the t h e serpentinites s e r p e n t i n i t e s represent r e p r e s e n t altered a l t e r e d harzburgite h a r z b u r g i t e and and l h e r z o l i t e (Rossell ( R o s s e l l and and Kalliokoski, Kalliokoski, this t h i s volume). volume). An An original o r i g i n a l composicomposilherzolite t i o n a l zoning zoning or o r layering l a y e r i n g may may be be reflected r e f l e c t e d by by wide wide variations v a r i a t i o n s in i n the t h e olivine olivine tional to t o pyroxene pyroxene ratios r a t i o s determined determined from from calculated c a l c u l a t e d mineral mineral modes, modes, but b u t the t h e scale scale of these t h e s e variations v a r i a t i o n s has h a s not n o t been been established. established. of + Serpentinite S e r p e n t i n i t e has has been been extensively e x t e n s i v e l y altered a l t e r e d to t o aa talc t a l c + dolomite dolomite ±Â magnesite magnesite ±2 chlorite c h l o r i t e assemblage assemblage in i n aa zone zone adjacent a d j a c e n t to t o the t h e Ropes Ropes ore o r e body. body. Major Major and and trace t r a c e element element compositions, compositions, including including gold, gold, were were determined determined for f o r aa suite s u i t e of of talc—carbonate talc-carbonate rocks rocks from from the t h e northern n o r t h e r n alteration a l t e r a t i o n zone. zone. From From this t h i s data d a t a relarelat i v e additions a d d i t i o n s and and losses l o s s e s of of chemical chemical components components were were computed computed by by two two methods: methods: tive The first f i r s t - aassuming s s u m i n g that t h a t alteration a l t e r a t i o n occurred occurred at a t constant c o n s t a n t volume, volume, and and the the The A 1 and and Sc Sc are a r e immobile immobile during during alteration a l t e r a t i o n while while volume volume second assuming assuming that t h a t Al second i s allowed allowed to t o change. change. Changes Changes calculated c a l c u l a t e d using using the t h e first f i r s t method method appear appear to to is be be more more consistent c o n s i s t e n t with w i t h observed observed mineralogical m i n e r a l o g i c a l changes changes than than those t h o s e calculated calculated by the t h e latter l a t t e r method. method. by Talc—carbonate Ropes Mine Mine appears appears to t o have have resulted r e s u l t e d in i n the the Talc-carbonate alteration a l t e r a t i o n at a t the t h e Ropes addition a d d i t i o n of of C02, CO2, Ca Ca and and Al, A l , and and the t h e removal removal of of H20 H2O and and Mg Mg from from the t h e serpentin— serpentini t e . Au Au abundance abundance in i n the t h e serpentinite s e r p e n t i n i t e samples samples analyzed analyzed were were found found to t o be be near near ite. c r u s t a l averages. averages. Talc—carbonate Talc-carbonate samples samples showed showed greater g r e a t e r variation, v a r i a t i o n , but b u t gengencrustal erally serpene r a l l y had had Au Au concentrations c o n c e n t r a t i o n s equal equal to t o or o r greater g r e a t e r than than those t h o s e found found in i n serpen— tinites. tinites. Gold may may have have been been transported t r a n s p o r t e d as a s aa carbonyl carbonyl or o r carbonate carbonate complex complex in i n aa Gold CO2 rich r i c h fluid f l u i d from from some some outside o u t s i d e source source to t o the t h e ore o r e host h o s t rock. rock. Subsequent Subsequent CO2 carbonate forming forming reactions r e a c t i o n s in i n the t h e ultraniafic u l t r a m a f i c rock t h e ore o r e host host carbonate rock surrounding the rock CO2 and/or rock sufficiently s u f f i c i e n t l y lowered lowered the t h e Pco2 and/or decreased decreased the t h e acidity a c i d i t y to t o allow allow for for structures d e p o s i t i o n of of gold gold in i n suitable suitable s t r u c t u r e s in i n the t h e ore o r e host h o s t rock. rock. deposition �38 Cobalt, Nickel, and Vanadium C o b a l t , Nickel, Vanadium Contents Contents of of Pyrite from Michiganime Slate, Michigan P y r i t e from Michigamme S l a t e , A . P. P. Ruotsala, R u o t s a l a , Paul P a u l M. M. Stadnik, S t a d n i k , T. T. J. Bornhorst (Dept. (Dept. of of Geol. Geol. A. & Geol. Engrg., Michigan Tech. Tech. Univ., Univ., Houghton, Houghton, MI M I 49931) 49931) Geol. Engrg., an oorganic—rich metasedimentary rock The Michigainme Michigamme SSlate l a t e iis s an r g a n i c - r i c h metasedimentary r o c k in in central Upper Peninsula of Michigan. central P e n i n s u l a of Michigan. The Michigan Geological G e o l o g i c a l Survey, Survey, with w i t h funding f u n d i n g from from the t h e Department of of Energy tested t e s t e d the t h e uranium potenpotential of the Marquette, Baraga and Iron with t i a l of t h e Michigamme in i n Marquette, I r o n Counties w ith ssix i x diamond drill d r i l l holes h o l e s (Trow, (Trow, 1979). 1979). In I n this t h i s study, s t u d y , pyrites p y r i t e s were were separated material nickel, s e p a r a t e d from ccore ore m a t e r i a l and analyzed for f o r cobalt, cobalt, n i c k e l , and with vanadium w i t h the t h e objective o b j e c t i v e of of determining d e t e r m i n i n g its i t s mode mode of of origin. origin. pyrites Price (1972), in in Most p y r i t e s fall f a l l into i n t o the t h e syngenetic s y n g e n e t i c field f i e l d of of P r i c e (1972), terms of of Co/Ni Co/Ni rratios; however, aa number number of of hhigh Co/Ni rratios were terms a t i o s ; however, i g h Co/Ni a t i o s were found which which ffall found a l l into i n t o the t h e volcanic—exhalative v o l c a n i c - e x h a l a t i v e massive massive sulfide s u l f i d e field. field. References Trow, J . , 1979, 1979, Final F i n a l report r e p o r t diamond—drilling diamond-drilling for f o r geologic g e o l o g i c informainformaTrow, J., Middle Precambrian Precambrian bbasins western of ttion i o n iin n tthe h e Middle a s i n s iin n tthe he w e s t e r n pportion o r t i o n of northern n o r t h e r n Michigan: Michigan: Geol. Geol. Surv. Surv. Div., Div., Michigan Dept. Dept. Nat. Nat. Re— ReLansing, Open—File ssources, o u r c e s , Lansing, Open-File Report UDOE UDOE OFR OFR GJBX—l62(79), GJBX-162(79), 44 44 p. p. Price, P r i c e , B.G., B.G., 1972, Minor elements in i n pyrites p y r i t e s from from the t h e Smithers Smithers map B.C. and e exploration of minor minor element studies x p l o r a t i o n aapplications p p l i c a t i o n s of studies aarea, r e a , B.C. (M.S. (M.S. Thesis): T h e s i s ) : Univ. Univ. of of British B r i t i s h Columbia, Columbia, Vancouver, Vancouver, 270 270 p. p. �39 Geochemistry Wisconsin Geochemistry of the the Volcanic Rocks of Northeastern Wisconsin J. SCHULZ Reston, Virginia 22092) KLAUS J. SCHULZ (U.S. (U.S. Geological Geological Survey, Survey, Reston, 22092) The early The early Proterozoic Proterozoic volcanic—plutonic volcanic-plutonic belt of north—central north-central northern half of Marinette Marinette County. Wisconsin is is well exposed in in the the northern area, the volcanic sequence has has been informally divided In this area, into Formation, the into four four formations formations (Jenkins, (Jenkins, 1973): 1973): the the Quinnesec Quinnesec Formation, the McAllister Peniene McAllister Formation, Formation,the theBeecher BeecherFormation, Formation,and andthe the PemeneForina— Formastratigraphic relationships relationships between these these are are still still tion. tion. Although stratigraphic not fully fully resolved, resolved, it it appears appears that that the the overall overall section section represents represents a a progression progression from from mafic mafic through through felsic felsic volcanics. volcanics. Although aa general general calc—alkaline calc-alkaline affinity affinity has been been recognized recognized felsic portions of this volcanic section, section, uncertainty for the more felsic still still remains remains as as to to the the geochemical geochemical affinities affinities of the the basaltic rocks rocks and their their possible possible petrologic petrologic relationship relationship to the the more felsic felsic volcanics. For For the the present present study, study, aa suite suite of samples samples was collected collected volcanics. elements, rare earth, earth, and other trace elements) for analysis (major (major elements, with emphasis with emphasis on on the the mafic mafic Quinnesec Quinnesec Formation. Formation. The The Quinnesec Quinnesec pillowed flows flows and associated associated diabases diabases range range from from basalt through through andesite andesite and show show little little evidence evidence of aa trend in in iron iron high, Al203 A1203 and and They have have variable, variable, though though generally generally high, enrichment. enrichment. They show a wide range range low Ti02 Ti02 contents. contents. The rare earth elements (REE) show low in both total total abundance abundance and and chondrite chondrite normalized normalized slopes. slopes. Most Most basalts basalts show show extreme extreme light light (L)REE (L)REE depletion depletion with [La/Sm]n [La/SmIn == .14.38 .14--38 Sturgeon Falls Falls (total range range .14—.76). .14-.76). Two gabbro samples from the Sturgeon (total sill, one of several large large gabbroic sills within the Quinnesec Quinnesec Forsill, mation, also mation, also show show significant significant LREE LREE depletion depletion suggesting suggesting possible possible LREE consanguinity with with the consanguinity the basalts. basalts. The andesites have enriched LREE relatively low ([La/SmJ ([La/SmIn == 1.23—1.47), 1.23-1.47), but relatively low total total REE REE abundances. abundances. Formation are andesitic whereas those Samples from the Beecher Formation those from the Pemene Pemene Formation from Formation are are rhyolitic. rhyolitic. The The rhyolites rhyolites have have higher higher REE REE abundances abundances and larger larger negative negative Eu anomalies anomalies than than the the andesites, andesites, but show show similar similar shaped, shaped, LREE—enriched LREE-enriched patterns. patterns. The The rhyolites rhyolites Rb/Sr ratios than than the the also have lower Sr (55—133 (55-133 ppm) and higher ~b/Sr andesites andesites ((Sr360 S r ~ 3 6ppm). 0ppm). The The data data suggest suggest the the following following conclusions: conclusions: 1. 1 . The The Quinnesec Quinnesec Formation Formation basalts and related related diabases diabases are are compositionally distinct from Proterozoic compositionally from the other early Proterozoic in upper Michigan (i.e. Badwater, etc.) etc.) basalts in (i.e. Hemlock, Badwater, which was highly depleted and were derived from from mantle which in large large ion ion lithophile lithophile elements. elements. 2. 2 . northeastern Wisconsin Wisconsin are The basalts and andesites of northeastern are not related by crystal crystal fractionation fractionation but represent seperate seperate melts melts from from compositionally compositionally distinct distinct sources. sources. 3. 3. The The overall overall chemical chemical characteristics characteristics of the the Quinnesec Quinnesec basalts basalts �40 suggest suggest affinities affinities with with basalts basalts in in recent recent island—arcs island-arcs back—arc basins rather than those of the ocean and back-arc the ocean floor floor or or continental continental regions. regions. The appearance appearance of of andesites andesites and more felsic felsic units with these these basalts also supports back—arc basin supports such such an an island—arc island-arc to back-arc environment. environment. Reference Reference Jenkins, R. A., 1973, Lake Superior . A., 1973, Institute Institute on on Lake Superior Geology, Geology, Jenkins, R 19th, p. 19th, p. 15—16. 15-16. �41 Geochemistry of of Fluid F l u i d Inclusions I n c l u s i o n s from from Archean Archean and and Phanerozoic Phanerozoic Gold Gold Geochemistry Deposits Deposits TED PAULL. J. SMITH, SMITH, PAUL L. CLOKE, CLOKE, and and STEPHEN STEPHEN E. E. KESLER KESLER (Department (Department of of TED J. Geological G e o l o g i c a l Sciences, S c i e n c e s , The The University U n i v e r s i t y of of Michigan, Michigan, Ann Ann Arbor, Arbor, MI MI 48109) 48109) F l u i d inclusions i n c l u s i o n s from from various v a r i o u s Archean Archean and and Phanerozoic Phanerozoic gold gold deposits deposits Fluid in i n metamorphic terrains t e r r a i n s were examined using u s i n g a specially s p e c i a l l y designed designed gas gas chromatographic chromatographic analytical a n a l y t i c a l system system and and conventional c o n v e n t i o n a l heating/freezing heatinglfreezing techniques. techniques. The The inclusion i n c l u s i o n analyses a n a l y s e s indicate i n d i c a t e that, t h a t , in i n most most cases, c a s e s , the the fluids CO f l u i d s are a r e H20—C02 H20-C02 or o r H20—CH4—C02 H20-CH4-C02 mixtures, m i x t u r e s , with w i t h trace t r a c e amounts amounts of of CO and N2. N2. and Heating and low and freezing f r e e z i n g measurements measurements indicate i n d i c a t e the t h e presence p r e s e n c e of of low salinity s a l i n i t y (<2 (<2 equiv. equiv. wt%NaCl), wt%NaCl), H20—C02 H20-C02 and and H20—CH4—C02 H20-CH4-CO2 fluid f l u i d inclusions, inclusions, confirming confirming our o u r analyses. analyses. Homogenization Homogenization of of the t h e inclusions i n c l u s i o n s occurred o c c u r r e d at at temperatures 220° to t o 380°C. 380°C Temperature and and f02 £ determinations determinations t e m p e r a t u r e s of of 220°C 2 were were made made by by plotting p l o t t i n g reaction r e a c t i o n lines l i n e s on on a02—teinperature a 0 t e m p e r a t u r e diagrams 2- utilizing u t i l i z i n g a recently r e c e n t l y developed developed equation e q u a t i o n of of state s t a t e for f o r supercritical supercritical H20-Coy-CH4 fluids. fluids. H20—C02—CH4 Our Our results r e s u l t s indicate i n d i c a t e that t h a t the t h e fluids f l u i d s obtained obtained equilibrium ' s near n e a r the t h e QFM QFM e q u i l i b r i u m at a t temperatures t e m p e r a t u r e s of of 340°C 340° to t o 500°C 500° and and f02ts f 02 buffer. buffer. Isochores, I s o c h o r e s , also a l s o calculated c a l c u l a t e d from from the t h e equation e q u a t i o n of of state, s t a t e , indicate indicate high h i g h pressures p r e s s u r e s of of 2000 2000 to t o 4000 4000 bars bars. �42 J a c o b s v i l l e Sandstone Sandstone Ridge Ridge in i n Keweenaw Keweenaw Bay Bay Jacobsville R. R. L. L. Wunderman Wunderman and and M. M. Rausch Rausch i s aa north—northeast n o r t h - n o r t h e a s t trending t r e n d i n g lake l a k e bottom bottom ridge r i d g e of of Jacobs— JacobsThere is yule v i l l eSandstone Sandstone in i n Keweenaw Keweenaw Bay Bay (Fig. (Fig. 1). 1 ) . AA recent r e c e n t scuba scuba dive d i v e conconfirms f i r m s the t h e presence p r e s e n c e of of subhorizontal s u b h o r i z o n t a l Jacobsville J a c o b s v i l l eSandstone Sandstone2020inm under under water w a t e r at a t aa point p o i n t 77 Km southeast s o u t h e a s t of of Portage P o r t a g e Entry Entry (88°22'W, (88O2ZvW, 46°56'N) 46'56'N) cropping A t this this cropping out o u t as a s aa detritus—free d e t r i t u s - f r e e north—west north-west facing f a c i n g scarp. s c a r p . At locality, l o c a l i t y , the t h e JJacobsville a c o b s v i l l e Sandstone is i s lithologically l i t h o l o g i c a l l y similar s i m i l a r to to nearby shore s h o r e exposures. exposures. Warren Warren (1981, (1981, Figs. F i g s . 46 46 and and 47) 47) shows shows that that this t h i s ridge r i d g e forms the t h e southeastern s o u t h e a s t e r n margin of of a steep—sided s t e e p - s i d e d valley valley so s o that t h a t similar s i m i l a r excellent e x c e l l e n t exposures of of bedrock are a r e likely l i k e l y to t o be b e found found on on the t h e northwest n o r t h w e s t ridge r i d g e face f a c e as a s well. w e l l . Being sheltered s h e l t e r e d from from the t h e lake, lake, t h e ridge r i d g e face f a c e more probably is i s related r e l a t e d to t o the t h e formation formation of the the t h e steep— steepsided being s i d e d vvalley a l l e y than than b e i n g the t h e result r e s u l t of of wave erosion e r o s i o n on aa lake l a k e cliff. cliff. Reference Reference Warren, E.J., E.J., Michigan Houghton, 1981, The bedrock topography topography of of the t h e Keweenaw Keweenaw Penninsula, Penninsula, (Ph.D. d i s s e r t a t i o n ) , Michigan Technological T e c h n o l o g i c a l University, University, (Ph.D. dissertation), 169 p. p. 169 Figure F i g u r e 1: 1: Location L o c a t i o n Map. Map. �43 ROPES GOLD MINE AND ITS I T S GEOLOGICAL SETTING SETTING Dean Rossell Kalliokoski D ean R o s s e l l and J. J. K alliokoski �44 THE THE ROPES ROPES GOLD GOLD MINE MINE AND AND ITS ITS GEOLOGICAL GEOLOGICAL SETTING SETTING Dean Rossell R o s s e l l and and J. J . Kalliokoski Kalliokoski INTRODUCTION INTRODUCTION Location Locat i o n The Ropes Gold Mine Mine is i s located l o c a t e d in i n Section S e c t i o n 29, 29, T48N—R27W, T48N-R27W, Marquette Marquette County, County, Michigan, Michigan, about t h r e e miles m i l e s north n o r t h of of Ishpeming Ishpeming and and aa quarter q u a r t e r mile m i l e west west of of Deer Deer Lake Lake (Figs. about three ( F i g s . 1, 1, 2). gold prosprosi s the t h e most most extensively e x t e n s i v e l y developed developed of of the t h e 20 20 or o r more more gold The Ropes Mine Mine is 2 ) . The pects p e c t s and and mines mines that t h a t comprise comprise the t h e Michigan Michigan gold gold belt. belt. History History Most i s summarized summarized from from Broderick Broderick (1945). (1945). The The Ropes Ropes ore ore Most of of the t h e following f o l l o w i n g history h i s t o r y is body body was was discovered d i s c o v e r e d in i n 1880 1880 by by Julius J u l i u s Ropes Ropes while w h i l e he h e was was prospecting p r o s p e c t i n g for f o r asbestos asbestos among among the t h e outcrops o u t c r o p s of of the t h e Deer Deer Lake Lake Peridotite. P e r i d o t i t e . Mining Mining operations o p e r a t i o n s at a t the t h e Ropes Ropes began in At i n 1882 1882 and and continued c o n t i n u e d until u n t i l 1897 1897 when when the t h e mine mine was was closed c l o s e d by by creditors. c r e d i t o r s . At the t h e time time of of closing, c l o s i n g , 15 1 5 levels l e v e l s had had been been developed developed to t o the t h e east e a s t and and west west of of the t h e Curry Curry shaft, s h a f t , that t h a t reached reached aa depth d e p t h of of 244 244 meters. meters. During During the t h e 15 1 5 years y e a r s that t h a t the t h e mine mine was was in i n operation o p e r a t i o n it i t produced produced 1250 1250 kg kg of of gold gold and and 6200 6200 kg kg of of silver s i l v e r from from 145,000 145,000 tons t o n s of of ore, o r e , averaging a v e r a g i n g 5.96 5.96 g/ton g / t o n gold gold and and 28.05 28.05 g/ton g / t o n silver s i l v e r (Morgan (Morgan and and DeCristoforo, D e C r i s t o f o r o , 1980). 1980). Around Around 1901 1901 some some 30,000 30,000 tons t o n s of of tailings t a i l i n g s were were cyanided. cyanided. In I n 1933 1933 the t h e Ropes property p r o p e r t y was was acquired a c q u i r e d by by the t h e Ishpeming Ishpeming Mining Mining Co., Co., which which continued continued surface s u r f a c e exploration e x p l o r a t i o n in i n the t h e area. a r e a . Calumet Calumet and and Hecla Hecla Mining Mining Co. Co. bought bought aa majority majority interest i n t e r e s t in i n the t h e Ishpeming Ishpeming Mining Mining Co. Co. in i n 1934. 1934. From From 1934 1934 to t o 1942 1942 they t h e y conducted conducted an an extensive e x t e n s i v e exploration e x p l o r a t i o n program program of of diamond diamond drilling, d r i l l i n g , drifting d r i f t i n g on on the t h e 15th 1 5 t h level, l e v e l , and and resampling resampling of of the t h e old o l d workings workings in i n an a n attempt a t t e m p t to t o find f i n d an an extension e x t e n s i o n of of the t h e Ropes Ropes ore ore body it body (Fig. (Fig. 3). 3 ) . Although Although this t h i s work work found found no no major major extensions e x t e n s i o n s of of the t h e ore o r e body, body, it did d i d disclose d i s c l o s e over over aa million m i l l i o n tons t o n s of of lower lower grade grade ore o r e in i n the t h e ore o r e host h o s t rock r o c k surrounding surrounding the 1st and and 15th 1 5 t h levels, l e v e l s , average average t h e old o l d workings. workings. These These zones, zones, located l o c a t e d between between the t h e 1st 0.13 0.13 oz/ton o z l t o n gold gold and and 0.7 0.7 oz/ton o z l t o n silver. s i l v e r . In I n 1942 1942 war time t i m e restrictions r e s t r i c t i o n s on on precious precious metal m e t a l mining mining stopped stopped operations o p e r a t i o n s at a t the t h e mine, mine, preventing p r e v e n t i n g further f u r t h e r exploration e x p l o r a t i o n below below the t h e 15th 1 5 t h level. level. In t h e Ropes Ropes Mine, Mine, began began aa new new expor— export h e present p r e s e n t owner owner of of the I n 1974 1974 Callahan Callahan Mining Mining Corp., Corp., the ation a t i o n program program to t o confirm c o n f i r m and and try t r y to t o expand expand the t h e low low grade grade ore o r e reserves r e s e r v e s established e s t a b l i s h e d by by the t h e Calumet Calumet and and Hecla Hecla Mining Mining Co. Co. To To date d a t e this t h i s work work has h a s included i n c l u d e d rehabilitation r e h a b i l i t a t i o n of of the t h e old o l d mine mine workings, an an extensive e x t e n s i v e surface s u r f a c e and and underground underground diamond diamond drilling d r i l l i n g camcampaign, worke x t r a c t i o n of of bulk b u l k samples samples for f o r metallurgical m e t a l l u r g i c a l tests, t e s t s , resampling resampling of of old o l d workpaign, extraction ings, remapping of of tthe i n g s , aand n d remapping h e ssurface u r f a c e and underground underground geology geology (Skillings, ( S k i l l i n g s , 1981). 1981). Previous P r e v i o u s Geological G e o l o g i c a l Studies Studies The i s by by Broderick, Broderick, who who was was the the The only o n l y detailed d e t a i l e d geological g e o l o g i c a l work work on on the t h e Ropes Ropes Mine Mine is mine mine geologist g e o l o g i s t for f o r Calumet Calumet and and Hecla Hecla Mining Mining Co. Co. In I n 1945 1945 Broderick B r o d e r i c k published p u b l i s h e d aa detailed d e t a i l e d description d e s c r i p t i o n of of the t h e Ropes Ropes ore o r e body body and and the t h e surrounding s u r r o u n d i n g peridotite. p e r i d o t i t e . SubSubsequent sequent published p u b l i s h e d work work on on the t h e geology geology of of the t h e surrounding surrounding area a r e a has h a s been been by by Boyum Boyum (1964, P u f f e t t (1966, (1966, 1974), 1974), Clark C l a r k and and others o t h e r s (1975), (1975), Cannon Cannon and and (1964, 1970, 1970, 1975), Puffett Klasner Klasner (1975), (1975), and and Morgan Morgan and and DeCristoforo D e C r i s t o f o r o (1980). (1980). The The latter l a t t e r provide p r o v i d e the t h e most most Information recent r e c e n t data d a t a on on the t h e overall o v e r a l l geology geology of of the t h e Ishpeming Ishpeming greenstone g r e e n s t o n e belt. b e l t . Information on the t h e ore o r e host h o s t rock r o c k comes comes from from an an unpublished unpublished mine mine report r e p o r t by by Creasy Creasy (1981). on (1981). �________ _______ 45 L o c a t i o n of t h e opes Gold Mine. Location of the Ropes Gold Mine. F i g u r1.e 1. Figure : :::::: —S'. I, / >j1 r ..— A • >< 7- A i ç.J c •••n'v Pv>,' t.JJ I < — r -, '. 47 A L NA Mine 1 0 Feet 4000 (cannon and Klasner, 1975: Clark and others.1975) Proterozoic Proterozoic . . ... . .., Marquette M a r ~ u e t Range t eRange Supergroup SupergrOUp (Cannon and Klasner, 1975; Clark and others,1975) 1-1 Archean Archean .... Granite Granite DeerLake LakePeridotite Peridotite I TAge3Deer relations uncertain ,;\,;:</ -5 '6 Field trip stops Field trip stops Age relations uncertain KitchiSchist Schist Kitchi ' r] Aggloherate Agglomerate 1-i Interned. to to fels. fels.voles. volcs. Intermed. GEOLOGYOF OFTHE THEAREA AREAAROUND AROUND GEOLOGY THE ROPES AND MICHIGAN GOLD MINES A c Amphibollte Amphiboilte F i g u r e 2. 2. Figure Regional geology of t h e Ropes Mine and Michigan Mine a r e a . Regional geology of the Ropes Mine and Michigan Mine area, �58 Composition of Serpentinites Because of difficulty in field recognition, no attempt was made during mapping In to distinguish pyroxene—rich and olivine—rich portions of the peridotite. general, olivine—rich ultramafics produce more magnetite when serpentinized than do the pyroxene—rich varieties. A large scale zonation of magnetic properties in the Deer Lake Peridotite, showing a highly magnetic core and less intensely magnetic margins (Morgan and DeCristoforo, 1980), suggests an olivine—rich core and pyroxene—rich margins. The chemical compositions of 10 representative serpentinites from the Deer Lake The MgO values reported in this study are signiPeridotite are given in Table 3. ficantly higher than those reported by Morgan and DeCristoforo (1980), but correlate well with those reported by Creasy (1981). After recalculating the chemical data to exclude volatiles, mineral modes were calculated for the serpentinite samples using a computer program. The dominant mineral phases in the calculated modes are olivine and orthopyroxene, with lesser amounts of diopside, magnetite, In the following paragraph chromite and, in pyroxene rich samples, of anorthite. The modal references to olivine and pyroxene also are to their calculated modes. The 10 samples in Table 3 are olivine to pyroxene ratios range from 0.28 to 1.93. plotted on an olivine—orthopyroxene—clinopyroxene ternary diagram in Figure 7. All of the analyzed samples from the Deer Lake Peridotite fall in or near the hartzburgite field. Ashely (1974), Coleman and Keith (1970), and Page (1967) report losses of Ca during serpentinization of primary ultramafic rocks. If substantial Ca has been lost from the Deer Lake Peridotite during serpentinization, the original ultramaf Ic rock may have had more diopside than shown in the calculated modes. Comparison of trace element abundances with calculated mineral modes reveals some In the samples analyzed in this study, A1203, Ti02 and Sc are engeneral trends. riched in pyroxene—rich serpentinites relative to the divine—rich ones. Increases in these abundances correlate with increasing chlorite in the serpentinite. Nb Cr303 and FeO show content appears to decrease with decreasing olivine content. The consistent pyroxene—rich samples. no consistent trends between olivine— and variation in the ratios of TiO2fAl2O3, Sc/Al203 for these samples imply that these serpentinites were originally derived from a single parent magma. Comparison of Serpentinite Compositions With Those of Other Ultramafics The determination of the origin of the Deer Lake Peridotite could have exploration significance. Morgan and Decristoforo (1980) noted that, based on their analyses, the composition of the Deer Lake Peridotite is close the komatiite field of Naldrett It follows that if the Deer Lake Peridotite represents komatiitic and Cabri (1976). volcanic rocks, the OHR might be an interflow tuff sequence, possibly with an associated, laterally extensive exhalite component. Many chemical criteria have been proposed to distinguish komatiitic rocks since the There now seems to be a con— recognition of ultramafic lavas in the late 1960's. census (Basaltic Volcanism Special Project, 1981) that komatiites are characterized 1) MgO values greater than 18 and less than 40 weight percent, but typically by: between 20 and 30 weight percent; 2) Tb2 less than 1%; 3) Ni greater than 100 ppm; In the serpentinite samples 4) Cr greater than 140 ppm; 5) CaO/Al203 0.8 to 1.1. analyzed for this study (with values recalculated to exclude volatiles; Table 2): �59 ANALYSES OF INITE SRMPLES SAMPLES RNRLYSES OF SERPENT SERPENTINITE 1 2 3 4 5 6 7 8 9 10 S102 RL203 FE203 FEO FEO MG0 M GO CR0 CRO NR2O 0 NR2 K20 K2 0 1-120+ H20+ T102 TI02 P205 P205 C02 C02 43.20 1.96 '42.55 .03 .00 42.18 39.88 41 .88 41.10 414 .146 1.71 .00 5.34 40.21 3.82 38.30 .98 .00 42.03 5.53 .00 .00 .00 2.07 .00 5.67 35.07 2.30 9.69 36.12 10.00 10.59 28 .60 .03 .00 .03 .00 .03 .01 .04 .02 27 .69 1.89 .06 12.21 31.85 3.14 5.43 37.73 1.48 5.58 34.29 4.36 9.70 6.70 6.20 8.20 6.80 .11 .01 .00 .02 .02 .05 .02 .07 .02 7.80 2.15 TOTAL TOTRL 102 .25 101 .06 100 .01 SC V CR Cu ZN .00 8.99 36.77 .27 .03 .00 11 85 .02 .03 .00 .05 .01 .00 .35 .04 .00 7.20 9.90 7.50 6.50 6.50 .27 .03 .214 .03 .01 .03 6.06 3.75 2.12 .01 .02 6 .8? .06 .01 5.08 .21 .02 .00 1.22 100 .00 100 .00 99.98 100.01 93.47 99.9? 97.87 19 126 19 123 8 15 82 7 s 17 43 70 2918 3343 3423 3940 2163 38 3* 22 13 60 62 66 50 60 98 7 12 52 25 59 49 37 49 1582 26 21 1 4 AU Table 33.. Peridotite. Peridotite. ppm. PPm. 17 .00 9.49 29.57 6 4667 .00 6.33 35.53 4.01 39 1989 27 5172 .00 .00 2.08 2274 20 64 1.60 .03 3 Selected S e l e c t e d analyses a n a l y s e s of of serpentinites s e r p e n t i n i t e s from the t h e Deer Lake Elements listed wt. l i s t e d as a s oxides o x i d e s in in w t . percent, p e r c e n t , others o t h e r s in in I' �60 OPX 0 PX a LherzOlite Wehrtde CPX CPX Clinopyroxenite Figure 7. Compositions of serpentinites from Table 3 plotted on Figure 7. of serpentinites from Coleman Table 3 and plotted on (Modified from Keith, nomenclatureCompositions ternary diagram. nomenclature ternary diagram. (Modified from Coleman and Keith, 1971). 1971). �61 1) 1 ) the t h e MgO MgO content, c o n t e n t , in i n every every sample, sample, is i s greater g r e a t e r than t h a n 30 30 weight weight percent, p e r c e n t , and and i s less l e s s than than s e v e r a l are a r e more more than than 40 40 weight weight percent; p e r c e n t ; 2) 2) Ti02 Ti02 in i n all a l l samples samples is several 1% and 1% and in i n most most samples samples is i s less l e s s than than 0.1%; 0.1%; 3) 3) for f o r all a l l samples samples both b o t h Cr C r and and Ni N i are are greater g r e a t e r than than 1000 1000 ppm; ppm; and and 4) 4) CaO/Al203 CaO/A1203 ratios r a t i o s range range from from 0.17 0.17 to t o 75.74. 75.74. The The wide wide variation v a r i a t i o n of of this t h i s ratio r a t i o probably probably reflects r e f l e c t s the t h e mobility m o b i l i t y of of Ca Ca during d u r i n g serpen— serpeni t can can be b e seen seen that t h a t Ti02, Ti02, t i n i z a t i o n and and carbonatization. c a r b o n a t i z a t i o n . From From this t h i s comparison comparison it tinization C r and and Ni N i fit f i t the t h e requirements requirements for f o r komatiite, k o m a t i i t e , but b u t all a l l would would be b e marginal marginal values. values. Cr Only some some of of the t h e MgO MgO values v a l u e s fit f i t the t h e criteria, c r i t e r i a , and and those t h o s e that t h a t do, do, also a l s o are a r e near near Only limit. t h e limit. the commonly used used plot p l o t for f o r distinguishing d i s t i n g u i s h i n g komatiitic k o m a t i i t i c rocks r o c k s from from tholeiitic t h o l e i i t i c rocks r o c k s is is AA commonly the t h e A1203 A1203 vs. v s . FeO/(FeO+MgO) FeO/(FeO+MgO) plot p l o t of of Naldrett N a l d r e t t and and Cabri C a b r i (1976) (1976) shown shown in i n Figure F i g u r e 8. 8. The The diagonal d i a g o n a l line l i n e in i n Figure F i g u r e 88 separates s e p a r a t e s plots p l o t s of of African A f r i c a n and and Canadian Canadian komatiites komatiites (x) from from those t h o s e of of tholeiitic t h o l e i i t i c Canadian Canadian synvolcanic s y n v o l c a n i c dikes d i k e s and and flows flows (o). ( 0 ) . All A l l ser— ser(x) pentinite t h e Deer Deer Lake Lake Peridotite P e r i d o t i t e (listed ( l i s t e d in i n Table Table 33 and and plotted p l o t t e d as a s solid s o l i d dots dots p e n t i n i t e of of the on Figure F i g u r e 8) 8 ) fall f a l l in i n or o r near n e a r the t h e komatiitic k o m a t i i t i c side s i d e of of the t h e diagram. diagram. However, However, aa number number on of (*) also a l s o fall f a l l well w e l l within within of samples samples of of Alpine—type Alpine-type ultramafics u l t r a m a f i c s (plotted ( p l o t t e d as a s stars s t a r s (*) t h e komatiite k o m a t i i t e side s i d eof o f the t h e diagram. diagram. This T h i s lack l a c k of of discrimination d i s c r i m i n a t i o n is i s noted noted by by Naldrett Naldrett the who who points p o i n t s out o u t that t h a t many many other o t h e r ultramafic u l t r a m a f i c and and mafic m a f i c rocks r o c k s that t h a t are a r e not n o t related r e l a t e d to to w i l l plot p l o t on on the t h e komatiitic k o m a t i i t i c side s i d e of of the t h e diagram diagram (Naldrett, ( N a l d r e t t , 1980). 1980). k o m a t i i t e s will komatiites On On the t h e basis b a s i s of of the t h e plot p l o t in i n Figure F i g u r e 88 the t h e Deer Lake Peridotiteiskomatiitic. P e r i d o t i t e i s k o m a t i i t i c . HowHowever, e v e r , the t h e very v e r y high h i g h values v a l u e s of of MgO MgO for f o r many many of of the t h e serpentinite s e r p e n t i n i t e samples samples do do not not ( B a s a l t i c Volcanism, Vol.canism, correspond correspond with w i t h one one of of the t h e diagnostic d i a g n o s t i c features f e a t u r e s of of komatiites k o m a t i i t e s (Basaltic These high h i g h MgO MgO values v a l u e s are a r e considered c o n s i d e r e d by by the t h e senior s e n i o r author author S p e c i a l Project, P r o j e c t , 1981). 1981). These Special Moreover, most most recent recent t o be be typical t y p i c a l of of intrusive i n t r u s i v e and and alpine a l p i n e type t y p e ultramafics. u l t r a m a f i c s . Moreover, to classifications c l a s s i f i c a t i o n s of of ultramafic u l t r a m a f i c rock rock types t y p e s have have been been based based on on tectonic t e c t o n i c setting s e t t i n g rather rather than than chemistry c h e m i s t r y alone a l o n e (Naldrett, ( N a l d r e t t , 1980), 1980), implying implying that t h a t both b o t h compositional c o m p o s i t i o n a l and and field field evidence evidence should should be b e considered c o n s i d e r e d for f o r aa valid v a l i d designation. designation. Talc-Carbonate Alteration Alteration Talc—Carbonate Serpentine, S e r p e n t i n e , olivine, o l i v i n e , and and pyroxene, pyroxene, the t h e primary primary constituents c o n s t i t u e n t s of of serpentinites s e r p e n t i n i t e s and and peridotites, C02 and and break b r e a k down down p e r i d o t i t e s , are a r e unstable u n s t a b l e in i n the t h e presence p r e s e n c e of of fluids f l u i d s rich r i c h in i n CO2 a c c o r d i n g to t o the t h e following f o l l o w i n g reaction: reaction: according + + CO2 == 33 magnesite magnesite ++ 11talc t a l c + 33 H20 Hz0 s e r p e n t i n e + 33 CO2 22 serpentine (Deere, et e t al., a l . , 1965). 1965). (Deere, The The serpentinites s e r p e n t i n i t e s of of the t h e Deer Deer Lake Lake Peridotite P e r i d o t i t e have have been been altered a l t e r e d extensively e x t e n s i v e l y to t o talc talc and carbonate c a r b o n a t e in i n the t h e vicinity v i c i n i t y of of the t h e Ropes Ropes Mine. Mine. Here Here zones zones of of talc—carbonate t a l c - c a r b o n a t e rock rock and extend extend over over 400 400 feet f e e t to t o the t h e north n o r t h of of the t h e ore o r e host h o s t rock, rock, and and over over 200 200 feet f e e t to t o the the Both zones apparently pinch out eastward, but persist downward, s o u t h (Fig. ( F i g . 4). 4 ) . Both zones a p p a r e n t l y p i n c h o u t eastward, b u t p e r s i s t downward, south I n general g e n e r a l the t h e distribution d i s t r i b u t i o n of of talc— talca t least l e a s t to t o the t h e present p r e s e n t levels l e v e l s of of exploration. e x p l o r a t i o n . In at carbonate c a r b o n a t e alteration a l t e r a t i o n appears a p p e a r s to t o be b e largely l a r g e l y controlled c o n t r o l l e d by by the t h e distribution d i s t r i b u t i o n of of the the OHR. Due Due to t o the t h e difficulty d i f f i c u l t y of of recognizing r e c o g n i z i n g low low to t o moderate moderate abundances abundances of of talc t a l c and and OHR. carbonate 4 , refer r e f e r only o n l y to to c a r b o n a t e in i n hand hand sample, sample, talc—carbonate t a l c - c a r b o n a t e zones, zones, shown shown in i n Figure F i g u r e 4, zones zones in i n which which talc t a l c and and carbonate c a r b o n a t e constitute c o n s t i t u t e the t h e majority m a j o r i t y of of the t h e rock. r o c k . This This criterionhas c r i t e r i o n h a s undoubtedly undoubtedly led l e d to t o an an underestimation u n d e r e s t i m a t i o n of of the t h e extent e x t e n t of of talc—carbonate talc-carbonate alteration. alteration. �62 20 0 15 xx x Komatiite Komatiite r) 0 10 Tholeiite Tholeiite 0 0 0 CN -J x x * 5 x .. x x 0 .0 .2 .4 .8 .6 FEO/FEO+MGO AL203 VS FEO/FEO±MGO + Figure Variation V a r i a t i o n of of A1203 A1203 with w i t h FeO/(FeO FeO/(FeO + MgO) MgO) wt. wt. percent percent F i g u r e 8. 8. ratio: ( - ) = serpentinites s e r p e n t i n i t e s of of the t h e Deer Deer Lake Lake Peridotite, Peridotite, r a t i o : (-)= (x)= (x)= komatiites k o m a t i i t e s (data ( d a t a from from Naldrett N a l d r e t t and and Cabri, C a b r i , 1976), 1 9 7 6 ) , (°)= ( o ) =tho— tho- leiites l e i i t e s from from Dundonald Dundonald Sill S i l l and and Theo's Theo's Flow Flow (Data (Data from from Naldrett Naldrett and l 9 7 6 ) , (*)= (*)= Alpine A l p i n e type t y p e lherzolites l h e r z o l i t e s and and harzburgites harzburgites and Cabri, C a b r i , 1976), (data T o t a l Fe Fe is i s calculated c a l c u l a t e d as a s FeO FeO and and ( d a t a from from Menzies, Menzies, 1977). 1 9 7 7 ) . Total all ( F i g u r e modmoda l l analyses a n a l y s e s are a r e calculated c a l c u l a t e d to t o exclude e x c l u d evolatiles. v o l a t i l e s . (Figure ified i f i e d from fromNaldrett N a l d r e t t and andCabri, C a b r i , 1976). 1976). 1.0 �63 P e r i p h e r a l to t o the t h e talc—carbonate t a l c - c a r b o n a t e zones, zones, carbonate c a r b o n a t e alteration a l t e r a t i o n in i n the t h e serpentinite serpentinite Peripheral o c c u r s as a s pseudomorphic replacements of of serpentine s e r p e n t i n e veins v e i n s by carbonate. c a r b o n a t e . Veins occurs Veins g e n e r a l l y increase i n c r e a s e in i n abundance near n e a r the t h e margins of of the t h e talc—carbonate t a l c - c a r b o n a t e zones, zones, so so generally t h a t a single s i n g l e hand sample sample may may contain c o n t a i n several s e v e r a l generations g e n e r a t i o n s of of veins. v e i n s . In I n these these that a r e a s , younger s e t s of of veins, v e i n s , composed of of coarse—grain c o a r s e - g r a i n carbonate, c a r b o n a t e , typically t y p i c a l l y crosscrossareas, younger sets c u t older o l d e r veins v e i n s of of serpentine s e r p e n t i n e replaced r e p l a c e d by by carbonate. carbonate. cut i s typically t y p i c a l l y gradational, gradational, The contact c o n t a c t between serpentinite s e r p e n t i n i t e and talc—carbonate t a l c - c a r b o n a t e rock r o c k is o n l y by aa gradual g r a d u a l lightening l i g h t e n i n g in i n color c o l o r of of the t h e rock, rock, as a s talc t a l c and and carbonate carbonate marked only i n c r e a s e at a t the t h e expense expense of of the t h e serpentine s e r p e n t i n e matrix. matrix. S e r p e n t i n i t e features, f e a t u r e s , such such increase Serpentinite patterns aass vvein ein p a t t e r n s and serpentine s e r p e n t i n e pseudomorphs after a f t e r olivine, o l i v i n e , are a r e commonly preserved preserved f o r some distance d i s t a n c e into i n t o the t h e talc—carbonate t a l c - c a r b o n a t e zone. zone. However, However, serpentinite s e r p e n t i n i t e features features for mrn clots clots aare re o b l i t e r a t e d in i n more intensely i n t e n s e l y altered a l t e r e d rock, r o c k , which commonly commonly contain c o n t a i n 33 mm obliterated and thin t h i n contorted c o n t o r t e d seams seams of of chlorite. c h l o r i t e . The degree d e g r e e of of alteration a l t e r a t i o n varies v a r i e s widely throughout the the n o r t h and south s o u t h alteration a l t e r a t i o n zones, zones, with w i t h pods of of relatively r e l a t i v e l y fresh fresh throughout north serpentinite p reserved w i t h i n the t h e mapped b o u n d a r i e s of of the t h e alteration a l t e r a t i o n zones. zones. The serpentinite preserved within boundaries rratio a t i o of t a l c to t o carbonate c a r b o n a t e generally g e n e r a l l y varies v a r i e s from about 2.0 2.0 to t o 0.5, 0 . 5 , but b u t several several of talc s m a l l zones of t a l c (steatite) ( s t e a t i t e ) have been found in i n the t h e mine. mine. Both dolodolosmall of almost pure talc m i t e and magnesite have been formed formed during d u r i n g alteration a l t e r a t i o n of of the t h e serpentinite, s e r p e n t i n i t e , dolomite dolomite mite OHR. b e i n g the t h e most abundant, abundant, particularly p a r t i c u l a r l y near n e a r the t h e OHR. being t h e contact c o n t a c t with w i t h the t h e OHR, OHR, the t h e talc—carbonate t a l c - c a r b o n a t e rock r o c k changes changes composition, composition, so s o that that Near the quartz mineral q u a r t z and chlorite c h l o r i t e become significant significant m i n e r a l phases and talc t a l c becomes a minor phase. phase. Chidester C h i d e s t e r and others o t h e r s (1978) (1978) have proposed that t h a t similar s i m i l a r carbonate—quartz carbonate-quartz zones zones in i n the the Belvidere body rrepresent of ttalc—carbonate B e l v i d e r e Mountains ultramaf u l t r a m a f iIc c body e p r e s e n t tthe h e ffinal i n a l sstage t a g e of alc-carbonate occurring aalteration, lteration, o c c u r r i n g along a l o n g zones where C02—rich C02-rich fluids f l u i d s travelled t r a v e l l e d most freely. freely. nature The locally l o c a l l y gradational gradational n a t u r e of of the t h e south s o u t h wall w a l l contact c o n t a c t between carbonate—quartz— carbonate-quartzchlorite OHR, suggest s u g g e s t that t h a t talc—carbonate t a l c - c a r b o n a t e alteration a l t e r a t i o n has h a s also a l s o affected affected c h l o r i t e rock r o c k and the t h e OHR, the This OHR. T h i s is i s supported s u p p o r t e d by large l a r g e differences d i f f e r e n c e s between trace t r a c e element element abundances abundances t h e OHR. in near OHR, and and those t h o s e in in i n samples n e a r the t h e contact, c o n t a c t , which reflect r e f l e c t the t h e composition of of OHR, talc—carbonate t a l c - c a r b o n a t e rocks r o c k s further f u r t h e r from from the t h e contact. c o n t a c t . A similar s i m i l a r overlap o v e r l a p of of alteration alteration from talc—carbonate t a l c - c a r b o n a t e rocks r o c k s to t o more felsic f e l s i c rocks r o c k s has h a s been reported r e p o r t e d at a t the t h e Campbell Red Lake and and Dickenson gold gold mines in i n Canada Canada (MacGeehan (MacGeehan and and Hodgson, Hodgson, 1980). 1980). A A more discussion petrographic i s under complete d i s c u s s i o n of of p e t r o g r a p h i c changes in i n the t h e talc—carbonate t a l c - c a r b o n a t e zone zone is preparation p r e p a r a t i o n by Rossell R o s s e l l (M.S. (M.S. thesis, t h e s i s , in i n preparation). preparation). Relationship R e l a t i o n s h i p of of Talc—Carbonate Talc-Carbonate Alteration A l t e r a t i o n to t o Gold Gold Mineralization Mineralization It h has been proposed proposed by w writers It a s been r i t e r s such as a s Pyke (1976) (1976) that t h a t ultramafic u l t r a m a f i c rocks r o c k s may be the bed" from which the t h e "source "source bed" t h e gold in i n many deposits d e p o s i t s has h a s been derived. d e r i v e d . Pyke his based h i s arguments largely l a r g e l y on on the t h e close c l o s e spatial s p a t i a l association a s s o c i a t i o n between between ultramaf u l t r a m a fIc ic Ontario rrocks o c k s and the t h e gold deposits d e p o s i t s at a t Timmins, Timmins, O n t a r i o and in i n other o t h e r large l a r g e Precambrian gold camps. camps. Additional A d d i t i o n a l support s u p p o r t for f o r this t h i s point p o i n t of of view view came came from from Gottfrled G o t t f r i e d and and others presented o t h e r s (1972), (1972), who p r e s e n t e d evidence suggesting s u g g e s t i n g that t h a t primary gold gold abundances in in ultramafic u l t r a m a f i c rocks r o c k s are a r e higher h i g h e r than t h a n in i n most most other o t h e r rock r o c k types. t y p e s . Anhaeusser and others others (1975), and Sager Sager and and oothers (1975), and t h e r s (1982) (1982) ddispute i s p u t e tthis h i s cconclusion, o n c l u s i o n , and show that, t h a t , on a basis, i s no higher, h i g h e r , and and in in worldwide b a s i s , the t h e primary gold content c o n t e n t of of ultramafic u l t r a m a f i c rocks r o c k s is i s lower, lower, than t h a n crustal c r u s t a l averages. averages. many cases c a s e s is Pyke (1976) (1976) proposes that t h a t one reason r e a s o n for f o r the t h e relationship r e l a t i o n s h i p of of ultramafic u l t r a m a f i c bodies b o d i e s to to gold m mineralization i s that t h a t substantial s u b s t a n t i a l amounts of of gold were released r e l e a s e d from from the the i n e r a l i z a t i o n is ultramafic u l t r a m a f i c rocks r o c k s during d u r i n g carbonatization. c a r b o n a t i z a t i o n . The senior s e n i o r writer w r i t e r has h a s tested t e s t e d the t h e hypohypothesis t h e s i s by obtaining o b t a i n i n g neutron n e u t r o n activation a c t i v a t i o n gold analyses a n a l y s e s for f o r a suite s u i t e of of samples samples from from the north the n o r t h talc—carbonate t a l c - c a r b o n a t e zone at a t the t h e Ropes Mine, Mine, and for f o r serpentinites s e r p e n t i n i t e s from from the the �64 Peridotite. T h i s data d a t a should permit permit an evaluation e v a l u a t i o n of of the the surrounding Deer Lake Peridotite. This degree d e g r e e of of redistribution r e d i s t r i b u t i o n of of gold and other o t h e r elements during d u r i n g carbonate c a r b o n a t e alteration. alteration. i s not n o t satissatisThe d i r e c t comparison of of chemical data d a t a expressed as a s weight percent p e r c e n t is direct factory with f a c t o r y for f o r determining chemical changes associated associated w i t h metasomatic alterations alterations (Kerrich particularly is p a r t i c u l a r l y true t r u e when substantial s u b s t a n t i a l changes in in ( K e r r i c h and Fyfe, Fyfe, 1981). 1981). This T h i s is i s the t h e case c a s e when serpentinite s e r p e n t i n i t e (sp. ( s p . gr. gr. sspecific p e c i f i c gravity g r a v i t y accompany alteration, a l t e r a t i o n , as a s is 2.60) alters 2.60) a l t e r s to t o talc—carbonate t a l c - c a r b o n a t e (sp. ( s p . gr. g r . 2.70—2.90). 2.70-2.90). C h i d e s t e r (1962), (1962), N a l d r e t t (1966), (1966). and Barnes (1973) (1973) have concluded that t h a t talc— talcChidester Naldrett ccarbonate a r b o n a t e alteration a l t e r a t i o n is i s aa constant c o n s t a n t volume volume process. p r o c e s s . For this t h i s and and other o t h e r reasons reasons d i s c u s s e d by o s s e l l (Thesis ( T h e s i s in i n prep.) p r e p . ) constant c o n s t a n t volume was assumed when calcucalcudiscussed by R Rossell l a t i n g rrelative e l a t i v e changes n cchemistry, h e m i s t r y , uusing s i n g aa method u t l i n e d b y c h i d e s t e r (1972). (1972). lating changes iin method ooutlinedbyChidester Relative R e l a t i v e aadditions d d i t i o n s and subtractions s u b t r a c t i o n s have been calculated c a l c u l a t e d from the t h e data d a t a in i n Table 4 and listed 5. of the t h e initial i n i t i a l parent p a r e n t rock is i s assumed l i s t e d in i n Table Table 5. The composition of to t o bbe e that t h a t of of serpentinite s e r p e n t i n i t e sample sample No. No. 33 (Table (Table 3). 3 ) . Reasons for f o r choosing this t h i s parent parent rock composition are a r e given given by by Rossell R o s s e l l (Thesis ( T h e s i s in i n prep.). prep.). Samples in i n Table 55 are are contact. l i s t e d from left l e f t to t o rright i g h t according a c c o r d i n g to t o decreasing d e c r e a s i n g distance d i s t a n c e from from the t h e OHR contact. listed v i s u a l l y estimated e s t i m a t e d from from thin t h i n section s e c t i o n are a r e listed l i s t e d below below each each sample. sample. Mineral modes visually V a r i a t i o n s in i n abundance of of C, C , H, Ca, Mg, i t h distance d i s t a n c e from from OHR contact contact Variations H, Ca, Mg, A Al1 and Au w with are a r e shown graphically g r a p h i c a l l y in i n Figure F i g u r e 9. 9. The large l a r g e increases i n c r e a s e s in i n C and Ca shown in i n Figure F i g u r e 9a 9a and 9b 9b correspond to t o increasing increasing abundances of of dolomite. dolomite. Losses in i n hydrogen throughout throughout the t h e zone zone (Fig. (Fig. 9) 9) correscorrespond to with pond t o the t h e loss l o s s of of serpentine, s e r p e n t i n e , and are a r e consistent consistent w i t h the t h e partial p a r t i a l dehydration dehydration n a t u r e of of the t h e reaction r e a c t i o n given given on on an an earlier e a r l i e r page. page. Major gains g a i n s in i n Al A 1 (Figure ( F i g u r e 9c) 9c) nature correspond with contact. correspond w i t h the t h e increasing i n c r e a s i n g abundance of of chlorite c h l o r i t e near n e a r the t h e OHR contact. All A l l of of the t h e altered a l t e r e d serpentinite s e r p e n t i n i t e samples listed l i s t e d in i n Table 33 and shown shown graphically g r a p h i c a l l y in in Ass n noted F i g u r e 9d 9d show show significant s i g n i f i c a n t losses l o s s e s of of Mg. Mg. A o t e d before, b e f o r e , many of of the t h e analyses analyses Figure of host Mg, suggesting of ore ore h o s t rock show apparent a p p a r e n t increases i n c r e a s e s in i n Mg, s u g g e s t i n g that t h a t Mg, Mg, and and possibly possibly Fe, have migrated from the Fe, t h e talc—carbonate t a l c - c a r b o n a t e zones into i n t o the t h e ore o r e host h o s t rock. rock. In of rrelatively uncarbonatized sserpentinite from tthe Deer Lake Lake PPen— eriI n five f i v e samples of e l a t i v e l y uncarbonatized e r p e n t i n i t e from h e Deer dotite, i s certainly certainly d o t i t e , gold has h a s an average a v e r a g e abundance of of 2.8 2.8 ppb (range (range 1—4 1-4 ppb) which is However, these values not n o t greater g r e a t e r than t h a n abundances in i n other o t h e r types t y p e s of of igneous igneous rocks. r o c k s . However, these v alues not may n o t represent r e p r e s e n t the t h e initial i n i t i a l gold content c o n t e n t of of the t h e peridotite p e r i d o t i t e if i f substantial s u b s t a n t i a l gold gold were removed during d u r i n g serpentinization. s e r p e n t i n i z a t i o n . Gold values v a l u e s in i n carbonatized c a r b o n a t i z e d serpentinite serpentinite samples showed greater variation, with an average abundance of 3.4 3.4 ppb and a range samples showed g r e a t e r v a r i a t i o n , w i t h of 11 ppb. ppb. As A s shown shown in i n Figure F i g u r e 9e 9 e gold values v a l u e s increase i n c r e a s e significantly significantly from trace t r a c e to t o 11 most intensely iin n tthe h e most i n t e n s e l y altered a l t e r e d rocks r o c k s near n e a r the t h e ore o r e host h o s t rock r o c k contact. c o n t a c t . From the t h e data data available, a v a i l a b l e , it i t appears a p p e a r s that t h a t gold values v a l u e s increase i n c r e a s e with w i t h increasing i n c r e a s i n g alteration a l t e r a t i o n sugsuggesting being is b e i n g added, added, not n o t removed, removed, during d u r i n g talc—carbonate t a l c - c a r b o n a t e alteration alteration g e s t i n g that t h a t gold is of of the t h e Deer Lake Peridotite. Peridotite. Kerrich may pplay K e r r i c h and Fyfe Fyfe (1981) (1981) have have suggested suggested that t h a t ultramaf u l t r a m a f iic c rrocks o c k s may l a y an important role r o l e in i n localizing l o c a l i z i n g the t h e precipitation p r e c i p i t a t i o n of of gold gold from from hydrothermal hydrothermal solutions. s o l u t i o n s . They They propose that t h a t gold may be b e transported t r a n s p o r t e d as a s carbonyl c a r b o n y l or o r carbonate c a r b o n a t e complexes complexes in i n C02— C02rich r i c h hydrothermal hydrothermal fluids. f l u i d s . Subsequent ccarbonate a r b o n a t e forming reactions r e a c t i o n s involving i n v o l v i n g ultra— ultramafic rocks r o c k s may trigger t r i g g e r gold precipitation p r e c i p i t a t i o n by reducing r e d u c i n g the t h e partial p a r t i a l pressure p r e s s u r e of of C02 CO2 and/or a n d / o r decreasing d e c r e a s i n g acidity a c i d i t y (Kerrich ( K e r r i c h and and Fyfe, Fyfe, 1981). 1981). �65 RNRLYSES OF OFTALC TRLCCARBONATE CRRBONRTEROCKS ROCKS ANALYSES 1 1 S102 5102 RL203 AL203 FEO FEO MGO MGO CRO CO NR20 NA20 KZO K20 H20+ H20+ TI02 T102 P205 P205 C02 C02 46.21 46.21 1.65 1.65 7 .06 7.06 26.55 26.55 TOTRL TOTAL 98.45 98.45 CR MN NI Cu ZN 3 26.83 5.62 5.28 47.86 2.01 4.20 20 .55 4.59 4.78 22.78 7.25 14 5 6 7 8 9 10 42 .04 39.77 2.06 5.55 45.56 1.03 5.38 39.30 1.17 46 .12 52 .74 1.13 1.29 7.114 5.39 28 .39 4 .81 .05 .01 29 .01 5 .09 .04 .01 1.00 14.30 3.80 5.10 5.00 .05 .09 .0? .05 27 .63 8 .29 .05 .01 1.40 .04 .06 30 .63 .04 .01 25 .13 10 .67 .03 .01 .04 .06 .03 .05 .03 .05 .01 1.94 4.51 23.39 .05 .01 .06 .01 1.40 2.50 .14 .05 .13 .08 24 .01 11 .80 .03 .01 .80 .04 .07 3.96 18.11 8.68 11.35 13.147 9.79 13.47 8.25 4.11 99.33 99.19 99.51 99.27 101 .11 99.22 98.23 100 .22 100.41 8 14 14 1? 19 17 114 11 12 9 50 1558 56 1443 1829 1844 38 89 37 22 1029 1473 1899 20 36 30 37 66 1805 1799 21 1603 27 1255 1704 1736 59 1305 1358 2264 2303 1478 951 2466 2040 606 2816 19 30 25 42 28 146 1846 2494 28 56 35 54 29 80 6 2 2 1 11.98 .98 .04 .04 .o 1 .01 2.50 2.50 .07 .0? .02 .02 1 2.36 .36 12 ------------------- SC V 2 54 .32 1430 2901 2? 53 AU 19.02 9275 3723 1079 21 65 10 T a b l e 4. 4. Table 114 .85 < S e l e c t e d analyses a n a l y s e s of of talc—carbonate t a l c - c a r b o n a t e rocks r o c k s from from the t h e North North Selected a l t e r a t i o n zone. Samples a r e a r r a n g e d a c c o r d i n g t o i n c r e a s i n g disalteration zone. Samples are arranged according to increasing disO r e Host Host Rock Rock contact. c o n t a c t . Elements l i s t e d as o x i d e s i n t a n c e from from the t h e Ore tance Elements listed as oxides in wt. percent, p e r c e n t , other o t h e rin. i n ppm. ppm. wt. 1.1 .04 .01 �66 . Sample Sample1/9 10 10 9 9 88 7 7 66 55 4 4 33 2 2 1 1 +34.7, +34.7 +17.2 +17.2 Si Sl +23.9 +23.9 +10.5 +10.5 —1.9 -1.9 +16.8 +16.8 —3.4 -3.4 +11.3 +11.3 +21.6 +21.6 —30.0 -30.0 Al +28.8 +16.4 +25.0 +12.5 +111.5 +118.3 +118.3 +526.0 +386.5 +78.8 Fe* Fe* —37.0 -37.0 —43.8 -43.8 —22.4 -22.4 —39.9 -39.9 —41.4 -41.4 —48.1 -48.1 —53.4 -53.4 —40.1 -40.1 —48.4 -48.4 —22.0 -22.0 Mg —16.0 —18.9 —17.2 —17.3 —28.7 —27.7 —28.7 —37.4 —34.0 —21.4 Ca —4.9 +246.5 +241.6 +503.5 +636.6 +1017.6 +752.1 +311.3 +411.3 +43.0 H —20.1 —16.9 —35.5 —75.6 —29.0 —82.0 —86.2 —55..6 —76.4 —56.9 Ti +21.2 —9.1 +21.2 —9.1 +51.5 —27.3 0.0 +184.8 +203.0 +48.5 P —9.1 +81.8 +81.8 +172.7 +263.6 +609.1 +354.6 +545.4 +236.4 +45.4 C +89.3 +288.2 +585.5 +392.0 +542.0 +489.7 +332.8 +827.9 +92.8 +554.2 Mn —44.4 —16.7 +75.9 +75.9 +29.6 +71.3 +38.9 +275.0 +73.7 +38.0 Ni +27.4 +7.8 +17.6 +7.8 +2.9 —11.8 —6.9 —47.6 —.13.2 +39.2 Estimated mineral mineral modes modes Serp Serp 40% 40% 35% 35% 37% 37% —— -- 30% 30% -- --- -- -- -- Talc Talc 40% 40% 40% 40% 30% 30% 55% 55% 35% 35% 43% 43% 50% 50% 30% 30% 40% 40% 35% 35 % .Carb Carb 15% 15% 20% 20% 30% 30% 40% 40% 30% 50% 50% 40% 40% 60% 60Z 45% 45% 55% 55% Chl --- --- tr tr 1% 1% 3% 3% 6% 6% 9% 9% 7% 7% 8% 8% 2% 2% 5% 5% 5% 5% 4% 2% 2% 1% 3% 3% 3% 5% 5% Clii Opaques Opaque~ Qtz 3% 3% Table 5. 5. Calculated C a l c u l a t e d percent p e r c e n t losses l o s s e s and and gains g a i n s of of various v a r i o u s elements elements Table during 4. Cald u r i n g talc—carbonate t a l c - c a r b o n a t e alteration a l t e r a t i o n for f o r samples samples from frbm Table Table 4. culations c u l a t i o n s made assuming assuming volume remained remained constant c o n s t a n t during d u r i n g alteraalteration t i o n and the t h e initial i n i t i a l composition for f o r all a l l of of the t h e samples was that that sample 3, 3 , Table Table 3. 3 . Samples Samples arranged a r r a n g e d according a c c o r d i n g to t o decreasing decreasing of sample distance d i s t a n c e from from the t h e OHR OHR contact. contact. �67 25 25 20 20 a a z I. aa 15 In 9 I0 *0 U 0r 5 1 10 20 30 40 0 ¶0 0 So 40 DISTANCE IN DISTANCE IN FEET FEET 50 DISTANCE IN IN FEET DISTANCE FEET VARIASION IN IN C WITH WITH DISTANCE DISTANCE FROM THE ORE ORE HOST HOST ROCK ROCK CONIfrCT CONTACT VARIASION VARIATION IN IN CA VARIATION CA WITh WITH DISTANCE HOST ROCK ROCKCONTACT CONTACT DISTANCE FROM FROM ORE HOST 7 U UI U S UI 40 a 2 z In a a C 35 N 0 a 3 0 a z 2 , 10 20 30 40 20 So 1 DISTANCE FEET DISTANCE IN IN FEET VARIATIONOF OF Al. Al. WITH FROM ORE ORE HOST HOST ROCK VARIATION WITH DISTANCE DISTANCE FHOM ROCK CONIACI CONIACT , t 10 20 30 40 1 50 DISTANCE OISTANCE IN IN FEET FEET VARIATIONIN IN MG FROM THE VARIATION MG WIJH W11H DISTANCE DISTANCE FROM THE ORE ORE HOST HOST ROCK ROCK CONTACT CONTACT 12 40 9 a 2 U, 30 a 0 6 N I 2 l0 30 DISTANCE IN IN FEET FEET VARIATION VARIATIONIN IN AD AU WITH WITH DISTANCE DISTANCEFROM FROMTHE THEORE OREHOST HOSTROCK ROCKCONTACT CONTCr t 0 0 TO 10 20 30 40 50 50 DISTMCE FEET FROU FROMCONTACT CONTACT DISTANCE IN IN FEET VARIATION WITH DIS DISiANCE FROM ORE ORE HOST HOST ROCK ROCK CONTACT CONTACT VARIATIONOF OF H H WITH lANCE FROM Plots P l o t s showing changes in i n composition of of altered a l t e r e d ser— serFigure F i g u r e 9. 9. pentinites from Table 3 with distance from the ore host rock conconp e n t i n i t e s from Table 3 w i t h d i s t a n c e from t h e o r e h o s t rock tact t a c t (left ( l e f t axis). a x i s ) . Right Right axis a x i s represents r e p r e s e n t s composition composition of of the t h e asassumed parent p a r e n t rock rock (sample (sample 3, 3 , Table Table 3). 3)- I �68 d i s t r i b u t i o n of of talc—carbonate The wide distribution tal-c-carbonate rock rock in i n the t h e vicinity v i c i n i t y of of the t h e Ropes Ropes Mine Mine r e q u i r e d the t h e addition a d d i t i o n of of C02 C02 from from aa very very large l a r g e volume volume of of C02—rich C02-rich fluids f l u i d s to t o the the required a r e a . The The presence p r e s e n c e oof f sseveral e v e r a l ggenerations e n e r a t i o n s of r o s s - c u t t i n g ccarbonate arbonate v e i n s in in of ccross—cutting veins area. t h e talc—carbonate t a l c - c a r b o n a t e rock rock and and the t h e nearby nearby serpentine s e r p e n t i n e suggest s u g g e s t that t h a t this t h i s introduction introduction the of correlation of CO2 CO2 probably probably occurred o c c u r r e d over over aa protracted p r o t r a c t e d period p e r i o d of of time. time. The The c o r r e l a t i o n t h e distribution d i s t r i b u t i o n of of the t h e OHR OHR and and talc—carbonate t a l c - c a r b o n a t e rock rock suggest suggest that t h a t the t h e OHR OHR between the s e r v e d as a s aa channel—way channel-way to t o supply supply C02—rich C02-rich fluids f l u i d s to t o the t h e serpentinite. serpentinite. may have served i t may be be that t h a t the t h e disruption d i s r u p t i o n of of the t h e serpentinite, s e r p e n t i n i t e , by by the t h e emplaceemplaceConversely, it Conversely, of the t h e OHR, OHR, created c r e a t e d the t h e necessary n e c e s s a r y permeability p e r m e a b i l i t y to t o facilitate f a c i l i t a t e the t h e talc— talcment of c a r b o n a t e alteration. alteration. carbonate Evidence Evidence for f o r Shearing Shearing in i n the t h e Deer Deer Lake Lake Peridotite Peridotite If i s an alpine—type, a l p i n e - t y p e , tectonically t e c t o n i c a l l y intruded i n t r u d e d mass, mass, there there I f the t h e Deer Lake Peridotite P e r i d o t i t e is b e evidence evidence for f o r considerable c o n s i d e r a b l e deformation deformation within w i t h i n and and around around the t h e body. body. This This should be i s reviewed in i n the t h e paragraphs p a r a g r a p h s that t h a t follow. follow. is The The Deer Lake Lake Peridotite P e r i d o t i t e has h a s undergone undergone considerable c o n s i d e r a b l e shearing s h e a r i n g in i n the t h e vicinity v i c i n i t y of of c l e a r e s t evidence evidence is i s exposed exposed along along the t h e ore o r e host h o s t rock rock and and probably probably elsewhere. elsewhere. The clearest the OHR intercepts i n t e r c e p t s the t h e outcropping outcropping t h e shore s h o r e of of Deer Lake where the t h e surface s u r f a c e trend t r e n d of of the t h e OHR serpentinites. ORH trend, t r e n d , in i n aa zone zone some some 200 200 feet f e e t wide, wide, the t h e serpentinites serpentinites s e r p e n t i n i t e s . Along Along the t h e ORH B y locally l o c a l l y with w i t h aa strong s t r o n g foliation. f o l i a t i o n . As A s noted noted earlier, e a r l i e r , such such recrystalrecrystala r e Type Type B, exposed are lized s e r p e n t i n i t e textures t e x t u r e s can can be b e correlated c o r r e l a t e d with w i t h shearing s h e a r i n g (Wicks (Wicks and and Whittaker, Whittaker, l i z e d serpentinite A t Deer Deer Lake Lake the t h e Type Type BB serpentinite s e r p e n t i n i t e has h a s been been dolomitized, d o l o m i t i z e d , altering a l t e r i n g the t h e color color 1977). At 1977). from from medium medium green green to t o aa yellowish y e l l o w i s h white w h i t e . Such dolomitization d o l o m i t i z a t i o n also a l s o suggests s u g g e s t s that t h a t the the zone had had enhanced enhanced permeability. p e r m e a b i l i t y . The The serpentinite s e r p e n t i n i t e outcrops o u t c r o p s to t o the t h e north n o r t h and and south south zone of of the t h e shear s h e a r zone zone are a r e prodominantly prodominantly Type Type A A serpentinite, s e r p e n t i n i t e , with w i t h abundant, abundant, closely closely spaced fractures, f r a c t u r e s , as a s well w e l l as a s aa number number of of picrolite p i c r o l i t e and and cross c r o s s fiber f i b e r serpentine s e r p e n t i n e veins, veins, f e a t u r e s also a l s o suggest s u g g e s t deformation deformation for for p a r t i a l l y replaced r e p l a c e d by by carbonate. c a r b o n a t e . These features now partially t h e production p r o d u c t i o n of of the t h e openings openings (Jahns, (Jahns, 1967). 1967). the To the t h e immediate immediate south s o u t h of of the t h e shear s h e a r zone, zone, outcrops o u t c r o p s show show elongate e l o n g a t e pods, pods, resembling resembling pillows, s e r p e n t i n i t e , ranging r a n g i n g in i n size s i z e from from several several of relatively r e l a t i v e l y unveined Type A serpentinite, p i l l o w s , of inches i n c h e s nnear e a r the t h e shear s h e a r zone contact, c o n t a c t , to t o several s e v e r a l feet f e e t further f u r t h e r away from the t h e contact. contact. The pattern i s formed formed by prominent, prominent, anastomosing, anastomosing, 22 to t o 55 cm cm wide ribbons r i b b o n s of of closely closely p a t t e r n is spaced sets of 1 to 2 mm, subparallel veins of cross—fiber serpentine outlining mm, s u b p a r a l l e l v e i n s of c r o s s - f i b e r s e r p e n t i n e o u t l i n i n g the the s e t s of 1 t o Morgan and (1980) notea n o t e a resemblance resemblance in i n shape shape between these these and DeCristoforo (1980) pods. structures pillows s t r u c t u r e s and lava lava p i l l o w s and suggest s u g g e s t that t h a t they t h e y may be evidence for f o r an extrusive extrusive However, they differ from pillows origin o r i g i n for f o r the t h e Deer Deer Lake Lake Peridotite. P e r i d o t i t e . However, they d i f f e r from p i l l o w s in i n their their lack l a c k of of asymetrical a s y m e t r i c a l top t o p indicators: i n d i c a t o r s : rounded rounded tops t o p s and and cuspate c u s p a t e bases. b a s e s . By contrast, contrast, the noted t h e authors a u t h o r s have n o t e d similarities s i m i l a r i t i e s between these t h e s e structures s t r u c t u r e s and shear s h e a r polyhedra described d e s c r i b e d by Jahns Jahns (1967) (1967) in i n alpine a l p i n e type t y p e ultramafics u l t r a m a f i c s in i n Vermont Vermont (Figure ( F i g u r e 10). 10). Jahns J a h n s describes d e s c r i b e s shear s h e a r polyhedra as a s pillow—like p i l l o w - l i k e masses of of less l e s s broken broken or o r sheared sheared serpentinite s e r p e n t i n i t e in i n aa matrix m a t r i x of of highly h i g h l y sheared sheared serpeninite. s e r p e n i n i t e . Shear polyhedra form form along the margins of intensely sheared serpentinite along the of i n t e n s e l y sheared s e r p e n t i n i t e and and progressively p r o g r e s s i v e l y increase i n c r e a s e in in size s i z e away from from the t h e shear s h e a r zone zone (Jahns, (Jahns, 1967). 1967). However, However, the t h e shear s h e a r polyhedra polyhedra described described by Jahns J a h n s do do not n o t contain c o n t a i n the t h e cross c r o s s fiber f i b e r serpentine s e r p e n t i n e veins v e i n s that t h a t are a r e prominent prominent at a t Deer Deer Lake. Evidence for f o r shearing s h e a r i n g in i n the t h e talc—carbonate t a l c - c a r b o n a t e zones surrounding s u r r o u n d i n g the t h e OHR, OHR, from from underunder1) local development of contorted ground openings openings and and drill d r i l l cores, c o r e s , include: include: 1 ) l o c a l of c o n t o r t e d foliafoliations with t i o n s in i n intensely i n t e n s e l y altered a l t e r e d talc—carbonate t a l c - c a r b o n a t e zones along along w i t h obliteration o b l i t e r a t i o n of of relict relict serpentinite s e r p e n t i n i t e features; f e a t u r e s ; 2) 2) intense i n t e n s e boundinaging of of chlorite c h l o r i t e schist s c h i s t layers, l a y e r s , thought thought to t o represent r e p r e s e n t mafic dikes, d i k e s , in i n the t h e talc—carbonate t a l c - c a r b o n a t e zone; zone; 3) 3) abundance of of fracture fracture filling both f i l l i n g carbonate c a r b o n a t e in in b o t h the t h e talc—carbonate t a l c - c a r b o n a t e zones zones and the t h e serpentinites; s e r p e n t i n i t e s ; and 4) 4) boudinage of quartz veins. boudinage of q u a r t z v e i n s . �69 Country rocks Marginal zone of intensely sheared ser~entinite Intermediate zone of shear polyhedrons Core of irregularly broken and sheared serpentinite diagram Idealized d i a g r a m showing shear s h e a r zones z o n e s around a Figure F i g u r e 10. 10. Idealized serpentinite s e r p e n t i n i t e body, body, Roxbury Dist., D i s t . , Vermont Vermont (Jahns, ( J a h n s , 1967). 1967). �70 There is i s much evidence e v i d e n c e for f o r deformation within w i t h i n the t h e Deer Lake Peridotite, P e r i d o t i t e , as a s one i s an a p p a r e n t lack lack would expect expect for f o r an a n alpine—type a l p i n e - t y p e intrusion. intrusion. S i m i l a r l y , t h e r e Similarly, there is apparent of of contact c o n t a c t metamorphic effects e f f e c t s by the t h e Deer Lake Peridotite P e r i d o t i t e on the t h e ore o r e host h o s t rock rock and tthe Kitchi he K i t c h i Schist S c h i s t as a s one one would expect e x p e c t from from an a n intruded i n t r u d e d hot h o t body. body. F inally, Finally, tthe h e OHR in i n the t h e Deer Deer Lake Lake Peridotite P e r i d o t i t e shows, shows aa close c l o s e analogy a n a l o g yto t o tthe h e septum of of country country rock in rock i n the t h e alpine—type a l p i n e - t y p e ultramafic u l t r a m a f i c body body in i n Ludlow Ludlow Township, Township, Vermont Vermont (Gregg, (Gregg, 1975). 1975). Thus, writers Thus, for f o r these t h e s e reaons r e a o n s the the w r i t e r s favor f a v o r the t h e alpine—type a l p i n e - t y p e peridotite p e r i d o t i t e model. model. Conclusions Conclusions 1. 1. The ore o r e host host intermediate intermediate 2. 2. The available a v a i l a b l e information i n f o r m a t i o n suggests s u g g e s t s that t h a t the t h e Deer Lake Peridotite, P e r i d o t i t e , surrounding surrounding rock, was was o originally pluton, it tthe h e oore r e hhost o s t rock, r i g i n a l l y aa hharzburgite—lherzolite arzburgite-lherzolite p l u t o n , and that t h a t it was probably tectonically t e c t o n i c a l l y emplaced into i n t o the t h e Kitchi K i t c h i Schists S c h i s t s as a s aa solid. solid. 33.. The juxtaposition j u x t a p o s i t i o n of of the t h e Deer Lake Peridotite P e r i d o t i t e and the t h e ore o r e host h o s t rock rock is i s at at part lleast e a s t in in p a r t the t h e result r e s u l t of of tectonism. t e c t o n i s m . This T h i s tectonism t e c t o n i s m may or o r may not n o t have occurred o c c u r r e d concurrently c o n c u r r e n t l y with w i t h the t h e tectonic t e c t o n i c emplacement of of the t h e Deer Lake Peridotite. Peridotite. 4. The substantial s u b s t a n t i a l talc—carbonate t a l c - c a r b o n a t e alteration a l t e r a t i o n of of serpentinite s e r p e n t i n i t e and and portions p o r t i o n s of of the the OHR required r e q u i r e d the t h e introduction i n t r o d u c t i o n of of large l a r g e quantities q u a n t i t i e s of of CO2 CO2 into i n t o these t h e s e rocks. rocks. 5. The extent e x t e n t of of bution b u t i o n of of the the 6. The gold gold content c o n t e n t of of the t h e serpentinites s e r p e n t i n i t e s of of the t h e Deer Lake Peridotite P e r i d o t i t e (1—4 (1-4 ppb) ppb) is higher i s nnot ot h i g h e r than t h a n typical t y p i c a l crustal c r u s t a l material. material. 7 points l i t t l e or o r no loss l o s s of of gold from from The eexisting x i s t i n g eevidence vidence p o i n t s to t o there t h e r e bbeing e i n g little serpentinites s e r p e n t i n i t e s during d u r i n g talc—carbonate t a l c - c a r b o n a t e alteration alteration. 8. of gold mineralization body: aa h higher Two ttypes y p e s of gold m i n e r a l i z a t i o n aare r e found in i n the t h e Ropes ore o r e body: igher grade v vein mineralization mineralization. ein m i n e r a l i z a t i o n and aa lower lower grade g r a d e disseminated disseminated m ineralization. 9. possible of o origin mineralization: There aare r e several several p o s s i b l e modes of r i g i n for f o r the t h e gold m ineralization: 1. A) 1. 2. 2. B) 1. B) 1. 2. 2. rock r o c k at a t the t h e Ropes Gold Mine probably consists c o n s i s t s primarily p r i m a r i l y of of to felsic volcanic rock t o f e l s i c volcanic rock. talc—carbonate i s , in i n part, p a r t , controlled c o n t r o l l e d by the t h e distridistrit a l c - c a r b o n a t e alteration a l t e r a t i o n is, OHR. OHR. disseminated The d i s s e m i n a t e d gold g o l d ore o r e may represent r e p r e s e n t an a n early e a r l y syngenetic syngenetic deposition, with OHR, prior prior d e p o s i t i o n , aassociated ssociated w i t h the t h e formation f o r m a t i o n of of the t h e OHR, to t o its i t s emplacement within w i t h i n the t h e Deer Deer Lake Lake Peridotite. Peridotite. high—grade vein The high-grade v e i n ore o r e may represent r e p r e s e n t aa remobilized r e m o b i l i z e d facies, facies, derived disseminated ore, d e r i v e d from the t h e early early d isseminated o r e , and deposited d e p o s i t e d in in sites prepared s i t e s that t h a t were structurally structurally p r e p a r e d during d u r i n g emplacement of of the OHR. t h e OHR. high—grade v vein—type ore be with mineralizing The high-grade ein-type o r e may b e epigenetic, epigenetic, w ith m ineralizing fluids a n outside o u t s i d e source, s o u r c e , and the the f l u i d s introduced i n t r o d u c e d into i n t o the t h e OHR from an gold deposited d e p o s i t e d in i n structures s t r u c t u r e s formed during d u r i n g emplacement of of the t h e OHR i n t o the t h e Deer Lake Lake Peridotite. Peridotite. into The disseminated d i s s e m i n a t e d ore o r e represents r e p r e s e n t s aa halo h a l o around around the t h ehigh, h i g h grade grade v e i n s introduced i n t r o d u c e d from from the t h e same same outside o u t s i d e source. source. veins . �71 C) C) The The disseminated disseminated and and vein—type vein-type ores o r e s were were formed formed independently independently of of each each other. other. D) D) Gold complex inaCO2—rich Gold was was transported t r a n s p o r t e d as a s aa carbonyl c a r b o n y l or o r carbonate c a r b o n a t e complex inaC02-rich fluid OHR. Subsequent Subsequent f l u i d from from some some outside o u t s i d e source, s o u r c e , and and introduced i n t r o d u c e d into i n t o the t h e OHR. carbonate—forming carbonate-forming reactions r e a c t i o n s in i n the t h e ultramafic u l t r a m a f i c rock r o c k surrounding s u r r o u n d i n g the t h e OHR OHR caused caused the t h e deposition d e p o s i t i o n of of gold gold in i n structures s t r u c t u r e s formed formed in i n the t h e OHR OHR during d u r i n g its its emplacement emplacement into i n t o the t h e peridotite. peridotite. ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS CallahanMining Mining Corporation Corporation for f o r making making available available The authors a u t h o r s would would like l i k e to t othank thankCallahan The some of of the t h e maps, maps, cross—sections, c r o s s - s e c t i o n s , and and rreports e p o r t s used used in i n the t h e preparation p r e p a r a t i o n of of this t h i s paper. paper. some They They would like l i k e to t o thank thank also a l s o Resource Resource Exploration, E x p l o r a t i o n , Inc., I n c . , in i n particular p a r t i c u l a r Grant Grant Tonkin Tonkin and Joe J o e Strapko, S t r a p k o , for f o r their t h e i r invaluable i n v a l u a b l e help. help. and This T h i s papers p a p e r s incorporates i n c o r p o r a t e s portions p o r t i o n s of of aa thesis t h e s i s in i n preparation by by Dean Dean Rossell, R o s s e l l , funded funded in by aa DMMMFC DMMMFC Fellowship Fellowship from fromHEW. HEW. i n part p a r t by the t h e Callahan Callahan Mining Mining Corporation Corporation and and by Thus D r s . T. T. Bornhorst Bornhorst and and William William Rose Rose for for Thus the t h e senior s e n i o r author a u t h o r would would like l i k e to t o thank thank Drs. help D r . W. W. Gregg Gregg for f o r assistance a s s i s t a n c e with w i t h photomicrographs. photomicrographs. Both Both h e l p along a l o n g the t h e way, way, and and Dr. of of us u s appreciate a p p r e c i a t e the t h e efforts e f f o r t s of of Karen Karen Rossell R o s s e l l and and Julene J u l e n e Erickson Erickson in i n getting g e t t i n g this this manuscript manuscript ready ready by by aa deadline. deadline. �72 REFERENCES REFERENCES Anhaeusser, C. W. S., Anhaeusser, C . R., R . , Fritze, F r i t z e , K., K . , Fyfe, F y f e , W. S., and Gill, Gill, Chemical mitive" Archean volcanics: mitive" volcanics: Chemical Geology, Geology, v. v. R. 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I., I., 1972, 1972, Distribution D i s t r i b u t i o n of of gold g o l d in in igneous i g n e o u s rocks: r o c k s : U.S. U.S. Geol. Geol. Survey Survey Prof. P r o f . Paper P a p e r 727, 727, 42 42 p. p. �73 Gregg, Gregg, W. W. J., J . , 1975, 1975, Structural S t r u c t u r a l studies s t u d i e s in i n the t h e Moretown and and Cram Hill H i l l units units near n e a r Ludlow, Ludlow, Vermont: Vermont: Unpublished Unpublished M.S. M.S. thesis, t h e s i s , State S t a t e Univ. Univ. New New York, York, Albany, p. Albany, 77 77 p. in Jahns, J a h n s , R. R. H., H . , 1967, 1967, Serpentinites S e r p e n t i n i t e s of of the t h e Roxbury Roxbury District, D i s t r i c t , Vermont, Vermont, in Wyllie, Wyllie, P. P . J., J . , ed., e d . , Ultramafic U l t r a m a f i c and and Related R e l a t e d Rocks: Rocks: Wiley Wiley and and Sons, Sons, Inc., I n c . , New New York, York, p. 137—160. 137-160. p. 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F., F., 1977, 1977, The The YelYellow Dog P Peridotite buried e r i d o t i t e and a possible possible b u r i e d igneous i g n e o u s complex of of Lower Kewee— Keweenawan nawan age a g e in i n the t h e Northern N o r t h e r n Peninsula P e n i n s u l a of o f Michigan: Michigan: U.S. U.S. Geol. Geol. Survey, Survey, O p e n - f i l e Report Report 77—93, 77-93, 65 65 p. p. Open—file Lewan, M. D., D . , 1972, 1972, Metasomatism Metasomatism and and weathering w e a t h e r i n g of o f the t h e Presque P r e s q u e Isle I s l e serpentin— serpentinLewan, M. Michigan Tech. Tech. Univ., Univ., Houghton, Houghton, ized i z e d peridotite, p e r i d o t i t e , Marquette, M a r q u e t t e , Michigan: Michigan: Michigan unpubl. unpubl. M.S. M.S. thesis, t h e s i s , 55 5 5 p. p. Moody, J. J. B., B . , 1976, 1976, Serpentinization: S e r p e n t i n i z a t i o n : aa review: review: Lithos, L i t h o s , v. v . 9, 9 , p. p. 125—138. 125-138. Morgan, Morgan, P.J., P . J . , and and DeCristoforo, D e C r i s t o f o r o , D. D. T., T., 1980, 1980, Geologic G e o l o g i c evolution e v o l u t i o n of of the t h e Ish— Ishpeming 11, p. p . 23—41. 23-41. peming Greenstone Greenstone Belt: B e l t : Precambrian Precambrian Research, R e s e a r c h , v. v. 11, Morris, M o r r i s , W. W. J., J . , and and Wilband, Wilband, J. J. T., T., 1977, 1977, Geochemistry Geochemistry of of the t h e Yellow Yellow Dog Dog plains plains 23 Inst. peridotite, p e r i d o t i t e , Marquette M a r q u e t t e County, County, Michigan Michigan (abst.): (abst.): I n s t . Lake Superior Superior Geology, Geology, Proceedings, P r o c e e d i n g s , Thunder Thunder Bay, Bay, Ontario, O n t a r i o , p. p. 35. 35. Naldrett, J . , 1966, 1956, Talc—carbonate T a l c - c a r b o n a t e alteration a l t e r a t i o n of o f some some serpentinized s e r p e n t i n i z e d ultra— ultraN a l d r e t t , A. A. 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M., M., 1983, 1983, Alteration A l t e r a t i o n of of the t h e Deer Lake Peridotite P e r i d o t i t e in i n the t h e vicinity vicinity of the t h e Ropes Ropes Gold Gold Mine, Mine, Marquette M a r q u e t t e County, County, Michigan: Michigan: M.S. M.S. thesis t h e s i s in in preparation, p r e p a r a t i o n , Michigan Michigan Tech. Tech. Univ. Univ. Sager, R., Meyer, Meyer, M., M., and Muff, Muff, R., R., 1982, 1982, Gold distribution d i s t r i b u t i o n in i n supracrustal supracrustal S a g e r , R., rocks Africa r o c k s from Archean greenstone g r e e n s t o n e bbelts e l t s of o f Southern Southern A f r i c a and from from Paleozoic Paleozoic ultramafic Alps: M Metallogenic u l t r a m a f i c complexes complexes of of the t h e European Alps: e t a l l o g e n i c and geochemical implications: i m p l i c a t i o n s : Econ. Econ. Geol., Geol., v. v. 77, 77, p. p. 1—24. 1-24. Sims, mineral Sims, P. P. K., K . , 1976, 1976, Precambrian tectonics t e c t o n i c s and m i n e r a l deposits, d e p o s i t s , Lake Superior Superior region: r e g i o n : Econ. Econ. Geol., Geol., v. v. 71, 71, p. p. 1092—1127. 1092-1127. Skillings S k i l l i n g s Mining Review, Review, 1981, 1981, Callahan C a l l a h a n nearing n e a r i n g decision d e c i s i o n on on major m a j o r project p r o j e c t for for Ropes 16. Ropes Mine: Mine: v. v. 70, 70, no. no. 39, 39, p. p. 16. Van Hise, H i s e , C. C. R., R., and Leith, L e i t h , C. C. K., K., 1911, The geology geology of o f the t h e Lake Superior S u p e r i o r region: region: U.S. U.S. Geol. Geol. Survey Survey Monograph Monograph 52, 5 2 , 641 6 4 1 p. p. - Wicks, F. F. J., J . , and Whittaker, W h i t t a k e r , E. E. J., J., 1977, 1977, Serpentine S e r p e n t i n e textures t e x t u r e s and and serpentinization: serpentinization: Canadian M Mineral., i n e r a l . , v. v. 15, 1 5 , p. p. 459—488. 459-488. �75 FIELD TRIP LOG ROPES GOLD MINE AND THE MICHIGAN GOLD MINE J. Kalliokoski Dean Rossell and J. �76 Log, Ropes Gold Gold Mine and and the t h e Michigan Gold Gold Mine Mine Road Log, Dean Rossell R o s s e l l and and J. J . Kalliokoski Kalliokoski Dean i s designed designed as a s aa one—day one-day excursion e x c u r s i o n to t o examine examine the t h e geological g e o l o g i c a l setting setting T h i s field f i e l d trip t r i p is This of the t h e Ropes Ropes and and Michigan Michigan gold gold mines. mines. The The trip t r i p involves i n v o l v e s five f i v e stops s t o p s (Fig. (Fig. 1), I ) , most most of on access.1 on private p r i v a t e property. p r o p e r t y . Please P l e a s e use u s e discretion d i s c r e t i o n in i n gaining g a i n i n g access.1 Proceed east e a s t from from Houghton to t o the t h e junction j u n c t i o n with w i t h County County Road Road 573 573 (traffic ( t r a f f i c light, light, Ishpeming). Turn left Ishpeming). l e f t and and continue c o n t i n u e around around Deer Deer Lake Lake for f o r 3.6 3.6 miles m i l e s (0.7 (0.7 miles m i l e s past past t h e Carp Carp Lake Lake intersection) i n t e r s e c t i o n ) to t o aa gravel g r a v e l side s i d e road road on on the t h e left. l e f t . Turn left, l e f t , continue continue the 650 650 feet. f e e t . Proceed on on foot f o o t 100 100 feet f e e t north n o r t h of of road road to t o aa pit p i t at a t base b a s e of of the t h e hill. hill. Stop 11—- Discovery Discovery Pit P i t (Fig. (Fig. ib) lb) Stop At A t this t h i s pit p i t Julius J u l i u s Ropes made made the t h e initial i n i t i a l discovery d i s c o v e r y of of the t h e Ropes Ropes Gold Gold Mine. Mine. Analyses of three t h r e e samples samples between the t h e pit p i t and and the t h e peridotite p e r i d o t i t e contact, c o n t a c t , uphill uphill the p i t suggest s u g g e s t the t h e ore o r e host h o s t rock to t o be b e an intermediate i n t e r m e d i a t e volcanic v o l c a n i c (Fig. (Fig. 2). 2). from the pit The contact i s exposed exposed c o n t a c t with w i t h the t h e strongly s t r o n g l y carbonatized c a r b o n a t i z e d Deer Deer Lake Lake Peridotite P e r i d o t i t e (DPL) (DPL) is a l o n g the t h e north n o r t h edge edge of of the t h e outcrop. o u t c r o p . This T h i s locality l o c a l i t y marks marks the t h e known known eastern e a s t e r n extent extent along of of the t h e ore o r e host h o s t rock rock septum, septum, the t h e host h o s t to t o gold gold mineralization. mineralization. In i n the t h e pit p i t is i s a quartz—chlorite—sericite q u a r t z - c h l o r i t e - s e r i c i t e schist s c h i s t with w i t h abunabunI n thin t h i n section s e c t i o n the t h e OHR in dant nun grains g r a i n s of of quartz. q u a r t z . To To the t h e north, n o r t h , six s i x feet f e e t south s o u t h of of the t h e contact contact d a n t 0.1 0 . 1 to t o 0.3 0 . 3 mm with w i t h the t h e talc—carbonate—altered t a l c - c a r b o n a t e - a l t e r e d peridotite, p e r i d o t i t e , the t h e rock r o c k displays d i s p l a y s in i n thin t h i n section s e c t i o n aa micro—breccia of darker quartzmicro-breccia texture t e x t u r e consisting c o n s i s t i n g oof f ssharply h a r p l y aangular n g u l a r fragments of d a r k e r quartz— nun quartz q u a r t z grains. g r a i n s . At A t the t h e talc—carbonate talc-carbonate s e r i c i t e matrix. m a t r i x . There There are a r e also a l s o aa few few 11mm sericite contact i s highly h i g h l y fractured, f r a c t u r e d , and sporadically s p o r a d i c a l l y replaced replaced c o n t a c t the t h e quartz—sericite q u a r t z - s e r i c i t e schist s c h i s t is by coarser c o a r s e r grained g r a i n e d sericite s e r i c i t e and and by younger younger veinlets v e i n l e t s of of chlorite c h l o r i t e and and carbonate. carbonate. OutReturn to t o the t h e gravel g r a v e l road road and and proceed proceed 450 450 feet f e e t west west to t o the t h e fork f o r k in i n the t h e road. r o a d . OutThis is also the T h i s i s a l s o t h e crops to the south are relatively uncarbonatized serpentinite. c r o p s t o t h e s o u t h a r e r e l a t i v e l y uncarbonatized s e r p e n t i n i t e . Continue 1200 feet along Continue 1200 f e e t a long approximate projection of the east end of the 15th level. approximate p r o j e c t i o n of t h e e a s t end of t h e 1 5 t h l e v e l . Reddish weathered outcrops along the road are the left fork to the shaft house. t h e l e f t f o r k t o t h e s h a f t house. Reddish weathered o u t c r o p s a l o n g t h e road a r e strongly s t r o n g l y carbonatized c a r b o n a t i z e d DLP DLP from from the t h e southern s o u t h e r n altered a l t e r e d zone. zone. S h a f t House House (Fig. (Fig. lb) lb) Stop 22 —- Shaft Stop The b buildings u i l d i n g s have been constructed c o n s t r u c t e d since s i n c e 1979 1979 as a s part p a r t of of the t h e Callahan Callahan Mining Mining Corp. Corp. frame is over the Curry The head i s t h e Curry shaft, shaft, The head on—going on-going exploration e x p l o r a t i o n at a t the t h e Ropes Ropes Mine. Mine. T h i s stop s t o p provides p r o v i d e s an an opporopporthe t h e principal p r i n c i p a l production p r o d u c t i o n shaft s h a f t from from the t h e late l a t e 1800's. 1800's. This s e c t i o n s. tunity to examine drill core, hand samples, and mine plans and cross sections. and p l a n s and c r o s s t u n i t y t o examine d r i l l c o r e , samples, g r a v e l road road follows follows Proceed on foot f o o t about 1200 1200 feet f e e t west past p a s t the t h e shaft s h a f t house. house. The gravel the contact of the ore host rock and the southern alteration zone of the Deer Lake t h e c o n t a c t of t h e o r e h o s t r o c k t h e s o u t h e r n a l t e r a t i o n zone of t h e Lake The road then turns south Peridotite K i t c h i Schist. S c h i s t . The road t h e n t u r n s s o u t h P e r i d o t i t e out o u t to t o the t h e contact c o n t a c t with w i t h the t h e Kitchi and follows Kitchi ( n o r t h ) and and the t h e DLP DLP (south). (south). i t c h i Schist S c h i s t (north) f o l l o w s the t h e contact c o n t a c t of of tthe he K he 1The Organizing Committee for f o r this t h i s 1983 1983 Field F i e l d Trip T r i p is i s appreciative a p p r e c i a t i v e of of the t h e permission permission given by D Dr. A.. Bouley, r . Bruce A Bouley, Chief Chief Geologist, G e o l o g i s t , Callahan Mining Corporation C o r p o r a t i o n to t o visit visit �______ ____ 77 R28W :} •_ I 27W -i••'--.._ .:::::)crv '"./A1 r. i'7 r< LN L lichigan Mine \I Proterozoic t 1- 0 Feet 4000 (Cannon and Klasner, 1975; Clark and others,1975) ' LA Marquette Range RangeSupergroup Supergroup Archean L T1 - Granite Granite IEIIIJ . pxa I-.> Deer Lake Peridotite Peridotite '5 '5 trip stops Field trip stops Age relations uncertain Age uncertain Kitchi Schist Schist Agglomerate GEOLOGY GEOLOGY OF THE AREAAROUND AREA.AROUND THE ROPES ROPES AND AND MICHIGAN MICHIGAN GOLD GOLD MINES MINES Intermed. to tels. volcs. Amphiboifte Deer Lake; ib, F i g u r e la, l a , Access to t o Deer l b , geology between Deer Lake Figure r,,1 e ?h-crn v i ~ h i oMfrip = nM i n ~ . tit h M �78 5 6 7 S102 s102 AL203 flL2 0 3 FE203 FE203 FEO FEO MG0 t4GO CR0 CRO NR2O NR20 (200 K2 1102 TI02 P205 P205 MNO MNO C02 c02 '48.39 15.07 10.28 .00 18.57 .60 50.05 15.68 8.27 '49.57 17.85 .18 .19 3.01 3.55 1.01 .08 .05 .00 TOTAL 95.24 SC 19 CR 131 171 NI 255 V Cu 10 ZN RB 119 68 SR 19 7.67 .00 .00 114.33 11.67 1.23 .98 .07 .05 .00 .35 .20 '4.54 .77 .17 .03 .00 94.40 92.82 20 124 175 191 < 10 95 79 26 13 94 48 178 < 10 138 114 20 Y 16 18 18 ZR NB 96 101 17 LA 17 15 129 21 12 12 CE 56 53 '42 Figure Figure 2. 2. Chemical analyses of the the ore host rock rock (by (by Bornhorst and and Rose, Rosey 1983). 1983)- Analyses Analyses in in wt. wt. percent. with talc—carbonate talc-carbonate rock; rock; percent. No. 5, 5 y contact contact with b), feet south south of of contact; contact; 7, 7 y discovery discovery pit. pit. b), 66 feet �Verde Antique Antique Quarry Quarry (Fig. ( F i g . ib) lb) Stop 33 —- Verde 79 The Deer Deer Lake Lake Peridotite P e r i d o t i t e is i s altered a l t e r e d extensively e x t e n s i v e l y to t o carbonate c a r b o n a t e and and talc t a l c along a l o n g the t h e Kitchi Kitchi The S c h i s t contact. c o n t a c t . In I n the t h e quarry q u a r r y the t h e serpentinite s e r p e n t i n i t e was was mined mined around around the t h e turn t u r n of of the t h e cencenSchist ttury u r y for f o r dimension dimension stone s t o n e ("verde ("verde antique" a n t i q u e " or o r "serpentine " s e r p e n t i n e marble"). marblet'). The contact c o n t a c t runs runs s l i g h t l y north n o r t h of of the t h e road. road. Thus, Thusy the t h e front f r o n t part p a r t of of the t h e pit p i t (now (now largely l a r g e l y removed) removed) slightly r o c k y but b u t some some remains remains on on the t h e west west side s i d e of of the t h e pit. pit. was primarily p r i m a r i l y talc—carbonate t a l c - c a r b o n a t e rock, was T h i s rock rock grades g r a d e s into i n t o moderately moderately carbonatized c a r b o n a t i z e d serpentinite, s e r p e n t i n i t e y now now exposed exposed along a l o n g the the This s o u t h and east e a s t sides s i d e s of of the south t h e quarry. q u a r r y . Carbonate Carbonate veins v e i n s are a r e abundant abundant in i n the t h e serpentinite, ~erpentinite~ w i t h as a s many many as a s four f o u r generations g e n e r a t i o n s seen seen in i n some some blocks. b l o c k s . Early with E a r l y veins v e i n s are a r e typically t y p i c a l l y carcarb o n a t e replacing r e p l a c i n g cross—fiber c r o s s - f i b e r serpentine s e r p e n t i n e and and picrolite. p i c r o l i t e . Younger veinlets bonate v e i n l e t s are a r e generally generally c o a r s e grained g r a i n e d carbonate c a r b o n a t e with w i t h no no pseudomorphic pseudomorphic textures. textures. coarse back to t o the t h e shaft s h a f t house, housey and and back back to t o intersection i n t e r s e c t i o n with w i t h CO C0573. Turn left l e f t and and Proceed back 573. Turn 1000 feet f e e t to t o where the t h e road road crosses c r o s s e s an an arm arm of of Deer Deer Lake. Lake. Be proceed 1000 Be careful; c a r e f u l ; the the road is i s narrow narrow and and traffic t r a f f i c can can be b e heavy. heavy. road S e r p e n t i n i t e along a l o n g Deer Deer Lake Lake (Fig. (Fig. 3) 3) Stop 44 —- Serpentinite Stop Outcrops along a l o n g the t h e shore s h o r e of of Deer Deer Lake Lake show show the t h e two two main main serpentine s e r p e n t i n e textural t e x t u r a l types types Outcrops d e s c r i b e d in i n the t h e text. t e x t . Samples Samples from from Outcrop Outcrop A A (Fig. (Fig. 3) 3) show show well—developed well-developed 1—5 1-5 mm mm described serpentine s e r p e n t i n e pseudomorphs after a f t e r olivine o l i v i n e and and aa probable p r o b a b l e cumulate cumulate texture. t e x t u r e . The serpen— serpent i n i t e is i s designated d e s i g n a t e d as a s "Type "Type A" A'' in i n the t h e text, t e x t y and and is i s the tinite t h e most most common common variety v a r i e t y on on o u t c r o p s of of DL?. DLP. outcrops At and lighter l i g h t e r in i n color c o l o r than than A t Outcrop Outcrop BB the t h e serpentinite s e r p e n t i n i t e is i s "Type—B", " T Y P ~ - B "finer—grained ~f i n e r - g r a i n e d and "Type—A", i s commonly commonly strongly s t r o n g l y foliated. f o l i a t e d . In In " T Y P ~ - A " shows ~shows no relect r e l e c t igneous igneous textures, t e x t u r e s y and and is the i s evidence e v i d e n c e of of shearing s h e a r i n g along a l o n g the t h e contacts c o n t a c t s between between the t h e ore o r e host h o s t rock rock t h e mine there t h e r e is and the t h e talc—carbonate t a l c - c a r b o n a t e zones. zones. Further, F u r t h e r y the t h e ore o r e host h o s t rock r o c k appears a p p e a r s to t o pinch pinch out o u t west west CO 573. 573. Thus, Thusy this t h i s zone zone of of non—pseudomorphic non-pseudomorphic serpentinite s e r p e n t i n i t e ("Type—B") ("Type-B1') may may reprerepreof CO sent s e n t the t h e extension e x t e n s i o n of of the t h e shear s h e a r zone zone beyond the t h e ore o r e host h o s t rock, r o c k y east e a s t into i n t o the t h e Deer Deer v e i n l e t s of of picrolite p i c r o l i t e and and cross—fiber cross-fiber Lake Peridotite. P e r i d o t i t e . These outcrops o u t c r o p s also a l s o display d i s p l a y veinlets Lake asbestos, a s b e s t o s , carbonate—replaced carbonate-replaced serpentine s e r p e n t i n e veinlets, v e i n l e t s y and and strongly s t r o n g l y jointed j o i n t e d peridotite. peridotite. At "Type-B" serpentinite s e r p e n t i n i t e occurs o c c u r s near n e a r the t h e waterline, w a t e r l i n e y in i n sharp s h a r p contact contact A t Outcrop Outcrop C, C y "Type—B" a r e formed formed with w i t h another a n o t h e r variety v a r i e t y that t h a t consists c o n s i s t s of of shear s h e a r polyhedra. polyhedra. These polyhedra are by by aa series s e r i e s of of anastomosing anastomosing sets s e t s of of subparallel s u b p a r a l l e l cross—fiber c r o s s - f i b e r serpentine s e r p e n t i n e veins, v e i n s y sursurrounding much less well rounding elongate e l o n g a t e bblocks l o c k s tthat h a t aare r e much less w e l l veined. v e i n e d . The The polyhedra polyhedra are a r e smaller smaller toward toward the t h e shear s h e a r zone, zoney and have been proposed as a s pillows p i l l o w s by Morgan and DeCristoforo Chemical These features f e a t u r e s are a r e discussed d i s c u s s e d in i n greater g r e a t e r detail d e t a i l in i n the t h e text. t e x t . Chemical (1981). analyses a n a l y s e s of of HR HR 197 197 and and HR 232 232 are a r e listed l i s t e d as a s Nos. Nos. 44 and and 10 10 in i n Table Table 33 in i n the t h e text. text. 41 Turn right r i g h t on on U.S. U.S.41 Proceed east and to t o U.S. U.S. 41. 41. Turn CO 573 573 to t o Cooper Cooper Lake Lake Road, Roady and e a s t along a l o n g CO right and 3.2 miles m i l e s to t o junction j u n c t i o n of of CO CO 478 478 (party ( p a r t y store s t o r e on on left). l e f t ) . Turn right and drive d r i v e about about 3.2 Turn left l e f t and and proproand t o junction j u n c t i o n with w i t h Diorite D i o r i t e Road Road (CO (CO 496). 496). Turn and continue c o n t i n u e 0.1 0 . 1 miles m i l e s to ceed 1.0 r i g h t fork f o r k and drive d r i v e 1.6 1 . 6 miles m i l e s to t o Gold Gold Mine Mine Lake Lake Road 1.0 miles mi1.e~to t o fork. f o r k . Take right r i g h t and and continue c o n t i n u e 0.4 0.4 miles miles (CO CU) marked by aa Gold Gold Mine Mine Lake Lake Realty R e a l t y sign. s i g n . Turn right (CO on foot f o o t along a l o n g dirt d i r t road road for for to t o dirt d i r t road road on on the t h e right, r i g h t y closed c l o s e d by by aa gate. g a t e . Proceed on extreme caution c a u t i o n around around fenced fenced areas a r e a s that t h a t mark mark 1300 1300 feet f e e t to t o old o l d mine mine workings. workings. Use extreme open shafts s h a f t s and and stopes. stopes. Stop 55 —- The The Michigan Mine The Michigan Mine operated o p e r a t e d from from 1890 1890 to t o 1898 1898 and and became the t h e second second largest l a r g e s t gold gold i n 1934, 1934, reopened in producer in i n the t h e Michigan gold gold belt b e l t —— 64 64 kg. kg. gold. gold. The mine was reopened mm— The minas processed. a mill hundrwl tens t m s of of ore was processed. The s e v e r a lhuftdred m i l l was constructed, c o n s t r u c t e d y and sevra1 -- �80 Figure F i g u r e 3. 3. S e r p e n t i n i t e outcrops, o u t c r o p s , shore s h o r e of of Deer Deer Lake. Lake. Serpentinite �81 eralogical e r a l o g i c a l zone zone was was exposed exposed about about 600 600 feet f e e t on on strike. s t r i k e . Six S i x shafts s h a f t s have have workings extend to a depth of 250 feet with levels at 60, 150, and extend t o a d e p t h of 250 f e e t w i t h l e v e l s a t 6OY 150, and 250 250 1972; Morgan and 1972; and DeCristoforo, D e C r i s t o f o r o , 1981). 1981). been been feet feet sunk and and sunk (Bodwell, (Bodwelly The The deposit d e p o s i t is i s situated s i t u a t e d in i n the t h e lower lower amphibolite a m p h i b o l i t e member member of of the t h e Kitchi K i t c h i Schist S c h i s t that t h a t is is intruded i n t r u d e d by by relatively r e l a t i v e l y fresh f r e s h appearing a p p e a r i n g quartz—feldspar q u a r t z - f e l d s p a r porphyry porphyry dikes. d i k e s . Quartz Quartz veins, veinsy erratic and w width found aalong e r r a t i c in i n strike, s t r i k e y dip. d i p and i d t h ggenerally e n e r a l l y aare r e found l o n g the t h e contact c o n t a c t between these these two two rock rock types. types. Pyrite—gold and the t h e property property P y r i t e - g o l d mineralization m i n e r a l i z a t i o n occurs o c c u r s along a l o n g the t h e margin margin of of quartz q u a r t z veins, v e i n s , and has t h e largest l a r g e s t weighing weighing over o v e r 15 1 5 oz., O Z . ~ h a s yielded y i e l d e d some some spectacular s p e c t a c u l a r high—grade high-grade specimens, specimensy the but b u t in i n general g e n e r a l the t h e values v a l u e s were w e r e sporadic. s p o r a d i c . Pyrite P y r i t e is i s the t h e principal p r i n c i p a l sulfide, s u l f i d e y with w i t h minor minor chalcopyrite, c h a l c o p y r i t e , galena, g a l e n a y sphalerite, s p h a l e r i t e y and and molybdenite molybdenite (Bodwell, (Bodwelly 1972). 1972). �____________________________________ CONSTITUTION CONSTITUTION OF OF INSTITUTE INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY ' A r t i c l e II Article Name Name The name of of the t h e organization o r g a n i z a t i o n shall s h a l l be b e the t h e 'Institute " I n s t i t u t e on on Lake Lake Superior Superior Geology. " Geology." A r t i c l e II I1 Article Objectives Objectives o b j e c t i v e s of o f this t h i s organization o r g a n i z a t i o n are: are: The objectives A. A. B. B. C. C. A r t i c l e III 111 Article To To provide p r o v i d e aa means means whereby whereby geologists g e o l o g i s t s in i n the t h e Great G r e a t Lakes Lakes region region may exchsnge exchange ideas i d e a s and and scientific s c i e n t i f i c data. data. may To To promote promote better b e t t e r understanding u n d e r s t a n d i n g of o f the t h e geology geology of of the t h e Lake Lake Superior Superior region. region. To plan p l a n and and conduct c o n d u c t geological g e o l o g i c a l field f i e l d trips. trips. To BY-LAWS I. I. Duties D u t i e s of of the t h e Officers O f f i c e r s and and Directors Directors A. A. Status Status 1. 1. No part p a r t of o f the t h e income income of of the t h e organization o r g a n i z a t i o n shall s h a l l inure i n u r e to t o the t h e benefit b e n e f i t of of I n the t h e event e v e n t of of dissolution d i s s o l u t i o n the t h e assets a s s e t s of of the the any member member or o r individual. i n d i v i d u a l . In any organization o r g a n i z a t i o n shall s h a l l be be distributed d i s t r i b u t e d to to (some tax t a x free f r e e urganization). organization). (some 2. 2. 3. 3. [To [To aavoid v o i d Federal F e d e r a l and State S t a t e income income taxes, t a x e s , the t h e organization o r g a n i z a t i o n should should be not n o t only o n l y "scientific" " s c i e n t i f i c " oro "educational" r " e d u c a t i o n a l "but b u talso a l s "non—profit."] o "non-profit."] be B. B. Ninn. Minn. Stat. S t a t . Anno. Anno. 290.01, 290.01. subd. subd. 44 ' 290.05(9) s. SOl(c)(3) 5Ol(c)(3) 1954 Internal I n t e r n a l Revenue Revenue Code Code s. 1954 A r t i c l e IV IV Article 2. 2. Membership Nembership 3. 3. s h a l l meet meet once once sa year, y e a r , preferably p r e f e r a b l y during d u r i n g the t h e month month of of The The organization o r g a n i z a t i o n shall p l a c e and and exact e x a c t date d a t e of of each e a c h meeting m e e t i n g will w i l l be b e designated d e s i g n a t e d by by A p r i l . The place April. t h e board b o a r d of o f directors. directors. the A r t i c l e VI VI Article C. C. Meetings Neetings 11. II. Directors Directors The The board board of of directors d i r e c t o r s shall s h a l l consist c o n s i s t of of the t h e Chairman, Chairman, Secretary—Treasurer Secretary-Treasurer and the t h e last l a s t three t h r e e past p a s t Chairmen; Chairmen; but b u t if i f the t h e board board should s h o u l d at a t any any time t i m e concons i s t of l e s s than t h a n five f i v e persons, p e r s o n s , by by reason r e a s o n of of unwillingness u n w i l l i n g n e s s or o r inability inability sist of less of any o f the t h e above persons p e r s o n s to t o serve s e r v e as a s directors, d i r e c t o r s , the t h e vacancies v a c a n c i e s on on the the of of board f i l l e d by by the t h e annual a n n u a l meeting m e e t i n g so s o as a s to t o bring b r i n g the t h e membership membership board may may be be filled of the t h e board b o a r d up up to t o five f i v e members. members. of A r t i c l e VII VII Article Officers Officers III. 111. B. B. A r t i c l e VIII VIII Article s h a l l be be elected e l e c t e d esch e a c h year y e a r by by the t h e board board of o f directors, directors, The Chairman shall s h a l l give q i v e due due consideration c o n s i d e r a t i o n to t o the t h e wishes w i s h e s of of any any group group that t h a t may may who shall promoting the t h e next n e x t annual a n n u a l meeting. m e e t i n g . Nis H i s term t e r m of o f office o f f i c e as a s Chairman Chairman be promoting w i l l terminate t e r m i n a t e at a t the t h e close c l o s e of of the t h e annual a n n u a l meeting meeting over o v e r which which he h e preprewill s i d e s or o r when his h i s successor s u c c e s s o r shall s h a l l have have been been appointed. a p p o i n t e d . He will w i l l then then sides s e r v e for f o r aa period p e r i o d of of three t h r e e years y e a r s as a s aa member member of of the t h e board board of of directors. directors. serve S e c r e t a r y - T r e a s u r e r shall s h a l l be be elected e l e c t e d at a t the t h e annual a n n u a l meeting. m e e t i n g . His His The Secretary—Treasurer t e r m of of office o f f i c e shall s h a l l be two two years y e a r s or o r until u n t i l his h i s successor s u c c e s s o r shall s h a l l have have term appointed. been appointed. Amendments Amendments T h i s constitution c o n s t i t u t i o n may be amended amended by by aa majority m a j o r i t y vote v o t e of of those t h o s e persons p e r s o n s who who This a r e personally p e r s o n a l l y present p r e s e n t at, a t , participating p a r t i c i p a t i n g in, i n , and and voting v o t i n g at a t any any annual annual are m e e t i n g of of the t h e organization. organization. meeting Keep Keep accurate a c c u r a t e attendance a t t e n d a n c e records r e c o r d s of of ell a l l annual a n n u a l meetings. meetings. Keep Keep accurate a c c u r a t e records r e c o r d s of of all a l l meetings m e e t i n g s of, o f , and and correspondence correspondence between, between, the t h e board b o a r d of o f directors. directors. Hold all a l l funds f u n d s that t h a t may may eccure a c c u r e as a s profits p r o f i t s from from annual a n n u a l meetings meetings or o r field f i e l d trips t r i p s and and to t o make make these t h e s e funds f u n d s svsilable a v a i l a b l e for f o r the the organization o r g a n i z a t i o n and operation o p e r a t i o n of of future f u t u r e meetings m e e t i n g s as a s required. required. It I t shall s h a l l be b e the t h e duty d u t y of of the t h e board board of of directors d i r e c t o r s to t o plan p l a n locations locations of o f annual a n n u a l meetings m e e t i n g s and and to t o advise a d v i s e on on the t h e organization o r g a n i z a t i o n end and financing financing of o f all a l l meetings. meetings. Dues and and Expenses Expenses 1. 1. There T h e r e shall s h a l l be b e no regular r e g u l a r membership membership dues. dues. 2. 2. Registration R e g i s t r a t i o n fees f e e s for f o r the t h e annual a n n u a l meetings m e e t i n g s shall s h a l l be b e determined determined by the t h e Chairmen Chairman in i n consultation c o n s u l t a t i o n with w i t h the t h e board board of of directors. directors. It It is i s strongly s t r o n g l y recommended recommended that t h a t these t h e s e be b e kept k e p t st a t aa minimum minimum to to encourage encourage attendance a t t e n d a n c e of of graduate g r a d u a t e students. students. Rules R u l e s or o r Order Order The The rules r u l e s contained c o n t a i n e d in i n Robert's R o b e r t ' s Rules R u l e s of o f Order Order shell s h a l l govern govern this this organization o r g a n i z a t i o n in i n all a l l cases c a s e s to t o which which they t h e y are a r e epplicsble. applicable. The officers o f f i c e r s of o f this t h i s organization o r g a n i z a t i o n shall s h a l l be b e aa Chairman Chairman and and aa Secretary—' SecretaryThe Treasurer. Treasurer. A. A. Preside P r e s i d e at a t the t h e annual a n n u a l meeting. meeting. Appoint all a l l committees committees needed needed for f o r the t h e organization o r g a n i z a t i o n of o f the the ennual a n n u a l meeting. meeting. Assume Assume complete c o m p l e t e responsibility r e s p o n s i b i l i t y for f o r the t h e orgsnizstion o r g a n i z a t i o n end and financing f i n a n c i n g of of the t h e annual a n n u a l meeting meeting over o v e r which which he h e presides. presides. It I t shall s h a l l be b e the t h e duty d u t y of o f the t h e Secretary—Treasurer S e c r e t a r y - T r e a s u r e r to: to: 1. 1. The The membership of the o r g a n i z a t i o n shall c o n s i s t of t h e board of directors. membership of t h e organization s h a l l consist o f the board of directors. g e o l o g i s t interested i n t e r e s t e d shall s h a l l be b e permitted p e r m i t t e d to t o attend a t t e n d and and participate p a r t i c i p a t e in in Any geologist v o t e at a t the t h e annual a n n u a l meetings. meetings. and vote A r t i c l e VV Article It It shall s h a l l be b e the t h e dutyof d u t y o f the t h e Chsirnsn Chairman to: to: IV. IV. Amendments Amendments These These by-lews by-laws may may be b e amended amended by sa majority m a j o r i t y vote v o t e of of those t h o s e persons p e r s o n s who who ere a r e personally p e r s o n a l l y present p r e s e n t at, a t , participating p a r t i c i p a t i n g in, i n , end and voting v o t i n g at a t any any ennuel annual meeting m e e t i n g of of the t h e organization; o r g a n i z a t i o n ; provided provided that t h a t such s u c h modifications m o d i f i c a t i o n s shell shall not n o t conflict c o n f l i c t with w i t h the t h e constitution c o n s t i t u t i o n as a s presently p r e s e n t l y adopted adopted or o r subsequently subsequently amended. �INSTITUTES INSTITUTES ON LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY INSTITUTE INSTITUTE NUMBER NUMBER 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 DATE -- PLACE PLACE Minneapolis, MN Minneapolis, Houghton, MI Houghton, MI East E a s t Lansing, Lansing, MI MI Duluth, I'IN Duluth, MN Minneapolis, MN Minneapolis, Madison, Madison, WI WI Port Ont. (Thunder Bay) P o r t Arthu-r, A r t h u r , Ont. Bay) Houghton, MI MI Duluth, Duluth, MN Ishpeming, I shp emin g , MI MI St. Paul, St. P a u l , MN Sault S a u l t Ste. S t e . Marie, Marie, MI MI East Lansing, MI E a s t Lansing, MI Superior, S u p e r i o r , WI WI Oshkosh, WI Oshkosh, WI Thunder Bay, Bay, Ont. Ont. Duluth, MN Duluth, Houghton, MI Houghton, MI Madison, WI Madison, WI Sault S a u l t Ste. S t e . Marie, Marie, MI MI Marquette, MI MI St. Paul, S t. P a u l , MN Thunder Bay, Bay, Ont. Ont. Milwaukee, WI WI Milwaukee, Duluth, MN Duluth, Eau Claire, C l a i r e , WI WI East E a s t Lansing, Lansing, MI MI IInternational n t e r n a t i o n a l Falls, F a l l s , MN Houghton, MI Houghton, MI Wausau, W WII Wausau, 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 In Michigan Technological Technological University University is is an an equal equal opportunity opportunity educational educational institutionlequal institution/equal opportunity Michigan opportunity employer. employer. � https://digitalcollections.lakeheadu.ca/files/original/47a23992a5300f3056d0a840ef01b365.pdf b1d42fe2b6fcf5b2fb62b0815cc007f1 PDF Text Text �---'--------......;;===================----------=====--------------==================.,......------'.. i" Michigan Technological University University /- ..-..;// ....::>' /tPl;SID~8;t;.~ /' ~ H'QH~A . _.'~ / ~7'" .:- .-":-'Y._~;---;;;r-;;.,.-;~--?~'-:~ - ----. --:..-- Y.~==-.:,- - _=_ -. ---._ __ HOUGHTON MI 49931 • -2< ' '1'~1J - rf'I 0'">" ~ III! :r::£'(P~ .- _.._. . . . . - .--- - ..- - . - . - . ,{'(}-(~.,c?". 'J<'£:: .f\ --' / (',{,!~,-- -~ .,~~ './ ---~. - -_. - . _ . ' - . N'-c.A ~ ~\ Seaman c···.· -' ••/ / ! --; , . .~r: ~; Mineral Museum . . .. --- (5th (5th floor) Memorial Union Union .. .,~=-'~" ::~::::-~':"'~~~:. .'.~' ~:-- - ----,- ...->--'-" / ~ —- - 1 (3rd floor) \\ / / // / r--. .. - ~f1Y- -. Geology -.—- ~~-::.~;,::;:~:~,:, * -.:• ,/ ..' ~C~ 0 ~.-:_-- - .. --7'- - " " . .. . -.., _ ...:>c.....- ~- // /' --;;.,;-. ---;.. - _~'~..rg;~.'~~~: ~_.-ifi,~.:.'~-': ~-F'i:rPJl' -~... ..e;- . ' ~ ... ?- • -~I)<0.rr - / PORTAGE LAKE / Commuter & DHH -) - _ ... - rv-l\l:rd- ~ (l"ri_,y,> 0 "'-0,,r ~ ( ,'."" f\,:,''''''- Qr4 'b-97? ?•j(4?it ,/7 r-5.jfy ,,, 5' //' - //.'/, /j1'J. HARONAVE' " - - clf i—__._ —__-'" = - - / J/ / ( /— — ,,, 5- --5 —'-_ \ -= 5J( 'n\\ \ 11 v'— r (" r -y"y' AdmInistration BuIlding Administration Building 4 ROTC ROTC BuildIng Building 5 Academic Academic Offices Offices BuIlding Building Electrical Energy Resources Resources Center Center ElectrIcal Energy 7 EERC-AE. Seaman Seaman Mineralogical Mineralogical Museum EERC·A.E. Museum (5th (5th Floor) Floor) 9 Alumni AlumniHouse-MT House-MT Fund Fund Humanities Center Center Arts and Humanities InstItute of of Mineral Mineral Research Research (Benedict (Benedict Lab) Lab) ,39- 'i\ '(! . 12 Institute CivIl-Geology Building Civil·Geology Hall 15 Fisher Hall library Forestry·lnstitute of Wood Research 19 ChemistryMetaurgyBuiing Chemistry·Metaliurgy Building MechanicalEngIneering-Engineering Engineering-Engineering Mechanics 20 Mechanical -3(Y- 24 Student Development Complex Student Development Complex Douglass Houghton Hall (DHH) Daniell Heights Housing -r4-,c' 34 Memorial Union Memorial UnionBuilding Building 37 Wadsworth Wadsworth Hall Hall \L7 -— - - I - - // rr-w-- fç,7 - FOOTBALL FIE LD -, / k/ 1 ' 9c'?1i-' /) J 14 (1 38 West West Coed Coed Hall Hall 38 39 Coed Coed Food Food Service Service 39 East East Coed Coed Hall 4t Central Heatmg Healing Plant 41 42 Physical Physical Plant Plant Storage Storage Building Building 42 Lakeside Laboratory 43 Lakeside 43 44 Storage-Service Storage-Service Building Buiiding (Pool (Pool Cars) Cars) 44 50 Gates Tennis Tennis Center Center 50 Gates 58 U.S. Forest Engineering Laboratory U.S. Forest Engineering A Visitors'Parking Parking Ares Area A Visitors )L. ç- - 9 - 40 Not appearing on on map map: Experimental Mine, Hancock Hancock Ford Forestry Center, Alberta Ford Alberta Keweenaw Research Center Center, Memorial Memorial Airport Airport Mont Ripley Ski Hill, Ripley Portage Lake Golf Course, Course, Houghton Houghton I ',S (\C'l(') '()r l ' r- (( .,.... .-,_ -( ,CY C �FIELD GUIDE TO THE GEOLOGY GEOLOGY OF OF THE THE KEWEENAW PENINSULA, PENINSULA, MICHIGAN BY J. Bornhorst Theodore J. William I. I. Rose, Rose, Jr. Jr William James B. B. Paces Department of of Geology and Geological Engineering Michigan Technological University University Houghton, Houghton, Michigan 49931 FOR SALE SALE AT: AT: E. R. R. Lauren Bookstore, Bookstore, Memorial Union E. Michigan Technological University Houghton, Michigan 49931 Houghton, Prepared as field trip trip guide guide for for the the 29th Annual Institute as aa field Annual Institute on Lake Superior Geology held held at at Michigan Michigan Technological Technolo~ical University on May 11—14, 11-14, 1983. 1983. FIRST EDITION May, 1983 May, COVER PHOTO: Miners Miners at at the the Mine(?) circa circa 1910. 1910. Baltic Mine(?) Michigan Technological University Archives and Copper Country Historical Collections. Collections. �PREFACE — It is presumptuous presumptuous for for us us to put together is based based mainly mainly on on the the work work It is to put together aa book which is of others. We have done so because hundreds of people come to of to the Keweenaw each year to to look look at at geological geological features features and and many many of of them them ask ask us us for for advice. advice. So we've tried to tried to communicate with people people who who are are doing doing serious serious geological geological field field trips. trips. This is is a first first draft of an evolving document, document, which we expect to to continually rerePlease help help us us make make it better by by suggesting changes, changes, finding finding mistakes mistakes and and Please it better vise. telling us what we've we've left left out. out. Starting with Douglass Douglass Houghton almost almost 150 years years ago, ago, dozens dozens of of geologists geologists have have contributed aa mountain of of geological on the the Keweenaw Keweenaw which which makes makes it it contributed geological information information on aa real challenge to to compile this this book. book. The greatest greatest contribution by far far has come come from from Walter Walter S. S. White, White, who who devoted devoted much of of his his professional professional career career to to Keweenawan Keweenawan whose impact geology and whose impact can can be traced traced to to virtually virtually every every page page of of this this book. book. of his his We hope that that we have faithfully faithfully transmitted his his ideas with a a fraction fraction of enthusiasm. ingenuity and enthusiasm. Houghton Houghton 30 March 1983 i1 �TABLE OF CONTENTS Page i PREFACE iii HOW TO USE THIS GUIDE GUIDE iv LIST OF OF STOPS STOPS vlii viii LIST OF MAPS ix LIST OF FIGURES xi LIST OF OF TABLES TABLES INTRODUCTORY NOTES ON THE GEOLOGY OF THE KEWEENAW PENINSULA 11 17 17 ROAD LOG AND STOP DESCRIPTION INDEX TO GEOLOGY ON NAPS MAPS IN IN THE FIELD FIELD GUIDE GUIDE 111 111 112 112 REFERENCES 11i i �HOW TO USE THIS GUIDE To make all the the stops stops listed listed in in this this guide guide would would take take three three days. days. If If you wish to to emphasize certain types types of of stops, stops, we we recommend recommend the the following following subsets: subsets: Suggested Stops Stops Sediments Sediments Volcanic Rocks Mineral Deposits Broad Coverage 5, 6, 8, 8, 9,. 16, 17, 17, 19, 19, 20, 20, 24 24 10, 13, 13, 16, 5, 6, 9, 10, 1, 15, 16, 16, 17, 17, 18, 18, 21 21 1, 3, 3, 11, 11, 12, 12, 13, 13, 14, 14, 15, 2,3,4,7,11,13,17,22,23 2, 3, 4, 7, 11, 13, 17, 22, 23 3, 6, 10, 10, 11, 11, 13, 13, 16, 16, 18, 18, 19, 19, 20, 20, 24 24 3, 6, Be imaginative and make up up your own own subset subset of of stops. stops. stops are are on on or or near near private private land. land. Please respect private property. property. The preMany stops Sent problems of access are minimal, but obviously we could ruin we don't don't sent problems of access are minimal, but obviously we could ruin things things if if we use low profile outdoor principles. principles. AA few few stops stops are are located located ot on old mine dumps. dumps. These can be hazardous, hazardous, especially especially where where bad bad ground ground occurs. occurs. Use common sense. sense. - have north north to to the the top top and and are are 1:24,000 1:24,000(4(4cmcmtoto1 Ikin). km). All maps have road log route on the the maps, maps, while while stars stars mark mark the the stops. stops. follow the the Dots follow Mineral collectors have long long flocked flocked to to the the Keweenaw to to collect its its unusual minerals. minerals. One of the best in the world located at this best mineral museums in world is located at the starting point point of of this field trip. trip. The Seaman Mineralogical Museum, Museum, open from 9:00—4:30 9:00-4:30 weekdays, weekdays, is is housed housed in the the EERC EERC Building, Building, Fifth Floor, in Floor, on on the the Michigan Michigan Tech Tech Campus. Campus. The mineralogical over the the Keweenaw and is collection includes includes samples samples from from all over is aa must for for all all rockhounds. rockhounds. 111 iii �STOPS LIST OF STOPS The following used to to help help you you design design your your own own field field trip trip following list of stops can be used to to see the geology of the the Keweenaw Peninsula. Peninsula. The location location of of stops stops are are shown shown in Figure la. la. The appropriate maps for for each stop and trip trip route are located in Figure Figure lb. lb. — — STOP MAP) (APPROPRIATE MAP) STOP DESCRIPTION STOP 11 (1) (1) Ophitic Scales Creek basalt flow and Keweenaw view, 7th 7th St., St., Houghton. Houghton. Waterway view, 2 2 (1) (1) Secondary minerals in in amygdaloid amygdaloid at at dump dump of of Isle Royale Mine, Dodgeville. Dodgeville. '-" 3 (2) (2) Section through a lava lava flow flow at at South South Range Range quarry. quarry. ....---4 (2) (2) Secondary minerals in in amygdaloid amygdaloid at at dump dump of of Baltic Mine. Mine. 5 5 (3) Glacial deposits on M—26 M-26 south south of of Houghton. Houghton. 6 6 (4) (4) Overlook of Keweenaw Waterway, Waterway, Houghton and the Range towns; towns; Quincy Quincy Hill, Hill, Hancock. Hancock. 7 7 (4 ) (4) Secondary minerals of amygdaloid at at dump dump of of Quincy Quincy Mine. Mine. 8 (6) (6) Flat—lying Flat-lying Jacobsville Jacobsville Sandstone Sandstone along along M—26, M-26, near Dollar Dollar Bay. Bay. 9 9 (7) (7) Hungarian Falls, Falls, near near Hubbell. Hubbell. Keweenaw Fault at Hungarian 10 10 (8) (8) Keweenaw Fault at at Natural Wall Wall Ravine, Ravine, near near Laurium. Laurium. 11 (9) (9) Secondary minerals in amygdaloid at at dump dump of of Wolverine Wolverine Mine. Mine. 12 (9) (9) Ophitic Scales Creek basalt flow, flow, at Scales Creek near Copper City. City. —- 13 ...../13 (9) (9) Lava flows flows of Portage Lake Volcanics and mineralized conglomerate with an excellent ized excellent view view of of the the central part of of the the Keweenaw Keweenaw Peninsula, Peninsula, Bumble— Bumbletown Hill. 14 (12) (12) Ophitic Greenstone flow and vein mineralogy at dump of Phoenix Mine. 15 15 (12) (12) part of of the Portage Lake Lake Section through through the the upper part the Portage Volcanics along along Eagle Eagle River. River. 16 (12) Contact between Portage Lake Volcanics Volcanics and Copper Contact Harbor Conglomerate Conglomerate at at Eagle Eagle River River Falls. Falls. ~. t/ iv �STOPS (Cont'd.) (Contld.) LIST OF STOPS STOP DESCRIPTION STOP (APPROPRIATE MAP) 17 17 (13) through the the upper upper part part of of the the Portage Portage Section through Lake Volcanics along Owl Owl Creek Creek and and amygdaloid! amygdaloid/ vein mineralogy at dump dump of of Copper Copper Falls Falls Mine. Mine. v"J.8 "18 (16) (16) Lava flows of the the Lake Shore Shore Traps Traps at at Esrey Esrey Park. Park. V19 \/19 (17) Overlook of Lake Superior Superior and and the the eastern eastern end end of of the Keweenaw Keweenaw Peninsula and outcrops of Copper the Harbor Conglomerate at at Brockway Mountain. Mountain. flO (17) (17) Copper Harbor Conglomerate Conglomerate at at Dan's Dan's Point. Point. 21 (20) (20) Diorite and granophyre stock stock at at Mt. Mt. Bohemia. Bohemia. 22 (21) Secondary mineralogy of of veins and and conglomerate conglomerate at Delaware Delaware Mine'. Mine~ The Delaware Mine is is open to to tourists for for aa fee. fee. 23 (28) Amygdaloid mineralogy of of dumps dumps at at Osceola Osceola Mine. Mine. 24 (30) at Hancock Hancock campground campground quarry. quarry. Nonesuch Shale at v �I ( I . ···i·9*··..······..·····;:;: ; ~ "'-~'L"'"alre Bailey . Eagle . . . f~~;I~.·.:::::::···:< . . . ""C~~r~·I La e M.,!dO'~ C ............ Delawar~.~.,2 ..'····· ....····· Copper Harbor 20 \ 0 " fifo" 5 IJ Eagle H ...r-nnr :._. _ - .~ .-:--~"::::~tS ~-~. Lak e Fanny Hooe Schlstter('.., •....1 (? ········\···'>... 21 = LakeV ~ Manitou Island Island ........ Phoenix .-:,., <f.2 .~.' i-~ Lake .../ "to A:::;!l\(~~:,..• o Kearsargei..,.J 1 ..i '···12 -< ~. McLain State Park McLain Park .rC"aiun;-~t·'· .f .-.,1.0... ~~ ~~ ~\ o~ C, Laurium 23*/ . Lake Linden ..... .... Scale Scale 1 0o M I 1 1 2 3 4 miles 4miles ~ Freda Atlantic South ~ ~ly ~ '" Painlsdale Pa in ed a le 12 Stopnumber number •2 Stop Figure Figure 1A: 1A: Route Route and and stop stop map map �SU ~~ \\ \ 17 o o~ 13~ ~ 23 o 12 'I-~ ... '" _0_" 27 ./' <~ t-<t-<. -.)~ ~ ~ \ o ~ c., 8 SCALE in in miles 01234 ,.... ji"Wiij o 1 2 ....., 3 p> 4 Dil2 Map number 12 ,.*" I'l + ~ " Figure 1B: 18: *'2 number Stop number Index of of 1:24,000 Index 1:24,000 scale scale maps maps �LIST OF OF NAPS MAPS Page MAP MAP 1 18 MAP MAP 2 22 MAP MAP 33 26 MAP MAP 44 31 MAP MAP 5 35 MAP MAP 6 39 MP MAP 77 42 MAP MAP 88 46 MAP MAP 9 49 MAP 10 MAP1O 60 MAP MAP 11 63 MAP 12 MAP 64 MAP13 MAP 13 71 MAP 14 MAP 74 MAP15 MAP 15 76 MAP 16 MAP 77 MAP17 17 MAP 79 MAP 18 MAP 82 MAP MAP 19 86 MAP2O t-1AP 20 87 MAP MAP 21 88 MAP 22 MAP 91 MAP MAP 23 95 24 MAP24 MAP 96 MAP25 MAP 25 98 MAP26 MAP 26 99 NAP MAP 27 100 MAP MAP 28 104 MAP MAP 29 106 MAP MAP 30 109 viii viii �LIST OF FIGURES Page vi Vi Figure 1: 1: Index map map of of route, Index route, stops and 1:24,000 scale scale maps. maps. Figure 2: 2: Location of the the Mid—Continent Mid-Continent Rift Rift System. System. 2 2 Figure 3: 3: Simplified geologic map, map, cross—section, cross-section, and and strati— stratigraphic column, column, western western Lake Lake Superior Superior region. region. 3 3 Generalized geologic geologic map of of the the western western Upper Upper Peninsula and stratigraphic stratigraphic section section of of the the Portage Portage Lake Volcanics. 4 4 Columnar stratigraphic Section section of of rocks rocks northwest northwest of of the Keweenaw Fault in the Calumet—Ahmeek the Calumet-Ahmeek area. area. 66 rocks Location of silicic to to intermediate intrusive rocks the Portage Lake Volcanics. in the Volcanics. 8 8 Figure Figure Figure Figure 4: 4: 5: 5: 6: 6: 7: 7: Schematic diagram showing interrelationships between northwest of of the major stratigraphic units units northwest the Keweenaw Fault in the the Keweenaw Peninsula. 10 Geologic and structure structure maps of of the the Keweenaw Keweenaw native native copper district. district. 13 and paragenesis of of secondary minerals Distribution and secondary minerals in Volcanics. in the the Portage Lake Volcanics. 14 14 Elemental mobility in in an an idealized idealized lava lava flow flow and and diagrammatic diagra~matic regional model for for metamorphism metamorphism of of the Portage Lake Volcanics. the 16 16 Figure 11: 11: Geologic cross—section cross-section for for Map Map 1. 1. 20 Figure 12: 12: Geologic profile of South Sou~h Range quarry. quarry. 21 21 Figure 13: 13: Speculative ice—marginal ice-marginal positions positions during during the the Wis— Wisconsin ice retreat. retreat. 27 Figure 14: 14: End moraine of the End the Keweenaw Bay Lobe glacier. glacier. 27 Figure Figure 15: 15: Enlarged view of ice—marginal ice-marginal positions. 28 Figure Figure 16: 16: High level drainage drainage through through the the Portage Portage Gap. Gap. 29 29 Figure Figure 17: 17: View from from Portage overlook overlook facing facing south. south. 32 32 Figure Figure 18: 18: Structures of the the Quincy Mine location. location. 36 Figure 19: 19: Geologic cross section section for for Maps Maps 4, 4, 5 and 30. 30. 37 37 Figure Figure 8: 8: 9: 9: Figure 10: 10: ix �Page Figure 20: 20: Relationships of of Jacobsville Sandstone. Sandstone. 40 21: Figure 21: Geologic sketch map of of Hungarian Falls Falls area. area. 44 Figure 22: 22: Wall Ravine. Ravine. Geologic sketch map of of Natural Wall 47 Figure 23: 23: Geologic Geologic map map and cross section, Wolverine Mine and and section, Wolverine arid cross vicinity. 51 Figure 24: 24: Thickness of of the the Kearsarge Kearsarge flow. flow. 52 Figure 25: 25: Paragenesis of secondary minerals in in the Kearsarge amygdaloid. 52 Cross section section of of Kearsarge Kearsarge amygdaloid amygdaloid showing showing the Cross the banding of of mineral assemblages. assemblages. 54 Distribution of quartz, quartz, microcline and high grade ore in in the the Kearsarge Kearsarge amygdaloid. amygdaloid. native copper ore 55 Figure Figure 28: 28: Outcrop map of of the the Allouez—Bumbletown Allouez-Bumbletown Hill Hill area. area. 57 Figure 29: 29: Map and section of the Greenstone flow between Seneca and the the Cliff Cliff Mine. Mine. 61 Figure 30; Figure 3O Map and section section of of the the Greenstone Greenstone flow flow near near Phoenix. Phoenix. 66 66 Figure Figure 31: 31: Stratigraphy of the Portage Lake Volcanics Volcanics above above the the Greenstone flow. flow. Greenstone 68 68 Plot of K20 and P205 content of 106 individual individual Portage Lake Volcanic flows flows in in stratigraphic stratigraphic order. order. 69 69 Schematic cartoon cartoonofdepositional Schematic of depositional environment environment of of the the Copper Harbor Conglomerate. Conglomerate. 83 83 Measured section of Copper Harbor Conglomerate at Dan's Dants cartoon of of the the depositional depositional environment. environment. Point and cartoon 84 84 Geologic map showing andesitic dikes near Mount Bohemia and occurrence occurrence and and paragenesis paragenesis of of secondary secondary and and opaque opaque and in the the dikes. dikes. minerals in 90 90 map and development of Sketch map of the the Keweenaw Keweenaw Fault Fault in in of Deer Deer Lake. Lake. vicinity of 93 93 Figure 26: 26: Figure 27: 27: Figure Figure 32: 32: Figure Figure 33: 33: Figure 34: 34: Figure 35: 35: Figure Figure 36: 36: Figure 37: 37: Figure 38: 38: Schematic illustration of the the funnelling effect on on Schematic illustration of funnelling effect fluids, Kingston Kingston conglomerate. conglomerate. mineralizing fluids, 102 102 Results of gravity gravity measurements across the Bear Lake on Map Map 29. 29. traverse plotted on 108 108 x �LIST OF TABLES Page Table 1: 1: Secondary minerals found found within within the the Portage Portage Lake Volcanics. Volcanics. 11 Table 2: 2: Major—element Major-element composition composition of of the the Kearsarge Kearsarge flow. flow. 51 Table Table 3: 3: Volume percent amygdule minerals from mapped assemblages shown in in Figure 26. 26. 54 Average major—element major-element composition of the the Scales Creek Creek flow. flow. 57 57 Table 4: 4: Table xi �INTRODUCTORY NOTES ON THE GEOLOGY OF THE KEWEENAW PENINSULA PENINSULA General Background The Mid-Continent Mid—Continent Rift Kansas to Lake Superior Superior Rift System extends northeasterly from Kansas to Lake It was was formed and then southeasterly through and through lower lower Michigan Michigan (Fig. (Fig. 2). 2). It formed about 1.1 1.1 to 1.2 b.y. b.y. ago ago (Keweenawan age) by by extensional extensional thinning of the the rigid rigid Precambrian Precambrian to 1.2 (Keweenawan age) thinning of Superior crustal block (Kiasner (Klasner and and others, others, 1982). 1982). Present day crustal thickness thickness the Lake Superior region, region, however, however, is is between between 40 40 and and 50 50 Km, Km, which which is is thicker thicker in the than than adjacent areas areas (Halls, (Halls, 1982). 1982). -— Peninsula is is located located on on the the margin margin of of the the Lake Lake Superior Superior Basin, Basin, The present Keweenaw Peninsula one of of the one the basins within the the Mid—Continent Mid-Continent Rift Rift System System (Fig. (Fig. 3). 3). The volcanic and sedimentary rocks rocks on the northwest side side of of the the Keweenaw Keweenaw Peninsula Peninsula generally generally dip dip toward Lake Superior and include the Portage Lake Volcanics, moderately toward Volcanics, Copper Copper Conglomerate, Nonesuch Shale Shale and and the the Freda Freda Sandstone. Sandstone. The Jacobsville Sand— SandHarbor Conglomerate, stone stone occupies the southeast side side of of much of of the the Keweenaw Keweenaw Peninsula Peninsula and and is is in in fault along the the Keweenaw Keweenaw Fault. Fault. The Jacobs— Jacobsfault contact contact with the Portage Lake Volcanics along ville Sandstone is however, it it is probably slightly younger than the the Freda Sandstone, Sandstone, however, is still most most likely upper Keweenawan in is still in age age (Kalliokoski, (Kalliokoski, 1982). 1982). At some time after the deposition of basin filling filling sediments, sediments, the Lake Superior region was was subjected to compression roughly region roughly normal normal to to the the basin basin axis. axis. These stresses in the the Keweenaw Keweenaw and and Isle Isle Royale Royale Faults, Faults, both both high high angle reverse reverse stresses re~ulted reulted in faults faults near near the margins of the the Lake Superior Superior Basin Basin (Fig. (Fig. 3). 3). This faulting steepened the dips the Peninsula Peninsula and and on on Isle Isle Royale. Royale. Definite age the dips of of strata exposed on both the relationships between between reverse reverse faulting faulting and and deposition deposition of of the the Jacobsville Jacobsville Sandstone Sandstone relationships are unclear: unclear: faulting syn- or wholly post—depositional. post-depositional. faulting may may be partially syn— The Lake Superior Syncline was affected affected by aa regional regional burial metamorphic and/or hydrothermal event. event. Remobilization of many elements, elements, particularly within the the Portage Lake Volcanics, Volcanics, caused lava flow caused strong alteration of of lava flow tops tops and and interbedded interbedded concon— glomeratic units. units. Native copper deposits of the the Keweenaw Peninsula are believed to to formed wholly or in in part the deposition of of the the Freda SandSandhave formed part after after the of much or all of stone (White, (White, 1968). 1968). Paleozoic geologic geologic processes processes were were largely largely atectonic. atectonic. Sediments associated with the the Michigan basin probably once covered the the Keweenaw Peninsula, Peninsula, as evidenced by the the isolated limestone at at Limestone Limestone Mountain Mountain and and Sherman Sherman Hill, Hill, isolated occurrence of of Ordovician limestone about 20 miles south about south of Houghton. The present day landscape of the the Keweenaw Peninsula is strongly strongly influenced by Pleistocene glaciation. is glaciation. Stratigraphy The bedrock geology of the the Keweenaw Peninsula consists of five major stratigraphic units. Portage Lake Volcanics, Volcanics, Copper Harbor Conglomerate, Conglomerate, Nonesuch Shale, Shale, Freda Sandstone and Jacobsville Sandstone Sandstone (Figs. (Figs. 33 and and 4). 4). The accumulated maximum thickness of of these these units units is is over over14,000 14,000in. m. The bedrock in the Keweenaw Peninsula is unconformably capped by a variety of is of glacial glacial deposits. deposits. �2 2 A. o0 -= KM t000 1000 KM ORIENTATIONS ORIENTATIONS OF SEGMENTS SEGMENTS OF THE MIDCONTINENT RIFT RIFT B. ---1\ l. I "----... N670,E N67 E "~ f, , 1. ----,j--, , ~ 0 N38 E( i---~~ ;:'-3~'E \ , 1 j 2: Location of the the Mid—Continent Mid-Continent Rift Rift System. System. A. Major Proterozoic A. Figure 2: rifts of of North North America America (from (from Burke, Burke, 1980). 1980). B. B. Orientation of and Paleozoic rifts individual the Mid—Continent Mid-Continent Rift Rift System System (from (from Kiasner Klasner and and others, others, individual segments of the 1982). �r- lie i ~ " II iA*' I 0 - Nipigon Sand,,,,",,. o JACOBSVILLE-BAYFIELD UP UPTO TO5000'+ 500O I f Cambrian &nd _ latesa: Kewc:etUlwu 49. '9" ONTARIO '\ Coppc:r Harbor Conalomcf1ue -/'-'-, '\;Z~'-S~10' /",-, - ""~O'~';ES o Kewecnaw&.l'l voleank: s.cquence, including Portage Lake Voleanic;s ,- __ ~ FREDA SANDSTONE SANDSTONE UP TO UP 70 12,000'+ 2000+ -1030 Ma (m,n.) IO30Mo(n,n.) 0:: W 0.. 0.. 0 MINNESOTA =:l .,. aa.. :3 :::> 47. 0 o 0:: (.!) (0 « WISCONSIN o I 50 I I o 45~ 45- I .,. I 93" I i ... 10(1 0:: I~"",""ES 100 I $0 ill , I ::2: \~')(Il(')Ll£"1RES I I .,. J 85" « C-) u LU w 0:: aa.. LAKE SUPERIOR REGION—distribution of of selected selected rock units. SUPERIOR REGION-distribution units, o0 —• :° .nç•0 .0 zz I— I- z Z COPPER HARBOR CONGLOMERATE 350' 350 -7000' -7000 zz « ~ I040Mo -1040Ma zz LU w UJ w 3: LU w 0:: o0 0:: 0 o Y: LU W aa.. 11 a.. PORTAGE LAKE PORTAGE VOLCANICS 9000' 9000 -15,000'. -(5,000. ::J I (include unnamed ufl0med (Include formation in west UP) formation west U.P.) VW ·YW ThUNDER BAY THUNDER REGION REGK>N KEWEENAW 1Sl..£ ROYALE [,lK£ SUPt.RIOR S£ ct jjjp LU W 1 .J P£HIN$ULA o co :E~ VERTICAL SCALE VERTICAL EXAGGERATED EXAGGERATED SOUTH RANGE RANGE SOUTH VOLCANICS (North Shore ~ Volcanics) Volconics) G]J t'ostvolcanic rrvludrg Poslvolcamc sodimenbo sc:dimenUry rocks. rocks. including the Copper Copper Harbor Harbor Conglom.::rale Conglomerate the tntrrbnddnd volcanic sedimentary ro<:h. rnck,. InltrbeJded VOIcMic and and seJimcntary nolading the the Portage Portage Lake Lake VolcanICS 'olratncs Including Prevolcanic Pynvolcanic rocks rock, a: indrcale relative relative directions directions Arrows indicate of movement along faults BESSEMER & BESSEMER B BARRON BARRON QUARTZ lIES QUARTZITES LU w ~ LAKE LAKE SUPERIOR SUPERIOR BASIN—cross BASIN--cross section. MIDDLE - I BASEMENT PRECAMBRIAN ,v•°°: I Figure 3: 3: Simplified geologic map, map, cross—section, cross-section, and and stratigraphic stratigraphic column column of of upper upper Precambrian rocks in the western Lake Superior region (map and cross—section from rocks in Lake Superior region (map and cross-section from Huber, column from from Daniels, Daniels, 1982). 1982). Huber, 1975; stratigraphic column w �4 NE SW NATIVE COPPER < aw 2 0 2 •° . .4 EEl > wo 0a—a- .4 F MINES — 2000 —, oo —1 1000 2000 3000 — 4000 5000 €000 — Location at onion within atratigraphic anc lion Aanraalmnln upFnn limIt at apiaatn & aaa'tn Approalmate Figure lawn, lion It at A. Generalized geologic map of upper Precambrian rocks of western Upper 4: B. GeneralPeninsula, Michigan. Hatched area is represented in cross—section in B. ized stratigraphic section of the Portage Lake Volcanics from Victoria to Copper Harbor (modified from Stoiber and Davidson, 1959). The major marker horizons and mines are shown. The dashed and dotted lines represent the approximate stratigraphic limits of secondary epidote and quartz and prehnite respectively. �Portage Lake Volcanics The Portage Lake Volcanics is a succession of more than 200 individual basaltic lava flows with a total thickness of 2500 m to 5200 m (Butler and Burbank, 1929; Huber, 1973; White, 1968) (Fig. 4). White (1960) recognized these volcanics as a thick pile of subaerial tholeiitic flood basalts. They are the product of rift zone magmatism and are comparable to the rift zones of East Africa and Iceland (Basaltic Volcanism Study Project, 1981; Chase and Gilmer, 1973; Green, 1977 and 1982; White 1960 and 1972). Volcanism was apparently controlled mainly by eruptions from fissures located under Lake Superior. The Portage Lake Volcanics are others, 1982). about 1,100 m.y. old (Van Schmus and Most of the lava flows are difficult to follow laterally with confidence. The Scales Creek, Kearsarge and Greenstone flows are the best documented laterally continuous flows. The Greenstone flow can be correlated to Isle Royale (Huber, 1975; Longo, 1982). There are thin conglomerate and sandstone beds throughout the section and these are excellent marker horizons (Fig. 4). The sediment inter— beds in all but the uppermost part of the Portage Lake Volcanics have been given names and are shown on the maps included in this field guide (Fig. 5). The inter— bedded sediments make up approximately 3 to 8% of the formation (White, l971a). The conglomerates of the Calumet area the host rocks for large native copper deposits. The lithology of the conglomerates is dominated by clasts of rhyolitic volcanic rocks (Merk and Jirsa, 1982). The frequency of interbedded sediments increases in Eventually volcanism waned and sediment deposition the upper part of the formation. became dominant, the overlying Copper Harbor Conglomerate. The dominant composition of the lava flows of the Portage Lake Volcanics is tholeiitic basalt. Dikes of mafic and intermediate composition cut the volcanic pile but are as unconmion. a whole Silicjc. volcanic and subvolcanic rocks comprise less than 1% by volume of the exposed Portage Lake Volcanics (Bornhorst, 1975; Grimes, 1977; Robertson, 1974; Robertson and others, 1979). They tend to be in the lower part of the stratigraphic section in the Keweenaw Peninsula (Fig. 6). The composition of volcanic rocks of the Portage Lake Volcanics was affected by both Primary magmatic differentiation has long been igneous and metamorphic processes. recognized both within and between tholejitic flows (Broderick, 1935; Broderick and For example, the Greenstone flow, the thickest Hohl, 1935; Cornwall, l95la and b). individual flow in the formation (Figs. 4 and 5), is chemically stratified due to Copper may have conceninternal differentiation (Cornwall, l951b; Longo, 1983). differentiation trated in the pegmatitic and more importantly in the flow tops. Work by Scofield (1976) demonstrated that copper can also be concentrated in the Rose and Grimes base of individual flows by gravitational setting of magnetite. (1979) showed the existence of three magmatic cycles within the Portage Lake Vol— canics which initiate with basalts that have high incompatible element abundances. The degassing of volatiles during and after eruption in an oxidizing subaerial environment was also important in that it allowed degassing of SO2 (Cornwall, 1951c). This created a sulfur deficient environment which favored the later deposition of native copper. A third pre—metamorphic process was deuteric or diagenic alteration of olivine and glass to hydrous minerals, the most important of which is chlorite. Ljvnat and others (1976) used '3D and '3180 to show that the basalts have undergone extensive isotopic exchange with low—temperature meteoric waters prior to metamorphism/hydrothermal mineralization. After emplacement the volcanic pile was subjected to extensive low—temperature, low—pressure hydrothermal/metamorphic alteraThe Portage Lake Volcanics on the Keweenaw Peninsula are in fact a classic tion. �6 Feet FR EDA SANDSTONE ci ,.,', Lava unit 0 AND fn .. COPPER HARBOR 0 NONESUCH SHALE CONGLOMERATE 0 06 0.-A 0 00 0 12,000 c a 15,000 =- - Lava unit c 000 o — QO 4 00 0 0 0 0-0 •0 0 o00 000 00 0 •2.0 . 00 . 0 0 0 11,000 c 14,000 1. .: PORTAGE LAKE LAVA SERIES Lava unit ci :0 10000 c 13,000 . Figure Columnar stratigraphic section of rocks northwest of the Keweenaw 5: Fault in the Calumet—Ahmeek area (from White and others, 1953). The labels for units within the Portage Lake Volcanics are consistent with those used on the maps in the field guide. �C phc paf T Hancock conglomerate (No. 17) Ashbed flow pp 9000 — -— Pewabic West conglomerate (No. 16) pk Kearsarge flow pv Wolverine sandstone (No, 9) 4000- poc Old Colony sandstone (unnumbered) 3000pg Greenstone flow pa Allouez conglomerate (No. 15) 4 orta - Lak 'r,Icanics ph Houghton conglomerate (No. 14) 7000 pi Scales Creek flow psc 2000 - Iroquois flow —— = pc - conglomerate TI (No. 13) 1000P0 pkc flow Kingston conglomerate (No. 12) Pcc Copper City flow PS 5000 St. Louis conglomerate (No.6) Figure 5 continued. �8 STUDY AREA Lake Superior COPPER HARBOR INDEX MAP OF NORTHERN MICHIGAN EAGLE RIVER Fish Cove I..: LacLo_ atiot Lake Cambrian Jacobsvil le Sandstone Upper Keweenawan Precambrian loge - .-.•. . . 10 Miles Figure 6: Portage Lake Lava Series Intrusive or extrusive body Bedrock geology of the Keweenaw Peninsula showing the location of silicic to intermediate volcanic and subvolcanic rocks (from Robertson, 1975). �9 locality of abundant and widespread low temperature alteration minerals (Table 1). Penetrative deformation did not accompany the metamorphic episode and primary textures are preserved even in the most intensely recrystallized areas. Copper Harbor Conglomerate The Copper Harbor Conglomerate conformably overlies and locally interfingers with the Portage Lake Volcanics (Fig. 3). It varies in thickness from about 100 m to 1800 m. The Copper Harbor Conglomerate is a red—brown basinward—thickening wedge of volcanogenic clastic sediments. These clastic sediments fine distally and up— section. Sandstones are lithic graywackes and conglomeratesare composed of volcanic clasts with a ratio of mafic to intermediate + silicic composition of about 2:1 (Daniels, 1982). Daniels (1982) has interpreted the Copper Harbor Conglomerate as Mafic to intermediate lava flows are a prograding alluvial fan complex (Fig. 7). interbedded in the exposed Copper Harbor Conglomerate (Fig. 5). These lava flows are termed the Lake Shore Traps and occur predominantly within the middle section of the formation. Nonesuch Shale — The Nonesuch Shale is a succession of gray—black siltstone, shale and sandstone which overlies and interfingers with the Copper Harbor Conglomerate (Fig. 3). The Nonesuch has a thickness of between 40 m and 215 m. The Nonesuch was deposited in a reducing, rift—flanking lacustrine environment initiated through disruption of drainages (Fig. 7) (Daniels, 1982). This differs from the over and underlying redbeds that formed in an oxidizing environment. Freda Sandstone The Freda Sandstone is a cyclic succession of red—brown, ferruginous, sandstone The Freda and mudstone overlying and gradational with the Nonesuch Shale (Fig. 3). It is dominantly fluvial in origin with has a maximum thickness of over 3700 m. The top of this greater compositional maturity than the Copper Harbor Conglomerate. formation is not exposed. Jacobsville Sandstone The Jacobsville Sandstone is a red to bleached white succession of coarse—to—fine— grained feldspathic and quartzose sandstone with varying amounts of siltstone, shale and conglomerate which rests in fault contact with the Portage Lake Volcanics in the Keweenaw Peninsula. Elsewhere it can be found overlying Middle Precambrian basement. Jacobsville is probably slightly younger than Freda Sandstone. Jacobsville has a Sandstones are fluvial in origin whereas conmaximum thickness of over 3,000 m. glomerates are believed to be alluvial fan deposits (Kalliokoski, 1982). Structure Structure of the Keweenaw Peninsula is dominated by the Keweenaw Fault (Fig. 4), a high angle reverse fault where older Portage Lake Volcanics are thrust to the Both units are affected by this major northeast over younger Jacobsville Sandstone. the normally flat—lying Jacobsville Sandstone is often strongly tectonic feature: deformed by drag folding near the fault contact and the Portage Lake Lavas are often highly fractured. The Keweenaw Fault cuts off the base of the Portage Lake Volcanic Series along its entire strike length so that the total stratigraphic thickness �__ 10 NONESUCH SHALE DEPOSITION POSSIBLE "LAVA-DAMMED LAKE" MODEL FOR SANDSTONE FREDA STREAM BRAIDED FLUVIAL BASIN MA IN BASIN CENTRAL FLUVIO-DELTAIC 0 00 0 O - LUVIQ°Th 0 o 00 0 o° x0 x 0 0 0 0 PORTAGELAKExVOLCxANICSxxX x O 0 0 x x _— o0xxXxx XXX 0 CONGLOMERATE 0 o_—T 0 ALLUVIAL°PLAIN OCOPPER HARBOR 0 0 x 00 x - x - x : x x tINTERFLOW 0 0 SEDIMENTS X -------- ±±± RELATIVE PAL ED F LO W DIRECTIONS Figure 7: Schematic diagram showing the interrelationships between major stratigraphic units found northwest of the Keweenaw Fault in the Keweenaw Peninsula (from Daniels, 1982). x �:ii Table 1: Secondary minerals found within the Portage Lake Volcanics, Keweenaw Peninsula, Michigan (from Butler and Burbank, 1929; Stoiber and Davidson, 1959; Jolly and Smith, 1972). Widespread Minerals Locally Important Minerals Rare Minerals Laumontite Analcime Apophyllite Prehnite Sericite Atacamite Pumpellyite Orthoclase /Nicrocline Bowlingite Quartz Chalcedony Brucite Epidote Thompsonite Chlorastrolite Albite Natrolite Chrysocolla Chlorite Chabazite Cuprite Hematite Native Silver Faujasite Sphene Sulfides Fluorite Calcite Arsenides Powellite Native Copper Datolite Serpentine Heulandite Stilbite Ankerite Tenorite Sulfates Tourmaline Clay Minerals Whitneyite Wairakiite �12 The regional tectonic as well as the total displacement along the fault is unknown. context of the compressional stresses which caused development of major reverse faults is unknown at the present time, although it is probably unrelated to processes which formed the Mid—Continent rift. — The Keweenaw strata dip moderately northwesterly toward the centr of the Lake This Superior Basin and their dip angles increase toward the base of the section. is in part due to modification attributed to the Keweenaw Fault, but White (1960) has demonstrated syn—depositional downwarpage of the basin. Thus, lava flows and sediments formed wedge—shaped beds thickening basinward such that a relatively constant horizontal datum level was maintained throughout the life of the basin. Smaller scale, post—depositional folds are also present as broad synclines and anticlines (wavelengths from 5 to 10 miles) (Fig. 8). The regional context of these folds is not clearly understood, however, they appear to predate major reverse Late high angle faulting occurred throughout the area and produced several faulting. major offsets of the Keweenaw Fault. This type of fracturing and faulting is partiSignificularly abundant in the upper portion of the section northeast of Mohawk. cant deposits of massive native copper later filled many of these cross—cutting channelways (summarized from White, 1968). Mineralization and Alteration The Keweenaw Peninsula is the location of a dormant billion—dollar copper mining district. From 1845 to 1968 the mines of the Keweenaw native copper district produced about 11 billion lbs. of refined copper (Weege and Pollack, 1971). The major ore producing horizons are geographically restricted to a 45Km long belt within the Portage Lake Volcanics in the Keweenaw Peninsula (Fig. 8a). There is a close relation— ship in both time and space between native copper mineralization and alteration in the Native copper, the principal ore mineral in the Portage Lake Volcanics (Fig. 9). Keweenaw Peninsula, occurs in amygdaloidal and brecciated flow tops, interflow conglomerate units, and fracture systems (Butler and Burbank, 1929; White, 1968 and 197la). The predominant native copper deposits are lenticular blanket—like ore bodies that are found along certain stratigraphic horizons such as the tops of lava flows and conWeege and Pollack (1971) estimated that 58.5 percent of the district glomerate beds. copper production came from flow top ore bodies and 39.5 percent came from conglom— erate ore bodies. The remaining 2 percent of copper production was from fissure (or vein) ore bodies. There are three main varieties of lava flow top recognized in the Keweenaw native 1) fragmental or flow top breccia; 2) nonfragmental! cellular copper district: or vesicular basalt; 3) "scoriaceous" or flow top breccia with a sandy or silty White (1968) estimated that 21 percent of the lava flow tops in the Portage matrix. Lake Volcanics are brecciated (fragmental). These flow tops consist of a rubble of The interstices between fragments and the vesicles are vesicular and massive lava. commonly filled with secondary minerals. Most of the major flow top (amygdaloid) copper ore bodies are of the fragmental type. White (1968) has estimated that uppermost 5 to 20 percent of most individual lava flows is vesicular and contains between 5 and 50 percent vesicles which are commonly filled with secondary minerals. The abundance of amygdules decreases downward and the middle and lower parts of flows The tops of these flows are locally termed cellular are amygdule—free massive basalt. Cellular amygdaloid may have traces of native copper but and often have smooth tops. �1968). White, (from district copper native Keweenaw B. the of Folds amygdaloids. in quartz of limit northwest approximate the is line dotted The amygdaloid. (ashbed) Atlantic 7) and amygdaloid; Royale Isle 6) amygdaloid; Osceola 5) amygdaloid; Pewabic 4) amygdaloid; Baltic 3) amygdaloid; Kearsarge 2) conglomerate; Hecla and Calumet 1) production: of order in number, bold the by identified are deposits Major 1968). White, (from district copper native Keweenaw the of map Geologic A. 8: Figure 3 •l �14 Eagle Harbor Section • o,f4 FEET Top of Portage Lake Lava Seriea I Hancock Congl. 2000 I-Il I Greenstone Flow Allouez Congl. — Houghton Congi. Calumet & Hacla Congl. 0 I - I - 2000 King8ton Congl. PUMPELLY lIE ZONE Kearaarge Amyg, 4000 Scale8 Creek Amyg. 8000 Upper Limit of Zone at Dehydration Gratlot Flow Bohemia Congl. 8000 10,000 Keweenaw Fault - I EPIDOTE ZONE 12,000 Micwcline — Chlorite —— — Epidote — — — — Pumpellyite — — — Prehnite — — — Copper — — — — Datolite — — — — Silver — — — — Ankente — — Quartz — — — — — - Sericite — — — — Colcte — — Arsenides — Sulfides — .-_ — — — — — Albite — — .._ Aduloria — — — — Saponite — — — Laumontite — — Analcime — — Sulfates(barite,anhydrrte, gypsum) Figure 9: A. Distribution of secondary minerals in the Eagle Harbor section of the Portage Lake Volcanics (compiled from Butler and Burbank, 1929; Jolly, 1974; Jolly and Smith, 1972; Stoiber and Davidson, 1959; White, 1968). Location of section is between Copper Falls and Delaware Mines shown in Figure 4. B. Paragenesis of secondary minerals in the flow tops and veins (from White, 1968). Solid black symbols are the more abundant minerals. Secondary minerals shown here are nonmagmatic and not of supergene origin. �15 — A few smooth topped flows show a tendency no ore deposits are only of this type. forming what are locally for the amygduies to be laterally interconnected in bands, important host rock for ore termed "coalescing cellular amygdaloid". This is an "ScoriaceouS" amygdaloid is used locally for flow top breccia at the Quincy Mine. filled with sandy or silty in which interstices between vesicular fragments are mineralized example of The Ashbed amygdaloid is the onl-y significantly detritus. this type. — native copper deposits, Conglomerates interbedded with lava flows are host for major of copper distrifundamental control The particularly in the vicinity of Calumet. Permeability is decreased by conglomerate. bution is the permeability of the host greatly on sedimen— Localization of ore depends abundant fine detrital material. which might bedrock topography tological and environmental factors, such as the conglomthickness of influence location of a stream channel resulting in differing erate. — right deposits are tabular and commonly crosscut the bedding at nearly Large masses of native copper weighing many tons were first angles to strike. the fissure deposits. These deposits are economically much less discovered in types. important than the other Fissure Copper sulfides are a minor constituent of the system, and are found as small veins cutting the flow top native copper deposits, joint—coatings in the conglomerate units, and in association with Mt. Bohemia intrusive (Butler and Burbank, 1929; Copper sulfidesandarsenides are paragenetically Broderick, 1931; Robertson, 1975). Significant copper sulfides with minor late in flow tops and conglomerates (Fig. 9b). native copper also occur at the base of the stratigraphically higher Nonesuch Shale and top of the Copper Harbor Conglomerate (Brown, 1971) at White Pine, approximately 70 Km southwest of most of the discovered mineralization in the Keweenaw Peninsula. The solutions that formed the White Pine deposit may have been related to those which formed the deposits in the Keweenaw Peninsula (Ensign and others, 1968). Vesicular and fragmented flow tops of the Portage Lake Volcanics were prevasively altered by hydrothermal fluids, producing low temperature metamorphic mineral associations occurring as amygduie and vein fillings as well as whole rock replacements in the most permeable hOrizons. The systematic metamorphic zoning varies vertically within the volcanic pile and is equivalent to zeolite, prehnite—pumpellyite facies (Jolly and Smith, 1972; Stoiber and Davidson, 1959), and possibly lower greenschist facies (Fig. 9a). The copper deposits lie stratigraphically within the pumpellyite The copper, in the deposits, may have been leached from dehydrated lava flows zone. (epidote zone) in the deep parts of the pile and migrated up dip and precipitated in the zone of hydration where conditions were sufficiently reducing (Jolly, 1974; Scofield, 1976; White, 1968). These workers and Cornwall and Rose (1957) suggest that most of the copper was probably initially tied up in Fe—Ti oxides and their oxidation released the copper. The oxidation reactions of magnetite to hematite and pumpellyite to epidote may occur along with native copper deposition (Jolly, 1974). The intensity and degree of alteration varies as a function of position within individual flows, position in the volcanic pile, and proximity to cross—cutting fractures (Jolly and Smith, 1972). Local controls, such as pre—alteration composition, appear to govern the assemblages of final alteration products and their major—element compositions. Figure 10 shows a summary of known elemental mobilities and a schematic picture of alteration conditions. �PERMEABILITY LITHOLOGY DIA GNOSTIC MINERALOGY Added to flow top Redistributed within flow Hgh '''''' e'°r : FLOW TOP - FLOW INTERIOR Low , None —r---- Pumpellyite Epidote Metadomain - Ca Al f .. Albitized Basalt Albite Chlorite Unmetamorphosed Basalt Ca—Plagiociase 16 ELEMENT MOBILITY from Outside flow - 114 Na Clinopyrosepe Olivme Si - - 1 H2 Lost from flow top Remained Immobile — K, Fe, Ti, Mg, Zn Cu —w- Cu(s) HO—*-HO 2 (p) 2 Ni Ce) Elements Remained Immobile I. DEPTH 4. TEMPERATURE I Basal chill zone ii Least—altered flow interior lIE Amygdular flow top Arrows denote tluid movement Figure 10: A. Possible elemental mobility pattern in an idealized lava flow in the pumpellyite and epidote zones within the Portage Lake Volcanics (based on chemical data of Jolly and Smith, 1972; Jolly, 1974; Scofield, 1976; Stoiber According to Jolly (1974) Cu and H20 were derived from and Davidson, 1959). the epidote (dehydration) zone and deposited in the pumpellyite (hydration) zone. Diagrammatic regional model for the Portage Lake Volcanics showing local B. thermal/chemical gradients superpositioned on the regional geothermal gradient and showing the movement of fluids along flow tops and bottoms and through frac— tures (modified from Jolly and Smith, 1972; Scofield, 1976). �17 ROAD LOG AND STOP DESCRIPTION Mileage MAP 1 0.0 Assemble at the Memorial Union on University. Begin the field trip the northeast side of the Union. on a kame terrace to the south of the campus of Michigan Technological from the circular drive lqcated on The Michigan Tech campus is located the Portage Lake. 0.1 Right turn. 0.2 Immediately after there is a right turn on to Townsend Drive. Left turn. The Quincy Mine can be seen on the ridge on the skyline. 0.55 Left turn on Agate Street, where we go up the steep hill on the south side of the Portage. We are climbing off of the kame terrace. 0.8 Right turn on Seventh Street. 1.0 STOP 1. Scales Creek flow on Seventh Street, City of Houghton. This stop is marked by a prominent ridge of ophitic basalt, which is an outcrop of the Scales Creek flow, one of the great Keweenawan flows, which can be traced continuously for a strike length of more than 160 Km along the Peninsula. It is about 70 m thick, with an amygdaloidal top which is typically not resistent and a prominent, ridge—forming, ophitic core. The ridge at this site can be followed down hill all the way to Shelden Avenue, where it is covered by glacial deposits. It can be traced across the valley, where it passes through the Ripley School, a prominent brick building across the Keweenaw Waterway. This bearing, about N3OE, is the regional strike of the Portage Lake Volcanics which dip about 500 to the NW. Another clue to the attitude of the rocks is given by the Quincy #2 shaft house on the horizon which heads up an inclined shaft down dip along the amygdaloidal ore bodies of lava flows just over 2000 m higher in the Portage Lake section. Throughout the Portage Lake section between Baltic and Mohawk, most amygdaloidal and conglomerate zones show well developed zeolite and prehnite—pumpellyite facies metamorphism and native Cu mineralization. At this site the amygdaloids just below the Scales Creek flow are strongly mineralized. One mine, the Sheldon Columbian, operated just a few hundred m to the east in the early 1900's. This same horizon is exploited by a series of shafts called Isle Royale Mines, for several km to the SW. Stop 2 is at one of these mine dumps. The most obvious geomorphological feature here is the Keweenaw Waterway, The waterwhose origin was thoroughly investigated by Warren (1981). way formed in a fault zone like many which crosscut the Portage Lake stratigraphy. A bedrock valley, more than 200 m deep formed along the fault as a result of stream superposition through a cover of flat—lying This valley, like others on the Keweenaw, was deepened and sediments. widened by glacial erosion, in a fashion similar to the finger lake The complex glacial deposits, consisting of region of New York State. moraines, terraces, varved clays and gravels were the result of the pattern of ice retreat from the region, which had profound and complex effects on the drainage patterns. �/ 71! /, )- - II 55 NJ/' C ft7 D— G N I - -. IStOP 2• -. // / J /1 /11 i// /1 9SGIS1eYaChASHAFT —/ / Li -- d \\\\ P L - 12 p /_ - K E C •==- — I / I ' H San ds1;i one ••°' - _ji _____ C0LL6E OF MINING AND YE CN0L0G \_y' __________________ 46' SSa 907 si _________ _____ \/ I A 1/ 1059 4 +1 /1 R2 Jdevii1e - - -: . 1M7 --- L . --;•: //r '-4 / A ______ T -- — 10 II /R 567/ -7 0 607 .4- - />7) // -/ t.• I - // - H - — NC - Map4 - , — - •MAP 1 �19 1.1 Left turn on Portage Street. 1.25 Grand Portage Mine dump on left. 1.45 At this spot the Scales Creek ridge is Near the Houghton water tower. slope exposed higher on the south of the Keweenaw Waterway. There are many bald knobs with more or less east—west trending deep glacial grooves on them. To the east of the prominent ridge, there are many mine oprIings from the series of Isle Royale shafts. The Adams Township takes its water supply from these Isle Royale mines which are now filled with water, and this is the source of water for Hancock and several other towns. 1.55 Cross Sharon Avenue and continue on Portage Street east of the City of Houghton fire station. 2.15 Right turn immediately followed by a left turn so we are now on Bridge Street heading south. 3.0 Entering Dodgeville. On the right hand side of the road is one of the prominent Isle Royale mine dumps. 3.2 Center of Dodgeville. If you turn on the road to the right through the Trailer Park, there is access to the Isle Royale mine dumps from Shaft No. 4 and 5. The Isle Royale Mine is described at Stop 2, continue ahead. 3.6 Junction to the Green Acres Road and make 3.7 STOP 2. Isle Royale Shaft No. 6 a right turn. mine dump on the Green Acres Road. The Isle Royale mine worked the top of the Isle Royale flow. Production from the Isle Royale amygdaloid began in 1855, the mine closed in 1948. A total of about 350 million lbs. of refined copper was removed from this mine (Weege and Pollack, 1971). The Arcadian Mine (see Map 4) may also work the Isle Royale amygdaloid. The Isle Royale flow varies in thickness but is about 70 to 150 ft. thick and lies just below the Scales Creek flow discussed in Stop 1. It dips about 50 to 60° to the northwest (Fig. 11). A gentle fold accounts for the curvature of the flow (see Map 1), Isle Royale syncline. The flow from the top down is characterized by fragmental zone, banded amygdaloid, foot inclusion zone, The fragmental zone consists of irregular fragments and massive main trap. of amygdaloid and fine—grained basalt ranging from small grains to tabular The vesicles and spaces between the blocks several feet in long direction. secondary minerals. The banded amygdaloid is an fragments are filled with considerable area. Amygdules are commonly abundant unbroken rock body over zone a banded appearance. Below the fragat certain horizons giving this amygdaloid is the foot inclusion zone which is indemental zone or banded foot inclusion The finite patches or inclusions of amygdaloid basalt. devoid of amygdules (summarized zones grades into massive basalt practically from Butler and Burbank, 1929). �L_, I. _J —, - - Le Vc ific Ss S iac 11: Cross section A—A' on Map 1 (from White, 1956). Labels are as follows for the Pewabic West conglomerate (pp), Creenstone Portage Lake Volcanic Series (P) and its subunits: flow (pg), Allouez conglomerate (pa), Calumet and Mecla conglomerate (pc), Kingston conglomerate (pkc), National sandstone (pn), Kearsarge flow (pk), Wolverine sandstone (pw), Scales Creek flow (psc), Bohemia conglomerate (pb), St. Louis conglomerate (ps), Baltic conglomerate (pbc), and Unnamed conglomerate (pu). Figure P ...vIIIe A' �21 Butler and Burbank (1929) recognized two distinct periods of alteration. The earliest alteration was oxidation which caused the development of This oxidation could essenhematite, which produced reddened basalt. alteration shortly after eruption. tially represent deuteric The second after the period of alteration was probably flows had been tilted. This period was complex and resulted in deposition of native copper. This stage :L divisible into three substages: 1) An early stage of deposition of epidote, pumpellyite quartz, calcite, most of the native copper and minor prehnite, alkali feldspar, and laumontite; 2) an intermediate stage characterized by the development of sericite with quartz, calcite, anhydrite, gypsum and minor barite; 3) a final stage of copper sulfides and arsenical copper accompanied by calcite, sericite, quartz, chlorite, and specular hematite occurring in numerous veinlets. Stoiber (unpubthe following estimate of the lished data) made percentage of alteration the Isle Royale Mine: quartz, 26— minerals on dumps from four shafts of 59; calcite, 5—39; prehnite, 6—32; pumpellyite, 1—17; epidote, 1—10; sericite, 0—12; chlorite, 0—3; K—feldspar, 0—trace. This dump and the ones near Dodgeville are freshly reworked and good specimens of native copper and alteration minerals can be found. 3.9 Junction M—26 at the Copper Country Mall and you are going to make a left turn. MAP 2 5.6 Entering Atlantic Mine. 6.9 Right turn at the sign that says South Range Village Limit and drive about 150 yards into the road and walk to the right through a notch up the hill another 60 meters to Stop 3, the South Range Quarry. NW SE Felsite bed 9 IEE Fragmental amygdaloid i Non-fragmental amygdaloid 190 FEET F(a) Masve basaft PegmatEte layer (a) and zone of thin Figure 12: Geologic profile of the South Range quarry along the northeast wall (from Cornwall, 1951; White, l97lb). Location of the quarry is shown in Map 2, Sec. 17, T54N, R34W. �22 C ;: 52 // p —q w• • . njflfe San .one I �23 STOP 3. South Range Quarry. South Range quarry provides an excellent cross sectional view of a massive to amygdaloid lava flow (Fig. 12) of the Portage Lake Volcanic Series. The base of the section is a conglomerate bed, about 4 m thick; it is exposed This is overlain by an 18 m thick fine— on the main path to the quarry. grained basalt flow, followed by a 42 m thick ophitic basalt flow and finally the lower 17 m of another ophitic basalt flow. The conglomerate is well indurated and consists mostly of pebbles and cobbles of rhyolite with subordinate clasts of basaltic lava set in a sandy matrix of similar composition. The clasts are subangular to sub— The overall character is similar to the Copper Harbor Conglomrounded. This conglomerate is erate which will be seen later in the field trip. one of a number of sedimentary beds which are interbedded with the Portage This particular bed is correlatable with the National Lake lava flows. Sandstone, a marker bed in the Nass—Rockland area. The basalt flow that occupies most the quarry face has features which The characterize the thicker flows of the Portage Lake Volcanics. lower half of the flow is massive basalt, overlain by a zone with progressively smaller pegmatitic layers, topped with cellular amygdaloidal basalt, and at the top a discontinuous layer of flow top breccia (called fragmental amygdaloid). A typical pegmatitic layer, consists of 4 cm to 1.3 m core of green amygdaloidal lava surrounded by a 4—9 cm border zone at the top and bottom. The border zone is composed of a medium to coarse grained aggregate of albite/oligoclase, augite, ilmenite, and magnetite. Pegmatitic layers toward the top of the zone are more amygdaloid. Quartz, prehnite, and a green or red cherty substance occurs in flattened vesicles The pegmatitic layers are products of cooling at the top of the layer. and differentiation as it cooled (description of pegmatitic layers from Cornwall, 1951). Amygdules and interfragmental spaces are filled with Locally the basalt is quartz and prehnite containing traces of copper. intensely epidotized or prehnitized. Outside of the Quarry and to the north are a series of glacially grooved outcrops in which the exposures of the pegmatitic zones are spectacular. Take a right turn on M—26, going into the town of 7.9 Return from Stop 3. South Range. 8.4 At stop sign in South Range, take a left turn. 8.6 Right turn at the church and immediately foiJowed by a left turn as the whole road jogs to the left. 8.7 Entering the town of Baltic. 8.8 Right turn. 9.2 The main road turns to the left, we go to the right on a small paved road driving past a concrete building towards some very large mine dumps. �24 9.4 STOP 4. Baltic Shaft No. 3 Mine Dump. The Baltic, Champion, and Trimountain mines worked the Baltic amygdaloid. Total proThe Baltic Mine opened about 1898, the others opened in 1902. duction from the Baltic amygdaloid was about 1.85 billion lbs. of refined copper which was the third largest producer in the Keweenaw native copper district (Weege and Pollack, 1971). The amygdaloid was developed for about 7 Km along strike and to the 38th level in the Baltic Mine. The Baltic flow is an ophite that varies considerably in thickness but The Baltic amygdaloid in many places is 17 m is around 50—70 m thick. or more in thickness and is composed of fragmental amygdaloid, the average stoping width is about 5—8 m. However, like all fragmental amygdaloids of the district, there are significant variations, e.g. the lode can thin to only a few feet thick composed of trappy or cellular amygdaloid. The lode dips at about 70°NW (summarized from Butler and Burbank, 1929). The abundant minerals associated with copper in the Baltic amygdaloid are Copper sulfides are unusually quartz, pumpellyite, epidote and carbonate. The sulfides characteristically occur in fissures that dip 75 abundant. Most of the copper sulto 900 and strike nearly parallel with the lode. fide in the lode is chalcocite associated with iron—bearing carbonate, there is some bornite and rare chalcopyrite. Native copper is irregularly distributed through the amygdaloid ranging from minute specks to masses weighing several tons. Native copper occurs at the margins of sulfide veins and it may occur with quartz in the center of veins. Sulfides are in general paragenetically late (Fig.9h Introduction) (summarized from Butler and Burbank, 1929). The majority of the dump at this stop is amygdaloid basalt. R. E. Stoiber (unpublished) made the following estimate of the percentages of the seconcalcite, 91; quartz, 5; epidote, 3; dary minerals in the dump as a whole: Paragenetically epidote and chlorite were early minerals; chlorite, 1. calcite, quartz and native copper were intermediate; and copper sulfides Excellent specimens of chalcocite and iron—bearing carbonate were later. can be found on this dump as well as native copper. 9.4 Retrace route in Baltic. 9.9 Stop sign in Baltic, make a left turn to go back in the direction of South Range. 10.1 Right turn, immediately followed at the church by a left turn. 10.3 In the center of South Range, right hand turn off M—26. 10.8 Passing the South Range Quarry, Stop 3. 12.5 M—26 jogs to the right at the center of Atlantic Mine �25 MAP 3 14.7 STOP 5. Glacial Deposit Near Pamida The Keweenaw Peninsula has probably been modified by all of the major glacial episodes of the Pleistocene. During maximum glaciation the entire Keweenaw Peninsula is believed to have been overridden by around 3000 m of ice. The present form of Portage and Torch Lakes is related to the final retreat of the Laurentide ice sheet in the Lake Superior The final glacial advance and stillbasin (shown in Figs. 13 and 15). stand over the Keweenaw Peninsula was made by the Keweenaw Bay Lobe, marked by an end moraine of Wisconsin stage (Fig. 14) (summarized from Warren, 198]). The earliest recognized channel cut by drainage through the Portage Gap area is the Huron Creek channel (Nap 3). The channel is waterworn bedSince there is no delta at the southern end rock due to southward flow. of this channel perhaps the source of water was a large lake where glacial The drainage sediments had time to settle before the water was removed. in Fig. 16 (summarized from pattern through the Portage Gap is shown Warren, 1981). A delta kame is just west of the Huron Creek channel and is the location The sediments, in this dissected knob, show strong of Stop 5 (Map 3). evidence of being deposited by a braided stream closely associated with Extreme variations in grain size and sorting occur within a a glacier. This suggests differing flow regimes during distance of a few meters. Poorly to well—worked unconsolidated sands predominate but deposition. Numerous cut—and poorly sorted pebble conglomerates are also present. Large striated boulders of basalt within fill structures are present. from a nearby glacier. This the gravel and sand must have originated large exposure is capped by a thin (less than one meter) poorly sorted clay till which thickens rapidly to the south; it is about 7 meters thick The later unit may be a flow till(?) at the top of the nearby hill. which slumped off the nearby glacier (description by S. Beske—Diehi and S. Nordeng, Dept. of Geol. & Geol. Engrg., MTU). 15.75 Between Junction of M—26 and US—4l, so turn right on US—4l past the Mobil and Erickson gas stations. 16.2 Excellent outcrop of basalt with exposed amygdaloid on both sides of the road. 16.35 Make a left U—turn back onto US—4l going one way back through the City of 1—loughton. 16.45 Amygdaloidal basalt with pegmatitic zones at Burger King Restaurant, Shelden Avenue, Houghton. This stop is an alternate to the South Range Quarry Stop. Excellent exposures of the cellular amygdaloid and pegmatitic interior of a thin Portage Lake lava flow are found to the west of the restaurant and along Montezuma The flow top is strongly metamorAvenue, just a few steps to the north. phosed with a variety of amygdule minerals of the prehnite—pumpellyite The green color of the basalt is due to the abundance of epidote. facies. Below the amygdaloid the basalt is virtually unmetamorphosed except where thin pegmatite zones cross it. �1I 4 0 6O7 R A T ) —. 4 I '',;ee1cii:.! 1 I 4 G 26 L E — ., �1981). Warren, 1976; Kalliokoski, 14: Figure (from glacier Lobe Bay Keweenaw the of moraine End / / e 80 Kilometers es ii M 0 F 0 Prest, 1975; Huber, (from America North central from retreat ice Wisconsin the during positions ice—marginal Speculative 13: Figure 1969). 46) (Fig. 1257A). Map Canada of Survey Geological 1969, Prest, K. V. (from basin Superior Lake the readvance, or surge, ice major Note Amenca. North central from RETREAT ICE WISCONSIN in H P H B NJ' y,.,. ,.4k,.,b,,,, Sh,,..,,d. K "fl". F 40 U j' ,)" L .• •' 27 �L-\' ii) o 5t - -- - -, - - - -?-- -- S — "0A P E - ( - -' - - .— T -"i /5S5 - S jS ji - !j ' - S -- I _\ S. S SI 5—- - QS.AUL -S-j - -- S - f I -- 1 S -' '< S S I \ /55( S ) - S7 sS S - - // HURP - ( ' )•J / - / At KE - /, .S\ 55 - - : S \_S . I / S 55 / - S S MUWAUKEE - 1 5 / S q S mo0/ S - - S. I :/fj'S.S ,jS/ :-r- S - /5 - \55 I - s - / /- S -S. _S___SS S 5CHICAGO Figure 55 S S S 55S\ /,/ ...5 I 5S / / —-S Enlarged view of ice—marginal positions during Wisconsin ice retreat 15: (from Prest 1969) . Note the major ice readvance in the Lake Superior Basin and withdrawal pattern over the Keweenaw Peninsula. S. �29 LAKE / WfSHBURN // / -.5 / I/ Figure 16: High level drainage through the Portage Gap during the Washburn Stage (from Warren, 1981). �30 16.9 Right turn on US—41/M—26 and crossing the Portage Lake Lift Bridge into Hancock. The bridge was built in 1957, and is designed to accommodate Great Lakes ore boats, who prefer the Keweenaw Waterway route to rounding Keweenaw The present bridge abuts the Hancock side of point in stormy weather. the canal at approximately the site of the old Quincy Mill where the tramway descended Quincy Hill from the mines. MAP 4 17.15 Left turn on TJS—41 into Hancock. 17.35 Right turn and immediately followed by US—41 going to the left but we go straight at 17.4. 17.5 Bear to the left on White Street. 18.0 Junction between White Street and Lincoln Drive which is US—41, we take a right turn. The fenced ground near this locality surrounds an area of recently caved ground, which is thought to be related to shallow stopes of the Hancock Mine. The detection and distribution of such openings is a problem of considerable concern to local authorities, since many mines had shallow workings, since towns grew up adjacent to mines and since maps of the underground workings are incomplete and/or inaccurate. 18.3 Turn off US—41 to the right to the overlook of the Keweenaw Waterway or Portage Lake which is Stop 6. STOP 6. Keweenaw overlook near Quincy Mine. This overlook, near the crest of Quincy Hill, allows a broad overview of all the previous stops and also the best general view of the Keweenaw The features which can be seen are, from east to west (left Waterway (Fig. 17). to right): 1) On the skyline, the knobby terrane of the Huron Mountains, which lie across Keweenaw Bay. The mountains are underlain by the Archean gneisses and granites of the Northern Complex, and are the main source 2) In the forearea for the extensive deposits of Jacobsville Sandstone. ground, underlying the flat topography of Jacobsville Sandstone is clearly The Jacobsville extends from the Keweenaw fault, which crosses visible. the Waterway just east of the Michigan Tech campus, across the Keweenaw The formation is genBay and under the Huron Peninsula (Pointe Abbaye). erally flat—lying, while all of the other rocks of the Peninsula dip north3) Within the town of Houghton several westward toward Lake Superior. ridges of basalt can be traced downhill, the most prominent being the The attitude of the Scales Creek flow horizon, where Stop 1 was made. Portage Lake flows and the alternation of resistent flow interiors and interflow conglomerates with less resistent flow tops makes site investigation work critical for construction projects, to accurately determine For example, depths to bedrock and to make hydrologic interpretations. site investigations of the extensive area south of the main campus, where the Michigan Tech Student Development Complex (visible from the overlook) is now located, provided the focus of several Masterts theses for students in Geological Engineering (Stevens, 1971; Hase, 1973). A �7 dVV i / 28 fl\ / I I // 4 _0 / i I / - 0 "HH< L -' / •/ -- - R - 2Z71L 7t z / r iA .•'.<;:Ir..r /1 // (( I _,_ t! II - r • G I / •0 - / / —: / \\ I. - / I I / • // 2? // / / Wewabic h(' / -.. // ---- / NA2 I II NA6 (CH!GAN 4N/ // A2!,'ll .fl. 1/ 2 A2/ /k' / // P -___-J ;LAK/E / 1 5 !s'c , \/ // , lI i//11 !r/z"v/ >1 - • _ wJI .1 L ./.7:E MaF5 - �View from Portage overlook facing south. Notable features include: 17: 1) Huron Mountains, 2) Flat—lying Jacobsville terrain, 3A) Scales Creek flow ridge, 3B) Student Development Complex, 4A) Houghton water tower at Isle Royale Shaft #1, 4B) Isle Royale dump 114, 4C) Isle Royale dump 115, 4D) Wheelkate Bluff (Trimountain, 5) Highway M—26, 6) Contact between the Portage Lake Volcanics and the Copper Harbor Conglomerate, 7) Houghton County Courthouse, 8) Quincy Smelter, 9) Michigan Technological University Main Campus. Previous stops are located with stars and stop numbers are prefixed with an S. Figure w �33 general map, showing the detailed bedrock geology of the City of Houghton (Holcomb, 1975) is used routinely by developers in the area. 4) On the skyline on the opposite side of the Waterway, beginning at the Houghton water tower a series of mine dumps representing the Isle This marks the Royale lodes can be seen extending into the distance. approximate route of the road between Stops 1 and 2, and shows the The knob on the skyline is Wheel— strike of the Portage Lake Lavas. kate Bluff near South Range which is one of several residual bedrock 5) The divided M—26 highhighs and is located just south of Stop 3. way is visible, traversing the glacial deposits described at Stop 5. 6) To the right, the Waterway traverses the upper contact of the Portage Lake Volcanics and the Copper Harbor conglomerate, Nonesuch Shale and Freda Sandstone. The Stop is the best single locality to observe the Keweenaw Waterway. The Waterway and the peninsula are named for an Indian word for Portage route, but to make the Waterway accessible to Lake Superior shipping, This canal work was necessary at both the northern and southern shores. The geological history of the Waterway was investwas completed in 1873. igated in detail by Warren (1981). This and other major bedrock valleys were formed by stream superposition as ancient rivers eroded through flat— But the valleys lying Paleozoic rocks into the tilted Keweenaw strata. Then the Pleistocene. were greatly deepened by glacial erosion during as the Keweenaw Bay sub—lobe retreated at the end of the Wisconsin glaciation, the Waterway allowed eastward drainage across the Peninsula to lower First, drainage occurred in the Portage Gap lake levels to the east. (between Houghton and Hancock) while a tongue of ice remained in what is As the ice retreated further, the valley now nowwestern Portage Lake. occupied by Portage Lake was formed by eastward drainage of successively Torch Lake was formed lower proglacial lakes in western Lake Superior. by a trapped block of ice which later melted in place to form the lake Warren's study includes a complete bedrock topographic map of basin. the Keweenaw and a series of maps showing the pattern of ice retreat, based on the distribution of glacial deposits. Houghton was named for Douglass Houghton, the geologist who sparked the Michigan copper mining boom by publishing his Michigan State Geologist Houghton was settled in 1852 and is the site of several Report in 1841. historic buildings, the most important of which is the Houghton County Courthouse (1887), a prominent yellow brick building with Jacobsville Sandstone facing and copper roof and a flag pole, on the hill above the main part of town. Hancock was settled in 1859. Across the road and just slightly up hill is Quincy Hill House (1871), the mine manager's house for the Quincy Mine. The Quincy No. 6 mine shaft house dominates the skyline behind the viewpoint. A map of the Quincy operations in its heyday are given in Figure 18. The inclined No. 2 shaft descends at about a 45° angle more than 3 Km (1.7 Km below the surface) making this one of North America'a deepest mines. The surface projection of the area mined is shaded on Map 4. 18.35 Right turn back on US—4l going up the hill. 18.75 Prominent outcrop of basalt with glacial grooves. �34 18.85 Right hand turn would lead to the Quincy Steam Hoist, we're in the center The Quincy Steam Hoist can be now of the Quincy Mine area (Fig. 18). visited during the summer months for a small admission charge. Inside is the largest steam mine hoist in the world. This great machine, invented by Bruno Nordberg and installed in 1920, could lift a 10 ton ore load at a rate of more than 1000 m per minute. The hoist is still in pristine condition and a full museum of the Quincy Mine is maintained inside as well. MAP 4 or 5 On the left hand side, immediately after 19.3 Turn right on Arcadian Road. the turn are some of the Quincy mine dumps, nearest Shaft No. 1. This will be Stop 7. Please respect private property signs and stay within the public right—of—way. STOP 7. Quincy Mine Dumps. The Quincy Mine worked the Pewabic amygdaloid. Production from the Quincy Mine began in 1856 and ended in 1967. Total production from the Pewabic amygdaloid was about 1 billion lbs. of refined copper, ranking fourth in the district (Weege and Pollack, 1971). Lankton and Hyde (1982) give an outstanding illustrated historical account of the history of the Quincy Mining Company which earned the name "Old Reliable" because it paid dividends so regularly. The Pewabic amygdalLoid deposit consists of a group of relatively thin flows. These basaltic flows are A geologic cross section is shown in Figure 19. Some texturally distinctly porphyritic with large feldspar phenocrysts. of the thicker flows have an ophitic texture. The tops of flows in some places are cellular whereas thick flows may be either cellular or fragmental. The amygdaloids of Pewabic flows are characteristically of a type Flows of this type typically have smooth termed ].ocally as coalescing. tops in which individual vesicles are larger than average, reaching an inch or more in diameter. VesiciLes in the same layer may coalesce to form a A series thin, jagged gash with a lateral extent of up to 12 feet or more. of such openings provided an almost continuous path for the flow of mineralizing hydrothermal solutions. Several such layers may occur in the same flow top. Where coalescing is well developed in the Pewabic amygdaloid there may be 2 to 10 layers from 3 to 5 feet thick. There is every gradation from coalesced layers of vesicles to those that show only a moderate tendency to collect in layers (summarized from Butler and Burbank, 1929). quartz is the most abundant secondary mineral assoCalcite is also abundant. ciated with native copper. Pumpellyite, epidote Laumon— and chlorite are common but not abundant and prehnite is present. tite and datolite are common in upper levels but not lower levels (summarized from Butler and Burbank, 1929). In the Pewabic lode, The majority of the dump at this stop is amygdaloidal to massive basalt. Secondary minerals in this dump are mostly quartz and calcite with lesser amounts of pumpellyite followed by epidote. Paragenetically epidote and pumpellyite seem to be early whereas quartz, calcite and native copper formed later. �__ 35 zz .../ ... 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';- .-;::~ -~_/. ." ~_. =--" ~ "'Ir)!~;'~~::[ • "' t.-" • "{"l'r J'\ : • ':". '" , "'-I' ~.~·:•. :t :, .~ •. '.. ..y~';" ;.~ ~,,"~ .~'. ~ J ',,- ~~ \0t"\' \", (/. 8 \"~ - • ""'. /\, ~.~., /' ~~. r ;' J 5inir: ,;:.O@ • ~ ••,. : ~~"~ / . .":./ ' ••• 0 ,', .. ';: . 'i' ~.- ---~ -J ' ' : . ' ' \VEl tV _ -- "'';'.', ~I)('I)'''' ~ Z ")~~ [1' •~ ,,' \: % ~~ ,~'-- ,.,~ - "I" ~ ,t; ~~ '~.~~",..~.~ ~ ~'f? ~.~ -':_. , 0®' R, .. , \Uti .. , . \ , ') fiu / " .",.. , j. 1'iin !'~inp ® #~:;~'s;ng- ~ .,. ,I Structures StructuH'.S of the the Quincy quincy 'A~G' .. h ';: ~ 'O6~/-,. '·~., ,., • .. /- • Figure 18: 18: ., . h'. i,; #.. . ~~---;- • II---~' J,:. ~, , •.•" . , . " ,®I'I. • ~ :---.-J.... ~ •. t. .... :;.:( ';:'~:\, ·1 " ~; '0\..;.), "~' " ~~i \.',' ~.~~~'i:::'--~., _~ --' .. i (~,",\~ .. /~.;/~~~,.~~I ,1r,-"\r .. ~,:,./... I -;:'1'" 'i'" . '''i;';~';cl:'' • , ',Ii', l'UI Franklin . , . , - ~ ,I, i/···' d,..... " " -![?'~' ..,.t .... ;l:~ '~~'-i.,~-",:~~"""... 6 -- , ~"" Pr I'is.,J)ir ,I .. >or ", ••h,c c- - - -. ~ (Y~'0'~0\ /~!e ,'" ',' u~ 8~~ _;t:,:~~'c~lL, N~6 ; _ , ' ~', @ ) . . W I Z . - ; - : - N 0 ? '~ -.----"'Cl.\ •• • .•~ . '"".•• , ~i~fr .. r '1'/" "J'II .. P~8bl('. •• ,-b~ ......, ~ ·~".I:.. ,I.', - ~ ,:_~. '~II '\!2~).J .... JuP<V,or"$~ '-~~> J!I ~ -______. ,;.,--::~ r'..... lt~ .•_, ~~_.:.- \ ~ ,\. ,'/ ~.~.~ ..••••·1".::"f! 4-ro CalumBt 4—eoca(umr "J,;t. ..... ~...",~" "~\"'':~'')\~;' ~. ,) , (,/",~ ~:;>{( \ :" ". ~ ':', \.-. " .... .., .. ', 5ord flaije 800rdinq ttouse /lhrth!5 OOX otDre 8. Abrth5 . Ii >;,,~/' (3. Jomei /1 Oa9r and i2w77pany fJ James, H ueaq8r cmcJ Wmp.'3ny Abrths /?;!..5ldence O<zorqe wr7e North::> .iderice •.~ -'9-~_ '., "0'., 6 =- .... ; ••-~ .,. , {i? IS Cat/)olle Olurcfiand arid Priest~ Prtest5 C.ti?olc 07urch /?Q.5idencØ R.e.:;ldence 5 9, :1' .. '. ~ . P<.-~ '.. 10 Clubhouse(öathhou5e) (l3athhouse) (0 Clubh,ue Ooctor:J Lbctcr f(e:,t.(Jence Rejtdene Dipetary DI,::;,oe=ary A9cnt5 f?e.5ldence idence k;Jent::> Z ,~ '. ~ I '----------:.~. ~;J: ~:h ~il!i t:/"2Ie' 1l: ~;H ica(e: ~ :~: 11T .~ "¥' '"F'""'C 'iIi: TT 4a:)}.~ i :1; 1um·:¥:-'.lf-----¥'-------, : r;11.. !I': Vl.U(1 • II] - , .\ I - 0 '~~•• ~ or, 'H~lJof A180 of C,e fuxaon me QlHncyMV74 kocy l.t:>cdctOn.,.no Locacror, a,ri Vte<nuy'(noC1dll} ------....... J0cation (['rom Lankton Lankton and and Tyde, Eyde, 1.982). 1982). location (crom Vnnty ( ~ ! 3 n~ a , l.v 0'> �s S' B- I I n ~l·(!,,.1 7""""- s .., c ~ 7/ 'N' J ~'C' ~ ~ "n",~ " .. .'!>'"<" ~teOa ~~ .".'_ L~ . I .J(VJ ' ~~,~eSUC; p ~ c -''' .c:= <' Copper Harbor Jacobsville -4000' I ., <P: ./ Figure 19: 19: Geological cross cross sectionfromB section from Bto to B' B' on on Map Map 30, 30, B' B' to to B" B" on on Map Map 4, 4, B" B" to to B"' B'" on on Map Map 5. 5. This This cross section section illustrates illustrates the the general general geologic geologic relationships relationships of of the the Keweenaw Keweenaw Peninsula. Peninsula. The successively by the the Copper Harbor Conglomerate, Conglomerate, the the Nonesuch Portage Lake Volcanics are overlain successively Shale and the the Freda Freda Sandstone. Sandstone. The Portage Portage Lake Lake Volcanics Volcanics are are in in fault fault (reverse) (reverse) contact contact with with the the Introduction). Labels for Jacobsville Sandstone Sandstone (see (see Fig. Fig. for the the Portage Portage Lake Lake Volcanics Volcanics (P) (P) younger Jacobsville are follows: Hancock conglomerate (phc), (phc) , Pewabic Pewabic West West conglomerate conglomerate (pp), (pp), Greenstone Greenstone flow flow (pg), (pg), are as follows: Allouez conglomerate Kear— canglomerate (pa), (pa), Calumet and and Hecla Hecla conglomerate conglomerate (pc), (pc), Kingston conglomerate conglomerate (pkc), (pkc), Kearsarge flow flow (pk), sarge (pk), Scales Creek flow (psc), (psc), Bohemia Bohemia conglomerate conglomerate (pb), (pb), St. St. Louis Louis conglomerate conglomerate (ps). (ps). W --.J �38 38 MAP 55 19.5 Entering Coburntown. Coburntown. This is is another one of the the communities that that sprung up around the the Quincy operations, operations, most of the the houses built and owned by by up Several ethnically distinct neighborhoods existed the company. Several existed "on "on the the hill" in in the the early early 1900's. 1900's. In lived on on the the In all all more than 6,000 people lived hill in in 1905. 1905. 20.45 Y in There is a Y in the road, road, we take the right hand branch which is essentially aa straight tially straight road with a sign sign saying saying Arcadian Arcadian Scenic Scenic View. View. 20.7 Passing a radio radio tower tower on on the the right. right. We are now crossing the the Scales Creek flow the top top of the small small ridge ridge (see (see Map Map 5). 5). The Arcadian Mine worked flow at at the an amygdaloid just just below below the the Scales Scales Creek Creek flow. flow. The amygdaloid may corcoran relate with the the Isle Isle Royale Royale amygdaloid discussed discussed at at Stop Stop 2. 2. North of the the road is is Shaft Shaft No. No. 11 of Mine. Stoiber (unpublished (unpublished date) date) of the Arcadian Mine. estimated the percentages of of non—metallic non-metallic secondary minerals in in the dump calcite, from Shaft No. No.11 as: calcite, 43; 43; prehnite, prehnite, 25; 25; quartz, quartz, 16; 16; K—feldspar, K-feldspar, 8; 8; epidote, epidote, 6; 6; pumpellyite, pumpellyite, 1; 1; chlorite chlorite 1; 1; and and laumontite, laumontite, trace. trace. 21.4 see the the largest largest part part of of Portage Portage Lake, Lake, Down to to the the right of of the the road road you you can can see of view is the field field of is basically Keweenaw Bay and the the Huron Huron Mountains. Mountains. Much of the flat—lying flat-lying Jacobsville terrane. terrane. 21.6 Road turns turns to to the the right right and and changes changes to to gravel. gravel. 21.8 descending off off the the Portage Lake Volcanic Volcanic Series Series across across the the Keweenaw We're descending Fault onto Jacobsville Sandstone. Sandstone. 23.0 have aa view of of the the Isle Isle Royale sands sands We are descending the the hill and and we have across Portage Lake in in Houghton. Houghton. These are tailings from the Isle Royale out and and into into Portage Portage Lake. Lake. dumps (Stop (Stop 2) 2) which were brought brought out 23.15 Junction with M—26 M-26 and and take take aa left left turn turn at at the the Portage Pottage Lake Lake Coal Coal Dock. Dock. 23.6 Entering Dollar Bay Bay on on M—26. M-26. MAP 66 25.2 of flat—lying Exposure of flat-lying cross—bedded cross-bedded redbeds of the Jacobsville Sandstone on the left hand side side of of the the road road (northwest (northwest side). side). STOP 8. 8. Jacobsville Sandstone. Sandstone. The Jacobsville Sandstone is a a fluvial fluvial succession of feldspathic feldspathic and quartzose quartzose sandstones, sandstones, conglomerates, conglomerates, siltstones, siltstones, and shales shales up to 1,000 m m thick (Fig. (Fig. 20a). 20a). There are no interbedded lava flows flows or cross—cutting cross-cutting dikes. The Jacobsville Sandstone is separated from the Portage Lake Valcanics Volcanics by the Keweenaw Fault, Fault, aa reverse reverse fault. fault. The Jacobsville Sandstone is is probably upper upper Keweenawan in in age and and may may be slightly younger than the the, Freda Sandstone. Sandstone. Current the Keweenaw Peninsula are to the northeast and east east Current directions directions in the suggests transport transport to to deeper parts parts of aa basin located located northeast of of which suggests Keweenaw Keweenaw Bay Bay (Fig. (Fig. 20b). 20b). West of Lake Gogebic thickness thickness and and current direc— directions tions suggest another deep deep part part to to the the basin. basin. East of Calumet, Calumet, near the the Keweenaw Fault (Stop (Stop 10) 10) the the Jacobsville Sandstone contains boulders of basalt which suggests a topographic topographic high in the the Portage Lake Volcanics north north of the the fault fault during during this this period period of of Jacobsville Jacobsville sedimentation. sedimentation. Metamorphosed �/ / / / ,0 /~(" / / // / .I,/""!' ... /Ci' ,;:"00' / , / /'pP .~ // /' ~ 56 / '-~~~ ..... / -....;,:~. / '086 • /// / //' // 39 // ." // II II II 1070 1070 , -I [ II II II II II II II II H \\ ,\ z , " \ 1068 ,__L_ — . II / / p- \\ H \' \\ \\ ,\. H "\\ ". —--•• , L ' p~~// ~\~. H... if] :=:;\ fr-- t1 16 II II r p N 0~ I~ 0 ,:;1'Q , '....... 0, NA/5Q .............. " II NAI3' II "'NA/5Q "" NA/3' " C'~ II :~<? H 1/ 1 0~ ....... .,,00 933 l ' ':O~ ....... CJO C, / 4, cL '\ 21 / ')0 -"',--- ""'--: ...... , . . . . ; /i /1 ~ ~\ \. 1 "( II II I I-=-- 4 A ~0 ...0 b~ --'~ , NAI7 NAI7 N-,~ Il /I It II J e~ ,~ ,000 ___ OFFSET _— OFFSET -4":t- ~0 14 i-- / KEWEENAW KEWEENAW FAULT FAULT c• \\ II .-:-1r;o.f6=====.=~ 15 N83 22 23 • 630 • : H Mill I,- 1 884 I, 'I ii I II" 'I. 913 / - "'-" '", / \. L )8 s. -T , --"J". /_-9_/ \ Stop8 602 602 \• \ "', - 0 V - II ii I, ou II * , H,;" II ,,'I; / CJ~ / ~O'" // 'so / / j .: // 668 ~ 11~ .~ /;:.~=J- ..--"--1-~~==-~;:./~ -: -- II JI-ij . - - If//// • -, ,... .~ .,;.: -:-- // // II /1I, // '1/ II // II /? /-::-~==;!/ 1, II ,726 26 / "// 11/ /,/ ,,/ ij "7 'l~' ,y 1- . 'l /,'l // 7, ~. /.1 ,'/ /1' ,,;1 ",' - "/ //' 800 :- H •- -j 4-\ Aap5 // / *0 ~0 27 62 // 26 ---- H >, \ "''-\ ,,----"'\ _ _ ;;:."'::- _F1_ \\ '\ \. '. 0,", "1L-B9~ --- ' , _ _ ,Q!=D_ M on pv, '\ ,--- ....—.. —'-.. 7 35 • 1 6 .. . MAP6 ~AAP ,,",, • �____ 40 Sandstone Thickness Current Directions 9400 Geophys. est. (ft.) 597 Weillft.l o 50 I j Km. B. A. I rocks Iron ranges 0 - 0 km mi 30 I 50 so N --...... ,. \ c. C. Figure 20: 20: Relationships of Jacobsville Sandstone Sandstone (from (from Kalliokoski, Kalliokoski, 1982). 1982). of Jacobsville Jacobsville Sandstone with minimum thickness denoted Thickness of denoted by +'. '+'. B. Current in the the Jacobsville Jacobsville Sandstone. Sandstone. C. Location of of Current directions in C. possible source areas iron formation staurolitic metasedimentary possible source areas of of iron formation and and of of staurolitic metasedimentary rocks. A. A. �41 iron-formation quartz-staurolite pebbles pebbles suggest suggest aa source source from from the the iron—formation and quartz—staurolite jacobsville Jacob sville sedimentation sedimentation was was preceded preceded by by aa long period of cratonic stability stability with with little little or or no no volcanic volcanic activity. activity. Erosion was was apparently initiated by late Keweenawan warping along the the mid—continent mid-continent rift rift system. system. The major movements on on reverse reverse faults faults were were after deposition (summarized (summarized from from Kalliokoski, Kalliokoski, 1982). 1982). after Jacobsville deposition southeast southeast (Fig. (Fig. 20c). 20~. sandstones varies from from subarkose subarkose to to quartz quartz sublithic sublithic Lithology of sandstones arenite. There are some some beds of of arkose arkose and and quartz quartz arenite. arenite. Grain size size varies from from fine fine to to coarse. coarse. Quartz grains show show evidence evidence of of volcanic volcanic and and metamorphic origin. origin. Microcline is relatively relatively unaltered unaltered and and plagioclase is is unaltered to to highly altered. altered. Other clasts clasts include: include: volcanic rocks, rocks, schist, the minerals epidote, epidote, biotite, biotite, muscovite muscovite and and chlorite. chlorite. schist, shale and the Sandstone varies in in color color from from red red to to aa cream—white cream-white or or purplish—red purplish-red color. color. The color depends on on the the alteration of of ferromagnesian ferromagnesian minerals minerals and and the the amount of iron oxide deposited deposited as as rims rims on on feldspar feldspar grains. grains. Ripple marked amount of bedding surfaces surfaces and and cross—bedding cross-bedding are are common common in in some some localities. iocalities. Sandstones are fluvial stones fluvial and conglomerates probably represent represent alluvial fan fan deposits (summarized (summarized from from Kalliokoski, Kalliokoski, 1982). 1982). At this this stop stop the the character character of of the the Jacobsville Jacobsville Sandstone Sandstone can can be be seen seen in in The exposures here can be the exposures on the left side of the road. the left side of the road. exposures here can be compared and contrasted to to Jacobsville that that will be seen at Stop 99 and Stop 10. 10. 25.9 the small small town town of of Mason. Mason. Mason was the the site site of company housing Entering the for for the Quincy mill operations operations from from 1890. 1890. 26.5 On the the right right hand hand side side of of the the road road is is an an old old dredge dredge which is is stuck stuck in in in Torch Torch Lake. Lake. This is the the C&H dredge #1, #1, built in in 1913, 1913, bought tailings in by Quincy in by in 1955 1955 and and used used until until 1967. 1967. 26.7 Now we pass pass the the remains remains of of the the main main buildings buildings of of the the Quincy Quincy Mill, Mill, built built in 1890 1890 to to accommodate accommodate steam stamps, required when when the Quincy operation operation in stamps, required the Quincy expanded to to the the Pewabic Pewabic Lode. Lode. 27.0 Along the road on the the left there there are more outcrops of flat—lying flat-lying Jacobsville Sandstone. 27.3 On the right, right, Torch Torch Lake. Lake. 27.7 On the right hand side of the the road road are tailings tailings which have been revegetated. revegetated. These tailings tailings now as we are entering Tamarack City are part of the the mill operation of the the Calumet && Hecla company mines and the the Calumet region region which have major mills located located at at Tamarack Tamarack and and Hubbell. Hubbell. 28.15 On the left hand side of the the road road are the the footings footings from from one of the the Tamarack Mills. MAP 7 28.6 On the right right hand side of the the road road are the the remains remains of a steam steam stamp stamp mill. mill. 28.7 Left turn, turn, going going up up the the hill hill toward toward Stop Stop 9. 9. Follow the paved road road which jogs a little little to to the the left left and and goes goes up up the the hill. hill. �__ _______ p 28 c/ / 5 \\ // ___ __ ___________ // i ''s / / //\ ;o367 /\' // TL 7 TL5 FaLls + 31 f I HIL / -LLVARY EM / 1 \ 36\ 42 MaD88 42 • J Cr C - Lake n en / 'S 'I I, ii' . T I \\\ \ II II II II /7 // 959 'I \ \ \ 12 1Ltp,9 . / mrs 1 \ &çubbell —;: -N ---- .. — •••S" 'so —\N ___--1-_ MapG ( MAP77 MAP \ �43 28.85 Cross the the old Copper Range Range railroad railroad grade. grade. 29.0 Sign indicating indicating Hungarian Hungarian Falls. Falls. This is is the the lower lower part part of of the the falls. falls. Continue going up the the hill, hill, straight straight ahead. ahead. 29.25 Junction of a a four—wheel four-wheel drive drive road road to to the the left. left. Stop and walk Stop here here and towards towards Tamarack reservoir/Hungarian reservoir/Hungarian Falls Falls upper upper part part where where excellent excellent exposures of of Jacobsville Jacobsville Sandstone Sandstone are are found found near near the the Keweeriaw Keweenaw Fault. Fault. STOP 9. 9. Hungarian Falls. Falls. The Keweenaw Hungarian Falls is is located located near near the the Keweenaw Keweenaw Fault Fault (Fig. (Fig. 21). 21). The Fault is reverse fault Volcanics and and Fault is aa reverse fault that that juxtaposes older older Portage Lake Volcanics the In this the younger Jacobsville Jacobsville Sandstone. Sandstone. In this locality, locality, the the Keweenaw Fault presumably dips dips at at a west similar to presumably a high angle to to the west to that that illustrated illustrated in Figure 19, in 19, Stop Stop 7. 7. The The Keweenaw Fault Fault at at the surface surface varies varies from from aa single fault single fault plane to to aa more complex complex fault fault zone, zone, such such as as described described hear near Structural relationship Lac La Belle. relationship of of beds beds near near the the fault fault also varies varies from steepened also steepened dips dips to to folds. folds. In general the the dip of the the In Portage Lake Volcanics and Jacobsville Sandstone Sandstone steepen steepen appropriately appropriately as one approaches the the fault. fault. as At Hungarian Hungarian Falls the At the fault fault contact causes very little little deformation of the Jacobsville Sandstone, the Sandstone, which which is is only only tilted tilted slightly. slightly. To To the west of of the fault fault at this this site site the the Portage Lake Volcanics are unusually shallow shallow If not not viewed in the If the context of of many many other other localities, localities, the the fault fault dipping. might not might not be recognized as such such a a profound feature, feature, and could appear as a a conformable contact. contact. The the fault fault exposure The contrast contrast between between the exposure here here and and that at at the the next next stop stop (Stop 10) at at Hungarian Hungarian Falls Falls is and illusthat (Stop 10) is striking striking and illustrates of rocks rocks along along this this major major feature. feature. trates the the structural variability of The Portage Portage Lake Volcanics near the The the Keweenaw Fault at Hungarian Falls conInterbedded sists of of basaltic lava flows sists flows with interbedded interbedded conglomerate. conglomerate. sediments make make up up aa small small part part of of the of the Portage sediments the stratigraphic stratigraphic section section of the Portage Lake Volcanics Volcanics and and are found found as relatively thin thin widely separated separated beds. beds. However, in the the Keweenaw Peninsula conHowever, here and at some other localities in glomerates glomerates within the Portage Lake Volcanics are either near or at the the fault contact. fault Walking downstream downstream along along the the stream stream to to the the upper upper and and lower lower falls falls allows allows examination of good exposures of Jacobsville Sandstone with cross bedding, of Sandstone bedding, interbedded shaly shaly and and conglomeritic conglomeritic horizons horizons and and many many typical arkosic redred— interbedded typical arkosic bed sedimentary features. features. 29.25 Turn around and and go go back back down down the the hill hill to to Tamarack Tamarack City. City. 29.8 Stop sign. sign. 29.9 Entering Hubbell 30.5 On the right are Calumet & & Hecla mill buildings which have recently recently been taken over over by by Michigan Michigan Tech Tech Ventures Ventures as as aa pilot pilot plant plant location taken location for for small small industries. Torch Lake is is still on the the right with many of the the tailings tailings out in in the the lake. lake. Stamp mill mill remains are straight Stamp straight ahead. ahead. Turn left left on on M—26. M-26. �Ta arack reservoir metal gra Jacobs yule sands tone 100 feet -.- z — fIIs D fault basalt c Ong!omer Figure 21: Geologic sketch map of the Hungarian Falls area (by J.M. Robertson, 1973). Basalt and conglomerate are part of the Portage Lake Volcanics. Note that north is toward the left margin of the page. �45 31.4 Entering the town of Lake Linden. The Houghton County Historical Museum is on the right hand side of the road. The building (1917) was donated by the C&H Company to the Houghton County Historical Society in 1963. Among the best displays are scale models of underground mines and a rich photographic record of the boom copper days. 32.2 Right turn on Ninth Street (the so—called Bootjack Road) in Lake Linden. 32.35 Follow the signs to the Lakes Left hand turn at two blocks after 32.2. This is Gregory Street. Drive—In Theatre. MAP 8 33.3 On the left hand side of the road is the Lake Linden cemetery. The road heads north along the Trap Rock River Valley. On the left hand side of the road at the top of the steep slope is the Keweenaw Fault. On the right hand side of the road is a flat—lying Jacobsville terrane. The Trap Rock River follows another of the glacially eroded, deep bedrock valleys described by Warren (1981). 34.5 Pavement ends. 34.6 The gravel road bears to the right. 34.9 Cross a bridge over the Trap Rock River. 35.0 Left turn at the Trap Rock Schoolhouse. 35.0 Cross the Trap Rock River again. 35.7 Left turn on to another dirt road that begins to go up hill. 36.1 Access to the Cross the railroad grade of the Copper Range railway. Natural Wall ravine for mapping purposes can be gained by walking a couple hundred yards to the left along this railroad grade and then walking along the stream valley up toward the fault line. 36.2 Poor exposures of flat—lying conglomerate beds within the Jacobsville Sandstone on the left hand side of the road. 36.4 Stop by an old wooden sign on the left hand side of the road. 200 meters to the left (south) to the Natural Wall ravine. STOP 10. Walk about Keweenaw Fault at Natural Wall Ravine. The Natural Wall is a bed of sandstone within the Jacobsville which has a near vertical attitude and because it is more resistant, it forms a On the sides of wall which extends outward from the walls of the ravine. the ravine the lithology of the Jacobsville here includes conglomeritic The attitudes of beds in the creek beds, sandstones and shaly horizons. flat—lying to the bottom change from east, to vertical and even locally overturned as the fault is approached. An anticline in the Jacobsville trends parallel to and 300 m east of the fault. West of the fault the Portage Lake Volcanics dip to the WNW at 35—40° (Fig. 22). �__ ______________ 7- II =" 46 -': '-,-; •=/_ rN. '/ - - -- - // _.>c I 0, /ö• - 0 -o ' Co 1 0 ' -, • - (,' I \Pj II '- (O' Cog,' ,,' ,< ' -Co " ,d/ ,-; d' / C 0 // / N' 0- N LU /12'i NN "N\ N • - - p\ -, F / ,,/, - /,,' -\ \\ ci 1 // , MI I, I, - e //4' / ,,,i'</ {7iiir ,,// \-" ,/\ / /IL[=== ci C ' \ —4 'C N ' " I -> (z,I4' , ,,\ k ," ". ,/,, =====' - ) -';tiiiiit V/11 __\\ — , 0- \ i I 17 -I ;3S? __WZZ ii4t - I ' P I - < - - r"N(N - ._:;:_ 4. ITC. - ,, ' 4- 0 - ci / .7 , il? -( _o— Sly) 07 I • — 1 : -I/,wI 0- —_. II 7___ /1/1/7- Co 'C I - ;r' 0 ,/ / - - \. \ ) - -/ // - I t - , NQN ci 0 - �47 . • : -. D / N -V l 'Ii 1 SC LE n thousmds of feet 1) // GN : I CL" HEA G.. 13Wfl1V — I I 11111! 1111 1-II 1111111 U II 111111 Figure 22: Geologic sketch map of the Natural Wall Ravine. Note that north is toward the right margin of the page. 2 �48 37.95 The beginning of pavement, we are entering the town of Laurium. 38.7 Left turn which is followed immediately by a right hand turn at the next stop sign on School Street. 38.8 Turn right. Junction of School Street and Calumet Avenue, which is US—41. This is Calumet, Michigan, the center of the Michigan Copper District, and a site of the Calumet & Hecla headquarters. Here Edwin Huribut discovered the Calumet conglomerate load in the early 1860's and this Greater became the most important ore body in the whole district. Calumet (including Red Jacket, Blue Jacket, Yellow Jacket, Laurium and Among many historic Rambaultown) had a population of 33,000 in 1910. buildings here are the Calumet Theatre (1900) and the C&H Community Library Building (1898). MAP 9 40.0 Entering Centennial 40.3 On the left hand side of the road you can see the Centennial Mine After closing in 1968, this mine was dewatered in the Shaft No. 6. This operation has since been abandoned. mid—l970's by Homestake. The Centennial Mine Shaft Nos. 3 and 6 worked the Calumet and Hecla The ore body lies up dip and northeast from the main ore conglomerate. body in the C&H conglomerate mined by the Calumet and Hecla Mine in the The C&H conglomerate yielded about 4.2 billion lbs. of Calumet area. refined copper, the largest lode in th district and is over one—third of the total production from the Keweenaw native copper district (total district production of about 11 billion lbs.). The C&H lode had the highest average grade in the district of 57 lbs. of Cu per ton of rock treated (Weege and Pollack, 1971). The Calumet and Recla conglomerate can be followed along strike for more Along most of this length it is less than about 1 m thick. than 65 Km. In the Calumet area it averages over 3 m thick and tends to thicken with The bed consists of north trending thicker and thinner zones depth. representing channels. At the Centennial Mine Shaft Nos. 3 and 6 thickness is often less than 3 m and the C&H conglomerate was deposited in The pebbles in conglomerate at Centennial a tributary stream channel. The pebbles in are almost all quartz—feldspar phenocrystic rhyolite. the main channel conglomerate are a quite varied suite of rhyolite and Main and granophyre with some quartz—feldspar phenocrystic rhyolite. tributary channel conglomerates tend to be coarser and contain less fine Outside of the 5—foot thickness contours the material where thicker. bed is usually shaly or sandy. At Centennial, copper mineralization tends to occur in bands with the bed and the intensity is related to the type and amount of interstitial material and location of pinch—outs or Higher grade areas are related to conglomerate with coarse barriers. sand or small pebbles as interstitial material, especially when pebbles Evidence and sand grains are quartz—feldspar phenocrystic rhyolite. also strongly suggests that the mineralized areas follow the axis of stream channels and grade is highest adjacent to the 5—foot thickness contour where the conglomerate bed increases greatly n thickness down These pinch—outs localized ore deposition from mineralizing soludip. Sedimentological relationships are tions that were migrating up—dip. �S. Q. -.7 4i 'J. idO I I, N N k-j: IC 7 /5 "4 -'-—--- —, I( - H I, C. dew b7 �50 important in exploring the conglomerate ore bodies (summarized from Wee and Pollack, 1971). 40.6 Entering Kearsarge, Michigan. 41.1 Stone boat on the 41.3 Right turn onto Water St1 .t just before the Wolverine Market. straight ahead on the main paved road. 41.5 STOP 11 is the Wolverine Mine dumps. There are dumps both on the right and left hand side of the road. The oner on the righL hand side of the road (south), just on the other side of some old buildings, ar somewhat dangerous because of bad ground. Mining in this are.a waS Very shallow (Shaft No. 3). The dumps on the left hand side of the road appear to be (Shaft ice. 2). much safcr Park along the road and walk about 100 in to right hand side of the road. Continue the north. The Wolverine Mine is one of seven different mines that worked the Kear— Centennial, South Kearsarge, &orth Kearsa rge, Ahneek. sarge amygdaloid: Allouez, Mohawk, and Seneca. Production of copper from the Kearsarge amygdaloid began in 1887 and stopped in 1967. About 2.3 billion lbs. of ref -i:ied copper Were produced frccn the Kearsarge amygdaloid making it the second largest producer of the Keweenaw native copper district (Weege and Underground workings are continuous far more than 12 Km Pollack, 1971). and extend down dip as much as 2500 m. The Kearsarge amygdaloid is one of the best documented ore bodies in the district. The Kearsarge flow has been recognized for a distance of around 55 Kit along strike, it lies directly above the Wolverine sandstone. The flow dips between 35 and 40 degt-ees to the northwest (Fig. 23). The interior of the Jt flow is a well developed ophite with a compositi:irI shown in Table 2. has an amygdaloid top that ranges from near zero up to 10 in in thickness. Just below the amygdaloid there is a zone in which the glow is distinctly Abundance and size ol porphyritic with tabular plagioclase phenocrysts. the plagioclase phenocrysts in this zone is variable but they can make up a large percentage of the rock and can be up to 2.5 cm in length. This zone. is probably the result of plagioclise floating during in situ crystallization of the flow. The stratigraphic and textural relRtionships makes this flow wore easiiv recognized than most. The near—surface thickness of the Kearsarge flow clearly shows that the most productive area is where it is thickest (Fig. 24). The flow top in the productive ares is Individual fragments mostly a fragmental amygdaloid (flow top breccia). are generally less than 15 cm in greatest dimension and contain nwnerous small amygdules. The fragmental amygdaloid makes up the uppermost part of the flow grading downward into banded cellular atnygdaloid with arnygdules This grades downward into a zone with fewer abundant at certain horizons. and large amygdules with less tendency to be found in bands and stilt further The amygdaloid top of the Kearsarg flow in downward into massive basalt. the mined area has an average thichness of around 2 rn (summarized from Butler and B'jrbsnk, 1929). �51 I A' A C ln,IIe 4000t1 Figure 23: Geologic map and cross section showing Mine and vicinity (modified from White and others, me Mine Shaft No. 2 dump (see Map 9). Labels are (pi); Calumet and Hecla conglomerate (pc); Osceola merate (pkc); Wolverine sandstone (pw); Old Colony conglomerate (ps). Table 2: Major—element composition of the Kearsarge flow (from Stoiber and Davidson, This is a weighted average exclu1959). sive of the top 12 feet and thus represents a close approximation to the original composition of the flow. the Kearsarge flow, Wolverine 1953). Stop 11 is the Wolver— Iroquois flow, as follows: flow (po); Kingston conglo— sandstone (poc); St. Louis Weight Percent Si02 A1203 Fe203* MgO CaO Na20 1(20 Ti02 MnO H20+ H20— CO2 Total ppm Cu 48.55 16.51 11.54 6.68 9.44 2.82 0.58 1.49 0.18 0.16 2.06 0.63 0.15 100.79 90 �52 300 Thickness 200 feet 100 Top of Wolverine sandstone C) CD 0 CD 0 a CD CD Butler and Burbank, 1929). Figure 24: Thickness of the Kearsarge flow (modified from from This is the near surface thickness along a strike distance of around 35 miles directly to Mandan (Map 20). The thickness is relative to the Isle Royale (Map ) underlying Wolverine Sandstone which is arbitrarily shown as horizontal. Th Chlorite Epidote Microcilne Hematite Prehnite Pumpellyite Quartz Sericite Native Copper Calcite early — TIME late Figure 25: Paragenesis of secondary minerals in the Kearsarge amygdaloid at the Wolverine Mine Shaft No. 2 (Paces and Bornhorst, unpublished data). The relationships are based on a limited megascopic and thin section study of samples from the Shaft No. 2 dump and may be modified slightly as research proceeds. The exact timing of the later minerals are difficult to determine because they do not occur together. �interior. flow Kearsarge the of outcrops find can one dumps 3 and 2 Nos. trace. quartz, and 1; Shaft the of vicinity the In prehnite, 10; epidote, 38; microcline, 51; calcite, minerals: of percentage following the estimated data) (unpublished Stoiber whole, a as dumps 2 and Nos. Shaft the For found. be can copper native with specimens Excellent 1 relationships. paragenetic their and assemblages mineral of variety a see to opportunity the have will you dump 2 No. Shaft Mine Wolverine the At trict. dis- copper native Keweenaw the in bodies ore amygdaloid of complexity the of illustration excellent an is amygdaloid Kearsarge the of area ductive pro- the within minerals amygdule of variation spatial and temporal The Bornhorst). and Paces of data unpublished of addition with 1959 Davidson, and Stoiber from summarized (mostly zones regional the within islands free prehnite and quartz are there that suggests data detailed zones. prehnite and quartz the within lies amygdaloid Kearsarge the Thus, scale regional a On mineralization. copper significant of limit the mark also may microcline of limit The boundary. zone quartz the straddle to appears ore copper richest The zones. mineral the than irregular more much is present copper native of amount The absent. is it until depth with irregularly decreases microcline of amount The depth. increasing with zone quartz the within content quartz in increase irregular an is There zone. quartz the within percent 15 about averages whole a as and depths shallower at percent 10 than less considerably is Quartz 27). (Fig. depth with vary mineralization copper native of grade and minerals amygdule the However, mineralization. copper native of grade the and banding between correlation strict no is There 25). (Fig. samples individual in seen relationships paragenetic the with consistent is This openings. remaining the in calcite of deposition finally and channel the of center the in epidote and quartz by followed channel solution the of parts outer the along first deposited been have would microcline and Chlorite channel. permeable a along moving solution hydrothermal a from minerals secondary of deposition by explained be may banding The 26). Fig. in corner wall hanging (north flow overlying the of base the in found is assemblage last The microcline. ± chlorite—calcite and epidote; ± calcite—microline calcite—epidote; quartz—epidote; microcline; ± calcite ± chlorite layer: amygdular the of top to bottom the mineral major five are from assemblages There bedding. to parallel roughly are bands The Table and 26 (Fig. 3). amygdaloid Kearsarge of bottom to top from minerals amygdule of arrangement banded a is there 3 No. Shaft Mine Ahmeek the In 25). (Fig. chlorite and calcite, copper, native quartz, are minerals formed latest the and minerals formed early are prehnite and microcline epidote, chlorite, Paragenetically spatially. and temporarily both vary assemblages mineral secondary The 1959). Davidson, and Stoiber from (summarized minerals amygdule secondary the with associated occurs copper Native sericite. and laumontite, pumpellyite, prehnite, chlorite, K—feldspar, epidote, calcite, abundant): of amounts lesser and quartz least to (most are whole, a as amygdaloid Kearsarge the in minerals filling space interfragmental and amygdule The plagioclase. replacing pseudomorphically pumpellyite fine—grained of consists basalt lyitized Pumpel— groundmass. cryptocrystalline to fine—grained a in set laths albite euhedral percent 60 about is basalt Albitized pumpellyitization. and albitization alteration: of types two by affected been has basalt top flow The oxidized. well is amygdaloid Kearsarge the in basalt The 53 �54 NORTH SOUTH Ii chlorite-mlcrocline-calcite SCALE Eli:; 10 0 3Oleet 20 copper ,, Contact between Kearsarge amygdaloid and overlying flow bottom Figure 26: Cross section of the Kearsarge amygdaloid showing the banding of amygdule mineral assemblages, Ahmeek Mine, 35th level, 399 to 500 feet south of Shaft No. 3 (from Stoiber and Davidson, 1959). The footwall is the bottom of the Kearsarge flow. Data from the back and walls are projected to a horizontal plane. In one mapped locality Stoiber and Davidson (1959) found a laumontite—quartz—calcite zone. Amygdule mineralogy of the various zones are given in Table 3 below. Table 3: Volume percent of amygdule minerals from mapped assemblages shown in Figure 26 (from Stoiber and Davidson, 1959). Mineral Assemblage Band Chlorite Chlorite— Microcline— Calcite Microcline— Calcite Quartz— Epidote Calcite— Epidote 0—3 45—82 0—47 5—10 0—trace 0—8 0 0 Volume Percent Amydule Filling Chlorite Microcline Calcite Epidote Pumpellyite Quartz 100 0 trace 0 69—74 15—25 0—5 0—1 0 0—6 0—5 1 2 0 2 0 0—1 90—96 0 87 12 0 trace 4—9 1 2 1 �copper SCALE 2 27: 4 SENECA N K (thousands of feet) W Distribution of quartz, microcline and high grade native Microcline present on hachured side of line only -" Lower limit of microcline l?igure A Over 10% quartz on hachured side of line Upper limit of quartz Very high grade copper ore NORTH KEARSARGE AHMEEK MO H ore in the Kearsarge amygdaloid (modified from Stoiber and Davidson, 1959). The Calcite and epidote are present in all zones. Kearsarge amygdaloid dips about 35 to 40 degrees to the northwest. Data from the incline are projected to a horizontal plane. CENTENNIAL WOLVERINE SOUTH KEARSARGE �56 41.5 Continue on the same road and in the same direction as before (.isr), away from Kearsarge. 42.1 There is a dirt road junction to the right, stop here. We are now in the vicinity of Scales Creek, which is the type section of the Scales Creek flow. This Is the sane flow seen at Stop 1, about 14 miles to the south, in Houghton. STOP 12. Scales Creek. This stop gives one an opportunity to look at the Scales Creek flow, a regionally extensive basaltic flow. This is the same unit observed at Stop 1, and it has been traced for more than 150 Km along the Keweenaw. There are outcrops of the Scales Cteek flow on both sides of the main road and along Scales Creek, just to the north and paralleling the road. The Scales Creek flow Is characteristically ophitle. This flow was studied, from drill core northeast of here, by Scofield (1976). The Scales Creek The massive flow has an amygdaloidal top and base and a massive interior. interior of this flow is believed to be for the most part geochemicallv unaltered (Table 4). Mineralogically primary and secondary minerals are present. Modes estimated for the massive interior are plagioclase, 40 percent; pyroxene, 48 percent; olivine, 10 percent; and opaque oxides, 2 percent. Primary plagioclase, pyroxene, and opaque oxides can be found but olivine is pseudomorphically replaced by talc, serpentine, and/or chlorite. In the amygdaloidal flow top no primary minerals are present but all have P]agioclase is been replaced by a suite of secondary alteration products. now albite with some replacement by sericite, chlorite, and puinpellyite; clinopyroxene is replaced by chlorite; olivi.ne is replaced by chlorite, epidote and pumpellyite, and opaque oxides are altered to hematite and sphene. Scofield (1976) has studied these changes in some detail. 42.1 Turn around and retrace route back to US—4l. 42.7 Passing the Wolverine mine dumps, Stop 11. 42.9 Right turn on 115—41 at Wolverine Market. 44.2 Entering the Village of Allouez. We have an excellent view of the southeast side of a prominent ridge. This ridge is held up by the Greenstone flow which is the thickest and volumetrically Largest single flow within the Portage Lake Voicanics. It wili be seen at Stop 14. 44.4 Left turn on a paved road called Bumbletownkoad, just before a Standard gas station. 44.6 Stay on the paved road, bearing right. 44.75 STOP 13. Allouez Conglomerate and flumbletown Hill (Fig. 28). The description of this stop is modified onj.y slightly from White (1971b). The stop begins with a survey of the dumps of the Allouez conglomerate mine (1869—1392, 1300T Cu). �Table 4: Average composition of three samples from the massive part of the Scales Creek flow (from Scofield, 1976). Weight Percent 5i02 47.57 A1203 16.10 Fe203* 12.54 MgO 7.67 CaO 10.00 Na20 2.24 K20 0.29 Ti02 1.43 97.84 Total 0 1000 L Figure 28: Outcrop map of the Allouez—Bumbletown Hill area (White, 197lb). 2000 FEET �58 The lithology of the conglomerate is best studied in the dumps. The largest boulders in this conglomerate are about 2 feet in diameter, and the median size is about 3 inches. A pebble count of boulders mafic rock, more than 8 inches across gave the following results: mostly amygdaloidal, 16 percent; quartz porphyry, 36 percent; feldspar porphyry, 11 percent; granophyre, 37 percent. The greater heterogeneity of this assortment suggests a less restricted source terrane than the one that supplied the Kingston and Houghton Conglomerates in this area; the Kingston, in particular, is made up almost entirely of fragments of quartz porphyry. These dumps are well known to rockhounds as a chryso— colla locality. Thin black veinlets cutting the conglomerate are calcite full of chalcocite dust. From the dump, it is a short walk to the top of the hill, which is an area of exceptionally good exposure and provides an opportunity to see several key units of the Portage Lake Lava Series. One has a unique view of both an area of intensive mining activity and of the general physiography of the Copper Range. From here, on a very clear day, one can see Isle Royale to the northwest. The Huron Mountains lie beyond Keweenaw Bay to the southeast. Bumbletown Hill is on the southwest side of Allouez Gap, a saddle crossing the Copper Range, similar to, but much less prounounced than, the valley at Houghton—Hancock. At this gap, the strike of the lava flows swings, going northeast from about N35°E to N50°E. Fractures and minor faults associated with this bend are probably the reason for the gap. To the northwest, the land slopes off very gradually toward Lake Superior, The southeast as it does through most of the length of the Copper Range. flank of the Copper Range has a steeper slope at the skyline, more or less along the line of the Keweenaw Fault. The low—lying plain between the fault and Keweenaw Bay to the southeast is underlain by flat—lying Jacobs— ville Sandstone. Looking northeast along the strike of the Copper Range, one can see the At Bumbletown cuesta form of the ridge upheld by the Greenstone Flow. Hill, this flow is only 85 m thick; it thickens abruptly to more than 300 m at the near end of the cuesta ridge. To the right of the Greenstone ridge, the more distant hills are upheld by lavas much lower in the section; dips of bedding are steep, and cuesta forms are less pronounced. The amygdaloidal top of the Kearsarge Flow has been the principal producer in this area. The line of shafts along its outcrop is a little more than a mile southeast of Bumbletown Hill, and the bottom levels are almost vertically below the surface trace of the Houghton Conglomerate (see outThis immediate area is unique in that five different and widely crop map). separated layers have been at least modest producers, suggesting a common Stratigraphically highest is the Allouez Conglomerate; plumbing system. dumps of the old Allouez mine (1869—1892, l3,000T copper) lie along the A small headframel200m N65°E of the foot of the hill, 300 m southeast. hilltop is the Allouez No. 3 Shaft, which produced (1944—1964) about l7,000T of copper from the Houghton Conglomerate (No. 14) and 2000T copper from the Iroquois Amygdaloid, 170 m stratigraphically beneath; The large headframe 6200 feet due both were found by diamond drilling. �59 east of the hilltop serves the shaft of the Kingstone Mine; this deposit, discovered in 1962 also by diamond drilling, is in the Kingston Conglomerate (No. 12), 300 m stratigraphically above the Kearsarge Flow. The outcrops on the top and upper slopes of Bumbletown Hill represent a series of andesite flows, some slightly porphyritic. The flows range Unlike the basaltic flows found below the up to 20 m in thickness. Houghton Conglomerate, these flows are not individually very extensive; the map shows two flows pinching out within this small area. As a group, the hilltop are stratigraphically equivalent the flows in the vicinity of whose and lithologically similar to those tops were mined at the Quincy Mine, just north of Hancock. The Greenstone Flow is exposed in a series of outcrops 160—300 m southIts thick amygdaloidal top is exposed at the end east of the hilltop. of a private roadway 200 m south—southeast of the hilltop. Columnar fine—grained basalt and ophitic basalt can be seen in exposures farther down the slope. 45.05 Take a left turn on US—4l and cross into Retrace route back to US—4l. Keweenaw County from Houghton County. 45.9 Entering Ahmeek. 46.25 Junction to Cliff Drive. MAP 10 47.65 49.5 Turn left on Cliff Drive. Passing Seneca Lake on the right hand side of the road. We are driving Along the road are along strike, near the base of the Greenstone flow. several small basalt outcrops mostly on the left side of the road, At this point the Greenstone Flow abruptly thickens to nearly 400 m. It dips northward at about 25° toward the Lake Superior Syncline. This lava flow can be traced along much of the Keweenaw and has been stratigraphically and geochemically correlated with a similar unit on Isle Royale, 90 Km away on the other side of the syncline (see Fig. Thus the areal extent 3a). of this great flow exceeds 5000 and its volume is of the order of 800— 1500 Km3 according to White (1960) and Longo (1983). It rivals the composite Roza flow (Columbia R.) as the largest known lava flow on earth, The Greenstone typically shows spectacularly developed pegmatites, ophitic horizons and columnar jointed areas. A cross section of the Greenstone Flow at this locality and a map of the zone where the flow thickens rapidly The pegmatoid zone is unusually thick in the northern are in Figure 29. part of this map. The ophitic zones of the flow are relatively unaltered portions and Longo (1983) has shown that the composition of these zones are remarkably constant and demonstrated the great chemical similarity of the composition of the Isle Royale and Keweenaw ophitic exposures of The rapid thickening of the Greenstone here was sugthe Greenstone Flow. gested by White (pers. comm., 1982) to be caused by the separation of the upper part of the flow into multiple flow units, which appear to be separate flows. To the north the flow may be a continuous, single flow unit, while to the south it may have been made up of many flow units. �—_ . ,.// ! • • ,•//Moh /7 0 ) / ( - / •1' 2 Io / ) ) �10 I EM 0 7 SCALE 1 mile Figure 29: Map and cross section showing vertical zones within the Greenstone flow between Seneca and the Cliff Mine (from Longo, 1983). I 92 1 2 20 15 225 285 680 (feet) Thickness Vertical Scale: 1"=200' Sub-ophite Pg: 2nd Pegmatoid Zone -Sub-ophite Pg: 1st Pegmatoid Zone LOp: Lower Ophite Pg: 3rd Pegmatoid Zone UOp: Upper Ophite Mel anophyre EM: Columnar Jointed Top of Flow Vesiculated Flow Top �62 MAP 10 and 11 50.0 Crossing the Cratiot River MAP 11 50.6 52.5 We are now driving on the southeast side of a prominent ridge which is held up by the Greenstone Plow. We are at the site of the Cliff Mine which was the first mine in the district. The dumps ind old footings for the mine building are mainly on the 1.eft hand side of the road and the townsite, of which little remains, is on the right hand side of the road. optional stop where one can look at the Greenstone Flow and the Cliff Mine dumps. In this region the Creenatone Flow is mainly ophitic basalt and sometimes shows quite well dev.loped coarse columnar jointing. The Cliff Mine worked the Cliff fissure. The mine operated discontinuously from 1845 to 1887. It produced a tote] of abcwt 38 million The productive portion of the fissure lies under lbs. of refined copper. the Creenstone Flow. The Cliff fissure is nearly at right angles to the attitude of bedding and dips steeply to the east. Most of the mineralization was confined to the fissure although SOL1C amygdaloids were mineralized (Cliff Mine suinmarizedtromsutler and Burbank, 1929). Many large masses of native copper were mined from the Cliff Mine and larger masses weighed up to 100 tons. The large 100 ton mass had to be cut, by hand, into smaller pieces, it could not be blasted (Clarke, 1976). Among the fissures rhr Cliff was the In addition to native copper and silver the followmost productive of silver. caling minerals are found at the Cliff Mine (not in order of abundance): cite, epidote, chlorite, laumontite, prehnite. datolite, thomsonite, chlora— strolite, apophyllite, adularia, gypsum, sphalerite, galena, pyrite and surface oxidation minerals. This is zir 53.1 Tunction of U5—41/M—26. Turn left (north). MAP 12 53.4 Entering Phoenix 54.5 Turn left on a dirt road just before (0.1 mile) the junction between US—41 It is about 100 meters from the paved road to the base of the and M—26. Phoenix Nine dump which is Stop 14. STOP 14. Phoenix Mine and Greenstone Plow. At this stop one can look at the Phoenix Mine dump and the lower ophite of The Phoenix Mine worked numerous veins below the the Creenstone Flow. Greenstone Flow. Like the Cliff Mine discussed at mileage 52.5, the Phoenix t'Iine was one of the. eatltet mines in tze d.Lstrict and opexattd off and cc'. from 1849 to 1917. It produced a total of about 17 million lbs. of refined The Phoenix Mine also worked the Ashbed copper (Butier and Burbank, 1929). ainygdaloid where it is mineralized in the vicinity of vein copper occurrences. The Phoenix Mine dump is notable for halfbreedS (native copper plus native silver) and for spectacular secondary analcite. Other minerals reported in the Phoenix Mine ares (Clarke, 1974a) include: pumpellyite, chlorite, natrolite, chlorastrolite, and apophyllire. �It I -t- /1 -iii - I I - 'I (/ If.-r: V- - I -/2 - // // 'i \ /_ 1;' FJ 'T 'ii L7 I - - C - L -.-. - - -c C: --- - - - // - - -:--- Efri /2- - -- r - -- / -: - • / - : '\-. = — — .1 / (r / . /9GOI H ,/ /7 - - // /I- , / I /2 --r - I ' -I \ C9 �_ oo __ - - 0 '. "/ - ' w. ta - '.;:.' Phoenix Ashbed1.. - Workings ! LI9 -- 0 / - /; 4 - / - r A9i-PhoenIx Mine - K Stop 11' MAP 12 -- �54.6 Flow. Greenstonie the cross and strike to perpendicular drive River. Eagle towards M—26 on left Turn 55.0 flow. the in middle cooling slower the represent which exposures, these on found be can cm 5 to up pyroxenes individual with texture, ophitic coarse Exceptionally road. the of left the to Flow Greenstone the of Outcrops 55.4 River. Eagle along traverse a begin also can one road, the up just 15, Stop At spring. the of periods water high the in done be can't This contacts. flow many at looking River Eagle to way the all here from downstream river the follow can You pools. deep many are there locality this in and road the of site the from m 25 about is River Eagle River. Eagle along seen be can Flow Greenstone the above flows the where stop optional an is This road. the of side hand right the on pull—out a is There 55.7 downstream. or upstream either River Eagle along traverse a begin to possible is it stop this At flow. Ashbed the of north River Eagle in bend sharp very a is There flow. Ashbed the crosses River Eagle locality this In right. the on pull—out road dirt maintained poorly a is There to begin and River Eagle Cross l951b). (l951a, Cornwall by papers in described was Flow Greenstone the of differentiation of petrology and chemistry The Sn Sc 28 Zr Zn Y V Sr 195 259 92 84 14 wt.% ppm 0.14 1.2 0.4 2.1 9.9 7.8 12.8 15.1 46.7 214 104 6 8 186 1680 11 66 Rb Ni Mn La Cu Cr Ba Ti02 K20 Na20 CaO MgO FeO* A1203 Si02 is: (1983) Longo of study from determined Flow, Greenstone unaltered the of composition average The 1877—1887. from 1,000 of population a had which Phoenix, of townsite the of and flow great the of strike the of view a is there Ridge Greenstone the of top the From observed. be all can zones ophitic and subophitic pegmatoid, the cliff the along exposures the following By 30. Figure in shown ophitic lower the is zone ophitic The Flow. Greenstone the of portion ophitic the of exposure spectacular a is there where hill the of top the to climb and ahead Proceed shaft. the above just zones fissure the of one pass then and dump the over up climb must you Flow Greenstone the at look To 65 �1 mIle PHOENIX (Longo, 1983). Figure 30: Section and map of the zonation of the Greenstone flow near Phoenix, Michigan SCALE I 78 540 5 62 8 170 35 25 250 (feet) Thickness I ____. ______ Lower Ophite Vertical Scale: 1"200' Bottom of Flow LOp: Sub-ophite Pg: Pegmatoid Zone _—Pg: Pegmatoid Zone Sub-ophite C' a.' Pegmatoid Lenses with intercalated lenses of ophites and sub—ophites Sub-ophite Pg: Pegmatoid Zone Pg UOp: Upper Ophite Ml: Melanophyric Zone Top of Flow �67 STOP 15. Eagle River Eagle River, Jacobs Creek and Owl Creek each make excellent stream traverses which are regularly mapped as an introductory exercise in the Michigan Tech field camp. At this point, approximately at the Ashbed amygdaloid, a traverse along the stream north to Eagle River allows excellent observations of the upper stratigraphy of the Portage Lake Volcanics. The Ashbed is a very distinctive fragmental amygdaloid traced over a distance of almost 100 Km in outcrop and drill holes. It is the second flow top below the Hancock Conglomerate (Fig. 31 and Map 12). The amygdaloid is a jumble of amygdaloid fragments and interstitial brown, fine—grained detrital material. The secondary minerals filling the amygdaloid are calcite quartz, chlorite and minor epidote. Some vesicles contain minute Exposures of the Ashbed are found both in flecks of Cu (White, 197lb). Small mines were found along this horiroadcut and within the streambed. zon in many places, from Atlantic Mine (near Stop 3) to Copper Falls (Stop 17) The stream traverse to Eagle River traverses the section shown in Figure 31. Among the features seen in the traverse are: 1) excellent sections through individual lava flows showing amygdaloidal tops, and massive melaphyric, 2) Interbedding of sediments glomeroporphyritic or ophitic lower portions. with the lava flows, which becomes more prevalent up section. 3) The occurrences of several dikes which cut the section at low angles. These dikes make up a very small portion of the volume of the section and may be analogous to the dikes described in the Tertiary lavas of eastern Iceland by Walker (1975). If you decide to take this traverse, it's best to to wet feet and the traverse is not advisable in the just resign yourself water. spring because of high The flows just above the Greenstone Flow are compositionally different from Although they are tholeiitic basalt like most of the Portage Lake Lavas. nearly all the PLy, these rocks are distinctly higher in K20 and other inLower in the stratigraphy below the Gratiot compatible elements (Fig. 32). flow another zone of K—enriched basalts occur. This caused Rose and Crimes (1979) to divide the PLV into three cycles of basaltic lavas each of which The cycles may reflect different begins with relatively K—enriched basalts. It is interesting to note that degrees of partial melting or fractionation. one of these cycles begins after emplacement of the Greenstone Flow. 55.9 There is an outcrop of amygdaloidal basalt on the left side of the road. Further off of the road is a rock dump from the Phoenix Ashbed workings (1855—1862, 1913—1917, 400T Cu). 56.6 Entering Eagle River. On the left is the road to Five Mile Point. The stone monument is a memorial to Douglass Houghton who was the first State He did pioneering geologic studies in the Keweenaw Geologist of Michigan. He drowned off Eagle River in 1845. Peninsula. 56.8 Cross Eagle River on the Eagle River Bridge. Park NE of the bridge. �COPPER HARBOR CONGLOMERATE 68 14000 Stratigraphy of Figure 31: the Portage Lake Volcanics above the Greenstone flow in the vicinity of Eagle River and Phoenix, Michigan (from Cornwall and Wright, 1954). Melaphyre Tongue of Copper Harbor conglomerate MelophyreS 13000— Ophihc flows; thickest flow pegmatific Melaphyres flows; thickest flow pegmatitic Melaphyres; thicker flows slightly glorneroporphyritic and ophitic 12000— —Hancock conglomerate (No. 17) gygaloid}t egrained rnelaphyreo, Ashbed porphyritic Melaphyres; thicker flows glomeroporphyritic and pegmatitic melaphyres, porphyritic lomeroporphyritiC flows Upper chill zone Greenstone flow PORTAGE LAKE LAVA SERIES �• .S •5 S .•• S • • • S. S • S S I • S S S. •• S • S •S S S S. S •. •S ::, S S. S. ••S. S • S • •S • S • • 2 S S S • 1(20 3 ' S M-O 5wt% 75 50 - 25— No. S •• • S S :. S S S S S . S • S :S. S. •5 S S • S S S • S S S S • S •:. S 55S • S S S S S S. • .2 S S S S • S .3 P205 I .4 .5 GS wt% top) sampled Figure 32: Plot of K20 and P205 content of 106 individual PLV flows in stratigraphic order (1 in drill holes across the section in the vicinity of Delaware by W. S. White (pers. comm., 1976) and reported GS represents the Greenstone flow horizon, M—0 represents the melaphyre—ophite line, by Rose and Grimes, 1979. a texturally traceable line in the PLV below the Gratiot flow in this area. The stratigraphic position is plotted by flow no. and is not to scale. 75. 50 25 No. S S 1 I �70 STOP 16. Eagle River Falls. The falls occur at the contact between the top of the Portage Lake Volcanics and the base of the Copper Harbor Conglomerate. There are some spectacular If the water is low, like it is potholes that have developed on this face. sometimes in the summer, you can see ropy surfaces on flows at the top of The contact dips about 30° NNW. The contact the Portage Lake Volcanics. relationships suggest very little erosion between the flow and deposition Under the bridge one of the basalt beds of the Copper Harbor Conglomerate. can get a good view of the lithology of the lower part of the Copper Harbor It consists of mostly rhyolite pebble conglomerates but inConglomerate. cludes many sandstone and even some shaley beds. There is an optional route to Eagle Harbor via Sand Dunes Drive given after the Garden City road log. NOTE: Eagle River to Eagle Harbor via Garden City Road MAP 12 56.85 Go straight after crossing the bridge. M—26 goes to the left which is the optional route. Passing in front of the Keweenaw County Courthouse and offices. 57.1 Gitche Gumee Bible Camp, continue on paved road. 57.2 Pavement ends. MAP 13 60.2 This is the Garden City Road. Junction with paved road. Turn left towards Eagle Harbor. 60.3 Cross Jacobs Creek. 60.5 Junction of a dirt road on the left. Continue ahead on paved road. From this road, a short distance to the west, there is access into Jacobs Creek, at the site of the Arnold Mine, along the Ashbed amygdaloid. This is the end of a traverse one can make across the upper part of the Portage It is recommended to begin the traverse at the lower end Lake Volcanics. of Jacobs Creek where it crosses M—26 (Sand Dunes Drive optional route to This is a very tough traverse with many steep and dangerous Eagle Harbor). There are excellent exposures of many individual lava points within it. At the Arnold Mine, one of the nearly conformable flows along Jacobs Creek. Geologic traverses made along massive dikes is exposed in the streambed. ahead), and Jacobs Creek allow Eagle River (Stop 16), Owl Creek (Stop 17 lateral variations in the upper part of the Portage one to look in detail at Lake Volcanics. �\\\\\ 71 — 1 :,, '' \" 'I J• I \\; ' lHwtl 0 . . 4. £L - Coooer Harbor Corg!omes an k ( ' \\ i \\ - MAP 13 I - 11 k I; �72 61.2 On the left is a roadside park with a tower. From the top of this tower there is an excellent view of Isle Royale on a clear day. You can also see some of the ridge—valley topography due to the dipping lava flows and conglomerates in this part of the section. 61.9 Dirt road that slants to the right goes to the old townsite of Copper Falls. Copper Fails was settled in about 1846 and had a population of 500 in 1877. Today there are a handful of residents. 62.2 Cross Owl Creek. 62.3 Road to the right goes upstream to the dumps of the Copper Falls Mine which is part of Stop 17 described below. 62.4 If you follow this road several hundred Road to the left goes downhill. meters, you will reach the 30—mile stampsands which are the tailings dump from the Copper Falls mining operation. From this stampsand you can gain access to the bottom of Owl Creek and can begin a one—hour traverse upIf you continue upstream beyond stream to the bridge along this road. the bridge, you will reach poor rock dumped along Owl Creek from the Copper Falls mining operation. By climbing out of the creek bed, to the east, one can reach a dirt road which will come out on the main road at 62.3 STOP 17. Owl Creek — Copper Falls Mine. Owl Creek is another one of the streams that cut across the upper part of The traverse begins downstream where the base the Portage Lake Volcanics. of the Copper Harbor Conglomerate and top of the Portage Lake VoiLcanics interfinger. There are excellent exposures of interbedded conglomerate! There are sandstone and lava flows along the bed and sides of Owl Creek. several well exposed amygdaloidal flows. The Copper Falls Mining Company worked several fissures and the Ashbed The mine operated from 1847 to 1893. It produced about 18 amygdaloid. million lbs. of refined copper from the Ashbed amygdaloid and about 9 Copper Falls million lbs. from fissures, mostly the Owl Creek fissure was the only mine in the north end of the district above the Greenstorie flow that paid dividends but was not a profitable venture (summarized from Butler and Burbank, 1929). The Owl Creek vein starts near the base of the Copper Harbor Conglomerate and extends through the Portage Lake Volcanic Series, probably into the Greenstone flow. The vein was productive only in the vicinity of the Ash— bed amygdaloid. The Ashbed flows are distinctly porphyritic. The amygda— bid is scoriaceous with a notable clastic component. In some localities The mineralpebbles and boulders of amygdaboid are set in a sandy matrix. ization of the Ashbed amydgdaloid is similar to that found in other amygda— bids in the Keweenaw Peninsula. At the Copper Falls Mine the more abundant minerals are: calcite, quartz, epidote, and pumpellyite. Datolite is abundant in the Ashbed near fissures. Datolite is abundant in fissures Native copper was more abundant toward the top part of such as Owl Creek. the deposit. Other minerals reported in the Copper Falls area include: �73 laumonitite, prehnite, native silver, adularia, analcite, apophylite, faugasite, natrolite, stilbite (summarized from Butler and Burbank, The Copper Falls Mine is stratigraphically one 1929; Clarke, l974b). highest in the Keweenaw native copper district and is near the top of the pumpellyite zone (see Figs. 4b and 9a in the Introduction). MAP 14 63.75 63.85 Crossing Eliza Creek There is a dirt road that goes off to the right. From this dirt road just a few hundred meters up hill you can begin a traverse upstream on Eliza Creek to get the exposures of the Portage Lake Lava flows of this region. 64.9 We are at Eagle Harbor where we join back up with M—26. Turn right on M—26. Eagle River to Eagle Harbor via Sand Dunes Drive (M—26). MAP 12 o At Eagle River Bridge make a sharp left turn, follow M—26. 0.1 Sharp right turn. MAP 13 3.05 Jacobs Creek Falls. From this point one can begin a traverse up Jacobs Creek that ends near the Arnold Mine on the Garden City Road (mileage There are excellent exposures of the upper part of the Portage 60.5). For those who are hardy, the stream Lake Vol.canics along Jacobs Creek. offers virtually continuous exposures through thin pahoehoe flows, especially in the first several hundred meters. This is a steep and rough traverse, and should not be attempted in high water periods. 4.9 Great Sand Bay. 5.9 The Lake Shore Traps form the offshore ridge. The Lake Shore Cat Harbor. Traps are mafic lava flows interbedded with the Copper Harbor Conglomerate. MAP 14 7.8 Right hand turn by the Eagle Harbor Store. 8.0 We are at the Junction of M—26 and Garden City Road Route. Return to Main Road Log Mileage. Stay on M—26. �/ - ( I - - - C..-;. *i . etC r Lake Superior - - '"1 it /// .. ( . / ci' iI - 41" 63gke ':yh ff \ ag H / I 8/AST GUARD O8 \..( GLE HARBOR (32 S ____ - . z-- .. �75 65.0 65.75 MAP 15 66.9 67.5 67.65 The harbor at Eagle Harbor is controlled by the occurrence of units which These are basalt flows which are inter— are called the Lake Shore Traps. bedded with conglomerates of the Copper Harbor Conglomerate and form typiThere are excellent exposures of the Lake Shore cally resistant ridges. Traps that occur at the Eagle Harbor Marina and continuing along the shore through Grand Marais Harbor and into Agate Harbor and eastward through small boat from the Copper Harbor. These are accessible by canoe or winds are on—shore. Marina, but don't try it if the Junction to the left to the Eagle Harbor Marina. Continue ahead on M—26. On the right hand side you can see the offA view of Grand Marais Harbor. shore islands and ridges which are controlled by the occurrence of the Lake Shore Traps. We are driving along a conglomerate ridge. this Road passes along the shores of Lake Bailey on the right hand side of Harbor Conglomerate conglomerate ridge. The ridges throughout the Copper the valleys are underlain by the tend to be held up by the conglomerates, On conglomerate. and shaley members within the more easily eroded sandy The (on the right) is Mount Lookout. the opposite side of Lake Bailey Vol— contact between the Copper Harbor Conglomerate and the Portage Lake canics runs through the back side of Mt. Lookout. sandstone On the left hand side of the road there are exposures of the members of the Copper Harbor Conglomerate. NAP 16 69.1 69.2 69.7 70.0 Crossing the Silver River there are excellent exposures of the Copper Brock— Harbor at this locality and along the left hand side of the road up look at the Copper Harbor way Mountain. This is an optional stop to At Eagle River Falls (Stop 16) one had the opportunity to Conglomerate. At this locality look at the basal beds of the Copper Harbor Conglomerate. of the formation, just bewe are stratigraphically in the more central part (20) one low abundant interbeds of Lake Shore Traps. At an upcoming stop The formation. will get the opportunity to look at the upper part of the of other stops. lithology of the sediments here can be compared to those the summit On the south side of the road at this stop a 3 Km trail leads to in the of Mt. Lookout (Map 15), one of the most spectacular viewpoints contact The summit is located on conglomerate, but very near the Keweenaw. with the Portage Lake Volcanics. Allow at least 1½ hours. this Junction to Brockway Mountai1 Drive. We are going to come back to Go to Park. point but we are going to first take a side trip to Esrey the left on M—26. shallow dipping We are now at the shore of Lake Superior where there are approxilava flows of the Lake Shore Traps. The road follows the shore mately parallel to the strike of the lava flows. STOP 18. Esrey Park. �___ ti del4f SI. dVV\I - - _; 3 3 - I p O4 • . —:- - .. ---— - —-I i20° - — - - _- ____________ — C- ——- S I - .. -. - )) Th of magflet .— Approxtmate posItlOfl °I/ .D - 1ff yi pa qtl V �- /_ \ * I r copper Copper L - _i_=-i j' - _ : - -— rbOr. -- - - - 4-.••• - 20 ,.:—.--—:- — ., Shore TrapS. _—- ,— -A Ashbed I T1ZH hc -.-- e -TiLak •:. ! ngtOmC rate ——-— - catedbY2lrb0 _____ tl / _______ - - _ �78 The rocks cropping Out at Esrey Park are lava flows of the Lake Shore Traps. The Lake Shore Traps consist of a number of lava flows interstratified within the Copper Harbor Conglomerate. The Lake Shore Traps extend from the tip of the Keweenaw Peninsula west and south to just north of Hancock. They lie stratigraphically near the middle of the Copper Harbor Conglomerate. They consist dominantly of mafic flows similar to those of the Some intermediate compositions have also been Portage Lake Volcanics. reported. The Lake Shore Traps represent the waning stages of Keweenawan volcanism in the Keweenaw Peninsula. Several of these flows have been traced offshore by prominent magnetic anomalies. The large outcrop between the parking lot and the lakeshore is the massive interior of a fine grained basaltic flow which strikes approximately parallel to the shore. The flow's amygdaloidal top can be observed along the lakeThe metamorphic grade of these rocks is substantially shore to the east. lower than that of the Portage Lake Volcanic Series, i.e. within the zeolite zone. Note the "fresh" appearance of massive interior basalt (with olivine phenocrysts) and the low temperature amygdaloidal minerals (in order of calcite, chlorite, laumontite quartz, adularia decreasing abundance): and analcite. 70.1 Turn around and head back towards the junction of Brockway Mountain Drive. 70.9 Sharp left turn onto the Brockway Mountain Drive followed by some more exposures of the sandy conglomerate zones within the Copper Harbor Conglomerate. We will drive for several kilometers along a conglomerate ridge with many conglomerate exposures. MAP 17 75.9 At the summit of Brockway Mountain we take a right turn a short distance to the observation site. STOP 19. Brockway Mountain Viewpoint. This high conglomerate ridge reaches an elevation of over 1300 feet and is one of the best known tourist stops in the whole Keweenaw. Excellent views of the ridge and valley topography of the northern shore of the Keweenaw can be had here, because the scrub vegetation allows a 360° panorama. The conglomerate here dips at about 20° to the north. To the west the Lake Shore Traps form prominent drowned ridges in the vicinity of Esrey Park. Lake Bailey (with the small island) and Lake Upsom occupy a topographically low valley of finer grained clastic sediments within the Copper Harbor Conglomerate. Just to the south of Lake Bailey the conglomerate ridge of Mt. Lookout can be seen, marking the contact between The inland the Copper Harbor Conglomerate and the Portage Lake Volcanics. lake almost directly south is Lake Medora, and just beyond the lake is a prominent ridge which marks the stratigraphic position of the Greenstone flow. In the distance, farther to the south across Lake Medora, Mount To the southBohemia (Stop 21) with a fire tower on top can be seen. west a distant ridge with white Air Force tracking buildings on it, marks Gratiot Mountain, which is underlain by andesitic dikes and small rhyolite bodies. To the east, Copper Harbor is visible and Lake Fanny Hooe (see Map 18) which occupies the same stratigraphic horizon as Lake Bailey. Beyond Copper Harbor to the east, East Ridge, a conglomerate ridge, is To the north, on the skyline 65 Km the prominent hill on the skyline. away is Isle Royale, easily visible on a clear day. The skyline of Isle �8- Map 16 _ —-- er — -- —--- i_ I 9 ( - Dans P9int N. _J I Lake Shore Tr,ps 26 __-1 —-- — -—--—- (3 — —c- - — et L - Stop 20 —= - - I /077 — Harbor — - — : 26 - - —- 4 Su;_5Or ILake —t . — ••- -- I -- -i_s -e I'.. —. .---.. - '''c —— — p /1) ( i— ) — -I --_----- ——. — --- - '.— —— —- .•1. .f.. .••\ '.4—.. 2! ..ii&' ) :jt .SM.c14— •Q=__ aSr.'; t .-..'—- — "••• SV,.fl -—__75 :nrftt - —-;. — _ ____ �80 Royale is the Greenstone Ridge, underlain by the Greenstone flow, which is apparently a continuous unit all the way from one side of the syncline to the other. It may be the largest single lava flow on earth, with a volume of more than 1500 Km3 (Longo, 1983). 75.9 MAP 18 79.45 80.5 MAP 17 81.7 83.35 We turn to the right and follow the road straight ahead toward Copper Harbor now going downhill and continuing along the ridge with excellent views all the way down. There is a pull—out on the right hand side of the road to give an excellent Copper Harbor is controlled by view of Copper Harbor and Lake Fanny Hooe. The islands offhsore including the occurrence of the Lake Shore Traps. Porters Island are underlain by lava flows. From the Copper Harbor Marina, with a small boat you can have access to excellent exposures of the Lake Shore Traps along the edges of Copper Harbor. There are exposures of the Copper Harbor Conglomerate along the road descending into Copper Harbor. Junction at M—26, turn left. We come to the shore of the lake again at a place called the Devil's Washtub. If you stop here by the right hand side of the road and take a short walk along the conglomerate along the shore, you come to wave washed exposures of the conglomerate at the Devil's Washtub. STOP 20. Dan's Point. There is a small gift shop observation tower on the right hand side of the road. Walk just a few yards down to the shore of Lake Superior to look at the lithology of the Copper Harbor Conglomerate and the occurrence of stromatolite in well exposed and wave washed exposures. Dan's Point consists of a lakeshore outcrop of Copper Harbor Conglomerate that is characteristic of the upper two—thirds of the formation (sometimes called the Outer Conglomerate). As a whole, the Copper Harbor Conglomerate is a red—brown, basin—ward thickening wedge of volcanogenic clastics which attains a maximum thickness of 1830 m (Daniels, 1982). A coarse conglomerate facies consisting of well—rounded, poorly sorted clasts of mafic to silicic volcanic rock fragments directly overlies and locally interfingers with the lavas of the Portage Lake Volcanics (Elmore, 1981). The conglomerate facies is generally clast—supported and contains a ratio of mafic to silicic intermediate clasts of about 2:1. The Copper Harbor Conglomerate fines both distally and upsection so that sandstone interbeds become more frequent in the upper two—thirds of the formation. Sandstones are predominantly subangular to angular lithic graywackes which exhibit current—ripples, festoon trough—cross beds, parting lineations and dessica— tion features. Laminated crystalgal carbonate horizons are interbedded within the conglomeratic and sandstone facies in the upper two—thirds of the formation. Stromatolites occur as laterally—linked drapes over cobbles, as laterally—linked contorted beds in mudstone—siltstone lenses and as poorly developed mats in coarse sandstone (Elmore, 1981). �81 The depositional environment of the Copper Harbor Conglomerate has been interpreted as a prograding alluvial fan complex (Fig. 33) with proximal— to—distal braided stream and sheet flood facies on coalesced alluvial fans and sand flats (Elmore, 1981; Daniels, 1982). Isolated cryptoalgal carbonate and ooid lenses formed in shallow, medial fan lakes receiving very low rates of sediment influx (temporarily abandoned stream channels) (Elmore, 1981). Paleocurrent indicators suggest sediment transport was from the southeast to northwest indicating that a basin was located toward the center of the rift zone (Daniels, 1982). The stratigraphic section of the "Outer Conglomerate" (that part of the Copper Harbor Conglomerate above the Lake Shore Traps) exposed at Dan's Point consists of about 80—90 ft. of interbedded conglomerates and sandPredominantly clast—supported conglomerate beds consist stones (Fig. 34). of rounded, cobble—to—small boulder—sized clasts with a matrix of coarse sand—sized sub—angular grains cemented with iron oxides. Conglomerate clasts are predominantly felsic volcanics (approx. 70%) with sub—ordinate basalt, pyroclastic, plutonic and metamorphic lithic fragments. Several silty—sandstone interbeds higher in the exposed section exhibit cross— bedding, current lineations, ripple marks, parting lineation and (reduction spots along bedding. In particular one should note the white stromato— lite (genus Colleria) horizon draping cobbles about one—third of the way up the exposed section. Algal growth occurred during a period of depositional quiescence and was halted by an influx of silty material followed by renewed conglomerate deposition. Please do not remove stromatolite from the outcrop. Good specimens can be found in the pebble beach. 83.35 MAP 18 86.65 87.1 Turn around and go back toward Copper Harbor on M—26. To the left is the junction Junction, again, to the Brockway Mountain road. to the Copper Harbor Marina. Continue straight ahead on M—26 to Copper Harbor. Junction between M—26 and US—4l in Copper Harbor. out of Copper Harbor. Turn right on US—41, south Copper Harbor was suddenly a boom town in 1843, following the discovery of Porter's Island was the site of the first governcopper in the vicinity. ment land office and in 1844 Fort Wilkins was built on the shores of Lake Fanny Hooe, to protect the miners from potentially hostile Indians. The lighthouse was built in 18o6. Fort Wilkins is now a state park with campMuch exploration activity took place in the ing facilities and a museum. fort and there are shafts and exploration pits immediate vicinity of the all along the land between Lake Fanny Hooe and the Harbor, mostly from In 1853 and for several decades thereexploration in the 1843—46 period. after mining activity took place south of the fort in a series of workings called the Clark Mine. The mineralization is of the fissure and amygdaloid type and consists of prehnite, epidote, analcite, quartz, laumontite, adularia, microcline, chlorite, datolite, calcite and several copper minerals including chalcocite, cuprite and tenorite as well as native copper. Agates are conspicuous in the amygdaloids here, and the area is well known for datolite collecting. One occurrence of manganese minerals in a fissure The manganese minerals found accounts for the name of Manganese Lake. brannite and manganite, orientite. The Estivant here were pyrolusite, of the Clark Mine lands which were deeded to Pine tract represents a part are now a nature preserve, containing some of the C&H Company in 1942 and Upper Peninsula. the last virgin pine tracts in the �L — -S. Cover P'-.. •.. . •• 963 W.AW __ -S ••. • ••- • . Copper :' - LL$i :;/ I• I /* • -, Shore p-----: •; - Lake tTTTTT+ Copp.r H - 4. • erJiarbr Lake Superior J z. HAYS — .) EXPLORATION Copper I 1 Copper Hao< _ '- .) --- ---- . !/ ;,j. �1982). Daniels, from (modified deposits stromatolitic containing lakes ephemeral shallow and deposits plain flood and stream braided fans, alluvial coalescing showing Conglomerate Harbor Copper the of environment depositional of cartoon Schematic 33. Figure — BAStNwARD 83 �I I I I I — IJj i: (T\ ; oooo00oqo;.ooy %o6,°fJ.. 0o:0 P ooj°Q4 ! I Ili. 9# I t'•' C' T rt CD C) CD CD- CD-. H- H. rtt)Q 0 o CD CD I H.t) H- t CD rl- CD CD H H- Fij 0 H. C -1 CD L) -C-- CO '-'1 CD C) CD CD- CD-. CD o '-1 oCDo CD- d 0 H. C 0 H- H- rrDrtCD '—j H- !10 00 H. H. (I) H- OC) H. rt H C o-r CD CD 0(J) H.H CD- CD CC rtH 00CC CD CD- 0HCD H- H- H- 0 0 rt H. C Hrt rt CDC) C) oCDCDCD CD CC H. 0 o o C)CDH H 0(000 0 C) CD CD OH CQ 0 H. CDHCD CD (I) H. CD rt HO -0 oCD 0 o- H. o H H H. HO 0C) 0 H- CI)—. CD c 00 (DrtC) H H. CD CCCD C CD-. C) CD CD H.CD 0 0 rt rt H- H. CD �85 Keweenaw Point, Horseshoe Harbor, East Bluff and other points of interest can be reached by taking an unmarked dirt road which goes eastward from the end of US—41. This road is rough and poorly maintained and may be followed around to Mandan. Horseshoe Harbor has excellent exposures of the Copper Harbor Conglomerate (Fig. 34). 88.2 MAP 19 91.45 MAP 20 94.3 94.55 MAP 21 97.3 MAP 20 101.4 101.6 Nice exposures of the Copper Harbor Conglomerate to the left of the road as we are going up the hill. Lake Medora on the right hand side of the road, Junction to the left to Mandan. Mandan now is only a few houses, it had 300 residents in 1910. Continue ahead on IJS—41. Road to the left. This is the entrance to the outer portion of the Keweenaw Peninsula, all on poorly maintained dirt roads. To visit Mount Houghton and Keweenaw point, you may exit here. Junction of the road to Lac La Belle, Turn left and continue to Stop 21 at Mt. Bohemia. If you wish to skip this stop, you may jump ahead to mileage 105.45. On the left hand side of the road is a large outcrop of amygdaloidal basalt of the Portage Lake Volcanics. These exposures are flows in the lower part of the formation below the Scales Creek flow (see Fig. 4 and in the Introduction). Dirt road turning off the main road to the left. This is STOP 21 at Mt. Bohemia, It is about one half mile walk up this road to. the summit of Mt. Bohemia; this is a four—wheel drive vehicle road. STOP 21. Mt. Bohemia. An intrusive body of diorite and granophyre crops out on the south slope of Mt. Bohemia. The majority of the intrusive body is a massive, medium— grained, miarolitic diorite. The major constituents of the diorite, are oligoclase and hornblende with lesser amounts of orthoclase, magnetite, uralitized augite, apatite, sphene, quartz, sericite, epidote, chlorite, and calcite. The later are alteration products or are introduced secondary minerals. The central core is a fine— to coarse—grained, miarolitic granophyre. The major constituents of the granophyre are albite, quartz and granophyric intergrowths of quartz and feldspar with lesser amounts of orthoclase, sericite, hornblende, apatite, sphene, magnetite and chlorite. Miarolitic cavities are lined with quartz, albite, calcite, chalcopyrite, and chalcocite (summarized from Cornwall, 1954). The Mt. Bohemia intrusive body yielded a Rb—Sr age of 1,130 ± 35 m.y. (Chauduri and Faure, 1968). The diorite and granophyre at Mt. Bohemia intrude basaltic lava flows of The basalts are slightly the lower part of the Portage Lake Volcanics. metamorphosed at the contact. The intrusive body is cut by the Lac La Belle This fissure is mineralized with fissure which trends north—northwest. copper sulfides, mostly chalcopyrite and bornite and in gangue of calcite, chlorite, and quartz (summarized from Juilland, 1965). �P —— _ ( Dl / 4r? 4 — / p 6 \ / - 'P E4 ' p \ai\ L0 ON pg - - • 0 .•, ) /- .5, - /000 S — J/ .• Map 18 �''' p — • -- :TI 'I -; I ,;.. - - • '------—4\1— _j '/ K __\ / 3Yk. - Flow Sci K * Stop 21 :...' ...P 20 7 — �MAP 21 -— = - - - I —___ I V = 1 = — - -I — E) ) MF35N / —- Rv er // • ' - — t/ I 7-IS --- • • ap23 •• 'P24 Map 20 I a \ I --:- / t Ifft /080/P\ \ ---------- - :\i - .-;: - _ (1 �89 Andesitic dikes are found in the vicini.ty of Mt. Bohemia (Fig. 35a). They average about 5 m in thickness. The dikes intrude flows of the Portage Lake Volcanics, two flow tops are shown in Figure 35a as alpha and beta. The dikes and amygdaloidal flow tops carry copper sulfides. Copper sul— fides in other parts of the district are found typically as fracture fillings. Native copper is typical of amygdaloids. A variety of secondary The and opaque minerals are found in the dikes and flow tops (Fig. 35). paragenetic sequence is consistent with that for the other deposits in the district (compare Fig. 35c and Fig. 9b in the Introduction). Copper sul— The copper and sulfur in this occurrence fides are paragenetically late. is believed to be of direct magmatic origin related to the magma source that produced the andesite dikes and Mt. Bohemia intrusive body. The emplacement of flows, subconcordant faulting and chronologic sequence is: fracturing, dike emplacement, renewed movement along subconcordant breaks, regional low—grade metamorphic/hydrothermal alteration, minor folding and faulting, and sulfide mineralization (summarized from Robertson, 1975) The road Up to the summit of Mt. Bohemia crosses flows of the Portage Lake Volcanics. The diorite and granophyre intrusive complex crops out to the southeast of the summit. Intrusive stocks are not common in the Keweenaw Peninsula, Most of these occur in the lower part of the Portage Lake Vol— canics and are rhyolitic in composition. Mt. Bohemia is the only occurrence of a diorite stock in the Keweenaw Peninsula. OPTIONAL SIDE TRIP TO Lac La Belle Discussion of complex relationships along the Keweenaw Fault and the Keweenawan rhyolite bodies, Go straight ahead (south) towards Lac La O At turnoff to Mt. Bohemia. Belle down hill. O4 Junction of roads to left and right at Lac La Belle. MAP 21 To Bete Grise turn left. (See Map 22) Bete Gi se is located on the shore of Keweenaw Bay on the Keweenaw Fault. Along the shoreline east of the point where the road reaches the shore are several exposures of the Keweenaw Fault which crosses on and off These may be visited in canoe or small boat. Also shore several times. to the east are several of the rhyolite bodies which are chiefly found in the lower part of the Portage Lake Volcanics. Three tenths of a mile north of Bete Grise, four—wheel drive road continues east of the paved road to Smith's Fisheries. The road intersects the Bare Hill Rhyolite body, a shallow Beyond the end of the road at Smith's Fisheries a trail continues intrusive. eastward along the shore to the mouth of the Montreal River. From here one may traverse up river to several falls over fine outcrops of basaltic flows or continue along the shore to the Fish Cove Rhyolite, a compositionally zoned shallow intrusive (Bornhorst, 1975). Inland and not far from Bete Grise is the Mt. Houghton Rhyolite. This is an extrusive rhyolite dome �14 55 495I 18 I /48\ 43/31 \ 'i2 47 32' 46 ._—-- 34 22A7flh777/' _____jB 36< 37 6 I g8 7 25 ffflaTImffl1/7"° 4 50 Lac La Belle Fissure - 60 0 EM DIIHe —-.40 Amygdaloid - °jk \-c'-\ v-s, <j r--,1 64 I 7___2t1 Mt. Boheiat'\ .Oiorite,>vt\ \ __-c 56.54 — 61 FIRE TOWER \ 0 loo2oo Amyqdoloids and dike projected to 1300 elevation - )iogy and drQ hole locations in the Mount Bohemia area (modi - from a preliminary Calumet and ilecla Mining Company map). Secondary minerals MINERAL Chlorite Vesicle- Frocture- fillings fillings in dike matrix 0 Epio'ote Quartz 0 0 0 0 ca/cite 5cr/cite Pumpe//y/te Microc/ine o 0 - o Hem Pyri 1, Cc, su/fides Noth Copper - Common o G Minor Nonpyrogenic 0 Rare 0 —Absent Minerals in the DPis MINERAL Pyrogenic I Deuteric Hydrothermal Supergene Magnet/fe Chlorite Pumpe//ylte 3cr/cite .- 'ucrt Microc/ine Su/idj Cha/capyr,te Ga/eva 5p/,o/er,fe ——— Epidote Colch Hei I, Hematite Z Pyrite —— —— — —— ti ——-—— ——— —— P2 ietic sequence of secondary minra1s in the dikes. Pink born,te Purple born/fe Diqenife Ojucleite Cha/coc/te Hematite I.E Cove/life —-— Paragenesis of opaque minerals in dikes and flow tops at Mount Bohemia. Figure 35: Geologic map showing andesitic dikes near Mount Bohemia and occurrence and paragenesis of secondary and opaque minerals in the dikes (from Robertson, 1975). �Y) 1 I I FauI.' Creek e I', r0 Houghton ,. ,iJ \'_ �92 with prominent flow banding and block and ash flow deposits on its flanks. Mt. Houghton is best approached from the Mandan Road (Map 19). Rhyolites make up less than 1% of the mass of the Portage Lake Volcanics Considerable textural variety of as seen in outcrop on the Keweenaw. rhyolites are found including intrusive and extrusive rhyolite and even But the abundance and variety of rhyolitic boulders small ignimbrites. and cobbles within the interflow conglomerates demands that a large number of rhyolitic source areas must underly the Jacobsville south and east of the Keweenaw Fault. To Gratiot River. Turn right and proceed ahead 1.2 miles on paved road. At the west end of Lac La Belle, in the vicinity of Deer Lake, the rocks south of the Keweenaw Fault are Portage Lake basalts (Fig. 36). These rocks may represent the lowest stratigraphic horizons exposed in the The area has been studied by geological and Portage Lake Volcanics. geophysical methods by DeGraff (1976) and his model for the development It is still of this unusual feature is shown graphically in Figure 36. another example of confusing deformation which is typical of this great A traverse down the Little Gratiot River from the Lac La Belle— thrust. Gay Road crosses many outcrops of the basalts. The fault—bounded, tilted body of Portage Lake Volcanics was defined by dense array of magnetic and gravity profiles and a few key drillholes, The attitude of the beds was altered by the faulting, but the rocks, like the rest of the Portage Lake Volcanics, have normal magnetic polarity. AFTER OPTIONAL SIDE TRIP to Lac La Belle return to main road log. MAP 21 101.6 At Mt. Bohemia turnoff. 105.45 Back at the junction of US—4l, 106.5 Dirt road to the right goes to Stop 22 at the Delaware Mine. on the dirt road and follow the signs to the Delaware Mine. 106.2 STOP 22. Turn around and retrace route back to US—41. Make a left turn towards Mohawk. Turn right Delaware Mine. The Delaware Mine, first known as the Northwest Mine, has had a long and It was operated by various companies from about unprofitable history. The mi:ie mostly worked veins for mass copper. Three shafts 1847 to 1887. were opened in 1881 to mine copper from the Allouez Conglomerate (#1, #2, The Allouez Conglomerate was seen at Stop 13. Total production from #3). the Delaware Mine was about 7.5 million lbs. of refined copper. As with other vein deposits in the Keweenaw, the Delaware Mine is a notable locality for datolite. Other minerals reported from the Delaware Mine poor rock piles include (not in order of abundance): chlorastrolite, prehnite, calcite, laumontite, analcite, chlorite, epidote, native copper and native silver (summarized from Clarke, 1975; Zelenka, 1978). �± \ -L Portage Lake VolcaflaS -o \ •Ro Gay Lee LaBeIle To sete Bo8e N N S S S llasalts and sandstones in a block south of the fault are exposed and overturned. l3asalts and sandstones in a block south of the fault are exposed and dip to the south. Classical fault contact between basalt and sandstone. Sandstone still exposed north of the IKeveenaw Fault. Sketch map of part of the Keweenaw Fault in the vicinity of Deer Lake, where the Figure 36: Portage Lake Volcanics are found south of the Keweenaw Fault. At right successive cross sections show stages in the development of the Keweenaw Fault at Deer Lake as envisioned by DeGraff (1976), P = PLy, J = Jacobsville. 11 \ Portage Lake VolcanicS 1' Mt Bohenja N Prior to faulting. �94 The Delaware Mine is open to tours for tourists during the summer months. It is owned and operated by Jack and Tom Poynter. At this stop one has the opportunity to look at the dumps from the Delaware Mine and to visit (for a fee) the underground workings. 106.35 MAP 23 109.0 Junction of Delaware Mine and US—4l. ahead towards Phoenix. Left turn on TJS—4l and continue Ahead we can see cliffs of the Greenstone flow. contact of the flow. Road nears the basal 110.3 Exposure of one of the flows beneath the Greenstone flow. 111.1 In the To the right one can see the Greenstone ridge in the background. foreground is the ghost town of Central and its associated dump piles. 111.45 Junction of paved roads to the right and left. Continue ahead on US—4l. The road to the left goes to Gratiot Lake and an Air Force Base; road to the right goes toward the ghost town of Central and the Central dump piles. The Central Mine worked a fissure vein striking nearly at right angles to bedding and dipping steeply to the east. The mine operated from 1854 to 1898 and produced about 52 million lbs. of copper. The fissure extends from just below the Greenstone flow to the Kearsarge Conglomerate. A strike fault at the Kearsarge Conglomerate offsets the vein to the west and below this it is not mineralized. The town of Central, settled in 1854, was settled mainly by Cornish immi— Although the area was mostly abandoned after the mine closed, grants. the descendants of these immigrants now living all across the country, hold a yearly reunion in July at the townsite. Later immigrant groups to the copper mining towns included: Italian, German, Croatian and Finnish people. MAP 24 112.8 Continue ahead on US—41. The road to the Junction of road to the right. right connects with an earlier part of this field trip at Jacobs Creek (mileage 60.3). 113.9 Another view of the ENE striking Greenstone flow holding up the prominent ridge. 114.6 Again another excellent view of the Greenstone flow ridge. MAP 12 115.4 Junction of M—26 and US—4l at Phoenix. There is an optional route from Phoenix to Ahmeek via US—41/M—26 given after the Five Mile Point road log. �- - - — ( I (L/ C4 ----i-I - - — .- —::; p- H. p p I 7 -- I I - 07 IL 1 ,. . - —y 24 — jge I — L — '7 :-fi0 L 2O' - J. - 1— y./ :' •O- c. . I 1 �_ ____ ___I de, • •-1-•r ,4. -— ".? ii /ç/)/11 \ I, ( // • ( - I \'\ •H \'\ .i • 1 —--\-- -, __ C _\ \\\ \\ \\ \\ \\ - -- \\ D — i4 i--, - I N -f I j 2 (fl ) \c \ LU — 1 copt 1 2 1 / ( - - C — /7 -- — - ••/// - 1 \\ '.1 1 -. - Map 1. �97 Phoenix to Ahmeek via Five Mile Point (a scenic route along the Lake Superior shore). MAP 12 115.4 Right turn toward Eagle River. 117.4 Left turn on to the road to Five Mile Point. MAPS 25 and 26 On the right hand side of the road is a turn—off to the Five Mile Point 112.2 In the front You must get permission to enter this area. lighthouse. yard of the lighthouse, there is a thin lava flow of the Lake Shore Traps with the Copper Harbor Conglomerate bed above and below it 121.5 MAP 27 126.9 Five Mile Point beach turn—off at the right hand side of the road. Along this beach there are many exposures of the Copper Harbor Conglomerate. Cross the Gratiot River. 128.45 A thin basalt flow, from a position just above the Greenstone flow, forms an outcrop here which displays a well—developed columnar jointing. The Greenstone flow itself shows spectacular columnar jointing in some areas, most notably along the Palisades shown on Isle Royale where columns 2 m In a few areas the colonade/entablature or more in diameter are found. jointing pattern described in Columbia River flood basalts is well— developed in the Greenstone. On the Keweenaw columnar jointed exposures in thin flow sequences are rare, probably because the underlying horizons were not water—saturated when covered by the next lava flow. 128.7 Stop sign. 128.8 Another stop sign. 130.0 Right turn which is immediately followed by a stop sign in front of a Join US—4l with a right turn. Directly ahead at about 11:00 church. This is a shallow mine that worked the Kingston is the Kingston Mine. Total proConglomerate. The Kingston ore body was discovered in 1962. duction was about 20 million lbs. of copper until mining stopped in 1968 The mine was left open as a research operation (Weege and Pollack, 1971). in the late 1970's. Go straight ahead. Turn left followed in block by a right turn. The Kingston Conglomerate is stratigraphically about midway between the It is overlàirt by a Calumet Conglomerate and the Kearsarge amygdaloid. A bedding plane fault separates the over60 m thick ophitic basalt flow. The conglomerate rests on a lying basalt from the Kingston Conglomerate. The Kingston Conglomerate can be traced along scoriasceous amygdaloid. strike for over 100 Km and ranges in thickness from 0.3 to 30 m. In vicinity of the ore body it averages about 13 m. Where the bed is thick it consists of a lower layer of shale and siltstone, 10—15 cm thick and an upper congloineratic layer (summarized from Weege and Pollack, 1971). �MAP 25 M — .', ór 5 :; %0 r - - - 07/ / - / i - V ' 4 ,<' /\ �99 Fivemile Poini 6NDH / TcUAR 'I / / —- I I J Sevenmile / /• !Point V I. '1 C7 7f q Map4-'7 MAP 26 r/ �100 : 2 I? Lake Shon I,> J7 • • ( MAP 27 Ma, •./. / �The Kingston Conglomerate is typical of rhyolite pebble conglomerates. Pebbles are largely subangular to subrounded quartz—feldspar porphyry. Quartz—free porphyritic and nonporphyritic rhyolite pebbles, common in Interstitial sand other conglomerates, are not present in the Kingston. Sandstone composition is similar to the peb— and sand lenses are common. The intensity of mineralization is related to the amount of matrix bles. present which is an indication of the original permeability. The main alteration minerals are kaolinite and chlorite. Introduced calcite and copper are found as fillings in healed fractures, interstitially filling A few individual pebbles are replaced voids and replacing the matrix. Economically important copper is found as rims around clasts by copper. Matrix filling takes place along and as matrix replacement or filling. texture bands parallel to bedding. Epidote and quartz are also found as introduced minerals. Bleached rock is commonly associated with mineralization in the Keweenaw native copper district but is not present in the Kingston ore body. The abrupt thinning of the conglomerate bed localized the ore body with high grade ore nearest the pinch—out (Fig. 37) (summarized from Weege and Pollack, 197; Brumleve, 1976). PHOENIX TO AHMEEK VIA US—4l/M—26. MAP 12 O Continue straight ahead on US—4l/M—26. 0.5 Bear left on US—41/M—26. Junction of US—41 and Cliff Drive. excellent view of the Greenstone flow ridge. Another MAP 10 5.2 Lumber mill on the left side of the road. 6.0 Entering Mohawk. 6.1 On the left hand side of the road are mine dumps from the Mohawk Mine. The Mohawk Mine worked the Kearsarge amygdaloid which is described at Stop 11. 7.0 MAP 9 The hill on the skyline with the four towers on it is Bumbletowfl Hill, the location of Stop 13. 7.9 Junction of US—41/M—26 and Cliff Drive in Ahmeek. 8.0 Junction of US—4l/M—26 and the road from Five Mile Point. RETURN TO MAIN ROAD LOG MILEAGE. 130.0 Junction of US—41/M—26 and the road from Five Mile Point. 134.1 Junction of US—41/M—26 and M—2O3. �-- - - -..-, .— contact - .' ore body footwall -..' N N N N N N N N N N N N - N ' contact ha ngwall •' N N Schematic illustration of the funnelling effect on mineralizing 37: fluids causing localization of ore deposition (modified from Butler and Burbank, 1929 by Brumleve, 1976). Figure basalt ridge -— r .YfJ FI :- I! C �103 There is an optional route from Calumet to Hancock via M—203/Mctain State Park given after the TJS—41/M—26 road log. Calumet to Hancock via US—4l/M—26. 134.1 Continue straight ahead on US—41/M—26. MAP 28 134.8 Flashing light 135.7 Continue straight ahead. center of Calumet. A right turn leads to the The Osceola Mine Shaft No. 13 can be seen on Southern edge of Calumet. Follow the right hand side of the road behind the Holiday gas station. Mileage is not logged the roads on Map 28 if you wish to go to Stop 23. to this stop. STOP 23. Osceola Mine Shaft No. 6. ProThe Osceola Mine worked the Osceola amygdaloid in the Calumet area. duction from the Osceola amygdaloid began in 1879 and continued until 1920 when mining activity stopped. The mine reopened between 1925 to 193L A total of The mine reopened in 1925 and production continued until 1968. about 600 million lbs. of refined copper was removed from this mine which The amygdaloid was ranks fifth in the Keweenaw native copper district. developed for about four miles along strike and to a depth of 4,500 ft. along incline (2,700 ft. vertically) (summarized from Weege and Pollack, 1971). The Osceola flow is an ophitic basalt and varies in thickness from 35 to The thickest part of the flow, near Calumet, has been the most 210 feet. The Osceola flow has been traced from the Cliff Mine to the productive. In the Calumet area the flow strikes N35°E and dips around Arcadian. The top of the flow is a well developed fragmental amygdaloid 37°NW. consisting of well oxidized, reddish, angular fragments of vesicular lava which typically range in size from a few inches up to a foot in diameter. The lode ranged in thickness from 1 ft. up to and sometimes greater than Amygdules and the voids in the brecciated flow top are filled 60 ft. mostly with calcite, epidote, K—feldspar, chlorite, and native copper. Quartz is present in certain areas and there is also minor amounts of The fragmental amygda— prehnite, pumpellylte, laumontite, and analcite. bid is frequently interrupted by sill—like layers of dense basalt which may have been emplaced by injection of lava from the interior of the flow into the solidified, brecciated crust. These dense basalt layers proNative copper vided barriers to the movement of mineralizing solutions. in the Osceola ranges from disseminated to small masses up to an inch in diameter to large masses weighing hundreds of lbs. (summarized from Weege and Pollack, 1971; Butler and Burbank, 1929). The Osceola Shaft No. 6 is at the southwest end of the ore body and was A barrier zone is believed to have the richest part of the deposit. funnelled mineralizing solutions moving up dip resulting in the high Textures and colors characteristic of fragmental copper contents. Stoiber (unpublished data) made amygdaloid can be seen in this dump. secondary minerals in the dump as a an estimate of the percentages of �Map. - S N 104 N -1 I. .H.. t. :: ,'I -- - .1 - I' •r- - I.- •- '\_ &__ - --- - -L /\ . /Q — :1: c-.- , '1 -/1 .1 N s 42 — 1 1 L-4y'-*- - _s / /-N / ' -- -— 5/ --- /ss 0 5, 'r' -x tL - / 7l, — / H -' /,- 26- k_ __,; -I' 'V 081 A LS34 p LS33 5/5 — '3 N Q33 /: A II 1&J - :', — L312 P28 — I �105 whole: calcite, 59; microcline, 29; prehnite, 4; epidote, 1; quartz, 1; These and pumpellyite, laumontite and native copper can be chlorite, 5. found on this dump. Bleaching of the basalt in vicinity of native copper can be seen in individual specimens. 135.7 Continue ahead on US—4l/M—26 towards Hancock. No Maps Until Hancock Turn left on White Street. 145.45 Junction of White Street on the left. 145.9 Right turn on Tezcuco 146.0 Stop sign at Quincy Street. Go straight ahead through this stop sign one more block to Hancock Street where you make a left hand turn. 146.55 Middle of the Portage Lake Lift Bridge. 146.8 Junction of US—4l/M—26. Stay left on US—4l to the left past the Mobil and Erickson gas stations. 148.1 Left hand turn off Townsend Drive back into the Michigan Tech Campus. Street in Hancock. CALUMET TO HANCOCK VIA M—203/McLain State Park. O Junction US—41/M—26 and M—203 on the edge of Calumet. turn on M—203. Make a right hand No Maps Until Near McLain State Park. 0.5 Village Limit of Calumet. 2.5 Junction of road to Calumet Township Waterworks Park. 4.2 Bear right on Y 4.6 Nice view of Lake Superior. MAP 29 6.7 with Continue straight ahead. another paved road. Continue on M—203. Road to the right is Lakeshore Drive which goes to Calumet Township Waterworks Park; road to the left is Salo Road to the Bear Lake Rhyolite. The Bear Lake Rhyolite cuts the Freda Sandstone bedrock. It is the youngest known igneous activity in the Keweenaw Peninsula. The Bear Lake Rhyolite is a minimum of 1054 ± 34 m.y. years old based on a K/Ar age date (White, 1968). 7.0 Exposures of sand dunes on the right. 7.5 Bear Lake on the left hand side of the road. glacial Bear Lake Channel. Cross on top of the filled �_ __ __ 106 /('i2 (/ F •... LVA A K E T;_ r I654 eøx COAST \GUARD 7( -' 715 2 792 ( 77 Lily Pond I' I' IIv,i )_i. = TO Hahc MAP 29 1J 26 . T BI 9 i ---V( / TTi N _ af n== c/ : 25 �107 The Bear Lake Channel (Map 29) represents a deep bedrock valley, the Although the Waterway was dredged extension of the Keweenaw Waterway. to the west of McLain Park, because the distance was less, the Bear Lake Channel is a much more profound feature, with more than 600 feet The definition of this and other similar bedrock valleys to bedrock. is shown by gravity data. One such traverse, plotted on the map, is See also the discussion of the origin of the displayed as Figure 38. Keweenaw Waterway under Stops 1, 5 and 6. 8.4 Entrance to McLain State Park and the other edge of the Bear Lake Channel. Camping facilities are located here. 9.2 Continue on M—203. Road to the right is to the Coast Guard Station; road to the left is the Bear Lake Road, location of gravity traverse. 10.6 Access road to Lily Pond. At this point the End Moraine of the Keweenaw Lobe, a great mass of glacial ice which was stabilized here during the Wisconsin glaciation, is crossed. The The regional distribution of this moraine is plotted in Figure 14. positions of lobes as they retreated at the end of the Wisconsin period are shown in Figure 15. 13.5 High Point Road, continue ahead on M—203. NAP 30 16.1 Cross Swedetown Creek. To the northeast along Swedetown Creek there are If one is interested in looking in more expcsures of Freda Sandstone. detail at the Freda Sandstone, excellent exposures can be found elsewhere. In the local area excellent exposures of Freda Sandstone are present along Redridge/Freda can the shore of Lake Superior between Redridge and Freda. be reached by following the Houghton Canal Road which begins on the west side of Houghton (see Fig. 17). 16.55 Access to Hancock Campground. The Nonesuch Shale is exposed in an abanThis is Stop 24 and doned quarry located just NE of the boat launch. mileage is not logged from the main road to the quarry. STOP 24. Hancock Campground. As a whole, the Nonesuch Shale consists primarily of siltstone with subordinate amounts of shale and sandstone. It can be distinguished from the formations above and below by its generally grayish color. Most Nonesuch Lithologically is a rippled, laminated siltstone with reddish—gray partings. siltstones and sandstones of the Nonesuch are composed of around 30 to 40 The rock fragpercent rock fragments and 60 to 70 percent mineral grains. ments are mostly volcanic with a 2:1 ratio of mafic to silicic + intermediate The Nonesuch is stratigraphically between the composition (Daniels, 1982). Copper Harbor Conglomerate and Freda Sandstone (Fig. 5). It is The Nonesuch crops out around the margin of the quarry at this stop. a fine— to medium—grained, gray to reddish brown sandstone with subordinate interbedded, reddish—brown laminated siltstone and shale (Cornwall and The attitude of bedding here is about N30°E, 25°W. Wright, 1956). �108 BEAR LAKE 9 8 7 6 5 4( I 2 I I 4 6 8 0 12 14 x 0 2 -3 Q) S a) Li Results of gravity measurements across the Bear Lake Figure 38: traverse plotted in Map 29. At top is Bouguer anomaly with regional In the middle the regional trend is subtracted to get the trend. solid line which is compared with the modelled topography (X's). Below is the model of the valley and the density difference of the bedrock (Freda Sandstone) and the valley fill (Warren, 1981). �109 n 'I - • McI31fl State Park / I V I t , .,, -I - .4 • // - -- ( ; c, '-.' / 'ir •i• 0 r -• -•• —;• I• • 30 JI_1_ - - �110 16.7 Hancock Beach. 16.85 Sharp left hand turn on M—203. 17.9 Turn right on the one—way road. Junction M—203 and US—41. US—4l back to the Michigan Tech Campus Edge of Hancock. Follow south �111 INDEX TO GEOLOGY ON MAPS IN THE FIELD GUIDE Map No. — — — Quadrangle Reference 1 Chassell White, 1956 2 South Range, Chassell White & Wright, 1956; White, 1956 3 Chasseli Warren, 1981 4 Chassell, Hancock White, 1956; Cornwall & Wright, 1956a 5 Chasseil, Hancock White, 1956; Cornwall & Wright, 1956a 6 Laurium Cornwall & Wright, l956b 7 Laur ium Cornwall & Wright, l956b 8 Laur ium Cornwall & Wright, 1956b 9 Ahmeek White & Others, 1953 10 Mohawk Davidson & Others, 1955 11 Mohawk Davidson & Others, 1955 12 Phoenix Cornwall, 1954a 13 Eagle Harbor Cornwall & Wright, 1954 14 Eagle Harbor Cornwall & Wright, 15 Delaware Cornwall, l954b 16 Delaware Cornwall, l954b 17 Lake Medora Cornwall, l954c 18 Lake Medora, Fort Wilkins Cornwall, l954c; Cornwall, 1955 19 Lake Medora Cornwall, l954c 20 Delaware Cornwall, 1954b 21 Delaware Cornwall, l954b 22 Lake Medora Cornwall, l954c 23 Eagle Harbor Cornwall & Wright, 1954 24 Eagle Harbor Cornwall & Wright, 1954; Cornwall, l954a 25 Phoenix Cornwall, l954a 26 Phoenix, Mohawk, Ahmeek Cornwall, l954a; Davidson & Others, 1955; White & Others, 1953 27 Ahmeek White & Others, 1953 28 Laurium Cornwall & Wright, 1956b 29 Hancock Cornwall & Wright, 1956a; Warren, 1981 Hancock Cornwall & Wright, 1956a MTU Campus Map (Cover Page) White, 1956; Hase, 1973 1954 �____________ _____________ 112 REFERENCES Basaltic Volcanism Study Project, 1981, Basaltic volcanism on the terrestrial planets: Pergamon Press, Inc., New York, 1286 p. Bornhorst, T.J., 1975, Petrochemistry of the Fish Cove rhyolite, Keweenaw Peninsula, Michigan, U.S.A.: Chemical Geology, v. 15, p. 295—302. Broderick, T.M., 1935, Differentiation in lavas of the Michigan Keweenawan: Geological Society of America Bulletin, v. 46, p. 503—558. Broderick, T.M. and Hohl, C.D., 1935, Differentiation in traps and ore deposition: Economic Geology, v. 64, p. 342—346. Brown, A.C., 1971, Zoning in the White Pine copper deposit, Ontonagon County, Michigan: Economic Geology, v. 66, p. 543—573. Brumleve, C., 1976, The petrology and fracture characteristics of a native copper bearing conglomerate, Kingston Mine, Keweenaw County, Michigan (M.S. thesis): Michigan Technological University, Houghton, 97 p. in Studies in Geophysics, Burke, K., 1980, Intracontinental rifts and aulacogens: Continental Tectonics, National Academy of Sciences, Washington, D.C., p. 42—49. U.S. Geolo- Butler, B.S. and Burbank, W.S., 1929, The copper deposits of Michigan: gical Survey Professional Paper 144, 238 p. the Mid—Continent Chase, C.G. and Gilmer, T.H., 1973, Precambrian plate tectonics: Gravity High: Earth and Planetary Science Letters, v. 21, p. 70—78. Chaudhuri, S. and Faure, G., 1968, Rubidium—strontium age of the Mount Bohemia intrusion in Michigan: Journal of Geology, v. 76, p. 488—490. Clarke, D.H., l974a, Lake Superior and Phoenix Mining Companies — Copper Mines of Keweenaw No. 4: Local Publication, Copper Mines of Keweenaw Series, 32 p. l974b, Copper Falls Mining Company — Copper Mines of Keweenaw No. 6: Local Publication, Copper Mines of Keweenaw Series, 36 p. No. 9: 1975, Northwest Copper Mining Association — Copper Mines of Keweenaw Local Publication, Copper Mines of Keweenaw Series, 28 p. 1976, The Cliff Mine — Copper Nines of Keweenaw No. 16: cation, Copper Mines of Keweenaw Series, 32 p. Local publi- Cornwall, H.R., l95la, Differentiation in lavas of the Keweenawan Series and the origin of the copper deposits of Michigan: Geological Society of America Bulletin, v. 62, p. 159—201. l95lb, Differentiation in magmas of the Keweenawan Series: Geology, v. 59, p. 151—172. Journal of l95lc, Ilmenite, magnetite, hematite, and copper in lavas of the Keweenawan Series: Economic Geology, v. 46, p. 51—67. �______________ ______________ Cornwall, H.R., 1954, Bedrock geology of the Delaware quadrangle, Michigan: U.S. Geological Survey Geologic Quadrangle Maps of the United States Map GQ 51. l954a, Bedrock geology of the Phoenix quadrangle, Michigan: U.S. Geological Survey Geologic Quadrangle Maps of the United States Map GQ 34. 1954c, Bedrock geology of the Lake Medora Quadrangle, Michigan: U.S. Geological Survey Geologic Quadrangle Maps of the United States Map GQ 52. 1955, Bedrock geology of Fort Wilkins quadrangle: U.S. Geological Survey Geologic Quadrangle Maps of the United States Map GQ 74. Cornwall, H.R. and Rose, H.J., Jr., 1957, Minor elements in Keweenawan lavas, Michigan: Geochemica et Cosmochimica Acta, v. 12, p. 209—224. Cornwall, H.R. and Wright, J.C., 1954, Bedrock geology of the Eagle Harbor quadrangle, Michigan: U.S. Geological Survey Geologic Quadrangle Maps of the United States Map GQ 36. 1956a, Geologic map of the Hancock quadrangle, Michigan: U.S. Geolo— gic'al Survey Mineral Investigations Field Studies Map MT 46. 1956b, Geologic map of the Laurium quadrangle, Michigan: gical Mineral Investigations Field Studies Map MT 47. U.S. Geolo- Oronto Group, MichiDaniels- P.A., Jr., 1982, Upper Precambrian sedimentary rocks: gan—Wisconsin: Geological Society of America Memoir 156, p. 107—133. Davidson, E.S., Espenshade, G.H., White, W.S. and Wright, J.C., 1955, Bedrock geology of the Mohawk quadrangle, Michigan: U.S. Geological Survey Geologic Quadrangle Maps of the United States Map GQ 54. DeGraff, J.M., 1976, Structural and age relationships of rocks associated with the Lac La Belle magnetic anomaly, Keweenaw County (M.S. thesis): Michigan Technological University, Houghton, 130 p. Elmore, R.D., 1981, The Copper Harbor Conglomerate and Nonesuch Shale: Sedimentation in a Precambrian intracontinental rift, Upper Michigan (Ph.D. dissertation): University of Michigan, Ann Arbor, 192 p. Elmore, R.D. and Van der Voo, R., 1982, Origin of hematite and its associated rema— nence in the Copper Harbor Conglomerate (Keweenawan), Upper Michigan: Journal of Geophysical Research, v. 87, p. 918—928. Ensign, C.O., Jr. White, W.S., Wright, J.C., Patrick, J.L., Leone, R.J., Hathway, D.J., Trammell, J.W., Fritts, J.J. and Wright, T.J,, 1968, Copper deposits in the Nonesuch Shale, White Pine, Michigan: in Ridge, J.D., ed., Ore Deposits of the United States, 1933—1967: American Institute of Mining, Metallurgy and Petroleum Engineering, p. 462—488. Fritts, C.E., 1952, A petrologic study of the Mount Houghton felsite, Keweenaw Peninsula (M.S. thesis): Michigan Technological University, Houghton, 42 p. Green, J.C., 1977, Keweenawan plateau volcanism in the Lake Superior region: Geological Association of Canada Special Paper No. 16, p. 407—422. �_____________ ____________ Green, J.C., 1982, Geology of Keweenawan extrusive rocks; of America Memoir 156, P. 47—55. Geological Society 114 Grimes, J.G., 1977, Geochemistry and petrology of Keweenaw rhyolites and associated rocks, Portage Lake Volcanics, Michigan (M.S. thesis): Michigan Technological University, Houghton, 80 p. Halls, H.C., 1982, Crustal thickness in the Lake Superior region: of American Memoir 156, p. 239—243. Geological Society Hase, H.W., Jr., 1973, Geological—geophysical site investigation of a portion of the Student Development Complex, Michigan Technological University, Houghton County, Michigan (M.S. thesis): Michigan Technological University, Houghton, 35 p. Holcomb, F.W., 1975, Urban Geological Map of the Eastern Half of the City of Houghton, Michigan (M.S. thesis): Michigan Technological University, Houghton, 87 p. Huber, N.K., 1975, The geologic story of Isle Royale National Park: Survey Bulletin 1309, 66 p. U.S. Geological Jolly, W.T., 1974, Behavior of Cu, Zn, and Ni during prehnite—pumpellyite rank metamorphism of the Keweenawan basalts, Northern Michigan: Economic Geology, v. 69, p. 1118—1125. Jolly, W.T. and Smith, R.E., 1972, Degradation and metamorphic differentiation of the Keweenaw tholeiitic lavas of northern Michigan, U.S.A.: Journal of Petrology, v. 13, p. 507—531. Juilland, J.D., 1965, Mineralization of the Mount Bohemia intrusive, Keweenaw County, Michigan (M.S. thesis): Michigan Technological University, Houghton, 78 p. Kalliokoski, J., 1976, End moraine map of northern Michigan—Wisconsin: Technological University Press, Geologic Map Series, Map hA. 1982, Jacobsville Sandstone: 156, p. 147—155. Michigan Geological Society of America Memoir Klasner, J.S., Cannon, W.F. and Van Schmus, W.R., 1982, The pre—Keweenawan tectonic history of southern Canadian Shield and its influence on formation of the mid— continent rift: Geological Society of America Memoir 156, p. 27—46. Lankton, L.D. and Hyde, C.K., 1982, Old Reliable — an illustrated history of the Quincy Mining Company: The Quincy Mine Hoist Association, Inc., Hancock, Michigan, 159 p. Livnat, A., Rye, R.O. and Kelly, W.C., 1976, Stable—isotope and fluid inclusion studies of the Keweenaw copper district, northern Michigan (abs.): Geological Society of America Abstracts with Programs, v. 8, p. 980—981. Longo, A.A., 1982, A geochemical correlation, with correlative inferences from petro— graphic and paleomagnetic data, of the Greenstone flow, Keweenaw Peninsula and Isle Royale, Michigan (abs.): Proceedings of the 28th Institute on Lake Superior Geology, p. 22—23. 1983, A geochemical correlation, with correlative inferences from petrographic and paleomagnetic data, of the Greenstone flow, Keweenaw Peninsula and Isle Royale, Michigan (M.S. thesis): Michigan Technological University, Houghton. �_______________ 115 Merk, G.P. and Jirsa, M.A., 1982, Provenance and tectonic significance of the Keweenawan interflow sedimentary rocks: Geological Society of America Memoir 156, P. 97—105. Prest, V.K., 1969, Retreat of Wisconsin and recent ice in North America: Survey of Canada Map 1257A. Geological Robertson, J.M., 1974, Major and minor element geochemistry of some late Precambrian dikes, Keweenaw County, Michigan (abs.): Proceedings of the 20th Institute on Lake Superior Geology, p. 27. 1975, Geology and mineralogy of some copper sulfide deposits near Mount Bohemia, Keweenaw County, Michigan: Economic Geology, v. 70, p. 1202— 1224. Robertson, J.M., Grimes, J.G. and Rose, W.I., Jr., 1979, Intermediate and silicic volcanic and subvolcanic rocks of the Portage Lake Volcanics, Michigan (abs.): Geological Society of America Abstracts with Programs, v. 11, p. 255. Rose, W.I., Jr. and Grimes, J.G., 1979, Cyclical compositional changes within flood Geological Society of basalts of the Portage Lake Volcanics, Michigan (abs.): America Abstracts with Programs, v. 11, p. 255. Scofield, N., 1976, Mineral chemistry applied to interrelated albitization, pumpel— lyitization and native copper redistribution in some Portage Lake basalts, Michigan (Ph.D. dissertation): Michigan Technological University, Houghton, 144 p. Stevens, A., 1971, A study of subsurface analysis of the proposed outdoor instruction area, Student Development Complex, Michigan Technological University, Houghton Michigan Technological University, Houghton, County, Michigan (M.S. thesis): 58 p. Stoiber, R.E. and Davidson, E.S., 1959, Amygdule mineral zoning in the Portage Lake Lava Series, Michigan copper district: Economic Geology, v. 54, p. 1250—1277, 1444—1460. Van Schmus, W.R., Green, J.C. and Halls, H.C., 1982, Geochronology of Keweenawan rocks of the Lake Superior region: A summary: Geological Society of America Memoir 156, p. 165—171. Walker, G.P.L., 1975, Intrusive sheet swarms and the identity of Crustal Layer 3 in Iceland: Journal of the Geological Society of London, v. 131, p. 143—161. Warren, E.J., 1981, The bedrock topography of the Keweenaw Peninsula, Michigan (Ph.D. dissertation): Michigan Technological University, Houghton, 169 p. Weege, R.J. and Pollack, J.P., 1971, Recent developments in the native—copper district of Michigan: Society of Economic Geologists, Guidebook for Field Conference, Michigan Copper District, Sept. 30—Oct. 2, 1971, p. 18—43. �__________ ___________ ____________ _____________ White, W.S., 1956, Geologic map of the Chassell Quadrangle, Michigan: gical Survey Mineral Investigations Field Studies Map MF 43. U.S. Geolo- 1960, The Keweenaw lavas of Lake Superior, An example of flood basalts: American Journal of Science, v. 258—A, p. 367—374. 1968, The native copper deposits of northern Michigan: ed., Ore Deposits of the United States, 1933—1967: Metallurgy and Petroleum Engineering, p. 303—325. in Ridge, J.D., American Institute of Mining, l971a, Geologic setting of the Michigan copper district: Society of Economic Geologists, Guidebook for Field Conference, Michigan Copper District, Sept. 30—Oct. 2, 1971, p. 3—17. 1971b, Field Trip A—2 —— Houghton to Calumet via South Range quarry and Society of Economic Geologists, Guidebook for Field Conference, Eagle River: Michigan Copper District, Sept. 30—Oct. 2, 1971, p. 68—75. 1972, Keweenawan flood basalts and continental rifting: Geological Society of America Abstracts with Programs, v. 4, p. 732—734. White, W.S., Cornwall, H.R. and Swanson, R.W., 1953, Bedrock geology of the Ahmeek quadrangle, Michigan: U.S. Geological Survey Geologic Quadrangle Maps of the United States Map GQ 27. White, W.S. and Wright, J.C., 1956, Geologic map of the South Range quadrangle, Michigan: U.S. Geological Survey Mineral Investigations Field Studies Map MF 48. 1960, Lithofacies of the Copper Harbor Conglomerate, northern Michigan: U.S. Geological Survey Professional Paper 400—B, p. B5—B8. Zelenka, B.R., 1978, The history of the Delaware Mine: Local Publication, 20 p. �i: r 2' V r 25 1. 4 14 Figure 1B: 15 r 1. 2 in mites SCALE 0 17 I r i 3 4 k12 18 12 i Stop n!Jmher Map number Index of 1:24,OOC caIe 'naps 0 r I 2 29 r 1 �'Freda McLain State Park Atlantic South Painesdale p4 Chassell Eagle rm 4 C, 0 1 4 Scate 2 o4? 3 + 4miteS Copper Harbor 12 Manitou Island Stop number Figure 1A: Route and stop map Michigan Technological University is an equal opportunity educational institution/equal opportunity employer. � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1983 Description An account of the resource Institute on Lake Superior Geology. Michigan Technological University, Houghton, Michigan. May 11-14, 1983. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1983 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/c2caa4000cd34c2d11aabbe70362e238.pdf 5aaa5cb9f07dbd04064727a8d6f121c6 PDF Text Text ___ ANNUAL THIRTIETH ANNUAL INSTITUTE INSTITUTE ON ON LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY SOUTH NORTH / U) //// ,ISLAND / / TRENCH /ANUE SM ARC 1OCEAN CRUST iL: I-. C) I- U) OLTZ — - _- i —--—- - -r + + + + + + + + + +++ + ++++++++ + + + + + + + + + + + + + +++ + + • + 4.4 + +++ ++ .4. — -7-- —/-ANIMIKIE -.— - — -- — — -— — —— — - -— —'-—S SEDIMENTS - 4 COLLISION + + + + + + + + + + + + + + + + + + + + + + ++ ++ + + + + + +++ + + + + + + + + + + 4- + + + + + + + + SNEISS DOMES W a u s a u , Wisconsin Wisconsin Wausau, A p r i l 24—28, 2 4 - 2 8 , 1984 1984 April �INSTITUTES INSTITUTES ON ON LAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY INSTITUTE NUMBER NUMBER INSTITUTE 11 22 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 II 11 12 12 13 13 14 14 15 15 16 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 - DATE DATE 1955 1955 1956 1956 1957 195 7 1958 1958 1959 1959 1960 1960 1961 1961 1962 1962 1963 1963 1964 1964 1965 1965 1966 1966 1967 1967 1968 1968 1969 1969 1970 1970 1971 1971 1972 1972 1973 1973 1974 1974 1975 1975 19 76 1976 1977 1977 1978 1978 1979 1979 1980 1980 1981 1981 1982 1982 1983 1983 1984 1984 1985 1985 PLACE Minneapolis, MN Houghton, Houghton, MI MI East E a s t Lansing, Lansing, MI MI Duluth, MN Minneapolis, MN Minneapolis, WII Madison, W Ont. (Thunder Port P o r t Arthur, Arthur, Ont. (Thunder Bay) Bay) Houghton, MI MI Duluth, MN Duluth, Ishpeming, MI Ishpeming, MI St. S t . Paul, Paul, MN MN Sault S a u l t Ste. S t e . Marie, MI MI East Lansing, Lansing, MI MI Superior, S u p e r i o r , WI WI Oshkosh, WI WI Thunder Bay, Ont. Ont. Duluth, Duiuth, MN Houghton, MI MI WII Madison, W Sault MII S a u l t Ste. S t e . Marie, Marie, M Marquette, MI MI S t . Paul, Paul, MN St. Thunder Thunder Bay, Ont. Ont Milwaukee, WI WI Duluth, MN Duluth, Eau Claire, C l a i r e , WI WI East E a s t Lansing, MI MI Falls, IInternational nternational F a l l s , MN Houghton, MI Wausau, Waus au , WI WI Kenora, Kenora, Orit. Ont. . �Award Award Guidelines Guidelines SAM SAM GOLDICH GOLDICH MEDAL MEDAL Preamble Preamble The The Institute I n s t i t u t e on on Lake Lake Superior Superior Geology was born on or o r around 1955, as a s documented do'cumented by by the t h e fact f a c t that t h a t the t h e 27th 27th annual annual meeting meeting will w i l l be be held h e l d in i n 1981. 1981. The The Institutes Institutes are i n their t h e i r continuing continuing objectives o b j e c t i v e s of dealing d e a l i n g with w i t h those aspects a s p e c t s of a r e exemplary exemplary in geology geology that t h a t are a r e related r e l a t e d geographically geographically to t o Lake Lake Superior; Superior; of of encouraging encouraging the the discussion d i s c u s s i o n of of subjects s u b j e c t sand andsponsoring w i l l bring b r i n g together together sponsoring field f i e l d trips t r i p s which which will geologists surveys, and andiindustry; g e o l o g i s t s from from tthe h e academia, academia, government government surveys, n d u s t r y ; and and of of maintaining maintaining an but an exceedingly exceedingly informal informal b u t highly h i g h l y effective e f f e c t i v emode mode of of operation. operation. During i t s existence e x i s t e n c e the t h e membership membership of of the t h e Institute I n s t i t u t e (that ( t h a t is, i s , those those During the t h e course course of of its geologists g e o l o g i s t s who who indicate i n d i c a t e an an interest i n t e r e s t in i n the t h e objectives o b j e c t i v e s of of the t h e I.L.S.G. I.L.S.G. by by attending) attending) has has become become aware aware of of the t h e fact f a c t that t h a t certain c e r t a i n of of their t h e i r colleagues colleagues have made particularly particularly noteworthy noteworthy and and meritorious meritorious contributions c o n t r i b u t i o n s to t o the t h e improvement improvement of of understanding understanding of of "Lake Superior" geologyand andiits "Lake S u p e r i o r " geology t s mineral mineral deposits. deposits. The by I.L.S.G. I.L.S.G. tot oSam The exemplary exemplary award award was was made made by Sam Goldich Goldich in i n 1979 1979 for f o r his h i s many many contributions t h egeology geology of ofthe t h eregion 50 years. years. regionextending extendingover overabout about50 c o n t r i b u t i o n s to t othe Award Award Guidelines Guidelines 1) 1) The The medal medal shall s h a l l be be awarded awarded annually annually by by the t h e Board Board of of Directors, D i r e c t o r s , I.L.S.G., I.L.S.G., to t o aa geologist whose name is a s s o c i a t e d with w i t h aa substantial s u b s t a n t i a l sustained s u s t a i n e d interest i n t e r e s t in, i n , or or g e o l o g i s t whose name is associated aa major SuperiorRegion. Region. thegeology geologyofofthe t hLake e LakeSuperior major contribution c o n t r i b u t i o n to, t o ,the 2) 2 ) The The Board Board of of Directors, D i r e c t o r s , I.L.S.G. I.L.S.G. shall s h a l l appoint appoint the t h e Nominating Nominating Committee. Committee. Their w i l l be be voted voted on on at a t the t h e annual annual business b u s i n e s s meeting. meeting. The The Their annual annual nominee nominee will initial i n i t i a l appointment appointment will w i l l be be of of three t h r e e members, members, one one to t o serve s e r v e for f o r three t h r e e years, y e a r s , one one for the member member with w i t h the t h e briefest b r i e f e s t incumbency incumbency to t o be be f o r two, two, and and one one for f o r one one year, y e a r , the chairman. chairman. After A f t e r the t h e first f i r s t year year the t h e Board Board of of Directors D i r e c t o r s shall s h a l l appoint appoint at a t each each spring memberwho who w i will l l s eserve r v e f for o r tthree h r e e years. y e a r s . In In the t h e third t h i r dyear year s p r i n g meeting meeting one one new new member this thismember member sshall h a l l be be the t h e chairman. chairman. The The Committee Committee membership membership should should reflect r e f l e c t the the main main fields f i e l d s of of interest i n t e r e s t and and geographic geographic distribution d i s t r i b u t i o n of of I.L.S.G. I.L.S.G. membership. membership. 3) 3) The Goldich Goldich Medal Medal Nominating Nominating Committee Committee shall s h a l l select s e l e c t the t h e medalist m e d a l i s t and and will will The make make its i t srecommendation recommendation tto o the t h e Board Board of of Directors D i r e c t o r s by byNovember November 1 t h a t year. year. 1 of of that 4)4) The The Board ~ o a r of dof Directors D i r e c t o r s normally normally will w i l l accept a c c e p t the t h e nominee nominee of of the the Committee, Committee, will w i l l inform inform the t h e medalist medalistimmediately, immediately, and andwill w i l have l haveone one medalengraved engraved medal appropriately a p p r o p r i a t e l y for f o r presentation p r e s e n t a t i o n at a tthe t h e May May meeting. meeting. I t is i s recpmmended recommended that t h a t the t h e Institute I n s t i t u t e set s e t aside a s i d e annually annually from fromwhatever whatever sources, sources, It such w i l l be be required r e q u i r e d to t o support support the t h e continuing continuing costs c o s t s of of this this award. award. such funds funds as a s will 5) 5) April ' 4 , 1981 1981 A p r i l 4, J. Kalliokoski, K a l l i o k o s k i , Chairman Chairman J. Bill B i l l Cannon Cannon Fred Fred Kehienbeck Kehlenbeck Glenn Glenn Morey Morey Greg Greg Mursky Mursky �region. To plan and conduct geological field trips. a c - m a a if 31 go a Â¥ a > 31 a a UJ a a w >à a 3 m - 0 c . 33 a 1) C u UE4-1 1) el U - + a s a c 3 - c- -- - aa m U .c IU 0 a. 33 el - n - 0 31 s U a >s 3 -m .c Id a 31 3 os 1) c a -1 a a -3 u à C -3 -- The rules contained in Robert's Rules of Order shall govern this organization in all cases to which they are applicable. Rules or Order Registration fees for the annual meetings shall be determined by the Chairman in consultation with the board of directors. It is strongly recommended that these be kept at a minimum to encourage attendance of graduate students. Ic 3 .c z0 I- - J= --- m 31 u a I- c U N M I- £- 0 U fat 0 u a c c 0 0 2 c amended. These by—laws may be amended by a majority vote of those persons who are personally present at, participating in, and voting at any annual meeting of the organIzation; provided that such modifications shall not conflict with the constitution as presently adopted or subsequently Amendments 1. ) in, and voting at 4-1 31 0 M eat ion. -5 w 1) > fleet lug oh the orgaril u M m Amendments u U Ia There shall be no regular membership dues. - 1-1 - This const Itiit ion may be amended by a maor1ty Vote of those persons who are personally present at, participating any annual 1)- Dues and Expenses 0 5 B. u a m I- c a a IV. c The Chairman shall be elected each year by the board of directors. who shall give due consideration to the wishes of any group that may be promoting the next annual meeting. his term of office as Chairman will terminate at the close of the annual meeting over which he presides or when his successor shall have been appointed. He will then serve for a period of three years as a member of the board of directors. The Secretary—Treasurer shall be elected at the annual meeting. His term of office shall be two years or until hits successor shall have been appointed. "0 A. s u a III. c a The officers of this organization shall be a Chairman and a Secretary— Treasurer. --:- 2. 2 1. -- Officers Keep accurate attendance records of all annual meetings. Keep accurate records of all meetings of, and correspondence between, the board of directors. Hold all funds that may accure as profits from annual meetings or field trips and to make these funds available for the organization and operation of future meetings as required. M It shall be the duty of the board of directors to plan locations of annual meetings and to advise on the organization and financing of all meetings. 3. 2. 1. c -1 c a u a c The board of directors shall consist of the Chairman, Secretary—Treasurer and the last three past Chairmen; but if the board should at any time consist of less than five persons, by reason of unwillingness or inability of any of the above persons to serve as directors, the vacancies on the board may be filled by the annual meeting so as to bring the membership of the board up to five members. II. - Preside at the annual meeting. Appoint all committees needed for the organization of the annual meeting. Assume complete responsibility for the organization and financing of the annual meeting over which he presides. It shall be the duty of the Secretary—Treasurer to: 3. 2. 1. It shall be the duty of the Chairman to: l?m Directors C. B. A. Duties of the Officers and Directors Â¥r The organization shall meet once a year, preferably during the month of April. The place and exact date of each meeting will be designated by the board of directors. Meetings The membership of the organization shall consist of the board of directors. Any geologist interested shall be permitted to attend and participate In and vote at the annual meetings. Membership Minn. Stat. Anno. 290.01, subd. 4 290.05(9) 1954 Internal Revenue Code a. SOI(c)(3) (To avoid Federal and State income taxes, the organIzation should be not only "acientitic" or "educational" but also "non—profit.") No part of the income of the organization shall inure to the benefit of In the event of dissolution the assets of the any member or individual. organization shall be distributed to (some tax free organization). I. BY-LAWS c Article VIII this organization are: on Lake Superior To provide a means whereby geologists in the Great Lakes region may exchange ideas and scientific data. To promote better understanding of the geology of the Lake Superior objectives of Status C. B. A. The Objectives "Institute 0 Article VII Name The name of the organization shall be the Geology." a Article VI Article V Article IV Article III Article II Article I CONSTITUTION OF INSTITUTE ON LAKE SUPERIOR GEOLOGY ___________________________________ 33- �TABLEOF OFCONTENTS CONTENTS TABLE . . . . . . B O A R D OF O F DIRECTORS DIRECTORS . . . . . . BOARD L O C A L COMMITTEES COMMITTEES. . . . . . . LOCAL G O L D I C H MEDAL MEDAL COMMITTEE COMMITTEE . . . GOLDICH S E S S I O N CHAIRMEN CHAIRMEN . . . . . . . SESSION G O L D I C H MEDAL MEDAL RECIPIENT RECIPIENT . . . . GOLDICH A N N U A L BANQUET B A N Q U E T SPEAKER SPEAKER. . . . . ANNUAL ACKNOWLEDGEMENTS. . . . . . . . ACKNOWLEDGEMENTS G E N E R A L INFORMATION INFORMATION GENERAL . . R E P O R T OF O F THE T H E CHAIRMAN CHAIRMAN REPORT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F i e l d Trip T r i p II . . . . . . . . . . . Field P o s t e r Papers Papers. . . . . . . . . . . Poster T e c h n i c a l Sessions S e s s i o n s II and a n d II. 11. . . . Technical C A L E N D A R OF O F EVENTS E V E N T S AND AND PROGRAM. PROGRAM. CALENDAR . . . . 1i iii i iii iii ill iii iv iv iv iv iv iv iv iv v V vii . vii vii . Vii vii . Vii . viii A n n u a l Banquet Banquet Annual ix Technical Technical . . . . . . . . . . . . S e s s i o n s III I11 and and I V . . . . . Sessions ix ix . . . . . . . . . xi xi F i e l d Trips T r i p s 22 and a n d 3. 3. Field ABSTRACTS ABSTRACTS �GENERAL INFORMATION GENERAL INFORMATI ON 30th 30th ANNUAL ANNUAL INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIORGEOLOGY GEOLOGY INSTITUTE Held Held at at HOLIDAY HOLIDAY INN INN Wausau, Wisconsin, Wisconsin, 54901 Wausau, 54901 April A p r i l 26, 26, 27, 27, 1984 1984 sponsored by sponsored by The Geology The Geology Department Department The University The U n i v e r s i t yofo Wisconsin-Oshkosh f Wisconsin-Oshkosh Program Chairman Chairmanand andEEditor Program ditor Gene L. LaBerge LaBerge Gene L. 1 �INSTITUTE BOARD BOARD OF OF DIRECTORS DIRECTORS G. L. L. LaBerge, LaBerge, Department of G. of Geology, University of of Wisconsin—Oshkosh Wisconsin-Oshkosh, Oshkosh, Wisconsin, 54901 Oshkosh, 54901 (1984) (1984) Engineering, T. 3. Bornhorst, Department T. J. Bornhorst, Department of of Geology Geology and and Geological Geological Engineering, Michigan Technological University, U n i v e r s i t y , Houghton, Houghton, Michigan, Michigan, 49931 49931 (1983) (1983) D. L. L. Southwick, Minnesota Geological Survey, Survey, 2642 2642 University University Avenue, Avenue, St. Paul, Minnesota, 55114 S t . Paul, 55114 (1982) (1982) tate U n i v e r s i t y , East F. W. F. W. Cambray, Department Department of of Geology, Geology, Michigan Michigan S State University, East Lansing, Michigan, 48824 Lansing, 48824 (1981) (1981) P. E. Myers, Department of P . E . Myers, of Geology, Geology, University of Wisconsin—Eau Wisconsin-Eau Claire, Claire, Eau Claire, C l a i r e , Wisconsin, 54701 54701 (1980) (1980) 3. K Kallioloski, Department of of Geology and Geological Engineering, Michigan J. a l l i o l o s k i , Department Michigan Technological University, U n i v e r s i t y , Houghton, Michigan, 49931 49931 (Secretary-Treasurer) (Secretary-Treasurer) SALES SALES t h e Abstracts A b s t r a c t sand andField Field T r iGuidebooks p Guidebooksmay maybe bepurchased purchased Copies of Copies of the Trip from . LaBerge , Geology , Uni v e r s i t y ooff from Gene GeneLL. LaBerge, GeologyDepartment Department, University Wisconsin-Oshkosh, Oshkosh, I , 54901. 54901. A Wisconsin—Oshkosh, Oshkosh, WWI, b s t r a c t s == $6.00; $6.00; Abstracts and III I 1 1= =$5.00 $5.00 each. each. Make Guidebooks I, Guidebooks I, III1and o: Makechecks checkspayable payable tto: I n s t i t u t eononLake LakeSuperior S u p e r i o rGeology. Geology. Institute 11 �LOCAL COMMITTEE L OCAL COMMITTEE Conference Chairman Chairman Gene L. L. LaBerge LaBerge Gene Trips Field F ield T rips P. K. P K. Sims, U.S. U.S. Geological Survey, Federal F e d e r a l Center, C e n t e r , Denver, Denver, Colorado, 80225 Colorado, 80225 Klaus J. J. Schuiz, Klaus Survey, National Center, Center, Schulz, U.S. U.S. Geological Survey, Reston, V Virginia, Reston, i r g i n i a , 22092 22092 Z e l l E. E. Peterman, U.S. Geological Survey, Survey, Federal F e d e r a l Center, Center, Zell Peterman, U.S. Denver, Colorado, Denver, Colorado, 80225 80225 Myers, Geology Department, Paul E. E. Myers, Department, University u n i v e r s i t y of of WisconsinWisconsinEau C l a i r e , Eau C l a i r e , Wisconsin, 54701 Claire, Claire, Wisconsin, 54701 W. L. L. Ueng, Ueng, D. W. D. K. K. Larue, Larue, R. R. L. L. Sedlock, D. D. A. A. Kasper, Kasper, S t a n f o r d University, University,, Stanford, Stanford, Department of Geology, Stanford California, C a l i f o r n i a , 94305 Registration R egistration LaBerge, Geology Department, Department, University U n i v e r s i t y of of WisconsinWisconsinS a l l y LaBerge, Sally Oshkosh, Oshkosh, Oshkosh, Wisconsin, Wisconsin, 54901 Oshkosh, 54901 Best Student Paper B e s t .Student Paper Committee Committee Paul E. Myers, Geology E . Myers, Geology Department, U n i v e r s i t y of of Wisconsin— WisconsinUniversity Claire, Eau C l a i r e , Eau Claire, C l a i r e , Wisconsin, Wisconsin, 54701 54701 W. Chandler, Minnesota Geological Survey, 2642 2642 U niversity Val W. Chandler, Minnesota Geological Survey, University Avenue, t . Paul, P a u l , Minnesota, Avenue, S St. Minnesota, 55114 Eugene C. C. Perry, P e r r y , Geology Department, Department, Northern Northern Illinois I l l i n o i s University, University, DeKaib,, Illinois, DeKalb I l l i n o i s , 61455 61455 GOLD ICH MEDAL MEDAL C COMMITTEE GOLD ICH OMMITTEE R. L. Buchheit, Meridian MeridianLand Landand andMineral MineralCompany, Company, Box Box 566, 566, L. Buchheit, Hibbing, Minnesota, 55746 55746 W. Cannon, U.S. U.S. Geological Survey, MS M S 954, National Center, Center, W. F. F. Cannon, Reston, Virginia, Reston, V i r g i n i a , 22092 22092 M. ~ a k e h e a dUniversity, University, M. F. Kehlenbeck, Department of Geology, Lakehead Bay, Ontario Thunder Bay, iii �SESSION SESSIONCHAIRMEN CHAIRMEN Robert of Geology, Robert L. L. Bauer, Bauer, Department Department of Geology, University University of of Missouri, Missouri, Columbia, Columbia, Missouri Missouri Theodore J. Bornhorst, Theodore J. Bornhorst,Department Department of ofGeology Geology and and Geological Geological Engineering, Engineering, Michigan Michigan Technological Technological University, U n i v e r s i t y , Houghton, Houghton, Michigan Michigan I. James Hoffman, Department Department of of Geology, Geology, University University of of WisconsinWisconsinJames I. Hoffman, Oshkosh, Oshkosh, Oshkosh, Oshkosh, Wisconsin Wisconsin Thomas R. Kalk, Kalk, Homestake Homestake Mining Mining Company, Company, P. P. 0. 0. Box Box 10628, 10628, Thomas R. Reno, Reno, Nevada Nevada John John S. S. Klasner, Klasner, Department Department of of Geology, Geology, Western Western Illinois Illinois University, U n i v e r s i t y , Macomb, Macomb, Illinois Illinois Gregory Gregory Mursky, Mursky, Department Department of of Geological Geological Sciences, Sciences, University University of of Wisconsin—Milwaukee, Wisconsin-Milwaukee, Milwaukee, Milwaukee, Wisconsin Wisconsin P e t e r A. A. Nielsen, Nielsen, Department Department of of Geology, Geology, University University of of Wisconsin— WisconsinPeter Parkside, Parkside, Kenosha, Kenosha, Wisconsin Wisconsin Klaus J. Schulz, Schulz, U. U. S. S. Geological Geological Survey, Survey, National National Center, Center, MS M S 954, 954, Klaus J. Reston, Reston, Virginia Virginia GOLDICH GOLDICH MEDAL MEDAL RECIPIENT RECIPIENT Richard Richard W. W. Ojakangas, Ojakangas, Geology Geology Department, Department, University University of of Minnesota—Duluth, Minnesota-Duluth, Duluth, Duluth, Minnesota Minnesota ANNUAL ANNUAL BANQUET BANQUET SPEAKER SPEAKER Dr. D r . Charles Charles Meyer, Meyer, 380 380 Smith Smith Road, Road, Sedona, Sedona, Arizona Arizona ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS Any this type type requires r e q u i r e s the t h e cooperation cooperation of of many many individuals individuals Any conference conference of of this who t i m e . As who are a r e willing w i l l i n gto t o give giveof of their t h e i rtime. A s general g e n e r a l chairman chairman II sincerely sincerely have had had by by the t h e many many people people I I a p p r e c i a t e the t h e widespread widespread cooperation cooperation II have appreciate have have asked asked to t o help h e l p make make the t h e conference conference aa success. success. AA special s p e c i a l thanks thanks goes goes to m y colleagues colleagues at a t UW—Oshkosh, UW-Oshkosh, especially t o my e s p e c i a l l y our o u r secretary s e c r e t a r y Sara Sara Margis Margis for for the t h e typing t y p i n g and and many many other o t h e rfunctions functionsshe shehas hasperformed. performed. II couldn't c o u l d n ' t have have done it without without you youall. all. done it iv �REPORT OF OFTHE THECHAIRMAN CHAIRMAN REPORT 29th INSTITUTE INSTITUTE 29th ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY ON 1983 29th Institute I n s t i t u t eon onLake Lake Superior Superior Geology Geology was was held h e l d May May 11—14, 11-14, 1983 1983 at at The 29th The The meeting meeting was was Michigan Technological Technological University Universityini nHoughton, Houghton,Michigan. Michigan. The Michigan theMichigan Michigan Tech Tech Department Department of of Geology Geology and and Geological Geological EngineerEngineersponsored by by the sponsored Regising in i n cooperation cooperation with with the the Division Division of ofEducation Education and and Public P u b l i c Services. S e r v i c e s . Regising t r a n t s numbered numbered 173, 173, including i n c l u d i n g 119 119 pprofessional r o f e s s i o n a l geologists g e o l o g i s t s and and 54 54 students. students. trants The program program included included aa pre-meeting pre-meeting one one day day field f i e l d trip t r i p to t o provide provide an an overview overview The Michigan, aa post-meeting post-meeting one one day day the geology geology of of the the Keweenaw Keweenaw Peninsula, Peninsula, Michigan, of the of f i e l d trip t r i p to t o the t h e Ropes Ropes and and Michigan Michigan gold gold mines mines near near Ishpeming, Ishpeming, Michigan Michigan and and field 70 persons persons participated p a r t i c i p a t e d in in four half—day half-day sessions s e s s i o n s of of technical t e c h n i c a l papers. papers. About About 70 four 60 participated p a r t i c i p a t e d in i n the t h e post-meeting post-meeting trip, t r i p , and and 31 31 about 60 tthe h e pre—meeting pre-meeting trip, t r i p , about The propropapers were were selected s e l e c t e d for f o r oral o r a l presentation p r e s e n t a t i o n at a t the t h e technical t e c h n i c a l sessions. s e s s i o n s . The papers I included 29th I n s t i t u t e were published i n two volumes. Volume ceedings of t h e ceedings of the 29th Institute were published in two volumes. Volume I included the accepted accepted abstracts a b s t r a c t s and and the t h e field f i e l d trip t r i p road road log l o g to t o the t h e Ropes Ropes gold gold mine. mine. the I1 was a geologic f i e l d guide f o r t h e Keweenaw Peninsula. Volume Volume II was a geologic field guide for the Keweenaw Peninsula. The Annual Annual Banquet Banquet was was held h e l d on on May May 12, 1 2 , 1983 1983 and and was was attended a t t e n d e dby by around around100 100 The people. Burt B u r t Boyum Boyum was was awarded awarded the t h e Institute's I n s t i t u t e 's Goldich ~ o l d i c Medal. hMedal. Unfortunately Unfortunately people. Burt was was o u t of of the the country countryand and Roy Roy Koski Koski accepted accepted the t h e medal medal in i n his h i sabsence. absence. Burt out Bob Reed was thanked by Ralph Marsden f o r h i s dedicated s e r v i c e f o r many years Bob Reed was thanked by Ralph Marsden for his dedicated service for many years a s the I n s t i t u t e ' s Secretary-Treasurer; this was Bob's l a s t meeting i n t h a t role. role. as the Institute 's Secretary—Treasurer; this was Bob 's last meeting in that The banquet address was given by D r . Stephen E. Kesler, University of Michigan, The banquet address was given by Dr. Stephen E. Kesler, University of Michigan, the CaribCaribwho compared n t r a s t e d precious e p o s i t s of e r t i a r y age age in i n the who comparedand andc ocontrasted preciousmetal metalddeposits of TTertiary bean to t o those thoseof ofArchean Archean age age in i nCanada. Canada. His H i s stimulating s t i m u l a t i n g talk t a l k provided provided a a fine fine bean touch tto o a meal meal of touch of prime primerib rib and andtrimmings. trinings. Dean Rossell, Rossell, graduate graduate student s t u d e n t at a tMichigan Michigan Technological Technological U n i v e r s i t y , received received Dean University, cashaward award of $200 ffor o r presenting p r e s e n t i n g the t h e best b e s t paper paper by by aa student. s t u d e n t . His of $200 H i s paper paper aa cash was eentitled n t i t l e d "Alteration " A l t e r a t i o n of of the the Deer Deer Lake e r i d o t i t e iin n tthe he v i c i n i t y of of the the was LakePPeridotite vicinity Ropes gold gold mine, mine, Marquette Marquette County, County, Michigan". Michigan". Dean Dean was co-leader of t h e ield Ropes was co—leader of the ffield ttrip r i ptot othe t h eRopes Ropesgold goldmine. mine. The The Best Student Paper Paper Coumtittee Committee recognized Best Student recognized aalll l s t u d e n t s for f o r their their good good p r e s e n t a t i o n s and i f f i c u l t to t o pick pick aa winner. winner. students presentations andfound founditit ddifficult the I n s t i t u t e and it is hoped t h a t t h Students p l a y an important r o l e i n Students play an important role in the Institute and it is hoped that thee q u a l i t y of of their theirpapers paperscontinues continuestot oimprove. improve. quality The Board Board of of Directors D i r e c t o r s of of the t h e Institute I n s t i t u t e met m e t on on May May 12, 12, 1983. 1983. Present Present at a t the the The T . J . Bornhorst (Chairman), D.L. Southwick, P.E. Myers, M.F. meeting were: meeting were: T.J. Bornhorst (Chairman), D.L. Southwick, P.E. Myers, M.F. Kehlenbeck, R.C. R.C. Reed Reed (Secretary-Treasurer) (Secretary-Treasurer) and and G.L. G.L. LaBerge LaBerge (incoming (incoming 1984 1984 Kehienbeck, Chairman). The Board took t h e following a c t i o n : Chairman). The Board took the following action: 1. 1. Accepted with w i t h thanks thanks the t h e continued continued offer o f f e r of of the t h e Minnesota Minnesota Geological Geological Survey Survey Accepted l i s t of of the t h e I.L.S.G. t o maintain maintain and and update update the t h e mailing mailing list I.L.S.G. to 2. 2. Accepted with w i t h enthusiasm enthusiasm the t h e offer o f f e r of of the t h e Ontario Ontario Geological Geological Survey Survey to t o host host Accepted t h e 31st 31st I.L.S.G. I.L.S.G. at a t Kenora, Kenora, Ontario Ontario in i n 1985. 1985. the 3. 3. Agreed that t h a t financing financing for f o r the t h e 1985 1985 meeting meeting in i n Kenora Kenora should should go go through through the the Agreed M.M. Kehlenbeck, Kehlenbeck, custodian. custodian. Canadian I.L.S.G. I.L.S.G. account, account, M.M. Canadian V �4. 5. Moved that t h a t the t h e summary summary report r e p o r t of of the t h e Chairman Chairman from from the t h e previous previous year, year, selection Award Constituion, the Goldich the t h e I n s t i t u t e ' s c o n s t i t u t i o n , t h e Goldich Award s e l e c t i o n rules, rules, a a list l i s t of of and location, and the address of the Secretary—Treasurer previous Institutes I n s t i t u t e s and l o c a t i o n , and t h e address of t h e Secretary-Treasurer (where previous Proceedings can be be obtained) obtained) be (where previous Proceedings Volumes Volumes can be included included iin n the the Proceedings Proceedings Volume. Volume. Institute's basis of Instructed I n s t r u c t e d that t h a t the t h e Chairman Chairman of of each each Institute I n s t i t u t e should should budget budget on on the t h e b a s i s of Excess money can be Excess money can be pre—registration w i t h the t h e goal g o a l of of breaking breaking even. even. p r e - r e g i s t r a t i o n with accumulated without I. I.R.S. R. S penalty. penalty. accumulated without . Moved Moved t hthat a t t transportation r a n s p o r t a t i o n to t o and and from from the t h e meeting meeting will w i l l be be paid p a i d for f o r the the This cost should be included in needed. This c o s t should be included in Goldich Award recipient, if Goldich Award r e c i p i e n t , i f needed. the t h e budget budget for f o r each each meeting. meeting. 7. Moved Moved that t h a t the t h eChairman Chairman of of each each Institute I n s t i t u t edecide decidewhat what expenses expenses are a r e reasonable reasonable 6. for f o r field f i e l d trip t r i ppresentation. presentation. 8. I t was was not n o t used used enough enough Decided to Decided t o discontinue discontinue the t h e I.L.S.G. I.L.S.G. Bibliography. Bibliography. It to of eeffort t o warrant warrant the t h e amount amount of f f o r t involved involved in i n updating. updating. 9. Discussed publication Discussed tthe he p u b l i c a t i o n of of aa special s p e c i a volume l volume of of papers papers as a s requested requested by by Tabled this issue until the 50th (via Dr. LaBerge). Dr. D r . Larue Larue ( v i a D r . LaBerge). Tabled this i s s u e u n t i l t h e 50th IInstitute. nstitute. 10. Noted papers extraneous extraneoust oto tthe Noted t that h a t papers h e ffield i e l d trip t r i pshould shouldnot n o tbe bepublished published in in BoardofofDDirectors' The Board i r e c t o r s ' ddesire e s i r e iis s to t o keep keep the the Proceedings Proceedings Volume. Volume. The the the Proceedings Proceedings Volume Volume uuncluttered. ncluttered. II. Appointed 1L.i.. i ~ . Kehlenbeck ~ . ( r e p r e s e n t i n g academia) academia) tto (representing o a a 3-year 3-year term term on on the the Medal Selection S e l e c t i o nCommittee. Committee. Dick Goldich Medal t h e1984 1984Chairman Chairman of Dick Buchheit Buchheit iiss the this thisCommittee. Committee. The The Board s t r u c t s the t h e Coxrnittee Committee tto o d e l i v e r the t h e name name of Boardi ninstructs deliver of t h e nominee nominee tto o the t h e Chairman Chairman by a t e r than than the by no no llater 12. of each each year. year. January 11 of January is Nominated G . Morey, Morey, JJ. . K a l l i o k o s k i , and r t hthe e I Institute's nstitute's Nominated G. Kalliokoski, and Paul PaulMyers Myersf ofor deadline necessary for f o r budget budget purposes. purposes. deadline i s necessary This This Secretary-Treasurer and i r e c t e d the t h e Chairman Chairman to t o accept accept other o t h e r nominations nominations Secretary—Treasurer andddirected from from the t h e membership. membership. The i l l be l e c t e d by by closed closed The new new Secretary-Treasurer Secretary—Treasurerw will be eelected b a l l o t vote vote of ofthe t h emembers members p resent. ballot present. 13. 14. I n s t r u c t e d the t h e new new Secretary-Treasurer o hold S . I.L.S.G. funds in i n an an Instructed Secretary-Treasurer tto hold UU.S. I.L.S.G. funds i n t e r e s t - b e a r i n g account account that t h a tpays pays the t h emaximum maximum i ninterest t e r e s t rrate a t e obtainable obtainable interest-bearing while high lliquidity. while maintaining maintaining high iquidity. i l l sell s e l land andhold holdProceedings Proceedings I n s t r u c t e d that t h a tthe t h eSecretary—Treasurer Secretary-Treasurer wwill Instructed Volumes from Volumes fromprevious previous meetings. The The eextra x t r a unsold unsold copies copies of of the t h eProceedings Proceedings Volumes w will i l l be o the t h e Secretary—Treasurer Volumes be given given tto Secretary-Treasurer aat t the t h e conclusion conclusion of of each each meeting. The eextra x t r a copies i l l be e p t until u n t i l the t h e next next year's y e a r ' smeeting meeting and and The copies wwill be kkept a f t e r that that after can be be discarded. discarded. Copies Copies of of previous previous volumes volumes can can be be obtained obtained can from t h e Secretary-Treasurer a t t h e c o s t of Xerox, s h i p p i n g and handling. from the Secretary—Treasurer at the cost of xerox, shipping and handling. The i l l be i s t e d on on the t h e back back of of the the The address address of of the t h e Secretary—Treasurer Secretary-Treasurer w will bellisted Proceedings Volume s o so t h athat t o rorders d e r s can r e c t e d t otot that hat o ffice. Proceedings Volume canbebed idirected office. 15. I n s t r u c t e d that t h a t the t h eSecretary-Treasurer Secretary-Treasurer print p r i n t I.L.S.G. I.L.S.G. s t a t i o n a r y and and make make Instructed stationary it available a v a i l a b l e to t o the t h e Chairman Chairman of of each each meeting. meeting. it Vi �16. 16. Moved that not be formalized beyond tthat t h a t the t h e Institute Institute n o t be formalized beyond h a t stated s t a t e d in i n the the Constitution. Constitution. 17. 17. Discussed and and suggested that t h a t group group travel t r a v e l arrangements arrangements for f o r the t h e 1985 1985 meeting in i n Kenora, Kenora, Ontario Ontario be investigated. i n v e s t i g a t e d . Ideas Ideas for f o r such transportation transportation included northward, perhaps perhaps arranged by by a UMD UND faculty included a bus from Duluth northward, faculty liaison, l i a i s o n , or o r possibly p o s s i b l y aa chartered c h a r t e r e d plane plane flight. flight. The The election e l e c t i o n for f o r aa new new Secretary—Treasurer Secretary-Treasurer was was held h e l d on on May May 13, 13, 1983. 1983. J. J. Kalliokoski, Kalliokoski, Department of of Geology and Geological Geological Engineering, Engineering, Michigan I ' m sure s u r e that t h a t the t h e Institute Institute U n i v e r s i t y , was elected e l e c t e d to t o the t h e post. p o s t . I'm Technological University, will w i l l benefit b e n e f i t from from Joe J o e 's ' s forthcoming effort e f f o r t as a s Secretary—Treasurer. Secretary-Treasurer. Financially Financially the 29th 29th I.L.S,G. I.L.S.G. concluded concluded with w i t h aa small small deficit. d e f i c i t . There is i s about about $2,900 $2,900 in in the U.S. account account and and about about $3,300 in i n the t h e Canadian Canadian account. account. t h e Institute's I n s t i t u t e ' s U.S. t a s k of t h e 29th 29th I.L.S.G. I.L.S.G. was an an enlightening e n l i g h t e n i n g experience experience in i n more more The task of organizing the ways than than one. I'm I ' m glad g l a d my responsibilities r e s p o n s i b i l i t i e s are a r e ending ending and and pass pass on on the t h e job job of of chairman Chairman to t o Gene Gene LaBerge, LaBerge, University University of o f Wisconsin, Wisconsin, Oshkosh. Oshkosh. 7Tdi Respectfully R e s p e c t f u l l y submitted, submitted, Theodore J. Bornhorst Bornhorst Theodore J. Chairman 29th 29th I.L.S.G. I.L.S.G. September September 21, 21, 1983 1983 , Houghton, Houghton, Michigan Michigan Vii vii �CALENDAR CALENDAR OF OF EVENTS EVENTS AND AND PROGRAM PROGRAII MONDAY, MONDAY, APRIL A P R I L 23, 2 3 , 1984 1984 - 6:00 6:00 p.m. p.m. - 9:00 9:00 p.m. p.m. DINNER DINNER AND AND ORIENTATION O R I E N T A T I O N FOR F O R PARTICIPANTS P A R T I C I P A N T S IN IN FIELD I. - Four Four Seasons Seasons Club, C l u b , Beecher, Beecher, F I E L D TRIP T R I P I. Wisconsin. Wisconsin. - TUESDAY, TUESDAY, APRIL A P R I L 24, 2 4 , 1984 1984 - 8:00 8:00 a.m. a.m. - 6:00 6:00 p.m. p.m. FIELD F I E L D TRIP T R I P I: I : GEOLOGY GEOLOGY OF O F THE THE EARLY EARLY PROTEROZOIC PROTEROZOIC ROCKS 1, Dunbar Dunbar ROCKS IN I N NORTHEASTERN NORTHEASTERN WISCONSIN-—Day WISCONSIN--Day 1, Gneiss-—Granitoid Sims, G n e i s s - - G r a n i t o i d Dome--P.K. Dome--P.K. S i m s , K.J. K . J . Schulz, Schulz, and E. Peterman. and ZZ.E. Peterman. . WEDNESDAY, WEDNESDAY, APRIL A P R I L 25, 2 5 , 1984 1984 - 8:00 8:00 a.m. a.m. - 4:00 4:00 p.m. p.m. - 7:00 p.m. - 10:00 1 0 : O O p.m. p.m. 7 : 0 0 p.m. -- 10:00 10:00 p.m. p.m. FIELD F I E L D TRIP T R I P I: I: GEOLOGY GEOLOGY OF O F THE THE EARLY EARLY PROTEROZOIC PROTEROZOIC ROCKS ROCKS IN I N NORTHEASTERN NORTHEASTERN WISCONSIN--Day WISCONSIN--Day 2, 2, The T h e northeastern northeastern Wisconsin W i s c o n s i n volcanic volcanic rocks-— rocks-K.J. K.J. Schulz, Schulz, P.K. P . K . Sims, S i m s , and and Z.E. Z . E . Peterman. Peterman. REGISTRATION, R E G I S T R A T I O N , LOBBY, LOBBY, HOLIDAY HOLIDAY INN, I N N , WAUSAU WAUSAU 7:00 7:00 p.m. p.m. - 10:00 1 0 : O O p.m. p.m. SMOKER SMOKER AND AND CASH CASH BAR, BAR, HOLIDAY HOLIDAY INN, I N N , WAUSAU WAUSAU 7:00 p.m. 7 : 0 0 p.m. POSTER POSTER PRESENTATIONS PRESENTATIONS Bruce and J.K. J . K . Greenberg--EARLY G r e e n b e r g - - E A R L Y PROTEROZOIC PROTEROZOIC B r u c e A. A. Brown B r o w n and STRUCTURES OF O F NORTHEASTERN NORTHEASTERN WISCONSIN W I S C O N S I N AS AS CONSTRAINTS CONSTRAINTS STRUCTURES ON ON PENOKEAN PENOKEAN TECTONIC TECTONIC MODELS MODELS A 1 U. U. Faister--MINERALOGY F a l s t e r - - M I N E R A L O G Y OF OF PEGMATITES PEGMATITES IN I N THE THE WAUSAU WAUSAU Al PLUTON, PLUTON, MARATHON MARATHON COUNTY, COUNTY, WISCONSIN WISCONSIN King, John John H. H. Karl, K a r l , John John S. S . Kiasner, Klasner, and and E l i z a b e t h R. R. King, Elizabeth William W i l l i a m J. J. Jones-—COMPOSITE J o n e s - - C O M P O S I T E MAGNETIC MAGNETIC MAP MAP OF O F WISCONSIN WISCONSIN PRECAMBRIAN PRECAMBRIAN FROM FROM NEW NEW COMPILATION COMPILATION OF O F DIGITAL DIGITAL AEROMAGNETIC AEROMAGNETIC DATA DATA Dennis and Joseph Joseph ManCUSO--GEOLOGY Mancuso--GEOLOGY OF O F THE T H ELONE LONE D e n n i s Mackovjak M a c k o v j ak and MOUNTAIN MOUNTAIN GOLD GOLD PROSPECT, P R O S P E C T ,NORTHEAST NORTHEASTNEVADA NEVADA M.G. Mudrey, M u d r e y , Jr. Jr. a n d Kalliokoski--METALLOGENY _J. Kalliokoski--METALLOGENY THE M.G. andJ. OFO FTHE LAKE LAKESUPERIOR S U P E R I O RPRECAMBRIAN PRECAMBRIAN P.A. METAMORPHIC MINERAL MINERALASSEMBLAGE ASSEMBLAGE P . A . Nielsen--MDB N i e l s e n - - M D B -- AA METAMORPHIC DATABASE FOR FOR THE THE PRECAMBRIAN PKECAMBRIAN OF O F THE THE LAKE LAKESUPERIOR SUPERIOR DATABASE DISTRICT DISTRICT viii viii �- WEDNESDAY, WEDNESDAY^ A APRIL P R I L 225, 5 , 1984 - continued P.A. P.A. Nielsen--METAMORPHIC Nielsen--METAMOFSHIC CONDITIONS CONDITIONSAND ANDEVOLUTION EVOLUTION A SUPRACRUSTAL SEQUENCE INTRUDED OF SEQUENCE INTRUDED BY BY THE THE OF DUNBAR GNEISS, G N E I S S f FLORENCE AND AND MARINETTE L W I N E T T E COUNTIES, COUNTIESf NORTHEASTERN NORTHEASTERN WISCONS WISCONS IN IX Hemzacek--PRECAMBRIAN J. Hemzacek--PRECAMBRIAN E.C, Jr., J. Feng and J. E . C o PPerry, e r r y , Jr., EVAPORITES: EVAPORITES: PRESERVATION PRESERVATION OF OF SULFATE SULFATE IN I N QUARTZ QUARTZ PSEUDOMORPHS AFTER GYPSUM PsETJDoMoR2Hs *WL PPetro——CRYSTALLIZATION *WmLa e t r o - - C R Y S T A L L I Z A T I O N HHISTORIES I S T O R I E S OF OF'EARLY FARLY PROTEROZOIC PROTEROZOIC PLUTONS FROM FROM NORTHERN NORTHERN WISCONSIN *ristopher A. Scholz-—LATE POST-GLACIAL *Christopher A. S c h o l z - - L AAND T E AND POST-GLACIALLACUSTRINE LACUSTRINE SEDIMENT DISTRIBUTION LANl SUPERIOR SUPERIOR SEDIMENT D I S T R I B U T I O N IN I NWESTERN WESTERN LAKE FROM SSEISMIC FROM E I S M I C REFLECTION EW?LECTION PROFILES PROFILES Michael J.. Schwartz M ichael J S c h w a r t z and P.A. P.A. Nielsen--REGIONAL N i e l s e n - R E G I O N A L CONTROLS CONTROLS ON ON ARCHEANMETALLOGENY METALLOGENY THEUPPER UPPER PENINSULA PENINSULA OF ARCHEAN I NINTHE OF MICHIGAN MICHIGAN *Jjfl Sikkila-—PETROGRAPHIC GEOCHEMICAL *Kevin S i k k i l a - - P E T R O G R A P H I CAND AND GEOCHEMICAL STUDY STUDY OF OF THE THE MOUNTBOHENIA BOHIA STOCK, LAKEVOLCANICS, VOLWICS, MOUNT STOCK,PORTAGE PORTAGE LAKE KEWEENAW PENINSULA, MICHIGAN KENEENAW PENINSULA, MICHIGAN W.R. TOTO THE GEOCHRONOLOGY W.R. Van VanSchmus-—RECENT Schmus--=CENT CONTRIBUTIONS CONTRIBUTIONS THE GEOCHRONOLOGY OF OF O F THE PRECAMBRIAN O F WISCONSIN WISCONSIN NOTE; All Best e l i g i b l efor f o rthe the B e sStudent t S t u d e nPaper t P a p e Award r Award NOTE: A l l Papers P a p e r s eligible are marked wwith an aasterisk are i t h an s t e r i s k ((*) *I . APRIL THURSDAY, THURSDAYf A P R I L 226, 6 , 1984 1984 77:30 : 3 0 aa.m. .m. - 4:30 4 : 3 0 p.m. p.m. REGISTRATION, LOBBY, REGISTRATION, LOBBY, HOLIDAY HOLIDAY INN, I N N fWAUSAU WAUSAU 8:00 a.m. a.m. 8:OO -- 5:00 pp.m. 5:OO .m. PRESENTATIONS needn onot POSTER PRESENTATIONS t sstay tay ( A u(Authors t h o r s need with posters) w i t h posters) - .m. 8:OO a.m. - 11:50 aa.m. 8:00 a.m. TECHNICAL SSESSION E S S I O N I, I, Kalk, Kalk ,Co—chairmen Co-chairmen John S. John S . Kiasner, Klasner,Thomas T h o m a s R. R. 8:00 a.m. 8:OO a.m. WELCOME 3 0 t30th h I -I.L.S.G.-—Gene L.S . G - - - G e n e L.L. LaBerge LaBerge WELCOME TO TO 88:10 : l O a.m. a.m. Warren W a r r e nC.CDay-—GEOLOGY . Day--GEOLOGY OF OF THE THERAINY RAINY LAKE LAKE AREA, AREA, NORTHERN MINNESOTA-REVISITED NORTHERN MINNESOTA-=VISITED 8:30 a.m. 8:30 a-m- 8:50 a.m. *Steven * S t e v e n Osterberg——STRATIGRAPHY O s t e r b e r g - - S T R A T I G R A P H Y OF O F THE THE HEADWAY-COULEE MASSIVESULZHIDE SULPHIDE PPROSPECT, HEADWAY-COUUE MASSIVE ROSPECTf M a AREA, m ONTARIO ONTARIO NORTHERN NORTHERN ONAMAN ONAMANLLAKE AREA, NW PPeter e t e r J. u d l e s t o n and David D a v i d L. L . Southwick--THE Southwick--THE J. H Hudleston -ROLE SHEAR IN I N DEFORMATION DEFORMATION ROLE OF TRANSCURRENT SHEAR OF THE ARCHEAN ARCHEAN ROCKS F THE VERMILLION VERMILLION OF THE ROCKS OOF DISTRICT, D I S T R I C T , MINNESOTA MINNESOTA ix �- continued continued THURSDAY, APRIL A P R I L 26, 2 6 # 1984 1984 THURSDAY, 9:10 a.m. D a v i d P. P . Moecher M o e c h e r and and L.G. L.G. Medaris, Medaris, Jr.--LATE Jr.--LATE David ARCHEAN METAMOWHIC CONDITIONS AT GRANITE ARCHEAN METAMORPHIC CONDITIONS AT GRANITE F A L L S f MINNESOTA MINNESOTA FALLS, 9:30 a.m. Anth.ony Mariano M a r i a n o and andH.H. H.H. t/oodard__POTASSIUM Woodard--POTASSIUM Anthony LMETASOMATISM OF TRONDHJEMITE MIGMATITE METASOMATISM OF TRONDHJEMITE MIGMATITE WALLROCK, VERMILION COMPLEXt NORTHERN WALLROCK, VERMILION COMPLEX, NORTHERN MIrnSOTA MINNESOTA 9:50 a.m. COFFEE BREAK 10:10 a.m. and Gregory G r e g o r y Mursky-—MOBILIZATION Mursky--MOBILIZATION R.L. Hackenberg H a c k e n b e r g and R.L. O F URANIUM AND THORIUM WITHIN THE REPUBLIC EPUBLIC OF URANIUM AND THORIUM WITHIN THE METAMORJ?HIC NODE, NORTHERN MICHIGAN METAMORPHIC NODE, NORTHERN MICHIGAN 10:30 a.m. Anthony W. h e p e c k and . J . Bornhorst-BornhorsteAnthony W. SShepeck andTT.J. 10:50 a.m. Thomas J. K i r s l i n g C.W. , C.W. Montgomery, M o n t g o m e r y , arid and E.C. E.C. Thomas J. Kirsling, CHARACTERIZATION OF THE ORE HOST ROCK AT CHARACTERIZATION OF THE ORE HOST ROCK AT THE ROPES GOLD GOLD MINE, MINE, ISHPEMING, ISHPEMING,MICHIGAN MICHIGAN THE ROPES P e r r Jr.-—RB-SR y Jr.--RB-SRANDAND OXYGEN ISOTOPE SYSTEMATICS Perry OXYGEN ISOTOPE SYSTEMATICS OFARCHEAN ARCHEAN GREY G m GNEISSES G N E I S S E SOFOF THE SOUTHWESTERN OF THE SOUTHWESTERN BEARTOOTH MOUNTAINS MOUNTAINS BEARTOOTH 11:10 a.m. KarlE.ESeifert--TRACE . S e i f e r t - - T F l AELEMENT C E ELEMENT GEOCHEMISTRY O r Karl GEOCHEMISTRy or 1 1 ~ 3a.m. 0a . m 11:30 P a t r i c Ryan k R y a and n and P aW. u l Weiblen——pT W. W e i b l e n - - P T Patrick Paul SOME LAICE SUPERIOR JCTWEENAWAN B A S I C LAYERE.. SOME LAKE SUPERIOR KEWEENAWAN BASIC LAYERL INTRUSIONS INTRUS IONS AND N I AND NI ARSENIDE MINERALS I N THE DULUTH COMPLEX ARSENIDE MINERALS IN THE DULUTH COMPLEX U : s O a.m. a.m. 11:50 LUNCH BREAK BREAK LUNCH ANNUAL MEETING, I L .S .G . BOARD OF DIRECTORS ANNUAL MEETING, I.L.S.G. BOARD OF DIRECTORS p.m. -1 : 2 0 p.m. 1:20 4 : 2 0 p.m. p.m. 4:20 TECHNICAL S E SESSION S S I O N I I tII, T hTheodore e o d o r e J.J. B ornnorst, TECHNICAL Bornhorst, J a m e s I. H o f f m a n , C o c h a i r m e n James I. Hoffman, Co—chairmen 1:20 p.m. andTheodore TheodoreJ. J. Bornhorst-J a m e s B. B. Paces P a c e sand James Bornhorst—— 1:40 p.m. S.A. H a u c k and E.W. Kendall--COMPARISON OF MIDDLE S.A.Hauck and E.W. Kendall--COMPARISON OF MIDDLE ALTEFATIONt PARAGENESIS AND AGE ASSOCIATE ALTERATION, PARAGENESIS AND AGE ASSOCIATE WITH NATIVE NATIVE COPPER COPPER MINERALIZATION MINERALIZATION OF OF THE THE WITH KEZGGARGE FLOWf KEWEENAW PENINSULAf MICHIGAN KEARSARGE FLOW, KEWEENAW PENINSULA, MICHIGAN PROTEROZOIC IRON OXIDE RICH RICH ORE O m DEPOSITS. DEPOSITS. PROTEROZOIC IRON OXIDE MID-CONTINENT S .A. SOUTH AUSTRALIA, SWEDEN, U MID-CONTINENT, U.S.A., SOUTH AUSTRALIA, SWEDEN, AND T m PEOPLES =PUBLIC OF CHINA AND THE PEOPLES REPUBLIC OF CHINA . 2 :00 p .m. R.D. P o w e l l - - C L I M A T I C INFERENCES OF IRON-E'OFlMATION R.D. Powell-—CLIMATIC INFERENCES OF IRON-FORMATION FROM ASSOCIATED DIAMICTI!I'E F A C I E S SEQUENCES, FROM ASSOCIATED DIANICTITE FACIES SEQUENCES, GRIQUALAND WEST SUPERGROUP, SOUTH AFRICA GRIQUALAND WEST SUPERGROUP, SOUTH AFRICA x �- THURSDAY, THURSDAY APRIL A P R I L 26, 26 1984 1984 - continued continued 2:20 p.m. . E. E . Schuessler S c h u e s s l e r and and E.C. E .C. Perry, P e r r y Jr.-—METAMORPHISM Jr --LMETAMORPHISM AND GRIQUATOWN GRIQUATOWN IRON IRON FORMATIONS OF OF KtJRUMAN KURUMAN AND F O M T I O N S AND AND . ASSOCIATED ASSOCIATED MAKGANYENE L W G A N Y E N E DIAMICTITE, D I A M I C T I T E l CAPE CAPE PROVINCE, PROVINCEl SOUTH SOUTH AFRICA: AE'RICA: AASTABLE STABLE ISOTOPE I S O T O P EINVESTIGATION INVESTIGATION 2:40 2 : 4 0 p.m. p-m- COFFEE COFFEE BREAK BREAK 3:00 3:OO p.m. p-m. *Erik AS TECTONIC * E r i k G. G. Shaw——DIKES Shaw--DIKES AS TECTONIC INDICATORS INDICATORS IN I N THE THE EASTERN EAS'IERN LAKE LAKE SUPERIOR SUPEFSORREGION-STRUCTURAL EGION-STRUCTURAL AND AND PALEOMAGNETIC PALEOMAGNETIC CONSIDERATIONS CONSIDERATIONS 3:20 3:20 p.m. pem. *Ted * T e d R. Repesky--MAGNETOTELLURIC &pesky--mGNETWEUURIC P R O F I L E OF OF THE THE PROFILE JACOBSVILLE JACOBSVILLE SANDSTONE SANDSTOm 3:40 p.m. W.F. E. Ranjthun--PRELININARY Kean D. D.Mercer M e r c eand r and E . Ramthun--PRELIMINARY W.F. Kean, PALEOMAGNETIC PALEOMAGNETIC RESULTS FROM FROM THE THEBARABOO BARABOO QUARTZITE AND THE THE ASSOCIATED M S O C I A T E D RHYOLITE F S Y O L I T E AND AND QUARTZITE AND GRANITE WISCONSIN GRANITE INLIERS I N L I E R SOF OFSOUTH SOUTHCENTRAL CENT= WISCONSIN 4:00 p.m. L.G. MICROSTRUCTURE Soroka and and J. J. Josch--MORPHOLOGY, Josch--MORPHOLOGYl L.G. Soroka AND AND ACCRETION A C C E T I O N RATE RATE OF OF RECENT RECENT ALGAL ALGAL STROMATOLITES STROMATOLITES FROM LAKE,OTTERTAIL OTTERTAILCOUNTY, COUNTYl MINNESOTA MINNESOTA FROM EAGLE EAGLE LAKE, 4:20 p.m. Richard Richard 6:00 p.m. SOCIAL S O C I A L HOUR--CASH HOUR--CASH BAR BAR. 7:00 ANNUAL ANNUAL BANQUET BANQUET p.m. A. Pau.U-—LOCALIZED P a u l l - - L O C A L I Z E D ACCUMULATIONS ACCUMULATIONS OF O F UPSIDE UPSIDE A. DOWN !XWN TRILOBITE T R I L O B I T E PARTS PARTS IN I N CAVITIES C A V I T I E S WITHIN WITHIN A A SILUBIAN S I L U R I A N REEF REZE' AT AT RACINE, R A C I N E l WISCONSIN WISCONSIN Announcement of 1985 1985 Meeting M e e t i n g in i n Kenora, Kenoral Ontario Ontario A n n o u n c e m e n t of P r e s e n t a t i o n of of Goldich Goldich Award A w a r d to t o R. R. W. W. Ojakangas Ojakangas Presentation by by S.S. S.S. Goldich Goldich G u e s t Speaker-—Dr. Speaker--Dr. Charles Meyer Meyer Guest Charles "THE "THE ORE O m METALS METALS IN I N EARTH W T H HISTORY" HISTORYtt FRIDAY, 2 7 , 1984 1984 FRIDAYl APRIL A P R I L 27, 8:00 8 : O O aa.m. . m . -- 1 11:50 1 : 5 0 a . a.m. m. 8:00 a.m. 8:30 a.m. T E C H N I ~ SESSION S E S S I O III, N I I I lKlaus Klaus J. J. Schulz S c h u l z and and TECHNICAL Robert Robert L. L. Bauer, B a u e r Co—chairmen Co-chairmen P.K. Sims, S i m s lZ•.E. Z.E. Peterman, P e t e m a n # and and Klaus Klaus 3. J. Schulz—— Schulz-BK. AA PARTISAN THE EARLY EARLY PROTEROZOIC PROTEROZOIC PARTISAN REVIEW WZVIEW OF OF THE GEOLOGY OF OF WISCONSIN WISCONSIN AND AND ADJACENT ADJACENT MICHIGAN MICHIGAN GEOLOGY and D.L. D.L. Southwick--EARLY S o u t h w i c k - - E A R L Y PROTEROZOIC PROTEROZOIC G - B . Morey M o r e y and G.B. GEOLOGY GEOLOGY OF O F EAST-CENTRAL EAST-CENTRAL MINNESOTA-A MINNESOTA-A REVIEW W I E W AND AND REAPPRAISAL REAPPRAISAL xi �- FRIDAY, FRIDAYr APRIL A P R I L 27, 2 7 r 1984 1 9 8 4 - continued continued 8:50 8:50 a.rn. a.m. Grant G r a n t M. M. Young--THE Young--THE HURONIAN HURONIAN SUPERGROUP: SUPERGROUP: AN AN EXAMPLE EXAMPLE OF OF AN EARLY EARLY PROTEROZOIC PROTEROZOIC PASSIVE P A S S I V E MARGIN MARGIN SEQUENCE SEQUENCE 9:10 9:lO Gene J . Schulz S c h u l z and and Paul P a u l E. E. G e n e L. L . LaBerge, L a B e r g e , Klaus K l a u s J. Myers--THE Myers--THE PLATE TECTONIC HISTORY HISTORY OF OF NORTH NORTH CENTRAL CENTRAL WISCONSIN WISCONSIN a.m. a.m. 9:40 9 : 4 0 a.m. a.m. 10:10 1 O : l O a.m. a.m. COFFEE COFFEE BREAK BREAK Klaus 3. J. Schulz--EARLY S c h u l z - - E A R L Y PROTEROZOIC PENOKEAN PENOmN IGNEOUS IGNFOUS ROCKS OF THE THE LAKE LAKE SUPERIOR SUPERIOR REGION: REGION: GEOCHEMISTRY GEOCHEMISTRY AND AND TECTONIC TECTONIC IMPLICATIONS IMPLICATIONS 10:30 a.m. *Warren SM ISOTOPIC * W a r r e n Beck--ND Beck--ND AND ANDSM I S O T O P I C STUDIES S T U D I E S OF OF THE THE QUINNESEC I NNORTHEASTERN NORTHEASTERN QUINNFSEC AND AND HEMLOCK HEMLOCK FORMATIONS FORMATIONS IN WISCONSIN AND AND ADJACENT ADJACENT MICHIGAN MICHIGAN 10:50 a.m. Timothy CONSTRAINTS T i m o t h yB.B.Hoist--PENOKEAN Holst--PENOKEANTECTONICS: TECTONICS: CONSTRAINTS FROM GEOLOGY IIN FROM STRUCTURAL STRUCTURAL GEOLOGY N EAST-CENTRAL EAST-CENTRAL MINNESOTA MINNESOTA 11:10 a.m. *Richard THE MULTIPLY * R i c h a r dC.CClark--MICROSTRUCTtJRES . Clark--MICROSTRUCTURES INI N THE MULTIPLY DEFORMED SLATE OF DEFORMED SLATE OF THE THETHOMSON THOMSON FORMATION, FORMATIONr EAST-CENTRAL MINNESOTA EAST-CENTMINNESOTA 11:30 a.m. G.A. Myers--BASEMENT F.W. Cambray, C a m b r a y t R.O. R . 0 . Meyer M e y eand r and F.W. G.A. Myers--BASEMENT COVER RELATIONS RELATIONS IN I NTHE TmMARQUETTE MARQUETTE AND AND REPUBLIC =PUBLIC COVER DISTRICTS, D I S T R I C T S MICHIGAN MICHIGAN 11:50 1 1 : S O a.m. a.m. -- 1:10 1 : l O p.m. p.m. LUNCH LUNCH BREAK BREAK 1:10 1 : l O p.m. p . m . -- 4:30 4 : 3 0 p.m. p.m. TECHNICAL S E SESSION S S I O N I V l IV, P e Peter t e r A.A.NNielsen i e l s e n and and TECHNICAL Gregory G r e q o r y Mursky, M u r s k y t Co—chairmen Co-chairmen 1:10 1 : l O p.m. p.m. and R.L. R.L. Sedlock--GEOLOGIC Sedlock--GEOLOGIC W.L. Ueng, U e n g l D.K. D.K. Larue L a r u e and W.L. HISTORY AND AND PALINSPASTIC P A L I N S P A S T I C RECONSTRUCTION RECONSTRUCTION OF OF THE THE HISTORY EARLY PROTEROZOIC PROTEROZOIC PENOKEAN PENOKBAN COLLISION C O L L I S I O N ZONE ZOm EARLY 1:30 1:30 p.m. p.m. John John S. S . K.lasner Klasner and and Dan D a n Osterfeld-—GRAVITY O s t e r f e l d - - G R A V I T Y MODELS MODELS OF OF GNEISS G N E I S S DOMES DOMES AND AND A A GRANITE GRANITE PLUTON PLUTON IN IN NORTHEASTERN IN NORTHEASTERN WISCONS WISCONSIN 1:50 p.m. FLichard O j a k a n g a s - - B A S ALOWER L LOWER PROTEROZOIC Richard W.W.Ojakangas--BASAL PROTEROZOIC GLACIOGENIC GLACIOGENIC FORMATIONS, FORMATIONStMARQUETTE MARQUETTE RANGE RANGE SUPERGROUP, SUPERGROTJF'r UPPER UPPER PENINSULA, PENINSULAr MICHIGAN MICHIGAN 2:10 p.m. S.S. S.S. 2:30 p.m. P.K. Sims--MIDDLE Z e l lE.E .Peterman P e t e n n a and n and Zell P.K. Sims--MIDDLE 2:50 p.m. COFFEE COFFEE BREAK BREAK Goldich--PRECAMBRIAN GEOCHRONOLOGY GEOCHRONOLOGY OF OF MINNESOTA MINNESOTA Goldich--PRECAMBRIAN PROTEROZOIC PROTEROZOIC EVENTS EVENTS IN I N NORTHEASTERN NORTHEASTERN WISCONSIN WISCONSIN AND AND ADJACENT ADJACENT RB-SR BIOTITE B I O T I T E AGES AGES MICHIGAN AS DEFINED BY MICHIGAN AS DEFINED BY RB-SR xii xii �FRIDAY, FRIDAY, APRIL A P R I L 27, 2 7 , 1984 1984 - continued continued - 3:10 p.m. Joseph Joseph J. J. Mancuso, M a n c u s o , Robert R o b e r t Brown, B r o w n , James J a m e s Harrison, Harrison, Alan Maharidge, M a h a r i d g e , Richard Richard Pennington P e n n i n g t o n and and Ronald R o n a l d Walden--GEOLOGY Walden--GEOLOGY OF O F THE THE GROVELAND GROVELAND MINE, MINE, FELCH DISTRICT, D I S T R I C T , MICHIGAN 3:30 p.m. Eugene E u g e n e C. C. Perry, P e r r y , Jr., J r a IS. S. Shen Shen and and C. C . Ueng—— Ueng-STABLE STABLE ISOTOPE I S O T O P E EVIDENCE EVIDENCEOF O FMETAMORPHISM METAMORPHISM AND AND HYDROTHERMAL ALTERATION, ALTERATION, NEGAUNEE NEGAUNEE IRON FORMATION, FORMATION, MICHIGAN MICHIGAN 3:50 p.m. Jeffrey K. G r e e n b e r g - - M A G H A T I S MAND AND THE BARABOO Jeffrey K. Greenberg--MAGMATISM THE BARABOO INTERVAL: INTERVAL: BRECCIAS, BRECCIAS, DIKES, D I E % , AND ANDMETASOMATISM METASOMATISM 4:10 p.m. Bruce AND THE THE B r u c eA.A.Brown-—LITHOLOGIC Brown--LITHOLOGIC DIVERSITY D I V E R S I T Y AND SEDIMENTARY-TECTONIC ENVIRONMENT DURING SEDIMENTARY-TECTONIC ENVIRO1ENT DURING DEPOSITION OF BARABOO B m O O INTERVAL INTERVAL (1760-1500 ( 1 7 6 0 - 1 5 0 0 MY) MY) D E P O S I T I O N OF ROCKS ROCKS 5:30 p.m. F I E L D TRIP TRIP II I1 DEPARTS DEPARTS FOR FOR IRON I R O N MOUNTAIN, MOUNTAIN, MICHIGAN MICHIGAN FIELD FROM FROM THE THE HOLIDAY HOLIDAY INN. INN. ( O v e r n i g h t in in (Overnight Dickinson D i d c i n s o n Inn.) IM.) SATURDAY, APRIL228, SATURDAY, APRIL 8 , 1984 1984 8:00 8:OO a.m. a.m. -- 5:00 5200 p.m. p.m. FIELD 11: EARLY EARLY PROTEROZOIC PROTEROZOIC TECTONOSTRATIGRApHIc TECTONOSTFUITIGRAPHIC F I E L D TRIP T R I P II: TERRANES TERRANES OF THE THE SOUTHERN SOUTHERN LAKE LAKE SUPERIOR S U P E R I O R REGION REGION by by W.L. W.L. Ueng, U e n g , D.K. D J C . Larue, L a r u e , R.L. R.L. Sedlock, S e d l o c k , and and D.A. D.A. Kasper, Kasper, Department D e p a r t m e n t of of Geology, Geology, Stanford S t a n f o r d University, Universityl Stanford, Stanford, California California 8:00 a.m. - 5:00 p.m. FIELD TRIP III: 111: GEOLOGY F I E L D TRIP GEOLOGY OF O F THE THE WAUSAU WAUSAU SYENITE S Y E N I T E COMPLEX, COMPLEX, by Paul P a u l E. E . Myers, Myers, Geology G e o l o g y Department, D e p a r t m e n t , University U n i v e r s i t y of of by W i s c o n s i n - E a u Claire, C l a i r e , Eau E a u Claire, C l a i r e , Wisconsin Wisconsin Wisconsin—Eau xiii xiii �(1) -I C) -I (1) w ABSTRACTS �Nd Studies Nd and and Sr S r Isotopic I s o t o p i c --S t u d i e s of of the t h e Quinnesec Quinnesec and --Northeastern and Adjacent Michigan N o r t h e a s t e r n Wisconsin Michigan Hemlock Hemlock Formations Formations in WARREN WAREEN BECK BECK (Dept. (Dept. of of Geology Geology and and Geophysics, Geophysics, University U n i v e r s i t y of of Minnesota, Minnesota, Minneapolis, 55455) Minneapolis, MN 55455) The Proterozoic P r o t e r o z o i c Penokean events e v e n t s of of the t h e southern s o u t h e r n Lake Lake Superior S u p e r i o r region region have recently terms of of Phanerozoic plate r e c e n t l y been been interpreted i n t e r p r e t e d iii i n terms p l a t e tectonic tectonic Two fundamentally fundamentally different d i f f e r e n t terrains t e r r a i n s may be found juxtaposed juxtaposed models. in i n the t h e northern n o r t h e r n Wisconsin—Upper Wisconsin-Upper Michigan Michigan region. r e g i o n . The northern n o r t h e r n terrain terrain has been interpreted i n t e r p r e t e d to t o represent r e p r e s e n t a continental c o n t i n e n t a l margin, margin, while w h i l e the the has terrain southern i s interpreted i n t e r p r e t e d to t o represent r e p r e s e n t an an s o u t h e r n volcano—plutonic volcano-plutonic t e r r a i n is The Penokean is interpreted i n t e r p r e t e d to t o represent r e p r e s e n t aa i s l a n d arc. arc. Penokean Orogeny Orogeny is island collision The following c o l l i s i o n event event between between these t h e s e two two terraines. terraines. f o l l o w i n g isotopic isotopic study study supports s u p p o r t s the t h e contention c o n t e n t i o n tthat h a t such models are a r e applicable a p p l i c a b l e to t o the the Penokean Penokean events. events. REE REE patterns p a t t e r n s from from tholeiitic t h o l e i i t i c basalts b a s a l t s and and gabbros gabbros from from the t h e southern southern terrain yield terrain y i e l d extremely LREE W E depleted d e p l e t e d signatures s i g n a t u r e s (Klaus (Klaus Schultz, S c h u l t z , 1983) 1983) similar to t o those t h o s e of of MOR MOR basalts. b a s a l t s . In I n contrast, c o n t r a s t , tholeiltes t h o l e i i t e s and and gabbros gabbros from the t h e northern n o r t h e r n terrain t e r r a i n yield y i e l d LREE LREE enriched e n r i c h e d patterns p a t t e r n s (Fox, (Fox, 1983), 19831, resembling continental c o n t i n e n t a l flood f l o o d basalt b a s a l t signatures. signatures. Tholeiitic and gabbros T h o l e i i t i c bbasalts a s a l t s and gabbros from the t h e southern s o u t h e r n terrain t e r r a i n define d e f i n e aa 143Nd/144Ndi sisochron with4.17 .95, . 9 5 ,and andananage a g eof of 1871 1871 ++- 57 57 my my o c h r o n withE& 4-17+ + (1~) . The The . age is i s interpreted i n t e r p r e t e d as a s aa ~crystallization r y s t a l l i z a t i o nage a g e and and is i s similar yimilar to U/Pb ages ages of of 1860 my o obtained t o U/Pb b t a i n e d for f o r several s e v e r a l granitic g r a n i t i c plutons p l u t o n s found found in in In the t h e southern s o u t h e r n terrain. terrain. I n contrast, c o n t r a s t , the t h e basalts b a s a l t s and and gabbros gabbros from from the the Other northern do not n o r t h e r n terrain t e r r a i n do n o t define d e f i n e aa Nd Nd isochron. isochron. Other isotopic i s o t o p i c data data suggest suggest however however that t h a t they they are a r e about about the t h e same same age age or o r slightly s l i g h t l y older. older. Calculating C a l c u l a t i n g initial i n i t i a l ratios r a t i o s for f o r 10 10 samples samples from from the t h e northern n o r t h e r n terrain terrain yields average 1143Nd/144Nd ofEdd=-2. Ed22.O4 This y i e l d s an average 4 3 ~ d / 1 4 4 ~ diinitial n i t i a l of 04 ++ 4.2. 4.2. This suggests suggests that t h a t the t h e source s o u r c e regions r e g i o n s for f o r the t h e two two terrains t e r r a i n s are ar; distinct, d i s t i n c t , with w i t h the the southern d e p l e t e d mantle source. source. s o u t h e r n tholeiites t h o l e i i t e s coming from a LREE depleted - The l a t e r therm_al thermal eevent v e n t of unknown orioriThe Rb/Sr Rb/Sr systematics s y s t e m a t i c s reveal r e v e a l aa later of unknown but but support support t h e above above thesis t h e s i s regarding r e g a r d i n g the t h e different d i f f e r e n t source source the regions r e g i o n s for f o r the t h e two two terrains. terrains. The northern n o r t h e r n terrain t e r r a i n ,yields i e l d s aa Rb/Sr Rb/Sr The errorchron ± 197 e r r o r c h r o n age of of 1550 + 197 my my (Lx), (LC),and andan an initial i n i t i a l °7SrI86Sr J7Sr/a6Sr ratio ratio w&eas the t h e southern s o u t h e r n terrain t e r r a i n suite s u i t e yields y i e l d s an a n age age of 0.70572 0.70572 + of + 14 (2s); (1); whereas of lY3 my my (1a), (LC), and and an an initial i n i t i a l 87Sr/86Sr 8 7 ~ r / 8 6of ~ r0.70258 ) of 1573 1573 ± 113 of 0.70258 + + 88 (2e (2-). age: overlap o v e r l a p the t h e age age of of emplacement emplacement of of the t h e very v e r y large l a r g e anorogenic ynorogenic Both ages Wolf Wolf River River Batholith, B a t h o l i t h , and and span span the t h e age age of of aa widespread widespread yet yet poorly poorly understood low—grade low-grade thermal thermal event event which affected a f f e c t e d much of of the t h e region region understood about 1700—1650 1700-1650 my my ago. ago. gin, gin, . + i n i t i a l 87Sr/86Sr 8 7 ~ r / 8 6ratio r~ a tri o (0.70572 (0.70572 + 1 4 ) from from the t h e northern n o r t h e r n terrain terrain The initial + 14) i s contained contained within w i t h i n the t h e field f i e l d for f o r continental contTnenta1 crustal c r u s t a l source s o u r c e regions regions is on i s not n o t clear c l e a r however however whether whether on an an 87Sr/86Sr a 7 ~ r / 8 6 evolution ~e rv o l u t i o n diagram. diagram. It is r e f l e c t s the t h e ccharacteristics h a r a c t e r i s t i c s of t h e source s o u r c e regions r e g i o n s of of the t h e Hemlock Hemlock this reflects of the i s aa reflection r e f l e c t i o n of of the t h e isotopic i s o t o p i c composition composition of of the the b a s a l t s , or o r rather r a t h e r is basalts, fluids f l u i d s which reset r e s e t the t h e Rb/Sr Rb/Sr systematics. systematics. I n contrast, c o n t r a s t , the t h e initial initial In 8 7 ~ r / 8 6 from ~ r the t h e southern s o u t h e r n terrain t e r r a i n (0.70258 (0-70258 + + 8) 8 ) is i s radically r a d i c a l l y difdif87Sr/86Sr from Ts contained c o n t a i n e d within w i t h i n the the f e r e n t from that t h a t of of the t h e northern n o r t h e r n terrain, t e r r a i n , and and is ferent 1 �field Hence the field for for source source regions regions for for basalts. basalts. Hence the Rb/Sr Rb/Sr systematics systematics are are consistent with the the Nd Nd isotopic isotopic systematics. systematics. In particular they they are are consistent with the thesis consistent with thesis that the the two two terrains terrains evolved evolved from from funfundamentally different source source regions, regions and damentally different and that that the northern northern terrain terrain tholeiites source region tholeiites and and gabbros gabbros were were generated generated from from aa source region with with a strong continental affinity, affinity* while the southern region tholeiites and gabbroic gabbroic sills were generated reservoir which sills were from aa reservoir which strongly generated from strongly resembles the modern day day MORE MORB source source regions. regions. For these these reasons reasons we we suggest that that this data is consistent suggest consistent with the existence existence of a suture suture zone between these two terrains, terrains* and that that this this data data supports supports the the above above mentioned plate plate tectonic tectonic model model of of the the Penokean Penokean events. events. 2 �Lithologic and tthe environment L i t h o l o g i c ddiversity i v e r s i t y and h e ssedimentary—tectonic e d i m e n t a r y - t e c t o n i c environment during deposition d uring d e p o s i t i o n of of Baraboo interval i n t e r v a l (176O—l500my) (1760-15OOmy) rrocks. ocks. Bruce A. A. Brown (Wisconsin (Wisconsin Geological and and Natural N a t u r a l History H i s t o r y Survey, Survey, 1815 1815 University Avenue, Nadison, Madison, W WII 53705) U n i v e r s i t y Avenue i s represented r e p r e s e n t e d by clastic c l a s t i c and and chemical chemical sediments sediments The Baraboo interval i n t e r v a l is deposited environment between between major major anorogenic anorogenic magmag— d e p o s i t e d iin n an eepicratonic p i c r a t o n i c environment matic m.y. ago (Greenberg (Greenberg and and Brown, Brown, 1984). 1984). This This m a t i c events e v e n t s 1760 and 1500 m.y. period of magmatism and ssedimentation followed tthe and cracra— p e r i o d of e d i m e n t a t i o n followed h e oorogenesis r o g e n e s i s and tonization t o n i z a t i o n of of the t h e Penokean Orogeny about about 1850 1850 m.y. m.y. ago. ago. Recent geologgeologic Wisconsin, and and ssubsurface i c mapping iin n ccentral e n t r a l Wisconsin, u b s u r f a c e sstudies t u d i e s iin n ssouthern outhern Wisconsin have produced significant new data on Baraboo interval significant d a t a on Baraboo i n t e r v a l rocks, rocks, of d deposition, history. ttheir h e i r environment of e p o s i t i o n , and their t h e i r tectonic tectonic h istory. The Baraboo interval b e s t known known for f o r red r e d quartzites, q u a r t z i t e s , such such as a s the the i n t e r v a l is best mapping and reexamination reexamination of of known Barron, Barrony Sioux, and and Baraboo. Baraboo. New mapping exposures, exposures, cores c o r e s and cuttings c u t t i n g s show show quartzite q u a r t z i t e in i n association a s s o c i a t i o n with w i t h argil— argililte, carbonaceous sslate, bedded chert, U t e y carbonaceous l a t e , bedded c h e r t , arkose, a r k o s e , siliceous s i l i c e o u s and and carbonate carbonate iron i r o n formation, formation, polymictic p o l y m i c t i c conglomerates, conglomerates, and and volcanogenic volcanogenic sediments. sediments. Att Baraboo, Baraboo, and and iin of ssoutheastern Wisconsin, aargillaA n the t h e ssubsurface u b s u r f a c e of o u t h e a s t e r n Wisconsin, rgillaceous rrocks, ceous o c k s , iiron r o n fformation, o r m a t i o n y and micaceous quartzite q u a r t z i t e occur occur in i n the t h e upper upper part parts p a r t of of the t h e section, s e c t i o n , above the t h e red r e d 4uartzites. q u a r t z i t e s . In In p a r t s of of central c e n t r a l and and northern Wisconsin, these n o r t h e r n Wisconsin, t h e s e lithologies l i t h o l o g i e s commonly commonly occur occur within w i t h i n aa few few distribution meters of the t h e base b a s e of of the t h e section. s e c t i o n . The areal a r e a l and vvertical ertical d istribution of depositional e p o s i t i o n a l environenvironof lithologies l i t h o l o g i e s aacross c r o s s Wisconsin Wisconsin suggests s u g g e s t s a complex d ment iin n which llocal o c a l hheterogeneities, e t e r o g e n e i t i e s y sstructural t r u c t u r a l oor r ttopographic, o p o g r a p h i c , ccontrolontrolled contemporaneous l e d the t h e distribution d i s t r i b u t i o n of of coarse c o a r s e sediments and allowed contemporaneous deposition d e p o s i t i o n of of mature quartz q u a r t z sandstones s a n d s t o n e s in i n one one area a r e a and and deposition d e p o s i t i o n of of shales presence of of volcanogenvolcanogen— s h a l e s and chemical sediments in i n another. a n o t h e r . The presence ic i c sediments suggests s u g g e s t s that t h a t local l o c a l rhyolitic r h y o l i t i c volcanism volcanism may may have have occurred occurred contemporaneously w i t h sedimentation, s e d i m e n t a t i o n , or o r that t h a t fresh f r e s h volcanic v o l c a n i c rocks rocks were were contemporaneously with exposed to within t o erosion erosion w i t h i n the t h e depositional d e p o s i t i o n a l basin. basin. The dominant deformational d e f o r m a t i o n a l structures s t r u c t u r e s in i n the t h e Baraboo Baraboo interval i n t e r v a l rocks rocks aare re o f t e n folds f o l d s overturned o v e r t u r n e d to t o the t h e south. s o u t h . Deformational i n t e n s i t y inoften Deformational intensity inccreases r e a s e s to t o the t h e east e a s t and and southeast. s o u t h e a s t . Greenschist G r e e n s c h i s t facies f a c i e s metamorphism metamorphism is is co=on comon throughout h e aarea r e a of exposure, exposure, with w i t h higher h i g h e r grade grade assemblages assemblages throughout tthe eevident v i d e n t only only iin n areas a r e a s where where tthese h e s e rocks r e iintruded, ntruded, p a r t i c u l a r l y by by rocks aare particularly granitic my age. age. g r a n i t i c rocks of 1500 1500 my i n t e r v a l was aa time t i m e of anorogenic anorogenic tectonic t e c t o n i c activity. activity. The Baraboo interval Early n the t h e interval, i n t e r v a l , rhyolitic r h y o l i t i c volcanism and sedimentation s e d i m e n t a t i o n were were probprobEarly iin m.y. ably contemporaneous. Anorogenic r e g i o n a l uplift u p l i f t at a t around 1630 1630 m.y. Anorogenic regional y e a r s ago may have been important important in i n the t h e initiation i n i t i a t i o n of of deformation deformation of of years t h e vvolcanic o l c a n i c and sedimentary rocks, r o c k s , as as w e l l as a s generation g e n e r a t i o n of of the t h e alkaalkathe well a g m a s which intruded i n t r u d e d the t h e already a l r e a d y deformed roëks rocks at a t around around 1500 1500 my. my. line m line magmas Greenberg, J * K . , and B.A. 3 . A . Brown, Brown, 1984, 1984, Cratonic C r a t o n i c sedimentation s e d i m e n t a t i o n during d u r i n g the the Greenberg, J.K., Proterozoic: P r o t e r o z o i c : aan n anorogenic connection in i n Wisconsin and and the t h e upper upper midmidw e s t , in i n press, p r e s s , Journal J o u r n a l of of Geology, March March 1984. 1984. west, 3 �Early Proterozoic E arly P r o t e r o z o i c structures s t r u c t u r e s of Northeastern N o r t h e a s t e r n Wisconsin Wisconsin as a s constraints c o n s t r a i n t s on Penokean tectonic t e c t o n i c models models ' B.A. BROWN BROWN (Wisconsin (Wisconsin Geological G e o l o g i c a l and N atural H i s t o r y Survey, Survey, 1815 UniUniB.A. Natural History versity W I 53705) 53705) v e r s i t y Avenue, Avenue, Madison, Madison, WI J.K. J . K . GREENBERG GREENBERG (Wisconsin (Wisconsin Geological G e o l o g i c a l and and Natural N a t u r a l History H i s t o r y Survey, Survey, 1815 1815 University U n i v e r s i t y Avenue, Avenue, Madison, Madisony WI W I 53705) 53705) N i a g a r a tectonic t e c t o n i c zone hhas a s been d e s c r i b e d by e v e r a l aauthors u t h o r s as a The Niagara described by sseveral suture which s u t u r e along alongw h i c h aa PProterozoic r o t e r o z o i c vvolcanic o l c a n i c aarc r c terrane t e r r a n e (Penokean (Penokean volcanic volcanic belt) onto of an b e l t ) to t o the t h e south, s o u t h , was accreted accreted o n t o the t h e ssouthern o u t h e r n margin of a n Archean craton c r a t o n during d u r i n g the t h e Penokean Penokean Orogeny. Orogeny. In I n modern plate p l a t e tectonic t e c t o n i c concepts concepts this t h i s interpretation i n t e r p r e t a t i o n implies i m p l i e s compressional compressional deformation d e f o r m a t i o n which which should s h o u l d be be identifiable both i d e n t i f i a b l e on b o t h sides s i d e s of the t h e aids axLs of of suturing. s u t u r i n g . Recent geological geological maps of of of the t h e region r e g i o n show that t h a t indeed i n d e e d sstructural t r u c t u r a l trends t r e n d s on bboth o t h sides s i d e s of the t h e Niagara zone zone are a r e roughly roughly parallel. p a r a l l e l . However, Xowever, analysis a n a l y s i s of of structural structural data d a t a collected c o l l e c t e d in i n mapping of the t h e Penokean volcanic v o l c a n i c belt b e l t has h a s raised r a i s e d seserious r i o u s questions q u e s t i o n s regarding r e g a r d i n g the t h e nature n a t u r e of the t h e suturing s u t u r i n g process p r o c e s s and and the the strict s t r i c t applicability a p p l i c a b i l i t y of of modern modern plate p l a t e tectonic t e c t o n i c analogues. analogues. The structural i s characterized c h a r a c t e r i z e d by by s t r u c t u r a l pattern p a t t e r n within w i t h i n the t h e volcanic v o l c a n i c belt b e l t is tight t i g h t to t o isoclinal i s o c l i n a l folds f o l d s and a regional r e g i o n a l foliation f o l i a t i o n which which strike s t r i k e roughly roughly parallel p a r a l l e l to t o the t h e belt b e l t margins. margins. Lithologic L i t h o l o g i c contacts c o n t a c t s and and foliation f o l i a t i o n are are generally parallel, g e n e r a l l y p a r a l l e l y and and steep s t e e p dips d i p s (70° (70' to t o vertical) v e r t i c a l ) are a r e predominant. predominant. The The trends t r e n d s of these t h e s e regional r e g i o n a l structures s t r u c t u r e s aare r e locally l o c a l l y reoriented r e o r i e n t e d around large smaller granitic g r a n i t i c plutons. p l u t o n s . AlAll a r g e gneissic g n e i s s i c granitoid g r a n i t o i d complexes, complexesy and and smaller though these t h e s e complexes may include i n c l u d e many different d i f f e r e n t granitoid g r a n i t o i d phases, p h a s e s , ininternal t e r n a l foliation f o l i a t i o n patterns p a t t e r n s are a r e generally g e n e r a l l y concentric. c o n c e n t r i c . Regional foliation foliation generally g e n e r a l l y does not n o t pass p a s s through through the t h e granites. g r a n i t e s . Exceptions E x c e p t i o n s are a r e cases cases where plutons plutons p l u t o n s are a r e located l o c a t e d adjacent a d j a c e n t to t o major faults f a u l t s or o r smaller plutons are a r e between larger l a r g e r complexes. complexes. Steeply S t e e p l y plunging p l u n g i n g folds f o l d s which refold r e f o l d the the earlier e a r l i e r regional r e g i o n a l foliation, f o l i a t i o n , and strong s t r o n g subvertical s u b v e r t i c a l lineations l i n e a t i o n s are a r e comcow monly developed near n e a r the t h e granitic g r a n i t i c contacts c o n t a c t s and between closely c l o s e l y spaced spaced plutons. p l u t o n s . Greenschist G r e e n s c h i s t facies f a c i e s metamorphism metamorphism has h a s affected a f f e c t e d the t h e entire e n t i r e belt, belt, and h higher i g h e r grade g r a d e metamorphic assemblages are a r e developed developed around around intrusive intrusive rocks. r o c k s . Isotopic I s o t o p i c data d a t a suggest s u g g e s t that t h a t the t h e granitoid g r a n i t o i d rocks r o c k s are a r e roughly roughly the the same same age age as a s the t h e volcanic v o l c a n i c rocks, r o c k s y with w i t h no no indication i n d i c a t i o n of of older o l d e r basement basement remobilization as is is typical t y p i c a l in i n the t h e mantled mantled gneiss g n e i s s domes domes of of the t h e terrane terrane r e m o b i l i z a t i o n as to pattern t o the t h e north. n o r t h . The overall o v e r a l l picture p i c t u r e is of of a tectonic—metamorphic tectonic-metamorphic p attern very similar to only t o that t h a t of of Archean granite—greenstone g r a n i t e - g r e e n s t o n e tterranes, erranes, o n l y in in younger rocks r o c k s (Greenberg (Greenberg and and Brown, Brown, 1983; 1983; Brown Brown and and Greenberg, Greenberg, 1983). 1983). Available higher—grade metamorphic metamorphic assemblages assemblages and A v a i l a b l e data d a t a suggest s u g g e s t that t h a t higher-grade increased i n c r e a s e d strain s t r a i n intensity i n t e n s i t y are a r e functions f u n c t i o n s of o f location l o c a t i o n with w i t h respect r e s p e c t to to intrusive i n t r u s i v e bodies b o d i e s rather r a t h e r than t h a n proximity p r o x i m i t y to t o the t h e proposed proposed suture. s u t u r e . There There is i s no no evidence e v i d e n c e of of an a n increase i n c r e a s e in i n either e i t h e r deformnational d e f o r m a t i o n a l intensity i n t e n s i t y or o r metametamorphism morphism across a c r o s s the t h e belt b e l t towards towards the t h e Niagara Niagara zone. zone. Structures S t r u c t u r e s within within the t h e Niagara zone suggest s u g g e s t vertical v e r t i c a l movement, movement, rather r a t h e r than t h a n horizontal horizontal thrusting t h r u s t i n g typical t y p i c a l of of most most Phanerozoic Phanerozoic sutures. sutures. L. �arguments p r e s e n t e d above ssuggest u g g e s t tthat h a t tthe h e Niagara t e c t o n i c zone The arguments presented Niagara tectonic may b be more analogous boundaries w within Superior e more analogous to t o subprovince boundaries i t h i n the the S uperior Province than t h a n to t o a modern zone zone of of continental—scale c o n t i n e n t a l - s c a l e collision. c o l l i s i o n . All A l l of of the t h e known Penokean volcanic v o l c a n i c rocks rocks are a r e chemically chemically more more like l i k e modern moderntuag— magmas m a s than t h a n Archean Archean greenstonas g r e e n s t o n e s (Greenberg (Greenberg and and Brown, Brown, 1983). 1983) the Both the chemistry and the of tthis t h e sstructural t r u c t u r a l sstyle t y l e of h i s tterrane e r r a n e ssuggest u g g e s t aa tectonic tectonic environment transitional between modern modern plate-margin plate—margin convergence convergence and t r a n s i t i o n a l between Archean k c h e a n block—boundary block-boundary interactions. interactions. . Brown, B r o w n , B.A., B.A., and and J.K. J.K. Greenberg, Greenberg, 1983, Gneiss Domes and Not so s o Gneiss Domes Wisconsin, (abs.) Domes in i n the t h e Penokean terranes t e r r a n e s of of Northern Wisconsin, ( a b s .) Twenty— Twentyninth 6. n i n t h Institute I n s t i t u t e on on Lake Lake Superior S u p e r i o r Geology, Geology, Houghton, Houghton, p. p. 6. J.K., and r o t e r o z o i c Volcanic Rocks Rocks Greenberg, J.K.,, and B.A. B.A. Brown, Brown, 1983, 1983, Lower Lower PProterozoic and & I L.G. L.G. Medaris, H e d a r i s , Jr., Jr., and their t h e i r setting s e t t i n g in i n the t h e Lake Lake Superior S u p e r i o r District, D i s t r i c t , in ed. ed. Early E a r l y Proterozoic P r o t e r o z o i c Geology Geology of of the t h e Great Great Lakes Lakes Region, Region, Geological Geological Society S o c i e t y of of america, America, Memoir Memoir 160, 160, p. p. 67—84. 67-84. 5 �Basement Basement Cover Cover Relations Relations in in the t h eMarquette Marquetteand andRepublic RepublicDistricts, Districts,Michigan Michigan W. (Department (Department ofof Geological Geological Sciences, Sciences, Michigan Michigan State State CAMBRAY, F.F. W. CAMBRAY, University,East EastLansing, Lansing,Michigan Michigan48324-1115) 48824-1 115 ) University, MEYER, R. 0.(Lagoven (Lagoven S.A., S.A., Org. Org. Geologia, Geologia, Apartado Apartado 234, 234,Maturin, Maturin, Edo. Edo. MEYER, R. 0. Monagas, Venezuela, Venezuela, Zona ZonaPostal Postal6201) 6201) Monagas, G. A. A. (Superior (Superior Oil Oil Company, Company, Geoscience Geoscience Laboratory, Laboratory, 12401 12401 MYERS, G. MYERS, Westheimer, Houston, TX 77077) Westheimer, Houston, TX 77077) ItItisisproposed proposed that t h a tthe t h eArchean Archeanbasement basementbetween betweenthe t h eMarquette MarquetteTrough Troughand and the as an essentially t h eRepublic Republic Trough Trough behaved behaved as essentially rigid rigid material during during both both the the subsidence subsidence and and the t h e deformation deformationassociated associatedwith withthe t h ePenokean PenokeanOrogeny. Orogeny. In In the t h e subsidence subsidence phase phase the t h e basement basement fractured fractured into into several several rift riftbounded bounded troughs troughs in in which which sediment sediment accumulated accumulated to t ogreater greaterthickness thicknessthan thanthe t h esurrounding surrounding areas, areas,particularly particularlythe t h eBanded BandedIron IronFormation. Formation. During deformation was was effected in During subsequent subsequent compression compression deformation in the t h ebasement basementby by ductile ductileshear shearalong along mafic mafic dikes dikes which which were intruded during tthe h e rifting. Using Usingthe the sense of of shear shearon onthese thesedikes dikesiti tcan canbebeshown shownthat t h a tthe t h emaximum maximum principal principal stress stress sense during east of of north northand andwas wasfocussed focussed near nearthe t h etrough troughmargins, margins, dosing was was east during dosing becoming normal tto becoming normal o them, them, aa feature f e a t u r eobserved observed in in the t h eelastic elasticdeformation deformation of of plateswith with holes holes ininthem. them. In In addition addition the t h e data d a t ashows shows that t h a t the t h emaximum maximum shear shear plates strain occurs occurs on ondikes dikeswhich which are a r eapproximately approximately45° 4 5 O to t o the t h emaximum maximumprincipal principal strain stress f e a t u r econsistent consistentwith withnon-rotational non-rotational deformation deformation by bysimple simple stressdirection, direction, aa feature shear on on the t h edikes. dikes. shear This This type type of of deformation deformation resulted resulted in in translation translationofofrigid rigidblocks blocksofofbasement basement with no no internal internaldistortion. distortion. The Theoverlying overlyingsediments sedimentsresponded respondedaccordingly. accordingly. At At with t h e margins margins of of the t h e troughs troughs reactivated reactivated faults faultsresulted resulted ininthe t h ebasins basins dosing closinglike like the t h e jaws jaws of of aa vice vice producing producing high high strain in in the t h e troughs troughs and and relatively relatively low low strain strain the on the t h e platforms platforms ininbetween. between. One One locality locality on on the t h e south south side side of of the t h eRepublic Republic on Trough exemplifies exemplifies this. this. In In flat f l a tlying lyinguncleaved uncleaved Kona Kona Formation Formation shales shales the the Trough reduction spots spots are a r e flattened flattenedininthe t h ebedding. bedding. In In the t h e adjacent adjacent tilted tiltedhorizons horizons the the reduction spots are areoblique oblique to t othe t h ebedding bedding with withthe t h eX1A2 X i X 2 plane cleavage. spots plane lying lying parallel parallel ttoo deavage. b �Microstructures Multiply Deformed Deformed S Slate of tthe Formation, X i c r o s t r u c t u r e s iin n tthe h e Elultiply l a t e of h e Thomson Formation, East—Central East-Central Minnesota Xinneso t a of Geology, Geology, U University RIChARD RICIIARD C. C. CLARK CLAFC (Dept. (Dept. of n i v e r s i t y of of Minnesota ?finnesota Duluth, Duluth, Duluth, Minnesota 55812) Duluth, Xinnesota Early Proterozoic Thomson Formation Formation cconsists of iintercalated The E arly P r o t e r o z o i c Thomson o n s i s t s of ntercalated slate, s l a t e , slaty s l a t y greywacke and metagreywacke units. units. The formation f o r m a t i o n was was multiply deformed dduring Penokean orogeny orogeny (1900—1800 m.y.) rresultm u l t i p l y deformed u r i n g tthe h e Penokean (1900-1800 m.y.) esulting with me i n two major phases of of folding folding w i t h axial—planar a x i a l - p l a n a r foliation. f o l i a t i o n . The i n g in second deformation affected evidence a f f e c t e d the t h e entire e n t i r e study s t u d y area, a r e a , whereas whereas evidence of deformation is is found found only o n l y iin n the t h e extreme ssouthern o u t h e r n portion portion of the t h e first f i r s t deformation Later deformation, p possibly Kee— of the t h e study s t u d y area. area. L a t e r minor deformation, o s s i b l y related r e l a t e d to t o Keewenawan rifting, r i f t i n g , resulted r e s u l t e d in i n the t h e development of of kink—bands kink-bands in i n some some areas. areas. In southernmost aareas by bboth major Penokean Penokean defonndeformI n the t h e southernmost r e a s aaffected f f e c t e d by o t h major ations a t i o n s a crenulation c r e n u l a t i o n cleavage c l e a v a g e has h a s formed formed iin n the t h e fine—grained f i n e - g r a i n e d slates. slates. M.icrostructural evidence M.icrostructura1 evidence suggests s u g g e s t s that t h a t the t h e crenulation c r e n u l a t i o n cleavage c l e a v a g e developed similar to t o that t h a tproposed proposed by by Gray Gray and and by aa solution—deposition s o l u t i o n - d e p o s i t i o n pprocess r o c e s s similar Durney (1979). The pprinciple behind the process r i n c i p l e behind t h e ppressure r e s s u r e ssolution olution p r o c e s s is is of ssoluble minerals tthe h e ssolution o l u t i o n ttransfer r a n s f e r of oluble m i n e r a l s from sites s i t e s of of high h i g h chemical chemical The difference potential p o t e n t i a l to t o sites s i t e s of of low chemical potential. potential. d i f f e r e n c e in i n chein— chemica]. potential can be directly related to stress variations around i c a l p o t e n t i a l can b e d i r e c t l y r e l a t e d t o s t r e s s v a r i a t i o n s microfolds The grains g r a i n s along the t h e limbs are a r e subject subject m i c r o f o l d s (crenulation—folds). (crenulation-folds). stress (and ttoo a a higher h i g h e r normal normal stress (and tthus h u s a hhigher i g h e r chemical potential) p o t e n t i a l ) than than grains in the hinge zones. Soluble (such as as qquartz) u a r t z ) are are S o l u b l e sspecies p e c i e s (such the t h e g r a i n s i n t h e h i n g e zones. then limbs zones (or of tthe s tto o tthe h e hhinge i n g e zones ( o r oout u t of h e system t h e n transferred t r a n s f e r r e d from tthe he W into quartz causing tthe of rrelatively into q u a r t z vveins) e i n s ) causing h e ppassive a s s i v e cconcentration o n c e n t r a t i o n of elatively insoluble p h y l l o s i l i c a t e s into i n t o mica—rich mica-rich zones zones (zona3. ( z o n a l ccrenulation r e n u l a t i o n cleavcleavi n s o l u b l e phyllosilicates age) orr iinto mica—rich ccleavage seams ((discrete age) o n t o ddistinct i s t i n c t mica-rich l e a v a g e seams d i s c r e t e ccrenulation renulation cleavage) cleavage) in i n the t h e former former limb Limb zones. Kink-bands are a r e common common in i n the t h e slates slates at a t the t h e ttype y p e locality l o c a l i t yata Thomson t Thomson Kink—bands Dam. Kink-bands can f i n e d aas s small-scale o l d s having having Kink—bands canb ebed edefined small—scalemonoclinal monoclinal ffolds p l a n a r limbs limbs and planar normally found foundi in rocks wwith and angular a n g u l a r hinge hinge zones zones normally n rocks ith a definite p l a n a r anisotropy a n i s o t r o p y (such (such as a s cleavage). c l e a v a g e ) . Several S e v e r a l models have definite planar been t o explain e x p l a i n the t h e formation of of kink—bands. kink-bands. Two models that t h a t have have proposed to t h e Thomson Formation are a r e the t h e rotation r o t a t i o n model model ccharacteristics h a r a c t e r i s t i c s found in the and the t h e jjoint—drag o i n t - d r a g model. model. r o t a t i o n model model proposes h a t as a s deformdeformThe rotation proposes tthat aation t i o n proceeds, proceeds, the t h e foliation f o l i a t i o n within w i t h i n the t h e kink—band kink-band is is rotated r o t a t e d through through iincreasing n c r e a s i n g angles. angles. S i n c e tthe h e ffoliation o l i a t i o n remains h e kink-band Since remains hinged hinged aatt tthe kink—band boundary it i t is geometrically geometrLcally necessary n e c e s s a r y ffor o r tthe h e ffoliation o l i a t i o n to t o part p a r t oorr d i l a t e as asrotation r o t a t i o noccurs occursthus t h u screating c r e a t i n volume g volume expansion. expansion. As otation dilate As rrotation passes a c r i t i c a l point t h e f o l i a t i o n begins t o close. I t is possible, possible, however, for f o r the t h e sspaces paces w i t h i n the t h e dilated d i l a t e d foliation f o l i a t i o n to t o be b e filled f i l l e d by within precipitating p recipitating m i n e r a l s (such as q u a r t z o r c a l c i t e ) t h u s 'jamming1 the minerals quartz or calcite) thus 'jamming' the kink—band at kink-band a t an an intermediate i n t e r m e d i a t e stage. s t a g e . The joint—drag j o i n t - d r a g model proposes that that c t u a l l y broken f f s e t by h e a r along a l o n g the t h e kink—band kink-band tthe h e ffoliation o l i a t i o n is is aactually broken and and ooffset by sshear d u r i n g deformation. deformation. F u r t h e r deformation a u s e s rrotation o t a t i o n of the boundary during Further deformation ccauses of the kinked foliation f o l i a t i o n accompanied by slip s l i p along a l o n g individual i n d i v i d u a l folia f o l i a within w i t h i n the the kink—band. Triagular-shaped kink-band. Triagular-shaped vvoids o i d s (which (which llater a t e r may e ffilled illed w i t h qquartz uartz may bbe with o r calcite) c a l c i t e ) develop along the t h e kink—band kink-band boundary causing c a u s i n g volume volume expanexpanor sion s i o n of the t h e rock. rock. passes a critical point the foliation begins to close. It is 7 �Kink—bands Formation ccontain of b both Kink-bands of of the t h e Thomson Formation o n t a i n ccharacteristics h a r a c t e r i s t i c s of oth models indicating i n d i c a t i n g that t h a t aspects a s p e c t s of both b o t h models were were probably p r o b a b l y in i n operation. operation. The foliation f o l i a t i o n can be seen s e e n as a s discontinuous d i s c o n t i n u o u s (sheared) ( s h e a r e d ) or o r continuous c o n t i n u o u s across across kink—band boundary boundary even w within tthe h e kink-band i t h i n different d i f f e r e n t parts p a r t s of of the t h e same same kink—band. kink-band. Triangular—shaped voids Triangular-shaped v o i d s and dilation d i l a t i o n zones zones between between individual i n d i v i d u a l folia folia now ffilled with ((both b o t h now illed w i t h qquartz) u a r t z ) aare r e ppresent r e s e n t iindicating n d i c a t i n g volume expansion expansion of the of t h e rock. rock. S i n c e volume expansion h e rrock o c k iin n aa hhorizontal o r i z o n t a l ddirecirecSince expansion of of tthe tion t i o n is i s involved, i n v o l v e d y the t h e kink—bands kink-bands must have have formed formed at a t aa high h i g h structural structural level l e v e l where confining c o n f i n i n g pressures p r e s s u r e s were were low. low. They are a r e also a l s o thought thought to to of tthe have formed late l a t e iin n t the h e sstructural t r u c t u r a l hhistory i s t o r y of r e a y ppossibly o s s i b l y as a s aa h e aarea, result of Middle Middle PProterozoic Keewenawan aactivity (1100 m.y.). m.y). r e s u l t of r o t e r o z o i c Keewenawan c t i v i t y (1100 Reference Gray, D. G. G. and and ~ Durney, D., W. W., l1979, Crenulation u i n e ~D. 97gy C r e n u l a t i o n ccleavage l e a v a g e ddifferentiaifferentiaGray D. of ssolution—deposition ttion: i o n : iimplications m p l i c a t i o n s of o l u t i o n - d e p o s i t i o n processes: processes: JJournal o u r n a l of of Structural l yNo. No. 1, 1, pp. pp. 73—80. 73-80. S t r u c t u r a l Geology, Geology, Vol. Vol. 1, 8 �Geology northern Minnesota—revisited Minnesota-revisited Geology of of the the Rainy Rainy Lake Lake area, area, northern 25046,DFC, DFC, WARREN WARRJIN C. C. DAY, DAY, U.S. Box 25046, U.S. Geological Geological Survey, Survey,Box Mail Mail Stop Stop 905, 905, Denver, ~enGer,CO CO 80225 80225 Recent Recent geologic geologic mapping mapping of of the the 2,700—m.y.—old 2,700-m.y.-old Rainy Rainy Lake Lake area area of of northern northern Minnesota Minnesota provides provides new new insight insight into into the the tectonic tectonic development development of of the the area. area. The The Rainy Rainy Lake Lake area area trends trends northeast northeast across across the the Minnesota— MinnesotaOntario Ontario international international border, and lies lies within the the western western extension extension of of The area area is is the the Superior Superior province. province. The the Wabigoon Wabigoon greenstone greenstone belt belt of of the bounded bounded on on the the south south by by the the Rainy Rainy Lake—Seine Iake-Seine River River fault fault and and on on the the The Minnesota Minnesota segment segment of of the the area area is is north Queticofault. fault. The north by by the the Quetico composed composed of of volcanic and subvolcanic subvolcanic intrusive intrusive rocks rocks intercalated intercalated with with volcaniclastic, volcaniclastic~epiclastic, epiclastic, and and chemical chemical sedimentary sedimentaryrocks. rocks. These These rocks rocks The volcanic volcanic rocks rocks are are grade grade upward upward into into volcanogenic volcanogenic graywacke. graywacke. The the mafic rocks rocks have have tholeiitic tholeiitic affinity affinity and and bimodal bimodal in in composition: composition: the the the felsic felsic rocks rocks have have calc—alkaline calc-alkaline affinity. affinity. In In Minnesota Minnesota all all of of the the rock rock types types have have been been metamorphosed metamorphosed to to upper upper greenschist greenschistfacies. facies. The The Minnesota portion of the Rainy Lake area has been affected by The first first was was large—scale large-scale folding folding that that three deformationevents. events. The three major major deformation produced produced an an S1 Sl schistosity schistosity subparallel subparallel to bedding CS0), (So), and southwest— southwestplunging The second second event event plunging F1 Fl parasitic parasitic folds folds and and L1 Ll mineral mineral lineations. lineations. The produced produced tight, tight, upward—facing, upward-facing, asymmetric asymmetric folds, folds, 1—3 1-3 km km in in scale, scale,an anS2 S2 penetrative penetrative cleavage, cleavage, and and northeast—plunging northeast-plunging F2 F2 parasitic parasitic folds foldsand and L2 L2 mineral mineral lineations. lineations. The The last last deformation deformation event event produced produced the the Rainy Rainy Lake— LakeSeine Seine River River fault. fault. In upward—facing F2 folds and upright stratigraphy In Minnesota, the upward-facing stratigraphy contrast F2 folds folds observed observed in in Ontario. Ontario. Poulsen Poulsen contrast with with the the downward—facing downward-facing F2 and and others others (1980) (1980) concluded concluded that that the the stratigraphic stratigraphic succession succession to to the the northeast northeast in in Ontario Ontario is is inverted, inverted, probably as a result result of of large—scale large-scale recumbent folding. folding. Another Another contrasting contrasting feature feature is is the the metamorphic metamorphic grade grade recumbent of of graywacke graywacke units; units; those those in in Minnesota being greensthist greenschist facies, facies, whereas whereas those sillimanite-bearing amphibolite amphibolite facies. facies. those in in Ontario Ontario being being sillinianite—bearing AA structurally structurally consistent consistent model for for the the region region places the the rocks rocks in in Minnesota Minnesota on on the the upper upper (upward—facing) (upward-facing) limb, limb, and the the rocks rocks in in Ontario Ontario on on the lower lower (downward—facing) (downward-facing) limb limb of of aa major major F1 Fl recumbent recumbent fold. fold. This the This hypothesis hypothesis suggests suggests that that the the higher higher metamorphic metamorphic grade grade in in Ontario Ontario could could reflect reflect the the higher higher temperature temperature and and pressure pressure conditions conditions experienced experienced by by the the lower, lower, more more deeply deeply buried buried limb limb of of the the recumbent recumbent fold fold (fig. (fig. 1). 1). The The new structural structural model differs markedly from that of Ojakangas (1972), new (19721, who proposed that that the the inconsistencies inconsistencies in in stratigraphy stratigraphy and and structural structural style style proposed were caused caused by by the the juxtaposition juxtaposition of internally internally coherent, coherent, fault—bound fault-bound were structural structural blocks. blocks. 9 �Although Although the the structural structural model model proposed here satisfies satisfies the the geometrical geometrical relationships, relationships, several several problems problems remain. remain. For For example, example, the the location location of of the the F1 Fl recumbent recumbent fold axis is not known, nor is is there there any any documented documented evidence evidence of of thrust thrust faulting faulting associated with with nappe nappe structures structures that that might might have have been been developed developed during during the the F1 Fl recumbent recumbent folding folding event. event. Only through structural model by through testing testing and revision of the proposed structural further further detailed detailed geologic geologic mapping can can the structural structural development of the the Rainy Rainy Lake Lake area area be be fully fully resolved. resolved. NW NN SCHEMATIC SCHEMATIC CROSS CROSS SECTION SECTION OF THE THE OF RAINY F A I N Y LAKE LAKE AREA AREA SE SE MINNESOTA MINNESOTA ONTARIO ONTARIO Figure Figure 1. 1. Schematic Schematic cross cross section section of of the the Rainy Rainy Lake Lake area. area. The The Minnesota Minnesota rocks rocks are are on on the the upright upright limb, limb, whereas whereas the the Ontario Ontario rocks rocks are are on on the the overturned overturned limb limb of of aa regional regional F1 Fl recumbent recumbent fold(s). fold(s). tn In Minnesota Minnesota the Fl fold fold has has been been refolded refolded by by asymmetric asymmetric F2 F2 folds folds that that have have steep steep the F1 northwest—dipping northwest-dippingfold foldhinges. hinges. References References cited cited Ojakangas, R.W., 1972, 1972, Rainy Rainy Lake Lake area: area: in in Sims, Sims,P.K., P.K., and andNorey, Horey,G.B., G.B., Ojakangas, R.W., eds., eds., Geology Geology of of Minnesota: Minnesota: aa Centennial Centennial Volume, Volume, Minnesota Minnesota Geological GeologicalSurvey, Survey,p. p. 162—171. 162-171. Poulson, Poulson, K.H., K.H., Borradaile, Borradaile, G.J., G.J., and and Kehienbeck, Kehlenbeck, M.M., M.M., 1980, 1980, An An inverted inverted succession succession at at Rainy Rainy Lake, Lake, Ontario: Ontario: Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences,v. v. 17, 17, p. p. 1358—1369. 1358-1369. 10 �Mineralogy of of Pegmatites Pegmatites in i n the t h e Wausau Wausau Pluton, Pluton, Marathon County, Countv. Wisconsin Wisconsin AL u U. u . FALSTER FXSTER (920 (920 McIntosh McIntosh Street, S t r e e t , Wausau, Wausau, WisconSin wisconsin 54401) 54401) The Wausau Pluton is a q quartz—rich phase of of g granitic quartz ssyenite— u a r t z - r i c h phase r a n i t i c .quartz yenitepyroxene is exposed exposed at a t Wausau, Wausau, Marathon Marathon County, County, pyroxene amphibole amphibole syenite s y e n i t e which which is Wisconsin. The The age age of the t h e body was determined to t o be 1,520 + + 25 25 m.y. may. (Van The (Van Schmus, S c h u s , 1980). 1980) The pluton p l u t o n is i s Cut c u t by by numerous numerouspegiriatitic pegmati& ddikes i k e s of generally g e n e r a l l y gentle g e n t l e dip. d i p . The Miarolitic M i a r o l i t i c cavities c a v i t i e s in i n these t h e s e dikes d i k e s yield y i e l d an astonishing a s t o n i s h i n g array a r r a y of o f accessory accessory minerals, m i n e r a l s , particularly p a r t i c u l a r l y Fe, Fe, Ti, T i , Be, B e , REE REE minerals minerals with w i t h lesser lesser amounts amounts Sb Sb and and Pb Pb bearing b e a r i n g species s p e c i e s and and rarely r a r e l y those those containing B, Nb, Nb, Ta. Ta. Variations V a r i a t i o n s in i n pocket constituents, c o n s t i t u e n t s , paragenesis, p a r a q e n e s i s , and and c o n t a i n i n g 3, morphology morpnology occur occur widely, not n o t only only from from pegmatite pegmatite to t o pegmatite pegmatite but b u t also also from from pocket pocket to t o pocket pocket within w i t h i n the t h esame samepeginatite. pegmatite. Pocket rupture, r u p t u r e , thermal thermal shock shock and and metasoinatic metasomatic eeffects f f e c t s are a r e very very often o f t e n seen. seen. - Several Several types types of of typical t y p i c a l assemblages assemblages can can be be distinguished: distinguished: a. Simple Simple pa.ragenesis paragenesis of pockets in i n small small dikes: dikes: Microcline, Microcline, albite a l b i t e and and quartz q u a r t z are a r e the t h e bulk minerals with few few accessories ~pseudomorphouslyreplaced replaced by by other other a c c e s s o r i e s like l i k e siderite s i d e r i t e (pseudomorphously Fe Fe minerals), m i n e r a l s ) , hematite, hematite, hisingerite, h i s i n g e r i t e , phenakite, phenakite, bertrandite, bertrandite, anatase. anatase . b. Complex Complex paragenesis paragenesis of of pockets pockets in i n larger l a r g e r dikes: dikes: Besides as above, c o n s i d e r a b l e variety v a r i e t y of of ~ e s i d e the st h e bulk bulk minerals minerals as above, aa considerable accessories a c c e s s o r i e s like l i k e sulfides s u l f i d e s and and sulfosalts s u l f o s a l t s (pyrite, ( p y r i t e , jamesonite, jamesonite, boulangerite, b o u l a n g e r i t e , and and others. o t h e r s . These are a r e unaltered u n a l t e r e d only if i f protected protected in i n other o t h e r mineral mineral phases.), p h a s e s . ) , siderite s i d e r i t e (replaced), ( r e p l a c e d ) , phenakite, phenakite, bertrandite, b e r t r a n d i t e , anatase, a n a t a s e , rutile, r u t i l e , brookite, b r o o k i t e , fluorite, f l u o r i t e , F—apatite, F-apatite, REE—minerals, FEZ-minerals, especially e s p e c i a l l y aa REE—rich FEZ-rich cheralite c h e r a l i t e and and others. others. c. Simple vuggy intermediate i n t e r m e d i a t e zones: zones: Simple paragenesis paragenesis of of vuggy Besides Besides the t h e bulk bulk minerals minerals large l a r g e amounts amounts of of hematite hematite and and less less cornonly ppyrite y r i t e ((replaced), r e p l a c e d ) , zzircon, i r c o n , ffluorite, luorite, F - a p a t i t e are are conmionly F—apatite found. found. d. Paragenesis of late l a t e stage s t a g e formation formation in i n solution s o l u t i o n etched e t c h e d zones zones near near Paragenesis pockets pockets with with quartz q u a r t z selectively s e l e c t i v e l y removed removed (and (and sometimes sometimes redeposited): redeposited): Besides Besides the t h e bulk bulk minerals minerals this t h i s environment environment is i s especially e s p e c i a l l y dominated dominated by by Ti T i oxides oxides (anatase, ( a n a t a s e , brookite, b r o o k i t e , rutile) r u t i l e ) and and often o f t e n accompanied accompanied by by i l m e n i t e , zircon, z i r c o n , bertrandite, b e r t r a n d i t e , cheralite c h e r a l i t e and and others. others. ilmenite, This is based based on on data d a t a collected c o l l e c t e d during d u r i n g excavation excavation of of over over This paper paper is it should should 760 pegmatite pegmatite pockets pockets in i n the t h e Wausau Wausau Pluton, Pluton, therefore, t h e r e f o r e , it 760 a fairly representative description. be be a f a i r l y r e p r e s e n t a t i v e d e s c r i p t i o n . 11 �PRECAMBRIAN GEOCHRONOLOGY IN MINNESOTA PRECAMBRIAN GEOCHRONOLOGY IN MINNESOTA S. GOLDICH GOLDICH (Department Engineering Colorado Colorado (Departmentofof Geological Geological Engineering, School of Mines, School Mines Golden, Go1 den CO CO 80401) 80401 ) S. - Orogeny has b u i 1dingl'.When When Orogeny hasbeen beendefined defined simply simply as as "mountain "mountain building". began studying geologists began studyingsimple simplemountains mountainsinindetail detail, they they found found that t h a t aa number number of geological geological processes processes were were involved. involved. These These can can be be defined simply as as mountain-building mountain-building or orogenic orogenic processes, processess but b u t the the defined simply only thing that agreeononi sis tthat there is only t h a t most most geologists geologists seem seem t otoagree h a t there is nothing simple about about mountain mountain building o rorogeny. orogeny. nothing simple building or The early early classification Precambrian The classificationofofthethe Precambrian rocks rocks ofofMinnesota, Minnesota summarized Grout (1951, GSA GSABull. Bull. 2Gs 26, 1017) 1017), divided the e teta lal. . (1951 the summarized byby Grout succession into into three uncon— succession three major majorgroups groups separated separated by by two two 'great" "great" unconformi t i e s . These These were of ofbath01 i t h i c intrusives in formities. werecut cut on on complexes complexes batholithic intrusives in andmetavol metavolcanic rocksre1 related to two folded metasedimentary metasedimentary and cani c rocks ated to two periods perf ods of orogeny. orogeny . K-Ar, early U-Pb agedeterminations determinationsf afailed K-Ars Rb-Sr, Rb-Srs and and early U-Pb age i l e d to resolve resolve the Laurentian Laurentian from fromthe theyounger youngerAlgoman A1 gomanorogeny. orogeny.The Theage agemeasurements measurments revealed aa complex complexgeological geologicalhistory history and andindicated indicated tthat revealed h a t the the time time interval was interval was small, smalls about about 50 50 m.y. m.y. Within W i t h i n recent recent years years notable notable imimprovementshave havebeen been made in analyticaltechniques techniquesand andininthe the ininprovements made i n analytical ages deterdeterparticularlyU-Pb U-Pb ages terpretation of of radiometric radiometric ages, ages s particularly mined onzircon zircon and andtititanite. tani t e . LateLate-tot opostkinematic postkinematicAlgoman A1 goman gramined on nites, the Minnesota geologists, are n i t e s , as asdefined definedbybyLawson Lawson and and the Minnesota geologistss are dated aatt 2,680 and the the Laurentian dated Zs680 Ma Ma and Laurentian orogeny orogeny at a t 2,735 Zs735 Ma. Ma. The The LaurLaupentian may may be be regarded regarded as as an an early earlyphase phase ofofthe theAlgornan Algoman orogeny orogeny as as has been beensuggested suggested a number of writers, local use, t e r s s b ubut t f ofor r local uses the the has by by a number of wri distinction is distinction i s useful. useful. New U-Pbdata datafrom fromeast-central east-central Minnesota Minnesota,1likewise, i kewise provide provide N ew U-Pb Ma).similar similar bbetter e t t e r resolution resolutionofofthe thePenokean Penokean orogeny orogeny (1,800-1870 (1 s800-1870 Ma), to the interval found in Wisconsin by Van Schmus and others. the interval found i n Wisconsin by Van Schmus and 12 �Maginatism and the Baraboo Baraboo Interval: Magmatism and Internal: Breccias, Dikes, Dikes, and Metasomatism Breccias, JEFFREY GREEIBERG (Wisconsin Geological and Natural History Survey, (Wisconsin Geological Survey, JEFFREY KK.O GREENBERG WI 53705) Madison, WI the known known expo=POIn breccias are arecoimnon common features features in in many of the In Wisconsin Wisconsin breccias The breccia The breccia sures of quartzites deposited during the Baraboo interval. sures quartzites during the Baraboo interval. white vein vein quartz matrix is is typically typically white quartz and partial voids containing containing clay clay quartz crystals. Dott (1970) and quartz crystals. Daiziel Dalziel and Dott (1970) previously attributed attributed the the an interpretation interpretation preprebreccias to to "explosive "explosive hydrothermal hydrothexmal activity't, activityft9an ferred ferred over over aa fault fault origin. origin. Fluid inclusions inclusions in in quartz quartz crystals crystals indiindicate cate temperatures temperatures of formation formation greater than expected from sedimentary fluids km fluids except except under ambient conditions at depths greater than 3 Ian below unlikely environment below the the Earth's Earth's surface. surface. This represents an unlikely brittle fracturing for the development of brittle fracturing and and undeformed uncieformed voids. voids. However, However, we have observed that all the breccias are associated with massive granite and and diorite, diorite, granitic granitic dikes and intrusions including massive pegmatites, and sometimes pegmatites, sometimes basaltic—andesitic basaltic-andesitic dikes. dikes. Most Most of of the the brecciated brecciated quartzites quartzites also also show showevidence evidenceof of metasotnatism metasomatism (late (late mag— magmatic?). metasomatic features matic?). Observed metasmatic features include: include: clay segregations segregations in which apparently contain contain feldspar pseudmorphs; pseudomorphs; unaltered in breccia which in altered quartzite; feldspar porphyroblasts in quartzite; tourmaline—quartz tourmaline-quartz veinlets in veinlets in quartzite; quartzite; and a d books books of of muscovite muscovite (to (to 11 cm cm diameter) diameter) . crystallized in vein quartz in vein quartz and and replacing replacing other other minerals minerals in in quartzite. quartzite. The above =antples examples of intrusion intrusion and metasomatism metasomatism occur in various various comThe above binations exposures of Baraboo, binations at at the the breccia breccia exposures Baraboo, Necedah, Necedah, Battle Battle Point, Point, Waterloo, Rib Mountain, and Hamilton Hamilton Mound. Waterloo, FUb Mountain, interpretation of the breccias is that they are analogous analogous Our present interpretation stockwork of quartz produced around around the the upper upper levels levels of of to the stockwork quartz veins veins produced porphyry-copper plutons. During During magma intrusion, intrusion* the the roof roof porphyry—copper mineralized mineralized plutons. rocks (quartzite) were were fractured fractured and and soaked soaked iii in hydrous fluids. rocks (quartzite) hydrous granitic granitic fluids. The fluids fluids and their particular effects vary vary with with distance distance from source plutons. Thus, plutons. Thus, as as in in some s m e Wisconsin examples, quartz Wisconsin examples, quartz veins and grade into into actual actual pegmatite pegmatite dikes dikes as as intrusions intrusions are are approached. approached. breccias grade The coincidence coincidence of quartzite breccias, intrusions, The intrusions, and metasomatism metasomatism have often often gone gone unrecognized. unrecognized. suggest controversial controversial relationships relationships which which have If isotopically isotopically dateable, dateable, the the intrusions intrusionscould couldspecify specifymininu.nn minimum ages If ages of within the units within the Baraboo Baraboo interval. interval. vailable =.vailable age agedata data are are confusing, confusing, quartzite exposures but the the quartzite exposures are are probably probably somewhere smewhere between between 1760 1760 and and 1500 1500 m.y. m.y. old. oldDalziel, I.WeD., and Dott, Dott, R.H., R.H., Jr., Jr., 1970, 1970, Geology Geology of of the the Baraboo Baraboo Dalziel, I.W.D., District, Wisconsin: District* Wisconsin: Wisconsin NaturaJ. History Historv Geological and and NaturaJ. Wisconsin Geological p. Survey, Information Circular Circular 17, 17, 164 164 p. Survey, Information 13 �Mobilization M o b i l i z a t i o n of of Uranium and Thorium Within the Metamorphic Node, Node, Northern Northern Michigan t h e Republic Metamorphic ROBERT L. L. HACKENBERG HACKENBERG (Conoco, (Conoco, Inc., I n c . , Lafayette, L a f a y e t t e , Louisiana) Louisiana) GREGORY (Dept. of of Geol. Geol. and and Geop. Geop. SSciences, University GREGORY MIJRSKY MURSKY (Dept. ciences, U n i v e r s i t y of of Wisconsin—Milwaukee, Wisconsin-Milwaukee, Milwaukee, Milwaukee, Wisconsin Wisconsin 53201) 53201) The paper summarizes the t h e results r e s u l t s of of uranium uranium and and thorium thorium neutron neutron activation a c t i v a t i o n analysis a n a l y s i s of of 150 150 samples samples from from regionally r e g i o n a l l y metamorphosed metamorphosed Precambrian Precambrian rocks, r o c k s , which comprise comprise the t h e Republic Republic metamorphic metamorphic node, node, northern Six ccentered e n t e r e d around the t h e city c i t y of of Republic, Republic, n o r t h e r n Michigan. Michigan. Six bee delineated llithologic i t h o l o g i c rock r o c k uunits, n i t s , whose metamorphism can can b d e l i n e a t e d wholly wholly orr p partly biotite, sillimanite o a r t l y by chlorite, chlorite, b i o t i t e , garnet, g a r n e t , staurolite, s t a u r o l i t e , and and sillimanite considered. iisograds, s o g r a d s , were considered. The data, i s summarized in i n Figure F i g u r e 1, 1, indicates i n d i c a t e s that t h a t mobilmobild a t a , which is ization of uranium might h have units i z a t i o n of a v e taken t a k e n place p l a c e in i n rock rock u n i t s which higher metamorphism. This is have been subjected s u b j e c t e d to to h i g h e r grades g r a d e s of of metamorphism. T h i s is particularly p a r t i c u l a r l y evident e v i d e n t in i n metagranodiorite, m e t a g r a n o d i o r i t e , shale, s h a l e , and and nietadiabase. metadiabase. granitic metavolcanics The trends t r e n d s for for g r a n i t i c gneiss g n e i s s and m e t a v o l c a n i c s are a r e inconclusive inconclusive because these t h e s e two two rock r o c k units u n i t s do do not n o t appear a p p e a r in i n areas a r e a s represented represented orr intermediate metamorphism. by low o i n t e r m e d i a t e grades g r a d e s of of metamorphism. The concentrations c o n c e n t r a t i o n s of of thorium thorium (Figure ( F i g u r e 2) 2) iin n ggeneral e n e r a l follow f o l l o w the the of uranium uranium cconcentrations o n c e n t r a t i o n s and suggest s u g g e s t that t h a t at a t higher h i g h e r grades grades ttrends r e n d s of of of metamorphism there t h e r e has h a s been some mobilization m o b i l i z a t i o n of of thorium. thorium. The study metamorphism may may pplay s t u d y indicates i n d i c a t e s that t h a t hhigher i g h e r ggrade r a d e metamorphism l a y aan n mobilization of uranium, uranium, and perhaps iimportant m p o r t a n t rrole o l e iin n tthe he m o b i l i z a t i o n of p e r h a p s thorium, thorium, and that i t may contribute c o n t r i b u t e to t o the t h e formation f o r m a t i o n of of ore—forming ore-forming fluids. fluids. t h a t it Concentration C o n c e n t r a t i o n and precipitation p r e c i p i t a t i o n of of uranium from from such such fluids f l u i d s may may result r e s u l t in i n economic economic uranium uranium deposits. deposits- lL �N.P. signifies s i g n i f i e s lithology l i t h o l o g y not n o t present p r e s e n t in i n that t h a t metamorphic metamorphic F i g u r e 1. 1. N.P. Figure of s amples zone. Numbers i n p a r e n t h e s i s a r e number zone. Numbers in parenthesis are number of samples analyzed. analyzed. 15 15 �F i g u r e 2. 2. Figure N.P. N.F. signifies s i g n i f i e s lithology l i t h o l o g y not n o t present p r e s e n t in ir! that that metamorphic zone. zone. Numbers in i n parenthesis p a r e n t h e s i s are are number of of samples samples analyzed. analyzed. 16 �Comparison of Middle Proterozoic Iron Oxide Rich Ore Deposits, Mid—Continent, U.S.M., South AustraHa, Sweden, and the Peoples Republic of China S. A. (Union Carbide Carbide Corporation, Corporation, p. S. A. HAUCK, HAUCK, (Union P. Q• 0. Box Box 1029, 1029, Grand Grand Junction, Colorado Colorado 81502) 81 502) E. W. (UnionCarbide Carbide Corporation, Corporation, p. E. W . KENDALL, KENDALL, (Union P. a. 0. Box Box 1029, 1029,Grand Grand Junction, Colorado Colorado 81502) 81502) Middle Proterozoic Ga) iron oxide Proterozoic (1.8—1.1 (1.8-1.1 Ga) oxide rich richdeposits depositscomprise compri se aa diverse diverse family family ofofeconomically economically important, important,multicommodity multicommodity ore ore depodepogenetic grouping sits genetically related. The s i t s which which appear appear genetically The genetic grouping of these these appears to a deposits (previously not well described) gap (or deposits (previously not well described) appears t o f i l l a gap (or many time—tectonic transition zone) in many time-tectonic ore ore deposit deposit classifications Ga) banded iron formations between Lower (2.5—1.8 Ga) BIF) between Lower Proterozoic Proterozoic (2.5-1.8 formations ((BIF) Camonfeatures features of of these and and Phanerozoic iron iron oxide oxide deposits. deposits. Common these iron oxide deposits deposits include: oxide include: (1) iron 20%Fe Fe as as magnetite magnetite and/or and/or hematite; hematite; iron'contents contentsgreater greaterthan than20% (2) anomalous concentrations of of base Go, Mo), anomalous t to o economic economic concentrations base metals metals (Cu, ( C u , Co, Mo), precious metals precious metals (Au, (Au, Ag), Ag), and and U; U; (3) associated associated geochemical geochemical enrichment enrichment (occasionally (occasionallyeconomic) economic) in in LREE, LREE, Ba, P, Ba, P, F, F, and and Th; Th; (4) intimate i ntimate primary primary mixture mixture of o f iron iron sulfides sulfidesand andhematite hematite and/or and/or nagmagnetite; (5) host host rock rock and and mineralization mineralizationages agesbetween between 1.8 1.8 and and 1.1 1.1 Ga; Ga; (6) close relationship to close spatial spatial and and temporal temporal relationship t o anorogenic anorogenic ffelsic e l s i c domidomiand intrusi intrusives (rapakivi v i granites and and ves (rapaki nated, bimodal volcanics and ferrodiorites) ofoflower ferrodiorites) lower crustal crustal and and mantle mantle origin; (7) ore deposition deposition ininananupper upper crustal crustalsubvolcanic subvolcanicenvironment environment and/or and/or intracratonic or sedimentary basins; basins; intracratonic o rmarginal marginal (tensional) (tensional )sedimentary (8) very exceedingone onebil billion very large largetonnage, tonnage, commonly commonly exceeding lion tons. tons. Examples Examples include the the Kiruna include Kiruna District, Sweden Sweden (Kiirunavaara, (Ki irunavaara, Rektorn, and and Hauki deposits), deposits), Baiyan BaiyanOBo, OBo, Inner Mongolia, Mongolia, Peoples Peoples Republic Republic of P R C ) , Pilot Knob-Pea and Olympic Olympic Dam, Dam, China ((PRC), Knob—Pea Ridge, Missouri, and South Austral Australia. South i a. fill The Middle deposits are are found found in in marmarThe MiddleProterozoic Proterozoiciron iron oxide oxide rich rich deposits t o intracratonic, intracratonic, tensional tensional basins basins overlying Lower Lower Proterozoic Proterozoic ginal to Archean shields shields (Churchill, (Churchill, Gawler, Baltic, rocks on on the the margins margins of of Archean North China). China). The The basins arkoses, sandstones, and and minor(?) minor(?) basins contain arkoses, carbonates (sebkha?), s i c volcanics. volcanics. SedimenSedimencarbonates (sebkha?),volcaniclastics, volcaniclastics, and and fel felsic (SEDEX) hematitic iron formations formations ((++Cu, Cu, Ca, Co, Mo, exhalative (SEDEX) tary exhalative hematitic iron Mo, Au, Au, Ag, U, U, LREE, F ) are are interbedded interbedded with with these thesesediments sedimentsand andmay may LREE, P, Ba, F) form form ore ore deposits deposits (Pilot Knob Outcrop, Outcrop, Olympic Olympic Darn, Dam, Baiyan OBo, OBo, Hau(Pilot Knob Hauk1) subvolcanic rriagnetite magnetite and and magnetite-hematite magnetite-hematite ore depodepoki). Related Related subvolcanic -+ Cu, Cu, Co, P, FF)) may may be these basins basins (Pea (Pea s i t s ((+ sits Go, Mo, P, be associated associated with with these Ridge, Pilot Kiirunavaara). Ridge, Pi lot Knob Knob Subcrop, Subcrop, K i irunavaara) . . A review review of the geochemistry of these iron oxide oxide rich deposits deposits A the geochemistry of these suggests aa more more or less continuous differenti ation series. seri es. Overall, suggests less continuous differentiation Ti02 and and P205 P205 (fluorapatite) (f 1 uorapat i t e ) with with there are general decreases iinn TiO corresponding LREE, base base and and precious precious metals, metals, UU (Th), ( T h ) , F, corresponding increases increases in LREE, F, trendsare arecompatible compatiblewith witha acontinuing continuingdifferentiation differentiation aria ana Ba. These These trends w i t hdecreasing decreasing P P and and TI (and (and increaincreaof an iron iron rich rich immiscible immiscible liquid liquidwith of an 17 �The ffinal sing s i n g oxygen oxygen fugacity) f u g a c i t y ) cconditions. onditions. The i n a l ore ore deposit d e p o s i t composition composition an tectonic and t e c t o n i c position p o s i t i o n of of the t h e iron i r o n oxide o x i d e rich r i c hdeposits d e p o s i t s iiss rrelated e l a t e d to to when and andand when when and where where in i n the t h e crust c r u s t liquid l i q u i immiscibility d i m m i s c i b i l ioccurs t y occurs whenand and wheret hthe where e i riron o n ooxide x i d e r rich i c h ddifferentiate i f f e r e n t i a t e is i s released. released. ggl.obal l o b a l pperiod e r i o d of o f ccratonic ratonic greenstone belt b e l t sstyle t y l e ooff The oore ttectonics. ectonics. The r e deposits d e p o s i t s may may be be rrelated e l a t e d to t o other o t h e r lower lower crustal crustal rock i.e., r o c k types t y p e s known known tto o have have formed formed dduring u r i n g the t h e Middle M i d d l e Proterozoic, P r o t e r o z o i c , i.e., anorthosite a n o r t h o s i t e massifs—rapakivi m a s s i f s - r a p a k i v i ggranites r a n i t e s and and ttheir h e i r associated a s s o c i a t e dmagmatic magmatic Lake, Adirondacks, segregation (Allard s e g r e g a t i o n Fe—Ti-P Fe-Ti -P oore r e deposits d e p o s i t s (A1 l a r d Lake, Adirondacks, Nelson, Va). Production Va) P r o d u c t i o n and and ddifferentiation i f f e r e n t i a t i o n of o f immiscible i m m i s c i b l e iiron r o n oxide o x i d e rich rich 1liquids i q u i d sduring d u r i n ganorthosite a n o r t h o s i templacement e emplacementmay maybebethe t hcommon e common denominator denomi n a t o r ffor o r the t h e origin o r i g i nofo upper f upper and and lower lower crustal c r u s t a l iiron r o n oxide o x i d e deposits. deposits. Pasproducesu puplift emplacement o fofa anorthosites n o r t h o s i t e s produces l i f t and and extension e x t e n s i o n ttoo form form ssive i v e emplacement Accompanying lowerc rcrustal marginal and iintracratonic n a l and n t r a c r a t o n i c basins. basins. Accompanying lower u s t a l ppartial a r t ia1 marg melting me1 t ng generates generates rapakivi r a p a k i v i granite g r a n i t e suites s u i t e s and and rrelated e l a t e d areally a r e a l l y extenextenCoeval, aalkalic, f e l s i c volcanics. volcanics. Coeval, l k a l i c , intermediate i n t e r m e d i a t e and and mafic maf i c volcavolcassive ive felsic m i n o r ) and and iintrusions n t r u s i o n s are a r e also a l s o related r e l a t e d to t oanorthosite a n o r t h o s i t eemplaceemplacennics i c s ((minor) Related Related Upper Uooer Proterozoic P r o t e r o z o i c (1.1-0.5 (1.1 -0.5 Ga)-Lower Gal-Lower Paleozoic Paleozoic anoroanoroment. ment kegenic events are are* rrepresented e p r e s e n t e d bybyaabortive b o r t i v e r rifting i f t i n g ((Keeweenawan, Keeweenawan, Adeg e m events laidean and/or aalkalic 1 aidean Geosyncline, Geosyncl ine, Oslo Oslo Graben) Graben) and/or l k a l i cplutonism p l u t o n i s m(Delamerian (Delarneri an Paleozoic Orogeny, South AAustralia Orogeny, South u s t r a l i a and and Inner I n n e r Mongolia). Mongol ia). Paleozoic and and younger younger carbonatites and kkimberlites maybe beone oneo of c a r b o n a t i t e s and i m b e r l i t e s may f t the h e llast a s t events events to t o characcharacterize t e r i z e this t h i scratonization c r a t o n i z a t i o nprocess. process. These ore o r e deposits d e p o s i t s formed during during stabilization s t a b i 1i z a t i o n tthat h a t followed f o l l o w e d the the a a Archean Archean . The central U.S., from The c e n t r a l U.S., f r o m Missouri M i s s o u r i to t o the t h e Great Lakes region, has sseveral e v e r a l areas areas ooff favorable f a v o r a b l e rock r o c k types t y p e s and and tectonic t e c t o n i c settings s e t t i n g scompatible compatible Careful with w i t h these these ore o r e deposits. deposits. C a r e f u l geophysical geophysical modeling modeling combined combined with with geochemicalandand shouldl elead geochemical g egeologic o l o g i c i n tinterpretation e r p r e t a t i o n should a d t otoi identification dentification ant, ooff ddrillable r i 1 l a b l e ttargets a r g e t s ffor o r another of o f these economically economical l y import important, ggiant i a n t ore o r e deposits. deposits. 18 �Penokean tectonics: tectonics: central c e n t r a l Minnesota Ninnesota geology Constraints C o n s t r a i n t s from from sstructural tructural g e ~ l o g yin ir! east— east- HOLST, T.B., T.B., Department Department of of Geology, Geology, U University of !4innesota Minnesota Duluth, HOLST, n i v e r s i t y of Duluth* Duluth, Minnesota 55812 Duluth, 55812 In past have been been sseveral plate I n the the p a s t decade there t h e r e have everal p l a t e tectonic tectonic a l l ininmodels for f o r the t h e early e a r l y Proterozoic P r o t e r o z o i c Penokean Penokean orogeny. orogeny. These all volve plate boundaries and and some ssuggest v o l v e convergent convergent p l a t e boundaries u g g e s t ccollision, o l l i s i o n , or or models which suggest multiple t e c t o n i c models s u g g e s t that t h a t the the m u l t i p l e collision. c o l l i s i o n . Other tectonic Penokean was an intracratonic event emphasize the role of basement. Penokean w a s a n i n t r a c r a t o n i c e v e n t emphasize t h e r o l e of basement. They suggest basement was rremobilized, and h high s u g g e s t that t h a t basement e m o b i l i z e d , and i g h heat flow con— concentratad fundamental boundary boundary iin basement, tthe Great c e n t r a t e d aalong l o n g aa fundamental n tthe h e basement* he G reat Tectonic Lakes T e c t o n i c Zone. Zone. Recent sstructural of eearly i n east— eastRecent t r u c t u r a l sstudies t u d i e s of a r l y PProterozoic r o t e r o z o i c rrocks o c k s in central Minnesota have have rrevealed which cconstrain c e n t r a l Minnesota e v e a l e d sseveral e v e r a l ffacts a c t s which onstrain Minnesota, the tectonic 1. In I n Minnesota* the t e c t o n i c models of of the t h e Penokean Penokean orogeny: orogeny: 1. o l d i n g , each rresultesultPenokean orogeny orogeny iinvolved two main main phases phases of of ffolding, Penokean n v o l v e d two The first f i r s t phase p h a s e of o f defordefor2. p e n e t r a t i v e tectonic t e c t o n i c fabric. fabric. i n g in i n a penetrative ing mation involved of northward-directed northward—directed nappes in i n v o l v e d the t h e development of in some some (Z approxand w was accompanied by by aa llarge approxa s accompanied a r g e fflattening l a t t e n i n g sstrain t r a i n (Z aareas, r e a s , and imately vertical) well-developed foliation. f o l i a t i o n . 3. 3. The second second imately v e r t i c a l ) and and a well—developed of deformation deformation lled development of of uupright phase of e d tto o tthe h e development p r i g h t ffolds, o l d s , and was horizontal of over w a s accompanied by a h o r i z o n t a l sshortening h o r t e n i n g of o v e r 60% 60% (Z (Z north— northssouth o u t h and h orizontal). horizontal). could ppossibly decollement While tthese h e s e ffeatures e a t u r e s could o s s i b l y bbe e eexplained x p l a i n e d by decollement gravity—gliding g r a v i t y - g l i d i n g off o f f a rising r i s i n g ddiapir i a p i r (McGrath (McGrath Gneiss?) Gneiss?) they are are with convergent pplate ccertainly e r t a i n l y aalso l s o cconsistent onsistent w i t h aa convergent l a t e boundary environenvironment, with southward-dipping subduction s u b d u c t i o n zone. zone. Further, F u r t h e r , the t h e fabric fabric ment* w i t h a southward—dipping within w i t h i n the t h e McGrath Gneiss suggests s u g g e s t s that t h a t it i t was not n o t a diapir, d i a p i r , but l ~ was w at s involved phase of of Penokean Penokean ddeformation, involved iin n tthe h e eearly a r l y phase e f o r m a t i o n y pperhaps e r h a p s as nappe ccores Pennine Nappe Nappe Zone Zone of of tthe Alps) o orr as "embryonic nappe o r e s (as ( a s iin n Pennine h e Alps) as recently r e c e n t l y suggested s u g g e s t e d in i n the & e Helvetic Helvetic nappe" basement shear s h e a r zones, zones * as Nappe Thus it Nappe Zone. Zone. i t seems that t h a t the t h e sstructural t r u c t u r a l evidence e v i d e n c e in i n east— eastcentral Minnesota iis most eeasily accounted ffor by aa cconvergent c e n t r a l Minnesota s most a s i l y accounted o r by o n v e r g e n t plate plate boundary model, cconsistent with growing body body of of sstructural boundary model, onsistent w i t h tthe h e growing t r u c t u r a l and petrologic p e t r o l o g i c eevidence v i d e n c e from Wisconsin and Upper Michigan. Michigan. 19 �The of of Transcurrent Shear Shear in i n Deformation Deformation of of the the The Role -Archean ---Rocks of of the the Vermilion District, D i s t r i c t , Minnesota Minnesota .. P.J. P J Hudleston, Hudles t o n l Department Department of of Geology Geology and and Geophysics, Geophysics University U n i v e r s i t y of of Minnesota, Minnesota, 551455; Minneapolis, MN Minneapolisl MN 55455; DL. D.L. Southwick, SouthwicklMinnesota MinnesotaGeological GeologicalSurvey, Survey,26142 2642 University U n i v e r s i t y Ave., A V ~ St. .S ~t . Paul, Paul, MN MN 551114. 551 14. Deformed and and metamorphosed sedimentary sedimentary and volcanic volcanic rocks of the the Vermilion district an east-west east—westt rtrending e n d i n g bbelt e l t between between higher grade grade rocks rocks of the the d i s t r i c t occupy occupy an Vermilion Granitio Vermilion G r a n i t i c Complex Complex t to o tthe h e north n o r t h and and the t h e Giants G i a n t s Range Range bbatholith a t h o l i t h to t o the the south. A l l the t h e measured measured sstrain, t r a i n , aa cleavage, cleavage, and and aa mineral mineral llineation i n e a t i o n iin n this this south. AU belt b e l t are are attributed a t t r i b u t e d to t o the t h e 'main' !maintphase phaseofofdeformation deformation (D2) (D2) that t h a t followed followed an an earlier whichl eleft e a r l i e r nappe—forming nappe-forming event event (D1), (Dl), which f t l little i t t l e evidence evidence of of fabric. fabric. Previous assumed that t h a t the t h e D2 deformation resulted r e s u l t e d from north-south north-south Previous work work has has assumed compression compression across a c r o s s the t h e district, d i s t r i c t , presumably presumably related r e l a t e d to t o diapiric d i a p i r i c intrusion i n t r u s i o n of of the the batholithic number of of observations observations now now lead l e a d us us b a t h o l i t h i c bodies bodies to t o the t h e north n o r t h and and south. south. AA number to that aa significant s i g n i f i c a n t component component of t h i s deformation deformation resulted r e s u l t e d from from t o believe believe that dextral d e x t r a l shear shear across a c r o s s the thewhole whole region. region. Thus Thus tthe h e Vermilion Vermilion ffault, a u l t , aalate—stage late-stage strike—slip that bounds bounds the t h e Vermilion Vermilion ddistrict i s t r i c t to t o the t h enorth, n o r t h lmay may s t r i k e - s l i p sstructure t r u c t u r e that simply s h e a r regime regime that t h a t was w a s much much simply be be the t h e latest, l a t e s t l more brittle b r i t t l e expression expression of of aa shear more time. Features Features that t h a t are a r e indicative i n d i c a t i v e of of shear shear more widespread widespread in i n space space and and time. include zones with with sigmoidal sinoidal foliation include ductile d u c t i l e sshear h e a r zones f o l i a t i o n patterns, p a t t e r n s , highly h i g h l y schistose schistose zones of shear c l a s t s or o rpyrite p y r i t ecubes cubes with with zones with with the t h e development development of shear bands, bands, feldspar f e l d s p a r clasts of this asymmetric of the asymmetric ppressure r e s s u r e shadows, shadows, and and the t h e fact f a c t that t h a tthe t h easymmetry asymmetry of t h e F2 F2 ffolds o l d s is is predominantly of the predominantly ZZf ofor r aat t least l e a s t 15 15km km south south of t h e Vermilion Vermilion ffault. ault. The presence of of a large of simple The presence l a r g ecomponent component of simple shear s h e a r may may hhelp e l p explain e x p l a i n addiaddi- tional t i o n a l structural s t r u c t u r a lfeatures f e a t u r e sini a n simpler a simplerway waythan than otherwise otherwise possible. possible. Just J u s t south south of of the t h e Vermilion Vermilion fault f a u l tthe t h ecleavage cleavagelocally l o c a l l ybecomes becomes folded folded and and aa new new spaced spaced cleavage developsi in o r i e n t a t i o n tot othe t h eold o l dcleavage cleavageaway away from from the the cleavage develops n aa similar orientation folds. than iinterpreting this as as evidence evidence for f o r an an additional a d d i t i o n a l episode episode of of f o l d s . Rather Rather than n t e r p r e t i n g this deformation, we consideri tit ttoo be deformation, w e consider be due due to t o aa single s i n g l eprocess process of ofcontinuous continuous shear: shear: aa foliation f o l i a t i o ndevelops developsand and after a f t e r aa large l a r g e strain s t r a i n local l o c a l perturbations p e r t u r b a t i o n s result r e s u l t in in folding f o l d i n g of the the old o l d foliation f o l i a t i o nand and the t h e development development of new one x i a l planar p l a n a r to to of a new one aaxial the type of of perturbation t h e folds. f o l d s . The The same same type p e r t u r b a t i o n can can lead l e a d to t o the t h e juxtaposition j u x t a p o s i t i o n of ofzones zones of ~f of constrictional c o n s t r i c t i o n a l and and flattening f l a t t e n i n g strains, s t r a i n s , aa distinctive d i s t i n c t i v e feature f e a t u r eof of the therocks rocks of the the Vermilion Vermilion district d i s t r i c t otherwise otherwise hard hard to t o account account for. f o r . The The strain s t r a i n pattern pattern requires north-south component component of of shortening s h o r t e n i n g in i n addition a d d i t i o n to t o shear. shear. The r e q u i r e s aa north—south D2 The D2 deformation deformation in i n the t h e Vermilion Vermilion district d i s t r i c t can can therefore t h e y e f o r e be be characterized c h a r a c t e r i z e d as a s one one of of transpression: ( ? ) crustal c r u s t a l blocks blocks to to transpression: oblique oblique compression compression between between two two more more rigid r i g i d (?) the the north n o r t h and and south. south. 20 �Preliminary P r e l i m i n a r y Paleomagnetic Results R e s u l t s from the t h e Baraboo Quartzite Quartzite Rhyolite and G Granite and the t h e Associated Associated R h y o l i t e and r a n i t e IInliersof n l i e r s of South Central C e n t r a l Wisconsin W.F. (Dept. of of GGeological and Geophysical W.F. KEAN, KEAN, D. D. MERCER, MERCER, E. E. RAMI'HTJN wlTHU?? (Dept. e o l o g i c a l and Sciences, W I 53201) 53201) S c i e n c e s , University U n i v e r s i t y of of Wisconsin—Milwaukee, Wisconsin-Milwaukee, Milwaukee, Milwaukee, WI The The Proterozoic P r o t e r o z o i c geology geology of of Wisconsin represents r e p r e s e n t s a fairly f a i r l y complex succession the s u c c e s s i o n of of tectonic t e c t o n i c events. e v e n t s . Of Of interest i n t e r e s t to t o this t h i s project p r o j e c t is the suite s u i t e of of rhyolitic r h y o l i t i c and and granitic g r a n i t i c inliers i n l i e r s of of the t h e Fox Fox River River Valley V a l l e y and and the t h e overlying o v e r l y i n g Baraboo Quartzite Q u a r t z i t e which span span the t h e time t i m e from from 1760 1760 m.y. may. ago to t o 1450 1450 m.y. m-y. ago. ago. A A total t o t a l of of 50 50 samples samples of of Baraboo Baraboo Quartzite Q u a r t z i t e were were collected c o l l e c t e d from from 15 1.5 sites samples were subs i t e s on both b o t h sides s i d e s of of the t h eBaraboo Baraboo Syncline. S y n c l i n e . The samples jected j e c t e d to t o both both alternating a l t e r n a t i n g field f i e l d (A.F.) (A.F.) demagnetization demagnetization and and thermal thermal demagnetization. remanence is demagnetization. The The rresults e s u l t s indicate i n d i c a t e that t h a t stable s t a b l eremanence is carried was set set before c a r r i e d by by hematite h e m a t i t e and and that t h a t the t h e magnetization m a g n e t i z a t i o n was b e f o r e the the major of the major ffolding o l d i n g of t h e syncline. s ~ c l i n e . The The within-site w i t h i n - s i t e directions d i r e c t i o n s are are tightly v a l u e s ranging from from 45 45 to t o 300, 300, and andct—95 a-95 t i g h t l y clustered c l u s t e r e dwith w i t hKK values values magneticddirections d e g r e e s . The The magnetic i r e c t i o n s aafter fter v a l u e s ranging ranging from from 118 8 tto o 55 degrees. unfolding u n f o l d i n g cluster c l u s t e r around around an an inclination i n c l i n a t i o n of 29° 29' and and aa declination d e c l i n a t i o n of of 1900. V.G.P. at a t about about 28°S, 2a0S, 90°W 90° which fits f i t s well w e l l with with 190° This T h i s gives g i v e s aa V.G.P. previously published North Torth American mericen Precambrian p r e v i o u s l y published Precambrian poles p o l e s for f o r the t h e time time range of of 220 220 m.y. may. ago ago to t o 1650 1650tn.y. may. ago. ago. We W e have have also a l s o obtained o b t a i n e d preliminary p r e l i m i n a r y results r e s u l t s from from several s e v e r a l rhyolites rhyolites from from the t h e Fox Fox River River Valley V a l l e y inliers. i n l i e r s . A.F. A.F. and and thermal thermal demagnetization demagnetization studies s t u d i e s show show these t h e s e samples samples to t o be b e magnetically m a g n e t i c a l l y softer, s o f t e r , but b u t reliable reliable directions d i r e c t i o n s can can be b e obtained. o b t a i n e d . Two dominant pole p o l e positions p o s i t i o n s are a r e found; found; is near n e a r 67°—87°N, 670-870N9 90°—150°W, 90°-150° and and the t h e other o t h e r is is near n e a r 2°—20°S, 2O-20°S one is 90°—120°W. 90'-120°W The The first f i r s t pole p o l e position p o s i t i o n is is reasonable r e a s o n a b l e for f o r 1630 1630 m.y. m.y. ago, ago, t h e second second is is similar similar to t o the t h e results r e s u l t s for f o r the t h e Baraboo Baraboo Quartzite. Quartzite. and the 21 �Composite Conposite Magnetic Yagnetic Ilap Flap of of Wisconsin Uisconsin Precambrian from fro^ New New Compilation Compilation of' Digital D i g i t a l Aerov!agnetic AeroL6amet i c Data Data of EIZABETH R. R. KING K I N G (U.S. (U.S. Geological Geological Survey, S u w e y YReston, Reston* VA VA 22092) 22092) ELIZABETH JOHN H. H. KARL EWU (Univ. (univ. of of Wisonsin, Wisonsiny Oshkosh, 0shkoshy WI W I 54901) 54901) JOHN JOHN SS. ELASNER KLASNER(Uestern (Ves t e r n Illinois I l l i n o i s Univ., Univ. Macomb, Macomb IL IL 61455) 61455) JOHN WILLIAM J. J. JONES JONCS (U.S. (U-S. Geological G e o l o g i c a l Survey, Surveyy Reston, R e s t o n y VA VA 22092) 22092) WILLIAM composite magnetic magnetic contour contour map map of of the t h e exposed exposed Precambrian Precambrian terrane terrane AA composite w i l l be be displayed d i s p l a y e d for f o r the t h e first f i r s t time. time. This This of northern n o r t h e r n Wisconsin Wisconsin will of mapy at a t aa scale s c a l e of of 1:250,000, 1:25OY00Oywas was prepared prepared from from 94 94 aeromagnetic aeromagnetic 15' 15' map, quadrangle Karl under under aa grant g r a n t from from the the quadrangle maps, mapsy which which were were compiled compiled by by Karl U.S. U.S. Geological G e o l o g i c a l Survey S u w e y from f r o u data d a t a he he obtained o b t a i n e d through through aa survey sur-~ey These conducted during d u r i n g 1973—77. 1973-77. These 94 94 recontoured r e c o n t o u r e d maps, mapsy at a t aa scale s c a l e of of conducted 1:62,500, 1:62y500y will w i l l replace r e p l a c e the t h e set s e t of of 86 8 6 maps maps currently c u r r e n t l y available a v a i l a b l e from fron t h e Wisconsin Wisconsin Geological G e o l o g i c a l and and Natural N a t u r a l History H i s t o r y Survey. Sumey. The The 20— 20- and and the 100—gamma of the t h e previous p r e v i o u s set, s e t y are a r e continuous continuous 100-gamma contours, c o n t o u r s y unlike u n l i k e those t h o s e of m e myriad myriad of of detail d e t a i l on on the the and match match at a t quadrangle quadrangle boundaries. b o u n d a r i e s . The and composite c m p o s i t e magnetic magnetic map map from from this t h i s new new compilation c o m p i l a t i o n results r e s u l t s in i n much much more more coherent c o h e r e n t patterns p a t t e r n s that t h a t highlight h i g h l i g h t the t h e contrasts c o n t r a s t s in i n magnetic n a g n e t i c character character of the t h e underlying u n d e r l y i n g Precambrian Precambrian terranes. terranes of . This %is magnetic magnetic map, mapy in i n conjunction c o n j u n c t i o n with w i t h simple s i m p l e Bouguer Bouguer and and filtered filtered g r a v i t y maps maps of of the t h e same same area, a r e a y allows a l l o w s the gravity of the the t h e westward westward extension e x t e n s i o n of t h r e e major major tectonic t e c t o n i c belts b e l t s or o r terranes t e r r a n e s proposed proposed by by Klasner Klasner and and others others three (in ( i n press) p r e s s ) for f o r an a n area a r e a that t h a t includes i n c l u d e s the t h e eastern e a s t e r n part p a r t of of the t h e area area shown in i n the t h e composite composite magnetic magnetic map. mapshown P J a s n e r y J. J. S., S a yKing, Kingy E. E. R., R e Y and and Jones, J o n e s y W. V. J., J a yin i n press, p r e s s y Geologic Geologic Iaasner, i n t e r p r e t a t i o n of s r a v i t y and magnetic d a t a f o r n o r t h ern of gravity and magnetic data for northern interpretation M c h i g a n and and Wisconsin: 1Jisconsin: Society S o c i e t y of of Exploration E x p l o r a t i o n Geophysicists Geophysicists Michigan S p e c i a l Publication P u b l i c a t i o n on on the t h e Utility U t i l i t y of of Regional Regional Gravity G r a v i t y and and Special lfagnetic Anomaly Anomaly Naps. Maps Magnetic . 22 �Rb—Sr Rb-Sr and Oxygen Isotope I s o t o p e Systematics S y s t e m a t i c s of of Archean Archean Grey Gneisses of of the t h e southwestern southwestern Beartooth B e a r t o o t h Mountains Mountains T.J. T . J . KLRSLING, KIRSLINGy C.W. C.W. MONTGOMERY, MONTGOMF3Y, and and E.C. E.C. PERRY, PEXRY, JR. JR. Geology, Geology, Northern Northern Illinois I l l i n o i s University, U n i v e r s i t y , DeKaib, DeKalb* IL IL (Department of 60115) 60115) Rb—Sr Rb-Sr and oxygen oxygen isotopic i s o t o p i c analyses a n a l y s e s were were performed performed on on samples samples of of Archean gneiss from from the t h e Cooke Cooke City C i t y region r e g i o n of of the t h e Bear— Beark c h e a n grey g r e y granitic g r a n i t i c gneiss tooth t o o t h Mountains, Mountains9 Montana. Montana. A A whole—rock whole-rock Rb—Sr Rb-Sr isochron i s o c h r o n date d a t e for f o r this this unit 2700 m.y. m.y. is u n i t of of about about 2700 is accompanied accompanied by by an an elevated e l e v a t e d initial initial 87Sr/86Sr 8 7 s r / 8 6 s r ratio r a t i o of of 0.7054. 0.7054. A more systematically—collected s y s t e m a t i c a l l y - c o l l e c t e d regional regional suite s u i t e of of these t h e s e grey gneisses g n e i s s e s hints h i n t s at a t an a n age in i n excess e x c e s s of of 33 b.y., b.y.> suggesting incompletely homogenized older h a t aan n incompletely o l d e r component comprised comprised suggesting tthat a portion whole—rock 6180 l8 values p o r t i o n of of the t h e gneiss. g n e i s s . Although Although whole-rock v a l u e s for f o r the the gneiss +8.00 °/oo, g n e i s s (average (average +8.00 O/ooY range +6.98 +6.98 to t o +10.03 +10.03 0/00 O/oo relative r e l a t i v e to to SMOW) o r i g i n * the t h e values v a l u e s are are SMOW) tend to t o indicate i n d i c a t e a primary magmatic origin, largely of oolder metasedimentary l a r g e l y indistinguishable i n d i s t i n g u i s h a b l e from from t5180 6180 vvalues a l u e s of l d e r metasedimentary units t h e gneisses g n e i s s e s (+7.87 (+7.87 to t o +11.00 +ll.OO O/ooy u n i t s now found as a s rafts r a f t s in the values v a l u e s which are a r e lower lower than t h a n expected). e x p e c t e d ) . AA composite composite source s o u r c e would be be more more consistent c o n s i s t e n t with w i t h the t h e Rb—Sr Rb-Sr data d a t a and and initial i n i t i a l Sr S r ratio. r a t i o . The The 2700 m.y. date 2700 may. d a t e reflects r e f l e c t s the t h e age a g e of of a regional r e g i o n a l thermal thermal event, e v e n t , perpervasive m i x t u r e of of primary primary v a s i v e throughout the t h e Beartooth B e a r t o o t h Mountains. Mountains. AA mixture differentiated d i f f e r e n t i a t e d magma, m a g m a * perhaps perhaps contemporaneous contemporaneous with w i t h this t h i s thermal thermal e v e n t * with w i t h assimilated a s s i m i l a t e d older o l d e r crustal c r u s t a l material m a t e r i a l would would account account for for event, both the t h e sstrontit t r o n t i u m and and oxygen oxygen isotope i s o t o p e data. data. 23 �Gravity models Gravity m o d e l s of o f gneiss g n e i s s domes domes and a n d aa granite g r a n i t e pluton pluton in i n nnortheastern o r t h e a s t e r n Wisconsin Wisconsin John S. S. Kiasner K l a s n e r (Department (Department of of Geology, G e o l o g y , Western W e s t e r n Illinois I l l i n o i s University, University, Macomb, Illinois I l l i n o i s 61455 aand n d U.S. U.S. Geological G e o l o g i c a l Survey) Survey) Dan Osterfeld O s t e r f e l d (Department (Department of o f Geology, Geology, Western W e s t e r n Illinois I l l i n o i s University, University, Macomb, Macomb, Illinois I l l i n o i s 61455) 61455) Three density models T h r e e 22—dimensional -dimensional d ensity m o d e l s of o f granitoid g r a n i t o i d bodies b o d i e s have have been b e e n prepared p r e p a r e d from gravity g r a v i t y profiles p r o f i l e s in i n northeast n o r t h e a s t Wisconsin. Wisconsin. The profiles p r o f i l e s cross c r o s s the t h e Dunbar gneiss g n e i s s dome, another a n o t h e r probable p r o b a b l e gneiss g n e i s s dome dome west w e s t of o f the t h e Dunbar Dome, Dome, and a n d the t h e east e a s t lobe l o b e of o f the t h e Hoskin Hoskin Lake Lake which is part ggranite r a n i t e ppluton l u t o n which i s cconsidered o n s i d e r e d aa p a r t of o f the t h e Dunbar dome. dome. Pock Rock density 45 hand specimens Sims iindicate d e n s i t y aanalyses n a l y s e s oof f 45 s p e c i m e n s collected c o l l e c t e d by by P. P . KK. . Sims ndicate domes, which which aare predominantly rrocks o c k s oof f tthe h e domes, re p r e d o m i n a n t l y gneissic, g n e i s s i c , are a r e on on the the average a v e r a g e of of 0.21 0 . 2 1 gm/cm3 less l e s s dense d e n s e than t h a n the t h e surrounding s u r r o u n d i n g generally generally mafic i s an a n average a v e r a g e of o f 0.30 0.30 m a f i c volcanic v o l c a n i c rocks. r o c k s . The Hoskin Lake granite g r a n i t e is d e n s i t y models models gm/cm3 less l e s s dense d e n s e than t h a n the t h e volcanic v o l c a n i c country c o u n t r y rock. r o c k . The density domes eextend iindicate n d i c a t e tthat h a t tthe h e ggneiss n e i s s domes x t e n d to to a a depth d e p t h of o f 1.6 1 . 6 km km (1 ( 1 mile). mile). Gravity model sstudies of llarge G r a v i t y model t u d i e s of a r g e ppost o s t kkinematic i n e m a t i c pplutons l u t o n s ((ott E o t t and and Smithson, 1 9 6 7 ) , of o f similar s i m i l a r areal a r e a l dimension d i m e n s i o n as a s the t h e gneiss g n e i s s domes, domes, ininS m i t h s o n , 1967), d i c a t e that t h a t most o f them are on the t h e order o r d e r of o f 10 1 0 km km thick, t h i c k , much much thicker thicker dicate most of domes and tthan h a n tthe h e domes a n d pluton p l u t o n of o f this t h i s study. s t u d y . They nnote, o t e , however, however, the the P r e c a m b r i a n granitic g r a n i t i c bodies b o d i e s tend t e n d to t o be b e thinner t h i n n e r than t h a n this t h i s and a n d that t h a t they they Precambrian may be b e thinned t h i n n e d by by erosion. e r o s i o n . Although A l t h o u g h the t h e gneiss g n e i s s domes of o f this t h i s study study a r e likely l i k e l y synkinematic s y n k i n e m a t i c and and n o t exactly e x a c t l y the t h e same same as a s the t h e granite granite are not plutons m o d e l l e d by by Bott B o t t and a n d Smithson, S m i t h s o n , they plutons modelled t h e y appear a p p e a r to t o be b e unusually unusually thin. thin. I t is ppossible o s s i b l e that t h a t vvarying a r y i n g densities d e n s i t i e s with w i t h depth d e p t h do do not n o t permit permit It a n accurate a c c u r a t e estimate e s t i m a t e of o f their t h e i r true t r u e depth. d e p t h . On the t h e other o t h e r hand, h a n d , the the an e a s t lobe l o b e oof f the t h e Hoskin Lake granite g r a n i t e body is i s aa discrete d i s c r e t e pluton. p l u t o n . Its Its east s h a l l o w depth d e p t h aand n d the t h e fact f a c t that t h a t it i t lies l i e s within w i t h i n aa prominent p r o m i n e n t south s o u t h dipdipshallow i t may be be allochthonous a l l o c h t h o n o u s and and is is p ing m agnetic g r a d i e n t suggests s u g g e s t s that t h a t it ping magnetic gradient truncated t r u n c a t e d at a t depth. d e p t h . One possible p o s s i b l e scenario s c e n a r i o is i s that t h a t truncation truncation ooccured c c u r e d aalong l o n g south s o u t h dipping d i p p i n g thrust t h r u s t faults f a u l t s that t h a t are a r e tectonically tectonically aassociated s s o c i a t e d with w i t h the t h e proposed p r o p o s e d fliagara N i a g a r a ssuture u t u r e which i e s aabout b o u t four four which llies m i l e s north n o r t h of o f the t h e Hoskin Hoskin Lake Lake pluton. pluton. I f this t h i s is i s correct, c o r r e c t , then t h e n the the miles If g n e i s s domes also b e allochthonous a l l o c h t h o n o u s features f e a t u r e s that t h a t are a r e truncated t r u n c a t e d at at gneiss domes may may also be ddepth e p t h by thrust t h r u s t faults. f a u l t s . Alternately; A l t e r n a t e l y , the t h e shallow s h a l l o w depths d e p t h s of o f the the g n e i s s domes n d granite g r a n i t e pluton p l u t o n may be b e due d u e to t o uplift u p l i f t and and erosion. erosion. gneiss domes aand Reference Reference B o t t , Y.H.P., m i t h s o n , S.B., S . B . , 1967, 1 9 6 7 , Gravity G r a v i t y investigation i n v e s t i g a t i o n of of Bott, M.H.P., and and S Smithson, s u b s u r f a c e shape s h a p e aand n d mass distribution d i s t r i b u t i o n of o f granite g r a n i t e batholiths: batholiths: subsurface G e o l o g i c a l Society S o c i e t y of o f America America Bulletin, B u l l e t i n , v. v. 7 8 , p. p . 879—906. 879-906. Geological 78, 24 �The The Plate P l a t e Tectonic Tectonic History History of of North-central North-central Wisconsin Wisconsin GENE GENE L. L. LABERGE LABERGE (Geology (Geology Department, Department, University U n i v e r s i t y of of Wisconsin-Oshkosh, Wisconsin-Oshkosh, Oshkosh, Oshkosh, WI W I 54901 54901 and and U.S. U.S. Geological Geological Survey) Survey) KALUS J. SCHULZ SCHULZ (U.S. ( U . S . Geological ~ e o l o g i c a Survey, lSurvey, Reston, Reston, VA VA 22092) 22092) KALUS 3. PAUL PAUL E. E. MYERS MYERS (Geology (Geology Department, Department, University University of of Wisconsin-Eau Wisconsin-Eau Claire, Claire, Eau Eau Claire, C l a i r e , WI W I 54701) 54701) Recent mapping in in north—central n o r t h - c e n t r a l Wisconsin indicates i n d i c a t e s the t h e presence of of three three Recent separate successions of Early Proterozoic volcanic rocks (Figure 1). Each s e p a r a t e successions of Early P r o t e r o z o i c v o l c a n i c rocks (Figure 1 ) . Each succession succession has has aa distinct d i s t i n c t lithology, l i t h o l o g y , structural s t r u c t u r a l pattern, p a t t e r n , and and metamorphic metamorphic grade. grade. These rocks tto the Archean Archean rocks o the t h e south south appear appear to t o be be best b e s texplained explainedby by These rocks rocks and and the aa plate p l a t e tectonic t e c t o n i c model. model. AA widespread widespread succession succession of of Early Early Proterozoic P r o t e r o z o i c quartzofeldspathic q u a r t z o f e l d s p a t h i c gneisses gneisses and amphibolite, derived mainly from subaqueous volcanic i s characterized characterized and amphibolite, derived mainly from subaqueous v o l c a n i c rocks rocks is by by amphibolite—facies amphibolite-facies metamorphism metamorphismarid and isoclinal i s o c l i n a l folding f o l d i n g about about westw e s t - to to northwest—trending northwest-trending axes. axes. These These metavolcanic metavolcanic rocks rocks were were intruded i n t r u d e d mainly mainly by by tonalites. t o n a l i t e s . Lithologies L i t h o l o g i e s are a r e characteristic c h a r a c t e r i s t i c of of island i s l a n d arcs, a r c s ,and andappear appear to t ohave have formed formed over aa north—dipping north-dipping subduction zOne zone (Figure (Figure2A). 2A). Dated the south south of of these t h e s e rocks rocks in i n central central Dated Archean Archean gneisses g n e i s s e s are a r e exposed exposed tto o the Wisconsin, Wisconsin, and and farther f a r t h e r south south typical t y p i c a l Archean Archean "greenstone "greenstone bbelt" e l t " llithologies i t h o l o g i e s of of iron—formations and foundi nind drill iron-formations and t u ftuffs f s a rare e found r i l l cores c o r e s and and aatt the the iron i r o nmine mine at at Black Black River River Falls. F a l l s . These These Archean Archean rocks rocks are a r e believed b e l i e v e d to t o be be part p a r t of of an an older older craton c r a t o n that t h a t collided c o l l i d e d with w i t h the the Early Early Proterozoic P r o t e r o z o i c island i s l a n d arc a r c(Figure (Figure2B). 2B). Metamorphism of the Early Metamorphism and and deformation deformation of E a r l y Proterozoic P r o t e r o z o i crocks rockswas was probably probably caused caused by by the t h e collision. collision. A A younger younger sequence sequence of of Early E a r l y Proterozoic P r o t e r o z o i c volcanic v o l c a n i crocks rocksunconforinably unconformably overlies overlies the the Archean Archean and and older o l d e r volcanic volcanic arc a r c in i n Marathon Marathon County County and and elsewhere. elsewhere. These These rocks rocks consist c o n s i s t of o fsubaqueous subaqueous bbasalt a s a l t to t o rhyolite r h y o l i t e that t h a t have have undergone undergone only only g r e e n s c h i s t - f a c i e s metamorphism, metamorphism, were were deformed deformed about about steeply s t e e p l y plunging plunging northeastnortheastgreenschist-facies trending w e r e extensively e x t e n s i v e l y intruded i n t r u d e d by by epizonal e p i z o n a l granites. g r a n i t e s . This This trending axes, axes, and and were succession isbelieved b e l i e v e dtot ohave haveformed formedata at continental—margin a continental-margin over overa asouthwardsouthwardsuccession is dipping zoneaas the ocean ocean bbasin dipping subduction subduction zone s the a s i n tto o the t h e north n o r t h closed closed (Figure (Figure2C). 2C). The The Niagara thethe boundary isinterpreted i n t e r p r e t e dtot be o be boundarybetween between these t h e s evolcanic volcanic Niagara fault f a u l t zone zone is assemblages andpplatform sedimentaryrocks rocksonont hthe Superiorccraton assemblages and l a t f o r m sedimentary e Superior r a t o n tto o the t h e north north (Figure (Figure2D). 2D). Deformation Deformation and andmetamorphism metamorphism associated a s s o c i a t e d with w i t h the the collision c o l l i s i o n of of these these volcanic Penokean Orogeny. volcanic belts b e l t swith w i t hthe t h eSuperior Superiorcraton c r a t o represent n r e p r e s e nthe t th e Penokean Orogeny. Dozens Dozens theArchean Archean and and Early Early u l t r a m a f i cbodies bodiesoccur occuralong alongthe t h boundary e boundarybetween between the of ultramafic of Proterozojc Proterozoic rocks rocks in i nCentral C e n t r a Wisconsin. l Wisconsin. In In addition a d d i t i o n to t onumerous numerous sulfide sulfide occurrences both Early Early PProterozoic n both r o t e r o z o i c ssuccessions, u c c e s s i o n s , aatt least l e a s tfour four occurrences (mostly (mostly ssmall) m a l l ) iin l o c a l i t i e swith w i t hsignificant s i g n i f i c a ngold t gold m i n e r a l i z a t i o nare a rknown e known in i nthe t h eproposed proposed localities mineralization collision c o l l i s i o nzone zoneini nCentral C e n t r aWisconsin. l Wisconsin. A of Early Early Proterozoic Proterozoic igneous igneousaactivity A third t h i r d and and youngest youngest ccycle y c l e of c t i v i t y is is represented represented by which unconformably unconformablyo overlie by rhyolites r h y o l i t e sat aWausau t Wausauand andCary CaryMound Mound which v e r l i e tthe h e older older sequences, are a r e gently g e n t l yfolded foldedabout aboutaxes axesplunging plunging100_200 10~-20Owest, west, arid and are a r e virtually virtually sequences, unmetamorphosed. r o c k s ~ w e l d e dt tuffs, u f f s , lahars, l a h a r sand , and flow-banded rhyolites-— rhyolites~ unmetamorphosed. These These rocks-—welded flow—banded a r e typical t y p i c a lcaldera c a l d e rtype a type rocks analogous o basin-and-range volcanic rocks in i n the the are rocks analogous to tbasin—and—range volcanic rocks Western Western United United States. S t a t e s . The rocks may The basin—and—range basin-and-range rocks may be be r e lrelated a t e d t otorrifting. ifting. Later of tthe River bbatholith Later faulting f a u l t i n gand andemplacement emplacement of h e Wolf Wolf River a t h o l i t h and and related related syenites s y e n i t e s during during the t h eMiddle Middle Proterozoic P r o t e r o z o i c has has further f u r t h e r complicated complicated the t h e geology. geology. 25 �________ 4 EXPLANATION EXPLANATION j — M I D D L E PROTEROZOIC PROTEROZOIC MIDDLE II.+l.+ + +f4. 90 E A R L Y PROTEROZOIC PROTEROZOIC EARLY Q R A N I T E AND A N D SYENITE SYENITE GRANITE [ A NO RTHO SITE QUA QUARTZITE RHYOLITE GRANITOID ROCKS [ii ARCHEAN ARCHEAN GREENSCHIST FAdES v0LCANIcS 777,,,,, QUARTZOFELDSPATHIC Q U A R T Z O F E L D S P A T H I C ONEISS QNEISS n I ii Q N E I S S , GREENSTONE QREENSTONE GNEISS, A N D GRANITE QRANITE AND 11111lllliIii1 Geological map map of of the t h e Precambrian Precambrian of of north n o r t h central c e n t r a l Wisconsin Wisconsin F i g u r e 1. 1. Geological Figure showing showing the t h e fault-bounded fault-bounded blocks blocks of of greenschist-facies g r e e n s c h i s t - f a c i e s volcanic volcanic rocks rocks alternating a l t e r n a t i n g with with amphibolite-facies a m p h i b o l i t e - f a c i e s volcanic v o l c a n i c rocks r o c k s and and the t h e Archean Archean rocks rocks to t o the t h e south. south. 26 26 �NORTH SOUTH // ——-1 SLANO ARC RNCH PLA1ORM SEIUENTS -— ANIMIKIE BASIN ,OCEAN CRUST — _. A B C ANIMIKIE SEDIMENTS - + + D Figure Figure 2. 2. . ++* ,—- -—- —.-----— — _s..—..— .-...-C - - —s.-.. — — —_. _ _.C + +4*4** + QMCS COLLISION GLL, I94 Block diacrransi lillustrating Elock diaqrams l u s t r a c i n q iie LISossth1e ~ 3 0 s s i bsequence l e sec;usnce of ofeven-as svencs in in the early tile e a r l y Proterocoic Proterozoic in i nWisconsin. \iisconsin. A. A. Developnt Development of of an anisland i s l a n darc a r cover overa anorth-dipping north-dipping subduction subduction offshore Platform sediments zone o f f s h o r e from the t h e Superior Superior Craton. Craton. Platform sediments formed ont the margin of of tthe formed on h e ppassive a s s i v e margin h e Superior Superior Craton. Craton. (Volcanic succession I.) I.) (Volcanic succession B. B. Archean craton c r a t o n from from the the' south south collides c o l l i d e s with the t h e island i s l a n d arc. arc. Continent-margin igneous activity C a c t i v i t y over a south-dipping south-dipping C.* Continent-margin basin subduction zone as a s the t h e ocean b a s i n on the t h e north n o r t h side s i d e of of the the island succession II, greenschist i s l a n d arc a r c closes. closes. (Volcanic succession 11, g reenschist facies f a c i e s rocks.) rocks. 1 D. D. C o l l i s i o n of t h e island i s l a n d arc a r c with the the p l a t f o r m sediments sediments and and Collision of the platform I11 - caldera—type caldera-type t h e Superior Craton. Craton. (Volcanic succession III the volcanics v o l c a n i c s in i n central c e n t r a l Wisconsin.) Wisconsin.) - 27 27 �Geology of of the t h e Lone Lone Mountain Mountain Gold Gold Prospect, P r o s p e c t , Northeast Northeast Nevada Nevada Geology MACKOVJAK and and JOSEPH JOSEPH MkNCIJSO WCUSO (Dept. Bowling Green Green DENNIS MACKOVJAK DENNIS (Dept. of of Geology, Geology, Bowling OH 43LO3) 43403) S t a t e University, U n i v e r s i t y , Bowling Bowling Green, Green, OH State The Lone Lone Mountain Mountain gold gold prospect prospect is i s located l o c a t e d in i n the t h e Independence Independence Range Range The of northeastern n o r t h e a s t e r n Nevada. Nevada. It It lies l i e s within w i t h i n the t h e Arseniéal A r s e n i c a l Gold Gold Belt Belt of of of C a r l i n y Getchell G e t c h e l l and and FMC—Freeport FMC-Freeport epithermal deposits d e p o s i t s along along with w i t h the t h e Carlin, epithermal mines (Fig. (Fig. 1). 1). mines Rock exposed exposed on on Lone Lone Mountain Mountain include: i n c l u d e : Ordovician Ordovician aflocthonous allocthonous Rock Silurianeugeosynclinal c h e r t s and s h a l e s (western f a c i e s rocks eueosynclinal cherts and shales (western facies rocks); ; Silu.rian— Devonian autocthonous miogeosynclinal Roberts Mountains Formation Devonian autocthonous miogeosynclinal Roberts Mountains Formation limestones ((eastern e a s t e r n ffacies a c i e s rrocks); o c k s ) ; and a r i o u s Tertiary T e r t i a r y intrusive i n t r u s i v e and and lixnestones and v various volcanic r o c k s y i n c l u d i n g t h e Nannies' Peak q u a r t z monzonite which forms volcanic rocks, including the Nannies' Peak quartz monzonite which forms t h e crest c r e s t of of Lone Lone Mountain. Mountain. the v a r i e t y of of siliceous s i l i c e o u s rocks rocks termed termed "jasperoids" " j a ~ p e r o i d s occur 'occur ~ w i t h i n the the AA variety within limestone beds beds of of the t h e Roberts Roberts Mountains Formation on on Lone Lone Mountain Mountain and and limestone Mountains Formation arsenic, g o l d y mercury, mercuryy arsenic, a r e associated a s s o c i a t e d with w i t h anomalous anomalous concentrations c o n c e n t r a t i o n s of of gold, are antimonyy and and thallium. t h a l l i u m . Field F i e l d and and laboratory l a b o r a t o r y investigation i n v e s t i g a t i o n by by the the antimony, authors identified i d e n t i f i e d four four types types of of jasperoids: j a s p e r o i d s : 1) 1)sandy sandy jasperoids, Jasperoids, authors which are a r e cavity c a v i t y filling f i l l i n g rocks rocks that t h a t consist c o n s i s t primarily p r i m a r i l y of of quartz q u a r t z sand sand which 2 ) fine-grained j a s p e r o i d s which a r e c a v i t y f i l l i n g rocks ; g r a i n s grains; 2) fine-.grained jasperoid.s, which are cavity filling rocks t h a t are a r e laminated laminated and and consist c o n s i s t primarily p r i m a r i l yofofsilt— s i l t -and. and clay—size c l a y - s i z e quartz quartz that g r a i n s ; 3 ) s i l i c i f i e d limestone j a s p e r o i d s , which a r e limestones in grains; 3) silicified limestone jasperoids, which are limestones in 4) J a s p e r o i d b r e c cias, which c a l c i t e has been replaced by q u a r t z ; a n d y which calcite has been replaced by quartz; and, ) jasperoid breccias, or which a r e c a v i t y f i l l i n g b r e c c i a s t h a t c o n s i s t o f fragments of any, which are cavity filling breccias that consist of fraents of any, or a l l of t h e p r e v i o u s l y l i s t e d rock t y p e s . Sandy j a s p e r o i d s , fine-grained all of the previously—listed rock types. Sandy jasperoids, fine-grained ( t h e "cavity " c a v i t y filling f i l l i n g jasperoids") j a s p e r o i d s " ) are are j a s p e r o i d s , and and jasperoid j a s p e r o i d breccias b r e c c i a s (the jasperoids, d e t r i t a l rocks t h a t occupy complex networks of s o l u t i o n c a v i t i e s and detrital rocks that occupy complex networks of solution cavities and f r a c t u r e s in i n the t h e coarse—grained coarse-grained limestone l i m e s t o n e of of the t h e Roberts Roberts Mountains Mountains fractures and/or interconnected i n t e r c o n n e c t e d bodies bodies as a s much much Formation. They They occur occur as a s isolated i s o l a t e d and/or Formation. a s one one thousand thousand feet f e e t in i n length. l e n g t h . Silicified S i l i c i f i e d limestone limestone jasperoids j a s p e r o i d s occur occur as i r r e g u l a r l y shaped shaped zones zones up up tto o thirty t h i r t y feet f e e t in i n length l e n g t h which which are are a s irregularly as adjacent to t o cavity c a v i t y filling f i l l i n g jasperoids. j asperoids adjacent . 'The solution s o l u t i o n cavities c a v i t i e s which which host h o s t the t h e cavity c a v i t y filling f i l l i n g jasperoids j a s p e r o i d s were were The formed and f i l l e d by k a r s t processes a f t e r t h e emplacement of t h e formed and filled by karst processes after the emplacement of the Nannies1 Peak Peak Intrusive. I n t r u s i v e . The The ddetritaJ. e t r i t a l qquartz u a r t z ggrains r a i n s iin n the t h e karst karst Nannies' c a v i t i e s were d e r i v e d from t h e coarse-grained l i m e s t o n e s of t h e Roberts Roberts cavities were derived from the coarse—grained limestones of the Mountains Formation. Mountains Formation. Multiple waves waves of of epithermal epithermal fluids, f l u i d s , related r e l a t e d to t o the t h e late l a t e Tertiary T e r t i a r y to to Multiple Recent igneous igneous system system on on Lone Lone Mountain, Mountainy moved moved preferentially p r e f e r e n t i a l l y through through Recent t h e filled f i l l e d solution s o l u t i o n cavities c a v i t i e s and and other o t h e r permeable permeable zones zones in i n the t h e Silurian— Silurianthe Devonian Roberts Roberts Mountains Mountains Formation. Formation. These These fluids f l u i d s deposited d e p o s i t e d early e a r l y and and Devonian l a t e calcite c a l c i t e in i n veins, v e i n s , silicified s i l i c i f i e d the t h e cavity c a v i t y filling f i l l i n g jasperoids j a s p e r o i d s and and late p o r t i o n s of of the t h e Roberts Roberts Mountains Mountains Formation Formation limestone, l i m e s t o n e , and and deposited deposited portions f i n e l y disseminated disseminated gold, g o l d y plus p l u s mercury, mercury, arsenic, antimony, and andthallium. thallium. a r s e n i c , antimony, finely We conclude conclude from from aa review review of of the t h e chronology chronology of of geologic geologic events events that that We have a f f e c t e d Lone Mountain t h a t t h e l o c a t i o n and d i s t r i b u t i o n of have affected Lone Mountain that the location and distribution of epithermal gold, g o l d y arsenic, a r s e n i c y antimony, antimonyy thallium t h a l l i u m and and accompanying accompanying epithermal 28 �silicification s i l i c i f i c a t i o n are a r e controlled c o n t r o l l e d more more by by the t h e "plumbing ''plumbing system" systemf1than t h a n by by the rocks in which they are found. t h e rocks i n which t h e y a r e found. The The epithermal e p i t h e r m a l fluids f l u i d s which which have have altered a l t e r e d and and mineralized mineralized the t h e rocks rocks of of Lone Lone Mountain Mountain are a r e related r e l a t e d to t o late late Tertiary T e r t i a r y to t o Recent Recent igneous igneous activity; a c t i v i t y ; however, the t h e mineralized m i n e r a l i z e d rocks rocks are are lower lower Paleozoic. Paleozoic. This This conclusion conclusion recognizing r e c o g n i z i n g the t h e importance importance of of the the "plumbing ffplumbingsystem" system1' rather r a t h e r than t h a n host h o s t rocks has serious s e r i o u s implications i m p l i c a t i o n s when vhen exploring for disseminated gold whether in Nevada or the exploring f o r disseminated in o r t h e Precambrian Precambrian volcanic—sedimentary volcanic-sedimentary terraines t e r r a i n e s of of the t h e Lake Lake Superior S u p e r i o r region. region. ' I '4 '4 '4 '4 '4 PANAMfl4T CITY, CSIILL,...' BALLARAT. CaflL-1— '——I Figure Figure 1. 1. Arsenical Arsenical gold gold belt belt of of Nevada Nevada (Modified from Joralemon, Joralernon,1978) 1978) (Modified from xx •e * * Lone Lone Mountain Mountain prospect prospect Gold Gold deposits deposits Conmiunities Communities 29 �Geology of of the t h e Groveland Groveland Mine, Minef Felch District, D i s t r i c t , Michigan Michigan JOSEPH ROBERT BROWNI BROWN, JAMES JAMES HAmSON, HARRISON, ALAN JOSEPH MANCtJSO, MANCUSOI ROBERT ALAX MAHARIDGE, WAR1DGEf RICHARD RICHARD PENNINGTON, PEN'NINGTONI RONALD RONALD WALDEN WALDEN (Dept. (Dept. of Geology, Bowling Bowling Green Green State OH 43403) 43403) S t a t e University, U n i v e r s i t y f Bowling Bowling Green, Green, OH The Groveland iron i r o n mine is is located l o c a t e d within w i t h i n the t h e Felch Felch Trough Trough in i n Central C e n t r a l Dickinson Dickinson County, County, Michigan. Michigan. The The Middle Middle Proterozoic Proterozoic rocks exposed expased in i n the t h e mine mine are a r e the t h e Randville Randville Dolomite, the t h e Feich Felch rocks Formation, Formation, the t h e Vulcan Iron I r o n Formation, FormationI and the t h e "northside "northside schist." gabbro sill s i l l intrudes i n t r u d e s the t h e northside n o r t h s i d e schist, s c h i s t I and and two two s c h i s t . " A gabbro nearly vertical nearly v e r t i c a l granite g r a n i t e dikes d i k e s trending trending north—south north-south cut c u t the t h e entire entire sequence. sequence. These rocks rocks were were folded, folded, faulted, f a u l t e d I and metamorphosed metamorphosed to amphibolite facies f a c i e s during during the t h e Penokean Penokean Orogeny. Orogeny. t o the t h e amphibolite The m metasedimentary exposed e t a ~ e d i m e n t a krocks ~ exposed in i n the t h e mine strike s t r i k e generally generally east-west east-west and dip d i p steeply s t e e p l y to t o the t h e north. north. James James et e t al. a l . (1961) (1961) and and Cumberlidge Stone (1964) (1964) concluded that t h a t the t h e Vulcan Iron Iron Cumberlidqe && Stone a s s y m e t r i c a l syncline syncline Formation Formation and surrounding surrounding rocks rocks form form aa tight, t i g h t , assymetrical More whose whose axial a x i a l plane plane dips d i p s to t o the t h e north n o r t h at a t approximately approximately 60°. 60° More recently r e c e n t l y (1978) (1978) the t h e Hanna Mining Company staff s t a f f proposed that t h a t the the rocks form aa faulted dipping ssteeply f a u l t e d inonocline monocline dipping t e e p l y to t o the t h e north n o r t h and and that c o r r e l a t i v e to t o the t h e Feich Felch t h a t the t h e "northside " n o r t h s i d e schist" s c h i s t " is not correlative Formation. Our (BGSUI 1982-84) 1982-84) suggests s u g g e s t s aa much much more more Our work in i n progress p r o g r e s s (BGSU, complex a array of rray o f faults f a u l t s and folds f o l d s to t o account for f o r the t h e repetition repetition of beds and the t h e apparent doubling in i n thickness t h i c k n e s s of of the t h e iron iron formation at a t the t h e mine mine site. site. formation Several Several faults f a u l t s are a r e clearly c l e a r l y visible v i s i b l e in i n the t h e mine. mine. The The east east i s bounded by a major fault f a u l t which strikes s t r i k e s NW—SE NW-SE he p i t is end of of tthe pit and dips d i p s steeply s t e e p l y to t o the t h e SW. SW. At A t this t h i s fault f a u l t the t h e iron i r o n formation formation terminates terminates abruptly a b r u p t l y against a g a i n s t Randville Randville Dolomite. Dolomite. Also, Also, aa set s e t of of faults E-W pparallel dip a r a l l e l tto o tthe h e iiron r o n formation and d ip f a u l t s sstrike t r i k e E-W f a u l t s offset o f f s e t the t h e granite g r a n i t e dikes dikes approximately vertically. v e r t i c a l l y . These faults and and appear to t o have right r i g h t lateral l a t e r a l and and normal normal components. components. A complex series s e r i e s of of nearly n e a r l y isoclinal i s o c l i n a l folds f o l d s is i s clearly c l e a r l y exposed exposed in of Randville Dolomite i n the t h e southwest southwest wall w a l l of of Dolomite in i n an outcrop of the t h e pit. p i t . This T h i s pattern p a t t e r n of of isoclinal i s o c l i n a l folding f o l d i n g may may be be characteristic characteristic of the t h e deformation of of all a l l the t h e metasedimentary units u n i t s in i n the t h e Feich Felch Trough. i s currently c u r r e n t l y in i n progress at a t the t h e mine mine and and Trough. More More work is elsewhere in Felch Trough in order tto better define i n tthe h e Felch i n order o b etter d e f i n e the t h e overall overall structure. structure. 30 - �References References James, H. L., L . , Clark, Clark, L. L. D., D . , Lamey, Lamey, C. C. A., A . , and and Pellijohn, P e l l i j o h n , E. E . J., J., James, H. 1961, in i n collaboration c o l l a b o r a t i o n with with Freedman, Freedman, J., J., Trow, Trow, J., J., and and 1961, K., Geology Geology of of central c e n t r a l Dickinson DickinsonCounty, County, Michigan: Michigan: Wier, K., Wier, U.S. Geol. Geol. Survey Survey Prof. Prof. Paper Paper 310, 310, 176 176p. p. U.S. Cumberlidge, J. J. T., T., and and Stone, Stone, J. J. G., G., 1964, 1964, The TheVulcan Vulcan IronIronCumberlidge, formation at a t the t h e Groveland GrovelandMine, Mine, Iron I r o n Mountain, Mountain, Michigan: Michigan: formation Econ. Geol., Geol., v. v. 59, 59, p. p. 1049—1106. 1049-1106. Econ. Birak, Birak, Donald Donald 3., J., 1978, 1978, Mineralogy Mineralogy and and petrology petrology of of the t h e Middle Middle Precambrian Precambrian rocks, rocks, Groveland g rove land Iron I r o n Mine, Mine, Dickinson Dickinson County, County, M.S. thesis, t h e s i s , Bowling Bowling Green GreenState State Msch.: Unpublished Unpublished M.S. Mich.: University, Bowling Bowling Green, Green, Ohio Ohio 43403, 43403, 149 149p. p. University, 3' �P o t a s s i u m Metasomatism Metasomatism of of Trondhjemite TrondhjemiteMigrnatite Miqmatite Walirock, Wallrock, Potassium V e r m i l i o n Complex, N o r t h e r n Minnesota Vermilion Complex, Northern Minnesota A . MARIANO MARIANO (Department (Department of of Geology, Geology, Beloit B e l o i t College, College, A. W I 53511) B e l o i t , Beloit, WI 53511) H . H . WOODARD WOODARD (Department (Department of of Geology, Geology, Beloit B e l o i t College, College, H.H. W I 53511) B e l o i t , Beloit, WI 53511) E x t e n s i v e collecting c o l l e c t i n g of of migmatite m i q m a t i t e walirock w a l l r o c k in i n the t h e southsouthExtensive e a s t e r n c o n t a c t zone of t h e Vermilion B a t h o l i t h h a s been eastern contact zone of the Vermilion Batholith has been c a r r i e d out o u t over o v e r the t h e past p a s t six s i x years y e a r s by by the t h e Beloit B e l o i t College College carried Department of of Geology. Geology. Potash P o t a s h feldspar f e l d s p a r distribution d i s t r i b u t i o n was was Department from the t h e Fourtown Fourtown Lake, Lake, Friday F r i d a y Bay, Bay, s t u d i e d in i n specimens specimens .from studied and Basswood Basswood Lake Lake West W e s t quadrangles q u a d r a n g l e s through through J a c k f i s h Lake, Lake, and Jackfigh f e l d s p a r staining, s t a i n i n g , cathodoluminescence, c a t h o d o l u m i n e s c e n c e , and and petrographic petrographic feldspar t e c h n i q u e s . The The specimens specimens investigated i n v e s t i g a t e d were were collected collected techniques. Granitefrom the t h e three t h r e e major major map map units u n i t s of of the t h e study s t u d y area. a r e a . Granitefrom (Mb) r i c h m i g m a t i t e (Mg) and b i o t i t e s c h i s t r i c h m i g m a t i t e(Mb) rich migmatite (Mg) and biotite schist-rich migmatite d i f f e r o n l y i n p e r c e n t a g e of g r a n i t i c m a t e r i a l (leucosome) differ only in percentage of granitic material (leucosome) r e l a t i v e to t o biotite b i o t i t e schist s c h i s t (paleosome). ( p a l e o s o m e ) . Leucocratic L e u c o c r a t i c biotite biotite relative i s t h e r o c k t y p e of t h e Vermilion b a t holith. a d a m e l l i t e (La) adamellite (La) is the rock type of the Vermilion batholith. The paleosome paleosome and and selvage s e l v a g e layers l a y e r s of of the t h e migmatites m i g m a t i t e s are are The ddevoid e v o i d of o f potash p o t a s h feldspar. f e l d s p a r . The The leucosomes leucosomes are a r e of of two two differdiffere n t r o c k t y p e s , t r o n d h j e m i t e and a d a m e l l i t e , depending on ent rock types, trondhjemite and adamellite, depending on amount of o f potash p o t a s h feldspar f e l d s p a r present. p r e s e n t . Leucosome Leucosome composition composition amount i s illustrated i l l u s t r a t e d in i n Fig. F i g . 1. 1. The The distribution d i s t r i b u t i o n of of the t h e potash potash is i s very v e r y selective s e l e c t i v e and andof' of a a non—gradational n o n - g r a d a t i o n a l nature. nature. ' ffeldspar e l d s p a r is T e x t u r a l relationships r e l a t i o n s h i p s indicate i n d i c a t e replacement r e p l a c e m e n t of of plagioclase plagioclase Textural i s late l a t e and and by potash p o t a s h feldspar. f e l d s p a r . Quartz Q u a r t z in i n the t h e leucosomes leucosomes is by r e p l a c e s the t h e feldspars. f e l d s p a r s . In I n the t h e field,the f i e l d , t h e pink p i n k adamellite adamellite replaces can be be seen s e e n cross c r o s s cutting c u t t i n g and and invading i n v a d i n g the t h e light l i g h t grey grey can t r o n d h j e m i t e l a y e r s and v e i n s . trondhjemite layers and veins. Specimens from from the t h e area a r e a mapped mapped as a s the t h e southeastern s o u t h e a s t e r n border border Specimens of t h e Vermilion b a t h o l i t h (La) show some c o m p o s i t i o n al of the Vermilion batholith (La) show some compositional l a y e r i n g w i t h r e s p e c t t o p o t a s h f e l d s p a r , a l t h o u g h t h e potash layering with respect to potash feldspar, although the potash i s much more uniform t h a n i n t h e f e l d s p a r d i s t r i b u t i o n feldspar distribution is much more uniform than in the leucosomes of of the t h e migmatites. m i g m a t i t e s . Textural T e x t u r a l relationships r e l a t i o n s h i p s indicate indicate leucosomes r e p l a c e m e n t of p l a g i o c l a s e by p o t a s h f e l d s p a r . replacement of plagioclase by potash feldspar. F i e l d and and laboratory l a b o r a t o r y evidence e v i d e n c e suggests s u g g e s t s that t h a t the t h e original original Field leucosome of of the t h e migmatite m i q m a t i t e walirock w a l l r o c k of of the t h e Vermilion Vermilion complex complex leucosome t r o n d h j e m i t i c . Later, L a t e r , through t h r o u g h potassium p o t a s s i u m metasomatism, metasomatism, was all a l l trondhjemitic. was much of of the t h e trondhjemitic t r o n d h j e m i t i c leucosome leucosome was was converted c o n v e r t e d to t o adamellite. adamellite. much The o r i g i n of some of t h e q u a r t z i n t h e s e m i g m a t i t e s may be The origin of some of the quartz in these migmatites may be the metasomatic p o t a s h f e l d s p a r . r e l a t e d t o t h e o r i g i n of related to the origin of the metasomatic potash feldspar. The rocks r o c k s mapped mapped as a s the t h e southeastern s o u t h e a s t e r n border b o r d e r of of the t h e Vermilion Vermilion The b a t h o l i t h show t h e same metasomatic r e l a t i o n s h i p s a the batholith show the same metasomatic relationships ass the m i g m a t i t e s , b u t on a more uniform b a s i s . I t i s p o s s i b l e that that migmatites, but on a more uniform basis. It is. possible t h e Vermilion b a t h o l i t h i t s e l f may have been a t o n a l i t i c o the Vermilion batholith itself may have been a tonalitic orr i n t r u s i o n which which was was later l a t e r transformed t r a n s f o r m e d to to t r o n d h j e m i t i c intrusion trondhjemitic a d a m e l l i t e through t h r o u g h extensive e x t e n s i v e potassium potassium metasomatism. metasomatism. If I f this this adamellite 32 �i s not n o t the t h e case, c a s e , than t h a n the t h e "batholith " b a t h o l i t h rocks" r o c k s " (La) ( L a ) examined examined is i n t h i s s t u d y a r e n o t t r u e b a t h o l i t h r o c k s b u t h i g hly in this study are not true batholith rocks but highly metasomatised ( g r a n i t i z e d ) w a l l rock. metasomatised (granitized) wall rock. A F i g u r e 1. 1. Plot P l o t of of the t h e relative r e l a t i v e percentages p e r c e n t a g e s of of modal modal quartz q u a r t z (Q), (Q), Figure a l k a l i f e l d s p a r ( A ) , and p l a g i o c l a s e (P) f o r t h e m i g m a t i t e alkali feldspar (A), and plagioclase (P) for the migmatite (La.). Percentages P e r c e n t a g e s are a r e plotted plotted leucosomes and and batholith b a t h o l i t hrocks r o c k s(La.). leucosomes on an I U G S c l a s s i f i c a t i o n t r i a n g l e . on an IUGS classification triangle. • - Trondhjemite leucosome leucosome Trondhjexnite - Adamellite leucosoe leucosome Adaxnelljte — £A — • Batholith rocks rocks -- Batholith 33 �LLate Archean Metamorphic Metamorohic Conditions - a t e Archean at at Granite G r a n i t e Falls, Fa11s ,Minnesota Minnesota - DAVIDP.P.MOECHER MOECHER (Dept. Geological Sciences, DAVID (Dept. Geological Sciences, U nUniversity i v e r s i t y ooff Michigan, Michigan, Ann Arbor, Arbor, Mi. Ann M i . 48109) 48109) L. GORDON MEDARIS, (Dept. Geology Geophysics, of L. GORDON MEDARIS, JR. JR. (Dept. Geology andand Geophysics, U nUniversity i v e r s i t y of Wisconsin-Madison, W i sconsi n-Madi son, Madison, Madison, Wi. W i 53706) 53706) . A detailed and bbarometric A d e t a i l e d geothermometric geothermometric and a r o m e t r i c iinvestigation n v e s t i g a t i o nhas hasbeen been completed Archeang granulite completed f ofor r Archean r a n u l i t e ffacies a c i e s gneisses gneisses aatt Granite G r a n i t e Falls, F a l l s , Mn. Mn. Garnetiferous and bbiotite-bearing G a r n e t i f e r o u s and i o t i t e - b e a r i n g variants v a r i a n t sofothe f t hhornblende-pyroxene e hornblende-pyroxene gneiss and ccordieritegneiss and o r d i e r i t e - and and orthopyroxene-bearing orthopyroxene-bearing vvariants a r i a n t s ooff the t h e gargarnet-biotite of oHimmelberg n e t - b i o t i t egneiss gneiss f Himmelberg(1968) (1968)contain contaia n number a numberofofassemblages assemblages ffor o r which which accurate accurate thermobarometric thermobarometric ccalibrations a l i b r a t i o n s have have recently r e c e n t l y been been calibrated. c a l ibrated. which occurs The composition composition ooff cordierite The c o r d i e r i t e(Mg/(Mg+Fe)=.80) (Mg/(Mg+Fe)=. 80) which r e q u i r e s metamorphic metamorphic cconditions o n d i t i o n s of of llocally o c a l l y in i n garnet-biotite g a r n e t - b i o t i t e gneiss gneiss requires approximately 710°C, 710°c 5.6kb, 5.6kb, and and X(H20)=.30 X(H20)=. SO (Lee (Lee and and Holdaway, Holdaway, 1977). 1977). Temperaturesoof 655°Cand and664 664°C havebeen been Temperatures f 65S° C have o bobtained t a i n e d f ofor r ccoexisting oexisting garnet g a r n e t and and clinopyroxene clinopyroxene (Ellis ( E l l i sand andGreen, Green, 1979) 1979) and and magnetite m a g n e t i t e and and ilmenite andLLindsley, i l m e n i t e (Spencer (Spencer and i n d s l e y , 1981), 1981) , in i n garnetiferous g a r n e t i f e r o u s hornblendehornblendeC o e x i s t i n g orthopyroxene orthopyroxene and n biobioandclinopycoxene clinopyroxenei in pyroxene gneiss. Coexisting pyroxene ttite-pyroxene i t e - p y r o x e n e ggneiss n e i s s yyield i e l d temperatures temperatures ffor o r clinopyroxene c l i n o p y r o x e n e consistentconsistently temperaturesf ofor l y around around 675°C 675 C ((Lindsley, L i n d s l e y , 1983), 1983), whereas whereas temperatures r oorthorthoGarnet, pyroxeneaare t o600°C. 600 C. Garnet, pyroxene r e l less e s s rreliable, e l i a b l e , ranging r a n g i n gfrom from500°C 500 C to ccordierite, o r d i e r i t e , and and biotite b i o t i t eini ngarnet-biotite g a r n e t - b i o t i t egneiss gneissexhibit e x h i b icomposit composittional i o n a l zoning zoning due due tto o partial p a r t i a l re—equilibration r e - e q u i l i b r a t i o n during d u r i n g cooling. c o o l i n g . The The rrims i m s of o f adjacent a d j a c e n t garnet g a r n e t and and cordierite c o r d i e r i t (Thompson, e (Thompson, 1976) 1976) and and garnet garnet and bbiotite and i o t i t e(Thompson, (Thompson, 1976, 1976, Ferry F e r r y and and Spear, Spear, 1978) 1978) yyield i e l dtempertemperwhereas cores oneg agarnet-cordierite aatures t u r e s of o f 620°C-630°C, 6 2 0 ~ ~ - 6 3C,0 whereas cores o fofone r n e t - c o r d i e r i t e ppair air yyield i e l d aatemperature temperature of o f660°C. 660 C. on the Pressure estimates based Pressure based on t h e assemblage assemblage orthopyroxenegarnet-plagioclase-quartz in garnet-plagioclase-quartz i ngarnetiferous g a r n e t i f e r o u shornblende-pyroxene hornblende-pyroxene gneiss (Bohlen gneiss (Bohlen and and oothers, t h e r s , 1983) 1983) and and garnet—biotite g a r n e t - b i o t i t e gneiss gneiss (Newton (Newton andPerkins, Perkins, 1982) 1982)l ilie and e iinn the t h e range range 4.7 4.7 to t o 5.3kb. 5.3kb. Application A p p l i c a t i o n of of barometer,based basedonont hthe Al-contentoof tthe h e orthopyroxene orthopyroxene barometer, e A1-content f oorthorthopyroxenei in pyroxene n eequilibrium q u i l i b r i u m with w i t h garnet g a r n e t (Harley ( H a r l e yand and Green, Green, 1982) 1982) is is pprohibited r o h i b i t e d for f o rthese thesegneisses gneisses because because ooff inappropriate i n a p p r o p r i a t e compositions. compositions. A A late l a t eArchean Archean metamorphic metamorphic geotherm geotherm of o f36°C/km 36Oc/km has has been been established e s t a b l i s h e d ffor o r the t h e gneisses gneisses aatt Granite G r a n i t e Falls, F a l l s , using u s i n gthe t h emost most reliable r e 1 i a b l eestimates estimatesofo temperature, f temperature,665°C, 665O~,based basedon on magnetite-ilrnenmagneti t e - i lmenite, i t e ,garnet-clinopyroxene, garnet-clinopyroxene,and andpyroxene pyroxenethermometry, thermometry, and and pressure, pressure, 5.0kb, on orthopyroxene-garnet-pl orthopyroxene-garnet-plagioclase—quartz 5. Okb, based based on a g i o c l ase-quartz e qequilibria. u i 1 ib r i a . Compared Compared t otoo tother h e r ggranulite r a n u l i t e terranes, t e r r a n e s , the t h emetamorphic metamorphic condicondittions i o n s at a t Granite G r a n i t e Falls F a l l s were were relatively r e l a t i v e l ylow lowini nterms termsofo temperature f temperature The ccalculated metamorphicgeotherm geotherm and pressure. The and a l c u l a t e d metamorphic i s is n onot t s isignifignifikyaniteccantly a n t l y different d i f f e r e n tfrom fromother o t h e rPhanerozoic Phanerozoic andalusitea n d a l u s i t e - and and kyanitesillimanite s i l l i m a n i t e facies f a c i e s series s e r i e s terranes. terranes. G r a n u l i t e facies f a c i e s conditions conditions Granulite mayhave havebeen beencaused caused same thermal regime may byby t hthe e same thermal regime t h that a t r eresulted s u l t e d iinn the Archean magmatism magmatism iin n the t h e southern southernCanadian Canadian t h e widespread widespread late l a t eArchean Shield. Shield. 3t �- Early Early Proterozoic P r o t e r o z o i c Geology Geology of of East-Central East-Central Minnesota Minnesota - AA Review Review and and Reappraisal Reappraisal G.E. G.B. MOREY MOREY and and DL. D.L. SOtJTHWICK, SOUTHWICK, Minnesota Minnesota Geological Survey, Survey, University University of of Minnesota, Minnesota, 2642 2642 University University Avenue, Avenue, St. St. Paul, Paul, Minnesota Minnesota 55114. 55114. Investigations I n v e s t i g a t i o n s by the t h e Minnesota Minnesota Geological Geological Survey Survey in i n east-central east-central Minnesota 15 years y e a r s have have shown shown that t h a t the t h e northwest northwest segment segment t h e past p a s t 15 Minnesota over over the of of the the Animikie Animikie basin b a s i n developed developed during d u r i n g early e a r l y Proterozoic P r o t e r o z o i c time t i m e over over and and approximately approximately parallel p a r a l l e l to to the the Great Great Lakes Lakes tectonic t e c t o n i c zone. zone. Although Although the the tectonic major Archean suture s u t u r e that t h a t clearly c l e a r l y remained remained an an imporimporis aa major t e c t o n i c zone zone is t a n t structural s t r u c t u r a l element element during during the t h e early e a r l y Proterozoic P r o t e r o z o i c evolution e v o l u t i o n of of the the tant Animikie is no no evidence evidence that t h a t the the zone zone ever e v e r defined defined aa Animikie basin, basin, there t h e r e is Proterozoic P r o t e r o z o i c continental c o n t i n e n t a l margin margin in i n Minnesota. Minnesota. Goldich 1961 were were the t h e first f i r s t to t o conclude conclude that that Goldich and and his h i s colleagues colleagues in i n 1961 the evolved through through an an eextensional t h e Aniinikie Animikie bbasin a s i n evolved x t e n s i o n a l sstage, t a g e , during which which stratified s t r a t i f i e d rocks rocks were were deposited, deposited, and and aa subsequent subsequent compressional compressional stage, stage, termed The Penokean Penokean deformation deformation was was viewed viewed by by termed the the Penokean Penokean orogeny. orogeny. The Goldich Goldich either e i t h e r to t o have have terminated terminated sedimentation, sedimentation, or o r to t o have have followed followed shortly s h o r t l y after a f t e r sedimentation sedimentation ceased. ceased. The The Penokean Penokean orogen oroqen can can be be divided divided into i n t o two two broad broad longitudinal l o n g i t u d i n a l zones zones on on the t h e basis b a s i s of of contrasting c o n t r a s t i n g styles s t y l e s of of deformation deformation and and grades grades of of metamorphism metamorphism -— aa northern northern stable stable zone zone and and aa southern zone termed termed tthe southern deformed deformed zone h e Penokean Penokean ffoldbelt. o l d b e l t . The The tectonic t e c t o n i c front front separating the two two zones zones coincides c o i n c i d e s with w i t h the the inferred i n f e r r e d northern n o r t h e r n edge edge of of s e p a r a t i n g the the the Great Great Lakes Lakes tectonic t e c t o n i czone zone in i nthe theArchean Archeanbasement, basement, and and isi smarked marked by by -- the t h e northern northern limit l i m i t of of aapenetrative p e n e t r a t i v ecleavage. cleavage. Little L i t t l edeformation deformation and and metamorphism occurred to the north n o r t h of of the the front, f r o n t ,whereas whereas south south of of metamorphism occurred t o the some some of of the the rocks rocks have have been been multiply m u l t i p l y folded folded and and metamorphosed. metamorphosed. it it Intrusive the orogen orogen include i n c l u d e small s m a l l to to moderate—size moderate-size plutons plutons I n t r u s i v e rocks rocks within within the of of late—tectonic l a t e - t e c t o n i c granodiorite g r a n o d i o r i t e and and sodic s o d i c granite, g r a n i t e , and and large l a r g e plutons p l u t o n s of of post—tectonic p o t a s s i c granite. g r a n i t e . Dikes, Dikes, sills, s i l l s , and and small s m a l l bodies bodies of of p o s t - t e c t o n i c potassic gabbroic, gabbroic, dioritic d i o r i t i cand and lamprophyric lamprophyric affinity a f f i n i t yalso a l s oare a r present e p r e s e nand t andwere were emplaced emplaced at a t different d i f f e r e n t times t i m e s throughout throughout the t h e evolution e v o l u t i o n of of the theorogen. orogen. Depositional ppatterns a t t e r n s rreflect e f l e c t contrasting c o n t r a s t i n g tectonic t e c t o n i c conditions c o n d i t i o n s in i n the the Depositional theAnimikie Animikie basin. basin. A northern and and southern southern segments segments of the northern A rrelatively e l a t i v e l y thin thin succession succession(2—3 (2-3 km) km) of of predominantly predominantly sedimentary sedimentary rocks rocks(Anirnikie (AnimikieGroup) Group) was w a s deposited deposited north n o r t h of of the the tectonic t e c t o n i c front, f r o n t , whereas whereas aa much much thicker t h i c k e r sucsucc e s s i o n (>6 ( > 6km) km) of of sedimentary sedimentary and ille cession and volcanic volcanic rocks rocks (Animikie (Animikie and and M Mule Lacs thefront. f r o n t . The Lacs Groups) Groups) was was deposited deposited south s o u t h of of the The depositional d e p o s i t i o n a l history history of these rocks rocks can can be be divided divided into i n t o five f i v ephases. phases. During During the the first f i r s t two two of these phases, phases, quartz—rich q u a r t z - r i c h rocks rocks derived derived from from source source areas a r e a s both both north n o r t h and and south south of of the t h e basin b a s i n were were deposited. deposited. In I n addition, a d d i t i o n , the the southern southern part p a r t of of the the basin b a s i n received received aa substantial s u b s t a n t i a l thickness thickness of of basic b a s i c volcanic volcanic rocks, rocks, carcarbonaceous bonaceous lutite, l u t i t e , and and iron—formation. iron-formation. During During the t h e third t h i r d phase, phase, aa variety variety of iron—formation iron-formation types types were were precipitated p r e c i p i t a t e d on on aa southward—facing southward-facing shelf, shelf, of the fourth f o u r t h phase phase represents r e p r e s e n t s aa transitional t r a n s i t i o n a l succession succession of of carcarwhereas the whereas bonaceous bonaceous lutite l u t i t e that t h a tformed formed as a s the the shelf s h e l ffoundered foundered into i n t odeep deepwater. water. During During the the last l a s t phase phase aa thick, t h i c k , southward—facing, southward-facing, flysch—like f l y s c h - l i k eclas c l a stic tic wedge wedge was was deposited deposited by by southward—flowing southward-flowing turbidity t u r b i d i t y currents. currents. 35 �The geologic history h i s t o r y outlined o u t l i n e d above above is i s broadly broadly comparable comparable with with that that of of the t h e Marquette Range Supergroup Supergroup in i n the t h e southeastern s o u t h e a s t e r n segment segment of of the the Animikie basin b a s i n in i n northern Wisconsin and and adjoining a d j o i n i n g Michigan. Michigan. Both sequences have sedimentological attributes a t t r i b u t e s similar s i m i l a r to t o those those of of Phanerozoic geosynclines and both can be best b e s t explained explained by by rifting r i f t i n g proproccesses e s s e s akin a k i n to t o those proposed to t o explain e x p l a i n the t h e opening opening of of aa Phanerozoic Phanerozoic protoceanic p r o t o c e a n i c basin. basin. However the t h e general g e n e r a l absence of structural s t r u c t u r a l and and litho— lithologic l o g i c evidence for f o r a cryptic c r y p t i c suture, s u t u r e , and and the t h e lack l a c k of of voluminous voluminous early early Proterozoic P r o t e r o z o i c volcanic v o l c a n i c rocks rocks like l i k e those those in i n the t h e Ladysmith—Rhinelander Ladysmith-Rhinelander volcanic v o l c a n i c belt b e l t of of northern Wisconsin raise r a i s e serious s e r i o u s problems for for paleogeographic reconstructions of ccentral Minnesota tthat con— r e c o n s t r u c t i o n s of e n t r a l Minnesota h a t iinvolve n v o l v e aa consuining suming ccontinental o n t i n e n t a l margin. However ssimilar imilar v o l c a n i c rocks may occur in in volcanic the subsurface subsurface of of Iowa Iowa and and southern Minnesota, Minnesota, and and their t h e i r absence absence from from ccentral e n t r a l Minnesota Minnesota may x p l a i n a b l e by e f t - l a t e r a l displacedisplacemaybebeeexplainable byaa major major lleft—lateral ment of of eearly Proterozoic age, perhaps concealed by the ment arly P r o t e r o z o i c age, t h e middle middle Proterozoic discontinuity P r o t e r o z o i c Midcontinent Midcontinent rift r i f t system. system. If I f such a d i s c o n t i n u i t y could could be i t would imply that t h a t the t h e volcanic rocks rocks of of north—central north-central demonstrated it Wisconsin and and the t h e rocks rocks of of the t h e Animikie Animikie basin b a s i n proper proper are a r e separate s e p a r a t e and and temporally discrete d i s c r e t e packages. packages. C o r r e l a t i o n s and paleogeographic rreconstructions e c o n s t r u c t i o n s aalso l s o aare r e hindered Correlations hindered by by an incomplete understanding of of the t h e deformational history h i s t o r y of of the t h e Penokean Penokean foldbelt. f o l d b e l t . For example T.B. T.B. Hoist Holst has shown shown that t h a t the t h e southern southern part p a r t of of i s characterized c h a r a c t e r i z e d by by an an t h e Penokean foldbelt f o l d b e l t in i n east—central e a s t - c e n t r a l Minnesota is the o l d e r "nappe—like" "nappe-like" structural s t r u c t u r a l geometry and aa superposed superposed younger younger older ""upright" u p r i g h t " sstructural t r u c t u r a l geometry, t h e "upright" " u p r i g h t " geometry geometry, whereas only the The iinferred n f e r r e d boundary boundary between between them them appears to occurs appears to o c c u r s tto o the t h e north. north. The s e p a r a t e rocks rocks of contrasting c o n t r a s t i n gmetamorphic metamorphic grade grade and and may may also a l s o correspond correspond separate tto o aa mappable break in i n aeromagnetic aeromagnetic data. data. Holst t e n t a t i v e l y concluded Hoist tentatively break was was the nose of of a major nappe—like nappe-like structure structure tthat h a t tthe h e sstructural t r u c t u r a l break during formed d u r i n g the t h e Penokean Penokean orogeny. orogeny. Alternatively, A l t e r n a t i v e l y , we u g g e s t t hthat a t the wessuggest th s t r u c t u r a l break break could could be be the t h e trace t r a c eofofa folded a f o l d e unconformity d unconformity beneath beneath the the structural Thomson Formation. The Thomson Formation. o s s i b l e presence presence in i n east—central e a s t - c e n t r a l Minnesota Minnesota of of The ppossible Proterozoic two eearly arly P r o t e r o z o i c successions separated s e p a r a t e d by aa major major pperiod e r i o d of folding of folding i s admittedly admittedly speculative. s p e c u l a t i v e . Nonetheless and metamorphism is Nonetheless it is now becoming obvious that t h a t the t h e evolution e v o l u t i o n of of the t h e Penokean Penokean foldbelt f o l d b e l t was was episodic w i t h alternating a l t e r n a t i n g periods of of compression and and periods p e r i o d s of of extenextene p i s o d i c with sion s i o n and sedimentation. sedimentation. Therefore we suggest s u g g e s t that t h a t the t h e Penokean Penokean orogeny orogeny should no longer longer be viewed viewed as a s a single s i n g l e event e v e n t sharply s h a r p l y marked marked in i n time. time. 36 �Metal].ogeny of the the Lake Lake Superior Superior Precambrian Metallo~env of Jr. M.G. M.G. MUDREY, MUDREY, Jr. (Wisconsin Geological and Natural History History Survey, Survey, 1815 University Avenue, Madison, Wisconsin 53706) 53706) J. J. KALLIOKOSKI KALLIOKOSKI (Department (Department of of Geology Geology and and Geological Geological Engineering, Engineering, Michigan Technological Technological University, University, Houghton, Houghton, Michigan Michigan 49931) 49931) For purposes purposes of of xnetallogenic metallogenic analysis, analysis, the the Lake Lake Superior Superior Precambrian Precambrian region region can can be be divided divided into into five five tectono—stratigraphic tectono-stratigraphic terranes: terranes: (1) (11 an an Archean an gneiss ~ n e i s s terrane terrane older older than than 3.0 3.0 Ga, Ga, and and (2) (2) an Archean Archean greenstone—granite sreenstone-granite terrane about about 2.7 2 * 7 Ca, Ga, the two two joined joined together together in in late late Archean time; an epicratonic cover on this Archean basement (3) time; (3) an epicratonic cover on this Archean basement of of an an Early Early Proterozoic Proterozoic iniogeoclina]. miogeoclinal assemblage assemblage and and associated associated epicratonic epicratonic rocks rocks (the (the Penokean Penokean orogen ororcen of of Minnesota—Michigan); Minnesota-Michigan); (4) (4) an Early Early Pro— Proterozoic assemblage terozoic eugeoclinal eugeoclinal assemblage of of intrusive and and extrusive extrusive rocks rocks with Archean with possible possible Archean basement basement (Wisconsin (Wisconsin inagmatic magmatic terrane) that that ! has aa cover cover of of intracratonic, intracratonic, an— anorogenic rhyolites, orogenic continental continental rhyolites, quartzites quartzites and and associated associated gran— granitic itic rocks rocks (Baraboo (Baraboo sepuence—4a) sequence-4a) and and is is intruded intruded at at 1.5 1.5 Ca Ga by by an— anorogenic orogenic alkalic alkalic granites granites (Wolf ( W a ..a River River seguence—4b); sequence-4b) ; and and (5) ( 5 ) aa Middle Middle Proterozoic Proterozoic (1.1 (1.1 Ga) Gal rift rift assemblage assemblage (Keweenawan (Keweenawan terrane— terraneMidcontinent Midcontinent rift rift system). system). - The The Early Proterozoic eugeoclinal Early Proterozoic eugeoclinal asassemblage attached the semblage was was attached to to the North North American American craton craton about about 1.85 1.85 Ca. Ga. The The Lake Lake Superior Superior craton craton has has L-.-..-..--. been stable been tectonically tectonically stable since since the Numbers the Keweenawan. Keweenawan. Numbers refer refer to to terranes. terranes. See See text. text. - 3' The The potential potential of of the the Archean Archean terrane terrane is is limited limited to to minor minor iron, iron, gold, gold, base base metals(?), metals(?), and and quality quality dimension dimension stone. stone. Greatest Greatest mineral mineral producproduction tion and and future future potential potential is is from from the the Proterozoic Proterozoic terrane. terrane. The Penokean Penokean orogen orogen contains contains the the major major iron—formations iron-formations in in aa basin basin in in The which the the sedimentary sedimentary fill fill thickens thickens southward southward from from about about 2,000 2,000 mm in in the the which Mesabi Mesabi and and Gogebic Gogebic iron iron ranges ranges on on the the northwest northwest to to about about 5,500 5,500 inm and and 8,000 8,000 inm in in the the Cuyuna Cuyuna and and Menominee Menominee ranges, ranges, respectively respectively The thinner thinner The sequences contain contain no no volcanic volcanic rocks, rocks, whereas whereas the the thicker thicker and and sedimento— sedimentosequences logically more complex miogeoclinal miogeoclinal sequences sequences south south of the the Mesabi Mesabi and and logically more complex east of of the the Gogebic Gogebic ranges ranges contain contain many many locally locally thick thick piles piles of of marine marine east tholejj.tic tholeiitic lavas. lavas. Other Other inetallogenic metallogenic settings on on the the Penolcean Penokean orogen orogen are related related to to Proterozoic Proterozoic unconformities unconformities and and subsequent subsequent epigenetic epigenetic enenare . . vironments. vironments. The The Wisconsin Wisconsin magmatic magmatic terrane, terrane, on on the the other other hand, hand, contains contains mineral mineral occurrences related related tà to both bothxuagntatism magmatism and temperature hydrothermal hydrothermal occurrences and high temperature deposition. deposition. Most Most important important are are the the massive massive sulfide sulfide deposits deposits along along aa belt belt of of fe].sic felsic to to intermediate intermediate calc—alkaline calc-alkaline volcanic volcanic rocks. rocks. These These 37 �bodies bodies exhibit exhibit many many similarities similarities to to the the Noranda— Noranda- and and Kuroko—type Kuroko-type ores ores including including general general form, form, mineral mineral zoning, zoning, disseminated disseminated footwall footwall mineralmineralization, and and mineralization mineralization succeeded succeeded by by aa period period of of sedimentation. sedimentation. ization, However, However, there there are are also also several several differences. differences. There There is is aa general general lack lack of of well well developed developed magnetic magnetic anomalies anomalies over over the the deposits deposits indicating indicating the the ababsence sence of of diagenetic diagenetic magnetite magnetite and and pyrrhotite; pyrrhotite; the the overlying overlying sediment sediment is is more a elastic than a chert; and although the major metal contents more a clastic than a chert; and although the major metal contents are are similar similar to to Archean Archean deposits, deposits, precious precious metal abundances abundances are are only only one—half one-half that that of of Canadian Canadian deposits, deposits, but but more similar similar to to those those in in Canadian Canadian Proter— Proter- ozoic deposits. deposits. ozoic Anorogenic Anorogenic sequences sequences include include the Baraboo, Baraboo, Wolf River River and and Keweenawan Keweenawan In In the the Baraboo Baraboo sequence sequence the the only only occurrences occurrences of of metallogenic metallogenic interest interest or or curiosity curiosity are are the the speculative speculative unconformity—related unconformity-related occuroccurrences rences of of uranium uranium and and the the minor, minor, thin thiniron—formations. iron-formations. The The Wolf Wolf River River sequence sequence contains contains minor minor occurrences occurrences of of U—Th, U-Th, REE, REE, and and possibly possibly Sn—W. Sn-W. By By contrast, the the Keweenawan Keweenawan is is aa copper—rich copper-rich province province and and contains contains major major contrast, stratiform stratiform. deposits deposits of native native copper copper in in basalts basalts and and interflow interflow congloconglomerates, merates, stratiform s t r a t i f o m deposits deposits of of copper copper sulfide sulfide in in black black shale, shale,. as as well well as Cu—Ni-(Co) Cu-Ni-(Co) concentrations concentrations in in the the basal basal part part of of the the Duluth Duluth Complex, Complex, as and Ti—V Ti-V concentrations concentrations in in melanogabbros melanogabbros of of the the Duluth Duluth Complex Complex and and and Mellen Intrusive. Intrusive. Mellen sequences. sequences. Some Some deposits deposits are are younger younger than than their their host host rocks rocks so so that, that, in in detail, detail, aa tectono-stratigraphic framework framework may may contain contain some some flaws. flaws. It It is is also also tectono—stratigraphic in some instances, younger epigenetic process have modified clear that that in some instances, younger epigenetic process have modified clear earlier earlier syngenetic syngenetic or or coeval coeval mineral mineral concentrations. concentrations. In In the the case case of of iron ores, ores, it it is is these these later later processes processes that that have have converted converted uneconomic uneconomic iron material material into into commercially comercially extractable extractable ores. ores. This study study was was undertaken undertaken to to set set the the mineral mineral deposits deposits in in this this region region This into into aa metallogenic metallogenic framework framework for for the the Lake Lake Superior Superior Precambrian Precambrian Volume Volume (DNAG). The DNAG DNAG text text will will ininof the the Decade Decade of of North North American American Geology Geology (DNAG). of clude abbreviated abbreviated descriptions descriptions of of the the more more important important mineral mineral deposit deposit clude types with with'data on past past or or current current production production (Keweenawan (Keweenawan copper; copper; Lake Lake types data on Superior iron iron ore) ore) or or on on reserves reserves or or resources resources Wisconsin Wisconsin zinc—copper; zinc-copper; Superior Minnesota Cu—Ni). Cu-Ni). Further, Further, the the tectono—stratigraphic tectono-stratigraphic framework framework allows allows Minnesota us to to propose propose metallogenic metallogenic settings settings for for still still other other kinds kinds of of mineral mineral us commodities, including including. Sn—W, Sn-W, diamonds, diamonds, petroleum, petroleum, and and Skellefta— Skellefta- and and commodities, Noril'sk-type nickel nickel occurrences. occurrences. Noril'sk—type 38 ��I Metamorphic Conditions and Evolution of a Supracrustal Sequence Intruded by the Dunbar Genesis, Florence and Morinette Counties, Northeastern Wisconsin PETER A. NIELSEN (Div. of Science, Univ. of Wis.-Parkside, Kenosha, Wi. 53141) A suite of lower Proterozoic graphitic-sulfidic metasediments and intercalated mafic to intermediate volcanics and volcaniclastics from Florence and Marinette Counties are described. The supracrustal sequence (Quinessic Fm of Dutton, 1971) is characterized by prograde metamorphic assemblages including: biotite-garnet-p I agioc lase-.quartz ± cordierite in metasediments, garnet amphibolites, and diopside-tremolite marbles. A late stage retrograde overprint is present in most samples studied to date. The most prevalent alteration includes: cordierite + pinite + sericite, garnet -. biotite + chlorite, and hornblende - actinolite + biotite ± chlorite. The local concentration of S in several horizons has led to the development of pyrite ± pyrhhotite with a loss of Fe from the silicate phases. The supracrustal sequence is intruded by pegmatites and quartz-.tourmaline veins analogous to those found within the Dunbar Gneiss Complex. The prograde assemblage suggests peak metamorphic conditions in the range 500-575°C at low to intermediate lithostatic pressure. The abundance of graphite, calcite, and pyrite ± pyrhhotite indicate that H2O <total and that CO2 and H2S were (at least on a local scale) major fluid components. Petrographic observations show an S1 foliation developed parallel to S0 bedding planes. A weakly developed S2 foliation developed during retrograde metamorphism and is defineciby second generation biotite. The S2 foliation is inclined to S1 by up to 900. Garnets in the graphitic-sulfidic pelites contain abundant oriented quartz inclusions producing a pseudo-tetragonal sector pattern. Occasional zoned plagioclase phenocrysts are preserved in the amphibiolites. The intruded Dunbar Gneiss ranges in composition from granite-granodiorite to biotite tonalite and locally contains abundant mafic inclusions. In many outcrops, the well foliated gneiss grades into migmatites. Multiple generations of pegmatite cut the Dunbar Gneiss and are highly deformed themselves. The gneiss displays a similar sequence of fabric develoment as that shown by the supracrustals (Sims, I 984, personal communication). Most of the samples discussed in this study were obtained from a series of diamond drill cores from the Bass Lake area, Florence County. These samples 'were made available by Kerr-McGee Corporation in Marquette, Michigan. Their cooperation is gratefully acknowledged. Dutton, C. E., 1971. Geology of the Florence Area, Wisconsin and Michigan, U.S.G.S. Professional Paper 633. '40 �- MOB Assemblage DataBase MOB -aa Metamorphic MetamorphicMineral Mineral Assemblage DataBasefor for the Precambrian the Lake LakeSuperior SuperiorDistrict District Precambrian ofofthe PETERA .A.NIELSEN NIELSEN (Divisionof of Science, PETER (Division Science, UW-Parkside, UW-Parkside, Kenosha, Kenosha, Wisconsin 53141) 53141) The MetamorphicDataBase DataBase(MDB) (MDB) databaseestablished established at i sisaa database a tUWUWThe Metamorphic Parksidedesigned designed facilitate the compilation, retrieval and Parkside t o tofacil i t a t e the compil ation, retrieval and subsequent plotting of data for for the subsequent plotting ofmetamorphic metamorphic mineral mineral assemblage assemblage data the consists of of two MOB consists two Precambrian Precambrianofofthe the Lake LakeSuperior SuperiorDistrict. District. MOB parallel LLOC data and other MLOC , one LLOCstoring storinglocation 1ocation data andthe the other MLOC para1 lel files, f i 1esone which contains containsaal list Relational Information which i s t of ofminerals minerals present. present. The The Relational Information ManagementSystem System(RIM) (RIM)supported supportedby by the the IBM used to Management IBM system system at a tUW—P UW-P i sis used to select user assemblages user specified specified 'critical' ' c r i t i c amineral l ' mineral assemblagesand andata tthe thesame same time retrieve corresponding LLOC LLOCcomponent. component. The retrievethethe corresponding The selected assemblages andcorresponding correspondinglocation locationdata data are are stored in an output i n an output assemblages and beprinted printed and andused usedasasinput inputt otoa aflatbed flatbedplotter plotter to ffile i l ewhich which may may be to producemaps mapsshowing. showing. arealdistribution distribution of produce thethe areal of specified speci fiedassemblages. assemblages. The relations between thevariables variables in in the The relations between the the LLOC LLOC f file i l e permit permit the the genergenerated ooutput u t p u t ffile i l e to to consist consist ofofdata data for fora asingle singlecounty, county,quadrangle, quadrangle, ated A complete sstate, t a t e , or or the theentire entireLake LakeSuperior SuperiorDistrict. District. A completeMOB MOB entry consists of line of of data consists of 22 componentscomponents- aa line of data datafor forLLOC LLOC and and aa column column of data inputconsists consistsofof an an identification identification number, for LLOC input number, county, county, forMLOC. MLOC. LLOC surfacesample,> sample,>0 depth core), latitude sstate, t a t e , depth depth ((0 0 == surface 0 = =depth i n in aa d rdrill i l l core), 1 a t i tude and longitude longitude (( degrees, degrees, minutes, minutes, and and seconds) seconds) age age of metamorphism metamorphism ( i(iff and known), termed ADINFO ADINFO which work known), and and aa string string termed whichindicates indicates the the type type of work which has has been beendone doneononthe thesample sample(thin (thinsection, section, microprobe data, bulk which microprobe data, bulk rock data, and contributor's name). rock chemical chemical data, and tth3 h i s contributor's name). The MLOC entry The MLOC entry consists of aa list thethe (equilibrium) mineral assemblage consists l i sof t of (equilibrium) mineral assemblageobserved observed in thin thin section sectionand and an an identification identificationnumber. number. Once the user mayselect select individual individual MDB, the user may Once aall l l data data are are entered entered into intoMOB, minerals or ccritical andobtain obtainaal list minerals or r i t i c a lmineral mineral pairs pairsororassemblages assemblages and ist of locations of locationswhere where the the specified specifiedassemblage assemblage occurs. occurs. I am am currently for the attempting to t o update update the theMetamorphic Metamorphic Mineral Mineral Assemblage Assembl age Map Map for the Lake Superior i s t r i c t(Morey, (Morey ,1978) 1978) incorporating incorporatingnew new data data and and Lake Superior DDistrict interpretations. IItt isi santicipated anticipated that that this this material material will will be be part part of aa contribution contributiontotothethe DNAG volume volume of the the Precambrian Precambrian of the Lake Lake DNAG of the SuperiorDistrict. District. AA sample s included i t h this Superior sampleinput inputform formi is included wwith abstract, and welcomeany any contributionsfor for inclusion abstract, and I would would welcome andand a l lallcontributions in MOB. MDB. in Morey, ., Metamorphism Metamorphism ininthe U .S .A. ,and and Morey, G.B G.B., theLake LakeSuperior Superiorregion, region, U.S.A., o crustal evolution; in Metamorphismofofthe theCanadian Canadian iits t s relation relationtot crustal evolution; in Metamorphism Shield,Geol. Geol .Surv. Surv.Can., Can.Paper , Paper 78-10,p.283—314, p .283-314, 1978 1978 Shield, 78—10, 4]. �L o c a t i o n ffile: ile: Location - LLOC County County ILOC 1 2 2 1 FLO FLO FLO FLO State State Depth Depth WI WI WI WI 140 .O 140.0 0. 0. Latitude Latitudeu 45 45 45 45 46 46 49 49 ' " 37.5 37.5 50.5 50.5 - Longitude " Longitude 88 88 22 5.2 22 5.2 88 17 88 5.2 17 5.2 ' SI I' Age Age PEN PEN PEN PEN ADINFO ADINFO IS TSPAN PAN IS TSPAN PAN M i n e r a l ffile: ile: Mineral MhOC MIiOC L i s t of o f minerals m i n e r a l s present p r e s e n t (( List no nomaximum) maximum) ifi fthe t h sample e sampleis i polymetamorphic, s polymetamorphic,It Is i trecommende1lhat i s recommendeflhat separate n codesand andages ages be b eassigned, assigned, along along separate identification i d e n t i f i c a t i ocodes with w i t h separate s e p a r a t e mineral mi n e r a l assemblage assemblage 1listings. is t i n g s . p t)* and LLOC LIOC are MLOC and r e iintegers n t e g e r sand and are a r e equal equal for f o r each each sample sample i In n tthe h e ffile i l e (MLOC=LLOC), (MLOC=LLOC), MLOC MLOC and are MLOC andLLOC hOCaare assigned a t t h e t i m e t h e d a t a a r e e n t e r e d i n t o MOB. are entered into MDB. assigned at the time the data MLOC MIOC M i n e r a l s present present Minerals QTZ EPI EPI IRE TRE CAL CAL 11 QTZ 22 BIO GAR GAR CTD CTD CIII CHLQTZ QTZPLA PLA BlO �Basal Lower Lower Proterozoic Proterozoic Glaciogenic Glaciogenic Formations, Formations, Basal Marquette Supergroup, Superqroup, Upper Upper Peninsula, Peninsula, Michigan Michigan Marquette RICHARD W. W. OJAKANGAS OJAWGAS (Department (Department of of Geology, Geology, University University of of Minnesota, Minnesota, RICHARD MN 55812) 55812) Duluth, MN Duluth, Three b a s a l Proterozoic formations i n t h e Upper Peninsula of Michigan Three basal Proterozoic formations in the Upper Peninsula of Michigan - the t h e Reany Reany Creek, Creek, Enchantment Enchantment Lake, Lake, and and Fern Fern Creek Creek -- are a r e interpreted i n t e r p r e t e d to to - The strongest s t r o n g e s t evidence evidence for f o r aa glaciogenic glaciogenic have had had glacial g l a c i a l origins. o r i g i n s . The have h i s t o r y is oversized lonestones (many of which a r e c l e a r l y dropstones) dropstones) history is oversized lonestones (many of which are clearly iinn laminated laminated shale-siltstone s h a l e - s i l t s t o n e beds beds that t h a t are a r e associated a s s o c i a t e d with with diamictites. diamictites. They are a r e interpreted i n t e r p r e t e d to t o have have been been dropped dropped into i n t o glaciomarine glaciomarine or o r glacia— q- l a c i o They llacustrine a c u s t r i n e environments environments from from either e i t h e r icebergs i c e bergs or o r ice i c e shelves. shelves. Other Other rock types types within within the t h e three t h r e e formations formations include include graded graded && ungraded ungraded clastclastrock " 4 ltetm-a MA-& AS 4.L..--Ap-: L.Aw= w L LLL= a a ~ ~- - 2supported conglomerate, conglomerate, sandstone, sandstone, and and siltstone. supported Most of the sand—sized g r a i n s in i n all a l l the t h e rock rock types types are a r e quartz. q u a r t z . The The Fern Fern Creek Creek and and Enchantment Enchantment grains Lake formations formations pass pass upward upward into i n t o formations Â'ormations of of quartz—sand; quartz-sand; the t h e Reany Reany Lake Creek has has aa faulted f a u l t e d upper upper contact. c o n t a c t . Microscopic Microscopic till till pellets p e l l e t s are a r e present present Creek i n t h e dropstone u n i t s of t h e Rean ,y Creek Formation. in the dropstone units of the Reany Creek Formation. LuALG. a ~ ~ e ~ uz as much i L t u ~ ~ a=. NU, unconformably UAGO~LOI-IMKJLY The three t h r e e formations, formations, separated separated by The as~ 80oukin, o v e r l i e Archean Archean basement. basement. They !rhey may may be be correlative c o r r e l a t i v e with with each each other, o t h e r , or or overlie s t i l l lower Proterozoic u n i t . t h e Reany Creek may be a younger b u t the Reany Creek may be a younger but still lower Proterozoic unit. ilnits Several workers workers have have proposed proposed correlations c o r r e l a t i o n s of of one one or o r more more of of the t h e units Several with the with the Gowganda Formation (interpreted to be of glacial origin) of t h e Huronian Hurc the Supergroup, 200 kin to the east in Ontario. The dropstone 6 u n i t - diamictite unit association in each unit strengthens this correlation. Radiomet ,oup Radiometric ages are not available in Michigan, but the Huronian Supergroup has been been bracketed between 2500 and 2100 rn.y. If any of the Michigan units ,its has prove to t o be uc younger Y U U A Y ~ Z than UILne Ontario uncarzo.gLacLogenxc rormaclons, then m e n another another prove the glaciogenic formations, i s i n d i c a t e d . e a r l y Proterozoic g l a c i a l episode early Proterozoic glacial episode is indicated. - 43 �Stratigraphy of the Headwav—Coulee Hassive Massive Sulfide S t r a t i g r a p h y of t h e Headway-Coulee Sulfide Prospect, P r o s p e c t , Northern Onaman Lake Area, Area, NW X? Ontario Ontario STEVE OSTERBERG (Dept. Geology, U University Minnesota—Duluth, (Dept. of of Geology, n i v e r s i t y of of Minnesota-Duluth, MM Duluth, ANN 55812) Headway—Coulee massive ssulfide within The Eeadway-Coulee u l f i d e pprospect, r o s p e c t , situated situated w i t h i n the the Archean Wabigoon g greenstone within located w i t h i n an intensely i n t e n s e l y altered altered r e e n s t o n e bbelt, e l t , is located succession m a f i c and and ffei.sic e l s i c metavolcanic, m e t a v ~ l c a n i cand and ~ intrusive i n t r u s i v e rocks. rocks. s u c c e s s i o n of of inafic Detailed mapping aand have shown tthat D e t a i l e d mapping d ppetrographic e t r o g r a p h i c sstudies t u d i e s have h a t the t h e vvolcanic olcanic l i t h o l o g i c a l units. units. ssuccession u c c e s s i o n can bbee divided d i v i d e d into i n t o several s e v e r a l distinct d i s t i n c t lithological Pillowed, Pillowed, massive, massive, and and breccjated b r e c c i a t d mafia m a f i c flows flows form form tthe h e bbase a s e of of the the volcanic vary v o l c a n i c succession s u c c e s s i o n and and are a r e about about 1.2 1.2 kzn k m 'thick. t h i c k . Flows v a r y from from aphan— aphanand have have an an amygdaloidal amygdaloidal ccontent iitic t i c to t o porp'nyritic, p o r p h y r i t i c , and o n t e n t ranging from from 00 to to mafia with a f i c flows are a r e interfingered interfingered w i t h and overlain o v e r l a i n by by lamlam8 percent. percent. The m inated bedded ffelsic hydrovolcanic rrocks, i n a t e d tto o tthickly h i c k l y bedded e l s i c hydrovolcanic o c k s , which range from crystal—rich and llapilli— and bblock—size c r y s t a l - r i c h aash s h and a p i l l i - and l o c k - s i z e ttuffs u f f s to t o aassociated s s o c i a t e d debris debris flow deposits. d e p o s i t s . These grade laterally l a t e r a l l y into i n t o thin t h i n ash—sized ash-sized deposits d e p o s i t s concontaining up tto fragments which which aare thought to t a i n i n g up o 15 ppercent e r c e n t fragments r e thought t o represent r e p r e s e n t reworked eequivalents q u i v a l e n t s of of the t h e hydrovolcanic hydrovolcanic rocks. rocks. Overlying Overlying the t h e hydrovolcanic hydrovolcanic units are tot obrecciated, units a r e spherulitic, ~ p h e r u l i t massive i cmassive ~ b r e c c i a t e d ,quartz—feldspar q u a r t z - f e l d s p a r porphyritic porphyritic is some some llava a v a flows flows which which may may or o rmay may not n o t be b e flow banded. banded. The The ffelsic e l s i c unit u n i t is 100 meters tthick 100 meters h i c k and extends extends along along sstrike t r i k e for f o rapproximately approximately 44 km; km; i t is is ooverlain v e r l a i n by pillowed to t o massive massive mafia m a f i c lavas. l a v a s . An An extensive e x t e n s i v e polymictic polpictic debris d e b r i s flow d e p o s i t which o n t a i n s cclasts l a s t s of a f i c and falsic f e l s i c volcanic, volcanic, deposit which c contains of m mafia g r a n i t e , and iiron granite, formation is iinterfingered with horizon r o n formation nterfingered w i t h the t h e felsic felsic h o r i z o n and have iits of the is bbelieved e l i e v e d tto o have t s oorigin r i g i n tto o tthe h e southwest of t h e study s t u d y area. area. it C r y s t a l - r i c h laminated tuffs t u f f s and tthickly h i c k l y bedded f r a g m e n t a l rocks Crystal—rich bedded fragmental and aassociated s s o c i a t e d ddebris e b r i s flow e p o s i t s aare r e bbelieved e l i e v e d tto o be t h e products p r o d u c t s of of flow ddeposits be the hydrovolcanic hydrovolcanic eruptions. e r u p t i o n s . Such eruptions form tuff cones with deposi— eruptions tuff w i t h deposittional i o n a l products dependent upon water to t o magma mapa ratios. ratios. Slumping and products dependent reworking would i n e l y laminated i s t a l eequivalents q u i v a l e n t s of reworking would produce produce ffinely laminated ddistal of such deposits deposits. . �Alteration, Alteration* Paragenesis Paragenesis and and Age Age Associated Associated with with Native Native'Copper Covper Mineralization Mineralization of of the the Kearsarge Kearsarge Flow, Flow* Keweenaw Keweenaw Peninsula, Peninsula* Michigan Xichigan James Paces and Theodore Theodore J. Bornhorst (Dept. (Dept. of of Geol. && Geol. Geol. Engrg., Engrg.* James B. Paces Michigan Michigan Technological Technological University, University* Houghton, Houghton* MI MI 49931) 49931) The The Portage Portage Lake Lake Volcanics Volcanics consists consists of of aa thick thick sequence sequence of of Keweenawan Keweenawan tholeiitic basalts which which hosts hosts a tholeiitic flood flood basalts a dormant dormant billion—dollar billion-dollar native native copper copper district. district. The The Kearsarge Kearsarge flow flow is is aa thick thick(60 (60kin) h)ophitic ophitic to to porphyritic porphyritic basalt basalt which which contains contains aa major major ore—producing ore-producing amygdaloidal amygdaloidal flow to10 10in m thick. thick. Seven Seven mines mines worked worked the the Kear— Kearflow top top ranging ranging from from00to sarge amygdaloid along a strike km and prosarge amygdaloid strike distance of more than than 12 12 km duced over 2.3 copper, the 2.3 billion lbs. of refined copper, the third third largest largest lode lode in the the district. district. Scoiber Stoiber and and Davidson Davidson (1959; (1959; Econ. Econ. Geol., Geol.* v. v. 54, 54*p. p. in 1250—1460) 1250-1460) documented an irregular irregular but generally symmetric symmetric banding banding of of secondary secondary minerals minerals within within the the flow flow top: top: chlorite chlorite and and microcline microcline were were deposited earliest earliest and farthest farthest away from from the zone zone of of highest highest permeapermeability, bility* later later epidote epidote and and quartz quartz were were confined confined to to the the most most permeable permeable horizons, horizons, and and calcite calcite filled filled the the remaining remaining pore pore space. space. Samples Samples of of Kearsarge Kearsarge flow flow top from from poor—rock poor-rock piles of the the Wolverine Wolverine Mine Mine confirm confirm this this broad paragenesis paragenesis on on aa single single amygdule amygdule scale. scale. Vesicle Vesicle walls walls are are lined with a thin layer of chlorite followed by a band of hematitehematite— dusted dusted microcline microcline crystals crystals which which terminate terminate in in euhedral euhedral pyramids. pyramids. Centers amygdules are filled with a complex combination combination of bladed Centers of amygdules epidote epidote with lesser lesser amounts amounts of fibrous fibrous prehnite, prehnite* euhedral euhedral to to anhedral anhedral quartz, quartz* native native copper, copper, and fine—grained fine-grained masses masses of of poorly—crystallized poorly-crystallized layer-silicates. Anhedral Anhedral calcite calcite fills fills remaining remaining open open pore pore space. space. layer—silicates. Rb—Sr Rb-Sr isotopic isotopic data data were obtained obtained from from aa suite suite of of secondary secondary minerals minerals from the the Wolverine Wolverine Nine. Mine. Early microcline microcline and chlorite chlorite define define an an iso— isofrom chron chron with an an age age of of 1,051 1,051 ±2 15 15 Na Ma and and an an initial initial Sr Sr ratio ratio of of 0.7145. 0.7145. The The age age of of the the Keweenawan Keweenawan lavas lavas within within the the Lake Lake Superior Superior basin basin has has been been constrained by a variety of workers and is best estimated estimated at about about 1,110 (Van Schmus Schmus and and others, others* 1982; 1982; Gaol. Geol. Soc. SOC. Amer. her. Memoir Memoir 156, 156, 1,110 Ma (Van Ma after after the the peak peak Thus* mineralization mineralization occurred occurred about about 50 50 Ma p. 165—171). 165-171). Thus, p. of ignous igneousactivity activity but but probably probably during during the the later later stages stages of of sedimentary sedimentary infilling of of the the rift rift basin. basin. Later calcites calcites and epidote epidote contain contain virvirinfilling tually tually no Rb and and have have Sr Sr ratios ratios which which cluster cluster about about aa value value of of 0.704. 0.704. They do do not not fit fit the the microcline—chiorite microcline-chlorite isochron. isochron. The The mineralizing mineralizing They fluids were apparently characterized by fluids by different early and late Sr isotopic compositions. compositions. We We interpret interpret this this data data as as evidence evidence for for variable variable isotopic sized fluid fluid convection convection during during the the evolution evolution of of the the mineralization mineralization event. event.' Whole-rock major and trace trace element chemical chemical compositions compositions have have been been Whole—rock determined across across aa 19.5 19.5in m section section of of the the Kearsarge Kearsarge flow. flow. It It is is determined apparent that some elements elements such P,y Sc, such as P Sc* YY,y and Zr have remained immobile while others have experienced a dramatic draktic redistriredistrilargely immobile bution during during the the metamorphic metamorphic event. event. Mass Mass balance balance calculations calculations have have bution been performed in an attempt attempt to determine whether trace trace elements elements (K, (Ky Rby.Ca and Sr in in particular) have behaved under open or closed closed rereRb, distribution distribution conditions. conditions. These These results results will will be be presented. presented. L.5 �Localized i n Cavities Cavities of tJpside—Down Upside-Down Trilobite T r i l o b i t e Parts P a r t s in Localized Accumulations Accumulations of w i t h i n aa Silurian. S i l u r i a n Reef t Racine, within Reef aat Racine, Wisconsin RICHARD RICHARD A. A. PAULL PAULL (Department (Department of of Geological Geological && Geophysical Geophysical Sciences, Sciences, The W I 53201) 53201) The University U n i v e r s i t y of of Wisconsin—Milwaukee, Wisconsin-Milwaukee, Milwaukee, Milwaukee, WI Outcropping in Wisconsin Wisconsin and and adjacent a d j a c e n t states s t a t e s are are Outcropping Silurian S i l u r i a n reef r e e f cores c o r e s in generally of dolomite flanked f l a n k e d by outward outward dipping, dipping, g e n e r a l l y structureless s t r u c t u r e l e s s masses of medium medium to t o thick t h i c k beds beds that t h a t flatten f l a t t e n and and grade g r a d e laterally l a t e r a l l y into i n t o thinner thinner Large irregular cavities coon in bedded interreef dolomite. r e common in bedded i n t e r r e e f dolomite. b r g e i r r e g u l a r c a v i t i e s a are Some reef r e e f cavities cavities many many reef r e e f cores, c o r e s , and and may may be b e present p r e s e n t in i n flank f l a n k beds. beds. Some result but r e s u l t from solution, solution, b u t others o t h e r s containing c o n t a i n i n g concentrated c o n c e n t r a t e d accumulations accumulations of of fossils f o s s i l s were primary primary features f e a t u r e s formed formed during d u r i n g reef r e e f growth. growth. AA partially p a r t i a l l y quarried q u a r r i e d Middle Middle Silurian S i l u r i a n (Niagaran) (Niagaran) reef r e e f in i n Racine Racine DoloDolomite Wisconsin, exposes about 20 elongate elongate m i t e at a t Quarry Lake Park, P a r k * Racine, Racine* Wisconsin, about 20 bell—shaped wide) 3' bell-shaped or o r equant cavities c a v i t i e s ranging up to t o 8.5' 8.5' wide, 3 ' high, h i g h , and and extending 6' inward inward from from the t h e face f a c e of of the t h e rock r o c k exposure. exposure. Many Many of of the the extending 6' cavities c a v i t i e s couldn't c o u l d n ' t be b e ewmirted examined safely s a f e l y and several s e v e r a l were nonfossiliferous. nonfossiliferous. The The base b a s e of three t h r e e out o u t of five f i v e cavities c a v i t i e s selected s e l e c t e d for f o r detailed d e t a i l e d examinaexamination numbers of of nnested e s t e d masses of of fossils f o s s i l s dominated by t i o n contained llarge a r g e numbers inverted i n v e r t e d (concave—up) (concave-up) cephalons and ppygidia y g i d i a of of the t h e trilobite t r i l o b i t e Bumastus t h a t similar s i m i l a r accumulations accumulations might sp. sp. Previous workers have suggested that represent: protected with r e p r e s e n t : (1) (1) a p r o t e c t e d living l i v i n g environment w i t h reworking by scavscavengers, e n g e r s , (2) (2) a favored molting site, s i t e , (3) (3) wave and current c u r r e n t accumulations accumulations behind ( 4 ) settling s e t t l i n g of of disarticu— disarticubehind obstacles o b s t a c l e s or o r within w i t h i n depressions, d e p r e s s i o n s , or o r (4) lated is also a l s o possible p o s s i b l e that that l a t e d fossils f o s s i l s washed into i n t o natural n a t u r a l cavities. c a v i t i e s . It is unique and selective might account for s e l e c t i v e predation p r e d a t i o n might f o r the t h e fossil f o s s i l deposits. deposits. within The fact f a c t that t h a t most (all?) ( a l l ? ) of of the t h e cavities cavities w i t h i n the t h e reef r e e f core c o r e were were The filled with clay adds to the enigmatic nature of these features. once once f i l l e d w i t h c l a y adds t o t h e enigmatic n a t u r e of t h e s e f e a t u r e s . with Flume and and settling s e t t l i n g experiments experiments w i t h chitinous c h i t i n o u s carapaces c a r a p a c e s and and full full Flume dorsal of tthe (Limulussp.) sp.) ddisclose i s c l o s e that that d o r s a l exoskeletons exoskeletons of h e horseshoe horseshoe ccrab r a b (Limulus only only free—fall f r e e - f a l l into i n t o a nnonagitated o n a g i t a t e d ccavity a v i t y aallows l l o w s a high percentage p e r c e n t a g e of of concave-up forms forms to t o accumulate. accumulate. This documentation, plus p l u s the t h e disartic— disarticconcave—up u l a t e d and incomplete n a t u r e of ulated nature of Bumastus Bumastus in with i n association association w i t h lesser lesser numbers of of other o t h e r fossil f o s s i lforms, forms, suggests s u g g e s t s selective s e l e c t i v e sorting s o r t i n gof ofdead dead numbers organisms by size s i z e and and shape shape as a s they organisms they washed washed across a c r o s s the t h e submerged submerged rreef eef f l a t before b e f o r e failing f a l l i n g into i n t odepressions. depressions. flat - Although Although t this h i s project p r o j e c t solved solved the t h emystery mystery of of upside—down upside-down t rtrilobites, ilobites, it it failed f a i l e dtot oprovide p r o v i d enew new insight i n s i g h t into i n t o the t h e origin o r i g i n and and clays w i t h i n rreef e e f cavities. cavities. clays within L.6 accumulation of �Precambrian Precambrian Evaporites: Evaporites: Preservation Preservation of of Sulfate Sulfate in in Quartz Ouartz Pseudomorphs Pseuclomorphs After After Gypsum Gypsum E.C. FENG* AND AND J. HEMZACEK H W A C E K (Northern (Northern Illinois Illinois University) University) E.C. PERRY, PERRY* J. FENG, The The average average sulfur sulfur isotope isotope composition com osition of of trace trace amounts amounts of of anhydrite anhydrite preserved preserved in in the the 22 XX 10 10 year year old old Kona Kona Dolomite Eolomite from from 33 distinct distinct localities localities near near Marquette, Marquette, Michigan Michigan is is 13.23 13.23 /oo loo (CDT) (CDT) with with 0 aa total total range range of of 1.2 1.2 too. Much of of this this sulfate sulfate is is preserved preserved as as. loo. Much microscopic microscopic inclusions inclusions in in quartz quartz pseudomorphs pseudomorphs after after gypsum, gypsum* but but at at least least one one rock rock contains contains distinct distinct sulfate sulfate crystals crystals that that dissolve dissolve on on Conspicuous pseudomorphs pseudomorphs are are weathering weathering leaving leaving aa pitted pitted surface. surface. Conspicuous associated associated with with large, large* silicified silicified stromatolites stromatolites at at aa quarry quarry 99 km km southwest southwest of of the the center center of of Marquette Marquette on on highway highway 480. 480. Other Other pseudomorphs from from this this quarry quarry are are replaced replaced gypsum gypsum crystals crystals up up to to about about pseudomorphs 33 cm cm long, long* which which occur occur in in maroon maroon carbonate carbonate mudstone. mudstone. Y The The significance significance of of the the discovery discovery of of sulfate sulfate in in the the Kona Kona Dolomite Dolomitc is well documented is that that marine marine evaporites, evaporitesy which contain contain aa well documented record record of of the the highly highly variable variable sulfur sulfur isotope isotope composition composition of of the the Phanerozoic Phanerozoic ocean, ocean* are are almost almost nonexistent nonexistent in the PPecambrian ecambrianexcept except for foraa few few sporadic sporadic occurrences occurrences that that are are 1.2 1.2 XX 10 10 years years old old or or younger. younger. If If sulfate sulfate is is preserved preserved in in some some of of the the numerous numerous reported reported occurrences occurrences of of Proterozoic and and Archean Archean sulfate sulfate pseudomorphs pseudomorphs and and if if this this sulfate sulfate has has Proterozoic not not suffered suffered serious serious isotopic isotopic fractionation fractionation during during diagenesis diagenesis and and metamorphism, metamorphismyit it may may be be possible possible to to extend extend the the important important sulfur sulfur isotope isotope record record of of exogenic exogenic processes processes back back to to aa time time of of low low atmospheric atmospheric 5 oxygen. oxygen. Leaching with sulfate sulfate from from the the Kona KonaDolomite Dolomitei~ticate iicate Leaching experiments with that that the the last last few few per per cent cent of of sulfate sulfate extracted extracted is is depleted depleted in in SS by by about about 11 °too. O/oo. If If this this can can be be extrapolated extrapolated to to diagenetic diagenetic and and metamorphic metamorphic processes processes responsible responsible for for replacement replacement of of evaporita evaporite minerals, minerals* it it suggests suggests that3he that3gheoriginal originalisotope isotopecomposition compositionmay may have have been than the the value value we we have have measured. measured. been moderately moderately higher higher in in SS than However, However* in in the the absence absence of of aa large large and and uniform uniform external external reservoir reservoir of of sulfate, sulfate*the the extremely extremely uniform uniform sulfur sulfur isotope isotope value value that that we we have have obtained, obtained* independent independent of of sulfate sulfate concentration concentration variations variations of of 20X, 20Xyis is an an encouraging encouraging indication indication that that the the original original sulfur sulfur isotope isotope composition composition of of sulfate sulfate in in the the Kona Kona Dolomite Dolomite is is preserved. presemed. To To test test whether whether or or not not processes processes that that encapsulate encapsulate sulfate sulfate in in silica silica produce produce significant significantsulfur sulfur isotope isotopefractionation, fractionation*we weare are collecting silicified silicified material material in in Phanerozoic Phanerozoic evaporites evaporites in in order order to to collecting compare compare the the isotopic isotopic composition composition of of trace trace sulfate sulfate inclusions inclusions with with sulfate sulfate in in the the main main evaporite evaporiteminerals. minerals. After finding finding preserved preserved sulfate sulfate in in the the Kona Kona Dolomite, Dolomite, we we After solicited the the help help of of colleagues colleagues in in assembling assembling the the most most comprehensive comprehensive solicited possible collection collectionof of similar similarmaterial material from fromother otherlocalities. localities. To To be be possible valuable, valuable,the the sulfur sulfur isotope isotope record record of of sea sea water water sulfate sulfate must must be be reasonably pseudomorphs rezsonablycomplete. complete. So So far far we we have have received quar qua9zz pseudomorphs after dter gypsum gypsum (or (or celestite) celestite) fro frogMontana Montana(1.2 (1.2 XX10 10 years), years)* Nabberu Xabberu Basin, Autralia Au tralia(1.4 (1.4 to to22XX 10 10 years), years), and and Barberton, Barberton*South South Africa Africa Basin, (3.4 (3.4 XX 10 10 years). years). We We shall shall be be grateful grateful for for material material from from other other Precambrian or or Phanerozoic Phanerozoic localities localities of of silicified silicified evaporites evaporites or or for for Precambrian information information about about such suchlocalities. localities. It It is is our our hope hope that that such such material, material* although inconspicuous, inconspicuousymay may be be common commonand, andyultimately, ultimatelyyuseful. useful. although 47 Lf7 �Stable Isotope Metamorphism and Hydrothermal Stable Isotope Evidence of Metamorphism Hydrothermal Alteration, Alteration, Negaunee Iron Iron Formation, Formation, Michigan Michigan E.C. E.C. PERRY, PERRY? S. SHEN, SHENy AND C. C. UENG (Department (Department of of Geology, Geology, Northern Northern IL 60115) 60115) Illinois University, DeKalb, IL University, DeKaib, A3equilibriuin Af8equilibrium siderite, siderite, and and particularly particularly quartz, quartz, concenconcentrate trate 00 with with respect respect to to magnetite. magnetite. This fractionation fractionation becomes becomes less at high high temperature temperature so so that thatdufing dung metamorphism metamorphism aa redistriredistribution occurs, from quartz quartz and and siderite. siderite. bution occurs, and and magnetite magnetite gains gains 0 0 from Because oxygen of carbonate and and quartz quartz in in iron iron formation formation1s magnetite, 6 % 0 of quantitatively more abundant abundant than than oxygen oxygen of magnetite, of varies magnetite in in metamorphosed iron iron formation formation typically typically varies considerably considerably as a function function of bulk composition composition and metamorphic metamorphic temperature. This patten is is not characteristic characteristic of of low low grade grade temperature. This pattern mgamorphic zones m~~amorphic zonesof 02the the Negaunee Negaunee Iron Iron Formation. Formation. Instead, Instead, the the manetite is 0 of ygnetite is almost almost constant constant throughout throughout aa given given core 6 0 whereas Cs6 0 0 of of quartz quartz and and siderite siderite varies varies considerably. considerably. We whereas with a interpret this to indicate equilibration of the rocks vith metamorphic fluid. metamorphic fluid. Over a large temperature temperature range range the the oxygen oxygen isotope fractionation between between magnetite magnetite and water water is almost constant, while while that between between quartz or siderite siderite and water varies varies constanty by several several per per mil. mil. Thus, a fluid dominated system syst-emwould behave behave as as the the Negaunee Negaunee Iron Iron Formation Formation does. does. Further Further evidence evidence for for hydrothermal hydrothermal fluid movement in in this this region region is is the the disequilibrium disequilibrium reversal in quartz-siderite quartz—siderite oxygen isotope isotope fractionation fractionation that reversal that Formation cores. cores. occurs near the the base of several several Negaunee Negaunee Iron Iron Formation Cs metamorphism of zone Average temperature temperature of metamorphism zone II iron iron formation formation wide area, asodeterminec! as0determined by quartz-magnetite quartz—magnetite geothermgeotherm— over a wide ometry, is 320 2 . 1133 C. One of the cores characterized characterized by this this ometry, C. temperature contains a zone in which reaction is is temperature which the following reaction grunerite ++ CO CO, + H,O. observed: siderite siderite + minnesotaite ininnesotaite == grunerite H,O. If a a large part part of of zone zone I I was was balanced balanced during during metamorphism metamorphism at a temperatures and pressures near those that would release temperatures volatiles volatiles by such such a reaction, reaction, rock rock permeability permeability may have have increased greatly at this locality opening conduits for fluids fluids conduits for expelled expellea from zones of higher grade metamorphism nearer the Republic trough. Republic trough. If this explanation is valid, valid, the the conduits, conduits, explanation is once formed, formed, must have remained open to circulation circulation of fluids fluids after the peak temperature of metamorphism metamQrphism since both both high and low isotope isotope "temperatures" "temperatures1'are are recorded recorded in in the the permeable permeable zones. zones. low + Sills emplaced before before the main main regional metamorphic metamorphic event cores that that we we have have studied. studied. These These occur in the upper parts of of 22 cores sills have produced distinctive contact metamorphic metamorphic effects in in underlying iron formation that are clearly presemed preserved in the oxygen isotope composition composition of of quartz, quartz, carbonate, carbonate, and and magnetite. magnetite. oxygen isotope isotope "temperatures" "temperatures" are are recorded recorded near near the the sills, sills, High mineral isotope but in the outer margins of the contact zones "temperatures" "temperatures1' frozen in by the earlier metamorphism lower than than frozen metamorphism are distinctly lower the temperature of regional regional metamorphism. metamorphism. temperature of L8 �In excellent correlation 1ists In at at least least one core an excellent ~ists between between amount amount of of carbonate carbonate in in aa specimen specinen and and the the 56'3 3content content of of the the carbonate. carbonate. This This relatign relatign holds holds over over aa range range of of 8 3 CC of of approximately approximately _70/oo -7O/oo to to —ii -11 /oo /oo and and aa carbonate carbonate content content of of 19 19 to to 6%. 6%. 49 �Middle Proterozoic in Northeast Wisconsin and and Proterozoic Events in Northeast Wisconsin Rb-Sr Biotite Biotite Ages Ages Adjacent Michigan Michigan as as Defined Defined by by Rb—Sr Adjacent ZELL E. PETEBMAN and ZELL E . PETERMAN and P. K. SIMS SIMS.(U.S. Geological Survey, Suneys Denver Denver (U.S. Geological Federal Centery Center, M MS Federal S 963, 963 Denver, Denver* CO CO 80225) 80225) Systematic variations variations of Rb-Sr Rb—Sr biotite ages for Proterozoic and Systematic for Early Proterozoic and Late from the Marquette Marquette km from Late Archean Archean rocks rocks in in aa transect transect extending extending 130 130kin trough in northern Michigan to northeastern northeastern Wisconsin record trough in record uplift uplift events The biotite events in in the the Middle Middle Proterozoic Proterozoic (Figure).. (Figure).. The biotite ages ages have have aa trimodal distribution with peaks at 1.58 (19 samples), samples)* 1.32 1.32 ±2 trimodal distribution 1.58 2± 0.07 Ga (19 0.04 Ga Ga (26 (26 samples), samples)* and and 1.14 1.14 ±2 0.03 0.03 Ga Ga (9 (9 samples). samples). The 1.58—Ga 1.58-Ga peak is is a composite composite containing the tightly clustered 1.63 ±2 0.03 Ga ages ages for for the southern complex complex in in northern northernMichigan Michigan(Van (VanSchinus Schmusand and Woolsey, W001sey~1975) 1975) the southern and slightly The 1.32 to the the south. south. The 1.32 Ga Ga peak peak is is slightly younger younger ages ages from from areas areas to defined by biotite ages in the Felch trough area area (Aldrich (Aldrich and others, others, an area area extending extending southward across across the central part of the 1965) and in an the Dunbar gneiss Dunbar gneiss dome dome in in northeastern northeastern Wisconsin Wisconsin into into the the body body of of Atheistane Athelstane south of the The western western third Quartz Monzonite of Cain (1964) south the dome. The third of of the the dome is characterized by biotite ages that range range from from 1.11 1-11 to to 1.17 1.17 Ga. This Ga. This age age zone zone merges abruptly abruptly to to the the east east with with the the zone zone of of interinterages, and the eastern part of the yields still mediate ages* the dome yields still older older ages ages ranging ranging from from 1.46 1.46 to to 1.63 1.63 Ga. Ga. biotite—hosted Rb-Sr Rb—Sr system have resulted Resetting of the biotite-hosted system could could have resulted from from pulses related to igneous activity* activity, recrystalli~ation~ recrystallization, or thermal pulses or rapid rapid uplift uplift and and cooling. cooling. At least least two of the age peaks reflect complete resetting setting of of the the systems systems as as suggested suggested by by the the limited limited dispersion. dispersion. The The 0.03 Ga Ga biotite biotite ages ages for Archean Archean rocks of the southern southern complex complex 1.63 2± 0.03 have been correlated have correlated with with an an isotopically isotopically widely widely recognized recognizedbut but geologigeologically Precambrian rocks cally cryptic event that has affected Precambrian rocks over over much much of of Wisconsin (Van Woolseyy 1975). 1975). The The resetting resetting of of biotite biotite Wisconsin (Van Schmus Schmus and and Woolsey, ages western third of the Dunbar Dunbar dome at 1.14 Ga occurred occurred ages in in the the western 1.14 ±2 0.03 Ga contemporaneously contemporaneously with with Keweenawan Keweenawan rifting rifting and and igneous igneous activity. activity. The The coincidence of age discontinuities discontinuities with with northwestnorthwest— and northeastnortheast— coincidence zones with vertical vertical lineations suggests trending shear zones lineations (Figure) (Figure) strongly stronglysuggests vertical uplift uplift was was a causative factor in producing that differential vertical age pattern. the age pattern. Rapid Rapid erosion, erosion* an an inevitable inevitable corollary corollary to to rapid rapid upuplift, would would have have contributed Early Early Proterozoic Proterozoic detritus to Keweenawan Keweenawan lift* sands. sands. The significance biotite ages The significance of the 1.32—Ga 1.32-Ga peak of biotite ages is is less less certain. certain. (1965) suggested suggested aa thermal thermal event event at at this this time, time, but but others (1965) Aldrich and others did not not elaborate elaborate on on aa possible possible cause. cause. Possibly, Possiblyy the the surface surface now now characterized by the 1.32—Ga 1.32-Ga age group was during was uplifted and cooled during which the biotite systems systems were only the Keweenawan from a depth at which partially partially reset. reset. so �References References Aldrich, L. T., Davis, G. L.* L., and James, T.* Davis* James* H. L., 1965, 1965, Ages of of minerals minerals Aldrich* from metamorphic and from metamorphic and igneous igneous rocks rocks near near Iron Iron Mountains, Mountains*Michigan: Michigan: Journal of v. 6, 6 * P. p. 445—472. 445-472. Petrology9 v. Journal of Petrology, Cain, A., 1964, Pembine area, 1964, Precambrian Precambrian geology of the the Pembine area* northnorthCainy J. A.* eastern Wisconsin: Papers of eastern Wisconsin: Papers of Michigan Michigan Academy Academy of of Science, ScienceyArt, Art, and Letters* Letters, v. 49, 49* p. 81—103. 81-103. and Van Woolsey, L L. Rb—Sr geochronology Van Schmus, Schmus, W. R., R.* and W001sey~ . L., 1975, 197Sy Rb-Sr geochronology of of the Republic area, Canadian Journal Journal the Republic area* Marquette Marquette County, County9 Michigan: Michigan: Canadian Earth Sciences, v. 12, 12, p. p. 1723—1733. 1723-1733. of Earth Sciences* v. 51 �8 8' 88° S 1.66 1.60 *1.69 •1.69 , I.65 -65 *11 .60 .60 63 5% : 55 1.62 . 1.62 MICHIGAN MICHIGAN 1.68 •1.39 ,1 .261.34 , 36 ' 46° 1.09 1.28 / , / 7 .32 .33 1.25 1.32' WISCONSIN 1.6 SHEAR •1.39 I \ 1 0MILES MILES 10 00 e KILOMETERS o0 •13 8 I 10 KILOMETERS 10 . Y" I .'% 1 - *I- 3 9 •1.39 # I.1 Rb-Sr biotite b i o t i t e ages ages for f o r Early E a r l y Proterozoic P r o t e r o z o i c and and Late L a t e Archean Archean rocks r o c k s in in Rb—Sr n o r t h e a s t Wisconsin and a d j a c e n t Michigan. Data a r e from A l d r i c h and northeast Wisconsin and adjacent Michigan. Data are from Aldrich and o t h e r s (196.51, Van Schmus and Woolsey (19751, and Peterman and Sims others (1965), Van Schinus and Woolsey (1975), and Peterman and Sims (unpublished). Note Note the t h e close c l o s e correspondence correspondence between between age age discontinui— discontinui(unpublished). t i e s and known and p r o j e c t e d s h e a r zones i n n o r t h e a s t Wisconsin. ties and known and projected shear zones in northeast Wisconsin. 52 52 �Crystallization C r y s t a l l i z a t i o n Histories H i s t o r i e s of of Early E a r l y Proterozoic Proterozoic Plutons from Northern Wisconsin from W.L. W.L. PETRO PETRO (Dept. (Dept. of of Geology Geology && Geophysics, Geophysics, University University of Wisconsin, Wisconsin, Madison, Madison, WI W I 53706) 53706) JA variety v a r i e t y of of Early E a r l y Proterozoic Proterozoic plutons p l u t o n s isi sexposed exposed plutoris in The p l u t o n s vary vary from from gabbro gabbro i n northern northernWisconsin. Wisconsin. The to t o granite g r a n i t eini ncomposition, composition, are a r emesozonal mesozonal to t ohypabyssal hypabyssal in i n level l e v e l of of emplacement, emplacement, and aare r e syntectonic s y n t e c t o n i c to to posttectonic p o s t t e c t o n i c with with respect r e s p e c t to t o the t h e Penokean Penokean orogeny. orogeny. Recent and petrographic etrographic work h a s established established Recent field f i e l d and work has crystallization c r y s t a l l i z a t i o n histories h i s t o r i e s for f o r the t h e plutons p l u t o n s arid and their their aureoles, a u r e o l e s , yielding y i e l d i n g important important information information on on the the petrologic p e t r o l o g i c evolution evolution of of this t h i s part p a r t of of the t h e crust c r u s t in i n the the Lake Lake Superior Superior region. region. The The plutons plutons generally g e n e r a l l y contain contain multiple m u l t i p l e generations generations mineral assemblages, indicating i n d i c a t i n g complex complex crystallicrystallization z a t i o n histories. h i s t o r i e s . Posttectonic P o s t t e c t o n i c hypabyssal hypabyssal plutons plutons contain contain relict r e l i c t euhedral euhedral or o r embayment embayment textures textures representing s i l i c a t e melt. melt. r e p r e s e n t i n g crystallization c r y s t a l l i z a t i o n from from aa silicate Posttectonic P o s t t e c t o n i c epizonal epizonal plutons, plutons, pegmatites, pegmatites, and and aplites aplites exhibit e x h i b i t textures t e x t u r e s which probably represent r e p r e s e n t crystallicrystallization z a t i o n at a t or o r near near the t h e solidus. s o l i d u s . Syntectonic Syntectonic mesozonal mesozonal plutons exhibit e x h i b i t textures t e x t u r e s representing r e p r e s e n t i n g subsolidus subsolidus crystallization. c r y s t a l l i z a t i o n . All A l l of of the t h e plutons p l u t o n s are a r e overprinted overprinted by low—grade alteration products. of of Previously Previously unreported unreported electron e l e c t r o n microprobe microprobe deterdeterminations minations of of mineral mineral compositions compositions have have been been made made for for plagioclase p l a g i o c l a s e and and potassium potassium feldspars, f e l d s p a r s , biotites, b i o t i t e s , horn— hornblendes, garnets, b l e n d e ~ ,znuscovites, muscovites, g a r n e t s , and and ilmenites. ilmenites. The The mineral compositions compositions allow allow estimations e s t i m a t i o n s of of the t h e intensive intensive mineral parameters during ccrystallization parameters obtained obtained during r y s t a l l i z a t i o n .• Possible Possible equilibria e q u i l i b r i a involving two two feldspars f e l d s p a r sand andplagioclase— plagioclase- hornblende yield y i e l d temperatures temperaturesofof600—700°C 600-700° ffor o r epizonal epizonal hornblende rocks rocks and and 00—600°C 400-600° for f o r mesozonal mesozonal rocks. rocks. Intrusion I n t r u s i o n of of Penokean and post—Penokean post-Penokean plutons plutons occurred across a c r o s s batholithic b a t h o l i t h i c dimensions dimensions in i n northern northern occurred Wisconsin. Wisconsin. Most Most of of the t h e Early Early Proterozoic Proterozoic metamorphism metamorphism in i n the t h e plutons and and their t h e i r aureoles a u r e o l e s probably probably occurred occurred during intrusion i n t r u s i o n and and cooling coolingofofthe t h eplutoris. plutons. during According to t o this t h i s interpretation, i n t e r p r e t a t i o n , Early Early Proterozoic Proterozoic iccording metamorphism metamorphism in i n northern northern Wisconsin Wisconsin was w a s autometamorphism autometamorphism and and contact c o n t a c t metamorphism metamorphism on on aa regional r e g i o n a l scale. s c a l e . These These new new data d a t a and and interpretations i n t e r p r e t a t i o n s place p l a c e important important constraints constraints on on models models for f o r the t h e thermal thermal evolution evolution of of this t h i s part p a r t of of the t h e crust. crust. 53 �Climatic C l i m a t i c Inferences I n f e r e n c e s of of Iron—Formation Iron-Formation from from Associated Associated Diamictite D i a m i c t i t e fades f a c i e ssequences, sequences, Griqualand Griqualand West West Supergroup, S u ~ e r g r o u p South , South Africa Africa R..D. POWELL POWELL (Dept. (Dept. of of Geology, Geology,N o r t h e r n Illinois I l l i n o i s University, U n i v e r s i t y , DeKaib, DeKalb, R.D. Northern 60115) I l l i n o i s60.115) Illinois Makganyene Ongeluk Lava Lava (-2.2 (2.2 Ga Makganyene Diamictite D i a m i c t i t e underlies u n d e r l i e s Ongeluk G a B.P.) B.P.) at at t h e base base of of the t h e Postmasburg Postmasburg Group Group in i n Cape Cape Province, P r o v i n c e , South SouthAfrica. Africa. the The i s interpreted i n t e r p r e t e d as a s glacigenic, g l a c i g e n i c , which which puts p u t s environmental environmental The diamictite d i a m i c t i t e is constraints c o n s t r a i n t s (e.g. (e.g. temperature) temperature) on on the t h e formation formation of of associated a s s o c i a t e d iron— ironformation sedimentary sedimentary rocks. rocks. formation In I n outcrops, o u t c r o p s , diamictites d i a m i c t i t e s are a r e interstratified i n t e r s t r a t i f i e d with w i t h conglomerate, conglomerate, sandstone, shale s h a l e and and pebbly pebbly mudstone. mudstone. Direct D i r e c t evidence evidence for f o r the t h e dia— diasandstone, tnictites is two two features f e a t u r e s of of clasts: c l a s t s : striated s t r i a t e d sursurm i c t i t e s bbeing e i n g glacigenic g l a c i g e n i c is f a c e s and and facetted, f a c e t t e d , flat—iron f l a t - i r o n shapes. shapes. Most Most clasts c l a s t s are are chert c h e r t and and faces s t r i a t i o n s are a r e well w e l l retained r e t a i n e d on on their t h e i r surfaces. s u r f a c e s . In I n some some areas a r e a s up up striations to t o 10 10 percent p e r c e n t of of the t h e clasts c l a s t s are are striated s t r i a t e d (a ( a high high proportion p r o p o r t i o n in i n many many Pleistocene s t r i a e orientaorientaP l e i s t o c e n e glacigenic g l a c i g e n i c successions), s u c c e s s i o n s ) , and and multiple m u l t i p l e striae t i o n s also a l s o occur. occur. Some Some clasts c l a s t s (up (up to t o 22 percent p e r c e n t locally) l o c a l l y ) have have aa tions f l a t - i r o n form form produced produced during d u r i n g basal b a s a l transport t r a n s p o r t in i n aa glacier. g l a c i e r . The The flat—iron oligomictic o l i g o m i c t i c clast c l a s t composition, composition, often o f t e n cited c i t e d as as evidence evidence against against Underlying for— foras aa source s o u r c e control. c o n t r o l . Underlying can be be explained e x p l a i n e d as glaciation, g l a c i a t i o n , can n a t i o n s , which r e probably h e ssource, o u r c e , comprise iron—formation iron-formation and and tnations, which aare probably tthe carbonate rocks. rocks. Both Both carbonate c a r b o n a t e and and (iron—rich) ( i r o n - r i c h ) shale s h a l e clasts c l a s t s did did carbonate Therefore, n o t survive s u r v i v e long long transport t r a n s p o r t by by Pleistocene P l e i s t o c e n e glaciers. g l a c i e r s . Therefore, not c h e r t is is the t h e most most likely l i k e l y component component of of glacigenic g l a c i g e n i c sediment sediment in i n the the chert Makganyene Diamictite. D i a m i c t i t e . Glacial G l a c i a l pavements pavements have have been been noted noted by by prepreMakganyene viOus v i o u s workers, workers, however, however, none none were were found found during d u r i n g this t h i s study. s t u d y . If I f many many then absence absence of of aa of of the t h e sequences sequences are a r e glacimarine g l a c i m a r i n e (see ( s e e below), below), then widespread pavement pavement can can be be expected. expected. widespread Other arguments arguments are a r e made made for f o r aa glacigenic g l a c i g e n i c origin o r i g i n of of the t h e diamic— diamicOther C i t e succession s u c c e s s i o n using u s i n g lithofacies l i t h o f a c i e s sequence sequence analysis. a n a l y s i s . Some Some of of the the tite a s s o c i a t e d sorted s o r t e d units u n i t s are a r e sheet—like s h e e t - l i k e sandstone sandstone bodies bodies up up to t o 12m 12x11 associated t h i c k . They They are a r e fine— f i n e - to t o coarse—grained, coarse-grained, occasionally o c c a s i o n a l l y pebbly pebbly or or thick. g r i t t y , and and are a r e apparently a p p a r e n t l y structureless s t r u c t u r e l e s s or o r exhibit e x h i b i t horizontal h o r i z o n t a l Lami— lamigritty, Basal n a t i o n , medium—scale medium-scale trough trough cross—bedding cross-bedding and and channel channelforms. forms. Basal nation, conglomerates occur occur in i n the t h e channel channel forms. forms. AA flaggy f l a g g y sandstone s a n d s t o n e facies facies conglomerates is common common at a t the t h e base base of of the t h e succession. s u c c e s s i o n . Asymmetrical Asymmetrical and and symmetrisyietri— is c a t rrippled i p p l e d sandstone u r f a c e s are a r e draped draped with w i t h shale. s h a l e . The The sandstones sandstones cal. sandstone ssurfaces a r e interpreted i n t e r p r e t e d as a s braided b r a i d e d stream s t r e a m deposits d e p o s i t s probably probably in i n interaction interaction are w i t h aa shallow shallow marine marine environment. environment. with fineOther sorted s o r t e d facies f a c i e s are a r e lensoid l e n s o i d channels channels of of structureless s t r u c t u r e l e s s fine— Other t o inedium—grained medium-grained sandstone within w i t h i n diamictite. d i a m i c t i t e . The The channels channels are are to s t a c k e d or o r isolated i s o l a t e d and and include i n c l u d e blocks blocks of of diamictite. d i a m i c t i t e . The The interton— intertonstacked guing of sandstone w i t h diamictite d i a m i c t i t e indicates i n d i c a t e s the t h e genetic g e n e t i c rrocesses processes guing with of both b o t h facies f a c i e s were episodic, e p i s o d i c , or o r that t h a t the t h e sandstone s a n d s t o n e channels channels were were of l i m i t e d in i n spatial s p a t i a l position. p o s i t i o n . This T h i s type t y p e of of sequence sequence has has been been dedelimited s c r i b e d in i n Pleistocene P l e i s t o c e n e subglacial s u b g l a c i a l lithofacies. l i t h o f a c i e s . The The sequence sequence may may be be scribed 54 �subaqueous where where tthe compound ppara—till chansubaqueous h e ddiamictite i a m i c t i t e iis s aa compound a r a - t i l l and the t h e channels i n t e r p r e t a t i o n presents p r e s e n t s aa n e l s are a r e subaqueous subaqueous outwash. outwash. A submarine interpretation because ffluvial extremely hhigh ddifficulty i f f i c u l t y because l u v i a l ttraction r a c t i o n ccurrents u r r e n t s rrequire e q u i r e extremely ish be maintained maintained aatt tthe base of of aa more more dense sediment cconcentrations o n c e n t r a t i o n s tto o be h e base sea water column. column. of ice-proximal ice—proximal One section s e c t i o n eexhibits x h i b i t s ffacies a c i e s aassociations s s o c i a t i o n s ttypical y p i c a l of D i a m i c t i t e grades into i n t o and Out o u t of pebbly pebbly subaqueous environments. Diamictite xmidstone, breccia/conglomerate bedsy beds, and and tthin mudstone, breccia/conglomerate h i n sandstone beds. beds. Another stacked debris-flow debris—flow noses noses tthat have sstructureless ssection e c t i o n comprises stacked h a t have tructureless ddiamictite i a m i c t i t e cores c o r e s and outer o u t e r fissile f i s s i l e zones zones exhibiting e x h i b i t i n g flow flow structure. structure. occur iin and submarine, submarine, gglacial and non-glanon—glaDebris flows occur n tterrestrial e r r e s t r i a l and l a c i a l and cial Alluvial c i a 1 environments. A l l u v i a l ffan a n ddeposits e p o s i t s have aa geometry and facies facies Terrestrial associations a s s o c i a t i o n s that t h a t exclude them from from consideration. consideration. T e r r e s t r i a l ice— icecontact c o n t a c t environments environments include i n c l u d e resedirnented resedimented ddeposits e p o s i t s tthat h a t cannot be be excluded as a s a possible p o s s i b l e interpretation i n t e r p r e t a t i o n at a t some some localities. l o c a l i t i e s . Submarine debris flows aare very rrare water uunless by aa d e b r i s flows r e very a r e iin n shallow water n l e s s iinfluenced n f l u e n c e d by glacier. glacier. The succession s u c c e s s i o n is i s considered considered glacigenic. g l a c i g e n i c . The glacier g l a c i e r must have melting had a m e l t i n g base base because because glacifluvial g l a c i f l u v i a l deposits d e p o s i t s are a r e conunon. common. Frozen glaciers Antarctica today llack debase g l a c i e r s llike i k e tthose h o s e iin n A n t a r c t i c a today a c k common ffluvial l u v i a l deposits. was vala s probably an ice i c e cap and/or v alp o s i t s . The terrestrial t e r r e s t r i a l glacier glacier w ley l e y glaciers g l a c i e r s based on, on, and south s o u t h of of the t h e Ganyesa Ganyesa Dome. Dome. The glacier glacier probably nnot a s probably o t an iice c e sshelf h e l f because margin ffacing a c i n g the t h e eepeiric p e i r i c sea wwas tidal t i d a l ranges were sufficiently s u f f i c i e n t l y large l a r g e to t o make make an a n ice i c e shelf s h e l f unstable, unstable, even if Therefore, w a s made made of of cold cold ice. ice. T i f the t h e glacier g l a c i e r was h e r e f o r e y the t h e glacier glacier ended as a s aa tidewater t i d e w a t e r terminus. terminus. Furthermore, Furthermorey the t h e presence of of volcanic volcanic ash in of the water i n some of t h e compound ppara—till a r a - t i l l iindicates n d i c a t e s an open w a t e r iiceberg ceberg necessarily zone environment close c l o s e to t o shore. shore. That n e c e s s a r i l y excludes an ice ice shelf s h e l f environment. environment . d r i l l cores c o r e s show an iintimate n t i m a t e aassociation s s o c i a t i o n of of d i a m i c t i t e and Deep drill diamictite l a s t i c marine t h a t iinclude n c l u d e llean e a n iron— ironchemical and cclastic marine sedimentary rocks rocks that formations. The Makganyene glacier, g l a c i e r , on a narrow sshelf h e l f aatt the t h e margin of the t h e eepeiric p e i r i c ssea, e a , probably s aatt ppresent r e s e n t glacial glacial of probably enhanced enhanced upwelling upwelling aas margins. That upwelling m may margins. y have enhanced chemical sediment deposideposittion i o n (iron—formation, (iron-formation, chert, c h e r t , carbonate). carbonate). The climate c l i m a t e was n o t exexnot treme (cf. (cf. A n t a r c t i ~ a )bbut ~u t cool c f . Alaska) h a t inAntarctica), cool temperate temperate ((cf. Alaska) and and tthat inon iinterpretations of oxygen oxygen iisotope analyfference e r e n c e pputs u t s cconstraints o n s t r a i n t s on n t e r p r e t a t i o n s of s o t o p e analyof associated sses e s of a s s o c i a t e d chemical chemical sediments. sediments. 55 �Magnetotelluric MagnetotelluricProfile Profileof of the theJacobsville JacobsvilleSandstone Sandstone Ted Engrg., R. Repasky Repasky (Dept. (Dept.of ofGeol. Geol.&& Geol. ~eol. Engrg.,Michigan MichiganTechnological Technological Ted R. MI 49931) 49931) University,Houghton, Houghton,MI University, Seven Seven magnetotelluric magnetotelluric soundings soundingswere were conducted conducted along along aa NW—SE W-SE line line across across the the Jacobsville Jacobsville Sandstone, Sandstone,between between Keweenaw KeweenawBay Bay and and the the They have have provided provided Keweenawfault faultin inMichigan's Mchigan's Upper UpperPeninsula. Peninsula. They Keweenaw the sandstone an estimate of the thickness and resistivity of and an estimate of the thickness and resistivity of the sandstoneand the underlying underlyingbasement. basement. the The 1818seconds) seconds)toto Thesoundings soundingswere were of of aalong longenough enoughperiod period (up (upto to1818 Initial obtain obtain data datafrom fromlayers layersat atleast leastseveral severalkilometers kilometersinindepth. depth. Initial interpretation interpretationis is that that the thesandstone sandstonemay may be be one one to to two two kilometers kilometersthick, thick, Tapiola/OtterLake Lake area, area,the the sandstone sandstoneis is and that that northwest northwest of of the the Tapiola/Otter and underlain by by the the Portage Portage Lake Lake volcanics volcanics of of aa higher higher resistivity. resistivity. To To underlain the southeast southeast of of this this area area the the sandstone sandstone is is underlain underlain by by aa body body of of the lower lower resistivity resistivity rock, rock, perhaps perhaps Michigamme Michigame Slates Slates which which are are known known to to outcrop at at the the head head of of Keweenaw KeweenawBay. Bay. outcrop — Lake rn / 'I / 1,0 I- 0 20 Miles 10 2030 Km Figure 1.1. Figure Location of of soundings soundings(stations (stations1—7), 1-71, Location j, Jacobsville Sandstone; fn, Freda Sandstone and j, Jacobsville Sandstone; fn, Freda Sandstone and Nonesuch Shale; Shale; cli, ch, Copper Conglomer3te; Nonesuch Copper Earbor Harbor Conglomerate; pl, Portage Lake Lava Series; m, Michigamme Slats. p1, Portage Lake Lava Series; m, Michigamme Slate. 66 �Sounding Results Results Depth Depth KM K P4 00 19 419 Resistivities in in Ohm—meters Ohm-meters 62 —.4 38 3 83 7 =2 12 16 11 —10 — 39 —2 71 24 21 6 4 39 2 2 3 3, 140 217 937 986 48 4. 4 123 4 6 5 • PROFILE 2OOO—"\.._--—.__________-- I ioooi;7 . I(I, E. -2000 .. :. - Ui Ui N-N ,,, Figure 2. Figure 2. Sounding locations Sounding locationson onaa geologic geologic cross cross section. section. (Meabref and and Iiinze, Hinse, 1970) 1970) (Meshref 57 7 SE �P t and and Ni N i Arsenide Arsenide Minerals Minerals in i nthe theDuluth DuluthComplex Complex Pt (Mineral Resources Research of PATRICK J. J.RYAN PATRICK RYAN (Mineral Resources ResearchCenter, Center,University University of Minnesota, Minneapolis, MN 55455)s Minnesota, Minneapolis, MI 551455)* PAUL W.W.WEIBUN (Minnesota Geological 2642 University Ave., PAUL WEIBLEN (Minnesota GeologicalSurvey, Survey, 26142 University Ave., 55114) St.Paul, Paul, St. MNMN551114) S p e r r y l i t e (PtAs2), (PtAs21, maucherite maucherite (Ni3tts2), (Ni3As21, and and possibly possibly niccolite niccolite Sperrylite (NUS) have d e n t i f i e d in i n massive massive sulfide s u l f i d esamples samples from from the the Duluth Duluth (NiAs) have been beeni identified Complex. was made made iin n the course of aa survey survey of of The iidentification d e n t i f i c a t i o n was Complex. The the course 1) from from the the three representative representativemassive massive sulfide s u l f i d esamples samples (Table (Table 1) three MINNAMAX Shaft Shaft (located about 8 km Babbitt,MN). MN). MINNAMA.X (located about 8 isouth south of of Babbitt, One ssperrylite p e r r y l i t e grain grain was w a s found found as aa aa small, small, c5 a micrometer, 5 micrometer,euhedral euhedral One elongategrain grain maucheritewhich which in i nturn turnwas was crystal in i na alarger, largery crystal elongate ofofmaucherite Quantitative Quantitative electron microprobe analyses i n d i c a t e a deficiency of A for electron microprobe analyses indicate a deficiency of Ass for 2, 1 & 2). Minor elements o t a l less less stoichlometric s p e r r y l i t e (Table atcichiometric sperrylite (Table 2, 1 & 2). Minor elementst total The s p e r r y l i t e grain has a very complex i n t e r n a l wt. 5. than two than two wt. %. The sperrylite grain has a very complex internal s t r u c t u r e which which cconsists o n s i s t s of of an an inclusion inclusion of of aa blade blade of of graphite graphite (?) (?I structure T h i s proved proved to t o be be too toofine— fineand aa complex complex myrmeketic m m e k e t i c intergrowth. This and grained (2 ( 2 micrometer micrometer wide o r quantitative q u a n t i t a t i v eanalysis, analysis,however, however, grained wideblebs) blebs) ffor data indicate i n d i c a t ethe thepossible possiblepresence presence of of graphite, graphite, precious precious q u a l i t a t i v e data qualitative are metal alloys, tellurides, t e l l u r i d e s and , andbismuth bismuthminerals. minerals. These These phases phases are metal postulated on on the the basis b a s i s of of positive p o s i t i v e identification i d e n t i f i c a t i o n of of C, C , Cu, Cu, Au, Au, postulated B i , and and Pb Pb peaks peaks in i n x—ray x-ray dispersive dispersive (EDX) (EDXI and and scanning scanningAuger Auger Te, Bi, Te, microprobe spectra. spectra. Pd Pd was w a s identified i d e n t i f i e d in i n only only one one x—ray x-ray spectra s p e c t r a in i n aa microprobe B i i n t h e s p e r r y l i t e grain. myrmeketic bleb r i c h i n myrmeketic bleb rich in Bi in the sperrylite grain. embedded i in n an of obalcopyrite—cubanite. chalcopyrite-cubanite. embedded an intergrowth of Maucherite was w a s found found in i n all a l l three three samples samples studied. studied. Maucherite It is It is llight i g h t microscopy microscopy from from other other sulfide s u l f i d e and and its white, white, high high reflectivity r e f l e c t i d t y and and very very faint f a i n t pink pink arsenide minerals mineral8 by by its arsenide It was was found found in i n five f i v e polished polished sections sections as as small s m a l l blebs blebs t i n t . It tint. as long long needle—like n e e d l e l i k e stringers s t r i n g e r s (0.01 (0.01 to t o 1.5 1.5 mm rn (10 micrometer) (10 micrometer) and and as It was found i n all three major s u l f i d e phases--pyrrhotite, long). It was found in all three major sulfide phases——pyrrhotite, long). pentlanditey and and chalcopyrite—cubanite chalcopyrite-cubanite intergrowthz——but intergrowths-but makes makes up up less less pentlandite, of the the massive massive ore o r e samples. samples. Although w t . %% of than one one wt. Although the the inaucherite maucherite than grains appear appearhomogeneous homogeneous in i n reflected r e f l e c t e d light, l i g h t , electron electron microprobe microprobe grains analyses show show aa wide a r i a t i o n in i n Ni/As N i / A s and and Fe/Ni Fe/Ni ratios ratios analyzes widerange rangeofof vvariation N i - A s grain g r a i n is is clearly c l e a r l y outside outside the the (Table 2,2,3—5). 3-51. One One analysis of aa Ni—As (Table analysis of range of of maucherite maucherite compositions compositions (2) (2) and and approaches approaches the the composition composition of of range 6 ) . n i c c o l i t e (Table 2, One micrometer-sized mauchrite gave gave niccolite (Table 2, 6). One micrometer—sizedgrain grain iinn mauchrite an EDX EDX sspectra p e c t m for f o rosmium. osmium. an distinguished iin n reflected reflected distinguished Platinum mineralization and maucherite maucherite have have been been reported in Platinum mineralization and reported in Keweenawan rock8 & 3), 31, but (2 & data reported reported here irst but the the data Keweenawan rocks (2 hereisis the the ffirst we are a r eaware aware of of in i n the the Duluth Duluth Complex. Complex. The i d e n t i f i c a t i o nwe The new new data data identification emphasizes the the need need for f o r evaluation evaluation of of the the ore ore recovery recovery procedures procedures emphasizes have iguored ignored special s p e c i a l problems problems related r e l a t e d to t o arsenide araenide which up up to t onow now have which w h a tphases The data data leaves leaves the the question questionofofwhat minerals. The phases are a r e responsible responsible minerals. f o r platinum platinum metal metal group group elements i n assay assay values values unreunrefor elementsother other than than PPtt in solved (14). (4). solved 58 �Table 1. Samples Samples of the the Duluth Duluth Complex Complex examined r aarsenide r s e n i d e minerals. Table 1. examinedf ofor Sample Sample Type Location MIX-A AMX-A 11 kg sample of massive massive kg sample ssulfide, u l f i d e , rich r i c h in i nchalco-. chalcoppyri y r ite—cubarii te-cubanitete Suppliedbyby MINNAMAX from an Supplied MINNAMAX from an u n s p e c i f i e d llocality. ocality. unspecified AMX—B AM-B kg sized kg s i z e d sample sample of of massive massive ssulfide, u l f i d e , rich r i c hini pentlan— n pentlanddite i te Suppliedbyby MINNAMAX from Supplied MINNAMAX drift #417, 1055 1055 feet d r i f tround round #k17, below reference r e f e r e n cine MINNAMt&X i n MINNAMAX below shaft. 25 kg kg random massive sulsul25 random massive From the shaft dump. From t h eMINNAMAX MINNAMAX shaft dump. AMX—C M - C fide f i d e ore o r esample. sample. . Electron E l e c t r o n microprobe microprobe analyses rsenide m i n e r a l s iin n the the Table Table 22. analysesofof aarsenide minerals Duluth Duluth Complex. Complex. 1 Analysis Sample AMX—A3 Sample 1 22 MIX—A9 33 MIX—Al AMX-A 1 55 k 4 MIX—A2 66 MIX—Bk MIX-B 1 sS .10 .09 .0k -04 .52 .11 Ass A Fe Co co Ni Ni Cu cu Zn zn PPtt kO.82 kO.30 117.09 47 09 116.93 118.08 .15 55.19 .77 .07 .76 .13 1.01 .10 .20 .62 62 1.15 2.27 11.69 2.38 2-38 50.06 50.06 3.18 1.97 .80 118.59 118.90 110.57 0 0 0 0 0 0 0 57.82 58.96 .13 .09 .11 100.117 101.19 100.50 101.112 101.51 .010 1.670 .008 1.612 .0112 .0511 .00k .006 .005 .010 .025 0 0 .908 .906 Anions Anions . Cations 1.679 1.679 1.000 1.000 1.620 1.000 1,000 Total T otal 2.679 2.679 2.620 2.620 Total s S AAss Fe Co co NNii Cu cu Zn zn Pt Pt .0110 .53 0 0 0 0 .06 -06 100.25 10025 .0011 -004 2.085 2.085 .037 037 .13k -134 2.828 2.828 0 0 0 0 .001 .001 0 .0511 .011 .018 2.081 .068 .179 2.750 2.122 2.800 .1311 .111 .319 .052 2.75k 2.627 0 0 0 0 0 0 .002 .002 .002 2.089 2.089 3.000 3.000 2.135 2.135 3.000 3.000 20 133 2.133 3.000 3.000 2.81 8 2.818 5.089 5.089 5.135 5.135 5.133 5133 5.818 5.818 59 3.000 3.00 �Notes to t o Table Table 2: 2: Analyses Analyses were were made made ononthe theARL. ARL nine spectrometer electron e l e c t r o n microprobe in Dept. of of Geology, Geology, University of of Wisconsin, Wisconsin, Madison. Madison. Operating Operating i n the Dept. conditions: conditions: 15 15 K.V., r e e rrepliepliK.V., 0.05 0.05 microamperes microamperessample samplecurrent; current;t hthree cate countingtime timessufficient c a t e analyses analyses with with counting u f f i c i e n t to t o give give accuracies accuracies of of + of amount present for major elements and ÷ 50 wt. % wt. % + 5 w t . % amount present f o r major elements and + 50 wt. % f o r elefor 5 -m e r i t s present ments present aatt less lessthan thanone onewt. w t . %. %.X—ray X-ray intensity i n t e n s i t y data d a t awere were reduced from mineral mineral standards standards with standard corrections. reduced from standard ZAP ZAF corrections. References: References : 1) 1) Watowich, 1978, AApreliminary preliminary geological geological view Watowich, SS.N., .No, 1978, view of the the MINNAMAX copper—nickel deposit DuluthGabbro: Gabbro: 39th MINNAMAX copper-nickel deposit i n in t hthe e Duluth Annual Mining Symposium, Symposium,University University of of Minnesota, Annual Mining Minnesota, Minneapolis, Minneapolis, Minnesota, Paper 19, Minnesota, Paper 19, p. p. 1—11. 1-1 1. 2) 2) Geul, Geul, J.J.D., J.J.D., 1970, 1970,Geology Geology of ofthe theDevon Devon and and Pardee Pardee townships townships and and the Stuart S t u a r t location: location: Ontario Department Department of Mines Mines Geological Geological Report 87, 52 Report 87, 52 p. p. 3) 3) Kullerud, G., P., 1980. G., Private P r i v a t ecommunication communication in i n Ramdohr, Ramdohr, P., 1980. The The ore ore L) 4) Schiuter, Schluter , R.B. R .B. and and Landstroin, Landstrom, A.B., A .B., 1976, 1976, Continuous Continuous ppilot i l o t plant plant minerals Press, Vi, minerals and and ttheir h e i r intergrowths, intergrowths, Pergamon Pergamon Press, V I , p. p. L02. 402. testing of Duluth Duluth Complex Complex sulphides, t e s t i n gconfirms confirms f].oatability f l o a t a b i l i t y of sulphides, Mining Journal, v. v. 177, #L, #4, p. p. 80—83. 80-83. Mining Journal, Engineering Engineering * * Present address: Magaetic Magnetic Peripherals 7801 7801 Computer Computer Avenue Avenue Minneapolis, MN MN 5535 55435 60 �L a t e and and Late Western Western Post-Glacial Lacustrine L a c u s t r i n e Sediment Sediment Distribution D i s t r i b u t i o n in in Post—Glacial Lake Superior from Seismic R e f l e c t i o n P r o f i l e s Lake Superior from Seismic Reflection Profiles A. SCHOLZ SCHOLZ (Department (Department of of Geology, Geology, University U n i v e r s i t y of of Minnesota, Minnesotay CHRISTOPHER A. CHRISTOPHER Duluth, ~ z n e s o t a 55812) Duluth, Minnesota 55812) During the t h e summers summers of of 1982 1982 and and 1983, 1983y University U n i v e r s i t y of of Minnesota Minnesota During r e s e a r c h e r s acquired over 700 km of h i g h r e s o l u t i o n s e i s m i c profiles profiles researchers acquired over 700 km of high—resolution seismic in the t h e extreme extreme western western end end of of Lake Lake Superior Superior between between Duluth Duluth and and the the in Apostle Islands. I s l a n d s . The The normal—incidence, normal-incidence, 3.5 3.5 kHz kHz single—channel single-channel seismic seismic Apostle system employed employed had had limited l i m i t e d penetration p e n e t r a t i o n of of Proterozoic P r o t e r o z o i c bedrock bedrock and and system t i l l s , but b u t produced produced aa clear c l e a r and and detailed d e t a i l e d acoustic a c o u s t i c picture picture Superior Lobe Lobe tills, Superior of t h e fine-grained l a t e and p o s t g l a c i a l l a c u s t r i n e sediments. of the fine—grained late and post—glacial lacustrine sediments. i t h eeastastThe Duluth Duluth sub—basin sub-basin has subdued bathymetry bathymetry compared compared wwith The has aa subdued e r n Lake S u p e r i o r ' s v a l l e y s and r i d g e s . The b a s i n between Duluth and ern Lake Superior's valleys and ridges. The basin between Duluth and t h e Apostle Apostle Islands I s l a n d s deepens deepens gradually g r a d u a l l y from from the t h e west west and and south, s o u t h , but but the trough runs p a r a l l e l to to q u i t e r a p i d l y from t h e n o r t h , such t h a t a deep quite rapidly from the north, such that a deep trough runs parallel t h e axis a x i s of of the t h e basin b a s i n along along the t h e Minnesota Minnesota shoreline. s h o r e l i n e . This This depression depression the is first f i r s t distinguishable d i s t i n g u i s h a b l e in in the t h e west west near n e a r the t h e mouth mouth of of the t h e French FrenchRiver, River, is it achieves a c h i e v e s aa maximum maximum u n t i l it and deepens deepens and and broadens broadens northeastward, northeastward until and depth of of 290 290 meters meters off o f f Silver S i l v e r Bay Bay Minnesota. Minnesota. depth The major major stratigraphic s t r a t i g r a p h i c components components of of the t h e basin b a s i n are are Keweenawan Keweenawan The tills c l a s t i c and v o l c a n i c rocks, unconsolidated Superior Lobe g l a c i a l tills clastic and volcanic rocks, unconsolidated Superior Lobe glacial of Wisconsinan age, and t h e p o s t and l a t e g l a c i a l l a c u s t r i n e sediments of Wisconsinan age, and the post and late—glacial lacustrine sediments T i l l reflectors r e f l e c t o r s are a r e commonly commonly broad, broad, of Superior Superior and and earlier e a r l i e r lakes. l a k e s . Till of d i f f u s e and n o i s y y and a r e r a r e l y t r a c e a b l e over more t h a n a few diffuse and noisy, and are rarely traceable over more than a few kilometers. They appear o n l y s p o r a d i c a l l y a c r o s s t h e basin. The conconkilometers. They appear only sporadically across the basin. The t i l l and and lacustrine l a c u s t r i n e sediments sediments is i s generally g e n e r a l l y parallel parallel ttact a c t between between the t h e till t o the t h e present—day present-day lake l a k e bottom bottom but but in i n places p l a c e s may may show show relief r e l i e f several several to meters greater g r e a t e r than than the t h e modern modern depositional d e p o s i t i o n a l surface. s u r f a c e . This This contact c o n t a c t is is meters one of t h e most d i s t i n c t i v e f e a t u r e s on almost a l l t h e r e c o r d s and i one of the most distinctive features on almost all the records and iss d e f i n e d by by aa crisp c r i s p even—to—wavy even-to-wavy or o r diffracted d i f f r a c t e d reflector r e f l e c t o r which which separates separates defined t i l l signature s i g n a t u r e from from the t h e highly highly t h e noisy, n o i s y , commonly commonly reflection—free r e f l e c t i o n - f r e e till the t r a n s p a r e n t lacustrine l a c u s t r i n e unit. unit. transparent The lacustrine l a c u s t r i n e section s e c t i o n typically t y p i c a l l y contains c o n t a i n s numerous numerous high high continuity continuity The even-to-wavy r e f l e c t o r s which mimic t h e t i l l l a k e sediment c o ntact. even—to—wavy reflectors which mimic the till—lake sediment contact. o n t h e o r d e r of 25 Maximum accumulations of fine-grained sediments, Maximum accumulations of fine—grained sediments, onthe order of 25 meters, occur i n t h e a x i s of t h e North Shore Trough. R e f l e c t o r s within meters, occur in the axis of the North Shore Trough. Reflectors within onlap t h e s teep tthis h i s unit u n i t are a r ecommonly commonly pparallel arallel b u t w i t h i n t h e trough but within the trough onlap the steep trough s i d e s and o c c a s i o n a l l y d i v e r g e down basin. Contorted r e f l e ctors trough sides and occasionally diverge down basin. Contorted reflectors in certain c e r t a i n areas a r e a s suggest suggest slumping slumping and the t h e lack l a c k of of lacustrine l a c u s t r i n e sediments sediments in and has taken taken place p l a c e on on the t h e flanks f l a n k s of of the t h e trough. trough. Section Section thickness t h i c k n e s s and and has r e f l e c t o r concentration c o n c e n t r a t i o n increase i n c r e a s e from from the t h e basin b a s i n edges edges to t o the t h e basin basin reflector L a c u s t r i n e sediment sediment isopachs isopachs are a r e grossly g r o s s l y parallel p a r a l l e l to t o the t h e bathybathydeeps. Lacustrine deeps. m e t r i c contours except i n t h e extreme western p o r t i o n of t h e a r e a where metric contours except in the extreme western portion of the area where an anomalous sediment d i s t r i b u t i o n occurs. Offf tthe h e French and Lester Lester an anomalous sediment distribution occurs. Of French and Rivers are a r e concentrations c o n c e n t r a t i o n s of of sediment sediment of of up up to t o 20 20 meters meters which which are a r e not not Rivers r e l a t e d t o t h e modern bathymetry o r modern sediment focusing e f f e c t s. related to the modern bathymetry or modern sediment focusing effects. i s an a r e a of e l e v a t e d a c o u s t i c baseBetween t h e two "mud patches," Between the two "mud patches," is an area of elevated acoustic basement, approximately approximately 50 50 meters meters below below the t h e present p r e s e n t lake l a k e level l e v e l and and buried buried ment, 61 �3—5 3-5 meters m e t e r s beneath fine—grained f i n e - g r a i n e d sediments, sediments, which which externally e x t e r n a l l y resembles resembles a a broad, broad, curved, curved, spit—shaped spit-shaped sand sand body. body. AA linear l i n e a r submerged submerged ridge r i d g e close close and and parallel p a r a l l e l to t o the t h e Wisconsin shoreline s h o r e l i n e also a l s o at a t depth d e p t h of of 50 50 meters meters appears shallow appears to t o be be an an ancient a n c i e n t low low lake l a k e level l e v e l strand s t r a n d line. l i n e . These shallow water water features f e a t u r e s suggest s u g g e s t the t h e past p a s t existence e x i s t e n c e of of aa low low lake l a k e stage s t a g e 50 50 meters meters below below current c u r r e n t lake l a k e level. level. 62 �Metamorphism of of Kuruman Kuruman and and Griguatown Griquatown Iron Iron Formations Formations and and Metamorphism Associated Makganyene Diamictitey Cape Provincey South Associated Makganyene Diatnictite, Cape Province, South Africa: AA Stable Stable Isotope Isotope Investigation Investigation Africa: E. SCHUESSLER SCHUESSLERAND AND E.C. E.C. PERRY, PERRYyJR. JR. (Northern (Northern Illinois Illinois University) University) E. 6 Oxygen isotope isotopegeothermoinetry geothermometry of cores of of 2200X106 2200x10 m.y. may.old old Oxygen of cores Kuruman and Griquatown Iron Formations and overlying Makganyene Kuruman and Griquatown Iron Formations and overlying Makganyene Diamictite*Postmasburg Postmasburg Group, Groupy from from cores cores near near Postmasburg, PostnxasburgyCape Cape Diamictite, Province* South Africa indicate a maximum temperature of Province, South Africa indicate a maximum temperature of metamorphismofofabout about250°C. 250°C Large Large variations variations diagenes/burial metamorphism in the r5 0 of carbonates on the scale of cm indicates that the the in the tS 0 of carbonates on the scale of cm indicates that iron formation acted as a series of closed subsystems during iron formation acted as a series of closed subsystems during diagenesislmetamorphism and and has has remained remai ed closed closed to to post— postdiagenesis/metamorphism metamorphic isotope isotope exchange exchange for for 2X10 2x10 years. years. Thus, Thusy apart apart from from metamorphic metamorphic effects, effects* these these Proterozoic Proterozoic South South African African iron iron forformetamorphic mations retain retain aa record record of of primary primary isotope isotopecomposition. composition. mations diagenesi./burial 9 Proterozoic hemical sediments, sedimentsyincluding including iron ironformations, formationsy Proterozoic1ghemical lk0 compared to modern cherts and carbonates. are depleted in are depleted in 0 compared to modern cherts and carbonates. AA possible explanation of this effect is high ocean temperature and possible explanation of this effect is high ocean temperature and The intimate intimate consequent low low chert—water chert-water isotope isotope fractionation. fractionation. The consequent association of Makganyene Diamictite of glacial origin and iron association of Makganyene Diamictite of glacial origin and iron formation (Powelly this volume) effectively rules out such an formation (Powell, this volume) effectively rules out such an explanation and this iron iron ormation formationwas was precipitated precipitated explanation and implieslbhat implies1hat this by about about 10 10 0100 compared to the the from water water depleted depleted in in 00 by from /oo compared to modern ocean. ocean. modern Carbon isotope isotope composition composition of of carbonate carbonate in in core core from from the the Carbon Makganyene Diamictite varies sympathetically with magnetite Makganyene Diamictite varies sympathetically with niagnetite content in in aa way way that that suggests suggests the the reaction: reaction: content FeCO 3Fe304. 5Fe 0 + C or a ic FeCO ++ 3Fe 04. 5Fe203 2 3 + (or2anlc) 3 3oxide iron minerals in This relat=onsh$p 8e~weLn carbona?e and This relationship between carbonate and oxide iron minerals in the diamictite diamictite matrix matrix reinforces reinforces the the interpretation interpretation that that these these the minerals were were produced produced from from active, activeychemically chemically deposited deposited iron— ironminerals rich precursor precursor phases phases and, and, thus, thus*that that diamictite diamictitedeposition depositionwas, wasy rich contemporaneous with with the the chemical chemical precipitation precipitation of of iron iron in part, party contemporaneous in formationminerals. minerals. formation . Oxygen isotopic isotopic study study of of two two iron iron formation formation cores cores helps helps Oxygen interpret diageneticlmetamorphic processes occurring in interpret diagenetic/metamorphic processes occurring inththe rocks. In In core core CS119, CSl1gy carbonate carbonate is is coarse—grained. coarse-grained. Its Its 6 00 rocks. varies by by only only 11 O/oo suggesting low-temperature exchange with varies /oo suggesting low—temperature exchange with magnetite and and Si02 SiO followed by carbonate recrystallizaf~on and magnetite followed by carbonate recrystallizaon and 2 of isolation from from further further isoto ic exchange. exchange. In In CS12O, CS120y 6 00 of isolation isotoRic carbonate varies varies by by several several g/00 loo and and is is correlated correlated on on aa cm cm scale scale carbonate consequence of of this this pattern pattern is is that that with per percent centinagnetite. magnetite. AA consequence with several apparent apparent siderite—magnetite siderite-magnetite oxygen oxygen isotope isotopetemperatures temperatures several from this core are about 100° higher than quartz-magnetite from this core are about 100°C higher than quartz—magnetite temperaturesy while while quartz—siderite quartz-siderite "temperatures" "temperatures" are are often often temperatures, O°C To below 0°C. To explain explain oxygen oxygen isotopic isotopic values values for for quartz, quartzy mag— magbelow netite* and siderite in @is core* it is necessary to postulate netite, and siderite in is core, it is necessary to postulate that siderite siderite exchanged exchanged 00 with with magnetite magnetite at at relatively relatively low low that temperatureythen then ceased ceased to to react react while while magnetite magnetite continued continued temperature, Be 63 �to exchange isotopes with quartz to temperatures of about 250°C. 250°C Thus, it appears that before crystallization crystallization siderite siderite is is more reactive than quartz whereas after recrystallization recrystallization it it is is relatively isolated from from further further oxygen oxygen isotope isotope exchange. exchange. Other explanations are inconsistent with isotope geothermometry. �Early Proterozoic ProterozoicPenokean Penokean Igneous Igneous Rocks Rocks of the Lake Lake of the andTectonic Tectonic Imp1 Implications Geochemi stry and ications Superior Region: Region: Geochemistry Klaus J. J. Schulz Klaus Schuqz U.S. U-S- Geological Geoloqical Survey Survey National Center, National cenier*M.S. M S . 954 934 VA 22092 22092 Reston, VA The composition of of igneous rocks from The nature nature and and composition igneous rocks from ancient terranes terranes can can provide significant insights into active during theirr provide significant intothe thetectonic tectonicprocesses processes active during thei recently only only limited limiteddata data were were available for f o r the the Early Early formation. Until recently formation- igneousrocks rocksofof the the Lake Proterozoic Penokean 1900-184OMa) igneous Lake Superior Proterozoic Penokean ( 1900—l840Ma) region, region* particularly particularly those those that thatconstitute constitutethe thevolcanic—plutonic volcanic-plutonic terrane terrane of of withthe the recent recent review review of of available major major northern Wisconsin. Wisconsin- However, However* with element data for for volcanic by by Greenberg element data volcanic rocks rocksofofthe theregion region Greenbergand andBrown Brown (1983), (1983)* the acquisition the acquisitionofoftrace—element trace-el ement data data (including (incl udi ngrare—earth rare-earth element el ement data) data) for f o r the thevolcanic volcanicrocks rocksofofupper upperMichigan Michigan(Fox, (Fox*1983) 1983)and and northern northernWisconsin Wisconsin (Schulz,* 1983), and the the documentation documentationofofthe the compositional compositional characteristics characteristics 1983) * and (Schulz of the others, 1983), the granitoid granitoid rocks rocks ininnorthern northernWisconsin Wisconsin (Schulz (Schulz and and others* 1983)* the nature compositional aaffinities igneous can f f i n i t i e sofofthethe igneousrocks rocks cannow nowbebemore more nature and and compositiona1 fully evaluated usedto to understand understandthe thetectonic tectonicactivity activity during fully evaluated and and used during the the Early Proterozoic evolutionofof the the region. Early Proterozoic Penokean Penokean evolution region- In upper igneousrocks rockswithin within the the dmi dominantly nantly sediupper Michigan, Michigan, Penokean Penokean igneous mentary MarquetteRange Range Supergroup consist basaltf1flows andgabbroic gabbroicsf1 sills, mentary Marquette Supergroup consist of of basalt ows and 1s * andlesser lesser amounts amounts basalticand andrhyoli rhyolitic volcaniclastic and of ofbasaltic t i c volcanic1 astic rocks. rocks. These suites are distinctly lesser rhyolite distinctlybimodal bimodal with withbasalt basaltand and.lesser rhyolitepredominant, predominant* show strong tholeiitic iron enrichment trends, and relatively highconcenconcenshow strong tholei i t i c iron enrichment trends * and re1 ativelyhigh rocks are are compositionally The rocks compositional 1y lithophilee (LIL)elements. trations of of large—ion large-ion lithophi1 (LIL) elements- The similar those of of the simil a r to to continental—rift continental - r i f t and and plateau plateau volcanics volcanics such such as as those Keweenawan Supergroup LakeSuperior Superiorregion region and and those those of the Keweenawan Supergroup of of thetheLake theColumbia Columbia River Basalt Basalt Group Group of of Washington, Washington*Oregon, Oregon, and and Idaho. Idahovolcanic within the In northern northern Wisconsin, Wisconsi n 9 Penokean Penokean vo1 canic sequences sequences within the volcanic— volcanicplutonic p1 utonic terrane terrane consist consist 0f of basalt basalt through through andesite andesite and and rhyolite rhyolite flows f1 ows and and These volcanic volcanic rocks w i t h associated associated subvolcanic subvol canic iintrusives. ntrusives- These rocks pyroclasti cs with pyroclastics are caic—alkalineand andare areenriched enrichedi ninLIL LILelements elements( i(i.e., -e. * are dominantly dominantly calc-alkaline [La/YbJN=2.5—9.4) aredepleted depletedinin high-f high—field—strength [La/Yb]N=2.5-9.4) b ubut t are iel d-strength elelements ements ( i(i.e., .e. * Hf, Hf, Zr, Zr, Ta, Ta*etc.) e t c - )and andare aresimilar similartot volcanic o volcanicsequences sequences found found in recent recent In contrast, the (e.g., New arcs). In the New Hebrides Hebrides and and Japanese Japanese arcs) iisland—arcs sland-arcs (e-gbasalts Formationfrom fromnortheastern northeasternWisconsin Wisconsin basalts of of the theQuinnesec Quinnesec Formation areare t htholeiitic oleiitic [LalYb]~ 0.09-0.89]* = =0.09—0.89], in character, character* are a r e strongly strongly depleted depleted in inLIL LILelements elements [i.e., [i .e-[La/Yb]N and are compositional compositionally similar basinbasalts basalts (e.g. (e.g.,* Lau and are 1y simi l a r to to recent recent back—arc back-arc basin Lau Basin) and is1 island—arc tholeiites (e.g(e.g.,* Scotia Basin) and and-arc tholeiites Scotia arc). arc). The Penokeangranitoid granitoid rocks rocks of of northern northernWisconsin Wisconsin show show aa temporal temporal The Penokean progressionfrom fromgabbro gabbroand and dioritethrough throughtonal tonalite to granite. These progression diorite i t e to rocks are mostly mostlyca1 calc—alkaline, althoughslslightly alkaline rocks are c-a1 kaline* although ightly a1 kali ne varieties varieties ((i.e. i .e. Marinette MarinetteQuartz QuartzDiorite, Diorite*northeastern northeasternWisconsin) Wisconsin) are are also also present. present. The granitoids granitoids show increasefrom fromnorth northt oto south southacross acrossthe theterrane terrane in in The show ananincrease ratios and are compositionally K20lNa20 ratios and overall Si02 Si02 contents. contents- They They are cmposi tional ly ttheir h e i r K20/Na20 similar modern, (e.g. Japan) Japan) simil a r to togranitoids granitoidsfound foundinin modern*evolved evolved island—arcs i s1 and-arcs (e.g., and continental continental convergent-plate—margin settings (e.g. (e.g.,* Sierra and convergent-plate-margi n settings SierraNevada Nevada batholith). bath01 it h ) 65 65 �The The nature and and geochemistry geochemistry of the the Early EarlyProterozoic ProterozoicPenokean Penokeanigneous igneous •rocks rocks of the the Lake Lake Superior Superior region region strongly strongly suggest suggest the the operation operation ofofplate— platetectonic processes largely similar similar to processes largely t o those those active active today. today. The The data support support basalt-rhyolite aa tectonic modelo fof1)1)early earlycrustal crustalrrifting tectonic model i f t i n g (bimodal (bimodal basal t-rhyol i t e volcanism, volcanism, upper upper Michigan) and and spreading, spreading, 2) 2)subsequent subsequent subduction subduction and and formation of a volcanicarc arc(tholei (tholeiitic, formation of a complex compl ex volcanic i t i c ,and and caic-alkaline cal c-a1 kal i nevolcanism vol cani sm and plutonism,northern northernWisconsin), Wisconsin), thearc arcf ifirst and plutonism, andand collcollision ision of ofthe r s t with with Archean crust on continental—margin Archean crust on the the south southand and then thenwith withthe the continental-marginsequence sequence and Archeancrust crust of of upper Michigan on onthe the north north (i.e., and Archean upper Michigan (i.e., thet hPenokean e PenokeanOrogeny). Orogeny). References References Fox, p., 1983, Fox, Thomas Thomas P., 1983, Geochemistry Geochemistry of the theHemlock Hemlock metabasalt metabasalt and and Kiernan Kiernan thesis, Michigan sills, County, s i l l s Iron , Iron County,Michigan: Michigan: Unpubl. Unpubl. MS MS thesis, Michigan State State p. 81 p. University, 81 Greenberg, Jeffrey K., Greenberg, Jeffrey K., and and Brown, Brown, Bruce Bruce AA., . , 1983, 1983, Lower Lower Proterozoic volcanic volcanic Geol. rocks andt htheir Superiorddistrict: rocks and e i r setting in in the the southern southern Lake Lake Superior i s t r i c t : Geol. Soc. Memoir 160, 160, p. p. 67-84. Soc. America America Memoir 67-84. Schulz, Klaus J., J., 1983, the volcanic volcanic rocks Schulz, Klaus 1983, Geochemistry Geochemistry ofof the rocks of of northeastern northeastern 29th,Houghton, Houghton, I n s t i t u t eononLake LakeSuperior SuperiorGeology, Geology ,29th, Wisconsin [abs.]: Wisconsin Eabs.: Institute Michigan, Michigan. Schulz, J., Sims, Schulz, Klaus Klaus J., Sims, P. P. K., K., and andPeterman, Peterman, Zell ZellE., E., 1983, 1983,Geochemistry Geochemistry of Early [abs.]: Geol. Early Proterozoic Proterozoic granitic granitic rocks, rocks, northern northern Wisconsin Wisconsin Cabs.]: Geol Soc. Abstracts wwith Soc. America America Abstracts i t h Programs, Programs, v.v. 15, p. p. 681. 681. . 66 �Regional Reqional Controls Controls of Lower Precambrian Precambrian Metallogeny in in the the Upper Upper Peninsula of Michigan Michigan MICHAEL J. J. SCHWARTZ SCHWARTZ (Dept. (Dept. of ofGeology, Geology,Univ. Univ.1Nis.-Parkside, Wis.-Parkside, Kenosha, Wi. W i.53141) 53 1 4 1 ) PETER PETER AA. . NIELSEN NIELSEN (Dept. (Dept. of Geology, Geology, Univ. Wis.-Parkside, Wis.-Parkside, Kenosha, Wi. 53141) Kenosha, Wi. 53 141) This is an attempt attempt at atfinding findingany anylarge largescale scaleregional regional controls controls of metallogeny metallogeny in in the theUpper UpperPeninsula Peninsula of of Michigan. Michigan. To limit limit the the extent toArchean Archean extent of this this study study we we are are restricting restricting the the scope scope of ititto and and lower lower middle middle Precambrian Precambrian sections sections and and not not including including the Keweenaw which regional Keweenaw which has has obvious obviousstructural structural controls controls at aa regional level. an information information base level. We We have have gathered gathered an base of structural structural and and lithologic trends ( 1 :250000) and andsmall smallscale scale trends from fromboth bothlarge largescale scale(1:250000) (1:24000) maps and and an an unpublished M.S. thesis by Bodwell (1:24000) maps unpublished M. S. thesis Bodwell (1972, (1972, all reported MTU). Bodwell Bodwell covered covered all reported metal metal locations locations and and this this was was used as as the the primary primary data-base. data-base. By plotting plottingstructure structureand andlithology lithologyon ona abase basemap mapand andmaking making overlays of different (Au ++ Cu + Ag, overlays of different metal metal associations associations (Au Ag, Au Au ++ Ag, Ag, Au ++ base base metal metal sulfides, sulfides, Cu Cu + Mo, Mo, base base metal metal sulfides) sulfides) regional regional structural/lithologic structural/lithologic metallogenic metallogenic patterns patterns are are shown, shown, if i f present. present. For purposes purposes of simplification simplificationthe theUpper UpperPeninsula Peninsulahas hasbeen been divided divided into into three threeareas: areas: The Marquette Marquette Range, Range, The TheGogebic-Watersmeet Gogebic-Watersmeet area, area, and and the the Crystal CrystalFalIs-Menomonee-lron Falls-Menomonee-Iron River River areas. areas. This is is based on on some somephysical physical separation separation of of these areas. areas. These These areas areas have have a common although stratigraphic stratigraphic columns columns are are not common Paragenesis Paragenesis although not. exactly exactly the thesame. same. After After following following this thisprocedure procedure hopefully hopefully some some relations relations will become apparent. apparent. At A t this thispoint pointmy myresearch research isis not notcomplete complete but but some some apparent trends are are present. present. In the the Gogebic-Watersmeet Gogebic-Watersmeet area area gold deposits deposits seem seem to be confined greenstone belt and the very gold confined to aa greenstone near In near proximity. proximity. In the northern northern Marquette Marquette Range Range base base metal metal deposits follow the the limbs limbs of of an an apparent apparent fold. Bodwell, Bodwell, Willard Willard H., H., 1972. 1972. Geologic Compilation Compilation and and Nonferrous Nonferrous Metal Metal Potential, Potential, Precambrian Precambrian Section, Sect ion, Northern Northern Michigan, Michigan, unpublished MS thesis, thesis, MTU. 67 . �Trace Trace Element Element Geochemistry Geochemistry of of Some Some Lake Lake Superior Superior Keweenawan Keweenawan Basic Layered Intrusions Intrusions . KARL KART,, E. E. SEIFERT SEIFERT (Dept. (Dept. of of Earth Earth Sciences, Sciences, Iowa Iowa State S t a t e University, U n i v e r s i t y , Ames, Ames, IA 50011) 50011) IA Seven REE (La, Ce, Lu), C e , Sm, Sm, Eu, Eu, Tb, Tb, Yb, Yb, and andL u ) , Ca, Co, Cr, C r , Th, Th, Hf, Hf, Ta, Ta, Sr, Sr, SevenREE Rb, Rb, and and Ba B a have been determined by instrumental i n s t r u m e n t a l neutron activation activation analysis a n a l y s i s (IRAA) (INAA) for f o r rocks rocks from from the t h e Duluth complex, complex, Mineral Lake Lake intruintrusion, s i o n , and the t h e Rearing Rearing Pond Pond intrusion. i n t r u s i o n . The The trace t r a c e element element characteristics characteristics of of the t h e various v a r i o u s units u n i t s comprising these t h e s e intrusions i n t r u s i o n s can be combined combined in in their t h e i r appropriate a p p r o p r i a t e abundances to t o dderive e r i v e the t h e ccharacter h a r a c t e r of of their t h e i r parental parental magmas. For For the t h e Mineral Lake intrusion, i n t r u s i o n , this t h i s calculated c a l c u l a t e d composition is is compared to t o a chill c h i l l zone zone sample sample and and found found to t o be b e markedly markedly different. different. Insufficient data Insufficient d a t a aare r e aavailable v a i l a b l e on the t h e Rearing Pond iintrusion n t r u s i o n to to calculate c a l c u l a t e aa parental p a r e n t a l magma magma composition. composition. The parental p a r e n t a l magma compositions are a r e compared to t o the The t h e most primitive primitive It North Shore Shore volcanic v o l c a n i c composition composition to t o test t e s t for f o r aa genetic g e n e t i c relationship. r e l a t i o n s h i p . It North i s not n o t possible p o s s i b l e to t o derive d e r i v e the t h e intrusive i n t r u s i v e parental p a r e n t a l maginas magmas from is from the t h e most most p r i m i t i v e North Shore vvolcanic o l c a n i c composition by magmatic differentiation differentiation primitive v a r i o u s parental p a r e n t a l tnagmas magmas can e l a t e d by can only only be be rrelated by more more complex alone. The various alone. models. 68 �-- - - Dikes as as Tectonic Tectonic Indicators Indicators -Dikes in Lake Superior Superior Region Region — in the the Eastern Lake Structural Structural and and Paleomagnetic Paleomagnetic Considerations Considerations - Shaw E.G. Geology, University of Torontof Toronto, Erindale Erindale E .G. Shaw (Dept. (Dept. of of Geologyf College, Mississaugaf Mississauga, Ontario, Collegef Ontario, Canada Canada L5L L5L 1C6) lC6) The majority of rocks have undergone undergone complex Early The majori* of Archean rocks Precambrian deformation, and thus, are of limited use use in defining Precdrian deformation, nature and timing of pst-Archean post-Archean tectonic the nature tectonic events. events- It It is is clear, however, from the abundance abundance of faults and shear-zones shear—zones in clearf however, areas that shield axeas that later later Precambrian Precambrian tectonic tectonic events events of of some some kind kind have have indeed indeed occurred. occurrd- Where aa shield shield is is overlain overlain by Middle to to Late volcanic/sedimentary sequences, sequences, tilting, fault Late Precambrian Precambrian volcanic/sedimentary displacement, displacementf and and other other deformational deformational features features can can often often be be directly directly observed observed and and constraints constraints placed placed on on the the age age and and extent extent of of part, howeverf however, such Precambrian cover deformation- For the the most partf deformation. rocks are confined to localized rocks localized areas areas on on shield shield margins. Ernst Ernst and and Halls Halls (1984) (1984) have shown from a study of dikes in Kapuskasing Zone, dike attitudes the I?apuskasing Zonef that that dike attitudes and and paleomagnetic paleomagnetic signatures may may be used as tectonic tectonic indicators indicators in in the the Canadian Canadian signatures Shield. study, dikes of the same swarm which In their studyf the same which differed differed Shieldfrom the norm b both attitude and paleomagnetic direction from the t h in in attitude and paleomagnetic direction were were used to association with with to show show aa westward tilting of the crust in association upthrusting upthrusting along along the the eastern eastern margin margin of of the the Zone. Zone. Patches of lakeward—dipping lakeward-dipping Keweenawan Kewenawan volcanics volcanics and and Patches sediments show show that sediments that the the shield shield along along the the coast coast of of Lake Lake Superior Superior has has been heen involved involved in in basin basin subsidence. subsidence. These These Keweenawan Kewenawan rocks, rocks, however, shore and thus however, are are only only rarely rarely found along the eastern shore define the are insufficient insufficient to define the full full extent extent of of shield shield deformation deformation with basin basin developentdevelonent. On On the the other hand, associated with handf dikes are are pervasive both pervasive b t h on the Lake Superior coast and in the interior of ield (1951) (1951) observed observed that the the dikes dikes in the the shield. shield- Muff Nuffield in the the Montreal Montreal River River Harbour Harbour area area dip dip NE; NE; dikes dikes north north and and east east of of the the lake have been been observed lake have observed to to be be near—vertical. near-vertical. This This is is an an ideal ideal environment in apply and environment in which to apply and extend extend the the findings findings of of Ernst Ernst and and Halls. Halls addition, the Montreal Montreal River follows major fault In additionf follows a ma-jor fault that that may may be be the the southern southern extension extension of of the the eastern eastern boundary bundary thrust thrust of of the was thought that if the Kapuskasing Kapuskasing Zone. Zone- It was of if faulting faulting had been been of major major extent, extentf an an overprint overprint dating dating from from fault fault movement movement (and (and Kapuskasing activity in in general) general)would uld be Kapuskasing activity be evident evident in in the the paleomagnetic signature dikes cutting paleomagnetic signature of of dikes cutting the the fault. fault. The The purpose of this study, thenf then, was was to use use the palemagnetic palemagnetic signature attitude of dikes to signature and attitude of dikes to 1) 1) determine determine the the nature nature and and Keweenawan extent of eastern—shore eastern-shore shield shield deformation deformation related relatedto toKeweenawari extent of basin subsidence subsidence and and 2) 2) look look for for signs signs of of Kapuskasing Kapuskasing activity activity along the the Montreal Montreal River River fault. faultalong 69 �Thirty—nine Thirty-nine paleomagnetic paleomagnetic sites sites comprising comprising aa total total of of 300 300 samples were collected from northwest—trending diabase dikes samples were collected from northwest-trending diabase dikes along along two two traverses traverses roughly roughly normal normal to to the the eastern eastern shoreline shoreline of of Lake Lake Superior Superior and and oblique oblique to to the the trend trend of of the the dikes. dikes. The The northern northern traverse, traverse, about about 45 45 km km long, long, follows follows the the Montreal Montreal River River to to the the Since it it was was important imprtant to to know know the the structure structure and and coast. mast. Since paleomagnetism paleomagnetism of of dikes dikes in in aa relatively relatively stable stable area, area, aa southern southern traverse—remote traverse-remote from frompossible possibleinfluences influencesof of Kapuskasing Kapuskasing and and Lake Lake Superior This traverse traverse is is defomation-waschosen chosenas asaacontrol. control. This Superior deformation—was located located 55 to to 10 10 km km south south of of the the northern northern traverse, traverse, 35 35 km km from from the the and and extends eastward eastward for aa distance distanceof of7070km. km. Twenty—three Wenty-three dikes dikes in inthe thesouthern southern traverse traverseand and sixteen sixteendikes dikesin inthe thenothern nothern mast, coast, traversewere weresampled. sampled. traverse paleomagnetic direction, direction?there thereappear appear to to be ke at at least least Based on on paleomagnetic Based four four ages ages of dike intrusions intrusions in in the theinterior interiorcorresponding correspnding to to Keweenawan, Keweenawan, Sudbury, Sudbury, Matachewan Matachewan and and an an undated undated dike dike set set which which cuts cuts aa Huronian Huronian outlier outlier and and has has aa similar similar paleomagnetic paleomagnetic direction direction to to that that of of Abitibi Abitibi and and Preissac Preissacdikes. dikes. All All sampled sampled interior interior dikes dikes trend NW to N, and beyond about two km from the shoreline, trend W to N, and beyond about two km from the shoreline, dip dip In the the field, field, less less than than 55 to to 10 10 degrees degrees from from the the vertical. vertical. In samples samples generally generally appear appear fresh, fresh, though though apparent apprent deuteric deuteric Dikes within within about about two two km km alteration is present present in in some some margins. margins. Dikes alteration is of more westerly of the the shoreline shoreline tend tend to to have have aa more westerly trend trend and and all all dip dip NE NE at at angles angles ranging ranging from from 45 45 to to 70 70 degrees. degrees. These These dikes, dikes, in in comparison caparison with with those those of of the the interior, interior, are are more m r e altered altered and and sheared, sheared, especially especially at at the themargins. margins. An An easterly easterly rotation rotation of of approximately approximately 40 40 degrees degrees about about aa NW NW returns direction of returns both b t h the the attitude attitudeand andpaleomagnetic paleomagnetic direction of the the coastal dikes dikes to tothose thoseof ofthe thecontrol controlgroup. group. This is isininagreement agreement coastal with to return the with the rotation rotation needed needed to the Keenawan EQweenawan rocks in in the the combinationofofrotated rotated attitudes attitudes and south to the the horizontal. horizontal. The The combination @ axis axis paleotnagnetic poles—andalso also the the large paleomagnetic ples-and large degree degree of ofshearing— shearing- indicates dips and andstrikes strikes of the indicates that thatthe thepresent presentanomalous anomalous dips the coastal dikes are due to to tectonic rotation rotation and and not to to aa geographic geographic in orientation orientation of of the thetensional tensionalenvironment environmentduring during change in emplacement. enplacement. In In addition, addition, the the study study shows shows that, that, at at least least locally, locallyr aa rim been tilted in rim of of shield shield no no more than than 22 km wide has keen in response respnse to subsidence subsidence in in the the Lake Lake Superior SuperiorBasin. Basin. to Preliminary structural structural and and palenagnetic palemagnetic data data from from the the NW NW Preliminary trending dikes dikes cutting cutting the the Montreal Montreal River River Fault Fault suggest suggestthat that trending little little activity activiw has has occurred occurred in in the the area area since since emplacement emplacement of of these dikes. dikes. these 70 �Characterization C h a r a c t e r i z a t i o n of of the t h e Ore Ore Host Host Rock Rock at a t the the Ropes Gold Gold Mine, Mine, Ishpexning, Ishpeming, Michigan Michigan Ropes Anthony W. Shepeck Shepeck and and Theodore Theodore J. J. Bornhorst Bornhorst (Dept. (Dept. of of Geol. Geol. && Geol. Geol. Anthony W. Engrg., 49931) M I 49931) Engrg., Michigan Michigan Technological Technological University, U n i v e r s i t y , Houghton, Houghton, MI Gold i s contained contained within w i t h i n an an Gold mineralization m i n e r a l i z a t i o n at a t the t h e Ropes Ropes Gold Gold Mine Mine is east—west east-west trending, t r e n d i n g , nearly n e a r l y vertical, v e r t i c a l , tabular, t a b u l a r , schistose s c h i s t o s e rock rock body body which The ore o r e host h o s t rock rock which .s i s surràunded surrounded by by the t h e Deer Deer Lake Lake Peridotite. P e r i d o t i t e . The (OHR) can be divided into four mappable units based on the relative (OIiR) d i v i d e d i n t o f o u r mappable u n i t s based on t h e r e l a t i v e abundance abundance of of layer l a y e r silicate s i l i c a t e minerals, m i n e r a l s , which which make make up up the t h e majority m a j o r i t y of of the OHR, and and whole whole rock rock chemical chemical composition: composition: 1) 1 ) mostly mostly sericite; sericite; t h e OHR, 2) 3 ) mostly mostly chlorite; chlorite; 2) about about equal e q u a l amounts amounts of of sericite s e r i c i t e and and chlorite; c h l o r i t e ; 3) and and 4) 4 ) chlorite c h l o r i t e and and carbonate. carbonate. Quartz Quartz is i s ubiquitous u b i q u i t o u s throughout throughout all all t h e units. u n i t s . Disseminated Disseminated pyrite p y r i t e and and lesser l e s s e r amounts amounts of of magnetite magnetite are are the also a l s o present. p r e s e n t . The The carbonate carbonate is i s dolomite dolomite with w i t h minor minor ankerite. a n k e r i t e . DisDisseminated seminated gold gold is i s most abundant abundant in i n the t h e more sericitized s e r i c i t i z e d and.silici— and.si1icified f i e d units. u n i t s . However, However, the t h e highest h i g h e s t gold gold values v a l u e s in i n the t h e mine mine are a r e assoassociated with quartz—sulfide veins which were the target for ciated with quartz-sulfide veins t h e t a r g e t f o r the t h e early early These veins v e i n s are a r e cross—cut cross-cut by by barren b a r r e n carbonate carbonate veins. veins. mining. These mining. The OHR units u n i t s can can be be The layer l a y e r silicate s i l i c a t e minerals minerals within w i t h i n the t h e various v a r i o u s OHR distinguished d i s t i n g u i s h e d by by composition, composition, structural s t r u c t u r a l type type and and textural t e x t u r a l criteria. criteria. In I n general, g e n e r a l , chiorites c h l o r i t e s are a r e clinochiore c l i n o c h l o r e but b u t in i n detail d e t a i l can can be be subdivided subdivided into: Ib chlorite, c h l o r i t e , relarelai n t o : Type Type 1) 1 ) an an early e a r l y fine—grained, fine-grained, lower lower ordered ordered lb tively with aa composition composition of of [(Mg11 2Fe08+2) t i v e l y enriched enriched in i n Mg Mg and Si [(Mgll.2Feo.8+2) S i with (Si71Al0g) is a (Si7.lAlc.g) 020 020(OH)16)] (OH)16)] which which commonly commonly defines d e f i n e s foliations f o l i a t i o n s and and is major and Type Type 2) 2) aa later l a t e r porphyroblastic, porphyroblastic, major component component of of the t h e matrix; m a t r i x ; and higher I I b chlorite, c h l o r i t e , which is i s relatively r e l a t i v e l y higher h i g h e r in i n Fe Fe and and Al A1 h i g h e r ordered ordered lib Seri— seriwith compositionofof[ ([(Mg.7Fe332) w i t h aa composition ~ ~71?e3. 8 . 3+2) ((Si58Al22) s i 5 8 ~ 1 2 . 2 )020 o~~ (OH)16]. (OH)16] cites Fe and and Mg Mg K, Al Al. muscovite muscovite with w i t h low low Na, N a , Fe c i t e s are a r e essentially e s s e n t i a l l y an an ideal i d e a l K, Type A) A) an an early e a r l y fine— fineand and can can also a l s o be b e subdivided subdivided into i n t o two two varieties: v a r i e t i e s : Type grained mica which which commonly commonly occurs o c c u r s in i n discrete d i s c r e t e blebs b l e b s or o r in i n torn torn grained 2. mica fragments; fragments; and Type B) B) a later l a t e r highly h i g h l y crystalline, c r y s t a l l i n e , coarser c o a r s e r 2m1 mica mica c h l o r i t e s are a r e rereThe Type Type 11 chiorites which which commonly commonly occurs occurs in i n the t h e matrix. matrix. The stricted s t r i c t e d to t o the t h e less l e s s intensely i n t e n s e l y altered a l t e r e d gold—poor gold-poor chlorite c h l o r i t e and and chlorite— chloritecarbonate carbonate units u n i t s of of the t h e OHR OHR whereas Type 22 chlorites c h l o r i t e s and and Type Type BB seri— sericites c i t e s are a r e predominantly found found in i n the t h e more gold—rich gold-rich sericite s e r i c i t e and and sericite—chlorite s e r i c i t e - c h l o r i t e units. u n i t s . The chlorite c h l o r i t e polytypes suggest suggest that t h a t the the later w a s formed formed at a t aa higher h i g h e r temperature temperature than than the the l a t e r Type 22 chlorite c h l o r i t e was earlier c h l o r i t e and e a r l i e r Type Type 11 chlorite and may be b e aa recrystallization r e c r y s t a l l i z a t i o n product product of of Type 1. 1. Their T h e i r compositions compositions reflect r e f l e c t the t h e composition composition of of the t h e fluid, fluid, Type rock and and water/rock w a t e r l r o c k ratios. r a t i o s . The overall o v e r a l l distribution d i s t r i b u t i o n of of the t h e various various types within reflection t y p e s of of layer l a y e r silicate s i l i c a t e minerals w i t h i n the t h e OHR may be a reflection of of hydrothermal hydrothermal gradients g r a d i e n t s established e s t a b l i s h e d during d u r i n g mineralization. mineralization. . zm1 The OHR is i s interpreted i n t e r p r e t e d as a s an an altered a l t e r e d and and sheared sheared rock rock and, and, as a s such, such, The OHR there i s only only speculative s p e c u l a t i v e evidence evidence as a s to t o the t h e original o r i g i n a l protolith. protolith. t h e r e is Whole—rock Whole-rock major and and trace t r a c e element element data d a t a on 63 63 samples samples indicate i n d i c a t e that that the t h e sericite, s e r i c i t e , sericite—chiorite s e r i c i t e - c h l o r i t e and the t h e cchlorite h l o r i t e units u n i t s are a r e composi— compositiortally than tthe t i o n a l l y ddifferent i f f e r e n t than h e Deer Lake Peridotite. P e r i d o t i t e . However, the the i s similar s i m i l a r iin n some e s p e c t s tto o tthe h e peridotite. peridotite. c h l o r i t e - c a r b o n a t e uunit n i t is chlorite—carbonate some rrespects Immobile element element ratios r a t i o s suggest suggest that t h a t the t h e sericite s e r i c i t e unit u n i t is i s similar s i m i l a r to to I=obile andesitic a n d e s i t i c members members of of the t h e Kitchi K i t c h i Schist. Schist. 71 �Petrographic Petrographic and and Geochemical Geochemical Study Study of of the the Mount Mount Bohemia Bohemia Stock, Stocky Portage Lake Lake Volcanics, VolcanicsyKeweenaw Keweenaw Peninsula, PeninsulayMichigan Michigan Portage Kevin Sikkila Sikkila (Dept. (Dept. of of Geol. Geol. && Geol. Geol. Engrg., Engrg.y Michigan Michigan Technological Technological Kevin , University, UniversityyHoughton, HoughtonyMI MI 49931) 49931) Mount 146 m) m) intruded intruded into into the the lower lower Mount Bohemii Bohemia is is aa small small stock stock (284 (284 xx 146 The majority majority of of Mount Mount Bohemia Bohemia section of of the the Portage Portage Lake Lake Volcanics. Volcanics. The section It has has aa stock is is an an altered, altered, medium— medium- to to coarse—grained coarse-grained diorite. diorite. It stock reconstructed reconstructed primary primary mineral mineral assemblage assemblage of of 45% 45% to to 50% 50% sodic sodic plagio— plagio(augite and and hornblende), hornblende), and and up up to to 30% to to 50% 50% mafic mafic minerals minerals (augite clase, 30% clase, considerable amounts amounts of of magnetite magnetite (exceeding (exceeding In addition, additionyconsiderable 3% quartz. quartz. In 3% 15% 15% in in some some areas) areas) are are more more or or less less ubiquitous ubiquitous throughout throughout the the rock rock the body body is is comcomsmall section section in in the the southeastern southeastern portion portion of of the body. AA small body. posed posed of of fine—grained fine-grained quartz quartz diorite diorite with with aa reconstructed reconstructed primary primary 30% quartz,. quartz,.. mineral mineral assemblage assemblage of of approximately approximately 60% 60% sodic sodic plagioclase, plagioclase, 30% A much smaller concentration of inagnetite, about 3%, 7% biotite. A much smaller concentration of magnetitey about 3%, and and 7% biotite. Presumably this quartz is found in this section of the intrusive. Presumably this quartz is found in this section of the intrusive. diorite diorite is is representative representative of of the the final final stages stages of of intrusive intrusive activity. activity. The alteration alteration The dioritehas dioritehasbeen been moderately moderately to to severely severelyaltered. altered. The The shows shows aa strong strong correlation correlation with with the the Lac Lac La La Belle Belle fissure, fissureyaa structural structural N20° through through the the intrusive, intrusivey indicating indicating aa preferential preferential feature striking striking N20°W feature channeling of of hydrothermal hydrothermal fluids. fluids. Potassium Potassium metasomatism metasomatism is is pervasive, pervasive, channeling although heaviest heaviest along along the the fissure, fissure, and and secondary secondary potassium potassium feldspar feldspar although is microscopically microscopically observable observable in in almost almost all all thin thin sections. sections. This, Thisycomcomis bined with with the the alteration alterationof ofprimary primarytnagnetite magnetite to to fine—grained fine-grained hematite, hematitey bined is responsible responsible for for the the pinkish pinkish coloration coloration that that gives gives hand hand specimens specimens the the is misleading appearance appearanceof syenite. Alteration Alteration products products which which are are misleading of aa syenite. epirelatable to to the the fissure fissure position position are: are: serpentine serpentine (from (from mafics); mafics); epi— relatable dote (from (from plagioclase, plagioclasey mafics); mafics); and and calcIte calcite (from (from plagioclase). plagioclase). AlterAlterdote ation products products whose whose abundance abundance is is inversely inversely related related to to the the position position of of ation the fissure fissure include: include: actinolite actinolite (from (from pyroxene) pyroxene) and and sericite sericite (from (from the plagioclase). Alteration Alteration of of mafic mafic minerals minerals to to chlorite chlorite occurs occurs everyeveryplagioclase). finewhere and and it it is is the the alteration alteration product product of of the the biotite biotite in in the the fine— where grained quartz quartz diorite. diorite. grained Geochemical variations variations within within the the intrusive intrusive follow follow aa few few general general Geochemical trends. Concentrations Concentrations of of mobile mobile elements elements such such as as Cu, Cu, Zn Zn and and Rb Rb are are treads. higher along along the the Lac Lac La La Belle Belle fissure. fissure. High High Rb Rb concentrations concentrations can can be be higher specifically correlated correlated with with the the presence presence of of secondary secondaryK—feldspar. K-feldspar. specifically and Ni Ni have have relatively relatively uniform uniform values values ZryVV and Immobileelements elementssuch suchas asZr, I=obile throughout the the diorite diorite rock rockbody. body. Cr Cr varies varies in in aa manner manner which which might might throughout be related related to to original originalmagmatic magmatic processes. processes. The The concentrations concentrations of of imimbe mobile elements elements are are distinctly distinctly different different between between the the main main diorite diorite mobile rock body body and and the the later—stage later-stage quartz quartz diorite. diorite. The Zr concentration concentration The Zr rock concentrations are are is higher higher in in the the more more silicic silicic rock, rocky and and Cr Cr and and VV concentrations is lower. lower. 72 �AA partisan partisan review review of of the the Early Early Proterozoic Proterozoic geology geology of of Wisconsin Wisconsin and and adjacent adjacent Michigan Michigan P. P. K. K. SIMS SIMS and and Z. Z. E. E. PETERMAN, PETERMAN, U.S. U.S. Geological Geological Survey, Survey, Denver, Denver, CO CO 80225; 80225; KLAUS J. SCHULZ, SCHULZ, U.S. U.S. Geological Geological Survey, Survey, Reston, Reston, VA VA 22092 22092 KLAUS J. in the the Two Two contrasting contrasting sequences sequences of of Early Early Proterozoic Proterozoic rocks rocks are are present present in Wisconsin—Michigan interbedded northern epicratonic epicratonic sequence sequence of of interbedded Wisconsin-Michigan region: region: aa northern sedimentary sedimentary and and volcanic volcanic rocks rocks (Marquette (Marquette Range Range Supergroup Supergroup of of Michigan) Michigan) overlying overlying Archean Archean basement, basement, and and aa southern southern terrane terrane dominantly dominantly composed composed of of volcanic volcanic and and granitoid granitoid rocks rocks and and generally generally lacking lacking Archean Archean basement basement (Wisconsin (Wisconsin magmatic magmatic zone). zone). The The boundary boundary between between the the two two terranes, terranes, at at least least in in northeastern northeastern Wisconsin, Wisconsin, is is the the Niagara Niagara fault. fault. The Supergroup is is composed composed of of three three depositional depositional cycles cycles The Marquette Marquette Range Range Supergroup separated separated by by minor minor unconformities. unconformities. In In general, general, the the deposits deposits fine fine upward: upward: basal basal clastic clastic and and chemical chemical deposits, deposits, accumulated accumulated in in rift rift basins basins and and on on platforms platforms (Larue (Larue and and Sloss, Sloss, 1980), 1980), are are succeeded succeeded upward upward by by quartzose quartzose sandstone sandstone and and the the major major iron—formations iron-formations of of the the region. region. These These strata strata are are overlain overlain by by aa southward—thickening southward-thickening wedge wedge of of turbidites, turbidites, areally areally restricted restricted iron—formations iron-formations and, and, in in more more southerly southerly parts, parts, intercalated intercalated submarine submarine volcanic volcanic rocks, rocks, which which are are mainly The depositional depositional patterns patterns indicate indicate aa shelf shelf prograding prograding mainly pillow pillow basalts. basalts. The into being derived derived principally principally from from into aa deep deep water water environment, environment, the the detritus detritus being exposed Deposition took took place place on on aa passive passive exposed Archean Archean rocks rocks to to the the north. north* Deposition continental Sedimentation ceased ceased before before or or during during the the main main pulse pulse of of continental margin. margin. Sedimentation deformation Deformation involved involved sub— subdeformation accompanying accompanying the the Penokean Penokeanorogeny. orogeny. Deformation horizontal horizontal compression compression accompanied accompanied by by substantial substantial shortening shortening of of the the supracrustal supracrustal sequence sequence (Cannon, (Cannon, 1973) 1973) and, and, later, later, dominantly dominantly vertical vertical tectonism tectonism associated associated with with the the development development of of diapiric diapiric gneiss gneiss domes domes caused caused by by reactivation An annular annular pattern pattern of of metamorphism metamorphism reactivation of of Archean Archean basement basement gneiss. gneiss. An around around some some of of the the gneiss gneiss domes domes was was superposed superposed on on regional regional greenschist greenschist metamorphism. metamorphism. The age age of of the the Marquette Marquette Range Range is is poorly poorly defined, defined, but but it it is is bracketed bracketed The between Ic dikes dikes in in basement; basement; Beck and Murthy, 1982) between 2,120 2,120 m.y. m.y. (maf (mafic 1982) and and 1,820 1,820 m.y., Mary, Mich., Mich., that that cuts cuts the the m.y., the the age age of of aa granite granite body body at at Lake Lake Mary, supergroup. supergroup. The The volcanic volcanic rocks rocks in in the the supergroup supergroup as as indicated indicated by by rhyolite rhyolite in in the the Hemlock Hemlock Formation, Formation, are are about about 1,900 1,900m.y. m.y. old old (W. (W. R. R. Van Van Schmus, Schmus, written written comm., corn., 1983). 1983). They They are are largely largely bimodal bimodal with with abundant abundant tholeiitic tholeiitic basalt basalt and and minor minor high high1(20 K20 rhyolite. rhyolite. The The basalt basalt shows shows strong strong iron iron enrichment, enrichment,and and high high Ti02 Ti02 and and incompatible—element incompatible-element contents contents (Fox, (Fox, 1983); 1983); it it is is compositionally compositionally similar similar to to continental continentalbasalts. basalts. Except Except in in aa broad broad sense, sense, aa coherent, coherent, integrated integrated view view of of the the Wisconsin Wisconsin magmatic zone is lacking, partly because of meagre exposures and magmatic zone is lacking, partly because of meagre exposures and partly partly because because of of the the inherent inherent difficulties difficulties of of deciphering deciphering thick, thick, complexly complexly disturbed disturbed volcanic As aa generalization, generalization,the the magmatic magmatic zone zone is is composed composed of of volcanic accumulations. accumulations. As calc—alkaline calc-alkaline volcanic volcanic and and intrusive intrusive rocks rocks having having overall overall island—arc island-arc affinities, affinities, and and more more restricted restrictedgranitoid granitoid gneisses. gneisses* AA key key area area for for understanding understanding the the stratigraphy, stratigraphy,metamorphism, metamorphism, and and tectonic tectonic evolution evolution of of the the magtuatic magmatic terrane terrane is is the the Dunbar Dunbar dome dome and and vicinity vicinity in in northeastern northeasternWisconsin. Wisconsin. The The dome dome is is aa large—scale, large-scale,antiforma]. antiformal fold— fold- 73 �interference structure in diameter, diameter, modified modified by by diapirism and and by by interference structure about about 20 20 kin km in intrusion intrusion of of tonalite, tonalite, granodiorite, granodiorite, and and granite. granite. It provides a window exposing older older gneiss gneiss that evolved at at aa deeper deeper crustal crustal level level than than the the widespread supracrustal supracrustal rocks. rocks. The gneiss and the immediately immediately adjacent adjacent amphibolite facies, facies, whereas the supracrustal rocks are amphibolite the regional regional metamorphic metamorphic The grade of the supracrustals supracrustals in in the the area is is greenschist greenschist facies. facies. The stracigraphic succession succession in the dome area, area, from from oldest oldest to stratigraphic to youngest, youngest, is is (1) (1) (2) shallowgneiss, miginatite, and amphibolite (Dunbar Gneiss of Cain, 1964), (2) shallow— gneiss, migmatite, and amphibolite (Dunbar Gneiss of 1964), water sedimentary rocks, (3) (3) basalt-andesite-dacite basalt—andesite—dacite (Quinnesec Formation), Formation), and and be younger younger than the major major deformation (4) (4) rhyolite. The rhyolite appears to be stratigraphic succession and metamorphism. In a broad sense, this stratigraphic succession appears appears to to fit gneiss—granitoid domes across across northern fit the other gneiss-granitoid northern Wisconsin. of Early Early Proterozoic Proterozoic rocks rocks has has been been A similarly complex stratigraphy of determined Wisconsin (LaBerge Myers, 1984). determined in in central central Wisconsin (LaBerge and Myers, 1984). At least least three three in successions of volcanic rocks are distinguished on on the the basis of of differences differences in composition, metamorphism, metamorphism, and composition, and structural structural fabric. fabric. An older, older, widespread widespread subaqueous basaltic subvolcanic intrusion intrusion subaqueous basaltic succession succession with with abundant abundant tnafic mafic subvolcanic breccias, breccias, mainly of amphibolite amphibolite facies, facies, is is overlain overlain locally locally by by subaqueous subaqueous felsic—intermediate of upper upper felsic-intermediate volcanic rocks and intercalated sedimentary sedimentary rocks rocks of weakly metamorphosed, metamorphosed, partly greenschist greenschist facies. facies. At Wausau, a still younger, weakly subaerial volcanic-sedimentary volcanic—sedimentary succession subaerial succession is is present. present. Distinct Distinct episodes episodes of of granite the younger younger granite emplacement emplacement followed followed extrusion extrusion of the the older older basalt basalt and and the volcanics volcanics at at Wausau; the the younger younger granites granites are are leucocratic leucocratic and and have have high high K20/Na20 ratios. The K20/Na20 The age of the volcanic successions successions relative relative to to the the Early Early associated with gneiss in Proterozoic gneisses and foliated tonalite associated with Archean Archean gneiss in central (Maass, 1983) 1983) is is equivocal, equivocal, but but we we interpret interpret the the volcanic volcanic central Wisconsin (Maass, successions as being younger; younger; the gneisses are representative successions representative of of aa deeper deeper crustal level than the volcanic rocks. crustal level than the volcanic rocks. All the Wisconsin (regardless All the volcanic rocks in in Wisconsin (regardless of of stratigraphic stratigraphic age) age) and and associated granitoid the associated granitoid rocks rocks have have U—Pb U-Pb zircon zirconages agesofofabout about1,850 1,850tn.y. m.y. zircon dating in northeastern Wisconsin (Van Schmus, Schmus, 1980). 1980). Detailed zircon in northeastern Wisconsin (Peterman, unpublished data) indicates that the volcanic and granitoid granitoid rocks rocks (Peterman, m.y., crystallized in the short time span of 30 30 m .y., from from 1,865 1,865 to to 1,835 1,835 m.y. m.y. ago. ago. The structure structure of the Early Proterozoic Proterozoic rocks rocks in in Wisconsin Wisconsin is is complex. complex. On scale, the terrane consists of generally a regional regional scale, generally large large structural structural blocks blocks having diversely oriented internal internal structures structures that are bounded by by ductile ductile deformation deformation zones zones ("shear zones"). zones"). The recordpronounced pronounced The deformation zones record flattening in inthe thefoliation foliation planesand anda astrong strongcomponent component of flattening planes of vertical vertical movement movement (Palmer, (Palmer, 1980). 1980). Although is is intense is Althoughdeformation defQrmation intenseininthe theshear shear zones, zones, it it is generally is in scope, and generally isyounger younger than than the prevailing internal internal regional in scope, and structural fabric within structural fabric within the the blocks. blocks. The boundary boundary between Proterozoic The betweenthe the northern northern and and southern Early Early Proterozoic terranes, as fault, isismarked terranes, as indicated indicated by by the the Niagara Niagara fault, marked by by structures structures indicative of variable indicative variable but generally generally high strain strain (Larue, (Larue, 1983). 1983). On On both sides both sides of of the fault, foliation that that is is fault, the rocks generally have a steep south-dipping south—dipping foliation subparallel to the fault and a generally steep southwest-plunging stretching southwest—plunging stretching lineation. These These data, data, together together with high-angle reverse faults faults on on the the north north lineation. high—angle reverse suggest that the side of the shear zone (Bayley and others, 1966), 19661, suggest the Niagara Niagara fault itself is steeply steeply inclined inclined southward. southward. The westward continuation continuation of of the the 7L. �fault is is conjectural, conjectural, although although aa fault fault is is shown shown on on the the regional regional geologic geologic map map fault (Morey and and others, others, 1982). 1982). (Morey Differences in in lithology, lithology, chemical chemical composition composition of of volcanics, volcanics, and and Differences metamorphic and and structural structural style style suggest suggest that that the the two two Early Early Proterozoic Proterozoic metamorphic Several plate plate tectonic tectonic models models involving involving terranes largely largely evolved evolved separately. separately. Several terranes to and collision collision have have been been proposed proposed to subduction, and some combination combination of of rifting, rifting, subduction, some explain the the evolution evolution of of the the Early Early Proterozoic Proterozoic rocks rocks in in the the Michigan—Wisconsin Michigan-Wisconsin explain segment of of the the Lake Lake Superior Superior region region as as well well as as the the nature nature of of the the Penokean Penokean segment orogeny (Van Schmus, 1976; Cambray, 1978; Larue and Sloss, 1980; and Greenberg Greenberg orogeny (Van Schmus, 1976; Cambray, 1978; Larue and Sloss, 1980; and and Brown, 1983). On the basis of new chemical and structural data, Schulz and Brown, 1983). On the basis of new chemical and structural data, Schulz and others (1984) have proposed a tectonic model of early crustal rifting and and others (1984) have proposed a tectonic model of early crustal rifting and and spreading, subsequent subduction and formation of a complex volcanic arc, spreading, subsequent subduction and formation of a complex volcanic arc, and collision of of the the arc, arc, first first with with Archean Archean crust crust on on the the south south and and then then with with the the collision Archean crust crust of of upper upper Michigan Michigan continental margin margin (epicratonic) (epicratonic) sequence sequence and and Archean continental Culmination of of the the orogeny orogeny was was on the the north north (the (the Penokean ~enokeanorogeny). orogeny). Culmination on approximately 1,850 1,850m.y. m.y. ago. ago. approximately REFERENCES REFERENCES Bayley, R. R. W., W., Dutton, Dutton,C. C. E., E.,and and Lamey,C.C.A., A *1966, , 1966, Geology Menominee Bayley, Lamey, Geology ofof thethe Menominee iron-bearing district, district, Dickinson Dickinson County, County, Michigan Michigan and and Florence Florence and and iron—bearing U.S. Geological Geological Survey Survey Professional Professional Paper Paper Marinette Counties, Counties, Wisconsin: Wisconsin: U.S. Marinette 513, 96 96 p. p. 513, R., 1982, 1982, Rb—Sr Rb-Sr and and Sm—Nd Sm-Nd isotopic isotopic studies studies of of Beck, Warren, Warren, and and Murthy, Murthy, V. V. R., Beck, Proterozoic mafic mafic dikes dikes in in northeastern northeasternMinnesota Minnesota[abs.J: [abs.]: Proceedings, Proceedings, Proterozoic 28th Annual Annual Institute Institute on on Lake Lake Superior Superior Geology, Geology, International International Falls, Falls, 28th p. 5. 5. Minnesota, p. Minnesota, Cain, J. J. 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S., S., 1984, 1984, The The volcanic—plutonic volcanic-plutonic terrane t e r r a n e of of northern n o r t h e r n Wisconsin: Wisconsin: Implications I m p l i c a t i o n s for f o r Early E a r l y Proterozoic P r o t e r o z o i ctectonisin, tectonism, Lake Lake Superior S u p e r i o r region: region: Program Program with w i t h abstracts, a b s t r a c t s , Geological Geological Association A s s o c i a t i o n of of Canada—Mineralogical Canada-Mineralogical Association A s s o c i a t i o n of of Canada Canada (in ( i n press). press). Van Van Schmus, Schmus, W. W. R., R., 1976, 1976, Early E a r l y and and middle middle Proterozoic P r o t e r o z o i c history h i s t o r y of of the t h e Great Great Lakes Lakes area, a r e a , North North America: America: Royal Royal Society S o c i e t y of of London London Philosophical Philosophical Transactions, T r a n s a c t i o n s , set. ser. A280, A280, no. no. 1298, 1298, p. p. 605—628. 605-628. 1980, Chronology Chronology of of igneous igneous rocks rocks associated a s s o c i a t e d with w i t h the t h e Penokean Penokean orogeny orogeny in G.B. and and Hanson, Hanson, G. G. N., N., eds., eds., Selected S e l e c t e d studies s t u d i e s of of i n Wisconsin, Wisconsin, iinMorey, n Morey, G.B. Archean Archean gneisses gneiss= and and lower lower Proterozoic P r o t e r o z o i c rocks, rocks, southern s o u t h e r n Canadian Canadian shield: shield: Geological Geological Society S o c i e t y of of America America Special S p e c i a l Paper Paper 182, 182, p. p. 159—168. 159-168. 76 �Morphologr_Accretion and acrost-tmMicrostructur Mor~holom,Accretion Rate and of Recent Algal Stromatolites Stromatolites from from Ottertail Co., Eagle XI1 Ehgle Lake, Lake Ottertail Co. MN L.G. L.G. SOROKA SOROKA (Dept. (Dept. of of Earth W t h Sciences, Sciences St. Cloud Cloud State State University, University St. 56301) st. Cloud, cloud, MN 56301) Earth Sciences, J.A. J.A. Roach Hosch (Dept. of of Earth Sciencesy St. Cloud Cloud State State University, UniversityySt. St. Cloud, MN 56301) 56301) cloud, MN m ' hardened, structures Hardened, high high relief relief organo—sedimentary organo-sedimentary carbonate carbonate structures (stromatolites) have been been discovered growing as cauliflower—like (stromatolites) have cauliflower-like mounds boulders in in water water depths depths of of between between 1 11 1 and 15m l5m mounds on on cobbles cobbles and. and boulders along Co., lake is The lake is along the the south south shore shore of ofEagle Eagle Lake, Lake,Ottertail Ottertail C O MN. . ~MI?. The an an exceptionally exceptionally clear, clear, hard—water, hard-water, kettle kettle moraine moraine lake. lake. The The stromatolites ( oncobbles cobblesand and boulders), boulders ) which which stromatolites begin as encrustations encrustations(on gradually columns 0.5 to gradually evolve evolve into into hemispheroidaJ. hemispheroidal columns to O.8m 0.8m in in height. height. The stromatolite surface The stromatolite surface is is covered covered by by aa green green mat mat of of filamentous filamentous algae botryoidal surface Cladophora aegagropila rabenhorst. A A botryoidal surface algae - Cladophora - gagropila rabenhorst. growth formmerges mergesinto intoan an interior interior with interconnecting growth form withnumerous numerous interconnecting cavities cavitieswhich which are are populated populated by by gastropods, leeches, leeches,and and other other organisms. organisms. X—ray X-ray diffraction most of the diffractionanalysis analysisindicates indicates that that most of the - lithified. lithified interior interior consists consists of of low—magnesium low-magnesium calcite. calcite. The The dominant dominant interior interior microstructure, microstructurey as as revealed revealed by thin—sections thin-sections and and scanning scanning electron anhedral calcite electron microscopy, microscopy, consists consists of of non—laminated., non-laminated, anhedral calcite crystals crystalsand. and diatoms. diatoms. This This inicrostructure microstructure suggests suggests that that settling lake lake carbonates carbonates have been trapped trappedand andbound. bound by by the the filamentous filamentous algae. algae. Subsequent cementation cementation occurs by photosynthesis induced precipitation Subsequent of of calcite calcite from from the the saturated saturated lake lake water. water. Observable Observable in in scanning scanning electron as well well as as in in thin-sections thin—sections are are areas areas which micrographs as which show show electron xuicrographs laminations. laminations. These laminated areas areasmake make up up less less than than 5% 5% of of the the stromatolite appear to to form stromatolite and and appear form in in recesses recesses where the thebioinduced. bioinduced precipitation is not being being diluted by by the more more rapidly lake rapidly settling settling lake settling precipitation is not carbonates. carbonates. This This bioind.uced bioinduced precipitate of aamosaic mosaic of of precipitate consists consists of smaller -5~. smaller uniformly uniformlysized sizedarthedral anhedral calcite calcite crystals crystals measuring measuring1 l-5. Preliminary Preliminary uranium—thorium uranium-thorium series dating of series datingsuggests suggeststhat thatthe therate rate of accretion O.5m accretion is is extremely extremely slow. slow. AA sample sample obtained obtained from from inside inside aa 0.5m thick strosiatolite stromatolite indicated in excess excess of of 10,000 10,000 years. years. thick indicated an age age in This observed observed stromatolite stromatolite formation formation in a relatively This relatIvely deep freshwater environment environment may necessitate necessitate a re-evaluation water re—evaluation of their generally pdeoenvironmental interpretation. accepted pa.leoenvironmenta]. accepted interpretation. 77 �Geologic and PPalinspastic G e o l o g i c HHistory i s t o r y and a l i n s p a s t i c Reconstruction R e c o n s t r u c t i o n oof f the the Early Collision E a r l y Proterozoic P r o t e r o z o i c Penokean Penokean C o l l i s i o n Zone Zone By W.L. Ueng, Ueng, D.K. D.K. Larue, Larue, R.L. R.L. Sedlock Sedlock W.L. Dept. ooff Geology, S t a n f o r dCA CA Dept. Geology, Stanford S t a n f o r d University, Un i v e r s it y ,Stanford 9+3O5 94305 Thereaare twopprincipal There r e two r i n c i p a l early e a r l y Proterozoic P r o t e r o z o i c tectonic t e c t o n i c elements elements in i n the t h esouthern southern Lake SSuperior Lake u p e r i o r rregion: e g i o n : aa northern n o r t h e r npassive p a s s i v emargin marginassemblage, assemblage, and and aa southern southern The magmaticaarc assemblage,j ujuxtaposed magmatic r c assemblage, x t a p o s e d aalong l o n g tthe h e Florence—Niagara F l o r e n c e - N i a g a r a f afault. ult. The passive margin assemblage, assemblage,r erepresenting terminusoof p a s s i v e margin p r e s e n t i n g t hthe e ssouthern o u t h e r n terminus f tthe h e Superior Superior province p r o v i n c e ooff the t h e Canadian Canadian Shield, S h i e l d , is i s locally l o c a l l yfragmented fragmented into i n t o two two discrete discrete blocks assemblage; b l o c k s next n e x t to t othe t h econtact c o n t a cwith t w i tthe h t hmagmatic e magmatic assemblage; the t h eFlorence—Niagara Florence-Niagara These terranes and Crystal and C r y s t a l Falls F a l l s terranes. terranes. These t e r r a n e s aare r e sstratigraphically t r a t i g r a p h i c a l l ycomparable comparable but disjunct b ut d i s j u n c t from from the t h e rest r e s t of o fthe t h epassive p a s s i v emargin. margin. Paired shear zones zoness straddle the P a i r e d shear t r a d d l e th e FFlorence—Niagara l o r e n c e - N i a g a r a f a ufault: l t : t otot the h e nnorth o r t h ooff the the fault, f a u l t ,highly-deformed h i g h l y - d e f o r m e d strata s t r a t aofo the f t hFlorence—Niagara e F l o r e n c e - N i a g a r a terrane t e r r a n e define d e f i n e the the northern shear zone; zone;t to off the n o r t h e r n shear o tthe h e south s o u t h ooff the t h e fault, f a u l t highly—deformed , h i g h l y - d e f o r m e d rocks rocks o the northern magmat i c tterrarle e r r a n e define d e f i n e the t h e southern s o u t h e r n shear shear zone. zone. n o r t h e r n margin margin ooff the t h e magmatic There hasbeen been material There has l i tlittle t l e oor r no no m a t e r i a l ttransfer r a n s f e r across a c r o s s tthe h e ffault. ault. shear zones zoneswere werepprobably formedd during shear r o b a b l y formed u r i n g t terrane e r r a n e aaccretion. ccretion. These paired These p aired •The by pprobably .The eentire n t i r e region r e g i o n has has been been deformed deformed by r o b a b l y ffive i v e deformation d e f o r m a t i o n events. events. This only T h i s has has been been pprecisely r e c i s e l y documented documented o n l y nnorth o r t h ooff the t h e Florence—Niagara F l o r e n c e - N i a g a r a f afault, ult, The pparallel but b u t preliminary p r e l i m i n a r y data d a t a to t o the t h e south s o u t h support s u p p o r t this t h i s contention. contention. The arallel deformation sharedbybyd idifferent d e f o r m a t i o n h histories i s t o r i e s shared f f e r e n t tterranes e r r a n e s i in n tthis h i s region r e g i o n indicate indicate regimeo of tthat h a t aa NNE NNE ooriented r i e n t e d sshortening h o r t e n i n g regime f t the h e ffirst i r s tdeformation d e f o r m a t i o n was was responsible responsible Throughout Fl ddeformation e f o r m a t i o n l left eft ffor o r the t h e terrane t e r r a n e accretion. accretion. Throughout t hthe e r eregion, g i o n , t the h e F1 a 90and anda as eseries a set s e t of o f penetrative p e n e t r a t i v e foliations f o l i a t i o n soriented o r i e n t e dN7OW N70W 90 r i e s o foft itight g h t folds folds which sometimes sometimesi ninvolved Archaenccrystalline r y s t a l l i n ebasement, basement, such such as as at a tthe t h eAmasa Amasa which v o l v e d Archaen Oval. The secondphase phaseo fofddeformation The second e f o r m a t i o n i is s characterized c h a r a c t e r i z e d by by planar p l a n a relements elements o r i e n t e d N65E N65E 90; e l olocally c a l l y ccrossfolded r o s s f o l d e d by h i s deformation. deformation. oriented 90;F1Fl elements elementsa rare by tthis The bending bendingo of Nl54oorientation The f ooriginally r i g i n a l l y N7OW—trending N7OW-trending F1 Fl s t rstructures u c t u r e s i ninto t o aa N15W rientation is bandccutting i s concentrated c o n c e n t r a t e d in i na a50 SOkm kmwide w i d e NE—trending NE-trending band. u t t i n g through t h r o u g h approximately approximately Crystal C r y s t a l Falls, F a l l s , Michigan, Michigan, up up toward toward tthe h e ssouthern o u t h e r n t tip i p of o f the t h e Republic R e p u b l i c trough. trough. To tthe F2deformation d e f o r m a t i o nband bandbends. bends the t h e Florence—Niagara F l o r e n c e - N i a g a r a FFault. ault. To h e southwest, southwest, this t h i sF2 The o c a t i o n oof f this t h i s band band was r o b a b l y c ocontrolled n t r o l l e d i in n ppart a r t by by structures s t r u c t u r e s in in The l location waspprobably the t h e underlying under1 y i n gbasement. basement. The p r e s e n t s one r o d u c t ooff The Amasa AmasaOval Ovalr erepresents onesuch suchpproduct crossfolding c r o s s f o l d i n g and and does does not n o t represent r e p r e s e n taagneiss g n e i s sdome. dome. We proposet hthat the LakeSSuperior waso originally We propose a t th e ssouthcentral o u t h c e n t r a l Lake u p e r i o r rregion e g i o n was riginally W-NW t r e ntrending d i n g s t r structures u c t u r e s r eresulting s u l t i n g ffrom rom tterrane errane a ccretion. c h a r a c t e r i z e d by by W—NW characterized accretion. This thet hNE—trending T h i s regional r e g i o n a l structure s t r u c t u r was e wasmodified m o d i f i e dbyby e NE-trending deformation d e f o r m a t i o n band band which rotated trending which r o t a t e dprevious p r e v i o u sW—NW W-NW t r e n d i n g sstructures. tructures. 78 �Recent Contributions C o n t r i b u t i o n s to t o the t h e Geochronology of of the the Precambrian of of Wisconsin Wisconsin W. of Geologyy Geology, University W. R. R. VAN VA8 SCHMUS SCHMUS (Department of U n i v e r s i t y of of Kansas, Kansas, Lawrence, Lawrence KS KS 66045) 66045) Continued U-Pb U—Pb age studies s t u d i e s on zzircons i r c o n s from Precambrian units units throughout ccentral and NN Wisconsin Wisconsin have have helped helped tto document iin more o document n more throughout e n t r a l and detail d e t a i l the t h e occurrence of of rocks r o c k s formed formed during d u r i n g the t h e main main phase phase of of the the Penokean Orogeny in our i n Wisconsin and have improved o u r understanding of of the of central c e n t r a l Wisconsin. Wisconsin. In I n addition, a d d i t i o n  rresults e s u l t s from t h e Archean block of several llocalities presence of of pre-Penokean pre—Penokean E Early o c a l i t i e s sseem e e m tto o confirm tthe h e presence arly Proterozoic P r o t e r o z o i c igneous igneous units u n i t s in i n Wisconsin. Based on p previous results, it best i t still s t i l l seems b e s t to t o bracket bracket r e v i o u s and new results the M a . The 1860 Ma. t h e main phase of of Penokean Orogeny Orogeny between between 1830 1830 and and 1860 tendency for f o r plutonic p l u t o n i c units u n i t s with w i t h ages ages in i n the t h e older o l d e r part p a r t of of this this more sstrongly pronounced, b but range to t o be more t r o n g l y ffoliated o l i a t e d iis s sstill t i l l pronounced, u t nnot ot universal. units u n i v e r s a l . Several Several u n i t s have aalso l s o been found that t h a t yyield i e l d apparent ages from from 1870 1870 to t o 1920. 1920. IIn n some ccases a s e s iit t iis s ppossible o s s i b l e tthese h e s e aare re with component iin but Penokean uunits nits w i t h an iinherited n h e r i t e d oolder l d e r component n tthe h e zzircons, ircons b ut with iif f so s o this t h i s is i s not n o t obvious. obvious. Furthermore, Furthermores in i n some cases cases w i t h ages of of 1890 to Maa this possibility Thus, t o 1915 1915 M p o s s i b i l i t y has h a s virtually v i r t u a l l y been been ruled r u l e d out. o u t . Thusy these around 1900 M Maa probably probably rrepresent e p r e s e n t ttrue r u e aages, g e s y and tthe h e rrocks ocks t h e s e ages around from which tthey were obtained obtained aare remnants h e y were r e ttentatively e n t a t i v e l y iinterpreted n t e r p r e t e d as remnants of one o orr more more o older, pre—Penokean (or Penokean) igneous of l d e r * pre-Penokean ( o r eearlier a r l i e r Penokean) suites. and scattered s u i t e s . Most of of these t h e s e units u n i t s are a r e tonalitic, t o n a l i t i ~deformed, deformed, ~ scattered no ssingle, coherent o older Proterozoic over a llarge a r g e aarea, r e a * sso o tthat h a t no i n g l e  coherent lder P roterozoic terrane t e r r a n e or o r domain can can be identified i d e n t i f i e d at a t present. present.  Tonalitic gneiss near Marshfield, Marshfield, along tthe of tthe T onalitic g n e i s s near h e nnorthern o r t h e r n edge of he Central Archean block, block, yyields with U—Pb i e l d s zzircons ircons w i t h complex U-Pb C e n t r a l Wisconsin Archean discordance However, iit discordance patterns. p a t t e r n s . However, t is i s clear c l e a r that t h a t tthese h e s e zzircons i r c o n s are are about 3000 M Ma old, with a o l d , cconsistent onsistent w i t h eearlier a r l i e r rresults e s u l t s ssuggesting u g g e s t i n g that that Archean tterrane may be be aa remnant remnant of of tthe gneiss—migmatite h e oolder l d e r gneiss-migmatite tthis h i s Archean e r r a n e may province of of the t h e southern southern Lake Lake Superior Superior region. region. Zircons separated separated gneiss from ffelsic elsic g n e i s s near Fifield F i f i e l d also a l s o indicate i n d i c a t e an an age age of of 2950 2950 to t o 3000 3000 Ma, suggesting tthat Archean block iin Wisconsin is Ma9 h a t the t h e Archean n ccentral e n t r a l Wisconsin i s rrelated elated Wisconsin. tto o tthe h e oolder l d e r gneisses g n e i s s e s in i n northwestern Wisconsin. overall by tthe s sstill t i l l one The o v e r a l l tectonic t e c t o n i c ppicture i c t u r e ppreferred r e f e r r e d by h e aauthor u t h o r iis which most most of of tthe Penokean igneous igneous ssuite of nnorthern Wisconsin wwas as iin n which h e Penokean u i t e of o r t h e r n Wisconsin n continental c o n t i n e n t a l margin arc a r c complexes, complexes9 and and that t h a t more more than t h a n one one formed iin distinct period magmatism within distinct p e r i o d of of subduction-generated subduction-generated m a g m a t i s m occurred w ithin tthe h e interval i n t e r v a l 1920 1920 to t o 1820 1820 Ma. M a . However, However, outcrop and geochronologic control c o n t r o l is i s still s t i l l insufficient i n s u f f i c i e n t to t o constrain c o n s t r a i n the t h e model precisely. precisely. 79 �The The Huronian Huronian Supergroup: Supergroup: An An Example Example of of an an Early Early Proterozoic Proterozoic Passive Passive Margin Margin Sequence Sequence GRANT GRANT M. M. YOUNG, YOUNG, (Department (Department of of Geology, Geologyl University University of of Western Western Ontario, Ontarior London, London, Ontario, Ontario, Canada) Canada) Information such aas those of of tthe Information on passive margin successions such s those h e ppen-Atlantic eri-Atlantic The stratigraphic s t r a t i g r a p h i c succession succession region region has has come come from from geophysical geophysical work work and and drilling. d r i l l i n g . The differs d i f f e r s in i n different d i f f e r e n t areas areas but but the t h e classical c l a s s i c a l model model involves involves alkaline a l k a l i n e volcanics volcanics and and continental c o n t i n e n t a l sediments sediments deposited deposited in i n fault-bounded fault-bounded troughs, troughs, followed followed by by evaporites evaporites and, and, above above the t h e "break—up" "break-up" unconformity, unconformity, aa continental c o n t i n e n t a l margin margin succession succession comprising comprising the t h e terrace t e r r a c e wedge wedge and and continental c o n t i n e n t a l rise r i s e successions. successions. Huronian stratigraphy s t r a t i g r a p h y has has largely l a r g e l y been been interpreted i n t e r p r e t e d in i n terms terms of of aa tripartite tripartite Huronian d i a m i c t i t e s l argillites a r g i l l i t e s and and sandstones sandstones in i n ascending ascending sequence. sequence. cycle involving involving diamictites, cycle It is i s here here suggested suggested that t h a t the t h e Huronian Huronian succession succession (10—12 (10-12 km km in i n max. max. thickness) thickness) It may may be be the t h e result r e s u l t of of continental c o n t i n e n t a l fragmentation. fragmentation. The The lower lower Huronian, Huronian, below below the the Groupl includes includes syn-nift s y n - r i f t volcanics volcanics chemically chemically akin akin to t o those those of of the t h e Afar Afar Cobalt Group, Cobalt Triangle and and largely l a r g e l y continental c o n t i n e n t a l clastic c l a s t i c sediments sediments such such as a s those those of of the t h e Mississagi Mississagi Triangle and and Serpent Serpent Formations. Formations. These These formations formations are a r e of of limited l i m i t e d distribution d i s t r i b u t i o n and and display display major major thickness thickness and and facies f a c i e s changes changes consistent c o n s i s t e n t with with contemporaneous contemporaneous fault f a u l t activity. activity. Evaporitic Evaporitic facies f a c i e smay may be be represented representedby bycarbonates carbonates of of the t h e Espanola Espanola Formation Formation near near the t h e top top of of the t h elower lowerHuronian Huronian succession. succession. s tthe h e base base of of the the The betweent hthe lowerand andupper upperHuronian Huroriiani sistaken takenaas The boundary boundary between e lower Gowganda Formation. Gowganda Formation. In In the t h e southern southern part p a r t of of the t h e Huronian Huronian outcrop outcrop bbelt e l t there t h e r e is is aa profound from aa bbasin—full condition ttoo one profound change change from a s i n - f u l l condition one in i n which which resedimented resedimented glacio— glaciogenic me boundary boundary iis s interpreted i n t e r p r e t e d to t omean mean aa sudden sudden tectonic tectonic genic rocks rocks predominate. predominate. The foundering of the foundering of t h e basin. basin. In angular unconformity I n more more northerly areas a r e a s there t h e r eisi s ananangular unconformity between andunderlying underlyinglower lowerHuronian Huronianformations formationsand ands tstill i l l farther farther between the t h e Gowganda Gowganda and north Formationl lies norththe t h eGowganda Gowganda Formation i e s directly d i r e c t l yononArchean Archeanbasement basement rocks. rocks. These These r e l a t i o n s h i p s indicate i n d i c a t eboth both local l o c a land andregional regionalsubsidence subsidence and and the t h e transition t r a n s i t i o nfrom from relationships aa dominantly dominantly continental c o n t i n e n t a l to t o marine marine shelf-type shelf-type sedimentation. sedimentation. Relationships Relationships at at the thet h"break—up" t h ebase baseofofthet hGowganda e Gowganda Formation Formation are a r eequated equatedtot o e "break-up" unconformity unconformity that many I t differs, differs, t h a tcharacterizes characterizes manyyounger younger continental c o n t i n e n t a lmargin marginassemblages. assemblages. It however, however, in i n bearing bearing evidence evidence of of contemporaneous contemporaneousglaciation. g l a c i a t i o n . Similar Similar resedimented resedimented glaciogenic glaciogenic facies f a c i e s are a r e associated associated with with late l a t e Proterozoic Proterozoic continental c o n t i n e n t a l fragmentation fragmentation in i n the t h e Cordifleran Cordilleranregion. region. Rocks Rocks of of the t h e lower lower Huronian Huronian do be represented represented in i nthe t h eLake LakeSuperior Superior do not not appear appear ttoo be region, probably probably because e eearly a r l y rrifting i f t i n g did d i d not not extend extend that t h a t far f a rwest west but butthe the region, becauset hthe transgressionassociated transgression~associated with the t h e regional regional subsidence subsidence phase phase led l e d to t o deposition deposition of of with glaciogenic and succeeding marine platformal facies f a c i e s of of the t h e Chocolay Chocolay Group Group and and glaciogeriic MilleLacs LacsGroup Groupwhich whichare a r econsidered consideredtot obebeequivalent equivalenttot othe t h eupper upper possibly the t h e Mule possibly . Huronian. Huronian The The tectonic t e c t o n i csetting s e t t i n gofofthe t hHuronian e Huronian and and equivalent equivalent rocks rocks remains remains obscure obscure but but thickness thickness and and facies f a c i e s changes changes and and regional regional paleocurrent paleocurrent data d a t a suggest suggest that t h a t they they were were formed in i n an an intracratonic i n t r a c r a t o n i c rift r i f t setting s e t t i n g with with subsequent subsequent ocean ocean opening opening to t o the t h e east east formed to t o explain explain the t h e regional regional subsidence subsidencein i nGowganda Gowgandatimes. times. The The subsequent subsequent history h i s t o r y of of e a r l y Proterozoic Proterozoic rocks rocks of of the t h e south south shore shore of of Lake Lake Superior Superior has has been been interpreted interpreted early by by several s e v e r a l workers workers to t o involve involve aa period period of of ocean ocean opening opening and and closure. closure. Reference Reference Jr., 1983, 1983, Early Early Proterozoic Proterozoic Geology Geology of of the t h e Great Great Lakes Lakes Medaris, L.G. L.G. Jr., Medaris, Region: Region: Geological Geological Society Society of of ?merica America Memoir Memoir 160, 160, 141 141p. p. 80 � https://digitalcollections.lakeheadu.ca/files/original/6ec5aceba816c6c0c46889c5593283e9.pdf fdb8576dcdd5eb0c3d227a7562f52037 PDF Text Text Thirtieth Annual Institute on Lake Superior Geology FIELD TRIP GUIDE 1 TO THE GEOLOGY OF THE EARLY PROTEROZOIC ROCKS IN NORTHEASTERN WISCONSIN 46 APRIL 24—25, 1984 �Guide to the Geology of the Early Proterozoic Rocks in Northeastern Wisconsin Field trip leaders P. K. Sims K. J. Schulz Z. E. Peterman Prepared for 30th annual meeting of the Institute on Lake Superior Geology Wausau, Wisconsin, 1984 �CONTENTS DUNBAR GNEISS - GRANITOID DOME P.K. Sims, Z.E. Peterman, and K.J. Schulz 1 GEOCHEMISTRY OF THE DUNBAR GNEISS - GRANITOID DOME, N.E. WISCONSIN K.J. Schulz, P.K. Sims, and Z.E. Peterman 24 FIELD TRIP LOG AND DESCRIPTIONS, DUNBAR GNEISS GRANITOID DOME P.K. Sims, K.J. Schulz, and Z.E. Peterman 43 VOLCANIC ROCKS OF NORTHEASTERN WISCONSIN Klaus J. Schulz 51 FIELD TRIP LOG AND DESCRIPTIONS, VOLCANIC ROCKS OF NORTHEASTERN WISCONSIN Klaus J. Schulz a 81 �DUNBAR GNEISS—GRANITOID DOME By P. K. Sims..!!, Z. E. Peterman!J, and K. J. Schulz-.i ..!Ju.s. Geological Survey, Denver, CO 80225 — U.S. Geological Survey, Reston, VA 22092 .1 I UI I I I I I �Introduction [ As a part of regional investigations of the geology of the Precambrian rocks in the eastern part of the Lake Superior region (Michigan and Wisconsin), northeastern Wisconsin was chosen as one of the key areas for study because of its apparently unique geology and relatively abundant outcrop. In particular, the Dunbar dome and adjacent areas were chosen for emphasis. This terrane contains varied gneisses, amphibolite, and abundant granitoid rocks, all of Early Proterozoic age, and contrasts markedly with the adjacent terrane in northern Michigan. The study area also is a part of the Early Proterozoic east—trending volcanic belt in northern Wisconsin that contains economically promising strata—bound massive sulfide deposits. In addition, northeastern Wisconsin provides the opportunity to further study the age, extent, and cause of Middle Proterozoic events that reset Rb—Sr whole— rock and mineral ages throughout most of the eastern part of the Lake Superior region, as first noted by Aldrich and others (1965). This summary of the geology, geochronology, and geochemistry of the rocks within and adjacent to the Dunbar dome is derived from papers in preparation by us and previous publications on the regional geology of adjacent areas to the north (Bayley and others, 1966; Dutton, 1971). Earlier reports on the ages of rocks in the general area by Banks and Cain (1969), Banks and Rebello (1969), Van Schmus, Thurman, and Peterman (1975), and Van Schmus (1980) were extremely useful. R. A. F Jenkins, M. G. Mudrey, Jr., and W. C. Prinz introduced us to the geology of the area, and together with many others stimulated our interest in the geology and mineral potential. Summary of Geology [ F The Dunbar dome is one of several domes in northern Wisconsin that have cores of gneiss, migmatite, and granitoid rocks and are mantled by inetavolcanic and inetasedimentary rocks. Both the basement (core) and the mantle (cover) are of Early Proterozoic age. The domes occur within an east—trending curvilinear, convex northward belt at least 60 km wide that lies adjacent to the boundary of this terrane (Wisconsin magmatic zone) with the Michigan terrane to the north. The Michigan terrane, as defined here, consists of epicratonic metasedimentary and metavolcanic rocks (Marquette Range Supergroup) that unconformably overlie Archean basement rocks (Sims, Card, and Lumbers, 1981). The proposed boundary (Larue, 1983) between the two terranes is the Niagara (or Florence—Niagara) fault zone. domes in northern Wisconsin provide windows that expose parts of an The extensive deeper crustal succession that lies beneath the thick pile of metavolcanic rocks in northern Wisconsin. Apparently, an Archean basement is lacking. However, a Nd—Sm isotopic study of two samples of Dunbar Gneiss (Cain, 1964) yielded ages of 2,130 Ma and 2,280 Ma, which probably indicates a component of Archean material in the source or a small degree of contamination of the magma during its ascent through Archean crust. Lead—isotope data on massive sulfide deposits and associated rocks in the Early Proterozoic belt of metavolcanic rocks in northern Wisconsin support this conclusion (Afifi and others, in press). 1 �The Dunbar dome is a complex antifornial structure consisting of a central core and three lateral protuberances from the core, named the Niagara, Pembine, and Bush Lae lobes, respectively (fig. 1). The dome occupies an area of about 470 km • The stratigraphic—tectonic evolution of the dome spanned the relatively short time of about 30 Ma, from about 1,865 Ma to 1,835 Ma ago, during the Early Proterozoic. The dome coincides with a deep gravity depression of about 20 milligals (Ervin and Hammer, 1974), which is the southeasternmost low of a family of lows that extend about 35 km to the northwest. The central core of the Dunbar dome is composed of biotite gneisses, migmatite, granite gneiss, and amphibolite, assigned to the Dunbar Gneiss of Cain (1964), and three granitoid bodies, which he called the Marinette Quartz Diorite, a megacrystic phase of the Newingham Tonalite (included by Cain (1964) in the Dunbar Gneiss), and a large elliptical body of Hoskin Lake Granite. The Niagara and Bush Lake lobes are composed of two other bodies of granite, which differ somewhat from the Hoskin Lake Granite. The Pembine lobe consists mainly of the Newingham Tonalite (formerly called Newingham Granodiorite by Cain, 1964). The granitoid bodies intruded the Dunbar Gneiss and a narrow fringing zone of the mantling Quinnesec Formation (volcanic succession) and stratigraphically older tnetasedimentary rocks, and apparently were emplaced in the order, from oldest to youngest, Marinette Quartz Diorite, Newinghani Tonalite, and Hoskin Lake Granite. Granite peginatite and aplite are abundant throughout the dome, especially in the Dunbar Gneiss. K—metasomatlsm, which was approximately contemporaneous with emplacement of the Hoskin Lake Granite, appreciably modified rock compositions in the northern part of the central core subsequent to their crystallization. Potassium was introduced during or after a cataclastic (ductile) deformation that recrystallized plagioclase and other minerals, to yield core—mantle (or mortar) textures and shears. The granitoid bodies were emplaced at relatively shallow crustal depths. The supracrustal (cover) rocks compose a steeply dipping succession that dominantly faces stratigraphically outward from the core. They consist mainly of metavolcanic rocks and layered, maf Ic sills, assigned to the Quinnesec Formation, and coeval subvolcanic rocks (Twelve Foot Falls Quartz DIorite of Cain, 1964). The cover rocks also include a more local, thinner older succession of metasedimentary rocks, principally impure quartzIte, stromatolitic marble, caic—silicate rocks, and biotIte schist (metatuff?). The volcanic rocks are interpreted as having been deposited in deep water, whereas the sedimentary rocks have shallow—water attributes. Granltoid rocks in the dome have general geochemical cale—alkaline characteristics, but the Marinette Quartz Diorite is slightly alkaline. The Dunbar Gneiss has relatively low Rb/Sr ratios (0.10—0.99) and steep rare earth element (REE) patterns ([La/Yb} = 25—43). They probably represent metamorphosed volcanic and related subvolcanIc intrusive rocks. The Newingham Tonalite Is compositionally homogeneous having high Sr (690), low Rb—Sr (0.066), and steep REE patterns ([La/Ybin = 43). It is compositionally similar to many Archean tonalites, and probably was derived by partial melting of a basaltic parent. The Hoskin Lake Granite and the closely associated granites of Spikehorn Creek and Bush Lake range in composition from granodiorite to granite, have relatively low Sr (58—300), high Th (23—40), 2 �p Rb/Sr >1, variable REE ([Lain = 57—163), and negative Eu anomalies. The Marinette Quartz Diorite and Hoskin Lake Granite show overlapping major and trace element compositions, which apparently reflect partial K—tnetasomatistn of the quartz diorite. U—Pb zircon ages of rocks in the dome are clustered in therange 1,865 Ma to 1,835 Ma. The oldest rocks, the Dunbar Gneiss and the Quiñnesec volcanics, are about 1,865 Ma old, whereas the Marinette Quartz Diorite and the Newingham Tonalite are inferred to be about 1,860 Ma. The youngest rock unit, the granite body of Spikehorn Creek in the Niagara lobe, has an age of 1,835*6 Ma. Rb—Sr whole—rock and mineral ages are consistently reset and are 100 Ma or more younger than the zircon upper intercept ages, as discussed on following pages. The Duabar dome is interpreted as a large—scale fold—interference structure resulting from cross folding modified by diapirism and emplacement of the granitoid intrusive rocks. Many of the criteria indicative of diapirism, as listed by Brun and others (1981), are observed in the dome: (1) cleavage parallel to dome boundaries, (2) steeply plunging lineation in dome boundaries, and (3) higher strain intensities located on dome boundaries. The Dunbar dome is surrounded by an asymmetrical annular zone of metamorphism in the cover rocks. An amphibolite—facies zone ranging from less than 0.5 km wide to at least 8 km wide lies adjacent to the core, and gives The amphibolite zone is widest on way outward to greenschist—facies rocks. the northern margin where it transects the Niagara fault zone (Dutton, Within the core, the Dunbar Gneiss has amphibolite—facies mineral 1971). The assemblages, as oes the northern part of the Marinette Quartz Diorite. Dunbar Gneiss was metamorphosed during dynamothermal metamorph-ism accompanying whereas the annular metamorphic pattern, superposed on previously metamorphosed greenschist—facies supracrustal rocks during a late stage evolution of the dome, was dominantly the result of thermal metamorphism. Granite—tonalite dikes were emplaced into rocks in the amphibolite—facies zone during the younger thermal metamorphism. The rocks in the Dunbar dome and surrounding environs compose part of a magmatic terrane, termed the Wisconsin magmatic zone, that differs in stratigraphy, structure, mineral deposits, and igneous rock chemistry from the epicratonic Michigan terrane to the north. Accordingly, we conclude that the Wisconsin magmatic zone evolved separately from the Early Proterozoic terrane to the north, and is an exotic terrane that was attached to the North American continent during the Early Proterozoic. Apparently the boundary between the two Proterozoic terranes is the Niagara fault, as suggested by Larue (1983). The doming was probably in response to collision of the two crustal blocks, which triggered the Penokean orogeny. Rock Units The Dunbar dome is composed of compositionally varied gneisses, assigned to the Dunbar Gneiss, and 5 younger intrusive units, which were emplaced, from oldest to youngest, in the order Marinette Quartz Diorite, Newingham Tonalite, Hoskin Lake Granite, granite of Bush Lake, and granite of Spikehorn Creek The Marinette Quartz Diorite and the Hoskin Lake Granite were named (fig. 1). 3 �_____ EXPLANATION (Figure 1) MIDDLE PROTEROZOIC Diabase EARLY PROTEROZOIC I XsgI Granite of Spikehorn Creek {g] Granite of Bush Lake [XhJ Hoskin Lake Granite [] Newingham Marinette Quartz Diorite ix1 IX1 Metagabbro sills X. Quinnesec Formation 1 Twelve Foot Falls Quartz Diorite of Cain (1963) Metasedimentary rocks I X1 Dunbar Gneiss of Cain (1964); includes abundant pegmatite and aplite and, in northeast part of central core, foliated intrusive megacrystic granodiorite Approximate contact Fault, bar and ball on downthrown side Fault, relative movement not known Facing direction of pillow lava Metamorphic isofacies—gs, greenschist facies; am, amphibolite fades. After Bayley and others, 1966. — — Metamorphic isograd—bi, biotite; gar, garnet. After Dutton, 1971. Note: Rocks listed in inferred order, from youngest to oldest. �Figure 1.——Geologic map of Dunbar Gneiss—granitoid dome. from Dutton and Linebaugh, 1967. a S In part modified �by Prinz (1965); the Dunbar Gneiss and the Newingham Tonalite, formerly called the Newingham Granodiorite, were named by Cain (1964). The granites of Bush Lake and Spikehorn Creek are new, informal names for granite bodies previously called Hoskin Lake Granite (Bayley and others, 1966; Dutton, 1971). The Dunbar Gneiss, as used herein, differs from the earlier usage by Cain in excluding a moderately large body of Newingham Tonalite that intrudes the Dunbar in the northeast part of the central core (fig. 1). The Dunbar Gneiss consists of partly migmatized biotite gneisses, lesser amphibolite, and granite gneiss of dominantly tonalite composition. Some of the granite gneiss contains conspicuous feldspar megacrysts. Granite pegmatite and aplite form abundant subcortcordant sheets and steeply dipping dikes in the gneiss and amphibolite. The Dunbar Gneiss has been metamorphosed to amphibolite fades. The Marinette Quartz Diorite is composed of intermediate and mafic rocks that seem to form a layered intrusive succession. The northern part of the body, adjacent to the Hoskin Lake Granite, has ainphibolite—facies mineral assemblages. The Newingham Tonalite is a remarkably uniform gray, medium—grained, foliated rock that is cut by dikes of similarly foliated, slightly porphyritic tonalite. It composes the Pembine lobe of the Dunbar dome and part of the central core. It intrudes the Dunbar Gneiss and the volcanic rocks of the Quinnesec Formation. The foliation in the Newingham Tonalite is a cataclastic (ductile) foliation that is oriented northeastward. The Hoskin Lake Granite is a complex, crescent—shaped unit along the northern margin of the dome. The type Hoskin Lake Granite (Prinz, 1965; Bayley and others, 1966) is a distinctive rock characterized by oriented 1—5 cm tabular crystals of K—feldspar. Much of this fades also has K—feldspar porphyroblasts that lie athwart the foliation in the rock. As noted by Cain (1964), the southern margin of the granite is gradational into biotite gneisses of the Dunbar Gneiss and the Marinette Quartz Diorite, and evidence for an origin of the border phase of the granite by K—metasomatism is compelling. The granite of Spikehorn Creek, which composes the Niagara lobe, is a massive, medium— to fine—grained rock that contains sparse, small K—feldspar phenocrysts. A similar, although somewhat coarser grained rock in the Bush Lake lobe (granite of Bush Lake) is assumed to be approximately equivalent in age to the granite of Spikehorn Creek. Formerly, both were called Hoskin Lake Granite (Bayley and others, 1966; Dutton, 1971). Structure The Dunbar dome is an irregular asymmetrical structure that interrupts and distorts the regional northwest—trending structural pattern in northeastern Wisconsin. It is characterized by a consistent parallelism of structures in the cover (supracrustal) rocks and in the margins of the core and by strongly foliated and lineated rocks, indicative of high strain, along the core—cover boundary. It has an estimated structural relief greater than 2 km. The outline of the dome is interpreted as resulting from polydeformation accompanied by diapirism and emplacement of granitoid rocks. 6 �Small—Scale Structures From examination of small—scale structures in the field, a sequence of four successive deformational events has been delineated in rocks within the core and the immediately adjacent cover rocks. The principal structures developed during the successive deformations are listed in table 1. Trajectories of the planar structures and lineations are plotted in figure 2. Core Zone F D1 structures——The oldest recognized structure is a pervasive foliation (S1) that is subparallel to compositional layering in the Dunbar Gneiss. It is defined mainly by a preferred orientation of biotite and hornblende. A lineation related to S1 has not been recognized. Migmatization of the Dunbar occurred during or prior to S1. Possibly, S1 formed as an axial plane structure to early, rootless isoclinal folds. 5O F [ [ r P D2 structures——Folds (F2) are conspicuous in the Dunbar Gneiss. A major antiform orientedN. 600 W. and plunging 35°—45° SE. has been delineated in the southwestern part of the Dunbar dome, and second order folds are common on the limbs. The folds are upright, slightly asymmetrical, open to closed structures. Except locally, the folds do not transpose the older foliation (S1) and layering (S0). An axial plane foliation (S2) is best developed in the relatively massive tonalitic Dunbar Gneiss, where it is defined mainly by oriented tabular feldspars and biotite. A lineation (L2) that is parallel to fold axes (F2) is best developed in mica— and hornblende—rich gnelsses and schists and is expressed by elongate minerals and mineral aggregates. D2 preceded emplacement of the granitoid rocks in the Dunbar dome. D structures——Structures related to D3 are abundant in the northeastern part ot the central core of the dome and in the Penibine lobe. The deformation consisted of two apparently distinct phases, designated D3 and D3s, respectively (table 1), which probably resulted from the same stresses. During an early phase, the Marinette Quartz Diorite acquired a foliation and was folded into dominantly open folds that plunge gently southwest (fig. 2). Presumably at the same time, the Dunbar Gneiss in the north—central part of the core was refolded; the folds plunge gently northeastward and a mineral lineation given by aimed biotite aggregates and hornblende was developed parallel to fold axes. Subsequently, after emplacement of the Newiugham Tonalite, continued stresses produced a nearly pervasive cataclastic (ductile) foliation (S3..) defined mainly by oriented biotite and quartz leaves in the intrusive rock. The foliation is dominantly oriented northeastward and dips moderately to steeply southeastward. In the contact zone between the Newingham Tonalite and the Dunbar Gneiss, the S3.. foliation crosscuts that (S1) in the Dunbar Gneiss. An associated lineation generally is absent. Adjacent to the southeastern margin of the central core (bc. B, fig. 2), F3.. folds, which are mainly Z—type asymmetrical folds, are superposed on previously folded Marinette Quartz Diorite; hinge lines plunge moderately southwestward and axial surfaces dip southeastward, parallel to the associated S3.. foliation. These structures adjacent to the margin of the core are assigned to D3, but in part could be D4 structures. 7 �I I I I Figure 2.——Interpretive structure map, Dunbar dome Planar and linear structures —4— Si, inclined vertical —.,'.c L, showing plunge —. L2 , —H* — -. — Fault, relative movement not known —— Trend of magnetic anomaly Locality referred to in text L3 S3, - L3 ---f-f- f.. —4-- Fault, bar and ball on downthrown side 3 ....LLL t —i-— I I I S4 Foliation and lineation of uncertain designation Major F2 antiform 8 -- �Table 1.——Structural sequence, Dunbar dome D1 Foliation parallel to layering in Dunbar Gneiss (S1). D2 Northwest—oriented folds in Dunbar Gneiss and Quinnesec Formation (F2). Foliation parallel to axial planes of folds (S2). Local. Lineation parallel to fold axes (L2). Local. D2, Stretching lineation (L2,) parallel to local steeply plunging folds (F2)1) in cover—rocks, north side dome. D3 Foliation parallel to layering in Marinette Quartz Diorite (S3). Lineatlon (L3) parallel to fold axes (F3). D3, Cataclastic foliation parallel to axial planes of asymmetrical folds, northeast—trending (S1). Lineation (L3..) parallel to fold axes (F3,). D4 Mylonitic foliation (S4) in core—cover boundary. Stretching lineation (L4). 9 �D4 structures——D4 structures occur in the core—cover boundary. Inasmuch as they obliterate or strongly modify older structures in the core they are interpreted as being the youngest structures, although they could have overlapped D3. The dominant structures are a mylonitic foliation and a stretching lineation defined by elongate clasts, rare folds, mullions, and slickenside striae. They are most intensely developed on the north margin of the core (D, fig. 2) where the foliation dips 700_800 S., and the lineatlon uniformly plunges 600 Sw. The zone of mylonitic foliation is as much as 500 m wide; the foliation decreases in intensity inward from the boundary, indicating that this deformation is strongly controlled by the core—cover boundary. A comparable steep mylonitic foliation exists along the northwest boundary of the central core, but the lineation is flatter. A steep foliation and mineral lineation also exists at the extreme southwest margin of the core of the dome. It should be noted that the Pembine and Niagara lobes lack in their contact zones. structures Mantle zone The mantling metavolcanic and metasedimentary rocks were deformed together with the Dunbar Gneiss on northwest—trending fold axes during D2, and subsequently were deformed in the core—cover boundary by D3 and D4. On a regional basis, folds and related mineral lineations in the supracrustal rocks plunge moderately to steeply either to the southeast or the northwest. On the southern margin of the Dunbar dome, inclusions of the Quinnesec Formation in the Newingham Tonalite (see figs. 1 and 2) are folded; the folds plunge moderately gently southeastward, subparallel to the major D2 antiforin axis in the Dunbar Gneiss, clearly indicating that folding in both rock types was coaxial. The northwest—trending foliation and southwest—plunging mineral lineation in the Quinnesec Formation on the northeast side of the Rush Lake lobe are tentatively considered as late—stage D2 structures, and are designated as S2, and L2, respectively (fig. 2). In this area, F2 folds (as discussed above seem to be absent, presumably because they have been obliterated by S21 and both of which have fabrics indicative of high strain. As shown in figure 2 (bc. E), S2 Is redeformed adjacent to the northwest boundary of the central core by D3 structures. In this area, S—type, asymmetrical folds that plunge moderately southwestward and have a southeast—dipping axial plane foliation are developed adjacent to the boundary. They persist intermittently for a distance of 0.8 km away from the boundary. The Quinnesec Formation on the north, overturned margin of the dome is intensely deformed and has a close—spaced foliation and a steeply plunging stretching lineation resulting from D4. Pillows in the lavas are both flattened and stretched, and have length—width ratios of about 5:1. The stretching lineation is similar to that in the Quinnesec Formation on the northeast side of the Bush Lake lobe, but is more intense. As noted earlier, the Quinnesec also is intensely deformed on the northwest margin of the dome, In the same way, the Quinnesec is refoliated but the lineation is flatter. adjacent to the southwest margin and has a moderately plunging lineation oriented westward. In the reentrant along the southeast margin of the central 10 I �' core (fig. 2), the Quinnesec has a steep southeast—dipping foliation, and pillows are somewhat flattened; a mineral lineation plunges about 600 SW. As shown on figure 2, the structures are assigned to D3, but could in part have resulted from D4. Large—Scale Structure The Dunbar dome is interpreted as a large scale fold—interference structure resulting from superposition of F2 and F3 folds modified by diapirism and the emplacement of granitoid intrusive rocks. The outline of the central core of the dome is mainly the result of superposed F2 and F3 folding. Its southern margin is the southwest limb of the major northwest—trending F2 antiform cored by Dunbar Gneiss. Small—scale structures indicate that the antiform plunges moderately southeast (fig. 2), and in the crestal area both the Dunbar Gneiss and the overlying Quinnesec Formation are intruded by the large body of Newingham Tonalite (see fig. 1). Presumably, the antiform is doubly plunging, to account for the westward closure of the dome, but this cannot be confirmed because of the absence of exposures in the extreme western part of the dome. The steeply dipping cover rocks along the western margin and fabrics indicative of high strain indicate that diapirism was intense in this boundary zone. Diapirism also modified the southern margin of the central core, as indicated by an intense foliation and west plunging mineral lineation. — The northwest and southeast margins of the central core of the Dunbar dome are subparallel to small—scale D3 structures, and are interpreted as the limbs of a major northeast—oriented antiform. The reentrant of Quinnesec Formation between the central core and the Pembine lobe, shown by the map pattern (fig. 2), is a major synform. The F3 flattening folds in the Quinnesec Formation within the reentrant and on the northwest margin indicate that the core rocks behaved in a more viscous manner than the cover rocks, perhaps indicating inflation of the core during D3. The northern, overturned margin of the central core, between the Hoskin Lake Granite and the Quinnesec Formation, was the site of intense D4 deformation, which nearly completely obliterated older structures. We interpret these structures as resulting from inflation of the core, especially its northern part. Evidence exists for at least one second—order diapir in the first order one, of the type described by Schwerdtner and others (1979). This is provided by the Niagara lobe, which is composed of nearly undeformed granite of Spikehorn Creek that transects at nearly right angles the outer (eastern) margin of the central core, composed here of Marinette Quartz Diorite. The granite in the Niagara lobe has a steep foliation near its walls, and the contact is in •part at least tectonic. The volcanic rocks of the Quinnesec Formation are molded around the margin of the dome. We conclude that the lobe of granite flowed differentially upward and outward in a plastic state during a late stage of dome inflation, in a manner similar to that described by Brun and others (1981). As a consequence of the second—order diapir, a "cleavage triple point" was developed in the supracrustal volcanic rocks at the intersection of the Niagara lobe and the eastern margin of the main dome. 11 �_ U Major Events (see caption) , p Rb—Sr Ages Biotite I U 000 0 0 0 0 Aplite dikes WR isochron (22 samples) U—Pb I I ' 0 0 0 o Zircon Ages Amberg Granite 0 Atheistane Quartz Monzonite Spikehorn Creek Granite o 0 0 0 o Newingham Tonalite Dunbar Gneiss Quinnesec Formation Sm-Nd Ages Dunbar Gneiss I 1.0 I I I 1.2 I 1.4 I 1.6 Age, I 1.8 I. 0 0 2.0 Ga Figure 3.——Summary of selected isotopic ages for rocks of the Dunbar gneiss dome and environs. The events shown are: (1) the main interval of Penokean igneous activity, (2) the post—Penokean 1,760—Ma igneous event, (3) the 1,600*50 Ma event that disturbed isotopic systems throughout much of the Precambrian of Wisconsin, (4) emplacement of the Wolf River batholith, and (5) Keweenawan igneous activity. Isotopic ages shown are from Aldrich and others (1965), Banks and Cain (1969), Banks and Rebello (1969), Van Schmus (1980), and USGS (unpublished Rb—Sr, U—Pb, and Sm—Nd ages). 12 �Following this reasoning, the Bush Lake lobe is possibly also a second order diapir. I I P We interpret the D1 structure in the Dunbar Gneiss as having formed than, and at greater crustal depths, than the regional deformation (D2) of the Dunbar Gneiss and the supracrustal rocks, for the deformation was accompanied by amphibolite—facies metamorphism and migmatization of the layered rocks; whereas D2 took place under less intense metamorphic conditions, indicative of relatively shallow depths. earlier Analysis of the regional geology indicates that the Dunbar dome was developed during regional deformation related to the Penokean orogeny. The regional structural fabric and perhaps also the persistent southwest—plunging stretching lineation in the core—cover boundary of the dome, could have The resulted from subhorizontal compression oriented north—northeastward. northeast elongation of the central core and of the Pembine granitoid lobe appear to be related to more local forces, perhaps thermal perturbations within the core of the dome, for D3 structures are virtually confined to the dome. An origin of the dome through stacking of thrust sheets was considered, but rejected, because of the lack of stratigraphic evidence and other structures suggestive of thrusting. Geochronology 4 The effects of repeated tectonic and thermal overprinting of rocks within and adjacent to the Dunbar dome are recorded in a spectrum of highly discordant isotopic ages (fig. 3). The principal units within the dome formed between 1,862*5 Ma and 1,835*6 Ma as shown by U—Pb zircon ages for the Dunbar Gneiss and granite of Spikehorn Creek, the oldest and youngest units, The supracrustal Quinnesec Formation has a U—Pb zircon age of respectively. 1,866*39 Ma (Banks and Rebello, 1969), which is not resolvable from the ages of the core rocks. The Athelstane Quartz Monzonite of Van Schmus and others (1975), cropping out southeast of the Dunbar dome, was approximately coeval with some of the core rocks as shown by a U—Pb zircon age of 1,836*15 Ma The Amberg Quartz Monzonlte of Van Schmus and others (Banks and Cain, 1969). (1975) intrudes the Athelstane Quartz Monzonite and is equivalent in age to high—level granitoids and felsic volcanic rocks in central Wisconsin (Smith, Data for two fractions of zircon from a sample of the Arnberg Quartz 1983). Monzonite (Van Schmus, 1980) define a chord with an upper intercept age of 1,756*19 Ma. Sm—Nd model ages of 2,130 and 2,280 Ma for two samples of Dunbar Gneiss (fig. 3) are substantially older than the crystallization ages defined by the Other Early Proterozoic igneous rocks in northern Wisconsin have zircon data. yielded similar "old" Sm—Nd ages (Nelson and DePaolo, 1982). The Sm—Nd ages, together with Pb—isotope data (Afifi and others, in press), strongly indicate a major involvement of Archean crustal material in the genesis of Early Proterozoic volcanic and plutonic rocks and syngenetic mineralization. 13 �Post—doming events have severely perturbed Rb—Sr. whole—rock and mineral Twenty—two whole—rock samples (5 to 10 kg each), representing both massive and gneissic units wiin e Dunbar dome, define a Rb—Sr isochron of 1,688*28 Ma, with an initial Sr ratio of 0.7038*0.0013 (fig. 4). Sr/ We attribute the disturbance of the Rb—Sr system at the whole—rock scale to open— system behavior related to cataclasis that variably affected all of the units in the dome. Recrystallization of biotite (and microcline where present) and sericitization and epidotization of plagioclase facilitated the mobility of Rb and Sr. Fluids undoubtedly played a major role in the migration of Rb and Sr as well as other elements. A relation between rock composition and degree of resetting is suggested by an isochrg agg of 1,733*43 Ma obtained by regressing only those samples with Rb! 6Sr ratios less than 3. This separation roughly divig9s t data according to rock type with the granites (sensu stricto) having Rb! Sr ratios greater than 3 and the tonalites and granodiorites having ratios less than 3. This correlation between rock composition and degree of resetting of the Rb—Sr system Is probably related to differences in physical properties of the rocks. The granites, being less biotitic and more quartz rich than the tonalites and granodiorites, probably deformed in a more brittle fashion, which led to a higher permeability and thus a greater opportunity for interaction with a fluid phase. Some of the units, although open systems on the sample—size scale (tens of centimeters), 9pea to have ematged closed at larger scales. For example, average Rb! 6Sr and 8 Sr/ Sr values calculated for the Dunbar Gneiss (11 samples) by weighting each sample by its Sr content, are used to calculate a model age of 1,875*70 Ma, using an initial Sr ratio of 0.7017. Although the uncertainty is large, a model age is indistinguishable from the crystallization age given by the U—Pb zircon data. ages. Rb—Sr biotite ages of rocks within the Dunbar dome decrease from east to west (figs. 3 and 5). This variation is part of a regional pattern of Rb—Sr biotite ages that extends north to the Marquette trough (Peterman and Sims, 1984). Within this area, 54 biotite ages define a tripartite distribution with well defined modes at 1,580*70 Ma, 1,320*50 Ma, and 1,140*30 Ma. The older group is a composite that contains the tightly clustered 1,630*30 Ma ages for Archean rocks of the southern complex in northern Michigan (Van Schmus and Woolsey, 1975) and slightly younger ages from areas to the south (fig. 5). Van Schmus and Woolsey correlated the 1.63—Ga ages with a cryptic event that has affected Precambrian rocks over much of Wisconsin (fig. 3). A younger resetting event at 1,140*30 Ma, recognized mainly in the western third of the Dunbar dome, occurred contemporaneously with Keweenawan (Middle Proterozoic) rifting and igneous activity. The coincidence of age discontinuities with northwest— and northeast—trending, vertically lineated shear zones (fig. 5) strongly suggests that differential uplift was a causative factor in producing the age pattern. Apparently, stresses attendant with rifting were transmitted over considerable distances and resulted in reactivation of existing faults and vertical adjustments of large magnitude. The intermediate group of ages, 1,320*50 Ma, does not correlate with any known events in the region (fig. 3). Aldrich and others (1965) suggested a thermal event at this time, but they did not elaborate on a cause. Possibly, the surface now characterized by the 1,320—Ma age group was uplifted and cooled during the Keweenawan from a depth at which the biotite systems were only partially reset. 14 �1.2 DUNBAR DOME (ALL SAMPLES) 1.1 C/) T = 1688 ± 28 Ma IR = 0.7038 ± .0013 1.0 Co Co 0.78 L.. U) 1= 1733± 43 Ma IR = 0.7032 ± 0.9 0.76 Co 0.74 0.8 0.72 0.70 0.7o 4 0.0 12 8 87Rb 0.8 1.6 2.4 16 / 86 Sr Figure 4.——Whole—rock Rb—Sr isochron for samples of all units within the Dunbar dome. The isochron of 1,68828 Ma is8aseg on all of the samples (22). The inset shows samples with Rb! 6Sr ratios of less than 3 (mainly tonalites and granodiorites). 15 20 �R • 1.66 * ,1 .69 '1.80 • .63 MICHIGAN .65 1.55 I I 1.62 .68 I ,1.39 46° •..' I S — / ,/ I: I I I WISCONSIN SHEAR ,136 •1.39 I 0 I 10 MILES 0 I 10 KILOMETERS •1.39 I I Figure 5.——Rb—Sr biotite ages in billions of years (Ga) for Archean and Early Proterozoic rocks in northeastern Wisconsin and adjacent northern Michigan. Data are from Van Schmus and Woolsey (1975) for the southern Complex, Aldrich and others (1965) for the Felch trough area, and Peterman and Sims (unpublished) for the Dunbar dome and vicinity. 16 I I �_ Evolution of Dome r [ r p p The stratigraphic—tectonic evolution of the Dunbar dome spanned a relatively short time of about 30 Ma, from about 1,865 to 1,835 Ma (table 2), during the Early Proterozoic. The first recognized event was the formation of the volcanic and plutonic (tonalitic) protoliths of the Dunbar Gneiss, probably as part of a succession covering a large area in an oceanic regime. Following an early deformation (D1) at moderate crustal depths and the rise of the Dunbar Gneiss to shallower crustal levels, quartz sand, dolomite, and volcanic tuff(?) were deposited unconformably on the Dunbar Gneiss in a shallow—water environment. Later, vast quantities of tholeiitic volcanic rocks (Quinnesec Formation) were deposited in deep water, probably in a back—arc basin (Schulz, 1984). Comagmatic, subvolcanic sills of maf Ic composition were intruded into the Onset of regional compression produced a northwest—trending, volcanic pile. generally steeply dipping, structural fabric (D2) In the basement and supracrustal successions. After culmination of the regional deformation (D2), the Marinette Quartz Diorite was emplaced in the northeast part of the Dunbar dome, apparently as a layered, crescent—shaped sheet essentially along the contact between the underlying Dunbar Gneiss and the overlying Quinnesec volcanics. Subsequently, the Newinghain tonalite was intruded. The Newingham was emplaced at the base of the Quinnesec Formation, and it contains abundant xenoliths of both the Quinnesec Formation and the Dunbar Gneiss in the contact zone. The Marinette Quartz Diorite was emplaced before or during deformation D3, which produced dominantly northeast—trending structures in the rock and was accompanied by amphibolite—facies metamorphism in the hotter and deeper(?) northern part of the dome. During later stages of the deformation (D3i), the Newingham Tonalite was emplaced and then deformed. The major structure imposed on it was a cataclastic (ductile) foliation that dominantly trends northeastward and has a northwest vergence. A major northeast—trending antiforin resulting from deformation D3 produced the northeast—trending margins of the central core of the dome. Concomitantly with rise of the thermal isograds in the dome, the Hoskin Lake Granite was emplaced along the northern margin of the dome during late stages of D3, mainly as a magma but in part by K—metasomatic replacement of the Marinette Quartz Diorite and the Dunbar At this stage, K—bearing fluids permeated parts of the central core, Gneiss. selectively replacing parts of the Marinette Quartz Diorite and the Dunbar Gneiss, apparently by migration of the fluid along more permeable cataclastic K—metasomatism continued In the northern, hotter part of the dome; and zones. rise and inflation of the central core produced a northward vergence, and was accompanied by rotation of the country rocks in the margins of the dome into Contemporaneously, the cover conformity with the core—cover boundary (D4). rocks adjacent to the central core were metamorphosed to amphibolite facies. The thermal metamorphic aureole was exeedingly wide on the northern and northwestern margins of the central core, where the amphibolite fades zone is at least 8 km wide, far in excess of that to be expected by conduction of heat from a magma such as the Hoskin Lake Granite. The thermal activity in the core led to the emplacement of abundant granitoid dikes in the inner (amphibolite grade) part of the metamorphic aureole. Continued rise of the geotherms in the northern segment of the dome led to development of a granitic magma (granite of Spikehorn Creek), which was emplaced by outward, diapiric 17 �1,865 1,860 —— H 1,835 . Age in Ma D1 Deformation of Dunbar Gneiss and supracrustal rocks on northwest axes, to produce regional structural fabric D2 —_——— — I_J J U I Formation of volcanic and plutonic (tonalitic) protolith of Dunbar Gneiss Foliation parallel to layering in Dunbar Gneiss of Cain (1964); metamorphism of Dunbar to amphibolite facies, migmatization, and intrusion of granite pegmatite and aplite Unconformity Deposition of shallow—water sediments Uncoriformi ty Deposition of a thick succession of tholeiitic volcanic rocks (Quinnesec Formation) Deformation on northeast axes (restricted areally), after emplacement of Marinette Quartz Diorite and Newingham Tonalite Emplacement of Hoskin Lake Granite, in part by K—metasomatism of older rocks Continued rise in isotherms centered on northern part of core accompanied by diapiric rise of dome, rotation of older structures into conformity with core—cover boundary, and metamorphism of adjacent cover rocks and northern part of core rocks Emplacement of granite of Spikehorn Creek and, possibly, granite of Bush Lake into Niagara and Bush Lake lobes, respectively, as diapirs; and intrusion of aplite and pegmatite into Dunbar Gnelss Quartz—tourmaline veinlets and fluorite in brittle fractures Event D3 D4 Deformation Table 2.——Stratigraphic—tectonic evolution of Dunbar dome - �! flow into the Niagara lobe, a second—order dome. The granite of Bush Lake was intruded at about the same time. At a late stage of evolution of the Dunbar dome, quartz and tourmaline were mobilized into brittle fractures both within and outside the core, and fluorite was mobilized locally into fractures in the Hoskin Lake Granite. Tectonic Environment r r- [ Recognition that the Dunbar Gneiss and, by implication, other bodies of crystalline rocks in northern Wisconsin are cores of domal structures exposing deeper crustal rocks has an important bearing on the Proterozoic stratigraphy and paleogeography of the region during Early Proterozoic time. Crystalline rocks of Early Proterozoic age, such as those exposed in the Dunbar dome, have not been delineated in northern Michigan despite extensive, detailed mapping, and it seems certain that they are absent or at least of minor significance. Also, in northern Wisconsin, volcanic rocks dominate the su#racrustal sequence, whereas Interbedded sedimentary and volcanic rocks characterize the Marquette Range Supergroup in Michigan. Chemically, the volcanic rocks in the two parts of the region differ substantially. Those in northern Michigan, as indicated by volcanic rocks in the Hemlock Formation, are largely bimodal with abundant tholeiltic basalt and minor high—K20 rhyolite. The basalt shows strong iron enrichment and high T102 and incompatible—element contents (Fox, 1983); they are compositionally similar to continental rift basalts, such as those of the Keweenawan in Minnesota. In contrast, the volcanic rocks of the Quinnesec Formation range from basalt through andesite to rhyolite, lack strong iron enrichment, and have back—arc basin compositional affinities (Schulz, 1984). Other contrasts in the two areas are marked differences in the mineral deposits contained in the Early Proterozoic successions (Sims, 1976). Iron—formations and associated enriched iron deposits are the dominant ore deposits in the Marquette Range Supergroup of Michigan, whereas massive sulfide deposits are dominant in northern Wisconsin and iron—formations are thin and sparse. A critical stratigraphic problem is the relationship of the shallow—water sedimentary rocks in the Dunbar dome to the shallow—water deposits at the base (Chocolay Group) of the Marquette Range Supergroup. We suggested earlier (Schulz and Sims, 1982) that the strata in both areas are possibly correlative; but the chemical differences in the overlying volcanic rocks and other differences, such as the volume of Early Proterozoic plutonism in the two terranes, now lead us to interpret the sedimentary rocks as being homotaxial rather than stratigraphically correlative. Data presented here, together with regional geologic relationships (fig. 1; Morey and others, 1982), are consistent with an interpretation that the Wisconsin magmatic zone is an exotic terrane that evolved in an oceanic—arc setting and was attached to the North American continent during the Early Proterozoic. Apparently the boundary between the two Proterozoic terranes is the Niagara fault zone, as suggested by Larue (1983). Probably the doming, which exposes the gneiss and granitoid rocks in the cores, was in response to collision of the two crustal blocks, which triggered the Penokean orogeny. The westward extent of the Wisconsin magmatic zone remains equivocal, for if 19 �indeed it does extend across the midcontinent rift system into Minnesota, only remnants of the vast accumulation of Early Proterozoic volcanic rocks apparently remain there. * The conclusions reached here support the earlier interpretation of Van Schmus (1976), based on broad geologic considerations, that the Early Proterozoic epicratonic successions in the Great Lakes area accumulated at a continental margin. A variant of this interpretation later was presented by Cambray (1978) and Larue (1983). The earlier interpretation of one of us (Sims, 1976; Sims and others, 1981) that the Early Proterozoic sequences in the Great Lakes area accumulated in an intracratonic setting no longer is tenable for the whole region. On the basis of new chemical and structural data obtained in this and other parts of Wisconsin and northern Michigan, Schulz and others (1984) have proposed a tectonic model of early crustal rifting and spreading, subsequent subduction and formation of a complex volcanic arc, and collision of the arc, first with Archean crust on the south and then with the continental margin Proterozoic sequence and Archean crust of northern Michigan on the north (the Penokean orogeny). 20 �REFERENCES CITED Afifi kfifa, Doe, B. R., Sims, P. K., and Delevaux, M. N., 198.4, U—Th—Pb isotopic chronology of sulfide ores and rocks in the Early Proterozoic metavolcanic belt of northern Wisconsin: Economic Geology (in press). Aldrich, L. T., Davis, G. L., and James, H. L., 1965, Ages of minerals from metamorphic and igneous rocks near Iron Mountain, Michigan: Journal of Petrology, v. 6, p. 445—472. Banks, P. 0,, and Cain, J. A., 1969, Zircon ages of Precambrian granitic rocks, northeastern Wisconsin: Journal of Geology, v. 77, p. 208—220, r Banks, P. 0., and Rebello, D. P., 1969, Zircon age of a Precambrian rhyolite, northeastern Wisconsin: p. 907—910. Geological Society of America Bulletin, v. 80, Bayley, R. W., Dutton, C. E., and Lamey, C. A., 1966, Geology of the Menominee iron—bearing district, Dickinson County, Michigan, and Florence and Marinette Counties, Wisconsin: U.S. Geological Survey Professional Paper 513, 96 p. Brun, J. P., Gapais, D., and LeTheoff, B., 1981, The mantled gneiss domes of Kuopia (Finland): Interfering diapirs: Tectonophysics, v. 74, p. 283—304. r Cain, J. A., 1964, Precambrian geology of the Pembine area, northeastern Wisconsin: Papers of Michigan Academy of Science, Art, and Letters, v. 49, p. 81—103. Cambray, F. W., 1978, Plate tectonics as a model for the environment of deposition and deformation of the early Proterozoic (Proterozoic X) of northern Michigan: Geological Society of America Abstracts with Programs, v. 10, no. 7, p. 376. Dutton, C. E., 1971, Geology of the Florence area, Wisconsin and Michigan: U.S. Geological Survey Professional Paper 633, 54 p. Dutton, C. E., and Linebaugh, R. E., 1967, Map showing Precambrian geology of the Nenominee iron—bearing district and vicinity, Michigan and Wisconsin: U.S. Geological Survey Miscellaneous Geologic Investigations Map 1—466 (scale 1:125,000). Ervin, C. P., and Hammer, S. H., 1974, Bouguer anomaly gravity map of Wisconsin: Wisconsin Geological and Natural History Survey (scale 1:500,000). Fox, T. P., 1983, Geochemistry of the Hemlock Metabasalt and Kiernan sills, Iron County, Michigan [Unpublished M.S. thesis]: East Lansing, Michigan, Michigan State University, 81 p. 21 �Larue, D. K., 1983, Early Proterozoic tectonics of the Lake Superior p region: Tectonostratigraphic terranes near the purported collision zone, in Medaris, L. G., Jr., Early Proterozoic geology of the Great Lakes region: Geological Society of America Memoir 160, p. 33—47. Morey, G. B., Sims, P. K., Cannon, W. F., Mudrey, M. G., Jr., and Southwick, D. L., 1982, Geologic map of the Lake Superior region, Minnesota, Wisconsin, and northern Michigan: Minnesota Geological Survey State Map Series 5—13 (scale 1:1,000,000). Nelson, B. K., and DePaolo, D. J., 1982, Crust formation age of the North American midcontinent: Geological Society of America Abstracts with Programs, v. 14, no. 7, p. 575. Peterman, Z. E., and Sims, P. K., 1984, Middle Proterozoic events in northeast Wisconsin and adjacent Michigan as defined by Rb—Sr biotite ages: Proceedings, 30th Annual Institute on Lake Superior Geology, Wausau, Wisconsin (in press). Prinz, W. C., 1965, Marinette Quartz Diorite and Hoskin Lake Granite of northeastern Wisconsin, in Cohee, G. E., and West, W. S., Changes in stratigraphic nomenclature by the U.S. Geological Survey, 1964: U.S. Geological Survey Bulletin 1224—A, p. A1—A77. Ramberg, Hans, 1967, Gravity, deformation and the Earth's crust: Press, London, 214 p. Academic Schulz, K. J., 1984, Early Proterozoic Penokean igneous rocks of the Lake Superior region: Geochemistry and tectonic implications: Proceedings, 30th Annual Institute on Lake Superior Geology, Wausau, Wisconsin (In press). Schulz, K. J., LaBerge, G. L., Sims, P. K., Peterman, Z. E., and Kiasner, J. S., 1984, The volcanic—plutonic terrane of northern Wisconsin: Implications for Early Proterozoic tectonism, Lake Superior region: Program with Abstracts, Geological Association of Canada—Mineralogical Association of Canada, London, Ontario, Canada (in press). Schulz, K. J., and Sims, P. K., 1982, Nature and significance of shallow water sedimentary rocks in northeastern Wisconsin [abs.]: Proceedings, 28th Annual Institute on Lake Superior Geology, International Falls, Minnesota, p. 43. Schwerdtner, W. M., Stone, D., Osadetz, K., Morgan, J., and Stott, G. M., 1979, Granitoid complexes and the Archean tectonic record in the southern part of northwestern Ontario: Canadian Journal of Earth Sciences, v. 16, p. 1965—1977. Sims, P. K., 1976, Precambrian tectonics and mineral deposits, Lake Superior region: Economic Geology, v. 71, p. 1092—1118. 22 �1980, Boundary between Archean greenstone and gneiss terranes in northern Wisconsin and Michigan: Geological Society of America Special Paper 182, p. 113—124. Sims, P. K., Card, K. D., and Lumbers, S. B., 1981, Evolution of early Proterozoic basins of the Great Lakes region, in Campbell, F. H. A., ed., Proterozojc basins of Canada: Geological Survey of Canada Special Paper 81—10, P. 379—397. Sims, P. K., Peterman, Z. E., Zartman, R. E., and Benedict, F. C., 1984, Geology and geochronology of granitoid and metamorphic rocks of Late Archean age in northwestern Wisconsin: U.S. Geological Survey Professional Paper 1292—C (in press). Smith, E. I., 1983, Geochemistry and evolution of the early Proterozoic, post—Penokean rhyolites, granites, and related rocks of south—central Wisconsin, U.S.A.: Geological Society of America Memoir 160, p. 113—128. Van Schinus, W. R., 1976, Early and middle Proterozoic history of the Great Royal Society of London Philosophical Lakes area, North America: Transactions, ser. A280, no. 1298, p. 605—628. 1980, Chronology of igneous rocks associated with the Penokean orogeny Geological Society of America Special Paper 182, p. in Wisconsin: 159—168. Van Schmus, W. R., Thurman, E. M., and Peterinan, Z. E., 1975, Geology and Rb—Sr chronology of middle Precambrian rocks in eastern and central Geological Society of America Bulletin, v. 86, p. 1255—1265. Wisconsin: Van Schmus, W. R., and Woolsey, L. L., 1975, Rb—Sr geochronology of the Republic area, Marquette County, Michigan: Canadian Journal of Earth Science, v. 12, p. 1723—1733. 23 �I Geochemistry of the Dunbar gneiss—granitoid dome, Northeastern Wisconsin by K. J. Schulz!', P. K. Sims2/, and Z. E. Peterinan2l U.S. Geological Survey, Reston, VA 22092 2/ U.S. Geological Survey, Denver, CO 80225 2L �Introduction Samples from the major rock units that make up the Dunbar gneiss— granitoid dome have been analyzed for major and trace elements (including rare—earth elements — REE) to determine their compositional characteristics and aid in deciphering their petrogenesis. Representative analyses are presented in tables 1 and 2 and shown graphically in figures 1 through 9. Dunbar Gneiss Samples of Dunbar Gneiss range from tonalite to granite, are calc—alkaline (figs. 1 and 2), and define general trends of decreasing Al203, FeOT, MgO, CaO, Ti02, Na20, and Sr contents and increasing K20 and Rb contents with increasing Sb2 content. Except for mafic amphibolite units found interlayered with the Dunbar Gneiss, samples in which Sb2 is less than 60 weight percent appear to be absent. The rocks have Rb/Sr ratios ranging from about 0.15 to 1.0 (fig. 4) and K/Rb ratios ranging from about 260 to 160; increasing Rb/Sr ratios correlate positively with Si02 content. The chondrite—normalized REE data for Dunbar Gneiss samples are shown in figure 5. All samples show steep patterns with relatively enriched light—REE (chondrite—norinalized La=[La]1q=71—360) and depleted heavy—REE ([La/Yb]N=45—18; except one example at 217). The sample with the steepest slope and most depleted heavy—REE is from a leucocratic layer within more biotitic tonalite gneiss. The two samples having the lowest total REE abundances have the highest S102 content (i.e., 75 and 74 weight percent). Except for these two samples, the rocks show small negative Eu anomalies. 25 �Table 1.—— Representative analyses of samples from the Dunbar Gneiss and Newingham tonalite. Si02 A1203 Fe203 FeO MgO CaO Na20 1(20 Ti02 P205 MnO H20 H20 CO2 1 2 3 4 61.7 17.5 1.02 4.41 1.64 3.20 4.22 3.16 0.82 0.18 63.6 16.3 0.88 4.07 1.64 3.87 4.21 2.42 0.82 0.26 0.09 0.37 0.05 0.03 75.0 13.5 0.08 1.22 0.22 1.25 3.17 4.51 0.14 <0.05 <0.02 0.24 0.10 0.03 49.8 15.7 1.50 6.70 8.50 11.6 2.24 1.06 0.35 <0.05 0.19 1.68 <0.01 <0.01 0.09 0.85 0.02 0.03 *Rb — — — — Sr y Zr Nb Th Ta Hf Cr Co Sc Zn Rb Ba Cs La Ce Nd Sm Eu Gd Tb Yb Lu 118 443 5 66.6 18.0 1.1 2.4 1.6 4.5 4.1 1.7 0.37 0.18 0.03 0.82 0.10 0.05 229 232 — 282 6 68.0 15.7 0.51 2.64 1.38 3.53 3.88 2.15 0.37 0.13 0.04 — L0I=0.51 — 67 656 7.8 68 — 126 14.5 3.6 10.0 3.78 6.75 7.8 10.2 5.13 74 137 883 5.65 35.1 61.8 27 5.1 1.17 4.4 0.66 1.16 0.20 3.1 10.3 3.95 7.6 25 9.9 8.0 — 117 810 4.9 63.2 119 34 7.13 1.76 — 0.94 1.55 0.21 2.2 12.2 2.58 2.39 17 1.34 1.05 26 250 1620 10.9 26.1 42.1 15.9 2.47 0.67 1.4 — 0.52 0.06 — 0.46 0.14 0.74 323 39.5 45.8 117 42 80 4.22 3.8 6.0 — 1.14 0.45 — 0.38 2.07 0.33 0.96 2.6 0.44 2.0 14 8.77 6.74 — 40 570 0.81 12.5 22.8 7.2 1.27 0.44 — 0.11 0.18 0.03 Major and minor elements by rapid rock methods or XRF *By XRF analysis +By instrumental neutron activation analysis. L0I = Loss on ignition 1—3 — Dunbar Gneiss 4 — Amphibotite within Dunbar Gneiss 5—6 — Newingham tonalite 26 1.8 6.0 1.75 3.4 42 6.97 4.5 — 69 961 6.1 27.9 52.0 17 2.67 0.77 — 0.26 0.42 0.06 — �H eOT I _ Dashed Brown, 1982). lines show field for igneous rocks from convergent plate margins (from Figure 1.--Fe01-MgO-Na20+K20 diagram for rocks of the Dunbar diie. Na20 +1<20 — — gO — I1 I I' �co r') CD .4 C-,. 0 0 \ 0 \0 QD 0•-• 0 0 U 0 • . wt.%SiO I S 0 DG owO co0 Oc No Lake Granite (may include MQD) (data plotted includes that of Cudzilo, 1978). Circle with star = Atheistane tuartz Monzonite. Figure 2.--Moclified Peacok diagram for rocks of the Dunbar dome. New = Newingham tonalite, DG = Dunbar gneiss, MQD = Marinette Quartz Diorite, HLG = Hoskin 0 U I• UiL II iJ �— 2w1% Na10 — ———— Falls quartz diorite. Other labels as in figure 2. Figure 3.--K2O-Na20 diagram for rocks of Dunbar dome. ATH = Atheistane Quartz Monzonite; 1FF = Twelve Foot r') (0 — E I00 Sr ppm 0 H IC 0 -t--- 0 l—— — a— I I Figure 4.--.Rb-Sr variation in rocks of Dunbar dome and Athelstane Quartz Monzonite. Aplites ciii) -— ___ �(A) Lo Ce II Nd I \AMPH I I I I 5n uGdTh DUNBAR I I 'lb IlL GNEISS I J Formation. H - ——— Figure 5.--Chondrite normalized REE for samples of Dunbar Gneiss (solid lines) and amphibolite enclaves in gneiss (Amph). Doted field for basalts of the Quinnesec — foo- 100_ Figure 6.--Chondrite normalized REE for samples of Newingham tonalite. II Ii �The amphibolites within the Dunbar Gneiss are basaltic in composition (Table 1) and are generally similar to the basalts of the Quinnesec Formation (Schulz, this volume) except for having higher 1(20 and relatively enriched La and Ce contents. The rare—earth elements Sm through Lu show a steep positive slope in the amphibolites (fig. 5) whereas the slope of La to Ce is distinctly negative. The steep positive slope of the heavy REE is similar to that observed for Quinnesec basalts which are strongly depleted in light REE (fig. 5), suggesting that the amphibolites were originally also depleted in light REE. The present enrichment of light REE (i.e., La and Ce) in the amphibolites, as well as 1(20, may have resulted from inter- action with their surrounding light—REE—enriched felsic gneisses during amphibolite facies metamorphism. On the bases of the field and geochemical data, the protolith for the Dunbar Gneiss is interpreted, to have been a sequence of interlayered inter- mediate to felsic volcanic and related intrusive rocks. The overall compositional similarity with intermediate to felsic rocks of recent magmatic arcs formed at convergent—plate margins (Brown, 1982; fig. 1) suggests that the Dunbar Gneiss protolith may have formed in a similar tectonic setting. The steep REE patterns suggest that the parent maginas were probably derived from mafic to intermediate, garnet—bearing sources (Hanson, 1981), perhaps at lower crustal levels. The trace—element characteristics of the Dunbar Gneiss samples are distinct from those of the structurally younger intermediate to felsic volcanic rocks of northeastern Wisconsin (Schulz, this volume); this difference supports the structural interpretation that the Dunbar Gneiss represents the product of an older cycle of magtnatic activity. 31 �Newingham Tonalite The intrusive Newingham tonalite is remarkably hongeneous in composition and shows only a small range in Si02 content (fig. 2). The tonallte is higher in A1203, MgO, CaO, and Sr and is lower in FeOT, Ti02, K20, and Rb than the Dunbar Gneiss (Table 1 and figs. 3 and 4). It is also characterized by lower Rb/Sr ratios (<.10) (fig. 4) and higher K/Rb ratios (>260). The samples show steep REE patterns (fig. 6) ([La/Yb]N=48—40) somewhat similar to those of the Dunbar gneisses but with mostly lower total REE abundances and show either no or slightly positive Eu anomalies. A strong correlation exists between increasing Rb/Sr ratio, increasing total REE abundance, and decreasing magnitude of the Eu anomaly. This correlation reflects the role of plagioclase fractionation in the magmas parental to these rocks. The Newingham tonalite is calcic (fig. 2) and is compositionally similar to Archean tonalites such as those of the Vermilion district of Minnesota (Arth and Hanson, 1975) and elsewhere (O'Nions and Pankhurst, 1978). Their low Rb/Sr ratios, high Sr contents, and strong heavy—REE depletions have been considered indicative of melts derived by partial melting of eclogite or garnet amphibolite (Arth and Hanson, 1972). However, the relatively high light—REE contents of the Newingham tonalite samples would preclude a typical tholeiitic basalt (which has depleted or flat light REE) as a parent (Hanson, 1981). A lithologically heterogeneous lower crust, probably more mafic than the source for the protoliths of the Dunbar gneisses (i.e., lower feldspar content at high grades of metamorphism), may have been the source of the parent magma of the Newingham tonalite. 32 b �r Marinette Quartz Diorite The Marinette Quartz Diorite (MQD) is distinct from the other units of the Dunbar dome in having alkalic to alkali—calcic affinities (fig. 2). These affinites are reflected in the high total alkali, Ti02, P205, and REE contents of the nre mafic samples (Table 2). The Marinette Quartz Diorite has a complex northern border zone where it is intruded by and is in contact with the Hoskiri Lake Granite. Throughout a broad zone, the MQD is variably metasomatized and partially assimilated by the Hoskin Lake Granite, resulting in intermediate to felsic compositions that overlap with those of the granite. Away from this broad contact zone, the MQD appears to be relatively inafic and more uniform in composition although more data are needed to fully establish its original compositional range. The chondrite—normalized REE patterns for samples of MQD are shown in figure 7. Most of the samples have similar steep REE patterns in which [La]N ranges from 170 to 340 and [Th]N ranges from 6.5 to 12. Samples mostly show a small negative or no Eu anomaly; the one sample having a large positive Eu anomaly contains abundant megacrysts of plagioclase. Two samples from within the contact zone of the MQD with the Hoskin Lake Granite have lower REE abundances than the other samples (fig. 7) and patterns similar to those of the Hoskin Lake Granite (compare figs. 7 and 8). The alkaline affinity and trace—element characteristics of the MQD suggest that the parent magma was alkaline, perhaps an alkali basalt. The relatively early occurrence of alkaline magmatism in a dominantly caic—alkaline magmatic terrane appears to be somewhat anomalous but may have an analogue in the early alkalic plutons present within the caic—alkaline plutonic belt of California (Miller, 1977). 33 �Table 2.—— Representative analyses of samples from the Marinette Quartz Diorite, I Hoskin Lake Granite, granites of the Bush Lake and Niagara lobes, and associated late aplites. Si02 A1203 Fe203 FeO MgO CaO Na20 1(20 Ti02 P205 MnO H20 H20 CO2 1 2 3 51.8 16.8 1.97 7.77 3.50 6.18 3.88 2.62 2.42 65.0 15.9 0.64 3.01 1.56 3.20 4.30 3.69 0.79 0.18 0.07 0.44 0.02 0.04 69.1 15.0 0.56 2.67 0.91 1.91 3.45 4.69 0.51 0.11 0.05 0.63 0.13 0.08 0.64 0.15 1.23 0.07 <0.01 *Rb — — — — Sr Y Zr Th Ta Hf Cr Co Sc Zn Rb Ba Cs La Ce Nd Sm Eu Cd Tb Th Lu 3.1 19.4 3.85 5.87 6.4 28.5 13.1 94 84 701 4.36 57.2 118 60 10.2 2.50 8.6 1.01 2.20 0.325 28 23 3.50 4.63 17 9.67 6.35 58 128 1050 153 279 73.0 13.7 0.31 1.78 0.41 1.06 3.51 4.63 0.18 <0.05 0.05 — L0I—0.44 — 244 117 15 163 — 137 5 6 72.7 13.6 0.27 2.07 0.40 1.19 2.74 5.48 0.27 0.09 0.04 0.39 74.6 13.7 0.23 0.96 0.15 0.65 3.43 5.06 0.03 <0.05 0.03 — 0.12 L0I0.28 0.02 329 58 154 57 1: 33.7 4.61 5.91 22 5.75 3.31 44 25.4 5.50 4.9 46 23 2.41 18 159 705 4.21 56.3 85.6 28 28 4.43 0.89 3.3 0.39 1.38 0.19 1.70 — 244 466 7.1 32.0 59.0 18 3.22 0.54 — 0.52 1.14 0.19 7 74.2 14.5 0 0.65 0.12 0.43 5.21 3.90 <0.02 <0.05 <0.02 — L0I=0.17 — 270 143 31 :.5 3.42 54.3 83.1 4.21 1.12 3.3 0.34 1.08 0.15 4 454 9.75 98 35 60 I 3.90 5.0 2.54 4.85 47 283 787 5.73 69 121 48 8.45 0.88 9.0 0.85 2.6 0.43 24.0 5.78 2.80 23.2 2.90 22 28 0.74 3.20 — 321 184 12.8 19.6 42 16 4.05 0.29 — 0.99 3.51 0.54 6.6 0.60 18.1 — 459 65 1.5 5 11 — 3.9 0.03 — 1.44 11.1 1.56 Major and minor elements by rapid rock methods or XRF *By XRF analysis +By instrumental neutron activitation analysis. LOI = Loss on ignition 1—2 — Marinette Quartz Diorite 3—4 — Hoskin Lake Granite (4 from Niagara lobe) 5—6 — Granite of the Bush Lake lobe 7 — Aplite dike cutting Dunbar Gneiss I �4oo I MARINETTE QUARTZ DIORITE S. 100 40 to— —— 4 I I LaCe I Nd I I I I 5M EtLS Th Figure 7.--Chondrite normalized REE for samples of Marinette Quartz Diorite. 35 I I YbLLL �Hoskin Lake Granite and Granites of the Bush Lake and Niagara Lobes The granites of the Niagara and Bush Lake lobes and the Hoskin Lake Granite share overall chemical similarities although systematic differences are recognized (Table 2). Relative to the more felsic segments of the Dunbar Gneiss, these granites have slightly higher K20, Ti02 and Rb contents and lower A1203, MgO, CaO, and Na20 contents. The granite of the Niagara lobe and the Hoskin Lake body are compositionally similar except that the Hoskin Lake Granite has a slightly higher K20 content. Rb/Sr ratios range from about 0.55 to 2.0 (fig. 4) and show a positive correlation with increasing Sb2 content; K/Rb ratios range from about 250 to 155 and show a negative correlation with increasing Si02 content. The samples show light—REE enrichment, small to moderate negative Eu anomalies, and decreasing light—REE abundance with increasing Si02; they also show only slightly fractionated heavy—REE (fig. 8). The granite of the Bush Lake lobe is compositionally distinct from that of the other two bodies in being slightly higher in average Sb2 and 1(20 contents and in having higher K20/Na20, U/Th and Rb/Sr ratios. The REE patterns are also distinctive (fig. 8) and have large negative Eu anomalies, relatively flat heavy—REE slope, and significant depletion in the light—REE with increasing Si02 content. Intruding the western part of the Dunbar dome are numerous garnet— bearing aplite and pegmatite bodies. The aplites are strongly depleted, relative to the granites, in FeOT, MgO, CaO, Ti02, P205, MnO, Sr, Zr, Ba, Eu, and light—REE but are enriched in Y, Ta, Nb, Rb, and the heavy—REE (Table 2 and figs. 4 and 8). They also show very low Zr/Hf (<17) and Nb/Ta (<4.7) ratios. 36 �400- 100 - AP- 40—— Bi N 10 I I I LaC.e I I Tb Nd Figure 8.--Chondrite normalized REE for samples of Hoskin Lake Granite (HL), Bush Lake granite (BL) and aplites cutting Dunbar Gneiss (AP). 37 �I The compositional characteristics of these aplites are not compatible with their derivation by partial melting of the Dunbar Gneiss. Rather, they are interpreted as the late—stage differentiates of the granite of the Bush Lake lobe. Shown in figure 9 are the relative enrichments and depletions in the average composition of the aplites relative to the least fractionated granite of the Bush Lake lobe (i.e., lowest Si02 and highest Sr contents). The enrichment and depletion patterns are similar to those documented by Hildreth (1979) for the compositionally zoned silicic Bishop tuff except for Al, Mn, Sm, Hf and Th. Hildreth (1979; 1981) discussed in some detail the problems related to explaining such elemental fractionations by any model of crystal settling or rock assimilation, and he proposed a model of liquid—state convection—driven thermogravitational diffusion to account for the relative geochemical enrichments and depletions. However, Mittlefehldt and Miller (1983) have recently suggested that fractionation / of REE—rich accessory phases (in particular, monazite) in conjunction with feldspar and ferromagnesian phases can also produce similar geochemical patterns in felsic magmas. Present data for the granite of the Bush Lake lobe and aplite association do not allow critical testing of the alternative hypotheses. It may be significant, however, that Th and the light REE are depleted in the aplites relative to the granite of the Bush Lake lobe (fig. 9), perhaps reflecting the fractionation of monazite (Mittlefehldt and Miller, 1983). 38 * �(0 (A) TT1 fl -fl -n - Figure 9.--Enrichment factors in average aplite relative to Bush Lake granite compared to those of the Bishop tuff (Hildreth, 1979). See text for discussion. —— = �Conclusions The ineta—igneous rocks of the Dunbar gneiss—granitoid dome show a progression with progression of time to more silicic and higher 1(20 compositions. This reflects, at least in part, a progressive change in the nature the sources providing the more evolved magmas. The overall caic—alkaline nature of these rocks and their changes in chemistry with time are similar to those observed in recent maginatic arcs formed at convergent—plate margins (Brown, 1982). The compositions of these gneissic and granitoid rocks, particularly when taken in conjunction with the geological and geochemical evidence from the surrounding volcanic rocks (Schulz, this volume), strongly suggest that plate—tectonic and maginatic processes largely similar to those recognized to be active today were already operative in the Early Proterozoic. 4O b �r t References Arth, J. G., and Hanson, G. N., 1972, Quartz diorites derived by partial melting of eclogite or amphibolite at mantle depths: r Petrol., Contrib. Mineral. v. 37, p. 161—174. Arth, J. G., and Hanson, G. N., 1975, Geochemistry and origin of the early Precambrian crust of northeastern Minnesota: Geochim. Cosmochim. Acta, v. 39, p. 325—362. Brown, G. C., 1982, Calc—alkaline intrusive rocks: their diversity, evolution, and relation to volcanic arcs, in Thorpe, R. S., ed., Andesites: New York, John Wiley and Sons, p. 437—461. Cudzilo, T. F., 1978, Geochemistry of Early Proterozoic igneous rocks in northeastern Wisconsin and Upper Michigan [Ph. D. thesis]: Lawrence, University of Kansas, 194 p. Hanson, G. N., 1981, Geochemical constraints on the evolution of the early crust. Phil. Trans. Royal Soc. London, A 301, p. 423—442. Hildreth, E. W., 1979, The Bishop Tuff: zonation in silicic magma Evidence for the origin of compositional chambers. Geol. Soc. America Special Paper 180, p. 43—75. Hildreth, E. W., 1981, Gradients in silicic magma chambers: for lithospheric magmatism: implications Jour. Geophys. Res., v. 86, p. 10153—10192. Mittlefehldt, D. W., and Miller, C. F., 1983, Geochemistry of the Sweetwater Wash Pluton, California: implications for "anomalous" trace element behavior during differentiation of felsic magmas: Geochim. Cosmochim. Acta, v. 47, p. 109—124. Miller, Calvin F., 1977, Early alkalic plutonism in the calc—alkalic batholith belt of California: Geology, v. 5, p. 685—688. 41 �O'Nlons, R. K., and Pankhurst, R. J., 1978, Early Archean rocks and geochemical evolution of the Earth's crust: p. 211—236. Earth Planet. Sci. Letters, v. 38, �I FIELD TRIP LOG AND DESCRIPTIONS DUNBAR GtIEISS — GRANITOID DOME :I By P. K. Sims, K. J. Schulz, and Z. E. Peterman —. .•a 2141 LISt D FLNCE _ ;:--_ *— I % 1 FERN'2 2 to!. — — I —i — .- !-••--• I —a.— J FLORENCE CO - -- ..-—.-- —-.——.——-—. ——--— - . .' OAGARA .. . —- a--—-— -. -2 ii ——-- -- IS4 -: MARINETTE CO - H OF UICHIGAU -: —J---___-1--_j_ --. . . S — — .-= - S 1-- —i -. -- - -—-- -- -—- DUNmAR4_L — --= GOODVAF2 - - . . .-.. —- —- - - —- -- I —=— —— —- . — — - OEECHER ii .. - ---ReId -.-.trip Dunbar . S - -I - —;: :i; L3 - ¼ L . -. �e. FIELD EXCURSION Road Log $ Log begins and ends at Dunbar, Wisconsin — at junction of First Street and U.S. highway 8. Descriptions of field stops are given separately on following pages. Mileage 0.0 Dunbar. 1.6 Junction of Marinette County highway U and U.S. highway 8. Continue westward. 4.5 Turn right (north) on secondary road to Coleman Lake Club. Permission should be obtained from Manager of the Coleman Lake Club of Goodman, Wisconsin. 6.2 Clearing at house and barn. Walk eastward about 800 feet to outcrops of Dunbar Gneiss (Stop 1). Return to vehicles and proceed south back to U.S. highway 8. 7.9 Junction with U.S. highway 8. 10.8 Drive west on U.S. highway 8. Turn left (east). I Junction of U.S. highway 8 with Marinette County highway U. left (north) on Co. U. Turn I 12.0 Turn left (west) on Spur Lake road (secondary road). 13.9 Outcrops on east side road (Stop 2) of Dunbar Gnelss. County highway U. 15.8 Junction, Spur Lake road and Co. U. 16.2 Outcrops on east side road (Stop 3). road cut (Dunbar Gneiss). Return to I I Walk eastward from blasted I 20.5 Junction Co. U and Co. B. Turn right (east) on Co. B and proceed due E (including dirt road) for 0.5 ml. 21.0 Turn right (south) on secondary road and proceed for 0.5 mi. will park here. Walk south on unimproved road to Stop 4. 21.7 (Stop 4). Gneiss. 22.4 Return to vehicles, and proceed north to Co. hy B. Junction of east—west secondary road. Turn left and proceed onto Co. B. 22.8 Farmhouse just east of junction of Co. B and Co. U. Obtain permission from owner. Walk south to outcrop (Quinnesec volcanics) behind barn. (Stop 5). Return to vehicles. Proceed east on Co. B. Cars Outcrop on knob is a highly deformed fades of Dunbar I I �Mileage 28.2 Junction of Co. B with north—south asphalt road. 31.6 Curve in road to left (east). 31.9 Outcrop south side of asphalt road on small knob. (Stop 6A). A companion outcrop (Stop 6B) to be observed is on north side of road, about 0.1 mile west of Stop 6. Return to east—west asphalt road and proceed east. 36.2 Junction asphalt road with County highway N. Turn right (south). Continue eastward. Turn right (east) on Co. N. 37.9 Railway crossing. Park and walk north along railway. (Stop 7) includes 3 separate outcrops, A, B, and C. Return to cars, and proceed east on Co. N into the town of Niagara. 39.9 Junction Co. N and U.S. highway 141. proceed through Niagara. 43.1 Junction of U.S. highway 8 with U.S. 141. 46.3 (Stop 8). Outcrop east side of highway exposing the contact zone between granite of Spikehorn Creek and Quinnesec volcanics. Return to cars and proceed south on U.S. 141—8 through Pembine. 52.4 Junction U.S. hy. 8 and U.S. 141—8. 58.0 (Stop 9). Outcrops on north side highway 8. proceed west to Dunbar. 61.2 Dunbar, Wisconsin. End of log. L5 Turn right on U.S. 141 and Proceed south on hy 141—8. Turn right (west) on hy. 8. Return to cars and �Description of Field Stops Stop 1. SW1/4 SW1/4 sec. 21, T.37N., R.18E., Goodman 7—1/2 minute quadrangle. Outcrops in partly grassy and wooded area, 1,000 feet east of Coleman Lake Club road. Large outcrops of Dunbar Gneiss——interlayered biotite gneisses with a few thin, intercalated layers of amphibolite, cut by abundant white pegmatite and pink aplite. Layers generally 1—24 inches thick. All rocks deformed by northwest—trending folds having steeply dipping limbs and axial planes striking N.45—50°W.; folds plunge 4O°SE. The foliation (S1) is subparallel to layering Some pegmatite shows incipient boudinage. (S0). On the northwest part of outcrop, foliation planes oriented N.80W., 45°S. have a crenulation and mineral lineation plunging 45° S.25°W. that is younger than F1. Probably it is related to strain near core—cover boundary. The northwest—trending folds and accompanying southeast— plunging lineation is virtually identical to the structure elsewhere in the Dunbar Gneiss in the central core of the dome. This gneiss has a U—Pb discordia age of 1,862*5 Ma. The Rb—Sr system in this rock has been reset, and a Rb—Sr biotite age on one sample is 1,125 Ma. Suggested additional stop; it will not be visited on this field excursion. SE1/4 SE1/4 sec. 19, T.37N., R.18E., Goodman quadrangle. Rock knob adjacent to cleared area, southeast of dirt Moderately homogeneous hornblende—biotite gneiss. Rock has road. a strong foliation and lineation, indicative of high strain. Foliation, N.5O°W., 900; lineatlon (mineral alinement), 800 S.50°E. Gneiss is cut by 2—3—inch blotite granite dikes and by pink pegmatite and aplite. The steeply plunging lineation is characteristic of structures of rocks in and near the core—cover boundary, where ductility contrasts during diapirism were large. One sample gave a Rb—Sr biotite age of 1.13 Ga. Stop 2. Center sec. 15, T.37N., R.18E., Dunbar 7—1/2 minute quadrangle. Excellent, partly lichen—free outcrops of migmatitic Dunbar Gneiss. -Consists mainly of compositionally layered rocks, biotite gneiss and lesser amphibolite, intruded by megacrystic biotite granite gneiss, granite pegmatite, and aplite. All rocks are Foliation: N.5O—55°W., 90°. Foliation, expressed by deformed. biotite and hornblende alinement, is generally parallel to compositional layering but locally transects intrusive contacts of niegacrystic granite gneiss at 100_150 angles. The protolith of the layered gneiss here and at Stop 1 is considered to be caic—alkaline volcanic rocks. 46 �Stop 3. SW1/4 SWl/4 sec. 13, T.37N., R.18E., Dunbar 7—1/2 minute quadrangle. Blasted outcrop of Dunbar Gneiss on east side Co. U and outcrops on ridge extending to east. The outcrop in road cut is site of USGS sample W143 and, apparently, of dated sample 5 of Banks and Cain (1969). Sample W143 gave a U—Pb zircon concordia upper intercept age of 1,862*5 Ma and a lower intercept age of 471*23 Ma. Aplite from this outcrop has a Rb—Sr model age of 1.4 Ga. The outcrops east of the road cuts are composed mainly of a megacrystic granite gneiss that contains rafts of layered amphibolite. Lineation in the amphibolite plunges 200_250 N.85°—90°E. Locally, the amphibolite is refolded by folds having N.50°W. steep axial surfaces. The granite gneiss has a pervasive N.70°W. foliation. The granite gneiss (Dunbar Gneiss) tonalite, and is interpreted Stop 4. has the composition of as a plutonic protolith. SE1/4 NW1/4 sec. 36, T.38N., R.18E., Dunbar 7—1/2 minute Rock knob near south end of north—south dirt road that quadrangle. connects with Florence County highway B. Biotite augen gneiss which is interpreted as an intensely deformed variety of Dunbar Gneiss. Foliation, N.75°E., 85°S.; lineatlon, 300 S.45°W. The high strain apparent in the rock is the result of strong ductile deformation in the vicinity of the core— cover boundary; the outcrop is less than 1,000 ft from the boundary. Stop 5. NW1/4 SW1/4 sec. 25, T.38N., R.18E., Dunbar 7—1/2 minute Outcrop south of farmhouse at junction of Florence quadrangle. Outcrop of County highways U and B. Ask permission of owner. metavolcanics and coarser grained metagabbro (amphibolite grade) of Quinnesec Formation. Two periods of folds are visible in the An older, dominant foliation (S2..), N.20°—4O°W., 45°SW. and rocks. accompanying lineation (L ..), 450 S.65°W., is deformed by small— scale asymmetrical folds F4) (S—type) that plunge 500 S.8O°W. The The folds have an axial plane foliation (S4), N.55°E. .900. younger deformation (D4) exhibits transitional brittle—ductile The outcrop is about 0.6 ml northwest of the core—cover behavior, boundary. The younger folds and foliation are interpreted as the result of flattening strain caused mainly by outward inflation (to the northwest) of the central core of the dome against the Similar asymmetrical folds (S—type) can be seen in metavolcanics. outcrops of the same rocks on the west side of highway U in SE1/4 SE1/4 sec. 26, T.38N., R.18E. L.7 �p Stop 6. Stop 7. SE1/4 sec. 28, T.38N., R.19E. Outcrops in rock knobs on both sides of asphalt road along bottom of section 28. Outcrops on south side of road (A) shows partial replacement of Dunbar Gneiss by K—feldspar, to yield Hoskin Lake—type granite; outcrop on north side of road is typical of much of the Hoskin Lake Granite (B). SE1/4 Outcrops along Chicago, Milwaukee, St. Paul and Pacific Railway north of Florence County hy. N, Iron Mountain 7—1/2 minute Secs. 7 and 18, T.38N., R.20E. quadrangle. Involves about a 2 mi walk along railway. A. Outcrop of Hoskin Lake Granite, 0.2 ml north of County highway N. The granite is coarse grained and has abundant large tabular K—feldspar grains that give a foliation, It contains inclusions of volcanic rocks N.85°W. 65°S. from the Quinnesec. Numerous fractures transect the granite. B. SW1/4 Outcrop in blasted cut, 0.2 ml north of station A. sec. 7, T.38N., R.20E. A 45—ft—wide wedge of intensely foliated amphibolite (Quinnesec Formation) occurs in the It strikes N.70°W. and dips 75°S. Hoskin Lake Granite. The adjacent granite is intensely fractured (brittle— ductile deformation). The wedge is interpreted as a tectonic block, faulted into the granite. Tourmaline veins are present in the southern part of the cut. C. Outcrop of Quinnesec volcanics, east side of railway SW1/4 sec. 7, T.38N., R.20E. The metavolcanics tracks. (amphibolite grade) have a strong, close—spaced foliation (S4) (N.80°W., 65°S.) and a steep stretching lineation (4) (62° S.15°W.) expressed by mineral alinement, rodding, boudins, crinkles, and flattened and stretched pillows. Deformed pillows can be seen on crest of knob, near south end of outcrop. Tight folds (F4) that plunge parallel to the linear fabric and have N.80°W., 65°S. axial surfaces can be observed at places. The high strain exhibited here is indicative of the intense deformation on the overturned, north margin of the central core of the Dunbar dome, and is controlled by the core—cover boundary. Qualitative estimates of stretched pillows indicate a maximum Deformation is indicative of length to width ratio of about 5:1. transitional brittle—ductile behavior. Suggested additional stop; it will not be visited on this Outcrop of metamorphosed Marinette Quartz Diorite, 0.2 mi south of County highway N on railway. The quartz diorite is a layered gneiss (amphibolite fades) that locally is cut by small dikes of 1-loskin Lake Granite and leucogranite. The layering dips moderately to gently and is folded into round—crested open upright folds that plunge 300 S.15W. A conspicuous mineral lineation is subparallel to fold hinges. trip. �Stop 8. SW1I4 sec. 1, T.37N., R.20E., Pembine NW 7—1/2 minute quadrangle, east side U.S. highway 8—141; blasted cut. Outcrop is the southern margin of the granite of Spikehorn Creek in the Niagara lobe against Quinnesec Formation. Contact of main body of granite is a steep fault whose surface is coated by chlorite. The granite is reddened by alteration of feldspar, and itself is faulted. It contains small inclusions of aiuphibolite. Dikes of granite of Spikehorn Creek and leucogranite intrude the Quinnesec on the south side of the faulted contact. Suggested additional stop: Outcrop 0.5 miles north of Stop 8; it will not be visited on this trip. This outcrop shows the contact of the granite of Spikehorn Creek with an inclusion of vólcanics from the Quinnesec. The granite, on north side of contact, is reddened, and in the contact zone contains veins of gray and smoky quartz, tourmaline, and pyrite. In the contact zone, the rocks have a cataclastic (mainly ductile) foliation and a steep lineation (plunges 75°SE.). A gray porphyry cuts the metavolcanic rocks in the southern part of the outcrop; both rock types are cut by dikes of red leucogranite. This lobe (Niagara lobe) of granite is interpreted as a diapir that bulged outward from the central core during a late stage in the evolution of the Dunbar dome, as evidenced by the uniformity of the granite, its lack of a penetrative foliation, and a foliation in the surrounding metavolcanics that conforms closely to the core—cover boundary. The granite is the youngest dated rock in the dome; it has a U—Pb zircon discordia age of 1,8366 Ma. Stop 9. (Time permitting) SW1/4 SE1/4 sec. 34, T.37N., R.19E., Dunbar NE 7—1/2 minute quadrangle. Smooth outcrops in cleared area, 150 ft north of U.S. highway 8, adjacent to trail. Contact zone of This outcrop of Newingham Tonalite contains Newingham Tonalite. inclusions of aniphibolite and biotite gneiss (Dunbar Gneiss). On east side of draw, the tonalite is reddened by surface alteration. In draw, contact can be seen between Dunbar Gneiss and the tonalite; it strikes N.55°E. and dips steeply. Foliation in the gneiss—is N.50°—55°E., 70°SE; foliation (S31) in tonalite is N.80°E., 65°SE. The foliation in the tonalite is younger than that in the gneiss; it crosseuts the contact but is only weakly developed in the gneiss. This structural relationship can be seen at many places in the contact zone between the Dunbar Gneiss and the Newingham Tonalite. Suggested additional stop; it will not be visited on this SE1/4 NW1/4 sec. 21, T.36N., RI9E., Twelvefoot Falls 7—1/2 minute quadrangle. Twelvefoot Falls on North Branch Pike River, in this stop is about 3.5 mu Twelvefoot Falls County Park. Note: south of U.S. highway 8, and can be reached via the Lily Lake Road. trip. L9 �Spectacular outcrops along the river expose the Twelvefoot Falls Quartz Diorite of Cain (1964). The outcrops are on the southern margin of a wide shear zone that strikes N.70°W. and dips 75°—85°N., and is more than a mile wide; lineations are nearly vertical. The same strongly foliated rocks at Eighteenfoot Falls on the northern line of section 21 also are sheared in the same fashion. At Twelvefoot Falls, relatively unsheared but highly altered quartz diorite occurs on the south side of the falls. Elsewhere, however, the quartz diorite has a strong, close—spaced foliation expressed by shears and alined muscovite and chlorite, which was formed by transitional brittle ductile deformation. At the falls, an 18—inch—wide dacite dike is parallel to a fault that strikes N.70°W. and dips ca. 80°N. Thin sections of rocks in the broad, northwest—trending shear zone (Twelvefoot Falls shear zone) show abundant shears, generally filled with chlorite or muscovite, and extreme alteration of hornblende and plagioclase. Garnet is a local metamorphic mineral. Microcline is present at places in fractures in the rocks. 50 �p 1* r1 Volcanic Rocks of Northeastern Wisconsin by Klaus J. Schulz U.S. Geological Survey, Reston, Va 51 22092 �INTRODUCTION Volcanic rocks of northeastern Wisconsin were examined as a part of the regional investigations of the geology of the Precambrian rocks in Wisconsin and Upper Michigan. The Pembine 15" quadrangle was chosen for particular emphasis because it contains relatively abundant outcrops of volcanic rocks and adjoins areas previously mapped or currently under investigation. The rocks in this area are the easternmost exposures of the east—trending volcanic—plutonic belt in northern Wisconsin that contains at least four stratabound, base—metal, massive sulfide deposits. The volcanic rocks of northeastern Wisconsin occur south of the Menominee and Iron River—Crystal Falls iron—bearing districts and are separated from rocks of the Marquette Range Supergroup by the Niagara fault zone (see Bayley and others, 1966; Dutton, 1971). The volcanic rocks were originally designated the "Quinnesec schist" by Van Hise and Bayley (1900) after outcrops of greenstone schists and associated tnafic intrusive rocks found at Quinnesec Falls on the Menominee River in southern Dickinson County, Michigan. The name was subsequently changed to Quinnesec Greenstone by Leith and others (1935) and to Quinnesec Formation by James (1958). James applied the term Quinnesec Formation to the belt of green— stone, amphibolite, and schist in the southern part of Dickinson County, Michigan, and the adjacent parts of Wisconsin. 52 �Although the name Quinnesec Formation is presently accepted and widely used to designate the volcanic and associated rocks in northeastern Wisconsin, Jenkins (1973) noted that at least four lithologically distinct volcanic units could be defined in the central part of the Pembine quadrangle. Jenkins considered three of these units sufficiently different from the lithologies of the type area of the Quinnesec Formation (Prinz, 1959; He pro- Bayley and others, 1966) to warrant their separate designation. posed the informal names McAllister formation, Beecher formation, and Pemene formation for these units. Recently, DePangher (1982) proposed that the Quinnesec Formation be designated the Quinnesec Group consisting of five lithostratigraphic units having formational status. For the purposes of this report, the informal nomenclature proposed by Jenkins (1973) for the volcanic rocks of the area is used (see fig. 1). I recognize that formal revision of the present stratigraphic nomenclature of the volcanic rocks of the area is warranted. However, such revision should not be undertaken until after present mapping and regional compilation efforts are completed. This summary of the geology and geochemistry of the volcanic rocks of northeastern Wisconsin is based largely on my work on the rocks in the Pembine 15" quadrangle (relatively detailed mapping in the north and reconnaissance mapping in the south) and the thesis studies of Hall (1971), Jenkins (1973), Cudzilo (1978), and DePangher (1982). Inasmuch as the mapping and regional compilation of the geology of the area are still incomplete, this summary represents only an interim report. volcanic rocks north and northwest of the Pembine quadrangle were 53 The �____ _____________________ EXPLANATION (Figure 1) Early Proterozoic Athelstane Quartz Monzonite Xsg Spikehorn Creek granite Xnt Newingham tonalite Marinette Quartz Diorite Granodiorite (includes diorite to granite) Xtq4,d X pT'2 v A1C AbC Twelve Foot Falls Quartz Diorite Pemene formation of Jenkins (1973): spherulitic rhyolite. dominantly micro— McAllister formation of Jenkins (1973): andesitic breccias. Beecher formation of Jenkins (1973): and felsic volcaniclastic rocks. Quinnesec Formation: basaltic and andesites, dacites, dominantly basalt and diabase with some andesite, metagabbro sills (Xmg), peridotite (Xp), tuff (Xqt), and breccia (Xqtb). --— ——— '-I * Approximate contact Fault Facing direction of pillow lava Strike and dip of bedding Field trip stop locations 51 �r ri I I I U 55 �described by Bayley and others (1966) and Dutton (1971), respectively, who also summarized earlier work in the region. Greenberg and Brown (1983) recently reviewed the major—element geochemistry of the volcanic rocks of northeastern Wisconsin. GENERAL GEOLOGY Volcanic and associated rocks are relatively well exposed in an arcuate belt east and north of the Dunbar gneiss—granitoid dome in Narinette and Florence Counties of northeastern Wisconsin. Volcanic rocks and associated sedimentary rocks are also exposed in scattered outcrops in a belt south of the dome (Cummings, 1978), but their stratigraphic relation— ships to the volcanic rocks to the east cannot be directly established because of intervening glacial cover. To the north and northeast, the volcanic sequence is truncated by the Niagara fault (Bayley and others, 1966 and Dutton, 1971), which marks a major discontinuity in the rocks of the region. North of this fault, rocks of the Michigamme Formation and other units of the Marquette Range Supergroup occur along with basement uplifts of Archean gneissic rocks. To the south, the supracrustal rocks of northeastern Wisconsin are bounded by the Atheistane Quartz Monzonite (Medaris and others, 1973); to the west of the Dunbar dome, outcrop is lost under glacial drift. 56 �The supracrustal sequence includes units of basalt, andesite, dacite and rhyolite flows and volcaniclastic material, and locally, sedimentary rocks including graywacke, black graphitic slates, and iron—formation. Pyritic to pyrrhotitic massive sulfide bodies are also present locally (Hollister and Cummings, 1982; LaBerge, 1983). Gabbro sills are common, particularly in the northern part of the sequence (Bayley and others, 1966). Serpentinite bodies, commonly with some associated gabbros are also present locally (see fig. 1). The units of the Dunbar gneiss—granitoid dome intrude the volcanic rocks west of the Pembine quadrangle, and the Atheistane Quartz Monzonite intrudes them to the south. Small intrusive bodies ranging from hornblendite and gabbro to granite and including lamprophyre dikes and plugs are widespread, particularly in the southeastern part of the volcanic sequence in the Pembine quadrangle. The Twelve Foot Falls Quartz Diorite (Wadsworth, 1962) intrudes volcanic rocks in the area south of the Dunbar dome (see fig. 1 of Sims and others, in this field guide). The supracrustal rocks and associated subvolcanic intrusive rocks are variably replaced by greenschist facies mineral assemblages throughout the eastern outcrop area but contain assemblages as high grade as amphibo— lite fades adjacent to the Dunbar gneiss—granitoid dome and further to the west. The rocks were regionally folded on northwest—trending axes and are now at or near vertical in attitude throughout much of the area, but they commonly lack a penetrative cleavage in the east. As a result, primary textures and structures are generally well preserved. Units generally face outwards from the margins of the Dunbar dome and Atheistane intrusion. 57 �P The volcanic and associated rocks are broken into several blocks or segments by high—angle faults. High—angle faults also appear to bound the major lithologic units in the Pembine quadrangle (Jenkins, 1973; see fig. 1). Because of uncertainties in the amount of displacement on these faults and the complexity of folding, detailed correlations between blocks have not been possible. As mentioned in the "Introduction", four major volcanic units have been recognized in the Pembine quadrangle (Jenkins, 1973); the Quinnesec Formation, the McAllister formation, the Beecher formation, and the Pemene formation. These formations, in the order listed, represent progressively more silicic rock units. Jenkins suggested that the order of naming above represented the order of decreasing age. This conclusion was based largely on an analogy with other volcanic terranes, which commonly show a progression to more silicic rock compositions with time. Insofar as this analogy is valid and applicable to the volcanic sequence in the Pembine quadrangle, the stratigraphic sequence proposed by Jenkins (1973) may be valid. However, significant lateral variations in the nature of volcanic rocks can also occur and could be difficult to decipher after deformation. Present geologic data support the interpretation that the Quinnesec Formation (as used by Jenkins) is the oldest volcanic unit. The relative ages of the other units, however, remain uncertain. The regional structure indicates that the McAllister formation may be younger than the Beecher formation but older than the Pemene formation. work is required to resolve the stratigraphy of these units. 58 Further I �Until recently, the age of the volcanic rocks in northeastern Wisconsin was a point of controversy. Van Hise and Bayley (1900) and Bayley (1904) originally interpreted the "Quinnesec schists" as early Precambrian principally because of the striking similarity of these rocks to Archean greenstones elsewhere in the Lake Superior region. Van Hise and Leith (1911) subsequently assigned the Quinnesec Formation to a pOst— Michigamme age (i.e. middle Precambrian) on the base of the interpretation of Hotchkiss that the Michigamme Formation graded upwards into volcanic rocks in Florence County, Wisconsin. Dutton later reinterpreted the relationship in this area and placed a fault between the volcanic rocks to the south and Michigamme Formation to the north. Bayley and others (1966) and Dutton (1971), while acknowledging that decisive field evidence to establish the age of the Quinnesec Formation was lacking, favored an early Precambrian age. Banks and Rebello (1969) reported a U—Pb zircon age of 1,866±39 Ma for a rhyolite sample from an area west of the Pembine quadrangle and south of the Dunbar dome. This age, which is not resolvable from the ages of the rocks of the Dunbar dome (see Sims and others, this field guide), is now generally taken as that of the volcanic sequence throughout northeastern Wisconsin although this rhyolite locality is isolated from the main areas of outcrop. Recently, Warren Beck of the University of Minnesota has obtained a similar age for the basaltic rocks of the Quinnesec Formation by the Sm—Nd technique (Beck, personal communication, 1984). Thus, the age of the volcanic rocks of northeastern Wisconsin now seems to be established as Early Proterozoic and not Archean as once thought. Their age is similar to that obtained for the massive sulfide 59 �deposits near Crandon, Monico, and Ladysinith to the west (Sims, 1976) and to ages of other volcanic and plutonic rocks of the northern Wisconsin magmatic terrane (Van Schmus, 1980). It is still uncertain, however, whether the Early Proterozoic inagmatic rocks of northern Wisconsin are significantly younger than the rocks of the Marquette Range Supergroup in Upper Michigan. STRATIGRAPHY The four lithostratigraphic units that compose the volcanic rock sequence in the Pembine quadrangle are described below. Although the rocks are metamorphosed at least to the greenschist facies, the prefix 'meta" is generally omitted throughout this report for simplicity. Quinnesec Formation The Quinnesec Formation, as used in this report, is the dominant volcanic unit in the Pembine quadrangle extending from the northern border to at least the middle of the quadrangle (fig. 1). thickness is not known because of the complexities Its stratigraphic of folding and faulting but is probably on the order of several thousand meters. The Quinnesec Formation consists predominantly of pillowed to massive tholeiltic basalt, diabase, and lesser pillowed and fragmental andesite. Andesite increases in abundance southward in the unit and is generally plagioclase and clinopyroxene phyric and aniygdaloidal. Basalt is generally pillowed, and pillow shape and size vary between areas. Locally, basaltic pillow breccia and highly variolitic pillow lava is encountered, particularly near the center of the quadrangle. 60 In the north—central �part of the map area, several distinctive tuff and breccia units are present (fig. 1). Fragments are very fine grained, light green, and commonly amygdaloidal and appear to be more siliceous than their matrix. Felsic tuffs and breccias are also present particularly in the southern part of the unit. (Felsic fragmental units were also reported by Bayley and others (1966) and Dutton (1971) to exist north and northwest of the Pembine area. Fine to medium—grained diabase is common throughout the unit and is particularly abundant in the northern part. A distinctive quartz bearing diabase extends over a wide area in the north—central part south of the tuff and breccia units (fig. 1). Dikes of diabase are locally identified and may represent feeders to overlying flows. Sedimentary rocks are rare within the Quirtnesec Formation. Where present, they consist mostly of chert, graywacke, slate, and iron—formation. Iron—formation, occurring as thin units interlayered with clastic sedimentary rocks or tuffs, consists of interlayered chert and siderite (Cummings, 1978). The Quinnesec Formation is intruded in the western part of the map area by the Marinette Quartz Diorite, the Newingham tonalite, and the Spikehorn Creek granite (fig. 1). To the south, it is in fault contact with the Pemene formation. 61 �McAllister Formation The McAllister formation extends in an east—west belt in the south— central h part of the map area (fig. 1) and ranges in thickness from about I 300 meters in the west to 3,000 meters in the east (Jenkins, 1973). The unit is steeply dipping; limited evidence indicates that it is probably northward facing. It consists of basaltic to andesitic breccia and locally massive flows. Fragments in the breccia are distinctive in containing large pyroxene crystals generally replaced by amphibole. Amygdules are also common in some fragments. An increase in fragment size to the east indicates that the source area for this dominantly volcaniclastic unit may be east of the present Menominee River. Beecher Formation The Beecher formation extends in a north—facing, east to southeast— striking belt in the southern part of the map area and is in contact to the south with the intrusive Athelstane Quartz Monzonite (fig. 1). unit is at least 3,000 meters thick (Jenkins, 1973). The The lower part consists dominantly of plagioclase and clinopyroxene phyric andesite and dacite lavas and pyroclastics. acidic fragmentals predominate. Upwards in the unit, bedded tuffs and Black slates are also locally present in the upper part of the unit. The lower part of the Beecher formation, where intruded by the Athelstane Quartz Monzonite, has a well—developed foliation and steeply plunging lineation. Dikes of Atheistane Quartz Monzonite are present only for a short distance from the intrusive contact. 62 �I Pemene Formation The Pemene formation occurs over a broad oval area in the south—central part of the map area (fig. 1) and is well outlined by the local topography. It is at least 2,000 meters thick and consists predominantly of micro— spherulitic, plagioclase—phyric rhyolite and rhyodacite lavas and breccias. The flows are interlayered with a few thin, graded sedimentary units, suggesting that the rhyolite flows were possibly extruded subaqueously. Individual flows were estimated by Jenkins (1973) to range from about 150 to 400 meters in thickness. The Pemene formation shows little evidence of a penetrative structural fabric. The flows show a southward dip in the north and are near vertical in the south. Jenkins (1973) interpreted the structure of the formation as an east—trending, asymmetric, doubly plunging syncline. INTRUSIVE ROCKS A variety of intrusive of the Pembine quadrangle. rocks is found within the supracrustal These range from sequence clearly synvolcanic bodies like the diabases to post—tectonic lamprophyric dikes and plugs. The intrusive rocks associated with the Dunbar gneiss—granitoid dome are discussed by Sims and others (this field guide) and are not further considered herein. 63 �Gabbro Bodies Numerous large gabbro bodies are present within the Quinnesec Formation, particularly north and northwest of the Pembine quadrangle (Bayley and others, 1966). These bodies are more or less conformable to the mafic lavas and probably represent synvolcanic sills. Two such bodies are present in the Pembine quadrangle (fig. 1). The smaller body in the northwest part of the area consists of medium to coarse— grained gabbro and diorite and locally contains abundant hornblendite to gabbro xenoliths. Intrusive breccia is locally developed where diorite dikes intruded the gabbro (e.g. road cut, Highway 8, NE1/4SE1/4, sec. 24, T.38N., R.20E.). A larger gabbroic body, named the Sturgeon Falls sill by Prinz (1959), occurs along the east side of the Menominee River in Michigan and trends southeast for a distance of at least 12 km. Both the upper and lower portions of this sill are fault bounded, the northern fault being an extension of the Niagara fault. The Sturgeon Falls sill is unique in having serpentinite and pyroxenite along the north side. The pyroxenite generally occurs between the gabbro and serpentinite but also forms narrow bands within the gabbro. and anorthositic gabbro compose the bulk of the sill. Gabbro Anorthosite is locally well developed within the gabbroic part of the sill whereas magnetite—rich gabbro composes the southwestern part. The overall strati— graphy of the sill, with ultramafic rocks along the northern side and magnetite gabbro along the southern side suggests that the sill faces southwest. The consistency of the stratigraphy further suggests that the body may represent a differentiated sill similar in many respects to the 6L S �Kiernan sills within the Hemlock Formation in Michigan (Bayley, 1959). However, the Sturgeon Falls sill is compositionally distinct from the Kiernan sills (see discussion below). On the basis of overall similarity in metamorphism, structure, and composition between the Sturgeon Falls sill and the Quinnesec Formation basalts, the sill is interpreted as synvolcanic in age, although Bayley and others (1966) considered the gabbroic sills as "post—Animikie" in age. Peridotite Bodies Several small peridotite bodies, now altered to serpentinite, occur in the south—central part of the map area, but the largest and best exposed body occurs in the north—central portion within the Quinnesec Formation basalt (fig. 1). This peridotite body trends east and outcrops discontinuously for a distance of about 4.5 km. The peridotite shows few primary textures, contains serpentinte and large magnetite crystals, and Is locally cut by veins of carbonate and cross—fiber asbestos. Mineralog— ically banded and massive gabbro, locally cut by mafic to ultramafic(?) dikes, occurs south of the periodotite and locally appears to also crosscut it. At the western end, the peridotite is cut by pyroxenite dikes composed of coarse (1—5 cm) amphibole pseudomorphs after pyroxene. Foliation and banding in the associated gabbro are more or less at right angles to the lithologic contacts. Also, dikes found cutting the gabbro and serpentinite do not appear outside the body. These features suggest that this serpentinite—gabbro body may be fault bounded and tectonically emplaced. 65 �Biotite—Pyroxene Diorites Several bodies of biotite—clinopyroxene—bearing diorite to quartz diorite intrude the Pemene and McAllister formations (fig. 1). Rocks range from fine to medium grained and contain variable amounts of amphibole, clinopyroxene, plagioclase, biotite and quartz. apatite are also present as minor phases. Opaque minerals and Most of the amphibole appears to be pseudomorphous after pyroxene. Miscellaneous Bodies Several small bodies of dacite porphyry and blue quartz—eye porphyry occur within the volcanic units in the southern half of the Pembine quadrangle. These probably represent subvolcanic intrusions related to the felsic volcanic rocks of the Beecher and Pemene formations. Several lamprophyre dikes and plugs have been identified within the map area. These are generally small bodies and are difficult to distinguish from mafic volcanic rocks in the lichen—covered outcrops of the area. The lamprophyres consist of prismatic hornblende and biotite crystals in a feldspar matrix. Atheistane Quartz Monzonite The Atheistane Quartz Monzonite intrudes the Beecher formation in the southern part of the Pembine quadrangle (fig. 1) and extends for an unknown distance to the south and west. It consists dominantly of medium to coarse grained quartz monzonite and locally contains numerous metavolcanic inclusions. The Atheistane Quartz Monzonite is dated at 1,836±15 Ma (Banks and Cain, 1969). The Amberg Granite, which intrudes the Athelstane Quartz Monzonite in the southern part of the map area, is 1,756+19 Ma (Van Schmus, 1980). 66 �GE OCHEMI STRY Representative analyses of volcanic rocks from units within the Pembine quadrangle are presented in Table 1. are shown in figures 2—8. Their compositional variations Greenberg and Brown (1983) recently reviewed the majorelement chemistry of volcanic rocks from northeastern Wisconsin and concluded that they are dominantly calc—alkaline and exhibit characteristics of rocks found in modern volcanic arcs. The data of this study confirm these conclusions and provide further information on the nature and evolution of the volcanic sequence. The overall caic—alkaline character of the northeastern Wisconsin volcanic rocks is shown by the AFM diagrams. (fig. 2) and Jensen cation (fig. 3) However, many of the basalts, diabases, and gabbros of the Quinnesec Formation are tholeiitic. Figures 2 and 3 also illustrate the marked compositional differences between the volcanic rocks of northeastern Wisconsin and those of the Marquette Range Supergroup in Upper Michigan, which are bimodal, show strong iron enrichment trends, and are enriched in Ti02 relative to those in northern Wisconsin. Chondrite—normalized rare—earth—element (REE) patterns for Quinnesec basalts and diabases are shown in figures .4 and 5. Most of the samples are characterized by marked light—REE depletions ([La/Yb]N=.lO—.54) even more extreme than is typical of ocean—floor basalts (fig. 4). REE abundances show a wide range ([YbIN7—25) that only poorly correlates with MgO content. The relative depletion of light—REE generally increases as REE abundance decreases, suggesting that these basalts may represent melts derived by progressive partial melting of the same mantle source. 67 �I Table 1.—- Representative analyses of volcanic rocks from the Pembine 0 Quadrangle, northeastern Wisconsin. I 2 1 Sb2 Al203 Fe203 FeO MgO CaO Na20 1(20 Ti02 '2S MnO H20 H20 49.7 16.3 1.9 6.7 8.1 12.8 2.0 0.27 0.53 0.09 0.18 1.4 0.17 47.8 15.9 3.2 8.0 8.8 11.5 0.81 0.10 0.43 0.07 0.17 3.2 0.08 CO2 4 3 53.4 15.5 48.4 15.5 2.1 7.7 4.1 2.5 9.5 7.7 9.8 2.1 5.8 4.7 0.27 0.18 1.1 1.2 0.19 0.14 3.4 0.09 0.15 0.18 Ba Zr Y Nb Cr 400 Co Sc 41 56 87 16 31 22 <5 105 53 59 1.1 0.17 7 8 70.2 13.4 0.97 4.2 0.78 74.6 13.5 0.84 1.3 4.7 2.2 0.19 5.9 0.43 0.12 0.13 0.96 0.10 0.29 0.09 0.03 0.65 0.11 2.1 1.3 1.7 .06 :.24 151 47 80 35 <5 14 37 43 0.093 2.20 0.22 135 104 80 25 307 104 392 1130 61 17 99 21 1005 166 43 8 <5 6 14 11 469 2 36 40 26 29 223 46 46 0.30 1.99 0.25 —— 0.27 — —— La Ce Sm Eu Tb Yb Cu 1.37 3.90 1.36 0.49 1.88 1.02 0.53 0.50 2.34 0.38 2.12 6.79 2.81 1.00 1.04 3.80 0.58 3.27 9.6 2.58 0.91 0.65 2.65 0.36 0.62 0.54 2.58 0.37 0.37 0.20 0.20 1.7 0.065 1.02 0.14 0.28 0.60 12.8 1.4 6.0 7.0 5.5 2.8 2.2 0.07 Ta Hf Th U —— 60.9 0.21 3.0 89 54 43 23 <5 56.2 16.5 2.4 7.6 3.8 8.0 3.4 0.34 0.92 0.16 0.18 3.1 <:.96 Sr 6 5 0.13 1.40 0.53 0.21 0.27 2.37 3.72 1.43 4.82 16.4 33.3 3.43 0.83 0.54 1.90 0.28 12.1 2.15 0.73 0.49 1.80 0.27 184 1.7 69 631 173 40 14 2 4.48 6.51 2.20 0.7 12.0 0.79 5.12 7.65 2.29 27.5 58.6 7.28 1.63 1.20 4.97 0.78 29.4 67.9 7.80 1.47 1.16 5.53 0.81 12.9 0.74 - 1 ii 1—2 3—4 5 6 7—8 Quinnesec diabases Quinnesec basalts Quinnesec andesite Beecher andesite Pemene rhyolites U 68 �0a, I I- 0w Li- 0 Cb4 + 0c1 z Figure 2.-—Fe01-—MgO—Na20+K20 diagram for volcanic rocks of Wisconsin (stipled field) compared to volcanic rocks ofnortheastern upper Michigan (dot—dash fields) and Monico area of Wisconsin (dashed fields). 69 �A1203 Cation % + Ti02 NE WISCONSIN MICHIGAN SI.c Aufl INI,I, (Ok,.a MgO •— •— — — • • rocks are all tholeiitic. i, u i — a 1•1 Figure 3.--Jensen cation diagram (Jensen, 1976) for volcanic rocks of northeastern Wisconsin (stars) and upper Michigan Rocks of northeastern Wisconsin plot mainly in the calc-alkaline field while the upper Michigan (dash uields) D FeO+ �The strong light—REE depletion indicates that this source had undergone prior partial melting. This conclusion has recently been confirmed by the Nd isotopic work of Warren Beck (Beck, personnal communication, 1984). These strongly light—REE depleted basalts are similar to those of the lower units of the Troodos Complex (Kay and Senechal, 1976). A smaller group of basalts from the Quinnesec Formation are only moderately depleted in light—REE (fig. 5). These are very similar in many respects to modern ocean floor basalts (figs. 5—8). The two gabbro samples from the Sturgeon Falls sill have light—REE depletion patterns similar to those of the basalts (fig. 4). The chondrite—normalized REE patterns for one Quinnesec Formation r andesite, two Beecher formation andesites, and three Pemene formation rhyolites are shown in figure 6. r in The samples show progressive enrichment light—REE, and, with increasing total REE abundances, show larger negative Eu anomalies. These REE patterns are typical of calc—alkaline volcanic rocks of modern arc systems (e.g., North Island, New Zealand, r Reid, 1983). The general island—arc compositional affinities of the northeastern Wisconsin volcanic rocks are further illustrated in figures 7 and 8 in terms of Y—Cr variations and Hf/Th—Ta/Th ratio variations, respectively. Like the volcanic rocks in modern arcs, the rocks of northeastern Wisconsin show marked depletions in high—valance cations like Zr, Hf, Ta, Y, and Ti. The basalt samples from the Quinnesec Formation that plot in the fields of mid—ocean ridge basalts in figures 7 and 8 represent the group of basalts in which light—REE are only moderately depleted (fig. 5). 71 �I I I Figure 4.-—Chondrite normalized REE for some Quinnesec Formation basalts and gabbros of the Sturgeon Falls sill. 40- MORB = field for mid-ocean ridge basalts. QzINNEsEc BsALrs N190 - 10 I 7Z - - 4 L Ce. SwEu. Tb Lu. Figure 5.--Chondrite normalized REE for some Quinnesec Formation basalts. Average MORB shown by dashed field. 72 �I 6.--Chondrite normalized REE for one Quinnesec Formation andesite (56.5, Si02), Figuretwo Beecher formation andesites (61-62, Si02) and three Pemene formation rhyolites (71-73.5, Si02). 73 �— I I I / I 10 iii I I / , '\ I, Yppm II • I I IAT — ,_ — \ I,/ / 50 I I MORB 'I 100 III —— —i I Ta/Th H — : is! • ±. similarity between Hemlock and Keweenawan volcanic rocks. Hemlock data from Fox (1983). Figure 8.--I-If/Th vs Ta/Th variation in volcanic rocks of northeastern Wisconsin (stars) (after Noiret and others, 1981). Note I.- I- — — —.: — — I_ Wisconsin volcanic rocks. IAT=Island arc tholeiite field; MORB=Iiid-ocean ridge basalt field. (After Pearce, 1982). Figure 7.--Cr-Y variation for northeastern 105 50 100 0 aa- E 500 1000 I I 4JJ �TECTONIC IMPLICATIONS Both the nature and geochemistry of the volcanic rocks of northeastern Wisconsin suggest that the rocks formed in a magtnatic arc similar in many respects to modern oceanic island—arcs (e.g., like those of the western Pacific, Hamilton, 1979). The presence of tectonically emplaced ultramafic rocks (ophiolite fragments(?)) with basalts of mid—ocean—ridge chemical affinities further indicates such an environment of formation. The general absence in Upper Michigan of magmatic rocks having similar affinities suggests that the associated subduction was to the south. The eventual collision of the maginatic arc formed as a result of the southward subduction probably resulted in the deformation event recognized as the Penokean Orogeny (Schulz and others, 1984). Thus, the Niagara fault zone, as proposed by Larue (1983), probably represents the zone of suturing between the magmatic arc terrane (northern Wisconsin volcanic—plutonic belt) and the Archean crust and miogeosynclinal cover sediments (passive margin sequence; Marquette Range Supergroup) to the north. One feature typical of many subduction—zone assemblages but notably missing from northern Wisconsin is a melange sequence representing rocks of a possible fore—arc basin and accretionary wedge. Drilling Project Recent Deep Sea drilling in the western Pacific, however, has shown that arc systems situated over steeply dipping Benioff zones commonly lack both fore—arc basins and abundant trench sediments (Uyeda, 1983). This finding suggests that the northern Wisconsin magmatic system may have formed over a steeply dipping subduction zone, thus precluding accumulation of a thick sedimentary wedge. 75 �The overall nature and geochemistry of the rocks of the northern Wisconsin volcanic—plutonic belt strongly suggest that tectonic processes during the Early Proterozoic generally were similar to plate—tectonic processes operating today. Although many aspects of the geology, tectonics, and paleogeography remain to be established for the Early Proterozoic rocks of the Lake Superior region, they now seem to represent another example of the Wilson cycle (i.e. opening and closing of an ocean basin) in the geologic record. 76 I �References Banks, P. 0., and Cain, J. A., 1969, Zircon ages of Precambrian granitic rocks, northeastern Wisconsin: Jour. Geology, v. 77, P. 208—220. Banks, P. 0., and Rebello, D. P., 1969, Zircon age of a Precambrian rhyolite, northeastern Wisconsin: Geol. Soc. America Bull., v. 80, p. 907—910. Bayley, R. W., 1959, Geology of the Lake Mary quadrangle, Iron County, Michigan: U.S. Geol. Survey Bull. 1077, 112 p. Bayley, W. S., 1904, The Menominee iron—bearing district of Michigan: U.S. Geol. Survey Mon. 46, 513 p. Bayley, R. W., Dutton, C. E., and Lamey, C. A., 1966, Geology of the Menominee iron—bearing district, Dickinson County, Michigan, and Florence and Marinette Counties, Wisconsin: U.S. Geol. Survey Prof. Paper 513, 96 p. Cudzilo, T. F., 1978, Geochemistry of Early Proterozoic igneous rocks in northeastern Wisconsin and Upper Michigan [Ph. D. thesis]: Lawrence, University of Kansas, 194 p. Cummings, M. L., 1978, Metamorphism and mineralization of the Quinnesec Formation, northeastern Wisconsin [Ph. D. thesis]: Madison, University of Wisconsin, 190 p. DePangher, Michael, 1982, The geology, geochemistry, and petrology of the Quinnesec Group east of Pembine, Marinette County, Wisconsin [M. S. thesis]: Salt Lake City, University of Utah, 210 p. Dutton, C. E., 1971, Geology of the Florence area, Wisconsin and Michigan: U.S. Geol. Survey Prof. Paper 633, 54 p. Fox, T. P., 1983, Geochemistry of the Hemlock metabasalt and Kiernan sills, Iron County, Michigan [M. S. thesis]: University, 81 p. 77 East Lansing, Michigan State �I Greenberg, J. K. and Brown, B. A., 1983, Lower Proterozoic volcanic rocks and their setting in the southern Lake Superior district, in Medaris, L. G., Jr., ed., Early Proterozoic geology of the Great Lakes region: Geol. Soc. America Mem. 160, p. 67—84. Hall, G. I., 1971, A study of the Precambrian greenstones in northeastern Wisconsin, Marinette County [M.S. thesis]: Milwaukee, University of Wisconsin, 80 p. Hamilton, Warren, 1979, Tectonics of the Indonesian region: U.S. Geol. Survey Prof. Paper 1078, 345 p. Hollister, V. F., and Cummings, M. L., 1982, A summary of the Duval massive sulfide deposit, Marinette County, Wisconsin: Geoscience Wisconsin, v. 6, p. 11—20. James, H. L., 1958, Stratigraphy of pre—Keweenawan rocks in parts of northern Michigan: U.S. Geol. Survey Prof. Paper 314—C, p. 27—44. Jenkins, R. A., 1973, The geology of Beecher and Pemene townships, Marinette County, Wisconsin [abs.]: 19th Institute on Lake Superior Geology, p. 15—16. Jensen, L. S., 1976, A new cation plot for classifying subalkalic volcanic rocks: Ontario Dept. Mines Misc. Paper 66, 22 p. Kay, R. W., and Senechal, R. G., 1976, The rare earth geochemistry of the Troodos ophiolite complex: Jour. Geophys. Res., v. 81, p. 964—970. LaBerge, G. L., 1983, LaSalle Falls — an exposed massive sulfide deposit in Florence County, Wisconsin [abs.]: Geology, p. 26. 78 29th Institute on Lake Superior 4 �Larue, D. K., 1983, Early Proterozoic tectonics of the Lake Superior region: Tectonostratigraphic terranes near the purported collision zone, in Medaris, L. G., Jr., ed., Early Proterozoic geology of the Great Lakes region: Geol. Soc. America Mem. 160, p. 33—47. Leith, C. K., Lund, R. J., and Leith, Andrew, 1935, Pre—Cambrian rocks of the Lake Superior region, a review of newly discovered geologic features, with a revised geologic map: U.S. Geol. Survey Prof. Paper 184, 34 p. Medaris, L. G., Jr., Van Schmus, W. R., Lahr, M. M., Myles, J. R., and Anderson, J. L., i973, Field trip locality 2 in Guidebook to the Precambrian geology of northeastern and northcentral Wisconsin, 19th Institute on Lake Superior Geology, p. 43—45. Noiret, Gerard, Montigny, Raymond, and Allegre, C. J., 1981, Is the Vourinós Complex an island arc ophiolite: Earth Planet. Sci. Letters, v. 56, p. 375—386. Pearce, J. A., 1982, Trace element characteristics of lavas from destructive plate boundaries in Thorpe, R. S., ed., Andesites: New York, John Wiley and Sons, p. 525—548. Prinz, W. C., 1959, Geology of the southern part of the Menominee district, Michigan and Wisconsin: U.S. Geol. Survey Open—File Report, 221 p. Reid, Frank, 1983, Origin of the rhyolitic rocks of the Taupo volcanic zone, New Zealand: Jour. Volcanology and Ceotherm. Res., v. 15, p. 315—338. Schulz, K. J., LaBerge, G. L., Sims, P. K., Peterman, Z. E., and Kiasner, John, 1984, The volcanic—plutonic terrane of northern Wisconsin——Implications for Early Proterozoic tectonism, Lake Superior region [abs]: Association of Canada, in press. 79 Geological �Sims, P. K., 1976, Middle Precambrian age of volcanogenic massive sulfide deposits in northern Wisconsin [abs.]: 22nd Institute on Lake Superior Geology, p. 57. Uyeda, Seiya, 1983, Comparative subductology: Episodes, v. 1983, p. 19—24. Van Hise, C. R., and Bayley, W. S., 1900, Description of the Menominee special quadrangle, Michigan: U.S. Geol. Survey Geol. Atlas, Folio 62, 13 p., 3 maps. Van Hise, C. R., and Leith, C. K., 1911, The geology of the Lake Superior region: U.S. Geol. Survey Mon. 52, 641 p. Van Schmus, W. R., 1980, Chronology of igneous rocks associated with the Penokean orogeny in Wisconsin: Geol. Soc. America Special Paper 182, p. 159—168. Wadsworth, W. B., 1962, Petrogenesis of a quartz diorite pluton near Pembine, Wisconsin [M.S. thesisi: Evanston, Ill., Northwestern University, 89 p. 80 �h I Field Trip Log and Descriptions of Stops to accompany Volcanic Rocks of Northeastern Wisconsin by Klaus J. Schulz 81 �r'.) ! — — '—I — / I COMM )NWEALT4 I 7*1 T IV p OJMAI\ i7 1I ii T.I7.I1 ,, /- : 5'H k.- H Ii.] Red trIp S tops, Dunber dome. .- 4 ,T IETTE MFffEA - . L!c •1 ± - ,f - - p a - STATCOFIICHIGAPI JH + To1z + — '"" Rock\ J!$i$I=t rip — L- : uit __ ____ I I., �Field Excursion Road Log Log begins at the Pembine Post Office, Wisconsin, on U.S. Highway 141—8 and ends with Stop H at Pemene Falls. Descriptions of stops are given separately on the following pages. Mileage 0.0 Pembine Post Office, Wisconsin, on U.S. Highway 141—8. 8.7 Junction with U.S. Highway 8. Proceed north. Turn right (east) and proceed to Norway, Michigan. 13.15 Turn right and proceed to Vulcan, Junction with U.S. Highway 2. Michigan. 14.8 Turn right on Main Street in Vulcan. Pass Vulcan Middle School on right. 15.5 Follow right fork in road onto River Road. 17.5 Bridge across Menotninee River. 17.95 Turn right onto secondary road going to Sturgeon Falls Dam. 18.1 Outcrop on west (right) side of road. of the Sturgeon Falls sill. STOP Al. Serpentinite Return to vehicles and proceed south. 18.5 Take left fork in road down to Sturgeon Falls Dam. 18.6 Outcrop to north (right). sill. STOP A2. Gabbro of the Sturgeon Falls Return to vehicles and proceed back through Vulcan and Norway to U.S. Highway 141—8 toward Pembine. Go south (left) on U.S. Highway 141—8 to intersection with Kremlin Road (just north of Pembine). 36.3 Junction with Kremlin Road. Turn left (east). 83 �Mileage 38.0 Railroad tracks (Soo line) and bridge across the South Branch Pemebonwon River. Park vehicles on right shoulder of road and walk along trail going east along the south side of the river. STOP B. Tuff unit of the Quinnesec Formation. Return to vehicles and proceed east on Kremlin Road. 40.35 Junction with dirt road going south. 40.75 Junction with east—west 43.35 Outcrop south side of road. Quinnesec Formation. back to Kremlin Road. Turn right. dirt road. Turn left. STOP C. Pillow basalt of the Return to vehicles, turn around and proceed (Note — We backtrack because beavers have flooded the dirt road further to the east). 46.35 Junction with Kremlin Road. Turn right and proceed east for about 2.3 miles. 48.65 Turn left (north) onto dirt road and proceed 0.35 miles. 49.0 Outcrops on both sides of road. STOP D. Foliated gabbros and massive diabases associated with large serpentinite body of the Quinnesec Formation. and Return to vehicles, turn around, return to Kremlin Road. 49.35 Turn left (east) onto Kremlin Road. 50.9 Junction with road to Pemebonwon Dam and Quiver Falls. right 51.05 Turn (south) and proceed 0.15 miles to railroad tracks. Cross railroad tracks (Soo line) and take sharp left onto dirt road. 51.8 Quiver Falls. Quinnesec STOP E. Formation. Pillowed and variolitic basalts of the Return to vehicles, turn around, and return to U.S. Highway 141—8 via Kremlin Road. 84 I �Mileage 60.25 Junction of Kremlin Road with U.S. Highway 141—8. Turn left (south) and proceed 3.75 miles to County Z. Turn left (east). 64.0 Junction with County Z. 70.85 Junction with Marek Road. Turn right (south), proceed 0.15 miles, and park. 71.00 Outcrop on east (left) side of road. of the McAllister formation. STOP F. Volcanic breccia Return to vehicles and continue south 1 mile. 72.0 Outcrop on east (left) side of road. rocks of the Beecher formation. STOP G. Felsic volcaniclastic Return to vehicles, turn around, and go back to County Z. 73.3 Turn right (east) onto County Z and continue east across the Menominee River. [ 77.45 Turn left (north) onto dirt road and proceed north about 1.05 miles to dirt road going down (west) to river. 78.5 Turn left onto dirt road toward river. 78.65 Pemene Falls. STOP H. Rhyolites of the Pemene formation. to vehicles and return via Return County Z to U.S. Highway 141. TRIP NOTE: time If END permits, we will make an additional stop. At intersection of County Z and Highway 141, turn left (south) and proceed about 4 miles to intersection of Highway 141 and Black Sam Road. southeast of intersection. 85 Outcrop is in field, �Description of Field Stops STOP Al. NW1/4SWI/4 sec. 26, T.39N., R.29W., quadrangle. Faithorn 7 1/2—minute Outcrop extends along low hill to the northwest. The knob next to the road and several outcrops to the northwest consist of serpentinite. The serpentinite is fine grained, is green to black, and is cut by thin seams of carbonate and asbestos. have a silky luster and are reddish brown. Many fracture surfaces The rock consists mostly of colorless antigorite, carbonate minerals, and magnetite. Rare chromite grains are also present. To the northwest along this outcrop, the serpentinite is interlayered with, and/or is cut by, fine grained diabase and porphyritic (plagioclase) diabase. Serpentinite is found at several localities along the north side of the Sturgeon Falls sill and appears to lie near the base of body. Locally, pyroxenite is found between the serpentinite and gabbro. STOP A2. Sturgeon Falls Dam, El/2 sec. 27, T.39N., R.29W. Faithorn 7 1/2—minute quadrangle. Outcrops of gabbro extend to the northwest and southeast and represent the major part of the Sturgeon Falls sill as presently exposed. Locally, the gabbro is cut by thin shear zones and contains basalt inclusions (near steps to dam). A major fault, which appears to truncate the top of the sill, passes southeastward along the river just west of these outcrops. The gabbros consist of varying proportions of plagioclase and pyroxene, which are mostly replaced by saussurite and amphibole, respectively. clinopyroxene is locally preserved and shows abundant, fine exsolution lamellae. To the southeast, the top of the sill consists of magnetic, magnetite—rich ( 3%) gabbro. 86 Fresh �Two gabbro analyses from this sill are given below; one an anorthositic gabbro and the other a magnetite—rich gabbro. The relative depletion in light REE and other trace—element characteristics shown by these samples are similar to those of the Quinnesec basalts, suggesting that they may be cogenetic. Also, the low trace—element abundances in both gabbro samples suggest that they are cumulate rocks. Composition of Sturgeon Falls sill r gabbro samples 2 1 Si02 A1203 Fe203 FeO MgO CaO Na20 1(20 Ti02 P205 MnO r 3.8 7.2 13.0 1.7 11.4 7.2 10.9 1.9 0.16 0.13 0.06 2.2 0.18 0.01 Rb 4 Sr 85 y Nb Ta Cr Co Sc Hf La Ce Sm Eu Tb Yb Lu 0.09 1.6 0.06 0.20 2.4 0.16 0.10 0.11 H20 Ba Zr Anorthositic 1.4 44.1 13.2 7.0 H20 Co2 1 — 2 — 49.3 21.6 <5 86 45 34 8 28 12 <5 12 <5 —— —— 124 39 3 74 29.6 0.21 62 0.46 0.39 1.07 0.44 0.31 0.19 0.78 0.12 0.79 2.3 0.80 0.33 0.25 0.88 0.17 gabbro Magnetite—rich gabbro 87 �Nl/2 sec. 36, T.37N., R.20E., Pembine 7 1/2—minute quadrangle. STOP B. Outcrops of intermediate to felsic tuffs are exposed along both sides of the South Branch Pemebonwon River. I Rocks consist of very fine grained, grayish—green to light—green tuffs and interlayered quartz eye tuffs. The rocks have a strong foliation striking N.60°E. and dipping 75°SE. and have a lineaton plunging 75°S.1O°W. Locally, plagioclase crystal tuffs (or porphyritic flows?) are also present. This unit strikes northeast, is intruded by the Newingham tonalite on the north, and is in apparent fault contact with the Quinnesec Formation basalts to the south. phyre. The unit is It is also intruded by quartz porphyries and grano— representative of felsic tuffs found within the Quinnesec Formation to the north and northwest. STOP C. SW1/4NE1/4 sec. 27, T.37N., R.21E., Faithorn 7 1/2—minute quad— rangle. Low open outcrop just south of road. This outcrop is relatively lichen free and shows pillows of basalt (or andesite?) of the Quinnesec Formation. Outcrops to the northwest consist of similar pillowed flows and pillow breccia. variolites are locally observed. N.8O°W. and generally face south. Amygdules and Pillows in this area strike about A sample from an outcrop to the northwest was analyzed and shows high Si02 (62.4 wt.%) and low MgO (4.3 wt.%) contents. However, the strong alteration of the sample (reflected in a very low CaO content — 3.3 wt.% — and high Na2O and 1(20 contents) makes this analysis suspect. 88 I �STOP D. NW1/4NE1/4 sec. 22, T.37N., R.21E. quadrangle. Faithorn 7 1/2—minute Outcrops extend both west and east of road. This stop is to examine some of the gabbroic and diabasic rocks associated with the large peridotite body in the north—central part of the map area. The peridotite is not exposed in these outcrops but occurs about 1/4 mile to the northwest. One of the most distinctive rock types exposed here is a strongly foliated gabbro (outcrop to left (west) of road). The gabbro is altered, and plagioclase is replaced by saussurite and pyroxene is replaced by amphiboles. The foliation strikes N.1O°—20°E. and dips 7O°NW.; it is almost at right angles to the strike of the ultramafic—inafic body and the strike of foliations in surrounding rocks. Locally in other outcrops, banded gabbros having mineral layering are present; this banding also strikes at a high angle to the trend of the body. Another distinctive rock type present in this outcrop is a fine—grained, gray, mottled diabase. The mottled appearance results from small (2—3 mm) oikocrysts of quartz (this is the myrmikitic basalt of G. I. Hall (1971, M. S. thesis, Univ. Wis., Milwaukee). More normal textured diabases of somewhat varying grain size are also present. These rocks lack the strong foliation of the gabbro but are similarly altered. In the outcrop area to the right of the road (east), the generally massive diabases are cut by thin (15 cm wide) dikes of diabase and pyroxenite(?). These dikes weather to a reddish brown and strike northwest. Similar dikes have been observed to the west but have not been recognized outside this ultramafic—inafic body. 89 �The relationship between the various gabbroic and diabasic rocks of these outcrops and elsewhere within this body remains uncertain. diabases represent dikes cutting the foliated gabbro? Could the Diabase is found crosscutting the ultramafic rocks of this body in outcrops to the northwest. Could they represent a system of sheeted dikes? Ultramafic rocks (not exposed at this stop) occur predominately along the north side of the body and at its western end. The ultrainafic rocks are all highly altered but locally show some preserved primary textures. Peridotite and pyroxenite appear to have been the main lithologies. At the western end of the body, large dikes(?) of coarse—grained, altered pyroxenite appear to cut and include serpentinite. Both the structural features of the rocks of this ultramafic—mafic body and the apparent restriction of dikes within it suggest that this body was tectonically emplaced. Could this ultramafic—mafic body represent a slice of Early Proterozoic ocean floor or is it just a disrupted differentiated sill? Samples have been submitted for chemical analysis, however, the altered nature of many of these rocks may preclude meaningful results. STOP E. Quiver Falls on the Menominee River. Sl/2, sec. 24, T.37N., R.21E., Outcrops exposed mainly Faithorn 7 1/2—minute quadrangle. along river bank. Follow road north to the river bank. Outcrops of largely undeformed pillow basalt of the Quinnesec Formation are exposed along the bank. This is one of the few places in the area where pillows can be viewed in three dimensions. They face south and appear to. be slightly overturned. The basalt is very fine grained, is light gray—green, and contains small, skeletal pseudomorphs of olivine. go �Return to parking area and take trail going south to river bank. Outcrop on the left (north) side of the trail presents one of the petrologic wonders of this area. At the top of the slope is a variolitic basalt in which the varioles are generally small. Down slope, these varioles are much larger (cm size) and compose the bulk of the flow. These structures are nre resistant to weathering than their surrounding matrix. The variolitic structures are round to ovoid, are pink, and are concentrically zoned. The zoning consists of a thin reddish—brown rim followed inward by a white zone and a pink core. The varioles consist of albite, an altered skeletal mafic phase (pyroxene?), microcrystalline material, quartz, and secondary carbonate minerals with hematite staining. Varioles found in basaltic rocks generally consist of radial growths of plagioclase formed as a result of rapid growth in cooling pillows or later devitrification of glass. host basalt. In composition, these are similar to their The varioles observed here, however, are more siliceous than their matrix and have textural features distinct from normal basaltic varioles. They most resemble the siliceous varioles described from Archean basalts of the Abitibi Belt of Ontario (Gelinas and others, 1976, Canadian Jour. Earth Sci., v. 13, p. 210—230), which have been interpreted as quenched immiscible liquids. Samples of the matrix and varioles from this outcrop are being analyzed to test this possibility. STOP F. NE1/4NE1/4 sec. 22, T.36N., R.2lE., Miscauno Island 7 1/2—minute quadrangle. Small hill on east side of road. This stop is to examine a typical exposure of the McAllister formation. The rock is a breccia consisting of porphyritic vesicular andesite fragments in a tuffaceous matrix. The fragments are characterized by 1—5—mm—long, 91 �dark—green hornblende pseudomorphs after clinopyroxene. be massive and lack flow structures. Units tend to Fragments appear to increase in size (>15 cm) in outcrops to the east, suggesting that a vent area is across the river in Michigan. STOP G. NW1/4NW1/4 sec. 26, T.36N., R.21E., Miscauno Island 7 1/2—minute quadrangle. Outcrop on hill on east side of road. This outcrop shows typical lithologies of the upper part of the Beecher formation. Lithologies range from fine—grained tuffs and crystal tuffs to coarser fragmental units. The coarser units contain rounded to sub— angular pink to white felsite and gray porphyritic dacite fragments in a Crystal tuffs mostly contain albitized feldspar pale to dark—green matrix. and a few quartz fragments. are to the north. In some tuff beds that show grading, tops The lower part of this formation consists mostly of dark—green porphyritic andesites and gray porphyritic dacites. STOP H. Pemene Falls, SW1/4SW1/4 sec. 16, T.37N., R.28W., Miscauno Island 7 Exposed 1/2—minute quadrangle. Outcrop along river bank. along the bank of the Menominee River at Pemene Falls are rhyolites of the Pemene formation. The rocks are dark gray to reddish gray, contain few phenocrysts, and are generally microspherulitic. Phenocrysts, many of which are glomeroporphyritic, consist of euhedral to subhedral albite. quartz and albite. The microspherules consist of radial intergrowths of Flow banding and breccias (flow breccia?) are observed in some outcrops west of this stop and probably represent upper and lower parts of rhyolite flows. Locally, thin felsite dikes can be seen cutting the rhyolites. 92 �Suggested additional stop (will not be visited on this trip unless time permits). STOP I. Low, open outcrop east side of U.S. Highway 141, NW1/4SW1/4 sec. 10, T.35N., R.2OE., Amberg 7 1/2—minute quadrangle. Outcrop consists of Athelstane Quartz Monzonite cut by dikes of Amberg Granite (after Medaris and others, 1973, 19th Annual Inst. Lake Superior Geology field guide). The Athelstane Quartz Monzonite intrudes the Beecher formation north of this stop and extends for several kilometers to the south and west. It is pink, medium to coarse grained, and allotriomorphic granular, and it contains both biotite and hornblende. Its distinctive appearance is due to the presence of pink perthitic microcline and white plagioclase. a cataclastic foliation. present in the outcrop. In the road cut, the Athelstane shows Small metavolcanic inclusions are also locally The Atheistane was dated by P. 0. Banks and J. A. Cain (1969, Jour. Geol., v. 77, p. 208—220) as 1,836+15 Ma, which is similar to the age of the Hoskin Lake Granite to the north. The Athelstane Quartz Monzonite is compositionally distinct from other granitoid rocks of the area in being significantly lower in Rb and having lower Rb/Sr and higher K/Rb ratios. The Amberg Granite is gray, medium to fine grained, and hypidio— morphic granular; it contains mainly biotite as the major ferromagnesian phase. Van Schmus (1980, Geol. Soc. America Special Paper 182, p. 159—168) determined the age of the Amberg as 1,756+19 Ma. Thus, it is equivalent in age to the high—level granitoids and felsic volcanic rocks in central Wisconsin. 93 � https://digitalcollections.lakeheadu.ca/files/original/a125dd7f19263dc54ad1df3ea5a18df2.pdf f9e418a6dd261cb50829c70f96e79ea8 PDF Text Text I Thirtieth Annual Institute on Lake Superior Geology FIELD TRIP 2 EARLY PROTEROZOIC TECTONOSTRATIGRAPHIC TERRANES OF THE SOUTHERN LAKE SUPERIOR REGION: FIELD TRIP GUIDE WITH SUMMARY Iron for.itlon PAINT RIVER GROUP YOltinics qqnrtzlt. BARAGA GROUP —I 71 FAULT CONTACT APRIL 28, 1984 �Early Proterozoic Tectonostratigraphic Terranes of the Southern Southern Lake Lake Superior Superior Region: Region: Field with F i e l d Trip Guide w i t h Summary Field F i e l d Trip Trip Leaders Leaders W. L. L. Ueng W. D. K. D. K. Larue R L. Sedlock R. L. D. A. A. Kasper D. Prepared for meeting of of tthe Prepared f o r 30th annual meeting he IInstitute n s t i t u t e on Lake Superior Geology Geology Wisconsin, 1984 Wausau, Wisconsin, 1984 �______ EARLYPROTEROZOIC PROTEROZOIC TECTONOSTRATIGRAPRIC T!lCTONOSTRATIGRAPHIC EARLY TERBAmSOP OFTHE TRESOUTHERN SOWl'EfERNLAZE LARZ SUPERIOR SUPERIOR REGION: REGION: TERRAZ!S TRIP GUIDE GUIDE WITH WITHSUMMARY SUMMARY FIELD TRIP FIELD W.L. Ueng ueng W.L. D.K. Lame Lame D.K. R.L. Sedlock Sedlock l.L. D.A. lasper Kasper D.A. Geology, Stanford Stanford University University Dept. Geology, Dept. Stauford CL CA 94305 94305 Stanford INTRODUCTION Geologic studies s t u d i e s in in the the Lake Lake Superior Superior region region Geologic ur~derventa a minor minor revolution revolution in i n 1976 1976 with with the the underwent The Ttm present present paper paper relies r e l i e s on on aa previous previous study study recently r e c e n t l y published published (Larue, (Lame, 1983) 1983) concerning concerning the the geology of the g e o l o w of the acuthcentral southcentral tot osoutheast southeastLake Lake P r w i o u s l y one cue of of us ussuggested suggested Superior Superior region. r e g i m . Previously (Lame, (Larue, 1983) 1983) that t h a t early e a r l yProterozoic Proterozoic rocks rocks of of the the publication of of Van V a n Schmue' Schma' paper the publication papers-king suiarizing the geolow and aud speculating about about early e a r l y Proterozoic Proterozoic geology Schen~ tectonicsofofthe theGreat GreatLakes Lakesregion. region. Van VanSchimia tectonics rock that aabelt b e lof t of calc-alkalinemagmatic ma-tic rock propoaed that proposed cab—alkaline extending across across northern aorthenaWisconsin Wisconsin represented represented the the extending Lake Lake Superior Superior region r e g i m can can be be described described in i n terms tenus of of aa 2) including: including: number of of discrete d i s c r e t e tarranea terranes (Pig. (Fig. 1,1, 2) number aa miogeocline udogeocline (terranes ( t e r r a n e s A,B), A,B), aa probably probably composite composite erge and magmatic terrane t e r r a (en) (mt) (Lab (Laberge andMeyers, Meyers, in in magnetic press) and and two tvo smaller, smaller, complicated complicated terranes terranes press) ccmposed of of miogeoclinal miogeoclinal lithologies, l i t h o l o g i e s , the the composed Florence—Niagara Florence-Niagara and and Crystal Crystal Falls F a l l s terraces terranes (FNt, (FNt, was suggested it was suggested that t h a t the the m t ) . In I n Larue Lame (1983), (19831, it Clt). had exhumed resmants remnants of ofanauAndean—type Andean-type arc a r cwhich whichhad exhumed formed on on an an older olderpassive passivemargin, margin, exposed exposed to t o the the formed north (Pig. (Fig. I). 1). Cambray Cambray (1978), (19781, Larue Larueand andSboss Sloss north (1980) and aud more more recently recencly Greenberg Greenberg and and Brown Brown (1983) (1983) (1980) proposed instead instead that t h a t an an arc arc terrane terrane collided collidedwith with proposed passive continental continental margin margin about about1.8—1.9 1.8-1.9 b.y. bay. ago. ago. aa passive — 4 GUNF I Vy 0 ONTARIO 404 * • 100% • I n Rocks Rocksyounger younger than than eaily eariy Proterozoic Proterozoic W°"° I.I plutonics and andvolcanics voicanks Marquette Range SuDergroup and equivalent rocks Archesn green8tomArcheangroenstone--1granlt. terran. granite terrano • 1Arch.an gneles ol Fig. Fig. 1 1 A. A. Location of of the t h e Lake Lake Superior Superior Region. Region. (After (After Morey, Morey, et Location e t al,1982) a1.1982) tarTan. �—2— this this deformation by examining examiningthe the sstructural deformation by tructural mt represents represents an m arc a r c terrane terrane that t h a t collided collided with u i t h and and mt probably overthrust the themiogeocline, miogeocline, and and that t h a t the the probably FNt kwere r e aalso l s o probably probably emplaced -laced during his CFt and and FNt during tthis CYt The fault f a u l t that t h a t separates separates major accretion event. event. The major the mt m t and and the the terranes t e r r a n e composed s composed of of miogeoclinal miogeoclind the l i t h o l o g i e sisi knoem s k n m as an the the Florence—Niagara Florence-Niagara ffault, ault, lithologies and may suture. and, mayrepresent represent aa suture. Proterozoic Proterosoic The present present paper paper is is aimed aimed at a t discussing discussing the the The f o l l w i n g points: 1) aa brief b r i e freview reviewofofthe thegeology geolw following points: 1) of the the southern southern Lake Lake Superior Superior region; 2) recent recent of region; 2) tlutwe vehave havemade made in i n the thesouthern southernLake Lake studies that studies Superior region region astride a s t r i d ethe t h eFlorence-Niagara Florence-Niagara Superior Specifically, we we present presentdata dataconcerning concerning f a u l t . Specifically, fault. s t r u c t u r a l evolution evolution of of the thearea areasurrounding surrounding the the structural We wwill i l l stress s t r e s s the thecomplicated complicated nature Y t u r e of of suture. We suture. The The rresponsibilities e s p o n s i b i l i t i e s for f o rwork work are a r e as a sfollows: follows: W.L. D.K. Larue, Larue, W.L. Ueng, Ueng, regional regional deformation deformatica model; model; O.K. regional regional studies; studies; R.L. R.L. Sedlock, S d l o c k , deformation deformation in in These magmatic D. Kasper, Kasper, geochemistry. geochemistrv. These m a p a t i c tterrane; e r r a e ; D. studies studies were were supported supported by by the t h e National National Science Science Foundation EAR 80—08202, 8048202, 81—08564) 81-08564) to t o O.K. D.K. Foundation(NSF (NSFLAP. Larue Larue and and by by the t h e U.S. U.S. Geological GeologicalSurvey. Survey. history I n addition, addition, we we present present h i s t o r y of of each each terrane. terrane. In some new new exciting e x c i t i n g data c?ataon on the t h egeochemistry geochemistry of of early early some shales shales in i n the the Lake Lake Superior Superior region. region. We We begin begin with with aa discussion discussion of of lithologies l i t h o l o g i e s in i n the the southern southern Lake Lake Superior Superior region, region, followed followed by by aa do not not attempt We do attempt structural s t r u c t u r a l analysis analysisand andsummary. sumnary. We to t o modify modify eexisting x i s t i n g tectonic t e c t o n i c models models in i n this t h i spaper. paper. IL' IM 2 t& "• 2 I I : FI 03 I z 0 I I C., II'a •' • AMASA OVAl. MARQUETTE TROUGH 3. Idealized NW—SE cross located i.n section of Florence Niagara and Crystal Falls terranes Fig. 2. CRYSTAL FAU.$ FI.osvsce-NsaeasA wAGUATIC TERRANS II- Q PAINT RIVER Fig. 1 -j o I' 'I. r 31,v&i) p - zUi 2Ui — I TEANU I WIST FLANK OF AMASA OVAL CAST FLANK OF AMA$A OVAL FCLCN TROUeH MANOUCYTE TROUGH I I I 4 A U I a I I I 44 . I I I I I ,. ZZ <a a Fig. Fig. 1 1 C. C. Stratigraphy of of units u n i t s discussed discussed in i n text. text. Stratigraphy �—3— OLOGY OF THE MIOOCLT.NE General - Older Precambrian Older Precambrian Precambrian Basement Basement.• Older Precambrian exposed only 2 is showniin basement shown n Figure 2 is exposed only Lfl i n the the miogeocline, and miogeocline, and can be be divided divided into i n t o two two types: types: Huronian (2.2—2.3 b.y.) Huroniau sstrata t r a t a (2.2-2.3 b.y.1 and andArchean Archean (>2.4 02.4 by.) b-y.) ccrystalline r y s t a l l i n e rocks (Van (Van Schmus, S c h s , 1976). 1976). ifuronian Eurmiau strata s t r a t a are a r e rrelatively e l a t i v e l y rare r a r e in i nthe t h eLake Lake Superior region (Van (Van Schmus, Schmus, 1976) 1976) and and aare r e not not Sims (1976) (1976) divided divided tthe he here. Morey and Sima discussed here. Lake Superior region rocks into Archean rocks i n t o aayounger younger Lake Superior region Archean (2.7—2.5b.y.), b.y.), northern, granits—greenstone (2.7-2.5 granite-greenstone southern, terrane an older older (>3.0 b.y.), southern, terrane and and au 03.0 b.y.1, Archeanrocks rocks iin n Figure gamiasic gneissic terrane t e r r a n e (Fig. (Fig. 1). 1). Archean 2 are 2 a r e iin n their t h e i r gneissic m e i s s i c terrana. terrane. Supergroup. a! Supergroup. Marquette Marquette The Chocolay Chocolay Group Group uncomfornably uuconfomably overlies o v e r l i e s older olderPrecambrian Precambrian basement, basement, consists of consists of basal basalconglomerate conglomerate overlain overlain successively by qquartaits, successively by u a r t z i t e , dolomite, dolanite, and and slate s l a t e and and of the is the t h elowermost lowermost unit u u i t of t h eMarquette Marquette Range Rauge Supergroup (Fig. (Fig. 23). 2B). Menominee Groups tstrata M m d n e e Group r a t a rrest e s t unconformably uuconformably on on consist of of quartaite Chocolay Group Group strata, s t r a t a , and a d consist q u a r t z i t e or or muddy overlain by muddy qquartzite u a r t z i t e overlain by banded bauded iron iron formation formation overlies Baraga Group Group o v e r l i e sthe t h Menominee e Mendnee (Pig. (Fig. 23). 2B). The Baraga Group Group aat t lleast e a s t locally l o c a l l yuncouformably, uuconform~bly, and aud consists consists of dominantly sandyand andmuddy muddyt uturbidites rbidites of dominantly deep—water deep-water sandy and volcanic volcanic uuits. units. and Sub terrane AA Subterrane The osiogeocliae miogeoclineMis divided divided iinto The n t o subterranes subterraues A A and (Fig. 2), have ddifferent and BB (Fig. 21, which which ham i f f e r e n t geologic geologic features but features but are a r e not not separated separatedby by any any apparent apparent maj majororsstructural t r u c t u r a l discontinuity. Boundaries and Distinguishins Distinguishing Features. Boundaries & Subterrane ItA is ia inferred i n f e r r e d to to be fault—bound f a u l t - b d on m the the west on the the south with west with with the the Cit CFtand and fault—bound fault-bound on tthe h e FNt, F N t , is ia overlain overlain to t othe t h eeast e a sby t byPhanerozoic Phanerozoic cover, cover, and and is is apparently apparently continuous continuous to t o the the nortwest nortwest is (sub terrane B) A is (subterrane B) and to t o the the north. north. Subtarrane Subterrane A unique with regard regard to to the the other terranes unique with terranes discussed because it it lacks here because lacks the thethick thicksequence sequence of ofBaraga Baraga Group volcanicsofof the the Cit Group volcanics CFt and and subterrane subterrane B, B, and and significant s i g n i f i c a n t mappable units u u i t s in i nthe t h eBaraga BaragaGroup Group composedofofmature mature (quartzose (quartzose and carbonate) composed carbonate) lithologies FNt. l i t h o l o g i e s as in i n the t h e FNt. of Stratigrephy. The oldest Stratigraphx. oldest Proterozoic Proterozoic rocks of those of of the Chocolay Group, subterrane A are those Group, which include l o c a l l y thick accumulations accumulatims of of quartzite quartzite include locally quartzitea and iron formation f0m.athII and dolomite. dolomite. Muddy quartzitea of of the the M e n k n e e Group uncmfomably overlie w e r l i e strata strata Menominee Group unconformably of the the Chocolay Group Group and and aare r e relatively r e l a t i v e l y thin. thin. of Baraga Group slates sandstones, locally i m sandstones, locally s l a t e s and ddirty with volcaniclastic (James and and others, others, volcaniclastic interbeds interbeds (James 19681, 1968), cap the sequence. sequence. Larue Larue and and Sloss Sloss (1980) and Larue (1981a) have have (1980) and Lame (l981a) suggested that t h a t the the Felch Felch and and Menominee Menominee s tstructural ructural suggested troughs were sedimentary basins during troughs during Chocolay Chocolay Group sedimentation. sedimentatim. This interpretation is based i n t e r p r e t a t i o n is on on the presence presence of of trough—parallel trough-parallel paleocurrent paleocurrent vectors from in the the areas areas frao cross—beds cross-beds iin n q u a r t z i t e in quartaite within s t r u c t u r a l troughs. troughs. The within the the structural The Felch basin basin was was n w expressed expressed by by bound on eeither i t h e r side sideby byplatforms, p l a t f o m a ,now exposed Archaen Archaen basement. basement. Archean basement is is exposed Archean basement a~the the northeast side side of the present only cmly on the Menominee Menominee trough. The southwest southwest margin margin of of the the Menominee The Menominee trough is is sstructurally complicated and and not not well well trough t r u c t u r a l l y complicated the basin basin may may understood. IIn uuderstood. n fact, f a c t , this t h i s side, s i d e , oof f the Menominee basin may may have been been open, have open, such such that t h a t tthe he M e n d n e e basin have had only have only one onewell—defined well-defined margin. margin. Group sedimentation, Felch During Menominee M e n d n e e Group sedimentation, the t h e Felch Menominee basins Menominee basins received received little l i t t l e sediment. sediment. basins became Apparently, tthe Apparently, h e basinn became iinactive n a c t i v e during during this this period, period, and and it it isisnot notknown known whether whether these these basins basins were reactivated during were reactivated duringBaraga BaragaGroup Group The complex complexsstructural sedimentation. The sedimentation. t r u c t u r a l and and overprinting of of these metamorphic overprinting these strata s t r a t a precludes precludes Baraga Group s e d i ~ t o l o g i canalysis. analysis. Baraga Group ddetailed e t a i l e d sedimentologic sediments represent represent products products of of regional regional deep-water deep-water sediments sedimentation. and and Sub terrane B is d different terrane BB is Miogeoclinal sub Hiogeoc1iaal subterrane i f f e r e n t from from it contains contains much greater greater subterrane A because it inafic igneous Proterozoic mafic volumes of early e a r l y Proterozoic igneous rocks. rocks. The basement basementofofsubterrane subterrane BB is Stratigraphy. S t r a t i g r a p b . The Archeangneiss gneisswhich whichf forms thecore coreofof aa large Archean o r m the large Figure dome, dme, the southern southern tip t i p of of which which is isshown shown in in F icre lfarquette Range r a t a mantle maatle the the RangeSupergroup Supergroups tstrata La. Marquette U. Chocolay Group Groupddolomites comprise tthe o l m i t e s comprise he dome. Chocolay lowermostpart part of of the sedimentary drape, and lowermost sedimentary drape, and are are overlain by volcanics and overlain by Baraga Baraga Group Group volcanics and sediment. sediment. particular a r t i c u l a r interest i n t e r e s t is is the the ICiernan Kiernan sills sills Of p iintrusive n t r u s i v e complex ccmplex which is is of of greatest g r e a t e s t thickness thickness to to the southwest of of the the domes domea (Fig. (Fig. 23) 2B) but but is is probably equivalent equivalent to probably t o sscattered, c a t t e r e d , smaller mafic intrusions i n t r u s i o n s that t h a t occupy occupy a a similar s i m i l a r sstratigraphic tratigraphic the perimeter pposition o s i t i m around a r d the perimeter of of the t h e dome d a m (Cannon, 1978). Where Where it it is is thickest, t h i c k e s t , the t h e iCiemnan Kiernan complex complex ultramafic rock c o n s i s t s of: 1)1)a acumulate—layered cumulate-layerad ultramafie consists base (lO0—300m); (100-3001~); 2) aa cumulate cumulate and aud isotropic i s o t r o p i c gabbro gabbro medial section and 3) k d ; and 3) aa pillow pillow basalt b a s a l t cap cap secticm(1—3 (1-3 1cm); medial byr ribbon charts and andt turbiditic d woverlain e r l a i n by i b b a ~cherta urbiditic ((>1 > l kion) ash beds m), and and iiron r o n formation formation (the (the beds ("lOO (-100 d, Mansfield member; —200m)in)(descriptions (descriptions from Gair member; a200 and and Weir, Weir, 1956; 1956; Bayley, Bayley, 1959; Weir, 1967). The Kiernan complex probablyoriginated originatedasastthe Xiernan c m p l e x probably h e ffloor l o o r of of aa volcanic within ccontinental volcanic basin basin within o n t i n e n t a l crust, c r u s t , during during deposition d e p o s i t i m of of Baraga Baraga Group Group sstrata t r a t a (Fox (Fox 1982; 1982; Wilband and and others, i n prep.). prep.). others, in Crystal Falls F a l l s Terrane Terrane Boundaries Boundaries and Distinguishing Features. Features. The CFt is roughly equidimensional in i n shape and is Cit is iinferred n f e r r e d to t o be fault—bound. fault-bound. The CFt i n fault fault Cit is in contact on m the t h e south with with the t h e FNt F N t (Fig. (Fig. lIt). 2A). Art An inferred ffault inferred a u l t to t o the the east separates separates the the Cit CFtfrom frcm tterrane e r r a e A, A, and and an au inferred i n f e r r e d ffault a u l t tto o tthe h e north separates the the CFt ( t h e latter l a t t e r two two Cit from terrane B B (the boundaries are ffault a u l t boundaries a r e inferred i n f e r r e d based on m truncation truncation of aeromagnetic trends sshown of h m on on the the map by Zietz Zietz and Kirby, Kirby, 1971). and 1971). There is insufficient outcrop to to define the exact boundaries boundaries of and of the southwest southwest arid 1; however, hawever, faults f a u l t s are are sides of of terrane terrane 1; west sides iinferred n f e r r e d based on m preliminary preliminary study study of of aeroinagnetic aerumagnetic anomalies. anamalies. Stratigraphy. S tratigraph~. N No unequivocal Chocolay o mequivocal Chocolay or Menominee M e n d n e e Group Group rocks are a r e present n the t h e Cit. CFt. present iin Baraga Group extrusive extrusive volcanics volcanics (Badwater(Badwater— Greenstone) r e iin n ffault a u l t contact Greens tone) aare contact with Chocolay i n the W of of the the Cit. CFt. Group strata s t r a t a of of the the E'Nt Flit in the S SW Presumably deep-water deep-water turbiditic t u r b i d i t i c sandstones sandstones and and p e l i t e s of of the the Paint Paint River—Group River-Group unconfommably(?) mconformably(?) pelites o v e r l i e Saraga Baraga Group Group strata s t r a t a (James (James and and others, others, overlie 1968). A deep-water storm-wave base) origin deep—water (below storm—wave base) origin �-4-. MAGMATIC TERRANE TERRAME 1: CRYSTAL FALLS TERRANE TERRANE 3: FLORENCE-NIAGARA TERRANE ARCHEAN BASEMENT FAULT - inferred FAULT 4s04s* Florence—NIagara Fault 1 2 PIne River Block Fig. 2 A. 3 Unnamed Block 4 Keyes Lake Block TerTanem in the south central Lake Superior region. (1983). I4AGNATIC TERRANE KIERNAN SILLS Iron formation volcanics PAINT RIVER GROUP m quartzlta I— BARAGA GROUP NENONINEE GROUP CHOCOLAY GROUP I FAULT . Inferred '2 FAULT >1 FAULT ,4 CONTACT CONTACT Fig. Fig. 22 B. B. Terrane aap of Terrae map of Fig. 2A 2A with with geology geology superimposed. super-osed- After Larue �—5— £5 is proposed because of of the t h e fine—grained, fine-grained, thin—beddednature nature of these thin-bedded these rocks; rocks; their their extent without ssignificant i g n i f i c a n t lateral l a t e r a l extent without evidence evidence of of deposits; intefingering with v i t h shallow—water shall-ter deposits; and and formation thicknessthicknesses within ttheir h e i r significant s i g n i f i c a n t formation no evidence sequences tthat sequences h a t show w evidence of of shall.owing. shallatring. The Terrane The Florence—Niagara Florence-Niagara Terrane PNtisis at Architecture. Architecture. The The FNt a t least l e a s t40 40ion km long long and cconsists and o n s i s t s of of aanumber number of major steeply—dipping steeply-dipping separate ddisparate faults f a u l t s that t h a t separate i s p a r a t e tithologies l i t h o l o g i e s and (3ayley and others, offset of f s e t metamorphic isograds isograds (Bayley others, major ffaults 1966; 1966; Dutton, 1970). Four of these these major a u l t s in in define tthree tthe h e Ft4t FNt define h r e e composite composite f fault a u l t sslices l i c e a with with width of about Ion;the the Pine Pine River? River, ccumulative u m l a t i v e width about 5—8 5-8 h; tthe h e Keyes Keyes Lake Lake and and an intermediate i n t k m e d i a t eunnamed uammed block ccalled a l l e d the t h e 8essie BessieRabbit Babbitblock blockby byLame U r u eand andIjeng Ueng will in the A# w i l l be be shown shown in the (submitted) (Pig. (Fig. ZA). (submitted) 2k). As composed structure s t r u c t u r e section, section, these these three threeblocks blocks are a r e ccmposed of additional addititma1 ffault a u l t slices s l i c e sand and thus thus aare r e composite. The contains Chocolay, Chocolay, The Pine Pine River block contains Mmtominee Baraga 3araga Group Menominee and and Baraga Group sstrata. t r a t a . The Beraga Groupcomprises comprisestb th. M Michigasme in tthe i c h i w e S Slate l a t e in h e Pine Pine Group block, and consists River block, c o n s i s t s mainly mainly of ppelites, e l i t e s , of of deep—waterorigin, origin, and probable deep-water and a fault—bound f a u l t - b o d uunit nit q u a r t z i t e representing representing 0.5 km thick of 0.5 thick of pebbly quartzite shallow—water deposition. ororf lfluvial u v i a l deposition. shallmmrater The intermediateffault The intermediate a u l t slice s l i c e isispoorly poorlyexposed, exposed, and pillow pillow and contains Paint River Group strata and s t r a t a and basalts b a s a l t s of ofthe theBadwater Badwater Greenstone Greenstone which vhich aare r e folded folded in syncline (Dutton, The Paint Paint i n aa SE—closing SE-closing syncline (Dutton, 1970). 1970). Th. River Group Group iin n this t h i s intermediate block contains contains two two principle p r i n c i p l e lithologies, l i t h o l o g i e s , iron i r o nformation formation and and slate slate vwith i t h thin t h i n graded graded sandstone sandstone interbeds. interbeds. Dutton plate (1970, p l a t e 5) 5 ) show. shmm tthat h a t th. thesouthwestern southwestern ffault ault that unnamed block truncates truncates t h a t defines the the unnamed ntetanorphic isograds, demonstrating the metamorphic themovement movement on on the the ffault a u l t occurred occurred after a f t e rregional regionalmetamorphism. mtawrphiam. i The Keyes Lake block is The is similar s i m i l a r to t o the t h e Pine Pine River block, River block, containing containing Chocolay, Cheeolay, Mencminee Manominee and and Baraga Group Groups strata. Baraga t r a t a . Michigasne X i c h i w e SSlate l a t e of tthe he Saraga Group Group includes includes another fault—bound Baraga fault-bound uunit n i t 0.3 0.3 Ion thick qquartzite km thick u a r t z i t e representing representing shallow shallow marine oorr fluvial f l u v i a l deposition, deposition, aalso l s o studied by Nilsen (1965). studied by (1965). Pillow 3adwater Greenstone Greenstone (Fig. (Fig. 23) Pillow baaalts basalta of of the the Badwater 2B) p a r t of of the the aare r e present iin n tthis h i s block blocki ninthe thevest st part florence Florence County County Quadrangle. Quadrangle. Magnetic terrane Magmatic terrane In the terrane, granitoid the magnetic magmatic terrane, g r a n i t o i d and and gneissic gneissic rocks of Penokean Penokean age r e mantled mantled by highly highly rocks age aare deformed deformedunits unitsofof three three major majorlithotypes: lithotypes: 1) 1) a schistose ssuite, u i t e , consisting of of felsic f e l s i c to to predominantly mafic metavolcanic metavolcanic rocks the rocks of of the ; 2) Quinnesec Formation (Bayley (Bayley and and others, 1966) 1966); 2) a inetasedimentary u i t e , consisting scattered metasedinentary rock rock ssuite, consisting of of scattered outcrops of u a r t z i t e and slate; s l a t e ; and and 3) 3) aa gabbroic gabbroic of q quartzite s u i t e , which which includes includes pillowed pillowed and and massive manaive basalt, basalt, suite, gabbroeofof varying varying cmposition, composition, and and llocal massive gabbrca ocal diabase dikes. The granitoid diabase dikes. granitoid and and gneissic rocks that form the the core core of t h a t form of the t h e magnetic magmatic terrace terrane have have been sshownb by by Schulz Schulz (1983) (1983) to t o have have calc—alkaline calc-alkaline a f f i n i t i e s , suggesting aa nagmatic magmatic arc origin. origin. The affinities, volcanic rocks rocks of c h i s t o s e suite s u i t e bear volcanic of the sschiatose geochemical of arc envirmments environments geochemical signatures signatures ttypical y p i c a l of (Cudzillo, 1978). (Cudzillo, 1978). The gabbroic gabbroic suite s u i t emay may be be interpreted as the the roots roots of of this t h i sarc arccomplex. complex. Archaen i n southcentral southcentralWisconsin Wisconsin Archaengneiss gneiss present present in (Fig. IA) ia not considered considered here. here. LA) is STRUCTURE Miogeocline and Crystal Crystal Falls F a l l s Terrane Terrane Structural S t r u c t u r a l features f e a t u r e s of of Early Early Proteroroic Proterozoic rocks rocks andCFt Cit north north of of the iin n the the iniogeocline FNt are are miogeocline and the FNt generally oriented E—W E-W except at a t the t h eAmasa Amasa Oval, Oval, generally oriented Smith Smith Creek Creek Uplift, U p l i f t ? Kiernan Kiernan SSills, i l l s , and and eastern eastern (Fig. 3). margin of of the Cit (Fig. 3). Most Moat structural structural 'margin t h e CFt troughs in E-W, such such troughs i n the miogeocline are a r e oriented E—W, as the Marquette trough, t h e Marquette trough, Felch trough, trough, and Calumet trough. The Sagola trough. Sagola structural s t r u c t u r a l basin, basin, however, hovever, WNW NW and becomes parallel p a r a l l e l to t o the the bends toward toward the the W Oval. The penetrative penetrative Uplift Smith Creek U p l i f t and Amasa Amasa Oval. formed during during tthe deformation ((see ffoliation o l i a t i o n fomed h e ffirst i r s t deformation see which i*this t h i sregion region whichcomeonly coumonlystrikes s t r i k e1*1W, s WNW, below) i'. also andbecomes becomesp parallel a l s o bends bends toward toward the t h eNNW NNW and a r a l l e l with with Transverse tto Amasa Oval. Oval. Transverse the of the the Amasa o these these the axis of structural s t r u c t u r a l bends, bends, tectonolithologic t e c t o n o l i t h o l o g i cassemblages assemblages change iin change n the the miogeoclinal miogeoclinal assemblage: assemblage: most most material ssignificantly, i g n i f i c a n t l y , the the amount amount of of volcanic volcanic m a t e r i a l in in the the Baraga Group Group increases increases dramatically dramatically tot othe the14—SW W-SW across the Amaaa Oval (from t o 3). B). across t h e Amasa (from subterrane subterr~A eA to deformation have have been been recognized Five phases of deformation miogeocline, CFt, and FNt TNt ofof tthe iin n the t h e miogeocline, CFt, and b e southern southern Lake Superior region based on cross—folds cross-folds and and is cross—cutting kleavages leavages (deformation t h e TNt FNt is cross-cutting ( d e f m t i o n in the considered in considered i n detail d e t a i l below)(iig. below)(Fig. 3). 3). Four of these phases aare r e characterized by ssteeply t e e p l y dipping dipping cleavages and axial cleavages a x i a l planes planes of minor folds. folds. These deformation fabrics regionally in f a b r i c s are a r e recognized recognized regionally in the t h e . area a r e a north of of magmatic magmatic terrane. terrane. The other P3, is deformation, F3, phase of deformation, M defined defined by subhorizontal cleavages which generally subhorizontal ccrenulation r m u l a t i o n cleavages dip d i p less l e s s than thau 35 35 degrees. degrees. This This set s e t of subhorizontal crenulatiom cleavage cleavage is recognized recognized subhorizontal crenulation everywhere Crystal Fells everywhere but iin n tthe he C rystal F a l l s terrane. terrane. TI, most pervasive pervasive F l , the t h e earliest e a r l i e s t and and -st characterized by tthe deformation, ia characterized h e following following defomation, is planar structures: structures: slaty s l a t y cleavage, c h i s t o s i t y , and cleavage, sschistosity, aaxial x i a l planfolds. In planes of minor folds. I n spite s p i t e of of later later deformations, aaxial x i a l planes of minor folds folds and deformations, planes of of tthis deformation, S SI, regionally ffoliations o l i a t i o m of h i s defomation, l , regionally sstrike t r i k e N7OW N70W and dip d i p vertically v e r t i c a l l y (for ( f o r example, example, Fig. Fig. 6k, Lame, 1983). Only in 6A, from Larue, i n the t h e neighborhood of of the Amasa Amasa Oval, Kiernan Sills, the S i l l s , and SE ppart a r t of of the the CFt have have Sl rotated by F2 Cit Si surfaces bean been passively rotated P2 orientation NNW. tto o an o r i e n t a t i o n of of NNW. Apical angles of of Fl Fl folds m ccharacteristically h a r a c t e r i s t i c a l l y ttight, i g h t , lless e s s than folds aare than 60 60 degrees, profiles degrees, and and fold p r o f i l e s can comuonly coaw~onlybe categorized iinto l C , and type 3 folds of categorized n t o type lB, LC, type 13, Ramsey's Ramaay's cclassification l a s s i f i c a t i o nscheme schema (1967). (1967). Apical of these NNW-trending NNW—trendimg F Fll folds folds a are angles of r e uusually sually extremely small amall such h a t isoclinal i s o c l i n a l folds folds and and such tthat transposed layerslayers are present. The tranapoaed a r enot notuncomeonly unconw~mlypresent. The ffoliation, o l i a t i o n , which vhich ranges ranges from f r m a closely c l o s e l y spaced spaced penetrative alignment of ppiety penetrative alignment of l a t y minerals minerals to to a spaced cleavage, comuonly ffoliation o l i a t i m or cleavage, conmuonly parallels p a r a l l e l s bedding, bedding, eespecially s p e c i a l l y in i n the Limbs limbs of of isoclines. isoclines. The P2 F2 deformation S l surfaces and and deformation refolded refolded the the $1 formed formed a a set s e t of of crenulation crenulation cleavages cleavages and and open open folds. Ax.al c r e n u l a t i m cleavages, cleavages, $2 S2 M a 1 planes and crenulation of t r i k e consistently c o n s i s t e n t l y N65E N6SE throughout throughout the the of F2, P2, sstrike ) , indicating i n d i c a t i n g that t h a t later l a t e r deformations deformations region (Pig. (Fig. 3 3), ffailed a i l e d tto o regionally r e f o l d Ti F l and and P2 F2 structures. structures. regionally refold Fold axes axes of of F2 f o l d s form f o m aa great g r e a t circle circle Fold P2 minor minor folds d i s t r i b u t i m on on stereogram stereogram because because the the P2 F2 distribution a t already already folded folded deformation represents represents folding folding of of an surface. Apical surface. 70 degrees degrees to to angles are a r ecomuonly coummly 70 Apical angles 120 degrees, and fold f o l d profiles p r o f i l e s indicate i n d i c a t e type type 13 1B and and 120 degrees, and 1IC C folds. folds. Depending on m host host rock rock lithology, lithology, �—6— ranges from ional crenulation cleavage crenulation cleavage of P2 F2 ranges from aa zonal cleavage cleavage in i n pelitic p e i i t i c rocks rocks to t o discrete, discrete, disccntinuäus cleavage iinn netavolcanics diacontinu6us cleavage metavolcanics or sandstones. IIn folds Si sandstones. n places, P2 F2 deformation deformation folds Sl folds or ffoliations o l i a t i o n s into i n t ominor minor chevron chevron folds or kinks. kinks. The deployment deployment of P2 F2 deformation deformation ffabrics a b r i c s is not not F2 minor homogeneousthroughout throughoutthe thearea area studied. studied. P2 homogeneous folds were were observed obserred only in inthe theCFt CFtand andthe theHemlock Hemlock Pormation sslates Formation l a t e s above the Fiernar& Kiernan SSills. i l l s . The The development P2 crenulation cleavages is is also also development of of F2 intense when most intense when Si S l surfaces surfaces are a r e oriented oriented NNW. BMW. The P3 deformation d•formmtioni sis characterized characterized by The F3 by subhorizontal crenulation crenulation cleavages cleavages (dips <(35 35 degrees) which iintersect degrees) which n t e r s e c t with Sl 31 foliations f o l i a t i o n s to t oform fom lineatione. abundant ation lineations. abundant subhorizontal crenul crenulation These subhorizontal cleavages dip These d i p away, away, on all all sides, sides, from tthe h e Amasa Amasa Oval Oval and and the the Peavy Pond Pond intrusive. These subhorizontal foliations intrusive. These f o l i a t i o n a indicate indicate subvertical shortening, subvertical shortening, probably probably associated associated with with Fig. 3. 3. Fig. uplift. basement u p l i f t . between this The rrelation e l a t i o n between t h i s phase deformation andbasement basementisisb ebest s t i illustrated l l u s t r a t e d by by deformation and tthe h e case case of of the the Peavy Peavy Pond t r u s i v e (Fig. 3 ) . The Pondi nintrusive (Pig. 3). of subhorizontal subhorizontal crenulation cleavages cleavages dipping away away from the Peavy Peavy Pond related Pond stock can reasonably be related of tthe Pondiintrusive. tto o the emplacement emplacement of h e Peavy Peavy Pond n t r u s i v e . So So iitt isisreasonable reasonable enough enough tto o bbelieve e l i e v e tthat h a t the the presence of subhorizontal crenulation c r e n u l a t i a i cleavages cleavages presence of subhorizontal dipping away from l s o the t h e result r e s u l t of of from hAmasa s a Oval is aalso Archean basement p l i f t even even though this t h i s uplift u p l i f t was was basementuuplift by any detectable any d e t e c t a b l e thermal thermal not accompanied by aactivity. c t i v i t y . In the t h e Peich Felch trough, trough,Calumet Calumet trough trough and and Taylor mine, subhorizontal cleavages Taylor mine, the the subhorizontal cleavages may nay aalso lso be related r e l a t e d to t o mobilization mobilization of crystalline be of crystalline basement. But d i f f i c u l t to to basement. n these But iin theseareas, areas,itit is difficult doiint the exact piece of pin down h e exact of basement basement involved. involved. This phase of deformation can subdivided iinto nto This phase of deformation can be be subdivided different d i f f e r e n t sets s e t sof ofsubhori.zontal subhorizontal crenulation crenulation cleavages based on which which part p a r t of basement uuplift plift baaed an of basement Deformation in Florence—Niagara and Deformation i n the the iniogeocline, miogeocline, Florence-Niagara and Crystal Crystal Falls Falls terranes. terranes. �—7— that t h a t each set s e t is is related r e l a t e d to. to. Rowever, However, cross—cutting cross-cutting relations r e l a t i o n s among among cleavages cleavages indicate indicate that t h a t the the time time slot s l o t for f o r formation formation of of these these subhorizontal subhorizontal cleavages cleavazes was was confined between between deformations, 14. Therefore Therefore it it seems seems that that F2 and andF4. deformations, 12 Archean Archean crystalline c r y s t a l l i n e basement basement of of the the study study area area was was regionally in the t h e Cit CFt (where no no regionally remobilized, renobilized, except in crystalline c r y s t a l l i n e basement if i f exposed), exnosed). during during this t h i s phase phase of s u b h o r i z o k a l ccleavage l e a v a g e in i n tthe h e INt FNt . o f deformation. deformation. Subborizontal problematic, but may maya also ber related problematic, but l s o be e l a t e d tto o this this period of regional period of regional uuplift. plift. is is The 14 deformation is marked marked by by sporadic sporadic The F4 deformation is occurrences steeply dipping occurrences of of NW—striking, NW-striking, steeply dipping minor minor fold erenulation planes, planes, fold axial a x i a l surfaces, surfaces,kink, kink. and andcrenulatiom which cross—cutppreexisting which cross-cut r e e x i s t i n g ffabric. a b r i c . The The solid solid evidence is shown shown by by refolding evidence of of this t h i s deformation is or or crenulating crenulating 13 F3 subhorizontal subhorizontal crenulation crenulation cleavages. minor folds folds observed observedinin the the ffield F4 minor ield cleavages. 14 70 degrees degrees to have apical angles angles ranging ranging from from 70 t o 120 120 have degrees. is represented represented by by aa set s e t of of F5 deformation deformation is 15 crenulations and steeply-dipping NS—striking US-striking crenulationa andsome some steeply—dipping open folds with open folds with apicat a p i c a l angles angles greater g r e a t e rthan than100 100 Fold pprofiles r o f i l e s indicate i n d i c a t e that t h a tmost most of of 15 F5 degrees. Fold Crenulation folds 1B and and lC 1C folds. Crenulation folds are a r e type type 13 cleavages of this cleavages of t h i sdeformation deformation range range from from a a zonal zonal cleavage tto o discontinuous, discontinuous, discrete discrete crenulation cleavage cleavage and is i scoenonly connonly present present whenever whenever the t h e 31 31 cleavage and surfaces EW. EW. surfaces are a r eoriented oriented In phasea of of I n spite s p i t e of of the the fact f a c t that t h a tfive f i v ephases deformation wererecognized recognizedi nintthis deformation were h i s region, only only the twoepisodes episodes of ofdeformation defoimation 11, Fl, and and 12, F2, t h e first f i r s ttwo were were eeffective f f e c t i v e in i n constructing constructing the the regional regional structural s t r u c t u r a l features. features. The extremely intense extremely i n t e nNNE—SSW s e NMB-SSW oriented of FFll constructed oriented shortening shortening regime regime of constructed aa series trending tright s e r i e sofofWNW WMU trending i g h t folds folds and and shear shear zones zones which which sometimes sometimes involved Archaen Archaen basement baaemant such as as the Oval, and Creek Uplift. Uplift. The the Amasa Amasa Oval, and Smith Smith Creek The 12 72 deformation folded the the eexisting 11 structural deformation cross croasfolded x i s t i n g F1 structural •f1O •XO$ trending features f e a t u r e s and locally l o c a l l y rotated r o t a t e d them them into i n t oNNW NNW trending structures. The crossfolding crossfolding origin o r i g i n of of Amasa Amasa Oval Oval s t r u c t u r e s . The instead is supported supported by by the the i n s t e a d of of gneiss gneiss doming doming is following following observations: observations: 1. The The ffact a c t that t h a t structures s t r u c t u r e s in i n strata s t r a t a of of the the Supergroup mantling mantling the Marquette Range Marquette Range Supergroup t h e Archean Archean basement of the Oval iindicate basement of the Amasa Amasa Oval ndicate crossfolding. crossfolding. 2. A NNW A sset e t of ofpenetrative penetrative NNW trending trending s u b v e r t i c a l foliations, f o l i a t i o n s , which is is pervasively pervasively subvertical developed developed in i n the the sediments sediments mantling mantling the the basement, is is found to t o be cross—cut cross-cut by later later deformation deformation fabrics f a b r i c s 52, S2, S3. S3. Both the the cross—cutting cross-cutting relations r e l a t i o n s and and the the correlation correlation with NNW trending trending Fl F l folds folds in i n Crystal C r y s t a l Falls Falls t e r r a n e indicate i n d i c a t e that t h a t this t h i s is a set s e t of of rotated rotated terrane Si S l foliations. foliations. 3. The The same same set s e t of of NNW NNW treading l i a t i o n s is is 3. trendingf ofoliations t h e most most prevalent prevalent foliation f o l i a t i o ndeveloped developedini nAmasa Amasa the Oval Oval Archean Archean basement. basement. 4. 4. Lack Lack of metamorphic metamorphic aureol aureol related r e l a t e d to t o Amasa Amasa Oval Oval discredits d i s c r e d i t s the t h e possible origin o r i g i n by by gneiss gneiss doming. doming. 5. The The subhorizontal subhorizontal crenulation crenulation cleavage cleavage 5. r e l a t e d to t o basement uplift u p l i f t cross—cuts cross-cuts which was related the NNW trending trending 31. Sl. t h e NNW The The presence presence of of 53 S3 subhorizontal subhorizontal cleavages cleavages in in t h i s region region indicates i n d i c a t e s that t h a t basement uplift u p l i f t presided presided this over over the the miogeocline miogeocline once. once. Rowever, However, the the major major structural s t r u c t u r a l features f e a t u r e s in i n this t h i s region region were constructed constructed mainly by o r i z o n t a l shortening shortening p r i o r to to mainly by periods periods of of hhorizontal prior basement basement uuplift. plift. Florence—Niagara Terrane Florence-Niagara Terrane The Florence—Niagara Florence-Siagara terrane t e r r a n e consists c o n s i s t s of of at at The e i g h t fault—bound fault-bound slices s l i c e s striking s t r i k i n g NU (Bayley eight NW (Bayley least least and and others, others, 1966; 1966; Dutton, Dutton, 1970; 1970; Larue Larue and and Gang, Ueng, in in prep.) is based based on on prep.) (Fig. (Fig. 4). 4). Recognition of faults f a u l t s is truncation truncation of of regional regional stratigraphy s t r a t i g r a p h y(Fig. ( f i g . 2A) 2A) (Bayley (Bayley and and others, 1966; 1966; Dutton, Dutton, 1970), 1970), changes changes in in structural or fabric f a b r i c across lithic lithic s t r u c t u r a l style s t y l e or boundaries, boundaries, and and stratigraphic s t r a t i g r a p h i c relations r e l a t i o n s (Larue (Lame and and Gang, Ueng, in i n prep.), prep.), as as discussed discussed below. below. Fault slices slices 3, 3, 7 and and 7A 7A are a r e defined defined on on the the basis b a s i s of of stratigraphy s t r a t i g r a p h y each represents shallow-marine to to fluvial f l u v i a l quartzices q u a r t z i t e scontiguous contiguous on on both both sides s i d e s with with apparently volcanogenic sslates apparently deep—water, d e e p w a t e r , volcanogenic l a t e s (Larue, (Larue, 1983). Contacts Contacts are a r e sharp, sharp, though no no obvious obvious 1983). P*it Rlv.r 3rou (Iron ormatton In bleci ,. 3ew.s, Gessnajon. MIhism,,. 31MlchlgçmmSlat. (quartzjt. ( q ~ r t ~ $tIDDI.d) Â¥tIpohd i f M•nomi• GrOUD Menominee aroup \.sdIm.ntary conteCt MOUNTAIN CllocoI.y Groi,p Pandall,. Dol.m*t. Contact Fig. 4. Geology of the Florence—Niagara terrane. �—8— truncations truncations aare r e present. present. All A l l fault f a u l tpackets packets except except packet 88 contain contain homoclinal homoclinal south—facing south-facing sstrata. trata. block, contains 3abbitt block, Packet 8, 8 , tthe h e Bessie Bessie Babbitt contains aa major fold. fold. Your Four different d i f f e r e n t types types of of structural s t r u c t u r a l fabric f a b r i c are are A l l are a m characterized characterized by by recognized in i n the t h eYNt. FNt. ALL aa dominant cleavage,oor byaaxial surfaces tthat dominant cleavage, r by x i a l surfaces hat Elongation lineationa lineations and steeply. Elongation sstrike t r i k eW—NW W-NW and d idip p steeply. associated associated with with such such foliations f o l i a t i o n splunge plunge down down ddip i p in in all where bulk bulk extension extension a l l cases cases except except in i npacket packet1,1,where fold axes, axes, aa llocally o c a l l y parallels p a r a l l e l sshallowly—plunging shallouly-plunging fold probable product of probable product of superimposed superimposed sstrains trains axes in packets packets 1) VoId f o l d axes (compaction andtectonic). tectonic). 1) (compaction and 1 and and 55 are a r e aubhorizontal subhorizontal or or shallowly shallowly plunging, plunging, 2) -Fold Fold axes axes in i n packets packets 22 NW—SE. 2) and trend E—W and E-W tto o HW-SE. and 77k plane (Fig. (Fig. 6B). 6B). and A are a r e girdled girdledini a n NW—SE a SW-SE plane Si, Sl, IN Mn I TT1S It Geologic map arly P r o t e r o i o i c rocks rocks Fig. mapofofeearly Proterozoic Fig. 5. 5. Geologic IM), MI, (?I, Iron Mountain Mountain ((IN), near Iron MI, Florence Florence (F), WI, and Niagara (N), WI. UI. WI, and Niagara (N), Florence-Uiagara Florence—Niagara (FH) Fault separates separates passive passivemargin margin (FE Fault assemblage assemblage to t o the thenorth north(Miogeo/Cracon (Miogeo/Craton— - autochthonous sedimentary sedimentary cover cover of Superior FNt = Superior Province basement; basement: YNt Florence-Niagara t eterrace; r r a e ; CFt Florence—Niagara Cit • Crystal Falls F a l l s terrace) t e r r a e )from frommagmatic magmatic aarc r c terrace terrane (mt) ranitoids (me) to t o the the south south (stipples ( s t i p p l e s— g granitoids and gneiss; ma netasedimentary rocks; rocks; gg and gneiss: os - metasedimentary = gabbroic gabbroic ssuite; u i t e ; v — metavolcanic schiacs). boundshigh high sstrain s c h i s t s ) . Jagged line l i n e bounds train belt e i t h e r side of of the the b e l t developed on either fault; f a u l t ; queried line l i n e denotes tentative tentative location location of boundary. Solid Solid llines ines bounding passive margin terranes and passive margin terraces and within FTNt U t are a r e faults; faults: ssolid o l i d Lines l i n e s in i ntat mt within aare r e lithologic l i t h o l o g i c contacts (after ( a f t e r K. Schulz K. Schulz and and P. S k , unpub. unpub. map) h a t way may aalso l s o be P. Sims, map) tthat ffaults. a u l t s . as * locations locations of slickenside slickenside sstriations t r i a t i o n s used used in i n stress s t r e s s axes axes calculations ext). V e r t i c a l l y lined lined calculations (see (see ttext). Vertically pattern denotes a u l t sslices l i c e s in in denoteslow-strain low-strainf fault TNt. FNt. - - - - • Fig. 66 Fig. 6*—c. Lower hemisphere stereographic 6a-e. stereographic Dl p r o j e c t i o n s of structural s t r u c t u r a l data d a t a for f o r Dl projections (accretion-related) deformation. C ircles (accretion—related) Circles - = ffold o l d axes; axes; squares squares— poles tto o aaxial xial 1, 2, 3 axes of the stress ellipsoid; Z are axes of strain eellipaoid. l l i p s o i d . a. a. miogeosyncline/craton miogeoayncline/craton folds; b. TNt folds; b. FHt folds with inferred i n f e r r e d X, Y, ZZ I, Y, sstrain t r a i n axes: s t r e s s axes axes from axes; c. c. FNt TNt stress fton slickenside sstriations t r i a t i o n s with with inferred i n f e r r e d951 95% slickeneide confidence i r c l e s ; d. d. tat m t folds; e. mt confidence ccircles; e. tnt stress s t r e s s axes. axes. surfaces; r e axes of the s t r e s s surfaces: 1, 2, 3 aare X, Y, e l l i p s o i d ; X, Y, Z a r e axes of s t r a i n intermediate aaxis of sstrain) have ((parallel p a r a l l e l tto o tthe h e intermediate x i s of t r a i n ) have been strained s t r a i n e d toward the direction d i r e c t i o n of of finite finite axes pparallel extension. Fold Fold axes a r a l l e l to t o the t h e intermediate intermediate extension. aaxis x i s of strain s t r a i n rotate r o t a t e less l e s s than t h a nthose t h o s e askew, askew, thus thus aa of fabric girdled The oorigin r i g i n of fabric girdled ddistribution i s t r i b u t i o n results. r e s u l t s . The understood, but but measured is poorly poorly understood, measured sstrains trains type 33 is indicate i n d i c a t e X/Z X/Z rratios a t i o s of of up up to t o 10, 10, and and therefore t h e r e f o r e the the fabric f a b r i c is is aalso l s o related r e l a t e d to t o large l a r g e strains. strains. Fabric representedi in seems represented n ffabric abric 3 3 with with aa Fabric 4 seems are 4, 6, 6, and 77 a 3) Fold axes in packets 3, 3, 4, r e steeply steeply 3) downthe theregional regional ffoliation. oliation. inclined and plunge plunge down in packet 8 also 4) Fold Fold axes in packet 8 a l s o plunge steeply but have been by cross—folds cross-folds with *4 N-S axial axial been complicated by The ffirst planes. i r s t three t h r e e fabrics f a b r i c s (1—3) (1-3) are are planes. The of ddifferent interpreted as a s products products of i f f e r e n t strain strain f a b r i c 2) 2) histories. h i s t o r i e s . The girdled fold axes ((fabric represents the the highly highly sstrained equivalent of of the represents t r a i n e d equivalent the f i r s t ffabric a b r i c type type (for ( f o rexample, example, Sanderson, Sanderson, 1973). 1973). first That iis, That s , initially i n i t i a l l ysubhorizontal subhorizontal fold foldaxes axes superposed superposed deformation deformation about about aaN—S N-S aaxial x i a l plane plane folds with planes aare (S2). Minor Minor folds with N—S N-S a xaxial i a l planes r e not (52). present elsewhere present elsewhere in i n the the FNt. Crenulations with TNt. Crenulacions aaxial x i a l surfaces surfaces parallel p a r a l l e l to t o those those described described in i n the the iniogeocline (12—V5) present sporadically, miogeocline (F2-F5) era a r e present sporadically, but but age age rrelations e l a t i o n s can not be specified s p e c i f i e d other other than than post—Si. pos t-Sl. FTNt. Nt. Metamorphism was relative Metamorphism r e l a t i v e complicated complicated in i n the the Early folding was not associated with �—9— Cross-folds iin n packet packet 88 significant s i g n i f i c a nmetamorphism. t metamorphism. Cross—folds pre—dated p r e d a t e d garnet grade grade metamorphism. metamorphism. S S ttrtke—s r i k e s llLp ip faulting f a u l t i n g(NW—striking) ( W s t r i k i n g ) with withassociated associated garnet garnet grade grade metamorphism metamorphism is is observed observed in i n packet packet 4. 6. Slickensid. Slickenside striations s t r i a t i m son on faults f a u l t swere -re studied studied (ma Fig. 4), calculated from (m i ninFig. 4 I yand and mean mean sstress t r e s s axes axas calculated from such data (technique of A. A. Michaels, Michaels, submitted). submitted). such data (technique of Results are a r e shown shown iinn Figure Figure 6C, 6C, and and stress s t r e s s axes axes Results parallel p a r a l l e l strain s t r a i naxes. axes. Magmatic Terrane Mamatic To To aa first f i r a approximation, t approximation, the thenorthern northern edge edge of of the terrane cam be bbest the magiaatic magmatic terrane can be e s t thought thought of of as a s aa wide highly highly strained 2-4 2-6 km km wide s t r a i n e d zone z m e that thatstrikes s t r i k eN7OW, s U7W, parallel (Fig. 53). p a r a l l e ltot othe t hFlorence—Niagara e Florence-Niagara FFault a u l t (Fig. 5B)In In detail, d e t a i l , the t h e penetrative penetrative vvertical e r t i c a l foliation f o l i a t i m that that defines ha8 been been refolded refolded defines the t h e shear shear zone zone fabric f a b r i c has about duringa asubsequent subsequent about subvertical subverticalaxes axes during deformation deformation event. went. In I n this t h i sregion region aa dominant dominant sstructural t r u c t u r a l feature f e a t u r e is is Gneiss dm*, done, which which SSims (pers. come., the t h e Dumbar Dtmbar Gneiss i w (pers. c~nm.~ 1982) 1982) invokes invokes to t o accoimt account for f o r variable v a r i a b l e foliat3.on foliation attitudes a t t i t u d e s at a t the the edges edges of of the the gneiss gneiss body. b*. Relative andl alater Relative timing timing of of gneise gneiss doming doming and t e r folding folding of the is the penetrative penetrative ffoliation o l i a t i a t near near the the fault f a u l t is unresolved. unresolved. Structural S t r u c t u r a lSynthesis Synthesis of of the the Magmatic Mamutic Terrane. Terrane. The D l , produced produced The eearliest a r l i e s t recognizable recornizable deformation, d e f o r m t i a x , Dl, aa penetrative, WNW—striking penetrative, subvertical, s G v e r t i c a 1regionally , regionally WlW-striking foliation f o l i a t i o n Si Sl with with aa steep steepdown—dip dom-dip mineral mineral B d i n a g e and and dismembered dismembered i sisoclinal oclinal lineation l i n e a t i o n 1.1. Ll. Boudinage folds indicate Early indicategreat g r e astrain t s t r a iaccompanied n accompmiedDI.. D l . Early metamorphism wassynkinamatic synkineaatic with with Dl D l and aad metamorphism MlMlwas probably attained amaphibolit. probably attained amphibolite ffacies a c i e s PT P-T conditions. Subsequent open opea to t o tight t i g h t folding folding conditima. Subsequent comprised 32; these these folds folds range cm to t o km km in in cmprised D2; range from f r m cm wavelength, have subvertical subvertical axes, wavelength, have axes, and and do do not not signify signifyaapenetrative penetrativedeformation defonnatim event. went. Retrograde M2, generated generated Retrograde thermal t h e w 1metamorphism, metamorphism, M2, randomly oriented amphibole amphiboleand andc hchlorite randmly oriented l o r i t e that that overprint It is is not not M l metamorphic metamorphic fabric. fabric. It overprint the Ml known orsyn—32. SF-D2. known whether 112 M2 iiss post— post- or Several Dl Several sstructural t r u c t u r a l features features indicate i n d i c a t e that t h a t Dl accompanied accompanied bybyggreat r e a t sstrain. t r a i n . Isoclinally Isoclinally folded folded compositional compositional layering and, and, in i n some some mnetaseditnencary metasedhentary rocks, rocks, bedding, bedding, is is almost almost always almys was was The The rresultant e s u l t a n t boudins bdins have or major major planes planea oriented oriented have ttheir h e i r long long axes axes or tectonically t e c t o n i c a l l y dismembered. dismembered. parallel p a r a l l e l to t o the the penetrative penetrative SSl l ffoliation. o l i a t i o n . Pressure Pressure shadows aroundsaue some mineralgrains grainslend lend support support ttoo shadows around mineral an of Ll an iinterpretation n t e r p r e t a t i o n of Ll as as a a stretching s t r e t c h i n g lineation. lineation. Finally, Finally,when when 32 D2 folding folding is is removed, removed, Dl D l fold axes axes define a great great circle c i r c l e distribution d i s t r i b u t i o n within aa constant N7OW N70W constant mean mean aaxial x i a l surface surfaceofofapproximately approximately (Fig. (Fig. 63). 6D). Renoval 3eanoval of of 32 D2 folds folds also a l s o yields y i e l d s aa point point maximum lineations plunging plunging maximum of of mineral mineral (stretching) ( s t r e t c h i n g ) lineations steeply steeply southwest. southwest. From From this t h i s geometry geometry we we infer infer axes D l to t o be XX axes of of the the strain s t r a i n ellipsoid e l l i p s o i d during during Dl subvertical, WNW—ESE, subvertical, Y subhorizontal subhorizontal WUW-ESE, and and ZZ corresponds with subhorizontal subhorizmcal NNE—SSW. NNE-SSW. Hence Renee XX corresponds with with S Sl, Ll, XY plane plane corresponds corresponds with l , and and the the Ll, the the XY shortening shortening direction d i r e c t i o n ZZ lies l i e n roughly roughly normal nonnal to t o 1170W N70W and Fault. and the Florence—Niagara Florence-Niagara Fault. Further Dl Further support support for f o r this t h i a orientation o r i e n t a t i m of of the t h e Dl strain s t r a i n axes axes was was recently recently obtained obtained from from slickenside slickenside striations m t . Using Using aa s t r i a t i o n s on on minor minor faults f a u l t s in i n the the at. computer computer program program developed developed by by Andrew Andrew Michael Michael of of Stanford Stanford University, we we calculated calculated axes axes of the the stress 1, 2, 2, 3) 3) that t h a t coincide coincide s t r e s s ellipsoid e l l i p s o i d (sigma (sigma 1, almost exactly with the strain Y, and X 2, Y, X s t r a i n axes, axes, Z, (Pig. (Fig. 6E). 6E). The close c l o s e agreement agreement of of axes axes markedlyddifferent orientations o r i e n t a t i o n s derived derived from f r a u two two markedly ifferent techniques, coupled with the the tiny t i n y 95% 95% confidence confidence circles c i r c l e s for f o r the t h e sigma sigaa values, values, strongly strongly indicate indicate NNE—SSW NNE-SSW shortening shortening and and subvertical s u b v e r t i c a l extension extension during during Dl. Dl. The earliest e a r l i e s tmetamorphism, metamorphism, Mi, M l , was was synkinematic synkinematic The Dl D l as a s evidenced evidenced by by alignment alignment of of relict relict amphibole mphibole grains g r a i n s within within the t h e Si S l foliation f o l i a t i mplane planeand and p a r a l l e l to t o Li. Ll. In I n thin t h i n section, s e c t i m , however, however, lLttle little parallel or or none of of the t h e original o r i g i n a l MMl 1 mineral assemblage can be be identified i d e n t i f i e d due due to t o retrograde retrograde metamorphism metamorphism during during with with M2. 112. During D2, D2, Dl D l layering layering was was folded folded about about subvertical s u b v e r t i c a l axes both at a t outcrop a t c r o p scale, s c a l e , where close close t o open open cm an to t o meter wavelength wavelmgth folds folds are a r e observed, observed, to and at a t map map sscale, c a l e , where wherehomogeneous hmogeneous domains domaim having and variable, but always always steep, steep, orientations o r i e n t a t i o n s of of Dl Dl foliation/layering f o l i a t i o n / l a y e r i n g are a r e best b e s t explained explained as a s limbs limbs of of open folds f o l d s with with wavelengths wavelengths measured measured in i n kin. km. Axial Axial open surfaces of of these these folds f o l d s are a r e variable v a r i a b l e but usually imply No penetrative penetrative imply E—W E-W to t o NW—SE W S E shortening. shortening. No S—surface acccmpanies 32. D2. S-surface or lineation l i n e a t i o naccompanies The preponderance prepcaderaace of randomly—oriented randomly-oriented green green amphibole andc hchlorite rocks ofof aall amphibole and l o r i t e i in n rocks l l lithocypes lithotypes suggests s q g e s t s tthat h a t the the magnetic magmatic terrane t e r r a n e experience experience late late N l amphibolite amphibolite thennal metamorphic metamorphic r retrogression e t r o g r e s s i m of Ml thermal facies f a c i e sassemblages assemblages tot o112 M2 greenschist facies facies assemblages. We havewnoddirect We have i r e c t evidence evidence ppertaining ertaining to M2 iiss post— post- or syn—D2. SF-D2. t o whether whether 112 AL& present present in i n the t h e magmatic magmatic terrane t e r r a n e are a r e local local Also areas in inwhich which crenulations c r e n u l a t i m s are a r edeveloped developed that that areas appear tto o be a r a l l e l to t ocrenulation c r e n u l a t i mcleavages cleavages in in appear be pparallel the FNt. However, miogeocline and and TNt. t h e miogeoclin. Hwever, we we do do not not have have enough data data at a t present present to t o conclude conclude whether whether aall ll enough def-tim phases obsemed n the the miogeocline miogeocline are are deformation phases observed iin present m t , and and whether whether the t h e ordering ordering of of present iin n th. t h e at, these these events events is similar. similar. RICH STRAIN BELT: NATURE OF THE 1ff—TNT BOUNDARY. The TNt mt and and northern northern tnt m t define aa high high as ttrain rain The b e l t , where fold fold axes axes have have been been locally l o c a l l y strained strained belt, i n t o parallelism p a r a l l e l i s u with with the the direction d i r e c t i o n of of finite finite into extension (Fig. (Fig. 5)(Larue 5)(Larue and and Ueng, Ueng, submitted; submitted; extension Sedlock and and tarmac, Larue, 1983). 1983). Other Other features features Sedlock associated with t h i s g r e a t s t r a i n a r e isoclinal isoclinal assocated with this great strain are folds, dismembered dimembered folds, f o l d s , type type 22 and and 33 folds folds (of (of folds, Ramsay, 1967) 1967) and and transposed layering. layering. Large Rainsay, Large thome inferred i n f e r r e d here here occur occur only only s t r a i n s such such as as those strains r a r e l y in i nrocks rocks north north of of the the FNt. FNt. The rarely The southern southern bomdary ofof the s t r a i n belt b e l thas hasnot notbeen been boundary the high high strain adequately defined. defined. We adequately conclude that F N ~and and We conclude t h a t the the FNt northern northern part part of of the t h e met m t represents represents a a high high strain strain belt b e l t straddling straddling the the Florence—Niagara Florence-Niagara Fault. Fault. is developed developed within within the the northern zone zone (FNt) (F'!?t)is northern me The miogeoclinal mna.ogeoclinal assemblage rocks, whereas the southern assemblage rocks, whereas the southern zone aaffects f f e c t s only onlyarc a r cassemblage assemblage rocks rocks (northern (northern zone part p a r t of of tnt). mt). Structural S t r u c t u r a l fabrics f a b r i c s are a r e nearly nearly @ig. 63—f). 6B-E). This i d e n t i c a l(Ftg. Ldentcal This high high strain s t r a i n belt belt probably formed formed during during terrane terrane accretion. accretion. probably Other zones zones of of high high strain s t r a i n including including shear shear Other zones occur occur locally l o c a l l y throughout throughout the t h e miogeocline and zones miogeocline and represent zones zones of of increased increased sstrain train probably represent resulting frcm localized localized weaknesses weaknesses in i n the the basement. basement. r e s u l t i n g from CEOCHE1fISTRY GEOCXEMISTRY Provenance of of Marquette Marquette Range Range Supergroup Supergroup Provenance �-10— sandstones sandstones is not not well wallconstrained constrainedbecause because Provenance Provenance studies s t u d i e s using using slate s l a t e geochemistry geochemistry have have been been made made by by Carrels Garrels and and MacKenzie MacKenzie (1971), (19711, Cameron Cameron and and Carrels Garrels (1981) (1981) and and others,, others,. who who used used geochemistry geochemistry to t o separate separate slates s l a t e s of of volcanic volcanic and and I n our our study, study, we we made made 106 106 continental continental provenance. provenance. In ternary 7) a r e showu shown (Pig. (Fig. 7) ternary diagrams diagrams of of which which 4 are diagenesis diagenesis and and metamorphism metamorphism has has altered a l t e r e dand and destroyed fragments such such tthat destroyed 1.LthLc l i t h i c fragments h a t modified modified assemblages exist. Petrographic assemblages exist. Petrographic studies s t u d i e s of of only mly s l i g h t l ymetamorphosed metamorphosed sandstones n d i c a t e s an an slightly sandstones iindicates older Precambrian Precambrian source for f o r the theChocolay, Chocolay, older Menoininee (Lame, 1981) Menominee (Larue, 1981) and and Baraga Baraga Groups Groups (Alvin, (Alwin, 1979). 1979). Rovever, Emever, aa ssignificant i g n i f i c a n t portion poztion of of the the late, Marquette Range Range Supergroup Marquette Supergroupisis represented represented by by sslate, whose provenance i f f i c u l t to to whose provenanceisis extremely extremelyddifficult establish e s t a b l i s hpetmographically. petrographically. To To try t r y to t ocharacterise c h a r a c t e r i z ethe theprovenance provenance of of the the slates, samples wesent seatabout about6060 samplesfrom f r a nthroughout throughout s l a t e s ,we average average argillite, a r g i l l i t e , average average granite g r a n i t e and and average average green. the Canadian Canadiau shield s h i e l d (Roaov (Ronov and and g r e e n stone t m e from from the Migdisw, 1971). 1971). In In addition, addition, analyses analyses of of the the Migdieov, 3adwater Badwater Greenstone Greenstone are a r e plotted p l o t t e d ini nFigure Figure7.7. Sample. our study study are a r e mostly mostly from f r a n the the Samples used used in i n our areas areas discussed discussed herein, herein, but but we we also a l s o included included samples samples from f r a u the t h e Marquette trough trough (especially ( e s p e c i a l l y the the S i a o Slate S l a t e of of the the Menominee M e n d n e e Group Group which which underlies underlies Siamo the t h e Negatntee Negauuee Iron Iron Formation). Formatirm). sectiai to t o the the the early e a r l yProterozoic Proterozoic section th. Barrangem—Maj antsCorporation, Corporation, who Barrmger-Majenta who made made major and and t r a c e element element studies s t u d i e susing usinginduced inducedcoupled coupledplasma platrace techniques (ICP). Several Several duplicate duplicatesamples sampleswere were techniques (IcP). sent 45%. Ton Tau Vogel Vogel sent and and errors e r r o r s were = r e in i n all a l cases l cases<5Z. Two Two basic basic populati.ons populations are a r e recognized recognized in i n the the (Michigan has (Xichigau State S t a t e University, . , 1980) 1980) has university, per¶ pers.e m c., ternary ternary diagrams diagrams presented presented herein herein ini nwhich which formational f o r n a t i o n a l groupings groupings occurred. occurred. Slates S l a t e s interbedded interbedded had had similar s i m i l a r success success with with them. than. CaO representing representing different d i f f e r e n tcombinations c m b i n a t i o n s of of major major and and minor elementsofof the the sslates, minor elements l a t e s ; and and also a l s o plotted plotted •2O K20 !m CU U B 5sdw s...i_ • Hdi U cI. C £ A Mu,amli. • Waws S o amco.y S avenge Thom, .. K,0 Fig. Fig. 7 7 Ternary Ternary plots p l o t s of of slate s l a t e geochemistry. geochemistry. 1(20 �—11— with ultramature ultramature quartzites q u a r t z i t e s and m d dolomites d o l d t e s ofof the the with ChocolayGroup Groupgenerally generallyplot p l o tini na atight t i g h tcluster cluster Chocolay Such near composition composition of of the theaverage averagegranite. granite. Such near potassic and andalulaLnous aluminous slates s l a t e swere wereprobably probably pOtasSC i l l i t i and c , and derived from a continental o r i g i n a l l yillitic, originally derived from a continental source. Slates S l a t efrom s frm e M e n d n e eand andBarags Baraga thet hMencminee source. (includingHemlock Hemlock Slates) S l a t e s )seem seemtot orepresent represent mixed (including mixed Some slates s l a t e sfrom fram source-continental plus plus volcanic. volcanic. Some source—continental theSismo SiamaSlate S l a t ehave havebulk bulkgeochemistry geochemistry similar s i m i l a rtot o the greenstones, probably probably indicating i n d i c a t i n gaavolcanogenic vo1caogenic greenscones, source. Although Although volcanic volcanicrocks rockshave havebeen been source. e Group recognized in i nthe theupper upperpart p a rof t the of ttlenominee h e M e n d n eGroup recognized is the the first f i r s t indication i n d i c a t i m that that (Prinz, 1976), 19761, this t h i s is (Prinz, pre-irm formatim t r a t a , specifically s p e c i f i c a l l the y t hSiamo e Siaw pre—iron formation sstrata, Gairand and S l a t econtain containvolcanogenic volcanogenic material. material. Gait Slate Thadm (1968) (1968) proposed, proposed, also a l s o cm m the t h e basis b a s i sofof Thaden geochemistry, that t h a tcertain c e r t a iof n of WeweSlates Slates geochemistry, thethe Wewe (uppennostomit m i t of of the t h e ChocolayCroup Chocolay'Group ini nthe the (uppermost s i n g l edata data !hrquette trough) trough)were werevolcanogenic. volcanogenic. AA single Marquette p l o t t e dini nFigure Figure7.7. pointfrom fromGait Gair and and Thaden Thadm ia point is plotted SUMMARY This This study study establishes e s t a b l i s h e s that t h a tthe theProterozoic Proterozoic ininthe t h esouth southcentral c e n t r aLake l LakeSuperior Superiorregion region have have suffered suffereda acomplicated, complicated,polyphase polyphasedeformation deformation The exact exact tectonic t e c t o n i c interpretation i n t e r p r e t a t i o nofofeach each history. history. The deformation deformatim event w e n t is is not not yet y e tfully f u l l understood. y understood. However, it isi sclear c l e a rthat t h athe t t hCFt, e CFt,E'Nt, E N t ,tat, m t ,and a d However, it rocks rocks miogeocline miogeocline have have undergone mdergone parallel p a r a l l e deformation l deformation El, r d n g aall l l deformations deformations except except Fl, By removing h i s t o r i e s . By histories. some assemblages some interesting i n t e r e s t i n gtectonotithological tectonolitho1ogical assemblages are a r eobserved: observed:thet hnon—volcanic e non-volcanic miogeocline miogeocline (subterrane A), submarine (aubterrane A), submarine tholeiitic t h o l e i i t i cvolcanics volcanicsofof subterrane subterrane B; B; basin basin floor f l o o r deposits deposits (Crystal ( C r y s t a lFalls Falls terrane), t e r r a e ) ,highly highlystrained s t r a i n e dfault f a u lpackets t packets(TNt), (FNt),and and the NE NEtot oSW SW in i nsequence. sequence. t h emagmatic magmatic terrane, terrane,from from These These assemblages assemblages were were juxtaposed juxtaposed together together by by the the end end of ofdeformation deformation Fl. Fl. Lacer Laterdeformations deformationswere were responsible r e s p m s i b l e for f o r rotation r o t a t i m of of the theregional regionalstructural structural features f e a t u r e s (Fig. (Fig. 8). 8). appearsthat t h avolcanism t volcanism conclusim, ititappears InI nconclusion, occurred Marquette Range occu=ed sporadically sporadi&llythroughout th~oughm tMarquette Range appearsthat t h aChocolay t Chocolay S u ~ e r x r o sedimentation. us~e d b t a t i m . ItItappears Supergroup Group ~ r & - s sediments e d - h e n t s were were derived exclusively exclusivelyfrom f r a naa with aa continental(older (olderPrecambrian) Precambrian) source, source, with continental minor influx i n f l u xofofvotcanogenic volcanogenicsedimentation sedimentatim minor its depositional depositional history. history. occurring late l a t e ini nits occurring Uncmformably overlying overlyingMenominee M e n d n e e Group uartzites Uncouformably Group qquartzites a l s orepresent representpurely purelycontinental continentalprovenance, provenance, but but also Siama Slate S l a t e turbidites t u r b i d i t - contain containsignificant s i g n i f i c a namounts t amounts Siano yetriot notascertained) ascertained)ofofvolcanogenic volcanogenic slates. slates. (asyet (as Volcanics are a r e also a l s ointerstratified i n t e r s t r a t i f i with e d with Mendnee Votcanics Mencminee Group iron formation formatim in i nthe theGagebic GogebicRange h g e (Prina, (Prim, Group Baraga Group Group sslates l a t e s also a l s ocontain containboth both 1976). Baraga 1976). continentally-derived, mixed, mixed, and and continentally—derived, volcanogenically-derived slates s l a t e s•. Thus, Thus, volcanism volcanism volcanogenically-derived seema to t o have have been been significant s i g n i f i c a n t and and long—lived lmg-lived from frm seems M e n d n e e Group through Baraga BaragaGroup Group Menaminee Group through sedimentatim. Volcanic Volcanic rocks rocks of of this t h i sage ageare are sedimentation. knto represent continental tholeiites t h o l e i i t e abased basedon on knotin to represent otherstudies studies(Fox, (Fox,1982; 1982;Cudzillo, Cudzillo,1978). 1978). other Pejemim Fig. 88 Fig. AP 1i Pt P a l i n s p a s t i c restoration r e s t o r a t i o n of of the the southern southern Lake Lake Superior Superior region. region. Palinepastic I. Cuupare with with Figure Figure 1. Compare �—12— 15.5 Field F i e l d Trip T r i pRoad Road Log Log Mileage 0.0 Leave Dickinson Dickinson Inn, Inn, Iron Leave Iron Mountain, Mountain, Michigan Xichigan (Fig. (Fig. at—i) EL-1) 0.1 Eight turn onto (U.S. 2). 2). Right m t o Stephenson Stephenson (U.S. south). (Go (Go south). 4.2 4.2 Town of Quitmesec 4.6 4.6 Excellent continuous Fumee Creek. Creek. Excellent Fume8 continuous of Randvilie exposure. of Good exposures Randville Dolomite. Dolomite. Good (This will w i l l be be Stop Stop aalgal l g a l structures. structures. (This 4). 8 -4 Norway. Town Tom of Norway. 13.1 Turn S t r e e t 1. ,Turn Flashingl light Flashing i g h t ((State S t a t e Street). of Loretto. Loretto. Town of left. (North). Tom left. (North). 13.7 Right on Right m paved paved' road. mad. 14.8 Left on m gravel gravel road. road. at—I RL-1 Stop 11 Sturgeon Falls F a l l s dam. dam. Park at at to end of road. road.. Obtain permission to look at a t rocks from from dam dam keeper. keeper. Excellent exposures expoeures of of Archean granitoid basement. Fern Creek g r a n i t o i d basement. Formation, Formation, and, and, down down the t h e road road aa piece, piece, Sturgeon Quartzite. Quartzite. Fern Creek and basal Quartzite Sturgeon Q u a r t z i t e represent represent b asal umits u n i t s of the the Chocolay Chocolay Group. Group. Pettijohn This outcrop outcrop is is famous famous because P e t t i j o h n (1943) (1943) and Tray (1948) claimed claimed tthat and T r w (1948) h ~ the the t Fern Fern Creek Creek More recently, recently, represents glacial represents g l a c i a l sedimentation. sedimentation. More tarot L a r w (1981a) (1981a) suggested suggested an an alluvial a l l u v i a lorigin o r i g i nwas wasmore more appropriate. Because Because the t h e rocks rocks aatt the t h e damsite damsite aare re extremely deformed, deformed, compelling compellingddata i l l probably probably extremely a t a wwill us (U. Last suamer, one never never be presented. ~ r e s e n t e d . Last s-er, one of of us (D. Leaper) Kaaper) sspent i e n t one m e week week studying studying the t h e Fern Fern Creek Creek was as as aa section, and and concluded concluded tthat h a t the t h e sequence sequence was whole fining—upward(see (seeFigure FigureRL-21, at—i),but but tthat whole fining-upuard hat several fining—upward severalsmaller smaller fining-upward and andcoarsening—upward coarsaing-upward conclude the basal cycles are cycles a r e apparent. apparent. We We conclude t hthat a t the basal sections represents channelized channelized deposits deposits sec tiom representS sequences), whereas the (fining—upward (fining-upuard sequences), the upper upper sandier sections represent progradation p r o g r a d a t i m of of sandier sheet—like sheet-like sand sand bodies (coarsening upward package of of channelized o v e r a l l package channelized en overall sequences). Such an sequences). bodies, capped by sheet—sand sheet-sand bodies, capped by by bodies overlain by .- Location map LocatLon map of Stops Stops 1—5. 1-5. (Map (Map courtesy of tourist t o u r i s tbureau) bureau) courtesy of �—13— perhaps is also a l s o allowable. allowable. perhaps aa glacial g l a c i a l fan fan delta d e l t a is nearshore nearshore sands sands of of the the Sturgeon Sturgeon Quartaite Quartzite seems seems best best interpreted i n t e r p r e t e d as a s the the flooding flooding of of aa fan fan delta. delta. That is, aa fat fandelta d e l t awith withmore moreproximal proximal channelized channelized That is, gravels gravels and and d i s t a l sheet sheet sands, sands, feeding feeding aa nearshore nearshore environment, envircument, was was drowned drowned by by aa rise r i s e in i n sea sea level. level. The The Sturgeon Sturgeon Quartzite Quartzite is is also a l s o an an interesting interesting i t s great g r e a t thickness thickness (( 700 m) m) and and unit, because because of of its unit, 700 extremely unidirectional u n i d i r e c t i o n a l paleocurrents paleocurrents (directed (directed extremely SE). SE). The The sedimentology s e d h e n t o l o g y of of the t h e Sturgeon Sturgeon Quartzite Quartzite distal Although we prefer p r e f e r the the fan fan delta d e l t a argument, argument, Although we is is discussed in i nLarue Larue (1980). (1980). discussed lOmi til 4o - plane P1 PI — plane laminated laminated - rippled rippled rr— RL—2 RL-2 15.5 Stratigraphic Fern Creek Creek Foretatin Formation dam (Stop (Stop 1). 1). Fern S t r a t i g r a p h i c section section at a t Fern Fern Creek Creek dam topping Numbers here here are a r e facies f a c i e s described described in i nappendix. appendix. topping in i n Sturgeon SturgeonQiiartzite. Quartzite. Numbers Leave dam. Leave Sturgeon SturgeonFalls F a l l s dam. toward toward Loretto. Loretto. Go Go back back 16.5 Right Xight on on main main road. road. 17.3 Left Left on cm road road (back (back to t o toretto). Loretto). Right Right on m U.S. U.S. 22 at a t Loretto. Loretto. 22 • 4 234. Left Left on on Section Section Street S t r e e t (town (townofof Norway). Norway). Section Forest Street. Section becomes becomes Forest Street. Left cm Pine Pine Drive. Drive. Left on 23.7 - black mdstone black— mudstone i nnudstones mudstones t h i n l y bedded bedded sandstones sandstones in thinly black black with with bars bars — Stop Hanbury 2~? Slates S l a t e snear near HaaburyLake. Lake. As As Stop2A shown shown in In Figure Figure 4& of of the thetext, t e x tLariie , Lameand and Ueng (submitted) (submitted) separate the the Ceng fault-bomd Florence—Niagara Florence-Niagara terrane fault—bound terrane (FNt) from f r m the t h e other other rocks rocks of of the the (FNt) Marquette Marquette Range Range Supergroup Supergroup and and on waderlying Archean Archean basement, basement, based based on underlying differences in i n structure s t r u c t u r eand and lithology lithology differences FNt. The The separation separation of of obsemed in i n the t h e FNt. observed FNt from from the the rest r e s tofofthe theLake Lake the PNt the Superiormiogeoc miogeocline was based based in i n large large Superior line was h b u r y Lake. Lake. part on on studies s t u d i e s made made at a t Ranbury part S t r a t a exposed exposed at a t Hanbury Ranbury Lake Lakeare are Strata thought Michigame thought to t orepresent representthethe Michigamne Formation of of the t h e Baraga BaragaGroup. Group. However, Formation Hwever, unlikeother other MichigamaeFormation Formation unlike Michigataite strata, s t r a t a , rocks rocks ata tflanbury Ranbury Lake Lake include include q u a r t z i t e s (probably (probably turbidites) t u r b i d i t e s ) and and quartzites dolomites (deep—water?). (deep-water?). dolomites Deep-water Deep—water �—14— a r e not present present qquartzites u a r t z i t e s and and dolomites dolomites are elsewhere in i n the t h e Lake Superior Superior region region iin n the Michigarene Formation tto Michigame Formation o our our the lithology lithology of of knowledge. knwledge. Therefore, the not Lake is strata s t r a t a exposed exposed aatt Ranbury Ranbury Lake is not ddirectly i r e c t l y comparable ccmparable to t o Nichigarane Xichigamma Formation F o m a t i m sstrata t r a t a iin n the miogeoclinal miogeocliual Superior region region (north Lake Superior realm realm of the Lake (north E'Nt). of the FMt). Lake rocks aat Ranbury Lake Secondly, Secondly, the the rocks t Eanhry great have experienced g r e a t strain. s t r a i n . Fold Fold axes axes have been been stretched stretched into i n t o local local direction parallelism p a r a l l e l i m with with the the d i r e c t i a of of bulk bulk This extension. is not not observed observed This is elsewhere in the t h e Lake Lake Superior Superior region regia elsewhere in except except perhaps perhaps near near the theRepublic Republic Mine. Mine- a stretching s t r e t c h i n g direction d i r e c t i o n observed elsewhere. elsewhere. Bedding is is locally locally transposed into transposed i n t o the the foliation foliation (Fig. RL-3A). RL—3A). Quartz veins are (Fig. are boudinaged and bowlinaged and folded llocally. ocally. 24.0 24.0 Folds (Fig. (Fig. RL—33) XL-3B) have have axes axes sub—parallel of extension, sub-parallel to t o direction d i r e c t i o n of extension, have attenuated attenuatedlimbs, limbs,aare have r e ttight i g h t to to isoclinal, i s o c l i ~ land ,aud have have probably undergone great g r e a t ffinite i n i t e strain. s t r a i n . Larue and Ueng (in (in preparation) suggest X/Z X/Z rratios preparation) a t i o s of of around arouad 10 10 aare r e required required to t o account account for for the observed fabric f a b r i c and and structures. structures. Att Stop A Stop 2k, ZA, 1ev l w outcrops outcrops by by the the show examples examples of near Hanbuq Ranbury of slate s l a t e near rroad o d show WNW, and Foliation Lake. F Lake. o l i a t i m strikes s t r i k e s WIW* and dips dips wrinkle llimeation ineatian steeply south. south. A wrinkle downthe thef ofoliation, plunges ~ l u n g e adown l i a t i o n , pparallel a r a l l e l to to -- .- RL—3 I&-3 Stop 2B. bend in road. 2B. Park near near bend road. Ask Stop permission p e r m i s s i a tto o trespass trespass from from nice nice people people hill in i n house hcuse before curve. curve. Hike up hill behind house house tto o crest, c r e s t , down down to t o small small pasture, up to bill pasture, t o next low h i l l where spectacular folds folds are a r e exposed. exposed. Fold of Formation, Stop Stop 2. Fold of Nichigasmie Hichigame Formation, 2. 25.7 25.7~ Turn around and backtrack to t o U.S. U.S. 2. 2. Left on m U.S. U.S. 22 (go (go west). west). 27.6 27.6 Right turn turn m d i r t road a f t e r "Begin Only" Only1' sign. outcrop. orientation o r i e n t a t i m from frrm the the previous outcrop. Att Stop 2, f o l d axes are a r e girdled g i r d l e d in in a A 2, fold A t Stop Stop 3, 3, constant mean axial a x i a l plane. plane. At axes aare ffold o l d axes r e aall l l aubhorizontal subhorizontal in i n the the Larue and same mean mean aaxial x i a l plane. plane. Larue and Ueng Ueng (submitted) suggestt hthat (submitted) suggest a t tthere h e r e iis s aa sstructural t r u c t u r a l discontinuity d i s c o n t i n u i t y tthat h a t separates separates the highly the highly strained s t r a i n e d rocks rocks of of outcrop 22 with the t h e less l e s s strained s t r a i n e drocks rocks observed observed in in the Mianro Munro mine. on dirt road after + Stop St0 3. 3. Munro Munro mine. Bayley and others Baytey and 1966) consider that t h a t the t h e Monroe mine (1966) Monroe mine exposes only m l y Trader's Trader's Iron—bearing Iron-bearing exposes member Vulcan IIron r m Formation. Formation. memberofof the the Vulcan These rocks rocksaare These r e tthin h i n bedded, bedded* ssiliceous, iliceous, and are are ttightly and i g h t l y folded folded locally. locally. The The regional t r u c t u r e ofofthe i t is regionalsstructure theppit is a south—dippinghomocline homocline cauplicated complicated by south-dipping minor folds. folds. Fold axes axes plunge plunge subhorizontally, and a subhorizontally, x i a l planes planes dip dip axial steeply. Some box steeply. box folds present and folds aare r e present have x i a l plane. plane. have one onesubhorizontal subhorizontal aaxial Slickenside striations s t r i a t i o n s on bedding Slickenaida surfaces are a r e distributed d i s t r i b u t e d iin n aa plane plane perpendicular the fold axis. perpendicular tto o the R ~ KRofmaun, S O ~ ~ Utthe h,e Canadian Canadiau Rams stromatotite stromatolite expert, expert, told t o l d us us (lP8l) (1?81) that that ttrace r a c e fossils f o s s i l s had had been described described aatt tthis his locality, l o c a l i t y , but but together together we found found none. none. The principal p r i n c i p a l point of of this t h i s outcrop outcrop is is changeinin fold fold axis the marked marked change Go back back to t o U.S. U.S. 22 and and proceed proceed NW NW (turn (turn 29.7 29.7 rright). ight). Exposed at Stop 4. Creek. Stop Fumee Fume Creek. 4. Exposed a t Fiance Fumee an excellent excellenthomoclinal hmoclinal Creek is an south—dipping south-dipping s esectionof c t i o n . of Randvilla Randville dolomite, dolomite, iin n fault f a u l t contact contact with with Michigasme Michigame Formation (Bayley and others, others, This T h i s upper upper ppart a r t of of the t h e Randville Randville contains almost no no clastic c l a s t i c detritus. detritus. Minor folds with axes f o l d s ,with axes subparallel s u b p a r a l l e l to to a r e present present a t Stop Stop 33 are those observed at locally l o c a l l y in i n cherty cherty beds. beds. Algal Algal RL4) on on sstructures t r u c t u r e s aare r e exposed (Fig. (Fig. BL—4) the t h e railroad r a i l r o a d grade perpendicular to t o the the 1966). creek. creek.. �—1.5— 1L—4 Cr'tptalgal structures, Stop 4 Go back to car. Proceed NW on U.S. 2. 30.2 Turn right at tovn of Quinnesec. 33.1 Turn left at Lake Antoine Rd. 34.3 Stop at Randvifle Quarry. Stop 5. You could spend months studying this outcrop. Strained and folded algal structures, strained msdcracks, minor folds, intraclastic dolomite, mud—draped ripples (Fig. RL—5) • Mote the abundance of coars.—grainsd sand in this lover part of the Randville. The sand is feldspathic and derived from a gremitic source. Excellent exposures of Exudville Dolomite are also found on the island lO m to the WNW. Structurally, the most interesting problem here is that the algal structures have beet stretched parallel to local fold axes (trending U, plunging 15—40°)(Fig. RL—5A). Most stretching i.ineations in the Florence—Niagara terrane plunge about 70—90°W. Fold axis parallel stretching lineationi can occur when a coiitpac ted rock is then strained. Another interesting structure is one we call "tornado" structures (Pig. (Fig. RL—5E,F). RL-SE,F). These These are a r e deformed d e f d algal a l g a l stromatolites strmnatolitesthat t h a have t havebeen been folded in folded such such that t h a t they they look, look, in cross—section, cross-section, like l i k e aatornado tornado couching touchhg dove. features of down. Other Other deformation deformaticm features of the the stromatolites s t r m a t o l i t e s include include folding folding of of individual individuallaminae. laminae. These These stroisatolites strmnatolitesobviously obviously represent represent intertidal i n t e r t i d a lstructures s t r u c t u r e sbecause because they they are are interstratified i n t e r s t r a t i f i e dwith with and—cracked mud-cracked strata. strata. Another Another interesting i n t e r e s t i n g point point to to reflect m is is the the nonstrous mmstroua thickness thickness r e f l e c t on (700 Dolomite in (700 m) m) of of the the P.andville Randville Dolumite i n the the FNt. FNt. Was Was this t h i s really r e a l l y deposited deposited on on Sturgeon Sturgeon Quartzite? Quartzite? �-16— RL—5 RL-5 of strained Plan P l a vi.ew dsu of s t r a i n e d cryptalgal cryptalgal stronatolite s t r a u a t o l i t edomes. domes. Lineation Lineation plunges plunges A. A. about W. &andville Randville Dolomite, Doldte, about 300 300 V. Stop Stop 5. 5. 3,C. B,C. Cross—sections Cross-sections of of strained strained Folded cryptalgal c r y p t a l g a l structures, s t r u c t u r e s , Stop Stop 5. 5. 1). D. Folded cryptalgal c r y p t a l g a l lamination. laminatim. E,F. E,F. Tornado Tornado structures s t r u c t u r e s (folded (folded algal a l g a l co1mins). columns). . G. Molar Molar teeth t e e t h ini nRandville Randville1)oloiaite, Dolomite, Stop Stop 5. 5. Origin Origin unknown. mhown. Proceed on at Lake Lake Antoine Antoine Rd. Rd. which which Proceed beccmes Margaret becomes Margaret Street. Street. 35.7 35 •7 Turn rright i g h t at a t U.S. U.S. 2. 2. From From here at the the Turn here on f i e l d guide guide gets gem sketchy sketchy iin n that the the field individual males miles aren't a r e n ' t counted. counted. individual H o v e v e r , there ia only only on. onemore more stop stop Rovever, there is left left i n this t h i s field f i e l d trip. t r i p . (Fig. (Fig. RL—6 RL-6 is is aa in map). map). RL—6 RL-6 Drive onU.S. U.S. 22 for Drive NW NW at for approximately 15 miles miles uuntil approximately 15 n t i l you you reach reach In the the the t h e town tm of of Florence, Florence, Wisconsin. Wisconsin. In c e n t e r of of town, tm, take take County County Road Road N U south south center (turn ( t u r n left l e f tfrom fromU.S. U.S. 2). 2). Drive Drive for for about on NNuuntil n t i l iitt intersects intersects about 33 miles miles on County Comity Road Road D. D. Turn Turn tight r i g h t at a t UD and and proceed proceed for f o r about about 11 mile mile until u n t i l you you see see the D a m public public the road road to t o the thePine PineRiver RiverDam Map Map showing showing Florence Florence and and vicinity, v i c i n i t y , Wisconsin Wisconsin and and Stop Stop 6. 6. of local l o c a l tourist t o u r i s t bureau) bureau) (Map courtesy of �—17— * ;_-_—ø ..*NATICN r1 —. ,uT — ,I * —. I em— . •1 I I .—— — —- RL-8 RL—8 Pebbly sandstones sandstonesini n "Michigamue Pebbly "Michigamue Layering sketched sketched Fornmtim" at a tStop Stop6A. 6A. Layering Formation" —F— i n at a t left. left. in — — - .—— RL-7 RL—7 '4— a Nfl1 Blowup of of Fig. Fig. RL—6 m - 6 with with geology, geology, from from Slow-up Duttm, Duttoti, 0 1971. 1971. access (see (sea Fig. Fig. RL—6). m-6). Take Take this t h i s road road access ( i t only m l y goes goes south) south) to t o the theend end and and park park (it near the the water water (see ( s e a Fig. Fig. RL—7). RL-7). near Walk back back up up the the road road¼k mile atile until until Walk reach the hill crest, outcrops are m. off to t othe thewest west150 150u. off you reach the h i l l c r e s t , outcrops a r e you 0 x/Y 4. Stop 6a 6a Stop isan auexposure exposure of of Stop 6a 6a is Stop pebbly quartaitic q u a r t z i t i csandstones sandstones (Fig. (Fig. RL—8) RL-8) pebbly i n the t h eflichiganme Michigamne Formation Fonuatim of of the the in 0 00 0 0 Florence-Niagara terraue. The rocks rocks are are Florence—Niagara tarrane. The exposed in i na asouth—facing south-facing homocline, humocline, exposed kiltmeter i n maximum about half halfa akilometer about in maximum thickness. Strata S t r a t aare a r ecomposed composed of of thickness. pebble beds, beds, sandstone sandstone beds beds and a d pebbly pebbly pebble sandstone beds beds are arecoemomly cam~mly sandstone plane-laminated or or cross—laminated. cross-laminated. plane—laminated 2• Sediments aare r e extremely rare Sediments extremely quartzose, quartzoee, tare a r g i l l i t epebbles pebbles are a r epresent. present. argillite Depositim occurred occurred in i n shalloti shallcw water water Deposition (Nilsen, 1965), 19651, possibly possibly by by fluvial fluvial (Nilsen, processes. processes. Pebbles in i n the the quartzite q u a r t z i t ehave havebeen been Pebbles stretchedinto i n t cigar—shaped o cigar-shaped stretched ( c m s t r i c t i a a lstrain)(Fig. s t r a i n ) ( F i gRL—9). . RL-9). (constrictioital Such extreme extreme sstrains t r a i n smake make paleocurrent paleocurrent Such s t d i e a (Nilsen, (Nilsen, 1965) 1965) doubtful. doubtful. studies Go back t o the thedam damand andwalk walkdown down to to Go back to the rocks rocksexposed exposed below b e l w the thedam. dam. the Y/z RL-9 RL—9 S t r a i ndata data(Rf/Ø ( ~ f /technique) $t e c h i q u e )from fromStop Stop6A 6A Strain ( h o l l w c i r c l e s , squares, t r i a n g l e s ) and (hollow circles, squares, triangles) and northern quartzite q u a r t z i t e (packet (packet 77 of of squares, squares, northern t r i a n g l e s ) and and northern northern quartzite q u a r t z i t e (packet (packet triangles) 7 of Fig. + f i l l e d c i r c l e s ) and Lake 7 of Fig. 4; filled circles) and Antoine area area (Stop (Stop 5)(hexagon). S)(hexagon). Antoine Lake �—18— Stop 6b. the spillway spillvay of 6b. Exposed Exposed aalong l m g the of the dam dam is is a spectacular spectacular homodtinal homoclinal (? top indicators i n d i c a t o r s are a r e rare) r a r e ) section s e c t i m of of sslate l a t e with llocal o c a l sandstone sandstone interbeda. interbeds. In I n the t h e hills h i l l s just j u s t north north of the t h e spilluay spillway are a r e highly deformed deformed volcanic rocks rocks (agglomerates (agglauerates of of Dutton, Dutton, 1970). 1970). Interesting I n t e r e s t i n g features features at a t the the damsite damsite are a r e foliations f o l i a t i m with v i t h . sstrongly t r a a g l y developed developed down down dip dip lineation. lineatiaa. This This lineation l i n e a t i m can can be shown shom to t o be be of of two two origins: aa stretching s t r e t c h i n g lineation lineatim and an intersection i n t e r s e c t i a a (foliation (foliatim x foliation) f o l i a t i m ) intersection. intersection. Zoned garnets garneta are a r e locally l o c a l l y present and and define define aashallowly—plunging sballwly-plunging l i n e a t i o n i n the dominant d d n u n t NW—trending Wtrending f o l i a t i m (Fig. BL—l0). BL-10). lineation in foliation (Fig. slates s l a t e s and and volcanics. volcanics. This This great g r e a t change change in accmpanied by i n stratigraphy s t r a t i g r a p h y is i s not accompanied any gradational g r a d a t i m a l changes, changes, and therefore therefore we conclude that t h a t Stop 6a and and 6b are are separated by aa major major fault. fault. separated by In I n susmarizing s m a r i z i n g the t h e FNt, F N t , the the occurrence of of shallow s h a l l w water wager quartzites quartzites in Stop 6a 6a and nd also i n two llocations o c a t i o n s ((at a t Stop a l s o to to the NW; see see Fig. Fig. 4) 6) in in contact contact with with deep—water volcanogenic shales d e e p w a t e r l olocally c a l l y volcanogenic shales suggests th8t both both quartzite q u a r t z i t e units u n i t s are are suggests that fault f a u l tbound. bound. Further, Further, the t h e changes changes in in structural s t r u c t u r a l style s t y l e between between slaty s l a t y rocks rocks and and those those of of the t h eChocolay Chocolay and and Menominee Mendnee Groups Groups suggests suggests aa fault f a u l t separation as as w e l l . Finally, F i n a l l y , if i f one one adds adds these these faults faults well. to t o those those previously previously described described by by Bayley and a d others others (1966) (1966) and aud Dutton D u t t m (1970), one one reaches FNt is a reaches the the conclusion conclusion that t h a t the the FNt collage collage of of fault f a u l t bound bound slices. slices. is a - Optional O p t i m a l Field F i e l d Stop Stop — Paint P a i n t River Dam Dam Location: Location: Return Return to t o Florence, Florence, Wisconsin, and proceed proceed NW on m U.S. U.S. 22 to to WisconsinT and Crystal Falls, When you you reach reach F a l l s , Michigan. Michigan. When the blinking blinking red l i g h t i n Crystal C r y s t a l Falls Falls (intersection on ( i n t e r s e c t i m with with M—69), M-69)* proceed proceed on U.S. U.S. I2 past pastthe theRed RedOwl Owl (one (one block, block, on on red light in and and iinto n t o the t h e left l e f t curve c u m of U.S. U.S. 2 (about (about 22 blocks blocks from from blinking red red light). l i g h t ) . Turn Turn rright i g h t on on the t h e Street s t r e e t next next to t o the theabandoned abandoned gas gas station s t a t i mand andproceed proceed down d m h hill, i l l , cross cross the t h e Paint P a i n t River River (about (about 11 mile) mile) and and park park in i n dirt d i r t lot l o t on a lleft. eft. right), right), Walk dam spillway. spillway. Walk over to t odam Geology: Geology: The Riverton The R i v e r t m iron iron formation formati- exposed exposed aatt this t h i sdamsite damsitewas was deformed by three t h r e e phases pbases of of deformation, deformation, deformed by the the 71, F l , 72, F2, and and 75 F5 events eveats discussed discussed in in m-10 RL—l0 Oriented SE), Oriented garnecs garnets (plunging (plunging SE), cross—cutting tineatian. Quarter cross-cutting down—dip d m - d i p lineation. Quarter Formation, Stop for f o r scale. scale. Michigmmse Michiganme Formation, St- 6B. 6B. Folds Folds with with steeply steeply plunging plunging axes axes disrupt d i s r u p t the theregional r e g i a a homocline l homocline and and can cun be be shown shmm to t o be be associated associated with with strike—slip s t r i k e s l i p fault f a u l t zones. zones. The The structural s t r u c t u r a l history h i s t o r y of of the the tlm text, t e x t ,tot form o forma acomplicated cauplicatedmosaic mosaic the of of folds. folds. Axial planes planes of ofFL F l folds folds comeonly and c o m ~ m l ysstrike t r i k e WNW WtW and d idip p v evertically, rtically, except except those those Fl F l folds foldscropping cropping out outon on the bankofof tthe t h e NE NE bank h e rriver i v e r (Figure (Figure Axial a-11). Axial planes planes ofofFL F l folds folds RL—Il). exposed NE bank bank were were rrotated o t a t e d by by aa exposed on m the t h eNE later l a t e r folding folding event event of of F5 F5 to t o aa NS NS orientation. o r i e n t a t i a a . Apical Apical angles augles of of FL F l folds folds generally type lb, ib, lcl cand generally show s h w type and type type 33 folds folds of Ramsay's Ramsay's cclassification l a s s i f i c a t i o nscheme scheme outcrop is discussed discussed in i nLarue Lame and and Ueng Ueng outcrop is (in ( i n preparation). preparation). The The dominant dauinunt NW NW The beds beds were were folded folded by by 71 F l to to (1967). Th. form two ssets e t s of of homoclinal homoclinal limbs limbs with with fom m strikes N5OW EV. Because Because the the s t r i k e of s of NSOW and and2W. foliation of the is aa product product of the earliest earliest f o l i a t i m is with with respect respect to t o the the flattening f l a t t e n i n g planes planes of of later not the l a t e r deformations. deformations. aare r e not the same, same, the the fold f o l d styles s t y l e s of of later l a t e deformations r deformations imprinted two limbs limbs are a r e also also imprinted on m these these two distinctively d i s t i n c t i v e l y different. d i f f e r e n t . In the the southwest part of of the southwest part the outcrop, outcrop, the t h e 72 F2 trending trending homocline homocline with bedding—parallel bedding-parallel during tthis deformation. deformatim. Metamorphism Metamorphism during his deformation l w grade. grade. The The def o m a t i m was was probably probably low second second ffoliation, o l i a t i o n Twhich which cross—cuts cross-cuts the the first f i r s t at a t high high angles, anglesToccurred occurred next, nextTand and was was associated associated with withbiotite—grade biotite-grade metamorphism. metamorphism. Strike—slip St r i k e s l i p faulting f a u l t i n g was was concurrent of folds concurrent with with development developwnt of folds with with steep steep axes axes occurred occurTed last l a s tand andwas Was also a l s o associated associated with with garnet garnet grade grade metamorphism. Garnets Garnets grew greu with with long long axes axes parallel p a r a l l e l to t o the theextension extension direction directim (subhorizontal). (subhorizontal). Suninary Swmary of of Stop Stop 6. 6. orientations o r i e n t a t i o a a of of these thesehomoclinal humoclinal limbs limbs deformation folded the the2W EW striking s t r i k i n g Fl Fl limb limb into i n t o aa series s e r i e s of of open open folds folds with with fold f o l d axes axes plunging 50 50 degrees NE, NET in i n aa NE—striking NE-striking axial a x i a l plane. plane. Apical Apical angles angles of of these these folds folds range range from from 100 100 to t o 120 120 degrees fold profiles degrees and and fold p r o f i l e s indicate i n d i c a t e type type lb l b and and Ic l c folds. folds. What What should should strike s t r i k eeven e v m the themost most casual casual observer observer about is the the contiguity contiguity of of about Stop Stop 66 is shallow s h a l l w water water quarazites q u a r t z i t e s with with deep—water deep-water These open open folds are Theae folds are the t h e result r e s u l t of of the the small small angle angle between between the EW trending trending 71 F l limb limb and and N65E N65E the 2W flattening planes of striking s t r i k i n g f l a t t e n i n g planes of 72 F2 deformation. A t the the northern northernend end of of deformatim. At this t h i s outcrop outcrop the t h e F2 F2 deformation deformation formed formed aa �—19— 1 1A Fl folding cr.stsd two homoclin.. (So) ThSSS honiOcSln•s w., r.foldsd by F2 aL—IIA,B Structure of the Paint River daetsite. SO wsr rsfold.d again by F3 See toad1og. �—20— sseries e r i e s of of much m c h ttighter i g h t e r folds, folds, with with fold fold SW, by by deforming deformingthe t hN5OW e N5OW plunging SW, Apical angles oriented angles of of Fll fold orimted F f o l d limb. Apical 80 comonly smaller than than 80 these folds are a r ecoamonly degrees degrees aand d ffold o l d pprofiles r o f i l e s indicate i n d i c a t e type type folds. These These ttight ight llb, b , ic l c and and type 33 folds. ffolds o l d s ppartially a r t i a l l y reflect r e f l e c t the the parallelism parallelism of the of t h e original. o r i g i n a l N5OW N5OW s tstriking r i k i n g FFl l fold fold limb with with the the shortmi-g sherteni..g ddirection limb i r e c t i o n of deformation regime. regime. F2 defamation the P2 axes axes Secause the P2 Because F2 deformation defonuation of aa previously previously represents folding of represents axes plunge folded surface, 12 F2 fold f o l d axes plunge aatt great angles and and define define aa g r e a t ccircle ircle various anglea distribution d i s t r i b u t i o n on on the the stereogran stereoRram RL—llB).. ( F ~ z . RL-llB).. (Pig. The F3, 13, 14 The F4 deformations, defonoatims, which which are are other outcrops ((see present iin n other s e e ttext) e x t ) aare re FS not not recorded in i n this t h i s outcrop. outcrop. The 15 deformation bends bands the eastern p part deformation a r t of of parallelism tthis h i s outcrop iinto nto p a r a l l e l i m with the river. Apical angles of P5 F5 folds folds are are coamonly 120 degreea degrees and fold p profiles comonly rofiles show type type ib, show lb, lic c folds. folds. - bank of tths On the t h e NE NE bank h e rriver,most iver;mst trendingfolds folds with with aapical of the the N—S N-S trending pical angles smaller than thau 80 80 degrees are a r e 11 Fl However, folds rotated by P5 F5 (Pig. (Pig. 11). 11). Uwever, there 15 folds exposed at NE there are a r e aa few feu FS a t NE bank judging from the ccharacteristic h a r a c t e r i s t i c 120 120 degree apical a p i c a l angle. angle. Groveland Kine Mine Grweland sec 31 T42N set 31 P.29W R29W T4m Location: mine Location: The Groveland G n e is a recently abandoned iron the i r o n mine in the Felch trough (see (see Pig. Fig.aL—i RL-1 or o rJames Jams and and Take M95 others, 1966 1966ffor location). Take others, o r location). M95 north about a b a t 12 miles from from Iron Mountain, turn east e a s t (right) ( r i g h t ) on County County Road R o d 569, and ffollow signs to and o l l w signs t o the theGroveland Groveland mine. mine. must have have permission permissiont otogget e t iinto n t o the the You mast pit! p it! Geology: G eolm: Mostspectacular spectacular in Moat i n tthis his pit is the Chocolay Group Randville p i t is Dolomite over Manominee Menknee D o l d t e i n f a u l t ccontact mtact 5 in fault Group Group Iron Iron Pormation; Formation; t hthis i s ffault a u l t is is iisoclinal s o c l i n a l folded. folded. Therefore, h i s fault fault Therefore, tthis represent a folded tthrust may represent h r u s t fault. fault. Unfolding the fault f a u l t reveals a m i n h minimum heave of several. hundred meters several hundred (Fig. RL—12). RL-12). (Pig. The mine also a l s o contains c m t a i n a numerous examples of of folds, folds, gorgeous gorgeous foliations, foliatiune, Idnks, k i n k , metamorphic minerals and on on and and on. on. East of of town town of Alpha T42N S E k SE ¼ sec 7 T42N P.32W R32w Location: Location: Start S t a r t from town town of of Crystal FFalls, the intersection Crystal a l l s , the i n t e r s e c t i o n of of Highway 69 and and Highway Uighway 2. Drive south Highway 2. 1)rive south on a Highway 2 for f o r 2.8 2.8 miles. miles. Take right right on the the iintersection n t e r s e c t i o n to t o town of Alpha. Alpha. Drive for f o r 0.7 0.7 miles. miles. Stop at a t a roadcut roadcut outcrop over over aa small small hill. hill. original N7OW Geology: The o riginal N 70W trending Fl folds iin trendmg n the Dunn Creek I&-12 R.endvitle Randville DDolomite o l d t e i ninftault a u l t contact contact over Croveland Mine, Vulcan IIron Vulcan r o n Formation, Formation, Groveland Xine, Contactisis iisoclinally west west face. face. Contact soclinally Pacing directions folded. Pacing folded. d i r e c t i munknown. unknown. slate NlSW s l a t e were folded by by 12 F2 ttoo aaH1SW Axial planes planes of trending oorientation. trending r i m t a t i o n . Axial of these fold6 foldsaare these r e sstill t i l l vertical. v e r t i c a l . Fold Fold styles s t y l e s of of these folds f o l d s are a r e still s t i l l similar similar to P1l folds exposed at t o tthose hme F a t Paint P a i n t River River dam dam except except with v i t h tighter t i g h t e r apical a p i c a l angles. angles. Fold Fold profiles p r o f i l e s coamonly commonly show s h m type type ib, l b , Ic, lc, folds. At A t the the eastern e a s t e r n and end of of and type type 33 fold.. outcrop, en SW oriented F2 P2 fold tthis h i s outcrop, an EW f o l d was refolded by N N—S 15 refolded -S oriented o r i m t e d F5 deformation. Fold axes here are deformation. are generally plunging north. north. sec 31 NW NU of of Stager Stager Lake Lake NW NW ¼ k see 31 242N TUN P.32W R32W Location: Start Location: S t a r t from from town town of of Highway 22 south. south. Crystal Falls. Falls. Take Righway Take rright ight 9.5 miles. miles. Take Drive for f o r roughly roughly 9.5 turn t u r n on the t h e intersection i n t e r s e c t i o n to t o Stager Lake. Drive for 2.4 miles miles northwest, northwest, Lake. f o r 2.4 passing Stager d i r t road road Stager Lake. Lake. Take a dirt cross the the rrailroad before the tto o cross a i l r o a d rright i g h t before the paved road road bends bends from from NW NW to t o NNE. NNE. You is will u i l l come come tto o an open f i e l d . There is field. another rrailroad another a i l r o a d track track about about 200 200 yards yards away from you in away i n the the southwest. southwest. Pick up up your and hhit i t this t h i s railroad railroad your backpack backpack and track. Hike track. Uike for f o r 3/4 314 mile toward NW on on This outcrop is tthis h track. track. ~ is present on on both both sides s i d e s of of the the track. track. Description: Descriptim: Deformed Deformed Dunn Creek Creek slate s l a t e here shows shows beautiful b e a u t i f u l isoclinal isoclinal and very very tight t i g h t folds. folds. They They are a r e 71 '?I folds and 72 folds which had been folds been rotated r o t a t e d by F2 deformation to t o a N—S N-S trending trending orientation. orientation. Fold profiles p r o f i l e s coumonly coammly show folds. Apical show ib, lb, lc, l c , and and type type 33 folds. angles are a r e cormonly coamonly smaller than than 30 30 degrees. degrees. Pold Fold axes axes are a r e generally generally gently gently dipping. dipping. Some dismembered isoclinal isoclinal folds are folds a r e present. present. The extreme extreme of these folds is probably probably fflattening l a t t e n i n g of folds is accumulated from f r a t strain s t r a i n regimes regimes of of Vt, Fl, 72, F2, and and 15. F5. �21 NW NW ofof PPeavy e a 7 Pond Pond NEI/4 m1/4 sec sec 24 24 232W R32W T42N T42N Ranlock dam dam NE1/4 NE1/4 sec see 18 18 231W R 3 l W T43N T43N Hemlock Prom From town town of of Crystal Crystal drive drive 4.2 4.2 miles milea east e a s t on on Highway Righ-y 69. 69. Turn Turn to t o south south at a t the the intersection intersection Drive 3.4 miles south to M a r y . Drive 3.4 miles south t o Lake Lake Mary. passing passing Lake Lake Mary. Mary. Turn Turn right r i g h t at a t the the Drive on on this t h i sgrl.t g r i t road road 3—way 3-way junction. junction. Drive toward for miles till till you t w a r d the t h e SW SW f o r 11miles you come cme to t o aa fork. fork. Take Take the the road road on on right r i g h t and and slowly slowly drive d r i v e for f o r another another 0.35 0.35 miles. miles. Stop Stop exactly exactly where where the the road road begins begins to to descend. outcrop in deacend. Search Search for f o r the the.outcrop i n the the woods woods to t o your your right r i g h t which which is is about &cut 20 20 yards yards away away from f r m you. you. Location: Go Go back back and and pass pass the the Location: me-lane bridge. bridge. Take Take right r i g h t turn turn one—lane heading heading north a t t h e t h r e e way way jtmctim. Drive Drive all a l l the the way way to t o the the end end junction. of the t h e road. road. Ask Ask for f o r permission p e m i s s i o n from from aa of very very nice n i c e person, person, Bob Bob Graph, o enter enter Graph, tto Location: Location: Falls, Falls, Geology: G e o l m : Examine Examine the the pelitic pelitic portion There are a r e three three p o r t i a of of the the outcrop. outcrop. There sets s e t s of of cleavages cleavages present present in i n the the rock, rock, i.e. i.e. one one set s e t of of slary s l a t y cleavage, cleavage, two two Sets sets of of crenulatiam c r e n u l a t i m cleavages. cleavages. The The Si S l slaty slaty cleavage NE and and is is crenulated crenulated by by cleavage strikes s t r i k e s NE S2 S2 which which strikes s t r i k e s N65E. N65E. Both Both Si S l and and 32 S2 cleavages cleavages dip d i p vertically. v e r t i c a l l y . However, Rowever, 33 S3 is is aa set s e t of of subhorizomtal subhorizontal crenulation crenulation cleavage and ccrosscutting cleavage dipping dipping NW NW aad rosscutting both both Si Sl and and S2. S2. The The 33 S3 crenulation crenulation cleavage cleavage here here belongs b e l m g s to t o aa group group of of subhorizomtal subhorizontal crenuiatiom c r e n u l a t i m cleavage cleavage dipping f r m the the Peavy Pea- Pond Pond dipping away away from intrusive, is located located SE SE of of where where Intrusive, which which is you you stand. stand. Neighborhood see 20 20 Neighborhood of of Mansfield Mansfield mine. mine. sec T43N T63N 2.31W R3lW - t h e darn. dam. the Geology: Geologp AA series s e r i e s of of fault f a u l tbound bound packets of of cherry cherty sediments sediments and and pillows pillows packets a the the cliff c l i f f at a t the the northern northern a r eexposed exposed on are end of of dam. d m . The end The rhythmic rhythmic banding banding of of sedimeuts here here are a r e mixtures mixtures of of sediments tuffaceous sediments sediments and and chert. chert. Graded Graded tuffaceous bedding isnot notcoamon. conmon. These These sediments sediments bedding is resemble ribbon r i b b m cherts c h e r t s which which represent represent resemble deep deep sea sea sediments sediments in i n orogenic orogenic beits. belts. Sane fallen f a l l e u blocks blocks on on the t h e northern northern bank bank Some of the the river, r i v e r , if i fyou you can can cross cross the the of river, r i v e r , show show depositional depositional contacts contacts among among t h r e e major major lithotypes, l i t h o t y p e s , the the massive massive lava lava three aad pillows, pillows, agglomerates, agglomerates, and and flown and flows ribbon ribbon charts. cherts. The The deployment deployment of of the t h one—mile e one-mile thick t h i c k differentiated d i f f e r e n t i a t e d sills s i l l s (Hiernan (Kiernan s i l l s . ) , pillow pillow lavas, lavas, ferrugenous ferrugenous sills), sediments (iron ( i r o n formation), formation), and and ribbon ribbon sediments t hneighborhood e neighborhoodof of Redockdam dam c h e r tininthe chert Hemlock and and Mansfield M u a f i e l d mine mine draws draws close close resemblance resemblance to t o the t h e upper upper part p a r t of of that the the ophiolite. It is t r u e that ophioiite. chemistry of of Hemlock Redock volcanics volcanics and and chemistry Kiernan s i l l s i s not depleted depleted enough enough to to It is true Kiernan silla is not Location: Locatim: Go Go back back to t o Highway Righway 69. 69. Drive Drive east east for f o r 300 300 yards yardson oaHighway Righway 69. 69. Take the sign sign of of Take left l e f t after a f t e r spotting spotting the HD.0CX EEMLOCK DAM. DAM. Drive Drive north north for f o r 2.8 2.8 miles miles till, Take the the right right ti11 you you come came to t o aa fork. fork. Take road Drive road passing passing the the one—lane oae-lane bridge. bridge. Drive for f o r another another 0.2 0.2 miles miles till t i l lyou you hit h i t the the first f i r s tseries seriea of of toed road cut cut outcrops. outcrops. Geology: Geoloa: north at the three Some Some Hemlock Redock pillows p i l l m and and are The slates slates a r e present present here. here. The exposed exposed aatt the the south south side side of of the theroad road are areaamixture mixtureofoftuffaceous tuffaceoussediments sediments and The slates s l a t e swere were baked baked by by the the and chert. chert. The neighboring Sills foam neighboring Hiernan Kiernan S i l l s tot oform abundant a F n d a n t porphyoblasts. porphyoblasts. Under Under m.croscope, tucroscopeT these these porphyroblasts porphyroblasts are are nothing uith nothing but but pockets pockets of of chert chertdoped dopedwith some tiny tourmaline same tiny toumaline crystals. c r y s t a l s . However, Rowever* slates slates porphyroblasts porphyroblasts in i n outcrops outcrops half half aa mile mile south show south of of here here cocnly comonly show chiastolite chiastolite pseudomorphs. pseudomorphs. Climb Climb up up the the northern northern hill h i l l of of this t h i soutcrop. outcrop. AA cliff c l i f f made made of of pillows ispresent presentata the t the westernend a d of of pillows is western this t h i s bill. h i l l . The The depositionai depositional surface surface outlined by the thepillows p i l l - faces faceswest west and and outlined by dips dips vertically. v e r t i c a l l y . This N-S striking s t r i k i n g and and This N—S vertically v e r t i c a l l y dipping dipping depositional depositional surface surface by the thebedding bedding of of slates slates i s paralleled paralleled by and and rhythmic rhythmic layering layering in i n ier'nan Kiernan Sills. Sills. .s Among Ammg the the over over2—mile 2-mile thick thickHemlock Redock volcanics volcaaics SW SW of the t h eAmasa Amasa oval, oval, pillows pillows a r e ubiquitously ubiquitously present prenent regardless regardless of of are stratigraphic s t r a t i g r a p h i c position. position. MORE. However, HouwerTthe the be characterized characterized be by by MORB. in front f r o n t of of geological setting s e t t i n g presented presented in geological you is is as very very rare r a r e case case in i n the t h eworld world you where a layered layered intrusion i n t r u s i o nwas was emplaced emplaced where i n t oaavery very thick thick pillow pillow basalt b a s a l tsequence. sequence. into SW of h s a N NWk 10 R32W TUN SW of Arnasa secsec 10 232W T44N A map map of Kelso Junction Junction Location: A Location: of Kelso quadr-.s.G.s. B u l l e t i n1226, 1226* quadrangle (U.S.G.S. Bulletin p l a t e 1) 1)will w i l lbe beneeded needed to t o get get to t o this this plate outcrop. outcrop. Start S t a r tfrom f r m Paint P a i n t River Riverdam dam (optional 1) and and drive d r i v e north. north. (optional outcrop outcrop 1) It It about 11 11miles miles of of driving. driving. isisabout Geolom: Some Some Hemlock Hemlock sslates l a t e sand and Geology: volcanicsare are exposedamong among several several volcanics exposed s m a l l mounds w m d s scattered s c a t t e r e d within within 100 100 yards yards small here. here. Three phases phases of of deformation deformation are are Three i n these these rocks, rocks* i.e. i.e. Fl, F l ,F2, E2* r e g i s t e r e d in registered s h m by by very very tight t i g h t folds folds and and F l isisshown Fl penetrative slaty s l a t y cleavage. cleavage. The aa penetrative The Fl Fl slaty s l a t y cleavage cleavage strikes s t r i k e s N15W N15Wand andisis coemonly conmonly present present all a l lthrough through the therocks rocks here. here. P2 F2 crenulation crenulation cleavage cleavage is is very very conmanly characterized characterized by by s u b t l e , but but isis coianonly subtle, s e t of of vertical v e r t i c a lcrenulation crenulation lineations lineations aa set P3. F3. showing on on netavolcanics metavolcanicsand and showing carbonaceous slates. s l a t e s . Stretched Stretched carbonaceous agglomerate pebbles pebbles plunge plunge vvertically e r t i c a l l y in in agglomerate p a r a l l e with l withF1xF2 E l f l 2 crenulation crenulation parallel l i n e a t i o n s . P3 E3 isis aa set s e t of of lineatione. subhorizontal crenulation crenulation cleavage cleavage that that subhorizontal Fl. dips25 25degrees degreeswest westand and croescuts crosscuts Fl. dips Some ssimilar i m i l a r sets s e t s of of subhorjzontal subhorizontal Some cleavagesdipping dippingaway awayfrom from the the Amasa Amasa cleavages oval have have been be- observed. observed. oval �—2 2— The subhorizocital flattening flattening plane The subhorizontal plane shoen by F3 13 cleavage cleavagehere here requires requires the the s h o m by basement to Oval basememt uplift ofofthe uplift theAmasa Amasa.Ova1 to account for the the vertical account for vertical shortening. shortening. basement However, the However, the uplift uplift of Archean basement later than ovalitas to in Amasa oval'has to occur occur later than in !,masa the 11 and 12 the Fl F2 deformation deformation because because 13 F3 Si and 52. cleavage crosscuts croascuts both Sl cleavage S2. Apparently, th. Apparently, themagnitude magnitude of this this uplift uplift wasminor minorsuch suchthat thatthe thedipa dip. of of the van the vertical Si vertical Slcleavage cleavage has has not been been rotated rotatedmuch. much. Peterson's Farm Peterson's T4IN SE1/4 R3OU T41N Sill4 sec sac 19 530W Location: Location: Start Start from fraa town town of of miles on Randvilie, Randville* drive drive south south for for 7.5 7.5 miles county road road 607. 607. Turn right and aud drive drive 2.2 miles to 2 .2 miles to the the end end of of the the road. road. Or when v h a you leave leave Randvills, Randville, drive drive south south for 6 6.5 State 95. Turn m State Turn left .5 miles on and drive for 1 1.2 and .2 miles till you hit 607 Make right right turntheading CComty -ty 607.• Malee u m heading for k mile. mile. Turn north for Turn left left and and drive another 2.2.2 miles till till you another 2 miles you hit the end end and ask of road. Get out out of of the the car and of the road. permission from from the the owner. m e r . The The outcrops outcrops permissica from are are scattered scattered about about 150 150 yards yards M15E N15E f rm you. You- Description: The The HMichiga i c h i g m slate slate these rocks rocks registered registered at at exposed in these i.e. least least 46deformations, defonuatiaw* i .e. 11, Fl, 13, F3* 14, F4, Almosta11 all the the pelitic politic portions purtims of of F15. 5. Almost these these rocks rock record 3 sets seCa of ofcleavages cleavages the best outcrop Rwever, the autcrop is is at at least. least. However, 15 feet feet wids an 8—foot tall, m 8-foot tall, 15 wide block block hill. Here Here sitting sitting atop a very gentle gentle hill. the 51 Sl slaty cleavage is ia crenulated by the S3 crenulatiom crenulatim cleavage. The crenulatiom S3fabric fabrici.e is so so intense intense crenulatim of of 33 that that it itresembles resembles bedding, bedding* but it it is is not. The cleavages were vere The 53 S3 crenulation crenulatim cleavages trending fold fold by by 14. F.5. folded into into a a NW trending 15 F5 crenulation crenulation cleavage is imprinted on everything exposed exposed here. here. To the the middle toward vest west end end of of this this outcrop, outcrop, another toward eubhorizomtal cleavage cleavage is clearly set of subhorizontal present. preseut. This set of subhorizontsl subhorizontal cleavage cleavage dips dipa SE SE and and may very very well well be be Peavy Pond related to to the the uplift of Peavy Pond intrusive. APPENDIX Facies descriptions Facies descriptions of stratigraphic stratigraphic section section at Fern Fern Creek dam (Stop (Stop 1). 1). Facies 1: Facies 1: Disorganized matrix—supported matrix-supported conglomconglomerate. erate. Mean grain grain size: size: 10 10 cm. cm. Sedimentary strucstructures: tures: massive (amalgamated?) (amalgamated?) beds, tectonically tectonically Facies , alligned alligned clasts clasts subparallel subparallel to to cleavage. cleavage. Facies thickness: thickness: 2-5 m. m. Lower Lower contact: contact: irregular. Upper Upper 2—5 debris contact: tabular, tabular, abrupt. abrupt. Interpretation: Interpretation: debris flow deposits. Facies 2: Pebbly Pebbly muddy muddy sandstone. sandstone. Mean grain Facies 2: size: Sedimentary structures: size: mu. Sedimentary structures: massive 0.5 mu. (amalgamated?) (amalgamated?) beds. beds. Facies thickness: thickness: 33 m. m. Lower Lower contact: tabular. tabular. Upper Upper contact: contact: not exposed. Interpretation: debris Interpretation: debris flow flow deposits. deposits. Facies 3: Facies 3: Ripple and plane—laminated plane-laminated fine fine grained grained sandstone. Mean grain 0.3 sandstone. grain size: size: 0 .3 cm. m. Bed thickness: thickness: 1—20 cm, mean — 33 cm. a,mean cm. SS:Sh SS:Sh •= 1—3. 1-3. Sedimentary 1-20 structures: ripple plane—laminations, convoluted structures: ripple and plane-laminations, bedding. Facies 1—2 n. bedding. Facies thickness: thickness: 1-2 m. Lower Lower contact: contact: tabular. Upper contact: contact: tabular or scoured. scoured. Interpretation: Lower Interpretation: Lower to to transitional transitional flow flow regime regime bedf oms. bedforms. Facies 4: 4: Interbedded Facies Interbedded sandstone sandstone and and shale. shale. ted Bed SH =<I-10. ' 1—10. thickness 1-30 1—30 cm. cm, mean — 10 10 cm. SS: SS: SH thickness structures: mud-draped mud—draped ripples, Sedimentary structures: Sedimentary ripples, diffuse diffuse plane plane laminations, laminations, massive massive beds. beds. Facies Facies thickness: thickness: Upper contact: 2—9 m. 2-9 m. Lower Lower contact: contact: tabular. Upper contact: tabular or scoured. Interpretation: Interpretation: Lower flow deposits interbedded with with suspended load deposregime deposits its. Facies 5:: Massive medium mediumto,coarse to coarse grained sandFacles 5 sand0.7 am. mu. SS:Sh SS:Sh = 10. 10. stone. Mean grain grain size: size: 0.7 Sedimentary structures: mud—draped ripples, Sedimentary structures: rare mud-draped ripples, diffuse plane laminations, laminations, massive massive (amalgamated?) (amalgamated?) beds. 11—12 m. beds. Facies Facies thickness: thickness: 11-12 m. Lower contact: contact: tabular, abrupt. Upper tabular, Upper contact: contact: tabular, tabular, abrupt. abrupt. Interpretation: Interpretation: Lower to transitional transitional flow flow regime regime sheet—flow deposits. deposits. sheet-flow Facies Fine—grained sandstone. Mean grain Facies 6: 6: Fine-grained grain size: size: ted thickness: thickness: 1—15 4 cm. 0.3 ma. mu. Bed 1-15 cm, mean mean — 4 cm. 0.3 SS:Sh = > > 10. SS:Sh Sedimentary structures: structures: ripples. ripples. 4—6 m m. . Lower contact: contact: tabular, tabular, Facies thickness: thickness: 4-6 abrupt. Upper contact: contact: gradational gradational into into the the Sturgeon Interpretation: Lower Sturgeon Quartzite. Interpretation: Lower to tc transitional transitional flow flow regime regime deposits. deposits. - - - �References Alwin, Alvin, Seven, Bevan, 1979, 1979, Sedimmitology Sedimmtology of of the the Tyler Tyler Pormation: Geological Formation: Geological Society Society of of America America no. 5, Abstracts with Programs, Programs, v. 11, 11, no. 5, p. p. 225. 225. 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Cudzilo, T.F., LI., 1978, 1978, Geochemistry Geochemistry of of Early Proterosoic Proterozoic Igneous Rocks, Northeastern Ph.D Wisconsin and h.D thesis thesis and Upper Upper Michigan. Michigan. P Univ. h i v . Pauses, Kansas, Lawrence, Lawrace, 194 1% pp. (-pub.). pp. (unpub.). Dutton, of the Florence area, Dutton, C.E., C.E., 1971, 1971,Geology G e o l m of area, Wisconsin Wisconsin and and Michigan: Michigan: U.S. U.S. Geological Survey Survey Professional Paper Paper 633, 633, p. p. 54. 54. Fox, Fox, T.P., T.P., 1983, 1983, Geochemistry of the t h eHemlock Hemlock metabasalt and andKiernan Riernanssills, metabasalt i l l s , Iron IronCounty, County, Michigan (M.S. Michigan SState (M.S. thesis): thesis): Xichigan Xichigan tate University, East East Lansing, Lansing, 81 81 p. p. 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James, H.L., L.D., Lamey, Lamey, C.L., C.L., and James, H.L., Clark, Clark, L.D., Pettijohn, P e t t i j o b , P.3., F.J., 1961, 1961, Geology Geology of central central Dickinson County, County, Michigan: Michigan: U.S. U.S. Geological Survey Professional P r o f e s s i o n d Paper Paper 310, 310, 176 176 p.James, p.James, H.L., Dutton, Dutton, C.E., C.E., Pettijohn, Pettijohn, 1.3., F.J., and Weir, W.L., and ore ore deposits deposits of of the Geology and t h e IIron ron River—Crystal River-Crystal Pails F a l l s district, d i s t r i c t , Iron Iron County, County, IC., 1968, K., 1968, Michigan: U.S. Michigan: U.S. Geological Geological Survey Survey Professional Professional Paper 570, 570, 134 134 p. p. Laberge, G., Meyers, P., Laberge, G., and Meyers, P., 1984, 1984, Two Two early early Proterozoic Proterozoic successions successions in i n central c e n t r a l Wisconsin Wisconsin Geological and ttheir h e i r tectonic t e c t o n i c significance: significance: Geological Bulletin, Society of Society of America America B u l l e t i n , in i n press. press. . Larue, D.K., 1981, 1981,The TheChocolay ChocolayGroup: Group: an an early early Larue, DL, Proterozoic cratonic Proterozoic c r a t o n i c sequence, sequence, Geological Geological Society of of America Bulletin, B u l l e t i n , v. p. 435. 435. v. 92, 92, p. D.K., 198lb, The early Menominee Larue, D.K., 1981b, The e a r l y Proterozoic Proterozoic Menominee Group Group siliciclastic s i l i c i c l a s t i c sediments sediments of of the the southern southern Evidence ffor Lake Superior Superior region: region: Evidence or sedimentation iin n platformal platformal and and basinal basinal setting: Journal of setting: of Sedimentary Sedimentaq Petrology, Petrolom, v. V. 51, p. p. 397—414. 397414. Larue, D.R., 1983, Procerozoic tectonics L a n e , D.K., 1983, Early Proterozoic t e c t o n i c s of of region: tectonostratigraphic tthe h e Lake Lake Superior region: teetonostratigraphic tcerranes e r r a n e s near the the purported purported collision c o l l i s i o n zone: zone: America, Memoir Geological Society of of America, Memoir 160, 160, , p. 33-47. p. 33—47. L.L., 1980, D.L, and Sloe., Larue, D.K., Sloss, L.L., 1980, Early basins of of the Lake Proterozoic sedimentary sedimentary basins t h e Lake Superior region: Superior region: Geological Society Society of of America Bulletin, B u l l e t i n , Pt. I, v. 91, 450-452; P a r t 11, v. 91, v. 91, 1836—1874. 1836-1874. Pt. I, v. 91, 450—452; Part II, W.L., 1984, and D.K., and Ueng, Ueng, W. L., 1984, Structural Structural Larue, D.K., history, h i s t o r y , ffinite i n i t e strain s t r a i nand and oblique oblique orientation orientation of folds in i n ffault a u l t packets of the early early Proterozoic terrane, Lake P r o t e r m o i c11 F lorence—Niagara o r a c e - N i a g a r a terrane, Lake Journal Superior region, Superior region, U.S.A.: U.S.A.: Journal of of Structural. Structural Geology, submitted. submitted. Geology, 1976, Boundary Sims, Morey, G.B., G.B., and and S b s , P.R., P.K., 1976, B o m d a q between between Moray, and iits two Precambrian W 0 Precambrian W tterranes e r r a n e s in Minnesota and ts geological significance: significance: Geological Society Society of of America Bulletin, B u l l e t i n , v. v. 87, 87, p. p. 141—152. 141-152. Moray, G.G., G.G., Simm, Sims, P.K., P.R., Canurn, Cannon, W.F., W.P., Mudrey, Mudrey, JJr., r., Morey, D.R., 1982, M.G., and M.G., and Southwick, Scuthwick, D.K., 1982, Geologic map of the of t h e Lake Lake Superior Superior Region, Region, Minnesota, Minnesota, Wisconsin, Wisconsin, and and Northern Northern Michigan. Michigan. Minnesota Minnesota Survey Geological S w e y State S t a t eMap Map Series S e r i e sS—13. S-13. Nilsen, Nilsen, LI., T.E., 1965, 1965,Sedimentology Sedimmtology of of middle middle Precambrian hAniaiikesn orence Precambrian i m i k e a n qquartz u a r t z iites, t e s , Fl. Florence County, Wisconsin: County, Wisconsin: Journal of of Sedimentary Sedimentary v. 35, p. 805—817. 805-817. Petrology, v. 35, p. Pettijohn, F.J., 1.3., 1943, Basal Ruronian Huronian c conglomerates Pettijohn, 1943, Basal onglmerates of Menominee M e n d n e e and Calumet districts, d i s t r i c t s , Michigan: Michigan: 'r. Journal of no. 6, of Geology, v. 51, no. 5 , p. p. 387—397. 387-397. Prinz, W.C., W.C., 1976, Correlative iron-foamations iron—formations and 1976, Correlative Prinz, volcanic rocks of Precambrian age, of Precambrian age, Northern Michigan: 22nd h Annual n u a l Institute I n s t i t u t e on Lake Michigan: Superior Geology, Geology, p. p. 47. 47. Ramsay, J.G., J.G., 1967, 1967, Folding Folding and and fracturing f r a c t u r i n g of of rocks: York, McGraw-Hill, McGraw—Hill, 568 rocks: New York, 568 p. p. Ronav, A.B., A.A., 1971, 1971, Geochemical Geochemical' Ronov, A.B., and and Migdisov, A.A., history of the crystalline h i s t o r y of c r y s t a l l i n e basement and and the sedimentary sedimentary cover of of the the Russian and and North American platforms: p l a t f m : Sedimentology, v. v. 16, 16, p. 137-185. p. 137—185. �Sanderson, D.J., D.J., 1973, of fold axes Sanderson, 1973, The The development development of axes oblique oblique tto o the the regional regional trend: trend: Tectonophysics, V. 16,p.p.55—70. 55-70. v. 16, Schulz, K.J., of the volcanic Schulz, K.J., 1983, 1983,Geochemistry Geochemistry of rocks of northeastern northeastern Wisconsin: Wisconsin: IInstitute n s t i t u t e of 39—40. meeting, p. p. 39-40. Lake Superior Geology, Geology, 29th meeting, Sedlock, R.L., Lt., and 1983, and Larue, Larue, D.c., D.K., 1983, Deformation and and metamorphism metamorphism of of a Penokean aarc r c and possible rout, north Wisconsin: ccollision o l l i s i o n zone, Wisconsin: Geological Geological Society Society of of America America Abstracts Abstracts with with Programs, Programs, v. 15, v. 15, p. p. 683. 683. Sims, P.K., 1976, S h , P.K., 1976, Precambrian Precambrian tectonics tectonics and mineral deposits, Lake Lake Superior Superior region: Economic Economic Geology, v. v. 71, 71, p. p. 10924127. 1092-1127. J.W., 1968, 1948, The The Sturgeon Sturgeon Quartzite Quartzite of the Trow, J.W., Menominee (Ph.D. thesis), Menominee District, D i s t r i c t , Michigan (Ph.D. thesis), University University of of Chicago, Chicago, 60 60 p. p. W.R., 1976, Van Schrus, Schmus, W.R., 1976, Early and middle Proterozoic Proterozoic history h i s t o r y of of the the Great Great Lakes Lakes area, area, Royal Society Society of London London North America: America: aoyal Philosophical Philosophical Transactions, Transactions, ser. ser. A, A, V. v. 280, p. 605—628. 605-628. p. and Anderson, Anderson, .T.L., J.L., 1977, 1977, Gaeisa Gneiss Van Schmua, Van Schmus, W.R., W.R., and of Archean age in the and migmatite of Archean age t h ePrecambrian Precambrian Geology, v.v. 5, of central basement of c e n t r a lWisconsin: Wisconsin: Geology, 5, p. 45-48. p. 45—48. igneous racks W.P.., 1980, Chronology Van Schmus, Schmus, W.R.,1980, Chronology of igneous rocks Penokean Orogeny Orogeny iinn associated with the the Penokean Wisconsin: Geological Society of America Wisconsin: America Special Special Paper Paper 182, 182,p.p.159—168. 159-168. Junctiot Weir, K.L., .L., Geology Weir, Geology of the Kelso Kelso Junction U.S. Michigan: U Quadrangle, Iron County, County, Michigan: .S. Geological SurveyBSulletin Geological Survey u l l e t i n 1226, 1226, 47 47 p. p. Zeitz, 1981, Aeromagnetic I., and Kirby, Kirby, J.R., J.L, 1981, I., and Aeromagnetic map map the western western part part of of the the northern northern peninsula peninsula of the of Michigan Michigan and part of of northern Wisconsin: Wisconsin: of U.S. U.S. Geological Survey Survey Map Map GP—750. GP-750. � https://digitalcollections.lakeheadu.ca/files/original/91870340a2a6b77947c39380cb574654.pdf 7e0f5344cc06f22c3e3a1ac3a078af35 PDF Text Text 30th 30th Annual Annual Institute on Lake Superior Superior Geology Geology FIELD TRIP 3 TH WAUSAU SYE NTTE CO M PLEX THEE WAUSAU SYENI E COMPLEX WA U S AU PLUTON W AU S A U N I NEM 1 L E P LU T 0 N miles April 28, 28, 1984, Wausau, Wausau, Wisconsin Wisconsin �30TH 3 0ANNUAL ANNUAL ~ ~ INSTITUTE INSTITUTEONONLAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY #3 FIELD TRIP TRIP #3 FIELD THE WAUSAU WAUSAU SYENITE SYEN I T E COMPLEX COMPLEX THE CENTRAL CENTRAL WISCONSIN* WISCONSIN* by P a u l E. E. Myers Myers Paul D e p a r t m e n t of o fGeology Geology Department U n i v e r s i t yofo Wisconsin f Wisconsin University Eau C l a i r e , W i s c o n s i n54701 54701 Eau Claire, Wisconsin K . Sood Sood Mohan K. Mohan Department D e p a r t m e n t of o f Earth E a r t hSciences Sciences Northeastern N o r t h e a s t e r n I Illinois l l i n o i s University University Chicago, C h i c a g o , Illinois I 1 1 i n o i 60625 s 60625 L o u i s A. A . Berlin Berlin Louis Department D e p a r t m e n t of o f Earth E a r t hSciences Sciences Northeastern N o r t h e a s t e r n I Illinois l l i n o i s University University Chicago, C h i c a g o , Illinois I 1 l i n o i 60625 s 60625 Falster A1 U. U. Faister Al 9 2 0 McIntosh M c I n t o s h Street Street 920 Wausau, Wisconsin Wisconsin Wausau, 54401 .54401 ** For F o r sale s a l e by b yPaul P a u l E. E. Myers, M y e r s , Department D e p a r t m e n t ooff Geology, G e o l o g y , University University o f Wisconsin, Wisconsin, of Eau Eau Claire, C l a i r e , Wisconsin Wisconsin 54701 5 4 7 0 1 [$6.00] [$6.00] �INTRODUCTION This Guidebook i sis aa major one used used in 1980 1980 for for the the 26th 26th Annual Annual This Guidebook major revision revision of one IInstitute n s t i t u t eononLake LakeSuperior SuperiorGeology. Geology. That waswritten written by That volume volume was by Sood, Sood, Myers, Myers, and Berlin. Berlin. Subsequent Subsequentmore moredetailed detailed mapping mappingand andanalyses analysesof of rocks and and and minerals minerals from the the southern southern portion portion of the havenecessitated necessitatedt hthis revision. AA from the Complex Complex have i s revision. comprehensive paper geology and and petrology petrology ofofthe the Wausau Syenite SyeniteComplex Complex comprehensive paperon on the the geology Wausau iiss forthcoming. forthcoming. Syenitic Weidman Syenitic rocks rocks ofofthe theWausau Wausau area area were were first Weidman (1907) (1907) as as f i r sdescribed t describedbyby part of aa general general report reporton on the thegeology geology of ofnorthern northern Wisconsin. Wisconsin. AA greater than than part of normal amount inint hthat a t report o the the mineralogy mineralogy of the normal amountofofattention attentionwas wasdevoted devoted report tto of the syenites. andSnyder Snyder(1(1944), Turner ((1948), syeni t e s . Emmons Emmons and 944), Turner 1 948), and and Giesse Giesse (1951) (1 951 ) subsequently subsequently studied studied mainly mainly the the mineral mineral associations associationsofofthe theWausau Wausau Syenite. Syenite. The The plutons plutons of of the the WausauSyenite Syenite Complex Complexwere weremapped mapped 1971—1976 part mappingproject project by Wausau in in1971-1 976 as as part ofofaamapping by Wisconsin Geological Geological and and Natural History HistorySurvey Survey(LaBerge (LaBerge and and Myers, Myers, 1984). 1984). the Wisconsin Koellner (1974) studied the units in the Koellner (1 974) studied the mineral mineral chemistry chemistry of the the various various mapped mapped units the Stettin S t e t t i n syenite syenite pluton. pluton. Her data have have been h i s guideguideHer excellent excellent data beenincorporated incorporatedinin tthis book with geochemical and and mineral mineral chemical-petrographic chemical-petrographic book with gratitude. Additional geochemical studies on by by Falster Falster (1984), (1984), Myers, Myers, Medaris,(University Medaris,(University of studies are being being carried on Wisconsin-—Madison), Madison),and and Sood (Northeastern University). Sood (Northeastern I1 1Illinois inois University). Wisconsin GENERAL GEOLOGY GENERAL GEOLOGY Central Wisconsin Central Wisconsin is i s on on the thesouthernedge southernedge of ofthe theexposed exposed Precambrian Precambrian Shield Precambrianrocks rocksare aresparsely sparsely exposed exposedthrough throughglacial glacial cover, 1 ) . The The Precambrian cover, ((Figure ~ i g u r e1). along streams, and andasasscattered scatteredi ninliers. The aeromagnetic aeromagneticmap mapbybyZietz Zietz and and others along streams, l i e r s . The (1978) anomaly gravity gravity map (1974) permit (1 978) and and the Bouguer Bouguer anomaly map by by Ervin Ervin and and Hammer Hammer (1 974) permit extrapolation ofofcontacts contactsbetween between isolate i s o l a t eexposures. exposures. Archeanmigmatites, migmatites, gneisses, gneisses, and andsschists are confined Archean c h i s t s of Archean Archean age age are confined to to lenticular region between l e n t i c u l a r fault f a u lslices t s l i c ein s the in the region betweenStevens Stevens Point Point and and Black Black River River Falls. Falls. They havebeen beenreferred referred tto 1984, p. p. 247) o informally informally (LaBerge (LaBerge and and Myers, Flyers, 1984, 2 4 7 ) as as the the They have "Stevens U-Pbzircon zircon age age dated dated aat than 2,800 2,800 m.y. m.y. old. t more more than "Stevens Point Point Complex," Complex," and and U-Pb by Van Schmus( 1 (1977, 1980).Syenitic Syeniticaugen augengneiss gneissa at a U—Pb by Van Schmus 9 7 7 , 1980). t NNeillsville e i l l s v i l l eyields yields a U-Pb gneisses and and amphibol amphibolites zircon age age of of 2,535 2,535 ++10 10m.y. m.y. (Van (VanSchmus, Schmus, 1980). 1980). Archean Archean gneisses ites occur north north of the been occur the Niagara ~Tagarafault f a u l tininnorthern northernWisconsin, Wisconsin,and andit ihas t has beensuggested suggested (LaBerge, oral communication, 1984)t hthat noArchean Archeancrust underlies the (LaBerge, oral communication, 1984) a t no crust underlies the region region betweenthese theseroughly roughlypara1 parallel east-northeast-trending fault between 1 el east-northeast-trending f a u l tsystems. systems. Older Proterozoic Proterozoic rocks regionare are quartz-sillimanite quartz—sillimanite sschist, Older rocks of the the Wausau Wausau region chist, biotite b i o t i t eschist, s c h i s tand , andamphibolite-grade amphibolite-grademetavolcanic metavolcanic rocks rocks northwest northwest of of the theAthens Athens Amphibolitic gneisses of volcanic n d t otonalitic nalitic gneisses of volcanic and and gabbroic gabbroic parentage parentage aand fault. f a u l t . Amphibolitic make ttoo trondhjemitic trondhjemiticorthogneisses orthogneisses makeupu pananeast—northeast—trending east-northeast-trending belt beltofofamphibo— amphibolite—grade amphibolite (Myers,.1974)in l974)in the 1 i te-grade rocks rocks comprising comprising the the Chippewa Chippewa amphi bol i t e complex compl ex (Myers, rocksofof similar similar lithology region region west west and and north north of ofMarathon Marathon County. County. Amphibolitic Amphibolitic rocks are interleaved with south of of are with Archean Archean migmatites migmatites in the the "Stevens "Stevens Point Point complex" complex" south MarathonCounty. County.The Theolder older succession successioni is Marathon s characterized characterized by by amphibolite-grade amphibolite-grade metametamorphic mineralogy mineralogyaand west-t to northwest—plungingisocl isoclinal n d westo northwest-plunging inal folds folds deformed deformed by by morphic moreopen, open,coaxial coaxial folds. folds. Basal Basal quartzite quartzite and rocks in more and pelitic p e l i t i cmetasedimentary metasedimentary rocks byby numerous tthis h i s older oldersuccession succession are are overlain overlainbybyvolcanic volcanicrocks, rocks,and andintruded intruded numerous syntectonic tonalites, granodiori t e(LaBerge s (LaBergeand andMyers, Myers, 1984, 1984, , andgranodiorites tonal i t e s ,trondhjemites, trondh jemi tes and p. 246). p. 246). Theyounger youngerEarly EarlyProterozoic Proterozoicsuccession successionconsists consistsprimarily primarily of of greenschist-facies greenschist-facies The calc-alkaline overlies basal t-rhyol i t esequence sequence that t h a t unconformably unconformably over1 i e s the older 01 der cal c-a1 kal ine basalt-rhyolite succession (Myers (Myers and 1980). Structures in in the thegreenschist greenschistsequence sequence succession and others, others, 1980). �—2— FIGURE 11 FIGURE GENERALIZED PRECAMBRIAN PRECAMBRIANGEOLOGY GEOLOGY GENERALIZED of of NEST-CENTRAL WISCONSIN* WISCONSIN* WEST-CENTRAL E X P L A N A T I O N EXPLANATION R a p a k i v i - t y p e g rgranites a n i t e s and s o c i a t e d i nintrusive t r u s i v e rrocks o c k s oof f tthe h e Wolf Wolf River R i v e r batholith batholith Rapakivi—type anda sassociated - S y e n i t e , quartz q u a r t zsyenite, s y e n i t equartz , q u a r tmonzonite z monzoniteof othe f t hWausau e Wausausyenite s y e n i t ecomplex complex Syenite, Quartzite E: Quartzite = - - - ' - - - U N ON C OFNORM F O RITY M —--.-——-'....—— I T Y '—'---—-'-UNC Metagabbro Metagabbro Anorthosite Anorthosite C a l c - a l k a l i n e i nintrusive t r u s i v e rrocks o c k s cconsisting o n s i s t i n g mmainly a i n l y o of f ggranite, r a n i t e , ggranodiorite, r a n o d i o r i t e , ttonalite, onalite, Calc—alkaline and quartz q u a r t z diorite; d i o r i t e ;commonly commonly ffoliated o l i a t e d and/or a n d / o r lineated lineated and Metasedimentary r orocks c k s i n including c l u d i n g p hphyllite, y l l i t e , cchlorite h l o r i t e schist, s c h i s t ,micaceous rnicaceous quartzite, quartzite, Metasedimentary t u f f a c e o u s sandstone, sandstone, ssiltstone; i l t s t o n e ; greenschist g r e e n s c h i s t facies. facies. tuffaceous Calc-a1 k a l i n e metavolcanic m e t a v o l c a n i c rrocks, ocks, m a i n l y bbasaltic a s a l t i c flows f l o w s and and aandesite n d e s i t e tto o rhyolite rhyolite Calc-alkaline mainly p y r o c l a s t i c rocks; r o c k s ; greenschist g r e e n s c h i s t facies facies - U N C ON N FCONFORM ORMITY —---U I LmMiphibolites illllhJ!IJ (?)T Y (?)—___—-—--- hphibol ites STRUCTURESYMBOLS SYMBOLS STRUCTURE 7 Approximate exposed edge o f Precambrian basement '7 Approximate exposed edge of Precambrian basement ---2 Contact, Contact, dashedwhere where inferred inferred —7 dashed C L> Contact based on aeromagnetic anomalies L7 Contact based on aeromagnetic anomalies R## F a u l toro rshear shearzone, zone, dashed dashed where where inferred; i n f e r r e d ; commonly c m o n l y wwider i d e r tthan h a n line line Fault ** From LaBerge LaBerge and 1984. From and Myers, 1984. �-3— trend and plunge plunge easterly. LaBerge trend northeasterly and and Myers Myers (1984) (1984) proposed LaBerge and proposed tthat hat the amphibolite—grade amphibolite-grade succession s pre—Penokean pre-Penokean in inage and t hthat a t i itt represents represents successioni is age and history. The majory yet-unrecognized yet-unrecognized part of aa major, of Wisconsin Wisconsin Precambrian Precambrian history. The amphibolitegrade succession with the theChocolay Chocolay Group Group in inwestern western Michigan Michigan and and grade succession may maycorrelate correlate with northern Wisconsiny while the the greenschist greenschist rocks rocksmay may correlate correlatewith withthethe Menomonie northern Wisconsin, Menomonie and/or Baraga Baraga Groups. Groups. The inal folds, fo1 ds higher highergrade grademetamorphism metamorphism and itic The isocl isoclinal andtonal tonalitic intrusives ininthe succession o l d e rpre-Penokean y pre-Penokean intrusives theolder older successionmay may thus thusrepresent representan an older, orogeny. The Proterozoic amphibolite-grade amphi bol i te-grade and and greenschist—grade greenschist-grade rocks ain The Early Early Proterozoic rocksare are over1 overlain nconformably and intruded intruded by by anorogenic anorogenic granites nconformablybybyrhyolite rhyolite pyroclastics pyroclastics and granites of of approximately 1760 1760may. n.y. age age (Smithy (Smith, 1978). 1978). Similar approximately Similar rocks rocks ininthe theBrokaw Brokaw area area ofWausau Wausau may o this t h i syounger youngersequence. sequence. Possibly north of may belong belong tto Possibly also also associated associated with these these volcanic volcanic and and intrusive intrusiverocks rocksare areyounger younger quartzites quartzitessuch such as as those those exposed Baraboo, F1 Flambeaü Ridge,and andBarron BarronHi1 Hills, ambeau Ridgey 1 s Wisconsin. Wisconsin. The Mountain exposed aat t Barabooy The Rib Mountain and MosineeHill Hill quartzites quartzites may also be beof of tthis and Mosinee may also h i s age. age. These These metasedimentary metasedimentary rocks are associated associated locally withdolomite, dolomiteyferruginous ferruginousslate, s l a t enietaconglomerate y metaconglomerate and and chert. chert. are locally with Widespreadfolding folding and and wrench wrenchfaulting faulting at n.y. ago of Widespread a tbetween between 1630-1600 1630-1600 m.y. ago was was of o producea asignificant significant resetting of Rb-Srisotope isotopesystems. systems. s u f f i c i e n tintensity i n t e n s i t to y tproduce sufficient resetting of Rb—Sr These wrenchf afault trend about the Stevens Stevens Point-Neillsville Point—Neillsville These wrench u l t systems systems trend about east—west east-west inin the area and and east—northeast east-northeast in region northwest northwestofofWausau. Wausau. The area in the region The Jump JumpRiver* River, Gilman, Gilmany Monico, andAthens Athensf afaults were probably probably developed developedororreactivated reactivated during during tthis Monicoy and u l t s were h i s major major kinematic event. kinematic event. Although the the Wausau SyeniteComplex Complex (WSC) intruded most thefaulting faulting Although Wausau Syenite (WSC) was was intruded a f tafter e r most of ofthe in this t h i sregion, regionysome some reactivation of of old oldfaults f a u l t scaused caused minor minor offsets o f f s e t s and and local local cataclasi s.. catacl asis,. THE WAUSAU THE WAUSAU SYENITE SYENITE COMPLEX COMPLEX The Wausausyenite syenitecomplex complex(WSC) (WSC) coeval Wolf Riverbath01 batholith are part part The Wausau andand coeval Wolf River i t h (WRB) (WRB) are 1,770 1,030 n.y.anorogenicy anorogenic,granite granite plutons plutons tthat of aa NE—SW—trending NE-SW-trending b e l tbelt of of 1 ¶77 t o to 1 ¶O3 may. hat extends from fromthe the Ba1 Baltic States (Figure t i c Shield Shield to t o the thesouthwestern southwestern United United States (Figure 2). extends 2). Theseplutons plutonsrepresent representthe the llast of Precambrian These a s t major major episode episode of Precambrian g granitic r a n i t i c intrusion in the (1983)has hascompared compared Anderson (1983) thethec hcharacteristics a r a c t e r i s t i c s of the Lake Lake Superior Superior region. regiono Anderson these anorogenic anorogenicplutonsy plutons,and andshows shows dominant rapakivia faffinity. these t h athat t thethe dominant typetype i s is of of rapakivi finity. crystallization According ttoo Anderson (1983, According Anderson (1 983 p. p. 133) 133) crystal 1 ization of ofthese these potassic, potassicyiron-enriched iron-enriched magmas placeaat temperatures between between640 640and and790° 790°Cand andlow lowt ototal t o took o k place t temperatures magmas t a l pressures, pressuresy generally lless than22 kb. kb. The Thepresent presentl i nlinear continuityofoftthis generally e s s than e a r continuity h i s belt b e l t of of roughly roughly coeval plutons and andt htheir apparentshallow shallowdepth depth intrusionsignify signify aa lack lack of coeval plutons e i r apparent of ofintrusion concludes major subsequent subsequentcontinental continental rearrangement rearrangemento rormajor majorup1 uplift. major i f t . He He concl udes tthat hat magmas crustal derivation derivationofofthe the magmas was was aa rresult e s u l t of ofthermal thermal doming doming in in the themantle mantle and and andand mangeritic magma emplacement tthat h a t cogenetic cogeneticanorthositic anorthositic mangeritic magma emplacementmay may have have played played an an active role heatofoffusion fusionaat lower crustal crustal levels. Anderson active role in ingenerating generating necessary necessary heat t lower Anderson of a p1 utonsdo do not notshow show aa consistent consistent age age progression progression of a track, t r a c k yand and feels that t h a t the theplutons that the wasrelated relatedtoto development development the thermal thermal event event was of of a faa ifailed l e d r irift. ft. Four concentrically-zonedy concentrically—zoned,cylindrical cylindrical alkaline plutons make Four alkaline plutons makeupu pthe theWSC. WSC. According to and others(1(l975a, 1981), TheSStettin ing to Van Van Schmus Schmus and others 975ay 1 l975b, 975by 1981 ) The t e t t i n syenite pluton p1 uton crystallized andNinemile Ninemilegranite granitepluton pluton crystallized crystallized WRB and crystallized 1,520 1 y520m.y. m.y. ago, agoywhile whilethe theWRB 1,500 m.y. n.y. ago. He feels that systemsare are clean clean enough enought oto assure assure tthat 1,500 ago. H e feels t h a tthe theU—Pb U-Pb systems hat the in ages This difference difference in radiometric the difference difference in ages iis s real. This radiometric age age is i s in inaccord accord with cross-cutting the ffield. The ooldest, alkaline with cross-cutting relationships relationships shown shown ininthe i e l d . The l d e s t y most most alkaline Stettin zone and S t e t t i n pluton pluton(Figure (Figure3,3,#1) # Ihas ) hasa wall a wall zone andcore corerimmed rimmed by by nepheline nepheline syenite. syenite. Following the emplacement theSStetting Fo1 lowing the emplacement ofofthe t e t t i n g pluton, p1 uton three threepipe—like pipe-1 i ke plutons p1 utonswere were intruded in series s e r i e ssouth-southwest south-southwest from fromWausau: Wausau: the Wausau pluton intruded in the Wausau pluton(Figure (Figure 3, #2), #2) the Rib pluton consisting consisting mostly the Rib Mountain Mountain pluton mostly of quartz quartz syenite syenitewith withnumerous numerous large xenoliths (Figure 3 # 3 ) , and and ffinally i n a l l y the the Ninemile Ninemile granite granite pluton pluton (Figure (Figure s3,y #4). #4). xenoliths (Figure 3, #3),  �-4- / / Figure F i g u r e 22 —-- Proterozoic P r o t e r o z o i c anorogenic a n o r o g e n i c granite g r a n i t ecomcomplexes p l e x e s of o f North N o r t h America America (Anderson, (Anderson, 1983, 1983, p. p. 135) 135) 042 miles Figure -- Components Components ooff the t h eWausau Wausau F i g u r e 33—— syenite s y e n i t e complex. compl ex. �—5-. The ssouthern o u t h e r n hhalf a l f of o fthe t h eWausau Wausau pluton p l u t o n was was stoped s t o p e d by b y the t h e Rib R i bMountain Mountain pluton, p l u t o n ,whose whose The were ooccupied ccore o r e and and ssouthern o u t h e r n rrim i m were c c u p i e d bby y t the h e NNinemile i n e m i l e ggranite r a n i t e pluton. pluton. G Granite r a n i t e and and monzonitea paplites qquartz u a r t z monzonite l i t e s fform o r m aappartial a r t i a l core c o r e rim r i m in i nthe t h esouthern s o u t h e r n lobe l o b e of o fthe t h eNine.Ninem i l e pluton, p l u t o n 9and and occupy occupy sseveral e v e r a l llarge, a r g e 9 irregular i r r e g u l a rareas areas west, west, southeast, s o u t h e a s t , and and north north mile of o f the t h eWasuau Wasuau complex. complex. S u b h o r i z o n t a l pegmatite p e g m a t i t e ddikes i k e s and and pods pods iin n the t h e Ninemile Ninemile Subhorizontal granite mineral g r a n i t e contain c o n t a i n miarolitic m i a r o l i t i cavities c c a v i t i whose e s whose m i n e r aassemblages l assemblages indicate i n d i c a t ethermal thermal shockand ands hshallow shock a l l o w c rcrystallization y s t a l 1 i z a t i o n (Faister, ( F a 1 s t e r 91984). 1984). Several Several younger, younger, possibly possibly related werei nintruded r e l a t e d quartz q u a r t z monzonite monzonite pporphyry o r p h y r y pplugs l u g s were t r u d e d a cacross r o s s f afaults u l t s t that h a t ccut u t the the The Wausau Wausau hasa as m small ssyenites. y e n i t e s . The p l pluton u t o n has a l l c core o r e oof f ggranite r a n i t e which w h i c h closely c l o s e l yresembles resembles N i n e m i l e ggranite. r a n i t e . IIn n general genera1 the t h e intrusive i n t r u s i v esequence sequence represents represents a a continual continual tthe h e Ninemile eenrichment n r i c h m e n t o of f t the h e ddifferentiating i f f e r e n t i a t i n gmagmas magmas i ninssilica. ilica. Figure which shows showst hthe F i g u r e 44 is i s aageologic g e o l o g i cmap map of o f Marathon Marathon County, County, which e ccontext o n t e x t ooff the the Wausaus ysyenite complex Wausau e n i t e complex andand i t sitsd discordance i s c o r d a n c e w iwith t h r erespect s p e c t t oto eeast-northeasterly ast-northeasterly trends A pportion o r t i o n of o f the t h e Wolf W o l f River R i v e r batholith b a t h o l i t hcan canbe beseen seen t r e n d s iin n the t h e older o l d e r rocks. rocks. A in i n the t h e eastern e a s t e r nquarter q u a r t e rofoMarathon f MarathonCounty. County. The Wolf The W o l f RRiver i v e r bbatholith a t h o l i t h is i sseparated separated from h e Wausau Wausau s ysyenite e n i t e ppluton l u t o n bby y aa major m a j o r fault f a u l tsystem systemwhich w h i c h bends bends abruptly a b r u p t l ywestward westward from tthe along a l o n g the t h e southern s o u t h e r n border b o r d e r of o fMarathon Marathon County. County. The The Wausau Wausau ssyenite y e n i t e complex complex occupies occupies the t h e concave concave pportion o r t i o n ooff this t h i s bend. bend. It I tisi spossible p o s s i b l ethat t h athe t t hsyenite e s y e n i tcomplex e complexhad had an an iimportant m p o r t a n t kkinematic i n e m a t i c iinfluence nfluence — - asast that h a t ooff aa knot k n o t --on onthe t h edevelopment development ooff the the ffaults, a u l t s , although a1 though the t h e syenite s y e n i t e iiss clearly c l e a r l yoffset o f f s e tby b ymany many ooff them them ((later l a t e r reactivation). reactivation). Figure showingt the F i g u r e 5 is i saageologic g e o l o g i cmap map of o fthe t h eWausau Wausau syenite s y e n i t e complex complex showing h e sstops t o p s ffor or tthis h i s ffield i e l d ttrip. r i p . Several x t r a stop s t o p descriptions d e s c r i p t i o n s are a r e included i n c l u d e dso sothat t h a one t onemay may Several eextra use The base base map mapf for use t the h e ffield i e l d guide g u i d e for f o r self—guided s e l f - g u i d e d f ifield e l d ttrips. r i p s . The o r the t h e geology geology is i s from f r o mLaBerge LaBerge and and Myers Myers 1984 1984 rreport e p o r t on on the t h eGeology Geology of o fMarathon Marathon County County being being published pub1 i s h e d by b y the t h e Wisconsin Wisconsin Geological G e o l o g i c a l and and Natural N a t u r a l Survey. Survey. Additional A d d i t i o n a l mapping mapping ssince i n c e submission submission oof f tthe h e map r tthe h e Survey e p o r t has e s u l t e d in mapf ofor Survey rreport has rresulted i n some some rrevisions e v i s i o n s -particularly p a r t i c u l a r l yofothe f t hWausau, e Wausau, Rib R i bMountain, Mountain, and and Ninemile N i n e m i l e plutons. p1 utons. Figure showingl olocations Some ooff i s aa topographic t o p o g r a p h i c map map showing c a t i o n s ooff stops s t o p s and and routes. r o u t e s . Some F i g u r e 66 is tthese h e s e wwill i l l not n o t be be vvisited i s i t e d dduring u r i n g t the h e f field i e l d trip t r i p owing o w i n g tto o time t i m e llimitations. i m i t a t i o n s . These maps werep lplotted ont the maps were o t t e d on h e ffollowing o l l o w i n g 15' 1 5 ' topographic t o p o g r a p h i c quadrangles quadrangles (clockwise ( c l o c k w i s e from f r o m the the Hamburg,MMerrill, nnorthwest: o r t h w e s t : Hamburg, e r r i l l ,Wausau, Wausau, and and Marathon. Marathon. �LATE PRECAMBRIAN EABLY PRECAMBRIAN MIDDLE PRECAMBRIAN SCALE Figure 4 -- Geologic map of Marathon County by LaBerge and Myers, 1979 Wisconsin Geological and Natural History 3urvey, Interim Copy. WISCONSIN GEOLOGICAL AND NATURAL HISTORY SURVEY Imt.ro Copy) MARATHON COUNTY,WIS. OF GEOLOGY EXPLANATION 0) �EXPLANATION EXPLANATION f - e-i STRUCTURE SYMBOLS SYMBOLS STRUCTURE a Alluvium go Glacial G l a c i a l outwash outwash gt Glacial G l a c i a l t till ill /-l.-#..-l N UJ t_> LATE LATE PROTERO- Contact: dashed dashed where where dashed f e r r e d ; dotdashedwhere wherei ninferred; tted e d where where covered covered UNCONFORMITY—.._---—... UNCONFORMITY- db Diabase Diabase Dike QD qp Quartz monzonite monzonite porphyry Quartz .~ o r.o h- v-r v . Granite aplite it e Granite apl Ninemile Ninemile granite g r a n i t e and and quartz monzonite monzoni t e Quartz syenite syenite Amphibole Amphibole ssyenite yenite Pyroxene-bearing te Pyroxene—bearingsyeni syenite zol C ZOIC AI '' ga ng qs as PS sv sa Syenitized Syeni t i z e d volcanic v o l c a n i c rocks rocks Syenite aplite it e Syeni t e apl Fault: dashed dashed where where iinferred; n f e r r e d ; dotted d o t t e dwhere where covered 70 70 \ S t r i k e and and ddip i p of o f layering layering Strike so 80 < S t i k e and and ddip i p oof f ffoliation oliation Stike (Border phase) phase) r.-I /'""-I is Hybrid Hybrid llensoidal e n s o i d a l syenite syenite Nepheline Nephel i n e ssyenite yenite ts Tabular Tabular syenite syenite ns LI MAP AREA I"- ig Leucocratic Leucocratic granite granite qm Quartz Quartz monzonite monzonite qd Quartz Quartz ddiorite i o r i t e and and ddiorite iorite vs Volcanogenic Vol canogenic sedimentary sedimentary rocks rocks -J LI Felsic F e l s i c volcanic v o l c a n i c rocks rocks iv Intermediate Intermediate volcanic rocks rocks my Mafic volcanic volcanic rocks rocks Mafic fv q Metaquartzite Metaquartzi t e bs Biotite B i o t i t e schist schist am Amphibolite Amphi bol it e Scale, miles Scale, miles .3 2 1984 1984 -- Figure5 5—— Figure GEOLOGIC MAP OF OF THE GEOLOGIC MAP WAUSAU COMPLEX, WAUSAU SYENITE COMPLEX, CENTRAL WISCONSIN WISCONSIN CENTRAL y Paul by PaulE. E. Myers Myers �—7- - // Wausau Pluton Rib Mountain Pluton a qm N r qd qm �0 -.5 r1 0 c-I- U, -.5 0 -I, 0) 3 (D c-I- 0 -S (D• m F i g u r e 6-- F i e l d t r i p r o u t e map f o r s t o p s 1 t h r o u g h 1 1 . — , GM *_ .— 0 0 3 —— — 0 - CONS I SW 1-625w 2 3 OW - ROAL 20 FEET SW - 16 — ' / 21 . J 4 - '1. •1 — 15W — 2$ - - - : lOW , .ci WAUSAU QUADRANGLE WISCONSIN—MARATHON CO. IS MINUTE SERIES (TOPOGRAPHIC) — 8945 WISCONSIN—MARATHON CO. IS MINUTE SERIES (TOPOGRAPHIC) MARATHON QUADRANGLE a 5 NILOMETSOS 21GM SifT - Mitts — —— —— STATE OF WISCONSIN �-9— STOP #1 STOP #1 - TITLE: TITLE- RIB MOUNTAIN SUMMIT SUMMIT - -GENERAL GENERALGEOLOGY GEOLOGY RIB MOUNTAIN LOCATION: R i b Mountain Mountain SState t a t e Park Park oobservation b s e r v a t i o n platform: p l a t f o r m : SE/4 SE/4 Sec. Sec. 8,8, T28N, T28N, Rib R7E; Wausau Wausau115' Quadrangle, Wausau West7.5' 7.5' Quadrangle R7E; 5 ' Quadrangle, Wausau West Quadrangle DATE:: DATE - March, March, 1984 1984 DESCRIPTION: Fromt hthis vantageppoint, can gget From i s vantage o i n t , one one can e t aa general general perspective p e r s p e c t i v e of o f the t h e major major elements ooff the elements t h e geology geology and and geography geography of o f the t h eWausau Wausau region. r e g i o n . This T h i s observation observation andaall edgeooff nnearly ttower o w e r and l l of o fRib R i bMountain Mountain are a r e on on the t h e upturned u p t u r n e d edge e a r l y vertical v e r t i c a lbeds beds ooff very v e r y coarse—grained c o a r s e - g r a i n e d mmetaquartzite e t a q u a r t z i t e wwith i t h ttops o p s facing f a c i n g southward. southward. Facing F a c i n g ddirection irection andooccasional iiss indicated i n d i c a t e dbyb ysparsely s p a r s e l yexposed exposed cross—bedding c r o s s - b e d d i n g and c c a s i o n a l rripple i p p l e forms. forms. The RRib Mountainqquartzite The i b Mountain u a r t z i t e is i s an an arcuate, a r c u a t e , keel-shaped keel-shaped xenolith x e n o l i t hembedded embedded in in quartz thet hnorthern q u a r t z ssyenite: y e n i t e : iti tisi situated s s i t u a t eon d on e n o r t h e r edge n edgeofo the f t h eRib R i bMountain Mountain syenite-quartz b' s y e n i t e - q u a r t z ssyenite y e n i t e ppluton, l u t o n , whose whose c ocore r e ( j(just u s t ssouth o u t h oof f hhere) e r e ) iiss occupied o c c u p i e d by ggranite r a n i t e and and qquartz monzoniteo of u a r t z monzonite f t the h e nnorthern o r t h e r n llobe o b e ooff the t h e Ninemile N i n e m i l e ppluton. luton. MosineeHHill oni it) Mosinee i 1 1 ssoutheast o u t h e a s t oof f hhere e r e ((the t h e knob knob wwith i t h tthe h e radio r a d i o antenna antenna on t ) and and Hardwood h i hill l l southwest Hardwood southwesto fofhere herea rare e s i similar, m i l a r , bbut u t ssmaller m a l l e r qquartzite u a r t z i t e xenolith xenolith remanents t hthat a t aare r e l olocated c a t e d i in n analogous s i t i o n s i nint hthe e ccylindrical y l i n d r i c a l Rib Rib remanents analogousp opositions Mountain ppluton. The qquartzite Mountain l u t o n . The u a r t z i t e xenoliths x e n o l i t h s form f o r m about about three—quarters t h r e e - q u a r t e r s o of f aa ccircle ircle with miles. w ith a a diameter d i a m e t e r ooff about about 55 m i l e s . Relict R e l i c t bedding b e d d i n g in i n the t h e quartzites q u a r t z i t e sata Mosinee t Mosinee H i l l (STOP (STOP ##2) 2 ) and H i l Hill l i s isp aparallel r a l l e l t to o eelongation l o n g a t i o n ddirection i r e c t i o n of o f the the Hill andHardwood Hardwood lenticular l e n t i c u l a r xenoliths. xenol it h s . A by 3M 3MCCorporation asaa ssource A large, l a r g e , abandoned abandoned qquarry, u a r r y , ooperated p e r a t e d by o r p o r a t i o n as o u r c e oof f roofing roofing ggranules, r a n u l e s , aaffords f f o r d s an an excellent e x c e l l e n t exposure exposure oof f tthe h e quartzites. quartzites. A A pporphyritic o r p h y r i t i c diabase diabase dike d i k e cuts c u t s through t h r o u g h qquartzites u a r t z i t e s on on tthe h e south s o u t h wwall a l l of o f the t h e quarry, q u a r r y , and and is i s traceable traceable 2 miles iinn float f l o a tforf oabout r about 2 m i l eto s tthe o t hwest—southwest. e west-southwest. The qquarry The u a r r y iis s located l o c a t e d on on the the west R i b Mountain M o u n t a i n aabout b o u t oone-half ne-half m i l e west here. west end end ooff Rib mile west ooff here. The endoof Rib Mountainq quartzite bodyi sis ooffset The eeast a s t end f tthe he R i b Mountain u a r t z i t e body f f s e t by by a a small northeasts m a l l northeast- trending t r e n d i n g ffault. a u l t . This T h i s ffault a u l t is i s parallel p a r a l l e l with w i t h larger l a r g e r faults f a u l t s of o f similar s i m i l a r trend t r e n d that that cut c u t the t h e edges edges of o f the t h e Rib R i b Mountain Mountain pluton. pluton. The Wausaup lpluton andt hthe Rib Mountain ppluton resemblance: ttheir The Wausau u t o n and e R i b Mountain l u t o n show show an an uncanny uncanny resemblance: heir Rib River ccontact o n t a c t is i s covered covered bby y R ib R i v e r aalluvium l l u v i u m jjust u s t north n o r t h of o fRib R i bMountain. Mountain. Each Each ooff tthe h e plutons p l u t o n s is i s cored c o r e d by b y granite, g r a n i t e ,and andeach each contains c o n t a i n s aa large l a r g emass mass of o f metaquartzite metaquartzite iinn its i t snorthern n o r t h e r nedge. edge. One One is i s tempted tempted to t o suggest suggest tthat h a t the t h e apparent a p p a r e n t "duplication" "duplication" was producedb by low-angle was produced y 1ow-angl e f afaulting. u l t i n g . However, e two u t o n s a are r e s significantly i g n i f i c a n t 1y However,t hthe twop ipl'itons different d i f f e r e n t ini nmineral m i n e r a lcomposition c o m p o s i t i o n and and in i n the t h e types t y p e s of o f xenoliths x e n o l i t h s making making up up ttheir heir has aa broad broad intermediate iintermediate n t e r m e d i a t e zones. zones. The The Wausau Wausau s syenite y e n i t e has i n t e r m e d i a t e zone zone of o famphibole amphibole ssyenite y e n i t e containing c o n t a i n i n g mainly m a i n l y metavolcanic m e t a v o l c a n i c xxenoliths, e n o l i t h s , while w h i l e the t h e Rib R i b Mountain M o u n t a i n pluton pluton intermediate zone iiss composed i n t e r m e d i a t e zone composed d odominantly m i n a n t l y o f of q uquartz a r t z s ysyenite e n i t e ( w(with i t h aat texture e x t u r e strongly strongly resembling andxenol xenoliths resembl i n g aarkose) r k o s e ) and it h s mmainly a i n l y o of f mmetaquartzite, e t a q u a r t z i t e , bbiotite i o t i t e schist, s c h i s t , and and amphibol amphi b o l iite. te . Interesting mode I n t e r e s t i n g questions q u e s t i o n s arise a r i s eas astot othe t h origin e o r i g and i n and modeofoemplacement f emplacement of o f these these Thesschists, xxenoliths. e n o l i t h s . The c h i s t s , amphibolite, a m p h i b o l i t e , and and possibly p o s s i b l y at a t least l e a s tsome some of o f the t h e metametaqquartzite u a r t z i t e xenoliths x e n o l i t h sshow show higher h i g h e r grades grades of o fregional r e g i o n a lmetamorphism metamorphism t than h a n iis s displayed displayed in complex i n the t h e rocks r o c k s surrounding s u r r o u n d i n g the t h e Wausau Wausau complex a t ati tits s ppresent r e s e n t llevel e v e l of o fexposure. exposure. It brought I tisi stherefore t h e r e f o r einferred i n f e r r ethat d t h athese t t h e sxenoliths e x e n o l i t hwere s were b r o u g h up t upfrom f r o maamore more highly highly metamorphosed basement. metamorphosed basement. Volcanic V o l c a n i c xxenoliths, e n o l i t h s , like l i k ethose t h o s eseen seenini nthe t h Wausau e Wausau syenite syenite aatt Stop S t o p 33 may may rrepresent e p r e s e n t mmaterial a t e r i a l ccollapsed o l l a p s e d iinto n t o the t h e pluton p l u t o n during d u r i n gcaldera c a l d e r asubsidence. subsidence. �-10STOP STOP ## 22 TITLE: Large Quartzite i o t i t e Schist Schist Xenoliths Xenoliths in inthe t h eCore Core Large Quartzite and andBBiotite Rim, Syenite Pluton R i m , Wausau Wausau Syeni t e Pl uton LOCATION:: South South end LOCATION end of Mosinee Mosinee Hill, HillNE¼, , NEkyNE¼ NEk Sec.27, Sec.27, T28N, TZ8N,R7E R7E Wausau15' 15' and and Wausau WausauWest West7.5' 7.5' quadrangles Wausau AUTHOR: Paul Claire Paul E. E. Myers, Myers, University University of ofWisconsin-Eau Wisconsin-Eau C laire DATE: DATE : February, February ,1980 1980 SUMMARY SUMMARY OF OF FEATURES: FEATURES: This abandoned 3-Mquarry quarryexposes exposesthe thesouth southend endofofaa large large quartzabandoned 3-M quartz- ite smallerxenolith xenolithofofbbiotite i t e xenolith xenolith and and aa much much smaller i o t i t e schist s c h i s t (Figure (Figure 1). 1). The lensoidal shape of the the large extrapolatedfrom fromshapes shapes The lensoidal shape of l a r g e xenoliths xenoliths isi sextrapolated with of smaller smaller ones ones throughout throughout the the intermediate intermediate zone. zone. Near Near iits t s contact contact with quartz syenite syenite the the qquartzite very fine-grained, fine-grained, iinquartz u a r t z i t e is i s impregnated impregnated wwith i t h very nterstitial t e r s t i t i a pink l pinkmicrocline microcl inewhich which selectively s e l e c t i v e l yreplaced replaced certain c e r t a i n layers layers The abundance abundance i n the the quartzite. q u a r t z i t e . The of of i ninterstitial t e r s t i t i a l K-feldspar K-feldspar diminishes diminishes in toward centerofof the the qquartzite toward t the h e center u a r t z i t e xenolith. Smaller Smaller qquartzite u a r t z i t e xenoxenoliths question of whether l i t h shave have been been thoroughly thoroughly granitized. granitized. The The question whether these these xenoliths were carried up up oor downalong alongthe thecylindrical cylindrical wall wall of the xenoliths were carried r down the Wausau syenitepluton plutoni sis sstill Wausau syenite t i l lnot notanswered. answered. Theonly only ssignificant occurrenceofofqquartzite andbbiotite The i g n i f i c a n t bedrock bedrock occurrence u a r t z i t e and iotite schist in ithe Wausau s c h i s t in in this t h i sarea areaisi as s asxenoliths xenoliths n the Wausau syenite syenite pluton. pluton. The The xenoliths following important xenoliths have have tthe h e following important ccharacteristics: haracteristics: showconcentric, concentric,zonal zonalddistribution 11.. They They show i s t r i b u t i o n and and orientation orientationaround around Ninemile pluton. tthe h e quartz quartz monzonitic monzonitic core—-the c o r e ~ t h eNinemile �—11— FIGURE 7--7--Profile south end end of Mosinee Mosinee Hill FIGURE Profile of of the south Hill 2. The occur one one mile outside the the core. core. The largest largest xenoliths occur mile outside 3. Thequartzite quartzite xenoliths xenoliths are The are the the largest largest because because ofof ttheir h e i r lower lower susceptibility totofragmentation susceptibility fragmentation and and assimilation. 4. Flow structure in in quartz quartz syeni syenite andfeldspar feldsparlenticulation lenticulation inFlow structure t e and dicate intrusion dicate intrusion of of the thequartz quartzsyenite syeniteas asaaviscous viscous crystal crystalmush. mush. 5. Mafic xenol xenoliths werebioti biotitized, i ths were t i zed, and and quartzite quartzite xenoliths xenol i thswere were Mafic addition of of KK 0 and Al granitized through through the the metasomatic metasomatic addition and A 1 00 with selective quartzitebybyf ine-grained fine-rained m?c?omcowith selective replacement rep1 acement ofofquartzite dine cl i nealong a1ongbedding bedding planes. planes . 6. Xenoliths north Xenoliths north of of the theRib RibRiver Riverare aredominantly dominantly metavolcanic metavolcanic rocks, rocks, whereasthe thexenoliths xenoliths south southof of Rib Rib River River are quartzite, whereas are dominantly dominantly quartzite, bbiotite i o t i t eschist s c h i sand t andvery verysubordinate subordinatenon-foliated non-foliatedmetadiabase. metadiabase. 7. Quartzgrains grainsi in the quartz quartz syenite syenite and andthe the outer outer part part of of the Quartz n the the Ninemile pluton Ninemi l e pl uton are a r e granular, granular, subangular, subangular, coarse coarse grained grained and and strained. THE THE NINEMILE NINEMILE PLUTON: PLUTON: The Ninemilepluton pluton has hasaa granite granite rim containing The Ninemile containing xenocrystic xenocrystic quartz. quartz. Samples taken at one-mile intervals across the pluton from north to Samples taken a t one-mile intervals across the pluton from north to south and and from from west west tto percentageof of xenocrystic south o east e a s t show show aa decreasing decreasing percentage quartz and an increasing increasing amount amountofof plagioclase plagioclase toward toward the the center center of the quartz and an the pluton. The Thecontact contactaat the Ninemile pluton is locally discordant, t the Ninemile pluton i s locally discordant, as as at at Black Creek1.7 1.7miles milesnorthwest northwest here. Miarolitic cavities, some Black Creek of ofhere. Miarol i t i c cavities, some f ifilled lled with along the the west w i t h large large quartz quartzcrystals crystalsare arecommon common along west side of of the theNinemile Ninemile 1 i z a t i on. They indicate shallow conditions of crystal They indicate shallow conditions of crystallization. pluton. pl uton. �—12- Figure 8--Block diagram o f t h e n o r t h e a s t e r n corner of t h e southern Figure corner southern segment8-Block of t h e diagram Wausau s of y e nthe i t e northeastern p l u t o n a t Mosinee H iof l l the showing abundant, segment Hill showing u ? r t z i t esyenite (q) andpluton b i o t iat t eMosinee s c h i s t (bs) x e n o l i t h sabundant, i n a floww e l l - o r i eof n t ethe d qWausau well—oriented quartzite (q) and biotite schist Cbs) xenoliths flowlaminated, l e n s o i d a l q u a r t z syeni t e (lqsy). The Ninemile q u ain r t zamonzlaminated, lensoidal quartz syenite (lqsy). o n i t e p l u t o n (am) I n t r u d e d the q u a r t z s y e n i t eThe w i tNinemile h o n l y aquartz l o c a l monzdiscordonite pluton (qm) intruded the quartz syenite with ance. The l e n s o i d a l s e n i t e i s bounded on t h e e a sonly t by aa local t h i n wdiscordall o f ance. The slensoidal syenite is bounded wall wofi t h which i s i t s e l f on i nthe f a ueast l t c oby n t aa c t thin eastward amphibole y e n i t e (asy) amphibole syenite (asy) which is itself in fault contact eastward f e l s i c volcanics. These rocks are c u t w i t h sharp discordance by with a felsic volcanics. are icut byreverse a diabase These (db) d i rocks k e which s cwith h a r a sharp c t e r i z ediscordance d b y a strong prominent prominent diabase (db) dike which is characterized by a strong reverse p o l a r i t y . The Qal i s Wisconsin R i v e r alluvium. The shaded r e c t a n g l e polarity. alluvium. The shaded rectangle shows t h e lThe c o a tQal i o n is of Wisconsin the p r o f i lRiver e in F i g u r e 7. shows the icoation of the profile in Figure 7. Fiqure 9-- Camera l u c i d a drawing o f slabbed specimen o f quartz s y e n i t e breccia Figure Cameraangular lucida drawing ( q )quartz , b i o tsyenite i t e s c hbreccia i s t (bs), c o n t a i9—-— n i n g aligned, c l a s t s of o f slabbed banded qspecimen u a r t z i t e of containing aligned, banded are quartzite biotite schist (bs), and feldspar feldspar ( f ) . Qangular u a r t z i t eclasts c l a s t of boundaries t y p i c a(q), l l y sutured and embayed and (f). QuartziteThis clastrock boundaries are typically sutured and embayed by K-feldspar metacrysts. i s i n t e r p r e t e d as a caldera r i m collapse by K—feldspar metacrysts. This rock is interpreted as a caldera rim collapse breccia. Specimen from the r i d g e west o f Rib Mountain. breccia. Specimen from the ridge west of Rib Flountain. �—13— Figure quartzite from the eeast side of of Figure 10-lo-- Granitized Granitized quartzite from the a s t side Mosinee Hill. Banding iiss relict Mosinee Hill. r e l i c tbedding. bedding. Figure 11-.— Coarsemicrocline microcline and and quartz quartz xenocrysts 11-- Coarse xenocrysts from quartz from the west side Mosinee Hill. quartz syenite syenite from the west side of Mosinee Hill. The ar Thematrix matrix iiss angul angular quartz grains quartz grains have have sstrain t r a i n laniellae. lamellae. The Width of of picture isi s3.4 3 . 4mm. mm. quartz and and K—feldspar. K-feldspar. Width �-14STOP STOP #3 #3 AUTHORS: AUTHORS: Mineralogy Bodies M i n e r a l o g y ooff Pegmatite Pegmatite B o d i e s iin n the t h e Ninemile N i n e m i l e Pluton Pluton North N o r t h Central C e n t r a l Sec0 Seco 19, 19, 1T28 28N, N, RR7 7E,E,Wausau Wausau 15t 1 5 ' Quadrangle. Quadrangle. South South side side of miles page 8 ]1 o f County County Highway Highway NN aabout b o u t 44 m i l e s west w e s t of o f US-51,[See US-51 .[See map, map, page and Paul PaulMyers, Myers,UUniversity Al A1 Faister, F a l s t e r , 920 920 McIntosh M c I n t o s h St., St., Wausau, Wausau, and n i v e r s i t y ooff DATE DATE:: - Wisconsin Eau CClaire W i s c o n s i n — Eau laire March, March, 1984 1984 TITLE: TITLE : LOCATION: - SUMMARY OF FEATURES: SUMMARY OF FEATURES: The Ninemile emplaceda at The N i n e m i l e ppluton l u t o n was was emplaced t sshallow h a l l o w ddepth e p t h ((probably p r o b a b l y less l e s s than t h a n 44 km) km) in i n the t h e core c o r e and and southern s o u t h e r n rrim i m of o f the t h e Rib R i b Mountain M o u n t a i n ppluton l u t o n and and iin n the t h e older o l d e r metametaandp lplutonic vvolcanic, o l c a n i c , metasedimentary, metasedimentary, and u t o n i c rrocks o c k s ssurrounding u r r o u n d i n g i tit.. The The Ninemile Ninemile pluton p l u t o n is i s composed composed oof f bbiotite-hornblende i o t i t e - h o r n b l e n d e granite g r a n i t e and and quartz q u a r t z monzonite, monzonite, and and iiss P e g m a t i t e pods pods locally l o c a l l y crowded crowded wwith i t h i inclusions n c l u s i o n s oof f qquartzite, u a r t z i t e , schist, s c h i s t , and and syenite. s y e n i t e . Pegmatite in N i n e m i l e pluton p l u t o n occur o c c u r as: a s : (1) ( 1 ) small s m a l l schlierenlike s c h l i e r e n l i k emasses, masses, (2) ( 2 )zoned zoned dikes dikes i n the t h e Ninemile with vugsi in ( 3simple, ) s i m p l e ,poorly p o o r l yzoned zoned bodies b o d i e s wwith i t h vugs n tthe h e iinternterw i t h miarolitic m i a r o l i t i ccavities, c a v i t i e s ,(3) mediate zone,and and( 4(4) showings eselective andc crystallization m e d i a t e zone, ) l late a t e stage s t a g e bbodies o d i e s showing l e c t i v e eetching t c h i n g and rystallization ooff accessory a c c e s s o r y minerals. m i n e r a l s. DESCRIPTION: The NNinemile Na—feldspar The i n e m i l e ppluton l u t o n is i scomposed composed ooff K—feldspar, K-feldspar, N a - f e l d s p a r ( t(together o g e t h e r uusually, sually, Quartz Q u a r t z grains g r a i n s have have rounded—polygonal shape, resemble like andand c l oclosely s e l y resemble g r agrains i n s f r ofrom m q u quartzite a r t z i t e 1i ke tthat hat r o u n d e d - p o l y g o n a l shape, Hematite andTTi—rich e m a t i t e and i - r i c h b biotite i o t i t e are are exposed exposed aatt Rib R i b Mountain M o u n t a i n and and Mosinee Mosinee HHill i l l. H Ninemile The N i n e m i l e ppluton l u t o n contains c o n t a i n s numerous numerous ppegmatitic e g m a t i t i c pods pods and and ddikes, ikes, llocally o c a l l yabundant. abundant. The which w h i c h aare r e sshallow h a l l o w ddipping i p p i n g eexcept x c e p t nnear e a r t hthe e mmargin a r g i n o of f t the h e ppluton, l u t o n , a factor f a c t o r suggesting suggesting pegmatite emplacementi nincconcentric zonesooff thermal p e g m a t i t e emplacement o n c e n t r i c zones t h e r m a l contraction. c o n t r a c t i o n .Deep Deepweathering weathering of o f the t h e Ninemile N i n e m i l e ggranites, r a n i t e s , especially e s p e c i a l l y in i n aa circular c i r c u l a zone r zonenear n e a r its i t srim, r i mhas , hasproduced produced which has been beenq quarried use as as ppaving aa ferruginous f e r r u g i n o u s gruss gruss w h i c h has u a r r i e d f ofor r use a v i n g mmaterials a t e r i a l s ffor o r over over abundance andt the 90 years. 90 years. The The abundance o f of f l ufluorite o r i t e and h e cconcentric o n c e n t r i c sstructure t r u c t u r e of o f the t h e Ninemile Ninemile pluton mosti nintense t e n s e wweathering e a t h e r i n g r ereflect f l e c t t the h e llocal o c a l effects effects p l u i o n suggest s u g g e s t t that h a t tthe h e zones zones oof most of e t c h i n g and and solution s o l u t i o n of o f quartz q u a r t zgrains g r a i n swith w i t hconsequent consequent o f the t h e formation f o r m a t i o n of o fHF HF to t o cause cause etching ddisaggregation i s a g g r e g a t i o n oof f tthe h e rock. rock. but as pperthite), b u t not n o t always always as e r t h i t e ) , quartz, q u a r t z , biotite b i o t i t and e andamphibole. amphibole. Pegmatite P e g m a t i t e Types Types and and Mineralogy Mineralogy Study N i n e m i l epluton p l u t o nis i hampered s hampered by b ypoor p o o rexposure. exposure. S t u d y ooff pegmatites p e g m a t i t e s in i n the t h eNinemile However,more moret hthan 800 c a v i t i e s ini nover o v e800 r 800pegmatite p e g m a t i t ebodies b o d i e shave have been been However, a n 800 m imiarolitic a r o l i t i c cavities examinedand and examined d edescribed s c r i b e d i n ind edetail t a i l bby y A.A. FFalster. a l s t e r . The The ssearch e a r c h ffor o r pegmatite p e g m a t i t e bodies bodies i s aided a i d e d considerably c o n s i d e r a b l y bby y s tstudying u d y i n g d idistribution s t r i b u t i o n oof f ccertain e r t a i n pplants, l a n t s , infrared i n f r a r e d aerial aerial is average ssize The average i z e •of o f pockets p o c k e t s is is photography, andssubtle photography, and u b t l e vvariations a r i a t i o n s in i ntopography. t o p o g r a p h y . The meters 15 ccentimeters dimension,a lalthough 4.5 xx 1.2 1.2 x 1 meters i n maximum maximum dimension, t h o u g h p opockets c k e t s upupt oto4.5 aabout b o u t 15 e n t i m e t e r s in IIn n addition a d d i t i o n to t oregular r e g u l a pockets, r p o c k e t s ,some some pegmatite p e g m a t i t e dikes d i k e s contain contain have have been been found. found. Some v every r y f ifine n e mmicrocrystalline i c r o c r y s t a l l i n e material m a t e r i a lhas hasbeen been taken t a k e n from f r o m these these vuggy vuggy zones. zones. Some vugs. vugs. masses 1. s c h l i e r e n - l i k emasses masses of o f small s m a l l size s i z eand andsimple s i m p l emineralogy. m i n e r a l o g y . These masses 1. Simple, Simple, schlieren-like are a r e common common i n in t h the e v i vicinity c i n i t y ooff larger l a r q e r dikes. d i k e s . Zoning Z o n i n g iis s generally g e n e r a l l y not n o t well w e l l developed. developed. Grain with G r a i n ssize i z e iincreases n c r e a s e s rregularly e g u l a r l y inward, inward, w i t h the t h e coarsest c o a r s e s t crystals c r y s t a l s ini nthe t h ehanging hanging wall Mineralogy: albite, w a l l near n e a r the t h e center c e n t e r (indicating ( i n d i c a t i n gvapor v a p o r nourishment). nourishment). M i n e r a l o g y : mmicrocline, i c r o c l i n e , a1 b ite, qquartz, u a r t z , and and a few few accessories a c c e s s o r i e s including i n c l u d i n g siderite s i d e r i t e(pseudomorphed (pseudomorphed bby y ggoethite, o e t h i t e , hematite, hematite, f e l d s p a r and and quartz, q u a r t z , and and and oother minerals), and ther m i n e r a l s ) , hematite, h e m a t i t e , hisingerite, h i s i n g e r i t e ,second second generation g e n e r a t i o n feldspar anatase,ssulfides, u l f i d e s , and and ssulfosalts. ul fosal ts. rrare a r e phenakite, p h e n a k i t e , anatase, 1 �—15— 2. zoned,t ytypically Complexly zoned, p i c a l l y l large a r g e ddikes i k e s wwith i t h wwell-formed e l l - f o r m e d mmiarolitic i a r o l i t i c cavities. cavities. 2. Complexly Dikes oof f tthis h i s kind k i n d are a r e typically t y p i c a l l ylarger l a r g e rthan t h a n10 1 0xx10 1 0xx0.2 0.2 meters meters and and eexhibit x h i b i t wellwellDikes defined with d e f i n e d zoning zoning w i t h wall w a l l zones, zones, intermediate i n t e r m e d i a t ezones, zones, and andcore c o r ezones. zones. While W h i l e the the wall w a l l zones zones aare r e usually u s u a l l y poorly p o o r l y defined, d e f i n e d , the t h eintermediate i n t e r m e d i a t ezones zones generally g e n e r a l l y consist consist of zonesoof o f graphic g r a p h i c zones, zones, blocky b l o c k y zones zones (usually ( u s u a l l y near n e a r cores) c o r e s ) and and pocket pocket zones f aaplite. pl i t e . Mineralogy microcline, i c r o c l i n e , albite, a l b i t e , and and quartz q u a r t z are a r e the t h e essential e s s e n t i a l minerals, minerals, M i n e r a l o g y i is s ddiverse: iverse: m often o f t e n occurring o c c u r r i n g ini ntwo twooro more r moresuccessive s u c c e s s i v e generations. g e n e r a t i o n s . Accessory Accessory m i n e r a l s include include minerals several s e v e r a l or o r numerous numerous s pspecies e c i e s o foft hthe e f following: o l l o w i n g : sulfides sul fides — - ppyrite, y r i t e , sphalerite, s p h a l e r i t e , galena; galena; - jamesonite, jamesonite, boulange i t e and and other o t h e r identified i d e n t i f i e dspecies; s p e c i e s ;carbonates carbonates sulfosalts— sulfosalts boulangeite s i d e r i t e (commonly (commonly r ereplaced p l a c e d b ybyF Fe' e m i n e r a l s 1like ike goethite, g o e t h i t e , hematite, h e m a t i t e , and and lepido1e p i d o siderite minerals c r o c i t e )calcite, c a l c i t emangano—calcite , mangano-cal c i t e and and ankerite(?); a n k e r i t e ( ? ) Be—minerals ; Be-mineral s such such as as phenakite, phenaki t e , crocite) b e r t r a n d i t e , bavenite, baveni t e , euclase, e u c l ase, and and beryl; b e r y l and ; andREE—rich REE-ri ch (Th-poor) bertrandite, (Th-poor)ccheralite, h e r a l it e , xenotime, monazite, and xenotime, monazite, and ssynchisite—parisite. ynchisite-parisite. Dikes showt hthe shock: i i.e. Dikes ooff this t h i s type t y p ecommonly commonly show e e feffects f e c t s oof f tthermal h e r m a l shock: . e . brecciated brecciated pockets pockets showing showing secondary secondary overgrowths overgrowths and and cementation. cementation. In a few cases the I n a few cases t h e pockets pockets were all1 fluids, were rrapidly a p i d l y evacuated evacuated oof f a1 f l u i d s and , andmetastable m e t a s t a b l e feldspar f e l d s p a r assemblages assemblages ccrystallr y s t a l 1ized while i z e d from f r o m eescaping s c a p i n g f lfluids uids w h i l e coating c o a t i n g aall l l earlier e a r l i e pocket r p o c k e tphases. phases. 3. with 3. Simple Simple bodies bodies w i t h extensive e x t e n s i v e vuggy vuggy rregions e g i o n s iinn the t h e intermediate i n t e r m e d i a t e zone. zone. These zoning. Wall Wall and andi interThese ddikes i k e s aare r e llarge, a r q e , thick, t h i c k ,and anddodonot n oshow t showwell—developed w e l l - d e v e l o ~ e d zoninq. ntermediate zones ccontain m e d i a t e zones o n t a i n patchy p a t c h y quartz q u a r t z cores. cores. Large c a v i t i e s are a r e rare, rare, Large mmiarolitic i a r o l it i c cavities but b u t myriads m y r i a d s ooff tiny t i n y vesicles v e s i c l e sabound abound in i n the t h e intermediate i n t e r m e d i a t ezone. zone. Maximum Maximum s size i z e ooff these t h e s e ccavities a v i t i e s is i sabout a b o u t 0.5 0.5 - -1.5 1.5centimeters. c e n t i m e t e r s .Dominant Dominant minerals m i n e r a l s are a r e microcline, microcline, albite, a1 b i t e , quartz, q u a r t z , and and tiny t i n y(<1.0 (<1.0 millimeter) m i l 1 i m e t e rhematite ) h e m a t i t ecrystals. c r y s t a l sAccessory . Accessory minerals minerals include i n c l u d e zircon, z i r c o n , fluorite, f l u o r i t e ,F—apatite. F-apatite. L a t e sstage tage m i l k y quartz q u a r t z veins v e i n s cut c u t these these Late milky dikes d i k e s in i n about about 50 50 percent p e r c e n t of o f the t h e cases. cases. 4. andc crystallization 4. Pegmatite Pegmatite bbodies o d i e s wwith i t h l alate t e sstage t a g e sselective e l e c t i v e eetching t c h i n g and r y s t a l l i z a t i o n of of accessory minerals. Although similar in many respects to the complexly A l t h o u g h s i m i l a r i n many r e s p e c t s t o t h e c o m p l e x l y zoned zoned large large accessory minerals. dikes described above, they differ in several significant respects. They typically d i k e s d e s c r i b e d above, t h e y d i f f e r i n s e v e r a l s i g n i f i c a n t r e s p e c t s . They t y p i c a l l y show ani ninward owingt to removalbby show an w a r d d diminution i m i n u t i o n i in n qquartz u a r t z ccontent o n t e n t owing o removal y ccorrosive o r r o s i v e ffluids. luids. Spaces originally filled with quartz were filled by graphic intergrowths Spaces o r i g i n a l l y f i l l e d w i t h q u a r t z were f i l l e d b y g r a p h i c i n t e r g r o w t h s of o fquartz quartz and growtho of wasaccompanied accompanied and feldspar. f e l d s p a r . Secondary Secondary growth f ffeldspars e l dspars was b y by c r ycrystallization s t a l 1 i z a t i o n of of Ti T i oxides o x i d e s (anatase ( a n a t a s e brookite b r o o k i t e rutile) r u t i l e )and and ilmenite. i l m e n i t e . Other Other m i n e r a l s include i n c l u d e Ti Ti minerals bearing b e a r i n g hematite h e m a t i t e (Ti (Ti = = 2-3 2-3 percent), p e r c e n t ) , zircon, z i r c o n , muscovite, muscovite, bertrandite, b e r t r a n d i t e , phenakite, phenakite, cheralite, xenotime, and others. c h e r a l i t e , xenotime, and o t h e r s . — Internal and44above) above) I n t e r n a l Evolution E v o l u t i o nofoMegmatite f MegmatiteDikes Dikes(Types (Types22and Development Development o f ofa av every r y t hthin, i n , fine-grained f i n e - g r a i n e d contact c o n t a c t zone zone (0.5 (0.5 -- 2 centimeters) centimeters) was zone containing c o n t a i n i n g elongate e l o n g a t e bbiotite. iotite. was ffollowed o l l o w e d bby y ccrystallization r y s t a l l i z a t i o n of o fan an extensive e x t e n s i v e wall w a l l zone Vapor nourishment ffed Vapor nourishment e d ccrystals r y s t a l s growing g r o w i n g down down from f r o m hangingwall. h a n g i n g w a l l . Finer F i n e r grained g r a i n e d parts parts of o f the t h e wall w a l lzone zone grew grew upwards upwards ffrom r o m t the h e ffootwall, o o t w a l l , with w i t hoccasional o c c a s i o n a ldevelopment development ooff a coarse-grained c o a r s e - g r a i n e d aggregate aggregate iinn pockets pockets of o f vapor vapor nourishment. nourishment. Rising R i s i n g vapors itially vaporsi ninitially formed coarse - f e l d s p a r i ning rgraphic a p h i c i nintergrowth t e r g r o w t h wwith i t h qquartz, u a r t z , and and llater a t e r blockky blockky formed coarseKK—feldspar K—feldspar. K-feldspar. Quartz Q u a r t z formed formed large l a r g emonomineralic m o n o m i n e r a l i c masses masses in i n the t h eupper—median upper-median ppart a r t of of the t h e dike. d i ken A A few few vvery e r y llarge a r g e crystals c r y s t a l s of o f siderophyllite s i d e r o p h y l l i t eformed formed at a tthe t h ecore c o r emargin. margin. As quenchmay mayhave havea faffected As the t h e pocket pocket stage s t a g e was was approched approched aa ppressure r e s s u r e quench f e c t e d t hthe e ffluid luid yielding y i e l d i n g an an aplite, a p l i t e , while w h i l e in i nother o t h e r sections s e c t i o n s of o f the t h e dike, d i k e , miarolitic m i a r o l i t i ccavities c a v i t i e sformed. formed. These bessingular, These ccavities a v i t i e s may may be i n g u l a r , relatively r e l a t i v e l ylarge l a r g eopenings, openings, oro they r t h e ymay maybe be extensive extensive areas areas iin n the t h e intermediate i n t e r m e d i a t e zone zone ooff tiny t i n yvesicles v e s i c l e swith w i t hmaterial m a t e r i aresembling l r e s e m b l i n ga asponge. sponge. At A t later l a t e stages, r stages,metasomatism metasomatism or o r hydrothermal hydrothermal replacement replacement of o f some some pocket p o c k e t consituents consituents sets other s e t s inwith i n - w i t halteration a l t e r a t i o nofo siderite, f s i d e r i t epyrite, , p y r i t eand , and o t h eminerals r m i n e r a l stot ogoethite, g o e t h i t e , hematite, hematite, hydration h y d r a t i o n of o f phenakite phenaki t e to t o bertrandite, b e r t r a n d i t e , corrosion c o r r o s i o nofo quartz f q u a r t and z andfeldspars f e l dspars(adularia— (adula r i a habit), h a b i t ) , pocket p o c k e t rupture r u p t u r e and and thermal t h e r m a l shock shock oof f pocket p o c k e t cconstituents, o n s t i t u e n t s , resealing r e s e a l i n g of o f the the pocket, pocket, and and continued c o n t i n u e d ccrystal r y s t a l growth growth or o rcomplete complete degassing, degassing, deposition d e p o s i t i o n of o fmetastable metastable feldspar microcline; f e l d s p a r assemblages assemblages ( h(high-sanidine, i g h - s a n i d i n e , oorthoclase, r t h o c l ase, and and iintermediate ntermediate m i c r o c l i n e ; R. R. Martin Martin pers. pers. com., corn., 1983), 1983), and and hhermetical e r m e t i c a l ssealing e a l i n g ooff the t h e pocket(any ~ o c k e(ta n y ffluid l u i d entering e n t e r i n gthe t h epocket pocket �_____ _____ -16— at a t this t h i stime t i m ewould w o u l d quickly q u i c k l yreact r e a c with t w i t hthe t h metastable e m e t a s t a b l ephases.) phases.) C o r r o s i v e ffluids luids Corrosive then t h e n remove remove qquartz u a r t z ffrom r o m ggraphic r a p h i c intergrowths. i n t e r g r o w t h s . uAlpine_typeu "Alpine-type'' m i n e r a l s are a r e then then minerals deposited The llatest a t e s t phase phase of o f pegmatite p e g m a t i t e eevolution v o l u t i o n involves i n v o l v e s the the d e p o s i t e d in i n voids. v o i d s . The formation f o r m a t i o n of o f clay c l a y minerals, m i n e r a l s , etching e t c h i n gofo fpocket p o c k e tconstituents, c o n s t i t u e n t s ,and anddestruction d e s t r u c t i o ndue due to and MMartin, t o weathering w e a t h e r i n g (Jahns, (Jahns, 1955 1955 and and 1982, 1982, Foord Foord and a r t i n , 1979, 1979, Martin, M a r t i n , 1982, 1982, Cern9. tern;. 1982, 1982, Falster, F a l s t e r , 1983.) 1983.) (1) (2) ?T,.z:;7\I /\ ,'K )( • )< )( • • X,('X,( X. / ,t )< x )( >. i ,'—/\ / t, — (3) . x (4) / \I' /"\I\— —— \ / —. • :._r— '. ..';'z( . • • . . • ,< X ''x x (X x . t71/\/\/\J— I/',/\ //,/_\/_I I/\ /N'' i,N\/—, //\ P e g m a t i t e schlieren: s c h l i e r e n : (2) ( I ) Pegmatite (1) ( 2 )Simple S i m p l e"vuggy" "vuggy" pegmatite p e g m a t i t e dike: d i k e :(3)( 3Zoned ) Zoned pegmatite p e g m a t i t e dike; d i k e ; (4) ( 4 )Zoned Zoned dike d i k e with w i t h solution-etched so1 u t i o n - e t c h e d regions. regions. E x p l a n a t i o nofo Symbols f Symbols Explanation ]L"S'i -L m p I= Aplite A p l i t econtact c o n t a c zone t zone I1- 1 Coarse feldspar feldspar Coarse Wall w a l lZone zone lzi Pocket ((or o r aplite a p l i t e unit) unit) Pocket Quartz Q u a r t zCore Core So1 u t i o n - e t c h e d region region Solution—etched Coarse Coarse quartz-feldspar q u a r t z - f e l dspar l o - - Types o fofppegmatite e g m a t i t e bbodies o d i e s i in n tthe h e Ninemile N i n e m i l e pluton. pluton. F i g u r e10—— Figure Types The and ttextural The Ninemile N i n e m i l e granite g r a n i t e itself i t s e lshows f showsmuch much compositional c o m p o s i t i o n a l and e x t u r a l variation: variation: miarolitic xenolithIc common, eespecially s p e c i a l l y that t h a t portion p o r t i o n of of m i a r o l i t i cavities c c a v i t i eand s and x e n o l i t h imaterial c m a t e r i are a l arecommon, the t h e Ninemile N i n e m i l e pluton p l u t o noccupying o c c u p y i n g the t h e southern s o u t h e r n rim r i mofo fthe t h eRib R i bMountain M o u n t a i npluton, p l u t o n ,where where much much sstoped t o p e d rrim i m materials m a t e r i a l s were were never n e v e r completely c o m p l e t e l y assimilated. a s s i m i l a t e d . Table T a b l e1 1 on on page page16 16 gives modal compositions taken andand E—W g i v e s brief b r i edescriptions f d e s c r i p t i o and n s and modal c o m p o s i t i o nfor s f17 o r samples 17 samples t a k einn N-S i n N-S E-W traverses t r a v e r s e s across a c r o s s the t h e pluton. p l uton. �-1 7- —17— TABLE TABLE 1 1 —- MODAL MODAL COMPOSITION COMPOSITION OF O F NINEMILE NINEMILE GRANITE GRANITEPLUTON PLUTON ** -- 1 K- SAMPLE SAMPLE NUMBER* NUMBER* KFel d Feld Plag e r t h Plag -Perth 24 12 28 12 24 72395 28 72395 12 51 72392A 51 12 72392A 723928 62 72392B . 62 62 72391A 66 62 72391A 55 10 72391B 55 72391B 46? 16 72393 46? 72393 10 57 10 10 72394A 10 72394A 23 99 47 72394B 23 72394B 33 30 32 72390A 30 72390A 55 60 72390B 60 72390B 21 12 28 21 72390C 12 72390C 8? 14 8? 72390D 30 14 723900 55 50? 30? 72389 30? 72389 42? 16? 55 72388A 16? 72388A 55 54 723888 723885 41 23 72387A 23 72387A 42 55 25 723878 42 72387B 55 70 72386 72386 37 i7 29 72385 72385 Q Q Bi Bi Am Am 35 35 Tr Tr - 31 31 2 35 35 2 — 29 29 3 — — 21 21 — — 35 35 2 21 21 — - 19 19 - — — 27 27 28 28 32 32 35 35 15 15 26 26 35 35 26 26 25 25 22 22 0.6 0.6 44 77 33 — 37 — — 65 65 76 76 40 40 -- - — 26 — — 10 I - 35 35 — -- 64 64 60? 60? 110 0 34 34 - — 1 16 16 99 40 40 28 28 31 31 22 33 99 Tr Tr - - 55 Tr Tr 22 22 15 15 22 22 25 25 26 26 88 60 60 55 15 15 — - - - 23 23 - — 77 55 34 34 - — 1 1 1 1 1 1 - 22 1 1 — <1 44 46 46 15 15 25 25 22 1 - — 1 88 10 10 — - — — 21 21 28 28 1166 -— 1 1 Rock C lassification North North Rock Classification Leucogranite Leucograni t e Biotite B i o t i t egranite granite Quartz Quartz syenite s y e n i t e W/ w/ xenocrystic xenocrystic quartz quartz Biotite B i o t i t egranite granite Leucogranite Leucogranite Gneissic Gneissic qsy qsy oorr granite g r a n i t e aplite aplite Hematiticquartz quartzmonzonite monzonite Hematitic veins Quartz Quartz syenite s y e n i t e or o r nnzonite m n z o n i t ew/ w/ qq veins B i o t i t equartz quartzmonzonite mnzonite Biotite Biotite B i o t i t egranite granite B i o t i t equartz quartzmonzonite mnzonite Biotite Altered biotite A l t e r e d b i o t i t egranite granite Leucogranite Leucograni t e Hornblende—biotite Hornblende-biotite granite granite Biotite B i o t i t egranite granite Biotite B i o t i t egranite granite Granite Graniteprotomylonite pmtomylonite Leucogranite Leucograni t e Biotite-hornblende Biotite-hornblendequartz quartzmonzonite monzonite sohh Sotth west 'West Hornblende-biotlte quartz moite Hornblende-biotite quartz moii% ite Leuco—quartz Leuco-quartz monzonite mnzonite Granite pmtomylonite Graniteprotomylonite Biotite B i o t i t egranite granite Nnphibole—biotite syenite Ampbi b o l e - b i o t i t e syeni t e (xennllth) (xennl it h ) Mafic syenogabbro Mafic syenogabbro (xenolith) (xenolith) Biotite syenite (xenolith) B i o t i t e syenite (xenolith) Schistose Schistose quartz—plagioclase quartz-plagioclase aplite aplite Quartz Quartzmonzonite monzonite flaser f l a s e rgneissl gneiss Quartz Quartzmonzonite mnzoni t e I — - -- - 1 — 72399 72399 72251 72251 72400 72400 72401A 72401A 72401B 72401B 72401C 72401C 72402A 72402A 72402B 72402B 7294 7294 72403 72403 2 -2 3 - 2 1 <1 - -- -- 1 Sample Sample Location LocationMap Map 1 1 I -"- FA<+ East - I �-18STOP #4 #4 STOP TITLE : TITLE: Metaconglomerate inclusion(?) in the thewest west edge edge of of the the Metaconglomerate inclusion(?)inin quartz quartz syenite in Rib Mountain Mountain Pluton Pl uton Rib NE/4, Sec. Sec. 22, 2 Z Y TT 28 28 N, N y RR 66E,E yMarathon Marathon 15' 15'Quadrangle Quadrangle [See [Seemap, mapypp 88 ]] NW14 NE/4 LOCATION: NW/4 LOCATION: AUTHOR: Paul E. E. Myers, Myersy University UniversityofofWisconsin Wisconsin—- Eau Eau Claire Claire Paul AUTHOR: March, DATE : Marchy1984 1984 DATE: DESCRIPTION: DESCRIPTION: Large Large boulder boulder piles piles south south of ofthe theroad roadcontain containnumerous numerous boulders boulders of highly highly deformed metaconglomerate which cutbybysmall small dikes dikes and and veins veins of quartz quartz syenite syenite deformed metaconglomerate which i s iscut Despite lack of outcrop here, the size, abundance, and uniqueness s i z e y abundancey and uniqueness Despite lack of outcrop herey the and granite. granite. and of that broken loose from a bedrock of this t h i srock rockindicate indicate t h aitt was i t was broken loose from a bedrockledge ledgeby byaafarmer farmer Ninemile granite isi sexposed exposed just east e a s tand and south south of of and hauled h i s pile. pile. Ninemile and hauledinto into tthis here, abundant hereyand and quartz quartzsyenite syenitewith with abundantmetasedimentary metasedimentary and and metavolcanic metavolcanic xenoliths xenoliths similar (Mosinee HHill) i l l ) isi sexposed exposed just east e a s t and and north north of of S t o p #2 #2 (Mosinee similartotothose thoseseen seen at a t Stop There is good enough exposure in this area to that there are There i s good enough exposure in t h i s area t o indicate t h a t there are here. here. several trendingf afaults which have have broken broken the the western N-S and and NE—SW NE-SW trending u l t s which western edge edge of the the several N-S Rib plutoninto into sslices. Rib Mountain Mountain pluton l i c e s . Thus, Thusy the the contact contact relations relations of ofthe therocks rocksseen seen inin these with distribution distribution of these rock rock piles, p i l e s ycombined combined with ofrock rocktypes types ininthe thesurrounding surrounding area, areay can usedtoto develop developa aconception conception relationshipsinin sspite can be be used of of t htheir e i r relationships p i t e of of the the lack lack of of exposure. exposure. The metaconglomerate containsf1flattened andfo1 folded clasts quartzite, The metacongl omerate contains attened and ded c1 a s t s of of banded banded quartzite metafine-grained or metasediment?), fine-grained biotite b i o t i t eschist s c h i sand t andgneiss gneiss(felsic ( f e l s volcanic i c volcanic or metasediment?) metamorphosed fine—grained rocks with porphyritic, morphosed fine-grained a n dandesitic(?) e s i t i c ( ? ) vo1volcanic canic rocks with re1relict i c t porphyriticy vesicular metadioritey and and metagabbro. metagabbro. One One cclast l a s t looks looks vesicular and and tuffaceous tuffaceous textures, texturesymetadiorite, beend idifferentially The cclasts l a s t s have have been f f e r e n t i a l l y flattened flattened with with simulsimul1 i keamphibole amphibole syenite! syeni te! The like Quartzite clasts, c l a s t sbecause y because taneous development of ofa ab ibiotite—chlorite o t i t e - c h l o r i t e ffoliation. o l i a t i o n . Quartzite taneous development of of resistance resistance to t oflattening, f l a t t e n i n gremained y remainedquite quiteround: round:the theschistose schistosemetavolcanic metavolcanic clasts clasts were greatly fflattened, were greatly l d t t e n e d y so so that t h a t their t h e i rlength/thickness lengthlthickness ratios r a t i o s are are up u p to t o 12. 12. of close kink-like folds A later l a t e r episode episode of close folding folding produced produced kink-like folds with with (Figure 11). 11 ). A (Figure consequent second-stagedeformation deformationofof the the cclasts. consequent second-stage lasts. Granitic thethe metaconglomerate Graniticdikes dikesand and veinlets veinletscutting cutting metaconglomerate discordantly discordantlyshow showaa pronounced reductioniningrain grain ssize thethe metacongomerate xenoliths -pronounced reduction i z e in the the vicinity v i c i n i t of y of metacongomerate xenoliths probably in the the water asaa rresult probably due due tto o a change change in water content content in in the the granite granitemagma magma as e s u l t of of Some of the contains granules of quartz Some of the granite contains granules quartz stoping fo much wallrock. stoping fo much wallrock. in tthis K-feldspar in h i s granite granite is is (xenocrysts?) up u p tto o 10 10 millimeters inindiameter. diameter. K-feldspar (xenocrysts?) relationships are are compatible compatiblewith with the the interpretation interpretation that These relationships that highly perthitic. p e r t h i t i c . These highly the rocks rocks here here are are near near the the contact contact between between aa xenolith-rich quartzsyenite syeniteand and the xenolith-rich quartz the (1 500 m.y.). m.y.). the younger younger Ninemile Ninemil e granite (1500 a Andesite Andesite cs cs Chlorite schist schist fv fv Felsic Felsic volcanics volcanics a Porphyritic Porphyritic andesite andesi t e Quartzite qq Quartzite md md Metadiorite Metadiorite pa pa g 11- - Texture Textureofofdeformed deformedand andmetamorphosed metamorphosed polymicti conglomerate. polymicticcconglomerate. Figure 11-Figure �—19— The The mmatrix a t r i x iis s foliated f o l i a t e dand and micaceous micaceous wwith i t h llenticular e n t i c u l a r fragments fragments of o f quartzoquartzoThe cclast l a s t 1lithologies it h o l o g i e s feldspathic andbbiotite. f e l d s p a t h i c rock r o c k (metavolcanic?), (metavo1 c a n i c ? ) , qquartzite, u a r t z i t e , and i o t i t e . The indicate i n d i c a t e deposition d e p o s i t i o n near n e a r the t h e contact c o n t a c t between between aa ccratonic r a t o n i c terrane t e r r a n e mantled m a n t l e d bby y qquartzite uartzite The volcanic portion of the conglomerate resembles those and and aa vvolcanic o l c a n i c terrane. t e r r a n e . The v o l c a n i c p o r t i o n o f t h e conglomerate resembles those possible exposednearby: nearby:t the exposed h e qquartzite, u a r t z i t e , however however has has no no present p r e s e n t nearby n e a r b y source. source. IItt isi spossible that the volcanics were overlain by platform quartzites, eroded, and then deformed t h a t t h e v o l c a n i c s were o v e r l a i n b y p l a t f o r m q u a r t z i t e s , eroded, and t h e n deformed first f i r s tby byflattening f l a t t e n i n gwith w i t development h development oof f foliation f o l i a t i o nand and then t h e n by b y close c l o s e folding folding These types of deformation are not seen in the greenschist facies ( F i g u r e 12). 12). These t y p e s o f d e f o r m a t i o n a r e n o t seen i n t h e g r e e n s c h i s t facies (Figure metavolcanic and pplutonic m e t a v o l c a n i c and l u t o n i c rocks r o c k s of o fcentral c e n t r aMarathon l MarathonCounty County — tthe h e region r e g i o n surrounding surrounding the t h e Wausau Wausau ssyenite y e n i t e complex. complex. - F i gure 1212- Sequence Sequence oof f deformation d e f o r m a t i o n in i n the t h emetaconglomerate. metaconglomerate. Figure F o l i a t i o n was was pprobably r o b a b l y developed d u during r i n g i n iinitial t i a l fflattening lattening Foliation developed ooff the t h e quartzite q u a r t z i t e clasts c l a s t s and and later l a t e rbuckled b u c k l e d by b y close-folding. close-folding. P a r t of o f the t h e chlorite c h l o r i t ewas was replaced r e p l a c e d by by biotite b i o t i t eduring d u r i n gemplaceemplacePart ment ooff the t h e Rib R i b Mountain Mountain pluton. pluton. ment The r o c k s showing showing t hthese e s e t ytypes p e s oof f ddeformation e f o r m a t i o n and t h o l o g y favor favor The absence absence ooff rocks andl ilithology t h e conclusion c o n c l u s i o n that t h a t tthey h e y represent r e p r e s e n t materials m a t e r i a l s carried c a r r i e dupwards upwards during d u r i n g syenite syenite the . empl acement emplacement. Figure Zoned F i g u r e 13—— 13-- Zoned d i k edikes s o f aofp aplitic l i t i c Nr'iineniile i n e m i l e ggranite r a n i t e ccutting uttjng foliated, f o l i a t e d , schistose s c h i s t o s ehiotite b i o t imetaconalomerate t e wetaconalomeratefrom f r o mLoc. LOC.72065 72065 �-20— STOP STOP #5 #5 TITLE: TITLE: Border B o r d e r Phases Phases ooff the t h eWausau Wausau Pluton Pluton LOCATION: LOCATION: WisconsinRRiver Wisconsin i v e r aatt Old O l d Technical T e c h n i c a l Institute, I n s t i t u t eWausau. y Wausau. NEkY 3sy NE¼, NEkY NE¼,Sec. Sec. 35, Wausau115' West7%' 7½' quadrangles. quadrangles. T29N, R7E. T29Ny R7E. Wausau 5 ' and and Wausau Wausau West Lfi'i, Ik1 i flI I R p• rir - 8 •'> . '°r 4. AUTHOR: AUTHOR: Paul E. E. Myers, University Paul Myersy U n i v e r s i t y of o f Wisconsin Wisconsin DATE DATE:: March, Marchy 1984 1984 -- Eau Eau Claire Claire SUMMARY OF FEATURES: SUMMARY OF FEATURES: Flow-lineated F l o w - l i n e a t e d amphibole amphibole ssyenite y e n i t e ccontaining o n t a i n i n g sheet-like s h e e t - l i k e masses masses ooff syenitized syenitized andmmafic aswwell as bblocky ssiliceous i l i c e o u s metavolcanic m e t a v o l c a n i c rrocks o c k s and a f i c s cschist h i s t as e l l as l o c k y xxenoliths e n o l i t h s ooff well bbiotite i o t i t eamphibolite a m p h i b o l i t eand andmetavolcanic m e t a v o l c a n i c rocks r o c k s resembling r e s e m b l i n g tthose h o s e aatt Brokaw Brokaw i is s we11 Xenolith e n o l i t h oorientrientexposed exposed aalong l o n g tthe h e overflow o v e r f l o w channel channel of o fthe t h epower powerdam dam ini nWausau. Wausau. X Thessyenite zonedy rrootless, o o t l e s s y steeply steeply aation t i o n is i s northwesterly n o r t h w e s t e r l y here. here. The y e n i t e i is s cut c u t by by zoned, with ddipping i p p i n g pegmatite p e g m a t i t e vveins eins w i t h quartz q u a r t z cores. cores. LLate a t e f fracture-filling r a c t u r e - f i l l i n g veinlets v e i n l e t s of of rreibeckite e i b e c k i t e are a r e locally l o c a l l yabundant. abundant. DESCRIPTION: Weidman's 203-208) "Wausau-typet' tWausau-type qquartz 907y p.p. 203-208) u a r t z ssyenite y e n i t e isi scomposed composed ooff Weidman's (1(1907, aalkali l k a l i feldspars: f e l d s p a r s : orthoclase, o r t h o c l a s e , microcline, m i c r o c l i n e yalbite, a l b i t e and y andmicroperthite m i c r o p e r t h i t eand and less less abundantb abarkevikite, r k e v i k i t e y hhedenbergite, e d e n b e r g i t e y f afayalite, y a l i t e , bbiotite, i o t i t e yand and quartz. q u a r t z . Accessory abundant minerals allanite(?). a p a t i t e ymagnetite, magneti t e y zzircon, i r c o n and and a1 l a n ite(?). m i n e r a l s i include n c l u d e f lfluorite, u o r i t e apatite, Cross-cutting throughout C r o s s - c u t t i n g relationships r e l a t i o n s h i p shere h e r etypify t y p i fthose y t h o sseen e seen t h r o u g h o uthe t t h Wausau e Wausau a j o r components components a rare e ddescribed e s c r i b e d below n oorder r d e r of o f decreasing d e c r e a s i n g age. age. pluton. Major belowi in pluton. M 1. The The ooldest l d e s t rrocks o c k s aare r e xxenoliths e n o l i t h s ooff schistose s c h i s t o s e biotite b i o t i t eamphibolite a m p h i b o l i t e and and slightly resembl i n gthose t h o s e ata tBrokaw. Brokaw. s1 i g h t l yaltered a1 t e r e dfelsic f e l s metavolcanics i c m e t a v o l c a n i c sresembling Sheet—like masses andf ofoliated S h e e t - l i k e masses o f of s i siliceous l i c e o u s and l i a t e d mafic m a f i c rocks r o c k s occur o c c u r on on the the These iinclusions end ooff the ~ i g u r e114, 4 y Loc. LOC. C). C). These n c l u s i o n s have have ssouth o u t h end t h e exposure exposure ((Figure a andn nearly a pronounced pronounced n onorthwesterly r t h w e s t e r l y s tstrike r i k e and e a r l y v vertical e r t i c a l dip. d i p . This T h i s fabric fabric iiss consistent c o n s i s t e n t with w i t h the t h e concentric c o n c e n t r i c structure s t r u c t u r eofo the f t h Wausau e Wausau pluton p l u t o n northnorthwest here. AA hhighly i g h l y altered a l t e r e d mafic m a f i c xenolith x e n o l i t h at a t Location L o c a t i o n AA (Figure ( F i g u r e 15) 15) west ooff here. has sswirled has w i r l e d ffoliation o l i a t i o nand and isi scut c u by t b yrootless r o o t l e s pegmatite s p e g m a t i t eveins v e i n swith w i t hK—feldK-feldSome o of f t hthe e mmafic a f i c vvolcanic o l c a n i c xenoliths x e n o l i t h s have have walls sspar par w a l l s and and quartz q u a r t z cores. cores. Some rrelict e 1 i c tporphyritic p o r p h y r i t i ctextures: t e x t u r e s mafic : m a f i xenoliths c x e n o l i t h sare a r enow nowbiotite-rimmed biotite-rimmed subhedralccrystals subhedral r y s t a l s ooff hastingsite h a s t i n g s i t e and and ferrohastingsite f e r r o h a s t i n g s i t e (Figure ( ~gure i 15,Loc. 15 LOC. B). 0). �—21- 4 N 0 1•> Figure 15-- Amphibol Amphibolite xenolith F i g u r e 15-i t e ((a) a ) xenol i t h with w i t h swirled swirled lineation l i n e a t i o n and and thin t h i n seams seams oof f ssyenite y e n i t e (Loc. (Loc. A, A, Fig. Fig. 14). Pegmatitic Pegmati t i c vveins e i n s have have KK-feldspar - f e l d s p a r (Kf) ( K f ) cores cores and and qquartz u a r t z (q) ( q ) cores. c o r e s . Late L a t e ffracture-filling r a c t u r e - f i l 1 i n gveins veins are a r e filled f i l l e dwith w i t hcoarse c o a r s elaths l a t h sofo sodic f s o d i camphibole. amphibole. Biotite B i o t i t eand and amphibole amphibole in i n amphibolite a m p h i b o l i t e are a r e about about the t h e same same ccomposition o m p o s i t i o n asast hthose o s e i in n tthe h e enclosing, enclosing, fflow—lineated l o w - 1 i n e a t e d ssyenite y e n i t e (determined ( d e t e r m i n e d by b y microprobe). microprobe). Figure F i g u r e14—— 14-- SSketch k e t c h map map showing showing llocations o c a t i o n s oof f points p o i n t s ooff interest interest Bar B a r sscale c a l e iin n sketch s k e t c h is i s 66 inches i n c h e s long. l o n g . View View is is oblique o b l i q u e toward t o w a r d northwest. northwest. 2. An An eearly, a r l y , flow-laminated, f l o w - 1 aminated, ffoliated o l i a t e d quartz q u a r t z syenite s y e n i t e containing c o n t a i n i n g llenticular enticular xenoliths x e n o l i t h s ooff porphyritic p o r p h y r i t i c felsic f e l s i cvolcanic v o l c a n i crocks r o c k s and and biotite b i o t i t eamphibolite amphibolite with w i t h relict r e l i cmafic t m a f i phenocrysts c p h e n o c r y s t s isi sexposed exposed at a t Location L o c a t i o n B. B. 3. Coarse—grained, amphiboleq uquartz Coarse-grained, f l flow-lineated o w - l i n e a t e d amphibole a r t z s syenite y e n i t e ccuts u t s tthe h e fine-grained fine-grained phase (Loc. B) phase (Loc. B ) with w i t h sharp s h a r p discordance. d i s c o r d a n c e . Although A l t h o u g h tthe h e llensoidal e n s o i d a l and and tabular tabular iinclusions n c l u s i o n s in i n this t h i srock r o c kshow show a a northwesterly n o r t h w e s t e r l y oorientation, r i e n t a t i o n , the t h eenclosing enclosing syenite s y e n i t eshows shows hhighly i g h l y discordant d i s c o r d a n t flow f l o w lineation l i n e a t i o n with w i t hswirls s w i r l sand andeddies eddies Considering C o n s i d e r i n g t the h e llack a c k of of suggesting andvviscosity. s u g g e s t i n g cconsiderable o n s i d e r a b l e tturbulence u r b u l e n c e and iscosity. deformation in the sheets of biotite amphibolite and siliceous metavolcanic d e f o r m a t i o n i n t h e s h e e t s o f b i o t i t e a m p h i b o l i t e and s i l i c e o u s m e t a v o l c a n i c rock r o c k iinn this t h i s syenite, s y e n i t e , aamodel model requiring r e q u i r i n g turbulent t u r b u l e n t flow f l o w in i nthe t h eenclosing enclosing syenite be prot o trouble. t r o u b l e . The The appearance appearance of o f discordance d i s c o r d a n c e may may be pros y e n i t e magma magma r uruns n s i ninto duced duced bby y o obliquity b l i q u i t y ooff lineation l i n e a t i o nwith w i t hrespect r e s p e c ttot othe t h eeroded e r o d e d rock r o c k surface. surface. 4. Late—stage, L a t e - s t a g e , r rootless" o o t l e s s " granite g r a n i t e pegmatite p e g m a t i t e veins v e i n s with w i t h quartz q u a r t z cores c o r e s probably probably rrepresent e p r e s e n t rresidual e s i d u a l lliquid i q u i d segregations s e g r e g a t i o n s along a l o n g incipient i n c i p i e n t thermal t h e r m a l contraction contraction The ppegniatites fractures f r a c t u r e s iin n the t h e crystallized c r y s t a l l i z e d syenite. s y e n i t e . The e g m a t i t e s may may dderive e r i v e from from uunassimilated n a s s i m i l a t e d ssiliceous i 1 i c e o u s rrocks, o c k s , possibly p o s s i b l y feldspathized f e l d s p a t h i z e d qquartzites. uartzites. 5. Coarse, amphibole( a(arfvedsonite andr i riebeckite) Coarse, ssodic o d i c amphibole r f v e d s o n i t e and e b e c k i t e ) ccrystallized r y s t a l 1 i z d d along along fracture appeart otoc ucut f r a c t u r e surfaces1and s u r f a c e s a n d appear t aall l l other o t h e r structures. structures. At Location B, m mafic and ffelsic L o c a t i o n B, a f i c and e l s i c xenoliths x e n o l i t h s are a r e aligned a l i g n e d N1OW, NlOW, v evertical r t i c a l iinn aa medium-grained medium-grained t a btabular u l a r s ysyenite e n i t e w iwith t h a af afabric b r i c ssimilar i m i l a r to t o that t h a tseen seen in i nthe t h emargin margin This h i s rock r o c k is i s cut c u tdiscordantly d i s c o r d a n t l ybyb coarse y c o a r s egray g r a yamphibole amphibole ooff the t h e Stettin S t e t t i n pluton. pluton. T �-22.-22. syenite. Thin, lenticular l e n t i c u l a a.plite r a p l i t veinlets e v e i n l e thave s have o r i e n t a t i oof n N75°W, o f N75OW,40°S 40° ananorientation s y e n i t e . Thin, These common podsand andv eveinlets These sshallow h a l l o w ddips i p s aare r e common i n in g rgranitic a n i t i c pods i n l e t s iin n the t h e syenite. syenite. The ssheet-like, h e e t - l i k e , foliated f o l i a t e dbiotite b i o t i amphibolite t e a m p h i b o l i tat e Location a t L o c a t i oCn has C has e appearance The thet happearance of o f aa dike d i k e (Figure ( F i g u r e 16), 1 6 ) , but b u t its i t scontacts c o n t a c t sare a r e highly h i g h l yconvoluted, c o n v o l u t e d , and and ffoliation oliation is i s deformed, deformed, aalthough l t h o u g h i tit iis s also a l s o locally l o c a l l ycut c u tby b ythe t h e syenite. s y e n i t e . The The cuspate cuspate edge haswhisps whispswwhich edge ooff the t h e amphibolite a m p h i b o l i t e sheet s h e e t has h i c h t atail i l oout u t into i n t o the t h e syenite syenite (Figure ( F i g u r e 17). 17). The The ttrace r a c e of o f lineation l i n e a t i o non onthe t h erock r o c ksurface s u r f a c egives g i v e sthe t h eimpression impression o f sharp s h a r p discordance d i s c o r d a n c e between between t hthe e aamphibolite m p h i b o l i t e ssheet h e e t and e l lineated i n e a t e d syenite. syenite. of andt hthe Irregularities I r r e g u l a r i t i e in s ithe n t hshape e shapeofothe f t hsyenite—amphibolite e s y e n i t e - a m p h i b o l i t e contact c o n t a c t can can give g i v e the the impression i m p r e s s i o n tthat h a t the t h e amphibolite amphibol i t e contains c o n t a i n s ssyenite y e n i t e inclusions i n c l u s i o n s (Figure ( F i g u r e 18). 18). The samea amphibolite is The same m p h i b o l i t e s sheet h e e t onont hthe e eeast a s t sside i d e ooff the t h e channel channel at a t Location L o c a t i o n DD is broken which can canbe bef fitted broken iinto n t o angular a n g u l a r fragments fragments which i t t e d back back together t o g e t h e r again. again. It It is i s therefore t h e r e f o r eapparent a p p a r e n t that t h a t the t h emechanical mechanical behavior b e h a v i o r ooff the t h e amphibolite a m p h i b o l i t e in i n the the syenite s y e n i t e varied v a r i e d significantly s i g n i f i c a n t l yover o v e rshort s h o r tdistances. distances. North North t — * Figure F i gure 16-16-- Deformed, Deformed, f foliated o l i a t e d biotite b i o t i t eamphibolite amphi b o l i t esheet s h e e tini namphiamphibole syenite at Location C. b o l e s y e n i t e a t L o c a t i o n C. Is I s iti a t dike a d i k which e whichwas was intruded i n t r u d e d at a tan an e a r l y stage s t a g e ooff syenite s y e n i t e ccrystallization, r y s t a l l i z a t i o n , then t h e n carried c a r r i e d to t o its its early p r e s e n t location l o c a t i o n during d u r i n g intrusion i n t r u s i o n of o fa asyenitic s y e n i t i crystal c c r y s t amush? l mush? present y can seen Slight, bebeseen S l i g h t ,but b u probably t p r o b a b l ysignificant s i g n i f i c a ndifferences t d i f f e r e n c ein s mineral i n m i n e rchemistry a l c h e m i s t rcan when amphiboleand andb ibiotite when amphibole o t i t e ccompositions o m p o s i t i o n s i in n vvarious a r i o u s inclusions i n c l u s i o n s are a r e compared compared t to o ttheir heir composition c o m p o s i t i o n iin n the t h e coarse coarse and and ffine i n e grained g r a i n e d varieties v a r i e t i e s ofo fthe t h eamphibole amphibole syenite. syenite. Table T a b l e 2 is i s aacompilation c o m p i l a t i o n of o fmicroprobe m i c r o p r o b e date d a t e for f o r these t h e s e minerals m i n e r a l s as as well w e l l as as i n the t h e syenite s y e n i t eand and in i nthe the plagioclase, p l a g i o c l a s e , which which is i s aa persistent p e r s i s t e n taccessory a c c e s s o r y mineral m i n e r a l in inclusions. i n c l usions. �—23- Figure edgeof of foliated, Figure 17-- Cuspate Cuspate edge f o l i a t e d ,sheet—like sheet-1 ikemass mass of biotite b i o t i t eamphibolite amphibolite ininlineated lineatedamphibole amphibole syenite. syenite. Bar scale scale iiss 66 inches Location C. Bar inches long. long. Location C. Figure 18-18—-Pseudoxenol Pseudoxenolith syeniteinin bbiotite Figure i t h of ofsyenite i o t i t eamphibamphibolite 01 i t e ata tLocation Location C. C. �-24- Figure Segmented amphibolite F i g u r e 19—— 19-- Segmented b i obiotite t i t e am p h i b o l i t e ssheet h e e t iinn lineated, l i n e a t e d , coarse-grained c o a r s e - g r a i n e d amphibole amphibole ssyenite. y e n i t e . Location L o c a t i o n D. D. Rule R u l e iis s six s i x inches i n c h e s long. long. TABLE 22 TABLE ANALYSESOF OFMAJOR MAJORMINERALS MINERALS SYENITESAND ANDINCLUSIONS INCLUSIONSAT ATFIELD FIELD TRIP STOP ELECTRON MICROPROBE MICROPROBE ANALYSES I NINSYENITES SFOP #5 #5 AMPHIBOLES WPHIBOLES Si02 Ti02 A12O3 FeO + FeO + MgO MgO CaO CaO MoO MnO Na20 K20 TOTAL rOTAL Fe2 03 I DESCRIPTION DESCRIPTION A/4* 43.30 1.44 6.64 Fe203 28.84 3.60 28.84 3.60 9.93 9.93 0.99 0.99 2.24 1.03 98.01 38.01 Green amphibole Green amphibole i n inf ofoliated l i a t e d bbiotite iotite amphibolite a m p h i b o l i t e xxenolith e n o l i t h in i n syenite syenite B/3 42.07 1.40 6.32 32.55 32.55 1.56 1.56 9.28 9.28 0.69 0.69 2.24 1.16 97.27 37.27 Medium—grained. Medium-grained. eearly a r l y phase phase amphiamphi- D/6 43.20 1.54 6.35 29.63 29.63 2.75 2.75 9.72 9.72 0.79 0.79 2.32 1.14 97.44 97.44 G/5 42.20 1.77 8.14 25.92 25.92 5.03 5.03 10.79 10.79 0.62 0.62 2.12 1.23 H/2 41.32 1.36 8.10 29.04 29.04 2.76 2.76 10.63 10.63 0.81 0.81 1.89 1.32 97.23 97.23 35.54 35.54 3.77 11.67 31.07 4.34 0.02 0.45 0.04 9.10 96.00 96.00 35.29 3.34 11.43 35.77 1.93 0.04 0.35 0.00 8.93 98.08 98.08 D/4 36.39 2.36 10.96 32.87 3.65 0.14 0.27 0.01 8.98 95.84 95.84 G/5 35.96 3.62 12.36 27.14 6.70 0.02 0.34 0.06 9.21 95.41 Yellow—orange Y e l l ow-orange t to o orange—brown orange-brown f ofolia 1i a in i n biotie—amphibole b i o t i e - a m p h i b o l e sschist chist HI? 35.64 3.49 12.82 30.74 3.91 0.02 0.52 0.02 9.19 96.35 96.35 Raggedyyellow—brown Ragged e l l o w - b r o w n wwith i t h green, green, anhedral amphibole amphiboleand andf lfluorite anhedral uorite bbole o l e syenite: s y e n i t e : green green amphibole amphibole olive o l i v e green green to t oolive o l i v ebrown brownamphiamphibbole o l e in i n lineated l i n e a t e damphibole amphibole syenite syenite green amphibole amphibolei in brownbbiotite n brown iotite 97.82 97.82 green cclots l o t s or o r plagioclase plagioclase BIOTI TES BIOTITES A/2 A12 8/1 I Green amphibolei in Green amphibole n lineated, l i n e a t e d ,coarse— coarsegrained g r a i n e d amphibole amphibole ssyenite, y e n i t e , late l a t ephase phase I Yellow—brownw with Yellow-brown i t h mmetamict e t a m i c t zzircon ircon iinn green green amphibole: amphibole: amphibolite a m p h i b o l i t e xeno. xeno. Olive O l i v e brown brown wwith i t h aapatite p a t i t e in i ngreen green amphibole amphibole cclusters lusters Yellow—brown Yellow-brown a nanhedral h e d r a l b ibiotite o t i t e with with ffluorite l u o r i t eini green n greenamphibole amphi b o l e PLAGIOCLASE FELDSPAR FELDSPAR D/2: 1.73%An 0/2: 1.73%An SampleLLocations: Sample ocations: G/3: G/3: 10.24-18.41%An 10.24-18.4l%An Avg. Avg. 13.12%An 13.12%An H/3: 8.83-l2.44%An 8.83-12.44%An H/3: Zoned Zoned Plag. Plag. = =1O.68—8.67%An. 10.68-8.67%An. SamplesA Aand andB Ba rare fromL oLocation 14: Sample SampleG Gi sisf from andHHi is i g u r e 14: r o m LLocation o c a t i o n CC, , and s from from Samples e from c a t i o n B Bi ninFFigure Location Location D 0 iin n Figure F i g u r e 14. 14. ** Field F i e l dnumber/number number/number of o f analyses a n a l y s e s averaged averaged �—25— -25STOP #6 STOP TITLE:: TITLE LOCATION: AUTHOR: Contaminated Amphibole Quartz Quartz Syenite Contaminated Amphibole Syenite—- Wausau Wausau Pluton Old quarry behind Old behind Employers' Employers1 Mutual Mutual Insurance Insurance Company Company ooffices, ffices, NW/4, SE/4, SE/4, Sec. Sec. 27, NW/4, 27, TT 29 29 N, N , RR 77E;E ;Wausau Wausau West West 7.5' Quadrangle Quadrangle Paul Paul E. E. Myers, Myers, University U n i v e r s i t yofo fWisconsin W i s c o n s i n— - Eau Eau Claire Claire April,1 , 1984 Apri 1984 DESCRIPTION: DESCRIPTION: Coarse pink and and brownish brownishgray grayamphibole amphibolequartz quartzsyenite syenite iiss well exposed in in Coarse pink we 11exposed relatively leadinginto into the the offices offices of of r e l a t i v e l y fresh fresh faces faces of of an an old old quarry quarry along along aa road road leading Four facies were Employers' Mutual Employers' Mutual Insurance InsuranceCompany. Company. Four were recognized: recoanized : (1) . ( 1 )brownish brownish gray quartz-bearing quartz—bearingsyeni syenite, (2) coarse, coarse, dark dark gray gray amphi amphibole syenite, ((3) 3 ) pink pink gray t e , (2) bole syenite, quartz syenite , and(4)( 4medium—grained ) medium-grained pinkish syeni t e with withabundant abundant volcanic vol canicxenoliths, xenol i thsand brown brownishgray grayamphibole amphibole quartzsyenite syenitewith withmagnetite magnetitesegr segrations. ations. brown t to o brownish quartz The pinksyeni syenites havea ad idistinctly higher Fe3+/Fe" Fe3/Fe ratio The pink t e s have s t i n c t l y higher r a t i o than than ) (See Table (See Table 33 ). Magnetite sheets and irregular masses occur in the medium— the gray gray syenites syenites Magnetite sheets and irregular masses occur in the mediumThe magnetitegrained syenite syenite along along the the road road on onthe the east east side side of of the grained the outcrop. outcrop. The bearing aeromagnetic on the themap map bearing quartz syenite syeniteforms forms aalarge, large,crescentic crescentic aeromagneticanomaly anomalyon by Tyson, and and Page, Page, (1963). (1963). The by Henderson, Henderson, Tyson, The anomaly anomaly iis s concentric concentricand andconcordant concordant with the the structure structureofofthe theWausau Wausau pluton. pluton. The concentric structure structure of this plutonisi accentuated s accentuatedby bythe theoccurrence occurrence The concentric t h i spluton large quartzite just north north of ofhere hereon on the thetree—covered tree-covered hhillside i l l s i d e of of numerous, numerous, large Unlike the Rib quartzite xenolith, xenoliths. Unlike Rib Mountain Mountain quartzite xenolith,this t h imass s masscomprises comprisesmany many Orientation of smaller quartzite blocks. of xenoliths xenoliths here here and and elsewhere elsewhere in the the smaller blocks. Orientation Wausau plutoni sisconcentric concentricand andnearly nearlyvertical vertical — aa factor strongly stronglysuggesting suggesting Wausau pluton subvolcanic emplacement withsuccessive successivecollapse collapse and and intrusion intrusion ofofmagma subvolcanic emplacement with magma into xenolithsaat concentric of the The xenoliths t tthis h i s location location concentric fracture systems systems of the caldera caldera rim. The are quite unlike pluton: they are unlikethose thoseanywhere anywhere eelse l s e in in the theWausau Wausau pluton: they consist almost almost showing pre-intrusion metamorphism. pre-intrusion metamorphism. eentirely n t i r e l y ofoffelsic f e l s ivolcanics c volcanics showingvirtually v i r t u a l lno y no (See Figure (See Figure 20 20 ). DATE: DATE : - - 0 meter (n detafled area) Figure 20-s i c volcanic i t h s (dotted) flow-1 ineated Figure 20-- Fel Felsic volcanic xenol xenoliths (dotted) in flow-lineated amphibole quartz syenite. amphibole quartz �-26— TABLE 33 TABLE Bulk compositionso foft hthe Bulk chemical chemical compositions e f ofour u r pprincipal r i n c i p a l quartz q u a r t z syenite syeni t e facies f a c i e s from from Employers' Mutual Mutual Insurance InsuranceCompany Company Quarry. Quarry. - Description Description — EW-5 EN-5 EW-3 EN-3 (WEST) (WEST) ( EAST) (EAST) NSI NSI (SOUTH) (SOUTH) BrownishBrowni shgray gray Coarse, Coarse, dark dark gray gray Pink Pink syenite, syeni te, with with volcanic v o l cani c xenoliths xenol it h s 1 SEI SE I (NORTH) (NORTH) Medium-grained Medi urn-grai nec syenite syeni t e 63.05 63.55 63.90 64.10 Ti02 0, 0.78 0.54 0.47 0.48 A1203 12.60 15.16 14.14 15.17 Fe203 1.91 1.25 5.42 4.58 FeO FeO 7.72 3.48 1.32 1.44 MnO ^In0 0.34 0.16 0.14 0.12 MgO w 0.41 0.16 0.45 0.09 CaO CaO 2.66 1.72 1.35 1.50 Na2O 1a20 4.80 5.52 6.32 5.17 4.22 5.67 6.34 5.57 H20 +zO 0.76 0.42 0.56 0.26 P205 0.22 0.06 0.05 0.06 CO2 ;02 0.28 1.92 0.62 0.09 BaO BaO 0.094 0.066 0.024 0.036 Zr02 Zr02 0.222 0.114 0.062 0.071 154 118 80 80 78 83 67 42 Si02 S i 0, n È,O 1(20 K2 Rb sr Rb Sr ppm P P ~ In with I n comparison comparison w i t h Nockolds' Nockol ds ' (1954) (1954) average average syenite syeni t e composition composi t i o n (see (see ), these these quartz q u a r t z syenites syenites aare r e rricher i c h e r in i nSi09 S i O and and total t o t a l iron i r o nand andpoor poor Table ), Table contents a'e a e also a l s olow lowcompared compared to to T h e i r Rb Rb and and SSrr contents in i n alkalies a l k a l i e s and and lime. lime. Their other o t h e r similar s i m i l a r rocks. rocks. * From Sood, Myers, Myers, and andBBerlin, From Sood, e r l i n , 1980, 1980, p. 21 21 6 �—27- STOP STOP #7 #7 TITLE: TITLE : Quartz-sillimanite-muscovite andqquartzite Quartz-sillimanite-muscovite sschist c h i s t and u a r t z i t e xxenoliths e n o l i t h s in in LOCATION: LOCATION: SE¼ SEk , AUTHOR: AUTHOR : Paul Paul E. E. Myers, Myers, University U n i v e r s i t y of o fWisconsin Wisconsin -- Eau Eau Claire Claire quartz q u a r t z syenite s y e n i t e of o fthe t h eWausau Wausau pluton. pluton. T29N,R7E; R7E;Wausau Wausau quadrangle[ F[Figure , NE¼, NEk, T29N, 1 515' ' quadrangle i g u r e 6] 61 - March, March, 1984 1984 DESCRIPTION: DESCRIPTION : DATE: DATE : Xenoliths mainly X e n o l i t h s in i n the t h eWausau Wausau ssyenite y e n i t e ppluton l u t o n aare re m a i n l y ssyenitized y e n i t i z e d mafic m a f i c and and interinterFelsic abundant, as as F e l s i c metavolcanic metavol c a n i c rocks r o c k s are a r e locally l o c a l l yabundant, at a t the t h e old o l dTechnical T e c h n i c a l School School (Stop ( S t o p 5), 5), and and may may rrepresent e p r e s e n t pportions o r t i o n s ooff the t h e volcanic volcanic mediate metavolcanic mediate metavol c a n i c rocks. rocks. cover which ccollapsed and were were sstoped c o v e r sequence sequence which o l l a p s e d and t o p e d bby y tthe h e rising r i s i n gsyenite s y e n i t magmas. e magmas. Mica Mica sschist c h i s t and and quartzite q u a r t z i t eare a r ecommonly commonly aassociated s s o c i a t e d i in n the t h e intermediate i n t e r m e d i a t e zones zones of of both and R Rib b o t h the t h eWausau Wausau and i b Mountain Mountain plutons p l u t o n s and andmay may represent r e p r e s e n tsamples samples ofo basement f basement rocks underlie C o n s i d e r a b l e v avariation r i a t i o n i in n 1lithology, it h o l o g y , r o c k s which w h i c h under1 i e the t h e volcanic v o l c a n i c rocks. r o c k s . Considerable size, s i z e , shape, shape, and and relative r e 1 a t i v eabundance abundance of o f xenoliths xenol i t h ssuggests suggestsmixing m i x i n gofo basement f basement and and cover c o v e r rocks r o c k s by b y complex complex subsidence subsidence and and resurgence resurgence ooff the t h e syenite s y e n i t emagmas magmas aatt shallow Not oonly n l y is i s the t h econcentric c o n c e n t r i c structure s t r u c t u r eofo these f t h e s eplutons p l u t o n sexpressed expressed s h a l l o w depth. depth. Not by a y e r i n g and and oorientation r i e n t a t i o n of o f xenoliths, x e n o l i t h s ,but b uxenolithology t x e n o l i t h o l o gshows y shows b y compositional c o m p o s i t i o n a l llayering a crude eachbluton. crude cconcentric o n c e n t r i c zzoning o n i n g wwithin i t h i n each luton. The dominantl i tlithology The dominant h o l o g y o of f xxenoliths e n o l i t h s aat t tthis h i s locality l o c a l i t yisi sillimanite—bearing s sillimanite-bearing lineated, 1 i n e a t e d , quartz-muscovite q u a r t z - m u s c o v i t e sschist c h i s t with w i t h aa pronounced pronounced t etectonite c t o n i t e ffabric a b r i c (Figure ( F i g u r e 21). 21 ). Figure Photomicrograph( w(with half—crossed F i gure 21—— 21 -- Photomicrograph i t h ha1 f - c r o s s e d ppolars) ol a r s ) of quartz-sillimanite-muscovite schist. s c h i s t . Elongated, Elongated, o f quartz—sillimanite-muscovite polygonal p o l y g o n a l qquartz u a r t z ggrains r a i n s show show ssimilar i m i l a r eextinction x t i n c t i o n positions positions and and eelongation l o n g a t i o n p aparallel r a l l e l t to o ssillimanite i l l i m a n i t e tufts. t u f t s . Width Width of of photomicrograph photomicrograph is i s4.0 4.0mm. mm. AA nearby metaquartzite n e a r b y xenolith x e n o l i t h isi scoarse—grained c o a r s e - g r a i n e d which which m e t a q u a r t z i t e with w i t h sutured s u t u r e d grains g r a i n sand and no no strain s t r a i n lamellae. l a m e l l a e . Sillimanite S i l l i m a n i t e isi sabsent. absent. This T h i s rock r o c kclosely c l o s e lresembles y resemblesthe t hmeta— e metaquartzites mineral q u a r t z i t e s ofo fRib R i bMountain. Mountain. The The strong s t r o n g contrast c o n t r a s t ini nthe t h etextures t e x t u r eand s and m i n e r acompol compositions s i t i o n s of o fthese t h e s e two two rocks r o c k s suggests suggests wwidely i d e l y ddifferent i f f e r e n t origins. o r i g i n s . Although A l t h o u g h sillimanite sillimanite can metasomatically metasomatic can form form m e t a s o m a t i c a l l y i nin metasomatic a uaureoles r e o l e s o f of g rgranitic a n i t i c pplutons, l u t o n s , iits ts o c c u r r e n c e hhere e r e i ninaasschistose c h i s t o s e r orocks c k s w with i t h a ad distinct i s t i n c t ttectonite e c t o n i t e fabric f a b r i ctends tends to to occurrence rule r u l e out o u t that t h a t possibility. p o s s i b i l i t y . (See (See Figure F i g u r e 22.) 22.) �-28- Figure 22-F i g u r e 22 -- Photomicrograph P h o t o m i c r o g r a p h o of f qquartz—sillimanite u a r t z - s i l l i m a n i t e sschist c h i s t (A) (A) and metaquartzite N o t e sutured s u t u r e d grain g r a i n boundaries b o u n d a r i e s and and and m e t a q u a r t z i t e (B). ( B ) . Note lack W i d t h of o f image image is i s1.5 1.5mm. mm. l a c k ooff sillimanite s i l l i m a n i t e in i n B. B. Width �—29— THE THE STETTIN STETTIN SYENITE SYENITEPLUTON PLUTON ?ç Wausau Pluton Figure Generalizedgeologic geologicmap map Figure 23-— 23-- Generalized o foft hthe e SStettin t e t t i n syenite s y e n i t e pluton. pluton. Excerpted Excerpted from 6 in i n this t h i sguidebook. guidebook. from Figure Figure 6 Although (1907)mapped mapped geologyofof nnorth-central Although Weidman Weidman (1907) t hthe e geology o r t h - c e n t r a l Wisconsin Wisconsin and near Wausau, and paid p a i d special attention a t t e n t i o ntot othe t hmineralogy e mineralogyofofthet hsyenites e syenites near Wausau, Emmons and Snyder (1944) hypothesized formation o f oft hthe e SStettin t e t t i n syenite syeni t e Emmons and Snyder (1944) hypothesized formation body by metasomatism metasomatism rocksalong alongshear shearzones zoneswwith body by of off efeldspathic l d s p a t h i c rocks i t h aalkalilkalirich r i c hsolutions s o l u t i o n sderived d e r i v e d from from aa subjacent subjacent granite g r a n i t e batholith. bath01 it h . Turner Turner (1948) (1948) studied accessoryminerals mineralsand and s t u d i e d the t h e heavy heavy accessory r a radioactivity d i o a c t i v i t y ofof tthe h e SStettin tettin pluton, described tthe petrographyofof tthis pluton, and and Geisse Geisse (1951) (1951) described h e petrography h i s pluton. pluton. PetPetrographic and and geochemical geochemi c a l i ninvestigation rographic v e s t i g a t i o n of of the t h emafic mafic minerals mineral sand andnepheline nephel i n e o f the t h e Stettin S t e t t i npluton p l u t o ninitiated i n i t i a t eanalytical d a n a l y t i cstudies a l s t u dwhich i e s which have been extended of have been extended by by the t h e work work of of Sood S00d and and Berlin B e r l i n (in ( i nSood sood and and others, others, 1980) 1980) The zonedSStettin (Figure2323) oval in The cconcentrically o n c e n t r i c a l l y zoned t e t t i n ppluton l u t o n (Figure ) i is s oval i n plan, plan, elongated with elongated nnortheasterly, ortheasterly, w i t h a length l e n g t h of of 5.5 5.5 miles m i l e s and and aa width w i d t h of of 4.0 4.0 miles. miles. Older 01 der volcanic v o l c a n i c rocks rocks enclosing enclosing the t h e pluton p i uton have have been been eextensively x t e n s i v e l y syenitized. syeni ti zed. The eastern and and southern southernmargin marginoof The eastern f tthe h e ppluton l u t o n is i saacomplexly complexly laminated laminated series series of of altered a l t e r e dvolcanic v o l c a n i cscreens screensand andpendants pendants and and various, various, contaminated contaminated iintruntrusive of the s i v e phases phases of t h e syenite s y e n i t e including i n c l u d i n gnepheline n m h e l i n e syenite. syenite. The The wall w a l l zone zone comprises discontinuous oouter comprises aa discontinuous u t e r rrim i m of gneissic g n e i s s i cnepheline nepheline syenite, syenite, and and an The intermediate i n t e r m e d i a t e zone zone (Stops (Stops an inner i n n e r layer l a y e r of o f tabular t a b u l a r syenite s y e n i t e (Stop (Stop # ).). The #6 #6 and and #7) #7) isi scomposed composed of o f amphibole amphibole and and pyroxene pyroxene ssyenite y e n i t e showing showing considerconsider- . �-30- able variation ini ncomposition able composition and and texture. The The amphibole amphibolesyeni syenite t e is i s comcommonly quartz-bearing. quartz-bearing. The monly core zone zone (Stop (Stop#8) #8) iiss one one mile in in diameter diameter The core and iiss located near the the north north end endof of the and located asymmetrically asymmetrically near the pluton. pluton. The The core zone comprises well-defined, cylindrical rim rim of indistinctly banded zone comprises a a we1 1-defined, cylindrical indistinctly banded nephnepheeline l i n e syenite syenite surrounding surrounding aa core core of of pyroxene pyroxene syenite. syenite. Field Field relations relations indicate the the following fol lowing intrusion intrusionsequence: sequence: (1) (1 ) pyroxene pyroxene syenite, (2) ( 2 ) nepheline neohel ine syenite, (4)(4) amphibole Numbers syeni t e , (3) (3)tabular tabularsyenite, syenite, amphibolesyenite. syenite. Numbers 33and and 44could could be be This evidence basedwholly whollyononf ifield reversed. This evidence i is s based e l d relations (Myers). (Myers). It It should that the as should also be be emphasized emphasized that the intrusion intrusionsequence sequencemay may not not be be the thesame same as work (Sood (Sood and t h i sguidebook) guidebook) and Berlin, Berlin, this the crystallization crystal 1izationseqence. seqence. Analytical work the suggests a t e age age ffor o r the the nepheline nephel ine syenite. (See (See discussion discussion of suggestsaavery veryllate of petrochemistry beginning beginningon onpage page31 31 ). A tabulationofofparagenetic parageneticrelations relations of of minerals A summary summary tabulation minerals in i n each each zone zone of from Koeliner Koel l n e r the Stettin w i t h modification modification from the S t e t t i n syenite syeni t e pluton pi uton isi spresented presented with 27, p. (1974) in Figure (1974) Figure 27, p. 36. 36. The section section on onMineral Mineralchemistry chemistryand andpetrology, petrology,originally originally contained The contained in #3 by by Sood Sood and and Berlin has has been been excerpted excerpted the 1980 1980 Wausau Wausau f ifield e l d trip t r i pGuidebook Guidebook #3 unchanged andincorporated incorporatedinin tthis unchanged and h i s guidebook. guidebook. �—31— MINERALOGY AND MINERAL MINERALOGY AND MINERAL CHEMISTRY CHEMISTRY (STOP NO'S (STOP NO's 88 through through 12) 12) M.K. Sood,P,E..Myers, PE. .Myers,and and LA. Beii M.K. Sood, L.A..Berlirt 1 The The pprincipal r i n c i p a l mineral mineral phases phases i in n SStettin t e t t i n Complex Complex a are r e pperthitic e r t h i t i c feldspars, f e l dspars, nepheline, nepheline, sodic sodic and and calcic c a l c i cpyroxenes, pyroxenes,and andsodic sodicamphiboles amphiboles whose whose representarepresentative t i v e chemistry chemistry is i s given given in i nTable Tab1 e and and ccharacteristics h a r a c t e r i s t i c sdescribed described below: below: Eel dspars Fel dsoars The major phase phaseo of The major f f feldspar e l d s p a r iiss aa microperthite m i c r o p e r t h i t eini nuniform u n i f o r mveins veinsshowing showing p a r a l l e l , subparallel, s u b p a r a l l e l ,orowavy r wavylamellar l a m e l l a rintergrowths, intergrowths, oro as r aspatches patches of o fone one parallel, feldspar f e l d s p a r in i n the t h e host. host. Both e r t h i t e and and aantiperthite n t i p e r t h i t e are a r e present, present, Both pperthite although thanaantiperthite. although perthite p e r t h i t eisi smore morecommon common than n t i p e r t h i t e . Frequently Frequently the t h e tabular tabular f e l d s p a r grains g r a i n sexhibit e x h i b iCarlsbad t Carlsbad t w i n n i nand g and l e sconinonly s commonlyMannebach Mannebach twinning. feldspar twinning less twinning. The pperthitic e r t h i t i c feldspar f e l d s p a r constitutes c o n s t i t u t e s 80 80 to t o90 90percent percent of o f the t h esyenites s y e n i t e s and and 60 60 to to The 75 percent ooff the 75 percent t h e nepheline nepheline syenites syenites (Table (Table 4). 4). ]50, b u t Distinct D i s t i n c tgrains g r a i n s of o falbite a l b i t have e havean anaverage average extinction e x t i n c t i o n angle angle of o f 15O, but are any of of the a r e not n o t common common i nin any t h e syenites. syenites. Microcline, as ddistinct M i c r o c l ine, also a l s o present present as i s t i n c t grains, grains, show show i its t s characteristic characteristic spindle-shaped and wavy wavye extinction, spindle-shaped ppolysynthetic o l y s y n t h e t i c ttwinning w i n n i n g and x t i n c t i o n , but b u t is i sless l e s sabundant abundant than than aalbite l b i t e as as individual i n d i v i d u a l grains. grains. The compositionsoof The bbulk u l k compositions f tthe h e pperthitic i f e l d s p a rwere s weredetermined determined e r t h i t i c alkali a1 k a lfeldspars for f o r nine n i n esamples samples of o f three t h r e emajor major zones zones of of the0Stettin t h e s t e t t i ncomplex. complex. The The samples samples were i n aa muffle m u f f l e furnace furnace for f o r48 48hours; hours; were homogenized homogenized t oto aa ssariidine a n i d i n e phase phase at a t 1050 1050 in then KBrO3 CuKcx and tthe 201feldspar f e l d s p a- r101 - 101 KBr03 CuKa was was measured measured and h e molecular percent percent ~ 2= 0=201 then 20 orthoclase using tthe o r t h o c l a s e was was determined determined using h e homogenized homogenized n anatural t u r a l mmicrocline-low i c r o c l i n e - l o w aalbite lbite x-ray The compositions compositions are a r e given given x-ray determinative d e t e r m i n a t i v e curve curve ooff Jones Jones eetal. t a1. (1969) (1969) The below below in i n Table Table 44 Table Table 44 THE THE MOLECULAR MOLECULAR PERCENT PERCENTORTHOCLASE ORTHOCLASEOF OFHOMOGENIZED HOMOGENIZED PERTHITIC PERTHITIC ALKALI ALKALIFELDSPARS FELDSPARSOF OFTHE THESTETTIN STETTINROCKS ROCKS Sample Sample 29 CuKa Mol Mol % % Or Or 1.40° 39 1.45 1.40 35 39 1.43 1.35 1.39 37 44 Core Core Zone Zone pyroxene pyroxene syenite syenite Intermediate I n t e r m e d i a t eZone Zone amphibole amphi b o l e syenite syeni t e 33 amphibole amphibole syenites syenites Rim Rim Zone Zone tabular tabu1 a r syenite syeni t e nepheline nepheline syenite syenite nepheline nephel i n e syenite syeni t e 41 The molecular percent percent orthoclase o r t h o c l a s eranges rangesfrom from3535to t44%; o 44%; however,Or% Or% The however, i s above above 40% 40% f for o r tthe h e nepheline nepheline ssyenites y e n i t e s and l e s s than than 40% 40% ffor o r the t h e nephelinenephelineis and iiss less free f r e e syenites. syeni t e s . �-32— The iintensity The n t e n s i t y ratios r a t i o s ofofthe the201 701peaks peaks of of rnicrocline microcline and and albite a l b i t ewere were determinedf ofor determined r tthe h e pperthitic e r t h i t i cfeldspars feldsparsbybyscanning scanning in i nboth both directions directionsbetween between 200 and230-20 23°-20CCukc l/8°-20 per per minute minuteusing using200 200counts countsper perf ufull 20 and u k a a tat1/8°-2 l l chart chart scale, seconds and and a chart c h a r t speed speed of 15 15 inches inches per per hour. hour. s c a l e , aa time time constant constant ofof5 5seconds The angular positions The angular positions were were averaged averaged from from three three scans. scans. Then Then the goniometer goniometer was exactly centered on on one one peak time and and the the intensity i n t e n s i t was y wasmeasured measured was exactly centered peak aatt a time using aa fixed time time ofoften tenseconds seconds with w i t h aa22second second time time constant. constant. The using The background intensity was measured at the midpoint between the two peaks. ground i n t e n s i t y was measured a t the midpoint between the two peaks. counts on onmicrocl microcline 2b1/l0 ss AA == number number ofof counts ine 201/10 B counts on on low low aalbite B == number number ofof counts l b i t e 201/10 201/10 Ss C of counts C == number number of counts on on the thebackground/b background/IO ss Then: The The i nintensity t e n s i t y r ratio a t i o I'o"a 0/I = (A (A - C)/(B C)/(B - C). C). The thethe bulk composition of of Or%/Ab% Or%/Ab% The iintensity n t e n s i t y ratio r a t i oand andthe thevalue valueof of bulk composition of the of ffor o r each each of the perthitic p e r t h i t i cfeldspars feldsparsstudied studied were were plotted plotted on on the the graph araph of Kuellrner (1959)(Figure24). Kuel lmer (1959) (Figure 2 4 ) . Fromt this as tto From h i s diagram, diagram, implications implications can can be be made made as o the t h e temperaturetemperature(B) From t hthe e pplots l o t s aa broadening broadening rratio a t i o (B) sstructural t r u c t u r a l state s t a t e of of the the feldspars. feldspars. From is obtained. i s obtained. the ddistortion The broadening rratio The a t i o isi saameasure measure ofof the i s t o r t i o n or o r structural structural The broadening ratio will decrease The broadening r a t i o will decrease mistakes mistakes iin n the two two phases phases ofof pperthite. erthite. with slower crystallization and lower temperature since these conditions slower c r y s t a l l i z a t i o n and lower temperature since these conditions are are ions favorable for of Si and favorable f o r the the attainment attainment ofofananordered ordered arrangement arrangement of and Al A1 ions in the the tetrahedral tetrahedral sites s i t e s ofofthe thefeldspar feldsparstructure s t r u c t u r e(Smith, (Smith,1974). 1974). The broadening thep eperthitic alkali of the kali feldspars feldspars of the Stettin Stettin The broadening r a tratios i o s f o for r the r t h i t i c a1 This is 0.9). This is rocks range from low (B = 0.30) to intermediate values (B rocks range from low (B = 0.30) t o intermediate values ( B = an indication indication of the of these an the low low temperature-structural temperature-structural sstate t a t e of these pperthites, erthites, correspondingt to the maximum intermediatemicrocline-low microcline-lowaalbite corresponding o the maximum t o tointermediate l b i t e series series determined from the positions of the 204 and 060 reflections. determined from the positions of the 204 and 060 r e f l e c t i o n s . // 8— 6 5 // 4 3 2 o / i .8 / // ,/ 5 4 // b',•'• • // / .1 .2 // / ///, /, /,/ / // / ,/ — — / — // / / / — — / / / // /// // / / // 24-- Plot compositions Figure 24—— Plotof of bulk compositions Or%/ versus I Olo/lafor / I f o r tthe h e 201 201 reOr%/Ab% Ab% versus 7 ••," / // 7 / ,/ / / /i / ii 11111! I .1 ., // // // / / /' q' / / . / / /71 // / .2 / // // // // / / / // / , / "/ // /7 //// 6 // / /. .4 .6 .8 1 O RTHOCLASE % ORTHOCLASE % ALBITE ALBITE % % f l e c t i o n s of of the thetwo twofeldspar feldsparphases phases fboctions S t e t t i n perthite p e r t h i t efor f odetermin-. r determinthe Stettin in the ation broadening r ratios a t i o s ((B) B ) aafter fter ation of broadening Kucilmen, 1959. Kucllmen, 1959. I I 2 I I 4 6 I 8 10 �-33TABLE 55 TABLE ELECTRON ELECTRONMICROPROBE MICROPROBECHEMICAL CHEMICALANALYSES ANALYSESOF OFMAJOR MAJORMINERALS MINERALS OF OF STETTIN STETTIN COPPLEX DUPLEX I Feidsoar Fpldi nar Si02 SiO, A1203 A1203 67.42 19.23 Ti02 T i O2 ---- FeO FeO -- MnO MnO -- 40.45 19.72 8.70 9.28 1.0 3.17 1.31 0.1 34.22 26.8 -—— ------ ---- CaO CaO 0.44 0.25 7.40 7.40 6.39 6.39 11.23 0.27 K20 K2 à 68.23 MgO MOO Na20 Na20 I bo1es 39.90 --- NnDI' nsy 48.1 Pyroxene Pyroxene DSV DSV 50.1 0.59 0.26 0.26 0.81 1.00 1.52 23.70 23.70 0.89 2.28 0.73 0.62 4.41 29.1 10.3 8.89 17.8 2.14 3.30 2.40 1.57 1.75 —— 20.30 20.30 0.57 0.57 N.D. N.O. tsv Fe-TI Fe-TI 50.8 ~ e o h eine* l Nehe1ine 46.5 OxIds Oxides 1.34 1.34 0.30 0.30 26.40 26.40 33.1 0.25 50.8 0.71 0.99 11.00 .oo 11 6.80 N.D. N.D. -- 0.18 0.18 ------- Fledspars Fledspars Based Based on 8 oxygens oxygens on Ainphiboles Based Amphiboles Based on 23 23 oxygens oxygens Si Si 2.987 2.988 2.988 6.73 6.43 6.43 Al 1.004 1.018 1.76 Al 0 0 1.52 1.52 0.118 0.118 Ti --- -- 3.89 3.89 0.515 0.515 4.61 Mg ---- Ca 0.021 0.012 1.765 1.765 Na 0.635 0.954 K 0.361 0.015 0.690 0.323 0.323 Fe 0.372 0.372 0 0 0.147 0.147 Pyroxene Based Based on 66 oxygens oxygens 2.001 1.990 2.074 2.074 0.010 --0.010 -0.42 0.017 0.064 0.42 0.017 0.064 -- ------ 0.13 15.20 5.46 5.46 —- -— Nepheline {epheline Based on on 32 32 oxygens oxygens 8.76 7.352 7.352 ------- Fe..Ti Fe-Ti Oxides Oxides Based on 24 24 oxygens oxygens 0.119 0.079 1.530 0.004 0.004 0.930 0.930 0.008 0.008 0.786 0.786 0.010 0.902 0.902 0.261 0.862 0.862 0.060 0.060 ---- 1.536 1.536 0.38 0.38 0.797 0.797 0.480 0.480 0.27 ------ 1.031 1.031 0.194 0.194 0.044 0.044 0.538 0.538 5.52 5.52 -- 0.172 0.172 —— -- 16.0 3.9 3.9 Di 3.5 3.5 Hd 75.1 25.2 25.2 60.8 60.8 Ae 11.19 .I9 --- * * 0.44 7.57 7.57 90.40 -— ATOMIC PROPORTIONS PROPORTIONS 0.361 -- —— -—— 0.29 1.315 - 20.310 20.310 0.272 --- 47.3 47.3 5.3 5.3 42.8 42.8 - * From From Koeliner Koellner (1974) (1974) Nephel i me ne Nepheline by iits r e c t a n g u l a r , blocky b l ocky Nephel i n e i is s ccharacterized h a r a c t e r i z e d by t s subhedral subhedral tto o euhedral, euhedral , rectangular, Nephaline ssyenite form a r a l l e l eextinction x t i n c t i o n iin n thin t h i n section. s e c t i o n . Nephaline y e n i t e pegmatites pegmatites con-. conform and andp parallel n hand hand specimen specimen t the h e nnepheline e p h e l i n e iiss cm llont. e n t . IIn ttam a i n nepheline n e p h e l i n e ccrystals r y s t a l s up up to t o 55 cm Alteration ppinkish i n k i s h and and greasy greasy in i nappearance. appearance. A l t e r a t i o n leaves leaves gray, gray, etched etched surfaces s u r f a c e s of of negative 8, and a n c r i n i t e isi common s common at a tSTOP STOP 8, and n e g a t i v e rrelief e 1 i e fagainst a g a i n s t feldspar f e l d s p a r and and quartz. quartz. Cancrinite r e p o r t s that t h a t the t h enephelines nephelines from from K o e l l n e r (1974) (1 974) reports paragonite paragoni t e has has been been rreported. e p o r t e d . Koeliner the andd deficient alkalies 15% and e f i c i e n t iin n a1 k a l i e s by by S i by byabout about 15% t h e Stettin S t e t t i n pluton p l u t o n are a r e enriched e n r i c h e d in i n Si about 13%. 13%. Pyroxenes Pyroxenes Both ssodic andccalcic occurinint hthe Both o d i c and a l c i c cclinopyroxenes l i n o p y r o x e n e s occur e SStettin t e t t i n pluton. p l u t o n . Representative chemical compositions compositions aare chemical r e ggiven i v e n in i n Table Tab1 e 55above. above. Aegiring A e g i r i n g and and aaegirine-augite egirine-augi t e may zonedwwith may oor r may may nnot o t be rimmed rimmed bby y ssodic o d i c amphiboles. amphiboles. Some Some a rare e c color o l o r zoned i t h bbright right green green rrims i m s and and ppale a l e yyellowish e l l o w i s h green green cores. cores. Average Average eextinction x t i n c t i o n angles angles of o fpyroxene pyroxene cores iiss 28°, This cores 28O, whereas whereas t hthat a t oof f tthe h e rrims i m s iis s 13 13 to t o 24°. 24'. T h i s suggests suggests an an outward outward increase inn aegiring increase i aegi r i n g content. content. Calcic Cal c i c pyroxenes pyroxenes (diopside—hedenbergite) ( d i o p s ide-hedenbergi t e ) aare r e iironronrich r i c h with w i t h aegirine a e g i r i n econtent c o n t e n tup uptot o10% 10% (Koeliner, ( K o e l l n e r , 1974). 1974). In I n general, general, Na Na ++ ~Fe3 e ^ +is is photomicrograph, FFigure highest h i g h e s t iinn the t h e wall w a l l zone. zone. See See photomicrograph, i g u r e 24. 24. �—34- Figure pyroxene ssyenite. F i g u r e 25—25-- Photomircograph Photomircograph oof f pyroxene y e n i t e . Zircon Zircon crystals by bdark c r y s t a l s (left ( 1 e of f t center) o f c e n t esurrounded r ) surrounded y d a arfvedson— rk arfvedsonite i t eand and aegirine-augite. a e g i r i n e - a u g i t e . Mafic M a f i c cluster c l u s t e r enclosed e n c l o s e d in in stained f e l d s p a r . Plane Plane ppolarized o l a r i z e d 1light. ight. s t a i n e d alkali a1 k a l ifeldspar. Amphibol Amphi b o les es b l u i s hgreen greensodic s o d i camphibole amphibole with w i t han anabsorption absorption The The dominant dominant mmafic a f i c mmineral i n e r a l iiss aa bluish scheme c closely l o s e l y rresembling e s e m b l i n g aarfvedsonite: r f v e d s o n i t e : XX == bbluish l u i s h green green or o r greenish g r e e n i s h blue; b l u e ; ZZ== scheme greenish g r e e n i s h brown brown oor r light l i g h tbrown. brown. Average Average eextinction x t i n c t i o n angle a n g l e is i s 16°. 16O. Late L a t e blue blue amphibole deepbblue; l u e ; ZZ == 1light i g h t blue. blue. amphibole i is s riebeckite r i e b e c k i t e with w i t h absorption a b s o r p t i o n sheme: sheme: XX == deep Extinction E x t i n c t i o n angle a n g l e of o f these t h e s e grains g r a i n s is i s very v e r y low. low. X-ray X-ray diffraction d i f f r a c t i o npowder powder patterns patterns of reflection o f the t h e riebeckite r i e b e c k i t e give g i v e 8.42A 8.42A ffor o r the t h e ll0] [110] r e f l e c t i compared o n comparedto t o8.50A 8.50A for for arfvedsonite a r f v e d s o n i t e [110] [I1 0 1 reflections. r e f 1 e c t i o n s . All A1 1ofo the f t h amphiboles e amphi b o l es are a r eiron—rich. iron-rich. Biotite Biotite Two Two vvarieties a r i e t i e s of o f biotite b i o t i t eoccur o c c u rsparsely s p a r s e l yini nthe t h eStettin S t e t t pluton: i n p l u t o dark n : d aorange— r k orange- brown, and llight brown, and i g h t olive o l i v egreen greentot obrown. brown. This T h i s indicates i n d i c a t e stwo two genetic g e n e t i cassociations associations of Mn2. Electron o f biotite b i o t i t ewith w i t hbimodal bimodal partitioning p a r t i t i o n i n gofo Ti, f T iFe2, , ~ e *Fe3, + , ~ eand 3 + , and ~n2'. E l e c t r omicro— n microprobe aanalysis n a l y s i s of o f biotite b i o t i t efrom s f r othe m t hStettin e S t e tpluton t i n p l uby t o nMyers by Myers shows e orange-brown probe shows thet horange-brown varieties v a r i e t i e s to t obe be Ti T iand and Fei+ rich. rich. Accessory Accessorv Minerals Mineral s Numerous havebeen beeni didentified. Numerous aaccessory c c e s s o r y mminerals i n e r a l s have entified. They They iinclude n c l u d e zzircon, i r c o n , fluorfl uor- apatite, a p a t i t e , fayalite, f a y a l i t e ,magnetite, m a g n e t i t e , sphene, sphene, f lfluorite, u o r i t e , ccalcite, a l c i t e , cancrinite, c a n c r i n i t e , allanite, a1 l a n i t e , pyrochlore, p y r o c h l ore, and andmany many others. others. Modal ccompositions o m p o s i t i o n s o fofSStettin t e t t i n rocks r o c k s are a r e included i n c l u d e d in i n Table T a b l e 6. 6 . (from ( f r o m Koeliner, K o e l l n e r , 1974). 1974). Modal �—35- TABLE TABLE 66 ?43DAL OF MODAL COMPOSITIONS COMPOSITIONS O F THE THE STETTIN STETTINROCKS ROCKS INTERMEDIATE INTERMEDIATEZONE ZONE Amphibole Amphibole Syenite Syenite ROCK TYPE - CORE CORE ZONE ZONE Tabular Tabular Syenite Syeni t e Pyroxene Pyroxene Syenite Syeni t e 66 and and 504 504 WALL MALLZONE ZONE Nepheline iepheline Syenite Syeni t e AMPLE NUMBERS* 10 77 503 100 uartz ephellne 7.1 6.6 2.9 1.4 26.4 17.6 6.6 80.7 83.5 90.3 83.0 87.4 80.2 63.6 75.7 61.4 8.6 0.2 5.1 13.6 5.5 4.1 0.5 19.1 8.4 4.6 29.5 0.2 0.6 0.4 0.4 1.0 Perthite lblte mphibole 0.5 11.2 0.6 Pyroxene Blotite' 0.2 Biotite (alter.) 0.6 Zircon 0.2 patite Fluorite 0.3 0.2 65 46 92 2 0.5 0.1 0.7 0.1 0.2 0.5 Calcite Calcite 0.3 0.1 Sphene Sphene Opaque minerals Opaque minerals AlteratIon 1.1 0.1 0.1 0.3 0.2 1.3 0.1 0.4 0.2 0.3 0.3 0.4 0.5 0.5 from from Sood, Sood, Myers, Myers, and and Berlin, Berlin, 1980, 1980, p. p . 28. 28. GXPLANAIION 0 Qel *JI,vh,m Qet Tin gr I including including localities l o c a l i t i e sofo fsamples samples and and ffield i e l d trip t r i pstops. stops. Granit, pay Pyranin, say *mpliib.i. Sy.ait. apap Stettin complex (after Myers. 1973) Figure of the Figure 26-.. 26%Geologic Geologic map map of the S t e t t i n complex ( a f t e r Myers, 1973) 4 I I Unt,ni.rmii Sp,nIe S,niI. aplit.  tay lty 1.b.,i., Itbultr Sp.iji. Sltiiite nay nç NiphnIia• Mtphtiint Syenit* Sytnitt lay Iiy ayv Syv nvb mvb L.n..Idi Lçmulday.niI. Sytniit ivfv i.lik FeliitV.k..,na hlimniti lulit Mrnlliislienka vçitrnk U.n mv Spanitiand Sltnifi~ç V,lc.niu Volconiti Irntjafed I n t t i a t t dMaftc MalitVeltanks Vsltanio �—36- FIGURE FIGURE 27 27 PARAGENETIC RELATIONS RELATIONS OF MINERALS IN EACH EACH ZONE ZONE OF OF THE THE STETTIN STETTINPLUTON PLUTON PARAGENETIC OF MINERALS - - - C R Y S T A L L I Z A T I O N CRYSTALLIZATION RROCK O C K TYPE T Y P E LU TABULAR SYENITE TABULAR (Myers, 1973) 1973) - -- - - SSEQUENCE E Q U E N C E - - —z zircon —I i rcon 4 —pyroxene4-!-pyroxene I —1 j_.alka1i ~ a kal l i feldspar— feldspar4 f—opaques_._ IÑopaques green amphiboles— - 1I green amphi bol es--4 I k1_biotite__I b i o t i te+ -J NEPHELINE NEPHELINE SYENITE SYENITE (Koellner, ( K o e l l n e r , 1974, 1974, P. 1 2 ) —nepheline -nephel i ne1-' -I I—alkali k a l kal i feldspar—I feldspar4 lI—olivine—I -olivine4 +pyroxene j I—pyroxene--I- opaques—l 1opaquesÑ —green g r e e n amphiboles.—4 amphi bol esÑ- Jbiotite—4 à ˆ - b i o tte-à PYROXENE SYENITE PYROXENE SYENITE (Koellner, (Koel 1n e r , 1974, 1974, p. P. 12) 12) I1.-alkali - a1 kal i feldspar—I f e l d s p a r -I I- a p a t i te-i Eapatite-i - opaques-l — opaques—I ivine----4 I— 01 olivine————.-$ + pyroxeneI— pyroxene— LU + — green g r e e n amphibole—S amphi boleÑ i—biotite—.. t- b i o t i t e 4 N1 pfrcarbonate.-4 carbonate-t i—blue I- bl ue amphibole— amphi bol e- LU H- LU AMPHIBOLE AMPHIBOLE SYENITE SYENITE (Koeliner, ( K o e l l n e r , 1974, 1974, p. 33) P. 33) I—alkali l- a1 kal i feldspar—I feldspar-l Iapatite4 k a p a t i te-1 LU I—opaques—4 kopaquesl +I—pyroxene p y r o x e n e 4—I )—green amphibole—I +green amphi bol e à ‘ tI—biotite—4 Ñbi0tite- H- I—blue IÑb ue amphibole— amphi bol e - FromSood, Sood,Myers, Myers,and andBerl Berlin, From in 1980, p. 24 24 1980, p. �—37— STOP STOP #8 #8 Nepheline syenite and syenitized volcanic rocks, Stettin pluton wall zone LOCATION: County Highway U on hill crest 0.5 mile east of Little Rib River; a- TITLE: Nepheline syenite and syenitized volcanic rocksy S t e t t in p1 uton wall zone LOCATION: County Highway U on h i l l c r e s t 0.5 mile e a s t of L i t t l e Rib River; , Sec. Sec. 18, 15' quadrangle. SSW W ,, SSW W , 18, T29N, T29N, R7E; R 7 E ; Wausau Wausau 15' quadrangle. (See Fig. 6). (See Fig. 6). Paul AUTHOR: Paul E. E . Myers, Myers, University University ofofWisconsin Wisconsin — - Eau Eau Claire AUTHOR: April, 1984 DATE DATE: April, 1984 SUMMARY OF OF FEATURES: SUMMARY FFATURFL: was Intrusion of of the theStettin S t e t t ipluton n pluton wasaccomplished accomplished by by peeling peeling slices s l i c e saway away from from the cylindrical andand carrying them upward causing much cylindricalwalls walls carrying them upwardwhile while causing muchmetasomatic metasomatic alteration a l t e r a t i o n through through the the addition addition of ofalkalies a1 kaliesand andalumina. alumina. The The border phases phases and aalterations l t e r a t i o n s typical and typical of of the the Stettin of the the eastern eastern border border of S t e t t i n pluton pluton are are well well exposed alongthe thehighway highwaya tatt hthis exposed along i s location. DESCRIPTION: The dominantrock rocktypes typesa at ( 1pyroxene, ) pyroxene,amphibole, amphiboleyand and The dominant t tthis h i s location location are: are:(1) olivine—bearing nephelinesyenite syenite pegmatite, pegmatite, and and variously variously syenitized olivine-bearing nepheline syenitized mafic mafic volcanic rocks. hybrid types types are are present volcanic rocks. Many Many hybrid present also. Through Throughaddition addition of K, K y Na, Na, and Al the volcanic rocks convertedlocally locally to of and A 1 the rocks were were converted t o aplitic a p l i t i rocks c rockscomposed composed of sodic amphibole(s), amphibole(s),b ibiotite, feldspar ((perthite). altered n d a1alkali ka1 i feldspar ~ e r t h i t e ) The ~ a1 sodic o t i t e $ aand The tered volcanic rocks canic rocks have have aa ccharacteristic h a r a c t e r i s t i csplotchy splotchyororstreaked streakedappearance appearance owing owing tto o local local pinkish color variation in in mineral mineral proportions: proportions: fine-grained fine-grained K-feldspar K-feldspar imparts imparts aa pinkish and tto o the the altered altered portions portions ofofthe thevolcanic volcanicrocks, rocksy andprimary primarypyroxenes pyroxenes are a r e altered ttoo Na-Fe Na-Fe pyroxenes. pyroxenes. 490' A B C 390' sv ==syenitized syenitizedvolconics volcanics syenite ns = nepheline nepheline syenite 2p0' 100' —EAST--'my 9' = syenite ss = syenite mv= mof Ic volcanic mv= mafic volcanic rocks rocks Geologics strip Figure 28—— 28-- Geologic t r i p map map along County C o u n t y Hiqhway Hiqhway U. U. The nephel nepheline syenite pegmatite pegmatiteaatt Location of very The ine syenite Location AA (Figure ( ~ i g u r 28) e28) isi scomposed composed of a n d 1 to 22 centimeter centimeter subhedral subhedral ccrystals rystals coarse subhedral ribbon perthite perthite and coarse subhedralgrains grainsof of ribbon of pinkish, nepheline (10—20%). (10-20%). Dark Dark mineral mainly dark dark green green to to pinkish$altered altered nepheline mineral iiss mainly Accessory minerals r e zircon, a p a t i t e $and and monazite, monaziteyellow green green amphibole. amphibole. Accessory mineralsaare zircon, apatite, B are composed composed ofofplagiocalse, The mafic Location B The mafic volcanic volcanic rocks rocks aatt Location plagiocalse, pperthitic erthitic a1 ka1 i feldspar, feldsparygreen green amphibole, amphiboley brown o t i t e y and and anhedral t iiss alkali brownb ibiotite, anhedralepidote. epidote.I It 1 locally cut cut by by syenite syenite veinlets. veinlets. have dark dark areas areas of residual residua1 mafic mafic rock rocknow now Syenitized volcanic rocks rocks at a t CC have Syenitized composed ofofanhedral 01 ivegreen green composed anhedralgreen greenamphibole amphibole( X(X= =dark darkyellow yellow green; green; ZZ == dark dark olive to brown) brown) clustered c1 ustered with with subhedral subhedral blue—gray amphibole (riebeckite) andcclots ti1 ue-gray amphi bo1 e (riebecki t e ) and l o t s of pale yellow—green yellow-green epidote. Brown o t i t e occurs coarser vvarieties. arieties. Brownb ibiotite occurs in in coarser �-38STOP #9 STOP TITLE: Contact relations and minerals in in the Contact relations and minerals the Wall Wall Zone, Zone, SStettin t e t t i n syenite syenite pluton pl uton LOCATION: County Highway t e t t i n Road, Road, Paul Highway O 0 aatt 10146 10146 SStettin Paul Knopp Knopp property, SEkYSE¼, SE%, Sec. 22, 22, T29N, T29N, R6E, R6E, Marathon Marathon 15' quadrangle, quadrangley(Sample SE¼, (Sample Location 92) 92) AUTHORS: P.E. P . E . Myers Myers and and M.KSbod M.KeSi50d DATE: DATE : February 1973, February 1973, February February 1980 1980 SUMMARY OF FEATURES: SUMMARY OF FEATURES: Theoutermost outermostrim rimofofthe theSStettin The t e t t i n pluton pluton is i s gneissic gneissic nepheline nepheline syenite syenite composed mainly alkali feldspar, perthi perthite, composed mainly of of a1 ka1 i feldspar, t e , nepheline, nephel iney aegirine, sodic sodic amphiboleand andbbiotite. amphibole i o t i t e . It I t isi sininsharp sharpcontact contactwith, with,and andveined veined by, by, tabular tabular syenite coarse,we1 well-oriented lathsof of perthite, perthi t e ysodic sodicamphiamphi syeni t e composed composed of ofcoarse, 1-oriented laths bole, pyroxene, lensoidal mafic essentially of of the bole, pyroxene, and and lensoidal mafic inclusions inclusions composed composed essentially the same minerals different porportions porportionsand andofoff finer grain size. The b ubut t inindifferent i n e r grain same minerals mafic inclusions inclusionsare arewe11 well-oriented parallel to to the the tabular tabular fabric of the mafic -oriented parallel the enclosing syenite syenite and andt oto the the wall wall of of the They contain contain large large perthenclosing the pluton. pluton. They perthite i n the the enclosing enclosing i t e porphyroblasts porphyroblasts of similar similarcomposition composition and and size s i z e as a s those those in weremined mineda tatt hthis Zircons from from tthis Zircons were i s ssite i t e in in the the 1950's. 1950's. Zircons his syenite. Zircons site 20m.y. m.y.bybyW.R. W .R. Van Van Schmus Schmus (oral comcoms i t ehave have given givenaaU/Pb U/Pb age age ofof1520 1520+ 20 munication). The chief chief questions questions to to be answereda tatt hthis The be answered i s ssite i t e are: are: (1) (1)how how were were the the nepheline syenite syenite and and tabular tabular syenite syenite emplaced, and(2) (2)to to what whatextent extent iiss nepheline emplaced, and the present metasomaticreplacement? replacement? present mineral mineral assemblage assemblage aa result resul tofofmetasomatic + �—39- The abundance abundance zirconand andhastingsite hastingsiteamphibole, amphibole,bbiotite The of ofzircon i o t i t e and and carbonate indicates miaskitic trend trend for forthe thenepheline n e ~ h e l i nand eandpyroxene pyroxene syenites. syenites. bonate indicates aa miaskitic The compositionsofof the the nepheline and pyroxene pyroxenesyeni syenites very similar similar The compositions nepheline and t e s aare r e very (Table (Table 6). 6). According According tto o Koeliner Koellner (1974, (1974 p. p. 144) 144) the syenite the amphibole amphibole syeni t e iiss agpiatic and and could could contain contain aa carbonatite carbonatitebody. body. agpiatic DESCRIPTION: DESCRIPTION: The nepheline syenite (Figure (Figure 30, The nephel ine syenite 303 Tables Tables 6 and and 7) 7) is i saagray, grayybanded banded rock here feldspar nephel nepheline, olivine, pyroxene, rock composed composed here of ofp eperthitic r t h i t i c feldspar i ne9 olivine pyroxeney magnetite, amphibole, amphibole,and andbbiotite. magnetite i o t i t e . Contorted Contorted aaplitic p l i t i cand andpegmatitic pegmatiticbands bands 1lie i e roughly roughly parallel parallel tot othe thewall wallofofthe thepluton plutonabout about1500 1500 feet f e e t south south of of here. here. The nepheline occurs occurs as as blocky, which weather b10cky~pinkish pinkishgrains grains which weathermuch muchmore more The nepheline readily than minerals, giving giving the the rock rock aa characteristic characteristic than the the associated associated minerals9 pitted pittedappearance. appearance. Nepheline Nepheline i sisppartially a r t i a l l y altered altered to to cancrinite cancrinite and and iron iron oxides. Banding9 Banding, and andmafic maficcontent contentof of the the nepheline nepheline syenite increase increase outoutward toward towardi its ward t s contact contact with w i t h syenitized syenitized mafic mafic volcanics volcanics which which tren tren westwestcommon addition tot othe theessential essentialminerals mineralslisted l i s t eabove, d abovey common northwesterly. In addition accessory minerals include include zircon and of unusually unusually large size accessory minerals and sphene sphene of size and and abundance, abundancey a papatite, a t i t e , f lfluorite, uori t e , allanite, a1 lani t e 9sodalite, soda1 i t e ,pyrochlore pyrochloreand and thorothorodatingofof the the zircons zircons from fromt this gummite(?). U/Pb U/Pb dating h i s site s i t e by by S. S. Goldich Goldich (oral (oral gummite(?). communication) gave gave aa minimum ageof of 1400 More recent recent analyses analyses of of comunication) minimum age 1400 m.y. m.y. More these zircons yielded aa U/Pb age of of 1520 W.R. Van Van Schmus Schmus yielded U/Pb age 1520 ++ 10 m.y. m.y. these zircons by by W.R. Thus, the SStettin t h z n the the Wolf Wolf Thus9 the t e t t i n syenite syenite is i s about about 20 20 million million years years older older than (oralcommunication). communication). River Bath01 i t h (oral River Batholith The gneissosity and andisoclinal isoclinal folding The gneissosity folding exhibited exhibited by by the the gneissic gneissic nephnepheline side of of the Stettin e l i n e syenite syenite of of the the wall wall zone zone on on the the south south side S t e t t i n pluton pluton suggestconsiderable considerabledifferential differential movement materialalong alongi its suggest movement ofofmaterial t s outer The extent extent to wasinvolved involved during during and wall. The to which which metasomatism metasomatism was and aafter f t e r ememplacement iiss not placement not known. known. However,metasomatism metasomatism was extensive,and andt hthat However9 was extensivey a t the nepheline syenite may consist in in large wall rocks. nepheline syenite may consist large part partofofmetasomatized metasomatized wall rocks. Zircon from red-brown, Zircon from tthis h i s locality l o c a l i t yis ideep s deep red-brownydoubly doublyterminated terminatedeuhedeuhedcrystalsdisplay display geniculate geniculate twinSome crystals in length. Some ral prisms prisms up up to to 14 14mm rnm in Chemicalanalyses analysesofof three three zircons from ning similar to to tthat of rrutile. from ning similar h a t of u t i l e . Chemical a nearby Sec. 22) 22) by by F.B. (NWg ofof Sec. F.B. Hall Hall (in ( i Weidman, n Weidmany1907, 1907Âp. p. 313) 313) nearby site s i t e(NW¼ indicates indicates an an A1203 A1203 content content of of between between 4.28 4.28 and and 7.80 7.80 percent percentand and an anFe903 Fe O3 Ca, Ti, Th and rare earths we'e Th and rare earths wege content between 1.21 and 4.47 percent. Cay Ti between 1.21 and 4.47 percent. sought but but not detected. sought detected. Brown pyrochiore octahedra octahedrauup to 22 mm mminin diameter diameterwere werefound foundaat Brown pyrochlore p to t tthis his location (1907, p. p. 308-309). location by byWeidman Weidman (1907, 308-309). Allanite isi sconfined confined mainly mainly to to petmatitic petmatitic portions portions ini nthe thenepheline nepheline syenite. syen i t e . Apatite and spheneofofunusually unusuallylarge larges isize show Apatite and sphene z e show a f faffinity i n i t y ffor o r clusters Large sphene crystals up to of mafic maf i c minerals mineral s in the the nepheline nephel ine syenite. syeni te. Large sphene crystal s up mminin length length can 77 mm can be be collected collected from fromnepheline nephelinesyenite syenitelenses lensesand andmasses masses near near iits t s contact contact with tabular tabular syenite. syenite. �-40- The tabular syenite The tabular syenite (Figure (Figure29, 2 9 ,Tables Tables66&i7)7 )is icomposed s composed dominantly dominantly of coarse coarse laths of of microperthite. microperthite. Vein patch type perthites Vein and and patch perthitespredompredominate. Poikilitic c amphi bole (hastingsite) (hastingsi t e )rims rimspyroxene pyroxene (intermediate (intermediate bebePoi ki1 i t i amphibole tween acmite andhedenbergi hedenbergite accordingt otoKoe1 Koeliner (1974, p. p. 65). 65). The tween acmi t e and t e according lner (1974, The tabular fabric orientation of fabric (Figure (Figure29) 29) isi scharacterized characterizedby by aarandom random orientation perthitic p e r t h i t i c feldspar feldspar tablets tablets in in aa plane plane parallel to t o the the outer outer wall wall of of the the pluton parallel to of mafic pluton and and parallel t o the thelong longdimensions dimensions of mafic inclusions. Perthitic PerthTtic feldspar tablets within within mafic mafic inclusions inclusions and and across across their t h e i r contacts contacts are are identical to t othose those ini nthe theenclosing enclosing tabular tabular syenite. syenite. The The inescapable conconclusions is that of of metasomatic t h a t the the perthitic p e r t h i t i cfeldspar feldspar isi sata least t l e a spartly t partly metasomatic clusions is origin. Veins of tabular syenite Veins of syenite locally locallycut cutthe thenepheline nepheline syenite syenite gneiss gneiss in the location. Mafic inclusions inclusionscomprise comprise from from the old old quarry quarry face face aatt this t h i s location. 5 to of the of mafic mafic inclusions t o 80 80 percent percent of the tabular tabular syenite. syenite. As As the volume volume of increases, amphibole, become increases, the the mafic maficminerals, minerals,mianly mianlysodic sodic amphiboley become coarsely coarsely poikilitic. Individual amphibole amphibole grains up u p to to 12 12centimeters centimeters long longwere were poi ki1 i t i c . Individual observed in aa small 1.5 miles observed in small roadside roadside excavation excavation 1.5 miles east-southeast east-southeast of here. here. Although Although the mafic mafic inclusions inclusionscontain containa amuch much higher higherpercentabe percentabe ofofpyroxene pyroxene and olivine than and olivine than the the enclosing enclosing tabular tabular syenite, syenite,they theyare areofofabout aboutthe thesame same chemical chemi ca1 composition. composi tion. The tabular syenite The tabular syenite forms forms the the outermost outermost layer layer on on the the north northand andwest west sides sides of the the Stettin S t e t t i npluton plutonwhere where the the nepheline nepheline syenite syenite is i sabsent. absent. The The abundance maficinclusions inclusionsincreases increasesoutward outwardi ninthe the tabular tabular syenite, abundance ofofmafic suggesting considerablecontamination contaminationbybythe thebasaltic basaltic wallrock. A A uunit nit suggesting considerable mapped lensoidalsyenite syenite and andaaclosely closely associated associated syenite syenite aplite mpped asaslensoidal a p l i t e(Myers, (Myers, 1973) are found found locally locally where 1973) are where the the nepheline nepheline syenite is i s absent. absent. The The lensoidal a1 syenite syenite is i san an aplitic, a p l i t i cgneissose y gneissose rock rock consisting consisting of of mafic mafic inclusions inclusions rich in syeniteaaplite The syenite p l i t e is is in biotite b i o t i t eenclosed enclosed in i n an an aaplitic p l i t i csyenite. syenite. The similar relatively free u t relatively f r e e of of mafic mafic composition bbut similar in i ntexture textureand and mineral mineral composition inclusions. Figure 29 29 Typical Typicalfabric fabricofof tabular syenite showingcoarse coarse Figure tabular syenite showing tablets of o fmicroperthite microperthite in inrandom random orientation to the the tablets orientation parallel parallel to wall of o f the the pluton. pluton. Microperthite Microperthite laths laths in inthe thelensoidal lensoidal mafic mafic inclusions tend tend to have have aa preferred to inclusions preferredorientation orientation parallel parallel to those those in in the theenclosing enclosing syenite. syenite. Some Some o fofthe thelaths laths crystallized crystallized across the edges edges ooff inclusions, inclusions,thus thusindicating indicating a metasomatic across a metasorriatic origin origin of o f at atleast leastpart partofo fthe themicroperthite. microperthite. �-41- Figure 30—— 30-- Photomicrograph syeniteshowing showing Figure Photomicrographofof nepheline nepheline syenite , rectangular nephel ine surrounded by a1 b i t eand and euhedral euhedral, rectangular nepheline surrounded by albite green amphibole. amphi bol e Crossed Crossed po1ars pol a r s green . Figure 31—— 31-- Photomicrograph syeniteshowing showing paraparaFigure Photomicrographofoftabular tabular syenite l l e l a1 ignment of p e r t h i t i c feldspar l a t h s o r t a b l e t s . llel alignment of perthitic feldspar laths or tablets. Crossed polars. pol ars. Crossed �-42STOP STOP #10 #10 TITLE: TITLE: LOCATION: LOCATION: "Moonstone" dikes in syenite of Intermediate "Moonstone" dikes in pyroxene—amphibole pyroxene-amphibole syenite IntermediateZone Zone the Stettin Stettim syenite syenite pluton. pluton. of the North side s i d e of ofCounty County Highway Highway UU, , 0.7 miles east e a s t ofofCounty CountyHighway Highway 0; North 0.7 miles SW:, SE4, SE?, Sec. Sec. 28, 28, T29N, T29N, R6E; R6E; Marathon Marathon 15' quadrangle [See [See Figure Figure 6] 61 SW, 15' quadrangle — &II 1) S F fl - AUTHOR: AUTHOR: Paul E. Myers, University of Wisconsin - April, 1984 April ,1984 DATE: DATE : - Eau Claire DESCRIPTION : DESCRIPTION: Coarsely crystallized syenite dikes containing containingpperthitic Coarsely crystallized syenite pegmatite pegmatite dikes e r t h i t i c feldspar feldspar crystals dark brownish amphibole-pyroxene u p tot o3535centimeters centimeterslong longcut cut dark brownishgray gray amphi bol e-pyroxene crystal s up moonstone" iiss characterized syenite in in this t h i sweathered weathered roadside roadside outcrop. outcrop. The The "moonstone" characterized by and brownish by aa soft s o f tirridescence irridescence and brownishsheen sheenimparted impartedbybyclose—spaced close-spaced ribbon ribbon green to bluish green amphibole I n t e r s t i t i a lpoikilitic poikil i dark t i c dark green t o bluish green amphibole perthite perthite lamellae. lamellae. Interstitial and dark greenish pyroxeneoccur occur bboth in the o t h in the pegmatite pegmatite dikes dikes and dark greenish brown brown tto o green green pyroxene and enclosing syenite. and enclosing syenite. A just north A large stone stone quarry quarry in the the woods woods just north of ofhere herewas was operated operated sporadically until by Mr. Mr. Gilbert Gilbert Schultz whoi sis, incidentally, disturbed until about about 20 20 years years ago ago by Schul t z who , incidentally, disturbed when rockhoundsinvade invade quarrywithout withoutpermission. permission.he hequarry quarryhas hasvertical vertical rock when rockhounds hishisquarry rock walls and deep water - DANGEROUS! syeniteinint hthis - DANGEROUS! TheThesyenite i s quarry quarry is is and is i s filled f i l l ewith d with deep water predominantly massive, brownish gray gray syenite massive, coarse—grained, coarse-grained, medium medium brownish syenitecomposed composed of perthite laths l a t h s with poikilitic p o i k i l i t amphibole i c amphiboleand andvery verysubordinate subordinategreen greenpyroxene. pyroxene. Pegmatite dikes exposed exposedininthe theSchul Schultz Quarryare arenearly nearly vertical vertical, ,reach t z Quarry reach 0.7 0.7 mm Pegmatite dikes width, and structure" (Figure and show show aaddistinctive i s t i n c t i v e "comb "comb structure" (Figure 32). 32). Interstitial I n t e r s t i t i a amphi-. l amphiboles boles are coarser coarser in in the the dikes, dikes,and andtend tendtot obebeconcentrated concentratedalong along dike dikemargins. margins. The dikes appear appeart otohave havecrystallized crystallized into opening conditions of The dikes opening fissures under under conditions arge, fresh fresh boulders boulders of of aa very very mafic mafic dike dikerock rock - lamprophyre lamprophyre Several 1large, extension. Several (?) the quarry, quarry, bbut ( ? ) wer wer observed observed ininthe u t ttheir h e i r relationship relationshiptot othe thesyenite syeniteisiunknown. s unknown. - / / / 'I — 1 / I" 6 inches ' , ,' '' /- \i' 0 ' — '... Figure 32—— "Comb"s tstructure 32-- "Comb" r u c t u r e in in syenite pegmatite dike pegmatite dike cutting cutting amphibole-pyroxene syenite in amphibole-pyroxene syenite the Schultz Schul t z Quarry Quarry 0.2 0.2 miles miles north of .north of here. here. Amphibole Amphibole is is poikilitic, occurs p o i k i l i t iand c , and occurswith withgreen green pyroxene. —I . '\ / I] \ — �-43STOP #11 #11 STOP - TITLE: TITLE : LOCATION: LOCATION: AUTHOR: AUTHOR: - DATE: DATE : Amphibole and Pyroxene PyroxeneSyenites Syenitesin in the Intermediate Amphibole and IntermediateZone Zone Marathon15' 15' quadrangle: quadrangle: See See Fig. Fig. 6. NW N W ,, SW SW ,, Sec. Sec. 14, T29N, T29N, R6E; R6E; Marathon 6. Paul Paul E. E. Myers, Myers, University University ofofWisconsin Wisconsin— - Eau Eau Claire April, April ,1984 1984 SUMMARY OF FEATURES: SUMMARY OF FEATURES : Massive and flow-lineated, flow—lineated,gray orange amphibole—pyroxene Massive and graytot opinkish pinkish orange amphibole-pyroxene syenite of onboth bothsides sidesofof the the road roadaat exposed on t tthis his of the the Intermediate Intermediate Zone Zone iis s well well exposed rock closely closelyresembles resemblesthe thepyroxene—bearing pyroxene-bearing syenite described described locality. 1 ocal i ty. This rock on page42. 42.The Thesyenites syenitesjust justnorth northand andwest westofofhere herecontain containl ilittle on page t t l e or orno no pyroxene, anddisplay display complex complexflow flow structures structures resembling those aatt the pyroxene, and resembl ing those the Old Old amphibolesyenite syenite north north of here The amphibole here contains contains Technical #5). The Technical IInstitute n s t i t u t e (Stop (Stop #5). the dominant mafice mineral mineral in abundant riebeckite. Although abundant riebeckite. Although the dominant mafice in the the pyroxenepyroxenebearing bearing syenite here here isi samphibole, amphibole, the thepyroxene pyroxene occurs occurs as as grains grainsrimmed rimmed by by Quartz-bearing aplites a p l i t e sare arecommon common in amphibole amphibole syenites they they were were amphibole. Quartz-bearing not in the n o t observed observed in the pyroxene-bearirg pyroxene-bearirtg syenites. syenites. DESCRIPTION: DESCRIPTION : Whereas the i s is c hcharacteristically a r a c t e r i s t i c a l l y pink outcrop, the the Whereas theamphibole amphibole pink in outcrop, pyroxene syeni t e i sis aa moderate-to-1 i ght oolive l i v e gray gray wwith i t h islands islands of pyroxene syenite moderate-to-light coarse mafics enclosed enclosedi nin coarse coarsetab1 tablets of randomly oriented fel felde t s of randomly oriented dcoarse mafics spar. spar. The amphibole syenite showsconsiderably considerablygreater greatertextural textural varThe amphi bole syeni t e shows variation, i a t i o n ,even evenata mesoscopic t mesoscopic scale. scale. Although A1 though vein-1 i ke and and iirregular rregular vein-like masses ofof zoned l i t e aare r e common common inina all l l outcrops, the the masses zonedpegmatite pegmatiteand anda paplite dominant rock medium-grained amphibole syenite aint dominant rock type type iiss medium-grained amphibole syenitewith withaaffaint t o conspicuous conspicuous lamination, r without created by by alignalignto lamination,with with oor without lineation created ment of feldspar feldspar tablets ment of t a b l e t s and and lensoidal lensoidal clots c l o t s ofofmafic maficminerals--mainminerals--mainly 1yamphibole amphibole and and subordinate subordinate pyroxene. pyroxene. Pegmatitic Pegmatitic phases phases of the theamam- syenitecontain containupuptot 12% o 12% quartzasascoarse coarsesegregations segregations cornmonphibole syenite quartz common1y rimmed rimmed by r i e b e c k i t i c )amphibole. amphibole. ly by blue blue ((riebeckitic) fibers. thin section, section, mafics mafics aare r e clustered In thin clusteredinin acicular acicular or or radiating radiating fibers. This the southwest containssmall smalls isill-like of tabular This zone zone tto o the southwest contains l l - l i k emasses masses of syenite. syeni t e . The major mineral mineral iiss micro-to micro-to mega-perthitic mega-perthi t i c feldspar feldsparsurrounding surrounding The major mafic minerals minerals which which seemingly a t e r than than the the feldspars. feldspars. The The the mafic seeminglyare arellater principal mafic mafic mineral mineral isi sbluish-green bluish-green arfvedsonite-riebeckite arfvedsonite-riebeckiteamphiamphibole (Table sometimes mantling mantl inq minor minor Fe-augite Fe-augite pyroxene. pyroxene. However, However, (Table ), sometimes pyroxene of tthis pyroxene iis s absent absent in in some some samples samples of h i s zone. zone. Alteration A1 t e r a t i o n of ofaniphiamphiboles to t o brown-red brown-red biotite b i o t i t eis icommon s common in in patches patches and and along along borders. borders. boles of aa dark dark The iinteresting n t e r e s t i n g feature feature of ofthe theamphibole amphibole grains grains isi scontainment containment of The blue riebeckitic r i e b e c k i t i cphase phase which which is i s most most common common only i s uunit. n i t . Some blue onlyi nint hthis Some amphiboles poikilitically amphi boles poi kil i t i c a l l yenclose encloseeuhedral euhedral feldspars feldspars (Figure (Figure ). ). Accessories include zircon which which isi scommonly commonly zoned, to Accessories include zircon zoned, quartz quartz (up to 12%), allanite. 12%), f fluorite, l u o r i t e , calcite, c a l c i t e ,FeTi-oxides, FeTi-oxides, apatite a p a t i t e and and a1 lanite. �-44- Figure Photomicrographofof amphibole amphibole syenite Figure 33—— 33-- Photomicrograph s y e n i t e showing showing poikilitic poi kil i t iamphibole c amphiboleenclosing enclosingeuhedral euhedral feldspar feldspar grains. grains. (From Sood, Myers, Myers, and andBerl Berling, ~ r o mSood, ing, 1980, 1980, p. p. 34). 34). with Figure 34-— 34-- Photomicrograph Photomicrograph of pyroxene syeni t e with Figure of pyroxene syenite zoned zoned aegirine-augite aeqi rine-auqi t emantled mantled by byarfvedsonite. arfvedsoni t eCrossed e Crossed polars. p. 35). 351, polars. (from (fromSood, Sood. Myers, Myers, and and Berline, Berl i n e ,1980, 1980, p. �-45STOP STOP #12 #12 TITLE: The Core CoreZone Zoneofofthe theSStettin The t e t t i n Syenite Syenite Plutori Pluton LOCATION: LOCATION: SW 1/4, SE SE 1/4 1/4 Sec. S W 1/4, Sec. 2, 129N, T29N, R6E; R6E; Hanthurg151 Hmburg 15' quadra,nle quadrangle William Powell requiredfor for entry. Powell property. property. Permission Permission required AUTHOR:: AUTHOR,: Paul E. Paul E. Myers Myers,, DATE: DATE : February, 1980, February, 1980, University University ofo Wisconsin f Wisconsin — - Eau Eau Claire April, Apri 1 ,1984 1984 SUMMARY OF FEATURES: SUMMARY OF FEATURES: The coreofof the the SStettin twoddistinct The core t e t t i n syenite syenite pluton pluton comprises comprises two i s t i n c t parts: parts: (1) banded (1 ) aa cylindrical cylindricalcore coremargin margin of of indistinctly indistinctly bandedororlineated, lineated,mediummediumgrained nepheline syenite syenite and and (2) (2) an grained nepheline an inner core core of of pyroxene pyroxene syenite. Bent Bent and crushed crushedfeldspar feldspar grains grains and and and a crude crude southeast-dipping southeast-dipping layering layering were were formed during during oorr after of the nepheline syenite formed a f t e remplacement emplacement of the core core margin. margin. The The nepheline magnetic anomaly about one one mile core margin margin produced produced aa pronounced pronounced donut-shaped donut-shaped magnetic anomaly about the southeast southeast corner corner of of iinn diameter. diameter. Drilling DrillingbybyBear BearCreek Creek Mining Mining Company Company inin the the inner core the core retreived retreived about about 250 250 feet f e e t of of core coreclassified classifiedbybycompany company geologists geologists carbonatite has been beenfound, found,a1although theaagpaitic as No carbonati t e has though the pal t i c trend trend of of as 1larvikite. arvi kite. No the rocks suggestst hthat suchaacarbonatite carbonatite iiss possible the rocks here here suggests a t such possible (Koellner, Koellner, 1974, 1974, p. 144). 144). p. ? DESCRIPTION: The nephelinesyenite syeniteofof the the core core margin marginhere herei sis indistinctly indistinctly banded The nepheline banded or or weatheredsurface surface paleyellowish yellowishgray graywith withppitting The weathered i s ispale i t t i n g due due to lineated. The fresh nepheline The fresh nepheline iiss pale pale greenish greenish differential differentialweathering weathering of of the thenepheline. nepheline. The brown andoccurs occursasaswe1 well-oriented, 1-oriented, subhedral subhedral to euhedral euhedral grains grains enclosed enclosed by by brown and The feldspars, feldspars, nepheline, up to to22cm cm long. long. The nepheline, and and islands islands tablets of of feldspar feldspar up of mafic ofm a f i c minerals minerals are are elongated elongated inina aplane planedipping dippingsoutheast southeastatabetween t between60 60and and This lamination is not parallel to the outer edge of the core margin at i s parall el to the outer edge of the core margin a t This 1 amination 70g. 70 . and broken brokenfeldspar feldspar and andnepheline nephelinegrains grainsand andlenticulation lenticulation Bent and tthis h i s location. location. Bent of mafic shearingduring duringororaafter mafic mineral mineral clusters suggest suggest shearing f t e r intrusion. �-46- The dominant w i t h40% 40% tabular microperthite microperthite(60% (60%orthoclase orthoclasewith The dominantmineral mineral iiss tabular An additional 25% of the rock i s subhedral t o euhedral oligoclase ribbons). ribbons). An oligalase additional 25% of the rock is subhedral to euhedral nepheline, which a r t i a l l y altered a l t e r e d to t o cancrinite. cancrinite. Mg-rich Mg-rich pyroxene pyroxene and and nepheline, whichi sisppartially pleochroic, olive o l i vbrown e brownamphibole amphiboleare a r of e of about equal abundanceand andmake makeup up pleochroic, about equal abundance about 20-30% 20-30% of rock. Accessory Accessory (2-5%) (2-5%) Mg-rich o l i v i n e and dark. brown about of the rock. Mg-rich olivine and dark.brown b i o t i t eaccompany accompany the n llenticular e n t i c u l a r clusters c l u s t e r sand and islands islands biotite theother other mafic maficminerals mineralsi in i n the nephel ine syeni t e . The b i o t i t e p a r t i a l l yrims rims occurring i n t e r s t i t i a l l y occurring interstitially in the nepheline syenite. The biotite partially the amphibole amphibole and formed a t at a a l alate t e stage rystallization. the andwas wasprobably probably formed stageofofccrystallization. donut-shaped magnetic magneticanomaly anomaly about about one one u n i produced t produceda apronounced, pronounced,donut-shaped This unit This Wiedman (1907, p. 251 ) reports unusually large and abundant i ndiameter. diameter. Wiedman mile in mile (1907, p. 251) unusually large and abundant The magnetite apparently magnetite octahedra octahedra from from streams streams northwest here. The magnetite northwest of here. magnetite iiss apparently i t h the livine. associated most associated mostclosely closelywwith the oolivine. �-47-. PETR0CHEMISTRY PETROCHEMISTRY** Chemicalcompositions compositionso foft hthe Chemical e SStettin t e t t i n rocks rocks are a r e presented presented in i n Table Table 77 Table 8compares averagecompositions compositions rocks ttoo those Table 8 compares average o f oft hthe e S Stettin t e t t i n rocks those of o f Nockold's Nockold's The average averageo of f t hthe e SStettin t e t t i n nepheline nephel i n e syenites syeni t e s show show ddistinct i s t i n c t differences differences (1954). The from samples,wwhile from Nockold's Nockold's average average syenite. s y e n i t e . These t e t t i n samplesy h i l e oonly n l y sslightly lightly These SStettin higher in Al903 NA2O higher CaO O3 and NA and 0 and h i g h einr FeO, i n FeO* CaOand andP205. P205. h i g h e r in i nsilica, s i l i c aare * alower r e lower i n A1 and Theamphibole amphiboleand and pyroxene in ssilica The pyroxene s y esyeniths, n i t $ s y a l salso o s ? islightly g h t l Y h higher igher i n i l i c a than than Nockold's Nockold's average average ssyenite, y e n i t e y are a r e lower lower ini nAl20., A1 0 MgO, MgOyCaO CaO and and 1(90, K2OY wwhile h i l e higher higher in q u a r t z ++ i nFeO, FeO*NA2O NA20 and andMnO. MnO. The The ddifferentiation i f f e r e n t i a t i o n 2 i?dices i d d i c e s (DI ( D I = normative normtive quartz albite oorthoclase r t h o c l a s e ++a1 b i t e + nepheline nepheline ++l eleucite u c i t e ++ kkalsilite) a l s i l i t e )(Thornton (Thornton and and Tuttle, Tuttle* 1960) rocks are are given g i v e n in i n Table Table 99 .. The The average averageDDI 1960) f for o r these these SStettin t e t t i n rocks I ffor o r these these rocks degreeo of rocks iiss 84.7, 84. 7*which which represents represents aa hhigh i g h degree f ddifferentiation. ifferentiation. However, However* nepheline ssyenites havet hthe 88.9 and and93.9 93.9r respectively, nepheline y e n i t e s have e hhighest i g h e s t DDI I ofof 88.9 e s p e c t i v e l y y indicating indicating the t h e greatest g r e a t e s t extent e x t e n t of o f differentiation d i f f e r e n t i a t i o among n among these these rocks. rocks. The aagpaitic The g p a i t i c indices i n d i c e s of o fthe t h eStettin S t e t t samples i n samplesare a rshown e shownini nFigure F i g u r 35—A. e 35-A. Rocks lower Si02 Si09 ccontent, Rocks oof f lower o n t e n t * the t h e nepheline nepheline bearing b e a r i n g rocks, r o c k s * have have lower lower agpaitic agpaitic thant the mre ssilica This iiss a reflection iindices n d i c e s than h e more i l i c a rich r i c h rocks. rocks. This r e f l e c t i o n of o f the t h e higher higher aluminaccontent, due t to o n t e n t * due o tthe h e presence presence oof f nnepheline, e p h e l i n e * iin n the t h e nepheline nepheline syenites. syenites. alumina The versusSi02 Si02 ((Figure increaseswwith The rratio a t i o Na20/K20 Na20/K20 versus F i g u r e 35C) 35C) increases i t h increasing i n c r e a s i n g Si02. Si02. This showstwo twotrends trendssuggesting suggestingt hthat This diagram diagram shows a t t hthe e SStettin t e t t i n rocks rocks belong belong to to two Amphiboleand andpyroxene pyroxenes ysyenites appeart to o l l o w aa continuous continuous two sseries. e r i e s . Amphibole e n i t e s appear o ffollow differentiation . I.Paw. normative normative compositions compositions d i f f e r e n t i a t i o nsequence. sequence. (Figures (Figures35E-G). 35E-G). CC.I.P.W. are presented The normative normativecompositions compositionso of analyzed SStettin The f tthe h e analyzed tettin presented in i n Table Table 99 of oNaA1SiO4, KA1SiO4 S i O and and aare r e plotted plotted rocks were were calculated c a l c u l a t e dini nterms terms f NaA1SiO4 KAlSi04 and and SiO All of Si02 K a l S i 0 4- S i 0 2 aatt 11000 0 0 0 bbars a r s PH 0 Figure f ~ i c j u r e 36). 36). A11 of iin n tthe h e ssystems y s t e m s NNaA1Si0 a A l S i 0 -- KalSiO4 2 tthe h e rocks rocks ffall a l l within w i t h i nthe ?helow lowtemperature temperature trough. trough. TABLE 77 TABLE nE — -— — —— {EMICAL COMPOSITIO OF STETTIN PLUTON ROCKS CHEMICAL COMPOSITION -— ROCK ROCK TYPE TYP — Sarrale Q w l e 9# 10 — CORE C ORE ZONE ZONE INTERMEDIATE ZONE ZONE froxene Syenite yeni te Anphibole Syenite Syeni t e 70 WALL ZONE jabular 503 503 108 64.70 64.70 61.95 59.75 61.S0** 65 — — Nepheline l i n e Syenite Syenite 6+504 6+504 — 46 22 5745 5695 56.95 92 92 sSb2 i o2 66.10 A1203 13.24 15.59 15.86 15.86 16.04 16.23 16.62 16.93 21.02 21.02 16.32 Fe203 2.61 2.36 2.45 2.45 3.13 2.55 2.55 5.20 2.58 2.93 2.93 3.41 FeO FeO 4.12 2.22 2.10 2.10 2.70 5.66 5.66 1.68 5.98 2.12 7.08 7.08 MgO M90 0.43 0.01 0.02 0.08 0.14 0.14 0.24 0.21 0.07 1.22 1.22 cao 0.70 0.50 0.95 0.95 1.10 2.15 1.43 2.64 0.51 4.03 %O3 Fe2° CaO • 5.92 6.92 7.07 7.07 6.51 5.97 6.49 6.71 7.81 5.01 K0 '5O 4.31 5.11 5.19 5.19 5.51 5.67 5.15 5.02 5.99 4.84 4.84 620 "zO 0.73 0.83 0.10 0.70 1.95 0.51 0.63 0.98 1.43 0.77 0.77 0.38 0.35 0.36 0.36 0.40 0.22 0.17 0.18 0.40 0.09 0.09 h2 CO2 c02 T1102 i o2 0.72 0.42 0.27 0.27 0.32 0.75 0.31 0.59 0.38 0.38 1.32 '05 2 '5 ' 0.11 0.04 0.06 0.07 0.13 0.13 0.07 0.13 0.50 0.50 0.49 0.49 nO Nlo 0.23 0.12 0.15 0.15 0.18 0.26 0.26 0.22 0.30 0.07 0.07 0.29 s 0.010 0.004 0.003 0.008 0.034 0.034 0.009 0.023 0.000 0.000 0.044 0.102 0.165 0.260 0.171 0.11 0.100 0.140 0.001 0.079 0.079 S ( l2r02 m2 0.03 Cl BaO Bao 0.013 0.010 0.024 0.024 0.150 0.071 -— Rb(pprn) P.~(PP~ Sr(ppm) 199. 44 0.010 0.01c 0.160 0.16( 0.345 0.02 0.103 0.086 152. 66. 133. 115. 105. 174. 174. 109. — — -—— Mar * Analyst-K. ~na1ys.t-K. Racial. Ramla1 , University U n i v e r s i t yofo fManitoba **Tabular **la u l a r yeni t e 0.105 0.105 0.241 0.143 0.215 *Modjfjed yenite *Modified fror.i f m r - i Sooci, S O O C ! ~ F!"ersy and Berlin, Uerl i r ~1980. 1989. * vers, and 57. I 54.10 65.20 0.025 0.025 0.02 0.02 0.208 0.208 102. 345. —. �-48-48TABLE TABLE 88 COMPARISON OF CHEMICAL CHEMICAL COMPOSITIONS COMPOSITIONS OF OF STETTIN COMPARISON OF STETTIN WITH WITHNOCKOLDS NOCKOLDS (1954) (1954)AVERAGES AVERAGES . Average Average SStettin tettin Nepheline Syeni t e Nephel ine Syenlte Syenite (Nockolds,1954) (~ockolds.1954) S102 sio2 56.17 Al203 A1203 Average Average Nepheline Nephel b e Average Average SStettin tettin Syenite Syenl t e Average Average Syenite Syeni t e (Nockolds, 1954) 1954) (Nockolds, 55.38 63.54 61.86 18.09 21.30 15.39 16.91 Fe203 2.97 2.42 2.62 2.32 FeO FeO 5.06 2.00 3.36 2.63 MgO w 0.50 0.57 0.14 0.96 CaO CaO 2.39 1.98 1.08 2.54 Na20 Na20 6.78 8.84 6.49 5.46 5.28 5.34 5.16 5.91 1.06 0.96 0.94 0.53* Ti02 1102 0.76 0.66 0.50 0.58 P205 p2° 0.37 0.19 0.08 0.19 0.22 0.19 0.19 0.11 Fe203 1(20 %O A 1120 "2O InÔ M~O' * Includes $ncludesonly o n l yH20 H20 from from Socd, Soc,d, Myers, Myers, and and Berlin, Berlin, 1980, 1980, p. p. 48. 48. TABLE TABLE 99 C.I.P.W. C.I.P.W. NORMATIVE NORMATIVECOMPOSITIONS COMPOSITIONSOF OFTHE THESTETTIN STETTINROCKS ROCKS 1 ROCK ROCK TYPE TYPE 10 Or 12.44% 25.61 Ab 44.05 Q CORE CORE ZONE ZONE Amphibole Amphi bole Syenlte Syeni t e Pyroxene Pyroxene Syenite Sveni t e L Sample Sample Numbers* Numbers* INTERMEDIATE INTERMEDIATEZONE ZONE 77 4.86% 30.06 51.92 503 2.80% 30.62 52.97 100 Ac Dl Mt Ii Pr Ru and and 504 504 1.79% 32.28 51.92 Tabular Tabular Syenite Syeni t e 65 65 47.72 30.62 52.44 2.22 1.28 3.41 7.22 5.31 1.04 1.36 0.12 0.02 2.36 5.91 1.89 0.51 0.76 0.01 1.36 5.89 3.88 0.54 0.46 0.01 1.65 2.70 2.70 3.28 0.61 0.01 Nepheline Nephel i n e Syenite Syeni t e 46 6.66 3.70 1.36 0.06 5.06 0.61 0.02 29.50% 35.62% 28.39% 56.48 1.47 7.93 3.00 38.39 34.16 4.26 8.10 4.67 9.82 3.70 1.06 0.06 Hl Tn 0.34 0.18 0.06 1.70 0.10 0.18 0.02 0.13 0.37 0.04 CC DI *Tabular *Tabular Syenite Syeni t e 2.11 14.86 0.96 4.17 0.76 10.65 4.86 2.43 0.06 0.91 C Z 92 1.62 Nm Ap 2 1.80% 33.40% 0.88 An Ne 01 My 66 WALL WALL ZONE ZONE 82.1 86.8 86.4 0.17 0.18 0.02 0.34 0.02 0.02 0.90 0.50 82.4 86.0 0.17 0.15 0.58 0.34 0.18 0.03 0.13 1.01 0.001 0.11 0.04 0.06 0.20 84.9 93.9 88.9 70.6 �__ _________________ __________________________ ________________ -49- Q2o I' 7)0 - 108 44 6 a 09 1 0 .. 0 108 65' 46 02 K 0 92 --08 30 60 70 50 60 S.O 94 70 SiO 94 IS® 20 4 I * 0 3 503 2 108 2l2 O 46 460 0 0 92 0 '10 97 0 I 50 70 60 60 50 70 0.05% 0 o ®20 ° 108 '8 65 0 92 . 6 77 IS C 92 l0 I IC 60 60 50 70 SiO % 70 507% 92 i 0 .5 3 046 0 2 20 l0 I 2 0.5 ,l0 60 5102 94 046 20 C 50 1.0 70 0.C 50 S \ " •" 65 "503 60 70 502 96 Figure F i g u r e 35-35-- Chemical Chemical trends t r e n d s of o f major major elements e l e m e n t s versus v e r s u s Si02 Si02 for p o 50) 50) f o r Stettin S t e t t i n pluton p l u t o n rocks r o c k s (from (from Sood Sood and and others, o t h e r s , 1980, 1980, p0 �-50DISCUSSION M. Sood and M. K. K. Sood andL.L. A.A. Berlin Due chemicaland andmineralogical mineralogicalheterogeneityy heterogeneity,the theorigin origin of of alkaline Due t to o chemical alkaline igneous rocks rocks iis, and may maybebethe ther result igneous s ininmany many cases, casesy very very complex complex and e s u l t of several several processes. Experimental icate Experimentalstudies studiesofofchemically chemicallyequivalent equivalentsynthetic syntheticsi1 silicate systems (Bai (Bailey systems 1ey and and Schairer, Schai r e r y1966; 1966; Hamilton Hami 1ton and and MacKenzie, MacKenziey 1965; 1965; Schairer, Schairer l a t t and and Edgar, Edgary 1970; 1970; Tuttle T u t t l eand andBowen, Boweny 1967; 1967; Sood Soodand andEdgary Edgar, 1972; 1972; Sood, Sood,PPlatt 1958) haveprovided providedaaphysicochemical physicochemicalframework framework to explain the crystallization 1958) have t o explain t h e crystal 1 ization behavior behavior of of alkali a1 ka1magmas. i magmas. Any petrogenetic model modelf for the formation thethe Wausau Any petrogenetic o r the formation of of alkaline a l k a l i n erocks rocksofof Wausau area must take take iinto area must n t o account: account: nature of the zoned nature thecomplex complex 11)) the zoned 2) 2) the presence quartz-bearingaaplitic the presence ofof quartz-bearing p l i t i c and and pegmatitic pegmatitic stages stages in in tthe h e intermediate intermediate ring of ofamphibole amphibole syenite; syenite; 3) 3) the the fenitized fenitizedzone zone surrounding surrounding the pluton; pluton; 4) 4) the presence volatile bearingmineral minerals (flourite, calcite, the presence ofofvo1 a t i l e bearing s (f1 ouri t e ca1 ci t e 'core" (?) i nmost most syenites, s y e n i t e s yand and in in the the quartz quartz monzonite monzonite "core" (?) aapatite) p a t i t e ) in of the Wausau pluton; t h e Wausau pluton; major and and ttrace geochemistryofof the the syenites. 5) major r a c e element element geochemistry 5) Consideration wwith the System SystemNephel Nepheline-Kalsilite-Silica Consideration i t h Respect Respect t oto the ine-Ka1 s i 1i te-Si 1 ica In normativecomposition composition rocksi sisplotted plotted iinn the 36 normative of of thethe S tStettin e t t i n rocks the In Figure Figure 36 along wwith i t h the t h e composition composition of system Nepheline-kalsilite-silica at H along a t 1Kb 1Kb PH system Nepheline-kalsilite-silica East Greenland Greenland (Wager, (Wagery 1965). 1965). the rocks intrusion, 22 East rocks from from Kangerdlugssuag Kangerdl ugssuag intrusion Theseanalyses analysesmay may interpretedt otoshow showa atrend trendofofssilica These be be interpreted i l i c a depletion depletionaway away from from the Si02 Si02 apex. apex. Rocksofoftthe IntermediateZone Zoneofofamphibole amphibole syenite plotinin tthe Rocks h e Intermediate syenite plot h e aalkali lkali feldspar-quartz region, near the alkali feldspar join, while pyroxene syenites near t h e a1 ka1 i fe1 dspar j o i n y w h i 1 e pyroxene syeni t e s fe1 dspar-quartz region, The positions positions of of the Zoneplot plotj ujust belowthe thea lalkali feldspar join. join. The the Core Core Zone s t below k a l i feldspar these syenites in the field show a silica depletion trend toward the center center these syenites i n the f i e l d show a s i 1 ica depletion trend toward the of the thecomplex. complex. From Figure36, 36, iitt appears amphibole appears that t h a t the t h etrend trendofofthese these amphiboleand andpyroxene pyroxene From Figure syenites iiss up the thermal thermal bbarrier, "over" the arriery feldsparsurface surface and and 1overt' syenites up the t h e alkali a1 kali feldspar which is similar to the interpretation by Wager (1965) for the nordmarkites, which i s s i m i l a r t o the i n t e r p r e t a t i o n by Wager (1965) f o r the nordmarkitesy pulaskites, pulaski t e s y and and foyaites foyai t e s of of the thealkaline a1 kal ineKangerdlugssuaq Kangerdl ugssuaq intrusion. (In the the nepheline-kalsilite-silica nephel ine-kalsil i t e - s i l i c asystem system at a t 55Kb Kb H PH o y these rock rock webs webs plot close close to t o the the feldspar feldsparcotectic c o t e c t i coro nephiline-feldspar r nephiline-feldspar 22 ccotectic. o t e c t i c . This is mineral paragenetic parageneticand andtextural texturalrrelations.) i s ininagreement agreement wwith i t h mineral e l a t i o n s . ) Further interpretations await the accumulation of additional data, i n t e r p r e t a t i o n s await the accumulation of additional d a t a y especially especially on on the the Wausaup1 pluton. Wausau uton. �—51— S i0 100 5 K A IS 1308 Nlephehne N e p h e l i n e ssss 100 / ,, 0 10 N aA ISs104 io4 ,, 20 20 . *- 30 30 / /'$6 01 / 8 2 0 / K a l s i l i t e ss 10 / / '/ 40 40 J 50 50 Weight cent. W e ~ g hper tper cent. V 60 60 70 70 -d 80 80 90 90 o 0 100 100 KAISIO4 KAlSiO4 Figure Figure 36-3 6 . - -Normative Normative compositions compositions ofof tthe h e SStettin t e t t i n rocks rocks (closed ( c l o s e d circles) circles) and and the t h e alkaline a l k a l i n erocks rocksofothe f t hKangerdlugssuaq e Kangerdlugssuaq intrusion, i n t r u s i o nEast y EastGreenland Greenland (open NaA1SiO4 (open circles) c i r c l e s (Wager, ) (Wager,1965) 1965)plotted p l o t t ein d the i n tsystem h e system NaA1Si04 --KA1SiO4 KAlSiO4 -Si02 Hamilton and 1963; Hamil ton andMacKenzie, MacKenzie 1965). 1965). Si02 at a tH2O P H==1000 ~ 1000 ~ bars b a r s(Fudali, (Fudali1963; �-52— How could such such inward inward ssilica How could i l i c adepletion depletionbebecaused? caused? Two Two possible explanations explanations are: are: (1) (1 ) Loss of the the volatile Loss of v o l a t i l e phase phase iineuilibrium n equilibriumwith with the themelt. melt. Such Such aa volatile alumina, a1 alkali, v o l a t i l ephase phase has has alumina, kali and and silica s i l i c aininthe thesame same propro- portion 1958; portion as a sfeldspars feldspars(Tuttle ( T u t t& l e Bowen, & Bowen? 1958;Mackenzie, Mackenzie?1960). 1960). The presenceofofap1 aplitic and feni fenitization i t i c and and pegmatitic pegmati t i c phases phases and tization The presence of beaa rreflection of the t h esurrounding surrounding volcanics volcanics may may be e f l e c t i o n of of separation separation of of volatiles v o l a t i l e into s i n tao gaseous a gaseousphase phase and and eventual eventual loss. l o s s . The The plot plot of pertinentsynthetic synthetic of the the Stettin S t e t t i nrocks rocks close c l o s e to t o cotectics c o t e c t i c s ini npertinent systems maybebeindicative indicativeofof ccrystallization systems may r y s t a l l i z a t i o nofofmajor majorphases phases crystallization within within narrow narrow temperature temperature 1limits. imi ts. Short Short crystal 1 ization intervals intervals are a r e also a l s o related r e l a t e d to t o silica s i l i c aand andalkali a l k a l content i contentwhich which control control volatile phases i n l i qand u i d gaseous and gaseous phases(Sood (Sood&&Edgar, Edgar? v o l a t i l edistribution d i s t r i b u t i oin n liquid 1970; Rhyaschi kov 1961). 1961 ) . 1970; Kogarko Kogarko && Rhyaschikov, (2) contribute to The The ssubstitution u b s t i t u t i o n of Fe3 ~ e A13 A' I ~' ~ in i n feldspars feldspars may may contribute to silic depletion w i t h crystallization crystal1 ization of of iron-rich iron-rich albite a1 b i t e s i 1 icq depletion with Fe-Alssubstitution (NaFe ~ 0i ) . Only Only aa small small amount amount ofof Fe-A1 u b s t i t u t i o n is is (NaFe 33Si20). thel liquid necessary2t8 f i x silica s i l i c aand and cause cause the i q u i d to t o shift s h i f tfrom from necessary th fix silica s i l i c asaturated saturatedtot osilica s i l i cundersaturated a undersaturatedtrend trend(Bailey (Bailey&&Schairer, Schairer? general iron-rich iron-rich and 1966). 1966). The The general and alumina-deficient alumina-deficient nature nature of of the syenites syenites inincomparison comparison tot oNockold's Nockold's(1954) (1954)averages averages and and aa limited 1imited Fe-content Fe-content of feldspars fe1 dspars favor favor such such substitution. substitution. The Nephelinesyenite syeniteinin the the SStettin The Nepheline t e t t i n pluton pluton may, may, therefore, t h e r e f o r e ?represent represent last l a s t residual residual liquids l i q u i d sinjected injectedinto i n t the o thesheared sheared wall wall zone. zone. ItI tmay may be be concluded concluded tthat h a t alkaline a1 kal inerocks rocksofofMarathon Marathon County County represent represent study of of silicate The study s i l i c a t esystems systems aa "genetically "geneticallyrelated r e l a t e dcomagmatic comagmatic series." s e r i e s . ' ' The and melting rocks have amply demonstrated t i n g relations re1 a t i o n of s of rocks have amply demonstratedthat t h magma a t magmacomposicomposi and me1 tion lies l i e sclose close to t othe theunivariant univariant lines l i n e soro rthe theinvariant i n v a r i a n tpoints, points?and and very very slight in iinitial s l i g h t changes changes in n i t i a lliquid l i q u icomposition d composition can can give give decidedly decidedly ddistinct istinct differences fferences in these these alkaline a1 ka1 inerocks rocksmay may be be Composi t i ona1 di trends. Compositional 1 i q u i d trends. liquid related compositionbybyfractional fractionalccrystallization r e l a t e d to t o slight s l i g hchanges t changes ininmagma magma composition rystallization I t isi simportant important to t o further f u r t h e r refine refine assimilationy or o r both. both. It o r by by wallrock wallrock assimilation, or geochemical data both both on on their t h e i r genetic genetic and and tectonic relations. r e l a t i o n s . Systematic geochemical rocks minerals are assess iiff these rocks and and minerals a r e needed needed t to o assess these rocks rocks are a r eformed formed from from mantle note the the low and Sr Sr contents contents ffor Rb and or mantle derived derived magmas magmas ( t e(tentatively n t a t i v e l y note low Rb Wausau rocks)which whichreached reachedc rcrust through recurrent recurrent fracture Wausau rocks) u s t through f r a c t u r esystems. systems. Such Such information will also information will a l s obe beUseful useful ininthe t h eestimation estimationofofeconomic economic mineral mineral potential potential thisarea. area.Such Suchrocks rocks form form ini nenvironments environments favorable favorable to t o the t h econcentration concentration of this of aa wide wide variety v a r i e t yofofelements. elements. . �—53— DISCUSSION DISCUSSION P.E. Myers Myers P.E. The of The ffour o u r plutons p l u t o n s ofo fthe t h eWausau Wausau syenite s y e n i t e complex complex share share many many ccharacteristics h a r a c t e r i s t i c s of lithology Moreovery they t h e yshow show l i t h o l o g yand and chemistry c h e m i s t r y which which llink i n k them them in i n age age and and oorigin. r i g i n . Moreover, a general genera1 ddifferentiation i f f e r e n t i a t i o n trend t r e n d from f r o m tthe h e peralkaline p e r a l k a l i n e SStetting t e t t i n g ssyenite y e n i t e wwith i t h iits ts nepheline n e p h e l i n e syenite s y e n i t e rim r i mand andcor c o rmargin m a r g i nthrough t h r o u g hthe t h eWausau Wausau and and Rib R i b Mountain Mountain plutons plutons which southeastward andf ifinally which aare r e ccharacterized h a r a c t e r i z e d bby y aasoutheastward i n cincrease r e a s e i n in s i lsilica, i c a * and n a l l y to to the A l t h o u g h tthere h e r e is i s no no t h e Ninemile N i n e m i l e ppluton l u t o n w with i t h i tits s ccore o r e r rim i m oof f aaplitic p l i t i c granite. g r a n i t e . Although obvious o b v i o u s sstructural t r u c t u r a l control c o n t r o l ofo fthe t h ecomplex, complexyiti does t doesoccupy occupy aa major m a j o r flexure f l e x u r e near near the andi nintermediate t h e boundary boundary between between mmafic a f i c and t e r m e d i a t e EEarly a r l ' y Proterozoic P r o t e r o z o i c metavolcanic m e t a v o l c a n i c rocks rocks on on the t h e west west and and ffelsic e l s i c to t ointermediate i n t e r m e d i a t emetavolcanic m e t a v o l c a n i c rocks r o c k s on on the t h e east. e a s t . The The complex complex l lies i e s only o n l y about about 25 25 miles m i l e swest west of o fthe t h eexposed exposed western w e s t e r n edge edge of o f the t h ecoeval coeval Wolf g r a n i tshares e sharesmany manymineralogical m i n e r a l o g i c a land and t h eNinemile N i n e m i l egranite Wolf River R i v e r batholith, b a t h o l i t h and * andthe chemical h a r a c t e r i s t i c s with w i t h the t h e Wolf W o l f River R i v e r batholith: b a t h o l i t h :they t h e yboth b o t hhave have rapakivi rapakivi chemical ccharacteristics affinities. p1 u t o npermit p e r m isome t someconclusions conclusions Aspects ooff concentric c o n c e n t r i c zoning z o n i n g ofo feach eachpluton a f f i n i t i e s . Aspects remain as as to t othe t h eactual a c t u amechanism(s) l mechanism(s) as i n t r u s i o sequence, n sequence*although a l t h o u g hproblems problems remain as to t o intrusion of o f emplacement. emplacement. Xenoliths absenti in Stettin X e n o l i t h s are a r e nnearly e a r l y absent n tthe he S t e t t i n pluton, p l u t o n ythe t h e oldest oldest p o s s i b l ybecause because the t h e conduit c o n d u i twas was developed developed more a p i d l y and/or and/or in more rrapidly sequence* possibly i n the t h esequence, The occurrence o c c u r r e n c e of o f metametabecause because tthe h e Stettin S t e t t i npluton p l u t o nhas hasbeen beenmore moredeeply d e e p l yeroded. eroded. The volcanic with v o l c a n i c xenoliths xenol i t h sclosely c l o s e l yresembling resembl i n grocks r o c k sexposed exposed nearby n e a r b y aalong long w i t h xenoliths xenol i t h s of micas schists andqquartzites o f high—grade h i g h - g r a d e mica c h i s t s and u a r t z i t e s suggests suggests cconsiderable o n s i d e r a b l e vvertical e r t i c a l mixing mixing of a l o n gthe t h ewalls w a l l sofothe f t hWausau e Nausauand and Rib R i b Mountain Mountain plutons. plutons. o f wallrock w a l l r o c kfragments fragments along These were ppenetrating These pplutons l u t o n s were e n e t r a t i n g a high-grade h i g h - g r a d e metamorphic metamorphic t eterrane r r a n e aatt depth, depth, aa factor f a c t o r suggesting s u g g e s t i n g the t h e presence presence of o f an an earlier e a r l i e Proterozoic r P r o t e r o z o i succession c s u c c e s s i o nbeneath beneath the the volcanic v o l c a n i c rocks. rocks. The The problem problem ooff the t h e "two "two Proterozoic P r o t e r o z o i csuccessions" s u ~ c e s s i o n shas ' has ~ been been recently and Myers Myers(1984.) (1984.)The Thex xenoliths r e c e n t l ydiscussed d i s c u s s e d by b y LaBerge LaBerge and e n o l i t h s iinn the t h e intermediate intermediate zones andRRib Mountainp lplutons zones ooff the t h e Wausau Wausau and i b Mountain u t o n s i nindicates d i c a t e s tthe h e initial i n i t i aemplacement l emplacement of o f syenite s y e n i t emagma magma dduring u r i n g aa ffirst i r s thigh—volume high-volume ssurge, u r g e * pprobably r o b a b l y wwith i t h venting v e n t i n g at a t the the surface. s u r f a c e . The The first-surge f i r s t - s u r g e magma magma t hthen e n c crystallized r y s t a l 1 i z e d inward i n w a r d from f r o m tthe h e dylindrical cylindrical walls, w a l l s , forming f o r m i n g the t h ewall w a l lzones. zones. Then Then (for ( f o rthe t h eWausau Wausau and and Rib R i b Mountain Mountain plutons), p1 u t o n s ) with and ccollapse w i t h repeated r e p e a t e d resurgence resurgence and o l l a p s e aalong l o n g ccylindrical y l i n d r i c a lshear shearzones, zonesythe t h edeeper deeper wallrock c o l l apse w a l l r o c kfragments fragments were were mixed mixed wwith i t h those t h o s e carried c a r r i e d downward downward bby y an a r l i e r collapse aneearlier phase. phase. This wou1 d eexplain x p l a i n the t h e tendency tendency ffor o r concentric c o n c e n t r i c elongation e l o n g a t i o n of o f xenoliths xenol i t h s T h i s would and and ttheir h e i r zonal zonal distribution. d i s t r i b u t i o n . IfI fthe t h esouthwesterly s o u t h w e s t e r l y track t r a c kofo the f t h plutonic e p l u t o n isequence c sequence i s possible p o s s i b l e that t h a t other o t h e rsyenitic s y e n i t i cplutons p l u t o n sexist e x i s in t i Wisconsin, n Wisconsiny can be be ggeneralized, e n e r a l i z e d * i itt is can but younger rrocks and gglacial The aeromagnetic aeromagneticmap map b u t are a r e obscured obscured beneath beneath younger o c k s and l a c i a l deposits. d e p o s i t s . The of many anomaliess isimilar o f Wisconsin Wisconsin shows shows many c i circular r c u l a r anomalies m i l a r tto o those t h o s e characterizing c h a r a c t e r i z i n g the the Wausau and Myers Myers, 1983, Wausau ssyenite y e n i t e (See (See LaBerge LaBerge and 1 983* Plates P l a t e s11 and and 2). 2). Features iindicating Features n d i c a t i n g shallow s h a l l o w intrusion i n t r u s i o ndepth d e p t h are: a r e :(1) ( 1abundance ) abundance of o f nearly nearly h o r i z o n t a l pegmatite p e g m a t i t e pods i a r o l i t i c ccavities a v i t i e s in i nthe t h eNinemile N i n e m i l e granite; granite; horizontal podsand andmmiarolitic ( 2 ) concentric, c o n c e n t r i c * cylindrical, c y l i n d r i c a l discordant d i s c o r d a n t structure s t r u c t u r e of o fthe t h eplutons, p l u t o n s yand and (3) ( 3 ) low low (2) metamorphic grade metamorphic grade andand r e lrelative a t i v e s i simplicity m p l i c i t y oof f sstructure t r u c t u r e in i n wallrocks. wallrocks. Some problems i s t cconcerning o n c e r n i n g t hthe e age e n e t i c r relationships e l a t i o n s h i p s of o f the the Some problemse xexist ageand andg genetic g r a n i t e aplite, a p l i t e which * whichoccupies o c c u p i e s aa large l a r g e area a r e a outside o u t s i d e the t h e plutons, p l u t o n s y but b u t isi sconfined confined granite mainly m a i n l y to t o the t h e region r e g i o nadjacent a d j a c e n t to t othe t h eNinemile N i n e m i l e pluton. p l u t o n . In I n essence, essence* the t h e aplite aplite is i s aa finer f i n e rgrained g r a i n e dvariety v a r i e t yofo the f t h eNinemile N i n e m i l e granite. g r a n i t e . However, Howevery mmiarolitic i a r o l i t i c cavities cavities and podsand andd idikes and pegmatite p e g m a t i t e pods k e s a rare e v every r y r arare r e i in n tthe h e aplite. a p l i t e . However, However* tthe h e aplite aplite may rrepresent e p r e s e n t an an early e a r l y phase phase of o f granite g r a n i t eintrusion i n t r u s i owhich n which precededemplacement emplacement of of may preceded the t h e Nineniile N i n e m i l e granite. g r a n i t e . The The aplite ap1 it econtains c o n t a i n splagioclase p l a g i o c l asephenocrysts p h e n o c r y s t sofo euhedral f euhedral plagioclase p l a g i o c l a s e and and tends tends tto o be be leucocratic: l e u c o c r a t i c : biotite b i o t i t eisi usually s u s u a l l ythe t h eonly o n l ymafic m a f i cmineral, mineral, and and its i t sabundance abundance i is s usually u s u a l l y less l e s s than t h a n 55 percent. p e r c e n t . Mantling M a n t l i n g of o fK-feldspar K - f e l d s p a r by b ysodic sodic p l a g i o c l a s e is i s common. common. I tIt i is s tentatively t e n t a t i v e l y concluded concluded t that h a t tthe h e ggranite r a n i t e aaplite p l i t e isi san an plagioclase early e a r l y intrusive i n t r u s i v ephase phase of o fthe t h eNinemile N i n e m i l e granite. granite. �-54Another problem problem concerns u a r t z monzonite monzoni t e pporphyry o r p h y r y p1 ugs (See (See F i g u r e 5). 5). Another concerns two two qquartz plugs Figure These ssmall m a l l pplug—like l u g - l i k e bbodies o d i e s c consist o n s i s t oof f aa light—colored, l i g h t - c o l o r e d , aphanitic a p h a n i t i c matrix m a t r i x and and These l a r g e K—feldspar K - f e l d s p a r pphenocrysts h e n o c r y s t s showing a r t i a l fragmentation f r a g m e n t a t i o n and and resorption. resorption. large showingp partial Quartz Q u a r t z phenocrysts p h e n o c r y s t s aare r e granular g r a n u l a r and and anhedral. anhedral. These l u t o n s aare r e strung s t r u n g out out These pplutons along County and a l o n g aa NW-SE NW-SE aaxis x i s across across Marathon Marathon County, and were were intruded i n t r u d e dthrough t h r o u g hpost—syenite post-syenite faults. They aare r e iinterpreted n t e r p r e t e d as as being b e i n g tthe h e "last " l a s t gasp" gasp1' of o f the t h eNinemile N i n e m i l e granite granite f a u l t s . They emplacement empl acement episode. Whole Whole rrock o c k and and trace t r a c e element element geochemistry geochemistry are a r eunder underway wayby b yMyers Myers and and Sood, Sood, while o s t u d mineralogy y m i n e r a l o g yand and mineral m i n e r a l chemistry c h e m i s t r y of o f the the w h i l e Falster F a l s t e r will w i l continue l c o n t i n u etot study pegmatites A comprehensive comprehensive ggenetic—petrological e n e t i c - p e t r o l o g i c a l model model p e g m a t i t e s iin n the t h e Ninemile N i n e m i l e pluton. pluton. A is be ppublished I tisi shoped hoped i s being b e i n gdeveloped, developed, and and should s h o u l d be u b l i s h e d wwithin i t h i n the t h e next n e x t year. y e a r . It that t h a t the t h e reader/participant r e a d e r / p a r t i c i p a n t may may f find i n d aa rresearch e s e a r c h pproject r o j e c t oof f iinterest n t e r e s t in i n this this relatively p a r tofo the f t h Precambrian e Precambrian shield s h i e l dofo Wisconsin. f Wisconsin. r e l a t i v e l ywell w e lexposed l exposed part P. wishes tto P. Myers Myers wishes o express express hhis i s gratitude g r a t i t u d etot othe t h eWisconsin WisconsinGeological G e o l o g i c a l and and Natural H i s t o r ySurvey Survey for f o rsponsoring s p o n s o r i n g field f i e l work d workduring d u r i nthe g t hsummers e summers of o f19711971N a t u r a l History 1976 1976 with w i t h Gene Gene LaBerge LaBerge in i n Marathon Marathon County. County. The The Survey Survey has has also a l s o provided p r o v i d e dmany many consultants. thin t h i n sections s e c t i o n s and and the t h e assistance a s s i s t a n c e of o f the t h e Survey Survey Staff S t a f f as as consultants. �A Figure — 37—- —S. EXPLANATION WAUSAU PLUTON —S. —S. S. Older caic-alkaline volcanic rocks, mainly andesite and rhyolite Quartzite Quartz diorite Alkalic extrusives, probably pyroclastics and subordinate flows Lensoidal quartz syenite with xenoliths of biotite schist and quartzite Syenitized volcanic rocks Gneissic nepheline and tabular syenite border facies Pyroxene syenite Amphibole syenite Ninemile quartz monzonite -S.' —•—. SOUTHEAST — Hypothetical northwest-southeast section across the Stettin and Wausau syenite plutons as they would have appeared about 1450 m.y. ago. Line A-A' represents the present land surface. rT1 1/i [; ...'I , / / '.—___, 01 01 �-56REFERENCES REFERENCES Anderson, J.L., 1980, 1980,Mineral Minerale qequilibria andc crystallization Anderson, J.L., u i l i b r i a and r y s t a l 1 i z a t i o n conditions conditions iin n the the Late Late Precambrian Precambrian rrapakivi a p a k i v i massif, massif, Wisconsin, Wisconsin, American American Journal Journal of o f Science Science v. v. 280, 280,P.p.289—332. 289-332. Anderson, J.L., 1983, Anderson, J.L., 1983, Proterozolc Proterozoic anorogenic anorogenic ggranite r a n i t e plutonism p l utonism of o f North North America, America, Geological Geological Society Societyofo America f AmericaMemoir Memoir 161, 161, p.p.133—154. 133-154. 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LaBerge, G.L., and LaBerge, G.L., and Myers, Myers, P.E., P.E., 1972. 1972. 1971 1971 Progress Progress report r e p o r ton onmapping mapping of o f Precambrian Precambrian geology geology of of Marathon Marathon County, County, Wisconin. Idisconin. His. His. Geol. Geol. Nat. Nat. Hist. Hist. Survey Survey Open Open FFile i l e Report, Report, p. p. 28, maps. maps. LaBerge, G.L., and 'Precambrian Geology Geology of o fMarathon Marathon LaBerge, G.L., and Myers, Myers, P.E., P.E., 1973. 1973. 'Precambrian County', County', ini nGuidebook Guidebook to t oPrecambrian Precambrian Geology Geology ooff Northeastern Northeastern and and Northcentral Wisconsin. Wis. Wis. Geol. Geol. Nat. Nat. Hist. H i s t Survey, . Survey,p.31—86. p.31-86. 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'Stettin to t o the thePrecambrian Precambrian Geology Geology ooff Northeastern Northeastern and and Northcentral Northcentral Wisconsin. Wisconsin. His. Wis. Geol. Geol. Nat. Nat.Hist. H i s tSurvey, . Survey,75—76. 75-76. Myers, P.E., The Wausau CentralWisconsin, Wisconsin,Abs., Abs.,I Institute Myers, P.E., The Wausau s ysyenite e n i t e o fofCentral nstitute on on Lake Lake Superior Superior Geology, Geology, p. 42, 42, 1976. 1976. Myers, M.L., and Wurdinger. S.R., S.R., Precambrian geology ooff the Myers, P.E., P.E., Cummings, Cummings, M.L., and Wurdinger, Precambrian geology the Chippewa Valley, 26th 26th Annual AnnualI Institute Chippewa Valley, n s t i t u t e on on Lake Lake Superior Superior Geology, Geology, Field F i e l d Trip T r i pGuide Guide #1, D. #1, 123 123 0. chemical compositions Nockolds, ~ o c k o l d s ,S.R. S.R. 1954. 1954. Average Average chemical compositions of of some some igneous inneous Soc. Amer. Amer. BBull., u l l . , V.65, V.65, p.p.1007-1032. 1007-1032. Geol Soc. rocks. Geol. . - Sims, P.1<., P.K., 1976, 1976, Precambrian Precambrian t tectonics e c t o n i c s and and mineral mineral deposits, deposits, Lake LakeSuperior Superior Sims, region, Economic Economic Geology, Geology, v.v. 71, 71,p. p. 1092-1127. region, 1092—1127. Sims, and Peterman, Peterman,Z.E., Z.E., 1983, 1983, EEvolution v o l u t i o n of o f Penokean Penokean ffold o l d belt. b e l t ,Lake Lake Sims, P.1<., P.K., and Superior Superior region, region, and and its i t stectonic t e c t o n ienvironment, c environment,Symposium Symposium on on the Proterozoic, Proterozoic, Geological Society ooff America Geological Society America BBulletin, u l l e t i n , v. v. 94, 94, p.p.000-000. 000-000. -Smith, Smith, J.V., J.V., 1974. 1974. Feldspar Feldspar Minerals, Minerals, V.1, V.l, New New York: York: Springer-Verlag, Springer-Verlag, p.627. p.627. M e l t i n g relations r e l a t i o n sofo undersaturated f undersaturated Sood, M.K., and Sood, M.K., and Edgar, Edgar, A.D., A.D., 1970. 1970. Melting alkaline a l k a l i n erocks. rocks. Meddelelsen Meddelelsen Om Om Gronland. Gronland. Bd. Bd. 181, 181. Nr. Nr. 12, 12, p. p. 41. 41. Sood, Sood, M.K. M.K., • and and Edgar, Edgar, A.D. A.D., • 1972. 1972. The system system ddiopside—forsteriteiopside-forsteriteThe nephel i n e - a l b i t e - l e u c i t e and s iimplication m p l i c a t i o n to t o the the genesis genesis of o f alkaline alkaline nepheline-albite—leucite andi tits rocks. rocks. 24th 24th mt. I n t .Geol. Geol. Congr. Congr. Montreal, Montreal, V. V. 14, 14, p.p.68—74. 68-74. Sood, M.K., P Platt, Sood, M.K., l a t t , R.G., R.G., and andEdgar, Edgar, A.D., A.D., 1970. 1970. Phase Phase r relations e l a t i o n s in in portions p o r t i o n s of o f the thesystem system diopside-nepheline--kalsilite-silica diopside-nepheline-kalsilite-silica and and their t h e i importance r importance in i n the the genesis genesis of o f alkaline a l k a l i n e rocks. rocks. Can. Can. Miner., Miner., V. V. 11, 11, p. p. 380-394. 380-394. Sood, M.K., Myers, P.E., and Sood, M.K., Myers, P.E., and Berlin, B e r l i n , L.A., L.A., 1980, 1980,The Thepetrology, petrology,geochemistry. geochemistry. and contact relations Wausau S t e t t iand n and Wausau syenite s y e n i t e plutons. plutons. Central Central Wisconsin. Wisconsin, and contact r e l a t i o n s of o fthe theStettin 26th 26th Annual Annual Institute I n s t i t u t eononLake LakeSuperior SuperiorGeology, Geology, Field F i e l dTrip T r i pGuidebook Guidebook #3, #3. 59p. 59~. �-58Internal I n t e r n a l structures s t r u c t u r e s and and geological geological ssetting e t t i n g of o f the the Sorensen, Sorensen, H., H., 1970. 1970. - three Khibinaand andLovozero Lovozero of o fthe theKola Kolapeninsula peninsulaand and three agpaitic a g p a i t i cintrusions i n t r u s i o n— s Khibina Can. Mm., Min., V. V. 10, 10,p. p299—334. . 299-334. Ilimaussaq, South South Greenland. Greenland. Can. Alkaline Sorensen, Sorensen, H., H., 1974. 1974. The The A1 k a l i n e rocks. rocks. New New York: York: Sons, Sons, p. p. 622. 622. John John Wiley Wiley and and Chemistry ooff igneous igneous rocks. rocks. Thorton, Thorton, C.P., C.P., and and TTuttle, u t t l e , 0.F., O.F., 1960. 1960. Chemistry J. Sci., I.I.Differentiation D i f f e r e n t i a t i o nIndex. Index. Am. Am. J. Sci., 258, 258, p.p.644-684. 644-684. Q.J. Geol. Geol. Soc. Soc. Problems oof f aalkali l k a l i rock rock genesis. genesis. Q.J. Tilley, T i l l e y , E.E., E.E., 1957. 1957. Problems Lond., Lond., V. V. 113, 113, p. p.323-360. 323-360. accessoryminerals mineralsand andr aradioactive Turner, Heavy accessory d i o a c t i v e studies studies of of Turner, D.S., D.S., 1948. 1948. Heavy Ph.D. ddissertation. i s s e r t a t i o n . Univ. Univ. of o fWisconsinWisconsinthe Wausau the igneous igneous rocks rocks ini nthe the Wausau area: area: Ph.D. Madison. Madison. O r i g i n ooff granite g r a n i t e iin n the t h e llight ight Tuttle, Bowen, T u t t l e , 0.F., O.F.,and and Bowen, N.L., N.L., 1958. 1958. Origin - of system NaA1Si3O8 KAlSi308 - Si02 Si02 -- lI20. H20. o f experimental experimentalstudies studiesin ithe n the system NaA1Si308- -KA1S13O8 Geol. . 74, 74, p. p. 153. 153. Geol. Soc. Soc. Am. Am. Mem., Mem., VV. Chronology ooff Precambrian Rocks i in Precambrian Rocks n Wisconsin, Wisconsin', Van W. R., R., 1973. 1973. 'Chronology Van Schmus, Schmus, W. in thePrecambrian Precambrian Geology Geology ooff Northeastern Northeastern and and Northcentral Northcentral i n Guidebook Guidebook to t o the Geol. Nat. Nat. Hist. H i s t .Survey, Survey, p.p.1—8. 1-8. Wisconsin. Wisconsin. Wis. Wis. Geol. Van Schmus,1976, 1976,E Early andMiddle MiddleProterozoic Proterozoichhistory Van Schmus, a r l y and i s t o r y of o f the theGreat GreatLakes Lakes area, area, North America, Society of Philosophical Transactions, America, Royal Royal Society o f London London Philosophical Transactions, ser. ser. A280, A280, no. 1298, . 605-628. 1298, p.p 605—628. Van Schmus, R., and 1981, Proterozoic chronology chronology and and evolution evolution Van Schmus,W.W.R., andBickford, Bickford, M.E., M.E., 1981, o f the themid—continent mid-continent region, region, North North America: America: in i nPrecambrian Precambrian Plate P l a t e Tectonics, Tectonics, of Kroner, 261—296. Kroner, A., A., ed., ed.. New New York York Elsevier E l s e v i e r Scientific ~ c i e n t i f Publication i c ~ u b l i c a tCo., i oCo., n p. p. 261-296. Van W.R.,Medaris, Medaris, L.G., L.G., and Van Schmus, Schmus, W.R., and Banks, Banks, P.O. P.O. 1975, 1975, 1975a, 1975a, Chronology Chronology of of Precambrian rocksi ninWisconsin, Wisconsin,I: I: The The Wolf WolfRiver Riverbbatholith, a t h o l i t h , aa rapakivi r a p a k i v imassif massif Precambrian rocks approximately 1500m.y. m.y.old, old, Geological GeologicatSociety AmericaB uBulletin, v. 86, approximately 1500 Society o of f America l l e t i n , v. 86, p. p. 907-914 907-914 Van W.R., Thurman,E.M., E.M., and and Peterman, Peterman, Z.E., Z.E., l975b, Van Schmus, Schmus, W. R., Thurman, 1975b, Geology Geologyand andchronchronology of of Precambrian Precambrian rocks Rb-Sr data o r tthe h e oolder l d e r rocks rocks in in ology rocksi ninWisconsin, Wisconsin,11: II: Rb-Sr dataf for eastern and and ccentral e n t r a l Wisconsin, Wisconsin, Geological Geological Society eastern Society ooff America America BBulletin u l l e t i n v. v. 86, 86, p. p. 1255—1265. 1255-1265. Wager, formand andi ninternal Wager, L.R., L.R., 1965. 1965. The The form t e r n a l sstructure t r u c t u r e ooff the t h e alkaline alkaline Kangerdlugssuaq Kangerdlugssuaq i intrusion, n t r u s i o n , East EastGreenland. Greenland. Mm. Min. Mag., Mag., V. V. 34, 34, p.p.487-497. 487-497. Weidman, S., 1907. Weidman, S., 1907. The Geology ooff North Central The Geology Central Wisconsin. Wisconsin. Nat. Bull., V. Nat. Mist. H i s t . Survey Survey Bull., V. 16, 16, p.p.697. 697. Wis. Geol. Geol. Wis. Wright, and studyoof Wright, T.L., T.L., 1968. 1968. X—ray X-ray and o poptical t i c a l study f aalkali l k a l i feldspars: feldspars: II I1 an andsstructural an X-ray X-ray method method f for o r determining determining tthe h e composition composition and t r u c t u r a l state s t a t efrom from measurement valuesf ofor p. 88-104. measurement o fof2020values r tthe h e rreflections. e f l e c t i o n s . A. A. Min, Min.,V.V.53,53, p. 88—104. Wright, ando poptical studyooff aalkali Wright, T.L., T.L., and andStewart, Stewart, D.B., D.B., 1968. 1968. X—ray X-ray and t i c a l study lkali feldspars: feldspars : III 1determination determination of o fcomposition composition and and sstructural t r u c t u r a l state s t a t efrom fromrefined refined unit-cell Mm., V. u n i t - c e lparameters l parametersand and2V. 2V. Am. Am. Min., V. 53, 53, p. p. 38-87. 38-87. � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1984 Description An account of the resource Institute on Lake Superior Geology. Wausau, Wisconsin. April 24-28, 1984. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1984 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/44dd6753bf6d405f82fdd2013485235c.pdf 85b48ae95ebbb0ab28ef6a43599bb2a8 PDF Text Text �TECHNICAL SESSIONS TECHNICAL SESSIONS AND AND ABSTRACTS ABSTRACTS FOR FOR THE THE 31ST ANNUAL 31ST ANNUAL INSTITUTE ON INSTITUTE ON LAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY HELD HELD AT INN OF INN OF THE THEWOODS WOODS KENORA, ONTARIO KENORA, ONTARIO MAY 9, 1985 MAY 8,8,9, 1985 WITh ThE IN CO-OPERATION CO-OPERATION WITH THE RES GEOLOG KENORA OFF RESIDENT IDENT GEOLOGIST I ST OFFICE, ICE,KENORA AND ThE AND THE ONTARIO GEOLOGICAL SURVEY, ONTARIO GEOLOGICAL SURVEY, ONTARIO MINISTRY NATURAL RESOURCES ()TARIO MINISTRY OFOF NATURAL RESOURCES PROGRAM CHAIRMAN EDITOR PROGRAM CHAIRMAI'.1AND AND EDITOR C, BLACKBURN C. E.I -BLACKBURN �1 a TABLE OF CONTENTS TABLE OF CONTENTS INSTITUTES LAKE SUPERIORGEOLOGY, 1955 1986 a, , , ,,.., , , , ., , , ii, ,a, ,.a, a,. , , , , 11 CONSTITUTION ThEINSTITUTE INSTITUTEON ONLAKE LAKE SuPIoR GEOLOGY CONSTITUTION OFOFTHE SUPERIOR GEOLOGY ..., , , , ,.. , , .,... , , , , , iii1 SAM ~ L D I C H MEDAL :AWARDGUIDELINESAND : AWARD GUIDELINES AND RECIPIENTS ~ C I PENTS I ,.,.,,..,,,,.,, , ,,,, ,, ,, , , , , , , v SAMGOLDICHMEDAL vi REPORT OFOF THE THE 19814 1984CHAIRMAN CHAIRMAN , l , l a , , , , l , l , , , , , , , , , , , , , , , , , , , ., ,..•.•.. ,,,,,, REPORT BOARD OF OF DIRECTORS DIRECTORS111111 l l l . l ~ . , l m lliii,,.. l ~ ~ l l Il lull.... ~ l , , , l llillIllIlli . l l , u , ~ , , , ...... , , , , , s ,viii v~i ,i ,1, , , , 1111 BJiRD LOCAL COtTITTEE COMMITTEE l l l l l l l l ~ l , ~ ~ l l l l l l l , l l l ~ l l , , l l s l u ~ . , . l , , l l l , , , ,i x, , , I_.oca_ BESTSrI.JDE!'rr STUDENTPAPEI PAPERCOtYv1ITfEE COWITTEE~ 6 ~ l , l o l B , . l l l l , l ~ , , , , , , ~ , ~ , , , ,I,x s , l , ~ , BESI ix GOLDICH NDAL.. MEDAL CoIT'1Ir'rEE COMMITTEE OL.DICl—1 FIELDTRIP TRIPlEADERS LEADERS ,,, l1l ,,l l, l , , l . , l l ~ l ~ , , , m l . ~ . l l , , , m , l l , ~ ~ ~ ixi, x, , ~ 8 ~ ~ o , , , SESSION CHAIRMEN1111111 . l , l l l l . l l , l l ~ ..... l l l l o......... l l l l ~ m all...... l l , . l l ~ l .. l , ... , , , l... ~ ~., ~ lx, , , , , o SESSION CI—IAIRr1EN x, i GOLDICH r"EDAI... MEDAL RECIPIENT . l B l , l . , ,,,,,... l l l l l l , ,1l , , l l , l l . , , ~ , l l , s. , ,... , ~ ,,1 , , ii , , , , ,Xl IECIPIENr ........, ANNUAL SPEAKER. , l l l , B ~ , l , l , , , , . l , , l l , , , , , , , , , , , , , , , , , , , , ~ x, i NUAL.. BANQUET BANQuET SPEPI(ER /i'i TECHNICALSESSIONS l l.. ,. ,.1aI . . l l , , s . l l l . . , l l , l ~ l m , l , l l ~ ~ , , Xii ,x li i, ~ ~ ~ ~ TECI—INICPJ... SESSIONS l . . l l . xiii x i 11 SESSION SESSION11 ONLAKE SUPERIOR GEOLOGY, 1955 TO TO 1986 INSTITUTES ON 11 a . • • a . • • a . . • • . . ~• . , F IEL...IJ , a ,, , . ~ • a , • , . , . . . . . . . . . . . . . . . • I I I I I I I I I I . . , . . . . . , , , 8. t . 8, • . • . . . • , , .~ , ,. ,~. ., . ~• . l , . . . . . . . . , , . • . . a . . . . . ,. 8 . . . . . . . . I I I I I I I I . a a . . • . • . , , . .8 , .~ ~ . . . . . I I . I I I I , . . , , , . ,. , . . , . l. , a , . . . . 3oL..IJICI—1 . I I • , . l . ,. ~ . . LX , ~ , ~ l l m ~ , , , 8 , , , . a . . • a . a a . i . a i . . . . I I I I I I I a . I . , , . . , . . I I I I I I I I I I . , I I I I I I . u I I I . , a . . a I I I I I I I , ~ . , .1 ,. 1• , . , .1 ., 1. .. 1 . , ., .. 1. ,. 1 . 1 ., .l 1. , . , . , ., 1. 1. 1. 1 . . .1 ,• 1 1 , 1 a , ,, 1. 1. * 1 , ,, ,, * , , # ,, SESSION SESSION33 ,a . a. , SESSION SESSION SESSION44 SESSION 22 ., , l , l . , , , 1 1 , , 1 1 l •l l l a l . ~i , . . , , , l l. l, , .l .l l. ' ., , ,, , , . . . . p a . ~ a 8a a a se a ~ ,i a l p , il i ., , , a il ,a al i , i ,l .@ i, a . l a a ., a u ,l . xi_r xiv 1 i, i, ,i , . , ,. ai ,a , a* ,i ,a , . , , , , , * , i i i . . p .a . , a p a l p i ~ , p p p p ~a p 8 i p 1. . ., ., , . ., .l .l ., ., .l l l . l . , . , . , . , a , , . l . l , l , l. ,. ,. ,. l. l, l. l. ,. l. ,. l. ,. l. * I , l l I, III POSTER PRESENTATIONSIIIIIIIIt l l , l . l l l , 111111 lllll,..la , , ,IiIaI , , , ,a l l ItlIllIllIll ll,,,,l,m l l ,I, , , ABSTRACTS /BSTRAC1'S POSTER PRESEI'1TA1"IONS I I I xv ~ ~ ~ ~ ~ a xvi xvi xvi 1 I xx xx . ., . , . l l l l s , , , t l , ~ ~ m , , ~ ~ ~ , ~ l . ,l ,. l , , , ,. l, l. l. l . , m , , ., ,l . l . , . , l, , l. l. ~ . l, ,• ,a lp •. .l . l . l . 8 . l . l t. m COVER COVER PHOTO; PHOTO; Sultana S u l t a n a Mine Mine (circa ( c i r c a1898) 1898) ; C o u r t e s y of o f Lake Lake of o f the t h e Woods Woods Courtesy Mueseum, Mueseurn, Kenora Kenora 1 ~ l ~ �INSTITUTES INSTITUTES ON LAKE LAKE SUPERIOR GEOLOGY INSTITUTE NUMBER 1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 DATE DATE 1955 1955 1956 1956 1957 1957 1958 1958 1959 1959 1960 1960 1961 1961 1962 1962 1963 1963 1964 1964 1965 1965 1966 1966 1967 1967 1968 1968 1969 1969 1970 1970 1971 1971 1972 1972 1973 1973 1974 1974 1975 1975 1976 1976 1977 1977 1978 1978 1979 1979 1980 1980 1981 1981 1982 1982 1983 1983 1984 1984 1985 1985 1986 1986 ii PLACE Minneapolis, M i n n e a p o l i s , MN Houghton, MI MI East E a s t Lansing, L a n s i n g , MI MI Duluth, D u l u t h , MN MN Minneapolis, M i n n e a p o l i s , MN MN Madison, WI WI Port P o r t Arthur, A r t h u r , Ont. Ont. (Thunder (Thunder Bay) Bay) Houghton, MI MI Duluth, D u l u t h , MN MN Ishpeming, Ishpeming, MI MI St. S t . Paul. P a u l . MN MN Sault S a u l t Ste. S t e . Marie, M a r i e , MI MI East E a s t Lansing, L a n s i n g , MI MI Superior, S u p e r i o r , WI W I Oshkosh, Oshkosh, WI WI Thunder Thunder Bay, Bay, Ont. Ont. Duluth, MN D u l u t h , MN Houghton, MI MI Madison, WI WI Sault S a u l t Ste. S t e . Marie, M a r i e , Ont. Ont. Marquette, M a r q u e t t e , MI MI St. S t . Paul, P a u l , MN MN Thunder Thunder Bay, Bay, Ont. Ont. Milwaukee, Milwaukee, WI WI Duluth, MN D u l u t h , MN Eau Eau Claire, C l a i r e , WI WI East MI E a s t Lansing, L a n s i n g , MI International I n t e r n a t i o n a l Falls, F a l l s , MN MN Houghton, Houghton, MI MI Wausau, Wausau , WI W I Kenora, Kenora, Ont. Ont. Hosted by by Wisconsin Wisconsin GS GS ?II'J �______________________________________ CONSTITUTION OF INSTITUTE ON LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY Article A r t i c l e II Name P The name of of the t h e organization o r g a n i z a t i o n shall s h a l l bbe e the t h e "Institute " I n s t i t u t e on Lake Superior Superior Geology. ' I Article A r t i c l e II I1 Objectives Objectives The objectives o b j e c t i v e s of o f this t h i s organization o r g a n i z a t i o n are: are: A. A. B. B. C. C. Article A r t i c l e III 111 To provide whereby geologists provide a a means whereby g e o l o g i s t s in i m the t h e Great G r e a t Lakes region region may exchange ideas i d e a s and and scientific s c i e n t i f i c data. data. To promote b better understanding of etter u nderstanding o f the t h e geology g e o l o g y of o f the t h e Lake Superior Superior region region To plan p l a n and conduct c o n d u c t geological g e o l o g i c a l field f i e l d trips. trips. Status Status of of organization No part part o f the t h e income o f the the o r g a n i z a t i o n shall s h a l l inure i n u r e to t o the t h e benefit b e n e f i t of of In any member or o r individual. individual. I n tthe h e eevent v e n t of of dissolution d i s s o l u t i o n the t h e assets a s s e t s of of the the organization o r g a n i z a t i o n shall s h a l l be b e distributed d i s t r i b u t e d to to (some ttax (some a x free f r e e organization). organization), [To Federal State [To aavoid void F e d e r a l and S t a t e income taxes, t a x e s , the t h e organization o r g a n i z a t i o n should should be o r 'educational" " e d u c a t i o n a l " but b u t also a l s o "non—profit."] "non-profit."] b e not n o t only o n l y "scientific" " s c i e n t i f i c " or 290,01, ssubd Minn. u b d , 44 Minn. Stat. S t a t . Anno. Anno. 290.01. If EE 29OO5(9) ' 2 90.05(9) 1954 Internal I n t e r n a l Revenue Code s. s o 50l(c)(3) 5Ol(c) ( 3 ) Article A r t i c l e IV IV Membership The membership of o f the t h e organization o r g a n i z a t i o n shall s h a l l consist c o n s i s t of o f the t h e board b o a r d of of directors. directors. b e permitted p e r m i t t e d to t o attend a t t e n d and and participate p a r t i c i p a t e in in Any geologist g e o l o g i s t interested i n t e r e s t e d shall s h a l l be and vvote meetings o t e aat t tthe h e aannual nnual m eetings. Article A r t i c l e VV Meetings Meetings The organization year, o r g a n i z a t i o n shall s h a l l meet once once a y e a r , preferably p r e f e r a b l y during d u r i n g the t h e month of of April. A p r i l . The place p l a c e and exact e x a c t date d a t e of of each e a c h meeting m e e t i n g will w i l l be b e designated d e s i g n a t e d by by tthe h e bboard o a r d of o f directors. directors. Article A r t i c l e VI VI Directors D irectors The board b o a r d of o f directors d i r e c t o r s shall s h a l l consist c o n s i s t of o f the t h e Chairman, Chairman, Secretary—Treasurer Secretary-Treasurer and the t h e last l a s t three t h r e e past p a s t Chairmen; Chairmen; but b u t if i f the t h e board b o a r d should s h o u l d at a t any any time t i m e conconsist by rreason s i s t oof f lless e s s tthan h a n ffive i v e ppersons, e r s o n s , by e a s o n oof f uunwillingness n w i l l i n g n e s s or o r inability inability of o f any of o f the t h e above persons p e r s o n s to t o serve s e r v e as a s directors, d i r e c t o r s , the t h e vacancies v a c a n c i e s on on the the board b o a r d may be filled f i l l e d by the t h e annual a n n u a l meeting m e e t i n g so s o as to t o bring b r i n g the t h e membership of o f the t h e board b o a r d up up to t o five f i v e members. members. Article A r t i c l e VII VII - Officers O fficers The officers o f f i c e r s of o f this t h i s organization o r g a n i z a t i o n shall s h a l l be b e a Chairman and and aa Secretary— SecretaryTreasurer. Treasurer. A. B. B. Article VIII A r t i c l e VIII The Chairman shall s h a l l be b e elected e l e c t e d each e a c h year y e a r by the t h e board b o a r d of o f directors, directors, who shall s h a l l give g i v e due d u e consideration c o n s i d e r a t i o n to t o the t h e wishes w i s h e s of o f any any group group that t h a t may may be b e promoting p r o m o t i n g the t h e next n e x t annual a n n u a l meeting. m e e t i n g . His H i s term t e r m of o f office o f f i c e as a s Chairman Chairman will w i l l terminate t e r m i n a t e at a t the t h e close c l o s e of o f the t h e annual a n n u a l meeting m e e t i n g over o v e r which which he he preprewill orr when his ssides ides o h i s successor s u c c e s s o r shall s h a l l have h a v e been b e e n appointed. appointed. He w i l l then then serve member of s e r v e for f o r aa pperiod e r i o d oof f three t h r e e yyears e a r s aass a a member o f the t h e board b o a r d of o f directors. directors. His The Secretary—Treasurer S e c r e t a r y - T r e a s u r e r shall s h a l l be b e elected e l e c t e d at a t the t h e annual a n n u a l meeting. meeting. H is term orr u until t e r m oof f ooffice f f i c e shall s h a l l bbe e two two yyears ears o n t i l his h i s successor s u c c e s s o r shall s h a l l have have been b e e n appointed. appointed. Amendments Amendments T h i s constitution c o n s t i t u t i o n may be b e amended by a majority m a j o r i t y vote v o t e of This of those t h o s e persons p e r s o n s who who a r e personally p e r s o n a l l y present p r e s e n t at, a t , participating p a r t i c i p a t i n g in, i n , and voting v o t i n g at a t any any annual annual are meeting m e e t i n g of of the t h e organization. organization. 111 iii - �BY -LAWS —LAWS II.. Duties D u t i e s of of the t h e Officers O f f i c e r s and and Directors Directors A. It I t shall s h a l l be the t h e dutyof d u t y o f the t h e Chairman Chairman to: to: 1. 1. 22.. 33.. B. It I t shall s h a l l be the t h e duty d u t y of the t h e Secretary—Treasurer S e c r e t a r y - T r e a s u r e r to: to: 1. 1. 2. 2. 3. 3. C. II. II. III. Preside P r e s i d e at a t the t h e annual a n n u a l meeting. meeting. Appoint all needed for organization Appoint a l l committees needed f o r the the o r g a n i z a t i o n of of the the annual a n n u a l meeting. meeting. organization and Assume complete responsibility r e s p o n s i b i l i t y ffor o r the the o r g a n i z a t i o n and of the meeting ffinancing i n a n c i n g of t h e aannual nnual m e e t i n g over o v e r which he he presides. presides. Keep accurate a c c u r a t e attendance a t t e n d a n c e records r e c o r d s of of all a l l annual a n n u a l meetings. meetings. of aall meetings of, Keep aaccurate c c u r a t e rrecords e c o r d s of ll m eetings o f , and correspondence correspondence between, the between, t h e board of of directors. directors. Hold all a l l funds f u n d s that t h a t may may aaccure c c u r e aass profits p r o f i t s from from annual a n n u a l meetings meetings orr field and tto make tthese o f i e l d trips t r i p s and o make h e s e funds f u n d s available a v a i l a b l e for f o r the the organization o r g a n i z a t i o n and operation o p e r a t i o n of of future f u t u r e meetings m e e t i n g s as a s required. required. It be duty of tthe of d directors plan I t shall shall b e the the d u t y of h e bboard o a r d of i r e c t o r s to to p l a n locations locations of meetings and to organization o f aannual nnual m e e t i n g s and t o aadvise d v i s e on tthe he o r g a n i z a t i o n and financing financing of all of a l l meetings. meetings. Dues and Expenses Expenses 1. 1. There shall s h a l l be b e no no regular r e g u l a r membership membership dues. dues. 2. 2. Registration meetings R e g i s t r a t i o n fees f e e s for f o r the t h e annual annual m e e t i n g s shall s h a l l be b e determined determined by the t h e Chairman in i n consultation c o n s u l t a t i o n with w i t h the t h e board b o a r d of of directors. directors. It recommended tthat be k kept I t is sstronglr t r o n g l y recommended h a t tthese h e s e be e p t at at a a minimum to to encourage attendance a t t e n d a n c e of of graduate g r a d u a t e students. students. Rules R u l e s or o r Order Order Rules The rules r u l e s contained c o n t a i n e d in i n Robert's Robert's R u l e s of of Order O r d e r shall s h a l l govern govern this this organization o r g a n i z a t i o n in i n all a l l cases c a s e s to t o which which they t h e y are a r e applicable. applicable. IV. IV. Amendments These by—laws by a majority by-laws may be b e amended by a m a j o r i t y vote v o t e of of those t h o s e persons p e r s o n s who are participating a r e personally p e r s o n a l l y present p r e s e n t at, at, p a r t i c i p a t i n g in, i n , and voting v o t i n g at a t any any annual annual meeting m e e t i n g of of the t h e organization; o r g a n i z a t i o n ; provided p r o v i d e d that t h a t such s u c h modifications m o d i f i c a t i o n s shall shall not with n o t conflict conflict w i t h the t h e constitution c o n s t i t u t i o n as a s presently p r e s e n t l y adopted a d o p t e d or o r subsequently subsequently amended. iv �SAM SAM GOLDICH GOLDICH HEDAL MEDAL Preamble Preamble The The Institute I n s t i t u t e on on Lake Lake Superior S u p e r i o r Geology Geology was was born b o r n on on or o r around around 1955, 1955, as a s documented documented w i l l be be held h e l d in i n 1981. 1981. The The Institutes Institutes by the t h e fact f a c t that t h a t the t h e 27th 2 7 t h annual annual meeting meeting will by are a r e exemplary exemplary in i n their t h e i r continuing c o n t i n u i n g objectives o b j e c t i v e s of o f dealing d e a l i n g with w i t h those t h o s e aspects a s p e c t s of of geology the geology that t h a t are a r e related r e l a t e d geographically g e o g r a p h i c a l l y to t o Lake Lake Superior; S u p e r i o r ; of o f encouraging e n c o u r a g i n gthe discussion d i s c u s s i o n of o f subjects s u b j e c t s and and sponsoring s p o n s o r i n g field f i e l d trips t r i p s which which will w i l l bring b r i n g together together geologists g e o l o g i s t s from from the t h e academia, academia, government government surveys, s u r v e y s , and and industry; i n d u s t r y ; and and of o f maintaining maintaining an exceedingly e x c e e d i n g l y informal i n f o r m a l but b u t highly h i g h l y effective e f f e c t i v e mode mode of o f operation. operation. an During During the t h e course c o u r s e of o f its i t s existence e x i s t e n c e the t h e membership membership of o f the t h e Institute I n s t i t u t e (that ( t h a t is, i s , those those geologists g e o l o g i s t s who who indicate i n d i c a t e an an interest i n t e r e s t in i n the t h e objectives o b j e c t i v e s of of the t h e I.L.S.G, I.L.S.G. bybyattending) attending) h a s become become aware aware of o f the t h e fact f a c t that t h a t certain c e r t a i n of o f their t h e i r colleagues c o l l e a g u e s have have made made particularly particularly has noteworthy and m meritorious of noteworthy and e r i t o r i o u s ccontributions o n t r i b u t i o n s tto o tthe h e improvement o f understanding u n d e r s t a n d i n g of of "Lake Superior" S u p e r i o r " geology geology and and its i t s mineral m i n e r a l deposits. deposits. "Lake was made made by by I.L.S.G. I.L.S.G. to t o Sam Sam Goldich Goldich in i n 1979 1979 for f o r his h i s many many The exemplary exemplary award award was The contributions c o n t r i b u t i o n s to t o the t h e geology geology of o f the t h e region r e g i o n extending e x t e n d i n g over o v e r about a b o u t5050years. years. Award Guidelines Guidelines Award The by the Board oof Directors, The medal medal shall s h a l l be be awarded awarded annually a n n u a l l y by t h e Board f D i r e c t o r s , II,L.SG., . L . S . G . , to t o aa geologist g e o l o g i s t whose whose name name is i s associated a s s o c i a t e d with w i t h aa substantial s u b s t a n t i a l sustained s u s t a i n e d interest i n t e r e s t in, i n , or or aa major major contribution c o n t r i b u t i o n to, t o , the t h e geology geology of o f the t h e Lake Lake Superior S u p e r i o r Region. Region. 1) 1) s h a l l appoint a p p o i n t the t h e Nominating Nominating Committee. Committee. The Board Board of o f Directors,I.L.S.G. D i r e c t o r s , I . L .S. G . shall 2) 2 ) The Their T h e i r annual annual nominee nominee will w i l l be be voted v o t e d on on at a t the t h e annual annual business b u s i n e s s meeting. meeting. The The i n i t i a l appointment appointment will w i l l be be of o f three t h r e e members, members, one one to t o serve s e r v e for f o r three t h r e e years, y e a r s , one one initial for f o r two, two, and and one one for f o r one one year, y e a r , the t h e member member with w i t h the t h e briefest b r i e f e s t incumbency incumbencytot obebe chairman. After A f t e r the t h e first f i r s t year y e a r the t h e Board Board of o f Directors D i r e c t o r s shall s h a l l appoint a p p o i n t at a t each each chairman. I n the t h e third t h i r d year year s p r i n g meeting meeting one one new new member member who who will w i l l serve s e r v e for f o r three t h r e e years. y e a r s . In spring t h i s member member shall s h a l l be be the t h e chairman. chairman. The The Committee Committee membership membership should s h o u l d reflect r e f l e c t the the this main membership. main fields f i e l d s of o f interest i n t e r e s t and and geographic g e o g r a p h i c distribution d i s t r i b u t i o n of o f I.L.S.G. I .L.S.G. membership. The Goldich Goldich Medal Medal Nominating Nominating Committee Committee shall s h a l l select s e l e c t the t h e medalist m e d a l i s t and and will will 3) 3) The make make its i t s recommendation recommendation to t o the t h e Board Board of o f Directors D i r e c t o r s by by November November 1 1of o f that t h a tyear. year. The Board Board of o f Directors D i r e c t o r s normally n o r m a l l y will w i l l accept a c c e p t the t h e nominee nominee of o f the t h e Committee, Committee, The will inform tthe medalist immediately, and will will inform he m e d a l i s t immediately, w i l l have have one one medal medal engraved engraved a p p r o p r i a t e l y for f o r presentation p r e s e n t a t i o n at a t the t h e May May meeting. meeting. appropriately 4) 4) I t is i s recommended recommended that t h a t the t h e Institute I n s t i t u t e set set aside a s i d e annually a n n u a l l y from from whatever whatever sources, sources, It such such funds funds as a s will w i l l be be required r e q u i r e d to t o support s u p p o r t the t h e continuing c o n t i n u i n g costs c o s t s of o f this t h i s award. award. 5) 5) April A p r i l 4, 4 , 1981 1981 J. J . Kalliokoski, K a l l i o k o s k i , Chairman Chairman Bill B i l l Cannon Cannon Fred Fred Kehienbeck Kehlenbeck Glenn Glenn Morey Morey Greg Greg Mursky Mursky RECIPIENTS RECIPIENTS 1979 Sam Sam Goldich Goldich 1979 Dutton 1981 Carl C a r l Dutton 1981 1982 Ralph Ralph Marsden Marsden 1982 1983 1983 Burton Burton Boyum Boyum 1984 1984 Richard R i c h a r d Ojakangas G j akangas 1985 1985 Paul Paul Sims Sins v �REPORT OF THE REPORT OF THE CHAIRMAN CHAIRMAN ONON LAKE SUPERIOR 330th 0 t hINSTITUTE INSTITUTE LAKE SUPERIORGEOLOGY GEOLOGY 1984 The AnnualI Institute was hheld The 330th 0 t h Annual n s t i t u t e on on Lake Lake Superior S u p e r i o r Geology was e l d AApril p r i l 24-28, 24-28, 1984 aatt the 1984 t h e Holiday H o l i d a y Inn I n nofo Wausau, f Wausau, Wisconsin. Wisconsin. Conference Conference rregistration e g i s t r a t i o nwas was 220, 220, including i n c l u d i n g professional p r o f e s s i o n a l geologists g e o l o g i s t sand and students. s t u d e n t s . The The program program cconsisted o n s i s t e d ooff one pre-meetingand andtwo twop opost-meeting one pre-meeting s t - m e e t i n g f i efield l d t trips r i p s and and two two days days ooff technical technical two-dayoor pre-meetingt rtrip The two-day r pre-meeting i p I to t o show show ffeatures e a t u r e s of o f the t h eDunbar Dunbar gneissgneisspapers. The andaassociated ggranitoid r a n i t o i d dome dome and s s o c i a t e d EEarly a r l y PProterozoic r o t e r o z o i c vvolcanic o l c a n i c rocks r o c k s in i n northeastern northeastern Wisconsin, Wisconsin, led l e d by by P.K. P.K. Sims, Sims, K.J. K.J. Schulz, Schulz,and andZ.E. Z.E. Peterman, Peterman, had had approximately approximately 60 Thepost-meeting post-meetingt rtrip II "Early 60 pparticipants. a r t i c i p a n t s . The i p 11 " E a r l y Proterozoic P r o t e r o z o i c Tectonostratigraphic Tectonostratigraphic Terranes ooff the Region', led Terranes t h e Southern Southern Lake Lake SSuperior u p e r i o r Region", l e d by by D.K. D.K. Larue, Larue, had hadapproximately approximately 25 pparticipants, of the 25 a r t i c i p a n t s , and and field f i e l dtrip t r i III p "Geology 111 "Geology o f tWausau h e WausauSyenite S y e n i t eComplex", Complex", led led by P.E. had aapproximately 12pparticipants. The ttechnical by P.E. Myers, Myers, had p p r o x i m a t e l y 12 a r t i c i p a n t s . The e c h n i c a l sessions sessions Onef full cconsisted o n s i s t e d ooff 51 51 papers, papers, of o f which which 13 13 were were poster p o s t e r presentations. p r e s e n t a t i o n s . One u l l day day of of devotedt to paperson ont hthe Proterozoic tthe h e technical t e c h n i c a l sessions sessions was was devoted o papers e EEarly arly P r o t e r o z o i c ooff the the Lake SSuperior Proceedingsoof conferencewere wereppublished f tthe h e conference u b l i s h e d i in n ffour our Lake u p e r i o r region. r e g i o n . Proceedings separate volumes; volumes;a abstracts andeach eacho foft hthe separate b s t r a c t s and e f ifield e l d trip t r i pguidebooks. guidebooks. The annual banquet banquetwas wash held onAApril The annual e l d on p r i l 26th, 26th, 1984, 1984, and and was was attended a t t e n d e d by by approximately 100people. people.WWilliam F. Cannon Cannonp rpresented qualifications i 11i a m F. e s e n t e d t h ethe qua1 i f i c a t i o n s ooff the the a p p r o x i m a t e l y 100 Goldich Medal rrecipient, G o l d i c h Medal e c i p i e n t , and andthe t h eMedal Medal was was presented presented to t oRichard R i c h a r dOjakangas Ojakangas by by SamGGoldich. banquetaddress address"The "TheOre OreMMetals Earth Sam o l d i c h . The The banquet e t a l s i in n E a r t h History H i s t o r y " was was presented by Dr. Charles The address addressccontained by Charles Meyer Meyer of o f Sedona, Sedona, Arizona. A r i z o n a . The o n t a i n e d aa wwealth e a l t h ooff information i n f o r m a t i o n on on tthe h e nature n a t u r e and and eevolution v o l u t i o n ooff ore o r e deposit d e p o s i t types. types. Two paper awards awardsoof $150.00 each eachwere wereppresented Two sstudent t u d e n t paper f $150.00 r e s e n t e d t this h i s year, y e a r , one one each each for Christopher A. Scholz, Scholz, ffrom f o r poster p o s t e r and and oral o r a l presentation. presentation. C h r i s t o p h e r A. r o m t the h e UUniversity n i v e r s i t y ooff Minnesota-Duluthr ereceived award Minnesota-Duluth c e i v e d t hthe e award f o for r t hthe e bbest e s t pposter o s t e r ppresentation r e s e n t a t i o n f for o r his h i s paper paper "Late L a t e and and Post—glacial P o s t - g l a c i a l LLacustrine a c u s t r i n e Sediment Sediment DDistribution i s t r i b u t i o n in i nWestern Western Lake Lake Superior Superior SeismicRReflection Beck, ffrom University ffrom r o m Seismic e f l e c t i o n PProfiles", r o f i l e s " , and and Warren Warren Beck, r o m tthe he U n i v e r s i t y of of Cities, Minnesota-Twin C i t i e s , received r e c e i v e d the t h e best b e s t student s t u d e n t oral o r a l presentation p r e s e n t a t i o n for f o r hhis i s paper paper "Nd and 'Nd and Sm Sm I Isotopic s o t o p i c Studies S t u d i e s of o fthe t h eQuinnesec Quinnesecand andHemlock Hemlock Formations Formations in i n Northeastern Northeastern Wisconsin and and Adjacent Adjacent Michigan'. awards were were ppresented Wisconsin Michigan". The The awards r e s e n t e d by by Val Val W. W. Chandler, Chandler, Chairman Chairman ooff the t h eStudent StudentPaper PaperAwards Awards Committee. Committee. The Boardo of The Board f DDirectors i r e c t o r s oof f tthe h e IInstitute n s t i t u t emet met on on April A p r i l 26, 26,1984. 1984. Present Present at at G.L. (Chairman),T.T.J. Southwick, G.L. LaBerge LaBerge (Chairman), J. Bornhorst, B o r n h o r s t , D.L. D.L. Southwick, F.W. Cambray, Cambray,P.E. P.E.Myers, Myers,J .3.KKalliokoski a l l i o k o s k i (Secretary-Treasurer) ( S e c r e t a r y - T r e a s u r e r ) and and C.E. C.E. Blackburn Blackburn F.W. (incoming Boardt otook (incoming Chairman Chairman ffor o r 1985). 1985). The The Board o k t hthe e f following o l l o w i n g action: action: the t h e meeting meeting were: were: 1. Accepted Accepted t hthe e i invitation n v i t a t i o n by by Charles Charles Blackburn B l a c k b u r n ooff the the Ontario O n t a r i o Geological G e o l o g i c a l Survey Survey to t o hold h o l dthe t h e1985 1985meeting meeting iinn Kenora, Kenora, Ontario. Ontario. 2. T e n t a t i v e l y accepted accepted t the h e iinvitation n v i t a t i o nof o fthe t h eWisconsin Wisconsin Tentatively Geological G e o l o g i c a l Survey Survey tto o hold h o l d the t h e1986 1986 meeting m e e t i n g in i nWisconsin. Wisconsin. vi �3. A motionby by KKalliokoski, byBornhorst, Bornhorst,t hthat A motion a l l i o k o s k i , second second by a t ffor or ffinancial i n a n c i a l reasons reasons tthe h e Institute I n s t i t u t ediscontinue d i s c o n t i n u e paying p a y i n g the the expenses expenses o of f t the h e rrecipient e c i p i e n t of o fthe t h eGoldich G o l d i c hMedal. Medal. Passed unanimously. Passed 4. Conference per Conference r eregistration g i s t r a t i o n should s h o u l d include i n c l u d e aa $1.00 $1 -00 per person charge tto person charge o maintain m a i n t a i n the t h e Goldich G o l d i c hMedal Medal account. account. The fundswwill i l l be be used used tto o strike s t r i k ethe t h emedals medals as as the the The funds need need aarises. rises. 5. 5. Replace Buchhei t on on the t h eGoldich G o l d i c hAward AwardCommittee Cornrni t t e e Replace Richard Richard Buchheit W i l l a r d Bodwell Bodwell with w i t h another another Member Member ffrom r o m IIndustry. n d u s t r y . Willard Comittee agreed agreed tto o serve serve a three-year t h r e e - y e a r term. term. The The Comrni t t e e ffor or 1985wwill 1985 i l l be be William W i l l i a mF.F.Cannon Cannon (U.S.G.S.), (U.S.G.S.), Chairman; Chairman; M.F. M.F. Kehlenbeck, Kehlenbeck, and and Bodwell. Bodwell. 6. Send Senda al ilist 6. s t of o f recipients r e c i p i e n t sofo fthe t h eGoldich G o l d i c hMedal Medal to t o the the incoming Chairman Chairmant otobe be i included incoming n c l u d e d iinn the t h e Proceedings Proceedings vvolume. o l ume . I would advice I would llike i k e to t o extend extend aa bit b i tofo hard—earned f hard-earned a d v i c e t otof ufuture t u r e IInstitute nstitute Chairmen. The The hhigh abstract i g h ccost o s t of o f printing p r i n t i n gand andbinding binding a b s t r a cvolumes t volumesand andguidebooks guidebooks necessitates we do donnot n e c e s s i t a t e s tthat h a t we o t pprint r i n t many many e extra x t r a ccopies o p i e s ( (II did). did). IIn n doing d o i n g so so we we ttie ie up tthe w i l not l n obe t berecouped. recouped. up h e IInstitut&s n s t i t u t e ' sresources resources in i n printing p r i n t i n gcosts c o s t s that t h a tprobably p r o b a b l y will So my mya advice So d v i c e i sis tto o print p r i n tonly o n l ya afew fewdozen dozen extra e x t r acopies copiesofo the f t h eguidebooks guidebooks and and abstracts. a bstracts. Serving a major S e r v i n g as as Institute I n s t i t u t eChairman Chairman has has been been a major learning l e a r n i n g experience. experience. It I thas has beenbboth Thewwillingness been o t h aa llot o t of o fwork work and and very very rewarding. rewarding. The i l l i n g n e s s ooff colleagues c o l l e a g u e s in in the Superior t h e Lake Lake S u p e r i o r rregion e g i o n tto o serve serve on on the t h e various v a r i o u s committees, committees, chair c h a i r sessions, sessions, lead lead field grateful myjob j o bmuch much easier, e a s i e r , and and IIam am g r a t e f u l for f o rthe t h ecooperation cooperation f i e l dtrips, t r i p setc., , e t cmade . , mademy off so o so many many i individuals. ndividuals. Respectfully submitted, Respectful l y submitted, / Gene L. LaBerge Gene L. LaBerge Chairman Annual I I.L.S.G. Chai rman 330th 0 t h Annual .L.S.G. Oshkosh, WI WI Oshkosh, May 21, 21, 1984 May 1984 vvii ii - �INSTITUTE BOARD OF DIRECTORS DIRECTORS ResidentResident Geologist, Ministry C . E. E . B1ackbu, Blackburn, G e o l o gofi sNatural t , M i Resources, n i s t r y o f N a t u r a l Resources, C. Robertson S St., Ontario, 808 Robertson t . , Kenora, Kenora, O n t a r i o , P9N 3X9 3x9 (1985) (1985) L. LaBerge, Department o off Geology, G. L G. . LaBerge, Geology, University U n i v e r s i t y of o f Wisconsin-Oshkosh, Wisconsin-Oshkosh, Oshkosh, Oshkosh, Wisconsin, Wisconsin, 54901 54901 (1984) (1984) T. J . Bornhorst, Bornhorst, Department Department of o f Geology Geology and and Geological Geological Engineering, Engineering, T. J. Michigan Technological University, U n i v e r s i t y , Houghton, Houghton, Michigan, Michigan, 49931 49931 (1983) (1983) Southwick, Minnesota Geological Survey, 2642 DD.. LL. . Southwick, 2642 University U n i v e r s i t y Avenue, Avenue, St. S t . Paul, P a u l , Minnesota, Minnesota, 55114 55114 (1982) F. W. Cambray, Cambray, Department of o f Geology, Michigan State S t a t e University, University, F. W. East E a s t Lansing, Lansing, Michigan, 48824 48824 (1981) (1981) J. J . Kalliokoski, K a l l i o k o s k i , Department Department of o f Geology Geology and and Geological Geological Engineering, Engineering, Michigan Technological Technological University, Michigan, 49931 499 31 Michigan U n i v e r s i t y , Houghton, Houghton , Michigan, (Secretary-Treasurer) ( S e c r e t a r y- T r e a s u r e r ) C o p i e s of o f the t h e abstract a b s t r a c t and field f i e l d guidebook guidebook Copies v o l u m e s may be b e purchased p u r c h a s e d from: from: volumes N.M. M.M. Kehienbeck Kehlenbeck D e p a r t m e n t of o f Geology Geology Department L a k e h e a d University University Lakehead Thunder Bay, Bay, Ontario Ontario PTV P7V 5E1 5E1 Costs: Costs: Abstracts $ 5.00 Abstracts $5.00 Field Field G u i d e b o o k $10.00 $10.00 Guidebook ((plus p l u s $2.00 $ 2 . 0 0 postage p o s t a g e and handling h a n d l i n g charges) charges ) c h e q u e s payable p a y a b l e to: to: Make cheques I n s t i t u t e on o n Lake Superior S u p e r i o r Geology Geology Institute viii viii �LOCAL COMMITTEE COMMITTEE LOCAL C. C. E . Blackburn: Blackburn: E. C . Beard: Beard: R.R. C. J . Parker: Parker: J. Conference Conference Chairman, Chairman, and and Technical Technical Sessions Sessions a Treasurer Treasurer Registration Registration C. C. C . Storey: S t o r e y : Poster P o s t e r Session Session C. M. M. R. Hailstone: Hailstone: R. Field F i e l d Trip T r i p Logistics Logistics All A l l at a t Ministry M i n i s t r y of o f Natural Natural Resources, Resources, 808 808Robertson RobertsonStreet, Street, Kenora, Ontario Ontario Kenora, BEST STUDENT STUDENTPAPER PAPER COMMITTEE COMMITTEE BEST - Gene LaBerge, LaBerge, Chairman, Chairman, Department Department of of Geology, Geology, University U n i v e r s i t y of o f Wisconsin Wisconsin, Gene Oshkosh, Wisconsin Wisconsin Oshkosh, Graham Borradaile, B o r r a d a i l e , Department Department of o f Geology, Geology, Lakehead LakeheadUniversity, University, Graham Thunder Bay, Bay, Ontario Ontario Thunder S c h u l z , United United States S t a t e s Geological Geological Survey, Survey, Klaus Schulz, Klaus Reston, Virginia Virginia Reston, GOLDICH MEDAL MEDAL COMMITTEE COMMITTEE GOLDICH W. W. F. F. Cannon, Cannon, Chairman, Chairman, United United States S t a t e s Geological Geological Survey, Survey, Reston, Virginia Virginia Reston, M. M. M. M, Kehienbeck, Kehlenbeck , Department Department of o f Geology, Geology, Lakehead LakeheadUniversity, University , Thunder Bay, Bay, Ontario Ontario Thunder Willard W i l l a r d Bodwell, Bodwell, Resource Resource Exploration, Exploration, Marquette, Marquette, Michigan Michigan FIELD TRIP TRIP LEADERS LEADERS FIELD R. Melling, Melling, Ottawa-Carleton Ottawa-Carleton Centre Centre for f o r Geoscience Geoscience Studies, Studies, David R, David Carleton C a r l e t o n University, U n i v e r s i t y , Ottawa, Ottawa, Ontario Ontario Watkinson, Watkinson, Ottawa-Carleton Ottawa-Carleton Centre Centre for f o r Geoscience Geoscience Studies, Studies, Carleton C a r l e t o n University, U n i v e r s i t y , Ottawa, Ottawa, Ontario Ontario DavidI-I. H. David John C. Davies, Davies, Ontario O n t a r i o Geological Geological Survey, Survey, 77 77Grenville G r e n v i l l eSt., St., John C. Toronto, Toronto, Ontario Ontario P. P . Mark Mark Smith, Smith, Ontario O n t a r i o Geological Geological Survey, Survey, 77 77 Grenville G r e n v i l l e St., St., Toronto, Toronto, Ontario Ontario Charles Charles E. E . Blackburn, Blackburn, Ministry M i n i s t r y of o f Natural Natural Resources Resources 808 808 Robertson Robertson St., S t . , Kenora, Kenora. Ontario Ontario ix �Gary P. P . Beakhouse, Beakhouse, Ontario O n t a r i o Geological G e o l o g i c a l Survey, S u r v e y , 77 77 Grenvi 1 l e St., St. , Grenville Ontario Toronto, O ntario Glen W W. Ontario Grenville St., . JJohns, ohns, O n t a r i o Geological G e o l o g i c a l Survey, S u r v e y , 77 77 G renville S t., Toronto, Toronto, Ontario Ontario Grenville Fred WW. Breaks, O Ontario . Breaks, n t a r i o Geological G e o l o g i c a l Survey, S u r v e y , 77 77 G r e n v i l l e St., St., Fred Toronto, Toronto, Ontario Ontario K . Poulsen, Poulsen, Geological G e o l o g i c a l Survey Survey of o f Canada, Canada, 601 601 Booth Booth St., St., Howard K. Ottawa, Ontario Ontario Don A. A. JJanes, a n e s , Ministry M i n i s t r y of o f Natural N a t u r a l Resources, Resources, Court Court House House Building, Building, Sioux S i o u x Lookout, Lookout, Ontario Ontario Richard C. C. Beard, Beard, Ministry M i n i s t r y of o f Natural N a t u r a l Resources, Resources, 808 808 Robertson Robertson St., St., Kenora, Kenora, Ontario Ontario SESSION CHAIRMEN CHAIRMEN Richard WW. Ojakangas, Geology Department, Richard . Ojakangas, Department, University U n i v e r s i t y of o f Minnesota, Minnesota, Duluth, Duluth, Minnesota Grenville John Wood, Wood, Ontario O n t a r i o Geological G e o l o g i c a l Survey, S u r v e y , 77 77 G r e n v i l l e St., St. , Toronto, Toronto, Ontario Ontario LeRoy Warren, Warren, Department of o f Natural N a t u r a l Resources, Resources, Hibbing, Hibbing, Minnesota Joop Langelaar, L a n g e l a a r , Norontex Exploration E x p l o r a t i o n Ltd., L t d . , Bedworth Bedworth Road, Road, Dryden, Ontario Dryden, Ontario Henry Lepp, Macalaster Department, Macalas t e r College College Lepp , Geology Department, St. S t . Paul, P a u l , Minnesota Mcllwaine, Ministry William 1-I. H. Mcllwaine, M i n i s t r y of o f Northern Northern Affairs, A f f a i r s , 435 435 James St. S t .South, South, William Thunder Bay, Bay, Ontario Ontario Everett, JJack ack E v e r e t t , Consulting C o n s u l t i n g Geologist, G e o l o g i s t , 1015 1015 North North Shore Shore Drive, Drive, Duluth, Duluth , Minnesota Michael Michael EE. . Cherry, C h e r r y , Ontario O n t a r i o Geological G e o l o g i c a l Survey, Survey, 77 77 Grenville G r e n v i l l e St., St., Toronto, T o r o n t o , Ontario Ontario x �GOLDICI-1 MEDAL RECIPIENT RECIPIENT GOLDICH MEDAL Paul Paul K. K . Sims Sims United U n i t e d States S t a t e s Geological G e o l o g i c a l Survey, S u r v e y , Denver Denver Federal F e d e r a l Centre, Centre, Denver Colorado Colorado ANNUAL BANQUET BANQUET SPEAKER SPEAKER Grant G r a n t M. M. Young, Young, Department Department of o f Geology, Geology, University U n i v e r s i t y of o f Western Western Ontario, Ontario, London, London, Ontario Ontario xi �TECHNICAL SESSIONS TECHNICAL SESSIONS A s t e r i s k denotes student s t u d e n t papers papers Asterisk Speakers Speakers are a r e underlined underlined xii �SESS S E S S ION I O N 1 1 Morning Wednesday, May 8 , 1985 1985 May 8, Co-chairmen: Co-chairmen: Jack Everett Everett and and Henry Henry Lepp Lepp 8:15 8:15 8:20 8:20 Opening Opening Remarks Remarks * T. Chartier Chartier * 8:40 8:40 9:00 9:OO * * 9:20 J. J . J. J . Mancuso Mancuso & C. C . W. W . Schick Schick Unconformity-type Unconformity-type uranium mineralization mineralization at a t the t h e Groveland Groveland Iron I r o n Mine, Mine, central central Dickinson County, County, Michigan. Michigan. C. L. L. Reichhoff Reichhoff Geology Geology of o f aa Lower Lower Proterozoic Proterozoic volcaniclastic v o l c a n i c l a s t i c sequence, sequence, Marathon County, Wisconsin. Wisconsin. J. J. G. G. 9:40 The the The texture t e x t u r e and and mineralogy mineralogy of o f the Lake Ellen E l l e n kimberlite, k i m b e r l i t e , Crystal C r y s t a l Falls, Falls, Michigan, Michigan, U. U . S. S . A. A. S. S. Kiasner Klasner 5 L, L o LaBerge LaBerge P. P. A. A. Nielsen 10:00 10: 00 Structural S t r u c t u r a l geology geology and and kinematics kinematics of of Early E a r l y Proterozoic P r o t e r o z o i c shear s h e a r zones zones in in central c e n t r a l Wisconsin. Wisconsin. Metamorphism Metamorphism of o f the t h e Dunbar Dunbar Gneiss Gneiss and associated a s s o c i a t e d supra-crustal s u p r a - c r u s t a l rocks: rocks: northeastern n o r t h e a s t e r n Wisconsin, Wisconsin, U. U. S. S . A. A. Coffee. Coffee. G. G. M. M. Young Young 6 H. W. W. Nesbitt Nesbitt Major Major element element geochemistry geochemistry of o f the the Gowganda Gowganda Formation, Formation, Ontario. Ontario. R. R . C, C. Johnson Documentaion Documentaion of o f aa subaqueously subaqueously emplaced emplaced volcanic v o l c a n i c horizon h o r i z o n in i n the t h e upper upper Portage Portage Lake Volcanics, Keweenaw Keweenaw Peninsula, Peninsula. Michigan. Michigan. 11:20 11:ZO J. J. Kalliokoski Kalliokoski & B. E . J. J. Welch Welch Caliche C a l i c h e paleosol p a l e o s o l in i n the t h e lower lower part p a r t of o f the the and Hecla Conglomerate, Centennial Calumet Calumet Conglomerate, Centennial Mine, Calumet, Calumet, Michigan. Michigan. 11:40 11:40 W, W. C. C. Hood Hood E& P. P . J. J. Vanstone Vanstone Economic Economic geology geology of o f the t h e rare r a r e element element pegmatites p e g m a t i t e s at a t Lilypad Lilypad Lake, Lake, northern n o r t h e r n Ontario. Ontario. 10:40 10~40 1-I. 11:00 11:OO 12:00 12 : O O * * Lunch. Lunch. xiii xiii �S E S S ION I O N SESS 22 Afternoon Aft e rn o on Wednesday, Wednesday, May May 8, 8 , 1985 1985 Co-Chairmen: Co-Chairmen: R. R. W. W . Ojakangas Ojakangas and and John John Wood Wood 2:OO 2:00 R. R. L. L . Morton, Morton, D. A. A. Groves, Groves, & D. J. NI. M. Franklin Franklin J. Volcanic V o l c a n i c stratigraphy s t r a t i g r a p h y and and nature n a t u r e of of t h e semi-conformable semi-conformable alteration a l t e r a t i o n zone zone the beneath b e n e a t h the t h e Mattabi M a t t a b i massive massive suiphide sulphide deposit, d e p o s i t , Sturgeon S t u r g e o n Lake, Lake, Ontario. Ontario. 2 :20 2:20 M. M. M. M. Kehienbeck Kehlenbeck Structure S t r u c t u r e of o f the t h e Beardmore-Geraldton Beardmore-Geraldton f o l d belt. belt. fold 2 :40 2:40 3:OO 3:00 M. J. J. Lavigne Lavigne Geological G e o l o g i c a l setting s e t t i n g of o f gold g o l d mineralization mineralization i n Beardmore-Geraldton. Beardmore-Geraldton. in P. P . W. W. Fralick F r a l i c k && B. NI. M. Scott Scott B. Controls C o n t r o l s on on the t h e genesis g e n e s i s of o f epigenetic epigenetic auriferous a u r i f e r o u s vein v e i n systems systems in i n Archean Archean chemical-siliciclastic c h e m i c a l - s i l i c i c l a s t i c submarine submarine fan fan deposits, d e p o s i t s , Geraldton G e r a l d t o n area, a r e a , Ontario. Ontario. NI. Coffee. Coffee. 3:20 3:20 3:50 3:50 H. H. G. G . Clark Clark Preliminary P r e l i m i n a r y metallogenic m e t a l l o g e n i c subdivision s u b d i v i s i o n of of the t h e Lake Lake of o f the t h e Woods Woods metavolcanicmetavolcanicmetasedimentary metasedimentary belt, b e l t , northwestern n o r t h w e s t e r n Ontario. Ontario. 4 : 10 4:10 M. M. G. G. Parr Parr 5 C . Boben Boben C. The The geological geological mineralization mineralization Mine, Mine, District District 44:30 : 30 :50 44 :50 *J J . Stix Stix B. B. A. A. Brown Brown setting s e t t i n g of o f gold gold observed o b s e r v e d at a t the t h e Scramble Scramble of o f Kenora, Kenora, N. N . W. W. Ontario. Ontario Volcanic V o l c a n i c facies f a c i e s of o f the t h e Andre: Andre": Bay Bay area, area, Lake Lake of o f the t h e Woods, Woods, Ontario. Ontario. The The deformational d e f o n n a t i o n a l history h i s t o r y of o f Archean Archean greenstones g r e e n s t o n e s in i n the t h e Central C e n t r a l Lake Lake of o f the the Woods Woods area, a r e a , northwestern n o r t h w e s t e r n Ontario. Ontario. xiv �SESS S E S S IION O N 3 Morning Thursday, May 9, 9 , 1985 1985 Co-chairmen and LeRoy LeRoy Warren Warren Co-chairmen:: Joop Langelaar and Opening Remarks Remarks 8:15 8:20 J. J. V. V. C. C. Green Green ?S W. W. Chandler Keweenawan dikes d i k e s of o f Minnesota. Minnesota- 8:40 M. M. GG. . Mudrey ?S PP.. E. E. Myers Myers Proterozoic P r o t e r o z o i c diabase d i a b a s e dike d i k e swarms swarms in in Wisconsin. 9:00 T. T. B. B. Hoist, Hoist, E. E . E. E . Mullenmeister J. C. & J. C. Green Keweenawan structural s t r u c t u r a l features f e a t u r e s at at tthe h e base of o f the t h e Duluth Complex Complex in i n the the near Dunka Pit Pit n e a r Babbitt, B a b b i t t , Minnesota. 9:20 9:40 D. M Miller * J . D. iller J. T. Wilband Magmatic pprocesses r o c e s s e s during d u r i n g the the Midcontinent Rift Midcontinent R i f t interval i n t e r v a l in i n northern northern Michigan: chemical and isotopic isotopic constraints. constraints. Coffee. 10:00 10:40 Petrogenesis P e t r o g e n e s i s ooff anorthositic a n o r t h o s i t i c rocks rocks of of the t h e Duluth Duluth Complex. Complex. D, G. W. Davis F R. Edwards Evolution of igneous complex complex o f an an Archean igneous from h high i g h precision p r e c i s i o n U-Pb U-Pb geochronology: geochronology : tthe h e Kakagi Lake Lake area, a r e a , N. N . W. Ontario, Ontario. 11:00 J. J . A. A. Percival Percival Metamorphism and and plutonism p l u t o n i s m in i n the the Quetico belt, b e l t , N. N . W. W. Ontario. Ontario. 11:20 R, H. Sutcliffe R. H. Sutcliffe well-preserved ell-preserved Mulcahy Lake Lake gabbro: gabbro : a w Archean layered l a y e r e d intrusion. intrusion. 11:40 D. D. A. A. Morrison Morrison W. W. C. C. Phinney, Phinney, F& E. Maczuga ft. The Mulcahy Lake gabbro and related related intrusions. intrusions. 12:00 Lunch. xv a �U SESSION S E S S I O N 4 4 Afternoon Thursday, May May 9, 9 , 1985 1985 Co-chairmen: Co-chairmen: i:30 1:50 . W.H. Cherry W. H . Mcllwaine M c I l w a i n e and and M.E. M E. C herry EE. . 00. . Owens E& J. Bornhorst T. J. J• D. *J. D. Vervoort Vervoort Geology Geology ooff Precambrian-hosted Precambrian-hosted precious precious metal metal prospects p r o s p e c t s in i n the t h e Fire F i r e Center Center and Holyoke mines area, a r e a , Marquette Marquette County, County, Michigan. Geology of o f the t h e Jap J a p Lake Lake area a r e a of o f the the eastern northeastern e a s t e r n Vermilion Vermilion district, district, n ortheastern Minnesota. 2:10 R. L L. R. . Bauer Multiphase fold f o l d geometry geometry along a l o n g the the ssoutheastern o u t h e a s t e r n margin of o f the t h e Vermilion Vermilion Granitic G r a n i t i c Complex, Complex, northeastern n o r t h e a s t e r n Minnesota. Minnesota. 2:30 T. L. T. L. Lawler & J . M. M. Seliner Sellner J. Ranier, Minnesota, Mineral potential R a n i e r , Minnesota, potential evaluation: e v a l u a t i o n : ooutcrop u t c r o p sampling, s a m p l i n g , geophysics geophysics and soil s o i 1 geochemistry. geochemistry. 2:50 D. D. Ela & The significance of strain The s i g n i f i c a n c e of s t r a i n ppatterns a t t e r n s in in deciphering d e c i p h e r i n g the t h e deformational d e f o r m a t i o n a l history h i s t o r y of of Archean rocks r o c k s in i n the t h e Vermilion Vermilion district, district, Minnesota. P. P. Ifudleston ifudleston 3:10 3:lO Coffee C offee 3:35 3 : 35 Announcement of o f best b e s t student s t u d e n t papers. papers. 3:40 3 :40 M. M. T. T. Corkery Stratigraphic S t r a t i g r a p h i c and structural s t r u c t u r a l evolution evolution off the o t h e Cross Lake supracrustal s u p r a c r u s t a l belt b e l t in in nnorthwestern o r t h w e s t e r n Superior S u p e r i o r Province, P r o v i n c e , Manitoba. Manitoba. 4:00 4:OO E. E. P. Moreton & P. R. Gerber R. Stratigraphy hydrothermal alteration S t r a t i g r a p h y and hydrothermal alteration Archean structural s t r u c t u r a l zone, zone, the the iin n an Archean Katisha K a t i s h a Lake Lake area, a r e a , Wabigoon Wabigoon Subprovince, Subprovince, N.W. Ontario. N.W. Ontario. 4:20 4 :20 B. B. J. J . Christie Christie & C. J. C. J. Hodgson Alteration A l t e r a t i o n and with w i t h a sheeted sheeted Red Lake Mine, Mine, 4:40 P. P. M. M. Berger, Berger, J . M. M. Dixon E& J. H. H. Helmstaedt Structural S t r u c t u r a l geology ooff nnorthern o r t h e r n Dome and southern s o u t h e r n McDonough Townships, Red Red Lake, Lake, Ontario. O ntario. xvi gold g o l d mineralization m i n e r a l i z a t i o n associated associated veinlet v e i n l e t zone zone at a t the t h e Campbell Balmertown, Balmertown, Ontario. Ontario. �U POSTER PRESENTATIONS Tuesday, May May 77 Wednesday, Wednesday, May 88 Thursday, T h u r s d a y , May May 99 4:00 - 110:00 0 : 0 0 p.m. p.m. 8:15 8 : 1 5 -- 5:00 p.m. 8:15 8 : 1 5 -- 5:00 5 : 0 0 p.m. I C. Anderson C. Correlation C o r r e l a t i o n of o f nnearly e a r l y continuous c o n t i n u o u s magnetic magnetic pprofiles r o f i l e s to t o lithology:case 1 i t h o l o g y : c a s e histories. histories. T. Anderson DD. . T. Remote sensing s e n s i n g application a p p l i c a t i o n in i n the t h e Cameron Cameron Lake Area, Ontario. A r e a , N.W. Ontario. T. T. Age of o f copper c o p p e r mineralization m i n e r a l i z a t i o n in i n the t h e flow flow tops t o p s of o f the t h e Portage P o r t a g e Lake Lake Lava Lava Series Series determined d e t e r m i n e d by paleomagnetic p a l e o m a g n e t i c methods. methods. D. Browning, D. S. S. Beske-Diehi, Beske-Diehl, J. J . Diehi, Diehl, 6 T. T. J. J. Bornhorst Bornhorst *G. T. Burgess *G. Chemical characterization Chemical c h a r a c t e r i z a t i o n and ppetrogenesis etrogenesi s Keweenawan d diabase off N Northern ooff Keweenawan i a b a s e dykes o orthern Michigan. KK.. D, D . Card Card Decade of o f North American Geology Geology (D-NAG) (D-NAG) geological g e o l o g i c a l and tectonic t e c t o n i c maps maps of o f the t h e southsoutheastern e a s t e r n Canadian Canadian Shield. Shield. Corfu FF. . C orfu & G,. M M,. Stott G Stott U-Pb U-Pb geochronology geochronology and tectonic t e c t o n i c history h i s t o r y of of the t h e Shebandowan belt, b e l t , northwestern n o r t h w e s t e r n Ontario. Ontario. FF.. GG,. G. G. R. R. Corfu, Corfu, P.o Beakhouse, P M. S Stott M. t o t t F15 H. S Sutcliffe H. utcliffe U-Pb U-Pb geochronology geochronology and tectonic t e c t o n i c history h i s t o r y of of the t h e Winnipeg River R i v e r granitoid g r a n i t o i d terrain, t e r r a i n , northnorthwestern w e s t e r n Ontario. Ontario. distri- . Crissman *S. EE, Geochemical Geochemical constraints c o n s t r a i n t s on on the t h e REE REE d i s t r i bution b u t i o n in i n the t h e Neguanee Iron I r o n Formation Formation of o f the the Empire Mine, Mine, Palmer, P a l m e r , Michigan. Michigan. R. M. M. Easton R. Easton Anomalous radiometric r a d i o m e t r i c ages a g e s from from the t h e Superior Superior Province, P r o v i n c e , Ontario: O n t a r i o : sense? s e n s e ? or o r non-sense? non-sense? T. Fitz T. Fitz & J. J . C. C . Green Green Large ignimbrites i g n i m b r i t e s in i n the t h e Keweenawan North Shore S h o r e Volcanic V o l c a n i c Group Group in i n Cook Cook County, County, Minnesota. Minnesota F4 J. W. Gell Geochemistry of M i l l Group: Group: the the o f the t h e Powder Powder Mill earliest e a r l i e s t lavas l a v a s of o f the t h e Midcontinent M i d c o n t i n e n t Rift R i f t in in Michigan. H. P. P . Gilbert Gilbert Stratigraphic S t r a t i g r a p h i c evolution e v o l u t i o n of o f the t h e Island I s l a n d Lake Lake ggreenstone r e e n s t o n e belt, b e l t , Manitoba. Manitoba. JJ.. K. K . Greenberg GreenbergF4S B, A. B. A . Brown Brown The central c e n t r a l Wisconsin Wisconsin Archean Archean block: b l o c k : new new eevidence v i d e n c e suggests s u g g e s t s a partially p a r t i a l l y reworked reworked granite/ granite/ W. Johns GG. . W. Facies F a c i e s interpretation i n t e r p r e t a t i o n of o f the t h e Berry Berry River R i v e r formation, formation, Lake of o f the t h e Woods. Woods. greens errane . g r e e n s ttone o n e tterrane, xvii �U ** W. J. W. J . Johnson Johnson T. T. The p petrology The e t r o l o g y and sedimentation s e d i m e n t a t i o n of o f the the Lower Proterozoic P r o t e r o z o i c Barron Barron Quartzite, Quartzite , nnorthwestern o r t h w e s t e r n Wisconsin. Wisconsin. Lawler F S LL.. Lawler Ranier, Minnesota, mineral R a n i e r , Minnesota, m i n e r a l potential potential sampling, g geophysics eevaluation: v a l u a t i o n : ooutcrop u t c r o p sampling, eophysics and soil s o i l geochemistry. geochemistry. J. J . NI. M. SSeliner ellner * E. The ppetrology e t r o l o g y of o f the t h e Longnose Peridotite Peridotite i t s relationship r e l a t i o n s h i p to t o the t h e Duluth Duluth ddeposit e p o s i t and its Complex. K. Lin$cheid R. Lundy * J. J . R. Minor folds f o l d s in i n the t h e Soudan Soudan Iron I r o n Formation, Formation, northeastern n o r t h e a s t e r n Minnesota. Minnesota. * D. D. MacTavish MacTavishF16 R. JJ. R. . Dutka The Atikokan cobalt—base c o b a l t - b a s e metals-platinum metals-platinum group elements e l e m e n t s project. project. A. A. * M. P. P. McDermott Chemical ccharacterization Chemical h a r a c t e r i z a t i o n ooff the t h e Unnamed Formation, Formation, aa ccentral e n t r a l vvolcanic o l c a n i c complex ooff Keweenawan age. age. * 0. D. R. R. D. D. H. H. L. B. L . B. K. K. H. H. Melling, M elling, Watkinson, Watkinson, Choriton, C horlton, Poulsen Poulsen The influence i n f l u e n c e of of shear s h e a r zone zone geometry geometry and and mineralization vvein e i n pparagenesis a r a g e n e s i s on gold-pyrite gold-pyrite m ineralization at a t Cameron Lake, Lake, northwestern n o r t h w e s t e r n Ontario. Ontario. 6 F1 E. E. Mulienmeister, Mullenmeister, T. B. Hoist, T. B. Hoist, 6 J. J . C. C . Green Green Structural S t r u c t u r a l analysis a n a l y s i s ooff the t h e nnortheastern ortheastern basal Mesabi Range Range and adjacent adjacent b a s a l Duluth Complex. B. Paces 6 B. T. T. J. Bornhorst Bornhorst Geology and geochemistry of o f lava l a v a flows flows within within the t h e Copper Harbor Conglomerate, Conglomerate, Keweenaw Peninsula, P e n i n s u l a , Michigan. Michigan. H. H. C. C. Palmer PalmerF16 The paleomagnetism of M i l l Group: Group: o f the t h e Powder Powder Mill with iits t s rrelevance e l e v a n c e tto o ccorrelation orrelation w i t h oother ther Keweenawan sequences and to t o tectonic t e c t o n i c developdevelopment of the t h e South South Range. Range. F1 J. J. F1 H. C. C. Halls H. ** E. EE.. Peterson Peterson The tectonic t e c t o n i c significance s i g n i f i c a n c e of o f the t h e Porphyritic Porphyritic Granite, Red G r a n i t e , Dickinson County, County, Michigan. Michigan. A. Ross * B. A. Ross Petrogenesis P e t r o g e n e s i s of o f the t h e Bardon Bardon Peak Peak peridotite, peridotite, Duluth Complex. * Platinum element m minerals P l a t i n u m group element i n e r a l s in i n the t h e Duluth Complex. T. T. Sabelin Sabelin W. A. W. A . Schieiss, Schleiss, T. J . Bornhorst, Bornhorst, T. J. A. P. Ruotsala A. P. Ruotsala P. M. M. Smith Smith P. 6 F1 vein mineralization wall A sstudy t u d y ooff v ein m i n e r a l i z a t i o n and w a l l rock alteration Mine, Keweenaw a l t e r a t i o n at a t the t h e Delaware Delaware Mine, County, County, Michigan. Michigan. The geological g e o l o g i c a l setting s e t t i n g at a t the t h e Duport Duport Mine, Mine, Cameron Island, I s l a n d , Shoal Shoal Lake. Lake. xviii xviii �U M. M. Swan, Swan, BB.. Keith, Keith, M. G. Parr M. G. Parr M. S. S. KK. . Thomson S DD. . Gliddon FT J. J. L . Welsh L. * S. S. FF. . Wright * 6 FT Magma series s e r i e s and and their t h e i r relationship r e l a t i o n s h i p to to greenstone g r e e n s t o n e gold g o l d metallogeny m e t a l l o g e n y in i n the the Lake Superior Lake S u p e r i o r Region. Region. The 1-lemlo Hemlo b abaritic r i t i c hhorizon; o r i z o n ; aa ppossibly ossibly ssyngenetic y n g e n e t i c Archean barite b a r i t e occurrence. occurrence. Preliminary geology P r e l i m i n a r y iinvestigations n v e s t i g a t i o n s iinto n t o tthe he g eology of o f the t h e Giants G i a n t s Range Range Complex, Complex, VirginiaVirginiaBiwabik area, Biwabik a r e a , N. N . E. E . Minnesota. Minnesota. Strain S t r a i n patterns p a t t e r n s in i n the t h e Kiruna K i r u n a district, district, northern n o r t h e r n Sweden; Sweden ; implications i m p l i c a t i o n s for for Proterozoic P r o t e r o z o i c deformation. deformation. xix �ABSTRACTS ABSTRACTS xx �U CORRELATION CORRELATION OF OF NEARLY NEARLY CONTINUOUS CONTINUOUS MAGNETIC MAGNETIC PROFILES PROF1LES - TO LITHOLOGY LITHOLOGY --CASE CASE HISTORIES HISTORIES TO I DR. CHRIS ANDERSON, DEPT. OF EARTH SCIENCES UNIVERSITY OF MANITOBA, WINNIPEG AA RESEARCH RESEARCH PROJECT P R O J E C T RELATING R E L A T I N G LITHOLOGY L I T H O L O G Y TO TOMAGNETIC MAGNET1 C MEASUREMENTS ALONGP PROFILES MEASUREMENTS ALONG R O F I L E S WWITH I T H AA STATION S T A T I O N SPACING S P A C I N G OF OF THE THE ORDER ORDER OF OF ONE ONE METRE METRE HAS HAS BEEN B E E NCONDUCTED CONDUCTED BY B Y THE T H EAUTHOR AUTHOROVER OVER PROJECTS HAVE H A V E BEEN B E E N COMPLETED COMPLETED AT A TA ANUMBER NUMBER T H E LAST L A S TDECADE. D E C A D E , PROJECTS THE OF AND P PATENTS OBTAINED OF LOCATIONS L O C A T I O N S ACROSS ACROSS CANADA CANADA AND ATENTS O B T A I N E D ON ON INSTRUINSTRUM E N T A T I O N FOR FOR R A P I D DATA D A T A ACQUISITION. ACQUISITION. MENTATION RAPID IN THIS (1) THE IN THIS PRESENTATION PRESENTATION RESULTS RESULTS WILL WILL BE BESHOWN SHOWN FROM FROM (1) THE FALCON FALCONLAKE LAKESTOCK, STOCK) BETWEEN BETWEEN THE THE INTERMEDIATE INTERMEDIATE INTRUSIVE INTRUSIVE AND AND THE HOSTRROCKS, (2) THE THE METAVOLCANIC METAVOLCANIC HOST O C K S / (2) THE EUCLID EUCLID LAKE LAKECHROMITE CHROMITE DEPOSIT D E P O S I T WITH W I T H THE T H E PROFILE P R O F I L EDATA D A T ACOVERING C O V E R I N G METAVOLCANICS1 M E T A V O L C A N I C S , MAFIC, MAFIC, AND ULTRAMAFIC INTRUSIONS# AND AND (3) (3)THE THEBIRD BIRD RIVER RIVER SILL SILL WHICH WHICH AND ULTRAMAFIC INTRUSIONS, THESE IS AALAYERED LAYERED BASIC BASIC TO T OULTRAMAFIC ULTRAMAFIC INTRUSIVE. INTRUSIVE, THESE SITES SITES IS ARE ALL ALLLOCATED LOCATEDININSOUTH—EASTERN SOUTH-EASTERN MANITOBA, MAN ITOBA, ARE THESE VARIATIONS OF THESE DATA DATA SHOW SHOW VARIATIONS OF BOTH BOTH POSITIVE POSITIVE AND ANDNEGATIVE NEGATIVE VALUES UP UP TO T OSEVERAL SEVERALTHOUSAND THOUSANDGAMMAS GAMMAS (NANO (NANO TESLAS) TESLAS)WITH WITH SOME SOME VALUES ANOMALY WIDTHS ONLY AA FEW FEWMETRES, METRES. THESE THESE VARIATIONS VARIATIONS CAN C A N BE BE ANOMALY WIDTHS OF ONLY RELATED R E L A T E D DIRECTLY D I R E C T L Y TO T O THE T H EOBSERVED OBSERVED LITHOLOGY. LITHOLOGY1 1 �U REMOTE SENSING --- APPLICATION APPLICATION IN I NTHE THECAMERON CAMERON LAKE LAKE AREA, AREA, N.WONTARIO N W ONTARIO -- -REMOTE_SENSING DR. D.T. ANDERSON, DEPT. OF EARTH SCIENCES UNIVERSITY OF MANITOBA, WINNIPEG THE LAKE AREA THE CAMERON CAMERON LAKE AREA IS IS OF OFCONSIDERABLE CONSIDERABLE INTEREST INTERESTBECAUSE BECAUSEOF OF A VARIETY VARIETY THE T H E ACTIVE A C T I V E REGIONAL R E G I O N A LGOLD GOLD EXPLORATION E X P L O R A T I O N BEING B E I N G CARRIED C A R R I E D OUT. OUT, A OF HAS NORTHERN OF TECHNIQUES TECHNIQUES HAS BEEN BEEN APPLIED APPLIED ININPARTS PARTSOFOF NORTHERNMANITOBA MANITOBA WHEREBY AND GEOPHYSICAL WHEREBY SSPECTRAL P E C T R A L AND G E O P H Y S I C A L REMOTE REMOTE SENSING S E N S I N G DATA D A T A HAVE H A V EBEEN BEEN INTEGRATED WITH GEOLOGYT OTOAASSIST INTEGRATED W I T H MAPPED MAPPED GEOLOGY S S I S T IIN N THE T H E INTERPRETATION I N T E R P R E T A T I O N OF OF THE T H E STRUCTURE STRUCTURE AND AND LITHOLOGY L I T H O L O G Y OF OF AN AN AREA. AREA, A A SIMILAR SIMILAR PROCEDURE PROCEDURE HAS HAS BEEN BEEN APPLIED APPLIED TO TOTHE THECAMERON CAMERON LAKE LAKE To TOTHIS T H I SEND, E N DTHE / T H AVAILABLE E A V A I L A B LAERIAL E A E R I APHOTOGRAPHS L PHOTOGRAPHSHAVE H A V EBEEN BEEN THE AVAILABLE AVAILABLE EXAMINED E X A M I N E D AND AND AAPHOTOLINEAMENT P H O T O L I N E A M E N TTREND TRENDMAP MAPPRODUCED. PRODUCED, THE AREA. AREA. GEOPHYSICAL G E O P H Y S I C A L SURVEY SURVEY DATA D A T A HAVE H A V E BEEN B E E N EXAMINED E X A M I N E D AND ANDAN ANANALOGOUS ANALOGOUS LINEAMENT LINEAMENT TREND TRENDMAP MAPPRODUCED. PRODUCED, MULTISPECTRAL MULTI SPECTRAL AND AND MULTITEMPORAL MULTITEMPORAL LANDSAT DATA LANDSAT DATA HAVE HAVE BEEN BEEN EXAMINED EXAMINED USING USING BOTH BOTHTHE THEPHOTOGRAPHIC PHOTOGRAPHIC IMAGERY AND TTHE YET IMAGERY AND H E DIGITAL D I G I T A LINFORMATION, I N F O R M A T I O N ,AND AND Y EANOTHER T ANOTHERANALOGOUS ANALOGOUS TREND-LINE MAP MAP PRODUCED. PRODUCED, THESE THESE THREE THREE LINEAMENT LINEAMENT MAPS MAPS HAVE HAVE BEEN BEEN TREND—LINE SUPERIMPOSED ON ONE ONE ANOTHER/ ANOTHER, AND S U P E R I M P O S E D ON AND UPON UPON THE T H E AVAILABLE A V A I L A B L EGEOLOGICAL GEOLOGICAL IT CAN MAPS OF OF THE T H E AREA, AREA, IT CAN BE B ESEEN SEEN THAT T H A T AAHIGH H I G HDEGREE DEGREE OF OF USEFUL USEFUL MAPS TH Is STUDY STUDY CONSISTED CONS IS T E D OF OF CORRELATION C O R R E L A T I O N EXISTS E X 1 S T S BETWEEN BETWEEN THESE T H E S E DATA. D A T A , THIS "MANUAL" "MANUAL" CORRELATION CORRELATION OF OF THE THE DATA, DATA, BUT BUTAUTOMATIC AUTOMATIC CORRELATION CORRELATION SHOULD AALSO L S O BBE E POSSIBLE. P O S S I B L E , TIME TIME AND AND EQUIPMENT E Q U I P M E N T CONSTRAINTS C O N S T R A I N T S PREPRESHOULD CLUDED CLUDED DDIGITAL I G I T A L CORRELATION C O R R E L A T I O N AAT T TTHIS H I S TIME. TIME. THE VALUE VALUE OF OF SUCH SUCH INTEGRATION INTEGRATION LIES IN THE THERAPID RAPIDOVERVIEW OVERVIEW THE LIES IN THAT IS IS POSSIBLE. POSSIBLE. THAT THE THE CLOSE CLOSE CORRELATION CORRELATION SUGGESTS SUGGESTS THAT THAT SPECTRAL SPECTRAL AND AND GEOPHYSICAL G E O P H Y S I C A L REMOTE REMOTE SSENSING E N S I N G INTERPRETATION I N T E R P R E T A T I O N MAY MAY GIVE G I V E VALUABLE VALUABLE INSIGHTS I N S I G H T S INTO I N T OEXPLORATION E X P L O R A T I O NMETHODOLOGY, METHODOLOGY, EVEN E V E N IN I NTHOSE THOSEAREAS AREASWHERE WHERE IT DETAILED MAPPING IS IS NOT DETA ILED GEOLOGICAL GEOLOG ICAL MAPPING NOT AVAILABLE. A V A ILABLE , FURTHERMORE, FURTHERMORE, MAY MAY DIRECT D I R E C T THE T H E GEOLOGICAL G E O L O G I C A L MAPPING M A P P I N G TO T O CRITICAL C R I T I C A LAREAS AREASWHERE WHERE THE THE ELUCIDATION E L U C I D A T I O N OF OF THE T H E STRUCTURAL STRUCTURAL STYLE S T Y L E MIGHT M I G H T MOST MOST READILY R E A D I L Y BE BE DERIVED, DERIVED. 2 �Multiphase Fold Geometry Along the the Southeastern Southeastern Margin of the the Vermilion Vermilion Granitic Granitic Complex, Complex, Northeastern Northeastern Minnesota University of Missouri, Columbia, Robert L. L. Bauer, Department of Geology, University Columbia, MO 65211. 6521 1. The Archean schist and migmatites the migmatites along the southern margin of the Vermilion Granitic Complex (VGC), (VGC), south south of of the the Lac Lac La La Croix Croix Granite, Granite, have have undergone three three periods of regional regional folding folding which are are differentially differentially developed developed and decipherable in in various portions portions of of the the terrane. terrane. A pervasive pervasive S1 S foliation foliation 1 in the schist is generally parallel parallel to bedding (S0) ( S ) except in the hinges of 0 rare minor Fl Fl folds. folds. Local graded bedding indicates indicates a downward—eastward downward-eastward structural facing in in the the S2 S foliation. foliation. We have interpreted interpreted this this facing facing and 2 reversals in facing in the Vermilion district to be a result of regional Ft Fl folding folding (Bauer and Hudleston, Hudleston, 1982). 1982). produced the the most most prominent prominent fold fold structures structures (F2), (F2), including including aa major major D produced e s t e r t Y plunging antiform along the the boundary of of the the Vermilion Cranitic Granitic westerly Complex and the the Vermilion Vermilion district district to to the the south. south. This east—west east-west trending trending boundary, marked strike-slip and dip—slip dip-slip faulting on the Vermilion and marked by strike—slip Haley faults, faults, follows follows the the axial surface surface trace trace of of the the antiform. antiform. Large-scale Large—scale parasitic folds folds on on this this structure structure are invariable invariable of of SS symmetry symmetry in in the the southern southern VGC and and occur occur on on the the northern northern limb limb of of the the antiform. antiform. These folds folds are are F2 folds of Z symmetry that occur in the Vermilion district on correlated with F 2 the southern limb limb of the the antiform. antiform. The orientation of F2 lineations are L lineations F fold fold hinges and coaxial L2 are 2 2 relatively constant in the VGC along the boundary with the Vermilion district, district, but in in the the Burntside Burntside Lake area, area, large—scale large-scale F2 F parasitic parasitic folds folds are are strongly strongly 2 noncylindrical, and and FF and noncylindrical, and L2 L vary vary from from SW SW to to NE NE plunging plunging within within the the local local S 2 2 axial surface. surface. This local noncylindricity is attributed to a combination of: (1) pre-F2 pre—F2 reorientation of S S0 and S1 S by intrusion of the Burntside tonalite, tonalite, 0 F2 synformal folding induced in part by gravitational and (2) to late—stage late-stage F 2 subsidence around a dense dense amphibolite amphibolite body. body. In the Norwegian Bay Haley and and Vermilion Vermilion faults, faults, Bay block, block, bounded bounded by by the the Haley F2 folds have been refolded by a doubly plunging, east—west—trending regional F east-west-trending 2 F3 fold cored by the F the Wakemup Bay Bay tonalite. tonalite. Northwesterly Northwesterly plunging, plunging, F3, F3 3' conical folds folds just just north of the the Vermilion fault fault also also fold fold large—scale large-scale F2 F 2 antiforms and synforms but are not associated associated with emplacement of granitic antiforms plutons such such as as the the Wakemup Wakemup Bay Bay stock. stock. Relationships between folding and the various granitic rocks rocks of of the the region indicate that the Burntside tonalite was emplaced prior to region to the the initiation of D D2; the Lac La Croix Granite was syn—D2; and the Wakemup Bay syn-D 2 2 but tonalite was emplaced post—D2, post-D but pre—D3. pre-D ' 2' 3' ' REFERENCES Bauer, R.L. R.L. and and Hudleston, P.J., P.J., 1982, 1982, F1 F recumbant recumbant folding folding in in the the western western Bauer, 1 Vermilion greenstone-granite terrane, terrane, NE NE Minnesota: Minnesota: Ann. Inst. Inst. Lake Lake Vermilion greeristone—granite Superior Geol., 28th, 28th, Proc., Proc., p. p. 4. 4. �U STRUCTURAL STRUCTURAL GEOLOGY GEOLOGY OF OF NORTHERN NORTHERN DOME DOME AND AND SOUTHERN MCDONOUGH RED LLAKE, SOUTHERN MCDONOUGH T OTOJNSHIPS, W N S H I P S , RED A K E , ONTARIO ONTARIO h Paula P a u l a M. M. Berger, B e r g e r , J. J . M. M. Dixon, D i x o n , and a n d H. H . Helmstaedt, H c l m s t a e d t , Department D e p a r t m e n t of o f Geological Geological S c i e n c e s , Queen's Q u e e n ' s University, U n i v e r s i t y , Kingston, K i n g s t o n , Ontario Ontario Sciences, and southern southern McDonough within Northern Northern Dome D o m e and McDonough TTownships, o w n s h i p s , within the Lake "greenstone" "greenstone"belt belt of the Red Red Lake of northwestern northwestern Ontario, O n t a r i o ,were were mapped scale with ongeological geological structures. structures. mapped on on a a 1:1000 1 : 1 0 0 0 scale with emphasis emphasis on Mafic Mafic to to ultramafic ultramafic metavolcanic rnetavolcanic rocks, r o c k s , felsic felsicmetavolcanic metavolcanic to to metavolcaniclastic metavolcaniclastic rocks, rocks, and and clastic clastic totochemical chemical metasedimentary greenschist grade, metasedimentary rrocks, o c k s , metamorphosed metamorphosed totogreenschist g r a d e , occur occur within supracrustal rrocks within the the area. area. These These supracrustal o c k s are are crosscut crosscut by by felsic felsic to tointermediate intermediate intrusives, intrusives, the the largest largestbeing being the the Planar, occur in in nearly nearly all P l a n a r , penetrative penetrative fabric fabric elements e l e m e n t s occur all exposures. cleavagei sisparallel parallel or exposures. This T h i s cleavage or at at a a low low angle angle to to contacts contacts oof f the the granitoid granitoid batholiths batholiths surrounding surrounding the the belt. belt. McKenzie Island Stock. McKenzie Island Stock. In and In the the study study area a r e a the the fabric fabricdips dipssteeply steeply andchanges changes gradually gradually and continuously in in strike and continuously strikefrom fromsoutheast southeastnear nearCochenour Cochenour to to northeast cleavageresulted resulted from northeast near near Slate S l a t e Bay. Bay. The T h e cleavage from bulk, bulk, inhomogeneous shorteningininaahorizontal horizontal direction, inhomogeneous shortening d i r e c t i o naccompanied , accompanied by by near—vertical near-vertical extension. extension. Competency contrastsbetween betweenrock rocktypes typesresulted resulted in in the Competency contrasts the development different structures. cleavageiis development o fofdifferent structures. The T h e cleavage s axial axial planar metasedimentary rnetasedimentary layers. layers. In In planar to to folds foldswithin withinthe the contrast, metavolcanic contrast, the thecleavage c l e a v a g e within withinthe the metavolcanicand andmassive massive metasedimentary unitsiis metasedimentary units s crosscut crosscut by by conjugate conjugate sets s e t s of o fshear shear fractures. shear fracture fracture planes fractures. The T h e shear planes maintain maintain aa constant constant orientation orientation of o f30° 3 0  from from the t h e penetrative, penetrative, flattening flattening fabric fabric and exhibit right—lateral and exhibit right-lateral slip s l i p along along the t h e clockwise c l o c k w i s e striking striking fracture left—lateral slip fracture planes planes and and left-lateral slipalong alongthe thecounterclockwise counterclockwise striking and fractures fractures striking fracture fractureplanes. planes. The T h e sshear h e a r zzones o n e s and fromed in a environment fromed in a ductile ductiletot obrittle—ductile brittle-ductile environmentsubsequent subsequent to to the the formation formation of o fthe t h ecleavage cleavage but butduring duringthe t h esame same deformational deformational event. Narrows,the theleft-lateral, left—lateral, northeast-striking northeast-striking event. Near Near PPost o s t Narrows, fracture several meters—wide fractureset setis iexpressed s expressedasas several meters-wideshear shearzones zones in in the the metavolcanic metavolcanic rocks. rocks. Pressure shadows garnets near s h a d o w s around around contact—metamorphic contact-metamorphic garnets near the Island Stock, the McKenzie McKenzie Island S t o c k , and and shear s h e a r zones z o n e s through through the the stock stock indicate that ititintruded thethedeformational indicate that intruded prior priortotoororearly earlyinin deformational history. history. Bedding iis s subparallel subparallel to tothe thecleavage c l e a v a g eexcept excepton onand and Bedding southeast Island where bedding sstrikes southeast of o f McKenzie McKenzie Island where bedding t r i k e s northeast northeast and and the the cleavage cleavage southeast. southeast. This T h i s geometry, g e o m e t r y , along along with with aa younging reversal a change c h a n g e in t r i k e ,suggests suggests the the younging reversal without without a in sstrike, presence deformational folds. folds. pre-"main-stage" deformational presence oof f early, e a r l y ,pre—"main—stage" All earlier earlierstructures structuresare a r ecrosscut crosscut by by a a second second brittleAll brittleductile ductile to to brittle brittleconjugate conjugate fracture fracture set. set. The T h e bisectrix of bisectrix of the acute acute angle angle between t r i k e s north north to to the betweenthe theconjugate conjugatepair pairsstrikes north—northeast. north-northeast. These These fractures occur throughout entire fractures occur throughout the the entire belt in strike. belt without without a a significant significantchange change in strike. 4 �U The The Deformational Deformational History History of of Archean Archean Greenstones Greenstones in in the Central Central Lake Lake of of the the Woods Woods Area Area Northwestern Northwestern Ontario Ontario Bruce Bruce A. A. Brown Brown Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey Survey 1815 1815 University University Avnue Avnue Madison, Madison, Wis, Wis. 53705 53705 Four Four distinct distinct deformational deformational events events have have been been identified identified in in the the Archean Archean greenstones of the the Central Central Lake Lake of of the the Woods area area of of northwestern northwestern Ontario. Ontario. These These events represent represent distinct distinct stages stages in in the the tectonic tectonic evolution evolution of of the the region region during during Archean Archean time. time. The The first first stage stage (D1) (Dl) produced produced upright, upright, isoclinal isoclinal folds folds (F1) (Fl) which which have shallowly shallowly plunging plunging to to nearly nearly horizontal horizontal axes, axes, and and aa penetrative penetrative axial axial planar foliation foliation (S1). (S,). F1 Fl folds folds are are expressed expressed as as large large scale scale planar anticlines anticlines and and synclines synclines traceable traceable across across much much of of the the adjacent adjacentregion. region. D1 Dl was was accompanied accompanied by by regional regional greenschist greenschist facies facies metamorphism metamorphism (M1). (MI), The (D,) produced produced steeply steeply plunging plunging folds folds and and aa complex complex The second second stage, stage, (D2) D, deformation deformation was was aa complex complex event. event. The D2 pattern of of ductile ductile shear shear zones. zones. The Style, Style, orientation, orientation, and and intensity intensity of of development development of of D2 D2 structures structures vary vary widely widely throughout throughout the the area. area. At aa given given locality, locality, it it is is common common to to find find more more than than one generation generation of of D2 D2 structures structures developed, developed, such such as as F2 F, folds folds suggesting that that stress stress overprinting aa D2 D, cataclastic cataclastic zone zone and and vice vice versa, versa, suggesting orientation and conditions conditions of of deformation deformation varied varied through through time time during during the the D event. event. Whereas Whereas D1 Dl structures structures were were uniformly uniformly developed developed across across the the D2 region, region, D2 D, structures structures are are most intensely intensely developed developed in in the the eastern eastern part part of of the the area, area, adjacent adjacent to to large large and and small small granitic granitic plutons. plutons. The The D3 D3 deformation deformation produced produced kink kink bands bands which which are are distributed distributed throughout throughout the the area, area, and and clearly clearly overprint overprint D1 Dl and and D2 D, structures structures and and fabrics. D4 D4 produced produced faults faults marked marked by by cataclastic cataclastic zones zones which which cross cross both both fabrics. the the greenstones greenstones and and the the adjacent adjacent granitoid granitoid rocks. rocks. D1 Dl and and M1 MI apparently apparently represent represent early early regional regional tectonism tectonism and and cannot be equated equated with with granitoid granitoid emplacement. emplacement. D2 D, and and localized localized contact contact cannot metamorphism metamorphism are are interpreted interpreted to to be be the the result result of of diapiric diapiric emplacement emplacement of of the the granitoid batholiths batholiths flanking flanking the the area area and and smaller smaller plutons plutons within within the the area. area. granitoid The complex complex geometry geometry and and sequence sequence of of D2 D, structures structures is is attributed attributed to to The continually continually changing changing deformational deformational conditions conditions during during the the rise rise and and expansion expansion of of these these intrusive intrusive bodies. bodies. The The origin origin of of D3 D, is is obscure, obscure, but but these these structures structures the result result of of regional regional stress stress imposed imposed during during the the late late stages stages of, of, or or may be the following pluton pluton emplacement. emplacement. D4 is is attributed attributed to to adjustment adjustment faulting faulting following which restored restored isostatic isostatic equilibrium equilibrium following following the the widespread widespread granite granite which emplacement during during the the D2 D, event. event. emplacement 5 �U I Copper Mineralization Topso foft ntue Lae Aje t h s F Flow l o ~To.1~ e P Portaje o r t a ~ eLas: A j e oof f Co->,?er M i n e r a l i z a t i o n in i n ti-ic Lava Series ~ y Paleomajnetic P a l e o i - n a j n e t i c Metuods MecnoJs Lava S e r i e s Determined D e t e r m i n e d oy "I Tim T i m D. D. Browninj, B r o w n i n g , Sue S u e BesKe—Diehi, B a s & ? - D i e h l , Jim J i m Diehl, D i e n l , and a n d Theodore T h e o d o r a J. J. Bornnorst Geol. Geol. B o r n n o r s t (Dept. ( D e p t . of of G e o l . and and G e o l . Enjrj., E n j r j . , Micnijan M i c n i j a n Tecunolojical Te~~nolojicdl University, M I 49931) 49931) U n i v e r s i t y , Houjhton, H o u g d t o n , MI Native N a t i v e ccooper o p p e r nmineralization i n e r a l i z a t i o n in i n tue t o e Portaje P o r t a g e Lake L a k e Lava L a v a Series S e r i e s occurs occurs wituin Ru—Sr w i t n i n amy-jdaloidal a i n y j i J a l o i d a l aand n d ~orecciated r e c c i a t e dttops o p s of o f lava l a v a flows. flows. RJ-Sr iatinj Jatinj mineralization oe aaround ± 1155 i-la r o u n J 11,051 , 0 5 1 +, Ma iindicates n d i c a t e s tthe h e aaje j e oof f m i n e r a l i z a t i o n tto o ae (Paces, .S.I. aaostract, o s t r a c t , 11984) 9 8 4 ) aas s compared c o m p a r e d to t o the t n e 1,110 1 , 1 1 0 Ma Ma aje a j e of of ( P a c e s , LL.S.I. The ineriors contain concaL-i majnatitc ,,-~djnecicz eextrusion. xtrusion. The relatively r e l a t i v a l ~uunaltered n a l t e r e d fflow l o w interiors whereas i s common common in i n the t n e mineralized m i n e r a l i z e d flow f l o w tops t o 2 s (Scofield, (Scofizld, w n e r e a s hematite h e m a t i t e is Pu.D. thesis, P'1.D. t h e s i s , M.T.U. M.T.U. 1976). 1 9 7 6 ) . The T h e remanent r e m a n e n t direction d i r e c t i o n associated a s s o c i a c e d witn irfici-i majnetite i s acquired a c q u i r e d during d u r i n g the t h e cooling c o o l i n g and a n d solidification s o l i d i f i c a t i o n of o f the tne tthe he m a g n e t i t e is magnetic e pparallel a r a l l e l tto o tthe h e eearth's arth's m a g n e t i c ffield i e l d ppresent r e s e n t at at llavas a v a s aand n d sshould n o u l d soe Dunn; tnat t n a t time. tine. D u r i n g mineralization m i n e r a l i z a t i o n of o f the t h e flow f l o w tops, t o p s , tne t n e orijinal orijinal Therefore, majuetite J i a g n e t i t e was altered a l t e r e d to t o secondary s e c o n d a r y hematite. hel-natite. T h e r e f o r e , the t n e primary .pri/nary remanence ~e r e m a n e n c e aacjuired c q u i r e d during d u r i n g the t h e solidification s o l i d i f i c a t i o n of o f tue t n e lavas l a v a s would w o o l J ue destroyed d e s t r o y e d and a n d replaced r e p l a c e d ooy y another a n o t h e r representing r e p r e s e n t i n g the t h e mineralization mineralization The ppurpose s t to o ddetermine e t e r i a i n e t the h e r relative e l a t i v z t itLe . a e of of eevent. vent. The u r p o s e oof f tthis n i s sstudy t u d y iis tue copper mineralization oy comparing the remanent directionu of t n a copper m i n e r a l i z a t i o n s y comparing t n e r e n a n e n t d i r a c t i o n s of mineralized m i n e r a l i z e d flow f l o w tops t o p s witn w i t n the t h e unaltered u n a l t e r e d flow f l o w interiors. interiors. Preliminary P r e l i m i n a r y tthermal h e r m a l ddemagnetization e m a g n e t i z a t i o n results r e s u l t s reveal r e v e a l two distinct Jistinct remanent r e m a n e n t directions, d i r e c t i o n s , one o n e associated a s s o c i a t e d with w i t n the c n e initial i n i t i a l cooling c o o l i n j of of rue m e represent llava a v a (magnetite ( m a g n e t i t ecomponent) c o m p o n e n t ),, and a n d another a n o t h e which r w h imay c h may r s 2 r tue e s ecopper n c t i i a co^,-)er mineralization m i n e r a l i z a tevent i o n e(hematite v e n t ( hcomponent). e m a t i t e c o m p o n e n t ) . Both Boch snow similar similar However, the declinations d e c l i n a t i o n s of o f around a r o u n d 295 295 degrees. degrees. However, t h e hematite n e m a t i t e component coia.ponant t o 10 10 cconsistently o n s i s t e n t l y eexnibits x n i o i t s ssteeper t e e p e r iinclinations n c l i n a t i o n s oon n the t n e oorder r d e r of o r 5 to degrees ÷33 ddegrees +40 ddegrees d e j r e e s (approximately ( a p L - i r o x i i n a t e l y +33 e g r e e s aand n d +40 e j r e e s inclination inclination directions Tuese respectively) r e s a e c t i v e l y ).. T nese d i r e c t i o n s aare r e consistent c o n s i s t e n t with v i t n the c n e directions predicted . p r e d i c t e d using u s i n g the t n e North N o r t h American A m e r i c a n polar p o l a r wander w a n d e r patn p a t i 1 for f o r Keweenawan Kaweznairfan t h e nematite n e m a t i t e cannot c a n n o t easily e a s i l y ue Je aage j e roccs. r o c i < s . The steeper s t e e p e r inclinations i n c l i n a t i o n s in i n the explained oy ttectonic prior e x p l a i n e d oy e c t o n i c ttilting i l t i n j towards t o w a r d s the t h e ppresent r e s e n t tilt t i l t direction 2 rior There mineralization. tto o m ineralization. T h e r e are a r e two t w o ppossiule o s s i o l e alternative a l t e r n a t i v e explanations e x p l a n a t i o n s of of (1) The The rrelatively tuese tiiese results. results. (1) e l a t i v e l y ssteep t e e p inclinations i n c l i n a t i o n s seen s e e n within w i t n i n the tiis Jmineralized i i n e r a l i z e d flow f l o w top t o p may may oc the t h e result r e s u l tof02polar p o l a rwander w a n d e wriich r w n i c n sug s u gjests jasts uetween time o e t w a e n tue tne some ppaleomagneticaily a 1 e o m a : j n e t i c a l l . y ssignificant i g n i f i c a n t pperiod e r i o d of o f time extrusion e x t r u s i o n of o f the t n e lavas l a v a s and a n d mineralization. mineralization. ( 2 ) The hematite hematite (2) crystallization, mineraliziation, may hhave i n e r a l i z i a t i o n , may a v e occurred o c c u r r e d over over a c r y s t a l l i z a t i o n , hhence e n c e tthe he m Ion; t i m e starting s t a r t i n g soon s o o n after a f t e r the t n e extrusion e x t r u s i o n of o f tue t n e lavas. lavas. l o n g pperiod e r i o d of o f time The hematite would tthen e aan n aaverage v e r a g e oof f tthe n e sshort—term hort-cera h e m a t i t e reinanence r e m a n e n c e would h e n soe changes magnetic c h a n g e s in i n the t h e eartu's eartn's m a g n e t i c ffield i e l d (secular ( s e c x l a r variation) v a r i a t i o n ) over o v e r tnat tnat On the time. t h e other o t n e r hand, n a n d , the t h e magnetite m a g n e t i t e remanent r m a n e n t direction direction -period > e r i o d of o f time. time on o n tue tile secular s e c u l a r variation v a r i a t i o ncurve c u r v euccause Jecause would represent represent a a point p o i n t in i n time At A t tthis n i s point point ttue n e lava l a v a cooled c o o l e d in i n aa relatively r e l a t i v e l y sshort n o r t period p e r i o d of o f time. tine. de do d o not n o t have h a v e adejuate a d e q u a t einformation i n f o r ~ i a t i oto nt ocuoose c n o o s euetween ~ecw/een iin n our o u r study, s t u d y , we tthese h e s e alternative a l t e r n a t i v e explanations. explanations. 6 �U CHEM I CAL CHARACTER LZAT ON AND IS OF CHEMICAL CHARACTER LZ AT IION AND PETROGENES PETROGEMES IS OFKEWEENAWAN KEWEEI'JAW AN DIABASE D I ABASE DYKES DYKES OF O F NORTHERN NORTHERN MICHISAN I 1 I. CH I GAN Gregory T. Durqess Department Uep<artm(ant oof f Geological Geological Sciences, Universy Sciiancaa, Michigan M i c h i g a n State State U n i varss b y East E a s t Lansing, L a n s i n g , Michigan M i c h i g a n 48824 48824 age Michigan, <ago diabase d i a b a s e dykes dykes of o-f Northern Northern M i c h i g a n , which which iintrude ntrude and Proterozoic metasediments, and early early Proterozoic metasadiments;, can be ha can subdivided into eastern and s u b d i vi. ded into e a s t e r n (Saraga (Baraga and Marquette M a r q u e t t o Cots.) Ca '5.) and western western (t3ogebic Thirty—four samples fourteen dykes i n the the (Goqebic Co.) swarms. Thirty-four samples +:rom Â¥fro "Fourteen dykes in east in e a s t and and twenty—two twenty-two samples samples rorn f r o m thirteen t h i r t e e n dykes dykes i n the the? west wore were Keweenawan Kewemawan Archean Archean basement basement analyzed analyzed, widest w i d e s t dykes dykes were were sampled sampled several s e v e r a l times t i m e s from f r o m the t h e chil:1 c h i l l marqin nargin are the a r e some subtle s u b t l e changes in i n the t h e major major oxides, o x i d e s , Â¥(Â¥r from the chill but c h i l l margin margin to t o the t h e interior, interior, b u t these t h e s e changes changes are a r e small s m a l l and a n d have have no no trends. and olivine consistent Quartz which consistent trends. Quarts d i v i n e thaieiites, tholeiites, which p l o t as as plot separate on TTi02 vsP205 P2O diagrams s e p a r a t e cclusters l u s t e r s on i02 vs diagrams similar s i m i l a r to t o those t h o s e noted n o t e d by by (1980) Wilband and are in In t h e east. ea'st. In Wilband and Wasuwanich Wasuwanich ( 1 9 8 0 ),, a r e recognized recognized i n the to dykes addition in found i n the the addition t o these, these, dykes a4 o f basaltic b a s a l t i c andesite a n d e s i t a are <are found western Although swarm. the western Although t h e TiO9—P,O TiOz-PzOs p l o t of of t h i s swarm swi'arm is i:::Â¥ plot this linear, it clustering east. linear, i t lacks l a c k s the t h e bimodal bimodal c l u s s t e r i n g noted n o t a d in i n the the east Characteristic C h a r a c t e r i s t i c major major oxide o x i d e abundance abundance ranges r a n g e s in i n the t h e bimodal bimodal clivine al i v i ne? i.(—2.:V., 13—iSV., MgO 7-El.!%, 7—8.X, Na20: 'rio2 tholeiites h o l e i i t e ' s are a r e A1203: 41203: 13-19X, MqO; l. A - 2 . 3 ' / . , 'TiQ2: and 0.5--1.5%, P2O: P205: 0.0—0.i6X, 0.05-0.167., and ffor o rthe t hquartz e q u tholeiites a r t z t h are oleiitare A1203: Al203; t2—1Y., Ti02: MqO: 3.7—7V., 3 . 7 - 7 % , Na2O Na2Q:2—2.8"/., 2-2.87., Ti02: 1.2—3.9X, 1.2-3.97., P205; 0,ti—O%. 0.15-a,,57.. 12-16%, MgO F'2O Sased the Based on geochemical geochemical grounds, grounds, t h e eastern e a s t e r n swarm 'swarm may have have been bean derived d e r i v e d from f r o m two two mantle m a n t l e sources s o u r c e s which which varied v a r i a d in i n depth d e p t h and and trace trace element content. The swarm may have content. The western western have formed formed by by +ractional fractional crystallization a Further c r y s t a l li s a t i o n a$ of a less l e s s varied v a r i e d source. source. Further interpr-otatiana interpretations based oS that t h a t data. data, baaed on trace t r a c e element data d a t a are a r e pending pending acquisition a c q u i s i t i o n o4 The The inwards. inwards. There There 7 �U Ii DECADE OF O FNORTH NORTHAMERICAN AMERICANGEOLOGY GEOLOGY(D-NAG) (D-NAG)GEOLOGICAL GEOLOGICAL r)ECADE A N D TECTONIC MAPS O F THE SOUTHEASTERN CANADIAN SHIELD; AND TECTONIC MAPS OF THE SOUTHEASTERN CANADIAN SHIELD; 588 Booth Booth St., St., Ottawa, O t t a w a ,Ontario, O n t a r i o ,K1\ K1A OEQ K.D. Card, C a r d , Geological Geological Survey Survey of of Canada, Canada, 588 K.D. OEL 1:5 million million sscale c a l e geological geological and e c t o n i c compilations compilations of of the t h eArchean Archean 1:5 and ttectonic Superior Province and surrounding P r o t e r o z o i c orogens r e v e a l s o m e lithological, Superior Province and surrounding Proterozoic orogens reveal some lithological, s t r u c t u r a l , m e t a m o r p h i c , and geochronologic p a t t e r n s t h a t bear on t h e tectonic tectonic structural, metamorphic, and geochronologic patterns that bear on the evolution of of this this part p a r t of of the t h eCanadian CanadianShield. Shield. evolution Superior Province Province has has northern northern(Pikwitonei, (Pikwitonei,Minto) Minto)and andsouthern southern(Minnesota (Minnesota Superior River Valley) high-grade gneiss regions c h a r a c t e r i z e d by t h e p r e s e n c e of granulites: granulites: River Valley) high-grade gneiss regions characterized by the presence of o n e of t h e s e ( M R V ) has rocks older t h a n 3.5 Ga. Between t h e high-grade regions one of these (MRV) has rocks older than 3.5 Ga. Between the high-grade regions a r e a l t e r n a t i n g , east-west trending belts o r subprovinces whose s u p r a c r u s tal are alternating, east-west trending belts or subprovinces whose supracrustal c o m p o n e n t s a r e dominated by metavolcanics o r by m e t a s e d i m e n t s . T h e components are dominated by metavolcanics or by metasediments. The metavolcanic-rich belts b e l t s(Abitibi, (Abitibi, Wabigoon, Wabigoon, etc.) a r e characterized c h a r a c t e r i z e dby bysinuous, sinuous, metavolcanic-rich etc.) are metamorphosed komatiitic-tholeiitic, calc-alkalic, and r a r e alkalic volcanic metamorphosed komatiitic-tholeiitic, caic-alkalic, and rare alkalic volcanic s e q u e n c e s with with volcanogenic volcanogenic cclastic l a s t i c and and chemical c h e m i c a l sediments. sediments. Intervening Intervening sequences m e t a s e d i m e n t a r y subprovinces (Quetico, Pontiac, etc.) consist mainly of of turbiditic turbiditic metasedimentary subprovinces (Quetico, Pontiac, etc.) consist mainly w a c k e and p e l i t e metamorphosed at g r a d e s ranging f r o m low greenschist upper wacke and pelite metamorphosed at grades ranging from low greenschist tot o upper amphibolite, and locally, g r a n u l i t e facies. Supracrustal s e q u e n c e s a r e c u t by amphibolite, and locally, granulite facies. Supracrustal sequences are cut by a b u n d a n t plutonic plutonic rocks, rocks, including including tonalitic t o n a l i t i c gneiss, gneiss, quartz q u a r t z diorite, diorite,and and abundant trondhjemite, younger granodiorite batholiths, and still younger g r a n i t e and and syenite syenite trondhjemite, younger granodiorite batholiths, and still younger granite plutons. Plutonic Plutonic rocks rocks that t h a tmay m a y represent r e p r e s e n tbasement b a s e m e n tto t othe t h esupracrustals s u p r a c r u s t a l s are are plutons. known in e w localities. Zircon dating dating demonstrates d e m o n s t r a t e sthat t h a tvolcanic, volcanic,plutonic, plutonic, known in only only aa ffew localities. Zircon deformational, and and metamorphic m e t a m o r p h i c episodes episodes of of relatively r e l a t i v e l y brief brief duration duration were were deformational, essentially synchronous synchronous over o v e r large l a r g e parts p a r t s of of Superior Superior Province, Province, but but there t h e r e are are essentially d e t e c t a b l e d i f f e r e n c e s in t h e a g e s of e v e n t s f r o m o n e a r e a t o a n o t h e r . In t h enorth north detectable differences in the ages of events from one area to another. In the (Sachigo, Uchi) major volcanism and plutonism o c c u r r e d b e t w e e n 3.0 and 2.3 G (Sachigo, Uchi) major volcanism and plutonism occurred between 3.0 and 2.8 Gaa 2.75 and and 2.7 2.7 Ga. Ga. InInthe t h esouth s o u t h(Abitibi, (Abitibi,Wawa, Wawa,Wabigoon) Wabigoon)major major and again again between b e t w e e n2.75 and volcanism and plutonism o c c u r r e d f r o m 2.75 t o 2.66 Ga. T h e c o n t e m p o r a n e i t y of of volcanism and plutonism occurred from 2.75 to 2.66 Ga. The contemporaneity short-lived m a g m a t i c episodes along t h e l e n g t h s of t h e s e belts s e e m s c o n s i s t e n short-lived magmatic episodes along the lengths of these belts seems consistentt with aa subduction-dominated subduction-dominated tectonic t e c t o n i cregime r e g i m efor f o rthe t h eSuperior SuperiorOrogen. Orogen. with L a t e tectonic t e c t o n i chistory historyofofSuperior SuperiorProvince Provincewas wasdominated d o m i n a t e dby by faulting. faulting. Late D e x t r a l t r a n s c u r r e n t f a u l t s trending EW a n d NW and sinistral f a u l t s trendingNE ME Dextral transcurrent faults trending EW and NW and sinistral faults trending f o r m subprovince boundaries in p a r t , as d o NE and EW trending thrusts. T h e most form subprovince boundaries in part, as do NE and EW trending thrusts. The most n o t a b l e product product of of faulting, faulting, the t h eKapuskasing Kapuskasing structural s t r u c t u r a lzone, zone, exposes exposes granulites granulites notable considered t o r e p r e s e n t lower c r u s t brought t o s u r f a c e along major YE trending considered to represent lower crust brought to surface along major NE trending f a u l t s that t h a t transect t r a n s e c tthe t h eeast-west east-westsubprovinces. subprovinces. faults Superior Province, Province, representing representing part p a r t of of aapreviously previously more m o r e extensive e x t e n s i v eArchean Archean Superior C r a t o n , i s bisected and surrounded by P r o t e r o z o i c orogens. The Early P r o terozoic Craton, is bisected and surrounded by Proterozoic orogens. The Early Proterozoic fold b e l t s (Ungava, Penokean) display lithological and t e c t o n i c zonation c o nsistent fold belts (Ungava, Penokean) display lithological and tectonic zonation consistent with t h e operation of p l a t e t e c t o n i c processes. with the operation of plate tectonic processes. 8 �— — a 0 2 r, C -V m oO 0 — o o — — — a 2 ; aV3 wan .o •a '— — — 0 on CV z C CVQ Ca—— .C - I0' 0 00> o30° - 31 < 0< r C) C) IC I Ir rT, Iz I C 0 0 N 0 m -I 0 -V 2 0 m C) m — — V t > C) I V �U THE TEXTURE TEXTURE AND AND MINERALOGY MINERALOGY OF OF THE THE LAKE LAKE ELLEN ELLEN KINBERLITE KIMBERLITE THE CRYSTAL FALLS, FALLS, MICHIGAN, MICHIGAN, USA USA CRYSTAL By Torrie Torrie Chartier Chartier By Michigan Technological Technological University University Michigan Houghton, MI MI Houghton, March, 1985 1985 March, H. Spence Spence The Lake Lake Ellen Ellen kimberlite kimberlite (figure (figure 1) 1) was was discovered discovered by by William William H. The and Klaus J. Schultz in 1966 and was described physically by Cannon and and Klaus J. Schultz in 1966 and was described physically by Cannon and Mudrey (1981). (1981). Hearn and the mineralogy mineralogy and and concluded concluded Mudrey Flearn and McGee McGee (1983) (1983) studied studied the that the mineral assemblages show equilibrium compositions of mantle that the mineral assemblages show equilibrium compositions of mantle 7 0 0 - 1 3 0 0 ~and and ~ at at depths depths derived inclusions inclusions were were formed formed at at temperatures temperatures of of 700—1300°C derived of 55-160 km, within the stability field of diamond. of 55—160 km, within the stability field of diamond. This isolated isolated kimberlite kimberlite occurence occurence has has raised raised considerable considerable interest interest This in view view of of the the widespread widespread discoveries discoveries of of diamonds diamonds in in the the glacial glacial overburden overburden in This has has prompted prompted kimberlite kimberlite exploration explorationin inthis thisregion. region. in Wisconsin. Wisconsin. This in Specimens from from six six represenative represenative sites sites on on the the Lake Lake Ellen Ellen kimberlite kimberlite diatreme diatreme Specimens were studied studied in in hand hand specimen specimenand and thin thin section texture and and were section for for diagnostic diagnostic texture mineralogy. The The characteristic characteristic features featureswere were then thenphotographed. photographed. The The purpose purpose mineralogy. was to to search search for for distinct distinct kimberlite kimberlitefacies faciesin inthe thebody. body. was The Lake Lake Ellen Ellen kimberlite kimberlite is is aa breccia breccia consisting consisting of of crustal crustal and and mantle mantle The derived xenoliths. Crustal xenoliths are most abundant and consist of derived xenoliths. Crustal xenoliths are most abundant and consist of Ordovician limestone limestone and and metamorphic metamorphic clasts clasts of of biotite biotite and andtalc talcschist. schist. Ordovician A smaller fraction of the xenoliths are of highly altered possible eclogitic A smaller fraction of the xenoliths are of highly altered possible eclogitic melilitic clasts now pseudomorphs of calcite. nodules and possible nodules and possible melilitic clasts now pseudomorphs of calcite. Around the the xenoliths, xenoliths, the the kimberlite kimberlite matrix matrix consists consists of of two two distinct distinct Around sizes of of olivine olivine grains: grains: small small (.5mm), (.5mm), rounded rounded to to subangular subangular grains grains in in sizes (.5-2mm), subhedral subhedralto toeuhedral euhedralxenocrysts. xenocrysts. The The the groundmass groundmass and and larger larger (.5—2mm), the fine grained grained olivine olivine is is usually usually completely completely replaced replaced by by calcite, calcite, serpentine serpentine fine and minor minor chlorite, chlorite, which which occurs occurs in inaa clastic clasticgroundmass of still still finer—grained finer-grained and groundnass of lithic clasts are coated alteration minerals. Some olivine xenocrysts and alteration minerals. Some olivine xenocrysts and lithic clasts are coated with a fine-grained magmatic kimberlite rind interpreted to be autolithic. with a fine—grained magmatic kimberlite rind interpreted to be autolithic. The only onlyniagmatic magmatic texture texture recognized recognized in in this this body body occur occur in in these these rinds. rinds. The The most most common common unaltered unaltered primary primary minerals minerals are are ruby—red ruby-red pyrope pyrope garnet, garnet, The ilmenite, and occasionally olivine, phlogopite and microscopic magnesium magnesium ilmenite, and occasionally olivine, phiogopite and microscopic apatite. None None of of the the specimens specimens showed showed pyroxene pyroxene minerals. minerals. Secondary Secondary apatite. minerals which commonly mask the primary mineralogy include serpentine (optically (optically minerals which commonly mask the primary mineralogy include serpentine identified as as antigorite), antigorite), calcite, calcite, phlogopite, phlogopite, chlorite, chlorite, and and microscopic microscopic identified millerite (NiS) (NiS) in incalcite. calcite. millerite The Lake Lake Ellen Ellen kimberlite kimberlite can can be be classified classified as as aa serpentine—carbonate serpentine-carbonate The kimberlite breccia according to the Skinner and Clement (1979) classification classification kimberlite breccia according to the Skinner and Clement (1979) scheme. Because of the lack of distinquishing features, the body is scheme. Because of the lack of distinquishing features, the body is interpreted to represent a single breccia phase. interpreted to represent a single breccia phase. 10 �U 48 N Lake Superior f Lake Ellen Kimberlite \ I A . . 46 N Lake bwisconsin 100 I______( Urn 88W 90 W Figure Figure 1. 1. Location Location map map for for the the Lake Lake Ellen Ellen kimberlite. kimberlice. -- REFERENCES REFERENCES Cannon, Cannon, W.F,, W.!?,, and and Mudrey, Mudrey, M.G., M.G., 1981. 1981. The The potential potential for for diamond—bearing diamond-bearing kimberlite kimberlite in in Northern Northern Michigan Michigan and and Wisconsin. Wisconsin. Geol. Geol. Survey Survey Circular Circular 862. 842. McGee, E.D,, and Hearn, Beam, B.C., McCee, E.D., B.C., Jr., Jr., 1983. 1983. Lake Lake Ellen Ellen kimberlite, kimberlite, Michigan, Michigan, USA, USA, USGS USGS Open—File Open-File Report Report 83—156. 83-156. Skinner, E.M.W. and and Clement, Clement, C.R., Skinner, E.M.W. C.R., 1979. 1979. Mineralogical Mineralogical classification classification of of southern southern African African kimberlites. kimberlites. Proceedings Proceedings of of the the 2nd 2nd International International Kimberlite 1:129-139. Kimberlite Conference, Conference, Vol. Vol. 1:129—139. 11 �U MINERALIZATION ASSOCIATED ALTERATION AND GOLD MINERALIZATION ASSOCIATED WITH WITH AA SHEETED SHEETED VEINLET VEINLET ALTERATION ZONE AT THE CAMPBELL RED LAKE MINE, MINE, BALMERTOWN ONTARIO ONTARIO Christie, B.J. Christie, B.J. and and Hodgson, Hodgson, C.J. C.J. Department Department of Geological Geological Sciences, Sciences, QueenTh Queen's University University Kingston, K7L 3N6, 3N6, Canada. Canada. Kingston, Ontario, Ontario, K7L The ore bodies at the Campbell Campbell Mine occur occur in in aa volcanic volcanic complex complex that that is composed of massive to pillowed basalt, basalt, with with lesser lesser andesite andesite and and rhyolite. These units are intruded rhyolite. intruded by by concordant concordant sills sills ranging ranging from from ultramafic to gabbroic ultramafic gabbroic in in composition. composition. The ultramafic lithologies lithologies and and flanking flanking zones of alteration are termed "altered "altered rock" rock" because because of of the the uncertain origin origin of some of these these petrologically petrologically distinctive distinctive rock rock bodies. bodies. In several several localities localities where there there is is aa well well developed developed cleavage, cleavage, the the unit is "altered rock" These veinlet zones". zones". These "altered rock" unit is characterized characterized by by "sheeted "sheeted veinlet zones are are broadly cleavage sub— zones broadly lenticular lenticularininshape shapeand andconsist consistofof cleavage subveinlets parallel stockwork, gold free, free, quartz—carbonate quartz-carbonate ±Â chlorite chlorite veinlets parallel to stockwork, cm wide. averaging about wide. They are typically spaced at 2.5 2.5 to 10 10 cm averaging about 1 cm basalt—ultramafic intervals. Most "sheeted veinlet zones" extend from basalt-ultramafic intervals. contacts into contacts into the the ultramafic ultramafic rock. rock. However some, some, such such as as the the 1958W 1958W "sheeted veinlet zone", are entirely within 'sheeted within the the "altered "altered rock" rock" unit. unit. These veinlet zones zones are thought to have formed formed by by extension extension normal normal to to the cleavage, cleavage, and by a process of incremental incremental opening opening and and simultaneous simultaneous outward growth of mineral fibres along the the vein—wallrock vein-wallrock contact. contact. Overprinting Overprinting the the veinlet zones zones are are small small pod pod or or pipe—like, pipe-like, subvertically orientated and often subvertically often spectacular spectacular high high grade grade gold gold bearing bearing siliceous replacement siliceous replacement zones. zones. These replacement replacement zones zones are are rich rich in in quartz, quartz, fuchsite, fuchsite, pyrite and native native gold, gold, ±k sphalerite sphalerite ±k arsenopyrite arsenopyrite ±k stibnite stibnite ±Â molybdenite. molybdenite. alteration—mineralization types occur in association A wide variety of alteration-mineralization with with the the "sheeted "sheeted veinlet veinlet zones". zones". The objective of this study study was to to petrologically and chemically characterize characterize these these and and investigate investigate their their relationship relationship to to the the gold. gold. The type of alteration alteration developed developed here, here, as as in in most gold gold deposits, deposits, depends depends on on the the nature nature of of the the host host rock. rock. In general general alteration in basalts is is much less carbon carbon dioxide dioxide rich rich than than that that in in the the "altered 'altered rock" due to the higher higher initial initial calcium, calcium, magnesium, magnesium, and and iron iron content of the the "altered "altered rock". rock". The The earliest type type of alteration alteration occurring occurring in in the the basalts basalts involves involves alkali depletion alkali depletion and and aluminium aluminium enrichment. enrichment. It is characterized characterized by by the the minerals garnet, garnet, biotite, andalusite, andalusite, chloritoid, chloritoid, sericite sericite and and magnesium magnesium chlorite, and appears appears to be spatially spatially related related to to the the basalt—"altered basalt-"altered chlorite, rock" contacts. contacts. The alteration alteration bears bears no no known known relationship relationship to to gold gold mineralization. mineralization. Synchronous with the early alteration alteration of basalts basalts is is aa chlorite—biotite—carbonate c h l o r i t e - b i o t i t e - c a r b o n a t e alteration alteration in in the the "altered "altered rock" rock" unit unit which which is characterized by the minerals chlorite, chlorite, biotite, biotite, coarse coarse grained grained carbonate, carbonate, and locally, locally, fine fine grained grained quartz—carbonate. quartz-carbonate. It can occur occur anywhere anywhere in in the "altered rock" rock" unit unit and and also also bears bears no no known known relationship relationship to gold mineralization. mineralization. Superimposed on these early alterations Superimposed alterations are are three three alteration alteration types types which which are are associated associated with with gold gold mineralization. mineralization. The The first first is is aa buff—brown buff-brown siliceous siliceous alteration alteration of of basalts basalts that that occurs occurs near the the basalt—"altered basalt-"altered rock" rock" contact. contact. It is characterized by the the characterized by 12 12 �U minerals minerals quartz, quartz, carbonate, carbonate, pyrite, pyrite, chlorite chlorite and and sericite, sericite, and and has has an an average average gold gold content content of of about about 1000 1000p.p.h. p.p.b. The unit. The other other two two alteration alteration types types occur occur in in the the "altered "altered rock" rockf1 unit. One One is is aa pistashio—green pistashio-green alteration alteration characterized characterized by by the the minerals minerals quartz, 100 cm cm wide wide quartz, carbonate, carbonate, sericite, sericite, and and pyrite. pyrite. It It occurs occurs as as 50 50 —- 100 envelopes on on 20 20 —- 30 30 cm cm wide, wide, banded auriferous auriferous quartz—carbonate quartz-carbonate veins. veins. envelopes The The The The average average gold gold content content of of this this alteration alteration type type about about is is 350 350 p.p.b. p.p.b. other that overprints overprints the sheeted veinlets, other is is aa silic:Lfication silicification that veinlets, and and consists consists of of quartz, quartz, minor carbonate, carbonate, minor minor biotite, biotite, minor minor chlorite, chlorite, pyrite pyrite and and locally locally gold, gold, arsenopyrite, arsenopyrite, sphalerite, sphalerite, stibnite stibnite and and molybdenite. molybdenite. The The alteration alteration occurs occurs in in small small pods pods or or pipe—like pipe-like bodies bodies and and is is probably probably fault fault controlled- In In some some areas areas gold gold grades grades in in silicified silicified "altered "altered or fracture fracture controlled. or rock" rock1'exceed exceed 15 15 ounces ounces per per ton. ton. Most Most of of the the alteration alteration and and mineralization mineralization associated associated with with "sheeted "sheeted veinlet veinlet zones" zones1'occurs occurs in in strongly strongly deformed deformed rocks rocks in in close close proximity proximity to to the the The contact, and fault or fracture zones basalt—"altered rock" contact. basalt-"altered rock" contact. The contact, and fault or fracture zones appear to have provided provided channelways channelways for for the the hydrothermal hydrothermal fluids fluids responsible responsible for for the the formation formation of of the the various various auriferous auriferous and and nonauriferous nonauriferous alteration—mineralization alteration-mineralization types types found found in in the the study study area. area. �PRELIMINARY METALLOCENIC SUBDIVISTON OF THE LAKE OF THE OODS METAVOLCANIC—METASEDIMENTARY BELT NORTHYiSTERN ONTARIO HilL CLARK CONSULTING GEOLOGIST 201 MELLICK AVENUE KENORA, ONTARIO Potential for gold and base metals within the Lake of the Woods east trending metavolcanic-metasedimentary belt Northwestern Ontario, has been shown by past exploration activity. This paper will summarize current planetary evolutionary hypothesis and past exploration work to develop a workable metallogenic subdivision of the area. The many 1970's saw the development of plate tectonic theory and geologists attemping to fit this type of dynamic system into Archean crustal mechanics. During the 19801s geologists are exploring the solar system by satellite. This activity may have impact of the same magnitude as plate tectonics on geologic an thinking. Planetary exploration has given us clues to the processes Heat flow rates, volcanic early Precambrian time. active in complexes on Mars and Jupiter's Red Spot as a heat transfer mechanism have been instrumental in rethinking Archean crustal evolution. Vertical tectonics and mantle plumes may hold the key to unlocking the mechanisms in operation during this period in georecently until time. Metavolcanic-metasedimentary belts logic have been viewed as simply a mixture of rock types: today we may view them as the end result of these processes. Examples will he brought forth for examination to help develop a metallogenic pattern. The Lake of the Woods metavolcanic—metasedimentary area can be viewed as east trending lithological belts, each with a distinct metailogeny. Internal structure may be one of the many features which provide evidence for this subdivision. The Lake of the Woods belt is represented by two base metal areas, two gold areas and apparently unmineralized area. Boundaries to these areas are an. marked by structural deformation zones or batholithic intrusions. Implications for mineral exploration in the Wabigoon Metavolcanic-metasedimentary belt and all other such belts in the Superior Province are highly significant. Planetary information and its effect on metallogenic subdivisions may give the exploration geologist a rational way of determining exploration targets in the Precambrian Shield of Canada. Following this rationale, the Lake of the Woods area may contain a gold camp, which at the turn of the century produced 55% of Ontario's gold, and a base metal area which have both been over looked until recently by explorationists. 14 �U geochronology andt etectonic g e o c h r o n o l o g y and c t o n i c hhistory i s t o r y ofofthe t h eShebandowan Shebandowan bbelt, elt, northwestern n o r t h w e s t e r n Ontario. Ontario. U-Pb F. F. Corfu, C o r f u , Ontario O n t a r i o Geological G e o l o g i c a l Survey, Survey, c/o c / oDepartment Department of o f Mineralogy Mineralogy and 100 QQueen's Park, Toronto, and Geology, Geology, Royal Royal Ontario O n t a r i o Museum, Museum, 100 u e e n ' s Park, Toronto, Ontario, O n t a r i o ,Canada CanadaM5S M5S2C6 2C6 G.M. 77 GGrenville G.M. SStott, t o t t , Ontario O n t a r i o Geological G e o l o g i c a l Survey, Survey, 77 r e n v i l l e Street, Street, Toronto, M5S 1B3 16'3 T o r o n t o , Ontario, O n t a r i oCanada , CanadaM5S The Shebandowan ThunderBay, Bay, eexhibits The Shebandowan b e belt, l t , wwest e s t oof f Thunder x h i b i t s evidence evidence for f o r two two major m a j o r periods p e r i o d s of o f deformation. d e f o r m a t i o n . The The ffirst i r s t period, p e r i o d ,which which caused have accompanied caused rregional e g i o n a l folding f o l d i n g across a c r o s sthe t h ebelt, b e lmay t , may have accompanied initial i n i t i adevelopment l development of of aa granitoid g r a n i t o i dcomplex complex to t o the t h e south. s o u t h . The The second produceda ar eregional second produced g i o n a l t rtranspression a n s p r e s s i o n aacross c r o s s t hthe e nnorthern o r t h e r n hhalf alf of w h i c h reflects r e f l e c t sa amajor m a j o rshortening s h o r t e n i n gacross a c r o s s the t h e Quetico Quetico be1 twhich o f the t h e belt metasedimentary metasedi'mentary s usubprovince b p r o v i n c e t otot hthe e nnorth o r t h and and ddextral e x t r a l shearing shearing along andssedimentary a l o n g the t h e Quetico Q u e t i c o Fault. F a u l t . Igneous Igneous and e d i m e n t a r y a activity, c t i v i t y , which which accompanied succeeded one accompanied o or r succeeded one o rort hthe e o other t h e r oof f these t h e s e deformation deformation periods, p e r i o d s , permit p e r m i t us us tto o set s e t absolute a b s o l u t e time t i m e constraints c o n s t r a i n t s on on this this sequence of events. sequence of events. The The sstratigraphy t r a t i g r a p h y ooff the t h e 9reenstone r e e n s t o n e bbelt e l t was was nnot o t ddated a t e d ddirectly, irectly, but Maf ofor but a a zircon z i r c o n age age of o f 2732 2732 +1U "'"1 Ma r aaqquartz-feldspar u a r t z - f e l d s p a r pporphyry o r p h y r y ssill ill -2 sets s e t s a minimum minimum d adate t e f o for r t hthe e eextrusion x t r u s i o n ofof iits t s host h o s t volcanic v o l c a n i c rocks rocks 8 north n o r t h ofofMiddle M i d d l Shebandowan e Shebandowan Lake. Lake. The d e f o r m a t i o n (D1) (Dl)preceded preceded or o r coincided c o i n c i d e d with wi h The ffirst i r s tperiod p e r i o dofofdeformation the t h e intrusion i n t r u s i o nofothe f t hShebandowan e Shebandowan Lake Lake pluton p l u t o n dated d a t e d at a t2696.1 2696.1 t 2 . i -2.3 Ma. Ma. This T h i s pluton p l u t o n appears appears to t o have have been been formed r i o r tto o the t h e extrusion extrusion formedp prior of anda1alkalic o f "Timiskaming—type" " T i m i skami n g - t y p e " c acaic-alkalic l c-a1 k a l ic and k a l ic pyroclastic p y r o c l as t i c rocks rocks and alluvial-fluvial and tthe h e ddeposition e p o s i t i o n oof f aassociated s s o c i a t e d a1 l u v i a l - f l u v i asedimentary l s e d i m e n t a r y rocks. rocks. This T h i s late l a t e supracrustal s u p r a c r u s t a l sequence sequence ooccurs c c u r s ssouth o u t h oof f tthe h e pluton p l u t o n in i n two two parallel groups that t h a tunconformably u n c o n f o r m a b l y ooverlie v e r 1 i e older 01 d e rKeewatin Keewati n volcanic vol cani c para1 l e l groups rocks. rocks. A A maximum maximum d adate t e f ofor r t hthe e ddeposition e p o s i t i o n oof f the t h e sediments sediments is is established Ma ffor or a a quartz-phyric quartz-phyric e s t a b l i s h e d by b y aa zircon z i r c o n age age of o f 2704.1 2704.1 + 1 - 8 Ma -1.6 trondhjemitic t r o n d h j e m i t i c clast c l as tini a n conglomerate, a conglomerate. A A trachytic t r a c h y t i c pyroclastic p y r o c l as t i c b r e c c i a from f r o m tthis h i s "Timiskaming-type" " T i m i s k a m i n g - t y p e " ssuite u i t e yyields i e l d s aa zircon z i r c o n age age of of breccia 2689.3 Ma, Ma, wwhich h i c h s slightly l i g h t l y but b u t significantly s i g n i f i c a n t l ypostdates p o s t d a t e s the the 2689.3 T!; crystallization c r y s t a l 1 iz a t i oof n othe f t Shebandowan h e Shebandowan Lake Lake pluton. p l uton. All A l l ofo the f t h eabove aboveunits u n i t shave havebeen been affected a f f e c t e d by b ythe t h esecond second period period of deformation d e f o r m a t i o n (D2). ( D ? ) . The The Burchell B u r c h e l l Lake Lake pluton, p l u t o n ,ananundeformed undeformed circular c i r c u l a r stock s t o c k of o fgranitic g r a n i t i to c t trondhjemitic o t r o n d h j e m i t i composition, c c o m p o s i t i o n ,postdates postdates the and appears appearst otobe beone oneofofaa sset t h e D2-deformation D2-deformation eevent, v e n t , and poste t of o f posttectonic t e c t o n i c plutons p l u t o n s wwithin, i t h i n , and and ssouth o u t h ofof tthis h i s belt. be1 t . Preliminary Preliminary zircon z i r c o n and and ttitanite i t a n i t e data d a t a from f r o m this t h i s intrusion i n t r u s i o nindicate i n d i c a t ean anage age of of 2684 2684 +Ol oMa. Ma. Because Because o f oft hthe e r erelatively l a t i v e l y large l a r g e error e r r o r the t h e age age is is -7 indistinguishable i n d i s t i n g u i s h a b l e from f r o m that t h a tofo the f t hdeformed e deformed"Timiskaming-type' "Timiskami n g - t y p e " volcanic v o l c a n i c rocks. r o c k s . Considering C o n s i d e r i n g ttheir h e i r errors, e r r o r s , the t h etwo twoages ages allow a1 l o w f o r aamaximum maximum t time i m e span 10 Ma o r "Timiskaming-type' " T i m i s k a m i n g - t y p e " volcanism, volcanism, for spanooff 10 Maf for D2-deformation andi nintrusion of the D2-deformation and t r u s i o n of t h e Burchell B u r c h e l l Lake Lake pluton. pluton. 15 �U This T h i s data d a t a indicate i n d i c a t e aa relatively r e l a t i v e l rapid y r a p i succession d s u c c e s s i o n of o fevents, events, between 2700and and2680 2680MaMa ago,i nincluding between aabout b o u t 2700 ago, c l u d i n g i nintrusion t r u s i o n of o f major major plutons, p l u t o n s , erosion, e r o s i o n ,sedimentation s e d i m e n t a t i o nand andvolcanism v o l c a n i s mand andaamajor m a j o r(D2) (DA d e f o r m a t i o n event. e v e n t . The The D2-deformation D 2 - d e f o r m a t i o n event e v e n t corresponds c o r r e s p o n d s to to deformation widely w i d e l y recognized r e c o g n i z e d late 1a t eArchean Archean crustal c r u s t a lshortening s h o r t e n i n gmanifested mani f e s t e d as as zones zones of o f transpression t r a n s p r e s s i o nnear n e a rsubprovince s u b p r o v i n c e boundaries, b o u n d a r i e s , major major s h e a r zones zones and t e ffaults a u l t s that t h a tborder b o r d e rand and transect t r a n s e c t the the shear andl alate subprovinces, andsshallowly-plunging s u b p r o v i n c e s , and h a l l o w l y - p l u n g i n g u upright p r i g h t f folds o l d s tthat h a t refold refold e a r l ie recumbent r recumbentstructures s t r u c t u r e sthroughout t h r o u g h o uthe t t hmetasedimentary e metasedi m e n t a r y earlier mineralization Go1 d m i n e r a l i z a t i o n i is s related r e 1 a t e d locally l o c a l l y to t othe the s u b p r o v i nces . Gold subprovinces. D2-deformation andr eregionally D 2 - d e f o r m a t i o n and g i o n a l l y tto o the t h e crustal c r u s t a l shortening s h o r t e n i n gevent; event; its i t sage ageisi sthus t h u sclosely c l o s e lbracketed y b r a c k e t e by d b the y t h presented e p r e s e n t e dU-Pb U-Pb data. data. Survey. Published with Pub1 i shed w i t h permission p e r m i s s i o n ooff the t h e Director, D i r e c t o r ,Ontario O n t a r i oGeological Geol o g i c a lSurvey. 16 �U andt etectonic U-Pb geochronology geochronology and c t o n i c hhistory i s t o r y of o f the t h e Winnipeg Winnipeg River River granitoid terrain, northwestern Ontario. g r a n i t o i d t e r r a i n , northwestern O n t a r i o . FF.. Corfu, Corfu, Ontario O n t a r i o Geological Geological Survey, Survey, do c/oDepartment Department of of Mineralogy Mineralogy and Geology, Royal 100 QQueen's and Geology, Royal Ontario O n t a r i o Museum, Museum, 100 u e e n ' s PPark, a r k , TToronto, oronto, Ontario, O n t a r i o ,Canada CanadaM5S M5S 2C6 2C6 Beakhouse,OOntario GeologicalSurvey, Survey,7777Grenvi Grenville GG.P. . P . Beakhouse, n t a r i o Geological l i e SStreet, treet, Toronto, Ontario, O n t a r i oCanada , CanadaM5S M5S 1B3 1B3 G.M. Grenville G.M. SStott, t o t t , Ontario O n t a r i o Geological Geological Survey, Survey, 77 77 Grenvil l e Street, Street, Toronto, T o r o n t o , Ontario, O n t a r i oCanada , CanadaMSS M5S 1B3 1B3 Grenville RR.H. . H . SSutcliffe, u t c l i f f e ,Ontario O n t a r i oGeological Geological Survey, Survey, 77 77 Grenvi 1 l e Street, Street, Toronto, Ontario, O n t a r i oCanada , CanadaM5S M5S 1B3 1B3 geochronological i t a n i t e and and PPreliminary r e l i m i n a r y U—Pb U-Pb geochronologi c a l d a tdata a f o rfor z i zircon, rcon, t titanite monazite fromt the WinnipegRiver Riverg rgranitoid monazi t e from h e Winnipeg a n i t o i d tterrain e r r a i n indicate i n d i c a t ea acomplex complex and history. and pprotracted r o t r a c t e d ggeological e o l o g i c a l hi story. Gneissic and ffoliated G n e i s s i c and o l i a t e d tonalites t o n a l i t e sfrom fromthe t h Cedar e CedarLake, Lake, Daniels DanielsLake Lake and Kenora Kenoraa rarea and e a a r eare i n tintrusive r u s i v e i ninto, t o , oor r ccontain o n t a i n iinclusions n c l u s i o n s oof f highly highly The ttonalite onal i t e fragmented, volumetrically fragmented, vol umetri cal l yminor minorsupracrustal s u p r a c r u s t a lsequences. sequences. The in Lake aarea Ma;t this i n the t h e Cedar Cedar Lake r e a yyields i e l d s aa zzircon i r c o n age age ooff about about 3170 3170 Ma; h i s is is the t h enorthern n o r t h e r n Superior Superior t h e ooldest l d e s t reliable r e l i a b l e zircon z i r c o n age age yyet e t identified i d e n t i f i e d ini nthe old, tonalites A tonalite tonal i t efrom fromKenora Kenora is i sabout about 2880 2880 Ma Ma 01 d , whereas whereas tonal i tes Province. A iinn the t h e Daniels Daniels Lake Lake area a r e a are a r eabout about2840 2840and and 2710 2710 Ma Ma oold. l d . These new new ddata, a t a , together t o g e t h e r with w i t h previously p r e v i o u s l ypublished p u b l i s h e dages agesofof3000-3040 3000-3040 Ma Ma at Ma Kenorassuggest a t Lac Lac Seul Seul and and 2830 2830 M a aat t Kenora u g g e s t t that h a t tonalite t o n a l i t eplutoruism piutonism took during aatt least took place p l a c e during l e a s t 55 periods. periods. Regional tectonics Regional t e c t o n i c s and and metamorphism metamorphism aare r e cconstrained o n s t r a i n e d by by ages ages on on llate a t e granitoid g r a n i t o i dintrusives i n t r u s i v eand s andmetamorphic metamorphic rocks: rocks: 1) andr eregional nappe-1 i ke s tstructures r u c t u r e s and g i o n a l uupright p r i g h t ffolding o l ding 1 ) Local Local nappe—like observed Kenorap post-date observed e east a s t oof f Kenora o s t - d a t e t hthe e f foliated o l i a t e d Daniels Daniels Lake Lake ttonalite onali t e at Ma,bbut a t 2710 2710 Ma, u t iis s older o l d e r than than the t h e crosscutting c r o s s c u t t i n g Lount Lount Lake Lake batholith batholith This h i s period p e r i o d of of deformation deformation to t o the t h e north n o r t h previously p r e v i o u s l ydated d a t e data 2702 t 2702Ma. Ma. T metamorphism iiss essentially e s s e n t i a l l ycoeval coevalwith withregional regional metamorphism in i n Kenora Kenora dated d a t e d at at about 2710MMa ana amphibolite andwith witht hthe e iintrusian n t r u s i o n of of about 2710 a bybyz izircons r c o n s i ninan m p h i b o l i t e and marginal ggranodiorite, i n t r u s i o nemplaced empl aced into i n t o the the ranodiori t e , a a sheet-like sheet-1 i ke intrusion tthe h e marginal subprovince subprovince iinterface n t e r f a c eata Kenora t Kenoraabout about2705 2705Ma Ma ago. ago. 2) follows regional 2 ) Late Late doming doming follows r e g i o n a l deformation. deformation. In the t h e Kenora Kenora area area the age of doming is constrained by titanite ages which t h e age of doming i s c o n s t r a i n e d by t i t a n i t e ages which iindicate ndicate 2700-2690 Ma Ma ago. ago. Doming Doming i in n the the ccooling o o l i n g tot obelow belowabout about500°C 500 C ata t2700-2690 Cedar Lakea rarea was Cedar Lake e a was e i either t h e r r erelated l a t e d tto o or o r post-dated p o s t - d a t e d aa late l a t ephase phase of o f aa protracted p r o t r a c t e d granulite g r a n u l i t efacies f a c i e metamorphic s metamorphic history hi s t o r yrecorded recorded by by metamorphicz izircons mafic ggranulite metamorphic r c o n s i nin aa mafic r a n u l i t e and and by by monazite monazite in i n aa Titanite i t a n i te ages ages of of ttonalite o n a l i t e and and aa granodiorite g r a n o d i o r i t eata about t about2680 2680Ma. Ma. T 2600-2590MMa CedarLake Lakea rarea showt hthat 2600-2590 a i nint hthe e Cedar e a show a t t this h i s crustal c r u s t a lsegment segment remainedaat muchl olonger than iin n g e r than n the t h e Kenora Kenora region. region. remained t eelevated l e v a t e d temperatures temperatures much Publishedwwith permissionofof tthe i t h permission h e Director, D i r e c t o r , Ontario O n t a r i oGeological Geological Survey. Survey. Published 17 17 �U STRATIGRAPHIC AND STRUCTURAL EVOLUTION STRATIGRAPHIC AND STRUCTURAL EVOLUTIOM OF THE THE CROSS CROSSLAKE LAKESUPRACRUSTAL SUPRACRUSTAL BELT BELT IN NORTHWESTERN SUPERIOR PROVINCE, IN PflDVINCE, MANITOBA MANITOBA Timothy Corkery, Corkery, Manitoba Department Department of Energy and M. and Mines, Mines, Geological Geological M. Tinothy Services Branch, Branch, Winnipeg, Winnipeg, Manitoba. Manitoba. The Archean supracrustal Lake—Pipestone Lake area supracrustal belt belt in the Cross Lake-Pipestone area contains contains evidence evidence of of two two distinct distinct episodes: episodes: an early period dominated by mafic volvolcanism, canism, followed by plutonic intrusion; intrusion; aa second second period period of of uplift, uplift, erosion erosion and deposition of subaerial—fluvial subaerial-fluvial dominated dominated sediments. sediments. These observations observations indicate that the development of the Cross Lake supracrustal supracrustal belt belt is is similar similar in character to other greenstone greenstone belts in the northern Superior Superior Province Province where where the dominantly volcanic succession succession (Hayes (Hayes River River Group) Group) is is unconformably unconformably over— overby a succession succession of dominantly sedimentary rocks (Oxford lain by (Oxford Lake Lake Group, Group, Island Lake Lake Group). Group). The early supracrustal supracrustal rocks rocks comprise comprise aa sequence sequence dominated dominated by by pillowed pillowed and and massive metabasalt flows flows with subordinate subordinate amoeboid amoeboid pillow pillow breccia. breccia. Near the the basalt sequence plagioclase plagioclase phyric massive and pillowed top of the basalt pillowed basalts basalts metasediments and occur. occur. Mafic volcanic metasediments and minor minor greywacke greywacke metasediments metasediments occur occur within the within the sequence. sequence. The early supracrustal supracrustal rocks rocks are are extensively extensively intruded intruded ultramafic sills sills and and dykes. dykes. On Pipestone Pipestone Lake, Lake, aa large large layered layered by mafic to to ultramafic anorthosite—gabbro anorthosite-gabbro complex complex contains contains titanium—vanadium titanium-vanadium enriched enriched magnetite— magnetiteilimanite layers. illmanite layers. These rocks rocks were intruded intruded by tonalite tonalite (U/Pb (U/Pb age age 2712 2712 Ma). Ma). overlying the early supracrustal Unconformably overlying supracrustal rocks rocks and and tonalite tonalite is is aa generally fining upward sequence sequence of metasediments. metasediments. Thickly Thickly bedded alluvial alluvial fan conglomerates conglomerates and high high energy energy fluvial fluvial sandstones sandstones up up to to 1500 1500 mm thick thick form form the base of the the sequence. sequence. Up to 250 250 m of thickly thickly bedded bedded sandstone sandstone and and thinly thinly bedded siltstone—sandstone siltstone-sandstone grade grade upward upward into into aa thin thin siltstone—shale siltstone-shale at at the the top of the metasedimentary sequence. sequence. Deformation Deformation and and metamorphism metamorphism occurred occurred concomitant concomitant with with development development of of major batholithic terrains terrains north north and south south of of the the supracrustal supracrustal belt. belt. Linear Linear to arcuate tectonic zones, zones, from 50 m to 100 100 m thick, thick, form form boundaries boundaries which which divide divide the supracrustal supracrustal belt into into aa series series of of blocks. blocks. Within these these tectonic tectonic Typically one zones zones both ductile ductile and brittle brittle features features are are abundant. abundant. Typically one to to meter thick shear zones occur at irregular seven meter irregular spacing, spacing, becoming becoming more more abundant abundant as as the the boundary boundary is is approached. approached. The rock rock between between the the shears shears ranges ranges from slightly deformed to completely transposed into into the the shear shear direction direction in in metathe boundary zone. zone. In these areas early mafic volcanic rocks rocks and and late late meta— sedimentary rocks rocks may be be tectonically tectonically interlayered. interlayered. Within Within the the blocks blocks original stratigraphic stratigraphic relationships relationships are are retained. retained. However, However, the the degree degree of of deformation and the grade of metamorphism varies from deformation from block block to to block. block. 18 �U - . GEOCHEMICAL CONSTRAINTSO NONTHE THEREE REEDDISTRIBUTION GEOCHEMICAL CONSTRAINTS I S T R I B U T I O N IN [N THE THE NEGAUNEE AT THE NEGAUNEE IRON I RON FORMATION FORM A T I ON AT THE EMPIRE EMPI RE MINE, M I ME, PALMER, PALMER, MICHIGAN M I CH I (?AN Susan Susan S. E. Crissman Cr- is'smari Department D e p a r t m e n t of raf Geological Geol a q i c a l Sciences, S c i e n c e s , Michigan M i c h i qan Stat State - 'm . - University U r i i vor?!:i fcy East Lansing, I 48824 East L a n s i n g , PI:[ 49824 I The The approximately approximately 2. 1 Ga 2.1 Ga old old Neqaunee Meqauriee Iron I r o n Formation F o r m a t i o n at at the the Empire Michigan Empire-? Mine M i n e near n e a r Palmer, Palmer, M i c h i g a n provides p r - a v i d o s an .an ex cel:lent, cili2eil: •cziient, albeit complex, of rock types to investiqate the elemental campl e x 7 spectrum spectrum of rock types to i n v e s t i g a t e the elemental distribution distribution and t y p i c a l Superior'-t:yp Superior--fcypo and (nineraloqical m i n e r a l ( ~ g i c a 1 variations variations o-f aa typical of This iron 1i m b of t t 7 a i r o n formation, 'formation. Thiia orebody o r e b o d y is i s located l o c a t e d on on the the s o u t h a a s t 1i(Th Marquette sync and sm is (eh Mi'arquotte s y n c11 i nnor o r iium u r n,, and metamarphi motamorpliiwn i5 minimal minimal c h , Ior . o ri ito ko facies).  ¥ f a d e s ) It I t precipitated p r e c i p i t a t e d dominantly dominantly a s a chert-siderite, c h e r t - s i d e r i t e , and and ehowo shows as extensive The alterations e x t e n s i v e replacement. replacement. The major m a j o r diagenetic diaqenetic a1 tor at ion:^ are r-;\re chert c h e r t to ta magnetite, and With magnetite, and siderite s i d e r i t e to t o magnetite m a g n e t i t e and and ankerite anherite, W it h postmetamorphic oxidation, magnetite post-metamorphic oxidation, magnetite2 was was replaced r e p l a c e d by b y martite, m a r t i t e , and and the t h e carbonates c a r b o n a t e s altered a l t e r e d to t o hematite h e m a t i t e or o r goethite. qoethite. The objective this investigation is the th a The a b j a c t i v e of of this investigation i s to t o evaluate ovalui-aka crystallochemical/environmental affecting controls the PEE crystallochemical/anvironmental controls a f f e c t i nq t h fc-a distribution in these pr-ecipitates.. distribution i n t h e s e low l o w temperature t e m p e r a t u r e chemical chemical p r - e c i p i kat(:-;s. Forty—five drill core Forty-five drill c o r e samples samples ffrom r o m the the* Empire E m p i r e Mine M i n e are are; b:i.nc:; beinq examined. They represent examined. r e p r a < 3 ~ ~five f ri ~v te facies f a c i e s distinguished d i a t i n q u i shed according i ~ ~ ~ ~ r to -to d the it h~e i q major mineral assemblaqe: chert, carbonates, ma j a r mineral chert, c a r b o n a t e ' s , maqnetite m a q n o t i te rich r ic h ore, ore, Siamo and interbeds. It is Siamo slate, slate, and clastic clastic interbeds, It i s anticipated i ~ r i t i c i p a t e d that that correlations reflect, c o r r e l a t i o n s of o? the t h e trace t r a c e elements e l e m e n t s with w i t h mineralogy f n i n e r a l a q y will w i l l r e " f 1 a c t the the influence i n f l u e n c e of a? partitioning p a r t i t i o n i n g coefficients c o e f f i c i e n t s on an the t h e REE REE distribution. distritautian, Seyeral significant correlations between trace! Several significant c o r r e l a t i o n s exist exist b e t w e e n the t h e trace elements, major The is elements, m a j o r oxides, o x i d e s , and and mineralogy. mineralogy. The LREE/HREE LREE/HREE ratio ratio i s highly h i g h l y antipathetic a n t i p a t h e t i c to t o siderite, s i d e r i t e , MqO, MqO, MnO MnO and and 002; C02; less l a s s so 'so with w i t h CaD. Can. The The correlation c o r r e l a t i o n with w i t h siderite s i d e r i t e agrees a g r e e s with w i t h what is i s expected w : p s c t e d based b a s e d on on crystallographic 1980). c r y s t a l l o g r a p h i c controls c o n t r o l s (Morgan (Morgan & Wandless, Wandless, 1980). T h e r e is is aa high high There positive REE with w i t h Ti02 T i 0 2 and and A1203. A1203, ' T h i s c:an can be p o s i t i v e correlation c o r r e l a t i o n of o-f the t h e REE This be interpreted i n t e r p r e t e d to t o mean that t h a t the t h e lanthanides l a n t h a n i d e s were were adsorbed a d s o r b e d onto o n t o detrital dstrital minerals, which m i n e r a l s , such such as as chlorite, chlorite, w h i c h were w e r e deposited d e p o s i t e d with w i t h the the chemical chemical precipitates. Europium Fe3+ ~ ~ 3 . 4and and . precipitates. E u r o p i u m correlates c o r r e l a t e s negatively negatively with with positively p o s i t i v e l y with w i t h Fe2+ Fez+ (e.g., (a.g., siderite). siderite). T h i s is i 5 consistant c a r i s i - i i t a n t with with bl-ii,:.? This h:? reducing proposed r e d u c i n g conditions conditions p r o p o s e d for ? o r the t h e precipitation p r e c i p i t a t i o n of of primary primary siderite, the s i d e r i t e , and and argues a r g u e s for for t h e presence p r e s e n c e of o f Eu2+ Eu2+ in i n the t h o basin b a s i n water. water. It It was w a s expected e x p e c t e d that t h a t the t h e diaqenetically d i a q e n e t i c a l l y enriched e n r i c h e d maqnetite m a q n e t i t e would w o u l d have h a v e aa negative n e g a t i v e correlation c o r r e l a t i o n with w i t h the t h e LREE/HREE LREE/HREE ratio r a t i o because b e c a u s e the t h e stability stability of complexes o f HREE'-carhonate HREE-carbonate compl e x e s exceeds e x c e e d s that t h a t of oS LREE—carhonate LREE-carbonate complexes compl e x e ~ s in iron'-transportinq (Graf, in i r - a n - t r a n s p o r t i n g ssolutions olutions (Graf, 1'984). 'The apparent a p p a r e n t LPEE LREE 1984). The enrichment in interpreted enrichment i n magnetite m a g n e t i t e is i s i n t e r p r e t e d to to t h a t the t h e HREE, 1-IREE, iiff mean that m o b i l i z e d during d u r i n g diagenesis, d i a g e n e s i a , were w e n s not n o t deposited d e p o s i t e d with w i t h the t h o iron. iron. mobilized Morgan, Morgan, J.W. J.W. distribution distribution soutast and and in i n 04: t Wandless, G.A., 19QO, R a r e earth earth el ctnent Wandless, G.A., 1990, Rare cioment some h y d r o t h e r m a l minerals: m i n e r a l '5: ovidorico far some hydrothermal evidence fr v o l " 4 4 , p.973-9S0. p . 9'73--980. c r y s t a l l o g r a p h i c control. c o n t r o l . Geochim. Geochim. Cosmochim., Cosmochim. , vol.44, crystallographic LL. Jr., 1984, valley—type J.L. Jr., 1*?Q4, Effects E f ? o c t s of of Mississippi Mississippi v a l Ilay-type mineral m i n o r ail izati ~ a t ion o non on REE REE patterns p a t t e r n s of a+ carbonate carbonate;! rocks r o c k s and and minerals minerals, Viburnum southeast Missouri. Viburnum trend, trend, southeast Missouri. Jour. t3oa.L s y vai.92, Jour. Geol. vol.92, p 3(:)7-324. p. 307-324. (3ra+ Bra+ . 19 �U Evolution E v o l u t i o n of o f an anArchean Archean igneous igneous complex complex ffrom r o m hhigh i g h precision p r e c i s i o n U-Pb U-Pb geochronology: N. W . Ontario. Ontario. geochronol ogy: tthe h e Kakagi Kakagi Lake Lake aarea, r e a , N.W. D.W.DDavis, Departmento of Geology,UUniversity D.W. a v i s , Department f Geology, n i v e r s i t y ooff Toronto, Toronto, Toronto, T o r o n t o , Ontario, O n t a r i o ,M5S M5S1A1 1A1 G.R. Departmentooff Earth G.R. Edwards, Edwards, Department E a r t h and and Atmospheric Atmospheric Science, Science, York York University, U n i v e r s i t y , 4700 4700 Keele K e e l e Street, S t r e e t ,Downsview, Downsview, Ontario, O n t a r i o ,M3J M3J 1P3 1P3 High on 10 Archean H i g h precision p r e c i s i o n U-Pb U-Pb ages ages determined d e t e r m i n e d on 10 rocks r o c k s from from the t h e Archean complex surrounding the Kakagi Lake area give a detailed c o m ~ l e xs u r r o u n d i n g t h e Kakagi Lake a r e a g i v e a d e t a i l e d ppicture i c t u r e of of igneous igneous eevolution, v o l u t i o n , ddefining e f i n i n g aa time t i m e span span oof f aatt least l e a s t 32 32 Ma Ma ffor or Ma The eearliest a r l i e s t age age is i s 2731.7 2731.7 ÷ 4.0 Ma developmentooff the development t h e complex. complex. The - 2.9 ffrom r o m aanalysis n a l y s i s ooff zircon z i r c o n and and baddeleyite b a d d e l e y i t e iin n aa gabbro gabbro iintruding n t r u d i n g the the This Katimiagamak Katimiagamak Group. Group. T h i s is i s the t h e oldest o l d e s tknown known unit u n i t in i nthe t h ecomplex complex and rrepresents ane pepisode and e p r e s e n t s an i s o d e o fofh ihigh g h i riron o n t tholeiitic h o l e i i t i cvolcanism. v o l c a n i s m . AA sslightly l i g h t l yyounger y o u n g e r age age of o f 2727.7 2727.7 ±Â 1.1 1.1Ma Ma from from a a dacite d a c i t e in i nthe t h eDash Dash Lake aarea Lake r e a pprobably r o b a b l y r represents e p r e s e n t s t hthe e bbeginning e g i n n i n g oof f ffelsic e l s i cvolcanism volcanism age ooff 2723.2 Maon onaa ttonalite An age 2723.2 ± 11.8 . 8 Ma o n a l i t e gneiss gneiss in i n the t h ecomplex. complex. An from the interior of the Sabaskong Batholith is indistinguishable f r o m t h e i n t e r i o r o f t h e Sabaskong B a t h o l i t h i s i n d i s t i n g u i s h a b l e Ma) from phaseo of f r o m tthe h e age age ooff a a massive massive bborder o r d e r phase f t the h e bbatholith a t h 0 1 it h (2724.4 (2724.4 Ma) and showsnonoe vevidence an oolder and shows i d e n c e o fofi ninheritance h e r i t a n c e ffrom r o m an l d e r sialic s i a l i component: c component. A phaseoof Kakagis sill A pegmatite p e g m a t i t e phase f tthe h e lowermost lowermost Kakagi i l l was was dated d a t e d at at Ma, wwhich maybebeo only 2724.8 2 - 5 Ma, h i c h may n l y sslightly l i g h t l y younger y o u n g e r than t h a n the t h e age age - 2.3 ooff intermediate i n t e r m e d i a t e volcanism v o l c a n i s m in i nthe t h eKakagi KakagiLake LakeGroup. Group. This T h i s iis s similar similar to t o the t h e age age of o fthe t h eSabaskong Sabaskong Batholith B a t h o l i t hand anddemonstrates demonstrates simultaneous simultaneous mafic m a f i c and and ffelsic e l s i c plutonism p l u t o n i s m as as well w e l l as as approximate a p p r o x i m a t e ssimultaneity i m u l t a n e i t y of of tonalitic t o n a l it i cplutonism p l u t o n i smini the n t hSabaskong e Sabaskong Batholith Bath01 it h and and intermediate intermediate vvolcanism o l c a n i s m in i n the t h eKakagi Kakagi Lake Lake Group. Group. Ma f from An age age ooff 2711.1 r o m aa ddacite a c i t e occurring o c c u r r i n g above above the the An 2711.1 ÷ 1 - 3 Ma ' 1-8 ' '- 1.L Kakagi Lake Group Groupshows showsa a13 13Ma Mat i time gapi in developmentofof the Kakagi Lake m e gap n development the ageoof oneoof volcanic phases The age f one f tthe h e ooldest l d e s t tonalitic t o n a l i t i cphases v o l c a n i c ppile. i l e . The Ma, Ma, wwhile h i l e tthe h e llatest atest of the of t h e Aulneau Aulneau BBatholith a t h o l i t h is i s2716.8 2716.8 g r a n o d i o r i t e phase phase is i s dated d a t e d at a t2709.6 2709.6 +t 3.9 3.3 Ma. Ma. T h i s shows shows granodiorite This 1.5 -— 1.5 that t h a t the t h e bulk b u l k of ofthe t h eAulneau Aulneau Batholith B a t h o l i t hwas was probably p r o b a b l y intruded i n t r u d e d over over a Maand andi nindicates a time t i m e span span ooff about about 77 Ma d i c a t e s t that h a t felsic f e l s i cvolcanism v o l c a n i sm above KakagiLake Lake Group t e p lplutonic u t o n i c aactivity ctivi t y above t hthe e Kakagi Group i s is c o ecoeval v a l w i twith h 1a late iinn the t h e Aulneau Aulneau BBatholith. atholith. The between The cconformable o n f o r m a b l e r erelationship 1 a t i o n s h i p between a1 all 1 oof f tthe h e vvolcanic o l c a n i c units uni t s showst hthat wasa ar erelatively shows a t rregional e g i o n a l ddeformation e f o r m a t i o n was l a t i v e l y late l a t eevent e v e n t and and nnot o t due due tto o iintrusion n t r u s i o n of o f the t h e large l a r g e batholiths, b a t h o l i t h s ,which w h i c h occurred occurred The end endoof dduring u r i n g volcanism. v o l c a n i s m . The f rregional e g i o n a l deformation d e f o r m a t i o n iinn the t h e area area g i v e n by b y the t h e ages ages ooff two two late l a t e tectonic t e c t o n i cplutons, p l u t o n s ,the t h eHeronry Heronry is i s given Lake Lake sstock, 1.2Ma Ma Lake sstock t o c k and and the t h e Stephen Stephen Lake t o c k , dated d a t e d at a t 2701.0 2701.0 ±z 1.2 and 2699.2 2699.2± 1.9 1.9 Ma, Ma, rrespectively. espectively. and g-9 �U Ii U-Pbaanalyses sphenei ninf ofour U-Pb n a l y s e s o of f sphene u r oof f the t h e samples samples i indicates n d i c a t e s variable variable age iiss from amountso of amounts f rresetting. e s e t t i n g . The The ooldest l d e s t sphene sphene age f r o m the t h eHeronry H e r o n r y Lake Lake agei is from the the  1.6 1.6 Ma), Ma), whereas whereas the t h e youngest y o u n g e s t sphene sphene age s from sstock t o c k (2699,2 (2699.2 ± Sabaskong (2673.7 ±6.6 6.6Ma), Ma),t the samplemost mosts strongly Sabaskong g ngneiss e i s s (2673.7 h e sample t r o n g l y aaffected ffected by by diapirism. diapirism. The duet oto ddiapiric The ddata a t a ssuggest u g g e s t t hthat a t rregional e g i o n a l deformation d e f o r m a t i o n ooccurred c c u r r e d due iapiric The ccentres of tthis rremobilization e m o b i l i z a t i o n ofof sslightly l i g h t l y older o l d e r batholiths. b a t h o l i t h s . The e n t r e s of his two of rremobilization e m o b i l i z a t i o n are a r e likely l i k e l ytot be o be twogneiss g n e i s sdomes domes near n e a r the t h e mouth mouth of Theseappear appeart otohave havebeen beenareas areas Sabaskong o fofr erelatively latively Sabaskong Bay. Bay. These llong-lived o n g - 1 i v e d heat h e a t flow f l o w as asindicated i n d i c a t e dbyb ythe t h younger e y o u n g e rsphene sphene ages. ages. 21 �ANOMALOUSRADIOMETRIC RADIOMETRICAGES AGESFROM FROMTHE THESUPERIOR SUPERIORPROVINCE, PROVINCE, ONTARIO: ANOMALOUS SENSE? NON-SENSE? SENSE? or o r NON-SENSE? R.M. Easton R.M. Easton PrecambrianSection, Section,OOntario Geological Survey, 77 77 G Grenville Precambrian ntario G e o l o g i c a l Survey, renville 1B3 Street, M5S S t r e e t , Toronto, Toronto, Ontario O n t a r i o M5S 1B3 Precise U-Pbzzircon agesoobtained P r e c i s e U-Pb i r c o n ages b t a i n e d oover v e r tthe h e llast a s t 55years y e a r s by byT.E. T.E. Krogh Kroghand and co-workers have pprovided co-workers at a t the t h eRoyal Royal Ontario O n t a r i oMuseum Museum have r o v i d e d aa chronologic c h r o n o l o g i c frameframe- work work ffor o r examining examining t the h e eevolution v o l u t i o n ooff individual i n d i v i d u a lgreenstone greenstone belts b e l t s and and the the sub-provincesooff tthe al. (1984) sub-provinces h e Superior S u p e r i o r Province P r o v i n c e iinn Ontario. O n t a r i o . Krogh Krogh eet t a1. (1984) summarizet hthe summarize e r eresults s u l t s oof f tthis h i s work. work. IIn n this t h i s paper, paper, the t h e significance s i g n i f i c a n c e of of anomalously youngand ando old Rb-Sr, KK-Ar andAAr-Ar age ddeterminations - A r and r - A r age e t e r m i n a t i o n s from from the the anomalously young l d Rb-Sr, Superior Provincei is assessedi nin1ilight S u p e r i o r Province s assessed g h t ooff the t h e work work of o f Krogh Krogh eett al. a1. (1984) (1984) and aa rrecent of geochronologic and e c e n t ccompilation o m p i l a t i o n of geochronologic ddata a t a ffor o r Ontario O n t a r i o (Easton, (Easton, 1985a). 1985a). In cases,i tit i is I n some some cases, s now now ppossible o s s i b l e t otoi ninterpret t e r p r e t tthe h e ssignificance i g n i f i c a n c e ooff radioradiometric m e t r i c ages ages hitherto h i t h e r t oregarded regarded as as curiosities. curiosities. IIn n the t h e Superior S u p e r i o r Province, Province, Rb-Sr, K-Ar 100 tto younger tthan Rb-Sr, K-Ar and and Ar-Ar A r - A r ages ages are a r e commonly commonly 100 o 150 150 Ma Ma younger h a n ccorresorrespondingU-Pb U-Pbz izircon ages;a ac hcharacteristic e.g. the ponding r c o n ages; a r a c t e r i s t i c ooff other o t h e r orogens, orogens, e.g. the Archean Slave P Province Orogen (Bear (Bear PProvince). Archean Slave r o v i n c e and and the t h e Proterozoic P r o t e r o z o i cWopmay Wopmay Orogen rovince) . Anomalous ages those 50Ma Mayounger younger Anomalous ages a r are e those t hthat a t a are r e >>50 o roro lolder d e r t hthan a n t hthe e ttypical ypical 2500 tto Maages ageso obtained by~b-Sr, Rb-Sr,K-Ar K-Ar and andAAr-Ar methodsf ofor Superior 2500 o 2600 2600 Ma b t a i n e d by r - A r methods r S uperior Superior Province anomalous ages Province Province rocks. rocks. S uperior P r o v i n c e anomalous ages f a fall l l i into n t o three t h r e e categories: categories: 1) ageswhich whiche xexhibit 1 ) Reset Reset ages h i b i t ddistinct i s t i n c t associations a s s o c i a t i o n s or o r trends. t r e n d s . These These include: include: a) boundaries,p particularly r e s e t ages ages present p r e s e n t along a l o n g subprovince subprovince boundaries, a r t i c u l a r l y K-Ar K-Ar a ) reset iisotopic s o t o p i c systems. systems. b) b ) reset r e s e tages ages near near province p r o v i n c eboundaries, boundaries, including i n c l u d i n both g b o tRb—Sr h Rb-Sr and and Ar Ar ages (e.g. resetting ages (e.g. r e s e t t i n gofofSuperior S u p e r i oand r andSouthern SouthernProvince P r o v i n c eages ages along a l o n g the the Resetting up ttoo 100 Grenville e s e t t i n g may may ooccur c c u r up 100 km km from f r o m the t h e boundary. boundary. G r e n v i l l e Front). Front). R 1800-1850 Structural t h ca. e ca. 1800-1850Ma MaKenyon Kenyon S tructural cc)) zones zones of o f reset r e s e tages, ages, e.g. e.g. the Zone Sachigo Subprovince. Subprovince. Zone iinn the t h e Sachigo d) agesaassociated d ) excess excess AAr r ages s s o c i a t e d wwith i t h f faulting a u l t i n g or o r major m a j o r geological geological sstructures, t r u c t u r e s , e.g. e.g. the t h eKapuskasing Kapuskasing Structural S t r u c t u r a l Zone. Zone. cases, tthe 2) Isolated r e s e t t i ngisi commonly I n many many cases, h e cause cause ooff the t h e resetting s commonly 2) I s 0 1a t e d reset r e s e tages. ages. In a recognized time a local l o c a l geologic g e o l o g i c ffeature e a t u r e tthat h a t was was nnot o t recognized a tatt hthe e tim e of ofi ninitial itial This K - A rages ages determined determined in in h i s situation s i t u a t i o napplies a p p l i e stot omany many of o fthe t h eK-Ar sampling. T tthe h e late l a t e 1950's, 19504s, early e a r l y 1960's. 1960's. 3) 3 ) Possible P o s s i b l e primary p r i m a r y ages ages that t h a t are a r eassociated a s s o c i a t e d with w i t hmagmatic magmatic events. events. These include: in c l ude : aa)) ages ages ooff carbonatite c a r b o n a t i t e complexes complexes wwithin i t h i n the t h e Superior S u p e r i o r Province, Province, which which correspond tto correspond o the t h e time t i m e ofo fmajor m a j o rmagmatic, magmatic, volcanic v o l c a n i cand andmetamorphic metamorphic events events in i n the t h e mid-continent m i d - c o n t i n e n t region r e g i o n of o f North N o r t h America, America, or o r major m a j o r structural s t r u c t u r a l zones, zones, or o r both b o t h (Figure ( F i g u r e 1). 1). whicha rare bb)) ages ages oof f iisolated s o l a t e d pplutonic l u t o n i c bodies bodies which e l olocally c a l l y nnot o t ssignificant, ignificant, but showr eregional b u t which which show g i o n a l ttrends r e n d s ((Figure F i g u r e 1). 1). Ages Ages wwithin i t h i n t hthe e f first i r s t and and third t h i r d category c a t e g o r y are a r e particularly p a r t i c u l a r l ynoteworthy, noteworthy, in in that agesc cluster t h a t the t h e observed observed ages l u s t e r aat t intervals i n t e r v a l s which which correlate c o r r e l a t e with w i t hchronologic chronologic tterranes e r r a n e s recognized recognized eelsewhere l sewhere i in n North N o r t h America America ((Figure F i g u r e 1). 1 ) . Although A1 though not not directly d i r e c t l y affected a f f e c t e dby bythese these events, events, the t h e Superior S u p e r i o r Province P r o v i n c e locally l o c a l l yprovides provides T h i s should s h o u l d be be considered considered aa record r e c o r d of of North N o r t hAmerican American magmatic magmatic episodes. episodes. This when when i ninterpreting t e r p r e t i n g future f u t u r e geochronologic geochronologic data data from from the t h e region. region. Easton, R.M., 1985a, GeochronologyCCompilation Easton, R.M., 1985a, Geochronology o m p i l a t i o n f ofor r OOntario; n t a r i o ; Ontario O n t a r i o GeolGeological o g i c a l Survey Survey Open Open FFile i l e Report Report and and 66 Preliminary P r e l i m i n a r yMaps. Maps. Easton, R.M., 1985b, 1985b,DDistribution Easton, R.M., i s t r i b u t i o n oof f chronologic c h r o n o l o g i c tterranes e r r a n e s iin n the t h e Grenville Grenville 22 �U Province, Eastern EasternNorth NorthAmerica; America; Geol. Geol. Assoc, Assoc. Can. Can. Abstracts, Abstracts, v.v. 10. 10. Province, F., 1984, Implications of precise U-Pb Krogh, T.E., Davis, D.H., and Corfu, F., 1984, I m p l i c a t i o n s o f p r e c i s e U-Pb Krogh, T.E., Davis, D.W., and Corfu, of the Superior Province; Geol. d a t i n g f o r t h e geological e v o l u t i o n o f t h e Superior Province; Geol dating for the geological evolution Assoc. Can. Can. Abstracts, 9, p.p. 79. 79. Assoc. Abstracts, v. v. 9, Van Schmus, M.R. and Bickford, M.E., 1981. Proterozoic P r o t e r o z o i cchronology chronologyand and ME., 1981. Van Schmus, W.R. and Bickford, A. Kroner, North America; in A. Kroner. e v o l u t i o n o f t h e mid-continent region, North America; i n evolution of the mid-continent region, , PrecambrianPlate P l a t eTectonics, Tectonics, Elsevier, El s e v i e r ,p.p.261-296. 261-296. e d i t . Precambrian edit., . based anomalous Figure 1: 1:Chronologic Chronologic history h i s t o r y of of the t h e Superior SuperiorProvince Province basedonon anomalous Figure K - A r and andRb-Sr Rb-Sr ages ages compared compared w i t h other o t h e r North NorthAmerican American data. data. K-Ar with AGE AGE Mo ininMo 10001000— I200 I 200 - 1400 1400 - 1600 1600 1800 800 2000 2000 - - - 2200 2200 2400 2400 2600 2600 - L^ 1 - typical R b - S r , re-setting /meto.event event re—sefting/meta. mogmotic event event mogmatic *'bused U-Pb Pbzircon zirconages ages based onon U- 23 I �U The Significance of Strain The Strain Patterns Patterns in in Deciphering Deciphering the Deformational History of Archean ~ r c h e a nRocks - ~eformatizal Vermilion ~District, Minnesota in the Vermilion i s t r i z ,Minnesota by Dan Ela and Peter Peter Hudleston Hudleston Department of Geology & Geophysics, University of of Minnesota Minneapolis, 55455 Minneapolis, MN 55455 The Vermilion district of of northern northern Minnesota Minnesota comprises comprises an an E—W E-W trending trending belt belt of multiply deformed sedimentary and volcanic rocks rocks of of Archean Archean age. age. The The district is separated from from the the higher—grade higher-grade rocks rocks of of the the Vermilion Vermilion Granitic Granitic Complex to to the the north north by by the the Vermilion Vermilion fault, fault, which which has has aa large large component component of of dextral strike—slip strike-slip movement. movement. An early nappe—forming nappe-forming event event was was followed followed by by aa second phase of deformation deformation which produced produced all all of of the the measured measured strain, strain, cleavage, cleavage, measurements in the lower—grade and lineations. lineations. Strain measurements lower-grade sedimentary sedimentary rocks rocks reveal reveal a complex pattern of deformation, deformation, which can can be be used used to to infer infer the the tectonic tectonic history of of the the belt. belt. The Magnitude and and symmetry symmetry of of strain strain in in the the rocks rocks varies varies in in parallel parallel bands. bands. The symmetry of the the strain strain varies from from constrictional constrictional to to flattening flattening in in ENE—trending ENE-trending bands which tend tend to to be lensoid lensoid in in map view, view, and and which which are are oblique oblique to to the the trace trace of the the ESE—trending ESE-trending Vermilion Vermilion fault. fault. The largest measured strains strains consistently consistently occur near the the Vermilion Vermilion fault. fault. Flattening strains strains also also predominate predominate adjacent adjacent to to the fault, then change symmetry several times times to to finally finally become become homogeneous homogeneous in in symmetry (constrictional), (constrictional), orientation, orientation, and and magnitude in in the the southern southern part part of of the district. district. The maximum extension of all samples showing constrictional extension directions directions (x) ( X ) of strain, plunge east at at angles angles between between 30 30 and and 65°. 65'. X in samples showing showing flatflattening strain plunges east or west, but near the the Vermilion fault fault all all plunges plunges are are west or more steeply east than than they they are are in in constrictional constrictional samples. samples. The maximum ( Z ) plunges plunges consistently less than 25° 25O to to the the north north or or shortening direction (z) south. south. A number of features in the the rocks indicate indicate aa large large component component of of dextral dextral simple shear in in the the deformation deformation history. history. The significance significance of of the the strain strain patterns patterns is is not not clear. clear. The alternating constrictional and flattening flattening zones zones preclude preclude their their origin origin by by homogeneous homogeneous coaxial coaxial strain or progressive simple simple shear. shear. These strain strain variations also also require require aa The model which can satisfy satisfy compatibility compatibility constraints constraints and and space space considerations. considerations. The area of consistent constrictional constrictional strains strains in in the the south south may may represent represent one one regional component of of the the strain. strain. Spatial correspondence of the the flattening flattening strains with the Vermilion fault fault suggests that that aa simple simple shear shear component component was was modified model of transpression added in in that that area. area. A modified transpression may explain explain how how H— Eby a concomitant inhomoge— plunging X axes are are reoriented reoriented to to become become W—pluriging W-plunging by inhomogeneous progressive Less progressive simple simple shear shear which which is is clearly clearly shown shown in in the the rock rock fabrics. fabrics. Less than vertical plunge of the some component component of of oblique oblique the X axes may necessitate some motion on on the the fault. fault. A second zone of flattening flattening strain strain may have have formed formed in in aa strain field which is reflected in in a smaller smaller dextral dextral strike—slip strike-slip fault, fault, or or it it may reflect reflect strain strain accommodation accommodation around around the the more more competent competent greenstone greenstone and and iron— ironformation coring the major anticlinal anticlinal structure structure in in the the area. area. 24 �U The The relatively relatively homogeneous homogeneous deformation deformation in in the the constrictional constrictional zones zones surrounded surrounded by by more more highly highly sheared sheared and and flattened flattened zones zones suggests suggests aa large—scale large-scale ana— analogue of of the the fabric fabric of of mylonite mylonite zones. zones. The The anastomosing anastomosing geometry geometry of of such such zones zones logue serves to to satisfy satisfy compatibility compatibility conditions conditions and and room room problems. problems. Such Such patterns patterns serves have have been been modelled modelled theoretically theoretically and and require require similar similar anastomosing anastomosing behavior behaviorinin the third third dimension dimension to to explain explain the the juxtaposed juxtaposed variations variations in in strain strain magnitude magnitude and and the symmetry. Similar Similar variations variations in in strain strain have have been been predicted predicted in in simple simple shear shear symmetry. 'b' direction direction to to give give an an overall overall flattening flattening regimes, with with extension extension in in the the 'b' regimes, strain. Perturbations Perturbations of of the the shear shear produce produce local local zones zones of of constrictional constrictional strain strain strain. at an an angle angle to to the the shear shear plane plane consistent consistent with with the the angle angle that that the the boundaries boundaries of of at zones zones of of constrictional constrictional and and flattening flattening strain strain in in the the Vermilion Vermilion district district make make with the the Vermilion Vermilion fault. fault. with In In aa general general way way the the strain strain patterns patterns observed observed in in the the Vermilion Vermilion district district can can be reasonably reasonably explained explained by by aa history history of ofN—S N-S shortening shorteningaccompanied accompaniedbybyinhornoge— inhomogebe neous dextral dextral simple simple shear shear which found found its its last last expression expression as as the the Vermilion neous fault. The The variations variations of of strain strain may may be be aa consequence consequence of of variations variations in in the the fault. relative relative intensities intensities of of shortening shortening and and shear, shear, large large perturbations perturbations of of the the shear) shear. or the the influences influences of of other other structures. structures. or 25 — �U in the the Keweenawan Keweenawan i\orth North Shore Large Large Igniinbrites Ignimbrites in Shore Volcanic Volcanic Group Group in in Cook Cook County, County, Minnesota Minnesota Thomas Thomas Fitz Fitz (Dept. (Dept. of of Geology, Geology, University University of of Minnesota—Duluth, Hinnesota-Duluth,Duluth, Duluth, MN 55812) MN 55812) Dr. Dr. John John C. C. Green Green (Dept. (Dept. of of Geology, Geology, University University of of Minnesota—Duluth, Minnesota-Duluth, Duluth, Duluth, MN MN 55812) 55812) Two Two thick thick and extensive extensive volcanic units units were studied in in the the North horth Shore Shore Volcanic Volcanic Group Group in in south—central south-central Cook Cook County, County, Minnesota. Minnesota. The The Kimball Kirnball Creek Creek quartz quartz latite latite is is 335 335 mm thick, thick, strikes strikes approximately approximately east—west, east-west, dips dips 10 10 degrees degrees south south and and can can be be traced traced 29 29 km krn along along strike strikebut but is is truncated truncated by by Lake Lake Superior Superior north—east north-east of of Grand Grand Marais. Marais. It It can can be be subdivided subdivided into into two two subunits subunits based based on on the the percentage percentage of of plagioclase plagioclase phenocrysts, phenocrysts, the the lower lower unit unit being being the the more more highly highly porphyritic. porphyritic. This This is is overlain overlain by approximately approximately 245 m of ophitic olivine olivine basalt flows flows of of the the Red Red Cliff Basalts (Green, 1972) and the 225 m thick Devil Track rhyolite. Cliff Basalts (Green, 1972) and the 225 m thick Devil Track rhyolite. The The Devil Devil Track Track rhyolite rhyolite can can be be traced traced 35 35 km km along along strike strike from from near near the the western end of Pike Lake eastward to the shore of Lake Superior western end of Pike Lake to the shore of Lake Superior where where it it too too extends extends an an unknown unknown distance distance under under the the lake. lake. Depending Depending on on assumptions assumptions as as to its its original original extent, extent, this unit appears to contain between 160 160 and 500 500 cu. cu. km km of of rhyolite. rhyolite. Closely Closely spaced spaced vertical vertical and and horizontal horizontal joints joints cause cause the the rocks rocks to to be be easily easily eroded eroded resulting resulting in in poor poor exposure exposure and and concealed concealed contacts. contacts. Texturally Texturally the the rocks rocks are are aphanitic, aphanitic, holocrystalline holocrystalline and and largely largely lack lack devitrification devitrification features. features. No No pyroclastic pyroclastic textures textures have have been been found. found. The The rocks rocks are are dominated by anhedral anhedral orthoclase orthoclase and platy, platy, randomly randomly oriented quartz quartz crystals crystals that that were were originally originally tridymite. tridymite. Tabular, Tabular, 1—2 1-2 mm rnm quartz quartz crystals, crystals, also also pseudomorphs pseudomorphs after after tridymite, tridymite, are are present in in some some small small cavities. There There are are some some oxidized oxidized pseudomorphs pseudomorphs of of clinopyroxene clinopyroxene but but cavities. blocky, blocky, subhedral subhedral magnetite magnetite is is the the dominant dominant primary primary mafic mafic mineral. mineral. It It is is partially partially weathered weathered to to hematite hematite giving giving the the rocks rocks their their red red color. color. The The lack lack of of flow flow banding banding and and vesicles, vesicles, the the very very large large volumes volumes and and aspect aspect ratios ratios (length/thickness) (length/thickness) of of 90 90 and and 160 160 for for the the Kimball Kimball Creek Creek and and Devil Track units respectively, suggest an origin by pyroclastic flows rather rather than than lava lava flows flows (Walker, (Walker, 1973). 1973). The The interpretation interpretation of of these these units units is that they were deposited by large, hot pyroclastic flows that deposited by large, hot pyroclastic flows that crystallized after emplacement similar similar to the rhyolitic tuffs tuffs of the San Juan region of of Colorado Colorado (Lipman, (Lipman, 1975a). 1975a). The The crystallization crystallization of of tridymite tridymite and orthoclase orthoclase destroyed destroyed any any pyroclastic pyroclastic textures. textures. The The tridymite tridymite subsequently subsequently inverted inverted to to quartz quartz during during burial. burial. Green, Green, John, John, C., C., 1972, 1972, North North Shore Shore Volcanic Volcanic Group. Group. In In Sims, Sims, P.K. P.K. and Morey, G.B. G.B. eds. eds. Geology Geology of of Minnesota: Minnesota: A Centennial Centennial Volume. Volume. Morey, Minnesota Minnesota Geological Geological Survey. Survey. Lipman, Lipman, P.W., P.W., 1975a, 1975a, Evolution Evolution of the Platoro Platoro caldera caldera complex complex and related volcanic volcanic rocks, rocks, Southeastern Southeastern San San Juan Juan Mountains, Mountains, Colorado: Colorado: U.S. U.S. Survey Prof. Prof. Paper Paper 852, 852, 128 128 p. p. Geol. Survey Walker, R. Soc. Soc. Land. Lond. A. A. Walker, G.P.L., G.P.L., 1973, 1973, Lengths Lengths of of lava lava flows. flows. Phil. Phil. Trans. Trans. 8. 274, 107—118. 107-118. 274, 26 �U CONTROLS ON THE GENESIS GENESIS OF OF EPIGENETIC EPIGENETICAURIFEROUS AURIFEROUS CONTROLS ON THE V E I N SYSTEMS SYSTEMS IN I NARCHEAN ARCHEAN CHEMICAL—SILICICLASTIC CHEMICAL-SILICICLASTIC SUBMARINE SUBMARINE VEIN FAN FAN DEPOSITS, DEPOSITS, GERALDTON GERALDTON AREA, AREA, ONTARIO ONTARIO andScott, S c o t tBrian, , B r i a nM. , M.Department Department F r a l i c k , Philip, P h i l i pW. , W.and Fralick, of University, o f Geology, Geology, Lakehead Lakehead U n i v e r s i t y , Thunder Thunder Bay, Bay, Ontario, O n t a r i o ,P7B P7B5El 5E1 In 1 9 2 0 ' s and and 30's 3 0 ' s aanumber number of o f occurrences occurrences of o f gold g o l d bearing bearing I n the t h e 1920's q u a r t z vein v e i nsystems systems were were discovered d i s c o v e r e d ini nthe the Beardmore-Geraldton quartz BeardmoreGera1dton Greenstone BBelt e l t nnorth o r t h of o f Lake Lake Superior. S u p e r i o r . Most Most vein v e i n systems systems are a r e located located Greenstone proximal with t o east—west east-west t rtrending e n d i n g f fault a u l t zones zones w i t h mineralization m i n e r a l iz a t i o n proximal to localized l o c a l i z e d in i n drag d r a g folds f o l d s and and ddilated i l a t e d ffractures r a c t u r e s iin na a variety v a r i e t y of o f rock rock t y p e s . Auriferous A u r i f e r o u s vein v e i nsystems systems and and associated a s s o c i a t e d replacement replacement sulphides s u l p h i d e s in in types. oxide Rock o x i d e facies f a c i e s iron i r o nformation f o r m a t i o nwere werestudied s t u d i e datathe t t hHard e Hard Rockand and MacLeod—Cockshutt Mines and Solomon's SolomontsPPillars MacLeod-Cockshutt Mines p l uplus s t hthe e MMcLellan c L e l l a n and illars occurrences occurrences tto o gain g a i n information i n f o r m a t i o n on on the t h e mineralization m i n e r a l iz a t i o nprocess. process. In In addition a d d i t i o n the t h e depositional d e p o s i t i o n a lenvironment environment of o f the t h e I.E. I . F .and andassociated associated siliciclastics belt. s i l i c i c l a s t i cwas s wasinvestigated i n v e s t i g a t e dthroughout t h r o u g h o u t the t h egreenstone greenstone be1 t. The (less The ooxide x i d e ffacies a c i e s LF. I.F. forms formsthin thin ( l e sthan s t h a5n mm) 5 mm)laminae laminaeand and packages packages ooff laminae laminae interbedded i n t e r b e d d e d with w i t h and and sometimes sometimes forming f o r m i n g the t h e EE d i v i s i o n of o f DE DE tturbidities. u r b i d i t i e s . The The cchemical-siliciclastic h e m i c a l - s i l i c i c l a s t i csuccessions successions are are division organized o r g a n i z e d into i n t oupward upward coarsening c o a r s e n i n g and and thickening t h i c k e n i n gpackages. packages. Both Both chemical chemical and and cclastic l a s t i c components components r represent, e p r e s e n t , i in n varying v a r y i n g proportions, p r o p o r t i o n s , deposition deposition from from dilute d i l u t esediment sediment gravity g r a v i t yflows f l o w sand andrainout r a i n o ubelow t belowstorm s t o r mwave wave base. base. The I.F. was was deposited d e p o s i t e d in i nshore shore The sstratigraphic t r a t i g r a p h i c succession succession indicates i n d i c a t e s I.E. proximal p r o x i m a l interchannel i n t e r c h a n n e lareas areason ona asubmarine submarine fan f a nforming f o r m i n gthe t h subaqueous e subaqueous o f aa fan f a ndelta d e l t asystem. system. p o r t i o n of portion ZONES OF IRON FORMATION ACCUMULATION OVERBAN}< VERBANK FLOW FLOW INACTIVE CHANNEL ACTIVE CTIVE CHANNEL CHANNEL Paleogeography Beardmore-Geraldton during off the Paleogeography o of f t the h e Beardmore-Geral d t o n a rarea ea d u r i n g ddeposition eposition o the As coarse eclastics As time t i m e progressed progressed tthe h e coarse lastics prograded southwardwidening wideningt hthe prograded southward e bbraidplain. raidplain. sedimentary sedimentary assemblage. assemblage. 27 I �U The veining event occurred concomitant with fol lowing aa The veining event occurred either either concomitant with or or following regional epi sode of deformation. Auriferous mineral i zation . F . is is regional episode of deformation. Auriferous mineralizationinin II.F. spaci a1 ly and probably genetical ly re1 ated t o extensive wall -rock spacially and probably genetically related to extensive wall-rock a1 terationincluding includingcarbonatization carbonatizationand andsulphidation. sul phidation.The Themineralogy mineralogy alteration of the occurrences indicates they were deposited from sulphide of the occurrences indicates they were deposited from sulphide rich, rich, alkaline tot oneutral neutralH20-C02 H20-C02 solutions. solutions. Under Under these these conditions conditions the the gold gold alkaline may have from depth depth by byreduced reduced sulphur sulphurcomplexes complexesand and may have been been transported transported from precipitated during wall-rock alteration of the I . F . b y b o t h a pH precipitated during wall-rock alteration of the I.F. by both a pH change and ZFe304 6Au(HS)y + +66H ~ '26FeS 6FeS2 ++ 8H 8Hz0 6Au change and the the reactions: 2Fe 0 ++ 6Au(HS)-T 0 +t6Au 34 2 ->2 2 22 t 4H2 2FeAsS t FeS2 t 4H20 t Z A u . Fe3O4 t 2Au(AsS2) Fe304 + 2Au(AsS2) + 4H2 2FeAsS + FeS2 + 4H20 + 2Au. + 28 �EARLIEST GEOCHEMISTRY OF G EOCHEMISTRY O F THE T H E POWDER MILL M I L L GROUF' GROUP: THE THE E A R L I E S T LAVAS LPiVAS THE THE NIL) M I D CONTINENT CONTINENT RRIFT I F T IN I NMICHIGAN MICHIGAN Jies W. OF OF Sell Sci ences, Michigan State Uni off G versi Department o Geological Dapar-tment o o l o q i c a l Science's, M i c h i gan S t a k e U r i i v e r - s i b1yy East E a s t Lansing, L a n s i n g , Michigan M i c h i g a n 48824 4Sf.324 etruded Powder Miii heo e;~:ti"nded M i 11 Group Group represents r e p r e s e n t ! %the t h 'first '~ f i r s t lavas l a v a s to to b Upper Midcontinent the development the; development oo f the the M i d c o n t i n e i n t Rift R i - F t in i n U p p e r vlichjqan. M i c h i qan. unique opportunity to These Keweenawan cenawan age age lava l a v a f1ows l a w s provide provide a u nique a ppartuni t y to one o$f the planet's oldest examine tthe h e iinitial n i t i a l eruptives eruptives ffrom rom one o the? planet's o l d e s t and and examine is(a exposed largest l a r - q e s t preserved pr-oaerved ri r i ft t systems. systems. The Powder Powder- Miii M i l l Group Gr-oup i o x posed southern qn over an area ovesr an a r e a of o f about a b o u t 160 160 km, km, +rom from s o u t h e r n Houqhton Houqhtori Courty, C o u n t y , Mi lvll:hi c h i q<,iri Mth:Lqan. Wisconsin, to Grandview, t.a Grandview, W i s c o n s i n , and is i s centred c e n t r e d around around IIronwood, ronwaod, IPlichiq<an, has IIts t s ttotal o t a l tthickness hickness h a s been estimated e s t i m a t e d at a t about a b o u t 6100 6100 m. m, Group is The Powder Mill M i l l i s divided d i v i d e d into i n t o two t w o Formations: F o r m a t i o n s : the t h e S:Lemns Siemens The lowermost Siemens C Creek Creek and the lowermost tthe he kesek t h e Kallander Kallander Creek. The 1300 rnm 0.6 of tthin and aandesite iows Formation about F o r m a t i o n represents represents a bout 1300 h i n bbasalt a s a l t and n d o s i t o flow:^ The overlying which w h i c h are a r e generally g e n e r a l l y less l e s s than t h a n 15 15 m m thick. thick, o v e r ly i ng Kallander Kal lander believed be about although only Formation Creek F ormation iis s b e l i e v e d tto o b e a b o u t 4500 m thick thick a lthough only Creek average The about a b o u t 1200 1200 m m is i s exposed. e:<posed. The a v e r a g e flow f l o w thickness t h i c k n e s s is is about a b o u t 25 2'5 m. mu (Hubbard,, els:Lte 'flows basalt These flows rrange a r i q e ffrom ram b a s a l t to t o quartz—bearing q u a r t z - b e a r i ng felsita (1-Iubbi'ar-d Powder Mill off 1975). All exposures the 1775) A ll e xposures o the Powder M i 11 Group west of o-f the t h e Keweenaw Ksweeriaw Lposures near vertical Fault F a u ldip t dip n ear v e r t i c a l and toward toward tthe h e northwest. northwo:st. Expaiuurc?!:ion a n tthe he east side east s i d e of o f the t h e Keweenaw Keweenaw Fault F a u l t are a r e flat f l a t lying. lying. by Wilband Preliminary Mill Group P reliminary iisotope s o t o p e work work on the t h e Powder Powder M i l l Group by W ilband of 0.7042+/— with an an isochran ((1984) 1.984) yyielded i e , l d e d .an isochrqn w ith an iinitial87Sr/SóSr nit1,all~~Sr/8a 6+~ ~0 .7043 + / off 1209 +/— 36 Ma. 4 0.0003 and an age o 1209 + / - 36 Ma. M a j o r element e l e m e n t data data from fr-cam 46 0.0003 and an age Major SiO' samples have been collected. Ranges o4 some sample's h a v e been c ollected. Ranges o af some oxides o x i d e s are: are; SiO12 18—4%. 70—48%; MqO 13—< 1"!.; CaO 1 1—< 1%; Al20, 16—10%; FeO 70-48Z;MgO 13-<17.;CaO 11-<17.;Al$):-!; 16-10%;FeQ (total FFe) o ) la-47.. There There a h high positive CaO. T h e r e is i s ia igh p o s i t i v e correlation c o r r e l a t i o n between b e t w e e n MqO MqG and and CaQ. Theres is i s also a h high negative correlation Al$z. a lso a igh n egative c o r r e l a t i o n between MqO MgO and and Al20,. Nine eighteen N i n e of o'f the t h e sampled lavas l a v a s are a r e olivine o l i v i n e tholeiites t l i o l e i i t e s and and e i q h t a e n are are quartz tholeiites. types byy A duality q uarts tholeiitas. duality oof lava lava t y p e s was was recoqnized recoqnized b Wilband Wasuwanich Portage W i l b a n d and W i ~ s ~ w a n i c(1980) h ( 1 9 8 0 ) in i n the t h e overlying overlying P o r t a q e Lake L a k e Lavas L a v a s and and These dykes tthe h e Keweenawan Keweenawan diabase d i a b a s e dykes. dykes. d y k e s are a r e believed be1 i e v e d to t o he he 'feeders -feeders both the This f'for ar both t h e Portage P o r t a g e Lake L a k e Lavas L a v a s and and the the? Powder Powder Miii M i l l Group. Group. T his duality in MgO v. TiO' d u a l i t y is i s also a l s o recognized recognized i n plots p l o t s o4 of MqO T i O z and A12(::):3 Ai1O', : F'205 for TTi02 iOz : P ~ d s 'For tthe h e Powder M i l l T r a c e element e l e m e n t data datia will will Mill Group. Trace be collected b e c o l l e c t e d to t o substantiate s u b s t a n t i a t e these t h e s e trends. trends. The during during . (total : Hubbard H. Hubhard H. A. A. ((1975) 1975) Lower c a n i c rocks r o c k s a-f M i c h i qiiin and Lower Koweenawan Keweenawan vol, volcanic of Michigan and W i s c o n s i n . U.S. U. S. c3eol, Geol S urvey J o u r . Research R e s e a r c h 3, 3 , 5Zc?--'-J4 J. Wisconsin. Survey Jour. 529—541, Wilband Age and and ssource of vvolcanics associated W i lbi31id J.T. J.T. ((1984) 1 9 8 4 ) Age o u r c e vvariation a r i a t i o n o-f o l c a n i c % (sissoci dtad with Keweenaw R w i t h Keweenaw i f t i n g . Trans. T r a n s . Am. Am. Geophys. Beophys. Union U n i a n 65, 6 5 , 1122. 1122Rifting. W i l b a n d J.T. J.T. and and Wasuwanich Wasuwanich F. F. Wilband ((1980) 1780) M o d e l s of a-f basalt b a s a l t petroqenesis: ptsti*-aqariei~'i.s: Models Lower Lower Keweenawan i abase ddikes i k e s and and Middle M i d d l eKeweenawan Keweeriawan Portage P o r t a g eLak:e Lake Keweenawand diabase L a v a s , Upper i c h i q a n . CContrib. antrib. M ineral. P atrol. 7 5 , 3t95-406,, Lavas, Upperl lMichigan. Mineral. Petrol. '75, 395—4O. 29 - - -- �U h STRATIGRAPHIC EVOLUTION EVOLUTION OF OF THE THE ISLAND ISLAND LAKE LAKE GREENSTONE GREENSTONE BELT. BELT, STRATIGRAPHIC MANITOBA MANITOBA 555-330 Graham Graham Ave.. Ave., Paul Gilbert. Gilbert, Geological Geological Services Services Branch. Branch, 555—330 Paul 4 E 3 Winnipeg, Manitoba. R3C Winnipeg. Manitoba. R3C 4E3 H. H. The Island Island Lake Lake greenstone greenstone belt belt in in the the northwestern northwestern The Superior Province consists of a lower, subaqueous, Superior Province consists of a lower, subaqueous. volcanosedimentary section section (Hayes (Hayes River River Group), Group), unconformably unconformably volcanosedimentary overlain by by fluvial fluvial deposits deposits and and younger younger turbidites turbidites (Island (Island Lake Lake overlain Group). The Hayes River Group was subjected to pre-Island Lake Group). The Hayes River Group was subjected to pre—Island Lake Group deformation, deformation, metamorphism, metamorphism, and and plutonism plutonism and and was was probably probably Group subaerially eroded before deposition of the younger sedimentary subaerially eroded before deposition of the younger sedimentary rocks. rocks. - Coarse volcanic volcanic breccia breccia and and relatively relatively shallow—water, shallow-water, Coarse vesicular basalt basalt in in the the eastern eastern part part of of the the belt belt suggest suggest aa more more vesicular proximal environment environment than than the the area area further further west. west. The The abandoned abandoned gold gold proximal mine in the the eastern eastern part part of Island Lake Lake occurs occurs at at aa mine in of Island volcanic/sedimentary interface within within the the Hayes Hayes River River Group. Group. volcanic/sedimentary interface Silicification and carbonatization are more widespread in this area Silicification and carbonatization are more widespread in this area than further west. Carbonatization may be partly related to than further west. Carbonatization may be partly related to possible sedimentary carbonate units (e.g. at the gold mine) but is possible sedimentary carbonate units (e.g. at the gold mine) but is 0.5 km of the Norrie Island carbonatite. This also extensive within also extensive within 0.5 km of the Norrie Island carbonatite. This intrusion, which which is is associated associated with with carbonatized carbonatized peridotite peridotite and and intrusion, intrusive breccia breccia containing containing mafic/ultramafic mafic/ultramafic clasts, clasts, is is emplaced emplaced intrusive close to to the the contact contact between between the the Hayes Hayes River River and and Island Island Lake Lake Groups Groups close in aa possible possible graben—like graben-like structure. structure. A zone of ultramafic in of A zone ultramafic intrusions extends extends through through the the central central part part of of the thegreenstone greenstonebelt, belt, intrusions and aa porphyritic porphyritic peridotite peridotite sill sill occurs occurs close close to to the the south south margin margin and of the the belt. belt. Regional Regional isoclinal isoclinal folding folding has has affected affected both both the the Hayes Hayes of River and and Island Island Lake Lake Groups Groups and and major major faults faults are are inferred inferred where where River stratigraphic discontinuities occur across the axial traces of some stratigraphic discontinuities occur across the axial traces of some folds. folds. 30 �U KEWEENAWAN KEWEENAWAN DIKES OF MINNESOTA John Green, Geology John C. Green, Geology Dept., Dept., Univ. of of Minn., Minn., Duluth, Duluth, MN MN 55812 55812 University Ave., St. Val W. Chandler, Chandler, Minn. Minn. Geol. Geol. Survey, Survey, 26)42 2642 University St. Paul, Paul, MN MN 551114 55114 Keweenawan dikes, many many of which were probably feeders for plateau basalt lavas, lavas, are concentrated in several swarms in northeastern Minnesota. Minnesota. Their Their general general trends trends probably probably show show the the direction directionof' of tensional tensional stress stress at different times and in different areas as the Midcontinent Rift system system evolved, evolved, and their their compositions compositions give give an an idea idea of of the the magmas magmas available available from from melting melting of of the the subcontinental subcontinental mantle mantle as as the the rift rift progressed. progressed. Time relations relations are inferred both from crosscutting intrusive intrusive relations studies of of polarity and pole relations and and from from paleotnagnetic paleomagnetic studies pole progression progression along the the Late Late Proterozoic Proterozoic track track (Halls (Halls and and Pesonen, Pesonen, 1982). 1982). The two oldest oldest swarms swarms show show reversed reversed polarity. polarity. The The Carlton Carlton County County swarm outcrop, trending swarm contains contains143 43 dikes dikes known known from outcrop, trending rather rather uniformly uniformly ~ 3 0 ~They . are found in the St. St. Louis Louis River River valley valley from from Carlton Canton and and N3O°E. Cloquet east through Duluth, and through the Jay Cooke State Park area west of Duluth, they cut the Lower Proterozoic Thomson Formation and some of the reversed - polarity lavas at Ely's polarity (R) (R) Keweenawan lavas Ely's Peak Peak beneath beneath the the Duluth Duluth Complex. Complex. Fe—rich basalt similar in composition to They are mostly rather evolved, Fe-rich many North Shore Volcanic Group (NSVG) (NSVG) lavas and the Columbia River plateau plateau basalts. basalts. A few normally polarized (N) (N) dikes, dikes, evidently evidently younger, younger, also occur in this same area, and several large N dikes with similar trend appear dramatically dramatically on on aeromagnetic aeromagnetic maps maps (Chandler (Chandler 1983). 1983). The The reversed reversed swarm shows a paleomagnetic pole position that closely corresponds corresponds to that previously determined by others for reversed lavas in Cook County and Logan Logan sills sills in in the the Thunder Thunder Bay Bay district. district. The occurrence occurrence of of large large RR dikes dikes up to 8 lavas or Duluth Duluth Complex 8 km km west west of of the the nearest nearest Keweeriawan Keweenawan lavas Complex suggests suggests that the R Ely's Ely's Peak basalts or their equivalent probably covered a considerably considerably wider wider area area before before Late Late Keweenawan Keweenawan erosion. erosion. - Another group of reversed reversed dikes dikes is is the the Grand Grand Portage Portage swarm swarm (Green, (Green, the coastal coastal zone zone of of northeastern northeastern Cook Cook 1981) which which is best exposed in the County Portage. They cut the reversed—polarity reversed-polarity Counìty from from Hovland Hoviand to to Grand Portage. Keweenawan lavas, lavas, the the Puckwunge Puckwunge Sandstone, Sandstone, and the underlying underlying Lower Lower Keweenawan Proterozoic Proterozoic Rove Rove Formation. Formation. At least 20 dikes are known, known, ranging from 1 to 145 thick;about about 30% 3O are 45 mm thick; are over over 10 10 mm thick. thick. They trend trend E.-W E-W to and to ENE and dip steeply steeply N. N. These These too too have have rather rather Fe—rich Fe-rich evolved evolved compositions. compositions. Several are plagioclase-porphyritic plagioclase—porphyritic and they were probably feeders for the Grand Portage Portage and and Hoviand Hovland lavas. lavas. 1 is found found in in the the Grand A major group of normally polarized dikes also is intrusions Portage area; these have been referred to as the Pigeon River intrusions by Geul Geul (1970). (1970). Consisting Consisting of at least 30—35 30-35 dikes, dikes, (most (most in in Canada) Canada) this this group contains contains many very large large ones ones over over 100 100 mm thick thick (some (some up up to to 500 500 m). m). trend N65 ~ E6 but but5 aa few few ~ are are transverse transverse with with N30—5 ~ 3 0 W- strikes. strikes. 5 ~ Most trend Several can can be be followed followed for for 15—20 15-20 km. km. They cut the Rove Fm, Several Fm, reversed Keweenawan lavas, Keweenawan lavas, and Logan Logan sills. sills. This This group group is is on on the the whole whole considerably more magnesian and primitive geochemically than the RR swarms swarms described, and represents represents aa major major tapping tapping of of new new mantle mantle melt melt after after just described, pole reversal. reversal. the R-È RN pole 31 �_____ I In 1I basalt dikes are known, all N, which In the City of Duluth about 44 cut cut the the Duluth Duluth Complex Complex and and the the NN lavas lavas above above it. it. Their Their trend trend is is variable variable but most are are N—S N-S with with aa 750 7 5 WW dip. dip. The The compositions compositions of of 10 10 analyzed analyzed samples ranges ranges from from fairly fairly primitive primitive to to more more evolved, evolved, but samples but generally generally are are not not as as Fe—rich Fe-rich as as the the RR dikes dikes of of Carlton Carlton County. County. Sixteen Sixteen N dikes south of Babbitt cut the Duluth Complex and trend transverse transverse to to the the general general rift, rift, about about N52 N52 ÷+ 15 1 5 WW (Morey (Morey and and Cooper, Cooper, Their 1976). Their extent extent is is not not well well defined defined nor nor is is their their chemistry. chemistry. Another Another 16 dikes between Ely and Moose Lake Lake in in the the Fernberg Fernberg Trail Trail area area (Green (Green et et al., Archean rocks rocks northwest northwest of of the the base base of of the the Duluth Duluth Complex. Complex. 1966) cut cut Archean al., 1966) Their Their polarity polarity is is not not established. established. Most NW; Most strike strike either either NN 65—70°E 65-70'~ or or NW; the the longest longest can can be be traced traced for for 10 10 km. km. These These have have aa range range of of basaltic basaltic compositions compositions rather rather like like those those of of the the Duluth Duluth area. area. The The 62 62 Minnesota Minnesota Keweenawan Keweenawan basaltic/diabasic basaltiddiabasic dikes dikes so so far far analyzed analyzed show show aa wide wide range range of of compositions compositions within each swarm, swarm, reflecting reflecting those those of of the the overlying overlying lavas. lavas. However, However, in in contrast contrast to to the the dikes dikes of of Michigan Michigan and Wisconsin, Wisconsin, there there is is aa preponderance preponderance of of more primitive primitive compositions compositions in in the N N group, group, and of of dikes dikes richer richer in in Fe, Fe, Ti, Ti, K, K, and and PP in in the the RR group. group. This This study study has has been supported in in part by the MNDNR Lithogeochemistry Lithogeochemistry Project. Project. References References Chandler, V. W., W., 1983, Aeromagnetic Aeromagnetic Map Map of of Minnesota: Minnesota: Carlton Canton and and Pine Pine Chandler, V. Counties., Counties., Minn. Geol. Geol. Survey, Survey, St. St. Paul. Paul. Geul, Geul, J. J. J. J. C., C., 1970, 1970, Geology Geology of of Devo Devo and and Pardee Pardee Townships, Townships,Ontario OntarioDept. Dept. Mines Mines Geol. Geol. Rept. Rept. 87 87 Green, J. J. C., C., 1981, 1981,Geol. Geol. Soc. Soc. Amer. Amer. Abstracts Abstracts with with Programs, Programs,v. v. 13, 13, p. p. Green, 271. 271. 9- Phinney, Phinney, W. W. C., C., and and Weiblen, Weiblen, P. P. W., W., 1966, 1966, Gabbro Gabbro Lake Lake Quadrangle, Quadrangle, Minn. Minn. Geol. Geol. Survey Survey Misc. Misc. Map Map M—2. M-2. Halls, Halls, H. H. C. C. and and Pesonen, Pesonen, L. L. J., J., 1982, 1982, Paleomagnetism Paleomagnetism of of Keweenawan KeweenawanRocks, Rocks, in in Geol. Soc. Soc. Amer. Amer. Memoir Memoir 156, 156, p. p. 173—202. 173-202. - Morey, G. G. B. B. and Cooper, Cooper, R. R. W., W., 1976, 1976, Bedrock Bedrock geologic geologic map of of Hoyt Hoyt Lakes Lakes — Money, Kawishiwi Kawishiwi Area, Area, St. St. Louis Louis and and Lake Lake Counties, Counties, NE NE Minn. Minn. Minn. Minn. Geol. Geol. Survey Survey open—file open-file map. map. 32 I I �i I Wisconsin Archean Block: Block: The Central Central Wisconsin Archean The New Evidence Suggests Suggests aa Partially Partially Reworked Reworked Granite/Greenstone Granite/Greenstone Terrane Terrane 3. J. K. K. Greenberg and and B. B. A. A. Brown Brown Wisconsin Geological and and Natural History History Survey Survey 1815 University Avenue Madison, WI 53705 1 A recently area of of central central Wisconsin, Wisconsin, which which includes includes most most of of Wood Wood recently mapped area and Portage counties, is typified by syn— and syn- to late—kinematic late-kinematic granitoid granitoid plutons plutons which intrude a predominantly volcanic volcanic terrane. terrane. The geology of this region is is analogous to granite/greenstone terranes common in in Archean shield shield areas areas and and analogous central Wisconsin area area was previously previously thought thought to to some younger provinces. provinces. The central of an extensive basement of Archean gneiss consist of gneiss overlain by by Proterozoic Proterozoic volcanic rocks and intruded and deformed around volcanic around 1850 1850 Ma. These These basement basement gneisses were were grouped with other gneisses in gneisses in southeastern southeastern Minnesota and and the the VaLley and and interpreted interpreted to to constitute constitute aa distinct distinct Archean Archean gneiss gneiss Minnesota River Valley provi;ce, separated from a granite/greenstone province, granite/greenstone terrane terrane to to the the north north by by aa major tectonic boundary. Our work in in central central Wisconsin suggests suggests that that the the two two major major lines lines of of evidence formerly used to infer terrane9*in in central central infer the the existence existence of of aa "gneiss "gneiss terrane" Wisconsin, age and and 1ithology;probably lithology,probably do do not not support this interpretation. Of Wisconsin,age the several available ages on Archean units, many are are younger younger than than similar similar rocks in southern southern Minnesota Minnesota or or nàrthern northern Wisconsin. Wisconsin. Most recent U/Pb dates from central Wisconsin are in in the range 2.5 2.5 to to 2.7 2.7 Ga, similar similar to to the the age age of of the proposed proposed granite/greenstone terrane in in northern northern Wisconsin and and Michigan. Michigan. Many of the newly designated designated Archean Archean units units and and other other potentially potentially Archean Archean units units are metavolcanic and metasedimentary lithologies, lithologies, such such as as those those exposed exposed at at DuBay in Portage County (interbedded Lake DuBay (interbedded felsic felsic and and mafic rocks) rocks) and and along along the Black River in in Jackson County (Algoma—type (Algoma-type iron iron formation formation and and amphibollte). amphibolite). There are numerous plutons plutons of of either either granite—granodiorite—tonalite granite-granodiorite-tonalite or or tonalite—hornblende diorite—gabbro tonalite-hornblende diorite-gabbro exposed in in the the area. area. Only a few ages are available for these rocks, but they are are generally generally thought thought to to be be early early Rock fabric and Proterozoic. Proterozoic. and contact contact relationships relationships indicate indicate that that the the intrusions were were syn to late kinematic, kinematic, commonly with massive cores and intrusions foliated margins. margins. The intrusive intrusive contacts contacts with volcanic—sedimentary volcanic-sedimentary country country rocks are extremely extremely complex. complex. Many rocks rocks previously previously mapped mapped as as diorites, diorites, gneisses, and syenites are actually contaminated—assimilated contaminated-assimilated contact contact lithologies. lithologies. Beyond the foliated foliated pluton—margins pluton-margins there there are are zones zones of of fine—grained and/or fine-grained gray "diorites" **diorites** and/or mixed mafic—felsic mafic-felsic rocks——texturally rocks--texturally "gneisses" "gneisses" with alternating bands of of granitic granitic and and mafic minerals. Where gneissic in aspect, these mechanically-mixed mechanically—mixed lithologies lithologies are are nearly nearly identical identical from the the plutons, plutons, in appearance with dated Archean gneisses. gneisses. Further away from only dikes and stringers of intrusive intrusive material are are present present in in the the country country rocks and intensity of metamorphism and and deformation deformation commonly commonly decreases. decreases. I I �I The presence of of Proterozoic Proterozoic gneissic gneissic zones zones in in central central Wisconsin Wisconsin has has possible possible tectonic implications implications for for at at least least some some of of the the Archean Archean and and supposed supposed Archean gneisses. gneisses. Geochronology and and geology geology have have been been thus thus far far unsuccessful unsuccessful in in specifying the timing at at which which these these rocks rocks became became gneisses. gneisses. In only a few few (Linwood and cases (t.inwood and Pittsville) Pittsville) are are the the gneissic gneissic structures structures almost certainly pre—Penokean. pre-Penokean. In other cases, Proterozoic tectonism tectonism probably probably converted converted Archean granite/greenstone granite/greenstone lithologies lithologiesinto intogneisses gneissesand andamphibo].ites. amphibolites. Orientations of minor folds folds and and foliations foliations vary vary widely widely throughout throughout the the area which has aa general general east—west east-west structural structural grain. grain. These structures and foliation within the plutons are generally parallel parallel near near the the pluton pluton contacts. contacts. Regional structural trends are reoriented within aa few few kilometres kilometres of of the the 1.5 1.5 Wolf River batholith, aa 9000 Ga Wolf 9000 km2 anorogenic anorogenic granite granite complex. complex. Metamorphism throughout throughout the the area area is is generally generally low low grade, grade, except except in in the the older older gneisses, gneisses, near the Wolf River batholith, and and in in some some other other contact contact zones zones where where middle antphibolite—facies amphibolite-facies rocks rocks occur. occur. Very low low grade grade Baraboo Baraboo interval interval metasedimentary metasedimentary rocks rocks (1760 (1760 to to 1630 1630 Ma) Ma) tend to reflect the composition of granite/greenstone granite/greenstone units units which they they apparently Ferruginous quartzite, apparently overlie overlie in in much of of central central Wisconsin. Wisconsin. Ferruginous quartzite, chert, argillite, and fuchsitic quartzite are are in in contact contact or or are are near near mafic and and metasedimentary rocks exposed near felsic ultramafic Equivalent metasedimentary felsic ultramaf Ic lithologies. lithologies. plutons and volcanic rocks are commonly lighter plutons lighter colored colored and and more sericite—rich. sericite-rich 34 �I Keweenawan Structural Structural Features Features at at the the Base Base of of the the Duluth Duluth Complex Complex in in the the Keweenawan Dunka Pit near Babbitt, Minnesota Dunka Pit near Babbitt, Minnesota U TIMOTHY B. B. HOLST, HOLST, EUGENE EUGENE E. E. MULLENMEISTER, MULLENMEISTER, JOHN JOHN C. C. GREEN, GREEN, Department Department of of TIMOTHY Geology, and Natural Resources Research Institute, University of Geology, and Natural Resources Research Institute, University of Minnesota Duluth, Duluth, Duluth, Duluth, Minnesota Minnesota 55812, 55812,and and PAUL PAULW. W. WEIBLEN, WEIBLEN, Minnesota Department of Geology and Geophysics, University of Minnesota, Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota Minnesota 55i55 55455 Minneapolis, number of of faults faults and and folds folds affect affect Animikie Animikie Group Group Rocks Rocks of of the the AA number northeastern Mesabi Mesabi Range (Mullenmeister (Mullenmeister and and others, others, this this volume). volume). northeastern Range Several of of these these are are found found in in the the Dunka Dunka Pit Pit region. region. In In addition addition to to these these Several there are are structures structures found found in in Animikie Animikie Group Group rocks rocks in in the the Dunka Dunka Pit Pit in in there close proximity proximity to to the the Duluth Duluth Complex Complex that that are are found found nowhere nowhere else else in in the the close northeastern Mesabi Mesabi Range. Range. These features features include include tight tight to to isoclinal isoclinal northeastern These small-scale folds folds (amplitudes (amplitudes and and wavelengths wavelengths aa meter meter or or less), less), and and some some small—scale unusual, undulatory sub-horizontal faults, faults, here here termed termed detachment detachment unusual, undulatory sub—horizontal features features. . The small—scale small-scale folds folds occur occur in in the the cores cores of of larger—scale larger-scale folds folds The (amplitudes on the order of ten meters) and associated with the detachment (amplitudes on the order of ten meters) and associated with the detachment features, in in the the upper upper plate. plate. Fold Fold vergence vergence and and attitude attitude is is quite quite features, variable. The folds always occur within the uppermost Biwabik Formation variable. The folds always occur within the uppermost Biwabik Formation (the "A" "Av layer layer of of Erie Erie Mining Mining Company) Company) or or the the lower lower portion portion of of the the (the Virginia Formation. Formation. In In the the cores cores of of the the small—scale small-scale folds folds there there is is aa Virginia well-developed axial—planar axial-planar foliation foliation in in the the calcite calcitematrix. matrix. well—developed The detachment detachment features features are are well—defined well-defined faults, faults, which which have have variable variable The dips (usually (usually shallow) shallow) and and can can be be traced traced for for up up to to tens tens of of meters meters across across dips the pit pit wall. wall. The lower lower plate plate rocks rocks are are typically typically undeformed undeformed or or may may the The contain aa broad broad gentle gentle anticline, anticline, and and are are generally generally of of the theUCtI llClllayer layer of of contain the upper upper portion portion of of the the Biwabik Biwabik Formation. Formation. The The upper upper plate plate rocks rocks are are the typically strongly strongly folded, folded, and and consist consist of of the the "A" "Attlayer layer of of the the upper upper typically Biwabik, or or the the base base of of the the Virginia Virginia Formation. Formation. Thus Thus the the detachment detachment Biwabik, features are are observed observed to to remove remove stratigraphy stratigraphy in in each each case. case. Eight Eight such such features detachment features features have have been been defined defined to to date. date. detachment The proximity proximity of of the the small—scale small-scale folds folds and and detachment detachment features features to to the the The Duluth Complex and their absence elsewhere, and the axial-planar foliation Duluth Complex and their absence elsewhere, and the axial—planar foliation in the the recrystallized recrystallized calcite calcite hornfels hornfels establishes establishes the the age age of of these these in structures as Keweenawan (syn-intrusion). structures as Keweenawan (syn—intrusion). features could could be be the the result result of of aa regional regional compression, compression, although although These features These this seems least likely. The detachment features cut out stratigraphy in this seems least likely. The detachment features cut out stratigraphy in the manner of the listric normal faults of the Basin and Range, and may be the manner of the listric normal faults of the Basin and Range, and may be the result result of of aa regional regional extension, extension, perhaps perhaps associated associated with with mid—continent mid-continent the rifting during the emplacement of the Duluth Complex. The folds are then then rifting during the emplacement of the Duluth Complex. The folds are interpreted as as having having formed formed under under local local compression compression in in the the overriding overriding interpreted plate of of the the detachment detachmentfault. fault. Alternatively, Alternatively, these these features features could could be be the the plate result of of body body forces forces (gravity) (gravity) forming forming slumps slumps at at the the country country rock—magma rock-magma result interface at at the the time time of of intrusion. intrusion. interface 35 n �ECONOMIC ECONOMIC GEOLOGY GEOLOGY OF OF THE THE RARE RARE ELEMENT ELEMENT PEGMATITES PEGMATITES AT AT LILYPAD LILYPAD LAKE, LAKE, NORTHERN NORTHERN ONTARIO ONTARIO Hood, Hood, William William C., C., W.C. W.C. Hood Hood Geological Geological Consulting, Consulting, P.O. P.O. Box 1AO; Vanstone, Vanstone, Box 1026, 1026, Lac Lac du du Bonnet, Bonnet, Manitoba, Manitoba, ROE ROE lAO; Peter J., J., Tantalum Tantalum Mining Mining Corp., Corp., P.O. P.O. Box Box 2000, 2000, Lac Lac du du Peter Bonnet, Bonnet, Manitoba, Manitoba, ROE ROE lAO 1AO The The tantalum tantalum potential potential of of the the Lilypad Lilypad Lake Lake pegmatite pegmatite field field was was recognized recognized in in 1979 1979 during during an an exploration exploration program program by by Tantalum Tantalum Mining Mining Corporation Corporation of of Canada Canada Ltd. Ltd. Exploration Exploration for for tantalum tantalum and and other other rare rare metals metals was was prompted prompted at at that that time time by by strong strong demand demand and and rising rising prices. prices. Previous Previous exploration exploration of of these these pegmatites pegmatites had had concentrated concentrated mainly mainly on on lithium lithium mineralization. mineralization. Bedrock geochemical geochemical surveys, surveys, using using lithium lithium as as the the pathfinder pathfinder Bedrock element, element, were were successful successful in in locating locating several several mineralized mineralized pegmatite pegmatite dikes. dikes. Geological Geological mapping mapping to to determine determine the the extent, extent, orientation, and and structural structural environment environment of of these these pegmatites pegmatites orientation, was was followed followed by by drilling drilling to to evaluate evaluate their their size sizeand andgrade. grade. albiteThe best best tantalum tantalum mineralization mineralization was was found found to to occur occur in in albiteThe enriched enriched dikes dikes occupying occupying late— late- to to post-tectonic post-tectonic fracture fracture systems. systems. The The limited limited tonnage tonnage of of these these pegmatites, pegmatites, subeconomic subeconomic tantalum tantalum grades, grades, and and falling falling tantalum tantalum prices prices caused caused abandonment abandonment of of the the project project in in 1982. 1982. Several geological geological characteristics characteristics of of the the Lilypad Lilypad Lake Lake Several pegmatite pegmatite field field provide provide important important guidelines guidelines for for exploration exploration of of pegmatite—hosted pegmatite-hosted rare rare metal metal deposits. deposits. In In common common with with several several other other pegmatite pegmatite districts districts in in the the Superior Superior Province, Province, the the T.1ypad T.i-lypadpegmatites pepatites occur occur on on the the margin margin of of the the English English River River gneissic gneissic belt, belt, suggesting suggesting aa genetic genetic link link to to the the sedimentary sedimentary gneisses gneisses of of this this terrain. terrain. Although Although zoning zoning within within the the Lilypad Lilypad pegmatite pegmatite field field is is not not well-defined, well-defined, it it is is believed believed that that the the tantalum-bearing dikes dikes occupy occupy upper upper marginal marginal positions positions within within tantalum-bearing the the field. field. Detailed Detailed chemical chemical data data is is not not yet yet available available from from these these pegmatites, pegmatites, but but their their mineralogy, mineralogy, including including pollucite, pollucite, lepidolite, lepidolite, colored colored tourmalines, tourmalines, and and fluorite, fluorite,indicate indicateaa high high degree degree of of magma magma fractionation. fractionation. 36 �_____ _____ I FACIES INTERPRETATION F THE OF THE THE WOODS WOODS INTERPRETATION O OF THE BERRY BERRY RIVER RIVER FORMATION LAKE OF Johns, Precambrian J o h n s , G.W., G.W., P r e c a m b r I a n Geology G e o l o g y Section, S e c t i o n , Ontario O n t a r l o Geological G e o l o g I c a l Survey, S u r v e y , Toronto. Toronto. The T h e Berry B e r r y River R l v e r formation f o r m a t l o n (Warciub ( W a r c l u b group) g r o u p ) occurring o c c u r r l n g along a l o n g Long L o n g Bay and and Lobstick L o b s t l c k Bay Bay IInn tthe h e Lake L a k e of o f the t h e Woods Woods area a r e a is Is a 2 km hlck s e q u e n c e oof f ccaIc a l c alkaline alkal lne d a c l t e pyroclastlc pyroclastlc a 2 km tthick sequence dacite rrocks. ocks. Sub units u n l t s within w l t h l n the t h e sequence s e q u e n c e were w e r e deposited d e p o s l t e d by b y a variety v a r l e t y of o f volcanic v o l c a n l c processes. processes. Sub Fades F a c l e s mapping m a p p l n g and a n d the t h e development d e v e l o p m e n t of of a a fades f a c l e s model m o d e l has h a s allowed a l l o w e d assessment a s s e s s m e n t of o f base b a s e metal metal potential. potential. The formation f o r m a t l o n was deposited d e p o s l t e d by b y two t w o phases p h a s e s of o f volcanism. volcanism. The o l d e r event e v e n t has has aa base b a s e of of The The older r e d e p o s l t e d ttuff uff o verl aln b y p r o x l m a l tto o d l s t a l ccoarse o a r s e and f lne p y r o c l a s t i c rocks r o c k s Including l n c l udlng redeposited overiain by proximal distal and fine pyroclastic he p r o x l m a l tto o ddistal l s t a l ppyrodlastlc y r o c l a s t l c ffades a c l e s on on the t h e west west unlts o a s h flow f l o w tuft. tuff. units off ash Overlying tthe proximal a r e redeposited r e d e p o s l t e d coarse c o a r s e pyroclastic p y r o c l a s t l c rocks r o c k s with w l t h interbedded l n t e r b e d d e d wackes. wackes. On the t h e east e a s t the t h e proximal p r o x lmal are tto o d lstal p y r o c l a s t l c rocks r o c k s were w e r e intruded l n t r u d e d by by subvolcanic s u b v o l c a n l c rocks. rocks. A thick t h l c k ash a s h flow f l o w tuft t u f f unit unit distal pyroclastic associated IIs s a s s o c l a t e d with w i t h this t h l s younger y o u n g e r event. event. O u t w a r d from f r o m the t h e subvolcanlc s u b v o l c a n l c rocks r o c k s and overlying overl ylng Outward tthe h e ash a s h flow f l o w tuft t u f f are a r e proximal p r o x l m a l coarse c o a r s e pyrociastlc p y r o c l a s t l c rocks. rocks. r o x l m a l tto o d l s t a l deposition d e p o s l t l o n facies facles v a r l e s ffrom rom d e b r l s flows f l o w s Iin n tthe he The The extensive pproximal distal varies debris e a s t , doubly d o u b l y graded g r a d e d subaqueous s u b a q u e o u s pyrociastic p y r o c l a s t l c flows f l o w s and a n dfal f a 1I—out I - o u t units u n l t s in I n tthe h e central c e n t r a l portion, portion, east, tto o debris d e b r l s flows f l o w s in I n the t h e west. west. D e b r l s flows f l o w s are a r e massive, m a s s l v e , Indistinctly l n d l s t l n c t l y bedded, b e d d e d , in I n tthe h e east east Debris and Subaqueous uff a n d poorly p o o r l y bedded b e d d e d in I n the t h e west. west. S u b a q u e o u s pyrociastic p y r o c l a s t l c flows f l o w s are a r e doubly d o u b l y graded g r a d e d with w l t h aa ttuft br.ccia The b r e c c l a base b a s e overlaln o v e r l a l n by b y thickly t h l c k l y laminated I a m l n a t e d tufts. tuffs. T h e tal f a l l -i—out o u t uunits n l t s cconsist o n s l s t of o f thinly thinly bedded horizons. p u m l c e o u s lap l a pliii f l l l tuft t u f f horizons. b e d d e d tufts t u f f s and a n d pumiceous lnterbedded with deposition lnterbedded w i t h tthe h e pproximal r o x l m a l tto o ddistal lstal d e p o s l t l o n ffades a c l e s are a r e conformable, conformable, discontinuous f low tuffs d l s c o n t l n u o u s massive m a s s l v e quartz—feldspar q u a r t z - f e l d s p a r and a n d feldspar f e l d s p a r porphyry p o r p h y r y ash a s h flow t u f f s with w i t h varied varled grain a rrange of quartz/feldspar g r a l n size, size, a ange o f q u a r t z / f e l d s p a r phenoclast p h e n o c l a s t ratios, r a t l o s , and and horizons h o r l z o n s of o f llithic l t h l c ciasts. clasts The distal The d l s t a l rredeposited e d e p o s i t e d ffades a c l e s Is I s reworked r e w o r k e d tuft, t u f f , lapilli l a p l l l l tuft, t u f f , heterol h e t e r o lithic l t h l c debrIs d e b r l s flow f low and Epiclastic a n d laher l a h a r with w l t h interbedded l n t e r b e d d e d wacke. wacke. E p l c l a s t l c teldspathic f e l d s p a t h l c wacke and a n d quartz—feldspar q u a r t z - f e l d s p a r wacke Wac k e Iis s ccorrelative o r r e l a t l v e with w l t h the t h e pyroclastic p y r o c l a s t l c deposits. d e p o s It s The eastern The e a s t e r n portion p o r t l o n of o f the t h e Berry B e r r y River R l v e r formation f o r m a t l o n Iis s vvent e n t ffades a c l e s chaotic, c h a o t l c , massive, masslve, quartz—feldspar q u a r t z - f e l d s p a r porphyry p o r p h y r y containing c o n t a l n l n g rafts, r a f t s , blocks b l o c k s and a n d xenol x e n o l liths t h s oof f ppyroclastic y r o c l a s t l c material. Outward O u t w a r d ffrom r o m tthe h e vvent e n t ffades a c l e s is I s the t h e proximal p r o x l m a l depositional d e p o s l t l o n a l ffades a c l e s coarse c o a r s e homolithic homo1 l t h l c pyroclastic ground The surge p y r o c l a s t l c rrocks o c k s with w l t h tthin h l n lnterbedded lnterbedded g r o u n d surge s u r g e or o r cloud c l o u d surge s u r g e tufts. tuffs. The surge deposits s h a l l low o w wwater a t e r environment. d e p o s i t s ssuggest uggest p y r o c l a s t l c flow f l o w deposition d e p o s l t l o n Iinn a shal pyroclastic environment. pml Point Bay Group Group I::i.I Warciub WarclubGroUp Group .-:-J Snake snakeBay BayFormation Fornation Granitoids ,j Granltoids -- BERRY RIVER FORMATION FORMATION UNITS OLDER UNITS OLDER diabase dike ashflow flow tuffs tuffs Jash fades — fault -vent vent facies proximal deposition (shallow (shallow water) -proximal — ldhk9Ic contact lithologic contact proximal—dIstal deposition (component of redeposition) redeposition) proximal-distal deposition -— stratigraphic distal redeposition distal redeposition stratigraphiccontact contact 0 1 2 3 4 5 fades boundary facies boundary 2__J epiclastic facies I .. ..... 23 - . .. kll01~1€atr • + •++ * I I I I I �I of aa Subaqueously Subaqueously Emplaced Emplaced V Volcanic Horizon Documentation of olcanic H orizon iin n tthe h e Upper Portage P o r t a g e Lake Volcanics, Volcanics, Keweenaw Peninsula, P e n i n s u l a , Michigan. Michigan. Rodney C. C . Johnson (Dept. (Dept. of of Geol. Geol. and and Geol. Geol. Engrg., Engrg., Michigan Michigan Technological Technological University, U n i v e r s i t y , Houghton, MI M I 49931) 49931) The Portage P o r t a g e Lake Volcanics V o l c a n i c s are a r e a series s e r i e s of of subareal s u b a r e a 1 flood f l o o d basalts b a s a l t s in i n which which to to date This d a t e no subaqueous igneous igneous activity a c t i v i t y has h a s been been documented. documented. T h i s paper p a p e r documents documents horizon within tthe h e eexistence x i s t e n c e oof f aa hhyaloclastic yaloclastic h orizon w i t h i n the t h e Portage P o r t a g e Lake Volcanics Volcanics (Figure 1). This minimum lateral ). T h i s hhorizon o r i z o n hhas a s aa minimum l a t e r a l extent e x t e n t along a l o n g strike s t r i k e of of (Figure 1 aapproximately p p r o x i m a t e l y 24 km from Owl Creek in i n the t h e northeast n o r t h e a s t to t o Seneca Seneca Lake Lake in i n the the southwest ppart of the Peninsula southwest a r t of t h e Keweenaw P e n i n s u l a and a thickness t h i c k n e s s of of between between 10 m. 1 0 and and 20 20 m. The hyaloclastic h y a l o c l a s t i c horizon h o r i z o n typically t y p i c a l l y lacks l a c k s any any textural t e x t u r a l homogeneity homogeneity either either vertically orr h horizontally of more more tthan few m nters. vertically o o r i z o n t a l l y oover v e r ddistances i s t a n c e s of h a n aa few e t e r s . In I n general, generaly tthe h e hhyaloclastic y a l o c l a s t i c hhorizon o r i z o n lies l i e s anywhere between two two textural t e x t u r a l end end members——a members--a Pillowed ppillowed i l l o w e d lava l a v a sequence and a true t r u e hyaloclastite. hyaloclastite. P i l l o w e d lava l a v a sequences s e q u e n c e s are are vesicular composed oof f eelliptical l l i p t i c a l to t o amoeboid v e s i c u l a r pillows. p i l l o w s . Vesicles V e s i c l e s are a r e commonly commonly cconcentric o n c e n t r i c and occasionally o c c a s i o n a l l y form form pipes. p i p e s . These pillows p i l l o w s frequently f r e q u e n t l y exhibit e x h i b i t chill chill hyalocalstite margins or o r "rinds", " r i n d s 1 ' , concentric c o n c e n t r i c cracks c r a c k s and and radial r a d i a l joints. j o i n t s . The h yalocalstite composed of of vvesicular, iis s composed e s i c u l a r , angular a n g u l a r fragments. f r a g m e n t s . Fragments Fragments rrange a n g e in i n size s i z e from blocks aash—sized s h - s i z e d to t o "rinds" " r i n d s " and b l o c k s from pillows. p i l l o w s . The smaller s m a l l e r fragments f r a g m e n t s are are frequently is f r e q u e n t l y ffinely i n e l y fractured f r a c t u r e d resembling r e s e m b l i n g perlitic p e r l i t i c texture. t e x t u r e . The hyaloclastite h y a l o c l a s t i t e is p r e h n i t e , epidote, e p i d o t e , microcline, microcline, very v e r y colorful c o l o r f u l due to t o the t h e secondary s e c o n d a r y minerals: m i n e r a l s : prehuite, native cchlorite, h l o r i t e y calcite, c a l c i t e , quartz, q u a r t z , and n a t i v e copper. copper. Field F i e l d work was conducted conducted at a t outcrops o u t c r o p s on o n Owl O w l Creek, C r e e k , near n e a r the t h e Copper Copper Falls F a l l s Mine, Mine, pillowed with and on Eagle E a g l e River. R i v e r . The outcrop o u t c r o p oon n Eagle E a g l e River R i v e r is is a a p i l l o w e d lava l a v a ssequence equence w ith p i l l o w s are a r e approximately a p p r o x i m a t e l y 50 50 cm cm in i n diameter, diameter, hhyaloclastite y a l o c l a s t i t e draped on o n top. t o p . The pillows have w well have e l l developed chill c h i l l margins that t h a t are a r e accentuated a c c e n t u a t e d by by red r e d oxidation, o x i d a t i o n , sparse sparse concentric O w l Creek Creek is is c o n c e n t r i c vvesicles, e s i c l e s , and contain c o n t a i n few pipe p i p e vesicles. v e s i c l e s . The outcrop o u t c r o p on o n Owl a p pillow—bearing i l l o w - b e a r i n g hyaloclastite. h y a l o c l a s t i t e . Pillows P i l l o w s range r a n g e in i n size s i z e from from 10 1 0 cm cm up u p to t o 11 mm and and Pillows occur are unoriented are u n o r i e n t e d in i n aa matrix m a t r i x of of hyaloclastite. hyaloclastite. P illows o c c u r singularly s i n g u l a r l y or o r in in iinterdigitated n t e r d i g i t a t e d masses. They generally g e n e r a l l y exhibit e x h i b i t well w e l l developed developed chill c h i l l margins, margins, concentric c o n c e n t r i c vvesiculation, e s i c u l a t i o n , concentric c o n c e n t r i c cracking, c r a c k i n g , radial r a d i a l joints, j o i n t s , and and occasionally occasional~y iinternal n t e r n a l cavities. c a v i t i e s . The hyaloclastite h y a l o c l a s t i t e occasionally o c c a s i o n a l l y exhibits e x h i b i t s crude c r u d e layering l a y e r i n g and and hyaloclastite Owl grading. wl g r a d i n g . An accurate a c c u r a t e estimation e s t i m a t i o n of o f the t h e thickness t h i c k n e s s oof f the the h y a l o c l a s t i t e oon n O Creek was n not o t possible p o s s i b l e since s i n c e the t h e horizon h o r i z o n is i s cut c u t by by aa fault. fault. The hyaloclastic h y a l o c l a s t i c horizon h o r i z o n has, h a s , in i n the t h e past, p a s t , been been included i n c l u d e d in i n aa unit u n i t called c a l l e d the the Ashbed, a frequently Ashbed includes Ashbed, f r e q u e n t l y mined horizon. h o r i z o n . The Ashbed i n c l u d e s rocks r o c k s that t h a t have been with ccharacterized h a r a c t e r i z e d aas s aa ppyroclastic y r o c l a s t i c flow flow w i t h scorreaceous, s c o r r e a c e o u s , highly h i g h l y oxidized, o x i d i z e d , and and ffrequently r e q u e n t l y welded textures. t e x t u r e s . Thus, Thus, as a s currently c u r r e n t l y shown shown on o n published p u b l i s h e d geological geological maps the i s sometimes sometimes the t h e pyroclastic p y r o c l a s t i c horizon h o r i z o n and and sometimes sometimes the the t h e Ashbed is E a g l e River R i v e r both b o t h horizons h o r i z o n s occur o c c u r with w i t h the t h e pyroclastic pyroclastic hhyaloclastic y a l o c l a s t i c horizon. h o r i z o n . On Eagle Ashbed and the t h e stratigraphically s t r a t i g r a p h i c a l l y separatal separated hhorizon o r i z o n identified i d e n t i f i e d aass the t h e Ashbed hyaloclastic h y a l o c l a s t i c horizon h o r i z o n unrecognized. unrecognized. The hyaloclastic d e s c r i p t i o n by Huber h y a l o c l a s t i c horizon h o r i z o n may crop c r o p out o u t on o n Isle I s l e Royale. Royale. A description (1975) of of aa ppyroclastic Ashbed and a picture (1975) y r o c l a s t i c uunit n i t ssimilar i m i l a r tto o tthe h e Ashbed p i c t u r e suggests s u g g e s t s it i t may may be the be t h e hyaloclastic h y a l o c l a s t i c horizon. h o r i z o n . The stratigraphic s t r a t i g r a p h i c position p o s i t i o n of of the t h e Isle I s l e Royale Royale unit unit of tthe horizon/Ashbed oon n the t h e Keweenaw Peninsula. Peninsula. iis s ssimilar i m i l a r tto o tthat h a t of h e hhyaloclastic y a l o c l a s t i c horizonfAshbed Although not Royale uunit may be be ccorrelatable with n o t seen s e e n by the t h e author a u t h o r tthis h i s IIsle s l e Royale n i t may orrelatable w ith the hyaloclastic on the h y a l o c l a s t i c horizon horizon o n the t h e Keweenaw Peninsula. Peninsula. 3388 I �I The presence p r e s e n c e of of the t h e hyaloclastic h y a l o c l a s t i c horizon h o r i z o n is i s significant s i g n i f i c a n t in i n that t h a t it it confirms confirms of aa body of of w water tthe h e eexistence x i s t e n c e of a t e r concurrent c o n c u r r e n t with w i t h volcanism. volcanism. T his m i g h t be This might consistent with Livnats (1983) (1983) hypothesis, h y p o t h e s i s y based based on o n oxygen oxygen isotope i s o t o p e data, d a t a y that that consistent w i t h Livnat's which m mineralized Lake V Volcanics were ssea water, tthe h e ffluids l u i d s which i n e r a l i z e d tthe h e PPortage o r t a g e Lake o l c a n i c s were ea w a t e r y aat t least least orr n not of w water iin n part. p a r t . However, However, whether o o t the t h e body of a t e r related r e l a t e d to t o the t h e hyaloclastic hyaloclastic horizon i s not n o t known. known. h o r i z o n was sea s e a water w a t e r or o r fresh f r e s h is I I I I I I I Figure F i g u r e 1. 1. Approximate location l o c a t i o n of of hyaloclastic h y a l o c l a s t i c horizon horizon l i n e ) and g e n e r a l i z e d stratigraphy s t r a t i g r a p h y near n e a r Eagle E a g l e River. River. (dashed line) generalized References: References : Hubery N . K e Y 1973, USGS Prof. P r o f . Paper P a p e r No. No. 754—C, 754-Cy p. p. C1—C32. Cl-C32. Huber, N.K., L i v n a t , A. 1983 Ph.D. Ph.D. Dissertation, D i s s e r t a t i o n , University U n i v e r s i t y of of Michigan, Michigany Livnat, A., 1983, 225 .p. 225 p. I I I I I I I 39 I I I �I ot 'Pne Petrology Petroloqy and and Sedimentation Sed~mentatlon ot tne tile iower Lower Proterozoic Protero~olc The Barron Barron tjuartzite, uuaxtzlte, Northwestern Aortnwestern Wisconsin hlsconsin University at ot dendy Jo Jo Johnson Johnson (Dept. (Dept. of of Geology, Geo.Logy,University Wendy Minnesota—Duluth, innesota 55812) Pilnnesota-Duluth, Duluth, Uuluth, Yiinnesota 55812 ) The The Barron Barron Quartzite Quartzite of of northwestern northwestern Wisconsin Wisconsin is is aa fine—grained, fine-grainedf quartz—cemented, quartz-cemented, butt butt to to red rea quartz quartz arenite arenlte with xlth scattered scattered quartz quartz pebbles pebbles and and aa thin thin basal basal quartz-pebble quartz-pebble thickness of of the the Barron Barron is 1s at at least lsast 225 2 2 5 inI I ~ conglomerate. Tne Tne thickness conglomerate. shown by drill core) and may be greater than 400 in. (as shown by drill core) and may be greater than 400 m. (as ?iafic dikes dlkss cut cut the the Barron Barron Uuartzite Quartzite out out are are as as yet yet undated. unaated. £4afic The Quartzite The primary primary framework framework component component of of the the Barron Barron Quartzite is common common quartz quartz (75%). ( 7 5 % ) . Polycrystalline Polycrystalline quartz quartz (grains [grainswitn vi1cr-i is component crystals), crystals), stretched stretched polycrystalline polycrystalline quartz quartz to 55 component 22 to (composites (composites of o numerous, numerous, suctured suctured crystals), crystals), recrystallized recrystallized quartz quartz (grains (grains made made up up of of numerous, numerous, small, small, polygonal polygonal crystals) 16% crystals) and and vein vein quartz.together quartz.togethermake make up up approximately approximately L6% of framework framework grains. grains. Multicycle ~ulticyclequartz quartz grains grains (common (common of quartz continuous of quartz grains grains which which have haveoptically optica~ly continuousoveryrowttis overgrowtt~s of quartz by other other quartz that that have have been been abraded abraded and and surrounded surrounded by overgrowths) are are also also present. present. Chert Cnert and and iron—formation iron-fornatlon overgrowths) rock rock fragments fragments occur occur but but are are rare. rare. Feldspar Feldspar is is absent. absent. Quartz Quartz cement, cement, which which occurs occurs as as optically optically continuous continuous overgrowths overgrowths on on quartz quartz grains, grains, is is common common (approximately (approximately9%) 9%) and and hematite hemstite cement cement constitutes constitutes less lessthan than1%. 1%. The The heavy heavy mineral suite suite is is composed composed almost ,almostentirely entirely of of rounded rounded zircon zircon mineral with with minor minor rounded rounded tourmaline tourmaline and and rutite, rutile, and and minor minor magnetite. magnetite. AA possible possible depositional depositional environment environment for for the the Barron aarron Quartzite plain which braidedal.LuviaJ. alluvial plain wnlch was was superseded supe~seded Quartzite is isaabraided by aa marine inarine shelf shelf environment. environment. Paleocurrent Paleocurrent data data are are by pattern towards variable. Most Nost localities localitiesshow showa auniiuodai. unlmodal pattern towards variable. the tne south, south, indicating indicating sediment sediment transport transport from from north north to to south. however, fiowever, polymodal polyinodal and and bimodal—bipolar bimoaal-9ipolar patterns patterns are are south. also present present at at some some outcrops. outcrops. AA unimodal unimodal pattern pattern probably probably also indicates environment while indicates aa fluvial fluvlal depositionai. dspositlonal environment while aa bimodal-bipolar bimoual-bipolar pattern pattern could could suggest suggsst aa tidally-influenced tidally-lnfluenceu marlne depositional depositional environment. environfuent. marine The The Barron Barron Quartzite Quartzite is is probably correlative correlative with with several quartzites in In the the iake L ~ K S several of of the tne other other Precambrian Precambrian quartzites Superior region, region, including including the the Baraboo, Baraboo, Sioux, Slouxf Flambeau, Flambeau, Superior Quartzites. Ot Ot these, these, the tne Baraboo Baraboo is 1s waterloo,and and£4cCaslin ~tlcCaslinQuartzites. aterloo, the the best best dated, dated, probably probably having havlng been been deposited deposited between between 1760 L760 and 1630 Lb30 Ma ~4a(Van (VanSchinus, Schmus, 1978; Van Schmus Schmus and and Bickiord, Bickiorci, and l98L). 1981.). N.K., l97Bf Geochronoiogy Geochronology of of the the southern southern Van Schmus, Schmus, W.R., Van 1978, Wisconsin rhyolites rhyolites and and granites: granitss: Geoscience Geoscience Wisconsin, hisconsln, Wisconsin v. 2, 2, p. p. 19—24. 19-24. v. 40 �I Schmus, 'PJ.L<.~ W.R., aand 1q81, PProtrozoic n d Sicktord, i c k k ~ r dij.E., q~. E . , 1981, rotsrozoic Van Schmust c n r o n o l o g y and a n d evolution evolution o of tne tilemicicontinent m i c i c o n t ~ n e n tregion rsgion crironology in Kroner, North A . * ed., ed.* Precambrian P r e c a m b r ~ a nelate Plate N o r t h America: in K r o n e r , A., Tectonics, * l ' e c t o n i c s t Elsevier, ~ l s e v G r *New Sew york, YorK* p. p . 261—296. 261-296. I I I I I I I I I I •1 I •1 I 41 I I I �and Hecla Hecla Conglomerate, Conglomerate, Caliche Paleosol P a l e o s o l in i n the t h e Lower Lower Part P a r t of of the t h e Caluinet Calumet and Mine, Calumet, Centennial Mine, Calumet, Michigan J. Kalliokoski J. K a l l i o k o s k i and Edwin J. J. Welch (Dept. (Dept. of Geol. Geol. and and Geol. Geol. Engrg., Engrg., University, M I 49931) 4993 1 ) Michigan Technological U n i v e r s i t y , Houghton, Houghton, MI The Calumet Calumet and Hecla Conglomerate, Conglomerate, a Keweenawan Keweenawan interfiow i n t e r f low sedimentary sedimentary unit unit about 1.1 b.y. b.y. in tthat h a t is i s about i n age consists c o n s i s t s aatt the t h e Centennial Mine of of aa felsitic felsitic upper p part and of of about about 1—2 of siltstone conglomerate upper a r t and 1-2 m of s i l t s t o n e and shale s h a l e along along the t h e base base fine—grained sediments there 1A). In I n these t h e s e fine-grained t h e r e is i s a complex complex sub—mature sub-mature (Figure 1A). profile represented by an upward increase ccaliche a l i c h e ssoil oil p r o f i l e represented i n c r e a s e in i n calcite c a l c i t e and and corresponding changes in corresponding i n ccalcite a l c i t e structures s t r u c t u r e s (Figure ( F i g u r e 1B) (Welch, (Welch, 1977). 1977). There is is All aalso l s o ccaliche a l i c h e ccalcite a l c i t e in i n the t h e felsitic f e l s i t i c conglomerate. conglomerate. A l l of of this t h i s calcite c a l c i t e predates predates period of of rregional tthe h e period e g i o n a l eepidote p i d o t e aalteration l t e r a t i o n as a s demonstrated on parts p a r t s of of the the 35—level where where tthis has been altered 35-level h i s ccalcite a l c i t e has a l t e r e d to t o epidote. epidote. Introduced ccalcite weight percent Introduced a l c i t e vvaries a r i e s from about 50 tto o 60 weight percent in i n some some upper layers of tthe weight p percent l a y e r s of h e bbasal a s a l uunit n i t to t o 10 weight e r c e n t and less l e s s in i n faintly f a i n t l y veined mudstone (Figure (Figure 1B). 1B). The introduced calcite c a l c i t e occurs in i n an upward grading grading microscopic v veinlets, sequence aas s microscopic e i n l e t s , thin t h i n rims on basalt b a s a l t clasts, c l a s t s , 33 cm cm oval o v a l nodules, nodules, horizontal h o r i z o n t a l lenticles l e n t i c l e s that t h a t may represent r e p r e s e n t coalesced coalesced and and flattened f l a t t e n e d nodules, nodules, K—fabrici is multi—generation veinlets, multi-generation v e i n l e t s , and and as a slayers l a y e r with s withK—fabric. K-fabric. K-fabric s the the designation with d e s i g n a t i o n ffor o r calcite—rich c a l c i t e - r i c h llayers ayers w i t h ffloating l o a t i n g clasts, c l a s t s ,produced produced by by under shallow overburden conditions replacement ccalcite a l c i t e under c o n d i t i o n s (Gile ( G i l e et e t al., a l . , 1965). 1965). overlain The above ttextural e x t u r a l sequence is is o v e r l a i n locally l o c a l l y by a second second similar s i m i l a r sequence. sequence. major features IIn n tthin h i n ssections e c t i o n s tthe h e major f e a t u r e s are a r e the t h e partial p a r t i a l to t o complete complete textural textural replacement of of feldspar replacement f e l d s p a r by calcite c a l c i t e and the t h e corresponding relative r e l a t i v e increase i n c r e a s e in in the proportions of the the p r o p o r t i o n s of t h e quartz q u a r t z and opaque components, components, and and the t h e exfoliation e x f o l i a t i o n of of biotite b i o t i t e cclasts l a s t s and clay c l a y chips c h i p s by introduced introduced calcite. c a l c i t e . Textures and and structures structures suggesting carbonatization c a r b o n a t i z a t i o n at a t a shallow depth are a r e the t h e K—fabric, K-fabric, and and aa soil soil mjcroreljef m i c r o r e l i e f structure s t r u c t u r e —— a llocal o c a l aantiforinal n t i f o r m a l f flexure l e x u r e iin n ccalichefied a l i c h e f i e d shale. shale. Subsequent Subsequent compaction is i s suggested by the t h e lensoid l e n s o i d shape shape of of calcite c a l c i t e nodules, n o d u l e s , and and wrinkles in i n vertically v e r t i c a l l y oriented o r i e n t e d calcite c a l c i t e veinlets. veinlets. -- The fine—grained fine-grained basal b a s a l unit u n i t has undergone undergone chemical chemical alteration a l t e r a t i o n during during ccarbonatization a r b o n a t i z a t i o n under ambient surface s u r f a c e conditions c o n d i t i o n s so s o that t h a t aa soil s o i l forming forming process process However, in and a profile p r o f i l e can can be identified. i d e n t i f i e d . However, i n the t h e conglomerate the t h e ccalcite alcite occurs o c c u r s in i n a less—recognizable less-recognizable form. form. White sparry s p a r r y calcite c a l c i t e rims pebbles pebbles and and fills fills interstices pebbles, i n t e r s t i c e s between p e b b l e s , generally g e n e r a l l y along subhorizontal s u b h o r i z o n t a l zones zones (Figure ( ~ i g u r elB). 1 ~ ) . This texture This t e x t u r e resembles resembles that t h a t described d e s c r i b e d by Gile G i l e and others o t h e r s (1966) (1966) as a s an an iintermediate n t e r m e d i a t e stage s t a g e of of caliche c a l i c h e in i n gravelly g r a v e l l y soils. s o i l s . Such cemented gravel g r a v e l can can be be unit described of it i t occurs in i n the t h e lower lower fine—grained fine-grained u nit d e s c r i b e d also a l s o as a s calcrete. c a l c r e t e . A bed of ((Figure F i g u r e IB). 1B). These kinds of of calcite—cemented calcite-cemented conglomerates conglomerates have have been been reported reported from an area a r e a that t h a t extends from 30 km km east e a s t of of Centennial Centennial (Davidson (Davidson et e t al., a l . , 1955) 1955) about 20 20 kkm southwest of of C Centennial, m southwest e n t e n n i a l , and are a r e very common in i n the t h e Copper Copper Harbor Harbor tto o about Conglomerate both on the (Wolff and and Huber, Huber, 1973). 1973). t h e peninsula and on Isle I s l e Royale Royale (Wolff Because nnative copper is abundant in Because a t i v e copper i s nnot o t abundant i n calcite—rich c a l c i t e - r i c h portions p o r t i o n s of of conglomerates, conglomerates, tthere h e r e is i s tthe h e ssuggestion u g g e s t i o n tthat h a t the t h e quantity q u a n t i t y and distribution d i s t r i b u t i o n of of native n a t i v e copper copper in in and H H conglomerate may may have been controlled tthe h e CC and c o n t r o l l e d by a pre—existing p r e - e x i s t i n g pedogenic pedogenic ccalcite. alcite. New analysis ked ssparry a n a l y s i s on on aa hand—p hand-picked p a r r y cca cite l c i t e from from aa calcite c a l c i t e rich r i c h layer l a y e r in i n the the +20.9; <S basal C: b a s a l unit u n i t gave gave values v a l u e s ((d 0: +20.9; C: —1.0) -1.0) that t h a t are a r e indistinguishable indistinguishable obtained by Livnat (1983) on all from tthose h o s e obtained a l l types t y p e s of of calcites c a l c i t e s in i n the t h e Portage Portage Lake Volcanics and and the t h e Copper Harbor Conglomerate. Conglomerate. He concluded that t h a t the the ranges in ccajites a l c i t e s had had undergone undergone homogenization homogenization and and that t h a t their t h e i r narrow ranges in C v values a l u e s denoted a CO2 CO source source from from either e i t h e r single s i n g l e magma or o r from from two two sources, sources, 2 one aa Precambrian Precambrian limestone. limestone. This probably probably was was the t h e caliche. caliche. 42 - �_________ ________ _________ _______ ________ _________ ___________ _________ The caliche c a l i c h e is i s interpreted i n t e r p r e t e d to t o have developed developed in i n slowly s l o w l y aggrading a g g r a d i n g sediments sediments This h i s ttook o o k place p l a c e during during were deposited tthat h a t were d e p o s i t e d on a basalt—floored b a s a l t - f l o o r e d fluvial f l u v i a l plain. plain. T of sslope of tthe tthe h e initial i n i t i a l sstages t a g e s of l o p e rreversal e v e r s a l of h e lava l a v a pplain, l a i n , ffrom r o m southerly s o u t h e r l y to to highly c a r b o n a t e accumulation in i n sediments sediments rrequires equires a h i g h l y seasonal seasonal northerly. n o r t h e r l y . Such carbonate and rrepresents about 15,000 y years e a r s of of weathering. weathering. ttemperature e m p e r a t u r e oor r ttropical r o p i c a l cclimate l i m a t e and e p r e s e n t s about paleolatitude been rreported The corresponding c o r r e s p o n d i n g Keweenawan p a l e o l a t i t u d e hhas a s been e p o r t e d tto o be about 30 degrees d e g r e e s north. north. o _io e0Ocp IIIIl l ?? - IIIIl l I1 c • 0 w 1•L• a, Ca a, E 2 a, - -— - - 'I—Il' 11-111 II — — a, o0 60 wt.% CALCITE CALCITE Generalized G e n e r a l i z e d ssections e c t i o n s at a t the t h e base b a s e of of tthe h e Calumet Calumet and Hecla Conglomerate. A,, stratigraphy; A s t r a t i g r a p h y ; thickness t h i c k n e s s about about 1.5 m; m; B, B , Modes of of occurrence o c c u r r e n c e of of calcalcite c i t e ((unpatterned). u n p a t t e r n e d ) . Numbers Numbers denote denote morphologic sstage t a g e of of the t h e caliche; caliche; calcite c a l c i t e abundance by chemical analysis. analysis. . A I I I I I I I I I B I References References Davidson, of the Davidson, E.S. E.S. and others, o t h e r s , 1954, Bedrock geology of t h e Mohawk Quadrangle, U.S. Geol. Michigan: U.S. Geol. Quadrangle Quadrangle Map Map GQ54, GQ54, scale s c a l e 1:2400. 1:2400. master L.H. and others, G i l e , L.H. o t h e r s , 1965, 1965, The K horizon: horizon: a m a s t e r soil s o i l horizon h o r i z o n of of carbonate carbonate Gile, Soil accumulation: S o i l Science, S c i e n c e , v. v. 99, 9 9 , p. p. 74—82. 74-82. Gile, Gile, L.H. and o others, genetic L.H. t h e r s , 1966, Morphological and g e n e t i c sequences in i n carbonate carbonate accumulation in i n desert d e s e r t soils: s o i l s : Soil S o i l Science, S c i e n c e , v. v. 101, 1 0 1 , p. p. 347—360. 347-360. Livuat, Alexander, 1983, Metamorphism and copper m mineralization i n e r a l i z a t i o n of of the t h e Portage Portage L i v n a t , Alexander, unpub. Ph.D. Univ. of Lake Lava Series, S e r i e s , northern n o r t h e r n Michigan: Michigan: unpub. Ph.D. thesis,. t h e s i s , Univ. of Mich., Mich., Arbor, 270 Ann Arbor, 270 p. p. 1 1 I 1 Origin of the mudstone at Welch, Edwin JJ., . , 1977, 1977, O r i g i n of t h e caliche—bearing c a l i c h e - b e a r i n g mudstone a t the t h e base b a s e of of the Calumet and and Hecla Hecla Conglomerate, Conglomerate, C Centennial Mine, Houghton Houghton County, County, MichiMichit h e Calumet e n t e n n i a l Mine, Unpub. M.S. M.S. thesis, Mich. Tech. Tech. Univ., Univ., Houghton, Houghton, M Mi, gan: Unpub. t h e s i s , Mich. i , 53 p. p. R.G., and Huber, 1973, The Copper Harbor Conglomerate (middle (middle Wolff Wolff,, R.G., Huber, N.K., N.K., 1973, U.S. Keweenawan) on Isle i t s regional r e g i o n a l implications: i m p l i c a t i o n s : U.S. Keweenawan) I s l e Royale, Michigan Michigan and and its Geol. Geol. Sur. Sur. Prof. P r o f . Paper 754—B, 754-B, p. p. B1—B15. B1-B15. LU i I �- STRUCTURE OF OF THE THEBEARDMORE BEARDMORE - GERALDTON GERALDTON FOLD FOLD BELT BELT STRUCTURE M. M. M. Kehienbeck Kehlenbeck M. Department Department of of Geology Geology Lakehead University University Lakehead BetweenBeardinore Beardmore and and Geraldton, Geraldton, complexly complexly folded foldedArchean ArcheanrnetametaBetween sedimentary and and metavolcanic metavolcanic rocks rocks form form an an intervening intervening terrain terrain bounded bounded sedimentary thethe Wabigoon on the thenorth northand and south south by by structures structuresofof Wabigoonand and Quetico Quetico subsubon provinces respectively. respectively. provinces The Beardmore Beardmore — Gerald.ton Geraldton fold belt is divisible into several The narrow, east-west east-west trending trending segments, segments, based based on on the the structural structural facing facing narrow, Structural facing facing directions directions are are either either east east or or direction of of folds. folds. Structural direction Depending on fold hinge line orientations, folds face upward, west. Depending on fold hinge line orientations, folds face upward, west. Where the the structural structuralfacing facing is is upward, upward,individual sideways,or or downward. downward. Where individual sideways, Where the the structural structural facing facing folds are are either either anticlines anticlinesor orsynclines. synclines. Where folds is antiformal is downward, downward, these these structures structuresare are synformal synformal anticlines anticlines or or antiformal Sideways structural structural facing facing is is associated associated with with neutral neutral folds. folds. synclines. Sideways synclines. Because Because of of variations variations in in structural structural facing facing within within and and between between narrow narrow segments, segments, the the fold fold belt belt as as aa whole whole represents represents aa disrupted disrupted and and discontinuous stratigraphy. stratigraphy. Discontinuities Discontinuities separating separating distinctive distinctive discontinuous segments segments are are zones zones of of pronounced pronounced shearing shearing which which are are coplanar coplanarwith with the the axial schistosity schistosity of ofthe thedominant dominantfolds. folds. axial Documented Documented reversals reversals in in the the structural structural facing facing direction direction between between the the segments segments of of the the fold fold belt belt suggest suggest that that the the last last folding folding episode episode Although no no refolded refolded occurred in in rocks rocks which which had had been been previously previously folded. folded. Although occurred folds folds were were observed observed in in outcrop, outcrop,the the presence presence of of an an earlier earlierschistosity schistosity has has been been recorded recorded in in several severalthin thin sections sectionsfrom from widely widely separated separatedlocalities. localities. The The second second folding folding was was in in response response to to an an inhomogeneous inhomogeneous fold-forming fold-forming shear component component accompanied accompanied by by aa homogeneous homogeneous compressive compressive strain. strain. The The shear shear shear component component formed formed folds folds of of various various amplitudes amplitudes and and wavelengths wavelengths with with shear shear planes planes everywhere everywhere parallel parallel to to the the axial axial surface surface of of these these folds. folds. Fold Fold hinge hinge lines lines parallel parallel the the intersection intersection of of the the shear shear planes planes and and the the surfaces undergoing undergoing folding. folding. Where Where the the shear shear direction direction lies lies in in the the surfaces surfaces surfaces undergoing undergoing folding, folding, no no folds folds developed developed although although the the rocks rocks show show strain component evidence of of internal internaldeformation. deformation. The The homogeneous homogeneous strain component evidence and. preserved preserved the the similar similarfold foldforms. forms. acted normal normal to the theshear shearplanes planesand acted Maximum extensive extensive strains parallel the shear shear direction, direction, and and shear shear disdisMaximum continuities continuities are are most most evident evident in in fold fold hinge hinge zones zones and and less less so so on on fold fold limbs where where the the layering layering and and axial axial planar planar schistosity schistosityare are commonly commonly subsublimbs parallel. parallel. - fold belt is divisible into several strains parallel the - The structural history Beardinore The structural historyofofthe the Beardmore - Geraldton Geraldton fold foldbelt beltmay may be summarized as follows: be sunuriarized follows: DDeformationand and metamorphism metamorphism of of sedimentary sedimentary and and volcanic volcanic rocks rocks Deformation D1 1 axial producing, at in part, part,folds foldsand and an an accompanying accompanying axial producing, at least least in tectonics including planar schistosity. schistosity. Gravity Gravity tectonics including thrusting thrusting planar may havebeen beenresponsible responsiblefor forthe the inversion inversion of of portions may have portions of of the stratigraphy. stratigraphy. the Development of similar folds by inhomogeneous shear and homohomoD2 D,, Development of similar folds by inhomogeneous shear and geneous strain strain in in surfaces surfaces of of variable variable orientation. orientation. Shear geneous Shear discontinuities discontinuities became became locally locally coneentrated concentrated as as shear shear zones zones in thin thin competent competent layers. layers. Large Large scale scale transposition transposition of of in individual, individual, shear shear zone zone bounded bounded segments segments led led to to the the disruption disruption of of the the stratigraphy stratigraphy of of the the fold foldbelt. belt. 44 I �I III I Geraldton I I I I Je/,j0 Structural facing_ of dominant folds upward 0 1Km sideways downward Eastern portion portion of of the the Beardmore—Geraldton Beardmore-Geraldton fold fold belt. belt. Eastern Individual segments segments reflect reflect variations variations in in the the plunge plunge Individual direction of of hinge hinge lines lines and and the the structural facing of of structural facing direction folds. The The segments segments are are separated separated from from each each other other fclds. by shear shear discontinuities. discontinuities. by 45 I I I I I I 1 I I I I �I STRUCTURAL STRUCTURAL GEOLOGY GEOLOGY AND AND KINEMATICS KINEMATICS OF OF EARLY EARLY PROTEROZOIC PROTEROZOIC SHEAR SHEAR ZONES ZONES IN I N CENTRAL CENTRAL WISCONSIN WISCONSIN . .- a. Klasner, Western Department Geol ogy, Western Illinois I 1 1 i noi s Department of o f Geology, Klasner, S. Macomb, inois 6145 and and G. G. L. L. LaBerge, LaBerge, Department Department Illin o i s 61455 Universi ty, Macomb Ill University, of University of Wisconsin, Oskosh, Oskosh, Wisconsin Wisconsin 54'701 49O1 f Wisconsin, o f Geology, Geology, U nivers t y o I J J. and in March C l a i r e Dells, Dells, March Rapids, Rapids, and Athens Athens in Rocks Rocks at a t Eau Eau Claire lend W i s c o n s i n have numerous 1 end c e n t r a l Wisconsin numerous structural s t r u c t u r a l features f e a t u r e s that that central themselves a n a l y s i s of o f the the nature n a t u r e and and kinematics k i n e m a t i c s of ot themselves to t o field f i e I d analysis deformation. At deformation. At EAU CLAIRE CLAIRE DELLS DELLS deformation d e f o r m a t i o n has has produced produced aa in p a r t i a l 1 y developed developed sigmoidal s i g m o i d a l pattern p a t t e r n in i n foliation f o l i a t i o n trends trends in partially finally foliations are progressively overprinted and which ENE ENE $01 i a t i ons a r e p r o g r e s s i v e l y o v e r p r i n t e d and f i na1 1 Y which Strain NNE foliation. replaced r e p l a c e d by by the NNE foliation. S t r a i n features f e a t u r e s in i n the the Dells Dells horizontal WNW elongation zone show zone show vertical vertical e l o n g a t i o n and and WNW horizontal shear crenulation Kink K i n k bands bands and andc r e n u l a t i o n folds f o l d s of o f foliation foliatian compression. Xenoliths indicate multiple i n d i c a t e mu1 o f intensely intensely t i p l e periods p e r i o d s of o f deformation. deformation. Xenol i t h s of deformed rock r o c k in i n the t h e Wolf Wolf River R i v e r batholith b a t h o l i t h near near the the Dells D e l l s suggest suggest deformed the deformation that d e f o r m a t i o n at a t the the Dells Del 1 s . predated p r e d a t e d intrusion i n t r u s i o n of of the that Structural batholith. batholith. S t r u c t u r a l measurements measurements near near MARCH MARCH RAPIDS RAPIDS indicate indicate from is separated the gneiss that tonal i t i c that tonalitic g n e i s s at at t h e rapids rapids is separated from metasedimentary and and metavolcanic m e t a v o l c a n i c rocks r o c k s to t o the the north n o r t h by by aa zone zone of of metasedimentary Foliation i n t e n s e brittle b r i t t l e deformation. deformation. F o l i a t i o n at a t MMarch a r c h Rapids Rapids south s o u t h of of intense folds Axes the the breccia b r e c c i a zone strikes s t r i k e s WNW and and dips d i p s steeply steep1 y N. N. Axes of of f a 1 d5 the fol iation plunge steeply to the E as do the long axes in in f o l i a t i o n plunge steep1 y t o the the l o n g axes of of The foliation shaped ellipsoidal shaped clasts c l a s t s in i n the the gneiss. gneiss. f o l i a t i o n and and E— Eellipsoidal open t r e n d i n g fold f o l d axes axes were were refolded r e f o l d e d into i n t o steep s t e e p N—plunging N-plunging open trending Foliation folds. folds. F o l i a t i on north n o r t h of o f the t h e breccia b r e c c i a zone zone strikes s t r i k e s ENE ENâ and dips dips doo the Folds steeply s t e e p l y S. S. F o l d s in i n bedding b e d d i n g plunge 300to 3 @ t o the the EE as asd the lorg long Foliation axes of o f ellipsoidal e l l i p s o i d a l clasts. clasts. F o l i a t i o n has has been been deformed deformed by by kink kink in ATHENS At ATHENS conspicuous conspicuous foliation fol iation i n felsic f e l s i c mylonite myloni t e bands. At Its strikes s t r i k e s NE NE and and dips d i p s steeply s t e e p l y NW. NW. I t s orientation o r i e n t a t i o n differs d i S f e r s from from The orientations structural o t h e r rocks r o c k s in i n the the region. region. The structural o r i e n t a t i o n s in i n all a1 1 other structural s t r u c t u r a l relationship r e 1 a t i onshi p between between nearby nearby bedded bedded rocks r o c k s and and mylonitic my1 on i % i c shear shear foliation f o l i a t i o n is i s nearly n e a r l y identical i d e n t i c a l with w i t h aa ductile d u c t i l e shear shear zone zone on on Foliation 1 highway S. highway U. U. S. 51near near Brokaw. Brokaw. F o l i a t i o n in i n mmetavolcanic e t a v o l c a n i c rocks rocks south s o u t h of of the the Athens f i t h e n s shear shear zone zone strikes s t r i k e s ENE ENE and and dips d i p s steeply s t e e p l y NW. NW. F o l d axes axes i n this t h i s region r e g i o n plunge gently gent1 y ENE ENâ and and the the X X axes axes of of Fold in gneiss ellipsoidal clasts Migmati ellipsoidal c l a s t s are nearly n e a r l y vertical v e r t i c a l.. M i g m a t itic tic g n e i s s at at Goodrich has Gaodrich Dells, Dells, 7 - m i l e s north n o r t h of o f Athens, has an an ENE— ENEabout 7—miles trending, v e r t i c a l foliation f o l i a t i on and and SW—plunging SW-pl ungi n g folds. $01 d5. t r e n d i n g , nearly near1 Y vertical - zones oof A l l three t h r e e areas a r e a s are a r e characterized c h a r a c t e r i z e d by by 1 l i ninear e a r zones f intense intense All d e f o r m a t i o n that t h a t diverge d i v e r g e trom f r o m the the regional r e g i onal structural s t r u c t u r a l fabric and +abr i c and deformation t h a t separate s e p a r a t e regions r e g i o n s with w i t h different d i f f e r e n t structural structural pictures. Eau that pictures. Eau C l a i r e Dells D e l l s and and Athens are a r e ductile d u c t i l e shear shear The March March Claire zones. The i t is i s possibly p o s s i b l y aa Rapids area a r e a is is a a zone zone of o f brittle b r i t t l e deformation; deformation; Rapids it ductile—brittle These shear d u c t i 1 e-br i t t l e zone zone of o f shear. shear. shear zones zones are a r e believed be1 i eved to ta have resulted r e s u l t e d from f r o m stresses s t r e s s e s that t h a t were were different d i f f e r e n t from t r o m those those that have that the regional r e g i o n a l structural s t r u c t u r a l fabrics f a b r i c s in i n the the three t h r e e areas. areas. produced the 46 -1 1 �GEOLOGICALSETTING SETTING OF GEOLOGICAL OF GOLD GOLD MINERALIZATION MINEFL4LIZATION IINN BEARDMORE-GERALDTON BEAJUMORE-GERALDTON LAVIGNE, Ministryofof Natural Natural Resources, LAVIGNE, M . JM.J., ., Ministry RED RED LAKE, Ontario is typical for most Archean greenstone belts, hosted by almost all lithologic is As A s is t y p i c a l f o r most Archean greenstone b e l t s , gold gold mineralization mineralization is hosted by almost a l l l i t h o l o g i c iin n the t h eBeardmore-Geraldton Beardmore-Geraldton camps camps is associations ccannot types, t h u s specific s p e c i f i c llithological i t h o l o g i c a l associations a m o t be used as as types, thus denominator. This fundamental genetic feature common a of is genetic f e a t u r e aa comon Archean gold mineralization. The host rocks Archean gold mineralization. The host rocks represent represent aabroad broadspectrum spectrum of time and and events, events, from from the t h eoldest o l d e s tvolcanic volcanicand andsedimentary sedimentary of geologic geologic time rocks Uniform gold ddistribution rocks to t o the t h eyoungest youngest Archean Archean intrusions. intrusions. Uniform gold istribution suggest that iin n all a l llithologic l i t h o l o g i ctypes types suggest t h athe t t hmechanism e mechanismof ofgold goldconcentration concentration processes associated is independent of tthe h e processes associated with with tthese h e s e rocks. It suggest that t h a t a ssingle i n g l e process process was was active a c t i v ethroughout throughout does, however, suggest t h e b e l t and a f f e c t e d a l l l i t h o l o g i e s uniformly on a regional s c a l e . each lithology on lithology responded ddifferently However, on a local l o c a l scale s c a l e each ifferently However, This process . This process affected a f f e c t e d young young intrusions i n t r u s i o n s which which post post t o t h e process. In date date the t h e supracrustals supracrustals and and subsequent subsequent iisoclinal s o c l i n a l folding. folding. I n Geraldton, Ckraldton, f i e l d r e l a t i o n s h i p s have c l e a r l y established t h a t t h e r e l a t i v e timing of those those hydrothermal process mineralization, p r o c e s s sresponsible responsible ffor o r gold mineralization, with respect t o t h e host rocks, w e r e t h e l a s t events i n t h e evolution The formation formation of of supracrustals of t h e greenstone b e l t . The s u p r a c r u s t a l swas was succeeded succeeded by tthe h e following sequence of events; isoclinal i s o c l i n a l folding, folding, regional felsic magniatic activity dextral d e x t r a l shear, mafic magmatic magmatic activity, activity f e l s i c magmatic a ctivity Dextral and finally f i n a l l y gold gold mineralization. mineralizatione Dextral shear shear was an an ongoing ongoing process process from to the from its its onset thru ko t h e last l a s t stages s t a g e s of of gold gold mineralization. mineralization. The common denominator The comon tto o all a l l gold mineralization in in high strain, tthis h i s belt b e l t is is tthe h e association association with zones of high s t r a i n , regional extent. iin n extent. This entire e n t i r e greenstone e l t has undergone pronounced greenstone bbelt d e x t r a l d u c t i l e shear. This has produced t h e r a t h e r unique l i n e a r , E-W trending volcanic This is E-W trending volcanic and and sedimentary sedimentary bbelts. elts. This is distinct d i s t i n c t from from lower strain s t r a i n greenstone belts b e l t s iin n which llithologic i t h o l o g i c packages do do not have regional preferred orientation. orientation. The present configuration of the can only of t h e belt b e l t can only be be produced produced as a s the t h e result r e s u l t of extremely extremely high high The stress. stress. The E-W E-W trending contacts c o n t a c t s between all a l l major lithologic lithologic units of high u n i t s are a r e zones of high strain. strain. Zones of of high high strain s t r a i n also a l s o occur Zones is found within these t h e s e llithologic i t h o l o g i c packages. packages. mineralization is Gold mineralization exclusively exclusively within within these t h e s e zones of high s t r a i n . I n Geraldton, Geraldton, these these In zones aalso l s o contain an anomalously anomalously high proportion proportion of both f e l s i c mafic and maf It appears ttherefore h e r e f o r e tthat h a t strain s t r a i n induced i c iintrusives. ntrusives permeability and hydrothermal hydrothermalaactivity permeability focused focused rnagmatic magmatic and c t i v i t y which which resulted resulted and mineralization. These zones of high sstrain iin n aalteration l t e r a t i o n and mineralization. train a re are easily all e a s i l y identified; identified; a l l primary volcanic, igneous and sedimentary sedimentary ttextures e x t u r e s have have been eeither i t h e r modified o bliterated. These zones zones orr o obliterated. also by tight may a l s o be identified i d e n t i f i e d by t i g h t repeated h e presence presence repeated folding and tthe of an high proportion of intrusions. an anomalously high IIn n conjunction intrusions. of high with t h e i d e n t i f i c a t i o n of high strain, s t r a i n , the t h e presence presence of of hydrothermal hydrothermal alteration, a l t e r a t i o n , serve to t o identify i d e n t i f y areas areas with with high high gold gold potential. potential. It is the belt and affected all lithologies uniformly on a regional scale. to the process. field relationships have clearly established that the relative timing with respect to the host rocks, were the last events in the evolution of the greenstone belt. , dextral ductile This has produced the rather unique linear, zones of high strain. . It felsic with the identification n 47 �I RANIER,MINNESOTA,NINERAL OUTCROP R4NIER,MINNESOTA,MINERAL POTENTIAL POTENTIAL EVALUATION: EVALUATI0N:OUTCROP SAMPLING, SAMPLINGy GEOPHYSICS GEOPHYSICS AND AND SOIL SOIL GEOCHEMISTRY GEOCHEMISTRY The i s located l o c a t e d east e a s t of of International I n t e r n a t i o n a l Falls, F a l l s y Minnesota, Minnesota, The Ranier Ranier area a r e a is just j u s t south s o u t h of of the t h e Canadian Canadian border. border. Outcrops Outcrops in i n the t h e area a r e a display d i s p l a y many many of of the same structural, lithologic and metamorphic characteristics as t h e same s t r u c t u r a l y l i t h o l o g i c and metamorphic c h a r a c t e r i s t i c s a s large large Canadian Canadian gold gold deposits. d e p o s i t s . At A t Little L i t t l e American American Island I s l a n d 500 500 tons t o n s of of gold gold bearing bearing rock was mined and milled in 1894, which would be ore grade at present rock and m i l l e d i n 1894, which would be o r e grade a t p r e s e n t day day prices. prices. Very low low frequency frequency electro—magnetic electro-magnetic traverses t r a v e r s e s at a t Little L i t t l e American d i s t i n c t i v e profile. p r o f i l e . The profile p r o f i l e defines d e f i n e s silicification silicific~tion I s l a n d y map aa distinctive Island, show aa vague vague indication i n d i c a t i o n of of Magnetometer observations o b s e r v a t i o n s show in i n aa fault f a u l t zone. zone. Magnetometer geologic units. u n i t s . These These characteristic c h a r a c t e r i s t i c VLF—EM VLF-EM profiles p r o f i l e s are a r e repeated r e p e a t e d at at geologic s e v e r a l locations. l o c a t i o n s . Detailed D e t a i l e d induced induced polarization p o l a r i z a t i o n surveys, s u r v e y s y coincident coincident several with w i t h VLF—EM VLF-EM surveys, surveys* define d e f i n e structural s t r u c t u r a l features f e a t u r e s and locate l o c a t e near surface surface disseminated disseminated sulf s u l fides. i d e s . Refraction R e f r a c t i o n sismic s i s m i c profiles p r o f i l e s tested t e s t e d one one such such structural s t r u c t u r a l feature f e a t u r e and and clearly c l e a r l y mapped mapped aa fault f a u l t zone. zone. They They also a l s o help help interpret i n t e r p r e t I.P. I.P. results. results. One mineral One of of the t h e goals g o a l s of of this this m i n e r a l potential p o t e n t i a l evaluation e v a l u a t i o n is i s to t o compare three These three three t h r e e geochemical geochemical sample sample media media over over gold gold bearing b e a r i n g lithologies. l i t h o l o g i e s . These vegetation; "Ao" (humus) horizon, and "A1" soil horizon. media media are: a r e : v e g e t a t i o n ; "Aott (humus) h o r i z o n , and "Altt s o i l h o r i z o n . A limited l i m i t e d number of of samples samples from from all a l l three t h r e e media media correlate c o r r e l a t e to t o help h e l p locate locate These are defined areas of interest and select drill sites. a r e a s of i n t e r e s t and s e l e c t d r i l l s i t e s . a r e d e f i n e d by by anomalous anomalous samples as a s high high as a s twenty twenty times times background. background. samples Two diamond drill d r i l l holes h o l e s confirm confirm structures, s t r u c t u r e s * silicification s i l i c i f i c a t i o n and and Mineralization M i n e r a l i z a t i o n is i s indicated i n d i c a t e d by assays a s s a y s of of short s h o r t core c o r e interinters e c t i o n s with w i t h anomalous anomalous gold gold content. c o n t e n t . These These include i n c l u d e one one six s i x inch inch interintersections DDH RR—1 RR-1 of of 3.56 3.56 ppm ppm gold. gold. The fault f a u l t structure s t r u c t u r e defined d e f i n e d by by s e c t i o n from from DDH section The DDH RR—2. RR-2. The highest highest r e f r a c t i o n seismic s e i s m i c methods methods was was further f u r t h e r tested t e s t e d by by DDH refraction gold gold assays a s s a y s for f o r this t h i s hole h o l e were located l o c a t e d in i n intersections i n t e r s e c t i o n s flanking f l a n k i n g the the indicated i n d i c a t e d fault f a u l t zone. zone. s u l f iides. des. suif Mineral potential Ranier area a r e a include: include: p o t e n t i a l evaluation e v a l u a t i o n methods methods for f o r Ranier (1) (1) a literature l i t e r a t u r e search; s e a r c h ; (2) (2) geophysical and and geochemical geochemical surveys surveys of of aa known m mineralized of these i n e r a l i z e d area; a r e a ; (3) (3) extension e x t e n s i o n of t h e s e surveys along a mapped area a r e a of of interest; i n t e r e s t ; (4) (4) tests t e s t s of of geophysical geophysical data d a t a with with outcrop outcrop and and collaborating c o l l a b o r a t i n g geophysical geophysical methods; methods; (5) (5) drill d r i l l holes h o l e s with with assays. a s s a y s . This This evaluation e v a l u a t i o n indicates i n d i c a t e s an an area a r e a of of excellent e x c e l l e n t precious p r e c i o u s metal metal mineral mineral potential. potential. If i t can can be obtained o b t a i n e d from from the t h e D.N.R. D.N.R. Minerals Minerals I f more information is i s desired, d e s i r e d , it MN 55746, phone phone (218) (218) 262—6767. 262-6767. D i v i s i o n y P.O. P.O. Box Box 567, 567y Hibbing, Hibbing* MN Division, By: T. T. L. L. Lawler Lawler J. J. M. M. Sellner Sellner 48 I �The Petroloov of the Lononose F'eridotite ERIC K. LINSCHEID (Department o-f Geology University of Minnesota Duluth, Duluth, MN 55812) The Longnose Peridotite deposit is a funnel shaped. titani-Ferous oxide rich layered ultramafic body located .E. of -4oyt Lakes Minnesota. The Peridotite lies 780m 8 km. above cese c- the atidge ver Troctolite——a basal vdde Proterozoic intrusion of the Troctolitic Series in the Duluth Eight units were distinguished in mapping the Complex. They range in surrounding, country rocks of the deposit. composition from troctolitic anorthosite to feldspathic dunite with anorthositic troctolite to troctolite being the most The units trend N.E and dip 10—25 degrees to the abundant. S.E.. youngin;. eastward. This trend is concordant with the VirQinia formation—Partridge River Troctolite contact. No contact was seen between the country rocks and the Longnose These strata are stratigraphically hich in the Feridotite. Frtride River Troctolite, which has been postulated to have formed b multiple intrusion of magma from the S.E. along the lower Froterozoic Virginia contact and middle Froterozoic North Shore Volcanic group. The deposit is t'tear dropu in plan view trends N.W.—S.E.. In long by 90m. to 488 m. wide. and is approximately Th2m the longitudinal section it forms an asymmetrical funnel; contact on the N.W. dips approximately 15—20 degrees to the 5.E., and the contact on the SE. dips approximately 70 degrees to the N.W.. The Peridotite appears to be layered with an outer shell of relatively oxide poor clinopyroxenite and an inner core of layeredq anomously rich ilmenite—magnetite duniteq peridotite. and picrite. with massive oxide zones occurring within some of the dunitic zones, the largest of which is 40m. Troctolitic anorthosite inclusions are common. thick. The dunitic zones are weakly to strongly serpentinized with minor secondary magnetite hematite, chlorite, talc and carbonate. The clinopyroxenite zone consists a-f titanaugite to hornblende, actinolite—tremolite. and and Fiagiociase may be altered to chlorite or clay. The talc. slightl-i altered oxides remain unaltered except for some occasional minor The Peridotite is ridden with near (nartltizatlor: of magnetite. vertical fractures which commonly nave slickensides. limenite and magnetite constitute the bulk of the ore combined) ulvspinel?. mineralogy with minor (less than Ilmenite—magnetite ha1copyrite, and an isotropic grey mineral. most commonly occur in a broken net—textured fashion, but may also be disseminated or massive. The contacts between these 5 tex -ures sequence can be gradational or sharp. The crystal I i zati on between ilmenite and rnagnetite varies within and i �I between units where either may be cumulate and the other interstitial or both may be cumulate in relation tD the silicate minerals_ Ilmenite exsolution lamellac commonly occur along octahedral cleavage in magnetite. An isotropic grey mineral (spinel?) commonly occurs in both ilmenite and magnetite. In magnetite it can -form along cleavage or as vermicular intergrowth with ilmenite alonq magnetite—ilmenite grain boundries. Ilmenite may contain faint white bands which are interpreted to be ulvospinel. Chalcopyrite is the major sulfide mineral averaging 1. or interstitial The troctolitic anorthosite inclusions appear to be Partridge River Troctolite which were raf ted upon intrusion o-f the Lorignose Peridotite into the Duluth Complex. 50 �Minor EQL F o l d s iu n the I r o nEQtQO.L F%rfiatiAnL !ua tfl Soudan .ici Northeastern Minnesota Northeastern Minnesota Geology (Department James R.. James R. (Department of of Geology University Uni v e r s i t y of o f Minnesota, Minnesota, Minneapolis. Minneapol i s . MN MN Lundy, Lundy, I and Geophysics, and Geophysics, 55455) 554 I part an Minor Minor folds f o l d s in i n the t h e Soudan Soudan Iron I r o n Formation F o r m a t i o n (SIF), (SIF), p a r t a-f of an terrane Archean greenstone/granite greenstone/granite t e r r a n e in i n northeastern n o r t h e a s t e r n Minnesota, Minnesota, Archean Previous have been been exmamined exmamined in i n detail. detail. P r e v i o u s work work suggests suggests the t h e preprehave This sence a llarge sence a-f of a a r g e recumbent recumbent nappe nappestructure.. structure. T h i s structure s t r u c t u r e and and associated a s s o c i a t e d minor folds f o l d s (Fl) ( F l ) have have been been redeformed redeformed during d u r i n g aa second second This tectonic t e c t o n i c event event (F2). (F2?. T h i s study s t u d y attempts a t t e m p t s to t o elucidate e l u c i d a t e the t h e geogeoboth metry and and nature n a t u r e (soft—sediment ( s o f t - s e d i m e n t or o r tectonic?) t e c t o n i c ? ? of o f folds f o l d s of of both metry with generations, w i t h a particular o a r t i c u l a r emphasis emphasis on on trying t r y i n g to t o understand understand generations, the early better b e t t e r the t h e nature n a t u r e of c l y folds f o l d s and and the t h e large l a r g e nappe—].ike nappe-1 ike study The structure. The SIF is especially a l l y useful u s e f u l for f o r this t h i s sort s o r t of of study structure of composition s i n c e it i t is i s made made up up a-f UT .Llayers d y e r -a o f ddifferent ifferent c o m p o s i t i o n and and comsince petence that t h a t became became folded f o l d e d on on a a small s m a l l scale s c a l e during d u r i n g both b o t h deforma— deformapetence tional t i o n a l events.. events. ranging wide variety v a r i e t y of o f fold f o l d shapes shapes is i s observed, r a n g i n g from from AA wide similar, broad warpings of the layering to concentric, broad warpings o f t h e l a y e r i n g t o c o n c e n t r i c , s i m i l a r , and and chevihevthese Using r o n shapes.. shapes. Using appropriate a p p r o p r i a t e quantitative q u a n t i t a t i v e techniques, techniques, these ron Fl shapes shapes are a r e described d e s c r i b e dini ndetail.. detail. F l folds f o l d s tend t e n d to t o be be of o f Class C l a s s 1C 1C F2 with o r Class C l a s s 22 shape, shape, w i t h wide wide variations v a r i a t i o n s in i n interlimb i n t e r l i m b angle. angle. F2 or folds consistent f o l d s tend t e n d to t o be be Class C l a s s 1C 1C in i n shape, shape, with w i t h -fairly fairly c o n s i s t e n t orienorienWhite t a t i o n s and and a much much narrower range range in i n interlimb i n t e r l i m b angle.. angle. White tations cherty l a y e r s consistently c o n s i s t e n t l y behaved behaved more more competently c o m p e t e n t l y than t h a n lean lean cherty layers j a s p e r or o r jaspilite layers. j a s p i 1it elayers.. jasper Detailed D e t a i l e d mapping mapping and and measuring measuring of o f fold f o l d axes, axes, axial a x i a l surfaces, surfaces, and other o t h e r structural s t r u c t u r a l elements has has been been done done in i n an an outcrop o u t c r o p showing showing Fl fine exceptionally f i n e fold f o l d interference i n t e r f e r e n c e patterns p a t t e r n s of of F l and and F2.. F2. exceptionally and F i e l d relationships r e 1a t i o n s h i p s suggest suggest sheath sheath folds f o l d s are a r e present, present, and that that Field of Fortuitous in t h e y are a r e Fl Fl i n age.. age. F o r t u i t o u s XV XY and and XZ X Z cross—sections cross-sections of they VZ and sheaths, and intersections i n t e r s e c t i o n s a-f o f fold f o l d axes axes on on opposite o p p o s i t e sides s i d e sa-f of YZ sheaths, cross—sections c r o s s - s e c t i o n s of o f sheaths sheaths suggest suggest that t h a t high h i g h strains s t r a i n s were were suffered suffered Shear direction during d u r i n gFl.. Fl. d i r e c t i o n during d u r i n g Fl F l is i s more more difficult d i f f i c u l t to t o assess assess t o movements movements during d u r i n g F2. F2. due to ' I , M Several lines l i n e s of o f evidence evidence seem seem to t o support s u p p o r t earlier e a r l i e r views v i e w s that that arose the l a r g e fold fold a r o s e at a t least l e a s t in i n part p a r t due due to t o downslope downslope soft— softlarge the wide variety This sediment sediment movement.. movement. T h i s evidence evidence includes: includes: v a r i e t y of o f fold fold non—uniform style s t y l e and and orientation o r i e n t a t i o n of o f Fl F l folds; folds; non-unif orm distribution d i s t r i b u t i o n of of the intrafolial nature these F l folds; folds; intrafolial n a t u r e of of t h e s e folds; folds; t h e likely likely Fl strains sheath folds development of of f o l d s and and associated a s s o c i a t e d high h i g h shear strains development during Fl. d u r i n g Fl. i 51 1 I I �I Unconformity-Type Uranium Uranium Mineralization Mineralization at at the the Groveland Groveland Unconformity—Type Iron Mine, Mine, Central Central Dickinson Dickinson County, County, Michigan Michigan Iron Joseph J. J. Mancuso Mancuso && Charles Charles W. W. Schick Schick Joseph Bowling Green State University Bowling Green State University Bowling Green, Green, Ohio Ohio 43403 43403 Bowling significant radiometric radiometric anomaly anomaly and and uranium uranium AA significant mineralization were detected immediately beneath the mineralization were detected immediately beneath the unconformity between Cambrian sandstone and underlying Lower unconformity between Cambrian sandstone and underlying Lower Proterozoic metasediments and metadiabases at the Groveland Proterozojc metasediments and metadiabases at the Groveland Iron Mine, Mine, Dickinson Dickinson County, County, Michigan. Michigan. Chemical Chemical analyses analyses of of 23 23 Iron samples taken from 0.1 to 1.0 meters below the unconformity samples taken from 0.1 to 1.0 meters below the unconformity yielded uranium uranium values values ranging ranging from from 0.8 0.8 to to 28.0 28.0 ppm. ppm. yielded (Background averages approximately 2 ppm.) This uranium (Background averages approximately 2 ppm.) This uranium mineralization can can be be compared compared to to the the unconformity—type unconforrnity-type uranium uranium mineralization ore deposits deposits in in the the Athabasca Athabasca Basin Basin of of Northern Northern Saskatchewan. Saskatchewan. ore The Groveland Groveland Iron Iron Mine Mine is is located located 16 16 miles miles northeast northeast The of Iron Iron Mountain Mountain in in Central Central Dickinson Dickinson County, County, Michigan. Michigan. The The of Lower Proterozoic Proterozoic rocks rocks of of the the Groveland Groveland Mine Mine area area are are found found in in Lower the Felch Felch Trough, Trough, and and are are bounded to to the the north north and and south south by by the Archean gneisses granites. The The rocks rocks in in the the trough trough consist consist Archeari gneisses and granites. of amphibolite, garnet mica schist, iron formation, marble and of amphibolite, garnet mica schist, iron formation, marble and quartzite which strike approximately E-W and dip nearly quartzite which strike approximately E-W and dip nearly vertically. These These metasediments metasediments were were folded, folded, faulted, faulted, intruded intruded vertically. by both granitic and gabbroic rocks and metamorphosed to the by both granitic and gabbroic rocks and metamorphosed to the b.y.). amphibolite facies during the Penokean Orogeny (1.85 amphibolite facies during the Penokean Orogeny (1.85 b.y.). Flat lying lying Upper Upper Cambrian Cambrian sandstone sandstone and and Pleistocene Pleistocene glacial glacial Flat drift overlie the Precambrian rocks. The sandstone is the the drift overlie the Precambrian rocks. The sandstone is Miner's Castle Member of the Munising Formation which is the Miner's Castle Member of the Munising Formation which is the upper member of the Upper Cambrian Lake Superior Sandstone upper of the Lake Superior Sandstone Group. Group. The Lower Lower Proterozoic Proterozoic rocks rocks underwent underwent extensive extensive erosion erosion The and weathering weathering after after the the Periokean Penokean Orogeny to the the and Orogeny and and prior prior to deposition of of the the Cambrian Cambrian Sandstone. Sandstone. The The weathering weathering produced produced deposition paleoregolith that that is is up up to to 30 30 meters meters thick. thick. The The most most aa paleoregolith important mineral mineral changes changes were were alteration alteration of of feldspars feldspars and and important mafic minerals minerals to to illite, illite, kaolinite kaolinite and and chlorite. chlorite. Analysis Analysis of of mafic the paleoregolith paleoregolith immediately immediately below below the the unconformity unconformity yielded yielded the 0.5% reductant reductant calculated calculated as as organic organic values ranging ranging from from 0.1 0.1 to to 0.5% values carbon. carbon. As aa working working hypothesis, hypothesis, the the following following genesis genesis is is As proposed: Oxidizing ground waters, carrying uranium in proposed: Oxidizing ground waters, carrying uranium in solution in in the the UU +6 +6 state state which which was was derived derived from from weathering weathering of of solution local Archean granite and gneiss highlands, passed through the local Archean granite and grieiss highlands, passed through the oxidized Upper Upper Cambrian Cambrian sandstone sandstone aquifer aquifer without without reaction. reaction. oxidized However, the altered basement rocks below the unconformity However, the altered basement rocks below the unconformity presented aa major major break break in in structure, structure, mineralogy mineralogy and and chemistry chemistry presented +6 and aa sudden sudden decrease decrease in in porosity porosity and and permeability. permeability. The The UU +6 and in the the oxidized oxidized fluids fluids reacted reacted with with the the reductant reductant in in the the in regolith immediately immediately below below the the unconformity unconformity reducing reducing the the regolith + 4 state state which which was was deposited deposited as as uraninite. uraninite. uranium to to the the UU +4 uranium 52 I �I Ii THE ATIKOKAN COBALT-BASE METALS-PLATINUM GROUP ELEMENTS PROJECT A.D. MacTavish MacTavish and and R.J. R.J. Dutka Dutka A.D. Ministry M i n i s t r y of of Natural Natural Resources, Resources, 435 James St. S t . South, Thunder Thunder Bay, Bay, Ontario Ontario p r o j e c t was initiated i n i t i a t e d in i n May, May, l98L 1984 to t o examine and document document The project the ccobalt, o b a l t , base metal p l a t i n u m group element element occurrences occurrences in i n the the the metal and platinum A t i k o k a n Area, Area, to t o study s t u d y in i n detail d e t a i l the t h e most significant s i g n i f i c a n t of o f these these occuroccurAtikokan rences and to t o stimulate s t i m u l a t e exploration. e x p l o r a t i o n . The detailed d e t a i l e d research r e s e a r c h will w i l l attempt attempt t o ooutline u t l i n e tthe he g e o l o g i c a l and t r u c t u r a l ssetting, e t t i n g , oore r e and s ilicate to geological and sstructural silicate p e t r o l o g y , petrochemistry p e t r o c h e m i s t r y and and potential p o t e n t i a l of o f the t h e occurrences. occurrences. petrology, I n i t i a l reconnaisance sampling, sampling, assaying a s s a y i n g and and geological g e o l o g i c a l mapping mapping Initial done during d u r i n g the t h e l98L 1984 field f i e l d season season and concentrated c o n c e n t r a t e d on on three t h r e e locations: locations: were done the Finlayson Area, the the F i n l a y s o n Lake Area, t h e Sapawe Sapawe Lake—Plateau Lake-Plateau Lake Lake Area, Area, and and the the Crooked Pine Pine Lake Lake Area. Area. This T h i s work has revealed r e v e a l e d the t h e presence presence of o f five five p r e l i m i n a r y 'deposit' ' d e p o s i t ' or o r 'occurrence' ' o c c u r r e n c e ' types. types. They were determined on on the the preliminary b a s i s of o f lithology, l i t h o l o g y , structure basis s t r u c t u r e and associated a s s o c i a t e d suiphide s u l p h i d e mineralogy, m i n e r a l o g y , which which m i g h t host h o s t cobalt, c o b a l t , base metal or o r platinum p l a t i n u m group group mineralization. mineralization. might 1) 1) 'The Quetico 'The Q u e t i c o Fault—Hosted F a u l t - H o s t e d Intrusions' I n t r u s i o n s ' contain c o n t a i n significant significant cobalt, c o b a l t , copper and nickel n i c k e l sulphides s u l p h i d e s closely c l o s e l y associated a s s o c i a t e d with w i t h disseminated disseminated to magnetite within t o massive m a g n e t i t e lenses lenses w i t h i n sheared, sheared, syntectonic s y n t e c t o n i c gabbroic g a b b r o i c to t o ultraultramafic m a f i c intrusive i n t r u s i v e rocks. rocks. A similar s i m i l a r potential p o t e n t i a l for f o r cobalt, c o b a l t , copper copper and and nickel nickel should exist within exist w i t h i n other o t h e r intrusions i n t r u s i o n s of o f this t h i s type. type. The The possibility p o s s i b i l i t y of of platinum p l a t i n u m group group enrichment enrichment is i s high h i g h in i n the t h e presence presence of o f copper copper and and nickel nickel sulph s u l p h ides. ides. I Quetico 2) 2 ) 'The 'The Q u e t i c o Intrusions' I n t r u s i o n s ' are a r e mafic maf i c to t o ultramafic u l tramaf i c bodies bodies exhibiting e x h i b i t i n g high h i g h local l o c a l concentrations c o n c e n t r a t i o n s of o f copper, copper, nickel, n i c k e l , cobalt, c o b a l t , platinum platinum and and palladium. p a l l a d i u m . The base base metals m e t a l s occur o c c u r in i n disseminated d i s s e m i n a t e d pods pods of o f chalcopyrite, chalcopyrite, pyrite p y r i t e and and pentlandite. p e n t l a n d i t e . The, The, as as yet y e t unidentified, u n i d e n t i f i e d , platinum p l a t i n u m group group minerals minerals are with a r e probably p r o b a b l y closely c l o s e l y associated associated w i t h the t h e chalcopyrite c h a l c o p y r i t e and and pentlandite. pentlandite. The The potential p o t e n t i a l for f o r base matal and platinum p l a t i n u m group group mineralization m i n e r a l i z a t i o n in i n these these o t h e r similar s i m i l a r bodies b o d i e s is i s high h i g h and should s h o u l d be be investigated i n v e s t i g a t e d further. further. and other 3) 3) The The deformed, deformed, banded chert c h e r t and iron-rich i r o n - r i c h chemical metameta- sediments sediments of o f the t h e Finlayson F i n l a y s o n Lake Lake Area locally l o c a l l y contain c o n t a i n copper, copper, cobalt c o b a l t and and minor ( ? ) sulphides. s u l p h i d e s . The The sulsulm i n o r zinc z i n c and and silver s i l v e r within w i t h i n primary p r i m a r y exhalative e x h a l a t i v e (7) phides, composed of of pyrrhotite, p y r r h o t i t e , pyrite, p y r i t e , chalcopyrite c h a l c o p y r i t e and and sphalerite, s p h a l e r i t e , are are phides, f i n e to t o coarse-grained, t o nodular, n o d u l a r , and d i s s e m i n a t e d to t o massive fine coarse-grained, banded to disseminated in i n appearance. 14) Shear zones and quartz q u a r t z veins v e i n s throughout throughout the the 4) and and 5) 5) Shear A t i k o k a n Area Area exhibit e x h i b i t localized l o c a l i z e d disseminated d i s s e m i n a t e d copper, copper, lead l e a d and and zinc z i n c minerminerAtikokan alization. a l i z a t i o n . Auriferous A u r i f e r o u s quartz q u a r t z veins v e i n s generally g e n e r a l l y have have associated a s s o c i a t e d base base metal metal m i n e r a l i z a t i o n occurring o c c u r r i n g either e i t h e r as semi-massive semi-massive lenses lenses or o r as as disseminated disseminated mineralization blebs. b l e b s . Cobalt was observed in with i n association association w i t h a possible p o s s i b l e splay s p l a y fault fault of o f the t h e Quetico Q u e t i c o Fault F a u l t Zone. Zone. D e t a i l e d research research is i s planned planned during d u r i n g 1985 1985 on on the t h e Quetico Q u e t i c o Intrusions Intrusions Detailed and and the t h e Quetico Q u e t i c o Fault-Hosted F a u l t - H o s t e d mafic m a f i c bodies. bodies. Reconnaisance Reconnaisance work will w i l l be be done done in i n the t h e Calm Calm Lake Lake Area, Area, the t h e Lumby Lumby Lake—Old Lake-Old Man Man Lake Lake Belt, Be1 t, and and portions p o r t i o n s of of the t h e Shebandowan Shebandowan Area. Area. 53 I �: CHEMICAL CHARACTERIZATION OF CHEMICAL O F THE THEUNNAMED UNNAMED FORMATION FURMATT.ON KEWEEMAWAM AGE A A CENTRAL VOLCANIC VOLCAN IC COMPLEX COMPLEX OF O FKEWEENAWAN Michael M i c h a e l Patrick P a t r i c kMcDermott McDormatt Science::; M i c h i g a n SState tate U n i v e r s i t y , Department o'f o-f Goloqical s o l o q i c a lSc:iences Michigan University, 49524 East Lansing MI. East L ansing M I . 48824 The unique Tho Unnamed Formation F o r m a t i o n provides provides a u n i q u e opportunity o p p o r t u n i t y to t o study s t u d y the the Proterozoic evolution off a e volution o a P r o t e r o s o i c volcanic v o l c a n i c system system tthroughout hrouqhout iits t's; Iwaning nning Formation off the the Keweenawan Keween<aw<an stages. o r m a t i on i s tthe h e youngest o Unnamed F stages. The Unnamed a sequence of subaerially I t iiss a si-ibaori a l 1y extruded c^~t+-udeid v o I c a r i i c s in i n Michigan. Michigan. voicanics lava and quartz—porphyry i ell ssite, a n d e s ite, to, fe ite, and quarts-porphyry l a v a ffl l aows ws i n tnterbedded e r b e d d a d with w i t h andesi subordinate sedimentary -Â¥subordinat s e d i m e n t a r y rocks. r o c k s . The The upper upper 770 770 m m a-f o f the t h e Formation F o r m a t i o n fforms arms Mountains. R Regionally Porcupine tthe h e uplands uplands o o f the the P o r c u p i n e Mountains. e g i o n a l l y the t h e the t h e Formation Formation measurable at iiss a v o l c a n i c p i l e which r e a c h e s i t s maximum maximum thickness t h i c k n e s s (neiasur<able at tthe h e surface s u r f a c e a-f o-f 2400 m m in i n the t h e Bergland B e r g l a n d and and Thomaston Thomaston quadrangles, quadrangles, Itt wedges km. south s o u t h of o f the t h e Porcupine P o r c u p i n e Mountains. I wodqos out o u t in i n the tho about about 8 km. and Greenland q quadrangle Greenland u a d r a n g l e to t o tthe h e east east and in i n the t h e Little L i t t l e Girl G i r l Point Point quadrangle west. q u a d r a n g l e to t o the t h e west. Portage The Unnamed Formation with underlying The Unnamed F o r m a t i o n is i s con-formable con-formabla w i t h tthe h e under1 yinq P ortage (PLL) series iti tbyb ydi'f'ferences di++or-cincss Lake Lava (PLL) s e r i e s and and is i s distinguishable d i s t i n g u i s h a b l efrom -from PLL are iin n rock r o c k type. t y p e . The The ma-fic mafic PLL a r e predominantly p r e d o m i n a n t l y basalts, b a s a l t s , whereas whereas those those grained and contain greater off o tthe h e Unnamed Formation F o r m a t i o n are a r e finer finer g r a i n e d and c o n t a i n a qr-eator off felsic The Harbor proportion porphyritic p roportion o p o r p h y r i t i c and and a felsic rrocks. ocks. The Copper Harbor with, the Conglomerate Conformably overlies, and con-formably o verlies, and iis s interbedded intorbodclod w ith, the? Formation 197). Unnamed F o r m a t i o n (Hubbard (Hubbard 1975) There major element element vvariation There iis s a large l a r g e spectrum spectrum a-F o f major a r i a t i o n within w i t h i n the the Silica content, which vvaries 49 to rrocks ocks o o-f the t h e Formation. S ilica c o n t e n t , which a r i e s f rfrom o m 45.8 t o '7 76 7., intermediate, X , can be used to t o discriminate d i s c r i m i n a t e basic, basic, intermediate3, and and acidic a c i d i c ;'flows. Â¥flows P2O On a-ff other CaD '-liD2 — P$g tthe he b asis o o t h e r c h a r a c t e r i s t i c oxidea, CaO TiClz basis MnO, and strong and tthe h e Na,O/K,O Na$I/KzO ratio, tthere here iiss a a s t r o n g dichotomy between + intermediate i n t e r m e d i a t e 'flows flows and a cidic f1ow<->. IIn n the the' between the t h e basic basic + and acidic iows. 'former former group he Na20/K2O r a t i o increases i n c r e a s e s tto o a m a x i , m u m which group tthe a maximuñ NaO/K.,O corresponds to to a a S i 0 2 content content o-f 65X, t h i s ratio r a t i o decreases decreases of 7., whereas this with increasing Major with increasing s i l i c a content i n the a cidic rrocks. ocks. Major acidic element modeling adequately model i n g cannot a d e q u a t e l y explain e x p l a i n these t h e s e oxide o x i d e abund<anc(as on the the abundances on basis a-F crystal -fractionation data basis o f crystal fractionation models. A l t h o u g h ttrace r a c e element element data models. Although are not complete, it are n o t complete, i t is i s suggested that that crustal m o l t i n g would crustal melting would betat best e x p l a i n the t h e origin o r i g i no-f o f the t h e acidic a c i d i c-flows. Â¥flows explain is It a volcanic pile which reaches its . characteristic oxides, - ratio, ratio silica content in the H. A. A. ( 1975) Lower Id. (197) and Wisconsin. and Wisconsin. U.S. U. 5 . Seal. Beol Hubbard Hubbard  - ¥ Kcaweenawan volcanic rocks M i c h i gan Keweenawan volcanic rocks of Michigan . Survey Survey Jour. J o u r . Research Research 3, 3, 329—41. 529-541 o 54 1 �I ZONE GEOMETRY GEOMETRYAND ANDVEIN VEIN PARACENESIS THE INFLUENCE THE INFLUENCE OF OF SHEAR SHEAR ZONE PARAGENESIS ON ATCAMERON CAMERON LAKE, LAKE, ON GOLD-PYRITE MINERALIZATION MINERALIZATIONAT NORTRWESTEIN NORTHWESTERN ONTARIO. . D.R. Poulsen3. D.R. ~Melling1, e l l i n ~D.H. D.H. l , wWatkinson', a t k i n s o n l , L.B. L.B. Chorlton2, c h o r l t o n 2 ,and andK.H. K.H. P oulsen 3 I The history h i s t o r y of of gold gold exploration e x p l o r a t i o n in i n the t h e Kenora—Fort Kenora-Fort Frances Frances area area Activity of n northwestern of o r t h w e s t e r n Ontario O n t a r i o dates d a t e s back back to t o the t h e mid—1800's. mid-1800's. A c t i v i t y peaked peaked between 1890 55 percent p e r c e n t of of 1890 and and 1910 1910 when when the t h e area a r e a accounted accounted for f o r over o v e r 55 Ontario's total Ontario's t o t a l gold g o l d production. production. Although the t h e area a r e a hosts h o s t s no no presently presently producing t h e recent recent i s again a g a i n high h i g h in i n view v i e w of o f the p r o d u c i n g gold g o l d mines, m i n e s , optimism o p t i m i s m is Cameron Lake Lake gold g o l d rush. rush. l o c a t e d 80 km south—southeast s o u t h - s o u t h e a s t of of The Cameron Cameron Lake Lake gold g o l d deposit, d e p o s i t , located Kenora, was Kenora, w a s originally o r i g i n a l l y discovered d i s c o v e r e d iin n 1960 1960 by by prospectors p r o s p e c t o r s working working for for Low gold with t tthat h a t ttime i m e ccoupled oupled w i t h aa ccomplex omplex Noranda Mines. Mines. Low g o l d pprices r i c e s aat subsurface s u b s u r f a c e geometry and poor poor outcrop o u t c r o p exposure exposure discouraged discouraged investment investment Four and dewelopment. F o u r separate s e p a r a t e diamond d i a m o n d drilling d r i l l i n g programs p r o g r a m s were were a n d development. conducted on the property prior to the discovery of a major conducted t h e p r o p e r t y p r i o r t o t h e d i s c o v e r y of a m a j o r zone z o n e of of gold Nuinsco/Lockwood joint 1983 by by the t h e Nuinsco/Lockwood j o i n t venture. venture. g o l d mineralization m i n e r a l i z a t i o n in i n 1983 Proven a t that t h a t time t i m e totaled t o t a l e d 1,287,000 1,287,000 tons t o n s grading g r a d i n g 0.154 0.154 P r o v e n reserves r e s e r v e s at oz/ton o z l t o n Au, Au, including i n c l u d i n g 807,000 807,000 tons t o n s grading g r a d i n g 0.194 0.194 oz/ton o z l t o n Au. Au. The Cameron Lake gold i s situated s i t u a t e d near near the t h e stratigraphic stratigraphic g o l d deposit d e p o s i t is ttransition r a n s i t i o n between b e t w e e n aa lower, l o w e r , mafic maf i c volcanic v o l c a n i c succession s u c c e s s i o n (Rowan (Rowan Lake Volcanics) mixed m mafic pyroclastic V o l c a n i c s ) aand n d aan n uupper p p e r mix-ed a f i c tto o ffelsic, e l s i c , ppartly artly p yroclastic ssuccession u c c e s s i o n (Cameron (Cameron Lake Lake Volcanics), V o l c a n i c s ) , but b u t within w i t h i n the t h e latter. latter. The and ooccurs deposit d e p o s i t is is epigenetic, e p i g e n e t i c , sstructurally t r u c t u r a l l y ccontrolled o n t r o l l e d and c c u r s in i n sheared sheared mafic maf i c metavolcanic m e t a v o l c a n i c rocks r o c k s adjacent a d j a c e n t to t o the t h e sheared s h e a r e d intrusive i n t r u s i v e contact contact with The sshear zone hhosting s i l l . The h e a r zone o s t i n g tthe h e ggold o l d ddeposit e p o s i t iis s aa w i t h a metagabbroic metagabbroic sill. dextral bbrittle—ductile, rittle-ductile, d e x t r a l strike s t r i k e slip s l i p system s y s t e m with w i t h an a n attitude a t t i t u d e of of 315/700 W and aa displacement Ore 315170' W and d i s p l a c e m e n t vector v e c t o r pitching p i t c h i n g 5' W. W. Ore sshoots h o o t s pitch pitch There w i t h i n the t h e plane p l a n e of of the t h e shear s h e a r zone. zone. T h e r e is is aapproximately p p r o x i m a t e l y 700 70' WW within Cameron Lake Shear llimited i m i t e d evidence e v i d e n c e to t o suggest s u g g e s t tthat h a t tthe h e Cameron S h e a r Zone Zone is is rrelated e l a t e d to t o the t h e regionally r e g i o n a l l y prominent prominent Pipestone—Cameron Pipestone-Cameron Fault. Fault. Three ddistinct have been been recognized recognized cutting Three i s t i n c t vveining e i n i n g eepisodes p i s o d e s have c u t t i n g the the mafic ccarbonatized arbonatized m a f i c metavolcanic metavolcanic rocks r o c k s of of the t h e Cameron Cameron Lake Lake Shear Shear Zone: Zone: early, veins (i) e a r l y , barren b a r r e n extensional e x t e n s i o n a l qquartz—carbonate u a r t z-carbonate v e i n s which have have (i) been buckled; buckled; major ((ii) i i ) aa m a j o r ssystem y s t e m of o f gold—bearing g o l d - b e a r i n g pyritic, p y r i t i c , quartz q u a r t z breccia breccia veins; veins ; (iii) ( i i i ) llate a t e cross—cutting c r o s s - c u t t i n g quartz—carbonate—chlorite—hematite—gold, quartz-carbonate-chlorite-hematite-gold, en—echelon en-echelon extension e x t e n s i o n veins. veins. ( i i ) breccia b r e c c i a veins v e i n s has has been been previously previously The significance s i g n i f i c a n c e of of the t h e stage s t a g e (ii) underestimated. They underestimated. They rrepresent e p r e s e n t aa s specific p e c i f i c oore r e ttype y p e wwhich h i c h ggenerally enerally The other, ggrades r a d e s greater g r e a t e r than t h a n 0.19 0.19 oz/ton o z l t o n Au. Au. o t h e r , lower lower grade g r a d e ore o r e type, type, consists c o n s i s t s of of pervasively p e r v a s i v e l y altered a l t e r e d carbonate—sericite—pyrite carbonate-sericite-pyrite rich rich phyllonitic Cameron Lake p h y l l o n i t i c rocks r o c k s and a n d occupies occupies a a large l a r g e volume v o l u m e of of the t h e Cameron Lake Shear Zone enveloping the t h e breccia b r e c c i a veins. veins. O I i I �I The The transition t r a n s i t i o n from f r o m ductile d u c t i l e cleavage c l e a v a g e development d e v e l o p m e n t to t o brittle brittle processes p r o c e s s e s within w i t h i n the t h e Cameron Cameron Lake Lake Shear S h e a r Zone Zone is i s manifested m a n i f e s t e d in i n the the formation f o r m a t i o n of of veins v e i n s and a n d vein v e i n breccias. b r e c c i a s . The The change c h a n g e from f r o m ductile d u c t i l e to to brittle b r i t t l e behavior behavior may be be the t h e result r e s u l t of of local l o c a l increases i n c r e a s e s in i n hydrothermal hydrothermal fluid f l u i d pressure p r e s s u r e which w h i c h facilitates f a c i l i t a t e s brittle b r i t t l e deformation d e f o r m a t i o n and a n d vein vein formation f o r m a t i o n by by reducing r e d u c i n g the t h e effective e f f e c t i v e normal normal stresses. s t r e s s e s . The The phyllonitic phyllonitic rocks s i n k for f o r the t h e gold—bearing g o l d - b e a r i n g fluids, f l u i d s , while w h i l e the t h e breccia breccia r o c k s formed f o r m e d aa sink veins v e i n s formed formed major major conduits c o n d u i t s enhancing enhancing fluid f l u i d circulation. circulation. The The localization l o c a l i z a t i o n of of economic economic quantities q u a n t i t i e s of of gold gold along a l o n g the t h e Cameron Cameron Lake Lake Shear Shear Zone Zone corresponds corresponds to t o the t h e development development of of oblique, o b l i q u e , secondary, secondary, At dextral, A t the the d e x t r a l , bedding—controlled b e d d i n g - c o n t r o l l e d sympathetic s y m p a t h e t i cshear s h e a r zones. zones. confluence s t e e p l y pitching, p i t c h i n g , dilatent dilatent t h e s e two t w o shear s h e a r systems s y s t e m s aa steeply c o n f l u e n c e of of these zone z o n e was w a s created c r e a t e d in i n which w h i c h ascending a s c e n d i n g hydrothermal h y d r o t h e r m a l . solutions solutions p r e c i p i t a t e d gold. gold. The The shear s h e a r zone zone model model serves s e r v e s to t o explain e x p l a i n the t h e complex complex precipitated subsurface s u b s u r f a c e geometry g e o m e t r y of of the t h e deposit, d e p o s i t , as a s well w e l l as as the t h e existence e x i s t e n c e of of hanging h a n g i n g wall w a l l and a n d footwall f o o t w a l l zones z o n e s on on either e i t h e r side s i d e of of the t h e main m a i n zone z o n e of of g o l d mineralization. mineralization. gold 1 Ottawa—Carleton Ottawa-Carleton Centre Centre for f o r Geoscience Geoscience Studies, S t u d i e s , Carleton C a r l e t on University, University, Ottawa, Ontario. Ontario. Ottawa, * Mineral M i n e r a l Deposits D e p o s i t s Section, S e c t i o n , Ontario O n t a r i o Geological G e o l o g i c a l Survey, Survey, Toronto, Toronto, Ontario. 2 Ontario. Economic Economic Geology Geology and and Mineralogy Mineralogy Division, D i v i s i o n , Geological G e o l o g i c a l Survey Survey of of Canada, Ottawa, Ottawa, Ontario. Ontario. Canada, 56 �PETROGENESIS OF OF ANORTHOSITIC ANORTHOSITIC ROCKS ROCKS OF O F THE THE DULUTH DrJLUTH COMPLEX COMPLEX PETROGENESIS I James D. Miller, M i l l e r , Jr., Jr., Minnesota Minnesota Geological G e o l o g i c a l Survey, S u r v e y , 2642 2642 University ~niversity Ave., St. St. James D. Ave., Paul, P a u l , Minnesota 55114 55114 The mafic m a f i c plutonic p l u t o n i c rocks r o c k s of of the t h e Middle Middle Proterozoic P r o t e r o z o i c Duluth Duluth Complex Complex in in northeastern >85%) n o r t h e a s t e r n Minnesota Minnesota include i n c l u d e aa wide wide variety v a r i e t y of o f plagioclase-rich p l a g i o c l a s e - r i c h (P1 ( P l >85%) rocks r o c k s belonging b e l o n g i n g to t o the t h e early—formed e a r l y - f o r m e d Anorthositic A n o r t h o s i t i c Series, S e r i e s , as a s well w e l l as a s younqer younqer rocks r o c k s dominated by troctolite t r o c t o l i t e and and olivine o l i v i n e gabbro g a b b r o (Troctolitic ( T r o c t o l i t i c Series). Series). Understanding U n d e r s t a n d i n g the t h e petrogenesis p e t r o g e n e s i s of o f the t h e anorthositic a n o r t h o s i t i c rocks, r o c k s , which which could c o u l d not n o t have have crystallized i s requisite r e q u i s i t e to t o understanding u n d e r s t a n d i n g the the c r y s t a l l i z e d directly d i r e c t l y from from basaltic b a s a l t i c liquids, l i q u i d s , is origin o r i g i n of of the t h e Duluth D u l u t h Complex. Complex. Field, F i e l d , petrographic, p e t r o g r a p h i c , and and petrochemical p e t r o c h e m i c a l studies s t u d i e s of of the t h e Duluth Duluth Complex Complex in i n the t h e Snowbank Snowbank Lake Lake quadrangle q u a d r a n g l e have h a v e been been useful u s e f u l in i n characcharacterizing t e r i z i n g the t h e kinds k i n d s of o f anorthositic a n o r t h o s i t i c rocks r o c k s that t h a t are a r e present p r e s e n t and and in i n establishing establishing their t h e i r genetic g e n e t i c relationship r e l a t i o n s h i p to t o one one another a n o t h e r and and to t o the t h e younger younger Troctolitic T r o c t o l i t i c Series Series rocks. rocks. . — The compositi~n, The major major anorthositic a n o r t h o s i t i c rock r o c k types t y p e s are a r e distinguished d i s t i n g u i s h e d by by modal modal composition, plagioclase p l a g i o c l a s e grain g r a i n size, s i z e , and and olivine o l i v i n e habit h a b i t (granular ( g r a n u l a r vs. v s . poikilitic; p o i k i l i t i c ; Miller M i l l e r and and Weiblen, 1 9 8 2 ) . Field F i e l d observations o b s e r v a t i o n s of of complex complex internal i n t e r n a l structures s t r u c t u r e s (based ( b a s e d on on Weiblen, 1982). lamination) l a m i n a t i o n ) and intrusive i n t r u s i v e and and stratiform s t r a t i f o r m contact c o n t a c t relationships r e l a t i o n s h i p s imply imply that t h a t the the Anorthositic A n o r t h o s i t i c Series S e r i e s rocks r o c k s formed formed from from diverse d i v e r s e magma magma types t y p e s during d u r i n g at a t least l e a s t three three major major stages s t a g e s of o f episodic e p i s o d i c intrusion. i n t r u s i o n . Reported Reported here h e r e are: a r e : 1) 1 ) what are a r e believed b e l i e v e d to to be b e the t h e physical p h y s i c a l and and chemical c h e m i c a l characteristics c h a r a c t e r i s t i c s of of the t h e magmas magmas that t h a t produced produced the the suite s u i t e of o f anorthositic a n o r t h o s i t i c rocks r o c k s and and how how these t h e s e characteristics c h a r a c t e r i s t i c s changed changed over o v e r the the intrusive 2 ) the t h e presumed presumed difference difference i n t r u s i v e history h i s t o r y of o f the t h e Anorthositic A n o r t h o s i t i c Series; S e r i e s ; and and 2) between between the t h e magmas magmas that t h a t produced produced the t h e Anorthositic A n o r t h o s i t i c Series S e r i e s and and the t h e younger younger Troctolitic T r o c t o l i t i c Series. Series. All All A n o r t h o s i t i c Series S e r i e s magmas magmas were were intruded i n t r u d e d into i n t o subvolcanic s u b v o l c a n i c chambers chambers at at Anorthositic depths d e p t h s of of about a b o u t 5—10 5-10 km km as a s crystal c r y s t a l mushes mushes containing c o n t a i n i n g as a s much much as a s 50 50 percent percent intratelluric Consequently, i n t r a t e l l u r i c plagioclase. plagioclase. C o n s e q u e n t l y , the t h e sequential s e q u e n t i a l intrusions i n t r u s i o n s of of these these viscous v i s c o u s magmas magmas considerably c o n s i d e r a b l y disrupted d i s r u p t e d the t h e internal i n t e r n a l structure s t r u c t u r e of o f previous p r e v i o u s crystal crystal accumulations. a c c u m u l a t i o n s . The The compositional c o m p o s i t i o n a l range r a n g e of o f complexly complexly zoned, zoned, intratelluric i n t r a t e l l u r i c pla— plagioclase g i o c l a s e (An (An 50—70) 50-70) is i s the t h e nearly n e a r l y same same for f o r all a l l anorthositic a n o r t h o s i t i c rock r o c k types. types. Textural, T e x t u r a l , modal, modal, and and mineral m i n e r a l compositional c o m p o s i t i o n a l data d a t a imply imply that t h a t the t h e compositional compositional diversity 1 ) in in d i v e r s i t y of o f the t h e plagioclase-laden p l a g i o c l a s e - l a d e n magmas magmas varied v a r i e d in i n two two general g e n e r a l ways: ways: 1) their and oother t h e i r MgO/MgO-4-FeO MgO/MgO+FeO ( I('mg') m g ' ) c ocomposition m p o s i t i o n and t h e r ccompositional o m p o s i t i o n a l pparameters a r a m e t e r s indicaindicat i v e of o f the t h e degree d e g r e e of o f differentiation; d i f f e r e n t i a t i o n ; and and 2) 2 ) in i n degree d e g r e e to t o which which the t h e magmas magmas were were tive olivine—saturated. olivine-saturated. I n general, g e n e r a l , olivine—undersaturated o l i v i n e - u n d e r s a t u r a t e d magmas magmas were were more more difdifIn ferentiated f e r e n t i a t e d (i.e., ( i . e . , lower lower tmg') I m g g ) than t h a n those t h o s e with w i t h olivine o l i v i n e on on the t h e liquidus l i q u i d u s upon upon intrusion. i n t r u s i o n . Most Most of o f the t h e compositional c o m p o s i t i o n a l diversity d i v e r s i t y was was apparently a p p a r e n t l y aa primary p r i m a r y characcharact e r i s t i c of o f the t h e Anorthositic A n o r t h o s i t i c Series S e r i e s magmas magmas as a s they t h e y were were intruded i n t r u d e d into i n t o the t h e Duluth Dull~th teristic Complex Complex as a s opposed opposed to t o having h a v i n g resulted r e s u l t e d from from differentiation d i f f e r e n t i a t i o n within w i t h i n the t h e Complex Complex chambers. chambers. The earliest e a r l i e s t stage s t a g e of o f Anorthositic A n o r t h o s i t i c Series S e r i e s magmatism magmatism produced produced medium— medium- to to The medium-coarse-grained troctolitic t r o c t o l i t i c anorthosites a n o r t h o s i t e s and and poikilitic p o i k i l i t i c olivine o l i v i n e anortho— anorthomedium—coarse—grained site. s i t e . These These early e a r l y magmas magmas had had the t h e highest h i g h e s t average a v e r a g e 'mg' Imgg composition c o m p o s i t i o n (25—30 (25-30 mole%) mole%) and and varied v a r i e d in i n the t h e degree d e g r e e to t o which which they t h e y were were olivine—saturated o l i v i n e - s a t u r a t e d upon upon intrusion. intrusion. O l i v i n e - s a t u r a t e d magmas magmas crystallized c r y s t a l l i z e d granular g r a n u l a r olivine o l i v i n e interstitial i n t e r s t i t i a l to t o pla— plaOlivine-saturated g i o c l a s e in i n troctolitic t r o c t o l i t i c anorthosite, a n o r t h o s i t e , whereas whereas those t h o s e that t h a t were were undersaturated u n d e r s a t u r a t e d in in gioclase olivine o l i v i n e produced produced poikilitic p o i k i l i t i c crystals. c r y s t a l s . Poikilitic P o i k i l i t i c olivine o l i v i n e probably p r o b a b l y formed formed by by r a p i d growth qrowth after a f t e r magmas magmas became became supersaturated s u p e r s a t u r a t e d with w i t h olivine o l i v i n e to t o the t h e extent extent rapid 57 I �I necessary n e c e s s a r y to t o nucleate n u c l e a t e crystals. crystals. In I n ccontrast o n t r a s t to t o the t h e early e a r l y stage, s t a g e , main stage stage magmas produced g a b b r o i c rock rock types. types. produced generally g e n e r a l l y coarser c o a r s e r grained g r a i n e d and and more more gabbroic Although the t h e average a v e r a g e 'mg' Img1 composition of of the t h e main stage s t a g e magmas was lower, lower, the the Although degree d e g r e e of of olivine o l i v i n e saturation s a t u r a t i o n was was similar s i m i l a r to t o that t h a t in i n the t h e early e a r l y stage s t a q e magmas. magmas. l a t e stage s t a g e magmatism, magmatism, olivine—undersaturated o l i v i n e - u n d e r s a t u r a t e d magmas magmas decreased d e c r e a s e d in i n relative relative During late abundance abundance such such that t h a t predominantly predominantly troctolitic t r o c t o l i t i c anorthosite a n o r t h o s i t e was was produced. produced. The The modal compositions compositions of of many many of of these t h e s e late l a t e stage s t a g e troctolitic t r o c t o l i t i c anorthosites a n o r t h o s i t e s approach approach t h o s e of of "normaF' "normal" troctolite t r o c t o l i t e (P1 ( P l <85%) < 8 5 % )implying implying a decrease d e c r e a s e in i n the t h e amount amount of of pla— plathose gioclase g i o c l a s e initially i n i t i a l l y entrained e n t r a i n e d in i n the t h e magmas. magmas. Moreover, Moreover, these t h e s e magmas maqmas were more c o n s i s t e n t l y saturated s a t u r a t e d with w i t h both both olivine o l i v i n e and and plagioclase p l a g i o c l a s e upon upon intrusion i n t r u s i o n into i n t o the the consistently Duluth Duluth Complex. Complex. The The late l a t e stage s t a g e Anorthositic A n o r t h o s i t i c Series S e r i e s magmatism magmatism is i s interpreted i n t e r p r e t e d to to be transitional t r a n s i t i o n a l to t o those t h o s e events e v e n t s which which produced produced the t h e Troctolitic T r o c t o l i t i c Series. Series. Petrochemical P e t r o c h e m i c a l data d a t a from from both b o t h rock rock series series of of the t h e Duluth Duluth Complex Complex and and from from aa v a r i e t y Keweenawan Keweenawan mafic volcanics v o l c a n i c s imply imply that t h a t the t h e parent p a r e n t magmas magmas were were derived d e r i v e d by by variety system fractionation f r a c t i o n a t i o n of of more more primitive p r i m i t i v e magmas magmas in i n mid— mid- to t o lower lower crustal crustal open system magma maqma chambers chambers (15—40 (15-40 km). km). Although Although Anorthositic A n o r t h o s i t i c Series S e r i e s magmas maqmas were were enriched enriched with w i t h plagioclase p l a g i o c l a s e crystals c r y s t a l s and and were, were, on on average, a v e r a g e , more more compositionally c o m p o s i t i o n a l l y evolved evolved than Troctolitic magmas, both than T r o c t o l i t i c Series S e r i e s magmas, ~ 0 t hseries s e r i e s were derived d e r i v e d from from the t h e same same primary primary magma Its composition can can be be approximated approximated by by tthe high-LU oohmaqma type. type. I t s composition h e pprimitive r i m i t i v e high-A1 livine v i n e tholeiites t h o l e i i t e s of o the t h e North Shore Shore Volcanic Volcanic Group Group (Green, (Green, 1981) 1981) and and is i s similar similar to t o MORE MORB except e x c e p t that t h a t it it is i s considerably c o n s i d e r a b l y enriched e n r i c h e d in i n incompatible i n c o m p a t i b l e elements. e l e m e n t s . Major Major element e l e m e n t data d a t a indicate i n d i c a t e that t h a t chinopyroxene c l i n o p y r o x e n e and and spinel, s p i n e l , in i n addition a d d i t i o n to t o olivine o l i v i n e and and p l a g i o c l a s e , were important i m p o r t a n t fractionating f r a c t i o n a t i n g phases, phases, as a s would would be be expected e x p e c t e d under under plagioclase, deep Kb). P l a g i o c l a s e was enriched e n r i c h e d in i n the t h e early e a r l y magmas magmas d e e p crustal c r u s t a l pressures p r e s s u r e s (5—10 (5-10 Kb). Plagioclase in i n part p a r t because of of the t h e effect e f f e c t of of pressure p r e s s u r e on on the t h e buoyancy buoyancy of of plagioclase p l a g i o c l a s e in in mafic m a f i c magmas. maqmas. AA decrease d e c r e a s e in i n the t h e amount amount of of entrained e n t r a i n e d plagioclase p l a g i o c l a s e and and aa trend trend p r i m i t i v e magma compositions with w i t h time time may may be related r e l a t e d to t o aa decrease decrease toward more primitive i n the t h e depth d e p t h of of source s o u r c e magma magma chambers chambers and and aa decreases d e c r e a s e s in i n the t h e residence r e s i d e n c e time time of of in primary magma in the crust, respectively. i s consistent c o n s i s t e n t with w i t h crustal crustal magma i n t h e c r u s t , r e s p e c t i v e l y . T h i s is This attenuation a t t e n u a t i o n as a s rifting r i f t i n g progressed. p r o g r e s s e d . The The transition t r a n s i t i o n from from Anorthositic A n o r t h o s i t i c to to Troctolitic T r o c t o l i t i c Series S e r i e s magmatism is i s comparable comparable to t o that t h a t observed observed at a t modern modern rift rift systems systems where the t h e rate r a t e of of spreading s p r e a d i n g increases i n c r e a s e s (Flower, (Flower, 1984). 1984). M i l l e r , J.D. J . D . and and Weiblen, Weiblen, P.W., P.W., 1982, 1982, 28th 28th I.L.S.G., I.L.S.G., p. 26. 26. Miller, p. Green, 1981, J.C., 1981, Basalt & s a l t Volcanism Volcanism Study Study Project, P r o j e c t , LPI, LPI, p. p. 30. 30. Green, J.C., Flower, Flower, M.F.J., M.F.J., 1984, 1984, Geology, Geology, v. v. 12, 12, p. p. 651. 651. 58 �I ALTERATION IIN STRATIGRAPHY AND ABD HYDROTHERMAL HYDROTHERMAL ALTERATION N AN AXARCHEAN ARCHEAN STRUCTURAL STRUCTUU STRATIGRAPHY SUBPROVINCE, N.W. N.W. ONTARIO LAKE AREA, AREA, WABIGOON WABIGOON SUBPROVIWE, ONTARIO ZONE, THE THE KATISHA KATISHA LAKE ZONE, W. Toronto Toronto Moreton, E.P., Esso Minerals Minerals Canada, Canada, 120 120 Adelaide Adelaide St. S t . W. Moreton, E.P., Esso M5W 1V9; lV9; and and Gerber, Gerber, R. R. Department Department of of Earth E a r t h Sciences, Sciences, University U n i v e r s i t y of of MSW \ Waterloo, Waterloo, Ontario N2L 3G1 The Katisha Lake area (92 30'OO" — 49 22'OO"), displays an a n exceptionally exceptionally I discrete well preserved Archean stratigraphic section comprising five discrete volcanic episodes centered around a major uplift zone. This tectonic tectonic rusive zone was the focus for associated shear zone development, intrusive activity and hydrothermal alteration. The basal b a s a l portion p o r t i o n of o r the t h e stratigraphy s t r a t i g r a p h y comprises the t h e Wapageisi wapageisi Lake Lake Group Group of of tholeiitic t h o l e i i t i c basalts b a s a l t s overlain o v e r l a i n by by heterolithic h e t e r o l i t h i c breccias, breccias, intruded l a y e r e d gabbro sill i n t r u d e d by a layered s i l l and capped by quartz q u a r t z porphyritic p o r p h y r i t ic f e l s i c volcanics. v o l c a n i c s . Uplift U p l i f t and and erosion e r o s i o n prior p r i o r to, t o , and and during d u r i n g the t h e capping caP P ~ % felsic The felsic f e l s i c volcanism, volcanism, led l e d to t o production p r o d u c t i o n of of an an angular a n g u l a r unconformity. unconformity. The -----7 - - 2 - - 0.. ---- L -aI -n- e Group n 2--*L<--l.-<,.*<,. overlying conglomerate, U V ~ L A Y A U Stormy ~~ L U S U I Y Lake W L U U ~ comprises G U U I ~ L A Z . C Z . a thin LUAU basal L J ~ z . polymictic p~ u~ A y ~ L L A L LuLLglomerate9 overlain o v e r l a i n by some some 500 m m of of dacitic d a c i t i c breccias, b r e c c i a s , followed followed by.a b y . a thick t h i c k sequence sequence A f t e r dacitic d a c i t i c volcanism, volcanism, aa series s e r i e s of of of of polymictic p o l y m i c t i c conglomerates. conglomerates. After vertical, v e r t i c a l , conjugate, c o n j u g a t e , ductile d u c t i l e shear s h e a r zones zones trending t r e n d i n g 120 120 and 180 180 formed formed Widespread carbonate c a r b o n a t e veining v e i n i n g and and in i n the t h e Wapageisi w a p a g e i s i Lake Lake Group Group rocks. -rocks. Widespread alteration a l t e r a t i o n occurred occurred in i n and and adjacent a d j a c e n t to, t o , these t h e s e shear s h e a r zones. zones. Synchronous Synchronous carbonate alteration non—shear! a l t e r a t i o n in i n the t h e Stormy Lake Group consisted c o n s i s t e d of of non-shear/ vein related areas of widespread pervasive carbonate—pyrite v e i n r e l a t e d a r e a s of p e r v a s i v e c a r b o n a t e - p y r i t e and and magnetite— magnetiteA series of composite, mafic to t o ultramafic ultramafic chiorite—pyrite c h l o r i t e - p y r i t e alteration. a l t e r a t i o n . A s e r i e s of composite, dykes dykes intruded i n t r u d e d into i n t o the t h e shear s h e a r zones zones during d u r i n g active a c t i v e carbonate c a r b o n a t e alteration alteration maybe maybe related r e l a t e d to t o subaqueous subaqueous trachy—basalt t r a c h y - b a s a l t flows flows which which extruded, e x t r u d e d , as a s part part of of the t h e Stormy Stormy Lake Lake Group, Group, some some 600 600 mm above above the t h e active a c t i v e shear s h e a r zones. zones. Later Later silicification with py, aasp silicification w i t h aassociated s s o c i a t e d py, s p and Au overprinted o v e r p r i n t e d the t h e carbonate— carbonatebearing b e a r i n g zones. zones. East—west East-west trending t r e n d i n g dextral d e x t r a l fault f a u l t zones zones with w i t h associated associated quartz of Stormy Lake Group sedimentation q u a r t z diorite d i o r i t e dykes marked the t h e end of s e d i m e n t a t i o n and maybe associated a s s o c i a t e d with w i t h batholith b a t h o l i t h emplacement emplacement and northward tilting t i l t i n g of of the the e n t i r e package. package. Late L a t e northeasterly n o r t h e a s t e r l y trending t r e n d i n g sinistral s i n i s t r a l faults f a u l t s associated associated entire with w i t h the t h e Manitou Fault F a u l t system system to t o the t h e west w e s t cut c u t all a l l the t h e above above rock rock types types and structures. structures. T I a •1 I I i I �THE THE MULCAHY MULCAHY LAKE GABBRO GABBRO AND AND RELATED RELATED INTRUSIONS INTRUSIONS ! Houston, Houston, TX, Houston, TX; TX; David DavidE.E.Maczuga, Maczuga,LEMSCO, LEMSCO, Houston, TX, 77058 77058 1 Donald Donald A.A. Morrison M o r r i s o n and and William W i l l i a m C. C. Phinney, Phinney, SN4 SN4 NASA/Johnson NASAIJohnson Space Space Center, The Mulcahy Lake gabbro gabbro is mafic The Mulcahy Lake i s a 63 63 square square km km llayered ayered m a f i c intrusion i n t r u s i o n which which resembles The intrusion resembles the t h e Skaergaard Skaergaard iinn many many respects. respects. The i n t r u s i o n iiss centered aatt 93.25W and49.35N, 49.35N,about about5050km kmsouthwest southwesto fofDryden Drydena tatt hthe southwestern llimits 93.25W and e southwestern imits of gabbroi nintrudes basaltic o f Eagle Eagle Lake. Lake. The The gabbro t r u d e s basal t i c t to o ssiliceous i 1iceous units u n i t s of o fthe t h eLower Lower Lake greenstone greenstone bbelt. Wabigoon Wabigoon SSeries, e r i e s , part p a r t of of the t h eCrow CrowLake—Savant Lake-Savant Lake elt. Two mafic be represented representedi nin tthe m a f i c to t o siliceous s i l i c e o u ssequences sequences may may be h e volcanics. volcanics. lliorites Diorites and ggranodiorites of the and r a n o d i o r i t e s of t h e Atikwa A t i kwa batholith b a t h o l it hintrude i n t r u d eboth b o t hgabbro gabbro and and volcanics.. v o l c a n i cs. Zircon my. (1). Z i r c o n from from the t h e gabbro gabbro yield y i e l d aaU/Pb UIPb age age of o f2733.2 2733.2 ÷1.01—0.9 +l.O/-0.9 my. ( 1 ) . PreviPreviously published zircon data (2) indicate crystallization of the batholith o u s l y p u b l i s h e d z i r c o n d a t a ( 2 ) i n d i c a t e c r y s t a l l i z a t i o n o f t h e b a t h o l i t h at at 2731.8 +1.61—1.3 2732.3+ I+1— .GI-1.3 my.my. t oto2732.3 - 2.9 2.9 my.,my., oneone t o to f i vfive e mmillion i l 1i o n years years at a tmost most 2731.8 +l The younger than than the younger t h e gabbro. gabbro. The vvolcanics o l c a n i c s vary vary from-2743 from-2743 to t o 2735 2735 my. my. approxiapproximately Sm—Nd analyses show gabbrowas wasdderived from aa source m a t e l y ((2). 2). Sm-Nd analyses show t h athat t t hthe e gabbro e r i v e d from source The i initial d e p l e t e d in i n light l i g h t rare r a r e earth e a r t h elements elements (1). (1). The n i t i a l SSr r ratio r a t i o of o f the the depleted gabbro i is s 0.7007, 0.7007, cconsistent o n s i s t e n t wwith i t h other o t h e r intrusives i n t r u s i v e s and and extrusives e x t r u s i v e s from from the the gabbro Wabigoon andQ uQuetico subprovinces, Wabigoon and e t i c o subprovinces, i n cincluding l u d i n g t hthe e AAtikwa t i kwa bbatholith, a t h o l i t h , and and sugsuggestive Rbddepletion g e s t i v e of o f aa moderate moderate Rb e p l e t i o n iin n the t h e source source compared compared t otot hthe e AAbitibi. bitibi. The iintrusion km The n t r u s i o n consists c o n s i s t s of o f aa llower o w e r and and middle m i d d l e zone zone each each about about two two km thick, t h i c k , aaone one km km thick t h i c kupper upper zone zone and and marginal marginal zones zones ooff variable v a r i a b l e thicknesses. thicknesses. The lower Each zoner erepresents Each zone p r e s e n t s a ad idistinct s t i n c t cooling c o o l i n g and and fractionating f r a c t i o n a t i n g regime. regime. The and mmiddle zonesf fractionated and i d d l e zones r a c t i o n a t e d from from the t h e floor f l o o upward r upwardwhereas whereas the t h e upper upper zone zone towards ffractionated r a c t i o n a t e d from frcin tthe h e roof r o o f downward downward towards t h ethe i n tinterior e r i o r oof f tthe h e intrusion. intrusion. Marginal zonesf rfractionated fromt hthe towardt hthe Marginal zones a c t i o n a t e d from e wwalls a l l s toward e i interior. n t e r i o r . The The primary primary phasesaare pyroxenes i including n c l u d i n g pigeonite, p i geoni t e , hornblende hornblende and and oxides. oxides. phases r e pplagioclase, l a g i o c l ase, pyroxenes Olivine t h e . b a s e ofo fthe t h elower lowerzone zoneand and i-n i-n the the O l i v i n e occurs occurs iin n ultramafic u l t r a m a f i c units u n i t s ata tthe-base upper zone, zone,i in upper n 'iron—rich i r o n - r i c h UUnits n i t s aatt the t h e top t o p of o fthe t h elower l o w e rzone, zone, and and -in i n a meterthick The oxides t h i c k marker marker horizon h o r i z o n near near the t h e base base of o f the t h e middle m i d d l e zone. zone. The oxides a re are chromite Plagioclase, chromi t e tto o chromian chromian sspinel p i n e l and and later 1a t e r magnetite. magneti t e . P I a g i o c l a s e , pyroxenes pyroxenes and and olivine Hornblende andmagneti magnetite 01 iv i neform formcumulates. cumulates. Hornblende and t e aare r e iritercumulus i n t e r c u m u l us phases. phases. The and fractionation The bbulk u l k composition composition is i s tholeiitic t h o l e i i t i c and f r a c t i o n a t i o n ffollows o l l o w s an ronan iiron— enrichment t trend r e n d wwith ith a a decreasing decreasing Mg/Mg+Fe r a tratio i o w with i t h sstratigraphic t r a t i g r a p h i c height height enrichment Mg/Mg+Fe andaa rrelatively and e 1 a t i v e l y constant constant ssilica i 1 ica content. content. Reversals iinn the Reversals t h eMg/Mg+Fe Mg/Mg+Fe r ratio a t i o in i npyroxenes pyroxenes and and concomitant concomitant changes changes in in showt hthat zoner erepresents oother t h e r phases phases show a t t hthe e mmiddle i d d l e zone p r e s e n t s an an i n influx f l u x o of f rrelatively elatively p r i s t i ne liquid l i q u i dfollowing f o 1 1 owingnearly n e a r l ycomplete complete fractionation f r a c t i o n a t i o n of o f the t h e pre-existing p r e - e x i s t i ng pristine liquid l i q u i dini nthe t h echamber. chamber. S m a l l e r sscale c a l e rreversals e v e r s a l s wwithin i t h i n tthe he m i d d l e zone self Smaller middle zonei titself i n d i c a t e further f u r t h e r introduction i n t r o d u c t i o n of of liquid l i q u i dasasthe t h emiddle m i d d l e zone zone m e l t ccrystallized. rystallized. indicate melt The betweenzones zonesa rare The ccontacts o n t a c t s between e c ccomplex i n ~ex l in interleavings t e r l e a v i nqs o of f ffractionated r a c t i o n a t e d and and less 1ess ffractionated r a c t i o n a t e d assemblages. assemblages. Relatively byccrystallizael a t i " e l y dense dense 1liquids iquid"s produced produced by r y s t a l 1 izapast ttion i o n near near the t h ewalls w a l l s(as ( a sliquid l i q umoved i d moved p a sthem) t them)appear appeartot have o havebeen beenconvected convected downward t oto form anomalously f fractionated r a c t i o n a t e d horizons h o r i zons in i n the t h e middle m i d d l e zone zone and and downward form anomalously possibly as we1 well. possi b l y the t h e lower lower zone zone as 1 Dike—like D i ke-1 ike uultramafic l t r a m a f i c cumulates cumulates ooff 01 i v i n e and and pyroxenes w i t h minor olivine with plagioclase p l a g i o c l a s e and and cchromite h r m i t e ooutcrop u t c r o p iin n Straight S t r a i g h t Lake, Lake, south south ofo fthe t h eMulcahy MulcahyLake Lake gabbro. Similar gabbro. S i m i l a r cumulates cumulates occur occur iin n the t h e upper upper zone zone of o f the t h e gabbro. gabbro. These 1latter a t t e rcumulates cumulates contain c o n t a i ncumulus cumul us chromian chrcini an sspinel p i n e l and and intercumulus intercumul us magnetite. magneti t e . The presence presenceofof i intercumulus The n t e r c u m u l u s mmagnetite a g n e t i t e i n dindicates i c a t e s t hthat a t t the h e ultramafics u l t r a m a f i c s are are co-magmatic presence ooff chrome—rich speciesi in co-magmatic wwith i t h the t h e gabbro. gabbro. The The presence chrome-rich species n both b o t h the the Straight and Mulcahy Lake S t r a i g h t Lake and u l t r a m a f i c s alike a1 ike suggests aa correlation correlation Lake ultramafics between tthe between h e two. two. IIff so, so, both b o t h tthe h e ffloor l o o r and and the t h e roof r o o f of o f the t h e intrusion i n t r u s i o n are are c h a r a c t e r i z e d by h e presence f uultramafic l t r a m a f i c cumulates p r e s e n t i n g t hthe e f first irst characterized by tthe presenceo of cumulatesr erepresenting productsofofc rcrystallization e i ninitial i t i a l liquid. 1i q u i d . products y s t a l 1iz a t i o n o foft hthe 6600 . �I Layered iintrusions n t r u s i o n s closely c l o s e l yresembling resembl i n g the t h eMulcahy Mulcahy Lake Lake gabbro gabbro in i n bulk bul k Layered composition, crystallization c r y s t a l 1i z a t i o nsequences sequences and and which which are a r e identical i d e n t i c a l in i n stratistrati- g r a p h i c age e nnorthern o r t h e r n pperiphery e r i p h e r y ofof tthe h e AAtikwa t i kwa bbatholith a t h o l i t h at a t Trap Trap graphic ageoccur occuronont hthe Lake, Nabish 80 km. km. (Chroniite (Chromite is i s aa Nabish Lake Lake and and Denmark Denmark Lake, Lake, aa distance d i s t a n c e of of 80 prominent phasei nin tthe Lake uultramafic). prominent phase h e Trap Trap Lake l t r a m a f i c ) . These These mmafic a f i c iintrusions n t r u s i o n s reprerepresent sent centers c e n t e r s of o fbasaltic basal t i niagmatism c magmatism active a c t i v esimultaneously, simultaneously, presumably presumably during during the t h e waning waning stages stages of development development of the t h eCrow CrowLake—Savant Lake-Savant Lake Lake greenstone greenstone belt. The belt. The aactivity c t i v i t y ofofthe t h mafic e maficcenters c e n t e rwas s waseclipsed e c l i p s e dbybyemplacement emplacement ooff the the batholith. b a t h o l it h . The development development ofof caic—alkaline calc-a1 k a l ine liquids l i q u i d smust musthave haveaccompanied accompanied The the succeeded onaavvery t h e mafic m a f i c magmatism magmatism o rorsucceeded i t iton e r y sshort h o r t time t i m e scale. scale. A A ddirect i r e c t petrogenetic p e t r o g e n e t i c link l i n kbetween between the t h egabbro gabbro and and the t h e intruded i n t r u d e d volcanics volcanics has has not n o t been been demonstrated. demonstrated. The The gabbro gabbro is i s somewhat somewhat f rfractionated a c t i o n a t e d compared compared to to intruded basal t s which which have have llight i g h t rare r a r e earth e a r t h element e l ement depleted d e p l e t e d patpati n t r u d e d pillow p i 1 l o w basalts terns. Isotopic terns. I s o t o p i c signatures s i g n a t u r e s allow a1 low aa co—magmatic co-magmatic relationship r e 1 a t i o n s h i p but b u t do do not not require r e q u i r e one. one. Whether gabbro and andi its Whether oor r nnot o t the t h e Mulcahy Mulcahy Lake Lake gabbro t s companion companion i intruntrui t i a1 representatives representatives s i o n s represent r e p r e s e n t end i n in t h ethe v ovolcanic l c a n i c c ycycle c l e o rorininitial sions endmembers members of o f aa plutonic p l u t o n i c cycle c y c l e petrogenetically p e t r o g e n e t i c a l l y ddistinct i s t i n c t from from the t h e former former is i s an an interestinteresting (3). i n g question q u e s t i o n (3). (1) ( 1 ) Morrison M o r r i s o n D., D., Davis DavisD.W., D.W., Wooden Wooden J.L., J.L., Bogard BogardD.D., D.D., Maczuga Maczuga D.E., D.E., Phinney Phinney W.C. and Ashwal AshwalL.D., L.D., 1985, Age of of the W.C. and 1985, Age t h e Mulcahy Mulcahy Lake Lake iintrusion, n t r u s i o n , NW NW Ontario, Ontario, and implications and imp1 i c a t i o n s for f o r the t h e origin o r i g i nofofgreenstone—granite greenstone-grani t e belts. be1t s In I n press, press, Earth Earth and Planet. Sci. D.W., and Planet. Sci. Letts. L e t t s .(2)( 2Davis C.E. and andKrogh Krogh T.E., T.E., 1982, 1982, ) Davis D.W., Blackburn BlackburnC.E. Zircon ages from from tthe Lakes area, area, Wabigoon Z i r c o n U—Pb U-Pb ages h e Wabigoon-Manitou Wabi goon-Mani t o u Lakes Wabi goon subprovince, subprovi nce , . northwest Ontario, CanadianJour. Jour.EEarth Sci. 19 northwest O n t a r i o , Canadian a r t h Sci. 19 p. p. 264. 264. (3) ( 3 )Davis DavisD.W. D.W. and and Edwards G.R., 1983, Edwards G.R., 1983, Zircon Z i r c o nU—Pb U-Pb ages ages from from the t h e Kakagi Kakagi Lake Lake area, area, Wabigoon Wabigoon Subprovi nce, northwest n t a r i o , Canadian Canadian Jour. arth S c i 19 19 p. p. 1235. 1235. Subprovince, northwest OOntario, Jour. EEarth Sci. . I I I I •1 I I 61 i I �I Volcanic Volcanic stratigraphy and nature of the the semi—conformable semi-confarmable alteratioin zone beneath the the Mattabi massive suiphide sulphide deposit, Sturgeon Lake, Ontario Morton, Department Department of of Geology, Geology University L. Morton, University of o+ Minnesota— MinnesotaL Duluth, Duluth Minnesota, Di-iluth, Duluth, Minnesota, 55812 55812 Groves, Newmont Exploration Ltd., Ltd. Duluth, D. A. . Groves, D. Newmont Exploration Duluth. Minnesota Minnesota 3. J. M. M. Franklin, Geological Geological Survey of Canada, Canada, 601 601 Booth Booth St., St.! Ottawa, Ontario R. hyalotuffs4 Subaerial and shallow shallow subaqueous subaqueous ma-Fic maf ic hyalotuf f s, lava lava and flow breccias, breccias, and and felsic lava flows and flows and pyroclastic flow and and fall fall deposits form a 2 pyroclastic 2 km k m thick succession beneath beneath the Mattabi Mattabi massive sulphide deposit. succession deposit. The The lowermost part o-F the succession succession is is composed composed of of massive and of the and flows and and flow flow breccias breccias which which are amygdaloidal ma-Fic maf ic flows interlayered with with repetitive sequences sequences of thinly bedded pillow lavas and hyaloclastites are absent felsic tuff; pillow absent from from this succession. this succession. Amygdaloidal Amygdaloidal felsic f elsic lavas lavas overlie over1 ie the the mafic maf ic flow succession succession and and are local1 locally capped by by a coarse explosion flow y capped believed to have initiated breccia. This breccia is believed initiated a a period period of ma-fic hydrovolcanic activity activity which which produced produced ash—laden of mafic hydrovolcanic ash-laden falls, surges, surges, and flows; these deposited thin to to thickly thickly Periods of water exclusion resulted in bedded hyalotuffs. bedded hyalotuf f s. in the formation of of scoria—rich scoria-rich beds. beds. These eruptions cone and and represent represent aa submergent submergent constructed aa tuf-f tuff cone hydrovolcanic cycle. cycle. Pyroclastic the immediate mine Pyroclastic flow flow deposits deposits -form form the -Footwall strata strata and and include include a) a) massive massive basal basal and overlying footwall These bedded bedded ash tuffs, and b) b) massive massive pumiceous pumiceous units. units. These deposits overlie overlie and and are are intercalated intercalated with with the thema-Fic mafic hyalotuf-f sequence. hyalotuf f sequence. The volcanic rocks beneath the the Mattabi deposit deposit have have hydrothermal alteration alteration and undergone hydrothermal and subsequent subsequent regional regional greenschist Within the the footwall greenschistmetamorphism. metamorphism. Within footwall volcanic volcanic sequencefour four chemically mineralogically sequence chemical 1 y and and mineralogical ly distinct alteration types types have have been been defined: defined: iron least altered, iron carbonate—chlorite, chioritoid, carbonate-chlorite, chloritoid, and sericite. sericite. Least Least altered rocks have been affected primarily by regional greenschist greenschist thus the freshest rocks rocks to ta be be facies metamorphism and are thus found in the area. area. They are largely largely confined to to mafic mafic flows flows hyalotuffs. Iron chloritoidand hyalotu-ffs. Iron carbonate-chlorite carbonate—chlorite and and chloritoid— type alteration form a widespread, semi—conformable semi-conformable zone zone beneath beneath the Mattabi Mattabi deposit; these these assemblages assemblages are are largely largely confined to t o felsic felsic pyroclastic pyroclastic flows flows and and lavas. lavas. Chloritoid Chioritoid believed to have formed formed from the interaction of iron—rich is believed iron-rich chlorite and a hydrous aluminum silicate silicate during during metamorphism. metamorphism. Sericite—type Sericite-type alteration envelopes and/or and/or crosscuts crosscuts the the earlier alteration. It I t is is semi— semiearlier iron carbonate-chlorite carbonate—chlorite type alteration. and is is most most abundant abundant within within conformable to stratigraphy and -felsic pyroclastic pyroclastic flow flow deposits. felsic An An alteration model is is proposed proposed in in which which seawater, seawater, trapped within within a thick, thick, submerged pile of mafic lava trapped lava flows flows and breccias, breccias, was heated and heated by by the Seidelman Beidelman Bay intrusion. intrusion. 6622 �I Thin, Thin, impermeable impermeable felsic f e l s i c lava l a v a fflows lows o v e r l i e the t h e mafic mafic overlie succession and and produced produced aa cap cap to t o the t h e hydrothermal h y d r o t h e r m a lreservo:ir. reservoir. High fluid f l u i d temperatures and low low water/rock w a t e r / r o c k ratios r a t i o s within w i t h i n the the rreservoir e s e r v o i r resulted r e s u l t e d in i n the t h e formation f o r m a t i o n of o f aa fluid f l u i d rich r i c hini nFe., Fe, Mn, Na, Na, and, and, presumably, Mn, presumably, C02. C 0 2 . The The C02 C 0 2 is i s believed b e l i e v e d to t o have have been derived d e r i v e d from f r o m diagenetic d i a g e n e t i c carbonate. carbonate. Deep-seated tectonism t e c t o n i s m within w i t h i n the t h e volcanic v o l c a n i c pile p i l e produced produced Deep—seated high—angle h i g h - a n g l e faulting f a u l t i n g which allowed a l l o w e d the t h e sudden sudden release r e l e a s e of of ffluids l u i d s from f r o m the t h e reservoir. reservoir. M i g r a t i o n of o f the t h e fluids f l u i d s through through Migration permeable pyroclastic p y r o c l a s t i c rocks r o c k s resulted r e s u l t e d in i n base—fixing b a s e - f i x i n g reactions reactions and the t h e formation f o r m a t i o n of o f the t h e semi—conformable, semi-conformable, ankerite—chlorite ankerite-chlorite alteration a l t e r a t i o n zone. zone. The fluids f l u i d s boiled b o i l e d as as they t h e y neared neared the the seafloor s e a f l o o r , and and siderite s i d e r i t e was was deposited d e p o s i t e d throughout t h r o u g h o u t the t h e rocks rocks Suiphide beneath the t h e discharge d i s c h a r g e area. area. S u l p h i d e minerals m i n e r a l s then then accumulated Later, accumulated on on the t h e seafloor. seafloor. L a t e r , near surface s u r f a c e interaction interaction off felsic o f e l s i c rocks r o c k s and warm seawater at a t high h i g h water/rock w a t e r / r o c k ratios ratios produced the t h e sericitic s e r i c i t i c alteration a l t e r a t i o n assemblage. assemblage. I I I I I I I •1 I 63 I I �STRUCTURAL ANALYSIS RANGE AND AND ADJACENT ADJACENT BASAL BASAL DULUTH DULUTH ANALYSIS OF THE NORTHEASTERN MESABI RANGE COMPLEX EUGENE MULLENMEISTER, MULLENMEISTER, TIMOTHY TIMOTHY B. B. HOLST, HOLST, JOHN JOHN C. C. GREEN, GREEN, Department Department of of Geology, Geology, and Natural Resources Research Research Institute, Institute, University University of of Minnesota Minnesota Duluth, Duluth, W. WEIBLEN, WEIBLEN, Department of of Geology Geology and and GeophyGeophyDuluth, Minnesota 55812, and PAUL W. sics, sics, University University of Minnesota, Minnesota, Minneapolis, Minneapolis, Minnesota Minnesota 55455 55455 I I Information Information on the the structural structural geology geology of of the the Biwabik Biwabik Iron Iron Formation Formation (BIF) (BIF) and and the base of the Duluth Complex for this poster poster session has been been compiled from state geological geological maps, maps, mining company company maps, maps, structure structure contour contour maps maps based based on on drill hole hole data, data, drill core logs and field observations. observations. The The data data covers covers aa mi. long portion of the northeastern northeastern Mesabi Range 24 mi. Range of of Minnesota, Minnesota, extending extending from the Embarras (T59N, RI6W), R16~),to to the the Dunka Dunka Mine Mine on on the the Embarras mine west west of of Aurora Aurora (T59N, south south side of Birch Lake Lake (T61N, (T61N, RI2W) ~ 1 2 and ~ and ) the the adjacent adjacent Duluth Duluth Complex Complex to to the the southeast. A total total of 31 31 faults faults in in the the BIF BIF and and 16 16 faults faults in in the the base base of of the the Duluth Complex Complex and several several folds folds are are inferred. inferred. Both the the BIF BIF and and Duluth Duluth Complex Complex are affected by six six of of the the faults. faults. Displacement along the faults, faults, fold amplitude and wavelength wavelength were estimated estimated from from the the structure structure contour contour maps. maps. ft. in Displacements along faults occurring in the iron formation range from 7 ft. the Peter Peter Mitchell Mine to to 450 450 ft. ft. along along the the Siphon Siphon Fault Fault west west of of the the Spring/Siphon SpringISiphon Mine. Mine. The displacement displacement is is greater greater than than 80 80 ft. ft. along along seven seven of of the the faults faults and 50 50 ft. or or less less along along the the remaining remaining 24. 24. N8OE) in the BIF, the downthrown For nine northeast—trending northeast-trending faults (N1OE (N10E to N80E) side is is to to the the southeast southeast for for five five and and to to the the northwest northwest for for three three with with one one unknown. 20 northwest—trending northwest-trending faults faults (N15W (N15W to to N5OW), N~OW),the the downthrown downthrown side side unknown. For 20 is divided evenly to to the the northeast northeast for for 10 10 and and to to the the southwest southwest for for'10. 10. There There are two N-S faults, one with N—S trending faults, with the east side down and one with the west side down. down. A total total of 16 16 faults faults give give aa cumulative cumulative east east side side down down displacement displacement side 1222 ft. ft. and and 14 14 faults faults give give aa cumulative cumulative west west side side down down displacement displacement of of of about 1222 about 705 ft. about 705 ft. Folding occurs in the iron formation formation north of Aurora and to the east through the Wentworth anticline north north of of Aurora Aurora trends trends generally generally E—W E-W for for Wentworth Mine. A broad anticline approximately It has an amplitude amplitude of about mi. about 150 150 ft., ft., and and aa map map distance distance approximately 44 mi. from from crest crest to to trough trough of of its its attendant attendant syncline syncline to to the the north north of of about about 0.5 0.5 mi. mi. The anticline anticline flattens flattens out out for for about about 1.0 1.0 mi. mi. west west of of the the Knox Knox Mine. Mine. It It is is apparent again east of the Knox Mine and continues for about 2.5 2.5 mi. mi. on a general general E—W E-W trend trend through through the the Wentworth Wentworth Mine. Mine. The amplitude amplitude increases increases to to 250 250 ft. and the map distance from crest to trough decreases to 600 ft. at the WentWent— E—W, it is offset to worth Mine. Mine. Although the general trend of the anticline is E-W, the north in several places giving it it aa sinuous sinuous axial axial trend. trend. Only one structure, structure, the the Siphon Siphon Fault, Fault, is is observed observed to to affect affect the the stratigraphic stratigraphic thickness of Animikie Animikie Group Group rocks. rocks. It trends N40W a vertical vertical displacedisplaceN4OW and has a ment of about about 450 450 ft., ft., down down to to the the northeast. northeast. There is an abrupt decrease decrease in in thickness of the Lower Cherty Member of of the the BIF from from west west to to east east across across the the fault, from 140 fault, 140 ft. west of the the fault fault to to 60 60 ft. ft. east east of of the the fault. fault. The The Lower Lower continues to thin gradually to the east until it disappears completely Cherty continues near the the south south side side of of Birch Birch Lake. Lake. The fault fault corresponds corresponds to a lithologic lithologic boundary in the Archean basement between Knife Lake Group metamorphosed metamorphosed sedimentary volcaniclastic rocks to the the east. east. and volcarticlastic rocks to to the the west west and and Giants Giants Range Granite Granite to 64 I �Displacement along faults occurring in the Duluth Complex is estimated for 11 11 of the 16 16 faults faults and range range from from 11 ft. in the Dunka to 360 360 ft. ft. at at the the Minnamax Minnamax Dunka Mine to faults and Project. displacement is greater than 100 ft. for five of the faults Project. The displacement 30 30 ft. or less less for for the the remaining remaining six. six. For nine northeast trending trending faults faults (NO5E (N05E to to ~ 5 5 in ~ )the the Duluth Duluth Complex, Complex, the the N55E) downthrown side is to the southeast for four, four, to the northwest for three and (N30~ to N5OW), ~ 5 0 the the ~ ) ~ unknown for two. two. For six northwest trending trending faults faults (N3OW unknown for to downthrown side is is to to the the northeast northeast for for four four and and to to the the southwest southwest for for two. two. downthrown side There is one N—S N-S trending trending fault fault with with the the west west side side down. down. The east east side side down down displacement for six six of of eight eight faults faults totals totals an an estimated estimated 630 630 ft. ft. The west side side displacement for down displacement displacement for for five five of of six six faults faults totals totals an an estimated estimated 650 650 ft. ft. Undulations at the base of the Duluth Complex are shown by structure contour maps in the Dunka Dunka Mine and and the the Minnamax Minnamax Project Project area. area. An antiform antiform structure structure begins at the northwest end of the Minnamax Project and trends S4OE S40E for about At this point the trend changes N70E for for about about another another 2.5 2.5 mi. mi. The The mi. At changes to to N7OE 0.5 mi. attendant synform to the north is parallel to the antiform structure for about 1.5 mi. mi. to the east and changes 1.5 changes to to a N—S N-S trend trend over over the the next next 0.7 0.7 mi. mi. The maximum mum amplitude amplitude of of this this antiform antiform structure structure is is about 350 350 ft. ft. with aa map distance distance from E—W trending from crest crest to to trough trough of of 1500 1500 ft. ft. Several E-W trending undulations undulations occur occur at at the the southeast southeast end end of of the the prospect. prospect. They can be traced for for about about 2000 2000 ft. ft. Axnpli— Amplitudes range N70W range from from 100 100 ft. ft. to to 450 450 ft. ft. with with aa wavelength wavelength of of 900 900 ft. ft. A N7OW trending antiformal antiformal structure structure occurs occurs in in the the Dunka Dunka Mine Mine area. area. It has an ampliampliof about 550 ft. ft. and and coincides with with an an anticline anticline observed in outcrop of the tude of underlying BIF in underlying in the the Dunka Dunka Mine. Mine. The highest grade of sulfide sulfide mineralization mineralization in the area area is is associated associated with with this this structure. structure. The pattern pattern of faulting faulting appears appears to to be be Archean basement basement litholbgies. litholbgies. affected by Archean All seven faults faults occurring in the BIF over an 11 mile stretch from the Siphon Siphon Fault to the east end of the Peter Mitchell Mine trend to the northwest. Here Here in the Dunka MineMine to theto eastthe the iron formation overlies Archean granite. and in the Dunka east the iron formation overlies Archean granite. and The northwest northwest trend is still present east of the Peter Mitchell Mine into into the Dunka Mine but it becomes more complicated where the BIF is intruded by the Duluth Complex. West of Duluth of the the Siphon Siphon structure, structure, the the dominant dominant northwest northwest fault fault patpattern is present present but complicated complicated by by aa northeast northeast component. component. Here the iron iron forfortern mation is folded and overlies Archean Knife Lake Group metamorphic rocks. This This indication indication that the style of deformation was controlled to some degree by the basement rocks rocks was suggested suggested earlier earlier by by White White (1954). (1954). • Co., Reserve Mining Co., Co., LTV Grateful appreciation appreciation is extended to Erie Mining Co., Corp., U.S. U.S. Steel corp. corp. and and Bear Bear Creek Creek Mining Mining Company Company for providing access steel Corp., mine properties and and to the Minnesota Minnesota Department Department of Natural Resources to data and mine for providing funding and data for for this this project. project. White, D.A., 1954, 1954, The The Stratigraphy Stratigraphy and and Structure Structure of of the the Mesabi Mesabi Range, Range, White, D.A., Minnesota: Minn. Geol. Survey 38, 92 92 pp Survey Bull. 38, •1 I 65 I �I Proterozoic Proterozoic Diabase Diabase Dike Dike Swarms Swarms in in Wisconsin Wisconsin M.G. M.G. MUDREY, MUDREY, Jr. Jr. (Wisconsin (Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, 1815 1815 University University Avenue, Avenue, Madison, Madison,Wisconsin Wisconsin53706> 53706) P.E. MYERS, (Department (Departmentof of Geology, Geology,University UniversityofofWisconsin—Eau Wisconsin-EauClaire, Claire, P.E. MYERS, Eau Claire, Claire, Wisconsin Wisconsin 54701) 54701) Eau I Regional geologic geologic mapping mapping and and analysis analysis of of regional regional aeromagnetic aeromagnetic maps maps Regional have identified identified two two areas areas of of mafic mafic dike dike swarms swarms in in Wisconsin: Wisconsin: (1) (1) aa central central have Wisconsin area, area, and and (2) (2) aa northern northern area area adjacent adjacent to to Keweenawan Keweenawan intrusive intrusive Wisconsin suites. There There appears appears to to be be little littledifference differenceininmajor majorelement elementchemistry chemistrybebesuites. tween the the two two swarms, swarms, although although the the northern northern swarm swarm and and some some of of the thecentral central tween swarm dikes dikes have have been been weakly weakly metamorphosed. metamorphosed. swarm The The dike dike swarm swarm in in central central Wisconsin Wisconsin is is defined defined principally principally from fromregional regional aeromagnetic aeromagnetic maps and and generally generally trends trends east east to to northeast. northeast. Individual Individual dikes dikes are are identified identified by by strong strong magnetic magnetic lows lows that that can can be be traced traced for forover over 260 260km tanand and continue beyond beyond the the limits limits of of the theavailable availableaeromagnetic aeromagnetic data. data. The The swarm swarm is is continue at at least least 120 120 km km wide wide and and is is lost lost at atits itssouthern southernmargin marginby by the thelimits limitsof of aero— aeromagnetic coverage. coverage. Isolated Isolated outcrops outcrops of of this this swarm swarm are are known known to to the the south. south. magnetic Some Some individual individual dikes dikes exceed exceed 80 80mm ininwidth. width. Where Where sampled, sampled, these these large large dikes dikes are are dominantly dominantly olivine olivine gabbro gabbro to to anorthositic anorthositic troctolite troctolite and and are are continental continental tholeiite, based based on on major major element elementchemistry. chemistry. In In detail, detail, the the dikes dikes can can be be diditholeilte, vided vided into into aa suite suite rich rich in in iron iron and and titanium titanium with with aa strong strong reversed reversed magnetic magnetic polarity polarity anda a n d amore moreaverage averagecontinental continentaltholeiite tholeiitesuite suitewith witha aweak weaknormal normalpopolarity signature. signature. Alteration Alteration is is minimal. minimal. Most Most of of the the recognized recognized swarm swarm is is larity hosted in in Proterozoic Proterozoicrock. rock. hosted The The northern northern dike dike swarm swarm is is defined defined from from outcrop outcrop with with supplemental supplemental defi— definition from from regional regional aeromagnetic aeromagnetic data. data. Aeromagnetic Aeromagnetic data data are are not not as as useful useful nition in in defining defining the the extent extent of of this this swarm swarm because because of of the the proximity proximity to to strongly strongly magmagnetized Keweenawan Keweenawan intrusives. intrusives. The The swarm swarm generally generally trends trends northwestward northwestward and and netized does not not appear appear to to be be as as continuous continuous as as the the central central swarm. swarm. Some Some individual individual does dikes dikes appear appear to to be be offshoots offshoots of of the theKeweenawan Keweenawan Mellen Mellenand andMineral MineralLake Lakeintruintrusive suites suites and and related related rock. rock. Locally Locally some some of of these these dikes dikes are are altered altered to to sive uralite and and chlorite, chlorite, probably probably by by subsequent subsequent metamorphism metamorphism of of the the adjacent adjacent uralite gabbroic complexes. complexes. AA few few dikes dikes cut cut the the Mellen Mellen granije. granite. gabbroic Another Another older, older, poorly poorly defined defined set set of of diabase diabase dikes dikes is is known known in in the the cencentral area, area, and and is is known known to to cut cut the the 1,760 1,760 Ma Ma rhyolite rhyolite and and granite granite in in southern southern tral Wisconsin. This This suite suite is is metamorphosed metamorphosed to to hornblende—chlorite—biotite hornblende-chlorite-biotite assemassemWisconsin. blages, has has aa weak weak tectonic tectonic fabric, fabric, and and is is calc—alkaline calc-alkaline in in composition. composition. Some Some blages, individual analyses analyses contain contain nepheline nepheline in in the the norm. norm. This This sodic sodic series series may may oc— ocindividual cupy the the same same fracture fracture system system as as the the younger, younger, fresher fresher swarm, swarm, but but generally generally cupy appears to to have have aa more more northwesterly northwesterlytrend. trend. appears Other Other post—Penokean post-Penokean dikes are are known known and and include include aa weakly weakly tectonized tectonized an— andesitic desitic suite suite in in the the Penokean Penokean orogen orogen and and aa granitic granitic suite suite in in southern southern Wis— Wis- consin. consin. event event. . These These are are probably probably related related to to the the 1,760 1,760 Ma Ma post—Penokean post-Penokean magmatic magmatic 66 a �I few diabase dikes are are known known in in the the area area between between the the northern northern and and cencenThis area area is is well well covered covered by by detailed detailed aeromagnetic aeromagneticsurveys; surveys;how-however, no strong magnetic magnetic lineaments are recognized, suggesting suggesting that that no magne distinctive swarm tically distinctive swarm exists. exists. A tral swarms. swarms. 6 6 Paleozoic cover cover 55 Keweenawan terrane terrane 4 4 Proterozoic anorogenic plutonic Proterozoic rock == Wolf River sequence rock sequence 3 3 Proterozoic quartzite = Baraboo Baraboo Proterozoic sequence sequence N I Proterozoicmetavolcanic metavolcanicand andplu-.plu2b Proterozoic Wisconsin inagmatic magmatic tonic rock == Wisconsin terraae terrane 2a Proterozoic Proterozoic metasedimentary metasedimentary rock rock == Proterozoic epicratonic Proterozoic epicratonic cover cover 1 Archean Archean terrane terrane I. A Sb2 Si02 Tb2 Ti02 A1203 A1203 FeOv FeOT MnO MnO MgO MgO CaO CaO Na20 Na20 K20 K20 P205 '2O5 49 2.3 13.8 14.6 0.2 5.1 8.6 2.7 1.1 0.4 49 1.4 13.6 11.7 0.2 5.9 9.0 3.2 0.9 0.1 I C B 51 1.0 16.4 8.8 0.2 6.3 8.6 3.2 1.2 0.3 high-Fe-Ti dikes, dikes, reverreverA avg. of 55 high—Fe-Ti sly polarized polarized(incl. (md. Rib sly Mountain). Rib Mountain). 8 B avg. of 66 low low Fe—Ti Fe-Ti dikes, dikes, weakly weakly reversely (?) ( ? ) polarized polarized normally and reversely (incl.Monico, Monico, Morse, Morse, Biron, Biron, Dudley). Dudley). (mci. C avg. of S5 sodic sodic dikes, dikes, weakly weakly po— polarized (incl. (mci. Montello, larized Montello, Prairie Prairie . Dell) Dell). I 1 I 67 I I I �U # METAMORPHISM METAMORPHISM OF OF THE THE DUNBAR DUNBAR GNEISS GNEISSAND AND ASSOCIATED ASSOCIATEDStJPRA—CRUSTAL SUPRA-CRUSTAL ROCKS: ROCKS: NORTHEASTERN NORTHEASTERN WISCONSIN, WISCONSIN, USA USA PETER PETER A. NIELSEN NIELSEN (Division (Division of of Science, Science, University University of of WisconsinWisconsin- Parkside, Parkside, Box Box 2000, 2000, Kenosha, Kenosha, WI WI U.S.A. U.S.A. 53141 53141 The The Quinnesec Quinnesec Formation Formation crops crops out out in in northeastern northeastern Wisconsin Wisconsin and and surrounds surrounds the the core core zone zone of of the the Dunbar Dunbar dome. dome. Metamorphic Metamorphic grade grade varies varies across across the the structure structure and and decreases decreases away away from from the the contacts contacts with with the the Dunbar Dunbar Gneiss Gneiss and and its its late late stage stage intrusive intrusive components. components. The Ic to The Quinnesec Quinnesec Formation Formationis is dominantly dominantlymaf mafic to felsic felsic volcanics volcanics and and volcaniclastics volcaniclastics (Schulz, (Schulz,1984). 1984). Local Local occurrances occurrances of of restricted restricted basin basin sediment sediment are are present present and and have have been been explored explored for for massive massive sulfide sulfide mineralization. mineralization. Their Their high high sulfide sulfide and and graphite graphite contents contents have have resulted resulted in in aa poor poor outcrop outcrop record, record, but but samples samples were were obtained obtained from from several several drill drill cores cores from from the the West West Bass Bass Lake Lake area area of of Florence Dunbar Gneiss Gneiss Florence County. County. The The supra—crustal supra-crustal rocks rocks and and the the Dunbar record record a a similar similar sequence sequence of of fabric fabric development development and and late late stage stage vein vein emplacement. emplacement. The The supra—crustal supra-crustal sequence sequence Is is characterized characterized by by prograde prograde metametamorphic morphic assemblages assemblages including: including: 1- biotite biotite -- garnet garnet — plagioclase plagioclase - quartz quartz + cordierite cordierite in in metameta1sediments sediments 2- garnet garnet — hornbJ.ende hornblende — plagioclase plagioclase ±+ quartz quartz in in metabasalts metabasalts 2— and, and, 3- diopside diopside — tremolite tremolite — calcite calcite + quartz quartz in in marbles. marbles. 3— - - - - - - Late Late stage stage metamorphic metamorphic effects effects are are present present in in most most samples. samples. most prevalent alteration includes: most prevalent alteration includes: garnet -à biotite biotite ++ chlorite chlorite garnet -+ cordierite pinite cordierite -+ Ñ pinite ++ sericite sericite 3- hornblende hornblende Ñ>— biotite biotite ++ actinolite actinolite ++ chlorite chlorite 3and, and, — epidote 4- Plagioclase Plagioclase Ñà epidote ++ albite albite 4- The The 1122— Beds Beds enriched enriched in in SS have have pyrite pyrite ++ pyrrhotite pyrrhotite ++ cha].copyrite chalcopyrite and show show a a loss loss of Fe Fe from from the the silicate silicate phases phases due due to to suifidation sulfidation reactions. reactions. The The supra—crustal supra-crustal sequence sequence and and the the Dunbar Dunbar Gneiss Gneiss are are cut cut by late late stage stage pegmatites pegmatites and and quartz-tourmaline quartz-tourmaline veins. veins. In In thin thin section, section, an an S1 S foliation foliation defined defined by by biotite biotite Is is parallel parallel to to bedding bedding planes planes (S0). ( S ) . Retrograde Retrograde biotite biotite defines defines a weak S2 S2 foliation foliation which by up up to to a which is Is inclined to to S, S by 900. Deformation 9 0 ' . Deformation of the the Quinessic Quinessic Formation Formation probably probably corresponds corresponds to to D2 and D4 D, (Sims (Sims et et al, all 1984) 1984) an in the the Dunbar dome. dome. Dunbar prograde metamorphic metamorphic assemblages assemblages restrict restrict peak peak metametaThe prograde The morphic conditions conditions to to 500—550°C 5 0 0 - 5 5 0 ~at at ~ low low to to intermediate intermediate morphic lithostatic pressure. pressure. Based Based on on the the abundance abundanceof of graphite graphitearid and lithostatic pyrite +÷ pyrrhotite, pyrrhotite, PH H and CO2 Con and and 0 << 'total H S were (at (at least major components components In in the fluid H2S least locally) locahy) major 68 phase. phase. 68 total I I �I The ranges in composition composition from The Dunbar Dunbar Gnei.ss Gneiss ranges from granite—grano— granite-granodiorite diorite to to biotite biotite tonalite, tonalite,and and locally locallycontains containsabundant abundantniafic mafic inclusions inclusions (Schulz (Schulzet et al, al, 1984). 1984). In In many many outcrops, outcropsfthe the gneiss gneiss grades grades into into migmatite. migmatite. The The similarity similarity between between the the deformational deformational and and metamorphic metamorphic histories histories of of the the Quinnesec Quinnesec Formation Formation and and the the Dunbar Dunbar Gneiss Gneiss suggests suggests that that they they were were coeval. coeval. The The lower lower metamorphic metamorphic grade grade recorded recorded in in the the Quinnesec Quinnesec Formation Formation is is attributed attributed to to aa smaller smaller extent extent of of erosion erosion due due to to higher higher density. density. The The core core of of the the Dunbar Dunbar dome dome was was formed formed at at the the peak peak of of metamorphism metamorphism by by bouyant bouyant emplacement Dunbar Gneiss. Gneiss. The The emplacement of of the the hotter hotter and and lower lower density density Dunbar time time required required to to form form the the Dunbar Dunbar Gneiss Gneiss protolith, protolithfthe the Quinessic Quinessic Formation Formation and and their their deformation deformation and and metamorphism metamorphism was was on on the the order order of of 30 30 million million years years (Sims (Simset et al, all1984) 1984). Schulz, Schulzf K.J., K e J a 1984, f1984f Volcanic Volcanic rocks rocks of of northeastern northeastern Wisconsin, Wisconsin,in: in: Guide Guide to to the the Geology Geoloqy of of the the Early Early Proterozoic Proterozoic Rocks Rocks in in 1 ThirtiethAnnual Annual Northeastern Wisconsin, Field Trip 1, Thirtieth Institute Institute on on Lake Lake Superior Superior Geology, Geology, p. p. 51-81 51-81 Schulz, Schulzf KJ., K ; J aSims, fSimsfP.K., P.K.#and andPeterman, Peterman#Z.E., Z . E q f1984, 1984,Geochemistry Geochemistrv of of the the Dunbar Dunbar Gneiss Gneiss Dome, Dome, N.E. N.E. Wisconsin, isc cons in^ in: in:Guide Guideto to the thl Geology the Early Early Proterozoic Proterozoic Rocks Rocks in in Northeastern Northeastern Geoloqy of of the Wisconsin, Field Trip Trip 1, 1, Thirtieth Thirtieth Annual Annual Institute Institute on on Wisconsin, Field Lake Superior Superior Geology, Geology,p. P O24—42 24-42 Lake Sims, Sims, P.K., P.K.# Peterman, Peterman#Z.E., Z.E.fand and Schulz, SchulzfK.J., K.J.,1984, 1984#Dunbar DunbarGneiss Gneiss -- Grani.toj.d Granitoid Dome, Dome, in: in: Guide Guide to to the the Geology Geology of of Early Early Proterozoic Rocks Rocks in in Northeastern Northeastern Wisconsin, WisconsintField FieldTrip Trip1,1 , Proterozoic Thirtieth Annual Annual Institute Instituteon on Lake Lake Superior SuperiorGeology, Geologytp. p . 1-23 1-23 Thirtieth I •1 I 69 1 I I �PRECAMBRIAN—HOSTED PRECIOUS METAL PROSPECTS GEOLOGY OF PRECAMBRIAN-HOSTED PROSPECTS IN I N THE THE AREA, MARQUIZTTE MARQUETTE COUNTY, FIRE CENTER AND HOLYOKE MINES AREAy COUNTYy MICHIGAN MICHIGAN Bornhorst (Department (~e~artmen oft Geology and and Geological Geological Eric 0. Owens and Theodore J. of E r i c 0. J . Bornhorst E n g i n e e r i n g , Michigan T e c h n o l o g i c a l University, U n i v e r s i t y y Houghton, Houghtony Michigan 49931) Engineering, Technological 2 During the t h e summer of o f 1984 1984 aa 66 km2 km area, a r e a , located l o c a t e d about about 19 19 km km northwest n o r t h w e s t of of Marquette, M a r q u e t t e y Michigan was geologically g e o l o g i c a l l y mapped at a t aa scale s c a l e of of 1:2,400. 1 : 2 y 4 0 0 . Mapping included of T49N, R27W and the i n c l u d e d aall ll o f section s e c t i o n 35, 3 5 , T49Ny t h e top t o p part p a r t of of section s e c t i o n 2, 2 y T48N, T48Ny R27W, including R27W, i n c l u d i n g the t h e inactive i n a c t i v e Fire F i r e Center C e n t e r gold g o l d mine and Holyoke silver s i l v e r mine. An of about about 30% ooutcrop u t c r o p ddensity e n s i t y of 30% allowed a detailed d e t a i l e d analysis a n a l y s i s of of the t h e field f i e l d geologic geologic relationships of aa sequence of r e l a t i o n s h i p s of of metamorphosed Archean and Lower Proterozoic Proterozoic volcanic, v o l c a n i c y sedimentary s e d i m e n t a r y and and intrusive i n t r u s i v e rocks. r o c k s . From oldest o l d e s t to t o youngest, y o u n g e s t , the t h e Archean metavolcanic m e t a v o l c a n i c units u n i t s are: a r e : pillowed p i l l o w e d basalt b a s a l t flows, f l o w s y a schistose s c h i s t o s e pyroclastic p y r o c l a s t i c horizon, horizony banded iron banded i r o n formation, f o r m a t i o n y and laminated l a m i n a t e d phyllitic p h y l l i t i c and schistose s c h i s t o s e volcanics v o l c a n i c s and and sediments. i s in i n fault f a u l t contact c o n t a c t with w i t h aa tectonized t e c t o n i z e d breccia b r e c c i a of of s e d i m e n t s . The latter l a t t e r unit u n i t is possible Archean—age; this unit p o s s i b l e Archean-age; this u n i t could c o u l d be lower lower Proterozoic P r o t e r o z o i c in i n age. a g e . The Archean metavolcanics m e t a v o l c a n i c s and and metasediments are a r e intruded i n t r u d e d by by gabbro gabbro and and rhyolite r h y o l i t e porphyry porphyry dikes of probable d ikes o f p r o b a b l e Archean age; a g e ; field f i e l d evidence e v i d e n c e indicates i n d i c a t e s the t h e rhyolite r h y o l i t e porphyry porphyry is is u n i t s described d e s c r i b e d above above are a r e overlain o v e r l a i n by by lower lower the t h e younger of o f the t h e two. two. The bedded units Proterozoic of section s e c t i o n 35, 35, P r o t e r o z o i c slates s l a t e s and and phyllites. p h y l l i t e s . Near the t h e northern n o r t h e r n boundary of of the lower Proterozoic Michigamme Formation is in fault q u a r t z i t e o f t h e lower P r o t e r o z o i c Michigamme Formation i s i n f a u l t contact c o n t a c t with with quartzite East—west trending Archean Archean ppillowed i l l o w e d bbasalt a s a l t flows. f l o w s . East-west t r e n d i n g Middle Proterozoic P r o t e r o z o i c diabase diabase dikes d i k e s of of Keweenawan age a g e intrude i n t r u d e the t h e Archean rock rock units. units. of The strike strike o f the t h e Archean and Lower Proterozoic P r o t e r o z o i c units u n i t s is i s approximately a p p r o x i m a t e l y N60°W ~ 6 0 ' ~ e x p o s e d y contacts c o n t a c t s between units u n i t s are a r e near n e a r vertical v e r t i c a l and and commonly commonly tto o N70°W. ~ 7 0 ' ~ . Where exposed, show eevidence v i d e n c e of o f faulting f a u l t i n g and and shearing. s h e a r i n g . Foliations F o l i a t i o n s are a r e manifested m a n i f e s t e d by by slaty s l a t y and and phyllitic and schistosity both p h y l l i t i c ccleavages l e a v a g e s and s c h i s t o s i t y in in b o t h the t h e Archean and Lower Proterozoic Proterozoic Except in Formation, rrocks. o c k s . Except i n the t h e Michigamme F o r m a t i o n y strike s t r i k e and dip d i p of of foliations f o l i a t i o n s (and (and bedding) bedding) are a r e generally g e n e r a l l y N60°W ~ 6 0 'to t o~ N75°W ~ 7 5 'and and ~ are a r e near n e a r vertical. v e r t i c a l . Evidence Evidence of of intense intense and shearing ddeformation e f o r m a t i o n and s h e a r i n g include i n c l u d e phaccoidal p h a c c o i d a l and schistose s c h i s t o s e structures, s t r u c t u r e s y tight tight ffolds, o l d s y ttransposed r a n s p o s e d layering l a y e r i n g and folded f o l d e d quartz q u a r t z lenses, l e n s e s y and boudinage. boudinage. These rocks rocks have been subjected s u b j e c t e d to t o greenschist g r e e n s c h i s t facies f a c i e s metamorphism. Mineralization zonesy M i n e r a l i z a t i o n occurs o c c u r s primarily p r i m a r i l y in i n quartz q u a r t z veins v e i n s and and in i n silicified s i l i c i f i e d shear s h e a r zones, and ttends be sspatially with and e n d s tto o be p a t i a l l y associated associated w i t h the t h e rhyolite r h y o l i t e porphyry dikes d i k e s and and banded banded ore minerals iron i r o n formation. f o r m a t i o n . Primary o re m i n e r a l s are a r e dominated by widespread pyrite p y r i t e with with minor occurrences o c c u r r e n c e s of o f chalcopyrite, c h a l c o p y r i t e , galena, g a l e n a y and and sphalerite. s p h a l e r i t e . No vvisible i s i b l e gold g o l d was was found. The main non—metallic n o n - m e t a l l i c alteration a l t e r a t i o n minerals m i n e r a l s include i n c l u d e nearly n e a r l y ubiquitous ubiquitous quartz, q u a r t z y locally l o c a l l y intense i n t e n s e sericite, s e r i c i t e y chlorite c h l o r i t e and biotite. b i o t i t e . Late L a t e stage s t a g e carbonate carbonate and q quartz—carbonate and u a r t z - c a r b o n a t e vveins e i n s cross c r o s s cut c u t all a l l previous p r e v i o u s mineralization. m i n e r a l i z a t i o n . The Fire Fire Center mine consisted of vertical C e n t e r ggold o l d mine consisted o f two v e r t i c a l shafts, s h a f t s y both b o t h located l o c a t e d on o n the t h e same same rhyolite r h y o l i t e porphyry dike. d i k e . The south s o u t h shaft s h a f t was sunk sunk along a l o n g the t h e sheared, s h e a r e d * silicified silicified with while north abbro* w h i l e the the n o r t h shaft s h a f t was apparently a p p a r e n t l y sunk sunk along a l o n g the t h e contact contact ccontact ontact w i t h ggabbro, with w i t h schistose s c h i s t o s e basalt. b a s a l t . The Holyoke silver s i l v e r mine was aa horizontal h o r i z o n t a l tunnel t u n n e l about about 550 feet h o s t rocks r o c k s are a r e silicified, silicified f e e t long l o n g dug in i n aa N19°E ~ 1 9 direction. 'd i~r e c t i o n . The host carbonatized, brecciated carbonatized, b r e c c i a t e d and schistose s c h i s t o s e metavolcanics m e t a v o l c a n i c s and and metasediments, metasediment~~ minor banded iron iincluding n c l u d i n g minor i r o n formation. f o r m a t i o n . Evidence to t o date d a t e suggests s u g g e s t s that that mineralization m i n e r a l i z a t i o n was probably p r o b a b l y epigenetic. epigenetic. 70 �I Geology And Geochemistry of of Lava Lava Flows Flows Within Within the t h e Copper Copper Harbor Harbor nd Geochemistry Conglomerate, Conglomerate Keweenaw Keweenaw Peninsula, P e n i n s u l a Michigan Michigan J. J . B. B. Paces and T. T. J. J . Bornhorst B o r n h o r s t (Department (Department of of Geology Geology and and Geological Geological E n g i n e e r i n g * Michigan Technological T e c h n o l o g i c a l University, U n i v e r s i t y * Houghton, Houghton, Michigan Michigan Engineering, 49931 49931) The Keweenawan Copper Harbor Conglomerate is i s aa rift—related, r i f t - r e l a t e d basin—ward basin-ward thickening t h i c k e n i n g succession s u c c e s s i o n of of terrestrial, t e r r e s t r i a l * coarse— c o a r s e - to t o fine—grained f i n e - g r a i n e d clastic clastic which interfinger with ssediments e d i m e n t s which interfinger w i t h and conformably overlie o v e r l i e the t h e Portage P o r t a g e Lake Lake Volcanics V o l c a n i c s (Daniels, ( D a n i e l s 1982). 1982). Northeast N o r t h e a s t of of Calumet, Calumet Michigan, Michigan* the t h e middle middle , portion p o r t i o n of o f the t h e Copper Harbor Conglomerate includes i n c l u d e s aa succession s u c c e s s i o n of of lava lava flows f l o w s known collectively c o l l e c t i v e l y as a s the t h e Lake Shore Shore Traps T r a p s (Lane, ( L a n e * 1911). 1911). T h i s unit unit This has h a s a strike—length s t r i k e - l e n g t h of o f over o v e r 90 90 km and and was deposited d e p o s i t e d in i n aa basin. b a s i n . The thickest t h i c k e s t section s e c t i o n (approx. ( a p p r o x . 600 m) is i s located l o c a t e d between between Copper Copper Harbor Harbor and and the the eeastern a s t e r n end of o f the t h e Keweenaw Peninsula. P e n i n s u l a . The Lake Shore Shore Traps T r a p s are a r e of of petrologic p e t r o l o g i c importance importance because b e c a u s e they t h e y represent r e p r e s e n t some some of of the t h e youngest youngest volcanic volcanic material m a t e r i a l erupted e r u p t e d throughout t h r o u g h o u t the t h e Lake Superior S u p e r i o r Basin. Basin. A Traps end of of tthe A 594 594 m section s e c t i o n through t h r o u g h the t h e Lake Shore T r a p s aatt tthe h e eeastern a s t e r n end he t o t a l of of 31 3 1 individual i n d i v i d u a l lava lava Keweenaw Peninsula P e n i n s u l a was mapped in i n detail. d e t a i l . A total flows f l o w s were identified i d e n t i f i e d (flow ( f l o w 11 at a t base, b a s e * 31 3 1 at a t top). t o p ) . Flow tthickness h i c k n e s s varies varies 4.4 tto 42.4 m m w with m. A 27 from 4.4 o 42.4 i t h aan n average a v e r a g e of o f 18.3 18.3 m. 27 m thick t h i c k interflow interflow conglomerate bed bed is conglomerate i s ppresent r e s e n t between flows f l o w s 10 1 0 and 11. Individual I n d i v i d u a l flows f l o w s show of o other ffeatures e a t u r e s ttypical y p i c a l of t h e r Keweenawan sub—aerial s u b - a e r i a l flood f l o o d basalts b a s a l t s including: including: amygdaloidal b o t t o m s * massive m a s s i v e flow f l o w interiors, i n t e r i o r s * vesicular, v e s i c u l a r y smooth, smoth* a m y g d a l o i d a l flow f l o w bottoms, pahoehoe pahoehoe flow f l o w tops t o p s and fragmental, f r a g m e n t a l * rubbley r u b b l e y flow f l o w tops. t o p s . Many flows f l o w s also also exhibit lower pportkn e x h i b i t vvertically—oriented e r t i c a l l y - o r i e n t e d vvesicle e s i c l e ccylinders y l i n d e r s iin n t the h e lower o r t i o n of of the the and thin, discontinuous, thin* d i s c o n t i n u o u s y horizontally—oriented, h o r i z o n t a l l y - o r i e n t e d * pegmatoid pegmatoid fflow l o w interior i n t e r i o r and layers upper Zeolite—grade i s common commn in in l a y e r s in i n the the u p p e r portions. portions. Z e o l i t e - g r a d e alteration a l t e r a t i o n is permeable permeable flow f l o w tops t o p s but b u t is i s minimal to t o non—existent n o n - e x i s t e n t in i n most most flow f l o w interiors. interiors. Geochemically, G e o ~ h e m i c a l l ythe t~h e Lake Shore Shore Traps T r a p s exhibit e x h i b i t tholeiitic t h o l e i i t i c evolutionary evolutionary AFM, nnormative, and iimmobile ttrends r e n d s oon n AFM* o r m a t i v e * SSi02, i 0 2 , and m m b i l e ttrace r a c e eelement l e m e n t ddiscrimination iscrimination plots. In plots. I n ggeneral, e n e r a l * lavas l a v a s become more evolved e v o l v e d from from the t h e base b a s e upwards. upwards. The lowest fflows l o w s (1, ( 1 , 2, 2, 3 4 ) are a r e Fe—rich F e - r i c h olivine o l i v i n e tholeiitic t h o l e i i t i c basalts b a s a l t s (47—50 (47-50 lowest 3,* and and 4) wt. w t . % Si02), S i 0 2 ) * followed f o l l o w e d by Fe—rich F e - r i c h olivine—bearing, o l i v i n e - b e a r i n g * tholeiitic tholeiitic b a s a l t i c - a n d e s i t e s with w i t h 50—53 50-53 wt. w t . %% Si02 S i 0 2 (flows ( f l o w s 5—22) 5-22) and tholeiitic tholeiitic basaltic—andesites t . % (flows ( f l o w s 23—31). 23-31). aandesites ndesites w i t h Si02 S i 0 2 oof f 54—58 54-58 w with wt. IIn n tthin h i n section, s e c t i o n * all all with rrocks o c k s aare r e largely l a r g e l y aaphyric phyric w i t h oonly n l y small s m a l l amounts of of plagioclase plagioclase phenocrysts. phenocrysts Groundmass i n e r a l s in i n the t h e basalts b a s a l t s include i n c l u d e 35—40% 35-40% plagioclase plagioclase Groundmass m minerals (An45-65; 15-252 clinopyroxene c l i n o p y r o x e n e (Wo (An4565), 15—25% (Wo3040, Fe/Mg 10—20% FefMg == 40—50), 40-50) 10-20% olivine olivine 3 0-40 * (Fo460), and and5—10% 5-10%Fe—Ti Fe-Ti oxides o x i d e s(mineral ( m m e r a l composition c o m p o s i t i o n determined d e t e r m i n e d by by (Fo4p-60 eelectron l e c ron m i c r o p r o b e ) . Groundmass m i n e r a l s in i n the t h e andesites a n d e s i t e s are a r e 40—50% 40-502 microprobe). minerals plagioclase (An5), 10—20% p l a g i o c l a s e (An 10-202clinopyroxene c l i n o p y r o x e n e (Wo3040, (Wo30-40 Fe/Mg FefMg == 30-40) 30—40), 5-15% 5—15% orthopyroxene, o r t h o p y r o x e n e 5—10% Fe—Ti Fe-Ti oxides o x i d e s and and 5—10% 5-10% late—stage l a t e - s t a g e intergranular intergranu l a r K—feldspar. K-feldspar. D e v i t r i f i e d intersertal intersertal g l a s s is i s ppresent r e s e n t in i n aall l l massive low Devitrified glass massive fflow interiors Diktytaxitic i n t e r i o r s (10—20%). (10-202). D i k t y t a x i t i c cavities c a v i t i e s are a r e common commn in i n most most flows. f l o w s . Flows 1 2 and 1 3 * located l o c a t e d just j u s t above the t h e interflow i n t e r f l o w conglomerate, c o n g l o m e r a t e , contain c o n t a i n distinct distinct 12 and 13, pphenocrysts h e n o c r y s t s oof f hhighly i g h l y rresorbed e s o r b e d plagioclase p l a g i o c l a s e and and quartz. quartz. . !%%! when Most major and and trace t r a c e eelements l e m e n t s show ccoherent o h e r e n t ppatterns a t t e r n s oof f vvariation a r i a t i o n when K20y pplotted l o t t e d versus v e r s u s stratigraphic s t r a t i g r a p h i c height. h e i g h t . Generally, G e n e r a l l y * SiO A1203* Na20, Na O y K20, Si0, A1203, and Rb increase i n c r e a s e from bottom to t o top t o p of o f the t h e sequence, s e q u e n c e * s hereas e r e a s FeO, F ~ oMgO, ~ ~ CaO, CaOy M ~ o , 71 rI1IIu!' I �I Ti02, P205, V, CafAl, Ca/Al, Cr, C r y Ni, N i , and Sr S r decrease. d e c r e a s e . Though these t h e s e trends t r e n d s apply apply to the succession general, i o n in in g e n e r a l y in i n particular, p a r t i c u l a r y numerous inconsistencies i n c o n s i s t e n c i e s rule rule out p a t t e r n s . The flows f l o w s below and and above above the the o u t simple s i m p l e evolutionary e v o l u t i ol~a r y patterns. conglomerate be grouped grouped ttogether : r a t e ccan a n be o g e t h e r oon n the t h e basis b a s i s of of repeating repeating iinterbedded n t e r b e d d e d conglomc Also, orr anomalous trends. A l s o y the t h e two two flows f l o w s (12 ( 1 2 and and o anomalous chemical—stratigraphic chemic: 3 1 - s t r a t i g r a p h i c trends. above tthe conglomerate aare anomalous w with high :he conglomerate r e anomalous i t h particularly particularly h igh 113) 3 ) ddirectly i r e c t l y above Si, K,y Rb and Zr Al, low A l , Fe, F e y Ca, Ca, Ti, T i , V and and P. P. As A s aa whole, whole, the t h e Lake Lake Si, K Z r and an(1 low Shore Traps a ~ sare a r e geochemically Eeoc:hemically more evolved than t h a n the t h e Portage P o r t a g e Lake Lake Volcanics Volcanics ..- - T -r-c which are a r e almost almost exclusively e x c l u s i v e l y hi—Al hi-A1 olivine o l i v i n e and and hypersthene h y p e r s t h e n e tholeiitic tholeiitic b a s a l t s . For similar s i m i l a r Si02 SiO contents, c o n t e n t s , the t h e Lake Shore Shore Traps T r a p s contain contain basalts. 2 substantially Ti, A 1 and and Ni N i (large (large l e s s Al s u b s t a n t i a l l y more T i , V, V , P, P y Zr, Z r y and Y and and less compositional c o m p o s i t i o n a l gaps). g a p s ) . A continuum exists, e x i s t s y however, however, for f o r Fe, F e y Mg, Mg, Ca, Cay Ca/Al, CaIAl, Cr, C r , total t o t a l alkalis, a l k a l i s * and and Rb. Rb. - - Qualitative Q u a l i t a t i v e petrogenetic p e t r o g e n e t i c interpretation i n t e r p r e t a t i o n of of the t h e present p r e s e n t geochemical geochemical data data suggests s u g g e s t s that t h a t crystal c r y s t a l fractionation f r a c t i o n a t i o n exerts e x e r t s at a t least l e a s t aa partial p a r t i a l control c o n t r o l over over magma ccompositions Traps. tthe h e magma o m p o s i t i o n s oof f tthe h e Lake Shore T r a p s . Major and trace t r a c e element element geochemical trends p l a g i o c l a s e and and t r e n d s suggest s u g g e s t that t h a t clinopyroxene, c l i n o p y r o x e n e , Fe—Ti Fe-Ti oxide, o x i d e , plagioclase Zircon eventually also apatite phases. a p a t i t e were significant s i g- n i f i c a n t fractionating fractionating p h a s e s . Z i r c o n e v e n t u a l l y a l s o - However, in reached r e a c h e d the t h e saturation s a t u r a t i o n limit. l i m i t . However, i n addition a d d i t i o n to t o fractionation, f r a c t i o n a t i o n , some some Petrographic and m major ttrace r a c e and a j o r eelements l e m e n t s aalso l s o suggest s u g g e s t open system behavior. behavior. P etrographic and geochemical geochemical eevidence and v i d e n c e ssupports u p p o r t s the t h e occurrence o c c u r r e n c e of o f upper u p p e r crustal crustal 1 2 and and ccontamination o n t a m i n a t i o n oof f several s e v e r a l lava l a v a flows f l o w s of of the t h e Lake Shore S h o r e Traps (flows ( f l o w s 12 t0 1 3 ) . Within the t h e remaining r e m a i n i n g flow f l o w succession, s u c c e s s i o n , magma magma mixing m i x i n g may may be be required r e q u i r e d to 13). , -,--two ---- geocnemxaL .--.,.- : - . * the eexplain x p l a .m adifferences l r r e r e n c e s in I n fractionation r r a~c c-l o- n.-a cLl .o -n - trends c&r e~ n a-s -between DeLween Lne LWO geochemical The petrogenetic groups: g r o u p s : lower lower flows f l o w s (1—9) (1-9) and and upper u p p e r flows f l o w s (16—31). (16-31). petrogenetic relationship r e l a t i o n s h i p between the t h e Lake Shore Traps T r a p s and the t h e Portage P o r t a g e Lake Lake Volcanics V o l c a n i c s is is ccurrently u r r e n t l y under investigation. investigation. . . . P ? - - L - L #- Reference Reference Daniels, 1 9 8 2 y Geol. Geol. Soc. SOC. Amer. Amer. Mem. Mem. 156, 156, p. p. 107—133. 107-133. D a n i e l s , 1982, Lane, Lane, 1911, 1 9 l l y Mich. Mich. Geol. Geol. Surv. Surv. Pub. Pub. 6, 6 , 983 983 p. p. 72 �I: PALEOMAGNETISM OF THE THE POWDER THE PALEOMAGNETISM POWDER MILL GROUP: ITS ITS RELEVANCE RELEVANCE TO TO CORRELATION CORRELATION THE WITh OTHER 'TECTONIC DEVELOPMENT DEVELOPMENT OF THE WITH OTHER KEWEENAWAN KEWEENAWAN SEQUENCES SEQUENCES AND AND TO TO*TECTONIC THE SOUTH SOUTH RANGE MNGE H.C. Palmer1and H.C. Palmer1and H.C. Halls. Halls. 22 p! m The Keweenawan Powder Powder Mill Group crops out as a 150 km—long dominantly The Keweenawan 150 km-long east—west striking belt in Xichigan Michigan and Wisconsin. A east-west A primary primary Keweenawan Keweenawan reverse magnetization has reverse magnetization has been been isolated isolated after after extensive extensive AF AF and and thermal thermal demagnetization demagnetization from 33 sites distributed along a strike length of 100 km W, 39°N, This reverse reverse magnetization magnetization yields yields aa pole pole (142 (142~~4, 39'~~ within the within the belt. belt. This A956.O°) which subset of of these these Ag5=6.00) which plots plots close close to to the the apex apex of of the the Logan Logan Loop. Loop. A subset within the reversely magnetized sites sites from from localties localties within the outcrop outcrop belt belt having having E—W E-W yield a a pole pole (147OW, (147°W, 42'~~ 42°N, Ag5=6.40) A956.4°) which which is is within within the the cluster cluster of strike yield Mellen Complex Complex other other reversely reversely magnetized magnetized Keweenawan Keweenawan paleopoles. paleopoles. Mellen ENE—trending segments within within magnetizations and Powder Mill magnetizations from ENE-trending dominantly E-W E—W trending the dominantly trending outcrop belt suggest suggest that that these these segments segments have have undergone counterclockwise undergone counterclockwise rotations. rotations. Normal magnetizations have been isolated isolated at at four four sites. sites. Poles Poles derived derived from from these these sites sites also also plot plot on on the the western arm western arm of of the the Logan Logan Loop. Loop. The The normal normal magnetizations magnetizations are are in in sites sites near sequence but the distribution of these near the the base of the stratigraphic sequence sites is not stratigraphically stratigraphically continuous. continuous. This This lack lack of of stratigraphic stratigraphic persistence, persistence, together together with aa higher higher metamorphic metamorphic grade grade at at the the normally normally magnetized sites, magnetizations are sites, lead us to believe that the normal magnetizations secondary. The The polar signature signature and the reversal stratigraphy stratigraphy of the Powder secondary. to those those of of other other Keweenawan Keweenawan volcanic volcanic sequences. sequences. Mill Group Group are are similar similar to (1968, 1972) 1972) which which led led to to the the belief belief that that The The paleomagnetic paleomagnetic results results of of Books Books (1968, Traps (Powder the South Range Traps (Powder Mill Group) ~roup)were were older older than than other other Keweenawan Keweenawan volcanic volcanic sequences sequences are are no no longer longer valid. The eastern eastern arm arm of of the the Logan Logan Loop Loop is undefined by Keweenawan Keweenawan data. data. I References: References: I K.G., Magnetization Keweenawan lava flows in the Lake of the lowermost Keweenawan Books, Books, K.G., Superior Superior area, area, U.S. Geological Geological Survey, Survey, Professional Professional Paper Paper 550—D, 550-D, p.D117—D124, p.Dll7-Dl24, 1968. 1968. Books, K.G., K.G., Paleomagnetism Books, Paleomagnetism of of some some Lake Lake Superior Superior Keweenawan Keweenawan rocks, rocks, U.S. U.S. Geological Survey, Geological Survey, Professional Professional Paper, Paper, 760, 760, 42 42 p., p., 1972. 1972. Department 1 1 Department of of Geophysics, Geophysics, University University of of Western Western Ontario, Ontario, London, London, Ont. Ont. F I I 2 Department 2 Department of of Physics, Physics, University University of of Toronto, Toronto, Erindale Erindale Campus, CampuslMississauga, MississaugalOnt. Ont. T I 73 1 I I ! �I THE GEOLOGICAL GEOLOGICAL SETTING SETTING OF OFGOLD GOLO MINERALIZATION MINERALIZATION OBSERVED THE OBSERVED N.W. ONTARIO ONTARIO AT THE THE SCRAMBLE SCRAMBLE MINEy DISTRICTOF OFKENORA, KENORAyN.W. AT MINE, DISTRICT P A R R Y M.G. u a r t z TTower, o w e r y 33451 3 3 4 5 1 Stransky S t r a n s k y Rd., RdeYEvergreen, E v e r g r e e n yCO C O80439 80439 PARR, M.G.( Q(Quartz U.S.A.) U.S.A.) BOBEN, (Dept.o fofGeol. Geol.&&Geol. Geol.EEngrg., BOBENy C. C. (Dept. n g r g e Y MMichigan i c h i g a n TTechnological e c h n o l o g i c a l Univ., UnivaY Houghton, M I 49931) 49931) Houghtony MI The The Scramble S c r a m b l e GGold o l d MMine, i n e y l located o c a t e d tten e n kilometres k i l o m e t r e s east e a s tofo Kenora, f K e n o r a swas was originally bybythe o r i g i n a l l developed y d e v e l o p e dini nthe t h elate l a t1890's e 1890's t h Scramble e S c r a m b l eGold GoldMining Mining Company L Limited i m i t e d and n t e r m i t t a n t lto y t1914 o 1914 y t hCanadian e C a n a d i a nHomestake Homestake Company and i intermittantly bybthe Gold Gold Mining M i n i n g Company Company Limited. L i m i t e d . Although A1 though a shaft s h a f t was was excavated excavated to t oabout about seventy seventy metres metres there t h e r e isi sno norecord r e c o r dofoproduction f p r o d u c t i obeyond n beyondbulk bu1 ksampling samplingand and mill m i l l testing. testing. The The ddeposit e p o s i t is i slocated l o c a t e data the t t h northwest e n o r t h w e send t endofothe f t hWabigoon e Wabi goonVol Vo1caniccani c- Plutonic Pl u t o n i c Belt Be1twithin w i t h imetavolcanics n m e t a v o l c a n i cand s andmetasediments metasediments which w h i c h outcrop o u t c r o p in i n aa northeast n o r t h e a s ttrending t r e n d i n gwedge wedge extending e x t e n d i n gfrom f r o mLake Lakeofofthe t h eWoods. Woods. North N o r t h of of this of the R i v e r Subprovince S u b p r o v i nce wwhilst h i 1s t t h i swedge wedge are a r e the t h e gneisses g n e i sses of t h e English E n g l is h River southeast area iis southeast oof f tthe h e area s the t h e Island I s l a n d Lake Lake ddiorite, i o r i t e y aa unit u n i tofo fthe t h eDryberry Qryberry Batholith Subprovince. Bath01 i t hwhich which ini nturn t u r nis ipart s p aof r t the of tWabigoon h e Wabigoon Subprovi nce. The Scramble Minei sisu underlain The S c r a m b l e Mine n d e r l a i n p predominantly r e d o m i n a n t l y b yby t h tholelitic o l e i i t i c pillowed pillowed flows, and occasional o c c a s i o n a l ffelsic elsic f l o w s yminor m i n o r mafic m a f i c tuffaceous t u f f a c e o u s units, u n i t s , exhalites e x h a l it e s and units u n i t s (see (see diagram diagram of of the t h estratigraphic s t r a t i g r a p h i csuccession). succession). All A11 the t h e volcanics volcanics on on the t h e property p r o p e r t y face f a c e and and dip d i p to t o the t h enorthwest. n o r t h w e s t . Foliation F o l i a t i o n tends t e n d s to to subparallel and aalso dips s u b p a r a l l e l bedding bedding and lso d i p s steeply s t e e p l y to t o the t h enorthwest. northwest. Deformed Deformed pillows, p i 11owsy shearing s h e a r i n g and and shear shear folding f o l d i n g occur occur throughout t h r o u g h o u t the t h eproperty p r o p e r t yand and are a r e well w e l l exposed e x p o s e d at a t the t h e mine m i n e site. site. Q u a r t z - t o u r m a l i n e veins v e i n s both both Quartz—tourmaline concordant andddiscordant concordant and i s c o r d a n t t oto ffoliation o 1 ia t i on are a r eubiquitous. u b i q u i t o u s . Nowhere Nowhere on on the the p r o p e r t y has has there t h e r e been been observed i q n i f i c a n t alteration a l t e r a t i o ndue due property observedany anyareas areaso fofs significant either e i t h e rtot oa primary a p r i m a r volcanogenic y volcanogenichydrothermal hydrothermal system s j s t e m or o r tot oa asecondary secondary shear shear zone zone related r e l a t e dhydrothermal hydrothermalsystem. system. Detailed D e t a i l e d studies s t u d i e s of o f the t h e nature n a t u r e ofofthe t h egold g o l dmineralization m i n e r a l i z a t i oare n a runderway e underway but as yet incomplete. Observations made to date, based on b u t as y e t i n c o m p l e t e . O b s e r v a t i o n s made t o d a t e y based on detailed detailed sampling mappingof oft hthe zonealong alongs tstrike, sampling and and mapping e oore r e zone r i k e , iindicate n d i c a t e that t h a t aa high high percentage p e r c e n t a g e ofof tthe h e ggold o l d i is s within w i t h i n the t h e exhalite e x h a l i t e unit. u n i t . This T h i s could c o u l dbe be either e i t h e r as as very v e r y fine f i n e grained g r a i n e d free f r e e gold g o l d or o r tied t i e dup upwith w i t hsuiphides. sulphides. Visible observed V i s i b l e gold g o l d has has been been observed i n int hthe e s isilicia l i c i a flooded f l o o d e d ffelsic e l s i c unit u n i t just just northeast n o r t h e a s t of of the t h e shaft. s h a f t . Since S i n c e tthe h e ggold o l d ccontent o n t e n t ofoft the h e f felsic e l s i c unit u n i t is is generally g e n e r a l l y less l e s s than than200 200 ppb ppb is i swould would appear appear that t h a t the t h eenriched e n r i c h e d values values in in the t h e felsic f e l s i cunit u n i are t a r edue due to t oremobilization r e m o b i l i z a t i o n of o fsilica s i l i c and a andgold g o l dunder under particular cartoon). p a r t i c u l a structural r s t r u c t u r acontrols l c o n t r o (see l s (see cartoon). Trace Trace chemistry c h e m i s t r y carried carried out on on twelve t w e l v e selected s e l e c t e dmineralized m i n e r a l i z e dsamples samples from from the t h e ore ore zone zone indicate i n d i c a t ea a out typical c go1system. d system. t y p i c a l tholeiitic t h o l e i 1 t igold Genesis ooff the t h e gold g o l d mineralization m i n e r a l i z a t i o nas asinferred i n f e r r e from d from o u t c r o pmapping mapping isi s Genesis outcrop summarized as ffollows. s u m m a r i z e d as o l l o w s . Pillowed P i l l o w e d flows f l o w s followed f o l l o w e d by b y mafic m a f i c tuffs t u f f sand and felsic auriferous f e l s i cvolcanism volcanism with w i t h distal d i s t a tuffs l t u f fand s and a u r i f e r o u schemical chemical precipitates precipitates s i l l yaa I n t r u s i o n of e l s i c sill, Intrusion of aa ffelsic possible p o s s i b l e feeder f e e d e r to to a a stratigraphically s t r a t i g r a p h i c a l l yhigher h i g h e rfelsic f e 1 s icentre, c c e n t r ecauses y causes remobilization r e m o b i l i z a t i o nofo fgold. g o l d . Finally, F i n a l l y ydeformation, d e f o r m a t i o n y regional r e g i o n a l folding f o l d i n gand and s h e a r i n g along a l o n g iinterflow n t e r f l o w boundaries b o u n d a r i e s rresults e s u l t s in i n small s m a l l scale s c a l e folding folding shearing w i t h i n the t h e interflow i n t e r f l o wunit u n iand t andmajor m a j o r remobilization r e m o b i l i z a t i o n of of gold g o l d and and silica silica within are a r epreserved preservedby byrenewed renewed mafic m a f i cvolcanism. volcanism. into i n t odilatent d i l a t e nzones t zones within w i t h i nthe t h ecompetent competent felsic fe1 s i cunits. units. 74 ~ �Stratigraphic column, Scramble Mine, showing gold distribution with respect to rock types. —S -S —.—- 50 E gold) fran — -S SS of charts dsto nmssive silica pzds in diiatanl mxxhng (+ with Iling by silica A cartoon of the structural elements observed at the Scramble Mine site. folds throuejsut thterflcs umeterial. z N — flow . pillowed tuft nmafic barren exhali te felsic unit exhalite tuff mnafic barren flow pillowed — — — — — — — — — — — — — ,— — — I I • Ui felsic mstits lmmlricate stacking of camçetmemt / — — .— — —. — — — — — — — —S - _ �METAMORPHISM AND N.W. ONTARIO METAMORPHISM AND PLUTONISM PLUTONISM IN IN THE THE QUETICO BELT, N.W. :John John A. A. Percival, Percival, Geological Geological Survey Survey of of Canada, Canada, 588 588 Booth Booth Street, Street, Ottawa, KIA0E4 OE4 Ottawa, Ontario OntarioKIA Reconnaissance study of 350 350 km km of strike length length of of the t h e1200-km-long 1200-km-long Quetico Quetico belt belt Reconnaissance of strike reveals reveals regional regional patterns patterns of of metamorphism metamorphism and and plutonism. plutonism. Located Located between between the the Wabigoon and h e Quetico belt consists consists of of aa marginal marginal Wabigoon and Wawa Wawagreenstone-granite greenstone-granite belts, belts, tthe metasedimentary metasedimentary schist schist unit unit and and an an interior interior complex complex of of metasedimentary metasedimentary schist schistand and gneiss rocks. Metamorphic gneiss and plutonic plutonic rocks. Metamorphic grade in marginal pelitic schists varies varies from from aa chlorite-muscovite chlorite-muscovite zone zone at at the t h e outer outer margin margin to t oaagarnet-sillimanite garnet-sillimanite zone zonetoward toward the the interior. Common Commonassemblages assemblages of of garnet-andalusite garnet-andalusite throughout throughout the t h emarginal marginal unit unit and and in in interior. the t h e interior interiorininthe t h eLac LacLa L aCroix Croixarea a r e aindicate indicatelow-pressure low-pressuremetamorphism metamorphism(bathozone (bathozone2). 2). Assemblages of and rare r a r ekyanite kyanitesome some60-150 60-150 km km east e a s tof ofLac L a cLa La Assemblages of staurolite-sillimanite and Croix conditions. Mineral Mineralassemblages assemblagesin in peraluminous peraluminous granitoid granitoid Croix suggest suggest bathozone bathozone 33 conditions. leucosome, and plutons plutons also also vary vary regionally regionally along alongstrike. strike. Sillimanite, leucosome, dykes and Sillimanite, in in association association with with garnet garnet and and muscovite, muscovite, isis common common in the t h e west; west; cordierite cordieriteisispresent presentonly only t o the t h eeast. east.Leucosome Leucosomeininmigmatites migmatitesisismainly mainlyintrusive intrusivein in the t h ewest westand andlocally locally derived derived to in east. These Thesefeatures featurestogether togethersuggest suggesta adeepening deepeninglevel levelof of erosion erosion from from west west to to in the t h e east. east. east. Two large plutonic complexes complexes characterize t h e interior interior of of the t h ewestern westernQuetico Quetico Two characterize the belt: the t h eVermilion Vermilion complex complex of Minnesota Minnesota and h e Quetico Park complex complex of The belt: and tthe of Ontario. Ontario. The Vermilion complex consists consists mainly mainly of of biotite granite Vermilion complex granite and and leucogranite leucogranitewith with metasedimentary schist schist inclusions. inclusions. A A zonation zonation in in plutonic rock types characterizes the metasedimentary characterizes the Quetico width. Peraluminous Quetico park park complex complex across iits t s 20-50 20-50 km km width. Peraluminous white granite of of the the Sturgeon Lake Lake hatholith batholith occurs in in the t h e centre c e n t r eof ofthe t h ecomplex complexand andisisflanked flankedby bysmall small Sturgeon 10-km-wide) plutons plutons of of pink pink biotite biotite ±+ magnetite magnetiteleucogranite, leucogranite,rarely rarely'with withinclusions inclusionsof of (( 10-km-wide) monzonite-diorite-hornblendjte. monzonite-diorite-hornblendite. Small small-(( 55km) km) plugs plugs of diorite-monzonite cut c u tmarginal marginal metasedimentary metasedimentaryschists. schists. composite section sectionthrough throughthe t h ebelt beltshows showssteeply steeplyinward-dipping inward-dipping margins marginsand and AA composite tadpole-shaped plutoris plutons derived source in in the t h e centre c e n t r eand and tadpole-shaped derived from from a metasedimentary source tonalitic rocks rocks of of the t h e greenstone-granite greenstone-granite terranes terranestoward toward the t h emargins. margins. AAback-arc back-arc basin basin tonalitic environment environment is is postulated postulated to t o account account for forearly earlydevelopment developmentof of an a nelongate elongatesedimentary sedimentary trough trough characterized characterizedby by high high heat heat flow flow which which led to t o later l a t e r deep deepcrustal crustalmelting meltingand and magma magma rise to t o high high structural structural level. level. Underplating Underplatingby bymafic maficmagmas magmaspossibly possibly contributed contributed to t o heat h e a t transfer transfer from from the t h e mantl mantlztot othe t h elower lowercrust. crust. 76 �1' The Tectonic Tectonic Significance Significance of of the t h ePorphyritic PorphyriticRed Red Granite, Granite, The Dickinson Dickinson County, County, Michigan Michigan EDWARD PETERSON,Department Department of of Geological EDWARD E.E. PETERSON, Geological Sciences, Michigan Michigan State State University, East EastLansing, Lansing, MI M I 48824-1115 48824-1 115 University, The The Porphyritic Porphyritic Red Red Granite Granite isisexposed exposed near near Feich FelchininDickinson Dickinson County, County, at1970 1970Ma Ma old old Michigan and by the t h e Rb/Sr RbfSr whole whole rock rock method method at Michigan and has has been been dated dated by (Van Schmus, per. Comm.). (Van Schmus, Comm.). Strain Strain studies studies using using the t h e grain grain center c e n t e r method method of of Fry Fry (1979) and h e deformed Talbut (1982) (1982) indicates two episodes episodes of of (1979) and tthe deformed dike dike method method of of Talbut deformation. deformation. The Thefirst firstisisan a nintrusive intrusivedeformation deformationcontrolled controlledby by the t h egeometry geometry of of the pluton appears tto be a regional pluton while while tthe h e second second appears o be regional deformation. deformation. New New major major element analysisindicates indicatest thha/2) granite has element chemical chemical analysis granite ~ has aa low low structural structural water water a 1.3, and and iti t isisnormative normative quartz quartz high K20 K 2 0content, content,Al/(Na+K+ Al/(Na+K+ 12) == 1.3, content, aa high chemical trends trends aare with Ssaturated. These S- or o r A-type A-type granites; granites; These chemical r e consistent consistent with however, major a t a cannot differentiate between them. them. however, major element element ddata differentiate between The The granite granite is composed composed of potassium potassium feldspar feldspar megacrysts megacrysts with with lesser lesser The The feldspar feldspar megacrysts,quartz, megacrysts,quartz, and and biotite are a r e all a l l elongated elongated within within the t h e foliation. foliation. The The biotite biotite defines a well developed LSfabric fabric where where tthe foliation is everywhere developed LS h e foliation everywhere parallel to to amounts of of quartz, quartz, biotite, biotite, and and magnetite magnetite ininthe t h egroundmass. groundmass. amounts I the t h e pluton's pIutonls margin margin and and the t h e lineatiori lineation is is steeply plunging. plunging. These These are a r every very common common features features among among diapiric structures. A Relative strain strain was was determined determined using using the t h e grain grain center c e n t e rtechnique techniqueof ofFry Frywhich which This study shows shows the the records records the t h e shape shape and and orientation orientation of of grain grain distributions. distributions. This The strain pattern pattern long axes of of the long axes the feldspar feldspar megacrysts megacrysts are a r esteeply steeplyplunging. plunging. The indicates plane planestrain strain(X1>A, (A >A == 1 >> XA 3) 3) at the t h e margin margin but but becomes becomes constrictional constrictional indicates diapiric structures 3) just inward. (+>A2 == AA3) inward? Modeled %odeled diapiric structures (Dixon, (Dixon, 1975) 1975) and and many many (A1>A2 natural deformed xenoliths xenoliths (Schwerdtner (Schwerdtner et et al., a!., 1983; 1983; Pitcher and and natural examples examples using using deformed 1 I i9 Berger, 1972) wide zone zone ofofvery verystrong strongmarginward marginward flattening flattening 1972) display display a wide narrow neutral surface, and a weak constrictional strain > weak strain toward toward A > AA ),1, aa (x (A = A, the in inthet hPorphyritic t h e midle. m i d l e . The 3Thedifferent differentpattern p a t t e r of n ofstrain strain e PorphyriticRed RedGranite Granitemay may be due ttoo the methods used in in measuring measuring strain strain in in tthat methods used h a t its i t s geometry geometry isis controlled controlled by the t h e growth patterns of of the t h e feldspars feldspars. fl Both Both the t h e pluton pluton and and its i t s associated associated pegmatites pegmatites show show signs signs of of aa post-intrusive post-intrusive deformation. m wide wideeast-west east-west left lateral deformation. A A large 25 m lateral shear shear zone zone occurs occurs in in the the southern southern part while while smaller smaller shear shear zones zones(3-40 (3-40 cm c m wide) wide) are a r ecommon common in in several several northeastern region region of of the The northeastern t h e pluton pluton displays displays fabric fabric crenulations crenulations and and areas. The highly highly contorted dikes with with steeply steeply plunging plunging fold axis. A strain analysis using deformed metadiabase dikes (Talbot, 1982) 1982) which which have have using deformed dikes (Talbot, intruded intruded the t h e pluton pluton were were used used to t orecord record the t h epost-intrusive post-intrusive deformation. deformation. These These dikes ccut u t across the t h e pluton's plutonls fabric and have foliations oblique oblique tto o their margins. margins. This oblique foliation foliation is produced by layer parallel shearing as the t h e dike dike rotates r o t a t e sin in This oblique produced by pole of of the response tto o tthe h e strain strain within within the t h e country country rock. rock. Connecting Connecting tthe h e pole the response margin stereonetproduces producesan a napproximation approximation of of margin tto o ' the t h e pole pole of of the t h efoliation foliationon onaastereonet t h e structural structural movement movement path. path. The The coherent coherent pattern pattern displayed displayed by by these these paths paths the have found on on tthe dikes to to decribe decribe tthe have been been used used with with lineations lineations found h e dikes h e type of of strain strain plunges to the south while plunges steeply t o t h e south while and the t h e strain strain axes. axes. This Thisanalysis analysisindicates indicatesAA A is gently plunging A plunging tto o the t h e northeast. northeast. AAcompanion companion study study using using Proterozoic-X Proterozoic-X diles a similar similar style of of d i t e s in in the t h e basement basement rocks rocks adjacent adjacent to t o the t h e pluton pluton suggests suggests a deformation. deformation. This This style in in the t h e Felch Felch area a r e a contrasts contrasts with with that that found found to t o the t h e north north I I �in in the theMarquette, Marquette,Michigan Michiganregion regionwhere wherethe t h ebasement basementhas hasbehaved behaved rigidly rigidly A (Myers, 1984). 1984). The The general general trend trend of ofthe t h ecompression compressionaxis axisisisthe thesame, same,however. however. (Myers, and 2 show the results of these strain studies for the granite 1 and 2 show t h e results of these strain studies for the graniteand and Figures Figures 1 basement rock, respectively. respectively. basement , There have have been been several several recent recent studies studies which which suggest suggest the t h e chemistry chemistryand and There mineralogy of granites are a r e functions functions of of their theirtectonic tectonicsetting setting(Chappel (Chappeland and mineralogy of granites al., 1984). 1984). Major Major element e e m e n t chemical chemical White, 1974; 1974; Pitcher, Pitcher, 1984; 1984; Pearce Pearce et a!., White, analysis analysis indicates the t h e granite granite isisstrongly stronglyperaluminous, peraluminous, has has aa high high 1(20 K 2 0 and and low low H 2 0 content, content, and and isis normative normative quartz quartz saturated. saturated. These These are a r e characteristic of of H20 Hercynian S-type (continental.collision~ (continental, collision)and andanorogenic anorogenic!l-type A-type (continental (continental rift rift Hercynian S-type or intraplate) intraplate) granites. granites. Major Major element element data d a t a of of these these two twotypes typesisisequivocal; equivocal; or however, however, they they strongly strongly contrast contrastwith withthe t h e1820-1840 1820-1840 Ma Maold oldgranites granitesofofWisconsin Wisconsin K 2 0content. content. CaO,MgO, MgO, A1203, A1203, and and higher higher K20 by their theirlower lowerCaO, by The Ma aage for tthe The 1970 1970 Ma g e for h e Porphyritic Porphyritic Red Red Granite Granite suggests suggests iitt may may be be related related t o the the formation formation of ofthe t h eFeich Felchtrough. trough. In In this thiscase case the t h epluton plutonmay mayrepresent represent aa to rifttype typegranite granitesubsequently subsequentlyintruded intrudedbybydiabase diabasedikes. dikes. These These dikes dikes intruded intruded rift this Ma (Sims (Sims et et this region region up up until untildeposition depositionofofthe t h eMichigamme MichigammeFormation Formationata t1900 1900Ma collision. al., from rift rift tot o collision. al.,1980). 1980). This Thiswould would suggest suggest a very short time t i m e sequence sequence from Figure 1 X1: ?3= 64/177 Figure F i g u r e 22 X1 11=68/168 681168 15/303 X2, 5/277 i2= 51277 20/39 A3 %= 21/10 21/10 REFERENCES REFERENCES Two contrasting contrasting granite granite types. types. B. W. W. and and White, White, A. A. 3.J. R., R., 1974. 1974. Two Chappell, B. Chappell, Pacific Geology, Geology, 2:173-174. 2:173-174. Pacific Finite strain strainand andprogressive progressive deformation deformation in in models models ot of Dixon, 3.3. 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A.; Pearce, discrimination diagramsfor for tthe discrimination diagrams h e tectonic tectonic interpretation interpretation of of granitic granitic rocks. rocks. Jour. Petrology, Petrology,2 25(4):956-983. 3our. 5(4):956 -983. Pitcher, W. W. 5., Set 1984. 1984. Granite Granite type type and and tectonic tectonicenvironment, environment, in Mountain Mountain Pitcher, Building Processes, Processes, Hsu, Hsu, K. K. 3.3. (ed.). (ed.). Acad. cad. Press, Press, London, London, United United Kingdom, Kingdom, Building p. 19-40. 19-4D. p. study of of Pitcher,,'*W.S.S. and and Berger, Berger, A. A. R., R., 1972. 1972. The The geology geology of of Donegal: Donegal: aa study Pitcher,W. granite, emplacing and ing. Wyley 435p. granite.e'mplacing and unroof unroofing. Wyley Interscience, Interscience,London, London,435p. Sims, P. P. K.; K.; Card, Card, K. K. D.; D.; Morey, Morey,G.G.B.B.and andPeterman, Peterman,Z.2.E., E.,1980. 1980. The The Great Great Sims, Lakes Lakes tectonic tectonic zone zone - a a major major crustal crustal structure structure in in central c e n t r a lNorth North America. Arnerica. Geol. kc. Amer. Amer. Bull., 13uIl., part part1,1,91:690-698. 91:690-698. Geol. Soc. Schwerdtner, W, and Sutcliffe, Sutcliffe, R. R.H., H., 1983. 1983. Strain Strain patterns patterns of of Schwerdtner, W. M.; M.; Scott, G. M. and cresentic cresentic granitoid granitoid plutons plutons inin the the Archean Archean greenstone greenstone terane terane of of Ontario. Ontario. Jour. Struct. Struct.Geol., Geol.,5:419—430. 5:419-430. :Jour. Obliquely foliated foliateddikes dikesas a sdeformed deformedincompetent incompetent single single Talbot, C. C. 3., I.,1982. 1982. Obliquely Talbot, layers. Bull., 93:450—460. layers*Geot. G ~ oSoc. LSot*Amer. Amera Bull*, 93:450-460* - 78 �I GEOLOGY OF A LONER PROTEROZOIC VOLCANICLA$TIC 3EQUENCE MARATHON COUNTY, vICON3IT Cohn o± ColinL.L.Reichhoff Reichhoff(Dept. (~ept. ofGeology, Geology,University University of of Minnesota— Ninneso taDuluth, I-QT 55812) 55812) Duluth, Duluth, Duluth,MN Geologic Geologic mapDing map~ingof of approximately auproximately21 21 km^ just just north north of of Wausau, Vausau, Wisconsin Wisconsin has has aided aided in in interpreting interpreting the the depositional depositional environment environment of of aa sequence sequence of of dominantly dominantly felsic—intermediate felsic-intermediate volcanic volcanic rocks rocks and and the the associated associated volcaniclastic volcaniclastic rocks. rocks. This This at—1860 m.y. (Van Schmus, 1980) m . y . (Van Schmus, 19SO) and and sequence has been dated at--1860 sequence has been dated lies lies in in Central Central Wisconsin disconsin near near the the southern southern margin margin of of the the exexnosed Lower Lower ProterozoiC Froterozoic volcanic—plutonic volcanic-plutonic belt. belt. These These rocks rocks posed have have been been metamorphosed metamorphosed to to lower lower greenschist greenschist facies facies and and are are generally generally only only mildly mildly deformed, deformed, dipping dipping to to the the west west at at 1O_300. 10-30". The The volcanic volcanic succession succession consists consists of of rhyodacitic rhyodacitic to to andesitic andesitic flows, flows, pyroclastic pyroclastic flows flows and and intrusives. intrusives. Volcanic Volcanic and and pyropyroclastic clastic textures textures are are locally locally well well preserved preserved and and include include perlitic perlitic cracks, cracks, devitrified devitrified shards shards and and pumice pumice fragments, fragments,and and fiamme fiamme within welded welded tuffs. tuffs. Massive Massive to to amygdaloidal amygdaloidal basalt basalt flows flows are are within minor minor components components of of the the sequence. sequence. Volcaniclastic Volcaniclastic sedimentary sedimentary rocks rocks represent represent aa major major portion gortion of of the the exposed exposed section section and and exhibit exhibit aa wide wide variety variety of of textures. textures. These These sedimentary sedimentary rocks rocks include include massive massive to to laminated laminated argillites argillites and and siltstones, siltstones, possibly possibly of of lacustrine lacustrine origin, origin, which which exhibit exhibit graded graded bedding bedding and and soft soft sediment sediment (including (includingdewatering) dewatering)deformdeform"Red beds" bedsv consisting consisting of of interbedded interbedded volcanic volcanic sandstones sandstones ation. "Red ation. and The and conglomerates conglomerates are are •present "present but are are poorly poorly exposed. exposed. The dominant crossdominant epiclastic epiclastic rock rock is is aa dark, dark, greenish—black, greenish-black,crossbedded bedded volcanic volcanic sandstone sandstone with with discontinuous discontinuous interbeds interbeds of of conglomerate, conglomerate, composed composed mainly mainly of of locally locally derived derived volcanic volcanic pebbles clasts of of quartzite quartzite and and tonalite. tonalite. pebbles but but also also including including clasts These These cross—bedded cross-bedded sandstones sandstones and and interbedded interbedded conglomerates conglomeratesare are interpreted interpreted as as fluvial fluvial deposits. deposits. This intermediateThis succession succession is is interpreted interpreted to to represent represent an an intermediate— source facies facies (Fisher (Fisher and and Schmincke, Schmincke, 1984) 1984) characterized characterized by by source rocks rocks formed formed by by pyroclastic yy-roclastic flow, flow, lava lava flow, flow, airfall, airfall, and and their their reworked products. products. The The tectonic tectonic interpretation interpretation is is based based on on reworked Dickinson's Dickinsonls(1974) (1974) model model of of magmatic magmatic arcs. arcs. This This model model places places volcanic intermediate-felsic composition compositionin inan anarc arc volcanic rocks rocks of of intermediate—felsic having having continental continental affinities affinities (crustal (crustalthickness thickness>15—20 >I 5-20 km). km). Using Using this this model, model, the the described described sequence sequence would would represent represent rocks rocks deposited deposited in in an an intra—arc intra-arc basin basin (graben) (graben) and and characterized characterized by by volcaniclastic volcaniclastic red red beds, beds, subaerial subaerial tuffs, tuffs, lacustrine lacustrine deposits deposits and conglomerates. conglomerates. and i I I P1 �U RJFiRN CS 3 i c k i n s o n , .R., ;/.R., 1974, 1 9 7 4 , Sedimentation S e d i m e n t a t i o n within w i t h i n and and beside b e s i d e ancient ancient Dickinson, modem, magmatic n a g m a t i c arcs. a r c s . In: In: JJott, Uot-b, JJr., r . , 3.5. Shaver, and modern P.H. and Shaver, 2.E. , eds., e d s . , Iiodern ?,iodern and n c i e n t ggeosynclinal e o s y n c l i n a l ssedimentation, edimentation, R.H., and aancient soc. 'ubl. p. P u b l . 19, 1 9 , p. p. 230—239. 230-239. i5oc. Econ. Econ. Paleont. P a l e o n t . Liineral. i - i i n e r a l . SSp. Fisher, Schmincke, H.-U., H.—U., 1984, F i s h e r , R.V. R.V. azid and Schmincke, 1 9 8 4 , Pyroclastic P y r o c l a s t i c Rocks. Rocks. Springer—Verlag, S p r i n g e r - V e r l a g , Berlin, B e r l i n , Heidelberg, H e i d e l b e r g , New York, York, Tokyo, Tokyo, 472p. Van Schmus, W.R., W.R., 1980, 1 9 8 0 , Chronology Chronology of of igneous i g n e o u s rocks r o c k s associated associated with w i t h the t h e Penokean Orogeny in i n Wisconsin. ',!/isconsin. Geological G e o l o g i c a l 3ociety Society of of America Special S p e c i a l Paper P a p e r 182, 1 8 2 , p. p. 159—168. 159-168. 80 �PETROGENESIS PETROGENESIS OF OF THE THE BARDON BARDON PEAK PEAK PERIDOTITE, PERIDOTITE,DULUTH DULUTHCOMPLEX COMPLEX BRIAN A.A. ROSS, f Geology n i v e r s i t y of o f Minnesota, Minnesota, MinMinBRIAN ROSS,Dept. Dept.oof Geologyand andGeophysics, Geophysics,UUniversity  neapolis, MN An An area area of of 55455 - 2.5 2.5 sq. sq. km mappedalong alongthe thebasal basal contact contact of Complex km was was mapped o fthe theDuluth Duluth Complex Three bands bands of unlayered unlayered around Peak, southwest off Duluth, Bardon Peak, southwest o Duluth, Minnesota. Minnesota. Three around Bardon gabbro paralleling gabbro p a r a l l e l i n gthe thecontact contactwere were located l o c a t e dini nananextensive extensivesequence sequence of o f rhythrhythnearest the the basal The band band ooff gabbro gabbro nearest basal contact is is m i c a l l y layered layered ttroctolites. r o c t o l i t e s . The mically interpreted ononthe wall magma i n t e r p r e t e dtot obebea amarginal marginalphase, phase, which which crystallized crystallized the w aof l l the o f the magma chamber. chamber. The The other two two bands bands of' o f gabbro gabbro possess possess ggradational r a d a t i o n a l lower lower contacts contactsand and sharp contacts wwith the host sharp upper upper contacts i t h the host troctolites, t r o c t o l i t e s and , andare arehypothesized hypothesized to t obe be The layers l a y e r s of o fgabbro gabbro and and underlying underlying layers l a y e r s dipping dipping east east ata tapproximately approximately 28°. 280. The troctolite macro—rhythmic t r o c t o l i trepresent e represent macro-rhythmic layers l a y e r sformed formedby byreplenishment replenishmentofomagma f magma in i naa sill—shaped chamber,wwith higher crystal sill-shaped chamber, i t h f rfractionation a c t i o n a t i o n and and higher c r y s t a lgrowth growth rates r a t e sresponrespons i b l e for f o rformation formationof' o fthe thegabbro. gabbro. sible The increasei in The increase n ccrystal r y s t a l growth growth rates r a t e s is is hypothesized be the the rresult hypothesized t to o be e s u l t of o f an an increase increase in i n the the amount amount oof f vvolatiles, o l a t i l e s , through through diffusion magma from dewatering dewateringoof country rock basalts. d i f f u s i o ninto i n tthe o the magma chamber chamber from f country basalts. Also the Bardon BardonPeak Peak areawere werei r irregular bodies ooff peridotite Also mapped mapped i ninthe f i efield l d area r e g u l a r bodies peridotite are circular Most ooff the bodies bodies are circular found iinn both both the the troctolite t r o c t o l i t eand andgabbro gabbro units. u n i t s . Most found in andare areooften contact wwith i ngeometry, geometry, and f t e n i in n gradational g r a d a t i o n a l contact i t h their t h e i r host host rock. rock. Dike— Dike- like not disrupt l i k eperidotite p e r i d o t i t ebodies bodieswere were found found which which ccut u t but b u t do do not d i s r u p t layering l a y e r i n g in i nhost host petrographic ttextures The petrographic e x t u r e s and and ccrystallization r y s t a l l i z a t i o nsequence sequence of o fthe thepen— perit r o c t o l i t e . The troctolite. primary ddifThe primary ifdotite and d o t i t e were were markedly markedly ddifferent i f f e r e n t from from the the troctolite troctolite andgabbro. gabbro. The ferences are the the mafic mafic minerals minerals eexhibit ferences are x h i b i t an an interlocking i n t e r l o c k i n gtexture, t e x t u r e ,and andplagioclase plagioclase i s always always anhedral anhedral and t e r s t i t i a l to t othe theother otherminerals. minerals. is andi ninterstitial 81 ItI twas wasdetermined determined I �the oolivine the pperidotite tthat h a t the the compositions compositions oof f the l i v i n e and and clinopyroxene clinopyroxene i in n the eridotite ccrystallized r y s t a l l i z e dfrom fromaamagma magma t hthat a t was l i g h t l y more more ffractionated r a c t i o n a t e d than than the melt melt wass slightly Compositionsofofthe the pplagioclase Compositions l a g i o c l a s e iin n the the which formed formedthe thet troctolite which r o c t o l i t eand andgabbro. gabbro. peridotite MnAncontents p e r i d o t i t ewere were found found to t o contain contain significantly s i g n i f i c a n t l higher y higher contentsthan thanplagio— plagio- clase clase iin n the the troctolite t r o c t o l i t eand andgabbro. gabbro. It I twas was concluded concluded tthat h a t the peridotite p e r i d o t i t ewas was formedby byaavvolatile—rich metasomatizingmelt meltt hthat replaced pplagioclase formed o l a t i l e - r i c h metasomatizing a t replaced l a g i o c l a s e iin n the the host rock with host w i t h olivine o l i v i n eand andclinopyroxene. clinopyroxene. Additionally, A d d i t i o n a l l y , iti tisi hypothesized s hypothesized that that the source source of o f the t h emetasomatizing metasomatizing melt melt was was intercumulus intercumulus melt, melt, which whichhad hadbeen been fluxed by volatiles v o l a t i l e sfrom fromdewatering dewatering of' o f the t h e country country rock. rock. fluxed by The metasomatizing metasomatizing The andand moved ffluid l u i d isi senvisioned envisionedtot ohave havebeen beenlocalized l o c a l i z e dini a n dilation a d i l a t i zone, o n zone, movedupward upward forming pipe—shaped peridotite iinn channeiways channelways forming pipe-shaped p e r i d o t i t e bodies. bodies. As from two drill d r i cores l l cores fromthe theWater Water Hen Hen intrusion, i n t r u s i o n , aalayered layered As aa ppart a r t of o f this t h i sstudy, study, two mafic mafic intrusion i n t r u s i o nalong along the thebasal basalcontact contactofofthe theDuluth DuluthComplex Complex south south of of Hoyt Hoyt Lakes, Lakes, Minnesota, Minnesota, were were examined. examined. Themany manys isimilarities the pperidotite The m i l a r i t i e s between between the eridotite coresand andaat BardonPeak Peak suggest thep eperidotite iinn the the Water Water Hen Hen cores t Bardon suggest t h athat t the r i d o t i t e i in n the Water Hen Heni nintrusion by a replacement Water t r u s i o n may may have have aalso l s o been been produced produced by replacement process. process. 82 ! 1 I �U Platinum Group Group Element Element Minerals Minerals in Platinum in the the Duluth Duluth Complex Complex TATIANA SABELIN SABELIN (Mineral (MineralResources ResourcesResearch Research Center, Center,University Universityof of TATIANA Minnesota,Minneapolis, Minneapolis,MNMN55455) 55455) Minnesota, Platinum Platinum group group element element (PGE) (PGE) minerals minerals with with trace traceamounts amountsof ofAu Auand andAg Ag from the the Duluth DuluthComplex Complexare aredescribed. described. The The minerals minerals were were found foundat at two two from different locations locations within within oxide-rich oxide-richportions portions of ofaadrill drillcore. core. The The different PGE minerals occur in an oxide( 65%)-plagioclase( 25-30%)-olivine( 5%) PGE minerals occur in an oxide( 65%)-plagioclase( 25-30%)-olivine( 5%) host and and an an olivine( olivine( 40%)-oxide( 40%)-oxide( 30%)-plagioclase( 30%)-plagioclase( 25%) 25%) host. host. TitanifTitanifhost erous magnetite magnetite is is the the dominant dominant oxide oxideand and is isassociated associatedwith withminor minorherhererous cynite and and ilmenite. ilmenite. Sulfide Sulfide mineralization mineralization in in these these rocks rocks is is minor minor cynite and is is primarily primarily of of the the finely finelydisseminated disseminatedtype. type. Chalcopyrite, Chalcopyrite, bornite bornite and and pentlandite pentlandite are are the the main main sulfide sulfidephases. phases. and The PGE PGE minerals minerals were were identified identifiedby by energy energy dispersive dispersivex-ray x-rayanalysis analysis The (EDS) (EDS) using using both both an an electron electron microprobe microprobe and and aa scanning scanning electron electron micromicroscope. They and two twolocked lockedcomcomThey consist consist of of five five monomineralic monomineralic grains grains and scope. posite grains. grains. EDS EDS spectra spectra were were collected collected from from each each of ofthe theindividual individual posite mineral grains grains and and from fromnumerous numerous points pointswithin withinthe thecomposite compositegrains. grains. mineral Approximate compuApproximate chemical chemical compositions compositions of of the the phases phases were were obtained obtainedby by computor-processing tor-processing the the net net peak peak counts counts of of the the elements elementspresent present in ineach each spectrum. The The analyses analyses were were then then correlated correlated with with published published microprobe microprobe spectrum. data on on PGE PGE minerals minerals in in order order to to identify identify the the phases. phases. The The mineral mineral names names data proposed proposed in in this this paper paper are are pending pending positive positive identification identificationby by quantitaquantitative analysis. analysis. tive The olivine-oxide-plagioclase The five five monomineralic monomineralic grains grains occur occur in in the the olivine-oxide-plagioclase They They are are subsubTwo hedral hedral to to euhedral euhedral and and range range in in size sizefrom from2x5 2x5to to 34x36 34x36micrometer. micrometer. Two grains grains are are associated associated with with magnetite, magnetite, chalcopyrite, chalcopyrite,bornite bornite and and silicate silicate The alteration products. products. One One grain grain occurs occurs as as an an inclusion inclusionin inilmenite. ilmenite. The alteration fourth fourth grain grain forms forms aa composite composite sulfide sulfide grain grain (70xl6 (70x16 micrometer) micrometer) with with The pentlandite, bornite and and chalcopyrite chalcopyrite and and occurs occurs in in plagioclase. plagioclase. The pentlandite, bornite Pt-Fe Pt-Fe alloy alloy is is distinguishable distinguishable from from the the sulfides sulfides in in reflected reflectedlight light The four four grains grains microscopy by by its its high high reflectivity reflectivity and and white white color. color. The microscopy have similar compositions and consist mostly of Pt with minor Fe have similar compositions and consist mostly of Pt with minor Fe and and The fifth fifth grain grain is is aa Ru Ru sulfide sulfide with with lesser amounts amounts of of Pd, Pd, Cu Cu and and Ni. Ni. The lesser It has has aa high high reflectivity reflectivity and and is is 0s and and traces traces of of Ir Irand andFe. Fe. It minor Os minor The mineral mineral resembles resembles laurite laurite in in both both its its comcomwhite with with aa grey grey tint. tint. The white The 10x20 10x20 micrometer micrometer grain grain is is euhedral euhedral position and and optical opticalproperties. properties. The position and occurs occurs as as an an inclusion inclusionin in plagioclase. plagioclase. and rock. Four Four of of the the five five grains grains consist consist of of aa Pt-Fe Pt-Fealloy. alloy. rock. The The composite composite grains grains were were found found in in the the oxide-plagioclase-olivine o x i d e - p l a g i o c l a s e - o l i v i n e host. host. measure l3x5 and and occur inand a Fe-Mg-Al-Si The grains grains measure 13x512x8 andmicrometer 12x8 micrometer occur in a Fe-Mg-Al-Si The alteration product associated with biotite and plagioclase. alteration product associated with biotite and plagioclase. One One grain grain consists of Pt-Fe alloy and three compositionally distinct Pd phases. distinct Pd phases. consists of Pt-Fe alloy and three compositionally EDS of the minerals indicate the presence of the presence following of the following EDS spectra spectra ofPd the Pd minerals indicate the elements elements (not (not listed listed in in order order of of abundance): abundance): Pd-Pt-Fe-Cu-Ni-Sn-Bi-As, Pd-Pt-Fe-Cu-Ni-Sn-Bi-As, Pd-Pt-Cu-Sn-Bi Pd-Pt-Cu-Sn-Biand and Pd-Fe-Sn-Bi-As. Pd-Fe-Sn-Bi-As. The The Pt-Fe Pt-Fe alloy alloy is is compositionally compositionally similar similar to to the the other other Pt-Fe Pt-Fe alloy alloy grains grains found found and and constitutes constitutes 85% 85% of of interthe grain. grain. The The second second grain grain contains contains very very fine-sized fine-sizedcomplex complex interthe Six phases phases were were identified identified by by EDS EDS growth of of numerous numerous PGE PGE minerals. minerals. Six growth 83 I 1 I �! analysis. analysis. The The texture t e x t u r e of o f the t h e grain g r a i n indicates i n d i c a t e s the t h e presence presence of o f additional additional phases phases but b u t they they were were too t o o fine-grained f i n e - g r a i n e d to t o be be resolved r e s o l v e d by by the t h e scanning scanning The phases phases identified e l e c t r o n microscope. microscope. The i d e n t i f i e d in i n this t h i s grain g r a i n are a r e an an Ir-Rh Ir-Rh electron sulfarsenide or irarsite, two Pt sulfarsenides with significant s u l f a r s e n i d e o r i r a r s i t e , two Pt s u l f a r s e n i d e s w i t h s i g n i f i c a n t Fe Fe and and Os 0 s and and traces t r a c e s of of Ag Ag (one (one of of which which also a l s o contained contained Pd Pd and and trace t r a c e amounts amounts of of Au), and traces t r a c e s of of Pd, Pd, Rh Rh and and Ag, Ag, A s and Au), aa Pt-Fe-Os Pt-Fe-0s phase phase with with minor minor Cu Cu and and As Pd arsenide a r s e n i d e with with Fe, Fe, Cu, Cu, Sn Sn and and Sb, Sb, and and aa Pd-Pt-Pb Pd-Pt-Pb arsenide. a r s e n i d e . Ag Ag may may aa Pd be be present p r e s e n t in i n the t h e Pd Pd minerals minerals as a s well w e l l but b u t was was difficult d i f f i c u l t to t o detect d e t e c t due due to to peak overlap o v e r l a p in i n the t h e EDS EDS spectra s p e c t r a for f o r Pd Pd and and Ag. Ag. Similarly, S i m i l a r l y , Au Au in i n other other peak Pt P t minerals minerals may may not n o t have have been been detected d e t e c t e d because because of o f peak peak overlap o v e r l a p for f o r Pt Pt and Au. Au. and This i s the t h e second second reported r e p o r t e d occurrence occurrence of of PGE PGE minerals minerals in i n the t h e Duluth Duluth This is Complex Complex and and the t h e first f i r s t identification i d e n t i f i c a t i o n of of Pd, Pd, Ir, I r , Ru, Ru, and and Os0 s - and and RhRhb e a r i n g phases. phases. This This find f i n d is i s also a l s o significant s i g n i f i c a n t because because the t h e minerals minerals bearing d e s c r i b e d here h e r e occur occur in i n rock rock containing c o n t a i n i n g disseminated disseminatedsulfides. s u l f i d e s . The The described sperrylite s p e r r y l i t e reported r e p o r t e d previously p r e v i o u s l y (1) (1) was was found found in i n massive massive sulfide s u l f i d e ore. ore. Considerably Considerably more more mineralogical m i n e r a l o g i c a l work work is i s required r e q u i r e d to t o evaluate e v a l u a t e the the potential p o t e n t i a l of of the t h e Duluth Duluth Complex Complex as a s aa producer producer of of platinum platinum group group metals. metals. The flotation flotation is also a l s o needed. needed. The The evaluation e v a l u a t i o n of o f ore o r e recovery recovery procedures procedures is The Of particular p a r t i c u l a r conconresponses responses of o f PGE PGE minerals minerals have have not n o t been been documented. documented. Of cern of alloys, a l l o y s , expecially e x p e c i a l l y of o f iron-platinum, iron-platinum, c e r n are a r e the t h e floatabilities f l o a t a b i l i t i e s of which may may not n o t be b e as a s floatable f l o a t a b l e as a s sulfides, s u l f i d e s , arsenides a r s e n i d e s and and sulfarsenides. sulfarsenides. which References : References: 1) 1) Ryan, P.J. P . J . and and Weiblen, Weiblen, P.W., P.W., 1984, 1984, Pt Pt and and Ni N i Arsenide Arsenide Minerals Minerals in in Ryan, •Duluth Duluth Complex Cabs), ( a b s ) , Ann. Ann. Inst. I n s t . Lake Lake Superior S u p e r i o r Geol., Geol., 30th, 30th, Wausau, Wisconsin, Wisconsin, 58-60. 58-60. Wausau, 84 I l �U AA Study Study Of Vein Mineralization and and Wall Rock Rock Alteration Alteration at at the the Delaware Delaware Mine, Mine, Keweenaw Keweenaw County, County, Michigan Michigan W.A. W.A. Schleiss, Scnleiss, T.J. T.J. Bornhorst, Bornhorst, and and A.P. A.P. Ruotsala Ruotsala (Dept. (Dept. of of Geol. Geol. and and Geol. Geol. Engrg., Engrg., Michigan Michigan Technological Technological University, University, Houghton, MI 49931) 49931) Houghton, MI 1 The Delaware Delaware Mine is is located located in in the the northern northern half half of of the the Keweenaw Keweenaw The Peninsula of of Upper Upper Michigan. Michigan. It opened in in 1848 1848 and and is is one one of of the tne Peninsula oldest oldest copper copper mines mines in in the the Michigan Michigan Native Native Copper Copper District. District. Mining Mining originally orii-jinally centered on a mass copper—oearing copper-ocarina fissure fissure known known as as the the Stoughtenourgh Stoujhtenourgh vein vein and and later later production production was was from from the the Allouez Allouez Conglomerate, Conglomerate, a copper—bearing copper-oearing conglomerate conglomerate which is is cut cut oy oy the the Stoujhtenourgh. The The mine closed closed in in 1887 1887 and and remained remained so so until until 1977 1977 Stoughtenurgh. when Tom Poynter Poynter purchased purcnased the the mine and reopened reopened the the first first level level for for public tours. tours. public The The mine was geologically mapped at at aa scale scale of of 1:1080. 1:1080. The The Allouez Allouez Conglomerate Conglomerate is is an an 88 meter thick stratified stratified conglomerate conglomerate consisting consisting of of rounded to suoangular suangular peübles peooles and and coooles coooles of of mostly mostly rhyolite rhyolite and and rarely rarely amygdaloidal amygdaloidal oasalt. oasalt. Exposed in in two two crosscuts crosscuts oelow oelow the the Allouez Allouez are are two two thin thin oasalt basalt flows. flows. The The Greenstone Greenstone Flow Flow is is stratigraphically stratigraphically above aoove the the conglomerate conglomerate but but not not exposed exposed in in the tne mine. ,nine. These These rocks rOCKs generally generally strike strike E—W E-W and and dip dip 25 25 degrees degrees north. north. Numerous Numerous mineralized tension tension fractures fractures with with generally generally northerly northerly strikes strikes and and near near vertical vertical dips dips transversely transversely cut cut the the oeds. oeds. Stereographic Stereographic projection of poles to planes for for the tne fractures fractures indicate indicate that tnat the the major stress stress field, field, sigma sigma one, one, was was approximately approximately N—S, N-S, parallel paragenetic sequence sequence parallel to to the the tension tension fractures. fractures. The general paragenetic for mineralization in the fractures fractures is, oldest oldest to to youngest: 1) 1) drusy drusy suohedral suonedral to anhedral anhedral grains grains of quartz; 2) euhedral eunedral to to anhedral anhedral microcline; muscovite, in part replacing microcline; 3) 3) fine fine •;rained grained muscovite, re,~lacing microcline; microcline; 4) native native copper; copper; 5) 5) coarse coarse grained grained anhedral anhedral calcite; calcite; and and 6) 6) rare rare copper sulfide. sulfide. copper Fluid inclusion inclusion studies studies of calcite calcite from from eleven eleven veins were were conducted conducted to constrain constrain the the temperature temperature of of the the mineralizing mineralizing fluids. fluids. Homogenization temperatures temperatures of 136 inclusions inclusions ranged ranged from from 80 80°C —Analyzed inclusions were 280°c uncorrected uncorrected for for pressure. pressure. inclusions were isolated, isolated, 280°C, did not follow oovious fractures, and showed follow oovious fractures, showed no evidence evidence of of necking necxing peas: down. A histogram suggests two and possioly three temperature peai<s: down. (A) (B)160—200 160-200C C(?) ( ? ),, and and (C) (C) 230—260°C. 230-260 C. Fluid inclusion inclusion (A) 110—130°C, 110-130 C, (B) homogenization homogenization temperatures temperatures must must oe oe corrected corrected for for pressure. pressure. Livnat's Livnat's (1983) inferred inferred pressure pressure of of 1.5 1.5 ko k for thispart this0part of of the the strafigraphic straigraphic column column yields yields aa pressure pressure correction correction of of +125 +I25 (peak C 325—385 325-385 C). C). The The pressure of pressure corrected corrected temperature temperature for for peak C seems seems too too high high in in light light of wall rock rock alteration alteration mineralogy, mineralogy, Livnat's (1983) (1983) prooaole prooaole temperature temperature of of lode lode copper copper mineralization, mineralization, and and comparison0to comparison to calcites calcites in in Tertiary Tertiary veins C are This veins where where temperatures temperatures ranging ranging from from 230—260 230-260'~ are common. common. This suggests perhaps little suggests that that the the pressure pressure was was less less than than 1.5 1.5 ico ko and perhaps little if if any pressure oressure correction correction is is needed. needed. At the present time time no no firm firxi conclusions conclusions can can oe oe drawn drawn from from the the fluid fluid inclusion inclusion data. data. Wall rock rocK adjacent adjacent to to veins veins is is mildly mildly to to intensely intensely chloritized, chloritized, sericibized, Plagioclase in in oasalt oasait is is sericitized, carbonatized, carbonatized, and and silicified. silicified. Plagioclase generally aloitized out where the oy veins veins plagioclase plagioclase the basalt oasalt is is cut cut by 85 I �iis s aaltered l t e r e d to t o sericite s e r i c i t e and and chlorite. chlorite. O l i v i n e is i s wholly w n o l l y or o r partly partly Olivine altered Interstitial a l t e r e d to t o serpentine. serpentine. I n t e r s t i t i a l material m a t e r i a l in i n the t h e oasalt o a s a l t (glass?) (glass?) has h a s oeen e e n predominantly p r e d o m i n a n t l y altered a l t e r e d to t o chlorite, c h l o r i t e , or o r replaced r e p l a c e d oy oy minor minor amounts of Rhyolite veins o f calcite. calcite. R h y o l i t e cclasts l a s t s in i n cconglomerate o n g l o m e r a t e adjacent a d j a c e n t to to v eins and ssilicified, with ttend e n d tto o ooe e lless e s s aaltered, l t e r e d , ddominantly o m i n a n t l y ccaroonatized a r o o n a t i z e d and ilicified, w ith calcite c a l c i t e and quartz q u a r t z filling f i l l i n g minute m i n u t e voids v o i d s and and fractures f r a c t u r e s in i n the t h e clasts. clasts. The rhyolite moderately r h y o l i t e cclasts l a s t s aare r e aalso lso m o d e r a t e l y tto o intensely i n t e n s e l y sstained t a i n e d with with a coating Samples o of wall c o a t i n g of o f iron i r o n oxide. oxide. Samples f w a l l rock r o c k taken t a k e n pperpendicular e r p e n d i c u l a r to to t h e vveins e i n s from f r o m ddirectly i r e c t l y aadjacent d j a c e n t tto o and p to t o aa maximum of o f one o n e meter meter the and uup away were cchemically of h e m i c a l l y aanalyzed n a l y z e d ffor o r aa ssuite uite o f 23 2 3 elements e l e m e n t s in i n order o r d e r to to determine All l l analyses a n a l y s e s were were d e t e r m i n e element e l e m e n t mooility m o o i l i t y during d u r i n g alteration. alteration. A Element m moollity ccorrected o r r e c t e d for f o r volume changes. changes. Element o o i l i t y calculations c a l c u l a t i o n s indicate indicate that were m massively a s s i v e l y aadded d d e d tto o 0ooth 0 t h rhyolite r h y o l i t e and oasalt oasalt t h a t Cu and and Ca were adjacent mineralizing a d j a c e n t to t o the t h e vveins e i n s ooy y the the m i n e r a l i z i n g fluids. f l u i d s . This T h i s is i s consistent consistent with w i t h the t h e formation f o r m a t i o n of o f calcite c a l c i t e and and native n a t i v e copper c o p p e r or o r copper c o p p e r sulfide. sulfide. K and Mg Mg w were generally most altered ere g e n e r a l l y aadded d d e d ooy y the t h e fluid f l u i d to t o tthe h e most a l t e r e d rock r o c k and were incorporated i n c o r p o r a t e d into i n t o sericite s e r i c i t e and and chlorite, c h l o r i t e , respectively. respectively. Na was was massively depleted m assively d e p l e t e d from f r o m the t h e rhyolite r h y o l i t e and and ddepleted e p l e t e d only o n l y in i n tne t n e most a l t e r e d obasalt a s a l t ddirectly i r e c t l y aadjacent d j a c e n t tto o tthe h e vvein; e i n ; Na removed oy the the altered Na was was removed Na depletion solution. s o l u t i o n . Na d e p l e t i o n prooably p r o o a o l y reflects r e f l e c t s the t h e breakdown breakdown of of Ni was m mobile was oonly pplagioclase. lagioclase. N i was o o i l e oout u t was n l y rredistriuted e d i s t r i o u t e d within w i t h i n the the Ba, Y Y, V, and Ti conglomerate. , Zr, Zr, V, T i were w e r e relatively relatively c o n g l o m e r a t e . The elements e l e m e n t s Ba, immocile during Att the immooile d u r i n g alteration. alteration. A t h e ppresent r e s e n t time t i m e a model is i s oeing minj developed of d e v e l o p e d to t o ddetermine e t e r m i n e the t h e nnature ature o f the t h e hydrothermal h y d r o t h e r m a l system s y s t e m for f o r vein vain mineralization i l l allow a l l o w for f o r a comparison comparison m i n e r a l i z a t i o n at a t the t n e Delaware D e l a w a r e Mine. Mine. T his w This will with w i t h the t h e more economically e c o n o m i c a l l y significant s i g n i f i c a n t lode l o d e deposits. deposits. Reference R eference . . Livnat, (Ph. D. D. D Dissertation), L i v n a t , A., A., 1983, 1 9 8 3 , (Ph. i s s e r t a t i o n ) , University U n i v e r s i t y of of Michigan, Michigan, Ann Arbor, 2 2 5 p. p. A r o o r , 225 86 1 �I I THE GEOLOGICAL GEOLOGICAL SETTING SETTINGATATTHE THEDLTPORT DUPORT MINE, MINE, CAMERON CAMERON ISLAND, ISLAND, THE SHOAL LAKE LAKE SHOAL Smith, P.M., P.M., Mineral Mineral Deposits DepositsSection,. Section,.Ontario Geological Smith, Ontario Geological Survey, Toronto Toronto Survey, The Ouport Mine Mine has has been been explored explored and and developed developed several several The Duport times since since its its discovery discovery in in 1896. 1896. Recent Recent drilling drilling has has times increased increased the the reserves, reserves, now now estimated estimated 1,927,000 1,927,000 tons tons grading grading 0.30 ounce ounce Au Au per per ton ton over over 9.75 9.75 feet feet (Northern (NorthernMiner, Miner , 0.30 October October 13, 13, 1983). 1983). Recently Recently an an 1l85m 1185m decline declinehas has been been driven driven to intersect intersect the the two two main main mineralized mineralized zones zones at at three three to levels. levels. limb of of aa northwest-trending northwest-trending Located on on the the western western limb rocated anticline, anticline, the the deposit deposit is is hosted hosted by by tholeiitic tholeiitic and and komatiitic komatiitic basalts basalts and and by by ultramafic ultramafic flows/sills. flows/sills. The Themafic mafic volcanics volcanics are are overlain overlain to to the the west west by by aa series seriesof of andesitic andesitic and and felsic felsic flows flows and and tuffs. tuffs. The The volcanic volcanic package package has has been been intruded intruded west west of of the the deposit deposit by by the the Snowshoe Snowshoe Bay Bay grano3iorite granodiorite hatholith, batholith,arid and immediately immediately to to the the east east by by the the Stevens Stevens Island Island diorite. diorite. Late Late felsic felsic and and mafic mafic dikes dikes cut cut all all lithologies. 1-ithologies.The The regional regional metamorphic metamorphic grade grade is is upper upper greenschist to to lower lower amphibolite amphibolite fades; facies;however, however,mineral mineral greenschist assemblages in in close close proximity proximity to to the the ore ore zones zones are are assemblages indicative of of lower lower greenschist greenschist grade grade metamorphism. metamorphism. indicative The mine mine lithologies lithologies consist consist of of metahasalt, metabasalt, metapyroxenite, metapyroxenite, The and varieties varieties of of chlorite chlorite schist. schist. Lithologies Lithologies close close to to the the and ore zones zones are are anomalous anomalous in in chlorite, chlorite, talc, talc, sericite, sericite, ore hiotite, biotite, epidote, epidote, carbonate, carbonate, magnetite, magnetite, and and pyrite; pyrite; the the ore ore zones zones themselves themselves are are quartz quartz and and suiphide sulphide rich rich and and contain contain varying amounts amounts of of feldspar, feldspar, muscovite, muscovite, sericite, sericite, pale—brown pale-brown varying biotite, biotite, epidote, epidote, carbonate carbonate and and chlorite. chlorite. The The two two main main ore ore zones, the the East East and and Main Main zones, zones, lie lie within within aa zone zone which which has has zones, recorded intense intense defocmation, deformation, the the Duport nuport Deformation Deformation Zone Zone recorded (DDZ). The DDZ DDZ is is aa reverse reverse fault fault system, system, several several hundred hundred (DDZ) . The metres 75 metres wide, wide, trending trending northeast, northeast, and and dipping dipping about about 75 degrees northwest. northwest. From From east east to to west west the the DDZ DOZ is is degrees characterized characterized by by chlorite—talc-carbonate chlorite-talc-carbonate schist schist and and amphibolite, grading grading to to zones zones of of actinolite—chiorite— actinolite-chloriteamphibolite, sericite schist schist and and finally finally to to basalt basalt breccia. breccia. Deformation Deformation sericite styles styles reflect reflect these these transitions, transitions, ranging ranging from from ductile ductile in in the east east to to brittle brittle +/— +/- ductile ductile in in the the west. west. Gold Gold is is hosted hosted the by well—defined well-defined quartz— quartz- and and sulphide—rich sulphide-rich zones. zones. It Itdisplays displays by strong association association with with arsenopyrite, arsenopyrite, but but is is also also found found aa strong with with pyrite, pyrite, pyrrhotite pyrrhotite and and chalcopyrite. chalcopyrite. There There are are are are least two two ages ages of of pyrite; pyrite; the the younger younger containing containing inclusions inclusions least of gold, gold, while while the the older older is is plated plated by by gold. gold. The The ore ore zones zones of show aa pronounced, pronounced, hut but discontinuous discontinuous sulp'nide—silica sulphide-silica show layering. Commonly Commonly aa well—developed well-developed biotite biotite (+/— ( + / - pyrite) pyrite) layering. halo halo surrounds surrounds the the ore, ore, and and in in places places extends extends past past ore ore lens lens terminations. terminations. In In general general the the ore ore parallels parallels the the schistosity, schistosity, I 1 �hut but locally locally it it fills fills branching branching interconnecting interconnecting fractures fractures and and does not not form form discrete does discrete zones. zones. Where Where felsic felsic dikes dikes intersect intersect ore-bearing system, system, dike margins are are brecciated brecciated to to the ore—bearing rnylonitized and and are are replaced replaced by by quartz, quartz,suiphides sulphidesarid and gold. gold. mylonitized suggested that that the the ore ore zones zones are are Recent underground work has suggested not continuous continuous as as previously previously believed, believed, rather rather they they are are aa not iT i: series of enechelon, enechelon, almond-shaped almond-shaped lenses, lenses, which which step step le let in the horizontal in the the in horizontal sense sense and and up up and and into into the the footwall ootwall in verical ver ical sense. sense. The The extensive extensive deformation, deformation, associated associated pervasive pervasive alteration, alteration, suggest that that the the ore—bearing ore-bearing zones zones and vein orientations, suggest are structurally structurally controlled. controlled. It It is is proposed proposed that that ore ore is is are hosted hosted by zones zones of of high high permeability, permeability, either either by by brittley brittley deformed felsic felsic dikes dikes or or by by permeable permeable channels channels created created by by deformed brittle brittle failure failure within within basalt, basalt, and and concentrated concentrated into into openings created created by by movement movement over over irregular irregular fault fault planes. planes. openings 88 I - I �VOLCANIC VOLCANIC FACIES FACIES 0 OFF THE THE ANDREW BBAY AY AREA, AREA, LAKE 0OF F THE WOODS, WOODS, ONTARIO ONTARIO JJohn ohn Department Department University University Toronto, Toronto, M5S M 5S Stix Stix of Geology o f Geology of o f Toronto Toronto Ontario Ontario 1A1 1A1 Basalt lava B asalt 1 ava fflows l o w s aand n d iintermediate n t e r m e d i a t e to to felsic felsic p yroclastic pyroclastic rrocks ocks o off Archean agee ccrop outt o onn eeither off aann eeast-trending i t h e r sside id e o a s t - t r e n d i n g ssyncline y n c l i n e in i n Andrew Andrew Archea n ag r o p ou I Bay, 2 20km Ontario. 0 kmsouth-southeast s outh-southeast of o f Kenora, Kenora, O n t a r i o . The basaltic b a s a l t i c assemblage assemblage reachess 55.4km pyroclastic reache . 4 k m in i n thickness thicknes s north n o r t h of o f Andrew Andrew Bay, Bay whereas tthe h e pyroclas ti c km oof km tthick rrocks o c k s ooverlie v e r l i e 00.9 . 9 km f bbasalt a s a l t aand n d aare r e uup p tto o 11.7 . 7 km h i c k ssouth o u t h oof f Andrew Andrew Bay. Massive aand pillowed basalts products off non-explosive volcanism, re p roducts o Bay. Massive nd p illowed b a s a l t s aare whereas whereas tuffs, t u f f s , lapilli l a p i l l i tuffs, t u f f s , and a n d debris d e b r i s flows f l o w s represent r e p r e s e n t products p r o d u c t s of of eexplosive x p l o s i v e volcanism. volcanism. , The tuffs deposits The t u f f s aand n d llapilli a p i l l i tuffs t u f f s aare r e massive d e p o s i t s that t h a t ccontain o n t a i n up o up tto 407.c crystals volume.Thes These rocks fragments, some which 40% r y s t a l s b by y volume. e rock s c carry a r r y l lithic i t h i c fragments , som e oof f which may orr flow-banded have may be b e welded tuffs tuffs o f low-banded lavas l a v a s that that h a v e been been transported t r a n s p o r t e d from near-ventt aareas. Many of presence off r e a s Many o f the t h e least-altered l e a s t - a l t e r e d tuffs t u f f s indicate i n d i c a t e the the p resence o near-ven pumice iin betweenc crystals rrelict e l i c t pumice n tthe h e iinterstices n t e r s t i c e s between r y s t a l s and lithic 1i t h i c fragments. Thee presenc presence pumice provides evidence Th e oof f pumic e provide s evidenc e ffor o r contemporaneous contemporaneous eexplosive xplosive volcanism By analogy modern-day environments, the v o l c a n i s m aand n d sedimentation. sedimentation. By analogy with withmodern-day the were el i likely marine 1 environmen environmentt bu butt n aa sshallow hallow m a r i n e tto o ssubaeria ubaeria 1 k e 1 y e rerupted u p t e d i in ttuff u f f sswer deposited marine environment environment below wave wave bbase d e p o s i t e d iinn aa marine a s e . The variable v a r i a b l e crystal crystal contentt of andd the high-temperaturee iindicators conten o f the t h e tuffs t u f f s an t h e lack l a c k of o f high-temperatur n d i c a t o r s iin n tthe he deposits magmatic aand/or post-magmatic loss mplies (1) ( 1 ) magmatic n d / o r post-magmatic loss o ine v itric d e p o s i t s iimplies off ffine vitric materia emplacementt aass resedimented deposits hott a n d (2) (2 ) emplacemen resedimente d d e p o s i t s rrather a t h e r than t h a n as a s ho m a t e r i a 1land pyroclastic p y r o c l a s t i c flows. f lows. . debris are The d ebris flows are heterolithic, poorly-sorted, heterolithic, poorly-sorted, and matrix-supported. and matrix-supported. They ccan an b normally-graded They bee ungraded, normally-graded,, rreversely-graded eversely-graded ffor o r tthe h e ccoarse o a r s e ffraction, raction, w i t h subrourided s ubrounded to t o subangular with one metre diameter. No bedding s i z e s to to o ne m e t r e in i nd i a m e t e r . No cclasts l a s t s of o f aall 1 1 sizes - iiss observed iinn these t h e s e breccias. b r e c c i a s . The The poorly-sorted, p o o r l y - s o r t e d , uunstratified n s t r a t i f i e d nnature a t u r e of o f the t h e deposits deposits i n d i c a t e s emplacement emplacemen t as a smass mas sflows flows• The d e b r i s flows f l o w s may indicates debris may have aa sshallow hallow marine to t o subaerial s u b a e r i a l volcanic v o l c a n i c provenance provenance but b u t subaqueous subaqueous depositional depositional marine setting. The rounding aand off c clasts, heterolithic nature eterolithi c n a t u r e of o f tthe s e t t i n g . The n d reworking o l a s t s ,h he 11 point point rrocks, o c k s , aand n d ppresence r e s e n c e oof f eessential s s e n t i a l pumice tthat h a t aappears p p e a r s vvesiculated e s i c u l a t e d aall ttoo aann oorigin r i g i n bby y sshoaling h o a l i n g tto o ssubaerial u b a e r i a 1 eexplosive x p l o s i v e eruptions. e r u p t i o n s . However, tthe he debris d e b r i s flows f lows rest r e s t upon upon a partly p a r t l y pillowed p i l l o w e d platform p l a t f o r m and and aare r e iintimately ntimately aassociated ssociate d w i t h turbidite t u r b i d i t e beds Thi s implies i m p l i e s the th e h eterolithi c m a t e r i a 1 has ha s with beds. This heterolithic material b e e n mixed aand n d ttransported r a n s p o r t e d into into d eeper w a t e r by mass fflow low p rocesses. been deeper water processes. . . , I n sum, the t h e bbasalts a s a l t s wer r u p t e d aand nd d e p o s i t e d subaqueously In weree eerupted deposited subaqueously, whereas tthe h e ppyroclastics y r o c l a s t i c s probably e r e eerupted r u p t e d iin n aa sshallow h a l l o w marine marine to t o subaerial s ubaerial probably wwere environmen t bu t d e p o s i t e dsubaqueously. subaqueously p y r o c l a s t i c s are a r e complexly environmentbutdeposited The pyroclastics iinterbedded n t e r b e d d e d aand n d eexhibit x h i b i t rrapid a p i d ffacies a c i e s changes. y r o c l a s t i c ddeposits e p o s i t s may changes. The The ppyroclastic may become more proximal west, vent-fades nott becom e mor e proxima 1 tto o t the h e west , bubut t s usubaerial b a e r i a 1 vent-f a c i e s r rocks o c k s aare r e no present p r e s e n t in i n this t h i s area. area. . fl n     89 1 I �U MULCAHY LAKE GPBBRO: MULCAHY LAKE GABBRO: WELL-PRESERVED ARCHEAN ARCHEAN LAYERED LAYERED INTRUSION INTRUSION AA WELL-PRESERVED Sutcliffe, S u t c l i f f e R.H., , R.H., Precambrian P r e c a m b r i a nGeology Geology Section, S e c t i o n , Ontario O n t a r i oGeological Geological Survey, S u r v e y , 77 77 Grenville G r e n v i l l e Street S t r e e t Toronto Toronto e we Mulcahy Mulcahy Lake Lake gabbro q a b b r o is is an a n iron—rich, i r o n - r i c h , tholeiitic t h o l e i i t i c layered layered intrusion 4 5 km km southwest s o u t h w e s t of of i n t r u s i o n located l o c a t e d in i n the t h e Wabigoon Wabiqoon Subprovince S u b p r o v i n c e 45 Dryden, Dryden, Ontario. O n t a r i o . The The gabbro q a b b r o is is one o n e of o f several s e v e r a l mafic m a f i c to t o ultra— ultramafic maÂi c intrusions i n t r u s i o n s which which are a r e intrusive i n t r u s i v e into i n t o tholeiitic t h o l e i i t i c to t o calc— calcalkaline a l k a l i n e metavolcanics m e t a v o l c a n i c s around a r o u n d the t h e periphery p e r i p h e r y of o f the t h e Atikwa— AtikwaLawrence w e l l preserved preserved Lawrence granitoid g r a n i t o i d batholith. b a t h o l i t h . The The exceptionally e x c e p t i o n a l l y well nature n a t u r e of o f the t h e Mulcahy Mulcahy gabbro g a b b r o makes makes it i t an a n ideal i d e a l location l o c a t i o n to t o study study the t h e relationship r e l a t i o n s h i p of o f mafic m a f i c plutonism p l u t o n i s m with w i t h crustal c r u s t a l development d e v e l o p m e n t in in the t h e Archean. Archean. The The intrusion i n t r u s i o n has h a s aa thickness t h i c k n e s s of o f 77 km km and and is is composed composed of o f three three zones are the t h e result r e s u l t of o f distinct distinct z o n e s and and aa marginal m a r g i n a l facies f a c i e s which which are cooling c o o l i n g regimes r e g i m e s and and fractionating f r a c t i o n a t i n g systems s y s t e m s (Morrison ( M o r r i s o n et e t al., al., 1982). 1 9 8 2 ) . The The lower l o w e r and and middle m i d d l e zones z o n e s represent r e p r e s e n t separate s e p a r a t e magma magma pulses p u l s e s which which crystallized c r y s t a l l i z e d from from the t h e bottom b o t t o m upward upward and and are are characterized c h a r a c t e r i z e d by by iron i r o n enrichment e n r i c h m e n t trends. t r e n d s . These T h e s e zones zones are are dominated d o m i n a t e d by b y orthopyroxenes o r t h o p y r o x e n e s and and plagioclase p l a q i o c l a s e cumulates. c u m u l a t e s . The The lower lower zone z o n e has h a s aa stratigraphy s t r a t i g r a p h y defined d e f i n e d by by the t h e appearance a p p e a r a n c e of o f cumulus cumulus phases o r t h o p y r o x e n e - p l ag i o c l a s e ,clino— cl inop h a s e s in i n the t h e following f o l l o w i n g order: o r d e r : orthopyroxene—plagioclase, pyroxene, p y r o x e n e , inverted i n v e r t e d pigeonite, p i g e o n i t e , magnetite m a g n e t i t e and and olivine. o l i v i n e . The The middle middle zone s i m i l a r stratigraphy s t r a t i g r a p h y but b u t in i n addition a d d i t i o n contains c o n t a i n s aa 20 20 zone has h a s aa similar meter meter thick t h i c k layer l a y e r of o f olivine o l i v i n e — clinopyroxene c l i n o p y r o x e n e — plagioclase plaqioclase cumulate lower part p a r t of o f the t h e middle m i d d l e zone zone and and c u m u l a t e which which occurs o c c u r s in i n the t h e lower can c a n be b e traced t r a c e d for f o r the t h e full f u l l 10 1 0 km km length l e n g t h of o f the t h e intrusion. intrusion. The is not n o t clearly c l e a r l y related r e l a t e d to to The upper u p p e r zone z o n e of o f the t h e Mulcahy Mulcahy gabbro q a b b r o is the t h e sequence s e q u e n c e in i n the t h e lower lower and and middle m i d d l e zones. z o n e s . These T h e s e rocks r o c k s are are interpreted i n t e r p r e t e d to t o represent r e p r e s e n t aa roof r o o f zone zone of o f mafic m a f i c to t o intermediate intermediate volcanic v o l c a n i c or o r subvolcanic s u b v o l c a n i c protolith p r o t o l i t h which which has h a s been b e e n metamorphosed metamorphosed to to aa pyroxene p y r o x e n e hornfels h o r n f e l s and and partially p a r t i a l l y melted. m e l t e d . Sills S i l l s ranging r a n g i n g in in composition c o m p o s i t i o n from from peridotite p e r i d o t i t e to t o gabbro g a b b r o and and granite g r a n i t e intrude i n t r u d e the the hornfels h o r n f e l s of o f the t h e roof r o o f zone. zone. The The iron—rich i r o n - r i c h nature n a t u r e of o f the t h e Mulcahy Mulcahy gabbro q a b b r o indicates i n d i c a t e s that t h a t the the magma was fractionated f r a c t i o n a t e d prior p r i o r to t o emplacement emplacement into i n t o the t h e metavolcanic metavolcanic magma was sequence. s e q u e n c e . Late L a t e peridotitic p e r i d o t i t i crocks, r o c k s ,occuring o c c u r i n qalong a l o n gzones z o n e s of of deformation d e f o r m a t i o n in i n the t h e vicinity v i c i n i t y of o f the t h e Mulcahy Mulcahy gabbro, g a b b r o , contain contain cumulate c u m u l a t e magnesian m a g n e s i a n olivine o l i v i n e and and chromite c h r o m i t e which which crystallized c r y s t a l l i z e d from from aa more more primitive p r i m i t i v e magma. magma. These T h e s e rocks r o c k s do d o not n o t appear a p p e a r to t o be b e part p a r t of of the t h e Mulcahy Mulcahy gabbro g a b b r o cumulate c u m u l a t e sequence, s e q u e n c e , however, however, they t h e y are are interpreted i n t e r p r e t e d to t o be b e derived d e r i v e d from from aa common common parental p a r e n t a l magma. magma. Although A l t h o u g h no no rocks r o c k s from from the t h e Mulcahy Mulcahy gabbro g a b b r o clearly c l e a r l y represent represent l i q u i d compositions, c o m p o s i t i o n s , the t h e sequence s e q u e n c e of o f cumulate c u m u l a t e phases p h a s e s provides provides liquid information i n f o r m a t i o n on o n the t h e density d e n s i t y relationships r e l a t i o n s h i p s of o f the t h e liquid. liquid. F r a c t i o n a t i o n of o f olivine o l i v i n e from from the t h e magma magma results r e s u l t s in i n aa decrease d e c r e a s e of of Fractionation density d e n s i t y of o f the t h e residual r e s i d u a l liquid. l i q u i d . If I f the t h e peridotites p e r i d o t i t e s are a r e olivine olivine cumulates c u m u l a t e s from from aa parental p a r e n t a l magma, magma, then t h e n the t h e magma magma pulses p u l s e s forming forming t h e lower lower and and middle m i d d l e zones zones may may represent r e p r e s e n t liquids l i q u i d s at a t or o r near n e a ra a the density d e n s i t y minimum. minimum. Further F u r t h e r fractionation f r a c t i o n a t i o n of o f plagioclase p l a q i o c l a s e and and p y r o x e n e , as a s developed d e v e l o p e d in i n the t h e lower l o w e r and and middle m i d d l e zones, z o n e s , causes c a u s e s the the pyroxene, density d e n s i t y of o f the t h e residual r e s i d u a l liquid l i q u i d to t o increase. i n c r e a s e . This T h i s apparent apparent c o n t r o l of o f density d e n s i t y on o n the t h e emplacement emplacement of o f the t h e two two magma magma pulses pulses control s u g g e s t s that t h a t crustal c r u s t a l filtering f i l t e r i n g has h a s restricted r e s t r i c t e d the t h e access a c c e s s of o f more more suggests primitive p r i m i t i v e magmas magmas to t o high h i g h crustal c r u s t a l levels. levels. T h e s e density d e n s i t y relationships r e l a t i o n s h i p s and and the t h e regional r e g i o n a l geology g e o l o g y suggest suggest These the P o n d i n g of o f mantle m a n t l e derived derived t h e following f o l l o w i n g sequence s e q u e n c eof o f events: e v e n t s : 1)1 ) Ponding p a r e n t a l magma magma at a t the t h e base b a s e of o f the t h e crust. c r u s t . 2) 2 ) Fractionation F r a c t i o n a t i o n of of parental o l i v i n e lowering l o w e r i n g the t h e density d e n s i t y of o f the t h e liquid l i q u i d allowing a l l o w i n g gabbro gabbro olivine plutons p l u t o n s to t o rise rise through t h r o u g h the t h ecrust. c r u s t . 3) 3 ) uplacement Emplacementof o f granitoid granitoid magmas magmas which which are a r ederived d e r i v e d from from melting m e l t i n g of o f crustal c r u s t a lrocks r o c k s with w i t h the the heat magmatism. 4) 4 ) uplacement Emplacement of o f late late maÂi cmagmatism. h e a t source s o u r c e provided p r o v i d e d by by mafic peridotitic p e r i d o t i t i c dikes d i k e s and and sills s i l l s along a l o n g fault f a u l t zones. z o n e s . This T h i s process process implies imp1 ies that t h a t mafic maÂi c metavolcanic m e t a v o l c a n i c rocks r o c k s in i n the t h e Wabigoon Wabiqoon Subprovince Subprov i n c e a r e underlain u n d e r l a i n by by less less dense d e n s e material m a t e r i a l and and may may also alsoexplain e x o l a i n the the are p a u c i t y of o f magnesian m a g n e s i a n basalts b a s a l t s and and komatiites k o m a t i i t e sin i n the t h e region. region. paucity - - - M o r r i s o n , D.A., D.A., Ashwal, Ashwal, L.D., L.D., Henry, Henry, D.J., D . J . , Maczuga, Maczuga, D.E., D.E., and and Morrison, Phinney, P h i n n e y , W.C., W.C., 1982, 1982, The The Mulcahy Mulcahy Lake Lake layered l a y e r e d norite, n o r i t e , 12th 1 2 t hLunar Lunar Lunar and and Planetary P l a n e t a r y Science Science and Planetary P l a n e t a r y Science S c i e n c eConference, C o n f e r e n c e ,Lunar and Institute, I n s t i t u t eHouston. , Houston. 90 90 �I MAGMA MAGMA SERIES AND AND THEIR THEIR RELATIONSHIP RELATIONSHIPTOTO GREENSTONE GREENSTONE GOLD GOLD METALLOGENY METALLOGENY IIN N THE THE LAKE LAKESUPERIOR SUPERIORREGION REGION Evergreen, COCO80439 M.M. (MagmaChem (MagmaChem Expl. Expl. Inc., Inc., 6949 6949Highway Highway 73, 73, Suite S u i t e10,10, Evergreen, 80439 SWAN, M.M. SWAN, U. S.A.) U.S.A.) KEITH, Inc., 10827 10827So. So.551st St., Suite KEITH, S.B. S.B. (MagmaChem (MagmaChem E x pExpi. l . Inc., 1 s t St., S u i t e202, 202, Phoenix, AZ AZ85044 85044 U.S.A.) U.S.A.) Phoenix, PARR, M.G. ( Q u a r t z Tower, Tower, 33451 33451 Stransky s t r a n s k y Rd., Rd., Evergreen, Evergreen,CO CO 80439 80439 U.S.A.) U.S.A.) PARR, M.G. (Quartz I Metal M e t a l and a n d trace t r a c e element e l e m e n t content c o n t e n t of o fgreenstone g r e e n s t o n e gold g o l d deposits d e p o s i t sofofthe t h Lake e Lake Superior S u p e r i o r Region R e g i o n ddisplay i s p l a y clear c l e a r empirical e m p i r i c a l relationships r e l a t i o n s h i p swith w i tmagma h magma series series chemistry c h e m i s t r y of o f spatially s p a t i a l l yand andtemporally t e m p o r a l l yrelated r e l a t e digneous igneousrocks. rocks. These These empirical empirical upon r e l a t i o n s h i p s , along a l o n g with w i t h similar s i m i l a empirical r e m p i r i c arelationships l r e l a t i o n s h i pbased s based upon aa worldworldrelationships, wide w i d e data d a t a base b a s e ooff 2500 2 5 0 0 mmineral i n e r a l ddeposits, e p o s i t s , is i s the t h e basis b a s i sfor f oa r afundamentally f u n d a m e n t a l l new y new petro—chemical rocks associated p e t r o - c h e m i c a l sserial e r i a l classification c l a s s i f i c a t i o of n oigenous f igenous r o c kand s and a s s o c i a t eco—genetic d co-genetic mineral m i n e r a l deposits d e p o s i t sthat t h a has t hasserious s e r i o u smineral m i n e r a expi l e x porati l o r a ton i o nas a swell w e l as l asearth e a r t hmodel model imp1 i c a t i o n s . According A c c o r d i n g tto o the t h e magma magma sseries e r i e s cclassification, l a s s i f i c a t i o n , gold go1 d deposits d e p o s i t s of of implications. the be ggrouped t h e Lake L a k e Superior S u p e r i o r Region R e g i o n ccan a n be r o u p e d i into nto 4 4 distinct d i s t i n c magma t magma series: s e r i e s : 1)1 ) magnesian, 2)2) calcic, c a l c i c , 3)3) calc—alkalic c a l c - a 1 k a l i cand and 4) 4) nepheline nephel i n e normative n o r m a t i v e alkalic a1 k a l i c(See (See rnagnesian, F i g u r e 1). 1). Less L e s s fundamental f u n d a m e n t a l breakdowns b r e a k d o w n s can c a n be be made made based b a s e d upon upon ddepositional epositional Figure vein vs. chemical sediment). e n v i ronment (e.g. v e i n vs. c h e m i c a l sediment). environment (e.g. The The notion n o t i o n of o f magma magma sseries eries — - aa ssuite u i t e of o f co-magmatic co-magmatic igenous igenous rocks r o c k s linked l i n k e dby by I differentiation s t h core e c o r concept e concept d i f f e r e n t i a t i o ntot an o aninitially i n i t i ahomogeneous l l y homogeneous mafic m a f i c parent p a r e n t - -isi the u p o n wwhich h i c h t the h e magma s e rseries i e s c l aclassification s s i f i c a t i o n i is s bbuilt. uilt. upon magma Before B e f o r e serial serial classification c l a s s i f i c a t i o n isi sattempted a t t e m p t e d spilitization s p i 1 it i z a t i o nand/or a n d / o r phyllic p h y l l i c and and argillic argilli c hydrothermal + CaO h y d r o t h e r m a l alteration a1 t e r a t i o are n a rfilteredout e f i l t e r e dby o uuse t b y of u sthe e o fA12O3/Na2O t h e A1 2 0 3 / N a T+0 K20 t K20 + CaO vs. Si02 SiO, variation v a r i a t i o ndiagram d i a g r a m (See (See Figure F i g u r e 2). The cclassification l a s s i f i c a t i o n first i r s divides t divides vs. 2). The igneous i g n e o u s rock r o c k series s e r i e sinto i n t2 o fundamental 2 f u n d a m e n t amegaseri l m e g a s e res i e s based b a s e d on on their t h e i aluminum r a1 uminurn 2). A A given g i v e n rrock o c k ssuite u i t e is i s thus t h u s first f i r s determined t d e t e r m i n e d to t obe be c o n t e n t (See (See Figure F i g u r e 2). content a1 u m i n u m - r i c h (peraluminous) ( p e r a l u m i n o u s ) oro raluminum—poor a1 u m i n u m - p o o r (metaluminous). ( m e t a l u m i n o u s ) . After A f t e r the the aluminum—rich megaseries igneousr o rock megaseries i sis ddetermined, e t e r m i n e d , t hthe e igneous c k i s isf ufurther r t h e r cclassified l a s s i f i e d iin n terms t e r m s ooff its its a1 k a l i n i t into y i n one t o one f 1magma 4 magma series. s e r i e s . In I n addition a d d i t i o n to t oconventional c o n v e n t i o n a l petropetroalkalinity of o14 chemical c h e m i c a l ccriteria, r i t e r i a ,these t h e s e series s e r i e s are a r e defined d e f i n e d by b y aa ppriori r i o r i "off " o f fplot" p l o tempi " e m prical irical knowledge knowledge aabout b o u t mmetal e t a l ccontents o n t e n t s oof f ttemporally e m p o r a l l y and and spatially s p a t i a l l yassociated a s s o c i a t e d mineral mineral systems. mineral alkalinity s y s t e m s . IIntegration n t e g r a t i o n ooff metal m e t a l cchemistry h e m i s t r y oof f m i n e r a l ddeposits e p o s i t s wwith i t h a1 kal i n it y aspects allows a s p e c t s of o f associated a s s o c i a t e d magma magma s eseries r i e s a1 l o w s t the h e ddetermination e t e r m i n a t i o n of of the t h e overall overall The sseries e r i e s aare r e ffurther u r t h e r divided d i v i d e d into into m e t a l l o g e n i c bias b i a sofo fthe t h emagma magma series. s e r i e s . The metallogenic subseries uponooxygen, s u b s e r i e s based b a s e d upon x y g e n , wwater a t e r aand n d i iron r o n content c o n t e n t of o f the t h emagma magma series. series. Additional A d d i t i o n a l divisions, d i v i s i o n s , that t h aof t orock f r o csystems, k s y s t e m s is , iaccomplished s a c c o m p l i s h e dby b yuse use of o f the the Differentiation T h o r n t o n and a n d Tuttle T u t t l e (1960) ( 1 9 6 0 ) to t o determine d e t e r m i n e levels l e v e l s of of D i f f e r e n t i a t i o nIndex I n d e xofo fThornton differentiation d i f f e r e n t i a t i o nwithin w i t h ian magma a magma series, s e r i e s , tot ointegrate i n t e g r a tconventional e c o n v e n t i o n a rock l r o c knames names to to the t h e magma magma s eseries r i e s c classification l a s s i f i c a t i o n and and to t o refine r e f i n ethe t h emetallogenetic m e t a l l o g e n e t i cbias b i a of s oaf magma a magma series s e r i e s to t othe t h esystem s y s t e m level. l e v e l .Once Once the t h e serial s e r i a geochemical l g e o c h e m i c a l character c h a r a c t e r of o f the the associated any aassociated a s s o c i a t e d magma magma s eseries r i e s i is s determined d e t e r m i n e d any s s o c i a t e d oore r e ddeposit e p o s i t can can be be further further c l a s s i f i e dini terms n t e r mof s oits f iemplacement t s emplacement e n v i ronment. classified environment. By classifying c l a s s i f y i n ggold g o l ddeposits d e p o s i t sofothe f t hLake e Lake S u p e r i oRegion r Region a c c o r d i n to g tmagma o magma By Superior according series, to t40 elements s e r i e s , their t h e ibulk r b u lmetal k m e t aand l a ntrace d t r a celement e e l e m e ncontent t c o n t e nup t up o 40 e l e m e n t scan c a nbe be p r e d i c t e d . These These eelements l e m e n t s a rare e l ilisted s t e d in i n the t h e Table Table below b e l o w by by gold g o l d deposit d e p o s i t type. type. predicted. Means and h e s e eelements l e m e n t s f for o r each each ggold o l d system system ttype y p e will w i l l be be presented presented Means andranges rangeso foft these a t the t h eposter p o s t e rsession. session. Also, Also, ore o r eand andgangue gangue mineralogy, m i n e r a l o g y , wall w a l l rock r o c k alteration, alteration, at element e l e m e n t zoning, z o n i n g , geophysical g e o p h y s i c a l ccharacteristics h a r a c t e r i s t i c s and and ultimately u l t i m a t e l yengineering e n g i n e e r i n gand and 9' 1• I �economic parameters l s o be be predicted p r e d i c t e d from from magma magma chemistry. chemistry. In I n gréenstone greenstone economic parameterscan canaalso g o l d exploration e x p l o r a t i o n greenstone greenstone belts be1 t s can can be be subdivided s u b d i v i d e d according a c c o r d i n g to t o magma magma sseries e r i e s to to gold predict p r e d i c t which w h i c h terranes t e r r a n e s are a r e capable c a p a b l e of o f hosting h o s t i n g aa given g i v e n gold g o l d deposit d e p o s i t type. t y p e . The The immediate i m p l i c a t i o n for f o r gold g o l d exploration e x p l o r a t i o nini nthe t h Lake e LakeSuperior S u p e r i o rRegion Region iiss that that immediate implication t h mineral e m i n e r aexploration l e x p l o r a t i o process, n process, save save tthis h i s practical p r a c t i c aapproach l a p p r o a c hcan canstreamline s t r e a m 1 inethe moneyand andu lultimately ttime i m e and and money t i m a t e l y iincrease n c r e a s e ggold o l d ddeposit e p o s i t discovery d i s c o v e r y rates. rates. KIRKLAND -- MAIN '-BREAK TYPE -,+BREAK TYPE I 0 + o PtRLUMWIOU$ s-.. C'J 1WAU10U$ z I ,t,O.l., VtTALUM•NOU* -J Ut ru ALRALtC STOt4OLV o LU -J C K70—Si02 K 0-SiO variation diagram diagram showing showing approximaTe approximale cFemicat i gneous rocks rocks associated associated with with czemica? position posit ion for for igneous 9oId deposit in the the Lake Lake Superior Superior region. gold deposit types types in Figure F i g u r e 11 Wt.% SiC2 A/CNK VAR VARIATION AICNK I AT I ON 2DLGRAM AGRAM FOR FOR WORLDWIDE WORLDW I DE IGNEOUS I GNE9US ROC<S 2OCKS Figure Figure 2 2 Tab 1e Tab1 e CHEMICAL NATURE F THE LAKE SUPERIOR REGION CHEMICAL NATURE OF OF GOLD GOLD DEPOSITS DEPOSITS O OF REGION Elements E I ements Elements Elements Nagma Vagma Series Series Magnesian Series Vagnesian Series In Commonly Enriched In y Enriched Common1 Mineral Deposit Type Type Mineral Deposit Homes take Homestake (Chem in is—Omega) (Cheminis-Omega) Catcic Calcic Series Series Timmns Timmins and and Grass Grass Valley Valley (La (La Maque) Maque) CaIc—alkal Ic Calc-alkalic Series i es Ser Hemlo and Hemlo and Red Lake Lake Au, Ag, Aul Agl Ni, Nil Cu, Cul Cr, Cr, Fe, Fel Mg, Mgl W, Wl (Cc, (ColZn, Zn, B) 6) Pb, Pbl U, U l Th, Thl Sn, Sn, Be, qe, Zr, Y, Li, Hg, Li, Hg, Nb, Nb, Zr, Y, Fe, Zn, Fel Au, Aul Ag, Agl Cu, Cul B, Bl Znl Pb, Nil W, W, Pb, C, Cl Co, Co, Ni, Platinoids, Platinoidsl Se, SelCd, Cdl Mn, Li Sl Mnl Li (Cr, (Cr, Mo, Mop As), ,4s), S, K, Kl Mg, Mg1 Na Na U, Th, Thl Rb, R b l Ce, CelBe, Be, Hg, Nb, Ba, F, F, Nb, Hg, Sb, Sb, Ba, Fe, Cu, Zn, Aul Fe, Cu, Znl Pb, Pbl Ag, Agl Au, Sb, Hg, S, Ba, W, Sbl 4 1 S I Ba1 W I Mo, b l Re, Rel Mn, Mnl (As, (AslSe, SelTi), TI), Ni, U, V i l Cr, Crl Sn, Snl F, Fl 9, Th, Ti, Thl Til B, Bl Li, Li, Be, 3e, Ba, Ba, Y, Y, Nb, Ta, Ta, platinoids), Na (Co, platinoids), (Col Va K K Nephel Nephe I i me ne Normative Normative Alk&ic Alkal ic Series Series Au, Aul platinoids, platinoidsl Cu, Cu, Pb, Pb, Zn, Ag, Mo, Znl Mop Ye Te (LREE (LREE Nb, Rb, Vb, Rb, La, La, Te, Tel Co, Co, Ni, Ni, Kirkland Kirk land Lake Lake Main Main Break Break K, Sr, Ba U l F, F, W, W, K, Srl Ba ,As) As) U, 92 Commonly DeQIeTed H Ta Ta Hg, Sb, TI, Mg (3, 5) �I I BARITIC HORIZON; THE (LEMLO ENL3 3ARIri'IC HORIZON; AAPOSSIBLY POSSIBLYSYNGFNETIC SYNGENETICARCHEAN ARCHEAN BARITE BARITE THE OCCURRENCE OCCURRENCE Thomson, K. and and Gliddon, Thomson, K. Gliddon, D., D . , Department Department of ofGeology, Geology,Lakehead Lakehead U n i v e r s i t y , Thunder Thunder Bay, Bay, Ontario, O n t a r i o f P7B P7B 5El 5El University, AA baritic b a r i t i c horizon horizon occurs occurs within w i t h i n Archean Archean supracrustal s u p r a c r u s t a l rocks rocks of of the t h e Hemlo Hem10 area, a r e a , northwestern northwestern Ontario, O n t a r i o , which which exhibits e x h i b i t s characteristics c h a r a c t e r i s t i c s that t h a t suggest suggest aa svngenetic i s likely. l i k e l y . This This baritic b a r i t i c unit u n i t crops c r o p s out o u t in i n 44 or o r 55 s y n q e n e t i c origin o r i g i n is locations km east e a s t of of the t h e town town of of Marathon, Marathon, and and appears appears l o c a t i o n s situated s i t u a t e d 55 to t o 13 13 km to t o parallel p a r a l l e l the t h e regional r e g i o n a l stratigraphy, s t r a t i g r a p h y , occurring o c c u r r i n gbetween betweenpillowed pillowedinafic mafic metavolcanics metavolcanics to t o the t h e south s o u t h and and intermediate i n t e r m e d i a t e to t o felsic f e l s i c pyroclastics p y r o c l a s t i c s and and metasediments The barite b a r i t e ia isthinly t h i n l y laminated laminated to t omassive massive metasediments to t o the t h e north. n o r t h . The and i s generally g e n e r a l l y interlaminated i n t e r l a m i n a t e d wIth w i t h chert, c h e r t , pyrite p y r i t e and/or and/or carbonate, carbonatef and is forming aa unit u n i t 11to t o 22 mm thick t h i c k which which is i s conformable conformable with w i t h the t h e associated associated forming rock rock units. u n i t s . Rock Rock lithologies l i t h o l o g i e s associated a s s o c i a t e d with w i t h the t h e baritic b a r i t i c unit u n i t include include deep w a t e r i s t a m e d basin-type basin-type sediments s e d h e n t s (pyritiferous ( p y r i t i f e r o u s graphitic q r a p h i t i c schists schists deep water/starved and and DE Dl7 turbiditic t u r b i d i t i c siltstones), s i l t s t o n e s ) , siltstones s i l t s t o n e s with w i t h green qreen mica—rich mica-rich (rip—up?) (rip-up?) clasts, c l a s t s , metapelites, m e t a p e l i t e s , green green mica mica schists, s c h i s t s , sericite s e r i c i t e schists, s c h i s t s , biotite— biotiteamphibolite amphibolite schists, s c h i s t s f mafic mafic metavolcanic metavolcanicflows flowsand andfragmentals., f r a q m e n t a l s , aa very very thin t h i n tuffaceous t u f f a c e o u s unitM u n i t * and and quartz-feldspar q u a r t z - f e l d s p a r porphyry porphyry dikes. d i k e s . Although Althouqh these these rock l i k e l y been been transposed transposed relative r e l a t i v e to t o one one another, a n o t h e r , their their rock units u n i t s have have likely persistent s u g g e s t s that t h a t their their p e r s i s t e n t presence presence at a t all a l l the t h e barite b a r i t e occurrences occurrences suggests i s real. real. a s s o c i a t i o n with w i t h the t h e barite b a r i t e is association In I n comparing comparing the t h e characteristics c h a r a c t e r i s t i c s of of the t h e Hemlo Hem10 baritic b a r i t i c horizon horizon with with those t h o s e of of other o t h e r documented documented Paleozoic Paleozoic to t o Archean Archean syngenetic syngenetic and and epigenetic epiqenetic barite it becomes becomes evident e v i d e n t that t h a t the the b a r i t e occurrences occurrences throughout throughout the t h e world, worldf it Hemlo Hem10 occurrence occurrence more more closely c l o s e l y resembles resembles syngenetic synqenetic than t h a n epigenetic epiyenetic deposits. d e p o s i t s . These These characterIstIcs c h a r a c t e r i s t i c s include: include: regional r e g i o n a l and and local l o c a l conformaconformab i l i t y of of the t h e bariti'c b a r i t i c uunit nit w i t h associated a s s o c i a t e d lithologies; l i t h o l o g i e s ; lateral lateral bIlity with continuity c o n t i n u i t y of 8 km; km; associated a s s o c i a t e d deep of the t h e baritic b a r i t i c horizon of possibly possibly 8 water/starved w a t e r l s t a r v e d basinb a s i n ? type type sedimentary sedimentary units u n i t s and and pillowed pillowed mafic mafic meta— metavolcanics; v o l c a n i c s ; thinly t h i n l y laminated laminated to t o thinly t h i n l y bedded bedded character c h a r a c t e r of of the t h e barite b a r i t e and and of i n t e r l a m i n a t i o n with w i t h chert, c h e r t " pyrite p y r i t e and and carbonate; c a r b o n a t e ; and and the t h e presence presence of interlamination rip—up rip-up clasts c l a s t s of of green green mica schist s c h i s t in i n sjltstones s i l t s t o n e s which stratigraphically stratigraphically o v e r l y the t h e baritic b a r i t i c unit. unit, overly I 'I I I '1 �U Geology of of the the Jap Jap Lake LakeArea Area of ofthe the Geology Eastern EasternVermilion VermilionDistrict, District,Northeastern NortheasternMinnesota Minnesota MinnesotaJEFFERYD. D. VERVOORT VERVOORT (Dept. (Dept.of ofGeology, Geology,University Universityof ofMinnesota— JEFFERY Duluth,MN. MN. 55812) 55812) Duluth, The Jap Jap Lake Lake area, area,located locatedat at the the eastern eastern end end of of the the Vermilion Vermilion The districtin innortheast northeastMinnesota, Minnesota, contains contains .a.a volcanic—sedimentary volcanic-sedimentarysuccession succession district typical of of many many Archean Archean greenstone—granite greenstone-granitecomplexes complexes of of the theCanadian Canadianshield, shield, typical as Proterozoicseen seen as well well as as lithologies lithologiesrepresentative representativeof ofthe thelower lowertotomiddle middle Proterozoic elsewherein in northern northernMinnesota. Minnesota. elsewhere Structurally, Structurally,this this Archean Archean sequence sequencerepresents representsthe thesouthern southern limb limb of ofaa The large antiform. antiform. The bedding bedding trends trends NW—SE NW-SE and and stratigraphic stratigraphicindicators indicatorsgive give large SW. The The lowest lowest stratigraphic stratigraphic unit, unit, here here named named the the Jap Jap Lake Lake topsto tothe theSW. tops Volcanic unit, unit, consists consists of of massive massive and and pillowed pillowed tholeiitic tholeiitic basalts basalts locally locally Volcanic intercalated with with thin thin mafic mafic tuffs, tuffs, pillow pillow breccias breccias and and hyaloclastites. hyaloclastites. intercalated Numerous mafic mafic to toultrarnafic ultramafic sills sills are are regularly regularly interlayered interlayered with with the the Numerous The basalts and and are are apparently apparently penecontemporaneous. penecontemporaneous. The base base of of this this unit unit has has basalts been intruded intruded and and apparently apparently removed removed by by the the 2.7 2.7 Ga Ga Saganaga Saganaga Tonalite. Tonalite. been Capping the the thick thick greenstone greenstone unit unit locally locally are are caic—alkaline calc-alkaline dacitic dacitic lava lava Capping The flowsand and an an associated associatedfragmental fragmental unit. unit. The entire entire volcanic volcanic sequence sequenceis is flows then overlain overlain by by aa thick thick blanket blanket of of volcanogenic volcanogenicsediments sediments and and later later capped capped then in the the early early Proterozoic Proterozoic (2.O (-2.0Ga) Galbybythe theGunflint GunflintIron IronFormation Formationand and Rove Rove in Intruding sequenceis isthe the Intruding the the top top of of this thissequence greywackesof ofthe theAnimikie AnimikieGroup. Group. greywackes Keweenawan Duluth Duluth complex complex (1.1 (-1.1 Ga). Gal. Keweenawan 17 samples samples from from the the Jap Jap Lake Lake Volcanic Volcanic Chemical analyses analyses performed performed on on 17 Chemical unit indicate indicate that that these these rocks rocks range range in in composition compositionfrom from high—Mg high-Mg tholeiitic tholeiitic unit basalts to to ultramafic ultramafic komatiltes komatiites as as defined defined by by the the Jensen Jensen cation cationdiagram diagram basalts to rocks are characterized by moderate (Jensen, 1976). 1976). These rocks are characterized by moderate to high high MgO% MgO% These (Jensen, (7-115 in in the the basalts basalts to to 20—32% 20-32% in in the the peridotite peridotite sills) sills) and and low low Ti02 Ti02 (7—11% The (0.6-1.0% in in the the basalts basalts to to O.3—O.k% 0.3-0.4% in in the the peridotite peridotite sills). sills). The (0.6—1.0% characterized by low Al203 (2-7%), high Mg values ultramafic sills are also characterized by low A1203 (2-7%), high Mg values are also ultramafic sills (-74 to ratios (0.9 (0.9 to to 3.1) 3.1) and and high high Ni Ni (700—1100 (700-1100ppm) ppm) (..71 to -831, .83), high CaO/A1203 CaO/Al203 ratios and Cr Cr contents contents (2300—3500 (2300-3500ppm). ppm). and Contact Contact metamorphism metamorphism has has been been locally locally moderate moderate to to severe severe in in the the Jap Jap Lake area. area. Adjacent to to the the Saganaga Saganaga batholith batholith hornblende hornblende hornfels hornfels facies facies Adjacent Lake plagioclase ++ assemblages can can be be seen seen in in the the basalts basalts (now (now hornblende hornblende ++ plagioclase assemblages biotite) as as well well as as in in the the peridotites peridotites (now (now tremolite tremolite ++ talc talc ++ secondary secondary dusty magnetite magnetite ++ chlorite chlorite ++ serpentine serpentine ++ calcite). calcite). forsteritic olivine olivine ++ dusty forsteritic Adjacent to to the the Duluth Duluth complex, complex, pyroxene pyroxene hornfels hornfels facies facies assemblages assemblages are are seen seen Adjacent biotite) in the the basalts basalts (augite (augite ++ plagioclase plagioclase ++ hornblende) hornblende) and and in in the the iron iron formation formation in (fayalite ++ hedenbergite hedenbergite ++ ferrohypersthene ferrohypersthene ++ magnetite magnetite ++ grunerite). grunerite). (fayalite Metamorphic Metamorphic effects effects from from the the Duluth Duluth complex complex can can be be seen seen as as far far as as 3000 3000 feet feet (map distance) distance) away away from from the the contact. contact. (map Based on on field, field, petrographic petrographic and and geochemical geochemical evidence, evidence,the the following following Based the archean volcanic—sedimentary pile. model is proposed for the origin of the archean volcanic-sedimentary pile. origin of the model is proposed for Tholeiitic basalts basalts were were erupted erupted subaqueously subaqueously at at significant significant water water depths depths and and Tholeiitic subsequently subsequently intruded intruded by by thin thin synvolcanic synvolcanic mafic mafic to to ultramafic ultramafic sills sills at at 94 94 , �I I shallow levels levels in in the the volcanic volcanic pile, pile, as as evidenced evidenced by by the the common common occurrence occurrence of of shallow quench textures textures on on the the sill sill margins. margins. The The cessation cessation of of tholeiitic tholeiitic volcanism volcanism quench also signalled signalled the the end end of of subaqueous subaqueous eruptions. eruptions. When When volcanism volcanism resumed resumed it it also be all had aa decidedly decidedly different different character: character: all later later eruptions eruptions appear appear to to ,be had subaerial and and have have caic—alkaline calc-alkaline affinities, affinities, possibly possibly signifying signifying genesis genesis in in subaerial an island island arc arc setting. setting. This largely largely dacitic dacitic volcanism volcanism is is believed believed to to be be This an genetically related related to to the the intrusion intrusion of of the the Saganaga Saganaga batholith, batholith, which which not not genetically for the felsic flows, but also was presumably only served served as as the the magma magma source source for the felsic flows, but also was presumably only responsible for for the the uplift uplift of of the the overlying overlying volcanic volcanic pile. pile. This This was was followed followed responsible by by rapid rapid erosion erosion and and deposition deposition of of the the thick thick pile pile of of volcanogenic volcanogenic sediments. sediments. I References References Jensen, L. L. S., S., 1976, 1976,AA New New Cation Cation Plot Plot for for Classifying Classifying Jensen, Subalkalic Volcanic Volcanic Rocks, Rocks, Ont. Ont. Dept. Dept. Mines, Mines, Misc. Misc. Paper Paper Subalkalic I 66, 17 17 p. p. No. 66, No. I 1 I I I I 'I I 1 95 i I �PRELIMINARY PRELIMINARY INVESTIGATIONS INVESTIGATIONSINTO INTO THE THE GEOLOGY GEOLOGY OF OF THE THE GIANTS GIANTS RANGE RANGE COMPLEX, COMPLEX, VIRGINIA-BIWABIK VIRGINIA-BIWABIK AREA, AFEA, N.E. MINNESOTA MINNESOTA James James L. L. Welsh Welsh Gustavus Gustams Adoiphus Adolphus College College St. MN 56082 56082 St. Peter, Peter, MN Geologic Geologic mapping mapping in in the the highlands highlands of of the the Giants Gi.antsRange Range Complex, Complex, from from east east of of Hwy. Hwy. 53 53 north north of of Virginia Virginia to to Hwy. Hwy. 135 135 north north of of Aurora, Aurora, has mignatitic wiit, unit, and has identified identified two two distinctive distinctive units: an older migmatitic aa younger younger hornblende-bearing hornblende-bearingunit. unit. The Hwy. 53 53 north The migmatite migmatite is is well well exposed exposed in in roadcuts roadcuts along along Hwy. of Virginia. Virginia. Four of Four separate separate phases phases within within this this body body have have been been identified: medium-grained, gneissic identified: 1) 1) pink to to grey, grey, medium-grained, gneissic biotite biotite tonalite; tonalite; 2) 2) agmatitic aptitic amphibolite amphibolite inclusions inclusions within within the the tonalite tonalite host; hornblende leucotonalite leucotonalite dikes which which host; 3) 3) mediuin-grained medium-grained hornblende crosscut 4) later later minor minor aplitic aplitic crosscut both both the the tonalite tonalite and and inclusions; inclusions; and and 4) banded amphibolitic amphibolitic gneiss gneiss marks marks the the southern southern dikes dikes and and veinlets. veinlets. AA banded migmatite Within the the area area mapped, mapped, the the migmatite boundary boundary of of the the migmatite. migmatite. Within occurs occurs only only in in the the Lookout Lookout Mountain Mountain area. area. The in the the mapped area area is is comprised comprised of of The remainder remainder of of the the Complex Complex in These rocks rocks are are pink pink to to grey, grey, mediummedium- to to hornblende-bearing hornblende-bearingrocks. rocks. These coarse-grained, coarse-grained,weakly weakly to to moderately moderately foliated, foliated, commonly commonly porphyritic, porphyritic, and and range range in in composition composition from from granodiorite granodiorite to to diorite, diorite, with with quartz quartz Amphibolite inclusions inclusions monzodiorite monzodiorite being being the the dominant dominant lithology. lithology. Amphibolite The hornblende hornblende bearing bearing unit unit is is clearly clearly are are common common within within these these rocks. rocks. The Along the the southern southern intrusive intrusive into into the the banded banded amphibolite amphibolite gneiss. gneiss. Along margin margin of of the the body body these these rocks rocks are are in in contact contact with with greenstone. greenstone. This not exposed, relatively sharp and is probably This contact, contact, though though not expased, is is relatively aa fault. fault. Foliations within both units are concordant, concordant, trending east by Foliations within Folding has been recognized with northeast. northeast. Folding has been recognized within within the theInigmatite, migmatite, with fold axes and mineral lineations plunging moderately to the east. fold axes and mineral lineations plunging moderately to the east. Hornblende Hornblende in in the the hornblende-bearing hornblende-bearing pluton appears to be similarly similarly aligned. As As structures structures in in the the greenstone greenstone have have aa similar similar trend, trend, aligned. the the fabric fabric in in the the plutonic plutonic rocks rocks is is interpreted interpreted to to be be tectonic. tectonic. 96 �I. MAGMATIC PROCESSES DURING THE MIDCONTINENT RIFT INTERVAL. IN NORTHERN MICHIGAN. CHEMICAL AND ISOTOPIC CONSTRAINTS John 1. Wilband I Department of Geological Sciences, Michigan State University East Lansing, Michigan 48924 C"1.3—0.9 Ga) rocks of the Lake Superior region The Keweenawan are preserved as several spacially and temporally separate plateau flood eruptions and/or related subvolcanic complexes. This magmatic activity was associated with the development of the Midcontinent Rift gravity anomaly, hence "the with its pronounced system CMCR) Midcontinent Gravity high". Michigan, two of these flood—type plateaus centers can be In which records the first CPMG) distinguished. the Powder Mill Group erupted lavas with eruptive centers near the Wisconsin—Michigan border, and the Portage Lake Lavas CPLLS) and overlying "un—named which records the abrupt formation" see McDermott, this program) cessation of rift related volcanism. Two dyke swarms which intrude Archean basement and early Proterozoic sedimentary basins, and small plug—like bodies, are the only exposed subvolcanic Keweenawan rocks similarities, the tholeiitic Based on petrochemical in Michigan. dykes are believed to b feeders for the overlying lavas of the PMG and PLLS. New data from the PMG yield an iiochron with 57Sr/56Sr — 0.7043 +/— 0.0003 and an age of 1209 +/— 136 Ma. The PLLS, which have eruptive centers to th northeast of the PMG, consist of two Colivine and of tholeiitic distinct, but intercalated, batches quartz) magma. Derivation of one batch from the other by micing or fractional crystallization modeling cannot adequately explain the element abundances. Two isochrons with similar ages were obtained for each batch. olivine tholeiite yielded an age of 1013 +/— 274 Ma and 875r/56Sr — 0.7029 and 1026 +/— 191 Ma with +/— 0.0006; 875r/56Sr — 0.7036 +/— 0.0005 for the quartz tholeiite. The "un—named" formation, with its high percentage of evolved rocks which include high potassium rhyolites and intercalated basaltic and andesitic flows, has a major element distribution which has an abrupt change at 65% silica. The origin of the acidic flows is melting than by fractional most easily explained by crustal crystallization of parent tholeiite magma. Petrochemical and isotopic data are interpreted to mean that the heat source which generated the PMG lavas moved notheastward relative and to the crust with time to produce the younger PLLS. The chemical isotopic duality of the PLLS suggest that proximal, but separated. magma chambers existed at this time, possibly derived by partial melting of REE undepleted upper mantle at different depths. 1 I I I I �. i: QIcI STRAIN PATTERNS .IN THE KLRUNft DISTRI-CT.9 NORTHERN SWEDEN;IMPLICATIONS IMPLICATIONS .....-- ...- --...- FOR .- .- .- FROTEROZOIC PROTEROZOIC -- .- --- -- DEFORMATION DEFORMATION .- .- --Stephen Stephen F. F. Wriqht, Wriqht, Dept. of Geology &St Geophysics, Geophysics, University University of of Minnesota, Minneapolis, MN MN 55455 55455 Early Early to to middle middle F'roterozoic Proterozoic supracrustal rocks occupy occupy aa supracrustal rocks large large area area o-f of northern the north north by by rocks rocks of of northern Sweden Sweden bordered bordered on the an an Archean Archean gneissic terrane terrane and and on on the the west west by by the the Caledonide Caledonide frontal frontal thrust. thrust. The Kiruna Kiruna district district includes includes broad broad belts belts of of The and metamorphosed metamorphosed supracrustal supracrustal rocks rocks composed composed of of bimodal bimodal deformed and volcanics, NE volcanics, volcaniclastic volcaniclastic sediments, sediments, and and quartz quartz arenites.. arenites. A NE striking striking eastern eastern belt, belt, hosting the the iron iron and and sulfide sulfide ores, ores, and aa NW NW striking striking western western belt belt are are symmetrically symmetrically disposed disposed about about an an apparently apparently younger, younger, unfoliated granite granite in in aa manner manner typical typical of of classic classic granite/greenstone qranite/greenstone terranes. terranes. fabric and and ininStructural fabric duced strains strains are inhomogeneously developed and are are attributed to to single major major phase phase of of deformation deformation —- the the Svecokarelian Svecokarelian oroqeny. orogeny. a single Extensive structural Extensive structural work work in in the the supracrustal rocks supracrustal rocks surrounding surroundinq the central granite has revealed the the following signisignificant 1..) Cleavage in in rocks rocks of of the eastern and f icant relationships: relationships: 1.) Cleavage and western belts is is steep and aligned roughly N—S N-S somewhat somewhat parallel parallel with 2..) Cleavage in rocks with the the granite granite boundaries. boundaries. 2 . ) Cleavage rocks north north and and south south of of the the granite granite is is also also dominantly dominantly aligned aligned N—S, N-S, oblique oblique to to the 3..) Bedding/cleavage Bedding/cleavage and and minor fold symmetry the granite granite borders. borders.3.) symmetry in in the the eastern eastern and and western, western belts belts both both indicate indicate structural structural vergence towards the granite (i.e. bedding dips away vergence towards the granite (i.e. dips away from from the the granite 4..) granite and and cleavage cleavage is is always always steeper steeper than than bedding). bedding). 4. ) E—W E-W shear shear zones zones with with dextral symmetry symmetry are are developed developed south south of of the the granite. 5.) Stretching ^i. ) Stretching lineations, lineations, minor minor fold fold axes, axes, and and granite. bedding/cleavage intersection plunge intersection lineations lineations congruously congruously plunqe moderately to t o steeply steeply to t o the the south south along along the the eastern eastern margin margin of of the 6.) the granite. granite. 6 . ) Facing directions are are consistently consistently away away from from the the central central granite. granite. These These structures structures suggest suggest E—W E-W shortening shortening concomitant concomitant with with large large wavelength wavelength buckling. buckling. Strain Strain measurements measurements were made made in in aa variety variety of of lithologies litholoqies bounding 1..) bounding the the central central granite granite and and reveal reveal the the following: followinq: 1.) AA considerable considerable heterogeneity heterogeneity o-f of strain strain magnitude magnitude between between the the varying varying lithologies lithologies ranging from highly strained schistose schistose conconglomerates glomerates to t o nearly nearly undeformed undeformed major major magnetite magnetite ore ore bodies. bodies. 2. 2.) Higher Higher strain magnitudes in in the the eastern belt than than in in the the western western and 3.) and southern southern belt. belt. 3.) Strain symmetry symmetry close close to t o plane plane strain. strain. 4..) Maximum shortening shortening strains strains (Z 4.) Maximum ( Z axes) are are dominantly dominantly E—W. E-W. 5. ) 5.) Maximum Maximum elongation elongation strains strains (X ( X axes) axes) plunge steeply steeply south south in in the the eastern Elongation strains eastern and and southern southern belts. be1 ts. strains plunge plunge northward northward in in the the western western supracrustal supracrustal belt. belt. The The strain strain patterns, patterns, structural structural symmetry, symmetry, and and distribution distribution strain strain intensity intensity just described described are are inconsistent inconsistent with with an an origin origin dominated dominated by by granite granite diapirism. diapirlsm. It is is proposed instead It instead that that deformation was was regionally regional 1y extensive extensive producing producing large large scale scale folds folds cored by syn—intrusive syn-intrusive granites and a regionally homogenous homogenous of of 98 �I strain strain Heterogeneities field. field. Heterogeneities are are thought thought to to result result -from -From the the large ductility contrasts contrasts in in the the supracrustal supracrustal rocks r o c k s and and the the large influence of large, newly intruded intruded granite granite bodies. bodies. SuperSuperlarge, stiff, sti-ff, newly is position position of of late late flattening flattening strains strains due due to to diapir diapir ballooning ballooninq is possible. possible. B1 . 7 q I I I I I I I I I I I I I I I �Element Geochemistry Geochemistry ooff the t h eGowganda Gowganda Formation, Ontario Major Element Formation, Ontario YOUNG, G.M. H.W.H.W. Department of of Geology, U nUniversity i v e r s i t y ooff YOUNG, G.M.and andNESBITT, NESBITT, Department Geology, Western Ontario, London, Western Ontario, London, Ontario O n t a r i oN6A N6A 5B7 5B7 Over 200 major major element ,most ooff which Over 200 element analyses analyses,most which are a r e new,are newyare available Formation,a dominantly gglaciogenic avai 1a b l e from from the t h eGowganda Gowganda Formation ,a dominantly l aciogeni c sedimentaryuunit sedimentary n i t forming forming part p a r t of o fthe t h eHuronian HuronianSupergroup. Supergroup. Most Most of of these analysesare arefrom fromd idiamictite anda argillites. a m i c t i t e mmatrix a t r i x mmaterials a t e r i a l s and rgillites. these analyses Deposition Formation and succeedi succeeding Huronian D e p o s i t i o n of o f the t h eGowgnada Gowgnada Formati on and ng Huroni an fforormations took took pplace under cconditions so tthat mations l a c e under o n d i t i o n s ooff regional r e g i o n a l subsidence subsidence so hat they preservedb oboth mainf ofold andi nin rrelatively t h e y aare r e preserved t h i nint hthe e main l d b belt e l t and e l a t i v e l y stable stable sshelf h e l f areas areas to t o the t h e north. n o r t h . There There are are three t h r e emain main areas areas of o f preservation preservation of Formation;t hthe BruceMines, Mines, Cobalt Cobalt and and W Whitefish o f the t h eGowganda Gowganda Formation; e Bruce h i t e f i s h Falls Falls areas. chemicalddata from tthe Whitefish areas. Most Most ooff the t h e new new chemical a t a aare r e from he W h i t e f i s h Falls F a l l s area, area, which had hadaamore moreb abasinal than tthe which s i n a l s setting e t t i n g than h e other o t h e r two. two. The averagemajor majorelement elementcomposition composition matrix The average o fofd diamictite iamictit e m a t r i x materials materials and and aargillites, r g i l l i t e s , giving g i v i n g equal equal weight w e i g h t tto o aall l l three t h r e e areas, areas, is i s as as follows;follows:Si02 1. 2. Ti0, Ti02 64.41 0.63 59.62 0.70 A1203 FeO FeO A12O3 Fend3 MnO MnO Fe203 15.08 2.08 17.28 2.94 3.58 5.06 MgO MgO CaO CaO Na20 Na20 0.08 3.13 1.53 4.46 0.09 3.27 1.07 3.88 K20 K20 P205 LO1 P205 LOl 1.84 0.14 2.84 0.16 2.71 3.03 analysesoof 1. is i s the t h e average average ooff 102 102 analyses f ddiamictite i a m i c t i t e matrix m a t r i x material. material. 105analyses analyseso fofa rargillites. 2. iiss the t h e average average oof f 105 gillites. With tthe exceptionooff CaO, CaO,which whichi sisddepleted With h e exception e p l e t e d i nint hthe e ddiamictites, i a m i c t i t e s , the the average composition of the diamictite matrix material corresponds losely average composi t i o n of t h e d i ami c t i t e m a t r i x m a t e r i a1 corresponds cclosely al.(1967) tto o the t h e estimate e s t i m a t e by by Shaw Shaw eet t a1. (1967) of o f the t h e average average composition composition ooff the the Archean basement Ontario. A Archean basement i ninp apart r t oof f Ontario. A similar,but s i m i l a r , b u t weaker, weaker, CaO-depletion CaO-depletion on on Archean basement iiss evident e v i d e n t ini nPleistocene P l e i s t o c e n etills t i l deposited l s deposited Archean basement ini nthe t h esame same region. The Cobalt Cobaltddiamictites and FeO FeOr erelative The i a m i c t i t e s are a r e enriched e n r i c h e d in i n CaO CaO and l a t i v e tto o the the average Gowganda anda rare depletedi nin Na Na90. average Gowganda d i adiamictite m i c t i t e and e depleted 0. DDiamictites i a m i c t i t e s from from the the Bruce Mines Minesarea areashow showr erelative Bruce l a t i v e depletion d e p l e t i o n ini nCaO CaO an an6FeO FeOand and are a r eNa90Na 0enriched. apparentwhen when thee enriched. SSimilar i m i l a r ppatterns a t t e r n s aare r e apparent t h ethe a r gargillites i l l i t e s oof f these areas comparedw iwith averagea rargillite areas aare r e compared t h t hthe e average g i l l i t e composition. composition. These These rresults esults are geology and and suggest suggest tthat a r e compatible compatible with w i t h the t h eobserved observed basement basement geology h a t the the chemical compositiono foft hthe matrix materials, chemical composition e d diamictite iamictite m atrix m a t e r i a l s , and and tto o a lesser lesser extent, be be used asaspeovenance e x t e n t , of o f the t h eargillites, a r g i l l i t emay s , may used peovenance indicators. i n d i c a t o r s . The The chemical composition composition ooff the Formation chemical t h e Gowganda Gowganda Formation i nint hthe e WWhitefish h i t e f i s h FFalls alls area mixed provenance provenancew iwith area suggests suggests aa mixed t h c contributions o n t r i b u t i o n s from from both b o t h regions. regions. Comparison averageGowganda Gowganda andddiamictite Comparison o foft hthe e average a r gargillite i l l i t e and i a m i c t i t e matrix matrix compositioni nindicates composition d i c a t e s d edepletion p l e t i o n i nins silica i l i c a (grain ( g r a i n size s i z e effect) e f f e c t ) and and the the mobile elementsCa Caand andNaNa i nint hthe e aargillites. r g i l l i t e s .Comparison Comparison of o f the t h e average average m o b i l e elements Gowganda with Gowganda a r argillite g i l l i t e composition composition w i t h that t h a t ofo the f t h eaverage averageAphebian Aphebian shale shale andGarrels, Garrels,1980, 1980,t to exclude data data from ((modified m o d i f i e d from Cameron Cameron and o exclude from the the Gowganda Formation) Gowqanda Formation) i n dindicates i c a t e s t hthat a t t hthe e 1latter a t t e risi much s muchmore more chemically chemically altered, Ti02 andand K20K20 and depleted a l t e r e d , being beingricher r i c h e in r i 5i02, n Si02, TiO2 and d e p l e t e din iCaO n CaOand andNa20. N ~ ~ o . 100 �I A index ooff alteration Young, A chemical chemical index a1 t e r a t i o n(CIA (CIAofoNesbitt f N e s b iand t t and Young,1982) 1982) was usedt to determinet the degreeoof weatheringi in was used o determine h e degree f weathering n tthe h e diamictite diamictite matrix m a t r i x materials m a t e r i a l sand and argillites a r g i l l i t eofs the o f Gowganda t h e GowgandaFormation. Formation.These These results r e s u l t s are a r einterpreted i n t e r p r e t e dtot indicate o i n d i c a tthat e t hthe a t tGowganda h e GowgandaFormation Formation in in the t h e southern southern part p a r t of o f the t h eHuronian Huronian outcrop o u t c r o p belt b e l t contains c o n t a i n s evidence evidence of of two major gglaciations by ddeposits an iinterglacial two major l a c i a t i o n s separated separated by e p o s i t s oof f an nterglacial period. period. References References Cameron, E.M. and and Garrels, Garrels, R.M. R.M. 1980. 1980. Geochemical Geochemical composition composition of o fsome some Cameron, E.M. Precambrian shales from Precambrian shales from the t h e Canadian Canadian Shield. S h i e l d.Chemical ChemicalGeology, Geology, v.28, p.181-197. p.181-197. v.28, Nesbitt, 1982. EEarly N e s b i t t , H.W. G.M. 1982. a r l y Proterozoic P r o t e r o z o i c climates c l i m a t e s and and H.W. and and Young, Young, G.M. plate chemistryoof p l a t e motions motions inferred i n f e r r e d from from major major element element chemistry f llutites. utites. Nature v.299, v.299, p.715—717. p. 71 5-71 7. Nature Shaw, D.M., RReilly, Shaw, D.M., e i l l y , G.A., G.A., Muysson, Muysson, J.R., J.R., Patterden, Patterden,G.E. G.E. and andCampbell, Campbell, F.E. F.E. 1967. 1967. An An estimate e s t i m a t e of o f the t h e chemical chemical composition composition of o f the the Canadian Precambrian Can.Jour. Jour.EEarth Canadian Precambrian S hShield. i e l d . Can. a r t h SSci. c i . v.4, v.4, p.829p.829853. 853. 1 I I I I I I 101 1 I I � https://digitalcollections.lakeheadu.ca/files/original/19e8abd9f1d6118035330430ab25f1cd.pdf e628cabb0aec31c93e60e9feb4cbf6e7 PDF Text Text Institute on Lake Superior Geology Thirty-First Annual Meeting KENORA, Ontario 1985 FIELD TRIP GUIDEBOOK �INSTITUTE INSTITUTE ON ON LAKE SUPERIOR GEOLOGY LAKE SUPERIOR GEOLOGY 31ST 3 1 sANNUAL ~ANNUAL MEETING MEETING KENORA, 1985 FIELDTRIP FIELDTRIP GUIDEBOOK GUIDEBOOK edited edited by GP G oP Beakhouse . Beakhouse R e s i d e n t Geologist Geologist Organized in i n conjunction c o n j u n c t i o n with w i t h the t h e Kenora Resident Organized Office O f f i c e and and the t h e Ontario O n t a r i o Geological G e o l o g i c a l Survey Survey �Copies of C opies o f the t h e abstract a b s t r a c t and field f i e l d guidebook guidebook volumes v o l u m e s may be b e purchased p u r c h a s e d from: from: M..M. M.M. KKehlenbeck ehlenbeck Department D e p a r t m e n t of o f Geology Geology Lakehead University University Thunder Bay, Bay, Ontario Ontario P7V 5E1 5E1 Costs: C osts: $5.00 Abstracts Abstracts $ 5.00 Field F i e l d Guidebook Guidebook $10.00 $10.00 ((plus p l u s $$2.00 2 - 0 0 postage p o s t a g e and handling h a n d l i n g charges) charges) Make cheques c h e q u e s payable p a y a b l e to: to: Institute I n s t i t u t e on o n Lake Lake Superior S u p e r i o r Geology The contributions The c o n t r i b u t i o n s oof f the t h e following f o l l o w i n g tto o the t h e production p r o d u c t i o n oof f this this volume aare volume r e gratefully g r a t e f u l l yacknowledged: acknowledged: whod rdrafted -— Barbara B a r b a r a Moore, Moore, who a f t e d mmost o s t o foft the h e ffigures i g u r e s and and designed d e s i g n e d the the ccover over Melenchenko, who who ttyped manuscript — - Anna BBranicky r a n i c k y aand n d JJoyce o y c e Melenchenko, y p e d tthe he m anuscript who pproof—read mostoof — Chris - C h r i s Drimmie, Drimmie, who r o o f - r e a d most f tthe h e volume volume Mary-Lynne Stuart -— Mary-Lynne S t u a r t and and Renate R e n a t e Aukstakalnis, Auks t a k a l n i s ,who who advised a d v i s e d on on of various v a r i o u s aspects aspects o f the t h e reproduction r e p r o d u c t i o n of o f this t h i s volume. volume. Deformed COVER PHOTO: PHOTO: Deformed mmafic a f i c d dike i k e ccutting u t t i n g 2.85 2.85 Ga Ga Wabigoon—Winnipeg River ggneissic n e i s s i c tonalite t o n a l i t e in i n the t h e Wabigoon-Winnipeg River ssubprovincial u b p r o v i n c i a l interface I n t e r f a c e zone, z o n e , Keewatin, K e e w a t i n , Ontario Ontario 11 �Preface Preface Kenor'a, Annual Institute K e n o r a , hhost o s t oof f tthe h e 331st 1 s t Annual I n s t i t u t e on o n Lake Lake Superior Superior Geology, G e o l o g y , is i s situated s i t u a t e d at a t the t h e north n o r t h end end of o f Lake Lake of o f the t h e Woods. Woods. It It is i s especially e s p e c i a l l y appropriate a p p r o p r i a t e that t h a t Kenora K e n o r a host h o s t the t h e 1985 1985 meeting m e e t i n g on on the t h e centenary c e n t e n a r y of o f Andrew Andrew Lawson's Lawson's first f i r s t publication p u b l i c a t i o n on on the t h e Lake Lake of of the t h e Woods area; a r e a ; he h e identified i d e n t i f i e d many many of o f the t h e problems p r o b l e m s we we are are debating a s aa classical c l a s s i c a l Archean Archean d e b a t i n g today t o d a y and and established e s t a b l i s h e d the t h e area a r e a as terrane. t e r r a n e . AA brief b r i e f summary summary of o f the t h e regional r e g i o n a l geologic g e o l o g i c setting s e t t i n g of of the the Kenora Kenora area, a r e a , based b a s e d on on the t h e discussions d i s c u s s i o n s in i n the t h e field f i e l d guides g u i d e s and and the the references r e f e r e n c e s cited c i t e d therein, t h e r e i n , follows. follows. Kenora i s located l o c a t e d within w i t h i n the t h e southwestern s o u t h w e s t e r n part p a r t of o f the the Kenora is Superior S u p e r i o r Province P r o v i n c e of o f the t h e Canadian C a n a d i a n shield. s h i e l d . The The Superior S u p e r i o r Province Province has h a s been b e e n subdivided s u b d i v i d e d into i n t o east—west e a s t - w e s t trending t r e n d i n g subprovinces s u b p r o v i n c e s consistconsisting i n g of o f greenstone—tonalite g r e e n s t o n e - t o n a l i t e terranes t e r r a n e s (Shebandowan—Wawa, (Shebandowan-Wawa, Wabigoon, Wabigoon, Uchi Uchi and and Sachigo S a c h i g o Subprovinces), S u b p r o v l n c e s ) , metasedimentary m e t a s e d i m e n t a r y gneiss g n e i s s terranes terranes (Ear M a n i g o t a g a n and and Quetico Q u e t i c o Subprovinces) S u b p r o v i n c e s ) and and bath— bath( E a r Falls F a l l s —- Manigotagan olithic o l i t h i c terranes t e r r a n e s (Winnipeg ( W i n n i p e g River R i v e r and and Berens B e r e n s River R i v e r Subprovinces). Subprovinces) * The The town town of o f Kenora K e n o r a lies l i e s on o n the t h e interface i n t e r f a c e between b e t w e e n the t h e Winnipeg Winnipeg River R i v e r and and Wabigoon Wabigoon subprovinces. subprovinces. The suprac r u s t a l The western w e s t e r n Wabigoon Wabigoon Subprovince S u b p r o v i n c e comprises c o m p r i s e s aa supracrustal assemblage a s s e m b l a g e of o f predominant p r e d o m i n a n t metavolcanic m e t a v o l c a n i c and and subordinate s u b o r d i n a t e meta— metasedimentary s e d i m e n t a r y rocks r o c k s and and granitoid g r a n i t o i d intrusions, i n t r u s i o n s , some some of o f batholithic batholithic dimensions. d i m e n s i o n s . Stratigraphic S t r a t i g r a p h i c analysis a n a l y s i s of o f the t h e rock r o c k sequences s e q u e n c e s within within the was aa t h e western w e s t e r n Wabigoon Wabigoon Subprovince S u b p r o v i n c e suggests s u g g e s t s that t h a t there t h e r e was consistent c o n s i s t e n t evolution e v o l u t i o n through t h r o u g h time t i m e with w i t h initial, i n i t i a l , quiescent, quiescent, submarine, s u b m a r i n e , mafic, m a f i c , tholeiltic t h o l e i i t i c volcanism v o l c a n i s m followed f o l l o w e d by by more more silicic, silicic, submarine c a l c - a l k a l i n e pyroclastic p y r o c l a s t i c volcanism v o l c a n i s m and and s u b m a r i n e and and subaerial, s u b a e r i a l , calc—alkaline related r e l a t e d clastic c l a s t i c sedimentation. s e d i m e n t a t i o n . More More than t h a n one o n e such s u c h cycle c y c l e may may be be present. p r e s e n t . Available A v a i l a b l e high h i g h precision p r e c i s i o n U—Pb U-Pb zircon z i r c o n geochronology geochronology suggest s u g g e s t that t h a t volcanism v o l c a n i s m and and plutonism p l u t o n i s m were w e r e synchronous s y n c h r o n o u s and a n d took took place p l a c e over o v e r aa relatively r e l a t i v e l y short s h o r t time t i m e interval i n t e r v a l between b e t w e e n 2755 2755 and a n d 2695 2695 Ma. Ma. The The metallogeny me t a l l o g e n y of o f the t h e western w e s t e r n Wabigoon Wablgoon Subprovince Sub p r o v i n c e is is diverse. d i v e r s e . Massive M a s s i v e sulphide s u l p h i d e deposits d e p o s i t s such s u c h as a s those t h o s e at a t South South Sturgeon S t u r g e o n Lake Lake and and numerous numerous gold g o l d deposits d e p o s i t s have h a v e received r e c e i v e d the t h e most most attention. a t t e n t i o n . Exploration E x p l o r a t i o n ffor o r gold g o l d mineralization m i n e r a l i z a t i o n has h a s recently recently intensified s i g n i f i c a ndiscovery t d i s c o v e r at y aCameron t Cameron i n t e n s i f i e d ini nthe t h ewake wake of o fa asignificant Lake0 Other Lake O t h e r types t y p e s of o f potentially p o t e n t i a l l y economically e c o n o m i c a l l y significant significant deposits d e p o s i t s include i n c l u d e disseminated d i s s e m i n a t e d copper c o p p e r and/or a n d / o r molybdenum, molybdenum, rare rare metal m e t a l pegmatites, p e g m a t i t e s , building b u i l d i n g stone s t o n e and and industrial i n d u s t r i a l minerals. minerals. Our Our perception p e r c e p t i o n of o f the t h e terrane t e r r a n e lying l y i n g to t o the t h e north n o r t h of o f the the Wabigoon Wabigoon Subprovince S u b p r o v i n c e has h a s changed changed dramatically d r a m a t i c a l l y within w i t h i n the t h e past p a s t ten ten years. a s the t h e English E n g l i s h River R i v e r Subprovince, Subprovince, y e a r s . This T h i s area, a r e a , referred r e f e r r e d to t o as is i s now now known known to t o consist c o n s i s t of o f two two different d i f f e r e n t types t y p e s of o f terrane t e r r a n e for for which separate s e p a r a t e subprovince s u b p r o v i n c e status s t a t u s has h a s been b e e n proposed; p r o p o s e d ; aa northern northern which s u p r a c r u s t a l domain domain (Ear ( E a r Falls—Manigotagan F a l l s - M a n i g o t a g a n Subprovince) S u b p r o v i n c e ) and and aa supracrustal southern s o u t h e r n plutonic p l u t o n i c domain domain (Winnipeg ( W i n n i p e g River R i v e r Subprovince). S u b p r o v i n c e ) . The The Ear Ear Falls—Manigotagan F a l l s - M a n i g o t a g a n Subprovince S u b p r o v i n c e consists c o n s i s t s predominantly p r e d o m i n a n t l y of of turbiditic t u r b i d i t i c metasedimentary m e t a s e d i m e n t a r y rocks r o c k s which which have h a v e been b e e n highly h i g h l y metametamorphosed morphosed and and partially p a r t i a l l y melted. m e l t e d . The The Winnipeg Winnipeg River R i v e r Subprovince Subprovince contains p r e - t e c t o n i c gneissic gneissic c o n t a i n s three t h r e e principal p r i n c i p a l rock r o c k suites; s u i t e s ; pre—tectonic granitoid g r a n i t o i d rocks, r o c k s , pre— p r e - to t o syn—tectonic s y n - t e c t o n i c sodic s o d i c plutons p l u t o n s and a n d late— l a t e - to to post—tectonic p o s t - t e c t o n i c potassic p o t a s s i c plutons. p l u t o n s . Subordinate, S u b o r d i n a t e , amphibolitic a m p h i b o l i t i c to to iii �granulitic, g r a n u l i t i c , predominantly p r e d o m i n a n t l y metavolcanic, m e t a v o l c a n i c , supracrustal s u p r a c r u s t a l inclusions inclusions aare r e ppresent r e s e n t in i n all a l l three t h r e e suites s u i t e s but b u t are a r e most m o s t abundant a b u n d a n t in i n the the gneissic g n e i s s i c rocks. rocks. In I n ccontrast o n t r a s t to t o tthe h e tightly t i g h t l y clustered, c l u s t e r e d , relatively r e l a t i v e l y young young ages ages of the Wabigoon Subprovince, Winnipeg River Subprovince o f t h e Wabigoon Sub p r o v i n c e , Winnipeg R i v e r S u b p r o v i n c e plutonism plutonism spanned 6 0 0 Ma Ma (2560 ( 2 5 6 0 to t o 3168 3168 Ma). Ma). Many of o f the t h e younger y o u n g e r rocks rocks s p a n n e d 600 appear These a p p e a r to t o represent r e p r e s e n t reworking r e w o r k i n g of of older o l d e r rocks. rocks. T h e s e relation-relationSubsships h i p s hhave a v e bbeen e e n interpreted i n t e r p r e t e d in i n terms t e r m s of o f the t h e Winnipeg River R i v e r Sub— pprovince r o v i n c e representing r e p r e s e n t i n g a basement b a s e m e n t complex complex that t h a t existed e x i s t e d prior p r i o r to to The interface Wabigoon Subprovince S u b p r o v i n c e volcanism v o l c a n i s m and and plutonism. plutonism. The interface between b e t w e e n the t h e two two subprovince s u b p r o v i n c e has h a s stratigraphic s t r a t i g r a p h i c(unconformable) ( u n c o n f o r m a b l e ), ttectonic, e c t o n i c , metamorphic m e t a m o r p h i c and and intrusive i n t r u s i v e aspects a s p e c t s and and defies defies a simplistic s i m p l i s t i c interpretation. interpretation. iv �CONTENTS CONTENTS Preface Preface Contents C ontents The Cameron Lake The L a k e Deposit D e p o s i t (D.R. ( D . R. Melling M e l l i n g and and D0H, D.H. Watkinson) Watkinson) Introductory I n t r o d u c t o r y Discussion Discussion Field F i e l d Guide Guide References R eferences Geologic G e o l o g i c Setting S e t t i n g and and Style S t y l e of o f Gold Gold Mineralization Mineralization Lake Woods aarea Davies, PM0 Smith, r e a ((J,C JoCoD a v i e s , P,M. Smith, iin n tthe he L a k e oof f t the h e Woods and CC.E . E . Blackburn) Blackburn) and Introductory I n t r o d u c t o r y Discussion Discuss ion Field F i e l d Guide Guide References R eferences Geological G e o l o g i c a l Relationships R e l a t i o n s h i p s in i n the t h e Vicinity V i c i n i t y of o f the the Wabigoon W a b i g o o n - Winnipeg W i n n i p e g River R i v e r Subprovincial S u b p r o v i n c i a l Interface Interface in Kenora area i n the the K enora a r e a (G.P ( G . P o Beakhouse) Beakhouse) IIntroductory n t r o d u c t o r y Discussion Discussion Field F i e l d Guide Guide References References Appendix Append ix A Volcanic V o l c a n i c Facies F a c i e s Interpretation I n t e r p r e t a t i o n of o f the t h e Berry B e r r y River River Formation (G.W. Johns) Johns) F o r m a t i o n (G.W. IIntroductory n t r o d u c t o r y Discussion Discuss ion Field F i e l d Guide Guide References R eferences Granitoid G r a n i t o i d Related R e l a t e d Mineralization M i n e r a l i z a t i o n in i n the t h e Dryden D r y d e n Area A r e a (F.W. (F.W. Breaks, R.C. BBeard, . A . Janes, J a n e s , RH. K.H. Poulsen) Poulsen) B r e a k s , R.C. e a r d , DDA. Discuss ion IIntroductory n t r o d u c t o r y Discussion Field F i e l d Guide Guide References R eferences V iiii ll v v 1 2 2 5 5 1 1111 13 13 1144 26 26 56 56 599 5 60 60 7788 96 9 6 101 101 105 105 106 106 131 131 153 153 157 157 158 158 170 170 185 185 �Deposit The Cameron Lake Lake Deposit IIntroductory n t r o d u c t o r y Discussion Discuss i o n and a n d Field Field Guide Guide 31st Annual Institute 3 1 s t Annual I n s t i t u t e on on Lake Lake Superior S u p e r i o r Geology Geology Kenora, K e n o r a , Ontario Ontario by D.R. D.R. Melling Mellinq D,H. D. H. Watkinson Watkinson Ottawa-Carleton O t t a w a - C a r l e t o n Centre C e n t r e for for Geoscience G e o s c i e n c e Studies Studies Carleton C a r l e t o n University University Ottawa, O t t a w a , Ontario Ontario K1S 5B6 5B6 �2 INTRODUCTION INTRODUCTION Lakeg ogold o c a t e d in i n northwestern northwestern The Cameron Cameron Lake l d d edeposit p o s i t isis llocated Ontario I t was was originally originally O n t a r i o about a b o u t 80 8 0 km km south—southeast s o u t h - s o u t h e a s t of o f Kenora. K e n o r a - It by two prospectors p r o s p e c t o r s working w o r k i n g for f o r Noranda N o r a n d a Mines Mines ddiscovered i s c o v e r e d in i n 1960 by Lowg ogold (Hunter ( H u n t e r et e t al., a l . , 1984). 1984 ) . Low l d p rprices i c e s aat t that t h a t time t i m e coupled c o u p l e d with with o m p l e x ssubsurface u b s u r f a c e ggeometry e o m e t r y aand n d poor p o o r ooutcrop u t c r o p exposure exposure a ccomplex Four discouraged d i s c o u r a g e d investment i n v e s t m e n t and and development. development. F o u r separate s e p a r a t ediamond diamond c o n d u c t e d on o n the t h e property p r o p e r t y prior p r i o r to t o the the d r i l l i n g programs p r o g r a m s were conducted discovery two d i s c o v e r y of o f aa major m a j o r zone z o n e of o f gold g o l d mineralization m i n e r a l i z a t i o n in i n 1983 1983 by b y two junior mining junior m i n i n g companies, c o m p a n i e s , Nuinsco N u i n s c o Resources R e s o u r c e s and a n d Lockwood Lockwood Proven Petroleum. t i m e totaled t o t a l e d 1,287,000 1 , 2 8 7 , 0 0 0 tons tons P etroleum. P r o v e n reserves r e s e r v e s at a t that t h a t time grading g r a d i n g 0.154 0 . 1 5 4 oz/ton o z / t o n Au, Au, including i n c l u d i n g 807,000 8 0 7 , 0 0 0 tons t o n s grading g r a d i n g 0.194 0.194 oz/ton o z / t o n Au Au (Nuinsco ( N u i n s c o Resources R e s o u r c e s Limited, L i m i t e d , 1983). 1983) drilling REGIONAL GEOLOGIC SETTING AND ITS ITS BEARING B E A R I N G ON GOLD MINERALIZATION Cameron western i e s in i n the the w e s t e r n portion p o r t i o n oof f the t h e Archean Archean Cameron Lake Lake llies Savant (Trowell S a v a n t Lake—Crow Lake-Crow Lake Lake metavolcanic—metasedimentary m e t a v o l c a n i c - m e t a s e d i m e n t a r y belt b e l t (Trowell The rregion by the et e t al., a l s f 1980), 1 9 8 0 ) . The e g i o n is is ddivided i v i d e d ggeologically e o l o g i c a l l y by t h e north— northwestsoutheast wes t - s o u t h e a s t trending, t r e n d i n g , northeast—dipping n o r t h e a s t - d i p p i n g Pipestone—Cameron P ipestone-Cameron Southwest Fault 1). S o u t h w e s t oof f tthe h e ffault a u l t lies l i e s the t h e north— n o r t h - to to F a u l t (Figure ( F i g u r e 1). east—facing, Kakag i Lake Lake greenstone g r e e n s t o n e terrain t e r r a i n (KLGT) (KLGT) (Schwerdtner (Schwerdt n e r e a s t - f a c i n g , Kakagi al., 1979) eet t a!.,, 1 9 7 9 ) aand n d tto o tthe h e nnortheast o r t h e a s t tthe h e ssouth—facing o u t h - f a c i n g Iowan Rowan Lake Lake is a a major m a j o r zone z o n e of of ggreenstone r e e n s t o n e terrain t e r r a i n (RLGT). (RLGT). The T h e fault f a u l t is ddeformation e f o r m a t i o n and a n d ddisplacement i s p l a c e m e n t which w h i c h strikes s t r i k e s over o v e r 100 1 0 0 km km in i n aa Exposure of the fault in nnorthwest—southeast o r t h w e s t - s o u t h e a s t direction. direction. E x p o s u r e o f t h e f a u l t i n the the Cameron Lake area is poor, often e i n g oobscured b s c u r e d bby y lakes l a k e s and a n d low low Cameron L a k e a r e a i s p o o r , o f t e n bbeing Correlation swampy depressions. depress ions C o r r e l a t i o n of o f lithologies l i t h o l o g i e s across a c r o s s the t h e fault, fault aalthough l t h o u g h suspected, s u s p e c t e d , has h a s not n o t been b e e n possible p o s s i b l e (Trowell (Trowell et e t al., a l . , 1980). 1980). The geology g e o l o g y of of the t h e RLGT RLGT is i s dominated d o m i n a t e d by b y the t h e Shingwak S h i n g w a k Lake Lake The fold Anticline. A nticline. f o l d hhas a s aa east—northeast e a s t - n o r t h e a s t trending t r e n d i n g axial a x i a l surface surf ace Based and and pplunges l u n g e s steeply s t e e p l y towards t o w a r d s the t h e southwest s o u t h w e s t (Kaye, ( K a y e , 1973). 1973). B a s e d on on field mapping field m a p p i n g and a n d lithogeochemical l i t h o g e o c h e m i c a l analyses, a n a l y s e s Blackburn B l a c k b u r n and and Hailstone H a i l s t o n e (1984) ( 1 9 8 4 ) have h a v e shown s h o w n that t h a t the t h e RLGT RLGT may be b e subdivided s u b d i v i d e d into into All the A l l rrocks o c k s hhave a v e been been t h e Powan Rowan Lake Lake and a n d Cameron Cameron Lake Lake Volcanics. Volcanics. The metamorphosed t o greenschist—facies g r e e n s c h i s t - f a c i e s assemblages. assemblages T h e Powan Rowan Lake Lake m e t a m o r p h o s e d to Volcanics V o l c a n i c s form form a a thick t h i c k ppredominantly r e d o m i n a n t l y ppillowed, i l l o w e d , subaqueous s u b a q u e o u s mafic maf i c flow f l o w ssuccession u c c e s s i o n in i n the t h e core core of o f the t h e Shingwak S h i n g w a k Lake Lake Anticline. Anticline. These by the mixed T h e s e rrocks o c k s aare r e ooverlain v e r l a i n by t h e Cameron Lake Lake Volcanics, Volcanics, a a m ixed succession s u c c e s s i o n of o f ssubaqueous u b a q u e o u s ppillowed i l l o w e d and a n d massive mass i v e mafic maf i c flows, f l o w s , and and South intermediate i n t e r m e d i a t e to t o felsic f e l s i c pyroclastics. pyroclastics. S o u t h oof f the t h e fold f o l d axis a x i s top top ddeterminations e t e r m i n a t i o n s ddefine efine a a ssteeply t e e p l y ddipping i p p i n g homocline h o m o c l i n e facing f a c i n g southsouthward. Subvolcanic sills were emplaced i l l s were e m p l a c e d at a t all a l l levels l e v e l s in i n the the S u b v o l c a n i c gabbroic gabbroic s Felsic t o folding. folding. F e l s i c porphyry p o r p h y r y sills s i l l s and a n d dikes, dikes, sstratigraphy t r a t i g r a p h y prior p r i o r to monzonite aand n d quartz quartz m o n z o n i t e sstocks t o c k s intrude i n t r u d e all a l l the t h e earlier e a r l i e r strata. strata. Blackburn and Hailstone (1984) have shown that the B l a c k b u r n a n d H a i l s t o n e ( 1 9 8 4 ) h a v e s h o w n t h a t t h e lower lower is ttholeiitic mostly ssuccession u c c e s s i o n (Rowan (Rowan Lake Lake Volcanics) V o l c a n i c s ) is h o l e i i t i c aand nd m o s t l y rather rather magnesium—rich, m a g n e s i u m - r i c h , while w h i l e the t h e upper u p p e r succession s u c c e s s i o n (Cameron ( C a m e r o n Lake Lake Volcanics) t o caic—alkaline c a l c - a l k a l i n e varieties. varieties V o l c a n i c s ) includes i n c l u d e s both b o t h tholeiitic t h o l e i i t i c to The most most ssignificant within i g n i f i c a n t ggold o l d ooccurrences c c u r r e n c e s aare re w i t h i n the t h e Cameron Cameron Lake Lake The Volcanics t o be b e associated associated V o l c a n i c s (Blackburn ( B l a c k b u r n and a n d JJanes, a n e s , 1983) 1 9 8 3 ) and and tend t e n d to with Several w i t h zones z o n e s of o f high h i g h strain. strain. S e v e r a l oof f these t h e s e occurrences o c c u r r e n c e s are are Two ssuch o r near n e a r gabbroic—volcanic g a b b r o i c - v o l c a n i c contacts. contacts. u c h gold— goldssituated i t u a t e d at a t or bearing, to b e a r i n g , hhigh i g h sstrain t r a i n zones, z o n e s , previously p r e v i o u s l y unnamed, unnamed, are a r e referred r e f e r r e d to a . �______ 3 + ++ : NOLAN ,+ + LAKE + + STOCK -I-t + + + + + + + + + + •+ + + + + + + + + + + + + + • + MIDDLE MIDDLE TO TOLATE LATEPRECAMBRIAN PRECAMBRIAN(PROTEROZOIC) (PROTEROZOIC) MAFIC MAFICINTRUSIVE INTRUSIVEROCKS ROCKS diabase diabase 00 1 1 - + + + + + + )+ + + 1 + + 22 kilometres kilometres gold occurrence occurrence AAgold EARLY EARLYPRECAMBRIAN PRECAMBRIAN(ARCHEAN) (ARCHEAN) LATE FELSIC INTRUSIVE LATE FELSIC INTRUSIVEROCKS ROCKS granite, granodiorite, granodiorite. diorite, diorite, monzodiorite, monzodiorite,monzonite, monzonite, quartz quartzmonzonite monzonite granite, EARLY EARLYFELSIC FELSICINTRUSIVE INTRUSIVEROCKS ROCKS [7''j feldspar porphyry, quartz porphyry, quartz—feldspar feldspar porphyry, quartz porphyry, quartz-feldspar porphyry porphyry MAFIC MAFICINTRUSIVE INTRUSIVEROCKS ROCKS IIJffJIjJJJJJ gabbro, quartzgabbro, gabbro,pyroxenite, pyroxenite, peridotite, peridotite, diorite gabbro, quartz diorite FELSIC FELSICTO TOINTERMEDIATE INTERMEDIATEMETAVOLCANICS METAVOLCANICS 1"""""")I rhyolite rhyolite, rhyodacite rhyodacite, dacite dacite,tuff tuff, lapilli—tuff lapilli-tuff, crystal crystallaptIli—tuff Iapilli-tuff,tuff—breccia tuff-breccia MAFIC MAFICMETAVOLCANICS METAVOLCANICS basalt,andesite andesite(pillowed (pillowedand and massive),pillow pillow breccia, tuff. lapilli-tuff,tuff—breccia tuff-breccia basalt, massive), breccia, tuff, lapilli—tuff, Figure Figure 1: 1: Geology G e o l o g y of o f the t h e Cameron Cameron Lake L a k e area a r e a (modified ( m o d i f i e d after a f t e r Kaye, Kaye, 1973). 1973). �4 here here a s the t h e Cameron Cameron Lake Lake and a n d nte MonteCristo C r i s t oShear S h e a rZones. Zones. as p r e s e n t l y the t h e principal p r i n c i p a l targets t a r g e t s for f o r exploration. exploration. presently These T h e s e are are THE GEOLOGY GEOLOGY OF O F THE THE CAMERON CAMERON LAKE LAKE GOLD GOLD DEPOSIT DEPOSIT THE The Cameron Cameron Lake Lake d e p o s i t is situated s i t u a t e d on o n the t h e north n o r t h shore s h o r e of of The m northwest of the point of about 700 Cameron Lake ( F i g u r e 1 ) a b o u t 700 m n o r t h w e s t o f t h e p o i n t o f Cameron Lake (Figure 1) a t the t h e Nuinsco N u i n s c o bush b u s h camp. camp. The T h e rocks r o c k s hosting h o s t i n g the the d e b a r k a t i o n at debarkation d e p o s it are a r e composed composed of of mafic maf i c volcanics v o l c a n i c s consisting c o n s is t i n g predominantly predominant1y deposit o f fine f i n e grained g r a i n e d pillowed p i l l o w e d and a n d massive m a s s i v e flows f l o w s with w i t h minor m i n o r occurrences occurrences of of t o felsic f e l s i c pyro— pyroo f pillow p i l l o w breccia b r e c c i a interlayered i n t e r l a y e r e d with w i t h intermediate i n t e r m e d i a t e to c l a s t i c rocks. r o c k s . Two Two gabbroic g a b b r o i c sills s i l l s intrude i n t r u d ethe t h eintermediate i n t e r m e d i a t earid and clastic ffelsic e l s i c pyroclastic p y r o c l a s t i c rocks. r o c k s . Quartz—feldspar Q u a r t z - f e l d s p a r porphyry p o r p h y r y sills s i l l s and and a r e also a l s o present. present. d i k e s are dikes The is located l o c a t e d within w i t h i n the t h e Cameron Cameron The Cameron Cameron Lake Lake gold g o l d deposit d e p o s i t is Lake Lake Volcanics V o l c a n i c s near n e a r the t h e contact c o n t a c t with w i t h the t h e underlying u n d e r l y i n g Powan Rowan Lake Lake It occurs in sheared mafic volcanic rocks adjacent I t o c c u r s i n s h e a r e d ma i c v o l c a n i c rocks a d j a c e n t to to V o l c a n i c s . Volcanics. t h e highly h i g h l y deformed d e f o r m e d intrusive i n t r u s i v e contact c o n t a c t with w i t h aa gabbroic g a b b r o i c sill. s i l l . The The the shear the Cameron Cameron Lake Lake gold g o l d deposit d e p o s i t is is aa brittle— brittles h e a r zone z o n e hosting h o s t i n g the ductile, d u c t i l e , dextral d e x t r a l strike—slip s t r i k e - s l i p system s y s t e m with w i t h an a n attitude a t t i t u d e of o f 315/700NE 315/700NE Its a n d aa maximum maximum strike s t r i k e length l e n g t h of o f over o v e r 1,000 1 , 0 0 0 m. m. Its width w i d t h varies varies and f r o m 11 1 1 mm to t o6 600 m. mo from Two Two planar p l a n a r fabrics f a b r i c s may be b e seen s e e n within w i t h i n the t h e zones z o n e s of o f high high strain; t o the t h e shear s h e a r zone, z o n e , and a n d aa planar planar strain; a a cleavage c l e a v a g e parallel p a r a l l e l to mineral m i n e r a l alignment a l i g n m e n t (flattening ( f l a t t e n i n g plane p l a n e foliation) f o l i a t i o n ) inclined i n c l i n e d at a t angles angles l e s s than t h a n 4450 5 0 to t o tthe h e sshear h e a r zzone o n e à The T h e intersection i n t e r s e c t i o n of o f these these less foliations f o l i a t i o n s defines d e f i n e s aa lineation l i n e a t i o n which w h i c h pitches p i t c h e s 85°E 850E within w i t h i n the the s h e a r zone. zone. T h i s l i n e a t i o n is p e r p e n d i c u l a r t o t h e i n f e r r e d shear displacement pitches 50W wwithin i t h i n tthe h e shear s h e a r plane. plane. d i s p l a c e m e n t vector v e c t o r which which p i t c h e s 50W T h r e e distinct d i s t i n c tveining v e i n i n g episodes e p i s o d e s have h a v e been b e e n recognized r e c o g n i z e d in i n the the Three c a r b o n a t i z e d rocks r o c k s of o fthe t h Cameron e Cameron Lake Lake Shear S h e a r Zone: Zone: carbonatized e a r l y , barren, b a r r e n , extensional, e x t e n s i o n a l quartz—carbonate quartz-carbonate stage i) early, v e i n s which w h i c h have h a v e been b e e n buckled; buckled; veins s t a g e ii) ii) major system s y s t e m of o f gold—bearing, g o l d - b e a r i n g , pyritic, pyritic, aa major stage q u a r t z - r i c h breccia—veins b r e c c i a - v e i n s (315/70°); ( 3 l5/7O¡ ; quartz—rich aa late s t a g e iii) iii) l a t e group g r o u p of o f cross cross cutting c u t t i n g en e n echelon echelon stage extension e x t e n s i o n veins v e i n s (360/900) ( 3 6 0 / 9 0 0 ) which w h i c h are a r e composed composed o f quartz—carbonate—chlorite—hematite—gold. q u a r t z - c a r b o n a t e - c h l o r i te-hemat i t e - g o l d of The ssignificance i g n i f i c a n c e of o f the t h e stage s t a g e (ii) ( i i ) breccia—veins b r e c c i a - v e i n s has h a s been been The p r e v i o u s l y underestimated. u n d e r e s t i m a t e d . They T h e y represent r e p r e s e n t aa specific s p e c i f i c gold—beargold-bearpreviously i n g rock r o c k type t y p e ata Cameron t Cameron Lake Lake which w h i c h commonly commonly c contains o n t a i n s ggreater reater ing o z / t o n Au. An. Pervasively P e r v a s i v e l y altered a l t e r e dcarbonate—sericite— carbonate-sericitet h a n 0.3 0 . 3 oz/ton than pyrite l a r g evolume v o l u m e of of the the p y r i t e rich r i c hphyllonitic p h y l l o n i t i rocks c r o c k which s w h i c hoccupy o c c u p y aa large lower Cameron Lake h e a r Zone n v e l o p e t the h e breccia—veins b r e c c i a - v e i n s are Cameron LakeSShear Zoneand andeenvelope are lower is readily g r a d e . This T h i s subdivision s u b d i v i s i o n of o f gold—bearing g o l d - b e a r i n g r orock c k t ytypes p e s is readily grade. visible diamond v i s i b l eini nsurface s u r f a c exposures e e x p o s u r e sofo fthe t h deposit e d e p o s iand t and d i a m o n d drill drill deposit is This lineation is perpendicular to the inferred stage i) . core. core. T h e breccia—veins b r e c c i a - v e i n s are h a r a c t e r i z e d bby y angular, a n g u l a r , often often The areccharacterized elongate e l o n g a t e fragments f r a g m e n t s oof f altered a l t e r e d basalt b a s a l which t w h i c h range r a n g efrom f r o m 1 mm mm to to g r e a t e r than t h a n 30 3 0 cm cm in i n size. s i z e . Breccia Breccia fragments f r a g m e n t s may may be b e in i n contact contact greater 1 or o r separated s e p a r a t e d by b y aa vein v e i n matrix m a t r i x (10 ( 1 0 to t o 50%) 5 0 % )of o f quartz, q u a r t z , carbonate, carbonate, a n d plagioclase. p l a g i o c l a s e . Commonly Commonly groups g r o u p s of o f fragments f r a g m e n t s can c a n be b e fitted fitted and t o g e t h e r like l i k e pieces p i e c e s in i n aa jigsaw j i g s a w puzzle. p u z z l e . Pyrite P y r i t e rarely r a r e l y exceeds exceeds together 5% 5 % and and is i s concentrated c o n c e n t r a t e d within w i t h i n the t h e fragments f r a g m e n t s and and forms f o r m s narrow narrow �5 envelopes Gold has e n v e l o p e s surrounding s u r r o u n d i n g the t h e breccia—veins. breccia-veins. h a s been b e e n seen s e e n in in hand as inclusions i n c l u s i o n s within w i t h i n pyrite pyrite h a n d sample s a m p l e and a n d polished p o l i s h e d thin t h i n section s e c t i o n as grains t o pyrite pyrite g r a i n s and and as a s free f r e e gold g o l d within w i t h i n the t h e matrix m a t r i x interstitial i n t e r s t i t i a l to grains. Minor ( l e s s than t h a n 1%) 1 % ) chalcopyrite c h a l c o p y r i t e and a n d rutile f u t i l e are a r e also also grains. M i n o r (less present. present. The The transition t r a n s i t i o n from f r o m cleavage c l e a v a g e development d e v e l o p m e n t to t o brittle b r i t t l e processes processes is manifested m a n i f e s t e d in i n the t h e formation formation w i t h i n the t h e Cameron Cameron Lake Lake Shear S h e a r Zone Zone is within of t o brittle brittle o f veins v e i n s and a n d vein—breccias. vein-breccias. The change c h a n g e from f r o m ductile d u c t i l e to The behavior b e h a v i o r may may be b e the t h e result r e s u l t of o f local l o c a l increases i n c r e a s e s in i n hydrothermal hydrothermal fluid f l u i d pressure p r e s s u r e which w h i c h f facilitated a c i l i t a t e d brittle b r i t t l edeformation d e f o r m a t i o n and a n d vein vein formation by rreducing t r e s s e s . The The f o r m a t i o n by e d u c i n g t the h e eeffective f f e c t i v e normal n o r m a l sstresses. phyllonitic p h y l l o n i t i c rocks r o c k s formed f o r m e d aa sink s i n k for f o rthe t h egold—bearing g o l d - b e a r i n g fluids, fluids, while b r e c c i a veins v e i n sformed f o r m e d major m a j o r conduits c o n d u i t s enhancing e n h a n c i n g fluid £ u i d w h i l e the t h e breccia cc iirc r c ul u l aatt iion. on. The The llocalization o c a l i z a t i o n of o f highly h i g h l yanomalous a n o m a l o u s quantities q u a n t i t i e s of o f gold g o l d along along the LakeS hShear Zoneisisr related e l a t e d to t o the t h e development d e v e l o p m e n t of of t h e Cameron Cameron Lake e a r Zone oblique, o b l i q u e ,secondary, s e c o n d a r y ,bedding—controlled b e d d i n g - c o n t r o l l e d sympathetic s y m p a t h e t i c shear s h e a r zones zones (275/700N) This (275/70ON).. T h i s is i l l u s t r a t e d o n aa dipping d i p p i n g longitudinal longitudinal section Note the t h e 7OOJ 7 O W pitch pitch s e c t i o n compiled c o m p i l e d from f r o m drilling d r i l l i n g (Figure ( F i g u r e 2). 2 ) . Note of o f the t h e gold g o l d shoots, s h o o t s , and a n d the t h e periodicity p e r i o d i c i t y of o f the t h e high h i g h grade g r a d e zones. zones. Figure i s aa simplified s i m p l i f i e d stereographic s t e r e o g r a p h i c projection p r o j e c t i o n of o f the t h e Cameron Cameron F i g u r e 33 is Lake Lake Shear S h e a r Zone Zone and a n d the t h e oblique, o b l i q u e , bedding—controlled, b e d d i n g - c o n t r o l l e d , sympathetic sympathetic splays. s p l a y s . The T h e pitch p i t c h of o f the t h e deposit, d e p o s i t , as a s defined d e f i n e d by by drilling, d r i l l i n g , is is coincident c o i n c i d e n t with w i t h the t h e intersection i n t e r s e c t i o n of o f the t h e these t h e s e two two shear s h e a r systems. systems. The t w o shear s h e a r systems s y s t e m s and and the t h e deposit d e p o s i t is is T h e relationship r e l a t i o n s h i p between b e t w e e n the t h e two illustrated i l l u s t r a t e d diagramatically d i a g r a m a t i c a l l y in i n Figure F i g u r e 4. 4. I t serves s e r v e s to t o explain explain It the w e l l as as t h e complex c o m p l e x subsurface s u b s u r f a c e geometry g e o m e t r y of o f the t h e gold g o l d shoots, s h o o t s , as a s well the t h e existence e x i s t e n c e of o f hanging h a n g i n g wall w a l l and a n d footwall f o o t w a l l zones z o n e s on o n either e i t h e r side side of A t this t h i s stage s t a g e the the o f the t h e main m a i n zone z o n e of o f gold g o l d enrichment. e n r i c h m e n t . At periodicity p e r i o d i c i t y of o f the t h ehigh h i g hgrade g r a d egold g o l dpods p o d s can c a n not n o t be b eadequately adequately explained. explained is illustrated on . FIELD F I E L D TRIP TRIP STOPS STOPS At A t this t h i s stop s t o pwe w ewill w i l examine l e x a m i n e excavated e x c a v a t e d exposures e x p o s u r e s (Figure ( F i g u r e5) 5) of o f the t h egold—bearing g o l d - b e a r i n g rrocks o c k s typical t y p i c a l of o fthe t h eCameron Cameron Lake Lake deposit. deposit. Emphasis w i l l be b e placed p l a c e d on o n the t h e following f o l l o w i n g aspects a s p e c t s of o f the t h e deposit: deposit: E m p h a s i s will 1) 1) 2) 2) 3) 3) K i n e m a t i c indicators i n d i c a t o r s useful u s e f u l in i n the t h e determination d e t e r m i n a t i o n of of Kinematic sense s e n s e of o f shear s h e a r (cleavage, ( c l e a v a g e , lineation, l i n e a t i o n , rotation r o t a t i o n and a n d foldfolding i n g of o f passive p a s s i v e and a n d nonpassive n o n p a s s i v e markers, m a r k e r s , minor m i n o r folds, folds, enechelon e n e c h e l o n veins); v e i n s ); Vein andi tits V e i n pparagenesis a r a g e n e s i s and s rrelation e l a t i o n to t o alteration, a 1 t e r a t i o n , gold gold deposition d e p o s i t i o n and a n d deformational d e f o r m a t i o n a l procesess p r o c e s e s s within w i t h i n the t h e shear shear zone; zone; Shear S h e a r zone z o n e geometry g e o m e t r y and a n d its i t s influence i n f l u e n c e on on gold g o l d deposition deposition and and exploration e x p l o r a t i o nmethods. methods. Discovery D i s c o v e r y Outcrop: O u t c r o p : This T h i s is is the t h e locality l o c a l i t ywhere where the was discovered. d i s c o v e r e d . The The outcrop outcrop t h e original o r i g i n a gold l g o l dshowing s h o w i n g was isis within w i t h i n the t h emain m a i n shear s h e a r system s y s t e m and and consists c o n s i s t s primarily primarily of o f pervasively p e r v a s i v e l y carbonatized c a r b o n a t i z e d pillowed p i l l o w e d basalt, b a s a l t , the t h e least least deformed d e f o r m e d of o f which w h i c h indicates i n d i c a t e s an anoverturned o v e r t u r n e d succession success ion STOP STOP A. A. topping A t the t h e southern s o u t h e r n edge e d g e of o f the the t o p p i n g toward t o w a r d the t h e south. s o u t h . At exposure is the t h e sheared s h e a r e d intrusive i n t r u s i v e contact c o n t a c t with w i t h the the e x p o s u r e is �6 feet F i g u r e 2: 2: Figure Longitudinal L o n g i t u d i n a l section s e c t i o n dipping d i p p i n g 65°N 65ON from f r o m the t h e baseline. baseline. Contours represent the value of grade times thickness C o n t o u r s r e p r e s e n t t h e v a l u e o f g r a d e t i m e s thickness (eg. ( e g . 0.2 0. 2 oz/ton o z / t o n Au Au over o v e r 50 5 0 feet f e e t == 10). 1 0 ) . The T h e contours contours are 7 5 drill d r i l l hole h o l e piercing piercing a r e based b a s e d on o n approximately a p p r o x i m a t e l y 75 points points. . �7 CAMERON LAKE SHEAR ZONE 3 15/65'- 70 S Figure F i g u r e 3: 3: Simplified S i m p l i f i e d stereographic s t e r e o g r a p h i c projection p r o j e c t i o n illustrating i l l u s t r a t i n g the the coincidence c o i n c i d e n c e of o f the t h e pitch p i t c h of o f ore o r e shoots s h o o t s with w i t h the t h e line line of o f intersection i n t e r s e c t i o n of o f the t h e Cameron Cameron Lake L a k e shear s h e a r zone z o n e and and bedding b e d d i n g controlled c o n t r o l l e d shear s h e a r zones. zones a Figure F i g u r e 4: 4: Diagramatic Diagramatic representation r e p r e s e n t a t i o n of o f the t h e spatial s p a t i a l relationship relationship between b e t w e e n ore o r e shoots s h o o t s and a n dthe t h enorth—west n o r t h - w e s t trending t r e n d i n gCameron Cameron Lake east a s t trending trending L a k e sshear h e a r zone z o n e and a n d north—east n o r t h - e a s t t to o e bedding b e d d i n g plane p l a n e shears. shears. �Figure 5: Local geology of discussed in the IÑ Cameron Lake gold deposit with the locations of outcrops text. the TI IÑ 0 m u-i a.' 0 i= >1 m c 0 .d �9 ffootwall o o t w a l l gabbro g a b b r o sill. s i l l . To the t h e north n o r t h is is a a tthin h i n interfiow interflow sedimentary unit (passive marker) which has s e d i m e n t a r y u n i t ( p a s s i v e m a r k e r ) w h i c h h a s been b e e n folded folded Several into i n t o the t h e plane p l a n e of o f the t h e shear s h e a r zone. zone. S e v e r a l early, e a r l y , stage stage markers) extension (i) ( i) e x t e n s i o n vveins e i n s (nonpassive (nonpass ive m a r k e r s ) are a r e present p r e s e n t in in this All t h i s exposure. exposure. A l l of o f these t h e s e have h a v e been b e e n shortened s h o r t e n e d and and Three buckled, b u c k l e d , commonly commonly ddisplaying i s p l a y i n g Z—fold Z - f o l d geometry. geometry. Three stage (ii) gold—bearing breccia—veins are present, one s t a g e ( i i ) g o l d - b e a r i n g b r e c c i a - v e i n s a r e p r e s e n t , one of o f which w h i c h i illustrates l l u s t r a t e s aa distinct d i s t i n c tbrecciated b r e c c i a t e d texture t e x t u r eand and howrrapidly Note how a p i d l y these these ggeometric e o m e t r i c ffit i t of o f fragments. f r a g m e n t s . Note swell. ttypes y p e s of o f veins v e i n s pinch p i n c h and a n d swell. This North STOP B. STOP B. N o r t h Trench: Trench: T h i s ooutcrop, u t c r o p , excavated e x c a v a t e d in i n 1984, 1984, is c r i t i c a l in i n terms of of understanding u n d e r s t a n d i n g the t h e geometry g e o m e t r y of of is critical Att the the t h e deposit. depos it. A t h e western w e s t e r n end e n d of o f this t h i s exposure e x p o s u r e the the intersection i n t e r s e c t i o n between b e t w e e n the t h e main m a i n shear s h e a r system s y s t e m (Cameron (Cameron Lake Lake Shear may bbe S h e a r Zone) Z o n e ) aand n d tthe h e bbedding—controlled e d d i n g - c o n t r o l l e d ssplays p l a y s may e clearly IItt is is at a t this t h i s intersection i n t e r s e c t i o n where w h e r e the t h e most most c l e a r l y seen. seen. dilatant, d i l a t a n t , permeable p e r m e a b l e conditions c o n d i t i o n s were developed d e v e l o p e d which which facilitated f a c i l i t a t e d the t h e migration m i g r a t i o n of o f the t h e gold—bearing gold-bearing hydrothermal The lline h y d r o t h e r m a l fluids. fluids. The i n e oof f intersection i n t e r s e c t i o n defines defines as defined d e f i n e d by b y drilling d r i l l i n g for for tthe h e ppitch i t c h oof f the t h e gold g o l d sshoots h o o t s as The 1 0 0 0 m. m. The large, l a r g e , sstage t a g e (ii), ( i i ), breccia b r e c c i a vein v e i n here here oover v e r 1000 The averaged 0 . 273 oz/ton o z / t o n Au Au over o v e r 22 2 2 channel c h a n n e l samples. samples. T he a v e r a g e d 0.273 is ccut u t bby y an a n array a r r a y oof f north—striking, n o r t h - s t r i k i n g , late, late, bbreccia—vein r e c c i a - v e i n is Note ( i i i ),, eenn eechelon c h e l o n eextension x t e n s i o n veins. veins. Note the the sstage t a g e (iii) bbarren, a r r e n , unaltered u n a l t e r e d bbull's u l l ' s nose n o s e structure s t r u c t u r e developed d e v e l o p e d east east of o f the t h e confluence c o n f l u e n c e of o f the t h e sympathetic, s y m p a t h e t i c , bedding—plane bedding-plane shear s h e a r and a n d the t h e main m a i n structure. structure. STOP C. Vic's The C. V i c ' s trench: trench: The extension e x t e n s i o n of o f the t h e large large breccia—vein b r e c c i a - v e i n s e e n i n t h e l a s t o u t c r o p is e x p o s e d i n t h i s t r e n c h b u t i t s s t r i k e is now p a r a l l e l t o t h a t o f t h e main m a i n sshear h e a r system. s y s t e m . To the t h e ssouth o u t h of o f the t h e breccia—vein breccia-vein occur maÂi c o c c u r relatively r e l a t i v e l y unaltered u n a l t e r e d and a n d undeformed u n d e f o r m e d mafic volcanics v o l c a n i c s and and to t o the t h e north, n o r t h , gold—bearing g o l d - b e a r i n g pervasively pervasively altered, a l t e r e d , phyllonitic p h y l l o n i t i c rocks. rocks, seen in the last outcrop is exposed in this trench but its strike is now parallel to that of the This STOP D. NC—19 trench: D c NC-19 trench: T h i s eexcavated x c a v a t e d exposure e x p o s u r e consists consists of c u t by zones z o n e s of o f cleavage cleavage o f relatively r e l a t i v e l y unaltered u n a l t e r e d basalt b a s a l t cut which w h i c h provide p r o v i d e aa small s m a l l scale, s c a l e , but b u t barren b a r r e n example e x a m p l e of t h e intersection t w o sshear h e a r systems s y s t e m s similar s i m i l a r to t o that t h a t seen seen i n t e r s e c t i o n of o f two Note the iin n the t h e north n o r t h trench. trench. Note t h e collar c o l l a r of o f DDH DDH NC—19, NC-19, 1 9 8 1 , which w h i c h intersected i n t e r s e c t e d 31.6 3 1.6 feet f e e t of o f 0.327 0. 327 ddrilled r i l l e d in i n 1981, is exposed e x p o s e d in i n Vic's Vic's o z / t o n Au (up ( u p dip d i p extension e x t e n s i o n of o f which w h i c h is oz/ton ttrench) r e n c h ) . Two distinct d i s t i n c t cleavages c l e a v a g e s and and the t h e lineat l i n e a t ion ion b e seen s e e n in i n this this pproduced r o d u c e d by b y their t h e i r intersection i n t e r s e c t i o n may may be ooutcrop. utcrop. of the . This IIsland s l a n d Trench: Trench: T h i s ooutcrop u t c r o p cconsists o n s i s ts of of basalt b a s a l t cut c u t by by aa small s m a l l quartz—feldspar q u a r t z - f e l d s p a r porphyry porphyry ddike i k e typical t y p i c a l of o f those t h o s e intersected i n t e r s e c t e d during d u r i n g drilling. drilling Although A l t h o u g h these t h e s e ddikes i k e s are a r e commonly commonly altered, a l t e r e d , they t h e y may may postdate Note the the p o s t d a t e the t h e formation f o r m a t i o n of o f the t h e gold g o l d deposit. deposit. ( i ) extension e x t e n s i o n vein v e i n which w h i c h has h a s been b e e n buckled buckled eearly, a r l y , sstage t a g e (i) (ii) aand n d rotated, r o t a t e d , and a n d the t h e fine—grained f i n e - g r a i n e d siliceous, s i l i c e o u s , stage s t a g e (ii) STOP E. STOP pillowed pillowed �10 b r e c c i a - v e i n eenveloped n v e l o p e d b ybya ap pyritic y r i t i c aalteration 1 t e r a t i o n halo. halo. breccia—vein STOP F. F. Blood B l o o d trench: t r e n c h : At A t this t h i s location l o c a t i o n we w e will w i l l examine examine STOP exposures e x p o s u r e s of o f weakly w e a k l y altered a l t e r e d and a n d cleaved c l e a v e d massive m a s s i v e and and p i l l o w e d b a s a l ts This outcrop, i n t e r p r e t e d to occur pillowed w i t h i n the t h e main m a i n shear s h e a r system, s y s t e m , does d o e s not n o t display d i s p l a y the the within pervasive p e r v a s i v e iron i r o n staining s t a i n i n g produced p r o d u c e d by b y the t h e weathering w e a t h e r i n g of of carbonates c a r b o n a t e s characteristic c h a r a c t e r i s t i c of o f the t h e outcrops o u t c r o p s tot othe t h eeast. east. However, H o w e v e r , even e v e n at a t this t h i s distance d i s t a n c e (approximately ( a p p r o x i m a t e l y 100 1 0 0 feet feet along isolated a l o n g strike) s t r i k e ) from f r o m the t h e centre c e n t r e of o f the t h e deposit, d e p o s i t , isolated stage ( i i ) brecciaveins b r e c c i a - v e i n s and andareas a r e a sofo f disseminated disseminated s t a g e (ii) pyritic p y r i t i c alteration a l t e r a t i o n are a r e found f o u n d suggesting s u g g e s t i n g that t h a t the the potential p o t e n t i a l for f o r additional a d d i t i o n a l economic e c o n o m i c gold g o l d occurrences o c c u r r e n c e s along along the t h e Cameron Cameron Lake Lake Shear S h e a r Zone Zone is is high. high. basalts. . This outcrop, interpreted to occur STOP G. G. Gabbro G a b b r o trench: t r e n c h : In I n this t h i s trench t r e n c h the t h e gabbroic qabbroic STOP sill s i l l which w h i c h occurs o c c u r s in i n the t h e footwall f o o t w a l l to t o the t h e deposit d e p o s i t isis Carbonate e x p o s e d . Note Note the t h e presence p r e s e n c e of o f quartz q u a r t z eyes. eyes Carbonate exposed. alteration a l t e r a t i o n and a n d incipient i n c i p i e n t shearing s h e a r i n g occur o c c u r on on the the northeastern n o r t h e a s t e r n edge e d g e of o f the t h e outcrop o u t c r o p indicating i n d i c a t i n g proximity p r o x i r n i t y to to the t h e footwall f o o t w a l l shear s h e a r zone z o n e and and the t h e mafic m a f i c volcanic v o l c a n i c hosts h o s t s toto t h e deposit. d e p o s i t . On On the t h e southeast s o u t h e a s t edge e d g e of o f the t h e outcrop o u t c r o p is is aa the contact c o n t a c t between b e t w e e n the t h e gabbro q a b b r o and a n d mafic m a f i c volcanics. v o l c a n i c s . This This is interpreted i n t e r p r e t e d as a s aa small s m a l l lobe l o b e of o f gabbro qabbro e x p o s u r e is exposure related t o the t h e larger l a r g e r (over ( o v e r 100 1 0 0 foot f o o t thick) t h i c k ) gabbro g a b b r o sill sill r e l a t e d to located l o c a t e d immediately i m m e d i a t e l y to t o the t h e south. south. . STOP H. H e Hunters H u n t e r ' s trench: t r e n c h : This T h i s exposure e x p o s u r e of o f sheared s h e a r e d and and STOP altered is considered c o n s i d e r e d representative representative a l t e r e d quartz—eye" " q u a r t z - e y e " gabbro g a b b r o is of o f the t h e barren b a r r e n footwall f o o t w a l l shear s h e a r zone z o n e encountered e n c o u n t e r e d during during Note Note the t h e development d e v e l o p m e n t of o f aa green g r e e n mica mica drilling drilling associated Th is green q reen a s s o c i a t e d with w i t h the t h e carbonate c a r b o n a t e alteration. a l t e r a t i o n . This mica mica is i s tentatively t e n t a t i v e l y interpreted i n t e r p r e t e d as a s aa chromium—bearing chromium-bearing phyllosilicate p h y l l o s i l i c a t e resulting r e s u l t i n g from f r o m the t h e alteration a l t e r a t i o n of o f the the gabbro g a b b r o which w h i c h contains c o n t a i n s an a n unusually u n u s u a l l y high h i g h primary p r i m a r y chromium chromium On the t h e southern s o u t h e r n margin m a r g i n of o f the t h e outcrop o u t c r o p are are c o n t e n t c On content. contacts c o n t a c t s with w i t h both b o t h unaltered u n a l t e r e d pillowed p i l l o w e d basalt b a s a l t and and sheared sheared intermediate i n t e r m e d i a t e pyroclastics. pyroclastics. I . Controversy C o n t r o v e r s y trench: t r e n c h : This T h i s outcrop o u t c r o p consists c o n s i s t s of of STOP I. STOP intermediate i n t e r m e d i a t e pyroclastics p y r o c l a s t i c s and and fine—grained f i n e - g r a i n e d bedded bedded Graded sediments G r a d e d bedding b e d d i n g indicates i n d i c a t e s an a n overturned overturned sediments. s u c c e s s i o n facing f a c i n g south. s o u t h . The T h e strike s t r i k e of o f this t h i s unit u n i t is is the the succession s m e as a s the t h e bedding—controlled, b e d d i n g - c o n t r o l l e d , sympathetic s y m p a t h e t i c splay splay same exposed o r e shoot shoot e x p o s e d in i n the t h e north n o r t h trench t r e n c h which w h i c h controls c o n t r o l s the t h e ore g e o m e t r y . Note Note the t h e thin t h i n mafic maf i c dikes d i k e s intruded i n t r u d e d along along geometry. b e d d i n q planes. planes bedding . ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS The study s t u d y of o f gold g o l d mineralization m i n e r a l i z a t i o n in i n the t h e Cameron Cameron —- Rwan Rowan Lakes Lakes The b e l t is is part p a r t of o f an a n M.Sc. PI. S c . thesis t h e s i s by b y David David R. R. Tvlelling Mell i n q in i n progress progress belt at a t Carleton C a r l e t o n University, U n i v e r s i t y , under u n d e r the t h e supervision s u p e r v i s i o n of o f David David H. H. W a t k i n s o n and and Lesley L e s l e y B. B . Chorlton. C h o r l t o n . The T h e authors a u t h o r s express e x p r e s s their their Watkinson gratitude K. Howard Howard Poulsen P o u l s e n and a n d Lesley L e s l e y B. B . Choriton C h o r l t o n for f o r their their g r a t i t u d e to t o K. d i r e c t i o n in i n the t h e field f i e l d and a n d for f o r reviewing r e v i e w i n g this t h i s contribution. contribution. direction �11 Funding provided F u n d i n g for f o r this t h i s project p r o j e c t is is in i n ppart art p r o v i d e d by b y Ontario Ontario Geoscience G e o s c i e n c e Grant G r a n t Award #193 # I 9 3 to t o David David H. H. Watkinson, W a t k i n s o n , and a n d through through the The t h e generosity g e n e r o s i t y of o f Nuinsco N u i n s c o Resources R e s o u r c e s Limited. Limited. T h e authors a u t h o r s would would also a l s o like l i k e to t o thank t h a n k Laird L a i r d Tomalty T o m a l t y and a n d Vic V i c Pitrie P i t r i e of o f Nuinsco Nuinsco Resources R e s o u r c e s Limited L i m i t e d for f o r providing p r o v i d i n g the t h e excavated e x c a v a t e d exposures. exposures. 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S e r . , scale scale 1 inch i n c h to t o 1/4 114 mile. m i l e . Geology G e o l o g y 1972. 1972. Nuinsco N u i n s c o Resources R e s o u r c e s Limited, L i m i t e d , 1983, 1983, Annual A n n u a l Report R e p o r t to t o Shareholders; Shareholders; 1 6p. 16p. 1 Schwerdtner, W.M., D., Schwerdtner, W .M., SStone, tone, D . , Osadetz, O s a d e t z , K., K., Morgan, M o r g a n , 3. J. and a n d Stott, Stott, G.M., G.M. , 1979, 1 9 7 9 , Granitoid G r a n i t o i d Complexes Complexes and a n d The The Archean A r c h e a n Tectonic Tectonic Record R e c o r d iin n The The Southern S o u t h e r n PPart a r t of o f Northwestern N o r t h w e s t e r n Ontario; O n t a r i o ; Canadian Canadian Journal J o u r n a l of o f Earth E a r t h Sciences, S c i e n c e s , Volume Volume 16, 1 6 , p.1965—1977. p . 1965-1977. Trowell, T r o w e l l , N.F., N. F . , Blackburn, B l a c k b u r n , C.E. C ÃE. and a n d Edwards, E d w a r d s , G,R., Go R . , 1980, 1980, Preliminary P r e l i m i n a r y Synthesis S y n t h e s is of o f the t h e Savant S a v a n t Lake—Crow Lake-Crow Lake Lake Metavolcanic—Metasedimentary Metavolcanic-Metasedimentary Belt, B e l t , Northwestern N o r t h w e s t e r n Ontario, O n t a r i o , and and its i t s Bearing B e a r i n g upon upon Mineral M i n e r a l Exploration; E x p l o r a t i o n ; Ontario O n t a r i o Geological Geological Survey, Accompanied S u r v e y , Miscellaneous M i s c e l l a n e o u s Paper P a p e r 89, 8 9 , 30p. 30p. A c c o m p a n i e d by b y Chart C h a r t A. A. �Geologic Setting S e t t i n g and and Style Style of of Gold Gold Mineralization M i n e r a l i z a t i o n in in the t h e Lake Lake of of The Woods Woods Area Area Introductory I n t r o d u c t o r y Discussion and and Field Field Guide Guide 31st 3 1 s t Annual Annual Institute I n s t i t u t e on on Lake Lake Superior Superior Geology Geology Kenora, Kenora, Ontario Ontario by 3,C. J . C . Davies Davies 411 41 1 Garrison Garrison Crescent Crescent Saskatoon, Saskatoon, Saskatchewan Saskatchewan P.M. P.M. Smith Smith Ontario O n t a r i o Geological Geolog i c a l Survey Survey 77 7 7 Grenville G r e n v i l l e St. StToronto, Toron t o , Ont. On t . C.E C cE Blackburn Blackburn Resident Resident Geologist Geologist Office Of % i c e Ministry M i n i s t r y of of Natural Natural Resources Resources 808 8 0 8 Robertson Robertson St. StKenora, Kenora, Ontario Ontario �14 SETTING REGIONAL GEOLOGIC GEOLOGIC SETTING --INTRODUCTION - - -,- Recent R e c e n t geological g e o l o g i c a l syntheses s y n t h e s e s (Trowell ( T r o w e l l et e t al a l 1980; 1 9 8 0 ; Blackburn B l a c k b u r n et et aL, a l . , 1985) 1 9 8 5 ) of o f the t h e western w e s t e r n Wabigoori Wabigoon Subprovince S u b p r o v i n c e of o f northwestern northwestern Ontario o tthe h e ggeneral e n e r a l cconclusion o n c l u s i o n that t h a t within w i t h i n the the O n t a r i o have h a v e led l e d tto 'greenstone" is aa general g e n e r a l chroriologic c h r o n o l o g i c pprogression rogress ion " g r e e n s t o n e " belts b e l t s there t h e r e is from mafic, from m a f i c , platformal p l a t f o r m a l volcanic v o l c a n i c sequences s e q u e n c e s upward upward into i n t o interinterClastic mediate t o felsic, f e l s i c , more pyroclastic, p y r o c l a s t i c , volcanic v o l c a n i c sequences. sequences. C las t i c m e d i a t e to with aand n d chemical c h e m i c a l ssediments e d i r n e n t s are a r e commonly commonly a associated ssociated w i t h the t h e upper upper These ssequences. equences. T h e s e ssyntheses y n t h e s e s hhave a v e i in n ggeneral e n e r a l bbeen e e n ccarried a r r i e d oout u t east east of rrecent oof f Lake Lake oof f the t h e Woods, Woods, wwhere h e r e c continuity o n t i n u i t y of e c e n t 1/4 1/4 mile m i l e geoqeologic mapping logic m a p p i n g bby y the t h e Ontario O n t a r i o Geological G e o l o g i c a l Survey S u r v e y hhas a s enabled enabled In stratigraphic s t r a t i g r a p h i c correlation c o r r e l a t i o n between b e t w e e n individual i n d i v i d u a l areas. areas. I n the the Woods (Figure 1 1 , two t w o areas a r e a s in i n which which nnorthern o r t h e r n ppart a r t oof f Lake Lake oof f the t h e Woods ( F i g u r e 1), mapping ddetailed etailed m a p p i n g hhas a s been b e e n done, d o n e , , oone n e in i n the t h e northwest, n o r t h w e s t , and a n d centred centred on Shoal Bigstone on S h o a l Lake, L a k e , aand n d the t h e oother t h e r in i n the t h e northeast n o r t h e a s t around a r o u n d Bigstone is presently Bay, are Bay, a r e separated s e p a r a t e d bby y aa central c e n t r a l area a r e a that t h a t is p r e s e n t l yunmapped. unmapped. Within t w o areas a r e a s the t h e general g e n e r a l sequence s e q u e n c e outlined outlined W i t h i n each e a c h oof f these t h e s e two above 1983): a b o v e hhas a s been b e e n demonstrated d e m o n s t r a t e d (Blackburn ( B l a c k b u r n and a n d Janes J a n e s 1983): correlation c o r r e l a t i o n oof f ssequences e q u e n c e s between b e t w e e n the t h e two t w o areas a r e a s has h a s not n o t yet y e t been been cconclusively o n c l u s i v e l y demonstrated. demonstrated In Crowduck Lake—Rush Lake-Rush Bay I n tthe h e nnorthwest, o r t h w e s t , tthe h e eeast—trending a s t - t r e n d i n g Crowduck fault f a u l t zone z o n e sseparates e p a r a t e s two t w o volcanic v o l c a n i c sequences s e q u e n c e s that t h a t can c a n be be ttentatively e n t a t i v e l y correlated, c o r r e l a t e d , notwithstanding n o t w i t h s t a n d i n g lack l a c k of o f geochronologic geochronolog i c Att Shoal iinformation, nformation. A S h o a l Lake a a lower lower mafic, m a f i c , tholeiitic t h o l e i i t i c volcanic volcanic sequence s e q u e n c e occupies o c c u p i e s the t h e core core of o f the t h e Gull G u l l Bay—Bag Bay-Bag Bay Bay anticline, a n t i c l i n e , and and is ssucceeded is u c c e e d e d upward upward oon n either e i t h e r limb l i m b by b y intermediate i n t e r m e d i a t e to t o felsic felsic At A t High High Lake, L a k e , north n o r t h of o f the t h e fault f a u l t zone, z o n e , aa ppyroclastic y r o c l a s t i c sequences. sequences. overlain lower rnafic m a f i c sequence s e q u e n c e is is o v e r l a i n unconformably u n c o n f o r r n a b l y by b y aa clastic clastic sedimentary ( Crowduck Lake Lake Group). Group). s e d i m e n t a r y ssequence e q u e n c e (Crowduck IInn tthe h e northeast, n o r t h e a s t , around a r o u n d Bigstone B i q s t o n e Bay, Bay,. recent r e c e n t mapping m a p p i n g has has demonstrated d e m o n s t r a t e d that t h a t a lower lower sequence s e q u e n c e of of mafic, maf ic, tholeiitic tholei itic core oof vvolcariics, o l c a n i c s , t that h a t llie i e iin n tthe h e core f aa bbroad r o a d ssouthwest o u t h w e s t plunging plunging are aantiform, ntiform, a r e overlain o v e r l a i n by by a a felsic f e l s i c to t o intermediate i n t e r m e d i a t e pyroclastic pyroclastic sequence e t al., a l . , 11985). 9 8 5 ) . Further F u r t h e r to t o the t h e north n o r t h in i n the the s e q u e n c e (Ayer ( A y e r et vicinity v o l c a n i c sequence s e q u e n c e that t h a t is is probably probably v i c i n i t y of o f Kenora, K e n o r a , aa mafic maf i c volcanic correlative with correlative w i t h that t h a t at a t Bigstone B i g s t o n e Bay, Bay, has h a s been b e e n isoclinally isocl i n a l l y folded f o l d e d about a b o u t nnortheast o r t h e a s t ttrending r e n d i n g axes. axes. Following F o l l o w i n g aare r e more more ddetailed e t a i l e d ddescriptions e s c r i p t i o n s of o f individual ind i v id u a l w i l l be b e visited v i s i t e d on o n the t h e field field ssub—areas, u b - a r e a s , aall l l except e x c e p t one o n e oof f which w h i c h will is included i n c l u d e d because b e c a u s e of o f its i t s key key ttrip: r i p : the t h e Shoal S h o a l Lake area a r e a is situation s i t u a t i o n in i n understanding u n d e r s t a n d i n g Lake Lake of o f the t h e Woods Woods stratigraphy, s t r a t i g r a p h y , and and t. tthe h e position p o s i t i o n of o f gold g o l d emplacement e m p l a c e m e n t wwithin i t h i n iit. - HIGH H I G H LAKE General G e n e r a l geology, g e o l o g y , adapted a d a p t e d from f r o m Davies Dav ies (1965), ( 1 9 6 5 1 , is is illustrated illustrated The ooldest 2. The l d e s t rrocks, ocks, a a thick t h i c k sequence s e q u e n c e of o f basaltic basaltic iin n Figure F i g u r e 2. and mmafic flows f l o w s and a f i c ssubvolcanic u b v o l c a n i c i intrusions, n t r u s i o n s , have h a v e been b e e n intruded i n t r u d e d by by r a n o d i o r i t e , porphyritic p o r p h y r i t i c granodiorite g r a n o d i o r i t e and a n d by porphyry porphyry t o n a l i t e , ggranodiorite, dikes. d i k e s . The T h e granitic g r a n i t i c complex c o m p l e x extends e x t e n d s west w e s t for f o r at a t least l e a s t 50 5 0 km km and, and, especially is characterized c h a r a c t e r i z e d by by e s p e c i a l l y in i n Manitoba, M a n i t o b a , the t h e dominant d o m i n a n t phase p h a s e is tonalite, �A Figure tH :1 —i HH" 1: A \ '/ 4 \ ?M?èrs / / 5I — Ar 0 lADY Figure2o 4 5 •A -- / - r - /1 'A / //-A/ I I j/, A o- - a' 4 - I — S / 'A 18athO!k L h MA4A'j Ar /4 - 7 Jot 0Figure3 K IA /// / ( WsI 'p/'4 4 /s,A AY/ / / /1/) 4t t H±1 \ A" / - C fT A I 'I Fig4 A I,? A I• / / /I / / I / / / '\ A"AA '1 AZ rugure5 Z - / )(AAAA A,AAAAAA-A / A / I ) / / A / / I 7 7- Figure 6 FI - T / / / — Dl c [ EARLY PAEAMRDIAN MIDDLE lOCATE PREY DMDAIAN PRECAMBRIAN CENOZOIC PHANEIIOZOIC h ^ J3 -^ -3 u IÑ (S n3 General geology of the Lake of the Woods Area (modified from Blackburn, 1981). 'A c Ui �91 OQ0 °O 0 . I Road Lake Shoal o + 4- )Oo C +D hO + + + + + + + + + + + + + 4 ++ + + + + + + f + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + .,++..++,+t+;+++ * + + + + + + Cl) + a — + xx \XX x x .CDOOOD) -." \x\x XXXX \xxx + + + + o O9 + + '+4' 4'-I + CD D + ++++++++++++ + +Ffl+ + + + CD ++ iU) f • + ++ + +-f + + + + C) I +nl -f + + + + + ('1++ ..+ + + + — CD _ +++ 0 V $ C) b O 3o.o 'N .m...:.:.:..:.. + oo -n Q.C)D) + .... CD nO o() + ° -. oj ++ c1;: 0O,Oo00 L \xxxx \xx \xxx + X xxxx\X X X (D X XXXXX\X ::::::::::::::::::X x xxxxxx'\ X + x X x X X x x o IÑ 0 + 11\i (1\1 3. l( c2:J 0g Ni E;;x:r# P-ij �17 euhedral e u h e d r a l microcline m i c r o c l i n e phenocrysts. p h e n o c r y s ts a At A t High High Lake, L a k e , large l a r g e basaltic b a s a l t i c blocks b l o c k s are a r e enclosed e n c l o s e d in i n and a n d cut cut by b y the t h e porphyritic p o r p h y r i t i c granodiorite g r a n o d i o r i t e and a n d related r e l a t e d dikes, d i k e s , and a n d are a r e interinterpreted t o be b e roof r o o f pendants p e n d a n t s in i n aa subvolcanic s u b v o l c a n i c intrusion. intrusion. The non— nonp r e t e d to The porphyritic p o r p h y r i t i c granodiorite q r a n o d i o r i t e locally l o c a l l y contains c o n t a i n s abundant, a b u n d a n t , small, s m a l l , round round mafic i t is is typically t y p i c a l l y less l e s s deformed d e f o r m e d than t h a n the the m a f i c inclusions; i n c l u s i o n s ; it porphyritic i t is is yyounger, o u n g e r , intruding i n t r u d i n g and and p o r p h y r i t i c granodiorite, g r a n o d i o r i t e , suggesting s u g g e s t i n g it deforming S u t h e r l a n d and a n d Colvine Colv i n e d e f o r m i n g the t h e porphyritic p o r p h y r i t i c granodiorite. g r a n o d i o r i t e . Sutherland (1979) ( 1 979 ) concluded c o n c l u d e d that, t h a t , although a 1 t h o u g h it it is is ppossible o s s i b l e that t h a t the t h e two t w o were were intruded i n t r u d e d in i n distinct d i s t i n c t events, e v e n t s , the t h e similar s i m i l a r composition c o m p o s i t i o n of o f both both rocks r o c k s suggests s u g g e s t s that t h a t they t h e y were more likely l i k e l y separate s e p a r a t e pulses p u l s e s of o f the the same s a m e intrusive i n t r u s i v e event. event. Both B o t h the t h e basalt b a s a l t and and the t h e porphyry p o r p h y r y are a r e overlain o v e r l a i n unconformably unconformably by Conglomerate, Crowduck Lake Lake Group. Group. C o n g l o m e r a t e , sandsandb y sediments s e d i m e n t s of o f the t h e Crowduck stone, s t o n e , greywacke, g r e y w a c k e , argillite a r q i l l i t e and a n d chert c h e r t have h a v e an a n apparent a p p a r e n t thickness thickness of 2 0 0 0 metres. metres. o f 2000 Tight T i g h t folding f o l d i n g of o f both b o t h the t h e sediments s e d i m e n t s and and felsic f e l s i c volcanics v o l c a n i c s is is associated a s s o c i a t e d with w i t h faulting f a u l t i n g and a n d shearing s h e a r i n g that t h a t extend e x t e n d into i n t o the t h e grano— granodiorite. d i o r i t e . The T h e over—all o v e r - a l l pattern p a t t e r n of o f both b o t h folds f o l d s and and faults f a u l t s indicates indicates dextral f a u l t s . , Within W i t h i n the the d e x t r a l movement along a l o n g the t h e east—trending e a s t - t r e n d i n g faults. porphyritic s e t of o f fractures f r a c t u r e s trends t r e n d s east— eastp o r p h y r i t i c granodiorite g r a n o d i o r i t e aa second s e c o n d set northeast. northeast. Mineralization is largely l a r g e l y confined c o n f i n e d to t o fractures f r a c t u r e s in i n the the M i n e r a l i z a t i o n is porphyritic t o shears s h e a r s in i n both b o t h the t h e adjacent adjacent p o r p h y r i t i c granodiorite g r a n o d i o r i t e and a n d to basalt b a s a l t and and the t h e overlying o v e r l y i n g conglomerate. c o n g l o m e r a t e . Molybdenite M o l y b d e n i t e and a n d chalco— chalcopyrite, a r e widely w i d e l y distributed d i s t r i b u t e d in i n the the p y r i t e , in i n trace t r a c e amounts, a m o u n t s , are porphyritic p o r p h y r i t i c granodiorite; g r a n o d i o r i t e ; they t h e y are a r e more more highly h i g h l y concentrated, c o n c e n t r a t e d , with with quartz, t o east—trending e a s t - t r e n d i n g faults, f a u l t s , and a n d are are q u a r t z , in i n shear s h e a r zones z o n e s adjacent a d j a c e n t to accompanied is also a l s o associated a s s o c i a t e d with w i t h pyrite, pyrite, a c c o m p a n i e d by b y minor m i n o r gold. g o l d . Gold G o l d is chalcopyrite and pyrrhotite in shears at or near the contact c h a l c o p y r i t e a n d p y r r h o t i t e i n s h e a r s a t o r n e a r t h e c o n t a c t with with basalt, b a s a l t , and and in i n quartz q u a r t z lenses l e n s e s and and irregular i r r e g u l a r masses m a s s e s in i n porphyry, porphyry, basalt b a s a l t or o r conglomerate c o n g l o m e r a t e where w h e r e there t h e r e are a r e complex c o m p l e x areas a r e a s of of competency A l l these t h e s e mineralization m i n e r a l i z a t i o n types t y p e s will w i l l be be c o m p e t e n c y contrast. c o n t r a s t . All illustrated 1, 22 and a n d 3). 3 ) . Pedora Pedora i l l u s t r a t e d by by field f i e l d trip t r i p stops s t o p s (Stops ( S t o p s 1, (1976) ( I 976 ) has h a s suggested s u g g e s t e d that t h a t mineralization m i n e r a l i z a t i o n is is arranged a r r a n g e d about a b o u t the the s o u t h e r n , non—porphyritic n o n - p o r p h y r i t i c granodiorite q r a n o d i o r i t e phase p h a s e in i n aa zonal z o n a l pattern, pattern, southern, and a n d that t h a t the t h e mineralizing m i n e r a l i z i n g fluid f l u i d may may have h a v e originated o r i g i n a t e d from f r o m the the southern s o u t h e r n phase. phase. SHOAL LAKE SHOAL LAKE - - General G e n e r a l geology, g e o l o g y , adapted a d a p t e d from f r o m Davies D a v i e s (1983), ( 1 983 ) , is is illustrated illustrated in Figure 3. i n F i g u r e 3. Tholeiitic T h o l e i i t i c basalts, b a s a l t s , interlayered i n t e r l a y e r e d with w i t h mafic maÂi c and and u l t r a m a f i c sills s i l l s and and minor m i n o r komatiitic k o m a t i i t i c basalts, b a s a l t s , are a r e overlain o v e r l a i n by by ultramafic calc—alkaline t o felsic f e l s i c pyroclastics. pyroclastics. Overlying c a l c - a l k a l i n e intermediate i n t e r m e d i a t e to Overlying these is an a n upper u p p e r sequence s e q u e n c e of o f mafic m a f i c flows f l o w s with w i t h some some felsic felsic t h e s e is volcanic s i l l - l i k e body body of o f anorthositic a n o r t h o s i t i c gabbro g a b b r o to to v o l c a n i c lenses. l e n s e s . AA sill—like diorite d i o r i t e (the ( t h e Stevens S t e v e n s Island I s l a n d Diorite) D i o r i t e ) lies l i e s near n e a r the t h e top t o p of o f the the tholeiitic The tthickness t h o l e i i t i c sequence. s e q u e n c e . The h i c k n e s s of o f the t h e northwest—facing n o r t h w e s t-f a c i n g volcanics is estimated e s t i m a t e d to t o be b e 9000 9 0 0 0 metres. metres. v o l c a n i c s is The The Canoe Canoe Lake L a k e stock s t o c k of o f altered a l t e r e d quartz q u a r t z diorite d i o r i t e terminates, t e r m i n a t e s , to to t h e southwest, s o u t h w e s t , against a g a i n s t the t h e tholeiitic t h o l e i i t i c basalts, b a s a l t s , and a n d aa major m a j o r anti— antithe dine i t . The The fresher f r e s h e r Snowshoe Snowshoe Bay Bay grano— granoc l i n eextends e x t e n d s southwest s o u t h w e s t from f r o m it. it d i o r i t e intruded i n t r u d e d the t h e intermediate i n t e r m e d i a t e to t o felsic f e l s i c sequence; s e q u e n c e ; it diorite continues c o n t i n u e s an a n unknown unknown distance d i s t a n c e into i n t o Manitoba M a n i t o b a and a n d is is of o f batholithic batholithic �+ + + + + + + + + + + + + + • __— + V ÷ + + + -- y/ "'i - 3: • / / —) / -. / / VOV V VVVV + + + • — • + + + + + + + + + + + -- + + V — •••. + + + + + + + + + + + + + + + + + + + + + + + + + + ÷ + + + + ÷ + + + + + + + + + + + + + + + + + + + + + + + + + + + , + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + ± + + + + + DlORlTE÷÷÷÷ + 1- + + * + + + + + + + + + + • ++ + + + + ÷ + v + + + + + + + + VV + VV + +++++++÷v VV + 2 + yyyy • VV + + + + + + + VVV : •,pc vYI__ Labyrinth Bay V VVVVVVV VVVVV OJ ::::::::::: + ++ + V + + + + 1- + + ••••,• + + + • + + + + + + + + + + + /'vvvvvvv + vvvvvv vvv + + + ÷ + +::: ' vI'vv + + + + +—* I- V + ÷ + + +' vv + + + + + + MINE+÷11+÷++÷+÷+/ .÷ + + + + + + + + *f+ + + + + V'- v + i" VV4VVVvv + + + + + / + + + + + + + + + V + + + + + + + + + + + S.. S7 Ptarmigan Bay upper volcanic rocks LIII middle cac—akahne intermediate and felsic volcanic rocks lower tholeiiflc to komatiitic mafic volcanic rocks and sills 0 + + •:•. VVV V + + + + + + + + + + + CANOE LAKE ++++++++++ + + MIKADO + + + + v• v VVV• vv V + vvvvvvvvv VVV VV VVV + + MINE vv OLYMPI V VV VV v V 0VVV VVV VVVV vSvvvV VV VVVV VVVVV vvvv VVV + + + + + + + + Echo Bay T. Geology of the Shoal. Lake area (modified from Davies and Smith, 1984). • [ij granitic intrusive rocks Figure / / / // / + + + + Day VV+++ vV Clytie vv VV • gold occurrence diorite, quartz duorite, gabbro, anorthositic gabbro —i,' / / ///1 ,> , / GRANODlORITE,/,', '/# // / — / RUSH BAY FAULT /. / CEDAR ISLAND MINE ShoalLake + + + 7 SNOWSHOE .47 + :+ + + ÷ + + + + + + + + r-4 + + — ::GROWDUCK LAKE ay �19 dimensions. d imens i o n s . In I n much much of o f the t h e Shoal S h o a l Lake L a k e area a r e a the t h e principal p r i n c i p a l foliation £0 i a t i o n direction North i s east—northeast. east-northeast. N o r t h of o f the t h e lake l a k e the t h e foliation foliation d i r e c t i o n is bends east as the Crowduck Lake—Rush Bay dextral fault is b e n d s e a s t a s t h e Crowduck Lake-Rush d e x t r a l f a u l t zone z o n e is approached. a p p r o a c h e d . Within W i t h i n aa "shadow " s h a d o w zone" z o n e " southwest s o u t h w e s t of o f the t h e Canoe C a n o e Lake Lake stock, v o l c a n i c s are a r e not n o t foliated, f o l i a t e d , but b u t aa series s e r i e s of of s t o c k , the t h e mafic ma i c volcanics east—southeast e a s t - s o u t h e a s t faults f a u l t s with w i t h aa large l a r g e vertical v e r t i c a l component c o m p o n e n t of o f movement has These are h a s offset o f f s e t the t h e volcanic v o l c a n i c stratigraphy. stratigraphy. T h e s e faults f a u l t s are interpreted i n t e r p r e t e d to t o be b e related r e l a t e d to t o emplacement e m p l a c e m e n t of o f the t h e Canoe C a n o e Lake Lake stock. Faults stock. F a u l t s with w i t h vertical v e r t i c a l displacement d i s p l a c e m e n t have h a v e also a l s o been b e e n interinterpreted p r e t e d to t o coincide c o i n c i d e with w i t h the t h e north n o r t h and and south s o u t h contacts c o n t a c t s of o f the the Snowshoe f a u l t i n q parallel p a r a l l e l to t o volcanic v o l c a n i c strati— stratiS n o w s h o e Bay Bay pluton; p l u t o n ; some faulting graphy q r a p h y may also a l s o be b e attributed a t t r i b u t e d to t o emplacement e m p l a c e m e n t of o f the t h e pluton. pluton. Most gold g o l d occurrences o c c u r r e n c e s are a r e in i n the t h e tholeiitic t h o l e i i t i c sequence. s e q u e n c e . Those Those associated a s s o c i a t e d with w i t h the t h e east—southeast e a s t - s o u t h e a s t faults f a u l t s typically t y p i c a l l y consist c o n s i s t of o f aa chioritic Silici— c h l o r i t i c shear s h e a r zone z o n e within w i t h i n which w h i c h aa felsite f e l s i t e dike d i k e occurs. occurs. Silicification, or lenses, l e n s e s , is is f i c a t i o n , commonly commonly in i n the t h e form f o r m of o f quartz q u a r t z veins v e i n s or accompanied a c c o m p a n i e d by b y pyrite, p y r i t e , traces t r a c e s of o f base—metal b a s e - m e t a l suiphides, s u l p h i d e s , and a n d rare rare visible v i s i b l e qold. g o l d . Some Some gold g o l d was w a s produced p r o d u c e d from f r o m fracture f r a c t u r e zones z o n e s of o f this this type a t the t h e Olympia O l y m p i a and a n d Cedar C e d a r Island I s l a n d Mines. Mines. t y p e at South—southeast S o u t h - s o u t h e a s t fractures f r a c t u r e s developed d e v e l o p e d near n e a r the t h e margin marg i n of o f the the Canoe At its intrusion. intrusion. A t the t h e Mikado Mikado Mine, Mine, C a n o e Lake L a k e stock s t o c k following f o l l o w i n g its gold i s associated a s s o c i a t e d with w i t h quartz q u a r t z veins v e i n s and a n d stringers s t r i n g e r s in i n such s u c h aa g o l d is fracture crosses basalt b a s a l t and a n d a thick t h i c k dike d i k e of o f quartz quartz f r a c t u r e which w h i c h crosses diorite. d i o r i t e . Pyrite, P y r i t e , chalcopyrite, c h a l c o p y r i t e , tetradymite t e t r a d y m i t e and a n d bismuthinite b i s m u t h i n i t e also also occur o c c u r in i n the t h e quartz. quartz. Fault F a u l t and a n d shear s h e a r zones z o n e s parallel p a r a l l e l to t o volcanic v o l c a n i c stratigraphy s t r a t i g r a p h y are are mostly m o s t l y narrow n a r r o w and a n d quartz q u a r t z veining v e i n i n g within w i t h i n them t h e m is is similarly s i m i l a r l y narrow narrow and a t the t h e Duport D u p o r t Mine M i n e is is much much wider, wider, a n d discontinuous. d i s c o n t i n u o u s . The T h e fault f a u l t at and a n d gold g o l d occurs o c c u r s with w i t h quartz q u a r t z in i n zones z o n e s where w h e r e competency c o m p e t e n c y contrast contrast accompanied a c c o m p a n i e d by b y brittle b r i t t l e fracturing f r a c t u r i n g resulted r e s u l t e d in i n greater q r e a t e r permepermeability There a b i l i t y (Smith ( S m i t h1984) 1 9 8 4 ). T h e r e is is a a strong s t r o n g association a s s o c i a t i o n of o f gold gold with it also a l s o occurs o c c u r s as as free f r e e grains g r a i n s associated associated w i t h arsenopyrite, a r s e n o p y r i t e , but b u t it with w i t h pyrrhotite, p y r r h o t i t e , pyrite p y r i t e and a n d chalcopyrite. chalcopyrite. . ECHO, CLEARWATER EC H O ,- ..-PTARMIGAN PTARMIGAN AND AND-------CLEARWATER BAYS BAYS 4 . - No N o recent r e c e n t systematic s y s t e m a t i c mapping m a p p i n g of o f this t h i s area a r e a has h a s been b e e n carried carried out ( 1 9 3 6 9 , but b u t it it is is ppossible o s s i b l e that t h a t most m o s t of of o u t since s i n c e that t h a t of o f Thomson Thomson (1936), the a r e equivalent e q u i v a l e n t to t o the t h e calc—alkaline c a l c - a l k a l i n e felsic felsic t h e vvolcanic o l c a n i c rocks r o c k s are sequence s e q u e n c e of o f Shoal S h o a l Lake. Lake. s e q u e n c e and a n d upper u p p e r mafic maÂi c sequence The The ddominant o m i n a n t sstructural t r u c t u r a l feature f e a t u r e is is the t h e Crowduck Crowduck Lake—Rush Lake-Rush Bay fault f a u l t zone z o n e in i n which w h i c h the t h e volcanic v o l c a n i c rocks r o c k s are a r e strongly s t r o n g l y to t o intensely intensely foliated. Carbonate is abundant, a b u n d a n t , bbut u t only o n l y in i n aa few f e w places p l a c e s is is foliated. C a r b o n a t e is there t h e r e evidence e v i d e n c e of o f much much mmobilization o b i l i z a t i o n oof f ssilica. i l i c a . Where Where deformation deformat ion has h a s been b e e n greatest, g r e a t e s t , thin t h i n quartz q u a r t z veinlets v e i n l e t s and a n d lenses l e n s e s occur o c c u r and a n d fine fine pyrite is disseminated d i s s e m i n a t e d in i n the t h e schists, s c h i s t s , but b u t only o n l y minor m i n o r amounts a m o u n t s of of p y r i t e is gold g o l d have h a v e been b e e n found. f o u n d . The T h e zone z o n e has h a s been b e e n traced t r a c e d to t o the t h e east e a s t at at least l e a s t as a s far f a r as asthe t h esouth s o u t hshore s h o r eofo fthe t h Northern e N o r t h e r nPeninsula: P e n i n s u l a : Ayer Ayer (1984) ( 1 9 8 4 ) has h a s recently r e c e n t l y suggested s u g g e s t e d its i t s continuation c o n t i n u a t i o n right r i g h t across across the the northern n o r t h e r n part p a r t of o f Lake Lake of o f the t h e Woods Woods to t o Andrew Andrew Bay. Bay. Around t o felsic f e l s i c pyroclastics pyroclas tics Around Clearwater C l e a r w a t e r Bay, Bay, intermediate i n t e r m e d i a t e to predominate p r e d o m i n a t e and a n d are a r e interlayered i n t e r l a y e r e d with w i t h basalt b a s a l t and and overlain o v e r l a i n by by fine fine clastic c l a s t i c sediments. sediments. e a s t - s t r i k i n g synclinal s y n c l i n a l axis a x i s lies l i e s along along An east—striking �20 tthe h e bbay, a y , and e l l - d e v e l o p e d ffoliation o l i a t i o n is is w i t h i n 330 0 degrees d e g r e e s of of and aa w well—developed within number oof eeast. a s t . AA number f qquartz—porphyry u a r t z - p o r p h y r y ddikes i k e s aalso l s o trend t r e n d east, e a s t , possibly possibly Quartz marking f n a r k i n q zones z o n e s of o f shearing. shearing. Q u a r t z veins v e i n s are a r e mainly m a i n l y in i n areas a r e a s of of iintermediate n t e r m e d i a t e llapilli—tuff a p i l l i - t u f f aand n d ttuff—breccia, u f  £ - b r e c c i a eespecially s p e c i a l l y in i n the the K e n r i c i a Mine Mine (Stop ( S t o p 44 on vvicinity i c i n i t y of o f the t h e former f o r m e r Kenricia on the t h e field f i e l d trip) trip). North 1 7 , foliated f o l i a t e d basalt basalt N o r t h oof f the t h e ppyroclastics, y r o c l a s t i c s , and a n d Highway 17, It with is iin outcrops o u t c r o p s over o v e r aa width w i d t h of o f i000m. 1000m. I t is n ccontact ontact w i t h granitic granitic may bbe rrocks o c k s tto o the t h e nnorth, o r t h , aand n d may e eequivalent q u i v a l e n t to t o the t h e tholeiitic tholeiitic sequence s e q u e n c e of o f Shoal S h o a l Lake. Lake. KENO RA KENORA A wedge—shaped w e d g e - s h a p e d area a r e a of o f volcanic v o l c a n i c and a n d sedimentary s e d i m e n t a r y rocks r o c k s extends extends northeast main n o r t h e a s t from f r o m the the m a i n body body oof f supracrustal s u p r a c r u s t a l rocks r o c k s in i n the the vicinity of Kenora K e n o r a (Figure ( F i q u r e 4). 4). IIntensely n t e n s e l y ddeformed e f o r m e d gneisses q n e i s s e s lie lie v i c i n i t y of tto o the t h e nnorthwest, o r t h w e s t , aand n d to t o the t h e east e a s t aare r e ggranitoid r a n i t o i d sstocks t o c k s which w h i c h may Tholeiitic be b e related r e l a t e d to t o the t h e Dryberry D r y b e r r y batholith. batholith. T h o l e i i t i c basalts b a s a l t s are are overlain o v e r l a i n by by fine—grained f i n e - g r a i n e d intermediate i n t e r m e d i a t e to t o felsic f e l s i c pyroclastics, pyroclas tics, which w h i c h are a r e in i n turn t u r n overlain o v e r l a i n by b y clastic c l a s t i c sediments. s e d i m e n t s . A gabbroic g a b b r o i c sill sill lies l i e s near n e a r the t h e top t o p of o f the t h e basaltic b a s a l t i c sequence. sequence, The principal p r i n c i p a l direction d i r e c t i o n of o f faulting, f a u l t i n g , the t h e weak to to strong strong foliation, and the trace of fold axes are all approximately f o l i a t i o n , and t h e t r a c e of f o l d axes a r e a l l approximately Att pparallel a r a l l e l to t o wedge boundaries b o u n d a r i e s and and converge c o n v e r g e to t o the t h e northeast. northeast. A the northwest side of the wedge mafic rocks are highly deformed t h e n o r t h w e s t s i d e o f t h e wedge m a f i c r o c k s a r e h i g h l y d e f o r m e d metamorphosed aand nd m e t a m o r p h o s e d bbut u t elsewhere e l s e w h e r e primary p r i m a r y features f e a t u r e s are a r e largely largely An ooval monzonite, ppreserved. reserved. An v a l sstock t o c k oof f pporphyritic o r p h y r i t i c qquartz uartz m o n z o n i t e . which which llies i e s on on tthe h e trace t r a c e of o f the t h e Airport A i r p o r t Anticline, A n t i c l i n e , is is only o n l y weakly weakly foliated. foliated. All A l l tthe h e known vvolcanic—hosted o l c a n i c - h o s t e d q gold o l d ooccurrences c c u r r e n c e s eexcept x c e p t one o n e are are are associated with quartz veins or silicified i n bbasalt a s a l t and a n d a r e a s s o c i a t e d w i t h q u a r t z v e i n s or s i l i c i f i e d in Fractured mineralized l i e in in sshears. hears. F r a c t u r e d aand nd m i n e r a l i z e d felsite f e l s i t e dikes d i k e s which w h i c h lie The mineralized ssheared h e a r e d basalt b a s a l t have h a v e also a l s o been b e e n investigated. investigated. mineralized zones z o n e s trend t r e n d northeast n o r t h e a s t and and are a r e interpreted i n t e r p r e t e d to t o be be related r e l a t e d to to Tourmaline movement along near—vertical axial planar shears, T o u m a l i n e and and movement a l o n g n e a r - v e r t i c a l a x i a l p l a n a r s h e a r s minor a r e associated a s s o c i a t e d with w i t h most most quartz q u a r t z veins; v e i n s ; chlorite, chlorite, m i n o r suiphides s u l p h i d es are hiotite, b i o t i t e , carbonate c a r b o n a t e and a n d suiphides s u l p h i d e s are a r e common common in i n the t h e sheared sheared basalt. basal t. o c c u r r e n c e s in i n the t h e Island I s l a n d Lake Lake quartz q u a r t z diorite d i o r i t e are are Gold occurrences Most of the mineralization with shearing. Most o f t h e m i n e r a l i z a t i o n is is iin n or or aassociated ssociated with shearing. Gold is near quartz veins which occupy zones of dilatancy. n e a r q u a r t z v e i n s which o c c u p y z o n e s o f d i l a t a n c y . Gold is with aassociated ssociated w i t h ppyrite, y r i t e , especially e s p e c i a l l y along a l o n g minor m i n o r ffractures r a c t u r e s in i n the the Dike—like quartz and the host diorite or quartz diorite. D i k e - l i k e bodies bodies q u a r t z a n d t h e h o s t d i o r i t e or q u a r t z d i o r i t e . e nnear e a r mmineralized i n e r a l i z e d a nand d s isilicified l i c i f i e d sshears h e a r s at at oof f ultra—mylonite u l t r a - m y l o n i t e l ilie three t h r e e ooccurrences. ccurrences Stop S t o p 5 on on the t h e field f i e l d trip t r i p illustrates i l l u s t r a t e s the t h e former f o r m e r type, t y p e , while while is hosted by the Island Lake mineralization at Stop 6 m i n e r a l i z a t i o n a t S t o p 6 is h o s t e d by t h e I s l a n d Lake quartz quartz diorite. diorite. . . BIGSTONE BAY Tholeiitic with T h o l e i i t i c basalts b a s a l ts w i t h an a n eestimated s t i m a t e d thickness t h i c k n e s s of o f 8000m 8000m are uunderlie n d e r l i e Bigstone B i g s t o n e Bay Bay aand nd a r e broadly b r o a d l y folded f o l d e d about a b o u t the t h e Hay Island Island �Fiqure 4: Geology of the Kenora area (modified from King, 1983). �22 Antiform A n t i f o r m (Figure ( F i g u r e 5). 5 ) . Mafic M a f i c and a n d ultramafic u l t r a m a f i c sills s i l l s or or flows, f l o w s , which which lie l i e near n e a r the t h e top t o p of o f the t h e sequence, s e q u e n c e , are a r e exposed e x p o s e d on o n the t h e south s o u t h limb limb of o f the t h e fold f o l d and a n d on o n the t h e northwest n o r t h w e s t limb l i m b near n e a r the t h e fold f o l d nose. n o s e . The The inafic by iintermediate t o felsic f e l s i c pyroclastics pyroclas tics r n a f i c r rocks o c k s aare r e ooverlain v e r l a i n by n t e r m e d i a t e to and a n d flows f l o w s which w h i c h occupy o c c u p y the t h e core core of o f the t h e Sultana S u l t a n a syricline; s y n c l i n e ; the the syncline t ohave h a v e been b e e n refolded refolded s y n c l i n e and a n d oother t h e r parallel p a r a l l e l folds f o l d sappear a p p e a r to about a b o u t the t h e Hay Hay Island I s l a n d Antiform. Antiform. G r a n o d i o r i t e of o f the t h e Dryberry D r y b e r r y batholith b a t h o l i t h occupies o c c u p i e s the t h e core core of of Granodiorite the B a s a l t s typically t y p i c a l l y show show little l i t t l e change c h a n g e in i n texture t e x t u r e or or t h e antiform. a n t i f o r m . Basalts The Quarry grain g r a i n size s i z e adjacent a d j a c e n t to t o the t h e contact, contact. Q u a r r y Island I s l a n d stock, stock, which w h i c h intruded i n t r u d e d the t h e top t o p of o f the t h e basalt b a s a l t sequence, s e q u e n c e , similarly s i m i l a r l y shows shows no no contact medium—grained i t consists c o n s i s t s oof f m e d i u m - g r a i n e d quartz q u a r t z diorite diorite c o n t a c t effects; e f f e c t s ; it with w i t h aa central c e n t r a l core core of o f porphyritic p o r p h y r i t i c granite g r a n i t e in i n the t h e northeast n o r t h e a s t part part of of Quarry Q u a r r y Island I s l a n d and a n d western w e s t e r n part p a r t of o f Sultana S u l t a n a Island. Island. On the t h e northwest n o r t h w e s t limb l i m b of o f the t h e antiform, a n t i f o r m , virtually v i r t u a l l y all a l l of o f the the gold to g o l d occurrences o c c u r r e n c e s are a r e associated a s s o c i a t e d with w i t h shear s h e a r zones z o n e s parallel p a r a l l e l to v o l c a n i c stratigraphy. s t r a t i g r a p h y . Quartz Q u a r t z veins v e i n s with w i t h pyrite, p y r i t e , many of o f which which volcanic contain s w e l l or or occur o c c u r as as c o n t a i n tourrnaline, t o u r m a l i n e , ttypically y p i c a l l y ppinch i n c h and a n d swell en—echelon e n - e c h e l o n lenses l e n s e s in i n the t h e chlorite c h l o r i t e schists. s c h i s t s . Visible V i s i b l e gold g o l d is is This erratically e r r a t i c a l l y distributed d i s t r i b u t e d in i n the t h e quartz. quartz. T h i s type t y p e will w i l l be b e viewed viewed a t Stop S t o p 77 on on the t h e field f i e l d trip. t r i p . On On the t h e south s o u t h limb, l i m b , the t h e volcanics volcanics at In vary v a r y in i n strike, s t r i k e , especially e s p e c i a l l y near n e a r the t h e granodiorite g r a n o d i o r i t e contact. contact. I n the the southeast s o u t h e a s t part p a r t of o f Bigstone B i g s t o n e Bay Bay and and extending e x t e n d i n g east e a s t to t o the t h e Islet Islet Lake Lake area, a r e a , several s e v e r a l east—southeast e a s t - s o u t h e a s t trending t r e n d i n g shears s h e a r s dip d i p south s o u t h and and show s h o w evidence e v i d e n c e of o f reverse r e v e r s e slip; s l i p ; the t h e shears s h e a r s are a r e carbonatized c a r b o n a t i z e d and and contain c o n t a i n pyrite p y r i t e and a n d narrow n a r r o w auriferous a u r i f e r o u s quartz q u a r t z veins. veins Several S e v e r a l old o l d workings w o r k i n g s are a r e in i n silicified s i l i c i f i e d and a n d carbonatized carbonat ized shears t o foliation f o l i a t i o n in i n the t h e intermediate i n t e m e d i a t e pyro— pyros h e a r s which w h i c h are a r e parallel p a r a l l e l to A t Middle M i d d l e Island I s l a n d aa shaft s h a f t was was sunk s u n k on o n aa strongly strongly e l a s t i c s . At clastics. carbonatized is associated a s s o c i a t e d with w i t h galena. galena. c a r b o n a t i z e d zone z o n e in i n which w h i c h gold g o l d is The T h e only o n l y important i m p o r t a n t gold g o l d production p r o d u c t i o n in i n the t h e Bigstone B i g s t o n e Bay Bay area area was west e s t sside i d e of o f Sultana S u l t a n a Island, I s l a n d , which which was aat t the t h e Sultana S u l t a n a Mine Mine oon n tthe he w Here operated 1 8 9 1 to t o 1906. 1906. Here gold—bearing g o l d - b e a r i n g vveins e i n s hosted h o s t e d by by o p e r a t e d from f r o m 1891 s h e a r e d quartz q u a r t z diorite d i o r i t e and a n d porphyritic p o r p h y r i t i c granite g r a n i t e of o f the t h e Quarry Quarry sheared most pproductive Island r e p o r t e d to t o have h a v e been b e e n most r o d u c t i v e aatt the the I s l a n d stock s t o c k were reported t w o intrusive i n t r u s i v e rocks. rocks. c o n t a c t between b e t w e e n the t h e two contact a -WITCH -- BAY Pillowed massive P i l l o w e d and and m a s s i v e tholeiitic t h o l e i i t i c basalts b a s a l t ~in i n the t h e Witch W i t c h Bay Bay area area were intruded i n t r u d e d by b y layered l a y e r e d sills s i l l s of o f peridotite p e r i d o t i t e to t o leucogabbro, l e u c o q a b b r o , and and the been t h e ssequence e q u e n c e hhas as b e e n folded f o l d e d about a b o u t east—trending e a s t - t r e n d i n g axes a x e s (Figure (Figure Intermediate 6) I n t e r m e d i a t e and a n d felsic f e l s i c volcanics v o l c a n i c s overlie o v e r 1 i e the t h e mafic maÂi c rocks. rocks. 6). Granodiorite G r a n o d i o r i t e of o f the t h e Dryberry D r y b e r r y batholith b a t h o l i t h cross—cuts c r o s s - c u t s this t h i s regional reqional f o l d structure. structure. fold Gold occurrences o c c u r r e n c e s are a r e in i n carbonatized c a r b o n a t i z e d shear s h e a r zones z o n e s iin n bbasalt. asaltis hosted h o s t e d by b y silicified s i l i c i f i e d and a n d pyritiferous p y r i t i f e r o u s schist s c h i s t or or by by The gold g o l d is The quartz t o 20 2 0 percent p e r c e n t sulphides. s u l p h i d e s c At A t the the q u a r t z veins v e i n s containing c o n t a i n i n g up up to Wendigo lie W e n d i q o mine m i n e and a n d Stella S t e l l a occurrence, o c c u r r e n c e , the t h e mineralized m i n e r a l i z e d shears s h e a r s lie stratigraphically s t r a t i g r a p h i c a l l y below b e l o w t hthe e p peridotitic e r i d o t i t i c bbase a s e o of f aa ssill. i l l . The The t o be b e at at a a ssimilar i m i l a r stratigraphic stratigraphic W i t c h Bay Bay ooccurrence c c u r r e n c e appears a p p e a r s to Witch The sshearing level. h e a r i n g is is believed b e l i e v e d to t o be b e related r e l a t e d to t o competency competency level. contrast s i l l . Two of o f these t h e s e deposits deposits c o n t r a s t between b e t w e e n the t h e basalt b a s a l t and and the t h e sill. will w i l l be b e seen s e e n on o n the t h e field f i e l d trip t r i p at a t Stops S t o p s 88 and a n d 9. 9. . �23 *** + top from grading piflow top shaft location * * shear zone and/or lineament anticline syncline + ii diabase *+ grariitoid intrusiois+. mafic intrusions ++ wacke felsic metavolcanics mafic * * * 01+2 Blindf old * DRYBERRY ++ (++ BATHOLITH Lake+*+*+*+c+# * Oblong + Lake+. top8 Figure F i g u r e 5: 5: Geology Bay aarea G e o l o g y of of the t h e Bigstorie B i g s t o n e Bay r e a (modified ( m o d i f i e d from f r o m Ayer, Ayer, 1984). 1984). �Figure 6: a.' ^-1 3 Geology of the Witch Bay area (modified from Davies and Smith, 194). �25 The T h e Wendigo W e n d i g o Mine Mine produced p r o d u c e d gold q o l d and a n d silver s i l v e r from f r o m 1936 1 9 3 6 to t o 1943 1943 and a n d copper c o p p e r during d u r i n g part p a r t of o f that t h a t period. p e r i o d . The T h e average a v e r a g e gold g o l d content content o r e was was 0.33 0 . 3 3 ounces o u n c e sper p e rtori. t o n . The T h e main m a i n quartz q u a r t z vein v e i n is is o f milled m i l l e d ore of in i n aa carbonatizecl c a r b o n a t i z e d cchloritic h l o r i t i c sshear h e a r zzone o n e which w h i c h sstrikes t r i k e s easterly e a s t e r l y and and d i p s steeply s t e e p l y north. n o r t h . The T h e vein v e i n was was up u p to to 75 7 5 cm cm wide w i d e but b u t averaged averaqed dips 30 c m , and a n d contained c o n t a i n e d up up to t o 50 5 0 percent p e r c e n t sulphides s u l p h i d e s (pyrite, (pyrite, 30 cm, p y r r h o t i t e and a n d chalcopyrite) c h a l c o p y r i t e ) as a s stringers s t r i n g e r s and a n d small s m a l l masses m a s s e s which which pyrrhotite are a r e concentrated c o n c e n t r a t e d at a t edges e d g e s of o f veins. veinsa CONTROLS ON MINERALIZATION MINERALIZATION CONTROLS ON ------------- Recent R e c e n t work w o r k by b y Davies D a v i e s and a n d Smith S m i t h (1984) ( 1 9 8 4 ) has h a s shown s h o w n that t h a t in i n the the q e n e r a l Lake L a k e of o f the t h e Woods Woods area: area: general 1 . The T h e majority m a j o r i t y of o f gold g o l d occurrences o c c u r r e n c e s are a r e hosted h o s t e d by b y tholeiitic tholeiitic 1. basalts s t r a t i g r a p h i c a l l y below below felsic f e l s i c volcanic volcanic b a s a l t s that t h a t occur o c c u r stratigraphically sequences sequences The T h e major major past—producing p a s t - p r o d u c i n g mines m i n e s (eg. ( e g . Wendigo) W e n d i q o ) and a n d the t h e recently recently active a c t i v e Duport D u p o r t property p r o p e r t y occur o c c u r near n e a r the t h e top t o p of o f this t h i s tholeiitic tholeiitic where preliminary p r e l i m i n a r y data d a t a indicate i n d i c a t e aa higher h i g h e r iron i r o n magnesium magnesium s e q u e n c e , where sequence, ratio. ratio. 2. 2. All A l l of o f the t h e occurrences o c c u r r e n c e s are a r e associated a s s o c i a t e d with w i t h faults f a u l t s or o r shear shear Most gold production has come from shears which Most g o l d p r o d u c t i o n h a s come f r o m s h e a r s w h i c h are are zones. zones. nearly n e a r l y parallel p a r a l l e l to t o volcanic v o l c a n i c stratigraphy. stratigraphy. 3. 3. 4. Hydrothermal H y d r o t h e r m a l solutions s o l u t i o n s were were rich r i c h in i n silica s i l i c a and a n d carbon carbon 4. most were were enriched e n r i c h e d in i n sulphur, s u l p h u r , potassium p o t a s s i u m and a n d boron. boron. d i o x i d e , and a n d most dioxide, Gold 5. G o l d may may have h a v e been b e e n carried c a r r i e d as a s aa sulphur s u l p h u r complex c o m p l e x in i n these these 5. solutions: its precipitation may have been enhanced by combining s o l u t i o n s : i t s p r e c i p i t a t i o n may h a v e b e e n e n h a n c e d b y combining sulphur s u l p h u r with w i t h iron. i r o n . If I f such s u c h conditions c o n d i t i o n s prevailed, p r e v a i l e d , iron—rich iron-rich basalts may have been the preferred site f o r gold g o l d deposition. deposition. b a s a l t s may h a v e b e e n t h e p r e f e r r e d s i t e for LE DGEM ENTS ACKNOWLE ACKNOW DGEMENTS Thanks t o : Bernard B e r n a r d Guarnera G u a r n e r a of o f Boise Boise Cascade Cascade T h a n k s are a r e due d u e to: Corporation, t o work work on o n the t h e Scramble S c r a m b l e property p r o p e r t y and and C o r p o r a t i o n , for f o r permission p e r m i s s i o n to for r e l e a s e of o f geological g e o l o q i c a l maps, m a p s , and a n d to t o Mike Mike Parr P a r r for for f o r the t h e release stimulating s t i m u l a t i n g discussion d i s c u s s i o n of o f the t h e epigenetic e p i q e n e t i c versus v e r s u s syngenetic synqenetic evidence a t the t h e Scramble; S c r a m b l e ; numerous n u m e r o u s students s t u d e n t s from f r o m the t h e University University e v i d e n c e at of Manitoba who under the direction of Lorne Ayres and o f M a n i t o b a who u n d e r t h e d i r e c t i o n o f Lome A y r e s a n d Bill Bill Brisbin, B r i s b i n , have h a v e cleared c l e a r e d outcrop o u t c r o p over o v e r many many years y e a r s at a t the t h e Conglomerate Conqlomerate Zone Zone unconformity; u n c o n f o r m i t y ; and a n d to t o Mike Hailstone H a i l s t o n e for f o r his h i s enthusiastic enthusiastic work Wajax pump pump during d u r i n g preparation p r e p a r a t i o n for f o r this t h i s field f i e l d trip. trip. w o r k with w i t h aa Wajax �26 ThE THE -- ------- IINTRODUCTION NTRODUCTION FIELD --TRIP TRIP field The f i e l d ttrip r i p route r o u t e utilizes u t i l i z e s existing e x i s t i n g roads r o a d s and a n d highways, highways, is designed d e s i g n e d to t o examine e x a m i n e major m a j o r aspects a s p e c t s of o f Lake Lake of of the t h e Woods aand n d is gold g o l d occurrences o c c u r r e n c e s without w i t h o u t going g o i n g onto o n t o the t h e lake l a k e itself. itself. 1, the t h e trip t r i p commences commences near n e a r the the On the t h e afternoon a f t e r n o o n of o f Day Day 1, Manitoba t o vview i e w sseveral e v e r a l ooccurrences c c u r r e n c e s within w i t h i n and a n d marginal marginal M a n i t o b a border, b o r d e r , to It tto o tthe h e High H i g h Lake Lake stock. stock. I t then t h e n pproceeds r o c e e d s east e a s t along a l o n g Highway Highway 17 17 (Trans Canada Highway) ttowards (Trans C a n a d a Highway) o w a r d s Kenora, K e n o r a , with w i t h one o n e stop s t o p along a l o n g the the r e c e n t past—producers past-producers way at a t the t h e Kenricia K e n r i c i a Mine, Mine, one o n e of o f the t h e more recent iin n the t h e area. area. On the 2, we w e will w i l l examine e x a m i n e aa number number of of t h e morning m o r n i n g of o f Day Day 2, mafic lowermost ma i c volcanics v o l c a n i c s of o f the t h e Kenora Kenora ooccurrences c c u r r e n c e s within w i t h i n the t h e lowermost 2, occurrences o c c u r r e n c e s are a r e viewed v i e w e d near near aarea. r e a . On the t h e afternoon a f t e r n o o n of o f Day Day 2, These Witch W i t c h Bay, Bay, including i n c l u d i n g the t h e former—producing f o r m e r - p r o d u c i n g Wendigo Wendigo Mine. Mine. These occurrences l i e in i n the t h e upper u p p e r part p a r t of o f the t h e lower lower mafic m a f i c volcanics, volcanics, o c c u r r e n c e s lie near with predominantly n e a r the t h e ccontact ontact w i t h the t h e ooverlying v e r l y i n g ccalc—alkaline, a l c - a l k a l h e f predominantly pyroclastic p y r o c l a s t i c suite. suite. DAY -- 1 1 Proceed P r o c e e d west w e s t from f r o m McLeod McLeod Park P a r k (Husky ( H u s k y the t h e Muskie) M u s k i e ) in i n Keriora Kenora along Highway 17 to the Shoal Lake Road turn off, a distance t o t h e S h o a l Lake t u r n o f f , a d i s t a n c e of of a l o n g Highway The 444 4 km. T h e Trans T r a n s Canada C a n a d a Highway runs r u n s parallel p a r a l l e l to, t o , and a n d in i n general general t o the t h e ssouth o u t h oof, f , the t h e boundary b o u n d a r y between b e t w e e n the t h e Wabiqoon Wabigoon and and jjust u s t to English E n q l i s h River R i v e r Suhprovinces. Subprov i n c e s Proceed Turn T u r n left l e f t (south) ( s o u t h ) on o n the t h e Shoal S h o a l Lake Lake road. road. P r o c e e d 2.8 2 . 8 km to to From this Laker oroad, the t h e High H i g h Lake a d , a aggravel r a v e l rroad o a d oon n t the h e rright. ight. From t h i s point point 3 . 2 km km aalong l o n g tthe h e ggravel r a v e l road r o a d to t othe t h eEvenlode E v e n l o d e molybdenite molybdenite pproceed r o c e e d 3.2 off Eco Explorations Eco E x p l o r a t i o n s LLtd. t d . aatt the t h e east e a s tend end of o fHigh H i q h Lake. Lake. pproperty roperty o . MINE STOP --1 EVENLODE EVENLODE MOLYBDENITE-GOLD MINE (F i(Figure g u r e 77)) --MJLYBDENITE—GOLD ----1 a Att the A t h e Evenlode E v e n l o d e property p r o p e r t y aanumber number of o f molyhdenitemolybdenitebearing quartz veins occur within ductile b e a r i n g q u a r t z v e i n s o c c u r w i t h i n d u c t i l e shear s h e a r zones z o n e s in in H i g h Lake Lake ssubvolcanic ubvolcanic tthe h e pporphyritic o r p h y r i t i c pphase h a s e of o f the t h e High The iintrusion. ntrusion. The vveins e i n s contain c o n t a i n low l o w to t o trace t r a c e amounts a m o u n t s of of ggold old. Four F o u r vveins e i n s of o f molybdenite—bearing r n o l y b d e n i t e - b e a r i n g qquartz u a r t z have h a v e been been The major identified i d e n t i f i e d on o n this t h i s property. property. The m a j o r ssurface u r f a c e and and work hhas 1 or No. No. 1 uunderground n d e r g r o u n d work a s bbeen e e n ddone o n e on o n the t h e Main, Main, or vein, v e i n , the t h e most recent r e c e n t work being b e i n g by b y Eco Eco Molybdenite Molybdenite The hheadframe Mines Ltd. t o 1982. 1982. The e a d f r a m e is is still still Mines L t d . from f r o m 1980 1 9 8 0 to standing, but the mill was removed from the site s t a n d i n g , b u t t h e m i l l was removed f r o m t h e s i t e in in 1984. 1 9 8 4. "The main 'The m a i n vein v e i n is is associated a s s o c i a t e d with with a a sstrong t r o n g shear shear zone z o n e striking s t r i k i n gabout a b o u tN.800W, N . ~ O ~ W and a, n d dipping d i p p i n g about a b o u t 80°N 8 0 0 ~in in its i t s central c e n t r a lportion, p o r t i o n ,but b u tmore more shallow s h a l l o w to t o the t h e east e a s tand and west. Obliteration development west. O b l i t e r a t i o n of o f feldspar f e l d s p a rphenocrysts, p h e n o c r y s ts , development of sericite, and minor silicification occur a d j a c e n t to to o f s e r i c i t e , a n d m i n o r s i l i c i f i c a t i o n o c c u r adjacent tthe h e shear s h e a r zone z o n e in i n which w h i c h qquartz u a r t z vveins, e i n s , lenses l e n s e s and and �_____ ______ _______ 27 + + + t + + -- + + + + , High High Lake Lake + + + + + + + + + + + + + + + + + + + + ÷ + + / + + + +' ++ + , , , - Figure F i g u r e 77 ; , , ' + + + -'+ + + + + + \\trench-4- + + + + + + + _+++ + + —_4 + + + + + + + + + + + + + + + + + + + + + -4- + + + + + + + 4- + + + + + + •-4- + + + + + + + + + + + + + + + + + + + + + + + + 4- + + + + + + + ÷ + + + + + --÷ + + + + + 1__ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + - + 4-J porphyritic granodiorite j-j basalt B " 'C' . — Stop 1 development muck -.... Geology o f the t h e Evenlode E v e n l o d e Molybdenite—Gold M o l y b d e n i t e - G o l d Mine Mine (after ( a Ât e r G e o l o g y of company company plans, p l a n s ,Assessment A s s e s s m e n tFiles F i l e sKeriora) Kenora) - + + + + tonallte and granodlorlte _—projection of veins to surface metadiabase 'ocations I + + + ÷ + 4- + + + + + 4- + + + ÷ + + + + + + + + + + + + + +4- + + ÷ + + + +,V —+++•+ + + + + +7 + + ++ +4+ + + + + + + + + + + 4- + + + + + + ÷ + + + + + + + + + + + + + + 4:++ + + - + + + + + + + + + +++ + + 4- + + +_•-+- + + + + 4- + + + + ++ +.+ +.++ + + + + + + + 4- - + + + +_--, 4-:÷ + + + + + ÷ + 4- + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + - + + + + + + + + \\ ++ + + + + + + + + + + + +\\ + + +'— + + + + + + + + 4- + + + ,pI—( w + + ± 4- + , , + + %f,-i ++ + : + - + +-+ + +,+ -+ + ,+ ++ +'+ + ++ ÷÷ + + -'+ + ÷shaft + -+ + +-V++ + + - + + +_ p 1— 4-/7+ 4 + 4- +.+ + + + + + + + + ++ ++ + + + + + + + +IjI, + +__.—-..+ ' + + + + + + �28 stringers s t r i n g e r s are a r e found. f o u n d . The T h e shear s h e a r zone z o n e has h a s been b e e n traced t r a c e d for for about a b o u t 2300 2 3 0 0 feet, f e e t , the t h e eastern e a s t e r n 1600 1 6 0 0 feet f e e t being b e i n g that that 'Drill— portion 'Drillp o r t i o n containing c o n t a i n i n g mineralized m i n e r a l i z e d quartz quartz.. indicated i n d i c a t e d ore' o r e ' over o v e r aa length l e n g t h about a b o u t 1200 1 2 0 0 feet...., feet.. r across across an a n average a v e r a q e width w i d t h of o f 4.7 4 . 7 feet, f e e t , and a n d to t o an a n average a v e r a g e depth d e p t h of of 508 5 0 8 feet, f e e t , has h a s been b e e n calculated c a l c u l a t e d at a t about a b o u t 126,000 1 2 6 , 0 0 0 tons tons grading p.51 ) . g r a d i n g 0.68 0 . 6 8 percent p e r c e n t molybdenite" m o l y b d e n i t e " (Davies, ( D a v i e s , 1965, 1 9 6 5 , p.51). Bulk B u l k sampling s a m p l i n g gave g a v e aa higher h i g h e r grade g r a d e (0.87 ( 0 . 8 7 percent percent molybdenite) 0.5 m o l y b d e n i t e ) and a n d 0.015 0 . 0 1 5 ounces o u n c e s of o f gold g o l d per p e r ton t o n (about ( a b o u t 0.5 grams g r a m s of o f gold g o l d per p e r tonne). tonne). The No. 2 2 vein v e i n ssystem, y s t e m , to t o the t h e southwest, s o u t h w e s t , trends trends T h e No. northeast n o r t h e a s t and a n d consists c o n s i s t s of o f one o n e dominant d o m i n a n t quartz q u a r t z vein v e i n and and several s h e a r zone z o n e 30—80 3 0 - 8 0 feet feet s e v e r a l subsidiary s u b s i d i a r y veins v e i n s within w i t h i n aa shear t r a c e d for f o r 700 700 w i d e . The The dominant d o m i n a n t vein, v e i n , which w h i c h has h a s been b e e n traced wide. feet, " is reported r e p o r t e d to t o average a v e r a q e 0.47 0 . 4 7 percent p e r c e n t molybdenite molybdenite f e e t , "is 2.2 foot f owidth, o t w with i d t hgold , waveraging i t h g o l .02—.05 d averaging .02-.05 o v e r aa 2.2 over The ounces is o u n c e s per p e r ton" t o n " (Davies, ( D a v i e s , 1965, 1965,, p.51) 0.51). T h e vvein e i n is The poorly be vvisited. p o o r l y exposed e x p o s e d a and n d wwill i l l nnot o t be isited. The No. N o . 33 vein vein strikes s t r i k e s northwest n o r t h w e s t and and dips d i p s 450 4 5 0 to t o 800 8 0 ^ northeast, n o r t h e a s t , with w i t h an an estimated 1 - 2 ppercent e r c e n t molybdenite. molybdenite. A A shaft s h a f t was was e s t i m a t e d grade g r a d e of o f 1—2 sunk fromiitt covers s u n k nnear e a r this t h i s vein v e i n arid a n d muck muck from c o v e r s the t h e vein vein completely. completely. . .. . .. Locality L o c a l i t y AA An An ooutcrop u t c r o p oof f unaltered u n a l t e r e d granodiorite, granodiorite, ----porphyry phase t y p i c a l oT the t h e p o r p h y r y p h a s e of o f the t h eHigh H i g h Lake Lake €TTT intrusion, occurs close to the road at the entrance to i n t r u s i o n , o c c u r s close t o t h e r o a d a t t h e e n t r a n c e t o the t h e property. p r o p e r t y . The T h e rock r o c k is is characterized c h a r a c t e r i z e dby b yrounded rounded quartz q u a r t z and a n d subhedral s u b h e d r a l plagioclase p l a g i o c l a s e phenocrysts p h e n o c r y s ts in i n an an aphanitic a p h a n i t i c matrix. matrix. main is exposed Locality L o c a l i t y BB The The m a i n vvein e i n is e x p o s e d iin n a a trench t r e n c h through through -----w h i c h a small s m a l l stream s t r e a m drains. drains. which £4olybdenite—bearing M o l y b d e n i t e - b e a r i n g quartz quartz occurs o c c u r s in in a a silicified s i l i c i f i e d shear s h e a r zone z o n e in i n which w h i c h the the was accompanied a c c o m p a n i e d by by d e s t r u c t i o n of o f feldspar f e l d s p a r pphenocrysts h e n o c r y s ts was destruction s e r i c iitt ii zzat a t iion. on. seric vei Locality A ffourth o u r t h vein, v e i n , between b e t w e e n the t h e No. No. 2 2 and a n d No. N o . 33 L o c a l i t y CC A G f n a s " been b e e n uncovered u n c o v e r e d in i n the t h e north n o r t h part p a r t of of a a 60 6 0 mm t r e n c h . The The 'vein' ' v e i n g strikes s t r i k e sabout a b o u tN1O0W. ~ 1 0 0 ~ddips i.p s ssteeply teeply trench. w e s t and a n d consists c o n s is ts of o f aa shear s h e a r zone z o n e in i n which w h i c h there t h e r e are are west narrow, is n a r r o w , discontinuous d i s c o n t i n u o u s quartz q u a r t z veins. v e i n s . Pyrrhotite P y r r h o t i t e is Assay associated a s s o c i a t e d with w i t h the t h e molybdenite. molybdenite. A s s a y data d a t a for f o r the the vein v e i n are a r e not n o t available. available. From the t h e Evenlode E v e n l o d e property p r o p e r t y return r e t u r n 2.2 2. 2 km km along a l o n g the t h e High H i q h Lake Lake The q r a n o d i o r i t e and road. T h e road r o a d ppasses a s s e s first f i r s t through t h r o u g h porphyritic p o r p h y r i t i c granodiorite and road. At then is cut c u t by b y porphyry. porphyry. A t the t h e northernnorthernt h e n through t h r o u g h basalt b a s a l t which w h i c h is most point p o i n t in i n the t h e road, r o a d , aa small s m a l l amount a m o u n t of o f gold g o l d and a n d silver s i l v e r was was recovered r e c o v e r e d from f r o m irregular i r r e g u l a r zones z o n e s of o f quartz q u a r t z exposed e x p o s e d in i n pits p i t s just just The north n o r t h of o f the t h e road. road. T h e surface s u r f a c e geology g e o l o g y here h e r e demonstrates d e m o n s t r a t e s the the Stop complexity c o m p l e x i t y of o f the t h e basalt—porphyry b a s a l t - p o r p h y r y relationship. relationship. S t o p near n e a r the the From the gate; t o the t h e north n o r t h is i s porphyry. porphyry. t h e parking p a r k i n g point point g a t e ; outcrop o u t c r o p to metrest to walk o aa fflagged l a g g e d ttrail, r a i l , and a n d south s o u t h on on the the w a l k east e a s t about a b o u t 120 1 2 0 metres t o Stop S t o p 2. 2. t r a i l to trail �29 STOP_2 STOP --- 2 THE BASE B A S E OF THE CROWDUCK LAKE LAKE GROUP: GROUP: THE THE UNCONFORMITYANDTHE CONGLOME~TEZONE" GOLD PROSPECT " --PA-------- At A t tthis h i s stop s t o p aa rather r a t h e rspectacular s p e c t a c u l a rexposure e x p o s u r e of o f the the unconformity t h e base b a s eofo fthe t hCrowduck e C r o w d u c k Lake L a k e Group G r o u p is is u n c o n f o r m i t y aatt the in i n close c l o s e proximity p r o x i m i t y to t o aa minor m i n o r but b u t structurally structurally significant s i g n i f i c a n t gold g o l d occurrence, o c c u r r e n c e , the t h e Conglomerate C o n g l o m e r a t e Showing. Showing. Locality B a s a l t , and a n d porphyry p o r p h y r y dikes d i k e s related r e l a t e d to t o the the L o c a l i t y A Basalt, iiTgfTLakeintrusion, a r e present p r e s e n t in i n the t h e western w e s t e r n part p a r t of of H i g h L a k e i n t r u s i o n , are this outcrop area and are overlain unconformably by t h i s o u t c r o p a r e a and are o v e r l a i n unconformably by sediments The s e d i m e n t s of o f the t h e Crowduck C r o w d u c k Lake Lake Group. Group. T h e sketch s k e t c h map by by Beakhouse ( t h i s volume, v o l u m e , p.86) p.86 ) illustrates i l l u s t r a t e s three three B e a k h o u s e (this sedimentary s e d i m e n t a r y units u n i t s that, t h a t , over—all, o v e r - a l l , show s h o w coarsening coarsening upward, s i l t s t o n e s and and thinly t h i n l y bedded bedded u p w a r d , from f r o m cherty c h e r t y siltstones sandstones s a n d s t o n e s at a t the t h e base, b a s e , through t h r o u g h pebbly p e b b l y sandstone s a n d s t o n e into into conglomerate. In addition, massive to thickly bedded conglomerate. I n add i t i o n , m a s s i v e t o t h i c k l y bedded sandstones s a n d s t o n e s occur o c c u r iin n the t h e north n o r t h part p a r t of o f the t h e outcrop o u t c r o p area. area. Relationships a r ecomplicated c o m p l i c a t e d by by R e l a t i o n s h i p s between b e t w e e n tthese h e s e units u n i t s are syn—depositional t h e original o r i g i n a l highly highly s y n - d e p o s i t i o n a l erosion e r o s i o n and a n d by the irregular i r r e g u l a r surface s u r f a c e upon u p o n which w h i c h deposition d e p o s i t i o n occurred. occurred. Noteworthy N o t e w o r t h y features f e a t u r e s at a t the t h e surface s u r f a c e of o f the t h e unconformity unconformity include; most notably i n c l u d e ; aa regolith, r e g o l i t h , most n o t a b l y developed d e v e l o p e d above a b o v e aa porphyry p o r p h y r y dike; d i k e ; possible p o s s i b l e evidence e v i d e n c e of o f syn—depositional syn-depos i t i o n a l faulting f a u l t i n g at a t the t h e southern s o u t h e r n contact c o n t a c t of o f the t h e porphyry p o r p h y r y with with basalts; b a s a l t s ; local l o c a l provenance p r o v e n a n c e of o f basaltic b a s a l t i c clasts c l a s t s in i n aa lens lens of o f conglomerate. conglomerate. The conglomerate is characteristically c h a r a c t e r is t i c a l l y heterolithic; h e t e r o l i t h ic; c o n g l o m e r a t e is porphyry clasts are predominant and conspicuously p o r p h y r y c l a s t s a r e p r e d o m i n a n t and c o n s p i c u o u s l y larger larqer than a n d felsic felsic t h a n oother t h e r types, t y p e s , which w h i c h include i n c l u d e mafic maf i c and volcanics, v o l c a n i c s , chert c h e r t and a n d iron i r o n formation. format ion. Soft—sediment deformation Sof t - s e d i m e n t d e f o r m a t i o n s t rstructures u c t u r e s i in n tthe h e finer finer sedimentary s e d i m e n t a r y rocks r o c k s include i n c l u d e slump s l u m p folds, f o l d s , load l o a d casts, c a s t s , and and flame f l a m e sstructures. tructures. is at a thigh h i g h angles a n g l e s to tobedding, b e d d i n g , and a n d parallel parallel F o l i a t i o n is Foliation to Minor t o clast c l a s t elongation e l o n g a t i o n and a n d fold f o l d axial a x i a l planes. planes. M i n o r folds folds show s h o w geometry g e o m e t r y similar s i m i l a r to t o regional—scale r e g i o n a l - s c a l e folding. folding. Quartz Q u a r t z and a n d qquartz—tourmaline u a r t z - t o u r m a l i n e v e veinlets i n l e t s f ifill l l fractures fractures in some l a s t s . The T h e vveinlets e i n l e t s are a r e oblique o b l i q u e to to i n s o m e pporphyry o r p h y r y cclasts. foliation f o l i a t i o nand a n dcommonly commonly pproject r o j e c t into i n t o the t h econglomerate conqlonerate matrix, c l e a r l y indicating i n d i c a t i n g their t h e i r late l a t e emplacement. emplacement. m a t r i x , clearly this point we return to the road, walk west to the gate and From t h i s p o i n t w e r e t u r n t o t h e r o a d , w a l k west t o t h e g a t e a n d south s o u t h 20m 20m t through h r o u g h t the h e bbush u s h tto o the t h e open o p e n outcrop o u t c r o p area. area. Locality PROSPECT L o c a l i tB y CONGLOMERATE B CONGLOMERATE PROSPECT ( F(Figure i g u r e 8) 8) ----- An embayment An embayment o f of t hthe e b basal a s a l cconglomerate o n q l o m e r a t e aat t this this location 1 5 m and a n d is is l o c a t i o n has h a s an a n average a v e r a g e width w i d t h of o f about a b o u t15m exposed exposed over The conglomerate o v e r aa length l e n g t h of o f 95m. 95m. c o n g l o m e r a t e is is enclosed e n c l o s e d t o t h e s o u t h , w e s t a n d n o r t h by f o l i a t e d b a s a l t and a n d consists c o n s i s t s of o f subrounded s u b r o u n d e d clasts c l a s ts in i n aa strongly s t r o n g l y foliated foliated to the south, west and north by foliated basalt �Filire B: 0Q 00 IKE 00 30 o metres ic QOC ROAD 0 Q of ooQooOa0 Q o oo0oo —— — — S Geolo'iy of the Canqiornerate Zone coil Pros[)ec (adapt.l from Davie , 1965). B trench stop location - GATE U �31 dark d a r k wacke w a c k e matrix. m a t r i x . Clasts C l a s t s are a r e mostly m o s t l y quartz q u a r t z porphyry porphyry and a n d granodiorite, q r a n o d i o r i t e , with w i t h lesser l e s s e r amounts a m o u n t s of o f feidsoar felds~ar p o r p h y r y and a n d mafic maÂi c volcanics, v o l c a n i c s , all a l l of o f which w h i c h may may have h a v e been been porphyry locally There is no n o distinct d i s t i n c t bedding, bedding, l o c a l l y derived. derived. T h e r e is although c l a s t size s i z e in i n general g e n e r a l increases i n c r e a s e s to to the t h e west. west. a l t h o u g h clast Clast C l a s t elongation, e l o n g a t i o n , which w h i c h is is slightly s l i g h t l y greater g r e a t e r near near contacts is parallel p a r a l l e l to t o the t h e east—trending east- t r e n d i n g c o n t a c t s with w i t h basalt, b a s a l t , is foliation; r a t i o s are a r e about about f o l i a t i o n ; average a v e r a g e width: w i d t h : length: l e n g t h : depth d e p t h ratios 1:2. 1 : 2 . 55:4. : 4. The ggeometric e o m e t r i c and a n d spatial s p a t i a l relationships r e l a t i o n s h i p s between b e t w e e n the the conglomerate c o n g l o m e r a t e and a n d basalt, b a s a l t , combined c o m b i n e d with w i t h the t h e strong strong east—trending eas t - t r e n d i n g foliation, f o l i a t i o n , suggest s u g g e s t that t h a t the t h e embayment embayment of of sediments s e d i m e n t s may may have h a v e been b e e n modified m o d i f i e d by b y tight t i g h t folding f o l d i n g about about a ssynclinal y n c l i n a l axis a x i s plunging p l u n g i n q 650 6 5 0 in i n an a n easterly e a s t e r l y direction. direction. Quartz Q u a r t z is is mainly m a i n l y present p r e s e n t as as lenses, l e n s e s , thin t h i n veins v e i n s and and irregular masses which w h i c h cut c u t across foliation, £0 i a t i o n , especially especially i r r e g u l a r masses in Quartz a l s o occurs o c c u r s in in i n the t h e vicinity v i c i n i t y of o f the t h e pit. pit. Q u a r t z also tension c l a s t s and a n d in i n aa t e n s i o n fractures f r a c t u r e s in i n aa few f e w granitic g r a n i t i c clasts porphyry p o r p h y r y dike d i k e in i n schistose s c h i s t o s e basalt b a s a l t at a t the t h enorth n o r t h edge e d q e of of the t h e outcrop. outcrop. P y r i t e is p r e s e n t i n p o c k e t s i n t h e irregular o f quartz q u a r t z and a n d as as disseminations d i s s e m i n a t i o n s in in i r r e g u l a r masses of quartz q u a r t z veins v e i n s and a n d along a l o n g slip s l i p and a n d foliation f o l i a t i o n planes, planes, especially e s p e c i a l l y in i n the t h e conglomerate c o n g l o m e r a t e matrix. matrix. M i n o r tourmaline tourmaline Minor is is also a l s o associated a s s o c i a t e d with w i t h the t h e quartz. quartz. The was the t h e source s o u r c e of o f aa 76 7 6 ton t o n bulk b u l k sample s a m p l e from from T h e pit p i t was which 0. 14 oz. o z . per p e r ton t o n was was w h i c h an a n average a v e r a g e gold g o l d recovery r e c o v e r y of o f 0.14 obtained o b t a i n e d in i n 1939. 1939. Extensive E x t e n s i v e drilling d r i l l i n g and a n d channel channel sampling was undertaken u n d e r t a k e n in i n 1944, 1 9 4 4 , but b u t only o n l y 11 1 1 core core s a m p l i n g was samples s a m p l e s of o f greater g r e a t e r than t h a n 1.5m 1.5m length l e n g t h had h a d gold g o l d assays assays exceeding The erratic 0.08 oz o z per p e r ton. ton. e r r a t i c nature n a t u r e of o f the the e x c e e d i n g 0.08 i s demonstrated d e m o n s t r a t e d by b y aa 1.8m 1.8m intersection intersection m i n e r a l i z a t i o n is mineralization which w h i c h assayed a s s a y e d 1.48 1 . 4 8 ounces o u n c e s of o f gold g o l d per p e r ton t o n (Davies, ( D a v i e s , 1965, 1965, p . 335) 5). p. The T h e presence p r e s e n c e of o f gold g o l d in i n quartz q u a r t z which w h i c h cuts c u t s across across foliation, f o l i a t i o n , indicates i n d i c a t e s the t h e late— l a t e - or o r post—tectonic p o s t - t e c t o n i c timing timing of o f mineralization. mineralization. Pyrite is present in pockets in the Return R e t u r n to t o the t h e Shoal S h o a l Lake Lake road, r o a d , turn t u r n left l e f t (north), ( n o r t h ) , and a n d proceed proceed about a c r o s s outcrops o u t c r o p s of of a b o u t 150m. 150m. Walk east e a s t along a l o n g aa trail t r a i l across conglomerate c o n g l o m e r a t e to t o the t h e Arsenic A r s e n i c Zone. Zone. - STOP 33--ARSENIC ZONE 9) ZONE GOLD PROSPECT PROSPECT (Figure (Figu ------GOLD --- The Arsenic A r s e n i c Zone Zone is is so s o called c a l l e d not n o t because b e c a u s e arsenic arsenic a major m a j o r component c o m p o n e n t but b u t because, b e c a u s e , of o f nine n i n e zones z o n e s explored explored by b y Electrum E l e c t r u m Lake Lake Gold G o l d Mines M i n e s Ltd. L t d . around a r o u n d 1960, 196 0, it i t was was the the only was identified. A t this this o n l y one o n e it-i i n w hwhich i c h a rarsenopyrite s e n o p y r i t e was i d e n t i f i e d . At occurrence, is associated a s s o c i a t e d with w i t h quartz q u a r t z that t h a t contains contains o c c u r r e n c e , gold g o l d is t o u r m a l i n e , pyrite, p y r i t e , arsenopyrite a r s e n o p y r i t e and a n d minor m i n o r pyrrhotite. pyrrhotite. tourmaline, The T h e quartz q u a r t z is is in i n irregular i r r e g u l a r veins v e i n s which w h i c h occur o c c u r in i n aa complex c o m p l e x of o f porphyry p o r p h y r y and a n d felsic f e l s i c pyroclastics p y r o c l a s t i c s or o r flows, flows, near p r o m i n e n t hill h i l l of of n e a r the t h e north n o r t h side s i d e of o f aa prominent conglomerate. A s at a t the t h e previous p r e v i o u s stop, s t o p , the t h e occurrence occurrence c o n g l o m e r a t e . As is is close c l o s e to t o the t h eunconformity u n c o n f o r m i t y at a tthe t h ebase b a s eofo the f t hCrowduck e Crowduck is is �Figure 9: Geology of the Prsenic Zone gold prospect N) w �33 Lake L a k e Group. Group. The relationship r e l a t i o n s h i p bbetween e t w e e n the t h e conglomerate c o n g l o m e r a t e and a n d the the The felsic is ddifficult i f f i c u l t to to f e l s i c volcanic v o l c a n i c and a n d sub—volcanic s u b - v o l c a n i c rocks r o c k s is ddetermine. etermine. IIn n aa pprevious r e v i o u s interpretation i n t e r p r e t a t i o n (Davies, ( D a v i e s , 11965) 965) was ssuggested were all iit t was u g g e s t e d that t h a t the t h e ffelsic e l s i c rocks r o c k s were a l l porphyry porphyry as aan n eeast—trending a s t - t r e n d i n g ddike, i k e , aand n d younger y o u n g e r than than tthat h a t ooccurred c c u r r e d as greywackes were identified i d e n t i f i e d north n o r t h and a n d south s o u t h of o f it. it. g r e y w a c k e s that t h a t were The The conglomerate c o n g l o m e r a t e in i n turn t u r n was was considered c o n s i d e r e d to t o be b e younger younger than I t was also a l s o noted n o t e d (Davies, (Davies, t h a n the t h e porphyry p o r p h y r y dike. dike. It was not n o t satisfactory, satisfactory, 11965) 9 6 5 ) tthat h a t this t h i s interpretation i n t e r p r e t a t i o n was since t o grade g r a d e into i n t o the the s i n c e the t h e greywacke g r e y w a c k e appeared a p p e a r e d to cconglomerate. onglomerate. O u r recent r e c e n t mapping m a p p i n g has h a s shown s h o w n that t h a t the t h e "porphyry "porphyry Our dike" d i k e " cconsists o n s i s t s of o f at a t least l e a s ttwo t w ophases p h a s e s of o f porphyry, p o r p h y r y , and a n d aa The pyroclastic unit. T h e ccontact o n t a c t between b e t w e e n the t h e main m a i n porphyry porphyry aand n d the t h e conglomerate c o n g l o m e r a t e aappears p p e a r s to t o be be an a n unconformity, unconformity, a n d G). G) aalong l o n g which w h i c h sshearing h e a r i n g has h a s occurred o c c u r r e d (Localities ( L o c a l i t i e s AA and This main This m a i n pphase h a s e oof f the t h e porphyry p o r p h y r y is is similar s i m i l a r to t o porphyry porphyry iidentified d e n t i f i e d eelsewhere l s e w h e r e as a s ppart a r t of o f the t h e High H i g h Lake L a k e stock. stock. A small s m a l l ooutcrop u t c r o p of o f pyroclastics p y r o c l a s t i c s (Locality ( L o c a l i t y E) 3 ) is is probably probably associated a s s o c i a t e d with w i t h this t h i s main m a i n porphyry p o r p h y r y phase. phase. E l s e w h e r e in in Elsewhere the i m i l a r transitions t r a n s i t i o n s from f r o m felsic felsic t h e High H i g h Lake L a k e area a r e a ssimilar porphyry composition p o r p h y r y iinto n t o pyroclastics p y r o c l a s t i c s of o fthe t h same e samecomposition s u p p o r t t h e i n t e r p r e t a t i o n t h a t t h i s p o r p h y r y is a ssub—volcantc u b - v o l c a n i - c intrusion. intrusion. D i k e s of o f porphyry p o r p h y r y clearly c l e a r l y cut cut Dikes main—phase tthe he m a i n - p h a s e pporphyry o r p h y r y (Locality ( L o c a l i t y F), F ) , but b u t the t h e timing t i m i n q of of t o deposition d e p o s i t i o n of o f the the ttheir h e i r eemplacement m p l a c e m e n t relative r e l a t i v e to conglomerate is not n o t clear. clear. c o n g l o m e r a t e is T h e hhighly i g h l y laminated, l a m i n a t e d , fine f i n e grained g r a i n e d grey q r e y rocks r o c k s on on the the The north C ) , formerly formerly n o r t h sside i d e oof f the t h e porphyry p o r p h y r y (Locality ( L o c a l i t y C), as ggreywacke iidentified d e n t i f i e d as r e y w a c k e (Davies, ( D a v i e s , 1965), 1 9 6 5 ) , are a r e here here mylonite t o be be a m y l o n i t e zone. zone. The m y l o n i t e may 'nay The mylonite cconsidered o n s i d e r e d to t o the t h e north. n o r t h . This T h i s mylonite mylonite uunderlie n d e r l i e the t h e swampy area a r e a to zzone o n e is i s pprobably r o b a b l y aassociated s s o c i a t e d with w i t h the t h e dominant d o m i n a n t easterly easterly trending trendinq faults. The T h e ggold—bearing o l d - b e a r i n g quartz q u a r t z veins v e i n s occupy o c c u p y fractures f r a c t u r e s that that clearly post—date: the main phase porphyry within which c l e a r l y p o s t - d a t e : t h e main p h a s e p o r p h y r y w i t h i n which they B, D D aand n d F); F); t h e y are a r e dominantly d o m i n a n t l y ddeveloped e v e l o p e d ((Localities L o c a l i t i e s B, some pebbles p e b b l e s and and tthe h e Sedimentary s . e d i m e n t a r y rocks, r o c k s , within w i t h i nwhich w h i c h some b o u l d e r s c o n t a i n l a t e f r a c t u r e s t h a t have been f i l l e d by quartz n d H); n d tthe h e late l a t e porphyry porphyry q u a r t z veins v e i n s (Localities ( L o c a l i t i e s A aand H); aand D , E and a n d F) F) . T h e i r rrelative e l a t i v e age a g e with with ddikes i k e s (Localities ( L o c a l i t i e s D, Their respect i s unknown. unknown. r e s p e c t to t o the t h e mylonite m y l o n i t e is Geometry G e o m e t r y oof f the t h equartz—tourmaline q u a r t z - t o u r m a l i n e veins v e i n s is is complex, complex, and However, a n d hhas a s not n o t been b e e n analyzed a n a l y z e d in i n detail. detail. H o w e v e r , there there t o bbe e ttwo w o ddominant o m i n a n t trends t r e n d s within w i t h i n the t h e main nain aappear p p e a r to pporphyry, o r p h y r y , one o n e northerly, n o r t h e r l y , the t h e other o t h e r southeasterly. s o u t h e a s t e r l y . These These a t Locality L o c a l i t y D. D. ddominant o m i n a n t trends t r e n d s are a r e especially e s p e c i a l l y evident e v i d e n t at Within W i t h i n tthe h e conglomerate, c o n g l o m e r a t e , qquartz—filled u a r t z - f i l l e d f fractures r a c t u r e s in in ppebbles e b b l e s and a n d boulders b o u l d e r s show s h o w consistent c o n s i s t e n t orientation o r i e n t a t i o n within within individual i n d i v i d u a l ooutcrops, u t c r o p s , but b u t this t h i s varies v a r i e s from f r o m outcrop o u t c r o p to to outcrop ( s e e Localities L o c a l i t i e sAA and a n d H). H). o u t c r o p (see IInn ssummary, u m m a r y , gold g o l d at a t the t h e Arsenic A r s e n i c Zone Zone is is contained contained within were emplaced e m p l a c e d into into w i t h i n qquartz—tourmaline u a r t z - t o u r m a l i n e v veins e i n s tthat h a t were pyroclastic unit. . support the interpretation that this porphyry is faults. boulders contain late fractures that have been filled by . �34 f r a c t u r e s developed d e v e l o p e d by b y brittle b r i t t l e failure f a i l u r e in i n felsic felsic fractures porphyry t o an an p o r p h y r y and a n d associated a s s o c i a t e d rocks, r o c k s , marginal m a r g i n a l to east—southeast—trending e a s t - s o u t h e a s t - t r e n d i n g mylonite m y l o n i t e zone. zone. ---- C r o w d u c k Lake Lake polymictic p o l y m i c t i c conglomerate, conglomerate, L o c a l i t y AA Crowduck Locality coriEflTg c o n t a i n i n g clasts c l a s ts of o f predominant p r e d o m i n a n t porphyry, p o r p h y r y , minor m i n o r dacite, dacite, and is in i n contact c o n t a c t with w i t h porphyry. porphyry. a n d rare r a r e basalt b a s a l t and and chert, c h e r t , is A narrow n a r r o w unit u n i t of o f inter—bedded i n t e r - b e d d e d sandstone s a n d s t o n e and a n d conglomerate conglomerate with 1-2 cm cm pebbles p e b b l e s lies l i e s immediately i m m e d i a t e l y adjacent a d j a c e n t to t o the the w i t h 1—2 The porphyry. The contact c o n t a c t with w i t h the t h e porphyry p o r p h y r y is is sharp s h a r p and and porphyry. A quartz q u a r t z vein v e i n occupying o c c u p y i n g aa fracture f r a c t u r e in i n the the sheared. A sheared. porphyry p o r p h y r y extends e x t e n d s aa few f e w centimetres c e n t i m e t r e s into i n t o the t h e sediments. sediments. Larger a t this t h i s locality l o c a l i t y show show L a r g e r conglomerate c o n g l o m e r a t e clasts c l a s ts at quartz—tilled q u a r t z - f i l l e d tension t e n s i o n fractures f r a c t u r e s that t h a t extend e x t e n d into i n t o the the matrix, m a t r i x , indicating i n d i c a t i n g their t h e i r late l a t e development. development. Locality Q u a r t z - t o u r m a l i n e veins v e i n s with w i t h associated associated L o c a l i t --y BB Quartz—tourmaline p y r ite,rrhotite, i t e , p y r r h o t i t e and , a n dminor m i n o rarsenopyrite a r s e n o p y r i t e occupy o c c u p y aa Other shear s h e a r zone z o n e trending t r e n d i n g 1400 1 4 0  in i n porphyry. porphyry. O t h e r veins v e i n s occur occur in i n minor m i n o r fractures. fractures. Locality M y l o n i t i z e d porphyry p o r p h y r y underlies u n d e r l i e s the t h e north north L o c a l i t y CC Mylonitized Strike slop s o f -ofEhe f i e outcrop o u t c r o p ridge. ridge. S t r i k e is is about a b o u t 1300, 1300, dipping d i p p i n g steeply s t e e p l y northeast. northeast. quartz—tourmaline vveins, A b u n d a n t quartz-tourmaline e i n s , showinq showinq L o c a l i t y D Abundant Locality_D two?5iinent m z e n t orientations, o r i e n t a t i o n s , one o n e approximately a p p r o x i m a t e l y north, n o r t h , the the other t w o phases p h a s e s of o f porphyry. p o r p h y r y . AA o t h e r southeast, s o u t h e a s t , occur o c c u rwithin w i t h i ntwo mafic v e r y narrow narrow m a f i c unit, u n i t , possibly p o s s i b l y aa dike, d i k e , parallels p a r a l l e l s and and very Grab in i n part p a r t follows f o l l o w s the t h e contact. contact. G r a b ssamples a m p l e s obtained o b t a i n e d from from the 1 0 oz oz t h e southeast s o u t h e a s t end end of o f these t h e s e outcrops o u t c r o p s contain c o n t a i n up u p to t o 10 per p e r ton t o n Au. Au. Locality C o n t a c t trending t r e n d i n g 1050 1 0 5 0 between b e t w e e n aa porphyry porphyry L o c a l i t y EE Contact a T R TiTfTyroclastic - ~ c f ~ y r o c l a s tphase ipch a s e of o f the t h e early e a r l y porphyry. p o r p h y r y . AA number number of o f clasts c l a s t s in i n the t h e pyroclastic p y r o c l a s t i c unit u n i t are a r e elongated elongated (1380) parallel ( 1 38O) p a r a l l e l to t o foliation f o l i a t i o n in i n the t h e conglomerates c o n g l o m e r a t e s and and Note quartz the m y l o n i t e zone. zone. q u a r t z veins v e i n s both b o t h in i n the the the mylonite porphyry p o r p h y r y and and the t h e pyroclastics. pyroclastics. Locality L o c a l i t y FF Two late l a t e porphyry p o r p h y r y dikes d i k e s intrude i n t r u d e the the The hhighly main—phase m a i n - p h a s e porphyry. porphyry. i g h l y irregular i r r e g u l a r nature n a t u r e of o f the the unconformity is seen s e e n here, h e r e , with w i t h aa deep d e e p embayment e m b a y n e n t of o f both both u n c o n f o r m i t y is wacke t h e conglomerate c o n g l o m e r a t e a nand d a ab abasal s a l wacke t oto a rargillite g i l l i t e unit unit the into into a a valley v a l l e y in i n the t h e porphyry. porphyry. -F---4- - Locality L o c a l i t y GG The T h e unconformity u n c o n f o r m i t y between b e t w e e n the t h e main—phase main-phase 7änd Crowduck Lake sheared, porpH'yFy'and Crowd uck conglomerates Lake c o n g l o m e r a t eis s is s h e a r e d , but but clasts c l a s t s of o f porphyry p o r p h y r y derived d e r i v e d in i n place p l a c e are a r e identifiable i d e n t i f i a b l e in in Note the t h e basal b a s a l part p a r t of o f the t h econglomerate. conglomerate. Note the t h e sigmoidal, s igmoidal, quartz—filled q u a r t z - f i l l e d t tension e n s i o n ffractures r a c t u r e s in i n the t h e contact c o n t a c t zone. zone. Locality Locality ----lor?ate c o n q l o m e r a t e is is seen s e e n at a t aa very v e r y shallow s h a l l o w angle a n g l e to to H H Weak bedding b e d d i n g in i n the t h e Crowduck Crowduck Lake Lake �35 foliation. foliation. N a r r o w quartz q u a r t z veins v e i n s cut c u t conglomerate c o n g l o m e r a t e in i n two two Narrow d o m i n a n t trends, t r e n d s , one o n e at a t 0850, 0 8 5 0 , another a n o t h e r at a t 1300. 1300. Unlike dominant Unlike A , where w h e r e clasts c l a s t s are a r e large, l a r g e , and a n d quartz q u a r t z veins v e i n s are are L o c a l i t y A, Locality ddominantly o m i n a n t l y confined c o n f i n e d to t o the t h e clasts, c l a s t s , the t h e clast c l a s t size s i z e here here is is ssmaller m a l l e r and a n d veins v e i n s cut c u t clasts c l a s ts and and matrix. matrix. From S t o Highway H i g h w a y 17. 17. At t o p 33 pproceed r o c e e d north n o r t h on o n Shoal S h o a l Lake L a k e road r o a d to Stop At t h e highway, h i g h w a y , tturn u r n rright i g h t (east) ( e a s t ) aand n d ccontinue o n t i n u e for f o r about a b o u t 30 3 0 km to to the is t h e Kendall K e n d a l l Inlet I n l e t Road. Road. F o r the t h e first f i r s t 11 11 km krn the t h e highway h i g h w a y is the For a p p r o x i m a t e l y pparallel a r a l l e l to t o regional r e g i o n a l foliation f o l i a t i o n and a n d passes p a s s e s throuqh through approximately T h e highway h i g h w a y crosses crosses v o l c a n i c rocks r o c k s (mainly ( m a i n l y felsic f e l s i c pyroclastics) pyroclastics) volcanic The ggranitic r a n i t i c rocks r o c k s for f o r the t h e next n e x t 10 1 0 km and a n d for f o r the t h e remainder r e m a i n d e r it i t is is iinn w e l l - f o l i a t e d basalts b a s a l t s and and intermediate i n t e r m e d i a t e to t o felsic f e l s i c tuff—breccia. tuff-breccia. well—foliated i g h t (south) ( s o u t h ) oon n the t h e Kendall K e n d a l l Inlet I n l e t Road and a n d proceed p r o c e e d south south T u r n rright Turn km to Kenricia ffor o r aabout b o u t 2 km t o the t h e vicinity v i c i n i t y of o f the t h e old old K e n r i c i a Mine. Mine. . . STOP 4. GOLD MINE_(Figure_10) 4. ---KENRICIA MINE ( F i q u r e 1 0 ) ------- Gold—bearing G o l d - b e a r i n g quartz q u a r t z veins v e i n s at a t this t h i s stop s t o p were were ddiscovered i s c o v e r e d in i n the t h e latter l a t t e r part p a r t of o f the t h e 19th 1 9 t h century. century. Three s u n k and a n d at a t that t h a t time t i m e the t h e property p r o p e r t y was was T h r e e shafts s h a f t s were sunk known as known as the t h e Three T h r e e Ladies L a d i e s Mine. Mine. IIn n tthe he m i d 1930's 1930's mid ssubstantial u b s t a n t i a l tonnages t o n n a g e s of o f gold g o l d ore o r e were were outlined o u t 1 i n e d by by Development ddrilling. rilling. D e v e l o p m e n t pproceeded r o c e e d e d on o n three t h r e e levels l e v e l s and and a a mill was constructed. During m i l l was c o n s t r u c t e d . D uring a a one—year o n e - y e a r period, p e r i o d , 2533 2533 oounces u n c e s oof f gold g o l d and a n d 521 521 ounces o u n c e s of o f silver s i l v e r were were recovered, recovered, ore and a n d the t h erecovery r e c o v e r y were were bbut u t bboth o t h tthe h e grade g r a d e of o f the t h e ore The mine bbelow e l o w eexpectations. xpectations. T he m i n e cclosed l o s e d in i n 1940. 1940. The is mainly m a i n l y underlain u n d e r l a i n by by intermediate i n t e r m e d i a t e to to T h e aarea r e a is f e l s i c llapilli—tuff a p i l l i - t u f f aand n d tuff—breccia, t u f f - b r e c c i a , having h a v i n g a combined combined o 3000 3 0 0 0 m, m , and a n d these t h e s e are a r e overlain o v e r l a i n by by at at tthickness h i c k n e s s of o f 200 200 tto lleast e a s t 800 800 m of o f fine f i n e pyroclastics p y r o c l a s t i c s and a n d related r e l a t e d sediments. sediments. An east—trending C l e a r w a t e r Bay e a s t - t r e n d i n g syncline s y n c l i n e extends e x t e n d s through t h r o u g h Clearwater and a n d the t h e entire e n t i r e section s e c t i o n from f r o m the t h e boundary b o u n d a r y of o f the t h e Wabigoon Wabiqoon Subprovince S u b p r o v i n c e to t o Clearwater C l e a r w a t e r Bay, B a y , which w h i c h includes i n c l u d e s about a b o u t 1000 1000 m oof f foliated f o l i a t e d basalt b a s a l t at a t the t h e base, b a s e , is is bbelieved e l i e v e d to t o be be ssouth o u t h facing. facing. The T h e principal p r i n c i p a l lithologies l i t h o l o g i e s on o n the t h e peninsula p e n i n s u l a where w h e r e the the veins v e i n s are located l o c a t e d are a r e tuff; t u f f , lapilli—tuff, l a p i l l i - t u f f , and and c l a s ts within within a a dark dark ttuff—breccia, u f  £ - b r e c c i a containing c o n t a i n i n g ddacitic a c i t i c clasts matrix. i s moderate m o d e r a t e to t o strong, s t r o n g , trending t r e n d i n g east east matrix. F o l i a t i o n is Foliation aand n d ddipping i p p i n g near n e a r vertical. vertical. C l a s t s are a r e aligned a l i g n e d within within Clasts the plane t h e foliation  £ 0 i a t i o n plane. Seven S e v e n qquartz u a r t z vveins e i n s hhave a v e bbeen e e n ddiscovered, i s c o v e r e d , although a1 though most N o . 11 and a n d No. No. 3 m o s t of o f the t h e work w o r k was w a s concentrated c o n c e n t r a t e d on o n the t h e No. 3 veins. All veins. A l l oof f the t h e vveins e i n s contain c o n t a i n carbonate c a r b o n a t e and a n d most ccontain o n t a i n black b l a c k tourmaline. tourmaline. M i n e r a l i z a t i o n consists c o n s i s t s of of Mineralization minor m i n o r pyrite p y r i t e and a n d chalcopyrite c h a l c o p y r i t e with w i t h traces t r a c e s of o f galena q a l e n a and and ( 1 9 3 7 ) has h a s described d e s c r i b e d three three nnative a t i v e gold. gold. Thomson (1937) ggenerations e n e r a t i o n s of o f quartz q u a r t z iin n the t h e No. No. 3 e i n ; qquartz—carbonuartz-carbon3 v vein; aate t e veins v e i n s are a r e cut c u t by by sugary, s u g a r y , faintly f a i n t l y bluish b l u i s h quartz q u a r t z in in which w h i c h tourinaline t o u r m a l i n e aand n d ssulphides u l p h i d e s ooccur c c u r along a l o n g thin thin felsic . �36 metres Kendall Inlet Clearwater Bay Lake of the Woods Figure F i g u r e 10: 10: Location at the Locat i o n of of gold—bearing g o l d - b e a r i n g vveins e i n s at theKenricia Kenricia Gold Gold Mine. Mine. �I 37 fractures, and these are cut by glassy white iuartz. largely restricted to the sugary quartz. Quartz veins in the Kenricia Mine area occur within zones where there has been a strong component of shear. These zones are parallel, or slightly oblique to regional foliation and contain concentrations of quartz, carbonate, tourmaline and biotite. Gold is restricted to quartz veins and to immediately adjacent altered wall GoLd is rocks. Here the lapilli—tuff is moderately IefocnedTith clasts elongate parallel to foliation. Locality A. vein has been traced for 475 m It is best exposed at the east end of the trenches where it is in contact with highly sheared wall rock. Fragments of wall rock are found throughout the vein but are concentrated near the margins. Quartz varies from suqary and white to coarse and clear; minor sulphides, tourmaline and hiotite are present in both types. The host schists contain up to 3% fine disseminated pyrite, are strongly silicified and are cut by quartz—carbonate veinlets. Coarse biotite is common at margins of the veinlets and alsd as flakes which cut across foliation and clast boundaries in th& host rocks. Analyses of sugary quartz, wall—rock schiat and clear quartz showed the gold content to be 310 ppb, 260 ppb and 505 ppb respectively. A second sample of clear quartz contained 855 ppb gold. Locality B. The No. 1 ffiirg5raximam width of 1.3 m. Some 20 m south of No. vein is an outcrop of strongly foliated dacitic lapilli—tuff. The rock is essentially a quartz—sericite—biotite—carhonate schist and contains rare broken remnants of sodic oliqoclase. An analyzed sample contained 3 ppb gold. 1 Locality D. At this locality several veins, E3TTEEWéTy known as No. la vein, comprise less tnan 30% of a zone of sheared dacitic lapilli—tuff. Bluish—white sugary quartz lies within the east—trending foliation plane as well as northeast—trending fractures, and encloses numerous fragments of wall rock. Veinlets of tourrnaline cross the quartz. The host schists contain carbonate and 3% euhedral pyrite. A sample of vein material contained 3590 ppb qold, and the pyritiferous schist contained 540 cob gobi. Return to Kenora. En route we will pass exposures of foliated volcanics and volcanogenic sediments. DAY 2 Proceed 5. 3 km east along Hiqhway 17 from the Thurist In formation Centre, to the junction of the Jones Road. Felsic pyroclastic �38 rocks r o c k s are a r e interlayered i n t e r l a y e r e d with w i t h basalts b a s a l t s near n e a r the t h e town, t o w n , hut b u t much much of of At the A t the the t h e route r o u t e passes p a s s e s through t h r o u g h massive, m a s s i v e , pillowed p i l l o w e d basalts. basalts. Highway 17 —- Jones J o n e s Road Road intersection, i n t e r s e c t i o n , quartz q u a r t z monzonite m o n z o n i t e with w i t h large large H i g h w a y 17 euhedral e u h e d r a l microcline m i c r o c l i n e megacrysts m e q a c r y s t s lies l i e s at a t the t h e southern s o u t h e r n edge e d g e of o f an an o v a l stock. s t o c k . Turn T u r n left l e f t (northeast) ( n o r t h e a s t ) on o n the t h e Jones J o n e s Road. R o a d . This This oval gravel g r a v e l road r o a d crosses c r o s s e s the t h e eastern e a s t e r n edge e d g e of o f the t h e quartz q u a r t z monzonite monzonite stock s t o c k up up to to the t h e railroad r a i l r o a d crossing c r o s s i n g and a n d then t h e n passes p a s s e s through t h r o u q h massive massive Proceed t o foliated f o l i a t e d basalt. basalt. P r o c e e d 1.6 1 . 6 km km beyond b e y o n d the t h e railroad r a i l r o a d crossing, crossing , to turn t u r n left l e f t (north) ( n o r t h ) on o n dirt d i r t tracks t r a c k s through t h r o u g h open o p e n clearings c l e a r i n g s and a n d then then west west through t h r o u q h light l i g h t bush b u s h to t o the t h e Scramble S c r a m b l e Gold G o l d Mine M i n e (total ( t o t a l distance distance 1 . 1 km km from f r o m the t h e Jones J o n e sRoad) R o a d. ) . The T h e dirt d i r t track t r a c k crosses crosses the t h e axial axial o f 1. Qf trace t r a c e of o f the t h e northeast—trending n o r t h e a s t - t r e n d i n g Airport A i r p o r t Anticline. Antic1ine. 1 STOP 55 SCRAMBLE STOP SCRAMBLE GOLD GOLD MINE M I N E (Figure ( F i g u r e 11) 11 ) --------------- Gold G o l d was was discovered d i s c o v e r e d on o n this t h i s property p r o p e r t y in i n the t h e 1890's 1890's and a n d several s e v e r a l interests i n t e r e s t s "scrambled" " s c r a m b l e d " to t o obtain o b t a i n aa working working option o p t i o n on o n it. i t . The T h e Scramble S c r a m b l e Gold G o l d Mining M i n i n g Company Company was was incorporated i n c o r p o r a t e d in i n 1897. 1 8 9 7 . Two Two shafts s h a f t s were were sunk s u n k and a n d some some underground u n d e r g r o u n d development d e v e l o p m e n t took t o o k place, p l a c e , but b u t there t h e r e was w a s no no gold g o l d production. p r o d u c t i o n . The T h e property p r o p e r t y lay l a y idle i d l e until u n t i l 1984 1 9 8 4 when when Boise B o i s e Cascade C a s c a d e Corporation, C o r p o r a t i o n , current c u r r e n t owners o w n e r s of o f the the property, p r o p e r t y , began b e g a n investigating i n v e s t i g a t i n g its i t s gold g o l d potential. potential. Bedrock B e d r o c k exposed e x p o s e d in i n aa recently r e c e n t l y stripped s t r i p p e d area a r e a consists c o n s is t s of o f northwest—facing n o r t h w e s t - f a c i n q pillowed p i l l o w e d basalt b a s a l t and a n d medium—grained med i u m - g r a i n e d basalts b a s a l t s that t h a t are a r e either e i t h e r subvolcanic s u b v o l c a n i c sills s i l l s or or coarser— coarserFelsite grained g r a i n e d flows. flows. F e l s i t e dikes d i k e s were were intruded i n t r u d e d into i n t o the the basalts, b a s a l ts , especially e s p e c i a l l y along a l o n g northeast— n o r t h e a s t- striking s t r i k i n g zones zones o f shearing. shearing. of Within W i t h i n the t h e stripped s t r i p p e d area, a r e a , sampling s a m p l i n g by b y Boise Boise p e r s o n n e l has h a s indicated i n d i c a t e d that t h a t gold g o l d isismore more abundant a b u n d a n t in i n aa personnel zone z o n e ssubparallel u b p a r a l l e l to, t o , and a n d immediately i m m e d i a t e l y southeast s o u t h e a s t of o f the the felsite f e l s i t e dikes. d i k e s . Our O u r ssampling a m p l i n g ssuggests u g g e s t s that t h a t gold g o l d values values a r e highest h i g h e s t (0.37 ( 0 . 3 7 oz. o z . Au Au per p e r ton t o n over o v e r 1.5 1.5m) m ) at a t locality locality are (Figure where ( F i g u r e 11) 11) w h e r e the t h e zone z o n e transects t r a n s e c t s aa felsite f e l s i t e dike. dike. The ddikes i k e s and a n d the t h e gold—bearing g o l d - b e a r i n g zone z o n e are a r e in i n aa zone z o n e of of strong is about a b o u t 20m 20rn wide, w i d e , sharply s h a r p l y bounded bounded s t r o n g shearing s h e a r i n g which w h i c h is t o the t h e northwest n o r t h w e s t (Locality ( L o c a l i t y D) D) and a n d southeast s o u t h e a s t by by to relatively r e l a t i v e l yundeformed u n d e f o r m e d ppillowed i l l o w e d bbasalts a s a l ts (Localities ( L o c a l i t i e sCCand and Remnants K). R e m n a n t s of o f mass m a s s i ive v e bbasalt a s a l t in i n the t h esheared s h e a r e d zone zone K) Major (Locality ( L o c a l i t y 3) J ) are a r e not n o tobviously o b v i o u s l y pillowed. pillowed. Major deformation within post—date deformation w i t h i n the t h e zone z o n e is is believed b e l i e v e dtot o pos t - d a t e G G . emplacement e m p l a c e m e n t o foft the h e ddikes i k e s because: b e c a u s e : the t h e dikes d i k e s themselves themselves are with a r e sheared, sheared, w i t h ffoliation o l i a t i o n in i n the t h e basalt b a s a l t cutting c u t t i n q the the dikes, d i k e s , at a t aa low l o w angle; a n g l e ; where w h e r e dikes d i k e s pass p a s s from f r o m undeformed undeformed rock r o c k into i n t o the t h e shear s h e a r zone z o n e they t h e y have h a v e suffered s u f f e r e d drag drag (Locality ( L o c a l i t y D); D ) ; ffold o l d sstyles t y l e s in i n basaltic b a s a l t i c rocks r o c k s of o f the t h e shear shear zone mimicked z o n e are are m i m i c k e d in i n the t h e narrow, n a r r o w , attenuated a t t e n u a t e d portions p o r t i o n s of of f e l s i c dikes. dikes. felsic Quartz quartz—tourmaline Q u a r t z and and q u a r t z - t o u r m a l i n e veins v e i n s occur o c c u r in i n both b o t h the the and the basalt host. been emplaced late because they fill shears in the fels ite. They d i k e s and t h e b a s a l t h o s t . T h e y commonly c o m m o n l y sshow h o w evidence evidence dikes o f folding f o l d i n g and a n d boudinage b o u d i n a q e (Localities (Localities I I aand n d 33), ) , hut b u t must nus t of have have been emplaced l a t e because t h e y f i l l s h e a r s i n t h e f e l s ite. �-----— 39 --- t- 0 0 22 - - 4 4 6 6 8 - - > 81 tuartz vein quartz vein 10 0 felsic dike felsic dike metres '' strongly stronglydeformed deformed felsic felsic dike dike brown" basalt "brown" basalt / a basalt flows flows '12 / fold style and sense F J m. sample location C Stop 5 locations -edge of deformation zone edge of deformation zone u2 .1 L ,?C^3> outcrop felsic dike -edge of Scramble deformation zone metres £ - pillow tops trenches shaft B Figure F i g u r e 1 11:: Stop 5 locations G e o l o g y oof f the t h e Scramble S c r a m b l e Gold G o l d aarea. rea. T h e aarea r e a enclosed enclosed Geology The lowermap map isisshown shown w i t h i n the t h e rectangle r e c t a n q l e in i nthe t h elower within eenlarged n l a r g e d above. above. �40 Abundant A bundant m i n o r folds f o l d s are a r e present p r e s e n t in i n the t h e shear s h e a r zone. zone. minor F2,F and These T h e s e are a r e predominantly p r e d o m i n a n t l y ZZ folds f o l d s (Localities ( L o c a l i t i e s E , F a n d G) G) Shear though t h o u g h SS folds f o l d s also a l s o occur o c c u r (Localities ( L o c a l i t i e sF Fand a n d3 J ). ). S hear ssurfaces u r f a c e s related r e l a t e d to t o the t h e development d e v e l o p m e n t of o f ZZ ffolds o l d s sstrike t r i k e at at a variety v a r i e t y of o f angles a n q l e s (approximately ( a p p r o x i m a t e l y N45°E) N45OE) but b u t are are iinvariably n v a r i a b l y ooblique b l i q u e to t o sshear—zone h e a r - z o n e boundaries b o u n d a r i e s (about ( about N52°E). N520~). Samples S a m p l e s ccollected o l l e c t e d aacross c r o s s the t h e sshear h e a r zone z o n e (1 ( 1 to t o 13, 13, Figure 1 1 ) show s h o w distinct d i s t i n c t petrographic p e t r o g r a p h i c and a n d geochemical geochemical F i g u r e 11) Relatively ( 1 aand n d 13) 13) ppatterns. atterns. R e l a t i v e l y unaltered u n a l t e r e d basalts b a s a l t s (1 contain c o n t a i n abundant a b u n d a n t hornblende h o r n b l e n d e (70—80%), ( 7 0 - 8 0 % ) , lesser l e s s e r feldspar feldspar minor ((10—25%), 1 0 - 2 5 % ) , mminor i n o r rretrograde e t r o g r a d e bbiotite i o t i t e aand nd m i n o r ilmenite ilmenite Toward aand n d carbonate. carbonate. T o w a r d the t h e centre c e n t r e of o f the t h e deformation deformation zone biotite zone b i o t i t e increases i n c r e a s e s at a t the t h e expense e x p e n s e of o f hornblende, h o r n b l e n d e , and and epidote e p i d o t e aand n d ssphene p h e n e aare r e present p r e s e n t in i nminor m i n o r amounts. amounts. Samples S a m p l e s ffrom r o m t the h e ccentral e n t r a l part p a r tare a r magnetite—bearing. e magnetite-bearing The is shown T h e ggeochemical e o c h e m i c a l p apattern t t e r n is s h o w n i in n ffigure i g u r e 12. 12. While W h i l e t the h e ppattern a t t e r n is is complex, c o m p l e x , tthere h e r e is, i s , coincident c o i n c i d e n t with with the t h e highest h i g h e s t gold g o l d contents, c o n t e n t s ,ana nincrease i n c r e a sin e iFe203, n F e 2 0 3MgO , MgO and and The K20, K20, aand n d aa decrease d e c r e a s e ini nCaO, CaO, Na20 Na2O and a n d Al203. Al2O3. The ccentral entral ppart a r t of o f the t h edeformation d e f o r m a t i o n zone z o n e is, i s , ini ngeneral, g e n e r a l marked , m a r k e d by by aan n increase i n c r e a s e in i n K20 K20 aand n d i in n t the h e ooxidation x i d a t i o n s state t a t e oof f iron. iron. . Pillowed Locality illowed L o c a l i t y AA P llavas a v a s ssoutheast o u t h e a s t oof f the t h e Scramble Scramble i d e of o f the the armatTn z o n e aare r e oobserved b s e r v e d o on n e either i t h e r sside a ^ : o r m a t i o n zone Although trail t r a i lleading l e a d i n gtoward t o w a r d the t h e airport a i r p o r runway. t runway. A l t h o u g h not not ttoo o o distinct, d i s t i n c t , tops t o p s are a r e interpreted i n t e r p r e t e d to t o be b e toward t o w a r d the the n n oorr tth h wwes e s t. t. ----- Locality P i l l o w e d bbasalts a s a l t s are a r e in i n contact c o n t a c t with with L o c a l i t y BB Pillowed E?ained c o a r s e r - g r amassive i n e d m a s mafic s i v e m a rocks f i c r o c kwith s w i t h2—3 2-3 mm mm The coarse hornblende h o r n b l e n d e porphyroblasts, porphyroblas t s , and a n d rare r a r e garnets. garnets. The coarse vvariety a r i e t y may be b e either e i t h e r coarse c o a r s e flows f l o w s or or subvolcanic subvolcanic sills. s i l l s . Pillows P i l l o w s are a r e elongate, e l o n g a t e , but b u t appear a p p e a r to t o face f a c e north. north. Several t o those t h o s e to to S e v e r a l fine—grairied f i n e - g r a i n e d ffelsic e l s i c ddikes, i k e s , ssimilar i m i l a r to be b e sseen e e n at a t the t h e Scramble S c r a m b l e shaft, s h a f t , cut c u t both b o t h rock r o c k types. types. Margins M a r g i n s of o f the t h e dikes d i k e s are a r e feathered, f e a t h e r e d , with w i t h small s m a l l shears shears displaying d i s p l a y i n g a dominantly d o m i n a n t l y dextral d e x t r a l horizontal h o r i z o n t a l component. component. Pillowed Locality L o c a l i t y CC P i l l o w e d llavas a v a s adjacent a d j a c e n t to t o the t h e stripped stripped ---. area a r e a aaroi r o u n dthe t h eScramble S c r a m b l eshaft s h a f t are a r e exposed e x p o s e d in i n aa number number Features s m a l l outcrops. outcrops. F e a t u r e s to t o oobserve b s e r v e are: a r e : distinct distinct oof f small shapes t o the the s h a p e s of o f larger l a r g e r pillows p i l l o w s indicating i n d i c a t i n g tops t o p s to with northwest; n o r t h w e s t ; smaller, s m a l l e r , amoeboid a m o e b o i d ppillows, illows, w i t h nno o cclear l e a r top top d i k e s feeding f e e d i n g the t h epillowed p i l l o w e d sequence; sequence; iindicators; n d i c a t o r s ; mafic maf i c dikes minor m i n o r ooffset f f s e t oof f pillow p i l l o w rims rims by b y shearing s h e a r i n g and a n d faulting. faulting. A felsic Locality L o c a l i t y DD f e l s i c dike d i k e is is aat t hhigh i g h aangle n g l e to to fTTatT6 F o I T Z t i oAn isharp A s h a rflexture p f l e x t u r eini nthe t h edike d i k e marks m a r k s the the nnorthwest o r t h w e s t boundary b o u n d a r y oof f the t h e Scramble Scramble deformation d e f o r m a t i o n zone. zone. Note also a l s o quartz—tourrnaline q u a r t z - t o u r m a l i n e vveins e i n s ccutting u t t i n g tthe h e ddike i k e aat t a high angle (approx. N400E) and occupying shear surfaces h i g h a n q l e ( a p p r o x . N40OE) a n d o c c u p y i n g s h e a r s u r f a c e s that t h a t extend e x t e n d into i n t o the t h e host h o s t basalt. basalt. �41 70 65 - 6055 - I... 50- Si02 I.. I 45 -J •I. 1817C 16- total iron as N Fe203 1514- A1203 13124-' 11— FeO CaO 0 ci Q. 9— 4-' 98- \ 7— 6- I 5H MgO H— E-. 43 ::AA FeO Fe203 23 Cc.'.. ...c........c: / K22 0 Au Au replicates replicates Figure F i g u r e 12: 12: "8, \ A-A B A ^*^ 00 sample number 11 sample pumber Au Au (ppb) (ppb) )6 16 ( / ' //A\\ ' ^> B F... F...• \.\.. // I BB B / NaO Na20 B B Â¥' c ......ic!% V- / \cB B / 'B / /3 DC CA B/';\ -A 22 17 17 33 66 77 88 99 10 10 80 80 2410 2410 80 80 360 3604075 4075130 130 85 85 2200 2200 75 75 75 85 2600 85 75 2600 370 5500 135 135 370 5500 125 345 345 2650 2650 125 \A-A L 11 11 12 12 13 13 4 99 77 21 21 40 40 980 980 45 45 40 40 1000 1000 5 960 960 Geochemical traverse t r a v e r s e across a c r o s s the t h e Scramble Scramble Geochemical deformation T h e location l o c a t i o n of of samples samples is is d e f o r m a t i o n zone. zone. The i l l u s t r a t e d in i n Figure Figure 11. 1 1 . Samples Samples 11 to t o 33 and and illustrated t o 13 1 3 are a r e mafic m a f i c metavolcanjc m e t a v o l c a n i c rocks; r o c k s ; 44 and and 55 6 to a r e strongly s t r o n g l y deformed deformed felsic f e l s i c dikes. dikes. are �42 -LLocalityE --o-c a l i t y E Pronounced P r o n o u n c e d Z—folding Z - f o l d i n g of o f aa tectonic t e c t o n i c fabric fabric iin n bbasaltic a s a l t i c lavas l a v a s within w i t h i n the t h e deformation d e f o r m a t i o n zone. zone. A number number a r e present p r e s e n t and a n d are a r e interpreted i n t e r p r e t e d to t o he be oof f felsic f e l s i c units u n i t s are early Fold e a r l y felsic f e l s i c dikes, d i k e s , rather r a t h e r than t h a n tuffs t u f f s or o r flows. flows. Fold axes d i f f u s e zone z o n e of o f brown—coloured brown-coloured a x e s plunge p l u n g e steeply. s t e e p l y . A diffuse basalt b a s a l t can c a n be b e traced t r a c e d toward t o w a r d Locality L o c a l i t y F. F. Locality L o c a l i t y FF S—folding S - f o l d i n g is is indicated i n d i c a t e d in i n the t h e "brown " b r o w n zone", zone", w h TEerrninates i c h t e r m i n a t e snortheastward n o r t h e a s t w a r d against a g a i n s t aa north—northeast north-northeas t ttrending r e n d i n g shear s h e a r surface. surf ace. IIntense n t e n s e 2Z—folding - f o l d i n g in i n felsic f e l s i c and and mafic is evident. e v i d e n t . Mafic M a f i c rocks r o c k s are are interpreted i n t e r p r e t e d to to ~ a f i rocks cr o c k s is Felsic be b e pillowed p i l l o w e d basalt b a s a l t flows. flows. F e l s i c units u n i t s are a r e dikes. dikes. L o c a l i t y GG A wide w i d e felsic f e l s i c ddike i k e can c a n be b e sseen e e n to t o ddip ip Locality steerthwestward Preliminary P r e l i m i n a r y grab qrab s t e e p l y n o r t h w e s t w a in r d ithe n t h eshaft. shaft samples s a m p l e s from f r o m the t h e property p r o p e r t y indicated i n d i c a t e d highest h i g h e s t gold g o l d values values within tto o be be w i t h i n rocks r o c k s aat t tthe h e sshaft, h a f t , both b o t h in i n the t h e dike d i k e and and Immediately the mafic i c volcanics, volcanics I m m e d i a t e l y southwest s o u t h w e s t of o f the the t h e ma shaft, n u m b e r of o f narrow n a r r o w quartz—tourrnaline q u a r t z - t o u r m a l i n e veins v e i n s occupy occupy s h a f t , aa number shear a t about about s h e a r surfaces s u r f a c e s in i n the t h e dike, d i k e , and a n d strike s t r i k e at N40—45°E. N 4 0 - 4 5 O ~ . This T h i s trend t r e n d is i s also a l s o seen s e e n in i n aa quartz q u a r t z vein vein within a sshear hear aalong l o n g sstrike, trike, w i t h i n the t h e bbasalts, a s a l t s , that t h a t ooccupies ccupies a zone ( Z-fold i n q ) z o n e exhibiting e x h i b i t i n g right—lateral r i g h t - l a t e r a l movement movement (Z—folding) . . . Locality L o c a l--i t y HH Two felsic f e l s i c units u n i t s interpreted i n t e r p r e t e d to t o be be dikes dikes mark margin m a r k the t h e south—east south-east m a r g i n oof f the t h e Scramble S c r a m b l e ddeformation eformation zone. 5 , Figure F i g u r e 11) 11) z o n e . One of o f these t h e s e dikes d i k e s (Sample ( S a m p l e 5, well ccontains o n t a i n s 1000 1 0 0 0 pppb p b ggold; old; w e l l aabove b o v e bbackground a c k g r o u n d vvalues a l u e s in in tthe h e basalt b a s a l t outside o u t s i d e the t h e deformation d e f o r m a t i o n zone. zone. A large l a r g e isolated i s o l a t e d quartz q u a r t z lens l e n s occurs o c c u r s here. here. is It is unclear. unclear. It could c o u l d be the t h e dislocated d i s l o c a t e d equivalent e q u i v a l e n t of o f aa wide wide quartz—tourmaline 20 metres northeast n o r t h e a s t of o f the the q u a r t z - t o u r m a l i n e vein v e i n 20 Scramble main S c r a m b l e shaft. shaft. IIn n tthe he m a i n felsic f e l s i c dike, d i k e , numerous numerous N~OOE, nnarrow a r r o w quartz—tourmaline q u a r t z - t o u r m a l i n e v veins, e i n s , sstriking t r i k i n gabout a b o u tN40°E, cross Toward c r o s s the t h e dike d i k e at a t aalow l o w angle. angle. T o w a r d LLocality o c a l i t y 3, J, nnumerous u m e r o u s examples e x a m p l e s oof f tthese h e s e can c a n be b e seen. seen. Locality L o c a l i t y II eEural ^ ^ F T e s F r U position e t u r a l p o s i t iof o n othis f t h i slens lens Examples E x a m p l e s oof f left—lateral l e f t - l a t e r a l shear, s h e a r , with with S—folds, are S -folds, a r e sseen e e n within w i t h i n the t h e main m a i n felsic felsic dike. Right—lateral dike. R i g h t - l a t e r a l sshear h e a r is is evident e v i d e n t within w i t h i n splays s p l a y s off off tthe h e ddike i k e into i n t o basaltic b a s a l t i c country c o u n t r y rock r o c k but b u t the t h e relationship relationship Deformed tto o the t h e ssinistral i n i s t r a lshears s h e a r sis iunknown. s unknown. D e f o r m e d amoehoil amoeboid ccur p i l l o w s , s i m i l a r t o t h o s e s e e n a t L o c a l i t y C , ooccur within w i t h i n the t h e Scramble S c r a m b l e deformation d e f o r n a t i o n zone, z o n e , on o n the t h e northwest northwest F r o m this t h i s point, p o i n t , looking looking sside i d e of o f the t h e main m a i n felsic f e l s i c dike. d i k e . From toward t o w a r d the t h e Scramble S c r a m b l e shaft, s h a f t , aa pronounced p r o n o u n c e d open—Z open-Z flexure flexure in is evident. evident. i n the t h e felsic f e l s i c dikes d i k e s is Locality L o c a l i t y J3 ã6Tted associated pillows, similar to those seen at Locality C, Locality Pillow L o c a l i t y KK P i l l o w lavas l a v a s ssoutheast o u t h e a s t of o f the t h e Scramble Scramble d e fition f o r m a t i ozone n z o nsuggesting e s u g g e s t i n gtops t o p stoward t o w a r dthe t h e northwest. northwest. - L -LocalityL -o c a l i .-t y L On On line OW oof Boise's l i n e 4+0 4+OOW f B o i s e ' s ggrid, r i d , aa trench trench �43 marks m a r k s the t h e location l o c a t i o n of o f an a n IP I P anomaly a n o m a l y that t h a t the t h e company c o m p a n y has has traced The geophysical t r a c e d from f r o m the t h e Scramble S c r a m b l e shaft s h a f t area. area. geophysical anomaly s t r i k e similar s i m i l a r to t o that t h a t of o f the t h e Scramble Scramble a n o m a l y has h a s aa strike deformation d e f o r m a t i o n zone. zone. . Return, t o Highway Highway 17, 1 7 , and a n d turn t u r n left(east). lef t(east) At R e t u r n , vvia i a Jones J o n e s Road, Road, to At the t h e crest c r e s t of o f the t h e first f i r s t hhill i l l which w h i c h the t h e highway h i g h w a y crosses crosses is is an an exposure e x p o s u r e of o f pillowed p i l l o w e d basalt b a s a l t with w i t h white w h i t e carbonate c a r b o n a t e filling filling inter—pillow i n t e r - p i l l o w gaps. g a p s . Reaction R e a c t i o n between b e t w e e n the t h e carbonate c a r b o n a t e and a n d the t h e basalt basalt has is cut c u t by by h a s generated g e n e r a t e d andradite a n d r a d i t e garnet g a r n e t and a n d epidote. epidote. The basalt b a s a l t is The granitic Beyond q r a n i t i c dikes. dikes. Beyond the t h e crest c r e s t the t h e outcrop o u t c r o p is is diorite d i o r i t e and and quartz q u a r t z diorite d i o r i t e of o f the t h e Island I s l a n d Lake L a k e intrusion i n t r u s i o n which w h i c h noses n o s e s out o u t aa short s h o r t distance d i s t a n c e to t o the t h e south. s o u t h . At A t the t h e Garbage G a r b a g e Dump Dump turnoff, t u r n o f f , 1.6 1 . 6 km km beyond b e y o n d the t h e south s o u t h end e n d of o f Hilly H i l l y Lake, L a k e , turn t u r n left l e f t (northeast) ( n o r t h e a s t ) and and bear m. To To the t h e left l e f t (northwest) ( n o r t h w e s t, ) , stripping s t r i p p i n g of of b e a r left l e f t for f o r 200 2 0 0 m. overburden has been carried out in the vicinity of the Silverman overburden h a s been c a r r i e d o u t i n t h e v i c i n i t y of t h e Silverman occurrence. occurrence. STOP 6A SILVERMAN ----- GOLD PROSPECT The T h e contact c o n t a c t between b e t w e e n massive m a s s i v e quartz q u a r t z diorite d i o r i t e of o f the the Island I s l a n d Lake L a k e intrusion i n t r u s i o n and a n d massive m a s s i v e basalt b a s a l t is is very v e r y near near the a r e a . The T h e contact c o n t a c t is is irregular i r r e g u l a r in i n detail, detail, t h e parking p a r k i n q area. but r e g i o n a l trend t r e n d of o f N65°E ~ 6 5 over o0v e~r aa distance d i s t a n c e of o f at at b u t has h a s aa regional least l e a s t 1.5 1 . 5 km. km. The T h e southeast s o u t h e a s t contact c o n t a c t of o f the t h e intrusion intrusion was probably p r o b a b l y fault f a u l t controlled c o n t r o l l e d and a n d post—emplacement pos t-emplacement mOvement t o the t h e fault f a u l t has h a s resulted r e s u l t e d in i n narrow narrow m o v e m e n t parallel p a r a l l e l to zones Inclusions z o n e s of o f mylonite m y l o n i t e in i n the t h e quartz q u a r t z diorite. diorite. I n c l u s i o n s of of basalt, some of o f which w h i c h have h a v e been b e e n partly p a r t l y digested, d i g e s t e d , are are b a s a l t , some locally l o c a l l y abundant. abundant. At A t the t h e Silverman S i l v e r m a n prospect p r o s p e c t aa number n u m b e r of o f shears shears trending t r e n d i n g about a b o u t N350E N35OE and a n d having h a v i n g near n e a r vertical v e r t i c a l dips digs contain c o n t a i n quartz, q u a r t z , tourmaline t o u r m a l i n e and a n d sulphides. s u l p h i d e s . The T h e main main workings 1 3 . 4 mm shaft s h a f t and a n d two t w o open o p e n cuts cuts w o r k i n g s consist c o n s i s t of o f aa 13.4 from Eron which w h i c h 184 1 8 4 tons t o n s of o f ore o r e were were shipped s h i p p e d for f o r milling m i l l i n g in in 1941. T h e average a v e r a g e gold g o l d content c o n t e n t of o f the t h e ore o r e was was 0.575 0 . 5 7 5 oz oz 1 9 4 1 . The per p e r ton. t o n . The T h e main m a i n vein v e i n was was up u p to to 50 5 0 cm c m wide w i d e but b u t was was discontinuous; d i s c o n t i n u o u s ; it i t was was emplaced e m p l a c e d within w i t h i n aa strong s t r o n g shear shear zone, a r e several several z o n e , and a n d where w h e r e the t h e main m a i n vein v e i n pinches p i n c h e s there t h e r e are parallel thin quartz veins within the shear. parallel thin quartz veins within the shear. The is sugary s u g a r y and a n d black b l a c k tourmaline t o u r m a l i n e is is T h e quartz q u a r t z is abundant locally. a b u n d a n t l o c a l l y . Pyrrhotite, P y r r h o t i t e , pyrite p y r i t e and a n d traces t r a c e s of of t o 22 percent. percent. c h a l c o p y r i t e are a r e present p r e s e n t in i n amounts a m o u n t s up u p to chalcopyrite Samples S a m p l e s of o f fresh f r e s h quartz q u a r t z diorite d i o r i t e and a n d highly h i g h l y sheared sheared quartz were q u a r t z diorite d i o r i t e adjacent a d j a c e n t to t o the t h e mined m i n e d vein v e i n were analyzed. Relative analyzed. R e l a t i v e to t o the t h e fresh f r e s h rock r o c k the t h e sheared s h e a r e d rock rock showed n e t loss l o s s of of Si02, S i O 2 , Al203, A l 2 0 3 , Na20, Na20, As, A s , Sb S b and a n d Pb, Pb, s h o w e d aa net and The g a i n of o f K2O, K20, 002 CO2 and a n d H2O. H2O. The gold g o l d content c o n t e n t of o f the the a n d aa gain fresh w a s lless e s s than t h a n 22 ppb p p b and a n d of o f the t h e sheared s h e a r e d rock rock f r e s h rock r o c k was 88 ppb. Ppb* Clearing C l e a r i n g aand n d bblasting l a s t i n g hhas a s been b e e n ccarried a r r i e d oout u t in i n the the area Here, a r e a between b e t w e e n the t h e Silverman S i l v e r - m a n vein v e i n and a n d the t h e road. r o a d . Here, quartz—tourmaline q u a r t z - t o u r m a l i n e veins v e i n s occur o c c u r in i n aa swarm, s w a r m , occupying occupying shear g e n e r a l N50°E ~ 5 0 trend. t0r e~n d . Small S m a l l drags d r a q s and and s h e a r zones z o n e s with w i t h aa general . �44 Z—folds Z - f o l d s indicate i n d i c a t e dextral d e x t r a l shear. s h e a r . Their T h e i r style s t y l e and and orientation o r i e n t a t i o n is is similar s i m i l a r to t o those t h o s e at a t the t h e Scramble. Scramble. Deformation D e f o r m a t i o n continued c o n t i n u e d after a f t e r emplacement e m p l a c e m e n t of o f the t h e veins, veins, since s i n c e they t h e y are a r e themselves t h e m s e l v e s drag—folded. drag-folded. IIn n pplaces l a c e s the the vveins e i n s ooccupy c c u p y sstrong t r o n g shear s h e a r zones z o n e s aa few f e w tens t e n s of of centimetres o r the t h e shears s h e a r s themselves t h e m s e l v e s are are c e n t i m e t r e s wide, w i d e , or apparently w h i l e the t h e immediate i m m e d i a t e host h o s t diorite diorite a p p a r e n t l y unaltered, u n a l t e r e d , while Granitoid is is eenriched n r i c h e d in i n tourmaline t o u r m a l i n e and a n d silica. silica. G r a n i t o i d veins, veins, which w h i c h occur o c c u r in i n both b o t h the t h e diorite d i o r i t e and a n d basalt b a s a l t inclusions inclusions are a r e cut c u t by b y felsite f e l s i t e dikes d i k e s that t h a t have h a v e been b e e n strongly s t r o n g l y sheared sheared parallel t o their t h e i r length. length. p a r a l l e l to Return km to R e t u r n to t o the t h e parking p a r k i n g area a r e a and and ccontinue o n t i n u e northeast n o r t h e a s t for f o r 00.8 . 8 km to The trail the t h e Treasure T r e a s u r e prospect. prospect. The t r a i l is is almost a l m o s t on o n the t h e quartz quartz but ddiorite—basalt i o r i t e - b a s a l t contact c o n t a c t for f o r about a b o u t 100 100 m m northeast n o r t h e a s t of o f Stop S t o p 6, 6, b ut there is llittle i t t l e bedrock b e d r o c k vvisible i s i b l e until u n t i l the t h e Treasure T r e a s u r e prospect p r o s p e c t is is t h e r e is reached. reached . STOP 6B 6B -- - ---- - TREASURE_GOLD (Figure TREASURE GOLD PROSPECT ( F i g u r e 13) 13) - -a The T h e mine m i n e was was developed d e v e l o p e d between b e t w e e n 1891 1891 and a n d 1900, 1 9 0 0 , when two main t w o sshafts h a f t s were sunk s u n k on o n the the m a i n zone z o n e and a n d a third t h i r d on a a separate t o the t h e southeast. s o u t h e a s t . Additional A d d i t i o n a l work work s e p a r a t e zone z o n e 200 200 mm to was ddone was o n e about a b o u t 1955 1 9 5 5 when when aa small s m a l l mill m i l l was was set s e t up. up. Recorded is about a b o u t 35 35 ounces o u n c e s of o f gold. gold. R e c o r d e d production p r o d u c t i o n is Quartz Q u a r t z ddiorite i o r i t e underlies u n d e r l i e s the t h e area, a r e a , the t h e main m a i n vein vein being n o r t h w e s t of o f the t h e contact c o n t a c t with w i t h basalt. basalt. b e i n g about a b o u t 400 4 0 0 m northwest The vvein i e s at a t tthe h e hhanging a n g i n g wall w a l l of o f aa shear s h e a r zone z o n e which which The e i n llies strikes s t r i k e s from f r o m N350E ~ 3 to ~5 and t o 5N50°E ~ a n~d0 dips d i p~s about a b~o u t 750 75O Thevvein's width is about a b o u t 15 1 5 cm, c m , but but nnorthwest. orthwest. The e i n ' s average average w i d t h is iitt widens w i d e n s to t o 60 6 0 cm cm and and iin n places p l a c e s pinches p i n c h e s out out Tourmaline is common common a nand d p pyrite y r i t e is is a a minor minor ccompletely. ompletely. T o u r m a l i n e is constituent. Gold constituent. G o l d ooccurs c c u r s aas s ffine i n e grains g r a i n s and and is also also l i p surfaces. surf aces ssmeared m e a r e d oon n sslip IItt has h a s been b e e n reported r e p o r t e d (Joop ( J o o p Langelaar, L a n g e l a a r , personal personal communication, c o m m u n i c a t i o n , 1 91983) 8 3 ) t hthat, a t , iin n the t h e main m a i n sshaft, haft, a a series series ooff qquartz u a r t z veins v e i n s is is present p r e s e n t at a t the t h e footwall f o o t w a l l of o f the t h e shear shear These t o the t h e hanging—wall hanging-wall zzone. one. T h e s e vveins e i n s are a r e at a t an a n angle a n g l e to manner ' f o l d e d ' in i n aa m a n n e r indicating i n d i c a t i n g normal normal vvein e i n but b u t are a r e 'folded' movement oon o h have a v e l ilittle t t l e llateral ateral n tthe h e sshear h e a r pplane, l a n e , aand n d s so The continuity. were either e i t h e remplaced emplaced continuity. T h e ffootwall o o t w a l l veins v e i n s were eearlier a r l i e rthan t h a nthe t h ehanging—wall h a n g i n g - w a l l vvein, e i n , or or both b o t h were were eemplaced m p l a c e d simultaneously s i m u l t a n e o u s l y within w i t h i n aa fault f a u l t zone z o n e and a n d its its associated a s s o c i a t e d pinnate p i n n a t e fractures. fractures. The main to curve c u r v e westward w e s t w a r d at a t its i t s south south m a i n vein v e i n appears a p p e a r s to end, e n d , and a n d possibly p o s s i b l y to t o terminate t e r m i n a t e against a g a i n s t aa mylonite m y l o n i t e which which t o the t h e southeast. southeast. T he sstrikes t r i k e s N65°E ~ 6 5 and a0n d~ dips d i p s 750 7 5 0 to The Chemical mylonite c m to t o 33 m. m. C hemical m y l o n i t e has h a s aa width w i d t h of o f from f r o m 10 10 cm aanalyses n a l y s e s of o f the t h e mylonite m y l o n i t e indicate i n d i c a t e that, t h a t , relative r e l a t i v e to t o the the enclosing more e n c l o s i n g quartz q u a r t z diorite, d i o r i t e , the t h e mylonite m y l o n i t e contains c o n t a i n s more ssilica i l i c a (69.5% ( 6 9 . 5 % vs v s 62.2%) 6 2 . 2 % ) and and soda s o d a (4.05% ( 4 . 0 5 % vs v s 3.35%) 3. 3 5 % )and and carbonate c a r b o n a t e (1.28% ( 1 . 2 8 % vs v s 0.13%), 0. l 3 % ) , but b u t contains c o n t a i n s less l e s s of o f other other metal oxides o x i d e s (notably ( n o t a b l y iron i r o n and a n d magnesium) m a g n e s i u m ) and and trace trace is less Theggold metals. m etals. The o l d ccontent o n t e n t oof f both b o t h rocks r o c k s is less than t h a n 22 . �45 3 1 - a Outcrop ~ u c k pile Granodiorite Mylonite Pit Quartz vein metres Figure 13: Figure 13: Geologyofof the the Theasure Geology Treasure gold gold occurrence. occurrence. �46 ppb. P P ~ Replicate R e p l i c a t e analyses a n a l y s e s of o f aa chip c h i p sample s a m p l e across a c r o s s 23 2 3 cm cm of of the main vein showed the gold content to be erratic t h e main v e i n showed t h e g o l d c o n t e n t t o b e e r r a t i c AA grab ( f r o m 20 2 0 ppb ppb to t o 17.7 1 7 . 7 ppm). ppm) g r a b sample s a m p l e of o f the t h e vein vein (from averaged a v e r a g e d 50 50 ppm ppm Au Au and a n d of of the t h e footwall f o o t w a l l schist s c h i s t about a b o u t 90 90 ppb Au. Au. Another A n o t h e r sample s a m p l e of o f the t h e mylonite m y l o n i t e near n e a r the t h e shaft shaft ppb 1 2 ppb ppb Au. Au. All A l l samples s a m p l e s contained c o n t a i n e d less l e s s than than c o n t a i n e d 12 contained ppm silver. silver. 22 ppm . Return R e t u r n to t o the t h e highway highway and and turn t u r n left l e f t (southeast) ( s o u t h e a s t ) for f o r aa distance d i s t a n c e of of 1 . 6 km. km. All A l l of o f the t h e highway highway cuts c u t s are a r e in i n basalt. b a s a l t . Thrn T u r n right right 1.6 (southwest) m , where where aa s o u t h w e s t ) down down aa cottage—access c o t t a g e - a c c e s s road r o a d for f o r about a b o u t 200 200 m, t r a i l leads l e a d s south s o u t h to t o the t h e Pine P i n e Portage P o r t a g e Mine. Mine. trail STOP 77 PINE PINE PORTAGE PORTAGE GOLD GOLD MINE MINE (Figure ( F i g u r e 11) 14) STOP Originally O r i g i n a l l y discovered d i s c o v e r e d in i n 1882, 1 8 8 2 , the t h e Pine P i n e Portage P o r t a g e mine mine gained i t s abundant a b u n d a n t visible v i s i b l e gold. gold. g a i n e d early e a r l y recognition r e c o g n i t i o n for f o r its m i l l had had been b e e n built b u i l t on o n an an W i t h i n 33 years, y e a r s , aa stamp s t a m p mill Within intermittent stream and some underground development was i n t e r m i t t e n t stream and some u n d e r g r o u n d d e v e l o p m e n t was c a r r i e d out. o u t . Since S i n c e that t h a t time t i m e the t h e property p r o p e r t y has h a s been been carried explored e x p l o r e d several s e v e r a l times. times. The i s hosted h o s t e d by by west—facing, w e s t - f a c i n g , north—northnorth-northThe prospect p r o s p e c t is east e a s t trending, t r e n d i n g , pillowed p i l l o w e d and and massive m a s s i v e basaltic b a s a l t i c flows, f l o w s , and and lies less than 50 m east of the steeply dipping contact l i e s l e s s t h a n 50 m e a s t o f t h e s t e e p l y d i p p i n g c o n t a c t o f the t h e Dryberry D r y b e r r y granodiorite g r a n o d i o r i t e batholith. b a t h o l i t h . The The of granodiorite is massive to weakly f o l i a t e d and and contains contains g r a n o d i o r i t e i s m a s s i v e t o weakly foliated Granitic dikes in t h e basalt basalt f e w basaltic b a s a l t i c inclusions. inclusions. G r a n i t i c d i k e s i n the aa few a r e rare. rare. are Vein i n f i l l s aa strongly s t r o n g l y sheared s h e a r e d and and faulted faulted V e i n material m a t e r i a l infills i s at a t least l e a s t 3.5 3 . 5 mm wide. wide. Near Near the t h e inclined inclined z o n e which which is zone shaft s h a f t the t h e vein v e i n strikes s t r i k e s approximately a p p r o x i m a t e l y north n o r t h and and dips d i p s from from N65° ~ 6 to t o5 75°E; 7 5~ O ~ it ; i t has h a s been b e e n traced t r a c e d north n o r t h about a b o u t 200 200 mm where where it i t curves c u r v e s slightly s l i g h t l y to t o the t h e east. e a s t . The The main m a i n vein v e i n follows follows the t h e well—defined w e l l - d e f i n e d hanging h a n g i n g wall w a l l of of the t h e zone z o n e and and has h a s an an irregular i r r e g u l a r footwall f o o t w a l l contact c o n t a c t and and is i s commonly commonly wider w i d e r where where t h e footwall f o o t w a l l amphibolite a m p h i b o l i t e is i s brecciated. b r e c c i a t e d . The The vein vein the consists c o n s i s t s of o f discontinuous d i s c o n t i n u o u s lenses l e n s e s of of quartz, q u a r t z , with with carbonate c a r b o n a t e and and inclusions i n c l u s i o n s of o f schist. s c h i s t . An An old o l d assay a s s a y plan plan shows shows that t h a t the t h e mineralized m i n e r a l i z e d section s e c t i o n had had aa maximum maximum width width o f up up to t o 55 m. m. of Along the t h e hanging h a n g i n g wall w a l l there t h e r e is i s aa zone z o n e of o f fault fault Along gouge g o u g e several s e v e r a l centimetres c e n t i m e t r e s wide, w i d e , characterized c h a r a c t e r i z e d by by a b u n d a n t clay c l a y minerals. m i n e r a l s . No No ssilicification i l i c i f i c a t i o n of o f this t h i szone zone abundant was was detected d e t e c t e d and and only o n l y low low gold g o l d contents c o n t e n t s were w e r e found. found. Relative byt hthe e f i n e d by e rrotation o t a t i o n of o f aa R e l a t i v e movement movement i sisddefined well—developed "3"f ofoliation "C" w e l l - d e v e l o p e d "S1' l i a t i o n iinto n t o the t h e plane p l a n e of o f the t h e"C" foliation f o l i a t i o nindicating i n d i c a t i nreverse g r e v e r movement s e movement(Simpson (Simpson and and 1 9 8 3 ). Later L a t e r "S"—shaped "S"-shaped t etension n s i o n ggashes a s h e s indicate indicate Schmid, 1983) Schmid, normal movement;t hthis mayhhave n o r m a l movement; i s may a v e r eresulted s u l t e d ffrom r o m rrelaxation elaxation o f applied a p p l i e d stress. s t r e s s . Quartz Q u a r t z post—dates p o s t - d a t e s the t h e major m a j o r period period of of o f movement, movement, occupying o c c u p y i n g structures s t r u c t u r e s parallel p a r a l l e l to t o the t h e "C" "C" fabric f a b r i c as a s well w e l l as a s the t h e tension t e n s i o n gashes. sashes. Pyrite P y r i t e is i s the t h e principal p r i n c i p a l sulphide. s u l p h i d e . Chalcopyrite, Chalcopyrite, . �47 / / / /- '+4-4+ +,_++ 1 7+ ++ /+ I \------ /I'I /-----+ I / + + --.-. ----\ -1 1 H ' Tailings1 / / \ \ - Geological Geologicalcontact contact Liii Basalt Outcrop Open cut Eu Muck 1 Figure Figure Granite Hornblende—chlorite schist 14: 14: Muck trench Foliation, Foliation, dip dip Pine Portage Prospect Prospect Pine 0 • 20 mstres Geology Geology of o f the the Pine Pine Portage P o r t a g e gold gold occurrence. occurrence. 40 I + + + + L.._—J shack —— + + + ++ ++ + Core _— + + + j11 / (. + + �48 ggalena a l e n a and a n d sphalerite s p h a l e r i t e are a r e present p r e s e n t in i n lesser l e s s e r amounts a m o u n t s and and tthere h e r e is is rare r a r e pyrrhotite, p y r r h o t i t e , twinned t w i n n e d ilmenite, ilmenite , arsenopyrite, a r s e n o p y r i t e , covellite c o v e l l i t e and a n d gold. g o l d . The T h e main m a i n gangue gangue minerals m i n e r a l s are a r e quartz, q u a r t z , ankerite, a n k e r i t e , calcite, c a l c i t e , and a n d mica mica and and Fine c l a y minerals. minerals. F i n e qold g o l d (less ( l e s sthan t h a n20 2 0microns) m i c r o n s ) is clay found f o u n d iin n tthe h e gangue g a n g u e a and n d a sasi inclusions n c l u s i o n s i in n ppyrite; y r i t e ; coarser coarser The ggold o l d is is erratically e r r a t i c a l l y distributed. distributed. T h e larger l a r g e r pyrite pyrite ggrains r a i n s are a r e zoned z o n e d and a n d in i n places p l a c e s enclose e n c l o s e silicates, silicates , Sphalerite ppyrrhotite, y r r h o t i t e , sphalerite s p h a l e r i t e or or chalcopyrite. chalcopyrite. S p h a l e r i t e is is Tellurium ggenerally e n e r a l l y found f o u n d in i n ribbons r i b b o n s of o f mafic ma i c schist. schist. T ellurium ( Forsgren hhas a s bbeen e e n ddetected e t e c t e d by b.y microprobe m i c r o p r o b e aanalysis n a l y s i s (Forsgren The 1980); present. 1 9 8 0 ) ; calaverite c a l a v e r i t e(AuTe2) ( A u T e 2 ) may may bbe e p resent. The most most characteristic h e high high c h a r a c t e r i s t i c f e a t u r e o f t h e m i n e r a l i z a t i o n is tthe t w i c e the t h e ggold o l d content; c o n t e n t ; most ssilver i l v e r content, c o n t e n t , being b e i n g about a b o u t twice g o l d occurrences o c c u r r e n c e s iin n the t h e Kenora K e n o r a aarea r e a hhave a v e aa ssilver ilver gold content c o n t e n t which w h i c h is is near n e a r or o r below b e l o w detection d e t e c t i o n limits. limits T h e ffault a u l t with w i t h which w h i c h the t h e Pine P i n e Portage P o r t a g e prospect p r o s p e c t is is The aassociated s s o c i a t e d extends e x t e n d s iinto n t o the t h e Dryberry D r y b e r r y batholith. bath01 i t h . Mineralization to M i n e r a l i z a t i o n may be b e largely l a r g e l y restricted r e s t r i c t e d to Forsgren irregularities i r r e g u l a r i t i e s in i n the t h e fault f a u l t plane. plane. F o r s g r e n (1980) ( 1 980 ) cconcluded o n c l u d e d that t h a t "this " t h i s epigenetic, e p i g e n e t i c , sheared s h e a r e d fissure f i s s u r e vein v e i n is is thought t h o u g h t to t o be b e the t h e result r e s u l t ooff wall w a l l rock r o c k alteration a l t e r a t i o n and and he aa is proposed p r o p o s e d to t o be llateral a t e r a l secretion. s e c r e t i o n . The T h e vein v e i n is rredistribution e d i s t r i b u t i o n ooff host h o s t rock r o c k chemistry c h e m i s t r y with w i t h induced induced Ca2, z 0 and a n d S. S. Meteoric water may he be the the vvolatiles olatiles C 0 2 , HHO ssource o u r c e of o f these t h e s e volatiles." volatiles feature of the mineralization is - ." Return R e t u r n aalong l o n g the t h e trail t r a i l which, w h i c h , in i n part, p a r t , coincides c o i n c i d e s with w i t h the the At northward A t the t h e highway, highway, n o r t h w a r d extension e x t e n s i o n of o f the t h e Pine P i n e Portage P o r t a g e fault. fault. across a c r o s s from f r o m the t h e road r o a d leading l e a d i n g to t o stop s t o p 7, 7, iirregular r r e g u l a r lenses l e n s e s and and vveins e i n s of o f tourmaline t o u r m a l i n e and a n d pyrite—bearing p y r i t e - b e a r i n q quartz q u a r t z occur o c c u r in i n the the The basalts. b a s a l ts The contact c o n t a c t oof f the t h e basalts b a s a l t s with w i t h the t h e Dryberry Drybe r r y well is w e l l eexposed x p o s e d in i n a hhighway i g h w a y cut, c u t , 350m 350m ssoutheast o u t h e a s t of of ggranodiorite r a n o d i o r i t e is Continue this e a s t for f o r 7.2 7 . 2 km to t o the t h e junction j u n c t i o n of o f Highway Highway t h i s point. point. C o n t i n u e east 71 5. 5 km to t o Rushing R u s h i n g River R i v e r Provincial Provincial 71 aand n d then t h e n turn t u r n right r i g h t (south) ( s o u t h ) 5.5 Fromhhere it is Park. is a further f u r t h e r 6.4 6 . 4 km km tto o the t h e turnoff t u r n o f f onto o n t o the the Park. From e r e it Witch A l l of o f the t h e rocks r o c k s along a l o n g the t h e route r o u t e thus t h u s far, f a r , and and W i t c h Bay Bay Road. R o a d . All kmaalong Witch BayRRoad, for f o r the t h e first f i r s t 55 km l o n g t the he W i t c h Bay o a d , a rare e p part a r t oof f the the The Dryberry o f the t h e Witch W i t c h Bay Bay Road Road is is D r y b e r r y batholith. batholith. T h e second s e c o n d 55 km of within w i t h i n bbasalts a s a l t s which w h i c h are a r e the t h e approximate a p p r o x i m a t e stratigraphic s t r a t i q r a p h i c equivalent equivalent At of a t the t h e Pine P i n e Portage P o r t a g e Mine. Mine. At a a junction j u n c t i o n about a b o u t 10 10 km km o f those t h o s e at from f r o m Highway Highway 71, 7 1 , turn t u r n to t o the t h e right r i g h t and a n d continue c o n t i n u e 300 300 mm to t o the t h e site site of o f the t h e former f o r m e r shaft s h a f t and a n d mill m i l l of o f the t h e Wendigo W e n d i g o Gold G o l d Mine. Mine. . THE WENDIGO GOLD-COPPER GOLD—COPPER MINE STOP STOP 88 THE M I N E (Figure_15) ( F i q u r e 15 Gold G o l d was was first f i r s t discovered d i s c o v e r e d on o n the t h e property p r o p e r t y in i n 1899, 1899, Work when an 18m shaft was sunk on the main vein. a n 18m s h a f t was s u n k o n t h e m a i n v e i n . continued c o n t i n u e d during d u r i n g the t h e next n e x t year y e a r and a n d about a b o u t 1000 1 0 0 0 tons t o n s of of The mine gold—copper o r e were were milled. milled. The m i n e lay l a y idle i d l e until until g o l d - c o p p e r ore when iit was re—examined t was r e - e x a m i n e d by b y Wendiqo W e n d i q o Gold G o l d Mines Y i n e s Ltd. Ltd. 11933 9 3 3 when O v e r tthe h e next n e x t ten t e n yyears e a r s considerable c o n s i d e r a b l eunderground u n d e r g r o u n d and and Over was mine ssurface u r f a c e work work w a s ddone o n e b before e f o r e t the he m i n e cclosed l o s e d i in n eearly arly Total 11943. 943. T o t a l production p r o d u c t i o n from f r o m the t h e property p r o p e r t y was was 67,000 6 7 , 0 0 0 oz oz �49 Las La 3.11. — — .— Gaqe• t.ak. 7 - — — — —— — - /• _V V — — /477 7— —V s7 — — 7——— 2 —— ., — .&I = = ?- -¥à ## A /// /// /// — — — -> ———-— —— — I shaft shaft I1 Basalt Basalt building building swamp swamp gravel gravel road road geological geotogical contact contact lault fault area area of of outcrop outcrop anticline. anticline,syncline synctine pillow pillow lacing facing 22 Porpbyritic Porphyritic Basalt Basalt 33 LeucocratiC Leucocratic t3abbro Gabbro 44 Melanogabbro Melanogabbro 5 S @ Field Field stop stop location location 00 -' dragf old dragfokj weak foliation foliation(inclined, (inclined. vertical, dip dip unknown) unknown) strong strong foliation foliation(inclined, (inclined, vertical, vertical, dip dip unknown) unknown) F i g u r e 15: 15: Figure Pendotfie Penctotite 190 100 200 200 metres Surface S u r f a c e geology g e o l o g y of of the t h eWendigo Wendigo Gold Gold Mine. Mine. 300 300 �50 of o f gold, g o l d , 14,762 1 4 , 7 6 2 oz o z of o f silver s i l v e r and and 1,886,246 1 , 8 8 6 , 2 4 6 pounds p o u n d s of of copper c o p p e r from f r o m 206,054 2 0 6 , 0 5 4 tons t o n s milled, m i l l e d , establishing e s t a b l i s h i n g the the Wendigo W e n d i g o as a s the t h e largest l a r g e s t past p a s t producer p r o d u c e r in i n the t h e western western Wabigoon Subprovince. S u b p r o v i n c e . Average A v e r a g e grade g r a d e of o f ore ore milled m i l l e d was was 0.33 0 . 3 3 oz o z of o f Au/ton. Au/ton. Wendigo Wendigo Mine Mine lies l i e s on o n the t h e south s o u t h limb l i m b of o f the t h e Hay Hay Island and 6) 6 9 within w i t h i n mafic maÂi c volcanics volcanics I s l a n d antiform a n t i f o r m (Figures ( F i g u r e s 55 and t o ultraznafic u l t r a m a f i c sills. s i l l s Metamorphic . M e t a m o r p h i c grade g r a d e is is a n d mafic maf i c to and Analogies lower lower ggreenschist r e e n s c h i s t facies. facies A n a l o g i e s between b e t w e e n the the stratigraphy s t r a t i g r a p h y here h e r eand a n data the t t hDuport e D u p o rMine t Mineon onShoal S h o a lLake Lake can twoo occur closet oto tthe op of c a n be be drawn; d r a w n ; t the h e two c c u r close h e .top o f aa lower lower mafic maÂi c volcanic v o l c a n i c cycle. cycle. Felsic F e l s i c pyroclastic p y r o c l a s t i c rocks r o c k s are a r eexposed e x p o s e d south s o u t h of o f the the mine m i n e aalong l o n g tthe h e north n o r t h shore s h o r e of o f Witch W i t c h Bay. Bay. The The felsic felsic rocks t o sericite sericite r o c k s are a r e intensely i n t e n s e l y deformed, d e f o r m e d , commonly to Only rarely schist. r a r e l y are a r e good g o o d relic r e l i c primary p r i m a r y textures textures schist. is the the locus l o c u s of o f an an p r e s e r v e d . The The ffelsic e l s i c sequence s e q u e n c e is preserved. extensive Bay—Witch Bay ffault e x t e n s i v e fault f a u lsystem, t s y s t e mthe , t Andrew h e Andrew Bay-Witch Bay ault zone z o n e (Figure ( F i g u r e 5), 5 1 , which w h i c h Ayer A y e r (1984) ( 1 9 8 4 ) suggests s u g g e s t s is is the the extension Lake—Rush Bayd dextral e x t e n s i o n of of the t h eCrouck Crowduck Lake-Rush Bay e x t r a l ffault ault zone z o n e (Davies ( D a v i e s and and Smith, S m i t h , 1984). 1 9 8 4 ) . The T h e ffault, a u l t , therefore, therefore, may extend e x t e n d from f r o m Indian I n d i a n Bay Bay of o f Shoal S h o a l Lake Lake to t o Witch W i t c h Bay Bay of of may Lake L a k e of o f the t h e Woods, Woods, aa distance d i s t a n c e of o f over o v e r 70 7 0 km. km. The mine The m i n e ssite i t e is i s primarily p r i m a r i l y underlain u n d e r l a i n by by porphyritic porphyritic and equigranular e q u i g r a n u l a r basalt, b a s a l t , which w h i c h has h a s been b e e n intruded i n t r u d e d by by gabbro s i l l s . Pillows P i l l o w s are a r e observed observed g a b b r o and a n d peridotite p e r i d o t i t e sills. locally l o c a l l y in i n tthe h e basalts, b a s a l t s , bbut u t ttop o p ddeterminations e t e r m i n a t i o n s are a r e often often Composition questionable. Compos i t i o n varies v a r i e s from f r o m tholeiite t h o l e i i t e to to questionable. high—iron is an an h i g h - i r o n tholeiite. t h o l e i i t e . The The porphyritic p o r p h y r i t i c basalt b a s a l t is excellent marker horizon, massive excellent m arker h o r i z o n , and a n d overlies o v e r l i e s the the m ass i v e basalt. basalt. Pillows observed near t h e s h a f t a r e a i n d i c a t e This tops is aa Mg—tholeiite M q - t h o l e i i t e and and t o p s to t o the t h e north. north. T h i s bbasalt a s a l t is characterized c h a r a c t e r i z e d by b y up up to t o20% 2 0 % white w h i t e feldspar f e l d s p a r phenocrysts phenocrysts less than t h a n 2.5 2.5 cm c m in i n diameter. diameter. less Much of o f thet hproperty e p r o piseunderlain r t y is by u ngabbro d e r l aand i n by g a b b r o a n d peridotite i t e c o mthick, p r i s idifferentiated n g t h i c k , sills. d i f f e r e n t i a t e d sills. p e r i d o tcomprising Fine—grained F i n e - g r a i n e d peridotite p e r i d o t i t e lies l i e s at a t the t h e base b a s e of o f some some sills sills The directly d i r e c t l y overlying o v e r l y i n g the t h e porphyritic p o r p h y r i t i c basalt. basalt. The eridotite, w e r i d o t i t e , where w h e r e less l e s s altered, a 1 t e r e d , is is composed composed principally principally of o f serpentine, s e r p e n t i n e , talc t a l c and a n d magnetite. m a g n e t i t e . Peridotite P e r i d o t i t e is is commonly overlain o v e r l a i n by by melagabbro m e l a q a b b r o transitional t r a n s i t i o n a l to to The m melagabbro is locally l o c a l l y magnetic m a g n e t i c and and leucogabbro. e l a g a b b r o is leucogabbro. displays more commonly commonly is is non— nond i s p l a y s rhythmic r h y t h m i c layering, l a y e r i n g , but b u t more Amphibole magnetic m a g n e t i c and a n d massive. massive. A m p h i b o l e has h a s replaced r e p l a c e d original original pyroxene. f e l d s p a r : p y r o x e n e ratio r a t i o was was close close p y r o x e n e . The T h e original o r i g i n a l feldspar:pyroxene to t o 50:50. 50:50. In I n places p l a c e s the t h e leucogabbro l e u c o g a b b r o is is porphyritic, porphyritic, containing c o n t a i n i n g feldspar f e l d s p a r phenocrysts p h e n o c r y s t s up up to t o 33 cm in i n diameter, diameter, similar t o those t h o s e observed o b s e r v e d within w i t h i n the t h e porphyritic p o r p h y r i t i c basalt; basalt; s i m i l a r to C o a r s e r peridotite p e r i d o t i t e occurs o c c u r s as a s dikes d i k e s and and as a s narrow n a r r o w layers layers Coarser in cores oof f the t h e ssills, i l l s , ssuggesting u g g e s t i n g that t h a t the t h e ssills i l l s may i n the t h e cores consist t h a n one o n e cycle. c y c l e . This T h i s peridotite p e r i d o t i t e locally locally c o n s i s t of o f more than Coarse displays d i s p l a y s excellent e x c e l l e n t rhythmic r h y t h m i c layering. layering. C o a r s e peridotite peridot ite dikes d i k e s and/or a n d / o r sills s i l l s intrude i n t r u d e the t h e host h o s t volcanics v o l c a n i c s in i n aa few few places. places. . Pillo observed near the shaft area indicate �51 Several S e v e r a l tight, t i g h t , east e a s t trending, t r e n d i n g , west w e s t plunging p l u n g i n g folds folds have h a v e been b e e n identified i d e n t i f i e d by b y means m e a n s of o f the t h e reversal r e v e r s a l of of differentiation s i l l s , and a n d by b y limited l i m i t e d top top d i f f e r e n t i a t i o n trends t r e n d s in i n the t h e sills, determinations Basalt B a s a l t located l o c a t e d within within d e t e r m i n a t i o n s in i n the t h e basalts. b a s a l ts. the t h e anticlinal a n t i c l i n a l cores c o r e s of o f these t h e s e folds f o l d s is is strongly s t r o n g l y foliated foliated to This is most noticeable n o t i c e a b l e in i n the t h e vicinity v i c i n i t y of of t o sheared. sheared. T h i s is the c l o s e to t o Gagne G a g n e Lake Lake where w h e r e wide wide t h e main m a i n shaft s h a f t and and close sections Notably, a r e strongly s t r o n g l y sheared. sheared. Notably, s e c t i o n s of o f basalt b a s a l t are strong is apparently a p p a r e n t l y absent a b s e n t from f r o m the t h e gabbro gabbro s t r o n g deformation d e f o r m a t i o n is bodies. The bodies. T h e texture t e x t u r e of o f the t h e leucocratic l e u c o c r a t i c gabbro g a b b r o shows shows virtually v i r t u a l l y no n o strain, s t r a i n , and a n d while w h i l e some some strain s t r a i n is is evident evident within i t does does w i t h i n both b o t h the t h e peridotite p e r i d o t i t e and a n d the t h e melagabbro, m e l a g a b b r o , it not n o t appear a p p e a r sufficient s u f f i c i e n t to t o be b e consistent c o n s i s t e n t with w i t h the t h e tight tight folding. folding. Gold G o l d mineralization m i n e r a l i z a t i o n is is restricted r e s t r i c t e d to to zones z o n e s of of silicification, s i l i c i f i c a t i o n , notably n o t a b l y to t o four f o u r east—trending e a s t - t r e n d i n g steeply steeply north—dipping n o r t h - d i p p i n g veins. v e i n s . All A l l the t h e veins v e i n s were were examined e x a m i n e d while while the mine the m i n e was was in i n operation, o p e r a t i o n , but b u t production p r o d u c t i o n was was restricted restricted to Veins t o the t h e No. N o . 11 vein. vein. V e i n s 2, 2 , 3 aand nd 4 4 are a r e located l o c a t e d about about 460 The e a s t of o f the t h e main m a i n shaft. shaft. T h e attitudes a t t i t u d e s of o f the the 460 mm east veins are slightly s l i g h t l y discordant d i s c o r d a n t to t o the t h e enclosing e n c l o s i n g lava lava v e i n s are flows The f l o w s (Figure ( F i g u r e 16) 16 ) . The veins v e i n s occupy o c c u p y aa zone z o n e about a b o u t 50 50mm w i d e w h i c h e x t e n d s to t h e p e r i d o t i t e c o n t a c t t o t h e north. They are north. a r e found f o u n d within w i t h i n both b o t h porphyritic p o r p h y r i t i c and and massive m a s s i v e b a s a l t , much o f w h i c h is l a r g e l y a l t e r e d t o chlorite schist. The s o u t h ( o r e p r o x i m a l ) s i d e o f t h e a l t e r e d to t o aa soft soft p e r i d o t i t e s i l l h a s b e e n i n t e n s e l y altered "talcy" Chlorite " t a l c y " rock. rock. C h l o r i t e schist s c h i s t proximal p r o x i m a l to t o the t h e main m a i n ore ore zone z o n e is is enriched e n r i c h e d in i n carbonate c a r b o n a t e and a n d quartz, q u a r t z , and a n d contains contains abundant minor a b u n d a n t epidote e p i d o t e and a n d zoisite-, zoisite, m i n o r ssphene, p h e n e , and a n d lesser lesser amounts a m o u n t s of o f clinozoisite, c l i n o z o i s i t e , opaques o p a q u e s and and sericite. sericite. The The No. No. 1 vein, v e i n , which w h i c h strikes s t r i k e s N8O0E ~ 8 0 and a0n d~ dips d i p s about about 790 7 9 0 to t o the t h e north, n o r t h , maintains m a i n t a i n s an a n average a v e r a g e width w i d t h of o f 30 30 cm, cm, pinching p i n c h i n g and a n d swelling s w e l l i n g to t o aa maximum maximum width w i d t h of o f 76 76 cm. cm. Quartz Q u a r t z contains c o n t a i n s pyrite, p y r i t e , pyrrhotite p y r r h o t i t e and a n d chalcopyrite. chalcopyrite. Locally, Little L o c a l l y , sulphide s u l p h i d e exceeds e x c e e d s quartz. quartz. L i t t l e of o f the t h e vein vein material m a t e r i a l is is presently p r e s e n t l y exposed. e x p o s e d . Thomson Thomson (1936) ( 1 936 ) estimated estimated that, t h a t , throughout t h r o u g h o u t the t h e mine, m i n e , half h a l f the t h e vein v e i n material m a t e r i a l is is sulphide, s u l p h i d e , a n d t h a t t h e s c h i s t i m m e d i a t e l y ad j o i n i n g t h e quartz In commonly well w e l l mineralized m i n e r a l i z e d with w i t h sulphic3es. sulphides. In q u a r t z isiscommonly g e n e r a l , s u l p h i d e s a r e i n s t r e a k s and l e n s e s w h i c h p a r a l l e l t h e s h e a r i n g . Milky—white, M i l k y - w h i t e , unmineralized unmineralized quartz q u a r t z veins, v e i n s , containing c o n t a i n i n g traces t r a c e s of o f ankerite, a n k e r i t e , may may be b e seen seen on a n d underground, u n d e r g r o u n d , locally l o c a l l y crosscutting c r o s s c u t t i n q the the o n the t h e surface s u r f a c e and mineralized t w o generations g e n e r a t i o n s of of m i n e r a l i z e d quartz, q u a r t z , indicating i n d i c a t i n g two silicification. s i l i c i f i c a t i o n . Faulting F a u l t i n g has h a s been b e e n observed o b s e r v e d in i n places, places, but b u t offsets o f f s e t s are a r e restricted r e s t r i c t e d to t o aa few f e w metres. metres. Petrographic P e t r o g r a p h i c work w o r k ccarried a r r i e d out o u t ini n1934 1 9 3 4and a n d1935 1935 (Canada ( C a n a d a Department D e p a r t m e n t of o f Mines M i n e s and a n d Resources, R e s o u r c e s , 1936) 1 9 3 6 ) showed showed native n a t i v e g o l d t o b e p r e s e n t as r e l a t i v e l y c o a r s e q r a i n s within w i t h i n grey g r e y translucent t r a n s l u c e n t quartz: q u a r t z : pyrite p y r i t e and a n d chalcopyrite chalcopyrite are a r e the t h e dominant d o m i n a n t sulphides, s u l p h i d e s , with w i t h minor m i n o r amounts a m o u n t s of of pyrrhotite, p y r r h o t i t e , s p h a l e r i t e , a n d a r s e n o p y r i t e . Brownell Brownell (1943) ( 1 9 4 3 ) noted n o t e d distinct d i s t i n c t mineralogical m i n e r a l o g i c a l changes c h a n g e s in i n the t h e vein vein . wide which extends to the peridotite contact to the basalt, much of which is largely altered to chlorite schist. The south (ore proximal) side of the peridotite sill has been intensely 1 and that the schist immediately adjoining the general, suiphides are in streaks and lenses which parallel the shearing. gold to be present as relatively coarse qrains sphalerite, and arsenopyrite. �Fiqure 16: Geoloqy of the 500 level of the Wendiqo Gold Mine (after Brownell, 1943). 1Ñ b IÑ c 1) 3 a2 0 u V IÑ 8 0 er-1 G- T? s c IÑ 01 N) �53 w h i c h were directly d i r e c t l y related r e l a t e d to t o aa sudden s u d d e n decrease d e c r e a s e in i n gold gold which content; c o n t e n t ; in i n the t h e upper u p p e r levels l e v e l s of o f the t h e mine, m i n e , gold g o l d was was accompanied a c c o m p a n i e d by b y pyrite p y r i t e and a n d chalcopyrite, c h a l c o p y r i t e , whereas whereas below below the is the t h e ddominant o m i n a n t sulphide s u l p h i d e and and t h e 335m level l e v e l pyrrhotite p y r r h o t i t e is a r e much much lower. lower. B r o w n e l l (1943) ( 1 9 4 3 ) suggested suggested ggold o l d contents c o n t e n t s are Brownell that t h a t this t h i s relationship r e l a t i o n s h i p is is essentially e s s e n t i a l l y temperature temperature ddependent, e p e n d e n t , ie. i e . pyrrhotite p y r r h o t i t e is is normally n o r m a l l y deposited d e p o s i t e d at at hhigher i g h e r temperatures t e m p e r a t u r e s than t h a n pyrite, p y r i t e , chalcopyrite c h a l c o p y r i t e and a n d gold. gold. Hee concluded H c o n c l u d e d that, t h a t , below b e l o w the t h e 335m 335m level, l e v e l , no n o additional additional ore might o re m i g h t be b e expected. expected. The is characterized c h a r a c t e r i z e d by b y intense i n t e n s e deformation d e f o r m a t i o n and and T h e area a r e a is l i e s within w i t h i n the t h e influence i n f l u e n c e of o f the t h e Andrew Andrew pprobably r o b a b l y lies Bay—Witch Since B a y - W i t c h Bay Bay fault f a u l t zone. zone. S i n c e the t h e rock r o c k assemblage a s s e m b l a g e is is heterogeneous, h e t e r o q e n e o u s , most of o f the t h e strain s t r a i n was was taken t a k e n up u p by b y the the least ( i . e . massive m a s s i v e and a n d porphyritic porphyritic l e a s t competent c o m p e t e n t rocks r o c k s (i.e. The contrasting bbasalt). asalt). The c o n t r a s t i n q competencies c o m p e t e n c i e s oof f the t h e two t w o major major rrock o c k types t y p e s (intrusive ( i n t r u s i v e vs v s extrusive) e x t r u s i v e ) resulted r e s u l t e d in i n zones z o n e s of of dilatancy d i l a t a n c y being b e i n g created c r e a t e d along a l o n g the t h e contact c o n t a c t between b e t w e e n the the These ttwo w o units. units. T h e s e zones z o n e s of o f dilatancy d i l a t a n c y acted a c t e d as a s permeable permeable cchanneiways h a n n e l w a y s along a l o n g which w h i c h hydrothermal h y d r o t h e r m a l fluids f l u i d s moved upwards. The upwards. T h e vertical v e r t i c a l zonation z o n a t i o n noted n o t e d by b y Brownell B r o w n e l l (1943) ( 1 943 ) may represent r e p r e s e n t two t w o ddistinct i s t i n c t sstability t a b i l i t y fields f i e l d s with w i t h the t h e 335 335 m level l e v e l corresponding c o r r e s p o n d i n g to t o the t h e stability s t a b i l i t y field f i e l d boundary. boundary. Locality_A This h i s locality l o c a l i t y is is sslightly l i g h t l y east e a s t of o f the t h e map map L ocality A T -bbounda7and o u n d a r y a n dshows s h o w srelatively r e l a t i v e l y undeformed u n d e f o r m e d porphyritic porphyritic bbasalt. asalt. Locality_B Locality B -- Relatively R e l a t i v e l y undeformed u n d e f o r m e d massive m a s s i v e basalt. basalt. Slightly Locality L o c a l i t y CC S ----l i g h t l y elongate e l o n g a t e ppillows i l l o w s within w i t h i n fine— fineCompare dgrainedTsalt. rained basalt. C o m p a r e this t h i s ooutcrop u t c r o p with w i t h more—deformed more-deformed rrocks o c k s which w h i c h will w i l l be b e seen s e e n later. later. Locality D L ocality D A t h i s outcrop o u t c r o p of o f highly h i g h l y deformed deformed Att this pporphyrTEtc o r p h y r l t i c bbasalt, a s a l t , remnant r e m n a n t feldspar f e l d s p a r phenocrysts p h e n o c r y s ts are are is rich r i c h in i n carbonate c a r b o n a t e and and bbarely a r e l y recognizable. recognizable. T h i s rock r o c k is This fine f i n e pyrite. pyrite. ---7- Locality BE From L o c a l i t yt h e oold ld m i n e ssite, i t e , follow f o l l o w the t h e trail t r a i l to to From the mine t h e wpassing e s t p a s s iover n g o vvarieties e r v a r i e t i eof s ochlorite f c h l o r i t eschist s c h i s t which which tTt A t this this hhave a v e undergone u n d e r g o n e various v a r i o u s degrees d e g r e e s of o f deformation. deformation. At l o c a l i t y , vvirtually i r t u a l l y undeformed u n d e f o r m e d pillowed p i l l o w e d porphyritic porphyritic locality, From make w e will will m a k e aa bbasalt a s a l t faces f a c e s north. north. From this t h i s point p o i n t we sill. ttraverse r a v e r s e north n o r t h across a c r o s s the t h e differentiated d i f f e r e n t i a t e d sill. Locality Locality ------ FF On tthe On h e north n o r t h sside i d e of of a a valley, v a l l e y , which w h i c h is is Ttertgd i n t e r p r e t to e d be t o bunderlain e u n d e r l a i by n b ytalc t a l cschist, s c h i s t , peridotite peridotite l i t t l e sign s i g n of o f deformation d e f o r m a t i o n and a n d is is ddisplays i s p l a y s little rrepresentative e p r e s e n t a t i v e of o f the t h e fine—grairied, f i n e - g r a i n e d , bbasal a s a l pportion o r t i o n oof f the the sill. ddifferentiated i f f e r e n t i a t e d sill. ----- Locality Melagabbro Locality G G M e l a q a b b r o in i n these t h e s e outcrops o u t c r o p s is enerally is qgenerally magnium rich, magnesium r i c h ,and a n dlocally l o c a l l y contains c o n t a i n s segregations, segregations, �54 iinclusions n c l u s i o n s or or veinlets v e i n l e t s of o f leucogabbro. leucoqabbro. foliation f o l i a t i o n is is evident. evident. IIn n pplaces l a c e s aa weak weak These are Locality L o c a l i t y HH T h e s e rrocks ocks a r e representative r e p r e s e n t a t i v e of o f the the I T r ' ~ ~ ~ zzone f o n~ e a bbetween e1 t w e e n melagabbro r n e l a g a b b r o and a n d leucoqabbro. leucoqabbro. Feldspar—actinolite is close c l o s e to t o 50:50, 5 0 : 5 0 , and a n d the the F e l d s p a r - a c t i n o l i t e ratio r a t i o is rock r o c k is is generally g e n e r a l l y massive, m a s s i v e , showing s h o w i n g little l i t t l e sign s i g n of of sstrain. train. Between L o c a l i t y II B e t w e e n localities l o c a l i t i e s H and a n d I, I , coarse c o a r s e feldspar feldspar Locality within p h e n o c r w s ooccur c c u r locally locally w i t h i n the t h e leucogabbro, leucoqabbro, indicating maf i c i n d i c a t i n g the t h e top t o p oof f the t h e first f i r s t ultramafic u l t r a m a f i c to t o mafic cycle. c y c l e . Primary P r i m a r y layering l a y e r i n g within w i t h i n outcrops o u t c r o p s of o f coarse coarse melagabbro m e l a q a b b r o and a n d peridotite p e r i d o t i t e can c a n be b e observed o b s e r v e d at a t this this llocal o c a l iity. ty. -TTeucogabbro. i n t r u d e s leucogabbro. At A t this t h i s location l o c a t i o n aa coarse coarse peridotite p e r i d o t i t e dike dike Contacts C o n t a c t s are a r e sharp s h a r p and and serpentine s e r p e n t i n e fills f i l l s fractures f r a c t u r e s in i n the t h e adjacent a d j a c e n t gahbro. qabbro. Locality L o c a l -i t y 3J Locality_K R e t u r n to t o the t h e mine m i n e site, s i t e , passing p a s s i n g over over L o -c a l i t y K Return df6med,pillowed, e f o r m e d , p i l l o w e dporphyritic , p o r p h y r i t i cbasalt b a s a l t and a n d chlorite chlorite The schist. schist. T h e oonly n l y present p r e s e n t exposure e x p o s u r e of o fthe t h emain m a i nWendigo Wendigo Here, the u n f o r t u n a t e l y , quite q u i t e poor. poor. Here, t h e chlorite chlorite v e i n i s , unfortunately, be examined e x a m i n e d further, f u r t h e r , as as there t h e r e are a r e several several sschist c h i s t can c a n be The ggood o o d vertical v e r t i c a l exposures e x p o s u r e s in i n the t h e general g e n e r a l area. area. The aadjacent d j a c e n t muck—pile m u c k - p i l e contains c o n t a i n s the t h e last l a s t material m a t e r i a l taken t a k e n from from the mine, t h e 335 3 3 5 mm level. level. the m i n e , and a n d probably p r o b a b l y caine c a m e ffrom r o m below the vein is, Return Highway 771, making R e t u r n tto o Highway 1, m a k i n g one o n e additional a d d i t i o n a l stop s t o p along a l o n g the t h e way. way. At At a a distance d i s t a n c e of o f 3.2 3. 2 km from f r o m the t h e road r o a d junction j u n c t i o n south s o u t h of o f the the Wendigo mill W endigo m i l l site, s i t e , turn t u r n sharp s h a r p left l e f t (north) ( n o r t h ) onto o n t o aa forest—access fores t-access Approximately a l o n g this t h i s road r o a d aa widening w i d e n i n g occurs o c c u r s at at a rroad. oad. A p p r o x i m a t e l y 500 5 0 0 m along A trail bend: is tthe h e ffinal i n a l sstop t o p on o n the t h e field f i e l d trip. trip. t r a i l leads leads b e n d : this t h i s is 0 m to t o Kite K i t e Lake, L a k e , and a n d half h a l f way way along a l o n g this t h i s trail t r a i l are are nnorth o r t h about a b o u t 660 the workings the w o r k i n g s ooff Witch W i t c h Bay Bay Gold Gold Mines M i n e s Ltd. Ltd. - STOP BAY GOLD--PROSPECT -- 99-----WITCH --- BAY The The ggeology e o l o g y in i n the t h e vvicinity i c i n i t y of o f Kite K i t e Lake L a k e has h a s not not Based it bbeen e e n mapped in i n detail. detail. B a s e d oon n aeromagnetic a e r o r n a q n e t i c data d a t a it would w o u l d aappear p p e a r that t h a t the t h e principal p r i n c i p a l lithologic l i t h o l o g i c units u n i t s of o f the the Wendigo ( i e . basalt, b a s a l t , gabbro g a b b r o and a n d peridotite) peridotite) , W e n d i g o mine m i n e area a r e a (ie. east—northeast eextend x t e n d eas t - n o r t h e a s t as a s far f a r as a s tthe h e ccentral e n t r a l ppart a r t of o f Kite Kite Lake, L a k e , where w h e r e they t h e y terminate t e r m i n a t e against a g a i n s t granodiorite g r a n o d i o r i t e of o f the the Dryberry D r y b e r r y bbatholith. ath01 i t h . Fine—grained F i n e - g r a i n e d basalt b a s a l t underlies u n d e r l i e s an a n area a r e a south s o u t h of o f Kite Kite Near the Lake. Near t h e ssouthernmost o u t h e r n m o s t tip t i p of o f Kite K i t e Lake L a k e an an L ake. b r e c c i a , from f r o m one o n e to to e a s t - s t r i k i n g zone z o n e of o f schist s c h i s t and and breccia, east—striking 7Q0, two metres wide t w o metres w i d e and a n d ddipping i p p i n g south s o u t h at a t from f r o m 550 5 5 ^ to t o 70^, contains c o n t a i n s some carbonate c a r b o n a t e and a n d one o n e or or more more quartz q u a r t z veins v e i n s and and The lenses l e n s e s with w i t h aa maximum width w i d t h of o f 45 45 cm. cm. T h e qquartz u a r t z is is fractured, f r a c t u r e d , encloses e n c l o s e s minor m i n o r silicified s i l i c i f i e d basalt, b a s a l t , and and ccontains o n t a i n s aabundant b u n d a n t cchalcopyrite h a l c o p y r i t e and a n d pyrite p y r i t e in i n and a n d near near , �55 some s o m e of o f the t h e fractures. fractures. T h e mineralization m i n e r a l i z a t i o n and a n d its its The stratigraphic position is similar to that at the s t r a t i g r a p h i c p o s i t i o n is s i m i l a r t o t h a t a t t h e Wend Wend igo. iqo. Two sshafts a p a r t have h a v e been b e e n sunk s u n k on o n the the h a f t s about a b o u t 30 30 m apart zone. c h i p sample s a m p l e across a c r o s s 50 5 0 cm c m of o f the t h e mineralized mineralized z o n e . A chip quartz a t the t h e east e a s t shaft s h a f t assayed a s s a y e d 1.93 1 . 9 3 ounces o u n c e s of of q u a r t z vein v e i n at gold g o l d per p e r ton. t o n . A third t h i r d shaft s h a f t was put p u t down down a a further f u r t h e r 75 75 m to t o the t h e east. e a s t . A fourth f o u r t h shaft s h a f t was w a s sunk s u n k on o n aa separate s e p a r a t e zone zone approximately t o the t h e southwest. s o u t h w e s t . The T h e zone z o n e is i s not not a p p r o x i m a t e l y 100 100 mm to exposed, material e x p o s e d , but but m a t e r i a l on o n the t h e dump indicates i n d i c a t e s that t h a t it it is is carbonatized, c a r b o n a t i z e d , sheared s h e a r e d basalt b a s a l t with w i t h minor m i n o r quartz q u a r t z and a n d with with chalcopyrite, c h a l c o p y r i t e , pyrite p y r i t e and a n d pyrrhotite. pyrrhot ite. �56 References References Ayer, J.A., 198)4, Bay A Area, J.A., 1 9 8 4 , GGeology e o l o g y oof f tthe h e BBigstone i g s t o n e Bay r e a , District D i s t r i c t of of Ayer, Kenora; p.19—224 i in Summary oof Ontario K e n o r a ; p.19-24 n Summary f FFieldwork, i e l d w o r k , 11984, 984, O n t a r i o GeoGeological l o g i c a l Survey, S u r v e y , Edited E d i t e d by by John J o h n Wood, Wood, Owen Owen L. L. White, W h i t e , R.B. R.B. Barlow, A. C . 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A . , 1983, 1 9 8 3 , Gold Gold Deposits D e p o s i t s in in Northwestern N o r t h w e s t e r n Ontario; O n t a r i o ; p.194—210 p.194-210 in i n The The Geology G e o l o g y of o f Gold Gold in in Ontario, A. C. Colvine, C o l v i n e , Ontario O n t a r i o Geological G e o l o g i c a l Survey, Survey, O n t a r i o , edited e d i t e d by A.C. Miscellaneous M i s c e l l a n e o u s Paper P a p e r 110, 1 1 0 , 27Bp. 278p. and Canada Department D e p a r t m e n t of o f Mines Mines and and Resources, R e s o u r c e s , 1936, 1 9 3 6 , Ore Ore Dressing D r e s s i n garid Metallurgical M e t a l l u r g i c a l Investigation I n v e s t i g a t i o n No.621; No.621; Investigations I n v e s t i g a t i o n s in i n Ore Ore Dressing D r e s s i n g and and Metallurgy, M e t a l l u r g y , Jan.—Jun., J a n . - J u n . , 1935, 1 9 3 5 , p.103—il6. p.103-116. Davies, 1965, D a v i e s , JJ.C., .C., 1 9 6 5 , Geology G e o l o g y of o f the t h e High High Lake—Rush Lake-Rush Bay Bay Area, Area, District D i s t r i c t of o f Kenora; K e n o r a ; Ontario O n t a r i o Department D e p a r t m e n t of o f Mines, M i n e s , Geological Geological Report R e p o r t 141, 4 1 , 557p; 7 p ; 2 maps, 1 1 inch i n c h to t o 1/2 1 / 2 mile. mile. Davies, J. C . , 1983, 1 9 8 3 , Gold Deposits D e p o s i t s of o f the t h e Lake Lake of o f the t h e Woods Woods Area, Area, D a v i e s , J.C., K e n o r a District; D i s t r i c t ; p.241-245 i n Summary Summary of o f Field F i e l d Work, Work, 1983, 1 9 8 3 , by by Kenora p.241—245 in Geological tthe h e Ontario Ontario G e o l o g i c a l Survey, S u r v e y , edited e d i t e d by by John J o h n Wood, Wood, Owen Owen L. L. White, W h i t e , R.B. R. B. Barlow, B a r l o w , and and A.C. A . C . Colvine, C o l v i n e , Ontario O n t a r i o Geological Geological Survey, Miscellaneous S urvey, M i s c e l l a n e o u s Paper P a p e r 116, 1 1 6 , 3l3p. 313~. Davies, . C . and and Smith, S m i t h , P.M., P.M., 1984, 1 9 8 4 , The Structural S t r u c t u r a l and and D a v i e s , JJ.C. Stratigraphic S t r a t i g r a p h i c Control C o n t r o l in i n the t h e Lake Lake of o f the t h e Woods Woods Area; A r e a ; p.l85—193 p.185-193 ~f' Fieldwork, F i e l d w o r k , 1984, 1 9 8 4 , Ontario O n t a r i o Geological G e o l o g i c a l Survey, Survey, iin n Summary if Edited Owen L. L. W White, R.B. Barlow, B a r l o w , and and A.O. A.C. E d i t e d by by John J o h n Woods, Wood, Owen h i t e , R.B. Colvine, C o l v i n e , Ontario O n t a r i o Geological G e o l o g i c a l Survey, S u r v e y , Miscellaneous M i s c e l l a n e o u s Paper P a p e r 119, 119, 3 09~ 309p. Forsgren, F o r s g r e n , F.M., P.M., 1980, 1 9 8 0 , AA study s t u d y of o f the t h e Pine P i n e Portage P o r t a g e Prospect, Prospect , Kenora K e n o r a District, D i s t r i c t , Ontario, O n t a r i o , Unpublished U n p u b l i s h e d B.Sc. B. Sc Thesis, T h e s i s , University University of o f North N o r t h Dakota. Dakota. King, H. L., 1983, 1 9 8 3 , Precambrian P r e c a m b r i a n Geology, G e o l o g y , Kenora—Keewatin K e n o r a - K e e w a t i n Area, Area, K i n g , H.L., Eastern Part E astern P a r t (NTS (NTS 52 E/163W) E/1 6SW) Kenora K e n o r a District, D i s t r i c t , Ontario; O n t a r i o ; Ontario Ontario Geological G e o l o g i c a l Survey, S u r v e y , Preliminary P r e l i m i n a r y Map ? k p P.2618, P.2618, scale s c a l e 1:15,840 1 : 1 5 , 8 4 0 or o r 11 inch i n c h to t o 1/4 1 / 4 mile. mile. . �57 Pedora, P e d o r a , J.M., J . M . , 1976, 1 9 7 6 , Mineralization M i n e r a l i z a t i o n of o f the t h eHigh H i g hLake Lake Pluton P l u t o n and and Unpublished M.Sc. Adjacent n p u b l i s h e d M. Sc. Thesis, T h e s i s , University University A d j a c e n t Country C o u n t r y Rocks; Rocks ; U oof f Manitoba, M a n i t o b a , Winnipeg, W i n n i p e g , Manitoba. Manitoba. Simpson, and Schrnid, Scbmid, S.M., S.M., 11983, Evaluation of . and 9 8 3 , An An E valuation o f Criteria C r i t e r i a to to Simpson, CC. GSA Bull., Deduce the t h e Sense S e n s e of o f Movement Movement in i n Sheared S h e a r e d Rocks. Rocks. Bull., V.94, p.1281-1288, p.1281—1288, 11 11 figures, f i g u r e s , November November 1983. 1983. V.94, Smith, S m i t h , P.M., P.M., 1984, 1 9 8 4 , The Geological G e o l o g i c a l Setting S e t t i n g of o f the t h e Duport D u p o r t Mine, Mine, Cameron Island, I s l a n d , Shoal S h o a l Lake; L a k e ; p.194—200 p.194-200 in i n Summary Summary of o f Fieldwork, Fieldwork, Ontario Geological 11984, 984, O ntario G e o l o g i c a l Survey, S u r v e y , Edited E d i t e d by by John J o h n Wood, Wood, Owen Owen L. L. White, W h i t e , R.B. R.B. Barlow, B a r l o w , and and A.C. A . C . Colvine, C o l v i n e , Ontario O n t a r i o Geological Geological Survey, S u r v e y , Miscellaneous M i s c e l l a n e o u s Paper P a p e r 119, 1 1 9 , 3O9p. 309~. Sutherland, and C Colvine, The G Geology .G., and o l v i n e , AA.C., .C., 11979, 9 7 9 , The e o l o g y and and S u t h e r l a n d , II.G., A r m , Canoe Canoe Lake, L a k e , and a n d High H i g h Lake Lake M i n e r a l i z a t i o n of o f the t h e Pickerel P i c k e r e l Arm, Mineralization Bodies; of Work, 1979, b y the the B o d i e s ; pp.233—243 . 2 3 3 - 2 4 3 in i n Summary o f Field F i e l d Work, 1 9 7 9 , by Ontario Geological Survey, by V. V.G. Mime, G. M i l n e , O.L. O.L. White, White, Ontario G eological S u r v e y , eedited d i t e d by R.B. Barlow, R.B. B a r l o w , and and C.R. C . R . Kustra, K u s t r a , Ontario O n t a r i o Geological G e o l o g i c a l Survey, Survey, Miscellaneous M i s c e l l a n e o u s Paper P a p e r 90, 9 0 , 245p. 245~. Thomson, Thomson, J.E., J . E . , 1936, 1 9 3 6 , Gold deposits d e p o s i t s on o n the t h e Lake Lake of o f the t h e Woods; Woods; Ont. Dept. O nt. D e p t . Mines, M i n e s , Annual Report R e p o r t for f o r 1935, 1 9 3 5 , Vol.44, V o l . 4 4 , Pt.4, Pt.4, pp.29-47. .29-47. Thomson, JJ.E., Thomson, . E . , 1937, 1 9 3 7 , Geology G e o l o g y of o f the t h e North N o r t h Central C e n t r a l Part P a r t of o f the the Lake of the Woods, Kenora District, Ontario: Ontario Lake o f t h e Woods, Kenora D i s t r i c t , O n t a r i o : O n t a r i o Department 4 5 , Part Part D e p a r t m e n t of o f Mines, M i n e s , Annual Annual Report R e p o r t for f o r 1936, 1 9 3 6 , Volume 45, p.1—43, Accompanied by 45b, scale 1:63,360 or 1 inch 3 , p.1-43, Accompanied by Map 4 5 b , s c a l e 1 : 6 3 , 3 6 0 o r 1 i n c h to to 3, 1 mile. 1 mile. Trowell, G . R . , 1980, 1980, T r o w e l l , N.F., N.F., Blackburn, B l a c k b u r n , C.E. C.E. and and Edwards, Edwards, G.R., Crow Lake Lake Meta— MetaIreliminary r e l i m i n a r y Synthesis S y n t h e s i s of o f the t h e Savant S a v a n t Lake Lake —- Crow volcanic, v o l c a n i c , Metasedimentary M e t a s e d i m e n t a r y Belt, B e l t , Northwestern N o r t h w e s t e r n Ontario, O n t a r i o , and and its its bearing b e a r i n g upon Mineral M i n e r a l Exploration; E x p l o r a t i o n ; Ontario O n t a r i o Geological G e o l o g i c a l Survey, Survey, Miscellaneous M i s c e l l a n e o u s Paper P a p e r 89, 8 9 , 3Op. 30p. �Geological G e o l o g i c a l Relationships R e l a t i o n s h i p s in in the t h e Vicinity V i c i n i t y of of the t h e Wabigoon W a b i g o o n —- Winnipeg W i n n i p e g River River Subprovincial S u b p r o v i n c i a l Interface I n t e r f a c e in i n the t h e Kenora K e n o r a area1 area1 Introductory I n t r o d u c t o r y Discussion D i s c u s s i o n and a n d Field F i e l d Guide Guide 31st 3 1 s t Annual I n s t i t u t e o n Lake S u p e r i o r G e o l o g y Kenora, K e n o r a , Ontario On t a r i o Annual Institute on Lake Superior Geology by G.P. G. P. Beakhouse Beakhouse Precambrian P r e c a m b r i a n Geology G e o l o g y Section Section Ontario O n t a r i o Geological G e o l o g i c a l Survey Survey 77 7 7 Grenville G r e n v i l l e Street Street Toronto, T o r o n t o , Ontario Ontario M5S M5S 1B3 133 1 This T h i s guide g u i d e is is published p u b l i s h e d with w i t h the t h e permission p e r m i s s i o n of o f the t h e Director Director of o f the t h e Ontario O n t a r i o Geological G e o l o g i c a l Survey Survey 1 �60 * THE THE RELATIONSHIP RELATIONSHIP OF OF SUPRACRUSTAL SEQUENCES SEQUENCES TO BASEMENT COMPLEX COMPLEX IIN N THE THE WESTERN WESTERN ENGLISH ENGLISH RIVER RIVER TO AA BASEMENT S UB PROVINCE * SUBPROVINCE* This T h i s introductory i n t r o d u c t o r y statement s t a t e m e n t is is a a modified m o d i f i e d vversion e r s i o n of o f aa paper p a p e r of of p u b l i s h e d eelsewhere l s e w h e r e ((Beakhouse B e a k h o u s e 1985) 1985). It is is t h e s a m e t i t l e published intended i n t e n d e d as a i n t r o d u c t i o n t o t h e r e g i o n a l c o n t e x t o f t h e f i e l d t r i p area. the sairte title It as a introduction to the regional context of the field trip area. . ABSTRACT ABSTRACT T h r e e ddistinctly i s t i n c t l y different d i f f e r e n t types t y p e s of o f terrane t e r r a n eare a r erecognized recognized Three within within and a n d immediately i m m e d i a t e l y adjacent a d j a c e n t to t o the t h e English E n g l i s h River R i v e r Sub— Subprovince. t e r r a n e forms f o r m s the t h e Uchi U c h i and and province. G r e e n s t o n e - t o n a l i t e terrane Greenstone—tonalite W a b i g o o n Subprovinces S u b p r o v i n c e s whereas w h e r e a s the t h e Ear Ear Falls F a l l s -— -- Mariigotagan M a n i q o t a g a n belt belt Wabigoon (EFMB) (EFMB) and a n d Winnipeg W i n n i p e g River R i v e r belt b e l t (WRB) (WRB) of o f the t h e English E n g l i s h River R i v e r Sub— Subprovince a r e paragneiss p a r a g n e i s s and a n d batholithic b a t h 0 1 i t h i c terranes, t e r r a n e s , respectively. respectively. p r o v i n c e are The T h e EFMB EFMB is is a major, m a j o r f linear l i n e a r sedimentary s e d i m e n t a r y basin b a s i n with w i t h detritus detritus d e r i v e d in i n adjacent a d j a c e n t terrains t e r r a i n s from f r o m laterally l a t e r a l l y equivalent e q u i v a l e n t volcanic volcanic derived rocks r o c k s and a n d granitic g r a n i t i c rocks. r o c k s . The T h e greenstone—tonalite g r e e n s t o n e - t o n a l i t e -- paragneiss paragneiss interface r e p r e s e n t s a facies f a c i e s change c h a n g e between b e t w e e n fundamentally fundament a l l y i n t e r f a c e represents different d i f f e r e n t depositional d e p o s i t i o n a l environments. environments. I n the t h e WRB, WRB, rare r a r e remnants remnants In of o f aa predominantly p r e d o m i n a n t l y volcanic v o l c a n i c supracrustal s u p r a c r u s t a l sequence s e q u e n c e occur o c c u r as as inclusions within metamorphosed inclusions w i t h i n hhighly ighly m e t a m o r p h o s e d and a n d deformed d e f o r m e d plutonic plutonic rocks Field F i e l d relationships r e l a t i o n s h i p s and a n d geochronological geochronolog ical r o c k s (orthogneiss). (orthogneiss) i n v e s t i g a t i o n s indicate i n d i c a t e that t h a t orthogneiss, o r t h o g n e i s s , together t o g e t h e r with w i t h certain certain investigations sodic ' K e n o r a n t volcanism v o l c a n i s m in i n the the s o d i c plutons, p l u t o n s , predate p r e d a t e widespread w i d e s p r e a d 'Kenoran' Wabigoon t o the t h e south. s o u t h . The T h e relatively r e l a t i v e l y potassic potassic W a b i g o o n Subprovince S u b p r o v i n c e to c o m p o s i t i o n and a n d slightly s l i g h t l y elevated e l e v a t e d Sr S r isotope i s o t o p e initial i n i t i a l ratios r a t i o s of of composition l a t e plutons p l u t o n s from f r o m the t h e central c e n t r a l axis a x i s of o f the t h e WRB W R 3 suggest s u g g e s t that t h a t they they late are a r e derived d e r i v e d from f r o m this t h i s earlier e a r l i e r crust. crust. V o l c a n o - p l u t o n i c activity, a c t i v i t y , perhaps p e r h a p s analogous a n a l o g o u s to t o that that Volcano—plutonic observed o b s e r v e d in i n the t h e greenstone—tonalite g r e e n s t o n e - t o n a l i t e terranes, t e r r a n e s , was was initiated i n i t i a t e d prior prior to 3 . 0 Ga G a and a n d led l e d to t o the t h e development d e v e l o p m e n t of o f aa 'pre—Kenoran' ' p r e - K e n o r a n t sialic s i a l ic t o 3.0 microcontinent m i c r o c o n t i n e n t now now represented r e p r e s e n t e d by b y the t h e WRB. WRB. S y n c h r o n o u s developdevelopSynchronous ment m e n t of o f volcano—sedimentary v o l c a n o - s e d i m e n t a r y sequences s e q u e n c e s in i n greenstone—tonalite greenstone- tonal ite t e r r a n e and a n d greywacke—turbidite g r e y w a c k e - t u r b i d i t e sequences s e q u e n c e s in i n paragneiss p a r a g n e i s s terrane terrane terrane o c c u r r e d adjacent a d j a c e n t to, t o , and a n d in i n part p a r t on, o n , this t h i s earlier e a r l i e r crust. c r u s t . This This occurred e a r l i e r crust c r u s t was greatly g r e a t l y thinned, t h i n n e d , or o r absent, a b s e n t , beneath b e n e a t h much much of of the the earlier Wabigoon W a b i g o o n subprovince. s u b p r o v i n c e . The T h e interfaces i n t e r f a c e s between b e t w e e n different d i f f e r e n t terranes terranes represent r e p r e s e n t either e i t h e r facies f a c i e s transitions t r a n s i t i o n s (EFMB—Uchi) (EFMB-Uch i ) or o r unconformities unconformities WRB-EFMB and a n d WRB—Wabigoon) WRB-Wabigoon) that t h a t are a r e loci l o c i for f o r subsequent subsequent (WRB—EFMB d e f o r r n a t i o n a l and a n d igneous i g n e o u s processes p r o c e s s e s that t h a t obscured o b s c u r e d the t h e primary primary deformational relationships r e l a t i o n s h i p s between b e t w e e n different d i f f e r e n t terranes. terranes . . �61 INTRODUCTION The was ffirst T h e English E n g l i s h River R i v e r bbelt e l t was i r s t ddefined e f i n e d as as a a ssubprovince u b p r o v i n c e of of the t h e Superior S u p e r i o r Province P r o v i n c e by b y Wilson W i l s o n and a n d Brisbin B r i s b i n (1963). (1 963). More recent recent mapping, ggeologic eologic m a p p i n g , particularly p a r t i c u l a r l y Project P r o j e c t Pioneer P i o n e e r (Manitoba ( M a n i t o b a Mines Mines and M c R i t c h i e and and Weber, W e b e r , 1971 1971)) and B r a n c h and a n d University U n i v e r s i t y of o f Manitoba; M a n i t o b a ; McRitchie Branch Operation Falls O p e r a t i o n Kenora Kenora — - Ear Ear F a l l s (Ontario ( O n t a r i o Geological G e o l o g i c a l Survey; S u r v e y ; Breaks Breaks shown that eett al. a l . 1978), 1 9 7 8 ) , hhas a s shown t h a t the t h e English E n g l i s h River R i v e r Subprovince S u b p r o v i n c e is is with aactually c t u a l l y ccompound, ompound, w i t h tthe h e Ear E a r Falls Falls — - Manigotagan M a n i g o t a g a n belt b e l t in i n the the b e l t in i n the t h e south s o u t h (Beakhouse ( B e a k h o u s e 1977; 1977; nnorth o r t h and a n d the t h e Winnipeg W i n n i p e g River R i v e r belt Breaks B r e a k s and a n d Bond, Bond, 1977). 1 9 7 7 ) . Breaks B r e a k s et e t al. a l . (1978) ( 1 9 7 8 ) refer r e f e r to t o these these a s the t h e Northern N o r t h e r n Supracrustal S u p r a c r u s t a l domain d o m a i n and a n d Southern S o u t h e r n Plutonic Plutonic bbelts e l t s as Regional domain, (see d o m a i n , respectively. respectively. R e g i o n a l ggeophysical e o p h y s i c a l investigations i n v e s t i g a t i o n s (see references r e f e r e n c e s in i n Beakhouse B e a k h o u s e 1977) 1 9 7 7 ) have h a v e added a d d e d important i m p o r t a n t information i n f o r m a t i o n on on the t h e tthird h i r d ddimension i m e n s i o n and, a n d , oon n the t h e basis b a s i s oof f a re—evaluation r e - e v a l u a t i o n of o f geoqeopphysical h y s i c a l ddata, a t a , Hall H a l l and a n d Brisbin B r i s b i n (1981) ( 1 981 ) suggested s u g g e s t e d that t h a t these t h e s e belts belts The sshould h o u l d be b e elevated e l e v a t e d to t o subprovince s u b p r o v i n c e status. status. T h e Ear Ear Falls F a l l s —Maniqotagan Winnipeg River M a n i q o t a g a n aand nd W innipeg R i v e r bbelts e l t s rrepresent e p r e s e n t two t w o fundamentally fundamentally different t o here h e r e as as d i f f e r e n t types t y p e s of o f "high—grade" " h i g h - g r a d e " terrane, t e r r a n e , referred r e f e r r e d to paragneiss Both are p a r a q n e i s s and a n d batholithic b a t h o l i t h i c terrane, t e r r a n e , respectively. respectively. B o t h are ddistinctly i s t i n c t l y ddifferent i f f e r e n t from f r o m greenstone—tonalite g r e e n s t o n e - t o n a l i t e or o r low—grade low-grade which Wabigoon tterranes erranes w h i c h ooccur c c u r in i n the t h e adjacent adjacent W a b i g o o n and a n d Uchi U c h i sub— subpprovinces r o v i n c e s (Figure ( F i g u r e 1). 1). This T h i s paper p a p e r will w i l l discuss d i s c u s s the t h e nature n a t u r e of o f these t h e s e two t w o types t y p e s of of ''high—grade' h i g h - g r a d e ' tterrane e r r a n e and a n d their t h e i r associated a s s o c i a t e d supracrustal s u p r a c r u s t a l rocks r o c k s and and ttheir h e i r relationship r e l a t i o n s h i p to t o each e a c h other o t h e r and a n d the t h e adjacent a d i a c e n t greenstone— qreenstoneEmphasis ttonalite o n a l i t e terranes. terranes. E m p h a s i s is is placed p l a c e d on o n the t h e broad b r o a d relationships relationships between b e t w e e n the t h e various v a r i o u s supracrustal s u p r a c r u s t a l assemblages a s s e m b l a g e s and a n d aa large l a r g e basement basement complex The c o m p l e x that t h a t pre—dates p r e - d a t e s some some of o f these t h e s e supracrustal s u p r a c r u s t a l rocks. rocks. T he English E n g l i s h River R i v e r Subprovince, S u b p r o v i n c e , together t o g e t h e r with w i t h adjacent a d j a c e n t parts p a r t s of o f the the Wabigoon 1 ) , is is W a b i g o o n and a n d Uchi U c h i greeristone—tonalite g r e e n s t o n e - t o n a l i t e SSubprovinces u b p r o v i n c e s (Figure ( F i g u r e 1), unique u n i q u e in i n that t h a t all a l l 3 types t y p e s of o f terrane t e r r a n e and a n d all a l l possible possible combinations c o m b i n a t i o n s oof f interfaces i n t e r f a c e s between b e t w e e n these t h e s e terranes t e r r a n e s are are rrepresented. epresented. LITHOLOGIES LITHOLOGIES T h e rocks r o c k s in i n the t h e English E n g l i s h River R i v e r Subprovince S u b p r o v i n c e can c a n be b e broadly broadly The ggrouped r o u p e d into i n t o 77 suites. suites. IIn n aapproximate p p r o x i m a t e oorder r d e r of o f decreasing d e c r e a s i n g age age t h e s e are a r e (1) ( 1 ) high—grade h i g h - q r a d e supracrustal s u p r a c r u s t a l (predominantly ( p r e d o m i n a n t l y meta— inetathese volcanic) v o l c a n i c ) remnants; r e m n a n t s ; (2) ( 2 ) oorthogneiss; r t h o q n e i s s ; ((3) 3 ) pparagneiss; a r a q n e i s s ; ((4) 4 ) internal internal ( 5 ) ssodic o d i c plutons; p l u t o n s ; ((6) 6 ) ppotassic o t a s s i c plutons; p l u t o n s ; (7) (7) ggreenstone r e e n s t o n e belts; b e l t s ; (5) mafic w i l l be b e described d e s c r i b e d only only m a f i c plutons p l u t o n s (Figure ( F i g u r e 2). 2). L i t h o l o g i e s will Lithologies briefly, b r i e f l y , more complete c o m p l e t e lithologic l i t h o l o g i c descriptions d e s c r i p t i o n s are a r e presented p r e s e n t e d by by Breaks e t al. a l . (1978) ( 1 9 7 8 ) and a n d Beakhouse B e a k h o u s e (1983). (1983). B r e a k s et Supracrustal Remnant' Suite Suite S u p r a c r u s t a l Remnant The T h e oorthogneiss r t h o g n e i s s ssuite, u i t e , and a n d to t o a lesser l e s s e r extent e x t e n t the t h e plutonic plutonic suites, s u i t e s , contain c o n t a i n minor, m i n o r , widely w i d e l y distributed, d i s t r i b u t e d , highly h i g h l y metamorphosed metamorphosed These and r a r e sedimentary s e d i m e n t a r y inclusions. inclusions. T hese a n d ddeformed e f o r m e d volcanic v o l c a n i c and a n d rare o r disruptdisruptiinclusions n c l u s i o n s aare r e usually u s u a l l y ssmall m a l l (<20m) ( < 2 0 m ) and a n d ddiscontinuous i s c o n t i n u o u s or Where the t o 1 km km thick t h i c k and a n d 55 km km long. long. the eed, d , bbut u t can c a n be b e up u p to inclusions i n c l u s i o n s ooccur c c u r in i n orthogneiss, o r t h o g n e i s s , intrusive i n t r u s i v e contact c o n t a c t relationships relationships indicate most i n d i c a t e tthat hat m o s t ssupracrustal u p r a c r u s t a l rremnants e m n a n t s are a r e older o l d e r than t h a n the the o r t h o g n e i s s (Gower, ( G o w e r , 1978; 1 9 7 8 ; Gower G o w e r and and Clifford, C l i f f o r d , 1981; 1981 ; ttonalitic o n a l i t i c orthogneiss However, Beakhouse, B e a k h o u s e , 1983; 1 9 8 3 ; Beakhouse B e a k h o u s e et e t al. a l . 11983). 983). H o w e v e r , some some 1 �62 / / God's Lake Ear Falls— Manigotagan Manitoba fl 1 FTfl1 1 0 100 200 kilometres F i g u r e 1: 1: Figure Map Map illustrating i l l u s t r a t i n g the t h e distribution d i s t r i b u t i o n of o f various v a r i o u s types t y p e s of of terranes t e r r a n e s in i n the t h e western w e s t e r n Superior S u p e r i o r province. province. Greenstone—tonalite t e r r a n e s include i n c l u d e the t h e Sachigo, Sachigo, G r e e n s t o n e - t o n a l i t e terranes Uchi, U c h i , Wabigoon Wabiqoon and and Wawa Wawa subprovinces. s u b p r o v i n c e s . The The Ear Ear Falls—Manigotagan a n d Quetico Q u e t i c o subprovince subprovince b e 1 t and F a l l s - M a n i q o t a q a n belt a r e paragneiss p a r a g n e i s s terraneS. t e r r a n e s . The The Berens ! 3 e r e n s River River are subprovince s u b p r o v i n c e and and Winnipeg W i n n i p e g River R i v e r belt b e l t are are b a t h o l i t h i c terranes. terranes. batholithic �_____ _____ 63 945 92 + * * + 4- + * * + *4- * + + 20 10 0 + * * + * * * * * * * + + * * * * * * * * * + * * * * * * * * * * I 30 I +kilomelres + + + + + 40 * * * -I- + + + + I + * + 50 I + + + * 4- * -' * * * * * + + * * + * * * + + * + * * * * * * * + + + * + * * + * + ''-l ',—'_/ + + + + - - /_\ + - - +1 + '- + ++ ::::I + — USA 51 ++:I4-I:I:Y * * +++++*+++*++*+ ::. ÷ + + * + + ++ ++ + + -51 + + * ::T + + Ear FaHs-Manigotagai • I;—. 4:::::.::::::: 5O + C-v i-'kk-(+ * + + + - + * + * * + * \S-\* + + + + * * * * + 4- + + + * * * * * + + 4- + + 4- * + ®c + + + / * * * * * * +*++ + + Quetico Th________ I granitoid rocks mafic plutonic rocks :--. -] metasedimentary rocks felsic metavolcanic rocks gneissic granitoid rocks [-J mafic metavolcanic rocks (unsubdivided) ::::: potassic plutonic rocks --J sodic plutonic rocks Figure F i g u r e 2: 2: + - 1 G e o l o g i c map of o f part p a r t of o f the t h e western w e s t e r n Superior S u p e r i o r province orovince Geologic including anigotaqan, i n c l u d i n g pparts a r t s oof f the t h e Uchi, U c h i , Ear E a r Falls F a l l s —- M Manigotagan, Winnipeg W i n n i p e g River, R i v e r , Wabigoon W a b i q o o n and a n d Quetico Q u e t i c o subprovinces. subprovinces. The i s ccompiled o m p i l e d pprimarily r i m a r i l y from f r o m Ferguson F e r g u s o n et et T h e ggeology e o l o g y is al. a l . (1970), ( 1 9 7 0 ) , Blackburn B l a c k b u r n (1981) ( 1 9 8 1 ) and a n d Breaks B r e a k s et e t al. a l . (1978). (1978). �64 . iinclusions n c l u s i o n s may be tectonic t e c t o n i c inclusions i n c l u s i o n s of o f younger y o u n g e r units. units M-phibolite Arnphibol i t e inclusions i n c l u s i o n s predominate. predominate. Some i n c l u s i o n s are a r e volcanic volcanic Some inclusions as as indicated i n d i c a t e d bby y tthe h e local l o c a l ppresence r e s e n c e oof f hhighly i g h l y ddeformed e f o r m e d pillow pillow In sstructures t r u c t u r e s. I n places p l a c e s the t h e pillowed p i l l o w e d units u n i t s are a r e interlaye i n t e r l a y e rred e d with with s i m i l a r , massive m a s s i v e amphibolites a m p h i b o l i t e s and and ccompositionally o m p o s i t i o n a l l y and a n d texturally t e x t u r a l l y similar, with w i t h coarse—grained c o a r s e - g r a i n e d amphibolites, amph i b o l i t e s , probably p r o b a b l y representing r e p r e s e n t i n g aa s e q u e n c e of o f massive m a s s i v e and a n d pillowed p i l l o w e d basaltic b a s a l t i c flows f l o w s and a n d related related sequence gabbro g a b b r o sills. sills. On h e oother t h e r hhand, a n d , many f the t h e inclusions i n c l u s i o n s are are On tthe many oof m a s s i v e amphibolite a m p h i b o l i t e of o f uncertain u n c e r t a i n origin. origin. o f these these massive Some of inclusions are mineralogically inclusions a re m i n e r a l o g i c a l l y and a n d texturally t e x t u r a l l y similar s i m i l a r to t o the the Others, a l s o be b e volcanic. volcanic. O t h e r s , however, however, vvolcanic o l c a n i c amphibolite a m p h i b o l i t e and a n d may may also s i l l s and a n d dikes. dikes. rrepresent e p r e s e n t ddisrupted, i s r u p t e d , younger y o u n g e r gabbroic g a b b r o i c sills Felsic F e l s i c volcanic v o l c a n i c rocks r o c k s have h a v e not n o t been b e e n conclusively c o n c l u s i v e l y identiidentiThe a primary primary f e l s i c vvolcanic o l c a n i c rocks r o c k s may be a ffied. ied. T h e ppaucity a u c i t y oof f felsic feature r may f l e c t ttheir h e i r less less f e a t u r e oof f this t h i s early e a r l y volcanism v o l c a n i s m oor mayr ereflect rrefractory e f r a c t o r y nature n a t u r eduring d u r i n gsubsequent s u b s e q u e n tmetamorphism m e t a m o r p h i s m aand n d ppartial artial melting al. Sedimentary et a l . 1983). 1983). S e d i m e n t a r y uunits n i t s aare r e rare r a r e and and m e l t i n g ((Beakhouse B e a k h o u s e et t o thick-bedded t h i c k - b e d d e d arkose a r k o s e and a n d greywacke, g r e y w a c k e , with with ccomprise o m p r i s e medium— m e d i urn- to interlayered c a l c - s i l i c a t e layers. layers. T hin-bedded , i n t e r l a y e r e d pelitic p e l i t i c and a n d calc—silicate Thin—bedded, is recognized ooxide—facies x i d e - f a c i e s iiron r o n formation f o r m a t i o n is r e c o g n i z e d on o n the t h e south s o u t h shore s h o r e of of tJmfreville U m f r e v i l l e Lake L a k e and a n d in i n the t h eCedar C e d a r Lake L a k e area a r e a(Westerman, ( W e s t e r m a n , 1977; 1977; Beakhouse, B e a k h o u s e , 1983). 1983). The widespread a s inclusions i n c l u s i o n s in in T he w i d e s p r e a d ddistribution i s t r i b u t i o n and a n d occurrence o c c u r r e n c e as old o l d tonalites t o n a l i t e s (discussed ( d i s c u s s e d below) b e l o w ) suggests s u g g e s ts that t h a t the t h e volcanic volcanic a m p h i b o l i t e , the the m e t a s e d i m e n t a r y , and a n d possibly p o s s i b l y many of o f the the amphibolite, metasedimentary, massive mass i v e amphibolite amph i b o l i t e inclusions i n c l u s i o n s are a r e remnants r e m n a n t s of o f an a n old, o l d , largely largely vvolcanic, o l c a n i c , supracrustal s u p r a c r u s t a l sequence. sequence. T h i s sequence s e q u e n c e may may have h a v e been been This ssimilar i m i l a r to t o the t h e greenstone g r e e n s t o n e terranes t e r r a n e s of o f the t h e better b e t t e r preserved p r e s e r v e d Uchi Uchi and a n d Wabigoon W a b i g o o n S Subprovinces, u b p r o v i n c e s , a nand d a appears p p e a r s to a v e been b e e n coextensive coextensive to hhave with Winnipeg It is tthe w i t h the the W i n n i p e g River R i v e r belt. belt. It is h e eearliest a r l i e s t sstage t a g e in i n the the development The d e v e l o p m e n t of o f the t h e belt. belt. T h e less l e s s abundant a b u n d a n t metavolcanic m e t a v o l c a n i c and and metasedimentary m e t a s e d i m e n t a r y inclusions i n c l u s i o n s in i n the t h e younger y o u n g e r plutonic p l u t o n i c suites s u i t e s may may hhave a v e been b e e n derived d e r i v e d either e i t h e r from f r o m this t h i s older o l d e r supracrustal s u p r a c r u s t a l sequence s e q u e n c e or or from f r o m aa younger y o u n g e r sequence. sequence. . Orthogneiss O r t h o g n e i s s Suite Suite The 2 ) is c o m p o s i t i o n a l l y and and T h e orthogneiss o r t h o g n e i s s suite s u i t e (Figure ( F i g u r e 2) is a a compositionally F els i c t e x t u r a l l y hheterogeneous e t e r o g e n e o u s assemblage a s s e m b l a g e of o f layered l a y e r e d gneisses. gneisses texturally Felsic pplutonic l u t o n i c components c o m p o n e n t s ppredominate r e d o m i n a t e aand n d uundeformed n d e f o r m e d i intrusive n t r u s i v e rocks rocks aand n d iinclusions n c l u s i o n s oof f supracrustal s u p r a c r u s t a l rocks r o c k s are a r e aa minor m i n o r component. component. T h e gneissic g n e i s s i c phases p h a s e s range r a n g e in i n composition c o m p o s i t i o n from f r o m quartz q u a r t z diorite diorite The to o m e d i u m - g r a i n e d , bbiotite i o t i t e or o r hornblende— hornblendet o granite. granite. F i n e - tto Fine— medium—grained, biotite b i o t i t e tonalitic t o n a l i t i c gneiss g n e i s s is is tthe h e ooldest l d e s t pplutonic l u t o n i c component c o m p o n e n t and and This was ccontains o n t a i n s inclusions i n c l u s i o n s of o f the t h e older o l d e r supracrustal s u p r a c r u s t a l sequence. sequence. T h i s was intruded wide i n t r u d e d bby y a w i d e variety v a r i e t y of o f fine—grained f i n e - g r a i n e d to t o pegmatitic, p e g m a t i t i c , quartz quartz ddioritic i o r i t i c to t o ggranitic r a n i t i c pphases, h a s e s , in in w h i c h the t h e ggneissosity n e i s s o s i t y rranges a n g e s from from which t o strongly s t r o n g l y developed, d e v e l o p e d , and a n d by b y mafic m a f i c dikes. d i k e s . The T h e mafic m a f i c dikes dikes w e a k l y to weakly metamorphosed t o amphibolite a m p h i b o l i t e facies; f a c i e s ; they they aare r e ddeformed e f o r m e d aand nd m e t a m o r p h o s e d to iintruded n t r u d e d many f the t h e ppost—tonalite o s t - t o n a l i t e ggranitoid r a n i t o i d phases p h a s e s but b u t are are many oof iintruded n t r u d e d by b y others. others. The T h e yneissosity g n e i s s o s i t y is is a a result r e s u l t of o f ppost—emplacement o s t - e m p l a c e m e n t deformation deformation metamorphism aand nd m e t a m o r p h i s m which w h i c h affected a f f e c t e d the t h e supracrustal s u p r a c r u s t a l remnants, r e m n a n t s , the the various v a r i o u s granitoid g r a n i t o i d phases, p h a s e s , and a n d the t h e mafic maÂi c dikes. d i k e s . Another A n o t h e r effect e f f e c t of of metamorphism was the t h e ddevelopment, e v e l o p m e n t , in i n many of o f the t h e rock r o c k units, units, tthe he m e t a m o r p h i s m was . �65 of o f concordant, c o n c o r d a n t , discontinuous, d i s c o n t i n u o u s , leucocratic l e u c o c r a t i c anatectic a n a t e c t i c lenses l e n s e s that that are l e s s than t h a n 1 cm c m thick. thick. compos i t i o n of o f these these a r e commonly commonly less The composition lenses is aa function f u n c t i o n of o f source s o u r c e rock r o c k composition c o m p o s i t i o n and a n d degree d e g r e e of of l e n s e s is melting. a r e quartz q u a r t z dioritic d i o r i t i ctot otonal t o n a litic itic m e l t i n q . Common Common associations a s s o c i a t i o n s are l e n s e s in i n amphibolite, a m p h i b o l i t e , tonalite t o n a l i t e to t o granodioritic g r a n o d i o r i t i c lenses l e n s e s in in lenses tonalitic t o granitic g r a n i t i c lenses l e n s e s in in t o n a l i t i c gneiss, g n e i s s , and a n d granodioritic q r a n o d i o r i t i c to granitoid g r a n i t o i d gneiss. qneiss. The variable v a r i a b l e degree d e g r e e of o f gneissosity g n e i s s o s i t y development d e v e l o p m e n t in i n the t h e post— postThe g r a n i t o i d phases, p h a s e s , and a n d the t h e differing d i f f e r i n g age a g e relationships relationships t o n a l i t e granitoid tonalite between b e t w e e n these t h e s e phases p h a s e s and a n d the t h e mafic maÂi c dikes d i k e s indicate i n d i c a t e aa considerable considerable t o and a n d during d u r i n g the the a g e span s p a n of o f granitoid g r a n i t o i d emplacement e m p l a c e m e n t prior p r i o r to age deformation. d e f o r m a t i o n . Pegmatitic P e g m a t i t i c and a n d aplitic a p l i t i c granitic g r a n i t i c dikes d i k e s and a n d plugs plugs that are t h a t postdate p o s t d a t e major m a j o r deformation d e f o r m a t i o n are a r e also a l s o common. common. They T h e y are probably p r o b a b l y temporally t e m p o r a l l y and a n d genetically g e n e t i c a l l y related r e l a t e d to t o the t h e potassic potassic plutonic p l u t o n i c suite. suite. The The complex c o m p l e x nature n a t u r e of o f the t h e orthogneiss o r t h o g n e i s s suite s u i t e results r e s u l t s from f r o m the the intimate i n t i m a t e admixture a d m i x t u r e of o f these t h e s e variably v a r i a b l y deformed d e f o r m e d rock r o c k types. types. Heterogeneity H e t e r o g e n e i t y is is manifest m a n i f e s t on o n two t w o scales. s c a l e s . On On the t h e outcrop o u t c r o p and a n d hand hand specimen s p e c i m e n scale s c a l e the t h e distinctive d i s t i n c t i v e layered l a y e r e d appearance a p p e a r a n c e is is aa consequence 1 ) primary p r i m a r y sedimentary s e d i m e n t a r y and a n d volcanic v o l c a n i c layering layering c o n s e q u e n c e of: o f : 1) (minor) ( m i n o r ), , 2) 2 ) transposition t r a n s p o s i t i o n of o f originally o r i g i n a l l y discordant d i s c o r d a n t structures structures into by intense i n t e n s e deformation, d e f o r m a t i o n , similar s i m i l a r to to i n t o essential e s s e n t i a l parallelism p a r a l l e l i s m by that t h a t described d e s c r i b e d by b y Myers M y e r s (1978), ( 1 9 7 8 ) , 3) 3 ) pre—emplacement p r e - e m p l a c e m e n t anisotropy anisotropy such s u c h as a s layering l a y e r i n g and a n d foliation f o l i a t i o n controlling c o n t r o l l i n g the t h e geometry g e o m e t r y of of intrusive i n t r u s i v e phases, p h a s e s , and a n d 4) 4 ) recrystallization r e c r y s t a l l i z a t i o n and a n d partial p a r t i a l melting me1 t i n g synchronous s t r e s s resulting r e s u l t i n g in in s y n c h r o n o u s with w i t h layer—normal, l a y e r - n o r m a l , principal p r i n c i p a l stress foliation f o l i a t i o n and a n d lenses l e n s e s of o f anatectic a n a t e c t i c melt m e l t being b e i n g oriented o r i e n t e d parallel p a r a l l e l to to layering. layering. AA larger l a r g e r scale s c a l e layering, l a y e r i n g , metres metres to t o hundreds h u n d r e d s of o f metres metres thick, thick, is is defined d e f i n e d by units u n i t s characterized c h a r a c t e r i z e d by particular p a r t i c u l a r assemblages a s s e m b l a g e s such such as a m p h i b o l i t e or o r granitoid g r a n i t o i d gneiss g n e i s s + anatectic anatectic a s tonalite t o n a l i t e ++ amphibolite layers. a r e not n o t continuous c o n t i n u o u s along a l o n g strike. strike. l a y e r s . These T h e s e units u n i t s are 1 -4- Paragneiss Paragneiss Paragneiss P a r a g n e i s s that t h a t is is composed c o m p o s e d principally p r i n c i p a l l y of o f plagioclase, ?lag ioclase , quartz q u a r t z and a n d biotite b i o t i t e with w i t h common common almandine a l m a n d i n e garnet g a r n e t and a n d minor minor s i l l i m a n i t e and a n d muscovite m u s c o v i t e is is the t h e dominant dominant K - f e l d s p a r , cordierite, c o r d i e r i t e , sillimanite K—feldspar, rock r o c k type t y p e of o f the t h e Ear E a r Falls—Manigotagan F a l l s - M a n i g o t a q a n belt. b e l t . In I n many many places places original t o 70 7 0 cm cm thick, t h i c k , can c a n be b e recognized recognized o r i g i n a l sedimentary s e d i m e n t a r y bedding, b e d d i n g , 55 to by b y variations v a r i a t i o n s in i n mineralogy, m i n e r a l o g y , texture, t e x t u r e , and a n d susceptibility s u s c e p t i b i l i t y to to anatexis. a n a t e x i s . The T h e bedding b e d d i n g is is particularly p a r t i c u l a r l y well w e l l defined d e f i n e d by b y inter— interlayered l a y e r e d fine— f i n e - to t o medium—grained, m e d i u m - g r a i n e d , granoblastic g r a n o b l a s t i c yneiss g n e i s s representing represent inq psammite p s a m m i t e of o f probable p r o b a b l e greywacke g r e y w a c k e composition, c o m p o s i t i o n , and a n d medium medium to to coarse—grained, coars e - g r a i n e d , porphyroblastic p o r p h y r o b l a s t i c gneiss g n e i s s representing r e p r e s e n t i n g semipelite s e m i p e l i t e or or siltstone. s i l t s t o n e . The T h e reversal r e v e r s a l of o f grain g r a i n size s i z e with w i t h the t h e psammite p s a m m i t e being being finer f i n e r grained g r a i n e d than t h a n semi—pelite s e m i - p e l i t e isis aa consequence c o n s e q u e n c e of o f metamorphic metamorphic recrystallization. N o r m a l graded g r a d e d bedding b e d d i n g is is recognized r e c o g n i z e d rarely r a r e l y by by r e c r y s t a l l i z a t i o n . Normal progressive p r o g r e s s i v e changes c h a n g e s in i n the t h e abundance a b u n d a n c e of o f biotite b i o t i t e and a n d garnet g a r n e t which which r e f l e c t original o r i g i n a l variations v a r i a t i o n s in i n clay c l a y content c o n t e n t (Van ( V a n de d e Kamp Kamp and and reflect Beakhouse, Other O t h e r sedimentary s e d i m e n t a r y structures s t r u c t u r e s such s u c h as a s cross— crossB e a k h o u s e , 1979) 1979) bedding b e d d i n g and a n d slump s l u m p structures s t r u c t u r e s are a r e rarely r a r e l y preserved. p r e s e r v e d . Pegmatitic Pegmat i t i c leucosome l e u c o s o m e originating o r i g i n a t i n g from f r o m the t h e partial p a r t i a l melting m e l t i n g of o f these t h e s e gneisses gneisses is i s abundant a b u n d a n t and and widely w i d e l y distributed. d i s t r i b u t e d . Metamorphic M e t a m o r p h i c mineral mineral assemblages a s s e m b l a g e s and a n d partial p a r t i a l melting m e l t i n g indicate i n d i c a t e widespread, w i d e s p r e a d , upper upper . . �66 amphibolite a i n p h i b o l i t e facies f a c i e s metamorphism m e t a m o r p h i s m (McRitchie ( M c R i t c h i e and a n d Weber, Weber , 1971b; 1971 b; Freund F r e u n d aand n d Turnock, T u r n o c k , 1971; 1 9 7 1 ; Harris, H a r r i s , 1976) 1 9 7 6 ) and a n d local l o c a l low l o w pressure pressure granulite f a c i e s conditions c o n d i t i o n s (Thurston ( T h u r s t o n and a n d Breaks, B r e a k s , 1978). 1978). g r a n u l i t e facies Because metamorphic B e c a u s e oof f the the m e t a m o r p h i c grade, g r a d e , the t h e sedimentology s e d i m e n t o l o g y of o f the the paragneiss p a r a g n e i s s progenitor p r o g e n i t o r is is difficult d i f f i c u l t to t o decipher, d e c i p h e r , but b u t van v a n de d e Kamp Kamp and a n d Beakhouse B e a k h o u s e (1979) ( 1 9 7 9 ) considered c o n s i d e r e d that t h a t the t h e paragneiss p a r a g n e i s s represents represents turbidites t u r b i d i t e s deposited d e p o s i t e d below b e l o w wave w a v e base. b a s e . The T h e provenance p r o v e n a n c e is is also also difficult d i f f i c u l t to t o resolve r e s o l v e because b e c a u s e the t h e primary p r i m a r y depositional d e p o s i t i o n a l mineralogy mineralogy must m u s t be b e inferred i n f e r r e d from f r o m metamorphic m e t a m o r p h i c mineral m i n e r a l assemblages a s s e m b l a g e s and and The c h e m i c a l compositions. compositions. The chemical c h e m i c a l and a n d mineralogical m i n e r a l o g i c a l composicomposichemical tion is ssuggestive u g g e s t i v e of o f immature immature t i o n of o f the t h e least l e a s t rnigmatitic m i g m a t i t i c pparagneiss a r a g n e i s s is sediments s e d i m e n t s (van ( v a n de d e Kamp Kamp and a n d Beakhouse, B e a k h o u s e , 1979). 1 9 7 9 ) . These T h e s e authors authors suggested s u g g e s t e d that t h a t relatively r e l a t i v e l y direct d i r e c t derivation d e r i v a t i o n from f r o m felsic f e l s i c volcanism volcanism explains e x p l a i n s certain c e r t a i n of o f the t h e chemical c h e m i c a l attributes a t t r i b u t e s of o f the t h e paragneiss. paraqneiss. Breaks e t al. a l . (1978), ( 1 9 7 8 ) , on o n the t h e other o t h e r hand, h a n d , argued a r g u e d that t h a t trace trace B r e a k s et element materials e l e m e n t abundances a b u n d a n c e s rrequire e q u i r e aa vvariety a r i e t y oof f ssource ource m a t e r i a l s ; high h i g h Cr Cr and a n d Ni N i reflect r e f l e c t mafic maÂi c or o r ultramafic u l t r a m a f i c sources s o u r c e s and a n d elevated e l e v a t e d Ba B a and a n d Rb Rb felsic f e l s i c sources. sources. The T h e interfaces i n t e r f a c e s with w i t h the t h e adjacent a d j a c e n t Winnipeg W i n n i p e g River R i v e r belt b e l t on on the the south s o u t h and a n d the t h e Uchi U c h i Subprovince S u b p r o v i n c e on o n the t h e north n o r t h are a r e modified m o d i f i e d by by faults f a u l t s and a n d plutonic p l u t o n i c activity, a c t i v i t y , but b u t primary p r i m a r y stratigraphic s t r a t i g r a p h i c relationrelationships some areas. a r e a s . In I n the t h e Rice Lake L a k e area area s h i p s have h a v e been b e e n preserved p r e s e r v e d in i n some of a r e considered c o n s i d e r e d to t o be, b e , in i n part, p a r t , aa o f Manitoba, M a n i t o b a , the t h e paragneises p a r a g n e i s e s are lateral l a t e r a l facies f a c i e s equivalent e q u i v a l e n t of o f the t h e Edmunds Edmunds Lake L a k e Formation F o r m a t i o n of o f the the Uchi M c R i t c h i e and a n d Weber, Weber, 1971b) 1971 b ) U c h i Subprovirice S u b p r o v i n c e (Campbell, ( C a m p b e l l , 1971 1971;; McRitchie In Ontario, In O n t a r i o , Thurston T h u r s t o n and a n d Breaks B r e a k s (1978) ( 1 9 7 8 ) noted n o t e d that t h a t the t h e paragneiss paraqneiss is is sstratigraphically t r a t i g r a p h i c a l l y equivalent e q u i v a l e n t to t o Cycle C y c l e II volcanic v o l c a n i c rocks r o c k s in i n the the Cerny Confederation a r e a of o f the t h e Uchi U c h i Subprovince. Subprovince. C e r n y et e t al. al. C o n f e d e r a t i o n Lake L a k e area ( 1 981 ) recognized r e c o g n i z e d a assimilar i m i l a r rrelationship e l a t i o n s h i p on o n tthe h e south s o u t h sside i d e of o f the the (1981) Ear Ear Falls—Manigotagan F a l l s - M a n i g o t a g a n b e 1belt t wwhere h e r e t hthe e p paragneisses a r a q n e i s s e s aare r e postulated postulated to t o be b e stratigraphically s t r a t i g r a p h i c a l l yequivalent e q u i v a l e n ot t othe t t hFlanders e F l a n d e rLake s L a k eFormation Format i o n Metaconglomerates in b e l tofo fManitoba. Manitoba. Metaconglomerates i n the t h e Bird B i r d River R i v e r greenstone g r e e n s t o n e belt o c c u r in i n both b o t h the t h e Edmunds Lake L a k e and a n d Flanders F l a n d e r s Lake L a k e Formations F o r m a t i o n s and and occur locally l o c a l l y at a t other o t h e r places p l a c e s near n e a r the t h e margins m a r g i n s of o f the t h eEar E a rFalls— Fallsb e l t (e.g., ( e . g . , Breaks B r e a k s et e t al., a l . , 1978), 1 9 7 8 ) , and a n d contain c o n t a i n aa M a n i g o t a g a n belt Manigotagan variety d e r i v e d from f r o m mafic maÂi c to t o felsic f e l s i c volcanic v o l c a n i c units, units, v a r i e t y of o f clasts c l a s ts derived mafic maÂi c to t o felsic f e l s i c plutons, p l u t o n s , and a n d sedimentary s e d i m e n t a r y units u n i t s including including ferruginous metasediments f e r r u g i n o u s cchemical hemical m e t a s e d i m e n t s ((Bateman, B a t e m a n , 11939 9 3 9 ; Breaks B r e a k s et e t al. a1 These 1978; 1 9 7 8 ; Cerny C e r n y et e t al. a l . 1981 1981 ; Campbell, C a m p b e l l , 1971 1971). ). T h e s e stratigraphic stratigraphic relationships more that m o r e proximal p r o x i m a l facies f a c i e s of o f the t h e paragneiss paragneiss r e l a t i o n s h i p s ssuggest u g g e s t that may v o l c a n o - s e d i m e n t a r y sequences sequences may occur o c c u r in i n the t h e greenstone—belt, g r e e n s t o n e - b e 1 t , volcano—sedimentary flanking f l a n k i n g the t h e Ear E a r Falls-Manigotagan F a l l s - M a n i q o t a g a n belt. belt. was apparently a p p a r e n t l y the t h e adjacent adjacent T h e provenance p r o v e n a n c e of o f the t h e paragneiss p a r a g n e i s s was The greenstone—granitoid g r e e n s t o n e - g r a n i t o i d terranes t e r r a n e s and a n d was was variable v a r i a b l e in i n composition, compos i t i o n , although a 1 t h o u q h volcaniclastic v o l c a n i c l a s t i c metasediments m e t a s e d i m e n t s may may be be regionally r e g i o n a l l y or or locallocally l y dominant d o m i n a n t (cf. ( c f Ojakangas, O j a k a n g a s , 1985). 1985). . . e B e 1 ts I n t e r n a l Greenstone G r e e n s t o n e Belts Internal Two Two relatively r e l a t i v e l y well w e l l preserved p r e s e r v e d greeristone g r e e n s t o n e belts be1 ts occur o c c u r entireentirely within ly w i t h i n the t h e English E n g l i s h River R i v e r Subprovince, S u b p r o v i n c e , along a l o n g the t h e boundary boundary between Manigotaqan belts. b e t w e e n the t h e Winnipeg W i n n i p e g R i v e r a n d Ear F a l l s - Manigotagan The Bird B i r dRiver R i vgreenstone e r g r e e nbelt, s t othe n elarger b e l and t , better t h e lpreserved a r g e r and b e t t e r preserved The of mafic to felsicr metavolcanic o f thet htwo e tbelts w o comprises b e l t s comprises n a f i c t o f rocks, e l s i c metavolcanic rocks, mafic cclastic l a s t i c metasedimentary m e t a s e d i m e n t a r y rocks r o c k s and a n d maf i c to t o ultramafic u l t r a r n a f i c intrusions intrusions River and Ear Falls - belts. �67 (Davies ( ~ a v i e et se t al. a l . 1962; 1 9 6 2 ; Karup—frloller K a r u p - M o l l e r a nand d Brurnmer 971; T r u e m a n 1975; 1975; Brummer 11971; Trueman Cerny C e r n y et e t al. a l . 1981). 1981 ) R e g i o n a l m e t a m o r p h i c g r a d e i n c r e a s e s o u t ward Regional metamorphic grade increases outward f r o m greenschist g r e e n s c h i s t to t o almandine—amphibolite a l m a n d i n e - a m p h i b o l i t e as a s the t h e belt b e l t grades g r a d e s into into from paragneiss M a n i g o t a g a n belt b e l t (Butrenchuk (Butrenchuk p a r a g n e i s s of o f the t h e Ear E a r Falls F a l l s —- Manigotagan 1970) 1970). c l a s t i c metasedimentary m e t a s e d i m e n t a r y rocks r o c k s are are F e l s i c metavolcanic m e t a v o l c a n i c and a n d clastic Felsic more abundant a b u n d a n t than t h a n in i n most most greenstone g r e e n s t o n e belts b e l t s of o f the t h e Wabigoon W a b i g o o n and and more u t tthis h i s may e f l e c t the t h e relatively r e l a t i v e l y small s m a l l size size U c h i SSubprovinces, u b p r o v i n c e s , bbut tJchi may rreflect of o f the t h e greenstone g r e e n s t o n e belt b e 1 t and and partial p a r t i a l engulfment e n g u l f m e n t by by younger y o u n g e r plutons plutons rather r a t h e r than t h a n any a n y primary p r i m a r y ddifferences. ifferences O t h e r greeristone g r e e n s t o n e bbelts, e 1 ts , Other h o w e v e r , ddo o llack a c k iintrusions n t r u s i o n s comparable c o m p a r a b l e tto o tthe h e layered, l a y e r e d , Cr-enrichCr-enrichhowever, ed Bird R i v e r s i l l . The T h e Separation S e p a r a t i o n Lake L a k e greenstone g r e e n s t o n e belt b e l t is is mainly m a i n l y massive m a s s i v e and and pillowed f l o w s with w i t h subordinate s u b o r d i n a t e qabbro q a b b r o and a n d peridotite peridot ite p i l l o w e d metabasalt m e t a b a s a l t flows i n t r u s i o n s and a n d oxide—facies o x i d e - f a c i e s iron i r o n formation; f o r m a t i o n ; metamorphic m e t a m o r p h i c grade g r a d e is is intrusions amphibolite a m p h i b o l i t e facies f a c i e s (Beakhouse, ( B e a k h o u s e , 1975). 1 9 7 5 ) . The The belt b e l t is is in i n fault fault contact c o n t a c t with w i t h paragrieiss p a r a g n e i s s tto o tthe h e north n o r t h and a n d the t h e southern s o u t h e r n margin marg i n is is aa 1 to t o 22 km km wide w i d e migmatitic m i g m a t i t i c zone z o n e with w i t h younger y o u n g e r plutons. plutons. Numerous N u m e r o u s gabbro, g a b b r o , and a n d iron i r o n formation f o r m a t i o n rafts r a f t s are a r e widely widely distributed d i s t r i b u t e d in i n the t h e younger y o u n g e r plutonic p l u t o n i c suites, s u i t e s , but b u t are a r e especially especially abundant a b u n d a n t along a l o n g the t h e north n o r t h margin m a r g i n of o f the t h e Winnipeg W i n n i p e g River R i v e r belt b e l t east east of o f Separation S e p a r a t i o n Lake L a k e where w h e r e they t h e y may may be b e an a n extension e x t e n s i o n of o f the the Separation a r e a south south S e p a r a t i o n lake l a k e greenstone g r e e n s t o n e belt, b e l t , and a n d in i n the t h e Sand S a n d Lake L a k e area of o f the t h e Separation S e p a r a t i o n Lake Lake belt. b e l t . These T h e s e rafts r a f t s lack l a c k the t h e intense intense deformation t h a t characterizes c h a r a c t e r i z e s the t h e early early d e f o r m a t i o n and a n d partial p a r t i a l anatexis a n a t e x is that supracrustal remnants. s u p r a c r u s t a l remnants. As A s noted n o t e d previously p r e v i o u s l y the t h egreenstorie—belt g r e e n s t o n e - b e 1 t sequences s e q u e n c e s appear a p p e a r to to be b e stratigraphically s t r a t i q r a p h i c a l l y equivalent e q u i v a l e n t to t o the t h e paragneisses p a r a g n e i s s e s of o f the t h e Ear Ear Falls—Manigotagan F a l l s - M a n i g o t a g a n belt b e 1 t (Cerny ( C e r n y et e t al., a 1 , 1981) 1981 ) and a n d to t o greenstone— greens tonebelt b e l t sequences s e q u e n c e s of o f the t h e tichi U c h iSubprovince. S u b p r o v i n c e . Contacts C o n t a c t s between b e t w e e n the the b e 1 t - p a r a g n e i s s assemblage a s s e m b l a g e and a n d the t h e older o l d e rorthogneiss— orthoqneissg r e e n s t o n e belt—paragneiss greenstone supracrustal s u p r a c r u s t a lremnant r e m n a n t assemblage a s s e m b l a g e have h a v e not n o t been b e e n observed. o b s e r v e d . However, However, a s w i l l b e d i s c u s s e d l a t e r , t h e r e l a t i v e a g e s o f t h e two assemblages a s s e m b l a g e s ccan a n be b e deduced d e d u c e d ffrom r o m iindirect n d i r e c t field f i e l evidence d e v i d e n c and e a n geo— d qeochronoloqic c h r o n o l o g i c data. data. . . ed Bird River sill. 1 . as will be discussed later, the relative ages of the two Plutonic P l u t o n i c Rocks Rocks e l s i c plutonic p l u t o n i c suites, s u i t e s , sodic s o d i cand a n d potassic, p o t a s s i c ,underlie u n d e r l i 80% e 80% Two f felsic Two of o f the t h eWinnipeg W i n n i p e g River R i v e r belt b e l t and and 50% 5 0 % of o f the t h e western w e s t e r n English E n g l i s h River River Subprovince p l u t o n scommonly commonly intruded intruded S u b p r o v i n c e (Figure ( F i g u r e 2). 2 ) . Potassic P o t a s s i cplutoris adjacent t h i r d (mafic) ( m a f i c ) suite s u i t e is is not n o tabundant. abundant. a d j a c e n t sodic s o d i c plutons. p l u t o n s . AA third The t w o settings: s e t t i n g s : 1)1 ) intruded i n t r u d e d into into T h e sodic s o d i c suite s u i t e occurs o c c u r s in i n two orthogneiss a n d 2) 2) o r t h o g n e i s s near n e a r the t h e margins m a r g i n s of o f the t h e Winnipeg W i n n i p e g River R i v e r belt, b e 1 t , and as a s diapiric d i a p i r i c intrusions i n t r u s i o n s into i n t o the t h e paragneiss p a r a g n e i s s of o f the t h e Ear E a r Falls F a l l s —Manigotagan M a n i g o t a q a n belt. b e l t . The T h e sodic s o d i c suite s u i t e includes i n c l u d e s quartz q u a r t z diorites, diorites , tonalites t o n a l i t e s and a n d granodiorites q r a n o d i o r i t e s that t h a t are a r e commonly commonly recrystallized r e c r y s t a l l i z e d and, and, in some cases, c a s e s , deformed. d e f o r m e d . Primary P r i m a r y igneous i g n e o u s textures t e x t u r e s are are i n some recognizable r e c o g n i z a b l e but b u t are a r e commonly commonly modified m o d i f i e d by by the t h e development d e v e l o p m e n t of o f aa foliation f o l i a t i o n or o r lineation. l i n e a t i o n . Weakly W e a k l y yneissic g n e i s s i c fabrics f a b r i c s are are present present locally, to l o c a l l y , near n e a r contacts, c o n t a c t s , and a n d probably p r o b a b l y originated o r i g i n a t e d in i n response r e s p o n s e to laminar l a m i n a r flow f l o w during d u r i n g emplacement e m p l a c e m e n t although a l t h o u g h certain c e r t a i n units u n i t s appear a p p e a r to to pre—date p r e - d a t e deformation. deformation. The is most m o s t abundant a b u n d a n t in i n the t h e west—central w e s t - c e n t r a l part part T h e potassic p o t a s s i c suite s u i t e is of o f the t h e Winnipeg W i n n i p e g River R i v e r belt b e l t where w h e r e it i t forms f o r m s large l a r g e batholiths batholiths �68 (Figure ( F i g u r e 2). 2). IIt t aalso l s o ooccurs c c u r s aas s sstocks, t o c k s , ddikes i k e s and a n d sills s i l l s throughout throughout ett al., a l . , 1978). 1 9 7 8 ) . This T h i s suite suite tthe h e English E n g l i s h River R i v e r Subprovince S u b p r o v i n c e (Breaks (Breaks e includes late i n c l u d e s ggranodiorites r a n o d i o r i t e s and a n d granites g r a n i t e s that, t h a t , except e x c e p t near n e a r late ffaults, a u l t s , lack l a c k the t h e ssecondary e c o n d a r y recrystallization r e c r y s t a l l i z a t i o n foliation foliation Primary ccharacteristic h a r a c t e r i s t i c of o f the t h e sodic s o d i c suite. suite. P r i m a r y planar p l a n a r and a n d linear linear a r e rare r a r e but b u t well w e l l preserved. preserved. fflow l o w sstructures t r u c t u r e s are Inclusions a r e found f o u n d in i n the the I n c l u s i o n s of o f virtually v i r t u a l l y every e v e r y older o l d e r suite s u i t e are potassic p o t a s s i c suite s u i t e but b u t individual i n d i v i d u a l units u n i t s are a r e characterized c h a r a c t e r i z e d by b y specific specific Potassic aassemblages s s e m b l a g e s of o f inclusions. inclusions. P o t a s s i c plutons p l u t o n s in i n the t h e Winnipeg Winnipeg River a r e characterized c h a r a c t e r i z e d by b y arnphibolite, a m p h i b o l i t e , oorthogneiss r t h o g n e i s s and and R i v e r belt b e l t are t o granodioritic granodioritic vvariously a r i o u s l y recrystallized r e c r y s t a l l i z e d quartz q u a r t z dioritic d i o r i t i c to inclusions Ear Falls Falls i n c l u s i o n s whereas w h e r e a s the t h e relatively r e l a t i v e l y small s m a l l plutons p l u t o n s in i n the t h e Ear — Manigotagan - M a n i g o t a g a n belt b e l t contain c o n t a i n variously v a r i o u s l y digested d i g e s t e d paragneiss paragneiss iinclusions. n c l us ions a FOR 'PRE-KENORAN' CRUST IIN THE WINNIPEG WINNIPEG RRIVER BELT EEVIDENCE V I D E N C E FOR 'PRE-KENORAN' CRUST N THE I V E R BELT The i s the t h e culminating c u l m i n a t i n g Archean A r c h e a n orogenic oroqenic T h e Kenoran K e n o r a n Orogeny O r o g e n y is It was eevent v e n t in i n the t h e Superior S u p e r i o r Province. Province. It w a s ooriginally r i g i n a l l y ddated a t e d as a s the the pperiod e r i o d between b e t w e e n 2390 2 3 9 0 Ma and a n d 2590 2 5 9 0 Ma (Stockwell, ( S t o c k w e l l , 1964) 1 9 6 4 ) based b a s e d on on These K - A r mineral m i n e r a l ages. ages. T h e s e ages a g e s are a r e now widely w i d e l y regarded r e g a r d e d as as K—Ar representing r e p r e s e n t i n g minimum cooling c o o l i n g ages a g e s and a n d the t h e age a g e and a n d definition d e f i n i t i o n of of ( e .g. Gower Gower and and t h e orogeny o r o g e n y has h a s been b e e n revised r e v i s e d repeatedly r e p e a t e d l y (e.g. the Clifford, ( 1 9 7 7 ) concluded, concluded, C l i f f o r d , 1981, 1 9 8 1 , Harland, H a r l a n d , 1983). 1 9 8 3 ) . Goodwin (1977) largely l a r g e l y oon n the t h e basis b a s i s of o f U—Pb U-Pb zircon z i r c o n ages, a g e s , that t h a t most m o s t metavolcanic metavolcanic metasedirnentary western aand nd m e t a s e d i m e n t a r y r rocks o c k s oof  tthe he w e s t e r n SSuperior u p e r i o r Province P r o v i n c e were were Ma, were were subsequently s u b s e q u e n t l y deformed deformed ddeposited e p o s i t e d between b e t w e e n 2710 2 7 1 0 and a n d 2760 2 7 6 0 Ma, metamorphosed aand nd m e t a m o r p h o s e d by by the t h e Kenoran K e n o r a n orogeny o r o g e n y and a n d had had been b e e n intruded i n t r u d e d by by Recent late— l a t e - or o r post—tectonic p o s t - t e c t o n i c plutons p l u t o n s by b y 2660 2 6 6 0 Ma. Ma. R e c e n t U—Ph U-Pb zircon zircon ddata a t a from f r o m the t h e western w e s t e r n Wabigoon W a b i g o o n Subprovince S u b p r o v i n c e (Hart ( H a r t and a n d Davis, D a v i s , 1969; 1969; Davis D a v i s eet t aal l . 1982; 1 9 8 2 ; Davis D a v i s and a n d Trowell, T r o w e l l , 1982; 1 9 8 2 ; Davis D a v i s and a n d Edwards, Edwards, with 1982; Blackburn e t al., a l . , 11984) 9 8 4 ) aagree gree w i t h this t h i s conclusion, c o n c l u s i o n , and and 1982; B l a c k b u r n et indicate i n d i c a t e tthat h a t vvolcanic o l c a n i c and a n d associated a s s o c i a t e d plutonic p l u t o n i c activity a c t , i v i t y here here t i m e interval i n t e r v a l of o f 2703 2 7 0 3 to t o aapparently p p a r e n t l y ooccurred c c u r r e d over o v e r the t h e restricted r e s t r i c t e d time 2755 Ma, and a n d that t h a t post—tectonic p o s t - t e c t o n i c plutons p l u t o n s were w e r e emplaced e m p l a c e d by b y 2695 2695 2 7 5 5 Ma, This is a useful u s e f u l standard s t a n d a r d against a g a i n s t which w h i c h to t o evaluate e v a l u a t e isotopic isotopic Ma. T h i s is Winnipeg aages g e s from f r o m the the W i n n i p e g River R i v e r belt b e l t because b e c a u s e of o f the t h e high h i g h precision precision a g e s and a n d the t h e proximity p r o x i m i t y to aand n d consistency c o n s i s t e n c y of o f the t h e ages t o the t h e Winnipeg Winnipeg River R i v e r belt. belt. Goodwin (1977) Ma) Lac L a c Seul Seul Goodwin ( 1 9 7 7 ) also a l s o recognized r e c o g n i z e d an a n older o l d e r (>3000 ( > 3 0 0 0 Ma) metaeevent, v e n t , and a n d ssubsequent u b s e q u e n t work w o r k has h a s recognized r e c o g n i z e d metavolcanic m e t a v o l c a n i c and a n d meta— pplutonic l u t o n i c rocks r o c k s intermediate i n t e r m e d i a t eini nage a g between e b e t w e e n2760 2 7 6 0and a n d3000 3 0 0 0Ma Ma (Nunes ( N u n e s a and n d TThurston, h u r s t o n , 11980; 9 8 0 ; BBeakhouse, e a k h o u s e , 1 91983; 8 3 ; C oCorfu r f u e teta al., l . , 1985). 1985). These a g e s complicate c o m p l i c a t e Goodwin's G o o d w i n ' s two—fold t w o - f o l d d distinction istinction T h e s e intermediate i n t e r n e d i a t e ages and Province, a n d ssuggest u g g e s t tthat, h a t , in i n some some parts p a r t s of o f the t h ewestern w e s t e r n Superior Superior P rovince, ccrustal r u s t a l evolution e v o l u t i o n may have h a v e proceeded p r o c e e d e d semi—continuously s e m i - c o n t i n u o u s l y for f o r 400 4 00 To facilitate Ma. f a c i l i t a t e ddiscussion i s c u s s i o n the t h e terms terms 'Kenoran' ' K e n o r a n ' and a n d 'pre— 'preKenoran' K e n o r a n ' are a r e used u s e d informally i n f o r m a l l y here h e r e to t o refer r e f e r to t o rocks r o c k s younger y o u n g e r and and It Ma. I t iis s eemphasized m p h a s i z e d that t h a t these these oolder, l d e r , respectively, r e s p e c t i v e l y , than t h a n 2760 2 7 6 0 Ma. terms a are terms r e adopted a d o p t e d for f o r convenience c o n v e n i e n c e only o n l y and a n d without w i t h o u t any a n y intent i n t e n t to to fformally o r m a l l y re—define r e - d e f i n e the t h e Kenoran K e n o r a n Orogeny. Orogeny. Field F i e l d Evidence Evidence The T h e oorthogneiss r t h o g n e i s s suite s u i t e intruded i n t r u d e d the t h e older o l d e r supracrustal supracrust a l remnant p h a s e s of o f the t h e orthogneiss o r t h o g n e i s s suite s u i t e predate predate r e m n a n t suite s u i t e and a n d most phases �69 the t h e plutoriic p l u t o n i c suites. s u i t e s . The T h e orthogneiss o r t h o g n e i s s is is interpreted i n t e r p r e t e d to t o be b e older older a n d Wabigoori Wabigoon t h a n the t h e paragneiss, p a r a g n e i s s , internal i n t e r n a l greenstone g r e e n s t o n e belts b e 1 ts and than s u b p r o v i n c e volcanism v o l c a n i s m based b a s e d on o n several s e v e r a l indirect i n d i r e c t field field subprovince relationships. relationships. 1) T h e orthogneiss o r t h o g n e i s s is is cut c u t by b y mafic ma i c dikes d i k e s (Bald, ( B a l d , 1981). 1981 ) Some 1) The Some of (6 o f these t h e s e dikes, d i k e s , such s u c h as a s those t h o s e in i n the t h e Tannis T a n n i s Lake L a k e area a r e a (6 o n Fig. F i g . 2), 2 ) , may may be b e feeders f e e d e r s to t o Kenoran K e n o r a n volcanism v o l c a n i s m (Clark ( C l a r k et et on al. a l . 1981), 1 9 8 1 ) , although a l t h o u g h Gower Gower (1978) ( 1 9 7 8 ) has h a s noted n o t e d that t h a t some some dikes d i k e s in i n the t h e Kenora K e n o r a area a r e a are a r e caic—alkaline c a l c - a l k a l i n e and a n d are are probably p r o b a b l y not n o t related r e l a t e d to t o the t h e basal b a s a l tholeiitic t h o l e i i t i c volcanism v o l c a n i s m in in the t h e adjacent a d j a c e n t Wabigoon W a b i g o o n Subprovince. Subprovince. 2) 2 ) Polymictic P o l y m i c t i c conglomerate c o n g l o m e r a t e at a t Perrault P e r r a u l t Lake L a k e in i n the t h e Winnipeg Winnipeg River R i v e r belt b e l t contains c o n t a i n s massive m a s s i v e and a n d foliated f o l i a t e d plutonic p l u t o n i c clasts clasts (Breaks e t al. a l . 1978). 1 9 7 8 ) . It I t is i s unlikely u n l i k e l y that t h a t the t h e foliated foliated ( B r e a k s et plutonic p l u t o n i c clasts c l a s t s were were derived d e r i v e d from f r o m syrivolcanic s y n v o l c a n i c plutons, plutons, and, a1 t h o u g h it i t cannot c a n n o t be b e established e s t a b l i s h e d that t h a t these t h e s e clasts c l a s ts a n d , although were were derived d e r i v e d from f r o m the t h e orthogneiss, o r t h o g n e i s s , they t h e y do d o demonstrate demonstrate the t h e existence e x i s t e n c e of o f an a n elevated e l e v a t e d granitoid g r a n i t o i d terrane t e r r a n e prior p r i o r to to the l a t e plutonism. plutonism. t h e late 3) 3 ) In I n the t h e western w e s t e r n end e n d of o f the t h e Ear E a r Falls—Manigotagan F a l l s - M a n i g o t a g a n belt, belt, orthogneiss cores of o f antiforms a n t i f o r m s and and o r t h o g n e i s s occupies o c c u p i e s the t h e cores structurally s t r u c t u r a l l y underlies u n d e r l i e s the t h e paragneiss p a r a g n e i s s representing r e p r e s e n t i n g aa possible p o s s i b l e basement—cover b a s e m e n t - c o v e r relationship r e l a t i o n s h i p (Ermanovics ( E r m a n o v i c s et e t al., al., 1979). 1 9 7 9 ) . However, H o w e v e r , tectonic t e c t o n i c juxtaposition j u x t a p o s i t i o n of o f these t h e s e units u n i t s is is also In a l s o possible. possible. I n the t h e Cedar C e d a r Lake L a k e area, a r e a , Westerman W e s t e r m a n (1979) ( 1 979) considered cores of of c o n s i d e r e d that t h a t the t h e Twilight T w i l i g h t paragneiss p a r a g n e i s s in i n the t h e cores domal d o m a l structures s t r u c t u r e s is is aa result r e s u l t of o f subhorizontal s u b h o r i z o n t a l tectonic tectonic interleaving i n t e r l e a v i n g of o f basement b a s e m e n t and a n d cover c o v e r sequences. sequences. 4) 4 ) The T h e earliest e a r l i e s t deformation d e f o r m a t i o n that t h a t affected a f f e c t e d the t h e orthogneiss o r t h o g n e i s s in in the t h e Cedar C e d a r Lake L a k e area a r e a may may not n o t be b e present p r e s e n t in i n the t h e Twilight Twilight paragneiss p a r a g n e i s s (Westerman, ( W e s t e r m a n , 1977) 1 9 7 7 ) implying i m p l y i n g that t h a t the t h e tonalites t o n a l ites were were emplaced e m p l a c e d and a n d deformed d e f o r m e d prior p r i o r to t o the t h e deposition d e p o s i t i o n of o f the the paragneiss p a r a g n e i s s progenitor. p r o g e n i t o r . Similarly, S i m i l a r l y , deformation d e f o r m a t i o n in i n the the paragneisses p a r a g n e i s s e s of o f the t h e Ear E a r Falls—Manigotagan F a l l s - M a n i g o t a g a n belt b e l t appears a p p e a r s to to be b e less l e s s complex c o m p l e x than t h a n in i n adjacent a d j a c e n t orthogneiss. o r t h o g n e i s s . However, However, it i t must m u s t be b e stressed s t r e s s e d that t h a t the t h e apparent a p p a r e n t differences d i f f e r e n c e s in in structural s t r u c t u r a l complexity c o m p l e x i t y of o f paragneiss p a r a g n e i s s and a n d orthogneiss o r t h o g n e i s s could could also a l s o be b e the t h e result r e s u l t of o f differing d i f f e r i n q ductility d u c t i l i t y contrasts c o n t r a s t s and and rheologic same deformation d e f o r m a t i o n event. event. r h e o l o q i c states s t a t e s during d u r i n g the t h e same The T h e field f i e l d relations r e l a t i o n s outlined o u t l i n e d above a b o v e give g i v e inconclusive i n c o n c l u s i v e results results about b e 1 ta b o u t the t h e age a g e relationships r e l a t i o n s h i p s between b e t w e e nthe t h egreenstorie g r e e n s t o n e belt— paragneiss p a r a g n e i s s assemblage a s s e m b l a g e aand n d tthe h e orthogneiss. orthogneiss. A t the present state o f k n o w l e d g e a1 t e r n a t i v e e x p l a n a t i o n s are p o s s i b l e f o r a l l o f t h e field f i e l drelations, relationa s , common a commonsituation s i t u a t i oin n isuch n s u ccomplexly h c o m p l e x l deformed y deformed t e r r a n e s . In I n spite s p i t e o f t h e s e p r o b l e m s , t h e f i e l d relations r e l a t i o n s can c a n be be interpreted t o indicate i n d i c a t e that t h a t the t h e orthogneiss o r t h o g n e i s s is is older o l d e r than t h a n the the i n t e r p r e t e d to greenstone g r e e n s t o n e belt—paragneiss b e 1 t - p a r a q n e i s s assemblage a s s e m b l a g eand a n disispre—Kenorari. pre-Kenoran. This This interpretation is supported s u p p o r t e d by b y geochronologic q e o c h r o n o l o g i c data. data. i n t e r p r e t a t i o n is . At the present state of knowledge alternative explanations are possible for all of the terranes. of these problems, the field Geochronological G e o c h r o n o l o g i c a l Evidence Evidence AA direct d i r e c t approach a p p r o a c h to to establish e s t a b l i s h the t h e existence e x i s t e n c e and and distribution d i s t r i b u t i o n of o f pre—Kenoran p r e - K e n o r a n crust c r u s t is is the t h e isotopic i s o t o p i c dating d a t i n q of o f those those rocks r o c k s interpreted, i n t e r p r e t e d , on o n the t h e basis b a s i s of o f field f i e l d relationships, r e l a t i o n s h i p s , to t o be b e the the oldest o l d e s t in i n aa particular p a r t i c u l a r area. a r e a . Supracrustal S u p r a c r u s t a l remnants r e m n a n t s are a r e difficult difficult �70 to to ddate a t e isotopically i s o t o p i c a l l y because b e c a u s e most most are a r e mafic m a f i c volcanic v o l c a n i c rocks. rocks. Rubidium — strontium s t r o n t i u m investigations i n v e s t i g a t i o n s oof f ssuch u c h rocks r o c k s are a r e hampered h a m p e r e d by by Rubidium a ssmall m a l l range r a n g e in i n Rb/Sr Rb/Sr which w h i c h limits l i m i t s precision, p r e c i s i o n , susceptibility s u s c e p t i b i l i t y to to open o p e n system s y s t e m behaviour, b e h a v i o u r , and a n d by b y low l o w Rb/Sr Rb/Sr which w h i c h results r e s u l t s in i n aa very very sslight l i g h t increase i n c r e a s e in i n initial i n i t i a l Sr Sr isotopic i s o t o p i c composition c o m p o s i t i o n for f o r meta— metaZircons are not a common primary morphically rotated isochrons. morphically rotated isochrons. Z i r c o n s are n o t a primary mineral be of of m i n e r a l in i n mafic m a f i c volcanic v o l c a n i c rocks r o c k s and, a n d , if i f present, p r e s e n t , they t h e y may may be metamorphic Zr derived d e r i v e d from f r o m the t h e alteration a l t e r a t i o n of of m e t a m o r p h i c origin o r i g i n with w i t h Zr ppyroxene y r o x e n e to t o amphibole. amphibole. Granitoid a r e more G r a n i t o i d ggneiss n e i s s components c o m p o n e n t s oof f the t h e orthogneiss o r t h o g n e i s s are appropriate a p p r o p r i a t e for f o r Rb—Sr Rb-Sr and a n d U—Pb U-Pb zircon z i r c o n investigation i n v e s t i g a t i o n —- - they t h e y may be relatively younger than the supracrustal remnants and b e r e l a t i v e l y y o u n g e r t h a n t h e s u p r a c r u s t a l r e m n a n t s a n d the the m e l t i n g of of ttonalite o n a l i t e gneiss g n e i s s but b u t they t h e y could, c o u l d , if i f derived d e r i v e d from f r o m the t h e melting ssuch u c h rocks, r o c k s , hhave a v e Sr S r isotope i s o t o p e initial i n i t i a l ratios r a t i o s that t h a t reflect r e f l e c t the the ccrustal r u s t a l residence r e s i d e n c e history h i s t o r y of o f their t h e i r precursor. p r e c u r s o r . The T h e rock r o c k type t y p e that that has a t t e n t i o n is is the t h e fine—grained f i n e - g r a i n e d tonalite tonalite h a s received r e c e i v e d the t h e most attention Radiometric ggneiss n e i s s component c o m p o n e n t of o f the t h e orthogneiss. orthogneiss. R a d i o m e t r i c dating d a t i n g of o f such such rocks is not without problems but they are amenable to a variety r o c k s is n o t w i t h o u t p r o b l e m s b u t t h e y a r e a m e n a b l e t o a v a r i e t y oof f types t y p e s of o f Rb—Sr Rb-Sr and a n d U—Pb U-Pb zircon z i r c o n investigation i n v e s t i g a t i o n (Beakhouse ( B e a k h o u s e 1983). 1983). The aavailable The v a i l a b l e ggeochronoloqical e o c h r o n o l o g i c a l ddata a t a for f o r the t h e orthogneiss o r t h o g n e i s s and and Winnipeg ssodic o d i c pplutons l u t o n s from f r o m the the W i n n i p e g River R i v e r belt b e l t sugqest s u g g e s t that t h a t these these rrocks o c k s aare r e sslightly l i g h t l y to t o ssignificantly i g n i f i c a n t l y oolder l d e r than t h a n volcanism v o l c a n i s m and and 'Pre—Kenoran' plutonism 3). ) 'Pre-Kenoran' p l u t o n i s m iin n the t h e Wabigoon W a b i g o o n SSubprovince u b p r o v i n c e ((Figure Figure 3 att Sen S e n Bay Bay on o n eastern e a s t e r n Lac Lac Seul Seul ttonalites o n a l i t e s hhave a v e been b e e n recognized recognized a (Krogh Tannis K r o g h e t a l . 1976a) 1 9 7 6 a ) ,, T a n n i s Lake Lake ( (Clark C l a r k eet t aal., l . , 1981; 1981 ; D.W. D.W. Davis, D a v i s , personal p e r s o n a l communication, c o m m u n i c a t i o n , 1983), l 9 8 3 ) , in i n the t h e Kenora K e n o r a area area ((Beakhouse, B e a k h o u s e , 1983) 1 9 8 3 ) aand n d hhave a v e been b e e n interpreted i n t e r p r e t e d (from ( f r o m combined c o m b i n e d U—Pb U-Pb zircon z i r c o n aand n d Rb—Sr Rb-Sr isotopic i s o t o p i c sstudies) t u d i e s ) to t o be b e present p r e s e n t in i n the t h e Cedar Cedar Lake L a k e area a r e a (Beakhouse, ( B e a k h o u s e , 1983). 1 9 8 3 ) . Rb—Sr Rb-Sr whole w h o l e rock r o c k ages a g e s tend t e n d to t o be be U—Pb zircon yyounger o u n g e r than t h a n U-Pb z i r c o n ages a g e s for f o r the t h e same s a m e units u n i t s and a n d the t h e poorer poorer Rb/Sr ages a g e s limits pprecision r e c i s i o n of o f the t h e Rb/Sr l i m i t s their t h e i r usefulness u s e f u l n e s s in i n inter-sub— inter-subPreliminary 3 other o t h e r localities localities pprovince r o v i n c e correlation. correlation. P r e l i m i n a r y ddata a t a from from 3 (Kenora, Daniels Cedar U—Pb zircon (Kenora, D a n i e l s Lake, Lake, C e d a r Lake) L a k e ) have h a v e minimum U-Pb z i r c o n ages ages rranging a n g i n g from f r o m 2837 2 8 3 7 to t o 3168 3 1 6 8 Ma Ma (Corfu ( C o r f u et e t al., a l . , 1985). 1985). IIn n aaddition, ddition, D.W. D.W. Davis D a v i s (personal ( p e r s o n a l communication, c o m m u n i c a t i o n , 1985) 1 9 8 5 ) has h a s determined d e t e r m i n e d aa age for a granitoid boulder in a conglomerate minimum a g e f o r a g r a n i t o i d b o u l d e r i n a c o n g l o m e r a t e near n e a r the the Winnipeg W i n n i p e g River—Wabigoon R i v e r - W a b i g o o n iinterface n t e r f a c e in i n the t h eSioux S i o u x Lookout L o o k o u t area a r e a of of 22897 8 9 7 Ma. Ma. The U—Pb T h e U-Pb z i rzircon c o n g egeochronological o c h r o n o l o q i c a l d adata t a ( (Figure F i g u r e 33) ) suggest suggest that River t h a t although a 1 t h o u g h the t h e Winnipeg Winnipeg R i v e r bbelt e l t had h a d aa more more protracted protracted hhistory i s t o r y than t h a n the t h eWabigoon W a b i g o o n SSubprovince, u b p r o v i n c e , t there here a r e some some ssimilarimilarare Mostl late— ities. Most a t e - a nand d p opost—tectonic s t - t e c t o n i c g r granitic a n i t i c pplutons l u t o n s iin n the the Winnipeg Ma and a n d 2705 2 7 0 5 Ma Ma W i n n i p e g RRiver i v e r belt b e l t were w e r e emplaced e m p l a c e d between b e t w e e n 2660 2 6 6 0 Ma This with w i t h tthe h e more more hhighly i g h l y ddifferentiated i f f e r e n t i a t e d granites g r a n i t e s emplaced e m p l a c e d llast. ast. T his with ccompares o m p a r e s ffavourably avourably w i t h the t h e age a g eofo f2695 2 6 9 5Ma Ma for for a a post—tectonic post-tectonic pplutori l u t o n (the ( t h e Taylor T a y l o rLake L a k e stock) s t o c k )from f r o mthe t hWabigoon e W a b i g o o n Subprovince Subprovince e t al. a l . 1982). 1 9 8 2 ) . Tonalitic T o n a l i t i c phases p h a s e s of o f the t h e granitoid g r a n i t o i d gneiss gneiss ((Davis D a v i s et ccomponent o m p o n e n t oof f the t h e oorthogneiss r t h o g n e i s s from f r o m the t h e Cedar C e d a r Lake L a k e area a r e a apparently apparently crystallized c r y s t a l l i z e d at a t approximately a p p r o x i m a t e l y tthe h e same same ttime i m e as a s volcanic v o l c a n i c and and tonalitic t o n a l i t i cplutons p l u t o n in s ithe n t Wabigoon h e W a b i g o o nSubprovince S u b p r o v i n c e but b u thave h a v emodel model Sr Sr iisotope s o t o p e iinitial n i t i a lratios r a t i o (approximately s ( a p p r o x i m a t e l y0.704) 0. 7 0 4 ) that t h a t ssuggest u g g e s t that that melting they t h e y ooriginate r i g i n a t e from f r o m the the m e l t i n g oof f oolder l d e r crust c r u s t (Beakhouse ( B e a k h o u s e 1983). 1983). This T h i s period p e r i o d of o f melting, m e 1 t i n g , crystallization c r y s t a l l i z a t i o n and a n d associated a s s o c i a t e d metametamorphism is broadly b r o a d l y equivalent e q u i v a l e n t to t o aa period p e r i o d of o f volcano-plutonic volcano-plutonic m o r p h i s m is . et al. ities. �- = 1 Late- tto o Post—Tectonic Post-Tectonic Plutons Plutons Late— • . > 0) a) .2C Pre- tto o Syn—Tectonic Syn-Tectonic Plutons Plutons Pre— < . . a+ conglomerate near near interface interface -ø-Tonalite Tonalite boulder boulder from conglomerate ,- .Late— -oLate- to t o Post—Tectonic Post-Tectonic Pluton Pluton . •Â +  c  0 0 +a .-D) n ;  *  -0 L I 1 2600 2600 2700 2700  -1 1 Pre- tto o Syn—Tectonic Syn-Tectonic Plutons Plutons Pre— Rocks Metavolcanic Rocks 2800 2800 1 I 2900 2900 3000 3000 I 3100 3 100 Time (Ma) (Ma) Time Figure Figure 3: 3: Summary Summary of o f U—Pb U-Pb z i zircon r c o n g geochronoloqy e o c h r o n o l o q y a available v a i l a b l e for f o r the t h eWinnipeq W i n n i p e g River R i v e r—Where Wahiqoon W a b i q o o n ssuhprovince u b p r o v i n c e area. area. W h e r e error e r r o r bars b a r s are a r e not n o t visible v i s i b l e they t h e y are a r e contained contained Symbols within w i t h i n the t h e size s i z e of o f the t h e symbol. symbol. S y m b o l s with w i t h arrows a r r o w s indicate i n d i c a t e minimum minimum Data Krogh Davis (207Ph/206Pb) Data are a r e from from K r o g h eet t aal. l . ((1976a,b), 1976a,b), D a v i s aand n d E&wards dwards ( 2 0 7 ~ b / 2 0 6 ~ bages. a)q e s . Beakhouse (1982), Davis e t al. a l . (1982), (1982), B e a k h o u s e (1983) ( 1 9 8 3 ) and and (1982), D a v i s aand n d Trowell T r o w e l 1 (1982), ( 1 9 8 2 ) , Davis D a v i s et Corfu C o r f u et e t al. a l . (1985) ( 1 9 8 5 ) with w i t h additional a d d i t i o n a l unpublished u n p u b l i s h e d data d a t a from f r o m F. F. Corfu C o r f u (personal (personal communication, c o m m u n i c a t i o n , 1985) 1 9 8 5 ) and a n d D.W. D.W. Davis D a v i s (personal ( p e r s o n a l communication, c o m m u n i c a t i o n , 1985). 1985) . �72 activity a c t i v i t yini nthe t hWabigoon e ~ a b i g o o Subprovince. nS u b p r o v i n c e . Metamorphic M e t a m o r p h i c zzircons i r c o n s from f r o m aa Kenora K e n o r a aarea r e a ttonalite o n a l i t e gneiss g n e i s sformed f o r m e d somewhat somewhat eearlier arlier (approximately M a , Beakhouse B e a k h o u s e 1983) 1 9 8 3 ) but b u t it i t is i s not n o t clear c l e a r if if a p p r o x i m a t e l y 2790 2790 Ma, this t h i s represents r e p r e s e n t s aa discrete d i s c r e t emetamorphic m e t a m o r p h i c eevent v e n t oor r a a single, single, protracted p r o t r a c t e d metamorphic m e t a m o r p h i c event. e v e n t . The T h e crystallization c r y s t a l l i z a t i o nage a g e(U-Pb (U-Pb zircon) of this t h i ssame s a m etonalite t o n a l i t gneiss e g n e i s(approximately s ( a p p r o x i m a t e l2830 y 2830Ma) Ma) is is z i r c o n ) of s i g n i f i c a n t l y older o l d e r than t h a n th t hvolcano—plutoriic e v o l c a n o - p l u t o n i c aactivity c t i v i t y in i n the the significantly Wabigoon W a b i g o o n S Subprovince u b p r o v i n c e b u but t n onotso t s o oold l d as a s the t h e "Lac " L a c Seul S e u l event" event'' (Goodwin ( G o o d w i n 1977). 1977). Sodic S o d i c ssuite u i t e plutons p l u t o n s in i n the t h eWinnipeg W i n n i p e g River R i v e r bbelt e l t are are c o n c e n t r a t e d along a l o n g the t h e northern n o r t h e r n and a n d southern s o u t h e r n marg m a r g i ins n s of t h e belt belt concentrated of the and a n d spatial s p a t i a l association a s s o c i a t i o n of o f sodic s o d i cplutons p l u t o n s and a n d orthogneiss o r t h o g n e i s s is is especially e s p e c i a l l y evident e v i d e n t along a l o n g the t h e southern s o u t h e r n margin. m a r g i n . Breaks B r e a k s et e t al. al. (1978; ( 1 9 7 8 ; 1981) 1 9 8 1 ) ppoint o i n t oout u t that t h a t the t h e sodic s o d i c suite s u i t e grades g r a d e s imperceptibly imperceptibly into i n t o orthogneiss o r t h o g n e i s s and and that t h a t the t h e former f o r m e r suite s u i t e "has " h a s evolved e v o l v e d over o v e r aa relatively These r e l a t i v e l y long l o n g period p e r i o d of o f intrusion". intrusion". T h e s e authors a u t h o r s consider consider that t h a t one o n e of of the t h e oldest o l d e s t dated d a t e d units u n i t s in i n the t h e Winnipeg W i n n i p e g River R i v e r belt, belt, the t h e tonalite t o n a l i t e gneiss g n e i s s of o f the t h e Sen Sen Bay Bay Complex, C o m p l e x , which w h i c h is is more more than than 3008 3 0 0 8 Ma Ma (Krogh ( K r o q h et e t al. a l . 1976a) 1 9 7 6 a ) is is aa sodic s o d i c pluton, p l u t o n . The T h e Dalles Dalles granodiorite g r a n o d i o r i t e has h a s aa minimum minimum (2O7Pb/206Pb) ( 2 0 7 ~ b / 2 0 6 ~ bzircon z) i r c o n age a g e of o f 2762 2762 Ma Ma (Beakhouse 1983) that is slightly older than Wabigoon Subprovince ( B e a k h o u s e 1983 ) t h a t is s l i q h t l y o l d e r t h a n ~ a b i q o o ns u b p r o v i n c e volcanism v o l c a n i s marid a n d plutoriism p l u t o n i s m (Figure ( F i g u r e 3). 3 ) . Although A l t h o u g h there t h e r e is is aa gradation b e t w e e n some some sodic s o d i c plutons p l u t o n s and and orthogneiss, o r t h o g n e i s s , many many sodic sodic g r a d a t i o n between plutons intruded orthogneiss at their present crustal levels. p l u t o n s intruded orthoq neiss at t h e i r p r e s e n t c r u s t a 1 l e v e l s . In I n the t h e sodic s o d i c suite s u i t e there t h e r e is is an a n apparent a p p a r e n t discrepancy d i s c r e p a n c y between between isotopic ages and field relationships. Identical i s o t o p i c ages and f i e l d r e l a t i o n s h i p s . I d e n t i c a l Rb—Sr Rb-Sr isochron isochron ages a g e s of o f 2630 2630 Ma Ma are a r e reported r e p o r t e d for f o r the t h e Dalles D a l l e s and and Melick M e l i c k sodic sodic plutons p l u t o n s from f r o m the t h e Kenora Kenora area a r e a(Wooden (Wooden 1978). 1 9 7 8 ) . The The emplacement e m p l a c e m e n t of of the t h e Dalles D a l l e s granodiorite g r a n o d i o r i t e is is responsible r e s p o n s i b l e for f o r the t h e last l a s t major major deformational d e f o r m a t i o n a l event e v e n t in i n the t h e Kenora K e n o r a area a r e a (Gower (Gower 1978; 1 9 7 8 ; Gower Gower and and Clifford C l i f f o r d 1981) 1 9 8 1 ) and and this, t h i s , combined c o m b i n e d with w i t h the t h e Rb—Sr Rb-Sr geochronologic geochronologic data, d a t a , suggests s u g g e s t s that t h a t this t h i s batholith b a t h o l i t h was was emplaced e m p l a c e d to t o its i t s present present crustal c r u s t a l level l e v e l during d u r i n g the t h e Kenoran K e n o r a n orogeny. o r o g e n y . The T h e minimum minimum U/Pb U/Pb zircon z i r c o n age a g e of o f 2762 2 7 6 2 Ma Ma (Beakhouse, ( B e a k h o u s e , 1983), 1 9 8 3 ) , however, h o w e v e r , indicates i n d i c a t e s pre— preKenoran K e n o r a n crystallization. c r y s t a l l i z a t i o n . Field F i e l d relationships r e l a t i o n s h i p s for f o r the t h e Melick Melick pluton p l u t o n are a r e also a l s o at a t variance v a r i a n c e with w i t h the t h e apparently a p p a r e n t l y young young Rb—Sr Rb-Sr age age and a n d suggest s u g g e s t that t h a t this t h i s unit u n i t was was emplaced e m p l a c e d relatively r e l a t i v e l y early e a r l y in i n the the deforniational Kenora d e f o r m a t i o n a l hhistory i s t o r y oof f tthe he K e n o r a area a r e a (Gower (Gower and a n d Clifford Clifford 1981 1981 ) . Taken T a k e n together, t o g e t h e r , the t h e evidence e v i d e n c e suggests s u g g e s t s that t h a t some some sodic sodic plutons p l u t o n s are a r e slightly s l i g h t l y to t o considerably c o n s i d e r a b l y older o l d e r than t h a n 'Kenoran' 'Kenoran' volcano—plutonic v o l c a n o - p l u t o n i c activity a c t i v i t y in i n the t h e Wabigoon W a b i g o o n Subprovince S u b p r o v i n c e and a n d are are similar s i m i l a r in i n age a g e to t o the t h e enclosing e n c l o s i n g tonalite t o n a l i t e gneisses. g n e i s s e s . Upward Upward mobilization m o b i l i z a t i o n of o f these t h e s e plutons p l u t o n s took t o o k place p l a c e during d u r i n g the t h e Kenoran Kenoran orogeny o r o g e n y and a n d is is responsible r e s p o n s i b l e for f o r the t h e intrusive i n t r u s i v e contacts c o n t a c t s and and the the last l a s t major m a j o r deformational d e f o m a t i o n a l event. e v e n t . The The Dalles D a l l e s batholih, b a t h o l i t h , in in particular, p a r t i c u l a r , has h a s many many of o f the t h e attributes a t t r i b u t e s of o f aa classical c l a s s i c a l mantled mantled gneiss g n e i s s dome dome (Eskota ( E s k o l a 1948). 1 9 4 8 ) . Kroner K r o n e r et e t al. a l . (1981) ( 1 9 8 1 ) describe d e s c r i b e aa similar s i m i l a r relationship r e l a t i o n s h i p for f o r tonalitic t o n a l i t i c gneisses g n e i s s e s from f r o m Finland. Finland. Deformational t o those t h o s e in i n the the D e f o r m a t i o n a l fabrics f a b r i c s and a n d structures s t r u c t u r e s similar s i m i l a r to orthogneiss o r t h o g n e i s s are a r e preserved p r e s e r v e d in i n some some of o f the t h e smaller s m a l l e r plutons, p l u t o n s , as a s for for example e x a m p l e the t h e Melic M e l i c c tonalite, t o n a l i t e , but b u t are a r e rare r a r eini nlarger l a r g e rplutons. p l u t o n s . The The absence a b s e n c e of o f early e a r l y eformational d e f o r m a t i o n a l fabrics f a b r i c s may may reflect r e f l e c t their their obliteration o b l i t e r a t i o n duriig d u r i l g upward upward mobilization m o b i l i z a t i o noro rlack l a c kofo fgrieissic gneissic �73 development d e v e l o p m e n t in i n the t h e interior i n t e r i o r of o f large, l a r g e , relatively r e l a t i v e l y homogeneous homogeneous b a t h o l i t h s that t h a t acted a c t e d as as buttresses b u t t r e s s e s against a g a i n s t which w h i c h deformation deformation batholiths took t o o k place. place. Geochemical Geochem i c a l Evidence Ev i d e n c e The The geochemical g e o c h e m i c a l characteristics c h a r a c t e r i s t i c s of o f the t h e potassic p o t a s s i c plutonic plutonic rocks r o c k s of o f the t h e Winnipeg W i n n i p e g River R i v e r belt b e l t support s u p p o r t the t h e interpretation i n t e r p r e t a t i o n that that pre—Kenoran p r e - K e n o r a n crust c r u s t was was extensive. extensive. T h e predominant p r e d o m i n a n t plutonic p l u t o n i c rocks rocks The of o f shield s h i e l d areas a r e a s are a r e tonalite t o n a l i t e and a n d related r e l a t e d rocks r o c k s (quartz ( q u a r t z diorite, diorite, trondhjemite a n d low—K l o w - K granodiorite; g r a n o d i o r i t e ; Glikson G l i k s o n 1979). 1 9 7 9 ) . Burke B u r k e and and t r o n d h j emite and Kidd ( 1 9 7 8 ) suggest s u g g e s t that t h a t granites g r a n i t e s are a r e rare rare in i n the t h e Superior Superior K i d d (1978) Province; P r o v i n c e : aa generalization g e n e r a l i z a t i o n that t h a t reflects, r e f l e c t s , in i n part, p a r t , the t h e emphasis e m p h a s is that t h a t has h a s been b e e n placed p l a c e d on o n greenstone—tonalite q r e e n s t o n e - t o n a l i t e terranes. terranes. L a t e - and and Late— post—tectonic p o s t - t e c t o n i c granodioritic g r a n o d i o r i t i c to t o granitic g r a n i t i c plutonic p l u t o n i c rocks r o c k s are are abundant a b u n d a n t in i n the t h e Winnipeg W i n n i p e g River R i v e r belt. belt. Typical T y p i c a l geochemical g e o c h e m i c a l characteristics c h a r a c t e r i s t i c s of o f Archean A r c h e a n plutonic plutonic r o c k s of o f tonalitic t o n a l i t i c affinity a f f i n i t y include i n c l u d e low l o w K20, K20, Rb, R b , K20/Na20, K20/Na20, Rb/Sr Rb/Sr rocks and a n d Sr S r isotope i s o t o p e initial i n i t i a l ratios r a t i o s with w i t h moderately m o d e r a t e l y enriched e n r i c h e d LREE LREE and and depletion d e p l e t i o n in i n HREE HREE and a n d YY (Glikson ( G l i k s o n 1979). 1 9 7 9 ) . Such S u c h characteristics c h a r a c t e r i s t i c s are are explained e x p l a i n e d by b y partial p a r t i a l melting m e l t i n g of o f aa metamorphically m e t a m o r p h i c a l l y transformed transformed tholeiitic t h o l e i i t i c basalt b a s a l t at a t mantle m a n t l e or o r lower lower crustal c r u s t a l depths d e p t h s (Hanson ( H a n s o n and and Qldich G o l d i c h 1972: 1 9 7 2 : Arth A r t h and a n d Hanson H a n s o n 1972, 1 9 7 2 , 1975; 1 9 7 5 ; Glikson G l i k s o n 1979). 1 9 7 9 ) . In In contrast, t h e potassic p o t a s s i c Lount L o u n t Lake L a k e batholith, b a t h o l i t h , from f r o m the t h e central central c o n t r a s t , the axis a x i s of o f the t h e Winnipeg W i n n i p e g River R i v e r belt b e l t has h a s relatively r e l a t i v e l y higher h i g h e r K20, ~ ~Rb, R b0, , K20/Na20, K 2 0 / N a 2 0 f Rb/Sr R b / S r arid a n d Sr Sr isotope i s o t o p e initial i n i t i a l ratios, r a t i o s , variable v a r i a b l e but but generally moderate g e n e r a l l y high h i g h LREE LREE aabundances b u n d a n c e s aand nd m o d e r a t e to t o high h i g hYYabundances abundances (Beakhouse geo— ( B e a k h o u s e 1983). 1 9 8 3 ) . Other O t h e r potassic p o t a s s i cplutons p l u t o n are s a reven e e v emore n more geochemically Lac du d u Bonnet B o n n e t ppluton; l u t o n ; Cerny C e r n y eet t al. al. c h e m i c a l l y eevolved v o l v e d ((e.g., e . g . , Lac 1981). 1981 ) . Certain C e r t a i n younger y o u n g e r plutonic p l u t o n i crocks r o c k (Dalmein, s ( D a l m e i nMpagenie , M p a g e n i e and and Sicunusa S i c u n u s a —- types) t y p e s ) from f r o m the t h e Kaapvaal K a a p v a a l craton c r a t o n of o f South S o u t h Africa A f r i c ahave have geochemical g e o c h e m i c a l ccharacteristics h a r a c t e r i s t i c s (Condie ( C o n d i e and a n d Hunter H u n t e r 1976) 1 9 7 6 ) ssimilar i m i l a r to to the t h e potassic p o t a s s i c suite s u i t eplutons. p l u t o n s . These T h e s e ccharacteristics h a r a c t e r i s t i c s are a r e not not compatible with compatible w i t h the t h e origin o r i g i n postulated p o s t u l a t e d for f o r tonalites t o n a l i t e s and a n d are a r e more more compatible c o m p a t i b l e with w i t h partial p a r t i a l melting m e l t i n g of o f pre—existing p r e - e x i s t i n g sialic s i a l i c crust. crust. The T h e initial i n i t i a l Sr S r isotopic i s o t o p i c composition c o m p o s i t i o n of o f the t h e Lount L o u n t Lake Lake batholith ( . 7 0 2 2 to t o .7044; . 7 0 4 4 ;Beakhouse ~ e a k h o u s1983) e 1 9 8 3 ) is is higher h i g h e r than t h a n that that b a t h o l i t h (.7022 considered considered 'normal' ' n o r m a l ' for f o r 2.7 2 . 7 —- 3.0 3. 0 Ga G a tonalites t o n a l i t e s (Peterman ( P e t e r m a n 1979). 1979). Such S u c h initial i n i t i a l ratios r a t i o s are a r e compatible c o m p a t i b l e with w i t h these t h e s e 2.63 2 . 6 3 —- 2.70 2 . 7 0 Ga Ga plutons p l u t o n s being b e i n g derived d e r i v e d from f r o m the t h e partial p a r t i a l melting me1 t i n g of o f aa source s o u r c e that that is is 200 2 0 0 to t o 400 4 0 0 Ma Ma older o l d e r having h a v i n g Rb/Sr R b / S r ratios r a t i o s comparable c o m p a r a b l e to t o those t h o s e of of tonalitic t o n a l i t i c gneisses g n e i s s e s from f r o m the t h e orthogneiss o r t h o g n e i s s suite s u i t e (Beakhouse ( B e a k h o u s e1983). 1983). The T h e production p r o d u c t i o n of o f large l a r g e volumes v o l u m e s of o f such s u c h magmas magmas implies i m p l i e s extensive extensive pre—existirig p r e - e x i s t i n g ssialic i a l i c crust c r u s t in i n the t h e Winnipeg W i n n i p e g River R i v e r belt. belt. BOUNDARY BOUNDARY PROBLEMS PROB LEM S primary nature of the t h e interfaces i n t e r f a c e s between b e t w e e n different different The The p r i m a r y n a t u r e o f t e r r a n e sare a r eofofundamental f f u n d a m e n t a limportance i m p o r t a n c efor f o development r d e v e l o p m e n t ofo fmodels models terranes for f o r Archean A r c h e a n crustal c r u s t a l evolution. e v o l u t i o n . These T h e s e iinterfaces n t e r f a c e s aare r e loci l o c i for for f a u l tting i n g and a n d iintrusive n t r u s i v e activity a c t i v i t y because b e c a u s e the t h e interfaces i n t e r f a c e s represent represent faul r e g i o n a l scale s c a l e discontinuities d i s c o n t i n u i t i e s in i n density, d e n s i t y , ductility d u c t i l i t yand and regional rheology; r h e o l o q y ; the t h e younger y o u n g e r events e v e n t s obscure o b s c u r e the t h e primary p r i m a r y stratigraphic stratigraphic relationships. t al. a l . 1978: 1 9 7 8 : Stone Stone r e l a t i o n s h i p s . The The Sydney S y d n e y LLake a k e FFault a u l t ((Breaks B r e a k s eet 1977) 1 9 7 7 ) forming f o r m i n g the t h e north n o r t hboundary b o u n d a r yof o fthe t hEar e E aFalls—Manigotaqan r Fa1 l s - Y a n i g o t a q a n belt isone o n e of o f the t h e largest l a r g e s tof o f the t h einterface i n t e r f a c efault f a u l systems. t s y s t e m s . This This b e l t is �74 Smaller fault f a u l t zone z o n e is is up up to t o 1 km wide w i d e and a n d has h a s numerous n u m e r o u s splays. splays. Smaller Stratigraphic fault a r e recognized r e c o g n i z e d along a l o n g other o t h e r interfaces. i n t e r f aces. S tratigraphic f a u l t zones z o n e s are relations a t the t h e interfaces i n t e r f a c e s can c a n be b e deciphered d e c i p h e r e d only o n l y where w h e r e fault fault r e l a t i o n s at and This a n d intrusive i n t r u s i v e activity a c t i v i t y were w e r e relatively r e l a t i v e l y minor. minor. T h i s can c a n be b e done done d i r e c t l y oonly n l y at a t the t h einterfaces i n t e r f a c ebetween s b e t w e e nthet hEar e E aFalls—Manigotagan r Falls-Manigotagan directly pparagneiss a r a g n e i s s and a n d the t h e Uchi U c h i Subpovince S u b p o v i n c e oon n t the h e nnorth o r t h and a n d the t h e Bird Bird River R i v e r internal i n t e r n a l ggreenstone r e e n s t o n e belt b e l t on o n the t h e south. south. The subprovince T h e contact c o n t a c t between b e t w e e n the t h e Uchi U c h i greenstone—tonalite g r e e n s t o n e - t o n a l i t e subprovince and as aa lateral lateral a n d Ear E a r Falls—Manigotagan F a l l s - M a n i g o t a g a n paragneiss p a r a g n e i s s originated o r i g i n a t e d as facies f a c i e s change c h a n g e between b e t w e e n fundamentally f u n d a m e n t a l l y different d i f f e r e n t depositional depositional The The ddistribution i s t r i b u t i o n of o f these t h e s eenvironments e n v i r o n m e n t s was was eenvironments. nvironments eestablished s t a b l i s h e dby b y2959 2 9 5 9Ma Ma ((the t h e aage g e oof f tthe h e ooldest l d e s t cycle c y c l e in i n the t h e Uchi Uchi belt; b e l t ; Nunes N u n e s a and n d T Thurston, h u r s t o n , 1 1980) 9 8 0 ) a nand d p epersisted r s i s t e d f for o r aat t least l e a s t 200 200 This Ma. T h i s implies i m p l i e s that t h a t the t h e subprovinces s u b p r o v i n c e s of o f the t h e western w e s t e r n Superior Superior Province a r e primary p r i m a r y features f e a t u r e s representing r e p r e s e n t i n g different d i f f e r e n t volcanic v o l c a n i c and and P r o v i n c e are sedimentary s e d i m e n t a r y environments e n v i r o n m e n t s and a n d are a r e not n o t aa consequence c o n s e q u e n c e of of ddifferential i f f e r e n t i a l uplift. uplift. The T h e nnature a t u r e oof f the t h e interface i n t e r f a c e between b e t w e e n the t h e Winnipeg W i n n i p e g River River bbatholithic a t h o l i t h i c terrane t e r r a n e and a n d the t h e adjacent a d j a c e n t Ear E a r Falls—Maniqotagan Falls-Manigotaqan paragneiss t e r r a n e s cannot c a n n o t be be p a r a g n e i s s and a n d Wabigoon W a b i g o o n greenstone—tonalite g r e e n s t o n e - t o n a l i t e terranes However, ddetermined e t e r m i n e d directly. directly. H o w e v e r , based b a s e d on o n both b o t h inconclusive i n c o n c l u s i v e field field ddata a t a and a n d more conclusive c o n c l u s i v e geochronologic q e o c h r o n o l o g i c data d a t a these t h e s e interfaces i n t e r f a c e s can can The t o be b e unconformities. unconformities. T h e Winnipeg W i n n i p e g River R i v e r —bbe e interpreted i n t e r p r e t e d to a pportion Wabigoon W a b i g o o n interface, interface, a o r t i o n oof f which w h i c h is i s the t h e subject s u b j e c t of o f this this ffield i e l d trip t r i p is i s discussed d i s c u s s e d more more fully f u l l y below. below. A first A f i r s t sstep t e p in i n understanding u n d e r s t a n d i n g the t h e nature n a t u r e of o f interfaces i n t e r f a c e s is i s to to define d e f i n e the t h e properties p r o p e r t i e s that t h a t distinguish d i s t i n g u i s h the t h e subprovinces s u b p r o v i n c e s and and As discussed llocate o c a t e the t h e transition t r a n s i t i o n on o n aa geologic g e o l o q i c map. map. As d i s c u s s e d above, a b o v e , the the Winnipeg W i n n i p e g River R i v e r belt b e l t differs d i f f e r s from f r o m the t h e Wabigoon W a b i g o o n subprovince s u b p r o v i n c e in in lower, p proportion 1 ) lower. r o p o r t i o n oof f s supracrustal u p r a c r u s t a l rrocks, o c k s , 22) ) ggenerally enerally hhaving a v i n g aa 1) 3 ) higher h i g h e r proportion p r o p o r t i o n of o f granite g r a n i t e in in hhigher i g h e r metamorphic m e t a m o r p h i c grade, g r a d e , 3) rrelation e l a t i o n to t o tonalite, t o n a l i t e , 4) 4 ) older o l d e r age a g e and a n d 5) 5 ) contrasting c o n t r a s t i n g structural structural Defining sstyle. tyle. D e f i n i n g the t h e position p o s i t i o n of o f this t h i s transition t r a n s i t i o n on o n the t h e ground g r o u n d is is not n o t aa trival t r i v a l problem. p r o b l e m . Between B e t w e e n Kenora K e n o r a and a n d the t h e Manitoba—Ontario Manitoba-Ontario pprovincial r o v i n c i a l boundary, b o u n d a r y , where w h e r e we w e will w i l l be b e examining e x a m i n i n g the t h e interface, interface, there is a a vvery e r y sharp s h a r p contact c o n t a c t between b e t w e e n older o l d e r gneisses g n e i s s e s of o f the the t h e r e is Winnipeg W i n n i p e g River R i v e r belt b e l t and a n d lavas l a v a s and a n d sedimentary s e d i m e n t a r y rocks r o c k s of o f the the Although meaningful Wabiqoon W a b i g o o n subprovince. subprovince. Although a a m e a n i n g f u l lithologic l i t h o l o g i c contact contact ccan a n be b e ddrawn r a w n on on a a map, m a p , the t h e metamorphic m e t a m o r p h i c transition t r a n s i t i o n (over ( o v e r 100—1000 100-1000 m)) is m i s not n o t sso o abrupt a b r u p t and a n d ddeformation e f o r m a t i o n associated a s s o c i a t e d with w i t h the t h e interface interface persists p e r s i s t s an a n unknown, unknown, but b u t significant s i g n i f i c a n t (<2 ( < 2 km) km) distance d i s t a n c e to t o the the north n o r t h and a n d south s o u t h of o f the t h e contact. contact. Between Vermilion B e t w e e n Kenora K e n o r a and and V e r m i l i o n Bay Bay the t h e location l o c a t i o n of o f the t h e interinterMost face f a c e is i s more uncertain. uncertain. Most workers w o r k e r s have h a v e placed p l a c e d the t h e sub— subprovincial p r o v i n c i a l boundary b o u n d a r y along a l o n g the t h e north n o r t h edge e d g e of o f the t h e Vermilion V e r m i l i o n Bay Bay This is based b a s e d largely largely ggreenstone r e e n s t o n e belt. belt. T h i s pposition o s i t i o n oof f the t h e interface i n t e r f a c e is on v o l c a n i c remnants r e m n a n t s within w i t h i n the the o n the t h e observations o b s e r v a t i o n s that t h a t 1 ) no volcanic Winnipeg W i n n i p e g River R i v e r belt b e l t are a r e comparable c o m p a r a b l e to t o the t h e Vermilion V e r m i l i o n Bay Bay green— greenterms of o f size s i z e and a n d degree d e g r e e of o f preservation p r e s e r v a t i o n and a n d 2) 2 ) tthe he sstone t o n e belt b e l t in i n terms llobate o b a t e fform o r m oof f the t h e Dryberry D r y b e r r y batholith b a t h o l i t h to t o the t h e south s o u t h of o f the the Vermilion V e r m i l i o n belt b e l t is is typical t y p i c a l of o f that t h a t observed o b s e r v e d for f o r batholiths b a t h o l i t h s within within Wabigoon Two observations tthe he W a b i g o o n subprovince. subprovince. o b s e r v a t i o n s suggest s u g g e s t that t h a t the the Vermilion V e r m i l i o n Bay Bay belt b e l t and a n d Dryberry D r y b e r r y batholith b a t h o l i t h could c o u l d be b e placed p l a c e d within within Winnipeg Firstly, tthe he W i n n i p e g River R i v e r belt. belt. F i r s t l y , the t h e Dryberry D r y b e r r y batholith b a t h o l i t h is is 1 . 1 ) �75 similar s i m i l a r to t o the t h e potassic p o t a s s i c plutons p l u t o n s of o f the t h e Winnipeg W i n n i p e g River R i v e r belt, b e l t , and and Wabigoon uunlike n l i k e oother ther W a b i q o o n ssubprovince u b p r o v i n c e bbatholiths, a t h o l i t h s , in i n terms t e r m s of of magnetic aaeromagnetic e r o m a q n e t i c signature, signature, m a g n e t i c susceptibility s u s c e p t i b i l i t y and a n d perhaps perhaps Secondly, ( H a l l , 1968; 196 8 ; Beakhouse, B e a k h o u s e , 1977). 1977) S e c o n d l y , an an llithology i t h o l o g y (Hall, amphibolitic a m p h i b o l i t i c "tail" " t a i l " extending e x t e n d i n g off o f f the t h e west west end e n d of o f the t h e Vermilion Vermilion Bay ggreenstone belt Winnipeg e l t is is folded f o l d e d along a l o n g with with W i n n i p e g River R i v e r belt belt Bay reenstone b gneisses l a r g e recumbent r e c u m b e n t structure s t r u c t u r e in i n the t h e Silver S i l v e r Lake L a k e area area g n e i s s e s into i n t o aa large ((Beakhouse B e a k h o u s e et e t al. a l . 1983). 1983). The T h e position p o s i t i o n of o f the t h e subprovince s u b p r o v i n c e interface i n t e r Âace between b e t w e e n Vermilion Vermil ion Breaks Bay and i s controversial. controversial. B r e a k s et e t al. a l . (1978) ( 1 978) a n d Sioux S i o u x Lookout L o o k o u t is locate l o c a t e the t h e subprovincial s u b p r o v i n c i a l boundary b o u n d a r y at a t the t h e sedimentary—volcanic sed imentary-volcanic Although some ccontact o n t a c t resulting r e s u l t i n g in in a a highly h i g h l y irregular i r r e g u l a r contact. contact. A l t h o u g h some of o f these t h e s e metasediments m e t a s e d i m e n t s are a r e highly h i g h l y metamorphosed m e t a m o r p h o s e d and a n d partially partially melted b e correlated c o r r e l a t e d with w i t h the t h e Warclub W a r c l u b Group G r o u p which w h i c h can c a n be be m e l t e d they t h e y can c a n be traced t r a c e d well w e l l into i n t o the t h e Lake L a k e of o f the t h e Woods Woods qreenstone g r e e n s t o n e belt b e l t (Trowell (Trowel1 must et e t al., a l . , 1980). 1 9 8 0 ) . The proposed p r o p o s e d boundary boundary m u s t therefore, t h e r e f o r e , at a t some some e t al. a l . 1978) 1 9 7 8 ) cross cross ppoint o i n t (not ( n o t illustrated i l l u s t r a t e d on o n the t h e map map of o f Breaks B r e a k s et An sstratigraphy. tratigraphy. An alternate a l t e r n a t e interpretation i n t e r p r e t a t i o n is i s that t h a t the t h e sub— subprovincial l i e s between b e t w e e n these t h e s e supracrustal s u p r a c r u s t a l rocks r o c k s and a n d the the p r o v i n c i a l boundary b o u n d a r y lies Unfortunately, granitoid is g r a n i t o i d rocks r o c k s to t o the t h e north. north. U n f o r t u n a t e l y , this t h i s contact c o n t a c t is poorly p o o r l y exposed. exposed. The T h e ssignificance i g n i f i c a n c e oof f the t h e ddiscussion i s c u s s i o n above a b o v e is i s not n o t simply s i m p l y to to point p o i n t out o u t that t h a t further f u r t h e r investigations i n v e s t i g a t i o n s are a r e required r e q u i r e d to t o ellucidate ellucidate Rather, tthe h e nnature a t u r e and a n d position p o s i t i o n of o f the t h e subprovincial s u b p r o v i n c i a l boundary. boundary. Rather, iit t sserves e r v e s to t o emphasize e m p h a s i z e that t h a t subprovince s u b p r o v i n c e interfaces i n t e r f a c e s must m u s t be be regarded a s imprecisely i m p r e c i s e l y bounded b o u n d e d zones z o n e s rather r a t h e r than t h a n aa line l i n e on o n aa r e g a r d e d as Within map. W map. i t h i n these t h e s e interface i n t e r f a c e zones z o n e s processes p r o c e s s e s characteristic c h a r a c t e r i s t i c of of either e i t h e r ssubprovince u b p r o v i n c e may operate o p e r a t e in i n addition a d d i t i o n to t o processes p r o c e s s e s uniquely uniquely t o the t h e interface i n t e r f a c e (eg. ( e g . faulting f a u l t i n g and a n d associated, associated, rrelated e l a t e d to ttectonically e c t o n i c a l l y controlled, c o n t r o l l e d , epiclastic e p i c l a s t i c sedimentation) sedimentation) Assuming A s s u m i n g the t h e argunents a r g u m e n t s presented p r e s e n t e d above a b o v e are a r e correct c o r r e c t and a n d the the Winnipeg be1 t represents r e p r e s e n t s an a n extensive e x t e n s i v e tract t r a c t of o f pre—Kenoran pre-Kenoran W i n n i p e g River R i v e r belt sialic s i a l i c crust c r u s t and a n d the t h e deposition d e p o s i t i o n of o f supracrustal s u p r a c r u s t a l sequences s e q u e n c e s in i n the the Wabigoon s i a l ic W a b i q o o n subprovince s u b p r o v i n c e post—date p o s t - d a t e the t h e formation f o r m a t i o n of o f this t h i s sialic ccrust, r u s t , there t h e r e are a r e two t w o alternate a l t e r n a t e interpretations i n t e r p r e t a t i o n s for f o r the t h e nature n a t u r e of of One alternative tthe h e interface. interface. a l t e r n a t i v e is i s that t h a t the t h e interface i n t e r f a c e is is a a tectonic t e c t o n i c contact c o n t a c t and a n d the t h e subprovinces s u b p r o v i n c e s were juxtaposed j u x t a p o s e d after a f t e r their their Alternatively, Wabigoon sequences fformation. ormation. A l t e r n a t i v e l y , the the W a b i g o o n ssupracrustal u p r a c r u s t a l sequences l i k e l y against, a g a i n s t , this this ccould o u l d have h a v e been b e e n ddeposited e p o s i t e d upon, u p o n , or o r more likely sialic s i a l i c crust c r u s t in i n which w h i c h case c a s e aa major m a j o r unconformity u n c o n f o r m i t y occurs o c c u r s within w i t h i n the the interface The l a t t e r interpretation i n t e r p r e t a t i o n is is supported s u p p o r t e d by by the the i n t e r f a c e zone. zone. T h e latter ppossible o s s i b l e ppresence r e s e n c e oof f feeder f e e d e r ddikes i k e s in i n the t h e Tannis T a n n i s Lake L a k e area a r e a and, and, more convincingly, by tthe c o n v i n c i n g l y , by h e presence p r e s e n c e oof f aan n ancient a n c i e n t boulder b o u l d e r in i n aa Davis, cconglomerate o n g l o m e r a t e nnear e a r Sioux S i o u x Lookout L o o k o u t (D.W. (D.W. D a v i s , personal personal ccommunication, o m m u n i c a t i o n , 1985). 1 9 8 5 ) . Clearly, C l e a r l y , intense i n t e n s e deformation d e f o r m a t i o n has h a s been been superimposed minor major s u p e r i m p o s e d on o n this t h i s unconformity u n c o n f o r m i t y and and m i n o r oor r m a j o r ddislocations islocations hhave a v e ooccurred c c u r r e d along a l o n g it. i t . It I t is is aalso l s o possible p o s s i b l e that t h a t the t h e Winnipeg Winnipeg River R i v e r tterrane e r r a n e could c o u l d have h a v e bbeen e e n jjuxtaposed u x t a p o s e d ((by b y t the h e ccbs l o s iing n g of o f an an oocean??) c e a n ? ? ) against a g a i n s t the t h eWabigoon W a b i q o o n subprovince s u b p r o v i n c e during d u r i n g volcanism v o l c a n i s m and and ssedimentation e d i m e n t a t i o n aand n d tthat h a t the t h e unconformable u n c o n f o r m a b l e r relationship e l a t i o n s h i p applies a p p l ies Wabiqoon. oonly n l y to t o the t h e youngest y o u n g e s t sequences s e q u e n c e s in i n tthe he W abiqoon. . . SUMMARY SUMMARY OF OF GEOLOGICAL G E O L O G I C A L RELATIONSHIPS RELATIONSHIPS Field, F i e l d , geochronobogical g e o c h r o n o l o q i c a l and a n d geochemical g e o c h e m i c a l evidence e v i d e n c e suggest s u g g e s t aa �76 c o m p l e x geologic g e o l o g i c history h i s t o r y spanning s p a n n i n g at a t least l e a s t 500 5 0 0 Ma. Ma. The T h e earliest earliest complex i s deposition d e p o s i t i o n of o f aa supracrustal s u p r a c r u s t a l sequence s e q u e n c e preserved p r e s e r v e d as as e v e n t is event i n c l u s i o n s in i n younger y o u n g e r plutonic p l u t o n i c rocks. r o c k s . The T h e rock r o c k types t y p e s in i n this this inclusions association a r e broadly b r o a d l y similar s i m i l a r to t o those t h o s e in i n the t h e better b e t t e r preserved, preserved, a s s o c i a t i o n are b e l t s , although a l t h o u g h felsic f e l s i c metavolcanic m e t a v o l c a n i c units u n i t s have have y o u n g e r greenstorie g r e e n s t o n e belts, younger n o t been b e e n identified i d e n t i f i e d conclusively. conclusively. not Tonalite T o n a l i t e gneiss g n e i s s of o f the t h e orthogneiss o r t h o g n e i s s suite s u i t e and a n d certain c e r t a i n of o f the the r e oolder l d e r tthan h a n 'Kenoran' ' K e n o r a n ' volcanism v o l c a n i s m in i n the t h e Wabigoon Wabigoon s o d i c plutoris p l u t o n s aare sodic More data d a t a are a r e required r e q u i r e d to t o establish e s t a b l i s h whether w h e t h e r these these S u b p r o v i n c e . More Subprovirtce. were all a l l formed f o r m e d 1) 1 ) during d u r i n g aa 3.0 3.0 —- 3.1 3.1 Ga Ga event e v e n t (Goodwin (Goodwin t o n a l i t e s were tonalites 1977) o r 2) 2 ) semi—continuously s e m i - c o n t i n u o u s l y from f r o m 3.1 3. 1 Ga Ga until u n t i l the t h e Kenoran Kenoran 1 9 7 7 ) or some tonalites t o n a l i t e s in i n the t h e Winnipeg W i n n i p e q River River o r o g e n y . The T h e antiquity a n t i q u i t y of o f some orogeny. b e l t suggests s u g g e s t s deposition d e p o s i t i o n of o f the t h e oldest o l d e s t supracrustal s u p r a c r u s t a l rocks r o c k s took took belt The p l a c e prior p r i o r to t o 3.0 3.0 Ga. Ga. T h e tonalitic t o n a l i t i c gneiss g n e i s s and a n d sodic s o d i c plutons plutons place a r e geochemically g e o c h e m i c a l l y similar s i m i l a r to t o rocks r o c k s of o f tonalitic t o n a l i t i c affinity a f f i n i t y that that are occur b a s a l t s of o f the t h e younger y o u n g e r green— greeno c c u r in i n bi—modal b i - m o d a l association a s s o c i a t i o n with w i t h basalts stone—torialite s t o n e - t o n a l i t e tterraries e r r a n e s aand n d ooriginate r i g i n a t e ffrom r o m the t h e partial p a r t i a l melting me1 t i n g m e t a m o r p h o s e d tholeiitic t h o l e i i t i c basalt. basalt. metamorphosed t o the t h e paragneiss p a r a g n e i s s in i n the t h e Ear Ear Falls—Manigotagan Falls-Maniqotaqan T h e precursor p r e c u r s o r to The b e l t was was deposited d e p o s i t e d synchronously s y n c h r o n o u s l y with w i t h volcano—sedimentary volcano-sedimentary belt time s e q u e n c e s in i n the t h e adjacent a d j a c e n t greenstone—tonalite g r e e n s t o n e - t o n a l i t e terranes. t e r r a n e s . The T h e time sequences resolved. i n t e r v a l over o v e r which w h i c h tthis h i s sedimentation s e d i m e n t a t i o n occurred o c c u r r e d iis s not not resolved. interval Volcanism a r e acommenced commenced by b y 2959 2959 V o l c a n i s m in i n the t h eUchi—Confederation U c h i - C o n f e d e r a t i o n Lakes L a k e s area SedimentMa aand n d ccontinued o n t i n u e d for for 220 2 2 0 Ma Ma (Nunes ( N u n e s and a n d Thurston T h u r s t o n 1980). 1980). SedimentMa ation a t i o n occurred o c c u r r e d synchronously s y n c h r o n o u s l y with w i t h the t h e oldest o l d e s t volcanic v o l c a n i c cycle cycle 1 9 7 8 ) and a n d probably p r o b a b l y continued c o n t i n u e d during durinq ( T h u r s t o n and a n d Breaks B r e a k s 1978) (Thurston d e p o s i t i o n of o f the t h e younger y o u n g e r volcanic v o l c a n i c cycles c y c l e s (P.C. ( P . C . Thurston T h u r s t o n 1982, 1982, deposition The p e r s o n a l communication). communication) T h e detritus d e t r i t u s for for the t h e paragneiss paragneiss personal was apparently a p p a r e n t l y derived d e r i v e d externally e x t e r n a l l y from f r o m flanking f l a n k i n q green— greenp r e c u r s o r was precursor s i a l i c microcontinent, m i c r o c o n t i n e n t , now now s t o n e terranes t e r r a n e s and a n d possibly p o s s i b l y from f r o m aa sialic stone represented r e p r e s e n t e d by by the t h e Winnipeg W i n n i p e g River R i v e r belt; b e l t ; they t h e y were were deposited d e p o s i t e d from from water. The The provenance provenance t u r b i d i t y currents c u r r e n t s in i n relatively r e l a t i v e l y deep d e e p water. turbidity i n c l u d e d felsic f e l s i c volcanics v o l c a n i c s which w h i c h are a r e locally l o c a l l y or o r regionally regionally included predominant, p r e d o m i n a n t , felsic f e l s i c plutonic, p l u t o n i c , mafic m a f i c volcanic v o l c a n i c and a n d pre—existing pre-ex is t i n g (see s e d i m e n t a r y units. u n i t s . Crustal C r u s t a l structure s t r u c t u r e perturbations p e r t u r b a t i o n s (see sedimentary references r e f e r e n c e s in i n Beakhouse B e a k h o u s e 1977) 1 9 7 7 ) are a r e aa manifestation m a n i f e s t a t i o n of o f the t h e tectonic tectonic r e g i m e associated a s s o c i a t e d with w i t h basin b a s i n development. development. regime The Ma, T h e major m a j o r thermotectonic t h e r m o t e c t o n i c event e v e n t between b e t w e e n 2660 2 6 6 0 and a n d 2760 2 7 6 0 Ma, resulted in the t h a t culminated c u l m i n a t e d with w i t h the t h e Kenoran K e n o r a n orogeny, oroqeny, r e s u l t e d i n t h e that g e n e r a t i o n of o f large l a r g e volumes v o l u m e s of o f felsic f e l s i c plutonic p l u t o n i c rocks r o c k s in i n all a l l sub— subgeneration p r o v i n c e s of o f the t h e western w e s t e r n Superior S u p e r i o r Province. P r o v i n c e . Plutonic P l u t o n i c rocks r o c k s of of provinces t h e greenstone g r e e n s t o n e subprovinces s u b p r o v i n c e s are a r e dominantly d o m i n a n t l y tonalitic t o n a l i t i c in in the composition c o m p o s i t i o n and a n d probably p r o b a b l y originated o r i q i n a t e d from f r o m the t h e partial p a r t i a l melting m e l t i n g of of were only o n l y slightly s l i g h t l y older o l d e r than t h a n the the m a n t l e derived d e r i v e d basalts b a s a l t s that t h a t were mantle p l u t o n s (Hanson ( H a n s o n and a n d Goldich, G o l d i c h , 1972; 1 9 7 2 ; Arth A r t h and a n d Hanson, H a n s o n , 1972, 1 9 7 2 , 1975; 1975; plutons G l i k s o n , 1979). 1 9 7 9 ) . In I n contrast, c o n t r a s t , geochemical g e o c h e m i c a l evidence e v i d e n c e indicates indicates Glikson, that t h a t the t h e extensive e x t e n s i v e potassic p o t a s s i c plutoriic p l u t o n i c rocks r o c k s in i n the t h e Winnipeg W i n n i p e g River River belt o f rocks rocks b e l t could c o u l d not n o t have h a v e originated o r i g i n a t e d from f r o m the t h e partial p a r t i a l melting m e l t i n g of d e r i v e d from f r o m the t h e mantle m a n t l e during d u r i n g the t h eKerioran K e n o r a n orogeny. o r o g e n y . Instead I n s t e a d they they derived apparently a p p a r e n t l y originated o r i g i n a t e d from f r o m the t h e partial p a r t i a l melting m e l t i n g or or upward upward q r e e n stonem o b i l i z a t i o n of o f aa "pre—Kenoran" " p r e - K e n o r a n " volcano—plutonic, v o l c a n o - p l u t o n i c , greenstone— mobilization t y p e , association. association. type, . �77 IMPLICATIONS FOR FOR CRUSTAL CRUSTAL EVOLUTION EVOLUTION The e o l o g i c a l history h i s t o r y spanning s p a n n i n g 500 5 0 0 Ma Ma T h e recognition r e c o g n i t i o n oof f a ggeological pposes o s e s certain c e r t a i n constraints, c o n s t r a i n t s , and a n d many questions, q u e s t i o n s , for f o r crustal crustal evolution The e v o l u t i o n in i n the t h e western w e s t e r n Superior S u p e r i o r Province. Province. T h e limited, lirnited, rreliable e l i a b l e geochronological q e o c h r o n o l o q i c a l data d a t a suggests s u g g e s t s semi—continuous s e m i - c o n t i n u o u s activity activity during d u r i n g this t h i s 500 5 0 0 Ma Ma interval i n t e r v a l rather r a t h e r than t h a n two t w o "accretion "accretion super—events" s u p e r - e v e n t s " (Goodwin, ( G o o d w i n , 1977). 1977). Sialic unknown eextent was a s ppresent r e s e n t prior p r i o r to t o the the S i a l i c ccrust r u s t oof f unknown xtent w ddeposition e p o s i t i o n of o f 'Kenoran' ' K e n o r a n ' supracrustal s u p r a c r u s t a l sequences s e q u e n c e s but b u t the t h e role r o l e of of The i s unclear. unclear. The tthis h i s ccrust r u s t in i n ssubsequent u b s e q u e n t crustal c r u s t a l evolution e v o l u t i o n is pre—Kenoran s i a l i c crust c r u s t has h a s been b e e n reworked r e w o r k e d and a n d intruded i n t r u d e d and and p r e - K e n o r a n sialic ddismembered i s m e m b e r e d bby y extensive e x t e n s i v e Kenoran K e n o r a n felsic f e l s i c plutons p l u t o n s derived d e r i v e d from f r o m the the melting ppartial artial m e 1 t i n q oof f ggreenstone—tonalite r e e n s t o n e - t o n a l i t e assemblages a s s e m b l a g e s of o f the t h e earlier earlier These ccrust. rust. T h e s e oolder l d e r vvolcanic o l c a n i c rocks r o c k s may be b e analogous a n a l o g o u s to t o the t h e better better preserved, p r e s e r v e d , pre—Kenoran p r e - K e n o r a n volcanic v o l c a n i c cycles c y c l e s now now recognized r e c o g n i z e d in i n green— greensstone t o n e belts b e l t s elsewhere e l s e w h e r e in i n the t h e Superior S u p e r i o r Province P r o v i n c e (Nunes ( N u n e s and a n d Wood Nunes 11980; 980; N u n e s and a n d Thurston T h u r s t o n 1980). 1980). T h e paucity p a u c i t y of o f mantle m a n t l e derived derived The Kenoran K e n o r a n volcanic v o l c a n i c aand n d pplutonic l u t o n i c r rocks o c k s i nint the h e ccentral e n t r a l ppart a r t of o f the the WRB were nnot o t emplaced e m p l a c e d tthrough h r o u g h tthe h e older older WRB s u suqgests q q e s t s t hthat a t t these h e s e rrocks o c k s were The c r u s t i n t h i s region. T h e presence p r e s e n c e of o f mafic m a f i c dikes d i k e s near n e a r the the southern s o u t h e r n margin m a r g i n oof f the t h e WRB, WRB, ppossibly o s s i b l y representing r e p r e s e n t i n g feeders f e e d e r s to to Kenoran K e n o r a n volcanism, v o l c a n i s m , aand n d tthe h e ooccurrence c c u r r e n c e oof f aan n ancient a n c i e n t granitoid granitoid Lookout bboulder o u l d e r in i n aa conglomerate c o n g l o m e r a t e near n e a r Sioux Sioux L o o k o u t i implies m p l i e s t that h a t the the may yyounger o u n g e r s usupracrustal p r a c r u s t a l s sequences e q u e n c e s may b e ,be, i n in p apart, r t , eensialic n s i a l i c bbut u t the the present p r e s e n t jjuxtaposition u x t a p o s i t i o n oof f relatively r e l a t i v e l y oolder l d e r and a n d younger y o u n g e r sequences sequences The may also a l s o be b e tectonic. tectonic. T h e ppaucity a u c i t y oof f ggranitoid r a n i t o i d rocks r o c k s originating originating from f r o m the t h e anatexis a n a t e x i s of o f sialic s i a l i c crust c r u s t in i n the t h e Wabigoon W a b i q o o n subprovince subprovince ssuggests u g g e s t s that t h a t a Winnipeg W i n n i p e g River R i v e r belt—type b e l t - t y p e basement b a s e m e n t complex c o m p l e x is is aabsent b s e n t or o r greatly g r e a t l y thinned t h i n n e d bbeneath e n e a t h tthis h i s area. area. The T h e rrecognition e c o g n i t i o n oof f lateral l a t e r a l facies f a c i e s relationships r e l a t i o n s h i p s between between greenstone g r e e n s t o n e and a n d paragneiss p a r a q n e i s s sequences s e q u e n c e s establishes e s t a b l i s h e s the t h e contemporacontemporanneity e i t y oof f tthese h e s e terranes t e r r a n e s and a n d implies i m p l i e s that t h a t the t h e belt—like, b e l t - l i k e , sub— subpprovince r o v i n c e structure s t r u c t u r e oof f the t h e western w e s t e r n Superior S u p e r i o r Province P r o v i n c e is is aa primary primary characteristic The c h a r a c t e r i s t i c and a n d not n o t aa consequence c o n s e q u e n c e of o f differential d i f f e r e n t i a l uplift. uplift. The ppattern a t t e r n of o f pre—existing p r e - e x i s t i n g sialic s i a l i c nuclei n u c l e i and a n d younger, y o u n g e r , coeval, coeval, interdigitating is i n t e r d i g i t a t i n g volcanic v o l c a n i c arcs a r c s and a n d sedimentary s e d i m e n t a r y basins b a s i n s is geometrically, g e o m e t r i c a l l y , though t h o u g h not n o t necessarily n e c e s s a r i l y genetically, g e n e t i c a l l y , analaqous a n a l a g o u s to to modern m o d e r n plate p l a t e tectonic t e c t o n i c regimes. regimes. crust in this region. ACKNOWLEDGMENTS ACKNOWLEDGMENTS L.D. R.H. McNutt, M c N u t t , P.C. P.C. Thurston T h u r s t o n and a n d an an L.D. Ayres, A y r e s , F.W. F.W. Breaks, B r e a k s , R.H. anonymous c r i t i c i s m at a t different different a n o n y m o u s reviewer r e v i e w e r ooffered f f e r e d constructive c o n s t r u c t i v e criticism sstages t a g e s in i n the t h e preparation p r e p a r a t i o n of o f the t h e paper p a p e r from f r o m which w h i c h the the introduction was modified. modified. P.C. T h u r s t o n also a l s o reviewed r e v i e w e d the the i n t r o d u c t i o n was P.C. Thurston W.C. revised r e v i s e d version v e r s i o n and a n d the t h e road r o a d log. log. W . C . Brisbin B r i s b i n visited v i s i t e d the t h e High High Lake-Tannis L a k e - T a n n i s Lake L a k e aarea r e a stops s t o p s with w i t h the t h e author a u t h o r and a n d shared s h a r e d his his The cconsiderable o n s i d e r a b l e understanding u n d e r s t a n d i n g of o f the t h e geology g e o l o g y of o f this t h i s area. area. T he i s ggrateful r a t e f u l to t o M. M. Sweeny who assisted a s s i s t e d in i n the t h e preparation preparation aauthor u t h o r is oof f stops s t o p s and a n d legions l e g i o n s of o f University U n i v e r s i t y of o f Manitoba M a n i t o b a field f i e l d school school students Barbara s t u d e n t s who stripped s t r i p p e d most of o f the t h e moss m o s s at a t stop s t o p 4. 4. B a r b a r a Moore patiently p a t i e n t l y and a n d skilfully s k i l f u l l y drafted d r a f t e d the t h e final f i n a l figures. figures. �78 ROAD LOG LOG AND DESCRIPTION DESCRIPTION OF OF STOPS STOPS ROAD 0.0 km W e will w i l l proceed p r o c e e d west west on on highway h i g h w a y 17 17 from f r o m Husky H u s k y the the We Muskie M u s k i e in i n the t h e town t o w n of o f Kenora. Kenora. En r o u t e t o t h e first En route to the first stop, is parallel p a r a l l e l to, t o , and a n d lies l i e s 1 to t o 22 kilo— kilos t o p , highway h i g h w a y 17 1 7 is metres south s o u t h of, o f , the t h e Wabigoon W a b i g o o n -- Winnipeg W i n n i p e g River R i v e r inter— interface f a c e (Figure ( F i g u r e 4). 4 ) . Moderately M o d e r a t e l y to to intensely i n t e n s e l y flattened f l a t t e n e d and and l i n e a t e d metavolcanic m e t a v o l c a n i c rocks r o c k s and a n d granitoid g r a n i t o i d rocks rocks lineated a r e exposed e x p o s e d in i n road r o a d cuts c u t s along along ( W i n n e t k a Lake L a k e stock) s t o c k ) are (Winnetka 1 this t h i s route. route. 2.5 km Junction J u n c t i o n with w i t h highway h i g h w a y 596 596 10.0 km Junction J u n c t i o n with w i t h highway h i g h w a y 641 64 1 11.2 km Junction J u n c t i o n with w i t h Kenora K e n o r a bypass bypass 23.7 km Junction For km we w e will will J u n c t i o n with w i t h Pye's P y e ' s Road. Road. F o r the t h e next n e x t 9.1 9 . 1 km traverse t r a v e r s e the t h e elliptical e l l i p t i c a l Winnetka W i n n e t k a Lake L a k e stock s t o c k that t h a t lies lies along a l o n g the t h e Wabigoon W a b i g o o n -- Winnipeg W i n n i p e g River R i v e r interface. i n t e r f a c e . This This stock s t o c k is is compositionally c o m p o s i t i o n a l l y zoned z o n e d with w i t h aa granite g r a n i t e to t o grano— granodiorite core and a n d aa hornblende h o r n b l e n d e diorite d i o r i t e rim r i m (Davies, (Davies, d i o r i t e core 1965) i t s elliptical e l l i p t i c a l geometry g e o m e t r y is, i s , in i n ppart, a r t , aa 1 9 6 5 ) and a n d its consequence c o n s e q u e n c e of o f post—crystallization p o s t - c r y s t a l l i z a t i o n deformation deformation (Brisbin, ( B r i s b i n , 1981). 1981 ) . 32.8 km The T h e contact c o n t a c t of o f the t h e Winnetka W i n n e t k a Lake Lake stock s t o c k with w i t h enveloping envelopinq Wabigoon m e t a v o l c a n i c rocks r o c k s is is exposed e x p o s e d in in W a b i g o o n subprovince s u b p r o v i n c e metavolcanic low l o w outcrops o u t c r o p s on on the t h e south s o u t h side s i d e of o f the t h e highway. highway. 35. 1 km 41.3 km Junction J u n c t i o n with w i t h the t h e Rush Rush Bay Bay Road Road Junction is J u n c t i o n with w i t h the t h e Royal R o y a l Lake L a k e Road. R o a d . The T h e first f i r s t stop s t o p is on the north side of the highway just beyond this o n t h e n o r t h s i d e o f t h e highway j u s t beyond t h i s unction. jj u nction. The series T h e lithologic l i t h o l o g i c diversity d i v e r s i t y of o f the t h e Keewatin K e e w a t i n series metavolcanic met a v o l c a n i c and a n d metasedimentary m e t a s e d i m e n t a r y rocks r o c k s cannot c a n n o t be be adequately a d e q u a t e l y represented r e p r e s e n t e d oon n t this h i s ffield i e l d trip. t r i p . Stops S t o p s 1A 1A and a n d 18 1B aare r e included i n c l u d e d t to o iillustrate l l u s t r a t esome some of o f the t h e factors factors which w h i c h ccomplicate o m p l i c a t e i interpretation n t e r p r e t a t i o n of o f these t h e s e rocks. rocks. 41.35 km Keewatiri K e e w a t i n sseries e r i e s Pillow P i l l o wLava Lava Outcrop s ign O u t c r o p oon n tthe h e north n o r t h side s i d e of o f the t h highway e h i g h w a y below b e l o w the t h e sign for f o r the t h e Royal R o y a l Lake L a k e Resort. Resort. In I n this t h i s outcrop o u t c r o p we w e will w i l l examine e x a m i n e aa ffine i n e grained, g r a i n e d , buff b u f f to to light l i g h tgreen g r e e nweathering, w e a t h e r i n g ,feldspar—phyric f e l d s p a r - p h y r i c pillowed p i l l o w e d flow. flow. STOP STOP 1A 1A In plagioclase I n thin t h i n section s e c t i o n the t h e rock r o c k consists c o n s i s t s of o f plagioclase phenocrysts up to 2 mm in longest dimension i n aa finer finer p h e n o c r y s t s u p t o 2 rnm i n l o n g e s t d i m e n s i o n in grained g r a i n e d matrix m a t r i x consisting c o n s i s t i n g of o f feldspar, f e l d s p a r , quartz, quartz, actinolite, I t is is difficult d i f f i c u l t to to a c t i n o l i t e , biotite b i o t i t e and a n d epidote. e p i d o t e . It estimate proportions of quartz and feldspar but veins estimate proportions of and feldspar but veins and a n d diffuse d i f f u s e patches p a t c h e s of o f quartz q u a r t z suggest s u g g e s t the t h erock r o c khas h a s been been ss iilicified. licified. �- — LIII EllllfflJ EE MINOR FOLD AXFS AND MINERAL LINEATIONS s 65 us Fiqure 4: T5uuS - -— UT UK LAKI N1F4BO Figure S _FLLANE U H - - — - 8 and 11 are outlined. BATHC)L ITH I 11111 WINNIPEG RIVER GRANITOID BELT I of figures 5, Geologic map of the Wabigoon—Winnipeg River interface between the Manitoba— Ontario border and Vermilion Bay (from Beakhouse et al., 1983). The location 1 Is... Figure - WABIGDON BELT METAVOLCANICS AMPI-IIBOLITE INCLUSION ZONES LCUNT LAKE INCLUSIONS) WITH GRANITE INTERLAYERS METASEDIMENTS AND DERIVED MIGMATITE TONALITE GNEISS (± S%AMPHIBOLITE TONALITE BATHOLITHPLUTON — LATE TECTONIC GRANODIORITE TO GRANITE INTRUSIONS_LATE TECTONIC UNMETAMORPHOSED MAF1C INTRUSIONS_POST TECTONIC 4O 2Okrr �80 I ::* = T Stop I 10 I-.. 0 - -:-:::--f:—:-- - + - = + CR0 GROUP Clastlc MetasedlmentaryRocks Rocks - C R O W DWOUCK UCK GROUP Metasedimentary A . Clastic u ZLI 3 00 $2 unconformity unconform~ty Hlgh Lake L a k e Porphyry Porphyry Intrusion lntrus~on High intrusive contact contact Mafic Maflc Intrusive lntruslve Rocks Rocks intrusive lntruslve contact contact The * T h e relative relative age a g e of of felsic felsic intrusive rocks that that intrude Intrude the basement basement complex complex with with respect to to the the older older z 1;; CWQ* ::--: Clastic Rocks ClastlcMetasedimentary Metased~mentary Rocks + 3; lntermed~ateto Felsic Felslc Metavolcanic Metavolcanic Rocks Rocks I 3 a Intermediate Rocks v V _j Mafic M aMetavolcanuc f ~ cMetavolcan~c Rocks w faulted faulted unconformity unconform~ty 0 4 LUhfflhlL aLate FelsicIntrusive Intrusive Rocks' Rocks t e Felslc Early Early Felsic Felslc Intrusive lntrus~veRocks Rocks' Basement Complex >yrn , Complex :gj s Figure g u r e 5: 5: x unconformity unconform~tyand and Wabigoon Wab~goon subprovince subprovmce lithologies litholog~es is I S not not known known. ** Rocks in the **Rocks the Keewatin Keewatin Series Series are are subdivided subdivided lithologically lithologically and and the the order order does does not not imply imply age age relationships. relationships. Geologic G e o l o g i c map of o f the t h e Tannis T a n n i s Lake—High L a k e - H i g h Lake L a k e area area generalized g e n e r a l i z e d from f r o m Davies D a v i e s (1965) ( 1 9 6 5 ) with w i t h additional additional information i n f o r m a t i o n oon n tthe h e ddistribution i s t r i b u t i o n of o f the t h e basement basement The complex c o m p l e x from f r o m Bald B a l d (1981). (1981 ) . T h e location l o c a t i o n of o f this t h i s map map is is illustrated i l l u s t r a t e d in i n figure f i g u r e 4. 4. �81 A chemical c h e m i c a l analysis a n a l y s i s of o f this t h i s rock r o c k (sample ( s a m p l e 84GPB8010, 84GPB80101 appendix) i s ddifficult i f f i c u l t to t o interpret i n t e r p r e t due d u e to t o this this a p p e n d i x ) is alteration. Elements alteration. E l e m e n t s whose w h o s e abundance a b u n d a n c e may not n o t be be pprofoundly r o f o u n d l y affected a f f e c t e d bby y this t h i s alteration a l t e r a t i o n suggest s u g g e s t that t h a t the the is not n o t simply s i m p l y aa r o c k was was geochemically g e o c h e m i c a l l y evolved e v o l v e d and a n d is rock silicified Relative s i l i c i f i e d basalt. basalt. R e l a t i v e to t o tholeiitic t h o l e i i t i c basals b a s a l s from from tthe h e area a r e a (samples ( s a m p l e s 83GPB323, 83GPB3231 84GPB8007 84GPB8007 and a n d 84GPB8009) 84GP58009) lower C Co, Cr, oI C r I Ni N i and a n d Ti T i and a n d higher h i g h e r Zr Z r and and tthis h i s rrock o c k hhas a s lower LREE. T h e fractionated f r a c t i o n a t e d REE pattern p a t t e r n (Lan/Ybn ( L a n / Y b n = 77)) is The is These aalso l s o distinctive. distinctive. T h e s e ccharacteristics h a r a c t e r i s t i c s are a r e similar s i m i l a r to to those t h o s e of o f certain c e r t a i n basaltic b a s a l t i c andesites a n d e s i t e s from f r o m the the Confederation C o n f e d e r a t i o n Lake L a k e belt b e l t (eq. ( e q . samples s a m p l e s 439 439 and a n d 448; 448; Thurston T h u r s t o n aand n d FFryer, r y e r I 11983) 9 8 3 ) hhaving a v i n g SSiO i O ? contents c o n t e n t s of of The aapproximately p p r o x i m a t e l y 55 5 5 percent. percent. T h e relative r e l a t l v e significance s i g n i f i c a n c e of of pprimary r i m a r y abundances a b u n d a n c e s and a n d geochemical g e o c h e m i c a l mobility m o b i l i t y accompanyaccompanyiing n g ssecondary e c o n d a r y aalteration 1 t e r a t i o n in i n ddetermining e t e r m i n i n g the t h e observed observed ccompositions o m p o s i t i o n s and a n d apparent a p p a r e n t calc—alkaline c a l c - a l k a l i n e affinity a f f i n i t y of of This is poorly p o o r l y constrained. constrained. T h i s poses poses a a problem problen tthis h i s rock r o c k is mafic iin n ccomparing o m p a r i n g the t h e cchemistry h e m i s t r y oof f m a f i c and a n d intermediate intermediate dikes d i k e s that t h a t cut c u t an a n interpreted i n t e r p r e t e d basement b a s e m e n t complex c o m p l e x to t o the the north n o r t h with w i t h that t h a t of o f the t h e flows f l o w s which w h i c h they t h e y may be b e feedinq. feedinq. 41.8 4 1 - 8 km STOP lB Series Metasedimentary 1B Keewatin Keewatin S eries M e t a s e d i m e n t a r y Pocks Rocks Outcrop O u t c r o p on o n the t h e north n o r t h side s i d e of o f the t h ehighway highway Thin metasedimentary Metasand— t o medium medium bbedded edded m e t a s e d i m e n t a r y rrocks. ocks. M etasandT h i n to metasiltstone sstones t o n e s predominate p r e d o m i n a t e but but m e t a s i l t s t o n e and a n d meta—argillite meta-arg i l l i t e (the ( t h e llatter a t t e r ooften f t e n ddisrupted) i s r u p t e d ) are a r e common in i n parts p a r t s of o f the the outcrop. Graded i s recognizable r e c o q n i z a b l e locally. locally. outcrop. G r a d e d bedding b e d d i n g is Although d e p o s i t e d in i n aa sedimentary sedimentary A l t h o u g h these t h e s e rocks r o c k s were deposited environment they are probably closely r e l a t e d to t o felsic felsic e n v i r o n m e n t t h e y a r e p r o b a b l y c l o s e l y related vvolcanic o l c a n i c activity. activity. Throughout much of T h r o u g h o u t much o f the t h e ooutcrop, u t c r o p I foliation f o l i a t i o n (mineral (mineral foliation s aatt a high hiqh f o l i a t i o n and a n d fflattening l a t t e n i n g of o f ffragments) r a g m e n t s ) iis angle a n g l e tto o bedding, b e d d i n g I mimicking m i m i c k i n g t the h e rregional e g i o n a l scale scale 1 9 6 5 ) . In In sstructure t r u c t u r eover o v e rmuch much of o f the t h e area a r e a (Davies, ( D a v i e s I 1965). intensely i n t e n s e l y ddeformed e f o r m e d zones, z o n e s I bedding b e d d i n g is i s transposed t r a n s p o s e d so s o as as The tto o bbe e essentially e s s e n t i a l l y parallel p a r a l l e l to t o the t h e foliation. foliation. The foliation i s parallel p a r a l l e l to t o the t h e axial a x i a l plane p l a n e of o f aa f o l i a t i o n is megascopic m e g a s c o p i c fold f o l d at a t the t h e crest c r e s t of o f the t h e roadcut. roadcut. 443.35 3 . 3 5 km JJunction u n c t i o n with w i t h Shoal S h o a l Lake L a k e Road Road 44.1 4 4 . 1 km JJunction u n c t i o n with w i t h Gundy Lake L a k e Road Road — - tturn u r n nnorth o r t h on o n Gundy Lake r e s e t odometer o d o m e t e r to t o 0.0. 0.0. L a k e Road Road —- reset 3.1 km 3.1 South t u r n lleft eft S o u t h Shore S h o r e Road junction j u n c t i o n —- turn 33.5 . 5 km Powerline P ower1i n e 44.05 . 0 5 km P i u t e Lake L a k e Road Road junction junctio— n - turn t u r n right riqht Piute 4.6 km km The Wabigoon Causeway C a u s e w a y a at t eend n d oof f Tannis T a n n i s Lake. Lake. The W a b i g o o n —Winnipeg W i n n i p e g River R i v e r iinterface n t e r f a c e lies l i e s along a l o n g the t h e south s o u t h shore s h o r e of of �82 Tannis Tannis ( F i g u r e 5). 5) T h e outcrop o u t c r o p on on the t h e north n o r t h side side Lake (Figure The ( w e s t side s i d e of o f road) r o a d ) consists c o n s is ts of o f foliatfoliato f the t h e causeway c a u s e w a y (west of s i m i l a r to t o those t h o s e at a t the the e d tonalite t o n a l i t e cut c u t by b y mafic m a f i c dikes d i k e s similar ed next stop n e x t stop a 5.05 5 . 0 5 km h Junction J u n c t i o n —- turn t u r n left left 5.15 5. 1 5 km km STOP w i t h Mafic Ma i c Dikes. Dikes. STOP 22 Tonalite T o n a l i t e with Outcrop on the west side of the O u t c r o p o n t h e w e s t s i d e o f t h e road. road. The principal p r i n c i p a l rock r o c k type t y p e in i n the t h e outcrop o u t c r o p is is aa fine f i n e to to medium medium grained, g r a i n e d grey, g r e y I strongly s t r o n g l y lineated l i n e a t e d biotite biotite tonalite. Clark tonalite. C l a r k et e t al a 1 (1981) ( 1 981 ) ddetermined etermined a a Rb—Sr Rb-Sr whole whole rock r o c k isochron i s o c h r o n age, a g e I based b a s e d on o n regional r e g i o n a l sample s a m p l e selection, selection, .0014). Recent 150 of -7028 .0014). R e c e n t U—Pb U-Pb o f 2950 2950 1 5 0 Ma Ma (Ri ( R i == .7028 zircon z i r c o n geochronology q e o c h r o n o l o g y on o n aa sample s a m p l e selected s e l e c t e d from f r o m this this outcrop o u t c r o p confirms c o n f i r m s the t h e antiquity a n t i q u i t of o f this t h i s unit u n i t and and indicates a minimum minimum (2O7Pb/2OPb) indicates a ( 2 0 7 ~ b / 2 0 P b ) age a g e of o f 3028 3 0 2 8 Ma Ma (D.W, ( D e w e Davis, D a v i s , 1984 1 9 8 4 personal p e r s o n a l communication). communication) The T h e tonalite t o n a l i t e here h e r e is is relatively r e l a t i v e l y "clean" " c l e a n " arid a n d contains contains only o n l y aa few f e w inclusions i n c l u s i o n s of o f massive m a s s i v e amphibolite a m p h i b o l i t e of of indeterminate origin. These amphibolite inclusions indeterminate origin. T h e s e a m p h i b o l i t e i n c l u s i o n s are are more discontinuous than more d i s c o n t i n u o u s t h a n the t h e mafic m a f i c dikes d i k e s cutting c u t t i n g the the outcrop o u t c r o p and a n d have h a v e subtle s u b t l e differences d i f f e r e n c e s in i n composition c o m p o s i t i o n and and texture but the possibility that they represent t e x t u r e but t h e poss i b i l i t y t h a t they r e p r e s e n t disrupted d i s r u p t e d dikes d i k e s cannot c a n n o t be b e totally t o t a l l y discounted d i s c o u n t e d on o n this this outcrop. Elsewhere, amphibolite inclusions with outcrop. Elsewhere amphibol i t e i n c l u s i o n s with calc—silicate calc-s i l i c a t e pods p o d s aand n d hhighly i g h l y sstretched t r e t c h e d pillows pillows demonstrate d e m o n s t r a t e aa vvolcanic o l c a n i c oorigin r i g i n for f o r some s o m e of o f the the inclusions i n c l u s i o n s and a n d provide p r o v i d e evidence e v i d e n c e for f o r pre—3.0 p r e - 3 . 0 Ga Ga volcanism v o l c a n i s m in i n the t h e Winnipeg W i n n i p e g River R i v e r belt. belt. The T h e tonalite t o n a l i t e is is cut c u t by b y deformed, d e f o r m e d f equigranular e q u i g r a n u l a r and and porphyritic (plagioclase phenocrysts) p o r p h y r i t i c ( p l a g i o c l a s e p h e n o c r y s t s ) amphibolitic amphibolitic mafic is not n o t well well m a f i c dikes. d i k e s * The T h e age a g e of o f the t h e mafic m a f i c dikes d i k e s is constrained c o n s t r a i n e d except e x c e p t that t h a t they t h e y are a r e younger y o u n g e r than t h a n the the tonalite G a ) and a n d older o l d e r than t h a n the t h e last l a s t deformation deformation t o n a l i t e (3.028 ( 3 . 0 2 8 Ga) and a n d certain c e r t a i n of o f the t h e variously v a r i o u s l y deformed d e f o r m e d granitic granitic pegmatite The p e g m a t i t e dikes. dikes. T h e age a g e of o f these t h e s e intrusive i n t r u s i v e phases p h a s e s and and deformation d e f o r m a t i o n is is not n o t constrained c o n s t r a i n e d here h e r e but, b u t , by b y analogy analogy with a r e a s in i n the t h e Winnipeg W i n n i p e g River R i v e r belt, b e l t f the t h e dikes dikes w i t h other o t h e r areas are a r e thought t h o u g h t to t o be b e older o l d e r than t h a n 2.7 2 . 7 Ga. G a . The T h e age age constraints c o n s t r a i n t s and a n d proximity p r o x i m i t y to t o the t h e Wabigoon W a b i g o o n subprovince subprovince metavolcanic r n e t a v o l c a n i c rocks r o c k s here h e r e led l e d to t o the t h e suggestion s u g g e s t i o n that t h a t the the dikes d i k e s cut c u t an a n older o l d e r basement b a s e m e n t complex c o m p l e x and a n d fed f e d Keewatin Keewatin series s e r i e s volcanism v o l c a n i s m (Bald, ( B a l d 1981; 1981 ; Clark C l a r k et e t al, a1 I 1981). 1981 ) Modal Modal and a n d chemical c h e m i c a l analyses a n a l y s e s of o f the t h e tonalite t o n a l i t e (sample (sample 321A) 3 2 1 A ) and a n d equigranular e q u i q r a n u l a r mafic m a f i c dike d i k e (sample ( s a m p l e 321B) 3 2 1 B ) are are presented p r e s e n t e d in i n the t h e appendix. appendixo x . , . P r o c e e d back b a c k towards t o w a r d s the t h e highway h i g h w a y for Proceed f o r 1.05 1 - 0 5 km km to t o the t h e junction j u n c t i o n with with the t u r n right r i g h t (west) t h e Piute P i u t e Lake L a k e Road Road —- turn ( w e s t ) —- proceed p r o c e e d 0.55 0 . 5 5 km. km. STOP W a b i g o o n —- Winnipeg W i n n i p e g River R i v e r Contact Contact STOP 33 Wabigoon The The Wabigoon-Winnipeg W a b i g o o n - W i n n i p e g River R i v e r contact c o n t a c t in i n this t h i s area area corresponds c o r r e s p o n d s to t o aa linear l i n e a r topographic t o p g r a p h i c depression d e p r e s s i o n and and �83 exposures e x p o s u r e s oof f the t h e contact c o n t a c t are a r e not n o t abundant. abundant. T h e outoutThe crops c r o p s on o n the t h e road r o a d immediately i m m e d i a t e l y before b e f o r e we w e stop s t o p and a n d most most oof f those t h o s e to t o the t h e north north o f the t h e road r o a d are a r e fine f i n e to t o medium of grained, g r a i n e d t foliated f o l i a t e d to t o gneissic, g n e i s s i c , dominantly d o m i n a n t l y tonalitic tonal itic rrocks o c k s cut c u t by b y mafic m a f i c dikes d i k e s (Figure ( F i g u r e 6). 6 ). T h e ooutcrops u t c r o p s to to The tthe h e ssouth o u t h oof f the t h e road r o a d cconsist o n s i s t oof f fine f i n e to t o medium grained, g r a i n e d amphibolitic a m p h i b o l i t i c mafic m a f i c volcanic v o l c a n i c rocks r o c k s with with interbedded i n t e r b e d d e d chert—magnetite c h e r t - m a g n e t i t e iron i r o n formation. formation. Some Some hhighly i g h l y ddeformed e f o r m e d pillow p i l l o w structures s t r u c t u r e s are a r e present p r e s e n t on o n the the The medium mafic llargest a r g e s t outcrop. outcrop. T he m e d i u m ggrained rained m a f i c rocks r o c k s may rrepresent e p r e s e n t sills s i l l s or o r transposed t r a n s p o s e d dikes. dikes. t h i n tuffaceous tuffaceous A thin near of hhorizon o r i z o n ooccurs ccurs n e a r the t h e north n o r t h side side o f the t h e thicker t h i c k e r iron iron formation f o r m a t i o n unit. unit. The mafic The m a f i c ddikes i k e s ccutting u t t i n g the t h e larger l a r g e r tonalite t o n a l i t e outcrops outcrops nnorth o r t h oof f the t h e road r o a d are a r e atypical a t y p i c a l in i n terms terms of o f their their The ccomposition o m p o s i t i o n and a n d heterogeneity. heterogeneity. T h e banding b a n d i n g and a n d calcic calcic ppods o d s within w i t h i n them t h e m resembles r e s e m b l e s those t h o s e associated a s s o c i a t e d with with metavolcanic m e t a v o l c a n i c amphibolite i n c l u s i o n s in i n the t h e Winnipeq Winnipeg a m p h i b o l i t e inclusions River R i v e r belt. belt. T hese m a f i c units u n i t s are These mafic a r e subparallel s u b p a r a l l e l to t o the the foliation f o l i a t i o n in i n the t h e tonalite t o n a l i t e but b u t at a t one o n e contact c o n t a c t (Figure ( F i g u r e 6) 6) aa low l o w angle a n g l e discordance d i s c o r d a n c e is is noted. noted. T h e relationships relationships The developed d e v e l o p e d in i n the t h e last l a s t stop s t o p description d e s c r i p t i o n and a n d context c o n t e x t in in highly w h i c h these t h e s e unusual u n u s u a l dikes d i k e s occur o c c u r affords a f f o r d s aa highly which It iinterpretive n t e r p r e t i v e though t h o u g h plausible p l a u s i b l e explanation. explanation. I t is is cconceivable o n c e i v a b l e that t h a t these t h e s e dikes d i k e s are a r e feeding f e e d i n g flows f l o w s within w i t h i n aa few metres (in deformed ( i n the the d e f o r m e d state) s t a t e ) of o f where w h e r e we we f e w tens t e n s oof f metres are is rreasonable a r e observing o b s e r v i n g them. them. IItt is e a s o n a b l e to t o expect e x p e c t that that tthe h e pprocesses r o c e s s e s (autobrecciation, ( a u t o b r e ~ c i a t i o ninteraction i~n t e r a c t i o n with w i t h sea sea water) w a t e r ) that t h a t produce p r o d u c e "volcanic" " v o l c a n i c " structures s t r u c t u r e s and and alteration a l t e r a t i o n iin n flows f l o w s would w o u l d pproduce r o d u c e s isimilar m i l a r ffeatures e a t u r e s in in tthe h e upper u p p e r pportions o r t i o n s of o f venting v e n t i n q dikes. dikes. The River T h e aactual c t u a l contact c o n t a c t between b e t w e e n the t h e Winnipeg Winnipeg R i v e r bbelt e l t and and Wabigoon W a b i g o o n s subprovince u b p r o v i n c e is not Immediately n o t exposed e x p o s e d here. here. Imnediately north n o r t h oof f the t h e road r o a d is i s a small s m a l l outcrop o u t c r o p of o f highly h i g h l y sheared sheared mafic m a f i c rock r o c k cut c u t by b y at a t least l e a s t one o n e deformed d e f o r m e d mafic m a f i c dike. dike. IItt i s not n o t known known if i f the t h e sheared sheared m a f i c rock r o c k is i s a flow f l o w or or is mafic dike. The highly dike. T he h i g h l y ssheared h e a r e d nature n a t u r e of o f this t h i s rock r o c k and a n d the the n e g a t i v e topographic t o p o g r a p h i c expression e x p r e s s i o n of o f the t h e contact c o n t a c t suqgests suqgests negative tthe he p r e s e n c e of o f aa fault. fault. Eoes t h i s fault f a u l t represent r e p r e s e n t aa presence Does this major dislocation d i s l o c a t i o n that t h a t juxtaposes j u x t a p o s e s two t w o unrelated unrelated a s s e m b l a g e s , at a t least l e a s t one o n e of o f which w h i c h is is allochthonous a l l o c h t h o n o u s or or assemblages, ddoes o e s iitt represent r e p r e s e n t a aminor m i n o r (or ( o rmajor) m a j o r )adjustment a d j u s t m e n t along along an a n original o r i q i n a l unconformity? unconformity? R e t u r n to t o Highway H i g h w a y 17 17 —- tturn u r n left l e f t (east) ( e a s t ) —- pproceed r o c e e d 0.75 8 . 7 5 km to to Return the Shoal the S h o a l Lake L a k e Road Road— pproceed r o c e e d south s o u t h on o n the t h e Shoal S h o a l Lake L a k e Road Road for for 22.9 . 9 km — turn t u r n rright i g h t (west) ( w e s t ) onto o n t o narrow n a r r o w road r o a d —- pproceed r o c e e d 0. k m west west 0.3 km oonn the t h e narrow n a r r o w road r o a d—- the t h e exposures a t s t o p 4 a r e located a p p r o x i m a t e l y 30 metres s o u t h o f t h e r o a d . exposures at stop 4 are located approximately 30 metres south of the road. STOP H i g h Lake L a k e Unconformity Unconformity STOP 44 High metabasalts e r i e s are are IIn n tthis h i s ooutcrop, utcropt m e t a b a s a l t s oof f tthe h e Keewatin K e e w a t i n sseries cut c u t bby y pporphyry o r p h y r y ddikes i k e s rrelated e l a t e d to t o the t h eHigh H i g h Lake Lake intrusion i n t r u s i o n and a n d both b o t h are a r e unconformably u n c o n f o r m a b l y ooverlain v e r l a i n by b y the the �84 fine to medium grained mafic roc with epidote pods chert-magnetite iron formation metabasah ..................................,.,,..,.,. . ... . ..... ....... .............. ..................... mafic dikes tonalite slightiywdiscordant c o n t a c t 1 - 0 5 10 15 20 metres Figure 6: 6: Figure G e n e r a l i z e d outcrop o u t c r o p map map of t o p 3. 3. Generalized of sstop �85 m e t aased sed im e n t a r y rrocks o c k s oof f the t h eCrowd Crowd uuck c k ggroup r o u p (Figure ( Figure met imentary 7). 7). The m e t a b a s a l t s (most (most oof f which w h i c h aare r e pillowed) p i l l o w e d ) and and The metabasalts High H i g h Lake Lake pporphyry orphyry d i k e are a r e exposed e x p o s e d on o n the t h e western w e s t e r n edge edge dike of o f the t h e outcrop. outcrop. I n this t h i s outcrop, o u t c r o p , the t h e Crowduck Crowduck group g r o u p is is divisible d i v i s i b l e into into In f o u r units u n i t s that t h a t reflect r e f l e c t aa general g e n e r a l coarsening c o a r s e n i n g upwards upwards four 7 ) Stratigraphic S t r a t i g r a p h i c relationships r e l a t i o n s h i p s are are t r e n d (Figure ( F i g u r e 7) trend c o m p l e x , however, h o w e v e r , because b e c a u s e many units u n i t s were were eroded e r o d e d prior prior complex, to t o or o r concomittant c o n c o m i t t a n t with w i t h deposition d e p o s i t i o n of o f overlying o v e r l y i n g units. units. Such w e l l displayed displayed S u c h scouring s c o u r i n g relationships r e l a t i o n s h i p s are a r e well immediately i m m e d i a t e l y east e a s t of o f the t h enorthernmost n o r t h e r n m o s t exposure e x p o s u r e of o f the the porphyry Near l o c a l i t y , the t h e effect e f f e c t of of p o r p h y r y dike. dike. N e a r this t h i s same locality, local l o c a l provenance p r o v e n a n c e in i n the t h e conglomeratic c o n g l o m e r a t i c facies f a c i e s is is illustrated by aa lense i l l u s t r a t e d by l e n s e oof f conglomerate c o n g l o m e r a t e richer r i c h e r in i n mafic mafic volcanic v o l c a n i c clasts c l a s t s than t h a n the t h e remainder r e m a i n d e r of o f the t h e outcrop. outcrop. Throughout most of o f the t h e conglorneratic c o n g l o m e r a t i c facies f a c i e s in i n this this T h r o u g h o u t most outcrop, o u t c r o p , clasts c l a s t s of o f the t h e porphyry p o r p h y r y predominate p r e d o m i n a t e and a n d are are conspicuously c o n s p i c u o u s l y larger l a r g e r than t h a n the t h e other o t h e r clast c l a s t types t y p e s which which include i n c l u d e relatively r e l a t i v e l y abundant a b u n d a n t mafic m a f i c to t o felsic f e l s i c volcanic volcanic rocks r o c k s and a n d minor m i n o r chert, c h e r t , iron i r o n formation f o r m a t i o n and a n d massive massive sulphides. s u l p h i d e s . The T h e thin t h i n to t o medium medium bedded b e d d e d sandstone—siltsandstone-siltstone s t o n e sequence s e q u e n c e exposed e x p o s e d near n e a r the t h e unconformity u n c o n f o r m i t y in i n the the eastern e a s t e r n part p a r t of o f the t h e large l a r g e outcrop o u t c r o p display d i s p l a y spectacular spectacular soft s o Ât sediment s e d i m e n t deformation d e f o r m a t i o n structures s t r u c t u r e s including i n c l u d i n g slump sl ump folds, f o l d s , load l o a d casts c a s t s and and flame f l a m e structures. structures. AA regolith uck group r e g o l i t h is is developed d e v e l o p e d beneath b e n e a t h the t h e Crowd Crowduck g r o u p and and is is most apparent a p p a r e n t in i n the t h e porphyry p o r p h y r y unit. unit. I t is is not n o t clear clear It how much of o f the t h e irregular i r r e g u l a r nature n a t u r e of o f the t h e unconformity unconformity surface t o pre—Crowduck p r e - C r o w d u c k group group s u r f a c e can c a n be b e attributed a t t r i b u t e d to topography. The topography. The presence p r e s e n c e of o f clasts c l a s ts with w i t h exposed exposed cross—sectional c r o s s - s e c t i o n a l areas a r e a s in i n excess e x c e s s of o f one o n e square s q u a r e metre metre clearly c l e a r l y requires r e q u i r e s at a t least l e a s t local l o c a l steep s t e e p gradients g r a d i e n t s to t o have have been mimics b e e n present. p r e s e n t . The T h e geometry g e o m e t r y of o f the t h e unconformity u n c o n f o r m i t y mimics the t h e pattern p a t t e r n displayed d i s p l a y e d by the t h e regional r e g i o n a l folding f o l d i n g with with east—west uck e a s t - w e s t ax ax ial i a l pplanes l a n e s that t h a t deforms d e f o r m s the t h e Crowd Crowduck group. g r o u p . The The orientation o r i e n t a tofi ofoliation n o f fino this l i a outcrop t i o n iisn t h i s o u t c r o p is approximately a p p r o x i m a t e l y p a r a l l e l t o t h e s e a x i a l p l a n e s and is markedly m a r k e d l y ddiscordant i s c o r d a n t to t o bedding b e d d i n g in i nthe t h Crowduck e Crowd uck group. group. These T h e s e observations o b s e r v a t i o n s suggest s u g g e s t that t h a t at a t least l e a s t part p a r t of o f the the irregularity i r r e g u l a r i t y of o f the t h e unconformity u n c o n f o r m i t y is is aa consequence c o n s e q u e n c e of of post—Crowd p o s t - C r o w d uuck c k deformation. d e f o r m a t i o n . In I n the t h e southwestern s o u t h w e s t e r n part p a r t of of the s il ts t o n e s of of t h e outcrop, o u t c r o p , thinly t h i n l y bedded b e d d e d sandstones s a n d s t o n e s and a n d siltstones the t h e Crowduck Crowduck group g r o u p overly o v e r l y the t h e regolith r e g o l i t h above a b o v e the the porphyry p o r p h y r y dike d i k e and a n d butt b u t t up up against a g a i n s t the t h e adjacent a d j a c e n t Keewatin Keewatin series s e r i e s metabasalt. m e t a b a s a l t . Similar S i m i l a r units u n i t s immediately i m m e d i a t e l y overlying overlying the t h e metabasalt m e t a b a s a l t are a r e several s e v e r a l metres metres sstratigraphically t r a t igraphically above a b o v e tthe h e base b a s e of o f the t h e sequence s e q u e n c e over o v e r the t h e porphyry p o r p h y r y unit. unit. Does Does this t h is represent r e p r e s e n t pre—Crowduck pre-Crowd uck topography t o p o g r a p h y or or prog p r o g rressive e s s i v e syn—depositional s y n - d e p o s i t i o n a l faul f a u lting? ting? Quartz Q u a r t z and a n d quartz—tourmaline q u a r t z - t o u r m a l i n e veins v e i n s cut c u t the t h e conglomerate conqlornerate and and in i n the t h e vicinity v i c i n i t y of o f the t h e High H i g h Lake Lake stock s t o c k are are associated a s s o c i a t e d with w i t h gold g o l d mineralization m i n e r a l i z a t i o n (Davies, ( D a v i e s , 1965). 1965). Locally, L o c a l l y , the t h e veins v e i n s appear a p p e a r to t o be be confined c o n f i n e d to t o porphyry porphyry clasts s u g g e s t i n g pre—erosional p r e - e r o s i o n a l veining v e i n i n g but b u t when when c l a s ts suggesting parallel to these axial planes and is �____ 86 conglomerate pebbly sandstone i.:: pebbly sandstone massive t o thickly thicklybedded b e d d e dsandstone sandstone massive to thinly bedded sandstone and siltstone thinly bedded sandstone and siltstone — — — — — unconformity I High Lake porphyry . . . intrusive intrusive contact • contact mafic metavolcanic rocks mafic metavolcanic rocks (pillowed and massive) ''i-iÑi (pillowed and massive) S K E E W A T I N SERIES KEEWATIN SERIES o 5 10 15 20 metres regolith original topography or syn—depositional faulting? F i g u r e 7:7: Fiqure Generalized outcrop o u t c r o p map map of of stop s t o p4.4 . Generalized I clasts �27 examined most oof e x a m i n e d in i n ddetail e t a i l most f these t h e s e have h a v e 'tails' ' t a i l s ' that that project p r o j e c t into i n t o the t h e matrix. matrix. Some vveins e i n s are a r e continuous c o n t i n u o u s and and The T h e concentration c o n c e n t r a t i o n of o f this this cclearly l e a r l y post—depositional. post-depositional veining v e i n i n g in i n porphyry p o r p h y r y clasts c l a s t s is i s interpreted i n t e r p r e t e d to t o be b e due d u e to to hheterogeneous e t e r o g e n e o u s ddeformation e f o r m a t i o n arisinq a r i s i n g from f r o m the t h e differing differinq mechanical m e c h a n i c a l properties p r o p e r t i e s of o f the t h e various v a r i o u s types t y p e s of o f clasts clasts aand n d matrix. matrix. The Crowduck T he C r o w d u c k ggroup r o u p hhas a s no n o obvious, o b v i o u s , ddirect i r e c t relationship relationship However, tto o the t h e Wabigoon—Winnipeg W a b i g o o n - W i n n i p e g River R i v e r interface. interf ace. H owever, when vviewed when i e w e d from from a a regional r e g i o n a l perspective, p e r s p e c t i v e , many Temiskaming—type t o be be T e m i s k a m i n g - t y p e supracrustal s u p r a c r u s t a l sequences s e q u e n c e s do d o appear a p p e a r to spatially s p a t i a l l y associated a s s o c i a t e d with w i t h subprovince s u b p r o v i n c e interfaces. i n t e r f aces. Other s i m i l a r sequences s e q u e n c e s occurring o c c u r r i n g near n e a r an an O t h e r examples e x a m p l e s oof f similar Rainy iinterface n t e r f ace iinclude n c l u d e tthose h o s e aat t R a i n y Lake, L a k e , Beardmore— BeardmoreGeraldton This G e r a l d t o n and a n d Kirkland K i r k l a n d Lake. Lake. T h i s observation o b s e r v a t i o n may may l a t e r tectonic t e c t o n i c activity activity rreflect e f l e c t the t h e concentration c o n c e n t r a t i o n of o f later and a n d associated a s s o c i a t e d tectonically t e c t o n i c a l l y controlled c o n t r o l l e d sedimentation s e d i m e n t a t i o n at at ssubprovince u b p r o v i n c e interfaces. interfaces. . Return east o hhighway i g h w a y aand n d pproceed roceed e a s t to t o the t h e jjunction u n c t i o n oof f highway h i g h w a y 17 17 R e t u r n tto and a n d 596 5 9 6 in i n the t h e town t o w n of o f Norman Norman (between ( b e t w e e n Keewatin K e e w a t i n and a n d Kenora)— K e n o r a ) - set set t o zero z e r o —- tturn u r n north n o r t h on o n 596. 596. oodometer d o m e t e r to 1.5 1 . 5 km Junction t u r n right right J u n c t i o n —- turn 1.6 1 . 6 km STOP 55 Marginal M a r g i n a l Granodiorite G r a n o d i o r i t e Unit Unit Wee will W w i l l stop s t o p near n e a r the t h e crest c r e s t of o f the t h e hill h i l l and a n d walk w a l k north north We on t o the t h e shores s h o r e s of o f Darlington D a r l i n g t o n Bay. Bay. We o n Highway 596 596 to will w i l l examine examine a a series s e r i e s of o f outcrops o u t c r o p s which w h i c h provide p r o v i d e aa This cross—section c r o s s - s e c t i o n of o f the t h e Marginal M a r g i n a l Granodiorite. Granodiorite. T h i s unit unit is i s continuous c o n t i n u o u s along a l o n g the t h e contact c o n t a c t between b e t w e e n metavolcanic metavolcanic Wabigoon rrocks o c k s oof f the the W a b i q o o n ssubprovince u b p r o v i n c e and a n d tonalitic tonalitic gneisses 3 0 km km g n e i s s e s of o f the t h e Winnipeg W i n n i p e g River R i v e r belt b e l t for f o r at a t least l e a s t 30 Along ((Figure F i g u r e 8). 8). A l o n g this t h i s length l e n g t h its i t s width w i d t h ranges r a n g e s from from less metres to l e s s than t h a n 100 1 0 0 metres t o approximately a p p r o x i m a t e l y 700 7 0 0 metres but but The metres i s typical. typical. T h e width w i d t h of o f the t h e unit u n i t here h e r e is is 2200 00 m e t r e s is aapproximately p p r o x i m a t e l y 350 metres metres and a n d displays d i s p l a y s relationships relationships i t s length. length. ttypical y p i c a l oof f the t h e unit u n i t along a l o n g its Figure IIn n the t h e first f i r s t ooutcrop u t c r o p at a t the t h e top t o p of o f the t h e hill h i l l (5A.; (5A; F igure 9) w e can c a n observe o b s e r v e the t h e sharp s h a r p contact c o n t a c t between b e t w e e n the the 9 ) we Keewatin The K e e w a t i n metavolcanics m e t a v o l c a n i c s and a n d Marginal M a r g i n a l Granodiorite. Granodiorite. T he most m o s t striking s t r i k i n g textural t e x t u r a l characteristic c h a r a c t e r i s t i c of o f the t h e grano— qranois the t h e presence p r e s e n c e of o f subhedral s u b h e d r a l to t o lenticular, lenticular, ddiorite i o r i t e is microcline They ppoikilitic oikilitic m i c r o c l i n e megacrysts. megacrysts. T h e y have h a v e some some characteristics c h a r a c t e r i s t i c s of o f both b o t h phenocrysts p h e n o c r y s t s and a n d porphyroblasts porphyroblasts magmatic bbut u t are a r e interpreted i n t e r p r e t e d to t o be b e late late m a g m a t i c megacrysts. megacrysts. Locally, l a t e blastic ' e l a s t i c growth g r o w t h or or L o c a l l y , eevidence v i d e n c e for f o r ssome o m e late microcline oovergrowth v e r g r o w t h oof f m i c r o c l i n e is is evidenced e v i d e n c e d by b y the the coexistence c o e x i s t e n c e of o f augen a u q e n and a n d subhedral s u b h e d r a l megacrysts. megacrysts. T he The is hhomogeneity o m o g e n e i t y oof f the t h e granodiorite g r a n o d i o r i t e in i n this t h i s outcrop o u t c r o p is ttypical y p i c a l oof f that t h a t ddisplayed i s p l a y e d along a l o n g strike s t r i k e in i n the t h e southern southern one t o the t h e Keewatin Keewatin o n e third t h i r d of o f the t h e unit u n i t adjacent a d j a c e n t to metavolcanic m e t a v o l c a n i c rocks. rocks. As A s we w e proceed p r o c e e d down the t h e hill h i l l we w e will w i l l briefly b r i e f l y examine e x a m i n e aa �+ + + Marginal Megacrystic Granodiorite [ffffffffff[ Mixed Gneissic Tonalite—Granitic Pegmatite Gneissic Tonalite LII1 Diorite Rat Portage Bay fault Mafic Metavolcanic Rocks L::III Clastic Metasedimentary Rocks I Intermediate to Felsic Metavolcanic Rocks Lake of the Woods I1IU' Geologic map of the Keewatin area (simplified from Gower (1978) with minor revisions). The location of this map is illustrated in fiqure 4. Dalles Batholith (tonalite to granodiorite) Figure 8: + .••. Proterozojc Duabase Dikes LIII Lulu Lake Granodiorite kilometres gtO' Bay ti,* . co �Figure 9: metres 100 200 + + + + + + + + + + + + + + + + + + —\ — -, \/ + + + + + + + + + + + + + + + + + + + + + + + Keewatin + 5D + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + -c-- + + + + + + + Winnipeg River + + + + + Geologic map of the Darling ton Bay bridge area illustrating the locations of stops 5 and 6. Refer to figure 8 for the location of this map. o Darlington Bay —— I + I"--1 banded gneissic tonalite with amphibolite enclaves mixed gneissic tonalite — granite pegmatite + ÷] marginal megacrystic granodiorite Wabigoon Subprovince metavolcanic rocks I, — '•. l_ �90 series s e r i e s of o f outcrops o u t c r o p s (SB, ( 5 B f CC and a n d D, D f Figure F i g u r e 9) 9 ) which which illustrate a c r o s s the t h e unit. u n i t . Note Note the the i l l u s t r a t e the t h e changes c h a n g e s across variable v a r i a b l e intensity i n t e n s i t y of o f fabric f a b r i c development, d e v e l o p m e n t f local local development b a n d e d character c h a r a c t e r (best ( b e s t seen s e e n in in d e v e l o p m e n t of o f aa banded outcrops 5i3 and a n d 5D) 5 D ) and a n d increasing i n c r e a s i n g abundance a b u n d a n c e of of o u t c r o p s 5B amphibolite seains a m p h i b o l i t e inclusions i n c l u s i o n s and a n d secondary s e c o n d a r y rnicrocline m i c r o c l i n e seams and a n d megacrysts. m e g a c r y s t s . Depending D e p e n d i n g on o n water water level, l e v e l , one o n e can c a n see see the t h e transition t r a n s i t i o n from f r o m Marqinal Marq i n a l Granodiorite G r a n o d i o r i t e to t o granitic granitic pegmatite—tonalite g n e i s s complex c o m p l e x in i n the t h e outcrops o u t c r o p s on on p e g m a t i t e - t o n a l i t e gneiss the t h e shore s h o r e of o f Darlington D a r l i n g t o n Bay Bay (outcrop ( o u t c r o p SE, 5Ef Figure F i g u r e 9). 9 ) . We We will w i l l examine e x a m i n e aa better b e t t e r exposure e x p o s u r e oof f this t h i s ccontact o n t a c t llaterin ater 'in t h e day. day. the AA modal m o d a l and a n d chemical c h e m i c a l analysis a n a l y s i s of of aa sample s a m p l e from f r o m outcrop outcrop Zircoris 5D i s presented p r e s e n t e d in i n the t h e appendix. appendix. Zircons 5D (sample ( s a m p l e 313) 3 1 3 ) is a p r e l i m i n a U—Pb r y U-Pb s e p a r a t e d from f r o m this t h i s sample s a m p l e yield y i e l da preliminary separated zircon 9 1 7 Ma Ma ((Corfu C o r f u eet t aal., l . , 1985) 1985). z i r c o n age a g e of o f 2705 2 7 0 5 ++ 9/7 The T h e unusual u n u s u a l geometry g e o m e t r y of o f this t h i s unit u n i t together t o g e t h e r with w i t h its its regional r e g i o n a l context, c o n t e x t , suggest s u g g e s t it i t was was emplaced e m p l a c e d into i n t o aa zone zone t w o ccontrasting o n t r a s t i n g terranes t e r r a n e s and and o f weakness w e a k n e s s t that h a t sseparated e p a r a t e d two of that t othe t h eemplacement e m p l a c e m e n t of o f the t h eMarginal Marginal t h a t subsequent s u b s e q u e n t to granodiorite, g r a n o d i o r i t e f this t h i s contact c o n t a c t was was tectonically t e c t o n i c a l l y active. active. The is T h e nature n a t u r e of o f the t h epre—emplacement p r e - e m p l a c e m e n t zzone o n e oof f weakness w e a k n e s s is not n o t clear c l e a r and a n d the t h e granodiorite g r a n o d i o r i t e precludes p r e c l u d e s direct direct i t could c o u l d have h a v e been been o b s e r v a t i o n of o f the t h e contact c o n t a c t but b u t it observation either O K fault. f a u l t . The T h e principal principal e i t h e r an a n unconformity u n c o n f o r m i t y or s geoe v i d e n c e for f o r an a n unconformable u n c o n f o r m a b l e relationship r e l a t i o n s h i pisi geo— evidence chronological: c h r o n o l o q i c a l : tthe h e ttonalites o n a l i t e s north n o r t h of o f the t h e contact c o n t a c t are are 2,83—2.88 Ga( B(Beakhouse, 2 - 8 3 - 2 . 8 8 Ga e a k h o u s e f 1 91983; 8 3 ; C Corfu o r f u e tet aal., l . , 1985) 1 9 8 5 ) and and a r e significantly s i g n i f i c a n t l y older o l d e r than t h a n volcanism v o l c a n i s m in i n the t h e Wabigoon Wabiqoon are subprovince, s u b p r o v i n c e although a l t h o u g h metavolcanic m e t a v o l c a n i c rocks r o c k s in i n the the vicinity o f the t h e interface i n t e r f a c e have h a v e not n o t themselves t h e m s e l v e s been been v i c i n i t y of Tholeiitic dated. T h o l e i i t i c mafic m a f i c dikes d i k e s such s u c h as a s at a t Tannis T a n n i s Lake Lake dated. are a r e not n o t recognized r e c o g n i z e d in i n the t h e Keewatin K e e w a t i n area. a r e a . Some Some deformed def~rmed narrow n a r r o w mafic r n a f i c dikes d i k e s cut c u t both b o t h the t h e gneisses g n e i s s e s and a n d grano— granodiorite d i o r i t e but b u t these t h e s e are a r e not n o t voluminous v o ~ u m i n o u sand, a n d as a s noted n o t e d by by Modal and Gower G o w e r (1978), ( 1 9 7 8 ) are a r e of o f calc—alkalirie c a l c - a l k a l i n e affinity. affinity. and c h e m i c a l analyses a n a l y s e s of o f two t w o such s u c h dikes d i k e s (samples ( s a m p l e s270 270 and and chemical 272) a r e presented p r e s e n t e d in i n the the 2 7 2 ) from f r o m the t h e Darlington D a r l i n g t o n Bay area a r e a are appendix. append ix . Proceed P r o c e e d across a c r o s s Darlirigton D a r l i n g t o n Bay Bay bridge bridqe Reset odometer o d o m e t e r to t o 0.0 0 . 0 km km at a t the t h e north north Reset 0.1 0. 1 km km STOP STOP 66 end e n d of o f bridge bridge Banded Banded Tonalite T o n a l i t e Gneiss Gneiss From F r o m here h e r e we w e will w i l l walk w a l k along a l o n g the t h e roadcuts r o a d c u t s on o n the t h e east east side t o Duffus D u f f u s Road Road and a n d examine e x a m i n e some sane s i d e of o fhighway h i g h w a y 596 5 9 6 up u p to e x p o s u r e s on o n this t h i s road r o a d immediately i m m e d i a t e l y west west of o f the t h e highway highway exposures (Figure ( F i g u r e 9). 9 ) . The T h e distinctive d i s t i n c t i v e banding b a n d i n g within w i t h i n these t h e s e rocks rocks is i s interpreted i n t e r p r e t e d to t o be b e a consequence c o n s e q u e n c e of o f the t h e intense intense d e f o r m a t i o n of o f aa heterolithic h e t e r o l i t h i cplutonic p l u t o n i complex c complex deformation consisting of: c o n s i s t i n g primarily p r i m a r i l y of: - fine f i n e to t o medium medium g rgrained, a i n e d f bhiotite iotite ± k hornblende h o r n b l e n d e ttonalite onalite — to t o leuco—torialite leuco- t o n a l i t e - fine f i n e grained g r a i n e d amphibolite a m p h i b o l i t e with w i t h associated a s s o c i a t e d diorite— d iorite— �91 quartz q u a r t z diorite diorite variously - v a r i o u s l y deformed d e f o r m e d granitic g r a n i t i c pegmatite p e g m a t i t e dikes dikes —- K— K - feldspar f e l d s p a r seams s e a m s and and megacrysts megacrysts Note N o t e the t h e tight t i g h t folding f o l d i n g and a n d shallow s h a l l o w angle a n g l e discordancies discordancies in i n gneissosity. g n e i s s o s i t y . Cross—cutting C r o s s - c u t t i n g relationships r e l a t i o n s h i p s between between the t h e vvarious a r i o u s tonalite t o n a l i t e phases p h a s e s are a r e present p r e s e n t but b u t are a r e not not abundant, a n i s o t r o p y in in a b u n d a n t possibly p o s s i b l y because b e c a u s e pre—existing p r e - e x i s t i n g anisotropy the t h e rock r o c k has h a s controlled c o n t r o l l e d the t h e emplacement e m p l a c e m e n t of o f subsequent subsequent intrusive i n t r u s i v e phases. p h a s e s . Discordant D i s c o r d a n t contacts c o n t a c t s are a r e difficult difficult to t o recognize r e c o g n i z e due d u e to t o intense i n t e n s e transposition t r a n s p o s i t i o n into i n t o the the plane p l a n e of o f the t h e gneissosity. gneissosity. - 3.4 3 . 4 km km STOP M e t a v o l c a n i c Amphibolite Amphibolite STOP 77 Metavolcanic The is on o n the t h e west w e s t side s i d e of o f the t h e road road !I'he outcrop o u t c r o p is approximately metres south s o u t h of o f the t h e junction j u n c t i o n between between a p p r o x i m a t e l y 100 100 metres Highway a n d 10). 10). Highway 596 596 and a n d the t h e Kenora K e n o r a bypass b y p a s s (Figures ( F i g u r e s 88 and The The principal p r i n c i p a l rock r o c k type t y p e in i n this t h i s outcrop o u t c r o p is is aa fine fine grained, t o banded b a n d e d amphibolite. amph i b o l i t e . g r a i n e d f equigranular, e q u i g r a n u l a r massive m a s s i v e to In I n lakeshore l a k e s h o r e exposures e x p o s u r e s 1 to t o 22 km km east e a s t of o f here h e r e on on the the Winnipeg W i n n i p e g River R i v e r system, s y s t e m f such s u c h banding b a n d i n g can c a n be be clearly clearly shown shown to t o represent r e p r e s e n t highly h i g h l y flattened f l a t t e n e d pillow p i l l o w structures. structures. Also diagnostic of a volcanic origin Also d i a g n o s t i c o f a v o l c a n i c o r i g i n are a r e the t h e presence presence of to o f calc—silicate c a l c - s i l i c a t e pods p o d s and and bands b a n d s that t h a t are a r e interpreted i n t e r p r e t e d to be b e metamorphosed m e t a m o r p h o s e d seawater s e a w a t e r alteration a l t e r a t i o n phenomena. p h e n o m e n a . With With the t h e exception e x c e p t i o n of o f the t h e example e x a m p l e discussed d i s c u s s e d at a t stop s t o p 3. 3 . such such calcium—rich c a l c i u m - r i c h mineral m i n e r a l assemblages a s s e m b l a g e s have h a v e not n o t been b e e n noted noted within a m p h i b o l i t e s for f o r which w h i c h aa mafic m a f i c dike d i k e origin o r i g i n can can w i t h i n amphibolites be demonstrated. b e demons t r a t e d . Concordant C o n c o r d a n t sheets s h e e t s of o f medium medium grained g r a i n e d biotite b i o t i t e tonalite tonalite constitute 25 percent of the outcrop. A narrow, A n a r r o w , fine fine c o n s t i t u t e 25 percent of t h e outcrop. grained g r a i n e d diabase d i a b a s e dike, d i k e f interpreted i n t e r p r e t e d to t o be be of o f Middle M i d d l e to to Late 1i t h o l o g i e s L a t e Precambrian P r e c a m b r i a n age, a g e crosscuts c r o s s c u t s all a l l other o t h e r lithologies in i n the t h e outcrop. outcrop. 1 3.5 3 . 5 km km Kenora K e n o r a bypass bypass 4.35 4 . 3 5 km km Amphibolitic A m p h i b o l i t i c metabasalt m e t a b a s a l t with w i t h pegmatite p e g m a t i t e dikes dikes (alternate ( a l t e r n a t e stop) stop) 4.9 4 . 9 km km STOP STOP 8A. 8 A . Pegmatite P e g m a t i t e —- Tonalite T o n a l i t e Gneiss G n e i s s Complex Complex We W e will w i l l stop s t o p at a t aa road r o a d into i n t o aa gravel g r a v e l pit p i t on on the t h e north north side s i d e of o f the t h e highway. highway. Outcrops O u t c r o p s on on the t h e south s o u t h side s i d e of o f the t h e road r o a d consist c o n s i s t of of tonalite g n e i s s with w i t h minor m i n o r ainphibolite a m p h i b o l i t e enclaves e n c l a v e s and and t o n a l i t e gneiss abundant a b u n d a n t pegmatoid p e g m a t o i d phases. p h a s e s . The T h e deformed d e f o r m e d pegmatoid pegmatoid rocks r o c k s occur o c c u r as a s concordant c o n c o r d a n t to t o sub—concordant s u b - c o n c o r d a n t sheets s h e e t s that that t o alkali a l k a l i granite g r a n i t e to to r a n g e in i n composition c o m p o s i t i o n from f r o m granite g r a n i t e to range microcline m i n o r quartz. q u a r t z . The The latter l a t t e r composition c o m p o s i t i o n is is m i c r o c l i n e 5 minor not n o t that t h a t of o f aa magmatic m a g m a t i c rock r o c k and and it i t is is likely l i k e l y that t h a t some some or o r all a l l of o f these t h e s e pegmatoid p e g m a t o i d phases p h a s e s are a r e generated g e n e r a t e d by by vapour v a p o u r phase p h a s e transfer t r a n s f e r and a n d metasomatism m e t a s o m a t i s n rather r a t h e r than than crystallized from silicate melts. Some c r y s t a l l i z e d f r o m s i l i c a t e me1 ts Some phases, phases however, h o w e v e r f do d o have h a v e granitic g r a n i t i c minimum minimum melt m e l t composition c o m p o s i t i o n and and it i t is is not n o t unreasonable u n r e a s o n a b l e to t o expect e x p e c t that t h a t the t h e presence p r e s e n c e of o f aa . �92 ++ + mixed gneissic tonalltegt-anit~cpegmatite gneissic tonalite amphibolite ( m e t a b a s a l t ) + -1 + + Figure F i g u r e 10: 1 0 : Geologic G e o l o g i cmap map of of an anarea a r e aalong a l o n Highway g Highway596 596 between between the the Rabbit Rabbit Lake Lake ffault a u l t and and the t h e Dalles D a l l e s batholith b a t h o l i t h with w i t h the the locations l o c a t i o n s of of stops s t o p s 77 and and 8. 8 . Refer R e f e r to t o figure f i g u r e 88 for f o r the the location l o c a t i o n of of this t h i smap. map. �93 vvapor a p o r pphase h a s e ccould o u l d initiate i n i t i a t e partial p a r t i a l melting m e l t i n g of o f the the The microcline ttonalite. onalite. T h e ggeometry e o m e t r y oof f the the m i c r o c l i n e rich r i c h phase phase ranges a n 2 swell r a n g e s from f r o m continuous c o n t i n u o u s planar p l a n a r sheets s h e e t s to t o pinch p i n c h and swell sheets s h e e t s to t o isolated i s o l a t e d microcline m i c r o c l i n e megacrysts. megacrysts. A number n u m b e r of of uundeformed n d e f o r m e d ggranitic r a n i t i c pegmatite p e g m a t i t e dikes d i k e s which w h i c h exhibit exhibit a r e present p r e s e n t in i n the the ccompositional o m p o s i t i o n a l and a n d textural t e x t u r a l zonation z o n a t i o n are outcrop. outcrop. STOP 8B. Standing 8B. S t a n d i n g oon n the t h e south s o u t h lip l i p (but ( b u t not n o t to t o close close are tto o the t h e edge e d g e —- there there a r e ddangerous a n g e r o u s overhangs) o v e r h a n g s ) of o f the the gravel w e s t of o f the the g r a v e l pit p i t approximately a p p r o x i m a t e l y 100 1 0 0 metres west turn—off, s e e on o n the t h e opposite o p p o s i t e side s i d e of o f the t h e pit pit t u r n - o f f I oone n e can c a n see D a l l e s bbatholith a t h o l i t h (furthest ( f u r t h e s t away), a w a y ) I in in eexposures x p o s u r e s oof f the t h e Dalles m e t a b a s a l t unit u n i t (Figure (Figure ccontact o n t a c t with w i t h an a n amphibolitic a m p h i b o l i t i c metabasalt Near the t h e bbottom o t t o m oof f the t h e pit p i t the t h e amphibolite a m p h i b o l i t e unit unit 110). 0 ) . Near is i s in i n contact c o n t a c t with w i t h pegmatite—tonalite p e g m a t i t e - t o n a l i t e gneiss g n e i s s such s u c h as as seen This s e e n in i n the t h e outcrops o u t c r o p s discussed d i s c u s s e d above. above* T h i s thin thin (approximately m e t r e s ) amphibolite a n p h i b o l i t e unit u n i t is is ( a p p r o x i m a t e l y 100 1 0 0 metres) laterally l a t e r a l l y ppersistent e r s i s t e n t for f o r approximately a p p r o x i m a t e l y 15 1 5 km k~ along a l o n g the the Dalles D a l l e s —- gneiss g n e i s s ccontact. ontact. A ssimilar i m i l a r amphibolite a m p h i b o l i t e unit u n i t occurs o c c u r s around a r o u n d the t h e Herb H e r b Lake Lake The ppluton l u t o n 38 3 8 km to t o the t h e east—northeast e a s t - n o r t h e a s t of o f here. here. T h e Herb Lake many oof L a k e ppluton l u t o n hhas a s many f the t h e ccharacteristics h a r a c t e r i s t i c s of o f the the Dalles D a l l e s bbatholith a t h o l i t h and a n d the t h e ggneisses n e i s s e s and a n d amphibolites amphibolites are r e ddeformed e f o r n e d into i n t o a large, l a r g e I recumbent, recumbentI aaround r o u n d tthis h i s unit unit a domed upwards nnappe—like a p p e - l i k e structure s t r u c t u r e domed u p w a r d s by b y the t h e Herb H e r b Lake Lake One ssample pluton e t al., a l . I 1983). 1983). One a m p l e from f r o m the the p l u t o n (Beakhouse ( B e a k h o u s e et rroot o o t zone z o n e oof f this t h i s complex c o m p l e x in i n the t h e Daniels D a n i e l s Lake L a k e area a r e a has has to that 1985) a similar age (2837 Ma, Corfu et al., a s i m i l a r a g e ( 2 8 3 7 MaI C o r f u e t a l . I 1 9 8 5 ) t o t h a t of of This the t h e banded b a n d e d tonalite t o n a l i t e gneisses g n e i s s e s in i n the t h e Kenora K e n o r a area. area. T his rraises a i s e s the t h e possibility p o s s i b i l i t y that t h a t the t h e 2.83—2.85 2 . 8 3 - 2 . 8 5 Ga G a grieisses gneisses in the Kenora area may be in large part allochthonous. be i n l a r g e p a r t a l l o c h t h o n o u s . i n t h e Kenora area 9.8 9 . 8 km Diorite STOP 99 ((optional) optional) D i o r i t e Intrusion I n t r u s i o n Breccia Breccia — - PPsuedo— suedocconglomerate onglomerate Outcrop O u t c r o p oon n the t h e north n o r t h side s i d e of o f the t h e highway highway This T h i s intrusion i n t r u s i o n bbreccia r e c c i a contains c o n t a i n s abundant a b u n d a n t fragments fraqments rrepresenting e p r e s e n t i n g a wide w i d e range r a n g e of o f rock r o c k types t y p e s and a n d resembles r e s e m b l e s aa Mafic M a f i c to t o ultramafic u l t r a m a f i c fragments fragments cconglomerate. onglomerate. Enclaves ppredominate. redominate. E n c l a v e s of o f similar s i m i l a r lithologies l i t h o l o g i e s are are common common in i n ddioritic i o r i t i c phases p h a s e s of o f the t h e Trout T r o u t Lake L a k e pluton p l u t o n to to Intermediate the t h e west w e s t and a n d may be b e cognate c o g n a t e inclusions. inclusions. Intermediate tto o ffelsic e l s i c fraqments f r a q m e n t s are a r e also a l s o present p r e s e n t and a n d probably probably The matrix rrepresent e p r e s e n t accidental a c c i d e n t a l inclusions. inclusions. T he m a t r i x of o f the the breccia b r e c c i a is i s a medium grained, g r a i n e d I equigranular, e q u i g r a n u l a r I hornblende hornblende diorite. ' d iorite. 110.8 0 . 8 km kn Sandy S a n d y Lake Lake 12.0 1 2 . 0 km JJunction u n c t i o n —- ccontinue o n t i n u e straiqht s t r a i g h t ahead a h e a d on o n Hiqhway H i q h w a y 596 596 115.95 5 . 9 5 km STOP 10 STOP 10 ((optional) o p t i o n a l ) Megacrystic M e g a c r y s t i c Grariodiorite Granodiorite We will examine low W e w i l l e x a m i n e low roadcuts r o a d c u t s occurring o c c u r r i n g on o n both b o t h sides s i d e s of of the road. t h e road. The made to T h e sstops t o p s made t o this t h i s point p o i n t are a r e not n o t truly truly �Figure 11: t 0 ''S (O rr —•l CD II I—ri (I • :1) c Ci) 0 (Ic3 0 (1 ct CD 11D i—a 0 CD —• r•—i• (I HQ G e o l o g i c map o f t h e T r o u t Lake a r e a ( f r o m B e a k n o u s e , 1 9 8 3 ) i l l u s t r a t i n g t h e l o c a t i o n s o f s t o p s 10 a n d 1 1 . T h e l o c a t i o n o f t h i s f i g u r e is i l l u s t r a t e d i n f i g u r e 4. 0 o 0 0 0 0 III 11111 11111.11111 11111 II.: 11111 IIIIIIIII 0 00000000000 0 11111 0 11I 1111i1i1 Ililililil 1I1i1i1I III 1 II II 11 I1I1I' IllIllIlIllIll II!IIIIIIIIIIIIIIIIIIIIII 00°::°O00°o:0° 0 0 000 :000 0 0• ::: o000::: 00 ::.iIiIiIiI :::.:.i II 11111 IiI: I II III:I:I" II91I1I1I1y1i1I1I1y1I1I1I1II III 1111111111 1111111111111111111111I111111111i11 IIIIIIIIIiIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIItIIII III I: II II I il I I I I IIIIIII 0 : I 1 (I) . 11 CD 5 Q— (t — + . _ E r CD Z C rc r -_________________ II IIII ililil .IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IhIhIhIhIhIIIhIhIhIhIhIhIhIhIhIhIhIhIIIIthIhIIII IIIIIIJIIIIIIIIIIIIIIIIIIIIIIII1.IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII III1II.'.I III 1 1 ihihii IIhIIhIIhIhIhIhIhIhIhIhIhIhIhIhIhIIIhIIIIIhIhIhII I1I1III 0 0 :I: 11111 ..ihIhi'ihi'ihihihihihiIhih. 11111I.:.:.:..:.;.OIIIIIIIIIIIIIIIIIIIIIIIIIIII I ''—' ' _______________ 1I1I'I'i riihihihihihihihihihihihihihihihihiIhiII IIIIIII...........\IC.l)IIIIIIIIIIIIIIIIIIIIIIIIIIIII HHHI ::::::::::::IIIHIIIIIIIIIIIHIIIIIIIIII hIhIIIhIhIhIIIhIIIIIIIhIhIhIhIhI iII:i II III IIL 00 0IIIIIIIIIIIIIIIIIIIIIIIII II1IIIIIII1IIl1III1II1l1I1i1I1I1IIII1IIIIII1I1III1II1I1I1 00000 Oo 0 0000 F) — _____ �95 r e p r e s e n t a t i v e of o f the t h e nature n a t u r e of o f the t h e Winnipeg W i n n i p e g River River representative as b e l t . This T h i s reflects r e f l e c t s the t h e emphasis e m p h a s i s of o f the t h e field f i e l d trip t r i p as belt. w e l l a s l o g i s t i c a l c o n s i d e r a t i o n s and t h e d e s i r e t o well as logistical considerations and the desire to k e e p field f i e l d trip t r i p participants p a r t i c i p a n t s awake. a w a k e . When When considering considering keep regional t h e W a b i q o o n W i n n i p e g R i v e r i n t e r f a c e f r o m the Wabigoon—Winnipeg River interface from aa regional i t is i m p o r t a n t t o k e e p i n m i n d t h at p e r s p e c t i v e perspective it is important to keep in mind that r e l a t i v e l y h i g h l y g e o c h e m i c a l l y e v o l v e d , m a s s i v e , late late relatively highly geochemically evolved, massive, t o p o s t t e c t o n i c g r a n i t i c r o c k s p r e d o m i n a t e i n t h e to post—tectonic granitic rocks predominate in the t o their their W i n n i p e g River R i v e r belt, b e l t , in i n marked m a r k e d contrast c o n t r a s t to Winnipeg p a u c i t y i n t h e W a b i g o o n s u b p r o v i n c e . paucity in the Wabigoon subprovince. l a t e plutonic plutonic Many of o f the t h e granodiorites q r a n o d i o r i t e s within w i t h i n the t h e late Many c o m p l e x e s a r e c h a r a c t e r i z e d by t h e p r e s e n c of complexes are characterized by the presencee of m i c r o c l i n e m e g a c r y s t s s u c h as a r e a b u n d a n t i this microcline megacrysts such as are abundant inn this o u t c r o p . This p a r t i c u l a r u n i t i s , h o w e v e r , a t y p i c a l in in outcrop. This particular unit is, however, atypical a r e a b u n d a n t i n p a r t s o f t h a t a m p h i b o l i t e i n c l u s i o n s that arnphibolite inclusions are abundant in parts of ( i n contrast contrast t h e unit u n i t and a n d both b o t h hornblende h o r n b l e n d e and a n d biotite b i o t i t e (in the t o b i o t i t e a l o n e i n most g r a n o d i o r i t e s ) a r e p resent. to biotite alone in most granodiorites) are present. T h e s e d i f f e r e n c e s , t o g e t h e r w i t h its a s s o c i a t i o n with w i t h aa These differences, together with its association ma i c p l u t o n ( F i g u r e 1 1 ) , s u g g e s t it may h a v e a mafic pluton (Figure 11), suggest it may have a d i f f e r e n t origin. origin. different 19.35 19.35 1 1 (optional) ( o p t i o n a l ) Trout T r o u t Lake L a k e quartz q u a r t z diorite diorite STOP 11 STOP 'The o u t c r o p o n t h e e a s t s i d e o f t h e r o a d c o n s i s t s o f The a r t z d diorite i o r i t e to to i n h o m o g e n e o u s h ohornblende—biotite r n b l e n d e - b i o t i t e q uquartz inhomogeneous d i o r i t e containing a wide v a r i e t y o f i n c l u s i o n s which a r e a l l more maÂi c t h a n t h e h o s t . The The nature n a t u r e of of the the . e n c l a v e s f o r m a c o n t i n u u m f r o m s h a r p l y b o u n d e d enclaves form a continuum from sharply bounded i n c l u s i o n s t o d i f f u s e l y bounded i n c l u s i o n s to d i f f u s e m a f i c rich r i c h patches. p a t c h e s . It I t is is not n o t clear c l e a rhow how much much of o f the the mafic a n d represent r e p r e s e n t disrupted d isrupted a m p h i b o l e could c o u l d be b e xenocrystic x e n o c r y s t i c and amphibole u l t r a m a f i c enclaves. e n c l a v e s . AA sample s a m p l e from f r o m this t h i s outcrop o u t c r o p yields yields ultramafic a U-Pb z i r c o n a g e o f 2 7 0 0 2 M a ( B e a k h o u s e 1 9 8 3 ) a U—Pb zircon age of 2700 ± 2 Ma (Beakhouse 1983). . outcrop on the east side of the road consists of diorite containing a wide variety of inclusions which are all more mafic than the host. inclusions to diffusely bounded inclusions to diffuse * R e t u r n to t o the t h e junction j u n c t i o n of o f Highway Highway 596 596 and a n d the t h e Kenora K e n o r a bypass b y p a s s —Return t u r n west w e s t (right) ( r i g h t ) on o n the t h e bypass b y p a s s and a n d proceed p r o c e e d 5.7 5 . 7 km km and a n d stop s t o p just just turn b e f o r e t h e b r i d g e o v e r t h e o l d M i n a k i Road a n d t h e r a i l r o a d before the bridge over the old Minaki Road and the railroad tracks. tracks. STOP 12 1 2 Marginal M a r g i n a l Granodiorite G r a n o d i o r i t e -- Tonalite T o n a l i t e gneiss g n e i s s contact contact STOP O u t c r o p o n b o t h s i d e s of t h e r o a d c o n t a i n t h e c o ntact Outcrop on both sides of the road contain the contact b e t w e e n t h e M a r g i n a l g r a n o d i o r i t e a n d w e l l b a n d e d between the Marginal granodiorite and well banded 8 ) . The T h e south s o u t h end e n d of of the the t o n a l i t i c yneiss g n e i s s (Figure ( F i g u r e 8). tonalitic o u t c r o p consists c o n s i s t s of o f intensely i n t e n s e l ysheared s h e a r e dmegacrystic megacrys t i c outcrop g r a n o d i o r i t e containing c o n t a i n i n g aa few f e w flattened f l a t t e n e damphibolite amphibolite granodiorite i n c l u s i o n s and a n d highly h i g h l y deformed, d e f o r m e d , discordant d i s c o r d a n leuco— t leucoinclusions ttonalite o n a l i t e dikes. d i k e s . The The north n o r t h end e n d of o f the t h e outcrop outcrop t o n a l i t e —- quartz quartz c o n s i s t s of o f banded b a n d e d amphibolite a m p h i b o l i t e —- tonalite consists d i o r i t e gneiss. g n e i s s . Sills S i l l s of o f highly h i g h l y deformed, d e f o r m e d , megacrystic megacrys t i c diorite g r a n o d i o r i t e are a r e difficult d i f f i c u l t to t o recognize r e c o g n i z e but b u t occur occur granodiorite t h r o u g h o u t much much oof f the t h e outcrop o u t c r o p but b u t decrease d e c r e a s e in in throughout a b u n d a n c e tto o the t h e north. north. abundance H i g h w a y 17, 1 7 , turn t u r n east e a s t and a n d return r e t u r n to to C o n t i n u e on on Kenora K e n o r a bypass b y p a s s tot oHighway Continue Kenora. Ken ora. �96 Re R e ferences ferences Arth, A r t h , J.G. J . G. and a n d Hanson, H a n s o n , G.N., G. N. , 1972. 197 2. 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Bird B i r d River R i v e— r - Winnipeg W i n n i p e g River R i v e r area: a r e a : in in Trueman, Summary o f F i e l d Work, 1 9 7 5 , M a n i t o b a D e p a r t m e n t o f M ines, Summary of Field Work, 1975, Manitoba Department of Mines, R e s o u r c e s a n d E n v i r o n m e n t a l M a n a g e m e n t , G e o l o g i c a l S e r vices Resources and Environmental Management, Geological Services B r a n c h , G e o l o g i c a l P a p e r 2/75. Branch, Geological Paper 2/75. v a n de d e Ramp, Kamp, P.C. P.C. and a n d Beakhouse, B e a k h o u s e ,G.P.., G.P., 1979. 1979. Paragneisses P a r a g n e i s s e s in i n the the van Pakwash L a k e a r e a , E n g l i s h R i v e r g n e i s s b e l t , n o r t h w e s t e r n Pakwash Lake area, English River gneiss belt, northwestern O n t a r i o : Canadian C a n a d i a n Journal J o u r n a l of o f Earth E a r t h Science, S c i e n c e , 16, 1 6 , p.1753—1763. p . 1753-1 7 6 3 . Ontario: W e s t e r m a n , C., C . , 1977. 1 9 7 7 . Tectonic T e c t o n i c evolution e v o l u t i o n of o f aa part p a r t of o f the t h e English English Westerman, R i v e r subprovince, s u b p r o v i n c e , northwestern n o r t h w e s t e r n Ontario: O n t a r i o : unpublished u n p u b l i s h e d Ph.D. Ph .D. River t h e s i s , McMaster McMaster University, U n i v e r s i t y , Hamilton, H a m i l t o n , Ontario, O n t a r i o , p.292. p . 292. thesis, W i l s o n , H.D.B., H. D. B . ,1971. 197 1. The The Superior S u p e r i o r province p r o v i n c e in i n the t h e Precambrian Precambrian Wilson, o f Manitoba: M a n i t o b a : in i n Turnock, T u r n o c k , A.C., A . C . , ed., e d . , Geoscience G e o s c i e n c e Studies S t u d i e s in in of M a n i t o b a , G e o l o g i c a l A s s o c i a t i o n o f C a n a d a , S p e c i a l P a p e r 9, 9, Manitoba, Geological Association of Canada, Special Paper p.41-49. p.41—49. W i l s o n , H.D.B. H . D . B . and a n d Brisbin, B r i s b i n , W.C., W.C., 1963. Nature N a t u r e of o f the t h e granitic granitic Wilson, 1963. c r u s t in i n the t h e Superior S u p e r i o r province: p r o v i n c e : Abstract, A b s t r a c t , Geological G e o l o q i c a l Society Society crust of America, A m e r i c a , 76th 7 6 t h Annual A n n u a l Meeting, M e e t i n g , p.180. p . 180. of W i l s o n , H.D.B. H. D . B . and a n d Morrice, Morrice, M.G., M.G., 1977. 1 9 7 7 . The The volcanic v o l c a n i c sequence s e q u e n c e in in Wilson, W.R.A., C o l e m a n , L.C. L.C. and a n d Hall, Hall, A r c h e a n shields: s h i e l d s : in i n Baragar, B a r a g a r , W.R.A., Archean Coleman, J.M., e d s , Volcanic V o l c a n i c Regimes R e g i m e s in i n Canada, C a n a d a , Geological Geological J.M., eds., A s s o c i a t i o n of o f Canada, C a n a d a , Spec. S p e c . Paper P a p e r 16, 1 6 , p.355—374. p.355-374. Association J . L . , 1978. 1 9 7 8 . Rb—Sr Rb-Sr isotopic i s o t o p i c studies s t u d i e s of o f Archean A r c h e a n rocks r o c k s of of Wooden, J.L., Wooden, t h e eastern e a s t e r n Lac L a c Seul S e u l and a n d Kenora K e n o r a areas, a r e a s , English E n g l i s h River River the s u b p r o v i n c e , Ontario: O n t a r i o : in i n Smith, S m i t h , I.E.M. I . E . M . and a n d Williams, ~ i l l i a m sJ.G., ,J . G . , subprovince, e d s . , P r o c e e d i n g s , 1 9 7 8 ~ r c h e a n G e o c h e m i s t r y F i e l d eds., Proceedings, 1978 Archean Geochemistry Field C o n f e r e n c e , University U n i v e r s i t y of o f Toronto T o r o n t o Press, P r e s s , Toronto, T o r o n t o , Ontario, Ontario, Conference, p.131-149. p.131—149. . . �101 101 APPENDIX APPEND1 X Modal and a n a l y s e s of e l e c t e d samples t h e field f i e l d trip trip Modal and chemical chemical analyses of sselected samples from the area area Table 1: Table 1: trip trip a n a l y s e s for f o r samples samples from from the the area a r e a of of the t h e field field Modal analyses -- -Metavolcanic ---~--, ~e t ~ Rocks~ l - ~ ~e s DD lices lk --- -----Winnipeg -.-Winnipe2 River ~ i v e r Belt -~elt Wabigoon Wabigoon Intermediate Intermediate 2/5 2/9 29JA 323 7 n?T2 9 0 7~ --- 3U9 3 - 312 7 2 373-------27ZS-X 272 --- - -------- 270 ---s A plagio— plag ioclase c l a s e 39.3 39. 3 K— Kfeldspar— feldsparquartz q u a r t z tr tr horn— hornblende 60.0 60.0 biotite b i o t i t e —muscovite— muscoviteepidote e p i d o t e 0.3 0.3 opaque opaque tr tr sphene 0.4 sphene 0.4 zircon —zircon apatite a p a t i t e tr tr allanite a l l a n i t e —carbonate— carbonate- 23.0 23.0 26.3 26.3 29.9 29.9 45.9 45.9 46.2 46.2 25.0 25.0 - - - 50.2 50. 2 1.2 1.2 48.6 48.6 4.55 4. — - - - - 2.0 2.0 1.6 1.6 0.3 0.3 1.4 1.4 73.7 73.7 59.0 59.0 11.2 11.2 67.7 67.7 67.5 67.5 0.4 0.4 - — — 0.3 0.3 1.2 1.2 tr tr - — — - — 0. 0.88 - tr tr tr tr - - tr tr - 0.5 0.5 - 61. 61. 11 3. 3.33 - - - 0.9 0.9 1.8 1.8 tr tr tr tr tr tr 59.4 61.9 1. 1 0.5 26.4 30.6 — 6.2 1.2 1.2 tr — 10.4 — 0.8 tr 58.9 0.3 30.5 0.9 6.9 — 66.4 6.8 71.5 69.7 2. 3 19.2 22.1 2.3 21.0 5.4 3.0 — — 5.7 0.7 0.6 1.8 2.2 0.7 — — — 1.0 — — tr tr tr tr tr tr tr tr tr tr tr tr tr — — — — — — — 0.3 - - tr tr tr tr - 1.6 1.6 0.6 0.6 - Granodiorites Granodiorites tr tr tr 71.0 71.0 0.2 0.2 0. 11 0. 0.4 0.4 - 1.2 1.2 1.8 - Tonal Tonalites ites plagioclase p l ag i o c l as e K—feldspar K-feldspar quartz quartz hornblende hornblende biotite biotite muscovite muscovite epidote epidote opaque opaque sphene sphene zircon zircon apatite apatite allanite allanite carbonate carbonate - 33.0 33.0 3.0 3.0 0.3 0.3 - Mafic Mafic -TTtT - - 31.3 31.3 — - ---- --.- 48.0 17.4 26.5 40.8 13.2 34.8 3.8 2.2 4.2 4.6 1.5 2.1 tr tr tr tr �L_c[L tt T a b l e 2: --- tiesfroin the area o the Chemical a n a l ~ s o f s e l e c t e d samples from t h e a r e a o f t h e f l e l d t r i p . 1 WINNIPEG WINNIFEG RIVER R I E R BELT BELT META.W)LCANIC METAWLCANIC Type WABIWON W I C X I O N META.OLCANIC METAKILCANIC R(EKS R E G Rock Type WINNIPEG RIVER BELT DIKE ROCKS ~ Sampl e SnipI Number umber N SIO2 5102 AI203 A'2° Fe F e203 93 Feo PeG MgO M@ c a4 CaO NaO Na9 K20 '(20 TIO2 1102 '2'5 MnO MeG 84GF- 84GFB- 323 8007 8009 54.0 51.2 15.5 1.22 9.09 4.23 9.73 2.68 0.10 1.17 0.04 0.23 13.7 1.49 50.1 14.4 2.04 9.31 .24 .76 B3GPB- CO2 820 9.67 83GF 8010 275A 279 62.5 50.2 14. 3 13. 8 51.2 13.9 2.30 8.36 8.39 0. 9 5.31 83GP8 3.96 8.00 6.86 83GP8 11.3 5.09 4.33 1.52 2.21 4.07 2.69 0.04 0.89 0.02 0.19 0.12 0.45 0.81 11.50 1.56 0.21 1.27 0.04 0.81 0.20 0.09 0. Il 0.97 0.04 0.26 0.77 0.02 0.18 0.07 0.56 0.22 0.87 0. 11 0.52 0.07 0.08 0.76 7.73 11.9 7.51 9 33 120 10 170 10 16 9) 70 90 160 16 12 13 85 67 42 20 86 Rb 8 Sr 110 8 83 LI 8 Ba Y 10. 4 1.01 16 MARGI NL GRANODR* ITE 1.93 10.8 6.64 9.74 2.26 1.30 1.19 0.04 50.9 13.6 3.02 9.96 5.78 83GFU 83GPB 83GP8 83GFB 270 272 304A 3218 50.8 14.3 54.2 55.3 12.5 13.7 2.93 2.37 5.09 4.95 9.55 7.50 10.2 8.52 1.61 9.60 6.47 11.9 0.05 0.25 0.03 0.01 0.04 0.07 0.03 0.07 0.70 0.12 0.68 0.12 0.98 0.08 0.08 1.05 0.08 0.58 0.06 0.87 0.24 0.47 0.12 1.04 0.06 0.30 92 78 155 43 129 41 253 570 89 42 133 66 22 65 69 113 98 117 <10 107 l0 <10 118 97 103 Pb <10 <10 <10 <10 <10 <10 Zn 92 82 72 82 122 91 3.71 0.21 81 69 3.41 0.85 0.19 13 95 1.55 4.49 0.20 9 125 34 81 0.73 1.12 1.45 0.43 3.42 1.29 0.05 0.25 39) 106 3.35 0.47 0.09 0.07 18 NI 1.52 1.31 0.93 120 43 0.40 1.17 18 50 2.98 2.67 5.02 1.31 0.93 0.28 0.03 120 8 16.1 1.83 80 114 72.7 16.3 1.37 610 Cu 72.1 14.5 0.38 100 22 213 72.0 14.1 1.82 6 29 73.2 15.9 1.37 0.70 0.15 0.14 125 118 64.0 0.79 0.57 0.22 0.15 22 110 22 1.06 51 10 43 94 560 105 17 20 800 8 90 24 435 20 370 155 94 35 17 183 65 43 116 13 44 10 38 <10 80 <10 76 82 65 45 <10 126 18 321A 16.1 0.43 76 3200 69.9 0.81 16 320A 12.8 3.18 11.3 5.65 10.3 1. 74 86 BSGFB 51.2 3. 53 39 650 56 770 83GPE 16.0 2. 76 0.21 83GF 63.9 2.87 12 41 310 1.78 1 55 365 83GP8 2.05 17 Ii 83GFB- 83GBP 262 2900 3.20 4.48 10.7 19 387 49 50.4 13.6 309 83GI3 312 12 304 172 20 29OA 83GfB 48 64 43 254 98 128 1 B3GPB 11 130 16 88 45 Zr Co Cr WINNIPEG RIVER BELT TONLITES ROCKS ~ ii 0.29 2.69 0.70 3.51 3.77 1.00 0.38 0.06 0.05 0.06 0.29 1.03 1.39 0.16 0.00 0.02 0.16 0.00 0.03 74.9 14.5 0.36 0.22 1.09 0.87 0.30 0.18 2.00 1.70 3.48 3.80 3.67 2.97 0.21 0.12 0.01 0.00 0.03 0.04 0.05 0.14 0.10 0.42 0.07 0.36 0.06 3.02 0.04 1.16 0.45 2.88 5.20 4.61 1.02 0.20 73.1 14.9 0.06 0.72 51 76 85 350 28 570 165 130 24 260 25 625 20 240 12 58 840 59) 6 7 6 2 3 4 225 195 180 120 90 120 95 14 6 8 <5 <5 5 <5 7 9 <5 <5 10 18 <5 10 10 7 II 25 24 8 6 6 9 <5 5 <5 5 <5 <5 10 <10 10 12 124 60 <10 34 14 41 26 22 38 44 30 59 21 21 3 31 15 43 10 28 5 55 19 1 4 315 34 660 46 250 22 380 3 11 115 6 11 41 160 La 5 3 6 15 6 4 13 9 7 51 36 4 4 Ce 12 8 13 29 13 9 10 15 12 17 74 26 55 103 53 12 8 103 Nd 9 6 10 14 9 6 tO 10 7 34 36 24 10 3 36 21 14 40 12 Sm 2 2 5 3 3 2 4 3 1 4 7 8 5 1 8 3 2 3 Sm 2 2 5 3 3 2 4 3 1 4 7 8 5 1 8 3 2 3 Eu 0.9 0.6 0.9 0. 9 0. 8 0.6 0.8 0.9 0.6 1.0 1.6 1.0 1.1 0.5 1.4 0.8 0.6 0.6 Gd 4 3 5 3 3 3 3 3 3 4 5 3 4 I 6 2 2 2 Dy 2.4 2.0 4.0 2. 3.3 2.7 1.4 1.3 2.4 2.1 0.9 1.3 0.8 2.7 1.0 0.9 0.6 1.2 2.3 4.0 2.7 1.2 1.5 2.3 2.0 1.3 1.9 2.2 1.6 3.5 Yb 2.9 1.8 1.6 0.8 4 83GFB- 83GF8 300 313 0.4 0.8 1 4 0.3 0.4 1 0.5 0.2 2 0.6 0.3 18 9 1 1 0.4 1 1.1 0.5 C) I'.) �103 100- 100- 10 Wabigoon Metavolcanics Metavolcanics Wabigoon i I x 8 3 G P B 3 2 3 ,84GPB8007, 84GPB8007,84GPB2009 84GPB2009 183GPB323, 1 I I I Lace LaCe Nd Nd l t I I SmEuGd SmEuGd Yb Yb Dy Dy 100 Lace LaCe 1 Nd Nd I Sm EuGd SmEuGd Yb Yb Dy Dy I 100- 10 - 1 Winnipeg River River Metabasafts Metabasalts Winnipeg 1 84GPB8010 • 84GPB8O1O 10 1 Winnipeg River River Dike DikeRocks Rocks Winnipeg I I 1 I I Lace LaCe I Nd Nd I I I l l SmEuGd SmEuGd I I Dy Dy F Ifl Winnipeg River Metabasalt 1 £83GPB270 •830P8272 •83GPB321B - Winnipeg River Tonalite Winnipeg River Tonalite I I I _iI___ L a c e Nd Nd LaCe I I Yb Yb l I I Dy Dy Yb Yb l I I Fe203+ FeO + Ti02 Fe203+FeO+T102 Wabigoon Metavolcanics Metavolcanics o0Wabigoon A Winnipeg River Metavolcanics Winnipeg River Metavolcanics DikeRocks Rocks o Dike 83GPB32 1B I SmEuGd SmEuGd CAcaic—alkaline calc-alkaline CA tholeiite TTtholeiite I"'/83GPB32lB see Grunsky ( 1 9 8 1) 1981) of for calculation ternary components ternary components A M A1203 MgO F i g u r e 12. 12. C h o n d r i t e normalized n o r m a l i z e d rare r a r e earth e a r t h element e l e m e n t abundances abundances Figure Chondrite and m a j o r e l e m e n t t e r n a r y c l a s s i f i c a t i o n d i a g r a m f o r samples and major element ternary classification diagramss for samples from t h e f i e l d t r i p a r e a . from the field trip area. �V o l c a n i c FFades acies AA Volcanic IInterpretation n t e r p r e t a t i o n of o f the t h e Berry B e r r y River R i v e r Formation1 Formation1 I n t r o d u c t o r y Discussion D i s c u s s i o n and a n d Field F i e l d Guide Guide Introductory 31st A n n u a l I n s t i t u t e o n L a k e S u p e r i o Geology 31st Annual Institute on Lake Superiorr Geology K e n o r a , O n t a r i o Kenora, Ontario by G.W. Johns Johns G.W. P r e c a m b r i a n G e o l o g y Section Section Precambrian Geology O n t a r i o G e o l o q i c a l Survey Ontario Geological Survey 7 7 G r e n v i l l e S t. 77 Grenville St. T o r o n t o , O n t . Toronto, Ont. 1B3 N5S 1B3 M5S 1 This T h i s guide g u i d e is is published p u b l i s h e d with w i t h permission p e r m i s s i o n of o f the t h e director d i r e c t o r of o f the the 1 O n t a r i o Geological G e o l o g i c a l Survey. Survey. Ontario �106 INTRODUCTION INTRODUCTION -Edy Theof s t uArchean d y o f A r cpyroclastic h e a n p y r o c l a s rocks t i c r o c khas s h aevolved s e v o l v e d from f r o m aa simple o the t h e ternary t e r n a r y classifica— classificas i m p l e tuff—agqloinerate t u f f - a g g l o m e r a t e ssubdivision u b d i v i s i o n tto tions N o w I an a n important i m p o r t a n t tool tool t i o n s oof f Fisher F i s h e r (1966) ( 1 9 6 6 ) and and Schmid Schmid (1981). ( 1 9 8 1 ) . Now, in Archean i n the t h e sstudy t u d y oof f A r c h e a n ppyroclastics y r o c l a s t i c s iis s ffades a c i e s analysis a n a l y s i s (Ayres, (AyresI Tasse 11977; 977; T a s s e eett aal., l e I 1978 1 9 7 8 and and Lichtblau L i c h t b l a u and and Dimroth, D i m r o t h I 1980). 1 9 8 0 ) . This This field  i e l d trip t r i p will w i l l examine e x a m i n e a deformed d e f o r m e d amphibolite a m p h i b o l i t e metamorphic m e t a m o r p h i c grade grade Archean A r c h e a n ssubaqueous u b a q u e o u s ppyroclastic y r o c l a s t i c sequence s e q u e n c e (the ( t h e Berry B e r r y River River formation) which formation) w h i c h tthe h e aauthor u t h o r hhas a s ssubdivided u b d i v i d e d iinto n t o vvolcanic o l c a n i c ffades. acies. The The purpose p u r p o s e oof f this t h i s field f i e l d trip t r i p is i s to t o examine e x a m i n e the t h e evidence evidence for  £ o the t h e subdivision s u b d i v i s i o n of o f the t h e Berry B e r r y River R i v e r formation f o r m a t i o n (Warclub ( W a r c l u b group) group) into volcanic IIt t iis s iimportant m p o r t a n t to t o sstudy t u d y Archean A r c h e a n pyro— pyrointo v o l c a n i c facies. facies. clastic f a c i e s model, m o d e l , when when c l a s t i c rocks r o c k s using u s i n g facies f a c i e s analysis a n a l y s i s because b e c a u s e aa facies w i l l lead l e a d to t o an a n understanding u n d e r s t a n d i n g of o f volcanic v o l c a n i c stratigraphy stratiqraphy ddeveloped, e v e l o p e d I will and ddepositional and e p o s i t i o n a l environment e n v i r o n m e n t and and thus t h u s the t h e placement p l a c e m e n t of o f known known o r e bodies. bodies. vvolcanogenic o l c a n o g e n i c ore The wasooriginally T h e formation f o r m a t i o n was r i g i n a l l y described d e s c r i b e d during d u r i n g aa 33 year year 1:15,840 detailed 1 : 1 5 I 840 d e t a i l e d mapping m a p p i n g programme programme c carried a r r i e d out o u t by b y the t h e Ontario Ontario Results Geological G e o l o g i c a l Survey. Survey. R e s u l t s of o f this t h i smapping m a p p i n g (Johns ( 3 J o h n sand a n d Richey, RicheyI 1982; 9 8 4 ) are are 1 9 8 2 ; Johns J o h n s and and Davison, D a v i s o n I 1983 1 9 8 3 and a n d J o h n s e t a l a I 11984) maps from aavailable v a i l a b l e as a s preliminary p r e l i m i n a r y maps f r o m the t h e Office O f f i c e of o f the t h e Mining Mining Additional Recorder, R e c o r d e r I Ministry M i n i s t r y of o f Natural N a t u r a l Resources, R e s o u r c e s I Kenora. Kenora. Additional were ccarried out arried o u t dduring u r i n g the t h e summer of o f 1984 1984 and a n d the the iinvestigations n v e s t i g a t i o n s were A preliminary facies p r e l i m i n a r y version v e r s i o n of o f the t h e model model f a c i e s model m o d e l was was developed. developed. iis s ooutlined u t 1 i n e d in i n Johns J o h n s (1984). ( 1984). The The Berry B e r r y River R i v e r formation f o r m a t i o n occurs o c c u r s 48 4 8 km southeast s o u t h e a s t of o f Kenora Kenora a n d 2) 2 ) outcropping o u t c r o p p i n q along a l o n g the t h e shore s h o r e of o f Long b n g Bay Bay and and ((figures f i g u r e s 1 and The fformation Lobstick i s ppart a r t oof f the the L o b s t i c k Bay, Bay, Lake Lake of o f the t h e Woods. Woods. The o r m a t i o n is Warciub W a r c l u b group, q r o u p I aa predominantly p r e d o m i n a n t l y metasedimentary m e t a s e d i m e n t a r y sequence, s e q u e n c e I found f o u n d in in the western the w e s t e r n portion p o r t i o n oof f the t h e Archean A r c h e a n Wabigoon subprovince s u b p r o v i n c e of o f the the Superior S u p e r i o r Province. Province. Johns et al., 1 SUPERIOR PROVINCE PROVINCE The of comprised o f Archean A r c h e a n age a g e rocks r o c k s with with The Superior S u p e r i o r Province, P r o v i n c e I comprised regional r e g i o n a l easterly e a s t e r l y trending t r e n d i n g structures, s t r u c t u r e s , extends e x t e n d s in i n Ontario O n t a r i o from from the t h e Manitoba M a n i t o b a border b o r d e r east e a s t to t o the t h e Quebec Q u e b e c border b o r d e r and and is i s overlairi o v e r l a i n to to by P Paleozoic t o the t h e south s o u t h by b y Proterozoic Proterozoic tthe h e nnorth o r t h by a l e o z o i c ssediments e d i m e n t s and a n d to The S Superior metasediments m e t a s e d i m e n t s and a n d metavolcanics. metavolcanics. The u p e r i o r Province P r o v i n c e has h a s been been subdivided s u b d i v i d e d into i n t o subprovinces s u b p r o v i n c e s based b a s e d on o n differences d i f f e r e n c e s in i n structural structural e t al., a l . , 1970). 1970). sstyles t y l e s and a n d lithology l i t h o l o g y (Stockwell ( S t o c k w e l l et These t e n d e n c y to t o decrease d e c r e a s e in i n age age T h e s e subprovinces s u b p r o v i n c e s show some tendency ffrom r o m north n o r t h to t o south s o u t h (Krogh ( K r o g h and and Davis, D a v i s I 1971 1 9 7 1 and a n d Krogh Krogh et e t al., al., and aare t o as a s the t h e Sachigo S a c h i g o subprovince, s u b p r o v i n c e I Berens Berens 11984) 9 8 4 ) and r e rreferred e f e r r e d to subprovince, River u b p r o v i n c e I Uchi Uchi subprovince, s u b p r o v i n c e , English E n g l i s h River R i v e r subprovince subprovince River s n t o the t h e Ear E a r Falls F a l l s—- Manigotagan M a n i g o t a g a n ssubprovince u b p r o v i n c e and and the the ((subdivided s u b d i v i d e d iinto Winnipeg W i n n i p e g 2River i v e r subprovince, s u b p r o v i n c e I Beakhouse, B e a k h o u s e I 1977), 1977 ) IWabigoon Wabigoon subprovince, Q u e t i c o subprovince s u b p r o v i n c e and and Abitihi A b i t i b i subprovince. s u b p r o v i n c e . The s u b p r o v i n c e I Quetico Berens B e r e n s River R i v e r and and Winnipeg W i n n i p e g River R i v e r subprovinces s u b p r o v i n c e s are a r ecomposed composed Ear Falls F a l l s—- Manigotagan Manigotagan ppredominantly r e d o m i n a n t l y oof f qgranitoid r a n i t o i d rocks r o c k s and a n d the t h e Ear The and Quetico s u b p r o v i n c e s are a r e metasedimentary m e t a s e d i m e n t a r y terranes. terranes The Q u e t i c o subprovinces remaining low r e m a i n i n g subprovinces s u b p r o v i n c e s are a r e characterized c h a r a c t e r i z e d by by comparatively c o m p a r a t i v e l y low metamorphic m e t a m o r p h i c grade g r a d e metavolcanics m e t a v o l c a n i c s and and subordinate s u b o r d i n a t e metasedimentary m e tased imentary rocks r o c k s intruded i n t r u d e d by by granitoid g r a n i t o i d batholiths. batholiths. . �107 Figure F i g u r e 1: 1: Location L o c a t i o n oof f Sioux S i o u x Narrows, Narrows, Ontario O n t a r i o with w i t h respect r e s p e c t to to that t h a t portion p o r t i o n of o f the t h e United U n i t e d States S t a t e s centered c e n t e r e d on on Duluth, D u l u t h , Minnesota. Minnesota. �_______ _____ ______ ________ _____ 108 * * * * * * * * + 4- * ***. * 4- * + * + + * ++:: + * + * * * * * + * * + * + * 4- .- + + * * + + * ** + * * + + * *++ — *::*+::::+45c USA ** **+ : * ++ +:::+ 51 * * :*1+>+*tI ——---- - + P4-S. * + + 'S * * * * * + + * * + + *_, * * * + + + + - _* + * * * H + + + + + * * * ** + + S.- + + + + + * + * 4- + + + + + * + + + 4- + + + + + + + * * * + + 4- + + ÷ ', + * + + + ::,* + + * + + + + + * * * + * * * * * * + + * * + + * * * * * * 4- * + + * + + + + + * * * * * + + + * * * + * + * * + •+ * + + + + + * + + + +_+ + + + 4- + * + * * * + + + * + + + + 4- + + + + + 4- + + + * + + + -'S + * + + + + * + + + * * + + + + + + + + + + * + * + + * + * + + * + * + + + + + + * + ++ granitoid rocks mafic plutonic rocks potassic pjütonic rocks 1::::::] metasedimentary rocks felsic metavolcanic rocks sodic plutonic rocks maf Ic metavolcanic rocks Lii gneissic granitoid rocks (unsubdivided) I F i g u r e 2: 2: Figure Location L o c a t i o n oof f the t h e Berry B e r r y River R i v e r formation f o r m a t i o n with w i t h respect respect to t o the t h egeneral g e n e r a lgeology g e o l o g yofo fthe t hwestern e w e s t e rWabigoon n Wabiqoon subprovince. subprovince. �109 - WABIGOON SUBPROVINCE SUBPROVINCE --TFre-WalqooFSTTbprovince i s aeast n e a sto t t onortheast n o r t h e a s t trending trending TWbfgoöiTUbprovince is an metavolcanic—metasediment—granitoid m e t a v o l c a n i c - m e t a s e d i m e n t - q r a n i t o i d terrane. terrane. I t is is bbounded o u n d e d on on It the by Winnipeg t h e north north b y the the W i n n i p e g River R i v e r subprovince s u b p r o v i n c e and a n d on o n the t h e south s o u t h by by the It t h e Quetico Q u e t i c o subprovince. subprovince. I t is is approximately a p p r o x i m a t e l y 200 2 0 0 km in i n width w i d t h and and is i s at a t least l e a s t 700 7 0 0 km km in i n length, l e n q t h , extending e x t e n d i n g beneath b e n e a t h Paleozoic P a l e o z o i c cover cover of o f the t h e James Bay Bay lowlands l o w l a n d s and a n d Williston W i l l i s t o n basin b a s i n to t o the t h e east e a s t and and west w e s t respectively. respectively Trowell T r o w e l 1 et e t al. a l . (1980) ( 1 9 8 0 ) studied s t u d i e d the t h e Wabigoon W a b i q o o n Suhprovince Subprovince b e t w e e n Kakagi K a k a g i (Crow) ( C r o w ) Lake L a k e and a n d Savant S a v a n t Lake L a k e and a n d made m a d e the t h e following following between observations. 1) metavolcanic—metasedimentary belts observations. 1 ) TThe h e metavolcanic-metasedimentary b e 1 ts generalgenerally 2) l y face f a c e inwards. inwards. 2 ) Thick T h i c k basal b a s a l high h i g h Mg Mq tholeiitic t h o l e i i t i c basalt basalt a s e m b l a g e s occur o c c u r at a t the t h e outer o u t e r edges e d g e s of o f the t h e greenstone g r e e n s t o n e belt. belt. 3) asemblages 3) Mixed M i x e d mafic maÂi c to t o felsic f e l s i c sequences s e q u e n c e s overlying o v e r l y i n g the t h e basal b a s a l assemblage assemblage occur o c c u r in i n the t h e internal i n t e r n a l portion p o r t i o n of o f the t h e greenstone g r e e n s t o n e belts b e l t s and a n d contain contain thick t h i c k sequences s e q u e n c e s oof f ma mafic i c fflows l o w s t that h a t are a r e mostly m o s t l y toward t o w a r d tthe h e top t o p of of the 4) t h e mixed m i x e d assemblage. assemblaqe. 4 ) Clastic C l a s t i c metasedimentary m e t a s e d i m e n t a r y rocks r o c k s are are associated mixed mafic a s s o c i a t e d with w i t h the the m i x e d ma i c to t o felsic f e l s i c portion p o r t i o n of o f the t h e meta— metaThe volcanic v o l c a n i c sequence. sequence. T h e metavolcanics m e t a v o l c a n i c s and a n d metasediments m e t a s e d i m e n t s have h a v e been been isoclinally i s o c l i n a l l y folded f o l d e d into i n t o synforms s y n f o r m s and a n d antiforms. antiforms. Available A v a i l a b l e high h i g h precision, p r e c i s i o n , U—Pb U-Pb zircon z i r c o n geochronological geochronolog i c a l investigations metavolcanic i n v e s t i g a t i o n s oof f intermediate i n t e r m e d i a t e to t o felsic felsic m e t a v o l c a n i c rocks r o c k s in in the Wabigoon the W a b i q o o n subprovince s u b p r o v i n c e suggest s u g g e s t that t h a t volcanism v o l c a n i s m occurred o c c u r r e d over over a a limited l i m i t e d time t i m e interval i n t e r v a l between b e t w e e n 2745 2 7 4 5 Ma Ma and a n d 2703 2 7 0 3 Ma Ma (Davis ( D a v i s and and Trowell, T r o w e l l , 1982; 1 9 8 2 ; Davis D a v i s and a n d Edwards, E d w a r d s , 1982, 1 9 8 2 , Davis D a v i s et e t al., a l . , 1982). 1982). Davis D a v i s and a n d Edwards E d w a r d s (1982) ( 1 9 8 2 ) have h a v e determined d e t e r m i n e d aa U—Pb U-Pb zircon z i r c o n age a q e of of 2713.9 Ma The 6.0/-4.4 Ma ffor o r the t h e Berry B e r r y River R i v e r formation. formation. T h e Warclub Warclub 271 3 . 9 ++ 6.0/—4.4 group, River s aa part, p a r t , can c a n be be q r o u p , of o f which w h i c h tthe h e Berry Berry R i v e r fformation o r m a t i o n i is . correlated c o r r e l a t e dwith w i t hthe t hAbram e Abramgroup q r o u pini the n t hDryden—Sioux e D r y d e n - S i o u x Lookout L o o k o u t area area where w h e r e aa preliminary p r e l i m i n a r y age a g e of o f 2716 2 7 1 6 Ma Ma oon n aa tuffaceous t u f f a c e o u s unit u n i t(Don (Don Davis, D a v i s , personal p e r s o n a lcommunication, c o m m u n i c a t i o n , 1983) 1 9 8 3 ) is is similar s i m i l a r to t o that t h a t age age determined These d e t e r m i n e d ffor o r the t h e Berry B e r r y River R i v e r formation. formation. T h e s e observations observations suggest s u q q e s t that t h a tthe t h Warciub e W a r c l u bgroup q r o u pis iamong s amonqthe t hyoungest e y o u n q e svolcano— t volcanosedimentary s e d i m e n t a r y sequences s e q u e n c e s in i n the t h eWabigoon W a b i g o o n subprovince. subprovince. LONG BAY LONG BAY BAY -- LOBSTICK LOBSTICK--BAY AREA AREA -.-- The T h e Long Lonq Bay Bay —- Lobstick L o b s t i c k Bay area a r e a is is within w i t h i n the t h e western western portion i s situated s i t u a t e d between b e t w e e n the the p o r t i o n of o f the t h e Wabigoon W a b i g o o n Subprovince S u b p r o v i n c e and a n d is Savant S a v a n t Lake L a k e —- Crow C r o w (Kakagi) ( K a k a q i ) Lake L a k e area a r e a studied s t u d i e d by b y Trowell T r o w e l l et e t al. al. (1980) Woods area ( 1 9 8 0 ) aand n d tthe h e cclassical l a s s i c a l Lake L a k e oof f the t h e Woods a r e a studied s t u d i e d by b y Lawson Lawson (1885) ( 1 8 8 5 ) (Figure ( F i q u r e 2). 2 ) . The T h e metavolcanic m e t a v o l c a n i c —- metasedimentary m e t a s e d i m e n t a r y rocks r o c k s are are bounded b o u n d e d by b y the t h e Dryberry D r y b e r r y Batholith B a t h o l i t h on o n the t h e northeast n o r t h e a s t and a n d the the Aulneau The A u l n e a u Batholith B a t h o l i t h on o n the t h e southwest. southwest. T h e forceful f o r c e f u l intrusion i n t r u s i o n of of these t h e s e two t w o bbatholiths a t h o l i t h s and a n d the t h e later l a t e rinternal i n t e r n a stocks l s t o c k have s h a v eproduced produced aa complex c o m p l e x s structural t r u c t u r a l pattern p a t t e r n (Figure ( F i g u r e 3). 3). A A ggeneral e n e r a l sstratigraphy t r a t i g r a p h y has h a s been b e e n developed d e v e l o p e d ffor o r the t h e area a r e a and and is Two i s outlined o u t l i n e d in i n Figure F i q u r e 4. 4. Two s stratigraphic t r a t i g r a p h i c domains d o m a i n s occur; o c c u r ; one one southwest Zonea nand to s o u t h w e s t of o f the t h ePipestone—Cameron P i p e s t o n e - C a m e r o n F Fault a u l t Zone d t the h e oother t h e r to . the To t h e northeast n o r t h e a s t (Blackburn, ( B l a c k b u r n , 1981). 1981 ) To date d a t e no n o correlation c o r r e l a t i o n has-been has- been attempted a t t e m p t e d between b e t w e e n them. them. Southwest Zone tthe S o u t h w e s t of o f the t h ePipestone—Cameron P i p e s t o n e - C a m e r o n FFault a u l t Zone h e northeast northeast facing f a c i n g Snake S n a k e Bay Bay formation f o r m a t i o nconsists c o n s i s tof s fine— o f f i n eand - a nmediurn—grained d medium-qrained mafic f l o w s , pillowed p i l l o w e d and a n d amygdaloidal a m y g d a l o i d a l flows f l o w s with w i t h horizons h o r i z o n s of of maf i c flows, autoclastic a u t o c l a s t i c breccia b r e c c i a and a n d pillow p i l l o w breccia b r e c c i a and a n d hyaloclastite h y a l o c l a s t i t e intruded intruded �Figure 3: Simplified structural geology map of the Long Bay — Lobstick Bay area. Refer to Figure 4 for the corresponding litho—stratiqraphic map. 5-2 m c CT' 4-1 c IÑ -4 H �_____________________ + F * * + + + •.' - + +4 + + fl flrnnn + + + + + + + + + +•• + + + + + + + * + + + lflt+++*+*+l +** + iay .oup \ * + * * + * + * * + + + * + + + + / * + + + 'L_ * + + + ...... I + + Point+ + y* intermediate intrusive intrusive rocks intermediate rocks inafic mafic intrusive intrusive rocks rocks metasediments and intermediate intermediate to telsic metasediments and felsic metavolcanics metavolcanics .intermediate to intermediate felsic metavolcanics to felsic metavolcanics mafic mat ic metavolcanics metavolcanics --- + + Stock + + + + Lake + . 1. - + + Viola + ,"* + + + 1-1 + + + + + 1:.:..:.:..:.:..:1 . . . * + + + + + + * + + lithologic contact 6 6 5 8 8 7 9 10 kilometres + + + + 19seke Warc!ub4O1JP,.. * + * Figure F i g u r e 4: 4: 3 + + * 2 4 - - 2- - kilometres - , 0 fault + + + + stratigraphic stratigraphic contact + + F + + F + * * + + + * + + * + + + + + F * * * + + + f * KqukLake Stck Stratigraphic S t r a t i q r a p h i c map of of the t h e Long Lonq Bay Bay —- Lobstick L o b s t i c k Bay Bay area. area. corresponding structural ffor o r tthe h e corresponding s t r u c t u r a l interpretation. interpretation. + + * + * •.,.•• : Refer Refer to t o Figure Fiqure 33 H t-' H I-1 H I-1 �112 by b y synvolcanic s y n v o l c a n i c gabbro g a b b r o sills. sills. The supracrustal s u p r a c r u s t a l rocks r o c k s northeast n o r t h e a s t of o f the t h e fault f a u l t zone z o n e are are subdivided s ubd i v i d e d into i n t o 55 informal i n f o r m a l metavolcanic—metasedimentary m e t a v o l c a n i c - m e t a s e d i m e n t a r y groups groups (Figure a r e the t h e Point P o i n t Bay Bay group, g r o u p , Populus P o p u l u s volcanics, volcanics, ( F i g u r e 4). 4 ) . They T h e y are Black B l a c k Lake L a k e volcanics, v o l c a n i c s , Gibi G i b i Lake L a k e volcanics v o l c a n i c s and a n d the t h e Warciub W a r c l u b group group which w h i c h includes i n c l u d e s the t h e Berry B e r r y River R i v e r formation. formation. The is the t h e Point P o i n t Bay Bay group g r o u p which w h i c h occurs o c c u r s around around T h e oldest o l d e s t unit u n i t is the I t consists c o n s i s t s of o f mafic m a f i c and and t h e margin m a r g i n of o f the t h e Dryberry D r y b e r r y batholith. batholith. It intermediate i n t e r m e d i a t e to t o felsic f e l s i c metavolcanics m e t a v o l c a n i c s and a n d metasediments m e t a s e d i m e n t s cut c u t by by thick t o mafic maf i c sills. s i l l s . It I t is i s overlain overlain t h i c k differentiated d i f f e r e n t i a t e d ultramafic u l t r a m a f i c to by i t s base b a s e has h a s been b e e n totally t o t a l l y removed r e m o v e d by by the the b y the t h e Warclub W a r c l u b group g r o u p and a n d its intrusion Roof i n t r u s i o n of o f the t h e Dryberry D r y b e r r y Batholith. Batholith. Roof pendants p e n d a n t s and a n d xenoliths xenoliths of o f the t h e Point P o i n t Bay Bay group q r o u p are a r e found f o u n d within w i t h i n marginal m a r g i n a l phases p h a s e s of o f the the batholith. batholith. The T h e Populus P o p u l u s volcanics, v o l c a n i c s , Black B l a c k Lake L a k e volcanics v o l c a n i c s and a n d Gibi G i b i Lake Lake volcanics v o l c a n i c s are a r e all a l l younger y o u n g e r than t h a n the t h e Point P o i n t Bay Bay group g r o u p and a n d are a r e over— overlain 4 ) . Their T h e i r mutual m u t u a l stratigraphic stratigraphic l a i n by b y the t h e Warclub W a r c l u b group g r o u p (Figure ( F i g u r e 4). relationships The a r e uncertain. uncertain. T h e Populus P o p u l u s volcanics v o l c a n i c s and a n d the t h e Black Black r e l a t i o n s h i p s are Lake L a k e volcanics v o l c a n i c s are a r e predominantly p r e d o m i n a n t l y mafic maf i c metavolcanic m e t a v o l c a n i c sequences. sequences. While W h i l e both b o t h sequences s e q u e n c e s contain c o n t a i n abundant a b u n d a n t massive m a s s i v e and a n d pillowed p i l l o w e d flows, flows, the t h e Populus P o p u l u s volcanics v o l c a n i c s also a l s o contain c o n t a i n mafic maf i c pillow p i l l o w breccia, breccia, hyaloclastite, maf i c pyroclastics p y r o c l a s t i c s and a n d intermediate i n t e r m e d i a t e flows f l o w s and and h y a l o c l a s t i t e , mafic pyroclastics. The a r e composed c o m p o s e d of o f interinterpyroclastics. T h e Gibi G i b i Lake L a k e volcanics v o l c a n i c s are mediate m e d i a t e and a n d mafic m a f i c pyroclastics p y r o c l a s t i c s with w i t h minor m i n o r mafic m a f i c flows f l o w s (Trowell, (Trowell, in i n prep.). prep.). The 4 ) overlies o v e r l i e s the t h e units u n i t s discussed discussed The Warclub W a r c l u b group g r o u p (Figure ( F i g u r e 4) above is structurally s t r u c t u r a l l y and a n d stratigraphically s t r a t i g r a p h i c a l l y complex. c o m p l e x . This This a b o v e and a n d is group 7 1 km km northeast n o r t h e a s t to t o Dryden D r y d e n where w h e r e it i t can c a n be be g r o u p can c a n be b e traced t r a c e d 71 correlated c o r r e l a t e d with w i t h the t h e Abram Abram group. g r o u p . It It consists c o n s i s t s predominantly p r e d o m i n a n t l y of of metasediments m e t a s e d i m e n t s with w i t h interbedded i n t e r b e d d e d intermediate i n t e r m e d i a t e to t o felsic f e l s i c pyro— pyroclastics. is e l a s t i c s . The T h e metasedimentary m e t a s e d i m e n t a r y portion p o r t i o n of o f the t h e Warclub W a r c l u b qroup q r o u p is compositionally North c o m p o s i t i o n a l l y varied. varied. N o r t h of o f the t h e Black B l a c k Lake L a k e volcanics v o l c a n i c s wackes wackes are a r e interbedded i n t e r b e d d e d with w i t h arenites a r e n i t e s while w h i l e south s o u t h of o f the t h e Gibi G i b i Lake Lake volcanics South v o l c a n i c s thin t h i n bedded b e d d e d arenite a r e n i t e and a n d siltstone s i l t s t o n e predominate. predominate. South of o f the t h e Black B l a c k Lake L a k e volcanics v o l c a n i c s wacke w a c k e predominates. p r e d o m i n a t e s . Thin T h i n beds b e d s of of magnetite a r e found f o u n d both b o t h north n o r t h and a n d south s o u t h of o f the t h e Black Black m a g n e t i t e ironstone i r o n s t o n e are Lake L a k e volcanics. v o l c a n i c s . The T h e variety v a r i e t y of o f lithologies l i t h o l o q i e s represent r e p r e s e n t various various depositional d e p o s i t i o n a l environments e n v i r o n m e n t s and a n d more more work w o r k is i s required r e q u i r e d to to reconstruct r e c o n s t r u c t the t h e paleoenvironment. paleoenvironment The T h e Berry B e r r y River R i v e r formation f o r m a t i o n (Figure ( F i g u r e4) 4 ) is i s aa 22 km krn thick thick sequence s e q u e n c e of o f intermediate i n t e r m e d i a t e to t o felsic f e l s i c pyroclastic p y r o c l a s t i c rocks r o c k s within w i t h i n the the Warclub Except W a r c l u b group. group. E x c e p t for f o r the t h e western w e s t e r n portion, p o r t i o n , the t h e formation formation faces 3 ) . It I t overlies, o v e r l i e s , with w i t h slight slight f a c e s uniformly u n i f o r m l y south s o u t h (Figure ( F i g u r e 3). unconformity, lower part p a r t of o f the t h e Warclub W a r c l u b group qroup u n c o n f o r m i t y , the t h e wacke w a c k e in i n the t h e lower and a n d is is overlain o v e r l a i n by by aa 20—100 2 0 - 1 0 0 mm thick t h i c k mafic m a f i c metavolcanic m e t a v o l c a n i c unit u n i t and and wacke e t al., a l . , 1984). 1 9 8 4 ) . The T h e isoclinally isoclinally w a c k e of o f the t h e Warclub W a r c l u b group g r o u p (Johns ( J o h n s et folded w e s t end e n d of o f the t h e formation f o r m a t i o n appears a p p e a r s to t o both b o t h overlie o v e r l i e and and f o l d e d west grade g r a d e laterally l a t e r a l l y into i n t o the t h e wacke w a c k e of o f the t h e Warclub W a r c l u b group. g r o u p . The T h e beddinq bedding and £0 i a t i o n planes p l a n e s have h a v e near—vertical n e a r - v e r t i c a l dips d i p s throughout t h r o u g h o u t the the a n d foliation strike s t r i k e length. length. . BERRY BERRY RIVER FORMATION FORMATION -- RIVER ThEting h e s e t t iof n g the o t tBerry h e B e rRiver r y R i v eformation r f o r m a t i o has n h a sbeen b e e noutlined outlined in I t is i s aa distinct distinct i n the t h e previous p r e v i o u s section s e c t i o n and a n d shown s h o w n in i n Figure F i g u r e4.4. It �113 u n i t of of subaqueously s u b a q u e o u s l y deposited d e p o s i t e d pyroclastics p y r o c l a s t i c s 20 2 0 km km long l o n g and a n d 22 km km unit thick. Rock thick. Rock units u n i t s were were mapped using u s i n g the t h e size s i z e classification c l a s s i f i c a t i o n of of Fisher ( 1 966 ) , making m a k i n q note n o t e of o f volcanic v o l c a n i c structures s t r u c t u r e s and a n d textures. textures. F i s h e r (1966), The T h e predominant p r e d o m i n a n t clast c l a s t and a n d matrix m a t r i x lithology l i t h o l o g y is i s both b o t h quartz— quartzfeldspar f e l d s p a r porphyry p o r p h y r y and a n d feldspar f e l d s p a r porphyry p o r p h y r y of o f dacite d a c i t e to t o rhyolite rhyolite composition. c o m p o s i t i o n . Thin, T h i n , fine—grained, f i n e - g r a i n e d , metasedimentary m e t a s e d i m e n t a r y horizons horizons composed c o m p o s e d of o f reworked r e w o r k e d pyroclastic p y r o c l a s t i c material m a t e r i a l are a r e interbedded i n t e r b e d d e d with with the t h e pyroclastics. p y r o c l a s t ics Size S i z e classification c l a s s i f i c a t i o n and a n d sorting s o r t i n g alone a l o n e did d i d not n o t provide provide sufficient s u f f i c i e n t information i n f o r m a t i o n to t o properly p r o p e r l y subdivide s u b d i v i d e the t h e sequence. sequence. Volcanic t o size s i z e and a n d sortsortV o l c a n i c textures t e x t u r e s and a n d structures, s t r u c t u r e s , in i n addition a d d i t i o n to ing, were used to develop subunits within the formation, i n g , were u s e d t o d e v e l o p s u b u n i t s w i t h i n t h e f o r m a t i o n , as a s outoutlined These l i n e d in i n Table T a b l e 1. 1. T h e s e subunits s u b u n i t s consist c o n s i s t of o f diagnostic d i a g n o s t i c vertical vertical sequences s e q u e n c e s of o f rock r o c k types t y p e s (after ( a f t e r Fisher, F i s h e r , 1966) 1 9 6 6 ) and a n d primary primary structures s t r u c t u r e s which w h i c h permit p e r m i t definition d e f i n i t i o n of o f distinct d i s t i n c t depositional depositional events. For events. F o r example, e x a m p l e , using u s i n g the t h e model m o d e l of o f Fiske F i s k e and a n d Matsuda M a t s u d a (1964, (1964, . their t h e sequence s e q u e n c e oof f primary p r i m a r y sstructures t r u c t u r e s expected e x p e c t e d in i n aa t h e i r Figure F i g u r e 66)) ,, the subaqueous m a s s i v e lower lower portion, p o r t i o n , which which s u b a q u e o u s ppyroclastic y r o c l a s t i c flow f l o w are: a r e : aa massive fines terms of o f non—vesicular n o n - v e s i c u l a r material m a t e r i a l and a n d an a n upper upper f i n e s upward u p w a r d in i n terms laminated t w o portions p o r t i o n s are are l a m i n a t e d portion, p o r t i o n , which w h i c h also a l s o fines f i n e s upward. u p w a r d . The The two often d o u b l y graded g r a d e d sequence. sequence. o f t e n referred r e f e r r e d to t o as a s aa doubly Examination E x a m i n a t i o n of o f aa sequence s e q u e n c e in i n the t h eBerry B e r r y River R i v e r formation formation mapped y r o c l a s t i c bbreccia r e c c i a wwith i t h ttuff u f f interbeds i n t e r b e d s in i n aapurely purely mapped asasp pyroclastic size s i z e and a n d sorting s o r t i n g classification c l a s s i f i c a t i o n (Fisher, ( F i s h e r , 1966) 1 9 6 6 ) outlined o u t l i n e d the the following f o l l o w i n g vertical v e r t i c a l sequence s e q u e n c e from f r o m base b a s e to t o top: t o p : 2.5 2 . 5 mm of o f homolithic homolithic c l a s t s ) pyroclastic p y r o c l a s t i c breccia b r e c c i a grading g r a d i n g inin( q u a r t z - f e l d s p a r porphyry p o r p h y r y clasts) (quartz—feldspar to t o lithic l i t h i c lapilli l a p i l l i tuff; t u f f ; clasts c l a s t s are a r e subangular s u b a n g u l a r and a n d quartz—feldspar quartz-feldspar tuff i s then t h e n overlain o v e r l a i n by b y 33 mm of o f moderately moderately t u f f matrix m a t r i x supported; s u p p o r t e d ; this t h i s is sorted, b e d d i n g is is s o r t e d , thickly t h i c k l y laminated l a m i n a t e d quartz q u a r t z feldspar f e l d s p a r tuff; t u f f ; bedding distinct d i s t i n c t and a n d regular r e g u l a r in i n this t h i s portion. portion. T h i s coarse coarse to t o fine fine This sequence s e q u e n c e is is then t h e n overlain o v e r l a i n by b y another a n o t h e r similar s i m i l a r assemblage. a s s e m b l a g e . The The above a b o v e vertical v e r t i c a l sequence s e q u e n c e of o f primary p r i m a r y structures s t r u c t u r e s and a n d rock r o c k type type compares ( 1 9 6 4 ) model m o d e l and a n d the the c o m p a r e s favourably f a v o u r a b l y with w i t h Fiske F i s k e and a n d Matsuda's M a t s u d a ' s (1964) sequence s e q u e n c e is i s most m o s t likely l i k e l y aa subaqueous s u b a q u e o u s pyroclastic p y r o c l a s t i c flow f l o w (Figure ( F i g u r e 5). 5). Individual I n d i v i d u a l subunits s u b u n i t s cannot c a n n o t be b e traced t r a c e d beyond b e y o n d single s i n g l e outcrops outcrops but b u t they t h e y do d o form f o r m unique u n i q u e packages p a c k a g e s that t h a t can c a n be b e traced t r a c e d for f o r considerconsiderable a b l e distance. d i s t a n c e . Subunits S u b u n i t s representing r e p r e s e n t i n g aa single s i n g l e depositional depositional process s u b a q u e o u s pyroclastic pyroclast ic p r o c e s s include i n c l u d e debris d e b r i s flow f l o w deposits, d e p o s i t s , subaqueous flow f l o w deposits, d e p o s i t s , block b l o c k and a n d ash a s h flow f l o w deposits, d e p o s i t s , fall—out f a l l - o u t tuff tuff deposits d e p o s i t s and a n d lapilli l a p i l l i tuffs t u f f s and a n d ash a s h flow f l o w tuff. t u f f . Table T a b l e 1 lists l i s t s the the criteria c r i t e r i a used u s e d to t o identify i d e n t i f y subunits s u b u n i t s within w i t h i n the t h e Berry B e r r y River River formation, f o r m a t i o n , and a n d aa brief b r i e f description d e s c r i p t i o n of o f each e a c h subunit s u b u n i t in i n the the formation is listed 1i s t e dbelow. below. f o r m a t i o n is 1 Debris Debris Flow F l o w Deposits D e p o s i t s (Stop ( S t o p 7) 7) Debris D e b r i s flow f l o w deposits d e p o s i t s within w i t h i n the t h e Berry B e r r y River R i v e r formation f o r m a t i o n are are compositionally c o m p o s i t i o n a l l y bimodal b i m o d a l (clasts ( c l a s t s of o f feldspar f e l d s p a r porphyry; p o r p h y r y ; quartz— quartzfeldspar f e l d s p a r porphyry) p o r p h y r y ) to t o heterolithic, h e t e r o l i t h i c , (clasts ( c l a s t s of o f feldspar f e l d s p a r porphyry; porphyry; quartz—feldspar q u a r t z - f e l d s p a r porphyry; p o r p h y r y ; fine f i n e grained g r a i n e d massive m a s s i v e intermediate intermediate volcanics; v o l c a n i c s ; felsic f e l s i c volcanics; v o l c a n i c s ; mafic maÂi c volcanics v o l c a n i c s and a n d sediments) sediments) matrix t o lapilli l a p i l l i tuffs. t u f f s . These T h e s e subunits subunits m a t r i x supported s u p p o r t e d tuff t u f f breccias b r e c c i a s to are a r e thick, t h i c k , massive, m a s s i v e , and a n d poorly p o o r l y bedded. b e d d e d . The T h e matrix m a t r i x in i n any a n y one one location t o the t h e majority m a j o r i t y of o f framework framework l o c a t i o n corresponds c o r r e s p o n d s in i n composition c o m p o s i t i o n to clasts. c l a s t s . The T h e debris d e b r i s flow f l o w deposits d e p o s i t s are a r e mostly m o s t l y tuff—breccia t u f f - b r e c c i a to to �T a b l e 1: -Table 1: Berry River Subunits_jdentified S u b u n i t s i d e n t i f i e d iin n tthe he B erry R i v e r formation f o r m a t i o n aand n d their t h e i r characteristics. characteristics. Flow Deposits D eposits Subaqueous S ubaqueous Pyroclastic P y r o c l a s t ic Flow F l o w Deposits Deposits Block B l o c k and and Ash Flow Ash Flow Depos D e p o sits its Fall F a l l Out Out Deposits D eposits Ash Flow Tuff T uff Reworked Debris D ebris Flow F l o w Deposits Deposits Bedd B e d d ing ing md i n distinct istinct ddistinct istinct distinct distinct ddistinct istinct aabsent bsent distinct distinct Grain! G rain/ clast c l a s t size size ccoarse oarse coarse coarse to t o fine fine ccoarse oarse to fine fine medium to fine fine coarse coarse to fine fine Sort S o r ti i fly ng poor poor moderate m oderate to t o poor poor ppoor oor moderate m o d e r a t e to to good good moderate to m o d e r a t e to ppoor oor mod m o dera e r att ee to t o good Grad G r a d ing ing aabsent b s e n t to to normal normal nnormal o r m a l and and rreverse everse aabsent b s e n t to to normal normal normal norm a 1 to to reverse reverse absent absent nnormal ormal Composition Composition to bbimodal i m o d a l to hheterol e t e r o l iithic thic bbimodal imod a 1 homolithic homo1 it h i c bimodal b imod a 1 qquart u a r t zz— feldspar feldspar pporphyry orphyry Pumice Pumice no yes yes yes Anyn g ulual ar rit A i t yy s uubround bround ssu ubround bround s ubang uular s ubang lar to t o angular angular ssubround u b r o u n d to to subany s u b a n g ular ular gas g a s escape escape features features rregularity e g u l a r i t y of of bbedd e d d ing i ng Subunit S ubunit Characteristics C haracteristics Debris D ebris 1Ñ I-' H h ' Unique U n i q u e features features ddouble o u b l e grading grading yes S s ubang uull aarr heterol h e t e r o l ithic ithic no no ssubround u b r o u n d to to rround ound iinterbedded nterbedded with w i t h wacke wacke �115 lapilli—tuff, l a p i l l i - t u f f , but b u t tuft t u f f in i n gradational g r a d a t i o n a l contact c o n t a c t with w i t h the t h e coarse coarse part p a r t of o f debris d e b r i s flow f l o w deposits d e p o s i t s forms f o r m s aa fine—grained f i n e - g r a i n e d top t o p in i n distal distal debris d e b r i s flow f l o w deposits. deposits. T h e debris d e b r i s flows f l o w s described d e s c r i b e d here h e r e are are The similar s i m i l a r to t o those t h o s e described d e s c r i b e d by b y Tasse T a s s e et e t al. a l . (1978) ( 1 9 7 8 ) in i n the t h e Abitibi Abitibi ss uubprov b p r o v iince. nce. Subaqueous a n d 11) 11) S u b a q u e o u s Pyroclastic P y r o c l a s t i c Flow F l o w Deposits D e p o s i t s (Stops ( S t o p s 99 and Subaqueous S u b a q u e o u s pyroclastic p y r o c l a s t i c flow f l o w deposits d e p o s i t s similar s i m i l a r to t o those those o r i g i n a l l y described d e s c r i b e d by by Fiske F i s k e and a n d Matsuda M a t s u d a (1964) ( 1 9 6 4 ) occur o c c u r in i n the the originally Berry B e r r y River R i v e r formation. f o r m a t i o n . Massive, M a s s i v e , compositionally compos i t i o n a l l y homolithic h o m o l i t h i c to to bimodal, b i m o d a l , tuft t u f f breccia b r e c c i a bases b a s e s are a r e overlain o v e r l a i n by b y caps c a p s of o f thickly thickly laminated o r quartz—feldspar q u a r t z - f e l d s p a r crystal c r y s t a l tuft. tuff T h e massive massive l a m i n a t e d feldspar f e l d s p a r or The portion p o r t i o n of o f the t h e flow f l o w is i s graded g r a d e d and a n d the t h e thickly t h i c k l y laminated l a m i n a t e d tuffs t u f f s are are subtly s u b t l y graded. graded. T h e s e subunits s u b u n i t s are a r e distinctly d i s t i n c t l y bedded b e d d e d with w i t h wellwellThese preserved p r e s e r v e d base b a s e and a n d upper u p p e r contacts. contacts. . Block B l o c k and a n d Ash Ash Flow F l o w Deposits D e p o s i t s (Stops ( S t o p s 33 and a n d 7) 7) AA block b l o c k and a n d ash a s h flow f l o w deposits, d e p o s i t s , aa product p r o d u c t of o f explosive explosive volcanism, v o l c a n i s m , consists c o n s i s t s of o f unsorted u n s o r t e d ash a s h deposits d e p o s i t s containinq c o n t a i n i n g large, large, generally g e n e r a l l y non—vesicular, n o n - v e s i c u l a r , jointed j o i n t e d cognate c o g n a t e blocks b l o c k s which w h i c h can c a n exceed exceed 55 m m in i n diameter d i a m e t e r (Fisher, ( F i s h e r , 1982). 1 9 8 2 ) . Block B l o c k and a n d ash a s h flow f l o w deposits d e p o s i t s in in the c pyrot h e Berry B e r r y River R i v e r formation f o r m a t i o nare a r ethickly—bedded, t h i c k l y - b e d d e d , homolithic h o m o l i t h i pyro— clastic e l a s t i c breccias b r e c c i a s that t h a texhibit e x h i b i tgrading. g r a d i n g . Thin T h i n tuff t u f f zones z o n e s are are occasionally as part o c c a s i o n a l l y preserved p r e s e r v e d as p a r t of o f these t h e s eblock b l o c k and a n d ash a s h flow flow deposits. d e p o s i t s . These T h e s e ttuff u f f zones z o n e s represent r e p r e s e n t either e i t h e r ash a s h cloud c l o u d deposits deposits or o r ground g r o u n d surge s u r g e deposits. d e p o s i t s . The T h e depositional d e p o s i t i o n a l characteristics characteristics displayed terms of o f the the d i s p l a y e d by b y these t h e s e deposits d e p o s i t s can c a n be b e explained e x p l a i n e d in i n terms depositional e t al. a l . (1973). (1973). d e p o s i t i o n a l model m o d e l proposed p r o p o s e d by b y Sparks S p a r k s et Fall—Out 11) F a l l - O u t Deposits D e p o s i t s (Stop ( S t o p 99 and a n d 11) Fisher F i s h e r and a n d Schmincke S c h m i n c k e (1984, ( 1 9 8 4 , their t h e i r Figure F i g u r e 7—1) 7-1 ) outlined o u t l i n e d the the characteristics c h a r a c t e r i s t i c s of o f submarine s u b m a r i n e fall—out f a l l - o u t tephra. t e p h r a . Characteristics C h a r a c t e r i s t i c s of of the t h e deposits d e p o s i t s formed f o r m e d in i n such s u c h an a n environment e n v i r o n m e n t preserved p r e s e r v e d in i n the the A r c h e a n are: a r e : thickness t h i c k n e s s of o f single s i n g l e layers l a y e r s commonly commonly less l e s s than t h a n 50 50 cm; cm; Archean sorting s o r t i n g good g o o d to t o poor; p o o r ; plane p l a n e parallel p a r a l l e l beds; b e d s ; normal n o r m a l gradinq g r a d i n q from from crystal c r y s t a l and a n d lithic l i t h i c rich r i c h bases b a s e s to t o shard s h a r d rich r i c h tops; t o p s ; and a n d grading grading may may be b e inverse i n v e r s e if i f pumice p u m i c e is is present. present. Fall—out a r e thick thick F a l l - o u t deposits d e p o s i t s in i n the t h e Berry B e r r y River R i v e r formation f o r m a t i o n are sub—units t h i c k l y laminated l a m i n a t e d to t o thinly t h i n l y bedded bedded s u b - u n i t s of o f interbedded, i n t e r b e d d e d , thickly crystal c r y s t a l tuft t u f f and a n d pumice p u m i c e crystal c r y s t a l lapilli l a p i l l i tuft. t u f f . Although A l t h o u q h bedding beddinq is i s regular r e g u l a r and a n d distinct, d i s t i n c t , contacts c o n t a c t s between b e t w e e n individual i n d i v i d u a l beds b e d s are are gradational. i s recessively r e c e s s i v e l y weathered w e a t h e r e d and a n d darker d a r k e r than than g r a d a t i o n a l . The The pumice p u m i c e is the t h e crystal c r y s t a l matrix. matrix. Ash Ash Flow F l o w Tuff T u f f Deposits D e p o s i t s (Stops ( S t o p s 44 and a n d 10) 10) Ross Ross and a n d Smith S m i t h (1961) ( 1 9 6 1 ) have h a v e defined d e f i n e d ash a s h flow f l o w tuft t u f f as a s consolconsolidated i d a t e d deposits d e p o s i t s of o f volcanic v o l c a n i c ash a s h resulting r e s u l t i n g from f r o m the t h e ash a s h flow flow eruptive e r u p t i v e process. p r o c e s s . They T h e y define d e f i n e the t h e ash a s h flow f l o w process p r o c e s s as a s aa turbuturbulent l e n t mixture m i x t u r e of o f gas g a s and a n d pyroclastic p y r o c l a s t i c materials m a t e r i a l s of o f high h i q h temperature temperature ejected e j e c t e d explosively e x p l o s i v e l y from f r o m aa crater c r a t e r or o r fissure, f i s s u r e , that t h a t travels t r a v e l s swiftswiftly l y down down the t h e slopes s l o p e s of o f aa volcano v o l c a n o or o r along a l o n g the t h e ground g r o u n d surface. surface. Ash Ash flow f l o w tuft t u f f deposits d e p o s i t s of o f varied v a r i e d thicknesses t h i c k n e s s e s are a r e found found throughout t h r o u g h o u t the t h e Berry B e r r y River R i v e r formation. f o r m a t i o n . They T h e y are a r e massive, m a s s i v e , homohomogeneous, fine—grained quartz—feldspar porphyry. Minor variations p o r p h y r y . M i n o r v a riations geneous, f ine-grained quartz-f eldspar �116 116 ERUPTIVE ERUPTIVE EVENTS EVENTS . - end! DEPOSITS DEPOSITS z mudstone mudstone 0 I— .0 ci turbidity turbidity currents, currents, fine fine ash, ash, minor minor pumice pumice lapilli lapilli LU 33- 0 LU I- z , - pumice pumice lapilli, lapilli, fine fine crystals crystals -J C S 0 0 LU subaqueous pyroclastic flow dense d e n s e fragments, fragments, large large crystal crystal fragments fragments . - A beginning \ pumice pumice fragments fragments in in ash a s hand and crystal c r y s t a l matrix matrix z 0 0 aLU 0-J LU lithic lithic and and pumice pumice fragments fragments fine fine ash ash F i g u r e 5: 5: Figure Schematic S c h e m a t i c drawings d r a w i n g s of o f aa submarine s u b m a r i n e eruption eruption producing p r o d u c i n g subaqueous s u b a q u e o u s pyroclastic p y r o c l a s t i c flows, f l o w s , and and subsequent s u b s e q u e n t appearance a p p e a r a n c e of o f the t h e deposits d e p o s i t s of o f such s u c h an an eruption e r u p t i o n (Easton ( E a s t o n and a n d Johns, J o h n s , in i n press). press). C) is C) Beginning B e g i n n i n g of o f eruption. e r u p t i o n . Vesiculating V e s i c u l a t i n g magma magma is Some erupted e r u p t e d into i n t o sea s e a water. water. Some fine f i n e ash a s h may may be be deposited d e p o s i t e d near n e a r the t h e vent. vent. Submarine B) B ) Climax C l i m a x of o f eruption. eruption. S u b m a r i n e eruption e r u p t i o n column column c a r r i e d much much ddebris e b r i s hhigh i g h into i n t o suspension. s u s p e n s i o n . Sorting Sorting carried splits s p l i t s the t h e debris d e b r i s into i n t ovarious v a r i o u s fractions. fractions. Buoyant Buoyant pumice d e n s e fragments, f r a g m e n t s , llarge a r g e crystals c r y s t a l s and and p u m i c e f floats; l o a t s ; dense settle around the compact c o m p a c t ppumice u m i c e l lapilli a p i l l i s e t t l e a r o u n d t h e vent, v e n t , and and a r e transported t r a n s p o r t e d llaterally a t e r a l l y in i n aa subaqueous subaqueous are Most flow. Most aash s h remains r e m a i n s in i n suspension. suspension. pyroclastic -p -y r o c l a s t i c flow. Steady pyroclastic of eruption. A) A ) End End o f e r u p t i o n . S t e a d y p y r o c l a s t i c flow f l o w ceases ceases as a s amount a m o u n t of o f erupted e r u p t e d material m a t e r i a l decreases d e c r e a s e s and a n d is is Later replaced r e p l a c e d by b y turbidity t u r b i d i t y current c u r r e n t flow. flow. Later turbidity currents contain finer and less t u r b i d i t y c u r r e n t s c o n t a i n f i n e r a n d l e s s dense d e n s e ash ash t h a t has h a s settled s e t t l e d from f r o m suspension. suspension. that As A s shown s h o w n in i n the t h e right—hand r i g h t - h a n d side s i d e of o f the t h e figure, f i g u r e , an an important i m p o r t a n t characteristic c h a r a c t e r i s t i c of o f subaqueous s u b a q u e o u s pyroclastic pyroclastic Each deposits d e p o s i t s are a r e their t h e i r doubly—graded d o u b l y - g r a d e d nature. nature. E a c h bed bed is graded, and the beds at the base of the is g r a d e d , a n d t h e b e d s a t t h e b a s e o f t h e sequence sequence contain c o a r s e r and a n d denser d e n s e r ash a s h than t h a n the t h e beds b e d s at a t the the c o n t a i n coarser Modified from Fiske and top t o p of o f the t h e sequence. sequence. M o d i f i e d from F i s k e and Matsuda M a t s u d a (1964) ( 1 9 6 4 ) and a n d Fiske F i s k e (1969). (1969). > C/) C/) �117 w i t h i n aa thicker t h i c k e r layer l a y e r indicates i n d i c a t e s deposition d e p o s i t i o n by b y aa number n u m b e r of of within separate s i n g l e cooling c o o l i n g unit. unit. s e p a r a t e events e v e n t s forming f o r m i n g aa single Petrography Petrography T h i n section s e c t i o n examination e x a m i n a t i o n of o f finer f i n e r grained g r a i n e d portions p o r t i o n s of o f the the Thin t o various v a r i o u s degrees d e g r e e s and a n d much f o r m a t i o n shows s h o w s recrystallization r e c r y s t a l l i z a t i o n to formation a 1 t e r a t i o n with w i t h secondary s e c o n d a r y carbonate, c a r b o n a t e , sericite s e r i c i t e and a n d epidote. e p i d o t e . The The alteration a n g u l a r i t y of o f ash—sized a s h - s i z e d crystals c r y s t a l s and a n d lithic l i t h i c fragments f r a g m e n t s can c a n often often angularity be b e observed o b s e r v e d but b u t generally g e n e r a l l y the t h e recrystallization r e c r y s t a l l i z a t i o n and a n d schistosity schistosity has destroyed all primary features. has destroyed a l l primary features. Geochemistry G e o c h e m i s t r y oof f the t h e Berry B e r r y River R i v e r Formation Formation Table l i s t s 20 2 0 whole w h o l e rock r o c k analyses a n a l y s e s of o f finer f i n e r grained grained T a b l e 2 lists clastic c l a s t i c samples s a m p l e s of o f the t h e Berry B e r r y River R i v e r formation f o r m a t i o n carried c a r r i e d out o u t by b y the the Geoscience G e o s c i e n c e Laboratories, L a b o r a t o r i e s , Ontario O n t a r i o Geological G e o l o g i c a l Survey, S u r v e y , Toronto. Toronto. According A c c o r d i n g tto o the t h e AFM AFM t ternary e r n a r y ddiagram i a g r a m oof f Irvine I r v i n e and a n d Baraqar B a r a q a r (1971) (1971) arid a n d the t h e Al—Fe—Ti—Mg Al-Fe-Ti-Mg m o l emolecular c u l a r p r o proportion p o r t i o n t eternary r n a r y ddiagram i a g r a m of of (1976), ( 1 9 7 6 ) , tthe h e ppyroclastic y r o c l a s t i c rocks r o c k s have h a v e caic—alkalic c a l c - a l k a l i c affinities a f fi n i t i e s (Figure T h e single s i n g l e high—magnesium h i q h - m a g n e s i u m tholeiitic t h o l e i i t i c basalt b a s a l t is is from from ( F i q u r e 6). 6 ). The the t h e thin t h i n metavolcariic m e t a v o l c a n i c unit u n i t capping c a p p i n g the t h e formation. formation. T h e clasclasThe sification s i f i c a t i o n schemes s c h e m e s of o f Irvine I r v i n e and a n d Baragar 2 ) and and B a r a g a r (1971) ( 1 9 7 1 ) (Table ( T a b l e 2) Jensen J e n s e n (1976) ( 1 9 7 6 ) (Figure ( F i g u r e 6) 6 ) respectively r e s p e c t i v e l y class c l a s s the t h e samples s a m p l e s as a s dacite dacite and rhyolite. No discernable trend was noted in the major and r h y o l i t e . No d i s c e r n a b l e t r e n d was n o t e d i n t h e m a j o r element The e l e m e n t chemistry c h e m i s t r y with w i t h respect r e s p e c t to t o stratigraphic s t r a t i g r a p h i c height. height. The close c l o s e c l u s t e r i n g o f t h e p o i n t s p l o t t e d i n F i g u r e 6 may i n d i c a t e a similar s i m i l a r magma magma s source o u r c e f for o r aall l l the t h epyroclastic p y r o c l a s t i csub—units. sub-units Figure F i g u r e 66 includes i n c l u d e s an a n AFM AFM t ternary e r n a r y diagram d i a g r a m (Irvine ( I r v i n e and and Baragar, B a r a g a r , 1971) 1 9 7 1 ) and a n d an a n Al—Fe—Ti—Mg Al-Fe-Ti-Mg molecular m o l e c u l a r proportion p r o p o r t i o n ternary ternary diagram (Jensen, 1976) of metasedimentary and metavolcanic d i a g r a m (J e n s e n , 1976 ) o f m e t a s e d i m e n t a r y a n d m e t a v o l c a n i c rocks rocks from f r o m the t h e rest r e s t of o f the t h e Warclub W a r c l u b group g r o u p within w i t h i n the t h e Long Long Bay Bay —- Lobstick Lobstick Bay Bay area. a r e a . Data D a t a for f o r these t h e s e plots p l o t s are a r e found f o u n d in i n Johns J o h n s (in ( i n prep) prep). These T h e s e plots p l o t s are a r e included i n c l u d e d to t o allow a l l o w comparison c o m p a r i s o n between b e t w e e n the t h e Berry Berry River R i v e r formation f o r m a t i o n and a n d the t h e metasediments m e t a s e d i m e n t s and a n d metavolcanics m e t a v o l c a n i c s of o f the the rest r e s t of o f the t h e Warclub W a r c l u b group group Jensen Jensen clustering of the points plotted in Figure 6 may indicate a . . FACIES FAC I E S MODELS MODELS Historically, H i s t o r i c a l l y , mapping m a p p i n g of o f Archean A r c h e a n pyroclastic p y r o c l a s t i c rocks r o c k s has has supplied d a t a to t o understand u n d e r s t a n d complex c o m p l e x stratigraphy. stratigraphy. s u p p l i e d insufficient i n s u f f i c i e n t data Figure s h o w s that t h a t the t h e complexity c o m p l e x i t y of o f volcanic v o l c a n i c stratigraphy stratigraphy F i q u r e 77 shows depends d e p e n d s on o n the t h e location l o c a t i o n of o f the t h e section. s e c t i o n . Mapping M a p p i n q by b y clast c l a s t size size parameters p a r a m e t e r s only o n l y will w i l l not n o t prove p r o v e useful u s e f u l in i n developing d e v e l o p i n g map map units u n i t s and and facies It f a c i e s models. models. I t is i s ddifficult i f f i c u l t to t o compare c o m p a r e ancient a n c i e n t and a n d modern modern pyroclastic p y r o c l a s t i c sequences s e q u e n c e s without w i t h o u t aa clear c l e a r idea i d e a of o f stratigraphy s t r a t i g r a p h y and and using u s i n g facies f a c i e s analysis a n a l y s i s aa stratigraphic s t r a t i g r a p h i c context c o n t e x t can c a n be b e developed. developed. Discrete D i s c r e t e packages p a c k a g e s of o f pyroclastic p y r o c l a s t i c subunits s u b u n i t s can c a n he b e traced t r a c e d and and correlated c o r r e l a t e d allowing a l l o w i n g for f o r the t h e development d e v e l o p m e n t of o f facies f a c i e s models. models. Through T h r o u g h development d e v e l o p m e n t of o f stratigraphy, s t r a t i g r a p h y , facies, f a c i e s , and a n d subunits s u b u n i t s within within Archean A r c h e a n pyroclastic p y r o c l a s t i c sequences s e q u e n c e s comparisons c o m p a r i s o n s can c a n be b e made with w i t h other other Archean pyroclastic sequences and they can then be compared A r c h e a n p y r o c l a s t i c s e q u e n c e s a n d t h e y c a n t h e n b e c o m p a r e d with with younger y o u n g e r pyroclastics p y r o c l a s t i c s thus t h u s assisting a s s i s t i n g in i n the t h e development d e v e l o p m e n t of o f paleo— paleoenvironmental e n v i r o n m e n t a l models m o d e l s for f o r Archean A r c h e a n volcanism. volcanism. Facies are based on a number F a c i e s a r e b a s e d o n a n u m b e r of o f parameters p a r a m e t e r s described d e s c r i b e d in in Fisher and Schmincke (1984): position relative to source, F i s h e r a n d S c h m i n c k e ( 1 9 8 4 ) : p o s i t i o n r e l a t i v e t o source, environment e n v i r o n m e n t of o f deposition d e p o s i t i o n and a n d primary p r i m a r y composition. composition. A - �Si02 52 55 55 500 4 I IÑ Proximal Distal 3 0 -4'44 CCJ w c E-i 0 Ll X !a '^ Tuft Ash Flow 0 3 4 Proximal "3 -4 E "3 0 Ll 0 Distal X 4 w &-i w c El Tuft Ash Flow .^ "3 r-1 E "3 Â¥4J 0 -4 L-i 0 X in Distal Proximal— Dacite 84 70 4 40 430 .-- 75 49 2 45 305 6 3 414-1 CCJ w 3 c El Tuft Ash Flow Rhyolite . 5 7 10 8 8 6 360 0.54 0.06 1.00 99.45 0.12 0.44 0.03 17.90 0.42 1.02 0.55 1.67 5.33 1.86 0.37 0.04 69.10 IÑ "3 Proximal Dacite 45 36 4 30 355 5 6 7 17 9 7 6 260 30 45 40 35 285 5 6 14 6 7 5 35 810 0.95 0.03 1.70 99.44 0.01 0.86 0.06 0.92 1.23 0.41 3.03 4.49 2.01 0.36 0.08 68.10 16.90 93.94319 49. 43213 83-GWJ 4172 Dacite Proximal Ash Flow IÑ Dacite 28 45 20 35 370 4 18 8 5 5 60 270 0.96 0.04 1.90 99.63 0.01 1.43 0.04 0.72 1.30 0.73 5.10 4.16 0.73 0.34 0.07 67.40 16.60 93.94560 83-GWJ 4173 49.42902 - -—- 4._______ 0.63 0.06 1.10 99.48 0.00 0.87 0.03 17.30 0.77 1.17 0.76 4.03 4.04 1.00 0.29 0.03 68.50 0 4 w tn w c E-i Tu f f a u [fl c 11 "3 .-I u u > tn 0 "3 Facies 0 Dacite 24 65 2 30 370 4 6 13 15 17 7 1 350 0.62 0.07 1.20 99.44 0.00 0.71 0.05 2.55 6.05 1.08 0.42 0.06 1.53 0.80 66.40 18.30 0.80 93.99126 49.42917 93.94431 662 82-GWiJ -3' Vocanic ... 12 4 5 8 320 0.32 0.07 1.00 99.29 0.02 0.65 0,06 0.33 0.03 1.61 2.27 4.90 0.34 0.34 0.95 70.30 17.10 93.98581 611 49. 44484 82-GWJ 0 in Dacite 48 45 2 35 490 5 12 28 8 5 320 0.98 0.12 1.60 99.86 0.01 1.06 0.05 16.80 0.73 1.39 0.49 2.34 4.95 1.32 0.29 0.03 69.30 93.94540 601 49. 44003 82-GWJ coin CM -7 Dacite 45 7 38 35 420 9 10 6 9 370 98.53 0.11 1.60 0.44 0.01 1.06 0.07 4.52 1.38 0.29 0.06 3.78 0.76 1.85 0.40 67.70 16.10 -G NJ Proximal Rhyodacite 45 32 22 125 60 3 51 6 10 8 620 0.05 1.20 99.55 1.51 0.01 0.18 0.04 0.08 0.81 2.95 1.26 1.87 73.20 16.50 0.33 0.89 0.37 93.94582 49. 42833 4174 83-GWJ in m ^' Irv me and Baragar rock name Andesite . 6 12 16 8 10 320 98.66 1.02 0.11 2.90 0.01 1.92 0.06 0.39 2.58 0.95 5.17 4,44 1.98 0.35 0.08 61.20 18.40 49.43382 93.97664 82 491 49. 43269 m Zr Zn I V Rb Sr Pb Sc Nd Ni Nb Li Co Cr Cu Ba Be Ce Total H20 LOl U20 S CO2 MnO P205 Ti02 1(20 MgO CaO Na20 FeO A1203 Fe203 94.12201 WElAJ -c Lonq itude i n h a ) 169 0 49. 48657 0 J 82-GWJ E Latitude A 81 -GWJ E c-0 5 0 2054 49.45833 94.07147 Q-GO 81 -GWJ 2050 O a No. Chemical analyses of samples from the Berry River formation (Geoscience Laboratories, Ontario Geological Survey, Toronto). The Irvine and Baragar (1971) rock name and the volcanic facies designation are at the bottom of the table. HI-AJ Sample Table 2: in (N 4 .ft "3 E 0 Ll & x .1-i "3 E Ll & 0 3 3 -4 E Ll & 0 0 2 .^ AJ in & 3 3. 3 3. Â¥ & I.- "3 .-I E "3 à n in & Co �Table Table 2 2 cont. cont. SSample a m p l e No. No. Latitude Latitude Lon2itude --o n g i t u d e L Si02 Si02 A1203 A1203 Fe203 Fe203 FeO MgO M gO Ca0 cao Na20 Na 20 K20 K20 Ti02 Ti02 p205 P 2° MriO MnO cCO2 o2 sS H^o"*" H20 H20 H20" LOl LO1 Total Total Ba Be Be Ce Ce Coo C Cr cr cCuu Lii L Nb Nd Nii N Pb Pb sScc Sr sr 83-GWJ 4176 49. 442677 49. 2677 993.95789 3 . 9 5 78.9 . 49. 43636 93.93486 67.10 67.10 50.20 14.50 68.90 0.644 0.6 1.85 1. 8 5 00.83 .83 3.09 3.09 44.60 .60 2.08 2.08 00.36 .36 0. 10 0. 10 00 05 05 1.34 1.34 00.02 .02 00.92 .92 0.06 0.06 22.20 .20 999.04 9.04 1.84 0.82 1.44 16.00 16.00 580 580 1 75 75 66 66 5 5 10 10 88 1 93 16.50 8.43 0.78 3.41 3.87 1.74 0.39 0.08 0.03 0.72 5.56 10.20 2 98 0.15 1.27 0. 12 0.18 2.00 0.21 0.01 0.86 0.06 1.30 99.61 1. 10 0.06 2.70 98.80 390 90 1 55 83—GWJ 5282 83—GwJ 5283 83—GWJ 49. 43636 49. 44095 93 .9287393.99055 66.00 15.80 1.57 69.30 15.70 0.29 5286 49. 44597 83-GWJ 5294 49. 44426 93.9892493.98683 66.30 16.90 0.53 65.40 17.80 1.11 1.65 2.13 1.65 1.78 1.41 1.30 0.60 4.71 4.72 1.30 0.45 1.19 3.78 4.81 1.94 0.41 3.77 5.06 1.29 0.40 0. 13 0.06 1.56 0.01 0.75 0.05 1.80 99.51 320 3.80 3.61 1.37 0.40 0.08 0.05 0.30 0.02 1.07 0.09 1.20 99.51 0. 10 0.08 1.06 0.01 0.08 0.05 0.56 0.02 1.70 98.96 0.06 0.01 0.78 0.04 0.60 99.27 64.80 6 4.80 64.10 0.82 0. 82 00.28 .28 3.36 3. 36 44.68 .68 1.86 1. 86 0.41 0.4 1 0.08 0.08 0.03 0.03 0.54 0.54 0.01 0.01 0.73 0.73 0.02 0.02 1.20 1 .20 100.08 1 00.08 1.58 1. 58 0.83 0 .83 5.14 5. 14 4.80 4 .80 1.59 1.59 0.42 0 .42 00.09 .09 0.10 0. 10 2.02 2 .02 00.01 .01 00.77 .77 00.07 .07 2.40 2. 40 999.76 9.76 0.96 16.30 1 6 . 30 1.24 1 .24 0.07 3.26 0.01 1.08 0.03 4.10 99.76 55 45 45 110 7 6 7 5 5 77 11 11 88 6 6 7700 6 1100 32 32 1144 6 6 1 204 64 7 10 7 10 7 6 5 26 16 6 38 30 16 9 12 10 10 7 5 7 7 6 6 6 10 12 8 35 35 5 5 6 45 4 4 315 3 15 30 30 5500 47 13 444 4 32 23 4 4 5 5 5 310 205 430 305 305 385 40 30 45 8 38 70 40 40 40 55 60 45 48 44 14 26 50 0. 38 0. 14 60 7 ---. 3.16 4.10 65 7 6 0.52 4.85 940 37 11 15.20 1.90 3350 50 44 ZZrr 70.00 70.00 16.80 1 6.80 0.47 0.47 380 3 80 111 110 49. 4369 93.9842193.00328 330 55 143 49. 44200 83—GwJ 5297 320 364 36 4 4455 50 49. 44313 93.98486 83—GWJ 5296 240 135 235 21 83—GWJ 5295 1 45 50 50 4400 yY Zn Zn 83—GWJ 5279 .96 184 vV ii KlJ 83—GWJ 4177 49.42537 2 35 55 4 360 36 0 400 /0 40 30 50 50 22 56 56 355 3 D 46 IIrv r v i me ne n1d an Ba B a rrag a g aarr rock rock Dacite D acite Basalt Dacite B asalt D acite (tholei ( t h o l e i itic) itic) Psh A s h Flow Flow Puuff ff T Prox P r o x iimal mal Dacite Dacite Dacite D acite Dacite Dac ite Dacite D acite Dacite Dacite Prox P r o x iimal mal —Distal -Dis t a 1 Ash A s h Flow Flow Puff Tuff Ash A s h Flow Flow Tuff Tuff Dacite Dac ite Dacite Dac ite nname ame Vo V ocan c a ni i cc Faci F a c i es es Prox P r o x imal imal P r o x iimal m a l Prox P r o ximal— imalProx Distal D is t a1 Ash A s h Flow Flow Puff T uff Ash A s h Flow Flow Tuff Tuff H H �FEO(TOTAL) Point No. No. Sample No. No. Sample 1 810WJ-2044 8 1 G W J - 2 0 4 4 lnt..Tuff Int..Tuff 1 8 1 G W J - 2 0 4 5 Wacke,Felcf Wacke,Feld. 22 81GWJ—2045 A 3 3 81GWJ-2049 8 1 G W J - 2 0 4 9 Int.,Tuff lnt.,Tuff 8 1 G W J - 2 0 5 1 WackeFefd Wacke.Feld. 4 81GWJ-205i FEOFE2O3+Tl 5 BIGWJ—2053 8 1 G W J - 2 0 5 3 Porph.Feld. Porph..Feld. 8 1 G W J - 2 0 5 5 Porph.,Qtz/Feld Porph.,Qtz/Feld. 6 81GWJ—2055 8 1 G W J - 2 0 4 8 Arenite Arenite 7 8IGWJ—2048 88 82GWJ—ooo 8 2 G W J - 0 0 0 8 Iflt.,Tuff lnt..Tuff 99 82GWJ—069 8 2 G W J - 0 6 9 1 Wacke Wacke 1 0 82GWJ-0092 8 2 G W J - 0 0 9 2 Wacko Wacke 10 Warciub Group CALC-ALKALINE NA2Ot K20 FEO(TOTAL) B A Point No. MOO MGO AL203 Sample No. 81GWJ-2050 8 1 G W J - 2 0 5 0 Int.,Tuff Int..Tuff 8 1 G W J - 2 0 5 4 Porph..Qtz/Feld. Porph..Otz/Feld. 22 81GWJ—2054 Int.,Tutf 3 3 82GWJ0169 82GWJ-0169 Int..Tuff 8 2 ~ w J - 0 4 9 1 Tuft T u f f Breccia Breccia 4 82GWJ0491 1 1 FEO+FE203-.TI THOLEIITIC Berry River Formation 55 82GWJ-0601 8 2 G W J - 0 6 0 1 Tuft Tuff 66 82GWJ—061 8 2 G W J - 0 6 111 Porptt,Feld. Porph..Feld. 77 82GWJ0662 8 2 G W J - 0 8 6 2 Lapilli L a p i l l i Tuft Tuff 8 8 836WJ—4 8 3 G W J - 4 1172 72 Porph.,OtZ/Feld. Porph.,Qtz/Feld. 99 83GWJ4 8 3 G W J - 4173 1 7 3 fnt.Tutt Int.,Tuff 10 1 0 83GWJ5279 8 3 G W J - 5 2 7 9 tnt.,Tuft Int..Tuff 11 1 1 830WJ—5282 8 3 G W J - 5 2 8 2 Porph..OtZ/Feld. Porph..Qtz/Fald. 12 1 2 836WJ—5283 8 3 G W J - 5 2 8 3 tnt.,Tuft Int.,Tuff 13 1 3 83GWJ-5286 8 3 G W J - 5 2 8 6 Tutt,Fetd. Tuff,Feld. 14 1 4 83GWJ—5294 8 3 G W J - 5 2 9 4 Tutf Tuff 15 1 5 83GWJ5295 8 3 G W J 5 2 9 5 Int.,Tutf Int..Tuff 16 1 6 83GWJ-5296 8 3 G W J - 5 2 9 6 TuttFeld Tuff,Feld 17 1 7 83GWJ—5297 83GWJ-5297 Porph.,Qfz/Feld. Porph.,Qtz/Feld. 18 83GWJ4174 18 8 3 G W J - 4 1 7 4 Tuft Tuff 19 83GWJ4176 19 8 3 ~ ~ ~ - , 4 1Tuft T7 u f6f Broccia Breccia 20 3GWJ4177 20 8 3 ~ ~ ~ - 4Mafic 1M 7a f i7cFfow Flow AL203 F i g u r e 6: 6: Figure A FM ternary t e r n a r y diagram d i a g r a m (Irvine ( T r v i n e and and Baragar, B a r a q a r , 1971) 1971 ) and and Al—Fe—Ti—Mg Al-Fe-Ti-Mq molecular molecular AFM p r o p o r t i o n ternary t e r n a r y diagram d i a q r a m (iensen, ( J e n s e n , 1976) 1976 ) of o f wackes w a c k e s and and pyroclastics p y r o c l a s t i c s from from proportion the t h e Warcluh W a r c l u b group g r o u p (top) ( t o p ) and and Berry B e r r y River R i v e r formation f o r m a t i o n (bottom). (bottom). H N) �121 A B I c#..41YE A B I C Figure F i g u r e 7: 7: stratigraphy s t r a t i g r a p h y will will comprise c o m p r i s e rrelatively elatively Continuous layers continuous layers stratigraphy s t r a t i g r a p h y of of mixed mixed layers l a y e r s and and lenticular l e n t i c u l a r units units stratigraphy s t r a t i g r a p h y of of llenticular e n t i c u l a r units units S t r a t i g r a p h i c sections s e c t i o n s through t h r o u g h aa volcano volcano Stratigraphic illustrating of i l l u s t r a t i n g the t h e continuity c o n t i n u i t y and a n d complexity c o m p l e x i t y of sstratiqraphy t r a t i g r a p h y in i n different d i f f e r e n t sections. sections. �122 P o s i t i o n Relative R e l a t i v e to t o Source Source Position F i s h e r and a n d Schmincke S c h m i n c k e (1984) ( 1 9 8 4 ) have h a v e subdivided s u b d i v i d e d this t h i s parameter parameter Fisher into: i n t e r m e d i a t e - s o u r c e facies f a c i e s and a n d distant distant i n t o : near—source n e a r - s o u r c e facies; f a c i e s ; intermediate—source These are relative terms and distance values vary with terms a n d d i s t a n c e v a l u e s v a r y with f a c i e s . T h e s e a r e r e l a t i v e facies. t o p o q r a p h y , eruption e r u p t i o n strength, s t r e n g t h , subaerial s u b a e r i a l vs. v s . subaqueous subaqueous topoqraphy, e n v i r o n m e n t etc.. e t c . . Williams W i l l i a m s and a n d McBirney M c B i r n e y (1979) ( 1 9 7 9 ) have h a v e provided provided environment terms; central c e n t r a l facies f a c i e s (0.5—2 ( 0 . 5 - 2 km km n u m e r i c a l estimates e s t i m a t e s for f o r these t h e s e terms; numerical f r o m vent); v e n t ) ; proximal p r o x i m a l facies f a c i e s (5—15 ( 5 - 1 5 km km from f r o m vent) v e n t ) and a n d distal d i s t a l facies facies from ( g r e a t e r than t h a n 5—15 5-15 km km from f r o m vent). v e n t ) . Providing P r o v i d i n g allowances a l l o w a n c e s are a r e made made (greater f o r differences d i f f e r e n c e s in i n method m e t h o d of o f deposition d e p o s i t i o n and a n d in i n the t h e mode mode of of for preservation, p r e s e r v a t i o n , these t h e s e concepts c o n c e p t s can c a n be b e applied a p p l i e d to t o Archean A r c h e a n pyrolastic pyrolast ic d e p o s i t s (Table ( T a b l e3). 3 ) . The T h e products p r o d u c t s listed l i s t e d in i n table t a b l e 33 for f o r each each deposits facies/zone f a c i e s / z o n e can c a n be be related r e l a t e d to t o aa large l a r g e central c e n t r a l vent v e n t composite composite v o l c a n o (Figure ( F i g u r e8). 8). volcano E n v i r o n m e n t of o f Deposition Deposit i o n Environment This T h i s method m e t h o d of o f facies f a c i e s analysis a n a l y s i s considers c o n s i d e r s all a l l physical, physical, chemical c h e m i c a l and a n d geological g e o l o g i c a l features f e a t u r e s that t h a t affect a f f e c t deposition. d e p o s i t i o n . Such Such t o be b e fully f u l l y exploited e x p l o i t e d in i n studies s t u d i e s of of f a c i e s models m o d e l s have h a v e yet y e t to facies A r c h e a n pyroclastic p y r o c l a s t i c rocks. r o c k s . The T h e facies f a c i e s model m o d e l of o f the t h e Berry B e r r y River River Archean formation l a t e r attempts a t t e m p t s to t o postulate p o s t u l a t e an a n environment e n v i r o n m e n t of of f o r m a t i o n presented p r e s e n t e d later depos ition. deposition. P r i m a r y Composition Composition Primary I n complex c o m p l e x aareas, r e a s , such s u c h as a s near n e a rvent, v e n ta , petrologic—chemical a petrologic-chemical In s e d tto o separate s e p a r a t e assemblages a s s e m b l a g e s into i n t obroad broad a p p r o a c h may may be approach be uused compositional t o aid a i d the t h edetermination d e t e r m i n a t i o n of of c o m p o s i t i o n a l ccategories a t e g o r i e s to s t r a t i g r a p h i c relationships. r e l a t i o n s h i p s . Note Note hhowever o w e v e r t hthat a t iif f this t h i s were were the the stratigraphic s o l e approach a p p r o a c h here h e r e then t h e n the t h e entire e n t i r e Berry B e r r y River R i v e r formation f o r m a t i o n would w o u l d be be sole classed a s one o n e facies f a c i e s (Figure ( F i g u r e 6); 6 ) ; calc—alkaline c a l c - a l k a l i n e dacite. dacite. c l a s s e d as --- FACIES------MODEL FOR FOR THE THE BERRY BERRY RIVER RIVER FORMATION FORMATION FACIES MODEL Figure F i q u r e 44 portrays p o r t r a y s the t h e stratigraphic s t r a t i q r a p h i c setting s e t t i n g of o f the the Various f o r m a t i o n within w i t h i n the t h eLong Long Bay—Lobstick Bay-Lobs t i c k Bay Bay area. a r e a . Various formation Subunits a r e shown shown in i n Figure F i g u r e 3. 3. S u b u n i t s based based s t r u c t u r a l complications c o m p l i c a t i o n s are structural u p o n rrecognition e c o q n i t i o n of o f depositional d e p o s i t i o n a l processes p r o c e s s e swere were erected e r e c t e d within within upon t h e formation f o r m a t i o n as a s previously p r e v i o u s l y described. d e s c r i b e d . These T h e s e subunits s u b u n i t s were were the categorized c a t e g o r i z e d in i n terms terms of o f distance d i s t a n c e from f r o m source, s o u r c e , environment e n v i r o n m e n t of of deposition d e p o s i t i o n and a n d degree d e g r e e of o f reworking r e w o r k i n g based b a s e d on o n primary p r i m a r y structures structures a n d lithological l i t h o l o g i c a l association. association. and The t w o episodes e p i s o d e s of of T h e Berry B e r r y River R i v e r formation f o r m a t i o n developed d e v e l o p e d during d u r i n g two e x p l o s i v e volcanism. v o l c a n i s m . The The first f i r s t episode e p i s o d e resulted r e s u l t e d in i n subaqueous subaqueous explosive deposition d e p o s i t i o n of o f the t h e proximal—distal p r o x i m a l - d i s t a l deposition d e p o s i t i o n facies f a c i e s along a l o n g with with t h i n ash a s h flow f l o w tuffs t u f f s (Figure ( F i g u r e 9). 9 ) . During D u r i n g the t h e second s e c o n d episode episode thin involving same volcano v o l c a n o (Figure ( F i g u r e 6), 6 ) , eruptions e r u p t i o n s may may have h a v e been been i n v o l v i n g the t h e same subaerial s u b a e r i a l but b u t deposition d e p o s i t i o n was was subaqueous s u b a q u e o u s in i n the t h e proximal p r o x imal d e p o s i t i o n facies. f a c i e s . AA thick t h i c k ash a s h flow f l o w tuff t u f f is is also a l s o associated a s s o c i a t e d with with deposition 9 ) . AA subvolcanic s u b v o l c a n i c quartz—feldspar quartz-feldspar t h i s eruptive e r u p t i v e event e v e n t (Figure ( F i g u r e 9). this porphyry was intruded i n t r u d e d into i n t o the t h e vent v e n t complex c o m p l e x of o f the t h e proximal proximal p o r p h y r y was Adjacent t o this t h i s is i s aa facies f a c i e s of o f reworked reworked d e p o s i t i o n facies. facies. A d j a c e n t to deposition c o a r s e to t o fine f i n e pyroclastics p y r o c l a s t i c s interbedded i n t e r b e d d e d with w i t h and a n d prograding p r o g r a d i n g into into coarse w a c k e s of o f an a n epiclastic e p i c l a s t i c facies f a c i e s (Figure ( F i g u r e 9). 9). wackes - . �123 Table T a b l e 3: 3: P r o d u c t s associated a s s o c i a t e d with w i t h the t h e four f o u r main m a i n volcanic v o l c a n i c facies facies Products o f aa central c e n t r a l vent v e n t as a s shown s h o w n in i n Figure F i g u r e 8. 8 . Johns J o h n s et e t al. al. of ( 1 9 8 3 ) . Adapted A d a p t e d from f r o m Williams W i l l i a m s and and McBirney M c B i r n e y (1979). ( 1 979). (1983). VENT FACIES FACIES VENT (0.5-2 ( 0 . 5 - 2 km from f r o m vent) vent ) dikes, d i k e s , sills s i l l s and and domes domes co—ignimbrite its c o - i g n i m b r i t e depos d e p o sits Depositional phreatomagmatic Depositional p h r e a t o m a g m a t i c deposits deposits talus t a l u s breccia, b r e c c i a , megabreccia megabreccia PROXIMAL FACIES FACIES (2—15 ( 2 - 1 5 km from f r o m vent) vent) air a i r fall f a l l deposits d e p o s i t s (tuffs) (tuffs) pyroclastic p y r o c l a s t i c flows flows subaqueous s u b a q u e o u s pyroclastic p y r o c l a s t i c flows flows lava l a v a flows f l o w s and and domes domes Depositional Depos i t i o n a l 1 Lahars Lahars Recognizable as pyroclastics pyroclastic R e c o g n i z a b l e a s p y r o c l a s t i c s p y r o c l a s t i c flows flows tuffs tuffs Red epos e p o sii tted ed Red Recognizable R e c o g n i z a b l e as a s volcanic v o l c a n i c sediments s e d iments debris d e b r i s flows flows arenites wac wac kkes es DISTAL D ISTAL FACIES FACIES (>5—15 0 5 - 1 5 km from f r o m vent) vent) air a i r fall f a l l deposits d e p o s i t s (tuffs) (tuffs) pyroclastic p y r o c l a s t i c flows flows subaqueous s u b a q u e o u s pyroclastic p y r o c l a s t i c flows flows lava l a v a flows flows Depos iitional tional Redeposited Redeposited / c 11ah a haarr ss Recognizable as pyroclastics pyroclastic R e c o g n i z a b l e a s p y r o c l a s t i c s p y r o c l a s t i c flows flows ( tufts tuffs ,debris flows arenites Recognizable R e c o g n i z a b l e as a s volcanic v o l c a n i c sediments sediments wac Wac kkes es ss il il ts ttones ones EPICLASTIC FACIES FACIES Redepos it e d Redeposited Tal T a l us us debris d e b r i s flows flows sediments s e d iments in i n crater c r a t e r lakes l a k e s (active, ( a c t i v e , extinct) extinct) perched ponds (Santiaguito) perched ponds ( S a n t i a g u i t o ) alluvial a l l u v i a l fans f a n s (Caribbean) (Caribbean) �Figure 8: Principal facies variation in volcanic rocks related to a large central vent Central zone is also known as the vent facies. composite volcano. Epiclastic facies can occur in all three zones. Products of each Easton and Johns (in press) modified zone/facies are listed in Table 3. from Williams and McBirney (1979). .4 1) T-4 d e n M4J4-1U.4 d r r - 1 Ul M -1-1 -1-1 IÑà a w s H �125 D e s c r i p t i o n of o f Volcanic V o l c a n i c Facies F a c i e s Components Components Description Each volcanic v o l c a n i c facies f a c i e s within w i t h i n the t h eBerry B e r r y River R i v e r formation f o r m a t i o n has h a s aa Each u n i q u e character, c h a r a c t e r , as a s described d e s c r i b e d below. b e l o w . Figure F i g u r e 10 10 illustrates i l l u s t r a t e s the the unique v a r i o u s s t y l e s o f d e p o s i t i o n f o r t h e f a c i e s o f t h e B e r r y R i v e various styles of deposition for the facies of the Berry Riverr f o r m a tion. ion. format D i s t a l Deposition D e p o s i t i o n Facies F a c i e s (Stops ( S t o p s 99 and and 11) 11 ) P r o x i m a l —- Distal Proximal The d e s i g n a t i o n p r o x i m a l d i s t a l d e p o s i t i o n f a c i e s does d o e s not not The designation proximal—distal deposition facies iindicate n d i c a t e aa facies f a c i e s progressing p r o g r e s s i n g from f r o m aa proximal p r o x i m a l setting s e t t i n g to t o aa distal distal setting. I t instead i n s t e a d refers r e f e r s to t o aa facies f a c i e s association a s s o c i a t i o n without without setting. It s u f f i c i e n t d i s t i n c t p r i m a r y f e a t u r e s w h i c h p e r m i t a s s i g n m e n t to to sufficient distinct primary features which permit assignment o n e e n v i r o n m e n t . T h e r e f o r e t h i s f a c i e s r e p r e s e n t s b o t h p r o x i m al one environment. Therefore this facies represents both proximal and d i s t a l e n v i r o n m e n t s . I t is a u n i t f o r m e d by d e p o s i t i o n and distal environments. It is a unit formed by deposition d i r e c t l y from f r o m the t h e volcano v o l c a n o without w i t h o u t significant s i g n i f i c a n t reworking. r e w o r k i n g . The The directly p r o x i m a l d i s t a l d e p o s i t i o n f a c i e s ex t e n d s t h e l e n g t h o f t h proximal—distal deposition facies extends the length of thee f o r m a t i o n (Figure ( F i g u r e 9). 9 ) . While W h i l e the t h e eastern e a s t e r n and and western w e s t e r n portions p o r t i o n s are are formation s i m i l a r , t h e c e n t r a l p o r t i o n is o f a d i f f e r e n t n a t u r e . similar, the central portion is of a different nature. w e s t the t h e deposits d e p o s i t s are a r emassive, m a s s i v e , interbedded, interbedded, I n the t h e east e a s t and and west In p o o r l y s o r t e d , c o a r s e , med ium and f i n e , c o m p o s i t i o n a l y homopoorly—sorted, coarse, medium and fine, compositionallyl homo— l i t h i c to t o bimodal b i m o d a l debris d e b r i s flows. f l o w s . The The bedding b e d d i n g planes p l a n e s between between d e p o s i t s are a r e generally g e n e r a l l y indistinct i n d i s t i n c t indicating i n d i c a t i n g rapid r a p i d accumulation. accumulation. deposits I n t e r b e d d e d w i t h t h e s e m a s s i v e d e p o s i t s a r e d i s c o n t i n u o u s ash ash Interbedded with these massive deposits are discontinuous f l o w t u f f . T h e s e d i s c o n t i n u o u s t u f f s a r e i n s i m i l a r s t r a t iflow tuff. These discontinuous tuffs are in similar strati— g r a p h i c p o s i t i o n s ( F i g u r e 9 ) i n d i c a t i n g e i t h e r e r o s i o n a f t er graphic positions (Figure 9) indicating either erosion after d e p o s i t i o n o r t o p o g r a p h i c c o n t r o l o f d e p o s i t i o n . F i g u r e 1 0, deposition or topographic control of deposition. Figure 10, A i s a s k e t c h o f t h e s e d e p o s i t i o n a l e v e n t s . s t a g e stage A is a sketch of these depositional events. The central c e n t r a l portion, p o r t i o n , particularly p a r t i c u l a r l y south—southwest s o u t h - s o u t h w e s t of o f Berry Berry The Lake c o n s i s t s o f d o u b l y g r a d e d s u b a q u e o u s p y r o c l a s t i c f l o w Lake consists of doubly graded subaqueous pyroclastic flow ( s e e Figure F i g u r e 5), 5 ) , massive m a s s i v e coarse c o a r s e and and medium medium clast c l a s t sized sized d e p o s i t s (see deposits d e b r i s f l o w d e p o s i t s , t h i c k l y l a m i n a t e d t u f f s and p u m i c e o u debris flow deposits, thickly laminated tuffs and pumiceouss l a p i l l i - t u f f fall—out f a l l - o u t deposits d e p o s i t s and a n d massive m a s s i v e tuffs t u f f s (see ( s e e Figures F i g u r e s 18 18 lapilli—tuff a n 1 9 , S t o p 9 and F i g u r e 2 0 , S t o p 1 1 ) . T u f f s d e p o s i t e d b y a s h an 19, Stop 9 and Figure 20, Stop 11). Tuffs deposited by ash l i t h o l o g ies f l o w mechanisms m e c h a n i s m s are a r e interbedded i n t e r b e d d e d with w i t h these t h e s e lithologies. Bedding flow Bedding t o d i s t i n c t . The p l a n e s b e t w e e n a l l u n i t s a r e g e n e r a l l y s h a r p planes between all units are generally sharp to distinct. The d e p o s i t s a r e c o m p o s i t i o n a l l y homo1 i t h i c t o b i m o d a l , m a t r i x deposits are compositionally homolithic to bimodal, matrix i s aa s u p p o r t e d and a n d show s h o w normal n o r m a l and a n d reverse r e v e r s e grading. g r a d i n g . Pumice P u m i c e is supported common c o n s t i t u e n t i n t h e f i n e r d e p o s i t s . F i g u r e 10 s t a g e BB outoutcommon constituent in the finer deposits. Figure 10 stage llines i n e s the t h e mechanism m e c h a n i s m of o f deposition d e p o s i t i o n for f o r this t h i s portion p o r t i o n of o f the the is in i n aa shallow s h a l l o w basin basin p r o x i m a l - d i s t a l deposition d e p o s i t i o n facies f a c i e s which w h i c h is proximal—distal w i t h i n the t h e more more massive m a s s i v e units. units. within lithic . F l o w Tuff T u f f Deposits D e p o s i t s (Stop ( S t o p 10) 10) Ash Flow Ash Ash f l o w t u f f o c c u r s a s d i s c o n t i n u o u s units u n i t s within w i t h i n the the Ash flow tuff occurs as discontinuous p r o x i m a l d i s t a l d e p o s i t i o n f a c i e s and a s a t h i c k c o n t i n u o u s unit unit proximal—distal deposition facies and as a thick continuous b e t w e e n t h e p r o x i m a l d i s t a l and p r o x i m a l d e p o s i t i o n f a c i e s between the proximal—distal and proximal deposition facies ( F i g u r e 9). 9 ) . The The ash a s h flow f l o w tuff t u f f deposits d e p o s i t s are a r e massive, m a s s i v e , broken b r o k e n and and (Figure t o f e l d s p a r e u h e d r a l c r y s t a l s u p p o r t e d q u a r t z f e l d s p a r t u f f euhedral crystal supported quartz—feldspar tuff to feldspar tuff. D i s t i n c t lithic l i t h i c clast c l a s t rich r i c h zones z o n e s of o f the t h e base b a s e or o r pumiceous pumiceous tuff. Distinct were n o t o b s e r v e d i n t h e t h i n n e r u n i t s . C l astic u p p e r p a r t s upper parts were not observed in the thinner units. Clastic were n o t e d i n t h e t h i c k e r u n i t i n d i c a t i n g t h e p o s sibility z o n e s zones were noted in the thicker unit indicating the possibility z o n e s , discontinuous d i s c o n t i n u o u s along along o f several s e v e r a l events. e v e n t s . These T h e s e clastic c l a s t i c zones, of s t r i k e may may represent r e p r e s e n t the t h e base b a s e of o f ash a s h flow f l o w deposits. d e p o s i t s . The The lack l a c k of of strike d i s t i n c t b e d s may b e a c c o u n t e d f o r by r a p i d a c c u m u l a t i o n o f distinct beds may be accounted for by rapid accumulation of were s e v e r a l ash a s h flows f l o w s cooling c o o l i n g as a s one o n e unit. unit. M i n o r lithic l i t h i c lapilli l a p i l l i were several Minor n o t e d t h r o u g h o u t t h e t h i c k c o o l i n g u n i t . T h e s e a s h f l o w t u f f s noted throughout the thick cooling unit. These ash flow tuffs �( Bj? Figure 9: Long +++1Granitoids ñt I 0 * 1 — + .ong Bay / + - — + + 3 + + :: 4 +............. kilometres 2 :++++++++ +++++I I epiclastuc tacies H :1 distal redeposition 5 + + + + + ++++++++** ++ :+::::+ * + * + + + ++ —--— stratigraphic contact facies boundary diabase dike fault lithologic contact +++::::j ash flow tuffs vent facies r proximal deposition (shallow water) y///////proximal—distal deposition (component of redeposition) L BERRY RIVER FORMATION O: C 0 4 r - f 0) ( 0 ( 0 C O U > I-) Vent facies is a subvolcanic quartz—feldspar porphyry intrusive into the base of a volcano. Proximal deposition facies is composed of coarse Schematic diagram of the facies distribution of the Berry River formation. Snake Bay Formation Warclub Group L. '±' Point Bay Group OLDER UNITS w.0 a o o + homolithic pyroclastics. Proximal—distal deposition facies contains a Distal redeposited and epiclastic variety of pyroclastic deposit types. facies are derived from the previous facies. e U4Ju-i en en a a q I\j H �127 were were deposited d e p o s i t e d during d u r i n g stage s t a g e A, A, B and a n d C, C , Figure F i g u r e 10. 10. Proximal P r o x i m a l Deposition D e p o s i t i o n Facies F a c i e s (Stops ( S t o p s 3, 3 , 4, 4 , 77 and and 8) 8) The proximal p r o x i m a l deposition d e p o s i t i o n facies f a c i e s occurs o c c u r s at a t the t h e east e a s t end e n d of o f the the The Berry B e r r y River R i v e r formation f o r m a t i o n nnorth o r t h oof f Lobstick L o b s t i c k Bay Bay aand n d iin n tthe h e central central part 9). I t isi composi— s composip a r t of o f the t h eformation f o r m a t i o nwithin w i t h i nLong Long Bay Bay (figure ( f i g u r e 9). It tionally t i o n a l l y homolithic h o m o l i t h i c pyroclastic p y r o c l a s t i c breccia b r e c c i a to t o tuff t u f f brecc.ia b r e c c - i a with with mostly quartzm o s t l y quartz—feldspar q u a r t z - f e l d s p a r pporphyry o r p h y r y cclasts l a s t s and a n d the t h e matrix m a t r i x isisquartz— feldspar f e l d s p a r tuff. t u f f . The The facies f a c i e s represents r e p r e s e n t s aa proximal p r o x i m a l environment e n v i r o n m e n t and and direct d i r e c t deposition d e p o s i t i o n by b y volcanic v o l c a n i c processes. processes. This f a c i e s is is composed composed of o f matrix m a t r i x supported, s u p p o r t e d , thickly—bedded, thickly-bedded , Th i s facies l a p i l l i s t o n e to t o pyroclastic p y r o c l a s t i c breccia b r e c c i a deposited d e p o s i t e d by b y the t h e block b l o c k and and lapillistone ash e t al. a l . 1973). 1 9 7 3 ) . Bedding B e d d i n g planes p l a n e s range range a s h flow f l o w process p r o c e s s (Sparks, ( S p a r k s , et from t o sharp s h a r p indicating i n d i c a t i n g rapid r a p i d accumulation. accumulation. Thin f r o m gradational g r a d a t i o n a l to Thin tuff t u f f beds b e d s separate s e p a r a t e some some block b l o c k and a n d ash a s h flow f l o w deposits d e p o s i t s and a n d grain grain size s i z e gradations g r a d a t i o n s occur o c c u r within w i t h i n these t h e s e beds. beds. T h e s e thin t h i n tuff t u f f inter— interThese beds b e d s are a r e the t h e surge s u r g e deposit d e p o s i t portion p o r t i o n of o f block b l o c k and and ash a s h flow f l o w subsubunits. u n i t s . Thin T h i n tuffs t u f f s overlying o v e r l y i n g the t h e main m a i n body b o d y of o f the t h e block b l o c k and and ash ash flow f l o w deposits d e p o s i t s exhibit e x h i b i t grain g r a i n gradation, g r a d a t i o n , suggesting s u g g e s t i n g they t h e y are are products p r o d u c t s of o f cloud c l o u d surge s u r g e deposition d e p o s i t i o n rather r a t h e r than t h a n ground g r o u n d surge s u r g e (stop (stop 3). 3 ) . Primary P r i m a r y features f e a t u r e s such s u c h as a s gas g a s escape e s c a p e structures s t r u c t u r e s are a r e found found within w i t h i n block b l o c k and a n d ash a s h flows f l o w s (stop ( s t o p 7). 7 ) . These T h e s e features f e a t u r e s are a r e limited limited to t o the t h e top t o p of o f cooling c o o l i n g units. units. Figure and DD outline o u t l i n e the t h e depositional d e p o s i t i o n a l environenvironF i g u r e 10 1 0 stages s t a g e s CC and ment m e n t envisaged e n v i s a g e d for f o r this t h i s facies. facies. Vent V e n t Facies Facies Vent t o the t h e eastern e a s t e r n end end of o f the the V e n t facies f a c i e s rocks r o c k s are a r e restricted r e s t r i c t e d to Berry is represented represented B e r r y River R i v e r formation f o r m a t i o n (figure ( f i g u r e 9). 9 ) . The The vent v e n t facies f a c i e s is by b y aa subvolcanic s u b v o l c a n i c quartz q u a r t z feldspar f e l d s p a r porphyry p o r p h y r y intrusion i n t r u s i o n cutting c u t t i n g the the proximal p r o x i m a l deposition d e p o s i t i o n facies. f a c i e s . Portions P o r t i o n s of o f the t h e porphyry p o r p h y r y are are massive, o r brecciated. b r e c c i a t e d . The The c l a s t i c or m a s s i v e , while w h i l e others o t h e r s are a r e subtly s u b t l y clastic porphyry is similar s i m i l a r in i n petrography p e t r o g r a p h y to t o the t h e clasts c l a s t s of o f the t h e proximal proximal p o r p h y r y is deposition d e p o s i t i o n facies. f a c i e s . Rafts R a f t s and a n d xenoliths x e n o l i t h s of o f the t h e proximal p r o x i m a l unit u n i t are are found f o u n d within w i t h i n the t h e vent v e n t facies f a c i e s intrusive. intrusive. The The similarity s i m i l a r i t y between b e t w e e n clasts c l a s t s of o f the t h e proximal p r o x i m a l deposition deposition facies w e l l as a s the t h e presence p r e s e n c e of o f rafts r a f t s and and f a c i e s and and the t h e porphyry p o r p h y r y as a s well xenoliths was emplaced e m p l a c e d into i n t o the t h e lower lower x e n o l i t h s suggests s u g g e s t s that t h a t the t h e porphyry p o r p h y r y was part p a r t of o f aa growing g r o w i n g volcanic v o l c a n i c edifice e d i f i c e and and may may have h a v e been b e e n the t h e magma magma chamber c h a m b e r feeding f e e d i n g the t h e block b l o c k and a n d ash a s h flows f l o w s overlying o v e r l y i n g the t h e thick t h i c k ash ash flow f l o w tuff t u f f (Figure ( F i g u r e 10, 1 0 , Stage S t a g e D). D). Distal D i s t a l Redeposited R e d e p o s i t e d Facies F a c i e s (Stops ( S t o p s 6, 6 , 99 and a n d 11) 11) Rocks Rocks of o f the t h e distal d i s t a l redeposited r e d e p o s i t e d facies f a c i e s occur o c c u r in i n two t w o strati— stratigraphic g r a p h i c positions. p o s i t i o n s . They T h e y are a r e found f o u n d at a t the t h e base b a s e of o f the t h e Berry B e r r y River River formation f o r m a t i o n south—southwest s o u t h - s o u t h w e s t of o f Berry B e r r y Lake Lake and a n d north n o r t h of o f Mist M i s t Inlet Inlet and M i s t Inlet I n l e t (Figure ( F i g u r e9). 9 ) . The The a n d at a t the t h e top t o p of o f the t h e formation f o r m a t i o n in i n Mist distal d i s t a l redeposited r e d e p o s i t e d facies f a c i e s exhibits e x h i b i t s primary p r i m a r y structures s t r u c t u r e s and and rock rock associations t y p i c a l of o f aa distal d i s t a l environment. e n v i r o n m e n t . Evidence Evidence a s s o c i a t i o n s (Table ( T a b l e 3) 3 ) typical for f o r re—working r e - w o r k i n g is i s shown shown on o n Table T a b l e 1.1 . South—southeast S o u t h - s o u t h e a s t of o f Berry B e r r y Lake Lake the t h e distal d i s t a l redeposited r e d e p o s i t e d facies facies has ( s e e Figure F i g u r e 18, 1 8 , Stop S t o p 99 and and Figure F i g u r e 20, 2 0 , stop stop h a s varied v a r i e d thickness t h i c k n e s s (see 11) 1 1 ) and and consists c o n s i s t s of o f moderately m o d e r a t e l y sorted, s o r t e d , thin t h i n to t o thick t h i c k bedded, bedded, cross c r o s s bedded, b e d d e d , graded g r a d e d reworked r e w o r k e d tuffs t u f f s and a n d lapilli l a p i l l i tuff. t u f f . Evidence Evidence �128 Stage AA Stage -- sea mad lev< Sea ource volcanic slope T7 active a volcanism volcanism m c slope \ active active faulting/slumping -7 active faulting/slumping P turbidity current tufts Warclub group metuseduments source aulcanic volcanic vent vent source Plinian type Eruptions Plunuan type Eruptions f pyroclastic flows flows and and tufts tuffs pyroclastuc StageBB Stage - -0 0 /-/ '-'-, ii sea lev fallout tephra Warclub group metaseduments StageCC Stage - -'' P ,- source volcanic volcanic vent vent source Phnian ttype y p e eruptions eruptions Pluniun block and ash f l o ws block and ash flows ash flows flows ash ciubgroupmefa5edim' J- - / - 7 n r^ , Stage D StageD source volcanic volcanicvent vent source Plinian ttype y p e eruptions eruptions Plinuan block and and ash ash flows flows block block and ash flow epiclastic facies �123 Figure F i g u r e 10: Stage A: S t a g e A: Stage S t a g e B: B: P r o p o s e d model o r the t h e development d e v e l o p m e n t oof f the t h e Berry Berry Proposed modelf for River R i v e r formation. formation. P r o x i m a l—- Distal D i s t a l Deposition D e p o s i t i o n Facies: F a c i e s : Debris D e b r i s flows flows Proximal and and ttuffs. uffs. A vvolcanic o l c a n i c eedifice d i f i c e is is constructed c o n s t r u c t e d by by explosive explosive A vvolcanism. olcanism. B u i l d i n g and and ooversteepening v e r s t e e p e n i n g oof f the t h e cone cone Building rresults e s u l t s in i n slumping s l u m p i n g of o f coarse c o a r s e pyroclastic p y r o c l a s t i c material material i n t o aa basin b a s i n in i n the t h eunderlying u n d e r l y i n g sediments s e d i m e n t s of o f the the into Warciub W a r c l u b ggroup. roup. IInterbedded n t e r b e d d e d t tuffs u f f s in i n this t h i ssequence sequence aare r e ddeposited e p o s i t e d ffrom r o m ffine i n e aash s h cclouds l o u d s eelutriated l u t r i a t e d ffrom rom less violent violent tthe h e turbulent t u r b u l e n t mass f l o w s and and from from less mass flows eruptions. A l t h o u g h these t h e s e thickly t h i c k l y bedded bedded deposits deposits eruptions. Although tthin h i n llaterally, a t e r a l l y , they t h e y do d o not n o t appear a p p e a r to t o grade grade laterally. laterally. T h e s e deposits d e p o s i t s are a r e best b e s t exposed e x p o s e d at a t the t h e east e a s t and and These w e s t ends e n d s of o f the t h e Berry B e r r y River R i v e r formation. formation. west PProximal r o x i m a l — ~Distal i s t a lDeposition D e p o s i t i o n Facies: Facies: Subaqueous Subaqueous P y r o c l a s t i c Flow Flow Deposit D e p o s i t and and Fall—Out F a 1 1-Out Deposits Deposits Pyroclastic The growing g r o w i n g edifice e d i f i c e approaches a p p r o a c h e s sea s e a level. level. The eeruption r u p t i o n ppattern a t t e r n changes c h a n g e s from f r o m single, s i n g l e , violent violent eexplosive x p l o s i v e events e v e n t s to t o a relatively r e l a t i v e l y continuous c o n t i n u o u s series series These oof f explosions e x p l o s i o n s that t h a t wane wane in i n energy. energy. T h e s e eruptions eruptions by Fiske Matsuda aare r e ssimilar i m i l a r to t o those t h o s e ddescribed e s c r i b e d by F i s k e and and M atsuda (1964) r o d u c i n g ddoubly o u b l y graded g r a d e d subaqueous subaqueous ( 1 9 6 4 ) pproducing which ppyroclastic y r o c l a s t i c flow f l o w ddeposits eposits w h i c h fill fill a a sshallow hallow basin b a s i n in i n the t h e underlying u n d e r l y i n g massive m a s s i v e deposits. deposits. The becomes ssubaerial eeruptive r u p t i v e ccolumn o l u m n becomes u b a e r i a l and and fine f i n e ttephra ephra ffalls a l l s oout u t tthrough h r o u g h air a i r and and water, w a t e r , producing p r o d u c i n g thin t h i n to to thick Thin l a p i l l i tuff. tuff Thin t h i c k bedded bedded tuff t u f f and and pumiceous p u m i c e o u s lapilli bbeds e d s oof f ash a s h flow f l o w tuff t u f f and and lapilli l a p i l l i tuff t u f f were were deposited Slumping from d e p o s i t e d at a t this t h i s time. time. Slumping from the t h e edifice edifice also massive, a l s o produced produced m a s s i v e , medium to t o coarse c o a r s e debris debris flow f l o w deposits. d e p o s i t s . These T h e s e deposits d e p o s i t s are a r e confined conÂi n e d to t o the the ccentral e n t r a l pportion o r t i o n of o f the t h eBerry B e r r y River R i v e r formation f o r m a t i o n and and aare r e bbest e s t exposed e x p o s e d between b e t w e e n Highway Highway 71 71 east e a s t to t o the the Berry B e r r y River. River. Proximal Deposition Proximal D e p o s i t i o n Facies: Facies: B l o c k and and Ash Ash flow flow Block Deposits D e p o s i t s and and Ash Flow Flow Tuffs Tuffs The voluminous v o l u m i n o u s eruptions e r u p t i o n s producing p r o d u c i n g the t h e proximal— proximaldistal d i s t a l deposition d e p o s i t i o n facies f a c i e s rocks r o c k s deflate d e f l a t e the t h e magma chamber resulting chamber r e s u l t i n g in i n local l o c a l volcano—tectonic v o l c a n o - t e c t o n i c subsubHomolithic, massive ssidence. idence. H omolithic, m a s s i v e block b l o c k and and ash a s h flow flow A ddeposits e p o s i t s were deposited d e p o s i t e d within w i t h i n the t h e depression. depression. massive ssequence e q u e n c e of o f thick, thick, m a s s i v e ash a s h flow f l o w tuffs, t u f f s , forming forming a a cooling c o o l i n g unit u n i t were were erupted, e r u p t e d , perhaps p e r h a p s subaerially, s u b a e r i a l ly, from This f r o m the t h e vent. vent. T h i s ddepression e p r e s s i o n later l a t e r becomes becomes the the ccenter e n t e r of o f renewed renewed vvolcanism o l c a n i s m in i n a shallow s h a l l o w water env e n v iironment. ronment P r o x i m a l Deposition D e p o s i t i o n Facies F a c i e s and and Redeposited R e d e p o s i t e d Facies Facies Proximal While W h i l e explosive e x p l o s i v e eruptions e r u p t i o n s continue c o n t i n u e to t o build b u i l d the the edifice e d i f i c e aa subvolcariic s u b v o l c a n i c qquartz—feldspar u a r t z - f e l d s p a r pporphyry o r p h y r y body iintrudes n t r u d e s the t h e base. base. The eruptions e r u p t i o n s produce p r o d u c e subaerial s u b a e r i a l block b l o c k and and ash a s h flow flow ddeposits e p o s i t s that t h a t prograde p r o q r a d e laterally l a t e r a l l y into i n t o aa shallow shallow water w a t e r environment. environment. S u r g e ddeposits e p o s i t s are a r e recognized r e c o g n i z e d between b e t w e e n block b l o c k and and ash ash Surge p r o x i m a l deposits d e p o s i t s extend ex t e n d aa fflow l o w deposits. d e p o s i t s . these These proximal f a i r ddistance i s t a n c e from the t h e vent v e n t as a s the t h e eruptions e r u p t i o n s were were fair subaerial s u b a e r i a l and and more more violent. violent Reworking oof f these t h e s e ddeposits e p o s i t s and and underlying u n d e r l y i n g units units Reworking r e s u l t e d in i n production p r o d u c t i o n of o f the t h e coarse c o a r s e distal distal resulted epiclastic r e d e p o s i t e d facies f a c i e s rocks r o c k s and and the t h e lateral l a t e r a l epiclastic redeposited ffacies a c ies wackes. wackes E r o s i o n and and ddegredation e g r e d a t i o n of o f the t h e subaerial s u b a e r i a l ediface ediface Erosion p r o d u c e the t h e overlying o v e r l y i n g wacke wacke of o f the t h e Warclub W a r c l u b group. group. produce - . Stage C: S t a g e C: Stage S t a g e D: D: . . . �130 for for reworking r e w o r k i n g in i n this t h i s portion p o r t i o n of o f the t h e facies f a c i e s include i n c l u d e the t h e moderate moderate sorting s o r t i n g and a n d presence p r e s e n c e of o f subrounded s u b r o u n d e d quartz q u a r t z and and feldspar f e l d s p a r crystals crystals a n d lithic l i t h i c clasts. c l a s t s . Along Along the t h e basal b a s a l contact c o n t a c t of o f this t h i s facies f a c i e s thin thin and beds west (see (see b e d s show s h o w evidence e v i d e n c e for f o r prograding p r o g r a d i n g from f r o m both b o t h east e a s t and and west 1 8 , stop s t o p 9). 9). F i g u r e 18, Figure N o r t h of o f Mist M i s t Inlet I n l e t at a tthe t h etop t o pofo the f t hBerry e B e r r yRiver R i v e rformation formation North 9 ) distal d i s t a l redeposited r e d e p o s i t e d facies f a c i e s rocks r o c k s consist c o n s i s t of o f interbedd— interbedd( F i g u r e 9) (Figure The ed, t o tuff. tuff. The presence p r e s e n c e of of e d , heterolithic, h e t e r o l i t h i c , graded g r a d e d tuff t u f f breccia b r e c c i a to volcanic v o l c a n i c clasts c l a s t s found f o u n d in i n the t h e Berry B e r r y River R i v e r formation f o r m a t i o n indicates i n d i c a t e s that that this i s associated a s s o c i a t e d with w i t h the t h e prograding p r o g r a d i n q Berry B e r r y River River t h i s facies f a c i e s is formation. formation. Evidence Mist Inlet I n l e t area a r e a includes: i n c l u d e s : sub— subE v i d e n c e for f o r reworking r e w o r k i n g in i n the t h e Mist round t o round r o u n d clasts, c l a s t s , poor p o o r to t o moderate m o d e r a t e sorting, s o r t i n g , normal n o r m a l grading, grading, r o u n d to heterolithic h e t e r o l i t h i c nature n a t u r e and and presence p r e s e n c e of o f wacke wacke interheds. i n t e r b e d s . This T h i s tuff tuff to t o pyroclastic p y r o c l a s t i c breccia b r e c c i a unit u n i t is is heterolithic, h e t e r o l i t h i c , poor p o o r to t o well w e l l sorted sorted c l a s t s . Wacke Wacke beds b e d s are a r e interbedded interbedded a n d graded g r a d e d with w i t h subrounded s u b r o u n d e d clasts. and with ( s e e Figure F i g u r e 16, 1 6 , stop s t o p 6). 6). w i t h these t h e s e reworked r e w o r k e d pyroclastic p y r o c l a s t i c rocks r o c k s (see Figure F i g u r e 10 1 0 stage s t a g e DD outlines o u t l i n e s the t h e model m o d e l for f o r the t h e deposition d e p o s i t i o n of of t h e s e rocks. rocks. these E p i c l a s t i c Facies Facies Epiclastic Quartz—feldspar Q u a r t z - f e l d s p a r wackes w a c k e s interdigitate i n t e r d i g i t a t e with w i t h and and overlie overlie proximal—distal p r o x i m a l - d i s t a l deposition d e p o s i t i o n facies f a c i e s rocks r o c k s in i n the t h e western w e s t e r n portion p o r t i o n of of The the t h e Berry B e r r y River R i v e r formation f o r m a t i o n (Figure ( F i g u r e 9) 9) west west of o f Mist M i s t Inlet. Inlet. The wackes t o very v e r y thick t h i c k bedded, b e d d e d , graded g r a d e d (AE (AE Bouma Bouma sequence) sequence) w a c k e s are a r e thick t h i c k to They a n d moderately m o d e r a t e l y sorted. sorted. They resulted r e s u l t e d from f r o m both b o t h reworking r e w o r k i n g of of and pyroclastic p y r o c l a s t i c deposits d e p o s i t s and a n d from f r o m the t h e distal d i s t a l turbiditic t u r b i d i t i c deposition deposition of D). o f block b l o c k and a n d ash a s h flows f l o w s (Figure ( F i g u r e 10, 1 0 , stage s t a g e D). SUMMARY SUMMARY The T h e Berry B e r r y River R i v e r formation f o r m a t i o n has h a s been b e e n placed p l a c e d in i n aa facies facies During context c o n t e x t and a n d as a s such s u c h aa stratigraphy s t r a t i g r a p h y has h a s been b e e n developed. developed. During the w e will w i l l examine e x a m i n e the t h e evidence e v i d e n c e for f o r the t h e proximal— proximalt h e field f i e l d trip t r i p we distal d i s t a l deposition, d e p o s i t i o n , proximal p r o x i m a l deposition, d e p o s i t i o n , ash a s h flow f l o w tuff t u f f and and distal distal r e d e p o s i t i o n facies. facies. redeposition MENTS ACKNOWLEDGEMENTS ACKNOWLEDGE T h e a u t h o r ggratefully r a t e f u l l y acknowledges a c k n o w l e d g e s the t h e assistance a s s i s t a n c e received received from P.C. Thurston and R.M. Easton and M. Easton in the discusf r o m P.C. T h u r s t o n and R.M. E a s t o n and M. E a s t o n i n t h e discussions s i o n s leading l e a d i n g to t o development d e v e l o p m e n t of o f the t h e model m o d e l and and reading r e a d i n g this this m a n u s c r i p t . Draughting D r a u g h t i n g and and setting s e t t i n g of o f the t h e figures f i g u r e s was was skillfully skillfully manuscript. Anna Branicky patiently done by Barb Moore and Krys Gil. Anna B r a n i c k y p a t i e n t l y did d i d the the d o n e b y B a r b Moore a n d Krys G i l . t y p i n g , re—typing, re- t y p i n g , re—re—typing re-re- t y p i n g typing, TTifhor .... �131 FIELD FIELD TRIP TRIP GUIDE GUIDE The The field f i e l d trip t r i p is i s designed d e s i g n e d to t o be b e completed c o m p l e t e d in i n one o n e day d a y with with 11 1 1 stops; s t o p s ; 44 on o n Lake Lake of o f the t h e Woods Woods and a n d 77 with w i t h road r o a d access. a c c e s s . Figures Figures 11 1 1 aand n d 12 1 2 show s h o w the t h e locations l o c a t i o n s of o f the t h e stops. stops. The w i l l commence commence with w i t h stop s t o p 33 but b u t if if T h e 1985 1 9 8 5 I.L.S.G. I.L.S.G. trip t r i p will conditions a n d 22 will will c o n d i t i o n s do d o not n o t permit p e r m i t the t h e use u s e of o f boats b o a t s then t h e n stops s t o p s 1 and be The b e visited. visited. The road r o a d guid•e q u i d - e sstarts t a r t s aatt the t h e Sioux S i o u x Narrows N a r r o w s bridge b r i d g e in in the t h e village v i l l a g e of o f Sioux S i o u x Narrows N a r r o w s on o n Highway Highway 71, 7 1 , 60 6 0 km km south s o u t h of of Highway Highway 17. 17. 1 1) 1) 2) 2) 3) 3) 4) 4) Several S e v e r a l points p o i n t s should s h o u l d be b e made made regarding r e g a r d i n g the t h e area: area: Lake Lake of o f the t h e Woods can c a n be b e treacherous t r e a c h e r o u s with w i t h respect r e s p e c t to to navigation It n a v i g a t i o n and and weather. weather. I t is i s advisable a d v i s a b l e to t o have h a v e aa navigation n a v i g a t i o n map of o f the t h e lake l a k e published p u b l i s h e d by b y the t h e Canadian C a n a d i a n Hydro— Hydrographic g r a p h i c Service, S e r v i c e , Department D e p a r t m e n t of o f Fisheries F i s h e r i e s and a n d the the Environment. These Environment. T h e s e maps are a r e readily r e a d i l y available a v a i l a b l e from f r o m local local outfiters. outfiters. The kccess Road" Roa& used i s aa "Forest " F o r e s t Access u s e d by b y heavy heavy The Maybrun Maybrun Road Road is trucks. w e l l off o f f the t h e right r i g h t of o f way. way. t r u c k s . Please P l e a s e park p a r k well Outcrops wet. O u t c r o p s are a r e slippery s l i p p e r y when when wet. This T h i s is is WOOD WOOD TICK TICK country. country. �paved paved highway highway -==== gravel road road -- geologic contact contact . - - fault/hneament faultAineament @ A field trip trip atop stop location location boat boat launch launch Early Precambrian Precambrian AA- mafic to to intermediate intermediate metavolcanics metavolcanics B -- intermediate Intermediate metavolcanics metavolcanics C-- metasediments metasediments C DD- ultramafic intrusive Intrusive rocks rocks E maticintrusive Intrusive rocks rocks E -—mafic F -- intermediate Intermediate to to felsic fel8ic intrusive intrusive rocks rocks Late Late Precambrian Precambrian G maf Icintrusive intrusive rocks(diabase) rocks(diabase) G -- mafic Pro vncIaI Park bet Launch Regina Bay Figure F i q u r e 11: 11: Navigation N a v i g a t i o n g guide u i d e t otot hthe e f ifield e l d ttrip r i p stop s t o p locations l o c a t i o n s in i n the t h e eastern e a s t e r n part p a r t of o f the the field f i e l d trip t r i p area. area. N-) �-paved highway -- ==--== gravel road - --(Z) A geologic contact faultllineament field trip stop location boat launch :arly Precambrian -mafic to intermediate metavokanici i- intermediate metavoicanics - metasediments 1-ultramafic intrusive rocks - mafic intrusive rocks -intermediate to felsic intrusive rock Figure F i g u r e 12: 12: Navigation N a v i g a t i o n guide g u i d e to t o the t h e field f i e l d trip t r i p stop s t o p locations l o c a t i o n s in i n the t h e western w e s t e r n part p a r t of of the the field trip area. f i e l d t r i p area. w �134 0.0 0.0 km km South S o u t h end end of o f the t h e Sioux S i o u x Narrows N a r r o w s Bridge B r i d g e on o n Highway Highway 71 71 (Figure ( F i g u r e 11). 11). Drive D r i v e south s o u t h on o n Highway Highway 71 71 through t h r o u g h Sioux S i o u x Narrows N a r r o w s for f o r 8.2 -8.2 km t o the t h e Gaudry G a u d r y Road. Road. km to - 8 . 2 km km 8.2 Gaudry G a u d r y Road Road (see ( s e e Figure F i g u r e 13 1 3 for f o r stop s t o p locations) l o c a t i o n s ) Turn T u r n left left o n t o the t h e Gaudry G a u d r y Road Road and and drive d r i v e towards t o w a r d s the t h e Whitefish W h i t e f i s h Bay Bay onto Indian Village . 9 km. I n d i a n Reservation Reservation V i l l a g e ffor o r -0.-.-0.9km. 9. 1 km kin 9.1 Park STOP 1: 1: STOP P a r k above a b o v e the t h e gravel g r a v e l pit p i t on o n the t h e left l e f t side s i d e of of the t h e road r o a d and and walk w a l k to t o outcrop o u t c r o p 'A' ' A ' (Figure ( F i g u r e 13). 13). Formation: Formation: Lithology: Lithology : Setting: Setting: Snake S n a k e Bay formation formation Mafic Maf i c metavolcanics metavolcanics Strike—southeast, dip-vertical, S t r i k e - s o u t h e a s t , dip—vertical, top—northeast. stratigraphic st r a t i g r a p h i c t o p - n o r t h e a s t F e a t u r e ( s ) : Feeder F e e d e r dike, d i k e , hyaloclastite, h y a l o c l a s t i t e , pillows. pillows. Feature(s): . The T h e best b e s t exposures e x p o s u r e s are a r e in i n the t h e cut c u t between b e t w e e n the t h e two two The feeder outcrops o u t c r o p s where w h e r e the t h e gravel g r a v e l has h a s been b e e n removed. removed. feeder d i k e ? in i n Figure F i g u r e 14, 1 4 , strikes s t r i k e s at a t 125° 1 2 5 0 and a n d dips dips dike, It vertically. I t consists c o n s i s t s of o f two t w o symmetrical s y m m e t r i c a l pparts; a r t s ; aa vertically. marginal m a r g i n a l zone z o n e chilled c h i l l e d against a g a i n s t the t h e country c o u n t r y rock r o c k and a n d aa central c e n t r a l zone z o n e chilled c h i l l e d against a g a i n s t the t h e marginal m a r g i n a l zone. zone. The is 77 cm thick t h i c k with w i t h aa 1.5—2.0 1 . 5-2.0 cm cm The marginal m a r g i n a l zone z o n e is thick t h i c k ddarker a r k e r coloured c o l o u r e d chilled c h i l l e d zone z o n e against a g a i n s t the t h e country country Concave c m apart apart rock. C o n c a v e up, u p , sub—parallel, s u b - p a r a l l e l , fractures f r a c t u r e s 1—7 1-7 cm rock. occur within this zone and dip 20 degrees into the o c c u r w i t h i n t h i s z o n e a n d d i p 20 d e q r e e s i n t o t h e o u t c r o p . These T h e s e fractures, f r a c t u r e s , 0.2—1 0.2-1 cm c m thick t h i c k in i n the t h e center center outcrop. are a r e carbonate c a r b o n a t e filled f i l l e d and a n d rarely r a r e l y occur o c c u r in i n the t h e central central The central zone. c m wide, w i d e , has h a s aa zone. c e n t r a l zone, z o n e , approximately a p p r o x i m a t e l y 44 cm The dike 2 mm chilled c h i l l e d margin m a r g i n against a g a i n s t the t h e marginal m a r g i n a l zone. zone. dike can 2 6 rn m tto o the t h e southeast. southeast. c a n be b e traced t r a c e d for f o r 26 The The The ddike i k e formed f o r m e d iin n two t w o stages. stages. The ffirst i r s t stage stage Reactivation f r o z e as a s a massive m a s s i v e fine f i n e grained g r a i n e d dike. dike. Reactivation froze magma f o r c e d new new magma t h rthrough o u g h t h the e c ecenter n t e r o of f tthe h e old o l d dike dike forced The fractures in the older marginal zone. producing producing f r a c t u r e s i n t h e o l d e r m a r g i n a l zone. The orientation o r i e n t a t i o n of o f the t h e fractures f r a c t u r e s indicates i n d i c a t e s that t h a t magma movement (in ( i n present p r e s e n t orientation) o r i e n t a t i o n ) had had an a n upward upward vector vector perpendicular p e r p e n d i c u l a r to t o the t h e fracture f r a c t u r e system. system. The is a a brittly b r i t t l y fractured, fractured, T h e host h o s t of o f the t h e feeder f e e d e r dike d i k e is The massive, m a s s i v e , fine—grained, f i n e - g r a i n e d , mafic m a f i c metavolcanic. metavolcanic. The carbonate—filled t h e r e is is c a r b o n a t e - f i l l e d fractures f r a c t u r e s may be b e early e a r l y —- there little l i t t l e evidence e v i d e n c e of o f penetrative p e n e t r a t i v e deformation d e f o r m a t i o n within w i t h i n the the The exposure outcrop. outcrop. e x p o s u r e on o n the t h e north n o r t h side s i d e of o f the t h e gravel gravel is fine f i n egrained g r a i n e dmafic m a f i cflows f l o w swith w i t hvery v e r ylarge l a r g eameboid ameboid p i t is pit shaped crn tthick h i c k selvages s e l v a g e s and and chilled chilled s h a p e d pillows p i l l o w s with w i t h1—2 1-2 cm (smile; m a r g i n s that t h a t have h a v e carbonate c a r b o n a t e filled f i l l e d concave c o n c a v e (smile) margins A 70 ccm fractures. fractures. A 70 m t hthick i c k hhyaloclastite y a l o c l a s t i t e to t o pillow pillow within b r e c c i a (Carlisle, ( C a r l i s l e ? 1963) 1 9 6 3 ) zone z o n e ooccurs ccurs w i t h i n the the breccia m e gapil a p i l l low o w ssequence. equence. meg Stratigraphically S t r a t i g r a p h i c a l l y overlying o v e r l y i n g the t h e megapillows m e g a p i l l o w s (east (east e n d of o f outcrop) o u t c r o p ) fine—grained, f i n e - g r a i n e d , massive m a s s i v e fflows l o w s hhave a v e tthick, hick, end b r i t t l e f r a c t u r e s f i l l e d w i t h s o Ât b l a c k ( o x i d i z e d r e d ) brittle fractures filled with soft black (oxidized red) �135 - 0 <^0 gravel pit 100 200 ----- gravel pit road B Figure F i g u r e 13: 13: field trip atop Locations o f field f i e l d trip t r i p Stop S t o p number number 1(A) 1 ( A ) and Stop Locations of and Stop nnumbers u m b e r s 2(8, 2 ( B , CC and a n d D) D) center massive flow massive flow I Figure F i g u r e 14: 14: FEEDER FEEDER DIKE DIKE I S k e t c h oof f the t h e ma i c feeder f e e d e r dike d i k e at a t Stop S t o p 1 (A (A o Sketch mafic onn Figure F i q u r e 13). 1 3 ) . The ddike i k e is i s bilaterally b i l a t e r a l l y symmetrical symmetrical t w o periods p e r i o d s of o f magma magma emplacement. emplacement. f o r m i n g during d u r i n q two forming 1 �136 hematitic hematitic mud and and scattered s c a t t e r e d carbonate c a r b o n a t e filled f i l l e d amygdules amygdules less l e s s than t h a n 44 mm mm in i n diameter. d i a m e t e r . AA sample s a m p l e of o f the t h e hematitic hematitic fracture f r a c t u r e filling f i l l i n g contained c o n t a i n e d 0.05—0.50 0.05-0.50 percent p e r c e n t copper c o p p e r as as well w e l l as a s greater g r e a t e r than t h a n 10 1 0 percent p e r c e n t iron i r o n (30 ( 3 0 element element quantitative q u a n t i t a t i v e spectrographic s p e c t r o g r a p h i c analysis a n a l y s i s by b y the t h e Geosciences Geosciences Laboratory, L a b o r a t o r y , Ontario O n t a r i o Geological G e o l o g i c a l Survey, S u r v e y , Toronto). Toronto) . 0.0 0.0 km km 0.24 0 . 2 4 km km 0.39 0 . 3 9 km km Return R e t u r n to t o vehicles v e h i c l e s and and drive d r i v e towards t o w a r d s Highway Highway 71 71 (Figure (Figure 13) m. 1 3 ) for f o r 240 2 4 0in. Turn T u r n at a t first m t l left e f t and and drive d r i v e to t o the t h e "Y" "Y" junction j u n c t i o n about about 150 rn. 150 m. If I f road r o a d (Figure ( F i g u r e 13) 1 3 ) is is blocked, b l o c k e d , park p a r k here h e r e taking t a k i n g care care not to block access to the sewage pond (follow your n o t t o b l o c k a c c e s s t o t h e sewage pond ( f o l l o w y o u r nose) o r road r o a d to t o gravel g r a v e l pit. pit. n o s e ) or STOP STOP 2: 2: Walk Walk through t h r o u g h the t h e gravel g r a v e l pit p i t to t o outcrop o u t c r o p BB (Figure ( F i g u r e 13). 1 3 ) . This T h i s is is an a n ongoing o n g o i n g (1985) ( 1 9 8 5 ) operation o p e r a t i o n and and if if the is active a c t i v e at a t the t h e time t i m e of o f your y o u r visit v i s i t please p l e a s e seek seek t h e pit p i t is permission t o enter. enter. p e r m i s s i o n to STOP STOP 2B: 2B : Formation: F o r m a t i o n : Snake S n a k e Bay Bay formation formation Lithology: Maf i c metavolcanics metavolcanics L i t h o l o g y : Mafic Setting: Strike—southeast, d i p - v e r t i c a l , strati— stratiSetting: S t r i k e - s o u t h e a s t , dip—vertical, graphic g r a p h i c top—northeast. top-northeast. Feature(s): F e a t u r e ( s ) : Flow F l o w contact, c o n t a c t , pillows, p i l l o w s , hyaloclastite, h y a l o c l a s t i t e , auto— autoclastic breccia c l a s t i c breccia At A t this t h i s stop s t o p we w e will w i l l examine e x a m i n e an a n east—south—easterly east-south-easterly striking v a r i e t y of of s t r i k i n g mafic m a f i c flow f l o w that t h a t displays d i s p l a y s aa variety structures. s t r u c t u r e s . The The flow f l o w grades g r a d e s from f r o m aa massive, m a s s i v e , fine—grain— fine-qrained, crystalline base through poorly defined pillows e d , c r y s t a l l i n e b a s e t h r o u g h p o o r l y d e f i n e d p i l l o w s into into aa hyaloclastite h y a l o c l a s t i t e to t o broken b r o k e n pillow p i l l o w breccia b r e c c i a top t o p (Figure (Figure 15). mm carbonate c a r b o n a t e filled filled 1 5 ) . Amoehoid Amoeboid pillows p i l l o w s rimmed rimmed with w i t h 1 mm amygdules a m y g d u l e s appear a p p e a r 1.3 1 . 3 mm below b e l o w the t h e flow f l o w top. t o p . The The pillows pillows grade g r a d e sharply s h a r p l y into i n t o aa variable v a r i a b l e thickness t h i c k n e s s of o f hyaloclastite hyaloclastite and and broken b r o k e n pillow p i l l o w breccia. b r e c c i a . The The pillow p i l l o w breccia b r e c c i a contains contains irregular < 6 4 mm mm in i n aa fine— finei r r e g u l a r pillow p i l l o w fragments f r a g m e n t s generally g e n e r a l l y <64 grained g r a i n e d chioritic c h l o r i t i c matrix. m a t r i x . The The elongation e l o n g a t i o n of o f pillows p i l l o w s and and embayment embayment of o f hyaloclastite h y a l o c l a s t i t e 30° 30 to t o bedding b e d d i n g represents r e p r e s e n t s aa flow t o the t h ewest—northwest w e s t - n o r t h w e s t ((right r i g h t to to f l o w front f r o n t advancing a d v a n c i n g to l e f t on figure 15). The issharp s h a r pand and T h e contact c o n t a c t with w i t h the t h e overlying o v e r l y i n g flow f l o w is irregular. The base is a 2 cm very fine vesiculated irregular. The b a s e i s a 2 c m v e r y f i n e v e s i c u l a t e d zone 6 0 cm cm to t o 1 mm massive m a s s i v e portion p o r t i o n grading grading z o n e overlain o v e r l a i n by by aa 60 into poorly i n t o coarse c o a r s e hyaloclastite—broken h y a l o c l a s t i t e - b r o k e n pillow p i l l o w breccia b r e c c i a —- poorly formed f o r m e d pillows p i l l o w s that t h a t have h a v e been b e e n sheared s h e a r e d and and carbonatized. carbonatized. 1 left on figure 15). 1 STOP STOP 2C: 2C : Figure F i g u r e 13 1 3 Outcrop O u t c r o p "C" "C" Formation: F o r m a t i o n : Snake S n a k e Bay Bay formation formation Lithology: Maf i c Metavolcanics Metavolcanics L i t h o l o g y : Mafic Setting: Strike—southeast, Setting: S t r i k e - s o u t h e a s t , dip—vertical, dip-vertical, stratigraphic s t r a t i g r a p h i top c t o— p - northeast northeast Feature(s): F e a t u r e ( s ) : Pillows, P i l l o w s , radiating r a d i a t i n gamygdules, a m y g d u l e s , epidote epidote alteration. a 1t e r a t i o n . �Figure 15: 4-1 a -1-1 a 0 IÑ 0 3 U-li) 4-1 0900 1200 The flow direction hyaloclastite, broken pillow breccia Sketch of the mafic flow top at Stop 2(B on Figure 13). is from right to left. Flow top breccia flow massive overlying massive flow I.. w IÑ C-> (1) - 4 IÑ w e 4-1 0 �139 STOP STOP 3: 3: Lobstick L o b s t i c k Bay. Bay. This T h i s stop s t o p is i s the t h e larger l a r g e r of o f two two l i t t l e islands i s l a n d s 20 20 m from f r o m the t h e mainland m a i n l a n d (Figure (Figure little 11). 11). Formation: Formation: Facies: Facies : Setting: Setting: Berry B e r r y River R i v e r formation formation Proximal P r o x imal Deposition Depos i t i o n Strike—east, S t r i k e - e a s t , dip—vertical, dip-vertical, stratigraphic s t r a t i g r a p h i c top—south top-south Feature(s): F e a t u r e ( s ) : Block B l o c k and a n d ash a s h flow; f l o w ; massive m a s s i v e portion p o r t r i o n and and cloud c l o u d surge s u r g e top. top. Massive, m a t r i x supported s u p p o r t e d pyroclastic p y r o c l a s t i c breccia b r e c c i a with with M a s s i v e , matrix subangular s u b a n g u l a r quartz—feldspar q u a r t z - f e l d s p a r pporphyry o r p h y r y cclasts l a s t s ini nquartz— quartzfeldspar f e l d s p a r tuff t u f fmatrix m a t r i xhave h a v e poorly p o o r l y defined d e f i n e d contacts. contacts. Essential cm and and minor minor E s s e n t i a l porphyry p o r p h y r y clasts c l a s t are s a r10—30 e 10-30 cm accidental a c c i d e n t a l mafic maÂi c cclasts l a s t s are a r e smaller. s m a l l e r . The The fine f i n e tuff tuff matrix m a t r i x increases i n c r e a s e s slightly s l i g h t l yini nabundance a b u n d a n c e toward t o w a r d the t h e top. top. A A 21 21 cm c m tthick h i c k quartz—feldspar q u a r t z - f e l d s p a r t tuff u f f bed b e d occurs o c c u r s on o n the the south s o u t h side s i d e of o f the t h e island i s l a n d between b e t w e e n two two pyroclastic p y r o c l a s t i c breccia breccia units u n i t s (Photo ( P h o t o 2). 2 ) . The The base b a s e of o f the t h e tuff t u f f is i s medium medium to t o fine fine grained g r a i n e d and and has h a s pronounced p r o n o u n c e d laminae. laminae. On On the t h e basis b a s i s of o f lack l a c k of o f bedding b e d d i n g in i n the t h e coarse coarse units, u n i t s , homolithic h o m o l i t h i c subangular s u b a n g u l a r clasts c l a s t s and and poor p o o r sorting sorting this t h i s sequence s e q u e n c e is i s interpreted i n t e r p r e t e d as a s aa block b l o c k and and ash a s h flow. flow. The The thin t h i n tuff t u f f interbed i n t e r b e d based b a s e d on o n the t h e association a s s o c i a t i o n with w i t h the the block b l o c k and a n d ash a s h flows f l o w s and and the t h e gradational g r a d a t i o n a l contact c o n t a c t with w i t h the the underlying u n d e r l y i n g breccia b r e c c i a is is interpreted i n t e r p r e t e d to t o be b e aa cloud c l o u d surge surge deposit. deposit. Overlying O v e r l y i n g the t h e tuff t u f f with w i t h aa sharp s h a r p but b u t irregular irregular contact i s aa similar s i m i l a r block b l o c k and and ash a s h deposit. deposit. c o n t a c t is . 400 400 mm east e a s t of o f Stop S t o p 33 (Figure ( F i g u r e 11). 11) S t o p on o n aa Stop long l o n g outcrop o u t c r o p sloping s l o p i n g steeply s t e e p l y inland. i n l a n d . This T h i s outcrop o u t c r o p has has moss moss on o n it i t and and can c a n be b e very v e r y slippery. slippery. STOP 4: STOP 4: Formation: Formation: Facies: Facies : Setting: Setting: Berry B e r r y River R i v e r formation formation Proximal P r o x i m a l Deposition Deposition Strike—east, S t r i k e - e a s t , dip—vertical, dip-vertical , Feature: Feature: top—south top-south Pumice P u m i c e in i n ash a s h flow f l o w tuff tuff stratigraphic stratigraphic Irregular c l a s t s of o f aa variety v a r i e t y of o f sizes sizes I r r e g u l a r chloritic c h l o r i t i c clasts (Photo ( P h o t o 3) 3 ) occur o c c u r near n e a r the t h e topographic t o p o g r a p h i c top t o p of o f the t h e ooututcrop. c l o t s , interpreted interpreted c r o p . These T h e s e quartz—feldspar q u a r t z - f e l d s p a r phyric p h y r i c clots, to t o be b e pumice, p u m i c e , occur o c c u r in i n aa fine—grained, f i n e - g r a i n e d , massive m a s s i v e quartz— quartzfeldspar f e l d s p a r tuff. t u f f . Two Two pumice p u m i c e bearing b e a r i n g horizons h o r i z o n s occur o c c u r in in zones z o n e s of o f silicification s i l i c i f i c a t i o n marked m a r k e d by by thin t h i n quartz q u a r t z veinlets. veinlets. Subtle S u b t l e lithic l i t h i c clasts c l a s t s are a r e seen. s e e n . The The pumice p u m i c e occurs o c c u r s in i n the the upper portion of two tuff u p p e r p o r t i o n o f t w o t u f f beds b e d s (units). ( u n i t s ) . Alteration A l t e r a t i o n to to chlorite c h l o r i t e and and silicification s i l i c i f i c a t i o n may may be b e pre—metamorphic. pre-metamorphic. �14 0 Photo 1: 1: Photo Cored Cored bomb bomb found found in i n aa 44 mm thick t h i c k mafic mafic breccia b r e c c i a at at Stop 2D. 2D. AA tuff t u f f accidental a c c i d e n t a l clast c l a s t is i s armored armored with w i t h aa Stop t h i n rim r i m of of amygdaloidal amyqdaloidal mafic mafic magma. magma. thin Photo 2: 2: Photo Cloud Cloud surge s u r g e tuff t u f f between between two two pyroclastic p y r o c l a s t i c breccias breccias The tuff is the upper portion 3. The t u f f i s t h e upper p o r t i o n of of aa a t Stop Stop 3. at Stratigraphic top is to b l o c k and and ash ash flow. flow. S t r a t i g r a p h i c top is t o the the block left. left. �141 Photo P h o t o 3: 3: Irregular I r r e g u l a r shaped s h a p e d pumice p u m i c e in i n aa quartz—feldspar q u a r t z - f e l d s p a r ash ash flow f l o w tuff t u f f at a t Stop S t o p 4. 4. T h e pumice p u m i c e now now consists c o n s i s t s of of The q u a r t z and a n d feldspar f e l d s p a r phenocrysts p h e n o c r y s t s in i n aa chloritic chloritic quartz matrix. matrix. (L -J I Photo 4: P h o t o 4: I Gas Gas escape e s c a p e structure s t r u c t u r e in i n the t h e upper u p p e r portion p o r t i o n of o f aa series s e r i e s of o f block b l o c k and a n d ash a s h flow f l o w deposits d e p o s i t s at a t Stop S t o p 7. 7. S t r a t i g r a p h i c top t o p is is towards t o w a r d s the t h e narrow n a r r o w apex a p e x of o f the the Stratigraphic triangular shaped feature. t r i a n g u l a r s h a p e d f e a t u r e . Gas G a s streaming s t r e a m i n g has has altered t o chlorite c h l o r i t e thus t h u s enhancing e n h a n c i n g the the a l t e r e d the t h e matrix m a t r i x to clasts c l a s ts . �142 STOP STOP 5: 5: A p p r o x i m a t e l y 22 km west w e s t of o f Stop S t o p 44 on o n the the Approximately l a k e s h o r e at a t the t h e west end e n d of o f Roberts R o b e r t s Lodge Lodge near n e a r the t h e boat boat lakeshore dock. dock. T h i s stop s t o p at a t the t h e end e n d of o f Roberts R o b e r t s Road Road may be be This reached Please 11). Please r e a c h e d by b y vehicle v e h i c l e from f r o m Highway Highway 71 71 (Figure ( F i g u r e 11). get g e t permission p e r m i s s i o n from f r o m the t h e lodge l o d g e for f o r this t h i s stop. stop. Formation: Formation: Lithology: Lithology : Setting: Setting: Feature: Feature: Berry B e r r y River R i v e r formation formation Mafic metavolcanics, Maf i c m e t a v o l c a n i c s , wacke wacke Strike—east, S t r i k e - e a s t , dip—vertical, dip-vertical, stratigraphic s t r a t i g r a p h i c top—south top-south Top T o p of o f Berry B e r r y River R i v e r formation formation The T h e Berry B e r r y River R i v e r formation f o r m a t i o n culminated c u l m i n a t e d in i n aa 20—100 20-100 mm thick The t h i c k unit u n i t of o f mafic maf i c pillowed p i l l o w e d flows. flows. T h e outcrop o u t c r o p on o n the the north is fine—grained f i n e - g r a i n e d porphyritic porphyritic n o r t h side s i d e of o f the t h e dock d o c k is (plagioclase) mafic ( p l a g i o c l a s e ) ma i c flow f l o w with w i t h poorly p o o r l y developed d e v e l o p e d pillows. pillows. Remnant pillow selvages are seen here. Better p i l l o w s e l v a g e s are s e e n h e r e . B e t t e r developed developed pillows p i l l o w s are a r e found f o u n d in i n outcrops o u t c r o p s among among the t h e cabins. cabins. The cm tthick The overlying o v e r l y i n g wackes w a c k e s have h a v e40—90 40-90 cm h i c k graded graded beds. Grain is well w e l ldeveloped d e v e l o p e d with w i t h 1 mm mm beds. G r a i n ggradation r a d a t i o n is subrounded feldspars and quartz grains in s u b r o u n d e d f e l d s p a r s a n d q u a r t z g r a i n s i n aa bbiotite i o t i t e rich rich matrix These cm t thick h i c k aargillite r g i l l i t e top. top. These m a t r i x grading g r a d i n g into i n t o 4—5 4-5 cm wackes, w a c k e s , based b a s e d on o n the t h e character c h a r a c t e r of o f the t h e grains, g r a i n s , represent represent reworking r e w o r k i n g and a n d redeposition r e d e p o s i t i o n of o f the t h e Berry B e r r y River R i v e r formation. formation. 1 STOP 6 : This T h i s location l o c a t i o n in i n Mist M i s t Inlet I n l e t is i s approximately approximately STOP 6: 11.5 1 1 . 5 km west w e s t of o f Stop S t o p 55 (Figure ( F i g u r e 12). 12). Berry B e r r y River R i v e r formation formation Distal D i s t a l redeposited redeposited Strike—east, S t r i k e - e a s t , dip—vertical, dip-vertical, stratigraphic s t r a t i g r a p h i c top—south top-south Feature(s): H e t e r o l i t h i c volcaniclastics, v o l c a n i c l a s t i c s , wackes wackes F e a t u r e ( s ) : Heterolithic Formation: Formation: Facies: F a c ies : Setting: Setting: The T h e coarse coarse volcanics v o l c a n i c s (Figure ( F i g u r e 16) 16 ) are a r e clast c l a s t supported supported 1.7 1.7 —- 4 m thick, t h i c k , predominantly p r e d o m i n a n t l y ungraded u n g r a d e d and and contain contain clasts o f feldspar f e l d s p a r porphyry, p o r p h y r y , intermediate, i n t e r m e d i a t e , mafic maÂi c and and c l a s ts of felsic Size i s noted noted f e l s i c metavolcanics m e t a v o l c a n i c s and and wacke. wacke. S i z e grading g r a d i n g is in Clasts, some beds. beds. C l a s t s , allowing a l l o w i n g for f o r deformation, d e f o r m a t i o n , are are i n some subrounded. The signs subrounded. s i g n s of o f reworking r e w o r k i n g (i.e. ( i.e. compositional compositional difference d i f f e r e n c e between b e t w e e n matrix m a t r i x and and clasts, c l a s t s , rounding r o u n d i n g of of clasts, heterogeneity of clast type and to c l a s t s , h e t e r o g e n e i t y o f c l a s t t y p e and the t h e ungraded u n g r a d e d to poorly p o o r l y graded g r a d e d nnature a t u r e oof f t the h e uunit) n i t ) ssuggests u g g e s t s t this h i s is i s aa debris d e b r i s flow f l o w (lahar) ( l a h a r )(c.f. ( c . f Fisher . F i s h eand r a nSchmincke, d S c h m i n c k e , 1984). 1984). The interbedded feldspar tuffs a r e thinner t h i n n e r bedded bedded The i n t e r b e d d e d f e l d s p a r t u f f s are than t h a n the t h e coarse c o a r s e volcaniclastics v o l c a n i c l a s t i c s and a n d contain c o n t a i n occasional occasional lithic l i t h i c clasts. clasts. Dark Dark grey, g r e y , fine f i n e grained, g r a i n e d , argillaceous a r g i l l a c e o u s wacke wacke and and lighter l i g h t e r grey g r e y feldspar f e l d s p a r and and quartz—feldspar q u a r t z - f e l d s p a r wacke wacke units units have h a v e variable v a r i a b l e bed bed thickness. thickness. The T h e heterolithic h e t e r o l i t h i c nature, n a t u r e , degree d e g r e e of o f sorting, s o r t i n g , and and rounding w e l l as a s the t h e wacke interbeds i n t e r b e d s suggest s u g g e s t the the r o u n d i n g as a s well volcaniclastics v o l c a n i c l a s t i c s have h a v e been b e e n reworked r e w o r k e d and and redeposited. redeposited. Provenance P r o v e n a n c e of o f the t h e unit u n i t was w a s the t h e underlying u n d e r l y i n g and and lateral lateral parts p a r t s of o f the t h e Berry B e r r y River R i v e r formation. formation. beds beds �143 MIST INLET: LAKE LAKE OF OF THE THE WOODS WOODS ............................................................... .................................................. wacke -....................................................................... a r g i l l a argillaceous c e o u s wacke o~l-feldspar tuff —feldspar tuff 0 0 - 0 0 o 0 O"Oo 0 0 0 0O.O OOOo.o 0 0 0 0 O O " O ~ o ~ O OoOoo 0 0 0 O 0 O 0 O 0 0 hert —tuft tuff breccia, breccia, upward tto o lapilli tuff fines upward wacke wacke metres metres - 10 n 10 - 88 tuff. tuff -argillaceous wacke rgiIIaceous wacke ........................ —lapillistone Ia liii st o tie ::::jjJ._Iapillistone 0 - 44 -2 1tuff . . . . . . . . . . . . '.— - 66 wacke wacke - 00 '—wacke -pyroclastic breccia breccia to t o tuff tuff —pyroclastic -feldspar tuff feldspar tuff A ~-pyroclastic breccia pyroclastic breccia A 0 A ;>:.:::::::.:.:.:.:.:.:.:.:.:.:.>>~.:.:.:.:.:.:.:.:.:.:.;*;;?>::::: :>::i^::&:k:&<^:^:::;^;:^cc:; -wacacke k e with with thin thin pyrociastic pyroclastic b r e c c i a horizons horizons breccia -feldspar tuff feldspar tuff pyroclastic breccia -pyroclastic breccia e wwacke acke -feldspar tuff '—feldspar tuff --wacke cke ..................... ...................................... ...& ..iS....ia,:....si....g...?........ :.... ............................ ......... .::x ........::.: ................................ .....:.:.......:.:.........................:: .:.x<.:.:.:.~.~z,.x<~.:.~ o oo A A Fiqure F i g u r e 16: 16: o O 0 Columnar C o l u m n a r mmeasured e a s u r e d s esection c t i o n ffrom r o m aa sshoreline h o r e 1 i n e outcrop outcrop in i n the t h e distal d i s t a lredeposited r e d e p o s i t e d facies f a c i e s at a tStop S t o p66 in i n Mist M i s t base ooff the is at Inlet. I n l e t . The The base t h e column c o l u m n is a t the t h e north n o r t hend end of the outcrop area. of t h e o u t c r o p a r e a . �144 Return R e t u r n tto o vvehicles e h i c l e s for f o r the t h e remainder r e m a i n d e r of o f the t h e field field The road r o a d log l o g will w i l l start s t a r t from f r o m the t h e north n o r t h end e n d of o f the the Sioux S i o u x Narrows N a r r o w s Bridge. Bridge. From the t h e north n o r t h end e n d of o f the t h e Sioux S i o u x Narrows N a r r o w s Bridge B r i d g e proceed proceed north krn to t o the t h e Maybrun Maybrun Road. Road. n o r t h on o n Highway 71 7 1 for f o r 10 10 km Figures F i g u r e s 11 1 1 arid a n d 12. 12. Turn T u r n right r i g h t (east) ( e a s t ) on o n the t h e Maybrun Maybrun Road Road for f o r 4.9 4 . 9 km. km. This This mileage STOP 88 aand is STOP n d wwe e wwill i l l r return e t u r n t otoi tito s o please please m i l e a g e is remember the t h e location. location. C o n t i n u e for for a a further f u r t h e r 0.6 0.6 km Continue ----km (Figure — ( F i g u r e 11). 11). trip. trip. 0.0 0 . 0 km km 10 krn 1 0 km 1 5 . 5 km km 15.5 - STOP 7: 7: (Figure ( F i g u r e 11) 1 1 ) is is aa large l a r g e area a r e a of o f outcrops o u t c r o p s on o n the the STOP left l e f t (north ( n o r t h side s i d e of o f the t h e road) r o a d ) (Figure ( F i g u r e 17). 1 7 ) . Please P l e a s e park park off i t is is used u s e d by b y large l a r g e trucks t r u c k s to t o haul h a u l pulp pulp o f f the t h e road r o a d as a s it wood. Berry B e r r y River R i v e r formation format ion Proximal P r o x i m a l deposition deposition Strike S t r i k e east, e a s t , dip—vertical, dip-vertical , stratigraphic s t r a t i g r a p h i c tops—south tops-south Feature(s): F e a t u r e ( s ) : Block B l o c k and a n d ash a s h flows, f l o w s , debris d e b r i s flows, f l o w s , lahars, lahars, gas g a s escape e s c a p e structures structures Formation: Format i o n : Facies: Facies : Setting: Setting: Figure F i g u r e 17 17 shows s h o w s the t h e location l o c a t i o n of o f outcrops o u t c r o p s as a s aa litho— lithologic l o g i c map and a n d separately s e p a r a t e l y the t h e interpretation i n t e r p r e t a t i o n of o f the the depositional were deposited deposited d e p o s i t i o n a l mechanism. mechanism. T h e pyroclastics p y r o c l a s t i c s were The as The a s block b l o c k and a n d ash a s h flows, f l o w s , debris d e b r i s flows f l o w s and a n d lahars. lahars. The lahars were deposited d e p o s i t e d in i n aa channel c h a n n e l within w i t h i n debris d e b r i s flows flows l a h a r s were (Figure ( F i g u r e 17). 17). The west end e n d of o f Figure F i g u r e 17 17 are a r e medium medium to to T h e units u n i t s at a t the t h e west coarse c o a r s e pyroclastics p y r o c l a s t i c s which w h i c h are a r e homolithic h o m o l i t h i c (quartz— (quartzfeldspar m a t r i x supported, s u p p o r t e d , poorly poorly f e l d s p a r porphyry p o r p h y r y clasts), c l a s t s ) , matrix sorted Up U p to t o 8—10 8-1 0 percent p e r c e n t pumiceous p u m i c e o u s lapilli lapilli s o r t e d and a n d graded. graded. occur Evidence o c c u r in i n units u n i t s at a t the t h e western w e s t e r n end. end. E v i d e n c e bearing b e a r i n g on on the 1 ) gas g a s escape escape t h e origin o r i g i n of o f these t h e s e units u n i t s includes: i n c l u d e s : 1) structures 4 ) ; 2) 2 ) their t h e i r homolithic, h o m o l i t h i c , poorly p o o r l y graded graded s t r u c t u r e s (Photo ( P h o t o 4); and 3 ) the t h e presence p r e s e n c e of of a n d poorly p o o r l y bedded b e d d e d character c h a r a c t e r and a n d 3) pumice. p u m i c e . The The above a b o v e are a r e consistent c o n s i s t e n t with w i t h these t h e s e units u n i t s being being deposited m e c h a n i s m s (c.f. ( c .f Sparks Sparks d e p o s i t e d by b y block b l o c k and a n d ash—flow a s h - f l o w mechanisms et e t al., a l . , 1979). 1979). A gas g a s escape e s c a p e structure s t r u c t u r e (Photo ( P h o t o 4) 4 ) is i s crudely crudely triangular t r i a n g u l a r in i n shape s h a p e with w i t h the t h e apex a p e x towards t o w a r d s the t h e strati— stratigraphic The m matrix g r a p h i c top. top. a t r i x has h a s been b e e n altered a l t e r e d to t o chlorite, chlorite, due t o gas g a s streaming, s t r e a m i n g , and a n d the t h e subround s u b r o u n d clasts c l a s t s enhanced. enhanced. d u e to Other O t h e r areas a r e a s of o f chlorite c h l o r i t e alteration, a l t e r a t i o n , though t h o u g h not n o t as a s well well defined d e f i n e d as a s Photo P h o t o 4, 4 , have h a v e been b e e n interpreted i n t e r p r e t e d as a s gas q a s escape escape structures. structures The presence p r e s e n c e of o f the t h e gas g a s escape e s c a p e structures s t r u c t u r e s and and pumice pumice indicates were deposited deposited i n d i c a t e s that t h a t these t h e s e block b l o c k and a n d ash a s h flows f l o w s were in i n a shallow s h a l l o w water w a t e r proximal p r o x i m a l environment. environment. In I n the t h e central c e n t r a l and a n d eastern e a s t e r n part p a r t of o f the t h e outcrop o u t c r o p area area one t o finer f i n e r heterolithic h e t e r o l i t h i c pyro— pyroo n e observes o b s e r v e s aa transition t r a n s i t i o n to clastics The e l a s t i c s with w i t h thinner, t h i n n e r , better—developed b e t t e r - d e v e l o p e d bedding. bedding. The . �H Ui F i g u r e 17: 17: Figure The outcrops Sketch of the thet hMaybrun S k e t c h of t h e outcrop o u t c r o p area a r e aata Stop t S t o7 p on 7 on e MaybrunRoad. Road. The o u t c r o p s were were The located l o c a t e d using u s i n gpace paceand andcompass compass methods. methods. The ppatterned a t t e r n e d iinterpretation n t e r p r e t a t i o n of of d e p o s i t i o n a l mechanisms in i n the t h e upper upper left l e f t portion p o r t i o n is is of of the t h e same same area a r e a as a s the the depositional o u t c r o p map. map. outcrop �146 most most common common clasts c l a s t s are a r e quartz—feldspar q u a r t z - f e l d s p a r porphyry p o r p h y r y with with with w i t h minor m i n o r siltstone s i l t s t o n e clasts c l a s t s in i n the t h e northern—most n o r t h e r n - m o s t outoutcrop c r o p (Figure ( F i g u r e 17). 17 ) . S u b r o u n d e d ^ fine—grained f i n e - g r a i n e d crystalline crystalline Subrounded, mafic t o the t h e block b l o c k and and r n a f i c clasts c l a s t s also a l s o occur. occur. I n contrast c o n t r a s t to In a s h - f l o w s , sorting s o r t i n g is is good g o o d to t o poor p o o r and and graded g r a d e d beds b e d s are are ash—flows, common. The bedding, b e d d i n g , sorting, s o r t i n g , and a n d heterolithic h e t e r o l i t h i c nature nature of were deposited d e p o s i t e d by by o f these t h e s e subunits s u b u n i t s indicate i n d i c a t e that t h a t they t h e y were debris d e b r i s flows f l o w s (c.f. ( c . f . Fisher F i s h e r and a n d Schmincke, S c h m i n c k e , 1984). 1984). T h r e e coarse c o a r s e volcaniclastic v o l c a n i c l a s t i c units, u n i t s , each e a c h with w i t h aa silt— siltThree stone s t o n e top t o p were deposited d e p o s i t e d in i n aa channel c h a n n e l within w i t h i n the t h e debris debris flows They f l o w s (Figure ( F i g u r e 17). 17). T h e y are a r e unsorted, u n s o r t e d , heterolithic h e t e r o l i t h i c with with elongate, c l a s t s are a r e fine— f i n e - and and e l o n g a t e , subangular s u b a n q u l a r clasts. clasts. Most clasts medium—grained med i u m - g r a i n e d mafic maÂi c metavolcanics m e t a v o l c a n i c s with w i t h approximately a p p r o x i m a t e l y 55 percent p e r c e n t white w h i t e aphanitic, a p h a n i t i c , felsic f e l s i c lapilli l a p i l l i throughout. throughout. The The matrix m a t r i x is is aa feldspar—hornblende f e l d s p a r - h o r n b l e n d e "tuff". "tuff" felsic The felsic clasts c l a s t s disappear d i s a p p e a r towards t o w a r d s the t h e top t o pand and the t h ematrix m a t r i xbecomes becomes aa light l i q h tbrown brown silty s i l t yarenite a r e n i t ewith w i t hcobbles c o b b l e sofo fsubround subround quartz—bearing The unsorted, q u a r t z - b e a r i n g pyroxene p y r o x e n e gabbro. qabbro. u n s o r t e d , hetero— heterolithic l i t h i c nature n a t u r e of o f the t h e volcaniclastic v o l c a n i c l a s t i c and and the t h e presence p r e s e n c e of of the t h e siltstone s i l t s t o n e top t o p suggests s u g g e s t s these t h e s e subunits s u b u n i t s are a r e lahars. lahars. The The tuffaceous t u f f a c e o u s matrix m a t r i x of o f the t h e southernmost s o u t h e r n m o s t lahar lahar contains c o n t a i n s rounded r o u n d e d quartz—bearing q u a r t z - b e a r i n g mmafic a f i c cclasts l a s t s and and quartz—feldspar is rusty, rusty, q u a r t z - f e l d s p a r pporphyry o r p h y r y cclasts. l a s t s . This T h i s llahar a h a r is weathering with weathering w i t h disseminated d i s s e m i n a t e d ppyrite y r i t e and and has has cross—cutting These T h e s e features f e a t u r e s suggest suggest veinlets c r o s s - c u t t i n g cherty c h e r t y veirilets. hot h o t emplacement e m p l a c e m e n t and a n d early e a r l y alteration. a l t e r a tion. The T h e complexity c o m p l e x i t y present p r e s e n t at a t this t h i s stop s t o p shows s h o w s that t h a t even even though t h o u g h aa single s i n g l e facies f a c i e s has h a s been b e e n assigned a s s i g n e d many many depositional d e p o s i t i o n a l processes p r o c e s s e s have h a v e occurred o c c u r r e d within w i t h i n this t h i s one one facies. facies. . . 0.0 0.0 km km T u r n around a r o u n d and a n d proceed p r o c e e d west west on o n the t h e Maybrun Maybrun road r o a d to t o STOP STOP Turn 88 (you remember tthe 0.6km. ( y o u remember h e sspot?) p o t ? ) aapproximately p p r o x i m a t e l y 0.6 km. 0.6 0.6 km km STOP STOP 8: 8: (Figure ( F i g u r e 11). 11 ). the t h e road. road. - F l a t outcrop o u t c r o p on o n the t h e north n o r t h side s i d e of of Flat Facies: Facies : Setting: Setting: Berry B e r r y River R i v e r formation formation Proximal P r o x i m a l deposition deposition Strike—east, S t r i k e - e a s t , dip—vertical, dip-vertical, Feature: Feature: top—south top-south Pyroclastic magma matrix matrix P y r o c l a s t i c breccia b r e c c i a with w i t h mafic ma i c magma Formation: Formation: stratigraphic stratigraphic Homolithic H o m o l i t h i c pyroclastic p y r o c l a s t i c breccia b r e c c i a with w i t h subangular subangular quartz—feldspar q u a r t z - f e l d s p a r porphyry p o r p h y r y clasts c l a s t s has h a s aa matrix m a t r i x of o f fine fine quartz—feldspar Locally magma occurs o c c u r s as as q u a r t z - f e l d s p a r tuff. tuff. L o c a l l y mafic maf i c magma discontinuous d i s c o n t i n u o u s blebs b l e b s with w i t h chilled c h i l l e d margins m a r g i n s wrapping w r a p p i n g around around clasts; c l a s t s and a n d tuffaceous t u f f a c e o u s matrix m a t r i x have h a v e been b e e n bleached bleached c l a s t s ; clasts for c m adjacent a d j a c e n t to t o the t h e mafic m a f i c magma. magma. The The outcrop outcrop f o r about a b o u t 1 cm has t o have h a v e formed f o r m e d by b y intrusion i n t r u s i o n of of h a s been b e e n interpreted i n t e r p r e t e d to rnafic magma iinto maÂi c magma n t o uunconsolidated n c o n s o l i d a t e d felsic f e l s i c pyroclastic pyroclastic breccia. breccia. This t o the t h e conclusion c o n c l u s i o n that that T h i s interpretation i n t e r p r e t a t i o n leads l e a d s to mafic maÂi c magmatism m a q m a t i s m must m u s t have h a v e been b e e n concomitant c o n c o m i t a n t with w i t h the the 1 �147 f e l s i c magmatism magmatism producing p r o d u c i n g the t h e Berry B e r r y River R i v e r formation. formation. felsic C o n t i n u e west west for f o r 2.6 2 . 6 km km toward_Highway t o w a r d H i q h w a y -71 resetting resetting Continue 71 o d o m e t e r a tat t h ethe B e r rBerry y R i v e rT7ET3. bridge. odometer Continue w e s t ffor o r -11.3km . 3 km Continue west -- 0 . 0 km km 0.0 B e r r y River R i v e r bridge. bridge. Berry 1 . 3 km km 1.3 STOP 99 (Figure ( F i g u r e 11 11 aand n d 12): 1 2 ) : included i n c l u d e d are a r e outcrops o u t c r o p s on o n both both STOP i s b u i l t up and t h e s i d es s i d e s of o f the t h e road. road. The r o a d sides The road is built up and the sides a r e soft s o f t so so care c a r e must m u s t be b e taken t a k e n while w h i l e parking. p a r k i n g . Watch Watch for for are l o g g i n g trucks! trucks! logging B e r r y River R i v e r formation formation Berry P r o x i m a l d i s t a l and i s t a l redeposited redeposited Proximal—distal andddistal dip-vertical S t r i k e - s o u t h e a s t , dip—vertical Strike—southeast, s t r a t i g r a p h i c top—southwest top-southwest stratigraphic C o n t a c t with w i t h the t h e Warclub W a r c l u b group g r o u p wackes, wackes , F e a t u r e ( s ) : Contact Feature(s): Formation: Formation: Facies : Facies: Setting: Setting: f a l l - o u t deposits, d e p o s i t s , subaqueous s u b a q u e o u s pyroclastic pyroclast ic fall—out f l o w s , double d o u b l e grading. grading. flows, The ccontact o n t a c t of o f the t h e base b a s e of o f the t h eBerry B e r r yRiver R i v e r formation formation The e x p o s e d in i n 22 outcrops outcrops a n d wackes w a c k e s oof f the t h e Warclub W a r c l u b ggroup r o u p is and is exposed m aapart p a r t oon n tthe h e north n o r t h side s i d e of o f the t h e road. road. Measured 30 in 30 Measured s e c t i o n s o f these t h e s e exposures e x p o s u r e s are a r e shown shown in i n the t h e center c e n t e r and and seEfönsöf A thin zone of distally A t h i n zone o f d i s t a l l y r i g h t columns c o l u m n s oof f Figure F i g u r e 18. 18. right r e d e p o s i t e d , reworked r e w o r k e d tuff t u f f separates s e p a r a t e s the t h e wacke wacke from f r o m the the redeposited, Note that t h a t detailed detailed p r o x i m a l - d i s t a l facies f a c i e s rocks. rocks. proximal—distal Note c o r r e l a t i o n cannot c a n n o t be b e made made between b e t w e e n these t h e s e two t w o closely closely correlation s p a c e d outcrops o u t c r o p s (Figure ( F i g u r e 18). 18). spaced is aa generalized g e n e r a l i z e d section s e c t i o n of of F i g u r e 19 19 (left ( l e f t column) c o l u m n ) is Figure A t h i c k l y t h e outcrop o u t c r o p on o n the t h e south s o u t h side s i d e of o f the t h e road. road. the A thickly t o thin t h i n bedded b e d d e d sequence s e q u e n c e of o f crystal c r y s t a l tuff t u f f and and l a m i n a t e d to laminated p u m i c e - c r y s t a l lapilli l a p i l l i tuff t u f f exhibits e x h i b i t s poorly p o o r l y defined defined pumice—crystal m u t u a l contacts. contacts. mutual to The distinct d i s t i n c t but b u t poorly p o o r l y defined d e f i n e d beds b e d s are a r e moderate m o d e r a t e to The w e l l sorted s o r t e d and and may may have h a v e been b e e n deposited d e p o s i t e d by by continuous continuous well f a l l - o u t through t h r o u g h water. water. fall—out O v e r l y i n g the t h e fall—out  £ a l l - o u deposits d e p o s i t s are a r e interbedded, interbedded, Overlying d o u b l y graded g r a d e d pyroclastic p y r o c l a s t i c flows, f l o w s , tuffs t u f f s and and wacke. wacke. These doubly These s o u t h e a s t on o n both b o t h sides s i d e s of o f the the a r e best b e s t exposed e x p o s e d 180 1 8 0 inm southeast are road. The right r i g h t column c o l u m n (Figure ( F i g u r e 19) 1 9 ) is i s aa generalized generalized road. The s e c t i o n of o f this t h i sexposure. exposure. section A t this stop the fall-out deposits underlie the c o a r s e r flow f l o w deposits. deposits coarser At this stop the fall—out deposits underlie the . 3.5 3.5 km km 0 . 0 km 0.0 km 1.9 1.9 km km Drive Drive - f o r 2.2 2 . 2 kin km to t o Highway H i g h w a y 71. 71. for Highway 71" Highway 71 R o b e r t sRoad Road 1.9km 1.9.- km T u r n lleft e f t and a n d drive d r i v e tot oRoberts Turn --STOP 10 10 (Figures ( F i g u r e s 11 1 1 and a n d 12). 1 2 ) . The The outcrop o u t c r o p is is on o n the the STOP n o r t h w e s t side s i d e of o f Highway Highway 71 71 opposite o p p o s i t e Roberts R o b e r t s Road. Road. northwest i s on o n aa curve c u r v e so so please p l e a s e park p a r k on o n Roberts R o b e r t s Road. Road. T h i s stop s t o p is This Formation: Formation: Facies : Facies: B e r r y River R i v e r formation formation Berry Ash fflow l o w tuff tuff Ash �Figure 18: • massive tuff reworked quartz feldspar 2m im 0 I— <r.2 Cr . o u > cc 2mquarzcrystai tu f 00000 o lapilli tuft — 2 0— r2 >2 0. n > z 0 >- ?i.0 x cc lapilli tuff oo ::::.:......... oL 0çQC °oOO1 a c0 c ro°0o1 OQ °4m tuft breccia 0 tuft breccia arenite reworked tuft reworked tuff 0.2-6cm discontmuous beds 575m wacke 30m <w 0 00000 lapilli tuff BERRY feldspar crystal 00 BERRY R VER o0 00 0 matrix RIVER FORMATION FORMATION 0 00000000 redeposition lapilli tuft redeposition reworked tufts 00 o prograding reworked tuffs distal source silty tuff distal source chert thinly laminated cc reworked tuft bleached contact chert . reverse graded --. BERRY RIVER FORMATION tuft indistinct beds 6cm reworked lithic-crystal tuft 1 2cm beds lithic lapilli tuft reverse graded lithic lapilli crystal tuft reworked tuft matrix recessive pumice zone reworked tuft bleached contact wacke-argillite found along the Maybrun Three measured sections from separate outcrops outcrops. The contact with Warciub qroup wackes is exposed in all lack of ioad. redeposited facies and the Note the varying thickness of distal The centre and correlation in the proximal—distal facies volcaniclaStics. right—side measured sections are from Stop 9. ath BERRY RIVER FORMATION primary deposition proximal t o distal tacies BERRY RIVER FORMATION redeposition, reworked tuff distal source WARCLUB GROUP P - 3 en (D .. rr �Figure 19: 4 ____ _________ _______ _________ ________ _____ _________________ __________ ___________ __________ ______________ ___________ .• •. ..Do I 149 \ C ____________ ______________________ __________ .:Oo tuff breccia- breccia massive homolithic o9 lapillituff oo p o o.Q tu ff lapilli tuft & tuft —:—:——:— lapilli tuft recessive clasts •:j tuft o pyroclastic breccia bimodal magnetite 0 c' ç tuft breccia pyroclastic breccia homolithic crystal-lithic lapilli tuff - thickly laminated tuft breccia tuft wacke & argillite c' o00 -0- ° -0 °o porphyryclasts quartz-feldspar tuffbreccialapilli tuft - -:.:y.-y.: tuff poorly laminated 0 0 — 2 E0 -— O 'o° tuft breccia- reworked thickly laminated tuft lapilli tuft °o0 • siltstone reworked tuft oO not to scale BERRY RIVER FORMATION tuff breccia lapilli tuft iyroclastic beccia \ o0Oi doubly graded not to scale • 0j)0000 ———,.—— :—:—:—:—: I —:—:—:—:— 2-3%bluequa'rtz —— I I I tuft-lapilli tuff tuft I 5% blue quartz I I i I \ 180m pumice Ii thu. - api I tu 0 -0 -._____ thin dark and light bed I I _—_——_—_ recessive clasts :—:——:—: lapilli tuft — :::::::::::::::::::::::: E —:—:—:—:— o——— c —:—:—:—_— 0 IapiII tuft tuft recessive _—_—_—_—_ pumice — ____ 0 primary deposition, subaqueous pyroclastic flows, proximal to distal faces Two generalized sections from two outcrop areas along the Maybrun road at Stop 9. Rocks in the left column overlie the sections on the center and right side of Figure 18 and the right column stratigraphically overlie rocks described in the left column. Fallout deposits progress up into a mixed assemblage of pyroclastic flow deposits, tuffs and wackes. r r 3 P W r-i I à ‘ ' c I-'-(D r+l--m1-- m x mr-iLQ m 0 0 t-tlm n o ; z r r 3 0)QJ rrrr LQoa �150 Strike—east—southeast, Settinq: S etting: S t r i k e - e a s t - s o u t h e a s t , dip—vertical dip-vertical Feature(s): Crystal F eature(s): C r y s t a l (quartz—feldspar) ( q u a r t z - f e l d s p a r ) tuff, t u f f , lithic lithic ci ts c l aass ts Anhedra A n h e d r a of o f quartz q u a r t z vary v a r y in i n size s i z e and and proportion p r o p o r t i o n across across the t h e ooutcrop, u t c r o p , whereas w h e r e a s euhedral e u h e d r a l to t o subhedrai s u b h e d r a l feldspar feldspar phenocrysts p h e n o c r y s t s do d o not n o t vary v a r y stratigraphically. stratigraphically. The pheno— phenocrysts c r y s t s are a r e supported s u p p o r t e d in i n a very v e r y fine—grained f i n e - g r a i n e d quartzo— quartzor e l i c t ash a s h matrix. matrix. M i n o r subrounded s u b r o u n d e d lithic lithic ffeldspathic e l d s p a t h i c relict Minor clasts This c l a s t s are a r e found f o u n d throughout. throughout. T h i s sstop t o p is i s just j u s t north n o r t h of of Pipestone—Cameron tthe he P i p e s t o n e - C a m e r o n Fault F a u l t and a n d much much of o f the t h e "ciastic" "clastic" of i s structural. structural. The vvariation ariation o f phenocryst phenocrys t ttexture e x t u r e is rratios, a t i o s , tuffaceous t u f f a c e o u s character c h a r a c t e r and and clastic c l a s t i c horizons horizons indicate was ddeposited i n d i c a t e that t h a t the t h e unit u n i t was e p o s i t e d by b y the t h e ash a s h flow flow mechanism. mechanism. There much ddebate T h e r e hhas a s bbeen e e n much e b a t e (not ( n o t quite q u i t e physical) p h y s i c a l ) as as to t o what w h a t this t h i s outcrop o u t c r o p represents. r e p r e s e n t s . What do d o you you think? think? 00.0 . 0 km Drive b a c k to t o the t h e Maybrun Maybrun Road ----1.9 1 . 9D r i v e north n o r t h on o n Highway 71 back kin. km A- 1.9 1 . 9 km . STOP 11 1 1 (Figure ( F i g u r e 12). 1 2 ) . This T h i s is is a a spectacular s p e c t a c u l a r outcrop o u t c r o p on on west e s t side s i d e of o f the t h e highway h i g h w a y opposite o p p o s i t e Maybrun Maybrun Road. Road. tthe he w Berry B e r r y River R i v e r formation formation Distal D i s t a l redeposited; r e d e p o s i t e d ; proximal—distal proximal-distal ddeposition eposition Strike—southeast, Setting: S etting: S t r i k e - s o u t h e a s t , ddip—vertical, i p - v e r t i c a l , strati— stratigraphic g r a p h i c tops t o p s folded f o l d e d at a t the t h e north n o r t h end e n d and and south s o u t h at a t the t h e south s o u t h end. end. Feature(s): Reworked tuffs, t u f f s , double d o u b l e grading, g r a d i n g , reverse r e v e r s e and and F e a t u r e ( s ) : Reworked normal n o r m a l grading grading Formation: Formation: Facies: F a c ies : Figure 20 is measured i s aa m e a s u r e d ssection e c t i o n sstarting t a r t i n g at a t the the F i g u r e 20 small s m a l l outcrops o u t c r o p s in i n the t h e ditch d i t c h just j u s t north n o r t h of o f the t h e main main eexposure. xpos u r e The T h e base b a s e of o f the t h e section s e c t i o n is is folded f o l d e d wackes w a c k e s and and pyro— pyroeclastics l a s t i c s of o f the t h e Warclub W a r c l u b group. group. The T h e distal d i s t a l redeposited r e d e p o s i t e d facies f a c i e s consists c o n s i s t s of o f folded, folded, The reworked bedded, b e d d e d , reworked r e w o r k e d tuff t u f f and a n d lapilli l a p i l l i tuff. tuff. reworked s u b r o u n d grains g r a i n s and a n d aa higher h i g h e r biotite biotite ppyroclastics y r o c l a s t i c s have h a v e subround matrix ccontent o n t e n t in i n the the m a t r i x than t h a n the t h e non—reworked n o n - r e w o r k e d material. material. This T h i s higher h i g h e r biotite b i o t i t e content c o n t e n t gives g i v e s the t h e weathered w e a t h e r e d surface surface a a brownish—buff b r o w n i s h - b u f f colour. colour. Three are T h r e e ddepositional e p o s i t i o n a l events e v e n t s not n o t seen s e e n at a t Stop S t o p 9 are The ppresent r e s e n t here. here. The first f i r s t unit u n i t (Figure ( F i g u r e 20) 2 0 ) above a b o v e the the reworked i s massively m a s s i v e l y bedded b e d d e d feldspar f e l d s p a r and and quartz— quartzr e w o r k e d tuffs t u f f s is Based feldspar f e l d s p a r crystal c r y s t a l tuffs. tuffs. B a s e d upon u p o n hiotite b i o t i t e content c o n t e n t and and angularity a n g u l a r i t y of o f phenoclasts p h e n o c l a s t s these t h e s e are a r e not n o t reworked. reworked. is the The second the s e c o n d depositiorial d e p o s i t i o n a l eevent v e n t (Figure ( F i g u r e 20) 2 0 ) is 5 ssubunits u b u n i t s of o f doubly d o u b l y graded, g r a d e d , subaqueous subaqueous ddeposition e p o s i t i o n of of 5 Each ppyroclastic y r o c l a s t i c flows. flows. Each hhave ave a a coarse c o a r s e clastic c l a s t i c base base t o tuff t u f f and/or a n d / o r laminated l a m i n a t e d tuff. tuff. ffining i n i n g south s o u t h to The third w a s the t h e deposition d e p o s i t i o n of of The t h i r d event e v e n t (Figure ( F i g u r e 20) 2 0 ) was . �________ 151 000 o00 0000 0 11Dm— cover cover lam prophyre lamprophyre bedded quartz-feldspar tuff, tuft, normal normal and andreverse-graded reverse-graded pumice pumice horizons, horizons homolithic homolithictuft tuffbreccia, breccia,massive massive tuff tuffbreccia, breccia, massive tuft, thinnly thinnly laminated tuft massive tuff, laminated tuff 10Dm— fault fault Primary deposition, fall fall deposits, deposits, note note presence presence of pumice pumice arc prophyre homolithic homolithic lapilli lapilli tuft tuffgrading gradinginto into thinnly thinnly laminated laminated tuff tuff 9Dm — 1 pyroclasticbreccia into homolithicpyroclastic brecciagrading grading into homolithic thickly thickly laminated laminated tuff Zff/7Z>E 8Dm-____ lamprophyre lamprophyre tuff tuff breccia, breccia, thin tuff tuff on on top top (homolithic) (homolithic) lam prophyre lamprophyre Primary Primary deposition, deposition,subaqueous subaqueous pyroclastic pyroclastic flows, proximal proximal to to distal distal facies facies -L OOO L)p 7Dm— p•zQp z C tuff grading into into tuff tuff )heterolithic) tuff breccia breccia qradinq (heterolithic) lani prophyre lamprophyre lapilli lapilli tuff tuffto t otuff tuffbreccia breccia - 0 UU- quartz-feldspar quartz-feldspar tuft, tuff,massive, massive,homogeneous homogeneous > >. 6Dm — : :: ::: reldspathic ~eldspathictuff, tuff,massise,laminated massive,laminated : ::: ////////// lam prophyre Iamprophyre quartz-feldspar quartz-feldspar tuft, tuff,massive massive Primary deposition, tuffs tufts prograding prograding distal distal source source I I U- tuff tuffbreccia brecciagrading grading into into thickly thickly laminated laminated tuffs tuffs 5Dm— lapilli laoilli tuft tuff feldspathic tuft feldspathic tuff reworked tuff, tuft, laminated laminated /////// lam prophyre Iamprophyre reworked reworked tuff, massive,laminated tuff,massive, laminated lam prophyre Iamprophyre 4Dm — reworked reworked tuff, tuff,massive, massive,laminated, laminated, -r cross-bedded, cross-bedded,graded graded Redeposition, Redeposition, reworked reworked tuffs, tuffs,distal distalsource source reworked reworked tuft, tuff lapplli lapilli tuft, tuff eldspathic 'eldspathic wacke w k k e (folded) (folded) 3Dm — 000 0000 00 0 0 0 2Dm— 0 1:.......... : :I .......... 1: 1: 1: I - 1Dm— 10m cover .°. lithic Iithic lapilli Iapilli tuff tuff (folded) (folded) feldspathic feldspathic wacke wacke quartz-feldspar quartz-feldspar porphyry porphyry feldspathic feldspatliic wacke wacke 0 Figure F i g u r e 20: 20: - feldspathic tuff, crystal crystal lithic lithic tuff, tuft, feldspathic tuff, lithic crystal crystal tuft tuff A m e a s u r e d ssection e c t i o n from f r o m Stop S t o p111 1ono nHighway H i g h w a y 71 71 A measured opposite The o p p o s i t e the t h eMaybrun M a y b r u n Road. Road. T h e bbasal a s a l portion p o r t i o n of of the r e s t of o f the the t h e section s e c t i o n has h a s been b e e n folded f o l d e d and a n d the t h e rest section s e c t i o n faces f a c e s south. south. T h e base b a s e of o f the t h e measured measured The s m a l l outcrops o u t c r o p s exposed e x p o s e d in i n the the s e c t i o n includes i n c l u d e s the t h e small section ditch d i t c h north n o r t h of o f the t h e main m a i n exposure. exposure. T h i s section section This includes Warclub a r c l u b group; g r o u p ; reworked r e w o r k e d tuffs t u f f s in i n the the includes W distal t u f f s , subaqueous subaqueous d i s t a l redeposition r e d e p o s i t i o n facies; f a c i e s ; tuffs, pyroclastic p y r o c l a s t i c flow f l o w and a n d fallout f a l l o u t deposits d e p o s i t s in i n the the proximal—distal p r o x i m a l - d i s t a l facies. facies. �152 thin t h i n bedded b e d d e d fall f a l l out o u t tuffs t u f f s and a n d lapilli l a p i l l i tuff t u f f and a n d tuff tuff breccia b r e c c i a deposited d e p o s i t e d by b y the t h e pyroclastic p y r o c l a s t i c flow f l o w mechanism. mechanism. T h e fall—out f a l l - o u t deposits d e p o s i t s have h a v e normal n o r m a l and a n d reverse r e v e r s e graded graded The pumice p u m i c e and a n d normal n o r m a l graded g r a d e d tuffs. tuffs. Here Here fall f a l l out o u t deposits d e p o s i t s overlie o v e r l i e subaqueous subaqueous a t Stop S t o p 99 they t h e y underlie u n d e r l i e them. them. p y r o c l a s t i c flows f l o w s whereas w h e r e a s at pyroclastic This T h i s is i s indicative i n d i c a t i v e of o f the t h e difficulty d i f f i c u l t y in i n attempting attempting pyroclastic p y r o c l a s t i c stratigraphy s t r a t i g r a p h y in i n the t h e Archean. Archean. TIME TIME FOR FOR AA BEER BEER �153 Re R e ferences ferences Ayres, A y r e s , L.D., L.D., 1977. 1 9 7 7 . Importance I m p o r t a n c e of o f stratigraphy s t r a t i g r a p h y in i n Early Early Precambrian C y c l i c Volcanism V o l c a n i s m at a t Setting Setting P r e c a m b r i a n Volcanic V o l c a n i c Terranes: T e r r a n e s : Cyclic Net N e t Lake, L a k e , Northwestern N o r t h w e s t e r n Ontario; O n t a r i o ; p.243—264 p. 2 4 3 - 2 6 4 in i n Volcanic Volcanic Regimes W. R.A. 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Ground Surge S u r g e Deposit: D e p o s i t : AA Third T h i r d Type T y p e of o f Pyroclastic P y r o c l a s t i c Rock; Rock; Nature, Nature, Volume Volume 241, 2 4 1 , p.63—64. p.63-64. Stockwell, S t o c k w e l l , C.H., C . H . , McGlynn, McGlynn, J.C., J . C . , Emslie, E r n s l i e , R.F., R.F., Sanford, S a n f o r d , B.V., B.V., �155 Norris, Donaldson, N o r r i s , A.W., A.W., D o n a l d s o n , J.P., J . A . , Fahrig, F a h r i g , W.F. W.F. and a n d Currie, Currie, K.L. K. L. 1970. 1 9 7 0 . Geology G e o l o g y of o f the t h e Canadian C a n a d i a n Shield, S h i e l d , in i n Geology G e o l o g y and and Economic E c o n o m i c Minerals M i n e r a l s of o f Canada, C a n a d a , edited e d i t e d by b y R.J.W. R.J.W. Douglas, Douglas , Geological G e o l o g i c a l Survey S u r v e y of o f Canada, C a n a d a , Economic E c o n o m i c Geology G e o l o g y Report R e p o r t No.1, No. 1 , 838p. 838p. Tasse, T a s s e , N., N . , Lajoie, L a j o i e , 3., J . , and a n d Dimroth, D i r n r o t h , E., E . , 1978. 1978. T h e Anatomy A n a t o m y and and The Interpretation I n t e r p r e t a t i o n of o f an a n Archean A r c h e a n Volcaniclastic V o l c a n i c l a s t i c Sequence, Sequence, Noranda N o r a n d a Region, R e g i o n , Quebec; Q u e b e c ; Canadian C a n a d i a n Journal J o u r n a l of o f Earth E a r t h Science, Science, Volume V o l u m e 15, 1 5 , p.874—888. p.874-888. Trowell, Geology i n prep. prep. G e o l o g y of o f the t h e Gibi G i b i Lake L a k e Area, Area, District District T r o w e l l , N.F., N.F. , in of o f Kenora; K e n o r a ; Ontario O n t a r i o Geological G e o l o g i c a l Survey S u r v e y Open Open File F i l e Report. Report. Trowell, B l a c k b u r n , C.E., C.E. , and a n d Edwards, E d w a r d s , G.R., G.R., 1980. 1980. T r o w e l l , N.F., N.F. , Blackburn, Preliminary Synthesis of the Savant Lake — C r o w Lake Lake P r e l i m i n a r y S y n t h e s i s o f t h e S a v a n t L a k e - Crow Metavolcanic M e t a s e d i m e n t a r y Belt, B e l t , Northwestern N o r t h w e s t e r n Ontario; Ontario; M e t a v o l c a n i c—- Metasedimentary and a n d its i t sBearing B e a r i n g upon u p o n Mineral M i n e r a l Exploration; E x p l o r a t i o n ; Ontario O n t a r i oGeological Geological Survey, S u r v e y , Miscellaneous M i s c e l l a n e o u s Paper P a p e r 89, 8 9 , 30p. 3 0 p . Accompanied A c c o m p a n i e d bby y Chart Chart A. A. Williams, W i l l i a m s , H., H., and a n d McBirney, M c B i r n e y , A.R., A.R., 1979. 1 9 7 9 . Volcanology; V o l c a n o l o g y ; Freeman, Freeman, Cooper C o o p e r and a n d Co., Co., San S a n Francisco F r a n c i s c o379p. 379p. �Granitoid G r a n i t o i d Related Related Mineralization M i n e r a l i z a t i o n in i n the the Dryden D r y d e n Area Area I n t r o d u c t o r y Discussion D i s c u s s i o n and and Field F i e l d Guide Guide Introductory 31st 3 1 s t Annual A n n u a l Institute I n s t i t u t e on on Lake Lake Superior S u p e r i o r Geology Geology Kenora, Ontario Kenora , Ontario by F.W. F.W. Breaks Breaks 110 110 Chan Chan Cresent Cresent f i a s k a t o o n , Saskatchewan Saskatchewan Saskatoon, S7K S7K 5N8 5N8 R.C. R.C. Beard Beard Ministry M i n i s t r y of o f Natural N a t u r a l Resources Resources 808 8 0 8 Robertson R o b e r t s o n St. St. Kenora, K e n o r a , Ontario Ontario D.A. D. A. Janes Janes Resident R e s i d e n t Geologists G e o l o g i s t s Office Office Ministry M i n i s t r y of o f Natural N a t u r a l Resources Resources P.O. P.O. Box Box 309 309 Sioux S i o u x Lookout, L o o k o u t , Ontario Ontario K.H. K . H . Poulsen Poulsen Geological G e o l o g i c a l Survey S u r v e y of o f Canada Canada 601 Booth St. 601 Booth S t . Ottawa, O t t a w a , Ontario Ontario K1A K I A 0E8 OE8 �158 GENERAL GENERAL GEOLOGY This T h i s field f i e l d trip t r i p examines e x a m i n e s the t h e diverse d i v e r s e granitoid q r a n i t o i d rocks r o c k s and and a s s o c i a t e d mineralization m i n e r a l i z a t i o n in i n the t h e Dryden D r y d e n area. a r e a . The T h e rocks r o c k s of o f this this associated area to a r e a are a r e transitional t r a n s i t i o n a l from f r o m the t h e Wabigoori Wabigoon Subprovince S u b p r o v i n c e northward n o r t h w a r d to t h e Southern S o u t h e r n plutonic p l u t o n i c domain d o m a i n (Winnipeg ( W i n n i p e g River R i v e r terrane) t e r r a n e ) of o f the the the English A l l field f i e l d stops s t o p s will w i l l be b e made within w i t h i n aa E n g l i s h River R i v e r Subprovince. Subprovince. All b o u n d a r y z o n e l i m i t e d b y t h e Wabigoon F a u l t on t h e s o u t h and by b y aa boundary zone limited by the Wabigoori Fault on the south and line marking line m a r k i n g the t h e maximum extent e x t e n t northward n o r t h w a r d of o f abundant abundant supracrustal 1 ). T h e precise p r e c i s e position p o s i t i o n of o f the the s u p r a c r u s t a l rocks r o c k s (Figure ( F i g u r e 1). The subprovince is debatable d e b a t a b l e and a n d is is largely largely s u b p r o v i n c e boundary b o u n d a r y within w i t h i n this t h i s zone z o n e is dependent s t r u c t u r a l or o r metamorphic m e t a m o r p h i c criteria criteria d e p e n d e n t on on the t h e lithological, l i t h o l o g i c a l , structural used u s e d to t o define d e f i n e it it but, b u t , for f o r the t h e purposes p u r p o s e s of o f this t h i s excursion, e x c u r s i o n , it it is is sufficient s u f f i c i e n t to t o note n o t e aa number number of o f general g e n e r a l characteristics c h a r a c t e r i s t i c s of o f the the zone: zone : 1 ) I t contains c o n t a i n s aa higher h i g h e r proportion p r o p o r t i o n of o f metasedimentary m e t a s e d i m e n t a r y rocks r o c k s and and derived d e r i v e d migmatitic m i g m a t i t i c stages s t a g e s (Table ( T a b l e 1) 1 ) than t h a n is is normal n o r m a l within within the et t h e main m a i n mass mass of o f the t h e Southern S o u t h e r n plutonic p l u t o n i c domain d o m a i n (Breaks ( B r e a k s et al., a l . , 1978) 19 7 8 ) and a n d the t h e Wabigoon Wabigoon Subprovince S u b p r o v i n c e to t o the t h e south. south. In In the t h e Dryden D r y d e n area, a r e a , the t h e Wabigoon Wabigoon Fault F a u l t marks m a r k s the t h e southern southern extent ( Z e a l a n dGroup) G r o u p )which which e x t e n t of o f these t h e s emetasedimentary m e t a s e d i m e n t a r y rocks r o c k s(Zealand are a r e dominantly d o m i n a n t l y oof f tturbiditic u r b i d i t i c origin. origin. 2) 2 ) The The pproportion r o p o r t i o n oof f exposed e x p o s e d pplutonic l u t o n i c rrocks o c k s rrelative e l a t i v e to to supracrustal s u p r a c r u s t a l rocks r o c k sincreases i n c r e a s e northward s n o r t h w a r dand a n dnorthwestward northwestward within w i t h i n the t h e zone. zone. 3) is ppresent within 3) A A ssteep t e e p metamorphic m e t a m o r p h i c g rgradient a d i e n t is resent w i t h i n this t h i s zone: zone: low l o w ggrade r a d e aassemblages s s e m b l a g e s i ninp pelitic e l i t i c rrocks o c k s aadjacent d j a c e n t to t o the the Wabigoon d i s t a n c e of o f 77 km to to Wabiqoon Fault F a u l t give g i v e way northward n o r t h w a r d over o v e r a distance high a r e inferred i n Âe r r e d h i g h grade g r a d e assemblages. a s s e m b l a g e s . Metamorphic M e t a m o r p h i c pressures p r e s s u r e s are to t o be b e relatively r e l a t i v e l y low l o w (Bartlett, ( B a r t l e t t , 1978; 1978; Breaks, B r e a k s , 1982). 1982). 4) 4 ) A suite s u i t e of o f gneissic g n e i s s i c granitoid g r a n i t o i d rocks r o c k s which w h i c h represent represent intensely metamorphosed intensely m e t a m o r p h o s e d and a n d deformed d e f o r m e d polycyclic p o l y c y c l i c intrusive intrusive phases o f the t h e main m a i n mass m a s s of o f the t h e southern southern p h a s e s are a r e characteristic c h a r a c t e r i s t i c of plutonic p l u t o n i c domain d o m a i n bbut u t aare r e absent a b s e n t from f r o m the t h e zone z o n e under under cons c o n s iderat i d e r a t ion. ion. 5) 5 ) Metavolcanic M e t a v o l c a n i c rocks r o c k s are a r e particularly p a r t i c u l a r l y abundant a b u n d a n t in i n the t h e eastern eastern part p a r t of o f the t h e zone z o n e and a n d form f o r m parts p a r t s of o f two t w o units u n i t s which w h i c h extend extend northeastward n o r t h e a s t w a r d out o u t of o f the t h e area a r e a of o f consideration. c o n s i d e r a t i o n . The The northern n o r t h e r n unit u n i t which w h i c h extends e x t e n d s to t o Gullwing G u l l w i n g Lake Lake (Figure ( F i g u r e 1) 1) forms f o r m s aa portion p o r t i o n of o f the t h eNorthern N o r t h e r n Volcanic V o l c a n i c Belt B e l t (Trowell ( T r o w e l l et et al., a l . , 1980) 1 9 8 0 )which w h i c h comprises c o m p r i s e s aa lower lower south s o u t h facing f a c i n g mafic mafic sequence and an a n upper upper s e q u e n c e composed composed largely l a r g e l y of o f magnesian m a g n e s i a n basalts b a s a l ts and mixed m i x e d intermediate i n t e r m e d i a t e to t o felsic f e l s i c metavolcanic—metasedimentary metavolcanic-metasedimentary sequence. s e q u e n c e . The T h e second s e c o n d unit u n i t which w h i c h includes i n c l u d e s the t h e Brownridge Brownridge Volcanics 1 ) forms f o r m s part p a r t of o f the t h e Central C e n t r a l Volcanic V o l c a n i c Belt Belt V o l c a n i c s (Figure ( F i g u r e 1) which mafic w h i c h comprises c o m p r i s e s ma i c t to o intermediate i n t e r m e d i a t e flows f l o w s with w i t h local local f e l s i c flows, f l o w s , autoclastic a u t o c l a s t i c breccias b r e c c i a s and a n d thin t h i n sedimentary sedimentary intervals e t al., a l . , 1980). 1 9 8 0 ) . AA third t h i r d unit, u n i t , comprising comprising ( T r o w e l l et i n t e r v a l s (Trowell mixed t o felsic f e l s i c metavolcanic m e t a v o l c a n i c rocks r o c k s occurs o c c u r s in i n the the m i x e d mafic maÂi c to western w e s t e r n part p a r t of o f the t h e zone z o n e in i n the t h e vicinity v i c i n i t y of o f Vermilion V e r m i l i o n Bay. Bay. 1 ) It felsic GRANITOID G R A N I T O I D ROCKS ROCKS WhilTiTvidual W h i l e v i d u aintrusions l i n t r u s i o n within s w i t h i nthe t h eboundary b o u n d a r y zone zone commonly commonly display d i s p l a y internal i n t e r n a l compositional composit i o n a l variations, v a r i a t i o n s , it i t is is possible p o s s i b l e to t o subdivide s u b d i v i d e the t h e granitoid g r a n i t o i d rocks r o c k s in i n aa general g e n e r a l way way into into . - . �Figure 1: General Geology of the Dryden Area. 01 �- T a b l e 1: 1: Table CLASSIFICATION FEATURES OfiETASEDI%NTARY OFMETASEDIMENTARY MIGMATITES ENGLISH CLASSIFICATION AND GENERAL FEATURES. MwTITES ENGLISH RIVER RIVER SUBPROVINCE, SUBPROVINCEe IGMATITIC M IGMATITIC STAGE STAGE LEUCOSOME: LEUCOSOME LEUCOSOME: LEKOSOME && PALEOSOME---RATIO-- DIAGNOSTIC MIGMATITIC MIGMATITIC STRUCTURE STRUCTURE GENERAL GENERAL PROCESSES PROCESSES DOMINANT EOALNAE GENERAL GENERAL FIELD FIELD FEATURES FEATURES PrOtOProto— metatex ite m e t a t e x ite <0.11 <o- Locally L o c a l l y stromatic strcinatic Sedimentary Sed i m e n t a r y bedding b e d d i n g or or llaminae a m i n a e may show show preservation preservat ion selective' IIncipient, n c i p i e n t , 'selective' aanatexis. n a t e x i s . Metamorphic Metamorphic differentiation d i f f e r e n t i a t i o n may be be iimportant mportant Characterized C h a r a c t e r i z e d by by intercalated i n t e r c a l a t e d fg Eg and mg—cg mg-cg porphyroblastic porphyroblastic wacke and pelite p e l i t e ccnponents. mponents. Podiform Pod i f o r m and a n d lensic l e n s i c potassic potass ic lleucosonies e u c o s c i n e s eexhibit x h i b i t cconfinement o n f i n e m e n t to to pelitic p e l i t i c horizons. h o r i z o n s . Hydrothermal Hydrothermal (qtz. ( q t z - vveins) e i n s ) mobilizate m o b i l i z a t e may may be be - important. Metatexite Metatex ite Stromatic S t r o m a t i c and/or and/or Phlebitic P hlebi tic 0.11 ttoo 0.6 0. 0.6 Local m c a l to t o moderate moderate ddegree e g r e e oof f anatexis anatexis Mobilizate M o b i l i z a t e ddeveloped e v e l o p e d i in n ssitu, itu, p o s s e s s e s biotitic b i o t i t i melanosonies c melanoscines possesses along a l o n g leucosome—paleosome l e u c o s o m e - p a l e o s o m e inter— interMobilizate fface. ace, M o b i l i z a t e (without (without melanosomes) me1 a n o s o m e s ) also a 1 so commonly common 1y -IInhomogeneous nhomogeneous Diatexite Diatex ite 0.6 tto 0.6 o 0.9 Oe9 Homogeneous Homog e n e o u s Diatex D i a t e x ite ite >0.9 injected i n j e c t e d along a l o n g prevailing prevailing foliation b e d d i n g surface surface f o l i a t i o n or bedding of o f paleosome. p a l m . SSchollen c h o l l e n structure structure especially e s p e c i a l l y character— characterLocally iistic. stic. L ocally sschlienitic c h l i e r i t i c or or nnebulitic e b u l it ic A n a t e x is rrelatively elatively Anatexis extensive, e x t e n s i v e , mobilizate mobil i z a t e essentially essentially aautochthnous utochthnous Homogeneous usually usually massive, mass i v e * Locally Iocally sschollen, c h 0 1 1 e n ~ schlieritic s c h l ier it ic or nebulitic nebulitic sstructures t r u c t u r e s apparent apparent Very advanced a d v a n c e d fusion;  £ ui o n ; Very m o b i l i z a t e probably probably mobilizate a 1 lloch o c h t thonous honous al Abbreviations-fied;ji b b r e v i a t i o n s : f g - f i n e g r a i n e dmedium—rained; ; mg - m e d i u m - 2 r a i n e d ; cgc g —- ccoarse oarse grained; C gained; CII 0 - -- Q R e p l e t i c n of o f disoriented disoriented Repletion p a l e o s o m e and a n d metatexite metatexite paleosome iinclusions n c l u s i o n s and a n d melanosome melanosome clum c l u m p s is is ddiagnostic. iagnostic. - U s u a l l y hholo—leucocratic o l o - l e u c o c r a t i c and and Usually s e v e r e 1 y ssenate. eriate. R a r e 1 y more severely Rarely m a f i c variants v a r i a n t s (CI ( C I 15 tto o 30) 3 0 ) may mafic rrepresent e p r e s e n t cases c a s e s of o f complete complete aanatexis n a t e x i s eeffecting f f e c t i n g resorption resorption of o f melanosome me1 a n o s o m e component c o m p o n e n t into into magmatic m a g m a t i c phase phase C o l o u r ,Index; I n d e x ; >> - Colour t h a n ; < - less less atenthan;<— - z a t e r than than �161 three t h r e e suites s u i t e s which w h i c h reflect r e f l e c t not n o t only o n l y compositional c o m p o s i t i o n a l variations v a r i a t i o n s but but their t o other o t h e r tectonic t e c t o n i c events: events: t h e i r timing t i m i n g relative r e l a t i v e to i) i ) aa pre— p r e - to t o syn—tectonic s y n - t e c t o n i c sodic s o d i c suite suite ii) a syn—tectonic peraluminous suite i i) a syn-tectonic peraluminous s u i t e iii) i i i ) aa syn— s y n - to t o post—tectonic p o s t - t e c t o n i c potassic p o t a s s i c suite. suite. The The essential e s s e n t i a l features f e a t u r e s of o f each e a c h suite s u i t e are a r e described d e s c r i b e d below b e l o w with with reference to the plutonic rock nomenclature of Streckeisen r e f e r e n c e to t h e p l u t o n i c r o c k nomenclature of S t r e c k e i s e n (1976). (1976). Sodic S-.o d i c Suite Suite The The phases p h a s e s within w i t h i n these t h e s e intrusions i n t r u s i o n s are a r e dominantly dominantly trondhjemite t r o n d h j emite and a n d granodiorite g r a n o d i o r i t e with w i t h rare r a r e granite. g r a n i t e . The The rocks r o c k s are are quite q u i t e uniform u n i f o r m in i n composition c o m p o s i t i o n and a n d commonly commonly possess p o s s e s s aa metamorphic metamorphic foliation. The rocks r o c k s are a r e generally g e n e r a l l y medium medium grained g r a i n e d and a n d contain contain f o l i a t i o n . The biotite b i o t i t e as a s the t h edominant d o m i n a n t mafic m a f i c mineral. m i n e r a l . In I n the t h e Dryden D r y d e n area a r e a this this suite s u i t e isisrepresented r e p r e s e n t e d by by small s m a l l plutons p l u t o n s and a n d sills s i l l ssuch s u c h as a s the the G o l d l u n d ttrondhjemite rondhjemite w i t h i n the t h e Central C e n t r a l Volcanic V o l c a n i c Belt B e l tand and by by Goldlund within stocks s t o c k s such s u c h as a s the t h eLateral L a t e r aLake l U k ebody body composed composed oof f foliated foliated biotite—bearing b i o t i t e - b e a r i n g granodiorite g r a n o d i o r i t e (McCarter, ( M c C a r t e r 1980) 1980 ) and and the t h e Broadtail Broad t a i l Lake body composed composed l i a t e d bbiotite i o t i t e and and Lake body o f of m amassive s s i v e t otof ofoliated hornblende—biotite h o r n b l e n d e - b i o t i t e granodiorite. granodiorite. A - - Peraluminous P eraluminous ------.-- Suite S -uite AA dominnt d o m i n a n t granitoid g r a n i t o i d element e l e m e n t in i n the t h e Dryden D r y d e n area a r e a is is the t h e Ghost Ghost Lake Lake Batholith. B a t h o l i t h . This his peraluminous, p e r a l u m i n o u s two—mica t w o - m i c i granitoid g r a n i t o i d was was previously p r e v i o u s l y mapped, m a p p e d , in i n part, p a r t by b y Moorhouse M o o r h o u s e (1939) ( 1 9 3 9 ) and a n d Satterly Satterly (1941) ( 1 9 4 1 ) and and completely c o m p l e t e l y delineated d e l i n e a t e d by b y Breaks B r e a k s et e t al. a l . (1976) ( 1 9 7 6 ) with with more The more recent r e c e n t detailed d e t a i l e d mapped mappedcompleted c o m p l e t e dbyb yBreaks B r e a k s(1984) ( 1 9 8 4 .) The batholith 280kin2, km2f is is elongated e l o n g a t e d and a n d is is broadly b r o a d l y concordant c o n c o r d a n t with with b a t h o l i t h isis280 east t o northeasterly n o r t h e a s t e r l y striking s t r i k i n g structural s t r u c t u r a l trends t r e n d s in i n adjacent ad] a c e n t e a s t to rocks. is distinguishable d i s t i n g u i s h a b l e from f r o m virtually v i r t u a l l y all a l l other other r o c k s . The T h e batholith b a t h 0 1 i t h is plutonic u n i q u e accessory accessory p l u t o n i c masses m a s s e s in i n the t h e region r e g i o n by b y virtue v i r t u e of o f aa unique mineral m i n e r a l suite s u i t e including i n c l u d i n g muscovite, m u s c o v i t e cordierite, c o r d i e r i t e sillimanite, sillimanite, Mn—garnet, r a r e duinortierite d u m o r t i e r i t e and a n d beryl. beryl. Mn-garnet tourmaline t o u r m a l i n e and a n d rare The T h e main m a i n exposed e x p o s e d mass mass of o f the t h e batholith b a t h o l i t h covers c o v e r s a a 40 4 0 km km long lonq area a r e a between b e t w e e n Eagle E a g l e River R i v e r and a n d Ghost G h o s t Lake Lake which w h i c h contains contains inhomogeneous t o homogeneous h o m o g e n e o u s diatexite d i a t e x i t e composed composed of o f coarse c o a r s e grained grained i n h o m q e n e o u s to granite g r a n i t e and a n d granodiorite g r a n o d i o r i t e with w i t h variable v a r i a b l e contents c o n t e n t s of o f biotite b i o t i t e and and muscovite. m u s c o v i t e . The T h e western w e s t e r n two—thirds t w o - t h i r d s of o f this t h i s mass mass probably probably represents lower sstructural t r u c t u r a l level l e v e l of o f the t h e intrusion i n t r u s i o n in i n that t h a t the the r e p r e s e n t s aa lower granitoid homogeneous, less homogeneous contain c o n t a i n less l e s stourmaline t o u r m a l i n eand and g r a n i t o i d rocks r o c k s are a r eless muscovite m u s c o v i t e and a n d form f o r m ttransitional r a n s i t i o n a lcontacts c o n t a c t with s w i t migmatized h migmatized metased rocksddisplaying i s p l a y i n g aassemblages s s e m b l a g e s ttypical y p i c a l of o f the the m e t a s e d i imentary m e n t a r y rocks second s e c o n d sillimanite s i l l i m a n i t e isograd. i s o g r a d . The The eastern e a s t e r n portion p o r t i o n of o f the t h e mass mass shows it s h o w s characteristics c h a r a c t e r i s t i c s of o f the t h e upper u p p e r level l e v e l of o f the t h e intrusion i n t r u s i o n as a s it has h a s an a n abrupt a b r u p t contact c o n t a c t with w i t h metasediments, m e t a s e d i m e n t ~few f~e w sedimentary sedimentary i n c l u s i o n s f abundant a b u n d a n t muscovite m u s c o v i t e and a n d tourmaline t o u r m a l i n e (locally ( l o c a l l y1010to t o 20 20 inclusions, percent) p e r c e n t ) and a n d potassic p o t a s s i c pegmatites p e g m a t i t e s which w h i c h typify t y p i f y the t h e cupola c u p o l a zone z o n e of of batholiths b a t h o l i t h s parental p a r e n t a l to t o rare r a r e element e l e m e n t pegmatites p e g m a t i t e s (Varlamoff, (Varlamoff 1972). l i e s in i n abrupt abrupt 1 9 7 2 ) . Along Along the t h e southern s o u t h e r n contact, c o n t a c t f the t h e batholith b a t h o l i t h lies contact l o w - to t o medium—grade m e d i u m - g r a d e metasediments m e t a s e d i m e n t s with w i t h no no c o n t a c t with w i t h low— appearance a p p e a r a n c e of o f assemblages a s s e m b l a g e s of o f the t h e second s e c o n d sillimanite s i l l i m a n i t e zone z o n e in in metapelitic m e t a p e l i t i c layers l a y e r s which w h i c h militates m i l i t a t e s against a g a i n s tin—situ i n - s i t u partial partial melting n e l t i n g in i n this t h i spart p a r tofo fthe t h body. e body. . �162 Potassic P o t a s s i c Suite Suite T h i s ssuite u i t e is is represented r e p r e s e n t e d in i n tthe h e Dryden D r y d e n area a r e a by by two t w o large large Thi masses, m a s s e s I the t h e Dryberry D r y b e r r y Batholith B a t h o l i t h and and the t h e Gullwing G u l l w i n g Lake Lake Batholith Batholith The pphases (Figure ( F i g u r e 1). 1) h a s e s within w i t h i n these t h e s e bodies b o d i e s are a r e predominantly predominantly monzonites and ggranites commonly mmassive qquartz uartz m o n z o n i t e s and r a n i t e s wwhich h i c h aare r e commonly assive; homogeneous and Unlike homogeneous a n d medium to t o coarse coarse grained. grained. U n l i k e the t h e sodic sodic ssuite, u i t e l these t h e s e rocks r o c k s are a r e generally g e n e r a l l y discordant d i s c o r d a n t with w i t h their t h e i r hosts h o s t s and and dikes s i l l s of o f similar s i m i l a r composition c o m p s i t i o n may be b e very v e r y abundant a b u n d a n t in in d i k e s and a n d sills The aadjacent d j a c e n t country c o u n t r y rocks. rocks. T h e greatest g r e a t e s t volume v o l u m e of o f rock r o c k in i n these these batholithic b a t h 0 1 i t h i c complexes c o m p l e x e s characteristically c h a r a c t e r i s t i c a l l y lacks l a c k s aa metamorphic metamorphic foliation  £ 0i a t i o n aalthough 1 t h o u g h contact—parallel c o n t a c t - p a r a l l e l foliations  £ 0i a t i o n s near n e a r the t h e margins marg i n s related t o emplacement, e m p l a c e m e n t I are a r e common common features. features. r e l a t e d to -- . ECONOMIC -o l-d -D GEOLOGY Gold G ~ t s --- -Gold G o l d ccurrences o G u r r e n c e s in i nthe t h eDryden D r y d e n area a r e a are a r e concentrated c o n c e n t r a t e d in i n the the Central Volcanic Central V o l c a n i c BBelt e l t iin n the t h e eastern e a L t e r n part p a r t of o fthe t h eboundary b o u n d a r y zone. zone. IIn n aa general g e n e r a l way, wayr tthe h e ggeological e o l o g i c a l ssetting e t t i n g of o f gold g o l d mineralization mineralization is similar i n t h i s a r e a is s i m i l a r to t othat t h a in t imany n manyother o t h e rgold g o l d 1camps camps in in Someo foft the Superior S u p e r i o r PProvince r o v i n c e ( (Colvine C o l v i n e e et t aal., l m r1984). 1 9 8 4 ) . Some h e ffeatures eatures oof f this t h i s gold—district g o l d - d i s t r i c t are: are: ii)) On a r e g i o n a l s c a l e r g o l d is l o c a l i z e d a t o r n e a r a m a j o r most vvolcanic—sedimentary o l c a n i c - s e d i m e n t a r y iinterface n t e r f a c e (Figure ( F i g u r e 1) 1 ) though though m ost individual i n d i v i d u a l deposits d e p o s i t s occur o c c u r within w i t h i n volcanic v o l c a n i c and a n d granitic granitic rrocks. ocks. wide morphologies iii) i ) AA w i d e vvariety a r i e t y oof f ddeposit eposit m o r p h o l o g i e s is i s present p r e s e n t including including veins rocks I en—echelon e n - e c h e l o n vein vein v e i n s and and sstockworks t o c k w o r k s in i n volcanic v o l c a n i c rocks, arrays i n t r u s i v e bodies, b o d i e s , carbonate c a r b o n a t e zones z o n e s in in a r r a y s in i n felsic f e l s i c intrusive volcanic rocks and and silicified s i l i c i f i e d shear s h e a r zones z o n e s in in v o l c a n i c and a n d sedimentary s e d i m e n t a r y rocks tuffs t u f f s aandlavas n d ' l a v a s (Blackburn ( B l a c k b u r n and a n d Janes, J a n e s I 1983). 1983). Gold mineralization by iiii) ii) G old m i n e r a l i z a t i o n is i s hosted hosted b y sstructures t r u c t u r e s bounded b o u n d e d by b y two two major faults f a u l t s which w h i c h roughly r o u g h l y parallel p a r a l l e l stratigraphic s t r a t i g r a p h i c trends. trends. Gold—quartz iiv) v) G o l d - q u a r t z vveins e i n s post—date p o s t - d a t e a lall l rrock o c k ttypes y p e s iin n the t h e area a r e a with with tthe h e possible p o s s i b l e exception e x c e p t i o n oof f some some ppost o s t ttectonic e c t o n i c granitoid granitoid iintrusions. ntrusions. Several t o small s m a l l bodies bodies vv)) S e v e r a l ooccurrences c c u r r e n c e s are a r e spatially s p a t i a l l y related r e l a t e d to composed composed of o f quartz q u a r t z and and feldspar f e l d s p a r porphyry. porphyry. The most most ssignificant The i g n i f i c a n t occurrence o c c u r r e n c e of o f gold g o l d in i n this t h i s area a r e a is is tthe he It Goldlund I t ccomprises o m p r i s e s en e n echelon e c h e l o n sets s e t s of o f extensional extensional G o l d l u n d deposit. deposit. is broadly broadly vveins e i n s which w h i c h ttransect r a n s e c t aa body body of o f trondhjernite t r o n d h j e m i t e which w h i c h is concordant with adjacent volcanic rocks. The veins c o n c o r d a n t w i t h a d j a c e n t v o l c a n i c rocks. T h e v e i n s appear a p p e a r to t o be be tthe h e product p r o d u c t oof f hydraulic h y d r a u l i c fracture f r a c t u r e oof f the t h e intrusion i n t r u s i o n and a n d the the is llikely rrelationship e l a t i o n s h i p bbetween e t w e e n g gold o l d a nand d t hthe e g granitoid r a n i t o i d r rock o c k is ikely pass ive passiv e aand n d s isimply m p l y t hthe e r eresult s u l t oof f bbrittle r i t t l e deformation d e f o r m a t i o n oof f aa competent unit. competent u n i t . T h i s s i t u a t i o n is s i m i l a r t o t h a t a t o t h e r deposits d e p o s i t s in i n Superior S u p e r i o r Province, P r o v i n c e " most notably n o t a b l y at a t the t h e Sigma Sigma Mine, Miner An important 1983). t aal., l . , 1983) An i m p o r t a n t ffeature e a t u r e of of V a l d'Or, d 1 0 r Quebec Q u e b e c ((Robert R o b e r t e et Val is tthe Goidlund G o l d l u n d is h e ppresence r e s e n c e oof f nnumerous u m e r o u s ddikes i k e s oof f qquartz u a r t z aand n d feldspar feldspar porphyry which p orphyry w h i c h cut c u t the t h e trondhjemite t r o n d h j e m i t e but b u t not n o t the t h e gold—quartz gold-quartz In some cases cases vvein—bearing veins. e i n - b e a r i n g sstructures t r u c t u r e s in i n the t h e trondhjemite trondhjemite veins. I n some Porphyries extend ex t e n d unmineralized u n m i n e r a l i z e d into i n t o porphyry p o r p h y r y dikes. dikes. P o r p h y r i e s of o f this this type t y p e are a r e common common features f e a t u r e s of o f many many gold g o l d depos d e p o sits i t s (McIntyre, (McIntyreI Hollinqer, H o l l i n g e r D3me) D o m e ) but b u t their t h e i r genetic g e n e t i c relationship r e l a t i o n s h i p to t o gold gold mineralization m i n e r a l i z a t i o n is is poorly p o o r l y understood. understood. DosTts in this area a regional scale, gold is localized at or near a major This situation is similar to that at other �163 Mo1yiteD M o l y b d e n--i t e Depos e---p o s its its - The The Lateral L a t e r a l Lake Lake granodioritic g r a n o d i o r i t i c stock s t o c k hosts h o s t s several several occurrences its contact c o n t a c t with w i t h rocks r o c k s of o f the the o c c u r r e n c e s of o f molybdenite m o l y b d e n i t e at a t its Northern Belt. This m i n e r a l 1 z a t i o n has h a s been b e e n described described N o r t h e r n Volcanic V o l c a n i c Belt. This mineralization by b y McCarter M c C a r t e r (1980), ( 1 9 8 0 ) Colvine C o l v i n e and a n d McCarter M c C a r t e r (1977) ( 1 9 7 7 ) and and Page P a g e (1984). ( 1 984). M o l y b d e n i t e occurs o c c u r s in i n quartz q u a r t z and a n d pegmatitic p e g m a t i t i c veins v e i n s which which are are Molybdenite w e l l developed d e v e l o p e d in i n aplitic a p l i t i c dikes d i k e s which w h i c h cut c u t the the p a r t i c u l a r l y well particularly granodiorite. The 1) as a s euhedral e u h e d r a l grains g r a i n s with with granodiorite. The molybdenite m o l y b d e n i t e occurs o c c u r s i) K—feldspar i i ) as rare r a r e euhedral euhedral K - f e l d s p a r and a n d phlogopite p h l o g o p i t e in i n pegmatites, p e g m a t i t e s f ii) grains i i i ) along a l o n g vein v e i n margins, margins i v ) as a s isolated isolated g r a i n s in i n quartz q u a r t z veins, v e i n s iii) iv) grains g r a i n s in i n quartz—vein q u a r t z - v e i n stockworks; s t o c k w o r k s ; v) v ) as a s narrow n a r r o w bands b a n d s and and lenses lenses parallel t o foliation f o l i a t i o n in i n wall—rocks w a l l - r o c k s and, a n d f vi) v i ) along a l o n g fractures f r a c t u r e s not not p a r a l l e l to parallel t o foliation f o l i a t i o n in i n walirocks w a l l r o c k s (Colvirie ( C o l v i n e and a n d McCarter, M c C a r t e r 1977). 1977). p a r a l l e l to Muscovite M u s c o v i t e and a n d pyrite p y r i t e are a r e common common accessories a c c e s s o r i e s to t o the t h e molybdenite molybdenite mineralization. Colvine mineralization. C o l v i n e and a n d McCarter M c C a r t e r (1971) ( 1 971 ) relate r e l a t e the the t o aa hydrothermal h y d r o t h e r m a l system s y s t e m developed d e v e l o p e d during d u r i n g the the m i n e r a l i z a t i o n to mineralization l a t e r sstages t a g e s of o f crystallization c r y s t a l l i z a t i o n of o f the t h e Lateral L a t e r a l Lake Lake stock s t o c k while while later Page P a g e (1984) ( 1 9 8 4 ) relates r e l a t e s it i t to t o post—tectonic pos t - t e c t o n i c emplacement e m p l a c e m e n t of o f pegmatites pegmatites which t o the t h e Lateral L a t e r a l Lake Lake intrusion i n t r u s i o n and a n d controlled controlled w h i c h are a r e unrelated u n r e l a t e d to by b y the t h e nearby n e a r b y Kathlyn K a t h l y n Lake Lake Fault. Fault. -- Rare—Metal R a r e - M e t a l- Pegmatites -P e-g m aptei gt ems a t i t e ~in Rare—metal R a r e - m e t a l pegmatites i n the t h e Dryden D r y d e n area a r e a were were first first described ( 1 9 6 5 ) who who termed t e r m e d their t h e i r concentration c o n c e n t r a t i o n the the d e s c r i b e d by b y Mulligan Mull i g a n (1965) "Dryden " D r y d e n Pegmatite P e g m a t i t e Field". F i e l d 1 ' . Regional Reg i o n a l zonation z o n a t i o n within w i t h i n this t h i s field field was ( 1 9 8 0 ) as a s outlined o u t l i n e d in i n Table T a b l e 2, 21 was first f i r s t recognized r e c o g n i z e d by b y Breaks B r e a k s (1980), resulting r e s u l t i n g in i n aa subdivision s u b d i v i s i o n into i n t o two t w o distinct d i s t i n c t pegmatite p e g m a t i t e groups groups (Terminology ( T e r m i n o l o g y aafter f t e r Cerny, C e r n y f 1982, 1 9 8 2 f p.8—9) p . 8 - 9 ) at a t Mavis Mavis Lake L a k e and and Gullwing—Tot Lakes separated by a distance of 9.7 km. G u l l w i n g - T o t L a k e s s e p a r a t e d b y a d i s t a n c e o f 9 . 7 km. The The geology g e o l o g y of o f the t h eMavis Mavis Lake Lake Pegmatite P e g m a t i t e Group Group is isdominated dominated by the Ghost Lake Batholith which represents the most by t h e G h o s t Lake B a t h o l i t h w h i c h r e p r e s e n t s t h e most plausible plausible source s o u r c e area a r e a for f o rthe t h erare—metal r a r e - m e t a l pegmatites p e g m a t i t e s based b a s e d upon u p o n the the following f o l l o w i n g ppetrologic e t r o l o g i c features f e a t u r e s and and chemical c h e m i c a l characterist-ics: characterist-ics : i) the advanced degree of geochemical fractionation t h e a d v a n c e d d e g r e e o f g e o c h e m i c a l f r a c t i o n a t i o n and and i1 difference sf 66 (Table ( T a b l e 3) 3) d i f f e r e n c e in i n plutonic p l u t o n i c units u n i t s such s u c h as a s GLB4, GLB4# 5, relative r e l a t i v e to t o the t h e main m a i n western w e s t e r n mass m a s s of o f the t h e batholith b a t h 0 1 i t h which w h i c h is is dominated d o m i n a t e d by b y plutonic p l u t o n i c unit u n i t GLB—1 GLB-1 (Breaks, ( B r e a k s in i n prep.). prep.) The The former t o exhibit e x h i b i t increased i n c r e a s e d levels l e v e l s of of f o r m e r plutonic p l u t o n i c units u n i t s tend t e n d to muscovite, with t o nil n i l biotite biotite m u s c o v i t e f tourmalirie t o u r m a l i n e aand n d ggarnet arnet w i t h ssparse p a r s e to in t o plutonic p l u t o n i c unit u n i t GLB—1; GLB-1; i n contrast c o n t r a s t to ii) i i ) sporadic p r e s e n c e of o f rare—metal r a r e - m e t a l mineralization m i n e r a l i z a t i o n (i.e. ( i .e beryl) beryl) s p o r a d i c presence within w i t h i n some some internal i n t e r n a l pegmatites p e g m a t i t e s (Dryden ( D r y d e n Airport A i r p o r t beryl beryl occurrence) t o u r m a l i n e -- quartz quartz o c c u r r e n c e ) and and in i n contact c o n t a c t pneuinatolytic p n e u m a t o l y t i c tourmaline deposits d e p o s i t s (Petrunka ( P e t r u n k a Tungsten T u n g s t e n Property P r o p e r t y at a t STOP STOP 5); 5); i i i ) contact iii) c o n t a c t metasomatic m e t a s o m a t i c selvedges, s e l v e d g e s developed d e v e l o p e d in i n mafic mafic metavolcanic m e t a v o l c a n i c host h o s t rocks, r o c k s which which exhibit e x h i b i t anomalous a n o m a l o u s trace t r a c e level level L i Cs, C s Be, B e , Rb, Rbf Sn Sn and a n d FF (Petrunka ( P e t r u n k a Thngsten Tbngsten e n r i c h m e n t in i n Li, enrichment Property P r o p e r t y at a t STOP STOP 5). 5). Significant GhostLake Lake S i g n i f i c a n t petrochemical p e t r o c h e m i c a l zonation z o n a t i o n within w i t h i n the t h eGhost Batholith B a t h o l i i h is is revealed r e v e i l e d by by ccertain e r t a i n trace t r a c e elements, e l e m e n t s f in i n particular p a r t i c u l a r B, Bf Ba, Ba Li, Li Rb, R b f Sr, S r Zr Z r and a n d REE REE ((Breaks, B r e a k s iin n pprep.). r e p . ) . Trends T r e n d s of of increasing F3, i n c r e a s i n g geochemical g e o c h e m i c a l ffractionation r a c t i o n a t i o n involving i n v o l v i n g enrichment e n r i c h m e n t of o f B, Be, with B e Ga, Ga Li, L i Nb, Nb and a n d Pb R b coupled coupled w i t h ddepletion e p l e t i o n of o f Ba, Ba Sr, S r Zr, Z r and and total t o t a l REE REE have h a v e been b e e n delineated d e l i n e a t e d within w i t h i n the t h e batholith b a t h o l i t h from f r o m the t h e main main . . �______________________________Assemblage1 _____________ 164 able 2: 22 Fable Geochemical Features Petroi P e t r o l o g i c a l and and Geochemical F e a t u r e s of of Rare-Metal—Bearing Rare-ZeLal-&ear1119 Pegsatites P e g m a t i t e s from From the t h e Dryden Dryden Field. Field.- Area/Occurrence Area/Occurrence Charactristic Charactristic Pegsatite P e g m a t i t e StructurR Structure Pegmatite P e q m a t i t e Mineral Hineral ~ s s e m b l a ~ ~ - Geochemical Aasoclation2 &.sociation2 Degree of (ate Degree OF b t e Stage Stage Replacueent bplacment Albitization A lbitization B—CBs—Cs) B-(Be-Ce) Absent Absent MaRie ~ a v i sLake u k e Pegmatit. p e g m a t i t e Group Dryden irFort Dryden AAirport occurrenm, Occurrence, Zealand x e a l a n d lbwnship mmnship Unzoned.i internal, Unmned, nternal, , barren uu.ually sually b a r r e n potassic p t ~ s i c pegmatitea Garnet +t Muscovite Garnet n u s c o v i t e +t Iburmaline m umaline + t Albite A l b i t e +t Quartz a l o c k y k—feldspar K-feldspar Q u a r t z +t Blocky + (Limegr.en t (Limegreen Beryl) mryl) Taylor Occurrence, Taylor Occurrence, Concession c o n c e s s i o n VII. V1 I , Zealand ?ownmhip Itenship zealand .arqinal m a s q i n a l to t oQost mostLaX. fah tkzoned potassic lhaoned p tdssic peqsatites p e g m a t i t e 8 developed developed Beryl (Sn—Nb>Ta— B e r y l ++lbur,salin. m u m a l i+nAlbite e + AB—Be— l b i t e 8-B-(Sn-~b>TaQuartz P)) +t Q uartz + t Graphic Graphic P K—feldspar K -feldspar + + Blocky Blocky k—feldspar R-feldapar t+ ((Colueblt. colmbite + Garnet t G a r n e t ++ Muscovite M u s c o v i t e +t Green *at ).patiits) Green te) p e t r u n k a Occurrence, Wcurrence, Petrunka Brownridge Brownridge and Zealand mmnship Zealand Townships p.g.atites Bathol B a t h o lith ith Unmned, t o u r m a l ins— ineUnmoned, toursal eenriched n r i c h e d fracture/pillow frecture/pillow ssalvage—controlled elvqemtrollad replaces.nt r e p l a c m e n t in i nBrownridg. Brownridge m i c estavolcanics metavolcsnics s.fa tIc Quartz t Plaqioclaae P l a q i o c l ~+ et Q uartz + Biot B i o t iits te ÷ + Scheel S c h e e l iit. te + + + (Pyrite 'Toursaline burmaline + ( P y r i t e ++ Holequletite Holmquia t i t o + t Fluorite?) PI w r i t e ? ) Incipient. all Incipient. % a l l pod. p a l s of of fine—grained, saccharoidal fine-grained , saccharoidsl splits a p l i t e (4 ( t Chriua Chrmium Mica ~ i c at4 Quartz W-artz + + aAlbit.) lbite) W—B—F— (Li—Sn—Be) W-B-P-(Li-Sn-Be) Ibeerved Sot C tat bservd Li— (Be—Rb-ra>Wb— Li-(&-Rb-Ta>NbB—Sn) 6-Sn) Moderate W e r a t e ddevelopeent w e l o p e n t of of aelbitization l b i t i a a t i o n (+ (t Garnet 4t Tantal T a n t a l iits t e ++ White W h i t s Beryl mryl Green *Fa.cov 7 Green s c w i t its e + t Quartz Clesv.landita) m a r t s t+ C leavelMdite) Falrservice e a i r s e r v i c e Property, Property, Brownr E x o m r i dIdge g e Township Tounship Main and sSouth u i n and o u t h Ions. an" Un zonedt to Unzoned o ccrudely rdely zoned zoned e x t e r n a l pegmatitea. peqnatitaa. externsl 4 Green Mu.cov Beryl Green H u s c w iits te Beryl + t+ Albite N b i t e 4.t Spodueens Spcdmene Contains C o n t a i n s r arandly n d m l y oriented, o r i e n t e d , Blocky Blocky K—feldspar K - f e l d s p a r +t last UstZone Zone ++ g r e e n primary p r h a r y spodLa.fle spodmene green phenocrysts p h e n o c r y ~ t s(Type (Type I1 epodtene e p c d m e m of o f H.inricfl, Heinrich, 1975) 1975) Quartz ( B l u e Apatite Apatite + t Q u a r t z t+ (Blue Garnet Garnet + t Toursaline T u t u m a l i n e4.t Tantal T a n t e l iits) te) Unmoned extetnal U nmnd ex ternal Primary sineralogy R imary m ineralcqy llarg.ly a r g e l y replaced. replaced. Bemnants Fmmndnts oof f blocky blocky k—feldspar, K - f e l d s p a r , spodue.ne. eiXdmelN, and and qquartz u a r t z sstill till discernible discernible p.geatitea pqmstltu Ta)Nb—B.— Ta>Nb-Be*B-( L(Li) i) ' Pervealve P e r v u l v e aalbitizatlon. lbitisation. Fast of mst o f peqeat p e g m a t iit. te White Beryl replaced r e p l a c e d by by 4. t White B~ryl 4. Green + rantal it. t T a n t a l i t e t Green Fascov Quartz m e c o v i its t e 4t ~ u a r t st+ C1.au.landitra C&elandi te Guliwing Lake—Itt Peqest Gullwing Iake-Tot fLake ah P w m a t its l t s Group QOuP Mica Point n ica P oint Gullwlng Lake, Gullwinq bh, rope R o wTownship lbmhip Crudely zoned, eexternal Cxudely so&, xternal potassic peq.atits ptassic m matite Muecovite Biotite Mumcwite ++ B i o t i t e ++ Albite N bite 4 t Quartz Quartz + t K—feldspar K - f e l d s p a r ++ (Molybdenits (mlybdenite Coluebite—Tantal ++ C o l m b i t - T a n t a l i t eits) ) (Nb>Ta-WO) (Nb>Ta*) Gullwinq Gullwinq Lake Iah Co.pl.x C o m p l ~external e~x t e r m 1 Green Green w'odten. m e n e +t Li— (TsCNb-Mo-Bn) (Ta(Nb—Mo—Sn) Li- Peg.atlte, P e g m a t i t e ,Webb !&bb Toimah T o m e h iipp Most ppeq.atlte. eqmatite. mt ooff dik, d i h consists c o n s i s t s of of .uBcov m u s c w iits—blot t m - b i o t i tits e peg.atltic p e g m a t i t i c granite. granite. ContaIns C o n t a i n s green g r e e n Type Wpm 1 s.podaens p o d m e n e of of B.inrlcb winrich I (1975) (1975) Muscovite t+ AAlbite Muscovite lbite + t Quartz t Blocky Blocky m artz + K—feldspar K-feldspar Albit. GreenYsaacovit. n ~ s c w i t 4et ~ l b i t4etGreen Quartz Q u a r t z +t Blocky Blocky k—feldspar K-feldnpar Incipient Incipient Moderateaalbitisation Moderate lbitization ddeveloped w e l o p a d in i n 22 sstages: tag-: I. e a r l ysediua—grained, mdium-grained, 1. early equ e q u iig g rranular anular + Biotite Tantal t ~ i o t i t4 e2 T a n t a lIts i t e +t usCOv l i u s c w iite te +Q Quartz + uarts + t Albite Albite 2. later, 2. l a t e r ,fine—gralnsd fine-grained u(apidol p i d o l Ite—Albite ite-Albite C a p l e x + Tantalit. Tantalite + t Beryl n e r y l ++ Garnet Garnet Lapidol +4 Lep1d01ite ++ Muscovite Muscwite t ClpvelapditeJ Cplez 4 it. + Clca!iteJ Coates Peqastite, CoatPaqaat it*, Webb m Township Webb mnship Peg.atlte P e g m a t i t e 215 215 5 m Southwest ooff Coates South-t coatPegmatite, P e q m a t i t e , Wsbb Webb Township m unship Tot Lake mt fake Pegsat iI tte, Pegmat e, Webbmmnship xnship Webb lUnzon.d, h z o n d , eexternal xternal potassic peq.etit• p taseic w matite Unxoned, eexternal Unmnad, xternal potas. p t a ~ sIc i cppeg.atite R3mstite -- complex C a p l e x eexternal xternal Contains peg.atlte. pegmatite. Contains pink p i n k Type Typ 2 2 spothnene epodmene off Beinrich o w i n r i c h (1975) (1975) Accessory ~ c c e s s o r ymminerals i n e r a l s pplaced l a c e d iIn n brackets. brackets. Minoreelements 22 Minor l e m e n t s pplaced l a c e d i in n bbrackets. rackets. Muecov its 4-+ A Albit. Muscovite l b i t e ++ Quartz m art; + t Graphic Graphic k-f K - f eeldBpar l d s p a r + (Molybdenite (mlybdenite Garnet 4+ Pyrite w r i t e t+ G arnet + + SSeaarskite marskite + t Sphalsrite Sphalerite Chalcopyrite + Beryl) t C h a l c o p y r i t e 4. t B eryl) nMo-e )Nb)Ta—Cu— (Nb>Ta-Cu- Muscovite 4t Albite A l b i t e +t 4 Blocky Quartz Blocky K—feldspar K-feldspar Quartz + + t (Colbite—Pantalite ( C o l m b i t e - T a n t a l i t e4.t Garnet Garnet + t Falybdenlte) mlyMenite) Nb>Ta?— (Mo) Nb>Ta?(-1 S p o d m e n e +t Pink Spodesene Pollucite Q u a r t z +t P o l l w i t e +t Quartz Albite N b i t e ++Blocky Blocky K—feldspar K - f e l d s p a r ++{(Fluorapatlte Flwrawtite 4t Garnet + Ibursaline) Garnet t mumeline) In—S-Be—RE!) Zn-840-REE) IIncipient n c i p i e n t repiscesent r e p l a c e m e n t by by fine—grsined f i n e - g r a i n e d aalbite l b i t e along along edge. Fast adgem of of K—feldspar. K-feldsparnost solybdenite mol y M e n i t e end and sarekite a m a ~ s k i associated t ea s s o c i a t e d with albitized cress IIncipient, n c i p i e n t , file—like film-like albitizatlon a l b i t i a a t i mand andaBeociated associated coiabite—tantal c o l m b i t e - t a n t a l iite t e In in with a l b i t i z e d a r e a s ccoarse u a r s e blocky b l o c & K—feldspar K-feldspar Li -Cs—Rb— Li-Cs-Rb- tensive aibitization Rtensive albitizatim developed -F-P -F+ )Ta>Nb—Be) ( ~ a > ~ b - ~ e )d w e l o w d iin n 22 sstages: tages: 1. sssccharoidsl a c c h a r o i d a l sodic sodic aplite (Blw Watite ++ Tourtualine m u m a l i n e 4 Quartz Wartz ++ ALb1t.a) Alblte) 2- tapidal u p i d o l ite—Albit. ite-Albite 2. Complex (+ (+ White mite complex Beryl B eryl + + Garnet Garnet ++ Trantalite anealite + + Sericite Sericite + + Lapidol + Quartz L e o i d 0 1 iite te + o u a r t z 4t C cl&l$ndite; split. (Blue gpatite llandite) �_______ Tablejmmy ofofP Petrol2!c GhoLBatholith. Summary e t r o l a i c Feat F e a t u r eures s o f Iof ~ t Irus r u s i Iv veP e - P hhs ~ s the t2h e GhoQ Lake B a t h o l i t h . T * 3: IIntrusive ntrusive -- P* Rock Rsk G LB—i GLB-1 Muscovite—biotite M u s c o v i t e - b i o t i t e and a n d biotite— biotitem u s c o v i t e ggranite r a n i t e and and rare rare muscovite Locally g ranodiorite. L o c a l l y cordierite— cordieritegranodiorite. bearinq beMuscovite—blotite ~ u s c o v i t e - b i o t i t e granite g r a n i t e to to g g rranod a n o d iioo rrite it e G LB -2 GLB-2 GLB—3 GLB-3 -GLB-4 G LB -4 GLB -5 GLB-5 Petroloatures IIntrusive n t r u s i v e Relations Relations e t r o l o ~ ~ u r e ~ Massive Coarse—grained M a s s i v e to t o weakly w e a k l y ffoliated. oliated. C o a r s e - g r a i n e d to to peginat itic, i t i c , inequig i n e q u i g rranular, a n u l a r generally generally pegmat . P- TE I hypidiomorphic—granular, hypidiomorphic-granularI - Mass, white—weathering w h ite-weathering aV faf fol -— occasf a1 Mass i v e t o c c a s ions-£0i a t e d fine— inedium—grained, f i n e - tto o m e d i u m - g r a i n e d I aallotriomorphic— llotriomorphic_9anular. Distinctive ranular. D g t i n c t i v e medium grey g r e y colour colour weakly foliated kMassive s % t o to weak1 y m ' i a t e d and o c c a s ~ o n a lyl lineated, medium—grained, lineated m e d i u m - g r a i n e d , allotriomorphic— allotriomorphicUniquep presence + ggranular. ranular. Unique r e s e n c e o foff fibrolite ibrolite+ + muscovite quartz quartz + m u s c o v i t e faserkiesel faserkiesel biotite granite + Muscovite ~ u s F o v i t eand a n d biotite—muscovite biotite-muscovite 5 garnet garnet ppegmatitic e g m a t i t i c leucogranite leucogcanite + + + tourmaline t o u r ~ ~i ~ n ea l garnet—muscoite— ~ S g r a i n e dg arnet-muscov itettourmaline o u r m a l i n e leucogranite leucogranite Massive to occasionT1 elayere M ~ S iSv e to o c c a ~ a l l $vaq ue layered - FTgraii granular hhypidiomorphic ypid iomorphic g ranula; - - MITe EodasionäI[y layered, ffne- trMuscov , -- l¶l\urnialine—quartz b u n n a l i n e - q u a r t z vveins eins Occurs as small O c c u r s as s m a l l masses m a s s e s and and dIkes dikes cross—cutting cross-cutting GLB—1. GLB-1. ftff and occasioT1fl TErisivereatTns No i n t r u s i v e r e l a t G MuscovTfftti muscov ~ u s c o v E e - b i te o t and i t e and m u s c oite— vitebiotite granite ggarnet arnet Mass i v e t ~ o c c a s i o n a lyl l a y e r e d I f i n e grained, usually g r a i n e d n allotriomorphic—granular, allotriomorph ic-granular usually ee3igranular 2igranular Mass Mass ive, i v e , h y p ~ o ~ p ch- qir a n u l a r w i t h distinctive d i s t i n c t i v i - randomly r a n d o m l i oriented oriinted bladed , b l a d e d rates a r 2 a trich e s r l in c h igreen n g r e e nmuscovite muscovite Massive, Mass i v e 2 y Tiypidiomorphc p * d ~ o r p h cg r a gran1ay n " m y be with aassociated ssociated w i t h fine—grained, f i n e - g r a i n e d , banded b a n d e d sodic sodic aplite. Contains o n t a i n s rare r a r e green g r e e n syngenetic syngenetic a p l ite. C beryl. beryl. Garnet—biot ii-6 m G a r nr e t - b i o t i t ite—tourfine--muscoT€e etourmaline-muscovite pegmatitic p e g m a t i t i c leucogranite leucog r a n i t e -G I J-7 ~ M u s c o vite—tourmal i t e - t o u r m a l ime n e potass p o t a s s ic ic . pegmatite p e g m a t i t e ?+garnet -garnet GLB—B GLB8 - . - --- tern ow.eas part %all veins c o n c e n t r a t e r n a r d s eastern p art Relatively ooff thost C h o s t Lake I d k e Batholith. Batholith. R e l a t i v e l ycommon common in i n metasedimentary m e t a s e d i m e n t a r y rocks r o c k s between b e t w e e n Dryden Dryden and and Thunder Featured T h u n d e r Lake. Lake- F e a t u r e d by b y locally l o c a l l y impressive impressive inetasomatic tourmaline metasomatic tourm a l i n e h a l o e s halohS2cks. i n host rp&. n i bserved. aadjacent d j a c e n t GLB—1 GLB-1 o or r 22 oobserved. GLB—3c ocontains GLB-3 n t a i n s llayers a y e r s and and small small pods ooff gradational g r a d a t i o n a l coarse— coarseraind_to_gmatiticranite grained t o m a~t i t i c r a n i t e Observed Observed as as veins v earwl w ~ e cutting c u t t i n g GLB—1 GLB-1 and a n d 2. 2. dies part ifed fy in No t e d on .on1 in eas Ghost Lake Batholith; Bath01 i t h ; intruded 7. i n t r u d e d by b GLB—6 GLB-6 and and 7. Crosscuts GLB-5 Cros r U s-cuLs yGLB-5 UI GLB-nx a n d r - cuts GLB ~r&%.-cuts Youngest Youngest g granitic r a n i t i c pphase h a s e inn Ghost Batholith. May G h o s t Lake Lake B atholith. May be be ccorrelative o r r e l a t i v e with w i t h exocontact, exocontact pegmatitic pegmat i t i c dikes d i k e s having having I ttounualine o u r m a l i n e babes h a l o e s and and zoned zoned garnet— g a r n e t - ttourmal o u r m a l me—green ine-green muscovite m u s c o v i t e dike d i k eon onHighway' Hiqhway' 17 - 17 1022 w e s t o f ~-,r ~ d & n . - Lm -- �166 northwestern n o r t h w e s t e r n mass mass of o f GLB—1 GLB-1 t o towards w a r d s t hthe e nnarrow a r r o w eeastern a s t e r n lobe lobe A t othe t h eMavis Mavis Lake Lake Pegmatite P e g m a t i t e Group. Group. A ssecond e c o n d ttrend r e n d of of aadjacent d j a c e n t to geochemical i s also a l s o developed d e v e l o p e d within w i t h i n the t h e batholiths batholiths g e o c h e m i c a l fractionation f r a c t i o n a t i o n is t o southwest s o u t h w e s t towards t o w a r d s plutonic p l u t o n i c unit u n i t GLB—3. GLB-3. aand n d ddirected i r e c t e d south s o u t h to T h e Mavis Mavis Lake Lake Pegmatite P e g m a t i t e Group G r o u p is is almost a l m o s t entirely e n t i r e l y contained contained The within is 8 km in i n sstrike t r i k e length l e n g t h and and w i t h i n the t h e Brownridge B r o w n r i d g e volcanics v o l c a n i c s and a n d is A well 1 . 4 km in i n breadth. breadth. w e l l developed d e v e l o p e d lateral l a t e r a l zonation z o n a t i o n of of ..8 8 tto o 1.4 The zonal is apparent a p p a r e n t over o v e r this t h i s strike s t r i k e length. length. zonal ppegmatites e g m a t i t e s is pattern p a t t e r n of o f typomorphic t y p o m o r p h i c mineral m i n e r a l assemblages, a s s e m b l a g e s internal i n t e r n a l structures, structures of a l b i t i z a t i o n and a n d characteristic characteristic ddegree egree o f replacement r e p l a c e m e n t stage s t a g e albitization geochemical g e o c h e m i c a l associations a s s o c i a t i o n s changes c h a n g e s progressively p r o g r e s s i v e l y at a t increasing increasing This ddistances i s t a n c e s from f r o m the t h e parental p a r e n t a l Ghost G h o s t Lake Lake Batholith. Batholith. T his is similar, s i m i l a r for f o r example, e x a m p l e to to ssuccession u c c e s s i o n of o f rare—metal r a r e - m e t a l ppegmatites e g m a t i t e s is that t h a t ddescribed e s c r i b e d in i n the t h e Yellowknife—Beaulieu Y e l l o w k n i f e - B e a u l i e u district d i s t r i c t (Hutchinson, (Hutchinson 1955), Preissac—Lacorne Quebec 1955) P r e i s s a c - L a c o r n e aarea r e a of of Q u e b e c (Mulligan, ( M u l l i g a n 1965), 1 9 6 5 ) and a n d the the Issia 1uvre t T b u v r e area a r e a of o f the t h e Ivory I v o r y Coast C o a s t (Varlamoff, ( V a r l a m o  £ f1972). 1 9 7 2 ) . The I s s i a eet degree w e s t to t o east e a s t in in d e g r e e of o f late—stage l a t e - s t a g e albitization a l b i t i z a t i o n increases i n c r e a s e s from f r o m west Mavis Lake tthe h e Mavis Lake Pegmatite P e g m a t i t e Group Group such s u c h that t h a t thin t h i n (1—3 ( 1 -3 mm width) width) ppegmatite e g m a t i t e ssheets h e e t s exposed e x p o s e d at a t the t h e East E a s t Zone Zone of o f the t h e Fairservice Fairservice Property e s s e n t i a l l y of o f secondary s e c o n d a r y mineral m i n e r a l assemblages. assemblages. P r o p e r t y consist c o n s is t essentially These white T h e s e mainly m a i n l y consist c o n s i s t of of w h i t e sodic s o d i c beryl beryl + + green g r e e n muscovite m u s c o v i t e ++ + cleavelandite Primary quartz quartz + c l e a v e l a n d i t e ++ ttantalite. antalite. P r i m a r y relict r e l i c t spodumene, spodumene mica, largely reen m i c a ragged ragged l a r g e l y cconverted o n v e r t e d into i n t o fine—grained f i n e - g r a i n e d albite a l b i t e ++ ggreen K—feldspar bblocky locky K - f e l d s p a r and a n d quartz quartz are nevertheless still Further rrecognizable. ecognizable. F u r t h e r west west at a t the t h e Main Main Zone Zone aalbitization l b i t i z a t i o n isismuch much less less ppronounced, r o n o u n c e d , consuming c o n s u m i n g between b e t w e e n 20 20 and a n d 50 5 0 percent p e r c e n t of o f primary primary pegmatite IIn n many instances i n s t a n c e s here h e r e the t h e albitization a1 b i t i z a t i o n appears appears p e g m a t i t e units. units directly t o aa rudimentary r u d i m e n t a r y quartz—rich q u a r t z - r i c h core core zone z o n e as a s at at d i r e c t l y related r e l a t e d to STOP STOP 4. 4. K, Cs, Sn, B,f Rb Metasomatic M e t a s o m a t i c release r e l e a s e of o f Li, Li K t C s Sn B R b and a n d FF can can ddevelop e v e l o p impressive i m p r e s s i v e endogenic e n d o g e n i c dispersion d i s p e r s i o n ppatterns a t t e r n s in i n mafic mafic metavolcanic a l b i t i z e d spodumene s p o d u m e n e pegmatites p e g m a t i t e s as as m e t a v o l c a n i c rocks r o c k s enclosing e n c l o s i n g albitized exemplified e x e m p l i f i e d by b y the t h e Main Main and and South S o u t h Zones Z o n e s of o f the t h e Fairservice Fairservice These mineralogically Property. m e s e elemental e l e m e n t a l concentrations c o n c e n t r a t i o n s are are m ineralcq i c a l l y P roperty. attributable a t t r i b u t a b l e tto o secondary s e c o n d a r y bbiotite, i o t i t e tourmaline, t o u r m a l i n e , and a n d holmquistite holmquistite w h i c h aare r e intensely i n t e n s e l y developed d e v e l o p e d within w i t h i n layers l a y e r s and a n d pods p o d s in i n proximal proximal which Five metasomatic mafic rocks. F i v e aanalyses n a l y s e s of o f these these m etasomatic m a f i c host h o s t rocks. assemblages, a s s e m b l a g e s (termed ( t e r m e d glimmerite g l i m m e r i t e in i n Russian R u s s i a n literature) l i t e r a t u r e ) from from Tot o t Lake Lake iimmediate m m e d i a t e contacts c o n t a c t s of o f Mavis Mavis Lake Lake and a n d Guliwing G u l l w i n g Lake Lake -- T Be, F,t Li, rare—metal a r e presented p r e s e n t e d in i n Table T a b l e 4. 4. B e t Cs, Cs, F Lit r a r e - m e t a l pegmatites p e g m a t i t e s are Rb aand Rb n d Sn Sn all a l l hhave a v e obvious o b v i o u s utility u t i l i t y in i n lithogeochemical l i t h o g e o c h e m i c a l surveys, surveys hhowever, o w e v e r in i n reconnaissance r e c o n n a i s s a n c e surveys s u r v e y s ddesigned e s i g n e d to t o locate l o c a t e rare—metal rare-metal pegmatite p e g m a t i t e fields, f i e l d s lithium 1i t h i u m represents r e p r e s e n t s the t h e most useful u s e f u l element element Pryslk d o c u m e n t e d several several ((Ovchinriikov, G v ~ h i n n i k o v 1976). 1~9 7 6 ) . P r y s l a k (1981) ( 1 981 ) documented impressive i m p r e s s i v e lithium l i t h i u m aureoles a u r e o l e s on on the t h e Main Main Zone Zone with w i t h the t h e largest largest by 1220 measuring 8 5 m by 1220 m and a n d containing c o n t a i n i n g maximum lithium lithium m e a s u r i n g 60 6 0 —- 1185 cconcentrations o n c e n t r a t i o n s of o f 4095 4 0 9 5 ppm. ppm. Pegmatite The Guliwing me G u l l w i n g Lake—Tot Lake-Tot Lake Lake rare—metal rare-metal P e g m a t i t e Group G r o u p (0.8 ( 0.8 2.2 tto o 2. 2 x 8.6 8 . 6 km in i n area) a r e a ) is is ssituated i t u a t e d bbetween e t w e e n the t h e northeast n o r t h e a s t end end of of mainly Guliwing G u l l w i n g Lake L a k e and a n d Tot T o t Lake and a n d is is m a i n l y confined c o n f i n e d to t o aa medium—grade, m e d i u m - g r a d e ! hhighly i g h l y deformed, d e f o r m e d southwest—striking s o u t h w e s t - s t r i k i n g mafic mafic metavolcanic m e t a v o l c a n i c uunit n i t which which envelopes e n v e l o p e s the t h e Lateral L a t e r a l Lake Lake Stock S t o c k (Breaks ( Breaks et Six e t al., al. 11978). 978). S i x rare r a r e metal pegmatites p e g m a t i t e s hhave a v e been b e e n ddiscovered i s c o v e r e d to to which ddate a t e ((Table T a b l e 22) ) w h i c h aare r e ddistinctive i s t i n c t i v e in i n sseveral e v e r a l ways from f r o m those those are, nevertheless, still . �___________ _________ S e l e c t e d themical ChemicalAnalyses1 A n a l y s e s 1 of o fMetasomatic Metasomatic S e l v a g e s Developed Developed a Selected Selvages att C o n t a c t s R a r e M e t a l P e g m a t i t s r o m t h e D r y k p e g m a t i t e F i , e l d . _—Mal Pegmatites from theDryderPegrnatiteFeld. - T a b l e 4: Table Spodumene Spod umene Pegmatite 2 P e g m a t i t e No. No. 2 Fairservice— F airserviceProperty P roperty o f Some Contacts of Some B B Be Be Cs F F Li Rb Sn Pa Nb 2 222 920 920 77650 650 6050 3790 68 <30 13 3.69% ine-holmquistite-biotite glimmerite) glimmerite) (tourmaline—holmquistite—biotite Pegmatite P e g m a t i t e No.2 No - 2 Taylor T a y l o r Beryl Beryl 5 20 5 20 1150 7250 2300 2210 762 <30 70 4.58% 18400 4600 7580 167 60 925 6.39% 5930 1900 4820 45 0 450 K20 ( tourmal Occurrence Occurrence ((biotite—rich b i o t i t e - r i c h glimmerite) qlimmerite) Gullwing G u l l w i n g Lake Lake Spoduinene Spodumene Pegmatite <5 P egmatite (biotite—rich ( b i o t i t e - r i c h gglimmerite) limmerite) lbt Lake Lake Spodumenelbt SpodumenePollucite P o l l u c i t e Pegmatite P e g m a t i t e 25 25 ((biotite—rich b i o t i t e - r i c h glimmerite) glimmerite) Gullwing G u l l w i n g Lake Lake Batholith att Batholith a STOP 6 STOP 6. N. D. N.D. 6 1140 I.-J 1122 1.60% 66 755 17,800 1400 1860 90 1010 1240 50 23.9 142 N.D. <10 N.D. 4.78% 7 3.70% 35 0.13% ( b i o t i t e - t o u r m a l me i n e glimmerite) g l immerite) (biotite—tourmal P e t r u n k a ¶Iingsten T u n g s t e n 44200 200 Petrunka P r o p e r t y at a tSTOP STOP 55 Property ((tourmaline t o u r m a l i n e +-+ bbiotite iotite met m e tasomatizeci a s m a t i z e d ppillow illow immediately sselvage e l v a g e immed iately below b e l o w scheelite—tounnaline s c h e e lite-tourmal i n e ssheet) heet) 3 3 iin n ppm u n l e s s otherwise o t h e r w i s e shown ppm unless = Not D N.D. = Determined etermined N.D. 1 3.7 N.D. �168 in i n the t h eMavis Mavis Lake Lake Pegmatite P e g m a t i t eGroup: Group: 1) Most Most ppegmatites e g m a t i t e s a are r e ssignificantly i g n i f i c a n t l y discordant d i s c o r d a n t to t o the the general 0 7 0 0 sstructural t r u c t u r a l trend t r e n d of o f host h o s t rocks. rocks. general 070° 2) Presence more P r e s e n c e of o f internally i n t e r n a l l yzoned zonedpegmatites p e g m a t i t e s exhibiting e x h i b i t i n gmore complex complex ggeochemical e o c h e m i c a l s pspecialization e c i a l i z a t i o n ii.e. .e . Li-Cs-Rb—Be--Ta>Nb Li-Cs-Rb-Be-Ta>Nb aand n d Li-Ta>Nb-Be--Mo. Li-Ta>Nb-Be-Mo. 3) no mineral i z a t ion ; no evidence e v i d e n c e oof f associated a s s o c i a t e d scheelite s c h e e l i t e mineralization; 4) absence a b s e n c e of o f tourmaline t o u r m a l i n e replacement r e p l a c e m e n t oof f host h o s t rocks, r o c k s , and and much more cconfined o n f i n e d development d e v e l o p m e n t of o f metasomatic metasomatic much more gl g l immerite i m e r i t e assemblages. assemblages. r e g i o n a l zonation z o n a t i o n of o f rare—metal r a r e - m e t a l pegmatite p e g m a t i t e types t y p e s not n o t as as 5) regional clearly c l e a r l y developed. developed. 6) parental p a r e n t a l granitic g r a n i t i c source s o u r c e area a r e a is is not n o t clearly c l e a r l y apparent. apparent. Most pegmatites p e g m a t i t e s of o f this t h i s group g r o u p are a r e oriented o r i e n t e d sub—perpendicular sub-perpendicular to t o the t h e curvilinear c u r v i l i n e a r contact c o n t a c t between b e t w e e n the t h e mafic m a f i c metavolcanic m e t a v o l c a n i c host host unit u n i t and and Lateral L a t e r a l Lake Lake Stock. S t o c k . Exceptions E x c e p t i o n s to t o this t h i s include i n c l u d e the t h e Mica Mica Point P o i n t columbite c o l u m b i t e pegmatite p e g m a t i t e (concordantly ( c o n c o r d a n t l y emplaced e m p l a c e d in i n the t h e mafic mafic metavolcanic it deflects d e f l e c t s north n o r t h to t o northeast n o r t h e a s t around around m e t a v o l c a n i c unit u n i t where w h e r e it western w e s t e r n terminus t e r m i n u s of o f the t h e Lateral L a t e r a l Lake Lake Stock) S t o c k ) and and the t h e Drope Drope 'Ibwnship Tbwnship ccolumbite—molybdenite o l u m b i t e - m o l y b d e n i t e ppegmatite e g m a t i t e exposed e x p o s e d at a t the t h e extreme extreme southern s o u t h e r n known known limit l i m i t of o f the t h e pegmatite p e g m a t i t e group. g r o u p . The The latter latter pegmatite t o foliation f o l i a t i o n of of clastic clastic p e g m a t i t e was was emplaced e m p l a c e d concordant c o n c o r d a n t to metasedimentary m e t a s e d i m e n t a r y host h o s t rocks. rocks. The The source s o u r c e area a r e a for f o r rare—metal r a r e - m e t a l pegmatites p e g m a t i t e s of o f the t h e Guliwing— GullwingTot T o t Lakes Lakes Group Group is is not n o t known known at a t present. p r e s e n t . The The Coates Coates Bay Bay Stock, Stock, located l o c a t e d near n e a r the t h e southwestern s o u t h w e s t e r n limits l i m i t s of o f the t h e pegmatite p e g m a t i t e group, group, could c o u l d represent r e p r e s e n t aa parental p a r e n t a l source s o u r c e region r e g i o n for f o r the t h e pegmatites p e g m a t i t e s but but has h a s not n o t been b e e n adequately a d e q u a t e l y studied. s t u d i e d . The The easternmost e a s t e r n m o s t part p a r t of of this this granitic pegmatitic g r a n i t i c stock s t o c k consists c o n s i s t s of o f garnet—muscovite g a r n e t - m u s c o v i t e pegmatitic leucogranite l e u c o g r a n i t e characterized c h a r a c t e r i z e d by by plumose p l u m o s eaggregates a g g r e g a t e sofo ffine—grairied fine-grained green g r e e n muscovite m u s c o v i t e and and quartz. quartz. The The relationship r e l a t i o n s h i p of o f rare—metal r a r e - m e t a l pegmatites p e g m a t i t e s of o f this t h i s pegmatite pegmatite group t o molybdenite—rich m o l y b d e n i t e - r i c h granitic g r a n i t i c pegmatites p e g m a t i t e s of o f the t h e Lateral L a t e r a l Lake Lake g r o u p to area, 4.8 km lun to t o the t h e east e a s t of o f the t h e Tot Tot lake l a k e pegmatite, pegmatite, a r e a , approximately a p p r o x i m a t e l y 4.8 is is presently p r e s e n t l y uncertain. u n c e r t a i n . Although A l t h o u g h these t h e s e molybdenite—rich molybdenite-rich pegmatites were not n o t included i n c l u d e d in i n the t h e study s t u d y of o f Breaks B r e a k s (in ( in p e g m a t i t e s were preparation) g e n e t i c relationship r e l a t i o n s h i p could c o u l d very v e r y well w e l l be b e involved involved p r e p a r a t i o n ),, aa genetic since s i n c e molybdenite m o l y b d e n i t e is is an a n accessory a c c e s s o r y in i n most most of o f the t h e rare—metal rare-metal pegmatites p e g m a t i t e s of o f the t h e Gullwing—Tot G u l l w i n g - T o t Lakes Lakes Pegmatite P e g m a t i t e Group. Group. -- Uraniferous egmatites U r a n i f e r o u s PPematites Uranium mi?Tization Uranium m i n e r a l i z a t i o within n w i t h i nthe t h eboundary b o u n d a r yzone z o n e is is concentrated c o n c e n t r a t e d in i n the t h e Vermilion V e r m i l i o n Bay Bay area. a r e a . These T h e s e occurrences o c c u r r e n c e s are are generally g e n e r a l l y concentrated c o n c e n t r a t e d along a l o n g the t h e margins m a r g i n s of o f potassic p o t a s s i c intrusions intrusions associated a s s o c i a t e d with w i t h the t h e Dryberry D r y b e r r y Batholith. B a t h o l i t h . The The mineralization mineral i z a t ion occurs coarse grained g r a i n e d to t o pegmatitic p e g m a t i t i c granitoid g r a n i t o i d rocks r o c k s and and o c c u r s in i n coarse contains c o n t a i n s uraninite, u r a n i n i t e , uranothorite u r a n o t h o r i t e and and allanite a l l a n i t e as a s common common minerals. m i n e r a l s . Most Most uuranium r a n i u m o occurrences c c u r r e n c e s i nint hthe e nnorthern o r t h e r n ppart a r t of o f the the English where E n g l i s h River a v e r Subprovince S u b p r o v i n c e occur o c c u r in i ninhomogeneous inhomogeneous ddiatexites i a t e x i t e swhere boundaries b o u n d a r i e s with w i t h supracrustal s u p r a c r u s t a l rocks r o c k s are a r e gradational g r a d a t i o n a l into i n t o pods pods of of uraniferous u r a n i f e r o u s granitoid g r a n i t o i d material. m a t e r i a l . In I n the t h e Vermilion V e r m i l i o n Bay Bay area area however, however, supracrustal s u p r a c r u s t a l host h o s t rocks r o c k s are a r e metavolcanic m e t a v o l c a n i c flows, f l o w s , tuffs tuffs and and associated a s s o c i a t e d sedimentary s e d i m e n t a r y rocks. r o c k s . Radioactive R a d i o a c t i v e mineralization m i n e r a l i z a t i o n in in this is confined c o n f i n e d to t o discrete d i s c r e t e pegmatitic p e g m a t i t i c leucocratic l e u c o c r a t i c dikes dikes t h i s case c a s e is �169 and sills s i l l s which w h i c h are a r e clearly c l e a r l y intrusive i n t r u s i v e into i n t o the t h e host h o s t rocks. rocks. and - Building B u i l d i n g Stone Stone om 1Tes soms $ i e of s the o f t hlate—tectonic e l a t e - t e c t o n i cpotassic p o t a s s i c suite s u i t e are a r e suitable suitable sources s o u r c e s of of monumental monumental and and building b u i l d i n g stone s t o n e in i n that t h a t they t h e y are are homogeneous, homogeneous, lack l a c k metamorphic m e t a m o r p h i c foliation £0i a t i o n and a n d locally l o c a l l y contain c o n t a i n few few joints. j o i n t s . The The Nelson N e l s o n Granite G r a n i t e Ltd. L t d . quarry q u a r r y near n e a r Vermilion V e r m i l i o n Bay Bay (STOP (STOP 2) 2 ) is is developed d e v e l o p e d on o n aa plug p l u g of o f granite g r a n i t e of o f this t h i s type t y p e within w i t h i n the the Dryberry 1983). D r y b e r r y Batholith B a t h o l i t h (Storey, ( S t o r e y , 1983). �170 THE THE FIELD FIELD TRIP TRIP The w i l l commence commence at a t the t h e Inn I n n of o f the t h e Woods, Woods, Kenora. Kenora. The field f i e l d trip t r i p will Proceed P r o c e e d approximately a p p r o x i m a t e l y 37 37 km km (23 ( 2 3 miles) m i l e s ) east e a s t along a l o n g the the Trans—Canada Trans-Canada Highway Highway (Hwy (Hwy 17) 1 7 ) to t o aa point p o i n t of o f intersection i n t e r s e c t i o n with w i t h the the C.P.R. r a i l line l i n e (overpass). ( o v e r p a s s ) . Proceed P r o c e e d an a n additional a d d i t i o n a l 650 6 5 0 mm east e a s t of of C.P.R. rail the s o u t h from f r o m the t h e highway h i g h w a y to to t h e overpass o v e r p a s s and a n d walk walk approximate a p p r o x i m a t e 250 250 mm south an a n area a r e a of o f stripping s t r i p p i n g and and trenching. trenching. --- STOP_1: BY BERG (HAWK N I U M OCCURRENCE OCCURRENCE STOP 1 : BYBERG_(HAWK_LAKE)_URANIUM ---. LAKE ) isU R Aconntrated UFTum Uranium mThèraITjàtion m i n e r a l i z a t i o n is c o n c e n t r a t e dini n masses masses and and 7 stringers coarse magnetite m a g n e t i t e within w i t h i n aa wedge—shaped wedge-shaped mass mass s t r i n g e r s of o f coarse of o f pegmatite p e g m a t i t e (Figure ( F i g u r e 2). 2). The pegmatites p e g m a t i t e s are a r e contained contained The within w i t h i n aa package p a c k a g e of o f mafic mafic volcanic v o l c a n i c rocks, r o c k s , now now largely largely hornblende h o r n b l e n d e schists. schists T h e s e volcanic v o l c a n i c rocks, r o c k s , along a l o n g the the These contact mass , are are very v e r y iron iron c o n t a c t with w i t h the t h e main m a i n pegmatite p e g m a t i t e mass, rich, r i c h , locally l o c a l l y magnetic, m a g n e t i c , and a n d layered l a y e r e d in i n appearance. appearance. The main m a i n showing s h o w i n g has h a s been b e e n explored e x p l o r e d by b y stripping s t r i p p i n g and and The 10 1 0 trenches, t r e n c h e s , one o n e open o p e n cut c u t 130 1 3 0 ft. f t . long, l o n g , scintillometer scintillometer surveys, s u r v e y s , and and 22 diamond diamond drill d r i l l holes. h o l e s . None None of o f the the uraniferous u r a n i f e r o u s zones z o n e s are a r e more more than t h a n 1.6 1.6 mm wide wide or o r 99 mm long. long. Earlier E a r l i e r work work by b y 3. J. Satterly S a t t e r l y of o f the t h e Ontario O n t a r i o Department D e p a r t m e n t of of 11ines Mines ssuggests u g g e s t s tthat h a t aalthough l t h o u g h aan n average a v e r a g e of o f 7 grab grab samples s a m p l e s from f r o m the t h e narrow n a r r o w magnetite—rich m a g n e t i t e - r i c h sections s e c t i o n s of o f the the pegmatite mass of of l b s U308 ~ 3 0 per 8P e r ton, t o n , the t h e main m a i n mass p e g m a t i t e ran r a n 1.9 1.9 lbs pegmatite p e g m a t i t e will w i l l probably p r o b a b l y run r u n less less than t h a n 11 lb l b U308 U308 per per ton. Ltd. in t o n . Diamond Diamond d drilling r i l l i n g by by Kerr Kerr Addison A d d i s o n Mines Mines Ltd. in 1975 1 9 7 5 iintersected n t e r s e c t e d one o n e zone z o n e that t h a t ran r a n0.41 0 . 4 1lbl U308 b U308 per p e r ton ton over b u l k sample s a m p l e collected c o l l e c t e d in i n the t h e early e a r l y 50's 50's o v e r 49 49 feet. f e e t . AA bulk had of 1.4 1.4 lbs I b s U308 U308 (chem. ( c h e m . equiv.) equiv.) had an a n average a v e r a g e content c o n t e n t of per p e r ton. ton. Uranium are Uranium minerals m i n e r a l s which w h i c h have h a v e been b e e n identified i d e n t i f i e d are uraninite, u r a n i n i t e , thorite, t h o r i t e , uranothorite, u r a n o t h o r i t e , uranophane, u r a n o p h a n e , and and B—uranotil. In I n 1977, 1977, 3. J. Douglas D o u g l a s Scott, S c o t t , formerly f o r m e r l y of of B-uranotil Eldorado material E l d o r a d o Nuclear, N u c l e a r , working w o r k i n g with w i t h magnetite—rich m a g n e t i t e - r i c h material from f r o m the t h e Byberg Byberg deposit, d e p o s i t , identified i d e n t i f i e d what what may may be b e either e i t h e r aa new new mineral m i n e r a l or or aa peculiar p e c u l i a r altered a l t e r e d allanite. allanite. Return R e t u r n to t o highway h i g h w a y and and proceed p r o c e e d eastward e a s t w a r d approximately a p p r o x i m a t e l y 43 43 km km (27 (27 miles) m i l e s ) to t o the t h e Nelson N e l s o n Granite G r a n i t e Quarry. Quarry. . . STOP STOP 2: 2: GRANITE GRANITE QUARRY QUARRY Exiiine Examine the t h e highway h i g h w a y exposures. e x p o s u r e s . The T h e "granite" " g r a n i t e 1 ' at at this t h i s locality l o c a l i t y is is distinctive d i s t i n c t i v e in i n its i t s uniform u n i f o r m pink p i n k colour, colour, consistent as c o n s i s t e n t texture t e x t u r e and a n d freedom f r e e d o m from f r o m fracturing f r a c t u r i n g as evidenced e v i d e n c e d by by the t h e highway h i g h w a y cut. cut. T h i s is i n d i s t i n c t contrast c o n t r a s t with w i t hthe t h esurrounding s u r r o u n d i n ggneissic g n e i s s i crocks r o c k sexposed exposed along It is is intrusive i n t r u s i v e into into a l o n g the t h e highway h i g h w a y on o n either e i t h e r side. s i d e . It the t h e gneissic g n e i s s i c granitoid g r a n i t o i d rocks r o c k s and and xenoliths x e n o l i t h s of o f these t h e s e can can be b e found f o u n d near n e a r the t h e contacts c o n t a c t s of o f the t h e body. body. Only Only the the central dimension s a t i s f a c t o r yasas d i m e n s i o n granite g r a n i t e due d u e to to c e n t r a l part p a r t isissatisfactory these t h e s e xenoliths. x e n o l i t h s . This T h i s granite g r a n i t e is iscurrently c u r r e n t l ybeing being quarried a s monumental monumental and and building b u i l d i n g stone s t o n e by by two two q u a r r i e d as companies, c o m p a n i e s , Nelson N e l s o n Granite G r a n i t e Ltd. L t d . on o n the t h e south s o u t h side s i d e of o f the the highway h i g h w a y and and Granite G r a n i t e Quarries Q u a r r i e s (GQI) ( G Q I ) Inc. I n c . (formerly (formerly Scotstown S c o t s t o w n Granite G r a n i t e and a n d Universal U n i v e r s a l Granite G r a n i t e Centre C e n t r e (1976) (1976 ) 7 This is in distinct �171 Byberg (Hawk Lake) Occurrence MacNicol Township District of Kenora metres I, •r 3 granitfr pegmatit - hornblende schist -Ii (metavolcanic) —I magn • • -• —'I— S —. - Geology and H.D. Figure F i g u r e 2:2: Geology G e o l o g yof o fthe t h Byberg e B y b e r gUranium U r a n i u m Occurrence. Occurrence. trench �172 L t d . oon n the t h e north n o r t h side. side. Ltd. The r a n i t e Ltd. Ltd. qquarry u a r r y was w a s first f i r s t oopened p e n e d in in The Nelson Nelson G Granite 1981, More 1981, pproducing r o d u c i n g stone s t o n e largely l a r g e l y for f o r monuments. monuments. More rrecently, e c e n t l y , hhowever, o w e v e r , the t h e pproduction r o d u c t i o n is is more evenly e v e n l y split split bbetween e t w e e n monumental monumental and construction c o n s t r u c t i o n uses. u s e s . Annual is on o n the t h e order o r d e r of o f 50,000 50,000 cubic c u b i c feet f e e t per per pproduction r o d u c t i o n is year. year. At A t the t h e present p r e s e n t time, t i m e , rough r o u g h blocks b l o c k s of o f approximately approximately 100 ccubic u b i c ffeet e e t are h i p p e d bby y ttruck r u c k to t o pplants l a n t s in i n New New 100 are sshipped Brunswick, B r u n s w i c k , Quebec, Q u e b e c , and a n d the t h e United U n i t e d States S t a t e s for f o r finishing. finishing. The company h has The a s constructed constructed a a ssmall m a l l plant p l a n t at a t the t h e quarry quarry ssite i t e so s o that t h a t sawn s a w n slabs s l a b s and a n d finished f i n i s h e d products p r o d u c t s may be be produced. produced o c k pproduced r o d u c e d in i n the t h e qquarries u a r r i e s is is pink, p i n k , medium The rrock g r a i n e d massive m a s s i v e biotite b i o t i t e granite: g r a n i t e : Modal n a l y s e s plot p l o t in in grained Modal aanalyses the close l o s e to t o the t h e ggranite r a n i t e — quartz quartz t h e ggranite r a n i t e ffield i e l d vvery ery c m o n z o n i t e boundary b o u n d a r y on the t h e Streckeisen S t r e c k e i s e n QAP QAP ddiagram. iagram. monzonite There is a a sslight l i g h t layering l a y e r i n g parallel p a r a l l e l to t o the t h e sheeting. sheeting. T h e r e is This is eevidenced by aa sslight T h i s is v i d e n c e d by l i g h t llightening i g h t e n i n g oof f the t h e ppink ink ccolour o l o u r oof f the t h e ffeldspar e l d s p a r aand n d biotite b i o t i t e is is roughly r o u g h l y aligned aligned pparallel a r a l l e l to t o these t h e s e layers. l a y e r s . Microcline M i c r o c l i n e crystals c r y s t a l s reach r e a c h up up tto o 1 cm c m in i n width w i d t h although a l t h o u g h the t h e texture t e x t u r e is is not not minor pporphyritic. orphyritic. A few few m i n o r quartz q u a r t z veins v e i n s up u p to t o 22 cm wide wide There Vertical are v e r y few f e w fractures. fractures. Vertical a r e present. present. T h e r e are very joints widely i d e l y spaced s p a c e d and in i n many parts p a r t s of o f the the j o i n t s are w outcrop Subhorizontal o u t c r o p are a r e not n o t evident. evident. S u b h o r i z o n t a l sheeting s h e e t i n g is is tthick. hick. Return highway aand R e t u r n tto o tthe h e highway n d pproceed r o c e e d through t h r o u g h tthe h e town town oof f Vermilion Vermilion Bay approximately a p p r o x i m a t e l y 27 27 km to the t h e Eagle E a g l e River R i v e r intersection i n t e r s e c t i o n (Hwy (Hwy 17 17 Continue C o n t i n u e eeastward a s t w a r d aapproximately p p r o x i m a t e l y 0.5 0.5 km krn further further and 596 ) and Hwy 596). ande xexamine aalong l o n g Highway Highway 1717and a m i n e t h the e o uoutcrop t c r o p a lalong o n g t hthe e nnorth o r t h sside i d e of of the t h e road. road. . - 1 . STOP STOP 3: - -- GHOST GHOST LAKE BATHOLITH_MIGMATITES BATHOLITH MIGMATITES relF1.zely X x i v e l yllarTzone a r g e z o n eofo t iiiiiFization m i g m a t i z a t i o n is is situated situated t o nnorthwest o r t h w e s t flanks f l a n k s oof f the t h e Ghost Ghost Lake Lake Batholith Batholith aadjacent d j a c e n t to eexhibiting x h i b i t i n g migmatitic m i g m a t i t i c sstages t a g e s (protometatexite, (protometatexite, metatexite) m e t a t e x i t e ) (Table ( T a b l e 1) 1 ) very v e r y similar s i m i l a r to t o those t h o s e encountered encountered iin n tthe h e northern n o r t h e r n ssupracrustal u p r a c r u s t a l terrain t e r r a i n of o f the t h e English English River Subprovince be1 t ) R iver S u b p r o v i n c e (Ear ( E a r Falls—Manigotagan F a l l s - M a n i g o t a q a n belt) Protometatexite Breaks ddelineated e l i n e a t e d by B r e a k s et e t àl., a l . , (1978). ( 1978). P r o t o m e t a t e x i t e is is ccharacterized h a r a c t e r i z e d by intercalation i n t e r c a l a t i o n ooff fine—grained f i n e - g r a i n e d wacke wacke and and medium—grained pelitic less than t h a n 15 15 cm cm medium-grained p e l i t i c layers, l a y e r s , usually u s u a l l y less which the iin n tthickness, h i c k n e s s , in i n which t h e ppelitic e l i t i c component contains contains sparse s p a r s e non—amalgamated non-amalgamated leucosome l e u c o s o m e patches. p a t c h e s . Note ffoliation o l i a t i o n llying y i n g aatt aan n aangle n g l e tto o bbedding e d d i n g oof f about a b o u t 20° 2 0 0 and and axial ccoplanar o p l a n a r with w i t h ax i a l ssurfaces u r f a c e s oof f small s m a l l sscale c a l e relatively relatively Development metatexite s i m i l a rtype t y p eS—folds. S-folds. Development o of f m etatex i t e oopen, p e n , similar in i n which w h i c h layers l a y e r s of o f thin t h i n hololeucocratic h o l o l e u c o c r a t i c mobilizate m o b i l i z a t e have have been b e e n iinjected n j e c t e d cconcordant o n c o r d a n t aand n d ssub—concordant u b - c o n c o r d a n t to t o bedding bedding is subordinate. Subisoclinal is subord i n a t e . S u b i s o c l i n a l to t o isoclinal i s o c l i n a S—folding l S - f o l d i n g of of is also a l s oapparent a p p a r e n tand andmay may ppelitic e l i t i cand a n dleucosome l e u c o s o m e layers l a y e r s is represent r e p r e s e n t tthe h e ffirst i r s t pphase h a s e of o f folding, f o l d i n g , although although interfering with p e n vvariety a r i e t y have have i n t e r f e r i n g relations relations w i t h the t h e more oopen A ~ �173 not n o t been b e e n observed o b s e r v e d in i n this t h i s particular p a r t i c u l a r area. a r e a . These These i s o c l i n a l folds f o l d s exhibit e x h i b i t coplanarity c o p l a n a r i t y of o f axial a x i a l planes p l a n e s and and isoclinal bedding. P o l i t i c units u n i t s are a r e characterized c h a r a c t e r i z e d by by the the b e d d i n g . Pelitic assemblage K - f e l d s p a r ++ cordierite c o r d i e r i t e ++ biotite biotite a s s e m b l a g e almandine a l m a n d i n e ++ K—feldspar + + quartz q u a r t z ++ plagioclase. p l a g i o c l a s e . Cordierite C o r d i e r i t e porphyroblasts p o r p h y r o b l a s t s can can be recognized r e c o g n i z e d as a s light l i g h t brown brown pits p i t s on o n weathered w e a t h e r e d surfaces. surfaces. Note Note also a l s o presence p r e s e n c e of o f sillimanite, s i l l i m a n i t e , mauve mauve cordierite, cordierite, and o f the t h e white white a n d rare r a r e blue b l u e dumortierite d u m o r t i e r i t e in i n some of intrusive i n t r u s i v e aanatecticmaterial. natectic material. Proceed miles) (9.25 m i l e s ) east e a s t along a l o n g Highway Highway 17b 1 7 b to t o vvillage i l l a g e of of P r o c e e d 14.8 14.8 km (9.25 Oxdrift. Oxdrift. STOP STOP 4: 4: GHOST GHOST LAKE_BATHOLITH LAKE BATHOLITH All ~igh1f7roadTeThxposures 7 a d s i d e e x p o s u r e s of o f white w h i t e granitoid granitoid ITiih rocks r o c k s between b e t w e e n the t h e Aubrey Creek C r e e k bridge b r i d g e east e a s t to t o the t h e Dryden Dryden cemetary the Ghost Ghost Lake Lake Batholith. Bath01 i t h . c e m e t a r y are a r e situated s i t u a t e d within w i t h i n the This T h i s roadcut r o a d c u t is is located l o c a t e d in i n the t h e western w e s t e r n part p a r t of of the the batholith ( F i g u r e 1) 1 ) and a n d features f e a t u r e s three t h r e e plutonic p l u t o n i c phases phases b a t h 0 1 i t h (Figure (GLB (GLB 1, 1, 2 2 aand n d 44 iin n Table T a b l e 33)) of o f this t h i s regionally r e g i o n a l l y extensive extensive S—type S - t y p e granitoid g r a n i t o i d complex. complex. Most of o f the t h e outcrop o u t c r o p consists c o n s is ts of o f inhomogeneous inhomogeneous diatexite d i a t e x i t e (GLB—1), (GLB-1 ) , characterized c h a r a c t e r i z e d by b y aa significant s i g n i f i c a n t proportion p r o p o r t i o n of o f metasedimentary m e t a s e d i m e n t a r y inclusions i n c l u s i o n s and and restite r e s t i t e (melanosome) (melanosome) patches. p a t c h e s . The latter l a t t e r may may locally locally contain significant sillimanite i g n i f i c a n t amounts amounts oof f s ill i m a n i t e and/or and/or contain s muscovite. m u s c o v i t e . These T h e s e minerals m i n e r a l s may may also a l s o appear a p p e a r within within enclosing e n c l o s i n g white, w h i t e , inequigranular, i n e q u i g r a n u l a r , medium— medium- to t o coarse— coarsegrained granite leucosome. g r a i n e d g r a n i t e l e u c o s o m e . Almandine garnet, g a r n e t , blue— bluegreen g r e e n apatite, a p a t i t e , and a n d rare r a r e deep—blue d e e p - b l u e cordierite c o r d i e r i t e may may also a l s o be be recognizable. recognizable. Dikes Dikes oof f fine—grained, f i n e - g r a i n e d , grey, g r e y , muscovite—biotite muscovite-biotite granite and coarse—grained, c o a r s e - g r a i n e d , white, white, g r a n i t e (GLB—2) (GLB-2 ) and holo—leucocratic h o l o - l e u c o c r a t i c granite g r a n i t e (GLB—4) (GLB-4) represent r e p r e s e n t later later intrusive Ghost Lake Lake Batholith. Batholith. i n t r u s i v e phases p h a s e s of o f the t h e Ghost Proceed P r o c e e d 8.8 8 . 8 km east e a s t along a l o n g Highway 17 17 to t o aa point p o i n t where it i t makes aa sharp s h a r p turn t u r n south. s o u t h . Continue C o n t i n u e through t h r o u g h Dryden Dryden for f o r 13.6 13.6 km. km. Turn Turn n o r t h on on Thunder Thunder Lake Lake Road Road and a n d continue c o n t i n u e for f o r 1.7 1.7 km. km. Turn north Turn northwest Lakea access n o r t h w e s t on on the t h e south s o u t h Ghost G h o s t Lake c c e s s r oroad, a d , t travelling r a v e l l i n g for f o r 1 ..55 km. Turn T u r n wwest e s t oon n ppoorly oorly m a i n t a i n e d ppowerline o w e r l i n e r road o a d aand n d t travel r a v e l for for maintained about km tto o point p o i n t where where road r o a d departs d e p a r t s north n o r t h from from powerline. powerline. a b o u t 1. 11 km Travel by aa ssteel 0.6 km km to t o base b a s e of o f small s m a l l ridge r i d g e marked marked by tee1 T r a v e l aa further f u r t h e r 0.6 gate g a t e (usually ( u s u a l l y locked). l o c k e d ) . Proceed P r o c e e d west west for f o r 0.27 0 . 2 7 kin km and and then t h e n turn turn south s o u t h on on one o n e of o f many many eexploration x p l o r a t i o n access a c c e s s roads r o a d s constructed c o n s t r u c t e d by by Sanmine and ttravel Sanmine EExploration x p l o r a t i o n IIncorporated n c o r p o r a t e d and r a v e l for f o rabout a b o u t0.0.37 37km. km. P r o p e r t y aaccess c c e s s rroads o a d s aare r e best b e s t travelled t r a v e l l e dby byfourwheel f o u r w h e e l drive drive Property vehicles. v e h i c l e s . Consult C o n s u l t figure f i g u r e 33 for f o r stop s t o p locations. locations. PLEASE PLEASE DO DO NOT NOT HAMMER HAMMER SURFACE SURFACE OF OF STRIPPED STRIPPED OUTCROPS. OUTCROPS. SELECT SELECT MINERAL MINERAL SPECIMENS SPEC IMENS FROM FROM LOOSE LOOSE BLASTED BLASTED MATERIAL MATERIAL ONLY. ONLY. STOP TUNGSTEN PROPERTY PROPERTY, SANMINE EXPLORATION STOP 5: 5: PETRUNKA PETRUNKA TUNGSTEN SANMINE EXPLORATION -INC. (EAST END) I N C . (EAST E N D ) f e1'iTeinera1ization z a t i ooccurs n o c c u r sini ngenerally generally "SchTeliteminerali flat—lying, undulating £a t - l y i n g , undulating . tourmaline—rich The t o u r m a l i n e - r i c h sheets. she'ets The sheets s h e e t s which which variably v a r i a b l y transect t r a n s e c t folation f o l a t i o n trends t r e n d s of o f host host �174 + + + + + + + +11+ + + + +. + + + + + + + + + + + + + + + + + + + + + + + + + + + + •¼\+ + + + + + + + + + + + +++ +++ + + +\l ++ + + ++÷++ + + ++ ÷ + + + + + + + + + + + +++ +++ ++ + +÷ + ++ + ++ + ++ + ++ + + + ++ + + + ++ + + + + + + + + ++ + + + + + ++++++ + + + + + + + + + + + + + + + + +++ + + + + +4+4. + + + + + + + ++ + + + + + + + + + + + + + + + + ++ ++ + + + + + + + + ++ +++ + + + + + + + + + + + + + 4+ + + +++++ + + + + + + + + + + + + + + +4. + GHOST LAKE BATHOLITH ++ ++ + + + + + ++ + +4+ ++ + ++ ++ + + + + + + + + + + + + + + + + + + + + + + + + + + + + +.+ + + + + + + +++4. + + + ++ + + + + + + + + + + + + + + + + + ++ ++ + + + + + ++ +++++ + + ++ + + + + + + + + + ++ +++ + + + + +4. +4. + + + + + ++ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + ++ + ÷+++÷+ + d + + • + + + + + + + + + + + + + + + + + + + + + ++ +o___.__.__,,__,__,__ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +5 +++ +4. + + + + ++*+ + + + +i_.._+ + + + + + + + + + + + + + + + + + + + + + + '+ + ABe+ V..+ + + + + + + + + + + + + + + + +4. + + + + + + + ÷\\_.+ + + + + + + + + + ++ + + + + + + + + + + + + •\'X+++ + + ++ + ++ + ++ + +++ ++ GPO5 + + ++ + + + + + + 4. ++ + ++ + +4. + +++ + + + +4. + + + + + + +4. + + + + + +'_ + +4. + ++ + - + + +++++++ ++++++_ + + •4. _—i + + + +4. + + + + + + + + + + + + - + + +'.. + (-. I :: ZEALAND METASEDIMENTS Thunder Lake a \^+\ x x Ghost Lake Batholith and Ghost and Zealand Zealand Stock Stock Porphyritic Biotite Granodiorite Porphyritic Granodiorite and and Granite Granite Zealand Metasediments (medium Zealand (medium grade ]metawackes, metapelites, metapelites, and andmagnetite— magnetitechert iron iron formation> formation) Brownridge Volcanics (massive (massive and and pillowed pillowed mafic metavolcanics with sparse sparse felsic metavolcanic metavolcanic tuff layers) layers) • field fieldtrip tripstop stop _—j bedding 4 bedding with dip 1 Lithophile Mineral Occurrence Occurrence Lithophile Mineral 2— "Si---bedding bedding (inclined, (inclined, overturned), overturned), -ft" top (arrow) (arrow) from from grain grain gradation gradation -igo foliation with dip dip .— strike M strikeofofbanding banding in in granitic granitic rocks rocks r facing direction of lava flows as indicated 9 . shape and packing by pillow facing direction of lava flows as indicated by pillow shape and packing F i g u r e 3: 3 : Geology G e o l o g y of o f the t h eMavis Mavis Lake Lake Pegmatite P e g m a t i t e Group. Group. Figure Be beryllium beryllium Lii L lithiulm Ta Ta tantalum tantalum W W tungsten tungsten �175 pillowed pillowed mafic maÂi c metavolcanics m e t a v o l c a n i c s are a r e up up to to 0.3 0 . 3 mm in in thickness 1 1 and a n d 19 19 degrees. degrees. Highest t h i c k n e s s and a n d dip d i p between b e t w e e n 11 Highest t o date d a t e occur o c c u r within w i t h i n these these l e v e l s of o f scheelite s c h e e l i t e found f o u n d to levels tourmaline t o u r m a l i n e sheets s h e e t s accompanied a c c o m p a n i e d by by ancillary a n c i l l a r y amounts amounts of of biotite, b i o t i t e , quartz, q u a r t z , plagioclase, p l a g i o c l a s e , pyrite p y r i t e and and possible possible lepidolite. is l e p i d o l i t e . An An identical i d e n t i c a l mineral m i n e r a l assemblage a s s e m b l a g e is developed d e v e l o p e d on o n several s e v e r a l spatially s p a t i a l l y associated, a s s o c i a t e d , ancillary ancillary fracture s e t s with w i t h relatively r e l a t i v e l y steep s t e e p dips d i p s (69—85°) (69-85O) and and f r a c t u r e sets along a l o n g 77 mm mm —- 55 cm c m wide w i d e pillow p i l l o w selvages, s e l v a g e s , the t h e latter l a t t e r of of which which have h a v e been b e e n intensely i n t e n s e l y replaced r e p l a c e d by by tourmaline t o u r m a l i n e and and biotite t h e vicinity v i c i n i t y of o f the t h e scheelite s c h e e l i t e mineralization mineralization b i o t i t e in i n the and C s and and a n d contain c o n t a i n trace t r a c e level l e v e l anomalous a n o m a l o u s enrichment e n r i c h m e n t in i n Cs Li L i (Table ( T a b l e 4). 4 ) . Scheelite, S c h e e l i t e , up up to to 55 by by 7.5 7.5 cm cm size, s i z e , is is predominantly p r e d o m i n a n t l y anhedral, a n h e d r a l , poikilitic, p o i k i l i t i and c , ahoney—brown n d honey-brown on on clean 3. 5mmchannel channel c l e a n weathered w e a t h e r e d surfaces. s u r f a c e s . Analysis A n a l y s i s of o f aa3.5 sample s a m p l e selected s e l e c t e d from f r o m aa flat—lying f l a t - l y i n g biotite—tourmaline biotite-tourmaline sheet s h e e t containing c o n t a i n i n g the t h e highest h i g h e s t scheelite s c h e e l i t e content c o n t e n t observed observed to t o date d a t e isisgiven g i v e nbelow b e l o w (in ( i nppm ppm unless u n l e s s otherwise o t h e r w i s e stated): s t a t e d ): W Be Cs FF W Be Cs Li Sn Au Li Sn Au 950 40 9,600 193 950 45 45 40 9,600 246 246 1 9 3 <2 < 2 ppb ppb Levels of tungsten are similar to those previously Levels of tungsten a r e s i m i l a r to those p r e v i o u s l y documented d o c u m e n t e d by by Noranda Noranda Mines Mines Limited L i m i t e dwho who reported r e p o r t e d channel channel samples s a m p l e s up up to t o 0. 0. 11 percent p e r c e n tW03 WO3 (Blackburn ( B l a c k b u r n and and Hailstone, Hailstone, 1983, 1983, p.12—13) p . 12-13) and a n d Selco S e l c o Incorporated I n c o r p o r a t e d who who obtained obtained grades up to 0.09 percent Wa3 (A. Pryslak, g r a d e s up t o 0 . 0 9 p e r c e n t W03 ( A . P r y s l a k , geologist, geologist, Selco S e l c o Incorporated, I n c o r p o r a t e d , personal p e r s o n a l communication, c o m m u n i c a t i o n , 1983). 1983). Return R e t u r n to t o main main property p r o p e r t y access a c c e s s road r o a d and and travel t r a v e l west w e s t for f o r 2.3 2 . 3 km km (1.5 ( 1 . 5 miles). miles). --- - , -stop is important in that it establishes a STOP STOP 6: 6 : PETRUNKA PETRUNKA TUNGSTEN PROPERTY SANMINE SANMINE EXPLORATION EXPLORATION - TUNGSTEN -- PROPERTY, INC. —I N C . (WEST (WEST END) END) ' T hTTs T s s t o p 1s i m p o r t a n t i n t h a t it e s t a b l i s h e s a genetic g e n e t i cconnection c o n n e c t i o nofo frare—metal r a r e - m e t a l mineralization m i n e r a l i z a t i o narid and *< associated a s s o c i a t e d boron boron metasomatism m e t a s o m a t i s m with w i t h the t h e Ghost Ghost Lake Lake Batholith. Bath01 i t h . This This large l a r g e stripped s t r i p p e d outcrop o u t c r o p exposes e x p o s e s the t h e rarely rarely observed o b s e r v e d contact c o n t a c t of o f the t h e Ghost Ghost Lake Lake Batholith B a t h o l i t h with with deformed The d e f o r m e d mafic maÂi c and a n d intermediate i n t e r m e d i a t e metavolcanics. metavolcanics The by c o n t a c t a t t h e w e s t p a r t o f t h i s o u t c r o p is d e f i n e d by an t ocoarse—grained coarse-grained a n interlayering i n t e r l a y e r i nof g omedium— f medium- to almandine—muscovite—tourmaline almand i n e - m u s c o v i t e - t o u r m a l i n e granite g r a n i t e with with calc—silicate m e t a v o l c a n i c s over o v e r35 35m. m. In In c a l c - s i l i c a t e bearing b e a r i n g mafic maÂi c metavolcanics places p l a c e sa abrown brownweathering w e a t h e r i n g1—8 1-8 cm cm wide w i d e biotite—rich biotite-rich metasomatic is developed d e v e l o p e d along a l o n g the t h e contact. contact. m e t a s o m a t i c sselvage e l v a g e is About to tthe About 550 0 mmt o h e eeast a s t the t h e contact c o n t a c t isismore more abrupt abrupt and an aoutermost a n d is ischaracterized c h a r a c t e r i z eby d by n o u t e r m o zone s t z o n(1—2 e (1-2mmwide) wide) of o f green g r e e n muscovite m u s c o v i t e enrichment e n r i c h m e n t which w h i c h rreverts e v e r t s inward inward to t o aa much l e s smicaceous m i c a c e o u almandine—muscovite—tourmalirie s almandine-muscov i t e - t o u r m a l i n e much less granite. off intense g r a n i t e . Impressive I m p r e s s i v e zones zones o i n t e n s e black b l a c ktourmaline tourmal i n e deposition thet hgreen e g r e emuscovite—rich n muscovite-rich d e p o s i t i o n occur o c c u r adjacent a d j a c e n ttot o granite. most extensive e x t e n s i v etourmaline—rich t o u r m a l i n e - r i c h zone z o n e (2 ( 2mm g r a n i t e . The The most wide) w i d e ) contains c o n t a i n s radiating r a d i a t i n gsheaves s h e a v e s of o f tourmaline t o u r m a l i n ewith with individual i n d i v i d u a l crystals c r y s t a l sup uptoto8 8cm cmini nlength, l e n g t hbrown , brown weathering w e a t h e r i n g biotite, b i o t i t e , and a n d actinolite. a c t i n o l i t e . These T h e s e pneumatolytic pneumatolytic . contact at the west part of this outcrop is defined �176 ddeposits e p o s i t s exhibit e x h i b i t anomalous anomalous enrichment e n r i c h m e n t in i n Be, B e , Cs, C s , Rb, Rb, Sn, Sn, F, F , and a n d BB (Table ( T a b l e 3). 3 ) . With increasing i n c r e a s i n g distance d i s t a n c e from f r o m the the bbatholithic a t h o l i t h i c ccontact o n t a c t a ggradation r a d a t i o n of o f the t h e tourmaline—rich tourmal ine-rich zzone o n e iinto n t o aalbite—quartz—rich l b i t e - q u a r t z - r i c h ppegmatitic e g m a t i t i c pockets p o c k e t s is is obvious. obvious. A c c e s s o r y , euhedral, e u h e d r a l , light l i g h t green g r e e n beryl b e r y l up u p to to Accessory, 5.4 m iin n bbasal a s a l ssections e c t i o n s occurs o c c u r s in i n these these 5.4 xx 6.5 6.5 c cm quartz—rich q u a r t z - r i c h masses. masses. Zoned u a r t z - t o u r m a l i n e veins, veins, Zoned qquartz—tourmaline exposed l i m i t s of o f the t h e stripped s t r i p p e d outcrop, outcrop, e x p o s e d near n e a r the t h e eastern e a s t e r n limits aare r e ggenerally e n e r a l l y ssubconcordant u b c o n c o r d a n t to t o hhost o s t rock r o c k foliation £0i a t i o n and and cclearly l e a r l y emanate e m a n a t e from f r o m the t h e Ghost Ghost Lake Lake Batholith. Bath01 i t h . R e t u r n to t o south s o u t h ciost Ghost Lake Lake access a c c e s s road, r o a d , turn t u r n north, n o r t h , and and proceed proceed Return Turn 1.5 km. km. T u r n eeast a s t on aa vvery e r y inconspicuous i n c o n s p i c u o u s oold l d drill d r i l l access access ffor o r 1.5 Park road r o a d and and follow f o l l o w for f o r 0.3 0 . 3 km. km. P a r k vehicle v e h i c l e and and walk w a l k on drill d r i l l road road 215 m. m. ffor o r aabout b o u t 215 STOP STOP 7: 7: --- ---- —- MPLVIS LAKE LAKE SPODUMENE-BERY SPODtJMENE-BERYL-TANTALITE PEGMATITES MAVIS L-TANTALITE PEGMATITES --- (FTR_SWICEROPERTY,_MAIN SERVICE PROPERTY, M A I NZONK) ZONE) -(FAIR This 12i76 12 x 76 mlensoidal—shaped m i e x d a l z h a p e d pegmatite p e g m a t i t e dike dike ooccurs c c u r s in i n foliated f o l i a t e d and and gneissic g n e i s s i c mafic m a f i c metavolcanics m e t a v o l c a n i c s arid and subordinate It It s u b o r d i n a t e fine—grained f i n e - g r a i n e d laminated l a m i n a t e d metawackes. metawackes eexhibits xhibits a a vague v a g u e internal i n t e r n a l zonation z o n a t i o n which w h i c h is is generally generally not n o t apparent a p p a r e n t in i n most most rare—metal r a r e - m e t a l ppegmatites e g m a t i t e s of o f the t h eMavis Mavis Lake Pegmatite Lake P e g m a t i t e Group. Group. A A qquartz—rich u a r t z - r i c h core o n e is core zzone is irregularly i r r e g u l a r l y and a n d asymmetrically a s y m m e t r i c a l l y ddistributed i s t r i b u t e d from f r o m the t h e dike dike centre These c e n t r e to t o north n o r t h contact. contact. T h e s e pod—like p o d - l i k e ddomains o m a i n s ccontain ontain cm iinn conspicious K—feldspars t o 33 33 xx 41 41 cm c o n s p i c i o u s blocky blocky K - f e l d s p a r s up up to ccross—sectional r o s s - s e c t i o n a l area, a r e a , and minor m i n o r beryl, b e r y l , green g r e e n spodumene, spodumene, muscovite, ggreen reen m u s c o v i t e , tourmaline, t o u r m a l i n e , blue b l u e apatite, a p a t i t e , and a n d orange orange garnet. garnet. Outer margins z o n e can c a n ggrade rade O uter m a r g i n s oof f the t h e core zone indistinctly i n d i s t i n c t l y into i n t o aan n aalbite—spodumene—quartz l b i t e - s p o d u m e n e - q u a r t z pegmatite pegmatite 4 7 percent p e r c e n t quartz q u a r t z and a n d 29 29 to t o 48 48 uunit n i t containing c o n t a i n i n g 37 37 ttoo 47 ppercent e r c e n t green g r e e n sspodurnene, p o d u m e n e , t hthe e l alatter t t e r being b e i n g hhighest i g h e s t levels levels recorded r e c o r d e d for f o r aany n y ppegmatite e g m a t i t e oof f the t h e Mavis Mavis Lake Lake Pegmatite Pegmatite Group. G roup. A third t h i r d zonal z o n a l unit u n i t is is developed d e v e l o p e d along a l o n g the t h e outer outer margins m a r g i n s of o f the t h e spodumene—rich s p o d u m e n e - r i c h unit u n i t and and contains c o n t a i n s the the assemblage muscovite—spodumene—albite—quartz— a s s e m b l a g e ggreen r e e n muscov ite-spodumene-albit e-quartzK—feldspar. to 7 ppercent e r c e n t while while K-feldspar. Spodumene contents c o n t e n t s drop d r o p to those K—feldspar It t o 55 55 percent. percent. It consists c o n s is ts t h o s e oof f K - f e l d s p a r increase i n c r e a s e to of o f coarse, c o a r s e , generally g e n e r a l l y anhedral, a n h e d r a l , coalescing c o a l e s c i n g white white K—feldspars K - f e l d s p a r s with w i t h interstitial i n t e r s t i t i a l quartz—spodumene q u a r t z - s p e d umene '"pockets". pockets" Small, white S mall, w h i t e to t o bbuff u f f coloured c o l o u r e d domains d o m a i n s (up ( u p to t o 11 x 33 m) of m) o f fine—grained, f i n e - g r a i n e d , equigranular, e q u i g r a n u l a r , saccharoidal s a c c h a r o i d a 1 sodic s o d ic aplite a p l i t e are a r e sparsely s p a r s e l y scattered s c a t t e r e d throughout t h r o u g h o u t the the sspodumene—rich p o d u m e n e - r i c h zone. z o n e . These T h e s e domains d o m a i n s consist c o n s i s t of o f albite, albite, muscovite, qquartz u a r t z aand n d accessory a c c e s s o r y ggreen reen m u s c o v i t e , apatite a p a t i t e and a n d an an unidentified brown m mineral u n i d e n t i f i e d brown i n e r a l (possibly ( p o s s i b l y aa phosphate) phosphate) This This type o be b e primary p r i m a r y iin n oorigin r i g i n as as t y p e oof f aplite a p l i t e aappears p p e a r s tto contacts with contacts w i t h bounding b o u n d i n g spodumene—rich s p o d u m e n e - r i c h units u n i t s are are iinvariably n v a r i a b l y ssharp h a r p aand n d exhibit e x h i b i t nno o evidence e v i d e n c e oof f replacement replacement ttextures. e x t u r e s . At A t STOP STOP 8, 8, identical i d e n t i c a l aplites a p l i t e s are a r e clearly clearly ttransected r a n s e c t e d bby y vveinlets e i n l e t s of o f coarser c o a r s e r albite a l b i t eand and green green . . . . �177 muscovite m u s c o v i t e (best ( b e s t observed o b s e r v e d on o n wetted w e t t e d surfaces) s u r f a c e s ) which which probably t o replacement r e p l a c e m e n t stage s t a g e aplites. a p l ites p r o b a b l y relate r e l a t e to Albite—rich A 1 b i t e - r i c h replacement r e p l a c e m e n t zones, z o n e s , commonly commonly peripheral peripheral to core zones, umene t o quartz—rich q u a r t z - r i c h core z o n e s , typify t y p i f yalla lspod l spodumene pegmatites p e g m a t i t e s of o f the t h eMavis Mavis Lake Lake area. a r e a . Approximately A p p r o x i m a t e l y 10 10 percent p e r c e n t of o f this t h i spegmatite p e g m a t i t e has h a s been b e e n intensely i n t e n s e l y albitized albitized to t o the t h e point p o i n t that t h a no t novestige v e s t i g of e oprimary f p r i m a r ymineralogy m i n e r a l o g y has has survived. a r e distinctly d is t i n c t l non—equigranular, y non-equigranular , s u r v i v e d . Textures T e x t u r e s are fine f i n e to t o medium medium grained g r a i n e d and a n d involve i n v o l v e aalbite, l b i t e , quartz, q u a r t z , green green muscovite, rare m u s c o v i t e , with w i t h accessory a c c e s s o r y white w h i t e beryl, b e r y l , garnet, g a r n e t , and a n d rare ilmenite. ilmenite. Columbite is C o l u m b i t e mineralization m i n e r a l i z a t i o n in i n this t h i s pegmatite p e g m a t i t e is sporadically s p o r a d i c a l l y distributed d i s t r i b u t e d and and clearly c l e a r l y associated a s s o c i a t e d with with replacement r e p l a c e m e n t stage s t a g e albitization, a l b i t i z a t i o n , as as evidenced e v i d e n c e d by by its its restriction blocky r e s t r i c t i o n to t o albitized a l b i t i z e rims d r i mof s osome f some b l o c kK—feldspar y K-feldspar aggregates a g g r e g a t e s and a n dspodumenes. spod umenes Proceed P r o c e e d aabout b o u t 660 0 mms osouth u t h t otos side i d e oof f hhill. ill. . . TANTALITE-BEARING TANTALITE-BEARING SPODUMENE_PEGMATITE_DIKE SPODUMENE PEGMATITE D I KE -Thlo T h e - l owe w ermos r m o s t tp pàE a x oö!ThTflr t a b T F G r cat c a t i ffIT t q , 26 268 m m I l o ngg STOP 8: STOP 8: . pegmatite p e g m a t i t e dike d i k e contains c o n t a i n s sparse s p a r s e disseminated d i s s e m i n a t e d t tantalite, antalite, distributed d i s t r i b u t e d uniformly u n i f o r m l y relative r e l a t i v e to t oother o t h e rpegmatites p e g m a t i t e s in in the t h e area. area. Maximum Maximum v avalues l u e s o of f ttantalum a n t a l urn (380 ( 3 80 ppm ppm oover v e r 0.9 0.9 m) m ) and a n d Nb Nb (210 ( 2 1 0 ppm ppm over o v e r 0.9 0.9 m) m) for f o rthe t h eMain MainZone ZoneMavis Mavis Lake area pegmatites p e g m a t i t e s occur o c c u r at a t this t h i s locality. l o c a l i t . The T h e rare rare Lake area lithium l i t h i u m amphibole a m p h i b o l e holmquistite h o l m q u i s t i t e[Li2(Mg, [Li2(Mg,Fe2)3 Fe ) 3Al2Si2022 Al2Si2022 s is subtly apparent in mafic metavolcanics above (OH)2] (OH)2] is s u b t l y a p p a r e n t i n m a f i c m e t a v o l c a n i c s a b o v e the t h e upper u p p e r 50 50 degree d e g r e esouth—dipping s o u t h - d i p p i n g contact. contact. Most Most oof f this t h i s pegmatite p e g m a t i t e isiscomposed composed oof f aa K—feldspar—rich K - f e l d s p a r - r i c h z ozone n e s i similar m i l a r t to o tthat h a t ata tSTOP STOP 7 7 but b u t can can be b e distinguished d i s t i n g u i s h e d by b y the t h econspicuous c o n s p i c u o u s development d e v e l o p m e n t of o f aa symplectic s y m p l e c t i cgreen g r e e nspodumene s p o d u m e n e ++ quartz q u a r t z intergrowth. intergrowth. Slender S l e n d e r spodumene spodumene pphenocrysts h e n o c r y s t s up u p to t o 1 mm long l o n g and and 12—19 12-1 9 cm c m wide w i d e are a r e oriented o r i e n t e d approximately a p p r o x i m a t e l y normal n o r m a l to t o the t h e lower lower pegmatite p e g m a t i t e contact c o n t a c t and and contain c o n t a i nfine—grained, f i n e - g r a i n e d , equigranular equigranular quartz A 4 4 to to q u a r t z comprising c o m p r i s i n g about a b o u t 30 3 0 percent p e r c e n t of o f the t h e host. host. A 55 cm cm wide w i d e quartz q u a r t z ++ green g r e e n muscovite m u s c o v i t e ++ albite a l b i t e carapace carapace 1 surrounds surrounds most most of o f tthe h e spodumerie—quartz s p o d u m e n e - q u a r t z intergrowths. intergrowths. The The entire e n t i r e intergrowth i n t e r g r o w t h is is typically t y p i c a l l y enveloped e n v e l o p e d by by coars coars ee—grained - g r a i n e d K—feldspar. K-feldspar. This T h i s pegmatite p e g m a t i t e also a l s o contains c o n t a i n s local l o c a l development d e v e l o p m e n t of o f aa quartz—rich q u a r t z - r i c h core core (accompanied ( a c c o m p a n i e d by by blocky b l o c k y K—feldspar, K-feldspar , white w h i t e euhedral e u h e d r a l beryl b e r y l up u p to t o 5.5x7 5 . 5 ~ 7an on in i n cross—sectional cross-sectional area, a r e a , and a n d spodumene) s p o d u m e n e ) and a n d pockets p o c k e t s of o f saccharoidal s a c c h a r o i d a l sodic sodic aplite a p l i t e similar s i m i l a r to t o that t h a t at a t STOP STOP7.7. Return t o drill d r i l l road r o a d and a n d walk walk short s h o r t distance d i s t a n c e east e a s t to t o top t o p of o f hill. hill. R e t u r n to - STOP 9: STOP 9 : ALBITIZED ALBITIZED SPODUMENE SPODUMENE PEGMATITE PEGMATITE WITH WITH METASOMATIC METASOMATIC --LAYERS_DEVELOPED IN LAYERS D E V E L O P E D I N HOST H O S T RROCKS OCKS-. -- Thfs This r e l aEivi7hiEiy t i v e l y 7 i g h lalbitized y a l b i t i z e dportion p o r t i o n of o f the the same same dike d i k e as a s that t h a t observed o b s e r v e d at a t Stop S t o p8 8exhibits e x h i b i t s well' well" �178 ddeveloped, e v e l o p e d , fine—grairied f i n e - g r a i n e d ssaccharoidal a c c h a r o i d a l aalbite l b i t e and a n d quartz. quartz. Glimmerite* bands are Glimrnerite* b ands a r e apparent a p p a r e n t in i nthe t h mafic e m a f i meta— c metavvolcanics o l c a n i c s immediately i m m e d i a t e l y nnorth o r t h oof f the t h e contact c o n t a c t and and ddisposed i s p o s e d cconcordant oncordant to oliation. The l i m r n e r i t e in in to ffoliation. The ggliirunerite this t h i s case caseisischaracterized c h a r a c t e r i z e by d benrichment y e n r i c h m e nin t ibronze— n bronzeb l a c k tourmaline, t o u r m a l i n e ,and a n d sporadic sporad ic ccoloured o l o u r e d bbiotite, i o t i t e ,black A ppartial hholmquistite. olmquistite. A a r t i a l chemical c h e m i c a l analysis a n a l y s i s is i v e n in in is ggiven Table T a b l e 4. 4. Geochemical G e o c h e m i c a l profiles p r o f i l e s for f o r distribution d i s t r i b u t i o n of o f mobile mobile elements Cs, Sn aand K , F, F, Li, L i , Rb, Rb, Cs, n d Be in i n mafic mafic e l e m e n t s K, m e t a v o l c a n i c hhost o s t rocks r o c k s as as aa function f u n c t i o n of o f increasing increasing metavolcanic No. 4 , ddistance i s t a n c e from f r o m northern n o r t h e r n contact c o n t a c t of o f Pegmatite P e g m a t i t e No.4, ssituated i t u a t e d 130 1 3 0 m east e a s t of o f this t h i s stop s t o p is is given g i v e n in i n Figure F i g u r e 4. 4. Return Ghost Lake access access rroad R e t u r n tto o ssouth o u t h Ghost o a d aand n d travel t r a v e l bback a c k to t o Highway 17. t o junction j u n c t i o n with w i t h Highway 601 and a n d turn t u r n north. north. 17. P r o c e e d west to Proceed T r a v e l ffor o r 4.8 4.8 km km to t o junction j u n c t i o n with w i t h Ghost G h o s t Lake Lake Road Road and a n d turn turn Travel east. east. P r o c e e d for f o r 23.5 2 3 . 5 km and turn t u r n west w e s t on on old o l d gravelled g r a v e l l e d logging logging Proceed km. rroad o a d for f o r 1.8 1.8 km. T u r n ssouthwest o u t h w e s t on on very v e r y poor p o o r clay—surfaced, c l a y - s u r f a c e d ,abandoned a b a n d o n e d logg l o g ging ing . Turn aaccess c c e s s road r o a d and a n d travel t r a v e l ini nfour—wheel f o u r - w h e e l ddrive r i v e for f o r 1.7 1.7 km. km. Walk 4 4 0 mm nnorthwest o r t h w e s t uup p vvery e r y poor, p o o r , partly p a r t l yovergrown o v e r g r o w n logging l o g g i n g road r o a d for f o r440 tto o ttop o p oof f hill. hill. f o r aabout b o u t 260 260 m north n o r t h along a l o n g pegmatitic pegmatitic Then walk walk for r i d g e to t o base b a s e of o f outcrop o u t c r o p area area on on north n o r t h slope. slope. ddike i k e forming f o r m i n g a ridge - - zondpmatite, - -disdaiTEto aniphibolitic STOP 110:__GULLWING 0 : GULLWING LAKE SPODUMENE PEGMATITE PEGMATITE STOP ThTh T his zoned p e g m a t i t e , d-i%corea%toasphibolitic metavolcanics, att the ma ic m e t a v o l c a n i c s , is is ssituated ituated a t h e northern n o r t h e r n end of of mafic aa 412 412 mml olong, n g , ccurvilinear, u r v i l i n e a r , pegmatitic p e g m a t i t i c ggranite r a n i t e dike dike a s t . Most Most oof f this this sstriking t r i k i n gN18°q N180W and and dipping d i p p i n g 52°—72° 520-720 eeast. pegmatite b l o c k yK—feldspar K - - f e l d s p a r + quartz quartz p e g m a t i t e consists c o n s i s t s of o f a ablocky coarsestggrain aassemblage s s e m b l a g e wwhich h i c h r erepresents p r e s e n t s t hthe e coarsest r a i n ssize i z e of of A small small core A core zone z o n e of of aany n y ppegmatite e g m a t i t e iin n the t h e Dryden Dryden Field. Field. muscovite uscovite sspodumene—blocky p o d u m e n e - b l o c k y KK—feldspar--quartz—albite - f e l d s p a r - q u a r t z - a 1 b i t e ++ m occurs The coarse light—green o c c u r s at a t the t h e lowest lowest exposure. exposure. The coarse light-green randomly measure e a s u r e uup p to t o 44 r a n d o m l y ooriented r i e n t e d spodumene spodumene pphenocrysts h e n o c r y s ts m x 100 cm cm( (parallel p a r a l l e l to t o 001) 0 0 1 ) and a n d 66 xx 40 40 cm c m (normal ( n o r m a l tto o x 100 001). 001 ). Two stages s t a g e s oof f replacement r e p l a c e m e n t aalbitization l b i t i z a t i o nhave h a v e been been identified d o m i n a n t and and i d e n t i f i e d within w i t h i n this t h i s pegmatite. p e g m a t i t e . The T h e most dominant eearliest a r l i e s t cconsists o n s i s t s oof f aan n eequigranular, q u i g r a n u l a r , albite—rich albite-rich assemblage a s s e m b l a g e accompanied a c c o m p a n i e d by b y minor m i n o r quartz, q u a r t z , muscovite, m u s c o v i t e , and and remnants This T h i s albitic albitic r e m n a n t s oof f primary p r i m a r y blocky b l o c k y K—feldspar. K-feldspar replacement r e p l a c e m e n t unit u n i t closely c l o s e l y follows f o l l o w s external e x t e r n a l contacts c o n t a c t s of of Gullwing mafic u l l w i n g Lake Lake Pegmatite P e g m a t i t e aand n d those t h o s e oof f several several m afic tthe he G and intermediate and i n t e r m e d i a t e metavolcanic m e t a v o l c a n i c xenoliths. x e n o l i t h s . A variant v a r i a n t of of tthis h i s aalbitic l b i t i c aassemblage s s e m b l a g e ooccurs c c u r s near n e a r the t h e upper u p p e r pegmatite pegmatite ccontact o n t a c t and and is is ffeatured e a t u r e d bby y an a n interesting i n t e r e s t i n g bbladed l a d e d texture texture muscovite fformed o r m e d bby y rrandomly a n d o m l y ooriented, r i e n t e d , tthin h i n bbiotite i o t i t e aand nd m uscovite . ----------* Russian Russian * metasomatic term for f o r a rrock o c k resulting r e s u l t i n g from from m etasomatic t r a n s f o r m a t i o n by by outward o u t w a r d dispersion d i s p e r s i o n of o f fluids f l u i d s enriched e n r i c h e d in i n such such transformation B, Li, eelements l e m e n t s as as K, K , B, Li, Cs, C s , F, F , Rb Rb which w h i c h were were released r e l e a s e d due d u e to t o late late s t a g e albitization a l b i t i z a t i o n of o f primary p r i m a r y spodumene spodumene ++ K—feldspar K - f e l d s p a r bbearing earing stage assemblages. ass embl a g e s . �179 E a. a. C 0 4- Ca 4- C a) C.) C 0 C.) 4C ci) E ci) a) distance from contact contact (metres) (metres) Geochemical F i g u r e 4: 4: Geochemical profile p r o f i l e within w i t h i n mafic metavolcanic rocks rocks Figure adjacent a d j a c e n t to t o the t h e contact c o n t a c t with w i t h aa pegmatite pegmatite dike. dike. �180 laths l a t h s up u p to t o 10 1 0 cm. cm. Sparse S p a r s e molybdenite m o l y b d e n i t e and and platy platy columbite—tantalite c o l u m b i t e - t a n t a l i t e can c a n be b e subtly s u b t l y intergrown i n t e r g r o w n with w i t h these these micas. micas A later l a t e r replacement r e p l a c e m e n t stage s t a g e is is finer—grained f i n e r - g r a i n e d and and specifically t o the t h e spodumene s p o d u m e n e core c o r e zone. z o n e . It I t is is s p e c i f i c a l l y confined c o n f i n e d to c h a r a c t e r i z e d by b y radiating r a d i a t i n g aggregates a g g r e g a t e s of o f platy, p l a t y , white white characterized to t o light l i g h t blue b l u e cleavelandite c l e a v e l a n d i t e accompanied a c c o m p a n i e d by b y green green muscovite, l o c a l lepidolite, l e p i d o l i t e , red—brown red-brown garnet, g a r n e t , light 1i g h t m u s c o v i t e , local green g r e e n beryl, b e r y l , and and platy p l a t y tantalite. t a n t a l i t e . Endogeneous E n d o g e n e o u s aureoles aureoles involving K , F, F, Li, L i , Cs, C s , Rb, Rb, Be, B e , and a n d Sn Sn are a r e much much less less i n v o l v i n g K, extensive e x t e n s i v e relative r e l a t i v e to t o rare—metal rare-metal pegmatites p e g m a t i t e s of o f the t h e Mavis Mavis Lake Lake Pegmatite P e g m a t i t e Group. Group. However, However, intense i n t e n s e metasomatic metasomatic activity a c t i v i t y is is obvious o b v i o u s within w i t h i n 3—5 3-5 cm cm of o f the t h e pegmatite pegmatite contact c o n t a c t and a n d these t h e s e brown—weathering b r o w n - w e a t h e r i n g bbiotite—rich i o t i t e - r i c h selvages selvages contain c o n t a i n the t h e highest h i g h e s tlevels l e v e l of s oF(1.84%), f F( 1 . 8 4 % )K20(8.82%), , K20 ( 8 . 8 2 % ) , Li(1 L i ( 1 1,000 1 , 0 0 0 pprn), R b ( 7 5 8 0 pprn), T a ( 1 0 0 ppm), p p m ) , Sn(320 S n ( 3 2 0 ppm) ppm) ppm), Rb(7580 ppm), Ta(100 and ppm) found and Zn Zn (2560 ( 2 5 6 0 ppm) f o u n d within w i t h i n in i n glimmerites g l i m m e r i t e s formed f o r m e d via via replacement r e p l a c e m e n t oof f mafic maÂi c metavolcanics m e t a v o l c a n i c s in i n the t h eDryden Dryden Field Field (Breaks ( B r e a k s iin n pprep., r e p . , and and Table T a b l e 4). 4). Return R e t u r n to t o Ghost G h o s t Lake Lake road r o a d and a n d proceed p r o c e e d north n o r t h for f o r 1.8 1.8 km. km. Turn Turn e a s t on old o l d gravelled g r a v e l l e d logging l o g g i n g road r o a d and a n d travel t r a v e l for f o r about a b o u t 1 km. km. east Park P a r k vvehicles e h i c l e s and a n d walk northeast n o r t h e a s t up u p undrivable, u n d r i v a b l e , clay c l a y surface surface logging t o aa junction. j u n c t i o n . Turn T u r n north n o r t h and and l o g g i n g road r o a d for f o r 1.35 1 . 3 5 km, km, coming coming to walk walk for f o r 345 345 m. m. . 1 Th T h e zzoned o n e d 'Ibt Tb t Lake Lake rare—metal r a r e - m e t a l pegmatfEe p e g m a t i t e represents represents STOP STOP 11: 11: TOT LAKE LAKE SPODUMENE-POLLUCITE SPODUMENE-POLLUCITE PEGMATITE PEGMATITE the t h e most most easterly e a s t e r l y known known occurrence o c c u r r e n c e of o f spodumene spodumene and and greatest g r e a t e s t degree d e g r e e of o f geochemical g e o c h e m i c a l specialization s p e c i a l i z a t i o n for f o r the the Dryden 1-6 mm Dryden Pegmatite P e g m a t i t e Field. F i e l d . This T h i s northwest—striking n o r t h w e s t-s t r i k i n g 1—6 wide, w i d e , 48 48 mm long l o n g dike d i k e lies l i e s sharply s h a r p l y discordant d i s c o r d a n t to to foliation £0i a t i o n trends t r e n d s of o f mafic maÂi c metavolcanic m e t a v o l c a n i c and and meta—ultramafic m e t a - u l t r a m a f i c host h o s t rocks. r o c k s . Presence P r e s e n c e of o f pollucite poll ucite (CsAlSi2O6), ore mineral m i n e r a l of o f cesium, c e s i u m , is is a unique unique ( C s ~ l S i 2 0 6 ) ,the t h e only o n l y ore feature f e a t u r e in i n the t h e area area and, a n d , elsewhere e l s e w h e r e in i n Ontario, Ontario, is is only only known a t Lily L i l y Pad Pad Lake, Lake, near n e a r Fort F o r t Hope Hope (Wallace, (Wallace, 1978). 1978) known at This T h i s mineral m i n e r a l is is confined c o n Âi n e d to to aa small s m a l l 1 xx 55 mm pod pod near n e a r the the well—layered w e 1 1 - l a y e r e d southeast s o u t h e a s t exposed e x p o s e d end e n d as as coarse, coarse, anhedral, anhedral, masses comprising c o m p r i s i n g about a b o u t 37 37 percent p e r c e n t of o f the t h e mode, mode, w h i t e masses white and a n d filling f i l l i n g interstices i n t e r s t i c e s between b e t w e e n relatively relatively earlier—formed, s p o d u m e n e phenocrysts. p h e n o c r y s ts e a r l i e r - f o r m e d , bladed, b l a d e d , pink p i n k spodumene Spodumene Spod umene may occur o c c u r as as relatively r e l a t i v e l y coarse, coarse, randomly randomly oriented o r i e n t e d blades b l a d e s up u p to to 1 x x 14 1 4 xx 38 3 8 cm cm near n e a r the the northwestern n o r t h w e s t e r n end e n d of o f the t h e exposure. e x p o s u r e . In I n proximity p r o x i m i t y to t o the the pollucite p o l l u c i t e zone, z o n e , finer—grained f i n e r - g r a i n e d spodumene spodumene exhibits exhibits sub—horizontal s u b - h o r i z o n t a l alignment a l i g n m e n t in i n longitudinally l o n g i t u d i n a l l y oriented oriented bands b a n d s with w i t h c—crystallographic c - c r y s t a l l o g r a p h i c axis a x i sapproximately a p p r o x i m a t e l ynormal normal to t o dike d i k e contacts. c o n t a c t s . These T h e s e bbands a n d s ccontain o n t a i n about a b o u t 70 7 0 percent percent spodumene alternate t e r n a t ewith w i t halbite—quartz—green a1 b i t e - q u a r t z - g r e e n s p o d umene aand n d a1 muscovite m u s c o v i t e aaplitic p l i t i c layers l a y e r s containing c o n t a i n i n g little 1it t lspodumene. e spodumene. A A ssignificant i g n i f i c a n t portion p o r t i o n of o f the t h epegmatite p e g m a t i t e has h a s been been subjected t o late l a t e stage s t a g e fracture—controlled f racture-controlled s u b j e c t e d to albitization. a l b i t i z a t i o n . This T h i s moderate m o d e r a t e to t o intense i n t e n s e albitizatiori a l b i t i z a t i o n was was effected e f f e c t e d by by hydrothermal h y d r o t h e r m a l fluids f l u i d s emanating e m a n a t i n g from f r o m aa now now . 1 . 1 �181 quartz—filled q u a r t z - f i l l e d central c e n t r a l branching b r a n c h i n g vein v e i n system s y s t e m extending ex t e n d i n g f o r virtually v i r t u a l l y the t h e complete c o m p l e t e exposed e x p o s e d dike d i k e length. l e n g t h . Near Near for t h e northwestern n o r t h w e s t e r n end, e n d , metasomatic m e t a s o m a t i c fronts f r o n t s oriented oriented the parallel p a r a l l e l to t o thin t h i n quartz—filled q u a r t z - f i l l e d fractures f r a c t u r e s intersect i n t e r s e c t pink pink p a r t l y altering a 1 t e r i n g these t h e s e (behind ( b e h i n d the the spodurnene phenocrysts, p h e n o c r y s ts , partly spodumene front)to tantalite-rich f r o n t ) t o fine—grained f i n e - g r a i n e d green g r e e n micas. m i c a s . AA tantalite—rich zone z o n e in i n the t h e same s a m e part p a r t of o f the t h e dike d i k e exhibits e x h i b i t s spodumenes spodumenes and a n d blocky b l o c k y K—feldspars K - f e l d s p a r s that t h a t have h a v e been b e e n completely completely r e p l a c e d by b y albite—green a l b i t e - g r e e n mica m i c a (cymatolite) ( c y m a t o l i t e ) and and albite, albite, replaced respectively. - a l b i t eite rreplacement e p l a c e m e n t assemblages assemblages respectively. L e p i d o l it Lepidol it ee—alb occur o c c u r locally l o c a l l y at a t the t h esoutheastern s o u t h e a s t e r n end end of o f the t h e dike d i k e and and are a r e specifically s p e c i f i c a l l y associated a s s o c i a t e d with w i t h the t h e pollucite p o l l u c i t e zone zone where w h e r e spodumenes spodumenes are a r e clearly c l e a r l y partially p a r t i a l l y replaced r e p l a c e d by by fine—grained f i n e - g r a i n e d lepidolite. l e p i d o l ite. Beryl B e r y l is is rarely r a r e l yfound f o u n d in i nthe t h eTot TbtLake Lake pegmatite, pegmatite, occurring t o anhedral a n h e d r a l crystals c r y s t a l s (up ( u p to to o c c u r r i n g as a s white w h i t e subhedral s u b h e d r a l to 2 x 4 cm in i n cross—section) c r o s s - s e c t i o n ) in i n albitic a l b i t i c replacement replacement zones. is noteworthy n o t e w o r t h y as a s fine—grained, fine-grained, z o n e s . Holmquistite H o l m q u i s t i t e is randomly r a n d o m l y oriented o r i e n t e d acicular a c i c u l a r purplish p u r p l i s h crystals c r y s t a l s on on the the surface s u r f a c e of o f a massive, m a s s i v e , medium—grained, m e d i u m - g r a i n e d , mafic m a f i c metavolcanic metavolcanic host h o s t reentrant r e e n t r a n t near n e a r the t h e southeast s o u t h e a s t end end (best ( b e s t seen s e e n on on wetted w e t t e d surfaces) s u r f a c e s ) and a n d in i n similar s i m i l a r adjacent a d j a c e n t rocks r o c k s for for distances t o 1 m from f r o m the t h e dike d i k e contact. contact. d i s t a n c e s up u p to Return R e t u r n to t o Ghost Ghost Lake Lake Road, Road, turn t u r n north, n o r t h , and a n d travel t r a v e l for f o r7.75 7 . 7 5km km to to junction. j u n c t i o n . Turn T u r n eeast a s t along a l o n g poor p o o r gravel g r a v e l road r o a d and and travel t r a v e l for f o r5 5km km to t o junction j u n c t i o n with w i t h Kathlyn K a t h l y n Lake Lake access a c c e s s road. r o a d . Turn T u r n south s o u t h and a n d travel travel for f o r about a b o u t 3.5 3 . 5 km. km. Proceed P r o c e e d aa sshort h o r t distance d i s t a n c e along a l o n g old o l d road r o a d to to west west to t o an a n outcrop o u t c r o p area a r e a with w i t h pits p i t s and a n dana nada dit. it. 1 STOP 12: STOP 12: - LATERAL LATERAL LAKE LAKE MOLYBDENITE MOLYBDENITE DEPOSIT DEPOSIT this T h i s property p r o p e r t y is is held h e l d by b y PT ~ i d g ~ M6iybdenum ~ o l ~ b d eMines Mines n u m Ltd. Ltd. and a n d covers c o v e r s the t h e eastern e a s t e r n contact c o n t a c t between b e t w e e n the t h e Lateral Lateral Lake Lake intrusion i n t r u s i o n and and intensely i n t e n s e l y foliated f o l i a t e d metavolcanic m e t a v o l c a n i c and and metasedimentary m e t a s e d i m e n t a r y rocks r o c k s (Figure ( F i g u r e 5). 5 ) . The The property p r o p e r t y has h a s been been explored e x p l o r e d by by an a n adit a d i t and and extensive e x t e n s i v e diamond diamond drilling, d r i l l i n g , most most recently r e c e n t l y by b y Rio R i o Tinto T i n t o Canadian C a n a d i a n Exploration E x p l o r a t i o n Ltd. Ltd. in in 1979—80. At A t this t h i s locality l o c a l i t y the t h e intrusion i n t r u s i o n is is composed composed of of 1979-80. foliated, t o coarse—grained coars e - g r a i n e d granodiorite, g r a n o d i o r i t e , pink pink f o l i a t e d , medium medium to aplite a p l i t e and and several s e v e r a l varieties v a r i e t i e s of o f pegmatite. pegmatite. Quartz—filled Q u a r t z - f i l l e d tension t e n s i o n fractures f r a c t u r e s are a r e oriented o r i e n t e d at a t aa high h igh angle a n g l e to t o foliation f o l i a t i o n and and cut c u t all a l lof o fthe t h eintrusive i n t r u s i v phases e phases (Page, 1 9 8 4 ) . Mineralization M i n e r a l i z a t i o n consisting c o n s i s t i n gof o fmolybdenite molybdenite ( P a g e , 1984). with w i t h lesser l e s s e r pyrite p y r i t e is is preferentially p r e f e r e n t i a l l y associated a s s o c i a t e d with with late l a t e feldspar f e l d s p a r and and muscovite—rich m u s c o v i t e - r i c h intrusive i n t r u s i v e phases. phases. Molybdenite is present p r e s e n t as a s scattered s c a t t e r e d flakes f l a k e s in in M o l y b d e n i t e is muscovite—bearing and vvein m u s c o v i t e - b e a r i n g p pegmatites e g m a t i t e s and e i n quartz. q u a r t z . Pyrite Pyrite and and muscovite m u s c o v i t e are a r e common common aassociates s s o c i a t e s of o f molybdenite m o l y b d e n i t e and and rare r a r e magnetite, m a g n e t i t e , bismuthinite b i s m u t h i n i t eand a n dtourmaliri,e t o u r m a l i n e have h a v e been been reported. reported. The most recent r e c e n t development d e v e l o p m e n t on o n this t h i s property p r o p e r t y has has The most resulted r e s u l t e d in i n aa published p u b l i s h e d reserve r e s e r v e estimate e s t i m a t e of of 14,300,000 14,300,000 tons . 0 8 %M0S2. MoS2. t o n s grading g r a d i n g .08% e a s t w a r d for f o r 8.6 8.6 Return t o Kathlyn K a t h l y n Lake Lake access a c c e s s road r o a d and R e t u r n to and continue c o n t i n u e eastward 72. Turn Turn right right km w i t h Highway Highway 72. km (5.4 (5.4 miles) m i l e s ) to t o the t h e intersection i n t e r s e c t i o n with �+ + I' + + + + + + + + + •_I__ LATERAL LAKE AREA '-. tz'_;l.. I + + + + + ÷ + + + + + + + + ÷ + + + + + -.—-— + + ++ + + ++ + ++++++ Stop 1 +++++ +++ + +. + + + + + + , 7 'I,— 1+ +1 adit after Page 1984 ' \' —JI' _\ —I I I—. rocks \.> \/ EJ metavolcanic sedimentary rocks granodiorite . Mo, Py occurrence I' powerline Lake Area. Figure 5 Generalized Geology of the Lateral '-I + + '+++++++ +++++++++ ++++++++++ +++++++++++++ ++++++++++++ +++++++++ _,ç-I/ ,_- v—' H �183 ( s o u t h ) and and proceed p r o c e e d 2.7 2 . 7 km km (1.7 ( 1 . 7 miles) miles) to t o the t h e Goldiund G o l d l u n d Mine Mine (south) access road. ( w e s t ) and a n d proceed p r o c e e d along a l o n g this t h i s road road a c c e s s r o a d . Turn right r i g h t (west) approximately km (1.5 ( 1 . 5 miles) miles) to t o the t h e mine. mine. a p p r o x i m a t e l y 2.4 2. 4 km STOP 13: GOLDLUND GOLDLUND MINE MINE STOP 13: The The G o l d l u n d ~ ~ is i t o p e r a t e d by Campbell Goldl ndposit is operated by Campbell Resources and ccontains R e s o u r c e s LLtd. t d . and o n t a i n s ppublishes u b l i s h e s reserves r e s e r v e s of of 600,000 .20o oz/ton o tthe h e 8800 0 0 f ft. t . level. level. 6 0 0 , 0 0 0 t tons o n s ggrading r a d i n g .20 z / t o n t to It I t is is hosted h o s t e d by aa tabular t a b u l a r northeasterly n o r t h e a s t e r l y striking s t r i k i n g body body of of is grossly g r o s s l y concordant concordant t r o n d h j e m i t e which intrudes i n t r u d e s and a n d is trondhjemite with w i t h mixed mixed mafic m a f i c to t o felsic f e l s i cmetavolcanic m e t a v o l c a n i c rocks r o c k s (Figure (Figure . 6). 6 ) AA large l a r g ediscordant d i s c o r d a n tbody bodycomposed composed oof f quartz q u a r t z and and feldspar f e l d s p a r porphyry p o r p h y r y occurs o c c u r s in i nthe t h emine m i n earea a r e and a andnumerous numerous dikes d i k e s of o f similar s i m i l a rcomposition c o m p o s i t i o n cut c u t the t h etrondhjemite t r o n d h j e m i t e and and the t h e volcanic v o l c a n i c rocks. r o c k s . The The ore ore zones z o n e s comprise c o m p r i s e cclusters l u s t e r s of of enechelon enechelon extensional e x t e n s i o n a l veins v e i n s which which transect t r a n s e c t the the trondhjemite: these trondhjemite: t h e s e sstrike t r i k e northerly n o r t h e r l y and and dip d i p at at moderate The m o d e r a t e angles a n g l e s to t o the t h e west. west. The v e i n s a r e f r a c t i o n s o f an a n inch i n c h to t o one o n e foot f o o t wide w i d e and and occur o c c u r at a t spacings s p a c i n g s of o f inches inches to t o several s e v e r a l feet. feet. v e i n s are a r e composed composed primarily p r i m a r i l y of o f quartz, quartz, The veins ankerite a n k e r i t e and p y r i t e with minor a c t i n o l i t e , b i o t i t e , tourmaline, t o u r m a l i n e , scheelite, scheel i t e , sphalerite, s p h a l e r i t e , galena, g a l e n a , chalcopyrite, chalcopyrite, pyrrhotite, i l r n e n i t e aand n d nnativegold. a t i v e g o l d . Most Most p y r r h o t i t e , tellurides, t e l l u r i d e s , ilmenite veins haloes v e i n s are a r e enveloped e n v e l o p e d by by "bleached" " b l e a c h e d " alteration a 1 t e r a t i o n haloes within w i t h i n trondhjemite: t r o n d h j emite: these t h e s e are a r e characterized c h a r a c t e r i z e d by by enrichments e n r i c h m e n t s of o f ankerite, a n k e r i t e , albite a l b i t e and and pyrite p y r i t e but b u t their their width correlate w i d t h and a n d intensity i n t e n s i t y of o f alteration a l t e r a t i o n does d o e s not n o t correlate directly d i r e c t l y with w i t h gold g o l d contents. contents. The The mine m i n e has h a s been been developed d e v e l o p e d by b y conventional conventional underground u n d e r g r o u n d stoping, s t o p i n g ,aa decline d e c l i n efrom f r o m surface s u r f a c e and and open open cuts c u t s at a t surface. s u r f a c e . Depending, Depending, on o n the t h e status s t a t u s of o f mining mining operations o p e r a t i o n s at a t the t h e time time of of the t h e field f i e l d trip, t r i p , one o n e or or more more areas a r e a s will w i l l be b e visited v i s i t e dtot oexamine e x a m i n e the t h e host h o s t trondhjemite, trondhjemite, porphyry p o r p h y r y ddikes, i k e s , qquartz u a r t z vveins e i n s and and aalteration 1 t e r a t i o n haloes. haloes. Return R e t u r n to t o Highway Highway 72 7 2 and a n d proceed p r o c e e d south s o u t h to t o the t h e intersection i n t e r s e c t i o n with with Highway Highway 17 17 to t o Kenora Kenora via v i a Dryden Dryden and and Vermilion V e r m i l i o n Bay. Bay. veins are fractions of and pyrite with minor actinolite, biotite, �Figure : Generalized Geology of the Goldiund Mine Area. — V' % '.1 shaft dump after Page 1984 zone pit decline J porphyry !I+ +1 trondhjemite ,"I--'-,'I metavolcanic rocks — �185 REF REF ERENC ERENCES ES Bartlett, B a r t l e t t , J.R., J. R., 1978, 1 9 7 8 , Metamorphic M e t a m o r p h i c trends t r e n d s in i n the t h e metasedimentary metasedimentary rocks r o c k s north n o r t h of o f Eagle E a g l e Lake, L a k e , Ontario; O n t a r i o ; unpublished u n p u b l i s h e d B.Sc. B.Sc. thesis, t h e s is, University U n i v e r s i t y of o f Western W e s t e r n Ontario, O n t a r i o , 73p. 73p. Blackburn, C. E. and and Hailstone, H a i l s t o n e , M.R., M.R., 1983, 1983, 1982, 1982, Report R e p o r t of o f the the B l a c k b u r n , C.E. Kenora p. 1-1 9 in i n Report R e p o r t of o f Activities Activities Kenora Resident R e s i d e n t Geologist; G e o l o g i s t ; p.1—19 Regional R e g i o n a l and a n d Resident R e s i d e n t Geologists, G e o l o g i s t s , 1982, 1982, edited e d i t e d by b y C.R. C.R. Kustra, O n t a r i o Geological Geological Survey, S u r v e y , Miscellaneous M i s c e l l a n e o u s Paper P a p e r 107, 107, Kus t r a , Ontario 211. 21 1. Blackburn, 1983, D.A., 1 9 8 3 , Gold Gold deposits d e p o s i t s in in B l a c k b u r n , C.E., C.E., and a n d Janes, J a n e s , D.A., N o r t h w e s t e r n Ontario; O n t a r i o ; p.194—210 p . 194-210 in i n The The Geology G e o l o g y of o f Gold Gold in in Northwestern Ontario; e d . A.C. A.C. Colvine; C o l v i n e ; Ontario O n t a r i o Geological G e o l o g i c a l Survey Survey O n t a r i o ; ed. Miscellaneous M i s c e l l a n e o u s Paper P a p e r 110, 1 10, 278p. 278p. Breaks, B r e a k s , F.W., F.W., 1980, 1 9 8 0 , Lithophile L i t h o p h i l e Mineralization M i n e r a l i z a t i o n in i n Northwestern Northwestern Ontario: Rare Element E l e m e n t Granitoid G r a n i t o i d Pegmatites; P e g m a t i t e s ; p.5—9 p .5-9 in i n Summary Summary O n t a r i o : Rare of o f Field F i e l d Work, Work, 1980, 1 9 8 0 , by by the t h e Ontario O n t a r i o Geological G e o l o g i c a l Survey, Survey, edited e d i t e d by b y V.G. V.G. Mime, M i l n e , O.L. 0. L. White, White, R.B. R.B. Barlow, B a r l o w , J.A. J. A. bertson, R o b e r t s o nand , a nA.C. d A.C. Colvine, C o l v i n e Ontario , O n t a r i oGeological G e o l o g i c a lSurvey, Survey, Miscellaneous M i s c e l l a n e o u s Paper P a p e r 96, 9 6 , 201p. 201p. Breaks, rare-metal pegmatites p e g m a t i t e s of o f the the B r e a k s , F.W., F.W., 1982, 1 9 8 2 , Metamorphism Metamorphism and a n d rare—metal Dryden D r y d e n area; a r e a ; p.4—12 p.4-12 in i n Stratigraphy S t r a t i g r a p h y and and Structure S t r u c t u r e of o f the the Western Wes t e r n Wabigoon Wabigoon Sub?ovince s u b p r o v i n c e and a n d its i t s margins, m a r g i n s , Northwestern Northwestern Ontario O n t a r i o ed. e d . C.E. C. E. Blackburn; B l a c k b u r n ; Geological G e o l o g i c a l Association A s s o c i a t i o n of of Canada, Field Trip guidebook No.3, Winnipeg. C a n a d a , F i e l d T r i p g u i d e b o o k No. 3, Winnipeg. Breaks, G h o s t Lake Lake area, a r e a , District D i s t r i c t of of B r e a k s , F.W., F.W., 1984, 1984, Eagle E a g l e River R i v e r — Ghost Kenora; Kenora; Ontariä O n t a r i o Geological Geological Survey, S u r v e y , Preliminary P r e l i m i n a r yMap Map P.2623, P. 2 6 2 3 , Geol. Geol. Ser., S e r . , scale scale 1 1 in i n to t o 1/2 1/2 mi. mi. Breaks, B r e a k s , F.W., F.W. , in i nprep., p r e p . ,Geology Geologyand a n dGeochemistry G e o c h e m i s t r y of o f the t h eDryden Dryden Pegmatite D i s t r i c t of o f Kenora; K e n o r a ; Ontario O n t a r i o Geological Geological P e g m a t i t e Field, F i e l d , District Survey S u r v e y Geological Geological Report. Report. Breaks, B r e a k s , F.W., F.W., Bond, Bond, W.D., W.D., Westerman, W e s t e r m a n , C.J. C . J . and a n d Harris, Harris, N., N . , 1976a, 1976a, Operation O p e r a t i o n Kenora—Ear Kenora-Ear Falls, F a l l s , Dryden—Vermilion D r y d e n - V e r m i l i o n Bay Bay Sheet, Sheet, District D i s t r i c t of o f Kenora; K e n o r a ; Ontario O n t a r i o Division D i v i s i o n of o f Mines, M i n e s , Preliminary Preliminary Map Map p.1203, p . 1 2 0 3 , Geol. G e o l . Ser., S e r . , scale s c a l e 1:63,360 1:63,360 or or 1 inch i n c h to t o 1 mile. mile. Geology G e o l o g y 1975. 1975. Breaks, Bond, W.D., W. D. , Harris, Harris, N., N., Westerman, Wes t e n n a n , C.J. C. J . and and B r e a k s , F.W., F.W. , Bond, Desnoyers, D e s n o y e r s ,D.W., D.W., 1976b, 1 9 7 6 b , Operation O p e r a t i o n Kenora—Ear Kenora-Ear Falls, Falls, D i s t r i c t of o f Kenora; Kenora; Ontario Ontario S a n d y b e a c h - R o u t e Lakes Lakes Sheet, S h e e t , District Sandybeach—Rute D i v i s i o n of o f Mines, M i n e s , Preliminary P r e l i m i n a r y Map Map p.1204, p . 1204, Geol. G e o l . Ser., S e r . , scale scale Division 1:63,360 1:6 3,360 of o f 1 inch i n c h to t o1 1 mile. mile. Geology Geology 1975. 197 5. Breaks, B r e a k s , F.W., F.W., Bond, Bond, W.D., W.D., and and Stone, S t o n e , Denver, D e n v e r , 1978, 1978, Preliminary Preliminary GeologicaL G e o l o g i c a l Synthesis S y n t h e s i s of o f the t h e English Engl i s h River R i v e r Subprovince, Subprov i n c e , Northwestern Ontario and a n d its its Bearing B e a r i n g Upon Upon Mineral Mineral N o r t h w e s t e r n Ontario E x p l o r a t i o n ; Ontario O n t a r i o Geological G e o l o g i c a l Survey S u r v e y Miscellaneous M i s c e l l a n e o u s Paper Paper Exploration; 72, 7 2 , 54p. 54p. Accompanied Accompanied by b y Map Mapp.1972, p . 1972, Scale S c a l e1:253,440. 1: 2 5 3 , 4 4 0 . Cerny, C e r n y , P., P., 1982, 1 9 8 2 , Anatomy Anatomy and a n d classification c l a s s i f i c a t i o n of o f granitic granitic p e g m a t i t e s ; p . 1-39 i n S h o r t C o u r s e i n G r a n i t i c Pegmatites P e g m a t i t e s in in pegmatites; p.1—39 in Short Course in Granitic S c i e n c e and a n d Industry; ~ n d u s t r y ; ed. e d . P. P. Cerny; C e r n y ; Mineralogical Mineralogical Science A s s o c i a t i o n of o f Canada, C a n a d a , Short S h o r t Course C o u r s e Handbook, Handbook, V.8. V. 8. Association Colvine, C o l v i n e , A.C. A.C. and a n d McCarter, McCarter, P., P., 1977, 1 9 7 7 , Geology Geology and a n d mineralization mineralization of o f the t h e Lateral L a t e r a l Lake Lake stock, s t o c k , District D i s t r i c t of o f Kenora; K e n o r a ; p.205—208 p.205-208 ini n Summary Summary of o f Fieldwork, F i e l d w o r k , 1977, 1 9 7 7 , by by the t h e Geological G e o l o g i c a l Branch, B r a n c h , ed. ed. V.G. V. G. Mime M i l n eete tal., a 1 ,Ontario O n t a r i oGeological G e o l o g i c a lSurvey, S u r v e y , Miscellaneous Miscellaneous Paper P a p e r 75. 75. - - 1 1 . 1 �186 C o l v i n e , A.C., A.C., A.J., C h e r r y , M.E., M.E., Durocher, D u r o c h e r , N.E., M.E., Fyon, Fyon, Colvine, Andrews, A.J., Cherry, A.J., L a v i g n e , M.J. M . J . Jr., J r . , Macdonald, Macdonald, A.J., A . J . , Marinont, Marmont, S., S., A.J., Lavigne, P o u l s e n , rCH., K.H., S p r i n g e r , J.S. J.S. and and Troop, Troop, D.G., D.G., 1984, An An Poulsen, Springer, 1984, i n t e g r a t e d model for f o r the t h e origin o r i g i n of o f Archean Archean lode l o d e gold gold integrated d e p o s i t s ; Ontario O n t a r i o Geological G e o l o g i c a l Survey, S u r v e y , Open Open File F i l e Report R e p o r t 5524, 5524, deposits; 84p. E.W., 1975, Economic Economic Geology and and mineralogy m i n e r a l o g y of o f petalite petalite H e i n r i c h , E.W., Heinrich, 1975, and a n d spodumene spod umene pegmatites; p e g m a t i t e s ; Indian I n d i a n Journal J o u r n a l of o f Earth E a r t h Sciences, Sciences, V.2, V.2, No.1, NO.1, p.19—29. p.19-29. Hutchinson, R.W., 1955, Regional Zonation of PPegmatites 1ss 1955, R egional Z o n a t i o n of e g m a t i t e s nnear e a r Ross H u t c h i n s o n , R.W., Lake, Mackenzie, Northwest NorthwestTrritories; Lake, District D i s t r i c t oof f Mackenzie, erritories; Geological G e o l o g i c a l Survey Survey of o f Canada, Canada, Bulletin B u l l e t i n 34. 3 4. McCarter, p., M c C a r t e r , P., 1980, 1980, Geology and mineralization m i n e r a l i z a t i o n of of the t h e Lateral Lateral Stock, D i s t r i c t of o f Kenora, Kenora, Northwestern N o r t h w e s t e r n Ontario; O n t a r i o ; unpublished unpublished S t o c k , District M.Sc. M.Sc. thesis, t h e s i s , Oregon Oregon University, U n i v e r s i t y , 141p. 141p. Moorhouse, 1939, W.W., 1939, Geology Geology of of the t h e Eagle Eagle Lake Lake Area; Area; Ontario Ontario Moorhouse, W.W., Department Department of o f Mines, Mines, Vol.48, Vol.48, pt.4, p t . 4 , p.1—31. p. 1-31. Accompanied by by Accompanied Map i n c h to t o 1 mile. Map No.48d, No.48d, Scale S c a l e 1 inch Mulligan, M u l l i g a n , Robert, R o b e r t , 1965, 1965, Geology Geology of o f Canadian C a n a d i a n Lithium L i t h i u m Deposits; Deposits ; Geological G e o l o g i c a l Survey Survey of o f Canada Canada Economic Economic Geology Geology Report Report 21. 2 1. Ovchinnikov, 1976, Ovchinnikov ,L.N., L. N., 1976, Lithogeochemical L i t h o g e o c h e m i c a l Methods Methods for f o r Prospecting Prospecting Rare—Element Rare-Element Pegmatites; P e g m a t i t e s ; Acad. Acad. Sci. S c i . U.S.S.R. U. S. S. R. Moscow, Moscow, 79pp. 79pp. Page, 1984, R.O., 1984, Geology of o f the t h e Lateral L a t e r a l Lake Lake Area, A r e a , District District Page, R.O., of of Kenora; Kenora; Ontario O n t a r i o Geological G e o l o g i c a l Survey, S u r v e y , Open Open File F i l e Report Report 5518, 551 8, 17 5p. 175p. Pryslak, P r y s l a k , A.P., A. P., 1981, 198 1 , Rafter R a f t e rProject P r o j e c— t F a i r s e r v i c e option o p t i o n No.1, No. 1 , Fairservice unpublished Files u n p u b l i s h e d rreport; e p o r t ; Assessment Assessment F i l e s Research R e s e a r c h Office, Office, Ontario O n t a r i o Geological G e o l o g i c a l Survey, S u r v e y , Toronto. Toronto. S a t t e r l y , J. , 1941, 194 1, Geology Geology of o f the t h eDryden—Wabigoon Dryden-Wabigoon aarea, r e a , Kenora Kenora District; D i s t r i c t ; Ontario O n t a r i o Department Department of o f Mines, Mines , Annual Annual Report R e p o r t for for 1941; 1941; v.50, v.50, pt.2, p t . 2 , p.1—57. p . 1-57. Accompanied by Map 5 0 e , s c ale Accompanied by Map 50e, scale 1:63,360 1 ~ 6 3 , 3 6 0or o r 11 inch i n c h to t o11 mile. Storey, S t o r e y , C.C., C.C., 1983, 1983, Preliminary P r e l i m i n a r y Report R e p o r t of of the t h e Building B u i l d i n g and and Ornamental Stone Ornamental S t o n e Inventory, I n v e n t o r y , Kenora Kenora and a n d Rainy Rainy River River Districts; Geological Districts Ontario ; Ontario G e o l o g i c a lSurvey S u r v e yOpen Open File F i l eReport R e p o r t 5446, 5 446, 143p., 14 3 p . , 20 20 tables t a b l e s and a n d 37 3 7 figures. figures. Streckeisen, S t r e c k e i s e n , A., A., 1976, 1976, To To each e a c h plutoriic p l u t o n i c rrock o c k its its proper p r o p e r name; name; Earth E a r t h Science S c i e n c e Reviews, Reviews, v.12, v. 12, p.1—33. p. 1-3 3. Trowell, T r o w e l l , N.F., N.F., Blackburn, B l a c k b u r n , C.E. C.E. and and Edwards, Edwards, G.R., G.R., 1980, 1980, P r e l i m i n a r y geological g e o l o g i c a l synthesis s y n t h e s i s of of the t h e Savant S a v a n t Lake—Crow Lake-Crow Preliminary Lake metavolcanic—metasedimentary m e t a v o l c a n i c - m e t a s e d i m e n t a r y belt, be1 t , Northwestern N o r t h w e s t e r n Ontario Ontario Lake and a n d its i t s bearing b e a r i n g upon upon mineral m i n e r a l exploration; e x p l o r a t i o n ; Ontario O n t a r i o Geological Geological Survey, S u r v e y , Miscellaneous M i s c e l l a n e o u s Paper P a p e r 89, 8 9 , 30p. 3Op. Varlanioff, N., 1972, 1972, C Central and W West African e n t r a l and est A f r i c a n rare r a r e metal m e t a l granitic granitic V a r l a m o f f , N., pegmatites, p e g m a t i t e s , related r e l a t e d aplites, a p l i t e s , quartz q u a r t z veins v e i n s and and mineral mineral deposits; M i n e r a l l i u m Deposita, Depos i t a , v.7, v. 7, p.202—216. p . 202-21 6. d e p o s its ;Mineralliuni Wallace, H., 1978, 1978, Geology of o f the t h e Opikeigen O p i k e i g e n Lake Lake Area, A r e a , District District W a l l a c e , H., of of Kenora Kenora (Patricia ( P a t r i c i a Portion); P o r t i o n ) ; Ontario O n t a r i o Geological G e o l o g i c a l Survey Survey Report R e p o r t 185, 185, 58p. 58p. Accompanied Accompanied by by Map Map 2379, 2379, scale s c a l e 1 inch i n c h to to 1/2 1/2 mile. mile. 1 1 - Satterly, J., 1 � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1985 Description An account of the resource Institute on Lake Superior Geology. Kenora, Ontario. May 6-11, 1985. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1985 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/447a6860028737df745d7974761e2c60.pdf b1fa75cb16513474e44fbc86c5e78652 PDF Text Text ������������������������������������������������������������������������������������������������������������������ https://digitalcollections.lakeheadu.ca/files/original/a7b558dc93da691333f1e1949b8696c9.pdf 25248eb71f780870062be75615a68e26 PDF Text Text ����������������������������������������������������������� https://digitalcollections.lakeheadu.ca/files/original/9fc774d21baf36760c0b5db050d7509e.pdf 65fb153ecfed13c8786f579e8d9310da PDF Text Text ���The following map was omitted from the printed field guide and included as a hand out during the meeting. It has been included here in the PDF to address that omission. The file was added on May 29, 2019. ������������������������������������������������������������ Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1986 Description An account of the resource Institute on Lake Superior Geology. Wisconsin Rapids, Wisconsin. April 29-May 4, 1986. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1986 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/5112d4ee1c22ab4b1871f1e3264eeb66.pdf 46f792ea23d8305833e7bae3ed9a151f PDF Text Text r IL 1 A Fl Ti Institute on Lake Lake Superior Geology N PROCEEDINGS PROCEEDINGS and ABSTRACTS ABSTRACTS Volume Volume 33, Part Part 11 HI 33rd 33rd Annual Annual Meeting Meeting May May 12 and 13, 13, 1987 1887 I I I p r p. r t r 'It Wawa, Ontario Ontario �- ERRATA ERRATA apologies to Explorations and David Baxter. - with with.apologies to Muscocho Muscocho .. .~-- Explorations and David Baxter. .. — . . .. .. . . . ~ ~ ..~ , . ... ~ ~~~. - last last line line should should read: read: page page xii xii — - Muscocho Muscocho Explorations Explorations Ltd. Ltd. (Toronto) (Toronto) — coffee coffee breaks breaks - lines lines 5—6, 5-6, sentence sentence omitted; omitted; lines lines should should read: read: page page 77 — . ~. . .... ..... ~ - .,- - . .. - . ~ . are are quartz quartz and and carbonate, carbonate, with with lesser lesser amounts amounts of of chlorite. chlorite. The The chief chief accessory accessory sulphide sulphide mineral mineral is is pyrite pyrite with with lesser lesser amounts amounts of of pyrrhotite, pyrrhotite, chalcopyrite, chalcopyrite, and and arsenopyrite. arsenopyrite. �INSTITUTE on on INSTITUTE LAKE LAKE PROCEEDINGS PROCEEDINGS GEOLOGY G EOLOGY and ABSTRACTS ABSTRACTS and 33, 33, Volume Volume SUPERIOR SUPERIOR Part Part 1 1 MEETING 33rd ANNUAL ANNUAL MEETING 33rd WAWA, WAWA, May May ONTARIO ONTARIO 12 and 12 and 13, 13, 1987 1987 Organizedbybythe theOntario OntarioMMinistry off Organized inistry o Northern Development Northern Development and and Mines: Mines : Wawa ResidentGeologist Geologist OOffice W awa Resident ffice and tthe and he Ontario Geological Ontario Geological Survey Survey ProgramChairmen Chairmenand andEditors: Editors: Program E.D. Frey E.D. Frey and and R.P. R.P. Sage Sage Vol. 33, Proceedings and and Abstracts Abstracts Vol. 33, Part Part1:1:Proceedings Part 2: Wawa Gold Field Part 2: Wawa Gold F i e l d TTrip rip Part 3: 3: Michipicoten Stratigraphy FField Michipicoten Iron I r o n Formation Formation Stratigraphy i e l d Trip Trip Part Part 4: Hemlo Gold Field Trip Part 4: Hem10 Gold F i e l d T r i p Part 5: Structural Zone 5: Kapuskasing Kapuskasing Structural Zone FField i e l d TTrip rip Part �TABLE TABLE OF OF CONTENTS CONTENTS .............................. Constitution Lake Superior Constitution of of the theInstitute I n s t i t u ton e on Lake SuperiorGeology Geology ........... By—Laws By-Laws o f oft hthe e I Institute n s t i t u t eon onLake LakeSuperior SuperiorGeology Geology ................ Sam Goldich Medal: delines Sam Goldich Medal :Award Award Gui Guide1 ines and and Recipients Recipients ............... Student Student Travel TravelAward Award ............................................. Institutes I n s t i t u t e sononLake LakeSuperior SuperiorGeology Geology ii iii iv iv v V vi vi ...................................... Vii vii Board ix Board ooff Directors Directors ............................................... Local Local Committee Committee ................................................ Best Best Student StudentPaper PaperCommittee Committee ..................................... Goldich GoldichMedal Medal Committee Committee .......................................... Field F i e l d Trip T r i pLeaders Leaders ............................................... Technical xi Technical Session SessionChairmen Chairmen ....................................... xi Goldich xi (Soldich Medal Medal Recipient Recipient .......................................... xi Banquet Speaker xi Speaker .................................................. xi Acknowledgements ................................................. xii Technical TechnicalProgram Program ................................................ xiii x i ii Abstracts Abstracts ........................................................ xxii xxi i Report Report of o fthe t h e1986 1986Chairman Chairman ix Y x x xA xi Acknowledgements i �U INSTITUTES ON ON LAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY INSTITUTES NUMBER NUMBER 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 DATE - PLACE - DATE PLACE MMinneapolis, i nneapol i s ,MN MN Houghton, Houghton, MI MI East Lansing, East Lansing, MI MI Duluth, Duluth, MN MN Minneapolis, MN MN Minneapolis, Madison, Madison, WI MI Port Arthur Port Arthur (Thunder (Thunder Bay), Bay), Ont. Ont. Houghton, MI Houghton, M I Duluth, MN Duluth, MN Ishpeming, MI Ishpaning, MI St. Paul, St. Paul, MN MN Sault Ste. Sault Ste. Marie, Marie, MI MI East Lansing, East Lansing, MI MI Superior, WI Superior, WI Oshkosh, WI Oshkosh, WI Thunder Bay, Bay, Ont. Thunder Ont. Duluth, MN Duluth, MN Houghton, MI Houghton, MI Madison, WI Madison, WI Sault Ste. Sault Ste. Marie, Marie, Ont. Ont. Marquette, MI Marquette, M I St. Paul, St. Paul ,MN MN Thunder Bay, Ont. Thunder Bay, Ont. Milwaukee, WI Milwaukee, WI Duluth, MN MN Eau Claire, Claire, WI Eau WI East Lansing, East Lansing, MI MI IInternational n t e r n a t i o n a l Falls, Fa1l s ,MN MN Houghton, MI Houghton, M I Wausau, WI Wausau, WI Kenora, Ont. Kenora, Ont. Wisconsin Rapids, Wisconsin Rapids, WI WI Wawa, Ont. Wawa, Ont. Marquette,MMI I ((tentative) tentative) Marquette, Duluth, MN MN ((tentative) tentative) Duluth, 1955 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 j U U U U -ii- �CONSTITUTIONOF OF INSTITUTE ON SUPERIOR GEOLOGY CONSTITUTION ON LAKE LAKE SUPERIOR GEOLOGY Article A r t i c l e II Name of the The name of t h e organization shall s h a l l be the t h e "Institute " I n s t i t u t e on on Lake Lake Superior Superior Geology."" Geology. Article A r t i c l e II I1 Objectives Objectives The objectives o b j e c t i v e s of of this t h i s organization are: are: A. A. BB.. C. C. Article I11 A r t i c l e III To provide a means means whereby whereby geologists g e o l o g i s t s in in the t h e Great Great Lakes Lakes region region may exchange ideas i d e a s and and scientific s c i e n t i f i c data. data. To promote promote b better To e t t e r understanding understanding of of the t h e geology geology of of the t h e Lake Lake Superior Superior region. region. To plan and conduct geological field f i e l d trips. trips. Status No part of the N o p a r t of t h e income income of of the t h e organization organization shall s h a l l inure Inure to t o the t h e benefit b e n e f i t of of any member or I n the t h e event of of dissolution d i s s o l u t i o n the t h e assets a s s e t s of of the the o r individual. individual. In organization shall s h a l l be distributed d i s t r i b u t e d to to (some tax t a xfree f r organization). e e organization). [To avoid Federal Federal and and S State [To avoid t a t e income income taxes, taxes, the t h e organization organization should should be not %on-profit ."I be n o t only only "scientific" " s c i e n t i f i c " or o r "educational" "educational" but b u t also a l s o "non—profit."] Minn. Stat. Anno. 290.01, Minn. S t a t . Anno. 290.01. subd. subd. 44 w vg ' 290.05(9) 290.05(9) 1954 s. 50l(c)(3) 501(c)(3) 1954 Internal I n t e r n a l Revenue Code Code s. Article IV A r t i c l e IV Membership Membership The membership of of the t h e organization organization shall s h a l l consist c o n s i s t of of the t h e board board of of directors. directors. Any permitted to Any geologist geologist interested i n t e r e s t e d shall s h a l l be permitted t o aattend t t e n d and pparticipate a r t i c i p a t e iin n t h e annual annual meetings. meetings. and vote at a t the Article A r t i c l e VV pMeetings eetings The organization shall s h a l l meet once once aa year, year, preferably p r e f e r a b l y during during the t h e month month of of April. April. The place and exact date d a t e of each each meeting meeting will w i l l be be designated designated by by tthe h e board of of directors. directors. Article A r t i c l e VI VI Ilirectors Directors The The board board of of directors d i r e c t o r s shall s h a l l consist c o n s i s t of of the t h e Chairman, Chairman, Secretary—Treasurer Secretary-Treasurer past l a s t three three p a s t Chairmen; but if i f the t h e board board should should at a t any any time time conconand tthe h e last of less reason of of unwillingness unwillingness or o r inability inability sist of less than five f i v e persons, persons, by reason of any of of the of t h e above persons to t o serve s e r v e as a s directors, d i r e c t o r s , the t h e vacancies vacancies on on the the may board m y be filled f i l l e d by the t h e annual meeting meeting so s o as a s to t o bring b r i n g the t h e membership membership of the t o five f i v e members. members. of t h e board up to Article A r t i c l e VII Officers O fficers of tthis organizition be aa Chairman and aa SecretarySecretary— The officers o f f i c e r s of his ~ r g a n i z ~ t i osshall nh a l l be Treasurer. A. A. B. B. Article VIII A r t i c l e VIII The Chairman shall shall be elected e l e c t e d each each year by by the t h e board board of of directors, directors, who shall t h e wishes of of any group that t h a t may s h a l l give due consideration consideration to t o the His be promoting the i s term of office o f f i c e as a s Chairman Chairman t h e next next annual annual meeting. meeting. H will of tthe annual meeting meeting over over which which he he prepreh e cclose l o s e of h e annual w i l l terminate aatt tthe sides orr when h his will i l l then then sides o i s successor successor shall s h a l l have have been been appointed, appointed. He w serve for t h r e e years y e a r s as a s aa member member of of the t h e board board of of directors. directors. f o r a period of three The Secretary—Treasurer Secretary-Treasurer shall s h a l l be elected e l e c t e d at a t the t h e annual annual meeting. meeting. His His term of of o office s h a l l be two two years y e a r s or o r until u n t i l his h i s successor successor shall s h a l l have have f f i c e shall been appointed. Amendments Amendments may be be amended by by aa majority majority vvote of those those persons parsons who who This cconstitution o n s t i t u t i o n may o t e of aare r e personally present at, a t , participating p a r t i c i p a t i n g in, in, and and voting v o t i n g at a t any any annual annual meeting meatins of of the the organization. organization. —iii— �BY-lAWS BY-LAWS I. I. Duties of Duties of the t h e Officers O f f i c e r s and and Directors Directors A. A. It sshall It h a l l be the t h e dutyof dutyof the the Chairman Chairman to: to: Preside 1. 1. P r e s i d e at a t the t h e annual annual meeting. meeting. needed for of tthe 2. Appoint all a l l committees needed f o r tthe h e organization of he 2. annual annual meeting. meeting. 3. 3. Assume complete responsibility r e s p o n s i b i l i t y for f o r the t h e organization and financing of of the t h e annual annual meeting over over which which he he presides. presides. B. It It shall s h a l l be the t h e duty duty of of the t h e Secretary—Treasurer Secretary-Treasurer to: to: 1. 1. Keep accurate accurate attendance attendance records records of of all a l l annual annual meetings. meetings. Keep a accurate records of of aall meetings o of, and correspondence correspondence 2. 2. Keep c c u r a t e records l l meetings f , and between, the between, t h e board of of director8. directors. meetings 3. 3. Hold aall l l fwids funds that t h a t may accure aass pprofits r o f i t s from annual meetings or o r field f i e l d trips t r i p s and and to t o make make these these funds funds available a v a i l a b l e for f o r the the organization and operation of organization of future f u t u r e meetings as a s required. required. C. C. Li It sshall h a l l be the t h e duty of of the t h e board of of directors d i r e c t o r s to t o plan p l a n locations locations of annual meetings and to and financing of t o advise on tthe h e organization and of all of a l l meetings. meetings. m ii. 1 1. Dues and Expenses 1-4 1. 1. There shall s h a l l be no regular r e g u l a r membership membership dues. dues. 2. 2. Registration R e g i s t r a t i o n fees f e e s for f o r the t h e annual meetings shall s h a l l be determined by the in consultation c o n s u l t a t i o n with with the t h e board board of of directors. directors. t h e Chairman in It is sstrong]. t r o n g l y recommended recommended that t h a t these t h e s e be be kept kept at a t aa minimum minimum to to encourage attendance of graduate graduate students. students. III. 1 11. Rules or o r Order Order The rules Robert's Rules of of Order shall rules contained in Robert's ahall govern this this organization in i n all a l l cases cases to t o which which they they are a r e applicable. applicable. IV. IV. Amendments Aoendments These bee amended by a majority v vote These by—laws by-laws may b o t e of of those t h o s e persons who personally present present aat, voting aatt any 6annual in, and voting nUWil aare r e personally t , pparticipating a r t i c i p a t i n g in, meeting of of the t h e organization; organization; provided that t h a t such modifications shall shall not orr subsequently n o t conflict c o n f l i c t with the t h e constitution c o n s t i t u t i o n as a s presently p r e s e n t l y adopted o amended. V 4 1j -iv- �Preamble Preamble SAM GOLDICH SAM GOLDICH MEDAL MEDAL The The IInstitute n s t i t u t eononLake LakeSuperior SuperiorGeology Geology was was born born on on or o r around around 1955, 1955, as as documented by the fact that the 27th annual meeting will be held i n1981. 1981. documented by t h e f a c t t h a t the 27th annual meeting w i l l be held in TheI Institutes The n s t i t u t e s are are exemplary exemplary i nin ttheir h e i r continuing continuing objectives objectives of o f dealing dealing with those aspects of geology that are related geographically w i t h those aspects o f geology t h a t are r e l a t e d geographically to t o Lake Lake Superior; of the discussion discussion ooff subjects sponsoringf field Superior; o f encouraging encouraging the subjects and and sponsoring ield geologists from thet hacademia, w i l bring l b r i ntogether g together geologists from e academia,government government ttrips r i p swhich which will surveys, and and industry; industry; and informal but but surveys, and ooff maintaining maintaining an an exceedingly exceedingly informal highly effective mode of operation. h i g h l y e f f e c t i v e mode o f operation. Duringthe the course courseoof During f iits t s existence existence the t h e membership membership o f oft hthe e I nInstitute s t i t u t e (that (that is, those geologists who indicate an interest in the objectives i s , those geologists who i n d i c a t e an i n t e r e s t i n the objectives ooff the the I.L.S.G. by become aware I.L.S.G. by attending) attending) has has become aware o f of thethe f a cfact t t hthat a t c ecertain r t a i n oof f ttheir heir colleagues have made particularly noteworthy and meritorious contributions colleagues have made p a r t i c u l a r l y noteworthy and meritorious contributions to understandingoof 'Lake Superior" Superior" geology and i its t o the the improvement improvement oof f understanding f "Lake geology and ts mineral deposits. m i neral deposits. The exemplary exemplaryaward awardwas wasmade made I.L.S.G.t otoSam SamGoldich Goldichi nin1979 1979f ofor The by by I.L.S.G. r hhis is many contributions to the geology of the region extending over about many c o n t r i b u t i o n s t o t h e geology o f t h e region extending over about 50 50 years. years. Award Guide1 Guidelines Award ines Themedal medals hshall beawarded awarded annually Board Directors,I.L.S.G., I.L.S.G., 1) The 1) a l l be annually byby t h the e Board o f of Directors, to a geologist whose name is associated with substantial sustained interest t o a geologist whose name i s associated w i t h substantial sustained i n t e r e s t in, or in, o raamajor major contribution c o n t r i b u t i o nto, to,the t h geology e geologyofo the f theLake LakeSuperior SuperiorRegion. Region. 2) The The Board Boardoof Directors, I.L.S.G. thet hNominating 2) f Directors, I.L.S.G. shall s h a lappoint l appoint e NominatingCommittee. Committee. Their annual nominee will be voted on at the annual business The meeting. The Their annual nominee w i l l be voted on a t t h e annual business meeting. oneto serve iinitial n i t i a appointment l appointment will w i l lbe beofo three f t h r e emembers, members, one'to serve ffor o r three t h r e e years, years, one for for two, with one two, and and one one for f o rone one year, year, the t h emember member w i t h the t h e briefest b r i e f e sincumbency t incumbency After ttoo be be chairman. chairman. A f t e r the t h e first f i r s year t yearthe t h eBoard Board of o f Directors Directors shall s h a l l appoint appoint member servef ofor three years. w i lwill l serve r three years. IIn n the the aatt each each spring spring meeting meeting one one new new member whowho The Committee membership tthird h i r dyear year this t h i smember member shall s h a l l be be the thechairman. chairman. The membership shouldr reflect off should e f l e c t the t h e main main f fields i e l d s of o f interest i n t e r e s tand and geographic geographic ddistribution istribution o I.L.S.G. membership. I.L.S.G. membership. 3) The TheSoldich GoldichMedal MedalNominating Nominating Committee selectt hthe medalistand andwwill 3) Committee s h ashall l l select e medalist ill make its recommendation to the Board of Directors by November 1 of that make I t s reconmendation t o t h e Board o f Directors by November 1 o f t h a t year. year. 4) The The Board Boardoof Directors normally f Directors normally will w i l laccept acceptthe t h enominee nominee of o fthe t h eCommittee, Committee, 4) one medal wwill i l l inform informthe t h emedalist medalistimmediately, immediately,and andwill w i have l l have one medalengraved engraved appropriately appropriately for f o r presentation presentationata tthe theMay May meeting. meeting. It isi srecommended 5) It recommended t hthat a t t the h e IInstitute n s t i t u t eset setaside asideannually annuallyfrom fromwhatever whatever 5) sources, such funds as will be required to support the continuing costs ooff sources, such funds as w i l l be required t o support t h e continuing costs this award. t h i s award. April A p r i l 4, 4, 1981 1981 J. Kalliokoski J. K a l l iokoski (Chairman),. (Chairman), . Bill Fred Kehlenbeck, 8111Cannon, Cannon, Fred Kehlenbeck, Glenn Morey, Glenn Morey, Greg Mursky Greg RECIPIENTS RECIPIENTS 1979 Sam Goldich, 1981 1981Carl Carl Dutton, Dutton, 1982 1982 Ralph Ralph Marsden, 1984 Burton Burton Boyurn Sam Goldich, Marsden, 1984 Boyum 1979 1987 Henry H Halls 1984 Richard Ojakangas, 1986 G.B. Morey, 1985 Paul Sims, 1984 Richard Ojakangas, 1985 Paul Sims, 1986 G.B. Morey, 1987 Henry alls —1— �STUDENT STUDENT TRAVEL TRAVELAWARD AWARD The 1986 Board Boardoof The 1986 f DDirectors i r e c t o r s established e s t a b l i s h e d the t h eTUG ILSGStudent Student Travel TravelAward, Award, to a r c i p i t a t i o n at a t the t h e annual annual IInstitutes. n s t i t u t e s . The awards awards t o support support student student pparcipitation will be made from the accrued interest from a special w i l l be made from t h e accrued i n t e r e s t from a s p e c i a l fund fund set s e t up up for for this t h i spurpose. purpose. This This award award iis s intended intended tto o help h e l p defray d e f r a y some some oof f tthe h e direct direct travel t r a v e l costs c o s t s to t o the t h e Institute I n s t i t u t eand andincludes i n c l u d e s aa waiver waiver of o f registration r e g i s t r a t i o n fees, fees, but excludes expenses for meals, lodging, and field trip b u t excludes expenses f o r meals, lodging, and f i e l d t r i p rregistration. egistration. j j J The numberand ands isize i l l be be determined determined by by the t h e annual annual Chairman Chairman i in n consulconsulThe number z e wwill tation with the Secretary—Treasurer and will be announced at the t a t i o n w i t h t h e Secretary-Treasurer and w i l l be announced a t t h eannual annual banquet. banquet. The considered bybythe The ffollowing o l l o w i n g general general criteria c r i t e r i awill w i be l l be considered t h annual e annualChairman, Chairman, who is responsible for selection: who i s r e s p o n s i b l e f o r s e l e c t i o n : 1) The have aactive The aapplicants p p l i c a n t s must must have c t i v e resident r e s i d e n t (undergraduate (undergraduate or or graduate) students tstatus time graduate) student a t u s a tatt hthe e tim e o foft hthe e I nInstitute, s t i t u t e , ccertiertified f i e dby bythe t h edepartment department head. head. 2) 3) 4) Students whoa rare authoron oneeither an ooral Students who e t hthe e ssenior e n i o r author i t h e r an r a l or or poster paper will be given favored consideration. p o s t e r paper w i l l be g i v e n favored consideration. ItItisi sdesirable d e s i r a b l efor f o two r twooro more r more students students tto o jointly j o i n t l yrequest request travel t r a v e l assistance. assistance. iJ In I n general, general, ppriority r i o r i t y will w i l lbe begiven given to t o those those iin n the t h e Institute Institute region r e g i o n who who aare r e farthest f a r t h e s taway. away. 5) I yJ Each requests shall bemade made award request h a l l -be i ninw writing, r i t i n g , . tto o the the Each t travel r a v e l award annual Chairman, with an explanation of need, possible annual Chairman, w i t h an e x p l a n a t i o n o f need, p o s s i b l e author author status s t a t u s oorr other o t h e r ssignificant i g n i f i c a n t details. details. WI j I ME j -vi-J �—a 0> Cr mI- Coo Zr —I a' rn rID —I C-u =0 -I, -In, -10 rn Lii C) -C r GD rn Cr Cr Cr taco —. C 0. 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The student-paper awards were presented by Wayne Zwickey t o K . W . Klewin o f N o r t h e r n I l l i n o i s U n i v e r s i t y f o r h i s paper, "The P e t r o l o g y and Geochemistry o f the P o t a t o River I n t r u s i o n (Eastern M e l l e n Complex), N o r t h e r n Wisconsin" and t o A . 0. Maharidge o f Bowling Green S t a t e U n i v e r s i t y f o r h i s paper " T e c t o n i c E v o l u t i o n o f t h e F e l c h Trough." 0-' Z Cth CD CC — CD 0) Oc-rr-rtS —Izrnzr —- 0 i'0C Q0—C- 0c)CDo 'CACDCLO = CD ID U) CD O 'Ii 0 0 re CD O(D.— LID ZLD)>< CDC-.P--Lfl0 Cr-. 0- rr0CO-(D OC GD-C U)0iI--(0 i—-I--OCLrr c-t fr--—. 0 C 5= (DO ' 0. S 0 CDCDrP. U) CDC)—4 r0 p--fl. U)0 0) C U)W0 (00) OhOCOCEr U) 4,S CD c-p COrP-CD CD . Ci) il CD . • —. S O I-.-Di CD I U) err— 0 00-0I 0 • CDoOh 0 0.S U)L CD —4 05 VCD0 CDCO (DO CL —- 0 L4 'ID fr--0t) Cr0 rO.-4P- OJOiN) 0O) O Oh — c-c- 5 (0 • 0.—IC) T. 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A p r i m a r y o b j e c t i v e o f t h e awards w i l l be t o a t t r a c t Canadian s t u d e n t s . A committee (M. M. Kehlenbeck, C. E. Blackburn, T . J. B o r n h o r s t ) w i l l submit the g u i d e l i n e s t o the Board. CDS' 2) t o t a l $2592.34 and As o f A p r i l 22, 1986, t h e U.S. accounts o f I.L.S.G. i n c l u d e $890 i n t h e G o l d i c h Medal Fund account. The Canadian account stands a t SCAN 6,209.34. The 32nd I.L.S.G. t u r n e d over an a d d i t i o n a l $1200.00 t o t h e U.S. account. 44U)fr—ctrU) N)QiO 1) rtC0SP-l -CD-s,00 .— -._- 0m r.—o-, 0 Ci 40 CD The I n s t i t u t e Board o f D i r e c t o r s met a t noon on May 1. Board members p r e s e n t i n c l u d e d J e f f Greenberg (Chairman), Bruce Brown ( C o - c h a i r ) , J. K a l l i o k o s k i ( S e c r e t a r y - T r e a s u r e r ) , Gene LaBerge, Ted B o r n h o r s t , C h a r l i e Blackburn, and Dave Southwick. Ron Sage was a l s o p r e s e n t as the 33rd I.L.S.G. Chairman. The Board took the f o l l o w i n g a c t i o n : . S 0. — C-i CD C p—4(0 C40--0. cJnh— U) 0 CrCr00- • Di 0 Cr 0(0Cr 0(40 ECOIDO c-rt0 flI—rr rr05-i, c-on— n. r-0Lnw0_C CD tC CD 0 P-D Wa rtCDOtI —IO-C (010 c-tO- ct 0 ' fr---—-0 -tOJ (D0) 1Oh0 Oct0 - rtOrt0- N)Ci0i -0-. 00 GDCh- 0. oi-, • c-p —.Crt CD CD 0 C CD CD CDC<n —. -, Oh S-i-.Or--Oip-- I--0U) p—-<% 'XfrCD CD(D ICE ac-or—I U)-C(09o o,CrctrCU). 0 5'0 I—p... Cr5 tCpQirt CDC xP—4 —1'{P-05 O-n C —iCi -co p-o-A> O)P (DO.Cfl0.P- 0. COS Ot4C CDCDrII0i--C.ct 00 C00.It o,or' rt 00) On M a y 1 the I n s t i t u t e ' s annual banquet f e a t u r e d e x c e l l e n t food, an award "ceremony," and t h e guest speaker. The Goldich Medal was presented by the e v e r - e n t e r t a i n i n g Dick Ojakangas t o G. 0 . Morey o f t h e Minnesota G e o l o g i c a l Survey. Through the m i d s t o f some t e c h n i c a l a d v e r s i t y , John Rogers of the U n i v e r s i t y o f North C a r o l i n a shared h i s i n s i g h t s i n t o t h e "Precambrian o f Peninsular I n d i a . " I 1 CD —r '(C rP I—rtLfl 0)0) CD,CCet N) 5N) (Oct -0U) .-" 0) Girt 4.EU)OZV'%Jt c-tIC 00-U) U)C CO —4 p-i 0.—CD (sin 'O -t.-OCLCDOWZ.--. -I OtfiWet rtP-0O-055 <o-ceeo0.m z0 nr--0)p--'.COCD 0(0W.— Lflrr0.U)CD.—0 rCA OhC.-w 0)0 U) c_. C,J S c -C = c-t r — h COO) Cr >CCA—p--o I-4-,Ep—c-t —— V '<aEO,SrtOpO)CrE,N)VCDOO(D05 0Dc-j O.OQi----4 50_CrU)(D-,Oh I--S no P-CDU)(0tI-.-0. COO- (Dr. O<0 ttr W0)rt U)0CD00--0.CD0aa mr-vlsi CDSCDCO rrCi—r-r- r—--4 The 32nd meeting o f the I n s t i t u t e on Lake Superior Geology was hosted b y the Wisconsin G e o l o g i c a l and N a t u r a l H i s t o r y Survey and h e l d from A p r i l 29 t o May 4, 1986 i n c e n t r a l Wisconsin. Meeting headquarters was the Mead I n n i n Wisconsin Rapids where t e c h n i c a l sessions took p l a c e on May 1 and May 2. Conference r e g i s t r a n t s numbered 207 w i t h s t u d e n t s c o m p r i s i n g j u s t over one t h i r d o f these. Two-day f i e l d t r i p s were h e l d b o t h b e f o r e and a f t e r the meeting. The pre-meeting t r i p 1, which was l e d by J e f f Greenberg and Gordon Medaris, v i s i t e d exposures o f p l u t o n i c r o c k s a s s o c i a t e d w i t h the Wolf River b a t h o l i t h on A p r i l 29 and exposures o f Baraboo i n t e r v a l metasedimentary and igneous r o c k s on A p r i l 30. There were 38 p a r t i c i p a n t s on t r i p 1. F i e l d t r i p 2 leader Randy Maass was j o i n e d by 24 people on May 3 and May 4 t o observe s t r u c t u r a l c o m p l e x i t i e s o f Archean gneisses and E a r l y P r o t e r o z o i c metavolcanic u n i t s i n c e n t r a l Wisconsin. Separate guidebooks were p u b l i s h e d f o r each t r i p . to t1TJ i::ii-" t; t—; CC Ltt i— c ri (4 N) REPORT OF THE C H A I R M A N 32ND INSTITUTE ON LAKE SUPERIOR GEOLOGY 1986 �j 3) I.L.S.G. I.L.S.G. abstracts a b s t r a c t sare a r enow now submitted s u b m i t t e d to t o the t h eAmerican American Geological G e o l o g i c a l IInstitute nstitute for f o rinclusion i n c l u s i oinn GEOREF. i n GEOREF. 4. Starting w i l l be be Institute Institute S t a r t i n g in i n 1987, 1987, tthe h e ttitle i t l e of o f the t h e I.L.S.G. I.L.S.G. publication p u b l i c a t i o n will This title on Lake Superior Geolov ProceedinQs and Abstracts. on Lake Superior Geology Proceedinas and A b s t r a c t s . This t i t l ewill w i lappear l appear J j on on the the title on the t h e cover cover and and on t i t l epage. page. The The publication p u b l i c a t i o n will w i l also l a l sappear o appearunder under volume aa volume designation, the 33rd I.L.5.G. at Wawa will publish 33. volume d e s i g n a t i o n , the 33rd I.L.S.G. a t Wawa w i l l p u b l i s h volume 33. These i l l enable enable tthe h e IInstitute n s t i t u t e to t oapply apply ini n1988 1988 for f o ran an These sstandardizations t a n d a r d i z a t i o n s w will ISBN andthereby thereby tto recognized pperiodical. I S B N number number and o become become aa recognized eriodical. 5. Meeting notices Meeting n o t i c e s for f o r those those meetings meetings to t o be be held h e l d in i nthe t h eU.S. U.S. should shouldinclude include 'This Institute is recognized as a non—profit the statement: the statement: " T h i s I n s t i t u t e i s recognized as a n o n - p r o f i t sscientific cientific J and IRS and educational e d u c a t i o n a l organization o r g a n i z a t i o nunder underthe t h1954 e 1954 I R SRevenue Revenue Code Code S.5Ol(c)(3 S.S01(c)(3) Therefore, Therefore, aall l l ggifts i f t s to t o the the Institute Institute (Employee (Employee Indent. I n d e n t .No. No.23—7326054). 23-7326054). are a r e tax tax deductible." deductible." J 6. on the R. R. W. W. Ojakangas Ojakangas is i sthe t h enew newmember member (1986—1989) (1986-1989) on t h e Goldich GoldichMedal Medal H. Kehlenbeck. Committee, replacing N. Coamittee, r e p l a c i n g M. M. Kehlenbeck. 7. To Best Student Paper To be be eligible e l i g i b l efor f oconsideration r c o n s i d e r a t i o for n f othe r the Best Student PaperAward Award the the Starting student must be senior author and must present the paper. s t u d e n t must be s e n i o r author and must p r e s e n t t h e paper. S t a r t i n g in i n 19:97 1987 J agreed agreed to t o prepare prepare the the sample sample ccertificate. ertificate. U the the prize p r i z e will w i l lconsist c o n s i s tofo fboth b o t haacheck check and and aa ccertificate. ertificate. Gene Gene LaBerge LaBerge 8. Ron Sager ereported the 1987 1987 I Institute Ontario i l l take takeplace place Ron Sage p o r t e d t hthat a t the n s t i t u t e ini nWawé Wawa O n t a r i o wwill 9. Although wereno nocclear Although tthere h e r e were l e a r ooffers f f e r s of o f sponsorship sponsorship ffor o r the t h e 34th 3 4 t h I.L.S.G. I.L.S.G. (1988), Gene LaBerge mentioned the possibility of a proposal to hold t h e p o s s i b i l i t y o f a p r o p o s a l t o h o l dthe the (1988), Gene LaBerge mentioned meeting in Michigan's Upper Peninsula in the vicinity of the Gogebic meeting i n Michigan's Upper Peninsula i n the v i c i n i t y o f the Gogebic Boardaalso discussedthe the ppossibility meeting Range. Range. The The Board l s o discussed o s s i b i l i t yofo a f a meetingini Sudbury n Sudbury andi ninclude May May 11 11 to t o May May I15 S and c l u d e s eseveral v e r a l e xexciting c i t i n g f ifield e l d ttrips. rips. U Ontario O n t a r i o for f o r1989 1989ororbeyond. beyond. As As in i n the t h eprevious p r e v i o u sthirty—one t h i r t y - o n e years, years, this t h i year's s y e a r 'completed s completedchairmanship chairmanship how I t is i sindeed indeedwonderful wonderfultot see o see howsosomany many has has been been an an educational e d u c a t i o n a l experience. experience. It people from ddifferent canwork workt otogether the people from i f f e r e n t organizations o r g a n i z a t i o n s can g e t h e r f ofor r th e I Institute's nstitute's Perhaps the only problem of note for the 32nd I.L.S.G. success. success. Perhaps the o n l y problem o f n o t e f o r t h e 32nd I.L.S.G. was was the thepoor poor pre—meeting responset otothe thenmailed pre-meeting response a i l e d r registration e g i s t r a t i o n forms. forms. ItI tisi svery very difficult d i f f i c u l t to to estimate e s t i m a t e pparticipation a r t i c i p a t i o n in i n meals, aeals, field f i e l dtrips t r i p and s andtechnical t e c h n i c a lsessions sessions (seating), (seating), etc. without reasonable early notice of two weeks or so before e t c . w i t h o u t reasonable e a r l y n o t i c e o f two weeks or so b e f o r ethe t h emeeting. meeting. II suggest consider iincreasing suggest tthat h a t future f u t u r e local l o c a lcommittees committees consider n c r e a s i n g t the h e ddifferential ifferential between pre—meeting feesand andfees feesf for on—site between pre-meeting r e gregistration i s t r a t i o n fees or o n - s i t e rregistration. egistration. should encourage more people to preregister. s h o u l d encourage more people t o p r e r e g i s t e r . This This My thanksagain againt to maket hthe I.L.S.G. (and (and tthe 32ndI nInstitute My thanks o aall l l who who make e I.L.S.6. h e 32nd s t i t u t e in in particular) a priceless gathering of the friends of the Precambrian. p a r t i c u l a r ) a p r i c e l e s s g a t h e r i n g o f t h e f r i e n d s o f t h e Precambrian. L ee ttfully f t f u l l ysubmitted, submitted, U J K 2 rman 'r Institute Institute Madison, Madison, Wisconsi Wisconsi July, J u l y , 1986 1986 —viii— -viii- I L �INSTITUTE BOARD INSTITUTE BOARD OF OF DIRECTORS DIRECTORS R.P. Sage Sage((with E.D. R.P. w i t h E. D. Frey, Frey, Mineral Mineral 0ev. Dev. Br., Br., Wawa), Wawa), Ontario Ontario Geological Geological Survey, M Ministry andMines, Mines,7777GGrenville St., Survey, i n i s t r y of o f Northern NorthernDevelopment Development and r e n v i l l e St., Toronto, Ontario M7A 1W4 (1987) Toronto, Ontario M7A 1W4 (1987) J.K. Greenberg Geological and and Natural Natural H History J.K. Greenberg ((with w i t h B.A. B.A. Brown), Brown), Wisconsin Wisconsin Geological istory Survey, 3817 Mineral Point 53705 (1986) (1986) Survey. 3817 Mineral Point Rd., Rd., Madison, Madison, Wisconsin Wisconsin 53705 C.E. Branch,MMinistry off Northern C .E. Blackburn, Blackburn, Mineral Mineral Development Development Branch, inistry o Northern Development and Mines, P.O. Box 5160, Kenora, Ontario P9N 3X9 Development and Mines, P.O. Box 5160, Kenora, Ontario P9N 3x9 (1985) (1985) G.L. Wisconsin—Oshkosh, Wisconsin-Oshkosh, G .L. LaBerge, LaBerge, Department Department ooff Geology, Geology, University Universitybf'of Oshkosh, Wisconsin 54901 (1984) Oshkosh, Wisconsin 54901 (1984) J. Kalliokoski, J. K a l l iokoski Department , Departmentofo fGeology Geology and and Geological Geological Engineering, Engineering, Michigan Michigan Technological University, 49931 (Sectretary(Sectretary— Technological University, Houghton, Houghton, Michigan Michigan 49931 Treasurer) Treasurer) —ix— �j I LOCAL COMMITTEE LOCAL COMMITTEE Ed Frey: Conference Programand andAbstracts Abstracts Editor Editor Ed Frey: Conference Co—chairman, Co-chairman, Program Ron Sage: Conference Programand andGuidebooks GuidebooksEEditor Ron Sage: Conference Co—chairman, Co-chairman, Program ditor ta-i Tern—Ann Hoffmann (MNDM, (MNDM, Wawa): Mailingand andRegistration Registration Terri-Ann Hoffmann Wawa): Mailing Barbara Leschishin Leschishin (MNDM, Wawa):MMailing andRegistration Registration Barbara (MNDM, Wawa): a i l i n g and Wendy Wing(MNDM, (MNDM, Wawa): andRegistration Registration Wendy Wing Wawa) : D r Drafting a f t i n g and Delio Wawa):FField Delio Tortosa Tortosa (MNDM, (MNDM, Wawa): i e l d TTrip r i p Assistance Assistance Gerry (MNDM, SaliltSte. Ste.Marie): Marie): FField Gerry Bennett Bennett (MNDM, Sault i e l d Trip T r i p Assistance Assistance J Ken Card (GSC, (GSC,Ottawa): Ottawa):FField Ken Card i e l d TTrip r i p Assistance Assistance I Mike M I ke Lockwood (Univ.Western WesternOntario) Ontario): Lockwood (Univ. : FField i e l d Trip T r i p Assistance Assistance Dave Walker (MNDM, (MNDM,Toronto): Toronto): DDrafting Dave Walker r a f t i n g and and Guidebook Guidebook Preparation Preparation Krystyna Toronto): Graphics Krystyna Gil G i l (MNDM, (MNDM. Toronto): Graphics I BEST STUDENT PAPER BEST STUDENT PAPER COMMITTEE COMMITTEE A.J. A.J. J Andrews,Ontario Ontario Geological Geological Survey, Andrews, Survey, Toronto, Toronto, Ont. Ont. J.J. Consulting Geologist, Geologist, Toronto, J.J. Brummer, Brumer, Consulting Toronto, Ont. Ont. P.K. P.K. Sims, Sims, United United States States Geological GeologicalSurvey, Survey, Denver, Denver,CO CO U GOLDICH GOLDICH MEDAL MEDAL COMMITTEE COMMITTEE W.A. Bodwell, Resource ResourceExploration, Exploration, Inc., Inc., Marquette, MI Marquette, MI W.A. Bodwell, J K.D. K.D. Card, Card, Geological Geological Survey Survey of o fCanada, Canada, Ottawa, Ottawa, Ont. Ont. R.W. Ojakangas,Dept. Dept. ooff Geology, R.W. Ojakangas, Geology, University U n i v e r s i t yofo Minnesota—Duluth, f Minnesota-Duluth, Duluth, Duluth, MN MN FIELD FIELD TRIP TRIPLEADERS LEADERS E.D. Development E.D. Frey, ~ r e yMineral ,MineralDevelopment Development Branch, Branch, Ministry M i n i s t r yofoNorthern f Northern Development and and Mines, Wawa, Wawa, Ont. Ont. T.L. Development T.L. Muir, Muir, Ontario OntarioGeological Geological Survey, Survey, Ministry M i n i s t r yofoNorthern f Northern Development and Mines, Toronto, Ont. ! and Mines, Toronto, Ont. j J I J.A. J.A. Percival, ~ e r c i v a Geological l , GeologicalSurvey Surveyofo Canada, f Canada, Ottawa, Ottawa, Ont. Ont. R.P. Development R.P. Sage, Sage, Ontario Geological Geological Survey, Survey, Ministry M i n i s t r yofoNorthern f Northern Development and Mines, Toronto, Ont. and Mines, Toronto, Ont. j Li �TECHNICAL TECHNICAL SESSION SESSIONCHAIRMEN CHAIRMEN T.J. T.J. Bornhorst, Bornhorst, Department Department of o f Geology Geology and and Geological Geological Engineering, Engineering, Michigan Technological University, MI Michigan Technological University,Houghton Houghton MI K.D. K.O. Card, Card, Geological Geological Survey Survey of o fCanada, Canada, Ottawa, Ottawa, Ont. Ont. A.M. Departmento fofGeology, Geology,UUniversity A.M. Goodwin, Goodwin, Department n i v e r s i t y oof f Toronto, Toronto, Toronto, Toronto, Ont. Ont. J.S. Geology,Western Western University, Dekalb, J.S. Klasner, Klasner, Department Department oof f Geology, I l lIllinois i n o i s University, Oekal b, IL IL G.L. of oWisconsin—Oshkosh, G.L. LaBerge, LaBerge, Department Department of o f Geology, Geology, University University f Wisconsin-Oshkosh, WI I 1 Oshkosh, Oshkosh, W I I F.R. Luther, Department of Geology, University of Wisconsin—Whitewater, F.R. Luther,Department o f Geology, u n i v e r s i t y of Wisconsin-Whitewater, Whitewater, WI Whitewater, WI R.J. R.J. Rupert, Rupert, Citadel CitadelGold GoldMines Mines Inc., Inc., Wawa, Wawa, Ont. Ont. R.H. R.H. Sutcliffe, S u t c l i f f e ,Ontario OntarioGeological GeologicalSurvey, Survey, Toronto, Toronto, Ont. Ont. i GOLDICH GOLDICH MEDAL MEDAL RECIPIENT RECIPIENT Henry C. Halls, Halls, Department off Geology, Henry C. Department o Geology, University U n i v e r s i t yofo Toronto—Erindale, f Toronto-Erindale, Toronto, Toronto, Ont. Ont. BANQUET BANQUET SPEAKER SPEAKER ,. 1 K. Poulsen, Geological Geological Survey Survey of o f Canada, Canada, Ottawa, Ottawa, Ont. Ont. K. Howard Howard Poulsen, —xi— �j ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS In thet hLocal Committee, thet hCo—chairmen I n addition a d d i t i o ntot othose thosecited c i t eon d on e Local Committee, e Co-chairmen wish wish to t o thank thank other other individuals i n d i v i d u a l sand andorganizations organizationswhose whose efforts e f f o r t sand andcooperacooperation apprecition t i o n have have contributed contributed to t o the t h eoperation operation of o fthe t h e33rd 33rdILSG. ILSG. Our Our apprecition also otherswho whow will ILSG i l l aaid i d the the Wawa Wawa ILSG a f tafter e r t hthis i s wwriting. riting. also goes goes tto o many many others - J Pam Aurora (MNDM—Toronto) manuscriptpreparation preparation Pan Aurora (MNDM-Toronto) — manuscript - Ann Wilson (Wawa) Ann Wilson (Wawa) —ccirculars irculars - Ann Ann May May (Wawa) (Wawa) - banquet banquet - Larry Larry Robinson Robinson and and others others of o fthe theWawa Wawa and and District D i s t r i cChamber t Chamberofo Commerce f Commerce conference conference assistance assistance Grant and sstaff Services Grant Southwell Southwell and t a f f ofo fthe theLeisure Leisure ServicesDepartment Department of o fthe theTownTown- ship ship of o f Michipicoten Michipicoten - conference conference f afacilities cilities - Township Michipicoten Council Council —use useo fofconference conference Township oof f Michipicoten f afacilities cilities - Algorna OreDDivision AlgomaSteel SteelCorporation CorporationLtd. Ltd. (Wawa) (Wawa) — f i efield l d t trip rip Algoma Ore i v i s i o n oof f Algoma assistance assistance - Bridget property access Bridget Lake LakeResources Resources Inc. Inc. (Wawa) (Wawa) — property access - CANAMAX Resources Inc. (Timmins) coffee breaks CANAMAX Resources Inc. Timmins) —coffee breaks - Citadel Inc. (Wawa) (Wawa) — f i field e l d ttrip r i p assistance assistance Citadel Gold Gold Mines Mines Inc. - Dunraine Ltd. (Toronto) Dunraine Mines Mines Ltd. (Toronto)— property propertyaccess access - Monk Gold and and Resources ResourcesLtd. Ltd. (Toronto) Monk Gold (Toronto) — property property access access - Muscocho Explorations Ltd. Ltd. (Toronto) Muscocho Explorations (Toronto)— property propertyaccess access -I j J J j J U U 1-I —xii— J �TECHNICAL TECHNICAL PROGRAM PROGRAM One Asterisk IIdentifies One Asterisk d e n t i f i e sStudent Student Papers. Papers. TwoAsterisks Asterisks IIdentify Two d e n t i f y Dual Dual (Oral (Oral & S Poster) Poster) Presentations. Presentations. Speaker/Presenter SpeakerIPresenter Underlined Underlined L I. L L 11 ft —xiii— �SESSION ONE ONE SESSION [ Tuesday Morning Tuesday Morning — May 12, 12, 1987 May 1987 i I 8:00 8:00 8:05 8:05 Allan A l l a n M. M. Goodwin Goodwin and and Ted Ted Bornhorst Bornhorst Co—chairmen: Co-chairmen: I I -- Opening Welcome Opening Welcome Conference Co—chairmen Conference Co-chairmen Greetings Development Greetings from from tthe h e Ontario Ontario Ministry M i n i s t r yofoNorthern f Northern Development && Mines Mines 8:20 K.D. K.D. Card Card Superior Province: Superior Province: the t h e product product of o fArchean Archean convergent pplate convergent l a t e tectonism tectonism 8:40 A. Turek A. Turek The meaning meaning ooff U—Pb andRb-Sr Rb—Sr agesi nin the the The U-Pb and ages Wawa area W awa area 9 :00 T.A. T. A. Vandall Vandal1 && D.T.A. D. T.A. Symons Synons Paleomagnetism Archean granitesi in Paleomaanetism o fofArchean aranites n tthe he Wawa area: definition W awa area: f u further rther de f i n i t i o n ooff the the apparent polar polar wander apparent wander path path 9 :20 R.I. Thorpe, R.I. Thor e, R.P. Sage, & J.M. J. M. Franklin Franklin F. F. Corfu Corfu && 9 :40 R.P. Sagee m . ... 10:40 11:20 11:20 11:40 12:00 precise IJ—Pb zirconage agef ofor trondhjemite AA precise 11-Pb zircon r aa trondhjem cclast l a s t ini nthe t h Dore e Coreconglomerate, conglomerate,Wawa, Wawa, Ontario Ontario coffee coffee 10:00 11:00 11:OO Leadisotope isotopeevidence evidencef ofor anoold Lead r an l d ccrustal rustal source ffor ore leads source o r many many ore leads in i nthe theWawa Wawa region reg d& . ** G.E. G .E. McGill McGill && C.H. Shrady t.H. Shrady Sequence folding, southwest Sequence o foff afaulting u l t i n g and and folding, southwest Michipicoten greenstone greenstonebbelt, Michipicoten e l t , Ontario Ontario G.E. McGill EkhmTf CC.H. H Shrady Shrad && Natureoof cleavage,f ofolding andsstrain Nature f cleavage, l d i n g and t r a i n in in tthe h e Michipicoten Hichipicoten greenstone greenstone belt, b e l t ,near nearWawa, Wawa, Ontario Ontario R.P. R. P. Bowen Bowen Geologyoof Geology f tthe h e Mishibishu Mishibfshu Lake Lake area area ** K.B. ** K.B. Heather Heather Gold mmineralization Gold i n e r a l i z a t i o n of o f the t h eMishibishu Mishi bishuLake Lake greenstone be1 beltt greenstone lunch lunch —xv— �j SESSION T TWO SESSION WO Tuesday Afternoon Afternoon Tuesday Co—chairmen: Co-chai rmen: - May 12, 1987 May 12, 1987 — j John John Klasner K l asner and andGene Gene LaBerge LaBerge U 2:00 2: OO ** E.C. ** E.C. Grunsky Grunsky Geology ooff the area, Ontario Geology the Batchawana Batchawana area, Ontario 2:20 2:20 W.T. W .T. JJolly olly Rhyolite R h y o l i t e and and basaltic b a s a l t i cvolcanism volcanism from from the the Huronian area, central Huronian ooff the t h e Thessalon Thessalon area, central Ontario Ontario 2:40 2:40 3:00 3:OO ** C. C.T. T. Barrie Barrie Geologyand ands tstructural Geology r u c t u r a l hhistory i s t o r y ooff the the Kamiskotia igneous igneous complex, complex,western westernAAbitibi Kamiskotia bitibi Subprovince, Subprovince, Ontario Ontario — "Basement—uplift" tectonics in "Basement-uplift" tectonics i nthe t h eKapuskasing Kapuskasing Structural Zone, Structural Zone, central c e n t r a l Superior Superior Province Province J.A. J.A. Percival Percival b, coffee 3:20 3 20 i Imprint of Imprint o f Archean Archean AAbitibi b i t i b i tectonics t e c t o n i c s on on the the 3:40 R.J. R.J. Shegeiski Shegelski 4:00 4:OO R.H. SSutcliffe R.H. utcliffe Contemporaneousl alate Contemporaneous t e Archean Archean mafic mafic and and granitoid Lac des des llies g r a n i t o i d magmatism magmatism i nin tthe h e Lac ies area, Wabigoon Subprovince, Ontario area, Wabigoon Subprovince, Ontario 4:20 4:ZO H.R. Williams H.R. Williams Fluid F l u i d induced induced structures structures in i nQuetico Quetico metasediments, northern northern Ontario metasediments, Ontario 4:40 4:40 ** W. ** W. Cannon, Cannon, J. Behrendt, 3. Behrendt, Fl. M. Lee, Lee, Proterozoic Lake Lake Superior Superior basin basin AA brief b r i e flook lookat aGLIMPCE t GLIMPCE D. Hutchinson, A. Green, Green, 0. ~ u t c h i n s o n ,A. C. Milkereit, C. Spencer, Spencer, B.B. M ilkereit, P. Morel, P. Morel, A. A. Davidson, Davidson, &6 D. 0. Teskey Teskey I Li s-A j j j U U U �SESSION SESSION Wednesday Morning Morning Wednesday Announcements Announcements 8:20 8:20 * — -- May 13, 13, 1987 May 1987 RoyRupert Rupertand andRichard RichardSSutcliffe Roy utcliffe Co—chairmen: Co-chairmen: 8:15 8:15 THREE THREE Conference Co—chairmen Conference Co-chairmen D.A. D.A. Baxter, Baxter, T.J. Bornhorst, 7.J. Bornhorst, && J.L. Van Aistine J.L. Van ~ lstine Geology,structure, structure, and Geology, and associated associated precious metal mineralization Archean precious metal m i n e r a l i z a t i o n of o fArchean rocks i in the vvicinity rocks n the i c i n i t y ofo fClark ClarkCreek, Creek, Marquette County, Marquette County, Michigan Michigan 8:40 8:40 R.C. R. C. Johnson, Johnson, T.J. Bornhorst, & T.J. Bornhorst, & J.L. Van Alstine J.L. Van A lstine Geology and and precious precious metal Geology metal mineraliza— mineralizaH i l l ' sLakes Lakes area, area, ttion i o n of o f the the Hill1s Marquette County, County, Michigan Marquette Michigan 9:00 9:OO T.J. Bornhorst T.J. Bornhorst && D.A. Baxter D.A. Baxter Geochemicalcharacter character ooff Archean Geochemical Archean rocks rocks from the east half of the northern from t h e east h a l f o f t h e northerncomplex, complex, upper Michigan: Michigan: aa progress progress report report upper 9:20 R.L. R. L. Bauer Bauer Refolding and andf ofold Refolding l d rreorientation e o r i e n t a t i o n during during pluton emplacement regional stress pluton emplacement i ninaa regional stress ffield, i e l d . Vermilion Vermilion granitic g r a n i t i ccomplex, complex, northeastern Minnesota northeastern Minnesota M.E. Bidwell && M .E. Bidwell R.L. Bauer R.L. Bauer two—stagesimple simpleshear shearmodel modelf ofor high AA two-stage r high fflattening l a t t e n i n g strains s t r a i n s ini nshear shear zones zones ooff the the ccentral e n t r a l Vermilion Vermilion ddistrict, i s t r i c t , northeastern northeastern Minnesota Minnesota 9:40 9:40 * coffee coffee 10:00 10:OO 10:40 11:00 D.C. Stewart && D.C. J.M. J. M. Mancuso Mancuso The "Hagar "Hagar Suite" Suite" and The and problems problems concerning and llocation tthe h e nature nature and o c a t i o n ooff the t h e northern northern boundaryo of the Wolf River River bath01 batholith ith boundary f th e Wolf I..Watkins, I Watkins, Rapakivi textures textures of Rapakivi o f central c e n t r a lMinnesota Minnesota G. Anderson, G. Anderson, && P. Erickson P. Erickson 11:20 P.A. P. A. Nielsen Nielsen 11:40 11:40 J.A. Peterson ** J.A. Peterson && C.A. Geiger C.A. Geiger 12:00 Petrologic evolution evolution ooff early Petrologic e a r l y Proterozoic Proterozoi c supracrustal rocks supracrustal rocks from from Florence Florence County, County 9 WI WI and ttheir of the and h e i r bearing bearing on on the t h e development development of the Dunbar Gneiss Dunbar The Hardwood Gneiss, a basic The Hardwood Gneiss, basictwo—pyroxene two-pyroxene ggranulite ranulite lunch lunch —xv ii— �SESSION SESSION WednesdayAfternoon Afternoon Wednesday -- May 13, 13, 1987 May 1987 M.L. Cummings M.L. Cummings Geochemistryo of Geochemistry f PProterozoic r o t e r o z o i c vvolcanic o l c a n i c hosted hosted formations in northern Wisconsin: formations i n n o r t h e r n Wisconsin: prospects prospects ffor o r gold gold mineralization mineralization D. Werbach Werbach AA rreview e v i e w ooff the t h e LaSalle LaSalle Falls F a l l smassive massive sulphide sul phide prospect prospect 2:40 R.R. Dahi, Dahl , D.H. m t k Watkinson, i n s o n , && J.J.W. W. McGoran McGoran TwoDuck DuckLake Lake Coldwell aalkaline Two I n intrusion, t r u s i o n , Coldwell lkaline complex, Ontario. Ontario. 1 1.. Geology and sstructure complex, Geology and tructure 3:00 R. Dahi, R. Dahl, D.H. m t k Watkinson, f n s o n , & JJ.W. .W. McGoran McGoran TwoDuck DuckLake Lake Coldwell a1 alkaline Two i n tintrusion, r u s i o n , Coldwell kal i n e complex, Ontario. 2. Petrology and complex, Ontario. 2. P e t r o l o g y and basebasemetal PGE geochemistry metal PGE geochemistry 2:20 * J ccoffee offee 3:20 3:40 4:00 J Ken Card Card and and Frank Frank Luther Ken Luther Co—chairmen: Co-chairmen: 2:00 FOUR FOUR * A. A . Davidson Davidson && 0. Van 0. VanBreemen Breemen Northeasternextension extensionoof Northeastern f tthe h e Proterozoic Proterozoic igneous terranes of mid—continental igneous t e r r a n e s o f m i d - c o n t i n e n t a l North North flmerica America J.F. Peterman, J.F. Peterman, Geological and and geophysical geophysicali investigation Geological nvestigation of graphite resources o f g r a p h i t e resources in i nupper upper Michigan Michigan 0. Droege, A.A.M. M. Johnson, Johnson, &i J.L. Van J.L. Van Aistine ~lstine 4:20 * 4:40 4:40 ** J.S. J.S. Springer Springer B.J. Prosen B.J. Prosen && A.M. Johnson A.M. Johnson Natural N a t u r a l brine b r i n e contamination contamination of o fgroundwater groundwater in the Keweenawan rocks of northern i n t h e Keweenawan rocks o f n o r t h e r n Michigan Michigan Mesozoicpaleogeography: paleogeography:i mimplications Mesozoic p l i c a t i o n s ffor or economic deposits north of Lake Superior economic d e p o s i t s n o r t h o f Lake Superior j -J j U -J —xviii— �C- POSTER POSTER PRESENTATIONS PRESENTATIONS May 11 11 Monday, May 12 Tuesday, May 12 May 13 13 Wednesday, Hay C.D. Anglin, J.M. Franklin, - brief MacLeod MacLeod Mine geology geology— aa b r i e f review review E.N. Berdusco E.N. Berdusco 3J.. Behrendt, Behrendt, M. M. Lee, Lee, 10:00 pan. 10:OO p.m. 5:00 5:00 p.m. p.m. 5:00 5:OO p.m. p.m. - Geochemistryo of scheelites associated with Geochemistry f scheelites with Archean gold deposits Archean gold hR. Jonasson, I.R. Jonasson, K. Bell, K. B e l l , &&E.E. Hoffman Hoffman W. W. Cannon, Cannon, -- 4:00 4:00 8:00 8:00 8:00 8: OO ** ** brief AA b r i e flook lookat aGLIMPCE t GLIMPCE 0. Hutchinson, 0. Hutchinson, A. A. Green, Green, C. Spencer, B. Milkereit, C. Spencer, B. M i l k e r e i t , P. A. Davidson, Davidson, && P . Morel, Morel, A. M. Teskey M. Teskey P.M. P. M. Eick Eick * Geochemistry andpetrography petrographyoof selected Early Geochemistry and f selected Early Proterozoic metadiabase Proterozoic metadiabase dikes from from Marquette Marquette County, Michigan County, Michigan R.E. R .E. Ernst Ernst && K. Bell K. Bell ** The great great AAbitibi The b i t i b i dyke dyke — ppetrological e t r o l o g i c a l overview overview R.J. R.J. Ferderer Ferderer && V.W. Chandler V.W. Chandler ** The The uutility t i l i t yofoWerner f Wernerdeconvolution deconvolution as as aa E.C. E. C. Grunsky Grunsky K.B. K. B. Heather Heather - geomagneticmapping mappingt otool geomagnetic o l in i n east—central east-central Minnesota Minnesota ** ** ** ** Geology ooff the area, Ontario Geology t h e Batchawana Batchawana area, Ontario Gold mineralization mineralization of Gold o f the t h eMishibishu Mishibishu Lake Lake greenstone bbelt greenstone elt M.A. JJirsa M.A. irsa Stratigraphic S t r a t i g r a p h i c evolution evolution of o f part p a r tofo fthe t h eArchean Archean M.J.P. Kuhns M.J.P. Kuhns && Applicability A p p l i c a b i l i t yofoaf sediment—hosted a sediment-hosted copper copper deposit model Solor Church model ttoo the t h eKeweenawan Keweenawan Solor Church Formation, Formation, R.J. Kuhns R.J. Kuhns metavolcanic bbelt, IItasca t a s c a County County metavolcanic e l t , northern northernMinnesota Minnesota Minnesota Minnesota G.L. LaBerge G.L. LaBerge Major llithological magmatic Major i t h o l o g i c a lunits u n i t in s ithe n t hWisconsin e Wisconsin magmatic terrane: data from fromddrill terrane: new new data r i l l cores cores G.A. G. A. Lehman Lehman U—Pb pitchblende from U-Pb d adatation t a t i o n oof f pitchblende from Dickinson Dickinson County, County, upper Michigan, Michigan, suggests suggestsr reactivation of upper e a c t i v a t i o n of Precambrianstructures structuresduring during formation formation of of the Precambrian the Michigan Basin Basin D.S. McPhee O.S. McPhee - Magnacon Project —Mishibishu Mishibishu Lake Lake greenstone greenstone Magnacon Project beltt be1 —xix— -xix- I �U - D.S. D. S. McPhee HcPhee MagmaProject Project —Michipicoten Michipicoten greenstone greenstone bbelt Magino elt J.D. MMiller, J.D. i l l e r , Jr. Jr. Bedrock geology geology ooff Keweenawan rocksi in Bedrock Keweenawan rocks n tthe he vicinity of Silver bay and Beaver Bay, v i c i n i t y o f S i l v e r bay and Beaver Bay, northeastern Minnesota northeastern Minnesota ' % - T.L. Muir T.L. Muir Stratigraphic S t r a t i g r a p h i c and and sstructural t r u c t u r a l considerations considerations on on the Hemlo gold deposit setting the Hemlo gold deposit s e t t i n g P.A. Nielsen P.A. Nielsen On thef afailure O n the i l u r e of o f the t h e midcontinent midcontinent rrift i f tsystem system to proceed to sea—floor spreading t o proceed t o sea-floor spreading W.I. Rose W.I. Rose Videof field Video i e l d trip t r i ptot othe t h eKeweenaw Keweenaw r irift ft R.J. Rupert R.J. Rupert Structural and geologyooff Citadel Structural and economic economic geology Citadel Gold Gold Mines Inc., Wawa, Ontario Mines Inc., Wawa, Ontario ' C.H. Shrady & G.E. McGill * Structural geology portion Structural geology of o f the t h esouthwestern southwestern p ortion of the Michipicoten greenstone belt, Ontario o f t h e Michipicoten greenstone b e l t , Ontario K.M. Sikkila K. M. S i k k i l a &8 W.J. Gregg U.J. Gregg * metasedi— AA sstructural t r u c t u r a l analysis analysisofoProterozoic f Proterozoic metasediments, northern Falls River, Baraga ments , northern Fa11s River, Baraga County, County, Michigan Michigan J.S. Springer J.S. Springer ** . JJ. Stevenson, Stevenson, J.M.. Mancuso, J M . , 3. Frizado, J. Frizado, Truskoski, &8 PP Truskoski, W. Kneller W. Kneller * D. D. Stone Stone T.J. Suszek T.J. Suszek &8 P.J. Meyer 'P.J. Meyer * 0. Tortosa 0. Tortosa Mesozoicpal paleogeography: implications Mesozoic eogeography: imp1 i c a t i o n s ffor or economic deposits north of Lake economic deposits north o f Lake Superior Superior j U L.A Solid S o l i d pyrobitumen pyrobitumen iin n veins, veins, Panel Panel Mine, Mine, Elliot Lake uranium district, E l l i o t Lake uranium d i s t r i c t , Ontario Ontario Geologyoof the Atikokan Geology f the Atikokan area, area, northwestern northwestern Ontario: an overview Ontario: an overview j Gravity and Gravity and magnetic magnetic evidence evidence for f o r rhomboid rhomboid sedimentary basins in the Wisconsin sedimentary basins i n t h e Wisconsinmagmatic magmatic terrane terrane U * Evidence ffor Evidence o r widespread widespread basement basement decollement decollement structures and related crustal structures and r e l a t e d c r u s t aasymmetry l asymmetryassoci— associated wwith limb ooff the ated i t h the t h e western western limb t h e inidcontinent midcontinent rift .1 Kremzargold gold deposit, deposit, District CANAMAX Kremzar D i s t r i of c t Algoma, o f Algoma. CANAMAX Resources Inc. — Kremzar Gold Mines Ltd. Resources Inc. Kremzar Gold Mines Ltd. rift G.R. G. R. Yule Yule U Reconnaissance geology gneissic Reconnaissance geology o f ofg rgranitic a n i t i c and and gneissic terrane, Wawa District terrane, Wawa D i s t r i c t R. R. Wunderman Wunderman &8 C.T. Young t.T. Young G.R. G.R. Yule Yule U . L I - U Structurally S t r u c t u r a l l y hosted hosted vein vein type type gold gold mineralization, mineralization, Goudreau—Lochalsh gold camp, Goudreau-Lochal sh go1d camp, D iDistrict s t r i c t of o f Algoma Algoma a.- It L �ABSTRACTS ABSTRACTS —xxi- �Geochemistry Geochemistrv of of Scheelites S c h e e l i t e s Associated Associated with w i t h Archean Archean Gold Gold Deposits Deoosi t s C.D. C.D. ANGLIN Survey of ANGLIN (Geological (Geological Survey of Canada, Canada, 601 601 Eooth Booth Street, Street, Ottawa, Ottawa, Ontario, O n t a r i o , K1A K I A OEB) OEB) J.N1. FRANKLIN (same) J.M. FRANKLIN (same) I.R. JONASSON I. R. JONASSON (same) (same) K. K. BELL BELL (Geology (Geology Department,Carleton Department,Carleton University, U n i v e r s i t y , Ottawa, Ottawa, Ontario) Ontario) E. E. HOFFMAN HOFFMAN (Nuclear (Nuclear Activation A c t i v a t i o n Services, Services, Hamilton, Hamilton, Ontario) Ontario) In I n the t h e study of o f gold g o l d deposits, deposits, fundamental fundamental questions questions remain remain regarding r e g a r d i n g the t h e criqin o r i g i n of o f the t h e ore—bearing ore-bearing fluids f l u i d s and and the If t h e absolute a b s o l u t e age age of o f mineralization. mineralization. I f tthe h e timing t i m i n g of of gold gold emplacement emplacement can can be be shown shown to t o be be related r e l a t e d to t o specific s p e c i f i c maymatic magmatic or metamorphic events, then very specific geological o r metamorphic events, then very s p e c i f i c g e o l o g i c a l criteria c r i t e r i a for f o r these these events events can can be be documented, documented, and and new new or or refined guidelines for exploration can be defined. To r e f i n e d g u i d e l i n e s f o r e x p l o r a t i o n can be defined. To date, date, attempts attempts to t o determine determine the t h e absolute a b s o l u t e timing t i m i n g of o+ emplacement emplacement 0+ of gold g o l d have have been been frustrated f r u s t r a t e d by by the t h e lack l a c k of o f suitable s u i t a b l e minerals minerals for f o r dating d a t i n g by by conventional conventional radiometric r a d i o m e t r i c dating d a t i n g techniques. techniques. This T h i s study study was was initiated i n i t i a t e d to t o follow f o l l o w up up aa suggestion suggestion by by Ludden common constituent constituent Ludden et. et. al. a l . (1984) (1984) that t h a t scheelite, s c h e e l i t e , aa common of o f gold—bearing gold-bearing veins, v e i n s , may may be be aa suitable s u i t a b l e mineral mineral for f o r Rb/Sr Rb/Sr and In and Sm/Nd Sm/Nd isotopic i s o t o p i c analysis. analysis. I n addition, a d d i t i o n , scheelite s c h e e l i t e may may be be suitable s u i t a b l e for f o r U/Pb U/Pb isotopic i s o t o p i c determination, determination, and and 0—isotope 0-isotope analysis. Boyle of: analysis. Boyle (1979) (1979) has has noted noted the t h e close c l o s e association a s s o c i a t i o n of scheelite s c h e e l i t e with w i t h gold g o l d mineralization, m i n e r a l i z a t i o n , and and pointed p o i n t e d out o u t that that scheelite s c h e e l i t e "occurs "occurs in i n [gold] [ g o l d ] deposits d e p o s i t s of of all a l l ages ages from from Precambrian For Precambrian to t o Tertiary". Tertiary". For this t h i s reason, reason, aa preliminary preliminary examination examination of of the t h e trace t r a c e element element and and REE REE contents c o n t e n t s of of scheelites s c h e e l i t e s from from gold g o l d deposits d e p o s i t s has has been been undertaken undertaken to to determine determine if i f the t h e levels l e v e l s of o f REE, REE, U U and and Sr S r would would be be sufficient sufficient for f o r isotopic i s o t o p i c study. study. To To date, date, more more than than 30 30 samples samples of of scheelite s c h e e l i t e have have been been collected c o l l e c t e d from from active a c t i v e or o r past p a s t producing producing gold g o l d mines mines or or prospects. 19 prospects. 19 samples samples were were analyzed analyzed for f o r their t h e i r trace trace element and rare earth element (REE) contents by element and r a r e e a r t h element (REE) c o n t e n t s by E. E. Hoffman, Hoffman. Nuclear Activation Services. All samples were associated Nuclear A c t i v a t i o n Services. A l l samples were associated spatially s p a t i a l 1y with w i t h gold, gold, and and several several contained contained native n a t i v e gold. gold. The The scheelite s c h e e l i t e samples samples typically t y p i c a l l y contain c o n t a i n several several tens t e n s of of ppm ppm of o f REE, REE, very v e r y abundant abundant strontium s t r o n t i u m and, and, in i n some some samples, samples, abundant The abundant uranium. uranium. The variation v a r i a t i o n in i n the t h e content content of of strontium strontium in i n scheelite s c h e e l i t e from from samples samples within w i t h i n aa single s i n g l e deposit d e p o s i t is i s generally g e n e r a l l y very v e r y restricted, r e s t r i c t e d , but b u t samples samples from from different different districts At d i s t r i c t s show show wide wide variations. variations. A t the t h e Sigma Sigma Mine, Mine, Sr Sr contents c o n t e n t s range range between between 100 100 and and 200 200 ppm, ppm, whereas whereas in i n Timmins Timmins scheelites s c h e e l i t e s typically t y p i c a l l y contain c o n t a i n 2400 2400 ppm, ppm, those those from from Geraldton Geraldton contain c o n t a i n an an average average of of 7i00ppm 7SOOppm and and those those from from Vellowknife Y e l l o w k n i f e are are highly The h i g h l y variable v a r i a b l e and and enriched enriched over over the t h e other o t h e r deposits. deposits. The contents S r in i n all a l l cases cases are a r e sufficient s u f f i c i e n t to t o permit permit c o n t e n t s of o f Sr —1— �U U determination d e t e r m i n a t i o n of of iinitial n i t i a l uvSr/FJtsr B'7Sr/-^eSr rratios, a t i o s , which g i v e an an which may give indication i n d i c a t i o n of of the t h e primary primary fluid f l u i d composition, composition, and andof of jnantlc mantle crustal versus c r u s t a l sources. sources. within with strontium, As w ith s t r o n t i u m , the t h e REE REE contents contents w ithin a a single single deposit d e p o s i t or o r district d i s t r i c t are a r e typically t y p i c a l l y quite q u i t e uniform, uniform, but but significant s i g n i f i c a n t variations v a r i a t i o n s exist e x i s t between between groups groups of o f deposits. deposits. Both the t h e Geraldton and and Sigma Sigma samples samples contain c o n t a i n between between 33 and and 10 ppm (avth-age 9ppm) La, La, whereas whereas tthe Timmins samples (average oof f 9ppm) h e Timmins have S r , the t h e REE: REE have 14 14 to t o 28 28 ppm ppm (average (average 23 23 ppm) ppm) La. La. As with w i t h Br, contents c o n t e n t s of o f scheelite s c h e e l i t e from from Yellowknife Y e l l o w k n i f e are a r ehighly h i g h l yvariable., variable, generally and g e n e r a l l y enriched enriched over over the t h e other o t h e r deposits. deposits. Chondrite—normalized Chondrite-normalized REE REE patterns p a t t e r n s illustrate i l l u s t r a t e two two features; 1) 1) all a l l samples samples have have aa significant significant features; positive p o s i t i v e Eu anomaly which may may indicate i n d i c a t e that t h a t Eu Eu was was transported reduced sstate 2 ) th3 the t r a n s p o r t e d iin n tthe h e reduced t a t e iin n tthe h e oore r e f fluid l u i d ; 2) PEE patterns may be be separated separated iinto two groups: groups i) samples i) samples R EE p a t t e r n s may n t o two Timmins, which have from Timmins, have a a relatively r e l a t i v e l y flat f l a t REE REE profile, p r o f i l e , with with anomaly, and ii) distinctive a d i s t i n c t i v e positive p o s i t i v e Eu ii)samples from Eu anomaly, Sigma in Sigma which display d i s p l a y a pattern p a t t e r n with with a a broad broad positive p o s i t i v e hump hump in The tthe h e intermediate i n t e r m e d i a t e REE's. REE's. The I3eraldton—Beardmore Geraldton-Beardmore samples samples show both b o t h types t y p e s of of profile. profile. interesting interesting both and heavy rrare IInn b o t h groups, groups, the t h e light light A d heavy a r e earths e a r t h s(LREE ' (LREE and HREE) HREE) have approximately and approximate1y the t h e same same chondrite—normalized chondri te-normal ized contents. Either E i t h e r the t h e samples samples with w i t h the t h e broad broad hump hump have have incorporated i n c o r p o r a t e d tthe h e 'middle" "middle" PEE REE more more efficiently e f f i c i e n t l y than than the the other group, or else the PEE compositions of the o t h e r group, o r e l s e t h e REE compositions o f t h e mineralizing m i n e r a l i z i n g fluids f l u i d s of of each each group group were were different. different. IIonic onic radius and charge conditions which controlled the PEE radius c o n d i t i o n s which c o n t r o l l e d t h e REE distribution d i s t r i b u t i o n in i n scheelite s c h e e l i t e should be be constant (with ( w i t h the the exception , and different exceptionofo fELI) Eu), and tthus hus d i f f e r e n t fluid f l u i d compositions compositions seem seem a more likely explanation off the differences likely e xplanation o the d i f f e r e n c e s in i n shape of of the the However, patterns. patterns. However, possible p o s s i b l e temperature temperature and and pressure pressure dependence of o f the t h e PEE REâ partitioning p a r t i t i o n i n g need need to t o be be considered considered further. further. J U U U j preliminary From our our p r e l i m i n a r y data, data, it i t is i s clear c l e a r that t h a t continued continued study of w i l l yield yield o f scheelite s c h e e l i t e and and other o t h e r accessory accessory minerals, minerals, will more information i n f o r m a t i o n on the t h e source source of o f mineralizing m i n e r a l i z i n g fluids f l u i d s for for gold go1d deposits. deposits. References References U Boyle, R.W., R.W., 1979; 1979; The geochemistry of o f gold g o l d and its i t s Boyle, deposits, Geological Survey deposits, Survey of o f Canada Canada Bulletin Bulletin no.280, no.280, 584p. 584p. Ludden, U.N., J.N., Daigneault, Daigneault, P., R., Robert, Robert, F., F., and andTaylor, T a y l o r , R..P., R.P., Ludden, 1984; Trace element mobility mobi 1it y in i n alteration a1t e r a t i o n zones zones associated with w i t h Archean Archean Au Au lode l o d e deposits. deposits. Economic Geology Geology v.79, v.79, no. no. 5,, p Economic 1131-1141. p 1131—1141. —2— U U �Geology andsstructural Geology and t r u c t u r a l history h i s t o r yofo fthe t h eKamiskotia Kamiskotia Igneous Complex, western Abitibi Subprovince, Igneous Complex, western A b i t i b i Subprovince, Ontario Ontario C. BARRIE (Department Geology,University University ooff Toronto, C. TUCKER TUCKER BARRIE (Department o f of Geology, Toronto, Toronto, M5S 1A1) 1A1) Toronto, Ontario Ontario M55 The The Kamiskotia Kamiskotia Igneous Igneous Complex Complex (KIC), (KIC), located located 30 30 km km west west of of Timmins, Tinunins, Ontario Ontario near near the the western western margin margin of of the the Abitibi Abitibi Subprovince, Subprovince, is is composed composed of of the the Kamiskotia Kamiskotia Gabbro Gabbro (KG), (KG), aa large large (>200 0 2 0 0 km2) km2) anorthositic anorthositic gabbroic gabbroic intrusion, intrusion, and and the the overlying overlying Kamiskotia Kamiskotia Volcanics Volcanics (XV), (KV), aa bimodal, bimodal, tholeiitic tholelitic volcanic volcanic pile pile that that hosts hosts significant mineralization 0 (>5 mu, tons significant massive massive sulfide sulfide mineralization 5 mil. tons The KIC is underlain by a Cu-Zn ore recovered). Cu-Zn ore recovered). The KIC is underlain by a 22 mm thick thick oxide—sulfide oxide-sulfide iron iron formation formation and and aa sequence sequence of of tholeiitic mafic volcanic rocks, and is intruded tholeiitic mafic volcanic rocks, and is intruded by by four four distinct distinct tonalitic tonalitic masses. masses. In In order order to to unravel unravel the the structural structural history history of of the the KIC, detailed structural mapping of penetrative and KIC, detailed structural mapping of penetrative and nonnonpenetrative penetrative fabrics fabrics is is presented, presented, along along with with preliminary preliminary U—Pb U-Pb geochronology qeochronology to to constrain constrain the the timing timing of of deformation deformation and and magmatism. magmatism. There There are are three three prominent prominent structural structural features features in in the the region. region. 1) 1 ) AA broad broad regional regional monocline monocline facing facing to to the the north north and and east east has has affected affected all all lithologies except three late tonalitic intrusions. 2) lithologies except three late tonalitic intrusions. 2 ) Contact Contact strain strain aureoles aureoles are are present present around around three three tonalitic intrusions, and extend up to tonalitic intrusions, and extend up to two two km km to to either either They are defined by a side of their contacts. side of their contacts. They are defined by a wellwelldeveloped developed flattening flattening fabric fabric parallel parallel to to the the contact contact accompanied by a strong elongation fabric accompanied by a strong elongation fabric locally. locally. There There is is evidence evidence for for overprinting overprinting of of one one contact contact strain strain A fourth tonalitic body aureole aureole on on another. another. A fourth tonalitic body located located at at the the center center of of the the KG KG does does not not have have an an associated associated contact contact strain strain aureole. aureole. It It is is characterized characterized by by clear clear magma magma mixing mixing textures textures between between tonalitic tonalitic and and gabbroic gabbroic material. material. 3) 3 ) AA predominately predominately east—trending, east-trending, non-penetrative non-penetrative fabric fabric crosscuts crosscuts stratigraphy stratigraphy and and is is pervasive pervasive throughout throughout the the region. region. this This fabric fabric is is particularly particularly well—developed well-developed in in the the felsic felaic volcanics volcanics of of the the KV. KV. +~ - 'k .' . a Preliminary Preliminary precise precise U—Pb U-Pb zircon zircon and and sphene sphene geochronology* indicates that the voluminous qeochronoloqy* indicates that the voluminous tholeiitic tholeiitic and calc-alkalic magmatism magmatism and and deformation deformation in in the the and calc-alkalic Kamiskotia Kamiskotia area area occurred occurred within within aa 15 15 Ma Ma interval. interval. Two Two samples samples from from the the KIC, KIC, aa quartz quartz pegmatitic pegmatitic gabbro qabbro from from the flow-banded rhyolite rhyolite from from the the XV KV are are coeval coeval the KG KG and and aa flow-banded at at 2705 2705 Ma. Ha. This This agrees agrees with with field field and and geochemical geochemical evidence evidence for for the the derivation derivation of of the the XV KV from from aa supracrustal supracrustal magma magma chamber chamber that that crystallized crystallized to to form form the the KG. KG. AA foliated foliated hornblende hornblende tonalite tonalite along along the the western western —3— �1-i U margin of One abraded sphene margin of the the KG is is 2697 2697 Ma. Ma. One sphene from this this sample is at 2692 fraction from is nearly concordant at 2692 Ma, suggesting a protracted cooling history, or a Ma, suggesting a protracted cooling history, or a dynamic metamorphic event 55 Ma after crystallization to reheat the reheat the sphene sphene past past its its blocking blocking temperature. temperature. AA foliated biotite tonalite from within margins of the foliated biotite tonalite within the margins KG has two nearly concordant zircon fractions KG has two nearly concordant zircon fractions at at 2692 2692 Ma. A third abraded fraction has a 207/206 age of 2926 Ma. A third abraded 2926 Ma and and is These data data can Ma is 4.6% 4.6% discordant. discordant. These can be be interpreted as as defining defining aa mixing mixing line line between between 2692 2692 Ma Ma interpreted and approximately 3500 Ma, indicating inheritance of and approximately 3500 Ma, indicating inheritance of xenocrystic zircon zircon from a much xenocrystic from a much older older crustal crustal component. component. work is Further work is in in progress progress to to analyze analyze older older zircon zircon populations, and and better better establish the evidence for very populations, old crust in the Kamiskotia area. old area. The KIC intruded into into previously existing crustal material composed of tholelitic tholeiitic mafic volcanics and an an older component, component, probably felsic During older felsic intrusive intrusive rock. rock. During the crystallization of the KG, KG, a caic—alkalic calc-alkalic tonalitic tonalltic magma was was injected into its center and mixed with the . mixed resident tholeiitic magma. Approximately 10 Ma later, resident later, a series of tonalitic intrusions were vertically emplaced intrusions into and and along along the margins of the KG, into KG, and subsequently expanded in situ to produce the well-developed well-developed flattening fabrics that characterize their contact strain aureoles. Between 2705 and 2695 Ma., Ma., a non— strain aureoles. nonpenetrative deformation event formed penetrative formed the large monoclinal structure across the Kamiskotia region. monoclinal region. Later north—south north-south compression compression formed formed the the regional regional easteasttrending, non-penetrative non—penetrative fabric. trending, fabric. With its magmatic magmatic and structural history, With history, the Kit KIC similar to several mafic intrusions that border is similar border granitoid terrane in granitoid in northwestern Ontario, Ontario, and appears Doze Lake to be comparable to the Sell Bell River and Dore Complexes in in Quebec. Bedding attitudes and structural structural are compatable compatable with predominately vertical vertical fabrics are movement of crustal material. There is little evidence movement material. There that modern day plate tectonic processes played a role role in the evolution of of the the KIC. KIC. Li j La U - U J J errors in in age age determinations are approximately +/—2 *All errors +/-2 Ma. Ages and errors will be modified as geochronologic work progresses. —4— U �Refolding andfold fold reorientation Refolding and reorientation during durin pluton regionalstress stressfield, field, pluton emplacement emplacement in ina aregional Vermilion Vermilion Granitic GraniticComplex, Complex, northeastern northeasternMinnesota Minnesota ROBERT BAUER (Department of Geology, Universityof of Missouri, Missouri, ROBERT L. L.BAUER (Department of Geology, University Columbia, Columbia, Missouri Missouri 65211, 65211, U.S.A.) U.S.A.) Archean schists and migmatites along along the the southern of the Archean schists and migmatites southern margin margin of the Vermilion southeastof of the the Lac La Croix Croix batholith batholith Vermilion Granitic Granitic Complex, Complex, southeast Lac La (LLB), undergonethree threeperiods periodsofofregional regional ductile ductile deformation. have undergone deformation. (LLB) , have Both of regional N—S Both F, F and and F F folds foldsformed formedasasa aresult result of regional N-Scompression. compression. However, F fdlds and local noncylindrical variations in ow eve?, F here f8lds and local noncylindrical variations inF9 F are are interpreted to be an indirect result of country rock interpreted here to be an indirect result of country rock teorientation reorientation during of the during the theemplacement emplacement of the LLB. LLB. F folds folds along along most most of of the thesouthern southern margin margin of of the theLLB LLB are are generally generally F cylndrical have relatively relatively constant cylindrical and and have constantSW-plunging SW-plunging hinges hinges and and east- striking in the the Burntside strikingaxial axialplanes. planes. However, However, in Burntside Lake Lake area, area, along along the the southeast margin of the LLB, large—scale F9 parasitic folds become southeast margin of the LLB, large-scale F parasitic folds become noncylindrical, noncylindrical,and andF,, F fold foldhinges hingesrange rangefrom fromSW SW to to NE NE plunging plunging within within the local F2 axial planes. In this same area, local tonalite the local Fn axial planes. In this same area, local tonaliteveins veinshave have undergone counterclockwise rotation undergone aa counterclockwise rotationproducing producingS—syninetry S-symetry drag drag patterns patterns in the local local F, in the the S. S foliation foliationcut cutby bythe theveins. veins. Both Both the F noncylindricity noncylindricity and the drag drag patterns patterns adjacent adjacenttotoveins veinsare areattributed attributed to to aa and the counterclockwise rotation of counterclockwise rotation of the thecountry countryrocks rocksalong along the thesoutheast southeast margin of the in aa continuing margin of the LLB LLB during during its itsprogressive progressiveemplacement emplacement in continuing N-S N-S compressional the LLB LLB continued, continued, aa doubly compressional regime. regime. As As emplacement emplacement ofof the doubly plunging parallel to plunging F F synform synform developed developed parallel tothe thesoutheastern southeastern margin margin of the the LLB, refolding both the earlier earlier F2 LLB, refolding both the Fn folds folds and and the the tonalite tonalite veins veins displaying displaying adjacent adjacent drag drag patterns. patterns. Other to WNW-trending axialplanes planes occur occur to to the Other F3 F3 folds folds with withW— W- to WNW-trending axial the southwest of the LLB wherethey theynoncylindrically noncylindrically refold regional southwest of LLB where regional F9 F folds 1986). The The FF folds folds(Bauer, (Bauer,1985, 1985, 1986). folds in in this thisarea areaare are interpreted interpreted to to have been reoriented reoriented to have been tothe theNW NW dJing duringemplacement emplacement of of the theLLB LLB and and then then refolded F3 during duringcontinued continuedN-S N-S regional regionalcompression. compression. refolded by by F3 These variations ininfold These variations foldgeometry geometrysuggest suggestthat thatemplacement emplacement of the theLLB LLB caused late—stagemodifications modificationsin in the regional caused late-stage regional fold foldgeometries geometriesbut butwas was not thethe N—S not responsible responsibleforfor N-Scompression compression which which caused caused the theF2 F2and and F3 F3 folds. folds. Bauer, Bauer, R.L., R.L., 1985, 1985,Geologic Geologicmap map of ofthe theNorwegian Norwegian Bay Bay quadrangle, quadrangle, St. St. Louis County, Minnesota: Minnesota Geological Survey, Miscellaneous Louis County, Minnesota: Minnesota Geological Survey, Miscellaneous Map Series, Map (scale == 1:24,000). Map Series, Map M—59, M-59, (scale 1:24,000). 1986, emplacement 1986, Multiple Multiplefolding foldinand andpluton pluton emplacement ininArchean Archean migmatites GraniticComplex, Complex, northeastern northeastern migmatites of of the thesouthern southern Vermilion Vermi ionGranitic Minnesota: Journal of of Earth Minnesota: Canadian Canadian Journal Earth Sciences, Sciences, v. 23, 23, p. p. 1753-1764. 1753-1764. 7 —5— �J Geology, structure, and associated precious metal mineralization of Archean rocks in the vicinity j of Clark Creek, Marquette County, Michigan D.A. BAXTER BAXTER and BORNHORST (Dept. o fofGeology D.A. andT.J. T.J. BORNHORST (Dept. Geology& &Geol. Geol. Engrg., Engrg., Michfgan Tech. Tech. U University, Michigan n i v e r s i t y ,Houghton, Houghton, MI M I49931) 49931) J .L. VAN VAN ALSTINE ALSTINE (Geological i v i s i o n ,Michigan Michigan Department Department ooff J.L. (GeologicalSurvey SurveyDDivision, M I 48909) 48909) Resources, Lansing, Lansing, MI Natural Resources, The Clark Creek Creekr region The Clark e g i o n l lies i e s within w i t h i n the t h eIshpeming Ishpeming Greenstone Greenstone BBelt e l t iin n the the nnorthern o r t h e r n portion p o r t i o n of o fMarquette Marquette County. County. This T h i s area area iiss currently c u r r e n t l y being being ttested e s t e d by by several several mining m i n i n gcompanies companies for f o r the t h epresence presence of o feconomic economic gold gold mineralization. m i n e r a l i z a t i o n . The The ooldest l d e s t rocks h e area r e ppart a r t of o f aa rocks observed observedi nin tthe area aare succesion ooff steeply s t e e p l y dipping d i p p i n gArchean Archean metavolcanics metavol cani c s known known as h e MetavolMetavolsuccesion as tthe canics canics of Silver S i l v e rMine MineLakes. Lakes. This T h i s group group was was named named ooriginally r i g i n a l l ybybyOwens Uwens lY85 (Michigan (MichiganGeological GeologicalSurvey SurveyDivision D i v i s i oReport n Report OFRand Bornhorst i n1985 and Bornhorst in OFR— 85—2; 85-2; 1985 east of the t h e Clark C l a r k Creek Creek region region 1985ILSG) ILSG)i ninan anarea areaimmediately imediately east and t o PPillowed i l l o w e d BBasalt, a s a l t , Pyroclastic, Pyrocl a s t i c , Iron I r o nFormation, Formation, and was wassubdivided subdividedi ninto and and Laminated Schist S c h i s tmembers. members. In I n 1986, 1986, Johnson Johnson and and oothers t h e r s (Michigan (Michigan Geological Survey OFR-86—2; Survey Division D i v i s i o Report n Report OFR-86-2; 1986 1986 ILSG) ILSG) rreported e p o r t e d on on an an area immediately t h ewest westwhich which contained contained foliated, f o l i a t e d ,non—foliated, n o n - f o l i a t e d , and and area imediately tot othe highly altered basalts of unknown stratigraphic relationship to the h i g h l y a1 t e r e d basal t s o f unknown s t r a t i g r a p h i c re1 a t i o n s h i p t o t n e Metavolcanics S i 1v e r Mine Mine Lakes. Lakes. Metavol canics ooff Silver J j This two areas areas and andr revision T h i s study study allows a l l o w s correlation c o r r e l a t i o n between between tthe h e two e v i s i o n ooff the the members Metavolcanicso of Lakest to members w iwithin t h i n t hthe e Metavolcanics f SSilver i l v e r Mine Mine Lakes o ((from f r o m ooldest l d e s t to to youngest): Willow Creek PPyroclastic youngest): Lower Lower Pillowed P i l l o w e d Basalt B a s a l t Member, Member, W i l l o w Creek y r o c l a s t i c and and Pillowed IIron r o n Formation Formation Member, Member, and and Upper Upper Pi1 lowed basalt b a s a l tMember. Member. The The Upper Upper Pillowed subdividedi ninto altered, P i 1lowed Basalt B a s a l t Member Member i sissubdivided t o hhighly i g h l y a1 tered, foliated, f o l i a t e dnon— , nonNumerous ffoliated, o l i a t e d , and and laminated 1aminated sschist c h i s t vvarieties. arieties. Numerous p ipillow 11ow sstructures t r u c t u r e s in in the t h e basalts b a s a l t s consistently c o n s i s t e n t l yshowed showed tthe h e ttop o p of o f beds beds to t o be be towards towards the t h e southsouthsouthwest. Wherev ivisible, andl ilithologic southwest. Where s i b l e , bedding bedding and t h o l o g i c contacts c o n t a c t s strike s t r i k ebetween between and~N75°W from NNO'W ~ O ' W and 7 5 'and ~ and d i pdip from 70"70° t o to v evertical, r t i c a l , ggenerally e n e r a l l y tto o the t h e southwest. southwest. The metavolcanics metavolcanics aare The r e iintruded n t r u d e d by by the t h eArchean Archean Metagabbro Metagabbro ooff Clark Clark Creek, Creek, which roughly roughly pparallels During the t h e Late L a t e Archean Archean the t h e area areawas was which a r a l l e l s bedding. bedding. During subjected ttoo aa period and metamorphism. subjected p e r i o d of o fintense i n t e n s edefomation deformation and metamorphism. Most Most field comes f i e l devidence evidence for f o rthis t h ievent s event comesfrom fromthe t h epresence presence of o fmappable mappable ftaults aults basedononl i lithologic based t h o l o g i c ccontact o n t a c t ddiscontinuities, i s c o n t i n u i t i e s , highly h i g h l y sheared sheared iintrusive ntrusive contacts, zoneso of contacts, and and zones f hhighly i g h l y ffoliated o l i a t e d to t oschistose s c h i s t o s ebasalts, b a s a l t s , many many of Most foliations have strikes which we interpret as shear zones. which we i n t e r p r e t as shear zones. Most f o l i a t i o n s have s t r i k e s of The Archean between N60°Wand and~N75'W 60. and and vvertical. e r t i c a l . The between N6O0W 7 5 w ' with i~t h ddips i p s between between 60 Rhyolite Intrusive of Fire Center Mine intrudes pre—existing rocks R h y o l i t e I n t r u s i v e o f F i r e Center Mine i n t r u d e s p r e - e x i s t i n g rocks in i n aa dike d i k e to t o sill—like s i l l - l i k emanner. manner. Field F i e l d relationships r e l a t i o n s h i p ssuggest suggestthat t h a these t t h e s erhyo— rhyoThe Archean rocks rocks are l i t e sare a r esyn— syn- to t o post—tectonic. post-tectonic. The Archean a r e unconformably unconformably lites Proterozoic ooverlain v e r l a i n by by quartzites q u a r t z i t e sand andslates s l a t e sof othe f t hLower e Lower P r o t e r o z o Michigamme i c Michigamme Formation. Formation wasmetamorphosed metamorphosedand andf afaulted Formati on. The The Michigamme Michi gamine Formati on was u l t e d near T h i s orogeny orogeny tthe h e end end of o f the t h eLower Lower Proterozoic P r o t e r o z o i cbybythe t h ePenokean Penokean orogeny. orogeny. This was was aalso l s o rresponsible e s p o n s i b l e ffor o r reactivation r e a c t i v a t i o nofo Archean f Archean faults f a u l t sand andminor m i n o rsecondsecondMiddle i d d l e Protero— Proteroary within a r y metamorphic metamorphic ooverprinting verprinting w i t h i n the t h eArchean Archean rocks. rocks. M diabase zzoic o i c (Keweenawan) (Keweenawan) diabase d i kdikes, e s , t ytypically p i c a l l y east—west east-west t r trending, e n d i n g , ccut u t aalll l Additional off the o t h e older o l d e r rock rock units u n i t s and and structures. structures. A d d i t i o n a l sstratigraphic t r a t i g r a p h i c details details will bepublished p u b l i s h e dini na 1987 a 1987Michigan Michigan Geological Geological Survey Survey Division D i v i s i o n Open Open FFile ile w i l lbe Report. Report. -6- U �Mineralization quartz— M i n e r a l i z a t i o n in i n the t h e region region exists e x i s t s ini ntwo twoforms: forms: 1) 1)epigeneti epigenetic quartz- carbonate—suiphi veins,and and2)2)disseminated di sseminatedsul sulphides altered carbonate-sulphide de veins, phides wwithin i t h i n a1 tered country rocks. The epigenetic quartz veins are often associated with country rocks. The epigenetic quartz veins are o f t e n associated with shear andf faults. The most most common common gangue mineralsi nin these these veins shear zones zones and a u l t s . The gangue minerals veins are carbonate,wwith amountso fofp pyrrhotite, are quartz quartz and and carbonate, i t h llesser e s s e r amounts y r r h o t i t e , chalcopyrite, chalcopyrite, and arsenopyrite. Disseminated mineralization is most prominent i in and arsenopyrite. Disseminated m i n e r a l i z a t i o n i s most prominent n the the highly altered variety of the Upper Pillowed Basalt Member but also h i g h l y a l t e r e d v a r i e t y o f t h e Upper Pillowed Basalt Member but a l s o occurs occurs This m mineralization ttoo aa much much llesser e s s e r degree degree iinn other o t h e r Archean Archean rock rock types. types. This ineralization consists of by minor minor amounts amountso fofppyrrhotite consists o f disseminated disseminated pyrite p y r i t eaccompanied accompanied by yrrhotite and chalcopyrite. The gangue minerals in the altered and chalcopyrite. The gangue minerals i n t h e a l t e r e d country country rocks rocks are are primarily Locally, galena and galena and p r i m a r i l y sericite, s e r i c i t e , quartz, quartz, chlorite, c h l o r i t e and . andcarbonate. carbonate. Locally. sphalerite are the dominant disseminated sulphide minerals. s p h a l e r i t e are thedominant disseminated sulphide minerals. 7 - A which yyielded A limited l i m i t e dnumber number of o f gold goldassays assays was was completed, completed, some some ooff which ielded anomalous values. values. The The highest highest values values were werefrom fromt hthe e hhighly i g h l y altered altered anomalous variety Member. Additional anomalous anomalous values values v a r i e t y ofo fthe t h eUpper UpperPillowed Pi1lowedBasalt Basalt Member. Additional for f o r gold goldwere were obtained obtained from from the t h eWil W i llow low Creek Creek Pyroclastic P y r o c l a s t i cand and Iron I r o nFormaFormation andBornhorst Bornhorst(1985) (1985)also also found found anomalous anomalousgold goldi in n tthis his Owens and t i o nMember. Member. Owens member which representaachemically chemicallyfavorable favorablehost host tfor member which wewe i n tinterpret e r p r e t t otorepresent or gold mineralization. An anomalouss silver obtained from An anomalous i l v e r assay assay was was obtained from an an area area gold mineralization. with enamineralization. mineralization. w i t h shear shear zone zone associated associated gal galena , —7— �Ii LI U - Mine Geology Geology - AA B Brief MacLeod Mine MacLeod r i e f Review Review N. BEROUSCO BERDUSCO E. N. E. (Algoma Ore Ore D Division, Wawa, O Ontario (Algoma i v i s i o n , Wawa, ntario P05 IKO) POS 1KO) ii located 235 235 kilometers The MacLeod MacLeod iiron The r o n oore r e (siderite) ( s i d e r i t e ) mine mine iiss located kilometers north off Wawa by highway, north kilometers n orth o Wawa by highway, n o r t h of o f Sault Sault Ste. Ste. Marie, Marie, 44 kilometers the Canadian and lies the Wawa Wawa Belt and l i e s within w i t h i n the B e l t of o f the Canadian Shield's S h i e l d ' s Superior Superior Province, downward extension extension oof the depleted depleted Helen Heln and a downward IItt iiss a f the and Province. single orebody together formed a Victoria orebodies which all V i c t o r i a orebodies which a l l together formed a s i n g l e orebody iin n The siderite—pyrite, the Helen the Helen IIron r o n Range Range (Goodwin, (Goodwin, 1964). 1964). The s i d e r i t e - p y r i t e , banded banded chert c h e r t iron i r o n formation formation is i s conformable conformable within w i t h i n underlying underlying felsic f e l s i c tuffs, tuffs, pillow lavas. overlying intermediate flows and agglomerate, and agglomerate, and o v e r l y i n g intermediate flows and p i l l o w lavas. limb of aa forms the south This continuous uninterrupted sequence This continuous u n i n t e r r u p t e d sequence forms the south limb of is overturned to the north, strikes east—west, dips syncline that s y n c l i n e t h a t i s overturned t o t h e north, s t r i k e s east-west, d i p s south an average average o off 60°and south an 60°an plunges plunges 35°east. 35Oeast. from 180 180 tto 730 meters MacLeod Mine which extends MacLeod Mine ssiderite, i d e r i t e , which extends from o 730 meters in length, 60 meters meters the shaft collar, averages 2 kilometers below below the s h a f t c o l l a r , averages 2 kilometers i n length, 60 which widens half of the mine, in width and in the east i n w i d t h and i n the east h a l f o f the mine, which widens tto o aa low iron high chert central silica maximum 150 meters, contains a maximum 150 meters, contains a low i r o n h i g h c h e r t c e n t r a l s i l i c a An average grade of from 33 tto 20 meters o 20 meters iin n width. width. An average iinn ssitu i t u grade of rrib i b from 3.86% S, Si02, 2.85% CaO, 5.60% 5.60* siderite Fe, 3.86% 5, 6.89% SiO,, 2.85* CaO, 35.3% Fe, 35.3% 6.89% s i d e r i t e iis: s: MgO, 0.70% 0.70% A1203, MgO, A 1 2 0 2.02% 2.02% Mn. Mn. the from the the s siderite contact, the descending descending order order from i d e r i t e ffootwall o o t w a l l contact, all the rocks may few meters each, o off any any o orr a may grade grade iinto a rocks nto a few meters each, l l ooff the interbanded and ffollowing ollowing interbanded cchert hert and ssiliceous iliceous ssiderite, iderite, orr dike, pyrite—argillite, p y r i t e - a r g i l l i t e , ffuchsite u c h s i t e bearing bearing felsic f e l s i c iintrusive n t r u s i v e sill sill o dike, encountering 60 60 meters ooff siliceous before 90 meters s i l i c e o u s ssiderite, iderite, before encountering tto o 90 the comon iinn the carbonated ffelsic pyroclastics. Chioritoid carbonated elsic p yroclastics. C h l o r i t o i d iiss common The massive underlying volcanics. volcanics. The massive siderite s i d e r i t e grades grades upwards upwards iinto n t o aa width and then 15 meters meters iin high high pyrite p y r i t e zone zone from from 33 tto o 15 n w i d t h and then into i n t o several several Some by upper volcanics. hundred meters of banded chert topped hundred meters o f banded c h e r t topped by upper volcanics. Some thin bands of zones in upper banded chert member contain the zones i n the upper banded c h e r t member c o n t a i n t h i n bands of The latter two minerals are also jasper, magnetite and pyrrhotite. jasper, magnetite and p y r r h o t i t e . The l a t t e r two minerals a r e a l s o not uncommon iin and they they freauently not uncommon n ssiderite i d e r i t e and f r e q u e n t l y occur occur with w i t h pyrite, pyrite, veins. Large ankerite and calcite in narrow quartz a n k e r i t e and c a l c i t e i n narrow quartz veins. Large iirregular rregular masses of masses o f metadiorite m e t a d i o r i t e generally g e n e r a l l y strike s t r i k e northeast northeast and and iintrude n t r u d e aall ll and lamprophyre dikes, rock Minor intrusions of types. rock types. Minor I n t r u s i o n s o f lamprophyre dikes, ssills, i l l s , and quartz—feldspar porphyry porphyry a are Four steeply quartz-feldspar r e also a l s o present. present. Four steeply dipping dipping diabase dikes width orebody. diabase dikes from from 10 10 tto o 20 meters meters iin n w i d t h traverse traverse the the orebody. Two iinn the the centre and one at east boundary Two c e n t r e and a t tthe h e east boundary strike s t r i k e northwest northwest while a west west boundary w hile a boundary dike d i k e strikes s t r i k e s northeast. northeast. U In In - The orebody orebody iis central offset att the east east c The s o f f s e t 107 meters meters nnorth orth a entral This east side diabase dike; dike; rrelative e l a t i v e displacement displacement iiss east s i d e northward. northward. This dike divides d ike d i v i d e s the the mine into i n t o MacLeod MacLeod West and and East. East. jj I La U II U ii U -8- U U �the Vugs of si zes are Vugs o f all a l l sizes a r e frequently f r e q u e n t l y intersected i n t e r s e c t e d especially e s p e c i a l l y iin n the in one area they are hangingwall banded chert of MacLeod East where hangingwall banded c h e r t o f MacLeod East where i n one area they are Several vugs vugs are interconnected 250 meters along strike. meters along interconnected for f o r 250 strike. Several are 10 10 to to in height and width. Most were water filled, coated with 30 meters 30 meters i n h e i g h t and width. Most were water f i l l e d , coated w ith and forms off calcite, marcasite, p pyrite and very very various assemblages various assemblages and forms o c a l c i t e , marcasite, y r i t e and galena rarely with amounts of chalcopyrite, marmatite, minute r a r e l y w i t h minute amounts o f c h a l c o p y r i t e , marmatite, galena oorr ssee len l e nii tte. e. 1961 58 The MacLeod Mine Mine has production since since 1961 and 58 has been been The MacLeod Iinn production and from all million tons of ore have been m Total ore med to 1986. m i l l i o n t o n s o f o r e have been mined t o 1986. Total o r e from a1 i 1939 since siderite three mines the same three mines iinn the same orebody orebody since s i d e r i t e mining mining began began iin n 1939 million 1939 1950, has been 8 million tons by open pit, and 79.3 1950, and 79.3 m i l l i o n has been 8 m i l l i o n tons by open p i t , 1939 surface drill hole tons from diamond d r i Il h o l e from from surface tons from underground underground since since 1949. 1949. AA diamond intersected siderite 1,200 meters below the shaft collar. i n t e r s e c t ,e d ,s. i d-e r i t e 1,200 meters below the .s h::a f t . c~ o,l l ,a r . . - . < .* . ; . .. - . ' . . .*> ... . ., , . ., . . .~~ !,* ., ..' .,< . , :. .* , ~, . .. ..... . .. . . . . . . . '< , 4 . . . , , . , .< . . - .. . . ., . . ... : : . <.,*- . . . , .~ . . , , 3 . . . . . .. .*. . < .. -. .. .", GOODWIN, GOODWIN, Range: A.M. Geochemical1 studies studies a att the the Helen Helen IIron A.M. 1964, Geochemica r o n Range: — 684 718. . . Economic Geology, Geology, Vol. Vol. 59, 59, 1964, 1964, pp. pp. - , , .- ,, . , .. . —9— . ., . ,.. <. +, ... .. . �s-I j A simple—shear model high flatteningstrains strains in A two—stage two-stage simple-shear model for for hiqh flattening in shear zonesofof the the central central Vermilion shear zones Vermilion district, district,northeastern northeasternMinnesota Minnesota U MATTHEW BIDWELL (Department Geology Geophysics, University of of MATTHEW E. E. BIDWELL (Department of of Geology andand Geophysics, University Wyoming, Laramie, Wyoming 82071) Wyoming, Laramle, Wyoming 82071 1 ROBERT BAUER (Department of Geology, University of Missouri, Missouri, Columbia, ROBERT L. L.BAUER (Department of Geology, Columbia, - of -- University Missouri 65211) Missouri 65211 ) Large—scale anastomosingshear shear zones zones up up to to 600 Large-scale anastomosing 600 meters meters wide wide deform deform basalt, tuff, lamprophyre, and graywacke in the central Vermilion basalt, tuff, lamprophyre, and graywacke in the central Vermilion district Mylonites in inthe thesbear shearz8nes zones districtjust justnorth northofofthe thetown town of of Ely. Ely. Mylonites have a relatively consistent C foliation orientation of N72 and have a relatively consistent C foliation orientation of N72E,E,6868SSand contain mineralliaeations li9eationsand nd striations stsiations with contain numerous numerous mineral with high high concentrations at S2Z S2 E, W, 56 56 and and a more more dispersed dispersed concentrations at E, 669and and544 S44W, concentration at N74 E, 33 Small-scale kinematic indicators, including concentration at N74 E, 33 Small-scale kinematic indicators, including actinolite S—C actinoliteporphyroblast porphyroblastfish, fish, S-C fabric fabricrelationships, relationships,shear shearbands, bands,and and extension with aa dextral indicatenon—coaxial non-coaxial deformation deformation with dextral extension fractures, fractures,indicate sense of shear. sense of shear. . Finite fromvariolitic variolitic pillow Finitestrain strainmeasurements measurements from pillowbasalts, basalts,agglomerate agglomerate clasts, and phenocrysts indicate large flattening strains clasts, and phenocrysts indicate large flattening strains in in the theshear shear zones (Fig. 1). of kk range from aa nearly nearly plane plane strain strain value Values of range from value of of zones (Fig. 1). Values 0.94 0.94 to to highly highlyoblate oblatevalues values of of0.06; 0.06; r rvalues values(=X/V (=X/Y+tY/Z Y/Z +1) +1) are are locally locallygreater greaterthan than15. 15. This range range in strain, strain,along alongwith withthe theabundant abundant kinematic against generation of the kinematic shear shear indicators, indicators,argues arguesagainst generationof the high high flattening flatteningstrains strainsvia viacoaxial coaxialdeformation. deformation. In In addition, addition, the the flattening flattenina strains by aa combination combination of simple strainscannot cannotreasonably reasonablybebeaccommodated accommodated by simple shear volumeloss loss - greater shear and and volume volume loss. loss. Excessive Excessive volume greaterthan than70% 70% -- is is required measured required to toattain attainthe the measured strains; strains;however, however, no no evidence evidence of of diffusive diffusivemass mass transfer transferwas was observed observed either either on on aa microscopic microscopic or or aa mesoscopic mesoscopic scale. scale. - - U Là U — Although strain path A1 though aa strain path involving involvingaacombination combination of ofprogressive progressive simple simple shear pure shear shearmay maybebecalled calledupon upon explainthe thestrain strain values shear and and pure totoexplain values in in Figure 1, we weconsider considerthe thepossibility possibilitythat thatthe thedifferential differential clustering Figure 1, clustering of of lineations striations on the CC foliation foliation and the distribution distribution of and the of lineations and and striations on the major and intermediate intermediatestrain strain axes axesininFigure Figure22isis aa result result of major and of superimposed simple shear. Possible strain paths consistent superimposed shear. Possible strain paths consistent with the the observed distribution of were observed distribution of flattening flatteningstrains strains werecalculated calculatedusing usinga atwo— twostage in which two simple simple shear shear events events with with different stage model model in which two differentdisplacement displacement vectors and displacement planes superimposed. and slightly slightlydifferent different displacement planesareare superimposed. AA difference in inthe theorientation orientationofofthe thedisplacement displacement planes planes is is required required because superimposedsimple simpleshear, sheatwith with different different shear because superimposed sheardisplacement displacement vectors planes,resultsinfinite finite plane vectors but parallel parallel displacement displacement planes,resultsin plane strains strains regardless regardless of ofthe theangle anglebetween between displacement displacement vectors. vectors. J U Relatively near plane-strain plane—strain values values obtained obtained from three Relativelylow—magnitude, low-magnitude, near three samples collected adjacent adjacent to to the mylonitic samples collected myloniticshear shearzones zones are are taken taken to to represent during the the initial initial simple represent strains astained attained during simpleshear shear event. event. An An angle the shear sheardisplacement displacementplanes planes thefirst first angle as as small snail as as 55 between between the ofofthe and secondevents events willproduce producelarge largefinite finite flattening flattening strains. and second will strains. The The best best fit usinginitial initial strain fitstrain strainpaths paths(Fig. (Fig.1)1)were were obtained obtained using strain values values ((ri) Y 1 of of 1.0 1.0 and and 2.5, 2.5, respectively, respectively,overprinted overprintedbybya asecond secondsimple simple shear shear with w i d aa -10- U �750 angle between the plane angle anglefrom fromthe thefirst first event and 1 0 ' shear shear plane event andasaa8.0 75' are angle between the as hi9h two vectors. yy values values as high as 8.0 are required required to to two displacement displacement vectors. produce the observed finite ttrains. oroduce the observed finite strains. 100 II x V I 2 3 4 5 0 7 S 5 10 11 12 13 14 15 I V z Flinn analyses Flinn plot plot of of finite finitestrain strain analyseswith withtwo two strain strainpaths paths of 1.0 and 2.5 and intervals 0.2, 0.5, 1.0, 1.5, for i 1.0 and 2.5 and 2y, intervals 0.2, 0.5, 1.0, 1.5, 2.0, 2.0, 2.5, 2.5, 3.0, 4.0, 6.0, 6.0, and and 8.0. 8.0. . , -. Figure 1. . .. '. " ,> . .. ,, ~ , a Ass aA £ ,. "' A A A A S 5.29 S •521 S —Is U.29 S Sot •18 •oe 5)0 Un S t44 •,26 •94 •.82 ..ft S S UI. A Figure Orientation of of minor minor (triangles), (triangles), intermediate (circles) Fi ure 2. 2. Orientation intermediate (circles) andma major (squares) axes finitestrain strain ellipsoids. ellipsoids. Numbers an or (squares) axes of of finite Numbers are are k values. values. -^-r —11— ~. .~. �k-J Character of Archean Rocks Rocks from Half Geochemical Character Geochemical of Archean from the the East East Half of the Northern Complex, Upper Peninsula, Michigan: of the Northern Complex, Upper Peninsula, Michigan: A Progress A Prnareqa Report Rennrt T.J. HURNHORST and and D.A. D.A. BAXTER BAXTER (Dept. (Dept. of of Geology Geology and and Geol. Geol. Engrg., Michigan Tech. University Houghton, MI Engrg., Michigan Tech. University Houghton, MI 49931) 49931) L The granite—greenstone Archean granite-greenstone The northern northern complex complex is is an an Archeari As a terrane located in Marquette and Baraga terrane located in Marquette and Baraga Counties. Counties. As a whole, it consists of more granitoid and gneissic rocks whole, it consists of more granitoid and gneissic rocks than greenstone. greenstone. yIn 21n the the eastern eastern half half of of the complex there there than the complex of exposed Archean rocks, one—third are about 1000 km are about 1000 km of exposed Archean rocks, one-third greenstone, which which are are unconformably unconformably overlain overlain by by Proterozoic Proterozoic greenstone, The Archean of the east half consists sediments. sediments. The Archean of the east half consists of of thouthousands of meters of dominantly subaqueous, mafic to sands of meters of dominantly subaqueous, mafic to felsic felsic volcanic flows, flows, pyroclastics, pyroclastics, and and volcaniclastic volcaniclastic sediments volcanic sediments that are intruded by gabbro and rhyolite and rhyolite dikes dikes and and sills, sills, and granitoid An Bxl Archean peridotite peridotite body body and granitoid plutons. plutons. An 8x1 km km Archean was also emplaced structurally within the volcanic rocks. within the volcanic rocks. All of of these these rocks have been been subjected deforma— All rocks have subjected to to intense intense deformafades. tion and and metamorphosed to to at at least least greenschist greenschist facies. data, weighted weighted for exposed Histograms of geochemical data, area, illustrate that the greenstone greenstone belt, belt, excluding granigrani— area, Basaltic toid plutons, is weakly bimodal in in character. character. Basaltic Pyroclas— type. Pyroclaslava flows are, by far, the the dominant dominant rock rocktype. tic volcanic rocks of andesitic to dacitic composition are histograms, rhyolites are lesser in the second mode in the histograms, abundance. On a Jensen cation diagram the basaltic flows abundance. and gabbroic intrusives are tholeiitic whereas andesitic pyroclastic rocks and rhyolite intrusives are pyroclastic are calc—alkalic. calc-alkalic. The granitoid rocks are calc-alkalic calc—alkalic and on the basis of modal mineralogy range range from quartz diorite to trondhjemite. trondhjemite. Within two two sections sections of basalt, where structural structural repetirepetition may may be low, low, we looked for stratigraphic geochemical Basalts and variations but no no coherent coherent trends trends were were found. found. Basalts the gabbros which which intrude them cannot be distinguished distinguished from one another geochemically, geochemically, suggesting that they are from genetically similar or possibly the same genetically same magma source. source. AA few INAA data for the basalts basalts show relatively flat to slightly LREE depleted patterns, 55 to to 9x 9x chondrites. chondrites. The last Archean Archean magmatic event in the greenstone belt The was the intrusion of relatively tabular rhyolite bodies and granitoid plutons. plutons. There is a textural continuum between the rhyolites and granitoid rocks which is further exressed by expressed by excellent excellent chemical chemical continuity continuity on on variation variation diagrams. Thus, Thus, a close genetic link exists between the diagrams. rhyolite and granitoid intrusives. intrusives. The rhyolites are are interpreted as the late-stage, late—stage, generally more-evolved more—evolved parts of the plutons. This investigation is an outgrowth of projects partially funded by the the Michigan Michigan Geological Geological Survey. Survey. —12— J 4 — j J �.2 in 'Ii L a: 0 in -J -C in .0 ill -.4 -C a. -I-. t -C 4'4- 0 0 0 a. 0 -.-. L in 4.' aC — 0 4-' C L 0 C i- riCi .i ..-. > C Ci L to I'. h. ) 01 > J LI) in .-. U -.4 Di 0 .—. 0 a, (0 0 I. -.4 in i-s aC — 0.-. -uU cm-c..-.-— m+'-UWC in.-.o JOW4J mLW'.-D ru a-) LW a-Cs--U-0 4-' 0 .—.in W-.4 o-.-sn-.-.N 01 9-in Ut ÷'.MWW inin>WLJCin W.JmOWU >-4, -C t CUCL U.-.D'0 E0CJ SCUWOU >•' in .4 Ifl-.-.uI t')fl Lfl .1J.C00 inC-.-.t0.-. WoOm tJLn 0-.-.inLOJ.t or 00+' C E0 0 W-...(fl4J OCt CO .4-al— in u 0 — 5Jc>-.'d-iin 15th U0 0.- in -.-.E_c>-Di.. 01 a..'.-. i- 0_c4,uOm4-4L WWWin..Jcu)-4J.cO -..4UlaC4-'-..in-.-.in uiuiu.-.-.-. in.—. COQIdO COW 4-' 0.-.Lin.-i OIL-i-' .Ift U IdO u •.-.tnw u..tr 4)3 in_cu n_cm mu SC-.-. •OOC 00 U'd4,U LO —c .., 0 in..4CM-inin Was.-.-.' L —m÷.0 4-'CIdL U—i-..L .fl.-.-.-..-'D —-.-tU--.4 in4-IOW .xo.-.ina UUWIVJO -1-'---L.inid>-0W-.4C_cSLL Jinflfl_cCLCiUO L'I 4flin qdinld 15 I I LC Un flC .4in U (JO-.-. LOCO •0-i.J .-. 0.dImLin>inmininW ..i4DI5JCU 03 in inC .-..SL..thin inOiU.-.4-_cW .-.W m.-.m_cWCinIdO-1L .C-.-.-nCin L-X u .'fl.uidn fl.-.m9-c omso-.-. u •.4Din -i-iOU inn.-. .'flWI CithinIUUOfl in >.C L Cci-. .—.inn-.-.lUW.-.LIflU — -.41_cin min_c-.Juu÷.C-.4 inCi U>0WSW -..-.-.WC.-.S9- Gs nin4JD'IdLD aininmI inin-,.EUfl.!C.--. LEU -.cenuam> -i-i mu_cu 4.1 -..C 53 in L-I-J-4-' mi— 0 mm-.. wLa.>—_cc rWfl÷'WW in 4-'O mdi Ci in 1.. UCJ in>- I U - -I-' .-.0 in. in.- 4- Om LW uo - 'dOW LIVC in 0. W.. U. oc vt.sc flWL-.--iI. 4-'Wm WE Wa. X in UU OE L .c U.-' -.4.... Em 4-'.-. ---.0 4-'.C 'n--, In C D'.o .4 C_c .—. mm 0 Ci L L.-4 0 'U4-JC EmO 9-in_c -.-i.--..W U .—.u-.-. no>— aJinci DSC Cm..-' u_cm Cfl '4- S LW -i-'--.a thin CUL in-.-.in in -.4mm flu ..ifl CS os—in Q 4-'.-. 0.0 q-.to F f l s i ~hypabyssal, nafic plutonic, t r a n s i t i o n a l migmatitic rocks bounding t h e supracrustal rocks and f e l s i c stocks and b a t h o l i t h s make u p most of t h e rocks underlying the nap area. .C IflWO —i-.'--. mm L L0 0550 IAE.' -.40c 0.0'L CCL COo UUU 0>- . in-i-a-.-' -x uOJ_c cc... LOn 1._c-ia 4-'L >-in C-.-. in_c OCUC a. LL.'DiD mmmc-.-' C 4-I inO +'E>. C .0 >—W-.-i C l a s t i c metacdimentary rocks comprise 15% of t h e supracrustal rocks and range from mudstone t o conglomerate. These rocks appear t o have been deposited b y t u r b i d i t y c u r r e n t s along submarine fans. 00mm-no'.EcE3li-0 9- 0>- Qi5>4,0 L÷'Umu .44-a'D C .4-'oZcL -.40 U1UL 10>-C .X..4flin LO UD. WOid-.. C.-. 5 .4 0 .C 4, in>-Lmin 0.rU ..-.Cq-OCL moot-.. .-i-.-.SU 4U.-i inS WDCWW10 OCLmWGiL Dci U_cL_c in C_c04-GSL U>.-._cW thU in.-4 W-'U) -.-'u_c--.OW—. Cu I—vC .C.-. fl_c 0. L a0. C CLin 0 • -4-'O W9-W> — ldon-.-.o '4-fl4-'UU 0 0 Win LLWW.X —0m..cmU C h f i c a l netasedimentary rocks make u p l e s s than 1% of the supracrustal rocks and a r e t y p i c a l l y magnetitic chert or Jasper interlayered w i t h magnetitic iron-rich rocks and appear t o be The cherty associated w i t h the waning s t a g e s of a volcanic cycle. portions nay be arkosic t o wicke and s u l f i d r a r e often associated w i t h the oxide portions in varying degrees. These rocks often wxhibit t h e e f f e c t s of deformation r a t h e r dramatically. -C: .coIn-E-.-' mo mom -.-.in.. UL C 0 -..EOCUCI fl.xfl0-.-4C in in - .—.9JL_cCOC II, C inLth.i.IUEO.J au-.-.-.-.0÷i -n-.4CUinO >.Li 0E0.C_c0Suq-Oin.X .-i÷'CSs -.4 in 0. D'U*- C-.-i .49- .... .C am-... >—.C .C4'9- in Sin -rid 04-' OlE -Lin W'. floinLOldoin .-.COinJaUinC.-. .-.UaC mlnELxO 001 0 WSLW €0_c -.-iLO ininU ..JCi.xmm +'C Oinri9Win.C.CL04J L> ins...ainau inLO n—° mm w-n-..m 3÷' inaL z÷minme.x 0-...-D mu-.-. 0 o.-ain.o-.-' inmin aa,rtWoe —acm .-s0t.ca. >-0 4.1.009inDia diW OIL -_ 00 i-.Cfl 5mW ..03>-.. 1dm mxli EL_c m Di 00101—. 0.-i OJCfl_-iUin mtm -inLU L >-WC 0 L4cicC0. 4,UUIin in..-.in 0 Cm 011105 IflC inU aOCCinD LC sin .11-i-i_cS.... in .Jin OOi in.--. Proceeding upward s t r a t i g r a p h i c a l l y , t h e supracrustal rocks consist of 15% nafic metavolcanic, oassive and pillowed b a s a l t i c , and l e s s e r andmsi t i c f lous and associated breccia5 and p y r o c l a s t i c rocks. Chemically, these rocks a r e magnesium- and i r o n - t h o i e i i t i c b a s a l t s , t h o l e i i t i c andesites and calc-alkaline b a s a l t s . The iron t h o l e i i t e predominatr. Intermediatr oetavolcanic f lows and basal t s p y r o c l a s t i c s make up about 4% of t h e supracrustal rocks and c o n s i s t of t h o l e i i t i c dacites and calc-alkaline andnsitf. Felsic metavolcanic flows and p y r o c l a s t i c rocks of c a l c - a l k a l i n e d a c i t f t o r h y o l i t e composition make u p about 3% of t h e supracrustal rocks. The intmrmediate and f e l s i c metavolcanics increase in proportion west of M i s h i b i s h u Lake. inWGaWIi I. -.-.tfl -I-jOqF0 II. in -— c-. LmL 00'.- 0 C CL 03_cO -.-. 0 .-.fli>- ..-i OW mcmua-.-' 0-.4+J..45in L fl-i-'LO-.-. 'I LW_c L CL.i-'Om mci n in in CE .xWiODI mmUac-_m -.4_n_c WCCCD OlinOOc '4-0-i-aCId -riE 0-4-s S 1d5..iW.-.. LUd 0 .fl4n 0004,4, C.C'.-iflc mi—-.--.-. CL UW in—. >-. Di >-L00 ..-.a-.-. .'4inL04-' U .cin---4 W4.aCLO uSOS -.-.uuum EQ DC '-4 0L ICWEWO 0 Oc.-'.cSs u-_-_xc inWa' OC-.-.L 0L0fl0 C.',... 4-'C-C --.-.l -0 4,0 Ui_c .-. 4-. 0 •.-.0-..mu c A considerable range of mineralogy and chrmical composition i s evident in t h e q r a n i t o i d rocks. The stocks intruding the supracrustal rocks tend t o be f a i r l y uniform in composition u h i l e t h e b a t h o l i t h i c rocks bounding t h e supracrustal rocks e x h i b i t a more varied composition and may be multiple i n t r u s i o n s or the product of a d i f f r e n t i a t e d magma. - —In O.W r: 4-' • inn.n.OL m .1 - LUJ .—1 oincJ-aCO0FL-,.r _j L_J in Ln no _J J j in-id0zm in -.4 .__t_J Oa,n>n minma, a. u_cc 0 in_cO-.. ni— -ninu.--.-.-. .1mm -.-i_c w gI.-.000W uD>-+'Ww -.-.co, uci mE--.-' 0.-au-.-,C Z— -riO -..Lm.nc.c-.-a i-'Os on ..-am-.-.mmO—-at-.-. C-ia CJL.-. in.4in Etj—.-,.0.'-.-. (Eta rwus_c-.-. -nm.--i u4-.-.u-ri.-—tO-En .0 OCU—DW WidLu-.-. Idin .-. 0..-' .0 ...oo 00th oInm-nea.--.u÷.>...L-.4 .-..xm mom_c .cLmO.-mn-.-. Ocr UWIdOWL .C4.'CC-C —.we—.ina 4J>-4Jin L)a-.inLac I—004U Din UDOn C-.-.O.4-'Li-iDCinO-.-.x ou> >Dinin-ri nClOinO & 'i-CC'U>-M-WC-.. z The Hishibishu Lake Area i s located about 35 kr w i t of Maua and about 80 km southeast of Hemlo. The M i s h i b i s h u Lake supracrustal belt i s about 33 k m long and 16 km uide and i s concave t o t h e south, by felsic bounded on either end by Lake Superior, enclosed b a t h o l i t h i c c o ~ p l e x e sand l o c a l l y intruded by younger f e l s i c plutonic rocks. The r a t i o of supracrustal t o b a t h o l i t h i c rocks is 2:3. S) .J .J LU to (Ontario Beological Survey, 77 Brenville, Toronto, Ontario -UJ en —I .._J ._J �I— 1.. m 01vOLD - - >.W In t.-tfl.-'-irnoimc.,-.u — OJL -,-.-.-.>mthD .rwmon 0-0 It, 1, Smq--oo ojo in dl a0 .-..dowmmiu LN>J-,.C 0-.-.uo ndi nm..-.-. ODmOM-in 0-1.0 E03L E-e-' Ui 04-' 0C >flO•..-,. CLZ -C ma, in ainmut -u djrn>-..'-.. r—U)m.-.L .-.wn 4-.-.-.030003ffl -,-.— OIC.X ma D4-.-. uo..JWauw .iiOI—>c-.-.0 ...o i,.mco. C-.-. Em Cdi >%flDifl LI. fr) U .CW .-.0tJ 0.mmmo..-.tO 03—Ln m .••,.4 viW -..j4-3E 010mW iii 1,4-3>03.-i >.)-9--,-.m.-.a. in 1,4.5 .cn 030 D'CO 0. >-. — U inc 03 ' CCO -..Ø' t.1i9 rn.-. ai÷'.-' 40cc €-'aj040 L.,-.Lfl.--.UI .-.-.m 0mo •-.>9-mCi CLO .W n QIC0 >-m mcci L-'-' in a0'ai.3 Co ma no, c•... c — 2m r • .4.iGiJ n.m in 40 >OU .CCirio,>03k.-0 mc o-wc t,-4 m÷.mc -a-cC *L.i.3 Wcai.-. wmn'o .xa,nmW .CLDL ULIflinin..'n> 0.IJinL03 WCW LI 03OJ-,-..-.C0c .-sL,-.,--wmwuu W0lmin0La m mr—. cn 0,> Cm 0'.-. -.-.rni.Wmaj-...c 03 C.-.)0L LU .-..Cfl COIL_..40 -n—coWcm-,. .—..-. >r C o.ir.. urn ..-.uzm .' 0L.t-.-. i-sm C rnm..J.._.n,mL 0 flEm---.-. ---40-.-4 .02 caJou CLCO-i-' ..-. CD mrnunm.s-'q4rnC03 innin 0.-..cc.,-.omwn. -.-'mrnu -.-...-..E 0-fl CLEL -..mmc.4-'Co'Eu >W WWcm OWC 0-..-.-.x . -.-44fl .-..--. 0Win-..,-.EnLI3 cm a.'UI —.c 0..mn C muir-rn —.--.-.c-.-'._-_wum -... 1, C Un' ciinin CC .fl. 0J.,..4-I E-r.-.-4 iii mc .n x.-. WI. m 0-.--.-. in mDnmEc -3'n mi-sW 0 .... The s u p r a c r u s t a l r o c k s have been f o l d e d i n t o an i s o c l i n a l synformal shape about an e a s t - t r e n d i n g a x i s w i t h s e v e r a l s u b p a r a l l e l p a r a s i t i c f o l d axes on e i t h e r side. F a u l t s and l i n e a m e n t s w i t h v a r y i n g degrees o f m o v f n t d i s p l a y d along them c u t a l l Archean l i t h o l o g i e s , b o t h p a r a l l e l and t r a n s v w s e . Shearing i s most i n t e n s e near t h e l a t e stagm i n t r u s i v e b o d i r . The main H i s h i b i s h u Deformation Zone i s a composite o f smveral shear zones. Shearing i s c h a r a c t e r i z e d by an increase i n the penetrative fabric, examples o f which a r e k i n k banding i n c l u d i n g c o n j u g a t e k i n k s e t s , c o m p o s i t i o n a l banding and t h r c dimensional chevron f o l d s . in 9-00. mU..-fl 4.3 -t 0 9- (04' 0 C 40 .C I—.m_ .4-' 03 Ci In > 03 -n-a1,0>.co ida' 0' mon.mn. ••• 4.3 03.—. '-4 -S tj c3 c =i - i a C WOO 1130 WDO L 03c CL •V GJ—C-'.c--' C WD2LOA-s 1.-Did 0' E-+LO' in tiiCjOU .-.E a3.CCUL-,-... •LC Ifl..-Jmom.i-.Jwoo SC DEm Dorm+s Ill ma, 40 DO mm> cLLcO,n'Lo, OLOW 1,IS1OD c'+.O..-.ct,'* 1,-4 -.-'..-'W --.0j .0 OCOOCI-.-LLO wL.-.-.-'a-,Lm— Ca. O0'-.'a9-CD—a LW ,cCOU X>.-.-. on uu 03+2 w L 1, 0>. 1.0 111am • Lwmc L>q-nt-4inindpinain -o to 0U O3LO .C 0 C WOLdm03m+iaW 030(0 mL- C 1, 03.-it ZoOq.-.-. .0 03cm—rn .-'—-,-.uin W÷'DWL-.-.COa, CL-1,DLOc> c0-.Jm.fl-.-. ..-. -n om mOlLffl'4->-mLiUOj>. 03 LOW 0..LW..j>.. I. Cot w.-.m -..ac 'omamo.O.—. LOD -.-.X.JC OW >0 -.-.cxED'c-.. c 03 -to -.-C-,-. 0 C4.' 03m 1,flC-.-.> .'C m>->-.,-.z_o'o I. L id.--.. 4.020>-.-. -4-' -rN-LCWt-SJLLW 0m flCOIaOI-.4C toE co-ww OCO 0—4 03cm .ca, 4.CVWWDQ.UI 4-Jo, E mc ES' mu •L 4-sauna, 1, C >-m-n n4i—. 00 0..-LOJCW 01DcmWW -t D 0. a' LELW.-4ffl xrnc-or003mm 030303PICW>WL>Lu-.-'fl-O OJLSI-. —.0 mu C 01 4- DtJ.0 Iii 0-4-' m 29- -.-. rnmxo,W-,l-.-.WD'o ,.mm÷scld-.-JnrnW..-. m>— Wmc WLCWLC .0 0301 .30303005 Q..-.W0W-.-.03 fln.oEv0n'n.Lo0m -.i03 uS..-.VlWmcin r.-. LCEucL c..-Ic.mE0,-.-'m 9- 0 di 3c L -.-. L .. 01 C03..m4-'>UICn0 Lm - .D-.. 0 flin9U C m.4.soa'cJoCuc LD CCL ....c0J 0011103 a'03 ..C n03€-4c-L.'03 ... M i n e r a l e x p l o r a t i o n i n t h e area has been recorded i n assessment f i l e r e c o r d s s i n c e 1907 and i s r e p o r t e d t o have begun b e f o r e t h e t u r n of t h e century. E a r l y e x p l o r a t i o n was f o r i r o n o r e and was c o n c e n t r a t e d near t h e David Lakes area. Gold e x p l o r a t i o n occurred b e t w ~ n1937 and t h e b e g i n n i n g o f U o r l d Mar 11. A f t e r t h e war g o l d e x p l o r a t i o n resumed and w i t h o n l y b r i e f b r e a k s c o n t i n u e d u n t i l t h e present. Some base metal e x p l o r a t i o n p r o j e c t s occurred from t i m e t o ti-, however, t h e s e programs w r e n o t o f a v e r y l a r g e s c a l e . The area i s p r e s e n t l y u n d w g o i n g r e l a t i v e l y i n t e n s e e x p l o r a t i o n f o r g o l d w i t h s e v e r a l companies i n v o l v e d in property (Valuation and f e a s i b i l i t y s t u d i e s on p r e v i o u s l y d i s c o v e r e d shonings. J ) fl =3 rj 1 =J 1 .CO.-4fl >1, .I' C—. C—.lt -—mmrn.-.m vOn. 2 0 -D • L—0.3 Ee.JC ..-.u cvi UL 4.3 -.. miii -.-.WL DLWW0a-.-' ..t.XNDW mow 2.m .JL L 03010 0.-.-i.I C -s-Ix .cOmE inL..JIIi >-fl0 Cr 0.0.3jfl 9-fl -—0- E mEm.c-.-' 1, EmwrnmWo Jc..4_JLE OiO rno-.ir ..4i0 9C.3 0300103 WWW.t OIIin.4JUiW .tuUuLcO am-.-.o C u W 3,QU fl—---40C4-iGJ C4-eJWWn wOmoim-.-. .ce>-.-.zinE .—E0,03÷'cO 0 1, 0 —4 COl L--'OL--.WD mm Dc., r)-0u .EDOCCOIW muLidOL> ola,-.-.mm i-i 0303.-scm = re000i 0 1, 1. L 0 0 Inn. C 03.—.a -a a.mm-,4m 0 idCa.O -€4 mc 9-..4 CLO' Lolca, o'-mn.-. U oWEmL. .,i4J .3C030J03 .-.mac VOL -.4L 03-.-. U glnint..-..0 DL. .4-Ira, m•.-. C L on CC+'C - The physiography i s c h a r a c t e r i z e d by low t o moderate r e l i e f , commonly broken by s t m p s i d e d h i l l s and r i d g e s 30 t o 200 m high. E l e v a t i o n s range from 183 l (Lake S u p e r i o r ) t o 300 m above sea l e v e l . P l e i s t o c e n e d e p o s i t s a r e varved c l a y s w i t h l e s s e r d e p o s i t s o f sandy Recent s u r f i c i a l d e p o s i t s outwash, t i l l , g r a v e l b a r s and d e l t a s . c o n s i s t o f a mantle o f o r g a n i c d e b r i s and r e c e n t e r o s i o n a l p r o d u c t s from bedrock and g l a c i a l d e p o s i t s . CI.4-3LWD 000 -o$n a' w>uwo .atnoL L034-0300+t)034J4J n,.—...-wowm UiCC co 303001003 0-.n-fl 0D'..-'Wuu 03.,. — ..'O —.0303 .min •L -...--. —r LL r)m> in .mWr Un. c÷'m-.-.d cojuCa.-' mm o mc LU LLC LUI+'o' Cal-nOD 4-' O'-.-.a-n • ma,dlnO •'in 0C c-.. cm U-4-i Ui-i-''-. cm>-.orn Metamorphic grade i s m a i n l y low t o m i d d l e g r e e n s c h i s t rank w i t h some c o n t a c t f a c i e s t o r p h i b o l i t e rank. M i d d l e t o L a t e Archean and P r o t e r o z o i c diabase d i k e s o f a t l e a s t 3 d i f f e r e n t ages c u t a l l Archean r o c k s i n t h e M i s h i b i s h u Lake Area. Several d i a t r e m e s and e r o s i o n a l r r n a n t s o f L a t e P r o t e r o z o i c l a v a s occupy t o p o g r a p h i c a l l y low areas near t h e shore o f Lake S u p e r i o r . These r o c k s do n o t appear t o have undergone metamorphism o r s t r u c t u r a l deformation. �AA Brief B r i e fLook LookataGLIMPCE t GLIMPCE W. CANNON (USGS,Reston, Reston, VA W. CANNON (USGS, VA 22092) 22092) 3. BEHRENDT, M. LEE (USGS, Denver, CC J. BE-T. M. LEE (USGS. Denver. CO 80225) 80225) 0. HUTCHINSON (USGS, WoodsHole, Hole, MA HUTCHINSON (USGS,WOO~S MA 02543) . 0. A. B. MILKEREIT, A. GREEN, GREEN, C. C. SPENCER, SPENCER, B. MILKEREIT, P.P.MOREL, MOREL, A.A. DAVIDSON, OAVIDSON, 0. TESKEY (GSC,I1Observatory ObservatoryCrescent, Crescent, Ottawa, 0. TESKEY (GSC, Ottawa, Ont. Ont. K1A K I A 0Y3) OY3) The Great GreatLakes LakesI nInternational The t e r n a t i o n a l Multidisciplinary M u l t i d i s c i p l i n a r yProgram Programon on Crustal Evolution Evolution(GLIMPCE) (GLIMPCE) was was conceived in i nNovember November 1985 1985 ttoo coordinate researchononfundamental fundamental problems problems of of coordinate multidisciplinary mu1t i d i s c i p1inaryresearch Participants crustal c r u s t a l evolution e v o l u t i o n of o fthe t h eGreat GreatLakes Lakes region. region. P a r t i c i p a n t s include include U.S. and Canadianfederal federalgeological geological surveys, surveys, sstate U.S. and Canadian t a t e and and pprovincial rovincial GLIMPCE has has geological surveys, manyuuniversity geological surveys, and and many n i v e r s i t y geoscientists. GLIMPCE tthe h e following f o l l o w i n g principal p r i n c i p a l aims: aims: To promote cooperative research 1.. To 1 promote cooperative researchand andcommunication communicationamong among researchers researchers i in n the region, region, To advocate advocatefunding fundingoof research i in 2. 2. To f research n the region, region, and and To cooperatively cooperatively fund 3. 3. To fund large l a r g e geophysical geophysical surveys. surveys. During tthe During h e first f i r s year t yearofoGLIMPCE, f GLIMPCE, tthree h r e e large l a r g e data data sets sets were were acquired. Seismic Seismicr reflection km acquired. e f l e c t i o n profiles p r o f i l e stotalling t o t a l l i n1350 g 1350 kmwere were obtained obtained by marine marine seismic seismic surveys surveys in i nLake Lake Superior, Superior, Lake LakeHuron, Huron, and LakeMichigan; Michigan;preliminary preliminaryrresults and Lake e s u l t s are displayed displayed in i n posters posters Duringt the throughout tthis throughout h i s meeting. meeting. During h e rreflection e f l e c t i o n survey, survey, aa large large data. set of refraction and wide—angle reflection data also was data. set o f r e f r a c t i o n and wide-angle r e f l e c t i o n data also was recorded aatt on—land recordings isites placedsstrategically on-1 and recording t e s placed t r a t e g i c a l l y around around the the recorded lakes and and with w i t h lake lakebottom bottomseismometers. seismometers. Data Data were were recorded by by teams from from the the University teams U n i v e r s i t y ofo fWisconsin—Madison, Wisconsin-Madison, UUniversity n i v e r s i t y of of Wisconsin—Oshkosh, Southern University, Western Wisconsin-Oshkosh, Southern I l l iIllinois n o i s University, Western Ontario Ontario University, University U n i v e r s i t yofoSaskatchewan, f Saskatchewan, the the Geological Geological Survey Survey of of Funding Canada (GSC),and andt the Canada (GSC), h e U.S. U.S. Geological GeologicalSurvey Survey(USGS). (USGS). Funding ffor or all through tthe GSC through h e Lithoprobe Lithoprobe a l lseismic seismicwork workwas was provided provided by by the t h eGSC Program and and by L o g i s t i c a l support support was was provided provided by by the the Program by the t h eUSGS. USGS. Logistical Ontario Geological Geological Survey Survey and and the the U.S. U.S. Coast CoastGuard. Guard. IIn n another another cooperative cooperative survey, survey, a anew newaeromagnetic aeromagnetic map map of Lake Lake Huron was funds from fromthe theGSC GSCand andthe t h eUSGS, USGS, the t h eGSC GSC Huron was produced. produced. With funds conducted survey and andproduced producedthe thepreliminary preliminary map napon onddisplay conducted t hthe e survey i s p l a y in in tthe h e poster poster session. session. Seismic rreflection Seismic e f l e c t i o ndata datafrom fromLake Lake Superior Superior reveal reveal aaremarkable remarkable imageoof Keweenawan basin strongr reflecR i f Rift t basin w iwith t h strong eflecimage f tthe h e asymmetric asymmetric Keweenawan andand sedimentary ttions i o n s from from the t h e intercalated i n t e r c a l a t e d rift r i fvolcanic t volcanic sedimentary horizons horizons Beneath extendingt to two-wayt rtravel times (T) (1) of extending o two-way a v e l times o f à 7 ss (( 5 20 km). km). Beneath the western end of the lake, the crust-mantle transition is t h e western end o f t h e lake. t h e crust-mantle t r a n s i t i o n i s represented bythe the base baseoof prominentband bando fofr ereflections represented by f aa prominent f l e c t i o n s tthat hat km)t to ddips i p s to t o the t h e south south from from TT —11.5 * 11.5 s (—'38 ( - 3 8 km) o TT —14s 14 s (-'40 ( - 4 0 km) km) and beneath beneatht hthe centeroof lake iti tcould and e center f tthe h e lake couldbe beas asdeep deep as as TT 17 5s The GGrenville (—56 ( - 5 6 km). km). The r e n v i l l e Front Front at a tthe t h ewestern westernend endofo fGeorgian Georgian Bay Bay is asaa spectacular spectacularseries seriesoof dipping reflections i s imaged imaged as f eeasterly a s t e r l y dipping reflections west tthat h a t truncate truncate a nearly nearly flat f l a thorizon horizon that t h a tlies l i e to s t the o the westbeneath beneath Lake Huron Huron aatt TT — Lake <x 6 s s ( —20 4 0 km). km). A A less less prominent prominent band bandofofsub— sub—'40 km) —35 km) 10 ss ( ~ 3 km) 5 t to o T a 12 12 5s ( -40 km) hhorizontal o r i z o n t a l reflections r e f l e c t i o n sata tT T— 10 maydelineate delineatet hthe baseo fofthe thec rcrust may e base u s t i in n tthis h i s region. region. - È —15— - - ( �6.1 Superior Superior Province: Province: The The product product of of Archean Archean convergent convergent plate p l a t etectonisni tectonism U K.D. K.D. CARD CARD (Geological (Geological Survey Survey of of Canada, Canada, 588 588 Booth Booth St., St., Ottawa, Ottawa, Ontario Ontario K1A K I A 0E4) OE4) Models for the the tectonic Models proposed proposed for tectonic evolution evolution of of the theArchean ArcheanSuperior Superior Province Province (SP) can be characterized as fixist (1,2,3) involving deposition of volcanics (SP) can be characterized as fixist (1,2,3) involving deposition of volcanics and and sediments in rifts rifts of sediments in of older older sialic sialic crust, crust, followed followed by by gravity gravity driven driven vertical vertical tectonism; or mobilist (4,5,6) with convergent plate tectonism, tectonism; or mobilist (4,5,6) with convergent plate tectonism, such suchas as in in the the NW NW Pacific where ongoing accretion is the result of subduction beneath Eurasia Pacific where ongoing accretion is the result of subduction beneath Eurasia (7,8). (7,s). SP SP greenstone greenstone belts, belts, from from 3.0 3.0 to to2.7 2.7 Ga Ga (9) (9) consist consist of of lower, lower, extensive, extensive, submarine plain tholeiitic tholeiitic pillow submarine plain pillowbasalts basaltsand and komatiites, komatiites, and and upper, upper, partly partly subaerial, of calc-alkaline calc-alkaline and tholeiitic subaerial, chemically diverse diverse central complexes complexes of and tholeiitic volcanics volcanics with with turbiditic turbiditicsediments sedimentsthat thatalso alsoform formthe thelarge, large, intervening intervening metasedimentary andalluvial/fluvial alluvial/fluvial metasedimentary belts belts (10). (10). Late Lateshoshonitic/alkalic shoshonitic/alkalic volcanics volcanics and sediments unconformably overlie older volcanics in some belts. SP greenstone sediments unconformably overlie older volcanics in some belts. SP greenstone sequences donot notresemble resemblethe thefill fill of of continental continental rifts, rifts, which sequences do which commonly commonly begin begin with alluvial sediments and end with volcanics (11,12), nor do they resemble Proterozoic alluvial sediments and end with volcanics (1 1,12), nor do they resemble Proterozoic greenstones depositedon onrifted riftS sialic begin with with terrigenous terrigenous greenstones deposited sialiccust custwhich whichcommonly commonly begin sediments and end with submarine volcanics. They do resemble sequences of island island sediments and end with submarine volcanics. They do resemble sequences of arcs that vary from immmature to mature and from ensimatic to ensialic (13,14). arcs that vary from immmature to mature and from ensimatic to ensialic (13,14). SP plain accumulations may may represent represent the lower parts SP submarine submarine plain parts of of accreted accretedarcs, arcs, seamounts, seamounts, or or upper oceanic crust, whereas whereas the the complexes complexes are are the the upper upper parts parts of of mature mature arcs arcsor or oceanic oceanic islands. islands. Bimodal Bimodalcycles cyclesmay mayrepresent represent back-arc back-arc volcanism volcanism on be the the on stretched stretched continental continentalcrust crustand and late latecycles cycles in in polycyclic polycyclicbelts beltsmay may be products products of of back-arc back-arc rifting riftingand and intra-arc intra-arc wrench wrenchfaulting. faulting. Superior Superiorturbidite turbidite belts belts ma' may represent represent the the fill fillofoftrenches, trenches,intra-arc intra-arcand andback-arc back-arcbasins, basins,and and transported transported deep-sea deep-sea fans. fans. Li —I SP and later, later, sodic suites suites and SP plutonic plutonic rocks, rocks, including including early, early, in inpart partsynvolcanic, synvolcanic, sodic in those ofofPhanerozoic Phanerozoic in part partsyntectonic, syntectonic, potassic potassic suites, suites, are generally similar to to those orogens. 3.0 to to2.65 2.65 Ga Ga and, and, like likethe thevolcanics, volcanics, display display orogens. They Theyrange range in in age age from from3.0 little littleevidence evidenceofofisotopic isotopicinheritance inheritancefrom fromappreciably appreciablyolder older(>3.0 P3.0 Ga) Gal crustal crustal sources sources(15). (1 5). Plutonic-supracrustal Plutonic-supracrustal contacts contacts are are mainly mainly intrusive intrusive or or tectonic; tectonic; unconformities arerare. rare. unconformitiesare SP trends and and metamorphic metamorphic zonation may be be partly partly attributable attributable to to SPstructural structural trends zonation may early orogenesis, but are mainly the products of late, polyphase events early orogenesis, but are mainly the products of late, polyphase events that that occurred south. Major Major occurred at a tabout about2.73-2.7 2.73-2.7 Ga Ga in inthe thenorth northand and2.7-2.68 2.7-2.68 Ga Gain in the the south. north-south compression and transpression resulted in early, ductile, isoclinal north-south compression transpression resulted in early, isoclinalfolds folds and later, increasingly brittle shear zones and wrench faults. Major recumbent and later, increasingly brittle shear zones and Major recumbent folds, beenmapped mappedinin some some belts belts(16,17,18). (16,17,18). folds,thrusts, thrusts,and anddeformation deformationzones zoneshave havebeen In In the the NW NW Pacific, Pacific, terrains terrainsof of lithological, litholo ical,structural, structural,and andmetamorphic metamorphiccomplexity complexity such (8) and and Japan 3apan (19) are variably variably deformed deformed and such as as the the Philippines Philippines (8) 19) are and ? metamorphosed metamorphosed subduction subduction complexes, complexes,arc, arc, back-arc back-arc and and trench trench sequences sequenceswith with abundant of about about 300 300 M Maa through through aa complex rocks accreted accreted over over aa period of complex abundantplutonic plutonic rocks sequence evident is evident sequenceofofthrusting, thrusting,rifting, rifting, wrench wrenchfaulting, faulting,and andisoclinal isoclinalfolding. folding. ItIt is that common, that Superior Superior Province Province and and the the NW NWPacific Pacific have have many manyfeatures features in in common, including including similar similarassemblages, assemblages, structural structuraland and metamorphic metamorphic styles, styles, scales, scales, and and time time Differences of komatiites in as the the absence absence of in the the NW NW Pacific Pacificand and the the Differencessuch such as lack belts rocks theSP SPcan can lackofofpaired pairedmetamorphic metamor~hic beltsand andabundance abundance of of plutonic ~Iutonic rocksininthe probably probably be attributed to &I hotter hotterArchean Archean mantle mantleand and the the relatively relativelyshallow shallow level levelof of erosion erosion in in the the NW NW Pacific. Pacific. frames. frames. ~- —16— ~ - ~ - - - - U U �REFERENCES REFEREN ES 1) 1 WBaragar, . R .W.R.A. A . and and McGlynn McGlynn 3.C., J.C., 1976, 1976, Geol. Gaol. Surv. Surv. Can. Can. Paper Paper 76-14; 2) Young, G.M., 1978, Geoscience Canada; 2) Young, G.M., 1978, decadence Canada; 3) U). p., 1985; in GAC and o n s trh u -Thurston, 'l G C Spec. Paper 28, 343-380; 33-380; 3) Ayres, Ayret, L. D. and 4) Langford,F.F. and Morin, M.A., 1976, Am. 4) Lang1ord.F.F. and Morin, M A , 1976, Am. Jour. 3our. Sci., Sd:,276, 276, 1023-1034; 1023-1034; 5) C.E., 64-72; 5) Blackburn, C & . , 1980, 1980, Geosci. Geosci. Canada Canada 7, 7,64-72; 6) Dimroth, E., Imreh, U., Goulet, N., and Rocheleau, M., ., Imreh, L., Goulet, N., and Rocheleau, M. , 1983, 1983, Can. Can. Jour. Jour. 6) Dimroth, E Earth Sci., 20, 1374—1388; 20, 1374-1388; 7) 7) Nur, A. and Ben-Avraham, Ben-Awaham, Z., Z., 1983, 1983, Terra Terra Scientific ScientificPubl.Co., PubLCo., Tokyo; Tokyo; 8) Hamilton, W., 1979,U.S.G.S. Prof. Paper 1078, 345 p. 9; 8) Hamilton, W., 1979,U.S.G.S. 9) 9) Davis, D.W.,Corfu, D.W.,Corfu, F., F., and and Krogh, Kro T.E., L.P.1. Tech. Rept. No. NO. 86-10, 86-10, 77-79; 77-79; 10) Ojakangas, R.W., 1985, in G.A.C.Spec. Paper 28, 23-47; 10) Ojakangas, R.W., 1985, in G.A.C . 11) 11) 12) 12) 13) 13) 14) 14) 15) 15) 16) 16) 17) 17) 18) 18) 19) 19) Van Am. Assoc. Assoc. Petrol. Geol., Van Houten, F.B., F.B., 1977, 1977, Bull. Bull. Am. Geol., 61, 61, 79-99; 79-99; 12) 12) Hoffman, P.F., Nature, in preparation; Hoffman, P.F., Nature in preparation; Sylvester, Attoh, K., and K.J., in in press, press, Can. Can. 3ovr. Jour. Earth Earth Sci.; Sd.; ~.J.,Attoh,~., and Schulz, K.J., Sylvester, P.3., Ludden, iN., C.,C., 1986, Geol.Mag., 153—166; J.N., Hubert, Hubert,C., C.,Gariepy Gariepy 1986, Geol-Mae.,123, 123, 153-166; Shirey, Geochem. Cosrnochem. Acta, 50, w e y , 5.5. saand Hanson, G.N., G.N., 1986, 1986, 50, - G 2631—265 1. 2631-2651. Paulsen, K.H., G.3., Can. Jour. K.H.9 Borradaile, k-k, GJ.9 Kehlenbeck, K M k k , M.M., MA., 1980, 1980, CmJOW. EarthSci., 17, 17,1358—1369; 1358-1369; McGill, G.E. .& and Shrady, Shrady, C.H., C.H., 1986, 1986, Jour. 3our Geophys. Res., 91, 91,E281-E289; E2814289; Hubert, and Ludden, Hidden, 3.N., J.N.9 1986, 1986, in in L.P.I. L.P.I. Tech. Tech. Rept. R-t. 86-10, 86-10, 121-123; 121-123; Hubert, C. C. and Taira, 51-63, Tokyo. A., 1985, 1985,DEUP DELP Pub Pub 3, 3,51-63, Tokyo. Taira, A., -, —17— �U -I A agef ofor trondhjemitecclast A precise precise U—Pb U-Pb z i rzircon c o n age r aatrondhjemite l a s t in i nthe theDore Dore conglomerate, conglomerate, Wawa, Wawa, Ontario. Ontario. F. (Ont. Geol.Surv., Surv.,c/o do Dept. F. CORFU CORFU (Ont. Geol. Dept. of of Mineralogy Mineralogyand and Geology, Geology, Royal Royal Park, Toronto, Toronto, Ont. O n tOntario a r i o Museum, Museum, 100 100 Queen's Queen's Park, Ont. M5S M5S 2C6) 2C6) R.P. (Ont.Geol. Geol.Siirv., Surv.,77 77GGrenville r e n v i l l e St., St., Toronto, Toronto, Ont. Ont. M55 M5S 183) 103) R.P. SAGE SAGE (Ont. j Trondhjemite predo— Trondhjemite clasts c l a s t sand and boulders, boulders, set setin ian matrix a m a t composed r i x composed predo- minantly characteristic m i n a n t l y of o f volcanic v o l c a n i c detritus, d e t r i t u s ,are area a c h a r a c t e r i s t icomponent c component of o f the the Dore greenstone belt, Subpro— Dore conglomerate conglomerate in i n the theMichipicoten Michipicoten greenstone b e Wawa l t , Wawa Subprovince. and associated associated sedimentary rocks are vince. The The Dore Dore conglomerate conglomerate and sedimentary rocks are laterally interfingered with felsic volcanic rocks belonging to l a t e r a l l y i n t e r f i n g e r e d w i t h f e l s i c v o l c a n i c rocks belonging t o the the second volcanism i in the bbelt. second ccycle y c l e oof f volcanism n the e l t . These These uunits n i t s are are overlain o v e r l a i n by by aa third cycle comprising intermediate to mafic volcanic rocks. The t h i r d c y c l e comprising intermediate t o mafic v o l c a n i c rocks. The distribution clasts suggests d i s t r i b u t i o nofothe f the c l a sin t s the i n conglomerate the conglomerate suggestsa provenance a provenance from a source in the west of the belt. Blue anatase from a source i n the west of t h e b e l t . Blue anatase isi sa aunique unique feature, feature, that t h a tmay may help h e l p in i n locating l o c a t i n gthe thesource source of o fthe thetrondhjemite. trondhjemite. A attempt tto date aa trondhjemite trondhjemite cclast A previous previous attempt o date l a s t by by analysing analysing bulk bulk zircon fractions was hampered by the highly metamict, U—rich zircon f r a c t i o n s was hampered by the h i g h l y metamict, U-rich nature nature of of the the zircons zircons which which yyielded i e l d e d very very discordant discordant analyses analyses (Turek (Turek eett al. a1. 1984). the analysis i f f e r e n tapproach approach based based on on the a n a l y s i s ofo f20-1 20-1ugugsamples samples 1984). AA ddifferent of the subordinate, carefully selected and strongly abraded, of the subordinate, c a r e f u l l y selected and s t r o n g l y abraded, clear clear zircons zircons provided providedconcordant concordant and and nearly n e a r l yconcordant concordant data data which which define d e f i n e an an age of 2698 +/—2 Ma. The various fractions analyzed comprised age o f 2698 + I - 2 Ma. The various f r a c t i o n s analyzed comprised longlongprismatic, prismatic, euhedral enhedral crystals, c r y s t a l ssubrounded , subroiindedgrains grainsand andapparent apparentcores coresand and single the mmatrix of aa clast. clast. All A l lthese these analyses analyses yyield ield s i n g l e zircons zircons from from the a t r i x of indistinguishable i n d i s t i n g u i s h a b l e results r e s u l t s indicating i n d i c a t i n gthat t h athe t thetrondhjemite trondhjemitedoes does not not contain contain any any older, older, inherited i n h e r i t ecomponent. d component. U jj The +/—2Ma Maage agef ofor the ttrondhjemite The 2698 2698 +/-2 r the r o n d h j m i t e is i ssimilar s i m i l ato r tU—Pb o U-Pb dates reportedbybyTurek Turekeett a1. al. (1982, dates of of 2696 2696+/—2 +/-2 and and 2698 2698 +1—11 + / - I 1 MaMareported (1982, 1984) 1984) ffor o r felsic f e l s i cvolcanic v o l c a n i crocks rockswithin w i t h i ncycle c y c l 2. e 2Since . Sincethe theDore Dorecongloconglomerate merate iis s stratigraphically s t r a t i g r a p h i c a l l yassociated associatedwith w i t hthese these volcanic v o l c a n i crocks rocks the the overlapping agesi nindicate of volcanism overlappingU—Pb U-Pb ages d i c a t e aa very rapid r a p i dsequence sequence of volcanismand and plutonism, and sedimentation plutonism, uplift, u p l i f t erosion , erosion and sedimentationspanning spanning only o n l ya afew fewMa. Ma. The The source source ooff the t h e trondhjemite trondhjemitedetritus d e t r i t uis s unknown. i s unknown.The TheU-Pb U-Pb age age indicates that it was not derived from older sialic crust documented i n d i c a t e s t h a t it was not derived from o l d e r s i a l i c c r u s t documented in 2800—2900 t U—Pb by U-Pbages agesofofabout about 2800-2900 Ma Ma (Turek (Tiirek eett al., a1 1984). 1984). AA i nthe thebelt be1by possible source may be the granitoid terrain to the west, one p o s s i b l e source may be the g r a n i t o i d t e r r a i n t o the west, one uunit n i t of of which was dated by Turek et al. (1984) at 2698 +/—1 Ma. Alternatively which was dated by Turek e t a1. (1984) a t 2698 + / - I Ma. A l t e r n a t i v e l y ., U the represented the the rrapidly the trondhjemite .trondhjemitemay may have have represented a p i d l y uplifted up1 i f t emagma d magma chamber of cycle 2 volcanic rocks. chamber o f c y c l e 2 v o l c a n i c rocks. Turek, P.E., VanVan Schmus, W.R., A., Smith, Smith, P.E.,andand Schmus, W.R.1982. ,1982. Rb—Sr Rb-Sr and andU-Pb U-Pb ages ages Turek, A., of of volcanism volcanism and and granite g r a n i t eemplacement emplacement iin n the Michipicoten Michipicoten belt— beltWawa, Ontario. Canadian CanadianJournal Journalooff Earth Sciences, Wawa, Ontario. Sciences, 19, 19. pp. pp. 1608— 16081626. 1626 - - - - -Turek, P.E., VanVan Schmus, U—Pb Turek, A., A., Smith, Smith, P.E., andand Schmns,W.R., W.R.,11984. 984. U-Pb zzircon i r c o n ages ages and the eevolution and the v o l u t i o n of of the theMichipicoten Michipicotenplutonic—volcanic p l u t o n i c - v o l c a n i c terrane terrane of of the theSuperior Superior Province, Province, Ontario. Ontario. Canadian Canadian Journal Journal of of Earth Earth Sciences, 21, pp.457—464. pp.457-464. Sciences, 21, U di -18- u �Geochemistry Geochemistry of of Proterozoic P r o t e r o z o i c Volcanic Volcanic Hosted Hosted Iron I r o n Formations Formations in in Northern Northern Wisconsin: Wisconsin: Prospects P r o s p e c t s for f o r Gold Gold Mineralization Mineralization L. MICHAEL MICHAEL L. CUMMINGS CUMMINGS (Department (Department of of Geology, Geology, Portland P o r t l a n d State S t a t e University, University, Portland, OR 97207) P o r t l a n d , OR 97207) Iron I r o n formation formation units u n i t s were were selectively s e l e c t i v e l y sampled sampled in i n drill d r i l l cores c o r e s at a t the the Wisconsin Core Repository in Milwaukee, Wisconsin during exploration Wisconsin Core Repository i n Milwaukee, Wisconsin during e x p l o r a t i o n for for possible p o s s i b l e gold—bearing gold-bearing uunits. n i t s . The q u a r t z as as The rocks r o c k s contain c o n t a i n grunerite g r u n e r i t e + quartz + the mineral t h ecommon common m i n e r a l assemblage. assemblage. Ferro—hornblende, Ferro-hornblende. fferro—actinolite, erro-actinolite, stilpnomelane, stilpnomelane, and and sulfide s u l f i d e minerals m i n e r a l s are a r e present p r e s e n t ini nvarying varyingproportions. proportions. Most units are well—bedded and contain alternating r o n ssilicate i l i c a t eand and Most u n i t s are well-bedded and c o n t a i n a l t e r n a t i n g iiron quartz q u a r t z beds. beds. The The grade grade ofofmetamorphism metamorphism ranges rangesfrom from upper upper greenschist greenschist facies f a c i e s to t o amphibolite amphibolite facies. f a c i e s . Samples Samples were were collected c o l l e c t e d from from 99 cores c o r e s from from throughout the Northern Northern Wisconsin Wisconsin volcanic v o l c a n i c belt. b e l t . Ten throughout the Ten elements, elements, including i n c l u d i n g Au, Au, Ag, Ag, Cu, Cu, Pb, Pb, Zn, Zn, Co, Co, Ni, N i , As, A s , Ba, Ba, Mn, Mn, BB(ppm) (ppm) and and Fe Fe (%), (%), were determined for a set of 48 samples. were determined f o r a set of 48 samples. Whenever Whenever possible, p o s s i b l e , the t h e samples samples were were approximately approximately 33 mm lengths l e n g t h s of of core. core. > . Gold Gold was was detected d e t e c t e d in i n concentrations c o n c e n t r a t i o n s > .02 .02 ppm ppm in i n cores cores from from Marinette Marinette County Corporation) and Mineral County (Duva]. (Duval Corporation) and Clark C l a r k County County (North (North Central C e n t r a l Mineral Ventures). Ventures). In I n Marinette M a r i n e t t e County County the the iron i r o n formations formations are are those t h o s e associated associated with with the t h e Duvál DuvalDeposit. Deposit. Geochemical Geochemical data d a t a indicate i n d i c a t e patterns p a t t e r n s that that distinguish d i s t i n g u i s h the t h e gold—bearing gold-bearing iron i r o n formations formations from from those t h o s e in i n which which gold gold was was absent a b s e n t or o r below below detection d e t e c t i o n limits. limits. These These include: i n c l u d e : concentration c o n c e n t r a t i o n of of Cu, Cu, Zn, Zn, Pb Pb are are low low in i n all a l l iron i r o n formation formationsamples samples(Cu (Cu< <1,000 1,000 ppm, ppm, ave. ave. 208 208 ppm; ppm; Zn Zn K< 1,350 1,350 ppm, ppm, ave. ave. 180 180 ppm; ppm; Pb Pb <50 <50 ppm, ppm, ave. ave. 99 ppm), ppm), however, however, gold—bearing gold-bearing iron i r o n formations formations contain c o n t a i n Zn>Cu, Zn>Cu, they they also a l s o contain c o n t a i n detectable detectable concentrations are not not c o n c e n t r a t i o n s of of Pb; Pb; gold—bearing gold-bearing iron i r o n formations formations are distinguishable the basis b a s i s of of Co:Ni; Co:Ni; Fe Feand and Mn Mnsuggest s u g g e s tthat t h a t variations variations d i s t i n g u i s h a b l e on on the in the concentrations of both elements within the section are favorable i n t h e c o n c e n t r a t i o n s of both elements w i t h i n t h e s e c t i o n are f a v o r a b l e for f o r gold gold association, a s s o c i a t i o n , where where the theconcentration c o n c e n t r a t i o nof of both both do do not not vary vary gold gold was not detected; As concentrations ranged from 10 to 50 ppm and, was n o t d e t e c t e d ; A s c o n c e n t r a t i o n s ranged from 10 t o 50 ppm and, asas aa group, group, were were on on the t h e average a v e r a g ehigher h i g h e r in i n gold—bearing gold-bearing iron i r o n formations; formations; B Bisis elevated in gold—bearing iron formations (71 ppm ave. / e l e v a t e d i n gold-bearing i r o n formations (71 ppm ave. / 18 18 ppm ppm ave.). ave.). Fifty—three F i f t y - t h r e e additional a d d i t i o n a l samples samplesofof the t h eiron i r o nformation formationsection s e c t i o n ini n Marinette County were analyzed by instrumental M a r i n e t t e County were analyzed by i n s t r u m e n t a l neutron neutron activation. activation. Samples Samples were were prepared prepared from from sections s e c t i o n s of of core c o r e containing c o n t a i n i n g 22 to t o 55 cm cm stratigraphic thickness. s t r a t i g r a p h i c t h i c k n e s s . Twenty—eight Twenty-eight samples samples contained contained Au Au concentrations l i m i t sand andranged ranged upuptot o.15 .15 ppm. ppm. c o n c e n t r a t i o n s greater g r e a t e r than than detection d e t e c t i o n limits The Thepersistence p e r s i s t e n c eofof stilpnomelane s t i l p n o m e l a n eini nassociation a s s o c i a t i o nwith w i t hgrunerite g r u n e r i t eand and quartz theaxnphibolite amphibolite facies f a c i e s of of metamorphism metamorphism q u a r t z under under conditions c o n d i t i o n sofof the suggests s u g g e s t s aa high high alkali a l k a l i content c o n t e n t ini nthe t h eiron i r o n formation. formation. Trace Trace element element concentrations c o n c e n t r a t i o n s show showstrong s t r o n gvariability v a r i a b i l i t yamong amongsamples. samples. These These differences differences are arerelated r e l a t e d tot omineralogy mineralogy ofof the t h esample sampleand andtot othe t h eintensity i n t e n s i t yofofthe the hydrothermal hydrothermalsystem systemata tthe t h etime timeofof deposition. deposition. Volcanic. V o l c a n i c -stratigraphy s t r a t i g r a p h y suggests s u g g e s t s that t h a t the t h e iron i r o nformation formation in i n Marinette Marinette County was deposited d e p o s i t e d within w i t h i n aa local l o c a basin l basinthat t h amay t mayhave havebeen been aa caldera. caldera. County was Basalt Basalt dikes d i k e s and and sills sillswithin w i t h i nthe t h iron e i r o formation n formation were were intruded i n t r u d e d while while the the sediments were unconsolidated. unconsolidated. These sediments were These basalts b a s a l t sare a r echemically chemically distinct distinct from from basalts b a s a l t swithin w i t h i n the t h elocal l o c a lvolcanic v o l c a n i csection. section. —19— �U t.1 Two thickLake LakeIntrusion. Intrusion,Coldwell ColdwellAlkaline AlkalineCunolex. Complex. tario Two Duck Ontario 1. Geology and Structure Structure L Geology and WATKINSON (Dept.Geo1 ogy, Carleton Carleton University U n i v e r s i t y and and DAHL R,. IiEfawa—Carleton Centre oscience Studies, Ottawa-Carleton Centre f o for r Geoscience Studies, Ottawa, Ottawa, Ontario, DAHL R., WATKINSON D.H. DH .. (Dept.Geology, Ontario, 586) 586) 800—543Granvi Granville McGORAN (FleckResources Resources Ltd., Ltd., 800-543 St., Vancouver, 1l e St., McGORAN AM.J.W. (Fleck B.C., B C .,. V6C V6C 1X8) 1x8) 1(15 K1S TheColdwell Coidwell Alkaline Alkaline Complex, onthe thenorth north shore shore ooff Lake Superior, iiss The Complex, on Lake Superior, composite intrusion layeredgabbroic gabbroict oto syeni syenitic ti c aa Proterozoic Proterozoic composite intrusion o f oflayered rocks. Along Along iits occurs an an arcuate arcuatebbelt rocks. t s eastern eastern boundary boundary occurs e l t of of layered layered gabbroic rocks rocks regarded as aa single intrusive gabbroic regarded as intrusiveunit u n(CURRIE, i t (CURRIE, 1980). AA platinum—group_element(PGE) (PGE) and copper depositwas wasoutlined outlined through platinum-group-element and copper deposit 1986; WAIKINSON 1986)i in recent exploration exploration (DM1 recent (DAHL et e t aT., al., 1986; WATKINSON etetalal., ., 1986) n the sameunit. unit. Detailed mapping (1:200),structural structural analysis same mapping (1:200), analysis and and logging logging ooff new new ddrill r i l l core coreoutlined o u t l i n e da adistinct d i s t i n ccoarse—grained t coarse-grained gabbroic gabbroic tto o monzonitic intrusion, the Two Duck Lake Intrusion, cross-cutting the monzonitic intrusion, the Two Duck Lake Intrusion, cross-cutting the copper—PGE layered gabbroic unit, and corresponding layered u n i t , and corresponding ttoo the copper-PGE mineralization. Two Duck Lake Intrusion is a N—S elongated dyke—shaped mineralization. Two Duck Lake Intrusion i s a N-S elongated dyke-shaped unit, ofol3Qn maximum width, width, continuously continuouslyexposed exposed for f o r1.5km. 1.5km. It It is is f 1%maximum discordant to the large scale stratigraphy of the layered gabbro, discordant t o large scale stratigraphy o f the layered gabbro, and and to c layeri ng, and c brecci a and t o its i t mesoscopi s mesoscopic layering, andexhi e x hbits i b i t smagmati magmatic breccia and xenolithic zones along the eastern (bottom) and western x e n o l i t h i c zones along the eastern (bottom) and western (top) contacts. Along contacts. Along the t h e eastern easternboundary, boundary, the t h ecoarse—grained coarse-grained gabbro gabbro intrudes foliated mafic and felsic Archean metavolcanics, the the i n t r u d e s f o l i a t e d m a f i c and f e l s i c Archeanmetavolcanics, ffoliation o l i a t i o n of o fwhich which isi ssystematically systematically subparallel subparallel tto o the the intrusion, intrusion, suggestingthat that it it was majorf fault was intruded intruded along along aa pre—existing pre-existing -major a u l t or or suggesting Steeply shear zone. zone. This This early structure structurehas hasthen thenbeen been reactivated. reactivated. Steeply dipping ttoo the becomes nothernpart, part,the theintrusion intrusion becomes more more dipping the west west ini nthe thenothern thethe coarse—grained coarse-grained fflat l a tsouthward. southward. Several Several phases phases ooff faulting faultingaffected affected gabbroic intrusion. intrusion. They are ooff various gabbroic They are various intensity, i n t e n s i t y , and and consist consist subvertical fault, and essentially of o f aamajor majorNNE NNE subvertical andaaconjugate conjugate network network of minor andSE SEtrending trendingfaults faults and andfractures. fractures. The Therelative relative offsets offsets of minor NE ME and along these these structures structures vary strike, and along vary along along strike, andare are responsible responsible for forsome some off the the intrusion. intrusion. o the discontinuities discontinuities of o f the CURRIE ological Survey Bulletin 287, OJRRIE K.L.,K.L.,Geological Survey of ofCanada Canada Bulletin 287, 1980. 1980. McGORAN JJ.W., G.A.C.—M.A.C.-C.G.U. DM11 WATKINSON D DJL, ., WATKINSON H.,. McGORAN U . ,. UC.-MAC.-CLU. JJoint oint DAHL RP., Annual Meeting, Meeting, May May 1986, 1986,program programwith withabstract, abstract, vol.11, Annual vol.11, p.61. p.61. WATKINSON DAHL McGORAN ibid., p.142. UATKINSON O.H.,D.H.,DAHL R., R.,McSORAN J.W., LW., ibid., p.142. J U Li U U -20- j U �Tv (kick Like LakeIntrusion, Intrusion, Coldwell CoidwellAlkaline Mkaline complex. complex.Ontario. (tario.. TMD Dude II. Petrology Petrology and base-metal /P( qeochi stry IL base-metallP6E qeocheçistr R., MATKINSON OJL (Department (Departmentoof Geology, Carleton Carleton University University WHL R. f Geology, ' SWd Ottawa-Carleton Centre for Geoscience studies, and Ottawa-Carleton Centre f o r Geoscience studies, Ottawa Ottawa DAHL WATKINSON D.H. Ontario, KiS Ontario, K1S 586) 586) McGORAN J J.W. (Fleck Resources Ltd., 800—543 Granville st., st., Vancouver HcGORAN M .. (Fleck Resources Ltd., 800-543 Granville Vancouver V6C BB.C., C. ,. V6C 1X8) 1x8) Detailed carried Detai 1ed petrological petrologi ca1and andgeochemical geochemicalcross—sections cross-secti ons have have been been carried out across Lake IIntrusion out across Two Two Duck Duck Lake n t r u s i o n iin n order order to t o identify i d e n t i f y any any and geochemical ppetrological e t r o l o g i c a l and geochemical sstratigraphy t r a t i g r a p h y oor r zoning, zoning, ttheir heir and geochemical and tto relationships, and relationships, o enlighten enlighten petrological p e t r o l o g i c a l and geochemical relationships with host Archean metavolcanics on the eastern margin, relationships with host Archean metavolcanics on the eastern margin, section and Coldwell Coldwell Eastern on the the western Typical section Gabbro on western margin. margin. Typical and Eastern Gabbro consists from bottom to top of 3 main subunits. consists from bottom t o top of 3 main subunits. of L AAfine to to medium-grained fine d m - g m l n e dhornblende hornblende gabbro gabbro to to monzodiorite Monzodlorite of ophitic to poikilitic textures (plagioclase, K—feldspar, augite, o p h i t i c t o p o i k i l i t i c textures (plagioclase, K-feldspar, augite, olivine, o l i v i n e , hornblende, hornblende, bbiotite, i o t i t e . apatite, apatite, chalcopyrite, chalcopyrite, cubanite, cubanite, pyrrhotite, ± [quartz, magnetite, pentlandite, prehnite, actinolite, actinolite, pyrrhotite, [quartz, magnetite, pentlandite, prehnite, chlorite, serpentine, recrystallized chlorite, serpentine, calciteJ) calcite]) including includingnumerous numerous recrystal 1ized and and partially melted xenoliths of metavolcanic material, and numerous p a r t i a l l y me1t e d x e n o l i t h s o f metavolcanic material, and numerous granophyric pods. pods. 2. coarset otoppegmatitic ferrogabbrot otof eferrodiorite 2. A A coarse e g m a t i t i c oolivine l i v i n e ferrogabbro r r o d i o r i t e ooff ol i lvi hypididiomorphi omorphi pegmati ctictextures textures (plagi oclase, ocl ase, augite, augite, 01 v i ne, ne, hypi c tcotopegmatiti Fe—Ti—oxides, biotite, apatite, [orthopyroxene, chalcopyrite, chalcopyrite, Fe-Ti-oxides, b i o t i t e , apatite, + [orthopyroxene, prehnite, cubanite, pyrrhotite, pyrrhotite, pentlandite, serpentine, actinolite, actinolite, prehnite, cubanite, pentlandite, serpentine, chlorite, calciteJ), cross-cut by numerous podsoof cross—cut by c h l o r i t e , calcite]), numerous pods f gabbro gabbro ttoo monzodiorite occur. monzodi o r it e pegmatites pegmatites where where granophyres granophyres may may occur. coarset to verycoarse-grained coarse—grainS gabbro 33. . AA coarse o very o l olivine i v i n e gabbro t otod idiorite o r i t e wwith ith augite, olivine, hypidiomorphic poikilitic iv i ne, te, 01 textures (plagioclase, (plagioclase, augi hypi d i omorphi c t otopoi k i 1iti c textures cubanite, pyrrhotite, orthopyroxene, biotite, biotite, apatite, apatite, chalcopyrite, chalcopyrite, cubani orthopyroxene, te, pyrrhoti te, ± [K—feldspar, epidote, chlorite, chlorite, pentlandite, Fe—Ti—oxides, pentlandite, Fe-Ti -oxides, + [K-feldspar, sphene, sphene, epidote, albite, prehnite, numerous albite, prehnite, actinolite, actinolite,calcite]), calcite]),including including numerous xenoliths xenoliths and blocks ooff equigranular from and blocks equigranular fine—grainS fine-grained olivine—biotite o l i v i n e - b i o t i t e gabbro gabbro from the Eastern Mostoof theseinclusions inclusionsdid did not not suffer Eastern Coldwell Coldwell Gabbro. Gabbro. Most f these suffer L ppartial a r t i a l melting melting as as did xenoliths xenoliths in i n subunit subunit 1. The abundance of hydrous and volatile—rich minerals near the the contacts The abundance o f hydrous and volatile-rich minerals near of the intrusion and the common association of pegmatites with o f t h e i n t r u s i o n and t h e common association o f pegmatites w ith xenoliths suggest that assimilation xenoliths suggest that assimilation took took place place at a tboth botheast eastand and west west boundariesoof intrusion and boundaries f t the h e intrusion and through through the xenolithic xenolithicmaterial. material.Base— Basemetal and PGE geochemical distributions follow the petrographic metal and PGE geochemical d i s t r i b u t i o n s f o l l o w t h e petrographic zoning, iinn that zoning, t h a t they they are areconcentrated concentrated assymetrically assymetrical 1y along along the the boundaries. The asymmetry of ore concentration is attributed boundaries. The ~ S F e t r Yo f ore concentration i s a t t r i b u t e d to to the bottom bottom by by gravity ppartial a r t i a l withdrawal withdrawal of o f assimilated assimilated material material from from the and concentration concentration ooff volatile/Cu+PGE—rich towardthe the top top ooff the and volatile/Cu+PGE-rich f l ufluids i d s toward intrusion. intrusion. + —21— �U U U Northeastern Northeastern Extension Extension of of the the Proterozoic Proterozoic Igneous Igneous Terranes Terranes of Mid—continental North America of Mid-continental North America A. A. DAVIDSON DAVIDSON and and 0. 0. VAN VAN Geological Survey Geological Survey of of BREEMEN BREEMEN Canada, Canada, U (Lithosphere Canadian Shield Shield Division, Division, (Lithosphere && Canadian 588 Booth Street, Ottawa, 588 Booth Street, Ottawa, Canada Canada KLA KIA OE4) 0~4) Granites Granites and and rhyolites rhyolites ranging ranging in in age age from from 1.8 1.8 to to 1.34 1.34 Ga Ga are are known known to underlie much of mid—continental North America west of the Phaneroto underlie much of mid-continental North America west of the Phanero— zoic zoic Michigan Michigan Basin. Basin. U—Pb U-Pb zircon zircon ages ages of of similar similar rocks rocks adjacent adjacent to to the the Grenville Ma; Killarney Killarney Grenville Province Province in in Ontario Ontario (Killarney (Killarney granite, granite, 1742 1742 Ma; porphyry, porphyry, 1732 1732 Ma; Ma; Bell Bell Lake Lake granite, granite, 1470 1470 Ma) Ma) suggest suggest that that the the mid— midcontinental continental terranes terranes extend extend northeast northeast beneath beneath and and beyond beyond the the Michigan Michigan Basin. Basin. Prevalence Prevalence of of similar similar U—Pb U-Pb zircon zircon ages ages obtained obtained from from meta— metagranitoid affected by by granitoid plutonic plutonic rocks rocks southeast southeast of of the the Grenville Grenville Front, Front, affected the the interpretation that the 1.15 1.15 to to 1.0 1.0 Ga Ga Grenvillian Grenvillian orogeny, orogeny, prompts promptstheinterpretation that deformed deformed equivalents equivalents of of the the mid—continental mid-continental Proterozoic Proterozoic rocks rocks form form the the bulk of the Grenvillian crust immediately east of Lake Huron. Farther Farther bulk of the Grenvillian crust immediately east of Lake Huron. east, east, pre—1.35 pre-1.35 Ga Ga terranes terranes are are tectonically tectonically occluded occluded by by 1.28 1.28 to to 1.25 1.25 Ga Ga Grenville Supergroup volcanic and sedimentary rocks and 1.26 to 1.22 Ga Grenville Supergroup volcanic and sedimentary rocks and 1.26 to 1.22 Ga Elzevirian themselves deformed deformed and and intruded intruded by by even even Elzevirian plutonic plutonic rocks, rocks, themselves younger Grenvillian plutons. Recognition of ca. 1.65 Ga and younger Grenvillian plutons. Recognition of 1.65 Ga and 1.5 1.5 to to 1.35 1.35 Ga Ga granitic, granitic, volcanic volcanic and and anorthositic anorthositic rocks rocks on on both both sides sides of of the the Grenville Sweden, Grenville Front Front in in Labrador Labrador and and in in the the Sveconorwegian Sveconorwegian Province, Province, Sweden, attests attests to to the the widespread widespread nature nature of of igneous igneous activity activity comparable comparable in in age age and type to that which characterizes the mid—continental terranes. and type to that which characterizes the mid-continental terranes. U U z. j U -j '-S U U —22— �Geochemistry Geochemistry and and Petrography Petrography of of Selected Selected Early Early Proterozoic Metadiabase Dikes Proterozoic Metadiabase Dikes from from Marquette County, Marquette County, Michigan. Michigan. P.M. EICK (Dept. (Dept. of of Geology Geology and and Geol. Geol. Engrg., Engrg., Michigan Michigan Technological University, Roughton, MI 49931) Technological University, Houghton, MI 49931) Early Early Proterozoic Proterozoic dikes dikes and and sills sills of metadiabase intrude the sediments of the Marquette Range Supergroup Supergroup and intrude the sediments of the Marquette Range and the Archean Granite—Greenstones throughout Marquette the Archean Granite-Greenstones throughout Marquette County, County, Michigan. Michigan. Between Between Champion Champion and and Marquette, Marquette, thirteen thirteen selected metadiabase dikes (.5—75 m wide selected metadiabase dikes (.5-75 m wide and and 44 km km long) long) were were studied. studied. One thick dike wasf .studied, - in detail for intra—intrusive intra-intrusive variations. variations. The metadiabase is is medium to coarsely crystalline, dark green to greenish black in in color, color, commonly commonly porphyritic, porphyritic, There is with ophitic to sub—ophitic textures. ophitic to sub-ophitic textures. There is 15—40% 15-40% groundmass, which is comprised of chlorite, calcite, biot— groundmass, biotite, amphiboles amphiboles and and quartz. quartz. Some sections have up to to 15% 15% large (.3—15mm) (.3-15m) phenocrystic relict plagioclase and pyrox— pyroxene crystals. They are altered with reaction rims of chlorite, hornblende hornblende (uralite), (uralite), and and biotite. biotite. The phaner— phaneritic mineral assemblage, other other than than the the phenocrysts, phenocrysts, accounts for for 35—75% 35-75% of the the rock, rock, and and is is composed composed of of the the following minerals minerals (vol. (vol. %): %): plagioclase, 18; 18; amphiboles, amphiboles, 15; chlorite, 15; calcite, calcite, 12; 12; quartz, quartz, 12; 12; pyroxene, 10; 10; biotite, 8; 8; opaques, opaques, 8; 8; apatite, apatite, 1; 1; and and sphene, sphene, 1. 1. The metamorphic grade is is low to middle greenschist facies, fades, but there there are are no foliations foliations visible visible in in hand hand specispecimens. There is extensive secondary mineral growth of mens. fibrous amphibole, felty chlorites chlorites with quartz, quartz, and and calcite calcite which is in micro—veinlets. There are multiple stages is in micro-veinlets. stages of oxy—exsolution oxy-exsolution in in titaniferous magnetites. magnetites. The The primary primary ilmenites have reaction rims of rutile and secondary conversion of the the rutile rutile to to sphene. sphene. Geochemical Geochemical data data thuggest suggest that the metadiabases are are tholeiitic in character. tholeiitic in character. The average chemical composition composition is 13.6; total total Fe Fe as as Fe FeO3, is (wt%): (wt%): Si02, 47.7; 47.7; A120.,, A1 0 13.6; 03, 17.3; 17.3; MgO, 8.3; CaO, 7.5; Na.,O, 1.9; K20, 1.3; TiO.,, 1.8; MgO, 8.3; CaO, 7.5; Na 02 3.9; K 0, 1.3; Ti0 1.3; P205, P 05, .4; PPM: V, V, 371; .4; and MnO, -0, .2. .2. In P?M: 3713 Cr, 264; 264; Nt, N?, 124; 124; Cu, 58; 58; Zn, Zn, 94; Rb, 27; 27; Zr, Sr, 337; 337; Y, Y, 24; 24; and and Zr, Zr, 134. 134. This compositional average reflects reflects the the data from from seven seven different different intrusive intrusive bodies. bodies. It should also be noted that there is is as much intra—intrusive intra-intrusive geochemical geochemical variation variation as as there there is is inter—intrusive inter-intrusive variation. variation. Further data analysis analysis is is curcurrently being performed. performed. , —23— , ~8, �- The Great Great Abitibi Abitibi Dyke petrological overview overview The Dyke — petrological J R.E. ERNST ERNST and and K. K. Sell R.E. Bell (Dept. of of Geology, Geology, Carleton Carleton University University & (Dept. & Ottawa—Carleton Centre for Geoscience Studies, Ottawa-Carleton Centre for Geoscience Studies, Ottawa, Ottawa, Ontario, Ontario, 1(15 5B6) 556) K1S The Abitibi Abitibi dyke dyke swarm, The swam, southeastern southeastern Superior Superior Province, Province, Canadian Canadian Shield, consists of at least 10 major dykes. The largest Shield, consists of at least 10 major dykes. The largest of of these, these, the Great Abitibi Dyke (GAD), is more than 600 km long, up toe0.25 the Great Abitibi Dyke (GAD), is more than 600 km long, up tor-"O.25 km wide wide and km and subvertjcal subvertical in in attitude. attitude. Previous workers have shown shown that that the age age of of the the GAD GAD and and probably probably the of the the rest rest of the swarm, swarm, is is 1.14 1.14 Ga Ga the (U—Pb data from from baddeleyite baddeleyite and (U-Pb data and K—Ar K-Ar data data from from biotite). biotite). .JJ The GAD GAD consists consists of of transitional weakly alkaline The transitional to to weakly alkaline olivine olivine gabbro gabbro to monzodiorite monzodiorite which which can be subdivided to can be subdivided into into two two compositional compositional groups groups (Unit Unit 1 (Unit 11 and and 2). 2). Rocks Rocks of of Unit 1 occur occur along along the the entire entire length length of of the the dyke, while while Unit Unit 2 rocks are are restricted dyke, 2 rocks restricted to to the the dyke dyke interior interior over over about half half of about of the the dyke dyke length. length. A Mg/ A linear linear relationship relationship between between the the Fo Fo content content of of olivines, olivines, the the Mg! (Mg + Fe) ratio of clinopyroxenes and the whole—rock Ba concentra(Mg + Fe) ratio of clinopyroxenes and the whole-rock Ba concentrations suggests suggests compositional compositional control by fractional tions control by fractional crystallization. crystallization. The range in chemistry (particularly for The range in chemistry (particularly for olivines) olivines) is is comparable comparable to to that found in large, layered, mafic bodies such as Kiglapait that found in large, layered, mafic bodies such as Kiglapait and and Skaergaard. Skaergaard. The variation in rocks can can be be modelled modelled The chemical chemical variation in Unit Unit 11 and and Unit Unit 22 rocks by fractionation of olivine and plagioclase from a magma by fractionation of olivine and plagioclase from a magma corresponding corresponding in.composition to to the most primitive, primitive, chilled—margin in.composition the most chilled-margin sample. sample. Some of these rocks could only have been derived, in in situ, if if olivine olivine and and plagioclase plagioclase settled settled out out to to deeper deeper levels levels in in the the dyke. dyke. synformal Feldspar alignment at at one one traverse traverse across across the the dyke dyke defines defines aa synforinal foliation (restricted (restricted to Unit 2) which suggests suggests that that the the dyke dyke dips dips southwards at about 75". Asymmetrical variation southwards about 75°. variation in in foliation foliation and and chemistry across across the dyke suggests suggests that that the the dyke dyke was was south—dipping south-dipping during intrusion. during intrusion. Incompatible—element spidergrams from the GAD are compared with data Incompatible-element The GAD patterns from igneous rocks of various tectonic settings. The abundances are similar and abundances similar to to those those of of Ocean Ocean Island Island Basalts Basalts and and some some Relative to these, the uncontaminated Continental Continental Flood Flood Sasalts. Basalts. Relative GAD is enriched in Ba, Eu, K, P, and Ti, Ti, and and depleted depleted in in Hf Hf and and Zr. Zr. -d The GAD GAD may may be be part part of of Lake Lake Superior Superior Keweenawan Keweenawan volcanism. volcanism. The age The and paleomagnetic signature signature of the the GAD, GAD, suggest suggest emplacement emplacement during during interval of Lake Superior Superior Keweenawan Keweenawan the lower 'narmal' 'normal' polarity interval stratigraphy. A positive Eu anomaly, anomaly, high high Al203 AlzOi and and other other aspects aspects cheistry of the GAD are similar to those of of some Lake Lake Superior Superior of the cheiatry Keweenawan volcanics. -J —24— 1 U �The U Utility The t i l i t yofofWerner WernerDeconvolution Deconvolutionasa sa Geomagnetic a GeomagneticMapping Mapping Tool in Tool i n East—Central East-Central Minnesota Minnesota R.J. (Department Geologyand andGeophysics, Geophysics,University University of R.J. FERDERER FERDERER (Department of ofGeology of MinMinnesota, nesota, Minneapolis, Minneapolis, MN MN 55455) 55455) V.W. CHANDLER (Minnesota Geological Survey, V.W. CHANDLER ( ~ i ~ e s o Geological t a Survey, St. st. Paul, Paul, MN MN 55114—1057) 55114-1057) Werner Werner deconvolution deconvolution is is an an inverse inverse magnetic magnetic modeling modeling technique technique used used to estimate position, depth, susceptibility contrast, and d i p parameters parameters t o estimate p o s i t i o n , depth, s u s c e p t i b i l i t y c o n t r a s t , and dip for f o r anomaly anomaly sources sources that t h a t can can be be approximated approximated by by thin t h i n sheets s h e e t s or o r planar planar interfaces. Related software was designed specifically for microcomi n t e r f a c e s . Related software was designed s p e c i f i c a l l y f o r microcom- puters the end end product product consists c o n s i s t s of of magnetic magnetic p u t e r s and and the source parameter source parameter maps maps plotted technique was applied to p l o t t e d at a t various various scales. scales. The tohigh—resolution high-resolution The technique was applied aeromagnetic data from east—central Minnesota flight (305 m aeromagnetic d a t a from e a s t - c e n t r a l Minnesota (305 f l i g h t lines l i n e sata 150 t 150m meant terrain samplingi intermean e r r a i n clearance, clearance, spaced m aapart p a r t with with a a 50 50 m m sampling nterspaced 400 400 m val). val). The of Werner Werner deconvolution deconvolution as a s aa structural s t r u c t u r a l and and lithologic lithologic The utility u t i l i t y of mapping mapping tool t o o l has has been been proven proven by by its its application a p p l i c a t i o n in i n areas a r e a s where where direct direct geological major syncline exist. tThe geological and and drill d r i l l hole hole information information exist. h e major syncline in i n the the North Cuyuna iron i r o n district d i s t r i c t is i s successfully s u c c e s s f u l l y represented represented by by North range range of of the t h e Cuyuna Results obtained north of tthin h i n sheet s h e e t solutions. solutions. Results obtained north of the the major major syncline syncline imply elongate, syncline. syncline. second, more more elongate, imply aa second, Along the the northeastern northeasterntwo— twoAlong thirds is represented t h i r d s of of the theSouth Southrange, range, the theiron—formation iron-formation is represented by by tthin hin sheets sheeta dipping dipping steeply s t e e p l y southeast, southeast, consistent c o n s i s t e n twith with observed observed data. data. Along the third, calculated t h e southwestern southwestern third, c a l c u l a t e d dips d i p s systematically s y s t e m a t i c a l l y change change tto o steeply steeply north. north. Northeast L a c s Lake Lake in i nthe theGlen GlenTownship Township area, area, a aknown known Northeast of of Mille MilleLacs syncline—anttcline pair is successfully represented by thin sheet solus y n c l i n e - a n t i c l i n e p a i r i s s u c c e s s f u l l y represented by t h i n s h e e t solutions bodiesaare t i o n s •. The The causative causative magnetic magnetic bodies r e ppyrrhotite y r r h o t i t e layers, l a y e r s , tthat h a t at a tone one time were considered consideredffor miningasasaa source source of of ssulfur, u l f u r , and/or and/or metametatime ware o r mining morphosed diabase morphosed diabase sills. sills. Werner deconvolution Werner deconvolution results r e s u l t s are a r e presently p r e s e n t l y being being interpreted i n t e r p r e t e d in i n areas areas of poorly understood geology. East of Mifle Lacs Lake, where several of poorly understood geology. East of Mille Lacs Lake, where s e v e r a l two—dimensional two-dimensional aeromagnetic aertmagnetic anomalies anomalies occur, occur, associated associated sheets s h e e t s and and interfaces i n t e r f a c e s have been characterized c h a r a c t e r i z e d and are are consistent c o n s i s t e n t with w i t h modern conconcepts the geology geology iin n the t h e region. region. Geologic c e p t s of of the Geologic ffeatures e a t u r e s represented represented by by these magnetite— and and p pyrrhotite—rich these results r e s u l t s may may include include magnetitey r r h o t i t e - r i c h lenses, lenses, sills sills and thrust faults. and dikes, dikes, limbs limbs of of folds, f o l d s , and and thrust faults. In has been used primarily primarily to to obtain the past, past,Werner I n the Werner deconvolution deconvolution has bean used obtain depth depth estimates estimates for f o r basins basins associated associated with with oil o i l exploration. exploration. This study study shows shows that t h a t the the technique kechnique also a l s o has great g r e a t potential p o t e n t i a l as as a mapping mapping tool t o o l for for Precambrian structural geology. Precambrian terranes terrams of of complex complex structural geology. —25— �Geology area, Ontario Geology ooff the t h e Batchawana Batchawana area, Ontario ERIC C. GRUNSKY Geological Survey,7777 St., Toronto, ERIC C. GRUNSKY ( O n(Ontario t a r i o Geological Survey, G rGrenville e n v i l l e St., Toronto, Ontario O n t a r i o M7A M7A 1144) 1W4) The The Batchawana Batchawana area a r e a has h a a been been subdivided s u b d i v i d e d into i n t o two two supracrustal a u p r a c r u s t a l and and three plutonic—gneissic, litho—tectonic domains. The two three plutonic-gneieaic, l i t h o - t e c t o n i c domaina. The twosupracrusta]. aupracrustal domains domaina are a r e predominantly p r e d o m i n a n t I y volcanic v o l c a n i c and and are a r e divided d i v i d e d into i n t o aa western v a t e r n and and an eastern domain. The plutonic terranes that enclose the supracrustal a n e a a t e r n domain. The p l u t o n i c t e r r a n e s t h a t e a c l o a e t h e a u p r a c r u s t a l rocks r o c k * has h a s been b e e n previously previously subdivided s u b d i v i d e d by by Card Card (1919) (1979) into i n t o the t h e Chapleau Chapleau Oneiss, G i r i a s . Ramsey Ramsmy Gneiss, G n e i a a , and and Algoma Algoma Plutonic P l u t o n i c domains. domains. Each Each of of these t h e s e five five litho—tectonic l i t h o - t e c t o n i c domains d o m a i n a are a r e geologically g e o l o g i c a l l y and a n d geochronologically geochrono1ogica11y distinct. d i s t i n c t . The T h e two t w o asupracrustal u p r a c r u a t a l domains d o m a i n s are a r a ddistinct i s t i n c t volcanic v o l c a n i c cycles cycles that t h a t are a r e spatially spatially separated s e p 8 r a c e d by bya amajor m a j o rtectonic t e c t o n i cevent e v e n tofof'-2715 -2715 Ma. Ma. The Tha oldest o l d e s t domain d o m a i n is i f the t h e western w e a t e r n supracrustal a u p r a c r u a t a l group g r o u p of of rocks r o c k s in in the t h e Batchawana B a t c h a w a n a greenstone" " g r e e n a t o n e " belt. b e l t . The T h e succession a u c c e a a i o n is i s principally p r i n c i p a l l y aa , homoclinal h o m o c l i n a l sequence a e q u e n c a of of submarine submarine tholeiitic t h o l e i i t i c mafic m a f i c volcanics v o l c a n i c s with w i t h minor minor intercalated i n t e r c a l a t e d sediments a e d i m e n t a and a n d felsic f e l s i c tuffs t u f f a (first ( f i r a t cycle). c y c l e ) . The The entire entire sequence a e q u e n c e defines define a a single a i n g l e volcanic v o l c a n i c cycle c y c l e and and is i s interpreted i n t e r p r e t e d as as a a mafic mafic plain p l a i n extrusive s x t r u a i v e environment e n v i r o n m e n tthat c h a t grades g r a d e * from f r o mthick c h i c k flows f l o w in i n the t h e west west with w i t h minor m i n o r intercalated i n t e r c a l a t e d tuffs t u f f a and a n d sediments a m d i m a n t i eastward e r t w a r d into i n t o aa distal distal facies f a c i e a equivalent e q u i v a l e n t containing c o n t a i n i n g more more abundant a b u n d a n t sediments. a e d i m e n t a . U/Pb U/Pb zircon z i r c o n data d a d from f e l e i c tuft t u f f in i n the t h e western w e a t e r n part p a r t of of the t h e succession a u c c e a a i o n yields y i e l d # an a n age age f r o m al felsic of o f —2729 -2729 Ma Ha (Corfu ( C o r f n and and Grunsky, Grunaky, in i n press). p r e a a ) . This T h i a sequence a e q u e n c e is i s bounded hounded to to the t h e north n o r t h by by post p o e t kinematic k i n e m a t i c intrusions i n c r u a i o n e of o f -"2668 -2668 Ha Ha and and by by gneisses g n e i e a e s of of the t h e Chapleau C h a p l x u gneiss g n e i a a domain. domain. The T h e southern s o u t h e r n part p a r t of o f the t h e sequence a e q u e n c e is is bounded bounded by by aa large l a r g e (-'2715 (-2715 Ma) Ma) granodioritic g r a n o d l o r i t i c intrusion i n t r u s i o n which predates predates the is t h e the t h e younger y o u n g e r eastern e a a t e r n supracrustal a u p r a c r u a t a l group. g r o u p . The T h e western w e a t e r n boundary b o u n d a r y is covered c o v e r e d by by Keweenawan Keweenawan volcanics v o l c a n i c aand a n dit i t is i a not n o t known known how how far f a r west w e s t the the sequence a e q u e n c e extends. e x t e n d a . The T h e eastern e a a t e r n margin m a r g i n of o f the t h e western w e s t e r n domain d o m a i n is i s bounded bounded by by aa fault f a u l t that t h a t possibly p o a a i b l y developed d e v e l o p e d around a r o u n d the t h e time t i m e of o f the t h e early early intrusions i n t r u a i o n a in i n the t h e Algoma Algoma Plutonic P l u t o n i c Domain Domain (—2715 (-2715 Ma). Ha). The e e a t e r n supracrustal a u p r a c r u a c a l domain domain (second (aecond cycle) c y c l e ) can c a n be be subdivided subdivided The eastern into i n t o an a n early e a r l y mixed mixed tholeiite—calc—alkalic t h o l e i i t e - c a l c - a l k a l i c volcanic v o l c a n i c succession a u c c e a a i o n that chat evolved c a l c - a l k a l i c environment. a n v i r o n m e n t . The The upper u p p e r part p a r t of of the the e v o l v e d upward upward into i n t o aa calc—alkalic succession a u c c s ~ s i o nis i a predominantly p r e d o m i n a n t l y tufts t u f f s and a n d sediments. a e d i m e n t s . U/Pb UIPb zircon z i r c o n age age determinations d e t e r m i n a t i o i r in i n the t h e eastern e a a t e r n supracrustal s u p r a c r u a t a l group g r o u pyield y i a l da arange r a n g eofof'—2111 -2711 to t o '-'2698 - 2 6 9 8 Ma Ha (Corfu ( C o r f u and a n d Grunsky, G r u n a k y , in i n press). p r o s ) . These T h e s e ages a g e s have h a v e been been determined d e t e r m i i r d from f r o m sites d t c in i n the t h e south a o u t h east e a a t part p a r t of of the t h e eastern e a a t e r n group. group. The The volcanics v o l c a n i c aini nthe t h enortheast n o r t h e a s tpart p a r tof o f the t h e area a r e a have h e v e been b a e ninferred i n f e r r e dto t o be b e of of approximately a p p r o x i m a t e l y the t h à same mame age a g e based baaed upon upon stratigraphic s t r a t i g r a p h i c correlations c o r r e l a t i o n s from from north n o r t h to t o south. a o u t h . The The lowest l o w e a t part p a r t of o f this t h i n succession a u c c e a s i o n is i s interpreted i n t e r p r e t e d as a s aa mafic m a f i c plain p l a i n environment e n v i r o n m e n t that t h a t evolved e v o l v e d upward u p w a r d into I n t o a shield a h i e l d volcano volcano environment e n v i r o n u n t as a a evidenced a w l d a n c e d by by the t h e increasing i n c r c a i n g component component of of calc—alkalic calc-elkalic pyroclastics p y r o c l f t i c e interbedded i n t e r b e d d e d with w i t h mafic m a f i c flows. flow. The The sedimentary a e d i m e n t a r y basin b a a i n in i n the t h e north—central n o r t h - c e n t r a l part p a r t of of the t h e belt b e l t began began as a a aa distal d i a t a l environment e n v i r o n m e n t to t o the t h e mafic m a f i c plain p l a i n volcanics v o l c a n i c a at a t the t h e base b a s e of of the the eastern e a s t e r n volcanic v o l c a n i c succession a u c c e a a i o n (second (aecond cycle). c y c l e ) . The The lower l o w e r part p a r c of of the t h e basin basin is i a comprised comprised of o f turbiditic t u r b i d i t i c sediments a e d i m e n t e of o f mafic m a f i c provenance p r o v e n a n c e with w i t h minor minor amounts amounce of o f interbedded i n t e r b e d d e d felsic f e l e i c tuffaceous c u f f a c a o u a units. u n i c a . Abundant A b u n d a n t turbiditic turbiditic sediments s e d i m e n t s interbedded l a t e r b e d d e d with w i t h conglomerates conglomerates derived d e r i v e d from f r o m the t h e pyroclastic pyroclaatic events e v e n t s to t o the t h e southeast a o u t h e e a t dominate d o m i n a t e the t h e middle m i d d l e to t o upper u p p e r part p a r c of of the t h ebasin. basin. The T h e basin b a a i n was waa probably p r o b a b l y active a c t i v e from f r o m early e a r l y in i n the t h e development d e v e l o p m à § nof o f the the eastern e a a t e r n succession a u c c e a a i o n until u n t i l the t h e onset o n a e t of o f plutonism p l u t o n i a m(-'2675 (-2675 Ma). Ha). The The southern a o u t h e r n boundary b o u n d a r y of o f the t h e sedimentary a e d i m e n t a r y basin b o i n is i a fault f a u l t bounded b o u n d e d with w i t h the the older o l d e r western w t e r n volcanic v o l c a n i c cycle. c y c l e . This T h i a fault f a u l t is i a aa major m a j o r disconformity diaconformity within w i t h i n the t h e supracrustal a u p r e c r u s t a l succession. aucceeeion. The The structural structural fabrics f a b r i c * of of the t h e two two volcanic v o l c e n i c domains domaina are a r e distinctly distinctly different. d i f f e r e n t . The The western w e a t e r n volcanic v o l c a n i c cycle c y c l e (first ( f i r a t cycle) c y c l e ) is l a only o n l y slightly alightly deformed deformed with w i t h northeasterly n o r t h e f t e r l y trending, t r e n d i n g , steeply s t e e p l y dipping d i p p i n g foliations f o l i a t i o n s and and subsequently s u b s e q u e n t l y intruded i n t r u d e d by by the t h e Griffin G r i f f i n Lake L a k e and a n d Pancake P a n c a k e Lake L a k e post— postkinematic k i n e m a t i c stocks s t o c k s (—2675 (-2675 Ma). Ha). LLarge a r g e sscale c a l e pplutonism l u t o n i a m ooccured c c u r e d aat'2715 t -2715 Ma Ma —' j J J —26— �and terminated the western western volcanic and terminated the v o l c a n i c cycle. cycle. A A major major fault/shear f a u l t l s h e a r system system bbounds o u n d s tthe h e wwestern e s t e r n volcanic v o l c a n i c domain d o m a i n and a n d the t h e sedimentary s e d i m e n t a r y basin. basin. TThis his of tthe ddisconformity i s c o n f o r m i t y wwas a s pprobably r o b a b l y active a c t i v e during d u r i n g the t h e development d e v e l o p m e n t of he sedimentary s e d i m e n t a r y basin. b a s i n . TThe h e oonly n l y known k n o w n gold g o l d occurrences o c c u r r e n c e s within w i t h i n the the ggreenstone" r e e n s t o n e " belt belt occur o c c u r in in proximity proximity to to this this fault. fault. TThe h e eastern e a s t e r n volcanic v o l c a n i c cycle c y c l e (second ( s e c o n d cycle) c y c l e ) is i s dominated d o m i n a t e d by by aa ddistinct i s t i n c t nnorthwest o r t h w e s t trending t r e n d i n g schistosity s c h i s t o e i t y in i n the t h e asouthern o u t h e r n and a n d central central domain. TTop pparts a r t s of of tthe h e domain. o p ddeterminations e t e r m i n a t i o n s in i n the t h e ssoutheast o u t h e a s t part p a r t of o f tthe he o r t h w e s t ttrending r e n d i n g zzone one bbelt e l t iindicate n d i c a t e ooverturning v e r t u r n i n g of o f the t h e ssequence. e q u e n c e . AA nnorthwest that extends extends ffrom the northern northern tto southern part part oof belt demarcates that r o m the o tthe h e southern f belt demarcates thrust. TThis aa zzone o n e oover v e r which w h i c h the t h e sequence s e q u e n c e is is thrust. h i s zone z o n e is i s ppart a r t ooff aa tightly folded syncline that extends into the north central part t i g h t l y f o l d e d s y n c l i n e that extends into t h e north c e n t r a l part of o f the the northeast—east trending trending ssyncline aarea r e a wwhere h e r e it it merges merges with w i t h aa northeast-east y n c l i n e from f r o m the the northeast group group of of volcanics. northeast volcanica. This This zone z o n e developed d e v e l o p e d in in part part due due to to active active ssubsidence u b s i d e n c e aassociated s s o c i a t e d wwith i t h aa mmajor a j o r sshield h i e l d volcano v o l c a n o environment environment accompanied by by later accompanied l a t e r contemporaneous contemporaneous tectonism—plutonism. tectonism-plutonism. to be be tthe TThe h e AAlgoma l g o a a PPlutonic l u t o n i c DDomain o m a i n aappears p p e a r s co h e ooldest l d e s t pplutonic lutonic Ma). TThis tterrane e r r a e ((—'2715 ~ 2 7 1 5 Ha). h i s ddomain o m a i n iiss ccharacterized h a r a c t e r i z e d by b y massive massive granodiorite, qquartz monzonite, end and granite granite pplutons granodiorite, u a r t z monzonite, l u t o n s wwith i t h asmall n a l I enclaves enclaves of a supracrustal of u p r a c r u s t a l mmaterial a t e r i a l situated s i t u a t e d between between the the major major intrusive i n t r u s i v e phases. phases. TThe h e ddomain o m a i n iiss distinctly d i s t i n c t l y llacking a c k i n g iinn aany n y ssignificant i g n i f i c a n t amounts a m o u n t s ooff gneiss /migmat it ics u supracrus material. gneiss/migmatitic p r a c r u a t tal a l material. 2675 GGa) (' TThe h e RRamsey a m s a y Gneiss G n a i a a DDomain o m a i n ("2675 a ) iiss ddominated o m i n a t e d wwith ith metasomatized and tec:onized equivalents (paragneiss) m e t e s o m a t i z e d a n d tec:onized e q u i v a l e n t s ( p a r a g n e i ~ a of )of the the eastern eastern 1supracrustal u p r a c r u n t a l domain. domain. TThe h e ddomain o m a i n is is ccharacterized h a r a c t e r i z e d by by linear l i n e a r zones z o n e s of of by mmassive ggneiss n e i s s intruded i n t r u d e d by a s a l v e to t o foliated f o l i a t e d felsic f e l s i c plutonic p l u t o n i c rocks. rocks. The The gneiss zzones gneiss o n e aare r e commonly c o a m o n l y gneiss g n e i s s at at the the borders borders and and migmatitic rigmatitic at at tthe he cores. TThese of aamphibolite h a à § linear l i n e a r zones tones strike s t r i k e northeasterly northeasterly and and are a r e of mphibolite cores. rank metamorphism. rank metamorphic. The T h e Chapleau C h a p l e a u Cneiss G n e i s s Domain D o m a i n is i s dominated d o m i n a t e d with with a a mixture m i x t u r e of of pparagneiss, a r a g n e i x , mmigmatite, i g m a t i t a , oorthogneiss, r t h o g n e i s s , ppegmatite, e g m a t i t e , aand n d intrusive i n t r u s i v e stocks. stocks. The T h e domain d o m a i n is i s distinctly d i s t i n c t l y more m o r e heterogeneous h e t e r o g e n e o u s relative r e l a t i v e to t o the t h e Ramsey Ramsey Gneiss G n e i s s Domain Domain and and the t h e Algoma A l g o m a Plutonic P l u t o n i c Domain. Domain. the Batchawana Batchawana Area Geology of the General CKology Qwral Keweenawan volcaniciand sediments mat ic to intermediate metavolcanics telsic to interdiate m*tavoIcSflIc3 fr—fl I I metasediments f} urpCtone plutonic and migmatituc rocks . i= late to post tectonic sauc vitrusive rocks ,,49.J metagabbro' • • s.- • J p;st Kewanawan CHAPLEAU GNEISS - MOfltflS H. DOMAIN • .. t..'.' s.dr.ntary4 2 AMSEY W'Z 1 7 — I ALGOMA PLUtONIC DOMAINS —C-- flAMSEY ONEISS -\v.vDOMAIN... 9 5 10 kulom.tres —27— 15 �j Cold M Mineralization Gold i n e r a l i z a t i o n ooff The The Mishibishu Mishibishu Lake Lake Greenstone Greenstone Belt Belt J KEVIN B. HEATHER HEATHER ((Ontario Geological Survey, Survey, 10th KEVIN B. O n t a r i o Geological 7, 10th Floor, F l o o r , 77 Crenville G r e n v i l l e SStreet, t r e e t , Toronto, Toronto, Ontario, Ontario, M7A M7A 1W4) 1W4) j The Mishibishu Mishibishu Lake Lake belt is located l o c a t e d 35 35 km km west west of o f Wawa, Wawa, Ontario Ontario The b e l t is and approximately approximately 80 km south south ooff Hemlo, Hemlo, Ontario. SO tan Deformation zones and Ontario. Deformation zones known gold gold occurrences occurrences found hhost o s t all a l l the t h e known found to t o date d a t e within w i t h i n the the Mishibishu Lake The Scuzzy Scuzzy L Little Lake (1), Granges-MacMillan Mishibishu Lake belt. b e l t . The i t t l e Lake ( I ) , Granges-MacMillan Magnacon ((3), Northwest (41, (4), h Nnichi Hollinger (6) (6) and and ((2), Z ) , Magnacon 3 ) , Northwest i c h i (5), (51, Hollinger Discovery (7) gold occurrences occurrences all Discovery (7) gold a l l occur occur within within aa lithologically l i t h o l o g i c a l l y and and structurally complex zone known as the Mishibishu Deformation Zone s t r u c t u r a l l y complex zone known as t h e Mishibishu Deformation Zone (MDZ) (Figure The N No Name Lake Lake (8) gold occurrence occurrence is 1). The o Name (8) gold is hosted hosted (MDZ) ( F i g u r e 1). within the Eagle River Deformation Zone (ERDZ), while no w i t h i n t h e Eagle River Deformation Zone (ERDZ), while no gold gold mineralization been found t h e Rook Rook Lake Lake m i n e r a l i z a t i o n hhas a s been found to t o date d a t e within within the Deformation Zone (RLDZ) (Figure 1). Deformation Zone (RLDZ) ( F i g u r e 1). The 40 40 kin long MOZ MDZ extends extends eastward eastward from from tthe East Pukaskwa The km long h e East Pukaskwa River, n north of Mishibishu, River, o r t h of Mishibishu, Mishi, Mishi, and and Katzenbach Katzenbach Lakes, Lakes, at a t which which it swings swings to t o tthe h e southeast s o u t h e a s t and and continues c o n t i n u e s to t o Lake Lake Superior Superior ppoint o i n t it 1). The MDZ MDZ v varies width from ((Figure F i g u r e 1). a r i e s iin n width from 200 ZOO tto o 500 500 mm and and is is The composed of composed o f several s e v e r a l anastomosing anastornosing shear s h e a r zones zones localized localized along along aa major major The metavolcanics metavolcanics tto of tthe volcanic-sedimentary contact. volcanic-sedimentary c o n t a c t . The o tthe h e nnorth o r t h of he MDZ cconsist MDZ o n s i s t of of massive massive to t o foliated f o l i a t e d mafic mafic to t o intermediate i n t e r m e d i a t e tuffs, tuffs, and vvolcanic The llapilli a p i l l i tuffs, t u f f s , crystal c r y s t a l tuft's t u f f s and o l c a n i c bbreccias. r e c c i a s . The metasedimentary rocks of interbedded interbedded MDZ cconsist o n s i s t of metasedimentary rocks to t o the t h e south south of o f the t h e MDZ polymictic polyinictic and and oligomictic o l i g m i c t i c conglomerates, conglomerates, wackes, wackes, quartz q u a r t z grits, g r i t s , and and Both the metavolcanic and aargillites. r g i l l i t e s . Both t h e metavolcanic and metasedimentary metasedimentary rocks rocks exhibit exhibit an iincreasing of sstrain an n c r e a s i n g sstate t a t e of t r a i n as as tthe h e MDZ MDZ is is approached, approached, with with rocks rocks within the core fo the I'VZ being intensely deformed and altered. w i t h i n t h e c o r e f o t h e MDZ i n t e n s e l y deformed and a l t e r e d . J J The MOZ MDZ is is characterized c h a r a c t e r i z e d by: by: The (a) development o of ( a ) tthe h e development f aa strong s t r o n g penetrative p e n e t r a t i v e foliation foliation (including 5, C, and C shear ( i n c l u d i n g S, C, and C' s h e a r fabrics), f a b r i c s ) , aa north-northeast north-northeast plunging stretching and asymmetric plunging s t r e t c h i n g lineation, l i n e a t i o n , syawnetric symmetric and asymmetric snail small scale scale folds f o l d s of of the t h e foliation, f o l i a t i o n , chevron chevron folds f o l d s and and cconjugate o n j u g a t e kink kink bands. bands. development o of ((b) b ) tthe h e development f vvariable a r i a b l e ddegrees e g r e e s of o f hydrothermal hydrothermal the form form of of cchloritization, h l o r i t i z a t i o n , carbonatization carbonat i z a t i o n aalteration l t e r a t i o n in i n the calcite and and aankerite), n k e r i t e ) , sericitization s e r i c i t i z a t i o n (÷ ( + green ((both b o t h calcite mica), s i l i c i f i c a t i o n , and and minor minor albitization. a l b i t i z a t ion. mica) silicification, , AA rrelatively e l a t i v e l y systematic s y s t e m a t i c ppattern a t t e r n oof f alteration a l t e r a t i o n minerals m i n e r a l s flanks f l a n k s tthe he auriferous a u r i f e r o u s zones zones within w i t h i n the t h eI'VZ. ?1. IIn n order o r d e r of o f increasing i n c r e a s i n g proximity proximity minerals tto o the t h e auriferous a u r i f e r o u s zones zones the t h e dominant dominant aalteration lteration m i n e r a l s are: are: ((1) 1 ) chlorite c h l o r i t e.s.+ ccalcite alcite - -+ ppyrite yrite (2) chlorite (2) c h l o r i t e ++ aankerite nkerite -+ ccalcite alcite + ppyrite yrite ± + + - sericite + a l c i t e + ppyrite yrite ((3) 3 ) chlorite c h l o r i t e ++ sericite ± ccalcite 4 -28- J —9 �mica ÷ + green mica + cchlorite hlorite nkerite + green + ppyrite yrite ±+ aankerite (Ll) sericite + (4) sericite Gradational ccontacts between each each of of tthese groups, Gradational o n t a c t s eexist x i s t between h e s e alteration a l t e r a t i o n groups, with tthe progression manifest manifest best mafic best within within tthe h e mafic with h e ooverall v e r a l l progression tnetavolcanic and more more ccryptically within the metavolcanic rrocks o c k s and r y p t i c a l l y within t h e metasediments. metasediments. knowngold goldoccurrences occurrences iin occurwithin within tthe AAll l l known n the t h e MDZ MOZ occur h e most most anda laltered is located l o c a t e d north n o r t h of o f the the iintensely n t e n s e l y deformed deformed and t e r e d p portion o r t i o n t hthat a t is Lake sstock, of monzonitic monzonitic tto Mishibishu Lake Mishibishu t o c k , aa llate a t e ttectonic e c t o n i c iintrusion n t r u s i o n of o quartz monzonitic composition. Both quartz—feldspar (QFP) porphyry (QFP) q u a r t z monzonitic composition. Both q u a r t z - f e l d s p a r porphyry and ffeldspar porphyry (FP) and e l d s p a r porphyry (FP) ddikes, i k e s , ttexturally e x t u r a l l y similar s i m i l a r to t o those those crosscutting the Plishibishu Lake stock, occur in close c r o s s c u t t i n g t h e Mishibishu Lake s t o c k , occur i n c l o s e proximity proximity to to of porphyry porphyry several r o t r a c t e d hhistory i s t o r y of s e v e r a l ooff the t h e gold gold occurrences. occurrences. AA pprotracted emplacement is with varying varying d degrees ddike i k e emplacement is eevident, v i d e n t , as as there t h e r e are are ddikes i k e s with egrees of alteration and deformation, ranging from weakly foliated with of a l t e r a t i o n and deformation, ranging from weakly f o l i a t e d with pporphyritic o r p h y r i t i c ttexture e x t u r e preserved preserved tto o intensely i n t e n s e l y foliated f o l i a t e d quartz q u a r t z ++ sericite ++ hhematite sericite ematite ± + ppyrite y r i t e schists. schists. - - Native gold -Native gold occurs o c c u r s ini nquartz q u a r t zveins v e i n (-4s (+ aankerite nkerite ± + aarsenopyrite r s e n o p y r i t e-4+ tourmaline + pyrite p y r i t e ±+ ggalena a l e n a i-+ cchalcopyrite h a l c o p y r i t e + ssphalerite p h a l e r i t e + tourmaline lbite + ± ± aalbite green which v vary sericite + g sericite r e e n mmica i c a +± cchlorite) h l o r i t e ) which a r y ffrom r o m several several - metres in ccentimetres e n t i m e t r e s to t o several several-metres i n width width and and are a r e several s e v e r a l tens t e n s of of metres in within zones up tto metres in metres i n llength, e n g t h , within zones up o several s e v e r a l metres i n thickness. thickness. Three ttypes mineralized q quartz Three y p e s ooff mineralized u a r t z vveins e i n s have have been been recognized: recognized: strongly boundinaged foliation—parallel pods of quartz, s t r o n g l y boundinaged f o l i a t i o n - p a r a l l e l pods of q u a r t z , laterally laterally continuous zones at aa continuous zones ooff quartz q u a r t z vveins e i n s which which ccrosscut r o s s c u t the t h e foliation f o l i a t i o n at low angle and likely occupying large shear fractures, iate quartzlow a n g l e and l i k e l y occupying l a r g e s h e a r f r a c t u r e s , l a t e q u a r t z ffilled i l l e d ffractures r a c t u r e s within within both both of o f above above vein vein types. types. between tthe majority of tthe There is is aa sspatial p a t i a l rrelationship e l a t i o n s h i p between he m a j o r i t y of he There known gold occurrences within the MOZ and major structures, commonly known gold occurrences within t h e MOZ and major s t r u c t u r e s , commonly by diabase t h e MDZ. MDZ. ffilled i l l e d by d i a b a s e dikes, d i k e s , that t h a t intersect the o Scuzzy Little (Dominion Explorers LimitedlAuj C Mishibishu Lake Greenstons Belt (T) Scuzzy UttlaLake LUalDominion Explarwi LimitadIUal MtaMUlM Lie O r ~ m l à §Â ¥ i ® Grsngss—MacMjllan(Grang,s Exploration (2) ~M~U-MMMIIIM~&M~U ~ x t ~ o f t iLimitecu umitmii an eBathelithic m ~ m Grsnltold a~r *u 4 1Rocks ~mi* Mishibishu N I ~ M N ~Lake ~akm ~ M Stock soak S Iron # 5- Lead Copper ® Tungsten Tlimtu .. Deformation 1 D d * n à ‘ t l ÃZones ZMà GJ 3 lMagnacon i ~ f l n ~ c o(Muacocho n i ~ u l c o cExplorations n o ~ x p t oufLimitedxhlj)(MI tm l~n i ti w x ~ ~ u ) ~ ~ Northwest 4 N o r t h ~ Ã(Westfield <§w n t f M dMinerals à ‘ n u a LimitedflAu) umitad~~~ul Amichi I(Westfield Minerals Umitadllml Limited)(M} s Amteill W U t f l l d MlnÈr> ® Hollinger Hollingw(Westfield IWÑtfiU Minerals M h i w ÃLimited)(Aga) UmltadlIJki) 0 Discovery Limited)(M) @ ~ i ~ o n(Westfield ~r wy u t f t aMinerals Minuall ~ u mitw~iw ® NNo @ O Name Nun* Lake LUr (Central ICWtlÈCrud,.C n i d aNoranda -N~ind8 Exploration UmitadIlJIu) Limited)(M) Eiptoratlon 8 8' —29— �Stratigraphic Archean S t r a t i g r a p h i cEvolution Evolution of of part p a r tofofthe the ArcheanItasca I t a s c aCounty County Metavolcanic Metavolcanic Belt, Belt, Northern NorthernMinnesota Minnesota MARK 057) MARK A. A. JIRSA JIRSA (Minnesota (Minnesota Geological Geological Survey, Survey, St. S t . Paul, Paul, MNMN55114—1 55114-1057) The southwestern—most ItascaCounty County metavolcanic metavolcanic belt beltis ithe s the southwestern-most exposed exposed The Itasca Archean metavolcanic terrane in the Superior Province, It Archean metavolcanic t e r r a n e i n the Superior Province. It lies l i e s4040km km west it by w e s t of of the the western western Vermilion Vermilion ddistrict, i s t r i c t , separated separated from from it by Giants Giants Range Range Granite Granite and and several s e v e r a l major major faults f a u l t s•. Rocks Rocks exposed exposed iin n the the southern southern part p a r t of of the t h e belt, belt, subject s u b j e c t of of this this in quadrangleaare i n the the Sherry Sherry Lake Lake 7—1/2—minute 7-1/2-minute quadrangle r e the the Volcanic andcclastic Volcanic and l a s t i c rocks rocks in i nthe theSherry Sherry Lake predominantly Lake area a r e a are a r e generally generallyupright uprightand andsteeply s t e e p l ydipping, dipping,with with predominantly east Locally e a s t and and southeast southeast younging younging directions. directions. Locally complex complex fold f o l d patterns patterns are the result r e s u l t of of at a t least least two two deformations, deformations, the the dominant dominant one one (D2) (D2) being being a r e the aa transpressional transpressional event. event. presentation. presentation. two Two contrasting contrasting cycles cycles of ofvolcanism volcanism and and sedimentation sedimentation exist e x i s t in i n the the Sherry Sherry Lake Lake area area (see (seefigure). f i g u r e ) . AA lower lower sequence sequence of of mafic mafic to t o felsic felsic volcanic volcanic and and clastic clastic rocks rocks capped capped by by iron—formation iron-formation is i s conformably conformably overlain predominantlyofof bbasaltic overlain by by aa second second sequence sequence composed composed predominantly a s a l t i c flows. flows. Both Both are a r e metamorphosed metamorphosed to to greenschist greenschist and, and, locally, locally, amphibolite amphibolite facies. fades. The The lower lower sequence sequence is is at a t least l e a s t 2500 2500 mm thick thick and and contains contains plagioclase— plagioclasephyric, pillowed, mafic to intermediate flows, blocky f e l s i c flows, flows, and and phyric, pillowed, mafic to intermediate flows, blocky felsic lenticular units of volcaniclastic and clastic rocks. The succession l e n t i c u l a r u n i t s of v o l c a n i c l a s t i c and c l a s t i c rocks. The succession becomes more felsic f e l s i c and and fragmental fragmental stratigraphically s t r a t i g r a p h i c a l l y upward upward becomes increasingly increasingly more (eastward), and finally passes into laminated, sulfide—, (eastward), and f i n a l l y passes into laminated, sulfide-, magnetite— magnetite- and and chert—rich andt utuff inferred to chert-rich iron—formation iron-formation and f f inferred to have have been been deposited deposited in in relatively r e l a t i d y deep, deep, quiet q u i e t water. water. The The upper upper sequence sequence is is 4000 4000 mm thick thick and and consists consists mainly mainly of of dark dark green, green, massive, In massive, pillowed pillowed basalt basalt and and rare r a r e lenses lenses of of fragmental fragmental basalt. basalt. In aa broad broad sense, senae, the the upper upper sequence sequence contains contains evidence evidence of of stratigraphically— stratigraphicallyupward upward shoaling shoaling processes. p r o o f s . The the basal basal and and central c e n t r a l parts p a r t s of of the the sequence sequence contain contain aa high high proportion proportion of of massive massive flows, flows, and and lack lack vesicles vesicles and and hyaloclastite These h y a l o c l a s t i t e units units implying implying deposition deposition in i n relatively r e l a t i v e l y deep deep water. water. These grade grade irregularly i r r e g u l a r l y to to more Bore pillowed, pillowed, vesicular vesicular and and fragmental fragmental flows flows upupward In the the uppermost upparmost part, p a r t , mafic mafic volcanism volcanism was was interrupted interrupted ward (eastward). (eastward). In by by aa pulse pulse of of dacitic d a c i t i cvolcanism volcanismand andsubsequent subsequentdeposition depositionofof a a400 400in— mthick heterolithic (dacite-dominated) conglomerate and tuff sequence. t h i c k h e t e r o l i t h i c (dacita-doalnatad) conglomerate and t u f f sequence. Dacite the northeastern northeastern basalts b a s a l t s may may Dacite porphyry porphyry dikes dikes which which irregularly i r r e g u l a r l y cut c u t the represent feeders or apophyses of this felsic volcanic source. The represent feeders o r apophyses of t h i s f e l s i c volcanic source. The dacite—bearing dacite-bearing clastic c l a s t i c sequence sequence is is overlain overlain by by fragmental fragmental basaltic b a s a l t i c rocks rocks inferred i n f e r r e d to t o have h a w been been deposited deposited in in relatively r e l a t i v e l y shallow shallow water, water, possibly possibly onto The onto the t h e flanks flanks of of ananemerging emergingfelsic f e l s i ccenter. center. The source source of of mafic mafic volcanic volcanic rocks rocks in i n the the upper upper sequence sequence may may be be represented represented by by large, large, semi— aemiconcordant concordant gabbroic gabbroic plutons plutons emplaced emplaced in i n the the lower lower sequence, sequence, and and smaller smaller mafic sills and and dikes dikes within within the t h e upper upper sequence. sequence. mafic sills AA four—stage four-stage depositional depositional model model is i s outlined outlined on on the the figure. figure. —30— 1 �SCHEMATIC STRATIGRAPHIC STRATIGRAPHIC SEQUENCE SCHEMATIC SEQUENCE Fragmental F r a g w n t a l mafic mafic volcanic volcanic rocks, rocks, rare r a r e flows flows 4 LU 0z Felsic F e l s i c volcanic volcanic breccia, breccia, conglomerate, conglomerate, tuft tuff , ,. .' .. . - . :. LU = 0' LU , . . ~ : , . ;*;. Pillowed b basalt dominant Pillowed a s a l t fflows l o w s dominant . C', . . .. .. . . .', . , ~. ----------------------- LU 0 0 = Massive b basalt flows dominant dominant Massive a s a l t flows 2. 0 LU — -c 4 0= Iron—formation and argillite interbedded with volcaniclastic ffine ine v o l c a n i c l a s t i c rocks rocks A4 1% Felsic intermediate volcanic volcanic rocks rocks and and to intermediate F e l s i c to volcaniclastic and eepiclastic ccoarse o a r s e to t o ffine ine v o l c a n i c l a s t i c and piclastic LU rocks )_ C'qAq / ..' cz$ZèjZ? LU 0 -I Mafjc to volcanic rocks rocks Mafic t o intermediate intermediate volcanic 1—soom . . DEPOSITIONAL SUMMARY DEPOSITIONAL SUMMARY 1 1 volcanism passing passing upward upward tto explosive ffelsic Mafic—intermediate volcanism Mafic-intermediate o explosive elsic and sedimentation. sedimentation. tto o intermediate intermediate volcanism volcanism and 2 2. of ffelsic volcanism (collapse?), Cessation of Cessation e l s i c volcanism ( c o l l a p s e ? ) , deepening deepening of of basin, basin, rrelative e l a t i v e tectonic t e c t o n i c and and volcanic volcanic quiescence. quiescence. 3. 3 Basin filling Basin f i l l i n g with w i t h mafic o a f i c flows. flows. • • Initial resurgence of nearby felsic source, shedding d debris ebris I n i t i a l resurgence of nearby f e l s i c source, basin. 4. flows $, l w and and water—laid w a t e r - l a d tuffs t u f t s into i n t.:o shallowing shallçylng.bÇsU . . f , . . .. . —31— , . ;.. , �Geology and Geology and Precious Precious Metal Metal Mineralization Mineralization of of the Hill's Hill's Lakes Lakes Area, Area, Marquette the Marquette County County Michigan Michigan Geol. and (Dept. of of Geol. and Geol. Geol. RR.C. .C. JOHNSON and T.J. BORNHORST (Dept. Engrg., Michigan Tech. Engrg., Tech. University, University, Houghton, Houghton, MI MI 49931) 49931) J.L. VANALSTINE (Geological J.L. (Geological Survey Survey Division, Division, Department Department of of Natural Resources, Resources, Lansing, Lansing, MI MI 48909) 48909) J j 2) The bedrock (13 km 2 ) area area including including The bedrock geology geology of of aa 55 mmi.2 i . (13 sections 3, 11, 12, 13 and 14 of T. 49 N., R. 28 W, sections 3, 11, 12, 13 and 14 of T. 49 N., R. 28 W, in in northern Marquette County, County, Michigan was mapped during the the summer of summer of 1986. 1986. Several abandoned prospects and trenches as well well as significant quartz veining and alteration are contained contained within within the the area. area. The oldest rocks in in the area are Archean tholeiitic pil— pillow basalts of the Upper low basalts of the Opper Pillowed Pillowed Basalt Basalt Member Member of of the the Hill's Lakes PyroPyro— Metavolcanics of Silver Mine Hetavolcanics Mine Lakes. Lakes. The Hill's clastic Member of the Metavolcanics of Silver Mine Lake clastic Member of the Metavolcanics of Silver Mine Lake crops out out in section 11 11 and crops in section and strikes strikes to to the the northeast northeast where where It is is composed composed of highly highly further exposures are expected. expected. It deformed, white to tan, pumiceous lapilli in a black, horn— deformed, hornblende—plagioclase—garnet, blende-plagiqclase-garnet, schistose schistose matrix and and has has aa The basalts have thickness in excess of 150 150 feet feet (46 (46 mm ). ). The been intruded by Archean gabbros gabbros and and diabase of of the the Meta— Metagabbro of Clark Creek. Creek. The mafic rocks rocks have been intruded intruded by the Archean Rhyolite Intrusive Intrusive of Fire Fire Center Mine the the Granodiorite of Rocking Chair Lakes. Lakes. The Granodiorite Granodiorite of of Rocking Chair Lakes is is generally massive, massive, tan tan to pink, and and composed of granodiorites, granodiorites, tonalites, quartz monzodiorimonzodiori— is composed Their massive massive nature, nature, association tes and quartz quartz diorites. diorites. Their with schistose amphibolite facies basalts, and the the intruintrusion along the hinge of the major fold in the area suggest in the suggest granodiorites are syntectonic. These rocks that the qranodiorites rocks are are cut cut by Archean quartz veins. The Archean units are intruded by veins. intruded by Lower Proterozoic Metadiabase and Keweenawan Diabase and and are unconformably overlain by Lower Proterozoic metasedi— metasedi- J J ments. The major major structure in the area is is a large large steeply steeply plung— plungfold. The fold symmetry is outlined by a gabbro sill sill the typigal Archean foliation in the pyroclastic pyroclastic u8it. unit. The typical in the area strikes The typical typcal Lower strikes NN 68 68 W and dips d i p s44 NN. . The Lower Proterozoic cleavage strikes strikes N 74° 74 W and and dips dips 51 51 SS. . This suggests that the Archean rocks cocks were relatively relatively unaffected unaffected by the Lower Proterozgic Proterozoic deformasion. deformation. The rhyolite dikes typically strike W, a strike subparallel strike NN 70 70 W to N 60 60 W, to the Archean foliation foliation in in the the area. area. This suggests that they intruded the axial planar foliation and, and, if if contempocontempowith the granodiorites, granodiorites, are also syntectonic. raneous with ing and -32- J �The pillowed basalts are metamorphosed from lower green— schist to upper amphibolite facies. The increase in metamorphic grade is associated with contact metamorphism related to emplacement of the granodiorite plutons. Lower greenschist facies metabasalts are characterized by chlori— te—actinolite—albite—clinozosite/epidote with minor carbonate and sericite and have relict magmatic textures. The upper amphibolite facies metabasalts are characterized by hornblende—calic plagioclase—hypersthene and are schistose. Altered basalts are found closely associated with faults The alteration forms varied retrograde and shear zones. assemblages of chlorite—albite—carbonate—epidote—sericite— quartz. The retrograde assemblages indicate that the mineralization in the area postdates the Archean metamorphism. The alteration is commonly associated with pyrrhotite and pyrite and locally is associated with quartz veins. Chal— copyrite and pyrite and occasionally sphalerite—galerza— arsenopyrite—pyrrhotite are commonly associated with the quartz veins. Several quartz veins in the area exceed 1000 ft. (300 m in width. The Cenin length and 20 ft. (6 m tral Section 14 Prospect consists of one shallow test This prospect is shaft, two pits and several trenches. located on a quartz vein hosted in altered basalts adjacent to a rhyolite dike. The dominant sulfide found at this prospect is pyrite. Within this area a limited number of gold assays were completed and several were anomalous. In addition, significant areas of alteration, numerous faults and shear zones, and several large quartz veins are favorable indicators of precious metal mineralization. ) ) —33— �-J J Rhyolite volcanism from from the the Huronian Huronian of of the the Thessalon Thessalon Rhyolite and and basaltic basaltic volcanism area, area, central central Ontario Ontario WAYNE WAYME T. T. JOLLY JOLLY (Dept. (Dept. Geol. Geol. Sci., Sci., Brock Brock Univ., Univ., St. St. Catharines, Catharines, Ont. L2S 3A1) Ont. L2S 3A1) The The bimodal bimodal Huronian Huronian volcanics volcanics of of the the Thessalon Thessalon region, region, central central Ontario, Ontario, are are composed composed of of interfingering interfingering caic—alkaline calc-alkaline rhyolite, rhyolite, tholeiitic tholeiitic basalt basalt and and andesite andesite flows, flows, and and minor minor pyroclastic pyroclastic sediments sediments The erupted in a developing continental rift zone environment. erupted in a developing continental rift zone environment. The rhyolites high-LILE, low—LREE low-LREE group group (75%) (75%) rhyolites are are subdivided subdivided into into 1) I) aa high—LILE, with Ba/La ratios greater than 50, low—LREE contents (LaN 100 - 50), SO), with Ba/La ratios greater than 50, low-LREE contents (LaN == 100 and and moderate moderate HREE HREE (ERN (ERN == 15), 15). and and 2) 2) aa low—LILE, low-LILE. high—LREE high-LREE group group (25%) (LaN == 150 150 — 200). 200). and high—LREE high-LREE (LaN (25%) with with Ba/La Ba/La less less than than 20, 20, and Batch melting calculations suggest the latter were generated Batch melting calculations suggest the latter were generated by by up up to to 20% melting in granulitic siliceous tonalite gneiss at deep levels, 20% melting in granulitic siliceous tonalite gneiss at deep levels, while while the the former former were were derived derived at at shallower shallower depths depths by by about about 30% 30% fusion fusion of of low—melting low-melting sources, sources, such such as as pegmatites pegmatites and and K—rich K-rich migmatitic aigmatitic leucogranites. leucogranites. - - Tholeiitic Tholeiitic flows flows are are subdivided subdivided into into 1) 1) an an upper upper basaltic basaltic unit, unit, characterized characterized by by lithophile lithophile element element ratios ratios approaching approaching chondritic chondritic levels 80 compared compared to to 110 110 in in chondrites), chondrites), low low REE REE and and (TiIZr == 80 levels (Ti/Zr nearly nearly flat flat HREE MUSE chondrite—normalized chondrite-normalized patterns patterns generated generated by by about about 20% 20% fusion fusion of of aa peridotitic peridotitic source, source, and and 2) 2) an an early early and and central central unit unit of of fractionated fractionated andesites andesites and and subordinate subordinate basalts, basalts, with with variable variable Ti/LILE TiILILE ratios ratios (Ti/Zr (Ti/Zr ranges ranges from from 35 35 in in early early types types to to 55 55 in in central central basalts), basalts), negative and Ti Ti anomalies anomalies on on distribution distribution diagrams, diagrams, and and high high negative K, K, Zr, Zr, and REE REE with with moderately moderately fractionated fractionated HREE HREE segments, segments, generated generated by by lesser lesser degrees degrees (from (from 10 10 to to 20%) 20X) of of perid3tite peridotite melting. melting. Garnet, Garnet, amphibole, amphibole, zircon, apacite and Ti—oxide phases remained residual in the zircon, apatite and Ti-oxide phases remained residual in the source source after but only only olivine, olivine, orthop orthop roxene, roxene, and and after generation generation of of early early flows, flows, but clinopyroxene clinopyroxene persisted persisted after after removal removal of of late late basalts. basalts. Many Many of of the the early early basalts, basalts, especially especially fractionated fractionated end—members, end-members, were were contaminated contaminated by by or or hybridized hybridized with with the the rhyolitic rhyolitic liquids liquids during during aa residence BaILa vs. vs. Rb/La RbILa ratio ratio diagrams, diagrams, residence period period at at crustal crustal levels. levels. Ba/La used contamination, reveal reveal that that basalt basalt used to to constrain constrain the the degree degree of of contamination, magma was was commonly commonly mixed mixed with with up up to to 40% 40% of of either either rhyolite rhyolite type. type. Compositions Compositions of of the the basalt basalt hybrids hybrids can can be be reproduced reproduced by by mixing mixing calculations. calculations. The The mantle mantle source source of of the the Huronian Huronian volcanics volcanics displays displays evidence evidence of of aa long All of of the the basalts, basalts, including including least least long and and complex complex history. history. All contaminated contaminated and and uncontaminated uncontaminated representatives, representatives. carry carry low low Ti Ti and and Nb Nb and high Rb, Ba, K, La, and Ce, indicating their source was hydrated and high Rb, Ba, K, La, and Ce, indicating their source was hydrated and metasomatically metasomatically enriched enriched in in tILE. LILE. Pronounced Pronounced negative negative anomalies anomalies characterize Ba, Nb, P, Ti, and HREE abundances due to withdrawal withdrawal characterize Ba, Nb, P. Ti, and HREE abundance* due to of basaltic liquids liquids prior prior to to the the metasomatic metasomatic episode, episode, probably probably during during Archean Archean time. time. U d �Applicability A p p l i c a b i l i t y of of aa sediment-hosted sediment-hosted copper copper deposit d e p o s i t model model to to the Keweenawan Solor Church Formation, Minnesota the Keweenawan Solor Church Formation, Minnesota MARY (Minnesota Geological Geological Survey, Survey, St. MARY JO JO P. P. ICUHNS KUHNS (Minnesota St. Paul, Paul, MN MN 55114) 55114) ROGER J. KUHNS (Department of Geology and Geophysics, University ROGER J. KUHNS (Department of Geology and Geophysics, University of of Minnesota, Minnesota, Minneapolis, Minneapolis, MN MN 55455) 55455) Large copperddeposits Large tonnage tonnage sediment—hosted sediment-hosted s tstratiform r a t i f o r m copper e p o s i t s occur occur within within many middle to late Proterozoic basins throughout the world. Prominent many middle to late Proterozoic basins throughout t h e world. Prominent North include White Spar Lake, North American American examples examples include White Pine, Pine, Michigan, Michigan, Spar Lake, MonMonAlthough and Redstone, Redstone, NWT. NWT. Although specific s p e c i f i c processes processes of of formation formation are are ttana, a n a , and unique at each locality, these deposits share many of the unique a t each l o c a l i t y , these d e p o s i t s s h a r e many of the same same basic basic characteristics: (1) thick ( 1 ) restricted r e s t r i c t e d to t oProterozoic Proterozoic age age rocks, rocks, ((2) 2 ) thick characteristics: basina]. sequences indicative of rapid subsi—dence and sedimentation, (3) b a s i n a l sequences i n d i c a t i v e of r a p i d subsi-dence and sedimentation, (3) basic b a s i c to t obimodal bimodal volcanic volcanic association, a s s o c i a t i o n , (4) ( 4 ) thick thick 'redbed" "redbed" host h o s t rocks, rocks, and ( 5 ) "green "green beds" beds* of of marine marine or o r lacustrine l a c u s t r i n e origin. origin. Source Source rocks rocks for for and (5) copper are probably underlying basalts, but in some cases may copper a r e probably underlying b a s a l t s , but i n some cases may be be the the redheds, Deposi—tion the copper copper generally generally seems seems to t o be be redbeds, themselves. themselves. Deposi-tion of of the controlled c o n t r o l l e d by by local l o c a l reduc—ing reduc-ing conditions conditions in i n thick t h i c k redbed redbed sequences. sequences. The sequence The Solor Solor church Church Formation Formation is i s aa fluvial/alluvial f l u v i a l / a l l u v i a l redbed redbed sequence within Midcontinent rift the Iceweenawan Keweenawan Midcontinent r i f t system. system. The t h e formation formation consists consists w i t h i n the of mters of of interbedded interbedded arkosic a r k o s i c sand—stone sand-stone and and limestone. limestone. of 580 580 to t o 980+ 980+ meters Numerous the primarily primarily Numerous grayish—green grayish-green siltstones s i l t s t o n e s and and shales s h a l e s occur occur within within the redbed the presence presence of of oncolites o n c o l i t e s suggests suggests organic organic activity activity redbed sequence, sequence, and and the during d u r i n g deposition. deposition. Copper Copper staining s t a i n i n g has has been been recognized recognized in i n core core samples samples from from the the Solor Solor Church Church Formation Formation as a s well w e l l as a s in i n underlying underlying basalts. basalts. Structural S t r u c t u r a l complexities complexities within within the t h e Keweenawan Keweenawan rift—parallel r i f t - p a r a i l e l faults f a u l t a assoassociated w i t h the the Solor Solor Church Church basin basin may may represent represent basin—growth basin-growth faults. faults. c i a t e d with These These faults f a u l t s would would provide provide important important conduits conduits and and focal f o c a l points p o i n t s for for copper—bearing fluids. copper-bearing f l u i d s . Clearly the above above description d e s c r i p t i o n of of the the Solor Solor Church Church Formation Formation shows shows C l e a r l y the to environments which host known stratiform to environments which h o s t known s t r a t i f o r m copper copper deposits deposits elsewhere. Furthermore, elsewhere. Furthermore, the the Precambrian Precambrian rocks rocks of of the the Lake Lake Superior Superior region are major sources of copper (the native copper deposits region are major sources of copper ( t h e n a t i v e copper d e p o s i t s of of the the Keweenawan Peninsula Keweenawan Peninsula in i n amygdaloidal amygdaloidal basalts b a s a l t s and and conglomerates, conglomerates, and and shale—siltstone—sandstone—hosted shale-ailtatone-sandstone-hosted copper copper at a t White White Pine, Pine, Michigan). Michigan). These These examples the presence presence of of copper copper and and its its mobility n o b i l i t y in i n aa examples demonstrate demonstrate the variety v a r i e t y of of host h o s t rocks. rocks. Therefore, t h e r e f o r e , if i f aa reasonable reasonable concentrating concentrating mechamechanism nism can can be be identified, i d e n t i f i e d , the the potential p o t e n t i a l for f o r large—scale large-scale copper copper concentraconcentrations the Solor Solor Church Church Formation. Formation. t i o n s exists e x i s t s in i n the similarities similarities —35— �Major Major lithological lithological units units in in the the New Data New Data from from GENE GENE L. L. LABERGE LABERGE Wisconsin Wisconsin magmatic magmatic terrane: terrane: Drill Core Drill Core (Geology Department, UW, UW, Oshkosh, Oshkosh, Oshkosh, Oshkosh, WI WI 54901 54901 (Geology Department, and U.S. Geological Survey) and U.S. Geological Survey) More More than than 250 250 exploration exploration drill drill cores cores from from central central and and northern northern Wisconsin Wisconsin have have been been examined examined and and their their locations locations plotted plotted on on 1:250,000 1:250,000 base base maps. maps. Because Because northern northern Wisconsin Wisconsin is is characterized characterized by by extremely extremely meagre meagre outcrop, outcrop, the the data data from from these these drill drill cores, cores, in in conjunction conjunction with with the 1987), the recontoured recontoured aeromagnetic aeromagnetic map map of of northern northern Wisconsin Wisconsin (Karl, (Karl, 1987), provide provide aa significant significant improvement improvement in in the the data data base base for for inferring inferring the the regional extent of major lithologic units in the Wisconsin magmatic regional extent of major lithologic units in the Wisconsin magmatic . j J terrane. terrane The The drill drill core core demonstrates demonstrates that that northern northern Wisconsin Wisconsin consists consists of of large large areas underlain by either greenschist facies volcanic, sedimentary and areas underlain by either greenschist facies volcanic, sedimentary and plutonic plutonic rocks rocks or or by by amphibolite amphibolite facies facies quartzofeldspathic quartzofeldspathic gneisses, gneisses, amphibolites In Rusk Rusk and and Price Price count— countamphibolites and and sillimanite—bearing sillimanite-bearing schists. schists. In ies, the highly foliated amphibolite facies rocks are intruded ies, the highly foliated amphibolite facies rocks are intruded by by isotropic The potassic granites granites that that appear appear to to be be postorogenic. postorogenic. The isotropic potassic aeromagnetic map of northern Wisconsin contains several rhomboid—shaped aeromagnetic map of northern Wisconsin contains several rhomboid-shaped areas areas in in Rusk Rusk and and Price Price counties counties with with subdued subdued magnetic magnetic expression expression that that are separated by areas of similar size with high amplitude, are separated by areas of similar size with high amplitude, short short wavewavelength length anomalies. anomalies. Drill Drill cores cores show show that that the the rhomboid—shaped rhomboid-shaped areas areas are are underlain argillite and and graywacke graywacke whereas whereas the the underlain mainly mainly by by graphitic graphitic argillite magnetically magnetically high high area area are are underlain underlain by by greenschist greenschist or or amphibolite amphibolite facies facies volcanic volcanic rocks. rocks. The rhomboid—shaped rhomboid-shaped areas areas are are also also charactercharacterized ized by by gravity gravity lows lows relative relative to to the the intervening intervening areas, areas, suggesting suggesting aa horst (LaBerge and and others, others, 1986; 1986; Suszek Suszek horst and and graben graben basement basement structure structure (LaBerge and and Meyer, Meyer, this this conference). conference). Linear Linear magnetic magnetic trends trends and and the the presence presence of of highly highly foliated foliated and and flattened flattened rocks rocks along along the the margins margins of of the the rhomboid— rhomboidshaped shaped grabens grabens suggest suggest that that the the boundaries boundaries are are faults. faults. Diabase Diabase dikes dikes and and ultramafic ultramafic rocks rocks are are present present along along some some boundaries. boundaries. j The The drill drill cores cores show show that that the the Wisconsin Wisconsin magmatic magmatic terrane terrane consists consists of of numerous Tlblockstl of disparate metamorphic grade. However, numerous "blocks" of disparate metamorphic grade. However, the the strati— stratigraphic graphic and and structural structural relationships relationships between between these these blocks blocks remain remain to to be be resolved. resolved. -1 REFERENCES REFERENCES Karl, Karl, J.H., J.H., 1987, 1987, "Total "Total Magmatic Magmatic Intensity Intensity Map Map of of Northern Northern Wisconsin", Wisconsin , Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, Map Map 86—7. 86-7. LaBerge, LaBerge, G.L., G.L., Klasner, Klasner, J.H., J.H., and and Suszek, Suszek, T.J., T.J., 1986, 1986, "Early "Early Proterozoic Proterozoic Horst—Graben Horst-Graben Structures Structures in in the the Magmatic Magmatic Terrane Terrane of of Northern Northern Wisconsin", Wisconsin", Abstract, Abstract, E0S, EOS, Trans. Trans. Amer. Amer. Geophys. Geophys. Union, Union, Vol. Vol. 67, 67, No. No. 44, 44, P. P. 1211. 1211. —36— �U—Pb pitchblende from from Dickinson County, U-Pb d adating t i n g o of f pitchblende County, upper upper Michigan, Michigan, suggests structures dduring suggests rreactivation e a c t i v a t i o n of o f Precambrian Precambrian structures u r i n g formation formation of of t h e Michigan M i c h i n a n Basin Basin the GEORGE LEHMAN (Minatome Corporation,Denver, Denver, Colorado GEORGE A. A.LEHMAN (Minatome Corporation, Colorado 80265) 80265) Exploratory ddrilling Exploratory r i l l i n ghas hasdelineated delineatedan an east—west east-west s tstriking, r i k i n g , north n o r t h dipping dipping degrees)b rbrittle Lake ((—60 4 0 degrees) i t t l e fault f a u l within t w i t h ithe n t hGene e Gene LakeGneiss, Gneiss,ananArchean Archean gneiss on tthe gneiss complex complex on h e north n o r t h edge edge of o f the t h eMiddle MiddlePrecambrian Precambrian Felch FelchTrough. Trough. The The bbrittle r i t t l e fault f a u l tclosely c l o s e l ycoincides coincides with, with, and and llocally o c a l l y cuts, cuts, aa mylonitic mylonitic fault t o t hdominant e dominantFelch FelchTrough Trough trend. trend. f a u l t which which in i n turn t u r nisi sparallel p a r a l l etol the Thus Precambrian Thus t the h e mmylonitic y l o n i t i c ffault a u l t isi sataleast t l e a sMiddle t Middle Precambrian ini nage ageand and the the brittle b r i t t l efault f a u l is t i younger. s younger. Pitchblende—carbonate occursasasspace spacef ifillings Pitchblende-carbonate m imineralization n e r a l i z a t i o n occurs l l i n g swhich which have have healed healed bbrittle r i t t l estructures structures within w i t h i nthe t h ehanging hanging wall w a l l and, and, less l e s s extensively, extensively, Four pitchblende the footwall of o fthe t h eeast—west east-west ffault. a u l t . Four pitchblendesamples samples were were t h e footwall analyzed U and and Pb Pb iisotopic s o t o p i c composition composition by by Teledyne Teledyne Isotopic I s o t o p i c Laboratory Laboratory analyzed ffor or U and were ccalculated denotes and tthe h e ratios r a t i o sofo206Pb*/238U f 206Pb*/238Uand and2O7Pb*/235U 207Pb*/235U were a l c u l a t e d ((**denotes are as as follows: radiogenic lead). lead). Ratios radiogenic Ratios are sample ## sample FR3 C18/4 C2/14 C3/10 206/238 2061238 .047040 .050370 .064910 .093450 207/235 2071235 .354300 .366770 .508890 .701320 Core sampleC1814 C18/4i sisconcordant, concordant,i nindicating possible m mineralization Core sample d i c a t i n g aa possible ineralization Core sample C2/14 and surface sample are normally event Core sample C2114 and surface sample FR3 FR3 are normally event at a t 317 317 m.y. m.y. discordant (assuminga as single remobilization) discordant and and (assuming i n g l e remobili zation) represent represent modification modification of "400 and—'SOO respectively. o f mineralizations m i n e r a l i z a t i o n swith w i tminimum h minimumages ages ofof-400 a n d - 5 0 0 mm.y. y . respectively. Core sample sampleC3110 C3/10 reverselydiscordant discordantand andr results modification rom m odification Core i sisreversely e s u l t s ffrom 400 m.y., m.y., again of o f mineralization, m i n e r a l i z a t i o n ,with w i ta h maximum a maximum age age of o f 400 againassuming assuming aa i n l e t s i in n core core indicate indicate Cross-cutting v eveinlets ssingle i n g l e remobilization remobilization event. event. Cross—cutting two, possibly three, three, mineralization/remobilization two, and and possibly mineral izationlremobil i z a t i o nepisodes. episodes. Concordia—discordiai nintercepts havebeen beenc acalculated employingaall Concordia-discordia t e r c e p t s have l c u l a t e d enploying l l four four An upperi nintercept of analyses and assuming assuminga as isingle remobilization. A analyses and n g l e remobilization. n upper t e r c e p t of 403 m.y. and and aa lower lower intercept 403 m.y. i n t e r c e p t ofo f4141m.y. m.y. were wereobtained obtainedusing usinga aprogram program written While w r i t t e nbybyHaxel Haxeland andWright Wright(1982, (1982,USGS USGSOpen Open File F i l eReport Report82—898). 82-898). no attempt attempt has beenmade madet otodetermune determune the data, data, the no has been thethe u nuncertainty c e r t a i n t y i nin the the ccorrelation o r r e l a t i o n ccoefficient o e f f i c i e n t of o f the t h e discordia d i s c o r d i a best best ffiti tisi s0.996 0.996 which which is is sufficiently good to support the conclusions to follow. s u f f i c i e n t l y good t o support t h e conclusions t o 400 m.y. m.y. oold wasppartly Theccalculated The a l c u l a t e d iintercepts n t e r c e p t s suggest suggest that t h a t 400 l d uranium urani um was artly remobilized between about 50 m.y. and the present, perhaps during the remobilized between about 50 m y . and t h e present, perhaps the erosion ooff Paleozoic erosion Paleozoic sstrata, t r a t a , outliers o u t l i e r sofowhich f whichoccur occurthroughout throughout the t h e area. area. Other iinterpretations Other n t e r p r e t a t i o n s include i n c l u d e episodic episodic mineralization m i n e r a l i z a t i o n ending ending at a t about about 300 m.y. m.y. oorr aa single s i n g l eepisode episode at a t500 500tot o300 300m.y. m y .which whichhas hasbeen been mobilized mobilized 300 more than once. more than once. The Felch Feicharea areai is on tthe Basin, indeed indeed iitt can can be be The s on h e margin margin ooff the t h e Michigan Michigan Basin, viewedas ason, on, oorr near, hingel line viewed near, aa north—south north-south hinge i n e between between aa sstable t a b l e shelf —37— �to the pperiodically The most t o the t h e west west and and the e r i o d i c a l l y subsiding subsiding basin basin tto o the t h e east. east. The most active period of deposition was during the Upper Silurian, averaging a c t i v e period o f deposition was d u r i n g the Upper S i l u r i a n , averaging 65 moof sedimentper perm.y., m.y.,over overt wtwice ther rate the next 65 m f sediment i c e the a t e oof f the next active a c t i v e period, period, the Misssissippian (—30 m/m.y. deposited). Note that the close t h e Misssissippian ( ~ 3 0m1m.y. deposited). Note t h a t t h e c l o s e of o f the the Silurian S i l u r i a n corresponds corresponds nicely n i c e l y with w i t hthe t h eupper upperconcordia—discordia concordia-discordia iintercept, ntercept, 405 vs. 403 m.y., and and tthe h e close close of o f the t h eMississippian Mississippiancorresponds corresponds cclosely losely 405 vs. 403 my., with the age of the one concordant sample, 310 vs. 317 w i t h t h e age o f t h e one concordant sample, 310 vs. 317 m.y. my. Therefore t is i s strongly s t r o n g l y indicated i n d i c a t e d tthat h a t the t h e space space f ifillings, l l i n g s , and and ffault, ault, Therefore i it are are Paleozoic Paleozoic in i n age age and and represent represent reactivation r e a c t i v a t i o nofo a f aPrecambrian Precambrian structure s t r u c t u r e ini nresponse response to t o the t h eformation formation ofo fthe t h eMichigan MichiganBasin. Basin. J This by Minatome Corporation, aa subsidiary This work work was was supported supported by Minatome Corporation, subsidiary ofo fCFP CFP (Total (Total Oil), O i l ) , and and Central Central Electricity E l e c t r i c i t yGreat Great Britain B r i t a i nas aspart p a r tofo a f auranium uranium exploration exploration program. program. PERIOD/EPOCH J SEDIMENTATION SEDIMENTATION RATE RATE . (meters/m.y.) (meters/m.y ) Jurassic Jurassic Pennsylvanian Pennsylvanian Mississippian Mississippian Devonian Upper Devonian — Upper — Middle Middle &8 Lower Lower Silurian — Upper Silurian Upper — Middle Middle - Lower Lower Ordivician O r d i v i c i a n— Upper Upper — Middle Middle — Lower Lower Cambrian Cambrian ----- 1.5 2.6 30.5 16.9 28.8 65.3 6.6 8.7 28.9 17.6 5.9 2.3 U/Pb U/Pb AGE AGE (rn.y.) H.Y 1 317 J 403 J -I J Li J J J -38- J U �Sequence Sequence of of Faulting Faulting and and Folding, Folding, Southwest Southwest Michipicoten Greenstone Michipicoten Greenstone Belt, Belt, Ontario. Ontario. E. . McGILL and CATHERINE H. SHRADY SERADY Dept. Dept. of Geology and Geography, Geography, GEORGE E University of Massachusetts, Amherst, MA 01003) 01003) complicated The The rocks of of the Michipicoten Michipicoten Greenstone Belt Belt record record aa complicated Our primary objective sequence of faulting, folding and intrusion. faulting, folding and intrusion. primary objective is is to determine the tectonic setting(s) settingcs) for the deposition of the the sedimensedimenThis requires tary and volcanic rocks rocks and and for for their their early early deformation. deformation. This requires determination of the structural sequence so that the effects determination of the structural sequence so that the effects of of younger younger deformation deformation can can be be removed. removed. This abstract reviews reviews the the evidence evidence pertainpertaining to this sequence in the ing the southwest southwest part part of of the the belt. belt. Localities Localities are are the text text (in (in 1 that are referenced in by letters located on Figure located Figure 1 by letters that referenced in the All localities are in Chabanel Towtiship, and all are parentheses). parentheses). localities are in Chabanel Township, and all are in or along the margins of the the fume fume kill. kill. At present, At present, we do do not not have have the the evidence evidence needed needed to to determine determine if if the the tectonic evolution evolution of the tectonic the Michipicoten Michipicoten Greenstone Greenstone Belt Belt occurred as an an essentially continuous continuous single single event event or or as aa series essentially series of of discrete discrete events events the separated by by intervals separated intervals of little little or or no no deformation. deformation. Very likely, likely, the truth lies lies between these truth these extremes. extremes. The structural structural style style did did change, change, one characterized characterized by by penetrative deformation deformation with with cleavage developfrom one stretching, to to one characterized and marked flattening and ment and marked flattening and stretching, characterized by by that appears appears to have occurred in the brittlelductile brittle/ductile transition faulting that regime. regime. We suspect suspect that that at at least least some some of of the the early early penetrative penetrative strucstructures developed in in aa single single evolving evolving event. event. The young faults faults probably probably represent discrete discrete later later events. events. The youngest major structure the Mildred structure in in the the area area we have mapped is is the late Lake fault fault (M-M'), of a a belt-wide (M-M'), one Lake one of belt-wide system system of of NNW-trending NNW-trending late faults. All rock units and major faults that intersect the Mildred Lake faults. Correlation of three fault are offset. offset. Correlation three contacts contacts and units units with with differdiffering attitudes attitudes across the fault indicates a sinistral net slip across the fault indicates a sinistral net slipofof3.2 3.2 kin. km. An unnamed fault fault (A-A') (A-A') west of of the the Magpie River River with 700 700 m of of sinistral sinistral separation separation is very likely likely aa young young NNW-trending NNW-trending strike-slip strike-slip fault fault also. also. Next oldest is (B-B"') that that strikes strikes parallel parallel to to the the strike strike is a fault fault (B—B''') of of bedding. bedding. This fault fault has caused a dextral separation separation of of diabase diabase dikes dikes of 100-200 100-200 m; m; the true net slip slip cannot cannot be be determined determined because because the the fault fault steeply dipping does not offset offset anything than steeply anything other does other than dipping diabase diabase dikes. dikes. Diabase dikes offset by this this fault fault are are commonly commonly distorted distorted as as well, well, sugsuggesting that, that, at the the level level of of modern modern exposure, exposure, deformation deformation was was in in the the brittle/ductile transition brittlelductile transition regime regime for for the the diabase. diabase. NE-trending NE-trending faults of moderate moderate apparent apparent displacement displacement (separations (separations of of 10's to 100's 10's 100's of meters) occur throughout throughout the area, but are most abundant near the dant the east east and and south south margins margins of of the the Pleistocene Pleistocene gravel gravel plain. plain. These faults probably probably occur beneath beneath the gravel as well, and and they they could could be responsible for the relative ease of erosion of the rocks beneath erosion the beneath the the Some gravel and along the Magpie River below Siderite Junction (SJ). gravel and along the Magpie River below Siderite Junction (SJ). Some Furthermore, of of these these faults faults offset offset diabase diabase dikes, dikes, generally generally dextrally. dextrally. Furthermore, faults that offset diabase dikes dextrally commonly offset faults that offset contacts in older rocks sinistrally. It is not entirely clear if this is rocks sinistrally. It is due to to a —39— �-j single post-diabase post-diabase oblique-slip oblique-slip event or to to fault fault reactivation, reactivation, but but we we suspect the the latter. latter. Because distinctive contacts in the older rocks can be NE faults faults at at the the SW SW end end of of Mildred Mildred Lake Lake be traced traced across across the the zone of NE there can be no Cc), (C), there can no major major fault fault passing passing through through that that location location (cf. (cf. "Magpie River River fault" fault" of Sage Sage et et al., al., OGS OGS Prelim. Prelim. Map Map P.2439); P.2439); instead, instead, a set of three or four four small faults faults is is responsible for for aa sinistral sinistral sepaseparation of (where the the "Magpie River fault" of about about 300 300 in m (where fault" follows follows the the river river below Siderite Junction there there is significant significant faulting faulting due due to to coincidence coincidence NE-trending faults of HE-trending faults with with older older bedding-related bedding-related faults). faults). IDiabase dikes truncate structures, and thus are truncate all thus are Diabase dikes all penetrative structures, younger than the younger the deformation deformation event(s) eventcs) responsible responsible for for the the steep steep dips, dips, metamorphism, cleavages, metamorphism, cleavages, and and strain strain that that characterize characterize the theArchean Archeaninetametasediments and metavolcanics. Major overturning occurred with or and metavolcanics. or before before the earliest resulting in in areally earliest cleavages, cleavages, resulting areally extensive extensive terranes terranes with bedding-related opposed stratigraphic tops that are juxtaposed by opposed stratigraphic tops are juxtaposed faults. These are described described in in more more detail faults. These pre-diabase pre-diabase structures structures are detail in in a companion abstract in in this this volume. volume. speculative working working hypothesis, As a somewhat speculative hypothesis, we propose propose that the earliest structures structures formed formed during during imbrication of volcanics earliest imbrication of volcanics and and poorly poorly consolidated sediments. consolidated sediments. The bewildering complexity of the the cleavages cleavages and and in part the would thus the stratigraphy stratigraphy would thus be be due due in part to the the tendency tendency for for each each imbricate slice to have its imbricate its own stratigraphy stratigraphy and and to to some some extent extent its its own own structure structure as well. well. The generally generally steep steep bedding bedding dips dips most most likely likely are are associated with aa later later but but still still pre-diabase pre-diabase NE-trending NE-trending cleavage. cleavage. In In most most places, places, the the effects effects of of younger younger faulting faulting and and diabase diabase intrusion intrusion are are relatively minor and and can can be be "removed" "removed" by by detailed detailed mapping. mapping. Unscrambling the earliest earliest events events is the the key key to to our our effort effort to to determine determine the the tectonic tectonic significance significance of of the the Michipicoten Michipicoten Creenstone Greenstone Belt. Belt. - - Early bedding-related Early bedding-related faults faults — Younger faults Younger faults -j sJ I" -J O feet 0 fast 3000 3000 1600 o 0meters (Titters 4000 B' Fig.1. Central Fig.l. CentralChabonel Chabanel Township Township —40— -40- �- Magnacon Project Mishibishu Lake Lake Greenstone Greenstone Belt Magnacon Project — Mishibishu Belt 0.5. D.S. McPHEE McPHEE (Muscocho Explorations Ltd., (Muscocho Explorations Ltd., Suite 601, Toronto, Ontario Suite 601, Toronto, Ontario 25 25 Adelaide Adelaide Street Street East, East, M5C 1Y2) M5C 1Y2) The Magnacon Project The Magnacon Project is is located located in in the the Mishibishu Mishibishu Greenstone Greenstone Belt Belt of the Superior Province, approximately 60 kilometers of the Superior Province, approximately 60 kilometers west west of of Wawa, Wawa, Ontario. Flanagan McAdam McAdam Resources Resources Inc. Inc. owns owns 50%. 50%, Muscocho Muscocho Explorations Explorations Ontario. Flanagan Limited Windarra Minerals Minerals Ltd. 25% of of the the property. property. Limited owns owns 25% 25% and and Windarra Ltd. owns owns 25% A A royalty royalty of of 3% 3% to to 5% 5% is is payable payable to to Westfield Westfield Minerals Minerals out out of of production. production. Presently, Presently, the decline, the project project is is at at an an advanced advanced exploration exploration stage stage with with aa decline, underground underground exploration exploration and and bulk bulk sampling, sampling, plus plus surface surface drilling drilling underway. underway. Auriferous hydrothermal Auriferous hydrothermal quartz quartz veins veins occur occur within within an an extremely extremely dilatant dilatant shear gold—bearing horizon is shear zone. zone. The host rock within the the gold-bearing is aa quartz— quartzsericite—ankerite +1— fuchsite fuchsite +1— +/- chlorite chlorite +1— +/- albite albite schist. schist. sericite-ankerite +/Mineralization Mineralization is is characterized characterized by by the the presence presence of of visible visible gold, gold, pyrite, pyrite, galena, Structurally, all galena, arsenopyrite, arsenopyrite, chalcopyrite chalcopyrite and and sphalerite. sphalerite. Structurally, all primary primary textures textures have have been been obliterated obliterated within within the the shear shear zone. zone. At At October October 1986, 1986, drill—indicated drill-indicated reserves reserves were were 1,032,435 1,032,435 tons tons grading grading 0.156 oz. gold per ton or 647,769 tons grading 0.219 oz. per 0.156 oz. 0.219 oz. per ton. ton. These These reserves reserves occur occur between between lines lines 79+00W 79+OOW and and 116+00W 116MOW and and to to aa depth depth of 450 feet. of 450 feet. Displayed will be map, sections map, sections and and polished specimens, specimens, photomicrographs photomicrographs of of —41— drill drill core, core, property property geology geology ore. ore. �j Magino Magino Project Project —- Michipicoten Michipicoten Greenstone Greenstone Belt Belt D.S. D.S. MePHEE McPHEE (Muscocho (Muscocho Explorations Explorations Ltd., Ltd., 25 25 Adelaide Adelaide Street Street East, East, Suite 601, Toronto, Ontario M5C 1Y2) Suite 601, Toronto, Ontario M5C 1Y2) The The Magino Magino Project Project is is aa joint joint venture venture between between Muscocho Muscocho Explorations Explorations Limited and McNellen Resources Inc. The property consists of of 55 Limited and McNellen Resources Inc. The property consists 55 claims claims located in the Goudreau—Lochalsh area, approximately 95 kilometers located in the Goudreau-Lochalsh area, approximately 95 kilometers by by road, road, northeast northeast of of Wawa, Wawa, Ontario. Ontario. The The gold gold on on the the Magino Magino property property occurs occurs mainly mainly in in aa series series of of parallel parallel quartz quartz veins veins and and alteration alteration zones zones within within aa large large mass mass of of trondhjemite trondhjemite which which intrudes intrudes aa series series of of mafic mafic flows. flows. Calculations 1986 drill drill Calculations of of drill—indicated drill-indicated tonnage tonnage at at the the end end of of the the 1986 programme programme gave gave aa total total of of 1,962,645 1,962,645 tons tons averaging averaging 0.251 0.251 oz. oz. gold gold per per ton. ton. These These preliminary preliminary reserves reserves occur occur to to aa depth depth of of 500 500 feet. feet. J The The 1986 1986 drill drill programme programme has has now now encountered encountered good good gold gold values values over over aa strike length of 5200 feet with the zones open at both ends. Although strike length of 5200 feet with the zones open at both ends. Although the the 1986 1986 drilling drilling has has been been concentrated concentrated on on the the zones zones within within the the intrusive, recent drilling has intersected additional intrusive, recent drilling has intersected additional zones zones at at or or near near the contact but within the volcanics. These will be tested in the the contact but within the volcanics. These will be tested in the current current drilling. drilling. AA decline decline ramp ramp of of 1600 1600 feet feet has has been been driven driven to to the the 200—foot 200-foot level level with with 1 drifting drifting occurring occurring on on several several gold gold zones. zones. The The display display will will consist consist of of drill drill core, core, hand hand specimens, specimens, maps maps and and drill drill sections. sections. j ii J -A -A ii -A -42- U j �Gaol .. .~ Bedrock Geology ogy of of Keweenawan ~eweenawanRocks Rocks in i n the tihe Vicinity v i c i n i t y of of Silver Silver Bay Bay and and Beaver Beaver Bay, Bay, Northeastern Northeastern Minnesota Minnesota ,..%' . & JAMES JAMES D. 0. MILLER, MILLER, JR. JR. (Minnesota (Minnesota Geological Geological Survey, Survey, St. St. Paul, Paul, MN MN 55114) 55114) Geologic Point Geologic mapping mapping in i n the the Silver S i l v e r Bay Bay and and Split S p l i t Rock ~ock Point NE NE 7.5' 7.5' quadrangles quadranglaa along along the t h e north north shore shore of of Lake Lake Superior Superior has has established e s t a b l i s h e d the the presence Middle Proterozoic (Keweenawan) presence of of a avariety v a r i e tof y of Middle Proterozoic (Keweenawan) mafic mafic plutonic plutonic and rocks amplaced emplaced in and hypabyssa]. hypabyasal rocks in a a thick thick sequence sequence of of dominantly dominantly basaltic basaltic volcanic volcanic rocks rocks of of similar The s i m i l a r age. age. The intrusive i n t r u s i v e rocks, rocks, collectively collectively assigned to the Beaver Bay complex, include at least assigned t o t h e Beaver Bay complex, include a t l e a s t three t h r e e temporally temporally distinct d i s t i n c t intrusive i n t r u s i v e suites; s u i t e s ; the t h e Lax Lax Lake Lake gabbro, gabbro, the the Beaver Beaver River River diabase, The theBeaver Beaver Bay Bay gabbro. gabbro. The complex complex aalso l s o includes includes two two diabase, and and the relatively Faulting, sills. Faulting, coeval coeval with w i t h magrnatic magmatic r e l a t i v e l y minor minor diabase diabase sills. intrusion, the sequence sequenceof of volcanic volcanicflows flowsand andminor minorinterf i n t e r f low low i n t r u s i o n , disrupted d i s r u p t e d the sedimentary rocks of the normally polarized (upper) North Shore Volcanic sedimentary rocks of the normally polarized (upper) North Shore Volcanic Group (MSVG), host h o s t rocks rocks for f o r the t h e BBC. BBC. Group (NSVG), Most range iin fromt tholeiitic Moat volcanic volcanic rocks rocks of of the theNSVG NSVG range n composition composition from holeiitic basalt to basaltic andesite, but some b a s a l t to b a s a l t i c a n d e s i t e , b u t some quartz—feldspar—porphyritic quartz-feldspar-porphyritic rhyolite r h y o l i t e flows flows also a l s ooccur. occur. Three Three ttextural e x t u r a l types types of of basaltic b a s a l t i cflows flows are are distinguished: ophitic basalt,plagioclase—porphyritic plagioclase-porphyritic o p h i t i c basalt, basalt, distinguished: ophitic o p h i t i c basalt, and Drill and intergranular i n t e r g r a n u l a r to t o intersertal i n t e r s e r t a l basalt b a s a l t and and basltic b a s l t i c andesite. andesite. Drill core c o r e (Green, (Green, 1982) 1982) and and exposures exposures to to the t h e east east of of the the field f i e l d area a r e a indicate indicate that siltstones and and sandstones sandstones and and volcanoclastic volcanoclastic t h a t interflow i n t e r f l o w arkosic a r k o s i c siltstones conglomerates conglomerates 'are a r e fairly f a i r l y common common in i n this this interval i n t e r v a l of of the the NSVG, NSVG, although although they Silver arerarely r a r e l yexposed exposedini the n the S i l vBay—Beaver e r Bay-Beaver Bay Bay area. area. Hornfels they are Hornfels of of volcanic thermal metamorphism volcanic and andsedimentary sedimentary rocks rocksresult r e s u llocally t l o c a lfrom l y from thermal metamorphism by by Beaver Beaver Bay Bay complex complex iintrusions. ntrusions. Subophitic Subophitic olivine o l i v i n egabbro, gabbro, granophyric granophyricgabbro gabbro and and gabbronorite, gabbronorite, mafic mafic granodiorite, and granophyre comprise the Lax Lake gabbro, q r a n o d i o r i t e , and granophyre comprise the Lax Lake gabbro, the the oldest oldest intrusive i n t r u s i v e rocks rocks in i n the thearea. area. Collectively, C o l l e c t i v e l y , these these rocks rocks define d e f i n e aaconcontinuous tinuous range range of of evolved evolved (Fe—Ti—rich) (Fe-Ti-rich) to t o highly highly evolved evolved (Si—K—rich) (Si-K-rich) comCOBpositions, implying a coeval evolution by differentiation. p o s i t i o n s , implying a coeval evolution by d i f f e r e n t i a t i o n . However, However, the the spatial the overall o v e r a l l shape shape s p a t i a l relationships r e l a t i o n s h i p s between between various various rock rock types types and and the of of the t h e Lax Lax Lake Lake body body are areobscured obscured by bya alack lackof of internal i n t e r n a l structures s t r u c t u r e s and and post—crystallization faulting. post-crystallization faulting. Both Both the the Lax Lax Lake Lake gabbros qabbros and and the the lava l a v a flows flows are a r e intruded intruded by by dikes dikes and and sills s i l l s of of Beaver Beaver River River diabase, diabase, typically t y p i c a l l y aa fine— fine- to t o medium—grained, medium-grained, ophitic o p h i t i c olivine o l i v i n e gabbro gabbro which which locally l o c a l l y grades grades into i n t o aa coarse—grained, coarse-grained, oxide—rich River diabases diabases aare oxide-rich ophitic o p h i t i cgabbro. gabbro. The The Beaver Beaver River r e unique unique iin n that that they they contain c o n t a i nnumerous numerous inclusions i n c l u s i o n s of of anorthosite, a n o r t h o s i t e , some some as a s much much as a s 100 100 meters meters in i ndiameter. diameter. The The inclusions i n c l u s i o n s tend tend to tobe be concentrated concentrated in i n the thelower lower parts p a r t s of of the t h e sills. sills. Typically, Typically, they they are a r e coarse—grained, coarse-grained, consist c o n s i s t almost almost entirely of calcic plagioclase (An 54—80, Morrison et al., 1983), and e n t i r e l y of c a l c i c p l a g i o c l a s e (An 54-80, Morrison e t a l . , 1983), and are Though less common, common, inclusions i n c l u s i o n s of of medium— mediuma r e commonly commonlytectonized. tectonized. Though less grained grained granite g r a n i t e and and aphanitic a p h a n i t i c felsite f e l s i t e also a l s o occur occur locally l o c a l l y in i n the t h e margins margins of both dikes and sills where they commonly are partially assimilated of both d i k e s and sills where they cormonly a r e p a r t i a l l y a s s i m i l a t e d by by the the diabase. diabase. The The basal b a s a l portions p o r t i o n s of of the the diabase diabase sills sills and and the the underlying underlying volcanics a ) granophyre granophyre dikes dikes volcanica are a r e commonly commonly intruded intruded by by thin t h i n (1(1 cm—i cm-1 m) which may have been generated by partial which nay have been generated by p a r t i a l melting melting of of the thevolcanics. volcanics. —43— �Theiron-rich iron—richBçave Beaver Bay gabbro theyoungest youngest intrusiveunit uniti in the The Bay gabbro i s is the intrusive n the area. Near the lakeshore, it consists of three zoned, elliptical-shaped area. Nur thà UAwhof, it consist* of thxà aonad, elliptical-shaped bodies which emplacedi ninthà theupper upperpart part of of aa thick w h i c h vwere m f ¥¥pUlc thickBeaver Beaver River River bodies sill. Each intrusion typically grades abruptly from a margin sill. Bxch intrusion typically grades abruptly from a marginofofcoarse— coarsegrained to commonly gabbro to to an grained topegmatitic, p w t i t i c ,van—textured, vari-taxturçd coÑonl granophyric granophyric gabbro an of interior medium—grained, well—laminated, moderately to locally locally i n t o r i o r of nÑdiua-qraLned moderçtel to wll-laminated, gabbronorite or or olivine Inclusions llayered, a y f d , gotabronorita olivine ferrogabbro ferroqabbro (Shank, ( S h m k , 1987). 1987). Inclusions of Beaver river diabase are especially common in one of the intrusions of Bçave r i v e r diab8ae a r e especially c o ~ o ni n one of the intrusions centered south of of Silver Inland, Beaver gabbro is is represented aenfrad Â¥oat SilvrBay. Bay. Inland, Beaver Bay Bay gabbro represented by an irregular—shaped intrusion of medium—grained ferrogabbro by an i r r d g u l a r - x ~intrusion of ndim-qr&inod ferroqabbro which which grades iinto was emplaced emplacedi ninthe the aaxial gradà n t o mafic oafic granodiorite granodiorif and and which which was x i a l porportion of Intrusionsofof tthis type are are ffairly Beavr River R i v r diabase diab8ae dike. dike. Intrusions h i s type airly tion of aaBeaver ccommon o~o thà area area to to the the northeast. northeast. niin n the relatively vinor minor Beaver relatively Beaver two Bay Complex intrueions intrusions are T wo Bay Complex are aa 15—20—meter—thick, aphanitic to fine—grained, intergranular diabase sill 15-20-Ñtu-thick Â¥phaniti to fim-graiifd, intargranular di-e sill ferrodiorite, Green, 1982) and aa 55-65-çeter-thick 55—65—meter—thick, 1982) and ((compositionally c o ~ p o i i t i o ~ l lfercodiorita, y Green, to mum-grained, medium—grained, hentitic-stained, hematitic—stained, slightly P1—porphyritic ophiophialightly Pl-porphyritic ffine i n e to diabasesill. sill. Petrogenetic relationships with other intrusive diçbà Petroapnatic relationships w i t h other intrusive rocks rocks uncertain, but the and texaare re u m a d h , but the ferrodiorite feeradiorite sill s i l l is is mineralogically  ¥ i o e r a ~ i c a l land texturally similar some Lax Lake gabbros and therefore may be an to t w d i ciliilu to xne Lax Lake gabbros and therefore nay be an offshoot Similarly, sills sills of of ophitic diabase are texoff are text of at that that suite. milt*. Similarly, ophitic similar to to Bkavr Beaver River River diabaae diabase and and may may bà be c comagnetic with it. tturally u r a l l y siçila o a a p t i c with it. ttic ic d this mapping Thia upping was w conducted conducted in i n conjunction conjunction with with the the U.S. U.S. Geological Geological Survey's COGDOHAP COGEOMAP program. Survey's progrç References Green, J.C., 1982, Geology Geology of of the the Milepost Milepost 7 7 Green, J.C., 1982, Minnesota: Minn. Geol. Survey, Report of Invest. H i w o t a : Wan. Gaol. Survey, Raport of Invest. area, Lake Lake area, 26, 12 p. 26, 12 County, County, Morrison, D.A. Morrison, D.A. and and others, other*, 1983, 1983, Pre—Keweenawan Pre-Kewmenaw~ anorthosite anorthosite inclusions inclusions Keweenawan the K Beaver Bay Bay and Italudi Duluth Coxplexes, Complexes, iinn the e w e l u w a n Beaver Minnesota: Hinnm8otA: Shank, S., S., Shank, Minnesota: Minifott: northeastern northeastern Geol. Soc. Am. Bull., Gaol. Soc. ta. Bull., v. v. 94, 94, p. p. 206. 206. Complex near Silver 1987, Potxoloqy Petrology of of the 1987, theBeaver Beaver Bay Bay C i ~ p l c xnear Silver Bay, Bçv GSAMÈtr Abstr. W with Programs, v. 19, 19, no. 4. GSA ith P r-, V. no. 4. —44— 4 �and SStructural on tthe Hemlo Gold Cold Deposit Deposit SStratigraphic t r a t i q r a v h i c and t r u c t u r a l CConsiderations o n s i d e r a t i o n s on h e Hemlo setting setting T.L. MUIR MUIR (Geologist, Precambrian Geology Geology SSection, Ontario Geological T.L. (Geologist, Precambrian ection, O n t a r i o Geological Survey, Toronto, Toronto, Ont., Ont., M7A 1W4). Survey, M7A 1W4). Initial of the Hemlo Gold Gold Deposit Deposit and and its I n i t i a l iinvestigation n v e s t i g a t i o n of t h e Hemlo its setting, setting, in the early 1980s, resulted in the interpretation of a relatively i n t h e e a r l y 1980s, r e s u l t e d i n t h e i n t e r p r e t a t i o n of a r e l a t i v e l y undeformed, homoclinal and undeformed, h m c l i n a l sequence sequence of of Archean Archean metavolcanic metavolcanic and metasedimentary units that contained a conformable, metasedimentary u n i t s t h a t contained a conformable, ssyngenetic yngenetic gold-bearing sinter Recently, more more detailed ((exhalative), e x h a l a t i v e ) , gold-bearing s i n t e r horizon. horizon. Recently, detailed surface mapping, drill core logging, and work in three mines, has has lled ed s u r f a c e mapping, d r i l l c o r e logging, and work i n t h r e e mines, to recognition of major lithological, structural, and alteration t o r e c o g n i t i o n of major l i t h o l o g i c a l , s t r u c t u r a l , and a l t e r a t i o n which have have introduced introduced ssignificant complications ffor ffeatures e a t u r e s which i g n i f i c a n t complications o r tthe he syngenetic model. These complications have forced a re—evaluation s y n g e n e t i c model. These complications have forced a re-evaluation of of now tthe h e setting s e t t i n gand and timing timingofofmineralization, m i n e r a l i z a t i o nand , and nowmounting mounting evidence, evidence, some of wtich is covered below, strongly supports an eepigenetic some of which is covered below, s t r o n g l y s u p p o r t s an p i g e n e t i c oorigin rigin gold deposit. ffor o r the t h e gold deposit. Nossiliceous No i l i c e o u s sinter s i n t e rhas hasbeen beenfound found ata Hemlo. t Hmlo. PPotassic otassic dominant form of the dominant form of of alteration a l t e r a t i o n of t h e mineralized mineralized metavolcanic and Some ffeatures rocks. metavolcanic and metasedimentary metasedimentary rocks. Some e a t u r e s ppoint o i n t to t o aa hydrothermal o origin with tthe is aassociated s s o c i a t e d with he hydrothermal r i g i n ffor o r the t h e barite b a r i t e tthat h a t is evidence for bedding iin ddeposit. e p o s i t . In I n any any case, case, evidence f o r bedding n tthe h e bbarite-bearing a r i t e - b e a r i n g rrocks ocks is equivocal. equivocal. is feldspathization is the f e l d s p a t h i z a t i o n is the L Gold and andmolybdenum molybdenum westernp apart Gold a r eare p r epresent s e n t i n in t hthe e western r t ofof tthe h e ddeposit eposit within to felsic felsicquartz—feldspar q u a r t z - f e l d s p a r porphyritic p o r p h y r i t i ccomplex complex within an an intermediate i n t e r m e d i a t e to and/or hypabyssal?), hypabyssal?),and andi nint the of the ((extrusive e x t r u s i v e andlor h e eeastern a s t e r n ppart a r t of t h e deposit deposit within laminated some within laminated metasediments metasediments which which show show evidence evidence of of some such, the tectono-metamorphicbanding bandingdue dueto to shearing. shearing. AAs tectono-metamorphic s such, the mineralization appearst otoccrosscut overa asstrike m i n e r a l i z a t i o n appears r o s s c u t sstratigraphy t r a t i g r a p h y over t r i k e length l e n g t h of of aa few few kilometres. kilometres. Majori isoclinal of the Major s o c l i n a l ffolding o l d i n g of the supracrustal s u p r a c r u s t a l rocks rocks has h a s taken taken place. This This is is cclearly place. l e a r l y eevident v i d e n t iin n rrocks o c k s sstructurally t r u c t u r a l l y ooverlying v e r l y i n g tthe he wtierer reclined, where e c l i n e d , antiformal a n t i f o r m a l synclines s y n c l i n e s have have been been ddelineated; elineated; Hence rocks structurally underlying the deposit have also been folded. folded. Hence rocks s t r u c t u r a l l y underlying the d e p o s i t have a l s o been the rocks hosting the mineralization have almost certainly been folded t h e rocks h o s t i n g t h e m i n e r a l i z a t i o n have almost c e r t a i n l y been folded and may be overturned. overturned. SStructurally t r u c t u r a l l y overlying o v e r l y i n g tthe h e eastern eastern may themselves themselves be part of the orebody are pelitic metasediments containing several P a r t of t h e orebodv are o e l i t i c metasediments c o n t a i n i n a s e v e r a l key key alteration/metamorphicmminerals (eg.a anthophyllite, n t h o p h y l l i t e , ccordierite, ordierite, alteration/metamo$hic i n e r a l s (eg. is aa rresult of ttight sstaurolite). t a u r o l i t e ) . This e s u l t of i g h t ffolding olding This sspatial p a t i a l association a s s o c i a t i o n is deposit deposit L is nnot which limits here; iitt is limits the t h e apparent apparent sstrike t r i k e eextent x t e n t ofoft this h i s uunit n i t here; o t aa which result of localized syngenetic alteration of sediments. r e s u l t of l o c a l i z e d syngenetic a l t e r a t i o n of sediments. L The andisis not not aa rresult The iisoclinal s o c l i n a l folding f o l d i n g ppredates, r e d a t e s , and e s u l t of, o f , dextral dextral whichisis manifest manifestas as sseveral of sstrong to intense sshearing h e a r i n g which e v e r a l zones zones of t r o n g to intense deformation, oone of which This is deformation, n e of which hhosts o s t s the t h emain main orebody. orebody. T h i s sshearing h e a r i n g is incipiently i n c i p i e n t l y developed developed locally l o c a l l ybetween between these t h e s e highly h i g h l ydeformed deformed zones, zones, and and significantly, hasaaffected least tthe s i g n i f i c a n t l y , the t h e shearing s h e a r i n g has f f e c t e d aat t least h e eearlier a r l i e r stages s t a g e s of of mineralization. m ineralization. —45— �Dislocation beddingand andi sisoclinal D i s l o c a t i o n along along bedding o c l i n a l ffold o l d limbs, limbs, by by dextral d e x t r a l and and ssinistral i n i s t r a lfaults f a u l t sresulting r e s u l t i n gfrom fromfolding f o l d i n gand/or and/or the t h edextral d e x t r a lshearing shearing andand medium—scale isevident e v i d e n tini nsmallsmallk d i u m - s c a l e sstructures. t r u c t u r e s . TThis h i s suggests suggests eevent, v e n t , is that bedding dislocation may have occurred on a mega—scale, which may may t h a t bedding d i s l o c a t i o n may have occurred on a mega-scale, which one of of tthe reasons why why sstratigraphy cannot be be matched matched cconsistently bbee one h e reasons t r a t i g r a p h y cannot onsistently major fold Considerable vertical component displacement aacross c r o s s major f o l d axes. axes. Considerable v e r t i c a l component displacement is suspected is suspected with with some some faults. faults. Transposition to folding f o l d i n g and/or a n d l o r shearing shearing is is present present T r a n s p o s i t i o n due due to particularly within noses of small— to medium—scale, p a r t i c u l a r l y within noses of small- t o medium-scale, ttight i g h t iisoclinal soclinal folds. However, the development of this feature on a f o l d s . However, t h e development of t h i s f e a t u r e on a large l a r g e scale scale has not not aaffected of tthe rocks. llikely i k e l y has f f e c t e d nnotable o t a b l e pproportions r o p o r t i o n s of h e ssupracrustal u p r a c r u s t a l rocks. This is because distinguishable lithologic units can generally be T h i s is because d i s t i n g u i s h a b l e l i t h o l o g i c u n i t s can g e n e r a l l y be some d distance ttraced r a c e d ffor o r some i s t a n c e along along strike. strike. Tectonic p pull—apart Tectonic u l l - a p a r t features f e a t u r e s due due to t o dductility u c t i l i t ycontrast c o n t r a s thave have developed The degree tto which in some tight isoclinal fold noses. o which developed in some t i g h t i s o c l i n a l f o l d noses. The degree these tectonic features sufficiently mimic primary fragmental ocks, t h e s e t e c t o n i c f e a t u r e s s u f f i c i e n t l y mimic primary fragmental rrocks, such tthat misidentification is iinevitable, is considered considered n e v i t a b l e , is such h a t ttheir heir m i s i d e n t i f i c a t i o n is minimal. Only Only one one n notable within tthe minimal. o t a b l e uunit, n i t , which which is is within h e oore r e ddeposit, e p o s i t , is is considered by considered by the t h e author author to t o be be aa possible p o s s i b l e tectonic t e c t o n i c breccia b r e c c i a due due to to Numerous units dductility u c t i l i t y contrast. c o n t r a s t . Numerous u n i t s of of deformed deformed pyroclastic p y r o c l a s t i c rocks, rocks, However, the and conglomerates conglomerates are are recognizable. recognizable. However, the vvolcaniclastic o l c a n i c l a s t i c rocks, rocks, and degree of of ttectonic and ttransposition of tthe degree e c t o n i c ffolding, o l d i n g , ddislocation, i s l o c a t i o n , and r a n s p o s i t i o n of h e rrocks ocks in precludes any any d delineation of primary growth faults so far. far. i n this t h i s aarea r e a precludes e l i n e a t i o n of primary growth f a u l t s so Possible P o s s i b l e conjugate conjugate shears s h e a r s in i n the t h e relatively r e l a t i v e l y isotropic i s o t r o ic quartz-feldspar appear, q u a r t z - f e l d s p a r pporphyritic o r p h y r i t i c complex complex appear, l o locally c a l l y a at t least, e a s t , tto o control some of of tthe mineralization These sshears are c o n t r o l some he m i n e r a l i z a t i o n and and alteration. a l t e r a t i o n . These h e a r s are likely zones of of sstrong and must must have have l i k e l y rrelated e l a t e d tto o tthe h e zones t r o n g ddextral e x t r a l sshearing, h e a r i n g , and been ccreated during a compressional event been r e a t e d during a compressional event which which involved involved pressures p r e s s u r e s and and stresses well well in excess excess of of tthose with lithostatic loading. stresses h o s e aattainable t t a i n a b l e with l i t h o s t a t i c loading. This T h i s strongly s t r o n g l y suggests s u g g e s t s that t h a t the t h e host h o s t rocks rocks must must have have been been deformed deformed and and major compressive compressive force a s eexerted. xerted. ttilted i l t e d ssubvertically u b v e r t i c a l l y bbefore e f o r e tthis h i s major f o r c e wwas The mineralization The timing timing of of m i n e r a l i z a t i o n is is thereby t h e r e b y constrained c o n s t r a i n e d to to post post deposition deposition and post folding of the host rocks. Zircon dating of several and post f o l d i n g of the h o s t rocks. Zircon d a t i n g of s e v e r a l rrocks ocks from w within and around around tthe 70 tto 90 M Ma from i t h i n and h e ddeposit e p o s i t indicates indicates a a 70 o 90 a ddifference ifference between age of of the the intermediate i n t e r m e d i a t e to to felsic f e l s i c qquartz-feldspar uartz-feldspar between tthe h e age porphyritic complex which locally hosts mineralization, and the p o r p h y r i t i c complex which l o c a l l y h o s t s the the m i n e r a l i z a t i o n , and t h e age age of major major granitic plutonism (eg. Cedar Lake Pluton) and numerous g r a n i t i c p l u t o n i a n (eg. Cedar Lake P l u t o n ) and numerous However, as as yet, ffeldspar e l d s p a r and and quartz-feldspar q u a r t z - f e l d s p a r porphyritic p o r p h y r i t i c dikes. dikes. However, y e t , no no clear between dike mineralization/ clear age age relationship r e l a t i o n s h i p between d i k e intrusion i n t r u s i o n and and m ineralization/ been established. established. aalteration l t e r a t i o n has has been ? J J j —46— �Petrologic evolution of early Proterozoic sucracnistal rocks from Florence County. WI and their bearingon onthe the d develonrent of ele- -the- Dunbar Gneiss . T . Peter of of Geology, tJW—Parkside, PeterA. A. Nielsen Nielsen(Dept. (Dept. Geology, OW-Parkside, Kenosha, Kenosha, WI) WI) 90 Kerr W samples ~ l e s obtained ~ f r a fran n & drill i l cores l - m provided & b y tbyh the e m - McGee have been Corporation petreographically. The The cores cores are are Corporation have been examined examined petreoqraphically. from restricted basins fran restricted basins with withshallow shallow water water sedinents. sediments. All All holes holes were w e r eoriented o A e n t etowards d t m - c the o n tcontact a c t - t hbetween e - d t h e the sedirrents and the Bush Lakes Granite. Samples represent upt oto300 300feet feet of of the the Bush Lakes Granite. mles represent up sedinentary sequence and show no coherent pattern of net amorphic Sedhntary sequeme and show m coherent pattern of mtamxphic grade as aa function the contact grade as function of of proximity proximity tto o the contact (the (the distance distance ranges fran 1.7 }cn to less than 100 m. ranges fran 1.7 km t o less than 100 m. The The rretasedinents range qfran franmicaceous micaceous quartz -zit- ites through timniqh marbles, graphite and sulfide sulfide rich ma&les, m t e and r i c h schists schistsand andruafic mafic volcaniclastics. Mineral aseitlages inply net amorphic conditions wlcaniclastics. Mineral asentolagw imply netamozphic conditions ranging from fran uppermost uppern'st greens chist fades facies ttoo amphibolite ranging greenschist au@iblite ffacies. ades. Assetlages include ~~ ~~garnet garnetarrphibolites, a q h i b o l i t e s , diopside dim* marbles ma&les and and biotite-garnet-cordierite—plagioclse—cpa.rtz schists. Nearly Nearly all all biotite-gamet-oordierite-plagioclse-quartz schists. samples have been affected by retrograde alteration due to fluids samples have been affected by retrograde alteration due t o fluids from the Bush fran the Bush Lake Lake Granite. Late stage stage quart veinslocally locally cut cut the Late quartz<-z-tourmalineveins the netasediitents, as et a.1., metasedtments, asoccurs occursini nthe theDunbar DmbarDone Done (Sims (Sins et al., 1985). 1985) Polyphase deformationis is evident An early early SS Polyphase deformation evident in inmost most samples. samples. An foliation bybiotite biotite is is parallel parallel to t o origional origional layerin4 layer& f o l i a t i o n defined defined by is (Sn). Retrograde biotite psoduces (S Retrograde biotite produces aa weak weak S5, ffoliation o l i a t i o n which which is in1ined to Thesefabrics fabrics & ae probably & t o Ss1by by up up to t o 90 90 w probably correlative correlative with D2 in the et al.) al.) with Dg and and D4 D4 in theDunbar Dunbar Done Done (Sims (Sirs et . Prograde minerala sasblages netamorphic Pnqrade mineral e l a g e srestrict restrictpeak peak metanorphic conditions at low conditionstot 500—550 o 500-550 at low tto o interrediate intermediatepressure pressure (4-5 (4-5 kbar). kbar) . Fluid pressure probably probablywas wasequal equalt otolithostatic lithostatic pressure; pressure; the Fluid pressure the fluid and ranged ranged from fromnearly nearlypure purewater water iin the fluidwas was heterogeneous heterogeneous and n the micaceous quartzites to micaceous quartzites t o fluid fluidwith withhigh highconcentrations concentrationsofofCO2 CO, and and 3 s in in carbonate, carbonate, graphite, graphite, and and sulfide sulfidebearing bearing layers. layers. The evolution of the done described described by by Sims et The evolution theDunbar Dunbar Gneiss done Sims et al., is sbdlar similar in (1985), is in style s t y l e to t othe thesupracnistals supmcmstalsdescribed descral., (1985), above. areas display amorphismfollowed followedbybylater later above. Both Both areas displayprograde proqradenet metanorphism retrograde net amorphism accatpanied by deformation. Sims et al. A x O g n c k metamz@lisn acaqmied by &foxmation. sins et al. (1985) show clear evidence that the Dunbar Done is a large scale (1985) s h o w d - e v i m W t h e - D o n e i s a m s d e fold-interference from fold-interference structure structureresulting resulting franpolyphase polyphasedeformation deformation and diapirism. I suggest that the two areas and that that diapirism. I suggest that the two areaswere wereco—eval co-eval and the differences in net amorphic grade between the Dunbar Gneiss and thedifferencesinmetamorphicgradebetweentheDunbarGneissand the supracrtstal rocks represent an an original original the Florence Florence County County siapracrustal rocks may may represent difference in in depth of burial burial - the having formed formedat at a depth of the Dunbar Dunbar having deeper level ~ ~ crustal M a nand dthen ~been~displaced ~ l to aa shallower c e level d t by not displaced displaced vvertically by diapirisu diapirisn while while the the supracrustals mpmxwhb were were not ertically to during D2Dnand asgreat greatananextent extent duringthe the andD4 D4 deformations. deformations. t o as - —47— o a ~ �-J lj Sims, P.K., P.K., Petennan, Petentian, Z.E., Z.E., and Schulz, KK.J., Sims. and Schulz, .J., 1985, 1985, The The Duitar Duribar Qeiss—granitoid dare: Implications for early Proterozoic W - u r a n i t o i d &me: ilmlications for earlv P ~ e m z o i c tectonic evolution tectonic evolutionofofnorthern northernWisconsin, Wisconsin, Geol. Geol.Soc. Soc. Am. am. Bull. ., 1101—1112. Bull. 96, 1101-1112. ~ ~ ~~A —I ~ U ci —I j J .3 j s-i U U -48- J �On the failure of the Midcontinent Rift System to proceed to sea—floor spreading Peter Peter A. A. Nielsen Mielsen(Departxrent (Department of Geology, Geology, University University of ofWisconsin Wisconsin Parkside, lcexsosna, iteriusna, WI WI 53141). 53141). Parkside, The system systemof of gravity gravity and anomaliesthat that extends Ole and magnetic magnetic anomalies extends from from Kansastto Superior and and then then southwards into central Kansas o Lake Lake Superior southwards into centralMichigan Michigan is one It reflects reflects aa is one of of the themost mostprominent prominent in inNorth N o r t h Anerica. America. It major geologic geologic feature feature which whichhas hasbeen beenidentified identified as as an abortive abortive major rifting craton - the rnidcontinentrift rift riftingof ofthe theNorth NorthAnerican American craton the midcontinent system Nurrerous authors authors system (ICES), @CIS), sinnarized summarizedininWold Wold&& Hinze, Hinze, 1982. 1982. Numerous haveproposed proposed that thisfeature featureisisa aresult resultofof 'activer 'active' rift ing have that this rifting processes hotspots spots intersecting intersecting the response tto o one one or more more hot the processes in response North Atrerican &&Dewey, toerican plate plateapproximately approximately1100 1100Ma Ma B.?. B.P.(Burke (Burke Dewey, Others (Tapponnier et al., al., 1982; 1973; van Schmus Hinze, 1985). Schnus &&Hinze, 1985). Others (Tacponnier et 1982; 1973; Gordon&&wHeupton, 1986)have havepresented presentedarguments argunentsthat that the the Gordon o n , 1986) tensional environtent ICRS tensional eiwironnenCrepresented representedbybythe the 1CRSmay may have have been been produced by Grerwille Orogenic Orogenic event. event. produced by the the Grenvifle - The t435is is unique uniquein in that that there The MSBS there is isno nothird thirdaim armassociated associated with with this failed RRR (Burke & &Dewey, this failed BRR triple t r i p l ejunction junction (Burke Dewey, 1973). 1973) Although true rifting rocksare are absent, absent, aa number nuiter of true riftingand andassociated associated mafic mafic rocks alkaline along thethe Coldwell Trend a l k a l b e intrusive intrusivecenters centers along Coldwall Trendmay may mark !nark the the position of this arm (Currie, 1976; Wieblen, 1982). The trace of this am (Currie, 1976; Wieblen, 1982) The trace of the potential also be be represented representedby bythe the suite suite of thirdarm armmay may also potential third north-trending mafic dikes tth are prominent north of Lake north-trmding m f l c dikes a c h are pranirmt north of Lake Superior. The presence of of a passive margin on the the w west Ole presence margin on est (receiving (receiving Belt Group andequivalent equivalent sediments) sedinents) coupled with aa continentGroup and coupled with continent collisional Grenvifle Orogeny) collisionalmargin margin on on the theeast east(the (the Grenville Orogeny) not only only prevented a sea-floor sea-floor spreading spreadingcenter centerfrom f r mdeveloping, developing, but also inhibited the developTentof of the the thirdarmof third ann of the but inhibitedthedevelopmt the conventional ' 'ERR' conventional PKR' ttriple r i p l e junction junctionfrom franforming. forming. . . Stress conditions Stress conditionsinposed imposedon onthe theNorth N o r t hAnerican Americanplate plate1100 1100Ma Ma B.?. suchthat thatgeneration generationofofa arift rift in in the B.P. were were such the direction of the the third thirdann arm of of the theideal idealERR RRR ttriple r i p l e junction junction was was prohibited prohibited (Fig. (Fig. 1) 1) and that that extension wasnot not oennitted permitted along extensionofofmore morethan than65-701cn 65-70km was alona the arms (the ?'EA mid—Michigan the two twosuccessful successful amis (the M3Aand andthe the mid-Michigan geophysical anomaly).. Global plate distribution, distribution, plate Global plate plateboundary boundary orientation, anomaly) plate boundary typeand andintxaplate intraplates&s stress distribution distribution control boundary type control whether continental continental lithosphere lithosphere can respond whether respond tto o hot hot spot spot induced induced Under unconfined. unconfined stress by stress by fonning forming an an ERR RRR t rtriple i p l e junction. Under extensional stress situations, extensional stress situations,continental continentallithosphere lithospherecan canform form an an ERRt rtriple junction in of aa hot hot spot RRR i p l e junction i n response response to t o errplacement emplacement of spot A new new divergent divergent boundary (Burke & Dewey, 1973). 1973). A (Burke & Dewey, boundary can can form form aa new new mid ocean ridge ridge system whereplate plate boundary conditions allow mid ocean system (ICR) @-%XUwhere boudary conditions This can occur when one or or more moreof of the the continued extension. This when one pre—existing plate bouxbries boundaries is is aa continentpre-existhg plate amthent-ocean ocean(C-O) (C-0) or or ocean-ocean (0-0) (0-0) comergent convergentboundary boundary(cf. (cf. the the break break up up of ocean-ocean The absence absenceof of an an oceanic oceanic free free face al.) Pangea). face (Tapponnier (Tapponnier et e t al.) Pangea) The for between for the theNorth North?aerican Americancontinent continent between1200 1200and andl000Ma lOOOMa B.?. B.P. causedthe the failure failure of the MS caused MESto t oproceed proceed to t o sea-floor sea-floor spreading. spreading. . —49— �j Burke, J.F., 1973, triple-junctions Burke, K., K., and and Des.ey, Dewey, J.F., 1973, Flute-generated Plume-generated triple-junctions Key plate Key indicators i.IXikdt0rs in inapplying applying p l a t e tectonics tectonics to t o old o l drocks, rocks, Journal Journal of 406—433 ofGeology, Geology,.J., Sl, 406-433 Currie, Sun. Currier K.L., K.L:, 1976, s 7 6 , The Sa4jne Rocks of m,Geol. -1. S-. of Canada, Can. Can. Bull. Bull. 239, 239. 229pp. 229co. Gordon, M.B., and and %I&, Herpton, M.R., M.R., 1986, 1986,Collision-induced Collision-induced rrifting: Gordon, M.B., ifting: The Riftof of North North America, Nierica, The Grenville GrenvilleOrogeny Orogeny and and the theKesceenawan Keweenawan Rift j Tectonophysics, T e c t ~ s i c s.]fl, m, , 1—25 1-25 Tapponnier, T ~ , R R., . P,Feltzer, e l t z e r , G., G., I.eoain, Wain,A.Y., A.Y., Atmijo, Annijo,R.., R., and andCobbold, Cokbld, P., tectonics in insi$its P., 1982, 1982, Propagating Propagating extrusion extrusion tectonics inAsia: Asia: New Mew insights from sinpie experiiients Geology, from siaple experimentswith withplasticine, plasticine, Geology,)aQi u,611-616 611-616 Van Scbmus,W. W.R., andHinze, Hinze,W.J., W.J., 1985, 1985, The Themidcontinent midcontinentrift rift Van Schmus, R., and system, Planet. Sci., system, kin. Arm. Rev. Rev. Earth Earth Planet. Sci., U, 13, 345—383 345-383 Wieblen, .W., 1982, intrusive rocks. -wan intrusive rocks. See SeeWold Wold & & Hinze Hinze Wieblen, PP.W., 1982, Keweenawan 1982, 1982,47—56 47-56 Wold, R.J., and V&ld, R.J., andHinze, Hiwe, W.J., W.J., editors, editors,1982, 1982,Geolocv and Tectonics 1 of the Lake Surior Basin, Geol. Soc. Mt. tn. 156 280 280 pp. s- j J J j J .4 j j -50- J �"Basement—uplift" tectonics in Structural Zone, "Basement-uplift" tectonics i n the t h eKapuskasing Kapuskasing Structural Zone, central Superior Province Superior Province J.A. PERCIVAL (Geological Survey Surveyof of Canada, 588Booth BoothSt., St., Ottawa, J.A. PERCIVAL (Geological Canada, 588 Ottawa, 0E4) Ontario KK1A I A OE4) The 500 500 km km long, long, NNE-trending NNE-trending Kapuskasing Kapuskasing uplift uplift exposes deep crustal sections The sections of of the east-west east-west striking strikingWawa-Abitibi Wawa-Abitibi and andQuetico—Opatica Quetico-Opatica belts belts of the central central Superior Province. Granulite to upper amphibolite fades rocks of the uplift uplift form form Superior Province. Granulite to upper amphibolite fades rocks of from south south to north entities: from three distinct geological-geophysical geological-geophysical entities; north the Chapleau, Chapleau, Groundhog River River and blocks. Chapleau consists of of Groundhog and Praserdale-Moosonee Fraserdale-Moosonee blocks. Chapleau block (CS) (CB) consists densegneissic gneissicand andanorthositic anorthositicrocks, rocks,with with high high seismic seismic velocities, velocities, in in the dense the upper upper amphibolite and and granulite facies, fades, metamorphosed metamorphosed at 7-9 7-9 kbar. It It is is iningradational gradational contact, across contact, across a a Conrad-like Conrad-like discontinuity, discontinuity, with with amphibolite-facies amphibolite-fades (5-6 (5-6 kbar) kbar) tonalitic rocks rocks with with lower lower seismic seismic velocity, velocity, of of the the Wawa Wawa belt to to the the west. west. In contrast, the eastern easterncontact contactofof CB CB with with the the Abitibi belt the well-defined well-defined contrast, the belt is the Ivanhoe Lake thrust, 35-3S0 NW-dipping NW-dipping Ivanhoe Lake thrust, imaged imaged by by seismic seismic reflection reflection as as a 35—38° structure. The Thepositive positivegravity gravityanomaly anomalyover overthe theblock blockisiscaused causedby bythe thepresence presence of dense surface, as as shown shown by by gravity gravity modelling modelling and and supported supported by by dense granulites granulites at surface, seismic refraction evidence which indicates anomalously thick (ca. 48 km) crust 48 seismic evidence which indicates anomalously thick beneath the structure, relative beneath the relativetot oregional regionalvalues valuesunder under 40 40 km. krn. Groundhog Groundhog River River block (GRB) consistsofof tonalitic tonalitic and Ic gneiss gneissininthe the granulite granulite ffades (7-8 kbar), kbar), (GRB) consists and maf mafic a d e s (7-a boundedononthe theeast, east,west west and andsouth southby bybrittle brittle faults. faults. It is is characterized characterized by by aa bounded arcuate gravity strong positive aeromagnetic aeromagnetic anomaly, anomaly, but but aasub—parallel, sub-parallel, arcuate avity anomaly anomaly exposing occurs up ttoo 40 40 km kin to t othe thewest. west.Fraserdale Fraserdale- Moosonee Moosoneeblock block(FMB), (FMB , exposingdeep deep levels of the diatexite and t h e Quetico Quetico belt, belt, consists consists of of paragneiss, paragneiss, diatexite and minor minor tonalitic tonalitic levels gneiss in in the granulite Thewedge-shaped wedge-shaped block block is is fault-bounded fault-bounded gneiss granulite facies facies(7-9 (7-9kbar). kbar). The and lies lies within within aa ttoo the the east east and and west, west, has has a strong strong positive positive magnetic magnetic anomaly anomaly and broad positive positive gravity anomaly. broad anomaly. AA65-km 65-km "gap" "gapnwithout withoutgranulites granulitesoccurs occursbetween between the the GRB GRB and and FMB. FMB. - 7 geological—geophysical models involving aa major Integrated geological-geophysical major SE-directed SE-directed thrust and normalmovement movementononbrittle brittle faults, faults, explain explain the thrust and later, W-side-down W-side-down normal diverse CS is is a northwest-dipping northwest-dipping tilted slab, slab, diverse characteristics characteristics of each each block: block: CB exposing an oblique obLiquecrustal crustal cross-section; cross—section;GRB GRBand andsouthern southernFMB FMBare arethrust thrust tips exposing an truncated by normal faults; an an arcuate arcuate normal fault faultcuts cutsout outgranulites granulitesininthe theGRB.GRBFMB gap; the northern FMB has pop-up geometry. The overail geometry, scale, FMB gap; northern FMB has popup geometry. The overall geometry, scale, timing and and chronology chronology of the the diverse diverse structures structures ininthe theKapuskasing Kapuskasing uplift uplift closely closely resemble those those in in Phanerozoic basement uplifts uplifts such as the Laramide province province of of resemble Phanerozoic basement such as the western western U.S.A. U.S.A. Early Early Proterozoic Proterozoiccooling coolingdates dates ininthe theKapuskasing Kapuskashg zone zone are are consistent with remote uplift effects of in the "Hudsonian" orogeny orogeny in the consistent with remote basement basement uplift of "Hudsonian" Churchill Province. Province. —51— �(j _._j 0 km 100 Granulite fades -14r j Regionalgeology geologyof of the thecentral centralSuperior SuperiorProvince Provinceshowing showingmajor major tectonic features Regional tectonic features associated with withthe theKapuskasing Kapuskasingzone, zone, a composite structure made up of the associated aand composite structure made up of the Chapleau (CB), Groundhog River (GRB) Fraserdale-Moosonee (FMB) blocks. Chapleau (CB), Groundhog River (GRB) and Fraserdale-Moosonee (FMB) blocks. TheVal Val Rita Ritablock block(VRB) bounded by by the theLepage Lepage(LF), (LF), Foxville (FF), Kineras (VRB) isisbounded The (FF), Kineras (KF)and and Saganash Saganash Lake Lake (SLF) (SLF) faults. faults. Additional Additional structures structuresFoxville indicated include the (NP) indicated include the Bad River (BRF) and Wakusimi River (WRF) faults and Ivanhoe Lake catadastic Bad River (BRF) and Wakusimi River (WRF) faults and Ivanhoe Lake cataclastic zone(ILCZ). (ILCZ). Geographical Geographicallocations locationsinclude includeCochrane Cochrane(C), (C),Chapleau Chapleau(Ch), (Ch),Hearst Hearst zone O K ) , Timmins ( 1 1 , and Wawa (W). (H), Kapuskasing (H), Kapuskasing (K), Timmins (1), and Wawa (w). c-i U I —52— �Geological Geological and and Geophysical Geophysical Investigation I n v e s t i g a t i o n of of Graphite Graphite Resources Resources in i n Upper Upper Michigan Michigan JILL JILL F. F. PETERMAN PETERMAN (Dept. (Dept. of of Mineral Mineral Economics, Economics, Michigan Michigan Tech. Tech. University, University, Houghton, Houghton, MI M I 49931) 49931 ) DAVID DAVID DROEGE DROEGE (Dept. (Dept. of of Geology Geology and and Geological Geological Engineering, Engineering, Michigan Michigan Tech. University, Houghton, MI 49931) Tech. University, Houghton, M I 49931 ) ALLAN ALLAN M. M. JOHNSON, JOHNSON, (BioSource (BioSource Institute, I n s t i t u t e , Michigan Michigan Tech. Tech. University, University, Houghton, MI 49931) Houghton, M I 49931 ) JACK JACK VAN VAN ALSTINE ALSTIME (Michigan (Michigan Geological Geological Survey Survey Division, Division, Dept. Dept. of of Natural M I 48909) 48909) Natural Resources, Resources, Lansing, Lansing, MI Graphite i n Baraga Baraga Graphite was was produced produced from from several s e v e r a l small small quarries q u a r r i e s in County, Michigan around the turn of the century for use County, Michigan around the t u r n of t h e century f o r use in i n coating coating foundry The graphite g r a p h i t e occurs occurs in i n the the and as a s aa battleship b a t t l e s h i p paint. paint. The foundry molds molds and Lower Slate Unit of the Lower Proterozoic (Proterozoic X) Michigamme Lower S l a t e Unit of t h e Loner Proterozoic (Proterozoic X) Michigamme Formation. the northern northern margin margin The strata s t r a t a crop crop out o u t sporadically s p o r a d i c a l l y along along the Formation. The of the Marquette Trough from Alberta on the west to the Hunboldt area area of the Marquette Trough from Alberta on t h e w e s t t o the Humboldt on the east, east, aa distance d i s t a n c e of of approximately approximately 50 50 km km (Klasner, (Klasner, 1972), 19721, on the (Bodwell, and Klasner Klasner 1977). 1977). Recent Recent work work by by Michigan Michigan (Bodwell, 1972), 1972), (Cannon (Cannon and Technological the Michigan Michigan Geological Geological Survey Survey Technological University University and and the established from 17% 17%to t o 30% 30%carbon. carbon. Three Three e s t a b l i s h e d that t h a t the the strata s t r a t a range range from billion tons of graphitic be contained contained in i n aa b i l l i o n tons of g r a p h i t i c material m a t e r i a l are a r e estimated estimated to t o be 1.6 km wide zone along the 50km strike length (Hwang, etal., 1986). 1.6 wide zone along t h e 50 km s t r i k e length (Hwang, %&., 1986). It I t is is known known that t h a t the the area a r e a is is structurally s t r u c t u r a l l y complex complex and and has has undergone undergone regional r e g i o n a l metamorphism metamorphism (LaRue (LaRue and and Sloss, Sloss, 1980; 1980; James, James, 1955). 1955). AA 1986 1986 literature l i t e r a t u r e search search revealed revealed scant s c a n t information information pertaining p e r t a i n i n g to to details the graphitic g r a p h i t i c slate s l a t e unit u n i t of of the the Lower Lower Michigamme Michigamme d e t a i l s of of the Formation. the Much of of the the early e a r l y prospecting prospecting work work was w a s done done prior p r i o r to t o the Formation. Much 1900's and during World War II; none of this work was published. 1900's and during World War 11; none of this work was published. Subsequent Subsequent work work in i n Baraga Baraga County County has has shown shown mappable mappable graphitic g r a p h i t i c units units (Klasner, 1972). However, detailed regional mapping (Klasner, 1972). However, d e t a i l e d r e g i o n a l mapping has has not not been been possible Core from from regional regional p o s s i b l e because because of of extensive extensive glacial g l a c i a l overburden. overburden. Core diamond drilling done in the mid 1970's for uranium exploration diamond d r i l l i n g done i n t h e mid 1970's f o r uranium e x p l o r a t i o n shows shows some some graphitic g r a p h i t i c zones. zones. This This core core was was available a v a i l a b l e for f o r study study and and was was used used to t o delineate d e l i n e a t e the t h e extent e x t e n t of of graphitic g r a p h i t i c zones. zones. During summer of of 1986, 1986, aa geophysical geophysical survey survey was was conducted conducted During the t h e summer using a VLF—EM (very low frequency electromagnetic) meter using a --EM (very low frequency electromagnetic) meter and and aa proton proton precession magnetometer. The EM readings have been correlated with precession magnetometer. The EM readings have been c o r r e l a t e d with known of unknown unknown known graphite g r a p h i t e occurrences, occurrences, and and compared compared with w i t h areas a r e a s of potential. p o t e n t i a l . Unfortunately Unfortunately the the interpretations i n t e r p r e t a t i o n s are a r e complicated complicated by by characteristics the overburden overburden and and individual i n d i v i d u a l conductor conductor response. response. c h a r a c t e r i s t i c s of of the However, However, filtering f i l t e r i n g techniques techniques combined combined with with magnetic magnetic data d a t a are a r e being being used used to t o enhance enhance the the graphitic g r a p h i t i c anomalies. anomalies. Ongoing the mineralogy, mineralogy, geology, geology, Ongoing research research involves involves study study of of the geophysical geophysical response, response, beneficiation b e n e f i c i a t i o n characteristics c h a r a c t e r i s t i c s and and economics economics of of the the graphite g r a p h i t e resource. resource. Aside Aside from from uses uses as a s an an industrial i n d u s t r i a l mineral mineral aa principle p r i n c i p l e application a p p l i c a t i o n considered considered for f o r the t h e graphite g r a p h i t e is is as a s aa reductant reductant in in steelmaking. steelmaking. —53— �I . REFERENCES REFERENCES ~, ..., ' . ~. .,., . . ~' Bodwell, w.A., W.A., (1972), Non—Ferrous Metal Bodwell, (1 972 ), Geologic Compilation and Non-Ferrous Potential, P o t e n t i a l , Precambrian Precambrian Section, Section, Northern Northern Michigan, Michigan, IM.S. [M.S. Thesis]: Thesis]: Houghton, Houghton, Michigan Tech. Tech. University, University, 73 73 p. p. Cannon, W.F. (1977), Cannon, W. F. and Kiasner Klasner J.S., J.S., (1977), Bedrock Bedrock Geologic Geologic Map Map of of Part of tthe Diorite the Southern P a r t of he D i o r i t e and Champion 7 1/2 Minute Quadrangles, Marquette County, County, M MI, U.S. Geological Survey Quadrangles, I , U.S. Survey Miscellaneous Investigations Series, Miscellaneous Investigations S e r i e s , Map 1—1058 1-1058 Scale 1:2400. 1:2400. I Hwang, J.Y., J.Y., Carlson, Carison, D D.H., Johnson, A.M. A.M. and Van A Alstine, .H., Johnson, l s t i n e , J., J., Hwang, (1986), Preliminary Investigation (19861, Preliminary I n v e s t i g a t i o n of Graphite Graphite Resources Resources in i n Michigan, Michigan, SME) AIME, AIME, N New Orleans, LA, LA, P Preprint, ew Orleans, r e p r i n t , 13 13 p. p. 115th Annual (Mtg. (Mtq. SHE) James H.L. H.L. (1955), (1955), "Zones "Zones of of Regional Metamorphism Metamorphism in i n the the Precambrian of Northern Michigan" Geol. Soc. 2\mer. Bull., V66, of Northern Michigan" Geol. Soc. h e r . Bull., V66, p. 1455-1488. p. 1455—1488. Klasner, Klaaner, J.S., J.S., (1972), (1972), Style S t y l e and and Sequence Sequence of of Deformation Deformation and and Pssociated Metamorphism Due to t o the t h e Penokean Penokean Orogeny Orogeny in i n the t h e Western Western Ketamorphism Due Associated Marquette Range, Range, Northern Michigan (Ph.D. tPh.D. dissert.]: dissert.1: Houghton, Michigan Tech. Tech. Univ., Univ., 131 131 p. p. and Stoss, LaRue, LaRue, D.K., D.K., Slosa, L.L., L.L., (1980), (19801, Early Early Proterozoic Proterozoic Sedimentary Basins of the the Lake Lake Superior Superior Region: Region: Summary. Geological of America B Bulletin, Society of u l l e t i n , Part P a r t I, V. v. 91, p. p. 450—452. 450-452. — U J J U U nj -54- U -J �The The Hardwood Hardwood gneiss, gneiss. aa basic basic two—pyroxene two-pyroxene granulite granulite J.W. J.W. PETERSON PETERSON (Department (Department of of the the Geophysical Geophysical Sciences, Sciences, University University of of Chicago, Chicago, Chicago, Chicago, IL IL 60637 60637 U.S.A.) U.S.A.) C.A. C.A. GEIGER GEIGER (Technische (Technische Universität UniversitSt Berlin, Berlin, Institut Institut für fur Mineralogie Mineralogie und und Kristallographie, Kristallographie, Ernst Ernst Reuter Renter Platz Platz 1, 1, 1000 1000 Berlin Berlin 12, 12, West West Germany) Germany) The Early Precambrain Precambrain age age outcropping outcropping in in The Hardwood Hardwood gneiss gneiss is is aa unit unit of of Early eastern—central eastern-central Dickinson Dickinson County, County, Michigan. Michigan. The The unit unit is is exposed exposed along along State State Route Route M—60 M-60 between between Foster Foster City City and and Hardwood, Hardwood, Michigan. Michigan. The The gengeneral eral lithology lithology of of the the unit unit is is described described by by James James et et al., al., 1961*, 1961*, and and consists consists of of garnet—hornblende—pyroxene garnet-hornblende-pyroxene gneiss, gneiss, plagioclase—quartz plagioclase-quartz gneiss, gneiss, hornblende—pyroxene hornblende-pyroxene gneiss, gneiss, amphibolite, amphibolite, garnet—quartz—mica garnet-quartz-mica schist, schist, and and micaceous micaceous quartzite. quartzite. This This assortment assortment of of rocks rocks is is suggestsuggestive of a supracrustal sequence. Samples containing garnet—hornblende— ive of a supracrustal sequence. Samples containing garnet-hornblendeclinopyroxene—orthopyroxene—plagioclase—quartz clinopyroxene-orthopyroxene-plagioclase-quartz have have been been examined examined petrographically, and analyzed with electron microprobe petrographically, and analyzed with electron microprobe techniques. techniques. The The pyroxenes pyroxenes have have been been previously previously interpreted interpreted as as primary primary igneous igneous crystals (James et al., 1961). High average calcium crystals (James et al., 1961). High average calcium content content of of the the clinopyroxene (> 42 mole Z Wo) as well as low average calcium content clinopyroxene (> 42 mole Z Wo) as well as low average calcium content of of the the orthopyroxene orthopyroxene (4 ( 4 33 mole mole ZZ Wo) Wo) indicate indicate aa lower lower temperature temperature (i.e. metamorphic) origin. The close textural proximity (1.e. metamorphic) origin. The close textural proximity of of the the pyrox— pyroxenes with porphyroblasts of garnet also supports a metamorphic enes with porphyroblasts of garnet also supports a metamorphic interinterpretation. pretation. Equilibrium Equilibrium assemblages assemblages of of garnet—clinopyroxene, garnet-clinopyroxene, and and orthopyroxene—clinopyroxene yield geotherinometric orthopyroxene-clinopyroxene yield geothermometric paleotemperatures paleotemperatures ranging Geobarometers ranging from from 730°—890°C. 730'-890°C Geobarometers that that utilize utilize assemblages assemblages of of garnet—plagioclase—orthopyroxene—quartz garnet-plagioclase-orthopyroxene-quartz yield yield paleopressures paleopressures greater greater than than 6.4 6.4 kbar. kbar. Garnet Garnet cores cores equilibrated equilibrated at at temperatures temperatures of o f d—'850— 850890°C, 89O0C, and and pressures pressures between between 7.4 7.4 and and 11.0 11.0 kbar. kbar. Garnet Garnet rims rims are are 16 16 mole % more depleted depleted in in caw Ca than mole ZZ richer richer in in iron, iron, and and 17 17 mole Z than garnet garnet cores. cores. These These differences differences represent represent aa re—equilibration re-equilibration in in temperature temperature down down to to 730—770°C, 730-77O0C, and and aa reduced reduced equilibrium equilibrium pressure pressure of of 6.4 6.4 to to 7.5 7.5 kbar. The presence presence of of apparently apparently metamorphic metamorphic clinopyroxene clinopyroxene and and ortho— orthokbar. The pyroxene, in conjunction conjunction with with calculated calculated temperatures temperatures and and pressures pressures of of pyroxene, in assemblages is opx-cpx-garnet-plagioclase-quartz, is assemblages bearing bearing the the phases phases opx—cpx—garnet—plagioclase—quartz, evidence evidence that that the the Hardwood Hardwood gneiss gneiss experienced experienced granulite granulite facies f a d e s metametamorphism requiring burial burial to to at at least least 25 25 km km depth. depth. morphism —— requiring -- * * James, James, H.L., H.L., Clark, Clark, L.D., L.D., Lamey, Lamey, C.A. C.A. and and Pettijohn, Pettijohn, F.J., F.J., 1961, 1961, Geology of central Dickinson County Michigan: U.S. Geology of central Dicklnson County Michigan: U.S. Geol. Geol. Survey Survey Paper Paper 310, 310, 176 176 pp. pp. —55— �Natural of Natural Brine Brine Contamination Cont-tion of Groundwater Grwater in an the t h e Keweenawan Keweenawa~ Rocks of Northern Michigan Rocks of Northern Michigan BARBARA BARBARA J. J. PROSEN PROSED (Dept. (Dept. of of Geology Geology and and Geological Geological Engineering, Engineering, Michigan Tech. University, Houghton, MI Michigan Tech. University, Houghton, M I 49931) 49931) ALLAN ALLAH M. M. JOHNSON JOHNSON (BioSource (BioSource Institute, I n s t i t u t e , Michigan Michigan Tech. Tech. University, University, Houghton, MI 49931) Houghton, M I 49931 j Former Former Michigan Michigan State S t a t e geologist, g e o l o g i s t , A.C. A.C. Lane Lane (1908) (1908) first f i r s t reported reported the presence of high concentrations of brines in the Keweenawan t h e presence of high concentrations of b r i n e s i n t h e Keweenawan rocks rocks of of Michigan. Michigan. Lane Lane coined coined the the term term "connate" "connate" to t o describe d e s c r i b e the t h e brines brines which which were were sometimes sometimes at a t concentrations concentrations greater g r e a t e r than than 15% 15%dissolved dissolved solids (150,000 mg/i) in the deep native copper mines s o l i d s (150,000 mg/l) i n t h e deep n a t i v e copper mines of of the the Portage Portage Lake Lava Series. Lake Lava S e r i e s . Less L e s s concentrated concentrated brines b r i n e s of of similar s i m i l a r composition composition have have been been encountered encountered in i n relatively r e l a t i v e l y shallow shallow water water wells w e l l s drilled d r i l l e d along along the t h e Lake Lake Superior Superior shore, shore, especially e s p e c i a l l y above above Upper Upper Keweenawan Keweenawan sedimentary sedimentary strata; strata; i.e., i.e., the t h e Nonesuch Nonesuch and and Freda Freda Formations. Formations. Working w e l l drillers d r i l l e r s in i n the t h e western western Working in i n cooperation cooperation with with water water well Upper Upper Peninsula Peninsula of of Michigan, Michigan, more more than than 100 100 brine b r i n e contaminated contaminated water water wells 37 wells wells were were sampled sampled and and analyzed analyzed wells were ware identified. i d e n t i f i e d . Of Of these, these, 37 for C l , SO4, SO4, Sr, S r , Mn, Mn, Ba, Ba, Al, Al, f o r aa number number of of cations c a t i o n s and and anions anions including including Cl, I, I, Zn, Zn, Cu, Cu, NO3, NO3, Br, B r , Fe, Fe, IC, K, Na, Na, Mg, Mg, and and Ca. Ca. The The total t o t a l dissolved dissolved solids solids ranged ranged as as high high as a s 24,000 24,000 mg/i mg/1 with w i t h an an average average value value of of 2800 2800 mg/i. mg/1. Elemental concentrations of the nine samples with chloride levels Elemental concentrations of the nine samples w i t h c h l o r i d e l e v e l s above above 1000 1000 mg/l, mg/1, in i n order order of of relative r e l a t i v e abundance, abundance, were: were: Cl, C l , Ca, Ca, Na, Ma, 504, SO4, Br, B r , Sr, Sr, Mg, Mq, Ba, Ba, and and I. I. Statistical S t a t i s t i c a l analyses analyses established e s t a b l i s h e d strong strong positive p o s i t i v e linear l i n e a r correlation c o r r e l a t i o n coefficients c o e f f i c i e n t s between between many many of of the t h e analyzed analyzed elements. elements. J 1\ number of of the the b brine A number r i n e contaminated contaminated wells wells were were situated s i t u a t e d some some distance inland from the Lake Superior shoreline. It was hypothesized hypothesized d i s t a n c e i n l a n d from t h e Lake Superior shoreline. I t was that that these these wells wells may may have have been been contaminated contaminated by by brine b r i n e migration migration along along vertical fissures which transect the Keweenawan rocks. v e r t i c a l f i s s u r e s which t r a n s e c t t h e Keweenawan rocks. To To test t e s t this this hypothesis hypothesis linearnents lineaments were were mapped mapped from from aerial a e r i a l photographs photographs and and satellite s a t e l l i t e imagery imagery and and compared compared to t o the the brine b r i n e occurrences. occurrences. Preliminary Preliminary data Geophysical field field d a t a are a r e not not adequate adaquate to t o confirm confirm this this hypothesis. hypothesis. Geophysical measurements measurements using using resistivity r e s i s t i v i t y methods methods are a r e proposed proposed to t o resolve resolve this this problem. problem. We them from W e favor favoraa model modelofof origin o r i g i nfor f o rthe t h ebrines b r i n e swhich whichderives derivesthem from the the Lake Lake Superior Superior Basin. Basin. Compaction Compaction of of t h e Keweenawan Keweenawan sediments sediments in i n the the the sediments sediments and and resulting r e s u l t i n g fluid f l u i d expulsion expulsion provides provides aa plausible plausible mechanism mechanism for f o r updip updip movement movement of of the t h e brines. brines. This This model model is i s similar s i m i l a r to to White's White's hypothesis hypothesis for f o r the t h e origin o r i g i nof of the t h enative n a t i v ecopper copperdeposits d e p o s i t sofof the the Keweenaw Keweenaw Peninsula Peninsula (White, (White, 1966). 1966). REFERENCES REFERENCES Lane, Lane, A.C. A.C. (1908), (1908),"Mine "MineWaters", Waters", Lake Lake Superior Superior Mining Mining Institute Institute Proceedings, Proceedings, pp. pp. 63—152. 63-152. White, White, W.S., W.S., (1966), (1966),"Tectonics "Tectonicsof of the theKeweenawan KeweenawanBasin: Basin: Lake Superior Region", USGS Prof. Paper 524—E. Lake Superior Region", USGS Prof. Paper 524-E. —56— Western Western j �Video yideo Field Field TriD Trio to to The The Reweenaw Keweenaw Rift Rift I. ROSE ROSE (Dept. (Dept. of of Geology Geology and and Geological Geological Engrg., Engrg., Michigan Michigan Tech. Tech. University, University,.Houghton, Houghton, MI M I 49931) 49931) W. 14. 1. 0 40 40 minute minute video video field field trip trip to to the the Reweenaw Keweenaw Peninsula Peninsula and and Isle Isle Royale Royale is is presented presented as as aa example example of of the the unique 1-n-iique ability ability of of this this median medium to to communicate communicate the the field field setting setting and and geologic geologic context context of of classical classical areas. areas. The The video video fl incorporates numerous ions incorporates aerial aerialviews viewswith with numerousground ground locat locations ItIt is meant for audiences ranging from high is meant for audiences ranging from high and and maps. maps. school erice classes t hrough geo 1 ogy graduate school earth earthSc science classes through geology graduate students whoare areinterested interested in in an an introduction introduction to students who to the the large scale flood basalt phenomena of the area arid large scale flood basalt phenomena of the area and the the Michigan CopperDistrict. District. Michigan Copper ItIt isishoped videofield fieldtrips trips will hoped that that such such video will allow allow better frequent interchange interchangeof cf field field observations better and and more more frequent observat ions among geoscient ists and educators working in areas areas ail all among geoscientists and educators working in over the world. The expansion of video systems and over the world. The expansion of video systems and the the availability of editing availability of editingsystems systems and and technical technical comniun i cat ions studentseager eagerfor for projects projects which communications students which demonstrate cornrnunicat ion communication demonstrate the the various variousadvantages advantages ofofvideo video for science purposes it forcertain certainnatural natural science purposes makes makes it possible possible for for scientists scientists with with little 1 itt le video background background to to produce produce high high quality results. The video will be run continuously quality resu.lts. The video will be run continuously during during the the poster poster session, session, with with the the author author available available for. for. quest ions and comments. quest ions and comments. —57— �-j —4 J J Structural Structural and Economic Geology Geology of of Citadel Citadel Cold Gold Mines Mines Inc. Inc. Wawa, Ontario (Citadel Gold Gold Mines Mines Inc., Inc., P.O. P.O. Box 54 J. RIJPERT RUPERT (Citadel 54 ROY J. Wawa, Ontario Ontario POS Wawa, POS 11(0) 1KO) J The Surluga Surluga and Jubilee Mines of Citadel Citadel Gold Mines Mines Inc. Inc. were were reopened reopened in in 1987. 1987. These former former gold producers producers are are both both located in or adjacent adjacent to to the the Surluga Surluga Fault Fault Zone. Zone. series of anastomosing anastomosing The Surluga Fault Zone is is defined by a series mud slips slips and breccia zones zones up to to 55 feet wide, within aa wider fault fault 50 to to 200 200 feet feet wide. It dips dips east-south-east east-south-east at 300 30 to to zone from 50 400. Slickensides consistently indicate 400. Slickensides indicate movement in a normal right lateral sense sense along along aa plunge plunge direction direction of of 15° 15' to to 200 20 south. south. The fault zone is clearly defined where intrusive intrusive dioritic unit, but cannot tuffaceous tuffaceous rocks rocks to to the the north north and and south. south. the diorities diorities are relatively fresh relatively fresh rocks. rocks. tiple tiple it crosses crosses a complex mul— mulbe readily readily traced traced into into Outside Outside the the fault fault ione, zone, J IJ J Within the the fault fault zone, zone, anastomosing anastomosing splay splay faults, faults, schist schist zones zones and quartz veins trend at a higher azimuth azimuth and have have aa lower lower dip dip angle than than the the fault fault zone zone as as aa whole. whole. Failure to recognize recognize this this relationship, and the relationship, the assumption assumption that that the the "shearing" "shearing" was was paralparallel to the fault was a major contributing contributing factor factor in in the the economic economic failure of the failure the Surluga Surluga Mine Mine in in 1970. 1970. zones and quartz veins parallel the Siliceous alteration zones the schis— schistosity tosity and and the the faults. Where siliceous siliceous alteration alteration is is most intense intense ore is is developed. developed. These ore zones zones are offset en echelon to the the left and progresssively beneath one one another another from from south south to to north. Mine isa classic The Surluga Mineisa classic example example of of en en echelon echelon dilatant dilatant zones zones related to to movement movement on on aa fault. fault. II 1, -58- J �Imprint I m p r i n t of o f Archean Archean AAbitibi b i t i b i tectonics t e c t o n i c s on on the t h e Proterozoic Proterozoic Lake Lake Superior Superior Basin Basin R.J. (EssoMinerals MineralsCanada, Canada,P.O. P.O.Box Box290, 290, Timmins, Timmins, Ontario R.J. SHEGELSKI SHEGELSKI (Esso P4N 7N6) P4N 7N6) Archean supracrustals form formssix Archean supracrustals i x lithotectonic, l i t h o t e c t o n i cvolcanic—sedimentary , volcanic-sedimentary facies associations: 1) Least differientiated consists f a c i e s associations : 1) Least d i f f e r i e n t i a tPRIMATIVE e d PRIMATIVECRUST CRUST consists of komati— of voluminous, voluminous, thick t h i c ksubmarine submarine Mg—tholeiitic M g - t h o l e i i t i c basalts b a s a l t swith w i t minor h minor komatiitic i t i clavas lavasand and ultramafic u l t r a m a f i c intrusions. i n t r u s i o n s . Flat f l a t paleotopography paleotopography ccollects ollects thin 2) The The tholeiitic t h o l e i i t iBASALT c BASALT t h i n but butextensive extensivepyritic—graphitic p y r i t i c - g r a p h i t i cmudrocks. mudrocks. 2) PLATFORM contains both minor ffelsics PLATFORM contains both MgMg andand F eFe—tholeiites, - t h o l e i i t e s , wwith i t h minor e l s i c sand and local mafic sedimentation near normal faults. upper lavas are l o c a l mafic sedimentation near normal f a u l t s . The The upper are vario— variolitic, a transition VOLCANIC COMPLEX 3) t h e CENTRAL VOLCANIC COMPLEX which which l i t i cforming , forming a t r a n s to i t i 3) o nthe t o CENTRAL contains two tthirds contains two h i r d s volume volume oof f ttholeiitic h o l e i i t i cand andcalc—alkalic c a l c - a l k a l i c basalts b a s a l t s or or andesites andesites and and one one tthird h i r dsubmergent submergent to t oemergent emergent dacite—rhyolite d a c i t e - r h y o l i t e cone cone complexes. more andemergent, emergent,ppyroclastic complexes. As As lavas lavas become become more f efelsic l s i c and y r o c l a s t i c flank flank facies f a c i e s develop develop and and fine f i n edownslope downslope into i n t o4)4)lateral l a t e rTURBIDITE a l TURBIDITEBASIN BASIN deposits deposits consisting debris and minorbut but more morel alaterally c o n s i s t i n g of o f quartzo—feldspathic quartzo-feldspathic debris and minor terally extensive deposits form form along extensive iron i r o n formations. formations. 5) RIFT RIFTBASIN—RIDGE BASIN-RIDGE deposits along lineaments as predominantly predominantlycalc-a1 calc—alkalic and1ocal locally alkalic 1ineaments as k a l i c and l y a1 ka1 i c lavas, 1avas , alluvial—fluvial a l l u v i a l - f l u v i asediments l sedimentsand and fault—bounded f a u l t-bounded t uturbidites. r b i d i t e s . 6) 6 ) CRATONIC CRATONIC NUCLEI basements telescoped versions otherl i lithotectonic NUCLEI asasbasements areare telescoped versions o f of other t h o t e c t o n i c assoassociations by sstable andi iron c i a t i o n s capped capped by t a b l e sshelf h e l f carbonates, carbonates, sstromatolites t r o m a t o l i t e s and r o n fforormations. mations. Areal Areal ddistribution i s t r i b u t i o n of o f lithotectonic l i t h o t e c t o n i c associations associations iin n the t h e Abitibi A b i t i b i terrane terrane suggests structures suggests tthat h a t earlier e a r l i e rdeposition depositionwas was favoured favoured along along regional regional structures which and recordshearing shearingasast their WNW and record h e i r latest l a t e smovements. t movements. which now now ttrend r e n d WNW This This is the i s the t h e direction d i r e c t i o nofo the f t h eboundary boundary between between t h e AAbitibi b i t i b i northern northern "internal "internal zone" southern "external "external zone". zone" and and southern zone". Possibly Possiblycontemporaneous contemporaneous ENE trendENE trend- ing i n g structures s t r u c t u r e s were were reactivated r e a c t i v a t e d and and ddilatant i l a t a n t during during later l a t e rdeposition depositionand and orogeny, and now host economic epigenetic ore deposits. Intersections orogeny, and now host economic epigenetic ore deposits. I n t e r s e c t i o n s of regional ttectonic faulto f these these two two trends trends produce produce aa regional e c t o n i c grain g r a i n of o fshear shearand and fault— bounded lozenges wwith bounded lozenges i t h apparent apparent east—west east-west eelongation. l ongat ion. Changes Orogeny produced a NNW—NNE Changes iinn regional regionalstress s t r e sduring s d u r the i n g Kenoran t h e Kenoran Orogeny produced a NNW-NNE fracture represented by by thet hMatachewan f r a c t u r eset set represented e Matachewandike d i kswarm e swarmand andKapuskasing Kapuskasing Structural Structural Zone Zone respectively. respectively. The The iinherited n h e r i t e d ENE ENE AAbitibi b i t i b i trend t r e n d controlled controlled deposition greenstone deposition of o fearly e a r l yProterozoic Proterozoic greenstonein i Wisconsin n Wisconsinand andHuronian Huronian deposition ooff the stable stab1 e shelf she1 f sedimentation sedimentation in i n Ontario. Ontario. Subsequent Subsequent deposition the Cobalt andNipissing Nipissingf lflood basaltswas wasi ninitiated Cobalt pplatform l a t f o r m and o o d basalts i t i a t e d aat t tthe h e interintersection and tthe southern termination termination of section of o fthe t h eENE tNE Huronian Huronian ttrend r e n d and h e southern o f the the NNW Matachewanddike NNW Matachewan i k e swarm. swarm. Younger analogoustrends trendse exist Younger analogous x i s t iin n the t h e Lake Lake Superior Superior basin. basin. The The Animikie Animi k i e strand byby thet hMesabi—Gunflint strand line, l i n e ,defined defined e Mesabi-Gunflint iron i r o nrange, range,trends trendsENE tNEand and is The NNW NNW f rfractures actures NNW ddilatent i l a t e n t fractures. fractures. The i s intersected intersectedby byaborted abortedNNW allowed and deposition deposition of allowed subsidence subsidence and o f the t h elacustrine—shallow lacustrine-shal lowmarine marine Sibley Sibley Group and subsequent deposition of the Nipigon—Logan sills. Group and subsequent deposition o f t h e Nipigon-Logan s i l l s . Long—lived Long-lived NNE NNE f afaults u l t s subparallel subparallel to t othe t h eKapuskasing Kapuskasing Structural S t r u c t u r a lZone Zone provided provided periodic access for alkalic intrusions such as the Coldwell complex at at p e r i o d i c access f o r a l k a l i c i n t r u s i o n s such as t h e Coldwellcomplex the t h eclose c l o s eofoKeweenawan f Keweenawan volcanism. volcanism. The The Keweenawan, Keweenawan, asast hthe e llast a s t major major extrusive e x t r u s i v e event event ini nthe t h ebasin, basin,produced produceda athick t h i c sequence k sequenceofofemergent emergent —59— �U tholeiitic The ttrace r a c e of o f the t h e axial a x i a lsurface surface t h o l e i i t i basalts c b a s a l t sand andfelsic f e l s i cextrusives. extrusives. The in i n the the western WNW easternp oportions basin as, as, respectively, western and and WNW i n in t h the e eastern r t i o n s oof f t the h e basin respectively, later l a t e rand and earlier e a r l i e r inherited i n h e r i t e d Abitibi A b i t i b istructural s t r u c t u r a ltrends. trends. The The ENE tNE AAbitibi bitib-i trend t r e n dwas was once once aain againpredominantly predominantlydilatent d i l a t e during n t d u r iKeweenawan n g Keweenawanvolcanism, volcanism, as which ooriginated trans-'AbitibiKeweenawan Keweenawan ddike i k e swarm swarm which riginated as evidenced evidenced by by the t h etrans—Abitibi from f i n a argument l argument from the t h e Aphebian Aphebian greenstone greenstone bbelt e l t axis a x i s ini nWisconsin. Wisconsin. AA final 11 byby Keweenawan of o f the t h eLake Lake Superior Superiorsyncline synclinedefined defined Keweenawan sstrata t r a t a isi sEPIE ENE U for Superior f o rAbitibi A b i t i btectonic i t e c t o n iimprint c i m p r i nint the i n t hLake e Lake Superiorbasin basinis i the s t hpresence e presence J of between o feither e i t h eENE r ENEoroWNW r WNW fault f a u l tcontacts contacts betweenArchean Archeangranite—greenstone granite-greenstone and and gneiss—amptiibolite gneiss-amphi bol i t e ccrustal r u s t a l remnants remnants wwithin i t h i n the t h e Lake Lake Superior Superior basin. bas1n. LI J U j j j j J j -60- J �Nature of Cleavage. Foldin2 and Strain in the Michinicoten Greenstone BelL Near Wawa. Ontario CATHERINE H. SHRADYand andGEORGE GEORGE McGILL (Department of E.ILMcGILL (Department of Geology Geology and Geography, Geography, University Universityof of Massachusetts, Massachusetts,Amherst, Amherst,MA MA01003). 01003). The rocks within withinthe theMichipicoten Michipicoten Greenstone Greenstone Belt Belt near near Wawa, Wawa, well exposed. exposed.This This and and the the generally low Ontario are exceptionally well metamorphic grade grade and and excellent excellent preservation preservation oof primary metamorphic f primary sedimentologicalfeatures featurespermit permit detailed detailedstructural structural analysis. sedlmentologlcal analysis. Development oof multiple phases of with associated Development f multiple of folding with associatedcleavages cleavages and shear zones zones characterizes the predominantly predominantly ductile earlier Archean deformation. These were subsequently subsequentlydissected dissected and and displaced displaced along faults faults and shear andShrady, Shrady, this this volume). volume). Strain along shear zones zones (McGill (McGlU and during the earlier earlier deformation deformation of of the the area areaisIsgenerally generallyheterogeneous heterogeneous although conglomerate conglomeratepebbles pebblesdeformed deformedvery veryearly early in in the the history of of this part strain. this part of of the theBelt Belt record record moderate, moderate, relatively relativelyhomogenous homogenous strain. Rootless tight to isoclinal Rootless tight isoclinal mesoscopic mesoscopic folds oof f probable soft sediment sediment slump origin and generally larger, meter—scale tight folds without generally larger, meter-scale tight folds without associated axial axial planar cleavage associated cleavage but of of probable probable tectonic origin are are among the oldest structures. Conglomerate oldest recogni2ed recogoiaad structures. Conglomeratepebbles pebbles lie lie within an an approximately approximately bedding bedding parallel cleavage, cleavage, the earliest earliest observed. This cleavage is only rarely rarely observed penetrative cleavage cleavage observed. cleavage is observed to to be axial planar to clastic dikes dikes parallel parallel to this be to folds. folds. The The existence oof f clastic suggests that, that, at early axial planar cleavage cleavage suggest* at least least locally, locally, this this cleavage cleavage developedin In incompletely incompletely consolidated consolidatedsediments. sediments. Mineral lineations Uneations developed principal extension and the thelong long axes axesofof deformed deformedpebbles pebblesdefine definea aNE—E NE-E principal extension within this thiscleavage cleavage plane. plane. Estimates Estimates of of the the axial axial ratios ratiosof of oblate oblate strain ellipsoids suggeststrain strain of of moderate moderate intensity intensity with little strain ellipsoids suggest little variation across faults are variation acrossthe thearea. area.Bedding—related Bedding-related faults are also also of of comparable relative relative age. age. Although Althoughthe theprecise preciserelation relation among comparable among the is not not at at present known, a early folds, folds, faults and this cleavage cleavage is of deformation deformation resulting resulting in in these structures structures isissuspected. suspected. continuum of Regionaloverturning overturning and and stratigraphic stratigraphic inversion Regional inversionsuggestive suggestive of of thrusting and with this phase and large large recumbent recumbent folds folds also is associated associated with phase of deformation. In In comparison, comparison, younger youngerdeformation deformationand andstrain strain are are o f deformation. Inhomogeneousand andhave havebad had little little effect, effect, except except locally locally (e.g. (e.g. in in shear Inhomogenwus zones) on the zones) the deformed deformed conglomerate conglomerate pebbles. pebbles. A younger, younger, generally A generallyNW—trending, NW-trending, moderately moderatelyNE—dipping NE-dipping is most most strongly developed inthe the western western and crenulation cleavage cleavage is developed in northwestern sections foldsare are rare. rare. northwestern sections of of the the area. area.Related Related mesoscopic mesoscopic folds —61— �-4 this and a NE— this and crenulating crenulatingall allprevious previoussurfaces surfacesisis a NEtrending cleavage that dips steeply SE and NW and is axial planar to trending cleavage that dips steeply SE and NW and is axial planar to folds oof opentototight tight geometry. geometry. Shear Shear zones zones parallel parallel the the axial axial surfaces surfaces folds f open of these folds. steepeningoof dipsprobably probably is is associated associated with with o f these folds. Regional Regional steepening f dips this deformation phase which appears more intensely developed in the the this deformation phase which appears more intensely developed in southern part is crenulated crenulated by by part of of the the area areamapped. mapped. This This older older cleavage cleavage is southern aa younger northeasterly trending axial planar cleavage with shallow younger northeasterly trending axial planar cleavage with shallow to moderate southeasterly southeasterly dips. dips. In Inaddition additionto tothose thosedescribed describedabove, above, are cleavages of only local development; some parallel faultsfollowed followed are cleavages of only local development; some parallel faults by diabase diabase dikes, dikes, others others are are oof variable attitude attitude and and uncertain by f variable uncertain association. association. Post—dating Post-dating The deformational deformationalhistory historyrecorded recordedby bythese thesestructural structural feautures feautures is is The more complex than previously recognized, with significant shortening more complex than previously recognized, with significant shortening and strain and shearing. and strain achieved achieved through through early earlyfolding folding and shearing. Subsequent Subsequent folding, cleavage cleavagedevelopment developmentand andassociated associatedstrain strain are are more local and folding, heterogeneousinincharacter. character. OOur observationsare are inconsistent inconsistentwith with a heterogeneous u r observations simple Archean deformational history dominated by either vertical simple Archean defarmational history dominated by either vertical motion or or horizontal compression motion compression resulting in an an uncomplicated uncomplicated suggest that that the complex nature of synclinal geometry. We We suggest complex nature of deformation in this part of the Michipicoten Greenstone Belt is more consistent with in this part of the Michipicoten Belt is more consistent with that recently documented in some other Archean terranes (e.g. the recently documented in some other Archean terranes (e.g. Barbeton Greenstone Greenstone Belt, Belt, de de Wit, Wit, 1982; 1982; the theNorseman—Wiluna Norseman-Wiluna Greenstone Belt, Martyn, 1986) and with that observedwithin within many many Greenstone Belt, Martyn, 1986) and with that observed Phanerozoic orogenic belts. Phaneroaoic belts. References Wit, M. M. J. J. 1982. Glidingand andoverthrust overthrust nappe nappe tectonics tectonics in in the 1982. Gliding de Wit, Barbeton greenstone belt, .1 Struct. 117—136. belt, J. Struct.Geol., Seol.,4,4,pp.pp. 117-136. Barbeton Martyn, J. E. 1986. Evidencefor forstructural structural stacking stacking and and repetition repetition in Martyn, J.E. 1986. Evidence the greenstones of of the Kalgoorlie district, Western Western Australia, Australia, In the Kalgoorlte district, Workshop on Tectonic Evolution of Creenstone Belts (M.J. J. de Wit Wit and Workshop on Ttctoaic Evolution of Srefastoae Btlts (M. L. D. L.P.1. TechRpt. TecftRpt. 86—10. Lunar and and L. D. Ashwal, Ashwal, eds.), cds.),pp. pp.150—152. 150-152. L.P.I. 86-10. Lunar Planetary Institute, Institute, Houston. Houston. —62— �Structural Geolov of the Southwestern Portion of the Michlnicoten Greenstone Belt. Ontario CATHERINE H. SHRADYand andGEORGE GEORGE McGILL (Department of Geology E. E.McGILL (Department Geology and Geography, University of Massachusetts, and Geography, University of Massachusetts,Amherst, Amherst,MA MA01003). 01003). The The Michipicoten ~ichipicotenGreenstone Belt Belt extends for about about150 150 kin k m ENE ENE from from the northeastern angle of Lake Superior. The eastern limit of the northeastern angle of Lake Superior. The eastern limit of the the belt belt isis the Kapuskasing zone zonethat that separates thehigh—grade high-grade Kapuskasing separatesthe theMichipicoten Michipicoten from the Abitibi Greenstone Belt. We are mapping key areas in from the Abitibi Greenstone Belt. We are mapping key areas in the the southwestern portion of the Belt at a scale of 400 = 1, tying these southwestern portion of the Belt at a scale o f 400' = I", these 4* areas Geological areastogether together with with11mIle mile== 4 " mapping mapping and andrecent recentOntario Ontario Geological Survey Surveypreliminary preliminarymaps mapsby bySage Sageand andothers. others.All Allof of our ourmapping mappingto to date has been within Chabanel Township, and most of it is in or date has been within Chabanel Township, most of is in or adjacent adjacent to to the the large large fume fume kill kffldownwind downwind from the the sintering sintering plant plant in in Wawa Wawa where where outcrops outcrops are are very veryabundant abundantand andeasily easilylocated. located. This This abstract of our ourdetailed detailed maps. maps. abstractaccompanies accompaniesaaposter posterdisplaying displayingsome some of The The rocks rocks of of our our area areamay maybebedivided dividedinto intothe thetraditional traditionallithologic lithologic types: types:rnafic—intermediate mafic-intermediate volcanics, wlcanlcs, intermediate—felsic intermediate-felsic volcanics, volcanics, clastic iron formation). clastic sediment5, sediments, and chemical chemical sediments sediments (including (including Iron formation). In In the thesouthwestern southwesternportion portionofofthe theMichipicoten MichipicotenGreenstone Greenstone Belt Belt there there is is aa northern northern(interior) (interior)terrane terraneconsisting consistingmostly mostlyof of intermediate intermediate to to mafic volcanics. These rocks dip north to northeast at intermediate mafic volcanics. These rocks dip north at Intermediate angles, angles, and are are overturned overturned (all (allindicators indicatorssuggest suggest southward southward or or southwestward southwestwardyounging). younging). Along Along the southern margin margin of of the the belt belt Is is aa thick volcanic rocks rocks with with minor iron formation that thick sequence sequence of of volcanic that youngs andhas hassteep steepnorth northororsouth southdips. dips.Between Betweenthese these youngs northward northwardand dominantly terranes isisan anextensive extensivebelt beltof of clastic clastic dominantly volcanic volcanic terranes sedimentary sedimentaryand andpyroclastic pyroclasticrocks. rocks.Much Muchof of our ourdetailed detailedmapping mapping has has been concentrated in this belt because of the abundance of good been concentrated in this belt because of the abundance of good indicators of younging younging direction, direction, and and because because cleavages cleavages generally generally are are indicatorsof better in the metasedimentary metasedimentary rocks rocks than they are batter developed developed in are in in the the rnetavolcanic metavolcanicrocks. rocks. In In the theeastern easternpart partofofChabanel Chabanel Township, Township, there there is is aa single, single, abrupt abrupt reversal reversalininyounglng younging direction direction within the sedimentary sedimentary belt belt that that Is is interpreted to be a fault (or a faulted isoclinal fold). One late fault interpreted to be a fault (or a faulted isoclinal fold). One late fault that is present present south south of of this this reversal, but thatgenerally generallyfollows follows bedding bedding Is but the Other bedding— thedisplacement displacementdoes doesnot notappear appeartotobebesignificant. significant. Other beddingrelated faults may be present but obscure due to lack of such related faults may be present but obscure due to lack of suchfeatures features as astruncation, truncation,obvious obviousshearing shearingand andlocal local stratigraphic stratigraphicinversion. inversion. Overall, thatthe thesedimentary sedimentarysequences sequences Overall, however, however, the theimpression impression isis that north and south of the one obvious younging direction reversal north and south of the one obvious younging direction reversal are arenot not severely severelydisrupted. disrupted. —63— �To the west, west, the widens rather rather To the the width width of of the the sedimentary sedimentary belt belt widens rapidly, in part due to Increasing thicknesses of Individual rapidly, in part due to increasing thicknesses of individuallithologic lithologic units, but units, but also also we w e suspect suspect due due to to fault fault imbrication imbrication (imbricatlon (imbrication is is very difficult the widest very difficult to to prove prove in in the the absence absence of of fossils!). fossils!). Within Within the widest part of and map map part of the the sedimentary sedimentary belt belt we we have have been been able able to to define define and lithologic "packages", most of which are bounded by contacts that we lithologic "packages", most of which are bounded by contacts that we believe are are early early faults, believe faults, based based on on the the presence presence of of one one oorr more more suggestive characteristics characteristics (deformed suggestive (deformed conglomerate conglomerate pebbles, pebbles, local local spaced spaced cleavages, gossans, mat ics sills, networks of quartz veins, narrow cleavages, gossans, mafics sills, networks of quartz veins, narrow linear topographic depressions,truncation truncation oof layering, oorr abrupt abrupt tops linear topographic depressions, f layering, tops reversals). In reversals). In addition, addition, the the sedimentary sedimentary belt belt appears appears to to be be separated separated from the the northern northern volcanic terrane by by aa fault from volcanic terrane fault that that we we have have been been able able to trace across almost the entire width of Chabanel Township. to almost the entire width of Chabanel Township. Tentatively, we we interpret Tentatively, interpret the the mapped mapped relationships relationships as representing representing a thrust—imbricated sequence of volcanic and sedimentary rocks, with with thrust-imbricated sequence of volcanic and sedimentary rocks, imbrication increasing increasingwestward westward within the area we have mapped. the area we have mapped. Becauseofofthe thefaulting, faulting,the theage ageofofthe therocks rocksinInthe thenorthern northern (interior) (interior) Because volcanic terrane relative to the volcanic rocks along the southern volcanic terrane relative to the wlcanic along margin of margin of the belt near near Wawa Wawa is is not not known known (no (no published published radiometric ages comefrom fromthe thenorthern northern volcanic volcanicterrane), terrane), nor do we we know the ages come sense of of relative relative movement movement across across the imbricate faults. Efforts Efforts to eliminate these uncertainties are underway. eliminate these uncertainties are underway. .1 —64— �fl Struct ural Mnal ysi s ofofPrc'terczcic MetMetasediments, ased iment s, fl Structural flnalysis Proterozoic Northern Falls Falls River. Michigan Northern River, Saraga Baraga County. County, Michigan SIRKILM arid GREGG (Dept. (Dept. of of Geology Geology and KK.M. . M. SIKKILfi. and W.W.J. J. GREGG and Geol. Gaol. Engrg., Michigan Tech. Univ., Houghton, MI 49931) Engrg., Michigan Tech. Univ., Houghton, M I 49931) The geologic geologic feature historically referred referred to The feature historically to as as the the "Baraga Basin" Basin" is is a a roughly roughly crescentic crescentic depression depression trending trending "Baraga east—west across across north-central north—central and and northeastern northeastern Baraga east-west Baraga County contains County in in the the Upper Upper Peninsula Peninsula of of Michigan. Michigan. IIt t contains deformed and and metamorphosed metamorphosed sediments sediments that that have have been deformed been correlated with correlated with the the lower lower Proterozoic ProterozoicMichigarnme Michigamme Formation. Formation, and is rocks of of the the Northern Northern Complex Complex to to and is bounded bounded by by flrchean flrchean rocks the the south south and and northeast. northeast. The The best bast exposures exposures of of the the structure structure within within the the Baraga Baraga Basin occur in the beds of the northward—flowing streams Basin occur in the beds of the northward-flowing streams draining into westernmost of these into Lake Lake Superior. Superior. The westernmost streams, the Falls River, was intensively mapped from streams, the Falls River, was intensively mapped from its its mouth in the village of L'Mnse to a terminal point mouth in the village of L'ftnw to a terminal point located located approximately one to the the south. Other Other aspects aspects approximately one mile mileupstrearii upstream to of the investigation included description of microstructural of the investigation included description of microstructural features and and geometric geometric analyses analyses of of various various elements elements cf features of the the rock fabric. rock fabric. The slates The slates and and metagreywackes metagreywackms of of the the Falls Falls River River area area are characterized by three roughly coaxial systems are characterized by three roughly coaxial systems cf of folds, folds, two of of which Style group two which are are mesoscopically mesoscopically distinct. distinct. Style group B. BI consists of a series consists series of tight to isoclinal isoclinal overturned folds folds with axes with axes that plunge shallowly to the the west—northwest west-northwest and east—southeast. Broal 1—scaleparasitic parasitic folds folds are are commonly commonly east-southeast. Small-scale associated with these The overall overall vergence vergence cf associated these larger larger folds. folds. The of the system suggests the suggests that the the field field area is is located located on on the the The axial—planar regional fold. long limb limb of of aa B1 B1 regional fold. The axial-planarfc.liati':'n foliaticm this style style group (Se) associated with this <S,) dips d i p s gently to the the southwest in in those those areas areas unaffected unaffected by by later later deformation. deformation. Microscopically, SI 5, varies in in appearance appearance from a Microscopically, well—developed continuous continuous slaty fabric well-developed fabric in in the the pelitic pelitic units units to an irregular domainal rough cleavage cleavage in in the the matrix—rich matrix-rich greywackes. In nearly nearly all all cases, cases, the mineral chlorite greywcckms. In chlorite defines the Matrix—poor varieties of defines the cleavage cleavage fabric. fabric. Matrix-poor greywacke display an an 5,—parallel SI-parallel flattening flattening of of clasts. clasts. Recrystallization textures are common in these R~crystallization textures are common in these rocks. rocks. A system of S, —parallel thrusts thrusts is is also also associated associated with this S,-parallel this style group. The fault fault zones are commonly cataclastized and style group. mineralized with quartz quartz and and carbonate. carbonate. Style group B B, considerable lateral . exhibits considerable lateral variation within the field area from north to south. To the the north, B, area from north to south. north, Em is best visualized as a series i s best series of of gentle gentle folds folds and and fabric. SI fabric. asymmetric flexures flexures in in the the previously previously existing existing 5, Fault zones zones have have also also been been visibly visibly folded folded in in some some locales. locales. trond roughly Fold axes appear to be horizontal and trend east—west. P sinuous sinuous crenulation is developed developed east-west. ft crenulation cleavage cleavage (B,) (9.) is —65— �j in the the proximity Cleavage domains in proximity of of the the B, B. hinges. hinges. Cleavage domains vary vary B. folds become tight at the Be folds become tight at the southern end is generally generally southern end of of the the survey survey line, line, and and S. S. is pervasive. Microscopically, S, is more strongly pervasive. Microscopically, Se is more strongly developed developed here than to here than to the the north, north, with with well—defined well-defined cleavage cleavage domains, domains, anastomosing and commonly commonly symmetrical symmetrical profiles. anastomosing rnorphologies morphologies and profiles. from from zonal zonal to to discrete. discrete. J — B deformation Bi deformation is is characterized characterized by by macroscopic macroscopic folds folds which overprint B, style group elements. Field evidence evidence is Field is which overprint Be style group elements. most most easily easily seen seen at at the the southernmost southernmost extent extent of of the the field field line S. cleavage cleavage line and and consists consists mainly mainly of of the the reorientation reorientationc'f of Sà attitudes. Originally east—west striking, nearly vertical attitudes. Originally east-west striking, nearly vertical crenulat ion cleavage cleavage planes planes have have been been rotated rotated more more than 70 crenulation than 70 degrees along a roughly east—west trending horizontal degrees along a roughly east-west trending horizontal axis. axis. Mesoscc'pic fold axes axes for for this this system system have have not not been Mesoscopic fold been precisely precisely located in the field. Pdditional field evidence in the field. additional field evidence in in the thefcrri form of is of a a localized localized steeply steeply dipping dipping spaced spaced cleavage cleavage CS3) (S,) is recognized outcr-ops at at the the terminus terminus of of the the survey survey line. line. recognized in in outcrops These These cleavage cleavage surfaces surfaces appear appear in in thin thin section section as as rough rough fractures and irregular fractures and irregular seams seams of of dark dark residual residual material material that that overprints overprints earlier earlier foliations, foliations, and and has has aa strike strike coincidental coincidental with with the the rotational rotational axis axis of of the the earlier earlier B, S. fabric. fabric. The operation operation of nappe—style nappe-style tectonism tectonism during during the the PenokeanOrogeny Orogenyhas hasbeen beenproposed proposed severalauthors authors in in Penokean byby several recent not be it may may not be the theonl9 onlymechanism mechanism recent years. years. fllthough Although it capable capable of producing producing the the structural structuralfeatures featuresobserved observed at at this and other locations in the Baraga Basin, it is a this locations in the Baraga Basin, it a tectonic tectonic model model that that is is consistent consistent with with known known field field evidence: evidence: 1) B fold 1) The B, fold systems systems in in the the region region display display aa vergence vergence indicative of a position on the long the long limb limb of of aa large— largescale overturned Fold scale overturned regional regional B1 Bi fold system. systems reflective limb reflçctiv of a position on the the short limb of a regional fold are not seen. of a regional fold are not seen. 2) S1—parallel thrust faults 2 ) Systems Systems of S,-pai-allel faults are are observable observable throughout the region, perhaps reflective the region, perhaps rçflectiv of of large— largescale overthrusting. scale overthrust ing. 3) 3 ) The The systematic systematic disappearance disappearance of of later—stage later-stage fold fold systems systems towards towards the the north, and and the the overall overall reduction reduction in the the intensity intensity of of deformation deformation towards towards the the north, north, is something observable on a regional scale, and reflective deform— reflective of a lateral lateral progression from a deformational foreland foreland to to aa hinterland. hinterland. 4) 4) Previous Previous work regarding multiply—deformed multiply-deformed terranes (overthrust (overthrust belts in particular) has shown that a single single progressive progressive tectonic tectonic event event can can produce produce poly— polyphase deformational deformational features features such such as as refolded refolded folds. folds. This This eliminates eliminates the the need need for for models models involving involving discrete deformat ion. discrete "pulses" "pulses" of of deformation. J J J j J -66- J -j �Mesozoic Mesozoic Paleogeography: Paleogeography: implications implications for f o r economic economic deposits north of Lake Superior deposits north of Lake Superior J. J. S. S. SPRINGER SPRINGER (Ontario (Ontario Geological Geological Survey, Survey, Sudbury, Sudbury, Ontario, Ontario, P3E P3E 5P9) 5P9) During During the t h e Mesozoic Mesozoic major major shifts s h i f t s took took place place in i n the t h e position p o s i t i o n and and attitude attitude of of the t h e North North American American crustal c r u s t a l plate p l a t e and and by by early e a r l y Cretaceous Cretaceous time time Africa Africa had had split s p l i t away away from from North North America America to t o form form the t h e Atlantic A t l a n t i c ocean. ocean. Great Great movements movements also a l s o took took place place in i n the t h e position p o s i t i o n of of magnetic magnetic north, north, influencing influencing global global weather weather patterns. patterns. For For long long periods periods the t h e Precambrian Precambrian Shield Shield stood stood as a s aa continental c o n t i n e n t a l massif massif subject s u b j e c t to t o intense intense tropical t r o p i c a l weathering, weathering, which which advanced advanced most most quickly quickly along along existing e x i s t i n g fracture f r a c t u r e zones zones or o r in i n rocks rocks of of susceptible s u s c e p t i b l e composition. composition. By late Jurassic time this process had developed a subdued By l a t e J u r a s s i c time t h i s process had developed a subdued surface surface of of advanced karst across parts of Minnesota on which quartz—feldspar advanced k a r s t across p a r t s of Minnesota on which quartz-feldspar debris, debris, supplied supplied by by the t h e granite g r a n i t e terranes t e r r a n e s of of Manitoba Manitoba and and Saskatchewan, Saskatchewan, was was slowly transported southwards across a gentle topogradient. slowly transported southwards across a g e n t l e topogradient. By By early e a r l y Cretaceous Cretaceous time time aa rapid rapid pulse pulse of of seafloor s e a f l w r spreading spreading and and renewed renewed sources of volcanism in the mantle caused rotation of the North sources of volcanism i n t h e mantle caused r o t a t i o n of t h e North American American plate. p l a t e . Mountain Mountain building building and and local l o c a l explosive explosive volcanism volcanism marked marked the western margin of the continent, whereas a shallow north—south t h e western margin of t h e continent, whereas a shallow north-south seaway seaway developed developed across across the t h e continental c o n t i n e n t a l midline. midline. Once Once again again the the Ontario Shield was a landmass Ontario Shield was a landmass upon upon which which terrestrial t e r r e s t r i a l materials m a t e r i a l s were were patchily SO* parallel p a r a l l e l now now ran ran from from about about Kenora Kenora to t o Cape Cape p a t c h i l y deposited. deposited. the The 50° Henrietta Henrietta Maria Maria and and the t h e climate climate on on the t h e eastern e a s t e r n shore shore of of the the inland inland sea s e a was was warm warm but but semi—arid. semi-arid. The The long long episodes episodes of of continental c o n t i n e n t a l weathering, weathering, the t h e subaerial s u b a e r i a l volcanism volcanism and and the t h e climate climate conditions conditions influenced influenced the t h e formation formation and and concentration concentration of of aa suite s u i t e of of economic economic mineral mineral deposits d e p o s i t s which which are a r e characteristic c h a r a c t e r i s t i c of of this this time. time. Kaolin, Kaolin, valuable valuable for f o r the t h e refractory r e f r a c t o r y properties p r o p e r t i e s of of iron—free iron-free aluminous i n addition a d d i t i o n have have aluminous materials, m a t e r i a l s , and and secondary secondary kaolins, kaolins, which which in special s p e c i a l plastic p l a s t i c properties, p r o p e r t i e s , were were formed formed worldwide worldwide in i n the t h e Mesozoic. Mesozoic. Volcanic Volcanic dusts, d u s t s , produced produced by by explosive explosive subaerial s u b a e r i a l volcanism, volcanism, have have been been subsequently weathered to special—use bentonitic clays. The hot, often subsequently weathered t o special-use b e n t o n i t i c clays. The h o t , often humid humid climate climate produced produced karst k a r s t depressions depressions filled f i l l e d with with concentrates concentrates such such as a s hematitic hematitic iron—ores iron-ores or o r carbonate—free carbonate-free clays. clays. Leaching Leaching of of carbonate carbonate from has left l e f t gravelly g r a v e l l y phosphate phosphate residues residues enriched enriched from carbonatite c a r b o n a t i t e bodies bodies has in rare earths and fluorine. i n r a r e e a r t h s and f l u o r i n e . Silica S i l i c a leaching leaching has has upgraded upgraded siderite siderite iron s o f t hematite—limonite hematite-limonite concentrate concentrate which which was w a s the t h e earliest earliest i r o n ores o r e s to t o aa soft Great Lakes iron ore. Great Lakes i r o n ore. The The common conmon theme theme of of these these deposits d e p o s i t s is is their t h e i r relationship r e l a t i o n s h i p to t o the t h e Mesozoic Mesozoic evolution of the North American Shield. evolution of t h e North American Shield. Ontario Ontario examples examples suggest suggest that that beneath beneath aa glacial g l a c i a l cover cover more more of of these these valuable valuable concentrations concentrations may may be be found and that t h a t the t h e importance importance of of this t h i s time time interval i n t e r v a l has has been been underunderfound and valued. valued. —67— �-a U Solid Pyrobitutxn Pyrobitumen iin Panel Mine, Mine, Elliot Solid n Veins, Veins, Panel E l l i o t Lake Lake Uranium Uranium District, Ontario Ratriet, Ontario JEFF STEVENSON, JOE MANCUSO, ,University,JOE HAHCUSO, JOE JOE FRIZADO, FRIZADO, Bowling Bowling Green Green JEFF State Bowling Green, Ohio 43403. State University, Bowling Green, Ohio 43403. TRUSKOSKI, Rio PPAUL AUL Â¥niUSKOSKI Rio Algom Algom Ltd. Ltd. Elliot E l l i o t Lake, Lake, Ontario Ontario P5A P5A 2K1 2K1 WILLIAM KNELLER, University of Toledo, Toledo, Ohio 43606 WILLIAM KHELLER, University of Toledo, Toledo, Ohio 43606 Globular blebs Globular blebs of o f solid s o l i d pyrobitumen pyrobitumen (thucholite (thuoholite of o f older older reports) are found in veins exposed in open stopes and r e p o r t s ) a r e found i n veins exposed i n open stopes and drifts d r i f t s in in The tthe h e Panel Panel Mine Mine in In the t h e Elliot E l l i o t Lake Lake Uranium Uranium District, District, Ontario. Ontario. The veins fill f i l l fractures fractures in i n the t h e 2.2 2.2 billion b i l l i o n year year old o l d Matinenda Matinenda veins Formation. The The blobs blebs a are mm) and Formation. r e small small (1—10 (1-10 ran) and free—form,varying free-formavarying shape from The surfaces from round round to t o disc, d i s c , twisted twisted or o r elongate. elongate. T he surfaces iin n shapa shiny and and pel-meated permeated w with Analyses show show the aare r e shiny i t h vesicles. vesicles. Analyses t h e blebs blebs be predominantly predominantly carbon with a a H/C H/C ratio r a t i o of of 0.51, 0.51, aa tto o be carbon with and aa 66 13C 13C value value of of —33°i6o(PDB). rreflectivity e f l e c t i v i t y (max (max Ro) Ro) of of 0.91%, 0.91%. and -33O/>o(PDB). j j Kaiman and and Horwood Kaimn Horuood (1976) (1976) concluded concluded that t h a t blebs blebs of of thucholite thucholite in the Milliken Mine were formed by the agglomeration and i n t h e Milliken Mine were formed by the agglomeration and polymeriztion of polymeriztion o f carbon carbon particles p a r t i c l e s from from the t h e exhaust exhaust of o f diesel diesel We propose that the pyrobitumen blebs in mining equipment. i n the the mining equipment. Me propose t h a t t h e pyrobltumen blebs Panel Mine are the result of the natural migration and maturation Panel Mine a r e t h e r e s u l t o f t h e 'natural migration and maturation of petroleum. The Precambrian petroleum migrated migrated into Precambrian petroleum i n t o the the of petroleum. The and with with ttime ffractures r a c t u r e s and i n e and and increased increased temperatures temperatures polymerization polymerization progressed and and tthe masses matured matured iinto blebs of of progressed h e ttarry a r r y masses n t o tthe h e blebs pyrobitumen. pyrobitumen. Blebs o of similar morphology morphology and and occurrence occurrence have have been been Blebs f similar reported from from fracture reported f r a c t u r e fillings f i l l i n g s in i n the the Cambrian Cambrian Bonneterre Bonneterre Formation from Magmont West West Mine Formation from tthe h e (tagmont Mine on on the t h e Viburnum Viburnum Trend, Trend, al. 1986) and in the Ordovician Missouri (Marikos,et Missouri (Marikos.et a l . 1986) and i n t h e Ordovician Trenton Trenton Formation in Both 1986). Both Formation i n Uyandot Wyandot County, County, Ohio Ohio (Haefner, (Haefner, ete tal., al., 1986). considered tto from locally l o c a l l y derived derived oil o i l that that aare r e considered o have have been been formed formed from was polymerized polymerized in was i n the t h e fractures. fractures. Based on on observations observations with with the Bued the petrographic petrogr8phie and and scanning scanning electron micrpscopes, microscopes, a paragenetic paragenetic sequence oof mineralization iin n electron f mineralization tthe h e ffractures r a c t u r e s and and the t h e occurrence occurrence of o f the t h e pyrobitumen pyrobituaen have have been been determined. Quartz Quartz was was the mineral to determined. t h e first first mineral t o crystallize c r y s t a l l i z e in i n the the followed by by a ffirst pyrite. The pyrite was ffractures r a c t u r e s followed i r s t generation pyrite. The p y r i t e was subsequently altered morphologically by partial dissolution. subsequently a l t e r a d lorphologioally by p a r t i a l dissolution. Petroleum migrated migrated iinto and wwas Petroleum n t o tthe h e ffractures n o t u r e s and u ppartially artially polymerized into polymePized i n t o blebs bleba which which were were encased e n c a ~ dby by fibres f i b r e s of o f sepiolite. sepiolite. generation ppyrite Near tthe h e end ooff sepiolite formation a second generation yrite was deposited. is in i n the t h e form form of of larger l a r g e r (5—15 (5-15 mm) was deposited. This ppyrite y r i t e is cubes. The ffact inclusions oof cubes. a c t tthat h a t tthis h i s ppyrite y r i t e contains Inclusions f and pyrobitunen pyrobitumen indicates ssepiolite e p l o l i t e and i n d i c a t e s that t h a t the t h e pyrobitumen formed formed h e same time time oorr just j u s t after a f t e r the t h e second second pprior r i o r tto o tthe h e ppyrite. y r i t e . AAtt tthe generation p pyrite formed, minor minor ppyrrhotite and galena galena y r r h o t i t e and generation y r i t e was formed, deposition began. mm) calcite c a l c i t e crystals c r y s t a l s cover cover and and deposition began. Large (5—20 (5-20 no) n tthe he overgrow the t h e blebs ooff pyrobitumen and aall l l other minerals iin fractures. fractures. —68— J J J J �The The source s o u r c e of o f the t h e organic o r g a n i c material m a t e r i a l which which produced produced the the petroleum is still in question. Willingham et petroleum is s t i l l i n q u e s t i o n . Willingham e t aal. l . (198k) (1984) ccited ited the t h e ooccurrence c c u r r e n c e of o f stratiform s t r a t i f o r m kerogens kerogens in i n the t h e Matinenda Matinenda Formation Formation Elliot Lake Region evidence for mats o of iin n tthe he E l l i o t Lake Region aass evidence f o r aancient n c i e n t mats f cyanobacteria. The other possible sources of organic material c y a n o b a c t e r i a . The o t h e r p o s s i b l e s o u r c e s o f o r g a n i c m a t e r i a l for petroleum formation f o r petroleum formation are a r e the t h e argillites a r g i l l i t e s and and siltstones s i l t s t o n e s of o f the the Mokim Formation. Mckim Format ion. REFERENCES REFERENCES Haefner, Haefner, R.F. R.F. Mancuso, Mancuso, J.J., J.J., Frizado, F r i z a d o , J.P., J.P., Shelton, S h e l t o n , K.L., K.L., and and Gregg, J.M., 1986, Crystallization temperatures and Gregg, J.M., 1986, C r y s t a l l i z a t i o n t e m p e r a t u r e s and stable stable carbon and oxygen isotopes carbon and oxygen i s o t o p e s of o f Mississippi M i s s i s s i p p i Valley—Type Valley-Type sulfides sulfides and associated carbonates, Trenton Limestone and a s s o c i a t e d c a r b o n a t e s , Trenton Limestone (Ordovician), (Ordovician), Wyandot County, Wyandot County, Ohio: Ohio: Geol. Geol. Soc. Soc. Amer. A m e r . Ann. Ann. Mtg. M t g . Abstracts Abstracts with Programs, p. 624(ab). with Programs, p. 624cab). Kaiman, S. 5. and Kaiman, and Horwood, Horwood, J.L., J.L., 1976 1976 An An unusual unusual "thucholite" " t h u c h o l i t e w from from Elliot Lake, Ontario: Ontario: Canadian Canadian Mineralogist, v. 1k, E l l i o t Lake, M i n e r a l o g i s t , v. 14, p. p. 422—428 422-428 Marikos, M.A., M.A., Laudon, Laudon, R.C. Marikos, R.C. and and Leventhal, Leventhal, J.S., J.S., 1986, 1986, Solid Solid insoluble i n s o l u b l e bitumen bitumen in i n the t h e Magmont Magmont West West Orebody, Orebody, southeast southeast Missouri: Leon. Missouri: Econ. Geology, Geology, v. v. 81, 81, No. No. 88 (in ( i n press). press). Willingham, T.O. Krinsley, Willingham, T.O. Nagy, Nagy, B. 0. and and Nagy, Nagy, L.A., L.A., K r i n s l e y , Dii. D.H. and and Mossman, D.J., 1985, Uranium—bearing stratiform organic Mossman, D.J., 1985, Uranium-bearing s t r a t i f o r m o r g a n i c matter matter in paleoplacers of the i n p a l e o p l a c e r s of t h e lower lower Huronian Huronian Supergroup, Supergroup, Elliot Elliot Lake—Blind River Lake-Blind River region, r e g i o n , Canada: Canada: Can. Can. Jour. Jour. Earth Earth Sci. S c i . 22, 22, p. p. 1930—194k. 1930-1944. —69— �j j The "Eager "Hager Suite" Suite" and Concerning the the Nature The and Problems Problems Concerning Nature and and Location Location of the the Northern Northern Boundary Boundary of of the the Wolf Wolf River River Batholith Batholith of J D.C. D.C. STEWART STEWART and and J.M. J.M. MANCUSO MANCUSO (Department (Department of of Geology, Geology, Bowling Bowling Green Green State University, University, Bowling Bowling Green, Green, Ohio Ohio 43403) 43403) State It contention of of this abstract that It is is the the contention this abstract that the the "Hager "Hager Granite Granite // Porphyry", which has previously been considered to be the Porphyry", which has previously been considered to be the northernnorthernmost unit in Wolf River most unit in the the Wolf River Batholith Batholith of of northeastern northeastern Wisconsin Wisconsin (Anderson and and Cullers, Cullers, 1978; 1978; Greenberg Greenberg and and Brown, Brown, 1984). 1984), is is neither neither (Anderson a member of the batholith, nor a granite. The northern—most member a member of the batholith, nor a granite. The northern-most member of the Wolf River Batholith is the "Belongia Granite" which has of the Wolf River Batholith is the "Belongla Granite" which has inintruded into into the the Eager-a Hager——a volcanic volcanic suite of felsic truded suite of felsic to to intermediate intermediate rocks——and into rocks-and into older older greenstones greenstones and and gneisses. gneisses. The extent extent of of the Hager Suite The the Eager Suite is is larger larger than than currently currently recogrecognized because exposures of this suite can be found nized because exposures of this suite can be found along along the the entire entire southern boundary boundary of of the Mccaslin Quartzite Quartzite in southern the McCaslin in regions regions currently currently mapped The disdismapped as as Belongia Belongia Granite Granite (Greenberg (Greenberg and and Brown, Brown, 1984). 1984). The tinction between between rocks rocks of of the Hager Suite tinction the Eager Suite and and the the Belongia Belongia Granite Granite can be made on the the basis of petrographic and/or and/or chemical chemical criteria. criteria. The felsic felsic member member of of the Hager Suite metarhyolite with with abunThe the Eager Suite is is aa metarhyolite abundant (20%) (20%) relic quartz phenocrysts that that commonly commonly display display resorpresorption embayments. The intermediate embayments. The intermediate members members of of the the suite suite show show an. an. tion increase in in mafic minerals and plagioclase and and rarely rarely contain contain the the quartz phenocrysts. Hager resorbed quartz phenocrysts. The eastern boundary of the the Eager appears to to have been intruded intruded by the the High Falls falls Granite; Granite; the the High High Falls is is currently thought thought to to be older older than than the the Hager Eager (Greenberg (Greenberg Au increase in metamorphic grade can be seen seen in in and Brown, 1984). 1984). An the pelitic components of the McCaslin Quartzite from east to west the pelitic components of the McCaslin Quartzite from east to west as the the High High Falls as Falls Granite Granite is is approached. approached. A similar gradient may be evident in the more mafic units of the the Hager Eager Suite. The boundaries, boundaries, extent The extent of of differentiation, differentiation, degree degree of of metamorphism, metamorphism, and timing of formation of the Hager Suite is being reevaluated. formation Eager Suite is Preliminary results results of of field works show Preliminary field and and chemical chemical works show that that the the Hager Eager Suite can be distinguished as a separte volcanic sequence from a separte volcanic sequence from the the other rocks knowledge of the character of this this rocks of the the region. region. A knowledge suite will be essential in in determining determining the the nature of the the northern northern boundary of the Wolf River Batholith. REFERENCES REFERENCES Anderson, J J.L. Cullers, R.L., R.L., 1978, 1978, Geochemistry Geochemistry and and evolution evolution Anderson, .L. and Cullers, of the Wolf River Batholith, a a Late Late Precambrian Precambrian rapakivi rapakivi massif massif Wisconsin, U U.S.A.: Precambrian Research, v.7, v.7, p.287—324. in north Wisconsin, .S.A.: Precambrian p.287-324. J.K. and Brown, B.A., B.A., 1984, 1984, Bedrock Bedrock geology geology of of Wisconsin: Greenberg, J.K. Northeast Sheet, Sheet, Wisc. Wisc. Geol. Nat. Hist. Surv., Surv., Regional Regional Map Map Series, Series Map No. 84—2. 84-2. —70— J �Geology Atikokan Area, northwestern Ontario: Geology of of the the Atikokan Area, northwestern Ontario: an an overview overview D. D. STONE STONE (Atomic (Atomic Energy Energy of of 601 Booth St., Ottawa, 601 Booth St., Ottawa, K1A KIA Canada Canada Limited/Geological Limited/Geological Survey Survey of of Canada, Canada, OES) OE8) Beginning Beginning late late in in the the nineteenth nineteenth century, century, geologists geologists have have more more or or less continuously studied Archean rocks in the Atikokan area, less continuously studied Archean rocks in the Atikokan area, with with The particular particular emphasis emphasis on on the the metavolcanic metavolcanic belt belt at at Steep Steep Rock Rock Lake. Lake. The first recorded survey of the area identified an unconformity overlain first recorded survey of the area identified an unconformity overlain by by conglomerate, conglomerate, dolomite dolomite and and tuff tuff formations formations along along the the northeastern northeastern These formations, margins These formations, which which comprise comprise margins of of the the Steep Steep Rock Rock belt belt (1). (I). the Rock Group, were studied extensively during the Steep Steep Rock Group, were studied extensively during open—pit open-pit mining mining of Early of the the iron iron ore ore zone zone at at the the top top of of the the dolomite dolomite unit unit (2). (2). Early workers workers thought thought that that the the Steep Steep Rock Rock Group Group was was one one of of the the youngest youngest supracrustal supracrustal sequences sequences in in the the area area (e.g. (e.g. 3), 3), but but recent recent lead lead isotope isotope studies yield an an age age of Harmion Lake tonalite Ga age age for for the the Madon Lake tonalite studies yield of 2.929 2.929 Ga Accordingly, the may be basement basement (4). (4). Accordingly, the overlying overlying Steep Steep Rock Rock Group Group may be older older than than most most metavolcanic inetavolcanic rocks rocks in in the the Wabigoon Wabigoon Subprovince Subprovince since since these Ga (5). (5). these tend tend to to be be in in the the range range of of 2.71—2.76 2.71-2.76 Ga I Three Three distinct distinct assemblages assemblages of of metavolcanic metavolcanic rocks rocks are are identified identified in in the the Steep Steep Rock Rock belt belt on on the the basis basis of of Atomic Atomic Energy Energy of of Canada Canada Limited's Limited's (AECL) mapping survey survey and (AECL) mapping and studies studies of of major major and and trace trace element element These consist of the lower lapilli tuff geochemistry. These consist of the lower lapilli tuff (ash (ash rock) rock) geochemistry. overlain by voluminous mafic pillow lavas, followed by intermediate overlain by voluminous mafic pillow lavas, followed by intermediate to to Erosion of felsic felsic flows, flows, tuffs tuffs and and breccias. breccias. Erosion of these these metavolcanic metavolcanic extrusives exposed tonalite extrusives and and exposed tonalite appears appears to to be be the the source source for for clastic elastic sediments in both the Quetico Subprovince and in narrow units sediments in both the Quetico Subprovince and in narrow units Several throughout the 1). Several phases phases of of felsic felsic the greenstone greenstone belts belts (Figure (Figure 1). plutonic and gneissic rocks occur outside of the supracrustal plutonic and gneissic rocks occur outside of the supracrustal belts. belts. Tonalitic gneisses containing Tonalltic gneisses containing thin thin amphibolite amphibolite units units are are extensive extensive in in the map area and can be correlated with the Marmion Lake tonalite the map area and can correlated with the Marmion Lake tonalite During or basement and early early supracrustal baseinent complex complex and supracrustal sequences. sequences. During immediately after the late stages of volcanism, the gneisses icoediately the stages the gneisses were Emplacement granitic intruded of granitic intruded by by several several "young" "young" tonalite tonalite plutons. plutons. Emplacement of magma, magma, such such as as the the Eye—Dashwa Eye-Dashwa pluton pluton at at 2.672 2.672 Ga, Ga, marked marked the the latest latest stage stage of of crustal crustal genesis genesis in in this this area. area. (1) (1) (2) (2) (3) (3) (4) (4) (5) (5) Smyth, H.L. 1891. 1891. American American Journal Journal of of Science, Science, 42, 42, 317—331. 317-331. Sayth, H.L. Jolliffe, Jolliffe, A.W. A.W. 1955. 1955. Economic Geology, 50, 50, 373—398. 373-398. GSC Memoir Memoir 28, Lawson, A.C. Lamon, A.C. 1912. 1912. GSC 28, 23. 23. HP 126, Davis, D.W. D.W. and Jackson, Jackson, M.E. M.E. 1985. 1985. OGS MP 126, 135—137. 135-137. Paper 28, 28, 89—123. 89-123. Blackburn, C.E. C.E. et.al. et.al. 1985. 1985. GAC Special Paper —71— �91° 45' 49000 49° 00 -4 j j j J -J fl -J —4 480 45' — 48° 4 5' ONTARIO ISTUDY AREA .1 91° 45' sr-45' Figure Figure 1: 1: Geology oof the Atikokan Atikokan area, area,northwestern northwesternOntario. tario. f the —72— �Gravity and Gravity and Magnetic Magnetic Evidence Evidence for f o rRhomboid Rhomboid Sedimentary Basins in Sedimentary Basins i n the t h eWisconsin WisconsinMagmatic Magmatic Terrane Terrane THOMAS SUSZEKand andPAUL PAULJ.J. MEYER MEYER(Department (Department o off Geology, J. J. SUSZEK Geology,UW—Oshkosh, UW-Oshkosh, THOMAS (lshkosh, M I 54901) 54901) Oshkosh, WI and PPrice Gravity and and magnetic magnetic data data from fromRusk, Rusk, Chippewa, Chippewa, Sawyer Sawyer and rice counties in counties i n northern northern Wisconsin Wisconsin indicate i n d i c a t ethe t h epresence presence of o fEarly EarlyProtero— Protero(Fig. 1) 1) zoic rhomboid rhomboid shaped shaped sedimentary sedimentary basins. (Fig. Gravity readings Gravity readings taken taken across across tthree h r e e basins, basins, the t h e boundaries boundaries of o f which which have been beendefined definedby bythe the aeromagnetic aeromagneticpattern, pattern, have have provided provideddata data ffor have or 2) twodimensional dimensional gravity g r a v i t ymodels. models. (Fig. tthe h e construction construction oftwo, o f -two,two (Fig. 2) The Ladysmith Ladysinith ggravity one basin in The r a v i t ymodel model,, which which spans spans one i nRusk Rusk and and Chippewa counties, was developed from data taken along a f t e e n mile mi1 e Chippewa counties, was developed from data taken along a f ififteen traverse w with taken aatt one thousandf ofoot traverse i t h readings readings taken one thousand o t iintervals. n t e r v a l s . This model model suggests an asymmetrical asymmetricalbasin basindeepening deepeningt otot hthe south wwith thickness suggests an e south i t h aa thickness of of approximately feet. o f sediments sediments of approximately tthirteen h i r t e e n thousand thousand feet. The Park Park FFalls The a l l s gravity g r a v i t ymodel, model, which which spans spans two two basins basins ini nSawyer Sawyer and and Price fromdata datagathered gatheredalong alongaaf fifty—four P r i c e counties, was was developed developed from i f t y - f o u r mile mile The model model of traverse wwith takenaat onehhalf mile traverse i t h readings readings taken t one alf m i l e iintervals. n t e r v a l s . The these sedimentthickness thickness ooff twelve these basins basins suggests suggests aa sediment twelve thousand thousand tto o sixteen sixteen Bothpprofiles modelsi nindicate thousand feet. feet. Both thousand r o f i l e s and and models d i c a t e t that h a t tthe h e ggravity r a v i t y highs highs correspondt to highs and and ggravity correspond o tthe h e magnetic magnetic highs r a v i t y lows lows to t o magnetic magnetic lows. lows. Drill D r i l lcore corefrom fromthese theseareas areas show show tthat h a t greenschist greenschist to t o amphibolite amphibolite grade metavolcanicand andg rgranitoid rocksuunderlie grade metavolcanic a n i t o i d rocks n d e r l i e t the h e ggravity r a v i t y highs, highs, and an'd graphitic t h e gravity g r a v i t y lows. 1ows. g r a p h i t i c argillites a r g i l l i t eand s andgraywackes graywackes underlie under1 ie the U 4 I 1 L1 LI 5 as-'I I -I I Os a — —_ J.3340k •.. • fled — a —73— I I I, I • — I fl C S N �—4 anti o.aticjn of Gravity Traverses the Sediriientary Basins(Xs) N(}RJIIWEST[RN WI SCONSIN Showipiij OF A[R(IiA(iNIJIC MAP OF A PORTION IL -, - •'.a a L_ L J_fl•.'I L L t_ I �Contemporaneous Archeanmafic niaficand andggranitoid Contemporaneous l alate t e Archean r a n i t o i d magmatism magmatism i in n the the Lac des lies area, Wabigoon Subprovince, Ontario Lac des l i e s area, Wabigoon Subprovince, Ontario Ri-I. Grenville St., R. H. Sutcliffe Sutcl i f f e(Ontario (OntarioGeological GeologicalSurvey, Survey, 917—77 917-77 Grenvil l e St., Toronto, Ontario M7A 1W4) - ""Toronto, Ontario M7A 1W4) The Lac Lac des des Ilies km north n o r t hofo fThunder Thunder Bay Bay The l e s area, area, located locatedapproximately approximately100 100km in the Wabigoon Subprovince, contains a suite of mafic to ultramafic i n t h e Wabigoon Subprovince, contains a s u i t e o f mafic t o u l t r a n a f i c Archean iintrusions n t r u s i o n s which which show show evidence evidence of o f being beingcontemporaneous contemporaneous wwith i t h llate a t e Archean tonal ite and granodiorite. The mafic to ultramafic and granitoid t o n a l i t e and granodiorite. The mafic t o ultramafic and g r a n i t o i d i intruntrusions are are emplaced emplaced gneissicb biotite formppart sions i n into t o o lolder d e r gneissic i o t i t e ttonal o n a l iite t e and and form a r t ooff tthe h e Wabigoon Wabigoon DDiapiric i a p i r i c Axis. Axis. The The t tholejitic h o l e i i t i c mafic mafic to t o ultramafic u l t r a m a f i c intrusions i n t r u s i o n s in i nthe t h earea area have have ssimilar imilar lithologic, tectonic, and metailogenic characteristics and define a a l i t h o l o g i c , t e c t o n i c , and metal logenic c h a r a c t e r i s t i c s and define circular c i r c u l a r structure s t r u c t u r eapproximately approximately 30 30 km km in i n diameter. diameter. The Lac Lacdes des Ilies The les Complex, thesei nintrusions, hostt to Pt Complex, t h the e l a largest r g e s t o fofthese t r u s i o n s , i sis host o ssignificant i g n i f i c a n t Pd, Pd, Pt mineralization as aa rresult multiple m i n e r a l i z a t i o n and and formed formed as e s u l t of o fthe t h eemplacement emplacement oof f m ultiple batches ooff magma minori nin—situ Themore moref rfractionated batches magma w iwith t h minor - s i t u f rfractionation. a c t i o n a t i o n . The actionated gabbroic rocks gabbroic rocks were were emplaced emplaced first f i r s and t andconsist c o n s iof s t plag—cpx—opx o f plag-cpx-opx and andplay— plagcpx cumulates. Theyounger youngeru lultramafic ol—cpx, cpx, cpx, cpx cumulates. The t r a n a f i c ssuite u i t e cconsists o n s i s t s ooff ol 01, , 01-cpx, cpx—opx, and cpx—opx—plag cumulates. The Tib Gabbro, the second largest cpx-opx, and cpx-opx-plag cumulates. The Tib Gabbro, t h e second l a r g e s t mafic consists ooff mafic intrusion, i n t r u s i o n , represents representsaamore more fractionated f r a c t i o n a t e dsequence sequence and and consists opx—cpx—piag cumulates grading zones cumulusa papatite, opx-cpx-plag cumulates grading t o tozones w iwith t h cumulus a t i t e , Fe—olivine Fe-olivine and magnetite. magnetite. AAll and l l of o fthe t h eintrusions i n t r u s i o nhave s havemarginal marginalzones zones characterized characterized by tthe gabbrot to hornblendite. by h e presence presence ooff hornblende hornblende gabbro o hornblendite. Late ggranitoid Late r a n i t o i d rocks rocks ranging ranging in i ncomposition composition from from hornblende hornblende t tonal o n a l i tite e tto o biotite granodiorite occupy the center of the circular structure defined b i o t i t e g r a n o d i o r i t e occupy t h e center o f t h e c i r c u l a r s t r u c t u r e defined b the Thehornblende hornblendet otonalite has ttextures by t h e mafic mafic intrusions. intrusions. The n a l i t e has e x t u r e s tthat hat indicate mixing between leucocratic tonalite and mafic magmas. These i n d i c a t e mixing between l e u c o c r a t i c tonal it e and maf i c magmas. These textures include include nnet veinedmafic maficdikes, dikes,mafic mafic" p"pillows" textures e t veined i l l o w s " i in n ttonalite, onalite, The rnixmixand hhybrid zonescharacterized characterized by by coarse, coarse, sskeletal and y b r i d zones k e l e t a l hornblende. hornblende. The ing textures occur within the tonalite pluton and at the contacts of i n g t e x t u r e s occur w i t h i n t h e t o n a l i t e p l u t o n and a t t h e contacts o f the the tonalite Mixing and and hhybridization t o n a l i t e pluton p l u t o n with w i t h the t h e mafic mafic intrusions. intrusions. Mixing ybridization appears tto widespread process process as as iindicated appears o have have been been aa widespread n d i c a t e d by by the t h edevelopment development of coarse throughoutt hthe pluton. of coarse sskeletal k e l e t a l to t o blocky blocky hornbiende hornblende throughout e t otonalite n a l i t e pluton. Breccia zones developedi in Breccia zones developed n tthe h e tonal t o n a lite i t emay may have have resulted r e s u l t e dfrom fromdegassing degassing chamberw with mafic magma magmaunderlying underlyingt the ooff aa zoned zoned magma magma chamber i t h mafic h e ggranitoid r a n i t o i dmagma. magma. Ther relationships mafic iintrusions i e s area area suggest suggest tthat h a t mafic ntrusions The e l a t i o n s h i p s iin n the t h e Lac Lac des des lIles played aa ssignificant The g r a n i t o magma i d magma genesis. genesis. The played i g n i f i c a n t role r o l eini late n l a Archean t e Archeangranitoid emplacement maficmagma magma generation ooff emplacement o f of mafic i n t ointo o l dolder e r c r ucrust s t r eresulted s u l t e d i nint the h e generation crustal mafic—felsic c r u s t a lmelts meltsand andthe t hdevelopment e developmentof ozoned f zoned m a f i c - f e l s imagma c magmachamixers. chambers. The compositions reflect between The rresultant e s u l t a n tmagma magma compositions r e f l e c mixing t mixing betweenthese theseend-members. end-members. —75— �Lead Many Ore Lead Isotope Isotope Evidence Evidence for f o r an an Old Old Crustal C r u s t a l Source Source for f o r Manv Ore Leads Leads in in the t h e Wawa Wawa Region Region R.I. R.I. ThORPE THORPE (Geological (Geological Survey Survey of of Canada, Canada, 601 601 Booth Booth St., St., Ottawa, Ottawa, Ontario Ontario [CiA 0E8) K I A OE8) 918—77 Grenville R.P. R.P. SAGE SAGE (Ontario (Ontario Geological Geological Survey, Survey, 918-77 Granville St., S t . , Toronto, Toronto, Ontario Ontario MSS M5S 1B3) 1B3) 601 Booth J.M. J.M. FRANKLIN FRANKLIN (Geological (Geological Survey Survey of of Canada, Canada, 601 Booth St., S t . , Ottawa, Ottawa, Ontario Ontario[CiA KIA OE8) OE8) Lead Lead isotope i s o t o p e analyses analyses for f o r galena galena from from deposits d e p o s i t s and and occurrences occurrences in in the because of of tthe t h e Wawa Wawa region region (Table (Table 1) 1 ) aare r e significant s i g n i f i c a n t because h e old old model model lead lead values for ages ages for f o r aa few few deposits d e p o s i t s and and the t h e high high 207Pb/201'Pb "'~b/"''~b values f o r many many of of the the in composition In these respects they are comparable specimens. specimens. I n these r e s p e c t s they a r e comparable i n composition ttoo leads from selected leads from s e l e c t e d localities l o c a l i t i e s in i n western western Superior Superior Province Province (Wabigoon (Wabigoon Subprovince) and are dissimilar to leads from Abitibi Subprovince. Subprovince) and a r e d i s s i m i l a r t o leads from A b i t i b i Subprovince. Application of Archean Application of Archean lead lead evolution evolution models models derived derived by by Thorpe Thorpe (in (in preparation) yields model lead ages greater than 2830 Ma for the preparation) y i e l d s model lead ages g r e a t e r than 2830 Ma f o r t h e 8CR BCH and and Ma .J J veins veins by by the t h e Abitibi A b i t i b i model, model, and and greater g r e a t e r than than about about 2870 2870 M a by by the the The latter model may apply because a comparable Western Superior model. Western Superior model. The l a t t e r model nay apply because a comparable Ma has zircon has been been reported reported for f o r tthe h e biotite biotite z i r c o n U—Pb U-Pb age age of of about about 2888 2888 Ma granite phase of the Hawk Lake oomplex (Turek et al., 198k), an external g r a n i t e phase of t h e Hawk Lake complex (Turek e t g . , 1984), an external pluton pluton that t h a t has h a s intruded intruded the t h e supracrustal s u p r a c r u s t a l rocks rocks of of Subcycle Subcycle 1 hosting hosting are thus old model ages a The leads with these mineralized zones. these mineralized zones. The leads with old model ages r e thus J — 1 restricted rocks aatt the r e s t r i c t e d tto o metavolcanic metavolcanic rocks t h e base base Other recognized recognized as a s the t h e oldest o l d e s t in i n the t h e region. region. Other of of the t h e section s e c t i o n that t h a t are are leads from localities leads from l o c a l i t i e s in in Sachigo property, property, Sachigo two and Subprovince, Ma, and iinn two Subprovince, also a l s o yield y i e l d model model ages ages greater g r e a t e r than than 2800 2800 Ma, cases c a s e s as a s great g r e a t as a s about about 3000 3000 Ma. Ma. Wabigoon Wabigoon Subprovince, Subprovince, and and from from the the Musselwhite Musselwhite J The The Kozak Kozak mineralization, mineralization, probably probably synchonous synchonous with with volcanism, volcanism, yields yields We and 2724 Superior) and model (W. Superior) 2724 Ma Ma ((Abitibi). Abitibi). W e model lead lead ages ages of of 2770 2770 Ma Ma (W. consider consider that that the t h e Abitibi A b i t i b i model model most most likely l i k e l y applies, a p p l i e s , but but this t h i s can can only only of model) of (W. Superior Superior model) dating. Model ages by zircon zircon dating. Model ages (W. 2657 f o r two two of of the t h e MacLeod MacLeod East East galenas galenas and and of of 2670 2670 Ma Ma Ma and and 2658 2658 Ma Ma for 2657 Ma for Leclair Township galena galena aare within aanalytical of ages for L e c l a i r Township r e within n a l y t i c a l uuncertainties n c e r t a i n t i e s of of a possibly iindicative a for plutons in area, f o r some some plutons i n the t h e area, possibly n d i c a t i v e of ggenetic enetic located The relationship. relationship. The Northern Northern Granite Granite (granitic ( g r a n i t i c gneiss) g n e i s s ) that that is is located along along the t h e northern northern boundary boundary of of the t h e greenstone greenstone belt b e l t has has aa zircon z i r c o n U—Pb U-Pb age age of of 2662 2662 ti 22 Ma, Ma, and and the t h e Troupe Troupe Lake Lake trondhjemite trondhjemlte is is apparently apparently of of the the same same age age (Turek (Turek et & al., &., 198k). 1984). be be confirmed confirmed Many Wawa region region plot p l o t well well above above tthe h e ffields i e l d s ffor or Many leads l e a d s from from tthe h e Wawa in the 2695 Superior Province massive suphide deposits with ages Superior Province massive suphide d e p o s i t s with ages i n t h e 2695 ttoo They and for 2770 2770 Ma Ma range, range, and f o r most most Superior Superior Province Province gold gold deposits. deposits. They mostly f o r Zimbabwe Zimbabwe gold gold deposits d e p o s i t s (Robertson, (Robertson, 1973; 1973; mostly lie l i e within within the t h e field f i e l d for Such 207Pb/201'Pb—enriched leads and unpublished data). l e a d s aare r e generally generally Such "'~b/"''~b-enriched and unpublished d a t a ) . high U/Pb U/Pb rratios interpreted evolved in had high that had atios i n t e r p r e t e d to t o have have evolved i n sources sources that time prior (p values) values) for f o r extended periods of of geological time p r i o r ttoo oore re have not formation, formation, sspecifically p e c i f i c a l l y iin n upper upper crustal c r u s t a l terranes t e r r a n e s tthat h a t have not been been These (e.g. Robertson, Robertson, 1973). subjected to t o high—grade high-grade metamorphism (e.g. 1973). These leads, leads, and some of those from from the t h e Wabigoon Wabigoon Subprovince, Subprovince, thus t h u s suggest suggest the the presence iin presence n these these regions of an ancient a n c i e n t lead l e a d source source of of "Minnesota "Minnesota River —76— j J �Valley—type". Wawa area Valley-type". IInn tthe h e Wawa a r e a these these leads leads aare r e from from within within or o r near near Subcycle 11 rocks. rocks. Subcycle The Th/U rratios The calculated c a l c u l a t e d Th/U a t i o s ffor o r the t h e lead lead sources sources of of the t h e Wawa Wawa region region galenas aare, with two two exceptions exceptions ((the BCH vein vein aatt aa value value of of 4.12 4.12 and and galenas r e , with t h e BCH the the epigenetic epigenetic vein vein in i n tthe h e Woman Woman River River iron i r o n formation), formation), iin n the t h e range range 4.00 The 4.00 to t o 4.07. 4.07. The uniformity uniformity in i n these these ratios r a t i o s suggests suggests that t h a t these these leads leads must must have have been been derived derived from from large l a r g e volumes volumes of of source source rocks, rocks, because because local local sources would be be expected expected to t o contribute c o n t r i b u t e leads leads with with much much more more variable variable sources would ratios. ratios. Galena Galena that, t h a t , with with calcite, c a l c i t e , pyrrhotite p y r r h o t i t e and and graphite, g r a p h i t e , occupies occupies aa late late fracture cutting ore in the Kremzar gold deposit, Goudreau area, has f r a c t u r e c u t t i n g o r e i n t h e Kremzar gold deposit, Goudreau a r e a , has a a very Assuming geologically it formed formed aatt aa geologically very radiogenic radiogenic composition. composition. Assuming it recent time, tthe calculated source source age age is r e c e n t time, h e calculated is 2680 2680 to t o 2735 2735 Ma M a if i f the t h e initial initial Pb composition of the source was in the range of the Hanson and Renabie Pb composition of t h e source was i n t h e range of t h e Ranson and Renabie compositions. compositions. Robertson, D.K., 1K., 1973, of the Earth 1973, AA model model discussing discussing the t h e early e a r l y history h i s t o r y of t h e Earth Robertson, the some Archean based on study of lead isotopes from veins in based on t h e study of lead i s o t o p e s from v e i n s i n some Archean cratons of Africa; Geochimica Acta, Cosmochimica Acta, Vol. 37, cratons of Africa; Geochimica eett Cosmochirnica Vol. 37, p. 2099—2124. p. 2099-2124. Turek, A., Smith, Turek, A., Smith, P.E. P.E. and and Van Van Schmus, Schmus, W.R., W.R., the the 1984, U-Pb U—Pb zircon ages and 1984, zircon ages and evolution of the evolution of of the t h eMichipicoten Michipicoten plutonio—volcanic plutonic-volcanic t eterrane r r a n e of the Superior Superior Province, Province, Ontario; Ontario; Vol. Vol. 21, 21, No. No. 4, 4, p. p. U57—464. 457-464. Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences, Table 1. data for and occurrences occurrences Load isotope Isotope data for deposits d e p o s i t s and Table 1. Lead in the Hawa twa region In the region Property Property .1 Vein J Vein ECH BCH Vein Vein Lakemount Lakemount Lakemount Lakemount Lakemount Lakemount Kozak Kozak Edwards Edwards pros. pros. MacLeod East MacLeod East MacLeod MacLeod East East MacLeod MacLeod East East Soocana Soocana Renabie Renabie Michipicoten Michipicoten Leclair L e c l a i r Twp. Twp. Rengold Rengold Braminco Braminco pros. pros. Hanson Ranson Kremzar Kremzar Vein Vein in in Woman Woman H. R. iron formation i r o n formation Model Ages Model Ages W. Superior W. Superior Abitibi Abitibi Model Model Model Model 207Pb/ 13.584 13.617 13.666 13.653 13.681 13.208 13.957 13.953 13.979 13.972 14.241 13.343 13.546 13.565 13.472 13.48 14.921 14.947 14.940 14.939 14.949 14.402 15.077 15.006 15.033 15.014 15.194 14.484 14.657 14.642 14.532 13.595 14.625 17.419 15.123 28.867 14.814 114.52 —77— 33.391 33.477 33.462 33.455 33.494 33.083 33.699 33.723 33.789 33.774 33.991 33.216 33.394 33.272 33.336 33.35 33.448 49.105 34.422 2838 2879 Ma Ma 2879 2838 2832 2873 Ma 2873 M a 2832 2788 2829 Ma 2829 Ma 2788 2798 2838 Ma 2838 Ma 2798 2824 Ma 2783 2824 Ma 2783 2724 2770 2770 Ma M a 2724 2670 2709 2709 Ma Ma 2670 2617 2657 2657 Ma M a 2617 2618 2658 2658 Ma Ma 2618 2649 Ma 2609 2649 Ma 2609 2548 2587 Ma 2587 Ma 2548 2678 2723 2723 Ma Ma 2678 2699 2699 Na Ma 2655 2655 2670 2627 2627 2670 Ma Ma 2654 2609 2654 Ma Ma 2637 2637 Ma Ma 2591 2591 2631 2587 2631 Ma M a 2587 anomalous anomalous 2066 2107 Ma Ma M a Ma M a Ma M a Ma Ma Ma Ma Na Ma Ma Ma Ma Ma Ma Ma Ma M a Ma Ma Ma Ma Ma Ma Ma Ma Ma Ma Ma Ma Ma Ma �Reconnaissance Geology of the Reconnaissance the Granitic Granitic and and Gneissic Gneissic Terranes Terranes in the Wawa District i n t h e m DELIO TORTOSA, (Ministry DKLIO (Ministry of Northern Northern Development Development and and Mines, Mines, P.O. Box P.0. Box 530, 530, Wawa, Wawa, Ontario, Ontario,P05 POS11(0) 1KO) geological the basis On basis of reconnaissance On the reconnaissance and and detailed geological mapping the Wawa District District over over the the past two two capping completed in in the together regional lake lake sediment/water sediment/water data, years, years, together with regional data. aeromagnetic data, aeromagnetic data, and studies studies by the the Geological Geological Survey Survey of of granitic Canada, Canada, aa preliminary gelogical gelogical evaluation evaluation of of the the granitic and gneissic terranes terranes in in the the Wawa District District is is in in progress. progress. into the Wawa area The The granitoid rocks rocks in the area can can be subdivided subdivided into three three main classes classes from f n r oldest oldest to to youngest: a) a) tonalite tonalite to to from gneiss "domes" or oval oval structures structures ranging granodiorite gneiss granodiorite "domes" or ranging from massive to well-layered well—layered gneiss gneiss containing volcanicmassive to containing metavolcanic— enclaves metamorphosed to ainphibolite metasedimentary me-basedimentary enclaves metamorphosed to amphibolite grade; grade; medium—to coarse—grained granodioriteto to quartz quartz monzonite nmdium-to coarse-grained granodiorite ronzonite size; ranging from large c) ranging large plutons to to batholiths batholiths in in size; c) late late quartz quartz diorite diorite to 1.0 syenite syenite plutons. plutons. b) b) The granitoid complexes complexes of the the Wawa Wawa District District have have geological geological which are similar to those described which are similar to those described by Schwerdtner et (1979). Some Some of al. (1979). of these these include: include: Schwerdtner eta].. 1) Tonalite gneiss domes d o e s displaying displaying aa transition transition from from a coarse—grained gneissic core core to coarse-grained 1.0 a marginal zone zone composed composed of layered tonalite tonalite gneiss gneiss containing containing arcuate—shaped arcuate-shaped metavolcanic metavolcanic —metasedimentary -metasedimentary segments. segments. characteristics characteristics j to Crescent-shaped of hornblende 2) Crescent-shaped plutons plutons of hornblende diorite diorite to 2) occupying quasi-concordant quasi—concordant sites sites granodiorite occupying granodiorite between gneissic "'domes" gneissic d m s " and and adjacent supracrustal supracrustal belts. belts. quartz A large large batholith from 3 batholithranging ranginginincomposition cc~position from quartz 3) A portion the central monzonite monzonlte to to granodiorite granodioriteand and occupying occupying Â¥th central portion of the a thestudy studyarea arearepresenting representing a of the granitoid granitoid terrane terrane in inthe post-tectonic period post-tmctonic periodofofemplacement. eaiplacaiaent. 4) Evidence of high and low ductility contrast between 4) the metavolcanic—metasedimentary gneissic/layered the metavolcanic-Botasedimentary segments segments and gaeissic/layered tonalites. tonalites The arcuate—shaped metavolcanic—metasedimentary 5) 5) The arcuate-shaped met-laanic-wtasedimentary enclaves can outer perimeter of the the can be the outer perimeter of enclaves be traced traced around around the synformal— gneissic "domes' and traced adjacent to larger gneissic "domes" adjacent to larger synformalshaped shaped metavolcanic-metasedimentary ntavolcanic-ntasedimentary belts. belts. J . —78— �I I I I I geological history of the granitic and gneissic terranes The The geological history of the granitic and gneissic terranes appears tonalite appears to to involve involvm an an early earlymagmatic magmatic period period of of tonalite intrusion into metavolcanic—metasedimentary rocks under intrusion into lae-tavolcanic-motasedloantary rocks under conditions high ductility ductility contrast. contrast. This This was was followed followed by aa conditions of of high period of auto—deformation with low contrasts period of auto-deformation with low ductility contrasts and the in the the development development of of gneiss gneiss domes domes which w h i c h resulted resulted in the infolding and fragmentation of the metavolcanicinfolding and fragmentation of the aetavolcanicmetasedimentary intense, post-tectonic oe-baaedhentary belts. belts. A period period of of intense, post-tectonic felsic plutonic activity followed, forming the large plutons felsic plutonic activity followed, forming the large plutons and and "central" "central" batholith. batholith. The The arcuate arcuate and and amoeboid amoeboid shape shape of of the metavolcanic—metasedimentary such as the the lae-tavolcaaic-BetaaediBentary belts belts such as the ductility Dayohessarah greenstonebelt belt and Dayohea8arah groanstone and the theMichipicoten Michipicoten greenstone gr-tone belt deformation thebroad broadscale scale deformationwhich which resulted resulted from from belt reflect reflectthe the the early early and and late late periods periods of of felsic felsic plutonic/gneissic plutonic/gneissic diapiric diapiric activity. activity. References: References : Schwerdtner, Schwerdtner, W.M., W.M., Stone, Stone, D., D., Stott, G.M. G- M.Stott. . .-- Osadetz, Osadetz, K., K., Morgan, Morgan, J., J., and and - 1979: and 1979: Granitoid Grani-boid complexes complex& and the the Archean Archean tectonic tectonic record partof ofnorthwestern northwesternOntario. Ontario. record in in the thesouthern southern part —79— �J The and Rb—Sr ages iin The meaning meaning of o fU—Pb U-Pb and Rb-Sr ages n the t h eWawa Wawa area area A. University A. Turek Turek (Department (Department oof f Geology, Geology, U n i v e r s i t y of o f Windsor, Windsor, Windsor, Windsor, Ontario Ontario N9B N9B 3P4) 3P4) U—Pb zirconages agesf ofor U-Pb zircon r tthe h e Michipicoten Michipicotengreenstone greenstonebelt b e lappear t appearchrono— chronostratigraphically correct. The greenstone belt and surroundingggranitic s t r a t i g r a p h i c a l l y correct. The greenstone b e l t and surrounding ranitic terrane occurred at terrane evolved evolvedaround around 2888 2888 to t o2615 2615Ma Ma ago. ago. Volcanism Volcanism occurred a t 2743, 2743, 2717, datedf fall Ma. Plutonic P l u t o n i c rocks rocks dated a l l into i n t o55events; events; 3 are coeval coeval 2717, and and 2696 2696Ma. with independent w i t h the t h eabove above volcanic volcanic periods periodswhile w h i l e2 2are are independentata2668 t 2668and and2888 2888 Ma. The 2668 Ma plutonism is probably part of the Kenoran orogeny, Ma. The 2668 Ma plutonism I s probably p a r t o f t h e Kenoran orogeny, while while j j J the Maggranite maybebea ar arafter t h e 2888 2888 Ma r a n i t e may f t e r ooff older o l d e r basement basement o or r r related e l a t e d tto o older older U The Rb—Srages ages obtainedf ofor rocks iin The Rb-Sr obtained r rocks n the t h e area area have have large l a r g eage ageuncertain— uncertainties notnot make t i e sand andchronostratigraphically c h r o n o s t r a t i g r a p h i c a l l do y do makesense; sense; probably probablybecause because they they are An attempt attempt at a t unmixing unmixing are hybrid hybridages, ages, between between primary primaryand andmetamorphic. metamorphic. An these these ages ages mathematically mathematically suggests suggests 55 possible possibleevents eventsaround around 2750, 2750, 2615, 2615, J volcanism volcanism asasy eyet t n onot t i didentified e n t i f i e d i in n tthis h i s belt. belt. 2510, The f first i r s t age age is i s essentially e s s e n t i a l l yaaprimary primary age age ffor or 2510, 2410, 2410, and and2330 2330Ma. Ma. The the t h e specific s p e c i f i crocks rocksdated, dated,the t h subsequent e subsequent ages ages are a r e thought thought to t obe bethermal thermal events. events. < J j J J J J j J J —80— -J �Paleomagnetism Archeangranites granitesi in area:f further Paleornagnetism o fofArchean n tthe h e Wawa Wawa area: urther definition of the Apparent Polar Wander Path d e f i n i t i o n of t h e Apparent Polar Wander Path l.A. Yandall University Ontario, (Department of of Geophysics, Geophysics, U n i v e r s i t y of of Western Western Ontario, T.A. Vandal1(Department London, Ontario Ontario N6A N6A 5B7) 5B71 London. D.T.A. Symons (Department Geology,u University D.T.A. Symons ( ~ e p a r t m e n to fofGeology, n i v e r s i t y ooff Windsor, Windsor, Windsor, Windsor, Ontario M9B N98 3P4) Ontario 3P4) Paleomagnetic measurements have been been completed completed on on about Paleomagnetic measurements have about 500 500 specimens specimens from and and Gamitagama Archean ggranitic r a n i t i cplutons plutonsin ithe n t hMichipicoten e Michipicoten Gamitagamagreen— greenfrom Archean stone belts, The The plutons plutons had stone belts. had all a11been beendated datedbybythe t h U—Pb e U-Pb zircon z i r c o nmethod method and also. Extensive Extensive AF and thermal thermal step AF and step and iinn most most cases cases by by other o t h e r methods methods also. demagnetization analysis was used to isolate stable remanence directions, demagnetization analysis was used t o i s o l a t e s t a b l e remanence d i r e c t i o n s . The 100) defines defines the = 5°, 5*, Dm Dm == lo0) the The ffirst i r s tpaleopole paleopole(HSE) (HSE) at a t20°W, 20*W, 37°S 3 7 * ~(Dp (Dp = '-2694 Ma position of the APWP. The pole position was established -2694 Ma p o s i t i o n o f the AWP. The p o l e p o s i t i o n was established by by averaging averaging single s i n g l ecomponent component remanences remanences i isolated s o l a t e d within w i t h i nthe t h Southern e SouthernGran— Granitic Terrane, Hawk Lake Granitic Complex and the Eastern External Granite i t i c Terrane, Hawk Lake G r a n i t i c Complex and t h e Eastern External Granite rock units. units. This apparentlyrecords recordst hthe rock This remanence remanence apparently e a cacquisition q u i s i t i o n ooff the the magnetization magnetization dduring u r i n g t hthe e l last a s t intrusive i n t r u s i v e event event of o f these these adjacent adjacent plutons. plutons. The second paleopole (NM) is derived from the Northern External Granite The second paleopole (MM) i s derived f r o m t h e Northern External Granite and and tthe h e Baldhead Baldhead River River Quartz QuartzMonzonite Monzonite which which have have U—Pb U-Pb zzircon i r c o n ages ages of of 2662 Ma and 2668 Ma respectively. They yield a single component reman2662 Ma and 2668 Ma respectively. They y i e l d a s i n g l e componentreman— ence which defines defines aa paleopole paleopole ffor ence which o r the#2665 the-2665 Ma Ma position p o s i t i o nofo the f t h APWP e APWP at at 16°E, 2005 (Dp = 12°, Dtn = 18°). The third paleopole (GD) comes from the The t h i r d paleopole (GD) comes from t70, he 16*E, 20*S (Dp = 12*, Dm = 18'). NNW—trending diabasedikes. dikes. They give aa position NNW-trending diabase They give p o s i t i o n of o f57°E, 5 7 * ~ 41°N , 4 1 " ~(Dp (Dp == 7O, Om 14°) which which agrees with Dm ==14") agrees w i t h poles polesdetermined determinedfrom fromthe t hMatachewan e Matachewanand and Hearst This result r e s u l t shows shows t that h a t aa ttectonically ectonically Hearst dike d i k eswarms swarms elsewhere. elsewhere. This stable s t a b l e craton craton existed e x i s t e d since since the t h e time t i m e of o fintrusion i n t r u s i o nata2633 t 2633Ma Ma and and also also These improves tthe MaMMatachewan improves h e precision p r e c i s i o nofothe f t h2633 e 2633 a Matachewan pole p o l eon onthe t h eAPWP. APWP. These results, paleomagneticdata datafrom fromt hthe eastern sside r e s u l t s , when when compared compared t to o paleomagnetic e eastern i d e ooff the the Kapuskasing Zone, also imply a1 so imply r e l arelatively t i v e l y 1 i tlittle t l e ttectonic e c t o n i c rotarotaKapuskasing S t rStructural u c t u r a l Zone, tion Subprovinces. A b i t i b iSubprovinces. t i o n or o rtranslation t r a n s l a t i obetween n betweenthe t h Wawa e Wawa and and Abitibi —81— �j -7 Rapakivi ttextures e x t u r e s of o f central c e n t r a lMinnesota Minnesota Ivan Watkins, Paul Erickson Ivan Watkins, Garry Garry Anderson, Anderson, and and Paul Erickson (Department (Department ooff Earth Earth Science, St. Cloud State University, S t Cloud, . Cloud,MN MN56301) 56301) Science, S t . Cloud State University,St. Crystalline St. Cloud C r y s t a l l i n erock rocksamples samples were were collected c o l l e c t e d from fromthe t h emapped mapped St. Cloud red red granite. The K—spar megacrysts, about 0.5 to 3 cm across, have rims granite. The K-spar megacrysts, about 0.5 t o 3 cm across, have rims like describedr rapakivi texture. IInn aa hand hand sample sample tthere here l i k ethe t h ecommonly commonly described a p a k i v i texture. are euhedral megacrysts showing little fracturing and subhedral are euhedral megacrysts showing l i t t l e f r a c t u r i n g and subhedral or or ovoidal megacrysts extensivef fracturing, ovoidal megacrysts wwith i t h extensive r a c t u r i n g , but b u t both bothtypes types have have an an easily observable rim on about fifty percent of the megacrysts. e a s i l y observable r i m on about f i f t y percent o f t h e megacrysts. The rrim i m ooff the t h e fractured f r a c t u r e dmegacrysts megacrysts isi scomposed composed ooff K—spar K-spar ccrystals r y s t a l s not not The The i m , ini nsome some iin n optical o p t i c a l continuity c o n t i n u i t ywith w i t hthe therest r e s tofo the f t h emegacryst. megacryst. The rrim, cases, has has an anooutline cases, u t l i n e made made bybyb biotite i o t i t e that t h a t isi smostly mostlyoutside o u t s i d ethe t h eK—spar K-spar The rrim but is rrim i m but i s included included in i n small small parts. parts. The i m iiss frequently frequently made made up up of of manyccrystals with between many rystals w i t h groundmass groundmass between i n dindividual i v i d u a l c crystals. rystals. The rrim i m ooff the t h eeuhedral euhedral megacrysts megacrysts is i salso alsocomposed composed ooff K—spar K-spar ccrystals. rystals. The Its from tthe anhedralrims rimsare aret hthat I t s main main ddifferences i f f e r e n c e s from h e anhedral a t t the h e ooptical p t i c a l contincontinuity notnot as as much groundmass u i t yisi sbetter b e t t eand r and much groundmass occurs. occurs. J J J J There are are iinclusions i n both b o t hthe t h efractured f r a c t u r e dand andeuhedral euhedral megacrysts megacrysts ooff There n c l u s i o n s in The most most quartz, biotite, plagioclase, K—spar relics, and chlorite. quartz, b i o t i t e , plagioclase, K-spar r e l i c s , and c h l o r i t e . The interesting inclusion is chlorite, without any apparent fracture i n t e r e s t i n g i n c l u s i o n i s c h l o r i t e , without any apparent f r a c t u r e along along The groundmass groundmassabout aboutt hthe megacrystscontains contains quartz, quartz, which iitt could could grow. grow. The e megacrysts which biotite, plagioclase, K—spar, chlorite, and other small crystals not b i o t i t e , plagioclase, K-spar, c h l o r i t e , and other small c r y s t a l s n o t yyet et iidentified. dentified. AAtt this t h i s time time we we are are looking looking at a t rapakivi r a p a k i v i from from the t h e Wolf Wolf River River Batholith Batholith for comparison purposes. f o r comparison purposes. j J -4 j j j J -82- j J �AA review review of of the the LaSalle Pails massive L a S a l l e F a l l s massive suiphide s u l p h i d e prospect prospect DAVID DAVID WEREACH WERBACH (Dept. (Dept. of of Geology Geology Northern Northern Illinois Illinois University, DeKalb, 601155 IL "60115) U n i v e r s i t y . DeKalb, IL -- The The Lasalle L a S a l l e Falls F a l l s massive massive sulphide s u l p h i d e prospect p r o s p e c t is is located l o c a t e d at a t the t h e Lasalle L a S a l l e Pails F a l l s (Pine ( P i n e Rapids) Rapids) on on the t h e Pine Pine River, R i v e r , Florence Florence County, County, northeastern n o r t h e a s t e r n Wisconsin. Wisconsin. The The prospect p r o a p e c t occurs occurs within w i t h i n aa graphitic gra h i t i c slate s l a t e in i n the t h e Quinnesec Quinnesec Formation Formation (Early (Early Pro-terozoic), P r o t e r o z o i c ? , nnear e a r the t h e contact c o n t a c t between between felsic tuffs to t o the t h e north, n o r t h , and and mafic mafic flows f l o w s to t o the t h e south. south. f e l s i c tuffs Topping Topping directions d i r e c t i o n s based based on on pillow p i l l o w structures s t r u c t u r e s are are equivocal e q u i v o c a l (Dutton, ( ~ u t t o n 1971). , 1971 ) . Petrographic P e t r o g r a p h i c and and geochemical geochemical analysis a n a l y s i s for f o r both both major major and trace element oxides, indicate that the Quinnesec and t r a c e element o x i d e s , i n d i c a t e t h a t t h e Quinnesec Formation i s comprised comprised of of tholeiitic tholeiitic Formation in i n the t h e study s t u d y area a r e a is basalts (some komatiitic) and calc—alkaline b a s a l t s (some k o m a t i i t i c ) and c a l c - a l k a l i n e andesites andesites and s i l l s and and volcanogenic volcanogenic and dacites, d a c i t e s , with w i t h minor minor gabbro gabbro sills sediments locally present. sediments l o c a l l y p r e s e n t . Just J u s t to t o the t h e south s o u t h of of the the prospect, p r o s p e c t , rocks r o c k s of of the t h e Dunbar Dunbar dome dome have have intruded i n t r u d e d the the Quinnesec QuinnesecFormation. Formation. All A l l units u n i t s in i n the t h e region r e g i o n have have been been metamorphosed metamorphosed to t o amphibolite a m p h i b o l i t e facies. f a d e s . AA penetrative p e n e t r a t i v e NW—SE NW-ST foliation f o l i a t i o n is i s present, p r e s e n t , along a l o n g with w i t h local l o c a l secondary secondary folds folds and and Shear s h e a r zones. zones. Secondary Secondary fold f o l d axes a x e s and and outcrop o u t c r o u data data indicate i n d i c a t e that that the t h e area a r e a has h a s been been isoclinally i s o c l i n a l l y folded, folded, possibly p o s s i b l y as as aa result r e s u l t of of movement movement along a l o n g the t h e Niagara Miagara Fault Piult Zone, which is less than two miles north. Zone, which i s l e s s than two m i l e s n o r t h . Drill D r i l l cores c o r e s from from near n e a r the t h e prospect p r o s p e c t as as well w e l l as as outcrop outcrop data approximately three miles to the northwest d a t a a u ~ r o x i m a t e l yt h r e e m i l e s t o t h e northwest indicate indicate that t h a t the t h e mafic maficand andfelsic f e l s i crocks r o c k sare a r often e o f t einter'oedcjed. n interbedded. Trace element data on units in an area Trace element d a t a on u n i t s i n an a r e a approximately ap?roximately three three miles that m i l e s to t o the t h e northwest northwest suggests s u g g e s t s the t h e possibility p o s s i b i l i t y that mineralization m i n e r a l i z a t i o n is i s greater g r e a t e r there t h e r e than t h a n at a t Lasalle LaSalle Falls. Falls. Thus the possibility exists that if there i s aa massive massive Thus t h e p o s s i b i l i t y e x i s t s t h a t i f t h e r e is sulphide s u l p h i d e deposit d e p o s i tin i n the t h e area, a r e a , it i t is i s more more likely l i k e l y to t o occur occur there. there. Dutton, C.E., 1971, 1971, Geology Geology of of the t h e Florence F l o r e n c e area, a r e a , Wisconsin Wisconsin Button, C.E., and and Michigan: Michigan: U.S. U.S. Geological Geological Survey Survey Professional P r o f e s s i o n a l Paper Paper 633, 633, 54p. 54~. —83— �-d J F luiu idd I inndduucced e d sts tr ruuc ct tuur ree5s 1i nn Qu Q ueeiit ci coo met m e tas a see di d imen m e nt tss , Ft n o r t h e r n O n t a r i o northern Ontario H. R. R. WI WI LU LLI MIS AMS Ontario OntarioGeological GeologicalSurvey, Survey,Toronto, Toronto,M7A M7AP44. 1W4. H. Sediment dewatering dewatering and and fluidisation fluidisationphenomena, phenomena, including including pillars pillarsand andhydraulic hydraulicfracture fracture Sediment and vein structures, have been identified within low grad* metamorphosed sedimentary and vein structures, have been identified within low grade metamorphosed sedimentary strataofofthe theQuetieo h e t i d oSubprovince. Subprovince.The Thestructures structuresare arecontained containedwithin withinsize sizegraded gradedand and strata form a 60 Km thicK, s t r e p l ~ dioping, ungraded lithic and frldsptthic wackts that ungraded lithic and feldspathic wackes that form a 60 km thick, steeply dipping, probablythrust thrustimbricated, imbricated,northwards northwardsyounging ywngingsequence. sequence. These These strata strataoccur occur within withinano and probably . , southofofthe theSeardmore—Geraldton Beardmore-Geraldton Belt. Belt. south .. j — J + Earlydewatering dewateringstructures structurrsare arecommon commonwithin withinthe thesediments, sediments,such suchas flames,convolute convolute Early as flames, and pillars. The pillars are rrmarhble far their size and shape, occurring lamination, lamination, and pillars. The pillars are remarkable for their size and shape, occurring orbell—shaped bell-shaped sfructures of slightly slightly a sparabolic parabolicor as structures up up to to 22 m m across. across.Fluidisation Fluidisation of structup* and a contemporaneous doming over it,indicate indicateaa laminated strata within the laminated strata within the structure and a contemporaneous doming over it, prc-lithification age for the struetwrs. Concentration of phyllosilicates occurs both pre—lithification age for the structures. Concentration of phyllosilicates occurs both within the pillars a s cirrus-shaped wisps, and around the margins of m o s t pillars. within the pillars as cirrus—shaped wisps, and around the margins of most pillars. intermittent^structurally structurallycontrolled controlledfluid fluidflow flow throughrocks rocKsmay may also alsobe be responsible responsible Intermittent, through for the initiation of bedding concordant breccia zonrs, listric structwes, and quartz for the initiation of bedding concordant breccia zones, listric structures, and uartz or after the imposition of a weaK regional veins. Them structurts drvrloped during veins. These structures developed during or after the imposition of a weak regional dipping steeply. steeply. cleavage. Mean Mean bedding cleavage. bedding and andcleavage cleavageorientations orientations birth both trend trend easterly, easterly, dipping Quaptz-filled extension fractures along both planar fabrics represent an early tectonic Quartz—filled extension fractures along both planar fabrics represent an early tectonic by a subseauent fluid-tnhtncrd brittle failure. These veins have been deformed phase of phase of fluid—enhanced brittle failure. These veins have been deformed by a subsequent of dextral dextralductile duetileshearing shearingthat thatfocussed focussedon onweak, we&, pelitic peliticunits unitsininthe thewacke wacKe episode of episode sequence. Cutting t h i s deformation fabric are bedding-parallel breccia zones consisting sequence. Cutting this deformation fabric are bedding—parallel breccia zones consistirQ ofcentimetre, ~entimetm or~smaller, smaller,unoriented unorirnted fragments fragmrnts set f t in inaa pelitic peiiticororvein veinquart: quartzmatrtx. matrix. of or 20 c m thicK and extend for up to 20 m along bedding striKe, The breccias maybe up t o The breccias maybe up to 20 cm thick and extend for up to 20 m along bedding strue, sometimes trrminating a s quart? s subtle discontinuities. sometimes terminating as quartz veins veins or or aas subtle listric listric discontinuities. J The structures s'tmctuTMdescribed dtscribed indicate indicateaa protracted protracted history historyofofdewatering dewatering during during The t h i s enormous pile of sediment. Thev are are compaction and s u b w q w r t deformation of compaction and subsequent deformation of this enormous pile of sediment. They simxlar ~ * p u t c to u r f s found within recently drilled accre'tiorwy prisms. similar to structures found within recently drilled accretionary prisms. -J J j —84— �Evidence for Widespread Basement Decolleisent Structures and Related Crustal Asyetry Associated with the Western Limb of the Nidcontinent Rift Richard Wunderman and and Charles Charles T. T. Young Young (Dept. (Dept. of of Geology Geology and and Geol. Geol. Engrg., Michigan Technological Univ., Houghton, MI 49931) Engrg., Michigan Technological Univ., Houghton, MI 49931) long, 18 stations) stations) across the AA magnetotelluric magnetotelluric (NT) (MI) survey survey (180 (180 km km long, the exposed Midcontinent Rift Rift (MCR) (NCR) and and associated associated adjacent adjacent crust crust indicate indicate exposed Midcontinent that major south that a a major south to to southeasterly southeasterly dipping dipping conductive conductive unit unit is is present present on The conductive (WOK) margin margin in in Minnesota Minnesota [1]. [I]. The conductive on the the western western off—rift off-rift (WOR) unit beneath the WOR has been followed MT data data and and unit seen seen dipping dipping beneath the WOR has been followed in in the the MT in compatible controlled—source audiofrequency MT (CSANT) data in compatible controlled-source audiofrequency MT (Cdata [2, [ 2 , 3]. 31. The unit has been traced northern The conductive conductive unit has been traced to to the the surface surface along along the the northern edge of the McGrath Gneiss, at the southern edge of the Animikie edge of the McGrath Gneiss, at the southern edge of the Animikie basin. This basin. This suggests suggests that that the the conductive conductive unit unit correlates correlates to to Animikie Animikie basin the upper contact of this unit represents a major basin rocks, rocks, and and the upper contact of this unit represents a major decollement in which Archean Archean McGrath McGrath Gneiss Gneiss has has been been emplaced emplaced over over decollement in which Lower Proterozoic Animikie basin rocks. Near the western edge Lower Proterozoic Animikie basin rocks. Near the western edge of of the the NCR the deepening conductive unit appears to thin or die out. Thus MCR the deepening conductive unit appears to thin or die out. Thus near may either near the the western western edge edge of of the the NCR, MCR, the the inferred inferred decollemont decollemont may either attenuate, be offset by Keweenawan faults, or it may continue the attenuate, be offset by Keweenawan faults, or it may continue into into the NCR as a structure too thin or resistive to be resolved with this MCR as a structure too thin or resistive to be resolved with this method. met hod. Geologic evidence supports a decollement along the southern margin of the Aninikie basin basin consistent consistent with with the the MT MT and and CSAMT CSAMT data data and and the the the Animikie interpretation discussed above. interpretations in interpretation discussed above. Some structural interpretations the Thomson Formation Formation of of the the Animikie Animikie basin basin suggest suggest an an early early Penokian Penokian the Thomson south dipping dipping nappe fold or thrust occurs there [4, 5, 61, 6], just east just east of where the the surface surface trace trace is is observed observed in in the the CSANT CSAMT data. data. A decolle— decollement is metamorphic grade is also consistent with other observations: observations: a) metamorphic and deformation increase southwestern margin margin of the AniAni— and increase toward toward the southwestern mikie basin adjacent b) inclusions inclusions adjacent the the proposed proposed decollement decollement [71, [TI, and b) in Late— to located south and southin Lateto post—Penokian post-Penokian igneous igneous stocks stocks 171 [TI located east east of of the the surface surface trace trace of of the the decollement decollement contain contain inclusions inclusions of of rocks rocks which are petrologically similar similar to to rocks of the the Thomson Formation suggesting that these sediments are tion of of the the Animikie Animikie basin basin [71, [TI, suggesting are present present at at depth. depth. In In contrast to to the the WOR WOR where where the the decollement decollement is is the the chief chief complexity, complexity, the MT data across the MCR in (-1 in Wisconsin indiindithe eastern off—rift off-rift (EOR) cate the the crust is is lithologically and structurally complex to depths of tens tens of of kilometers. kilometers. The central central NCR MCR itself itself appears appears as as an an elongate elongate plateau or horst and MT results are consistent with a body consisting of multiple mafic mafic igneous intrusive sheet dikes overlain by a basaltic basaltic pile. Resolution of the deep roots of the NCR from the surrounding pile. the roots the MCR from the surrounding crust is is difficult with with available available data. data. Proprietary Iowa undisclosed), traverse Iowa MT data data 181 [81 (specific (specific location undisclosed), traverse the MCR NCR with one site site on on each each off—rift off-rift margin. margin. The MT data data east east and and west of of the the NCR MCR in in Iowa Iowa appear appear analogous analogous to to those those obtained obtained along along the the off—rift off-rift margins to to the the north north on on the the EOR EOR and and WOR WOR respectively. respectively. For For example, the one available site west of the rift in Iowa shows a —85— �j -j Further studies nearby nearby intrabasement intrabasement conductive conductive zone. zone. Further studies are are indicated indicated but the conductive zone could be caused by decollement in but the conductive zone could be caused by decollement in aa situation situation similar The Iowa Iowa MT MT site site east east of of the rift similar to to the the WOR WOR in in Minnesota. Minnesota. The the rift again reflects extreme crustal complexity. COCORP data in Kansas again reflects extreme crustal complexity. COCORP data in Kansas [9, 19, 10] (COK) (COK) show show a a prominent prominent continuous continuous east east dipping dipping feature feature in in the the 101 basement to to the the west west of of the the MCR MCR which which extends extends at at least least to to the the main main basement low rift axis. This structure has been interpreted as: 1) "... a rift axis. This structure has been interpreted as: 1) a low angle detachment similar to those seen in the Basin and Range..." or angle detachment similar to those seen in the Basin and Range or 2) "... a sill similar to the Duluth Cabbro in Lake Superior..." [9]. a sill similar to the Duluth Gabbro in Lake Superior. [91. 2) Again, east Again, east of of the the rift, rift, extreme extreme crustal crustal complexity complexity is is seen seen in in COK COK The LOR data [io] similar to SOR MT MT data data [lo] similar to the the EOR data discussed discussed above. above. The EOR corn— complexity is consistent with with Alpine Alpine nappes nappes or or the the roots roots of of island arcs island arcs plexity is consistent [10] in in both both the COK and [lo] the COK and the the MT MT data. data. ."... ..." .." "... decollement and and observed crustal asymmetry in MT and and COK data The decollement in the MT are here here interpreted a Penokian Penokian continental margin are interpreted to to suggest suggest that that a continental margin preceded the emplacement of of the the MCR MCR and and that that the the younger younger rift rift strucstrucpreceded the emplacement If essentially a ture is is essentially a tectonic tectonic reactivation reactivation of of this this structure. structure. If and crustal asymmetry are indeed present and and widespread widespread decollement and indeed present be quite compatible to recent models models of Phanerozoic rift this would be genesis [111. genesis [11 I. J J J References: References: 91—92. 11 Wunderman, Wunderman, R., R., 1986; 1986; 32nd 32nd Annual Annual Inst. Inst. Lake Lake Superior Superior Geol., Geol., 91-92. ElectroMagnetic Surveys Inc., 1985; Rep. 8417, v. 1, Berkeley) CA. 2 ElectroMagnetic Surveys Inc., 1985; Rep. 8417, v. 1, Berkeley, CA. 3 Lawler, T. and M. Vadis, 1986; 32nd Annual Inst. Lake Superior 3 Lawler, T. and M. Vadis, 1986; 32nd Annual Inst. Lake Superior Geol., 49. Geol., 49. 4 Rolst, 4 Holst, TT.B., .B., 1985; 1985; J. J. Struct. Struct. Geol., Geol., v. v. 7, 7, 375—383. 375-383. HoIst, T.B., 1984, Geol., v. 12, 135—138. 5 5 Holst, T.B., 1984, Geol., v. 12, 135-138. 6 Holm, D O.K., 1986, 32nd 32nd Annual Annual Inst. Inst. Lake Lake Superior Superior Geol., Geol., 32-33. 32—33. 6 Holm, .K., 1986, 7 A Centennial VolKeighin et al., 1972; in Geology of Minnesota —— 7 Keighin al., in A Centennial Vol(Sims and Morey, eds.), eds.), Minn. Minn. Geol. Geol. Surv. 240—254. ume (Sima Surv. publ., publ., 240-254. 8 Phoenix 8 Phoenix Geophysics, Inc., Inc., 1985; 1985; Nonexclusive lionexclusive Iowa Iowa Midcontinent Midcontinent Rift Rift MT Data Data and HI and 2—d 2-d Model. Model. 9 et al., al., 1984; Tectonics, v. v. 3, no. no. 3, 367-384 367—384 9 Serpa et v. 11, 11, 25—30. 25-30. 10 Brown et et al., al.. 1983; 1983; Geology, Geology, v. 11 Bosworth et al., 11 al., 1986; 1986; Eos, Transactions, American Geophysical no. 29, pp. v. 67, no. pp. 577, 577, 582—583. 582-583. Union, v. 2 F -- J j Support for for BLU: RLW: & IW, 1W, Minnesota Geol. Geol. Surv. Surv. Grant-in-aid Grant—in—aid for Support GC 6 Students, Trek and Trail Sporting Goods (winter camping equipment). ment). Acknowledgements: Dal Stanley Anderson and others Aclounrladg~ents: Stanley (consultation), (consultation), R9. . Anderson others at .5. Phoenix Geophysics, Denver (MT modeling aid); D. McDowell, at Phoenix Geophysics, Denver modeling aid); D. McDowell, J. Paces, V. Chandler, C. Morey, .5. Diehl (discussion), T. Seiss, Paces, V. G. Morey, J. Diehl (discussion), T. Seiss, Kitchen, the the Lynch Lynch family, family, and and many many others MM. . Kitchen, others (field (field work). work). -86- J J -j �Kremzar GoldDeposit, Deposit, DDistrict Kremzar Gold i s t r i c tofo Algoma f A1 goma - .CANAMAX Resources Inc. — Kremzar Gold CANAc l t d Mines Ltd.. G.R. Resources Inc.,255 255Algonquin Algonquin Blvd. Blvd. West, G.R. Yule Yule (CANAMAX (CANAMAX Resources Inc., West, Timmins, Timmins, Ontario P4N 2R8) Ontario P4N 2R8) - Drill geological reserves at the Kremzar Gold Mines D r i l indicated l indicated geological reserves a t CANAMAX t h e CANAMAX —Kremzar Mines Ltd. Ltd. gold golddeposit depositare arecalculated calculatedata932,000 t 932,000 tonnes tonnesgrading grading8.6 8.6 grams grams gold gold per on rresults per tonne tonne iinn five f i v esubparallel subparallelmineralized mineralizedzones, zones, based based on e s u l t s of of diamond recentddrill diamond ddrilling r i l l i n gprior p r i oto r t September o September1986. 1986. Aditional A d i t i o n a l recent r i l l results results to have t o the the west west confirming confirming continuity c o n t i n u i t y of of the t h e'B'' BHorizon ' Horizon havenot n o been t been included. included. In Mines, operators operators ooff the dine I n 1940, 1940, O'Brien O'Brien Gold Gold Mines, t h e then then producing producing C l i n eLake Lake Gold Mine, ooutlined tonnesoof gold m mineralization Gold Mine, u t l i n e d 64,000 64,000 tonnes f gold i n e r a l i z a t i o n grading grading 7.9 7.9 gg Au per tonne tonne iin fall1ofo f1984, Au per n 17 17 ddrill r i l lholes holesononthe t h e'New 'New Zone'. Zone'. Since Since tthe h e fa1 1984, CANAMAX's evaluation 'NewZone' Zone' gold gold bearing bearing structure CANAMAX'S evaluation o foft hthe e 'New s t r u c t u r ehas hasexpanded expanded reserves ananunderground reserves ssubstantially. u b s t a n t i a l l y . In I n the t h e fall f a lof l o1985 f 1985 underground exploration exploration program was initiated, based on drill indicated geological program was i n i t i a t e d , based on d r i l l i n d i c a t e d geological reserves reserves of of 790,000 tonnes grading grading 7.9 7.9 grams gold per off the 790,000 tonnes grains gold per tonne. tonne. Results Results o t h e underunderground programshowed showed ground eexploration x p l o r a t i o n program e x cexcellent e l l e n t c ocorrelation r r e l a t i o n wwith i t h t hthe e eearlier arlier drill d r i l lresults. results. Auriferous Auriferous quartz quartz veins veins within w i t h i nmafic maficmetavolcanics metavolcanics on on the t h eKremzar Kremzar project project are localized within NW and NE striking biotitized shear zones. a r e l o c a l i z e d w i t h i n NU and NE s t r i k i n g b i o t i t i z e d shear zones. Mineralized mainly of ized veins veins are arecomposed composed mainly o f cherty chertyblue—grey blue-grey quartz, quartz,K—spar, K-spar, and and sericite. minerals s e r i c i t e . Accessory Accessory minerals i n cinclude l u d e p y pyrite, r i t e , p ypyrrhotite, r r h o t i t e , bbiotite, iotite, chlorite, very ffine c h l o r i t e , carbonate, carbonate, and and very i n e free f r e e gold. gold. Native gold gold occurs occurs mainly mainly as as very very fine f i n e free f r e e gold gold "dust "dust clouds", clouds", as as fine f i n eindividual i n d i v i d u aspecks, l specks,and andon on the majority t h e boundaries boundaries oof f ffine i n e anhedral anhedral tto o subhedral subhedral ppyrite y r i t e grains. grains. The The m ajority of veins oblique oblique to t o the the o f the t h e gold g o l d is i srestricted r e s t r i c t e dtot 2nd o 2ndorder ordersigmoidal sigmoidal veins shear zone, tthat dip NW within w i t h i n the t h e shear shear shear zone, hat d i p vertically, v e r t i c a l l y ,and andplunge plungetot othe t h eNW zone structure. This n aa ductile—brittle d u c t i l e - b r i t t l eshear shearzone zone This deposit deposit has has formed formed iin zone structure. environment strongb but restricted wallrock aalteration. A l l obserobserenvironment wwith i t h strong ut re s t r i c t e d wallrock l t e r a t i o n . All vations from hand handsamples, samples,f r ofrom m d rdrill i l l core, core, and and from from detailed detailed vations have have been been from underground investigations. underground investigations. On displaywwill and On display i l l be be a a typical t y p i c a l section section of o f drill d r i lcore l core anditsi tcorresponding s corresponding drill d r i l section, l section,a alongitudinal l o n g i t u d i n asection, l section,and andplan p l a nofo fthe t h edeposit, deposit, as as well well as as hand hand samples. samples. * , .. . ~~ ~ + ., .., . : . .. , ,: .. ., . . .,.. , - . ! , . . . , ., . ., .. , .. —87— , , r . �j - Structurally Lochalsh S t r u c t u r a l l yhosted hosted vein vein type typegold goldmineralization, m i n e r a l i z a t i o nGoudreau , Goudreau —Lochalsh camp,DDistrict ggold o l d camp, i s t r i c tofo Algoma f Algoma J G.R. (CANAMAX Resources 255A1Algonquin Blvd. West, West, Timmins, G.R. YULE YULE (CANAMAX Resources Inc.,Inc.,255 gonquin Blvd. Timmins, P4N 2R8) Ontario PAN 2R8) Ontario J Since Resources commenced search goldmmineralizSince CANAMAX CANAMAX Resources Inc.,Inc., commenced t h e the search f o rfor gold ineralization terrane, gold a t i o n ini nthe t h eWawa Wawa greenstone greenstone terrane, gold has has been been noted noted to t o be be hosted hosted within major and minor structures transecting all lithologies, except w i t h i n major and minor structures t r a n s a c t i n g a l l l i t h o l o g i e s , except the diabase dike It also apparent tthat t h e late l a t eKeweenawan a l s obecame became apparent hat Keweenawan diabase d i k eswarm. swarm. It the Goudreau—Lochalsh area hosted the major criteria for gold deposits. the Goudreau-Lochalsh area hosted t h e major c r i t e r i a f o r gold deposits. In entered joint—venture with I n 1983 1983 CANAMAX CANAMAX entered i ninto t o jo i n t - v e n t u r e agreements agreements w i t h Algoma Algoma Steel Steel Corporation and and wwith GoldMines MinesLtd., Ltd., a Corporation i t h Kremzar Kremzar Gold a subsidiary subsidiary ofo fAlgoma Algoma Steel holdings in the Steel Corporation, Corporation, to t o explore explore their t h e i large r l a r gland e land holdings i n t Goudreau— h e GoudreauLochalsh area. CANAMAX has since defined major auriferous structures, Lochalsh area. CANAMAX has since defined major auriferous structures, responsible for the many gold occurrences of the area, which responsible f o r t h e many gold occurrences o f t h e area, which eluded eluded previous workers. previous workers. The hhistoric gold camp northernf l aflank The i s t o r i cGoudreau—Lochalsh Goudreau-Lochalsh gold camp i s is on on t h ethe northern n k oof f tthe he Wawa greenstone terrane. The lithology of the region is typically Wawa greenstone terrane. The l i t h o l o g y o f t h e region i s t y p i c a l l y Archean metavolcanicrocks, rocks,ranging rangingfrom fromf efelsic Archean metavolcanic l s i c ttoo mafic mafic composition, composition, with w i t h minor, minor, but b u t regionally r e g i o n a l l yextensive, extensive,carbonate—sulphide carbonate-sulphide iiron r o n formations formations markingt hthe majorl ilithologic marking e major t h o l o g i c contact. contact. Goldmmineralization campi sissstructurally t r u c t u r a l l y controlled c o n t r o l l e d by by the the Gold i n e r a l i z a t i o n wwithin i t h i n tthe h e camp major east-northeast east—northeasttrending, trending,low lowangle anglereverse reversef fault major a u l t system system rreferred eferred Zone, and andby by subsidiary subsidiary minor ttoo as as the t h eGoudreau Goudreau Shear Shear Zone, minor splays splays and and shear shear fractures units the the latel aKeweenawan fractures that t h a ttransect transectalla rock l l rock u n except i t s except t e Keweenawandiabase diabase dikes. LLithologies dikes. i t h o l o g i e s found found tto o host host these these gold gold bearing bearing structures s t r u c t u r e s include include mafic and andffelsic sulphide—carbonate mafic e l s i c volcanics, volcanics, felsic f e l s i intrusives, c i n t r u s i v e and s , and sulphide-carbonate iron i r o n formation. formation. J U j Hydrothermala lalteration these sstructurally Hydrothermal t e r a t i o n oof f these t r u c t u r a l l y prepared prepared conduits conduits iiss also also essential ffor Wallrockaalteration essential o r gold gold mineralization. mineralization. Wallrock l t e r a t i o n includes includes potassic potassic metasomatism theb ibiotization the mafics maficsand ands esericitization metasomatism (i.e.(i.e. the o t i z a t i o n oof f the r i c i t i z a t i o n ooff sulph— tthe h e ffelsics), e l s i c s ) , silicification, s i 1 i c i f i c a t i o ncarbonatization, , carbonatization,chloritization, c h l o r i t i z a t i o nand , and sulphdization (pyrite, pyrrhotite, chalcopyrite, arsenopyrite, and sphalerite). d i z a t i o n ( p y r i t e , p y r r h o t i t e , chalcopyrite, arsenopyrite, and s p h a l e r i t e ) . The GoudreauShear Shear Zone, a major zone low angle reverse The Goudreau Zone, a major zone o f of low angle reverse f afaulting, u l t i n g , is is host to gold deposit. deposit. Splays Splays of t othe t h eMagino—Muscocho Magino-Muscocho gold o f the t h eGoudreau Goudreau Shear Shear Zone, trending northwest at 35 — 45 degrees to the structure, host Zone, t r e n d i n g northwest a t 35 45 degrees t o t h e s t r u c t u r e , host several other occurrences, namely golddeposit deposit,, othergold gold occurrences, name1the y t hCANAMAX—Kremzar e CANAMAX-Kremzar gold These northwest northwest tthe h e Cline C l i n e Lake Lake past past producer, producer, and and the t h e Markes Markes prospect. prospect. These trending splays trending splays appear appear tot ohave havean anextensional extensional.component, component, suggested suggested by by ont hthe GoudreauShear Shear Zone, tthrust h r u s t movement movement on e Goudreau Zone, a l lallowing o w i n g f ofor r aal larger a r g e r dilat— dilatancyooff the the splays, thus witdths, witdths, and ancy splays, and and thus and therefore t h e r e f o r e tonnage tonnage ppotential. otential. Minor conjugate conjugate northeast northeast ttrending Minor r e n d i n g splay splay structures s t r u c t u r e ssuch suchas asZones Zones 22 and and 33 on tthe property are are also also auriferous. auriferous. These Theseminor minorstructures structures are on h e Kremzar Kremzar property tonnageppotential. comprescconsistantly o n s i s t a n t l y narrow, narrow, and and thus have have lower lower tonnage o t e n t i a l . AA compres— sional component may be be responsible, responsible, component ooff the t h emajor majorGoudreau Goudreau Shear Shear Zone Zone may making minorsplays splaysa at itighter structure. making t hthe e minor g h t e r structure. - J -4 —88— J �-j I C) a E ft C) a) it it LC -I-) U, 4-, -Cr- i :i r i —, :i 1 — Ji I Ci TI i±I L....1 ! I I I I I I I I I I I I I I I I I I CNC r it .r- 43 U, 4) .-. (0 0 C) 0 C )<CC) _o -c C) -c rSL 4-) 0 •!- I— (0 0' .— U1 -C C ci -w I— C) >, r 4- L (0010 it,— a) t_ it -C 4' 4-) a) 4-' r LF -C Ci 4JC,(0 4-' (0 it 4-) 3 L C) LrL 0 4-' it it -r Li—C .C I/I r- C) >, 0 U, C ro o'.o WOE 4-' C) o (I) w L a' r'--f-- C) -I-' -0-C C, C -0-c r+J a F Circa L -o (0 This e x h i b i t w i l l I l l u s t r a t e t h e s t r u c t u r a l l y c o n t r o l l e d gold minerali z a t i o n which transacts a l l t h e various l i t h o l o g i e s w i t h i n t h e gold camp and t h e r e s u l t i n g hydrothermal a l t e r a t i o n assemblages. �AUTHOR AUTHOR INDEX INDEX ........... 821 ............. . .......... ........ 5,10 3 5. 10 6,12 ............. 6. 12 .............. 151,24 .................. 1. 24 ........... 8 ....... 106,12,32 .......... 6.12. 32 .............. 13 ................ 15 ............... 16 ........... 25 ................. 18 ...... 19 .................. 20,21 20. 21 Anderson, Anderson. Gary Gary Anglin, Anglin. C.D C.D. Barrie, Barrie. C. C Tucker Tucker Bauer, Robert Bauer. Robert LL Baxter, Baxter. D.A D.A. Behrendt, Behrendt. 3J Bell, B e l l . KK Berdusco, Berdusco. E.N E.N. Bidwell, Bidwell. Matthew Matthew E. E Bornhorst, Bornhorst. T.J T.J. Bowen, Bowen. R.P R.P. Cannon, Cannon. WW Card, K.D. Card. K.D Chandler, Chandler. V.W V.W. Corfu, Corfu. FF Cummings, Michael LL Cunnings. Michael Dahl, Dahl. RR Davidson, Davidson. AA Droege, Droege. David David Eick, Eick. P.M P.M. Erickson, Erickson. Paul Paul Ernst, Ernst. R.E R.E. Ferderer, Ferderer. R.J R.J. Franklin, Franklin. J.M J.M. Frizado, Frizado. Joe Joe Geiger, Geiger. C.A C.A. Green, Green. AA Gregg, Gregg. W.J W.J. Grunsky, Grunsky. Eric E r i c CC Heather, Heather. Kevin Kevin BB Hoffman, Hoffman. EE Hutchinson, 0D Hutchinson. Jirsa, Jirsa. Mark Mark AA Johnson, Johnson. Allan A l l a nMM Johnson, R.C. Johnson. R.C Jolly, Wayne J o l l y . Wayne TT Jonasson, Jonasson. hR I.R. Kneller, Kneller. William William Kuhns, Kuhns. Mary Mary Jo Jo PP Kuhns, Roger Kuhns. Roger JJ LaBerge, LaBerge. Gene Gene LL Lee, M Lee. M Lehman, Lehman. George George AA McGill, George McGill. George EE McGoren, McGoren. J.W J.W. McPhee, McPhee. 0.5 D.S. Mancuso, Mancuso. J.M J.M. Meyer, Meyer. Paul Paul 3J MilkereTt, M i l k e r e i t . BB Miller, M i l l e r . Jr., Jr.. James James 0D Morel PP Muir, Muir. T.L T.L. 82 1 3 15 8 10 13 15 16 25 18 19 .............. ............ ............... ........... .............. ........... ........... ............. ............. ................. .............. .......... ......... ............... ............ ............ ......... ............ ........... ........... ......... ......... ........... .......... ................... ......... 39,61,63 ......... ............ ............. ............ ............ ............. ..... .................. ............... 15,22 15. 22 53 53 23 23 82 82 24 24 25 25 1,76 1.76 68 68 55 55 15 15 65 65 26 26 28 28 1 15 15 30 30 5 3,56 53. 56 32 32 34 34 1 1 68 68 35 35 35 35 36 36 15 15 37 37 39.61. 63 20,221 1 20. 41,42 41. 42 68,70 68.70 73 73 15 15 43 15 15 45 45 1 47,49 ........ 47. 49 .......... 51 ........ 5553 .......... ....... 5756 .............. ........... 5818. 18,76 .............. 76 ......... 59 39,61,6 3 ..... 39.61. 63 ........... 6515 .............. .......... 67 ......... 68 ........... 7170 ................ ........ 73 ......... 75 .......... 8115 ............... ............ 76 .......... 78 ......... 8068 ................ 6,32,53 ....... 226.32. 53 ........... ........... 81 ........... 82 20,21 ......... 8320. 21 .......... .......... 84 ...... 85 ........ 8587. 87,88 .............. 88 Nielsen, Peter Peter AA Nielsen. Percival J.A. Percival. J.4. Peterman, Jill F Peterman. Jill F Peterson, J.W Peterson. J.W. Prosen, Barbara Prosen. Barbara J. J Rose, Rose. W.I W.I. Rupert, Rupert. Roy Roy JJ Sage, R.P Sage. R.P. Shegelski, Shegelski. R.J R.J. Shrady, Catherine H Shrady. Catherine H. Sikkila, S i k k i l a . K.M. K.M. Spencer, CC Spencer. Springer, Springer. 3.5. J.S. Stevenson, Stevenson. JJeff eff Stewart, Stewart. D.C. D.C. Stone, Stone. DD Suszek, Suszek. Thomas Thomas JJ Sutcliffe, S u t c l i f f e . R.H. R.H. Symons, D.T.A. Symons. D. T.A. Teskey, 0. Teskey. D Thorpe, R.I. Thorpe. R.I. Tortosa, Tortosa. Delia Delio Truskoski, Truskoski. Paul Paul Turek, AA Turek. Van Alstine, J.L Van Alstine. J.L. Van Van Breenien, Breemen. 00 Vandall, Vandall. T.A T.A. Watkins, Ivan Watkins. Ivan Watkinson, Watkinson. D.H D.H. Werbach, Werbach. David David Williams, Williams. H.R H.R. Wunderman, Richard Wundennan. Richard Young, Charles TT Young. Yule, G.R Yule. G.R. —90— 53 55 56 57 58 59 65 15 67 68 70 71 73 75 81 15 76 78 68 80 22 81 82 83 84 85 85 � https://digitalcollections.lakeheadu.ca/files/original/c8d8c053aa0e63109723bb2132dd3fc8.pdf e87a531a6c2b257913b28ed87343a403 PDF Text Text Institute on Lake Superior Geo'ogy i r t y - T h i r dAnnUal Annual Meeting Me ThirtyThrd WAWA, ONTARR:) May 12 and 13, 19B7 GeoIogy of Ww Area God MbieraUaton Sponsored by Onlaria Ministry Ministry ofofNorthern and Wnes fi/iinics NorthernDevelopment DeIopment and OntarIo VVtw Resiclont Uoloqit U Nice Volurr)e a :: Par 2 �OF GEOLOGY O F WAWA AREA GOLD MINERALIZATION MINERAL1 ZATI ON E. D. D. Frey Frey Ontario O n t a r i o Ministry M i n i s t r y of o f Northern N o r t h e r n Development Development and a n d Mines Mines Wawa Resident s Of Office R e s i d e n t Geologist' Geologistt s £ic P.O. P . 0 . Box 530 530 Wawa, Ontario 1KO Wawa, O n t a r i o PUS POS 1KO Institute I n s t i t u t e on Lake Superior S u p e r i o r Geology 33rd Annual Meeting 3 3 r d Annual Meeting Wawa, Wawa, Ontario Ontario 11957 987 Fieldtrip F i e l d t r i p Guidebook Volume 33, Volume 33, Part P a r t 22 �FOREWORD FOREWORD T h i s guidebook guidebook is i s aa candidate c a n d i d a t e for f o r the t h e most-delayed most-delayed production production This award. award. conducted the t h e original original y e a r s have passed p a s s e d since s i n c e I conducted Three years f i e l d t r i p twice t w i c e during d u r i n g the t h e Wawa Wawa ILSG ILSG meeting. meeting. fieldtrip C i t a d e l Mine Mine The Citadel h a s test t e s t milled m i l l e d its i t s underground underground development development and and continues c o n t i n u e s to to has explore e x p l o r e on on surface. surface. C i t a d e l Gold Gold Mines Mines Ltd. Ltd. has h a s acquired a c q u i r e d the the Citadel P a r k h i l l Mine Mine and and has h a s conducted conducted extensive e x t e n s i v e surface s u r f a c e stripping s t r i p p i n g on on Parkhill that t h a t property p r o p e r t y and and surrounding s u r r o u n d i n g prospects. prospects. Ranson prospect p r o s p e c t was was The Ranson o p t i o n e d to t o FinNeth FinNeth Explorations E x p l o r a t i o n s Ltd. Ltd. in i n late l a t e 1987 1 9 8 7 and and has has been been optioned thoroughly t h o r o u g h l y sampled sampled and and evaluated. evaluated. some some of of these t h e s e new new data. data. incorporates The guidebook incorporates No changes changes have have affected a f f e c t e d the t h e other o t h e r sites sites No visited v i s i t e d during d u r i n g the t h e ILSG I L S G meeting. meeting. ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS I thank t h a n k Dello D e l i o Tortosa, T o r t o s a , Wawa Wawa Resident R e s i d e n t Geologist, G e o l o g i s t , for f o r providing p r o v i d i n g the the dedicated d e d i c a t e d time t i m e necessary n e c e s s a r y for f o r completion c o m p l e t i o n of of this t h i s project. proj ect. Contract Contract geologists g e o l o g i s t s Rosa Rosa Stewart S t e w a r t and and Ann Ann Wilson Wilson prepared p r e p a r e d the t h e figures. figures. Wilson Wilson reviewed r e v i e w e d the t h e text. text. Ann Ann Ron Sage, Sage, Ontario O n t a r i o Geological G e o l o g i c a l Survey, Survey, also a l s o provided p r o v i d e d continued c o n t i n u e d support. s u p p o r t . Any Any rremaining e m a i n i n g eerrors rrors or o r word word fog f o g are a r emy my responsibility. responsibility. Toronto, Toronto, fieldtrip would not exist without the co-operation of the This T h i s f i e l d t r i p would n o t e x i s t w i t h o u t t h e c o - o p e r a t i o n of t h e property property owners owners and and operating o p e r a t i n g companies companies listed l i s t e d below. below. Their T h e i r open open access a c c e s s policies p o l i c i e s have contributed c o n t r i b u t e d greatly g r e a t l y to t o the t h e continuing continuing exchange of of observations o b s e r v a t i o n s and and ideas i d e a s on on Wawa geology geology and and gold gold mineralization m i n e r a l i z a t i o n that t h a t characterize c h a r a c t e r i z e the t h e Wawa Wawa exploration e x p l o r a t i o n community. community. I thank t h a n k the t h e management management and and staff, s t a f f , as a s noted, n o t e d , of: o f : Citadel C i t a d e l Gold Gold Mines Mines Ltd. Ltd. -- Roy Roy Rupert Rupert and and Alison A l i s o n Leroy; Leroy; Monk Gold Gold and and Resources Ltd.; Ltd. ; and and Bridget B r i d g e t Lake Lake Resources Resources Inc. Inc. �—2— - 2 NTRODUCTI ON ON I NTRODUCTI The fieldtrip f i e l d t r i p provides p r o v i d e s aa one one day day overview o v e r v i e w of of the t h e variety v a r i e t y of of lithological of g gold bearing quartz vein l i t h o l o g i c a l and structural s t r u c t u r a l settings s e t t i n g s of old b earing q uartz v ein m i n e r a l i z a t i o n in i n the t h e Wawa Wawa area. area. mineralization The route r o u t e traverses t r a v e r s e s the the historical h istorical g o l d mining m i n i n g area a r e a south s o u t hof ofWawa Wawa and and includes i n c l u d e s several s e v e r a l as as gold yet y e t minor o c c u r r e n c e s that t h a t are a r e of of interest i n t e r e s t for f o r their t h e i r geological geological occurrences ssetting e t t i n g (Fig. (Fig. 1). 1). 10 stops s t o p s were selected s e l e c t e d for f o r their t h e i r interest interest The 10 and large l a r g e group g r o u p accessibility. accessibility. occurrences o c c u r r e n c e s are a r e known known (Fig. (Fig. numerous additional a d d i t i o n a l gold gold However numerous 1)) and and aa comprehensive comprehensive review 1 r e v i e w of of the the local gold mineralization l o c a l lithostructural l i t h o s t r u c t u r a l relationships r e l a t i o n s h i p s of of g old m ineralization remains r e m a i n s to t o be be done. done. The mineral m i n e r a l development history h i s t o r y of of Wawa began began in i n June J u n e 1897 1897 with of Wawa Lake by by w i t h the t h e discovery d i s c o v e r y of of gold g o l d on the t h e southwest s o u t h w e s t sshore h o r e of local l o c a l native n a t i v e William W i l l i a m Teddy. Teddy. Wawa d discovery The Wawa i s c o v e r y coincided c o i n c i d e d with with the t h e Kiondike K l o n d i k e gold g o l d rush r u s h and and many many westward-bound westward-bound prospectors prospectors sstopped t o p p e d at a t Wawa on on their t h e i r steamer s t e a m e r journey j o u r n e y across a c r o s s Lake Lake Superior. Superior. The first f i r s t Wawa gold g o l d rush r u s h ended ended in i n 1906 1906 after a f t e r numerous numerous shortshortlived l i v e d mining m i n i n g developments d e v e l o p m e n t s of o f low low tonnage. tonnage. Gold exploration exploration rrevived e v i v e d in i n the t h e 1930s 1930s and and resulted r e s u l t e d in i n fifteen f i f t e e n mines mines tthat h a t produced produced tthrough h r o u g h tthe h e early e a r l y 1940s. 1940s. The total production t o t a l gold gold p r o d u c t i o n from from the t h e Wawa Wawa area a r e a has h a s been b e e n less l e s s than t h a n 200,000 200,000 ounces. ounces. The next n e x t cycle c y c l e of of gold g o l d exploration e x p l o r a t i o n was was stimulated s t i m u l a t e d by b y the the record r e c o r d high h i g h gold g o l d price p r i c e of of 1980 1980 and and the t h e Hemlo Hemlo discoveries d i s c o v e r i e s two two years y e a r s later. later. Continued C o n t i n u e d high h i g h demand and a sustained s u s t a i n e d acceptable acceptable price of eexploration has p r i c e have h a v e maintained m a i n t a i n e d the t h e level l e v e l of x p l o r a t i o n tthat hat h a s rresulted esulted in i n recent r e c e n t mine mine development development activities a c t i v i t i e s and and production p r o d u c t i o n decisions. decisions. An accidental a c c i d e n t a l result r e s u l t of of the t h e intensive i n t e n s i v e gold g o l d prospecting p r o s p e c t i n g was was �Occurrences. Gold and Geology General Area Wawa Occurrence Gold © A Mine Gold Producing Past IA Stop Trip Field v V Rocks Intrusive Mafic Rocks Metavolcanics Malic Sediments Quaternary T1 vV V \N\\\\ \\\ \\ \N\NN \N\\N\\\ v v STOCK LAKE 4vt41 vvvVvvVVVVVVV\\\\\\\\\\N\\\\\\N\N\\N N /\NN\\\\\\\N\\JV\\/,VVVVV/ -' /\N\N\N\\\\NNYvV.iV\4-VVVVVVVVV+\N\\\N\\. vVVVV\\\\\ vvvvvv\\\N. V ,Y'VVVVVVVVV VVVV V Li: Rocks Intrusive Felsic vVV VV Figure Rocks Metavolcanic Felsic Rocks Plutoruc Felsic vVVVVVVvVVV 1. Lillill VVVVVVBHOGET \VVVV - V vvV'\ \N\NNN\\ VVVVVV\\\\\NN\ v/vVv\vVvVvVVvvVVVVVvK/'P/) -vv Y -P; \JVvVvVVVVVVVYji! vVvVVVVVVV \VVVVVVVV')'/' \VVVVV vvvV:/P ,vVvv-c 1-NNNN\\N\-%\NNN\\NNwyvvV-,/ vVvvVvvVVVVVVVVVVVVVV V \V /v\,\\ VVVVVM VVVVVVV//N\N\N\N\N\\NN\N\\ \\\\ \\\\\\ CNNNN vVvvVVV\ V-VVVVVvVVvVVvVVVVV vv V VVVVVVVV jV vv V - -'/ \\\N\\ 4- 4 I + 4 1 4- 4 vvvvVV /VVVVVVV\V /vVVVVVVV 4-j 'vvVvvv\t -+VVVV4L.' yvvvv\ Superior 4 t + 4- If 4- 1 4- 4 4- 4 +4-f t f4-1 1-44-444-4 114NQ STOCK :*4-+ /_ - 4CEHIENtJAY N'"-' + + 4 j\\\ H Lake + -4- 4- 4- 4 F + + 4- 4- 1— 1— 4- 1- ,,C',. -4- 4- 1- _l- 4- - * / / 0 / // ;P_,\ "'';iP,;/ '//_J ,! - 4/—\, l/_/I\ ,\j\_ 4\)i'--ç P \ 1 4 ± 4 + 4- 4- 4- 4- 4- 4- N 4 /; 4 > A V v �—4— t h e discovery d i s c o v e r y of of iron i r o nore o r eini n1898. 1898. the I r o n mining mining became became the the Iron m a i n s t a y of of the t h e Wawa Wawa economy economy until u n t i l reduced r e d u c e d demand demand for f o r steel steel mainstay f o l l o w i n g World World War War II forced f o r c e d the t h e closure c l o s u r e of of the t h e Helen Helen and and Magpie Magpie following mines by by 1920. 1920. mines I r o n mining mining revived r e v i v e d in i n the t h e late l a t e 1930s, 1930~ prompted ~ by aa Iron prompted by provincial p r o v i n c i a l bounty b o u n t y of of two two cents c e n t s per p e r ton t o n in i n 1937 1937 and and the t h e onset o n s e t of of 11. The The open open pit p i t Helen Helen Mine Mine re-opened re-opened in i n 1939 1939 and and by by World War WarII. World 1960 had had developed d e v e l o p e d into i n t o the t h e George GeorgeW. W. MacLeod MacLeod Mine, Mine, which which 1960 c o n t i n u e s to t o operate o p e r a t e today t o d a y as a s an a nunderground undergroundsiderite s i d e r i t emine. mine. continues Modern Modern geological g e o l o g i c a l mapping mapping of of the t h e Wawa Wawa area a r e a by by the t h e provincial provincial government has h a s been been completed completed by by the t h e Ontario O n t a r i o Geological G e o l o g i c a l Survey Survey government (Ministry ( M i n i s t r y of of Northern N o r t h e r n Development Development and and Mines) Mines) at a t aa scale s c a l e of of 1: 15, 840 (1 ( 1 inch i n c h == 1./4 114 mile). mile). 1:15,840 This T h i s work work includes i n c l u d e s preliminary preliminary maps (Sage, (Sage,ete al. t al, . , 1982a—1982d; 1982a-1982d; Massey, Massey, ete tal. a l .,, 1982a-1982c; 1982a-1982c; and and maps Mandziuk, et e t al., a l . , 1981) 1981) and and open open file f i l e reports r e p o r t s (Massey, (Massey, 1985; 1985; Mandziuk, Sage, in i n press). p r e s s 1. Sage, GEOLOGICAL SETTI NG GEOLOGI CAL SETTING Wawa Wawa is i s in i n the t h e south s o u t h central c e n t r a l part p a r t of of the t h e Michipicoten M i c h i p i c o t e n greenstone greenstone belt, b e l t , within w i t h i n the t h e Wawa Wawa Subprovince Subprovince of of the t h e Superior S u p e r i o r Province P r o v i n c e of of the the Canadian Shield S h i e l d (Fig. ( F i g . 2). 2). Canadian The The Michipicoten M i c h i p i c o t e n greenstone g r e e n s t o n e belt b e l t is is composed composed of of supracrustal s u p r a c r u s t a l metavolcanic m e t a v o l c a n i c and and metasedimentary m e t a s e d i m e n t a r yrocks, rocks, that t h a t have have been been divided d i v i d e d into i n t o three t h r e e volcanic v o l c a n i c cycles c y c l e s (Sage, (Sage, 1986). 1986). Each Each cycle c y c l e consists c o n s i s t s of of mafic m a f i c to t o felsic f e l s i c metavolcanic m e t a v o l c a n i c rocks r o c k s and and a s s o c i a t e d subvolcanic s u b v o l c a n i c intrusions. intrusions. associated The The volcanic v o l c a n i c cycles c y c l e s are are of overlain o v e r l a i n by by iron i r o n formation f o r m a t i o n or o r clastic c l a s t i c metasedimentary m e t a s e d i m e n t a r y rocks r o c k s of v o l c a n i c origin. origin. volcanic �GAMITAGAMA LAKE GREENSTONE BELT / Figure 2. General Geology of the Michpicoten Greenstone Belt MSHIBISHU LAKE GREENSTONE BELT + 4-J f ,#+/ B ELI Granitic Intrusive Rocks (internal) Metavolcanic-Metasedimentary Supracrustal Rocks L + ft 1- 4 V+ LEGEND Granite-Gness Pluflonic Rocks (external) GA EENS TO NE MICHPICOTEN (fl �—6— - 6 The mafic m a f i c volcanic v o l c a n i c compositions c o m p o s i t i o n s vary v a r y from from basaltic b a s a l t i c to to p e r i d o t i t i c komatiite k o m a t i i t e in i n the t h e oldest o l d e s t cycle, c y c l e , to t o tholeiitic t h o l e i i t i c basalts basalts peridotitic i n the t h e two two younger younger cycles. cycles. in The rrocks o c k s are a r e massive and pillowed pillowed f l o w s and minor minor accumulations a c c u m u l a t i o n s of of tuff. tuff. flows The iintermediate n t e r m e d i a t e to to ffelsic e l s i c rocks r o c k s of o f the t h e three t h r e e cycles c y c l e s are a r e pyroclastics p y r o c l a s t i c s and minor flows flows of o f rhyolite r h y o l i t e and and dacite, d a c i t e l of of caic-alkalic c a l c - a l k a l i c affinity. affinity. M i c h i p i c o t e n Iron I r o n Formation, Formationl dominated by siderite s i d e r i t e in i n the the Michipicoten Wawa area, a r e a l caps caps the t h e oldest o l d e s t volcanic v o l c a n i c cycle. cycle. The clastic elastic m e t a s e d i m e n t a r y rocks r o c k s that t h a t overlie o v e r l i e the t h e younger younger cycles c y c l e s consist c o n s i s t of of metasedimentary u n u s u a l l y well w e l l preserved p r e s e r v e d siltstones s i l t s t o n e s to t o conglomerates c o n g l o m e r a t e s that t h a t have have unusually d e p o s i t e d in i n aa variety v a r i e t y of of marine marine and and non-marine non-marine settings. settings. been deposited s t r a t i g r a p h i c thicknesses t h i c k n e s s e s of of the t h e mafic m a f i c and and felsic-intermediate felsic-intermediate The stratigraphic s e c t i o n s of of the t h e oldest o l d e s t cycle, c y c l e l in i n the t h e Wawa Wawa area, a r e a l are a r e approximately approximately sections 1800 m and and 900 900 m, ml respectively. respectively. (SageI 1986; 1986; (Sage, Sagel et e t al. a l .,, Sage, 1987; 1987; Sage, in Sagel i n press) press) Michipicoten The M i c h i p i c o t e n greenstone g r e e n s t o n e belt b e l t is i s enclosed e n c l o s e d within w i t h i n Early Early P r e c a m b r i a n granitic g r a n i t i c and and gneissic g n e i s s i c rocks r o c k s that t h a t are a r e younger younger than t h a n the the Precambrian supracrustal s u p r a c r u s t a l rocks. rocks. The supracrustal s u p r a c r u s t a l rocks r o c k s have been intruded i n t r u d e d by by felsic ccoeval o e v a l tto o younger stocks s t o c k s of of a variety v a r i e t y of of intermediate i n t e r m e d i a t e to t o felsic ccompositions. ompositions. These events e v e n t s have been dated d a t e d by the t h e U-Pb zircon zircon method and rrange from 2888 2888 +1/ - 9 Ma Ma to t o 2663 2663 +/+ / - 66 Ma Ma (Turek, ( T u r e k I et et method and a n g e from aal. l., 1988; 1988; Turek, Turekl et e tal. a l ., 1990). 1 990). Michipicoten The M i c h i p i c o t e n greenstone g r e e n s t o n e belt b e l t has been metamorphosed mainly to t o greenschist g r e e n s c h i s t grade. grade. Amphibolite grade g r a d e metamorphism metamorphism has has altered a l t e r e d the t h e supracrustal s u p r a c r u s t a l rocks r o c k s along a l o n g the t h e margin of of the t h e greenstone greenstone belt b e l t and adjacent a d j a c e n t to t o the t h e larger l a r g e r intrusions. intrusions. mineralization exclusively Gold m i n e r a l i z a t i o n iis s hosted h o s t e d almost almost e x c l u s i v e l y iin n quartz quartz �— - 7— 7- v e i n s and and lenses l e n s e s or o r pods pods within w i t h i n shear s h e a r zones zones and and breccia b r e c c i a zones. zones. veins Only minor u a n t i t i e s of of gold g o l d have have been been reported r e p o r t e d from from adjacent adjacent Only minorqquantities wall wall rocks. rocks. These gold g o l d depositional d e p o s i t i o n a l settings s e t t i n g s occur o c c u r in i n aa variety v a r i e t y of of These lithologies. lithologies. T h e i r orientation o r i e n t a t i o n and and character c h a r a c t e r appear a p p e a r to t o be be Their c o n t r o l l e d by the t h e competency competency of of the t h e host h o s t rock r o c k and and its i t s behaviour behaviour controlled during d u r i n g the t h e shearing s h e a r i n g and/or a n d / o r other o t h e r deformation. deformation. Common elements e l e m e n t s of of Common t h e gold g o l d occurrences o c c u r r e n c e s are: a r e : their t h e i r lack l a c k of of preferred p r e f e r r e d host h o s t lithology, lithologyl the the t h e presence p r e s e n c e of of recrystallized r e c r y s t a l l i z e d quartz, q u a r t z l and and minor minor amounts amounts of of sulphide s u l p h i d e minerals. minerals. The presence p r e s e n c e and intensity i n t e n s i t y of of alteration a l t e r a t i o n also also appears a p p e a r s to t o be an a n important i m p o r t a n t factor f a c t o r in i n evaluating e v a l u a t i n g individual i n d i v i d u a l gold gold occurrences. occurrences. Al though tthe A 1 though h e rrelationship e l a t i o n s h i p remains unclear, unclear) significant s i g n i f i c a n t gold g o l d occurrences o c c u r r e n c e s rarely r a r e l y occur o c c u r outside o u t s i d e of of aa zone zone of of pronounced pronounced alteration. alteration. JUBILEE STOCK STOCK STOP STOP 1: 1: - - V e r t i c a l Rockcut, Rockcutl SE SE side s i d e of of Highway Highway 101, 101, High Vertical km NE from from Surluga S u r l u g a Road Road Intersection I n t e r ~ e c t i o n-2 km high-level The Jubilee J u b i l eStock e S t (Fig. o c k ( F i g . 1) 1 ) iis s aa h i g h - l e v e l subvolcanic s u b v o l c a n i c intrusion intrusion The which varies v a r i e s in i n composition c o m p o s i t i o n from from diorite d i o r i t e to t o quartz q u a r t z diorite d i o r i t e and and granodiorit e . granodiorite. It I t is i s finef i n e - to t o medium-grained, medium-grained) equigranular e q u i g r a n u l a r to to locally l o c a l l y porphyritic. porphyritic. The stock s t o c k intrudes i n t r u d e s felsic f e l s i c and intermediate intermediate fragmental f r a g m e n t a l metavolcanic m e t a v o l c a n i c rocks r o c k s of of the t h e lower l o w e r volcanic v o l c a n i c cycle. cycle. A U-Pb U-Pb z i r c o n age a g e of of 2745 2745 +/+ / - Ma Ma obtained o b t a i n e d from from the t h e stock s t o c k identifies i d e n t i f i e s it it zircon as a s coeval c o e v a l with w i t h the t h e metavolcanic m e t a v o l c a n i c rocks r o c k s of of the t h e lower l o w e r volcanic v o l c a n i c cycle cycle + / - 10 10 Ma Ma and 2749 2749 +/— + / - 22 Ma, Mal Turek, Turekl et e t al., al. (2744 +/— 1982). 1 982). ssurface u r f a c e expression e x p r e s s i o n of of the t h e stock s t o c k is i s approximately a p p r o x i m a t e l y 88 km km sq. sq. The �—8— - 8 - m a r g i n a l zones z o n e s of o f the t h e stock s t o c k form form an a n intrusive i n t r u s i v e breccia breccia The marginal contact. contact. The central i s dioritic d i o r i t i c to t o granodioritic g r a n o d i o r i t i c in in c e n t r a l stock s t o c k is i s partly p a r t l y encircled e n c i r c l e d by a massive m a s s i v e quartz-feldspar quartz-feldspar c o m p o s i t i o n and a n d is composition porphyry. p orphyry. p o r p h y r y may occupy a ring r i n g fracture f r a c t u r e associated associated The porphyry w i t h caldera c a l d e r a formation f o r m a t i o n during d u r i n g the t h e intrusion i n t r u s i o n of o f the t h e Jubilee J u b i l e e Stock. Stock. with ((Sullivan, S u l l i v a n , et e t al., al., 1985; 1985; sage, Sage, 1986 & in i n press) press) The Jubilee J u b i l e e Stock S t o c k is i s highly h i g h l y variable, v a r i a b l e , both b o t h within w i t h i n its its compositional c o m p o s i t i o n a l range r a n g e and a n d texturally. texturally. The v variability The a r i a b i l i t y is i s displayed displayed within w i t h i n small s m a l l areas a r e a s and and often o f t e n within w i t h i n individual i n d i v i d u a l outcrops. outcrops. A lso Also c o n t r i b u t i n g to t o its i t s mapping complexity c o m p l e x i t y are a r e abundant a b u n d a n t xenoliths x e n o l i t h s of of contributing metavolcanic m e t a v o l c a n i c rocks r o c k s that t h a t locally l o c a l l y comprise c o m p r i s e up to t o 50% 50% of o f the t h e intrusion intrusion and display d i s p l a y great g r e a t size s i z e variation. variation. (Sullivan, ( S u l l i v a n , et e t al. al., , 1985) 1985) The fieldtrip f i e l d t r i p will w i l l examine examine aa 100 100 m m length l e n g t h of of aa large l a r g e vertical vertical roadcut r o a d c u t of o f diorite d i o r i t e and a n d quartz q u a r t z diorite d i o r i t e on on the t h e south s o u t h side s i d e of of Highway Highway 101. 101. Annually, A n n u a l l y , renewed rock r o c k falls f a l l s provide p r o v i d e fresh fresh exposures e x p o s u r e s of o f the t h e stock s t o c k and and related r e l a t e d features: f e a t u r e s : multisized multisized xenoliths, x e n o l i t h s , quartz q u a r t z vein v e i n occupation o c c u p a t i o n of o f minor minor shears, s h e a r s , and a n d hematitic hematitic and a n d carbonate c a r b o n a t e alteration. alteration. JUBILEE J U B I L E E TUFFS TUFFS STOP 2: STOP 2: - - Roadcut and Hillside H i l l s i d e Outcrops, O u t c r o p s , SE SE side s i d e of of Highway 101, Highway 101, SW SW of o f Surluga S u r l u g a Road IIntersection ntersection - Quartz Q u a r t z feldspar f e l d s p a r crystal c r y s t a l tuffs t u f f s are a r e an a n abundant a b u n d a n t component of o f the the felsic f e l s i c metavolcanic m e t a v o l c a n i c rocks r o c k s south s o u t h of o f Wawa Wawa Lake. Lake. They consist consist mainly m a i n l y of o f fine f i n e to t o medium grained g r a i n e d quartz q u a r t z and feldspar f e l d s p a r and and minor minor quantities q u a n t i t i e s of o f sericite, s e r i c i t e , carbonate, c a r b o n a t e , chlorite, c h l o r i t e , epidote, e p i d o t e , and and biotite. b iotite. The quartz q u a r t z content c o n t e n t is i s 10% 10% to t o 15% 15% and a n d quartz q u a r t z crystals crystals �—9— - 9 - are a r e often o f t e n up up to t o 55 mm mm in i n diameter. diameter. Q u a r t z in i n the t h e tuffs t u f f s is is Quartz e n r i c h e d 33 to t o 55 times t i m e s over o v e r that t h a t of of the t h e felsic f e l s i c flows f l o w s in i n the t h e area. area. enriched L i t h i c fragments f r a g m e n t s up to t o lapilli l a p i l l i size s i z e are a r e common common and confirm c o n f i r m the the Lithic pyroclastic p y r o c l a s t i c origin o r i g i n of of the t h e tuffs. tuffs. P r e v i o u s l y , most of these t h e s e and Previously, most of o ther p o r p h y r y i t i c pyroclastic p y r o c l a s t i c rocks r o c k s of of the t h e area a r e a had been been mapped mapped other porphyryitic as a s felsic f e l s i c intrusives. intrusives. (Sage, in i n press) press) (Sage, The wavy bedding of of the t h e tuffs t u f f s visible v i s i b l e along a l o n g the t h e road r o a d dips dips gently g e n t l y away away from from the t h e Jubilee J u b i l e e Stock. Stock. t u f f s also a l s o are a r e mapped mapped as as The tuffs t o the t h e stock s t o c k and and are a r e interpreted i n t e r p r e t e d to t o be the t h e re-worked re-worked conformable to p y r o c l a s t i c products p r o d u c t s of of the t h e emplacement emplacement of of the t h e stock. stock. pyroclastic Elsewhere iin n tthe h e vicinity v i c i n i t y of of the t h e stock s t o c k polymictic p o l y m i c t i c tuff t u f f breccias b r e c c i a s are a r e more more common. common. (Sage, et 1982; Sage, (Sage, e t al., a l . , 1982; Sage, in i n press) press ) STOP STOP 3: 3: CITADEL MINE CITADEL -- South on the t h e Surluga S u r l u g a Road, Road, 1 km from iits t s Intersection Intersection with w i t h Highway Highway 101 1 0 1 -- (Fig. ( F i g . 3 The Citadel 3) was developed developed on seven C i t a d eMine l Mine ) was s e v e n levels l e v e l s to t o aa depth 687 d e p t h of of 950 950 feet f e e t in i n the t h e late l a t e 1960s 1960s and and produced produced 1,1 , 6 8 7 ounces ounces of of gold g o l d and 43 43 ounces ounces of of silver s i l v e r in i n 1968. 1968. Re-evaluation R e - e v a l u a t i o n and exploration exploration since 500 ttons of pproven s i n c e 1987 1987 has h a s yielded y i e l d e d 358, 358, 500 o n s of r o v e n and probable p r o b a b l e ore ore reserves r e s e r v e s with w i t h aa grade g r a d eofof0.0.215 215 oz. oz. Au/ton. 000 An additional a d d i t i o n a l 150, 150,000 tons Au/ton aalso have been been t o n s of of possible p o s s i b l e reserves r e s e r v e s grading g r a d i n g 0. 0. 23 2 3 oz. oz. Au/ton l s o have outlined. outlined. ((Citadel C i t a d e l Gold Gold Mines Mines Inc. Inc. , 1988 1988 Annual Report) Report) , During 1989, 1989, Citadel C i t a d e l Gold Mines Mines Inc. I n c . continued c o n t i n u e d underground operations o p e r a t i o n s tto o sample and to t o assess a s s e s s the t h e quality q u a l i t y and mineability m i n e a b i l i t y of of ore o r e reserves r e s e r v e s in i n the t h e Jubilee J u b i l e e shear s h e a r zone. zone. This T h i s work terminated t e r m i n a t e d in in September 1989 1989 and tthe h e recalculation r e c a l c u l a t i o n of of reserves r e s e r v e s is i s in i n progress. progress. �10Dm (Modified from Citadel Gold Mines nc) Figure 3. Citadel Mine Exploration and Development - Jubilee and Minto Mines Development. lOOft 0 —H--- Minto Mine (past producer) Citadel Mine (under development) �- 1111 - — Also A l s o in i n 1989, 1989, a a six s i x month long l o n g test t e s t milling m i l l i n g program p r o g r a m processed processed 5 7 , 9956 56 t o n s oof f oore r e aand n d pproduced r o d u c e d 4737 4 7 3 7 Troy T r o y ounces o u n c e s of o f gold. gold. 57, tons The ore o r e zones z o n e s occur o c c u r within w i t h i n the t h e northeast n o r t h e a s t (0200) ( 0 2 0 ) trending trending JJubilee u b i l e e shear s h e a r zone. zone. ssouth. outh. They dip d i p 30° 30 to t o 40° 40 east e a s t and a n d plunge p l u n g e to t o the the The surface s u r f a c e projection p r o j e c t i o n of o f the t h e mineralization m i n e r a l i z a t i o n within w i t h i n the the i s 1800 1800 feet f e e t long l o n g and a n d 200 200 to t o 300 300 feet f e e t wide. wide. JJubilee u b i l e e shear s h e a r is Gold is finely d i s e m m i n a t e d in i n pods p o d s and a n d lenses l e n s e s of o f quartz q u a r t z within within is finely disemminated s e g m e n t s of o f the t h e shear s h e a r zone, zone, within w i t h i n the t h e Jubilee J u b i l e e Stock. Stock. segments Ore a p p e a r s to t o be b e further f u r t h e r restricted r e s t r i c t e d to t o areas a r e a s of o f carbonatized c a r b o n a t i z e d and and appears l o c a l l y silicified s i l i c i f i e d sericite s e r i c i t e and a n d chlorite c h l o r i t e schists s c h i s t s within w i t h i n the the locally w i l l provide p r o v i d e an a n overview o v e r v i e w of o f the the J u b i l e e Stock. S t o c k . Citadel C i t a d e l geologists g e o l o g i s t s will Jubilee ccurrent u r r e n t exploration e x p l o r a t i o n and a n d development d e v e l o p m e n t plan p l a n for f o r the t h e property. property. The Minto M i n t o and a n d Jubilee J u b i l e e mines mines and a n d the t h e newly newly developed d e v e l o p e d Old O l dTom' Tom1ss Zone a re p r o g r e s s i v e l y deeper d e e p e r extensions e x t e n s i o n s of o f a south s o u t h plunging p l u n g i n g zone zone Zone are progressively o f m i n e r a l i z a t i o n (Fig. ( F i g . 33). ). of mineralization a n d Jubilee J u b i l e e mines together together The Minto and p r o d u c e d 37, 37, 6678 7 8 oounces u n c e s oof f g o l d and a n d 1, 1, 123 u n c e s oof f ssilver i l v e r bbetween etween produced gold 123 oounces 1929 and a n d 1944. 1944. STOP 4: STOP 4: JUBILEE SHEAR JUBILEE SHEAR (OLD (OLD TOM' TOM' S ZONE) ZONE) - - East E a s t side s i d e of o f South S o u t h end e n d of o f Jubilee J u b i l e e Lake, Lake, on o n lower lower Hillside, H i l l s i d e , 20 2 0 m North N o r t h of o f South S o u t h end e n d of o f llake, a k e , Surluga Surluga Road follows f o l l o w s West Shore S h o r e of o f Jubilee J u b i l e e Lake Lake -- The south s o u t h end e n d of o f Jubilee J u b i l e e Lake provides p r o v i d e s an a n excellent e x c e l l e n t perspective perspective on tthe h e eroded e r o d e d lineament l i n e a m e n t that t h a t forms forms the t h e surface s u r f a c e expression e x p r e s s i o n of o f the the JJubilee u b i l e e shear s h e a r zone. zone. An abandoned decline d e c l i n e of o f unknown depth depth meters), on tthe ((exceeding e x c e e d i n g ttwenty wenty m e t e r s ) , aand n d aage, g e , on h e ssoutheast o u t h e a s t sside i d e of of Jubilee J u b i l e e Lake was the t h e site s i t e of o f early e a r l y mining m i n i n g of of a a quartz q u a r t z lens l e n s within within �- 12 12 —- — the the Jubilee J u b i l e e shear. shear. The site s i t e provides p r o v i d e s aa good good introduction i n t r o d u c t i o n to t o the t h e character c h a r a c t e r of of the the The quartz q u a r t z veins v e i n s that t h a t are a r e typical t y p i c a l of of the t h e Wawa Wawaarea. area. F e a t u r e s to t o note note Features are a r e the t h e sharp s h a r p contacts c o n t a c t s of of the t h e veins v e i n s and and host h o s t rock, r o c k , reverse reverse fault fault movement indicators, i n d i c a t o r s , the t h e fine f i n e to t o medium medium grained, g r a i n e d , recrystallized recrystallized movement form form of of the t h e quartz, q u a r t z , the t h e general g e n e r a l scarcity s c a r c i t y of of suiphides, s u l p h i d e s , rare rare visible v i s i b l e gold g o l d on on intergrain i n t e r g r a i n boundaries b o u n d a r i e s and and adjacent ad-j a c e n t to t o suiphides, sulphides, and the t h e unusual u n u s u a l odour odour released r e l e a s e d on on breakage b r e a k a g e of of the t h e quartz. quartz. and The The l a t t e r appears a p p e a r s to t o be be characteristic c h a r a c t e r i s t i c of of gold g o l d bearing b e a r i n g quartz q u a r t z veins veins latter in i n the t h e area a r e a and and consists c o n s i s t s of of aa pungent pungent garlic g a r l i c odour, odour, possibly p o s s i b l y aa m e r c a p t a n or o r another a n o t h e r gas gas from from inclusions i n c l u s i o n s in i n the t h e quartz. quartz. mercaptan Recent Recent surface s u r f a c e prospecting p r o s p e c t i n g and and channel c h a n n e l sampling s a m p l i n g of of the t h e vein vein in i n the t h e vicinity v i c i n i t y of of the t h e decline d e c l i n ehas hasyielded y i e l d e dupuptot o0.0. 65 65 oz. oz. Au/ton Au/ton over o v e r aa width w i d t h of o f five f i v e feet. feet. The average a v e r a g e assay a s s a y result r e s u l twas was0.0.26 26 The oz. Au/ton. 02. Au/ton. The The vein v e i n strikes s t r i k e s 0200 020Âand and dips d i p s 37° 37' southeast. southeast. C i t a d e l Gold Gold Citadel Mines Mines Inc. I n c . has has identified i d e n t i f i e d the t h e vein v e i n underground underground as a s part p a r t of of the t h e Old Old Tom' Zone, tthe Tom'ss Zone, h e aapparent p p a r e n t down-plunge down-plunge extension e x t e n s i o n of of the t h e Jubilee Jubilee Mine Mine orebody orebody (Fig. ( F i g . 3). 3). STOP STOP5:5: PARKHILL PARKHILL MINE M I N E (PAST (PASTPRODUCER) PRODUCER) - Mine Mine Gate Gate is i s on on West West side s i d e of of Surluga S u r l u g aRoad, Road, of of Citadel C i t a d e l Mine Mine -- - km South South 44 km The The Parkhill P a r k h i l l Mine Mine was was the t h e largest l a r g e s t gold g o l d producer p r o d u c e r in i nthe t h eWawa Wawaarea. area. It I t produced produced aa total t o t a l of of 54,301 5 4 , 301 ounces ounces of of gold g o l d and and 2,896 2, 896 ounces ounces of of silver s i l v e r from from 125, 125, 778 ttons o n s of of ore o r e milled, m i l l e d , yielding y i e l d i n g an a n average a v e r a g e grade grade of 0. 4 3 2 oz.Au/ton. oz. Au/ton. of 0.432 The The earliest e a r l i e s t production p r o d u c t i o n reported r e p o r t e d was was 16.8 16. 8 �13 — - 13 — oz. o of f gold g o l d from from 99 tons t o n s of of ore o r e in i n 1904. 1904. Mining stopped s t o p p e d until until 1929 and then t h e n resumed resumed from from 1931 1931 through t h r o u g h 1938. 1938. P r o d u c t i o n peaked Production iin n 1935 1935 with w i t h 9, 9, 618. 618. 77 ounces e c o v e r e d from from 20, 20, 871 o n s milled. milled. ounces rrecovered 871 ttons S u r f a c e clean-up c l e a n - u p from from 1940 1940 to t o 1944 1944 yielded y i e l d e d additional a d d i t i o n a l gold. gold. Surface Mine development ) iincluded n c l u d e d 14 llevels e v e l s to to a a vertical vertical development (Fig. ( F i g . 44) depth d e p t h of o f 1,1,244 2 4 4 ft. f t .,, 30, 000 ft. 30,000 f t . of of drifting, drifting, cutting, c u t t i n g , and and 5,000 5 , 0 0 0 ft. f t . of raises. raises. fft. t. inclined i n c l i n e d shaft. shaft. 4 , 000 ft. 4, 000 ft. of cross of cross Access of a 1,877 1, 877 Access was was by way of Extensive E x t e n s i v e development in i n this t h i s style s t y l e was was ttypical y p i c a l of o f the t h e narrow-vein n a r r o w - v e i n gold g o l d mines mines of of that t h a t era. era. The property property remained r e m a i n e d dormant until u n t i l Dunraine Dunraine Mines Mines Ltd. Ltd. began a a modern modern surface surface and underground u n d e r g r o u n d exploration e x p l o r a t i o n program program in i n 1980. 1980. The main gold-bearing g o l d - b e a r i n g quartz q u a r t z veins v e i n s are a r e a series s e r i e s of of quartz quartz lenses l e n s e s of o f short s h o r t strike s t r i k e length l e n g t h (up ( u p to t o 125 125 feet) f e e t ) and and more more extensive extensive down dip d i p dimension, d i m e n s i o n , approximately a p p r o x i m a t e l yin i nthe t h eratio r a t i oofof1:1:4. 4. The quartz width q u a r t z llenses e n s e s have an a n average average w i d t h of of two feet f e e t and a maximum maximum width w i d t h of o f six s i x feet. feet. occupy a zone of of iintense They occupy a zone n t e n s e schistosity schistosity 0 0 0 that t h a t strikes s t r i k e s 090 0 9 0 and dips d i p s 30 3 0 tto o 48 4 8 to t o the t h e south, s o u t h , crosscutting crosscutting metavolcanic m e t a v o l c a n i c and and metasedimentary m e t a s e d i m e n t a r y host h o s t rocks r o c k s that t h a t strike s t r i k e 0500 050 tto o 070°. 0 70. The h o s t rocks r o c k s are a r e Jubilee J u b i l e e Tuff Tuff and a polymictic p o l y m i c t i c volcanic volcanic host breccia b r e c c i a in i n the t h e vicinity v i c i n i t y of of the t h e Jubilee J u b i l e e Stock S t o c k (Sage, (Sage, in i n press). press). Goldun Age Resources R e s o u r c e s entered e n t e r e d a joint j o i n t venture v e n t u r e in i n 1986 1986 with with Dunraine D u n r a i n e Mines Mines Ltd. Ltd. and completed an a n extensive e x t e n s i v e evaluation e v a l u a t i o n of of the the underground workings to u n d e r g r o u n d workings t o the t h e 7th 7 t h level l e v e l to t o test t e s t a proposed p r o p o s e d model model of of paleoplacer p a l e o p l a c e r gold g o l d concentration c o n c e n t r a t i o n and and to t o test t e s t the t h e potential p o t e n t i a l for f o r gold gold rrecovery e c o v e r y by stope/drift s t o p e / d r i f t washing washing and and tailings t a i l i n g s processing. processing. ttest e s t yielded y i e l d e d ore. ore. Neither N either The program iincluded n c l u d e d more tthan h a n 13,000 1 3 , 0 0 0 feet f e e t of of underground u n d e r g r o u n d diamond diamond drilling. drilling. �It, C. -, (I) C, 0 CD :IJcc CD (I) C CD a CD (I) a 0 -' Shaft, drift, and slope dimensions exaggerated for clarity (0 • ' a (Dunraine Mines Ltd. 198 1 Annual Report) :3 :3 CD 0 2 CD CD () (0 CD :3- CD C (C -fl Figure 4. Parkhill Mine - 1938 Development Plan �- 15 15 - — — Subsurface S u b s u r f a c e geology observed o b s e r v e d by by the t h e author a u t h o r to t o the t h e 3rd 3 r d level level and reported E. r e p o r t e d on on the t h e 7th 7 t hlevel l e v e lbybyJ.J.E. communication, communication, T i l l s l e y (personal (personal Tillsley s dominated by a massive, massive, fine f i n e grained grained 1987) iis t u f f , that t h a t is i s devoid d e v o i d of of sedimentary s e d i m e n t a r y structure, s t r u c t u r e , and and is is tuff, s t r a t i g r a p h i c a l l y below below massive massive to t o pillowed p i l l o w e d mafic m a f i c flows. flows. stratigraphically A A f r a g m e n t a l unit, u n i t , consisting c o n s i s t i n g of of coarse c o a r s e lapilli l a p i l l i to t o bomb bomb sizes, sizes, fragmental occurs o c c u r s at a t the t h e east e a s t end end of of the t h e mine. mine. t r a n s i t i o n of of clast c l a s t shape shape A transition to t o a flattening f l a t t e n i n g fabric f a b r i c marks marks aa high h i g h strain s t r a i n area, a r e a , possibly p o s s i b l y aa shear shear Lamprophyre of vvarious Lamprophyre d dikes i k e s of a r i o u s attitudes a t t i t u d e sare a rcommon. e common. This T h i s exploration e x p l o r a t i o n program program concluded concluded tthat h a t no no mineable mineable ore ore zone. zone. remains remains it. it. above the t h e 14th 1 4 t h level, l e v e l , although a l t h o u g h ore o r e potential p o t e n t i a l exists e x i s t sbelow below The quartz q u a r t z veins v e i n s were were well w e l l explored e x p l o r e d and and completely c o m p l e t e l y mined mined by by previous p r e v i o u s workers, w o r k e r s , leaving l e a v i n g only o n l y minor minor ppillars. illars. concluded concluded The program lso The program aalso that t h a t the t h e gold g o l d recovery r e c o v e r y potential p o t e n t i a l from from subsurface s u b s u r f a c e clean— clean- up is i s minor minor due due to t o low low volume. volume. Sampling the t h e surface s u r f a c e muck muck piles piles and tailings t a i l i n g s yielded y i e l d e d an a n average a v e r a g e of of 0.01 0. 0 1 oz.Au/ton oz. Au/ton and and aa maximum maximum of of 0.025 0. 025 oz.Au/ton. oz. Au/ton. The original o r i g i n a l fieldtrip f i e l d t r i p examined examined two two outcrops o u t c r o p s of of metagreywacke metagreywacke (water—laid ( w a t e r - l a i d ttuff?) u f f ? ) that t h a t contain c o n t a i n truncated t r u n c a t e d bedding bedding and and minor minor crossbedding. crossbedding. Recent overburden o v e r b u r d e n stripping s t r i p p i n g reveals r e v e a l s these t h e s e rocks r o c k s to to be clastic c l a s t i c metasediments or o r crystal c r y s t a l tuffs t u f f s interbedded i n t e r b e d d e d with with coarser c o a r s e r tuff t u f f breccias b r e c c i a s and and massive massive crystal c r y s t a l and and lapilli l a p i l l i tuffs. tuffs. The The gold g o l d bearing b e a r i n g silicified s i l i c i f i e d zone zone strikes s t r i k e s east, e a s t , transecting t r a n s e c t i n g the the subvertically s u b v e r t i c a l l y dipping d i p p i n g pyroclastic p y r o c l a s t i c rocks r o c k s at a t aa low low angle. angle. A late late lamprophyre dike d i k e occupies o c c u p i e s the t h e centre c e n t r e of of the t h e shear s h e a r zone zone and and has has aa fenitized f e n i t i z e d alteration a l t e r a t i o n halo h a l o parallel p a r a l l e l to t o it. it. The The zone zone of of alteration alteration consists c o n s i s t s of of replacement r e p l a c e m e n t of of quartz q u a r t z by by aa blue b l u e sodic s o d i c iron i r o n amphibole amphibole �- 16 16 —- — ( x - r a y diffraction d i f f r a c t i o nidentification identification Sage, personal personal bybyR.R.P.P. Sage, (x-ray communication, communication, STOP 6: 6: STOP I988 ) 1988). . MONK DEFORMATION DEFORMATION ZONE ZONE MONK - - Stripped Stripped Area 10 10 mm West West of of Monk Monk Access Access Road, Road, 0. 0 . 55 km km Area South of of Access Access Road Road Intersection I n t e r s e c t i o n with w i t h High High Falls F a l l s Road Road -South O b s e r v a t i o n s in i n the t h e vicinity v i c i n i t y of o f the t h e Monk Monk Prospect P r o s p e c t (see ( s e e Stop S t o p 7) 7) Observations and several s e v e r a l other o t h e r less l e s s developed d e v e l o p e d prospects p r o s p e c t s suggest s u g g e s t that t h a t the t h e area area and i s part p a r t of of aa wide wide zone zone of of highly h i g h l y strained s t r a i n e d metavolcanic m e t a v o l c a n i c rocks, rocks, is The The Monk Monk zone zone has has here h e r e named named the t h e Monk Monk deformation d e f o r m a t i o n zone zone (Fig. ( F i g . 5). 5). aa minimum minimum width w i d t h of of one one kilometre k i l o m e t r e and and aa strike s t r i k e length l e n g t h of of over over Its I t s strike s t r i k e varies v a r i e s slightly s l i g h t l y but b u t is i s consistently consistently t h r e e kilometers. kilometers. three a b o u t 1400 140 and and its i t s dip d i p is i s vertical. vertical. about The The deformation d e f o r m a t i o n zone zone will will be be examined examined at a t this t h i s site s i t e in i n order o r d e r to t o compare compare its i t s features f e a t u r e s here, h e r e , aa barren b a r r e n prospect, p r o s p e c t , with w i t h those t h o s e at a t the t h e Monk Monk Prospect, P r o s p e c t , a gold g o l d occurrence. occurrence. The deformation d e f o r m a t i o n zone zone as a s viewed viewed at a t this t h i s stop s t o p is i s characterized characterized by intensely i n t e n s e l y flattened f l a t t e n e d breccia b r e c c i a fragments fragments of of quartz q u a r t z feldspar feldspar s e r i c i t e schist. schist. sericite The The abundance abundance of of sericite s e r i c i t e suggests s u g g e s t s aa felsic felsic composition c o m p o s i t i o n for f o r the t h e protolith. protolith. ratios r a t i o s from from4:4:11to t o14: 14:1. 1. The fragments f r a g m e n t s exhibit e x h i b i t flattening flattening Both the t h e fragments f r a g m e n t s and and the t h e matrix matrix contain c o n t a i n abundant abundant euhedral e u h e d r a l feldspar f e l d s p a r megacrysts, megacrysts, 1 cm cm by by 22 mm. mm. 1 Concordant Concordant with w i t h the t h e foliation f o l i a t i o n are a r e narrow narrow zones, zones, up up to t o 10 10 cm cm wide, wide, of of foliated f o l i a t e d mafic m a f i c tuff t u f f (?), (?), a c r o s s the t h e outcrop. outcrop. across continuous continuous for f o r their t h e i r strike s t r i k e length length The tectonic t e c t o n i c preservation p r e s e r v a t i o n of of such such ustratigraphy?t " s t r a t i g r a p h y " iis s cconsistent o n s i s t e n t throughout t h r o u g h o u t the t h e deformation d e f o r m a t i o n zone. zone. Remnants of of prep r e - or o r syn-deformation s y n - d e f o r m a t i o n quartz q u a r t z veining v e i n i n g are are recorded r e c o r d e d by dismembered and and ptygmatically p t y g m a t i c a l l y folded f o l d e d narrow narrow vein vein �P++! g g a nite S mafic metavolcafliCS Figure 5. Monk Deformation Zone - Michipicoten River Area Gold Occurrences WAWA felsic metavolcaniCS felsic intrusive A prospect (orientation unknown) prospect (orientation known) deformation zone boundary (position approximate) past producing mine (orientation known) �- 18 18 —- — segments and and tear t e a r drop d r o p shaped s h a p e d quartz q u a r t z nodules. nodules. segments The nodules n o d u l e s have have The c u r v e d tails t a i l s or o r sigmoidal s i g m o i d a l shapes s h a p e s that t h a t indicate i n d i c a t e rotational rotational curved movement but b u t they t h e y do do not n o t provide p r o v i d e consistent c o n s i s t e n t kinematic kinematic movement information. information. Z - f o l d s up up to t o 20 20 cm cm amplitude a m p l i t u d e within w i t h i n the t h e sericite sericite Z-folds schist s c h i s t plunge p l u n g e 50° 5 0 to t o the t h e southeast. southeast. Intersection I n t e r s e c t i o n lineations l i n e a t i o n s in in t h e schist s c h i s t also a l s o plunge p l u n g e southeast s o u t h e a s t but b u t more more steeply, s t e e p l y , 70° the 7 0 to t o 75°. 75. Minor Minor quantities q u a n t i t i e s of o f suiphide s u l p h i d e mineralization m i n e r a l i z a t i o n accompany accompany some some of of t h e quartz q u a r t z veins v e i n s however however no no gold g o l d has h a s been been reported r e p o r t e d from from this t h i s part part the of the t h e deformation d e f o r m a t i o n zone. zone. of 7: STOP 7: STOP MONK PROSPECT PROSPECT MONK - - Total Total NW of of S Scott Trenches, T r e n c h e s , Stripping, S t r i p p i n g , and and Adit, A d i t , 300 3 0 0 in m NW c o t t Falls F a l l s -- production p r o d u c t i o n from from several s e v e r a l bulk-sampling b u l k - s a m p l i n g programs, programs, since s i n c e gold gold was was discovered d i s c o v e r e d on on the t h e property p r o p e r t y in i n 1936, 1936, has h a s been been less l e s s than t h a n 100 100 ounces. ounces. The last l a s t exploration e x p l o r a t i o n program program ended ended in i n 1987, 1987, and and the the property p r o p e r t y is i s currently c u r r e n t l y dormant. dormant. Gold Gold mineralization m i n e r a l i z a t i o n is i s concentrated c o n c e n t r a t e d in i n aa series s e r i e s of of en e n echelon echelon quartz q u a r t z veins v e i n s which which strike s t r i k e 050° 050' and and dip d i p 45° 45' northwest. northwest. Assays Assays from early e a r l y surface s u r f a c e and and recent r e c e n t subsurface s u b s u r f a c e sampling s a m p l i n g consistently consistently y i e l d e d 0. 0. 5 ounce g o l d per p e r ton. ton. yielded ounce gold Tonnage calculations c a l c u l a t i o n s are a r e not not available. available. The shallow-dipping, s h a l l o w - d i p p i n g , northeast-trending n o r t h e a s t - t r e n d i n g mineralized m i n e r a l i z e d veins veins transect transect a a zone zone of of weakly weakly mineralized m i n e r a l i z e d quartz-carbonate q u a r t z - c a r b o n a t e veins v e i n s (the (the "main m a i n zone") z o n e " ) that t h a t are a r e concordant c o n c o r d a n t with w i t h the t h e regional r e g i o n a l southeastsoutheasts t r i k i n g foliation. foliation. striking The The zone zone consists c o n s i s t s of of a a 33 to t o 44 m m wide section section of of vertical v e r t i c a l quartz q u a r t z veins v e i n s and and stringers, s t r i n g e r s , which which are a r e contained contained �- 19 1 9 —- — within w i t h i n aan n iintensely n t e n s e l y sericitized, s e r i c i t i z e d , carbonatized, c a r b o n a t i z e d , and silicified silicified host h o s t rock. rock. d e g r e e of of alteration a l t e r a t i o n obscures o b s c u r e s host h o s t rock rock The degree i d e n t i f i c a t i o n ; however property p r o p e r t y mapping mapping suggests s u g g e s t s an a n intermediate intermediate identification; t o mafic m a f i c volcanic v o l c a n i c assemblage. assemblage. to The "main " main zone" zone" and the t h e associated a s s o c i a t e d shallow-dipping s h a l l o w - d i p p i n g mineralized mineralized veins v e i n s occur o c c u r at a t the t h e apparent a p p a r e n t southwestern s o u t h w e s t e r n margin margin of of aa regional regional of intense i n t e n s e flattening f l a t t e n i n g strain, s t r a i n , the t h e Monk Monk deformation d e f o r m a t i o n zone zone (cf, (cf, zone of S t o p 6). 6). Stop SSTOP T O P 8: 8: CENTENNIAL STOCK - - Roadside Outcrop Hill H i l l 1 km km N of of High Falls F a l l s -1 The Centennial km The C e n t e n n i a l Stock S t o c k occupies o c c u p i e s 77 sq. sq. k m of of tthe h e northwest n o r t h w e s t corner corner of of Naveau Township and and adjacent a d j a c e n t McMurray McMurray Township Township to t o the t h e north north Fig. 1 & 5). 5). 1 Itt consists white I c o n s i s t s of of a grey g r e y to to w h i t e granodiorite g r a n o d i o r i t e to to t r o n d h j e m i t e , massive massive to t o weakly foliated f o l i a t e d and and medium medium to t o coarse coarse trondhjemite, grained. g rained. distinguished presence IIt t iis s d i s t i n g u i s h e d by the the p r e s e n c e of of grey-blue g r e y - b l u e to to opalescent o p a l e s c e n t quartz-eye q u a r t z - e y e phenocrysts p h e n o c r y s t s that t h a t are a r e up up to t o 33 mm mm diameter. diameter. On its i t s southwest s o u t h w e s t margin, margin, massive massive granodiorite g r a n o d i o r i t e grades g r a d e s into i n t o aa fine fine porphyry. grai g r a i nned e d graniti g r a n i t icc quartz q u a r t z-p1 - p lagi a g i oocl c l aas s e e porphyry. dikes d i k e s occur o c c u r within w i t h i n the t h e stock. stock. Graniti G r a n i t i c apli a p l i ttee Small xenoliths m)) of x e n o l i t h s (up ( u p to t o 0. 0. 5 m mafic m a f i c metavolcanic m e t a v o l c a n i c flows flows are a r e also a l s o common, common, but b u t not n o t abundant. abundant. Felsic xenoliths F elsic x e n o l i t h s have not n o t been observed, o b s e r v e d , even though t h o u g h the t h e stock stock iintrudes n t r u d e s felsic f e l s i c metavolcanics. metavolcanics. (Fig. (Fig. 66)) A series s e r i e s of of discrete d i s c r e t e shears s h e a r s strikes s t r i k e s southeast s o u t h e a s t (1400) (1 4 0 ) across a c r o s s the t h e stock. stock. They are wide) a r e usually u s u a l l y narrow (<10 ( < 10 cm cm w i d e ) zones of of iintensely n t e n s e l y foliated, f o l i a t e d , black b l a c k cataclastic c a t a c l a s t i c rock. rock. Quartz Q u a r t z eyes are are �'- — 7Q, / 0 V till Ii 45 2 cw 2 nI%tl \\ 'tIIflltt' 7/ p7 / 2 Qv 2 I // 70/ 60 1) / 1 OU.4P -- 80 1IN \ThIflhi rut //open cut Ov/ - 70 (l/llhJIIII1ENTENNiAL UV MINE 2 V 0 - 7/ I 100 ft. ft. /i 2 •75 'I meters rnc>lers 80 LAMPROPHYRE DIKE DIKE LAMPROPHYRE DIABASE DIKE DIKE DIABASE 2 Th\ 100 100 00 CENTENNIALSTOCK STOCK CENTENNIAL granodlortte granodiorite XENOLITHS MAFIC XENOLITHS MAFIC Shaft )iiPit -1'Trench -i-I / 2,1 2 Field Trip Stop '3 —— ——— 2 Figure 6. Centennial CentennialMine Mine - Surface Surface Geology Geology Figure (afterWAWA WAWA ASSESSMENT ASSESSMENT FILE FILE 'iVP 1985) (after WP NaveauNaveau-1.t. S.M SM. Sears, t985) �- 21 21 — - — preserved p r e s e r v e d within w i t h i n them them and and the t h e feldspars f e l d s p a r s are a r e fractured f r a c t u r e d and and Where they t h e y have have been been mapped mapped in i n the t h e Centennial C e n t e n n i a l Mine Mine stretched. stretched. area a r e a (Fig. ( F i g . 6) 6 ) they t h e y are a r e spaced s p a c e d about a b o u t 100 100 m apart a p a r t and and have have strike strike lengths l e n g t h s of o f several s e v e r a l hundred hundred meters. meters. is i s unknown. unknown. Their T h e i r sense s e n s e of of displacement displacement Quartz Q u a r t z veins v e i n s of of the t h e same same orientation o r i e n t a t i o n and and up up to t o aa metre m e t r e in i n width w i d t h occupy occupy portions p o r t i o n s of of several s e v e r a l of of the t h e shears. shears. These These veins v e i n s host h o s t the t h e known known gold g o l d mineralization m i n e r a l i z a t i o n within w i t h i n the t h e stock s t o c k (Fig. ( F i g . 55 6). && 6). The Centennial C e n t e n n i a l Stock S t o c k hosts h o s t s two two minor minor past p a s t producing p r o d u c i n g gold gold mines: mines: the t h e Norwalk Norwalk Mine, Mine) 60 ounces ounces (1904 (1904 & 1910), 1 9 1 0 ) 1 and and the the ounces of Centennial C e n t e n n i a l Mine, Mine) 510 ounces ounces of of gold g o l d and 30 ounces of silver s i l v e r from 8 6 1 2 tons t o n s of of ore o r e (1939) ( 1 9 3 9 ) (Fig. ( F i g . 55 && 6). 6). 8612 Both mines mines were shallow shallow operations o p e r a t i o n s with w i t h their t h e i r deepest d e e p e s t drifts d r i f t s at a t 200 200 feet f e e t and and 250 250 feet, feet) respectively. respectively. Historical H i s t o r i c a l information i n f o r m a t i o n on on these t h e s e operations o p e r a t i o n s is is sparse s p a r s e but b u t it i t suggests s u g g e s t s that t h a t mining mining ceased c e a s e d for f o r financial, financial) management, management) and/or a n d / o r labour l a b o u r reasons r e a s o n s rather r a t h e r than t h a n ore o r e depletion. depletion. Although A l t h o u g h the t h e shear-vein s h e a r - v e i n system s y s t e m of of the t h e Centennial C e n t e n n i a l Stock S t o c k has has yielded significant quantities of gold, it is analogous in n o t y i e l d e d s i g n i f i c a n t q u a n t i t i e s of g o l d ) i t i s a n a l o g o u s i n not many many r respects e s p e c t s tto o the t h e mineralization m i n e r a l i z a t i o n at a tthe t h eMagino Magino Mine, MineI in in production production near n e a r Goudreau Goudreau since s i n c e 1988. 1988. The most noteable noteable difference, d i f f e r e n c e ) in i n addition a d d i t i o n to t o gold g o l d content, c o n t e n t ) is i s the t h e absence a b s e n c e of of The Maginoo ore The Magino r e iis s within within siliceous thet hWebb s i l i c e o u s zones zones and and veins v e i n s of ofthe t h esheared s h e a r e dportion p o r t i o nofof e WebbLake Lake byssericite i t is i s accompanied accompanied by e r i c i t e and and t r o n d h j e m i t e stock s t o c k and and it trondhjemite a l t e r a t i o n in i n the t h e Centennial C e n t e n n i a l Stock. Stock. alteration potassium potassium feldspar f e l d s p a r alteration. alteration. �- — STOP 9: STOP 9: 2222 — - BRIDGET LAKE STOCK & IIRON R O N FORMATION - - Rock C u t and a n d Surface S u r f a c e Stripping, S t r i p p i n y , SE SE Side S i d e of o f Highway Highway 17, 17, Cut 112 2 kkm m S o u t h of o f Turnoff T u r n o f f to t o Wawa Wawa -South This T h i s stop s t o p displays d i s p l a y s the t h e character c h a r a c t e r of o f the t h e Bridget B r i d g e t Lake Stock S t o c k and and i t s unusual u n u s u a l intrusive i n t r u s i v e relationship r e l a t i o n s h i p with with a a magnetite-chert m a g n e t i t e - c h e r t iron iron its fformation o r m a t i o n and a n d mafic m a f i c flows. flows. IIt t iis s aalso l s o tthe he s ite o f a a high h i g h grade grade site of g old o c c u r r e n c e l related r e l a t e d to t o shearing s h e a r i n g within w i t h i n the t h e iron i r o n formation. formation. gold occurrence, The Bridget B r i d g e t Lake Stock S t o c k is i s a quartz q u a r t z feldspar f e l d s p a r porphyry p o r p h y r y that t h a t has has aa ssurface u r f a c e expression e x p r e s s i o n of o f about a b o u t 22 sq. sq. km. km. I t outcrops o u t c r o p s about about 6 6 km km It s o u t h of o f the t h e mouth mouth of o f the t h e Michipicoten M i c h i p i c o t e n River R i v e r (Fig. ( F i g . 1). 1). south Its Its c o m p o s i t i o n l texture t e x t u r e and a n d intrusive i n t r u s i v e relationships r e l a t i o n s h i p s here h e r e and a n d at a t the the composition, next n e x t stop s t o p suggest s u g g e s t that t h a t it i t is i s aa high h i g h level, l e v e l ) subvolcanic s u b v o l c a n i c intrusive. intrusive. The stock s t o c k consists c o n s i s t s of o f aa medium medium grained g r a i n e d feldspar f e l d s p a r porphyry p o r p h y r y with with minor m i n o r blue b l u e quartz q u a r t z eyes. eyes. The feldspar f e l d s p a r phenocrysts p h e n o c r y s t s are a r e white white andesine 1 cm in a n d e s i n e laths, l a t h s ) subhedral s u b h e d r a l to t o euhedral e u h e d r a l and a n d up to to 1 i n length, length) in i n a fine f i n e grained g r a i n e d ground g r o u n d mass mass of o f quartz q u a r t z and a n d feldspar f e l d s p a r and a n d minor minor amounts of o f chlorite, c h l o r i t e l calcite, c a l c i t e ) sericite, s e r i c i t e ) and a n d sphene. sphene. phenocrysts p h e n o c r y s t s are a r e anhedral a n h e d r a l and a n d clear. clear. The quartz quartz The porphyry p o r p h y r y texture t e x t u r e is is generally g e n e r a l l y massive m a s s i v e except e x c e p t where it i t is i s strongly s t r o n g l y foliated f o l i a t e d in i n local local sshear h e a r zones. zones. (Massey, (Massey) 1985) 1985 1 The iron i r o n formation f o r m a t i o n consists c o n s i s t s of o f alternating a l t e r n a t i n g layers l a y e r s of o f chert chert and a n d magnetite m a g n e t i t e in i n thicknesses t h i c k n e s s e s that t h a t vary v a r y from from 11 mm mm to t o 5-10 5-10 cm, cmJ aand nd up to t o >30 > 3 0 cm cm for f o r some some•chert c h e r t layers. layers. ffrom r o m 20% 20% to t o 70%. 70%. The magnetite m a g n e t i t e content c o n t e n t varies varies Grunerite as of G r u n e r i t e occurs occurs a s sspheroids pheroids o f radiating radiating ffibres i b r e s in i n some chert-magnetite c h e r t - m a g n e t i t e laminae. laminae. The iron i r o n formation f o r m a t i o n layering l a y e r i n g is i s commonly commonly contorted c o n t o r t e d into into �— - 23 23 — - complex flow(?)-folding  £ l o w ( ?- f o l d i n g or o r planar p l a n a r disruptions. disruptions. IIt t iis s concordant concordant and a n d interfolded i n t e r f o l d e d with w i t h a massive m a s s i v e mafic m a f i c flow f l o w at a t the t h e northeast n o r t h e a s t end e n d of of tthe h e roadcut. roadcut. t llies i e s ssubhorizontally u b h o r i z o n t a l l y on o n the t h e upper upper F u r t h e r ssouth o u t h iit Further surface s u r f a c e of o f the t h e porphyry. porphyry. o r p h y r y discordantly d i s c o r d a n t l y intrudes i n t r u d e s the the The p porphyry mafic m a f i c flow f l o w but b u t does d o e s not n o t display d i s p l a y a clearly c l e a r l y intrusive i n t r u s i v e contact c o n t a c t with with the t h e overlying o v e r l y i n g folded f o l d e d iron i r o n formation. formation. Coarse C o a r s e ggrained r a i n e d visible v i s i b l e gold g o l dwas was exposed e x p o s e d in i n 1981 1981 by by trenching trenching adjacent 30 mmssoutheast a d j a c e n t to t o aa pit p i of t ounknown f unknown vintage, v i n t a g e , 30 o u t h e a s t oof f the the highway. The gold g o l d occurs o c c u r s in i n aa vertical v e r t i c a l bed bed of o f sheared, sheared, rrecrystallized e c r y s t a l l i z e d chert. chert. The shear s h e a r zone z o n e is is a a few few centimeters c e n t i m e t e r s wide wide where it aand n d iis s ttraceable r a c e a b l e to t o the t h e vertical v e r t i c a l roadcut r o a d c u t where i t is i s exposed e x p o s e d in in the t h e underlying u n d e r l y i n g porphyry p o r p h y r y as a s aa zone zone of o f intense i n t e n s e foliation, f o l i a t i o n , without without ssilicification i l i c i f i c a t i o n or o r any a n y gold g o l d mineralization. mineralization. RANSON MINE RANSON M I N E (PAST (PAST PRODUCER) PRODUCER) STOP STOP 10: 10: -- km Bush Bush Roadf Road, Accesa Access Road Road B Begins End of 1. 1. 6 6km e g i n s aatt NW South Side S i d e of of Highway Highway 17, 17/ 11 kkm m S o u t h of o f Turnoff T u r n o f f to t o Wawa Wawa -- The Ranson Ranson Mine Mine (Fig. ( F i g . 7) 7 ) consisted c o n s i s t e d of of aa 200 2 0 0 ft. f t . adit a d i t along a l o n g the t h e HH vein v e i n and a n d aa stope s t o p e raise r a i s e to t o surface. surface. All A l l development d e v e l o p m e n t work and and mining m i n i n g occurred o c c u r r e d during d u r i n g aa few few months months in i n 1939. 1939. An on on site s i t e mill m i l l processed p r o c e s s e d 774 774 tons t o n s of o f ore o r e and a n d recovered r e c o v e r e d 156 156 ounces o u n c e s of o f gold g o l d for for a a grade g r a d e of o f 0.0. 20 20 oz. 02. /ton. /ton. The property p r o p e r t y was dormant d o r m a n t until u n t i l acquired a c q u i r e d by Bridget B r i d g e t Lake Lake Resources R e s o u r c e s in i n 1982. 1982. The company built b u i l t an a n access a c c e s s road r o a d and and prospected p r o s p e c t e d the t h e vein v e i n systems s y s t e m s known known from from early e a r l y records. records. Visible Visible gold was d discovered g o l d was i s c o v e r e d on o n the t h e E vein v e i n and a n d several s e v e r a l ounces o u n c e s recovered recovered from mill. f r o m hand h a n d cobbed c o b b e d samples s a m i l e s with w i t h the t h e use u s e of o f aa portable p o r t a b l e mill. In In �l/ /2 I / I / 2; 2/ / GABBRO F / •2m / —— \ dsz I \lOcm 20-30cm / \\EVf JIN '.23 B.VEIN,toocm / 0Ocm I C-VEIN / / / / m I' I / / 80cm 80co lS0c/ / / / ' // 1 --_ ,.. QFP' /0 V El raIse 30cm / I-. / -• vein I I / / GAB8RO aim —._ - ---i F/ / (WAWA ASSESSMENr FItE WPIabao 10 FinNeth Eioio,ation Inc, 3 LuLes 198?) / H VEIN Figure 7. m H.vElN;cH Ouaitz rekispar Porphyry iron Formation / /: GABERO P GEOLOGY & VEIN WIDTHS / 1L /OFF A / / I BRlDTL PESOUES INC veflohithis / MhCROGA8BAO / ?aocm IF QFP / T..1 "!jocm / F VEIN with —— '— \AICROGABBRO ero ma / 2/ () I / / MICROGAa ./ a S .-.. --.r / I / / / ' p GABORO ICROG8BR9 QFP I &I 2/ / 'MEDtUM GRAINED / GAB8RO / / '. I / / / / / ". / / / OFF / / / ".. _..f / // /'' 1-a-Si -. �— - 25 25 —- addition, a ddition, a b o u t 35 ounces were recovered r e c o v e r e d from 188 188 tons t o n s test test about milled m i l l e d by by Pamour Pamour Mines Mines Ltd. Ltd. in i n Timmins. Timmins. The veins v e i n s are a r e hosted h o s t e d by the t h e Bridget B r i d g e t Lake Stock S t o c k quartz quartz ffeldspar e l d s p a r porphyry p o r p h y r y and and gabbro g a b b r o (Fig. ( F i g . 7). 7). two stocks: stocks: o r p h y r y is i s mapped mapped as as The p porphyry a e s t e r n body of o f grey, grey, h e t e r o g e n e o u s quartz q u a r t z feldspar feldspar a w western heterogeneous porphyry p o r p h y r y that t h a t contains c o n t a i n s late l a t e phase p h a s e segregations s e g r e g a t i o n s of of finer f i n e r grained grained granite g r a n i t e and xenoliths x e n o l i t h s of of mafic m a f i c and felsic f e l s i c composition; c o m p o s i t i o n ; and and an an eastern e a s t e r n iintrusion n t r u s i o n of of similar s i m i l a r composition c o m p o s i t i o n but b u t homogeneous homogeneous and and xenolith x e n o l i t h free. free. Both porphyry p o r p h y r y stocks s t o c k s are a r e intruded i n t r u d e d by by gabbro. gabbro. The gabbro gabbro v a r i e s from a coarse c o a r s e grained g r a i n e d plagioclase-pyroxene p l a g i o c l a s e - p y r o x e n e rock r o c k to t o an an varies aphanitic, a p h a n i t i c , phenocryst p h e n o c r y s t free f r e e micrograbbro m i c r o g r a b b r o in i n chilled c h i l l e d margins near near tthe h e porphyry p o r p h y r y stocks. stocks. eastern porphyry has The e astern p o r p h y r y sstock tock h a s been intruded i n t r u d e d by numerous numerous veins v e i n s and and dikes d i k e s of of microgabbro. microgabbro. Banded chert-magnetite occurs Banded c h e r t - m a g n e t i t e iron i r o n formation formation o c c u r s along a l o n g the the northern n o r t h e r n contact c o n t a c t of of the t h e quartz q u a r t z feldspar f e l d s p a r porphyry p o r p h y r y and and along a l o n g the the margins oof gabbro andddikes within s o u t h e r n margins f g a b b r o vveins e i n s and ikes w i t h i n tthe h e eastern eastern southern p o r p h y r y stock. stock. porphyry Contacts C o n t a c t s between the t h e iron i r o n formation f o r m a t i o n and the the gabbro g a b b r o are a r e reactive r e a c t i v e and and commonly commonly show brecciation b r e c c i a t i o n of of the the magnetite m a g n e t i t e layers l a y e r s by by silica s i l i c a remobilized r e m o b i l i z e d from from the t h e cherty c h e r t y beds. beds. Chioritic C h l o r i t i c alteration a l t e r a t i o n of of the t h e porphyry p o r p h y r y is i s common common and and extensive extensive adjacent a d j a c e n t to t o the t h e gabbro g a b b r o veins v e i n s and and dikes. dikes. Carbonate C a r b o n a t e alteration a l t e r a t i o n of of the t h e host h o s t is i s pervasive p e r v a s i v e within w i t h i n the t h e auriferous a u r i f e r o u s veins. veins. Sericite S e r i c i t e is is aalso l s o abundant a b u n d a n t as a s aa coating c o a t i n g on on minor minor slip s l i p planes. planes. A penetrative 1 0 5 and and dips d i p s 80° 8 0 SW, SW, p e n e t r a t i v e cleavage c l e a v a g e strikes s t r i k e s 105° paralleling p a r a l l e l i n g the t h e gabbro-iron g a b b r o - i r o n formation f o r m a t i o n contact. contact. 0 0 0 SW, quartz q u a r t z veins v e i n s strike s t r i k e 100 100" to t o 110 110" and dip d i p 80 80" S W, Shear S h e a r zone hosted hosted �— 2266 - -— cconcordant o n c o r d a n t with w i t h the t h e trend t r e n d of of the t h e shear s h e a r zone. zone. s h e a r zone zone is is The shear 70 tto o 80 meters m e t e r s wide and and has has aa dextral d e x t r a l sense s e n s e of of motion. motion. quartz vein property The q uartz v e i n systems s y s t e m s of of the the p r o p e r t y have a minimum and an a n average a v e r a g e width w i d t h of of one one a g g r e g a t e strike s t r i k e length l e n g t h of of 1000 1000 m and aggregate meter. Two meter m e t e r widths w i d t h s are a r e common common at a t depth. depth. alteration a l t e r a t i o n is i s minimal minimal to t o absent. absent. rock Wall rock Where p r e s e n t it i t is i s sericitic sericitic present in i n the t h e quartz q u a r t z feldspar f e l d s p a r porpyhry porpyhry and and chioritic c h l o r i t i c in i n the t h e gabbro. gabbro. The The veins v e i n s occupy shear s h e a r fractures f r a c t u r e s and and many many display d i s p l a y crack-seal c r a c k - s e a l zones zones to to 15 cm wide, wide, ssuggesting 1 5 cm u g g e s t i n g multiple m u l t i p l e episodes e p i s o d e s of of hydraulic h y d r a u l i c emplacement. emplacement. Exploration E x p l o r a t i o n to t o date d a t e suggests s u g g e s t s the t h e presence p r e s e n c e of of possible possible reserves, r e s e r v e s , near-surface, n e a r - s u r f a c e , of of 10,000 10, 000 to t o 30,000 30,000 tons t o n s from from the t h e D, D, and H veins v e i n s with w i t h an a n average a v e r a g e grade g r a d e 0. 0. 2 2 to t o 0. 0. 6 6 oz. oz.Au/ton. Au/ton. E, E, Large samples from tthese vein samples from h e s e vveins e i n s and and tthe he C C v e i n have have ddefined e f i n e d tthe h e gold g o l d as as fine f i n e grained, g r a i n e d , non-uniformly non-uniformly ddistributed, i s t r i b u t e d , and and primarily p r i m a r i l y associated associated with with suiphide s u l p h i d e minerals. minerals. �— 27 REFERENCES Mandziuk, Z.L. 1981, P Precambrian geology Z. L. and Studemeister, S t u d e m e i s t e r , P.A., P. 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D. and Calvert, C a l v e r t , T., T. , 1982d, 1982d, P r e c a m b r i a n geology g e o l o g y of of Chabanel Township, Township, Algoma District: D i s t r i c t : Ontario O n t a r i o Geological Geological Preliminary 840. 15,840. Survey P r e l i m i n a r yMap MapP.P.2439, 2439, Scale S c a l e1:1:15, Survey Sage, Sage, R. Geology of of Chabanel, Chabanel, Esquega, Esquega, L Lastheels R. P.P., , i in n ppress, r e s s , Geology a s t h e e l s and McMurray Townships, District of Algoma: Ontario Townships, D i s t r i c t of Algoma: O n t a r i o Geological Geological Survey Open Open File F i l e Report Report 5586, 5586, 523 523 p. p. R. R. �— 28 Sullivan, Sullivan, — R.W., 1985, U-Pb zircon R . W . , Sage, Sage, R.P., R. P . , and and Card, Card, K.D., K.D., 1985, U-Pb z i r c o n age age of tthe of h e Jubilee J u b i l e e Stock S t o c k in i n the t h e Michipicoten M i c h i p i c o t e n greenstone greenstone belt 361-365 i in Geolgical e o l g i c a l Survey b e l t near n e a r Wawa, Wawa, Ontario, O n t a r i o , p. p. 361-365 n G of Canada Paper B, 637 p. of P a p e r 85-lB. 85-lB, Current C u r r e n t Research, Research, Part P a r t B, 637 p. R. P.P., and Van Van Schmus, R., Turek, A . , Sage, R. , and Schmus, W. W. R . , 1990, 1990, Advances in in Turek, A., geochronology of of the t h e Michipicoten M i c h i p i c o t e n greenstone g r e e n s t o n e belt: belt: IInstitute n s t i t u t e on Lake Superior S u p e r i o r Geology, Geology, Proceedings P r o c e e d i n g s and and Abstracts. (in A bstracts. ( i n press) press) Turek, A . , Van Van Schmus, Schmus, W.R., W. R . , and and Sage, Sage, R.P., R. P . , 1988, 1988, Extended Turek, A., volcanism v o l c a n i s m in i n the t h e Michipicoten M i c h i p i c o t e n greenstone g r e e n s t o n e belt, b e l t , Wawa, Wawa, Ontario: Mineralogical O n t a r i o : Geological G e o l o g i c a l Association A s s o c i a t i o n of Canada Canada -- Mineralogical Association Annual Meeting, Meeting, Program w with A s s o c i a t i o n of o f Canada Annual ith Abstracts, p. 127. A b s t r a c t s , v. v. 13, 13, p. 127. Turek, 1982, Rb-Sr Rb-Sr and U-Pb A. , Smith, Smith, P.E., P. E . , and and Van Van Schmus, Schmus, W.R., W. R. , 1982, Turek, A., ages a g e s of o f volcanics v o l c a n i c s and and granite g r a n i t e emplacement emplacement in i n the t h e Michipicoten Michipicoten belt, Wawa, Ontario: O n t a r i o : Canadian Canadian Journal J o u r n a l of of Earth E a r t h Sciences, Sciences, b e l t , Wawa, v. 19, 1 9 , p. p. 1608-1626. 1608—1626. �— - 29 29 - LIST LIST OF FIGURES Figure F i g u r e 1. 1. Wawa Area General Geology and Gold Occurrences Occurrences Figure F i g u r e 2. 2. General G e n e r a l Geology of the t h e Michipicoten M i c h i p i c o t e n Greenstone G r e e n s t o n e Belt Belt Figure F i g u r e 3. 3. Citadel C i t a d e l Mine Exploration E x p l o r a t i o n and and Development Development -- JJubilee ubilee and Minto Mines Development Development Figure 4. F i g u r e 4. Parkhill 1938 Development Plan P a r k h i l l Mine -- 1938 Plan F i g u r e 5. 5. Figure Monk Deformation Michipicoten Deformation Zone Zone -- M i c h i p i c o t e n River R i v e r Area Gold Occurrences Occurrences Figure 6. F i g u r e 6. Centennial C e n t e n n i a l Mine -- Surface S u r f a c e Geology Geology Figure 7. F i g u r e 7. Ranson Prospect P r o s p e c t -- Geology and Vein Widths � https://digitalcollections.lakeheadu.ca/files/original/0d5e2404cf86f8c0cd09e874bc54d539.pdf a1b06ae6e6d6b18fc5bcf643d4b01b57 PDF Text Text ������������������������������������������������������������������������������������� https://digitalcollections.lakeheadu.ca/files/original/9fb80bcae67b4ebd07fb14adbabd2fdd.pdf 5052087fe87fa65daa8b16946d6910cf PDF Text Text ����������������������������������������������������������� https://digitalcollections.lakeheadu.ca/files/original/8786c509eb186e81797fcf04ae095105.pdf 09bf7145eb17aace4568c122d2ba2511 PDF Text Text r I F F I I Institute on Lake Lake Superior Superior Geology Geol Thirty-Third Annual Meeting THE ICAPUSKASING UPLIFT: ARCHEAN GREENSTONES AND GRANULITES n 0 50 km n P a Wawa, Wawa, Ontario. Ontario Vol. Vol. 33, Part Part 55 P ii �THE THE KAPUSKASING KAPUSKASING UPLIFT: ARC-lEAN ARCHEAN GREENSTONES GREENSTONES AND GRANULITES GRANULITES 3.A. 3.A. Percival Percival Geological Geological Survey of Canada, Canada, 588 Booth Street Street Ottawa KIA OE4 0E4 Ottawa KIA Annual Institute Institute on Lake Superior Superior Geology 33rd Annual Geology Wawa, Ontario Ontario Wawa, Vol. 33, Part 55 Vol. 33, �I ' I à I I I TABLE OF CONTENTS TABLE OF CONTENTS Page h U ZI:?GEOLOGICAL ~GE~L-FRAMEWORKOFTHEKAPU~KA~INGUPLIFT PART FRAMEWORK OF THE KAPUSKASING UPLIFT Introduction Introduction RegionalSetting Setting Regional Geophysical characteristics of south-central Superior Province Geophysical characteristics of south-central Superior Province General Geology ofthe theWawa Wawa- Abitibi Abitibi Region General Geology of - - 1 1 i 1 2 Region I)1) Greenstone- Granite GraniteTerranes Terranes Greenstone 2)2 ) WawaGneiss GneissTerrane Terrane Wawa 6 6 9 9 Kapuskas'ingStructural StructuralZone Zone Kapuskasing Relationshipof ofKapuskasing Kapuskasingstructural structural zone to adjacent subprovinces Relationship zone to adjacent subprovinces Structure of the Kap~crustal crass-section Structure of the Kapuskasing crustal cross-section ATcheanevolution evolutionofofthe tileKapuskasing ingcrustal crustatstructure structure Archean Uptiftofofthe theKapuskasing Kapustasingstructure structure Uplift 3)3 ) I 13 13 21 21 25 29 32 PART II: ROAD LOG Summary Summary DayI:1: Stops Stops1-1 1-ltoto1-10; 1-18;Geology Geologyof ofthe the Wawa subprovince, Day Wawa subprovince, Wawa to C h a p k u Wawa to Chapleau Day 2: Stops2-1 2-1toto2-9; 2-9sGeology Geologyofofthe theKapuskasing Kapuskasing structural Day 2: Stops structural zone in the Chapteau-Poleyet area zone in the Chapleau-Foleyet area 34 34 34 39 ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS 46 REFERENCES REFERENCES t \^ PARTI PART t Figure1 1 Figure F i r e22 Figure Figure3 3 Figure Figure44 Figure Figure5 5 Figure Figure66 Figure figure7 7 Figure Eggre88 Figure 1 1 46 LETOF OFILLUSTRATIONS BAUSTKATIONS LIST Geoiogyof of central centralSuperior SuperiorProvince Province Geology Geologyof ofthe theWawa-Chapleau-Foleyet Wawa-Chapteau-Foleyetarea area Geology Crustedthickness thicknessininthe theLake LakeSuperior Superiorarea area Crustal Bouguergravity gravitymap m p Bouguer Pressurebased basedon enhornblende hornblendeAl A1content content Pressure Geology of of the theKapuskasing Kapuskasing structural structuralzone zoneand andvicinity vicinity Geology Geologyof of the theShawmere Shawmereanorthosite anorthositecomplex complex Geology Metamorphicmineral mineralassemblages assemblagesin inthe theChapleau-Foleyet Chageau-Fokyet area Metamorphic 2 3 4 5 11 11 12 12 15 15 area 1717 �U Figure 9 Figure 10 Figure 11 Figure 12 Metamorphic reactions and P-I conditions for Kapuskasing granulites Paleo-pressure map for the Chapleau_Foleyet area Figure 13 Concorcfia diagram for zircon samples Gravity profile and crosssection for Kapuskasing zone in the Chapleau area Seismic reflection profile Figure 14 Figure 15 Restored vertical section 40Ar/39Ar age spectra Page 19 21 22 23 24 26 32 PART II Figure 22 Location of outcrops at Stop 2-5 42 3 j J �st I 8 PART ft PART b GEOLOGICAL GEOLOGICALFRAMEWORK FRAMEWORK OF OF THE THE KAPUSKASING KAPUSKASING UPLIFT INTRODUCTION The purpose purposeofofthe the trip trip is is to to examine examine the the characteristics characteristics and The and interrelationships interrelationships of of Archean high-grade gneiss gneiss terranes terranes of of the Superior Province. A Archean greenstone-granite greenstone-granite and high-grade Superior Province. A 300-km long west transect westtot oeast east transect between Wawa Wawa and Timmins, Ontario will be be used ttoo illustrate illustrateregional-scale regional-scale relationships. Figure Figure 11 shows the the major major geological features features of the theSuperior Superior Province Province and and Figure 22 traces trip route. The traces the the trip The first first day day will will be spent spent examining features features of of the the Michipicoten belt, a dominantly dominantly metavolcanic metavolcanic portion of the theWawa Wawa subprovince, subprovince, and and contact of the contact relationships between the the Michipicoten Michipicoten supracrustal supracrustal rocks and intrusions of Wawa domal gneiss gneiss tterrane. Wawa domal Onday daytwo, two,the theWawa-Kapuskasing Wawa-Kapuskasing boundary boundary will willbe be e r r a e . On examined, features of examined, as well as features of the theKapuskasing Kapuskasing structural structuralzone, zone, including including the the Shawmere anorthosite complex, high-grade gneisses, and the Ivanhoe Lake cataclastic cataclastic high-grade gneisses, zone separating zone from from those of of the Abitibi separating rocks of the the Kapuskasing Kapuskasing zone Abitibi Belt. . REGIONAL REGIONAL SETTING SETTING The Superior Province Province is is an an Archean Archean tterrane composed of of east-west east-west trending belts e r r a composed of alternate alternatevolcanic-rich volcanic-rich and and sediment-rich sediment-rich character, character,termed termedsubprovinces subprovinces(Fig. (Fig. 1). I). The continuity continuity of of the the east-west east-west belts belts is is interrupted interrupted by by aa northeast-trending northeast-trending zone zone of of highhighgrade metamorphic rocks, rocks, the Kapuskasing structural zone zone (Thurston (Thurstonet et al., al., 1977). Kapuskasing structural 1977). At its its southern end, the Kapuskasing structure is fault-bounded fault-bounded on on the the southeast southeast but but the Kapuskasing structure western contact contactisiscomplex complexand and gradational gradationalover over120 120 km to low-grade low-grade rocks of the the Michipicoten belt near near Lake Lake Superior Superior (Percival (Percivaland and Card, Card,1983; 1983;1985) 1985) (Figs. (Figs. I1and and 2). 2). The Kapuskasing Kapuskasing"high", "high",aaprominent prominentnortheasterly northeasterly gravity and aeromagnetic aeromagnetic anomaly, was interpreted indicate pronounced interpretedby byWilson Wilson and and Brisbin Brisbin (1965) (1965) tto o indicate pronounced upwarp of the the Conrad Conrad discontinuity. Bennett Bennettetetal. al.(1967) (1967)concluded concluded that that the theKapuskasing Kapuskasing structure structure is aa complex complex horst uplifted during during the Proterozoic. Proterozoic. The Theassociation associationofof1,100-1,000 1,100-1,000 Ma Ma alkalic that the alkalic rock-carbonatite rock-carbonatitecomplexes complexesled ledBurke Burkeand and Dewey Dewey (1973) (1973) tto o suggest that the Kapuskasing structure is a failed arm of the the Keweenawan Keweenawan rift structure. structure. Watson Watson(1980) (1980) Kapuskasing structure postulated postulated that thatthe theKapuskasing Kapuskasingzone zone was was uplifted uplifted during during late late Archean Archean or or early early Proterozoic sinistral transcurrent movement. transition aatt the movement. The The low-to-high-grade low-to-high-grade transition the southern of the the structure southern end of structurehas has been been interpreted interpreted as asan an oblique oblique cross-section of the crust uplifted along an east-verging east-verging thrust (Percival and Card, Card, 1983). 1983). Recent earthquakes in the region region indicate that that the thestructure structureisisstill stillactive active(Forsyth (Forsythand Morel, 1982; Forsyth et et a!., al.,1983). 1983). �-2- Figure1.1. Geology Geologyof of the thecentral centralSuperior SuperiorProvince. Province. Inset: Inset:positive positive gravity anomalies Figure gravity anomalies dark stipple b-25 mGal); limes (-25 mGal t o -35 mGal); blank (<-35 mGal). dark stipple @-25 mGal); lines (-25 mGal to -35 mGal); blank (<-35 mGal). GEOPHYSICALCHARACTERISTICS CHARACTERISTICSOF OFSOUTH-CENTRAL SOUTH-CENTRAL SUPERIOR PROVINCE GEOPHYSICAL SUPERIOR PROVINCE mapshowing showing apparent apparent crustal crustalthickness thicknessininthe theLake Lake Superior region, based on AAmap Superior region, based on seismic refraction studies, was presented by Halls (1982) (Fig. 3). These data show that seismic refraction studies, was presented by Halls (1982) (Fig. 3). These data show that �— 3— C C) C Co p1 0 4) U) p4 L b 1-i 4) t r4 C) 4-) r1 C) (Ti .1-I -p rl 4) --1 'p Cli U) C) 0 I— C) 'C a) 4.) :2 )< E o C) C) Co C o III IllIlillIjillIlIl lillillIlIl 1.17 — 111,1,1, —'t t :2 0 5 o.w c r-1 Ci, C D 0 a) a) Ct >1 Co ' CO •- w C 0 — Co Co E 0 'C) c 0 (0 C Ia) — C) — E 0) (N C Co o 0 — ct Ct 5 E 0 L. — > -C C) o c0 —t CC) ox rn Ii1'llI El! E C a) Ct Cl) .u) a) C) 0CtCOC — 0 —o — .9 — 0(0 2Co(0 0 E > 0 o c 0 (:' (0 N 0- 0 a) — C) iiiipj 0 0 .0 -o 111111r11111111,J; I.- C (0 Ct —1 �J U I Initial 1986). Ellis, and Boland 1986; West, and Northey 1985; al., et (Northey interpretation of stages preliminary in still are zone, Kapuskasing the beneath structure crustal examine to 1984 in conducted study, refraction major a of Results velocities. mantle and crustal averaging of necessity the to due partly and areas some in coverage insufficient of because partly preliminary, as thickness crustal apparent of map contour the viewed Halls east. the to km —35 to abruptly drop zone Kapuskasing the beneath range km 39 the in Values zone. Kapuskasing the of boundary eastern the with associated Moho to depth in decrease step—like a be to appears there addition, In Timmins. near km 35 to Wawa near km 45 about of values from easterly decreases Province Superior the of crust the of thickness apparent the advised. was map using in caution extreme and Halls by listed are data of Sources 1982). Halls, (after area Superior Lake the in crust the of thickness Apparent 3 Figure 1 j 2 U U 3 j -4U �-585° 470 810 Figure 4. Bouguer gravity map superimposed on simplified geology. (Gravity values in mGal), with 5 mGal Contour interval are from Earth Physics Branch maps 44078, 44084, 48078 and 48084). Checks - greenstone belts; dots -Kapuskasing unpatterned_undjyided granitoid rocks. gneiss; interpretation indicates that the crust is at least 48 km thick beneath the Kapuskasing zone and thins abruptly to about 40 km to the southeast; high seismic velocities characterize the high-grade rocks of the Kapuskasing zone (0. Northey, oral communication, 1985; Cook, 1985; Fountain and Salisbury, 1986). The Bouguer gravity anomaly map for the Wawa-Timmins region is shown in Figure 4. In general, areas underlain by metavolcanic rocks have associated positive gravity anomalies and granitoid..gneissic rocks have negative anomalies. The Kapuskasing structural zone has an assoçiate linear positive gravity anomaly extending �—6— from from James JamesBay b y in in the the north north to t o some some 50 50 km km southwest southwest of of Chapleau. Chapleau. In In the the WawaWawaChapleau.-Foleyet Chapleau-Foleyet area, the the gradient gradient isisgradual gradual on on the the west west and and abrupt abrupt on the east, east, suggesting contact between betweenthe theKapuskasing Kapuskasing zone and Abitibi Abitibi suggesting a west-dipping contact subprovince. In this thisregion, region,the thegravity gravityprofile profile(Fig. (Fig.12) 12)shows shows aa paired pairedhigh—low high-low subprovince. In anomaly. anomaly. The The trough trough of of the the low low is coincident with the fault fault at a tthe theeastern easternboundary boundaryof of the the Kapuskasing Kapuskasing zone. zone. To the north, as itit coalesces coalesces with with the the north, the thepositive positiveKapuskasing Kapuskasinganomaly anomaly broadens broadens as east-west east-west gravity gravity high high associated with with the the Quetico-Opatica Quetico-Opatica metasedimentary metasedimentary subprovince. J j 1 GENERAL GENERAL GEOLOGY GEOLOGY OF OFIL-fE THE WAWA WAWA -- ABITIBI ABITIBI REGION REGION Three Three distinct distinct types types of of terrane terraneare arerecognized recognized in inthis thispart partof ofthe theSuperior Superior Province: Province: 1) greenstone-granite greenstone-granite belts, belts, 2) 2) regions regionsdominated dominated by by orthogneiss orthogneiss in in the the amphibolite fades, facies, and 3) 3)heterogeneous heterogeneousgneisses gneisses in in the the granulite granulite to t oupper upper amphibolite amphibolite fades. facies. Differences between terranes terranes in in metamorphic metamorphic grade grade and and pressure pressure suggest suggest that that the the terrane terranetypes typesrepresent representcrustal-scale crustal-scaleniegalayers megalayers(Percival (Peruvaland andCard, Card,1985), 1985),the the components components of the the upper upper and and middle middle continental crust. crust. The TheWawa Wawaand and Abitibi Abitibi belts belts are are greenstone-granite terranes; of terrane type terranes; the theWawa Wawa gneiss terrane is an example of type 22 and zone represents type and the the Kapuskasing Kapuskasing zone type 33 terrane terrane(Fig. (Fig. 2). 2). ~ j j 4.: 1) 1) Greenstone-Granite Greenstone-Granite Terranes Terranes a The partofofthe thevolcanic-rich volcanic-richWawa Wawasubprovince, subprovince,Isiscomposed composed The Michipicoten Michipicoten belt, part mainly IC and mafic andfetsic felsiccomposition composition(Goodwin, (Goodwin, mainly of metavolcanic metavolcanicrocks rocksofofultrarnafic, ultramafic,maf 1962), with intercalated intercalated greywacke, 1962), with greywacke, conglomerate, chert chertand andiron iron formation, formation,mainly mainly siderite. as well as downward-facing downward-facing strata strata siderite. Dome Dome and basin structures structures(Goodwin, (Goodwin, 1962) 1962) as and and overturned overturned structures structures(Attoh, (Attoh, 1980) 1980)have have been recognized. recognized. Metamorphic Metamorphic grade grade ranges amphibolite facies facies (Fraser (Fraser et al., ranges from sub-greenschist sub-greenschist to amphibolite al., [978). 1978). Several Severalsuites suitesof of intrusive ranging from from peridotite peridotite to intrusive rocks rocks include include synvolcanic synvolcanic bodies ranging t o granodiorite, granodiorite, younger younger granodiorite granodiorite batholiths, batholiths, and and still stillyounger younger granite graniteand andsyenite syeniteplutons plutons (Card, (Card, 1982). 1982). The of the southern part of The supracrustal rocks ro of the the belt belt were weredivided divided into three three major (1962). A lower lower cycle, cycle, consisting of of roafic major cycles cycles by by Goodwin Goodwin (1962). rnafic and felsic felsic volcanics, volcanics, isis capped iron formation, formation, mainly mainly siderite, siderite, but with lesser pyrite-, capped by by Michipicoten-type Michipicoten-type iron U - 7 �r —7- I chert- and and graphite-rich graphite-rich rocks. rocks. The Theassociated associatedJubilee JubileeStock, Stock,aa high-level high-level subvolcanic SU~VO~C~N intrusion, was was emplaced emplaced within aa caldera caldera structure structure(Sage, (Sage, 1980). 1980). The middle cycle cyc Icvolcanics volcanicsoverlain overlain by byclastic clastic metasediments metasediments and and comprises maf comprises mafic and felsic tuffs an breccias. The breccias. The clastic clasticsediments, sediments, including including the the Doré Dor6 conglomerate, conglomerate, wacke, wacke, siltstone, siltstone, and an I crossbeddedarkose, arkose,a are thef facies equivalentsofof the the felsic felsic pyroclastics and crossbedded r e the a d e s equivalents and are formed mainly of detritus detritus eroded eroded from the t h e felsic felsic centres. centres. The Theupper upper cycle cycle comprises comprises intermediate to felsic -dacite) tuffs tuffs and quartz-feldspar porphyry. porphyry. Recent felsic (andesite (andesite -&cite) and quartz-feldspar Recent (pers.comm., comm., 1986) 1986)indicates indicatesonly onlytwo twocycles cycleswithin within tthe work by Sage Sage (pers. h e main volcanic pile. The Abitibi Abitibi subprovince The subprovince is is dominated dominated by a thick thick sequence sequence of volcanic volcanic and and I J I I I I I fl of the sedimentary rocks of t h e Abitibi Abitibigreenstone greenstonebelt belt(Jensen, (Jensen, 1981; 1981; 1985). 1985). The supracrustal successiontypically typically comprises comprisessequences sequencesofofultramafic, ultramafic, mafic, mafic, and and felsic felsic volcanics. succession volcanics. high proportion of volcanic volcanic detritus. detritus. Intercalated turbiditic turbiditicsedimentary sedimentary rocks rocks contain contain aa high In the Abitibi Abitibibelt, belt,the t h euppermost uppermostgroup, group, the t h eTimiskaming, Timiskaming,isisan anunconformity-bounded unconformity-bounded sequenceofof alkal~c alkalic volcanics and fluviatile fluviatile sediments sediments(Hyde, (Hyde,1980) 1980) localized localized along along major major sequence east-west fault east-west faultzones. zones. Large areas areas of of the Abitibi Abitibi greenstone Large greenstone belt belt are aremetamorphosed metamorphosed to t o greenschist greenschist prehnite-pumpellyite Ifacies acies rocks rocks are common common in in tthe Timminsh e Timminsffacies; a d e s ; subgreenschist, subgreenschist, prehnite-pumpellyite Rouyn area areaand andnarrow narrowaureoles aureolesofofamphibolite amphibolite ffacies rocks occur occur adjacent adjacent tto Rouyn a d e s rocks o plutonic plutonic bodies (Jolly, (Jolly, 1978). 1978). The supracrustal supracrustal rocks rocks of of the Abitibi The Abitibisubprovince subprovince display display evidence evidence of polyphase polyphase orientations. deformation in the t h e form form of of major majorand and minor minor structures structuresof ofseveral severalages ages and orientations. In the Abitibi Abitibigreenstone greenstone belt, older northerly-trending folds folds are are overprinted overprinted by by easteaststructures west trending major and minor folds, forming formingmajor major dome dome and and basin basin structures (Pyke, 1982). The Themajor majorisoclinal isoclinal folds folds with with east-west east-west striking striking subvertical (Pyke, 1982). subvertical axial axialplanes, planes, steeply-plunging minor folds, folds, subvertical axial plane foliation, foliation, and steeply-plunging minor and steeply steeply plunging plunging stretching stretching lineation lineation were were probably probably formed formed under under subhorizontal, subhorizontal, generally generally north-south north-south major compression. compression. Toward Towardtthe southernmargin marginofofAbitibi Abitibi belt the major h e southern t h e major folds are overturned northward, and and in the the adjacent adjacent Pontiac Pontiac subprovince, subprovince; folds folds are a r e recumbent. recumbent. The Cadillac-Larder Lake fault fault zone, between tthe Abitibi The Cadillac-Larder zone, which constitutes the the boundary boundary between h e Abitibi and probably has hasboth both transcurrent transcurrent and and thrust components and Pontiac subprovinces, subwovinces. orobablv comDonents of movement. Several suites of intrusive rocks in the Abitibi subprovince can be distinguished on I I of composition, composition, structural structural relationships, the basis basis of relationships, setting, setting,and andage a g e(Card, (Card, 1982). 1982). The The sills, dykes and and plutons plutons ranging rangingin in composition composition from from oldest suite includes synvolcanic sills, peridotite typically quartz diorite peridotite to t o granodiorite; granodiorite; the more more felsic intrusions aare r e typically diorite and and trondhjemite. Gneissic Gneissic plutonic plutonic rocks rocks of of tonalite tonaliteand and granodiorite granodiorite composition, composition, �—8— commonly containing amphibolitic amphiboliticenclaves, enclaves, occur occur in in the the northeastern and commonly containing and southwestern southwestern Abitibi subprovince. Massive felsic plutonic plutonic rocks rocks intrude intrude both both the the greenstones and the Abitibi subprovince. Massive felsic gneissic rocks in in the form of simple and and composite composite plutons plutons and and batholiths. batholiths. They They form several suites, suites, including including early early granodiorites, granodiorites, younger younger granite granite batholiths, batholiths, and andstill stillyounger younger syenite-diorite plutons. plutons. Contacts Contactsbetween between the theplutons plutons and and the the country country rocks rocks are are commonly concordant and and steeply steeply dipping; dipping;dominant dominanteast-west east-weststructural structural trends are commonly concordant are locally deflected about about the theintrusions. intrusions. A time framework for events events in in the theMichipicoten Michipicoten and and Abitibi Abitibi belts belts can can be be constructed U-Pb zircon dates. In the western Abitibi Abitibi belt, volcanic volcanic rocks rocks range in in constructed from from U-Pb age from Nunes and and Jensen, Jensen, 1980), with late late to 2,703 2,703 Ma Ma (Nunes and Pyke, 1980; 1980; Nunes 19801, with from 2,725 2,725 to alkaline Group) aatt 2685 Ma, Ma, and and in in the the Michipicoten Michipicoten belt, from from alkaline volcanics volcanics (Timiskaming (Timiskaming Group) 2,749 a t 2737, 2737, 2744 2744 (Turek (Turek et etal., al., 1982) 1982)and and2745 2745 2,749 tto o 2,696 Ma, with synvolcanic plutons at Ma (Sullivanetetal., al., 1985). 1985). A number numberofoflatelate- ttoo post-tectonic plutons M a (Sullivan plutons from from the the Abitibi Abitibi and Michipicoten Michipicoten belts have zircon dates dateswithin within aafew fewmillion million years yearsof of2,680 2,680(Icrogh (Krogh et et al., al., 1982; 1982;Frarey Frareyand and Krogh, Krogh, 1986). 1986). Thus Thus the themain main Abitibi Abitibi and and Michipicoten Michipicoten supracrustal supracrustal sequences sequences and and early earlyintrusions intrusionsdeveloped developed between between 2,750 2,750 and and 2,700 2,700 Ma Ma ago. The dates on volcanics and late late plutons bracket the volcanics and the age age of of deformation deformation and and regional regional metamorphism Ma ago. Major a ago. Major volcanic, plutonic, and metamorphism aatt between between 2,700 2,700 and 2,680 2,680 M tectonic tectonic events events of of relatively relatively brief brief duration durationwere wereessentially essentiallysynchronous synchronous throughout throughout the Abitibi and Wawa subprovinces, a region some 1,200 km wide. wide. The Wawa subprovinces, 1,200 km long and 200 km The lithologic and age similarities similaritiesbetween between the theAbitibi Abitibiand andWawa Wawa subprovinces subprovinces strongly strongly suggest original continuity, now structural zone. now interrupted by the Kapuskasing Kapuskasing structural Diabase dyke dyke swarms swarms of of late late Archean Archean and and Proterozoic age are present present throughout throughout the region. The Theoldest oldestdykes, dykes, the thenorth-trending north-trending Matachewan Matachewan swarm swarm of of the the Abitibi subprovince, Rb-Sr age age of of 2633 2633 Ma Ma (Gates and Hurley, Hurley, 1973). 1973). NorthwestNorthwestsubprovince, have a Rb-Sr striking subprovince are are petrographically petrographically similar to t o and and have have been been striking diabase diabase dykes dykes in in Wawa Wawa subprovince paleomagnetically correlated correlatedwith withthe theMatachewan Matachewanswarm swarm(Ernst, (Ernst,1981; 1981;Ernst Ernstand and paleomagnetically Halls, subprovincesare are thus thus inferred inferred ttoo have been tectonically Halls, 1984). 1984). Abitibi Abitibi and Wawa Wawa subprovinces tectonically time. Northeast-striking Northeast-striking tholelltic tholeiiticdykes dykesare areabout about2105 2105Ma Ma old old stable cratons cratons by by this time. stable (Gates 1973);northwest northwest olivine diabase diabase dykes (Gates and and 1-lurley, Hurley, 1973); dykes (Sudbury (Sudbury swarm) swarm) are a r e about about 1250 Ma Ma old old (Van (VanSchmus, Schmus,1975); 1975);and andeast-northeast east-northeast olivine diabase diabase dykes dykes (Abitibi (Abitibi swarm) swarm) are M aold old(Lowden (Lowdenand andWanless, Wanless,1963). 1963). are approximately approximately1100 1100Ma �r 1 2) 2) 4 I I I I $ I I I I I I I The belt is intruded intruded ttoo the The Michipicoten Michipicoten belt the southeast southeast by by tonalitic tonalitic gneiss and plutons plutons of gneiss terrane terrane (Fig. 2). The consist of of aatt least of the theWawa Wawa domal domal gneiss (Fig. 2). The rocks in this region consist least four four lithologic lithologic components: components; (1) (1)hornblende-plagioclase hornblende-plagioclase ±+ clinopyroxene clinopyroxene mafic and rare rare paragneiss paragneiss xenoliths, xenoliths, ranging ranging from centimetres centimetresto totens tensofofmetres metresininmaximum maximumdimension, dimension, making most makingup up55to to 50% 50% of of individual individual outcrops, and enclosed in (2) the volumetrically most abundant abundant phase, phase, hornblende-biotite hornblende-biotite tonalitic tonaliticgneiss gneisswhich which is iscut cutby by (3) (3) concordant concordant to to discordant discordant layers layers of of foliated foliatedto t ogneissic gneissicbiotite-hornblende biotite-hornblende granodiorite, granodiorite,which whichin in turn turn are arecut cutby by (4) (4)late late discordant discordant quartz quartz monzonite monzonite pegmatite. Xenolith-rich Xenolith-rich tonalitic tonaliticgneiss gneiss units units alternate alternateon on aa 55 to to 10 10 km krn scale with xenolith-poor xenolith-poor units and can be be traced traced for for distances distances of of at a tleast least50 50km. km. Layering Layeringininmafic maficxenoliths xenolithsisislocally locallydiscordant discordant to tolayering layering in in enclosing enclosing gneiss. gneiss. Small Small folds folds of of layering layering in in tonalitic tonaliticgneiss gneiss are arecommonly commonly truncated truncated by by layers layers of of foliated foliatedgranodiorite. granodiorite. Tonalite Tonalitegneiss gneisshas hasa aminimum minimumU-Pb U-Pb zircon zirconage ageof of2707 2707 Ma, M a(Percival (Percivaland andKrogh, Krogh, Ma, partly partly reset resetby bythe theintrusion intrusionofofgranodiorite granodioritesheets sheetsata 2677 t 2677Ma 1983) 1983)(Fig. (Fig. 5). 5). The The layers layers of of granodiorite granodiorite on on the cm cm to to km km scale scale in the the gneiss gneiss terrane terrane can can be be correlated correlatedby byzircon zircongeochronology geochronologywith with discordant discordantplutons plutonsof of 2680 2680Ma Ma age age in in the the greenstone greenstone belts, belts, suggesting suggesting that that the the plutons plutons have have deep roots in the gneissic gneissic terrane. In In the the area areabetween betweenthe theMichipicoten Michipicotenbelt beltand andKapuskasing Kapuskasingzone zone (Fig. (Fig. 2) 2) the the orientation orientationof of foliation, foliation,gneissosity gneissosityand and axial axial surfaces surfacesof of small smallfolds foldspermit permitdefinition definitionof of several severalstructural structuraldomains domainscharacterized characterizedby bydomal domalgeometry geometry(Fig. (Fig. 6). 6). The Thespacing spacing of of major major domal domal or or antiformal antiformalculminations culminations is is on on the the order order of of 20 20 to t o25 25 km, km, although althoughmany many smaller smaller culminations culminations are arealso alsopresent. present.The TheHighbrush HighbrushLake Lakeand andRacine RacineLake Lakedomes domeshave have cores coresof of tonalite-granodiorite tonalite-granodioritegneiss gneisswhereas whereasthe theChaplin C h a p lLake i Lakedome domeand andMissinaibi MissinaibiLake Lake arch planar fabric fabricin in the the archhave have granitic graniticcores coresflanked flanked by by foliated foliated to to gneissic gneissic rocks. AAplanar homogeneous homogeneous granitic rocks, defined by by lenticular quartz quartz and and biotite biotitealignment, alignment,isis generally generally concordant concordant to t ogneissosity gneissosity in in mantling mantling gneiss. gneiss. The Thestructural structuraldomes domesmay maybe be related relatedtotothe theemplacement emplacementofofplutons, plutons,possibly possiblyby bydiapiric diapiricrise. rise.The TheRobson RobsonLake Lakedome, dome, adjacent adjacentto t othe theKapuskasing Kapuskasiig structural structuralzone, zone, has has aa core coreof of interlayered interlayeredmafic maficgneiss, gneiss, paragneiss paragneiss and and tonalitic tonaliticgneiss. gneiss. InIngeneral, general,asymmetric asymmetricsmall smallfolds foldsofofgneissic gneissiclayering layeringdo donot nothave have aa consistent consistent sense senseof of asymmetry asymmetrywith with respect respectto todomal domalculminations culminations and and are are therefore thereforenot notcongruent congruent with withthe thedomes. domes. Near Nearsome somedomal domal crests, crests,the theorientation orientationofofgneissic gneissiclayering, layering,small small folds are widely variable to chaotic and definee aa pattern foldsand and lineations 1 patternof ofcoalescing coalescing domes. domes. I Wawa Wawa Gneiss Terrane Terrane �- 10 - geobarometer for calc-alkaline igneous rocks is based on the Al content of hornblende (l-lammarstrorn and Zen, 1986): A P= —3.92 + 5.03 Allotal Application of the barometer to a suite of tonalites from the Wawa gneiss terrane suggests suggests that thatthe thepressure pressureofofigneous igneouscrystallization crystallizationincreases increasesfrom fromabout about55kbar kbarininthe the central over Kapuskasing 6 kbarnear nearthe the Kapuskasingzone zone(Fig. (Fig. 5). 5). These These centralpart partofofthe theterrane terranetoto over6 kbar results areintermediate intermediatebetween betweenindependent independentpressure pressureestimates estimatesfor forthe theMichipicoten Michipicoten resultsare belt basedon onsphalerite-pyrrhotite sphalerite-pyrrhotitegeobarometry geobarometry(Studemeister, (Studemeister,1983) 1983)and and beltof of2-3 2-3kbar, kbar, based for 6-8kbar kbarbased basedon ongarnet-pyroxene-plagioclase_quartz garnet-pyroxene-plagioclase-quartz forthe theKapuskasing Kapuskasingzone zoneof of6-8 barometry barometry(Percival, (Percival,1983). 1983).AAvalue valueofof8 8kbar kbarnear nearWawa Wawaisisderived derivedfrom fromaabiotite biotite tonalite tonalhewhich whichcontains containshornblende hornblende only on adjacent to contacts with amphibolite; the hornblende hornblendeisisprobably probablyxenocrystic. xenoaystic. Metasedimentary Metasedimentaryrocks rocksoccur occurini two locations in the eastern Wawa subprovince. AAdiscontinuous, discontinuous, antiformal antiformalto t odomal domalbelt beltofofparagneiss paragneisswest westofofthe theRacine RacineLake Lakedome dome may 6). maybe becontinuous continuous to t othe theeast eastwith withparagneiss paragneissofofthe theKapuskasing Kapuskasingzone zone(Figs. (Figs.22and and6). Stretched-pebble Stretched-pebble metaconglomerate metaconglomerateoccurs occursininassociation associationwith withquartz quartzwacke wackeand and amphibolite Thepolymictic polymictic(tonalite, (tonalite,granodiorite, granodiorite,metame amphibolitein inthe thevicinity vicinityof of Borden Borden Lake. Lake. The andesite, andesite,metasediments, metasediments,amphibolite, amphibolite,vein veinquartz), quartz),clast-supported clast-supported rock rockcontains contains cobbles cm)with withaaprominent prominentshallow shallow cobblesranging rangingfrom fromequant equanttotoconstricted constricted(1.5 (1.5mmx x7 7x x7 7cm) northeast plunge. In cross-section the clasts vary from equidimensional to northwestdipping ellipses. The Floranna Lake complex is a strongly lineated and foliated complex crescentic pluton plutonof ofintermediate intermediatecomposition compositionthat thatoccurs occursbetween betweenthe theRobson RobsonLake Lakeand andRacine Racine Lake medium-grained Lakedomes. domes. The Themargins marginsofofthe thecomplex complexare arefinefine-toto medium-grainedhypersthene.hypersthenebiotite contains medium-grained biotitegranite, granite,whereas whereasthe thecore core contains medium-grainedrnonzonite rnonzoniteand anddiorite dioritewith with rare raregabbro gabbroand andcoarse coarsebiotite-clinopyroxene biotite-clinopyroxene melagabbro melagabbrolayers. layers. The Theleast-deformed least-deformed interior igneous(?) interiorportions portionscontain containrelict relict igneous(?)clinopyroxene clinopyroxeneand andfeldspar feldsparaugen augenphenocrysts. pheno Migmatitic Migmatiticquartz quartzmonzonite monzonitelayers layersconstitute constituteupuptot o10% 10%ofofsome someoutcrops. outcrops.The The complex complexhas hassimilar similarstructural structuraland andlithological lithologicalcharacteristics characteristicstotocrescentic crescenticplutons plutonsofof the theWabigoon Wabigoonsubprovince subprovinceof of northwestern northwesternOntario Ontario(Schwerdtner (Schwerdtneretetal., al., 1979,1983; 1983 1979, Sutcliffe 1979). Sutcliffeand andFawcett, Fawcett, 1979). The donial region a semi-continuous Theeastern easternlimit limitofofthe the domal regionis is a semi-contin"ous zone zoneofofnorth, north, northeast easterly-dipping and northeastand andnorthwest northweststriking, striking,gently gently easterly-dippinggneissosity gneissosity andeasterlyeasterlyplunging 6)6may plunginglineation. lineation. This Thiscurvilinear curvilinearfeature feature(Fig. (Fig. ) mayrepresent revresentthe theeastern easternextremity extremity �I I I I I I I — 11 2.6 0 0 a) Ia -0 interior intermediate edge 8 S S.- I. U (3) ¼ I I a S a2E 6- (I, 0 4 (4 Lu — 0 0 • .40 •• 5 A 150 Wowa I &ne/ss Terr one 100 I I I I I - — . 50 L8r() N Structural Zone I I I I ao >' 0 Kop uskasing S 0 A.4 I p p 2 I_ '4' ---------- 0 9-1.6 C Distance Distance from from Ivanhoe Ivanhoe Lake Lake cataciastic cataclastic zone, km km Al/n A/ in Horn b/en de Barometer Hornblende Barometer ............ ...,......... .. b'} . .. . . ., Wa wa/ / 4•97 I I 0 I I 1 •1 24 0 0 I I 0--- r 0 -S. 1* I I I — to 11.0 &ne/ss V / A bit/b - V , ,. / Belt 5.1 Terrane 50 0 km Figure Figure 5.5. a)a) Plot Plotof ofhornblende hornblende composition composition vs vs spatial spatial distribution. distribution. Vertical Vertical array arrayof of points represents representswithin-sample within-sample compositional variation. Hornblende at a t far far left leftisis points variation. Hornblende probably xenocrystic, xenocrystic, from from adjacent adjacent amphibolites amphibolites of of Michipicoten Michipicoten belt. Dashed-line Dashed-line box box probably representsindependent independentpressure pressure estimates estimatesfrom fromgranulites granulitesofofthe theKapuskasing Kapuskasing zone. zone. represents b)b) Map Map showing average pressure in kbar, kbar, based based on on hornblende hornblende geobarometry geobarometry in in the theWawa-Chapleau Wawa-Chapleau area. area. �63'Oo' LEGEND Proterozoic Alkalic rock—carbonatite complex: I: Lackner Lake complex; n: Nemegosenda Lake Lake complex; comple%s: a: Shenango Shenango complex Complex 1100 t i 0 0 Ma Ma intrusions intrusions Archean I m + massive granite, granodiorite, grenodiorite, with minor minor tonalite tonalite diorite—monzonite intrusive complex; minor hornblendite, granite diorite-monzonite intrusive 2707-2668 Ma Me sequence sequence 2707—2668 foliated foliated to to flaser flaser tonalite tonalite I@ tg;4 tonalite—granodiorite tonelite-granodiorite gneiss; gneis metavolcanic metavolcanic rocks, rocks, mainly mainly metabasalt metabasait . :: ---------- ~....' - Shawmere Shawmere anorthosite anorthositecomplex: complex: metamorphosed metamorphosed gabbroic gabbroic anorthosite, anorthosite, anorthosite, anorthosite, gabbro, gabbro, minor minor tonalite tonalite pre—2765 pre-2765 Ma sequence sequence Amq gneiss: highhigh Ca,AI basaltic composition, with gneiss: Ca,AI basaltic composition, withtonalitic tonaliticleucosome ieucosome "fl-i,maficmafic lAp 0 ' / ^ 2749-2696 Ma sequence sequence 2749—2696 flaser ic tonalite flaser diorite dioritetotomat mafic tonalite— includes inciudesminor minorgabbro, gabbro .._.:j .-.--hornbiendite, granodiorite granodiorite hornblendite, "'Bsojl I metasedimentary metasedimentery rocks rocks (includes (includes metaconglomerate metaconglomerste with with tonalite tonalite cobbles zircon date date of of 2664±12 cobbles with with aa U—Pb U-Pb zircon 2664±1Ma) Ma) paragneiss- quartz-rich paragneiss— quartz—richcomposition, composition,wi with up to 15% tonalitic leucosome — fault; fault; Ivanhoe ivanhoe Lake Lake cataclastic cstaclasticzone zone Figure Figure 6. 6. Geology Geologyof ofthe theiCapuskasing Kapuskasing structural s t r u c t u r a l zone zone and and vicinity. vicinity. �I I I I I I I - I -13of of aa first-order first-order dome domeof of 75-100 75-100 km km diameter, diameter, of of which which the t h e individual individual structural structural domains domains are a r e higher-order higher-order domes domes of of similar similarscale scaleand andspacing spacingtot othose thoseofofthe theWabigoon Wabigoonsubprovince subprovince (Schwerdtner (Schwerdtner and and Lumbers, Lumbers, 1980). 1980). Dome development development can can be be temporally temporally related related to t o the the formation formation of of minor minor structures structuresin in gneiss. gneiss. The Thediscordant discordant foliations foliationsin in mafic mafic gneiss gneiss predate predate the thegneissic gneissic layering layering in the tonalite-granodiorite tonalite-granodiorite host. host. Small Smallfolds foldsof of this thisgneissic gneissiclayering layering in in turn turn predate layers. Crosscutting predate intrusion intrusion of granodiorite layers. Crosscutting pegmatite pegmatite dykes dykes and and sills are still still younger younger and are a r e probably probably the t h e same same age age as asthe thehomogeneous homogeneous plutonic plutonic rocks rocks which which locally locally have by lenticular quartz grains, have a planar planar fabric defined by grains, biotite alignment, alignment, fracture fracture cleavage, of granulation. granulation. The cleavage, or minor minor planar zones of The absence absence of aa consistent consistent sense sense of asymmetry asymmetry of small small folds with respect to t o domal domal culminations culminations and the t h e random random orientation orientation of of re-orientation of small small folds folds near dome crests argue in favour of re-orientation of of pre-existing pre-existing small small folds layering during duringthe the latest latest doming. doming. The folds and gneissic gneissic layering The quartz-lenticle foliation foliation and and fracture plutonic rocks rocks cannot cannot be be readily readily attributed attributed to fracturecleavage cleavagein inhomogeneous homogeneous plutonic to magmatic magmatic flow flow and therefore suggest suggest that that the the plutons plutons were were emplaced emplaced at their their present present structural structurallevel levelat a tsub-solidus sub-solidus temperature, possibly possibly relating to t o late l a t e diapiric diapiric rise. rise. 3) Kapuskasing Structural Zone The The Kapuskasing Kapuskasing structural zone zone comprises comprises northeast-striking, northwest-dipping northwestdipping belts tonalite, and belts of of paragneiss, paragneiss, mafic mafic gneiss, gneiss, gneissic gneissic and xenolithic tonalite, and rocks rocks of of the the Shawmere Shawmere anorthosite anorthosite complex complex (Bennett (Bennett et et al., al., 1967; 1967; Thurston Thurston et et al., al., 1977) 1977) (Figs. (Figs. 22 and and 6). 6). Migmatitic layered with with garnet, biotite, Migmatitic paragneiss paragneiss is compositionally layered biotite, quartz-rich quartz-rich and and rare rare graphitic graphitic varieties. varieties. Concordant Concordanttonalitic tonaliticleucosome leucosome constitutes constitutes up up to to 20 Ic gneiss 20 per per cent cent of of many many outcrops. outcrops. Enclaves Enclavesand andlayers layersofofmaf mafic gneiss in in paragneiss paragneiss occur occur on on the the10 10cm cm to t o 11km km scale. scale. Migmatitic Migmatiticmafic maficgneiss gneiss isis characterized characterizedby by garnetgarnetclinopyroxene-hornblende-plagioclase-quartz-ilmenite+orthopyroxenemineral mineral clinopyroxene-hornblende-plagioclase-quartz-ilmenite÷orthopyroxene assemblages assemblages and and generally contains concordant tonalitic tonalitic leucosome. leucosome. Layering, Layering, on on the the i1to t o10 10cm c m scale, scale,isisproduced produced by by variable variable proportions proportions of minerals. minerals. Table Table11presents presentstwo two sets setsof of whole-rock whole-rock analyses analyses from from adjacent adjacentanhydrous anhydrous (garnet-clinopyroxene-plagioclase(garnet-clinopyroxene-plagioclasequartz)and and hornblende-bearing hornblende-bearing layers from mafic gneiss in two different locations. locations. quartz) From From the t h e analyses analyses iti tisisunclear unclear whether whether the t h elayering layeringisisaapreserved preservedcompositional compositional heterogeneity heterogeneity or or aa product product of of metamorphic metamorphic differentiation. differentiation.The Thebulk bulkcomposition composition corresponds correspondsto t ohigh highcalcium calcium(10-15 (10-15wt% wt%CaO), CaO),high high alumina alumina(13.4-17.2 (13.4-17.2 wt% wt%A1203) AIn03) basalt basalt - I I I �- 14 Table Table 1: 1: e Si02 Si02 Ti02 1102 A1203 Whole rock chemical analyses of Whole of mafic gneiss from the the Kapuskasing Kapuskasing zone, with CIPW norms. Analyst: I: granulite layer, Analyst: R. R. Charbonneau, Charbonneau, GSC GSC Lab. 1: layer, P79-475 P79-475 CIPW norms. (Gt-Cpx-Pl-Qz, 5% 2: amphibolite amphibolite layer, P-475 (Gt-Cpx-PI-Qz, 5% Nb); Hb); 2: P-475 (Gt-Cpx-Pl-Qz, (Gt-Cpx-PI-Qz, 25% 25% Nb); Hb); 3: granulite (Gt-Cpx—Pl,trtrQz); Qz);4:4:amphibolite amphibolitelayer, layer, P79-371 granulitelayer, layer,P79—371 P79-371 (Gt-Cpx-PI, (Nb 40%, 40%, Gt Gt 15%, 15%, Cpx Cpx 15%, 15%,PI Fl20%); 20%);5:5:average averageofofthree three mafic gneisses from (Hb the the KSZ KSZ (79-84A, (79-84A, 123, 123, 299); 6: 6: high-alumina basalt basalt (Ringwood, (Ringwood,1975). 1975). 1 2 3 4 5 6 47.8 46.6 52.5 43.1 47.8 49.9 1.0 1.3 0.81 0.81 1.81 1.59 15.5 15.6 17.2 13.4 16.2 17.0 Fe203 1.3 2.2 2.2 5.7 3.4 1.5 FeO FeO 9.1 9.4 8.5 12.8 8.5 7.6 MnO MnO 0.27 0.19 0.32 0.3 0.32 0.2 MgO MgO 4.53 5.29 3.64 9.25 5.41 8.2 13.50 11.4 CaO CaO Na20 Na20 K20 K2 fl20 Co2 C02 Ni Ni Cr Total Total QZ OR AB AN DI HE EN PS P0 PA MT IL AP CC 15.4 14.2 11.2 10.0 2.0 2.4 2.8 1.6 2.3 2.8 0.25 0.41 0.12 0.58 0.33 0.2 0.5 1.1 0.3 1.6 0.8 2.3 2.0 0.4 0.1 0.6 0.014 0.014 0.0095 0.0098 0.024 0.019 0.018 0.018 0.014 0.015 100.0 1.5 1.49 17.02 32.77 11.42 12.80 6.05 7.83 1.9 1.55 0.12 5.26 100.4 2.44 20.46 30.81 11.52 10.90 3.64 3.95 3.01 3.60 3.21 1.55 0.14 4.58 100.6 100.6 100.4 CIPW CIPW Norm Norm 6.6 6.6 0.71 3.47 0.71 23.63 13.72 13.72 33.92 28.03 28.03 6.99 10.20 8.28 6.41 8.28 5.80 5.39 7.89 3.89 9.26 7.36 3.18 8.37 2.24 3.06 3.06 0.26 0.24 0.26 0.24 0.91 0.46 0.91 0.46 100.2 100.1 100.1 1.95 1.95 19.8 32.97 13.77 13'77 10.58 4.96 4.43 4.43 1.54 1.0 1.0 23.5 33.4 33.4 1-54 4.95 4.95 1.90 0.19 0.19 1.44 1.44 1.21 1.21 18.9 9.4 9.3 2.2 2.2 2.5 2.5 �t I I I I R mafic gneiss in the 95-220 and 1212(Table 1). Nickel and chromium abundances abundance5 ofof mafic gneiss aare r e in 95-220 and 190ppm ppmranges rangesrespectively respectivelyand andare arenot notdefinitive definitive in distinguishing between 190 between basaltic igneousand andmarly martysedimentary sedimentaryparentage parentagefor for the the rock rock type. type. igneous In the the area area of of Figure Figure 6, 6,four four linear, linear, northeast-striking northeast-striking bodies bodiesofof flaser-textured flaser-textured tto In o foliated diorite foliated dioriteand and mafic mafictonalite tonaliteoccur occurdominantly dominantlywithin withinparagneiss paragneiss terranes. terranes. These These ff' SHAWMERE ANORrHOSITE COMPLEX Megacrystic qabbrac anorthosile // Banded zone cpabbrO/anar I hosite/qarneti let I' I Anorthosite zone I 5 / hornbleedet / 'a Tonahtic racks Liiiilii Paraqnetss —— $ — —— km —— I I I Ia p - I I _—_—_— 1 / ____iii___ ±61r'- / / ---- — / / - / —:——7 a C' / /-';Y/ / — :Y / // // / - // / /// -: Renee / _/ / / / ,:-:i / Catty / *34B \/ a- 1 ii / /r //c/:-/// / /-/ _—_/ -/ — /1—- /— a / J-& -- - -- I I / /-:j // 7 // I',) / /-;: I / z __ / _// / / / / — Mat a yneiss. amohibolute FseIt ___I — ;;/ /ft\/// // S Luneament / ". E::E J ?- couNrAt ROCKS $ / '1- / ronalilic rocks ___ // C Border zone-am phibolite. mat'c gnetss 4à2 — - - -yI / IMd::y 3 4A / // 13.:c::_J -- —-—— / ' -: - —:—:—-- — - 8300----f ':':nFigure 7. - t' a / 8230 Geologyof of the the Shawmere Shawmereanorthosite anorthositecomplex complex (after (after Riccio, 1981 and Geology 1981 and Percival, 1981). 48 �- 16 - medium- to coarse-grained, coarse-grained, locally locally migmatitic migmatitic rocks mediumrocks consist consist of of hornblende, hornblende, biotite biotite and and per cent cent quartz plagioclase, with up to 10 plagioclase, 10 per quartz as as well well as as orthopyroxene, orthopyroxene, clinopyroxene clinopyroxene and and hornblendite and rare pyroxenite pyroxenite occur cm to garnet. Gabbro, as layers layers 10 10 cm to rare garnet. Gabbro, hornblendite and rare occur locally locally as cii thick, generally within 2 km km of of paragneiss contacts. 2 2m present south south of of the t h e main main Discrete belts of of xenolithic xenolithic and and gneissic gneissic tortalite tonalite are present and small small bodies are present present to to the north. anorthosite complex and body of the the Shawmere Shawmere anorthosite The southern southern belt belt is made up of of coarse coarse garnet-hornblende-biotite-plagioclase-quartz garnet-hornblende-biotite-plagioclase-quartz made up and garnettonalite containing enclaves of of mafic gneiss, paragneiss, hornblendite and orthopyroxene-hornblende-biotite rocks. orthopyroxene-hornblende-biotite rocks. Southwest Southwest along along this belt, garnet decreases decreases in composition is is granodioritic. granodioritic. Inclusions abundance and the composition Inclusions in this area area are are amphibolite, amphibolite, and cummingtonite-hornblende-biotite cummingtonite-hornb!ende-biotite rocks. hornblendite, and rocks. The Shawmere Shawmere anorthosite anorthosite complex (Thurston et et al., al., 1977) 1977) consists of a main main northern body, measuring 55 xx 15 km. km. The 50 km and a smaller mass, mass, measuring The bodies bodies taper to to body, 15 15 x 50 the northeast and and thus thus have haveconcordant concordantcontacts. contacts. Gneissic and southwest and Gneissic textures textures prevail in in the the outer outerportions portionsof ofthe themain mainbody, body,whereas whereas primary primaryigneous igneous minerals minerals and and textures are preserved preserved in the interior interior(Simmons (Simmons et et al., al.,1980). 1980). The Themain mainbody body comprises comprises four distinct (1)aaborder border zone zone of of distinctlithological-textural lithological-texturalunits units(Riccio, (Riccio,1981; 1981;Fig. Fig.7): 7):(1) rnigmatitic, foliated migmatitic, foliatedtot ogneissic gneissicgarnetiferous garnetiferousamphibolite, amphibolite,(2)(2)a abanded banded zone zone consisting consisting of 11 ttoo 30 30 cm-thick layers layers of anorthosite, anorthosite, gabbro, gabbro, garnet-rich, and and ultramafic ultramafic rock, rock, (3) (3)an an anorthosite zone gabbro and (14) megacrystic gabbroic gabbroic anorthosite (4)aamegacrystic anorthosite zone containing containing minor gabbro zone with plagioclase phenocrysts cm and and minor minor anorthosite, anorthositic phenocrysts to t o 50 cm anorthositicgabbro, gabbro, gabbro and andmelagabbro. melagabbro. AA 1 km km wide wide body bodyofoffoliated foliated garnetiferous tonalite tonalite is gabbro is present present within the the outcrop outcrop area of the anorthosite. anorthosite. Its Itsgenetic geneticrelationship relationshipto t othe theanorthosite anorthosite complex is not clear although although ititappears appears to tobe be temporally temporallyrelated related(Simmons (Simmonsetetal., al.,1980). 1980). southern body body consists consistsdominantly dominantly of of coarse coarse gabbroic anorthosite. The southern The orientation orientation of gneissosity and lithological lithological contacts the prominent prominent The gneissosity and contacts make make up up the east-northeast structural structural grain of the structural zone. zone. Gneissosity in all east-northeast the Kapuskasing Kapuskasing structural Gneissosity in rock types is folded or warped gently-plunging (0-25°) northeast-trending axes. warped about gently-plunging (0-25O) northeast-trending axes. The folds vary from from isoclinal "Z"sense senseasymmetry asymmetrywhen when viewed viewed toward toward isoclinalwith withconsistent consistent"Z" the east to northwest-facing northwest-facing monoclinal flexures. flexures. Axial Axialsurfaces surfacesare arerarely rarelyaccompanied accompanied by a foliation foliation defined defined by by flattened flattened quartz quartzgrains. grains. The Thetrend trendofoflineations lineationsand andfold foldaxes axesisis northeast-southwest throughout throughout this part of but plunge plunge direction direction northeast-southwest of the theKapuskasing Kapuskasing zone, zone, but varies on on aa regional regional scale scale from from dominantly dominantly southeasterly southeasterly in in the the south south tto northeasterly in o northeasterly the north. Between lineations are are within within 10° Between these these areas, areas, lineations 1O0 of horizontal horizontal and and abrupt changes plungedirection direction occur occur on on the the 100 m m scale. scale. Both Both regional regional and and local local plunge plunge changes inin plunge reversals can be be related related to aa gently gently southeast-plunging southeast-plunging warp axis. reversals can �r LI I - 17 - I A A I I I I 'A -4- -s A 'c -e A Sc "INDEX MINERAL' ISOGRADS (teeth point p up—grade) 0 A / Clinopyroxene / -f n A A Garnet — cIinopyroxene Orthopyroxene A A I 'Lfl A A 4, / 1' A A4 A n I I I I I I I I I I I . . LEGEND LEGEND 1 SYMBOLS SYMBOLS Alkalic rock-carbonotite complex Granitic Graniticrocks rocks ' Anorthositic Anorthositic rocks rocks . Retrograde Retrograde greenscllst greemctist fades facies laI Unsubdivided — Unsubdivldedgreenschist ÇMnSchist amphibolite amphibolite facies facie* supra— supracrustal crustal rocks rocks Cataclastic ASSEMBLAGES ASSEMBLAGES MAFIC(BASALTIC) (BASALTIC)GNEISS GNEISS MAFIC C HbHb-P1PI —Hb—PI CE Gt Gt-Hb-PI nfl Cpx—Hb—PI Cpx-Hb -PI ttton ton Q Gt Gt—Cpx-Hb-PI -Cpx-Hb-PI -Qz -02 GI~t—Cpx —Qz ton -CPX-Hb—PI -~b-PI -02—-ton Gt -ton Gt—Opx-Cpx-Hb—PI -0px-Cpx-Hb-PI—Qz -02-ton DIOR ITIC ROCKS ROCKS DIORITIC A Hb—Bt-PI Hb-Bt-PI -Qz -02 r A Hb—Bt Hb-Bt—P1 -PI—Qz -02—ton -ton AA Cpx-Hb—Bt Cpx-Hb-Bt—P1 -PI -02 -ton -Qz -ton AA Opx-Cpx-Hb—Bt Opx-Cpx-Hb-Bt—P1 -PI -Qz -02-ton -ton PARAGNEIS PARAGNEISSS 00 BtBt—P1 -PI —Qz±Hb -0ztHb(+sfauroliteØ) (*stniirnl~te 0) 0<SGt—Bt Gt -Bt -P1 -PI -QztHb -0ztHb AA Opx—Gpx—Hb—Pl ±Qz opx-OPX-H~-PI to2 CC Gt Gt-Hb-PI -Hb-PI ±Qz Hb-PltQz C Hb-Pl e0Opx-Bt-PI Opx-Bt -PI-Qz -02 ANORTHOSIT1C ROCKS ROCKS ANORTHOSITIC e0 GtOpxHb-PItQz Gt-Opx-Hb-PltQz ULTRAMAFIC +ULTRAMAFIC ROCKS ROCKS CCGt—Bt-PI —Qz—ton Gt-Bt-PI -02-ton± tHbHb opx-cpx-~b(+Pp (<-PI.+) Opx-Cpx—Hb 4) cM -Opx-Bt—PI -Qz—ton(+Kspe) 1 -op~-Bt-pI -O~-~O~(+KSD:È Opx-Cpx-Bt-Pl -Qz-ton zone . Figure Metamorphicmineral mineralassemblages assemblagesand andindex indexmineral mineralisograds isogradsIfor part of ofthe the Figure8.8. Metamorphic or part Chapleau-Foleyet garnet;Opx Opx- orthopyroxene; orthopyroxene;Cpx CpxChapleau-Foleyet area. area. Gt Gt- -garnet; clinopyroxene; clinopyroxene;Hb Hb- hornblende; hornblende; Bt Bt- -biotite; biotite; P1 PI- -plagiocase; plagiocase;Ksp Ksp- -feldspar; feldspar; Qz Qz- quartz; quartz;ton ton- -tonalitic tonaliticsegregations. segregations.(after (afterPercival, Percival,1983) 1983) - - - - �- 18 - Two high-grade high-grade metamorphic metamorphic zones canbe bedistinguished distinguishedininthis this part part of of the the Two Kapuskasing structural zone. zone. Assemblages characteristic of Kapuskasing structural Assemblages characteristic of aa lower-grade lower-grade garnetgarnetclinopyroxene-plagioclase zone zone are are developed developedinin mafic mafic gneiss. gneiss. Orthopyroxene, in clinopyroxene-plagioclase Orthopyroxene, present present in four areas (Fig. 8; areas in most rock types, is is diagnostic of aa higher-grade higher-grade orthopyroxene zone zone (Fig. Percival, 1983). 1983). A continuous reaction resulting resulting in of hornblende in mafic A continuous reaction in decomposition decomposition of hornblende in mafic rocks rocks to to produce garnet garnet and and clinopyroxene clinopyroxene may may be bewritten: written: hornblende plagioclase^±garne ± garnet + clinopyroxene + + quartz quartz + ll2O (1) + clinopyroxene +H 20 ornblende ++ plagioclase (1) The coexistence over large areas areas of of this divariant and tonalitic tonalitic leucosome xistence over divariant assemblage assemblage and leucosome veinlets suggests that the the reaction reaction was liquid over over aa range range veinlets suggests that was anatectic anatecticand and also also produced produced aa liquid of P-I conditions (Fig. 9): 9): hornblende ++pplagioclase garnet + ÷ clinopyroxene clinopyroxene ++ tonalite tonalite hornblende l a g i o c l a s e±e garnet (2) (2) A reaction leading leadingtto the production production of of orthopyroxene orthopyroxene in in mafic mafic rocks is: is: A possible possible reaction o the hornblende ++garnet garnete ± orthopyroxene + clinopyroxene clinopyroxene ++ H20 H20 hornblende (3) (3) The evolved evolved water would The would presumably presumably have have been been taken up by anatectic anatecticLiquids. liquids. In paragneiss, paragneiss,aare reaction producing orthopyroxene yroxen in the presence of anatectic melt is: is: . . biotite + quartz ÷ plagioc1ase orthopyroxene + gra.rtodioritic (4) ' biotite + + plagioclase^sorthopyroxene + grandioritic liquid * . - .. > ..~. .'. ..,. diagram summarizing summarizing continuous continuous reactions reactions in in the mafic - - ' - : AA P—I P-T diagram mafic system system and and apparent metamorphic conditions on various mineral geothermometers conditions based based on geothermometers and and geobarometers, is presented in Figure Figure 9. 9. Apparent Apparentpressures, pressures,based based on onNewton Newtonand and geobarometers, Perkins' (1982) (1982)garnet-clinopyroxene-plagioclase garnet-clinopyroxene-plagioclasequartz quartz barometer, barometer, are a r e plotted plotted on on aamap map Perkins' have aan averagevalue valueofof 6.3 6.3 kbar. kbar. This 10 and have n average This barometer apparently apparently in Figure 10 by 1-1.6 underestimates pressure pressure by 1-1.6 kbar (Newton (Newton and and Perkins, Perkins, 1982; 1982; Ghent et et al., al., 1983) 1983)and and hence an an average average value valueof of 7.8 7.8 kbar kbar is is suggested. suggested. Apparent temperatures, temperatures, based based on the hence Ellis garnet-clinopyroxene thermometer thermometer (Fig. 9) 9)are a r e in in the t h erange range 700700Ellis and and Green (1979) (1979) garnet-clinopyroxene 800°C. Metamorphic on water water barometry 80O0C. Metamorphic fluids fluidswere were probably probably depleted depleted in H20, H20, based based on (Percival, 1983) and the the presence presenceof of carbonic carbonic fluid inclusions 1983) and inclusions (Rudnick (Rudnick et et al., al., 1984). 1984). The assemblage assemblageaimandine almandinegarnet-clinopyroxene-plagioclase-quartz garnet-clinopyroxene-plagioclase-quartz is diagnostic The of the regional egionalhypersthene hypersthene zone zone according according to t o Winkler Winkler(1979, (1979, p. p. 260, 260, 267-268). 267-268). de de Waard Waard (1965)and andGreen Greenand andRingwood Ringwood (1967) (1967)suggested suggestedthat that this this assemblage forms as an an (1965) forms as alternative to anulite-facies toorthopyroxene-plagioclase orthopyroxene-plagioclaseduring during high-pressure high-pressure gr granulite-facies alternative metamorphism. Turner attachesaadifferent different significance significance to t o the theassemblage, assemblage, metamorphism. Turner (1981) 0981) attaches �I I I I I - 19 - 12 I 0 4 0$ I $ 9. I 0 0 I I . II 7. .0 I 0) 0) 0) .5 3 11.5 S 0 Gt-Cpx—Hb—PI—Oz Gt-Cpx- Hb-PI-Qz C 0 Ct Gt—Opx—Cpx—Hb—PI -0px-Cpx-Hb-PI 0 0 Gt—Opx—Bt—PI—Oz Gt-Opx-Bt-PI-Qz I. 4. I I S •• 0. I I S. . 0 3 I I S 0 700 800 Temperature (°C) Figure Figure 9. 9. Summary of reactions applicable to mafic Summary of mafic rocks rocks arid and metamorphic pressuretemperature temperature estimates. estimates. Temperatures Temperatures are arederived derived from from the garnet- clinopyroxene and Green, Green, 1979) 1979) and pressures from clinopyroxene thermometer thermometer (Ellis (Ellis and garnet-pyroxene-plagioclase-quartz garnet-pyroxene-plagioclase-quartzbarometers barometers(Newton (Newtonand and Perkins, Perkins, 1982). 1982). �-20regarding based ononBinns' regarding it it as as transitional transitionalfrom fromamphibolite amphiboliteto t ogranulite granulitefades fades based Binns'(1964) (1964) study. In the present study area, the location of the garnet-clinopyroxene-plagioclase study. In the present study area, the location of the garnet-clinopyroxene-plagioclase zone hornblende-plagioclase÷clinopyroxene rocks zone between between hornblende-plagioclase+clinopyroxene rocks and and orthopyroxene-bearing orthopyroxene-bearing rocks suggests suggeststhat that it it characterizes amphibolite-granulite facies transition. characterizes the the amphibolite-granulite facies transition. rocks Although is the the same that in Although the the assemblage assemblage is same as as that in the theAdirondacks Adirondacks(de (deWaard, Waard,1965) 1965) and and temperature Bohlen and Essene, 1977),the the path path of temperature conditions conditions were were similar similar(Cf. (cf. Bohlen Essene, 1977), metamorphism different. In In the the Grenville Grenville Province, Province, the the development development of of garnetgarnetmetamorphism was was different. clinopyroxene hasbeen beenattributed attributed tto isobaric cooling clinopyroxene assemblages assemblages has o isobaric cooling of orthopyroxeneorthopyroxeneand Schrijver, plagioclase granulites (Martignole 1971; Whitney, 1978) whereas in plagioclase (Martignole and Schrijver, Whitney, 1978) whereas in the the Kapuskasing Kapuskasing zone, zone, garnet garnet and and clinopyroxene formed formed during during prograde reactions. Rounded zircons of Rounded zircons of probable probable metamorphic metamorphic origin origin from from Kapuskasing Kapuskking mafic maficgneiss gneiss gave a concordant date date of of 2,650 2,650 Ma Ma and and from fromaaleucosome leucosome layer layerininparagneiss paragneiss of 2,627 2,627 Ma Ma (Percival (Percival and and Krogh, Krogh, 1983; 1983; Fig. 11). 11). Further Furtherwork workon onmetamorphic metamorphiczircon zirconhas has extended (Krogh et et al, A al, 1986). 1986). A extended the the range range of of metamorphic metamorphic dates dates to t o 2696-2616 Ma Ma (Krogh minimum age of of emplacement emplacement for foliated tonalite minimum age tonalite from from the theShawmere Shawmere complex complex is provided by by zircons (2,765 (2,765 Ma) Ma)but butthe the U-Pb U-Pb system system has has been been strongly affected affected by by the the high-grade Krogh, 1983). 1983). The rocks rocks intruded by by tthe high-grade metamorphism metamorphism (Percival and Krogh, h e tonalite tonalite are thus t h e Abitibi Abitibi and and Michipicoten Michipicoten belts. thus older older than than dated dated volcanic volcanic rocks rocks of of the Quartz-bearing gabbroic anorthosite contains contains zircon zircon with with two two habits: habits: red-stained red-stained resorbed grains with with meta-igneous meta-igneous appearance, appearance, and equant, multifaceted, colourless colourless grains of probable probable metamorphic origin. Both Bothpopulations populations have have aa U-Pb U-Pb age ageof of 2649 2649Ma Ma (3.A. Sullivan, unpublished unpublisheddata), data),interpreted interpreted as tthe (LA. Percival and R.W. R.W. Sullivan, h e time time of of metamorphic The analysis analysis of of the coarsest coarsest resorbed resorbed grains grains plots slightly slightly to the the metamorphic cooling. cooling. The right line, suggesting suggesting an an older older component. component. right of of the the2649 2649Ma Ma discordia discordia line, At least least two two swarms swarms of fresh fresh mafic mafic dykes dykes transect transect metamorphic metamorphic rocks rocks of of the the Kapuskasing zone. East-northeast-striking, Kapuskasing zone. East-northeast-striking, southeast-dipping southeast-dippingKapuskasing Kapuskasingdykes dykes are are11to to 10 m m wide, wide, sparsely sparsely plagioclase plagioclase porphyritic, porphyritic, mediummedium- to to fine-grained, fine-grained, ophitic, green-grey gabbro. Northeast-trending Northeast-trending olivine-bearing olivine-bearing dykes dykes may may belong belong to t o the the Abitibi Abitibi swarm. swarm. Several rock-carbonatite complexes Several small alkalic rock-carbonatite complexes are associated with the the Kapuskasing zone. The Kapuskasing zone. The more more northerly northerlybodies bodieshave haveK-Ar K-Ar dates datesofof1655 1655tot o1720 1720Ma, Ma, whereas those in the the south south have have dates datesof of 1050 1050to t o 1100 1100 Ma Ma (Gittins et e t al., al., 1967). 1967). Thin Thin lamprophyre dykes and andaa rare rare diatreme diatreme breccia are are associated associated with with the the complexes; complexes; lamprophyre dykes biotite biotite from fromaalamprophyre lamprophyre dyke dyke in the Chapleau-Foleyet Chapleau-Foleyet area gave a K-Ar K-Ar date date of of 1144 I144 +±31 31 Ma (Stevens eta!., e t al.,1982). 1982). 4 i 1 $ Li �r I I I I I I 1 $ I I -21 - PALEOPRESSURE PALEOPRESSURE ESTIMATES ESTIMATES Equilibria Equilibria I I I 032—8.3 / 024- ,+. 29-6.5 21 —& 53 .1W( DC 0 22— 8.i;9,9 W 06.7 enstatite=1/3 grossular ~ 6 . Anorthite+ 7Anorthite+enstatite=1/3 gross + 2/3 pyrope+quartz 0+ 2/3 pyrope+quartz (Perkins (Perkins&SNewton, Newton,1981) 1981) 2 06.7W 0 6 . 7 ~Garnet—orthopyrOXene Garnet-orthopyroxene A (Wood, (Wood,1974) 1974) 06.79 06.7~33Anorthite=grOSSUIart Anorthite=grossular+ 2 sillimanite÷ciuartz (Ghent, 1976) 07-6.7 2 0-6.2 14—' 0 10—6.6 013—4.29.9W 013-L2.9.9W >20 1 1.3,COW 17-6.5 — 48°00 - 2 1—6.7 0 Chapeat 10 0 40 I I I 6-7.3 2 3—5.4 06.7 grossular 06.7 Anorthite+diopside=2/a ~northite+diopside=~/s grossu ÷+ 1/3 pyrope+quartz V3 pyrope+quartz I I 3 1-6.00 km km Figure Figure10. 10. Paleopressure Paleopressure map Symbols represent rock map of of the Chapleau-Foleyet Chapleau-Foleyet area. area. Symbols type paragneiss; squares squares - mafic mafic gneiss; gneiss; triangles triangles - orthogneiss). orthogneiss). type (circles (circles- paragneiss; Numbers Numbers to to the the right rightofofthe thedash dashare arepressure pressure estimaters estimators(kbar) (kbar)keyed keyed to tothe the equilibrium equilibriumused used to t o derive derive the t h e value. value. The The6.3 6.3 kbar kbar reference referenceline lineisisbased based on on garnet-dinopyroxene-plagioclase-quartz equilibrium. (afterPercival, Percival,1983) 1983) garnet-clinopyroxene-plagioclase-quartz equilibrium. (after - - - RELATIONSHIP OF OFKAPUSKASING KAPUSKASING STRUCTURAL STRUCTURAL ZONE ZONE TO TOAD3ACENT ADJACENTSUSPROVINCES SUBPROVINCES RELATIONSHIP The The contact contactbetween between the theKapuskasing Kapuskasing structure structureand and Abitibi Abitibisubprovince subprovinceisis aa zone zone of faulting faultingand andcataclasis, cataclasis,the theIvanhoe Ivanhoe Lake Lake cataclastic cataclasticzone, zone, that thatseparates separates the the two two of terranes of of contrasting contrasting lithological, lithological, structural, structural,and and metamorphic metamorphic characteristics. characteristics. The The terranes �- 22 — 2O6 b 238 u 0.55 2800 1• 14 '4, 0N 2 0.50 'Ix Paragneiss Paragneiss leucosorne leucosome ( Vv Mafia Mafic gneiss gneiss (2) (2) 013 Shawmere Shawmere tonalite tonalite (3) (3) (vanttoe Ivanhoe Lake Lake ptuton pluton (4) (4) 0a Gneissic Gneissic tonalite tonalite (5) (5) v- 0¡ ' + OneissicGneissic- foliated granodiorite granodiorite (6) (6) 7 0 0.45 ZO7Pb 235u 12.0 13.0 14.0 15.0 Figure Figure 11. 11. Concordia Concordia diagram diagram with with isotopic isotopic ratios ratiosof of zircon zircon samples. samples. Ab: Ab:abraded abraded (Krogh, N: non-magnetic (Frantz); MI: magnetic at : non-magnetic MI: magnetic atj0l oside side tilt tilt (Krogh, 1982); 1982); N (Frantz); (Frantzk pr: pr: prismatic; prismatic; an: an: anhedral. anhedral. Solid Solidlines lines are areempirical empiricallead-loss lead-loss trajectories; Ma trajectories;dashed dashedline: line: hypothetical hypothetical lead-loss lead-loss trajectory trajectory(projects (projectstoto0 0Ma lower lower intercept); intercept); dash-dot line: empirical mixing xing line. line. (after (afterPercival Percivaland and Krogh, Krogh, 1983) 1983) zone zone is is defined defined in part by by positive, positive, linear north-northeast-trending north-northeast-trending aeromagnetic aeromagnetic anomalies pairedhigh high(Kapuskasing) (Kapuskasing) --low low (Abitibi) (Ab'itibi) anomalies and and coincides coincideswith withthe thetrough troughofofa apaired gravity and12). 12). gravityanomaly anomaly(Figs. (Figs.44and The Ivanhoe Ivanhoe Lake cataclastic zone is is characterized characterizedby bynarrow narrowveinlets veinletsof offinely finely The cataclastic zone comminuted rock rock which which form form discontinuous, discontinuous, randomly-oriented randomly-oriented pods pods and networks. networks. Two Two comrninuted foliatedtotomassive, massive,semi-opaque semi-opaque typesof of fault faultrocks rockscan canbe bedistinguished. distinguished. The Thefirst firstisisfoliated types mylonite, cataclasite cataclasiteand andblastomylonite, blastomylonite, partly partly or or totally totallyrecrystallized recrystallizedtot ofine finegrained grained mylonite, epidote, chlorite, chlorite, carbonate, carbonate, and and actinolite. actinolite. The Thesecond secondtype typegrades gradesfrom from cataclasite cataclasitetoto epidote, pseudotachylite with with aphanitic, aphanitic,almost almostopaque opaquematrix matrixand androunded, rounded,embayed embayed pseudotachylite monomineralic rnonomineralicporphyroclasts. porphyroclasts. �r I I o - 23 - - -5 It: .- > F 0 -to- .3c. -so- m CB - 0 10 kkrn m I I I 20 Shawmere Shawmere anorthosite anorthosite complex complex PROTEROZOIC 1100 Ma alkalic-rock complex ARCHEAN Massive granite. granodiorite (G2.70) I I I I I I 4 Ivanhoe Ivanhoe Lake cataclastic cataclastic zone zone 1 I Tonalitic gneiss (G.270) H Metavolcanic rocks (Gz2.90) Anorthositic rocks (G~2.82) (G2.82) Anorthositic rocks Kapuskasing gneisses (G2.52) Kapuskasing zone zone gneisses (G=2.82) Figure Figure12. 12. Generalized Generalized west-east west-east cross-section cross-section from fromthe theWawa Wawa domal domal gneiss gneiss terrane, terrane, through structural zone zone into into tthe Abitibi subprovince, through the t h e Kapuskasing Kapuskasing structural h e Abitibi subprovince, showing showing gross gross crustal structure. The The gravity gravity model modelbased based on on the t h e average average rock rock densities: densities: tonalitic tonaliticgneiss gneissand andgranite: granite:2.70; 2.70; metavolcanics: metavolcanics: 2.90; 2.90; Kapuskasing structural zone Kapuskasing structural zoneand and lower lower crust: crust:2.82 2.82 g/cm g/cm 3.3. The cataclastic zone The dip of the the Ivanhoe Ivanhoe Lake cataclastic zoneisisnot notwell wellconstrained constrainedgeologically. geologically. Although fault-rock veinlets are Although some fault-rock are parallel parallel to t ogneissosity gneissosity and and therefore thereforedip dipgently gently northwest, northwest, many many others others have have random random orientation. The Thejuxtaposition juxtapositionofofhigh-grade high-grade against displacement across across the the cataclastic cataclastic zone. against low-grade low-grade rocks indicates reverse displacement zone. The The associated associated paired paired gravity gravity anomaly anomaly is i s characteristic characteristic of of many many well-documented well-documented overthrust terranes terranes(Smithson (Smithsonetetal., al.,1978; 1978;Fountain Fountainand andSalisbury, Salisbury,1981) 1981) and suggests that that the the Ivanhoe cataclastic zone Ivanhoe Lake cataclastic zone is is the t h esurface surfaceexpression expression of of aanorthwest-dipping northwest-dipping thrust thrust fault fault(Fig. (Fig. 12). 12). AAshort short(10 (10km) km) seismic reflection survey survey over the zone indicates aa reflector reflectorininthe t h eappropriate appropriateposition positionwith withaatrue truenorthwesterly northwesterlydip dipofof38-40° 38-40-(Cook, (Cook,1985; 1985; Fig. Fig. 13). 13). The boundaryvaries variesinincharacter character over over its its length. length. North The Wawa-Kapuskasing Wawa-Kapuskasing boundary North of of Bonar Bonar Lake, Lake, it i t is is aafault, fault,with withdistinct distinctaeromagnetic aeromagneticexpression, expression,which whichdiverges diverges westward westward into into Wawa Wawa tonalites tonalites toward toward the thesouthwest. southwest. South SouthofofBonar BonarLake, Lake,the t h eboundary boundaryhas has T �_______________ - 24 — 24 a a LINE KAP LINE KAP - s-P. ____.i —. b — 2I -1 1sw 5 km 400? —-.-——---- :200 LINE KAP b 5.P. n_fl- 201 -1 5km W — A —C N S C — B — —— —— - A B 5.0. Figure 13. a ) Figure 13. a) Seismic reflection profile over the eastern Kapuskasing zone. The data Seismic reflection profile on left the Kapuskasing continuity of zone. reflections is are plotted with east overbecause the eastern The data are plotted with east on left Reflection because theAcontinuity better in this orientation. is likely from the Ivanhoeis Lake of reflections better in this zone; orientation. cataclastic reflections B a r e from t h e Abitibi Reflection A is within likely from the subprovince. Lake cataclastjc zone; reflections B are from within the Abitibi Ivanhoe subprovince. b) Line drawing interpretation of a ) (after Cook, 1985). b) Line drawing interpretation of a) (after Cook, 1985). �'I -25- I I I J I I I I $ gradational lithogical, structural and lithogical, structural and metamorphic metamorphic characteristics. Mafic Maficgneiss gneiss with with minor paragneiss paragneiss is typical of the minor the Kapuskasing Kapuskasing zone but also occurs in in the the Robson Robson Lake Lake dome with characteristic structural style subprovince. GarnetGarnetdome style of the the Wawa Wawa subprovince. clinopyroxene-hornblende-plagioclase assemblages are common commonhere, here, suggesting suggestingthat that the clinopyroxene-hornblende-plagioclase assemblages are metamorphic similar to that in the structural zone. zone. The metamorphic grade grade is similar the Kapuskasing Kapuskasing structural The discontinuous paragneiss paragneiss belt belt that extends 30km kminto intothe theWawa Wawasubprovince subprovince extends for for up upto t o30 discontinuous may also be be a part of lithological sequence. sequence. Tonalitic of the the Kapuskasing Kapuskasing lithological Tonalitic gneiss gneiss can be be traced eastward eastward from from the the Borden Borden Lake area, where it i t has has the the complex complex structures structures characteristic of characteristic of the theWawa Wawa subprovince, subprovince, into strongly foliated and lineated gneiss typical of the the Kapuskasing Kapuskasing zone. zone. The change in in structural structural style The change style from from domal domal in in the the eastern easternWawa Wawa subprovince subprovince to ENEbelts belts in inthe the Kapuskasing Kapuskasingstructural structural zone zonecan can be be used usedto to define define aa transitional transitional linear ENE boundary zone zone between betweenterranes terranes with with contrasting structural boundary structural styles, styles,but butno nosharp sharpline linecan can drawn on on this this bask. basis. South be drawn South of Chapleau, the orientation orientation of of gneissic gneissic layering layering changes changes eastward from horizontal horizontal near near the theHighbrush Highbrush Lake Lake dome, through a zone with a superimposed upright uprighteasterly easterly foliation, foliation, ttoo strong northeast-striking, superimposed northeast-striking, northwest-dipping northwest-dipping north-south-trending structural structural culmination coincides with with the eastern gneissosity. A north-south-trending eastern domes of of the Wawa subprovi.nce.East Eastofof the the culmination, culmination, lineations plunge plunge easterly easterly domes Wawa subprovince. toward a structural structuraldepression depression into into which which southwest-trending southwest-trending lineations of the southern southern Kapuskasingzone zonealso alsoplunge. plunge. To To the the north, lineations plunging northeasterly off the Kapuskasing plunging northeasterly the Lake arch arch appear ttoo be continuous with with northeastnortheastnortheastern flank flank of the the Missinaibi Missinaibi Lake plunging, reclined reclined folds in in tthe structural zone plunging, h e northern Kapuskasing Kapuskasing structural zone (Percival, (Percival, 1981 1981a,b). a,b). Cataclastic veinlets veinlets characterize the the faulted faulted contact contactbetween between mafic maficgneiss gneiss and and tonalitic tonalitic gneiss southwest southwest of of Kapuskasing KapuskasingLake. Lake. To To the the south, south, the the gradational nature of gneiss lithological contacts as well as the structural lithological structural and and metamorphic metamorphic continuity continuity between between high-grade gneisses gneissessuggests suggeststhat that the the contacts contacts were etablished prior tonalites and high-grade prior ttoo metamorphism and doming, doming, and and that that rock units of of the theKapuskasing Kapuskasing zone zone locally occur the Wawa Wawatonalite-granodiorite tonalite-granodiorite gneiss. gneiss. Based structurally below below the Based on on the the change change in in average rock density density across across this thisdiffuse diffusesubhorizontal subhorizontalboundary, boundary, Percival Percival(1986) (1986) suggested that it could represent an exposed mid-crustal mid-crustal (Conrad) (Conrad)discontinuity. discontinuit STRUCTURE OF THE THE KAPUSKASING KAPUSKASING CRUSTAL CROSS-SECTION I $ The The transition from from the the Michipicoten Michipicoten belt to t o the the eastern eastern boundary boundary of the the �- 26 - 0 C 4-. 0 04a. fl-I 0 5 :::::::::::. Ct E o . V CD U, ci) 67 __:::_::.c_:c.: C s a, r ——— i! iiiiii: ::::::::::::::::::::•— —15 T::::E:::::::::: :::.. — — — .. — -. ——— a — .A>2,765 — 25 \Ivanhoe Ivanhoe Lake Lake cataciastic cataclasticzone zone Figure Figure 14. 14. Restored Restoredvertical verticalsection sectionthrough throughthe theMichipicoten Michipicotenbelt, belt,domal domalgneiss gneiss terraneand andKapuskasing Kapuskasing zone. zone. Numbers Numbersare a r ezircon zircondates dates(÷4 (54Ma) Ma)on onigneous igneous terrane and meta-igneous rocks (after Percival and Card, 1983). Kapuskasing Kapuskasing zone can be interpreted interpreted as asan anoblique oblique crustal crustal cross-section cross-section based basedon onthe the following: following: 1)1)metamorphic metamorphic grade gradeincreases increaseseastward eastwardfrom fromlow lowgreenschist greenschistfacies faciesininthe the Michipicoten Michipicoten belt belt(Studemeister, (Studemeister,1983) 1983)through through amphibolite amphibolite facies faciesin inthe theWawa Wawadomal domal gneiss gneissterrane terranetotoupper upperamphibolite amphiboliteand andgranulite granulitefades faciesininthe theKapuskasing Kapuskasing zone; zone;2)2)the the proportion proportion of of plutonic plutonicto t osupracrustal supracrustalrocks rocksincreases increaseseastward eastwardininthe theWawa Wawasubprovince; subprovince; 3)3)the theoldest oldestrocks rocks(>2,765 b2.765 Ma) Ma)are a r eininthe theKapuskasing Kapuskasing zone zone at atthe theinferred inferredbase baseofofthe the section; section;4)4)the thegravity gravityanomaly anomalycan canbebebest bestmodelled modelledbybyusing usingaawest-dipping west-dipping crustal crustalslab slab (Fig. (Fig.12); 12);and and5)5 ) rocks rockswith withseismic seismicvelocities velocities typical typicalof of the theupper uppercrust crustare a r enot notpresent present �r I -27the Kapuskasing zone. The three major terrane types recognized in the Abitibi-Wawa region can be be related region can related to t o depth depth zones zones in in the the crust crustbased based on on metamorphic metamorphic evidence evidence and and consistent seismicvelocity velocitycharacteristics characteristics of of the the crust consistent with with known known seismic crust of of the t h e Superior Superior Province. crust is of supracrustal supracrustal rocks rocks of of the the greenstone Province. Thus Thus the the uppermost uppermost crust is made made up up of greenstone belts and and discordant discordant plutonic plutonic rocks. rocks. Beneath megalayer made made up up of of variably variably belts Beneath is is aa megalayer deformed felsic felsic ttoo intermediate deformed intermediate plutonic plutonic rocks, rocks, with with large-scale large-scale domal domal geometry. geometry. With With increasing depth within within this this layer, layer, the the attitude attitude of from sub-vertical, sub-vertical, increasing depth of gneissosity gneissosity changes changes from near zone. The near greenstone greenstone contacts, contacts, to t o sub-horizontal, sub-horizontal, near near the the Kapuskasing Kapuskasing zone. The lowermost lowermost exposed megalayer is represented represented by exposed megalayer by the t h e Kapuskasing Kapuskasing zone, made made up of aa heterogeneous heterogeneous lithological assemblage assemblage aatt high metamorphic grade. grade. Moderate high metamorphic Moderate dips dips of of lithological lithological layering lower crustal crustal attitude attitude rotated layering aare r e interpreted as as the t h e dominant dominant sub-horizontal sub-horizontal lower rotated passively uplift. passively during uplift. Construction of of a generalized generalized crustal crustal cross-section cross-section (Fig. (Fig. 14) 14) requires requires several several Construction assumptions: 1)the the dip dip of of the the crustal slab is constant; 2) assumptions: 1) 2) pressure is a function of depth de so that estimates of the estimates of of metamorphic metamorphic pressure pressure can be used used to derive tthe h e thickness of section; 3) the metamorphic assemblages assemblages aare r e the product product of of aa single single metamorphic metamorphic event; event; post-metamorphic vertical displacement on faults within 4) post-metamorphic and 4) within the the section section is isnegligible. negligible. The highest-grade highest-grade assemblage from tthe area is garnet-andalusite in h e Wawa Wawa area in indicating aa maximum maximum pressure pressure of of 3.3 3.3 kb kb and and aa depth of of metagreywacke (Ayres, (Ayres, 1969), 1969), indicating about 11 km (Carmichael, (Carmichael, 1978). 11 km 1978). Similar pressures, in the t h e 2-3 2-3 kb kb range, are arebased based on on sphalerite-pyrrhotite geobarometry on rocks rocks from Gutcher Lake, 30 km km northwest of o Wawa (Studemeister, 1983). 1983). The The range range of of pressures pressures estimated estimated from Wawa (Studemeister, from the t h eKapuskasing Kapuskasing garnet-clinopyroxene-plagioclase-quartz zone, based on Newton Newton and Perkins' Perkins' (1982) (1982) garnet-clinopyroxene-plagioclase-quartz barometer, is is 5.4 5.4 to to 8.4 8.4 kb kb (average (average of of 6.3 6.3 kb, kb, Percival, Percival, 1983) 1983) but the t h e lower lower values values may may result from re-equilibration re-equilibration during during cooling. cooling. These These values values correspond ttoo depths of 18 18 ttoo km (average (average 21 21km). km). The The minimum minimumerosion-level erosion-leveldifference difference isis therefore therefore 7 km, but the 28 km the closer ttoo 15 km. The maximumdip dipestimates estimates over over aa difference is is probably probably closer 15 km. The minimum minimum and maximum 100. constantly-dipping slab 120 km long long aare constantly-dipping 120 km r e approximately 5° 5O and lo0. The dips of of post-metamorphic post-metamorphic dykes dykes in in the the Kapuskasing Kapuskasing zone zone and and eastern easternWawa Wawa providean anindependent independentestimate estimateofoft the tilt of of tthe subprovince may may provide h e tilt h e slab in this area. dykes dip dip NE NE at at 75' 75° ttoo 85° and ENE ENE Kapuskasing Kapuskasing dykes dykes dip dip SE SEaatt 70 70° ttoo 85° 85' and 85"'. Matachewan dykes ' on measurements measurements of of dykes dykeswith withvertical vertical exposure exposureininroadcuts. roadcuts. Post-metamorphic based on Post-metamorphic maf Icdykes dykesinint the Shieldgenerally generallyhave havenear-vertical near-vertical orientations, rnafic h e Shield orientations, as asdo do Matachewan Matachewan dykes in the Abitibi subprovince (Thurston et a!., 1977; Mime, 1972). The consistent nonin I I fl I pLi I I I ' �- 28 - vertical dip may thus have resulted from large-scale crustal rotation. To restore the dykes of both both swarms swarmsto to vertical, vertical, a dykes of a 14° 14O counter-clockwise counter-clockwise rotation rotation about about an an axis axis trending 038° is necessary. necessary. Thus 14°northwesterly northwesterly dip dip is is indicated indicated in in this trending 038'' is Thus aa 14" this eastern eastern area. area. The difference difference in The in dip dip estimate estimateprovided provided by by these these two twomethods methods may may be be due due to to uncertainties in the the calculations, calculations, faulty or real uncertainties in in the the data data used used in faultyassumptions, assumptions, or real differences differences in in dip dip from from east east to t o west. west. The The overall overall dip dipmust must flatten flattentot othe thenorthwest northwestand andisisreversed reversed northwest northwest of of the t h e Michipicoten h4ichipicoten belt beltwhere whereErnst ErnstU981, (1981, p. p. 87; 87; 1983) 1983) reported reported consistent consis 85° SW dipsofof Matachewan Matachewandykes. dykes. Therefore, Therefore, an an intermediate intermediate dip 85O SW dips dip value value of of 10° 10' If dips flatten perpendicular tto the fault fault was for construction construction of perpendicular o the was chosen chosen for of Figure Figure 14. 14. If dips flatten toward the the northwest, northwest, this this will will result of the toward result in in over-estimation over-estimation of of the the true true thickness thickness of the section. The generalized section section is is a a valid valid representation representation provided provided that that(1) (I)aa single si The generalized regional event affected affected all (2) late late vertical vertical regional metamorphic metamorphic event all of of these these rocks, rocks, and and (2) displacement along faults isisnegligible Wawa negligiblebetween betweenthe theIcapuskasing Kapuskasingzone zone and and eastern e displacement along faults subprovince. In subprovince. In view of of the thecomplex complex relationships relationships described described and and uncertainties uncertainties involved, involved, these simplifications simplifications may information which be these may be be unwarranted; unwarranted; however, however, the information which can can be derived from an exposed exposedcross-section cross-sectionthrough throughpart partofofthe thecrust crust is is potentially potentially valuable derived enough permit some enough tto o permit some speculation. The generalized crustal cross-section, cross-section, constructed constructedusing using aa dip dipof of10° 10' (Fig. (Fig.14), 14),has has at its upperamphibolite amphibolite tto its base base a sequence sequence ofof upper o granulite granulite facies faciesgneiss gneiss and anorthosite, unknown,and andof ofwhich whichsome some55tot o10 10km km isisexposed exposed in i the the full fullthickness thicknessofofwhich whichisisunknown, Kapuskasing zone. Structurally Kapuskasing zone. Structurallyabove aboveand and separated separated by by an an analogue analogue of the the Conrad Conra an estimated estimated 10 tto km thickness thicknessof of tabular tabular ba batholiths discontinuity (Percival, (Percival, 1986) 1986) is an o 15 km of gneissic and xenolithic tonalite. sheetsand anddeepdeepgneissic and tonalite. Massive Massivegranitic graniticrocks rocksoccur occurasassheets rooted plugs at this this structural structural level. upper 5-10 km, both both granitic granitic rocks level. In the upper 5-10 km, rocks and and plugs at gneissic migmatitic migmatitic haloes surroundthe thelow-grade low-gradeMichipicoten Michipicotenbelt. belt. The interfaces gneissic haloes surround between the the adjacent, adjacent, generally horizontal megalayers undulating surfaces surfaces with with between megalayers are undulating several kilometres kilometres of of relief, domesatatintermediate intermediate structural structural levels as gneiss gneiss domes several relief, manifest manifest as and as as intrusive intrusive bodies bodies aatt higher levels. and In the western Superior Superior Province, two seismic seismic discontinuities discontinuitiesat at16-19 16-19and and 21-22 21-22 km, define upper, km, upper, middle and and lower crust (Hall (Hall and and Brisbin, Brisbin, 1982). 1982). Using Usingthe theKapuskasing Kapuskasing model, boundary between betweenaastructurally structurally higher model, the upper upper discontinuity corresponds corresponds tto o the boundary granitoid gneissic subjacent heterogeneous heterogeneous high-grade high-grade gneiss gneiss complex, granitoid gneissic layer layerand and aasubjacent whereas the lower discontinuity, corresponding to the middle-lower crustal boundary, is �I I I I I I I -29probably aa metamorphic metamorphic isograd (orthopyroxene (orthopyroxene isograd?) within withinthe theheterogeneous heterogeneous gneiss. Woods (1985)studied studiedelectrical electrical conductivity conductivity in Woods (1985) in the theKapuskasing Kapuskasing region with with aa large-scale array. Although large-scale magnetometer magnetometer array. Although the t h elower lowercrust crustisisanomalously anomalously conductive conductive in in the area (Duncan et al., al., 1980), there is is no no conductivity conductivity anomaly associated associated with with the 1980), there (Duncan et Kapuskasing zoneofofmidmid-t otolower lowercrustal crustalorigin. origin. This was wasinterpreted interpreted tto indicate that that Kapuskasing zone o indicate the conductivity the result of in conductivity anomaly anomaly at depth depth is the & situ fluids fluids which which were were lost during uplift uplift ofofthe theKapuskasing Kapuskasing structure. Similar gravity Similar models models of mega-layered mega-layered continental continental crust crustare arebased based on on seismic seismic and and gravity data (Smithson and Brown, Brown, 1977; 1977;Berry Berryand andMair, Mair,1980). 1980). Other Other inferred inferred cross-sections (Smithson and cross-sections through the the crust crust (Ivrea (Ivrea zone, zone, Pikwitonei Pikwitoneiregion, region,Musgrave, Musgrave, Fraser Fraser ranges; ranges; Fountain Fountain and and Salisbury, haveinincommon commonaadownward downwardincreasing increasingmetamorphic metamorphic grade grade and and aa thick, thick, Salisbury, 1981)have intermediate-depth intermediate-depth amphibolite-facies amphibolite-fades section section of of quartzofeldspathic quartzofeldspathicgneiss, gneiss, corresponding gneissterrane terrane of of the Wawa Wawasubprovince. subprovince. In In the the central corresponding tto o the domal gneiss Superior Province section, intrude and and assimilate assimilate both the section, these these gneisses gneisses intrude the overlying overlying supracrustal succession successionand andparts partsofofthe theunderlying underlyingcomplex. complex. The entire section down The entire down tto o I ' I 20 addedt to the crust crust in the interval 20 km was was added o the intervalbetween between 2750 2750and and 2680 2680 Ma. Ma. The The prepreexisting as thick thick as present present continental continental crust crust existing crust crust may may have, have, but but need need not have have been been as prior to to the the major major thickening thickeningevent. event. The Thehigh highmetamorphic metamorphic grade grade in in this this older older crust crust can can be accounted accountedfor for by by burial, burial, first first by later by by intrusion intrusion of of by aa volcanic volcanic pile pile and and somewhat somewhat later tonalite tonalitesheets. sheets. ARCHEAN ARCHEANEVOLUTION EVOLUTION OF OF THE THE KAPUSKASING KAPUSKASING CRUSTAL CRUSTAL STRUCTURE STRUCTURE I The and mafic gneiss of the The oldest rocks so far far recognized, recognized, paragneiss paragneiss and gneiss of the Kapuskasing zone, aare considered part part of a sedimentary-volcanic Kapuskasing zone, r e considered sedimentary-volcanic succession succession deposited deposited $ probably also prior to and probably probably as asaastratiform stratiform body t o 2765 2765 Ma M a ago and body at a t depths depths of less less than than 20 20 km, as inferred from from the the presence presence of relict relictolivine olivine(Thurston (Thurstonetetal., al., 1977; 1977; Kushiro Kushiro I I I I prior prior to t o2765 2765 Ma Ma ago. ago. The TheShawmere Shawmere anorthosite anorthositewas was emplaced emplaced into intothis thissuccession, succession, and by Simmons et al. (1980), the intrusion intrusion may represent the As suggested suggested by Simmons et (1980), the the and Yoder, 1966). 1966). As differentiation basalt differentiationproduct productofoftholeiitic tholeiitic basaltmagmas magmaswhich whichalso also erupted erupted at a t surface. surface. Major Major eruption eruption of ofvolcanic volcanicrocks rocksand anddeposition deposition of ofsediments sedimentsoccurred occurredbetween between al.,1982) 1982)and andbetween between 2725 2725 and and 2749 and 2696 2696 Ma Ma ago in the Michipicoten Michipicotenbelt belt(Turek (Tureketetal., 2749and 2703 M Ma ago in in the western Abitibi a ago Abitibibelt belt(Nunes (Nunesand and PyRe, Pyke, 1980). 1980). The lowermost volcanics are dated by the U-Pb are generally generally mafic maficand and so so have have not been been dated U-Pb zircon method. method. �- 30 - including ultramafic, ultramafic, mafic, and trondhjemitic to Synvolcanic intrusions, including Synvolcanic to granodioritic granodioritic bodies, were intruded into into the theMichipicoten Michipicoten and and Abitibi Abitibi piles piles 2750 2750 ttoo 2700 MMa ago. Large Large volumes volumesofoftonalite tonalite intruded intruded beneath beneath and andadjacent adjacent tto the greenstone 2700 a ago. o the at this thistime. time.The Theminimum minimumage ageofof2707 2707Ma Mafor forWawa Wawa tonalite tonalh? (Fig. (Fig. 11) 11)isisgiven given by by aa belts at concordant point point and and is is therefore therefore probably close tto the age of of crystallization. nearly concordant probably close o the The tonalites tonalites could could be be the the subsurface expression expression of of magmas magmas that that produced produced &cites dacites in the The upper parts of the upper the volcanic volcanic piles. piles. Tonalite Tonaliteintrusions, intrusions,now now gneissic, gneissic, engulfed engulfed and and represented as detached fragments of the the lower lower parts parts of of the thegreenstone greenstone succession succession (now (now represented rnafic mafic xenolith trains), possible possible older, older, tonalite tonalitebasement basementenclaves enclaves(e.g. (e.g. 1-lillary Hillmy and and Ayres, 1980), 1980),and andthe thewestern western parts parts of of the Kapuskasing which extend extend into the Ayres, Kapuskasing zone which tonalite gneiss gneiss terrane. The Thetonalitic tonaliticrnagmas magmasmay mayrepresent representjuvenile juvenilemaginas magmas derived derived from the mantle, or may products of partial partial melting melting of of aa heterogeneous heterogeneous lower lower from may be the products crust similar to zone. The t o that that exposed exposed in in the the Kapuskasing Kapuskasing zone. The tonalitic tonalitic intrusions intrusions have have imposed amphibolite-facies amphibolite-facies aureoles on metavolcanic metavolcanic host host rocks; rocks; considering considering the thevolume volume imposed sufficient ttoo account for most of of tonalite, the the heat heat from fromthese thesemagmas magmas was was probably probably sufficient the metamorphism of the volcanics. metamorphism of volcanics. Tonalitic Tonaliticmagmatism magmatismthus thusmay mayhave havecoincided coincided with with regional metamorphism metamorphismand andacted actedas asthe the main mainagent agentofofheat heat transfer transfer into the upper regional upper crust (cf Wells, Wells, 1979). 1979). Isoclinally Isoclinallyfolded foldedgneissosity gneissosityininthe thetonalite tonalite demonstrates demonstrates that major (cf major deformation post-dates post-dates these these intrusions. intrusions. The age of of major deformation Abitibi and and Wawa Wawa subprovinces is closely deformation in in the the Abitibi Ma, the the approximate approximate age age of of the youngest volcanics of of the main youngest volcanics main bracketed between 2696 Ma, pile, and 2680 Ma,the the approximate approximateage ageofoflatelate- to post-tectonic plutons plutons (Frarey (Frarey and 2680 Ma, In supracrustal supracrustal rocks rocks at at high high crustal levels, this this deformation deformation produced produced Krogh 1986). 1986). In upright to vertically-plunging structural features upright vertically-plunging structural features as as well well as as thrusts thrusts and and nappe-like nappe-like structures etal., al.,1981; 1981; Gorman German et et al., al., 1978; 1978; Thurston and Breaks, Breaks, 1978). 1978). At structures(Poulsen (Poulsen et deeper structural structural levels, levels, the thedeformation deformationresulted resultediningneissosity gneissosity and and subsequent subsequent folds folds in in plutonic rock rock and and paragneiss, paragneiss, followed followedby bylater later doming. doming. Forceful emplacement of plutonic massive plutons plutons also also deflected deflected structural structural trends massive trends in in country country rock rock into into concordance concordance with with of these bodies. at 2680 2680Ma, Ma, the margins of bodies. Following Following intrusion of the the massive massive plutons at subprovinces. There there was was relative relative tectonic tectonicquiesence quiesencein inAbitibi Abitibi and and Wawa Wawa subprovinces. There is is evidence, however, of continued activity activity in in the theKapuskasing Kapuskasing zone. zone. High-grade metamorphic rocks of of the Kapuskasing yield concordant U-Pb High-grade Kapuskasing zone yield U-Pb zircon dates of 2696 Ma. U-Pb U-Pb zircon dates dates are a r e generally generally considered considered to t o record record 2696 ttoo 2616 2616 Ma. case are a r eof of metamorphic metamorphic origin. origin. the age of crystallization of of the the zircons, zircons, which which in in this this case interpretation would This interpretation would imply imply tthat h a t metamorphism metamorphism in in the t h e Kapuskasing Kapuskasing zone occurred �r I 1 I I 3 I I P I I I 2696 Ma ago,up upt to 60M Ma aftertectonic tectonic stabilization of of much much of of the the rest of 2696 ttoo 2616 2616 M a ago, o 60 a after of Superior province. A discrete burial and metamorphism metamorphismevent, event,restricted restricted tto burial and o the Superior province. Kapuskasing zone, could explain the deformed, metamorphosed metamorphosed conglomerate conglomerate cobbles cobbles from Borden Lake which which have have aa zircon zircon date date of 2664 2664 Ma Ma (Percival et al., al., 1981). 1981). However, However, Borden Lake an anomalously young zircon zircon date date of of 2552 M Ma on aa trondhjemitic trondhjemitic cobble from the anomalously young a on the weakly weakly metamorphosed Ma Doré conglomerate conglomerate near Wawa, reported by Turek et et metamorphosed >2696 >2696 M a Dore Wawa, reported by Turek al. (1984), suggests that that the date (1984), suggests date on on the theBorden Borden Lake Lake conglomerate conglomerate cobble cobble may may not represent the age of crystallization of the source source pluton. pluton. In In addition, addition, tectonic mechanisms which which could could lead lead tto of the 500 krn wide wide o deep burial of 500 km long xx 50 50 km Kapuskasing "sliver"are are unknown unknownand andseem seemt otobe beunlikely unlikelyafter after termination termination of of the major Kapuskasing "sliver" tectonism theAbitibi Abitibiand andWawa Wawasubprovinces. subprovinces. It is more likely that aa single single tectonism ininthe protracted protracted metamorphic metamorphic event eventwas wasresponsible responsible for forproducing producing the the observed observed characteristics. One must must therefore examine the assumption that zircons zircons are a r e closed closed to t o lead lead loss loss immediately following crystallization, regardless of the following crystallization, the cooling cooling history. Slowly Slowly decreasing temperatures from decreasing metamorphic temperatures from peak levels of 800°C 800° could could result result in in lead lead diffusion years after after crystallization, provided that there diffusion out out of of zircon zircon for several million million years provided that is temperature" for zircon. 50°C was was estimated is some finite "blocking "blocking temperature" zircon. AAvalue value of of 700 700 ± -+ 50° for this hypothesis ttoo explain for zircon blocking blocking by Mattinson (1978). (1978). Invoking Invoking this explain the theyoung young "metamorphic" "metamorphic" dates dateswould would allow allow aa simpler simpler geological geological history historyinvolving involving only only the the metamorphism with later fluid metamorphism at at 2700 2700 to t o 2680 2680 Ma M a with fluid circulation and and possible possible ductile shear at at depth. depth. The east-northeast structural The prominent prominent east-northeast structuraltrends trendsininthe theKapuskasing Kapuskasing zone zone are are the the result of of relatively relatively late late tectonism. tectonism. The Thestructural structuralgrain grainisisdefined defined by by the orientation orientation of inigmatitic axes. This nigmatiticand and gneissic gneissiclayering layering folded folded about aboutshallow-plunging shallow-plunging ENE ENE axes. This folding folding event event therefore therefore post-dates post-dates crystallization crystallization of of tonalitic tonaliticmelts, melts,thought thought to t ocoincide coincide with with the netamorphic peak. units that can be the inetamorphic peak. Similarly, Similarly, structurally structurally complex complex tonalitic gneiss units traced into the Kapuskasing have a strong, strong, superimposed superimposed traced from from Wawa Wawa subprovince into Kapuskasing zone have ENE ENE foliation foliation and lineation in in the theKapuskasing Kapuskasing zone zone(Percival (Peruvaland andCoe, Coe,1981). 1981). If the the correlation correlation is isvalid valid between between massive massive granodiorite dated at a t 2680 2680 ± Ma and granodiorite granodiorite -+ 3 Ma gneiss then the the ductile gneiss adjacent to to the theKapuskasing Kapuskasing zone in the Abitibi subprovince, subprovince, then strain strain occurred occurred after after2680 2680 Ma Ma but pre-dated pre-dated post-metamorphic post-metamorphic cooling. cooling. This This timing timing is consistent that sinistral sinistral transcurrent transcurrent movement consistent with with the thesuggestion suggestion of of Watson Watson (1980) 0980) that movement occurred occurredalong alongthe theKapuskasing Kapuskasing zone zone during during emplacement emplacement of of the theMatachewan Matachewandyke dyke swarm swarm at at 2633 2633 Ma Ma (Gates and Hurley, Hurley, 1973). 1973). Late Late Archean Archean deformation deformation could could have have promoted promoted resetting resettingofof2700-2680 2700-2680 Ma Ma zircons zircons to toages agesdown downto t o2616 2616Ma. Ma. �- - — 32 32 — UPLIFT UPLIFT OF OF THE THE KAPUSKASING KAPUSKASING STRUCTURE STRUCTURE The age of of uplift of the Kapuskasing constrained. Evidence Kapuskasing zone is not well constrained. Evidence of of late lateArchean Archean transcurrent transcurrentmovement movementwas wascited citedby byWatson Watson(1980) (1980) and Percival Percival and and Coe Coe (1980), however its its magnitude was probably probably small, small, judging judging by bythe the minor minor apparent apparent offset (1980), however offset of occurred aatt that of the the Abitibi-Opatica Abitibi-Opatica contact contact (Fig. (Fig. 1). I). Major Major thrusting thrusting could could also also have occurred that time, time, setting settingU-Pb U-Pb and andK-Ar K-Ar isotopic isotopicsystems systemsininthe thehigh-grade high-graderocks rocksata t2,650-2,250 2,650-2,250 Ma. Ma. Geochronological evidence indicates indicates activity activity at Ma. Three Three alkalic alkalic Geochronological evidence at 1,655-1,850 1,655-1,850 Ma. rock-carbonatite rock-carbonatite complexes complexesnear nearKapuskasing Kapuskasiighave haveK-Ar K-Ar dates datesofof1,655-1,720 1,655-1,720 Ma Ma (Gittins (Gittins et et a!., al., 1967). 1967). AAbiotite-whole-rock biotite-whole-rock Rb-Sr Rb-Sr isochron isochron from tonalite of of the the Shawmere arid others, others, 1980). 1,850Ma Ma (Simmons (Simmons and 1980). A A whole-rock whole-rock Shawmere anorthosite anorthositecomplex complexisis1,850 40Ar/39Ar analysis of blastomylonite from from the Ivanhoe Lake Lake cataclastic cataclastic zone gave aa '+o~r/^~ r of date dateof of 1,720 1,720Ma Ma (Percival, (Percival,1981; 1981;Fig. Fig. 15). 15). 3-0 25 to 2.0 0) 0l C 02 Co a a I.e 1.0 0.2 0.4 0.6 0.8 1.0 Fraction Fraction 39Ar " ~ rre'eased released Figure Figure15. 15. 40Ar/39Ar 40Ar/39Ar age agespectra spectrafor forhornblende, hornblende,plagioclase plagioclaseand andwhole-rock whole-rock separates separatesfrom fromnear near the theIvanhoe IvanhoeLake Lake cataclastic cataclasticzone. zone. Increasingly Increasinglyhigh high release releasetemperature temperature from from left lefttotoright. right.Width Widthofofbars barsare are2o-uncertainty 2uuncertainty estimates. estimates. �ii I 17 I I I I I I I I I I I I I I I -33rock-carbonatite complexes in the southern Three alkalic rock-carbonatite southern Kapuskasing Kapuskasing zone have of 1,050-1,100 Ma (Gittins (Gittins et at., K-Ar K-Ar dates of 1,050-1,100 Ma al., 1967). 1967). Plagioclase Plagioclase from from amphibolite4n amphibolite-in tthe he of tthe Ivanhoe Lake Lake cataclastic cataclastic zone footwall of h e Ivanhoe zone yields a 40Arf39Ar ^O~r/39Arplateau at at 1107 1107 Ma Ma (Fig. 15), suggestingmild mildresetting, resetting, possibly possiblydue duet otofaulting. faulting. Lower concordia intercepts intercepts (Fig. 15), suggesting Lower concordia of zircon discordia in tthe Ma (Percival (Percival and and Krogh, Krogh, 1983) 1983)may mayrelate relatetto of h e range 827-1,108 827-1,108 Ma o ago. uplift 1,100-1,000 1,100-1,000 Ma ago. events along along tthe structure with major The coincidence of Proterozoic events h e Kapuskasing Kapuskasing structure orogenic activity activity elsewhere Shield suggests suggeststhat thatt hthe structure is is an anintracratonic intracratonic orogenic elsewhere in tthe h e Shield e structure basementuplift uplift related to possibly an anearly early Proterozoic Proterozoic basement t o aa distant distant compressional compressional event, possibly collision in the Churchill Province to t o the t h e northwest northwest (Percival (Percivaland andMcGrath, McGrath, 1986). 1986). �- 34 - PART lb ROAD LOG . KAPIJSKASING UPLIFT: UPLIFT: ARCHEAN THE KAPUSKASING ARCHEAN GREENSTONES GREENSTONES AND AND GRANULITES GRANULITES SUMMARY Variousstructural structural levels within tthe Various h e central centralSuperior Superior Province Province will will be be examined examined to to demonstrate their characteristics characteristics and and interrelationships. interrelationships. Starting Startingwith with the thelowest-grade lowest-grade area, we we will will progress up-grade up-grade through an rocks in the Michipicoten Michipicoten belt of the t h e Wawa Wawa area, unbrokenoblique obliqueccrustal cross-section into tonalitic gneisses and granulites of the unbroken r Kapuskasing zone. DAYI Geology of the Geology of the Wawa Wawa Subprovince, Wawa ttoo Chapleau Chapleau in well-preserved well-preserved supracrustal rocks of of tthe h e Michipicoten Michipicoten belt The first day begins in and ends ends in in the the lowest lowest structural structural levels gneiss terrane (Fig. and levels of the the Wawa Wawa gneiss (Fig. 2). 2). Exposures Exposures near Wawa willdemonstrate demonstrate lithological, lithological,structural structural and and metamorphic metamorphic characteristics characteristics of Wawa will of the low-grade terrane. To rocks ocks and and internal low-grade terrane. To the theeast, east,the thetransition transitiontot ogneissic gneissicplutonic pi characteristics gneiss terrane will be examined. W characteristicsof of the t h eWawa STOP 1-1: 1-1: Doré STOP Dore Conglomerate Conglomerate(E. (E.and andW. W. sides sidesof of Hwy Hwy 17) 17) The Dore Doré isis aa thick, thick, coarse polymictic polyrnictic conglomerate unit tthat h a t isis overlain overlain by by The metavolcanic rocks at2696 2696 Ma Ma (Turek (Turek et et al., al., 1982) 1982)and and underlain underlain by by rocks of cycle cycle HI, 111, dated dated at older inetavolcanic metavolcanic rocks. rocks. Eastward f a d e s transition transitionfrom from Doré Dore conglomerate conglomerate older Eastward there there is is aa facies of wacke, siltstone, cross-bedded cross-bedded arkose and conglomerate called the the into a sequence of "Eleanor Slate". Slate". At this locality, coarse felsic tuff-breccias to "Eleanor t o the t h enorth north are aresucceeded succeeded southward by by aa sequence sequence of of wacke wacke (reworked (reworked tuff?) tuff?) and and Dore Doré conglomerate. conglomerate. Bedding southward Bedding and foliation dip approximately 45° 45" eastward eastward and and may may face facedownward downward (west). (west). The Dore Dare consists of of pebbles pebbles and and boulders boulders of of mafic mafic and and felsic volcanics, The volcanics, quartz quartz porphyry, iron iron formation formation and andtrondhjemite trondhjemiteininaa schistose, schistose, chloritic chloritic matrix. matrix. The The pebbles pebbles porphyry, aare r e flattened flattenedininthe thefoLiation foliation plane plane and and elongated elongated in in the the east-plunging east-plunging rodding rodding lineation. lineation. Variations in pebble pebblepacking packingand andsize sizedefine definecrude crudestratification stratification units. units. A Variations in A single trondhjemitic boulder apparent age age of of 2552 2552 Ma Ma boulder yielded discordant zircons with an apparent (Turek et et al., at., 1984), approximately 150 150M Ma youngerthan thant hthe stratigraphicage age of of the the unit unit 1984), approximately a younger e stratigraphic (Turek likely that that the source of of the based on zircon zircon dates of bracketing volcanic volcanic rocks. rocks. It is likely based trondhjemitic boulders syn—volcanic M a age. trondhjernitic bouldersand andcobbles cobblesis is syn-volcanic plutons plutonsofof2744—2735 2744-2735 Ma �r I 1-2: Helen Iron Range Section at McLeod Mine, Algoma Ore Properties Ltd. The McLeod Mineextracts extracts siderite siderite and and pyrite pyrite from from the base of the McLeod Mine the Helen Helen iron iron range. This 1800 m m thick unit of intermediate to t o felsic felsic Thisiron iron range range lies lies at a t the thetop topof of aa1800 metavolcanics metavolcanics consisting of oligomictic and polymictic breccia, thin thin bedded bedded to t o massive massive tufts, flows, and andcrystal crystal tuffs. tuffs. These tuffs, lapilli lapilli tuffs, tuffs, spherulitic spheruliticflows, flows, flow flow banded banded flows, These intermediate to felsic felsic metavolcanics metavolcanics are areintruded intruded by by gabbro gabbro ttoo quartz quartz diorite diorite dykes dykes and intermediate to sills sills that that reach reach290 290m m thickness. thickness. The intermediate intermediate to dominantly massive massive and and t o felsic felsicmetavolcanics metavolcanicsoverlie overlieaadominantly pillowed of intermediate to ed sequence of t o mafic mafic metavolcanics. metavolcanics. The The mafic to t o felsic felsic metavolcanics metavolcanics are arebimodal bimodal in in composition composition and represent the the oldest cycle cycleof ofvolcanism volcanism(Fig. (Fig. 14). 14). The The iron formation caps the first firstvolcanic volcanic cycle cyclein in the theMichipicoten Michipicoten greenstone greenstone belt belt and and from from the the stratigraphic stratigraphicbottom bottom to totop t o pconsists consistsof of five fivelithologic lithologic rock rock types types that that are are gradational gradational into into each other. Upper Upper and and lower lower contracts are sharp. sharp. From From stratigraphic stratigraphic bottom bottom to t o top top the t h eiron iron formation formation consists consists of of siderite, siderite, pyrite, pyrite, banded banded chert, chert, thin chert-wacke-magnetite, and graphite-pyrite. thin bedded bedded chert-wacke-magnetite, graphite-pyrite. AAU-Pb U-Pb isotopic isotopic age age of of approximately has been been obtained obtained from from the the crystal M a has crystal tuffs tuffslying lyingimmediately immediately below below approximately 2749 2749 Ma the the iron iron formation formation (Turek (Turek et et al., al., 1982). 1982). Overlying intermediate to Overlying tthe h e iron formation are massive massive pillowed pillowed intermediate t o mafic mafic inetavolcanics inetavolcanics of of cycle cycle two. two. The The area area of of the themine minedisplays displays numerous numerous major and minor faults, and and contains contains several a1Proterozoic Proterozoic diabase diabase dykes that strike strike northeast northeast and and northwest. northwest. Beneath areaofofapproximately approximately1800 1800mmby by 750 750 m m has has been been Beneath the theiron iron formation formationan anarea outlined outlined that that contains containschloritoid. chloritoid. These Thesecrystals crystalsare aregenerally generallyup upto t o22mm mrn in in diameter diameter and and are a r erandomly randomly oriented with with respect ttoo the schistosity. schistosity. Chloritoid Chloritoid alteration alterationoccurs occurs above above the the iron iron formation formation as aswell, well, in in less less abundant abundant quantities. quantities. The The volcanics volcanics above above and and below below the the iron iron range range are arepervasively pervasivelysoaked soakedwith with carbonate. carbonate. Carbonate Carbonatealteration alterationisisofofregional regionalextent extentand andoccurs occursin inall allrock rock types, types, volcanic, volcanic. sedimentary, sedimentary, and and intrusive. intrusive. STOP il I I I I I I I I I I I I I Spherulitic rhyolite rhyolite(100-200 (100-200 m m south south of of gate gateon onMcLeod McLeod Mine Mine road) road) Stop 1-3 1-3 Spherulitic Stop This This stop stop contains containsthe thebest bestexposure exposureofofaaspherulitic spherulitic(hollow) (hollow)flow flowbanded banded felsic felsic & . flow Mine area. area. The flow within within the the McLeod McLeod Mine The spherulitic spherulitic unit unit isis overlain overlain by by aa flow flow breccia breccia containing well well developed developed fiamme fiamme and and this this unit unit isisin in turn turnoverlain overlainby by aa massive massivetuff tuffwith with containing scattered scattered lapilli-size lapilli-size clasts. clasts. This Thisexposure exposure lies lies in in the the lower lower part of of the the felsic felsic part part of of the the �— 36 - oldest oldest cycle cycle of of volcanism. volcanism. Stratigraphic Stratigraphic tops tops are are north north and and the t h esection sectionisisoverturned, overturned, dipping along Wawa atWawa Wawa dipping south. south. Interpreted Interpretedfaulting faulting along WawaLake Lakeand andbeach beachdeposits depositsat prevent any estimate as to how far above the contact with the intermediate prevent any estimate as t o how far above t h e contact with t h e intermediate to t o mafic mafic pillowed metavolcanics this this felsic felsic section pillowed and and massive massive metavolcanics section occurs. occurs. Return Return to t o Hwy Hwy 101 101 - 00.0 km - Junction Me, Wawa. Junction of of Highway Highway IOIE 101Eand and Broadway Broadway Ave, Wawa. Proceed Proceed east east on on 00.0 km Highway Highway 101. 101. - 20.9 20.9 km -- Stop Stop 1-4: 1-k Mafic Maficgneiss gneiss - tonalite tonalitecontact contactzone zone(N. (N.and andS.S.sides sides of of Hwy Hwy101) 101) , A Ic gneiss A large large enclave enclave of of maf mafic gneiss is enclosed in and and intruded by tonalitic tonaliticgneiss gneissininaa migmatitic migmatiticzone zone marginal marginal to t o the the Michipicoten Michipicoten greenstone greenstone belt. The Thehornblendehornblendeplagioclase considered tto represent deformed, metamorphosed plagioclase gneiss is considered o represent metamorphosed Michipicoten volcanics and and metagabbro. metagabbro. In In this this exposure exposurei titisiscut cut by byearly earlytonalitic tonalitic intrusions, intrusions, llate ate aplitic apliticand and pegmatitic pegmatiticdykes, dykes, and and still stilllater latermafic maficand andlamprophyric lamprophyricdykes. dykes. The Thegneiss gneiss displays subvertical foliation, foliation, mineral displays subvertical mineral lineation, lineation,and and tight tightsteeply-plunging steeply-plunging isoclinal isoclinal minor folds. 45.1 45.1 km km Jct. Jct. Hwy. Hwy. 651. 651. Continue Continueeast. east. * , - 68.5 gneiss Budd and 68.5 km Stop Stop1-5: 1-5: Xenolithic Xenolithictonalite tonalite gneissatat BuddLake Lake(N. (N. andS.S.sides sidesofofHwy Hwy101) 101) This This complex complex outcrop outcropconsists consists of of several severalphases: phases: 1) 1) xenoliths of mafic maficgneiss, gneiss, interpreted interpreted as asrafts raftsofofthe t h eMichipicoten Michipicotenmetavolcanic metavolcanicsequence, sequence, 2) 2)gneissic gneissic tonalite tonalite with small, wispy mafic xenoliths, cut by 3) foliated to gneissic hornblende-epidote- biotite-sphene tonalite, all cut by 4) pink-white granitic pigmatite. Hornblende from foliated wt% ,41203, A1203, indicating indicating crystallization crystallization at foliated tonalite tonalite(3) (3) contains contains 10.4 10.4 wt% approximately approximately5.6 5.6 kbar kbar(Hammarstrom (Hammarstromand andZen, Zen, 1985). 1985). Continue east on 101 94.4 km Stop 1-6; Tonalite gneiss and maf Ic dykes (N. and S. of Hsy 101) Tonalite northeast-trending mafic Tonalite gneiss gneiss iiss cut by northwest- and and northeast-trending mafic dykes dykes with wit chilled dykes (Ernst and chilledmargins. margins. The Theolder oldernorthwest-striking northwest-strikingHearst Hearst dykes (Ernst andHalls, Halls,1980, 1980,1984) 1984) occur have aa similar similar trend and occur west west of of the t h eKapuskasing Kapuskasing zone. zone. The The dykes dykes have and similar similar �- r I (I I I I 1 I I I I including plagioclase plagioclase phenocrysts phenocrystsand andtholeiitic tholeiitic composition, composition, tto characteristics, including o Matachewan dykes dykes east east of of the Kapuskasing zone. The Kapuskasing zone. The Matachewan Matachewan dykes dykes have an Rb-Sr Rb-Sr Matachewan whole-rock age of 2633 ± 75 M Ma (Gates and andHurley, Hurley, 1973). 1973). Ernst and Halls (1980, a (Gates (1980, 1984) 1984) whole-rock 2633 + also reported reported similar paleomagnetic poles poles for for the two zone 50 50 km km wide wide also two swarms. swarms. InInaa zone " zone, the the Hearst dykes average average 44 m m in in width and west of the the Kapuskasing Kapuskasing zone, and have have a consistent easterly easterly dip dip of of 80 80° (Ernst, (Ernst, 1983; Percival, 1981). 1981). The Thetonalitic tonalitic gneiss is thinly thinly consistent 1983; Percival, gneiss is layered and and has hassparse sparsemafic maficxenoliths. xenoliths. Gneissosity appearstto havechaotic chaotic orientation orientation Gneissosity appears o have but is subhorizontal onaverage. average. There Thereisisevidence evidencefor forat at least least two two sets setsofof structure: structure: an an but subhorizontal on older gneissosity gneissosity is is reoriented reoriented by by younger younger subhorizontal subhorizontalfoliation foliation to t o give give complex complex patterns. sigmoidal patterns. Continue east 122.2km km Stop 1-7: 122.2 1-7: Highbrush Highbrush Lake Lake Dome Dome (N. (N.side of Hwy Hwy 101) 101) Small domes domesexposed exposedininroadcuts roadcutshere hereare aretypical typicalofof the the local local and and possibly possibly of of the the Small regional-scalestructural structural pattern. pattern. The rock type is fine-grained, fine-grained, thinly-layered thinly-layered regional-scale The main main rock biotite and biotite and hornblende-biotite hornblende-biotite gneiss gneiss with with local localaugen augen of potash potash feldspar. The outcrop outcrop consists consists of of several several domes domesor orcanoe-shaped canoe-shapedfolds foldswith withaarolling rolling easteastThe west mineral mineral and andstretching stretchinglineation. lineation. Small parts west Small intrafolial intrafolialfolds foldsare arepresent present in in some some parts as are areamphibolitic amphibolitic xenoliths, xenoliths,locally locally with with clinopyroxene. clinopyroxene. Pink Pink granitic granitic of the outcrop, outcrop, as and sills sills cut cut gneissic gneissic layering layering in in some some areas. areas. Late sub-horizontal highpegmatite dykes dykes and are common commonininthe the vicinity vicinity of strain zones zones are of the thetransition transitionzone zonebetween betweenWawa Wawa and and Kapuskasing gneisses. gneisses. Continue east - I 131.6km km - Junction Junction of of Highway andHighway Highway129. 129. Follow Follow 101E, lOlE, 129N toward Highway 101 101 and 129N toward 131.6 1 132.9 km Chapleau Stop 1-8: 1-8: Xenolithic tonalite (w. side side of of Hwy Hwy Stop tonalite with withhorizontal horizontalshear shear zones zones (W. 101—129) 101-129) 1 I I I Xenolith alignment and gneissosityhave havesub-vertical sub-verticalorientations orientations in in the the central central and gneissosity thin part of this this road-cut. road-cut. Layering Layeringbecomes becomes horizontal horizontal and and mafic mafic xenoliths xenoliths become become thin and bottom bottom of of the mafic layers in 1/2 112 m-thick horizontal horizontalshear shear zones zones near near the top and outcrop. �139.5 - — 38 — km . Junction )unction of of Highways and 129N: 129N: Proceed north km Highways 1OIE 101E and north on on Highways Highways 101-129 101-129 through Chapleau. Chapleau. Follow Follow the t h eMissinaibi Missinaibi Provincial Park Park signs north of town on gravel road. road. Proceed Proceednorth northand andeast easton onpark parkroad roadand andlogging logging roads roads leading ttoo the the Chapleau Chapleau River. River. - 178.3 FlorannaLake LakeComplex Complex Stop 1-9: 1-9: Floranna 178.3 km - Stop The Floranna Floranna Lake Lake Complex Complexisisaacomplex complexcrescentic crescentic pluton plutonofof intermediate intermediate composition. composition. The The western western margin margin consists of lineated, h e a t e d , fine fine grained grained granite granite with with orthopyroxene and and biotite. biotite. inside Inside the the marginal marginal unit is is lineated diorite diorite to t o monzonite rnonzonite containing hornblende-rimmed augenclinopyroxene clinopyroxenephenocrysts. phenocrysts. The Thecentral central part of the hornblende-rimmed augen the complex is foliated hornblende-clinopyroxene-biotitediorite, diorite, gabbro gabbroand and foliated and and lineated lineated hornblende-clinopyroxene-biotite melagabbi-o. well-exposed eastern eastern contact contact of melagabbro. The well-exposed of the thecomplex complexshows shows extremely extremely attenuated attenuatedand and contorted contortedlayering layering in in granite granite of of the thecomplex complex adjacent adjacent to t o rocks rocks of of the the Robson Lake dome dome tto the east. Robson Lake o the Clinopyroxene augen diorite-monzonite diorite-monzonite C l i p y r o x e n e augen These coarse-grained monzonite. medium- to coarse-grained monzonite. RodRodThese rocks are strongly lineated, mediumshaped shaped clinopyroxene clinopyroxene phenocrysts, rimmed rimmed by by hornblende, hornblende, make make up up some some 20% 20% of the the rock. rock. Original Originaloutlines outlines of of feldspar feldspar grains grains are arevisible visible but but these theseare arenow now polycrystalline polycrystalline aggregates. aggregates. j-y, - 179.3 - Foliated and lineated h e a t e d diorite dioritewith with gabbro gabbro and and melagabbro melagabbro layers layers Igneous clinopyroxene with with hornblende hornblende overgrowths overgrowths and and granitic leucosome leucosome layers layers are are present. present. - 183.2 Granulitegneiss, gneiss,Robson Robson Lake Lake dome dome 183.2 km - Stop Stop 1-10: 1-10: Granulite The of tthe complexisisaa foliated foliated to to augen-textured, augen-textured, The easternmost exposure of h e igneous complex xenolithic porphyritic granite granite with with leucogranite leucogranite veinlets veinlets parallel ttoo foliation xenolithic hornblende hornblende porphyritic on on the the 11 mm-2 mm-2 cm scale. scale. The Thelayering layeringisisfolded foldedabout aboutnorthwesterly-plunging northwesterly-plunging axes. axes. Parts Partsof of the theoutcrop outcropare a r efine-grained fine-grained and andmylonitic myloniticwith with highly highly attenuated attenuatedlayering. layering. To of interlayered mafic To tthe h e west, the t h e Robson Robson Lake dome consists of mafic and and tonalitic tonalitic gneiss. gneiss. Near Near the thecontact contactwith withthe theFloranna FlorannaLake LakeComplex, Complex, the t h e layering layering in in rocks in the dome concordant tto west, however, however, the the attitude attitude is dome is concordant o the contact and and dips steeply west, is horizontal Ic rocks eastin in the thecore coreof of the thedome. dome. AtAtthis thisoutcrop outcropthe themaf mafic rocks consist consist horizontal farther farther east of garnet-clinopyroxene-hornblende-plagioclase-quartzassemblages, assemblages, with with layering layering of garnet-clinopyroxene-hornblende-plagioclase-quartz defined and hornblende-rich defined by by different different proportions proportions of of minerals, minerals,including including garnet-rich garnet-rich'and hornblende-rich varieties. varieties. Concordant Concordanttonalitic tonaliticlayers layerslocally locallyhave havelarge largeclinopyroxene clinopyroxenecrystals crystalsrimmed rimmed by by hornblende, hornblende, in clots up ttoo 4 cm. The Thelayering layering isisfolded folded about about upright upright isoclinal isoclinal folds folds locally. locally. �r I I I I I I I -39inclusions of of mafic gneiss gneiss in in granite granite of granite in mafic gneiss and inclusions Small dykes of granite in indicate an indicate an intrusive intrusivecontact contactbetween betweenthe theFloranna FlorannaLake LakeComplex Complexand and Robson Robson Lake dome. The interpretation interpretation of the Lake dome, dome,which whichhas hasthe thestructural structural attributes attributes The the Robson Robson Lake of the domal gneiss gneissterrane terraneand andthe thelithological lithological characteristics characteristics of t h e Wawa Wawa domal of Kapuskasing Kapuskasing zone, is is that rocks zone underlie underlie the Wawa domal zone, rocks like likethose those exposed exposed in the the Kapuskasing Kapuskasing zone Wawa domal terrane been exposed exposedhere hereininaastructural structural culmination. culmination. terrane and and have have been Return to t o Chapleau Chapleau DAY 2 Geologyof of the Kapuskasing KapuskasingStructural Structural Zone Zone in in the the Chapleau-Foleyet Chapleau-Foleyet Area Geology In this this section we will will examine In examine the t h e rocks rocks and and structures of of the t h e Wawa Wawa domal doma' gneiss -- Kapuskasing Kapuskasingzone zoneboundary boundaryand andofofthe theKapuskasing Kapuskasingzone zoneitself itself along along gneiss Highway 101. 101. - 0.0 km km 0.0 I I I I I I I * ii. and Highway Highway 129 south south of of Chapleau. Chapleau. Proceed Junction of Highway Highway 101E 101E and Proceed east on Highway 101. 101. 2-1: Borden 13.0 km km Stop 101) Lake conglomerate conglomerate (S. (S. side of Hwy 101) 13.0 Stop 2-1: Borden Lake This outcrop outcrop consists consists of of stretched-pebble stretched-pebble metaconglornerate metaconglomerate with with aa strong rodding rodding This weak, gently gently north-dipping north-dipping foliation. foliation. The lineation and and weak, The rock rockisisaaclast-supported clast-supported conglomerate containing 10% 10%matrix matrix of of garnet-hornblende-biotite-quartz. garnet-hornblende-biotite-.quartz. The The cobbles, cobbles, conglomerate which range range up uptto m in in length, length, aare felsic metavolcanics, metasediments,granodioritegranodioriter e felsic metavolcanics, metasediments, which o 1m amphibolite, with rare hornblendite tonalite, plagioclase-porphyritic plagioclase-porphyritic meta-andesite meta-andesite and and amphibolite, and vein vein quartz. quartz. The and The metaconglomerate metaconglomerate is spatially spatially associated associated with amphibolite and and paragneissto tothe the south southon onBorden BordenLake, Lake,and andisiscut cutby bygranite, granite, however, however,tthe stratigraphic h e stratigraphic paragneiss relations of relations of the thesupracrustal supracrustal rocks rocks are areunknown. unknown. An aggegate aggegateofoftonalitic tonalitic cobbles extracted from the An cobbles extracted the metaconglomerate metaconglomerate yielded yielded Ma (Percival et et al., 1981). 1981). The The zircons zircons have have aa corroded corroded zircons dated at at 2664 2664 ±+ 12 12 M a (Percival appearanceand andproduced produceddiscordant discordantdata datapoints pointsand andhence hencet hthe interpretation of of the the data appearance e interpretation open. Rather than recording recording the the original original crystallization crystallization age of the source pluton for for is open. Rather than age of source pluton the cobbles the zircons zircons probably probablydate dateaalater later deformation-metamorphic deformation-metamorphic event. event. The cobbles the The source pluton plutonfor for the the cobbles cobblesmay maybe besimilar similart otothat that which which provided providedmaterial material for for the source Doré conglomerate. Dor6 �— 40 - Continue east on 101 Continue . .. - .. 2-2: Mafic 25.9 km Stop 2-2: 25.9 Mafic gneiss gneiss xenoliths xenoliths with with amphibolitic amphibolitic margins margins (N. (N. side of Hwy Hwy 101) 101) This exposure exposuredemonstrates demonstrates an an important important aspect aspect of between the This of the boundary boundary between Kapuskasingzone zoneand andWawa Wawagneiss gneiss terrane. Aside Asidefrom fromthe thelarge-scale large-scale structural structural Kapuskasing terrane. terrane and contrast between between the the domal domal Wawa Wawa terrane and the t h e linear linear belts beltsin inthe theKapuskasing Kapuskasing zone, intrusive relations relations are also instructive. The intrusive Theoutcrop outcropconsists consists of of two two main main components: components: (1)coarse-grained coarse-grainedhornblende-biotite hornblende-biotitetonalite, tonalite, the the dominant dominant rock rocktype type tto the west, west, and and (1) o the (2) medium mediumgrained grained mafic mafic gneiss gneiss consisting consisting of of garnet-clinopyroxene-hornblendegarnet-clinopyroxene-hornblende(2) plagioclase-quartz assemblages. assemblages. Small xenoliths of of mafic mafic gneiss gneiss in intonalite tonalite have have plagioclase-quartz Small xenoliths margins, up up tto cm thick, thick, consisting consisting of of hornblende-plagioclase. hornblende-plagioclase. Dykes Dykesofoftonalite tonalite margins, o several cm cutting mafic gneiss gneiss are are bordered bordered by mafic rock with hornblende-plagioclase hornblende-plagioclase assemblages. The assemblages. The interpretation of of age age relationships relationships is that that the thehigh-grade high-grade metamorphism that that produced the garnet-clinopyroxene assemblages in mafic gneiss metamorphism gneiss preceded the the intrusion intrusion of of tonalite. tonalite. Water preceded Water in in the the tonalite tonalitemagma magma was was presumably presumably ,. crystallization and and hydrated hydrated the the adjacent less-hydrous mafic rock. rock. released upon upon crystallization less-hydrous mafic Althoughthe the tonalite tonalite at this outcrop has not been dated, iti t probably either to Although probably belongs belongs either Ma tonalite gneiss gneiss suite suite or ttoo the 2680 group of of plutons. plutons. The high-grade the >2707 >2707 M a tonalite 2680 Ma M a group high-grade metamorphismisistherefore therefore older olderthan than 2680 2680Ma. Ma. This Thisisisininconflict conflictwith withthe thedirect direct dates dates metamorphism of metamorphic zircons from the as 2616 2616 Ma. Ma. of the Kapuskasing Kapuskasing zone that yield yield ages ages of of as aslow low as The conflict conflict has led ttoo the that the The the suggestion suggestion (Percival (Percival and and Krogh, Krogh, 1983) 1983) that the Kapuskasing Kapuskasing gneisses, although although metamorphosed metamorphosed prior prior tto 2680 M Ma ago,remained remainedat at high high temperatures temperatures gneisses, o 2680 a ago, where radiogenic lead diffused readily out of zircon until at least 2616 Ma ago. Continue east 37.0 km 37.0 2-3: Thinly-layered Stop 2-3: Thinly-layered tonalitic gneiss gneiss and diatreme diatreme breccia breccia (N. (N. side side of of Hwy Iiwy 101) 101) Fine grained grained tonalitic tonalitic gneiss Fine gneiss aatt this exposure is strongly foliated and layered on a 1-5mm mmscale scalewith withgarnet, garnet,hornblende hornblendeand andbiotite-rich biotite-richlayers. layers. Extremely Extremelyattenuated attenuated 1-5 intrafolial folds folds are are present present locally. locally. Units foliation intrafolial Units characterized characterized by by extremely planar foliation such as as this this aare relatively rare in tthe zone. Although the orientation orientation of of such r e relatively h e Kapuskasing Kapuskasing zone. Although the foliation in this exposure exposure is typical typical for for the theKapuskasing Kapuskasing zone, zone, most most Kapuskasing Kapuskasing gneisses gneisses coarse-grained and andlayered layeredwith withdistinctive distinctiveleucocratic leucocratic portions. portions. In are mediummedium- tto o coarse-grained addition, the the layering layering in in the the typical gneisses gneisses is is warped warped about about gently gently northeast northeast or or addition, southwest-plungingaxes. axes. The fine grain size and thin thin planar layering in this outcrop southwest-plunging suggest aa relatively relatively late, high-strain suggest high-strain flattening flattening or shearing shearing event. �r —41 - I? d A A thin thin diatreme diatremedyke dykeoccurs occursininthis thissame sameexposure. exposure. ItIt has has not not been been dated dated but but presumably presumably is part of of aa set set of of lamprophyre lamprophyre dykes dykes of 1100 . ~ l l 0Ma 0M aage age(Stevens (Stevens et et a!, al, 1982) 1982) that are particularly particularly common thatoccur occurininthe t h eKapuskasing Kapuskasing zone zone and and are common in the the area area between between the I I I Lackner Lakecomplexes. complexes. Both Both the the matrix matrix and fragments in the Lackner and and Nemegosenda Nemegosenda Lake the dyke dyke are be identified. identified. These are altered, altered, but but some some fragments can be These include include tonalitic tonaliticgneiss, gneiss, spinel spinel n Continue Continue east east on on Hwy Hwy101 101 lherzolite not occur occur in the Iherzoliteand and massive massive pink granite. As Asmassive massive granite granite does does not Kapuskasing zone,the thegranite granite fragments fragments are arerelatively relatively exotic. Their Kapuskasing zone, Theirsource sourcewas was probably below Kapuskasingzone, zone,possibly possiblyiningranite graniteofofthe the Abitibi Abitibi belt, below the Kapuskasing belt, which which according according to t o the the gravity gravitymodel, model, lies liesvertically verticallybelow belowatata adepth depthofof—15 -15 km. km. ' 52.1 52.1 km km Stop KapuskasingGneiss Gneiss (S. (S. side side of of Hwy Hwy101) 101) Stop 2-4: 2-4: Kapuskasing Layered ruafic in situ tonalitic tonaliticleucosome, leucosome,and and crosscrossmafic gneiss gneiss with concordant & cutting cuttingtonalitic tonaliticand andpegmatitic pegmatiticdykes. dykes. Layering Layeringononthe the5 5tot o1010cm c mscale scaleisisgiven givenby by I alternating of similar alternatinghornblende-rich hornblende-rich and and garnet-pyroxene-rich garnet-pyroxene-rich layers layers(see (see analyses analyses of layers layers in Table 1). 1). Metre-scale Metre-scale blocks blocks of mafic mafic gneiss gneiss in breccia give parts of the outcrop moutcrop aa chaotic chaoticappearance. appearance. These These structurally structurallycomplex complexpanels panelsare areseparated separated by. bym- scale high-strain high-strain zones with gently rolling, north-dipping, foliation. zones with north-dipping, pronounced pronounced foliation. Continue Continue east east on on Hwy Hwy101 101 59.8 59.8 km Stop Stop2-5: 2-5: Kapuskasing Kapuskasinggneisses gneisses (N. (N. and and S. S. sides sides of Hwy Hwy 101) 101) There are several several features features of of interest interest at this this outcrop outcrop (Fig. (Fig. 23): 23); Mafic Maficgneiss gneiss is present on the northwest side side of the the road. road. ItIt isis aa coarse coarse grained grained rock rock consisting consisting of of three threetypes types of of layers layerson on the the5-100 5-100 mm mm scale: scale: i)i)relatively relativelyanhydrous anhydrous A. I I I I I rnafic and quartz, quartz, with some mafic rock rock made made up of garnet, clinopyroxene, clinopyroxene, plagioclase and some hornblende to analyses analyses I1 && 3, 3, Table Table 1); ii) more hornblende (analogous (analogous to 1); ii) more hydrous hydrous layers layers containing containingless less garnet garnet and and clinopyroxene clinopyroxeneand and more morehornblende hornblende (analogous (analogous to t o analyses analyses 22 &&4, 4, Table Table1); I); and and iii) iii)tonalitic tonaliticleucosome leucosomelayers, layers, both both concordant concordant to t o layering layering and and transverse transverse in the amphibole-rich amphibole-rich mafic rocks. rocks. Note Note that that the thetonalite tonalitehas has no no retrogressive retrogressive effect effect on on adjacent anhydrous mafic gneiss. gneiss. The tonalitic tonalitic leucosome anhydrous mafic leucosome veinlets are are considered considered ttoo be in situ anatectic anatecticmelt meltsegregations segregationsdeveloped developed during prograde prograde metamorphic reactions of the outcrop, submicroscopic (see reaction 2). 2). In the western end of submicroscopic symplectites of orthopyroxene-plagioclase identified by form barely-visible coronas orthopyroxene-plagioclase identified by microprobe microprobe analyses, analyses, form coronas around garnet, clinopyroxene clinopyroxene and andhornblende. hornblende. Analyses Analysesofof the the symplectite symplectite minerals, at around garnet, at �-- 42 42 lower size size limit limit of of microprobe microprobe resolution, resolution, aare reported along along with with those those of of tthe tthe h e lower r e reported h e other minerals in in the the rock, rock, in in Table Table 2.2. The minerals The rock contains three three plagioclase plagioclase compositions. compositions. An39 Ana9 is present in in coronas coronas whereas worm-like worm-like intergrowths intergrowths of of An35 An35 and and An50 Anro make up tthe he matrix plagioclase. plagioclase. The mineral mineral compositions compositions yield yieldestimates estimates of of 735°C usingtthe and Green Green The 735'C using h e Ellis and (1979)garnet-clinopyroxene garnet-clinopyroxenethermometer thermometer and and 6.2 6.2 kbar kbar using usingtthe garnet-clinopyroxene(1979) h e garnet-clinopyroxene- plagioclase-.quartzbarometer barometer (Newton (Newtonand andPerkins, Perkins,1982). 1982).At Atthe thesame sametemperature temperature tthe plagioclase-quartz he and matrix matrix garnet yield 9.1 coronal minerals and 9.1 kbar kbar with tthe h e garnet-orthopyroxenegarnet-orthopyroxeneplagioclase-quartzz Newton and Perkins Perkins barometer. barometer. plagioclase-quart Newton and Kapuskasing dike Kapuskasing dike 1 B, . . A A orthopyroxeneorthopyroxeneplagioclase coronas 22Dm 0m 0 I I I orthopyroxene bearma bearing orthopyroxene metasedimentary imentary rock '7 ic and tonalitic gneiss Figure 23. 23. Location Location of of outcrops outcrops at at Stop Stop 2-5. 2-5. - A Kapuskasing Kapuskasingmafic maficdyke dykecuts cutsthe theeastern easternend endofofthe theoutcrop. outcrop. The overal overall BB.. A attitude SE although although tthe h e margin is offset by by numerous small attitudeof of the t h edyke dykeisis070/75 070175 SE sinistral faults. The Theouter outer22cm c mof of the themargin margin isischilled. chilled. Sparse Sparseplagioclase plagioclase phenocrysts phenocrysts are present in olivine-bearing gabbro. gabbro. Several in the t h e dominantly dominantly medium medium grained ophitic olivine-bearing Several dykes of of this swarm been dated by tthe dykes swarm have been h e whole-rock whole-rock K-Ar K-Ar method method and and yield yield "ages" "ages" and 3649 3649 Ma, Ma,indicating indicatingt the presence of of excess argon between 2367 2367 and h e presence (Stevens et et al., 1982). al, (1986) (1986)estimated estimated an age of 2040 2200 Ma Ma based based on (Stevens 1982). 1-lanes Hanes etet al, 2040 -- 2200 dyke and and its its baked baked country country rock. rock. ^40Ar/39Ar ~ r / ^ ~ ranalyses of a Kapuskasing Kapuskasing dyke Homogeneousmetasedimentary metasedimentary rock C. Homogeneous South of the road is a flat outcrop of medium grained rock with the h e assemblage . . �r I I I I I I I I I I I I I 1 1 I — 43 - Table 2. 2. Microprobe Microprobeanalyses analyses of minerals minerals in coronitic coronitic mafic mafic gneiss, gneiss. Stop Stop 2-5 2-5 1 2 4 3 Si02 Si02 38.01 51.57 49.06 42.29 hO2 Ti02 0.00 0.34 0.03 2.03 A1203 20.99 2.92 4.75 12.98 Cr203 0.22 0.21 0.34 0.08 28.06 11.81 31.20 18.43 0.70 0.81 13.35 1.39 0.17 9.28 8.32 0.00 11.34 22.65 11.41 0 27 0.74 0.52 1.95 Cr203 10* FeO* MnO MnO MgO MgO CaO CaO Na 0 Na20 2 K20 K2 4.11 0.00 0.08 0.00 0.69 Total Total 100.67 101.79 101.45 99.31 Si Si 2.973 1.908 1.885 6.252 Aliv Aliv 0.00 0.092 0.115 1.748 Alvi Alvi 1.935 0.035 0.100 0.513 Ti Ti 0.00 0.009 0.001 0.226 Cr c r 0.014 0.008 0.010 0.009 0.0 0.087 0.042 0.288 1.835 Mg Me 0.040 0.479 0.278 0.003 0.625 0.960 0.026 0.764 Ca Ca 0.697 0.898 0.057 1.990 0.021 2.044 1.807 Na Na 0.041 0.053 0.039 0.559 K K 0.00 0.004 0.00 0.130 3+ pe3 Fe 2÷ 2+ Fe Fe Mn Mn (0) (0) * * (12) (6) (6) (23) 1: 1: garnet; garnet; 2: 2: clinopyroxene; clinopyroxene; 3: 3: orthopyroxene; orthopyroxene;4: 4: hornblende hornblende Total Fe3 by Total iron as FeO; Fe3+ bystoichiometry stojcHiornetry Specimen Specimen also also contains contains quartz quartzand andplagioclase plagioclase(An33 Art88 in syrnplectite) symplectite) Ann8 in I 1.:jyt- mntrir. in matrix, �- 44 - z. Plagioclase garnet-orthopyroxene-biotite-plagioclase-quart garnet-orthopyroxene-biotite-plagioclase-quartz. Plagioclase occurs occursas asporphyroblasts porphyroblasts to is up uptto mm. The t o 22 cm cm and and orthopyroxene orthopyroxene is o5 5 mm. The rock rock has has the the same same mineral mineral assemblage assemblage as as high-grade in tthe zone but but lacks lacks tthe high-grade paragneiss paragneiss in h e Kapuskasing Kapuskashg zone h e migmatitic migmatitic layering layering typical typical of of paragneiss. paragneiss. Application Application of of the the garnet-orthopyroxene-plagioclase-quartz garnet-orthopyroxene-plagioclase-quartz geobarometer geobarometer yields values values in in excess excess of and Perkins yields of 11 11 kbar kbar by by both both Newton Newton and and Perkins Perkins (1982) (1982) and Perkins and and Chipera (1985) calibrations. calibrations. Chipera Interlayered mafic mafic and tonalitic gneiss D. Interlayered and tonalitic gneiss D. complex relations relations between Ic and and tonalitic tonalitic gneiss. outcrop demonstrates This This outcrop demonstrates complex between maf mafic gneiss. Isoclinal folds of of layering layering are are truncated truncated by Isoclinal folds by tonalite tonalitepods pods and and dykes, dykes, suggesting suggesting multiple multiple generations of of tonalite. tonalite. Thin generations Thinmylonite mylonite seams seams are are sub-parallel sub-parallel to t o gneissic gneissic layers. layers. Continue east 67.0 km km Stop 67.0 Stop 2-6: 2-6: Xenolithic Xenolithictonalitic tonaliticgneiss gneiss(S. (5.side sideof ofHwy Hwy101) 101) This outcrop outcrop consists consists of of mediummedium-t to coarse-grained tonalite tonalite made up of of garnet, garnet, This o coarse-grained hornblende, biotite, biotite, plagioclase plagioclase and and quartz. quartz. AA variety hornblende, variety of of xenoliths xenoliths includes includes mafic gneiss gneiss (garnet-.clinopyroxene-plagioclase-quart z),amphibolite, amphibolite,biotite-rich biotite-rich schists and spinel (garnet-clinopyroxene-plagioclase-quartz), pyroxenite. Amphibole-rich rims characterize characterize the pyroxenite. Amphibole-rich rims t h e high-grade high-grade inclusions. inclusions. Continue east 69.2 km Stop 2-7: Ivanhoe Lake cataclastic cataclastic zone 69.2 km Stop 2-7: Ivanhoe Lake zone(S. (S. side sideof ofHwy Hwy 101) 101) The outcrop outcrop is is on ont the western, high-grade high-grade side sideofoft the cataclastic zone and consists h e western, h e cataclastic The of migmatitic garnet-clinopyroxene-hornblende-plagioclase-quaitz of migmatitic mafic mafic gneiss gneiss with with garnet-clinopyroxene-hornblende-plagioclase-quartz assemblages. ItIt is assemblages. is transected transactedby by numerous numerous small fault offsets offsetsand and by by one one major major cataclasite thin section, section, this black black aphanitic material is cataclasite vein. vein. In In thin is seen seen to t o consist consist mainly mainly of (recrystallized) (recrystallized) fine fine actinolitic actinoliticamphibole amphibole and and of porphyroclasts porphyroclasts of hornblende. hornblende. AA 39 40Ar/39Ar whole-rock analysis of material from art age age plateau plateau at analysis of from this this vein vein yielded yielded an A r / Ar whole-rock 1720MMa (Fig.15). 15). On Ont hthe west side sideofoftthe outcrop aare rusty-weathering 1720 a (Fig. e west h e outcrop r e thin (3 cm) rusty-weathering lamprophyre dykes. dykes. Tonalitic by cataclasite cataclasite are of the lamprophyre Tonalitic rocks rocks cut cut by a r eexposed exposed 150 150 m north of highway on an overgrown road. Continue east �r I I U I I metavolcanics, Abitibi 2-8: Mafic km Stop 70.5 km 70.5 Stop 2-8: Mafic metavolcanics, Abitibi subprovince subprovince (N. (N. side sideof of Hwy Hwy 101) 101) on the eastern, low-grade the IL,CZ and is is the the westernmost This outcrop is on low-grade side of the ILCZ and belt. It is aa fine hornblendegrained, layered hornblendeof rnetavolcanics metavolcanics of of the Abitibi belt. fine grained, exposure of clinopyroxene rock rock with with local local rusty-weathering rusty-weathering patches. plagioclase + patches. ± clinopyroxene The structural characteristics characteristics of the east-west strike of of The structural t h e outcrop, outcrop, including including east-west isoclinal small small folds, folds,aare typical of of the the Abitibi layering, vertical dip dip and steeply-plunging steeply-plunging isoclinal r e typical Abitibi belt. Chlorite belt. Chloriteand and epidote epidote are are common common tto o tthe h e east along strike, where where the belt is wider, wider, suggesting an an easterly easterly decrease in metamorphic grade. grade. suggesting 40Ar/39Ar of hornblende hornblende and and plagioclase plagioclase from from this this outcrop outcrop by by tthe Analyses of he A ~ I A ~ method (Fig. (Fig. 15) show showaa plateau plateau for for hornblende hornblende at at 2567 M Ma and aa saddle-shaped saddle-shaped spectrum spectrum method a and plagioclase with with aa plateau plateau at 1107 Ma. The for plagioclase 1107 Ma. The plagioclase plagioclase plateau may may be due to t o argon argon loss resulting resulting from from aa mild mild thermal thermal event, event, possibly possiblyrelated related tto faulting. loss o faulting. 72.3 km km Turn main road. road. 72.3 Turn north on on logging logging road follow main side of 87.2 km km Stop 2-9: 2-9: Shawmere of road) 87.2 Shawmere gabbroic anorthosite (w. (W. side mainly coarse-grained coarse-grained gabbroic anorthosite anorthosite with The outcrop is mainly with hornblende hornblende and I I • I 1 I I I I I minerals. Ultramafic Ultramaficlayers layersconsisting consistingof of orthoortho- and andclinopyroxene clinopyroxene rare garnet as mafic minerals. with hornblende hornblende rims rims and and sparse sparse plagioclase plagioclase to 3 cm, occurs occurs in in layers layers and and pods pods up to to 44 m m with Mafic and and ultramafic ultramafic layers are structures thick. Mafic thick. are locally locally folded folded into into shallow shallow NE-plunging NE-plunging structures with aa prominent prominent lineation. lineation. One part of the with the outcrop outcrop is is a spectacular spectacular coronitic coronitic gabbroic gabbroic anorthosite with football-sized football-sized plagioclase megacysts. megacysts. Coronas Coronas have have orthopyroxene orthopyroxene or clinopyroxene cores; cores; orthopyroxene orthopyroxene has has successive successive hornblende hornblende and and pale pale garnet garnet rims; clinopyroxene clinopyroxene has has hornblende hornblenderims rims and andrare rare orthopyroxene orthopyroxene cores. cores. clinopyroxene Return to Hwy 101. km END 134.1 km END OF OF DAY DAY 2. 2. Return to t o Wawa. Wawa. �- 46 ACKNOWLEDGEMENTS Weberimproved improvedthe themanuscript. manuscript. C.W. by P.C. W. Weber Reviews by P.C. Thurston and W. C.W. Jefferson is thanked for editorial editorial revisions. revisions. . . . REFERENCES REFERENCE in the the Attoh, K., K., 1980. Stratigraphic relations of the the volcanic-sedimentary volcanic-sedimentary successions in Wawa greenstonebelt, belt, Ontario. Ontario. In Current Research, part 5 Current,Research, part A. A. 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U-Pb U-Pb zircon zircon age age of of the the Jubilee Jubileestock stockinin the Research, part B. t h eMichipicoten Michipicotengreenstone greenstone belt belt near near Wawa, Wawa, Ontario. InInCurrent C Geological GeologicalSurvey Survey of of Canada, Canada, Paper Paper 85-IB, 85-10, pp. pp. 361-365. 361-365. Sutcliffe, studies on the Sutcliffe,R.R.and andFawcett, Fawcett,3.3., J.J., 1979. 1979.Petrological Petrologicaland andgeochronological geochro Rainy Rainy Lake Lake granitoid granitoidcomplex, complex,northwestern northwestern Ontario; Ontario;aaprogress progress report. report. In In Current Current Research, Research, part part A. A. Geological GeologicalSurvey SurveyofofCanada, Canada, Paper Paper 79-lA, 79-LA, pp. pp. 377-380. 377-380. Thompson, hompson, A.B., A.B., 1976. 1976. Mineral Mineral reactions reactions in in pelitic politicschists schistsH. 11. Calculation Calculatio of some P-T-X phase phase relations. relations. American AmericanJournal JournalofofScience, Science,276, 276,pp. pp.425—454. 425-454. Thurston, F.W., 1978. 1978. Metamorphic Metamorphic and andtectonic tectonic evol evolution of the UchiThurston, P.C. P.C. and and Breaks, Breaks, F.W., English River River subprovince. subprovince. InInMetamorphism Metamorphism ininthe t h eCanadian Canadian Shield. Shield. Geological Geological English Survey SurveyofofCanada, Canada,Paper Paper78-10, 78-10, pp. pp. 49-62. 49-62. Thurston, Thurston,P.C., P.C., Siragusa, Siragusa,G.M., G.M., and andSage, Sage, R.P., R.P., 1977. 1977. Geology Geologyofofthe t h eChapleau Chapleau area, area, Districts DistrictsofofAlgoma, Algoma,Sudbury Sudburyand and Cochrane. Cochrane. Ontario OntarioDivision DivisionofofMines MinesGeological Geological Report Report157, 157,293 293p.p. �- 514 - Turek, Smith, P.E., W.R., 1982. Turek, A., A., Smith, P.E., and and Van Van Schmus, Schmus, W.R., 1982. Rb-Sr Rb-Sr and and U-Pb U-Pb ages agesof of volcanism volcanism and granite emplacement in the Michipicoten Ontario. Canadian and Michipicoten belt, Wawa, Wawa, Ontario. Canadian lournal Journal of Earth Earth Sciences, Sciences, 19, pp. 1608-1625. 1608-1625. Turek, A., Smith, P.E. and Van Schmus, W.R., W.R., 1984. 1984. U-Pb P.E. Van Schmus, U-Pb zircon ages ages and and the t h e evolution evolution Turek, A., of plutonic-volcanicterrane terrane of tthe of tthe h e Michipicoten Michipicoten plutonic-volcanic h e Superior Superior Province, Province, Ontario. Ontario. Canadian Journal of Earth Earth Sciences, Sciences, 21, 21, pp. pp. 457-464. 457-464. Turner, Field and Tectonic Aspects. Turner, F.)., F.J., 1981. 1981. Metamorphic Metamorphic Petrology; Petrology; Mineralogical, Mineralogical$e~~.~n~Je$o,n~~,~sp^cts. Second edition. McGraw-Hill, McGraw-Hill, New New York, York, 524 524p. p. .,.z. + ~2b7b&; <;:, 5 3 ,;';<:,~, .:q Van Schinus,W.R., W.R.,1975. 1975. On Ont the age of of tthe dike swarm. swarm. Canadian Van Schmus, h e age h e Sudbury Sudbury dike Canadian Journal Journal of of Earth Earth Sciences, Sciences,12, 12,pp. pp.1690-1692. 1690-1692. Wanless, R.K., 1969. 1969. Isotopic age map Wanless, R.K., map of Canada. Canada. Geological GeologicalSurvey Surveyof of Canada, Canada,Map Map Â¥ 9- 1256A. 1256A. Watson, 3., 1980. and history of of the Kapuskasing structural zone, The origin and Kapuskasing structural zone, Ontario, Ontario, Watson, J., 1980. The Canada. Canada. Canadian Canadian Journal Journal of of Earth EarthSciences, Sciences, 17, 17, pp. pp. 866-876. 866-876. Wells, P.R.A., P.R.A., 1979. 1979. Chemical and thermal evolution of Archean Wells, Archean sialic sialic crust, crust,Southern Southern West Greenland. Greenland. Journal Journal of of Petrology, Petrology, 20, 20, pp. pp. 187-226. 187-226. Whitney, P.R., 1978. of garnet "isograds" in granulite facies rocks of Whitney, P.R., 1978. The The significance of "isograds" in the t h e Adirondacks. Adirondacks. In Metamorphism Metamorphism in the t h e Canadian Canadian Shield. Shield. Geological GeologicalSurvey Survey of of Canada, Paper Paper 78-10, 78-10, pp. pp. 357-366. 357-366. Wilson, H.D.B.,and and Brisbin, Brisbin,W.C., W.C.,1965. 1965. Mid-North Mid-North American American ridge ridge structure structure (Abstract). Wilson, H.D.B., (Abstract). Geological Society of America, Special Special Paper Paper 87, 87, pp. pp. 186-187. 186-187. Winkler, H.G.F., 1979. 1979. Petrogenesis Petrogenesis of of Metamorphic MetamorphicRocks. Rocks. 5th 5th edition. edition. SpringerWinkler, H.G.F., SpringerVerlag, Berlin, Berlin, 1-Ieidelburg, Heidelburg, New York. York. Wood, B.)., 1974. Wood, B.J., 1974. The The solubility of alumina in orthopyroxene coexisting with with garnet. garnet. Contributions Contributions to t oMineralogy Mineralogy and Petrology, Petrology, 46, 46, pp. 1-15. 1-15. Woods, D.V.,1985. 1985. Large-scale Large-scale electromagnetic electromagnetic induction investigation of the Woods, D.V., the Kapuskasing structural In Current Current Research, Research, part partA. A. Kapuskasing structural zone, zone, northern northern Ontario. Ontario. In Geological Geological Survey Survey of of Canada CanadaPaper Paper85—lA, 85-1A, pp. pp. 533-542. 533-542. .-, .*. � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1987 Description An account of the resource Institute on Lake Superior Geology. Wawa, Ontario. May 12-13, 1987. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1987 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/0ac2b7d90fa70da0fc171bbd32248ac5.pdf 10dbf180b065de6c5397d0231466198b PDF Text Text _________ Thirty-fourth Annual Meeting Marquette, Michigan Mayl2and 13, 1988 Institute on Lake Superior Geology Proceedings and Abstracts Volume 34, Part 1 22p0 LINEF,F,UNMIGRATED UNMIGRATED UNE 24p0 u 00 10 km 10km �34th ANNUAL LAKE SUPERIOR INSTITUTE ON LAKE SUPERIOR GEOLOGY GEOLOGY INSTITUTE Proceedings and Abstracts Proceedings Abstracts Marquette, Michigan Michigan May 12 1 2 and 13, 13, 1988 1988 Organized by John Hughes, Northern Michigan University John Kiasner, Klasner, Western Illinois Illinois University University Klaus Schulz, S. Schulz, U. U. S. Geological Survey Survey Klaus Program Program Chairman Chairman and and Editor: Editor: Volume Volume 34. 34. John Kiasner Klasner John Part 1 Program Program and Abstracts Abstracts Part 2 Field Guidebooks Guidebooks COVER Seismic time section section with inset inset showing the location of line line FF in Lake Superior. Superior. The seismic seismic is from the GLIMPCE section is program in the Great Great Lakes. Lakes. S volcanics; S == sediments; sediments; V == volcanics; AP == Archean-Proterozoic AP terrane. Archean—Proterozoic terrane. �PURCHASE OF PROCEEDINGS PROCEEDINGS AND ABSTRACTS AND FIELD GUIDEBOOKS The Proceedings and Abstract and the Field Guidebooks for for the the 34th Annual Annual Institute on Lake Superior Geology may be purchased by contacting: contacting: John Kiasner Klasner Geology Department of Geology Western Illinois University Macomb, Illinois Illinois 61455 61455 PROCEEDINGS AND ABSTRACTS, VOLUME 34. 34. PART PART 11 ----------- 4OO $4.00 FIELD GUIDEBOOKS, GUIDEBOOKS, VOLUME VOLUME 34, 34, PART PART 22 - - - - - - - - - - - - - - - $5.00 $5OO Issues Issues of Proceedings and Abstracts and Field Guidebooks from from previous meetings may be purchased by contacting the Secretary— SecretaryTreasurer: Treasurer: Joe Kalliokoski Kalliokoski Department of Geology and Geological Engineering Michigan Technological University Houghton, Michigan 49931 49931 �TABLE OF OF CONTENTS CONTENTS TABLE Institutes on on Lake Lake Superior Superior Geology Geology to to 1988 1988 Institutes Constitution of of the the institute Institute on on Lake Lake Superior Superior Geology Geology Constitution By Laws Laws on on the the Institute Institute on on Lake Lake Superior Superior Geology Geology By Goldich Medal Medal Guidelines Guidelines Goldich Student Travel Travel Award Award Student 1 1 ii ii iii iii iv iv v v Board of of Directors Directors Board vi Local Committee Committee Local vi Best Student Student Paper Paper Committee Committee Best vi vi vi vi Goldich Medal Medal Committee Committee Goldich vii Field Trip Trip Leaders Leaders Field vii Technical Session Session Chairs Chairs Technical vii Goldich Medal Medal Recipient Recipient Goldich viii Banquet Speaker Speaker Banquet viii viii Acknowledgements Acknowledgements vi ii viii Report of of the the Chairs Chairs of of the the 33rd 33rd Annual Annual Institute Institute Report Calender of of Events Events Calender Abstracts Abstracts vii vi i vii viii ix ix xi1 xii xvi i i xviii �INSTITUTES ON ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY INSTITUTES INSTITUTE NUMBER NUMBER INSTITUTE DATE DATE 1 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1 22 3 3 44 55 66 77 88 99 10 10 11 11 12 12 13 13 14 14 15 15 16 16 17 17 13 18 19 19 20 20 21 21 22 22 23 23 24 24 25 25 26 26 27 27 28 28 29 29 30 30 31 31 32 32 33 33 34 34 PLACE PLACE M i n n e a p o l i s , MN MN Minneapolis, Houghton, MI MI Houghton, E a s t Lansing, L a n s i n g , MI MI East D u l u t h , MN MN Duluth, M i n n e a p o l i s , MN MN Minneapolis, Madison, W I Madison, WI P o r t Arthur, A r t h u r , Ont. Ont. (Thunder (Thunder Bay) Bay) Port M I Houghton, Houghton, MI D u l u t h , MN MN Duluth, Ishpeming, MI Ishpeming, MI S t . P a u l , MN St. Paul, MN S a u l t Ste. S t e . Marie, M a r i e , MI MI Sault E a s t Lansing, L a n s i n g , MI MI East S u p e r i o r , WI WI SuDerior, Oshkosh, WI WI O3hkosh, Thunder Bay, Bay, Ont. Ont. Thunder MN D u l u t h , Duluth, MN Houghton, MI MI Houghton, Madison, W Madison, WII S a u l t Ste. S t e . Marie, Marie, Ont. Ont. Sault M a r q u e t t e , M I Marquette, MI S t . Paul, P a u l , MN MN St. Thunder Bay, Ont. Thunder Bay, Ont. WI Milwaukee, WI Milwaukee, D u l u t h , MN MN Duluth, Eau Claire, C l a i r e , WI WI Eau E a s t L a n s i n g 241 East Lansing,, MI I n t e r n a t i o n a l F a l l s , MN MN International Falls, Houghton, M I Houghton, MI Wausau, WI WI Wausau, Kenora, Ont. Kenora, Ont. WI Wisconsin Rapids, R a p i d s , WI Wisconsin Wawa, Ont. Ont. Wawa, MI M a r q u e t t e , MI Marquette, 1 �_________________________ CONSTITUTION CONSTITUTION OF OF INSTITUTE INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY Article II Article Article II I1 Article Name Name Article Article VII VII Officers Officers The The name name of of the the organization organization shall shall be be the the "Institute "Institute on Lake Lake Superior Superior Geology." Geology." on The The officers officers of of this this organization organizationshall shall be be aa Chairman Secretary-Treasurer. Chairman and and aa Secretary-Treasurer. Objectives Objectives The The objectives objectives of of this this organization organizationare: are: A. A. The The Chairman Chairman shall shall be be elected elected each each year year by by the the board board of of directors, directors, who who shall shall give give due due consideration consideration to to the the wishes wishes of of any any group group that that may may be be promoting promoting the the next next annual annual meeting. meeting. His His term term of of office office as as Chairman Chairman will will terminate terminate at at the the close close of of the the annual annual meeting meeting over over which which he he presides presides or or when when his his successor successor shall shall have have been been appointed. appointed. He He will will then then serve serve for for aa period period of of three three years years as as aa member member of of the the board board of of directors. directors. B. 6. The The Secretary—Treasurer Secretary-Treasurer shall shall be be elected elected at at the the annual annual meeting. meeting. His His term term of of office office shall shall be be two two years years or or until until his his successor successor shall shall have have been been appointed. appointed. A. A. To To provide provide aa means means whereby whereby geologists geologists in in the the Great Lakes Lakes region region may may exchange exchange ideas ideas and and Great scientific scientific data. data. B. B. To To promote promote better better understanding understanding of of the the geology geology of of the Lake Lake Superior Superior region. region. the C. To plan and conduct geological field trips. C. To plan and conduct geological field trips. Article III 111 Article Status Status No No part part of of the the income income of of the the organization organization shall shall inure inure In the the to the the benefit benefit of of any any member member or or individual. individual. In to event event of of dissolution dissolution the the assets assets of of the the organization organization shall shall be be distributed distributed to to (some tax tax free free organizatt3iT. organization). (some (To Federal and (To avoid Federal and State State income income taxes, taxes, the the organization organization should should be be not not Only only "scientific" "scientific" or or "educational" but also "non—profit".) "educational" but also "non-profit".) Minn. Minn. Stat. Stat. Anno. Anno. 290.01, 290.01, subd. subd. 44 ht-'- I-i. ' 290.05(9) 290.05(9) 1954 (3) 1954 Internal InternalRevenue RevenueCode Codea.s.501(c) 501(c)(3) - 1-'• Article IV IV Article Article VV Article Article VI VI Article Membership Membership The The membership membership of of the the organization organization shall shall consist consist of of the board board of of directors. directors. Any geologist geologist interested interested the shall shall be permitted to to attend attend and and participate participate in in vote at at the the annual annual meetings. meetings. and vote Meetings Meetings The The organization organization shall shall meet meet once once aa year, year, preferably preferably during during the the month month of of April. April. The The place place and and exact exact date date designated by by the the board board of of of each meeting will be designated directors. directors. Directors Directors The The board of directors directors shall shall consist consist of of the the Chairman, Chairman, Secretary—Treasurer, Secretary-Treasurer, and and the the last last three three past past ChairChairmen; men; but if if the board should should at at any any time time consist consist of of less than five persons, persona, by by reason of unwillingness unwillingness or 01 or inability inability of any of the the above above persona persons to to serve serve as as directors, directors, the the vacancies on on the the board board may may be be filled by by the annual meeting meeting so as to bring the the membership membership of of the the board board up up to to five five members. members. Article Article VIII VIII Amendments Amendments This This constitution constitution may may be be amended amended by by aa majority majority vote vote of of those those persons persons who who are are personally personally present present at, at, participating participating in, in, and and voting voting at at any any annual annual meeting meeting of of the the organization. organization. �- BY-LAWS BYLAWS I. I. Duties of of the the Officers Officers and and Directors Directors Duties A. A. It shall shall be be the the duty duty of of the the Chairman Chairman to: to: It 1. 1. 2. 2. 3. 3. B. B. at the the annual annual meeting. meeting. Preside at Preside all committees committees needed needed for for the the organization organization of of Appoint all Appoint the annual annual meeting. meeting. the Assume complete complete responsibility responsibility for for the the organization organization Assume and financing financing of of the the annual annual meeting meeting over over which which he he and presides. presides. It shall shall be be the the duty duty of of the the Secretary-Treasurer Secretary-Treasurerto: to: It Keep accurate accurate attendance attendance records records of of all all annual annual Keep meetings. meetings. 2. Keep Keep accurate accurate records records of of all all meetings meetings of, of, and and 2. corres?ondence between, between, the the board board of of directors. directors. corresrondence 3. Hold Hold all all funds funds that that may mav accure accure as as profits profits from from annual annual 3. meetings or or field field trips trips and and to to make make these these funds funds meetings available for for the the organization organization and and operation operation of of future future available meetings as required. meetings as required. 1. 1. C. C. 11. II. Dues and and Expenses Ex-oenses Dues 1. 1. 2. 2. III. III. It shall shall be be the the duty duty of of the the board board of of directors directors to to plan plan It locations of annual meetings and to advise on the locations of annual meetings and to advise on the organization and and financing financing of of all all meetings. meetings. organization regular membership membership dues. dues. There shall shall be be no no regular There for the the annual annual meetings meetings shall shall be be Registration fees fees for Registration determined by by the the Chairman Chairman in in consultation consultation with with the the determined the board board of of directors. directors. It It is is strongly strongly recommended recommended that that the these be kept at a minimum to encourage attendance of these be kept at a minimum to encourage attendance of graduate students. students. graduate Rules of of Order Order Rules The rules rules contained contained in in Robert's Robert's Rules Rules of of Order Order shall shall govern govern The this organization orqanization in in all all cases cases to to which which they they are are applicable. applicable. this IV. IV. Amendments Amendments amended by by aa majority majority vote vote of of those those These by-laws by-laws may may be be amended These persons who are personally present at, particinating in, and and persons who are r'ersonally present at, particiating in, voting at anv annual meeting of the organization; provided voting at any annual meeting of the organization; provided that such such modifications modifications shall shall not not conflict conflict with with the the that constitution as presently adopted or subsequently amended. constitution as presently adopted or subsequently amended. iii iii �Award CudaUnes SAN GCLD:C: 4EDAL Preamble Preamble The tnszituz an wasborn born an onor o raround around The InsT:itx-:3 on l aaie k e Sueror S u p e r i o rGecloav Geoioqy as 1 9 5 5 , aas s dec-sexad 'ay the =he acz fac-: that that tne cke27th 2 7 t h annual a n n u a l meetn: neecn,; 1955, iocmentd by will w i l l be be held h e l d in i n1981. 1981. The The 1nsT:i'curss a r e exemiar'a x e n g l a r y in i n their :heir tnsttutes are continuinc c o n c i ~ u i n cx ~:ecz;es : e c i z ~ , - of e sofdealing d e a l i n g with w i t h those 3 o s e aseczs a s p e c t sofofgeology geolsqy that Si-aerier: of of en— ent h a t are a r e related r e l a c e dgeograchically ~ ~ e o g r a p n i c a . lto l t' /ocake Lake Superior courauxng =r:a i s c i s s i o n oof r sub?ec-ss p o n s o r i n g ffield ield couraging the ddiscussion sabjects and ands sonscring t r i o s whch whick will v i l lbring b r i n atocether z o a e t h e rgeologists q e o i o c i s t sfrom fromthe t h eacademia, academia, trios government sur-J-eys, and indus'czy; and of of maintaining s i a i n c a i n i n g an an government surevs, and industr'; and exceedlv e x c e e d l v informal i n 5 m a l but b u t highly h i a h l y effective e f f e c t i v e mode mode of peraelon. of ooerazion. Durina i t se:istence e x i s t e n c ethe t h rserttbership e .'nembershiu of o f the the During tthe h e course c o u r s e of of its Institute I n s - c i t u t e that k h a 'is, c i those s , t h o sgeologists e q e o l o a i s c who s who indicate i n d i c a t e an a n interest interest in i n the t h e objectives obyectiq.'es of of the t h e I.L.S.G. 1.Ii.S .G. by by attending) a t t e n d i n g ) has h a s become become aware aware of of the t h e fact S a c t that t h a t certain c e r t a i n of of their t h e i r colleagues c o l 1 e a c u e s have have made nocaworthy and and meritorious m e r i t o r i o u s contributions contributions mace particularly p a r t i c u l a r l y noteworthy to 'ake Suerior" t o the t h e iprcvement i a p r o v e z e n c of of understanding understandinu ofof"Lake Superior" geology and iits qeoloay and t s mineral m i n e r a l degosits. degosits. The I .L.S . G . to t oSam Sam Gcldich G o l d i c h in in The exemclar-. exemniary award awardwas :/as made made by by I.L.S.G. 1979 hsi smany off the 1 9 7 9 ffor or h many contributions c o n t r i b u t i o n s to t o the t h e geology geology o t h e region reuion extending 50 years. years. e x t e n d i n g over o v e r about a b o u t 50 Awrd Guidellnes 1) 1) Thu "he xmedal e d a l sshall n a l l be be awarded awarded aannually n n u a l l y by by the t h e Board 3 o a r d of of Directors, is associated 2.:. G. , to t oa ageologist q e o l o a i s twnose wnose name name is assoczated D i r e c t o r s , 1..L.3.G., subszanzal sustaned interest in, or a major con— Â¥;= --~ - -.-- u t ~ oto, n i^.e geology geoloqy ofofShe a ~ eSSueror u s e r z o r region. region. trbuton the theLtaie with :.r~^. aa s u b s z . i n i ~ ^ . lsus-ca1r.ea Lnceras-c i n , o r a ^layor con- The ofSDirectors, acoint the The 3Board o a r t 05 i r e c t o r s , I .I.L.S.C. L.3.3. s shall h a l l aoooint: the at a t the *e annual a n n u a lbusiness b u s i n e s smeeting. neecina. The The iinitial n i t i a l apointment appoinment will w i l l be be of ofthree 5 r e members, e members, one one to t o serve s e r v e for f o r three t h r e e years, y e a r s , one one for thebbrefest riefest f o r two, two, and and one a n e for f o r one one year, y e a r , the t h e rnemoer rnemner wwith i t h the incumoencv incumbency to t o be bechairman. chairman. After A f t e r the =he first f i r s t ;year y e a rthe t h eBoard 3oard of of Directors Direc-iors shall s n a i lappoint angoin-c at a teach each string s ? r i n a meeting meeting one onenew new member who member vno x iwill 1 l s serve e r v e ffor o r three t h r e e years. y e a r s . In I n the t h e third t h i r d year year this t h i smember m e m e r sshall n a l l be be the t h echairman. chairman. The The Corrittee Committeemembership membership should s h o u l d rref e f lluct e c t the t h e main main ffields i e l d s of of interest i n t e r e s - cand and geograthic geographic 2) 2) ominating i l l be b e voted voced on on !lominaci.ncCommittee. Commxtitee. Their T h e i r annual a n n u a l nominee xominee wwill distribution dis-cribuizion of of I.L.S.G. I.L.S.G. membership. niembership. Committee 3) 3 ) The The Goidich Goidzcr. :edal Medal ominating ^lom.~natina Committee shall s n a i l select s e l e c t the the medalist and w i l lmake m a k e its ~ recommendation t recormenda'c~on s tto o the t o e Board 3 o a r c of of medai~s'c anc. will Directors by Iovember !roveainer 1, L, of of that c h a t year. year. DLrec=ors by 4) 4 ) The The Board Board of of Directors D i r e c t o r s normally normally will w i l l accept a c c e p t the t h enominee nominee of w i l linform inform the t h emedalist m e d a l i s timmediately, immeaiacely, of the t h eCommittee, Comi=-cee, will an engraveda ~apropatalv and.will w i l have l have one one medal medal engraved p r o p r i a t e l yfor Sor prepresentation s e n t a t i o n at a t the t h e Iay .lay meeting. meeting. 5) 5) It I t is is recommended recommended that t h a t the the Institute I n s t i t u t e set see aside a s i d eannually annually from whatever w i l l be be required r e q u i r e d to to from w h a t e v e r ssources, o u r c e s , such such funds funds as a s will support s u p p o r t the t h e continuing c o n t i n u i n g costs c o s e s of of this t h i saward. award. April 4 , 1981 1981 A p r i l 4, J. J. Kalliokoski, K a l l i o k o s k i ,Chairman Chairman Bill B i l lCannon Cannon Fred Fred Kehlenbeck Kenienbeck Glenn Glenn 4orey Yoray Greg Greg Murskv Mursky iv �STUDENT TRAVEL TRAVEL AWARD AWARD STUDENT The 1986 1 9 8 6 Board Board of o f Directors D i r e c t o r s established e s t a b l i s h e d the t h e ILSG ILSG Student Student The T r a v e l Award Award to t o support s u p p o r t student s t u d e n t participation p a r t i c i p a t i o n at a t the t h e annual annual Travel I n s t i t u t e s . The The awards a w a r d s will w i l l be b e made made from f r o m the t h e accrued a c c r u e d interest interest Institutes. s p e c i a l fund f u n d set s e t up up for f o r this t h i s purpose. p u r p o s e . This T h i s award a w a r d is is f r o m aa special from i n t e n d e d to t o help h e l p defray d e f r a y some some of o f the t h e direct d i r e c t travel t r a v e l costs c o s t s to t o the the intended iinstitute n s t i t u t e and a n d includes i n c l u d e s aa waiver w a i v e r of o f registration r e g i s t r a t i o n fees, f e e s , but but meals, lodging, l o d g i n g , and a n d field f i e l d trip trip e x c l u d e s expenses e x p e n s e s for f o r meals, excludes s i z e w i l l b e d e t e r m i n e d by by the the r e g i s t r a t i o n . The number a n d registration. The number and size will be determined a n n u a l C h a i r m a n i n c o n s u l t a t i o n w i t h t h e S e c r e t a r y T r e a s u r e r and and annual Chairman in consultation with the Secretary Treasurer w i l l b e a n n o u n c e d a t t h e a n n u a l b a n q u e t . will be announced at the annual banquet. The following f o l l o w i n g general g e n e r a l criteria c r i t e r i a will w i l l be b e considered c o n s i d e r e d by by the the The a n n u a l Chairman, C h a i r m a n , who who is is responsible r e s p o n s i b l e for f o r the t h e selection: selection: annual 1 ) The The applicants a p p l i c a n t s 'must 'must hhave a v e aactive c t i v e resident r e s i d e n t (undergraduate (undergraduate 1) t i m e o f t h e institute, institute, o r g r a d u a t e ) s t u d e n t s t a t u s a t t h e or graduate) student status at the time of the c e r t i f i e d b y t h e d e p a r t m e n t h e a d . certified by the department head. 2 1 Students S t u d e n t s who who are a r e the t h e senior s e n i o r author a u t h o r on on either e i t h e r an a n oral o r a l or or 2) p o s t e r paper p a p e r will w i l l be b e given g i v e n favored f a v o r e d consideration. consideration. poster 3 ) It I t is is desireable d e s i r e a b l e for f o r two t w o or o r more more students s t u d e n t s to t o jointly jointly 3) r e q u e s t travel t r a v e l assistance. assistance. request 4 4) I n general, g e n e r a l , priority p r i o r i t y will w i l l be b e given g i v e n to t o those t h o s e in i n the the In I n s t i t u t e region r e g i o n who who are a r e farthest f a r t h e s t away. away. Institute 5 ) Each Each travel t r a v e l award a w a r d request r e q u e s t shall s h a l l be be made made in i n writing, w r i t i n g , to t o the the 5) a n n u a l C h a i r m a n , w i t h a n e x p l a n a t i o n o f n e e d , p o s s i b l e annual Chairman, with an explanation of need, possible a u t h o r status s t a t u s or o r other o t h e r significant s i g n i f i c a n t details. detailsauthor V �BOARD BOARD OF OF DIRECTORS DIRECTORS 1988 1988 J. J. S. Klasner (with J. D. Hughes and K. of Kiasner (with K. J. 3. Schulz), Department of Western Illinois Illinois University, University, Macomb, Illinois Illinois Geology, Western 61455 61455 1987 1987 Sage (with R. P. 'Sage (with E. D. Frey) Ontario Geological Survey, Ministry of Northern Northern Development Development and and Mines, Mines, 77 77 Grenville Grnville Street, Street, M7A 1W4 Toronto, Ontario 1W4 1986 1986 Wisconsin Geological and J. K. Greenburg (with (with B. B. A. A. Brown) Brown) Wisconsin Natural History Survey, 3817 Mineral Point Road, Madison, 53705 Wisconsin 53705 1985 1985 C. E. Blackburn, Mineral and and Development Development Branch, Branch, Ministry Ministry of of Kenora, Northern Development and Mines Mines P. P. 0. 0. Box Box 5160, 5160, Kenora, Ontario P9N 3X9 Ontario 3x9 Secratary-Teasurer Secratary-Teasurer J. Kalliokoski, Department of Geology and Geological Engineering, Michigan Technological Technological University, University, Houghton, Houghton, Michigan 49931 49931 Michigan LOCAL COMMITTEE COMMITTEE J. D. D. Hughes: Hughes: Conference Co-Chair; Conference Co-Chair; Local arrangements arrangements 3. J. S. S. Kiasner: Klasner: Conference Co—Chair; Co-Chair; Program and Abstracts Abstracts editor, editor, mailings and regitration regitration K. J. J. Schulz: Schulz: arrangements and Conference Co-Chair; Co-Chair; Field trip arrangements and field guidebook editor, banquet banquet speaker speaker BEST STUDENT STUDENT PAPER COMMITTEE COMMITTEE G. W. Adams: Adams: Exploration, Noranda Exploration, G. L. LaBerge: G. LaBerge: P. Sage: Sage: R. P. Rhinelander, Rhinelander, Wisconsin University of of Wisconsin—Oshkosh, Wisconsin-Oshkosh, Wiscons in Wisconsin Ontario Geological Geological Survey, Survey, vi Oshkosh, Oshkosh, Toronto, Ontario �GOLD1 CH MEDAL MEDAL COMMITTEE COMMI TTEE GOLDICH J. J. J. Brummer: Brummer: J. K. D. D. K, Brununer Consulting, Consulting, Toronto, Toronto, Ontario Ontario Brummer Card: Geological Geological Survey Survey of of Canada, Canada, Ottawa, Ottawa, Ontario Ontario Card: R. J. J. Oiakarigas: Ojakangas: University Minnesota R. Uriiver3ity of of Minnesota, Minnesota, Duluth, Duluth, Minnesota FIELD TRIP TRIP LEADERS LEADERS FIELD D. A. A. Baxter: Baxter: Michigan Michigan Technological Technological University, University, Houghton, Houghton, D. Michigan Michigan J. Bornhorst: Bornhorst: Michigan Michigan Technological Technological University, University, Houghton, Houqhton, T. J. T. Michigan Michigan B. C. C. Boyurn: Boyum: B. Cleveland-Cliffs, Inc. Inc. Ishpeming, Ishpeming, Michigan Michigan Cleveland-Cliffs, A. Brozdowski: Brozdowski: Callahan Callahan Mining Mining Corporation, Corporation, Negaunee, Negaunee, Michigan Michigan R. A. R. C. Gallup: Gallup: California California Institute Institute of of Geology, Geology, Long Long Beach, Beach, C. California Ca i i for n i a W. R. R. Gregg: Gregg: Michigan Michigan Technological Technological University, University, W. Michigan Michigan € C. C. Johnson: Johnson: R. Michigan Michigan Wm. Kangas: Kangas: Wm. Houghton, Houghton, Michigan Technological Technological University, University, Michigan Houghton, Houghton, Cleveland-Cliffs, Inc., Inc., Ishpeming, Ishpeming, Michigan Michigan Cleveland-Cliffs, J. S. S. Klasner: Klasner: Western Western Illinois Illinois University University and and U. U. S. S. Geological Geological J. Survey, Macomb, Macomb, Illinois Illinois Survey, L. MacLellan: MacLellan: M. L. M. Michigan Michigan R. G. G. Reed: Reed: R. Michigan Geological Geological Survey, Survey, Michigan G. W. W. Scott: Scott: G. P. K. K. Sims: Sims: P. Michigan Technological Technological University, University, Michigan Lansing, Michigan Michigan Lansing, Callahan Mining Mining Corporation, Corporation, Callahan U. S. S. Geological Geological Survey, Survey, U. Houghton, Houghton, Neqaunee, Michigan Michigan Negaunee, Denver Colorado Colorado Denver TECHNICAL SESSION SESSION CHAIRS CHAIRS TECHNICAL R e L. L. Bauer: Bauer: R. University of of Missouri, Missouri, Columbia, Columbia, Missouri Missouri University F. W. W. Cambray: Cambray: Michigan Michigan State State University, University, Lansing, Lansing, Michigan Michigan F. W. F. F. Cannon: Cannon: W. U. S. S. U. Geological Survey, Survey, Reston, Reston, Virginia Virginia Geological J. Hinze: Hinze: Purdue Purdue University, University, West West Lafayette, Lafayette, Indiana Indiana W. J. W. M. M. M. Kehienbek: Kehlenbek: M. Lakehead University, University, Lakehead vii vii Ontario Ontario �S. S. W. Nicholson: Nicholson: W. J . M. M. J. Washington, D. D. C. C. Washington, Paces: Paces: Michigan Michigan Technological Technological University, University, Michigan Michigan D. Southwick: Southwick: Minnesota Minnesota Geological Geological Survey, Survey, D. Minnesota Minnesota Houghton, Houghton, Minneapolis, Minneapolis, GOLDICH GOLDICH MEDAL MEDAL RECIPIENT RECIPIENT Walter S. S. White, White, U. S. S. Geological Geological Survey Survey (retired). (retired). Medal Medal Walter U. awarded awarded by by D. D. H. M. Davidson, Davidson, Northern Northern Illinois Illinois University University BANQUET SPEAKER SPEAKER BANQUET P. F. F a Hoffman: Hoffman: P. Geological Geological Survey Survey of of Canada, Canada, Ottawa, Ottawa, Ontario Ontario ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS Several Several people people and and organizations organizations assisted assisted in in preparation preparation of of the 34th 34th Annual Annual ILSG. ILSG. Without Without their their help help the the many many tasks tasks in in preprethe paring paring this this meeting meeting could could not not have have been been done. done. We We would would like like to to thank thank the the following following people people and and organizations organizations for for their their help. help. Diana Robertson Robertson and and the the office office of of Non—Residential Non-Residential Programs Programs at at Northern Northern Michigan Michigan University University for for logistical logistical assistance. assistance. The Department Department of of Geography, Geography, Earth Earth Science, Science, Conservation Conservation and and Planning at at Northern Northern Michigan Michigan University University Planning The Department of Geology at Western Illinois Illinois University Gretchen Gretchen Kiasner Klasner for for assistance assistance in in handling handling finances. finances. Cathy McCormick and and Corrine Corrine Weaver Weaver for for help help with with typing, typing, logistics, and and mailing. mailing. logistics, Callahan Callahan Mining Mining Corporation Corporation for for assistance assistance with with field field trips. trips. Michigan Technological Technological University University for for assistance assistance with with Michigan transportation for for field field trips. trips. transportation Geological Survey Survey for for providing providing mailing mailing lists lists and and Minnesota Geological labels labels viii vili �33rdINSTITUTE IYSTITUTS ON ON LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY 33rd WAWA, WAWA, ONTARIO ONTARIO -- 1987 1987 Lake Superior S u p e r i o r Geology Geology was was held held The 33rd 33rd meeting m e e t i n g of of the t h e Institute I n s t i t u t e on on Lake The h o s t s d by by i nWawa, Wawa, Ontario O n t a r i o from from 10 10 to t o 15 1 5 May May 1987. 1937. The meeting messing was hosted in t h e Ontario O n t a r i o Ministry M i n i s t r y of of Northern N o r t h e r n Development Devel0pmer.t and and Mines Mines -- Wawa Wawa Resident Resident the G e o l o g i s t Office O f S i c e and and the t h e Ontario O n t a r i o Geological Geologies! Survey. Survey. Technical T e c h n i c a l sessions sessions Geologist were held h e l d on on 12 1 2 and and 13 1 3 May May ini n the t h e corrnunity community arena a r e n a and and posters a o s t -^s - were were were d i s p l a y e d in i n the t h e adjacent a d j a c e n t curling c u r l i n g clubhouse. c l u b h o u s e . Registered R e g i s t e r e d attendance screndance displayed was 255, 255, including i n c l u d i n g 30 30 students. s t u d e n t s . P:e—registraticn P r e - r s g i s t r a t i m totalled t o t a l l e d 220. 220. Four Fou; crc—meeting, or?-meeting, three t h r s s repeated r e p e a t e d post p o s t meeting, meeting, and two two duolicate d u p l i c a t e field field trips o f 245 2 4 5 participants, p a r t i c i p a n t s , many many t r i p s during d u r i n g the t h e meeting m e e t i n g attracted a x r a c t s d aa total t o t a l of attending a t e n d i n 5 two two of of the t h e five f i v e individual i n d i v i d u a l tours. t o u r s . Bernie Berr.ie Schnieda:s S c h n l e d e r s became became a n excellent e x c e l l a n t substitute s u n s t i t u c s for f o r Tom Tom Muir Mui; when when illness i l l n e s s forced f o r c e d Tom's Tom's absenc2 aksencs an f:om from leadership l e a d e r s h i p of o i aa review r e v i e w of of Hemlo Henlo geclacy g e c l o c y attended a t t e n d e d by by 47. 47. John John Percival P e r c i v a l conducted c o n d u c t e d two two 2—day ?-day transects t r a n s e c t s of of the t h e Kapuskasing Xapuskasincj Structural 3t;xt'~ral f o r 40 40 visitors. v i s i t o r s . Ron Ron Sage Sage led l e d 33 3 3 participants p a r t i c i p a n t s through t h r o u g h the t h e st:a— sxaZone for tigraphy of the Michipicoten Iran Formation an two field trips, t i g r a p h y o f t h e X i c h i g i c o t s n I r o n Formation on two f i e l d t r i p s . rawa Wawa ea wasexamined examinedbyby 96 9 6 during d u r i n g two two field f i e l d trips t r i p s led led AreaGold GoldMineralitation M i n e r a l i z a t i o nwas mine of G.W. MacLead MacLeod side:ita s i d e s i t e mine of the t h e Algoma Algorra Steel Stsel Staf: of of the t h e G.W. 3d Frey. F r e y . Staff by Ed C o r p o r a t i o n hosted h o s t e d 29 29 visitors v i s i t o r s on on two two half—day h a l f - d a y tours. t o u r s . Separate S e p a r a t e guide— guideCorporation books books. were were published p u b l i s h e d for f o r three t h r e e of of the t h e field f i e l d trips t r i p s and a fourth f o u r t h is is in in p r e p a r a t i o n for f o r the t h e Wawa Wawa gold g o l d tour. t o u r . AA guidebook guidebook was was not n o t published p u b l i s h e d for for preparation t h e MacLead MacLeod Mine Mine tour. tour. the Thirty-three 29 posters p o s t e r s were were displayed displayed T h i r t y - t h r e e papers p a p e r s were were presented p r e s e n t e d orally o r a l l y and and 29 during d u r i n g the t h e technical t e c h n i c a l sessions. s e s s i o n s . K. M. Lockwood Lockwood replaced r e p l a c e d the t h e last-minute l a s t - m i n u t e cancancellation c e l l a t i o n of of two two papers p a g e r s by by R. R. Dahi, Dahl, et e t al., a l . , with wich an a n impromptu i m o r o a p t u review r e v i e w of of Fifteen chioritoid c h l o r i t o i d alteration a l t e r a t i o n in i n the t h e Wawa Wawa area. area. F i f t e e n students s t u d e n t s presented presented eight t a s k for f o r the the e i g h t papers p a p e r s and eight e i g h t posters p o s t e r s and provided provided a challenging c h a l l e n g i n g task the Best Student presented Tony Andrews Student Awards Committee, Committee. Andrews p r e s e n t e d t h e Z e s t S t u d e n t Paper Paper Student Award to t o Matthew E. E. Bidwell, B i d w e l l , Univ. Univ. of of Wyoming, Wyoming, for f o r his h i s paper p a p e r "A "A two— twostage s t a g e simple—shear s i m p l e - s h e a r model for f o r high h i g h flattening f l a t t e n i n g strains s t r a i n s in i n sshear h e a r zones of of the t h e central c e n t r a l Vermilion V e r m i l i o n district, d i s t r i c t , northeastern n o r t h e a s t e r n Minnesotan. MinnesotaR. R.L. R.L. Bauer, Bauer, Univ. Univ. of of Missouri, M i s s o u r i , was was co—author. c o - a u t h o r . The The Best Best Student S t u d e n t Poster P o s t e r Award Award went went to K. Sikkila, Tech. Univ., Univ., ffor A structural t o Kevin M. S i k k i l a , Michigan Tech. o r hhis i s pposter o s t e r "A structural analysis a n a l y s i s of o f Proterozoic P r o t s r o z o i c inetasediments, metasediments, >northern n o r t h e r n Falls F a l l s River, R i v e r , Ba.&&@ co—authored by by W.J. W.J. Gregg, Gregg, Michigan T6c'h. TéEñ. Univ. County, Michigantt, Michigan", co-authored Univ. Each award award consisted c o n s i s t e d of of $150.00 $ 1 5 0 . 0 0 provided p r o v i d e d from from registration r e g i s t r a t i o n fees. f e e s . Six Six students s t u d e n t s received r e c e i v e d waiver w a i v e r of of registration r e g i s t r a t i o n fee f e e and and $50.00 $ 5 0 . 0 0 each e a c h as as a Student S t u d e n t Travel T r a v e l Award. Award. These funds funds also a l s o were were provided provided by registration registration receipts. receipts. The The annual a n n u a l banquet b a n q u e t on on 12 1 2 May May at a t the t h e Union Union Hall H a l l was an a n outstanding outstanding feast, f e a s t , catered c a t e r e d for f o r 229 229 people p e o p l e by by the t h e Voyageur Voyageur Restaurant. R e s t a u r a n t . Allan Allan Goodwin presented Erindale p r e s e n t e d the t h e Goldich G o l d i c h Medal Medal to t o Henry Halls, Halls, E r i n d a l e College— ColleqeUniv. Univ. of of Toronto. T o r o n t o . The guest q u e s t speaker s p e a k e r was was Howard Howard Poulsen Poulsen; Geological Geological Survey S u r v e y of o f Canada, Canada, who who reviewed reviewed the t h e relationship r e l a t i o n s h i p between bet-ween tectonics t e c t o n i c s and gol'd g o l d mmineralization i n e r a l i z a t i o n throughout t h r o u g h o u t Canada. Canada. The ILSG ILSG Board Board of of Directors D i r e c t o r s held h e l d aa luncheon luncheon meeting meeting on on 12 1 2 May. May. In In attendance were Co-chairmen Ed Frey and Ron Sage, Bruce Bro, a t t e n d a n c e were Co-chairmen Ed F r e y and Ron Sage, Bruce Brown, Charlie Charlie Blackburn, Blackburn, Gene Gene LaBerge, LaBerqe, and and Fred Fred Kehienbeck. Kehlenbeck. Also Also present p r e s e n t were were Ted Ted Bornhorst B o r n h o r s t and the t h e 34th 3 4 t h ILSG ILSG team team of of John John Kiasner, K l a s n e r , John John Hughes Hughes and and ix �The Board Board took took the the following following action: action: Klaus Schulz. Schulz. The Klaus 1.As As of of 22 April April1987 1937 the the U.S. U.S. account account totalled 3 3 0 5 3 . 2 l and and the the 1. totalled $O63.21 Goldich Medal ?edai Fund Fund was was $1153.92. $1153.92. As As of of12 12May May 1937 1337 the theCanadian Canadian Goldich account total was $5507.51. The 33id ZL3G submittad $3839.56 account total was $5507.61. The 33rd LLSG submitted $3839.56 ($2637.55 pofit) Canadianaccount accountininDec. Dec.1937 1237and and ($2637.56 profit) totothethe Canadian C$255.00 to the Goldich Medal Fund. C$255,00 to the c-oldich Medal Fund. 2. Ted Ted 3ornhorzt 3ornnorstmoved moved that-the custodianofofthethe Canadianaccount account 2. thatthe custodian Canadian be present present at at all all businessmeetings. meetings. Motion Motion passed passed unanimously. unanimously. be business 3. Gene Gene .LeBes;e aoved that thatinterest in-rarast cc~3inedU.S. Y.S. and and 3. noved onsnthethe combined .a2er;e Canac:an ac=cui"ttsbe be used used for forStuden: SfczdentTravel TravelAwards. Awards. Motion Mocion Canadian accounts :assed unanImously. iinaninously. ItItwas wasnoted notad that that ititisisdesirable desirabletotohave have passed $ 1 0 , 2 C O . L.-. aac." account and that no meetin? shcuLd be planned $10,000. in each account and that no meeting should be planned to lose losemoney. xney. to 4. The The ILGG is aa non-profit non-profitorganization organization underU.S. U.S.law lawand anddonadona4. LLG is under tions are are tax taxdeduc:ible. deductible. This This fact factshould should be be noted notsd on tions on all all circulars for U.S. meetings. circulars for U.S. meetings. 5. There There is isno no need need to to publish publishthe theby—laws by-laws of the organization organization 5. of the foreach eachmeeting. meeting. for in 6 . Student Studentpaper pager and and poster poster awards awards should should be be $150.00 $150.00 each, 6. each, in The awards awards should be part part the currency cxzency of of the the meeting meeting site. site. The the should be Co-authored pacers now acceptable, ofthe themeeting meetingbudget. budget. Co—authored of papers are are now acceptable, provided that the student student is isthe thesenior seniorauthor. author. provided that the 7. Ted Ted Bornhorst Bornnorst and and Charlie Charlie Blackburn Blackburn prepared prepared guidelines for 7. guidelines for by the Board. Student Travel Awards that were accepted Student Travel Awards that were accepted by the Board. Klaus Schulz Schuizrecommended recommended that thenew new awards awards requirements requirementsbe be Klaus that the sent to tointerested interestedgeology geologydepartments. degartments. sent 3. The The Proceedings Proceedings and guidebooks 3. andAbstracts Abstractsvolume volumeand andfield field trip trip guidebooks now have now havevolume volumeand andpart partnumbers numberstotoallow allowproper properlibrary library indexing. The The P. P. & & A. A. title title hasbeen beenstandardized. standardized. indexing. has 9. Dr. Dr.J.J. J.J.(Joe) (Joe) Brummer, consulting consultinggeologist, geologist,Toronto, Toronto, is is the the 9. Brurtuner, W.A. Bodwell. Bodwell. new iember Medal Committee, Committee, reglacing new memberofofthe the Goldich Goldich Medal replacing W.A. be Michigan and and will The 1933 1938 iL3G meet in in Marquette, Marquetta, Michigan 10. The 10. ILSGwill will meet will be organized by John Klasner, John Hughes, and Klaus Schulz. organized by John Kiasner, John Hughes, and Klaus Schulz. The 1989 1989 ILSG in Duluth, Duluth,Minnesota Minnesota and and chaired chaired by by The LLSGwill will be be in 1990 meeting meetingmay may be be in inThunder Thunder Bay, Bay, Ont. Ont. Dick Ojakangas. Ojakangas. The The 1990 Dick 11. Gene Gene Laberqe will forthe theBest BestStudent Student 11. L1aberge willprepare preparea acertificate certificate for Poster Awards Awards and the winners. winners. The The Paper && Poster Paper and send send them them to to the certificatewill will state title of paper/poster, date, and ILSG certificate state title of paper/poster, date, and ILSG and will will signed awardcommittee. committee. The The locationand location bebesigned bybythethe award winners' names should be published in the Chairman's report. winners' names should be published in the Chairman's report. We hope hope Chairingthe the33rd 33rdILSG ILSG has has been been an an education education in in organization. organization. We Chairing thatthe theWawa Wawa meeting meeting has has demonstrated demonstrated that small communities communities with with that that small sufficient accommodations accommodations can sufficient can host host futureILSGs. ILSGs. The The absence absence of of custom custom future x x �facilities insDired innovation here, as it can elsewhere. We again thank all who rtade the Wawa rneeting possible and those who provided encouragernent and support. The ILSG is a priceless gathering of friends in the geological fraternity working in the Lake Superior Toronto, Ontario RP. Sage region. We know of no better way to keep in touch with new ideas on the region than through the ILSG. Respectfully submitted, E.D. Frey Wawa, Ontario CoChai:en, 33rd ILSG January l87 xi I-' X �CALENDER OF EVENTS EVENT'S AND PROGRAM PRE-MEETING FIELD FIELD TRIPS TRIPS TUESDAY, May 10, 1988 1988 TUESDAY, 8:00 8:OO a.m. a s m oto to 5:00 5:OO p.m. p.m. Field Trip 11 -— -- Archean geology and mineralization mineralization of of the the Marquette Greenstone Belt (day Marquette (day one of a two-day two-day field trip) trip) W?3DNESDAY. May 11, 1988 1988 WEDNESDAY. 8:00 8:OO a.m. to to 5:00 5:OO p.m. p.me -- Archean geology geoloqy and mineralization mineralization of of the the Field Trip 11 —Marquette Greenstone Belt (day Marquette ( d a y two of a two—day two-day field trip) trip) 8:00 8:OO a.m. to to 5:00 5:OO p.m. p.m. Field Trip Trip 22 —— -- Marquette Marquette Mineral District District of of Michigan: Michigan: Mining Mining history and geology GET TOGETHER TOGETHER REGISTRATION AND WELCOME GET 1988 WEDNESDAY. May WEDNESDAY, l&y JJ- 1988 4:00 to 7:00 4:OOp.m. p.m. to p.m. 7:OO p.m. Registration at the the Ramada Inn Inn Convention Convention Center Center 7:00 p.m. p.m. 7:OO Welcome get together, together, poster poster displays, displays, cash cash bar. bar- TECHNICAL TECHNICAL SESSIONS SESSIONS THURSDAY, 1988 THURSDAY. May 12, 1988 Morning Co-Chairs: Co-Chairs: Geology of the Keweenawan Rift Rift William J. J. Hinze and James James B. B. Paces Paces Welcoming remarks remarks 8:15 $:I5 a.m. a.m. F. F. G. R. C. 8:20 a.m. a.m. W. A. D. 3. J. Cannon Cannon Green Hutchinson Hutchinson Behrendt 8:40 a.m. a.m. S. W. Nicholson Nicholson Paces 3. B. Paces J . B. W. F. Cannon Cannon Variations in in structural structural style style of the the Midcontinent Rift beneath Lake Superior Superior Development of of the Midcontinent Midcontinent Lake Superior Rift in in the the Lake Superior region: Petrologic region: Petrologic and and geochemical constraints for qeochemical for aa tectonic model model xii x ii �9:00 9:OO a.m. a.m. J. J e B. B. D. D. W. Paces Paces Davis Davis 9:20 a.m. a.ma 9:20 K. W. Kiewin Klewin J. J. H. Berg Berg Chemostratigraphy of of the the lower lower division division lavas lavas of of the the Mamairise Mamainse Point Point Formation and implications implications for for rifting tectonics tectonics Coffee break break 10:00 a.m. 1O:OO a.m. 10:20 a.m* a.m. C. 10:20 J, J. M. M. precision Implications of a high precision U-Pb age dates on zircons from U-Fb from on Portage Lake volcanic ba3alts basalts on subsidence rdtes, rates, Midcontinent Rift subsidence lava flow repose periods, lava periodsp and magma macpa production rates rates P. F. G. Geophysical and petrological Ervin petrological characteristics of Olmsted Olmsted of the the Clam Clam Lake Lake constraint on a Mudrey, Jr. intrusion -— Jr. intrusion -- a on the thc time time of Keweenawan basin basin developdevelopmentt men 10:40 a,m. 10:40 a o m . R. R 6 P. P a Meyer Meyer V. Green WW.* V. Comparison Comparison of of the the Keweenawari Keweenawan and and Gregory Rifts from from the study study of teleseismic delay delay times times and Bouguer gravity 11:00 a.m, Mudrey, JJr. Midcontinent Rift model based ll:€ a - m a MM.e GG.a Mudrey, K - Hidcontinent A.* B. A B a Dickas Dickas upon Gregory Rift tectonic tectonic and and sediment sediment geometries geometr i e s 11:20 a.m. P. A. 11:20 a.m. A. Nielsen The Keweenawan Rift: a kinematic model for its its origin and evolution 11:40 1 1 ~ 4 0a.m. a-m. Lunch, Lunch- THURSDAY. THURSDAY. Afternoon Board of Directors luncheon luncheon 12.1988 12,1988 Geology of the Keweenawan Rift/Miscellaneous Co-Chairs: W. F. Cannon and S. S. W. W. Nicholson Nicholson 2:00 2:OO p.m. p.ma F. W. Cambray A tectonic model for for the the Midcontinental Rift System 2:20 2:20 p.m. p e m e M. L. Manson* Manson* H. C C. H. . Halls Halls A 2:40 2:40 Hinze p.m. W. W e 3. J. Hinze W. C. Kelly Scientific drilling into into the the Midcontinent Rift System 3:00 3:OO p.m. p .me Coffee break break submersible dive on on Superior Superior Shoals: Shoals: plans and prospects xiii x iii �3:20 p.m. p.ma V. W. R. J. 3:40 p.m. B. SainiEidukut* Sulfide mineralization and and associated associated in anorthositic anorthositic hydrous silicates in rocks from from the the Duluth Complex Complex 4:00 p.m. T. Lewchuk* Lewchuk* p.m. M. M. T. D. A. Syrnons Symons D e T. T. A. Paleomaqnetism of of the the Clay—Howells Clay-Howells Paleomagnetism carbonatite carbonatite and and Keweenawan Keweenawan motion motion on KSZ on the the KSZ 4:20 p.m. p.m. M. M. D. D. Thompson* Thompson* C. C - P. P. Ervin Ervin Refraction analysis analysis of of the the GLIMPCE GLIMPCE Refraction marine marine reflection reflection profile profile in in Georgian Georgian Bay Bay 4:40 p.m. p.m. 5:00 p.m. T. J. Boerboom Boerboom p e m &T. An An unusual unusual apatite—rich apatite-rich nelsonite—, nelsonite-, pyroxenite—, pyroxenite-, and and hornblendite— hornblenditebearing bearing intrusion intzusion of of post—Penokean post-Penokean age, age, central central Minnesota Minnesota 5:30 p.m. Cash Cash Bar Bar 6:30 p.m Banquet Banquet FRIDAYS FRIDAY, Morning Morninq Chandler Chandler Ferderer Ferderer Copper-nic!<el mineralization mineralization of of the the Copper—nickel Duluth Complex, Complex, northeastern northeastern Minnesota, Minnesota, a gravity gravity and magnetic maqnetic perspective perspective W. Michigan Michigan kimberlite kimberlite province province W. Jarvis Jarvis J. J. Kalliokoski Kalliokos~i MaY 1988 May 13. 1988 Geology mineral Geoloqy and and mineral deposits Archean rocks rocks deposits of of Archean Co-Chairs: R. R. L. L. Bauer Bauer and and M. M. M. M. Kehienbeck Kehlenbeck 8:20 8:20 p.m. p.m. T. T. J. J. Bornhorst Bornhorst An introduction introduction to to the the geology qeoloqy and and An mineral deposits deposits of of the the Archean Archean mineral Marquette Greenstone Greenstone Belt, Belt, Michigan Michigan Marquette 8:40 8:4Q a.m. a.m. G. G. B. B. J. J. W. W. R. R. A. A. A. A. S. S. B. A. B. A. Comparison of of two two parts parts of of the the Comparison Dead Dead River—Ishpeming River-Ishpeminq Greenstorie Greenstone Belt: Belt: evidence for for correlation correlation of of volcanic volcanic evidence stratigraphy stratigraphy 9:00 9:OO a.m. J. W. W. Norby Norby a.m. J. History History of of precious precious metal metal exploration/development in in the the Dead Dead exploration/development River-Ishpeming Greenstone Greenstone Belt Belt River—Ishpeming 9:20 9:20 a.m. a.m. R. R. L. L. Bauer Bauer Multiple folding folding and and regional regional fold fold Multiple patterns patterns in in the the northern northern Vermilion Vermilion granitic granitic complex, complex, NE NE Minnesota Minnesota Margeson Margeson Norby Norby Brozdowski Brozdowski Carter Carter Bouly Bouly xiv xiv �9:40 9 ~ 4 0 a.m. a.me J. R. R . Tabor* Tabor* P. J. Hudleston Hudleston Deformatign history of of the the Quetico Quetico Deformation inetasediments along along the the northern northern metasediments of the Vermilion granitic granitic margin of complex, northern Minnesota 10:00 a.m. Coffee break 10:20 a.m. B. L. Brasaemle* qeobarametry of of Stratigraphy and geobarometry Stratigraphy monzodiorites from the Giants Giants Range Range monzodiorites Minnesota Batholith, northeastern Minnesota 10:40 a.m. G. J. Hudak* The The stratigraphy stratigraphy and physical physical volcanology vo~canology associated associated with with the the F-group volcanogenic volcanogenic massive massive sulfide sulfide F—group Sturgeon Lake, Lake, northwestern northwestern deposits, Sturgeon Ontario Ontario 11:00 1l:QO a.m. a.m. W. K. M. Kehienbeck Kehlenbeck B. E. Seemayer Seemayer late Archean Archean clastic clastic sequence—fill sequence-fill A late of a fault-bounded fault-bounded basin basin structure structure of 11:20 11:2Q a.m. acme The magnetic fabric fabric and structure structure The the Quetico Quetico slates slates at at the the of the Quetico-Wabigoon interface, interface, northwest northwest Quetico—Wabigoon Ontario Ontario P. Sarvas Sarvas G. G e J. J e Borradaile Rorradaile 11:40 a.m. Lunch Lunch FRIDAY. FRIDAY, May Afternoon Afternoon 1988 Rocks/ Geology of of Early Early Proterozoic Proterozoic Rocks! Geology Miscellaneous Miscellaneous Co-Chairs: Co-Chairs: F. F. W. W - Cambray Cambray and and D. D. L. L. Southwick Southwick 1:00 1:OO p.m p - m P. P e K. K. Sims Sims K. J. J. Schulz Schulz Z. Z. E. E. Peterrnan Peterman W. R. R . Van Van Schmus Schmus Evolution of of the the Early Early Proterozoic Proterozoic Evolution Wisconsin magmatic magmatic terrane terrane of of the the Wisconsin Penokean Penokean orogen oroqen 1:20 1:20 p.m. p.me P. P. F. F. Hoffman Hoffman Animikie Animikie Group: Group: A Penokean Penokean foredeep? foredeep? 1:40 1:4O p.m. D. D. L. Southwick Southwick G. B. Morey Tectonic Tectonic imbrication imbrication and and foredeep foredeep development in in the the Penokean Penokean orogen, oroqen, development east—central east-central Minnesota Minnesota 2:00 2:QO p.m. p.m. S. S. D. D. Stahl Stah1 Early Penokean Penokean deformation deformation in in the the Early Peavy Pond Pond area, area, northern northern Michigan: Michigan: Peavy evidence evidence from from the the Michigarnme Michigamme Formation and the Peavy Peavy Pond Pond igneous igneous Formation complex complex D. J. Matty Matty 2:20 2 : 2 0 p.m. p.me J. R. R. K. K. G. S. S. W. J. J. L. L. Klasner Klasner Ojakangas Ojakangas Schulz Schulz LaBerge LaBerge for development development of of an an Evidence for Early Early Proterozoic Proterozoic overthrustoverthrustnappe nappe system system in in the Penokean Penokean orogen orogen of of northern northern Michigan Michigan xv �2:40 p.m. p.m. J. C. Palmqu.st Palmqt-'.st tectonicsArchean and Proterozoic tectonics— northern Michigan, a speculative speculative synthes is synthesis 3:00 3:OO p.m. pain. Coffee break break Coffee 3:20 3:20 p.m. G. L. L. LaBerge LaBerge p.m. G. J. J. S. S. Kiasner Klasner new look look at at The Baraboo Quartzite: Quartzite: A new an an old old problem problem 3:40 3:40 p.m. p.m. P. P. K. K. Sims Sims Z. 2 . E. E. Peterman Peterman J. Klasner J. S. Kiasner -- relevance relevance The Mountain Mountain shear shear zone zone -— The to to age age of of quartzite quartzite at at McCaslin McCaslin and and Thunder Mountains, northeastern northeastern Thunder Wiscons in Wisconsin 4:00 4:OO p.m. p.m. W. T. Jolly Jolly stratigraphy of of the the Geochemical stratigraphy Huronian Huronian continental continental volcanics, volcanics, Ontario: Relative Relative contributions contributions of of mantle mantle heterogeniety, heterogeniety, open-system open-system magmatism andcrystal crystal fusion maqmatism and fusion 4:20 4:20 p.m. A. U. U. Faister Falster p.m. A. Emplacement, mineralogy, Emplacement, mineralogy,and and internal internal evolution evolution of of a highly hiqhly evolved evolved Li-pegmatite Li-pegmatite in in Florence Florence County, County, W. W. B. B. Simmons Simmons Wiscons in Wisconsin 4:40 4:40 * * p.m. B. H. H. Boyum Boyum The origin oriqin and extent extent of of the the hard hard and and The soft soft iron iron ores ores of of the the Maquette Maquette Range, Range, Michigan Michiqan Papers Papers eligible eligible for for student student competition competition POSTER POSTER PAPERS PAPERS The The authors authors of of poster poster papers papers have have been been requested requested to to be be at at their their poster poster displays displays during during the the first first part part of of the the lunch lunch breaks breaks on on Thursday Thursday and and Friday Friday and and at at the the end end of of the the tecnical tecnical sessions sessions on on Thursday. Thursday. C. C. D. D. Anderson Anderson and and R. I?. Argenal Axgenal -— -- New New VLF-EM VLF-EM field field parameters sarameters D. A. Baxter* Baxter* and and T. T. J. J. Bornhorst Bornhorst --- Multiple Multiple discrete discreternafic mafic D. A. intrusions intrusions of of Archean Archean to to Keweenawan Keweenawan age, age, western western Upper Upper Peninsula, Peninsula, Michigan Michiqan T. T. M. M. Boduz* Bodus* and and W. W. F. F. Kean Kean --- Preliminary Preliminary paleomagnetic paleomaqnetic study study of of the the Amberg Amberg and and Atheistane Athelstane granites granites in in northeastern northeastern Wisconsin Wisconsin M. M. Cohen*, Cohen*, J. J. Mancuso, Mancuso, J. J. Frizado, Frizadol and and D. D. Stewart, Stewart, E. E. Berdusco Berdusco —— -Paragenetic Paraqenetic relationships relationships among among siderite, sideritel magnetite, magnetite, calcite, calcite, quartz, quartz, and and sulfides sulfides in in the the MacLeod MacLeod Siderite Siderite Mine, Mine, Wawa, Wawa, Ontario Ontario D. D. H. M. Davidson, Davidson, Jr. Jr. --- Precambrian Precambrian Red Red Bluff Bluff granite granite complex, complex, West Comparison West Texas: Texas: Comparison with with other other Mid—Proterozoic Mid-Proterozoic rapakivi rapakivi granites granites xvi �J. Feeny* Feeny* and and W. W. F. F. Kean Kean -- Paleornagnetism of Keweenawan age 3. of Falls Keweenawan hasalts from the TaylorPaleomagnetism Falls-St. Croix Croix area ofage basalts from the Taylor Falls—St. Falls area of Wisconsin and and Minnesota Minnesota Wisconsin - R. J. J. R. Ferderer* --.Application of Werner dec~nvolution to the Ferderer* Application of Werner deconvolution to the Penokean fold-and-thrust belt, east-central Minnesota Penokean fold-and—thrust belt, east-central Minnesota J. Fronk Fronk*and andD. D. C . Stswart -- An investigation into the chemical J. C. Stewart -— An investigation into the chemical processes causing the the formation of unakite in the Waupaca processes causing adamellite of Wisconsinformation of unakite in the Waupaca adamel].ite of Wisconsin -- T. H. M. Han Han -— Genesis Genesis and metamorphism of magnetite in Biwabic IronT. and District, metamorphism of magnetite in Biwabic Iron— Formation, Mesabi Minnesota Formation, Mesabi District, Minnesota P. P. K. Jongewaard* Jongewaard* -— -- Stratigraphy Stratigraphy and physical K. and physical footwall rocks to the the Sturgeon Sturgeon Lake footwall rocks to Lake deposits, Nki Ontario deposits, MW Ontario volcanology of the volcanology of the massive sulphide massive sulphide L. MacLellan* MacLellan* and and T. T. J. J. Bornhorst Bornhorst -- Geology, Geology, structure and M. L. M. —— structure and Marquette County, mineralization of the Reany Lake area, mineralization of the Reany Lake area, Marquette County, Michigan Michigan Mudrey, Jr., Jr., and and B. B. A. A. Brown Brown —— -- Bedrock Bedrock geology of the Mudrey, geology of the Superior map sheet, Wisconsin Superior map sheet, Wisconsin M. G.G. M. Peterson* and and C. C. A. A . Geiger -- Two generations of garnet Peterson* Geiger —— Two generations of garnet growth in the Hardwood gneiss, Dickinson County, Michigan growth in the Hardwood gneiss, Dickinson County, Michigan R . Schneiker* Schneiker* and and W. W. F. F. Kean Kean -- AA paleomaqnetic study of the R. paleomagnetic study of the Hamilton Mound area of Adams Adams County, County, central central Wisconsin Hamilton Mound area of Wisconsin J. 3. W. W. - K. J. J. Schulz, Schuiz, P. P. K. K. Sims, Sims, and and Z. Z. E. E. Peterman Peterman ——A --A post-tectonic K. post-tectonic rare-metal-rich granite in the southern complex, Upper rare—metal--rich granite in the southern complex, Upper Peninsula, Michigan Peninsula, Michigan and T. T . J. J à Bornhorst -- The Small* and Small* Bornhorst -— The Marquette County, Michigan: northern northern Marquette County, Michigan: Reany Creek Formation, Reany Creek Formation, Archean or Proterozoic? Archean or Proterozoic? P. 3. J. Wagner Wagner and and M. M. K. K. Sood Sood -— -- Geochemistry Geochemistry and petrology of the P. and petrology of the Athelstane granite, Marinette County, Wisconsin Wisconsin Atheistarie granite, Marinette County, S. M. M. Wee Wee and and J. J. T. T. Wilband Wilband -- Geochemistry and tectonic S. Geochemistry -— and tectonic significance of Early Proterozoic igneous rocks, rocks, northern significance of Early Proterozoic igneous northern Michigan and northeastern Wisconsin Michigan and northeastern Wisconsin J. R. R. 3. J. 3. * L. Welsch Welsch -— -- Preliminary Preliminary structural analysis of Archean rocks L. structural analysis of Archean rocks in the Virginia Horn area, area, northeastern Minnesota in the Virginia Horn northeastern Minnesota * Papers Papers eligible eligible for for student student competition competition xvii xvii �POST POST MEETING MEETING FIELD FIELD TRIP TRIP j,. 1988 L U 8:00 8 : O O a.m. a.m. to to about about 7:00 7:OO p.m. p.m. Field Trip Trip 33 —— -- Evidence Evidence for Early Proterozoic ?roterozoic overthrusting overthrusting in in northern northern Michigan Michigan and and Wisconsin. W i s c o ~ s i n ~This field field trip trip terminates terminates in in Iron Mountain, Mountain, Michigan, Michigan, which which has has air air service. service. The The bus bus will will return return to to Marquette. Marquette. SATURDAY. V W xviii �ABSTRACTS �NTT VLF-::J FITLD ?ATIRS by Chris :Iris rgenai P. Anderson 3. m t i e r s o n and a9fL Poger ?.ozer t i ~ ? e i ; d :innipeg, Manitoba, ,:inni?eg, Xanitoba, Canada and the The primary r a n s m i t t e r md the i ~ r i r n a r yfield f i e l d from the t h e VLF ttransmitter secondary ffield from aa conductor conductor combine combine aatt aa llocation i e l d from ocation resulting 3 ' 5 field f i e l d ellipse. e l l i ? s e . Conventional measurements mezisure~ents r e s u l t i n g in i n aa EM are with ith a r 5 of of' the t h e angle the t h e major aaxis x i s of of the t h e ellipse e I l i ; ~ s emakes w a h horizontal o r i z o n t a l plane -?lane (sometimes (sometimes called c a l l e d the t h e in-'hase in-,>base measurement) and. of tthe measurement) and tthe h e rratio a t i o of h e xminor i n o r and major mz.jor axes axes field ellise tthe c, e fielcl e l l i x eexoressed e x x e s z e 6 as a s >ercent e r c e n t(sometimes (zmetir:er called measurement). r quaem-ture ne2surene;i~ c ~ l l e ?the t h e out-of-hase out-of- ~ h a or s eoquadrature In 7lace In > l a c e of tthe h e ratio r z t i omeasurement, measurement9some sor2e systems s y s t e z s measure ::~XLIL-S tthe h e secondary secondary ffield i e l d strength s t r e n g t h which often o f t e n is i s exoressed ex~ressed as ercent above a s a2 3ercent above tthe h e primary ?rimary ffield. ield. Based on field f i e l d experience e x y e r i e n c e and model ccalculations alculations measurement of of we have found that t h a t the t h e measurement of the t h e direction d i r e c t i o n of the component of t h e hhorizontal o r i z o n t 2 1 com2onent of the t h e secondary field f i e l d gives gives a That is, good indication i n d i c a t i o n of of the t h e strike s t r i k e of of the t h e conductor. c o n 2 u c t o ~ . Yh~2.t is, without tthe h e ddirection irection w i t h o u t a secondary secondzry field f i e l d is i s at a t right risht angles a g l e s to t o the t h e direction 2 i r e c t i o n to t o the t h e VLF 7LL2 station. s t a t i o n . iith Yitk the the resence of direction will ill Yresence of a strong s t r o n g secondary field, f i e l d , the the d irection w be c controlled be o n t r o l l e d by the t h e conductor conductor and and will w i l l be be at a t right r i g h t angles anglss For nmoderate tto o the t h e strike s t r i k s of of the t h e conductor. c o n d u c t o r , For o d e r z t e secondary secongmy fields, f i e l d s * the t h e effect e f f e c t can can be evaluated e v a l u a t e d and and using u s i n g this this information c m be be calculated. ~alculate6~ i n f o r m a t i o n the t h e strike s t r i k e of of the t h e conductor conductor can This ~ roceedure ? a r t i c u l a r l y important i m ~ o r t a n tin i n areas a r e a s of of This r o c e e d u r is ei s particularly multile m u l t i 3le conductors. conductors. IIn n tthe h e ccase a s e of of three t h r e e field f i e l d vectors v e c t o r s at a t aa- station, stztion* namely, namely, the t h e Primary x i m a r y field, f i e l d , a strong s t r o n g secondary field f i e 1 2 from Troy a bed bed rock rock conductor, and a secondary field c o n d u c t o r , and f i e l d ffrom r o m overburden having q u a d r z t u r e component, con?onent, the t h e calculations c a l c u l a t i o n s and an? h a v i n s mostly a2. quadrature f r o m ffield i e l d . and ar-d model moc?el ddata a t a clearly c l e a r l y show shoi! the the rresults e s u l t s from of uusing llimitations i - ~ i t z t i o n sof s i n g tthe h e rratio a t i o data d a t a in i n interpretation. inte~~retz+ign. " of 01 >. 1 �inaii,r, th2 resu1t of uiti1e-conducor nJ effects and non— 1anar field vectors result in a triaxial field elli?soid which can be artially resolved as of the interpretation. 2 �I MULTIPLE FOLDING AND REGIONAL FOLD PATTERNS IN THE NORTHERN VERMILION GRANITIC COMPLEX, NE MINNESOTA Robert L. Department Bauer of Geology, University of Missouri Columbia, Missouri 65211, USA The western Vermilion Granitic Complex of the southwestern Quetico Subprovince is a highly deformed amphibolite facies (M1) The principal rock units are paragneiss and biotite schist that contain variable concentrations of veins and lenses of early tonalite—granodiorite and younger granite of the adjacent Lac La Croix batholith. These granitic units are interlayered with biotite schist on scales as great as several kilometers and are folded along with the schist into a series of easterly trending folds. The distribution of these folds has migmatite complex. been well established by reconnaissance geologic mapping (Southwick and Ojakangas, 1979) and more recently by regional aeromagnetic patterns (Chandler, 1983). Analysis of multiple fold geometries along the northern margin of the Vermilion Granitic Complex, in the Kabetogama and Namakan Lakes area, indicates that the large—scale regional fold patterns observed in the complex correlate with the youngest of three periods of folding. The oldest deformation produced a strong bedding—parallel foliation (el) in the schist and local sinistral/north-side—down shear parallel to S1. Well-developed asymmetric pull-apart structures in early tonalite veins parallel to bedding in the schist indicate the kinematics of shear. The second deformation generated easterly plunging F2 folds and a D2 IS fabric that locally aligns M1 sillimanite—muscovite tufts parallel to a axial plane foliation (S2) and F2 fold hinges. In the mignatitic rocks described here, the F2 folds are of S—symmetry and fold the D1 asymmetric pull—apart structures and S1 foliation. Further to the north, in the less migmatitic biotite schist north and west of Kettle Falls, the F2 folds are of Z—symmetry (Tabor, this volume) and indicate the presence of a major upright east-west—trending F2 antiformal trace along the Kabetogama peninsula between Rainey and Kabetogama Lakes. Stratigraphic tops are invariably to the north on the southern (migmatitic) limb of this major F2 structure and change to the south on the northerr limb, indicating a downward structural facing of the regional F2 antiformal syncline (Fig. 1). F2 fold axial planes, which are steeply dipping along the northern margin of the complex, dip more gently to the north as one proceeds to the south toward the more migmatitic part of the Here the F2 folds of S—symmetry are refolded by upright F3 folds of Z—symmetry on the northern limb of one of the large east-west—trending, easterly plunging antiformal structures recognized during reconnaissance mapping (Fig. 2). An intense D3 linear fabric occurs parallel to the regional F3 fold hinges, and a locally well—developed S3 crenulation foliation deforms both and the M1 sillimanite—muscovite tufts aligned in S2. complex. 3 �N- / I,/' Inf erred structure Inferred structure // / '/ / 0 / ,1 / Fig. Fig. F I, / Observed Observed rnl->tinnc;t-,Jps relationships 1 2/ Schematic Schematic cross cross section section illustrating illustrating the the relationship relationship among F2 F2 folding, folding, inferred inferred F1 Fi folding, folding, and and stratigraphic stratigraphic younging young ing among directions directions (given (givenby by bar bar and and ball ball symbols). symbols). 1l F2 F3 Fig. Fig. 22 Schematic Schematic cross cross section section illustrating illustrating the the relationship relationship between between F2 F2 and and F3 F3 folding. folding. This This section section is is south south of of the the cross cross section shown in inFigure Figure1.1. section shown 4 �U Preliminary analysis of this deformation sequence and the orientation of the structures generated suggests the following sequence of events: Northwest—directed compression resulted in early recumbent folding. Associated northwest—directed shear on the lower limb of this structure produced the asymmetric boudins with sinistral/north—side—down displacement. Continued north- to northwest—directed compression lead to F2 refolding of the lower (overturned) F fold limb and resulted in the downward—facing easterly plunging F2 folds. Progressive overturning of these F2 folds to the south (possibly during emp].acement of the Lac La Croix batholith), in a regime of continued north to northwestdirected compression, lead to F3 refolding of F2 folds about a similar easterly plunging axis. A significant feature of this sequence of deformation is its development in a relatively constant north— to northwest—directed compress ional regime. REFERENCES CITED Chandler, V.W., 1983, Aeromagnetic map of Minnesota, St. Louis County, total intensity anomaly. Minnesota Geological Survey, Aeromagnetic Map Series, Map A—2, St. Paul, scale 1:250,000. Southwick, D.L. and Ojakangas, R.W., 1979, Geological map of Minnesota: International Falls sheet. Minnesota Geological Survey, St. Paul, scale, 1:250,000. Tator, J.R., this volume, Deformation history in the Quetico metasediments along the northern margin of the Vermilion Granitic Complex, NE Minnesota. 5 �Multiple Discrete Discrete Mafic Mafic Intrusions Intrusions of of Archean Multiple Archean to to Keweenawan Age, Age, western western Upper Keweenawan Upper Peninsula, Peninsula, Michigan Michigan D.A. BAXTER and Ti. D.A. BAXTER and T.J.BORNHORST BORNHORST (Department (Department of of Geology Geology and andGeological Geological Engineering, University Houghton, MI MI 49931) 49931) Engineering, Michigan Michigan Technological Technological University The bedrockofof the the western Upper Peninsula Peninsula of of Michigan Michigan concon The Precambrian Precambrian bedrock western Upper tains gabbro and diabase intrusions of of varying age, origin, tains gabbro and diabase intrusions varying age, origin, and size. size. Previous studies assignedthese thesemafic mafic rocks, rocks, on on the the basis studies have have typically typically assigned basis of of alteration alteration and and orientation, to to one of Archean, Lower Lower Proterozoic, Proterozoic, and and orientation, of three three broad broad age agegroups: groups: Archean, Middle Proterozoic In contrast, Middle Proterozoic (Keweenawan). (Keweenawan). In contrast, detailed detailed mapping mapping by Kantor Kantor (1969) (1969) documented more more than than three three ages documented ages of mafic mafic intrusions intrusions in in the theSugarloaf Sugarloaf Mountain Mountain area, north of area, of Marquette. Marquette. In this this study, study, we we suggest suggest that at at least least six six separate separate intrusive events intrusive events occurred occurred based based on careful careful examination examination of textures, textures, mineralogy, mineralogy, and degree in hand hand sample, thin section, and degree of metamorphism metamorphism in sample, thin section, and outcrop outcrop (Figure (Figure 1). The local setting of of each The local geologic geologic setting each body body must must also also be be taken taken into intoconsideration. consideration. The oldest oldest mafic mafic intrusions intrusions in region are dike dike and and sill-like sill-like gabbro gabbro bodies bodies The in the region within the Marquette within Marquette Greenstone Greenstone Belt. Belt. The The gabbro gabbro typically typically consists consists of plagioplagioclase, amphibole, amphibole, and and varying of secondary clase, varying amounts amounts of secondary sericite sericite and retrograde retrograde rocks of of the greenstone belt are cut gabbro and volcanic volcanic rocks greenstone belt cut by by gneissic gneissic chlorite. The gabbro tonalite to to granodiorite plutons which whichare are in in turn turn cut by tonalite granodiorite plutons by thin thin discontinuous, discontinuous, tabular, amphibolite tabular, amphibolite bodies bodies such as as those those at at Wetmore Wetmore Landing. Landing. Although Although xenoliths xenoliths of greenstone belt plutons, we we interpret interpret these these tabular tabular of greenstone belt rnafic mafic rocks rocks exist exist in in the plutons, bodies as as mafic on the mafic intrusions intrusions based based on the appearance appearance of of their their margins. margins. Foliation bodies in Foliation in these dikes dikes is parallel rocks which which leads these parallel to the the surrounding surrounding gneissic gneissic rocks leads to to the the conclusion Archean deformation deformation event post-date the conclusionthat that the the dikes dikes pre-date pre-date an an Archean event but but post-date tonalite to granodiorite tonalite granodiorite plutonic plutonic activity. activity. The occurred in in aa span The next next mafic rnafic intrusive intrusive activity activity occurred span of time time bracketed bracketed by by the the Archean deformation event event and and the the deposition of the sediments of the Archean deformation deposition of sediments of the Lower Lower Proterozoic Marquette Supergroup. These dikes dikes are are porphyritic Proterozoic Supergroup. These porphyritic and typically typically trend trend north-south (±12°). (212"). They They contain contain 4i to cm (4 (4 to to 1 inch) euhedral euhedral to to subhedral subhedral to 3 cm phenocrysts phenocrysts of plagioclase plagioclase (approx. (approx. An70). Anm). The dikes dikes range range from from 9-60 9-60 meters meters (30-200 feet) feet) in (30-200 in width width and andare arevariably variablymetamorphosed. metamorphosed. Cannon Cannon (1975) (1975) noted noted that that some dikes dikes in in the Republic and cut the Archean some Republic area area are distinctly distinctly porphyritic porphyritic and the Archean granites and gneisses, but do not granites and gneisses, but not cut cut the theEarly EarlyProterozoic Proterozoic sediments. sediments. Puffett (1975) also also noted noted the the existence of coarsely porphyritic mafic mafic dikes (3975) existence of coarsely porphyritic dikes which which may may be be Archean in age. We tentatively tentatively interpret interpret these Archean age. We these porphyritic porphyritic mafic dikes dikes as as equivalent Archean Matachewan Matachewan Dike Ontario which which have have an an age age equivalent to to the Archean Dike swarm swarm of of Ontario of 2690±93 Ma (Gates and Condie and and others (1987) of 2690293 Ma and Hurley, Hurley, 1973). 1973). Condie (1987) state state that that Matachewan dikes in in Ontario Matachewan dikes Ontario cut Archean Archean lithotectonic lithotectonic trends trends and and are areconsequently consequently younger than the last event in the younger than last major major Archean Archean tectono-thermal tectono-thermal event the area. area. This is is consistent with with our our observations in the western consistent observations in western Upper Peninsula Peninsula of Michigan. Michigan. The Matachewan dikes are are cut by Matachewan dikes by both both Lower Lower Proterozoic Proterozoic and and Middle Middle Proterozoic Proterozoic (Keweenawan) diabase diabase dikes dikes on on Sugarloaf (Keweenawan) Sugarloaf Mountain Mountain (Kantor, 1969). 1969). This mafic This mafic intrusive intrusive event event may may include include some some relatively relatively non-porphyritic non-porphyritic dikes dikes as as well. well. 1 Following the deposition deposition of of most Following the most of the the Lower Lower Proterozoic Proterozoic Marquette Marquette SuperSupergroup, a swarm swarm of finefine- totocoarse-grained coarse-grained gabbro gabbro and and diabase diabase intrusives intrusives cut all all group, pre-existing These dikes dikes and and sills pre-existing rocks. rocks. These sills have have been been previously previously interpreted interpreted as as related to the 1974). Michigamme Formation Formation (Cannon, (Cannon, 1974). related the Clarksbbrg Clarksburg Member Member of of the theMichigamme They They consist consist of pyroxene/hornblende, pyroxene/hornblende, chlorite, chlorite, plagioclase, plagioclase, epidote, sericite, sericite, and and variable amounts variable amounts of secondary secondary carbonate. carbonate. Intrusive Intrusive bodies bodies range range from from 10 cm to to over 175 (6 inches over 175 meters meters (6 inches to >> 500 500 feet) thick but but orientation orientation is is highly highly variable, variable, feet) thick and therefore and therefore not not useful useful as aa tool tool for for identification. identification. These intrusions are Early Early These intrusions Proterozoic inin age age and and have during the PenoProterozoic have been been deformed deformed and and metamorphosed metamorphosed during Penokean kean orogenic orogenic event. event. 6 �____________________________ _______________________ _______________________ _______________ ________________ ______________ ___________________________ ___________________ ____________________________ _________________ In Marquette Marquette County, County, there there are are at at least least two two groups groups ofofKeweenawan Keweenawan diabase diabase In dikes. dikes. The The older older of of these these is is aa set set of of fine-grained fine-grained diabases diabases that that trend trend approxiapproximately mately north-south north-south (±15°). (215O). They commonly consist slightly altered altered pyroxene, pyroxene, They commonly consist of of slightly plagioclase, amphibole, generally less less than than 30 30 meters meters (100 (100 plagioclase, amphibole,and and chlorite, chlorite, and and are are generally feet) thick. thick. The younger younger intrusives intrusives trend trend east-west east-west (±10°), (±lo0)cross-cut cross-cut the the older older Keweenawan diabase, medium to coarse-grained, and be over over 200 200 meters meters Keweenawan diabase, are are medium to coarse-grained, and can be (600 (600 feet) thick. thick. The younger younger dikes dikes also also have have aa strongly strongly reversed reversed remnant remnant magnetization, and occasionally have a coarse-grained magnetization, and occasionally have coarse-grained granophyric granophyric interior. interior. Cannon (1975) (1975) mentioned existence of "undeformed" diabase which cut cut Cannon mentioned the the existence of "undeformed" diabase dikes dikes which folded sediments sediments of of the the Marquette Marquette Supergroup Supergroup and the Lower Lower ProteroProterothe folded and also also cut cut the zoic zoic dikes dikes and and sills sills which which intrude intrude the thesediments. sediments. We We interpret these these undeformed undeformed dikes as early early (north-south) (north-south) Keweenawan Keweenawan mafic mafic intrusions. intrusions. There There are multiple multiple ages ages of mafic mafic intrusive intrusive rocks rocks in the the western western Upper Upper Peninsula. Peninsula. We Archean mafic maficintrusives: intrusives: 1) 1) We propose propose three distinct distinct groups groups of of Archean post-plutonic/pre-deformation; and postpost-volcanic/pre-plutonic; 2) 2) post-plutonic/pre-deformation; and 3) 3) postdeformation! deformation/ pre-Early pre-Early Proterozoic Proterozoic sedimentation sedimentation (Figure (Figure 1). 1). This is is followed followed by by intrusives of Early age and and by two intrusives of Early Proterozoic Proterozoic age two ages ages of of Keweenawan Keweenawan (north-south (north-south and then the youngest Archean, the the Early Early then east-west) east-west) intrusives. intrusives. Previously, Previously, the youngest Archean, Proterozoic, and the oldest Proterozoic, and oldest Keweenawan Keweenawan (north-south) (north-south) were were combined combined together together as as the Metadiabase Metadiabase of Early Early Proterozoic Proterozoic age age (Clark (Clark and and others, others, 1975; 1975;Cannon, Cannon,1975; 1975; Cannon, Gair and Cannon, 1974; 1974; Gair and Thaden, Thaden, 1968; 1968; Puffet, Puffet, 1974). 1974). It It is not not possible possible to to base base aa field of age on the the trend field determination determination of age simply simply on trend of individual individual intrusives intrusives or the the degree degree of alteration alteration and and deformation. deformation. For example, example, aa N-S N-S trending trending dike dike which which isis known to be known to be Keweenawan Keweenawan in age age contains contains alteration alteration of the the primary primary mineralogy mineralogy to to chlorite, chlorite, carbonate, carbonate, and and sericite sericite and andhas hasweakly weakly foliated foliatedmargins margins(Owens, (Owens,1986). 1986). These are being with further These preliminary preliminary results results are being confirmed confirmed with further laboratory laboratory and and field field work. This study study was was partially partially funded funded by by aa grant grant from fromthe theMichigan MichiganGeological Geological Survey. Survey. <E-W Keweenawan Keweenawan Diabasj ~iabase] Mid Continent Continent Rifting Rifting < N-S Keweenawan Diabasel ~iabasel ..jj-S 0 0 N Penokean Penokean Orogeny Orogeny 0 Baraga L o w e Proterozoic r ProterozoicDiabas1 ~iabase) -lilLower Group Marquette Marquette Supergroup Supergroup —4 Menominee Group Chocolay Group —1Matachewan Intrusionsj 03 2 J- I Late Archean deformation and and metamorphism metamorphism _j ..cZ"Wetmore < " w e t m o r e Landing" Landing" Intrusions! ~ntrusions] 1 Tonalite toto granodiorite granodiorite 1 plutons plutons 1 -zZGabbro ~ a b b r Intrusions! ~ntrusions] o \ Marquette Marquette Greenstone Greenstone 1 1 Belt Belt volcanism volcanism 1 Figure Figure 1. 1. Schematic Schematic diagram diagram of of mafic maficintrusion intrusion relative relativechronology. chronology. 7 �REFERENCES Cannon, W.F., W.F., 1975, Bedrock Geologic Geologic Map Map of of the Republic Cannon, 1975, Bedrock Republic Quadrangle, Quadrangle, Marquette Marquette County, County, Michigan: Michigan: U.S. U.S. Geological Geological Survey, Survey, Miscellaneous Miscellaneous Investigations Investigations Series Series Map, 1-862. 1-862. Cannon, W.F., Map of the Cannon, W.F., 1974, 1974, Bedrock Bedrock Geologic Geologic Map the Greenwood Greenwood Quadrangle, Quadrangle, Marquette Marquette County, County, Michigan: Michigan: U.S. U.S. Geological Geological Survey, Survey, Geologic Geologic Quadrangle Quadrangle Map, Map, GQ-1168. GQ- 1168. Clark, L.D., and Kiasner, Map of of Clark, L.D., Cannon, Cannon, W.F., W.F., and Klasner, J.S., J.S., 1975, 1975, Bedrock Bedrock Geologic Geologic Map the Negaunee Quadrangle, Marquette Marquette County, County, Michigan: U.S. Geological SurGeological Surthe Negaunee SW SW Quadrangle, Michigan: US. vey, vey, Miscellaneous Miscellaneous Map Map Series, Series, GQ-l226. GQ- 1226. K.C., Bobrow, D.J., and Condie, K.C., Bobrow, D.J., and Card, Card, K.D., K.D., 1987, 1987, Geochemistry Geochemistry of PrecamPrecambrian Mafic Dykes of the brian Dykes from the the Southern Southern Superior Superior Province Province of the Canadian Canadian Shield, Shield, in: Mafic Dyke W.F. Fahrig Fahrig editors, editors, Geological Geological Association Association in: Dyke Swarms, Swarms, H.C. H.C. Halls Halls and and W.F. of Canada Paper 34, of Canada Special Special Paper 34, p. p. 95-108. 95-108. Gair, Gair, J.E. J.E. and and Thaden, Thaden, R.E., R.E., 1968, 1968, Geology Geology of of the the Marquette Marquette and andSands Sands Quadrangles, Marquette Marquette County, County, Michigan: U.S. Geological Geological Survey Survey Prof. Prof. Paper 397, Quadrangles, Michigan: U.S. Paper 397, 77 pp 77 PP. Gates, Gates, T,M. T.M. and and Hurley, Hurley, P.M., P.M., 1973, 1973, Evaluation Evaluation of Rb-Sr Rb-Sr Dating Dating Methods Methods Applied Applied to Matachewan, Matachewan, Abitibi, MacKenzie MacKenzie and and Sudbury Sudbury Dike Dike Swarms Swarms in in Canada: Canada: 10, p. 900-919. Canadian Journal of Earth Canadian Journal Earth Sciences, Sciences, v. v. 10, 900-919. Kantor, J.A, Kantor J.A., 1969, 1969,Assimilation Assimilation and and Dike Dike Swarms Swarms in in the the Sugarloaf Sugarloaf Mountain Mountain Thesis, Michigan Michigan Technological Technological UniverArea, Area, Marquette Marquette County, County, Michigan: Michigan: M.S, M.S. Thesis, sity, Houghton, Houghton, Michigan, Michigan, 83 83 pp. pp. Owens, E.O., E.O., 1986, Geology and and Precious Precious Metal Metal Mineralization of Owens, 1986, Precambrian Precambrian Geology Mineralization of the Fire Center the Center Area, Area, Marquette Marquette County, County, Michigan: Michigan: M.S. M.S. Thesis, Thesis, Michigan Michigan TechnoTechnological University, University, Houghton, logical Houghton, Michigan, Michigan, 152 152 pp. Puffet, W.P., W.P.,1974, 1974, Geology Geology of the the Negaunee Negaunee Quadrangle, Quadrangle, Marquette Marquette County, County, Michigan: U.S. U.S. Geological GeologicalSurvey, Survey,Prof. Prof. Paper Paper 788, 788, 53 53 pp. Michigan: 8 �Preliminary Preliminary Paleomagnetic Paleomagnetic Study Study of of The The Amberg Amberg and and Atheistane Athelstane Granites Granites in in Northeastern Northeastern Wisconsin Wisconsin Theresa M. M. Bodus Bodus Theresa and and William William F. F. Kean Kean Department Department of of Geosciences Geosciences University University of of Wisconsin—Milwaukee, Wisconsin-Milwaukee, WI WI 53201 53201 The The Amberg Amberg and and Athelstane Athelstane granites granites of of Marinette Marinette County, County, Wisconsin Wisconsin have have compositions compositions which which are are similar similar to to the the Penokean Penokean granites but the the ages ages tend tend to to overlap overlap with with granites of of Northern Northern Wisconsin, Wisconsin, but the the post post Penokean Penokean granites granites of of south south central central Wisconsin. Wisconsin. In In addition, addition, the the grey grey Amberg Amberg granite granite cross-cuts cross-cuts the the pink pink Atheistane Athelstane granite granite and and gives gives an an Rb/Sr Rb/Sr age ageof of1650+m.y.a. 1650+m.y.a. This This study study was was started started to to help help define define the the chronology chronology of of the the ignious ignious intrusives intrusives and and to to determine determine if if there there is is any any similarities similarities between between the the paleopole paleopole positions positions of of these these samples samples and and those those of of the the 1760 1760 m.y. m.y. old old granites granites and and rhyolites rhyolites of of south south central centralWisconsin. Wisconsin. Ten Ten oriented oriented hand hand samples samples were were collected collected from from the the intrusives intrusives and and analyzed analyzed for for magnetic magnetic stability stability and and magnetic magnetic directions. directions. Preliminary Preliminary results results indicate indicate about about half half the the samples samples were were stable stable enough enough to to provide provide well well clustered clustered magnetic magnetic directions. directions. In In addition, Amberg and and the the addition, the the magnetic magnetic directions directions for for the the Amberg Atheistane Athelstane granites granitesare arenot notsimilar. similar. The The magnetic magnetic direction direction of of the the Amberg Amberg granite graniteseem seem to to be be associated associated with withthe the1650 1650m.y. m.y. associated overprint overprint whereas whereas the the Athelstane Athelstane pole pole positions positions may may be be associated with in.y. with either either1760 1760m.y. m.y.oror1450 1450 m.y. It It is is further further suggested suggested that that the the Amberg Amberg and and Atheistane Athelstane granites granites are are not not simply simply single single intrusives, intrusives, but but are are probably probably the the main main components components in in aa large large intrusive intrusivecomplex. complex. 9 �An Unusual Apatite-Rich Nelsonite-, Nelsonite-, Pyroxenite-, and Homblendite-Bearing An and Hornblendite-Bearing Intrusi Intrushof of Post-PenokeanAge, Age, Central Centmi Minnesota Minnesota Post-Penokean Texrence J. Boerboorn, Minnesota Geological Survey, 2642 University Ave., SL Paul, Minnesota 55414 A A small small pluglike pluglike intrusion inmsion in incentral tendMinnesota Minnesota contains containsvery veryapatite-rich apatite-richrocks rocks rangingfrom from nelsonite nelsonite (oxide-apatite (oxide-apatie rock) m k )to topyroxenite, pyroxenite*hornblendite, hornblendite*and and diorite. dionte. As As ranging judgedfrom frommagnetic magneticdata, data,the theplug plughas hasaadiameter diameterofofabout a b u t2.5 2.5km, kmvand andisisconcentrically concen~ly judged zoned Petrochemical Petrochemicaldata data indicate indicatethat thatthe theplug pius is issubalkalic s u b W c to alk1ic W c in in composition composition zoned. is characterized by atypically high values d Fev Ti* P, and H g q but is depleted and and is aracterized by atypically high values of Fe, Ti, P. and H20, but is depleted inhKK and Si. Si The l%e distinctive disthaivemagnetic magneticanomaly anomaly(Fig. (Fig. 1), I)*combined combined with rock distnbution dismbution and panems defines defies aa plug-like plug-Iike geometry geomeuyand andconcentrically-zoned concenmcally-mnedintrusion inmsion2.5 2.5km laninin patterns, diamm.It intrudes It intrudes conglomeratic rocksofofEarly M yProterozoic Proterozoicage, age,and andisislocated Iocatedalong dung diamer. conglomeratic rocks thetrace sacof of the the Great GreatLakes Lakestectonic tectoniczone, zoneqaamajor rna~ur E-NEtrending m n h gstructural smb u n c h yinin the E-NE boundary east-caml Minnesota. Mimesom This E sintrusion intrusionforms ~OITXIS oneofofmany manysharp, sharp,small s dmagnetic magnetic east-central one aresynsynano& in central central Minnesota. Mimesom Regional Regionalrelationships rehionshipsimply implythat thatthese theseplutons plutonsare anomalies in topost-tectonic p o s t m n i c with regard regard to to the the Penokean Penokm orogeny. q e n y . AAfew fewscattered scatteredoutcrops outmpsofofthe the to plutonedst, exis&and anditithas hasbeen beenintersected intmectedbyby1212drill CM holestotaling totaling250 250m, m,which which were were pluton holes drilled in the 1900s during iron-ore drilled ly early in the 1930s duxing iron-meexploration. explcmion. The type in outcrop outcrop is rtlanocradc mianocratictotomesocratic mesomaticferrodiorite; f e d o r i t e ;the the The dominant dominant rock type latter lattercontains cmtains pegmatitic pegmatiticveins veins and andanorthositic anorthositicsegregations. segregations.Hornblendite Hmblendieisis gradmad into into pyroxenite, ppxenite*which whichtogether togetherwith withnelsonite nelsoniteform fomaasignificant significantfraction hctionofof gradational theintruaion. on. Approximately AppximateIy 80% 80% of the core faxage the footageisishornblendiee/pymxenite, hornblendite/pyroxenite,10% l0 nelsonire, nelsonkvand and 10% 10% diorite. diorite-The Thenelsonite, nelsonite,pyroxenite, pymxeniteqand andhornblendite hornblenditeare arelocated located withinthe theferrodiorite femdionte in in aa horseshoe-shaped horseshoe-shapedwoe, m e *and andare areseen s e nonly odyinindrill drillcore. cores within The Theferrodiorite femdioriteisismediummedum-totocoarse-grained coarse-pined and and consists consistsdominantly dominantlyof of andesk (Anjgjo), ( b m ) ferTopargasitic ,fermpargasiuchornblende, hmblende,actinolite, actinolite9apatite, apatite*magnetite, magnetite*ilmenite, henite* andesine augite(Ca43Mg37Fej) Ca43Mg37Fe20)and andlesser lesseramounts amountsof ofalbite. dbite. Apatite Apatiteisisprominent prninentininthe the augite meladicxite, volume. Layering meIadicxite9comprising cornpising as as much as as 15% 15% of of the the modal zmdaâvolumes Layeringdefined definedby by eithercumulus c m d u s or ur flow-aligned flow-aligned plagioclase plagioclaiecrystals crystals and and by by centimeter-scale centimeter-scalemodal modal either v a r i of of~feldspar feldspar ~ and hornblende hornblendeisisconcordant c o n h t with with the the edge edge of of the the intrusion intrusionand and variations and dips dipssteeply steeplytowards towardsthe thecenter. center* Hornblendite Xmblendite and andpyroxenite pymxeniteare aredark darkgreen, green,medium mediumgrained, grained,and andequigranular. equigranuh, The tworock rocktypes typesare aregradational, pdationa17depending dependingmainly d yupon uponthe thedegree degreetotowhich whichpyroxene pymxene Thetwo hasbeen beenreplaced replaced by by hornblende hornblendeand andactinolite. a c ~ o l i t eDominant .Dominantminerals mineralsininboth bothrock rocktypes types has include includeprimary primary and andsecondary smndaxyferropargasitic ferropargasitichornblende, hornblende*augite augite(C&39Mg29Fe), (agMg~gFa), actinolixe, oxides, and apatite. a c t i n o h Fe-Ti Fe-Ti oxides* apatite. Tabular Tabularzoned m e d magmatic magmatic hornblende homblendeisiscommon, common, and dark andconsts co& ofofa red-brown a red-brownferropargasitic fmpargasiriccore corerimmed -ed by byrhythmic rhythm~c darkgreen greenand a d coIorle overgrowths ofofincreasing cmlurles avergrowths increasingactinolitic actinofiticcontent. contentTextural T e x Mevidence evidenceshows showsthat that cumulus cumulusaugite augitewas wasreplaced replacedby bymaginatically magmaticaIlyrelaxed related prismatic pismaticferropargasitic fmpargasitic hornbIeie, and and hornblede* andboth bothaugite augite andhornblende hornblendewere weresubsequently subsequentlyreplaced replacedby byfibrous fibrous actinoli~.In Inextreme extremecases casesthe therock rockisiscomposed composedofofaafelted feltedmat matofofactinolite xrholitethat thathas has actinolixe. all primary pt i m~q grain grain boundaries, boundaries-Modes Modsofofoxides oxidesrange m g efrom from10% 10%toto80%, 8Q%,and ad o b ~all obliterazed the magmatic thelatter latterrocks rocksgrade grade into intonelsonite. n e l ~ n i tVery eVery ~ minor minoramounts amountsofofinterstitial, interstitial9 mgmatic sphene andcalcite calciteare arepresent pxesentininboth bothhornblendite hmblenditeand andnelsonite. rielsorite. spheneand Black B k kand andwhite, white*strongly stronglymagnetic magneticnelsonite nebnite contains containsvariable variableamounts amountsof of chlorite. chloriteactinolite, aainolite*homblende, hmblende*and andpyroxene. pyroxene.Oxides Oxidesconsist consistofofequant equantmagneute magnetitegrains, grains, which whichcontain amainabundant abundant(111) (1 11)exsolved exsolvedlamellar lamellarilmenite, ilmenite*asaswell wellasasgrains grainsofoflate late 10 �anbedralilmenite. ilmenite.Grains Grainsofofprismatic prismaticaparite +te are arcaaprominent prominent feature of the nehmite. anhedral feature of the nenite. Thisintrusion intrusioncontains containsappreciable appreciabkapatite apatiteand andtherefore thereforeititcould couldbe be a pmi?de This a possible P. By analogy w i t h other a p ~ r i c h bodies it could also be a source @-rare saxrce of sce of P. By analogy with other apanie-rich bodies it could also be a source of rare e a r t h elemems Limited analyses of the neisonite and ppxenite show up to 15% Ti%, earth elements. Limited analyses of the lsonite and pyroxenite show up to l TiC)2, and 50% F q Q ; this implies that the plum could also be a source of these comxxiities. and 50% Fe203; this implies that the plinon could also be a source of these conodities. 15%apatite apatiteora10% 1Wofree free Akhough none noneof ofthe thematerial materialnow nowavailable availablecontains mntainsmore morethan than15% Although k n i t e not tied up in magnetite, the exking c m (7 cm per 1.5 m) was p h k i y biased ilmenite not tied up in magnetite, the exing core (7 cm per 1.5 m) was probaby biased tcnvard the theiron-rich iron-richunits. units.ItItisisalmost h o s ta acertainty certaintythat thataasimple simple drilling drilling pproam r o g mwould ~would toward imcrsect intmals of considerable apatite mntent andor zones containing econanic intersect intervals of considerable apatite content and/or zones containing econccuc beenhanced enhancedby bythe thewellwellamunts of of recoverable m v e r a b l e ilmenite. ilmenite.Exploration Explcmionwould wouldbe amounts cumrained size sizeofofthe thepluton phtonand andby bythe thefact fictthat thatititisisburied buriedby byno nomore morethan than30 3Gmmof of constrained g l a d material. glacial material. Fi-gure 1.1.Aerornagetic Ammageticmap mapofofthe thePhilbrook Philbrmkarea area(modified (modifiedfrom h mthe theMinnesotz Minnesotz Figure Gedogical Sumey, Legislative Commission on h4innesota Resources, aemmapcncmap map Geological Survey, Legislative Commission on Minnesota Resources, aeromaznenc of h e Motley 7.5 quadrangle.) showing lrxations of outcrops and d r i l l holes used i n this of the Motley 7.5 quadrangle.) showing locations of outcrops and drill holes used in this s d y Outcrops. . Outcrops;drill s;drillholes— holes-. sny. 11 �An to the Geology of the An Introduction Introduction to Geology and Mineral Mineral Deposits Deposits of the Archean Marquette Archean Marquette Greenstone Greenstone Belt, Michigan Michigan T.J. BORNHORST (Department of of Geology T.J. BORNHORST (Department Geology and Geological Geological Engineering, Engineering, Michigan Michigan Technological Technological University, University Houghton, Houghton9 Michigan Michigan 49931) 4993 1) The Marquette Belt occupies occupies an an area area of of about Marquette Greenstone Greenstone Belt about 125 125 mi2 mi2 (325 (325 km2) km2) The geology in northern northern Marquette Marquette County, County7Michigan. Michigan. The geology is is complex. complex. The belt belt consists of of several thousand feet feet of subaqueous mafic to silicic consists several thousand subaqueous mafic silicic flows flows and and pyroclastics is dominated dominated by tholeiitic tholeiitic basalt, basalt, with with pyroclastics and volcaniclastic vokaniclastic sediments. sediments. It is rocks are are intruded a scattering scattering of of compositions compositions towards towards rhyolite. rhyolite. These These rocks intruded by by gabbro gabbro The belt and rhyolite and rhyolite dikes, and and by by granitoid granitoid plutons. plutons. The belt includes includes two two peridotite peridotite Stratigraphic correlations correlations are complicated complicated All rocks rocks are of of Archean Archean age. age. Stratigraphic bodies. All of the the belt will by the the existence existence of faults faults and and shear shear zones. zones. Stratigraphy Stratigraphy of will be be by discussed, with suggestions for improving discussed, with suggestions for improving the current current stratigraphic stratigraphic nomenclature. nomenclature. All of these All these rocks rocks have have been been metamorphosed metamorphosed from from greenschist greenschist to to amphibolite amphibolite facies vertica1 facies and subjected subjected to to multiple multiple deformation deformation during the the Archean, Archean* Near vertical dips Regionally,the the belt belt isis affected affected by dips are quite quite common. common. Regionally, by two two major major Archean Archean The Carp shear zones. zones- The Carp River River Falls Falls Shear Shear Zone Zone trends trends E-W E-W and lies lies along along the the is cut cut by by much much less less deformed deformed mafic mafic dikes dikes of of southern boundary of of the southern boundary the belt. belt- It is The full width width of of the the shear shear Archean Archean age (Baxter (Baxter and Bornhorst, Bornhorst, this this volume). volume). The zone is is unknown because part part of of itit was zone unknown because was reactivated reactivated during during the the Penokean Penokean orogeny, orogeny? juxtaposing sediments against against more more altered and juxtaposing less less deformed deformed Lower Lower Proterozoic Proterozoic sediments and The Carp Shear Zone Zone may may be be part part of of the sheared Archean rocks. rocks- The Carp River River Falls Falls Shear the sheared Archean Great Lakes Great Lakes Tectonic Tectonic Zone Zone of Sims Sims (1980, (l98Q9Geol, GeoL Soc. Sot- Amer. Amer- Special Special Paper 182, 182, p. p* second major structural structural zone, zone, Dead Dead River River Basin Basin Shear Shear Zone, Zone?trends trends 113-124). The second NW-SE and and bisects too was was reactivated reactivated NW-SE bisects the belt, belt7with with unknown unknown displacement. displacement. It too Stratigraphic correlation correlation across across this this zone zone is is tenuous. tenuous. during the during the Penokean Penokean orogeny. orogeny. Stratigraphic Of Of the the numerous numerous base base and and precious precious metal metal orebodies orebodies and occurrences occurrences known known in in Most of of the the belt, belt7 the the Ropes Ropes Mine Mine is is the the most most significant. significant. Most the occurrences occurrences are are the interpreted to be with faults faults and shear interpreted be epigenetic, epigenetic, spatially spatially associated associated with shear zones, zones, and and structures may may be important Regional structures important in in localizing localizing syn- to synto post-tectonic. post-tectonic. Regional mineralization. Precious Precious metal metal mineralization mineralization is accompanied accompanied by sulfide sulfide minerals, minerals, especially pyrite pyrite with with lesser of pyrrhotite, pyrrhotite7 chalcopyrite, chakopyrite, and and arsenopyrite, arsenopyrite, especially lesser amounts amounts of and by and by non-metallic non-metallic minerals minerals such such as quartz, quartz, carbonate, carbonate7 chlorite, chlorite, and and sericite. sericite-. The The present data data permits that there there have present permits the tentative tentative suggestion suggestion that have been been at at least least two two major pulses major pukes of of mineralization. mineralization. The potential potential for discovery discovery of of new new economic economic deposits in in the deposits the Marquette Marquette Greenstone Greenstone Belt Belt isis indicated indicated by byanomalous anomalousgeochemical geochemical Au of numerous quartz and and carbonate Au values, values, the occurrence occurrence of numerous quartz carbonate veins, veins, areas areas of pervasive alteration, areas areas of of relatively abundant faults faults and shear zones? and and the the pervasive alteration, relatively abundant shear zones, overall geologic geologic setting. setting. 12 �THE ORIGIN ORIGINAND AND EXTENT EXTENTOF OFTHE THEHARD HARDAND ANDSOFT SOFTIRON IRONORES ORESOF OF THE THE MARQUETTE MARQUETTE RANGE, RANGE MICHIGAN MICHIGAN THE BurtonH.H.Boyurn Boyum Burton 1shpeming9Michigan Michigan49849 49849 Ishpemlng, ABSTRACT ABSTRACT The Marquette D iDistrict s t r i c t i is s llocated o c a t e d iin n the the north n o r t h central c e n t r a l part p a r t ofo fthe t h eUpper UpperPeninsula Peninsula of o fMichigan Michigan as as The MarquetteMineral Mineral r e l a t i v e l yminor minoroccurrences occurrences of o f gold g o l d and and of of relatively o f Middle Precambrian age. The pprincipal rincipal m i n e r a l i z a t i o n iiss Iron i r o n with w i t h other other shown iin n Figure Figure I.I * The shown mineralization The host host rocks rocks are arefound foundini the n the Marquette RangeSupergroup Supergroup copper. The copper. Marquette Range There are are of Middle Precambrian age. There several iron-formation iron-formation memberswith w i t hthe the NegauneeIron—Formation Iron-Formation the the principal p r i n c i p a l locus locus of o fhigh h i g hgrade grade iron i r o nores. ores. several members Negaunee i s the the thickest t h i c k e s treachreachA1 though generally generally similar s i m i l a r tot othe theother o t h eiron—formations r iron-formations of o fthe t h eLake Lake Superior Superior Region, Although Region,i Itt Is i n g aa stratigraphic s t r a t i g r a p h i cthickness thickness ofofover over1,300 1,300 meters meters (3500 (3500 feet), f e e t ) , It I t differs d i f f e r salso a l s oini nthat t h aItt contains i t contains a minimum ing a minimum o f arillaceons argillaceonsoroarenaceous r arenaceous facies. facies. of The The " s o f t " ores ores are goethite, s osoft, f t , f rfriable i a b l e tto o earthy earthy oorr plastic. p l a s t i c . The The "hard" "hard1' ores ores are a r edense dense 'soft1' are hematite hematiteand and goethite, There aare r e t three h r e e ddistinct i s t i n c t structural s t r u c t u r a l locations l o c a t i o n s for f o r the t h eores, ores* The The soft s o f tones ones There t o specular specularhematite hematiteand andmagnetite. magnetite. to are found found at a t the the base base of of the the Negaunee Negaunee Iron-Formationp g e ngenerally e r a l l y i n In f a fault u l t sstructures t r u c t u r e s wwith i t h intrusive i n t r u s i v edikes; dikes;and and are Iron—Formation, on large l a r g e iintrusive n t r u s i v e ssills, i l l s , also also in i n structures s t r u c t u r e s related r e l a t e d to t o faulting. f a u l t i n g . The The hard found near t o p of o f the the on hard ores ores are are found near the the top Negaunee Iron—Formation. Iron-Formation. The The Marquette t h e Lake Lake Superior Superior Region Region to t o have have both both hard hard Negaunee Marquette Range Rangei sisthe the only only one one iInn the and soft s o f t ores. ores* and The regional regional metamorphism metamorphism has ranging l o r i t e in i nNegaunee Negaunee and u l k of of The haszones zones rangingfrom fromc hchlorite and Ishpeming, Ishpeming,where wherethe the bbulk the soft s o f t ore ore was was found, b i obiotite, t i t e , ggarnet, a r n e t * s staurolite t a u r o l i t e tto o ssillimanite. i l l i m a n i t e . Most Most o t h e hard hard ore o r e was was found found in in the found,through through off the the higher orders o f metamorphism. the higher orders of metamorphism. From 1846 t a l of 57599009119 long tons of o firon i r o ore n o rhave e have beenproduced producedand andshipped shippedfrom from From 1846through through1986 1986a at ototal of 575,900,119 long tons been the Marquette Marquette Range, Range* i including n c l u d i n g concentrates e l l e t s from from low low grade grade operations. operations. Of O f the t h e natural, n a t u r a l *high h i g hgrade grade the concentrates and andppellets ores 186,607,540 186,607*540 tons f o ofootwall t w a l l s osoft f t ore, tons were i n tIntrusive r u s i v e s isill l l structure s t r u c t u r e soft s o f tore oreand and ores tonswere were ore,54,092,030 54,092,030 tons were 6O935OS944tons were were hard hard ore. ore. 60,350,944 The extent the ores ores are l l u s t r a t e dby by their t h e i r plan p l a n and and thickness thickness as e l a t e d tto o structural s t r u c t u r a l controls. controls. The extent of of the are iIllustrated as rrelated Hypotheses oof f oorigin r i g i nare arediscussed. discussed. Hypotheses UPLANATION FGURC I •EOI.GS' UPCWIS&ø$ 9PC. 'SICA flU, .1 W((haS*l Og S dIOCIL I •**CLS.kI As •QC,I lAO, '0.1111o $1401.1. 105(1 PItt PSI '04.10 14.14(1 O W.P(* PINISIW,& t -. - Figure 1 — Generalized a l f ooff the t h e Upper Upper Peninsula Peninsula of of Michigan Michigan Figure Generalizedgeology geologyo fofthe thewestern westernhhalf 1 13 �STRATIGRAPHY AND GEOBAROMETRY OF MONZODIORITES FROM THE STRATIGRAPHY THE GIANTS RANGE BATHOLITH, NORTHEASTERN MINNESOTA BATHOLlTH, MINNESOTA of Geology Bruce L. Brasaemle, Brasaemle, Department of Geology Minnesota, Minneapolis, Minnesota, Minneapolis, MN MN 55455 and Geophysics, University of Mapping in the the northeastern part of the northeastern part the Archean Archean Giants Giants Range Range batholith batholith (in near Ely, the Bear Minnesota has Bear Island Island quadrangle), near Ely? Minnesota has revealed a suite suite of five mappable composition from mappable granitic granitic units ranging in composition from hornblende hornblende monzodiorite monzodiorite to granodiorite are comparable the Farm granodiorite (Fig. (Fig. 1). 1). These These units units are comparable toto the F a m Lake Lake facies facies of of the tlie Giants by Green Giants Range Range batholith batholith proposed proposed by Green (1970) (1970) for for granitic granitic rocks rocks in the Gabbro Gabbro Lake Lake quadrangle. All All of of the thegranitoids granitoids in the the Bear Bear Island Island quadrangle quadrangle are are generally generally mediummedium- to to coarse-grained, and variably porphyritic with microcline being the most The different are distinguished on the common type type of common of phenocryst. phenocryst. The different granitic units are distinguished on the especially modal basis of of texture texture and and modal modal mineralogy, mineralogy, especially modal abundances abundances of quartz, Contacts hornblende, and/or Contacts between between the units, where observable, andfor biotite. observable, are Dikes of the quartz monzodiorite (Agqm) gradational. (Agqm) cut the hornblende stratigraphic relations of of Agmd monzodiorite (Aghm), monzodiorite (Aghm), but but the stratigraphic Agmd to to the other units field. Nevertheless, it is plausible to could not could not be be deciphered deciphered in in the field to assume assume that that the units are genetically related. related* The The "mg' "mg"values values(Mg/(Mg+Fe)) (Mg/(Mg+Fe)) of of hornblende hornblende and/or whole rocks rocks (based (basedon on ~Fe+ e + only) +only)suggest suggest a adifferentiation differentiation sequence sequence of of the the and/or whole principal units: + Agmd Agmd + Agqm (see (see Table 1). 1). Aghm —> principal units: Aghm - Pressure determinations based on hornblende stoichiometry stoichiometry (Hammarstrom Assuming that that the and and Zen, Zen9 1986; 1986; Hollister Hollister and and others, others, 1987) 1987) are are shown shown in in Fig, F i g 1. 1- Assuming the stratigraphic and geobarometric deductions are correct, correct, two structural models The observed for the could could account account for the observed observed geologic geologic relations. The observed distribution of 1) these granitic rocks could represent: 1) the faulted record of aa composite of asymmetric folding of of such intrusion (Fig. 21, 2), or 2) intrusion (Fig. 2) a product product of asymmetric folding such an an intrusion intrusion (Fig. (Fig. less plausible becauseofof the the lack lack of Model 11 seems seems less plausible because of field field evidence evidence for for faults faults 1. faults shown other other than than the the regional regional northeast northeast trending trending faults shown in in Fig. 1. 3). References References Brasaemle, B. L., Southwick D. L., L., and Brasaemle, B, Southwick De and Sims, Sims* P. K., K., in in prep., prep., Bedrock Bedrock geologic geologic map map of of Minnesota Geological Louis County, Bear Island Bear Island quadrangle, quadrangle, St. St* Louis County7 Minnesota: Minnesota: Minnesota Geological Miscellaneous Map Map Series, Survey Miscellaneous Series, scale scale 1:24,000. 1:24,000. Gabbro Lake 1970, Lower Green, J. I. C., 1970, Lower Precambrian Precambrian rocks rocks of the Gabbro Lake quadrangle, Special Publication Minnesota Geological Survey northeastern Minnesota: Survey Special Series, SP-13, Series, SP-13. 96p. 96p. An empirical 1986, Aluminum M., and Hammarstrom, J. M., and Zen, Zen, E., E., 1986, Aluminum in in hornblende: hornblende: An empirical 1297-1313. igneous geobarometer: igneous geobarometer: American American Mineralogist, Mineralogist, v. 71, 71, p. p. 12971313. Hollister, L. S.$ S., Grissom, G. C., K., Stowell, Stowell, H. H., H., and and Sisson, Sisson, V. V. B., B ~1987, ,1987, H011ister~L. Grissom, G. C., Peters, Peters, E. Ee K., of Al Confirmation of the Confirmation of the empirical empirical correlation correlation of A1 in hornblende hornblende with with pressure American of solidification of solidification of caic-alkaline calc-alkaline plutons: American Mineralogist, Mineralogist, v. v. 72, p. p. 23 1-23 9. 231-239. 14 �Fig. Fig. 11 Schematic Schematic map map of granitic granitic units of the Giants Giants Range Range batholith batholith in in the the Bear Bear Island Island quadrangle quadrangle (modified (modified from Brasaemle, Brasaemle, and and others, in in prep.) prep.) 15 �—. — Fig. 2 Faulting Faultingof of aacomposite compositeintrusion intrusionto toaccount account for for observed observed geologic geologicrelations relationsof of granitic graniticunits. units. Fig* 3 Asymmetric Asymmetricfolding foldingof of aacomposite corn ositeintrusion intrusion Fig. to to account account for observed observed geologic geologic relations r e h o n s of granitic graniticunits. units. Table Table 1. 1. Monzodiorite Monzodioritewhole wholerock rockand andhornblende hornblendeanalyses. analyses. II Whole Rock Analyses Analyses Whole Rock Unit Samo! # Aghm 3A Oxides (wt %) 'YO) Oxides (wt Si02 ~ i 0 2' ' 56.3 Al203 17.7 A1203 17-7 Ti02 0,63 Ti02 0.63 Fe203 2.57 Fe203 FeO 3.32 FeO MnO 0.10 MnO MgO 3.38 CaO 4,93 Na20 5.40 K20 2,84 P205 0SO Total 97.67 Mg/(Mg+Fe2+) 0,645 0.645 (atomic) (atomic) Agmd 148 64,9 64-9 17.5 17.5 0,37 0-37 1.21 1.21 1.92 1.92 0.05 1.92 3.90 6.20 2.25 O1 Agqm 19 71.0 71.O 16.3 16~3 0.13 0-13 0.55 0.67 0.03 0.65 1.84 5.90 2.73 Hornblende Hornblende Analyses Analyses Aghm Aghm Agmd Agmd Agqm Agqm Unit Unit SmnIA S m e # 333A 3A 148 146 Oxides Oxides (wt (wt %) O/O) 48.21 Si02 48.21 Si02 6.88 A1203 A1203 6~88 0,94 T102 Ti02 0-94 14.34 MgO MgO 14-34 14.40 FeO FeO 14-40 0.40 MnO MnO 11.35 CaO 47.53 43.74 7.56 7*56 8.02 8-02 0.75 0-75 0.77 13.02 13~02 12.18 12.18 16.40 16.40 17.94 17.94 0.34 0.34 0.60 0.60 11,46 11.06 Na20 K20 1.36 0.68 O0 100.60 99.86 0.641 0.641 0.635 1.48 0.81 319 319 1.35 1,03 Cations Cations (based (basedon on 23 23 oxygens) oxvaens) Unit Unit ' Anhm ~ a h m~Acmd q m d"'A,m AQQ~ ampIe# 146 319 319 14 S a m ~ l e# 33A 33A Si 7.04 6.97 6.69 AI(iv) 0.93 1,03 1.31 Al(tot) 1.18 1.31 1.45 Al(vi) 0.22 0.28 0.14 Ti 0.10 0.08 0.09 Mg 3.12 2.85 2.78 Fe+2 Mn Ca Na K Mg/ (Mg+Fe) 16 1.76 0.49 1.77 0.37 0.13 1.95 0.42 1.80 0.42 0.15 0.640 0.594 2.30 0.08 1.81 0.40 0.20 0.548 �A TECTONIC TECTONIC MODEL MODELFOR FORTHE THEMID-CONTINENTAL MID-CONTINENTALRIFT RIFTSYSTEM SYSTEM A F. William William Cambray Cambray F. Department of Geological Sciences Department of Geological Sciences Michigan State University Michigan State University 48824-1l1.S East Lansing, Lansing,MI MI48824-1115 East The opening opening vector vector of of the the MRS MRS isisrestricted restricted totoananapproximate approximatenorth-south north-south direction direction The because its its Continuous continuous nature 180' of Lake because nature through through almost almost 1800 of arc arc from from Kansas, Kansas, north north to to the Lake Superior Region Region and and then then south souththrough through Michigan, Michigan, has has been beenestablished establishedby bygravity, gravity, Superior magnetic and and seismic seismic reflection reflection studies. studies. Motion Motion on on such such aa rift riftsystem systemwould would be belargely largely magnetic extensional in regions at right angles to the opening vector and increasingly transtensional extensional regions at right angles to the opening vector and increasingly transtensional as the the angle angle decreased. decreased. This Thisseems seemsto to be beborn bornout outby by the thegreater greaterwidth width of of the the basin basin in in the the as east-west trending Lake Superior portion when compared with the narrower geophysical east-west Lake Superior portion when compared with the narrower geophysical anomalies on on the the more more north-south north-south sections. sections. InInaddition, addition9the therift riftfits fitsan anasymmetric asymmetricmodel model anomalies such as as that that of ofWernicke Wernicke (1981, (1981, 1985) 1985) or Lister Lister et et al. al.(1986) (1986) in in the theLake LakeSuperior Superiorregion. region. such The south south side side appears appears to to be be the thelower lowerplate platewith with the thegreater greaterthickness thicknessand and more more complex complex The pattern of of sediments sediments close close to to that that margin. margin. The Thelower lower plate plate uplift uplift close close to to the theupper upperplate plate pattern margin described Lister et al. al. model model is is represented represented by by the the deep deep level level of of erosion erosion margin described in in the the Lister exposing the the higher higher grade grade metamorphic metamorphic rocks rocks on on the the northwest northwest exposing the Duluth Duluth Gabbro and the Finally, the MRS has been involved in a later compressional shore of Lake Superior. shore of Lake Superior. Finally, the MRS has been involved in a later compressional event. The Thevector vectorofofmovement movementfor forthis thisphase phase would would also also be be restricted restricted to toan anapproximately approximately event. north-south direction in a rigid crust. The thrusting and folding in the Lake Superior north-south direction a rigid crust. The thrusting and folding in the Lake Superior region is related related to tothis thismovement. movement. Elsewhere Elsewhere the the motion motion must must have haveinvolved involved various various region TheSt. St.Croix Croix Horst Horst and and its its continuation continuation to to the the south south could could be be amounts of transpression. transpression. The amounts described as a positive flower tested in in described flower structure structure in in this this setting. setting. The The model model can can be further tested the field field by by collecting collecting kinematic kinematic data from £ro fault surfaces surfaces and finite strain data data from from fold fold the structures. The Thedetachment detachmentfault faultshould shouldbe beexposed exposedto tothe thenorth northand andwest westof ofthe thegabbro. gabbro. structures. 17 �Variations V a r i a t i o n s in i n Structural S t r u c t u r a l Style S t y l eofo fthe t h eMidcontinent M i d c o n t j n e n t Rift R i f Beneath t Beneath Lake Lake Superior Superior USGS,Reston, Reston,VVirginia W e FF.e Cannon, Cannonp USGSu irginia AA, e G. G* Green, Green# Geological G e o l o g i c a l Survey Survey ofo fCanada, Canada, Ottawa, Ottawa9Canada Canada D, R. Hole, Massachusetts I?. Hutchinson, Hutch i n s o n #USGS, USGS8Woods Woods Hole, Massachusetts 3, J Q C. C- Behrendt, Behrendt, USGS, U%S, Denver, Denver9 Colorado Colorado W, Recent deeps eseismic Recent deep i s m i c r ereflection f l e c t i o n profiles p r o f i l e sby bythe t h eGreat G r e a tLakes Lakes Program ononCrustal Program C r u s t aEvolution l Evol u t i o(GLIMPCE) n (GLIMPCX 1 IInternational n t e r n a t i o n a lMultidisciplinary Mu1t i d i s c i p l 1 nary only nnot ot o n l y show show ddetails e t a i l s ooff the t h e deep deep sstructure t r u c t u r e ooff the t h e Midcontinent Midcontiment RRift ift beneathLake LakeSSuperior beneath u p e r i o r b but u t aalso l s o iIndicate n d i c a t e structural s t r u c t u r a l changes changes along a l o n g the the trend r i fthat t t h asuggest t suggestchanges changes iin n the t h e rifting r i f t i n gprocess. process. These new new t r e n d of o f the t h e rift data, combined an iinterpretation data, combined w iwith t h p opotential t e n t f a 1 f ifield e l d data, d a t a 8 support s u p p o r t an n t e r p r e t a t j o n of of rifting r i f t i n gand andsubsidence subsidence of o f discrete d i s c r e t eblocks b l o c k shaving h a v i n gdimensions dimensions of o f aa few few tens tens Individual I n d l v i d u a l blocks b l o c k s appear appear to t o have have flexed flexed tto o aa few few hundred hundred kkilometers. ilometers. during being d u r i n g subsidence subsidence rrather a t h e r tthan han b e i n g ccompletely o m p l e t e l y rrigid. f g l d . IInn some some areas, areasr subsidence as 10 10 km kmappears appearst otohave haveoccurred occurredppurely by ccrustal f as as much much as u r e l y by rustal subsidence oof flexing Boundariesooff tthe f l e x i n g within w i t h i n an an individual ind-ividual block. block. Boundaries h e blocks, blocks, however, however* are On sseismic a r e probably probably ffaults. aults. On e i s m i c llines, i n e s , boundaries boundarfes are a r eshown shown by by abrupt abrupt changes and/ora tattitude changes i nint hthickness i c k n e s s and/or t i t u d e oof f rrift—filled i ft-f i 1 l e dvolcanic vo1 c a n i c and and sedimentary cases, sseismic imageso of sedimentary rocks. r o c k s - In I n some some cases, e i s m i c images f t the h e ffault a u l t planes planes were obtained. obtained. were I n western western Lake Lake Superior, t h e rift r i fappears t appearsto t b.e o beananasymmetric asymmetric graben graben In Superior, the 3 0 kml e nnorth, o r t h , whereas e ccentral e n t r a l ppart art o t h e lake, lakep deepest b('30 deepest km)on ont hthe whereasi nint hthe off the tthe h e graben graben is i s deepest deepest on on the t h e south. south. AA zone zone of o f accommodation accommodation between between t h e s e two n f e r r e d aalong l o n g aa prominent f f s e t iin n the t h e gravity gravity these two grabens grabensi sis i inferred prominento offset ppattern a t t e r n extending e x t e n d i n g from from jjust u s t west west of o f Isle I s l Royale e Royaletot onear nearOntonagon, Ontonagon, Michigan. M ichigan@ The sstructure t r u c t u r e beneath beneath eastern e a s t e r n Lake Lake Superior S u p e r i o r is i smore more symmetrical, symmetrical, and and an an The area a r e a at a t least l e a s t80 80km kmwide wide appears appears to t ohave have subsided subsided uniformly u n i f o r m l yabout about15 15km, kmu w i t h little l i t t l or e ono r no t i l t i nbefore g , b e f undergoing o r e undergoing a d d i t i o n a15 l 15 more with tilting, ananadditional kmkmofo fmore complex complex subsidence. The The TThiel h i e l ffault, a u l t , aastructure s t r u c t u r elong l o n grecognized recognized from from p o t e n t i a l field f j e l ddata, data,extending e x t e n d i n gfrom fromnear n e a rMarathon, Marathon, Ontario, O n t a r i o 8 to t o near near potential Marquette, Michigan, M i c h i g a n 8isi proposed s proposed accmmodationzone zonebetween between Marquette, asas anan accommodation structures s t r u c t u r e s in i n the t h e eastern e a s t e r n and and ccentral e n t r a l lake. lake. The a t t e r n in i nBouquer Bouquer gravity g r a v i t yanomalies anomal i e s beneath beneath much much ooff the the The unusual unusual ppattern 1lake, ake, where where ttrends r e n d s ooff linear 1 ineargravity g r a v i t yanomalies anomal i e s end end abruptly abrupt1 y or o rshow show sharp sharp changes n t e r p r e t e d t to o rreflect e f l e c t the t h e outlines o u t 1 i n e s of o f discrete discrete changesi nintrend, trend,i sis i interpreted blocks b l o c k s ooff prerift p r e r i fbasement. t basement. The The Independent independent movement f tthese h e s e blocks blocks movemento of d u r i n g rrifting i f t i n g controlled c o n t r o l 1ed tthe h e tthickness h i c k n e s s o fofb abasalts s a l t s t h athat t f i 1filled l e d t hthe e r rift. if t during Detailed D e t a i l e d cconfiguration o n f i g u r a t i o n oof f tthe h e rrift, i f t ,therefore, t h e r e f o r e ,may may be be inherited i n h e r i t e d from from o l d e r structures s t r u c t u r e sini n t hArchean e Archeanand andLower Lower Proterozoic P r o t e r o z o i cbasement basement tthat h a t were were older the asf afaults rreactivated e a c t i v a t e d as u l t s dduring u r i n g r rifting. ifting. 18 �COPPER—NICKEL COPPER-NICKEL MINERALIZATION MINERALIZATION OF OF THE THE DULUTH DULUTH COMPLEX, COMPLEXf NORTHEASTERN MAGNETIC PERSPECTIVE PERSPECTIVE NORTHEASTERN MINNESOTA: MINNESOTA: AA GRAVITY AND MAGNETIC Val Val W. W. Chandler Chandler and and Robert R o b e r t J. J. Ferderer, F e r d e r e r f Minnesota Minnesota Geological G e o l o g i c a l Survey, Surveyf 2642 2642 University U n i v e r s i t y Avenue, Avenuer St. S t . Paul, P a u l r Minnesota Minnesota 55114—1057 55114-1057 It I t is i s now now generally g e n e r a l l y accepted a c c e p t e d that t h a tinteraction i n t e r a c t i obetween n betweenmagmas magmas of the t h e Duluth Duluth Complex (MiddlePProterozoic) and tthe Complex (Middle r o t e r o z o i c ) and h e sulfur—rich s u l f u r - r i c h Virginia V i r g i n i a Formation Formation (Early (Early Proterozoic) Cu-Ni sulfides s u l f i d e s near n e a r the t h e base base P r o t e r o z o i c ) played p l a y e d aa key key role r o l e in i n forming forming the t h eCu—Ni of o f the t h e complex, complex, but b u t many many details d e t a i l s regarding r e g a r d i n g their t h e i r evolution e v o l u t i o n remain remain unknown unknown (Ripley, ( R i p l e y , 1986). 1 9 8 6 ) . Gravity G r a v i t y and and high-resolution h i g h - r e s o l u t i o n aeromagnetic a e r o m a g n e t i c data d a t a are a r e useful useful i n elucidating e l u c i d a t i n g the t h e structural s t r u c t u r a l setting s e t t i n g for f o r the t h e Cu-Ni Cu-Ni sulfide s u l f i d e deposits d e p o s i t s in i n the the in Hoyt Hoyt Lakes-Kawishiwi Lakes-Kawishiwi area. a r e a . The The sulfide s u l f i d e deposits d e p o s i t s themselves themselves generally g e n e r a l l y lack lack aa direct d i r e c t gravity g r a v i t y and and magnetic magnetic signature, s i g n a t u r e f but b u t associated a s s o c i a t e d inclusions i n c l u s i o n s of of wall wall rock, r o c k , as a s well w e l l as a s structures s t r u c t u r e s near n e a r the t h e base b a s e of of the t h e complex, complex, can c a n produce produce s t r o n g magnetic magnetic signatures s i g n a t u r e s especially e s p e c i a l l y if i f any any involve i n v o l v e the t h e Early E a r l y Proterozoic Proterozoic strong Biwabik Biwabik Iron I r o n Formation. Formation. For For example, example, contact c o n t a c t metamorphosed metamorphosed iron—formation iron-formation in i n the t h e Babbitt B a b b i t t area a r e a produces produces aa prominent, p r o m i n e n t , northeast-striking n o r t h e a s t - s t r i k i n g magnetic magnetic signature. s i g n a t u r e . AA spur—like s p u r - l i k e eastward e a s t w a r d projection p r o j e c t i o n of of this t h i s signature s i g n a t u r e reflects r e f l e c t s aa step—like s t e p - l i k e structure s t r u c t u r e in i n the t h e basal b a s a l contact c o n t a c tat a tthe t h eNIINNAMAX MINNAMAX deposit. d e p o s i t . Detailed Detailed magnetic MINNAMAX area a r e a indicates i n d i c a t e s that t h a t the t h e Biwabik Biwabik Iron Iron m a g n e t i c modeling modeling of of the t h e MINNAMAX Formation Formation thins t h i n s appreciably a p p r e c i a b l y across a c r o s s this this step—like s t e p - l i k e structure s t r u c t u r e and and ultimately ultimately pinches p i n c h e s out o u t aa short s h o r t distance d i s t a n c e down down dip d i p between between the t h e complex complex and and the the underlying i s improved improved if i f more more iron— ironu n d e r l y i n g Archean Archean granite. g r a n i t e . The The fit f i t of of the t h e model model is i s included i n c l u d e d several s e v e r a l kilometers k i l o m e t e r s farther f a r t h e r down down dip d i p along a l o n g the t h e basal basal f o r m a t i o n is formation contact. contact Several S e v e r a l kilometers k i l o m e t e r s south s o u t h of of the t h e MINNAMAX MINNAMAX deposit, d e p o s i t f well w e l l within w i t h i n the the interior i n t e r i o r of of the the complex, complexf prominent prominent magnetic magnetic anomalies a n o m a l i e s sharply s h a r p l y outline o u t l i n e an an area a r e a containing c o n t a i n i n g abundant abundant inclusions i n c l u s i o n s of of hornfelsed h o r n f e l s e d wall w a l l rock. rock. These These anomalies a n o m a l i e s demonstrate d e m o n s t r a t e that t h a t areas a r e a s of of interaction i n t e r a c t i o n between between wall w a l l rock r o c k magma maqma and and are a r e not n o t restricted r e s t r i c t e d to t o the t h e basal b a s a l contact c o n t a c t of o f the t h e complex. complex. Many Many of of the t h e sulfide s u l f i d e deposits d e p o s i t s in i n the t h e Hoyt Hoyt Lakes—Kawishiwi Lakes-Kawishiwi area a r e a lie lie along a l o n g northwest-striking n o r t h w e s t - s t r i k i n g lineaments l i n e a m e n t s observed o b s e r v e d in i n derivative—enhanced d e r i v a t i v e - e n h a n c e d gravity gravity and and aeromagnetic a e r o m a g n e t i c data. d a t a . The The lineaments l i n e a m e n t s cut c u t both b o t h the t h e complex complex and and the the surrounding s u r r o u n d i n g wall w a l l rocks r o c k s and and are a r e believed b e l i e v e d to t o represent r e p r e s e n t late l a t e Archean Archean faults faults that t h a t were were reactivated r e a c t i v a t e d during d u r i n g emplacement emplacement of of the t h e complex. complex. These These lineaments lineaments support s u p p o r t Weiblen Weiblen and and Morey's Morey's (1976) ( 1976) idea i d e a that t h a t northwest—striking n o r t h w e s t - s t r i k i n g faults faults enhanced sulfide s u l f i d e deposition, d e p o s i t i o n r either e i t h e r by by providing p r o v i d i n g conduits c o n d u i t s for f o r volatiles v o l a t i l e s or or enhanced by by enhancing enhancing wall w a l l rock r o c k interaction i n t e r a c t i o n along a l o n g fractures. fractures. G r a v i t y and and magnetic magnetic modeling modeling of o f the t h e Hoyt Hoyt Lakes-Kawishiwi Lakes-Kawishiwi area area Gravity indicates 15O to t o the t h e southeast. southeast. i n d i c a t e s that t h a t the t h e base b a s e of of the t h e complex complex dips d i p s about a b o u t 15° The The models models indicate i n d i c a t e that t h a t in i n the t h e Hoyt Hoyt Lakes-Kawishiwi Lakes-Kawishiwi aarea r e a the t h e Biwibak Biwibak Iron Iron Formation Formation and and presumably presumably the t h e overlying o v e r l y i n g Virginia V i r q i n i a Formation Formation dip d i p subparallel subparallel to i t s subsurface s u b s u r f a c e extension. extension. t o the t h e basal b a s a l contact c o n t a c t and and may may locally l o c a l l y occur o c c u r along a l o n g its Under Under these t h e s e conditions c o n d i t i o n s magma magma ascending a s c e n d i n g along a l o n g the t h e basal b a s a l contact c o n t a c t would would have h a v e aa lengthy l e n g t h y reaction r e a c t i o n time time with w i t h the t h e Virginia V i r g i n i a Formation, Formation, which which is i s conconsistent s i s t e n t with w i t h results r e s u l t s of of sulfur s u l f u r and and oxygen oxygen isotopic i s o t o p i c studies s t u d i e s (Ripley, ( R i p l e y f1986). 1986). Model Model studies s t u d i e s south s o u t h of of the t h e study s t u d y area a r e a indicate i n d i c a t e that t h a t the t h e base b a s e of of the t h e complex complex there t h e r e dips d i p s much much more more steeply s t e e p l y and and abruptly a b r u p t l y truncates t r u n c a t e s the t h e Virginia V i r q i n i a Formation Formation (Ferderer, ( F e r d e r e r ! 1982). 1 9 8 2 ) . The The consequent c o n s e q u e n t decrease d e c r e a s e in i n reaction r e a c t i o n surface s u r f a c e of of the the 19 �Virginia V i r g i n i a Formation Formation might might explain e x p l a i n the t h e lack l a c k of of significant s i g n i f i c a n t Cu-Ni Cu-Ni sulfides s u l f i d e s in in t h e southern s o u t h e r n part p a r t of of the t h e Duluth Duluth Complex. Complexa the Acknowledgment Acknowledgment This T h i s study s t u d y was was supported s u p p o r t e d by by the t h e Legislative L e g i s l a t i v e Commission Commission on on Minnesota Minnesota Resourceso Resources, References R e f e r e n c e s Cited Cited R e J e , 1982, 19€ Gravity G r a v i t y and and magnetic magnetic modeling modeling of o f the t h e southern s o u t h e r n half h a l f of of F e r d e r e r , R.J., Ferderer, the t h e Duluth Duluth Complex, Complex, northeastern n o r t h e a s t e r n Minnesota: Minnesota: Unpublished, Unpublished, M.A. M.Ae thesis, thesisp Indiana 99 p. p. I n d i a n a University, U n i v e r s i t y , 99 Ripley, R i p l e y r E.M., E.M., 1986, 1986r Application A p p l i c a t i o n of of stable s t a b l e isotopic i s o t o p i c studies s t u d i e s to t o problems of of magmatic magmatic sulfide s u l f i d e ore o r e genesis g e n e s i s with w i t h special s p e c i a l reference r e f e r e n c e to t o the t h e Duluth Duluth Complex, 9Friedrich F r i e d r i c h and and others, o t h e r s , Geology Geology and and metallogeny m e t a l l o g e n y of of Complexr Minnesota, Minnesotar in copper c o p p e r deposits: d e p o s i t s : Berlin, B e r l i n r Heidelberg, H e i d e l b e r g r Springer—Verlag, S p r i n g e r - V e r l a g , p. p. 25—42. 25-42. Weiblen, W e i b l e n r P.W., P e w e , and and Morey, Morey, G.B., G.B.r 1976, 197€Textural T e x t u r a l and and compositional c o m p o s i t i o n a l characcharacteristics t e r i s t i c s of of sulfide s u l f i d e ores o r e s from from the t h e basal b a s a l contact c o n t a c t zone zone of of the t h e South South in Kawishiwi i n Mining Mining Kawishiwi intrusion, i n t r u s i o n r Duluth Duluth Complex, Complex, northeastern n o r t h e a s t e r n Minnesota: Minnesota: Symposium, Symposiumr 37th 3 7 t h Annual, Annual, and and American American Institute I n s t i t u t e of of Mining Mining and and Metallurgical N e t a l l u r g i c a l Engineers, E n g i n e e r s r Minnesota Minnesota Section, S e c t i o n , 4th 4 t h Annual Annual Meeting, Meetingr Duluth, Duluthr 1976, 1976, Proceedings: P r o c e e d i n g s : Minneapolis, M i n n e a p o l i s , University U n i v e r s i t y of of Minnesota, Minnesota, Continuing Continuing Education E d u c a t i o n and and Extension, E x t e n s i o n , paper p a p e r 22, 2Zr 24 24 p. p. 20 �Paragenetic Relationships Relationships Among Among Siderite, Siderite, Magnetite, Magnetite, Paragenetic Calcite, Quartz, Quartz, and and Sulfides Sulfides in in the the Macleod Macleod Siderite Siderite Mine, Mine, Calcite, Wawa, Ontario Ontario Wawa, J. Mancuso, Mancuso, J. J. Frizado, Frizado, D. D. Stewart Stewart M. Cohen, Cohen, 3. M. Bowling Bowling Green Green University, University, Bowling Bowling Green, Green, Ohio Ohio 43403 43403 E. Berdusco Berdusco E. Algoma Ore Ore Division, Division, Wawa, Wawa, Ontario Ontario POS POS 1KO 1KO Algoma The Macleod Macleod Mine Mine is is located located four four kilometers kilometers north north of of The Wawa, Wawa, Ontario Ontario and and lies lies within within the the Helen Helen Iron Iron Range Range in in the the Wawa Greenstone Greenstone Belt Belt of of the the Superior Superior Province Province of of the the Wawa Canadian Shield. Shield. The The mine mine is is an an underground underground siderite siderite mine mine Canadian that began began production production in in 1949 1949 and and has has continued continued to to the the that present. It It has produced produced an an estimated estimated 80 80 million million tons tons of of present. ore through through 1986. 1986. ore The The siderite—pyrite—banded siderite-pyrite-banded chert chert iron iron formation formation is is conformable between between underlying underlying felsic felsic tuffs tuffs and and overlying overlying conformable intermediate flows flows and and pillow pillow lavas. lavas. The The iron iron formation formation intermediate and adjacent adjacent volcanics volcanics form form the the south south limb limb of of an an overturned overturned and syncline plunging plunging approximately approximately 35 35 degrees degrees to to the the east. east. syncline The overturned overturned limb limb strikes strikes east—west east-west and and dips dips The approximately 60 60 degrees degrees to to the the south. south. The The age age of of the the iron iron approximately formation has has been been determined determined by by U—Pb U-Pb dating dating of of underlying underlying formation volcanics to to be be 2750 2750 Ma. Ma. before before present. present. volcanics The iron iron formation formation consists consists of of aa thin, thin, basal basal banded banded The chert member member (1—2m) (1-2m) overlain overlain by by the the massive massive siderite siderite chert (30-loom). The The siderite siderite member member is is overlain overlain by by massive massive (30—lOOm). (3-15111)grading grading to to aa banded banded chert chert member member several several pyrite (3—15m) pyrite hundred meters meters in in thickness. thickness. The The mine mine itself itself is is located located hundred within the the massive massive siderite siderite member. member. within Mine mapping mapping in in the the massive massive siderite siderite and and petrographic petrographic Mine analyses of of selected selected samples samples indicate indicate the the following following analyses paragenetic sequence: sequence: paragenetic 1. Magnetite Magnetite filling filling fractures fractures and and partially partially 1. replacing siderite. siderite. replacing 2. Calcite Calcite filling filling fractures fractures crossing crossing magnetite magnetite and and 2. siderite. siderite. 3. Multiple Multiple episodes episodes of of quartz, quartz, sulfide, sulfide, and and 3. tourmaline veining. veining. tourmaline The origin origin of of magnetite magnetite in in Precambrian Precambrian iron iron formations formations The has long long been been an an unresolved unresolved problem. problem. Theories Theories proposed proposed has vary from from primary primary sedimentary sedimentary through through diagenetic diagenetic and and vary metamorphic to to exhalative. exhalative. In In the the MacLeod MacLeod Mine Mine the the metamorphic magnetite is is definitely definitely secondary secondary because because it it selectively selectively magnetite replaces siderite and fills fractures. replaces siderite and fills fractures. 21 �PRECAMBRIAN RED RED BLUFF BLUFF GRANITE GRANITE COMPLEX, COMPLEX, WEST WEST TEXAS: TEXAS : COMPARISON WITH OTHER MID-PROTEROZOIC "RAPAKIVI" "RAPAKIVI " GRANITES . Donald M. M. Davidson, Davidson, Jr. Jr Department of Geology Northern Illinois Illinois University, University, DeKaib, IL 60115 60115 DeKalb, IL Red Bluff Granite Complex is exposed exposed over an area of 20 The Red 20 The square km k m in in the the Franklin Franklin Mountains, Mountains, near near El El Paso, Paso, Texas. Texas. The units and an intrudes metasedimentary RBGC RBGC intrudes supracrustal units and an ignirnbrite cap cap (Harbour, (Harbour, 1960). ignimbrite 1960). in this b.y. have been mapped ey. Seven phases phases have mapped thus thus far far in this 11 b batholith. Two early microgranite microgranite sills are spatially spatially separated separated three-phase ring ring complex complex by by aa younger 6 6 km k m from from aa three-phase younger tin—bearing tin-bearing biotite granite granite which which cores cores the the complex. complex. A riebeckite granite granite is is all aplites cut phase, although the youngest phase, cut all the although pegmatites pegmatites and and aplites units. units. granite are except the the riebeckite All phases phases except riebeckite granite are medium to to Several coarse—grained with equigranular, porphyritic textures. coarse-grained porphyritic textures. Several phases display Quartz and alkali phases display rapakivi rapakivi texture. texture. Quartz alkali feldspar feldspar riebeckite granite The constitute 90% 90 of constitute of minerals observed. observed. The riebeckite granite typically exhibits an ineguagranular, typically inequagranular, hypidiomorphic texture and and to 38%). 38). contains plagioclase plagioclase as a major major mineral mineral component component (up to contains Riebeckite crystals crystals show strongly Riebeckite strongly preferred orientations orientations and Elsewhere the unit granulated textures are observed granulated observed locally. locally. Elsewhere unit is is pegmtitic (Ray, pegmatitic (Ray, 1982; 1982; McCutcheon, McCutcheon, 1982). 1982) rapakivi granites, granites, the RBGC is is As with many mid—Proterozoic mid-Proterozoic rapakivi but marginally peraluminous (Al203>K20+CaO+Na20), but with (A1203>K20+CaO+Na20), SiO2 peralkaline tendencies. tendencies. Moreover, Moreover, the RBGC is is enriched enriched in in Si02 and strongly depleted depleted in Al2O3, Al203, MnO, MnO, MgO, MgO, and CaO CaO compared compared with with (Anderson, such bodies of similar age 1983) other such bodies of similar age (Anderson, 1983) or the the "average" a v e r a g e " granite of of Nockolds Nockolds (1978). (1978). RBGC show high K, Ba, and REE values suggestive Units of the RBGC.show derivation Plotted on a Rb/Nb—Y derivation from from aa crustal crustal source. source. Plotted on Rb/Nb-Y tectonic discrimination tectonic discrimination diagram (Pearce (Pearce and and others, others, 1984) data 1984) data for the RBGC fall fall in in the the "within "within plate" plate" field. field. However, such aa does not category does not preclude preclude aa relationship to to subducting subducting true, this may represent lithosphere. If the lithosphere. If true, this batholith represent the westernmost manifestation of of the the Grenville Grenville orogeny. orogeny. of of 22 �REFERENCES REFERENCES Anderson, Anderson, J.L., J.L., 1983, 1983, Proterozoic Proterozoicanorogenic anorogenicgranite graniteplutoriism plutonism of of North America: America: Geological Geological Society Society of of America America Memoir Memoir 151, 161, North p.133-154. p,133—154. Harbour, R.L., R.L., 1960, 1960, Precambrian Precambrian rocks rocks at at North North Franklin Franklin Mountain, Mountain, Harbour, Texas : American Association Association of of Petroleum Petroleum Geologists Geologists American Texas: Bulletin, V. v. 44, 44, p.1785—1792. p.1785-1792. Bulletin, T., 1982, 1982, Petrology Petrology and and geochemistry geochemistry of of the the T., Northern Franklin Complex, Precambrian Red Bluff Granite Complex, Northern Franklin Granite Precambrian Red Bluff unpublished Mountains, El El Paso Paso County, County, Texas: Texas: unpublished MS MS thesis, thesis, Mountains, University of of Texas, Texas, El El Paso, Paso, p.177. p.177. University McCutcheon, McCutcheon, Nockolds, S..R., S.R., and and others, others, 1978, 1978, Petrology Petrology Nockolds, Cambridge University University Press, Press, 435p. 435p. Cambridge for for Students: Students: Ray, Ray, D.R., D.R., 1982, 1982, Geology Geology of of the the Precambrian Precambrian Red Red Bluff Bluff Granite Granite 'aso Complex, Complex, Fusselman Fusselman Canyon Canyon area, area, Franklin Franklin Mountains, Mountains, El El P aso MS thesis, thesis, University University of of T Tex, County, Texas: Texas: unpublished unpublished MS ~ : o ,s County, El Paso, Paso, 295p. 295p. El and and others, others, 1984, 1984, Trace Trace element element distribution distribution discrimination diagrams diagrams for for the the tectonic tectonic interpretation interpretation of of discrimination granitic rocks: rocks: Journal Journal of of Petrology, Petrology, v. v . p.956—983. p.956-983. granitic Pearce, J..A., J.A., Pearce, 23 �GEOPHYSICAL GEOPHYSICAL AND AND PETROLOGICAL PETROLOGICAL CHARACTERISTICS CHARACTERISTICS OF OF THE THE CLAM CLAM LAKE LAKE INTRUSION--A CONSTRAINT CONSTRAINT ON ON THE THE TIME TIME OF OF KEWEENAWAN KEWEENAWAN BASIN BASIN INTRUSION--A DEVELOPMENT DEVELOPMENT C. Patrick Patrick Ervin Ervin C. Dept, of of Geology, Geology, Northern Northern Illinois IllinoisUniv. Univ, Dept. DeKalb, IL IL 60115 60115 DeKalb, F. Olmsted Olmsted James F. James Center for Earth & Env. Sci., SUNY-Plattsburgh SUNY-Plattsburgh Center for Earth & Env. Sd., Plattsburgh, NY NY 12901 12901 Plattsburgh, M.G. Mudrey, Mudrey,Jr. Jr. M.G. Wis. Wis. Geol. Geol. && Nat. Nat. Hist. Hist. Surv., Surv., 3817 3817Mineral MineralPoint PointRd. Rd. Madison, WI WI 53506 53506 Madison, The The Clam Clam Lake Lake gravity gravity and and magnetic magnetic anomalies anomalies are are associated associated gabbro, with aa layered, layered, mediummedium- to to course—grained, course-grained, mafic—rich mafic-rich gabbro, with probably probably of of Keweenawan Keweenawan age age (Mudrey (Mudrey and and others, others, 1982), 19821, intruded intruded into an an Archean Archean granite granite gneiss. gneiss. The The intrusion intrusion is is located located aa few few into kilometers kilometers south south of of the the Mellen Mellen Complex Complex and and has has been been penetrated penetrated by by two, two, nearly—coincident nearly-coincident boreholes-—one boreholes--one vertical vertical and and one one inclined inclined 65O to to NNW. NNW. 65° The The northern northern Wisconsin Wisconsin aeromagnetic aeromagnetic data data show show the theintrusion intrusion to to be be marked marked by by aa 7000 7000 gamma gamma anomaly anomaly with with aa wavelength wavelength of of only only 5.5 5.5 km, km, indicating indicating aa highly highly magnetic, magnetic, shallow shallow source. source. The The field field configuration configuration suggests suggests the the presence presence of of aa significant significantremanent remanent polarization, which has has been been confirmed confirmed by by paleomagnetic paleomagnetic analysis analysis polarization, which (Kean and and Swingen, Swingen, 1981). 1981). After After reduction—to-the-pole, reduction-to-the-pole, the the (Kean magnetic magnetic anomaly anomaly is is slightly slightly oval oval with with an an east—northeast east-northeast trending trending axis and and with with aa narrowed, narrowed, westward westward elongation, elongation, suggesting suggesting axis Model analysis analysis yields yields an an possible possible extension extension along along aa fracture. fracture. Model average average susceptibility susceptibility contrast contrast of of 0.026 0.026 cgs cgs units units for for aa source source exhibiting exhibiting surface surface relief relief and and having having aa thickness thickness significantly significantly greater greater than than its its depth depth of of burial, burial, which which is is only only slightly slightly over over 20 20 at one one point. point. mm at The The same same source source configuration, configuration, using using aa density density contrast contrast of of 0.5 0.5 g/cc, g/cc, also also yields yields aa satisfactory satisfactory fit fit to to the the residual residual Bouguer Bouguer anomaly anomaly calculated calculated from from aa small small gravity gravity survey survey made made over over the the intrusion. intrusion. Cores Cores from from both both drillholes drillholes were were sampled sampled for for laboratory laboratory analysis. Although Although the the holes holes are are only only about about 152 152 mm apart, apart, analysis. susceptibility susceptibility and and density density values values are are significantly significantly different different between between the the two, two, and and both both give give generally generally higher higher values values than than the the geophysical geophysical modeling modeling suggests suggests to to be be representative representative of of the the body. body. The The differences differences are are probably probably reflective reflective of of the the proximity proximity of of the the holes to to the the edge edge of of the the intrusion. intrusion. The The most most extreme extreme values values holes occur occur in in the the hole hole believed believed to to be be closest closest to to the the contact. contact. The The variation variation in in compositon compositon is is due due largely largely to to changes changes in in cumulate phases. phases. Oxide Oxide poor poor zones zones are are composed composed of of cumulus cumulus cumulate plagioclase plagioclase (An46-50) (~n46-50)and and clinopyroxene clinopyroxene (Wo.4l, (Wo.41, En.47, En.47, Fs.09, Fs.09, Ac.03) Ac.03) with with oxides oxides restricted restricted to to the the postcumulus postcumulus fraction. fraction. In In 24 �contrast, the the oxide—rich oxide-rich layers layers include include magnetite magnetite and and ilmenite ilmenite in in contrast, the cumulus fraction as well. Strongly oriented plagioclase Strongly oriented plagioclase the cumulus fraction as well. occurs in in both both types types of of layers layers parallel parallel to to their their boundaries boundaries and and occurs This is most obvious at about 30 to the axis of the drill core. This is most obvious the axis of the drill core. to at about 300 and quite quite striking striking in in the the oxide—rich oxide-rich layers. layers. The The orientation orientation and increases to to about about 40° 40' in in deeper deeper parts parts of of the the core, core, suggesting increases suggesting aa flattening, possibly possibly related related to to the the boundary boundary of of the the intrusion. flattening, intrusion. Major Major and and selected selected trace trace element element data data were were obtained, obtained, along along with microprobe microprobe data data of of major major mineral mineral phases, phases, to to help help characterize characterize with Ti02; however, however, no no the body. body. The The unit unit is is extremely extremely rich rich in in Ti02; the abnormal abnormal concentrations concentrations of of vanadium vanadium or or other other trace trace elements elements were were detected. detected. Banding Banding in in the the cores cores suggests suggests that that the the intrusion intrusion has has been been rotated 10° lo0 to to 20° 20 from from the the vertical, vertical, while while the the paleomagnetic paleomagnetic rotated data show show no no evidence evidence of of rotation rotation (Kean (Kean and and Swingen, Swingen, 1981). 1981). This This data implies that that the the body body was was either either (a) (a) emplaced emplaced in in aa tipped tipped implies position or or (b) (b) magnetization magnetization was was acquired acquired after after tipping. tipping. The The position mineral chemistry chemistry clearly clearly indicates indicates that that the the magnetite—ilmenite magnetite-ilmenite mineral temperature-oxygen fugacity fugacity is is subsolidus subsolidus (around (around 600°C), 600°C) which which temperature—oxygen is above the hematite and magnetite blocking temperatures. We is above the hematite and magnetite blocking temperatures. We conclude, conclude, therefore, therefore, that that the the NRM NRM was was acquired acquired when when the the intrusion intrusion was in in aa subsolidus subsolidus stage stage in in its its cooling cooling history, history, and and that that was tipping of of the the body body occurred occurred during during or or very very slightly slightly after after tipping emplacement. emplacement. This This suggests suggests that that significant significant rotation rotation and and evolution evolution of of the the Keweenawan basin basin occurred occurred in in the the middle middle Keweenawan Keweenawan during during Keweenawan emplacement emplacement of of plutonic plutonic bodies bodies and and during during extrusion extrusion of of the the lavas. lavas. REFERENCES CITED CITED REFERENCES Kean, W.F., W.F., and and Swingen, Swingen, R.A.,1981, R.A.,1981, Paleomagnetism Paleomagnetism of of aa Keweenawan Keweenawan Kean, age intrusive intrusive near near Clam Clam Lake, Lake, Wisconsin, Wisconsin, Geophys. Geophys. Res. Res. Let., Let., age v. 8, 8, p. p. 579—582. 579-582. v. Mudrey, M.G., M.G., Jr., Jr., Brown, Brown, B.A., B.A., and and Greenburg, Greenburg,J.K.,1982, J.K.,1982, Bedrock Bedrock Mudrey, geologic map map of of Wisconsin, Wisconsin, Wisconsin Wisconsin Geological Geological && Natural Natural geologic History Survey, Survey, Madison, Madison, Wisconsin. Wisconsin. History 25 �EMPLACEMENT, EMPLACEMENT, MINERALOGY, MINERALOGY, AND AND INTERNAL INTERNAL EVOLUTION EVOLUTION OF OF AA HIGHLY HIGHLY EVOLVED Li-PEGMATITE Li-PEGMATITE IN IN FLORENCE FLORENCE COUNTY, COUNTY, WISCONSIN WISCONSIN EVOLVED U. Faister, Falster, Wm. Wm. B. B . Simmons, Simmons, Dept. Dept. of of Geology Geology and and Alexander U. Alexander of New New Orleans, Orleans, Lakefront, Lakefront, New New Orleans, Orleans, LA LA Geophysics, University University of Geophysics, 70148 70148 ' Recent investigation investigation of of several several highly highly evolved evolved grariitic granitic Recent pegmatites peqmatites in in Florence Florence County, County, Wisconsin, Wisconsin, have have make make it itpossible possible to determine determine numerous numerous details details of of their their origin, origin, their their paragenesis paragenesis to and their their internal internalevolution. evolution. and One large large pegmatite pegmatite in in particular particular was was studied studied in in detail. detail* One aa with in maximum dimension, This pegmatite may exceed 300m in maximum dimension, with 300m This pegmatite may exceed thickness of of up up to to 4.5m. 4.5m. The The pegmatite pegmatite invaded invaded the the surrounding surrounding thickness heavily country rock rock concordantly, frequently frequently engulfing engulfing heavily concordantly, country tourmalinized screens screens of of country country rock rock in in the the pegrnatite pegmatite and and tourmalinized causing tourmalinization tourmalinization in in the the surrounding surrounding countr' countryrock rock as well, causing as well. 0 The The pegmatite pegmatite strikes strikes N20 ~ 200W'to to ~ N35 ~ 3 05W'and ~ and dips dips 60 60 —65 -65" in in aa westerly westerly exhibits a striking partitioning direction. This This pegrnatite pegmatite exhibits partitioning of of Mn Mn direction. and Fe Fe along along its its length. length. The The northern northern end end is is Mn-enriched Mn-enriched and and and contains tourmaline tourmaline var. var. rubellite, rubellite, lepidolite, l e p i d ~ l i t e ~spodumene, spodumene, contains and mangano—columbite/tantalite, lithiophilite, fillowite mangano-columbite/tantaliteà and fillowite lithiophilite, The southern rhodizite, besides besides quartz, quartz, microcline, microcline, and and albite. albite. The southern rhodizite, segment is is enriched enriched in in both both Mn Mn and and Fe Fe and and lacks lacks lithiophilite lithiophilite and and segment rnangan— heterosite—purpurite, fillowite, containing instead heterosite-purpurite, manganinstead containing fillowite, Spodumene mangan-huhnerkobelite(?la Spodumene occurs occurs alluaudite, and and mangan-huhnerkobelite(?). alluaudite, abundantly in in the the core core zones zones in in crystals crystals several several times times larger larger abundantly than those those from from the the northern northern segment. seqment. Rubellite Rubellite does does not not occur occur than in this this section section but but Fe—rich Fe-rich blue—black blue-black tourmaline tourmaline is is found found ininits its in place. place. The tourmaline tourmaline in in both both segments segments occur occur in in large large quantity quantity in in The the outer outer wall wall and and contact contact zone, zone, as as well well as as in in the the inner inner the lack of of tourmaline tourmaline in in most most of of the the other other intermediate zone. zone. AA lack intermediate All phosphates appear with tourmaline zones is is conspicuous. conspicuous. All phosphates appear with tourmaline in in zones the inner inner intermediate intermediate zone zone and and the the core core zone. zone. They They are are absent absent the in the the other other units. units. in From country country rock rock distortion distortion it it appears appears that that the the intruding intruding From The south—easterly direction. pegmatitic melt invaded from a south-easterly direction. The from a invaded pegmatitic melt the most likely likely source source of of this this and and neighboring neiqhborinq pegmatites pegmatites is is the most Hoskin Hoskin Lake Lake granite, granite, aa Precambrian Precambrian intrusive intrusive of of an an age age of of 1,650 1,650 million years. years. million The following following list list of of minerals minerals has has been been identified identified to to The date (EDS, (EDS,petrographically petrographically and and by by wet wet chemistry): chemistry): date . in the the Microcline-oerthits is is the the most most abundant abundant mineral mineral phase phase in Microcline-perthit The color It forms blocky grains up to 15 cm across. pegmatite. It forms blocky grains up to 15 c m across. The color pegmatite. ranges from from grayish grayish white white in in the the northern northern segment segment to to reddish reddish in in ranges the southern section, the southern section. Albite, Albite, var. var. cleavelandite, cleavelandite, evidently evidently with with low lowanorthite anorthitecontent, content, is widespread widespread and and also also forms formslate latestage stagemetasornatic metasomatic units. units. The The is color ranges ranges from from aa bluish bluish gray gray to to white white to to red red brown. brown. color 26 �Quartz, of of aa distinctly distinctly gray gray (and (and not not smoky) smoky) color color is is less less abundant than than the the feldspars. feldspars. Masses up to to several several tens tens of of centimeters occur occur occasionally. occasionally. (rubellitel occurs abundantly abundantly in in Tourmaline, variety, elbaite (rubellite) some of the the zones. zones. Deep-blue tourmaline appears appears to to be be an an elbaite elbaite var iety. variety. Spodumeme strictly S ~ o d ~ m e moccurs e strictly in in the the core core zones. zones. Crystals up to to 30 30 cm have been recovered from the core zones in in the southern segment. segment. Lepidolite Leoidolite is is abundant throughout the pegmatite and forms forms patches patches and stringers of purple to pinkish—lilac pinkish-lilac or rarely yellowish flakes (commonly (commonly around 1—2mm 1-2mm in in diameter) diameter) and and masses masses and and occasionally some coarse books books up up to to 1.5cm 1.5cm in in diameter. diameter. Polytlithionite has been identified identified from from near the spodumene core cors masses resembling topaz where it it is found in masses topaz crystals crystals in in outline, outline, thus possibly indicating complete alteration of earlier existing topaz. topaz. The size of these lumps lumps ranged from from 1cm 1cm to to 6cm, 6cm, the the color color greenish yellow. is a greenish yellow. muscovite has been tentatively identified from a patch in Lithian muscovite in where it occurs as bright golden-yellow the intermediate zone where books up to to 5mm 5mm across. across. ADatite occurs throughout the pegmatite pegmatite with the bulk Apatite bulk near the blue, the size up to 5mm in contact. The color is deep blue, in maximum contact. dimension. Apatite occurs also as the white core in dimension. in lithiophilite nodules near the the spodumene spodumene core. core. It is rimmed by lithiophilite and finally finally by by fillowite. fillowite. Lithiophilite Lithioohilite occurs in in the intermediate intermediate and core zones zones of of the the northern segment. northern segment. The size of the nodules nodules reaches reaches aa maximum maximum of of 2cm, Zcm, and generally has a tan to to salmon-pink salmon-pink color, color, in in some some cases cases rimmed by black Mn-oxides. Mn-oxides. Fillowite occurs as a light light tan tan rim rim over over lithiophilite lithiophilite nodules. nodules' Heterosite-~urourite Heterosite-purDurite of the Fe-richer Fe-richer variety was found only at purplish—brown the southern segment as nodules up to 3cm and of purplish-brown color, rimmed by a so far unidentified unidentified white white mineral mineral and be an outer layer layer of of light light blue blue tourmaline. tourmaline. Mangan-alluaudite also was only Manuan-alluaudite only found found at at the the southern southern segment. segment. olive—brown nodules up to 2cm 2cm in in diameter.Mangandiameter.ManganIt formed olive-brown huhnerkobelite occurs with mangan-alluaudite as as brownish brownish masses masses up to 1cm 1cm in in diameter. diameter. This is is the first first reported reported occurance occurance for for this Mn-rich Mn-rich variety. variety. Mangan—huhnerkobelite Mancran-huhnerkobelite occurs occurs with with mangan-alluaudite mangan-alluaudite as as brownish brownish masses up to to 1cm 1cm in in diameter. diameter. This is is the first first reported reported occurance for for this this Mn—rich Mn-rich variety. variety. 27 �Mangano—columbite Yanqano-columbite and mangano-tantalite manqano-tantalite both occur occur throughout throughout the the pegmatite in in small amounts in in crystals of reddish-black color, color, up up 2mm in in maximum maximum dimension. dimension. It is remarkable that both both occurred occurred to 2mm only mm apart in in the the same same sample. sample. Rhodizite is is probably the most remarkable mineral from from the the pegrnatite. glassy, tan colored grains up to 4mm pegmatite* It was found as glassy, 4mm near the contact contact of of the the intermediate intermediate and and wall wall zones. zones. Only Only 22 other localities produced rhodizite: the first first is is near Swerdlovskz, in the Wral Ural Mountains., Mountains., USSR, and the second is Swerdlovskz, is near Mania, Madagascar. Madagascar. The internal internal evolution is is believed to have taken taken the the following pegmatitic magma, magma, highly enriched in following path: path: The pegmatitic in volatiles, Li, Rb, Cs, B invaded invaded the country country rock rock along along bedding bedding planes and planes of of weakness. weakness. Some partial melting meltinq of of the the of country rock may also have occurred, liberating the alkalies of low meltinq melting point and and possibly possibly B. B. A thin contact contact zone z o n e up up to to e.l few mm formed first, immediately followed by a thick wall zone zone up up to 20 2 0 cm. c m * Possibly at this time an interfering influence, influence! either a fluid phase contributed by b y the country rock, or a ph/Eh differential, caused NAA caused profuse profuse crystallization crystallization of of tourmaline, tourmalineo NAA data suggest suggest that the rubellite may indeed indeed have have formed formed relatively relatively Cs. early, despite its its high Mn/Fe Mn/Fe ratio, ratio, it it is is very very low low in in Rb Rb and and Cs. These elements occur abundantly abundantly in in the the deep deep blue blue tourmaline, tourmaline, indicating a higher degree of differentiation. indicatinq differentiationm As the the intermediate zones began began E forming, magma fluxed by lithium intermediate o ~ m i n gaa~ magma prevented precipitation of tourmaline and tetraborate may have prevented inner phosphates (due (due to lack lack of of aqueous aqueous fluid), fluid). Once the inner intermediate zone began to form, form, free free aqueous aqueous fluid fluid began began to to exsolve, resulting in destabilizing of the tetraborate flux, fluxf and an2 in crystallization crystallization of large amounts of of tourmaline tourmaline and and phosphates. phosphatese The fluids enriched in Li eventually gave rise to the spodumene core and to replacement units of lepidolite and albite throughout throuqhout the pegmatite. pegmatite- Finally, escaping fluids, rich in in B, created aa tourmalizied halo in in the the surrounding surrounding country country rock. rock. miarolitic cavities in To date, no evidence of miarolitic in the pegmatite has been been found. found. , 28 �Paleomagnetism Paleomagnetisn of of Keweenawan Keweenawan Age Age Basalts Basalts From From The The Taylor Taylor Falls-St. Falls-St. Croix Croix Falls Falls Area Area of of Wisconsin Wisconsin and and Minnesota Minnesota John John Feeney Feeney and and William F e Kean Kean William F. Department Department of 05 Geosciences Geosciences University of of Wisconsin-Nil'iaukee Wisconsin-KilGaukee University Milwaukee, Milwaukee, WI WI 53201 5320 1 Ten Ten oriented oriented hand hand samples samples from from the the St. St. Croix Croix Falls Falls area area were measured measured for for magnetic magnetic characteristics. characteristics. A.F. A.F. demagnetidemagnetiwere zation zation and remanence remanence acquisition acquisition studies studies indicate indicate that that the the remanence remanence is is carried carried by by magnetite. magnetite. Most Most samples samples show show aa single single The paleopole paleopole directions directions are $re component of of magnetization. magnetization. The component predominately with latitudes latitudes ranging ranging from from S40 S40° to to ~10' Nb0 predominatelv reversed with The The basalts basalts are are probably probably middle middle Keweenawan Keweenawan in in age, age, based based on on known known reversal reversal patterns patterns for for Keweenawan Keweenawan time. time. 29 �APPLICATION OF OF WERNER DECONVOLUTION TO THE THE PENOKEAN PENOKEAN BELT9EAST-CENTRAL EAST-CENTRAL MINNESOTA MINNESOTA FOLD-AND-THRUST BELT, R.J. FERDERER FEFUIERER (Department (Department of Geology Geology and and Geophysics, Geophysics, University University of Minnesota, Minnesota7 R.J. Minneapolis, MN 55455; Minneapolis, 55455; and Minnesota Geological Survey, 2642 University Ave., St. 55114) Ave., St, Paul, MN 55114) The geology of the Penokean orogen in east-central Minnesota has recently been reinterpreted by Southwick Southwick and others others <1988). (1988). These authors authors have have divided divided the the orogen orogen several tectonic elements, elements, including including a fold-and-thrust fold-and-thrust belt and and the main bowl bowl of the the into several Animikie basin. The fold-and-thrust fold-and-thrust belt ?At has been further further divided divided into into three three zones zones which which Animilcie basin. The The discontinuities discon~uities are defined defined by are bounded by major structural discontinuities. The are changes metamorphic grade, stratigraphy, stratigraphy, and structural structural style. changes in metamorphic defining structures structures Werner deconvolution has proven to be a useful tool for defining This inverse inverse magnetic magnetic modeling modeling associated with the Penokean fold-and-thrust belt* belt. This technique (k)or or thickness, thickness, and and dip dip estimates estimates technique yields yields position, position9depth, depth, susceptibility susceptibility contrast contrast (k) for anomaly sources by thin thin sheets sheets or or planar planar interfacesinterfaces, Results sources that can be approximated by Results the above-mentioned above-mentioned obtained within two areas areas that lie along dong two of the presented here were obtained nature. structural discontinuities, and provide new information on their name. One area studied straddles the Malmo M a h o structural discontinuity, discontinuity, a southwardsouthwarddipping dipping thrust zone zone that that separates separates the internal internal and and medial zones zones of the fold-and-thrust fold-and-thst belt. The beltThe presence presence of of this this feature featureis is strongly strongly supported supported by a magnetotelluric modeling Young, 1987). Consistent study ((Wunderman W u n d e m and Young? Consistent intermediate intemediate to steeply southward dipping along dipping thin sheet sheet solutions S O ~ ~ were O ~ obtaitied obtaified S dong the mapped location of the discontinuity discontinuity (Fig. 1). in this area (Fig I)*Depth Depth estimates estimateshave have an average average value of 95 m, m9and k estimates (calculated for a sheet thickness of 50 m) have an average value of 0.0230 cgs. cgs- The existence existence of consistent thin sheet solutions over a strike strike length of at least least implies that that the anomaly anomaly source source is related to the discontinuity, discontinuity,and and may may represent represent 40 km implies itself. Pyrrhotite-rich the fault zone itselfPynhotite-rich graphitic graphitic phyllite are common throughout the foldthrustaand-thrust n d - b s t belt and one of these units may have acted as a plane of slippage for the thrust. Alternatively, Alternatively, a layer layer of magnetite magnetite and/or pyrrhotite pynhotite may have formed formed in the the fault fault zone, zone, processes during during faulting, faulting,or or after afterdeformation* deformation. It is also associated with metamorphic processes conceivable conceivablethat that the thin sheet sheet solutions solutions represent a magnetic magnetic layer layer oriented oriented subparallel subparallel to to Formation. The presence of a northwest-trending, leftthe fault zone, within the Denham Formation. lateral strike-slip strike-slip fault fault is is also also indicated indicated (Fig. (Fig. 11b)). b)). A second second area of study lies on the boundary between the fold-and-thrust fold-and-thrust belt and and main bowl of the Animikie basin. basin. A the nuin A major major north-directed north-directed thrust is mapped in this elements mentioned area, as well as an unconformity between rocks of the two tectonic elements mentioned above. Holst Holst(1984) (1984)defined definedaa boundary boundary between between areas areas affected 'affected by one and by two major km east east of of this this area. area. The boundary was interpreted phases of folding, approximately 55 km to be the outermost limit of the hinge of a major north-directed, isoclinal, isoclinal9recumbent fold that is probably a thrust nappenappe. Southwick Southwickand and others others (1988) (1988) extended this boundary, boundaq, based on sparse sparse drilling drilling data, to the northeastern edge of the area considered here. here* 30 �Interface Interface solutions solutions were were obtained obtained north of the mapped mapped thrust fault, fault, and have have Thin sheet sheet solutions solutions were obtained over a orientations which are consistent with it. it. Thin distance along strike, north of the fault and south of the westward distance of greater greater than 15 15 km along Holst's boundary. boundary. Forward Forwardmodeling modelingwas wasperformed performedusing using both both interface interface extension of Hoist's sheet solutions solutions to establish establish which source type is more appropriate for the and thin sheet Thethin thin sheet sheet solutions solutions are are favored based on similarity between anomaly in question. The calculated calculated and and observed obsemed anomalies. anomalies. The Thethin thinsheet sheetsolutions solutionsdip dipapproximately approximately65° 650NN and and are are associated associated with with average averagedepth depth and and kk estimates estimatesof of 300 300m mand and0.0100 0.0100cgs, cgs, respectively. respectively. Because Because of the proximity of the thin sheet solutions solutions to the mapped location location of Holst's Holst'sboundary, boundary,ititisisproposed proposedthat thatthe thesheet sheetmay maycorrespond correspondto toaaunit, unit,possibly possiblyaalean lean iron-formation, located located within within the the nappe nappe hinge hinge so so that that northward northward dips dips would would be be expected. expected. iron-formation, The large large depth depth estimates estimates may may represent represent an an unconformity unconformity separating separating rocks rocks of of the the nappe nappe The h n t from from overlying overlying sediments sedimentsthat that were were derived derived from from the stacked stacked thrust thrust pile pile to to the the front south. ItItisisalso alsopossible possiblethat thatthe theupper upperportion portionof ofthe thenappe nappefront fronthas hasbeen beenfaulted faultedout, out, possibly possibly by by the thethrust thrustmapped mappedin inthis thisarea. area. For For both both of of the the areas areas considered, considered, the the absence absence of interface interface solutions solutions associated associated with thrust thrust faults faults may be be explained explained by a low susceptibility susceptibility contrast contrast between the footwall footwall and and hanging hanging wall. Except Exceptfor foriron-formation, iron-formation,most most supracrustal supracrustal rocks in the Penokean orogen wealdy magnetic. magnetic. Therefore, orogen in east-central Minnesota are weakly Therefore,strong strong susceptibility susceptibility contrasts contrastsacross acrosslow-angle low-anglefaults faultsininthese theserocks rocksare arenot notlikely. likely. Acknowledgments Acknowledgments This This research research was was funded funded by by the the Legislative Legislative Commission Commission on on Minnesota Minnesota Resources. Resources. References ReferencesCited Cited Holst, Holst, T.B., 1984, 1984, Evidence Evidencefor fornappe nappedevelopment developmentduring during the the early early Proterozoic Proterozoic Penokean Mimesota: Geology, Geology,v. v. 12, 12,p. p. 135-138. 135-138. Penokean orogeny, orogeny, Minnesota: Southwick, P.L., 1988, Geologic Southwick, D.L., Morey, G.B. and McSwiggen, P.L., Geologic map map (scale (scale 1:250,000) 1:250,000) of of the the Penokean Penokean orogen, orogen, east-central east-centralMinnesota, Minnesota,and andaccompanying accompanyingtext: text: Minnesota MinnesotaGeological GeologicalSurvey SurveyReport Reportof of Investigations Investigations37 37(in (inpress). press). Wunderman, Wunderman,R.L., R.L., and andYoung, Young,C.T., C.T., 1987, 1987,Evidence Evidencefor forwidespread widespreadbasement basement decollement decollementstructures structuresand and related related crustal crustal asymmetry asymmetry associated associated with with the the western western limb limbof of the theMidcontinent MidcontinentRift Rift(abs.): (abs.): Institute Instituteon onLake LakeSuperior superiorGeology, Geology, Proceedings Proceedingsand andAbstracts, Abstracts,v. v. 33, 33,Pt. pt. 1,1,p. p. 85-86. 85-86. 31 �• 0156 •353,2 1km II 069 and c) susceptibility contrast solutions, all obtained along the Malmo structural discontinuity. Depth estimates are in meters and susceptibility estimates are in cgs units, a •99 01 6. g Fig. 1, Werner deconvolution thin sheet; a) depth, b) dip, 069 •103 •ni•120 •96 •.Q22? S oi4• 02090 022 ?025.02b0 0302 2...1_j5BI ..os \ 3 O2O1 C °" ! b ________________________ 4 �An An investigation investigation into into the the chemical chemical processes processes causing causing the the formation adamellite of of Wisconsin Wisconsin formation of of unakite unakite in in the the Waupaca Waupaca adamellite JODY FRONK FRONK and and Dion Dion C. C. Stewart Stewart(Department (Departmentof ofGeology, Geology, JODY Bowling Bowling Green Green State State University, University, Bowling Bowling Green, Green,OH OH 43403) 43403) Unakite, Unakite, an an epidote-chlorite-rich epidote-chlorite-richred red granite, granite,is islocally locally developed developed in in the the Waupaca Waupaca ademellite, ademellite,which which is is the the southern southernmost most Inthe the pluton in in the the Wolf Wolf River River batholith batholith of of northern northernWisconsin. Wisconsin. In pluton Johnson Johnson Quarry Quarry near near the the city city of of Waupaca Waupaca the the unakite unakite occurs occursin in narrow (20 (20centimeter) centimeter)linear linearzones. zones. Forty Forty samples samples were were collected collected narrow at at regular regular one-meter one-meter intervals intervalson on two two traverses traversesrunning running perpendicularto tothese thesezones. zones. Detailed Detailed mapping mapping of of the the quarry quarry was was perpendicular used used to to establish establish the the orientation orientation of of the the zones zonesand and the thelocation locationof of each sample sample relative relative to to the the unakite unakitezone. zone. Both Both modal modal and and chemical chemical each analyses analyses were were conducted conducted on on the the rocks rocks and and their their consituent constituentminerals minerals from both both traverses. traverses. from Results Results show show that that unakite unakite occurrence occurrence is is spatially spatiallyrelated relatedto to the presence presence of of fracture fracturejoints. joints. Three Three distinct distinct zones zones are are the developed in in the the field field in in aa symmetrical symmetricalpattern pattern around around the the developed fracture joints. joints. Each Each zone zone can can be be characerized characerized by by its its mineral mineral fracture alterations and and either either the the formation formation and/or and/or disappearance disappearance of of alterations The outer most zone is represented by specific minerals. The outer most zone is represented by specific minerals. relatively relatively unaltered unaltered adamellite, adamellite,having having aa strongly strongly developed developed rapakivi rapakivi texture texture and and aa mode mode of of 17% 17% quartz, quartz, 11% 11% biotite, biotite, 62% 62% perthitic microcline, microcline, 6% 6 % plagioclase plagioclase (Ab (Ab== 93), 93), and and 4% 4% accessories accessories perthitic predominately predominately apatite, apatite, sphene, sphene,opaques opaques and and zircon. zircon. The The first first zone of of alteration alteration is is recognized recognized by by the the appearance appearance of of chlorite chlorite and and zone the progressive progressive disappearnce disappearnceof ofbiotite. biotite. The The second second zone zone is is the recognized recognized by by the the appearence appearence of of epidote epidote in in the the groundmass, groundmass,and and aa decrease in in the the amount amount of of microcline, microcline, which which becomes becomes progressively progressively decrease more red red in in handspecimen. handspecimen. The The central central zone, zone, in in the the fracture fracture more lineament, lineament, is is recognized recognized by by aa large large increase increase in in epidote epidote including including the the conversion conversion of of the the rapakivi rapakivi rims rims to to epidote, epidote, aa slight slight increase increase in plagioclase plagioclase (Ab (Ab== 99+), 99+), aa large large decrease decrease in in microcline, microcline, and and the the in conversion of of perthite perthite to to antiperthite antiperthite (bulk (bulkmineral mineral Ab=63, Ab=63, Or=36, Or=36, conversion An=l) An=1). . Mass balance balance calculations calculations using using modal modal abundances, abundances,mineral mineral Mass chemistry, chemistry, and and bulk bulk rock rock chemistry chemistry (both (bothmajor major oxides oxides and and trace trace elements) show show that that the the "unakitization" "unakitizationtl process is is accomplished accomplished by by elements) process both redistribution redistribution of of ions ions among among the the rock-forming rock-forming minerals minerals of of the the both adamellite adamellite and and the the addition addition and/or and/or subtraction subtraction of of ions ions to/from to/from the the rock by by aa hydrothermal hydrothermal fluid. fluid. Calcium Calcium is is redistributed redistributed from from rock plagioclase plagioclase to to epidote, epidote, and and is is added added to to the the rock rock by by the the fluid. fluid. Maanesium and and iron iron are are redistributed redistributed from from biotite biotite to to chlorite. chlorite. Magnesium Aluminium redistributed from from microcline microcline and and plagiolase plagiolase to to ~ l k i n i u mis is redistributed chlorite and and epidote. epidote. Sodium Sodium is is partially partially redistributed redistributed from from chlorite Potassium is is perthite perthite and and plagioclase plagioclase to to antiperthite antiperthite and and albite. albite. Potassium partially partially redistributed redistributed from from biotite biotite and and microcline microcline to to antiperthite, antiperthite, but but is is largely largely removed removed from from the the system system by by the the fluid. fluid. These These types types of of chemical chemical alteration alteration are are broadly broadly synonomous synonomous with with the the characteristics of of "propylitic "propyliticalteration". alteration". characteristics 33 �Genesis Genesis and and Metamorphism Metamorphism of of Magnetite Magnetite in in Biwabik Biwabik Iron—Formation, Iron-Formation,Mesabi Mesabi District, District, Minnesota Minnesota by by Tsu-Ming Tsu-Ming Han Han The The Cleveland—Cliffs Cleveland-Cliffs Iron IronCompany Company Abstract Abstract The The Bjwabik Biwabik iron—formation iron-formationin in the the Mesabi Mesabi District Districtextends extends east—northeast east-northeast for for contact The eastern end has been subjected to a progressive The eastern end has been subjected to a progressive contact about 120 miles. 120 miles. about Four metamorphic metamorphic metamorphism metamorphism by by the the intrusion intrusion of of the the Duluth Duluth Gabbro GabbroComplex. Complex. Four zones have have been been established established by by French French (1968) (1968) within within the the iron—formation iron-formation along along zones (Zone These zones zones are are unaltered unaltered (Zone the strike strike toward toward the the contact contact of of the the complex. complex. These the 3), and highly (Zone metamorphosed moderately 1 1, transitional (Zone 21, moderately metamorphosed (Zone 3 ) , and highly (Zone 2), transitional 1), metamorphosed (Zone (Zone W metamorphosed ). . iron-formation in in The following following diagram diagram shows shows the the mineralogy mineralogy of of the the Biwabik Biwabik iron—formation The Gabbro as a function of distance from the Duluth different metamorphic metamorphic zones zones as a function of distance from the Duluth Gabbro different contact. contact. tOO iltIl In 50 I—till ZONE 111111 0I I ZONE 4 ZONE 2 I i.. Gre.nolit. C)ianiosic — — Minnesotoite I a— U . a. Stilpnom.ton. FoIc o. 1.0 5 ai as Ñ — t3runer,te-Cummungtonite Orunentç-Cumm~nqton~t blend. Blue Blue•gr.en -green bern hornblende , Ned.nberqttt Hedenberqitt Ferroty.r3then. Foyalite i Quartz — Sideri?. — AnUritC •UI au I — — Hematite Magn.ttte ••• 111111 too 50 COlcite Calcite mmmm U... Pynt. u I.. Pyrrbef it, aaa 111111 I0 11111 l_......L_ I.0 5 Distance from f r o m Contact Contact (mtles) (miles) Distance Modified Modified from from French,(l968) French,(1968) 34 0.5 I I 0.I �This study study deals deals with with the the genesis genesis of of magnetite magnetite in in the the iron—formation, iron-formation,based based This on on its its internal internal microstructures, microstructures, and and the the effect effect of of the the progressive progressive metamorphism on on the the internal internal microstructures microstructures of of the the magnetite magnetite in in the the respective respective metamorphic metamorphic zones. zones. Polished sections sections prepared prepared from from the the magnetite—rich magnetite-rich specimens specimens of of the the iron— ironPolished formation formation were were microscopically microscopically examined examined and and reexamined, reexamined,before before and and after after an anininduced oxidation. oxidation. The The oxidation oxidation was was done done by by heating heating the the polished polished sections sections in in aa duced stagnant air air furnace furnace at at about about 300°C 300° for for three three to to four four days. days. This This oxidation oxidation stagnant process process is is rather rather selective selective and and takes takes place place along along either either or or both both the theoctahedral octahedral planes on planes or or the the preexisting preexisting structural structural weaknesses weaknesses of of the the magnetite, magnetite,depending depending on the degree degree of of metamorphism. metamorphism. the The The magnetite studied studied was was free free from from martitization, martitization, except except for for traces traces of of magnetite This magnetite occurs as granules, hematite hematite inclusions inclusions In in some someof of it. it. This magnetite occurs as granules, laminae, laminae, and and single single or or coalesced coalesced octahedra octahedra in in all all the the metamorphic metamorphic zones zones classified. classified. the induced oxidation results show the magnetite coexisting with However, the induced oxidation results show the magnetite coexisting with laylayHowever, ered type type silicates silicates oxidizes oxidizes along along the the preexisting preexisting structural structural weaknesses, weaknesses, ered whereas the the magnetite magnetite associated associated with with chain chain type type silicates silicates oxidizes oxidizes mostly mostly whereas along its its octahedral octahedral planes. planes. along In In the the unaltered unaltered and and transitional transitional zones, zones, the the hematite hematite generated generated by by the the ininduced oxidation oxidation of of magnetite magnetite outlines outlines the the size, size, morphology morphology and and microstructures microstructures duced of of the the preexisting preexisting inclusions inclusions within within the the magnetite. magnetite. These These inclusions inclusions have have been been The interpreted interpreted as as "preexisting l'preexisting hematite" hematite1' (Han (Han 1987 1987 and and 1986). 1986). The existing existing hematite inclusions inclusions observed observed in in the the magnetite magnetite before before the the induced induced oxidation oxidation are are hematite These actually actually unreplaced unreplaced portions portions of of the the preexisting preexisting hematite. hematite. These preexisting preexisting They hematite inclusions inclusions vary vary widely widely in in apparent apparent morphology. morphology. They may may be be platy, platy, hematite bladed, hexagonal, rhombohedral, colloform, wedge—shaped, and lath—shaped bladed, hexagonal, rhombohedral, colloform, wedge-shaped, lath-shaped or in in other irregular irregular forms. forms. They They exhibit exhibit various various types types of of microstructures, microstructures,such such as as other vuggy, vuggy, microgeodic, microgeodic, botryoidal, botryoidal, etc. etc. In In the the moderately moderately metamorphosed metamorphosed zone, zone, the the induced induced oxidation oxidation takes takes place place prinprincipally along along the the cleavage cleavage planes planes of of the the magnetite. magnetite. However, However, the the outlines outlines of of cipally the the preexisting preexisting hematite hematite inclusions inclusions and and their their arrangements arrangementsare are still still traceable traceable in most most of of the the specimens. specimens. in The magnetite magnetite from from the the highly highly metamorphosed zone zone oxidizes oxidizes almost exclusively exclusively The The internal internal microstructures microstructures created created by by the the preprealong along the the octahedral octahedral planes. planes. The existing hematite has been almost completely obliterated. existing hematite has been almost completely obliterated. Genetically, it it is is believed believed that that the the preexisting preexisting hematite hematite functioned functioned as as the the Genetically, principal principal nuclei nuclei responsible responsible for for the the development development of of much much of of the the magnetite magnetite in in the Biwabik Biwabik iron—formation. iron-formation. The The existing existing magnetite magnetite was was largely largely developed developed by the the bethe replacement replacement and and overgrowth overgrowth that that occurred occurred concurrently concurrently at at the the interface interface between tween the the hematite hematitenucleus nucleusand andits itsgarigue gangue host. host. The The development development varies varies in in magmagnitude from from very limited limited to to rather rather extensive, extensive, as as indicated indicated by by the the differences differences nitude in size size and morphology morphology between between the the existing existing magnetite magnetite and and its its nucleus. nucleus. In In gengenin magnetite larninae, existing eral, eral, the size, size, orientation orientation and and outlines outlines of of the the existing magnetite laminae, granules, granules, and and coalesced coalesced octahedra octahedra are are dictated dictated by by the the corresponding corresponding features featuresof of This clearly demonstrates that the magnetite is the preexisting hematite. This clearly demonstrates that the magnetite is not not preexisting hematite. the primary mineral mineral and and may may also also suggest suggest that that the the so—called so-called carbonate carbonate facies facies and and aa primary 35 �silicate facies fades either either originally originally contained contained hematite hematite or or were were oxide oxide fades facies bebemagnetitization, carbonatization, carbonatization, and fore the postdepositional postdepositional changes changes -- magnetitization, and fore the silication. silication. The The developed by overgrowth on, magnetite developed magnetite by the the replacement replacement of, of, and overgrowth on, hematite hematite centripetal ionic diffusion diffusion of Fe++ was apparently apparently the nuclei suggests that the centripetal the Iron was probably initially deposited process. Iron probably initially deposited as as aa key magnetite-forming magnetite—forming process. oxide gel ferric oxide gel associated associated with with siliceous siliceous mud. mud. This This gel gel could could have have dehydrated dehydrated to colloform layers and granules or could have crystallized to hematite cryscrysto tals with different different microstructures. microstructures. The gel could also have reacted with carsource for for the as a bon to produce produce Fe++ Fe++ which which served served as a principal principal source the magnetite magnetite development. development. The The magnitude magnitude of of magnetite magnetite enrichment enrichment was, was, of of course, course, determined determined by the Fe++ Fe++ supply which, in turn, turn, was controlled by the availability availability of of oxyoxyMagnetite development by centripetal and ferric oxide gel. gen, carbon, carbon, ferric oxide gel. centripetal difdifgen, early stages fusion fusion probably occurred occurred during during late late diagenesis diagenesis or or in in the the early stages of of regional regional metamorphism. metamorphism. References References Iron— French, B.M. B.M. 1986 Progressive Contact Metamorphism of the Biwabik IronFrench, Formation, Mesabi Range, Formation, Range, Minnesota. Minnesota. Minnesota Geological Survey Survey Bull. I5. 45. Microstruotures of Magnetite Magnetite as Guides Guides to Its Origin Origin in Some Han, T.M. Han, T.M. 1978 Microstructures Fortschritte der Precambrian Iron—Formations. Precambrian Iron-Formations. Fortschritte der Mineralogie, Mineralogie, Vol. Vol. 56, 56, p. 1O5—12. 105-142. Origin of Magnetite Magnetite in Precambrian Iron-Formations Iron—Formations of Han, T.M. (in (in press) Origin Han, T.M. Abstr. Terra Terra Cognita, Low Metamorphic Grade. Abstr. Cognita, The The Journal Journal of of the the Metamorphic Grade. 6, 1986, Union of of Geosciences, Geosciences, No. No. 3, 3, Vol. 6, 1986, p. 563. 563. European Union 36 �SCIENTIFIC SCIENTIFICDRILLING DRILLINGINTO INTOTEE THEMIDCONTINENT MIDCONTINENT RIFT RIFTSYSTEM SYSTEM William H i l l i a m j. J. Hinze(1) I?inzeO and and William W i l l i a m C. C . Kelly(2) Kelly (2) Approximately Approximately Minnesota Minnesota aa at at 100 100 geoscientists geoscientists workshop workshop entitled entitled recently recently convened convened "Scientific "Scientific in in Drilling Drilling Duluth, Duluth, of of the the of defining Midcontinent Rift R i f t System" Systemn ffor o r tthe h e purpose purpose of d e f i n i n g the t h e generic g e n e r i c and and Midcontinent s p e c i f i c scientific s c i e n t i f i c objectives o b j e c t i v e s of' of drilling drilling specific into into the Rift t h e Midcontinent Midcontinent Rift System and and to t o recommend recommend and and prioritize p r i o r i t i z e drilling d r i l l i n g sites. sites. System was was sponsored by by sponsored Deep Deep Continental Crust, Crust, Inc., Inc., Continental Observation Observation paleo-rift paleo—rift midcontinent midcontinent Sampling Sampling of of the the Earth's Earth's the t h e Department Department of of Energy Energy and and several s e v e r a l state state surveys MRC. surveys interested i n t e r e s t e d in i n the t h e MRC. old old and and This This workshop workshop , The The Midcontinent Midcontinent Rift R i f t (MCR), (MCR) an an 1100 1100 Ma Ma system system extending extending for f o r more more than than 2000 2000 km km across a c r o s s the the region, region, offers offers excellent excellent opportunities opportunities for for studying studying well as a s problems problems dealing d e a l i n g with with the the c o n t i n e n t a l rifting r i f t i n g processes processes as a s well continental e v o l u t i o n of of continents. continents. evolution The The MCR MCR is is unique unique among among rifts rifts because because it it contains m of c o n t a i n s as a s much aass 30 km o f rift—related r i f t - r e l a t e d volcanic volcanic and and sedimentary sedimentary rocis rocics Ga were were and several s e v e r a l crustal c r u s t a l provinces provinces having having aa range range in i n age age of o f about about 22 Ga and c u t by by the t h e crustal c r u s t a l disruption. disruption. cut Our direct d i r e c t knowledge knowledge oof f the t h e MCR MCR is i s largely l a r g e l y limited l i m i t e d to t o evidence evidence obtained obtained from restricted restricted from outcrops outcrops in in the the Lake Lake Superior S u p e r i o r region region and and cuttings r i f t is is c u t t i n g s obtained obtained from from widely distributed d i s t r i b u t e d drill d r i l l holes h o l e s where the t h e rift covered covered by Phanerozoic Phanerozoic by geophysical geophysical have have studies s t u d i e s and and sedimentary sedimentary rocks rocks of of the the craton. craton. However, However, drilling d r i l l i n g of of the t h e overlying overlying Phanerozoic Phanerozoic strata strata pinpointed manya rareas alongt hthe pinpointed many e a s along e l elength n g t h o foft hthe e rrift i f t where where hholes o l e s less less ( 1 ) Department Department of of Earth Earth and and Atmospheric Sciences, Purdue Purdue University, University, (1) West West Lafayette, IN I N 147907 47907 ( 2 ) Department of of Geological Geological Sciences, Sciences, (2) University MI University of of Michigan, Ann Ann Arbor, Arbor, MI 37 1006 C.C. 1006 C.C. 148109—1063 48109-1063 Little L i t t l e Building, Building, �than 5-ian 5-KIU iin n depth can bbee drilled d r i l l e d to t o adequately adequately sample sample the t h e Proterozoic Proterozoic rocks and investigate i n v e s t i g a t e their t h e i r stratigraphic s t r a t i g r a p h i c and and structural s t r u c t u r a l relationships. relationships. These relationships and the These r e l a t i o n s h i p s and t h e sampled rocks rocks can can ne De used used to t o study study the t n e two two MCR: primary scientific s c i e n t i f i c objectives o b j e c t i v e s of of' drilling d r i l l i n g into i n t o the t h e MCR: 11)) To investigate i n v e s t i g a t e the t h e physical p h y s i c a l and snd chemical chemical processes processes involved involved in in the of ccontinental rifts, sspecifically MCR; and and p e c i f i c a l l y tthe h e MCR; t h e origin o r i g i n and eevolution v o l u t i o n of o n t i n e n t a l rifts* To To 2) 2) continental continental iinvestigate n v e s t i g a t e crust crust rrifting ifting process; and mantle specifically specifically interaction interaction to to identify identify during tthe he the the mantle reservoirs r e s e r v o i r s iin n the t h e continental c o n t i n e n t a l lithosphere l i t h o s p h e r e and and the t h e asthenosphere asthenosphere that that have hzve acted acted aass sources ffor o r rift rift basalts b a s a l t s and presumably presumably reflect r e f l e c t tthe he differing d i f f e r i n g ages of of the t h e crust c r u s t and the t h e related r e l a t e d mantle. mantle. These two two primary following reasons. reasons. themes aare re pparticularly articularly attractive attractive for for tthe he First, F i r s t * they are a r e focused focused on on major major geologic g e o l o g i c problems problems broad ggeneric which can be a applied having broad e n e r i c implications, i m p l i c a t i o n s , which p p l i e d to t o the t h e study s t u d y of of rifts. oother t h e r intraplate i n t r a p l a t e rifts. Second, they Second, t h e y can be be addressed addressed only o n l y with with fresh fresh samples obtained by drilling; samples d r i l l i n g ; existing e x i s t i n g outcrops outcrops and and drill d r i l l hole hole samples samples aare r e inadequate. inadequate. initially, initially, Third, tthe Third* h e drilling d r i l l i n g program program can can be staged staged such such that that can be be made ssignificant i g n i f i c a n t pprogress r o g r e s s can made with with several s e v e r a l relatively relatively low—cost low-cost shallow to t o intermediate i n t e r m e d i a t e depth hholes, o l e s , the t h e results r e s u l t s of o f which will will serve s e r v e to t o aid a i d in i n siting s i t i n g and prioritizing p r i o r i t i z i n g possible p o s s i b l e deeper holes. holes. Fourth, Fourth* ddrilling r i l l i n g tto o achieve achieve the t h e purposes purposes of of the t h e primary primary themes themes will w i l l provide provide a basic basic framework iinto n t o which oother ther sstudies, tudies, such aass sedimentology, geophysics, geophysics, metamorphic geology, geology, fluid f l u i d chemistry and movement, movement* etc. e t c . can can / be integrated. integrated. In I n fact, f a c t , the t h e vast v a s t majority m a j o r i t y of of the t h e "secondary nsecondary science" sciencew oobjectives b j e c t i v e s aare r e really r e a l l y essential e s s e n t i a l ingredients i n g r e d i e n t s that t h a t support support the t h e primary primary themes. Fifth, wee anticipate a n t i c i p a t e that t h a t the t h e drilling d r i l l i n g environment environment of of the t h e MCR 14CR F ifth* w will w i l l be be as as benign benign as a s one one can can expect expect to t o encounter. encounter. Finally, F i n a l l y , and and most most significantly, s i g n i f i c a n t l y y tthe h e two two primary primary objectives O D J ~ C ~can, c~a nV* ~ffor oSr the t h e most most part, p a r t * be be achieved with core c o r e samples samples from from the t h e same same drill d r i l l holes. holes. 38 �We W e propose propose as a s aa first first stage s t a g e of of the t h e MCR MCR drilling d r i l l i n g program program two two 3.5— 3.5- to to J4.5—im—deep first iin 4.5-Km-deep ddrill r i l l hholes, o l e s , tthe h e first n southern Minnesota and and the t h e second second i n northern northern Kansas. Kansas. in Because Ekcause of of our our current c u r r e n t knowledge, knowledge, the t h e drilling drilling program could be initiated i n the t h e near near future f u t u r e with with minimum minimum pre—drilling pre-drilling i n i t i a t e d in studies. studies. In we recommend recommend that t h a t site s i t e selection s e l e c t i o n studies s t u d i e s begin begin in in I n addition, a d d i t i o n , we the t h e eastern e a s t e r n Northern Northern Peninsula of Michigan, Michigan, for f o r the t h e purpose purpose of of locating locating d r i l l sites sites to t o sample sample the t h e 20—km—thick 20-km-thick tholeiitio t h o l e i i t i c basalt b a s a l t section s e c t i o n in in drill eastern Lake Superior. Superior. e a s t e r n Lake 39 �ANIMIKIEGROUP: GROUP: A A PENOKEAN PENOKEAN FOREDEEP? FOREDEEP? ANIMIKIE Paul F. F. Hoffman Hoffman Geological Survey Survey of of Canada, Canada, 312-538 Booth St St., Ottawa, Ontario Ontario KIA K 1A 0E4 OE4 Geological 3 12-588 Booth ., Foredeeps (foreland (forelandbasins) basins)a rare linearasymmetric asymmetricbasins basinst hthat migrate in in front front of, Foredeeps e linear a t migrate and They develop (Fig. 1). 1). They and become become incorporated incorporated within, within, foreland foreland thrust-fold thrust-fold belts belts (Fig. of the continental thrust sheets. as a flexural flexural response response to t o loading loading of continental lithosphere lithosphere bby y thrust sheets. Many foredeeps evolve evolve from from oceanic trenches when ted ccontinental Many foredeeps when rif rifted m t h e n t a l margins margins are are drawn into into subduction subduction zones zones(Fige (Fig.219 2),but butthey theymay mayalso alsoresult result from from intracontinental intracontinental drawn thrusting. Taiwan thrusting. Taiwan Strait, Strait,the t h ePersian-Arabian Persian-Arabian Gulf, Gulf, and and the t h e Ganges Ganges River River basin basin aare re examples of active foreJeeps f o r d e e p s in in progressive progressive stages of of devlopment. examples of Active in front by by flexural flexural forebulges forebulges and and behind behind by by Active foredeeps foredeeps are bounded bounded in progradirig thrust-fold belts (Fig. Foredeep migration migratim causes causes diachronous diachronous prograding thrust-fold (Fig. 3). Foredeep of lithofacies, deposition of lithofacies, recognized recognized by by the t h efollowing following diagnostic diagnostic stratigraphic stratigraphic sequence (fig. 4): sequence (Fig. 4): (1) (1) pre-foredeep p r e - f o r d e e p deposits deposits (e.g. (e.g, passive-margin passive-margin shelf shelf sediments); sediments); (2) short-lived erosional disconformity caused by by the (2) short-lived erosional discmformity caused t h e migrating migrating forebulge; forebulge; (3) (3) transgressive outer-ramp outer-ramp (strandline (strandline ttoo foreslope) transgressive foreslope) lithofacies; lithofacies; (4) axial axial turbidites, whIch may shoal upward which m a y shoal upward tto o fluvial fluvial sediments sediments that that are a r ecommonly commmly eroded eroded away away during immediately immediatelysubsequent subsequentthrust-fold thrust-folddeformation. deformation. Foredeep outer-ramps aare during Foredeep outer-ramps re possibly caused caused by commonly broken by normal commonly broken normal faults, possibly by lithospheric lithospheric bending bending stresses. The stresses. The outer-ramp outer-ramp lithofacies lithofacies are a r e typically typically chemical, chemical, starved starved of of terrigenous terrigenous sediment, from areas of of sediment, and and the t h e axial axial turbidites turbidites are arecommonly commonly derived derived along strike from more However, m o r e advanced advanced orogeny orogeny (e.g. (eeg. foreland promontories). p r m on tories). Xowever , terrigenous terrigenous sediments in in some some foredeeps foredeeps may may be be derived derived directly directly from from tthe sediments h e foreland foreland (e.g. (e.g. Nile Nile of tthe ccone o n e of h e eastern Mediterranean). Mediterranean). The Group (Marquette (Marquette Range one of of several possible The Animikie Animikie Group Range Supergroup) Supergroup) isis me possible foredeep sequences sequencesofof Early Early Proterozoic Proterozoic aage identified in in the foredeep g e identified t h e Canadian Canadian shield shield on thwnflexed Archn crust (Hoffman, 1987). It It was was deposited deposited on cbwnflexed Archean crust between between the the (Hoffman, 1987). Penokean thrust-fold Penokean thrust-fold belt tto o the t h e south, south, related related to accretion of the t h e Early Proterozoic island-arc island-arc terrane of Wiscmsin, and and the t h e Archean Archean foreland foreland to to Proterozoic of central centralWisconsin, pre-foredeepdeposits deposits aare tthe h e north. north. Accordingly, Accordingly, t hthe e pre-foredeep r e tthe h e Milles Milles Lacs Lacs and/or and/or Chocolay groups, groups, outer-ramp outer-ramp sediments sediments are represented represented by bythe t h eMenominee Menominee Group, Group, Chocolay and and the t h e axial axial deposits deposits by by the t h eBaraga Baraga Group. Group. As As with other other Early Early Proterozoic Proterozoic foredeeps in in Canada, foredeeps Canada, the t h e Animikie Animikie Group Group is characterized characterized by outer-ramp outer-ramp ironironfformation o r m a t i m and axial tholeiitic tholeiitic volcanism. volcanism. Traditionally, tthe h e Animikie Animikie Group a s an a n evolving evolving passivepassiveTraditionally, Group has has been been interpreted interpreted as margin prism. prism. Testable margin Testable predictions predictions of of the t h e foredeep foredeep model model for for the t h eAnimikie Animikie Group Group are: (1) (1) the t h e age a g e of of Animikie Animikie Group Group deposition deposition (U-Pb (U-Pb dating of of flows oorr tuffs) should be close close to be t o that t h a t of of the t h ePenokean Penokeanorogeny orogeny(ca. (ca. 1.85 1.85Ga), Gal, and and(2) (2) the t h eAnimikie Animikie Group Group m a y be be derived derived from from the t h e Early Early Proterozoic Proterozoic arc a r c terrain terrain (U-Pb (U-Pb dating dating of of turbidites may detrital zircons detrital zircons or o r Nd-Sm Nd-Sm model model age a g e of of terrigenous terrigenous sediment). sediment). However, However, an an Archean source source terrain is Archean is not not excluded excluded in the t h e foredeep foredeep model. model. Preliminary PreliminaryNd-Sm Nd-Sm to an a n Early E k l y Proterozoic Proterozoic source source for for the t h eAnimikie Animikie Group Group turbidites turbidites ddata a t a point point to al., 1987, 1987, 1988). 1988). ( k o v i c h et a!., (Barovich References Barovich, K.M., Ekovich, K.M., Patchett, P.J., a n d Peterman, Peterman, Z., 2,1987, 1987, Origin Origin of of 1.9-1.7 1.9-1.7 Ga P.L, and Penokean continental crust of Penokean ctntinental of the t h eLake LakeSuperior Superiorregion: regim :Eos, Eos, v.68, v.68, p.1547. p.1547. Barovich, K.M., Z.E., and a n dSims, Sims, P.K., P.K., 1988, 1988, Nd Nd isotopes isotopes K.M., Patchett, P.L, P.J., Peterman, Peterman, Z.E., and tthe h e origin of 1.9-1.7 1.9-1.7 Ga Penokean Penokean continental t h e Lake Lake Superior Superior continental crust of the region: Geological region: Geological Society Society of America Bulletin, Bulletin, in review. review. Hoffman, P.F., P.F., 1987, Early Proterozoic foredeeps, foredeep Hoffman, 1987, Early foredeep magmatism, magmatism, and and Superior-type iron-formations h e Canadian Canadian shield, shield, in Proterozoic Superior-type iron-formations of of tthe Uthospheric r k e rA., A*, , ed., ed American AmericanGeophysical Geophysical Union, Union, Evolutim :~Krner, Lithospheric Evolution: Geodynamics Series, v.17, Geodynamics v.17, p.85-98. p.85-98. ., 40 �___ ____ Paul F. F. Hoffman Hoffman ANIMIKIE GROUP: A A PEPJOKEAN PENOKEAN FOREDEEP? ANIMIKIE GROUR fold-and-thrust FOREDEEP outer clS pheric ntinentol crust i i i ::::. :::: :: : mantle o an ic crust F'oceanic fold—and- I I fold-and* 00 0 100 200 300 + 4:0 with foredeeps foredeeps Fig. Fig. 1. 1. Tectonic elements associated with and nomenclature used usedininthis this paper. paper. Note the step-like and nomenclature step-like a m p The The geonormal faults forming h e outer normal forming on on tthe outer rramp. IS strictly strictly schescheof the fold-and-thrust fold-and-thrust belt is metric form of matic. — active I foredeep - II II m IIIItUlt!!IlI!tIIIlIIIlII I I initial-rif passive-margin trench-foredeep initial-riftt passive-margin trenchforedeep deposits deposits deposits deposits Fig. 2. Evolution of an an oceanic trench (A) Fig. Evolution of (A) into a foresubduction of rifted deep (B) by byattempted attempted subduction of a rif ted continental a l margin. margin. direction of direction of foredeep migration '" I.,., flexed plate foredeep deposits iron sb ssei r m j fold—and—thrust fold-and-thrust wedge wedge Foredeep migration migration causes the site s i t emarked marked by by Fig. 3. Foredeep Fig. a black triangle to t o experience uplift and erosion erosion aatt time 12, deposition deposition of of outer-ramp outer-ramp sediment aatt 13, T2, T3, deposition deposition of axial-zone axial-zone sediment sediment aatt 14, of T4, and incorporation into the the allochthonouswedge wedgeaat 15. Note actively deforming deforming allochthonous t T5. of the the progressive progressive sedimentary infilling of t h e foredeep foredeep diachronous process also in a direction with time, aa diachronous parallel to t o the the foredeep foredeep axis. axis. 41 fluvial "molasse" "molasse" m . • outer—ramp outer-romp ddeposits eposits I I 1 axial turbidites axial sequence pre-foredeep sequence stratigraphic sequences. sequences. Fig. 4. Typical foredeep stratigraphic Middle columncorresponds correspondst to site of of the black Middle column o tthe h e site black Figure 3. Paleocurrent directions directions are a r e mainly mainly triangle in Figure 3. Paleocurrent axial. �BANQUET BANQUET TALK TALK UNITED PLATES O OFF AMERICA: ORIGIN AND AND EARLY EARLY EVOLUTION EVOLUTION OF OF LAURENTIA LAURENTIA (2.0 (2.0 TO TO 1.0 Ga) 1.0 Gal F. Hoffman Hoffman Paul F. Geological SurveyofofCanada, Carda, 312-588 Booth Booth St., St., Ottawa, Ont. KIA OE4 0E4 Geological Survey The me stable Precambrian Precambrian lithosphere lithosphere of of North North America America and and Greenland Greenland (Laurentia) (Laurentia) isis weldedby byaa system of 2.0 system of 2.0 - 1.8 Ga Ga aan n aggregate aggregate of of former former microccntinents, micmcmtinents, welded The microcontinents, microcontinents, clustered clustered in in tthe colEsion (Hoffman, 1988). 1988). The h e northern na-them collision zones (Hoffman, mainly of of Archean two-thirds of of Laurentia, are composed composed mainly Archean crust. crust. The collision collision two-thirds Laurentia, are forelands have have sheif-foredeep zones (Fig. zones (Fig. 1) 1) are a r e asymmetric: asymmetric: their their forelands shelf-foredeep prisms prisms of of relatively low low metamorphic metamorphic grade, grade, deformed deformed by byearly earlythin-skinned thin-skinned thrusting thrustingarK! and subsequent thick-skinned folding; folding;their their hinterlands hinterlands have have linear calc-alkaline subsequent thick-skinned calc-alkaline and and crustal-aratectic crustal-ana t e c t i c magmatic magmatic zones, zones, and and systems systems of of obliqueoblique- and and strike-slip str ike-slip shear shear zones andlor post-collisional post-collisional indentation-extrusion indentationextrusion zones related to to oblique oblique subduction subduction and/or The inferred tectonics. The tectonics. inferred sutures sutures are arecommonly commonly cryptic, cryptic, but butthe t h eTrans-Hudson Trans-Hudson orogen preserves preserves a 400-km-wide orogen 4OO-km-wide internal zone in in Manitoba Manitoba and a n d Saskatchewan Saskatchewan that that belts of of former oceanic In northern northern Quebec, the ccontains m t a i n s belts oceanic island i s l a d arcs. In t h eforelarK! foreland of of the collision zone zone preserves preserves aa 400x80-km klippe inin which which a continentalt h e sai-ne same collision 400x80-km klippe continentalmargin is overthrust margin rift assemblage assemblage is overthrust by by transitional transitional oceanic oceanic crust, overthrust overthrust in in turn an imbricated imbricated ophiolite, ophiolite, complete complete with with "sheeted "sheeted dikes" dikesf1 and and maficmaficturn by by an al., 1988). The of the ultramafic cumulates The location location of t h e exposed exposed uitramafic a m u l a t e s (St-Onge (St-Onge et al., Precambrian shield, as as opposed opposedt to covered Precambrian Precambrian platform, platform, is apparently o tthe h e covered Precambrian shield, controlled by by tthe ccntrolled h e distribution distribution of of Archean Archean crust, crust, perhaps perhaps reflecting reflecting its i t s greater greater buoyancy due due tto depleted mantle lithosphere. lithosphere. buoyancy o aa depleted 3uvenile Proterozoic crust, composed of former Juvenile Proterozoic composed of former island island arcs a r c s and and other other oceanic oceanic crustal relics, was was accreted to t othe t h eassembled assembled microcontinents microcontinent s prior prior to t o 1.6 1.6 Ga Ga and and during western Laurentia, In western Laurentia, crust of of ca ca2.2 2.2 Ga Ga during tthe h e 1.25-1.0 1.25-1.0 Ga Ga Grenville Grenville orogeny. omgeny* In (LA.Bowring, &wring, aage g e was was accreted accreted beginning beginning about about 1.9 1.9 Ga GaininWopmay Wopmayorogen orogen(S.A. appears to unpublished data) and and appears t o be b ewidespread widespread ininthe t h parautochthonous(?) e parautochthcnous(?) Cordillera from from California California tto Alaska. In In southeastern and southern Laurentia, belts Cordillera o Alaska. Ga crust of 1.9-1.8 1.9-1.8 Ga crust were were accreted accreted in in the t h ePenokean Penokeanand andMakkovik-Ketilidian Makkovik-Ketilidian orogens, 1.8-1.7 1.8-1.7 Ga Ga crust crust in the t h e Yavapai-Central Yavapai-Central Plains Plains orogen, orogen, and and 1.7-1.6 1.7-1.6 Ga Ga orogens, crust in These belts extend in the t h eLabrador Labrador and and Mazatzal Mazatzalorogens omgens(Hoffman, (Hoffman, 1988). 1988). These extend crust for 5000 km along along strike (including Baltic equivalents) equivalents) and and total 1200 foe 5000 km (including Baltic 1200 km km in in width width south of Archean crust crust isis rrare of the t h eWyoming Wyoming province province (Fig. (Fig. 1). 1). Archean a r e tto o absent absent (Patchett about 1.7 1.7 Ga, Ga, aa possible possible sea-level sea-level highstand highstand resulted in and Arndt, 1986). 1986). Beginning Beginning about in the t h e deposition deposition of of clastic clastic sediments sediments in in widely distributed distributed cratonic basins basins (eg. (eg. Baraboo, Athabasca, Thelon, J3arabo0, lhelon, Hornby). Hornby). From at least least 1.5 1.5 to t o1.3 1.3 Ga, Ga, epizonal epizonalsyenogranite syenogranite batholiths batholiths and and layered layered gabbro gabbro From masfs and/or anorthosite anorthosite m a s g f s were wereemplaced emplaced across much of southern aand nd southeastern Laurentia. In In many many areas, areas, the t h eMiddle MiddleProterozoic Proterozoic"anorogenic" 'lanomgenict' magmatism lacks lacks associated associated rift rift faulting, thick magmatism thick alluvial alluvial sedimentation, sedimentation, and and syn-ri synqi fftt (isostatic) and and post-rift post -rift (thermal) (thermal)subsidence subsidence normally normally expected expected as asconsequences ccn sequences of lithospheric Rather than lithospheric stretching. Rather than attributing attributing the t h e magmatism magmatism to t o extensional extensional tectonism, it isis suggested above aa mantle mantle tectonism, suggested tthat h a t tthe h e then then young young Laurentia Laurentia sat above "superswell" (Pribac and Davies, superswells aare tlsuperswell'l Davies, 1987). Such Such superswells r e products products of deep deep convective upwellings, expressed as topographic ccnvective upwellings, expressed topographic and and geoidal geoidal highs highs arK! and hotspot hotspot clusters having having diameters diameterson on tthe clusters h e order order of of 5000 5000 km. km. The proposed proposed Middle Middle The Proterozoic caused thermal thermal erosion Protem zoic superswell superswell czused e m s i m of of the t h eLaurent Laurentian ian lithospheric lithospheric mantle, of mantle mantle melts melts into the continental crust, and mantle, injection injection of a n d extensive extensive crustal crustal melting. melting. Components Components of of uplift uplift were were both both temporary, temporary,due dueto t othermal thermalexpansion, expansion, and and permanent, permanent, due due to t o magmatic magmaticcrustal crustalunderplating underplating(McKenzie, (McKenzie, 1984). 1984). Only Only the the Archean cratons whose whose tectospheric tectospheric m roots Archean cratons o t s hal h d not not been been disrupted disrupted by, by, for for example, example, Early Proterozoic subduction zones remained relatively unaffected; unaf f e t e d ; Early Proterozoic crust crust was was extensively extensively remelted. - 42 �UNITED UNITED PLATES PLATESOF OFAMERICA AMERICA F. Hoffman Hoffman Paul F. Figure 1. 1. Precambrian Precambrian tectonic elements elements of of Laurentia Laurentia and and Baltica. Baltica. Uppercase FIgure Uppercase names are a r e Archean Archean provinces provinces (former (former microcontinents); microcont inent s); lowercase lowercase names names are are names Proterozoic orogens. orogens. Greenland Greenland is is restored restored prior prior to t orefting reftingfrom fromNorth NorthAmerica; America; Proterozoic Baltica possible pre-lapetus pre-Iapetus position. position. Abbreviations: Abbreviations:BH=Black BH=BlackHills; Hills; Baltica isisshown shown in in aapossible BL=Belcher foldbelt; CH=cheyenne CH=Cheyenne belt; CS=Cape CS=Cape Smith Smith belt; belt; FR=Fox FR=Fox River River belt; belt; BL=Belcher GL=Great Lakes Lakes tectonic tectonic zone; zone;GS=Great GS=GreatSlave SlaveLake Lakeshear shearzone; zone;KL=Killarney KL=Killarney GL=Great magmatic KR=Keweenawan rift; rift; MK=Makkovik MK =Makkovik magmatic zone; zone;KP=Kapuskasing K P=Kapuskasing uplift; uplift ;KR=Keweenawan orogen; orogen; MO=Mistassini-Otish MOsMistassini-Otish basins; basins; MRV=Minnesota M RV=Minnesota River River Valley Valley terrarie; terrane; SG=Sugluk terrane; THThompson SG=Sugluk terrane; TH=Thompsonbelt; belt;TS=Transscandinavian TS=Transscandinavian magmatic magmatic zone; zone;WR= WR= Winisk Winisk River River fault. fault. 43 �UNITED PLATES PLATES OF OF AMERICA AMERICA Paul F.Hoff man F.Hoffman The The protracted thermomagmatic thermomagmatic assault by by the the superswell superswell caused caused thinning thinning and weakening of much of the weakening of much of t h e Laurentian Laurentian lithosphere, lithosphere, and and has has implications implications for for injection injection of deformation in the of the t h e Mackenzie Mackenzie dike swarm, deformation t h e Grenville Grenville orogen, orogen, and and magmatism magmatisin in the t h e Keweenawan Keweenawan rift. The 1.3 1.3 Ga Ga Mackenzie Mackenzie dike dike swarm swarm presents presents problems problems in in accounting for its width (1800+ km) if caused by rifting and its length (2400+ for i t s width (1800+ km) if caused b y and its length (2400+km) km) if if caused Alternatively, hotspot. Alternatively, tthe h e dikes dikes may may represent represent leakage leakage from from caused by by aa hotspot. extensive in intrallthosçeric tralithosphericmelt-ponds melt-ponds emanating emanating from from the t h e mantle mantleupwe!ling. upwelling. Dike Dike orientation may may only record the t h e ambient ambient intraplate intraplate stress stressregime, regime, generally generally related related to forces at plate plateboundaries. boundaries. Accordingly, Accordingly, tthe h e dikes dikes may may parallel parallel forces generated generated at compressional stress trajectories generated coeval(?) orogen orogen marginal marginal to t o the the compressional stress generated by b y aacoeval(?) Beaufort Sea, inferred inferred from from seimic seimic reflect reflection profiling. Recent Beaufort Sea, ion profiling. Recent seismic seismic reflection reflect ion profiling shows that .25-1.0 Ga) t h a t much much of of the t h ecollisional collisionalGrenville Grenvilleotogen orogen(1(1.25-1.0 Gal is is thrust thrust imbricated to t o the the base base of of the t h ecrust. crust.The Theorogen orogenisisalso alsounusual unusual in in lacking lacking preserved preserved foreland foreland basins basins oorr other evidence evidence of aa flexural flexural response response to t o orogenic orogenic loading. loading. These These observations suggest aa thin lithospheric observations suggest lithospheric mantle mantle and and low low flexural flexural rigidity rigidity during during Grenvillian The rift has Grenvillian deformation. deformation. The 1.1 1.1 Ga Ga Keweenawan Keweenawan rift has an a nextraordinary extraordinary thickness (15-20 synclinal structure is is due due to t o volcanic volcanic thickness (15-20km) km)ofofbasalt basalt(its (its post-rift post-rift synclinal loading). loading). Theoretical Theoretical calculations calculations show show that t h a t magma magma generation genera tion in in rifts r i f t s isis critically critically dependent 19871, consistent with with dependent on on potential asthenosphere asthenosphere temperature t e m p e r a t u r e (White, (White, 1987), anomalously hot asthenosphere asthenosphere beneath beneath tthe anomalously hot h e rift. Among the many many unsolved unsolved problems problems regarding regarding tthe Among the h e early evolution evolution of of Laurentia Laurentia are (1) Did Didtthe Archn microcontinents common ancestry ancestry in in a r e the t h e following: following: (1) h e Archean microcontinent shave haveaacommon l a t eArchean-early Archean-early Proterozoic Proterozoic supercontinent? supercontinent? (2) (2) Did Did Laurentia Laurentia belong a late belong to to a Middle Proterozoic supercontinent tthat h a t broke broke up up prior prior to t othe t h eGrenvillian Grenvillian collision? collision? Middle Proterozoic supercontinent (3) was tthe hinterland tthat separated from (3) What What was h e Grenville Grenville hinterland h a t presumably presumably separated from Laurentia Laurentia during the t h e opening opening of lapetus? Iapetus? References Hoffman, United plates plates of of America, America, the the birth of of a craton: Early P.F., 1988, 1988, United Early Hoffman, P.F., Proterozoic Proterozoic assembly assembly and and growth growth of of Laurentia; Laurentia;Annual AnnualReview Reviewof ofEarth Eartharid and Planetary PlanetarySciences, Sciences,v.16, v.16, p.543-603. p.543-603. McKenzie, A possible possible mechanism mechanism ffor epeirogenic uplift; Nature, McKenzie, 1)., D., 1984, 1984, A o r epeirogenic Nature, v.307, v.307, p.616—618. p.616-618. Patchett, Patchett,P.3., P.J., and andArndt, Arndt,N.T., N.T., 1986, 1986,Nd Nd isotopes isotopes and and tectonics tectonicsof of1.9-1.7 1.9-1.7 Ga Ga crustal crustalgenesis; genesis; Earth Earth and and Planetary Planetary Science Science Letters, Letters,v.78, v.78, p.329-338. p.329-338. Pribac, Pribac, F., F., and and Davies, Davies, G.F., G.F., 1987, 1987, Mantle Mantle superswells: superswells: regressions regressions arid and rifts? rifts? (abstract); (abstract); Eos, Eos, v.68, v.68, p.1451. p.1451. St—Onge, S t a g e , M.R., M.R., Lucas, Lucas, D.3., D.J., Scott, Scott, D.i, D.J., and andBegin, Begin,N.3., N.J., 1988, 1988,Thin-skinned Thin-skinned imbricat ion and and subsequent subsequent thick-skinned thick-skinned folding foldingofofrift-fill, rift-fill, transitional-crust, imbrication and ophiolite suites in the t h e 1.9 1.9 Ga Cape Smith Belt, northern Quebec, Quebec, in Current Research, Part Part C; C ;Geological Geological Survey Survey of of Canada, Canada, Paper Paper 88-IC. 88-1C. In In press. Research, White, and igneous igneous underplating underplating in in sedimentary White, R.S., R.S., 1987, 1987, Volcanism Volcanism and sedimentary basins basins and and XIX General GeneralAssembly, Assembly, International International rifted continental continentalmargins margins(abstract); (abstract);XIX rifted Union of Geodesy and Geophysics, Vancouver, Union of Vancouver, v.1, v.1, p.183. p.183. 44 �THE STRATIGRAPHY AND PHYSICAL VOLCANOLOGY ASSOCIATED WITH THE F-GROUP VOLCANOGENIC MASSIVE SULFIDE DEPOSIT, STURGEON LAKE, NORTHWESTERN ONTARIO George George J. J. Hudak Hudak (Dept. (Dept. of of Geology, Geology, University University of of Minnesota Minnesota -Duluth, Duluth, Duluth, Duluth, MN MN 55812) 55812) The The F—Group F-Group volcanogenic volcanogenic massive massive sulfide sulfide deposit, deposit, situated situated 77 Km. west of the the Mattabi massive sulfide sulfide deposit deposit in in the the Archean Wabigoon Wabigoon greenstone greenstone belt, belt, is is located located within within an an intensely intensely altered altered succession succession of of mafic to felsic felsic metavolcanic metavolcanic rocks and and associated associated intrusive intrusive rocks. rocks. This This deposit deposit yielded yielded rocks nearly nearly 400,000 400,000 tons tons of of Zn-Cu—Pb—Ag Zn-Cu-Pb-Ag ore ore prior prior to to its its depletion depletion in in 1984. Detailed Detailed mapping and petrographic petrographic studies studies allow allow the the 1984. volcanic volcanic succession succession associated associated with with this this deposit deposit to to be be divided divided into into several several distinct distinct lithological lithological units. units. These These are: are: bedded, bedded, scoria—rich scoria-rich volcaniclastic volcaniclastic rocks rocks which which a) form form the the base of of the the volcanic volcanic succession succession and and are are up up to 110 110 meters meters thick: thick: to massive, massive, poorly sorted sorted mesobreccia mesobreccia deposits deposits which b) overlay overlay the the volcaniclastic volcaniclastic rocks rocks throughout throughout the the entire field field area. area. These These heterolithic heterolithic deposits deposits entire are are up up to to 150 150 meters thick thick and contain contain from from 20-70% 20-70% basaltic basaltic and and dacitic dacitic fragments fragments which appear appear to to be be derived derived from from volcanic volcanic rocks rocks which which underlie underlie the the scoria—rich scoria-rich volcaniclastic volcaniclastic rocks: rocks: a series series of of quartz quartz phyric, phyric, pumice—rich pumice-rich pyroclastic pyroclastic c) flow flow deposits deposits which which are are up up to to 110 110 meters meters thick thick and and are are locally locally interfingered interfingered with, with, and and grade grade into into the the mesobreccia mesobreccia deposits. deposits. These These pyroclastic pyroclastic flows flows and and associated form the immediate associated ash ash tuft's tuffs form immediate footwall footwall rocks rocks to to the the F—Group F-Group massive massive sulfide sulfide deposit: deposit: a 250 250 meter thick thick series series of of well well bedded ash ash and and d) quartz quartz phyric, phyric, pumice-rich pumice-rich pyroclastic flow flow deposits. To To the the east, east, these these rocks rocks host host the the Mattabi Mattabi deposits. orebody. orebody. a a series series of of more massive massive pyroclastic pyroclastic flows flows which which e) contain contain 1—6 1-6 mm diameter diameter quartz quartz and and plagioclase plagioclase crystals. These These flows flows comprise comprise the the uppermost uppermost units units crystals. associated associated with with the the F-Group F-Group orebody. orebody. The The scoria—rich scoria-rich volcaniclastic volcaniclastic rocks rocks are are the the reworked reworked equivalents cone deposit deposit located equivalents of of aa scoria scoria cone/tuft' cone/tuff cone immediately immediately east east of of the the field field area, area, and and are are believed believed to to have have been deposited deposited in in shallow shallow water. water. The The mesobreccia mesobreccia and and quartz quartz been crystal—rich crystal-rich pyroclastic flows flows are believed to represent represent deposits deposits formed formed during the collapse collapse of a caldera caldera combined with simultaneous felsic felsic volcanism. volcanism. The The F—Group F-Group massive massive sulfide sulfide simultaneous deposit was formed formed prior to a second second cycle cycle of explosive explosive volcanism that that deposited deposited the bedded, bedded, quartz-phyric, quartz-phyric, pumice-rich pumice-rich pyroclastic which host host the the Mattabi Mattabi massive massive pyroclastic flows flows and and ash ash tuft's tuffs which sulfide deposit deposit to to the the east. east. The The uppermost uppermost quartzquartz- and and sulfide plagioclase—phyric plagioclase-phyric pyroclastic flows flows represent represent the last last phase of explosive explosive volcanism volcanism associated associated with with the the caldera. caldera. 45 �MICHIGAN KINBERLITE PROVINCE MICHIGAN KIMBERLITE PROVINCE W. JARVIS W. JARVIS Jack Murphy, Murphy, Trustee, 49920 90, Crystal Crystal Falls, Falls, Michigan Michigan 49920 Jack Trustee, P.O. Box 90, J. KALLIOKOSKI KALLIOKOSKI University, Houghton, Houghton, Michigan Michigan 49931 49931 Michigan Technological Michigan Technological University, The disclosure disclosure by Mudrey (1981) by Cannon Cannon and and Mudrey (1981) of of the the presence presence of of the the The Lake Ellen kimberlite in Michigan pointed Lake Ellen kimberlite in the the Upper Peninsula Peninsula of of Michigan pointed to to the the historical diamond finds finds in Great Lakes Lakes possibility that the source of historical in the the Great possibility that the James Bay could be be other than region could than in in the the James Bay lowlands lowlands of of Ontario Ontario as as had had region Jack Murphy, been previously previouslyassumed. assumed. Jack Murphy,Trustee Trustee(Dow (DowChemical ChemicalCompany), Company), with whom whom we we are are associated, associated, has has been been actively actively exploring exploring since since 1982 1982 for for other Lake Ellen other expressions expressions of of the the Lake Ellen kimberlite kimberlite field, field, and and has has looked looked at at potential of those kimberlites kimberlites that the economic potential that have have been been found. found. This This reports on six found, which which occupy occupy a paper reports a northnorthpaper six additional additional ld.mberlites kimberlites found, west trending trending belt extending extending from from the the Powers/Hermansville Powers/Hermansville area area to to Lake Lake Ellen Ellen (Fig. (Fig. 1). 1) . WISCONSIN GEOLOGY L Pvot.rozoic granite gn.i.e I-. L Prot. matlc volcanic rocks • 463O MICHIGAN GEOLOGY x7oJ Jurassic kimb.rlltes (Sits No.) I Ordoviclan s.dHiisnts Cambrian s.dim.nts / L Prot.s.d. and Voic. rockal Amass I (iron formation solid black) ] kI Arch.an rocks —'." Fault , 'I ) 46 -T . 'i -7 -j >'i ;... V ,><r r- r'\1. lounti :s : 7 x 873O" FIG. Bedrock geology geology of of the Marquette—Iron Mountain FIG. 1. 1. ~edrock the Marquette-Iron Mountain region region of of Michigan—Wisconsin, showing bodies. the location location of kimberlite bodies. Michigan-Wisconsin, showing the ofImown known kimberlite It now generally It is is now generally accepted that thatininMichigan Michigan the thePrecambrian Precambrian Shield Shield Archean terranes is made made up up of of two two sutured sutured Archean terranes across across which which were deposited deposited is margin and lower Proterozoic Proterozoic passive passive margin and rift rift basin basin assemblages assemblages of of sedimentary sedimentary lower and and volcanic volcanic rocks, rocks, some some possibly possibly 2.1 2.1 b.y. b.y. old. old. These These rocks rocks underwent underwent aa 46 �period period of of tectonism tectonism estimated estimated at at about about 1.9 1.9 b.y., and and were were cut cut by by east—west east-west striking striking post—orogenic post-orogenic diabase diabase dykes. dykes. Thus, Thus, one one requirement requirement that that the the search search for for diamondiferous diamondiferous kimberlites kimberlites be be conducted conducted on on stable stable portions portions of of cratonic cratonic blocks blocks was was satisfied. satisfied. In the the region region of of our our kimberlite kimberlite finds finds the the structures structures in in the the Archean Archean In Proterozoic cover trend from westerly to deformed basement and basement and deformed Proterozoic cover trend from westerly to northwest northwest (Fig. 1). 1). (Fig. 73 kimberlite kimberlite intrudes intrudes flat—lying flat-lying lower lower Paleozoic Paleozoic shallow shallow The Site Site 73 The thissedimentary sedimentarycover cover sea basin basin margin margin sedimentary sedimentary rocks. rocks. At one time this sea extended to the thewest west and and northwest northwest as as evidenced evidenced by outliers outliersatatLimestone Limestone extended Palaeozoicrocks rocksin in all all the Mountain and and by by abundant abundant xenoliths xenoliths of of lower Palaeozoic the Mountain discovered discovered kimberlites. kimberlites. The The Lake Lake Ellen Ellen kimberlite kimberlite was was dated dated by by Cannon Cannon and and Mudrey Mudrey as as post post lower lower Palaeozoic Palaeozoic by by the the presence presence of of Ordovician Ordovician limestone limestonexenoliths. xenoliths. The The additional kimberlites kimberlites are are also also post post lower lower Palaeozoic, Palaeozoic, some some with with 66 additional Devonian Devonian fossils fossils (J. (J. Humi, Huml, personal personal communication, communication,1987). 1987). Macrocrystal Macrocrystal zircons zircons (3mm) (3mm) recovered recovered from from Site Site 73 73 mineral mineral concentrates concentrates have have been been dated dated at at 155 155 m.y. using using the the fission—track fission-track method method (Craig (Craig Chesner, Chesner, personal personal communication, communication, 1987) 1987) and and aa potassium—argon potassium-argon age age of of 190 190 m.y. m.y. was was obtained obtained from from phiogopite phlogopite from from the the same same kimberlite kimberlite (Craig (Craig Smith, Smith, personal personal communication,1987). 1987). Based Based on on these these age age determinations determinations and and their their similar similar communication, modes modes of of occurrence, occurrence, we we conclude conclude that that all all of of the the kimberlites kimberlites are are Mesozoic, Mesozoic, probably probably Jurassic. Jurassic. The The compositions compositions of of garnet garnet and and chromium chromium spinel spinel from from kimberlite kimberlite can can be be used used as as guides guides to to the the possible possible presence presence of of diamond diamond by by comparing comparing them them (and garnet and (and their their abundance) to to the the compositions compositions of of garnet and spinel spinel occurring occurring as as inclusions kimberlites (Gurney inclusionsinindiamond diamondand and in inknown known diamondiferous kimberlites (Gurney and Switzer, 1973; 1973; Gurney, Gurney,1984; 1984;Harte, Harte,etetal, al, 1980; Sobolev, Sobolev, et et al, al,1973; 1973; has two two proven proven parageneses: parageneses: eclogitic Sobolev,1984). 1984). Diamond Diamond has eclogiticand and perido— peridoSobolev, titic. The garnet garnet population population at at each each of of the the kimberlites kimberlites was was examined examined for for titic. The compositions kimberlitescontaining containingdiamonds diamonds compositions comparable comparable to to those those found found in in kimberlites ofaaknown known peridotitic peridotitic paragenesis paragenesis (Gurney's (Gurney'sG—10 G-10 garnets). garnets). For For the the Lake Lake of Ellen Ellen and and Bacon Bacon kimberlites, kimberlites,aapreselection preselectionofofgrains grainswas wasmade made to to ensure ensure inclusion with diamond diamond inclusion that all allcolor colorgroups groupswere were represented. represented. Garnets with that compositions, CaO and and higher higher Cr203 Cr203 than than compositions,or oreven evencompositions compositionswith withlower lowerCaO McGee has has reported reported aa similar similar the lherzolite lherzolite field, field, are are rare rare (Fig. (Fig. 2). 2). McGee the 69, 70 70 For the the Site Site 69, low low G—10 G-10 population population for for Lake Lake Ellen Ellen (McGee, (McGee,1987). 1987). For and and 73 73 kimberlites, kimberlites, only only lilac, lilac, purple purple or or mauve mauve garnets garnets were were sent sent for for with a analysis. This analysis. This produced produced aa plot plot with a bias bias toward toward garnet garnet compositions compositions However, aa large largeamount amount of of mineral mineral concenconcenfalling falling near near the the G—10 G-10 field. field. However, trate trate was was examined examined for for the the selection selection of of these these grains grains and, and, according according to to the criteria, the significant population population of the Gurney criteria, the lack of a significant of G—10 G-10 garnets garnets suggest be highly highly diamondiferous diamondiferous (Gurney, (Gurney, 1984; 1984; Boyd Boyd suggest the the pipes pipes may may not not be and and Gurney, Gumey, 1982). 1982). A Michigan kimberlites A number of ofchromium chromium spinels spinels from from each each of of the the Michigan kimberlites were -but no no spinels spinels of of diamond diamond inclusion inclusion field field compositions compositions were also also analysed analysed-but were were found. found. Literature Literature sources suggest that thatinindiamondiferous diamondiferous kimberlites, kimberlites, up up to to about about 12% 12% of of the the spinel spinel population population falls falls in in the the diamond diamond inclusion inclusion compositional field. field. compositional Based Based on on our our work work we we conclude conclude that that these these particular particular kimberlites kimberlites are are unlikely unlikely to to be be economically economically diamondiferous diamondiferous and and also, also, that that they they are are not not the the probable probable specific specific source source for for the the large large diamond diamond finds findsin inWisconsin. Wisconsin. However, in the the garnet garnet population population does does However, the the presence presence of of G—10 G-10 compositions compositions in indicate indicate that that the the source source region region for for the the kimberlite kimberlite magma magma was was within within the the diamond by diamond stability stability field field of of the the upper upper mantle, mantle, as as was was also also indicated indicated by McGee McGee and and Hearn Hearn (1982), (1982), and and that that the the potential potential for for diamonds diamonds in in other other kimberlites kimberlites in in this this area area remains remains strong. strong. 47 �Lake Ellen Site 69 (2 pipes) Bacon I :• F I.. I... I I.. ;.• I' cSo3 .1;.. .1' 4 ' It. •' t-._ 2 4 c.e S IS S I SiteTO(2 S i t e 7 0 ( 2pipes) pipes) I. 1 / 8 I I. 1 1 1 Site S i t e73 73 -.- " . * — -.-'4.-. • :.4. I 'S I, FIG. Cao v. v. Cr203 CrgOaplots plots for for selected selected garnet garnet grains grains from from each each of of FIG. 2.2. Gao the The dashed dashed lines lines correspond correspond to to the the 85 85 percentile percentile lines lines thekimberlites. kimberlites. The of Gurney. of Gurney. References References Boyd, Boyd, F.R. F.R. and and Gurney, Gurney,J.J., J.J., 1982, 1982,Low Lowcalcium calciumgarnets: garnets: keys keysto to craton craton structure structureand anddiamond diamondcrystallisation. crystallisation. Carnegie Carnegie Institute,Washington, Washington, Yearbook, Yearbook,v. v.81, 81,p.p.261—267. 261-267. Institute, Cannon, F. and Cannon,W.W.F. and Mudrey, Madrey,M.G., M.G., Jr., Jr., 1981, 1981,The Thepotential potentialfor fordiamond— diamondbearing bearing kinberlite kimberlitein innorthern northernMichigan Michigan and andWisconsin. Wisconsin. U.S. U.S. Geol. Geol. Survey Survey Circular Circular 842, 842,15 15p.p. correlation between between garnets garnets and and diamonds diamonds in in kimber— kimberGurney,J.J., J.J., 1984, 1984,AA correlation Gurney, lites, E. and lites,in inGlover, Glover,J.J.E. and Harris, Harris, P.G., P.G., eds., eds., Kimberlite Kimberlite occurrences occurrencesand and origin: origin: aa basis basis for forconceptual conceptualmodels modelsin inexploration. exploration. University University of of Western WesternAustralia, Australia,Geology GeologyDept. Dept. and andUniv. Univ. Extension ExtensionPublication. Publication. Harte, Harte,B., B., Gurney, Gurney,J.J., J.J., Harris, Harris,J.W., Jew., 1980, 1980,The The formation formation of of peridotite peridotite suite suiteinclusions inclusionsin indiamond. diamond. Contrib. Contrib.Mineral. Mineral.Petrol, Petrol,v.v.72, 72,p. p. 131—190. 131-190. McGee, McGee,E.S., E.S., 1987, 1987,Garnet Garnetxenocryst xenocrystanalyses: analyses: potential potentialfor fordiamonds diamondsin in kimberlite,north—central north-centralMontana Montanaand andthe theLake LakeEllen Ellenkimber— kimbertheWilliams Williamskimberlite, the lite, lite,northern northernMichigan. Michigan. U.S. U.S. Geol. Geol.Survey SurveyOpen—file Open-fileReport Report87—418, 87-418,1515p.p. Sobolev, N.V., 1984, 1984,Kimberlites Kimberlitesofofthe theSiberian Siberianplatform: platform: their Sobolev,N.y., theirgeologigeological caland andmineralogical mineralogicalfeatures featuresin: in: Glover, Glover,J.E. J.E. and andHarris, Harris,P.G., P.G., eds., eds., Kimberlite Kimberliteoccurrence occurrenceand and origin: origin: aabasis basisfor forconceptual conceptualmodels modelsininexexploration. UniversityofofWestern WesternAustralia, Australia,Geology GeologyDept. Dept. and andUniv. Univ. ploration. University Extension 143-166. ExtensionPublication Publication8,8,p.p.143—166. 48 �GEOCHEMICAL STRATIGRAPHY STRATIGRAPHY OF OF THE HURONIAN GEOCHEMICAL HURONIAN CONTINENTAL CONTINENTAL VOLCANICS, VOLCANICS, ONTARIO: ONTARIO: RELATIVE CONTRIBUTIONS CONTRIBUTIONS OF MANTLE MANTLE HETEROGENEITY, SYSTEM MAGMATISM AND RELATIVE HETEROGENEITY, OPEN OPEN -- SYSTEM CRUSTAL FUSION FUSION CRUSTAL Wayne T. Jolly (Department (Department of Geological Geological Sciences, Sciences, Brock Brock University, University, St. Catharines, Catharines, Ontario, Ontario, Canada Canada L2S 3A1) 3A1) L2S The 1500 1500 m thick thick sequence sequence of of Huronian Huronian flood flood basalts basalts at at Thessalon, Thessalon, Ontario, Ontario, contains interlayered low—Ti, low-Ti, enriched enriched continental continental tholeiites tholeiites and and two two distinct distinct varieties varieties of crustally crustally derived derived rhyolite rhyolite (1, (1, 2). 2). The stratigraphic stratigraphic succession succession is divided into four volcanic cycles, cycles, each each of which includes includes early early mafic mafic and late late felsic felsic phases. phases. Basalts Basalts of mafic phases phases were were erupted erupted from from aa progresprogressively fractionating, fractionating, periodically periodically replenished replenished magma source source of of the the type type O'Hara and Mathews (3), envisaged by O'Hara ( 3 ) , probably probably located located at at the the density density discondisconmarking the boundary between the tinuity marking the crust crust and lithospheric lithospheric upper upper mantle. mantle. Magmas of the the earliest earliest volcanic volcanic sequence sequence underwent underwent simultaneous simultaneous contamination contamination by siliceous, siliceous, depleted depleted material material of of lower lower crustal crustal affinities affinities and and gabbroic gabbroic fractionation with an assimilation/fractional assimilation/fractional crystallization fractionation crystallization (AFC) ( A X ) ratio ratio of 0.4. 0.4. Subsequent Subsequent cycles cycles do not display display AFC—type AFC-type contamination, contamination, suggesting suggesting that a solid basaltic layer layer formed formed at at the the top top of of the the main main tnagmatic magmatic source source body cutting cutting off contact contact with with the the lower lower crust crust (see (see also also 4). 4). Crustal Crustal fusion fusion during during the the mafic phase phase of of each each volcanic volcanic cycle cycle eventually eventually produced so much rhyolitic liquid that basalt magmas magmas no no longer longer passed passed freely freely surface; basalts are uncommon to the surface; uncommon in in felsic phases. When When present present they they predominant contaminant are are invariably invariably highly highly contaminated. contaminated. The predominant contaminant was was derived derived by an an average average of of 20% 20% fusion fusion of of high—LILE, high-LILE, relatively relativelylow—LREE low-LREEleucograriitic leucogranitic upper crustal crustal material material (1), (I), but but low—LILE, low-LILE, high—LREE high-LREE liquids liquids from from low—degree low-degree melting of depleted depleted siliceous siliceous tonalite tonalite at at deeper deeper levels levels were were also also present. present. Resulting Resulting hybrid magmas magmas form form two two mixing mixing lines lines between between basalt basalt compositions compositions and the individual individual rhyolite rhyolite types; types; basalt—rhyolite basalt-rhyolite mixing mixing ratios ratios as as high high as as 40:60 are are common common in in the the central central part part of of the the stratigraphic stratigraphic section. section. During During volcanfc cycle, cycle, rhyolites the final volcanic rhyolites were not erupted, erupted, and and crustal crustal contamination contamination became less less common, common, probably probably because because volcanic volcanic vents, vents, conduits conduits and and feeders feeders had become insulated insulated by marginal marginal chilled chilled zones, zones, as as suggested suggested elsewhere elsewhere (5) (5) The beginning of each each successive successive volcanic volcanic cycle cycle presumably presumably occurred occurred following crustal cooling during the interim, interim, and was was marked by by replenishment replenishment of the main main magma reservoir at depth and renewed renewed mafic volcanic volcanic activity. activity. Initial magmas of each cycle were relatively relatively uncontaminated, uncontaminated, but but compositions compositions of mafic end—members end-members at at any any given given Mg* Mg* became became progressively progressively less less siliceous siliceous and less enriched in in LILE LILE and and LREE LREE with with time. time. For example, example, early early flows flows display display La/Y, Sr/Y, Sr/Y, and Cu/Y Cu/Y ratios ratios of of 0.6, 0.6, 6.0, 6.0, and and 0.8 0.8 respectively, respectively, compared compared to to La/Y, 1.0, 8.0, and 2.0 in central central basalts and 1.2, 15, 15, and and 3.0 3.0 in in late late basalts. basalts. addition, absolute Ti02 content increased In addition, increased from from 0.75 to to over over 1.25%, 1.25%, while while Ti/Zr Ti/Zr ratios ratios gradually gradually rose rose from from 35 35 to to stabilize' stabilize at about 85 in in late late basalts. basalts. Enrichment Enrichment of early early basalts basalts cannot cannot be be attributed attributed to to crustal crustal contamination, contamination, since both Sr and Cu are also enriched in in these these basalts, basalts, while while compositions compositions of both upper and lower crustal crustal contaminants, contaminants, as as reflected reflected by by compositions compositions of the accompanying rhyolites, rhyolites, are highly depleted depleted in in these these components. components. Therefore, Therefore, the the variations variations are are considered considered to to reflect reflect heterogeneity heterogeneity in in the the 1-ithospheric mantle source. lithospheric mantle source. Basalts of the first volcanic volcanic cycle cycle were were composed composed of the most enriched enriched magma magma type. type. This This liquid liquid was subsequently subsequently progressively progressively diluted in the main reservoir reservoir by influx influx of aa new, new, less—enriched less-enriched magma, magma, giving giving rise to a mixing line line between between the the two two types. types. The The original original magma magma was was largely largely flushed from the system system by late late stages stages of Huronian Huronian volcanism volcanism (6). (6). 49 �Both Both basalt types types exhibit exhibit enrichment enrichment in in incompatible incompatible element element abundances, abundances, but but negative negative anomalies anomalies for for the the more more refractive refractive lithophile lithophile elements, elements,including including Nb, mantle—normalized diagrams Nb, P, P, Zr, Zr, and and Ti, Ti, and positive positive anomalies anomalies for for Sr on mantle-normalized diagrams are are features features characteristic characteristic of of islnd islnd arc arc tholeiite tholeiite basalts basalts (2). (2). It It is is suggessuggested that enrichment enrichment of the the Huronian Huronian subcontinental subcontinental lithospheric lithospheric mantle mantle occurred occurred through through ancient ancient subduction subduction of of crustal crustal material, material, probably probably during during formation formation and and consolidation consolidation of of the the continental continental crust. crust. The The Huronian Huronian basalts basalts resemble, resemble, in in both both tectonic tectonic setting setting and and geochemistry, geochemistry, widespread widespread Mesozoic Mesozoic flood flood basalts basalts erupted break—up, including the Farrar Group erupted in in association association with continental continental break-up, of of Antarctica Antarctica (7), (7), and and the the Parana Parana and and equivalent equivalent Etendeka Etendeka continental continentalbasalts basalts of of south south Brazil Brazil and and Namibia Namibia (8, (8, 9) 9) respectively. respectively. References References 1) 1) Jolly, Jolly, W. W. T., T., 1987, 1987, Can. Can. J. J. Earth Earth Sci. Sci. 24, 24, 1360—1385. 1360-1385. 2) W. T., T., 1987, 1987, Earth Earth Planet. Planet. Sci. Sci. Lett. Lett. 85, 85, 401—415. 401-415. 2) Jolly, Jolly, W. 3) and Mathews, Mathews, R. R. E., E., 1981, 1981, J. J. Geol. Geol. Soc. Soc. 3) O'Hara, O'Hara, M. M. J. J. and London London 138, 138, 237—277. 237-277. 4) 4) Huppert, Huppert, H. H. E. E. and and Sparks, Sparks, R. R. S. S. J., J., 1980, 1980, Contr. Contr. Mineral. Mineral. Petrol. Petrol. 75, 75, 279—289. 279-289. 5) 5) Cox, Cox, K. K. G. G. and and Hawkesworth, Hawkesworth, C. C. J., J., 1985, 1985, J. J. Petrol. Petrol. 26, 26, 355—377. 355-377. 6) 6 ) Jolly, Jolly, W. W. T., T., 1988, 1988, Contrib. Contrib. Mineral. Mineral. Petrol. Petrol. (in (in press). press). 7) 7) Kyle, Kyle, P. P. R., R., 1980, 1980, Contrib. Contrib. Mineral. Mineral. Petrol. Petrol. 73, 73, 89—104. 89-104. 8) 8) Petrini, Petrini, R. R. et et al., al., 1987, 1987, J. J. Petrol. Petrol. 28, 28, 701—726. 701-726. 9) 9) Hawkesworth, Hawkesworth, C. C. J. J. et et al., al., 1984, 1984, Nature Nature 311, 311, 331-335. 331-335. 50 �0 8 04 0 0 0 0 E a a 0 N a -J 0 1 0 N N 0 0 0 N E a. 8 0 0 0 C', 0 0 8 8 I', • SSau3uj 51 !UdOJ6!4OJ4S �STRATIGRAPHY STRATIGRAPHY AND AND PHYSICAL PHYSICAL VOLCANOLOGY VOLCANOLOGY OF OF THE THE FOOTWALL FOOTWALL ROCKS ROCKS NW ONTARIO ONTARIO TO THE THE STURGEON STURGEON LAKE LAKE MASSIVE MASSIVE SULFIDE SULFIDE DEPOSIT, DEPOSIT. NW TO K. JONGEWAARD, University University of of PETER K. JONGEWAARD, PETER 55812 Minn., 55812 Minn., Minnesota-Duluth, Duluth, Duluth, Minnesota-Duluth, Sturgeon Lake Lake massive massive sulfide sulfide deposit deposit sits sits atop atop aa 66 Sturgeon volcanic and succession of xnafic to felsic succession of mafic to felsic volcanic and volcaniclastic rocks rocks of of the the Savant—Sturgeon Savant-Sturgeon Lake Lake metavolcanic— metavolcanicvolcaniclastic metasedimentary 2.1m.t. m. t. metasedimentary greenstone greenstone belt. belt. The The ore ore deposit deposityielded yielded2.1 of of high—grade high-grade Zn—Cu—Pb—Ag-Au Zn-Cu-Pb-Ag-Au ore ore from from 1974 1974 to to 1980. 1980.Despite Despite regional greenschist greenschist and and local local amphibolite amphibolite grade grade metamorphism metamorphism and and regional variable amounts amounts of of hydrothermal hydrothermal alteration, alteration, seven seven distinct distinct variable volcanic footwall succession. succession. volcanic units units have have been been identified identified in in the the footwall This subdivision subdivision is is based based on on preserved preserved primary primary textures, textures, fragment fragment This types, composition, composition, and and regional regional stratigraphic stratigraphiccorrelation. correlation. types, Mafic km, of of the the Mafic volcanic volcanic rocks rocks comprise comprise the the lowermost lowermost 33 km. footwall succession, succession, and and are are composed composed of of massive, massive, brecciated, brecciated, footwall amygdaloidal, may consist consist of of up up to to amygdaloidal, and and pillowed pillowed flows. flows. Pillows Pillows may 70% 70% rounded rounded amygdules, amygdules, indicative indicative of of shallow shallow water water extrusion. extrusion. The The mafic volcanic volcanic rocks rocks are are overlain overlain by by aa thick thick (1 (1 km.), km.), laterally laterally mafic extensive heterolithic heterolithic breccia, breccia, composed composed of of angular angular lapilli— lapilli- to to extensive block—sized mafic block-sized mafic mafic and and felsic felsic volcanic volcanic fragments fragments set set in in aa mafic matrix. This This breccia breccia is is intercalated intercalated with, with, and and overlain overlain by by aa matrix. quartz—phyric quartz-phyric pumice—bearing pumice-bearing ash—flow ash-flow tuff, tuff, which which reaches reaches aa 150 in. m. This This tuff tuff marks marks the the first first largelargemaximum thickness thickness of of 150 maximum volume eruption eruption of of felsic felsic material material in in the the succession. succession. The The ash— ashvolume flow tuff tuff is succeeded succeeded upward upward by by debris debris flow flow and and bedded bedded is flow epiclastic epiclastic deposits, deposits, which which contain contain fragments fragments of of the the underlying underlying units units as as well well as as bomb—sized bomb-sized juvenile juvenile pumice. pumice. Overlying Overlying the the debris debris flow km. sequence sequence of of massive massive to to bedded bedded flow deposits deposits is is aa thick thick 11 km. ash-flow quartz/plagioclase-phyric ash-flow tuffs. tuffs. Massive Massive quartz- and and quartz/plagioclase—phyric quartz— in thickness, whereas bedded 250m. m. in thickness, whereas bedded units units consist consist units are are up up to to 250 units m. basal basal beds beds composed composed of of crystals, crystals, of normally-graded normally-graded 10—30 10-30 in. of lithic lithic lapilli, lapilli, and and pumice pumice overlain overlain by by thinly—bedded thinly-bedded ash ash units. units. The top top of of this this sequence sequence is is the the immediate immediate host host to to the the Sturgeon Sturgeon The to tuaf Ic Thin Lake massive sulfide sulfide deposit. deposit. Thin axnygdaloidal amygdaloidal mafic to massive Lake intermediate form the the hangingwall hanginwall to intermediate lavas lavas cap the succession succession and. and form to the orebody. The The volcanic volcanic succession succession is is intruded intruded by by intermediate intermediate the orebody. 25% of of the the rocks rocks to mafic mafic sill—like sill-like bodies bodies which which comprise comprise up up to to 25% to in the the area. area. in A major major north—trending north-trending synvolcanic synvolcanic structure structure divides divides the the area of area into into two two distinct distinct stra.tigraphic stratigraphic sequences. sequences. To To the the west west of the the structure, structure, basal mafic flows flows are are overlain overlain by by the the breccia—ash— breccia-ashflow flow tuff—debris tuff-debris flow flow sequence. sequence. East East of of the the structure structure the the basalts basalts are immediately immediately overlain overlain by by fragment—poor fragment-poor ash-flow ash-flow tuffs tuffs which which are thin rapidly rapidly and and pinch pinch out out eastward. eastward. It It is is believed believed this this thin structure represents represents the the eastern eastern topographic topographic margin margin of of the the structure Sturgeon which has has been been traced westward 20 Sturgeon Lake Lake caldera. caldera which westward for for up up to to 20 km. Owing Owing to to unique unique circumstances circumstances of of regional regional deformation deformation and and km. erosion, fill and and outflow outflow facies fades resulting erosion, both intracaldera fill resulting from from caldera caldera collapse collapse can can be be studied studied in indetail. detail. The The km.thick km. thick 52 �A LATE ABCHEAN CLkSTIC SEQUCE — FILL OF A FAULT-BOUNDED BASIN ST1JCTU M.M. Kehlenbeck arid M.M. and B.E. B.E. Seemayer Seemayer Dept. of Dept. of Geology, Geology, Lakehead Lakehead University, University,Thunder ThunderBay, Bay,Ontario OntarioP7B P7B5E1 5E1 - North west of of Thunder Bay, Ontario, Ontario, the of the Thunder Bay, the Archean Archean bedrock bedrock of the North and and west Wawa subprovince includesseveral several exposures exposuresofof cl clastic Wawa subprovi nce includes a s t i csedimentary sedimentaryand and intercalated volcanic form isolated outcrop intercalated volcanicrocks. rocks. These These clastic cl a s t i csequences sequences form outcrop 80km ka long long belt b e l tfrom fromThunder ThunderBay Bay areas l e n t i c u l ashape r shapewhich whichdelineate delineateanan80 areas of of lenticular west to t oShebandowan. Shebandowan. These These rocks are arecommonly commonly designated as as aa younger younger sequence sequence compared compared to to the Archean volcanic and and sedimentary sedimentaryterrane terranew with whichthey theyare arei in contact. i t h which n contact. Archean volcanic the The terms terms "Timiskaming" "Timiskarning" or or post-Keewatin" The "oost-Keewatin" have have been been suggested suggested ffor o r these these clastic Shegeiski, a s t i csequences sequences (?lacdonald, (!4acdonald, 1938; 1938; Shegel ski, 1980). 19SO). In In most most cases cases the the cl designation of on ccertain designation of these these rocks rocksas asaayounger younger sequence sequence iiss based based on ertain lithological similarities Abitibi h establishedTimiskaming Timiskann'ng sstrata t r a t a iin n the the Abi t i bi lithological simi 1a r i t i ewith s w i t established belt (Quebec), and on structural and stratigraphic discontinuities along b e l t (Quebec), and on structural and straticraohic discontinuities along the the contacts wwith i t h "Keewatin' "Keewatin' volcanic volcanic rocks. rocks. contacts More recently Borradaile Brown (1987) (1987) have have used used the term term More recently Borradaileand andBrown "Shebandowan group" r cclastic l a s t i csedimentary sedimentary rocks rocksnear nearShebandowan. Shebandowan. Their Their work work "Shebandowan group"f ofor showst hthat rocks are are iisoclinally s o c l i n a l l yfolded foldedand and that t h a tthe thedeformation deformationwas was shows a t tthe h e rocks accompaniedbybythe thedevelopi'ient development single tectonic and magnetic ffabric. e tectonic and magnetic a b r i c . Based Based accompanied of ofa asing1 on bedding-cleavage relationships, showt hthat the folds, folds, Borraaai l e and and Brown Brown show a t the on beddi ng-cl savage re1 ationships, Borradaile wheretraceable, traceable, have east-west axi axial moderatelyt oto strongly strongly whera have east-west a1 surfaces surf aces and and moderately curved hinge n e s , and and tthat h a t locally the the folds folds developed developed iin n inverted inverted strata. strata. curved hingel ilines, They suggest a t the grouo" i s aist at l e aleast s t partly n ffault a u l t contact contact They suggestt hthat the "Shebandowan "Shebandowan group" partlyi in with w i t h the the adjacent adjacent volcanic volcanicrocks rocks("Keewatin (Yeewatin group"), group"),although although they theywere were unable unable which would wouldpermit permitdocumentation documentation relationship. tto o locate locate exposures exposures which of oft hthis i s relationship. Corfu and from rocks rocks of U-Pb ages ages from Corfu and SStott t o t t (1986) (1986) have have reported reported precise precise U-Pb the Shebandowan Theirr eresults show theclclastic rocks of of the t. Their s u l t s show t h that a t the a s t i c rocks the the Shebandowan be1 belt. a years "Keewatin" "Shebandowan group" "Shebandowan group"are areabout about40 40M Ma yearsyounger youngerthan thanthe the adjacent adjacent "Keewatiri" volcanic rocks. They They suggest r the l a s t i c rocks rocks of of volcanic rocks. suggestthe theage ageofofdeposition depositionf ofor thecclastic Tiniiskaming-type a t at 2 62689Ma. 8 9 2 ~ a . This obtained from a a l alatitic t i t i c breccia breccia Timiskaming—type Thisage agewas was obtained from reDresentativeofof calc-a1 calc-alkaline representative kal i ne to t o alkalic a1 kal i cvolcanic volcanicrocks rockswhich which are are interfingered w i terrestial t h t e r r e s tsediments i a1 sediments suggesting contemporaneous 1ateral ly interfingered laterally with suggesting contemporaneous t e cl a s t fror. from aa volcanism and volcanism andsedimentation. sedimentation.A Aporphyritic porphyritic trondhjeni trondhjemite clast conglomerate which part ofofthe theclastic c l a s tsequence i c sequence formed 2704*2Ma Ma ago ago and and conglomerate which iiss part formed 2704±2 represents age the sequence. sequence.InIn contrast, contrast, an repi-esents a maximum maximum age f o for r d deposition e ~ o s i t i o nofof the an age age of of 273353 from i l l isi a s minimum a minimin age age ffor o r aa sequence sequence ofof older 2733t3 from aa porphyry porphyry ssill older volcanic rocks the north. rocks exposed exposed t to o the 53 �The variety of The clastic clasticsequence sequence is i s composed composed ofof aa variety of rock rocktypes typeswhich which include clastic include sandstone, sandstone, ssiltstone, i l tstone,greywacke, greywacke, arkose, arkose, conglomerate, conglomerate, cl astic volcanic volcanic rocks, iron formation. rocks, and and minor minor occurrences occurrences ofof iron formation. Spatially Spatiallythese these rock rocktypes types are are intimately severaltypes typesoccur occurin in a single intimately associated, associated, and and commonly commonly several single outcrop. outcrop. Because thecomplex complex nature theirdistribution, distribution, iitt isi snot n o possible t possibletot omap map Because ofofthe nature of of their any particular rock distance in in the the field. field. any particular rock type type for any any distance In outcropsthe therecognition recognitionofof bedding beddingi is not difficult. difficult. However, In many many outcrops s not However, iti tisi typical marked in in bedding ito find to find markedvariations variations beddingattitudes a t t i tudesfrom fromone oneoutcrop outcrop s t y ~cal to to another another as as well we1 1 as as inina asingle singleexposure. exposure.These These variations variationsininbedding bedding attitudes separatedbby small faults. faults. attitudesare arecommonly commonly separated y small In sequence, In the the eastern eastern portion portion ofofthe theclastic clastic sequence,bedding beddingofofmore more consistent consistent orientation orientation can can be be traced traced in in several several outcrops. outcrops. Here Here too, local local way—up the strata strata can way-up ofofthe can be be determined determined from from graded graded beds beds and and cross-bedding. cross-bedding. Based onthese theseobservations, observations,the the rocks rocks appear appeart oto indicate indicate aa synformal Based on synformal structure structure although no fold closures observedinin the the ffield. although no closures were were observed ield. In most exposures, but particularly in those where finefine-grained grainedand and In most exoosures, b u t particularly in thosewhere semipelitic semi pel i t i c rocks rocks occur, occur, aacontinuous continuous slaty slatycleavage cleavage isi sobservable. observable. This This cleavage cleavage iiss also also present present in incoarser coarser grained grained rocks rocks where where iti tforms formsan an anastomosing pattern. anastomosi ng pattern. In outcropsofof the the clastic clastic sequence, andparticularly particularly in the In most most outcrops sequence, and the finer rocks, thethe bedding and finergrained, grained,well welllayered layered rocks, bedding andcontinuous continuouscleavage cleavagehave have been folded. In exposuresthis thissmall smallscale scalefolding folding has led to t o the the been folded. In many many exposures has led development chevron folds folds possessing narrow hinge hinge zones zonesand andstraight straight limbs. limbs. development ofof chevron possessing narrow In outcrops,polycl polyclinal hinge In some some outcrops, i nal folds folds with with multiple mu1 tip1 ehinges hingesand and non-parallel non-para1 1 el hinge lines In all lines have have developed. developed. In all cases cases these these noncylindrical noncylindrical folds foldspossess possess aa subvertical subvertical axial axialplanar planarcrenulation crenulationcleavage cleavagewhich which strikes strikesbetween between northeast northeast and northwest. In In general and northwest. general fold fold hinge hinge lines linesplunge plungesteeply steeplynorthward. northward. Although Although the folds folds are arebest bestdeveloped developed in inthe themore more laminated laminated rock rock types, clastic rocks. some unstratified types, they they are are also also present present in the the coarser coarser clastic rocks. InInsome sheets of conglomerate, the individual clasts are buckled into folds sheets of conglomerate, the individual clasts are buckled folds with with angular folds ininthe angular hinges, whereas whereas folds thematrix matrixhave havehinges hingeswhich whichare aremore morerounded. rounded. In one case, refolding refolding of of earlier about north north striking strikingaxial axialsurfaces surfaceshas has one case, earlier folds foldsabout been observed. observed. been Near the contact with of the Near the with the themetavolcanic metavolcanic rocks, rocks, many many outcrops outcrops of the clastic are cut cut by faults. These clasticsequence sequence are by faults. These structures truncate truncate the the small-scale small-scale folds and all earlier and a11 earlierstructures. structures. InIntypical typicaloutcrops outcrops several several faults of of variable patterndividing dividing the outcrop outcrop into into variable orientation orientationproduce produce an an anastomosing anastomosi ng pattern lensoidal portions variation in portions ininwhich whichprevious ?ravious structures structuresshow show marked marked variation in orientation. itI is uncommon near t inot s not uncommon tto o find earlier earlierstructures structuresinin nearorthogonal orthogonal relationships segments.Evidence Evidence faulting is re1 ationshipsbetween between adjacent adjacent fault—bounded faul t-bounded segments. forforfaulting is 54 �particularly particularlypronounced pronounced in rocks rocks of of the the western western part part of of the theclastic c l a s t isequence c sequence along the contact of the contact along the contact with with the thevolcanic volcanicsuccession. succession. Exposures Exposures of contact occur occur here the rocks markeddevelopment development myloniticschistosity. schistosity. mylonitic here and and the rocks show show aa marked of of aa evidence supports a u l t relationship relationship between between the astic Field evidence supportsthe theffault the cl clastic sequence andthe the adjacent adjacent volcanic volcanic terrane. Along sequence and Along the thewestern western and and southern southern margin, outcrops thecontact contactprovide provided idirect evidenceofoffaulting faulting in margin, numerous numerous outcrops of ofthe r e c t evidence in the mylonitic of ffault mylonitic schistosity schistositydeveloped develooed in in the the rocks. rocks. Elsewhere, Elsewhere, zones zones of ault breccia truncations of of regional regional structural structural trends distinctive brecci a and and truncations trends and and di s t i ncti ve lithologies 1i tho1 ogi es reflect ref 1ectthis t h i sdiscordant discordant relationship. re1 a t i onshi p. Internally, the rocks of the Internally, the rocks of theclastic c l a s t isequence c sequence include include aa wide wide variety of types contact with with each other in in individual types which which are are commonly commonly ininf afault u l t contact each other individual outcrops. Abundantsmall smallf afaults greatlyobl obliterate earlier i e r structural structuraland and outcrops. Abundant u l t s greatly i t e r a t e earl stratigraohic relationships. re1 ationships. Collectively Collectivelythese thesefeatures featuresmay may indicate that that the the stratigraphic clastic c l a s t i csequence sequence as as aa whole whole represents represents aa strongly stronglyimbricated imbricateddown—faulted down-faulted block. In addition f a u l t i n s , the the clastic c l a s t i csequence sequence ddiffers i f f e r s structurally addition to tr.e the faulting, from rocks. A north—southstriking striking subvertical subvertical crenulation A north-south crenulation from the metavolcanic metavolcanic rocks. cleavage scale north-plunging north-pl ungi ng folds. folds. The The structures structures cleavage iis s axial axi a1 planar pl anar to t o small small scale fold fold the thecontinuous continuous slaty slatycleavage cleavage as as well as as the the bedding. bedding. This This crenulation crenulation cleavage has not not been observedinin the the adjacent cleavage has been observed adjacent volcanic rocks. rocks. Mesoscopic foldsi in the rocks rocks of of the clastic are rare, nor n the c l a s t i csequence sequence are nor Mesoscopic folds could bedetermined determined from from systematic systematic observations observations of of could such such structures structuresbe bedding—slaty cleavagere1 relationships. beddi ng-sl aty cleavage ationshi ps. The mayreoresent representananooutlier The cclastic l a s t i csequence sequence may u t l i e r of of younger younger rocks rocks in in fault f a u l tcontact contactwith withthe thevolcanic volcanicterrane. terrane.Field Fieldobservations observationstotodate datesuggest suggest that representsthe thef filling sequence as as aa whole whole represents i l l ingofofa afault-bounded fault-bounded that the the clastic cl a s t i csequence basin structure. structure. The The tectonic tectonichistory historyofofthis t h basin i s basin i s complex mayhave have basin is complex andandmay included periods periods of of transtension transtensionand and transpression transpression which which affected affectedthe theArchean Archean included crust regionally regionallyand andclosely closely coincide with boundary betweenthe theQuetico Queticoand and crust coincide with thethe boundary between Wawa subprovi nces. Wawa subprovi nces. Borradaile, G.H., 1987. 1987. The Borradai l e yG.J. G.J. and andBrown, Brown, G.H., The Shebandowan Shebandowan Group: "Timi skami ngGroup: "Timiskaminglike"Archean Archean rocks rocks ininnorthwestern northwestern Ontario. Ontario. Canadian Canadian Journal Journal of of Earth Earth like" Sciences, 24, pp.185—188. 185-188. 24,pp. Corfu, F. and Stott, G.M., 1986. U-Pb Corfu, F. and S t o t t , G.M., 1936. U-Pb ages o r late l a t emagmatism magmatism and and regional regional ages ffor t , Superior SuperiorProvince, Province,Canada. Canada. Canadian Canadi an deformation ininthe theShebandown Shebandown Be1 deformation Belt, Journal pp.1075-1032. 1075-1032. Journal of of Earth EarthSciences, Sciences, 23, 23,pp. Macdonald, R.D., 1938. 1938. Geology Geology of Gorham Township andand vicinity. Ontario Macdonald, R.D., of Gorham Township vicinity. Ontario Department Mines, Annual AnnualReport, Report,v.v.48, 48, part part 3, Department ofof Mines, 3, 18 18 p. p. Shegelski, R.J., R.J., 1980. Shegelski, 1980.Archean Archeencratonization,emergence cratonization,emergenceand andred redbed beddevelopment, development, 1 2 , pp. pp. 331-347. 331-347. Lake Shebandowan Shebandowan area, Canada. Precambrian Lake area, Canada. Precambrian Research, Research, 12, 55 �PROTEROZOIC OVERTHRUST-NAPPE OVERTHRUST-NAJ?PE EVIDENCE FOR DEVELOPMENT OF AN EARLY PROTEROZOIC SYSTEM IN THE PENOKEAN OROGEN OF NORTHERN MICHIGAN KLASNER, J.S., 3.2., Department of Geology, Western Illinois KLASNER, Illinois University U.S. Geological Survey, Survey, Macomb, Macomb, IL IL 61455; 61455; OJAKANGAS, OJAKANGAS, R.W., R.W., and U.S. Department of Geology, University of Minnesota, Duluth Duluth and U.S. Geological Survey, Duluth, Duluth, MN MN 55812; 55812; SCHULZ, K.J., K.J.-, U.S. U.S. GeoloGeological Survey, MS 954, National Center, Reston, VA 22092; 22092; and G.L., Department of Geology, University of Wisconsin, LABERGE, G.L., Oshkosh,and U.S. U.S. Geological Survey, Oskosh, WI 54901 Oshkosh,and 54901 Evidence for development of an Early Proterozoic thrust-nappe thrust-nappe system is found in 1900—Ma 1900-Ma rocks at several localities localities in in northern northern Michigan. At Falls River in in L'Anse, north-verging, recumbently recumbently folded slates and graywackes of the Michigamme Formation Formation have have nearly nearly flat—lying, flat-lying, axial planar foliation (Sikkila, (Sikkila, 1987, 1987, and Sikkila Sikkila and and Gregg, 1987). 1987). About 20 20 km k m south of L'Anse, flat—lying flat-lying Early Early Prot— Proterozoic quartzite occurs occurs at at Canyon Canyon Falls. Falls. The quartzite is is separseparated by thrust faults from from stratigraphically higher slates, slates, phyl— phyllites, and metaqraywackes metagraywackes of the Michigamme Formation at Little 1 ites, and Mountain and Taylor Taylor Mine. Mine. Bedding at Little Mountain and Taylor Mine is overturned toward the north and has steeply south-dipping foliation (see foliation (see Fig. Fig. 1). 1). At Plumbago Creek similar overturned slates slates and phyllites have steep south-dipping foliation foliation that projects projects Archean gneiss. gneiss. A drill-hole about 10 10 km km east of Taylor beneath Archean Mine penetrates Archean gneiss. gneiss. The gneiss has shallow—dipping shallow-dipping penetrative cleavage and is is underlain by graphitic slate slate and and quartquartzite, suggesting that the gneiss was overthrust above the the slate. slate. About 110 km to the the west, west, in in Ironwood, Ironwood, Michigan, Michigan, bedding beddng in in graywacke gr~ywackeand slate slate of of the the Tyler Tyler Formation Formation is is oriented oriented N75 N75 5, E, 70°NW. 70 NW. These rocks have a prominent cleavage that that is is oriented oriented N75°,, 58°NW. broad—scale, north-dipping N75 58 NW. The Tyler are part of a broad-scale, homocline that that formed formed during during the the 1100-Ma 1100-Ma rift rift event. event. The Tyler Tyler strata are overlain overlain by by nearly nearly concordant concordant Keweenawan Keweenawan strata. strata. Reorientation Reorientation of of the the Tyler Tyler to to its its position position prior prior to toKeweenawari Keweenawan deformation shows subhorizontal bedding and gently gently south-dipping south-dipping foliation compatible with a north-verging north-verging thrust-nappe thrust-nappe system. system. Thirty km east of of Ironwood, Ironwood, hyaloc&astitgs hyalocastitgs of of the the Emporer Emporer Formation have have a foliation foliation oriented oriented N30 N30 E, E, 30 30 SE. SE. This shallow shallow south dipping foliation is characteristic of the thrusted Early Proterozoic terrane described above and is is interpreted interpreted to to have have north—verging thrust-nappe thrust—nappe system been formed by the same north-verging system that affected the the Tyler Tyler and and Michigamme Michigamme Formations Formations near near L'Anse. L'Anse. Such evidence for for north—verging north-verging thrust thrust faulting faulting was was previously recognized by Cannon Cannon and and Kiasner Klasner (1972), (19721, Klasner Klasner (1972), (19721, and Klasner Kiasner (1978) (1978) and and was wa interpreted Cannon (1973), (19731, and interpreted as a decollement. The field guide for lement. for this this meeting meeting by by Kiasner Klasner and and others, others, (1988) provides provides additional additional data on the nature of Early (1988) Early Proterozoic Proterozoic overthrusting in northern northern Michigan. Michigan. overthrusting in The data presented above span a distance of well over 100 100 km indicate that that Early Early Proterozoic Proterozoic rocks rocks from Ironwood to L'Anse and indicate 56 �and Archean gneiss of the Penokean orogen in in this region are part of a broad-scale north-vergging north-vergqinq thrust-nappe thrust-nappe system, system, probably probably the the same thrust-nappe system as that described by Hoist Holst (1984), (1984), 300 300 km to the west in in Minnesota. Minnesota. REFERENCES REFERENCES W.F., 1973, The Penokean orogeny in northern Michigan, In Cannon, W.F., In G.M. Young (ed.), GeologG.M. (ed.), Huronian Huronian stratigraphy stratigraphy and and sedimentation: sedimentation: Geological Association of Canada Special Paper 12, 12, p. p. 253-271. 253-271. J.S., 1972, 1972, Guide to Penokean Penokean deformadeformaCannon, W.F. and Klasner, J.S., tional style and regional metamorphism of the Western Marquette In W.I.Rose W.I.Rose (ed.), (ed.), Field description and road road Range, Michigan, In logs: logs: 18th Annual Institute on Lake Superior Superior Geology, Geology, Houghton, Houqhton, Mich., p.B1-B38. p.B1-B38. Mich., Holst, T.B., T.B., 1984, Evidence for nappe development during the Early Proterozoic Penokean Penokean orogeny, orogeny, Minnesota: Minnesota: Geology, v. v. 12, 12, 135-138. p. 135—138. Klasner, J.S., J.S., 1972, Style and sequence of deformation and associated metamorphism due to the Penokean orogeny in the western Marquette Michigan: PhD. dissertation, Michigan Technological Range, northern Michigan: University, Houghton, Mich., 132p. University, Mich., 132p. KLasner, J.S., J.S., 1978, Penokean deformation and associated metamorphism in the western Marquette Range, northern northern Michigan: Michigan: Geological Society Society of America Bulletin, Bulletin, v. v. 89, 89, p. p. 711—722. 711-722. Klasner, J.S., J.S., Sims, A structural traverse ing Early Early Proterozoic R.J. field guide, guide, In K.J. tute on Lake Lake Superior Superior P.R., Gregg, P.K., Gregq, W.J., W.J., and Gallup, Gallup, Christina, Christina, 1988, 1988, across a part of the Penokean orogen illustratillustratoverthrusting in in northern northern Michigan: Michigan: text and and Schulz Schulz (ed.), (ed.), Field Field guides: guides: 34th Annual InstiInstiGeology, Geology, Marquette, Mich. Mich. p. C1—C32. C1-C32. Sikkila, K.M., 1CM., 1987, A structural analysis of Proterozoic metasediments, northern Falls River, River, Baraga Baraga County, County, Michigan: Michigan: Master of of Science Science thesis, thesis, Michigan Technological Technological University, University, Houghton, Houghton, Mich. Mich. 103 p. 103 p. Sikkila, K.M. K.M. and Gregg, Gregg, W.J., W.J., 1987, 1987, A structural analysis analysis of of ProProterozoic metasediments, metasediments, northern Falls River, Baraga Baraqa County, Michv. 33, 33, igan (abs.): (abs.)/: 33rd Annual Institute Institute on Lake Superior Superior Geology, Geology, v. igan part 1, 1, pp. pp. 65—66. 65-66. 57 �2 11111, Mu.j.Iuh. 2. Mint I op lot FIGURE 1. — N20W 3 C.*p, FtIIt 'S. N ¼ BASEMENT — N16°E I I 4 I N III It — I I 4s' a.M tiPS.. t _N2OW ESitulo. Si IKIItStI.. I-. btd Slit0 • Fold ,.., Is 8.Sdiag 5, A, I 67 II II Sd SI Falsil —. l5i tC tot inie.t S $t (sUn kKOI•S F FACIIK ROOILIP 'as i ii CPOflttCTI kk k t ___Sin,ina "It.lAitst I. A structural traverse extending southward from Falls River to Covington Mich. and along highway U.S. 141 illustrating the structural relation between Falls River, Little Mountain, Taylor Mine, Plumbago Creek, Lower hemisphere Canyon Falls, and points southward. illustrate orientalion of bedding (SO), stereoplots foliation (Si), and fold axes in SO (black dots) From Klasner dnd others (1988). along the profile. See text for discussion. pI.mt.go 'S. _N30°E !j — — a a a — — — — — a — — a — a a vs r a Foil, Cise A — N2rE �CHEMOSTRATIGRAPHY OF THE LOHER DIISIOfl LAVAS OF THE MiHAINSE POINT FORMATION fiND IMPLICATIONS FOR RIFTING TECTONICS Kiewin. K l e x i n . K. K . 4. H . ,, aand n d Berg, Berg, University, U n i v e r s i t y , DeKalb, DeKalb, Ii T l J. Northern J.H. H . . , iDepartment 2 e p a r t m e n t oof f Geology, G e o l o ~ : , ~ ,N o r t h e r n I Illinois llinois b115 ball5 Detailed Detailed e a s t e r n shore shore eastern sstudy t u d y oof f eexposures x p o s u r e s of o f the t h e Mamainse M a m a i n s e Point P o i n t Formation F o r m a t i o n along a l o n g the the of o f Lake L a k e Superior S u p e r i o r in i n Ontario O n t a r i o reveals r e v e a l s at a t least l e a s t six s i x recognizable recognizable The (1973). T h e llowermost o w e r m o s t uunit n i t ( (3e ~ 3 @ mm uunits n i t s within w i t h i n the t h e Lower L o w e r Division D i v i s i o n of o f Annells A n n e l l s (1973). thick) consists of olivine—phyric basaltic and picritic flows that are heavily t h i c k ) c o n s i s t s of o l i v i n e - p h y r i c b a s a l t i c and p i c r i t i c f l o w s t h a t a r e h e a v i l y more ddissected i s s e c t e d by b y calcite c a l c i t e veins v e i n s aand n d aappear p p e a r tto o be be m o r e aaltered l t e r e d than t h a n fflows l o w s hhigher i g h e r up up (olivines ( d i v i n e s in i n this t h i s and a n d all a l l other o t h e r units u n i t s are a r e altered a l t e r e d to t o secondary s e c o n d a r y minerals). minerals). This by aa ssecond (28e mm thick) T h i s unit u n i t is i s overlaizi o v e r l a i n by e c o n d uunit n i t (5200 t h i c k ) of o f similar s i m i l a r olivineolivinephyric p h y r i c flows, f l o w s , but b u t without w i t h o u t the t h e uubiquitous b i q u i t o u s ccalcite ' a l c i t e vveins e i n s aand n d aappearing p p e a r i n g tto o be be Near less altered. altered. N e a r the t h e middle m i d d l e of o f this t h i s unit u n i t are a r e two t w o or o r three t h r e e very v e r y mafic m a f i c flows floss The that t h a t are a r e komatiitic k o m a t i i t i c in i n terms terms of o f major—element m a j o r - e l e m e n t chemistry. chemistry. T h e upper u p p e r part p a r t has has several s e v e r a l flows f l o w s that t h a t ccontain o n t a i n small s m a l l iinclusions n c l u s i o n s ((i $ 1 cm) c m j of o f wehrlite s e h r l i t e or o r spinel spinel swehrlit.e e h r l i t e ( (the t h e dolivine i v i n e aand n d ppossible o s s i b l e sspinel p i n e l are a r e altered a l t e r e d to t o secondary s e c o n d a r y mtnerals). m~nisrals:~. Overlying O v e r l y i n g this t h i s is i s the t h e third t h i r d unit, u n i t , the t h e very v e r y distinctive d i s t i n c t i v e "daisy " d a i s y stone" stone" ( 25 m This tthick). hick). T h i s unit u n i t consists c o n s i s t s of o f 2—3 2-3 thin t h i n and a n d one o n e very v e r y thick t h i c k flows f l o s s of' of pplagioclase—phyric l a g i o c l a s e - p h y r i c ferrobasalt f e r r o b a s a l t containing c o n t a i n i n g locally l o c a l l y abundant a b u n d a n t 3—cm 3-cm pla5ioclasa plasiuclass The sspherulites. pherulites. T h e ffourth o u r t h unit u n i t (5øø ($500m m thick) t h i c k ) isi scomposed c o m p o s e dof' o f olivine—phyric oli-jine-phyric Especially bbasaltic a s a l t i c and a n d picritic p i c r i t i c flows. flows. E s p e c i a l l y in i n the t h e lower l o w e r part, p a r t , this t h i s unit u n i t has h a s much much coarser c o a r s e r olivine o l i v i n e phenocrysts p h e n o c r y s t s than t h a n the t h e unit u n i t below b e l o w the t h e daisy d a i s y stone s t o n e unit u n i t < oiiiine oil.-ins Above aa transitior phenocrysts p h e n o c r y s t s in i n both b o t h units u n i t s are a r e typically t y p i c a l l y skeletal). skeletal). Abovs t r a n s i t i o n zone z o n eof' of alternating a l t e r n a t i n g olivine—phyric o l i v i n e - p h y r i c and a n d plagioclase—phyric p l a g i o c l a s e - p h y r i c flows, f l o w s , is i s the t h e t'ifth f i f t h unit unit ('4ø@ This ( - ~ 4 0m @ thick) t h i c k ) consisting c o n s i s t i n g of o f plagioclase-phyric p l a g i o c l a s e - p h y r i c basaltic b a s a l t i c flows. flows. T h i c unit u n i t is is ttopped o p p e d by the t h e uppermost u p p e r m o s t (sixth) ( s i x t h ) unit u n i t (z14•ØØ (2400 ma t thick) h i c k ) cconsisting o n s i s t i n g oof f aaphyric phyric Near N e a r the t h e base b a s e of of this t h i s bbasaltic a s a l t i c flows f l o w s interspersed i n t e r s p e r s e d with w i t h aa few f e w ophitic o p h l t i c basalts. basalts. unit u n i t is i s the t h e "basaltic " b a s a l t i c breccia" b r e c c i a " noted n o t e d by b y Annells A n n e l l s (1973). (1973). Thus T h u s far f a r we we have h a v e analyzed a n a l y z e d flows f l o u s from f r o m the t h e four f o u r oldest o l d e s t units u n i t s and a n d found found major geochemical differences between them. The basal unit is dominated m a j o r g e o c h e m i c a l d i f f e r e n c e s b e t w e e n them. T h e b a s a l u n i t i s d o m i n a t e d by by llow—Ti02 o w - T i 0 2 ((1.ø—1.b 1.0-1. 6 nwt%) t % ) bbasalts a s a l t s aand n d ppicrites, i c r i t e s , bbut u t tthese h e s e aalternate l t e r n a t e llocally o c a l l y uwith ith The high—TiOz h i g h - T i 0 2 (up ( u p to t o 2.'t 2. 4 wwt%) t % ) basalts b a s a l t s and a n d picrites. picrites. T h e second s e c o n d unit u n i t contains c o n t a i n s only only The the t h e low—TiOz l o w - T i 0 2 flows f l o w s with w i t h generally g e n e r a l l y less l e s s altered a l t e r e d chemistry. chemistry. T h e komatiitic komatiitic The mentioned MgO ccontents 18—23 wwt. fflows lows m e n t i o n e d aabove b o v e hhave a v e HgO o n t e n t s oof f 18-23 t%. T h e daisy d a i s y stone s t o n e unit u n i t is is a a very—high—Ti02 v e r y - h i g h - T i 0 2 ferrobasalt, f e r r o b a s a l t , and a n d analyses a n a l y s e s support s u p p o r t an a n accumulation a c c u m u l a t i o n model m o d e l for for The the t h e plagioclase p l a g i o c l a s e spheruljtes. spherulites. T h e oolivine—phyric l i v i n e - p h y r i c flows f l o a s above a b o v e the t h e daisy d a i s y stone stone Figures uunit n i t are a r e high—Ti02 h i g h - T i 0 2 (1.4—2,7 ( 1 . 4-2. 7 wt%) u t % ) basalts b a s a l t s and a n d picrites. picrites. F i g u r e s 1, 1, 2, 2, and . . ~ n d33 sshow h o a that t h a t except e x c e p t for f o r the t h e lowest l o w e s t unit u n i t the t h e other o t h e r units u n i t s have h a v e distinct d i s t i n c t geochemical gsochemical A ccharacteristics h a r a c t e r i s t i c s and a n d trends. trends. A plot p l o t of o f Ti02 T i 0 2 vs. vs. flow f l o w I! (Fig. ( F i g . 2) 2) rreveals e v e a l s some within oof f the t h e systematic s y s t e m a t i c iinternal n t e r n a l vvariation ariation w i t h i n uunits, n i t s , bbut u t aalso l s o tthe h e pprofound r o f o u n d aand nd aabrupt b r u p t changes c h a n g e s between b e t w e e n most m o s t of o f the t h e units. units. These T h e s e field f i e l d and a n d ggeochemical e o c h e m i c a l ccharacteristics h a r a c t e r i s t i c s hhave a v e aallowed l l o w e d uus s tto o ccorrelate orrelate this t h i s main m a i n section s e c t i o n of o f the t h e MPF MPF that t h a t starts s t a r t s at a t Mica M i c a Bay Bay with a i t h the t h e Alona A l o n a Bay Bay secsection MPF based b a s e d on o n reconnaissance r e c o n n a i s s a n c e field f i e l d and a n d compositional c o m p o s i t i o n a l examination e x a m i n a t i o nof' of t i o n of o f the t h e MPF Contrary the t h e Alona A l o n a Bay Bay section. section. C o n t r a r y to t o the t h e speculation s p e c u l a t i o n of o f Annells A n n e l l s (1973), (1q73",the the Alona A l o n a Bay section s e c t i o n starts s t a r t s high h i g h up u p in i n our o u r second s e c o n d unit u n i t (alternatively, ( a l t e r n a t i v e l y , tthe h e first first two t w o units u n i t s are a r e extremely e x t r e m e l y thinned t h i n n e d at a t Alona A l o n a Bay). Bay). IIn n aany n y eevent, v e n t , although a l t h o u g h prepreviously v i o u s l y unrecognized, u n r e c o g n i z e d , the t h e daisy d a i s y stone s t o n e unit u n i t occurs o c c u r s relatively r e l a t i v e l y near n e a rthe t h ebase b a s eof' of the t h e Alona A l o n a Bay section, s e c t i o n , and a n d it i t is i s underlain u n d e r l a i n by by the t h e low—Ti02 l o x - T i O ; olivine—phyric olivine-phyric Rare lavas l a v a s and a n d overlain o v e r l a i n by b y the t h e high—Ti02 h i g h - T i 0 2 olivine—phyric o l i v i n e - p h y r i c lavas. lavas. R a r e small small plagioclase p l a g i o c l a s e spherulites s p h e r u l i t e s are a r e present p r e s e n t in i n the t h e Alone A l o n a Bay Bay daisy d a i s y stone s t o n e unit, u n i t , but but otherwise o t h e r w i s e it i t is i s free f r e e of o f the t h e abundant a b u n d a n t large l a r g e spherulites s p h e r u l i t e s that t h a t characterize c h a r a c t e r i z e the the Mica Bay daisy Mica d a i s y stone. stone. (2a 59 �He He believe b e l i e v e that t h a t the t h e magma magma chemistry c h e m i s t r y of o f these t h e s e primitive p r i m i t i v e la;as. l a ; a s , the t h e prospro;-;rressive e s s i v e changes c h a n g e s in i n magma magma chemistry c h e m i s t r y within s i t h i n each e a c h unit, u n i t , . and a n d the t h e abrupt a b r u p t . changes changes i l l uultimately l t i m a t e l y pprovide r o v i d e iimportant m p o r t a n t sstratigraphically—controlled tratigraphicallv-controlled bbetween e t w e e n uunits n i t s wwill a n s w e r s to t o maflor m a i o r qquestions u e s t i o n s r regarding e g a r d i n g tthe h e ttectonic e c t o n i c ddevelopment. evelo~ment.m a g m a t i c e',.'oiaanswers magmatic evolittion. i o n , mantle m a n t l e structure s t r u c t u r e and a n d dynamics, d y n a m i c s , and a n d crustal c r u s t a l integrity i n t s g r i t y during d u r i n gthe t h eriftirig fifting For pprocess. rocess. F o r example, e x a m p l e , the t h e lowermost l o a e r m o s t unit u n i t contains c o n t a i n s lavas l a v a s that t h a t may have have were very v a r y rich r i c h in in o r i g i n a t e d from f r o m two t w o separate S e p a r a t e mantle m a n t l e sources, s o u r c e s , both b o t h of o f which w h i c h were originated LILE, u t oone n e (producing ( p r o d u c i n g the t h e high—Ti02 h i g h - T i 0 2 lavas) l a v a s ) richer r i c h e r than t h a n the t h e other. other. A lternaLILE, bbut Alternamagmas were were bbeing modified eing m o d i f i e d bby y ccrustal r u s t a l assimilation a s s i m i l a t i o n while while ttively, i v e l y , some s o m e of' o f t the h e magmas others o t h e r s were were not, n o t , or o r at a t least l e a s t less l e s s so. so. D u r i n g the t h e eruption e r u p t i o n of o f the t h e second s e c o n d unit, unit, During o n l y the t h e less—enriched l e s s - e n r i c h e d source s o u r c e was being b e i n g tapped t a p p e d and a n d magmas became b e c a m e progressively progressively only more m o r e primitive. primitive. PPresumably r e s u m a b l y the t h e plumbing p l u m b i n g system s y s t e m was was becoming b e c o m i n g better b e t t e r developed, developed, This aallowing l l o w i n g primitive p r i m i t i v e lavas l a v a s an a n ever—more e v e r - m o r e direct d i r e c t route r o u t e to t o the t h e surface. surface. T his was aabruptly ferrobasalts eepisode p i s o d e was b r u p t l y tterminated e r m i n a t e d bby y the t h e eeruption r u p t i o n oof f hhighly i g h l y eevolved v o l v e d ferrobasalts After fforming o r m i n g the t h e daisy d a i s y stone s t o n e unit. unit. A f t e r oonly n l y 3-4 3-4 eruptions e r u p t i o n s of o f this t h i s highly h i g h l y evolved evolved magma system less magma, aa new new primitive p r i m i t i v e magma s y s t e m took t o o k oover, v e r , erupting e r u p t i n g progressively p r o g r e s s i v e l y less primitive p r i m i t i v e lavas l a v a s ssomewhat o m e w h a t similar s i m i l a r to t o the t h e high—Ti02 h i g h - T i 0 2 laas l a v a s of o f the t h e basal b a s a l unit. unit. Because B e c a u s e it i t appears a p p e a r s difficult, d i f f i c u l t , if i f not n o t impossible, i m p o s s i b l e , to t o relate r e l a t e the t h e three t h r e e magma magma ssystems y s t e m s represented r e p r e s e n t e d by by the t h e flows f l o w s oof f the t h e ddaisy a i s y stone s t o n e and a n d the t h e units u n i t s above a b o v e and arid below, b e l o a , profound p r o f o u n d changes c h a n g e s in i n magma magma sources s o u r c e s arid a n d tthe h e crustal c r u s t a l plumbing p l u m b i n g system s y s t e m must must have h a v e been b e e n taking t a k i n g place p l a c e across a c r o s s this t h i s interval. interval. PPerhaps e r h a p s tthe h e llow—hO: o x - T i O : magma magma source l i t h o s p h e r - i c mantle. mantle. s o u r c e was lithospheric l i t h o s p h e r i c mantle m a n t l e or o r involved i n v o l v e d aa component c o m p o n e n t of o f lithospheric mark time wwhere Its I t s termination t e r m i n a t i o n ccould ould m a r k tthe h e ppoint o i n t iin n time h e r e tthe h e aasthenospheme s t h e n o s p h e r 1 . c diapir diapir This finally f i n a l l y eroded e r o d e d through t h r o u g h to t o the t h e base b a s e of o f the t h e crust. crust. T h i s would w o u l d have h a v e accelerated accelerated rifting r i f t i n g of o f the t h e crust c r u s t and a n d could c o u l d have h a v e resulted r e s u l t e d in i n the t h e disruption d i s r u p t i o nand a n dtapping t a p p i n gat' of crustal c r u s t a l magma magma chambers c h a m b e r s containing c o n t a i n i n g highly h i g h l y evolved e v o l v e d magmas, magmas, thus t h u s forming f o r m i n g the the New evolved e v o l v e d daisy d a i s y stone s t o n e unit, unit. N e w magma magma generation g e n e r a t i o n would w o u l d subsequently s u b s e q u e n t l y be b e derived derived Alternative solely s o l e l y from f r o m the t h e asthenospheric a s t h e n o s p h e r i c subeontinental s u b c o n t i n e n t a l mantle. mantle. A l t e r n a t i v e models m o d e l s are are models i l l be b e ggreatly r e a t l y iimproved m p r o v e d with xith ppossible, o s s i b l e , aand n d tthe h e cconstraints o n s t r a i n t s oon n tthese hese m o d e l s wwill Nevertheless, models Keweenaan iisotopic s o t o p i c results. results. N e v e r t h e l e s s , ddynamic y n a m i c ttectonic ectonic m o d e l s ffor o r tthe he K exeenaiian rrift i f t wwill i l l ddepend e p e n d hheavily e a v i l y oon n aaccurate c c u r a t e aand n d ddetailed e t a i l e d cchemostratigraphic h e m o s t r a t i g r a p h i c studies studies of o f the t h e erupted e r u p t e d lavas. lavas. . REFERENCE REFERENCE The 1973, Annells, .N., 1 9 7 3 , Proterozoic P r o t e r o z o i c flood f l o o d basalts b a s a l t s of' o f eastern e a s t e r n Lake L a k e Superior: Superior: The A n n e l l s , RP.,N,, Gaol. Keweenawan Keweenawan volcanic v o l c a n i c rocks r o c k s of' o f tthe h e Mamainse M a m a i n s e Point P o i n t area, a r e a , Ontario, Ontario, G eol. Surv. S u r v . Canada C a n a d a Paper P a p e r 72—10, 7 2 - 1 0 , 51 51 p. p. FIGURES NOTE FOR FIGURES 1, open Asterisks A s t e r i s k s == uunit n i t 1, o p e n squares s q u a r e s == uunit n i t 2, 2, oopen p e n triangles triangles Some of the unit stone)1 solid squares = s t o n e ) , s o l i d s q u a r e s = u n i t 4. 4. o f t h e samples s a m p l e s from from not n o t been b e e n analyzed a n a l y z e d for f o r chromium. chromium. 60 == unit unit 3 3 (daisy (daisy units u n i t s 1 and a n d 22 have have 1 �Cu 3 2 0 33 5 5P I I 1 0 Fig. a a I 0 3 15 a mu au,. 10 MgO Fig. I a %a 0 xD I 2 20 a 0 25 3 0 0 I 0 I I a. I 0 I Fig. I a 2 1000 CR Fig. 4 I 0 2 1500 — I. •1. JLD 0 1111111 I 500 1 3 2 I 0 80 go 2000 3 70 60 50 40 30 20 10 0 CU 0 -,-1 I— 0 -J IL FLOW # I 0 0.3 0.2 0 Ti02 + n - i W ^ L n r n ^ J C D t D 0 I— WI Cu 0 0 0.1 0.0 Ti02 0 0 0 0 0 0 0 0 0 w �THEBARABOO EARABOO QUARTZITE: OUARTZITE: THE ?,lE?! LOOK LOCK AT ATAN A?! OLD CLDPROBLEM PRO3LE4 A.4NEW GEYE L. L. LABERGE, LABERGE, Geol. Geol. Dept., Dept., UW—Oshkosh, UJ-Oshkosh, Oshkosh, Oshkosh, WI VI and and U.S.G.S. U.S.G.S. and and JOHN JOIIN S. S. GENE KLASNER, Geol.Dept., Dept.,Vestern WesternI Illinois SLASXER, Geol.. l l i n o i sUniv., Univ*,Macomb, Yacomb, IL I Land andU.S.G.S. U.S.G.S. i n c l u d i n g the t h e Baraboo Baraboo c e n t r a l . and and southern s o u t h e r n Wisconsin, Idisconsin, quartzires, q u a r t z i r e s , including InI n central Quartzite, Q u a r t z i t e , represent r e p r e s e n t the t h e southernmost southernmost occurence occurence of of Precambrian Precambrian rocks r o c k s in i n the the Lake Lake Superior S u p e r i o r region, r e g i o n , but but their t h e i r stratigraphic s t r a t i g r a p h i c and and tectonic t e c t o n i c relations r e l a t i o n s to t o the the sedimentary rocks r o c k s of o f the t h e iron i r o n districts d i s t r i c t s to t o the t h e north n o r t h is is uncertain. uncertain. sedimentary Originally, O r i g i n a l l y , the t h e Baraboo Baraboo Quartzite Q u a r t z i t e and and associated a s s o c i a t e d slate, slate, dolomite, dolomite, and and iron— ironwere called c a l l e d "Huronian" "Huronian" and and correlated c o r r e l a t e d with w i t hthe t h eiron—bearing iron-bearing rocks r o c k s of of formation were formation the VanHise Hise and andLLeith, t h eLake Lake Superior S u p e r i o r region r e g i o n(Weidman, (Weidman, 1904; 1904; Van e i t h , 1911; 1911; Leith, L e i t h , and and o t h e r s 1935). 1935). Subsequently, Subsequently, Dalziel Dalziel. and and Dott Dott (1970), (l97O), Smith Smith (1978), ( l 9 7 8 ) , Van Van Schmus Schmus others (1978), (1978), and and Greenberg Greenberg and and Brown Brown (1983, (1983, 1986) 1986) suggested suggested that t h a t the t h e quartzites q u a r t z i t e s in in t h e r e f o r e , substantially substantial.1.y southern southern Wisconsin Idisconsin are are younger younger than t h a n 1,760 l V 7 6 0Ma M a and, and, therefore, Deformation of of younger younger than t h a n the t h e Proterozoic P r o t e r o z o i c sedimentary sedimentary rocks r o c k stot othe t h enorth. n o r t h . Deformation the t h e quartzites q u a r t z i t e s has h a s been been attributed a t t r i b u t e d to t o aa postulated p o s t u l a t e d plate p l a t e tectonic t e c t o n i c event e v e n t that that occurred 1,630 1,630 Ma Ma ago ago and and was was buried buried beneath beneath Paleozoic P a l e o z o i c rocks r o c k s to t o the t h e south south occurred (Smith, 1978; 1978; Dott, D o t t v 1983; 1983; Cambray, Cambray, 1987). 1987). (Smith, Recent ??ecent geologic g e o l o g i c studies s t u d i e s (LaBerge (J4aBerge and and Kiasner, Klasner, 1986, 1986, and and preparation) p r e p a r a t i o n ) in in central c e n t r a l . and and southern s o u t h e r n Wisconsin 14?isconsinsuggest s u g g e s t that t h a t the t h e quartzite q u a r t z i t e occurrences o c c u r r e n c e s in i n this this area a r e a are are older o l d e r than t h a n currently c u r r e n t l y interpreted i n t e r p r e t e d and and that t h a t they they are a r e remnants remnants of of aa major south—vergent south-vergent thrust—fold t h r u s t - f o l d system. system. Our Our studies, s t u d i e s , presented presented below below and and major shown shown in i n Figures F i g u r e s 11 and and 22 suggest s u g g e s t that t h a t the t h e quartzite q u a r t z i t e was was present p r e s e n t and and was was thrust thrust southward and southward before b e f o r e 1,760 1,760 Ma, kv and probably probably before b e f o r e 1,850 1,850Ma. !la. At A t Baraboo, 3arab00, the t h e relation r e l a t i o n of of the t h e quartzite q u a r t z i t e to t o adjacent a d j a c e n t rhyolite r h y o l i t e is is Dal.zie1. and and Dott . D o t t (1970) (1970) suggested suggested that t h a t the t h e quartzite q u a r t z i t e is is problematical. Dalziel problematical. stratgraphically s t r a t g r a p h i c a l l y above, above, and and younger youn'ger than, t h a n , adjacent a d j a c e n trhyol.ite, r h y o l . i t e , which which is is inferred inferred t o be be 1,760 1,760 Ma. ?fa. However, flowever, Stark S t a r k (1930, (1930, 1932) 1932) suggested suggested that t h a t rhyolite r h y o l i t e crops c r o p s out out to on the t h e upturned upturned northern n o r t h e r n limb limb of of the t h e Baraboo 3araboo Syncline, S y n c l i n e , which which indicates i n d i c a t e s that that on t h e quartzite q u a r t z i t e is i s older o l d e r than t h a n the t h e rhyolite. r h y o l i t e . Although Although not n o t unequivocal, unequivocal., our our field fie1.d the A t Hamilton Ramilton Mounds, Younds, the the i n v e s t i g a t i o n s support s u p p o r t Stark's S t a r k ' s (1932) (1932) interpretation. i n t e r p r e t a t i o n . At investigations deformed is intruded i n t r u d e d by by an a n undeformed undeformed granitoid g r a n i t o i d dike d i k e dated dated at a t 1,764 1,764 deformed quartzite q u a r t z i t e is A t Vesper Vesper Ma, Ma, which which indicates i n d i c a t e s pre—1,764 pre-19764 Ma M a deformation deformation of of the t h e quartzite. q u a r t z i t e . At quarry, q u a r r y , quartzite q u a r t z i t e that t h a t has h a s aa steep—dipping steep-dipping tectonic t e c t o n i c fabric f a b r i c occurs o c c u r s within w i t h i n 33 min of of an a n undeformed undeformed granite g r a n i t e that t h a t is i s identical i d e n t i c a l . to t o granite g r a n i t e at a t Cary Cary Mound Yound dated dated at at 1,832 Ma; ?la; we w e infer i n f e r that t h a t the t h e 1,832—Ma 1,832-Ma granite g r a n i t e intruded i n t r u d e d the t h e already a l r e a d y deformed deformed 1,832 . q u a r t z i t e . Along Along Hamann Hamann Creek Creek in i n western western Marathon Farathon County, County, quartzite q u a r t z i t e boulders bou1.ders •quartzite. occur in i n aa conglomerate conglomerate that t h a t is is interbedded interbedded with w i t h 1,850—Ma—old 1,850-?fa-old volcanic v o l c a n i c rocks rocks occur T h i s requires r e q u i r e s the t h e presence presence of of aa 1,850—Ma 1,850-!la quartzite quartzite (LaBerge and and Myers, Hyers, 1983). 1983). This (LaBerge c e n t r a l .Wisconsin. I/isconsin. Sillirnanite—bearing S i l l i m n i t e - b e a r i n g qquartzite u a r t z i t e xenoliths x e n o l i t h sini nthe t hWausau e Vausau central pluton probably probably represent r e p r e s e n tuplifted u p l i f t ehigh—grade d high-grade basement basement rocks r o c k s that t h a t are a r e not not pluton to tunderlie of the the exposed, but but are a r einferred inferred o u n d e r l1,850—Ma—old i e 1,850-Ma-old vvolcanic o l c a n i c rrocks o c k s of exposed, r e g i o n (LaBerge (LaBerge and and Myers, ?fyers, 1984). 1984). region in in Therefore, T h e r e f o r e , the t h e availabl.e availab1.e sstratigraphic t r a t i g r a p h i c evidence evidence indicates i n d i c a t e s that t h a t the the quartzites q u a r t z i t e s in i n central c e n t r a l and and southern s o u t h e r n Wisconsin iscon cons in may be be older o l d e r than t h a n 1,850 1,850 Ma ?la (Figure 1). 1 ) . Thus, Thus, they t h e y appear appear to t o pre—date pre-date the t h e 1,850—Ma 1,850-Ha Penokean Penokean orogeny. orogeny. We ?!e (Figure suggest suggest that t h a t the t h e quartzites q u a r t z i t e s represent r e p r e s e n t remnants remnants of of aa once—extensive once-extensive sequence sequence of of Early Early Proterozoic P r o t e r o z o i c platform p l a t f o r m sedimentary .sedimentary rocks r o c k s deposited d e p o s i t e d on on the t h e passive p a s s i v e margin margin The The exact e x a c t age age of of the the of of an a n Archean Archean craton, c r a t o n , now now exposed exposed in i n central c e n t r a l . Wisconsin. l!isconsin. sedimentary sedimentary rocks rocks is i s unknown, unknown, but, b u t , inasmuch inasmuch as a s they they appear appear to t o pre—date pre-date the the Penokean Penokean Orogeny, Orogeny, they they may may be be roughl.y roughly equivalent e q u i v a l e n t to t o the t h e Marquette I l a r q u e t t e Range Fange Supergroup supergroup of of northern n o r t h e r n Michigan. Yichigan. As A s shown shown in i n Figure F i g u r e 2, 2, the t h e platform ? l a t f o r m sediments sediments 62 �are a r e interpreted i n t e r p r e t e d to t o have have been been thrust t h r u s t southward southward onto onto the t h e Archean Archean craton c r a t o n as a s it it (see collided t h e Wisconsin Visconsin Magmatic ?,lagmaticterrane t e r r a n e (see col.1.ided with the t h e island i s l a n d arc a r c rocks rocks of of the earlier e a r l i e r studies s t u d i e s of of LaBerge, LaBerge, 1986; 1986; LaBerge LaBerge and and others, o t h e r s , 1984a, 1984a, b). b). REFERENCES CITED CITED Cambray, F.W., 1987, The Cambray, F.V., The Baraboo 3araboo Syncline; The The Shape Shape and and Refolding Refolding Explained Explained as as aa Result Result of of Superposition Superposition of of Simple Simple Shear Shear on on aa Pre—Existing Pre-Existing Fold: Fold: Abstract, G. G. S. S. A., A., Minneapolis, Ninneapolis, p. p. 192 192 Abstract, Daiziel, I.V*D., and and Dott, Dott, R.H., R*H., jr. jr. 1970, 1970, Geology Geo1.ogy of of the t h e Baraboo Baraboo District, District, D a l z i e l , I.W.D., Wis.: and Nat. Nat. HHist. Survey IInfor. Circular nfor. C i r c u l a r 14, 14, 164 164 p. p. Idis* : Geol.. Geol.. and i s t . Survey The Proterozoic Proterozoic red red quartzite q u a r t z i t e enigma enigma in i n the t h e north— northDott, R.H., Jr. Jr. 1983, 1983, The Dott, R.H., G. S. A. Memoir Memoir 160. 160. central. United SStates: central. United t a t e s : Resolved by plate p l a t e collision? col.lision? G. S. A. Greenberg, J. K., K., and Brown, Brown, B.A., B-A., 1983, Middle Proterozoic P r o t e r o z o i c to t o Cambrian rocks Greenberg, J. in i n central central. Wisconsin: !$isconsin: Anorogenic Anorogenic sedimentary sedimentary and and igneous igneous activity: a c t i v i t y : Wis. Vis. Geol. Geol.. and and Nat. Hat. Hist. R i s t . Survey Survey Field F i e l d Trip T r i p Guide Guide Book Book No. 80. 8, 8 , 50 50 p. p. Greenberg, J*K., Brown, Brown, B.A., B.A., and and Medaris, Medaris, L.G. L.G. Jr., J r * ,1986, 1986,The TheWol.f Wolf River River Greenberg, J.K., Batholith 32ndAnnual. Annual. Inst. Inst. GuidebookField F i e l d Trip T r i p1,1,32nd B a t h o l i t h and and Baraboo Baraboo Interval: I n t e r v a l : Guidebook on Lake Superior Geology, b!isconsin Rapids. Rapids. Ge01.ogy , Wisconsin LaBerge, La3erge, G.L., G*L., 1986, 1986, The Proterozoic P r o t e r o z o i c Geology of of the t h e Lake Superior Region. Eegion. in 50th Annual Annual. Tn—State T r i - S t a t e Fiel.d Fie1 d LaBerge, G.L. G. L. and and Mode, Xode, 'I.N., !!.!I., Guidebook. Guidebook. 50th Conference. Conference. LaBerge, 1985, Evidence for f o r a major south—directed south-directed LaBerge, G.L., G.L., and Klasner, Kl.asner, J.S., J.S., 1986, Early G. Ear1.y Proterozoic P r o t e r o z o i c thrust t h r u s t sheet s h e e t in i n south south central central. Wisconsin: Visconsin: Abstract, A b s t r a c t , G. S. A. A. San San Antonio, Antonio, TX. TX. S. LaBerge, LaBerge, G.L., G.L*, and and Klasner, Klasner, J.S. J.S. (in ( i n preparation), p r e p a r a t i o n ) , Major Ikijor south south directed directed thrusting t h r u s t i n g of of Early Early Proterozoic P r o t e r o z o i c quartzites q u a r t z i t e s in i n south southcentral. central. Wisconsin: !!isconsin: Implications I m p l i c a t i o n s of of the t h e Penokean Penokean Orogeny. Orogeny. LaBerge, La9erge, G.L., G.L., and and Myers, Myers, P.E., P.E., 1983, 1983, The Precambrian b e c a m b r i a n geology geology of Marathon County, Vis. : Wis. Vis. Geol. Geol.. and and Nat. Hat. lUst. Hist. Survey Survey Info. Info. Circular C i r c u l a r 45, 45, 83p. 83p. County, Wis.: LaBerge, Myers, P.E., P.E., 1984, Proterozoic successions in LaBerge, G.L., G.L., and Myers, 1984, Two eearly arly P r o t e r o z o i c successions in . central c e n t r a l Wisconsin b!isconsin and and their t h e i r tectonic t e c t o n i c significance: s i g n i f i c a n c e : G. G. S. S. A. A. Bull. Full.. pp. pp. 246-253. 246—253. LaBerge, Myers, P.E., ?*E., 1984a, 1984a, The plate p l a t e tectonic tectonic LaBerge, G.L., G.L., Schulz, S c h u l . ~IC.J., ,K.J., and Myers, history Wisconsin: Abstract. h i s t o r y of of central central. IJisconsin: Abstract. 30th Annual Inst. I n s t . on Lake Superior Superior Geology, Geology, Wausau, Wausau, p. p. 25—27. 25-27. LaBerge, J., Myers, P.E., P.E., 1984b, Proterozoic Plate K. J *, and Myers, 1984b, "Early "Early P roterozoic P late G.L., Schulz, Schulz, K. LaBerge, G.L., Tectonics: G. S. S. A. A. Reno,NV. Reno ,NIT. Tectonics: Evidence Evidence from from north n o r t h central c e n t r a l . Wisconsin,"Abst. W i s c o n s i n ,"Abst C. Leith, Pre—Cambrian rocks of L e i t h , C.K., C.K., Lund, Lund, R.J., R.J., and Leith, L e i t h , AA.* 1935. 1935. Pre-Cambrian of the t h e Lake Superior region, region, with revised r e v i s e d geologic geologic maps. maps. U.S.G.S. U.S.G.S. Prof. Prof. Paper Paper 184. 134. Smith, E.I., E.I., 1978, 1978, Precambrian Precambrian Rhyolites Rhyolites and and Granites G r a n i t e s in i n South—Central. South-Central. Smith, Wisconsin: IJisconsin: Field F i e l d Relations R e l a t i o n s and and Geochemistry: Geochemistry: Geological. GeoI.ogica1. Society S o c i e t y of of America Bulletin, B u l l e t i n , vol. vol. 89, 89, pp. pp. 875—890. 875-890. Stark, J. T., T., 1930, 1930, Pre—Cambrian Pre-Cambrian water—laid water-].aid tuff t u f f in i n the t h e Baraboo, 3arab00, Wisconsin, Wisconsin, S t a r k , J. District.: District.: Jour. Jour. Geol., Geol.., Vol. Vol. 38, 38, pp. pp. 466—471. 466-471. Stark, District, Wisconsin: !$isconsin: Jour. Jour. 1932, Igneous Igneous rocks rocks in i n the t h e Baraboo Baraboo District, S t a r k , J.T., J-T., 1932, Geol., Geol*, Vol. Vol.. 40, 40, pp. pp. 119—139 119-139 W.R., 1978, 1978, Geochronology of of southern southern Wisconsin Visconsin rhyolites r h y o l i t e s and and Van Schmus, Schmus, W.R., Van granites; p. 19—24. 19-24. Val* 2, 2 , p. g r a n i t e s ; Geoscience Geoscience Wisconsin, Visconsin, Vol.. Van Hise, use, C.R., C.R*, and and Leith, L e i t h , C.K., C.K., 1911, 1911, Geology Geology of of the t h e Lake Lake Superior ' s u p e r i o r Region. Region. U.S. U.S. Geological GeologicaT Survey Survey Monograph Konograph 52. 52. Weidman, The Baraboo Iron-Eearing Iron—Bearing District District of of V!isconsin Wisconsin: Wisconsin : :*!isconsin Weidman, S., S., 1904, 1904, .=The X i i i , 190 190 p. p Geological. and Natural. Natural Ristory History Survey Survey B Bulletin No. Xiii, GeoI.ogica1. and u l l e t i n ?To. . . 63 �__________________________________ }40 TOUATEO. ItLiUANITE.aEARIN6 QUAflT2I1 C RIB MOUNTAIN XENOUTN IN 500 MA SYENITE NAT iNTRUOBS GI1EENS0WST.ACBS I 130 MA VCS.CAMCS. PRE—1,850 Ma • - :? ... . 4.—'. .. .•-—', '. VO1.C.5N OUARTZITE PRE.OATES lOSE MA. OEFCRME0O.LAR1E ERREO 100* INTRUOEO BY U9OEFCRM*0 I5MARO VESPER QUARRY GAAMTL PRE—1,832 Ma JARTZITE AND DEFORMATION PRE-QATES 1332MA. OEFGRMEOQUM1TE INT.J0E0 BY 1154 MA . ' . INTERBEDOED WITH OEFORMED 1550 MA ° PRE-1,850 Ma • • METMIORPSW 10 SIWMANITE GRAOE PRIOR 10 1550 MA. aNR1 BA0EPS 19 CGI.C*.IERATE NAMANN CREEK L...._ — O.MR1'ZrTE OEPOSITEO AIO : -- GRAMTE. HAMILTON MOUNDS : ••-4- PRE—1,764 Ma CUAR1ZITE AND OEFORMATION PQE.OAT3 1704 MA. —Y..•.,.•_'• OEFCRMEO OUARTZTTE IS STRATIGRAP,.IICAIY 8ARABOO SYNCLINE 5*1.0W UNOEFOI1MED hOE MA YOJTE. CUANTZIT* AND OSFORMATION PRE.OATES PRE—1,76o Ma 1760M& Figure Figure 1. 1 . Location Locationmap map and and a-ge age rrelationships e l a t i o n s h i p s of o f quartzites quartzites in in central c e n t r a land andsouthern southernWisconsin. Wisconsin. QUARTZITES OF OF SOUTHERN SOUTHERN WISCONSIN WISCONSIN QUARTZITES RAEO BE A ARAB 00O Y NC N C LINE LINE SSY NECEDAH N E C E D A H HAMILTON HAMILTON MOUNDS MOUNDS QUARRY QUARRY VESPER VESPER HAMANN HAMANN QUARRY Q U A R R Y CREEK CREEK RIB MOUNTAIN MOUNTAIN I— 44'4 4AA 4. 4 A 4 1754 MA A 4 4 ARCHEAN ARCHEAN I.\ g 1532 MA 4 CONTINENTAL CONTINENTAL FORELAND - FORELAND EAU EAU PLEINE P L E I N E FAULT F A U L TZONE ZONE ACCRETED ACCRETED VOLCANIC VOLCANIC TERRAINE Figure 2. 2 . Diagramatic Djagramat,!~cross—section c r o s s - s e c t i o n of o f the the proposed proposed tectonic tectonic Figure r e l a t i o n s h i p s ofo fthe t h esouthern southernWisconsin Wisconsin quartzites. quartzites. relationships 64 �PALEOMAGNETISM O F THE TH3CLAY-HOWELLS CUY-HOmLLS CARBONATITE CAFBONATITEAND ANDKEWEENAWAN KE-ENAWAN MOTION ON PALEOMAGNETISM OF MOTION THE KSZ LewchukI M.T.# SymonsI D . T . A a I Department of Lewchuk, M.T., and Symons, D.T.A., of GeologyI Geology, University of Windsor, Windsort Windsor, Windsort Ontario, OntarioI Canada Canada N9B N9B 3P4 3P4 The Clay-Howells Clay-Howelis Complex is of i s llocated o c a t e d approximately 130 km eeast a s t of HearstI Ontario, Ontario, at a t 49950'N, 4 9  ° 5 0 ' ~82°05'W 8 2 O 0 5 ' ~within tthe he n o r t h end of h e Kapuskasing Hearst, north of tthe It (KSZ) of the t h e Superior Superior Province Province of of the t h e Canadian Canadian Shield. Shield. It S t r u c t u r a l Zone (KSZ) Structural i s a large l a r g e aviform 'U6 km2 km2 that t h a t i s composed composed dominantly dominantly of of syenite syenite is oviform pluton of "16 with with minor minor carbonatite. c a r b o n a t i t e . It I t was emplaced into i n t o an an Archean gneissic g n e i s s i c terrain terrain of of the t h e amphibolite a m p h i h l i t e to t o granulite g r a n u l i t e facies f a c i e s with with Middle Middle Precambrian Precambrian diabase diabase dikes. dikes. The complex is age (Rb/Sr 107216 Ma) n age The complex i s Late Precambrian iin (Flb/Sr 1072516 Ma) with w i t h aa relatively relatively fresh texture. f r e s h unmetamorphosed unmetamorphosed t e x t u r e . Field F i e l d and and geophysical geophysical ddata a t a iindicate n d i c a t e tthat h a t the the is complex wasprobably probablyformed formedbybyt hthe passive iintrusion complex was e passive n t r u s i o n of of several s e v e r a magmatic l magmatic pulses l a t e fault f a u l t may cut c u t the t h e northeast n o r t h e a s t corner p u l s e s with with similar s i m i l a r compositions. compositions. A late of the t h e complex. complex. Detailed of 194 Detailed AF and and thermal demagnetization of 194 specimens specimens from 21 sites sites (18 from from tthe h e iintrusion, n t r u s i o n , two from from the t h e dikes d i k e s and and one one from from the t h e host h o s t gneisses) gneisses) was completed completed using using aa CTF CTF cryogenic cryogenic magnetometer magnetometer in i n aa shielded shielded room. room. The The 18 1 8 syenite s y e n i t e sites s i t e s define d e f i n e aa consistent c o n s i s t e n t unit u n i t mean mean direction d i r e c t i o n of of 294.2°, 294.2O, 27.1° ( N == 18, 18, kk == 26,ccg5 2 6 , a g ~== 7.0) which which yields y i e l d s aa pole p o l e position p o s i t i o n of of l78.8°E, 178.8O~~ 27.1' (N 26.5°N (D == 4.1, 26.5O~ (Dp 4.11 Dm Dm == 7.6) for f o r the t h e Clay—Howells Clay-Howells Complex. Complex. AA rudimentary rudimentary contact c o n t a c t test t e s t with with the t h e three t h r e e Archean Archean ssites i t e s proved proved inconclusive. The The sscatter catter of of the t h e site s i t emeans means about about the t h e unit u n i tmean mean direction d i r e c t i o n does does not not indicate i n d i c a t e aageographgeographical alongt hthe i f any any -- did d i d not not i c a l bias b i a sso sothat t h apost—intrusive t p o s t - i n t r u s i v e movement movement along e ffault a u l t -- if produce tilting rotations. produce t i l t i n g r o t a t i o n s . The concordant concordantwith w i t hthe t h eapparent apparentpolar p o l a rwander wander The ppole o l e ffor o r the t h e intrusion i n t r u s i o nisi s path rocks of of Palmer p a t h for f o rKeweenawan Keweenawan rocks Palmer and Davis (1987). (1987). It It plots p l o t sat a tapproxapproximately 107510Ma on the the Logan Logan Loop Loop which. which is i s in i n agreement agreement w i t h the t h e Rb/Sr Rb/Sr age age 1075210~aon with of l072t16 i s that that 1072216 Ma Ma for f o r the t h e Clay—Howells Clay-Howells Complex. Complex. Therefore Therefore the t h e conclusion conclusion is the Its concordant pole pole t h e complex records r e c o r d s an untilted, u n t i l t e d f primary primary remanence. remanence. Its s i g n i f i c a n t uplift u p l i f t or o r rotation r o t a t i o n of of the t h e KSZ KSZ indicates i n d i c a t e s that t h a t there t h e r e has has been been no significant since since the t h e intrusion i n t r u s i o n of the t h e Clay—Howells Clay-Howells Complex Complex and and that that all a l l significant significant geotectonic geotectonic activity a c t i v i t y on on the t h e KSZ KSZ m.ust must ppredate r e d a t e l072tl6Ma. 1072216Ma. 65 �Geology, Structure and Mineralization Geology, Structure Mineralization of the the Reany Reany Lake Lake Area, Area, Marquette Marquette County, County,Michigan Michigan Marv L. L. MacLellan MacLellan and and Theodore Theodore J. Bornhorst Bornhorst (Department (Department of Geology and GeoMary of Geology and Geological Engineering, Engineering, Michigan Michigan Technological Technological University, University, Houghton, I-Ioughton, Michigan Michigan 49931) 49931) logical During mi2 area area of of the theMarquette MarquetteGreenstone GreenstoneBelt Belt During the the summer summer of of 1987 1987 aa 55 mi2 was was mapped mapped at at aascale scaleofof1:6000. 1:6000. This Thisarea areaincludes includesSection Section 36, 36,T49N, T49N.R27W, R27W, Section Section 31, 31, T49N, T49N, R26W, R26W, Section Section 1, 1, T48N, T48N, R27W, R27W, and and Sections Sections 6,7, 6,7, T48N, T48N.R26W. R26W. The The Reany Reany Lake Lake Area Area isis outlined outlined in in Figure Figure11below. below. 1 SI Figure 1.1. Figure Regional Regional geology geology and and location location map map of of the Reany Reany Lake Lake area. area. the 100 icc K.. This This study study was was undertaken undertaken in in order order to to extend extend detailed detailed mapping mapping of of the the northern northern Marquette Marquette Greenstone Greenstone Belt Belt to to the theeast. east.Previous Previousdetailed detailed mapping mapping has has been 1985),Johnson Johnson been done done to tothe thewest westofofthis thisarea areabybyOwens Owensand andBornhorst Bornhorst(ILSG (ILSG1985), et.al. of the units et.al. (ILSG (ILSG 1987) 1987) and and Baxter Baxter et.al. et.al. (ILSG (ILSG 1987). 1987). Nomenclature Nomenclature of units isis still still in in aaprocess process of of evolution evolution but but has has been been retained retained from from one one study study to to the the next next asas much much as as possible. possible. Figure Figure 22 shows shows the the stratigraphic stratigraphic correlation correlation of of the theunits units identified identified in in the the Reany Reany Lake Lake area. area. The The majority majority of of the thearea areaisiscomposed composed of of Archean Archean pillowed pillowed basalts basalts interbedded interbedded with two two mudflow mudflow breccias breccias and and an aniron iron formation formation and and intruded intruded by by Archean Archean gabbro gabbro and and rhyolite rhyolite dikes. dikes. Mapping Mapping in in this this area area extends extends nearly nearly 2000' 2000' lower lower into into the thesection section than thanprevious previousdetailed detailedstudies studiesdue due to to the thepinch pinchOut outofofa downfaulted a downfaultedblock blockofofMichigamme MichigammeFormation. Formation. With With the the exception exception of of the thelower lower breccia breccia member member and andthe thebottom bottomseveral several thousand thousand feet feet of of pillowed pillowed basalt, basalt, the the majority majority of ofthe theArchean Archeanvolcanics volcanics and and intrusives intrusives can can clearly clearly be be correlated correlated to the the west. west. This This isis especially especially true of of the theIron Iron Formation Formation Member Member and and the the Breccia Breccia Member Member of of Reany Reany Lake Lake which which persist, persist, relarelatively tively unchanged, unchanged, for up up to to four four miles miles totothe thewest westofofthis thisarea area(Owens (Owensand and 66 �Bornhorst, ILSG upper part part of of Bornhorst, ILSG 1985, 1985, Baxter Baxteret,al., et.al., ILSG ILSG 1987). 1987).Other Otherunits unitsinin the the upper Archean sequence vary in character. character. To the the west, west, the Archean sequence can can also also be be traced traced but but they they vary there To the there appears appears to be be aa greater greater number number of of recognizable recognizable pillow pillow structures. structures. To the west, there there is aa greater greater amount amount of of quartz quartz and and carbonate carbonate alteration alteration whereas whereas in the west, in the Reany Lake Lake area area sericite sericite and and chlorite chloriteare arecommon. common. Owens Owens and andBornhorst Bornhorst (ILSG (ILSG Reany 1985) mapped Laminated Schist Member, Member, composed composed of laminated phyllitic phyllitic and and 1985) mapped aa Laminated of laminated schistose volcanics, the Altered, Altered, and and Foliated Foliated Basalt Basalt schistose volcanics,this this isis now now correlated correlated with with the Varieties of the Pillowed Pillowed Basalt Basalt Member. Member. The Reany Lake area area includes includes aa lower lower Varieties of the The Reany breccia unit stratigraphically below called the breccia unit stratigraphically belowdetailed detailedstudies stuaiestotothe the west. west. ItIt is is called Breccia Member Bismark Creek, polymictic breccia lies along a major major Breccia Member of of Bismark Creek, a polymictic breccia which which lies NW-SE trendingshear shear zone. zone.This Thisunit unit isis truncated truncated by by gabbro and itit is uncertain NW-SE trending gabbro and uncertain whether to the west whether it continues continues to west of of the the Reany Reany Lake Lake area. area. The Archean Archean volcanic volcanic and intrusive intrusive rocks rocks are are unconformably unconformably overlain overlain by the the Reany this unit is Reany Creek Creek Formation, Formation, this is discussed discussed in detail detail by by Small Small and and Bornhorst Bornhorst (ILSG 1988).To Tothe the south south of of the the Reany Formation isis an an upfaulted block of of (ILSG 1988). Reany Creek Creek Formation upfaulted block highly basalts and and rhyolites rhyolites which which pinches pinches out out to highly foliated foliated Archean Archean pillowed pillowed basalts to the the west. The uncertain. The overlain by by slates slates of the the west. The relative relative age age is is uncertain. The entire entire area area is overlain Michigamme Michigamme Formation. Formation. All All of the the preceding preceding units units have have been been Cut cut by by Middle Middle Proterozoic Proterozoic Keweenawan Keweenawan diabase dikes. dikes. All pre-Keweenawan pre-Keweenawan rocks rocks have have been been metamorphosed metamorphosed to to greenschist greenschist facies. facies. The Archean and is near Archean units units typically typically have have aa foliation foliation which which strikes strikes N70°W N70° and near vertical vertical to steeply steeply north dipping. dipping. The The gabbro gabbro and and rhyolite rhyolite dikes dikescommonly commonly parallel parallel this trend. generationsofof faults faults are are evident evident in in the trend. Several Several generations the Reany Reany Lake Lake area. area. The The older (Archean) faults tend tend to parallel the trend (Archean) faults parallel the trend of foliation foliation and and are are quite quite continuous. They 10-100 foot wide zones zones of very high high foliation foliation continuous. They are are marked marked by by 10-100 foot wide of very and abundant The older older faults faults are are frequently truncated or or off-set abundant alteration. alteration. The frequently truncated off-set by by later (Archean (Archean but possible possible reactivated reactivated during during the the Lower Lower Proterozoic). Proterozoic). N-S trending faults. These These younger younger faults faults are are reflected reflected by by 10-50 trending faults. 10-50 foot wide wide zones zones of of moderate to strong moderate to strong foliation foliation and and are frequently frequently marked marked by by distinct distinct ravines. ravines. Evidence favoring precious precious metal metal mineralization mineralizationinin the the Reany Evidence favoring Reany Lake Lake area area appears appears to be be less less abundant abundant than than totothe thewest. west.Mineralization Mineralization occurs occurs primarily primarily as as disseminated sulfides within altered disseminated sulfides altered Country country rocks. rocks. There There are arevery veryfew fewquartz— quartzcarbonate-sulphide veinswhich whichare are abundant abundantinin the the areas areas to the carbonate-sulphide veins the west. west. MineralizMineralization is is most most abundant abundant adjacent adjacent to to the the major major NW-SE NW-SE trending trending shear shear zones zones and and next next to or or within within the therhyolite rhyolitedikes. dikes.Metallic Metallic minerals minerals generally generally consist consist of of disseminated disseminated pyrite and and widely widely scattered scatteredchalcopyrite. chalcopyrite. This project project was was funded funded by by the theMichigan MichiganGeological Geological Survey Survey and and Michigan Michigan Technological University. University. 67 �__ tnfr4u vii I I CoieIaion cf MaØ kit$ Sodimen* Sediment, ond Volcanici Mlconb and Peroean Orogeny JLeuutv otecoic xnlq Xms }li kI L_ J Fault .kcM.i&a..sr I*1 U— lAd lAy I IMl Fot Aif j IAI IAmbi Keweenawan Diabase Diabase Keweenawan ;:sIq Michigame Formation Formation (Slates/Quartzites) (~lates/~uartzites 1 Xms/q Michigamme Reany Creek Creek Formation Formation Reany Yd AXa AXa AXs AXs AXb AXb s r Agr Ar Ag A9 %? Aga Abr Art Art 2: Apb Aba Ab f Abf Ai f Aif Amf Amf Amb Axnb Undifferentiated Undifferentiated Slates Slates Basal Conglomerate Basal Conglomerate Granodiorite of of-Rockin Chair Lakes Lakes Granodiorite Rocking Chair Intrus~veof of Fire $ire Center Center Mine Mine Rh o l ~ t eIntrusive Rhyolite ~ a g b r oof of Clark Clark Creek Cr=ek Gabbro Altered Variety Var~ety Altered Undifferentiated Foliated Foliated Pillowed Basalt Undifferentiated Highly Foliated Foliated Rhyolite Rhyolite Pillowed Basalt Highly Volcanics of of Silver Silver Mine Mine Lakes Lakes Volcanics Pillowed Basalt Basalt Member Member Pillowed Altered Basalt Basalt Variety Variet Altered A$tered and and Foliated ~ o y i a t e dBasalt Basalt Hi hly Altered Highly jormatlon Member Member Iron Formation Iron Breccia Member Member of of Reany Reany Lake Lake Breccia Breccia Member Member of of Bismark Bismark Creek Creek Breccia and Rhyolite Rhyolite and Variety Variety Figure 2. 2. Stratigraphic Stratigraphic Correlation Correlation chart chart for for the the Figure Reany Lake Lake area. area. Reany 68 �ASUBMERSIBLE SUBMERSIl3LEDWE DIVE ON ON SUPERIOR SUPERIOR SHOALS: SHOALS: PLANS PLANSAND AND PROSPECTS PROSPECTS A M.L.Manson & & H.C.Halls, H.C.Halls, Dept. Dept. of of Geology, Geology, University University of of Toronto, Toronto, Erindale ErindaleCampus, Campus, M.L.Manson Mississauga, Ontario, Canada L5L L5L1C6 lC6 Mississauga, Areview reviewisisgiven givenof ofaaplanned plannedGeological Geologicaland andGeophysical Geophysicalstudy study of of the the Superior SuperiorShoals, Shoals,Lake Lake A Superiorundertaken undertakenas aspart partof ofthe theJuly July 1988 1988Great Great Lakes Lakes Manned Manned Submersible SubmersibleProgram Program(NOAA (NOAA Superior National Underwater Underwater Research Research Program). Dives are are to tobe becarried carriedout outusing using aa NOAA NOAA 2600 2600 ftft National Program). Dives submersible for for the the purpose purpose of of orientated orientated sample samplecollection collection with, with, ititisishoped, hoped,supplementary supplementary submersible dredge sampling sampling and and photography tethered ROy, ROV, over over aa period period of of one one to to one one and and aa dredge photography from fromaa tethered A concurrent series of side scan sonar and ship-borne magnetometer surveys will half days. half days. A concurrent series of side scan sonar and ship-borne magnetometer surveys will provide important bathymetric and geological data. provide important bathymetric and geological data. The Superior Superior Shoals Shoals lie lie at at the theintersection intersection of of the theIsle IsleRoyale Royaleand andThiel Thielfaults faultsand and occur occur The about half way along the Trans-Superior Tectonic Zone defmed to the north by the Slate about half way along the Trans-Superior Tectonic Zone defined to the north by the Slate Islands crypto-explosion structure and a line of intrusive alkaline complexes. The shoals are Islands crypto-explosion structure line of intrusive alkaline complexes. The shoals are known from fromprevious previous dredging dredgingand andbathymetric bathymetric work work to to consist consistof of aa northern northern ridge ridge of of red red and and known grey sandstones sandstones and and aa southerly southerly one one composed composed of of amygdaloidal amygdaloidal basalt. Theselithologies lithologiesare are grey basalt. These consistent with with Middle Middle to to Upper Upper Keweenawan Keweenawan volcanic The shoals shoals consistent volcanic and and clastic clastic assemblages. assemblages. The 60kilometer kilometerradius radiusininLake LakeSuperior. Superior. representthe theonly onlyoutcrop outcropof ofthese theserocks rockswithin withinaa60 represent be; Priorities of the project will Priorities of the project will be; 1. To To further further understanding understanding of of the the stratigraphy stratigraphy and and structure structure of of the the eastern easternLake LakeSuperior superior 1. Basin, particularly in relation to the Trans-Superior Tectonic Zone and to recently acquired Basin, particularly in relation to the Trans-Superior Tectonic Zone and to recently acquired GLIMPCEseismic seismicreflection reflectionprofiles. profiles. GLIMPCE 2. To Toinvestigate investigateanomalous anomalouspalaeomagnetic palaeomagnetic signatures signatures suggested suggested from from crudely crudely orientated orientated 2. chips collected collected previously previously by surface scuba scuba dive. Data gained gained from from these these suggest suggest aa reversed reversed chips by surface dive. Data magnetisationfor forthe theKeweenawan Keweenawanvolcanics volcanicswith withaacurious curiousoverprint overprintof ofunknown unknownorigin originwhich which magnetisation may be be due duetotoreheating reheatingeffects effects(due (duetotointrusions intrusionsorortotooverlying overlyingnormally normallymagnetised magnetisedflows flows may similar to to those those on on Isle IsleRoyale) Royale) or ormay maybe berelated relatedtotothe theSlate SlateIslands Islandsexplosive explosive event. event. AA similar will be be aimed aimed atatresolving resolving these these questions questions and and will will further further further program program of of collection collection will further knowledge of Keweenawan faulting, alkaline complexes and diatremes in the area. knowledge of Keweenawan faulting, alkaline complexes and diatremes in the area. 3. To Tostudy studyaspects aspectsofofnative nativecopper coppermineralisation mineralisationreported reported (Kirkham (Kirkham& &Franldin Franklin1981) 1981) 3. from samples dredged by the 1980 Cousteau expedition and models of basin wide fluid motion. from samples dredged by the 1980 Cousteau expedition and models of basin wide fluid motion. Workwill willbe bedone donein in co-operation co-operationwith withR.V. R.V. Kirkham Kirkham& &J.M. J.M. Franidin, Franklin,Geological GeologicalSurvey Surveyof of Work Canada (copper mineralisation, M o c k geology), J. Klasner, Western Illinois University (rock Canada (copper mineralisation, bedrock geology), J. Kiasner, Western fflinois University (rock fabric),and andW.C. W.C. Kelly, Kelly,University U~versity of Michigan Michigan(metamorphic (metamorphicphase phaseequilibria, equilibria,fluid fluidinclusions inclusions fabric), of and stable stableisotope). isotope). and Finally, an an overview overview of ofthe themechanical mechanicalproblems problemsof ofunderwater, underwater,remote remoteoriented orientedsample sample Finally, collection will willbe be given. given. collection 69 �COMPARISON OF OF TWO TWO PARTS PAFiTS OF OF COMPARISON THE DEAD DEAD RIVER-ISHPEMING RIVER-ISHPEMING GREENSTONE GREENSTONE BELT: BELT: THE EVIDENCE EVIDENCE FOR FOR CORRELATION CORRELATION OF OF VOLCANIC VOLCANIC STRATIGRAPHY STRATIGRAPHY by by G. W. Norby, Norby, G. Bradford Bradford Margeson, Margeson, John John W. Robert A. A. Brozdowski, Brozdowski, Alan Alan S. S e Carter, Carter, Bruce Bruce A. A. Bouley Bouley Robert CALLAHAN CALLAHAN MINING MINING CORPORATION CORPORATION EXPLORATION EXPLORATION DEPARTMENT DEPARTMENT 25 25 Industrial Industrial Park Park Road Road Negaunee, 49866 Negaunee, Michigan Michigan 49866 Detailed Detailed geologic geologic mapping mapping by by Callahan Callahan Mining Mining Corporation Corporation in in the the Dead Dead River-Ishpeming River-Ishpeming Greenstone Greenstone Belt Belt has has shown shown similarities similarities in in volcanic—sedimentary volcanic-sedimentary stratigraphy stratigraphy and and intrusive intrusive events events between between I ) the the west west end end of of the the south south arm arm of of the the belt, belt, and and 2) 2) the the south south 1) half half of of the the north north arm arm of of the the belt. belt. The The west west end end of of the the south south arm arm of of the the belt belt comprises, comprises, from from WNW to to ESE, ESE, aa consistently consistently southeastward-facing southeastward-facing sequence sequence of of 1) 1) WNW pillowed to to massive massive basalt, basalt, subordinate subordinate basalt basalt tuff, tuff, associated associated pillowed hypabyssal hypabyssal gabbroic gabbroic sills sills and and dikes, dikes, and and minor minor mafic mafic graywackes; graywackes; dacite tuff, and porphyritic interlayered basalt, 2) a zone of interlayered basalt, dacite tuff, and porphyritic zone of a 2) hypabyssal 3 ) dacite dacite tuff, tuff, which which hosts hosts aa discondisconhypabyssal dacite dacite sills; sills;3) tinuous trend trend of of banded banded quartz—magnetite quartz-magnetite iron iron formation formation and and tinuous quartzose quartzose graywacke; graywacke; 4) 4) volcanic volcanic conglomerates conglomerates and and tuff tuff breccias. breccias. Fine grained grained serpentinized serpentinized peridotite peridotite strikes strikes northeast northeast and and cuts cuts Fine AA the the overall overall mafic mafic to to felsic felsic transition transition at at an an acute acute angle. angle. northeast trending trending line line of of granitoid granitoid plugs plugs intrudes intrudes the the above above northeast mafic section. section. The The extreme extreme northwest northwest and and west west parts parts of of the the mafic basalt section, section, in in proximity proximity to to the the bounding bounding granitoid granitoid terrane, terrane, basalt is is at at amphibolite amphibolite facies, facies, the the remainder remainder of of the the above above section section is is at at greenschist greenschist facies. facies. The The south south half half of of the the north north arm arm of of the the belt belt comprises, comprises, from from 1) north to to south, south, aa consistently consistently south south facing facing sequence sequence of of 1) north pillowed pillowed basalt, basalt, subordinate subordinate basalt basalt tuff, tuff, and and hypabyssal hypabyssal gabbroic gabbroic 2) aa zone zone of of interlayered interlayered basalt, basalt, mafic mafic graywacke, graywacke, sills; 2) sills; hypabyssal porphyritic porphyritic dacite dacite intrusions intrusions transitional transitional to to dacite dacite hypabyssal trend quartz—magnetite tuff, and and aa discontinuous discontinuous trend of of quartz-magnetite iron iron tuff, 3 ) dacite dacite tuff tuff and and porphyritic porphyritic hypabyssal hypabyssal dacite dacite formation; 3) formation; intrusions. An An east east trending trending line line of of granitoid granitoid plugs plugs intrudes intrudes intrusions. The northernmost part of the basalt the mafic mafic section. section. The northernmost part of the basalt section section the is is at at amphibolite amphibolite facies, facies, the the more more southerly southerly part part of of this this arm arm is is at at greenschist greenschist facies. facies. The The data data suggests suggests that that the the above above two two sequences sequences have have similar similar volcanic—sedimentary volcanic-sedimentary rock rock successions, successions, intrusive intrusive events, events, facing facing Although gradients. metamorphic directions, and and metamorphic gradients. Although minor minor directions, two sequences, differences exist exist between between the the two sequences, the the strong strong differences It is similarities suggest suggest aa common common heritage. heritage. is proposed proposed that that similarities separated sequences presently spatially these two two presently spatially separated sequences of of Archean Archean these rocks were were originally originally on—strike on-strike parts parts of of the the same same terrane terrane which which rocks has by opening opening of of the the early early has been been separated separated and and somewhat somewhat rotated rotated by Proterozoic Proterozoic Dead Dead River River Basin. Basin. 70 �Comparison Comparison of of the the Keweenaw Keweenaw and and Gregory Gregory Rifts Rifts from from the the Study Study of of Teleseismic Teleseismic Delay Delay Times Times and and Bouguer Bouguer Gravity Gravity R.P. R.P. Meyer Meyer and and W.V. W.V. Green, Green, Department Department of of Geology Geology and and Geophysics, Geophysics, University University of of Wisconsin-Madison Wisconsin-Madison Parameters Parameters that that can can be be equally equally well well studied studied in in aa billion-year-old billion-year-old rift and and an an active active modern modern continental continental rift rift are are the the focus focus of of an an ongoing ongoing rift study in in the the midcontinent midcontinent Keweenaw Keweenaw rift rift in in the the vicinity vicinity of of the the PettyPettystudy Ray Ray profile profile northwest northwest of of Minneapolis Minneapolis and and in in the the Gregory Gregory rift rift in in the the region region of of greatest greatest uplift, uplift7northeast northeast of of Nairobi, Nairobi,Kenya. Kenya. The The parameters parameters being being used used are are teleseismic teleseismic delay delay times times of of near-vertically-arriving near-vertically-arriving waves waves from from distant distant earthquakes earthquakes and and Bouguer Bouguergravity. gravity. The The data data show show that that the the slope slope of of the the regression regression of of delay delay time time on on Bouguer Bouguer anomalies anomalies is is five five times times as as steep steep for for African African data data as as for for midcontinent midcontinentdata. data. Why Why are are the the seismic milligal so so much much greater greater in inAfrica? Africa? We seismic delays delays per per milligal We believe believe that that the the answer answer lies lies in in the the existence existence of of partial partial melt melt underlying underlying the the active active rift. rift. Further, Further, in in the the Keweenaw Keweenaw rift rift we we find find that that the the slope slope of of the the regression regression of of delay delay times times on on Bouguer Bouguer anomalies anomalies is is typical typical of of other other older older tectonic tectonic features, features*such suchas as the the Sierra SierraNevada. Nevada. Other significant significant results results are are that that these these rifts rifts are are asymmetric asymmetric Other features features consistent consistent with with aa model model employing employing alternating alternatinghalf-grabens. half-grabens. We We find find this this at at the the Gregory Gregory rift, rift*and and note note that that GLIMPCE GLIMPCE and and other other seismic seismic profile profile data data across across Lake Lake Superior Superior also also support support an an alternating alternating half-graben half-grabenKeweenaw Keweenawrift riftmodel. model. We We also also find find as as much much variation variation in in delay delay time time along along the the Gregory Gregoryrift riftas asacross acrossit. it. 7]. �SUPERIOR MAF' MAP SHEET, BEDROCK GEOLOGY GEOLOGY OF OF THE THE SWERIOR SHEET, WISCONSIN M.G. M.G. Mudrey, Mudrey, Jr., and and B.A. B.A. Brown, Brown, Wisconsin Geological Geological and and Natural Natural History History Survey, 3817 Mineral Point 53705, (in Survey, 3817 Mineral Point Road, Road, Madison, Madison, WI WI 53705, {in cooperation cooperation with the the U.S. Geological Survey) U.S. Geological Survey) ABSTRACT ABSTRACT Reconnaissance Reconnaissance mapping, examination examination of of newly acquired acquired drill drill core, core, and and reanalysis of geophysical data in northwestern Wisconsin is preliminary reanalysis is in U.S. Geological Survey as part of of the COGEOMAP the COGEOIYAP progress in in cooperation with the U.S. Initial work has resulted in a new new preliminary preliminary 1:250,000 bedrock bedrock Initial work program. program. units on the do not differ differ geologic geologic map. map. The The broad lithologic lithologic units the new map do significantly from those on previous maps; however, the relationship relationship and significantly Archean metavolcanic metavolcanic rock, significance rock, significance of of the the various various units units has has changed. changed. Archean granite, southwest trending trending belt south south of the Gogebic Gogebic granite, and gneiss occupy a southwest The southeast southeast corner of the corner of the map sheet is is underlain by Early Proterozoic Proterozoic Range. Range. The metasedimentary metasedimentary rock, rock, mafic mafic to to intermediate intermediate volcanic volcanic rock, rock,and and iron ironformation. formation. The Proterozoic succession succession on the Gogebic Range which is The Early Proterozoic the Gogebic is probably contemporaneous age with the rock to the southeast southeast in the Mercer Butternut contemporaneous in age area Proterozoic Keweenawan area is is in in turn turn unconformably unconformably overlain by Middle Proterozoic of the tectonic tectonic setting setting of the volcanic reevaluation of the upper Keweenawan volcanic rock. rock. AA reevaluation sedimentary separate presentation at this sedimentary rock rock succession succession is is discussed discussed in in a separate this meeting (A.B. (A.B. Dickas Dickas and and M.G. M.G. Mudrey, Mudrey, Jr.). Jr.). meeting unconformity between the The regional mconfomity the Chocolay Group (represented (represented on the Gogebic Range Range by the Menominee Group Group west Gogebic the Bad River Dolomite) and the the Menominee (represented (represented by the the Palms, Palms, Ironwood Ironwood and and Tyler Tyler Formations) Formations) is is confirmed, confirmed, suggesting suggesting regional regional folding, folding, uplift uplift and and erosion erosion during during the the Early Early Proterozoic; Proterozoic; the regional ite and and the regional unconformity unconformity between between the the basal basal Keweenawan Keweenawan Bessemer Bessemer Quartz Quartzite the the Tyler Tyler Formation Formation indicates indicates deformation, deformation, uplift and erosion prior to to Subsequently, the the units were tilted tilted to to the the north deposition of deposition of the the Bessemer. Bessemer. Subsequently, into the the Lake Lake Superior Superior syncline. syncline. into Future work will concentrate on establishing the relationship relationship between the Future the tectonic history of of the Proterozoic rock of the Gogebic Gogebic Range Range and that in tectonic the Early Proterozoic southeast corner corner of the area, south south of the intervening block block of Archean the southeast of this project is to better map map the Archean rock and rock. rock. An additional goal of the relationship relationship between the granitegreenstone granite—greenstone terrane south of Hurley clarify the and the and the gneiss gneiss exposed exposed further further to to the the southwest. southwest. 72 �MIDCONTINENT RIFT RIFTMODEL MODEL BASED BASEDUPON UPON MIDCONTINENT GREGORY AND SEDIMENTATION SEDIMENTATION GEOMETRIES GEOMETRIES GREGORY RIFT RIFT TECTONIC TECTONIC AND M.G. M.G. Mudrey, Mudrey, Jr., Jr., Wisconsin Wisconsin Geological Geologicaland andNatural Natural History HistorySurvey, Survey, 3817 3817 Mineral Mineral Point Point Road, Road, Madison, Madison, WI WI 53705, 53705, and and WI 54880 54880 A.B. Dickas, Dickas, University University of of Wisconsin—Superior, Wisconsin-Superior, Superior, Superior, WI A.B. ABSTRACT ABSTRACT Middle Middle Proterozoic Proterozoic tepetate—type tepetate-type sedimentation sedimentation growth growth geometries geometries on on aa major major scale scale have have been been identified identifiedwithin within the theMidcontinent MidcontinentRift Rift System System from from Lake Lake Superior Superior reflection reflection profiles profiles (GLIMPCE), (GLIMPCE), on—shore on-shore Wisconsin Wisconsin drill drill core core (Bear (Bear Creek Creek Mining MiningCo.), Co.), and and outcrop outcropanalysis. analysis. These These geometries geometries are are in in the the form form of of structurally structurally independent independent basins basins in listric movement movement along along axially—oriented axially-orientedfault fault in which which differential differential listric systems systems have have created created sedimentation sedimentation wedges wedges of of alternating alternating isopach isopach polarity. Within the the area area of of study study from from northwestern northwestern Wisconsin Wisconsin into into polarity. Within the the eastern eastern sector sector of of Lake Lake Superior Superior this this regional regional geologic geologic setting setting appears appears to to be be structurally structurally similar similar to to that that reported reported along along the the Gregory Gregory Rift Rift of of Kenya, Kenya,Africa. Africa. Midcontinent Midcontinent Rift Rift tectonic tectonic models models published published since since 1956 1956 have have emphasized emphasized aa centrally centrallypositioned positionedhorst horst bounded boundedby by parallel parallelfaults faults within within aabroader broadergraben grabenor orrift. rift. These Thesesystems systemsformed formedin inthe theinner inner border border of of flanking flankingasymmetric asymmetricbasins basinsof ofsedimentation. sedimentation. Fault Fault throws throws were were implied impliedto to have have been been equivalent equivalent resulting resulting in in supra—horst supra-horst sedimentation both parallel parallel and and sedimentationpackages packages of of similar similar thickness, thickness, both perpendicular to the rift axis. perpendicular to the rift axis. New analysis of New analysis of core, core, particularly particularly depth depth constraints constraints associated associated Orontostrata strataand andpre—Oronto pre-Orontoage agevolcanic volcanicrock, rock, principallywith with Oronto principally permits series of of permits the the portrayal portrayal of of the the Midcontinent Midcontinent rift rift trend trend as as aa series sub—basins sub-basins separated separated by by "accommodation "accommodationzones." zones." Three Three identified identified sub—basins sub-basins are are believed believed to to have have developed developed independently independently in in the the study study area area in in response response to to rift rift stress stress and and fault fault movements movements of of contrasting contrasting magnitude. magnitude. This This resulted resulted in in sedimentation sedimentationisopach isopachpolarities polaritiesthat that are are symmetric symmetricparallel, parallel, but but asymmetric asymmetricperpendicular, perpendicular,totothe therift rift axis. axis. From From west west to to east east these thesepolarity polarity orientations orientationsare aresouth southinin Bayfield Bayfield County, County,Wisconsin Wisconsin (Brule (BruleBasin), Basin), north northonshore onshoreand andoffshore offshore Ontonagon, Ontonagon,Michigan Michigan(Ontonagon (OntonagonBasin), Basin), and andsouth southoffshore offshoreMarquette, Marquette, Michigan Michigan(Manitou (ManitouBasin). Basin). AA fourth fourthbasin basin (Cariboo (Cariboo Basin) Basin) is is located located southeast southeast of of the the Manitou Manitou Basin, Basin, but but is is poorly poorly defined defined from from geologic geologic and and geophysical geophysicalconstraints. constraints. The Theaccommodation accommodationzones zones are are generally generally situated of fluctuating fluctuating sedimentation sedimentation patterns patterns and and situated within within the the region region of are arespecifically specificallyidentified identifiedby byoffsetting offsettingBouguer Bouguergravity gravitypatterns. patterns. Although Although this this Middle Middle Proterozoic Proterozoicmodel model may may not not be be representative representative of 20to to40 40m.y. m.y. developmental developmentalhistory historyofofthe theentire entire ofthe theentire entire20 length lengthof ofthe theMidcontinent MidcontinentRift Rift System, System,it itdoes doesencourage encouragedevelopment development of ofnew new models models pertinent pertinent to to rift rift evolution evolution and and the the discovery discovery of of associated associatedbase—metal base-metaland andhydrocarbon hydrocarbonresources. resources. 73 �COMPARISON AFRICANAND AND MIDCONTINENT RIFT ELEMENTS1 COMPARISON EAST EAST AFRICAN ELEMENT ELEMENT AFRICAN AFRICAN MODEL MODEL U.S. MODEL U.S. MODEL SYSTEM SYSTEM EAST AFRICAN EAST AFRICAN RIFT RIFT MIDCONTINENT RIFT RIFT MIDCONTINENT BRANCH BRANCH EASTERN EASTERN WESTERN WESTERN MID-MICHIGAN GRAVITY HIGH2 MID—MICHIGAN GRAVITY HIGH2 MID-CONTINENT GRAVITY GRAVITY HIGH2 HIGH2 ZONE ZONE CRRROUY (KENYA) (KENYA) GREGORY 500—700 500-700 km km STEFANIE (CHOW BAHIR) T.AKK SUPERIOR3 STIPRRTOR3 LAKE CENTRAL IOWA3 NORTHEASTERN KANSAS3 SOUTHERN MICHIGAW in length in length TANGANYIKA USNO—OMO—KIBISH UNIT4 UNITq 80—160 km 80-160 km in length in length L/W ratio ratio 2—4/1 L/W 2-4/1 TURKANA TURKANA SUGATA SUGATA BARINGO—BOGORIA5 BARINGO-BOGORIAS NAKURA—NAIVASHA5 NAKURA-NAIVASHA5 MAGADI-NATRON5 MAGAD I-NATRONS MANITOU ONTONAGON ONTONAGON BRULE BRULE CARIBOU CARIBOU BLOCK8 BLOCK6 width 10 km width 10kin L/W ratio ratio 4—10/1 4-10/1 RECOGNIZED RECOGNIZED RECOGNIZED RECOGNIZED - --------------- 'After rift rift Scale 1After Scale classification classification by by Rosendahi Rosendahl (1987). (1987). The The architectural elements should should be considered typical, typical, rather rather than architectural correlative, examples. correlative, examples. 2Known principally principally as as geophysical geophysical entity 3After 3After Dickas Dickas (1986) (1986) 4Fundainental rift building building block block 4Fundamental rift Keisler (1986) 5After =After Bosworth, Bosworth, Lambiase Lambiase and and Keisler (1986) 6lnfrastructure of rift 8Infrastructure of rift units units References Cited: References Cited: Bosworth, William, Joseph, and and Keisler, Keisler, Ron, Ron, 1986, Bosworth, William, Lainbiase, Lambiase, Joseph, 1986, AA new new look look at at Gregory's Rift: The The structural structural style style of of continental continental rifting: rifting: EOS, EOS, v. v. 67, 67, no. 29, 29, p. p. 577—582, 577-582, 583. 583. Dickas, A.B., A.B., 1986, Seismologic analysis of arrested stage stage development of Dickas, 1986, Seismologic the Midcontinent Midcontinent Rift: Geoscience 11, p p. v. 11, . 45—52. 45-52. the Geoscience Wisconsin, Wisconsin, v. Rosendahi, B.R., B.R., 1987, rifts with with special Rosendahl, 1987, Architecture of continental rifts reference Earth and Planetary reference to East Africa: Annual Reviews of Earth Science, v. 15, 15, p. p. 445—503. 445-503. Science, v. 74 �Isle Isle Royale Royale Flexure Flexure \ D ! ! - 4' Apostle LAKE L A K E SUPERIOR SUPERIOR —4 Ui Keween Detachment Douglas Douglas ,' hite Pine ~lexurei' I 4T ] 1 I I I / / I S F I DEPOCENTER AXIS DEPOCENTER AXIS DETACHMEN DETACHMENT 1 FAULT FAUp FLEXURE Fm p""nw 3 1 MANITOU BASIN 2 Lake Owen Detachment KM Flexure CARIBOU BASIN BASIN 50 0 ] ONTONAGON BASIN - I1 I BRULE BASIN PRE—RIFT ROCK RE-RIFTROCK SCHEMATIC -CHEMATlC CROSS CROSSSECTION SECTION I WESTERN LAKE LAKESUPERIOR SUPERIOR STRUCTURE STRUCTURE 1 �DEVELOPMENT DEVELOPMENT OF OF THE MIDCONTINENT MIDCONTINENT FUFT RIFT IN THE THE LAKE LAKE SUPERIOR SUPEFUOR REGION: FLEGION: PETROLOGIC AND A N D GEOCHEMICAL GEOCHEMICAL C O N S T U I N T S FOR MODEL CONSTRAINTS FOR A A TECTONIC MODEL S.W. Nicholson, Dept. ofofGeology, Geology, University u a i v d t y of Minnesota, Minneapolis, Minneaph, Minnesota 55455 55455 =ti and the US. Geological U.S. GeologicalSurvey, Survey,MS MS 954, 954, Reston, k t o a , Va. Va. 22092 22092 3.B.Paces, Paces, Dept. of ~ e o land o g yaGeological d Geologica~ hgineahg, Michigan TechnologicalUniversity, u a i v d t y ,Houghton, Houghton, J.B. Dept. of Geology Engineering, Michigan Technological Michigan Michigan49931 49931 W.F. U.S.UGeological Survey, MS W.F.Cannon, Cannon, S . Geological Survey, MS911, 911.Restou, Raton, Va. Va. 22092 22092 and isotopic isotopic data with Integration of new geochemical geochemical and with new new geophysical geophysical and geochronological data data for western Lake Superior provides an excellent opportunity opportunity to develop a tectonic and magmatic magmatic model model for for the the evolution evolution of of the the Midcontinent Midcontinent rift. Basalt Basaltcompositions compositionsbecame became more more primitive primitive as as the therift riftevolved, evolved,which whichsugsuggests that the theextent extentofofcrustal crustalattenuation attenuationinfluenced influencedthe the.composition composition of of the the volcanic rocks rocks that were were erupted. erupted. basaltic rocks rocks exhibited exhibited a broad variation in As the Midcontinent rift evolved, basaltic through quartz tholeiites composition, ranging from olivine through tholeiites [1,2]. [1,2]. This This discussion discussion focus on on the the North Shore volcanic group group in in Minnesota Minnesota and and the Portage will focus Portage Lake Lake volcanic for which which the most v o l c ~ group cgroup in Michigan for most complete complete chemical chemical and and isotopic isotopic data data have have been been compiled. compiled. The The older older North North Shore Shorebasalts basdts generally generallydisplay display more more chemically evolved evolved compositions compositions (Mg# (Mg# 2 440—55), showingenrichment enrichment in incomQ-551, showing patible patible trace traceelements elements[1,3]. [1,3]. Younger Younger basalts, including including most of of the the Portage PortageLake Lake volcanic group group [5] [5] and and some of of the North volcanic North Shore Shorebasalts basalts[1,2], [1,2],are areless-evolved less-evolved olivinetholeiites tholeiites(Mg# (Mg 2 65-70 65—70and andhigh highcompatible compatibletrace-element trace-element abundances). abundances). olivine The most primitive The primitive tholeiites tholeiites occur at the the top top of of the the Portage PortageLake Lakesection section and and repflood baalts basalts in the rift. Chemical resent the youngest flood Chemicalvariations variations among among basalts baalts can be attributed attributed largely largely to to crystal crystal fractionation fractionation in subcrustal subcrustal to to intracrustal intracrustal which were weresubject subject to to replenishment, replenishment, periodic periodic tapping, tapping, crustal magma chambers, which contamination, contamination,and and minor minor variations variationsin inparent parentmagma magmacomposition composition[4,51. [4,5]. Nearly one hundred Nd Nd isotopic isotopic analyses have been obtained obtained for for rocks rocks from from the North the North Shore Shore[3,6] [3,6] and the the Portage PortageLake Lake[5,7] [5,7] volcanic volcaaic groups. Despite Despite chemical values at at 1100 1100 Ma Ma cluster cluster about 0 (Fig. cal variations G a t i o n s among the the basalts, basalts,the theENd C N values ~ (Fig. 1)[3,6,8,9]. The range of values for basalts from the North Shore is from about -9 1)[3,6,8,9]. range d u e s basalts from the North Shore is from about—9 whereasbasalts basalts from from the the Portage Lake to +3.5 [3,61, [3,6], whereas Lake group group show show aa more more narrow narrow to +1.4 +1.4 [5,7]. range of values, from about —2 -2 to [5,7]. However, However, the strong strong clustering clusteringof of values around 0 implies implies that that most most of the basalts values around baalts in in the thewestern westernLake Lake Superior Superior region were derived derived from from aa similax similar mantle mantle source. source. The region were The wide wide range rangeininenriched enriched isotopic compositions for for North North Shore basalts suggests some crustal contarninasuggests some crustal contamination [10]. [lo]. The more restricted restricted composition composition of of the Portage Portage Lake Lake basalts basalts suggests suggests less involvementofofaacrustal crustal component. component. Within the Portage less involvement Portage Lake Lake group, group, the the 76 �amount of crustal component component decreases decreases upsection upsection and and virtually virtually disappears disappears dur[51. Strongly enriched Nd C N values values ~ at 1I00 Ma Maofof—13 -13 ing the the latest lateststages stagesofofrifting rifting[51. at 1100 to —16 -16 obtained Portage Lake Lake areas areas obtained for for some somerhyolites rhyolitesin inthe the North North Shore Shore and and the Portage [6,8] melting of of Archean Archean crust did did occur occur locally. locally. However, However, [6,81indicate indicatethat that partial melting rhyolites show show isotopic compositions similar basalts, which which most rhyolites similar to to those of of the basalts, suggests derivation from a similar source to that of of the thebasalts basalts[8]. [8]. reflection profiles profiles suggest suggest that that In western Lake Lake Superior, GLIMPCE GLIMPCE seismic seismic reflection the main main depositional depositional basin basin of of the the rift rift was was confined confined between between two major faults, faults, Fault on the north and the Kewmaw-Lake Keweenaw-Lake Owen Fault the Isle Isle Royale-Douglas byale-Douglas Fault Inthis thisarea, area,subsidence subsidence along dong the rift axis axis accommodated up to 30 30 on the south. In km of rift-related volcanics volcanics and sediments. sediments. The The Portage Portage Lake Lake volcanic volcanic group group in in Michigan, which which are are the the youngest youngest rift-related rift-related flood floodbasalts, basalts, lies lieswithin within this this major depositional basin. basin. However, However, the North North Shore Shore volcanic volcanic group in Minnesota Minnesota lies lies within basin (about (about 5 km deep) deep) to the northwest northwest of of the Isle Isle within a broad broad shallow shallow basin Royale-DouglasFault. Fault. This shallow basin probably probably developed during the early Royale-Douglas shailow basin developed during early stages of volcanicrocks rocksoccur occuratatthe the base base of of the North of rifting (reverse-polarity (reverse-polaxity volcanic Shore group), group), but was active at least least until until major major subsidence subsidence occurred along dong the the rift axis. axis. Hence, Hence, the North North Shore Shore and and Portage Portage Lake Lake volcanic volcanic groups were not emplaced in the same structural structural setting. setting. Integration of of these these data leads model: In the early early stages stages Integration leads to to the the following following model: of rifting, rifting, thick continental crust impeded of impeded the rapid ascent ascent of of basaltic basaltic magma magma and permitted permitted magma magma interaction interaction with with walirock. wallrock. Early Early basalts basdts preserve preserve chemical and isotopic of fractional fractional crystailization crystallization aand isotopic evidence of d ccrustal m t d assimilation assimilation enroute enroute to the plate extension, the surface. surface. As As the thecrust crustthinned thinnedduring duringcontinued continued.plate extension, magma magma established, and magmas that ascended conduits became established, ascended more rapidly had had less less opportunity opportunity for for crustal crustalinteraction. interaction.Younger Youngerbasalts basaltsshow show more more primitive primitive compocompoor isotopic isotopic evidence evidenceofofcrustal crustalcontamination. contamination. The The basin sitions and less cchemical h e m i d or in which the North North Shore Shore group group resides resides is underlain underlain by by continental crust crust which which was thinned no more than to GLIMPCE data; comthan aa few few kilometers, kilometers, according to compositions of the North Shore rocks reflect reflectsome somecrustal crustalcontamination. contamination. In Shore volcanic rocks In contrast, contrast, the the Portage PortageLake Lake group group lies at the the edge edge of of the major depositional basin beneath which which the crust crust was was greatly greatly thinned thinned or orperhaps perhapscompletely completelyseparated sepaated dikes and a d sills sills [11]. [ll].The The compositions compositions of the the youngest youngest and replaced replaced by sheeted sheeted dikes and most suggest little little or no most primitive primitive basalts basalts of of the thePortage Portage Lake Lake Volcanics Volcanic3 suggest no interaction between basaltic magma and the continental crust in which the rift between basaltic magma and continental crust which developed. developed. Thus, Thus, the thevariation &ation ininthe thechemical chemicalcha.ractertistics charactertistics of of the volcanic volcanic rocks can be used to qualitatively infer the extent of crustal attenuation. 77 �REFERENCES 1. Green, of Keweenawm Keweenawan extrusive rocks, Ri. Wold and WLffinze, 1. Green, LC., J.C., 1982, 1982, Geology Geology of extrunive rocks, h jRJ. Wold and W L h , ed., ed., Geolog GeoJm and tectonics of the the Lake Lake Superior SuperiorBasin: Baaia Geological Geological Society %ety of of America, Americb Memoir Memoir 156, 156, p. 47—55. 47-55. Baaalticvolcanvolcan2. Basaltic Volcanism Study Study Project, Project, 1981, 1981, Pre-Tertiary Pre-Tertiary continental continentalflood floodbasalts, b a d t o , th Basaltic 2. B d t i c Volcanism ism on the terrestrial urn ternatrialplanetr planet&Pergamon PergamonPress, Prezu,p.p.30—77. 30-77. 3. Brannon, Brannon?J.C., J.C.,1984, 1984,Geochemistry G e ~ c h e m i of ~ of t successive q s u 6 v elava lavaflows flowsofofthe theKeweenawa.n Xeweenawan North NorthShore ShoreVolVolGroup: St. Louis, Missoun, hub9 hhmuri, Ph.D. %D. dissertation, dissertation,312 312pp. pp. canic G m u v Washington Washington University, university, st. 4. Miller, in 4. Miller, J.D., LD., 1987, 1987, The Thegeology geology and and petrology petrology of of anorthositic anorthadticrocks KO& inthe theDuluth Duluthcomplex, complex,SnowSnowbank Lake quadrangle9 quadrangle, northeastern bar& northeastern Minnesota M n n e a o tUniversity ~UnivedtyofofMinnesota,. b f h u o t + Minneapolis, Minneapolis, Minnesota, Minnesota, Ph.D. dissertation, Ph.D. M a t i o n , 436 436 pp. pp5. Paces, Paces, LB., J.B., 1988, 1988,Geochemical Geochemical and and isotopic isotopic evaluation evaluation of of the themamgatic mamgaticprocesses, proasses, evolution evolution and mantle in lflood basalt basalt in development development of of the the major majorKeweenaw Keweauw continental continem~ t aflood mantle source murce involved inw~ l v d Univexbasin: Kmmenaw Peninsula, Peninsula, Michigan: Michigan: Michigan MichiganTechnological Tech1;ohgicd Univerhuh Portage PortageLake LakeVolcanica, Volcanica,Keweenaw ILty,Houghton, Rougliton, Mi&ga Michigan, Ph.D. dissertation mty, 6. Dosso, L., The nature of mantle: isotopic study (Sr, 6. hmo, L ., 1984, 1984, The of the the Precambrian Precambrian snbcontinental suLmntinental mantle: (Sr, Pb, the Keweenawan Xeweenawan volcanism VO~C~I&SII of the North North Shore Shore of of Lake Lake Superior: Superior: University UniversityofofMinnesota, Mhneaota, Nd) of the Minneapolis, Minnesota, Ph.D, Ph.D. dissertation, 221 221 pp. pp. bGnneapolis, Miieaota, 7. Nicholson Nichobn (in (ii prep) prep) S.W. and 1100-Ma midcontinent midcoutinent rift development: evidence 8. NIcholson, Nkhohn, S.W. and Shirey, Shirey, S.B., S.B., 1987, 1987,1100-Ma evidence from Nd of volcanic rocks, rocks, northern northern Michigan: b t o ~ i composition composition c of Keweenawan Kmeenawan volcanic Michigan: Geological G d o g i c d Society and Sr Sz isotopic of America, Abstracts with Program, v. 19, p. 788. nor 9. Paces, LB. and Bell, K., (in review), Enriched shallow lithospheric mantle beneath the Superior Province: Nd-Sr isotopic evidence from uncontaminated 1.1 Ga znidcontinent rift olivine tholeiites, t-9 Keweenaw Peninsula, Michigan: submitted Acta neweenaw remnsum, ~ ~ g aS nU D: I I U ~ ~to soGeochimica ucocxwmu et a Cosmochimica -mocnmuca t a (Sr9 10. Dosso, L., 1985, The The nature of mantle: hisotopic data (Sr, Nd, Nd, Pb) mbcontinentd mantle: t o p i c da 10. Doom, L., a~fthe Precambrian subcontinent.al on the the North Shore of of Lake Supexim. Superior. (abet.), f the (atmt.), Terra Ten aCognita, the Keweenawan Xeweenawan volcanism ~01cani.sm oof Cognita,v.5, v.5, p. 207. 20711. Lee, Milkereit, 11. Bebrendt, Bduendt9J.C., J.C., Green, Green,A.C., A.C.*Cannon, uamon,W.F., w .r Eutchinson, nusamson,D.R., UXL, M , M.W., M.w ., muereit,B., B., Agena, Agena, results ead@from W.F. WSFsand and Spencer, Spencer, C., C., 1988, 1988, Crustal Crustal structure structure of of the theMidcontinent hfidcontinent rift rift system: syatem: r GLIMPCE profiles: Geology, Geology,v.v. 1fJ9 16, p. p. 81-85. GLMPCE deep deep seismic eeismic reflection d e c t i o n profiles: - ., 20 u PORTAGE LAKE VOLCANIC8 PORTAGE VOLCANlCS NORTH SHORE VOLCANICS U' a. I' 0 10 U' m z H 0 —10 0 —6 E Nd 5 at 1100 Mi Fig. 1: 1Nd values at 1100 Ma cluster around 0 for volcanic rocks in both the Portage Lake and North Shore volcanic groups with <-. 56% Si02. 78 �Vrnric 1N RThT: A ICNETIC MT1 P ITS (IGIN Peter P e t e r A. A. Nielsen, NielsenI &parbentof of GeolcqyI WParksideIKeriosha, KenoshaIWI WI53141 53141 Departxrent Geology, UW—Parkside, The P f S ) has has been been modelled mcdelled as a passive passive The Midcontinent Midcontinent Rift Mft Systen System(ICRS) structureIoroimpactogen, r h p a c t q e n tcaused causedbybythe the Grenville Orogenyand and as as an an active, activeI or or structure, Grenvifle Orogeny p1un p l u m induced induced structure. structure. II show, showI that based on stress that based on an an analysis analysis of of the stress conditions conditions present present in in the the North North Anerican Amrican Plate Plate(NAP) OW?) from fm - 1400-1000 1400-1000 Ma Pb b.p./ b.p., - the wasananactive activerrr rrr ttriple theICRS MXS was r i p l e junction. junction. Global G l o b a l pplate l a t e distribution distributioncould could not accczidate acccmcdateunconfined unconfined extension extension of ofthe theNAP NAP and this thisprevented preventedthe theMRS M3.5 not from proceeding tto from proceeding o sea-floor spreading spreading (Figure (Figure 1). 1). The KPS no classical t h i r dam annassociated a s s m i a t e dwith with The ICRSisisunique uniqueininthat thatthere there is is no classical third it. it. Howeverf the Coldwell Trend, Trendf a series However, the Coldwell Ma alkaline intrusive intrusive seriesofof1130—1110 1130-1110 M a alkaline centers represent the the location of the the third thirdarm. arm. centers may may represent Stress distribution distributionwas was primarily primarily aa function function of of the the nature nature of of the theNorth North Stress Aitrican American Plate' Plate'ss continental continental margin margin typs typs of plate plate types as as well well aass the types boundaries boundaries present. present. The TheNAP NAP was was characterized characterized by by passive passive continental continentalmargins margins in w e s tand andnorth northand andby by an an active activecontinental continentalconvergent convergent margin =gin in i n the the i nthe t h ewest east. weremid-ocean mid-ocean ridges in in the thewest west and and Plateboundaries, boundaries, therefore, thereforeIwere east. Plate north in the east east and and southeast. southeast. These These boundary boundaq northand and aa convergent convergent boundary boundary in conditions stress field f i e l d that that was was dominantly dominantly inward inward directed directed conditions produced p r & W a stress ccipression, cmpressionfcomprised cmprisedof of west west and and northwest, northwestf directed directed capression carpression at a t its its eastern Grenvifle easternmargin margin (the (thesite siteofofthe the M l l eOrogeny), Orogeny) I eastward eastwarddirected directed ccaiipression the westernf western, passiveI passive, continent-ocean margin (site (site of conpression aat t the continent-ocean margin of Belt E!dt Group directed Group and equivalent sedinentation), sedimntation) I and andpossibly possiblysouthward -s directed compression along of aa 1200 1200 Ma Pb rrifting i f t i n g center). center) . compression alongthe the northern northern margin margin(the (thesite site of The of an The absence absence of an oceanic oceanic free free face face by by 1160 1160 Ma Pb (ocean-continent (ocean-continent or o rocean-ocean man-ocean convergent convergent margin) margin) bounding bounding the the NAP NAP coupled coupled with w i t h the the net net conpressive cmpressive stress stress fields pinned NAP, fieldseffectively effectively pinnedthe the NAPI limited l i m i t e d rifting rifting to t o65-7 65-700 kin, hf prevented the the CRS KRS from frcan proceeding p r c e d h g to t o mid-ocean mid-ocean ridge status s t a t u s and and precluded precluded the the active activestage stage of 05rifting r i f t i n galong alongthe t h eam anndefined &fined by by the theColdwell Coldwell trend. trend. The me systen system of ofgravity gravityand andmagnetic magneticanomalies a n d i e s that thatextends extendsfrom frmKansas Kansas to to Lake -s iinto n t o central mtralMichigan Michigan and and into i n t oeasterrn easternOhio Ohio Lake Superior and and then southwards isisone most prominent oneofofthe the most prcminentini North n NorthAmerica. mica. ItItreflects reflects a majorgeologic geologic a major event identified as thethe North American been identified asan anabortive a b r t i v erifting r i f t i n of g of North American event which which has been - the theCRS, K3Sfsuninarized m i z e dini nWold Wold&& Hinze, Hinze' 1982. 1982. craton craton — NUIFTOUS authors authors have have Numerous proposed this feature processes proposed tthat h a t this feature is isaaresult resultofofactive activerifting rifting processesini response n response to Plate w aroximately t oone oneor o rmore more hot hot spots spots intersecting intmeingthe theNorth NorthAmerican American Plate roximtely 1250 &&Dewey, I& b.p. b.p.(Burke (Emke Ikweyt 1973; 1973; van mnSchnius Schmus & & Hinze, 1985). 1985). Others Others 1250 to t o1100 1100Ma (Tapponnier et al., al.!1982; 1982;Gordon Gordon&& Htpton, HeqtonI1986) 1986)have havepresented presentedarguments arguments (Tappnnier et that t h a t the t h e tensional tensionalenvironment environment represented represented by by the t h eCRS MIGmay m y have have resulted resultedfrom frm the event. theGrenvifle WileOrogenic 0rcqen.i~ mt. The thethe Keweenawan The petrology petrologyand andgeochnistry geochdst.ryofof Kewemwan igneous igneous rocks, mcJcsIasasexposed exposed 1) nultiple source require that: ini nthe Lake Superior region, the Lake Superior regionf require that: 1) multiple source regions regions and contributed contributedmagma; magma; 2) 2) partial partialmelting m l t i n goccurred occurredover overaarange rangeofofdepths; ckpths; and 3)3)one sources was REE oneoro more r moreofofthe the sources was FEEundepleted. undepleted. . They were: were: Three l'hreemagma magma series s e r i e swere were proposed proposed by by Weiblen Weiblen (1982). (1982) They 1) 1) o l e i i t e (alkalic, (alkalicIhigh high Ti), T i ) Iand and alkaline C02-poor),2)2)quartz quartzt htholeiite alkaline(C02—ric.h ( a 2 - r i c h t otoC02-por) 79 �3) olivine olivine tholeiite t h o l e i i t e(low (lowalkali, alkali, high highAl). Al) . The The first firsttwo twoseries series have REE 3) have REE patterns and and initial initialSrSrratios r a t i ocompatible s compatiblewith w i t hderivation derivationfrom from aa mantle mantleplurre plume patterns The olivine olivine tholeiites t h o l e i i t ehave s have FEE source (Weiblen, (Weiblen, 1982; 1982; Wilband, Wilband, 1985). 1985) . The source REE patterns and bulk compositions which correspond closely t o mid-ocean ridge patterns and bulk coiTositions which correspond closely to mid—ocean ridge b a s a l t s (Weiblen, 1982) . basalts (Weiblen, 1982). The order order of of eirplacerrent emplacement of threemagma magma series from The of the the three series and andthe the transition transition from PEE undepleted, plume derived melts t o M3BB type melts strongly supports the REE undepleted, plurre derived malts to MDRB type malts strongly supports the hypothesis that that the theMRS 1CRS forned formed as riftsystem. system. hypothesis as an an active active rift Recent and and current current research research in i nthe thebest bestexposed exposedGrenvifle G r e n v i l l erocks rocks(Brown (Brown et et Recent al., 1986; Easton, 1986; Windley, 1986, summarized in M o o r e et a l . 1986) al., 1986; Easton, 1986; Windley, 1986, surrinarized in Moore et al. 1986) constrain stress stress distribution distribution along along aa region a r a l l e l tto o the the strike s t r i k e of of the the constrain regionpparallel Coldwell Trend, thatby by1160 1160 Ma Ma b.p. NW directed was Coldwell. Trend, and and indicate indicate that b.p. NW directed thrusting thrusting was prominent. Davidson Davidson (personal communication, 1987) suggests that these major prominent. (personal catinunication, 1987) suggests that these major NW compressional shear zones represent thrust t i v i t y that &dfted NW ccmpressional shear zones represent thruststacking stackinga cactivity that shifted SE with timedue due to t olocking lockingup upand andstepping steppingback back of of Benioff Benioff zones. zones. Any Any SE with tine sutures associated associated with with this thisactivity a c t i v i t yare arenow now cryptic. cryptic. The The timing timing of ofthis this NW sutures NW directed stress p a r a l l e l t o the Coldwell Trend and the Grenville Front provide directed stress parallel to the Coidwell Trend and the Grenville Front provide the necessary necessary stress f i e l d to t oprevent prevent any any rrifting i f t i n g along along this this possible possible third third the stress field rift arm. T h e absence of any rift-type cracking along the Coldwell trend rift arm. The absence of any rift-type cracking along the Coidwell trend strongly argues argues against r the r it is in inthe theregion region strongly againstaapassive passiveorigin originf ofor theM3^St CRS,f ofor it is parallel t o crustal thickening, that crustal flexure amd f a i l u r e should occur. parallel to cnistal thickening, that crustal flexure and failure should occur. The absence The absenceofofany anycontrols controlsononthe thedistribution distributionofof Central CentralMstasedimentary tasedirrentary Belt age age rocks rocks south south of of the theAdirondacks, Adirondacks, their spotty distribution distribution in innorthern northern Belt their spotty Quebec and Newfoundland (Figure Easton, 1986) coupled with with the the Quebec and absence absence In in Newfoundland (Figure 2,2, Easton, 1986),, coupled apparent truncation of the SE trending arm of the M3RS in the vicinity of the apparent truncation of the SE trending arm of the MS in the vicinity of the west end end of of Lake Lake Erie, and the change iin n orientation of the theGrenville G r e n v i l l eFront Front west Erie, and the change orientation of that the M3RS is not passive in origin. south of Lake Erie strongly argue south of Lake Erie strongly argue that the MRS is not passive in origin. zJsIc The Midcontinent Midcontinent Rift System was riple The Rift System wasananactive, active, plume plurreinduced inducedrrr rrr ttriple Near constant constant stress stressmagnitude magnitude and and orientation orientationfrom from the thewestern western and and junction. Near junction. northern margins margins of of the theNorth N o r t h Arterican American Plate coupled w i t h changing changing stress northern Plate coupled with stress conditionson on the theeastern easternmargin marginprevented preventedthe thearm armdefined definedby bythe theCoidwell Coldwell conditions Trend fran from rifting r i f t i n goroproducing r producingmafic maficvolcanics. volcanics. Evolving Evolving stress stressconditions conditions Trend l a t e rstopped stoppedfurther furtherrifting rifting Michigansegrrent segment and and ffinally i n a l l y along along the the later ononthethe Michigan The 1CRS Grenville Orogenyoverlapped overlapped in time, Lake Superior Superior segnent. segment. The Lake S andand thethe Grenville Orogeny in tine, The only only effect of the the but there therewas was no no genetic geneticrelationship relationshipbetween betweenthe thetwo. two. The but effect of Grenville Orogeny was t o cause the failure of the M^RS t o proceed t o sea-floor Grenville Orogeny was to cause the failure of the ICRS to proceed to sea-floor spreading. spreading. 80 �500 0 1000 kiIaI,S* ..•..•..•:;' Figure 2, fran Easton, BTtTCQAPBY BIx,IasAmY R.L., Chappel, J.F., Wrer Vriore,J.Mer J.M.,and andThompsonr Thcqson, P.H.r P.H., 1975, An Brown, R.L., Bmmr -lr J.F.# 1975# An island arc Grenvifle Province of enigmatic island arcand and ocean ocean closure in tthe h e Gremdlle southeastern Ontario, Canada, v. v. 2, Ontarior Canada, Canada, Geoscience Geoscience Canadar Zt pp. p.141-144 141-144 Burke, K.C.A. K.C.A., and and Dewey! Dewey,J.F., 1973Plume Plunegenerated generatedt rtriple i p l e junctions: junctions: Key Key Burker J.F. 1973 indicators in plate in applying -lying p l a t e tectonics tectonics to t oold oldrocks, rocksrJournal JournalofofGeology, Geolcgy, v. 86, 406—433 8Grpp. p. 406-433 Easton, R.M., Grenvifle Province, in Eastonr R.M. 1986, 1986, Geochronology ~ n 0 ofof the 1 Gmmille ~ Promhcer hMoore, Wrer J.M., J.M., Davidson,A.A., and andBBaer, A.J., Davidsonr a a r A. J. eds. eds. The The Grenville G r e m L l l e Province, Provincer Geolocical Geolcdcal Association of of Canada Canada SpecialPaper SpxialPaper 31, 3Ir pp. s.127-173 127-173 Gordon, M.B.! M.B., and andHen@onl Henpton,MM.R., 1986,Collision-induced Collision-inducedr rifting: .R. 1986r i f t i n g : The The Gordonr Grenville of North North Anerica, G r d l l e Orogeny Orcgeny and the the Keweenawan -wan R Rift i f t of Amricar Tectonophysics, v. v. 127, 127,pp.1—25 p.1-25 Tectonophy~ics~ Moore,J J.M., Davidson,A.A.,and andFaerr Baer,A.A.J., Wrer . M e r Davidsonl J e teditors, editorsr1986, 1986, The The Grerivifle Grenville Province, P r & n e r Geological Geolcgical Association of of Canada Canada Special Paper 31, 31r 358 358 pp Van Sdxnusl Schmus,W.R.r W.R.,and andHimet Hinze,W.J., W.J..,198Sr 1985,The The xnidcontinent riftsystemt systn, van midcontinent rift the Earth V. 13r 13, pp. Annual Earth and and Planetary Planetaxy Sciences, Sciencesr v. p. 345-383 345-383 Annual Reziews Reviews of the 1982 in Wieblen, P.W., intnisive rocks, K e w e n a w a n intrusive rockst 1982 in Wold, Wold, R.J., R . J e r and Wieblenr P.War 1982, 1982r Keweenawan Hinze, W.J., editors, editorsr1982, 19821Geology Wlm and and Tectonics Tectonics of the t h e Lake Lake Superior Swerior Hinzer W.J.r ir 156156 280 pp. 47-56 Basin, Geological Easi.~~ Geoloaical Society Societv of Axrica America Wmir 280pp., R. p. 47-56 Wilband, J.T., 1985, processes during during the the Midcontinent Rift 198SrMagmatic Magmatic precesses Midcontinent R ift Wilbandr J.T.l interval ininnortheastern Qienical and and isotopic isotopic constraints, intnortheasternMichigan: Michigan: Chemical constraintsr Proceedings of the the Annual Institute on Proceedings of Annual Institute onLake Lake Superior %prior Geology, Geologyr v.31,p.97 v. 31rp. 97 Windley, B.F., 1986r 1986, CCrparative of Windeyr B.Fmr a p r a t i v e Tectonics T-onics of the theWestern Western Grenville and tthe he and BBaer, A.J., eds. h t'bore, Wrer J.M., J . M e r Davidson, Davidsonl AA., e r and a a r A.J:r eds. Himalayar in Western Himalaya, The Grenville The G r e n v i l l e Province, P r & n e r Geological Geolwical Association of of Canada Canada Special SceaaI, Paper 31, 341—348 Parer 31rpp. p. 341-348 Wold,R.R.J., Geology Woldr J. and and Hinze, Hinzer W.J., W. J. editors, editorsr1982, 1982# !%elmand and Tectonics Tectonic$ of the Basin, Geological Societyof of AAnerica moir 156 cal Sccietv m e r i c a P~ITDU 156 the Lake Lake Superior Smerlor E ~SUI~ Geol 280 pp. p. 81 1986. �History History of of Precious Precious Metal Metal Ex,loration/Development Ex~loration/Develo~ment Ishpeming Greenstone Greenstone Belt Belt in the the Dead Dead River River — Ishpeming in - JOHN W. W, NORBY NORBY (Callahan (CallahanMining Mining Corporation, Corporation,Exploration ExplorationDept, Dept, JOHN 25 Industrial Industrial Park, Park, Negaunee, Negaunee, MI MI 49866) 49866) 25 - The Dead Dead River River - Ishpeming Ishpeming Greenstone Greenstone Belt Belt (DIGB) (DIGB)is is located located The in in northern northern Marquette Marquette County, County, Michigan Michigan and and is is part part of of the the Archean Archean Gold Superior Province. Province. Gold was was first first discovered discovered in in the the DIGB DIGB by by Superior Michigan's first State Douglass Houghtonl Michigan's first State geologist geologist (1837(1837Houghton, Douglass 1845)# who who panned panned the the metal metal from from an an undisclosed undisclosed location location between between 1845), silver veins veins LIAnseand and Marquette. Marquette. In In the the mid—1860s mid-1860s base base metal metal - silver L'Anse in the the middle middle DIGB DIGB were were worked worked for for their their lead, leadl needed needed in in the the in production production of of minie minie balls balls used used by by Federal Federal armies armies fighting fighting the the Civil Civil War, War, and and for for their their silver silver credits. credits. - In In 1880, 1880, Julius Julius Ropes Ropes discovered discovered the the mine mine that that was was to to bear bear his his name name in in the the southwest southwest DIGB. DIGB. From From 1882 1882 to to 1897 189'7 the the Ropes Ropes Gold Gold Mine produced produced 41,280 41,280 oz oz Au Au and and 193,500 193,500 oz oz Ag. Age Two Two other other mines mines Mine the have have recorded recorded production production from from this this era: era: the Michigan Michigan Mine Mine (875 (875 the Fire Center Mine (97 oz) in the southwest DIGB, and oz) in the southwest DIGB, and the Fire Center Mine (97 02) in oz) in the middle middle DIGB. DIGB. Numerous Numerous additional additional prospects prospects in in the the southwest southwest the DIGB were were developed developed in in the the late late 1880s 1880s and and worked worked sporadically sporadically DIGB until until the the 1893 1893 depression. depression. At At the the turn turn of of the the century, century,cyanid.cyanidization ization of of Ropes Ropes tails tails and and mill mill amalgam amalgam netted netted 2,645 2,645oz ozAu. AU* In In 1934, 1934, the the 69% 69% rise rise in in gold gold price price to to $35 $35 US US stimulated stimulated renewed activity. activity. From From that thqt year year through through 1942 1942 Calumet Calumet and and Hecla Hecla renewed Consolidated Consolidated Copper Copper Co. Co. developed developed lmT 1mT grading grading 0.13 0.13 oz/ton oz/ton Au, Aul 0.7 0.7 In oz/ton oz/ton Ag Ag in in the the Ropes Ropes Gold Gold Mine. Mine. In 1936, 1936# Norgan Norgan Gold Gold Mining Plining Co. conducted conducted aa reconnaissance reconnaissance program program throughout throughout the the belt, belt, Co. Fire Center drill test of the a 13—hole culminating in culminating in a 13-hole drill test of the Fire Center trend. trend. US gold gold The 1942 1942 War War Powers Powers Act Act halted halted the the development development of of US The properties. properties. During the the 1960s 1960s and and 70s, 70s1 .the .the DIGB DIGB was was the the subject subject of of During massive sulfide sulfide exploration, exploration, but but much much of of the the generated generated core core was was massive assayed assayed for for precious metals, metals, providing information information to to later later gold gold prospectors. Callahan Callahan Mining Corp. Corp. purchased purchased the the Ropes Ropes Gold Gold Mine Mine prospectors. in 1975. 1975. After the the US US abandonment abandonment of of the the gold gold standard standard in in 1973 1973 in of that that commodity commodity throughout throughout the the and subsequent subsequent rise rise in in price price of and decade, exploration exploration in in the the belt belt switched switched to to gold gold in in the the early early decade, 1980s. In 1983, 1983, Callahan Callahan made made the the decision decision to to mine mine the the Ropes Ropes In 1980s. The orebody, and and production commenced commenced in in September September 1985. 1985. The Ropes Ropes orebody, Gold Gold Mine Mine had had produced produced 83,671 831671 oz oz Au Au and and 113,014 113,014 oz oz Ag Ag through through the the third third quarter quarter of of 1987, 1987, bringing bringing total total precious precious metal metal production production in in the the DIGB DIGB to to approximately approximately 128,500 128,500 oz oz Au Au and and 306,500 306,500oz oz Ag. Ag. 82 , �CHRONOLOGY CHRONOLOGY Precious Precious Metal Metal Exploration/Development Exploration/Development Dead Ishpeming Greenstone Greenstone Belt Belt (DIGB) (DIGB) Dead River River — Ishpeming - 1837 - 1845 Douglass Houghton discovers Douglass Houghton discovers placer placer gold gold at at unrecorded L'Anse and and Marquette. Marquette. unrecorded location location between between L'Anse mid mid 1860s 1860s Base silver veins veins in in middle middle DIGB DIGB worked, worked, Base metal metal - silver including Silver Creek prospect including Silver Creek prospect (4 (4 shallow shallow shafts), shafts), Silver Silver Lakes Lakes mines mines (2 (2 shafts, shafts, adit, adit, winze), winze), Lead Lead pits. pits. 1864 - 1865 Holyoke Holyoke precious precious and and base base metal metal mine mine developed developed (526 (526 ft ft adit, adit, 64 64 ft ft winze), winze), no no production. production. 1880 Julius Julius Ropes Ropes discovers discovers gold gold west west of of Deer Deer Lake. Lake. 1882 — 1897 Ropes Gold and and Silver Silver Co. Co. produces produces 215,000 215,000tons tons at at Ropes Gold 0.192 oz/ton Au, 0.90 oz/ton Ag from Ropes Mine. oz/ton Au, 0.90 oz/ton Ag from Ropes Mine. 0.192 late late 1880s 1880s East—west East-west quartz quartz vein vein trend trend in in extreme extreme southwest southwest DIGB Prospects DIGB explored. explored. Prospects include include Lake Lake Superior Superior Gold, Gold, Lake Lake Superior Superior Iron, Iron, Superior, Superior, Breitung, Breitung, Grayling, Grayling, and and Mockler Mockler Brothers, Brothers, plus plus Michigan Michigan Mine. Mine. Nearby Nearby Peninsula Peninsula prospect prospect also also worked. worked. 1887 — 1894 Michigan working,^), Michigan Mine Mine in in operation operation (2,065 (2,065ft ft of of workings), produces produces 3,500 3,500 tons tons at at 0.25 0.25 oz/ton oz/ton Au. Au. 1891 — 1893 Fire 225 tons tons at at 0.43 0.43 Fire Center Center Mining Mining Co. Co. produces produces 225 oz/ton oz/ton Au Au from from Beaver Beaver shafts shafts and and Crescent Crescent tunnel. tunnel. 1899 — 1901 Corrigan, treat Ropes Ropes tails, tails, Corrigan, McKinney McKinney and and Co. Co. treat 30,000 eqv oz oz Au. Au. mill amalgam amalgam yield yield 2,645 2,645 eqv 30,000 tons tons && mill 1932 Yellow gold explored, explored, Plains glacial glacial drift drift gold Dog Plains Yellow Dog surface ft). (500ft). samples, 66 drill drill holes holes (500 bulk samples, surface bulk 1934 Michigan Mine dewatered dewatered by by Marquette Marquette Mines Mines Co., Co., Michigan Mine 500 500 tons tons milled, milled, no no recorded recorded production. production. 1934 - 1942 Calumet and Consolidated Calumet and Hecla Hecla Consolidated Copper Copper Co. Co. evaluates evaluates Ropes Ropes Gold Gold Mine, Mine, 2,550 2,550 ft ft underground underground development, development, 94 94 underground underground drill drill holes holes (10,885 (10,885 At holes on on property property ft). At surface, surface, drills drills 66 holes ft). (1,564 (1,564ft), ft), 33 holes holes east east of of Ropes Ropes (1,278 (1,278ft), ft), 88 holes holes west west of of Ropes Ropes (4,109 (4,109 ft), ft), and and 55 holes holes at at Bjork-Lundeen Bjork-Lundeen prospect prospect (2,109 (2,109ft). ft). 1936 Norgan Norgan drills drills - Gold Gold Mining Miming Co. Co. prospects prospects entire entire DIGS, DIGB, 13 13 holes holes (1,999 (1,999 ft) ft) along along Fire Fire Center Center trend. trend. 83 �- Precious Metals Exploration/Development, Exploration/Developmentt cont. cont. DIGB Precious CHRONOLOGY - DIGB CHRONOLOGY 1966 1966 Cleveland—Cliffs Iron The Cleveland-Cliffs Iron Company Company (CCI) (CCI) drill drill holes. tests tests Michigan Michigan Mine, Minet 3 holes. 1968 — 1971 explores Humble Oil and Humble Oil (later (later Exxon) explores middle middle and Exxon) sulfide, analyzes southwest southwest DIGB DIGB for for massive massive sulfide, analyzes for for Drills 2 2 holes iron precious metals. precious metals. Drills holes into into iron formation and 2 into topographic formation topographic low low (2,000 (2,000 ft). ft). 1970s (Bethlehem Steel Steel and and CCI). CCI). Beth-Cliffs JV (Bethlehem 1975 presents Ropes Resource Exploration, Resource Exploration, Inc. Inc. (REI) (REI) presents Ropes which Callahan Mining Corp. Gold Mine data data to to Callahan Mining Corp. which Arcadian Copper from purchases property property from Arcadian Copper Mine Mine Tours (owner Tours (owner since since 1955). 1955). 1972 — 1985 Superior Oil Co. Co. and and Nicor Nicor Mineral Mineral Ventures Ventures JV JV Superior Oil massive DIGB for massive prospects middle and northwest northwest DIGB several geophysical and/or geochemical sulfide, several geophysical and/or geochemical sulfide, manager thru anomalies RE1 project project manager thru 1983. 1983. anomalies drilled, drilled, REI several to switches to Emphasis switches gold that that year, yeart several Emphasis additional additional targets targets drilled. drilled. During both phases phases of of 14 holes exploration JV exploration JV drills drills 14 holes (4,700 (4#700 ft) ft) on on Holyoke Holyoke property. property. 1977 - 1981 NOMEX AU JV JV (Chevron (Chevron and CCI) CCI) explores explores southwest southwest Bjork—Lundeen prospect holes 4 DIGB, drills drills 4 holes at Bjork-Lundeen prospect DIGB, (2,729 ft) and 4 (2#729ft) 4 holes holes west west of of Ropes Ropes (1,680 (lt680ft). ft). 1979 - 1981 REI Mine, Callahan Callahan evaluates evaluates Ropes Ropes Gold Mine, RE1 project project manager. manager. Drills 18 surface holes (12,724 (12*724ft) ft) into into into IP IP anomaly anomaly (802 (802 ft), ft), plus plus 8,000 8,000 orebody and 2 into ft ft of underground underground drilling. drilling. 1984 psnt 1984 —- psnt Kerr—McGee Kerr-McGee drilling. drilling. 1983 1983 St. Joe American Corp. prospects patchwork of land in northern northern and and southern southern DIGB, DIGBt no no holes holes drilled. drilled. - 1985 1983 — 1985 1983 - psnt 1984 1984 - psnt Corp Corp prospects prospects middle DIGB, DIGB, actively actively develops production makes Callahan makes production decision, decisiont develops Callahan ft level. Ropes Gold Mine to to 900 900 ft level. Acquires and and renovates renovates iron iron ore ore flotation flotation mill mill in in Champion. Champion. for additional on Callahan Callahan prospects prospects for additional reserves reserves on Ropes property property and and in in other areas areas within hauling hauling radius radius of of Ropes Ropes mill, mill, actively actively drilling. drilling. - prospects southwest Dodge prospects Phelps Dodge southwest DIGB, DIGB, drills drills 11 Phelps hole east eas-tof of Ropes Ropes (824 (824 ft). ft). - Au, 0.28 0.28 ml' at 0.087 0.087 oz/ton Au, Callahan Callahan mills mills 1.25 mT orebody above above 1284 1284 ft ft level. level. oz/ton Ag from Ropes orebody 1985 1985 - 1986 1986 9/87 9/85 — 9/87 9/85 84 �IMPLICATIONS IMPLICATIONS OF HIGH PRECISION PRECISION U-Pb AGE AGE DATES DATES ON ON ZIRCONS ZIRCONS FROM FROM PORTAGE LAKE LAKE VOLCANIC VOLCANIC BASALTS ON MIDCONTINENT RIFT SUBSIDENCE SUBSIDENCE RATES, RATES, LAVA LAVA FLOW FLOW REPOSE PERIODS PERIODS AND AND MAGMA MAGMA PRODUCTION RATES RATES JAMES JAMES B. PACES, PACES, Dept. Dept. Geology Geology & &Geological GeologicalEngrg., Engrg., Michigan Technological University, Houghton, Houghton, MI 49931 Technological University, 4993 1 DON W. DAVIS, DAVIS, Jack Satterly Geochronology Geochronology Laboratory, DON W. Royal Ontario Museum, Queen's Park, Park, Toronto, Ontario M5S Museum, 100 Queen's M5S2C6 2C6 Recent U-Pb zircon Recent high high precision precision U-Pb zircon dating dating of of Keweenawan-aged Keweenawan-aged rocks rocks in the the western western Lake Lake Superior Superior region region has has revealed revealed that basaltic basaltic igneous igneous activity activity associated associated with with the the Midcontinent Midcontinent Rift (MCR) (MCR) was was initiated initiated around around 1109 1109Ma1. ~ a ' . Dates of similar similar quality quality which which record record the the cessation cessation of extensive extensive flood flood basalt basalt extrusion extrusion do not not exist. exist. In In this this paper, paper, we we report the upper report new new dates dates which which constrain constrain the upper age age limit limit of of MCR MCR mafic mafic volcanism, volcanism, and and use use these data to to estimate estimate rates rates of of rift-related rift-related tectonic tectonicand andigneous igneousprocesses. processes. STRATIGRAPHY The Portage Portage Lake Lake Volcanics Volcanics (PLV), (PLV), northwest northwest Michigan, Michigan, represents the youngest youngest flood basalt-filled basalt-filled portion portion of of the theMCR MCR in the region2. The thick pile (3-5 the western western Lake Superior Superior region2. (3-5 km) km) of normal normal magnetic magnetic polarity, polarity, predominantly predominantly olivine olivine tholeiite tholeiite lavas isis conformably conformably overlain overlain by Oronto Oronto Group Group sediments. sediments. lavas This sequence of rocks sequence of rocks therefore therefore records records a major major transition transition in in MCR tMCR evolution evolution from from dominantly dominantly volcanic volcanic to to sedimentary sedimentary rif riftfilling material. material. filling Figure Figure 11 shows shows generalized generalized stratigraphic relationships in the the Keweenaw Peninsula. Peninsula. Highly differentiated differentiated pegmatoid pegmatoid layers layers within within two PLY PLV flows, flows, the the Greenstone Greenstone Flow Flow and and Copper Copper City City Flow Flow (GSF (GSF and CCF CCF respectively), respectively), were were sampled sampled for zircon zircon stratigraphic horizons horizons represented represented by these these extraction. The stratigraphic flows are separated by 2600-3100 of flood basalts and minor 2600-3100 m of sediments. A single single lava lava from from aa series series of of flows flows interflow sediments. (Lake Shore Traps, LST) within the Shore Traps, the Copper Copper Harbor Harbor ConglomConglomis separated erate was was also also sampled. sampled. LST LST magmatism magmatism is separated from from the GSF 700 m m of GSF horizon horizon by approximately approximately 700 of PLY PLV lavas lavas and and 800-1000 800-1000 m of coarse coarse clastic clastic sediment. sediment. RESULTS Ages from U-Pb U-Pb data on Ages were were determined determined from on multiple multiple fracfracabraded zircon zirconseparates. separates. All data points points plot plot close close to to tions of abraded the concordia concordia curve suggesting suggesting that problems problems of lead lead loss loss and and inheritance are are minimal. minimal. Six Six zircon zircon fractions fractions from from the the two two PLY and two PLV samples samples and two fractions fractions from the the LST LST sample sample yield yield 1.3 Ma and and 1094.1 1094.1 ± 2 3.6 3.6 Ma Ma respectively respectively 1095.1 ±2 1.3 ages of 1095.1 (based on zero errors on on all (based on zero age age lower lower intercepts; intercepts; errors all data data are are quoted at at 95% 95%confidence confidence levels). levels). PLY PLV and and LST LST ages ages are are quoted unresolvable from present data. data. Within Within the PLY PLV section, section, unresolvable from the present separate ages GSF and 1.7 separate ages for for the the GSF and CCF CCF horizons horizons are are 1094.4 1094.4 ±k 1.7 and 1096.0 1096.0 ± k 1.9 1.9 Ma Ma respectively. respectively. The GSF-CCF GSF-CCF age age Ma and difference and and one one sigma sigma error error isis1.6±1.3 1.6k1.3 Ma. Ma. The age reported reported for for the the PLY PLV isisconsistent consistent with with slightly slightly older, older, reverse reverse magnetic magnetic polarity polarity lavas l a v a from from the the Black Black Bay Bay Peninsula (upper Osler Peninsula (upper Osler Group, Group, 1097.6±3.7 1097.6k3.7 Ma'). ~ a ' ) . These age age C5 Fig. Fig. 11 (1cm) (km) C., S 0 I (1094.1 3.6 a S a 0. 0. 0 0. 1 —I. GSF (1094.4 1.7) C) 0 1 (I, 0 z 0 -ii 0 > —3 w -I w CCF (1096.Otl.9) 00. Keweenaw Fault �- relationshipssuggest suggestthat that all all of of the normal relationships normal polarity flood flood basalts with the polarity basalts associated associated with the western Lake Lake Superior Superior segment segment of of the MCR western were produced produced over over aa period of 2-3 were period of 2-3 Ma. Ma. However, an an age age reported reported from from a porphyrHowever, porphyritic intrusive/subintrusive intrusive/subintrusive unit uniton onMichipi— Michipicoten Island is ~sig- ) Island (1086.5 (1086.5 +1.3/—3.0 +1.3/-3.0 ~Ma3) a is nificantly younger than than PLY nificantly younger PLV or or LST LST ages ages reported here. reported here. This This large large age age difference difference implies that either 1) implies that 1) volcanic volcanic rocks rocks in the the eastern MCR are much eastern MCR much younger younger than than those those to west, 2) 2) the Michipicoten Michipicoten Island Island the west, to the Formation represents aa much later, Formation represents later, isolated isolated magmatic episode, episode, or or 3) intrusion magmatic intrusion occurred occurred much later later than deposition much deposition of the the volcanic volcanic host rocks. RATES OF SUBSIDENCE RATES geochronologic and stratiCombined geochronologic graphic data can be used to estimate estimate minimum rates rates of rift-related minimum rift-related subsidence. subsidence. The assumption assumption underlying underlying this this calculation, calculation, maintenanceofof a near maintenance near horizontal horizontal deposidepositional surface, is is supported supported by flow morphology, primary primary slope variations4, morphology, variations4, and distributions of interf low sediments. distributions interflow sediments. An average thickness thickness of of 2850 average 2850 m between between the the GSF ens4 i n n /^~PPo-GSF and and C'F CCF b~Awnnm horizons and +ha the age &WAA&Ulm -6- differMa yields yields subsidence subsidence rates rates ence of 1.6-1.9 ence 1.6- 1.9 Ma Although higher higher rates rates of 1.5 1.5 to to 2.0 2.0 mm/yr. mim/yr. Although may occur along MCR axis, the values MCR axis, the values may occur along-the - - - -- calculated from GSF-CCF GSF-CCF data are comparcalculated from able with able with rates rates of of tectonic tectonic subsidence subsidence in in other continental continental grabens (typically (typically 1-2 mm/yr; range range of of 0.2-10 mm/yr). The mm/yr; 0.2-10 mm/yr). The large large error in the error the reported reported LST LST age age reduces reduces the the significance of of similarly calculated rates rates for significance similarly calculated PLY subsidence the GSF-LST the GSF-LST interval. interval. PLV subsidence rates rates are roughly roughly an an order order ofofmagnitude magnitude those calculated greater than greater than those calculated from Osler Osier Group Group data (0.l2-0.24 (0.12-0.24 mm/yr). mm/yr). However, 1.5-2 mm/yr subsidence over the 12-13 1.5-2 mm/yr subsidence over 12-13 Ma Ma period period of of MCR MCR magmatic magmatic activity activity (1108(11081095 1095 Ma) Ma) would would have have resulted in the accumulation of 18—26 kmof of rift-fill. rift-fill. This 18-26 km thickness added to to 8-10 thickness added 8-10 km km of of overlying overlying post—magmatic sediments5'6 post-magmatic sediment^"^ yields total totalrift— riftfill values values in in close close agreement agreement with with recent recent seismic reflection reflection results7. results7. OULU LJiU UAJ.J.&dL- LAVA IODICITY LAVA REPOSE PER PERIODICITY Average interflow Average interflow repose periods periods can can also be estimated estimated from the the GSF-CCF GSF-CCF data. data. also Up to 140 140 separate separate cooling cooling units are recogrecognizable over this stratigraphic stratigraphic interval, however the the presence however presence of of compound compound flows flows reduces this number to to approximately approximately 65-70 65-70 86 major lava major lava flows. flows. Therefore, Therefore, the the average average repose period between successive successive major eruptions eruptions is is estimated at 20-30 Ka. Somewhat longer repose repose may may typify erupSomewhat longer er'uptions separated by by interf low sedimentary tions interflow sedimentary units while units while shorter shorter repose repose periods periods may may be be typical of of the majority typical majority of of PLY PLV flows flows which which directly overlay the underlying flow top. top. RATES OF OF MAGMA MAGMA PRODUCTION Finally, magma proproFinally, minimum minimum rates rates of of magma duction have been for the duction have been calculated calculated for the CCFCCFGSF interval. interval. Total Total volume volume of eruptive eruptive products is speculative products speculative given present present expoexposure. Minimal and "probable" sure. Minimal "probable" estimates estimates of the original original areal areal extent extent of PLY PLV lavas lavas are are shown shown in Figure Figure 22 (modified (modified after afterGreen8). re en^). Constant thickness thicknessacross acrossthe the basin basin is asConstant assumed (axial (axial thickening thickening is counteracted sumed counteracted by marginal thinning). Estimates of minimal marginal thinning). Estimates minimal . and "probable" volumes for for the and "probable" volumes the GSF-CCF GSF-CCF interval are are approximately approximately 40,000 and 100,000 km3 km3 respectively respectively which 100,000 which result result in ma ma production between 2-6x10"~ magma production rates rates between 2-6x102 km4/yr. Although these km /yr. Although these values values may may be be underestimatedby byaa factor factor of of 2-5, 2-5, they underestimated they fall fall within within the the range range of of values values estimated estimated for for h-@-1^ and basaltic magma production production in in other other rift and hot spot hot spot settings settings (Iceland ~ km3/ yr; (Iceland 5xl02 5x 1o ' km3/yr; Columbia River Basalts 7x102 km3/yr; Basalts 7x10'~ km3/yr; and and Columbia River Hawaii 3-10xl02 krn3lyr)'. Hawaii 310x10-2 km3/yr)9. 5 iB'adUJ.LJ.W LJ.J.Ue.LJ.f.U Davis and Sutcliffe Sutcliffe (1985) (1985 GSA GSA Bull Bull 96: 96: 1572. 1572. 2 Green (1982) (1982) GSA GSA Mem Mem 156: 156: 47. 47. Palmer and and Davis Davis (1987) (1987) Precambrian Res Res 37: 37: 157. 157. White (1960) (1960) Am J Sci Sci 5 258A: 367. 5Daniels 258A: 367. Daniels (1982) (1982)GSA GSAMem Mem156: 156:107. 107. 6Kalliokowski GSAMem Mem 156: 156: 147. 147. '7Behrendt 6 ~ a l ~ o k o w s(1982) k(1982) i GSA ~ehrendt 8 (1988) Green (1983) (1988) Geology Geology 16: 16: 81. (1983) Tectonophysics Tectonophysics 94: 413. 9Swanson 94: 413. g~wansonat et a!. al. (1975) (1975) Am Am JJ Sci Sci 278: 275: 877. 877. I Fig. Fig. 22 'Probable" Area �- Archean and and Proterozoic Proterozoic Tectonics Tectonics - Northern Michigan A Speculative Speculative Synthesis Synthesis John Palmquist, Geology Department C. Palmquist, John C. Lawrence University, University, Appleton, WI 54912 Lawrence 54912 tectonic interpretations offered as an attempt These eclectic These eclectic tectonic interpretations are offered attempt to to Penokean orogeny call ancestry of of the the Penokean orogeny and to call attention attention to to the the Archean Archean ancestry to apparent conflicts previously published reconcile reconcile the the apparent conflicts in in previously published ideas ideas about about the the nature nature of of the the Penokean Penokean deformation deformation (vertical (vertical vs. horizontal horizontal tectonics) tectonics) and views concerns the nature concerns the the contrasting views nature of basement-cover basement-cover interaction interaction the contrasting Two (brittle ductile basement-cover (brittle basement basement blocks blocks vs. vs. ductile basement-cover relationships). Two conflicting tectonic tectonic concepts have been sets of of conflicting concepts have been presented in in both both the the sets One concerning concerning the the question district and the the region.. region. One question of of the the role role of the the district and the Penokean was it Archean Archean basement basement behavior behavior during during the Penokean - was it ductile ductile or or brittle? brittle? The second conflict has to do with with reconciliation of the The the steep steep fault fault zones zones surfaces of folds and near near vertical vertical axial axial surfaces folds and and cleavages cleavages with with the the recumbent recumbent and folding folding in in adjacent adjacent areas. areas. - Archean scenario. Archean scenario. A southern southern gneissic gneissic terrane terrane (southern (southern complex) complex) and complex) were juxtaposed northern northern greenstone-granitic greenstone-granitic terrane terrane (northern (northern complex) juxtaposed in in proto-continental collision Zone (GLTZ) (GLTZ) of of proto-continental collision to form the Great Lakes Tectonic Zone Dextral shear shear along along the the GLTZ GLTZ may have have created created aa series series of low low Sims, ( 1980). Dextral Sims, (1980). Compeau Creek pressure zones the emplacement pressure zones which which guided guided the emplacement of the the Compeau Creek plutons plutons into syntectonic syntectonic relations with the greenstones of the northern complex and southern complex. Strain in the the Archean Archean of the the southern the the gneiss gneiss of complex. Strain patterns patterns in Vermilion District, Minnesota have been shown greenstone belt of the greenstone belt of the Vermilion District, Minnesota have been shown by by convincing example Schultz-Ela example Schultz-Ela (1986) (1986) to to indicate indicate dextral dextral transpression. transpression. AA convincing pull-apart associated with the the South pluton emplaced emplaced in of a granite of a granite pluton in a pull-apart South Ainorican Shear Shear Zone Zone of of France France is given by American is given by Guineberteau Guineberteau and and others, others, (1987). (1987). were intruded multiple ages Diabase dikes Diabase dikes of multiple ages were intruded along along fractures fractures and and faults faults in in northern and southern both both the the northern southern complexes complexes as as an an accompaniment accompaniment of of regional regional the syntectonic emplacement. Later of uplift and/or and/or "relaxation" "relaxation" of the syntectonic emplacement. Later uplift remobilization remobilization of of the the complexes complexes is is indicated indicated by by the the deformation deformation patterns patterns in in dismembered and of the gneissic terrain terrain and by dismembered and contorted contorted remnants remnants of the southern southern gneissic remnants appear early The appear as diffused, early dikes dikes in in the the northern northern complex. complex. The remnants diffused, Some feldspathized feldspathized amphibolites amphibolites and schlieren schlieren in in the the Compeau Compeau Creek Creek gneiss. gneiss. Some Mona of these these amphibolite amphibolite "ghosts" "ghosts" may may represent represent incomplete incomplete assimilation assimilation of Mona schist (Stonehouse, (Stonehouse, 1970). 1970). schist rift become the the Marquette The Penokean orogeny. orogeny. The rift destined to to become Marquette began to to close'by closeby transpression synclinorium began transpression (Cambray, (cambray, 1984) 1984) along the the site site southward directed subduction under the of the the GLTZ. GLTZ. A southward subduction zone zone somewhere somewhere under the of Wisconsin juxtaposed juxtaposed the the Baraga, Baraga, Menominee present present area area of of northern northern Wisconsin Menominee and and Chocolay Groups in wedge Chocolay Groups in an an accretionary accretionary wedge (Larue and Ueng, Ueng, 1985). (Larue and Underthrusting wedge comprised Underthrusting of the the footwall footwall caused the piling up of a wedge comprised of of a a series series of thrusts, thrusts, including including the the crystalline crystalline cored cored nappe nappe preserved preserved in in the the Felch Felch District District (Maharidge (Maharidge and and others, others, 1986). 1986). As As the the thrust thrust sheets sheets advanced advanced subducting northward (the footwall may have been actively subducting relatively relatively northward (the footwall may have been actively southward), toward have been southward), toward the the foreland, foreland, their their leading leading edges edges may may have been diverted diverted diverged around topographic buttresses, buttresses, into topographic lows, into topographic lows, i.e., i.e., diverged around topographic thrusts were southern complex. complex. Where the possibly possibly the the gneisses gneisses of of the the southern Where the thrusts were thickly stacked, stacked, depressed depressed geotherms geotherms formed formed the the metamorphic metamorphic nodes nodes at at 87 �Watersmeet, Peavy Watersmeet* Peavy and and Republic Republic (Attoh, (Attoh* 1986) following following aa thermal thermal lag. lag. The The have caused northward thinning thinning of the the tectonic tectonic load would have caused thermal thermal weakness weakness toward the the foreland. The anisotropy Archean rocks to slope slope up toward foreland. The anisotropy in in the the Archean rocks to modified the transpressional the shortening transpressional tectonic averted the shortening direction direction and modified tectonic trends to trends to allow allow Penokean Penokean reactivation reactivation of of Archean Archean structures. structures. Differential Differential thermal thermal weakening weakening of of diverse diverse foreland foreland (footwall) (footwall) Archean rocks rocks would allow allow some portions the footwall to yield whereas other some portions of of the footwall to yield as as brittle brittle blocks blocks whereas other initially weaker weaker or more portions, more heated, portionsy either either initially heatedy would fail fail by foldingj foldingyplastically the hanging hanging wall plastically flowing, flowingy or melting into the wall rocks. rocks. Ellis Ellis (1988) (1988) explored foreland and explored the the idea idea that that thrusting thrusting migrates toward the the foreland and that that the the internally by analyzing footwall/foreland secton will begin begin to to deform aeform internally analyzing the the footwall/foreland secton strength of a strength a rheologically rheologically simple simple two-layer two-layer lithosphere lithosphere under under compression. compression. This This interpretation interpretation resolves resolves the the dilemma dilemma of of the the vertical vertical axial axial surfaces surfaces seen at with the seen at the the east east end end of of the the Marquette Marquette synclinoriuxn synclinorium with the horizontal horizontal axial axial basement planes planes in in the the west. west. The The evidence evidence of of aa block-like block-like behavior behavior of of the basement Klasner and the the draping draping of of the the supracrustal supracrustal rocks rocks (Marquette (Marquette and and Republic Republic -- Klasner indications of the indications of a and and Cannon, Cannon* 1974) 1974) in in seeming seeming conflict conflict with with the a ductile ductile interaction interaction of of basement basement and and cover cover (Watersmeet (Watersmeet area) may also also be resolved resolved by were raised basement (footwall) the interpretation interpretation offered offered here here -- the the basement (footwall) rocks rocks were raised through the the ductile-brittle ductile-brittle transition transition as the ductile environment from aa ductile environment through as the from orogeny. Penokean orogeny. footwall/foreland deformed deformed internally during the Penokean At the the footwall/foreland ductile east end east end of of the the Marquette Marquette synclinorium, ~ynclinorium~ ductile greenstones greenstones appear appear to to have have cover rocks interacted with the interacted with the metasedimentary metasedimentary rocks rocks because because basement basement and and cover rocks properties (Carter Where have have similar similar mechanical mechanical properties (Carter and Palmquist, Palmquisty 1986). 1986). Where stronger stronger gneisses gneisses were were uplifted uplifted en bloc bloc the the weaker, weaker* layered layered metasediments metasediments over basement blocks in are draped over basement blocks in the the fashion fashion of the Rocky Mountain are draped Laramide thrusting. In the foreland uplifts foreland uplifts associated associated with with Laramide thrusting. In the Rockies, Rockiesy basement and more homogenous homogenous crystalline crystalline basement a cooler however* a and a cooler thermal thermal however, a more behave in more uniform, structure structure caused caused the the basement basement rocks rocks to to behave in a more uniformy brittle, brittle, region, the GLTZ of block-like fashion. In the block-like fashion. In the Lake Lake Superior region, the GLTZ of the the Archean zones of weakness that localized the Marquette Marquette synclinorium foreland created zones Presumably, the vertical vertical axial axial surfaces Basin. and the the Dead Dead River River Basin. Presumablyy surfaces at the the horizontal axial surfaces east end of the Marquette synclinorium and the horizontal surfaces on on resulted from the same same north-south north-south shortening shortening event, west have the have resulted from the event* the the the west Recumbent isoclinal Penokean footwall/foreland Penokean footwall/foreland compression. compression. Recumbent isoclinal folds folds described described might be be interpreted interpreted by (Kiasner, (Klasner* 1972) at the west end of the synclinorium might Group as as these rocks escaped escaped the over of of the as the the spilling spilling over the Baraga Baraga .Group these rocks the and were flattened gravitational confinement the footwall confinement of of the footwall "jaws" "jawst' and flattened by gravitational force. force. the crust, Where the the tectonic tectonic loading has sufficiently sufficiently heated the crusty basement basement ductile along with the metasedimentary rocks became ductile gneisses have became along with the rocks gneisses have Differential mechanical susceptibility (Watersmeet node). node). Differential thermal thermal and and mechanical susceptibility in in (Watersmeet strain along ductile zones zones leaving rocks may have concentrated concentrated strain the basement the basement rocks bloc (Republic free to intermediate (Republic node). node). intermediate areas areas unaffected unaffected and and free to deform deform en & locally reset radiometric clocks conditions may locally Thus, reset radiometric clocks without without Thus, metamorphic metamorphic conditions everywhere during penetratively deforming penetratively deforming or or remobilizing remobilizing the the basement basement everywhere during the the Penokean Penokean metamorphic metamorphic event. event. 88 �REFERENCES REFERENCES Attoh*K. K. 1986, 1986* Metamorphic Metamorphic Pressures, Pressures*Temperatures Temperatures and and Early Early Proterozoic Proterozoic Attoh, Geotherms in in Northern Northern Michigan Michigan [Abstract], [Abstract]$ Thirty-second Thirty-second Ann. Ann. Inst. Inst. on on Geotherms geology*p. p. 5-6. 5-6. Lake Superior Superior geology, Lake Cambray* W.F., W.F.* 1984, 1984* Proterozoic Proterozoic Geology, Geologyy Lake Lake Superior Superior South South Shore, Shore* Cambray, Geological Geological Association Association of of Canada Canada Field Field Trip Trip Guide Guide5. 5. Carter, Carter* P.J., P.J.* and and Palmquist, Palmquist* J.C., J.C.* 1986, 1986* Strain Strain Analysis Analysis of of Deformed Deformed Archean Archean Pillow Lavas, Lavas* Mona Mona Schist, Schist* Marquette Marquette County, Countyy Michigan, Michigan* U.S.A. U.S.A. Pillow [Abstract]. [Abstract]. Thirty-second Thirty-second Ann. Ann. Inst. Inst. on on Lake Lake Superior Superior Geology, Geologyyp. p. 16. 16. 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D.K. and and Ueng, Ueng, W.L., W.L.* 1985, 1985* Florence-Niagara Florence-Niagara terrane: terrane: An early early Larue, Proterozoic accretionary accretionary complex, complexy Lake Lake Superior Superior region, region* U.S.A., U.S.A.y Proterozoic Geological Geological Society Society of of America America Bulletin, Bulletinyv. v. 96, 96*p. p. 1179-1187. 1179-1187. Maharidge, Maharidge* A.D., A.D.* Mancuso, Mancuso* J.J. J.J. and and Onasch, Onasch* C.M., C.M.* 1986, 1986$ Tectonic Tectonic Evolution Evolution of of the the Felch Felch Trough Trough [Abstract], [Abstract]? thirty-second thirty-second Ann. Inst. Inst. on on Lake Lake Superior Superior geology, p. p. 53-54. 53-54. geology, Schultz-Ela, D.* 1986, 1986* Strain Strain Models Models for for the the Evolution Evolution of of- the the Vermilion Vermilion Schultz-ElayD., Ann. Inst. Thirty-second Minnesota District, District* Minnesota [Abstract], [Abstract]* Thirty-second Ann. Inst. on on Lake Lake Superior Geology, Geologyyp. p. 71-72. 71-72. Superior Sims, Sims* P.R., P.K.* 1980, 198OY Boundary between Archean Greenstone and Gneiss Terranes in Northern Northern Wisconsin Wisconsin and and Michigan, Michigan* Geological Geological Society Society of of America America Special Special Paper 182, 182* p. p. 113-124. 113-124. Paper Stonehouse, Stonehousey H.B., H.B.* 1970, 19709 Precambrian Precambrian of of the the Marquette Marquette Area, Areay Michigan, Michigan* in in Guidebook Guidebook for for Field Field Trips, Trips* Geological Geological Society Society of of America, America*North-Central North-Central Sec., Set.* Michigan Michigan Basin Basin Geol. Geol. Soc., S O C . East ~East Lansing, Lansing*p. p. 159-177. 159-177. 89 �Two of aarnet Jwo aenerations of cmrnet arowth arowthininthe theHardwood Hardwoodaneiss. aneissL Dickinson Cauntv. Ilichiaon Michiam DiekinsunCounty. 4.W. PETERSON PFTERSON (Department of the theGeophysical Qeophysiwl Sciences, SciencessUniversity Universityof Chicago, ChicagosChi -, IL J.W. (Department of Chicago, ft 60637U.S.A.) U.S.A) 60637 CA* QEIQER ( Technixhe UniversiM Berlin Ernst C.A. GEIGER (Techniache Universitat Berlin,I nstitut InstitutfW für Mineralqie Mineralogie und undKristallqraphie, Kristailogrophie, Ernst Reuter ReuW Plat2 P1aQ 1, I , 1000 1000BerlIn Berlin12, 12,West WetGermany) hrmany) The Hardwood Hardwoodgneiss gneissisisaaunit unitof ofEarly Early Precambrian Precambrian age outcropping in age outcropping ineastern—cantral eastern-central Dickinson general lithology of the described by )ames et at a]., al., D i c k i mCounty, bunty*Michigan. Michip. The Thegeneral lithdqyof theunit unitwas wus&cribd by James * 1961* pyroxene gneiss* gneiss, plagioclequartz plagioclase—quartz gneiss* gneiss, 196 1 and andconsists consistsofofgarnet— garnet- hornblende— hornblende-pyroxene hornblende— pyroxenegneiss, gneiss,amphibolite, amphibolite, garnet-quartz-sillimanite-mica garnet—quartz—sillimanite— micaschists schist,and andquartzite. quartzlte. hornblen&-pyroxene Two generations of pyroxene Two generations cd garnet garnet growth growthcan mbe bedistinguished distinguishedininthe thegarnet—hcrnblende— garnet-hurnblende-pyroxene units. anhedr& porphyroblasts porphyroblasts of garnet, units Generation Generation Iiconsists consists of of subhedral to anhedral garnet*1.0—2.5 1 .O-2.5 mm in in diameter, matrix of diameter*set set ininaafine—grained fine-grained matrix ofplagioclase plqioclaseand and hornblende. Many Many of these garnets contain rutile up to 100 100urn pmlong. long. Some &me garnets garnets contain amtain inclusions inclusionsof cpx, cpx, opx, opx, and and contain needles needles ofofrutile up to plagioclase, thoughthis this is not common. common. InclusionInclusion—free garrietshave havedistinct distinctrims. rims. h Generation II1 p?cgia3ase,though free prnets eration 1 consists, 00um wide) generation((I) rims consistssin in part, part*ofof distinct distinctrims rims(80— (80- 11OOpm wide) on the gmeration I ) garnets. garnets. These These rims contain aa band of contain of irrqularly-shaped irragularly—shaped oxide blebs blebs (5(5—10 10pm urndimensions) dimensions)which which forms forms a sharp sharp contact diffuse contact with the ant& with m n k t with the interior interior(generation (generation1)I )portion portionofofthe thegarnet garnetand anda diffus remainder garnet rim. rim. Generation remainder of the garnet Qeneration(II) (11)garnet prnetgrowth g m t hisisalso alsorepresented representedby by50— 50- 100 I 00 i.jm pm diameter geometric grains grains are commonly commonly cored coredwith with oxide oxideblebs blebssimilar similar diameter euhedral euhedral garnets. garnets. These These geometric to those rims of t h w in the rims of generation generation(I) ( I garnets. ) garnets.These Thesecores coresare are—25 -25 .Lrn pm inindiameter diameterand andconsist consistofof several m inindimension. -5 jim dimension.The Theeuhedral euhedralgernets garnetsare arecommonly mmmonlylocated located several individual individualoxide wick blebs blebs—5 around rims of larger generation relative location wound the rims uf the larger generation ((I)I )garnets. garneb. Because Bemuse of the relative laxtionof of oxide blebs the ares cores of of euhe$ral euhedral garnets garnetsand andthe therims rims of sub-8nhedrid sub—anhedralgarnets* garnets,we weinfer infer that bkbs between the that both contemporaneously,and andatataadistinctly distinctly different different time both rims rimsand and euhedr& euhedral garnets grew mtemp~ranmusly~ timethan thanthe the garnets. generation ((I)I)garnets. generation In samples, no nollarge (generation I) gamete In some same samples, a m (generation I) garnetsare arepresent. present.However, However,augen—shaped augn-shaped areas 10 euhdral euhedral garnets* garnets, eech areas (—1.5 (-1 -5 mm rnm by 1I mm) mm) are arepresent presentwhich whichcontain contain5— 5- 10 em31 150—200 150-200 .im pm butbut areare riddled inclusions in gamnets rarely cored with oxides, riled with with inclusions These pgeometric m e t r i c garnets areare rarely mred with in diameter. These of cpx, have been beenthe thelaxtions locationsof of1arq large generation generation cpx, plagioclase, phgitclasesand and hornblende. hornblenck. These These augen augem may have (I) subsequentlyrecrystallizd recrystallized to (1)gamete garnetswhich whichexperienced experiencedlater laterpenetrative penetrativedeformation deformationand and subsequently the, euhedral generation (II) gamnets. A difference In whole—rock the small, euhedral pneration ( 11) prnets. A difference in whole- rockbulk bulkcomposition cornpusitionmay m8y explain explainthe thelack lackofofoxide mi&cores. mre. Electron reveal mmpositional compositionaldifferences differencesbetween betweenthe thetexturally texturally Electron microprobe microprobe analyses reveal thermobarometry indicates equilibration equilibration defined generation(I) (I) and and(11) (II) gamete. defined generation garnets. Quantitative Quantitative thermobarometry conditions 850—950C and kbar for for generation ((I)Igarnets, 8- 111 1 kbar ) grnets,and andP—I P-T conditions mnditionsof anditions of 850-950° and 8— 650-750C (II) gamete. 650-750°and and7-8 7-8kbar kbarfor forgeneration generation (11) garnets. The recognition of two growth at least portion of The recognition two generations gmerations of garnet growth l e d records rear& one portion of the the decompression—cooling history for for this terrane, and discriminate between ~mpression-mUnghistory thishigh—grade high-gr& terrane, and may discriminate between Archean Proterozoic metamorphic Archean and Proterozoic metamorphicevents. events. * James* H.L. Clark,L.D., L.D. Lamey,C.A. Lamey, C.A. and and Pettijohns F.J., 1961, 196 I ,Geology h l a of ~ Dickinm James, H.L.,Clark, Pettijohn, F.U., of~central central Dickinson County Michigan: U.S. Geol. Survay Paper Paper3310, U.S. b l.Survey 10, 11 76 pp. 90 �SULFIDEMINERALIZATION MINERALIZATIONAND ANDASSOCIATED ASSOCIATEDHYDROUS HYDROUSSILICATES SILICATESIN IN SULFIDE ANORTHOSITICROCKS ROCKSFROM FROMTHE THEDULUTH DULUTHCOMPLEX COMPLEX ANORTHOSITIC Bernhardt Saini—Eidukat, S a i n i - E i d u k a t ? Dept. Dept. of of Geology Geology and and Geophysics, Geophysicst Bernhardt University U n i v e r s i t y of of Minnesota, Minnesota? Minneapolis, Minneapolis? Minnesota Minnesota 55455 55455 The The principal p r i n c i p a l sulfide s u l f i d e minerals m i n e r a l s in i n anorthositic a n o r t h o s i t i c rocks r o c k s of o f the the D u l u t h Complex, Complexf Minnesota, M i n n e s o t a ? are a r e chalcopyrite, c h a l c o p y r i t e t pyrite p y r i t e and and Duluth pentlandite. p e n t l a n d i t e . They They occur o c c u r as a s interstitial i n t e r s t i t i a l void—filling, v o i d - f i l l i n g ? included, i n c l u d e d ? and and fine—veini-et t y p e s ? similar s i m i l a r to t o those t h o s e observed o b s e r v e d in in f i n e - v e i n l e t textural t e x t u r a l types, troctolitic series rocks r o c k s (Weiblen (Weiblen and and Morey, Morey? 1976). 1976) t r o c t o l i t i c series A n a l y s e s of o f biotites b i o t i t e s in i n Duluth D u l u t h Complex Complex anorthositic a n o r t h o s i t i c and and Analyses t r o c t o l i t i c rocks r o c k s show show higher h i g h e r chlorine c h l o r i n e contents c o n t e n t s in i n biotites biotites troctolitic a s s o c i a t e d with w i t h sulfide s u l f i d e mineralization. m i n e r a l i z a t i o n . Substitution S u b s t i t u t i o n of o f chlorine chlorine associated ( C l ) in i n biotite b i o t i t e depends d e p e n d s on on temperature, t e m p e r a t u r e ? Cl C l activity a c t i v i t y during during (Cl) e q u i l i b r a t i o n f and a n d the t h e Mg!(Mg+Fe) Mg/ (Mg+Fe) ratio r a t i o ("mg") (llmgll) of o f the t h e biotite biotite equilibration, i s known known in i n the t h e case c a s e of of (Munoz? 1984) 1 9 8 4 .) . Only Only the t h e latter l a t t e r parameter p a r a m e t e r is (Munoz, the C l with with t h e Duluth Duluth Complex. Complex. The The expected e x p e c t e d correlation c o r r e l a t i o n of of increasing i n c r e a s i n g Cl decreasing i s observed o b s e r v e d (Table ( T a b l e 1), I ) , but b u t the t h e highest h i g h e s t Cl C l found found d e c r e a s i n g "mg" lvmgvlis also A t this t h i s point p o i n t it it is i s not not a l s o correlates c o r r e l a t e s with w i t h high h i g h sulfide s u l f i d e content. c o n t e n t . At known C l content c o n t e n t reflects r e f l e c t s dominantly dominantly aa magmatic magmatic enrichment enrichment known if i f the t h e Cl with C l when when SS was was added added to t o the the w i t h differentiation, d i f f e r e n t i a t i o n ? or o r the t h e addition a d d i t i o n of of Cl system system (Ripley, ( R i p l e y ? 1981) 1981). It I t has h a s been been proposed p r o p o s e d that t h a t Cl—complexing Cl-complexing fluids f l u i d s may may play p l a y an an important i m p o r t a n t role r o l e in i n the t h e metallogenesis m e t a l l o g e n e s i s of o f platinum p l a t i n u m group g r o u p element element (PGE) deposits d e p o s i t s (Balihaus ( B a l l h a u sand andStumpf S t u m p1, f l ? 1986; 1986; Boudreau, Boudreau? Mathez Mathez and and (PGE) McCallum? 1986) 1 9 8 6.) . Preliminary P r e l i m i n a r y analyses a n a l y s e s of of Duluth Duluth Complex Complex rocks r o c k s show show McCallum, aa correlation N i and and c o r r e l a t i o n of of enrichment enrichment of of chlorine c h l o r i n e with w i t h whole whole rock r o c k Cu, Cut Ni PGE PGE enrichment. e n r i c h m e n t . Although Although at a t this t h i s point p o i n t in i n the t h e investigation i n v e s t i g a t i o n the the role C l in i n metal m e t a l concentration c o n c e n t r a t i o n is i s equivocal, e q u i v o c a l r it it is i s hoped hoped that that r o l e of o f Cl further with w i l l provide p r o v i d e exploration e x p l o r a t i o n geologists geologists w i t h a tool t o o l for for f u r t h e r study s t u d y will t a r g e t i n g PGE PGE deposits d e p o s i t s in i n the t h e Duluth Duluth Complex. Complex. targeting . References : References: and B a l l h a u s f C.G. C.G. a n d E.F. E . F . Stumpfl, S t u m p f l ? 1986, 1986? Sulfide Sulfide Ballhaus, mineralization in the Merensky Reef: m i n e r a l i z a t i o n i n t h e Merensky R e e f : evidence evidence silicates Contr. Mm. Pet., Pet., s i l i c a t e s and fluid f l u i d inclusions. inclusions. C o n t r . Min. and a n d platinum platinum from from hydrous hydrous 94, 9 4 ? 193—204. 193-204. A . E . ? Mathez, Mathez? E.A. E - A . and a n d 1.S. I . S . McCallum, McCallumf 1986, 1986? Halogen Halogen Boudreau? A.E., Boudreau, geochemistry g e o c h e m i s t r y of o f the t h e Stillwater S t i l l w a t e r and a n d Bushveld B u s h v e l d Complexes: Complexes: evidence e v i d e n c e for f o r transport t r a n s p o r t of o f the t h e platinum—group p l a t i n u m - g r o u p elements e l e m e n t s by by Cl—rich J . Petr., P e t r . ? 27, 2 7 ? 967—986. 967-986. C l - r i c h fluids. f l u i d s . J. F—OH 1984, Munoz? J.L., J.L. 1984 F-OH and a n d Cl-OH C l - O H exchange e x c h a n g e in i n micas m i c a s with with Munoz, In: Bailey, applications to hydrothermal ore deposits. a p p l i c a t i o n s t o h y d r o t h e r m a l o r e d e p o s i t s . I n : B a i l e y ? S.W. S.W. (ed.) Micas,t Rev. (ed.) w Rev. Mineral. M i n e r a l . 13, 1 3 ? Mineral. M i n e r a l . Soc. SOC. Am., Am. Virginia, Virginia, 469-494. 469—494. Ripley, E . M m f 1981, 1981r Sulfur S u l f u r isotopic i s o t o p i c studies s t u d i e s of of the t h e Dunka Dunka Road Road Cu—Ni Cu-Ni R i p l e y f E.M., deposit, 7 6 ? 610—620. 610-620. d e p o s i t ? Duluth Duluth Complex, Complexr Minnesota. Minnesota. Econ. Econ. Geol., Geol . 76, Weiblen, Weiblenf P.W. P .W. and a n d G.B. G . B . Morey, Morey? 1976, 1976? Textural T e x t u r a l and and compositional compositional characteristics of sulfide ores from the basal c h a r a c t e r i s t i c s of s u l f i d e o r e s from t h e b a s a l contact c o n t a c t zone zone of of the South Kawishiwi intrusion, Duluth Complex, Northeastern t h e S o u t h Kawishiwi i n t r u s i o n ? D u l u t h Complext N o r t h e a s t e r n University Minnesota. M i n n e s o t a . Proc. P r o c . 37th 3 7 t h Ann. Mi Min. Symp., Symp. U n i v e r s i t y of of Minnesota. Minnesota. 91 �2 3 34.45 5.16 13.93 0.04 18.98 9.93 37.87 3.27 16.55 0.06 10.00 15.66 0.09 0.42 9.55 1 Si02 1102 Ti02 Al203 A1203 Cr203 CQ03 FeO FeOTT MgO MI0 cCaO ao Na20 Na20 K20 K20 32.48 3.33 cCls 0.19 25.88 6.39 0.05 0.33 8.93 0.46 TOTAL TOTAL 92.45 92.92 -0=Cl -O=CI 92.35 92.82 93.68 93.63 Si Si 5.36 5.46 5.61 Ti Ti Al1 A 0.41 0.61 2.80 0.02 3.57 1.57 0.36 2.89 0.01 2.51 0.01 0.11 n.d. 0.11 1.88 0.13 1.94 0.12 15.87 15.71 Cr Fe Fe Mg Mg Ca Ca Na Na K K cClI TOTAL TOTAL 14.41 n.d. 0.37 9.62 0.44 2.60 2.34 0.21 0.01 1.24 3.46 0,01 0.12 1.81 0.05 15.56 1..Analyses Table I Analyses of biotites in Duluth Complex rocks. n.d. = not detected. n.d. Numbers the basis basis of of22 220. Numbers of ions on the 0. 1. Troctolitic Troctolitic Series. Series. INCO 2B, Gabbro Lake Ql~ad. Q'iad. 1. INCO Test Pit sample 26, Anorthositic Series. Sulflde.bearing 2. Anorthositic Sulfide-bearinganorthosite. Gabbro Gabbro Lake Lake Quad., BL.27A-87 BL-27A-87 3. Anorthositic Anorthositic Series, late stage. Troctolitic anorthosite, sample 30814 308A of Miller 3. (Geology and Petrology of Anorthositic Rocks in the Duluth Complex, Snowbank Lake Quadrangle, Quadrangle, Northeastern Northeastern Minnesota. Minnesota. Ph.D. Ph.D. Thesis, 1988) 1986) 92 �I THE MAGNETIC FABRIC AND STRUCTURE OF THE QUETICO SLATES AT THE QUETICO-WABIGOON INTERFACE, NORTHWESTERN ONTARIO. PERRY SARVAS and GRAHAM .3. BORRADAILE. Department of Geology, Lakehead University, Thunder Bay, Ontario, Canada. u Recent studies of magnetic fabric in tectonites be many workers have repeatedly revealed a strong correlation between principal magnetic susceptibility directions and principal finite strain directions. These observations have led to this study of magnetic fabric in the Quetico slates to assist structural investigations. The Archean Quetico metasedimentary belt, at the interface with the Wabigoon volcanic—plutonic subprovince, is characterized by sheath—folded greywacke-slate sequences of very low metamorphic grade. The sequences show a lateral metamorphic gradient towards the center of the Quetico subprovince, where migmatites are found. The sheath folds close to the belt bounday are primary, isoclinal and are believed to result from pervasive dextral transpression of the northern margin of the Quetico subprovince. The Quetico metasedimentary rocks have a polyminerallic magnetic mineralogy, comprised of a small trace (<2 weight U of highly magnetic grains (magnetite and pyrrhotite) and a much more substantial proportion of weakly magnetic minerals Both fractions are believed to contribute (phyllosilicates). significantly to both the magnetic susceptibility and the magnetic susceptibility anisotropy of the rocks. The magnetic fabric of the Quetico slates is predominantly The minimum magnetic susceptibility tectonic in derivation. directions are consistently perpendicular to continuous cleavage These cleavage planes parallel the major structural planes. trends and metamorphic isograds, corresponding to the major episode of pervasive regional deformation/metamorphism. In places, a weak remnant sedimentological magnetic fabric is preserved. The directions of maximum and intermediate magnetic susceptibilities vary throughout the area. This may be due to the influence of the phyllosilicates on the lithological magnetic susceptibility anisotropy (phyllosilicates have an oblate magnetic susceptibility ellipsoid, with poorly defined maximum and intermediate susceptibility directions). Also, the complexities introduced from a polyminerallic magnetic mineralogy, and a subordinate sedimentological magnetic fabric, could have influenced the orientations of the principal magnetic susceptibilities. 93 �A A Paleomagnetic Paleomagnetic Study Study of of the the Hamilton Hamilton Mound Mound Area of of Adams County, County, Central Wisconsin Robert Robert Schneiker Schneiker and William F. Kean Department Department of of Geosciences Geosciences University Wisconsin—Milwaukee University of of Wisconsin-Milwaukee Milwaukee, Milwaukee, WI WI 53201 53201 The The Hamilton Hamilton Mound area area represents represents aa complex complex intrusion intrusion into into precambrian measurements were precambrian quartzites. quartzites. Magnetic measurements were made made on on the the granitic granitic intrusion, intrusion, the the complex complex mixed mixed zone zone and and the the quartizites. quartizites. The viscous to The granite granite proved proved to to be be too too magnetically viscous to provide provide reliable palemagentic reliable palemagentic directions. directions. The The magnetism in in the the quartizite appears appears to be caused by hematite, based on on A.F. A.F. and quartizite thermal demagnetization thermal demagnetization studies. studies. The The pole position position of of the the quartizite, after quartizite, after aa correction correction for for local local structure structure is is N15°, ~15O, W120°, ~ 1 2 which which 0 ~ is is similar similar to to the the position position for for the the Baraboo Baraboo type type quartzites of quartzites of Wisconsin Wisconsin and and Minnesota. Minnesota. The is The mixed zone zone has has a a magnetism which is directions are magnetite. The magnetic directions are well magnetite. The provide a provide a pole pole position position at at S20°, s20° W75°. ~ 7 5 ~This This . represent the the last represent last age age of of intrusion intrusion at at about about 94 primarily primarily carried carried by clustered clustered and and position probably position probably 1600 1600 m.y.a. m.y.a. �A POST-TECTONIC POST-TECTONIC RARE-METAL-RICH RARE-METAL-RICH GRANITE GRANITE ININTHE THESOUTHERN SOUTHERNCOMPLEX, COMPLEX, UPPER UPPER A PENINSULA, PENINSULA, MICHIGAN. MICHIGAN. SCHULZ, K.J., Survey, Reston, Reston, VA VA 22092; 22092; Sims, Sims, P.K. P.K. SCHULZ, K.J., U.S.Geologica1 U.S.Geological Survey, and Z.E., 80225. and Peterman, Peterman, Z. E., U.S.Geological U.S. Geol ogicalSurvey, Survey,Denver, Denver,CO CO 80225. We repert herein herein preliminary results We report resultsofofa geochemical a geochemical and and Rb-Sr Rb-Sr isotopic granite from the northern isotopic study study of ofaasmall smallundeforined undeformed granite from the northern part of of the Southern miles south Southern Complex, Complex, 22 miles south of ofHumboldt Humboldt in in the theUpper Upper Peninsula Peninsula of granite, which of Michigan. Michigan. The The granite, which is of of probable probable Early Early Proterozoic Proterozoic age, age, is is coinpositionally similar to composi tionally similar torare-metal-rich rare-metal -richgranites granitesand andsuggests suggests aa possible potential potential for forSn-W Sn-W (Ta-Nb) (Ta-Nb) mineralization mineral ization ininupper upperMichigan. Michigan. The granite, which wasfirst first discovered briçfly The granite, which was discovered and and bri flydescribed described by by Hoffman (1987),is roughly circular outline, about17/1/ miles Hoffman (1987) ,is roughly circular in inout1 ine, about miles in 8 diameter, diameter, and and intrudes the the Archean Archean Bell Creek Creek granite granite and an gneisses gneisses of of the Southern Thegranite granite is is generally massive, mediumSouthern Complex. Complex. The massive, finefine-toto mediumgrained equigranular to to hypidiomorphic granular, nonfoliated, nonfoliated, and light grained equigranular hypidiomorphic granular, and light red to brick brick red. red. AA prominant prominant biotite and(or) lineation 1 ineation is is red biotite foliation foliation and(or) present locally near joints are present locally near the the margins. margins. Fractures Fractures and and joints are ubiquitous ubiquitous and typically are Kand typically arecoated coated with withmicas. micas. The The mineralogy mineralogy consists of of Kfeldspar, albite, muscovite, a1 bi te,quartz, quartz,biotite, biotite, muscovite,and andaccessory accessory fluorite fluoriteand and zircon. Accessory uranothorite, col columbite, euxenite, cassiterite, Accessory uranothorite, umbi te, euxeni te, cassiterite, molybdenite, (1987). According and topaz topaz were were reported by by Hoffman Hoffman (1987). According to to the the molybdeni te, and IUGS classification of plutonic 1976), this this body body is is IUGS classification plutonic rocks rocks (Streckheisen, (Streckheisen, 1976), an a1 kal i -feldspar granite. granite. an alkali-feldspar The granite isischaracterized The granite characterizedbybyhigh highSi02 Si02(>74 (>74%), %),low lowFeO(11 FeO (<2 %), (<0.2 %) %), CaO(~0.5 (<0.5%) %), andTi02 1102(<0.02 (<0.02%) %), andnear'iiual near'eual %) , MgO MgO (<0.2 , CaO , and , and Na20 and KK,O (4-5 %) %) contents. The Na 0 and 0 (4-5 The trace traceelements elementsRb Rb (350-1000 (350-1000ppm), ppm), Pb Pb (20-70 (26-70 ppmj, ppm?, VY (28-115 (28-115 ppm), ppm), Nb Nb (35-209 (35-209 ppm), ppm), and and Ta Ta (21-36 (21-36 ppm) ppm) are are strongly (<I7ppm), ppm),BaBa(<20 (<20ppm), ppm),and andEu Eu (<0.07 (<0.07ppm) ppm) strongly enriched, enriched,and andSrSr(<17 are strongly stronglydepleted depletedcompared compared to toaverage average granites. granites.The TheREE REE have have U-shaped chondrie normalized normalizedpatterns patterns with with very large U-shaped chondrite large negative negative Eu Eu anomal i es (Eu/Eu (Eu/Eu <0.025). <O.O25). anomalies Age Age determination by by the theRb-Sr Rb-Sr method method on on three threewhole whole rock rocksamples samples defined preliminary age ageofof 1733 1733/_25 a Sr initial ratio ratio of /_25 MaMa andand a Sr initial of defined aa preliminary 1.55). Although Although this this isisa minimum about 0.81T/_0.078 0.817+/0.078 (Model (Model I,I,MSWD MSWD = =1.55). a minimum about age, granite may age, ititsuggests suggeststhat thatthe the granite mayhave havebeen beenemplaced emplaced during the the Early Proterozoic, with the Proterozoic,perhaps perhapscontemporaneously contemporaneously with the ca. ca.1760 1760Ma Ma anorogenic magmatism Wisconsin. An magmatism inin Wisconsin. An Early Proterozoic Proterozoicpost-Penokean post-Penokean age wouldbe becompatible compatiblewith withthe the lack lack of age would of penetrative penetrativedeformation deformation and and mineral alteration in this mineral alteration this granite. granite. Compositional featuresofofthe the granite granite stock stock are are similar similar to Compositional features tothose those of Sn-W mineralized kal i -feldspar granites of of the theArabian Arabian Shield Shield Sn-W mineral ized a1alkali-feldspar (Jackson Ramsay,1986) 1986)and andthe the Nigerian Nigerian Younger Granite province Younger Granite province (Jackson and and Ramsay, (Kinnaird others, 1985), 1985),and andtotothe thetopaz topazrhyolite rhyolite suite of of the the (Kinnaird and and others, Western UnitedStates States (Chri (Christiansen and others, others, 1986). Western United sti ansen and 1986). Highly Highly evolved, evolved, rare-metal-rich granite stocks, or cupolas, typically occur rare-metal -rich granite stocks, or cup01 as, typically occur in clusters clusters or linear are related related to larger lineararrays arraysthat thatcommonly commonly are larger granite granitebodies bodies as, as, for 1986).ItIt is is for example, example, in in the theArabian Arabian Shield Shield (Jackson (Jackson and and Ramsay, Ramsay, 1986). interesting to lies on tonote note that thatthe thegranite granitenear nearHumboldt Humboldt lies on the the 95 �northeastern edgeofof aa large large negative negative gravity gravity anomaly that is northeastern edge anomaly that is roughly roughly coincident coincident with withthe theRepublic Republicmetamorphic metamorphic node; node; this thisanomaly anomalyhas hasbeen been subjacent granite granitepluton pluton(Kiasner (Klasnerand and others, others, 1985). 1985). attributed totoaasubjacent Although highly greisenized rocks rocks have have not Although highly greisenized not been beenfound foundinin the the granite near trace-element-enriched nature nature and and the possible possible near Humboldt, Humboldt,its its trace-element-enriched occurrence thearea area suggests suggests this this region region occurrenceofofother other similar similar intrusions ininthe Peninsulaof of Michigan Michiganmay may containa asignificant significant potential of the the Upper Upper Peninsula contain for Sn-W for Sn-W (Ta-Nb) (Ta-Nb) resources. resources. REFERENCES REFERENCES Christiansen, E.C., Christiansen, E.C., Sheridan, Sheridan, M.F., M.F., and and Burt, Burt,D.M., D.M., 1986, 1986,The TheGeology Geology and Geochemistry Geochemistryof of Cenozoic Cenozoic Topaz TopazRhyolites Rhyolites from from the Western and Western United States: Geological States: Geological Society Society of ofAmerica America Special Special Paper Paper 205, 205, 82 8 2 p. Hoffman, M.A., M.A., 1987, Hoffman, 1987, The The Southern Southern Complex: Complex: Geology, Geology, Geochemistry, Geochemistry, Mineralogy and Mineral Chemistry Mineralogy and Mineral Chemistry of ofSelected SelectedUraniumUrani urn-and and Thorium-Rich Thori urn-Ri ch Granites: unpublished disseration, PhD di sseration, Michigan Michigan Technological Techno1 ogical unpubl i shed PhD University, 382 University, 382pages. pages. Jackson, N. N.J. C.R., 1986, 1986, Post-Orogenic Post-Orogenic Fel Felsic Jackson, J. and and Ramsay, Ramsay, C.R., sic Plutonism, Pl utoni sm, Specialization in the Mineralization and and Chemical Chemical Specialization the Arabian Arabian Shield: Shield: Transactionsof of the the Institute Institute ofofMining Transactions Mining and and Metallurgy Metallurgy (Sect. (Sect. B: B: Appl. Appl . earth earth sd.), sci.), v.v.95, 95,p. p.B83-B93. B83-B93. Kinnaird, J.A., J.A., Batchelor, Batchelor,R.A., R.A., Whitley, Whitley,J.E., J.E.,and andMacKenzie, MacKenzie, A.B., A.B., 1985, Geochemistry, Mineralization andHydrothermal HydrothermalA1Alteration of the i zati on and terat i on of 1985, Geochemi stry, Mineral Nigerian High ProducingGranites, Granites, in High Nigerian High Heat Heat Producing High Heat Heat Production Production Granites, HydrothermalCirculation Circulation and andOre OreGenesis: Genesis:Institute Institute of Hydrothermal of Mining Mining and and Metallurgy, p. p. 169-195. 169-195. Kiasner, J.S., Klasner, J.S., King, King,E.R., E.R., and andJones, Jones, W.J., W.J., 1985, 1985,Geologic Geologic Interpretation ofofGravity Interpretation Gravityand andMagnetic Magnetic Data Data for forNorthern Northern Michigan Michigan and and Wisconsin,inin Hinze, Hinze,W.J., W.J., editor, editor, The Utility ofofRegional Wisconsin, The Utility Regional Gravity Gravity and and Magnetic Anomaly AnomalyMaps: Maps: SocietyofofExploration Exploration Geophysicists, Geophysicists, p. 267-286. 267-286. Magnetic Society Streckeisen, A., Earth A., 1976, 1976,To ToEach Each Plutonic PlutonicRock Rock Its ItsProper ProperName: Name: Earth Science 12, p. 1-33. Science Reviews, Reviews, v. 12, 1-33. 96 �The Mountain Shear Zone——Relevance Zone--Relevance to age of quartzite quartzite at McCaslin and Mountain Shear Thunder northeastern Wisconsin Thunder Mountains, Mountains, northeastern Wisconsin CO 80225; 80225; P.K. SIMS SIMS and and Z.E. Z.E. PETERNAN, PETERMAN, U.S. U.S. Geological Geological Survey, Survey, Denver, Denver, CO P.K. J.S. KLASNER, KLASNER, Western Western Illinois Illinois University, University, Macomb, Macomb, IL IL 61455 61455 J.S. The Mountain shear zone zone is a discrete, 1- to 2.5-km-wide discrete, 1— 2.5—km—wide zone of rocks that trends N.55°—60° ~ . 5 5 ~ - 6E .0 ~and largely obliterates regional mylonitic rocks E. obliterates the regional north-trending fabrics fabrics (S0/S1) (So/Sl) in in metavolcanic rocks of early north—trending metavolcanic and granitoid rocks Proterozoic ("1860 Ma) age age (Sims (Sims and and others, others, 1986; 1986; Sims, Sims, in in press). press). An An (1860 Ma) quartz diorite diorite body (Hines Quartz Quartz Diorite) body that intruded the undeformed quartz the shear zone has a U-Pb U—Pb upper upper intercept age age of of 1812.7±3. 1812.7±3.6 Ma, Ma, which which provides provides a firm age on on the the shearing. finn minimum age A deformed within the deformed conglomerate conglomerate (Baldwin (Baldwin Conglomerate) Conglomerate) within the shear shear zone zone of granitic granitic gneiss gneiss and and metavolcanic metavolcanic rocks derived derived from the contains clasts of evolving evolving shear shear as as well as as clasts clasts of quartzite quartzite as as much as as 25 25 cm cm in in diameter diameter was the (Lahr, 1972). The source for quartzite clasts almost certainly was (Lahr, 1972). Mountains, less than 20 km to quartzite now exposed at McCaslin and Thunder Mountains, the north. Thus, Thus, inasmuch inasmuch as the Baldwin Conglomerate was deformed during the shear deformation, deformation, and prior to emplacement of the Hines Hines Quartz Diorite, Diorite, the quartzite clasts and their parent rocks are older than 1812 Ma. quartzite clasts their parent rocks are older than 1812 Ma. The quartzite at McCaslin and Thunder Mountains unconformably overlies the Waupee Volcanics (Olson, (Olson, 1984), 1984), which were deformed deformed on on northeast—trending northeast-trending fold fold axes axes and and metamorphosed quartzite was metamorphosed prior prior to to quartzite quartzite deposition. deposition. The quartzite was deformed deformed later later westward—plunging syncline into a westward-plunging syncline (Nancuso, (Mancuso, 1960). 1960). in the Lake Superior show a great disparity The quartzite quartzite bodies in Superior region region show deformation, yet yet all of them generally have have been presumed presumed to in intensity of deformation, 1981), inasmuch as the be younger than 1760 1760 Ma (see Van Schmus and Bickford, 1981), Wisconsin disconformably overlies 1760 Ma Baraboo Quartzite in southern Wisconsin rhyolite (Daiziel rhyolite (Dalziel and Dott, Dott, 1970; 1970; Van Van Schmus, Schmus, 1978, 1978, 1980). 1980). The The establishment establishment of the the quartzite at McCaslin and Thunder Mountains as being older older than than 1812 1812 Ma Ha suggests that other strongly deformed quartzite bodies, such as the Flambeau suggests Perhaps these Quartzite, 160 west, possibly Quartzite, 160 km km to the the west, possibly are are of of comparable comparable age. age. Perhaps these quartzites were deposited during a tectonically tectonically quiescent interval between quartzites "'1850 1850 Ma and and 1812 1812 Ma. Ma. Because in the north-central north—central United States may Because the quartzite quartzite bodies in differ more, and have undergone differ in in age age by as much as as 50 50 Ma, or perhaps more, different tectonic histories, histories, the term "Baraboo interval" (Dott, (Dott, 1983) should different be restricted restricted to those those quartzite quartzite bodies bodies known known to to be be younger younger than than 1760 1760 Ma. Ma. REFERENCES CITED REFERENCES CITED Dalziel, Dalziel, I.W.D., I.W.D., and and Dott, Dott, R.H., R.H., Jr., Jr., 1980, 1980, Geology Geology of of the the Baraboo Baraboo District, District, Wisconsin: Wisconsin Geological Geological and Natural History Survey Information Wisconsin: Information Circular 17, Circular 17, 164 164 p. p. Dott, Proterozoic red quartzite enigma in the northnorth— R.H., Jr., Jr., 1983, 1983, The Proterozoic Dott, R.H., Resolved by by plate plate collision?, collision?, in inMedaris, central United States: central States: Resolved Medaris, L.G., L.G., Jr., ed., ed., Early Proterozoic region: Jr., Proterozoic geology geology of of the the Great Great Lakes ~akesre~ion: Geological Society Geological Society of America America Memoir Memoir 160, 160, p. p. 129—141. 129-141. 97 �Lahr, M.M., M.M., 1972, geology of Lahr, 1972, Precambrian geology of a greenstone g r e e n s t o n e belt b e l t in i n Oconto County, Wisconsin and geochemistry of of the t h e Waupee Waupee metavolcanics: m e t a v o l c a n i c s : M.S. M.S. thesis, thesis, University U n i v e r s i t y of of Wisconsin, Wisconsin, Madison, 62 62 p. p. Mancuso, J.J., J.J., 1960, of the Mancuso, 1960, Stratigraphy S t r a t i g r a p h y and sstructure t r u c t u r e of t h e McCaslin District, District, Ph.D. Wisconsin: Ph.D. thesis, t h e s i s , Michigan State S t a t e University, U n i v e r s i t y , East E a s t Lansing, Lansing, 101 101 p. p. Olson, J.M., 1984, of the 1984, The geology of t h e llower o w e r Proterozoic P r o t e r o z o i c McCaslin Formation, Formation, Olson, J.M., northeastern n o r t h e a s t e r n Wisconsin: Wisconsin: Geoscience Wisconsin, v. v. 9, 9 , p. p. 1—19. 1-19. Sims, P.Kç P.K., iin Geologic map map of of P Proterozoic Mountain, Oconto Sims, n ppress, r e s s , Geologic r o t e r o z o i c rrocks o c k s nnear e a r Mountain, County, Wisconsin: County, Wisconsin: U.S. U.S. Geological G e o l o g i c a l Survey Miscellaneous M i s c e l l a n e o u s Investigations Investigations Series 1-1903, scale s c a l e 1:24,000. 1:24,000. S e r i e s Map 1—1903, Sims, P.K., P.K., Day, Day, W.C., W.C., and K Kiasner, J.S., 1986, Early Proterozoic Sims, l a s n e r , J.S., 1986, The E arly P r o t e r o z o i c Mountain sshear h e a r zone, zone, northeastern n o r t h e a s t e r n Wisconsin: Wisconsin: Geological G e o l o g i c a l Society S o c i e t y of of America America Abstracts with 752. A bstracts w i t h Programs, Programs, v. v. 18, 1 8 , p. p. 752. Van Schmus, Schmus, W.R., W.R., 1978, 1978, Geochronology of of the t h e southern s o u t h e r n Wisconsin rhyolites r h y o l i t e s and and Wisconsin, v. v. 2, 2 , p. p. 19—24. 19-24. ggranites: r a n i t e s : Geoscience Wisconsin, Van Schmus, W.R., 1980, Schmus, W.R., 1980, Chronology of of igneous i g n e o u s rocks r o c k s associated a s s o c i a t e d with w i t h the the Penokean orogeny iin Wisconsin, & inMorey, Morey, G.B., G.B., and and Hanson, Hanson, G.N., G.N., eds., eds., n Wisconsin, Selected of Archean gneisses S e l e c t e d sstudies t u d i e s of g n e i s s e s and and lower lower Proterozoic P r o t e r o z o i c rocks, rocks, ssouthern o u t h e r n Canadian Canadian Shield: S h i e l d : Geological G e o l o g i c a l Society S o c i e t y of of America Special S p e c i a l Paper 182, p. 182, p. 159—168. 159-168. Van Sebmus, W.R., and Bickford, M.E., 1981, Schmus, W.R., B i c k f o r d , M.E., 1981, Proterozoic P r o t e r o z o i c chronology and evolution inK Kroner, e v o l u t i o n of of the t h e Midcontinent region, r e g i o n . North America, America, & r o n e r , A., A . , ed., ed., Precambrian p plate Elsevier Scientific Publishing Precambrian l a t e ttectonics, ectonics, E lsevier S cientific P u b l i s h i n g Co., Co., Amsterdam, Amsterdam, p. p. 261—296. 261-296. 98 �EXPLANATION EXPLANATION ml PALEOZOIC PALEOZOIC (570 (570 Ma Ma and and younger) younger) !-?a) EARLY PROTEROZOIC (1600—2500 (7600-2500 Ma) CRrnbrian and.tone Cambrian sandstone MIDOLE PROTEROZOIC ( 900-1 600 Ma) Ma) MIDDLE PROTEROZOIC (900—1600 'Yi Y,i, Hager quartz porphyry quartz p o r phyr y ys, Hager Rhyolite '1,,, Hines Q u a r t z DDiorit iorlte Hines Quartz Xbc Baldwin Conglomerato High FalL Granite Quartzi te Belongia Granite 1 yw9 1 xh xq X Wolf R i v e r Granite Granite Wolf River -'—--'-- Mangerite Grani to Waupen Vo1anics Mylonite in Mourita'n sshear h e a r zone .4 Bedding $ Bedding -4 + Foliation 4 F oliation 6 // Fault Fault + —'• Geologic map GeolOgiC map Fold Fold of part of of northeastern n o r t h e a 9 t e r n Wisconsin X i s c o m i n (Compiled ( C o m p ~ l eby dbyP.1<. P.K. Sims, Slmg, 1988) 7988) OF > 99 �Evolution Evolution of of the the Early Early Proterozoic Proterozoic Wisconsin Wisconsin magmatic magmatic terrane terrane of of the the Penokean Penokean orogen orogen K.J. SCHULZ, SCHULZ, U.S. U.S. P.K. SIMS, SIMS, U.S. U.S. Geological Geological Survey, Survey, Denver, Denver, CO CO 80225; 80225; K.J. P.K. Geological Survey, Survey, Reston, Reston, VA VA 22092; 22092; Z.E. Z.E. PETERMAN, PETEEMAN, U.S. U.S. Geological Geological Geological Survey, SurveyyDenver, Denver, CO CO 80225; 80225;W.R. W.R. VAN VAN SCHMUS, SCHMUS,Department Departmentof of Geology, Geology, University University of of Kansas, Kansas, Lawrence, Lawrence,KS KS 66045 66045 The 1) is is aa major major Early Early Proterozoic Proterozoic tectonic tectonic belt belt The Penokean Penokean orogen orogen (fig. (fig* 1) along along the the southern southern margin margin of of the the Archean Archean Superior Superiorcraton. craton. It It consists consists of of aa northern continental—margin continental-margin assemblage assemblage that that overlies overlies an an Archean Archean basement basement and and aa northern southern volcanic—plutonic volcanic-plutonic (oceanic (oceanic arc) arc) assemblage, assemblage, termed termed the the Wisconsin Wisconsin southern maginatic magmatic terrane. terrane. The Ma along along the the The two two terranes terranes were were juxtaposed juxtaposed at at about about 1860 1860 Ma Niagara Niagara fault, fault, aa 10—km—wide 10-km-wide paleosuture paleosuture zone zone containing containing aa dismembered dismembered ophiolite ophiolite (Schulz, (Schulzy1987). 1987). The The Wisconsin Wisconsin magmatic magmatic terrane terrane consists consists of of two two known known subterranes subterranes separated 7-km-wide zone zone of of high high strain strain (Eau (Eau Pleine Pleine shear shear zone) zone) presumed presumed separated by by aa 7—km—wide to to be be aa paleosuture. paleosuture. The The northern, northern, and and major, major, subterrane, subterrane,which which is is exposed exposed along along aa strike strike length length of of 275 widthof of150 150kin, km, is composed composed 275 km km and and across across aa width dominantly dominantly of of greenschist—facies, greenschist-facies, and and locally, locally, lower lower amphibolite—facies amphibolite-facies volcanic volcanic rocks rocks deposited deposited in inthe the interval interval1860—1870 1860-1870Ma. Ma. These These rocks rocks are are mainly mainly calc—alkaline calc-alkaline felsic felsic to to mafic mfic volcanic volcanic rocks rocks similar similar to to volcanic volcanic sequences sequences in in recent recent island island arcs, arcs, but but include include tholeiitic tholeiitic basalt basalt compositionally compositionally similar similar to to back—arc back-arc basin basin basalts basalts and and island—arc island-arc tholeiites tholeiites(Schulz, (Schulz,1984). 1984). AA more more restricted, restricted, younger, younger, greenschist—facies greenschist-facies volcanic volcanic succession succession (1840—1850 (1840-1850 Ma) Ma) overlies overlies older older tholeiitic tholeiitic basalt basalt near near Wausau, Wausau, in in the the area area southeast southeast of of the the Athens Athens shear shear zone. zone. It It consists consists of of felsic felsic calc—alkaline calc-alkaline volcanic volcanic rocks, rocksy also also of of island—arc island-arc affinity, affinity, and and associated associated subvolcanic(?) subvolcanic(?) quartz quartz diorite diorite (LaBerge (LaBerge and and Myers, Myers, 1984). 1984). The exposed south south of of the the Eau Eau Pleine Pleine shear shear zone, zone, The southern southern subterrane, subterraneyexposed consists volcanic succession, succession, approximately low-grade felsic felsic to to inafic mafic volcanic approximately consists of of aa low—grade 1860 which unconformably unconformably overlies overlies aa possibly possibly continuous continuous Archean Archean M a old, old, which 1860 Ma basement. basement. Interlayered Interlayered with with the the volcanic volcanic rocks rocks are are ferruginous ferruginouschert, chert, quartzite, quartzite, conglomerate, conglomerate,and and carbonaceous carbonaceousargillite. argillite. The The Archean Archean gneisses gneissesare are exposed exposed widely widely in in the the major major river river valleys valleys in in central central Wisconsin. Wisconsin. AA moderately moderately widespread widespread red red alkali—feldspar alkali-feldspar granite, granite,1835 1835 Ma Ma old, oldy intrudes the volcanic rocks in the southern subterrane and the Wausau intrudes the volcanic rocks in the southern subterrane and the Wausauarea. area. It It is is cogenetic cogenetic with with two two known known small small patches patches of of rhyolite, rhyolite, welded welded tuff, tuff, and and volcanogenic volcanogenic graywacke graywacke (LaBerge (LaBerge and and Myers, Myers, 1984) 1984) which which probably probably are are caldera caldera related. related. Granitoid Granitoid rocks, rocks,mainly mainly ranging ranging in inage agefrom fromabout about1860 1860Ma Matoto1760 1760Ma, Ma, compose the Wisconsin Wisconsin magmatic magmatic compose about about one—quarter one-quarter of of the the exposed exposed part part of of the terrane. terrane. Calc—alkaline Calc-alkaline (volcanic—arc) (volcanic-arc) intrusive intrusivebodies bodies(1840 (1840MaMaand andolder) older) characterize characterize much much of of the the northern northernsubterrane. subterrane. They They are are presumed presumed to to be be of of mantle mantle origin originmodified modified by by aasubduction subductioncomponent. component. Near Near the the Niagara Niagara fault faultzone zone in in northeastern northeastern Wisconsin, Wisconsin, the the dominant dominant granitic granitic intrusive intrusive rocks rocks are are collision—zone collision-zone intrusions, intrusions,as as defined defined by by Harris Harrisand andothers others(1986). (1986). They They include include both both syn—collisional syn-collisional and and post—collision post-collision plutons, plutons, and and apparently apparently were were generated generated during during continent—arc continent-arc collision collision(-1860 (-1860Ma) Ma) from frommelting meltingofof continental They can can be be distinguished distinguished from from volcanic—arc volcanic-arc plutons plutons continentallithosphere. lithosphere. They 100 �through through their their higher higher Nb Nb and and Ta Ta values. values. The 1835 1835 Ma and the the still still younger younger 1760 1760 Ma granitic bodies are post-tectonic post—tectonic and have have characteristics characteristics of A-type A—type granites. Presumably they were derived derived as as partial partial melts melts of of evolved evolved crust. crust. Structurally, the 1860—1870 volcanic rocks rocks in in the the northern northern subterrane subterrane Structurally, 1860-1870 Ma volcanic have a dominant east-trending, east—trending, steep foliation foliation that is axial planar to tight intersection lineation; lineation; primary structures folds and a related mineral or intersection commonly commonly are are partly partly preserved. preserved. The The main main east—trending east-trending structural structural grain grain is is inferred modified inferred to have have resulted resulted from from north—south north-south collision. collision. It was modified zone, emplacement subsequently by gneiss domes adjacent to the Niagara fault zone, diverse orientation, and and discrete discrete (-1815 of granitoid bodies, major faults of diverse Ma) shear shear (ductile (ductile deformation) zones zones that that locally locally obliterate obliterate older older structures. The 1840—1850 structures. 1840-1850 Ma volcanic rocks southeast of the Athens shear zone dip steeply and are folded on northeast-trending northeast—trending axes, axes, whereas whereas the 1835 zone 1835 Ma M a volcanic rocks rocks are are virtually virtually undeformed. In In contrast, contrast, the the -1860 -1860 Ma Ma volcanic volcanic rocks rocks and and Archean Archean basement basement rocks rocksitt in the the southern southern terrane terrane have have aa nearly pervasive steep stretching lineation and accompanying mylonite that is superposed ott older Archean Archean and and Early Early Proterozoic Proterozoic structures. These These mylonitic mylonitic superposed on older structures pre-date pre—date the 1835 Ma magmatism, magmatism, and possibly resulted from arcarc— structures continent continent collision collision along along the the Eau Eau Pleine Pleine shear shear zone zone at at about about 1840 1840 Ma. Ma. summary, the Wisconsin Wisconsin magmatic magmatic terrane is aa composite composite arc arc system that In summary, records interval of calc—alkaline records a major interval calc-alkaline and tholeiitic volcanism at 1860— 18601870 restricted younger younger interval interval of of caic—alkaline calc-alkaline volcanism volcanism at at 1870 Ma and aa more restricted 1840—1850 Ma. Granitoid intrusive 1840-1850 intrusive rocks accompanied and followed the -1840 Ma Ma along the Eau volcanism. Following final assembly of the terrane at -1840 volcanism. Pleine Pleine shear shear zone, zone, intraplate intraplate magmatism magmatism in in the the south south produced produced post—tectonic, post-tectonic, possibly caldera—related caldera-related rhyolite rhyolite and and cogenetic cogenetic alkali alkali feldspar feldspar granite. granite. This This relatively local magmacism was followed by more widespread magmatism at 1760 local magmatism 1760 Ma, which which was Ma, was coeval coeval with with the theanorogenic anorogenicrhyolite—granite rhyolite-granitetuagmatisut magmatism in in southern southern Wisconsin Wisconsin (Smith, (Smith, 1983; 1983; Anderson Anderson and and others, others, 1980). 1980). REFERENCES CITED CITED Anderson, R.L., Van Schmus, .L., Cullers, Cullers, R.L.,andand Van Schmus,W.R., W.R.> 1980, 1980,Anorogenic Anorogenic Anderson, JJ.L., mid—Proterozoic of tnetaluminous andperaluminous peraluminousplutonism plutonismin in the metaluminous and the mid-Proterozoic of Wisconsin, Contributions p. Wisconsin, U.S.A.: U.S.A.: Contributions to to Mineralogy Mineralogy and and Petrology, Petrology, v. v. 74, 74, p. 3 11-328. 11—328. 3 Harris, N.B.W., Pearce, Pearce, J.A., J.A., and and Tindle, Tindle, A.G., A.G., 1986, 1986, Geochemical Geochemical Harris, N.B.W., characteristics of collision—zone in Coward, Coward, M.P., M.P.y and and Ries, Ries, characteristics collision-zone magmatism, magmatism, & Publication A.C., eds., A.CeY eds., Collision Collision tectonics: tectonics: Geological Geological Society Special Special Publication no. lgy 19, p.p .67—81. 67-81. Myers, P P.E., Proterozoic successions successions in LaBerge, G.L., G.L., and Myers, .E., 1984, 1984, Two Early Proterozoic LaBerge, Geological Society central Wisconsin Wisconsin and their central their tectonic tectonic significance: significance: Geological Society of of America Bulletin, Bulletin, v. v. 95, 95$ p. p. 246—253. 246-253. 1984, Volcanic Volcanic rocks rocks of of northeastern northeastern Wisconsin, Wisconsin, in g Sims, Sims, P.K., P.K., Schulz, K.J., 1984, Schulz, 1C.J., Schulz, K.JeY K.J., and Peterman, Peterman, Z Z.E., eds., Guide to the geology of the Early .E., eds., Schulz, Proterozoic rocks l y 30th 30th Annual Annual Proterozoic rocks in in northeastern northeastern Wisconsin: Wisconsin: Field trip 1, Institute Institute on on Lake Lake Superior Superior Geology, Geology, Wausan, Wausau, Wisconsin, Wisconsin, 93 93 p. p. Geological 1987, an Early Proterozoic Proterozoic ophiolite ophiolite in 1987* in the the Penokean Penokean orogen: orogen: Geological Association of Association of Canada Canada Programs Programs with with Abstracts, Abstracts, v. v. 12, 12, p. p. 87. 87. Sims, Sims, P.K., P.K., 1987, 1987, Metallogeny Metallogeny of of Archean Archean and and Proterozoic Proterozoic terranes terranes in in the the Great Great U.S. Lakes region——A Lakes region--A brief brief overview: overview: U .S. Geological Geological Survey Survey Bulletin Bulletin 1694—E, 1694-E, p. 56—74. 56-74. p. 101 �Smith, Smith, E.I., E.I., 1983, 1983, Geochemistry Geochemistry and and evolution evolution of of the the early early Proterozoic Proterozoic post— postPenokean Penokean rhyolites, rhyolites, granites, granites, and and related related rocks rocks of of south—central south-central Wisconsin, inMedaris, U.S.A., & Medaris, L.G., L.G., Jr., Jr., ed., ed., Early Early Proterozoic Proterozoic geology geology Wisconsin, U.S.A., of the Great Lakes region: Geological Society of America of the Great Lakes region: Geological Society of America Memoir Memoir 160, 160, p. p. 113—128. 113-128. 102 �90° 46° 45° FIGURE 1. GEOLOGIC MAP OF PENOKFAN OROGEN, EASTERN LAKE SUPERIOR REGION, FIGURE 1. GEOLOGIC MAP OF PENOKEAN OROGEN, AND WISCONSIN MAGMATIC TERMNE. SHOWING CONTINENTAL-MARGIN ASSEMBLAGE EASTERN LAKE SUPERIOR REGION, SHOWING CONTINENTAL—MARGIN ASSEMBLAGE MAGMATIC (Modified from Sims, 1987.) C r o s s h a tAND c h pWISCONSIN a t t e r n , Archean g n eTERRANE. iss; blank a r e a s , (Modified Archean Eau P lgneiss; e i n e s h eblank a r ( s uareas, ture) E a r l y P r ofrom t e r o zSims, o i c r o1987.) c k s ; â‚ Crosshatch P a l e o z o i c spattern, t r a t a . E, Early Proterozoje rocks; Paleozoic strata. zone; J , Jump River s h e a6, r zone; A, Athens s h e aE, r zone; PI, Mountain shear Eau Pleine shear (suture) zone; shear zone; A, Athens shear zone; N, Mountain shear M , I rRiver o n Mountain; M, Marquette. zone. J, I Jump zone. IM, Iron Mountain; M, Marquette. 103 �The TheReany ReanyCreek CreekFormation, Formation,Northern NorthernMarquette MarquetteCounty, County,Michigan: Michigan: Archean Archean ororProterozoic? Proterozoic? J.R. J.R. SMALL SMALL and andT.J. T.J.BORNHORST BORNHORST (Department (Department of ofGeology Geologyand andGeological Geological Engineering, Engineering, Michigan Michigan Technological Technological University University Houghton, Houghton, MI MI49931) 49931) The The Reany Reany Creek Creek Formation Formation consists consists of of aavariety varietyofofclastic clasticsediments sediments and anE-W E-Wtrending trendingelongate elongate belt, belt, less less than than 1.5 1.5km kmwide, wide, and crops crops out out ininan along along the the north north shore shore of ofthe theDead DeadRiver RiverStorage StorageBasin BasinininMarquette Marquette There are are three threestratigraphic stratigraphic units units (Puffett, (Puffett, 1969): 1969): 1) 1) aabasal basal County. There County. conglomerate composedofof an an eastern eastern lens lens in sections sections 2 and and 3,3,T48N, T48N, conglomerate composed R26W, R26W, a western western lens lens in in section section 6, 6, T48N, T48N, R26W, R26W, and and the the Breccia Breccia of of HolyHolyoke oke Mine Mine of of Owens Owens and andBornhorst Bornhorst (1985); (1985); 2) 2) aa middle middle succession succession of of slate slate and plutonic); and and 3) an upper and greywacke greywacke with with dispersed dispersed clasts clasts (dominantly (dominantly plutonic); upper unit ofofarkose, arkose,quartzite, quartzite,slaty slatygreywacke, greywacke,and andconglomerate. conglomerate. The The basal basal unit sediments overlie, or or are are in fault sediments unconformably unconformably overlie, fault contact contact with withArchean Archean To the the south, south, the the upper upper unit unit is is in in fault fault volcanic rocks rocks to to the the north. north. To volcanic Clasts were were sampled sampled throughout throughout the the contact with withArchean Archeanvolcanic volcanicrocks. rocks. Clasts contact formation formation and and include: include: granite, granite, granodiorite, granodiorite, rhyolite, rhyolite, mafic mafic volcanics, volcanics, slate, slate, and iron-formation. iron- formation. and Both Both the the age age of of the theformation formation and and its its mode mode of of origin origin have have been been debated. ItIt has hasbeen beenproposed proposed as a sArchean Archean totoLower LowerProterozoic Proterozoic in in age ageand and debated. parts parts of of itithave have been been interpreted interpreted to to be be either either tillite tillite (Puffett, (Puffett, 1969) 1969) or or aa mass flow flow deposit deposit(Mattson, (Mattson,1983). 1983). This This study study focused focused on on the the question question of of mass VanHise and Leith Leith (1911) (1911) assigned assigned the unit unit to to the age age of of the theformation. formation. VanHise the the the Upper Upper Huronian Huronian due due to tothe thepresence presence of ofiron-formation iron-formation clasts clastswhich which they thought thought to tobe beMiddle MiddleHuronian. Huronian. However, However, these these clasts clasts are are quite quite they similar similar to the the iron-formation iron-formation found found to the the north north in in the theArchean Archean stratistratigraphic and similar graphic succession succession and similar to iron-formation iron-formation within within the the Reany Reany Creek Creek W. A. A. Kelly Kelly(1936, (1936, Formation Formation as as described described by byOwens Owensand andBornhorst Bornhorst(1985). (1985). W. in in Engel, Engel, 1954) 1954) referred referred to to the theunit unitasasbeing beingTimiskaming, Timiskaming, ororsub-Huronian sub-Huronian (Archean), (Archean), in in age age based based on onlithology lithology and and on onan anangular angularunconformity unconformity Engel between between slates slates and and aaquartzite quartzitecorrelated correlatedasasLower LowerProterozoic. Proterozoic. Engel (1954) the unit unit to the (1954) assigned assigned the the sub-Huronian, sub-Huronian, but but stated stated there there was was aa Puffett (1969) (1969)named named possibility possibility that itit was was Middle MiddleororLower LowerHuronian. Huronian. Puffett the the unit, unit, Reany ReanyCreek CreekFormation, Formation, and andsuggested suggested aaLower LowerProterozoic Proterozoic age. age. However, However, he also also stated stated that that itit could could be beequivalent equivalent totothe theTimiskaming. Timiskaming. Owens (1985) favored favored an an Archean Archean age age for the Owens and Bornhorst Bornhorst (1985) the Breccia Breccia of of Holyoke Mine Mine (basal (basalconglomerate). conglomerate). At At the theHolyoke Holyoke Mine Mine Area, Area, they they Holyoke observed is deformed, and that folds observed that the the basal basal conglomerate conglomerate is deformed, and folds in in iron iron formation formation are vertically vertically plunging, plunging, a style style of of deformation deformation more more like like the the A shear shear zone zone follows follows the the basal basal Archean than than the theLower LowerProterozoic. Proterozoic. A Archean contact contact of of the the Reany Reany Creek Creek Formation Formation (Breccia (Breccia of Holyoke Holyoke Mine) for for about about 22 km is is entirely within Archean km until until i it entirely within Archeanrocks rocks(MacLellan (MacLellanand andBornhorst, Bornhorst, (1987) concluded concluded that that the Reany Finally, Weeks Weeks (1987) Reany Creek Creek this volume). volume). Finally, this Formation filled a basin as a result Formation filled basin which which was was truncated truncated as result of of Archean Archean faulting faulting along along the the Dead Dead River River Shear ShearZone. Zone. No such such dikes dikes cut cut Rhyolite dikes dikes are are common common cutting cutting Archean Archean rocks. rocks. No Rhyolite sediments age in the Geologic sediments of Lower Lower Proterozoic Proterozoic age the Marquette Marquette area. area. Geologic mapping mapping by Puffett Puffett (1969) (1969) showed showed no rhyolite rhyolite dikes dikes cutting cutting the the Reany Reany Creek In one one Two possible possible dikes dikes were were found found in in the the basal basal unit. unit. In Creek Formation. Formation. Two locality, there is aa poorly locality, there poorly exposed exposed tabular tabular rhyolite rhyolite body, .5 .5 meters meters by by 10 10 104 �meters, at at an oblique meters, oblique angle angle to to bedding. bedding. This exposure could This exposure could be be either aa dike or In another locality, or an an unusually unusually large, large, elongate elongate clast. clast. In locality, a well well exposed tabular rhyolite exposed tabular rhyolite body body cuts aa schist. schist. Identification of the parent Identification of parent to to the schist schist is is uncertain. uncertain. It may may be be Archean Archean volcanics volcanics or sediments sediments of Reany Reany Creek Formation. Formation. If Archean, Archean, the the rhyolite rhyolite and and surrounding surrounding schists schists are part part of aa fault Unfortunately, these these data data are faultbounded bounded block. block. Unfortunately, are inconclusive inconclusive with respect respect to the the age age of of the theReany ReanyCreek CreekFormation. Formation. The age of the Reany Creek Creek Formation Formation isisequivocal. equivocal. The formation formation is is The the Reany in unconformable or fault contact unconformable or contact with with Archean Archean rocks. rocks. There There is no no evidence to rule out evidence to out conclusively conclusively an Archean Archean or an an Early Early Proterozoic Proterozoic age. age. It should should not be be presumed presumed that that the the Reany Reany Creek Creek Formation Formation is is Early Early ProProterozoic in age. terozoic age. REFERENCES Engel, T. Jr. Engel, Jr. (1954) (1954) The The Stratigraphy Stratigraphy and Petrography Petrography of the the Holyoke Holyoke Meta-sediments of of the Dead [M.S. Meta-sediments Dead River River Basin, Basin, Marquette Marquette County, County, Michigan, Michigan, [M.S. Thesis]: East Lansing, Thesis]: East Lansing, Michigan Michigan State State University, University, 72p. 72p. Mattson, S.R. S.R. (1983) (1983) The The Reany Reany Creek Creek Formation: Mattson, Formation: aa Mass Mass Flow Flow Deposit Deposit of Possible Post Post Menominee MenomineeAge: Age:Proceedings Proceedingsand andAbstracts, Abstracts,29th 29th Institute Institute on on Lake Possible Superior Geology, Geology, Houghton, Houghton, MI., MI., 1983, 1983, p.27 p.27 Owens, E.O. and Bornhorst, Owens, E.O. Bornhorst, T.J. (1985) (1985) Geology Geology and precious precious metal metal mineralizmineralization of the ation the Fire FireCenter Centerand andHolyoke HolyokeMines Mines Area, Area, Marquette Marquette County, County, Michigan: Michigan: Michigan Geological Geological Survey Survey Division, Division, Department Department of of Natural Michigan Natural Resources, Resources, Open Open File File Report OFR-85-2, Report OFR-85-2, 105p. 105p. Puffett, W.P., W.P., (1969), (1969), The Reany Reany Creek Creek Formation, Formation, Marquette Marquette County County MichiMichigan, U.S. Survey Bulletin Bulletin 1274-F, 1274-F, 25 25 p. gan, U.S. Geological Geological Survey VanHise, C.R., and and Leith, C.K., VanHise, C.R., C.K., (1911) (1911) The Geology Geology of the the Lake Lake Superior Superior Region; U.S. Survey Monograph Monograph 52, 52, p. 287-288 Region; U.S. Geological Geological Survey 287-288 Weeks, V.L., (1987) (1987) Gravity Gravity and and Magnetic in the South-Central Weeks, V.L., Magnetic Investigations Investigations in South-Central Part of Part of the theIshpeming Ishpeming Greenstone Greenstone Belt, Belt, Marquette Marquette Co. Co. Michigan, Michigan, (M.S. [M.S. Thesis]: Thesis]: Houghton, Michigan University, 60 p. Houghton, Michigan Technological Technological University, p. 105 �TECTONIC TECTONIC IMBRICATION IMBRICATIONPtND AND FOREDEEP FOREDEEP DEVELOPMENT DEVELOPMENT IIN N THE THE PENOKEAN PENOKEAN OROGEN, OROGEN, EASTEASTCENTRAL MINNESOTA MINNESOTA CENTRAL G.B. Morey Morey D.L. Southwick Southwick and and G.B. D.L. Minnesota Minnesota Geological Geological Survey, survey, 2642 2642 University University Avenue, Avenue, St. st. Paul, Paul, MN MN 55114 55114 Geophysical Geophysical data d a t a (chiefly ( c h i e f l y aeromagnetic), aeromagnetic), together together with with the t h e results r e s u l t s of of scientific and industrial drilling, have led to the recognition of several s c i e n t i f i c and i n d u s t r i a l d r i l l i n g , have l e d t o t h e recognition of s e v e r a l structural s t r u c t u r a l discontinuities d i s c o n t i n u i t i e s within within the t h e Cuyuna Cuyuna iron—mining iron-mining district d i s t r i c t and and contiguous tiguous terrane t e r r a n e in i n east—central e a s t - c e n t r a l Minnesota. Minnesota. These These discontinuities d i s c o n t i n u i t i e s separate separate structural s t r u c t u r a l panels panels of of differing d i f f e r i n g stratigraphy, s t r a t i g r a p h y , structural s t r u c t u r a l style, s t y l e , and and metametabe zones zones of of thrust t h r u s t faulting. f a u l t i n g . Regionally Regionally the the morphic grade, grade, and and appear appear to t o be morphic thrust—faulted, t h r u s t - f a u l t e d , tectonically t e c t o n i c a l l y imbricated imbricated terrane t e r r a n e constitutes c o n s t i t u t e s aa fold-and— fold-andthrust t h r u s t belt b e l t that t h a t was was emplaced emplaced onto onto the the southern southern margin margin of of the t h e Superior Superior craton c r a t o n early e a r l y in i n the the deformational deformationalhistory h i s t o r yofof the t h ePenokeari Penokean orogen. oroqen. Lubricate Imbricate thrusting t h r u s t i n g and and recumbent recumbent folding f o l d i n g may may have have begun begun as a s early e a r l y as a s the the time 30—2180 m.y. in.y. and and continued continued eepisodically t i m e interval i n t e r v a l 21 2130-2180 p i s o d i c a l l y for f o r 300 300 m.y. m.y. or or more. From From south south to to north north the t h e thrust—bounded thrust-bounded structural s t r u c t u r a l panels contain more. rocks rocks metamorphosed metamorphosed at a t successively successively shallower shallower crustal c r u s t a l depth; depth; deformation deformation occurred occurred under under conditions conditions ranging ranging from from amphibolite amphibolite facies f a c i e s in i n the t h e southernsouthernmost McGrath-Little Falls F a l l s panel panel (Fig. (Fig. 1) 1 ) to t o lower lower greenschist g r e e n s c h i s t facies f a c i e s in i n the the most McGrath—Little North range range of of the t h e Cuyuna Cuyuna district. district. North Geophysical Geophysical and and drilling d r i l l i n q data d a t a also a l s o indicate i n d i c a t e that t h a t the t h e east-northeast e a s t - n o r t h e a s t strucstructural the fold—and—thrust fold-and-thrust belt b e l t are a r e overlapped overlapped unconformably on t u r a l trends t r e n d s of of the the the lower lower strata s t r a t a of of the the Animikie Animikie Group Group along along the t h e south south margin t h e north north by by the The of of the t h e main main bowl bowl of of the t h e Animikie Animikie basin basin (Fig. (Fig. 1). 1). The deformation deformation within within the t h e main main bowl bowl decreases decreases regionally r e g i o n a l l y and and systematically s y s t e m a t i c a l l y from south—southeast south-southeast to the Mesabi iron i r o n range range at a t the t h e north north margin t o north—northwest, north-northwest, until, u n t i l , along along the of the Animikie Animikie Group Group dip d i p gently gently of the t h e basin, b a s i n , the t h e unfolded unfolded basal b a s a l strata s t r a t a of of the southward southward and and rest r e s t with with angular angular unconformity unconformity on on Archean Archean basement. basement. We We interpret i n t e r p r e t the t h e main main bowl bowl of of the the Animikie Animikie basin to t o be a tectonic t e c t o n i c foredeep foredeep that t o loading loading of continental c o n t i n e n t a l crust c r u s t by t h a t developed developed as a s aa flexural f l e x u r a l response response to thrust t h r u s t sheets s h e e t s and and nappes nappes in i n the t h e fold—and—thrust fold-and-thrust belt b e l t to t o the t h e south. south. Tectonic transport t r a n s p o r twas was from from south—southeast south-southeast tto o north—northwest, north-northwest, and and the the Tectonic Animikie foredeep probably probably migrated migrated cratonward cratonward iin Animikie foredeep n the t h e same same sense. sense. and ddrilling F i n a l l y , geophysical geophysical and r i l l i n g data d a t ahave have revealed revealed two two other o t h e r basins basins Finally, f i l l e d by by sedimentary sedimentary strata s t r a t a comparable comparable to t o the t h e Animikie Animikie Group Group that t h a t lie lie between between the t h e fold—and—thrust fold-and-thrust terrane t e r r a n e of of the the Cuyuna Cuyuna district d i s t r i c t and and the t h e cratonic cratonic Archean rocks. rocks. These, These, named named the the Long Long Prairie P r a i r i e basin basin and and the the f o r e l a n d of of Archean foreland Nimrod I ) , are a r e interpreted i n t e r p r e t e d to t o be remnants remnants of the t h e formerly formerly Nimrod outlier o u t l i e r (Fig. (Fig. 1), more extensive extensive Animikie Animikie foredeep. foredeep. more filled 106 �ANIMIKIE ANIMIKIE 8ASN BASIN dikes (Early Prot,) &J Possible riftud—margin terrane .,4 Rocks of Archean age LOCATION MAP KILOMETERS 1 1.• Generalized tectonic t e c t o n i c map of of the t h e Penokean orogen orogen of of east—central east-central fold-and-thrust belt b e l t of of Early Early Proterozoic P r o t e r o z o i c age age consists c o n s i s t s of of Minnesota. A fold-and—thrust the t h e McGrath—Little McGrath-Little Falls, F a l l s , the the Moose Moose Lake Lake - Glen Glen Township, Township, and and the t h e Cuyuna Cuyuna South South range range structural s t r u c t u r a l panels; panels; the t h e panels panels are a r e bounded bounded by by structural structural discontinuities d i s c o n t i n u i t i e s inferred i n f e r r e d to t o involve involve significant s i g n i f i c a n t thrusting. t h r u s t i n g . The North range of the i s interpreted i n t e r p r e t e d as a s an an early e a r l y foredeep foredeep that t h a t has has t h e Cuyuna Cuyuna district d i s t r i c t is of the been tectonically t e c t o n i c a l l yincorporated incorporatedini nthe t hexternal e e x t e r nzone a l zone of tfold—and— h e fold-andbeen major foredeep foredeepofof Early Early PProterozoic A major r o t e r o z o i c age, age, but b u t consequent consequent t h r u s t mass. mass. A thrust t o some and perhaps much deformation in i n the t h e fold—and—thrust fold-and-thrust belt, b e l t , conconto sists of of the t h e Animikie Animikie basin, b a s i n , the t h e Long Long Prairie P r a i r i e basin, b a s i n , and and the t h e Nimrod Nimrod out— outl i e r . The sedimentary sedimentary fill f i l l of of these t h e s e basins b a s i n s rests r e s t s unconformably unconformably on on cra— craher. tonic t o n i c basement basement of of Archean Archean age age along along the t h e northwest northwest margins margins of of the the basins. basins. Figure Figure - 107 �EARLY EARLY PENOKEAN PENOKEAN DEFORMATION DEFORMATION IN INTHE THE PEAVY PEAVY POND POND AREA, AREA, NORTHERN NORTHERN MICHIOAN: UICHIOAN: EVIDENCE EVIDENCEFROM FROMTHE THEMICHIGAMME MICHIGAMMEFORMATION FORMATIONAND ANDTHE THEPEAVY PEAVYPOND PONDIGNEOUS IGNEOUSCOMPLEX COMPLEX Steven andDavidd. Davithi. flatly, Matty, Geology Dept.,Central Central Michigan Michigan Univ., Univ., Mt. Pleasant, M Steven D. D. Stahl and Geology Dept., MI 48859 48859 INTRODUCTION INTRODUCTION In areaof ofnorthern northern Michigan, the Inthe the Peavy Peavy Pond area the Early EarlyProterozoic ProterozoicMichigamme NichigammeFormation Formation (PPC). Both bythe thePeavy PeavyPond Pond igneous complex (PPC). Bothunits unitswere weredeformed deformedand and was intruded intrudedby was metamorphosed during the the Proterozoic Proterozoic Penokean Penokeanorogeny orogeny(e.g., (e.g.,Attoh, Attoh, 1984, 1984, 1986 metamorphosed during 1986a,a,b). b). Detailed structural analysis Detailed structural analysisofofthe themacroscopic macroscopic fabric fabricelements elements in i nthe the Michigamme Michigamme Formation in in and to the the PPC PPCsupports supports an anarc-continent arc—continentcollision collision model modelwith with north north over and adjacent to over south south shortening. structure isi saanorth—closing with the shortening. The Thedominant dominantPenokean Penokean structure north-closing fold fold nappe nappe with the PPC PPC iinn the core core and and the upper and and lower lower limbs limbsjuxtaposed juxtaposed by bypostnappe postnappe faulting faultingassociated associated with withthe theBush BushLake Lake (BLF). Fault (BLF). Fault OBSERVATIONS OF OF STRUCTURAL STRUCTURAL FEATURES FEATURES OBSERVATIONS For presentation, we study area area into into the following following domains: Forease ease of presentation, we have have subdivided the stud/ domains: Domain Domain I1consists consistsofofthe theMichigamme MichigammeFormation Formationnorth northofofthe theBLF BLFand andadjacent adjacenttotothe thePPC; PPC; Domain Domain 22 comprises Includesigneous igneousrocks rocksofof comprisesenclaves enclaves of Michigamme Michigamme Formation Formation within withinthe thePPC; PPC;Domain Domain33includes the the PPC; PPC; and andDomain Domain 44 contains containsrocks rocksofofthe theMichigamme MichigammeFormation Formationtotothe thesouth southofofthe theBLF BLFand and adpent totothe thePPC. PPC. adjacent Domah11 £7ffl81fl Minor structural fabric Minorfolds foldsdominate dominate the structural fabricofofthe thegreenschist greenschisttotoamphibolite amphibolitefacies faciesMichigamme Michigamme Formation north of Formationexposed exposed to the north of the the BLF. BLF. Six Sixgenerations generationsofoffolds foldsare arerecognized. recognized.The Theoldest oldest three (Fl,1,F2, three generations generations (F F2,F3) F3)predate predateregional regionalmetamorphism. metamorphism. They Theyposess posess the following of axial axial planar planar foliation; WSW—ENE 1 ) absence absence of foliation;2)2)consistence consistencewith with WSW-ENE common characteristics: common characteristics: 1) shortening; shortening; 3) 3)asymmetry asymmetryindicative indicativeofofWSW WSWtotoENE ENE overriding; overriding;4)4)quartzo—feldspathic quartzo-feldspathic layers layers defining folds; 5)5)micaceous micaceouslayers layersdefining definingClass Class33folds; folds;and and6)6)rounded roundedhinges hingesand andthe the definingClass Class 11 folds; reduction of hinge to limb limb ratio age. Fl, F 1 ,F2, F2,and andF3 F3appear appear to to be be coaxial, but but the ratiowith withdecreasing decreasing age. data not conclusive conclusivein in part part due duetototheir their insufficient insufficient number dueto totheir their reorientation reorientation data are not number but but also also due by polyphasedeformation. deformation. F 11are aretight tight to isoclinal isoclinal folds (SO). F2 folds of of beds beds (SO). F2are areclose closetoto by subsequent subsequent polyphase tight, axialsurfaces surfaces(Si (51))))folds foldsofofSO SOand and tight, shallowly shallowlytotomoderately moderatelyinclined inclined(with (withrespect respecttotoF F11axial Si. inclined (with S1.F3F3are areopen opentotoclose, close, moderately moderately to steeply inclined (withrespect respectto to Si) S1)folds foldsofofSO, SO, Si, 31and ,and F2 axial surfaces (52). (32). Younger are markedly different different from style, attitude, attitude, and geometry: apperently apperently Younger folds are fromFF11—F3 4 3 i ninstyle, and geometry: synmetamorphic almost ideal ideal chevrons chevrons (interlimb (interlimb angle synmetamorphic F4 F4 folds are almost angleclose close to 700, 70° hinge hinge region region very with axialplanar planar foliation foliation ((34) verysmall) small)ofofearly early3—surfaces 5-surfwithmoderately moderately well well developed developed axial 3-4)ini nthe the hinge. The shorteningand andnorthward northwardoverriding overriding which which iiss The sense sense ofof 3344 asymmetry indicates indicates N—S N-5 shortening (e.g. Cambray, 1978). consistent with withPenokean Penokean kinematics (e.g. consistent Cambray, 1978). Fifth striking, Fifthand and sixth sixthgeneration generationfolds foldsare areopen open to to gentle. F5 F5isi sdefined definedby byaa N8OW—N8OE N80W-N80E striking, steeply dipping dipping foliation foliation(35); (55);it isitconsistent steeply i s consistent withwith N—S N-5 shortening shortening and and is ipost—F4 s post-F4because because55 5 5isi s neither parallel paralleltoto34 3 4nor norfolded foldedby byF4. F4. F6 F6folds foldsS5; 55; this thisgeneration generationisi sconsistent consistentwith withE—W E-W neither F5and andF6 F6are areregional regionaldeformations deformationspresent presentini nseveral severalPenokean Penokeanterrenes. terranes. shortening. F5 Domarh 2 Don7ern 2 Enclaves of the the Michigamme MichigammeFormation Formationwithin within the PPC PPCare arecharacterized characterizedbby minor folds folds with with Enclaves of y minor superimposed equigranular equigranular texture texture that that isi slocally locallyfoliated, foliated.These Thesefolds foldsare arecorrelated correlatedtotoDomain Domain11 Fl, they are are similar similar in the intrusion intrusion of F 1 ,F2, F2,and andF3 F3because because they instyle. style.F FI 1—F3 -F3 therefore predate predate the of the the PPC. Domain22 Michigamme Michigammerocks rocks are are stoped stopedblocks, blocks,attitude attitude measurements measurementsof offabric fabric PPC. Because Because Domain Domain I1 surfaces surfacesmay may of Domain Domain 2 surfaces elements iinn these blocks blocks are are moat; moot; parallelism parallelism of surfaces with with Domain or fortuitous. Nonetheless, onthe the or may may not not be fortuitous. Nonetheless, the the orientation orientationofofthe thefoliation foliationsuperimposed superimposedon xenolithic xenolithicblocks blocksisi ssteeply steeplydipping dippingand andstrikes strikesN8OE—N8OW. N80E-N80W. The The equigranular texture texturewas was 108 �developed foliation developed by by contact metamorphism, metamorphism,and andthe theevent eventwhich whichproduced producedthe thelate—stage late-stage foliation postdatesPPC PPC emplacement. emplacement. postdates Doma~h33 Dornern Two BLF; one onestrikes strikes Two steeply dipping dipping foliations foliationsare arepresent presentini nthe thePPC PPCon on both both sides sides of the BLF; N8OE-.N8OW andi is crosscut by by the second, second,which whichstrikes strikes NI O—20E. On Onthe thebasis basisof ofparallelism parallelism N80E-N80W and s crosscut N10-20E. of surfaces, surfaces, the the former former isi scorrelated correlatedtotoDomain Domain I1F5 F5and andthe the letter latterisi scorrelated correlatedtotoDomain Domain11F6. F6. of Dams/# 4 Dome/n I Domain Domain 44 consists consistsofofsillimanite—grade sillimanite-grade Michigamme MichigammeFormation Formationexposures exposurestotothe thesouth southofofthe the BLF thePPC. PPC.Minor Minor folds are ubiquitous, but flattened to to tight to BLF and &adjacent p e n t totothe but they they have have been flattened to isoclinal isoclinalwith withquartzo—feldspathic quartzo-feldspathic leyers layersdefining definingClass Class 22 folds. folds. This Thisflattening flatteningmakes makes differentiation differentiationand andcorrelation correlationofofDomain Domain44folds foldsto to Domain Domain 11 Fl F 1,,F2, F2, or orF3 F3impossible. impossible. Ductile andflattened flattenedgarnets garnetsare areprevalent prevalent iin theseexposures. exposures. Estimates, that are Ductileboudinage boudinage and n these necessarily novolume volumestrain, strain, of finite necessarilylow lowand and assume no finiteextension extensionderived derivedfrom fromthe themeasurement measurementofof boudins from 75 boudins range from 7 5 to to 85 8 5percent; percent;ini nflattened flattenedgarnets garnetsthe theestimated estimatedfinite finiteextension extensionranges ranges from 95 95toto105 105percent. percent.The Themean mean finite finitestrain strainellipsoid ellipsoidIsi soriented orientedsuch suchthat: that: 1) 1 ) the the from intermediate intermediateaxis axisplunges plungesshallowly shallowlyand andtrends trendsapproximately approximatelyE—W; E-W; 2) 2)the themaximum maximumextension extension axis plunges plunges shallowly shallowly and and trends N—S; N-S; and axis and3) 3) the themaximum maximumcompression compressionaxis axisi sisnear nearvertical. vertical. The The presence presence of rolled rolledgarnets, garnets,rolled rolledboudins, boudins,and andfolded foldedboudins boudinsindicate indicatethat thatthe themechanism mechanism of deformation deformation was not pure shear instead extreme shear of shear but Instead extremesimple simple shear shearwith with near horizontal horizontal shear plane N—Strending trendingshear sheardirection. direction. This event event iiss correlative correlative totoDomain it is plane and N-S Domain11 F4 F4because because it is syn—metamorphic; asymmetry (S ( S over over N) N)are arethe the syn-metamorphic; moreover, the the closure closure direction directionand andsense sense of asymmetry same in i nboth bothdomains. domains. same INTERPRETATIONS INTERPRETATIONS The andsurrounding surrounding Michigamme Formation fold nappe nappe(recumbent (recumbent fold, The PPC and Formation define define aa Penokean Penokean fold fold, allàchthonous, extremesimple simpleshear sheari ninlower lower"short" "short or allkhthonous, extreme or"overturned" "overturned" limb limband andparasitic parasiticfolds foldsini n upper with faulted lower limbs have been documented upper "upright" "upright"limb). limb).Nappes Nappes with faulted lower limbs have been documentedelsewhere elsewhere in i n the the Penokean foldbelt belt(e.g. (e.g.Hoist, Holst, 1984), 1984), but ductle lower lower limb limb is Penokean fold but the recognition of a ductle i s apparently apparently unique juxtaposes the upper Peavy area. The ThePPC PPC is i s ininthe thecore coreofofthe thenappe nappeend and the BLF juxtaposes upper unique to to the the Peavy (Domain (Domain 1) 1 )and and lower lower (Domain (Domain 4) 4)limbs. limbs.The Theextreme extremesimple simpleshear shearassociated associated with withthe the development fold nappe nappeobscured obscuredthe theearly early fabric fabric elements — development of the Penokean Penokean fold elements in i nthe thelower lowerlimb limb - this eventsi in rocksof ofthis this limb, limb, which thisreorientation reorientationprohibits prohibitsthe therecognition recognitionofofearly earlyPenokean Penokean events n rocks comprise the exposuresinin thePeavy PeavyPond Pondarea. area. comprisethe the overwhelming overwhelmingmajority majorityofofexposures Structural Structuralanalysis analysisofofthe theMichigamme MichicjammaFormation Formationini nand andadjacent adjacentto tothe thePPC PPC indicates that the the structures compatible only structuresassociated associatedwith withthe thePenokean Penokean orogeny are compatible only with withan anarc—continent arc-continent collision similar to Cambray((1978). collisionmodel model similar tothat thatproposed proposed by Cambray 1978). Our Our work workalso also implies, implies,however, however, that previously. thatthe thepaleogeography paleogeographymust must have have been been more complex than than has has been proposed previously. REFERENCES REFERENCES Attoh, of Early Early Proterozoic Attoh. K., K.. 1984, 1984.Some Someconstraints constraintson onthe thethermal thermalceouses caouses of Proterozoic metamorphic - zones Assoc. i n & in i nnorthern northernMichigan: Michigan:Geol. Oeol. Asm.Can. Can.— Mm. Min.Assoc. Assoc.Can. Can. Ann. Ann. Meeting. Meeting. Attoh, Early Proterozoic Attoh, K., K., 11 986a, Metamophic Metamophic pressures, pressures, temperatures temperatures and and Early Proterozoic geotherms geotherms iinn northern ononLake northernMichigan: Michigan:32nd 32ndAnnual AnnualMeeting fleetingInstitute Institute LakeSuperior SuperiorGeology. Oeology. Attoh, K., 986b, Early geotherms Penokean K., 11986b, EarlyProterozoic Proterozoiccrustal crustal geothermsduring during Penokeanmetamophism metamophism ini n - northern Assoc. Min.Assoc. Asm. Can. Can. Ann. Meeting. Meeting. northernMichigan: Michigan:Geol. Oeol. Assoc.Can. Can.— Mm. Cambray, modelfor forthe theenvironment environmentofofdeposistion deposistionand anddeformation deformation Cambray, F., F., 1978, 1978,Plate Platetectonics tectonicsososaamodel of the Early Michigan: (3eol. Soc. Am. Abst. w northern flichiqan: 0eol. Soc. Am. Abst. w Prog., Procj., Earlv Proterozoic Proterozoic(Precambrian (PrecambrianX)X)ofofnorthern 10, p. p. 376. 376. j.Q., 984, Evidence B., 11984, Evidence for fornappe nappedevelopment development iinn the the Early EarlyProterozoic ProterozoicPenokean Penokeanorogeny, orogeny, Hoist, 1. B., Minnesota: Geology, J2, p. 135—138. HOISTT. 109 �DEFORMATION HISTORY OF OF THE THE QUETICO QUETICO METASEDIMENTS METASEDIMENTS ALONG THE THE NORTHERN NORTHERN DEFORMATION MARGINOF OFTHE THEVERMILION VERMILIONGRANITIC GRANITICCOMPLEX, COMPLEX,NORTHERN NORTHERNMINNESOTA. MINNESOTA. MARGIN PJ.,Dept. Dept.ofofGeology Geologyand andGeophysics, Geophysics,University UniversityofofMinnesota, Minnesota, Tabor, J.R., J.R., and and Hudleston, Hudleston, PJ., Tabor, Minneapolis, MN, MN, 55455. 55455. Minneapolis, Arnphibolite-grade(M1) (Mi)pelitic pelitic schists schists and and younger younger minor minor leucogranites leucogranites and and pegmatites pegrnatites of of the the Amphibolite-grade trending belt of Archean supracrustals supracrustals that Rainy Lake LakeDistrict District in in northern northernMinnesota Minnesota dominate dominate the E-W trending Rainy borders the the northern northern margin margin of ofthe thehigher-grade higher-grademigmatites migmatitesand andgneisses gneissesof ofthe theVermilion VermilionGranitic Granitic borders Complex of the Quetico Gneiss Belt. Belt. The (VGC),the thesouthwestern southwesternextension extension in northern northern Minnesota of The Complex (VGC), structural structuraldevelopment developmentof of the theschist schistbelt beltinvolved involvedthe thetemporal temporalpartitioning partitioningof of the the strain strainassociated associatedwith with aa dynamic both E-W dextral shear dynamic dextral dextral transpressive transpressive deformation deformation involving both shear and and N-S N-S horizontal horizontal flattening. flattening. Theearly earlystage stageof of deformation deformation involved involved two two phases phases of of pervasive pervasive folding, folding, the the first first possibly recumbent recumbent The and and nappe-like nappe-like and and the the second second upright upright and and isoclinaL isoclinal. Minor Minorfolds folds across across much much of of the the width width of of the the schist schist arepreodniinantly preodminantly F2 F2 and and of 2Z' symmetry,with withminor minor'perturbed' 'perturbed'areas, areasof of 'S' 'S' symmetry symmetryrepresenting representing belt are belt symmetry, either undulations undulations in the the hinge hinge lines lines of of minor minor F2 F2 folds folds or or major major F2 folds. folds. However, However,approaching approachingthe the either southern aredominant dominantin inthe theschists schists(Bauer, (Bauer, F2 folds folds of of 'S 'S' symmetry symmetryare southern margin of the the schist schist belt belt minor minor F2 1988), suggesting suggesting that that aa major major F2 F2fold folddoes doesindeed indeedunderlie underliethe theschist schistbelt beltwhose whosenorthern northernlimb limbforms forms 1988), much of the the width width of of the the belt. belt. Reversal Reversalininstratigraphic stratigraphictops topsfrom fromnorthnorth-totosouth-facing south-facingacross acrossthe the much northern limb of this this major major F2 F2 fold fold suggests suggests the presence of a major major F1 F i fold. fold. Minor MinorF1 FlF2 fold northern F2 fold alsosupport supportthis. this. interferencepatterns patternsalso interference Mesoand microstructural microstructural evidence evidence along along the the Rainy Lake-Seine River Fault (RLSRF), (RLSRF),the themajor major Meso- and fault fault defining definingthe the boundary boundary between betweenthe theschist schistbelt belt and andthe theRainy RainyLake LakeWrench WrenchZone Zoneto tothe thenorth, north,suggest suggest E-W E-W near-horizontal near-horizontaldextral dextralshear sheardominated dominatedthe theintermediate intermediatestage stageof ofthe thetranspressive transpressivedeformation deformationand and was localized localized into the RLSRF RLSRFasasthe theschists schistsalong alongthe thenorthern northern margin margin of of the the belt beltcooled cooledfrom from was amphibolite-to togreenschist-facies greenschist-faciesconditions. conditions. amphiboliteThe veins crosscutting Thelack lackof ofevidence evidencefor forshear, shear,the thepresence presenceofoftectonized tectonizedpegmatite pegmatiteveins crosscuttingF1F2 FlF2fold fold interference of conjugate shear shear bands bands and zones in the interference patterns patterns and the presence presence and orientation of the 110 �and pegmatites suggest the N-S leucogranites and N-S horizontal horizontal flattening flattening component component of of the thetranspression transpression the later stages of the deformation. Quartz dominated the Quartz and and calcite calcitelattice lattice preferred preferred orientation orientation (LPO) (LPO) of a ductile component component of of N-S N-S horizontal horizontal flattening flattening in in the analyses also suggest an increased dominance of RLSRF RLSRFduring duringgreenschist-facies greenschist-faciesconditions. conditions. In the center of the the schist schist belt, belt, quartz quartz LPO LPO patterns patterns suggest: 1) leucogranites and pegmatites have also experienced experienced both E-W E.W dextral 1) the schists schists bordering the leucogranites dextral N-S flattening, 2) 2) schists located away away from from the the intrusives intrusives have have experienced experienced only only E-W E.W dextral dextral shear and N-S shear and 3) the N-S horizontal flattening. Quartz the leucogranites leucogranites and and pegmatites pegmatites have experienced experienced only N-S Quartz 120 LPOpatterns patternsfrom fromthe thesouthern southernmargin margin of of the theschist schistbelt belt bordering bordering the the inigmatite migmatite terrane to the south to those measured measured along along the the northern northernmargin marginof ofthe thebelt beltininthe theRLSRF RLSRF and to those in the were similar to enveloping the margins schists enveloping margins of the the leucogranites leucogranitesand and pegmatites pegmatites in in the the center center of of the the belt, belt, indicating indicatingthe the schists to the south have also experienced experienced both both E-W E-W dextral dextral shear shear and and N-S N-S flattening. flattening. schists have also It is suggested partitioning of of strain across the width suggested that this sequence of structural structural development and partitioning consequence of the rotation of the regional kinematic framework framework of deformation deformation and and of the schist belt is a consequence in the ductility of the the schists schists and and intrusives. intrusives. Initially, while bedding was was nearneartemporal variations in horizontal, the schists accommodated the coaxial coaxial component of the transpression horizontal, accommodated the component of transpression and deformed deformed homogenously by by pervasive pervasive folding. folding. Minor homogenously Minor noncoaxial noncoaxial strain from this episode episode of the the deformation deformation is is rucorded in the asymmetric quartz LPO patterns in schists in the center of the belt. belt. Following Following pervasive pervasive recorded upright and and isoclinal isocinal F2 favorableorientation orientation to to accommodate accommodate the upright F2 folding, folding, the the schists schists were were in in aafavorable noncoaxial component component of of the the transpression. transpression. However, noncoaxial However, the schists schists were were also also cooling, cooling, and and therefore therefore hardening, such such that that E-W E-W dextral dextral shear shear was was heterogeneously heterogeneouslylocalized localizedinto intothe theRLSRF RLSRF along along the the hardening, northern margin of of the belt. Subsequently, Subsequently,the the regional regional kinematic kinematic framework framework rotated rotated such that that ductile ductile N- flattening occurred occurredinin the: the: 1) 1) RLSRF, RLSRF, 2) S horizontal horizontal flattening 2) leucogranites leucogranites and and pegmatites pegmatites and and schists schists enveloping their margins and 3) schists schists along along the the southern southern margin of the the belt belt bordering bordering the the migmatite migmatite terrane to to the south. The terrane Thebulk bulk of ofthe theschist schistbelt beltdefromed defromedby by brittle brittle faulting faulting during during this this stage stage of of the the deformation. deformation. increased ductility ductility necessary The increased necessary for for the aforementioned aforementioned areas areas to accommodate accommodate the late component component of N-S horizontal flattening was was a consequence consequence of: of: 1) 1) strain strain heating heating in in the RLSRF along along the the northern northern 111 �margin of of the schist belt, 2) contact heating supplied supplied by by the the plutons plutons in in the center of the belt and 3) margin 3) regional metamorphic heating supplied by by the the VGC VGC along the southern margin margin of of the the belt. belt. At At this this time, time, significance of the rotation of the regional kinematic framework are unclear. unclear. the reasons and tectonic significance framework are ..........this this volume. Bauer, R.L., R.L.,1988, 1988, Multiphase Multiphase folding folding , 112 �REFRACTION REFRACTION ANALYSIS ANALYSIS OF OF THE THE GLIMPCE GLIMPCE MARINE MARINE REFLECTION REFLECTION PROFILE' IN GEORGIAN GEORGIAN BAY PROFILE IN BAY Michael D. Thompson Thompson and and C. C. Patrick Patrick Ervin Ervin Dept. of Geology, Geology, N. Illinois Illinois Univ., Univ., DeKaib, DeKalb, IL IL 60115 60115 In 1986, a multichannel, marine reflection reflection survey survey was was made made along a profile across across Georgian Georgian Bay Bay and and Lake Lake Huron Huron (GLIMPCE (GLIMPCE Line Line J) employing employing a streamer streamer length length of of approximately approximately 33 km. km. Part Part of of the data within Georgian Bay, Bay, beginning with shotpoint shotpoint 1598 1598 north north of Cabot Head and and extending extending westward westward to to shotpoint shotpoint 2174 2174 north north of of Cove Island Island in in the the entrance entrance of of the the bay, bay, were were reprocessed reprocessed using using an an automatic automatic picking algorithm algorithm to to obtain obtain arrival arrival times times for for the the refracted energy. refracted energy. Both a refractor refractor offset offset correction correction and and aa lake lake bottom topography correction were incorporated into the topography correction were incorporated into the inversion inversion of the first first arrival arrival data data to to obtain obtain aa velocity—depth velocity-depth section section along along the the profile. profile. the eastern eastern portion po rtion Preliminary analysis of the data shows Prelimi nary analysis shows the to be domina dominated (<0.5') dipping (<0.5°) .ted by laterally continuous, continuous, westward westward dipping gentle dip dip is is refractors, probably of of Ordovician Ordovician age. age. The gentle fractors, probably consistent regional geologic consistent with with the theregional geologic structure, structure, and and the the computed computed velocities velocities are are within the the range range of of values values expected expected on on the the basis basis Assuming that velocities of the known known lithologies lithologies in in the the area. area. velocities on the order of 6.1 km/s mark the the top top of of the the Precambrian Precambrian 6.1 to to 6.6 6.6 km/s basement (Mereu obidon, 1971), ( ~ e r e uand Jobidon, 19711, the the interpreted interpreted velocity velocity structure beneath this portion of the the profile suggests suggests that that the the depth of the the westward deepening deepening basement basement surface surface ranges ranges from from 300 300 to 400 400 m. m. The western part of the the profile profile track track overlies overlies near—surface, near-surface, high—velocity high-velocity Silurian Silurian dolomite, dolomite, which which tends tends to to mask mask the the refractions refractions from from underlying underlying layers. layers. In this this instance, instance, refractions refractions from the Precambrian Precambrian surface surface are are not observed observed because because first arriving arriving energy energy until until•beyond 'beyond the the they do not become become the the first limits of the further problem arises arises in in the the limits the receiving receiving array. array. AA further shallow water areas where bottom sediment sediment refractions refractions are are often often absent absent due due to to the the large large source—to—first—receiver source-to-first-receiver distance distance relative to relative to the the refractor refractor depth. depth. Because refractor depths depths are are calculated cumulative fashion, fashion, lack lack of of information information for for the the calculated in in a cumulative undetected shallow layers precludes precludes calculation calculation of reliable reliable depths depths for for the the deeper deeper interfaces. interfaces. This This analysis analysis demonstrates demonstrates that that marine marine reflection reflection data data can can be reprocessed reprocessed relatively cheaply to obtain additional additional However, the information on the shallow shallow velocity velocity structure. structure. However, the technique is ineffective ineffective in the extremely extremely shallow shallow water overlying overlying the unusually—high, near—surface velocities unusually-high, near-surface velocities found found in in the the entrance entrance to the the bay. bay. REFERENCES REFERENCES CITED CITED R.F., and Jobidon, Jobidon, G., 1971, 1971, A Seismic Seismic Investigation Investigation of of Mereu, R.F., the Crust and Moho on a Line Perpendicular Perpendicular to to the the Grenville Grenville Front, Canadian Jr. of Front, of Earth Earth Sci., Sci., v. v. 8, 8, p. p. 1553—1583. 1553-1583. 113 �GEOCHEMISTRY GEOCHEMISTRY AND AND PETROLOGY PETROLOGY OF OF THE THE ATHELSTANE ATHELSTANE GRANITE, GRANITE. MARINNETTE MARINNETTE COUNTY, COUNTY. WISCONSIN WISCONSIN R. J. J. Wagner Wagner and and M. M. K. K. Sood Sood Department Department of Earth Earth Sciences Sciences Northeastern Northeastern Illinois I1 linois University University Chicago, Chicago, Illinois, Illinois, 60625 60625 The The Athelstane Athelstane Granite Granite lies lies in in the the northern northern part part of of is roughly roughly Marinette Marinette County, County, northeastern northeastern Wisconsin. Wisconsin. It is oval shaped pluton pluton that that covers covers an an area area of of 2226 mi. (585 26 mi. (585 Van Schmus km. Schmus et al., (1975) (1975) obtained obtained an an Rb/Sr Rb/Sr isotope isotope km.). age of 1810+/—50 m.y. for 1810+/-50 m.y. for the the Athelstane Athelstane Granite, Granite, and and considered it to to be a part of the the Penokean Penokean Northeastern Northeastern considered it Wisconsin Wisconsin orogenic orogenic and and plutonic plutonic complex. complex. The The Athelstane Athelstane Granite Granite has has relatively sharp sharp contact contact relations relations with with the the Quirinesec Quinnesec metavolcanics (1905+/—50 m.y.). Quinnesec metavolcanics (1905+/-SO m.y.1. Quinnesec xenoliths xenoliths in in Athelstane Athelstane are are thermally thermally altered. altered. Locally, Locally, the the Athelstane Athelstane Granite Granite is isintruded intrudedby by 1760+/—10 1760+/-10 m.y. m.y. old oldArnberg Amberg Granite Granite (Van (Van Schmus, Schmus, 1980). 1980). 9 "4. The is aa medium medium to to coarse coarse grained grained The Atheistane Athelstane Granite Granite is pink granite granite with average average modal composition composition of of microperthitic microcline (39.1%), (39.1%),Ans0-rn An20_ plagioclase microperthitic microcline plagioclase (24.9%), bluish quartz quartz (26.5%), (26.5%), biotite biotite (3.8%), (.8%), and (24.9%), bluish and hornblende hornblende (1.2%). (1.2%). Accessory Accessory minerals minerals include include apatite, apatite, sphene, and and magnetite. magnetite. Modal compositions compositions plot in in the the sphene, Granite Granite field field of of Streckeisen's Streckeisen's (1976) (1976)quartz—alkali quartz-alkali feldspar-plagioclase feldspar-plagioclase feldspar feldspar diagram. diagram. Micrographic Micrographic growths growths are are present. present. Retrogressive Retrogressive reactions reactions seen seen include include sericitization sericitization of of plagioclase, plagioclase, and and the the replacement replacement of of hornblende hornblende by by biotite biotite or or chlorite. chlorite. Major element element chemistry of the the Atheletane Athelstane rocks rocks shows shows that they they are are calc—alkaline calc-alkaline and and marginally marginally peraluminous. peraluminous. The The S102 SiQ2 varies varies between between 67 67 to to 75 75 weight weight %. %. KoO, FeO, Fed, TiO2, TiOo, 1(20, and and P205 P205 are are high, high, whereas whereas MgO, MgO, CaO CaO and and to to aa certain certain extent extent Na20, Na 0, are are low, low, when compared compared to to granitoids granitoids with similar similar is generally greater greater than than Na20, with with siTica si ica contents. contents. K20 is total alkalis alkalis (Na20+K20) (Na20+K 0 ) between between 6.1 6.1 to to 8.5 8.5 weight weight %. "is The The (K20+Na20)/CaO and Fe Fe/(FeO+MgO) < K O+Na2Q)/Ca0 and /(FeO+MgO) ratios ratios of of 1.5 1.5 to to 3.5 3.5 and and 0.75 0. 5 to to 0.86 respectIvely, respectively, are are similar similar to to anorogenic anorogenic granite, granite, but different different from from other other Penokean Penokean granites. granites. Harker Barker variation diagrams diagrams (S102 (S102 vs. other major oxides) show show aa limited role played by fractional fractional crystalization. crystalization. Both Both Zr Zr limited (130—410 ppm.) and Ba (630—2380 (130-410 ppm.) (630-2380 ppm.) ppm.) are are relatively relatively higher higher than other other Penokean Penokeangrariltes. granites. Ba—Rb-Sr Ba-Rb-Sr relations relations do do not not than show show extensive extensive effects effects of of metasomatism metasomatism or or late late fluxing fluxing of of magma 1975). magma with with volatiles volatiles (El—Bouseily (El-Bouseily and and El-Sokkary, El-Sokkary, 1975). ? Y 8 114 �Petrographic, chemical chemical (Figures (Figures 1—3), 1-31, and and field field Petrographlc, relations of of the the Athelstane Athelstane Granite Granite have have greater' greater affinity affinity to to relations anorogenic than than synorogenic synorogenicgranite graniteplutoris. plutons. Clearly, Clearly, the the anorogenic Athelstane Granite Granite is is aa late late orogenic orogenic (or (or perhaps perhaps even even post post Atheistane orogenic) intrusion intrusion that that certainly certainly did did not not originate originate during during orogenic) the main stage stage of of the the Penokean Penokean orogeny. orogeny. the Plots of of the the compositions compositions of of Athelstane Athelstane rocks rocks in in the the Plots albite-orthoclase-silica minima albite—orthoclase-sil Ica system system containing polybaric minima 19835, suggest suggest that that the the granite granite magma magma projections (Anderson, (Anderson, 1983), projections was probably probably generated generated at at approximately approximately 35 3 5 km. km. depth, depth, and and was emplaced at at about about 10 10 km. km. depth. depth. emplaced It is is therefore therefore proposed proposed that that the the Athelstane Athelstane Granite Granite It magma was was generated generated by by aa moderate moderate degree degree of of partial partial melting melting magma of crustal crustal material, material, probably probably aa mixture mixture of of Archean Archean and and of Penokean crust crust transitional transitional to to tonalite-gabbro tonalite-gabbro composition. composition. Penokean This This study study was was supported supported by by aa grant grant to to N. M. K. K. Sood Sood from from the Committee Committee on on Organized Organized Research. Research. the J. L., L., 1983, 1983, Proterozoic Proterozoic anorogenic anorogenic granite granite Anderson, J. Anderson, p. plutonism of of North North America: America: Geol. Geol.Soc. Soc.America AmericaMern. Mem. 161, 161, p. plutonism 133-154. 133-154. Anderson, J. J. L., L., and and Cullers, Cullers, R. R. L., L., 1987, 1987, Crust-enriched, Crust-enriched, Anderson, mantle-derived torialites tonalites in in the the early early Proterozoic ProterozoicPeriokean Penokean mantle—derived orogen of of Wisconsin: Wisconsin: Journal Journal of of Geology, Geology, v. v. 95, 95, p. p. 139-154. 139-154. orogen El-Bouseily, A. A. M., M., and and El-Sokkary, El-Sokkary, A. A. A., A., 1975, 1975, The The El-Bouseily, Relation Between Between Rb, Rb, Ba, Ba, and and Sr Sr in in Granitic Granitic Rocks: Rocks: Chemical Chemical Relation v. 16, 16, p. p. 207-219. 207-219. Geology, v. Geology, Streckeisen, A. A. L., L., 1976, 1976, To To each each plutonic plutonic rock rock it's it's proper proper Streckeisen, name: E. E. Sd. Sci. Review, Review, number number 12, 12, P. P. 1—34. 1-34. name: Van Schmus, Schmus, W. W. R., R., 1980, 1980, Geochronology Geochronology of of igneous igneous rocks rocks Van associated with with the the Penokean Penokean Orogeny Orogeny in in Wisconsin: Wisconsin: in in Morey, Morey, associated G. B., B., and and Hanson, Hanson, C. G. N., N., eds., eds., Selected Selectedstudies studiesofofArcheari Archean C. and lower lower Proterozoic Proterozoic rocks, rocks, southern southern Canadian Canadian Shield: Shield: Geol. Geol. and p. 159-169. 159-169. Soc. America America Spec. Spec. Paper Paper 182, 182, p. Soc. Van Schmus, Schmus, W. W. R., R., Thurman, Thurman, E. E. N., M., and and Peterman, Peterman, Z.E., Z.E., 1975, 1975, Van Geology and and Rb-Sr Rb-Sr chronology chronology of of middle middle Precambrian Precambrian rocks rocks in in Geology v. eastern and and central central Wisconsin: Wisconsin: Geol. Geol. Soc. Soc. America America Bull., Bull., V. eastern 86, p. p. 1255—1265. 1255-1265. 86, 115 �Q Figure 1 A P p 0N Figure 2 N z+ 0 N 80 55 50 55 70 75 80 S0p 3 S S Figure 3 Figure 3 £ I 0 U £ 3 2 C 5 Wl. 4n.,n 0 U thsls.n. 0 1.0 0.2 OIPw Normally. Figures Figures 1-3. 1-3. QUsrtz/(OrtftoclSss...AIbj.+Aflo,thlt,) Figure Q—A-P Diagram (modal Figure 11 is a Q-A-P (modal Quartz—Alkali Quartz-Alkali Feldepar—Plagioclase Feldspar-Plagioclase Feldspar) Feldspar) comparing comparing the the Atheistane pluton to the other Penokean plutons of northern Athelstane and northeastern northeastern Wisconsin. Wisconsin. Figure 22 is is aa plot plot of of Total Total Alkalis Alkalls (K20 ++ Na20) vs. Si02 (weight (weight %s) %s) for for the the Athelstane pluton compared to to other other Penokean Penokean plutons plutons of of shows the CIPW-normative corundum Wisconsin. Wisconsin. Figure 3 show3 corundum vs. vs. quartz/feldspar ratio for the Atheistane quartz/feldspar Athelstane pluton compared compared to to the other Penokean Penokean plutons plutons of of Wisconsin. Wisconsin. Box ABCD Is is the the zone of normal normal granltes granites (from ( f r m Fernandez—Alonso Fernandez-Alongo et et al., al., 1986). 1986). 116 �Geochemistryand and Tectonic TectonicSignificance Significance of Early Earlv Proterozoic Proterozoic Igneous Igneous Rocks. Rocks, Geochemistry Northern NorthernMichigan Michiganand and Northeastern NortheasternWisconsin Wisconsin Soo So0 Meen Meen Wee Wee and and John JohnT. T. Wilband, Wilband, Department Departmentof ofGeological GeologicalSciences, Sciences,Michigan Michigan State StateUniversity, University,East EastLansing, k i n g ,MI MI48824 48824 Early Early Proterozoic Proterozoic igneous igneous rocks rocks in northern northern Michigan Michigan and and northeastern northeastern Wisconsin consist of of a complex assemblage of of lavas, lavas, sills sills and and dikes. dikes. These Wisconsin consist complex assemblage Theserocks rocks were were metamorphosed metamorphosed atatvarying vaqing degrees degreesduring duringthe thePenokean PenokeanOrogeny Orogeny(1.82-1.85 (1.82-1.85 Ga). of the area Ga). The The tectonic tectonic evolution evolution of area has has been been attributed attributed to toplate platemargin margin processes, processes, arc-continental arc-continentalcoffision collision processes, or intracratonic intracratonicmobilization. mobilization. The the tholeiitic tholeiiticfield fieldinin an an AFM AFM diagram. diagram. A A The analyzed analyzed rocks rocks fall Within within the northern tholeiitic tholeiiticassemblage assemblageofofdike dikeswarms swarmsand andvolcanic volcanicpiles pilescontaining containingpillow pillow northern lavas (Hemlock (Hemlock and and Badwater Badwater Greenstones) Greenstones) can can be bedistinguished distinguishedfrom from aasouthern southern lavas magmatic with arc-related chemical characteristics. characteristics. Mafic magmatic assemblage with Mafic rocks rocks of the the dike dike swarms, swarms, the the Hemlock Hemlock volcanics, volcanics, and the Badwater Badwater Greenstones Greenstonesevolved evolved from from tholeiitic tholeiitic basalts basalts with with subalkaline subalkalineaffinities. affinities. Virtually Virtually all all rocks rocks plots plots within within the the subalkaline subalkaline field of the Ol-Ne-Q 01-Ne-Q diagram. The Theabsence absenceof of the thealkaline alkalinebasalt basaltfield field within within the the region region could could mean mean that thatearly earlyProterozoic Proterozoic magmas magmas were were generated generated atat relatively relatively shallow shallow depth, depth, under under the theinfluence influenceof of aa high high geothermal geothermalgradient. gradient. Based CaO/Ti02 and andA1203 A1203 vs. vs. Ti02 Ti02plot, plot, itit Based on on chemical chemical characteristics and CaO/TiO can arederivatives derivativesofofhi-Ti hi-Ti can be be sugested suggestedthat thatthe therocks rocksofofthe thenorthern northernassemblage assemb ageare MORB MORB like like tholeiites tholeiites from from relatively relatively undepleted undepleted source(s). source(s). The The elemental elemental distributions lava and and dike dikeswarms swarms in in the the northern northernassemblage assemblagehave haveled ledus ustoto distributionsof of the thelavas conclude concludethat thatthe thedikes dikesserved servedasasfeeders feederstotothe thevolcanic volcanicpiles. piles. Other data datasupport supportcontamination contamination processes. processes. For Forexample, example,ininsome somedikes, dikes, Other Si02 S O 2 and and Rb/Sr RbISrare areenriched e ~ c h eatdatthe themargins marginscompared compared to to the thecenters centersand and may may represent emplacement or or crystallization. crystallization. The The Zr/Y ratio represent assimilation assimilation during emplacement ratiofor for the ( > 10)isismuch much higher higher than thanthe themore moreprimitive primitiveflows flowsand and the supracrustal supracrustal rocks rocks (>10) dikes. dikes. Evolved Evolvedrocks rockswith withprogressively progressively higher Zr/Y ratios ratiosmay may have haveresulted resultedfrom from assimilation systems. Furthermore, assimilation within ponded magma systems. Furthemore, Ce/Yb Ce/Yb vs. vs. Ce Ceplots plots can can be beinterpreted interpretedtotorepresent representassimilation-fractional assimilation-fractionalcrystallization crystallizationrather ratherthan thansimple simple fractionalcrystallization. crystallization. Finally, Finally,ininspider spiderplots plotsofofsuite suiteaverages, averages,the thedike dikeswarms, swarms, fractional Hemlockvolcanics, volcanics, and and Badwater Badwater Greenstones Greenstonesare medistinctively distinctivelydepleted depletedininNb Nbwith with Hemlock respect Nb anomaly anomaly isis calculated calculated asas respect toto its its neighboring neighboring elements, elements, where where the the Nb Nb/chon. (Thlchon. ++ La/chon.)/2 La/chon.)/2 (Ueng (Ueng etet al., al., 1987). 1987). The The decrease decrease Nblchon. - - (Th/chon. approximates approximates an anexponential exponentialfunction functionwith withincreasing increasingdifferentiation differentiationindex. index. This This implies impliescontinuing continuingassimilation assimilationthroughout throughoutthe thedifferentiation differentiationhistory. history. The Thetectonic tectonicsettings settingsofofthe thedike dikeswarms, swarms,Hemlock Hemlockvolcanics, volcanics,and andBadwater Badwater Greenstones Greenstoneswere weretested testedbybypreviously previouslydeveloped developedtectonic tectonicdiscrimination discriminationdiagrams. diagrams. In InTi-Zr-Y Ti-Zr-Y plots lots(Pearce), (Pearce),the themajority majority of of the therocks rocksplot plotininthe thewithin withinplate platebasalt basalt field, field,and andaafairly airly large large number number in in the the calc-alkaline calc-alkaline and ocean ocean floor floor basalt region. In In Nb-Zr-Y Nb-Zr-Y plot plot (Meschede), (Meschede), the the data datamostly mostly fall fall in in the the within within plate plate tholeiites tholeiites and and PPNbapex apexmay mayreflect reflect typeMORBs. MORBs. The Thesubparallel subparallel"vertical" "vertical"trends trendsaway awayfrom fromthe theNb type the of crustal Nb. The The other other the aforementioned aforementioned assimilation assimilation of crustal rocks rocks depleted depleted in in Nb. possibility possibility is is that that the theP-type P-typeMORBs MORBscan canbe begenerated generatedbybygradual gradualdecompression decompression during duringrifling. rifting. This Thisdecompression decompressionenabled enabledconcurrent concurrentmelting meltingofofzoned zoned source sourceofof upper, upper,more moredepleted depletedmantle mantleand andlower lowerenriched enrichedmantle. mantle.InIntectonic tectonicdiscrimination discrimination diagram diagramusing usingHf-Ta-Th Hf-Ta-Th(Wood), (Wood),most mostsamples samplesfrom fromthis thisinvestigation investigationplot plotoutside outside the Ta, thetectonic tectonicfields. fields. This Thissuggests suggeststhat thatthe therocks rockshas hasbeen beencontaminated contaminatedsince sinceHf, Hf,Ta, and andTh Thare arevery verysensitive sensitivetotocrustal crustalcontamination. contamination. InInsummary, summary,there thereisisno noclear clear definition definitionof of tectonic tectonicsetting settingfor forthe theearly earlyProterozoic Proterozoicrocks rocksof ofthe thearea. area.However, However, Nesbitt),most mostofofthe thenorthern northern CaO/Ti02and andAl,O3/TiO2 A1303/Ti02vs.vs.Ti02 Ti02 plots(Sun (Sun&&Nesbitt), CaO/Ti02 plots assemblage assemblage rocks rocks äluster c uster along along an an undepleted undepleted source source trend; trend;whereas whereasthe thesouthern southern ? k' 117 �"magmatic arc" arc"rocks rocksofofthe the Quinessec Quinessecplot plot in in aa depleted source region. region. Because Because arc-related rocks are commonly commonlydepleted depletedininTTiO rocks are i 0 and are enriched in A1203/Ti02 compared to MORBs MORBs or continental continental tholeiitic tholeiitic %asalts, northern compared basalts, the the rocks rocks of of the northern assemblage assemblage are are probably probably best assigned assigned as as having having aa rift related origin. origin. Interpretations of these rocks, Interpretations of of the the chemical chemical characteristics characteristics of rocks, based on on modern modern analogs, favor an extensional analogs, favor extensional tectonic tectonic regime, regime, such such as would would develop develop by by arcarccontinent by previous previous investigaters. investigaters. continentcollision collisionprocesses processessuggested suggested by 118 �Preliminary Structural Preliminary Structural Analysis Analysis of of Archean Archean Rocks Rocks in in the the Virginia Virginia Horn area, areaI Northeastern Minnesota Minnesota J.L. WELSH WELSH (Department (Department of GeologyI J.L. Gustavus Adoiphus Adolphus College, CollegeI Geology, Gustavus St. St. Peter, PeterI1'2 MN 56082) 56082) Detailed mapping in Detailed mapping in lower lower greenschist greenschist grade grade Archean Archean rocks rocks northeastern Minnesota Minnesota (the within the the Virginia Horn area of northeastern (the defined by the unconformable unconformable superjacent prominent Z-fold 2-fold defined superjacent Biwabik Iron Formation of the Mesabi Iron Range), has Iron Fomation Iron Range)# has revealed revealed the the presence presence of of at at least least one one major major period periodof offolding folding(F].) (Fl) and and aa series northeasterly trending trending faults series of of northeasterly faults which which postdate postdate the the folding. The identified primarily primarily on folding. The fold fold event is identified the basis basis of of on the reversals folds are are reversals in in stratigraphic stratigraphic top top indicators. indicators. Minor Fl folds rare, where present they are tight to rareI but where are tight to isoclinal isoclinal in in style style and and well developed steeply steeply plunging. plunging. A moderately to well developed axial axial plane foliation foliation is is present present in in these these folded folded rocks. rocks. informally designated One prominent fault, faultI here informally designated the the Fayal Fayal fault, greenstone occupying faultI separates separates the the greenstone occupying the the ridge ridge west west of of Gilbert Gilbert with with the the greywacke—slate greywacke-slate sequence sequence present present east east of of Eveleth Eveleth (Fig.). Another Another fault, faultI here informally informally designated designated as as the the Pike Pike (Fig.) River sequence from River fault, faultI separates separates this this same same metasedimentary metasedimentary seqyence from greenstone greenstone to to the the west, westI in in the the northern northern portions portions of of the the study study The Pike. area. phyllonitic rocks area. Strongly Strongly phyllonitic rocks mark mark its its presence. presence. The Pike. River River fault fault is is more more difficult difficult to to delineate delineate to to the the south south as as it it metasedimentary sequence appears to cut into the metasedimentary sequence and and trends trends parallel parallel to to bedding. In In this this southern southern area area the the Pike Pike River River fault fault interpreted to occupy a phyllonitic zone is interpreted zone which which separates separates aa distinctive distinctive conglomeratic conglomeratic unit unit from from the the more more turbiditic turbiditic greywacke—slate between these greywacke-slate sequence. sequence. Located between these two two major faults faults occur a group group of inferred subsidiary faults, occur inferred subsidiary faultsI that that strike strike obliquely to obliquely to the the main main fault fault trend. trend. These These subsidiary subsidiary faults faults are are identified by topograhic lineaments, identified lineamentsI changes changes in in strike strike of of bedding bedding (in the easternmost easternxnost of of these these faults) faults) and and local local silicification silicification (in the and/or sericite-.carbonate alteration of the rocks and/or sericite-carbonate alteration rocks along along them. them. The The localization localization of alteration alteration zones zones along along some some of of these these faults, and the occurrence faultsI and the occurrence of abundant abundant sericite sericite and and carbonate carbonate in in many of many of the the metasedimentary metasedimentary rocks rocks suggests suggests that that large large volumes volumes of of fluids passed through through these these rocks, probably using fluids rocksI probably using the the faults faults as as conduits. Therefore these these faults faults and conduits. Therefore and their their associated associated alteration alteration zones mineral exploration zones may be useful useful guides for for mineral exploration in in the the area. area. The The Pike Pike River River fault fault lies lies essentially essentially on on trend trend with with the the Waasa Waasa fault fault further further to to the the northeast, northeastI and and thus thus could could have have regional regional significance. significance. The occurrence occurrence of of these these faults faults in in the the Archean Archean rocks rocks of of the the area area also also suggests suggests aa possible possible genetic genetic relationship Proterozoic structure relationship to to the the Proterozoic structure of of the the of of the the Virginia Virginia Horn itself. Horn itself. 119 �Vif Virginia 0 fault Eveleth El El Gilbert fault 1— —i miIes I. Sketch map Virginia Horn Horn area, area, showin showin Fig. Sketch Fig. mapofof Archean Archeanrocks rocksinin the the Virginia the distribution di j t r i bution of metasedimentary(ms) (ms)and andmetavolcanic metavol canic(mv the of metasedimentary rocks, and and major The boundary boundary shown rocks, major faults. faults. The shownininthe thevicinity vicinity (mvj of the the cities c i t i e sofofVirginia, Virginia, Eveleth,and andGilbert Gilbertmarks marks the the of Eveleth, unconformity between between the the Archean Archean rocks and the the superjacent superjacent unconformity rocks and Proterozoic rocks. rocks. Proterozoic 120 � https://digitalcollections.lakeheadu.ca/files/original/019747c29e8c82d96f5b64350c5a0b6b.pdf cb43ca8d828e1d80a5ab6c9e3009ff8a PDF Text Text Thirty-fourth Annual Meeting Marquette, Michigan May l2and 13, 1988 Institute on Lake Superior Geology Field Trip Guidebooks Volume 34, Part 2 — - —— —'—-—----:i-e-,-' — "4... �34th 34th ANNUAL ANNUAL INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY INSTITUTE Field Trip Trip Guidebooks Guidebooks Field Volume Volume 34, 34, part part 22 Marquette, Marquette, Michigan Michigan May 12 12 and and 13, 13, 1988 1988 May Organized Organized By By John John Hughes, Hughes, Northern Northern John John Klasner, Klasner, Western Western Klaus Klaus Schulz, Schulz, U. U. S. S. Michigan Michigan University University Illinois Illinois University University Geological Geological Survey Survey Edited Edited by by Klaus Klaus Schulz Schulz Cover: Cover: 1 Line ScandinavianLine drawing drawing of of Scandinavianstyle style headframe headframe and and modern modern head— headframe frame at at Cleveland Cleveland Cliff's Cliff's Cliff Cliff Ishpeming, mine, iron shaft shaft iron mine, Ishpeming, Michigan. Michigan. �TABLE OF OF CONTENTS CONTENTS TABLE FIELD TRIP TRIP 11 FIELD An Introduction Introduction to to Archean Archean Geology Geology and and Precious Precious Metal Metal An Mineralization of of the the Marquette Marquette Greenstone Greenstone Belt, Belt, Michigan. Michigan. Mineralization Geological Overview Overview of of the the of of the the Marquette Marquette Greenstone Greenstone Geological Michigan Belt, Michigan Belt, T.J. Borrihorst Borrlhorst T.J. Al A1 -- Al8 A18 Geological Framework Framework of of aa Part Part of of the the Marquette Marquette Geological Greenstone Belt Belt North North of of the the Dead Dead River River Storage Storage Basin Basin Greenstone D.A. 3axter Baxter and and M.L. M.L. MacLellan MacLellan.................... D.A. A19 A19 -- A31 A31 Geology of of the the Ropes Ropes Mine Mine Geology R.A. Brozdowski. R.A. Brozdowski A32 ~ 3 —-2 A53 ~ 5 3 Geological Field Field Trip Trip to to the the Marquette Marquette Greenstone Greenstone Belt: Belt: Geological 1 to 11 Part I, Day 1 Road Log Stops 1 to 11 Stops Part I, Day 1 Road Log TJ. T.J.Bornhorst, Bornhorst,D.A. D.A.Baxter, Baxter,M.L. M.L.MacLellari, MacLellan, and and R.C. Johnson Johnson...................................... R.C. A54 A54 -- A64 A64 Geological Field Field Trip Trip to to the the Marquette Marquette Greenstone Greenstone Belt: Belt: Geological Road Log Log -- Stops Stops AA to to EE Part II, 11, Day Day 22 Road Part T.J. Bornhorst Bornhorst and and D.A. D.A. Baxter Baxter T.J. A65 A65 -- A71 A71 Geological Field Field Trip Trip to to the the Marquette Marquette Greenstone Greenstone Belt: Belt: Geological Part III, 111, Callahan Callahan Mining Mining Corporation Corporation Ropes RopesMine Mine Part Property Property R.A. Brozdowski Brozdowski and and G.W. G.W. Scott Scott....... R.A. A72 A72 - A73 A73 ................................... .................................. ..................... ............. FIELD TRIP TRIP 22 FIELD Marquette mineral mineral district district of of Michigan, Michigan, mining mining history history Marquette and geology. and geology. Burton H. H. Boyum Boyum and and Robert Robert C. C. Reed Reed....... Burton Bi Bl —- B15 B15 Marquette mineral mineral district district of of Michigan Michigan with with emphasis emphasis on on Marquette MINING HISTORY HISTORY and and GEOLOGY GEOLOGY MINING Burton H. H. Boyum, Boyum, Robert Robert C. C. Reed Reed and and Wm. Wm. Kangas Kangas Burton B16 B16 -- B33 B33 ........... ...... FIELD TRIP TRIP 33 FIELD structural traverse traverse across across aa part part of of the the Penokean Penokean orogen orogen AA structural illustrating Early Early Proterozoic Proterozoic overthrusting overthrusting in in northern northern illustrating fieldquide. Michigan: text text and and fieldcuide. Michigan: John J. Gregg Gregg and and John S. S. Klasner, Klasner, Paul Paul K. K. Sims, Sims, Wm. Wm. J. Christina Gallup Gallup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cl Cl -- C36 C36 Christina 1 �FIELD TTRIP FIELD RIP 1 1 Geological of the Geological Overview Overview of the Marquette Greenstone Marquette Greenstone Belt, Michigan Michigan T.J. Bornhorst T.J. Bornhorst Department of Geology Department Geology and and Geological Geological Engineering, Engineering, Michigan Technological University, Houghton, Michigan Technological University, Houghton, Michigan Michigan 49931 49931 INTRODUCTION The name Greenstone Belt Belt isis applied applied to to the belt name Marquette Marquette Greenstone belt of of dominantly dominantly Archean volcanic rocks rocks which which underlies underlies an an area area of of about Archean volcanic about 125 125 mi2 mi2 (325 (325 km2) km2) in in \ The belt occupies northern occupies the the eastern eastern northern Marquette Marquette County, County, Michigan Michigan (Figure (Figure 1). 1). The part of of the the northern northerncomplex, complex, an anextensive extensive terrane terrane ofofArchean Archeangranite-greenstone granite-greenstone Lower Proterozoic (750 km2) north north of of the (750 mi2; mi2; 1950 1950 km2) the Marquette Marquette trough. trough. Lower Proterozoic sediments, sediments, which fill fill the Marquette and overlie the complex, bury the Great which Marquette trough trough and overlie the complex, bury Great Lakes Lakes Tectonic Tectonic Zone, Zone, a major major regional regional Archean Archean structural structural zone zone described described by by Sims Sims (1980). (1980). The Marquette The Marquette Greenstone Greenstone Belt Belt represents represents the southwestern southwestern extension extension of the the Wawa Wawa Subprovinceof of the the Superior Province of of the Canadian Subprovince Superior Geologic Geologic Province Canadian Shield Shield as defined defined focus of of this overview (and of of the The specific specific focus overview (and the by Card Ciesielski (1986). (1986). The by Card and andCiesielski accompanyingfield fieldtrips) trips) isis the the greenstone belt, which which occupies occupiesabout about one-fifth one-fifth of accompanying greenstone belt, the entire the entire Archean Archean northern northern complex. complex. The Marquette of several The Marquette Greenstone Greenstone belt Consists consists of several thousand thousand feet of of subaqueous subaqueous These are mafic to silicic flows flows and andpyroclastics, pyroclastics, and andvolcaniclastic volcaniclastic sediments. sediments. These to silicic The belt also intruded also intruded by gabbro gabbro and and rhyolite rhyolite dikes dikes and and by by granitoid granitoid plutons. plutons. The includes two intrusive intrusive peridotite peridotite bodies, bodies, one one in in vicinity of the includes two vicinity of the Ropes Ropes Mine Mine and and All these the other other at at Presque Presque Isle. Isle. All these rocks rocks are Archean, Archean, about about 2700 2700 to 2500 2500 Ma Ma metamorphic grade grade old (Morgan (Morgan and and DeCristoforo, DeCristoforo, 1980; 1980; Trow, Trow, 1979). 1979). Their metamorphic ranges from from greenschist to amphibolite amphibolite facies facies and and they they have ranges greenschist to have been subjected subjected to to multiple deformation multiple deformation during the the Archean. Archean. There are numerous There numerous gold gold and base base metal occurrences occurrences throughout throughoutthe the belt belt (Bodwell, (Bodwell, 1972) 1972)but but the the Ropes Ropes Mine Mine is the metal the most significant most significant to date date (Brozdowski, (Brozdowski, this volume; volume; Bornhorst Bornhorst and others, others, 1986; 1986; Brozdowski and others, Archean rocks rocks are are unconformably unconformably overlain overlain by by Brozdowski others, 1986). 1986). The Archean A-i �Keweenawan EarIy Proterozoic ::i::Archean granitoids and gneiss 50 0 I km A Archean Southern Complex 'S Paleozoic Greenstofle Figure1: 1: Regional Regionalgeological geologicalsetting settingofofthe theMarquette Marquette GreenstoneBelt Beltwhich which Figure is shown in solid black. black. is shown in solid A—2 �and, in in fault faultcontact contactwith, with,Lower LowerProterozoic Proterozoicsediments. sediments. Greenstone Belt Belt was was proposed proposed for for these same The name name Ishpeming Ishpeming Greenstone same rocks rocks by by However, this this name name isis abandoned here in favor Morgan and DeCristoforo Morgan DeCristoforo (1980). (1980). However, abandoned here favor of Marquette Belt because becausethese theseArchean Archeanrocks rocksdo do not not crop crop out out in Marquette Greenstone Greenstone Belt in Ishpeming (Lower (Lower Proterozoic Proterozoicsediments sedimentscrop cropout out in in Ishpeming) whereas they they do Ishpeming Ishpeming) whereas do crop out out in the crop the City City of of Marquette. Marquette. Further, Further, the belt belt is is located located in in northern northern Marquette County. Marquette County. The rooks rooks of the the belt belthave havebeen beenstudied studiedand anddiscussed discussedby bynumerous numerousgeologists. geologists. For a historical the reader reader isis referred referred to to the work For historical background background the work of of Morgan Morgan and and based on on work work by by the author and This overview overview isis based and his his DeCristoforo (1980). (1980). This students, and and on on work (1968), Puffett (1974), (1974), Clark Clark and students, work by Gair Gair and and Thaden Thaden (1968), others (1975), Cannon and and Klasner and on the others (1975), Cannon Klasner (1977), (1977), and the geological geological studies studies summasummarized MacLellar (this (this volume). volume). rized by by Baxter Baxter and andMacLellari. STRATIGRAPHY STRATIGRAPHY As by the the literature from other As documented documented by literature from other parts parts of of the the Superior Superior Province, Province, stratigraphic correlations across across regional regionalfaults faults or or shear shear zones stratigraphic correlations zones are quite quite tenuous tenuous and and error. The stratigraphy stratigraphy of the the Marquette Marquette Greenstone Greenstone Belt Belt will will be be subject to error. discussed in two two separate parts because because the the belt belt is traversed discussed in separate parts traversed obliquely obliquely by by the the Dead Dead River 2). For purposes purposes of of description, description, River Shear Shear Zone, Zone, a probable probable major major fault fault (Figure (Figure 2). the greenstone belt has has been been subdivided subdivided into into aa northern northern and and a southern the greenstone belt southern part; part; other other faults necessitate that the the southern southern part part be be further divided faults necessitate that divided into into an an "eastern "eastern two-thirds" and aa "western two-thirds" "western one-third". one-third". Northern Part Northern The rocks of the northern The rocks of northern part of of the the belt belt have have been been described described by by Baxter Baxter and and rocks are are dominated dominated by by pillowed pillowed and and massive massive basalt basalt MacLellan MacLellan (this volume). volume). The rocks lava mudflow breccias breccias and and iron-formations; iron-formations; this thisassemblage assemblage lava flows with with interbedded interbedded mudflow These rocks are are has 2). These has been named named the the Volcanics Volcanics of Silver Silver Mine Mine Lakes Lakes (Figure (Figure 2). cut by of gabbro and all by dikes dikes and and sill-like sill-like bodies bodies of gabbro and all are cut cut by by dikes dikes of of rhyolite rhyolite A-3 ��it: u 0 a; -J z 0 E- DEAD RIVER PLUTON GRANITOID ROCKS SEDIMENTS 3 1-1 n 4 ca $ n Of. n 21-1 1 z MONA SCHIST KITCHI SCHIST PERIDOTITE z Cd z E- z u 0 n. 0 E- Cd m "3 0 E- 01 u a: u vs LIGHTHOUSE POINT MEMER Ed s Cd 2: E-i x 1-1 u 1-1 SHEARED RHYOLITE TUFF MEMBER a: I 0 I m Cd Of. AGE RELATION UNCERTAIN I Of. ARCHEAN 0 Ill I w ARCHEAN z PROTEROZOIC Q LEGEND ______ ca w Ln Ill Ill 3 E- w E- u 1-1 0 ?-i s Of. 0 Cd 2Cd a: m Of. Cd rn z Cd z ^ Cd Cd K u x 2 Cd z 4 z 0 z m x 4 1-1 1-1 0 VOLCANICS OF SILVER MINE LAKES LOWER BASALT MEMBER NEALY CREEK MEMBER Cd Ed z u z Of. Cd > 1-1 n m Ill 0 m u n 2u �Figure 2: Southern extents of the Dead River Geology of the Marquette Greenstone Belt, Michigan. and Carp River Falls Shear Zones are shown. Numbers and letters represent stops for field Cannon and Kiasner (1977), Clark and others (1975), trips (this volume). Compiled from: Puffett (1974), Bodwell (1972) and Gair and Thaclen (1968). �plutons intrude intrude the the northern northern part part of the and Granitoid plutons the and plutons plutons of of granodiorite. granodiorite. Granitoid greenstone belt to to the northeast greenstone belt northeast (see (see Day Day 2 Road Road Log, Log, Stop Stop E). E). The The granitoid granitoid rocks rocks of of the theMarquette MarquetteQuadrangle Quadrangle were were mapped mappedasasCompeau Compeau This name name has has also also been been assigned assigned more more Creek Gneiss Gneiss by Gair Gair and andThaden Thaden(1968). (1968). This recently crystallinerocks iocks in in the the region recently to similar-looking similar-looking crystalline region south south of the the Marquette Marquette trough l), and and ininessence, essence, signifies signifies "undifferentiated "undifferentiated plutonic plutonic rocks rocks of of trough (Figure (Figure 1), Creek Gneiss Gneiss should should be be used used only only in that Marquette County". County". The name name Compeau Compeau Creek that context context or prhaps, perhaps, be beabandoned. abandoned. Southern Southern Part Part The rocks of the rocks of the southern southern part part of the the belt, belt, south south of of the the Dead Dead River River Shear Shear Zone, Zone, have have been been mapped mapped by Gair Gair and and Thaden Thaden (1968), (1968), Puffett Puffett (1974), (1974), Clark Clark and and others others (1975), (1975), and Cannon Cannon and and Klasner Klasner(1977). (1977). Much Much of the the following following is is based based units (Figure (Figure 2) 2) in in the southern their work. work. The major major lithologic lithologic units southern part of of the the on their belt are: Kitchi Schist, Schist, Deer Deer Lake Lake Peridotite, Peridotite, Dead Dead River Pluton Pluton and and are: Mona Mona Schist, Schist, Kitchi other unnamed as Compeau Creek Gneiss Gneiss and and as as graunnamed granitoid granitoid plutons plutons (mapped (mapped as Compeau Creek nite). Relative The Relative age age relations relations among among these these major major lithologic lithologic units units are are uncertain. uncertain. The contact the Mona as a shear Kitchi Schists Schists was was mapped mapped as shear zone zone by by contact between between the Mona and and Kitchi top direction within a few Clark and and others others(1975). (1975). In addition, addition, stratigraphic stratigraphic top direction within few miles of the NE whereas whereas the Kitchi Kitchi Schist Schist miles of the contact contact indicates indicates that Mona Mona Schist Schist faces faces NE (1983) has has suggested suggestedthat that the the contacts contacts of of the Deer faces SE. SE. Rossell Rossell (1983) Deer Lake Lake Peridotite are structural and not Peridotite are not stratigraphic, stratigraphic, making making age age relations relations uncertain. uncertain. Although between the plutonic Although contacts contacts between plutonic rocks rocks and and volcanics volcanics rocks rocks are arecommonly commonly faults or shear shear zones, zones, the the plutonic plutonic rocks rocks in in close close proximity proximity to to the thegreenstone greenstone belt belt can be be interpreted interpreted to to intrude intrudethe thevolcanics, volcanics, based based on onsmaller smallerintrusive intrusiverelationships relationships and contact contact metamorphic metamorphic features. features. In view view of the the fact fact that thatfaults faults complicate complicate the the study study of of the the stratigraphy stratigraphy of of to resort even even the the southern southern part part of of the thegreenstone greenstone belt, belt, itit is necessary necessary to resort to to A-7 �describing describing the the stratigraphy stratigraphyofofthe theeven evensmaller smaller"eastern "easterntwo—thirds" two-thirds" and and"western "western one-third" areas. areas. of the southern The eastern eastern two-thirds two-thirds of southern part part of of the the belt belt Eastern Eastern Two-Thirds. Two-Thirds. The This name name should should perhaps perhaps be modified modified in in consists of the consists of the Mona Mona Schist Schist (Figure (Figure 2). 2). This the future future to tothe the"Mona "Mona Group" Group" because because the the Mona Mona Schist Schist can be be subdivided subdivided into into units (currently scale which which should should be elevated (currently termed termed members) members) at 1:24000 1:24000 scale elevated to to status. In addition, addition, the the rocks rocks that that are aremapped mapped asasthe theMona Mona"Schist" "Schist" formation status. have to the North have an an identifiable identifiable protolith protolith and and consequently, consequently, according according to North American American Code the parent parent lithology lithology term term should should be be used Code of Stratigraphic Stratigraphic Nomenclature, Nomenclature, the used in in for present Nevertheless, for present purposes purposes the term term Mona Mona name instead instead of of schist. schist. Nevertheless, the name Schist will be retained Schist will retained as as will will the thecurrently currentlyrecognized recognized four fourmembers: members: Lower Lower Member, Member, Nealy Nealy Creek Creek Member, Member, Sheared Sheared Rhyolite Rhyolite Tuff Member, Member, and andLighthouse Lighthouse Point Member. Member. The Lower Lower Member Member of of the theMona MonaSchist Schistconsists consists mainly mainly of ofsubaqueous subaqueousmassive massive and pillowed Day I1 Road pillowed tholeiitic tholeiitic basalt basalt lava lava flows flows (see (see Day Road Log, Log, Stops Stops 1 and 2, 2, this this volume) volume) with minor minor interbedded interbedded volcaniclastic volcaniclastic and and tuffaceous tuffaceous rocks. rocks. The member member crops crops out in in aa 25 25mi2 mi2(65 (65 km2) km2) area and and is is over over 10,000 10,000 feet feet (3300 (3300 m) m) thick, thick, top direction direction in the Stratigraphic top the Lower Lower assuming there is no assuming there no structural structural repetition. repetition. Stratigraphic Member is to the Member is the north. north. The Nealy lie the Nealy Creek Creek Member Member is considered considered to ove overlie the Lower Lower Member. Member. ItIt consists of a variety schistswhich whichcrop cropout out in in a quartz-chlorite-sericite-feldspar schists consists of variety of of quartz—chlorite-sericite-feldspar mi2 (18 (18 km2) km2) area. area. The schists schists appear to to be be mostly mostly greywacke greywacke and and shale shale (see (see 7 mi2 Day Day 11 Road Road Log, Log, Stop Stop 11, 11, this this volume), volume), but but in ingeneral general the theschistose schistose texture texture prevents member prevents recognition recognition of volcaniclastic volcaniclastic or tuffaceous tuffaceous textures. textures. This member (perhaps 3000 feet feet (1000 m) thick) thick) is the only unit in the (perhaps 3000 (1000 m) only significant significant sedimentary sedimentary unit the greenstone belt. belt. The Sheared Tuff Member Sheared Rhyolite Rhyolite Tuff Member is considered considered to overlie overlie the the Nealy Nealy Creek Creek rocks which consists of light-colored, light-colored, porphyritic porphyritic volcanic volcanic rocks which crop out out in in Member. It consists Member. A- 8 �of tabular aa 1.3 1.3 mi2 mi2(3.4 (3.4 km2) km2) area. area. The The common common lithology lithology consists consists of tabular fragments fragments of of porphyritic by fine-grained porphyritic rhyolite rhyolite surrounded surrounded by fine-grained matrix matrix of quartz, quartz, sericite sericite and and are quartz quartz and and feldspar, feldspar, and and make make up up 10 to 50 chlorite. Phenocrysts Phenocrysts are 50 percent percent of of chlorite. This the rhyolite rhyolite (Puffett, (Puffett,1974). 1974). In In some some outcrops outcrops there there are aregranitic graniticfragments. fragments. This the rock rock was was interpreted interpreted by by Puffett Puffett(1975) (1975) as asan anintensely intenselydeformed deformed pyroclastic pyroclastic deposit. deposit. The lies north north of the The Lighthouse Lighthouse Point Point Member Member lies the Nealy Nealy Creek Creek Member Member and and mi2(18 (18km2) km2)area. area. This This member member encompasses encompasses two different different crops out out in in'aa77mi2 crops relatively coarse-grained coarse-grained amphibolite, amphibolite, and and layered layered amphibolitic amphibolitic schist schist lithologies: lithologies: relatively Morgan and and DeCristoforo DeCristoforo (see (see Day Day 22 Road Road Log, Log, Stops Stops C C and and D, D,this thisvolume). volume). Morgan (1980) (1980) have have interpreted interpreted the the coarse-grained coarse-grained amphibolite amphibolite to be be gabbro. gabbro. The The layers layers in in the the layered layered amphibolite amphibolite are are interpreted interpreted as as flattened flattened pillows pillows and and the the material material between between the the layers layers isis often oftenwell-foliated. well-foliated. The The flattened flattened pillows pillows may may be due due to to that much This author author suggests suggests that much of the the deformation. This primary processes processes or to to deformation. primary flattening flattening is due due to tohigh highstrain. strain. The western western one-third one-third of the the southern southern part part isisunderlain underlain Western One-Third. One-Third. The Western by Kitchi Kitchi Schist Schist and and Deer Deer Lake LakePeridotite Peridotite(discussed (discussed under under Intrusive IntrusiveRocks) Rocks) be changed 2). The The name name "Kitchi "Kitchi Schist" Schist" should should likewise likewise be changed to "Kitchi "Kitchi (Figure 2). Kitchi Schist Schist crops crops out in in aa 12 12mi2 mi2(30 (30 km2) km2) area area and and consists consists of of Group". The Kitchi To the the east east of of the the Deer Deer Lake Lake Peridotite Peridotite itit consists consists of of dominant lithologies. lithologies. To three dominant quartz-sericite quartz-sericite phyllites phyllites and and schists, schists, commonly commonly containing containing feldspar feldspar phenocrysts phenocrysts and and lithic lithic fragments, fragments, (see (see Day Day 22 Road Road Log, Log, Stop Stop A, A, this thisvolume) volume)and andcoarse coarsebreccias breccias (see Day 22 Road Road Log, Log, Stop Stop B, B, this thisvolume). volume). The phyllites phyllites and and schists schists are areandesite andesite to dacite dacite in in composition composition and and are are interpreted interpreted as as interbedded interbedded pyroclastic pyroclastic fall and and coarse breccias breccias consist consist flow deposits, deposits, volcaniclastic volcaniclastic sediments, sediments, and lava lava flows. flows. The coarse of porphyritic porphyritic andesite-dacite andesite-dacite clasts clasts surrounded surrounded by quartz-sericite-chlorite quartz-sericite-chlorite matrix. matrix. The breccias sorted, but but locally along the the south shore of breccias are mostly mostly poorly poorly sorted, locally along of Deer Deer layering isisconspicuous conspicuous (Brozdowski, (Brozdowski, 1988, 1988, personal personal communication). communication). They They Lake layering A- 9 �are areinterpreted interpretedasassubaqueous subaqueousmudflows mudflowsand andpyroclastic pyroclastic flow flowdeposits. deposits. To Tothe the west west of ofthe theDeer DeerLake LakePeridotite, Peridotite,the theKitchi KitchiSchist Schistconsists consistsofofmafic maficvolcanic volcanicand and gabbroic gabbroic rocks rocks which whichmay mayunderlie underliethe theintermediate intermediatecomposition compositionvolcanic volcanicrocks rockstoto theeast east(Brozdowski, (Brozdowski, this thisvolume; volume;Brozdowski Brozdowski and andothers, others,1986). 1986). Stratigraphic Stratigraphictop top the direction consistently direction ininthe theKitchi KitchiSchist Schistis is consistentlysouth south(Brozdowski, (Brozdowski,1988, 1988,personal personal communication). communication). IntrusiveRocks. Rocks. The TheDeer DeerLake LakePeridotite, Peridotite,now nowpredominantly predominantlya aserpentinite, serpentinite, Intrusive mi2(5(5 km2) km2) area area (see (see Field Field Guide GuidetotoCallahan CallahanMining Mining crops out out in' i daa22mi2 crops Corporation Corporation Ropes Ropes Mine Mine Property, Property, this volume), volume), and is is surrounded surrounded by by Kitchi Kitchi Serpentine pseudomorphs pseudomorphs after olivine olivine and and pyroxene pyroxene are are Schist (Figure (Figure2). 2). Serpentine Schist Insome someserpentinite serpentinite there thereare are common and and the therock rockcontains containseuhedral euhedralmagnetite. magnetite. In common Foliated serpentinite serpentinite occurs occurs near near textures textures which which are areindicative indicative ofofcumulate cumulateorigin. origin. Foliated Near the the Ropes Ropes Mine, Mine, the theserpentinite serpentiniteisis the contacts contacts and and atatthe theRopes RopesMine. Mine. Near the Bornhorst and and altered altered also also to to aatalc-carbonate talc-carbonate rock rock(Bornhorst (Bornhorstand andothers, others,1986). 1986). Bornhorst others others (1986) (1986) interpret interpret the the Deer Deer Lake Lake Peridotite Peridotite as as an andiscordant discordantintrusive intrusivebody body with with structural structural contacts contacts whereas whereas Brozdowski Brozdowski and others others (1986) (1986) agree agree on on the theoverall overall intrusive intrusive nature nature of of the the body body but butinterpret interpretitsitscontacts contactsasasbeing beingmore moreconcordant concordant and hence hence more moresill-like. sill-like. and Where recognized, recognized, Dikes Dikes of of Archean Archean gabbro gabbro cut cut the theMona Monaand andKitchi KitchiSchists. Schists. Where these these intrusions intrusions were were mapped mapped most most commonly commonly as as metadiabase metadiabase of of uncertain uncertain age age Dikes of of rhyolite rhyolite cut cut the thebasalt basalt relations relations (Puffett, (Puffett, 1974; 1974; Gair Gair and andThaden, Thaden,1968). 1968). Dikes and and gabbro, gabbro, but but the theage agerelationship relationship between between the the rhyolite rhyolite dikes dikes and andthe thegranitoid granitoid plutons plutons is is less less clear; clear; only only aa few fewsimilar-appearing similar-appearing rhyolite rhyolite dikes dikes cut cutthe theplutons. plutons. The The textures textures of of the therhyolite rhyolitedikes dikesare areporphyritic porphyritic(most (most common), common), aphanitic, aphanitic, and and granular (least (leastcommon). common). Porphyritic Porphyritic rhyolite rhyolite is is composed composed of phenocrysts phenocrysts of of granular quartz quartz with with or or without without feldspar feldspar set setinina avery veryfine-grained fine-grainedgroundmass. groundmass. The The granular granular rhyolite rhyolite dikes dikes show show aa textural textural continuum continuum totogranitoid granitoid plutons. plutons. Undifferentiated part of of Figure 2) 2) and and the theDead Dead Undifferentiated granitoid granitoid plutons plutons (southwest (southwest part A—1O �River Pluton Pluton cut cutthe thegreenstone greenstonebelt. belt. The The Dead Dead River River Pluton Pluton isisaacomposite composite River pluton pluton and and consists consists of of granodiorite, granodiorite, diorite, diorite, and andsyenite syenite(Puffett, (Puffett,1974). 1974). The The southwestern southwestern granitoid granitoid plutons plutons have have been been poorly poorly studied, studied, but butmost mostare areprobably probably At the thePeppin PeppinProspect Prospect(3.5 (3.5 miles miles NW NW of of the theRopes RopesMine), Mine),Boben Boben granodiorite. At granodiorite. (1986) described described aa trondhjemite. trondhjemite. The The Archean Archean granitoid granitoid plutons plutons are areinterpreted interpreted asas (1986) syn- totopost-tectonic. post- tectonic. synGEOCHEMISTRY GEOCHEMISTRY There There aie are now now over over200 200major majorand andtrace traceelement elementanalyses analyses from fromthe theMarquette Marquette Most trace trace element element data data have have been been determined determined by by XRF X R Fand and GreenstoneBelt. Belt. Most Greenstone Geochemically the basaltic basaltic lava lava flows flows and and gabbroic gabbroicintrusives intrusives about 20 20 by byINAA. INAA. Geochemically about are are tholeiitic, tholeiitic, whereas whereas the the andesite andesite to to dacite dacite fragmental fragmental rocks rocks and andrhyolite rhyolite Although variable, variable, the the chemical chemical compositions compositions of of the the intrusives are arecalc-alkalic. calc-alkalic. Although intrusives basalts composibasalts and gabbros gabbros overlap overlap to the the extent extent that that they they must mustbe beconsidered considered compositionally tionally similar, similar, and and totohave havesimilar similarpetrogenetic petrogenetichistories. histories. To To demonstrate demonstrate that the the belt belt isis dominantly dominantly basalt basalt with with aa scattering scattering of of compositions compositions towards towards rhyolite, rhyolite, Bornhorst Bornhorst and and Baxter Baxter (1987) (1987) multiplied multiplied the thesurface surface area area of of each each major major unit unit of ofthe thegreenstone greenstone belt belt (as (as an anindication indication of of volume volume Of the the lesser lesser relations) relations) by by the therepresentative representativeaverage averagechemical chemicalcomposition. composition. Of number number of of silicic silicic rocks, rocks, more more compositions compositions fall near near the the andesite-dacite andesite-dacite boundary boundary than i.e., the thebelt beltisisvery verymildly mildlybimodal. bimodal. than on on either either side, side, i.e., The The few few analyses analyses of of granitoid granitoid plutonic plutonic rocks rocks suggest suggest that that the the granitoids granitoids are are calc-alkalic in in affinity. affinity. On On aa variety variety ofofcompositional compositional diagrams, diagrams, the the rhyolite rhyolite dikes dikes caic-alkalic that that cut cut the the greenstone greenstone belt belt lie lie on on similar similar trends trends with with the the plutonic plutonic rocks rocks and and The rhyolite rhyolite dikes dikes overlap overlap the the chemical chemical composition composition of the the more more silicic silicicplutons. plutons. The are parts of are interpreted interpreted as as late-stage, late-stage, generally generally more more evolved evolved parts of the the plutons plutons that that intrude the the greenstone greenstone belt. belt. intrude METAMORPHISM METAMORPHISM The The rocks rocks of of the thegreenstone greenstone belt beltwere weremetamorphosed metamorphosed from from greenschist greenschist toto A-li �amphibolite facies facies during during the Archean. During the Penokean Penokean orogeny, orogeny, the amphibolite Archean. During Archean rocks rocks were were subjected subjected to to greenschist facies metamorphism metamorphismand, and, in in areas areas of of Archean greenschist facies amphibolite facies, facies, this denoted by retrograde amphibolite this Penokean Penokean metamorphism metamorphism isis denoted retrograde assemassemblages. Archean greenschist facies facies was was elevated elevated to to the Archean regional regional greenschist the amphibolite amphibolite facies facies in relatively relatively restricted restricted areas. areas. STRUCTURE STRUCTURE Archean structural structural geology of the Marquette Archean geology of Marquette Greenstone Greenstone Belt Belt is dominated dominated by by E-W, to N-S N-S faults, faults, but but some data suggest suggest that that the the belt belt has E-W, NW-SE, NW-SE, to some data has been been subFor example, from north north of of the jected to to multiple multiple deformations. deformations. For example, from the Dead Dead River River jected Storage Basin, Johnson Johnson and and others have described Storage Basin, others (1987) (1987) have described an Archean, Archean, steeplysteeply- plunging, anticline with with dimensions on the the order of This fold plunging, synformal synformal anticline dimensions on of miles. miles. This fold requires aatt least Archean deformation. deformation. requires least two two periods periods of of Archean Similarly, the Mona-Kitchi Similarly, the Mona-Kitchi structural relationship relationship described describedearlier earlierrequires requiresatat least least two two periods periods of of Archean structural Archean deformation. The Archean Archean rocks rocks are are overlain overlain by by Early Early Proterozoic Proterozoic supracrustal supracrustal rocks rocks which which were deformed were deformed during the the Penokean Penokean orogeny orogeny (1900 (1900 to to 1800 1800 Ma). Ma). Although reactiAlthough reacti- vation of Archean Archean structures structures during during the the Penokean Penokean orogeny orogeny can can be be documented documented vation clearly, various various lines lines of of evidence evidencesuggest suggestthat thatmost mostofof the the structure structure in in the clearly, greenstone belt belt represents greenstone represents Archean Archean deformation. deformation. Local Local Faults and Shear Shear Zones Zones dips steeply; dips near In the the Marquette Marquette Greenstone Greenstone Belt Belt most most stratification stratification dips steeply; dips near The rocks are variably foliated, but but on vertical vertical (+1_be) (+/-lo0) are are quite quite common. common. The rocks are variably foliated, on both both a local local and and regional regional scale scale there there are are linear linear zones zones along along which which the foliation foliation is is better better zones of of higher These zones higher strain may may be be faults faults developed developed than than in in surrounding surrounding rocks. rocks. These Where stratigraphic stratigraphicunits unitsare are offset offset they they are mapped mapped as as faults. faults. or shear shear zones. zones. Where North North of the the Dead Dead River River Storage Storage Basin Basin many many high high strain strain zones zones are are too too small small Faults are are of of brittle-ductile brittle-ductile and and to show to show at 1:6000 1:6000 (1 inch inch equals equals 500 500 feet). feet). Faults ductile types, ductile types, and and displacement displacement may be be mostly mostly vertical. vertical. A-12 These faults faults are are also These also of �two older roughly E-W faults truncated two general general ages: ages: older roughly E-W truncated by by younger younger N-S N-S faults faults (Johnson and and others, others, 1987). 1987). (Johnson South South of the the Dead Dead River River Storage Storage Basin, Basin, Clark Clark and and others others (1975) (1975) interpreted interpreted the distinct Kitchi Kitchi and and Mona to be aa Mona Schists Schists to the contact contact between between the the lithologically lithologically distinct shear shear zone zone (Figure (Figure 2), and and contacts contacts of of the the Deer Deer Lake LakePeridotite Peridotitehave havealso alsobeen been interpreted interpreted as either either faults faults or orshear shearzones zones(Clark (Clark and andothers, others,1975; 1975;Rossell, Rossell, 1983). 1983). Regional Regional Faults Faults and Shear Shear Zones Zones The Belt is affected The Marquette Marquette Greenstone Greenstone Belt affected by by two two regional regional Archean Archean shear shear along the the entire southern Extending along southern boundary boundary of of the the greenstone greenstone zones (Figure 2). 2). Extending belt isis the the Carp CarpRiver RiverFalls FallsShear Shear Zone Zone (Puffett, (Puffett,1974). 1974). Rocks Rocks along along this shear shear zone are both both intensely intensely foliated foliated and altered altered (see (see Day Day I1Road RoadLog, Log,progression progression the full full width However, the width of the the shear shear zone zone isis from Stops Stops 11 to 3, 3, this thisvolume). volume). However, from not not known known since since a part part of ofititwas wasreactivated reactivatedduring duringthe thePenokean Penokean orogeny, orogeny, juxtaposing juxtaposing more more altered and and sheared sheared Archean Archean rocks rocks against against less less deformed deformed Early Early width of of this this zone zone is is up to exposed width to 1500 1500 ft f t (450 (450 m) m) Proterozoic sediments. sediments. The exposed as documented documented by by detailed detailed mapping mapping (Brozdowski, (Brozdowski, 1988, 1988,personal personal communication). communication). Since this shear is cut by Since this shear zone zone is by much much less less deformed deformed mafic mafic dikes dikes of of Archean Archean age age (Baxter and Bornhorst, 1988), itit must must be be Archean Archean in in age. age. This shear zone zone may may be be (Baxter and Bornhorst, 1988), part of of the theGreat GreatLakes LakesTectonic TectonicZone ZoneofofSims Sims(1980). (1980). The second cuts through second major major structural structural zone zone cuts through the middle middle of of the the greenstone greenstone belt and As and isis termed termed the the Dead Dead River River Shear Shear Zone Zone (Puffett, (Puffett, 1974) 1974) (Figure (Figure 2). 2). As recognized by Puffett Puffett (1974), the shear recognized by (1974), the shear zone zone lies lies within within the the Sheared Sheared Rhyolite Rhyolite Tuff Member of the Mona Member of Mona Schist Schist (near (near the east east end end of of the theDead DeadRiver RiverStorage StorageBasin). Basin). In this with the interpretathis area area detailed detailed gravity gravity and and magnetic magnetic data data are consistent consistent with interpretation of of aasteeply steeplydipping dippingshear shearzone zone(Weeks, (Weeks,1987). 1987). The Dead Dead River River Shear Shear Zone Zone can be be extended extended to to the the west west ititwas wasreactivated reactivated during duringthe thePenokean Penokean orogeny, orogeny, juxtaposing Archean and and Early Early Proterozoic Proterozoicrocks rocksinin aa manner manner similar similar to to the Carp juxtaposing Archean Carp Falls Shear Shear Zone. Zone. In the the west, west, the the existence existence of the the shear shear zone zone isis indicated indicated River Falls A-13 �by by well-foliated well-foliated and and altered altered Archean Archean rocks rocks along along the Archean Archean and Early Early ProteroProterozoic zoic contact contact (see (see Day Day 11 Road Road Log, Log, Stop Stop 5,5, this this volume). volume). ItIt isisproposed proposed that that the the eastward of this shear eastward extension extension of shear zone zone follows follows the Lighthouse Lighthouse Point Point Member Member of the the Mona Mona Schist Schist which which is interpreted interpreted as as having having been been subjected subjected to to high high strain strain(see (see Road Road Log Log Day Day 2, 2, Stops Stops C C and and D). D). Thus, Thus, the the Dead Dead River River Shear Shear Zone Zone represents represents aa NW-SE NW-SE trending trending fault, with with unknown unknown displacement, displacement, that that bisects bisects the the Marquette Marquette Greenstone Greenstone Belt. Belt. PRECIOUS PRECIOUS METAL 'METALMINERALIZATION MINERALIZATION Of Of the the numerous numerous base base and and precious precious metal metal occurrences occurrences in in the the belt belt(Bodwell, (Bodwell, 1972), the Ropes 1972), the Ropes Mine Mine is the the most most significant significant orebody orebody to to date date (Figure (Figure 2). 2). The The Ropes Ropes Mine Mine has has been been described described by byBornhorst Bornhorst and andothers others(1986) (1986)and andBrozdowski Brozdowski It has has been been mined mined for for Au Au and and others others (1986) (1986) and and ininthis thisvolume volumebybyBrozdowski. Brozdowski. It Metallic minerals minerals are are dominated dominated and Ag Ag and and has has aa Au/Ag Au/Ag ratio ratio of of about about 11 to to 5.5. Metallic and by by pyrite, pyrite, with with lesser lesser other othersulfides 'sulfidessuch such asastetrahedrite, tetrahedrite,galena, galena,and andchalcopyrite. chalcopyrite. Certain Certain parts parts of of the the Ropes Ropes Mine Mine show show aa good good correlation correlation between between abundance abundance of Au Au and and fine finepyrite pyrite(Brozdowski, (Brozdowski, this thisvolume). volume). Non-metallic Non-metallic alteration alteration minerals minerals are are dominated dominated by by quartz quartz and and carbonate carbonate with with varying varying amounts amounts of of sericite, sericite, chlorite chlorite talc. The The ore ore host host rock rock for for the theRopes Ropesorebody orebody isis interpreted interpreted by byBornhorst Bornhorst and talc. and others others (1986) (1986) and and Brozdowski Brozdowski and others others (1986) (1986) as as aa dacitic daciticvolcaniclastic volcaniclastic rock rock and Bornhorst Bornhorst agree agree that the Both Brozdowski Brozdowski and the within within the the Deer Deer Lake Lake Peridotite. Peridotite. Both mineralization epigenetic,but but differ differ in their mineralization isis epigenetic, their interpretation interpretation of of mechanism mechanism of of and others (1986) emplacement. Brozdowski Brozdowski and (1986) suggest suggest that precious precious metals metals were were emplacement. concentrated concentrated by hydrothermal hydrothermal fluids fluids related related to to emplacement emplacement of peridotite peridotite sills sills Bornhorst and others others (1986) (1986) suggest suggest that the the orebody orebody was was (Deer Lake Lake Peridotite). Peridotite). Bornhorst (Deer syntectonic and that that hydrothermal fluids followed followed aa zone of relatively syntectonic and hydrothermal fluids zone of relatively high high strain, strain, (this volume) volume) describes describesaa structural structural genetic Brozdowski (this genetic model model for shear zone. zone. Brozdowski a shear the Ropes orebody. Ropes orebody. Other less less important important occurrences occurrences of of mineralization mineralization present present as asdisseminations disseminations A- 14 �and in in quartz quartz veins, veins, are are associated associated with with all the the major major Archean Archean rock rock types. types. Most of the the occurrences occurrences are interpreted interpreted as as epigenetic, epigenetic, but at at some some poorly poorly studied studied localities the the mineralization localities mineralization may be be syngenetic. syngenetic. The description The description that that follows follows applies to epigenetic applies epigenetic mineralization. mineralization. Mineralization is commonly spatially associated associated with with faults and Mineralization is commonly spatially and shear shear zones, zones, and is interpreted and interpreted as synsyn- to to post-tectonic. post-tectonic. Sulfide Sulfide minerals minerals are significant significant indicators of precious indicators precious metal metal mineralization. mineralization. quartz and quartz-carbonate quartz-carbonate veins. veins. Pyrite and in Pyrite occurs as disseminations disseminations and in Pyrrhotite, chalcopyrite, Pyrrhotite, chalcopyrite, and arsenopyrite arsenopyrite are are less less abundant abundant than pyrite. pyrite. In studies studies carried carried out out atatMichigan MichiganTechnological Technological % University, no anomalous Au or or Ag Ag values were obtained obtained from from any any sample University, no anomalous Au values were sample of of rock rock and galena or quartz quartz vein vein that that was was free free of of sulfides. sulfides. Sphalerite Sphalerite and galena are found found at at some some occurrences, and these tend to occurrences, and these minerals minerals tend to be be more more commonly commonly associated associated with with anomalous Ag, whereas whereas the the yellow Abundance of anomalous Ag, yellow sulfides sulfides are associated associated with Au. Au. Abundance sulfides in a rock, as measured measured by by abundance abundance of sulfur, sulfur, isis poorly poorly correlated correlated with with sulfides in rock, as chlorite, and and sericite occur as the abundance of Au. the abundance of Au. Quartz, Quartz, carbonate, carbonate, chlorite, as wall-rock wall-rock alteration quartz and carbonate alteration minerals; minerals; quartz carbonate also also occur occur as as vein veinminerals mineralsassociated associated with precious with precious metal metal anomalies. anomalies. The that there there appear The present present data permit permit the the tentative tentative suggestion suggestion that appear to have have been at least been least two two major major pulses pulses of ofmineralization. mineralization. An early pulse An pulse resulted resulted in in pervasive quartz quartz and and carbonate carbonate alteration alteration and and was was accompanied accompaniedby by gold, gold, pyrite pyrite and pervasive other yellow sulfide minerals, and abundant other yellow sulfide minerals, and abundant chlorite chlorite and and sericite. sericite. Quartz-carbonate veins are associated with this early veins associated with early pulse. pulse. Detailed Detailed studies by by Callahan Callahan Mining Mining Corporation (Brozdowski, 1988, personal personal communication) communication) indicate indicate that significant Corporation (Brozdowski, 1988, significant occurrences of of gold mineralization with structures parallel occurrences mineralization are associated associated with parallel and and conjugate to layering conjugate layering between between rock rock types. types. A later later pulse pulse of of mineralization mineralization was was dominated by quartz-carbonate dominated by quartz-carbonate veins containing containing base metal metal sulfides sulfides (pyrite, (pyrite, galena, galena, sphalerite, with little little or or no at the sphalerite, with no Au), Au), although although the the relatively relatively abundant abundant galena galena at the Ropes Mine Mine may may be be an an exception. exception. The The extent extent of country country rock rock alteration alteration associassociRopes ated ated with this this latter latter pulse pulse may may have have been been less less than than that that associated associated with with the the earlier earlier A-15 �pulse. At At some some individual individual prospects prospects aa paragenetic paragenetic succession succession of of metallic metallic and and pulse. non-metallic non-metallic minerals minerals can be be recognized recognized within within aapulse. pulse. SUMMARY SUMMARY The The Marquette Marquette Greenstone Greenstone belt belt consists consists of of several several thousand thousand feet feet ofofsubaqueous subaqueous mafic mafic to to silicic silicicvolcanic volcanic flows, flows,pyroclastics, pyroclastics, and andvolcaniclastic volcaniclastic sediments. sediments. These These are are intruded intruded by by gabbro gabbro and and rhyolite rhyolite dikes dikes and and by by granitoid granitoid plutons, plutons, all all of ofArchean Archean The belt belt also alsoincludes includes two twoperidotite peridotitebodies. bodies. age. The age. All All of of these these rocks rocks have have been been 1 metamorphosed from greenschist to amphibolite metamorphosed from greenschist to amphibolite facies facies and subjected subjected to to multiple multiple deformation. Precious Precious metal metal mineralization mineralization is is dominantly dominantly epigenetic. epigenetic. The The Archean Archean deformation. geologic history of of the geologic history the belt belt isisobscured obscured by byunconformably-overlying unconformably-overlying Early Early Proterozoic sediments and and by deformation Proterozoic sediments deformation during during the the Penokean Penokean orogeny. orogeny. The potential potential for for discovery discovery of of new new economic economic deposits deposits of precious precious metals metals in in the the Marquette Marquette Greenstone Greenstone Belt Belt is is denoted denoted by by anomalous anomalous Au Au values, values, quartz quartzand and carbonate carbonate veins, veins, areas areas of of pervasive pervasive alteration, alteration, areas areas of of relatively relatively abundant abundant faults faults and and shear shear zones, zones, and andoverall overallgeologic geologic setting. setting. ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS I thank thank the the present present and andformer formergraduate graduate students students who who have have spent spent many many hours hours working on the geology of the Belt and and with working on geology of the Marquette Marquette Greenstone Greenstone Belt with whom whom I have have They include: include: D. D. Baxter, Baxter, C. C. Boben, Boben, R. R. Johnson, Johnson, M. M. had many many fruitful fruitfuldiscussions. discussions. They MacLellan, have benefited benefited from from numernumerMacLellan, E. Owens, Owens, D. D. Rossell, Rossell, and and T. T.Shepeck. Shepeck. I have Michigan Geological Geological ous Kalliokoski. The Michigan ous conversations conversations with with my my colleague, colleague, J.J.Kalliokoski. Survey, of Natural Survey, Department Department of Natural Resources Resources and the the Department Department of of Geology Geology and and Geological University have Geological Engineering, Engineering, Michigan Michigan Technological Technological University have supported supported my my D. Schueller Schueller and and D. D. program program of research research on on the theMarquette Marquette Greenstone GreenstoneBelt. Belt. D. paper was was improved improved by by Baxter provided comments commentson onaa draft draft of this Baxter provided this paper. paper. This paper the reviews reviews of of J.J.Kalliokoski, Kalliokoski,Michigan Michigan Technological Technological University, University, and and K. K.Schulz, Schulz, S. Geological Geological Survey. Survey. U. S. A-16 �REFERENCES Baxter, T.J., 1988, Mafic Intrusions of Baxter, D.A. D.A. and Bornhorst, Bornhorst, T.J., 1988, Multiple Multiple Discrete Discrete Mafic Intrusions of Archean to Keweenawan Archean Keweenawan Age, Age, western western Upper Peninsula, Peninsula, Michigan, Michigan, [abs.]: [abs.]: ProceedProceedings and Abstracts, ings Abstracts, 34th 34th Institute Institute on on Lake Lake Superior Superior Geology, Geology, Marquette, Marquette, Michigan, Michigan, (this volume). volume). Boben, comparison of of three three precious Boben, C.A., C.A., 1986, 1986, Geological Geological comparison precious metal metal prospects prospects in in Marquette County, County, Michigan: M.S. Thesis, Thesis, Michigan MichiganTechnological Technlogical University, Marquette Michigan: M.S. Houghton, 77 p. Houghton, p. Bodwell, W.A., W.A., 1972, 1972, Geologic Geologiccompilation compilationand and non-ferrous non-ferrous metal potential, Bodwell, potential, Precambrian Precambrian section, section, northern Michigan: Michigan: M.S. M.S. Thesis, Thesis, Michigan Michigan Technological Technological University, University, Houghton, Houghton, 106 106 p. p. 1 Bornhorst, T.J. T.J. and Baxter, character of of Archean Bornhorst, Baxter, D.A., D.A., 1987, 1987, Geochemical Geochemical character Archean rocks rocks from the the east east half half ofofthe theNorthern NorthernComplex, Complex,Upper UpperPeninsula, Peninsula,Michigan: Michigan: Institute Proceedingsand and Abstracts, Abstracts,v.v. 33, 33, part part 1, Institute on Lake Lake Superior Superior Geology Geology Proceedings 1, p. p. 12. 12. Bornhorst, T.J., T.J., Shepeck, A.W. and and Rossell, Rossell, D.M., D.M., 1986, 1986, The The Ropes Ropes gold Bornhorst, Shepeck, A.W. gold mine, Marquette County, Michigan, U.S.A.: in in MacDonald, MacDonald,A. A. J., 1., Ed., Ed., Proceedings of Marquette County, Michigan, U.S.A.: Proceedings of Gold on the the Geology of Gold, Toronto, Gold 86, an an International International Symposium Symposium on Geology of Toronto, 1986, 1986, p. p. 2213-227. 13-227. Brozdowski, R.A., Gleason, Gleason, R.J. R.J. and and Scott, Brozdowski, R.A., Scott, G.W., G.W., 1986, 1986, The Ropes Ropes Mine: Mine: A A pyritic gold deposit Archean volcaniclastic volcaniclastic rock, rock, Ishpeming, Ishpeming, Michigan, Michigan, U.S.A.: U.S.A.: pyritic deposit in in Archean A. J., in MacDonald, MacDonald, A. J., Ed., Ed., Proceedings Proceedings of Gold Gold 86, 86, an anInternational International Symposium Symposium on on the Geology of Gold, the Geology of Gold, Toronto, Toronto, 1986, 1986, p. p. 228-242. 228-242. Cannon, and Klasner, map of of the Cannon, W.F. W.F. and Klasner, J.S., J.S., 1977, 1977, Bedrock Bedrock geologic geologic map the southern southern part of the part the Diorite Diorite and andChampion Champion 77 1/2-minute 1/2-minute quadrangles, quadrangles, Marquette Marquette County, County, Michigan: U. S. Michigan: S. Geological Geological Survey Survey Miscellaneous Miscellaneous Investigation Series Series Map Map 1-1058. 1-1058. Card, K.D. of the #I. Subdivisions Subdivisions of the Superior Superior Card, K.D. and and Ciesielski, Ciesielski, A., A., 1986, 1986, DNAG DNAG #1. Province of the Province of the Canadian Canadian Shield: Shield: Geoscience Geoscience Canada, Canada, v. v. 13, no. no. 1, p. 5-13. 5-13. Clark, L.D., Clark, L.D., Cannon, Cannon, W.F. W.F. and Klasner, Klasner, J.S., J.S., 1975, 1975, Bedrock Bedrock geologic geologic map map of the Negaunee quadrangle, Marquette Marquette County, Negaunee SW SW quadrangle, County, Michigan: Michigan: U. S. S. Geological Geological Survey Survey Geologic Geologic Quadrangle Quadrangle Map Map GQGQ-1226. 1226. Gair, J.E. and Gair, and Thaden, Thaden, R.E., R.E., 1968, 1968, Geology Geology of the the Marquette Marquette and and Sands Sands quadrangles, Geological Survey Professional Professional quadrangles, Marquette Marquette County, Michigan: Michigan: U. U. S. S. Geological Paper Paper 397, 397, 77 p. p. Johnson, R.C., Bornhorst, T.J. and VanAlstine, 1987, Geologic Geologic setting setting of of Johnson, R.C., Bornhorst, T.J. VanAlstine, J.L., J.L., 1987, precious metal metal mineralization mineralizationinin the the Silver Silver Creek Creek to to Island Island Lake Lake area, Marquette precious Marquette County, Michigan: Michigan Geological GeologicalSurvey SurveyDivision, Division,Department Department of of Natural County, Michigan: Michigan Natural Resources, Open-File Open-File Report Report OFR-87-4, OFR-87-4, Supersedes OFR-86-2, 134 Resources, Supersedes OFR-86-2, 134 p. Morgan, evolution of of the Morgan, P.J. P.J. and DeCristoforo, DeCristoforo, D.T., D.T., 1980, 1980, Geological Geological evolution Ishpeming Greenstone Greenstone Belt, Belt, Michigan, Ishpeming Michigan, U.S.A.: U.S.A.: Precambrian Precambrian Research, v. v. 11, p. 23-41. Puffett, W.P., of the Puffett, W.P., 1974, 1974, Geology Geology of the Negaunee Negaunee quadrangle, quadrangle, Marquette Marquette County, County, Michigan: U. U. S. Geological Professional Paper Paper 788, 788, 51 p. Michigan: Geological Survey Survey Professional p. A-17 �Rossell, D.M., 1983, 1983, Alteration Alterationofof the the Deer Rossell, D.M., Deer Lake Peridotite Peridotite near the the Ropes Ropes Mine, Marquette County, Mine, County, Michigan: Michigan: M.S. M.S. Thesis, Michigan Michigan Technological Technological University, Houghton, sity, Houghton, 83 p. Sims, P.K., 1980, and gneiss Sims, P.K., 1980, Boundary Boundary between between Archean Archean greenstone greenstone and gneiss terranes terranes in in northern Wisconsin and Michigan: Geological Society Society of of America northern Wisconsin and Michigan: Geological America Special Paper 182, 182, p. 113-124. 113-124. Trow, in the Trow, J., 1979, 1979, Final Final report report diamond diamond drilling drilling for geologic geologic information information in the Middle Precambrian basins basins in in the the western Middle Precambrian western portion portion of of northern northern Michigan: Michigan: Michigan Michigan Geological Survey, Survey, Department Departmentofof Natural Natural Resources, Resources, Open-File Open-File Report Report UDOE Geological OFR GJBX-162(79), 44 p. OFR GJBX-162(79), 44 Weeks, V., V., 1987, 1987, Gravity Gravity and and magnetic investigationsinin the the south-central Weeks, magnetic investigations south-central part part of the the Ishpeming Ishpeming Greenstone Greenstone Belt, Belt, Marquette Marquette County, County, Michigan: Michigan: M.S. M.S. Thesis, Thesis, Michigan Houghton, Michigan ~Tchnological t k h n o l o ~ i cUniversity, aUniversity, l Houghton, 61 61 p. p. A-lB �Geological Frameworkofof aa Part of Geological Framework of the theArchean Archean Marquette Marquette Greenstone Belt North Greenstone Belt North of the the Dead Dead River River Storage Storage Basin Basin D.A. D.A. Baxter Baxter and and M.L. M.L. MacLellan MacLellan Department Department of of Geology Geology and andGeological Geological Engineering, Engineering, Michigan Michigan Technological Technological University, Houghton, Houghton, Michigan Michigan 49931 49931 INTRODUCTION INTRODUCTION The Archean Archean Marquette Marquette Greenstone Greenstone Belt Belt underlies underlies approximately approximately 125 125mi2 mi2(325 (325 km2) of northern km2) of northern Marquette Marquette County County in in Michigan's Michigan's western western Upper Upper Peninsula Peninsula / belt is divided greenstone belt divided into northern northern and and southern southern portions portions by by (Figure (Figure 1). 1). The greenstone a structural structural zone zone which which parallels parallels the the Dead Dead River River Storage Storage Basin Basin (Bornhorst, (Bornhorst, this this volume). The southern southern part of of the the greenstone greenstone belt belt and and the the metasediments metasediments of the the volume). part of the Marquette The northern northern part the Marquette Supergroup Supergroup were were mapped mapped by by the theU.S.G.S. U.S.G.S. The belt was and the remainder was partially partially mapped mapped by the the U.S.G.S. U.S.G.S. and remainder was was included included on on the the 1:60,000 compilationmap map of of the northern aim of of 1:60,000 compilation northern complex complex by by Bodwell Bodwell (1972). (1972). The aim this paper of the paper is is to to briefly briefly describe describe the the geology geology of the northern northern part of of the the Archean Archean Marquette Belt based based on on detailed Marquette Greenstone Greenstone Belt detailed mapping mapping of the the southwest southwest 25 25 mi2 mi2(65 (65 km2). km2). Archean Archean rocks rocks of the the northern northern part partconsist consist ofofdominantly dominantlysubaqueous subaqueous mafic mafic lava and pyroclastic of lava flows, flows, and minor, minor, interbedded interbedded volcaniclastic volcaniclastic and pyroclastic deposits deposits of All of of these these rocks rocks are are assigned assigned to to intermediate and iron formation. intermediate composition composition and formation. All the Yolcanics of Silver Mine Lakes, Lakes, an an informal formation name name used used to to distinVolcanics of Silver Mine informal formation guish strata from guish these these strata from the remainder remainder of the the Mona Mona Schist Schist which which is situated situated on on the the southern side of of the southern side the Dead Dead River River Shear Shear Zone, Zone, an an Archean Archean structural structural zone zone with with aa large, large, but but unknown, unknown, degree degree of ofmovement. movement. The volcanic volcanic package package has has been been intruded intruded by by gabbro gabbro and and subsequently subsequently by rhyolite rhyolite and and granodiorite granodiorite of of Archean Archean age. age. The rhyolite rhyolite is is interpreted interpreted as as aa more more evolved evolved equivalent equivalent of of the the granodiorite granodiorite to to tonalite 1987). tonalite plutonic plutonic rocks rocks (Bornhorst (Bornhorst and and Baxter, Baxter, 1987). A- 19 �T5ON T49N T48N o• 0 30 60 60 90 90 30 M iles Miles 0 o I I I 50 100 100150 150 50 I 1 I Km. Km. Regional geology geology and location location map map of of the the Figure 1.1. Regional Figure Marquette Marquette Greenstone Greenstone Belt Belt (modified (modifiedfrom from Morgan and DeCristoforo, 1980). Morgan and DeCristoforo, 1980). A-20 �VOLCANICS VOLCANICS OF SILVER SILVER MINE MINE LAKES LAKES The Volcanics 'The Volcanics of Silver Silver Mine Mine Lakes Lakes (MacLellan (MacLellan and and Bornhorst, Bornhorst, 1988) 1988) are are named for a succession of Archean Archean volcanic volcanicunits unitsthat thatcrop crop out out in in the vicinity named for succession of vicinity of and Bornhorst, Silver Mine Mine Lakes. Lakes. Detailed Detailed mapping mapping (MacLellan (MacLellan and Bornhorst, 1988; 1988; Baxter and and Silver others, and others, and Bornhorst, has distinothers, 1987; 1987; Johnson Johnson and others, 1987; 1987; Owens Owens and Bornhorst, 1985) 1985) has guished guished five members: members: Pillowed Pillowed Basalt Basalt Member, Member, Breccia Breccia Member Member of Bismark Bismark Creek, Member of of Reany Creek, Breccia Breccia Member Reany Lake, Lake, Iron Iron Formation Formation Member, Member, and the the Hill's Hill's of the Lake Pyroclastic Pyroclastic Member Member (Figure (Figure 2). 2). Relative Relative ages ages of the members members are are based based on on the presence presence of of pillows pillows as as top top indicators indicators in in the thePillowed Pillowed Basalt Basalt Member. Member. The The members are too members are too small small to to be be distinguished distinguished at at74 7+minute minutequadrangle quadranglescale scale (1:24,000). Pillowed Pillowed Basalt Basalt Member Member This member member has been been subdivided subdivided into three three varieties, varieties, normal, normal, foliated, foliated, and and contacts between between these these varieties varieties are are altered, altered, based based on on various various criteria. criteria. The contacts gradational. gradational. dark green green to green-black This variety variety is commonly commonly dark green-black in in Normal Normal Variety. Variety. This color, color, fine-grained fine-grained to to aphanitic, aphanitic, and and massive massive to to moderately moderately foliated foliated (see (see Day Day 11 Visible mineralogy mineralogy includes very very Road Road Log, Log, Stops Stops 6 and and 10, 10, this this volume). volume). Visible fine-grained and sericite, fine-grained chlorite, chlorite, very very fine-grained fine-grained plagioclase plagioclase and sericite, and rarely rarely fine-grained plagioclase plagioclase crystals crystals often show show relict relict fine-grained amphibole. amphibole. Very fine-grained Elongate, variably variably flattened pillows pillows are are found found locally locally igneous igneous microlite microlite textures. textures. Elongate, and range feet (30-250 (30-250cm) cm) inin length length and and 3-30 range from from 1—8 1-8 feet 3-30 inches inches (8-76 (8-76 cm) cm) in in thickness. Some pillows show show small small bands bands of of vesicles vesicles (1/16-1 (1/16-1 inch, 2-25 Some pillows 2-25 mm) mm) is common common to find find interpillow interpillow void void space space filled filled with with the chilled chilled margins. margins. It is along the fewplaces, places, stratigraphic stratigraphic tops tops have have been been to gray gray carbonate carbonate material. material. In aa few tan to determined cuspate pillows pillows shapes. shapes. determined from the the cuspate Quartz and quartz-carbonate veinsfrom fromless lessthan than 1/16 1/16 inch inch (2 (2 mm) Quartz and quartz-carbonate veins mm) to 99 veins can can inches (23 cm) in width width can can be be found foundthroughout throughout this this variety. variety. The veins inches (23 cm) A-21 �___________________________ Correlation of Archean Archean Units Units and Volcanic and Sedimentary Rocks Rocks Intrusive Rocks Rocks c Granodiorite Granodiorite of Rocking Rocking Chair Lakes Lakes rhyolite Intrusive Rhyolite Intrusive of of Altered Fire Center Center Mine Mine Variety I Gabbro of Gabbro of I Altered Altered 1 1 Clark Creek Creek 1 Variety 1 7 Foliated Variety Variety Highly Altered Variety Hill's L a k e Pyroclastic Pyroclastic Member Hiils Lake Member j [ Volcanics of Silver Mine Lakes Silver I Iron Formation Member Member a. P- Breccia Member Member of Reany Reany Lake Lake Breccia Member Member of Bismark Bismark Creek Creek Figure 2. A 2 A-- 222 �carry up up to to5% 5% sulfides sulfides and and there there may may be be up uptoto2% 2%disseminated disseminated sulfides sulfides in in the the carry sulfides occur occur throughout throughout much much of of this unit adjacent Disseminated sulfides unit and and adjacent basalts. basalts. Disseminated are usually usually >> 95% 95% pyrite pyrite with with minor minor amounts amounts of of chalcopyrite, chalcopyrite, pyrrhotite, pyrrhotite, and and are arsenopyrite. arsenopyrite. This variety variety ranges ranges in in color color from from medium medium gray-black gray-black to to Foliated Foliated Variety. Variety. This It has has an an aphanitic aphanitic texture, texture, aaphyllonitic phyllonitic to to schistose schistose fabric, fabric, and and isis green-black. green-black. It composed dominantly of of chlorite composed dominantly chlorite with lesser lesser amounts amounts of plagioclase plagioclase and/or sericite, sericite, quartz and andqarbonate. carbonate. Some Some exposures exposures contain contain up up to to40% 40% secondary secondary carbonate carbonate quartz (ankerite) (ankerite) as as the the matrix matrix of ofbrecciated brecciated basalt. basalt. Other Other exposures exposures contain contain alternating alternating light light and and dark dark layers layers which which are are interpreted interpreted as as tectonic tectonic layering layering resulting resulting from from highly elongated elongated pillows. pillows. The The alternating alternating layers layers originated originated from from darker darkerpillow pillow highly interiors Some outcrops may may also also have have interiors surrounded surrounded by by lighter lighter colored colored pillow pillow rinds. rinds. Some originally originally been been basalt basalt tuffs and and the the layering layering may may reflect reflecthighly highlyelongated elongated lithic lithic pyrite is is found fragments. Disseminated Disseminated pyrite found throughout throughout this variçty variety and and can can occur occur fragments. locally locally in in concentrations concentrations up up toto30%. 30%. The highly highly altered altered variety variety of of the thePillowed Pillowed Basalt Basalt Highly Highly Altered Altered Variety. Variety. The Member is dark Member is dark to light light gray gray in color color and takes takes on a green green hue hue near near the the gradagradational tional contact contact with with the the normal, normal, less less altered altered variety variety (see (see Day Day 11 Road Road Log, Log, Stops Stops 44 The basalt basalt is is aphanitic aphanitic to to very very fine-grained fine-grained and andisiscomposed composed 5, this this volume). volume). The and 5, of varying varying quantities quantities of of chlorite, chlorite, carbonate, carbonate, sericite, sericite, plagioclase, plagioclase, and and quartz. quartz. The The rocks rocks are are predominantly predominantly chioritized, chloritized, with with carbonatization, carbonatization, sericitization, sericitization, and and silicification The fabric fabric varies varies from from massive massive to to very very silicification occurring occurring in in varying varying degrees. degrees. The the degree degree of of foliation in this Typically, the foliation in this variety variety is as as high high as as the the highly foliated. foliated. Typically, highly rare cases, cases, deformed deformed and andundeformed undeformed pillow pillow structures structures foliated basalt basalt variety. variety. In rare can still still be be observed observed on onweathered weatheredsurfaces. surfaces. Disseminated mineralizationisismost most abundant abundant in in this this variety Sulfide Disseminated mineralization variety of of basalt. basalt. Sulfide minerals can reach reach up to minerals can to 20 20 volume volume percent percent of of the theoutcrop, outcrop, but buttypically typicallyaverage average veins, similar similar to to those Quartz and quartz-carbonate quartz-carbonate veins, those found found in in the the 2 4 % . Quartz only 2-6%. general, both both types types of of foliated foliated variety, variety, also also occur occur in in this this variety. variety. In general, A- 23 �mineralization mineralization are are related related totowell wellfoliated foliatedstructural structuralzones. zones. Breccia Member Member of ofBismark BismarkCreek Creek Breccia The TheBreccia Breccia Member Member of of Bismark Bismark Creek Creek isislocated located along alongaamajor majorNW-SE NW-SE trending trendingstructural structuralzone, zone,the theWillow WillowCreek CreekShear ShearZone Zone(MacLellan (MacLellan and andBornhorst, Bornhorst, 1988) (see (see Day Day 11Road Road Log, Log, Stop Stop9,9,this thisvolume). volume). There There ar areatatleast leastthree threetypes types 1988) ofofclasts clastsininthis thisunit: unit:boudinaged boudinagedporphyritic porphyriticrhyolite rhyolite(similar (similartotothe theRhyolite Rhyolite Intrusive The Intrusive of of Fire FireCenter CenterMine), Mine),wispy wispygabbro, gabbro,and andboudinaged boudinagedgranodiorite. granodiorite. The clasts in shape and range from 1/2 to le&oidal to elongate elongate in shape and range from to 3/4 3/4 inches inches (1-2 (1-2 clasts are are lensoidal cm) cm) for for the thelensoidal lensoidal type, type, and and up up to to 4-6 4-6 inches inches (10-15 (10-15 cm) cm) in in width width by by 3-6 3-6 feet feet (1-2 meters) meters) ininlength lengthfor forthe theelongate elongatetype. type. Clasts Clasts are are supported supported in in an an (1-2 Both the the matrix matrix and and the therhyolite rhyolite clasts clasts contain contain up uptoto epidote-rich basaltic basalticmatrix. matrix. Both epidote-rich This unit unit isisinterpreted interpretedasasa amudflow mudflowbreccia. breccia. 5% disseminated disseminated pyrite. pyrite. This 5% Breccia Member Member of of Reany ReanyLake Lake Breccia I The The Breccia Breccia Member Member of Reany Reany Lake, Lake, best best exposed exposed near near Reany Reany Lake, Lake, isis aa breccia breccia with with aa strike strikelength length of ofatatleast least5 5miles miles(8(8kilometers) kilometers)(see (seeDay Day 1 1Road Road Log, Stop Stop 8,8,this thisvolume). volume). The The unit unitisiscorrelative correlativewith withthe theMudflow MudflowMember Member Log, described by by Baxter Baxter and andothers others(1987). (1987). The The breccia breccia clasts clasts are are white, white, gray, gray, or or described brown whereas the the matrix matrix weathers weathers to to aa brown on on both both weathered weathered and and fresh fresh surfaces, surfaces, whereas The lower lower light light green-tan green-tan color color and and isisaagreen-black green-black color coloron onfresh freshsurfaces. surfaces. The portion portion of of the theunit unitcontains containsvery veryfew fewlarge largeclasts clastsand andwas wasmapped mappedasasclast-poor, clast-poor, whereas whereas the the upper upper portion portion contains contains up up to to 35% 35% clasts clasts of of all allsizes sizes and andwas wasmapped mapped In some some exposures, exposures, there there isis second second clast-poor clast-poor zone zone as the theclast-rich clast-rich horizon. horizon. In as above the the clast-rich clast-rich zone. zone. above The The clast-poor clast-poor horizon horizon has has equant equant to to oblong, oblong, sub-angular sub-angular totosub-rounded sub-rounded grains grains of of volcanic volcanic rock rock which which rarely rarely exceed exceed 1/3 1/3 inch inch (1 (1 cm) cm)ininsize. size. The The matrix matrix is is medium medium to to fine-grained, fine-grained, intermediate intermediate totomafic maficinincomposition, composition,with withoccasional occasional The clast-poor clast-poor horizon horizon isis 1/16 to to 1/8 1/8inch inch(1-3 (1-3mm) mm)grains grainsofoffeldspar. feldspar. The 1/16 interpreted mudflow or or aa reworked reworked tuff tuff deposit. deposit. interpreted as either either aa well-sorted well-sorted mudflow A- 24 �In the horizon the the clasts clasts are matrix In the clast—rich clast-rich horizon matrix supported. supported. Shapes vary vary from Shapes highly elongate to to sub-equant and rounding highly elongate sub-equant and rounding from very very angular angular to to rounded. rounded. The The more more equant equant clasts clasts are generally generally 1/3-4 113-4 inches inches (1-10 (1-10 cm) cm) across across while while the the elongated elongated fragments can reach reach lengths of up to fragments can lengths of to 10 10inches inches (25 (25 cm). It is is important important to to note note that about of the This, coupled about 50% 50% of the clasts clasts are are white, white, gray, gray, and and black black cherts. cherts. This, coupled with with the fact fact that that aacherty chertyiron-formation iron-formation overlies overlies this this unit, unit, suggests suggests that that these these cherts cherts may may have have formed formed in in aa volcanic volcanic vent vent region region and andwere werebrecciated brecciated during duringexplosive explosive Theremaining remaining clasts clasts are are fine-grained, fine-grained, porphyritic porphyritic andesites. andesites. eruptions. lhe The matrix is very very similar similar to the the material material in in the the clast-poor clast-poor horizon. horizon. Therefore, matrix Therefore, we we t also also interpret interpret the the clast-rich clast-rich horizon horizon as as aamudflow mudflow breccia breccia deposit. deposit. Iron Formation Formation Member Member The Iron Iron Formation Formation Member, Member, which which overlies overlies the Breccia Breccia Member Member of of Reany Reany Lake, consists consists ofof gray, gray, dark dark gray, Lake, gray, to black black banded banded rock with with alternating alternating bands bands of micro-crystallinechert chertand and magnetite, magnetite,or or iron-rich iron-rich chert chert (see micro-crystalline (see Day Day 11 Road Road Log, Log, Stop 10, Stop 10, this this volume). volume). In some the unit unit is is a black, some localities, localities, the black, cherty cherty iron iron formation containing formation containing up to to 2-5% 2-5% disseminated disseminated sulfides, sulfides, mainly mainly pyrite. pyrite. These cherty layers are cross-cut which may may contain contain up up to 20% cherty layers are cross-cut by carbonate carbonate veinlets veinlets which 20% suif ides. sulfides. At Clark Clark Creek, Creek, the the iron iron formation formation is is gray gray in in color color and andshows shows very very distinctive distinctive interlayering of micro-crystalline interlayering of micro- crystalline quartz quartz and and massive massive magnetite. magnetite. This locality locality also also contains clots clots of of sulfides through the the rock, often contains sulfides scattered scattered through often associated associated with with the the carbonate veins that fill 5% carbonate veins fill tension tension gashes. gashes. The sulfides sulfides comprise comprise a maximum maximum of of 5% of the whole whole rock. rock. Hill's Hill's Lake Lake Pyroclastic Pyroclastic Member Member The Hill's of white white to tan The Hill's Lake Pyroclastic Pyroclastic isis aa breccia breccia composed composed of tan dacite dacite clasts clam in aa black in black schistose schistose basalt basalt matrix. matrix. The clasts are flattened The clasts are flattened and and give give vertical vertical The metamorphic gradeofof this this unit unit is metamorphic grade is lower lower surfaces surfaces a banded banded appearance. appearance. The clasts consist consist of plagioclase plagioclase and quartz with with minor minor hornblende, hornblende, and quartz amphibolite. The clasts A-25 �The matrix matrixisiscomposed composedofofhornblende, hornblende,plagioclase, plagioclase,biotite, biotite, sericite, and andepidote. epidote. The sericite, and garnet, garnet, with withminor minorsericite, sericite,chlorite, chlorite,tourmaline, tourmaline,and andclinozoisite/epidote clinozoisite/epidote and (Johnson and and others, others,1987). 1987). (Johnson GABBRO OF OFCLARK CLARKCREEK CREEK GABBRO The The Gabbro Gabbro of of Clark ClarkCreek Creek(MacLellan (MacLellan and and Bornhorst, Bornhorst, 1988) 1988) is is named named for for gabbro gabbro intrusives intrusives that that cut cutthe theVolcanics Volcanics of of Silver Silver Mine Mine Lakes Lakes near nearClark ClarkCreek Creek and 10, 10,this thisvolume). volume). The The gabbro gabbro isismedium medium toto (see Day Day 11Road RoadLog, Log, Stops Stops5,5, 8,8, and (see dark dark green-black green-black on on aafresh freshsurface, surface,holocrystalline, holocrystalline, medium medium to to very verycoarsecoarseThe mineralogy mineralogy is is blue-green blue-green grained, and and massive massive to tostrongly strongly foliated. foliated. The grained, amphibole, chlorite, and minor amphibole, plagioclase, plagioclase, chlorite, minor pyrite, pyrite, magnetite, magnetite, and andpyrrhotite. pyrrhotite. The The more more foliated foliated zones zones within within the the gabbro gabbro have have aamuch muchhigher higherpercentage percentage ofofchlorite chlorite which causes causes aa deeper deepergreen greencolor. color. which There There is is also also an an altered altered variety variety of of gabbro gabbro which which is is medium medium to to dark dark gray gray inin color color with with plagioclase plagioclase crystals crystals forming augens augens surrounded surrounded by chlorite, chlorite, carbonate, carbonate, This rock rock has has an an undulating, undulating, schistose schistose texture on on the the quartz, and andsericite. sericite. This quartz, foliation surface. surface. The The intensity intensity of of alteration alteration isis greater greater near near zones zones of ofintense intense foliation foliation. foliation. RHYOLITE RHYOLITE INTRUSIVE INTRUSIVE OF OF FIRE FIRECENTER CENTER MINE MINE The The Rhyolite Rhyolite Intrusive Intrusive of of Fire FireCenter CenterMine Mine(Johnson (Johnson and andothers, others, 1987) 1987)has has three three common common textural textural types types and cuts cuts the the volcanics volcanics and and the the gabbro gabbro(see (seeDay Day1 1 The first first two, two, porphyritic porphyritic and and 7, this thisvolume). volume). The Road Log, Log, Stops Stops 5,6, 5,6, and and 7, Road The third third isis aphanitic, aphanitic, but but granular, granular, are are grouped grouped together together as as the thenormal normalvariety. variety. The since itit is is typically typically altered, altered, itit isistermed termed the thealtered alteredvariety. variety. since Quartz-porphyritic Quartz-porphyritic rhyolite rhyolite is the most most common common textural textural type, type, with with anhedral anhedral phenocrysts of quartz, 1/16 1/16 to to 5/16 5/16 inches inches (2-8 (2-8mm) mm)across. across. The The other other porphyporphyphenocrysts of quartz, ritic ritic type type isisquartz-feldspar quartz-feldspar porphyritic porphyritic rhyolite, rhyolite, with with phenocrysts phenocrysts of of subhedral subhedral potassium feldspar and/or and/or plagioclase as well well as anhedral potassium feldspar plagioclase as anhedral quartz quartz of of similar similar size. size. The The matrix matrix in in both both types types isisfine-grained fine-grained totoaphanitic aphanitic and andconsists consists of of quartz, quartz, A- 26 �from dark gray Color varies varies from gray to to light light gray gray carbonate, carbonate, feldspar, feldspar, and and minor minor sericite. sericite. Color The granular granular type type isisgenerally generally light light pink pinkwith withroughly roughlyequidimensional equidimensional to to pink. pink. The quartz Disseminated quartz and and feldspar feldspar grains, grains, 1/16 1/16 to to 3/16 3/16inches inches(2-5 (2-5mm) mm)across. across. Disseminated sulfides sulfides are present present in in amounts amounts of of usually usually less less than than 1%. 1%. The The altered altered variety variety is is aalight lightgreen greentotogreen-gray, green-gray-aphanitic, aphanitic,schistose schistose rock. rock. identified in in the thefield fieldprimarily primarily by bycolor color and andlack lackofofvisible visiblegrains. grains. The The It isis identified rock is is composed composed of partially partially recrystallized recrystallized quartz, quartz, feldspar, feldspar, and and interstitial interstitial sericite sericite which may may define define aa crude crude foliation. foliation. There are are up up toto8% 8%disseminated disseminated sulfides sulfides in in which the altered altered variety. variety. the GRANODIORITE GRANODIORITE OF ROCKING ROCKING CHAIR CHAIR LAKES LAKES The Granodiorite Granodiorite of Rocking Rocking Chair Chair Lakes Lakes was was named named by by Johnson Johnson and and others others (1987) plutons which which intrude intrude the Volcanics (1987) for dominantly dominantly granodioritic granodioritic plutons Volcanics of Silver Silver intrusive contacts contacts are are often often sheared sheared Mine Mine Lakes Lakes and Gabbro Gabbro of of Clark Clark Creek. Creek. The intrusive of Fire Fire Center Rhyolite Intrusive Intrusive of Center Mine Mine is interpreted interpreted as aa and/or faulted. faulted. The Rhyolite late-stage, late-stage, more more evolved evolved equivalent equivalent of the the granodiorite granodiorite plutons plutons (Baxter, (Baxter, 1988; 1988; t Johnson 1987; Bornhorst Bornhorst and and Baxter, Baxter, 1987). 1987). Johnson others, 1987; The Granodiorite of Rocking Granodiorite of Rocking Chair Chair Lakes Lakes is medium medium gray gray to light light pink, pink, medium to coarse to allotriomorphic granular, and and is medium to coarse grained, grained, hypidiomorphic hypidiomorphic to allotriomorphic granular, composed dominantly of of granodiorite composed dominantly granodiorite with with lesser lesser tonalite, tonalite, quartz quartz monzonite, monzonite, quartz quartz monzodiorite, and quartz diorite monzodiorite, and diorite (using (using aaStreckeisen Streckeisen diagram). diagram). The The massive massive granodiorite is composed of plagioclase, K-feldspar, quartz, quartz, amphibole, granodiorite is composed of plagioclase, K-feldspar, amphibole, and minor minor more amphibole-rich amphibole-rich sericite, sericite, epidote, epidote, chlorite, chlorite, apatite, apatite, and and carbonate. carbonate. A more granodiorite, owing it's it's origin granodiorite, owing origin to the the assimilation assimilation of amphibole amphibole from from the the mafic mafic country country rocks, rocks, is typically typically aa darker gray gray in in color color and and mediummedium- to to fine-grained. fine-grained. The altered altered variety variety is red red to to orange, orange, finefine- totomedium-grained, medium-grained, and and isis cross-cut cross-cut by by foliated variety, variety, found found along along intrusive intrusive contacts, contacts, is aa stockwork stockwork quartz quartz veins. veins. The foliated mineralogy of of gray gray to black, black, fine-grained fine-grained totoaphanitic, aphanitic, schistose schistose mylonite. mylonite. The mineralogy this of plagioclase, chlorite, K-feldspar, K-feldspar, quartz, quartz, and minor this variety variety consists consists of plagioclase, chlorite, minor apatite, apatite, A-27 �sericite, and epidote sericite, epidote (Johnson (Johnson and and others, others, 1987). 1987). STRUCTURE STRUCTURE The rocks The rocks in the the northern northern part part of of the theMarquette Marquette Greenstone Greenstone Belt Belt were were affected in the Archean affected by several several deformational deformational episodes episodes in Archean and and Lower Lower Proterozoic Proterozoic The first first event event folded, folded, sheared, sheared, faulted, faulted, and andmetamorphosed metamorphosed the the (Penokean). Archean rocks of the Archean rocks the Marquette Marquette Greenstone Greenstone Belt Belt in in Archean Archean time. time. A later later event event folded, folded, faulted, faulted, and and metamorphosed metamorphosed the the Lower Lower Proterozoic Proterozoic sediments sediments and diabase diabase / of the and had had a less the Marquette Marquette Range Range Supergroup Supergroup and less definite definite effect effect on on Archean Archean minor reactivation reactivation of of Archean Archean faults faults may may have have taken rocks. Some Some minor taken place place during during between Archean Archean and and Penokean Distinguishing between Penokean metathe Penokean Penokean deformation. deformation. Distinguishing morphismisis difficult difficult since since they they are are both both greenschist facies,but but in in the Island morphism greenschist facies, Island Lake Area where Archean Archean metamorphism metamorphism reaches reaches amphibolite amphibolite facies, facies, Penokean Penokean metamormetamorArea phism is denoted and fabrics phism denoted by by retrograde retrograde assemblages assemblages and fabrics (Johnson (Johnson and and others, others, 1987). 1987). Foliations in the region Foliations in region are are defined defined by by slaty, slaty, phyllonitic, phyllonitic, and andschistose schistose cleavages and generally These cleavages cleavages generally trend trend N70°W. N70¡W These cleavages are most most prominently prominently displayed in in the lepidoblastic displayed lepidoblastic textured, mafic mafic rocks. rocks. Most in the Most foliations foliations in the Archean rocks rocks are are interpreted interpreted to to have Archean have been been formed formed during the the Late Late Archean Archean tectonic event. event. The Archean Archean rocks rocks in the the area area of of Silver Silver Mine Mine Lakes, Lakes, Clark Clark Creek, Creek, and Silver Creek lie lie on the and Silver Creek the southern southern limb limb of of aasteeply steeply plunging, plunging, synformal synformal anticline (Johnson The nose anticline (Johnson and others, others, 1987). 1987). The nose of of this this regional regional fold fold is is exposed exposed to to the of Silver Creek where where the the hinge hinge region region of of this the northwest northwest of Silver Creek this structure structure has has been been intruded intruded by the the Granodiorite Granodiorite of of Rocking Rocking Chair Chair Lakes. Lakes. There are are several generationsofof faults faults in in the region There several generations region that that faults faults probably probably formed Archean deformational deformational event. event. The oldest formed during during various various pulses pulses of the the Late Late Archean oldest faults faults in the the area area generally generally trend trend southeast-northwest southeast-northwest to east-west, east-west, are are generally generally ductile ductile in nature, nature, and and would would be be termed termed shear shear zones zones in in Ontario. Ontario. A large large structural structural zone, zone, the Dead Dead River River Shear Shear Zone, Zone, also also trends trends southeast-northwest, southeast-northwest, and and was was This zone initiated during the zone is typified typified by by steeply steeply dipping, dipping, phyllonitic phyllonitic initiated the Archean. Archean. This A-28 �to highly highly schistose schistose volcanic volcanic rocks. rocks. It originated originated as an Archean Archean ductile ductile shear shear zone zone which subsequentlyhad had aa minor minor portion portion reactivated reactivated as as aa relatively brittle fault relatively brittle which subsequently during the the Early Early Proterozoic. Proterozoic. Earlier faults and and shear are truncated, Earlier Archean Archean faults shear zones zones are truncated, and locally locally offset by by slightly slightly younger, younger, north-south north-south to to northeast-southwest northeast-southwest trending trending Archean Archean faults. faults. The deformational regimefor for these these faults faults was was relatively relatively brittle brittle in in contrast deformational regime contrast to the the older older ductile faults. faults. It is is likely likely that that movement movement along along these these faults faults took took place place in the the waning stages' stages'ofof the the Archean Archean deformational deformationalevent eventbecause becausethey theyoffset offset the the zone waning zone of highly altered basalts. highly basalts. MINERALIZATION Mineralization in the region Mineralization in region exists exists in in two two forms: forms: 1)1)disseminated disseminated sulfides sulfides within altered 2) quartz-carbonate-sulfide quartz-carbonate-sulfide veins. veins. within altered country rocks, rocks, and and 2) Disseminated mineralization most prominent prominent in in the the highly mineralization isis most highly altered altered variety of of the thePillowed Pillowed Basalt Member Member and and in in the Iron Basalt Iron Formation Formation Member, Member, but but also also occurs occurs occasionally occasionally in pyrite and sporadic other Archean Archean rock rock types. types. It consists consists of disseminated disseminated pyrite sporadic minor minor pyrrhotite and The alteration minerals in in the country alteration minerals country rocks rocks are are and chalcopyrite. chalcopyrite. The primarily primarily chlorite, chlorite, sericite, sericite, carbonate, carbonate, and and quartz. quartz. The veins of quartz of chlorite, The veins of quartz and and carbonate, carbonate, and lesser lesser amounts amounts of chlorite, are often often associated with shear zones associated with zones and and faults. faults. The chief chief sulfide sulfide mineral mineral is pyrite pyrite with with much much lesser lesser amounts amounts of chalcopyrite, chalcopyrite, arsenopyrite, arsenopyrite, and pyrrhotite. pyrrhotite. Locally, galena Locally, galena and sphalerite sphalerite are the the dominant dominant sulfide sulfide vein vein minerals. minerals. In general, general, it appears appears that that two two episodes episodes of of mineralization mineralization have have affected the the volcanicsand and intrusives intrusivesofof the the northern northern part part of the volcanics the Marquette Marquette Greenstone Greenstone Belt. Belt. The early early episode episode produced produced the majority majority of of the the disseminated disseminated mineralization mineralization and was likely likely controlled controlled by by the the location of the east-west was location of east-west trending trending faults faults and and shear shear for the the production of zones This event event was was also also responsible responsible for production of zones of intense intense zones. This carbonatization, sericitization, and chioritization. chloritization. The second second episode episode produced produced carbonatization, sericitization, primarily carbonate-quartz veins with primarily carbonate-quartz veins with associated associated galena, galena, sphalerite, sphalerite, and chalcopyrite chalcopyrite A— 29 �These veins veins are are localized localized near near the the areas areas of ofyounger, younger,north-south, north-south, mineralization. These mineralization. brittlefaults. faults. Anomalous Anomalous precious precious metal metal values values can be be found found associated associated with with both both brittle episodes of of hydrothermal hydrothermalmineralization. mineralization. episodes GEOLOGICHISTORY HISTORY GEOLOGIC The The earliest earliest event event in in the theregion region north northofofthe theDead DeadRiver RiverStorage StorageBasin Basin was was the the extrusion extrusion of of the thesub-aqueous, sub-aqueous, tholeiitic, tholeiitic, pillow pillow basalts basalts that that form formthe thePillowed Pillowed Basalt Member Member of of the theVolcanics Volcanics of of Silver SilverMine MineLakes. Lakes. The The age age of of these thesebasalts basalts isis Basalt / about about 2.7 2.7 Ga Ga based based on on the theradiometric radiometric age age dating dating of of aarhyolite rhyoliteintrusive intrusivewhich which cuts basalt basalt beneath beneath the theClark ClarkCreek CreekBasin Basin(Trow, (Trow,1979). 1979). During During eruption eruption of of the the cuts basalts, basalts, several several thin mafic mafic to to intermediate intermediate volcanic volcanic mudflow mudflow breccias breccias that that contain contain locally abundant abundant iron iron formation formation debris debris were were deposited. deposited. Continued Continued extrusion extrusion of of locally subaqueous lava lava flows flows produced produced additional additional pillow pillow basalts. basalts. The The volcanic volcanic pile pile was was subaqueous then intruded intruded by by dikes dikes and andsills sillsofofgabbro gabbro(Gabbro (GabbroofofClark ClarkCreek). Creek). The The mafic mafic then rocks deformed and and intruded intruded by by syn- to rocks were were synchronously synchronously deformed to post-tectonic post-tectonic rhyolite rhyolite and granodiorite granodiorite (2.7 (2.7 Ga). Ga). The The rhyolites rhyolites may may represent represent differentiated differentiated portions portions of of and the the granodiorite granodiorite plutons plutons (Bornhorst (Bornhorst and and Baxter, Baxter, 1987). 1987). An An episode episode of synsyn- to to post-tectonic post-tectonic hydrothermal hydrothermal alteration alteration resulted resulted in in the theprecious preciousmetal metalmineralization. mineralization. The The Late Late Archean Archean deformation deformation and and hydrothermal hydrothermal activity activity also also produced produced the the foliated foliated and and altered altered varieties varieties of of the thePillowed Pillowed Basalt Basalt Member Member of of the theVolcanics Volcanics of of Silver Mine Mine Lakes. Lakes. Silver ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS The The co-operative co-operative research research effort which which made made this this study study possible possible was was funded funded by of the by the the Michigan Michigan Geological Geological Survey Survey Division Division of the Department Department of of Natural Natural Resources Resources and the the Department Department of of Geology Geology and andGeological Geological Engineering Engineering atat Michigan Michigan This paper paper has has benefited benefited from from discussions discussions with with Ted Ted Technological University. University. This Technological Bornhorst, Rod Rod Johnson, Johnson, Jo Jo Kalliokoski, Kalliokoski, and and Eric Eric Owens. Owens. Careful Careful review review of of this this Bornhorst, paper paper by by Ted TedBornhorst, Bornhorst, Jo JoKalliokoski, Kalliokoski, and andKlaus KlausSchulz Schulzare arealso alsoacknowledged. acknowledged. A- 30 �REFERENCES REFERENCES Baxter, Baxter, D.A., D.A., 1988, 1988, Geology, Geology, Geochemistry, Geochemistry, and and Hydrothermal Hydrothermal Alteration Alteration Associated with Precious in the Clark Associated with Precious Metal Metal Mineralization Mineralization in Clark Creek Creek Region, Region, Marquette Marquette County, County, Michigan: Michigan: M.S. M.S. Thesis, Thesis, Michigan Michigan Technological Technological University, University, Houghton, Michigan Michigan (in (in preparation). preparation). Houghton, Baxter, Baxter, D.A., D.A., Bornhorst, Bornhorst, T.J., T.J., and and VanAlstine, VanAlstine, J.L., J.L., 1987, 1987, Geology, Geology, Structure, Structure, and Metal Mineralization Mineralizationofof Archean ArcheanRocks Rocksinin the the Vicinity Vicinity of and Associated Associated Precious Precious Metal Clark Clark Creek, Creek, Marquette Marquette County, County,Michigan: Michigan:Michigan MichiganGeological Geological Survey SurveyDivision, Division, Department of Natural Open File File Report Department of Natural Resources, Resources, Open Report OFR-87-8, OFR-87-8, 54 54 pp. pp. Bodwell, Bodwell, W.A., W.A., 1972, 1972, Geologic Geologic Compilation Compilation and Nonferrous Nonferrous Metal Metal Potential, Potential, Precambrian Precambrian Section, Section, Northern Northern Michigan: Michigan: M.S. M.S. Thesis, Thesis, Michigan MichiganTechnological Technological University, University, Houghton, Houghton, Michigan, Michigan, 106 106 p. p. Bornhorst, T.J, and Baxter, Character of of Archean Bornhorst, T.J. Baxter, D.A., D.A., 1987, 1987, Geochemical Geochemical Character Archean Rocks Rocks from the the East East Half Half ofofthe theNorthern NorthernComplex, Complex,Upper UpperPeninsula, Peninsula,Michigan: Michigan: Institute Proceedingsand andAbstracts, Abstracts,v.v.33, 33, part part 1, Institute on Lake Lake Superior Superior Geology Geology Proceedings 1, p. 12. 12. Johnson, Johnson, R.C., R.C., Bornhorst, Bornhorst, T.J. T.J. and and VanAlstine, VanAlstine, J.L., J.L., 1987, 1987, Geologic Geologic Setting Setting of of Precious in the the Silver Precious Metal Metal Mineralization Mineralization in Silver Creek Creek to Island Island Lake Lake area, area,Marquette Marquette County, Michigan: Survey Division, Division, Department Department of of Natural Michigan: Michigan Michigan Geological Geological Survey Natural Resources, Open-File Report, OFR-86-2, 134 Resources, Open-File Report, OFR-87-4, OFR-87-4, Supersedes Supersedes OFR-86-2, 134 p. p. MacLellan, M.L. and Bornhorst, 1988, Geology, Geology, Structure, Structure, and and MineralizMineralizMacLellan, M.L. Bornhorst, T.J., 1988, ation ation of of the theReany ReanyLake LakeArea, Area,Marquette MarquetteCounty, County,Michigan: Michigan:Michigan MichiganGeological Geological Survey Department of of Natural Natural Resources, Resources, Open Open File File Report, Report, (in preparaSurvey Division, Division, Department preparation). Morgan, Evolution of of the Morgan, P.J. P.J. and and DeCristoforo, DeCristoforo, D.T., D.T., 1980, 1980, Geological Geological Evolution the Ishpeming Greenstone Belt, Belt, Michigan, Michigan, U.S.A.: U.S.A.:Precambrian PrecambrianResearch, Research,v.v. 11, 11, p. Ishpeming Greenstone 23-4 1. 23-41. Owens, Owens, E.O. E.O. and and Bornhorst, Bornhorst, T.J., T.J., 1985, 1985, Geology Geology and and Precious Precious Metal Metal MineralizMineralization ation of the the Fire FireCenter Centerand andHolyoke HolyokeMines MinesArea, Area, Marquette Marquette County, County, Michigan: Michigan: Michigan Survey Division, Division, Department Department of of Natural Resources, Michigan Geological Geological Survey Resources, Open Open File File Report OFR-85-2, OFR-85-2, 105 105 p. p. Report Trow, Trow, J., J., 1979, 1979, Final Final report report on on diamond diamond drilling drilling for forgeologic geologic information information in in the Middle basins in in the western Middle Precambrian Precambrian basins western portion portion of of northern northern Michigan: Michigan: Michigan Survey Division, Division, Department Department of of Natural Resources, Michigan Geological Geological Survey Resources, Open Open File File Report Report UDOE UDOE OFR GJBX-l62(79), GJBX-162(79), 44 p. p. A-31 �Geology of of the Ropes Geology Ropes Gold Gold Mine Mine R.A. R.A. Brozdowski Brozdowski Callahan Callahan Mining Mining Corporation Corporation Exploration Exploration Dept. Dept. 25 Industrial 25 Industrial Park Park Rd. Rd. Negaunee, Negaunee, Michigan, Michigan, 49866 49866 INTRODUCTION The mine is is located in the south-west The Ropes Ropes gold gold mine located in south-west part of of the the Archean Archean Marquette Greenstone Greenstone Belt, Belt, 5.8 5.8 km km northwest of the Marquette northwest of the town town of of Ishpeming, Ishpeming, Michigan, Michigan, 43', in at latitude latitude 46° 46' 32', 32', longitude longitude 87° 87' 43', in the the Sl/2 Sl/2NW1/4 NW1/4 Section Section 29, 29, T48N, T48N, R27W, R27W, / Ishpeming Township, Township, Marquette County, Ishpeming County, Michigan, Michigan, USA. USA. The mine The mine can be be reached by by traveling from US Hwy reached traveling northward northward from Hwy 41, west west via via paved paved County County Road Road west via via unpaved 573, then west unpaved County County Road Road GCL (the (the Ropes Ropes mine mine access access road). road). 573, HISTORY Julius Ropes, Julius Ropes, a druggist druggist and and prospector prospector from fromIshpeming, Ishpeming, Michigan, Michigan, discovered discovered a gold-bearing gold-bearing quartz stringer stringer in 1880 1880 while while prospecting prospecting for asbestos asbestos and serpentine "marble"ininlow lowground groundnear near the the east east end end of of the serpentine "marble" the present-day present-day Ropes Ropes prospectingresulted resultedinin discovery discoveryofof the the outcrop Continued prospecting outcrop of the the mine property. property. Continued Ropes main ore zone 250 m m west west of of the Ropes main zone approximately approximately 250 the initial initial discovery discovery (Allen, (Allen, 1912). 1912). The original The original Ropes Ropes mine operated operated sporadically sporadically from 1882 1882 to to 1897, 1897, producing 1029 Kg Kg of of Au Au and and 2057 2057 Kg of of Ag Ag from from 195,000 195,000 tonnes tonnes of of ore. ore. The producing 1029 The property idle, except property remained remained idle, except for minor minor cyanidization cyanidization of tailings, tailings, until until Calumet Calumet and Hecla Copper Co. Co. conducted extensive surface surface and underground Hecla Consolidated Consolidated Copper conducted extensive underground exploration from from 1935 to 1942 tonnes of of ore exploration 1935 to 1942 and outlined outlined 1,393,000 1,393,000 tonnes ore averaging averaging 3.98 3.98 The relatively low grade gradeofof the the deposit at a time g/tonne Au g/tonne Au (Broderick, (Broderick, 1945). 1945). The relatively low deposit at time of controlled of controlled gold gold prices, prices, combined combined with with wartime wartime restrictions restrictions on precious precious metals metals mining, precluded precluded any any production production at at that time. Mining Corporation mining, time. Callahan Callahan Mining Corporation of Phoenix, Arizona, Arizona, purchased purchased the the property property from from Arcadian Arcadian Copper Copper Mine Mine Tours Tours in Phoenix, 1975, began began exploration explorationinin 1979, 1979,and and made madeaa decision decisiontoto develop develop the the mine mine in in mid 1975, mid began in in September 1985, and and isis now Production began September 1985, now about about 1,800 1,800 tonnes tonnes per 1984. 1984. Production day. A-32 �GEOLOGY OF SW PART PART OF OFTHE THEMARQUETTE MARQUETTEGREENSTONE GREENSTONE BELT BELT GEOLOGY OF THE SW Rocks in the Rocks in the southwest southwest part of of the the Marquette Marquette Greenstone Greenstone Belt, Belt, which which host host the the Ropes of the lower Ropes mine, mine, generally generally have mineral mineral assemblages assemblages of lower greenschist greenschist facies, facies, except except in proximity proximity to the the granitoid granitoid rocks rocks which which bound bound the the greenstone greenstone belt, belt, where where amphibolite facies rocks rocks are charamphibolite facies facies assemblages assemblages occur. occur. The greenschist greenschist facies char- acterized by a sub-vertical acterized by sub-vertical planer planer foliation, foliation, defined by by aa weak weak parallelism parallelism of of aphanitic phyllosilicate minerals, which which is commonly phyllosilicate minerals, commonly conformable conformable to flow flow margins margins in volcanic volcanic rocks, rocks, graded graded bedding bedding in in graywackes, graywackes, and and compositional compositional layering layering in units units such such as as chert-magnetite chert-magnetite iron iron formation. formation. There There are relict relict cumulate cumulate textures textures in serpentinized peridotite, pillows in basalt, serpentinized peridotite, pillows in basalt, and and bipyramidal bipyramidal and and embayed embayed quartz quartz grains, and lithic Therefore, rocks grains, lithic fragments fragments in in volcaniclastic volcaniclastic rocks. rocks. Therefore, rocks with with readily readily recognizableprimary primarystructures structuresand andtextures texturesare arereferred referredtotohere here in in by by their recognizable sedimentary or igneous names as as recommended recommendedinin the the North North American Code of of sedimentary or igneous names American Code Stratigraphic nomenclature; the the prefix "meta-" Stratigraphic nomenclature; "meta-" is is impli€d. implied. Hydrothermally altered altered rocks in in the vicinityofof the the Ropes Ropes mine mineare are referred referred to to by by their rocks the immediate immediate vicinity dominant assemblageslisted listedinin decreasing decreasingorder order of of abundance, dominant mineral mineral assemblages abundance, such as "quartz—sericite-chlorite "quartz-sericite-chlorite rock." rock." The southwest part of the to ESE, southwest part the greenstone greenstone belt belt comprises, comprises, from from WNW WNW to ESE, aa sequence of: of: (1) pillowed sequence pillowed to massive massive tholeiitic tholeiitic basalt, basalt, associated associated hypabyssal hypabyssal gabbroic gabbroic sills and dikes, dikes, and and subordinate subordinate mafic-volcanic mafic-volcanic derived derived graywackes; graywackes; (2) sills (2) an inter—layeredzone zoneofofbasalt, basalt,dacite dacitetuff, tuff,and and porphyritic porphyritic dacite dacite sills; sills; (3) (3) dacite dacite tuff tuff inter-layered with subordinate tuff breccia, with subordinate tuff breccia, which which hosts hosts banded banded quartz-magnetite quartz-magnetite iron formation formation and quartzose immediately west west of of the Ropes (4) serpentinized, serpentinized, and quartzose graywacke graywacke immediately Ropes mine; mine; (4) and talc-altered fine grained grained peridotite, peridotite, which which is carbonatized carbonatized and talc-altered in proximity proximity to to the the conglomeratesand andtuff tuff breccias brecciasofof dccitic dcitic composiRopes mine; and (5) (5) volcanic volcanic conglomerates composiRopes mine; tion. The volcanic units strike strike ENE, ENE, dip subvertically, and top consistently to the The volcanic units subvertically, and consistently to the southeast, based based on pillow southeast, pillow facing facing directions directions and and graded graded bedding bedding (Callahan (Callahan Mining Mining Corporation geologic mapping core logs). logs). The serpentinized Corporation detailed detailed geologic mapping and and drill core serpentinized peridotite has a relict, peridotite has relict, fine fine grained grained cumulate cumulate texture texture and and was was likely likely aahypabyssal hypabyssal A- 33 �sill sill complex complex emplaced emplaced within within the the volcanic volcanic section, section, based based on its its fine finegrain grainsize sizeand and local local complex complex interlayering interlayering with with the thevolcanic volcanicrocks. rocks. The The rocks rocks which which most most directly directly host host the the Ropes Ropes mine mine represent represent one one ofofsix sixknown knownlocalities localitieswhere wherevolcanic volcanic rocks rocks are are interlayered interlayered with withthe theserpentinized serpentinizedperidotite peridotite(Callahan (CallahanMining Mining Corporation Corporation detailed detailed geologic geologic mapping mapping and drill drill core core logs); logs); other othervolcanic volcanic inliers inliers may may exist exist in in poorly poorly totonon nonoutcropping outcropping low low ground ground throughout throughout the the outcrop outcrop belt belt of of the serpentinized serpentinized peridotite. peridotite. the The The Ropes Ropes mine mine isis located located to to the thesoutheast southeast of of the thebasalt-to-dacite basalt-to-dacite transition transition The zone 1). The zone and and the the layers layers of ofbanded bandediron ironformation formationand andgraywackes graywackes(Figure (Figure1). , Ropes gold gold deposit depositisishosted hostedbyby quartz-sericite-chlorite rock interpreted asas Ropes quartz—sericite—chlorite rock interpreted hydrothermally altered dacite dacite tuff on hydrothermally altered on the thebasis basis ofofthe theprogressive progressivedevelopment development of of This alteration alteration gradationally gradationally replaces replaces and and pervasive pervasive quartz quartz and and sericite sericitealteration. alteration. This finally finally totally totally pseudomorphs pseudomorphs feldspar feldspar phenocrysts, phenocrysts, matrix feldspar, feldspar, and and felsic felsiclithic lithic fragments fragments in the the tuffs tuffsasasthe theRopes Ropesmine mineisisapproached approached from fromthe thewest. west.Similar Similar less less mobile mobile trace trace element element abundances abundances and and similar similar chondrite-normalized chondrite-normalized rare rare earth earth patterns dacite tuff patterns between between unaltered unaltered (except (except for for greenschist greenschist facies facies metamorphism) metamorphism) dacite to thethe quartz—sericite-chlorite quartz-sericite-chlorite rock rock which which hosts hosts to the thewest westofofthe theRopes Ropesmine mineand and the the Ropes Ropes deposit deposit also also provides provides evidence evidence for foraacommon commonorigin origin(Callahan (CallahanMining Mining Corp., unpublished unpublished data). data). Corp., GEOLOGY GEOLOGY OF OF THE THEMINE MINEAREA AREA There There are are four four main main rock rock types types within within the the immediate immediate mine mine area area: (1) (1) Fine Fine grained the ore zones, quartz-sericite-chlorite rock rock encloses encloses the zones, strikes strikes N70°E N70° and and dips dips grained quartz-sericite-chlorite This rock rock type type is is bounded bounded to the the north north and and south south by, by, (2) (2) fine fine steeply south. south. This steeply grained, grained, carbonate-quartz-chlorite carbonate-quartz-chlorite rock rock which which isismassive massivetotocompositionally compositionallylayered layered quartz-sericite-chlorite rock rock and and the the The quartz-sericite-chlorite on aascale scaleofofseveral severalmillimeters. millimeters. The on carbonate-quartz-chlorite carbonate-quartz-chlorite rock rock are are locally locally complexly complexly interlayered, interlayered, particularly particularly Contacts between between the two two rock rock 1, 2, 2, 3). 3). Contacts within and west west of the the mine mine (Figures (Figures 1, within The carbonate-quartz-chlorite carbonate-quartz-chlorite rock rock is is flanked flanked types are are generally generally sharp. sharp. The types A- 34 �'-4 U II L± - E1 Ti EXPLANATION FOR FIGURE 1 Basalt tuff Basalt (includes pillowed and glomerophyric basalt) Fine-grained mafic intrusions Graywacke and siltstone Banded quartz-magnetite iron formation Dacite tuff, tuff breccia and flows, minor andesite flows; altered to quartz-sericite-chlorite rock in mine area Compositionally layered to massive carbonate-quartz chlorite rock Carbonate-talc rock Carbonatized, serpentinized peridotite N Ct, Serpentinized fine-grained peridotite Ill LI : JHIH Quartzite Graywacke Geology v r -. JJpdip projection to surface of orebodies Shaft Fault (dotted where inferred) Field trip stop Paved road Unpaved road inferred) Contact (dotted where Symbols �a Figure 1. Geologic Map of the Ropes Mine area. Explanation on preceding page. �EXPLANAT ION EXPlANATION ELEVATION (ft.) ELEVATIO Serpentinized finefineSerpentinized IH I Ii 1400 grained peridot peridotite, grained ite, locally carbonatized carbonatized locally Carbonate-talc Carbonate-talc rock rock Compositionally Compositionally layered to to massive massive layered carbonate-quartzcarbonate-quartzchlorite chlorite rock rock 1200 LI 1000 I Quartz-sericiteQuartz-sericitechlorite rock rock chlorite Orebody Orebody >2 gg Au/tonne Aultonne >2 800 Mine Levels Levels Mine L 600 L L 400 Scale Scale 100 100 L 200 200ft. ft. 0 61 m. 200 100 L 61 rn. 200 ft. L Sea Sea Level Leva 0 Figure 2.2. Figure Ropes Ropes Mine Mine 600 600 EE Cross-Section Cross-Section looking SS 80° 80' WW looking — 200 400 A-37 �Scale 61 m. -H 200 ft. Figure 3. Geologic plan maps of the Ropes Nine. See Fig. 2 for explanation. �successively,on onboth both the the north north and and south successively, south sides, sides, by, (3) (3) fine fine grained, grained, massive massive to to moderately foliated, foliated, carbonate-talc carbonate-talc rock, rock, and and (4) fine moderately fine grained, grained, totally totally serpentinized serpentinized peridotite retains aa relict cumulate peridotite which which commonly commonly retains cumulate texture after after original original olivine olivine This rock is is carbonatized carbonatized to varying varying degrees degrees near near its its contacts contacts and lesser lesser pyroxene. pyroxene. This between the carbonate-quartz-chlorite Contacts between carbonate-quartz-chlorite rock rock with with the the carbonate-talc carbonate-talc rock. rock. Contacts and the carbonate-talc rock and and the and the carbonate-talc carbonate-talc rock, rock, and between between the carbonate-talc rock serpentinized peridotite are generally over one to serpentinized peridotite generally gradational gradational over to several several meters. meters. The preservation of relict relict feldspar and lithic and the total The preservation of feldspar and lithic clasts, clasts, and total thickness thickness of quartz-sericite-chlorite rock, rock, increases gradationally westward westward from from the Ropes quartz-sericite-chlorite increases gradationally Ropes main main ore zone (Figure 1) 1) over over aa distance of several hundred meters meters into into aa large body of of ore zone (Figure distance of several hundred large body dacite that has dacite has moderately moderately aligned aligned twinned twinned plagioclase plagioclase phenocrysts, phenocrysts, bipyramidal bipyramidal quartz, and volcanic quartz-sericite-feldspar-chlorite quartz, volcanic rock fragments fragments in in an an aphanitic aphanitic quartz-sericite-feldspar-chlorite matrix characteristic matrix characteristic of of aacrystal—lithic crystal-lithic tuff. The dacite dacite locally locally contains contains intervals intervals of lapilli-sized lapilli-sized'fragments. fragments. rock isis restricted largely The carbonate—quartz-chlorite carbonate-quartz-chlorite rock largely to the thin intervals intervalsup uptoto 22 m m thick the mine mine area area (Figure (Figure 1), l), although although thin thick occur occur up to to The thickest 400 m west west of the the Ropes Ropes main main ore ore zone. zone. The thickest intervals intervals of carbonate-talc carbonate-talc 400 rock rock occur occur within within the mine mine area area (Figure (Figure 1); 1); however, however, thin intervals intervals of talc-rich talc-rich rock at the contacts rock occur occur at numerous numerous localities localities at contacts of, and and also also in, in, serpentinized serpentinized Serpentinized peridotite peridotite peridotite away peridotite away from the the mine mine area area(Rossell, (Rossell,1983). 1983). Serpentinized occurs up to to 2 km of the and up km northeast northeast of the Ropes Ropes mine mine and up to to 55 km km southwest southwest of the the occurs up mine in aa northeast mine northeast trending trending set set of of outcrops, outcrops, approximately approximately 600 600 m wide wide (Clark (Clark et.al., 1975). et.al., 1975). MAJOR ROCK ROCK TYPES TYPES IN IN THE ROPES MAJOR ROPES MINE MINE PROPERTY PROPERTY Quartz-Sericite-Chlorite Rock Quartz-Sericite-Chlorite Rock The main The main host host for gold gold is is light light green, green, massive massive to slightly slightly foliated, foliated, fine fine This rock rock isis up grained, up to 40 40 m m grained, quartz-sericite-chlorite quartz-sericite-chlorite rock with with relict relict clasts. clasts. This thick on on the 800 toward the the surface and toward the east thick 800 Mine Mine Level, Level, but but narrows narrows toward surface and toward the to less than than 6 m m thick. thick. to less is complexly It is complexly interlayered interlayered with carbonate-quartz-chlorite carbonate-quartz-chlorite A-39 �rock, rock, especially especially west west of the the Ropes Ropes main main ore ore zone zone (Figure (Figure 1) 1) and and in inthe themine mine and3). 3). The The rock rock has has equant equant quartz quartz grains grains 50 50 toto100 100microns microns inin (Figures 22 and (Figures diameter diameter in in aarandomly randomly oriented oriented totomoderately moderately aligned aligned sub-20 sub-20 micron micron quartz, quartz, sericite, and and minor minor chlorite chloritematrix. matrix. Randomly Randomly oriented oriented totomoderately moderatelyaligned, aligned, I1 toto sericite, 22mm, mm, angular, angular, rectangular rectangular mats mats of of sub-10 sub-10 micron micron sericite sericite and andminor minorquartz quartzare are enveloped enveloped in this this matrix matrix and and have have an anexternal external habit habitvery verymuch muchlike likethe theplagioclase plagioclase phenocrysts phenocrysts in the the thicker, thicker, more more massive, massive, lateral lateral equivalent equivalent of of this this rock rock This textural textural change change isisgradational gradationaleastward eastward immediately west west of of the themine. mine. This immediately toward toward the the orebody orebody over over aa distance distance of of aafew fewhundred hundred meters meters and andisischaracterized characterized by by increasing increasing alteration alteration of of the theplagioclase plagioclase phenocrysts phenocrysts to to sericite sericite and andan anincrease increase in in the the abundance abundance of of quartz quartz and and sericite sericite ininthe thematrix, matrix,with witha acorresponding corresponding quartz-sericiteTherefore, the the sericite-rich sericite-rich mats mats in in the thequartz-sericitedecrease in in feldspar. feldspar. Therefore, decrease chlorite pseudomorphs after afterplagioclase plagioclase chlorite rock rock of of the themine mineare areinterpreted interpretedasaspseudomorphs constituteup up to to 20 The sericite sericite pseudomorphs pseudomorphs constitute 20 percent percent of of the the rock. rock. phenocrysts. The phenocrysts. mm inindiameter diameterand andcomposed composed ofofmicrocrystalline microcrystalline aggreaggreUncommon clasts, clasts, I1 to to 22 mm Uncommon gates gates of of quartz, quartz, may mayrepresent represent pseudomorphs pseudomorphs of of quartz quartz phenocrysts phenocrysts which which now now exhibit exhibit subgrain subgrain development, development, or or alternatively, alternatively, some some may may be bechert chertfragments. fragments. Chlorite-quartz Chlorite-quartz fragments, fragments, which which may may be be more more mafic mafic volcanic volcanic rock rock fragments fragments or or pseudomorphed mafic mineral occur less in the rock. pseudomorphed mafic mineral phenocrysts, phenocrysts, occur less commonly commonly in rock. Chlorite componentofof the the rock Chlorite is generally generally a subordinate subordinate component rock at less less than than 10% 10% and and occurs occurs both dispersed dispersed in the the matrix matrix and and locally locally as as coarser coarser laths laths which which define define aa slight foliation. foliation. Ferroan Ferroan dolomite dolomite is locally locally a minor minor component component of the the matrix. matrix. slight The rock rock isislayered layered locally locally with with 55 mm mm thick, thick, planer, planer, sericite-rich sericite-rich and andalternate alternate The more chlorite—rich chlorite-rich laminae. laminae. more Gold Gold abundance abundance is generally generally greatest greatest where where very very fine to to aphanitic aphanitic pyrite pyrite to 8% 8% of the the rock, rock, quartz quartz and and sericite sericite are are most most abundant, abundant, and and chlorite chlorite comprises 55 to comprises is does not not apply apply in in the case is least least abundant abundant (this generality generality does case of of the the chloritic, chloritic, pyritic, pyritic, farthest farthest eastern eastern rim rim of of the the Ropes Ropes main main ore ore zone, zone, as asdiscussed discussed in in the the subsequent section section on on"The "TheOrebodies"). Orebodies"). Rock with with greatest greatest gold gold abundance abundance subsequent A-40 �contains contains only only trace trace amounts amounts of of carbonate, carbonate, compared compared with higher higher but but still stillminor minor concentrations of carbonate quartz-sericite-chlorite concentrations of carbonate in less less auriferous auriferous parts parts of of the thequartz-sericite-chlorite Fine pyrite, pyrite, 50 50 to to 100 100 microns microns in in diameter, diameter, is is dispersed dispersed in the the rock rock matrix matrix rock. rock. Fine and and is and less less commonly commonly within within the the sericite sericite pseudomorphs pseudomorphs after plagioclase plagioclase and is not not confined confined only only to to quartz quartz veinlets veinlets or or totofoliation foliationplanes. planes. Coarser Coarser pyrite, pyrite, 0.5 0.5 to to I1 mm mm in in diameter, diameter, occurs occurs near near quartz quartz veinlets veinlets and and also alsoalong along chioritic chloritic foliations. foliations. This This relatively relatively coarse coarse pyrite is is enclosed enclosed locally locally by by quartz quartz over-growths, over-growths, and and isis occasionally pulled apart along Rock characterized characterized by by only only coarser coarser occasionally pulled along the the foliation. foliation. Rock less than than 11 mm Quartz veinlets veinlets less mm thick thick comprise comprise up up to to several several pyrite pyrite is is not not ore. ore. Quartz percent Quartz in in the theveinlets veinletscommonly commonly percent of the the rock rock and andare arerandomly randomly oriented. oriented. Quartz Rock outside outside of of the theore orezones zones has has undulatory undulatory extinction extinction and and local local mortar mortar texture. texture. Rock is is characterized characterized by by <2% <2% very very fine fine pyrite. pyrite. Carbonate-Quartz-Chlorite Carbonate-Quartz-Chlorite Rock Rock Carbonate-quartz-chlorite Carbonate-quartz-chlorite rock rock envelopes envelopes the afore-mentioned afore-mentioned quartz-sericitequartz-sericite- chlorite with it, particularly chlorite rock rock and and isis complexly complexly interlayered interlayered with particularly toward toward the the west west carbonate-quartz-chlorite rock rock contains contains end of of the theRopes Ropesmine mine(Figure (Figure1). 1). The The carbonate-quartz-chlorite end abundant abundant ferroan ferroan dolomite, dolomite, and and lesser lesser quartz quartz and andchlorite. chlorite. Minor sericite sericite occurs occurs in some and minor some specimens, specimens, and minor talc talc in others, others, but but these these two two minerals minerals are aregenerally generally quartz-sericite-chlorite rock rock are aresharp; sharp; Contacts with with the the quartz-sericite-chlorite mutually exclusive. exclusive. Contacts however, minerals are are present present in in the however, minor minor carbonate carbonate minerals the quartz-sericite-chlorite quartz-sericite-chlorite rock rock near carbonate-quartz-chlorite rock, rock, and and minor minor sericite sericite isis near its its contacts contacts with with the the carbonate-quartz-chlorite present present in in the the carbonate-quartz-chlorite carbonate-quartz-chlorite rock rock near its its contacts contacts with with the the quartzquartz- this rock rock contains contains up up to 150 Typically, this 150 ppb ppb Au. Au. sericite-chlorite sericite-chlorite rock. rock. Typically, Quartz-rich Quartz-rich parts parts of of the thecarbonate-quartz-chlorite carbonate-quartz-chlorite rock rock are arelocally locally slightly slightly pyritic pyritic and contain contain up to to 1 ppm ppm Au. Au. The carbonate-quartz-chlorite layered on on aa carbonate-quartz-chlorite rock is is commonly commonly compositionally compositionally layered Layering is defined defined by by scale of several several millimeters, millimeters, but but locally locally isismassive. massive. Layering parallel, parallel, fine to to medium medium grained, grained, white white carbonate carbonate laminae, laminae, chlorite chlorite foliation, foliation, and and A-41 �quartz-chlorite-rich laminae. quartz-chlorite-rich laminae. with carbonate-talc with carbonate-talc rock. rock. The rock rock is is increasingly increasingly talcose talcose toward toward the the contact contact Coarse grained, barren, barren, white white dolomite dolomite veins veins up up to to 55 Coarse grained, thick cut across of the rock. cm thick across all other other features features and and comprise comprise <1% ~ 1 %of rock. Carbonate- quartz-chloriterock rockoccurs occursnot notonly onlyininthe themine, mine,but butalso alsoininaa layer layer up up to to 60 quartz-chlorite 60 m thick on on the north l), where where itit contains contains thin thin layers layers of of thick north side side of of the the mine mine (Figure (Figure 1), the the other three three main main rock rock types. types. Serpentinized Peridotite Perdotite and Carbonate-Talc Serpentinized Carbonate-Talc Rock Rock The interlayered The interlayered quartz-sericite-chlorite quartz-sericite-chlorite rock rock and and carbonate-quartz-chlorite carbonate-quartz-chlorite rock rock are bounded bounded on the the north north and andsouth south by bysill-like sill-like masses masses of ofserpentinized serpentinized peridotite. There are several peridotite bodies bodies within within the There several smaller smaller serpentinized serpentinized peridotite carbonate-quartz-chlorite rockon on the the north north side carbonate-quartz-chlorite rock side of the the Ropes Ropes mine. mine. The larger larger of these peridotite masses massesforms formsthe the north north wall wall of of the Ropes these minor minor serpentinized serpentinized peridotite Ropes mine The rock 1, 2). 2). The rock is dark dark gray gray to to green, green, fine finegrained grainedserpentine serpentine mine (Figures (Figures 1, containing lesser talc talc and and carbonate, containing lesser carbonate, and minor minor chlorite, chlorite, with with accessory accessory chromite chromite Commonlyitit has has aa relict texture of of 1 to and magnetite. to 33 mm mm serpenserpenmagnetite. Commonly relict cumulate cumulate texture 1 tine pseudomorphs after olivine olivine and and pyroxene, pyroxene, which which are are surrounded surrounded by by rims rims of of pseudomorphs after talc and although locally locallythe the rock rock isis dark dark green, talc and carbonate, carbonate, although green, felted felted textured textured serpentine. The serpentinized toward its serpentinized peridotite peridotite isis increasingly increasingly carbonate—rich carbonate-rich toward borders, although borders, although relict texture texture isiscommonly commonly continuously continuously preserved. preserved. Au abundance isis typically typically less less than than 30 30 ppb ppb in the the serpentinized serpentinized peridotite, peridotite, even even in abundance close close proximity proximity to the the mine. mine. Massivetoto well well foliated, foliated, gray gray to to dark dark green, Massive green, very fine fine grained grained carbonate-talc carbonate-talc rock occurs around the margins 3). The rock occurs around margins of serpentinized serpentinized peridotite peridotite (Figures (Figures 1, 2, 2, 3). carbonate-talc rock rock has contacts over over one one to several carbonate-talc has gradational gradational contacts several meters meters with with serpentinized peridotite peridotiteand and with with talc-rich talc-rich parts of serpentinized of the the carbonate-quartz-chlorite carbonate-quartz-chlorite rock. The in the The carbonate carbonate mineral mineral in the carbonate-talc carbonate-talc rock rock is is dominantly dominantly ferroan ferroan ranges from from <30 <30 ppb ppb to approxiAu abundance abundance ranges approxidolomite with minor dolomite minor magnesite. magnesite. Au mately ppb in the mately 100 100 ppb the carbonate-talc carbonate-talc rock. rock. A- 42 �The The spatial spatial association association of carbonate-talc carbonate-talc rock rock with with the the margins margins of of serpentinserpentinized ized peridotite, peridotite, the thegradational gradational contacts contacts with with serpentinized serpentinized peridotite, peridotite, and and the the similar similar less less mobile mobile trace trace element element composition composition of the the carbonate-talc carbonate-talc rock rockand and serpentinized with regard regard to Cr serpentinized peridotite, peridotite, especially especially with Cr content, content, suggests suggests that that the the carbonate-talc carbonate-talc rock rock isisthe thealtered alteredmargins marginsofofserpentinized serpentinizedperidotite peridotitemasses. masses. SUMMARY OF OF MINERAL MINERALCOMPOSITION COMPOSITION SUMMARY Minerals Minerals in in rock rock samples samples from from selected selected traverses traverses across across and along along the the strike strike of of Although detailed detailed the Ropes Ropes deposit deposit were wereanalyzed analyzedby byelectron electronmicroprobe. microprobe. Although the mineral is not dealt mineral chemistry chemistry is dealt with with here, here, aa brief brief summary summary of ofgeneral general trends trends isis included included in in this thisfield fieldguide guide(Callahan (CallahanMining MiningCorporation, Corporation, unpublished unpublished data). data). Chlorite Chlorite occurs occurs in in nearly nearly all all rock rock types, types,but butitsitscomposition compositionand andabundance abundance In general, general, the the Fe/Mg Fe/Mg ratio ratio ofofchlorite chloriteincreases increases toward toward the the center center are variable. variable. In are of of the thequartz-sericite-chlorite quartz-sericite-chlorite rock rock and andaway awayfrom fromserpentinized serpentinized peridotite. peridotite. The The chlorite rocks and clinochlore chlorite isis mostly mostly sheridanite sheridanite in inthe thequartz—sericite-chlorite quartz-sericite-chlorite rocks clinochlore in in the other other major majorrock rocktypes. types. the Talc Talc increases increases in iron iron content content from from serpentinized serpentinized peridotite peridotite toward toward quartzquartzTalc sericite-chiorite quartz-sericite-chlorite rock rock itself. itself. Talc sericite-chlorite rock, rock, but isis absent absent in inthe thequartz-sericite-chlorite compositions show aa narrow compositions show narrow range, with with an an Fe/(Fe+Mg) Fe/(Fe+Mg) cation cation ratio ratio between between 0.0 0.0 and 0.11, 0.1 1, centered centered atat0.05. 0.05. and Sericite Sericite is restricted restricted mostly mostly to the the quartz-sericite-chlorite quartz-sericite-chlorite rock rock and and is is minor minor inin carbonate—quartz-chlorite rock,where wherethese these two two rocks rocks are are in carbonate-quartz-chlorite rock, in contact. contact. The The sericite sericite is is an an FeFe- and andMg-bearing Mg-bearing muscovite, muscovite, with with FeO FeO and and MgO MgO contents contents of of as asmuch much asas The sum sum of of Mg+Fe Mg+Fe cations cations in the the sericite sericite structural structural formula, formula, several wt.% wt.% each. each. The several on 22oxygens, oxygens, isisbetween between 0.4 0.4 and and1.2 1.2cations, cations, centered centered atat0.6 0.6cations. cations. on the the basis basis of of 22 No in the rocks No consistent consistent trends trends in in sericite sericite composition composition were were recognized recognized in rocks of of the the mine. Ropes mine. Carbonate are common to all rocks Carbonate minerals minerals are common to rocks and are are dominantly dominantly low low iron iron Low iron iron dolomite dolomite is aa minor minor component component in in dolomite and and lesser lesser pure pure dolomite. dolomite. Low dolomite A— 43 �quartz-sericite-chlorite quartz-sericite-chlorite rock, rock, but but isis aamajor majorcomponent component in in the theother otherthree threemajor major rock types types atatthe theRopes Ropesmine. mine. Calcite Calcite isisminor minorininquartz-sericite-chlorite quartz-sericite-chlorite rock. rock. rock Magnesite Magnesite is is commonly commonly a major major component component of of the theserpentinized serpentinized peridotite peridotite and andthe the Serpentine isis major major ininthe theserpentinized serpentinizedperidotite. peridotite. carbonate-talc rock. rock. Serpentine carbonate-talc Disseminated Disseminated chromite chromite is minor minor in in the theserpentinized serpentinized peridotite peridotite and andcarbonate-talc carbonate-talc rock. rock. The The differences differences ininmineral mineralcomposition composition probably probably reflect, reflect, in inlarge largepart, part,original original differences differences in in bulk bulkcomposition composition between between serpentinized serpentinized peridotite peridotite and and the thedacitic dacitic volcaniclastic protolith protolith of of the thequartz-sericite-chlorite quartz-sericite-chlorite rock. rock. Talc Talc and andchlorite chlorite volcaniclastic compositions compositions are more more Mg-rich, Mg-rich, and and Mg-carbonate Mg-carbonate minerals minerals are are also also more moreabunabundanttoward towardthe theserpentinized serpentinizedperidotite. peridotite. dant STRUCTURE STRUCTURE The The dominant dominant structural structural element element in the the Ropes Ropes mine mine area area is is aaN70°E N70° subsubvertical vertical foliation foliation defined defined by by the thealignment alignmentofofaphanitic aphaniticphyllosilicate phyllosilicate minerals, minerals, The overall overall strike strike which which isis generally generally parallel parallel to to the thelayering layeringbetween betweenrock rocktypes. types. The A slight, slight, of of the theRopes Ropesmain mainore orezone zonealso alsonearly nearlyparallels parallelsthis thisfoliation. foliation. A sporadically and is sporadically present present sub-vertical sub-vertical second second foliation foliation strikes strikes N45°E N45OE and is defined defined by by generally generally slightly slightly coarser coarser grained grainedphyllosilicate phyllosilicatelaths. laths. Several Several ore-related ore-related structural structural elements elements characterize characterize the the Ropes Ropes deposit: deposit: 1)1)aa series series of of N55°E N55OE to to N65°E N65OE striking, striking, vertically vertically dipping, dipping, steeply steeplywestward westward plunging, plunging, auriferous auriferous quartz quartz vein-dominated vein-dominated pods pods occur occur progressively progressively further east east in in occur at, at, or south successively deeper levels of the the mine. mine. These These pods pods occur south of, of, the the successively deeper levels south crypticzones zonesofofsignificantly significantlyhigher higher south side side of of the theRopes Ropesmain main ore orezone; zone; 2)2)cryptic grade grade Au Au mineralization, mineralization, defined defined solely solely on the the basis basis of of assay assay data, data,are arecontained contained more more centrally centrally within within the the Ropes Ropes main main ore orezone. zone. The The middle middle parts parts of of these these higher higher grade trend of the grade zones zones strike across across the overall overall N80°E N80"E trend the orebody orebody ininen-echelon en-echelon fashion fashion at at approximately approximately N55°E, N55OE, while while the extremities extremities of these these higher higher grade grade transverse N70° trend, trend, thus thus forming forming aalow lowangle anglesigmoidal sigmoidal transverse zones zones have have a nearly nearly N70°E A- 44 �pattern across the ore zone This pattern pattern can can best at the pattern across the zone (Figure (Figure 5). 5). This best be recognized recognized at 250 ft. ft. elevation in the the mine, the east east end end of 250 elevation in mine, toward toward the of the the Ropes Ropes main main ore ore zone zone (Figure 3). 3). Both Both of the the above above structural structural elements elements can can be be regarded regarded as asextensional extensional features. features. The quartz pods are are evidence of silica The quartz vein dominated dominated pods evidence of silica addition addition in incipient incipient voids. voids. The higher zones within within the the main main ore ore zone, The higher grade grade transverse transverse zones zone, while while not strictly strictly veins, may have have been been zones of increased veins, nonetheless nonetheless may zones of increased permeability permeability to ore ore fluids. fluids. A comparison with shear shear zone zone models models presented presented in in Ramsay and Huber (1983) comparison with Ramsay and (1983) demondemon- strates strates that the the above above structural structural elements elements are best best interpreted interpreted as as extensional extensional features, features, and and that that the the rocks rocks containing containing the the Ropes Ropes deposit deposit can can be be considered considered to to represent aa structural some degree degree of of simple shear, with aa represent structural setting setting involving involving some simple shear, Figure 55 compares compares the the component of of positive volume change change in in the shear component positive volume shear zone. zone. Figure theoretical orientation orientation of of extensional extensionalvein vein arrays arrays developed developedinin aa shear theoretical shear zone zone as aa result of positive in aa shear _result positive volume volume change change in shear zone zone with with the theobserved observed geologic geologic relations of ore related relations of related structural structural elements elements at the the Ropes Ropes mine: mine: ititisisgeometrically geometrically correct that en-echelon 45' to to correct en-echelon fissure fissure systems systems will always always make make angles angles of less less than than 450 the trend trend of of the theshear shearzone zoneinincases caseswhere wherepositive positive volume volume change change isis involved involved relationshipsatat the the Ropes Ropes mine mine between between the the two (ibid). The observed observed geometric geometric relationships two ore related above, and and the shear related structural structural elements elements discussed discussed above, shear zone zone "walls" "walls" (the nonfoliated serpentinized peridotite), peridotite), are are consistent consistent with with the the required nonfoliated serpentinized required acute acute angle angle of shear required relative relative sense sense of shear in in the the present present day dayhorizontal horizontal relationship. The required plan view view of of the WSW and and south south plan the Ropes Ropes mine mine area area is, is, therefore, therefore, north north side side to tothe theWSW the midpoints of the midpoints of the side side to the the ENE, ENE, as as illustrated illustrated in in Figure Figure 5. 5. Connecting the quartz vein vein dominated dominatedpods podsatat the the Ropes Ropes mine mine gives givesthe the true true sense sense of of shear shear in in the quartz third dimension as lying lyingalong alongaaline lineoriented orien.eddown downtotothe the ENE ENE and and up up to to the third dimension as considerationofof the the plan WSW (Figure (Figure 5). WSW 5). A simultaneous simultaneous consideration plan and and long long section section views views necessitatethat that the the south south side side of of the zone necessitate zone had had an an ENE ENE and and downward downward net net compocomponent while the the north nent of movement, movement, while north side side of the the zone zone had had aaWSW WSW and upward upward net net component component of movement. movement. A-45 �R o o e s Production S h a f t \ .E .*l.-Northwes+ 2 Ore Zone Major Gold Gold Ore Ore Types Types Major 1. 1. Light Light green green to to tan tan quartz-sericite quartz-sericiterock, rock,with with lenses lensesof of light light gray gray cherty cherty quartz quartz rock rock containing containing pyrite-tetrahedriteChalcO pyrite-tetrahedrite-chalcopyrite-galena. Pyrite Pyrite content content of of this this ore ore type type does does not not pyrite-galena. correlate with with gold gold grade grade correlate 2. Light Light green green quartz-sericite-chloritepyrite quartz-sericite-chlorite-pyriterock. rock. Good Good 2. correlation Au grade. grade. correlation between between fine-grained fine-grained pyrite pyrite content content and and Au 3. Dark Dark green green quartz-chlorite-pyrite quartz-chlorite-pyriterock. rock. Consistently Consistently high high 3. fine-grained fine-grained pyrite pyrite content content and and high high gold gold grade. grade. 4. Figure 4. Figure Ropes Ropes Mine Mine long-section long-section looking looking NN 100 lo0 WW A - 446 6 A- �_____ A A A B ELANATION w near vertical vertical foliation foliation near of Ropes Ropes orebody orebody outline of outline 9-> Au zone of of higher-grade higher-grade Au zone mineralization mineralization L— contact between between serpentinized serpentinized contact component) component) (with down down (with component component) arrow in in plan plan arrow view projection projection view of plane of of plane of shear shear true sense senseof of shear sheardetermined determined true by connecting midpoints of by connecting midpoints of extension views extension views verticalprojection projectionof of quartz quartz vertical vein-dominated pods (extension vein—dominated pods (extension veins) onto ontothe the plan plan view view veins) quartz-vein dominated dominated pods pods quartz—vein projected onto ~ 8 long 0 ~ projected onto N80°E long section section (with up up (with 0 <\s maximum stretch stretch direction direction maximum (vein (vein opening opening direction) direction) <y 7 peridotiteand and dacite daciteCuff Cuff (with (wi~h peridotite associated rocks) rocks) associated strike of of layering layeringin in rocks rocks strike Figure5: 5: Figure Schematic structural structural diagrams diagrams of of the the Ropes Ropes Mine Mine Schematic A is plan view, inset after Ramsay and Huber, A is plan view, inset after Ramsay and Huber, 1983, Figure Figure 3.21A; 3.21A; BB is is N80°E N 8 0  °vertical vertical long long section sectionview view 1983, A-47 �THEOREBODIES OREBODIES THE The The Ropes Ropes mine mine main main ore orezone zone isissteeply steeplydipping, dipping, 335 335mmininmaximum maximumstrike strike length, length, 12 12 m m ininaverage averagethickness, thickness, and and 600 600 mmininpresently presentlydefined defineddown-dip down-dip occurswithin withinthe thequartz-sericite—chlorite quartz-sericite-chlorite rock, rock, and andisis 4). ItItoccurs extent (Figure (Figure4). extent characterized The total total characterized by by disseminated disseminated pyrite pyrite with with only onlyminor minorquartz quartzveins. veins. The stated stated property property tonnage, tonnage, including including historic historicproduction production through through1987 1987and andgeologic geologic Based on on reserves, reserves, is is approximately approximately 2.5 2.5 million million tonnes tonnes at 3.25 3.25 g/tonne g/tonne Au. Au. Based available from the the upper available information information from upper third of of the the Ropes Ropes main main zone, zone, the the Ag Aggrade grade 12g/tonne. g/tonne. estimated at at 12 isis estimated The The Ropes Ropes main main ore ore zone zone can can be be divided divided longitudinally longitudinally into into three three major major ore ore types of the types based based on on the the physical physical characteristics characteristics of the ore, ore, as as illustrated illustrated ininFigure Figure4.4. In In plan plan view, view,these theseore oretypes typesform formcrescent—shaped, crescent-shaped, concentric shells, shells, with with the the convex convex side side of each each ore ore type type toward toward the the east east and and the theconcave concave side side toward toward the the of the west. The The convex-to-the-east convex-to-the-east geometry geometry of the ore ore type type zones, zones, along along with with an an west. overall cutoff of Au and a sharp overall gradual gradual western western cutoff Au mineralization mineralization and sharp eastern eastern cutoff, cutoff, suggests that the suggests that the flow flow vector vector for for the themineralizing mineralizing fluids, fluids, relative relative to to the the present-day present-day surface, surface, may may have have been been upwards upwards from the the deep, deep, southwest southwest end end of of the the deposit deposit toward toward the the shallower shallower northeast, northeast, high high grade grade keel keel of of the thedeposit. deposit. The The Ropes Ropes main main ore zone zone is is cut cut by by an aneast-striking, east-striking, southsouth- dipping, dipping, low low Offset of of units units across across angle reverse reverse fault fault zone zone at at the the 900 900 mine mine level level (Figure (Figure 2). 2). Offset angle the greater atat the the south south side side of of the the mine the fault fault zone zone is is generally generally greater mine than than at the the north north orebody thins thins down down dip toward toward the fault fault zone, zone, but but thickens thickens below below it. it. The orebody side. The side. Several bodies exist exist on the Several other gold-mineralized gold-mineralized bodies the Ropes Ropes property. property. The The Northwest ore zone is a small Northwest ore zone is small ore zone zone to to the the northwest northwest of of the theRopes Ropes main main ore ore Significant intersections intersections of gold-mineralized gold-mineralized rock, rock, comparable comparable in in zone (Figure (Figure 4). 4). Significant zone grade grade and and width width to to the theRopes Ropes main main ore orezone, zone, have have been been encountered encountered in in deep deep drilling 370 370 m m below below the theRopes Ropesmine mine1284 1284level level(Callahan (CallahanMining Mining Corporation Corporation news release, release, July July 20, 20,1987). 1987). news In general, general, most most gold gold occurs occurs associated associated with sub-100 sub-100 micron micron sized sized pyrite pyrite A-48 �which the mass which is is dispersed dispersed throughout throughout the mass of the the quartz-sericite-chlorite quartz-sericite-chlorite rock, rock, as as well well as as on on fractures, fractures, foliations, foliations, and andalong alongquartz quartzveinlets. veinlets. However, However, in in certain certain ore ore types types the the modal modal abundance abundance of pyrite pyrite does does not not show show aastrict strictcorrelation correlationwith withgold gold grade 4). Native Native gold, gold, of of variable variable fineness, fineness, occurs occurs as as grade (see (see explanation, explanation, Figure Figure 4). approximately approximately 3 to to 10 10 micron micron sized sized grains grains ininthe thefollowing followingspecific specificsites: sites: 1)1) attached attached to the the surface surface of of the the fine fine grained grained pyrite, pyrite, 2) 2) included included as as fine fine blebs blebs within within the the fine fine grained grained pyrite, pyrite, 3) 3) on on fractures fractures within within the fine fine grained grained pyrite, pyrite, and 4) 4) at at grain boundaries boundaries of of fine fine grained grained quartz quartz and andsericite. sericite. A A volumetrically volumetrically minor minor grain amount amount of coarse coarse free free gold gold occurs occurs on on fractures fractures in in quartz quartzstringers stringers and andlenses. lenses. Silver Silver occurs occurs as electrum, electrum, native native silver, silver, argentiferous argentiferous tetrahedrite, tetrahedrite, argentiferous argentiferous galena, and and rare raredyscrasite. dyscrasite. galena, Pyrite over 95% 95% of of the metallic Pyrite comprises comprises over metallic minerals minerals in the the flotation flotation mill mill concentrate, galena, argentiferous argentiferous concentrate, followed followed by by chalcopyrite chalcopyrite at at1%. 1%. Argentiferous galena, , tetrahedrite, magnetite, and and rutile rutile are present tetrahedrite, sphalerite, sphalerite, hematite, hematite, magnetite, present in in trace trace amounts. amounts. Fine Fine grained, grained, white white to to light light gray gray sugary-textured sugary-textured auriferous auriferous quartz quartz veins veins are are concentrated at and and south concentrated at south of the the extreme extreme south south side side of of the the Ropes Ropes main main ore orezone. zone. Individual quartz veins veins are are rarely rarely up up to Individual quartz to aa meter meter thick, thick, but butcollectively collectively these these veins, veins, interlayered with quartz-sericite-chlorite rock, form form pods pods up up to aa maximum quartz-sericite-chlorite rock, maximum of of 88 interlayered with m thick thick and and 30 30 m m ininstrike strikeand andplunge plungeextent. extent. The pods pods strike strike approximately approximately N65°E, compared to to the the N80°E overall trend trend of of the Ropes N65OE, compared N8VE overall Ropes main main ore ore zone, zone, plunge plunge steeply further east east at deeper steeply to the the west, west, and and occur occur progressively progressively further deeper levels levels of the the Ropes Ropes mine, mine, as as discussed discussed in in the thesection sectionon on"Structure". "Structure". Accessory minerals in in these Accessory minerals these quartz quartz pods pods include: include: pyrite, pyrite, minor minorargentiferous argentiferous tetrahedrite and chalcopyrite, and rare free tetrahedrite galena, galena, and chalcopyrite, and free gold, gold, molybdenite, molybdenite, and and dyscrasite. Trace tourmaline tourmaline and native native Ag Ag were were reported reported by byBroderick Broderick(1945). (1945). dyscrasite. These contain 44 to to 77 g/tonne g/tonne Au Au and andapproximately approximately 20 20 g/tonne g/tonne Ag. Ag. These pods pods typically typically contain Although these pods pods are are higher higher than than average grade ore, ore, the the higher Although these average grade higher grade grade parts parts of of the quartz-sericite-chlorite rock ore ore of of the Ropes quartz-sericite-chlorite rock Ropes main main ore ore zone zone are are not not zoned zoned A-49 �about about the thepods; pods; rather, rather, the thehigher highergrade gradeparts partsofofthe themain mainore orezone, zone,characterized characterized by bydispersed dispersed pyrite, pyrite, occur occur more more centrally centrally within within the the trend trendofofquartz-sericitequartz-sericiteestimatedthat thatthe theexisting existingand andmined minedout outpods podsconstitute, constitute,inin chloriterock. rock. ItItisisestimated chlorite 5%ofof the the ore oreatatthe theRopes Ropesmine. mine. total,approximately approximately5% total, DISCUSSION DISCUSSION The Theserpentinized serpentinized peridotite peridotite bodies bodies have have contact contact relations relations with with the thebordering bordering and and interlayered interlayered volcanic volcanic rocks, rocks, as as well well as as internal internal relict relict fine finegrained grainedigneous igneous texture, consistent consistent with withtheir theirintrusion intrusionasashypabyssal hypabyssalsills. sills. Serpentinization Serpentinization texture, preserved preserved igneous igneous textures, textures, and and was was most most like'y likelyatatnear nearconstant constantvolume volume(Best, (Best, This constant constant volume volume serpentinization serpentinization process process would would have havenecessarily necessarily 1982). This 1982). released The released large large amounts amounts of MgO MgO and and Si02 Si02 to to the thesurrounding surrounding rocks rocks(ibid). (ibid). The voluminous voluminous carbonate-quartz-chlorite carbonate-quartz-chlorite rocks, rocks, which which bound bound and and are areinterlayered interlayeredwith with the the Ropes Ropes gold gold deposit, deposit, are arecomprised comprised primarily primarily of of weakly weakly ferroan ferroan dolomite dolomite and and Their origin origin could could conceivably conceivably be attributed attributed to to such such aarelease release ofof lesser quartz. quartz. Their lesser MgO of the MgO and and Si02 Si02 during during serpentinization serpentinization of the peridotite peridotite enclosing enclosing the trend trend of of volcanic rocks rocks at at the theRopes Ropesmine. mine. volcanic The The Ropes Ropes orebodies orebodies are are overall overall tabular, tabular, stratiform stratiform and andstratabound strataboundalteration alteration zones as dacite tuff quartz-sericite-chlorite rock rock interpreted interpreted as tuff on on the thebasis basis of of zones in in quartz-sericite-chlorite relict relict fragmental fragmental crystal-lithic crystal-lithic textures textures preserved preserved in and and near near ore. ore. These These pseudomorphs pseudomorphs are clearly clearly gradational gradational to feldspar feldspar phenocrysts phenocrysts and and lithic lithicfragments fragments in tuffs tuffswest west ofofthe theRopes Ropesmine. mine. Additionally, Additionally, the the mine mine rocks rocks have haveabundances abundances in Gold of of less less mobile mobile trace trace elements elements indicative indicative of of aadacitic daciticcomposition. composition. Gold mineralization at the the Ropes mine is is restricted to these mineralization at Ropes mine restricted to these rocks, rocks, and itit appears appears that that these receptive host host for K20 K20 these originally originally feldspar-rich feldspar-rich rocks rocks provided provided a chemically chemically receptive and and Au Au bearing bearing solutions, solutions, which which altered altered the the feldspar feldspar totosericite. sericite. Possibly, Possibly, either either better better permeability permeability in the the tuffs tuffs relative relative to to the thedense densecrystalline crystalline peridotite, peridotite, or or else else aa ductility ductility contrast contrast between between the the volcanic volcanic rocks rocks and andperidotite, peridotite, facilitated facilitated The bounding bounding peridotite peridotite near near the the preferential focussing focussing of of ore orebearing bearingsolutions. solutions. The preferential A- 50 �mine and appears to have mine isisextensively extensively carbonatized carbonatized and appears to have been been aa sink sink for forC02, CO2, possibly contained contained in in the thesame sameAu-bearing Au-bearing solutions. solutions. possibly Certain structural elements elementssuch such as as aa series of quartz Certain ore—related ore-related structural quartz vein vein dominated dominated pods pods south south of the the Ropes Ropes main main ore ore zone, zone, and andtransverse transverse zones zones of of higher higher gold grade grade in in the theRopes Ropesmain mainore orezone, zone,have havegeometric geometricrelations relationsconsistent consistent with with gold an an origin origin as asextensional extensional features features in inaashear shearzone zonewith withpositive positivevolume volumechange. change. Structural Structural elements elements indicate indicate that that the the net netcomponent component ofofmovement movementduring duringsome some stage stage of of gold gold mineralization mineralization was was north north side side up up totothe theWSW WSW and andsouth southside sidedown down to the theENE, ENE,relative relativetotothe thepresent-day present-day ground groundsurface. surface. Furthermore, Furthermore, the the overall overall to concentric, to the east of the major concentric, convex convex to east geometries geometries of major ore ore types types in in the theRopes Ropes main main ore ore zone, zone, combined combined with with the the gradual gradual western western cutoff cutoff ofofgold goldmineralization mineralization and and sharp sharp eastern eastern cutoff cutoff in in front front ofofthe thehigh highgrade gradeeastern eastern"keel" "keel" of of the thedeposit, deposit, suggests that the flow suggests that flow vector vector for for mineralizing mineralizing fluids, fluids, relative relative to to the the present present day day surface, surface, may may have have been been upwards upwards from from the the deep deep southwest southwest part of of the the deposit deposit toward the the shallow shallow eastern eastern high high grade gradeedge. edge. toward Timing Timing of of gold gold mineralization mineralization can be be demonstrated demonstrated as being being later later than than deposition deposition of the the volcanic volcanic rocks rocks which which host host the the Ropes Ropes deposit, deposit, because because alteration alteration associated associated with with the Ropes Ropes deposit deposit affects affects the the serpentinized serpentinized peridotite, peridotite, which, which, on on the the basis basis of of relict relict fine finegrained grainedigneous igneous texture texture and andinterlayering interlayering with with the thevolcanic volcanic rocks, rocks. appears appears to be be aahypabyssal hypabyssal sill sill complex, complex, and, therefore, therefore, intrusive intrusive into into the the of the Emplacement of the peridotite peridotite may may have have been beenpreferentially preferentially volcanic section. section. Emplacement volcanic controlled by an controlled by an early-formed early-formed structure structure which which appears appears to have have exerted exerted aa control control on on the the original original distribution distribution of of volcanic volcanic and and sedimentary sedimentary units: units: the the peridotite peridotite occurs occurs at at or or near neara amajor, major,partially partiallyinterlayered interlayeredtransition transition between between basalt basalt and anddacite dacite This transition transition is is accompanied accompanied by aa zone zone of of sedimentary sedimentary units units pyroclastic rocks. rocks. This pyroclastic including banded banded iron iron formation formation and andquartzose quartzosegraywackes. graywackes. This This major major transition transition including in the by sediments, could represent represent aa break the volcanic volcanic section, section, accompanied accompanied by sediments, could break or or zone zone of flexure of the flexure which which controlled controlled the position position of the interface interface between between the the two two partly partly Such aa boundary boundary between between contrasting contrasting contemporaneous major volcanic volcanic facies. facies. Such contemporaneous A-51 �volcanic volcanic facies facies may may have have been been controlled controlled by aa zone zone of of crustal crustalweakness weakness which which facilitated facilitated intrusion intrusion of upper upper mantle mantle derived derived peridotite, peridotite, as as well well as as provided provided aa conduit The trend trend of ofvolcanic volcanic rock rock which which conduit for forfocussing focussinggold goldbearing bearingsolutions. solutions. The hosts hosts the Ropes Ropes deposit deposit is near near this this transition, transition, and and strikes strikes away away from from the thetransition transition at at an an acute acuteangle. angle. The The Ropes Ropes environment environment may may represent represent a splay splay or or second second order order of ore types structure structure off off the the more more major major break. break. The The observed observed zoning zoning of types at at the the Ropes is consistent consistent with with fluid fluid flow from Ropes mine, mine, as as discussed discussed previously, previously, is from the the direction direction of of the the inferred inferred major major break break to to the the west west of of the theRopes Ropes mine, mine, toward toward the the Persistent or recurrent recurrent movement movement along along the inferred inferred major major present-day ENE. Persistent present-day ENE. structure structure which which controls controls the distribution distribution of major major volcanic volcanic fades, facies, could could have have provided action to assist provided a seismic seismic pumping pumping action assist in moving moving large large volumes volumes of mineralmineralcould also also account account for for the ore Such movement movement could ore related related ized ized hydrothermal hydrothermal fluid. fluid. Such structural observed in in the structural elements elements observed the Ropes Ropes main main ore ore zone, zone, which which indicate indicate relative relative movement during at least movement during least part part of ofthe thegold goldmineralizing mineralizingprocess. process. CONCLUSIONS CONCLUSIONS Gold at the Ropes Gold mineralization mineralization at Ropes mine mine occurs occurs primarily primarily with with fine fine grained grained pyrite rock interpreted interpreted as as altered quartz-sericite-chlorite rock altered dacite tuff. tuff. pyrite dispersed dispersed in quartz-sericite-chlorite The may represent represent aa splay off aa more The Ropes Ropes environment environment may splay off more major major early early formed formed structure basalt structure which which controls controls the distribution distribution of the the two two major majorvolcanic volcanic facies: facies: basalt dacite pyroclastics. pyroclastics. The The serpentinized serpentinized peridotite, peridotite, as as well well as as gold gold bearing bearing and dacite solutions, may have have used solutions, may used this this structure as as aa conduit. conduit. ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS The author author thanks thanks Glen Glen Scott, Scott, Ropes Ropes mine mine Chief Chief Geologist, Geologist, who who was was instruinstru- mental much of of the mental in defining defining mappable mappable units units and compiling compiling much the geology geology at the the paper benefited benefited from from editing editing and and revision revision by by Klaus KlausSchulz, Schulz, Ropes mine. mine. This paper Geological Survey. Survey. U.S. Geological A-52 �REFERENCES Allen, of Michigan Allen, C., C., 1912, 1912, Mineral Mineral Resources Resources of Michigan with statistical statistical tables tables of of production and and value production value of mineral mineral products products for 1910 1910 and and prior prior years: years: Michigan Michigan Geological and and Biological Survey, Publication Publication 8, p. Geological Biological Survey, p. 365-366. 365-366. Best, M.G., M.G., 1982, and metamorphic W. H. H. Freeman Freeman and Best, 1982, Igneous Igneous and metamorphic petrology: petrology: W. Company, San San Francisco, Company, Francisco, p. 398-399. 398-399. M., 1945, Geology of of the Ropes 1945, Geology Ropes Gold Gold Mizie, Mice, Marquette Marquette County, County, Broderick ,, M., Michigan: Economic EconomicGeology, Geology,v.v.40, 40, ## 2, p. p. 115-128. 115-128. Michigan: Clark, L.D., map of Clark, L.D., Cannon, Cannon, W.F., W.F., and Klasner, Klasner, J.S., J.S., 1975, 1975, Bedrock Bedrock geologic geologic map the Negaunee Negaunee SW SW Quadrangle, Quadrangle, Marquette Marquette County, Michigan: Michigan: U.S. U.S. Geological Geological SurSurvey, Map Map ##GQ-1226, GQ-1226, Scale Scale1:24000. 1:24000. Ramsay, J J.G., and Huber, .G.,and Huber, M., M., 1983, 1983, The techniques techniques of modern modern structural structural Ramsay, geology, v. 1: Strain Strain analysis: analysis: Academic AcademicPress, Press,Inc., Inc., Orlando, Orlando, Florida, Florida, p. p. 48-50. 48-50. v. 1: % Rossell, D.M., 1983, 1983,Alteration Alterationofofthe the Deer Deer Lake Lake Peridotite Peridotiteinin the the vicinity of Rossell, D.M., vicinity of the Ropes the Ropes Mine, Mine, Marquette Marquette County, County, Michigan, Michigan, (unpublished (unpublished M.S. M.S. thesis): thesis): Michigan Michigan Technological University, University, Houghton, Houghton, Michigan, Michigan, 83 p. Technological p. A-53 �Geological Geological Field Field Trip to to the theMarquette Marquette Greenstone Greenstone Belt: Belt: Part Part II Day Day 11Road RoadLog Log- - Stops Stops 11toto1111 T.J. T.J.Bornhorst, Bornhorst,D.A. D.A.Baxter, Baxter,M.L. M.L.MacLellan, MacLellan, and andR.C. R.C.Johnson ~ohnson* Department Department of ofGeology Geologyand andGeological GeologicalEngineering Engineering Michigan MichiganTechnological Technological University UniversityHoughton, Houghton,Michigan Michigan49931 49931 *Currently with *Currently withKerr-McGee Kerr-McGeeCorporation Corporation NOTE: on the NOTE: Additional Additional information information on the geologic geologic setting setting of the the field field trip tripstops stopsmay may be be found foundininpapers papersbybyBornhorst Bornhorstand andbybyBaxter Baxter&&MacLellan MacLellanininthis thisvolume. volume. Refer totoFigure Figure1:1:Route Routeand andStop StopMap Map Refer Mileage Mileage 0.0 0.0 Ramada Inn, Inn, Marquette Marquette StartDay Day1 1 -- Ramada Start Assemble at at the the entrance entrance of ofthe theRamada RamadaInn. Inn. From From the theRamada Ramada Inn Innturn turn Assemble right (west) to Washington Street and proceed toward junction with U.S. right (west) to Washington Street and proceed toward junction with U.S.41. 41. At At At 6.4 6.4 mi, mi, 1.3 mi, mi, turn turnright right(west) (west)totoU.S. U.S.4141and andproceed proceedtoward towardNegaunee. Negaunee. At 1.3 pull off offtotothe thetight lightshoulder shoulderalongside alongsideofofoutcrops. outcrops. pull 6.4 6.4 Stop11 -- Pillowed Pillowed Basalt Basalt Stop The The dominant dominant volcanic volcanic lithologies lithologies in the the Marquette Marquette Greenstone Greenstone Belt Belt are are massive massive and pillowed pillowed tholeiitic tholeiitic basalt, basalt, the the massive massive variety variety appearing appearing to to be be more more abundant At this this abundant perhaps perhaps because because typical typical mossy mossy outcrops outcrops may may obscure obscure the thepillows. pillows. At stop stop are are excellent excellent three threedimensional dimensional views views of ofrelatively relativelyundeformed undeformedpillowed pillowed basalt. basalt. The in shape with dimensions around 1'1' X X 4' The pillows pillows are ellipsoidal ellipsoidal in shape with dimensions around 4' X X 5'; 5'; attitude attitude Cusps on on pillows pillows indicate indicate of of bedding bedding strikes strikesapproximately approximately E-W E-W and anddips dips85°N. 85ON. Cusps There are arealso alsocharacteristic characteristicradial radial that that here here stratigraphic stratigraphic top top is is to to the thenorth. north. There fractures fractures and and interpillow interpillow void void spaces spaces filled filled with with quartz quartzand andcarbonate. carbonate. This This locality locality was was mapped mapped most most recently recently by by Puffett Puffett(1974) (1974)asasLower LowerMember Member Location: NW+, NWi, section section 20, 20, T48N, T48N,R26W. R26W. of the theMona MonaSchist. Schist. Locaticn: of At 7.6 7.6 mi, mi, pass pass the the road road totoMarquette MarquetteCounty County Continue west west on on U.S. U.S. 41. 41. At Continue At 8.6 8.6 mi, mi, large large outcrop outcrop on on opposite opposite side side of of highway highway (south) (south) is is Stop Stop 22 Airport. At Airport. (for (for safety safety proceed proceed 0.1 0.1 mi mi west, west, make make aa U-turn U-turn just just before before the the Carp Carp River, River, and and proceed east to outcrop; when finished finished proceed proceed east east 0.05 0.05 mi, mi, make make aa U-turn proceed east outcrop; when U-turn to to U.S. 41 41 west). west). U.S. A-54 �ARCHEAN ARCHEAN PROTEROZOIC [ r ++++++ DEAD RIVER PLUTON GRANITOID ROCKS 1 SEDIMENTS I I U. I 03 z Cd "I E- M E- +I >-i 0 >< x a; n Cd a. 4 Cd x 01 BASALT MEMBER z (Xl tn VOLCANICS OF SILVER MINE LAKES LOWER NEALY CREEK MEMBER SHEARED RHYOLITE TUFF MEMBER LIGHTHOUSE POINT MEMER MONA SCHIST KITCHI PERIDOTITE AGE RELATION UNCERTAIN I LEGEND a. w �"-4 C) -H z (I) 0 4-i (ID 1J 4-i z 0 4-i 'Ii cj 4-i C A-56 �Stop Deformed Pillowed Pillowed Basalt Stop 22 -- Slightly Deformed 8.6 The vertical The vertical road cut cut consists consists of of slightly slightly deformed deformed pillowed pillowed basalt. basalt. Pillow rinds rinds are not not easily easily visible visible in the the vertical vertical face face but but are aremore moreconspicuous conspicuous on on the the are flattened glacially polishedsurface surfaceon on the the top top of the glacially polished the outcrop. outcrop. Pillows Pillows are flattened and and rinds rinds have have feathered feathered edges; edges; bedding bedding strikes strikes roughly roughly E-W. E-W. Foliation strikes strikes N86°W N86OW dips 84°S. 84's. Quartz Quartz and carbonate carbonate veins veins containing containing aa few percent percent euhedral euhedral and dips Flat-lying fractures fractures are filled filled dominantly dominantly with with pyrite parallel pyrite parallel this foliation. foliation. Flat-lying carbonate. This was mapped most recently recently by by Puffett (1974) This locality locality was mapped most (1974) as the the Lower Lower Member of the Member the Mona MonaSchist. Schist. Location: Location: SW+, SWi, section section 28, 28, T48N, T48N. R26W. R26W. Proceed west west on on U.S. U.S. 41 41 and and at at 8.75 Proceed 8.75 mi cross cross bridge bridge over over Carp River. River. At 9.3 mi, 9.3 mi, pull pull off off to tothe theright rightshoulder shoulderalongside alongside aa number number of of small smalloutcrops. outcrops. Deformed .Archean Volcanic Stop Volcanic Rocks Rocks Stop 33 -- Deformed-Archean 9.3 The rocks The rocks in this this road road cut cuthave havea awell-developed well-developed close-spaced close-spaced foliation foliation (N75-88°W, dip dip 70-89°S) which produces (N75-88OW, 70-89"s) which produces a slate-like slate-like appearance. appearance. These rocks These rocks are There are two two lithologies lithologies in within Archean Carp Carp River River Falls Falls Shear Shear Zone. Zone. There within the Archean this outcrop: outcrop: chlorite chlorite schist schist from from aabasaltic basaltic parent, parent,and andquartz—sericite quartz-sericite schist schist from from The quartz-sericite schist isis aa tabular a rhyolitic rhyolitic parent. parent. The quartz-sericite schist tabular shaped shaped body body near near the the center center of the the outcrop, outcrop, and and isis probably probably aa dike dikebased based on onanalogous analogous lithologies lithologies to the the north. Near end of the Near the extreme extreme eastern eastern end the outcrop outcrop are are probable probable pillow pillow rinds rinds which suggest suggest the the basalt of the which basalt parentage parentage of the chlorite chlorite schist. schist. Flat—lying fractures, fractures, Flat-lying similar to to Stop Stop 2, 2, are present present in the the basalts basalts but not not in in the therhyolites. rhyolites. similar This most recently recently by by Puffett (1974) This locality locality was was mapped mapped most (1974) as Undifferentiated Undifferentiated Greenstone. Location: Location: S+, S+, section section 29, T48N, T48N, R26W. R26W. 10.2 mi, enter enter City City of of Negaunee Negaunee and and continue continue Proceed west Proceed west on U.S. U.S. 41. 41. At 10.2 At 13.8 mi, traffic light through Negaunee on U.S. 41 and towards Ishpeming. At 13.8 mi, traffic light at at through Negaunee U.S. 41 and towards Ishpeming. 41, turn right right (north) (north) to to County County Road Road junction of County junction County Road Road 573 573 and and U.S. U.S. 41, on left, stay 14.2 mi, pass pass cemetery cemetery on stay on on main main road, road, now now called called Deer Deer Lake Lake 573. 573. At 14.2 At 14.9 14.9 mi, mi, Deer Deer Lake Lake is is visible visible on on right, right, continue continue ahead ahead on on main main road. road. Avenue. At At 16.7 mi, junction with Cooper Lake Road Road on on left, left, stay At 16.7 mi, junction of County County Road Road 573 573 with Cooper Lake stay on on At 17.5 mi, gravel road to to the the Ropes Mine on on the the left left (the 17.5 mi, gravel road Ropes Mine (the field field trip will will 573. At 573. A- 57 �stop stop at at Ropes Ropes on onDay Day 2), 2),continue continueon on573. 573. At At 22.4 22.4 mi, mi, at atY-intersection, Y-intersection, go go left left to At 27.7 27.7 mi, mi, to the the North North Dead Dead River River Road; Road; road road turns turns to to gravel gravel atatthis thispoint. point. At the Archean rocks rocks of of the theClark ClarkCreek Creekarea. area. At At 28.8 28.8 mi, mi, the hills hills on on the theright rightare areArchean cross cross bridge bridge over over the the Dead Dead River; River; Archean Archean rocks rocks of of the theSilver SilverCreek Creek area areaare are exposed exposed in the the steep steeptopography topography ahead. ahead. At At 28.95 28.95 mi, mi, intersection intersection of of North North Dead Dead River River Road Road and and Silver Silver Lake Lake Road, Road, proceed proceed right right (east) (east) on on North North Dead Dead River River At 30.2 30.2 mi, mi, outcrops outcrops of ofMichigamme Michigamme Formation Formation in in roadbed. roadbed. At At 30.8 30.8 mi, mi, Road. Road. At At 31.1 31.1 mi, mi, turn turn left left totodirt dirtroad roadtowards towardsGrigg Grigghunting hunting cross cross over over Silver Silver Creek, Creek, At camp. At At 31.4 31.4 mi, mi, park park atathunting hunting camp camp and and walk walk about about 400 400 'eet feetN20-25°E N20-25OE camp. from the cabin to the Silver Creek prospect located on the side from the cabin to the Silver Creek prospect located on the side of of the thevalley. valley. 31.4 31.4 Stop44—- Silver Silver Creek Creek Prospect Prospect Stop The The The Silver Silver Creek Creek Prospect Prospect consists consists of of several several shallow shallow shafts shafts and and trenches. trenches. The prospect by aa quartz vein (up (up to to 4 ftf tthick) prospect is dominated dominated by quartz and and carbonate carbonate vein thick)which which contains contains galena galena and sphalerite sphalerite as the the major major sulfides, sulfides, lesser lesser amounts amounts of of pyrite pyrite and and chalcopyrite, and trace chalcopyrite, and trace amounts amounts of arsenopyrite arsenopyrite and and pyrrhotite. pyrrhotite. Pyrite Pyrite replaces replaces 120 ppm ppm Ag Ag and and one of A mineral mineral separate separate of galena galena contained contained 120 of pyrrhotite. pyrrhotite. A sphalerite contained less less than than 1 ppm yellowsulfide sulfideseparate separate(chalcopyrite, (chalcopyrite, sphalerite contained ppm Ag. Ag. AAyellow pyrite 180 ppb ppb Au. Au. AAgrab grabsample sample of of white whitemassive massive pyrite and and pyrrhotite) pyrrhotite) contained contained 180 quartz quartz vein vein from from the the rock rock piles piles at at this this prospect prospect contained contained 38 ppb Au Au and and 44ppm ppm Ag. Ag. The vein vein isishosted hosted by byaltered alteredpillow pillow basalt. basalt. The This by Johnson This locality locality was mapped mapped most most recently recently by Johnson and others others (1987) (1987) and is is designated as the Highly designated as Highly Altered Altered Variety Variety of of the the Pillowed Pillowed Basalt Basalt Member Member of of the the N E k section 25, 25, T49N, T49N. R2SW. R28W. Location: NE+, Volcanics of Silver Mine Mine Lakes. Lakes. Location: Volcanics of Silver Proceed back to to North River Road Road and and turn left Proceed back North Dead Dead River left (east) (east) at at 31.5 31.5 mi. mi. At At 31.8 31.8 mi, mi, turn left left and and proceed proceed to to dirt dirtlogging logging road, road, turn turn right rightand andfollow followlogging logging At 32.1 32.1 mi, mi, park, park, continue continue walking walking on on dirt dirt road road about about950 950 road north, north,0.O5mi. 0.05mi. At feet (generally up slope) (generally up slope) to Stop Stop 5a; 5a; cross cross altered altered rhyolite rhyolite at about about 700 700 feet. feet. 32.1 32.1 Stop 5 -- Section Section 30 Alteration Alteration Zone Zone Stop This This area is very very close close to the the Dead Dead River River Shear Shear Zone, Zone, an Archean Archean zone zone of Alteration intensity intensity varies varies from outcrop outcrop to to outcrop, outcrop, strain and and deformation. deformation. Alteration high strain Chlorite is is ubiquitous ubiquitous throughout throughout the the as as does does the the dominant dominant type type of of alteration. alteration. Chlorite alteration alteration zone, zone, whereas whereas sericite sericite and carbonate carbonate are are locally locally abundant abundant alteration alteration this zone Alteration along along this zone is interpreted interpreted to to be be synchronous synchronous with with the the products. products. Alteration A- 58 �The stop has been been divided divided into three three parts parts which which will will be be described described deformation. The separately. This locality most recently recently by by Baxter locality was was mapped mapped most Baxter and others others (1987) (1987) and lithologies are are designated designated as as the the Highly lithologies Highly Altered Altered Variety Variety of the the Pillowed Pillowed Basalt Basalt Memb'r of of Clark Member of the the Volcanics Volcanics of Silver Silver Mine Mine Lakes, Lakes, Gabbro Gabbro of Clark Creek, Creek, and and Location: NW+, section 30, T49N, Rhyolite Intrusive Intrusive of of Fire Center Rhyolite Center Mine. Mine. Location: NWi, section T49N, R27W. R27W. 5a. The 5a. The Cliff Cliff Outcrops Outcrops This set of outcrops rocks and and intrusives of altered This outcrops contains contains altered altered gabbroic gabbroic rocks intrusives of altered on the south outcrop on south side of the the valley valley isis mainly mainly altered altered rhyolite porphyry. porphyry. The outcrop gabbro gabbro with with a fault-bounded fault-bounded block block of of altered altered rhyolite, rhyolite, which which strikes strikesapproximately approximately N50° dips 750 75O to the east, east, along along the the eastern eastern contact. contact. The western western contact contact of N50°E and dips this rhyolite block has has aa similar strike and and aa dip of this rhyolite block similar strike of about about 40° 40Âtowards towards the the east. east. The maximum east-west thickness thicknessofof the the rhyolite rhyolite block block isis 50 50 feet. Mineralization The maximum east-west is concentrated along the the faulted contact is concentrated along contact between between the altered altered gabbro gabbro and and altered altered rhyolite. Pyrite is the Pyrite the dominant dominant sulfide sulfide phase, phase, with with arsenopyrite arsenopyrite and and chalcopyrite chalcopyrite outcrop on on the the north north side side of The small small outcrop of the the occurring in much occurring much lesser lesser amounts. amounts. The valley is a slightly valley is slightly less less altered altered example example of the the gabbro. gabbro. 5b. The Hillside 225 feet feet east 5b. Hillside Outcrop Outcrop (about (about 225 east of 5a) 5a) These outcrops outcrops are are located locatedalong alongthe the north north side side of of the These the valley valley on aa gently gently Near the the south south end of of upward hill, and upward sloping sloping hill, and are are mainly mainly highly highly altered altered basalt. basalt. Near the outcrop the outcrop is aa rhyolite rhyolite porphyry porphyry contact contact trending trending about about N10°W NlWW and dipping dipping 50° 50' east. This is is aa good good location location to to observe observe quartz-carbonate quartz-carbonate veining veining along along the the contact contact between rhyolite between rhyolite and altered altered basalt. basalt. Between this this outcrop outcrop and and Stop Stop 5c 5c there are Between are several several smaller smaller outcrops outcrops on the the north and south with rare north south side of of the the valley valley of of predominantly predominantly altered altered basalts basalts with rhyolite dikes. dikes. A- 59 �5c. 5c. The The Island Island Outcrop Outcrop (about (about 225 225 feet east east of of 5b) 5b) This is in the This outcrop outcrop is the middle middle of of the thevalley valley which which isisotherwise otherwise outcrop-free. outcrop-free. The entire outcrop outcrop is highly highly altered altered basalt basalt with with the exception exception of the the western western 1/4 1/4 which is is cut by which by rhyolite. rhyolite. Proceed back back toto North North Dead Dead River River Road Road and and turn turn left (east) Proceed (east) at 32.3 32.3 mi. mi. At 34.3 mi, mi, bridge 34.3 bridge over over Clark Clark Creek, Creek, park park near near bridge. bridge. Across Across the Clark Clark Creek Creek bridge, the the road bridge, road is is known known as as Red Red Road. Road. 34.3 Stop Stop 6 (optional) (optional) -- Pillowed Basalt and and Rhyolite Rhyolite The outcrops directly beneath beneaththe the western westernside sideofof the the bridge The outcrops directly bridge are predompredom- are vertical inantly Archean Archean pillowed pillowed basalt. basalt. These These pillows pillows are vertical and and show show younging younging direction toward S30¡W S30°W. A A fault contact direction toward contact (seen (seen when when the water water level level isis low) low) juxtaposes aa rhyolite rhyolite porphyry porphyry on on the the east against juxtaposes against the pillow pillow basalt basalt on the the west. west. A few normal toto the the main main fault fault show of the few small small (inch (inch scale) scale) zones zones normal show shearing shearing of gives the the rhyolite This structural structural interleaving interleaving gives rhyolite a basalt basalt into the the rhyolite. rhyolite. This feet to the pseudo-pillowed appearance. The large large cliff, cliff, visible visible about about 1500 1500 feet the north north pseudo-pillowed appearance. The of of the the bridge, bridge, is is the the type type locality locality for for the the Gabbro Gabbro of of Clark Clark Creek. Creek. This locality locality was was mapped mapped most most recently recently by Baxter Baxter and and others others (1987) (1987) and and contains Member of of the Volcanics of Silver contains the the Pillowed Pillowed Basalt Basalt Member Volcanics of Silver Mine Mine Lakes Lakes and and Rhyolite Intrusive Intrusive of of Fire Rhyolite Fire Center Center Mine. Mine. Continue north on Red Continue north Red road. road. low relief outcrops. low outcrops. 35.0 35.0 Location: SE+, section section 29, T49N, Location: SE4, T49N, R27W. R27W. At 35.0 mi, pull off to At 35.0 mi, pull off to the the right right shoulder, shoulder, near near Stop 7 (optional) Stop (optional) -- Granular rhyolite These outcrops are are along along the the upward upward slope slope on on the the east east side side of the These outcrops the road. road. Even this rock Even though though this rock is is holocrystalline, holocrystalline, itit has has been been included included with the the other other rhyolites based on on its similar rhyolites based similar major major and and trace trace element element chemical chemical composition, composition, e.g., e.g., calc-alkaline rhyolite on aa Jensen calc-alkaline rhyolite Jensen diagram. diagram. The granular granular rhyolite rhyolite Consists consists of microcline and albite, albite, but is microcline and is now now moderately moderately altered altered to to sericite, sericite, Quartz, quartz, and and minor minor Some sulfide sulfide mineralization mineralization can can be be found in epidote chlorite. Some in localized localized zones zones epidote and chlorite. A- 60 �of of the theoutcrop, outcrop, mainly mainly on on the thesouth southside. side. This This locality locality was was mapped mapped most most recently recently by by Baxter Baxter and andothers others(1987) (1987)asas NWi. section 28, 28, T49N, T49N,R27W. R27W. Location: NW+. Rhyolite Rhyolite Intrusive Intrusive of Fire Fire Center Center Mine. Mine. Location: Continue Continue north north on on Red Red road. road. At At 35.05 35.05 mi. mi. cross cross Deer Deer Creek Creek and turn turn right right (east) after the the bridge tridge to aa dirt At 35.35 35.35 mi, mi, cross cross Deer Deer Creek Creek (east) immediately immediately after dirtroad. road. At at the the top of aa hill, At 35.5 35.5 mi, mi, 3-way 3-way irtersection intersection at hill, take take road road to tothe theright. right. again. again. At At At 36.0 36.0 mi, mi, flat flat area areaisispart partofofthe theClark ClarkCreek Creekbasin basinconsisting consistingofofLower Lower Proterozoic Formation;prominent prominentoutcrops outcropson on the the left are Proterozoic Michigamme Michigamme Formation; are Archean Archean At 36.6 mi, pull over to small side road on the right and walk about200 200 rocks. At 36.6 mi, pull over to small side road on the right and walk about rocks. feet southwest to outcrops on small knob. feet southwest to outcrops on small knob. 36.6 36.6 - Stop Stop 88 - Breccia Breccia This This outcrop outcrop is is the the best bestknown knownexposure exposure of ofa amember memberwhich whichgeomorphologigeomorphologiStratigraphic top is is towards towards the thesouth-southwest, south-southwest, cally cally tends tends to to form form aadepression. depression. Stratigraphic member consists consists of at at consistent consistent with nearby nearby pillowed pillowed basalt basalt top top indicators. indicators. This member The lowest lowest part of of this this member member isis interpreted interpreted least least three three lithologic lithologic breccia breccia units. units. The to to be be aasubaqueous subaqueous pyroclastic pyroclastic and/or and/or fine-grained fine-grained mudflow mudflow deposit, deposit, devoid devoid of of Above this is is aa breccia breccia with with aalarge largeproportion proportion of offragments fragments large large fragments. fragments. Above representing The majority majority of of fragments fragments are are representing a wide wide range range ofoflithologies. lithologies. The heterolithologic heterolithologic porphyritic porphyritic volcanic volcanic rocks rocks of of probable probable andesite andesite composition, composition, now now extensively These fragments fragments are equant equant to to slightly slightly elongate elongate and and extensively altered. altered. These are of iron-rich The other other fragments fragments are iron-rich chert chert which which sub-angular to to sub-rounded. sub-rounded. The sub-angular occurs from equant occurs in shapes shapes ranging ranging from equant to highly highly elongate, elongate, with with angular angular to to breccia is interpreted interpreted as as aa subaqueous subaqueous mudflow, mudflow, of sub-angular edges. edges. This breccia relatively An unbrecciated unbrecciated cherty cherty iron-formation iron-formation overlies overlies relatively near-vent near-vent facies facies origin. origin. An this breccia, the chert chert clasts must have have been breccia, consequently consequently the clasts must been derived derived from prepreexisting existing chert deposits deposits that formed formed in in aaless lessstable stableenvironment. environment. This member member has has undergone undergone a relatively relatively large large amount amount of of strain, strain,demonstrated demonstrated are many many replacement replacement by flattened flattened clasts, clasts, compared compared to to adjacent adjacent members. members. There are pods, of mainly pods, consisting consisting of mainly pyrite, pyrite, throughout throughout the the member member indicating indicating hydrothermal hydrothermal alteration. alteration. The large large outcrops outcrops to the the south south of of the the breccia breccia member member are are of ofrelatively relatively A-61 �This showsaa wide wide range range of of grain due to This gabbro gabbro shows grain size, size, probably probably due unaltered gabbro. unaltered gabbro. the localized which produced produced finer-grained finer-grained zones the localized fault movement movement which zones within within the the overall coarse-grained overall coarse-grained rock. rock. This locality was mapped most recently recently by by Baxter This locality was mapped most Baxter and others others (1987) (1987) and and contains the the Breccia Member of of Reany contains Breccia Member Reany Lake Lake of the the Volcanics Volcanics of of Silver Silver Mine Mine Lakes and and Gabbro of Lakes of Clark Clark Creek. Creek. Location: SW+, section 27, 27, T49N, SWi, section T49N, R27W. R27W. Location: Retrace route to to Red Red road Retrace route road at first first Deer Deer Creek Creek bridge bridge and turn turn right right (north) (north) on the the main main gravel/dirt gravel/dirt road road and and at at 41.3 41.3 mi mi turn turn right Continue on right at 38.0 38.0 mi. mi. Continue (south) to gravel At 46.3 mi, turn turn left (east) to dirt road, (south) gravel County County Road Road 510. 510. At 46.3 mi, (east) to road, the the Park near and walk walk 1200 1200 feet feet east east on on the road, Holyoke Holyoke Trail. Park near intersection intersection and road, then then 160 160 feet southeast southeast to Stop Stop 9. 9. 49.5 49.5 Stop 99 Stop -- Breccia These outcrops, located located along along the the extension of the These outcrops, extension of the Willow Willow Creek Creek Shear Shear Zone, Zone, The matrixconsist of aa breccia matrixconsist of breccia member member interbedded interbedded with with pillowed pillowed basalt. basalt. The supported breccia consists consists of of several several types types of of flattened to 1:20) supported breccia flattened clasts clasts (1:10 (1:lO to 1:20) in aa basaltic matrix. basaltic matrix. The margins of some clasts are are feathered. The clasts The margins of some clasts feathered. The clasts vary vary in size size from lensoidal 1/5 inch inch fragments to 44 inch wide feetlong long fragments. fragments. fragments to wide and and 66 feet from lensoidal 115 Clast types Clast types include include rhyolite, rhyolite, gabbro, gabbro, and and granodiorite. granodiorite. The rhyolite The rhyolite clasts clasts are are porphyritic with 20% phenocrystsinin aa fine-grained, porphyritic 20% plagioclase plagioclase phenocrysts fine-grained, quartz, quartz, plagioclase, plagioclase, and chlorite chlorite matrix. matrix. The granodioritic granodioritic clasts are porphyritic porphyritic with with40% 40%plagioclase plagioclase phenocrysts in in fine-grained, phenocrysts fine-grained, quartz quartz and and chlorite chlorite groundmass. groundmass. The gabbro gabbro clasts clasts are are medium-grained, sub-ophitic sub-ophitic with with plagioclase, plagioclase, chlorite chlorite and and amphibole. amphibole. The matrix medium-grained, matrix of the of mainly chlorite and and epidote epidote with with up to 5% pyrite. pyrite. of the breccia breccia consists consists of mainly chlorite to 5% This breccia breccia is interpreted interpreted as as aa subaqueous subaqueous mudflow mudflow which which has has undergone undergone a high high amount amount of strain. strain. This locality This locality was was mapped mapped most most recently recently by by MacLellan MacLellan and and Bornhorst Bornhorst (1988) (1988) and is of Bismark Creek of of the Volcanics of is designated designated as the the Breccia Breccia Member Member of Bismark Creek Volcanics of Location: SE+, SEk section section 31, 31, T49N, T49N, R26W. R26W. Silver Mine Lakes. Silver Lakes. Location: Continue south on County 48.4 mi, mi, pull pull off off to to right rightshoulder shoulder Continue south County Road Road 510. 510. At 48.4 Be careful, careful, this (outcrops on on other other side of (outcrops of road). road). Be this road road is heavily heavily traveled traveled at times. A-62 �51.4 Basalt, and and Gabbro Gabbro Stop 10 -- Iron-Formation, Basalt, Stop This outcrop outcrop consists consistsofof iron iron formation formationinin contact contacttoto the the north north and south with This between the the massive massive basalt. basalt. To the the west west the the basalt basalt is is cut cut by by gabbro. gabbro. The contact between iron-formation is is approximately approximately 55 basalt basalt and gabbro gabbro follows follows the the highway. highway. The iron-formation exclusively of of fine, black feet thick thick and andtrends trendsN30°W. N30°W It is is compcsed compcsed almost almost exclusively black chert which To the west which contains contains scattered scattered magnetite magnetite grains grains and abundant abundant pyrite, pyrite. To west of this is generally layered with with 1/2 inch this locality, locality, the the iron-formation iron-formation member member is generally layered inch chert and and magnetite magnetite bands. bands. Although the magnetite content can can be highly Although the magnetite content highly variable, the iron-formation variable, iron-formation produces produces aa strong strong magnetic magnetic signature. signature. dark green to dark to black, black, fine-grained fine-grained and and relatively relatively non-foliated. non-foliated. The basalt basalt is is The gabbro The gabbro is is medium-grained, ophitic ophitic to to sub-ophitic, sub-ophitic, and is medium-grained, is composed composed of equigranular equigranular amphiamphibole, plagioclase bole, plagioclase and chlorite. chlorite. This locality was mapped mapped most most recently recently by by Puffett (1974) This locality was (1974) as the the Lighthouse Lighthouse A more Point of the of uncertain more Point Member Member of the Mona Mona Schist Schist and and Metadiabase Metadiabase of uncertain age. age. A satisfactory correlation isis with with the Pillowed satisfactory correlation Pillowed Basalt Basalt and Iron Iron Formation Formation Members Members of of the Volcanics of Silver Mine Lakes Lakes and and the the Gabbro Volcanics of Silver Mine Gabbro of Clark Clark Creek Creek as as mapped mapped Location: SE+, SEi, section 5, 5, one mile mile to to the theeast eastby byMacLellan MacLellanand andBornhorst Bornhorst(1988). (1988). Location: T48N, T48N. R26W. R26W. 48.8 mi, mi, intersection intersection with with North North Continue Continue south on County County Road Road 510. 510. At 48.8 At 50.6 mi, pull off to right At 50.6 mi, pull to right Basin Road and pavement begins, Continue south. Basin Road and pavement begins, continue south. Walk east east across shoulder, just just before across road road shoulder, before going going downhill downhill and and across across a bridge. bridge. Walk along an an abandoned along abandoned portion portion of 510 510 to to small small outcrops. outcrops. 53.6 Stop Stop 11 (optional) (optional) -- Archean greywacke This outcrop of black, This outcrop consists consists of black, quartz-feldspar-sericite-chlorite quartz-feldspar-sericite-chlorite schist with with This rock rock is interpreted interpreted as as minor minor disseminated disseminated pyrite; pyrite; foliation foliation trends trends westerly. westerly. This greywacke. This extends eastward eastward for for 8 miles This particular particular member member extends miles and and represents represents The the only the only major major sedimentary sedimentary unit within within the the Marquette Marquette Greenstone Greenstone Belt. Belt. The member consists consists of of greywacke member greywacke and slate. slate. A- 63 �This This locality locality was was mapped mapped most most recently recently by Puffett Puffett (1974) (1974) as as the theNealy Nealy Creek Creek Location: Sf, Si,section section 10, 10,T48N, T48N,R26W. R26W. Member of of the theMona MonaSchist. Schist. Location: Member Continue Continue south south on on County County Road Road 510. 510. At At 50.85 50.85 mi, mi, cross cross bridge bridge over over the the At 52.9 mi, bear left and at 53.0 mi, turn left(east) (east) Dead Dead River RiverStorage StorageBasin. Basin. At 52.9 mi, bear left and at 53.0 mi, turnleft and to to the the east east end endofofCounty CountyRoad Road502. 502. At At 53.6 53.6 mi, mi, turn turn left left (east) (east) to to U.S. U.S. 41 41 and return return to to the theRamada Ramada Inn InnininMarquette. Marquette. END END OF OF DAY DAY 11 Acknowledgements and References References in Day Acknowledgements and Day 22 Road Road Log. Log. A- 64 �Geological Field Trip Trip to to the Marquette Belt: Part II Geological Field Marquette Greenstone Greenstone Belt: I1 Day Day 2 Road Road Log Log -- Stops Stops A to EE T.J. T.J. Bornhorst Bornhorst and and D.A. D.A. Baxter Baxter Department Department of of Geology Geology and andGeological Geological Engineering Engineering Michigan Technological Technological University, University, Houghton, Houghton, Michigan Michigan 49931 49931 NOTE: The field field trip trip for forDay Day22includes includes aalate latemorning morning to to afternoon afternoon stop stop at at the the NOTE: The There is aa separate separate guide, guide, Part Part III, 111,authored authored by byBrozdowski Brozdowski and and Ropes Mine. Mine. There Ropes Additional information on on the thegeologic geologic of Callahan Callahan Mining Mining Corporation. Corporation. Additional Scott of setting of the setting of the field field trip trip stops stops may may be be found found in in the thepaper paperby byBornhorst Bornhorst (this (this volume). volume). Refer Refer to to Day Day 11Road Road Log, Log, Figure Figure 1:1: Route Route and and Stop Stop Map Map Mileage Mileage Start Start Day Day 22 -- Ramada Ramada Inn, Marquette Marquette 0.0 Assemble at the the main Assemble at main entrance entrance of the the Ramada Ramada Inn. Inn. Turn Turn right right out out of of the the parking to U.S. parking lot of of the the Ramada Ramada Inn Inn to toWashington Washington Street Street to U.S. 41 and and then then west west At 13.8 13.8 mi, mi, turn turn right right (north) (north) at at traffic traffic light light to toCounty County Road Road towards Ishpeming. Ishpeming. At towards At 14.75 14.75 mi, mi, pull pull off off to to the theright rightshoulder shoulder 14.6 mi, mi, hairpin hairpin turn turn left. left. At 573. 573. At 14.6 alongside of of outcrops. outcrops. alongside 14.75 14.75 Stop Stop A -- Schist Schist These These rocks rocks are foliated foliated quartz-sericite quartz-sericite schists schists with with angular angular carbonate carbonate clots clots rocks are are N70° and dips dips 84°S. 84OS. The rocks Foliation strikes N70°W scattered throughout throughout them. them. Foliation intermediate (dacite) arid and have rocks intermediate in composition composition (dacite) have a calc-alkalic calc-alkalic affinity. affinity. These rocks are interpreted interpreted totobebesubaqueously subaqueously deposited deposited volcaniclastic volcaniclastic sediments sediments or orpyroclastic pyroclastic deposits, and are are an important of the the southwestern part of of the deposits, and important component component of southwestern part greenstone belt. belt. This locality most recently recently by by Clark locality was was mapped mapped most Clark and others others (1975) (1975) as as the the Kitchi Location: NW+, NWL section 34, 34, T48N, T48N,R27W. R27W. Kitchi Schist. Schist. Location: 14.9 mi, mi, Deer Deer Lake Lake is is on on right. right. At Continue NW NW on County County Road Road 573. 573. At 14.9 15.55 mi, pull pull off to 15.55 mi, to the theright rightshoulder shouldernear nearglacially glaciallypolished polished surface. surface. 15.55 15.55 Stop Stop B -- Breccia Breccia The breccia outcrop and and on the The breccia is exposed exposed in aa glacially glacially polished polished outcrop the lake lake shore. shore. A-65 �On Onthe thepolished polished surface, surface, the the clasts clasts vary vary from from 10" 10" X X 14" 14" down down to to the the size size of ofthe the matrixgrains. grains. Larger Larger clasts, clasts, up to to 2' 2, XX4'4'inincross crosssection, section,are arepresent present ininthe the matrix lakeshore shoreoutcrops. outcrops. Clasts Clasts greater greater than than 1/2" 1/2" make make up up about about 20% 20% of of the therock rockand and lake thereisisananobvious obviousstratification stratificationininclast clastsize. size. Shape Shape of of clasts clastsvaries variesfrom from there Theclasts clastsare areandesite-dacite andesite-dacite(near (nearcompositional compositional very-angular totorounded. rounded. The very-angular division) division) inincomposition compositionwith withsmall smallchemical chemicalvariation variationbetween betweenindividual individualclasts clasts studiedtotodate. date. This This breccia breccia isisinterpreted interpretedasasa asubaqueously subaqueouslydeposited depositedmudflow mudflow studied breccia. breccia. This Thislocality locality was was mapped mapped most most recently recently by byClark Clarkand andothers others(1975) (1975)asas Location NE+, N E k section section33, 33,T48N, T48N.R27W. R27W. agglomerate facies facies of of the theKitchi KitchiSchist. Schist. Location agglomerate At 17.5 17.5 mi, mi, turn turn totoleft lefton ongravel gravelroad road toto Continue on onCounty CountyRoad Road573. 573. At Continue See Field Field Trip TriptotoCallahan CallahanMining MiningCorporation CorporationRopes RopesMine Mine the Ropes RopesMine. Mine. See the Property (this (thisvolume). volume). Property At 34.2 34.2 mi, mi, enter entercity cityofofMarquette Marquette Retrace route routeback backtowards towardsMarquette. Marquette. At Retrace and and atat34.5 34.5 mi, mi,make makeaaleft leftturn turnononWashington WashingtonStreet Street towards towards the the Ramada Ramada Inn. Inn. At At 34.95 34.95 mi, mi, turn turn left left totoRublein Rublein Street Street and and at at 35.1 35.1 mi, mi, turn turn right right totoRidge Ridge Pull over over and and park park atat35.3 35.3mi, mi,near nearsmall smalloutcrops outcrops on onright rightshoulder. shoulder. Street. Pull Street. Stop CC (optional) (optional) -- Schists Schists Stop 35.3 35.3 AA small small roadcut roadcut on on the thesouth southside sideofofRidge RidgeStreet Streetexposes exposeswell-foliated well-foliated Foliation strikes strikes roughly roughly E-W E-W and and dips dipsvertical. vertical. On On the the chlorite-sericite schists. schists. Foliation chlorite-sericite north north side, side, about about 200 200 feet feet through through the the trees, trees, there thereisisa aclearing clearingwith withglacially glacially polished outcrops. outcrops. On On the the way way totothe theclearing clearingthere thereare arelayered layeredamphibolitic amphibolitic polished A banded, banded, tabular tabular body body ofofquartz-sericite quartz-sericite schists D). A schists (discussed (discussed further at at Stop Stop D). schist schist is is well well exposed exposed at the the clearing; clearing; this is is interpreted interpreted as as aa rhyolite rhyolite dike. dike. The The contorted contorted banding banding is either either due due to to primary primary flow flow banding banding and/or and/ordeformation. deformation. We We consider consider the the latter latterinterpretation interpretation the themost mostlikely. likely. This This locality locality was was most most recently recently mapped mapped by Gair Gair and and Thaden Thaden (1968) (1968) as as the the Location NE+, NEi, section section 22, 22, T48N, T48N, Lighthouse Lighthouse Point Point Member Member of of the theMona MonaSchist. Schist. Location R25W. R25W. A-66 �Continue Continue east east on Ridge Ridge Street Street and at at 35.4 35.4 mi, mi, turn turnright righttotoLincoln LincolnAvenue. Avenue. Continue straight straight on on At Washington At 35.5 35.5 mi, mi, turn turnleft leftatattraffic trafficlight lightto to WashingtonStreet. Street. Continue Washington Street past past the the Ramada Ramada Inn, Inn, from 36.1 Washington Street 36.1 mi mi until until 36.6 36.6 mi, mi, where where At 37.1 37.1 mi, mi, Washington Street ends at Washington Street at Lake LakeStreet. Street. Turn Turn left left on onLake LakeStreet. Street. At make make aa right right turn turn atatthe theentrance entrancetotothe theMaritime Maritimemuseum museum and andcontinue continue on onroad road to to the the Coast Coast Guard Guard Station Station and and park.. park.. 37.25 37.25 D -- Lighthouse Lighthouse Point Point Member Member Stop D Stop You from the U.S. You must must obtain obtain permission permission from U.S. Coast Coast Guard to to visit visit this this locality. locality. No rock rockhammers hammersallowed!! allowed!! No Excellent on Lighthouse Lighthouse Point Point provide provide a view Excellent shoreline shoreline exposures exposures on view of of Archean Archean We will will walk walk around around the the point point noting noting the thelocalities localities shown shown and and Proterozoic Proterozoic rocks. rocks. We in detail This area area was was most most recently recently mapped mapped in detail by Gair Gair and and Thaden Thaden on Figure Figure 2. 2. This on (1968) as the Lighthouse Point Member Member of of the Mona (1968) as Lighthouse Point Mona Schist Schist cut by by Early Early ProteroProteroLocation: NW+, NWL section 24, 24, T48N, T48N,R25W. R25W. zoic zoic and and Keweenawan Keweenawan diabase diabase dikes. dikes. Location: Stop Stop Dl. Dl. Archean, (basaltic) schist schist isis cut by Archean, thinly thinly layered, layered, amphibolitic amphibolitic (basaltic) by aa tabular, tabular, porphyritic porphyritic rhyolite rhyolite dike dike trending trending roughly roughly parallel parallel to to the t h elayering. layering. The The layers layers on on Lighthouse Point, as aa whole, Lighthouse Point, whole, strike strike approximately approximately E-W E-W and and dip dip70°N. 70°N This This layered layered schist schist was was mapped mapped by Gair Gair and and Thaden Thaden (1968) (1968) as as the the Lighthouse Lighthouse Point Point The layers layers in in the the schist schist are areinterpreted interpreted asasflattened flattenedpillows pillows (basalt). (basalt). Member. Member. The The mechanism of flattening could be be primary, primary, but but we interpret mechanism of flattening could interpret high high strain strain as as the the most most important important means means of of flattening. flattening. The The rhyolite rhyolite is is interpreted interpreted as as an anlate-tectonic late-tectonic rhyolite dikes dikes in in the greenstone belt are more Archean dike. dike. Some Some rhyolite greenstone belt more strained strained than than others. others. The are cut by The Archean Archean rocks rocks are by two two N-S N-S trending trending diabase diabase dikes that are are metamorphosed to greenschist greenschist facies facies and and are are distinctly metamorphosed to distinctly younger younger than the the layered layered and Thaden Thaden (1968) (1968) interpreted interpreted these these dikes dikes as as Early Early amphibolite-grade amphibolite-grade schist. schist. Gair and However, Baxter Baxter and Bornhorst Bornhorst (1988) (1988) suggest suggest these these porphyporphyProterozoic Proterozoic in in age. age. However, ritic ritic dikes dikes are are Archean Archean in in age, age, correlative correlative with with the theMatachewan Matachewan dike dike swarm swarm in in Ontario. Ontario. A- 67 �EXPLANATION EXPLANATION Keweenawan Keweenawan @Diabase Diabase ProterOzoiC proterozolc Diabase Diabase Archean Archean9 ? Gabbro Gabbm Rhyolite UhyoIitO Archean Archean Ala Layered L a y e r e dAmphlbolitic AmphiboliticSchist Schist — Contact Contact -----Fault Fault Pd Ag Ar 0 I 50 50 100 100 I ftf t If Ala F i g u r e2:2: Figure Geology Geology of of Lighthouse L i g h t h o u s e Point, P o i n t , Marquette, M a r q u e t t e , Michigan. Michigan. Modified Modified slightly s l i g h t l y from from detailed d e t a i l e d map map by by Gair G a i r and and Thaden (1968). ( 1 9 6 8 ) . Numbers Numbers at a t localities l o c a l i t i e s described described Thaden i n text. text. in A-68 �Walk over ridge ridge to to other side A relatively relatively unmetamorphosed, unmetamorphosed, Walk over side of of the the point. point. A E-W diabasedike dikecrops cropsout out along along the the crest crest of of the E-W trending trending Keweenawan Keweenawan diabase the ridge. ridge. Stop Stop D2. D2. There There are are bodies bodies of of comparatively comparatively massive, massive, fine fine to tomedium-grained medium-grained (Archean?) (Archean?) body must must have have been been gabbro within within the the layered layered amphibolilic amphibolilic schist. schist. This body relatively late-tectonic due due to to the relatively late-tectonic the lack lack of of foliation/strain foliation/strain as as compared compared to the the amphiboliticschist schistand and gabbro gabbro are are cut cut by aa Layered amphibolitic surrounding layered layered schists. schists. Layered metamorphosed metamorphosed (Proterozoic?) diabase dike. dikeStop D3. D3. Intense Intense foliation foliation has has obliterated obliterated layering layering at this this location; location; interpreted interpreted as as aa higher higher strain strain zone zone within within the the layered layered amphibolitic amphibolitic schist. schist. Stop Stop D4. D4. Layered schist is cut Layered amphibolitic amphibolitic schist cut by by aametamorphosed metamorphosed (Proterozoic?) (Proterozoic?) diabase diabase dike and and layered layered amphibolite amphiboliteschist schistare arecut cut by by a thin, dike. The metamorphosed metamorphosed dike thin, relatively E-W trending trending diabase diabase dike dike of Keweenawan The relatively unmetamorphosed, unmetamorphosed, E-W Keweenawan age. age. The metamorphosed diabasedike dike isis offset offset by aa small metamorphosed diabase small NW-SE NW-SE trending trending fault. fault, Retrace Retrace route back back to to Lake Lake Street. Street. At 37.4 37.4 mi, mi, turn turn right right totoLakeshore Lakeshore Blvd. Blvd. and proceed 38.2 mi, mi, junction junction proceed along along the the lakeshore lakeshore towards towards Presque Presque Isle Isle Park. Park. At 38.2 with Fair Fair Avenue, Avenue, stay stay on on Lakeshore Lakeshore Blvd. Blvd. and at at 38.7 38.7 mi, mi, Lakeshore Lakeshore Blvd. Blvd. joins joins Pine 38.8 mi, mi, excellent excellent view view of active active iron iron ore ore docks docks and and Presque Presque Isle Isle Pine Street. Street. At 38.8 (an Archean, Archean, serpentinized serpentinized peridotite peridotite unconformably unconformably overlain overlain by by Jacobsville Jacobsville 39.3 mi, mi, turn turn left lefttotoHawley Hawley Street Street before before power power generating generating plant. plant. Sandstone). At 39.3 Sandstone). At 40 40 mi, mi, turn turn right right(north) (north)totoCounty County Road Road 550. 550. At 43.6 43.6 mi, pass pass turnoff turnoff to to Sugarloaf Mountain overlook overlook (requires (requires climb climb along along aa maintained Sugarloaf Mountain maintained trail trail with with steps). steps). At 43.8 on both 43.8 mi, mi, large large granitoid granitoid gneiss gneiss outcrops outcrops on both sides sides of the the road. road. At 44.9 44.9 mi, pathway to to Harlow Harlow Lake, Lake, into into a mi, turn turn right right towards towards the the lakeshore, lakeshore, opposite opposite pathway small parking area. area. small 44.9 Stop E£ -- Plutonic Plutonic rocks rocks at a t Wetmore Wetmore Landing Landing Stop Walk around the the gate gate and and down down aa dirt road Walk around road to to the thelakeshore lakeshore and and proceed proceed east. east. Walk SE along along the the road Walk SE road above above the the beach beach totolarge largerounded roundedwave-washed wave-washed outcrops outcrops to view of granitoid view features features characteristic characteristic of granitoid rocks rocks which which intrude intrude the the volcanic volcanic rocks rocks A-69 �of the theMarquette MarquetteGreenstone GreenstoneBelt. Belt. of The dominant dominant rocks rocks are aregneissic gneissictonalite tonalitetotogranodiorite. granodiorite. These These plutonic plutonicrocks rocks The are are cut cut by bytonalite tonalitedikes dikesofofvarying varyingage, age,by bymafic maficdikes dikes(amphibolite), (amphibolite), and and by by The mafic mafic dikes dikes are are irregular irregular in in plan plan view view and and veins of of quartz quartzofofvarying varyingage. age. The veins are deformed deformed(Baxter (Baxter and andBornhorst, Bornhorst,1988). 1988). Ductile Ductile to to brittle brittle shear shear zones zones cut cut the the are rocks; epidote epidote isis associated associated with with the the brittle brittleshears. shears. These These outcrops outcrops display display the the rocks; complex history history experienced experienced by by the thegranitoid granitoid rocks. rocks. These These features features are are often often complex obscured obscured in inmore moretypical typicalmoss-covered moss-covered outcrops. outcrops. This This locality locality was was most most recently recently mapped mapped in in detail detail by by Gair Gairand andThaden Thaden(1968). (1968). Location: SE+, SEi7section section 29, 29, T49N, T49N,R25W. R25W. Location: Return to toRamada Ramada Inn. Inn. Return END OF OFDAY DAY 22 END ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS This This field field trip tripwould would not notbebepossible possiblewithout without support supportby bythe theMichigan Michigan Geological Survey, Department Department of of Natural Natural Resources Resources and and the Department Geological Survey, Department of of Geology University for an Geology and Geological Geological Engineering, Engineering7 Michigan Michigan Technological Technological University an This field field guide guide on-going on-going program program of of research research on on the theMarquette Marquette Greenstone Greenstone Belt. Belt. This has has benefited benefited from fromreviews reviews by byJ.J.Kalliokoski, Kalliokoski,Michigan MichiganTechnological Technological University, University, and K. K.Schulz, Schulz7U. U.S.S.Geological GeologicalSurvey. Survey. and REFERENCES REFERENCES Baxter, Baxter, D.A. D.A. and and Bornhorst, Bornhorst, T.J., T.J., 1988, 1988, Multiple Multiple Discrete Discrete Mafic Mafic Intrusions Intrusions of of Archean Archean to to Keweenawan Keweenawan Age, Age7western western Upper UpperPeninsula, Peninsula7Michigan Michigan[abs.]: [abs.]: ProceedProceedings ings and and Abstracts, Abstracts, 34th 34th Institute Institute on onLake LakeSuperior Superior Geology, Geology7Marquette, Marquette, Michigan Michigan (this volume). volume). (this Baxter, Baxter, D.A., D.A.7 Bornhorst, Bornhorst, T.J., T.J., and and VanAlstine, VanAlstine7J.L., J.Le71987, 19877Geology, Geology7Structure, Structure, and Metal Mineralization Mineralizationofof Archean Archean Rocks Rocks in in the and Associated Associated Precious Precious Metal the Vicinity V i c i ~ i t yof of Clark Clark Creek, Creek7Marquette Marquette County, County,Michigan: Michigan: Michigan MichiganGeological Geological Survey Survey Division, Division7 Department of Natural Open File File Report Department of Natural Resources, Resources7 Open Report OFR-87-8, OFR-87-8, 54 54 p. p. Clark, Clark7L.D., L.D., Cannon, Cannon7 W.F., W.Fe7and and Klasner, Klasner, J.S., J.S., 1975, 1975, Bedrock Bedrock Geologic Geologic Map Map of of the the Negaunee Negaunee SW SW Quadrangle, Quadrangle, Marquette Marquette County, County7Michigan: Michigan: U.S. U.S. Geological Geological SurSurvey, vey7Miscellaneous Miscellaneous Map Map Series, Series, GQ-1226. GQ- 1226. A-70 �Gair, J.E. and Gair, and Thaden, Thaden, R.E., R.E., 1968, 1968, Geology Geology of the the Marquette Marquette and and Sands Sands Quadrangles, Marquette County, Michigan: Quadrangles, Marquette Michigan: U.S. U.S. Geological Geological Survey Survey Professional Professional Paper Paper 397, 397, 77 p. p. Johnson, R.C., R.C., Bornhorst, T.J., and VanAistine, Johnson, Bornhorst, T.J., VanAlstine, J.L., J.L., 1987, 1987, Geologic Geologic Setting of Precious Metal Mineralization Mineralizationinin the the Silver Creek to Island Precious Metal Silver Creek Island Lake Lake Area, Area, Marquette Marquette County, Michigan Geological Geological Survey Survey Division, Division, Department Department of of Natural County, Michigan: Michigan: Michigan Resources, Open File File Report OFR-86-2, 134 Resources, Open Report OFR-87-4, OFR-87-4, Supersedes Supersedes OFR-86-2, 134 p. p. MacLellan, M.L. M.L. and and Bornhorst, T.J., 1988, MacLellan, Bornhorst, T-J., 1988, Geology, Geology, Structure, and and MineralizMineralization Reany Lake LakeArea, Area,Marquette MarquetteCounty, County,Michigan: Michigan: Michigan Michigan Geological Geological ation of the the Reany Survey Division, Department Departmentofof Natural Natural Resources, Resources,Open OpenFile File Report Report (in (in preparaSurvey Division, preparation). Puffett, W.P,, W.P., 1974, 1974, Geology Geology of the the Negaunee Negaunee Quadrangle, Quadrangle, Marquette Marquette County, County, Michigan: U.S. 788, 53 53 p. p. Michigan: U.S. Geological Geological Survey, Survey, Professional Professional Paper Paper 788, A-71 �Geological Field Trip Trip to the Belt: Geological Field the Marquette Marquette Greenstone Greenstone B e k Part III I11 Callahan Callahan Mining Mining Corporation Corporation Ropes Ropes Mine Mine Property Property R.A. R.A. Brozdowski Brozdowski and G.W. G.W. Scott Scott Callahan Callahan Mining Mining Corporation Corporation Exploration Exploration Dept. Dept. 25 25 Industrial Industrial Park Park Rd., Rd., Negaunee, Negaunee, Michigan, Michigan,49866 49866 NOTE: Additional information informationononthe theRopes RopesMine Minemay maybe be found found in in the paper NOTE: Additional paper by by Brozdowski Brozdowski in this this volume. volume. STOP STOP 1. le (Outcrop (Outcrop is 225 m west west of of the the intersection intersection of of the theRopes Ropesmine mineaccess access road road with road curves to south with the the paved paved highway: highway: Park where where access access road curves to south and and walk walk the the Julius Ropes Ropes made made final final 40 40 m m west west along along the the cut cut line line totoa asmall smallprospect prospect pit). pit). Julius his of gold his initial initial discovery discovery of gold at or or near near this this spot spotinin1880, 1880,and andsubsequently subsequently discovered the Ropes main ore ore zone The outcrop outcrop in the the pit pit isis discovered the Ropes main zone 250 250 m to to the the west. west. The a fine quartz-sericite-chlorite rock with with fine grained, grained, massive massive to to moderately moderately foliated, foliated, quartz-sericite-chlorite I abundant abundant 0.2 mm mm quartz quartz grains grains and and 11 -- 22 mm rectangular rectangular mats mats comprised comprised of of aphanitic The aphanitic sericite sericite in aa matrix matrix of of aphanitic aphanitic quartz, quartz, sericite, sericite, and andchlorite. chlorite. The sericite sericite mats mats are are interpreted interpreted asaspseudomorphs pseudomorphs after afterfeldspar feldsparphenocrysts, phenocrysts,because because progressively more sericite sericite altered progressively more altered feldspar feldspar phenocrysts phenocrysts are observable observable in in this this same same feldspar remains remains rock rock type type as as the the Ropes Ropes mine mine isisapproached approached from from the thewest. west. No feldspar the north Toward the north side side of the the pit pit isiswell well foliated foliated within within or east east of of the the mine. mine. Toward quartz-sericite quartz-sericite rock rock in in contact contact with with massive, massive, rusty rusty brown brown weathering weathering carbonatecarbonatequartz rock rock with with white whitecarbonate carbonate veins. veins. 2. STOP 2. to a letter (105 According to letter written written (105 m at at azimuth azimuth 285 285 degrees degrees from from stop stop 1). 1). According by by Julius Julius Ropes Ropes in in 1890, 1890, these these two two small small quarries quarries were were excavated excavated in the the late late 1880's to provide provide carbonate carbonate flux flux for for a nearby 1880's to nearby iron iron ore ore blast blast furnace. furnace. The north north wall wall of both both quarries quarries is is aafine finegrained, grained,well wellfoliated, foliated,light-green light-green carbonate-talc carbonate-talc rock Massive, rock with with lenses lenses of of blue-green blue-green talc talc and and white whitecarbonate carbonateveins. veins. Massive, carbonate-quartz rock occurs occurs toward toward the the south south ends ends of of the eastern carbonate-quartz rock eastern walls walls of of both both A-72 �serpentinized peridotite peridotite crops crops out uphill quarries. quarries. Brown Brown weathering, weathering, carbonatized, carbonatized, serpentinized uphill from the the quarries. quarries. from STOP STOP 3. 3. (Park (Park across across highway highway from from Ropes Ropes mine mine access access road, road, follow follow path pathsoutheastward southeastward peridotite at at this locality The serpentinized serpentinized peridotite locality has has aa well well to shore shore of of Deer Deer Lake). Lake). The developed fine grained texture of of 3-5 3-5 mm mm serpentine pseudomorphs pseudomorphs after after developed fine grained cumulate cumulate texture and lesser lesser pyroxene. pyroxene. The rock rock has has curvilinear curvilinear fracture fillings fillings of olivine and asbestos. chrysotile asbestos. STOP 4, 4. Examine drill core core and and hand of various various types types of of ore and Examine drill hand specimens specimens of and major major types types of wall wall rock rock from from the theRopes Ropes mine mine property. property. View View geologic geologic maps maps of Ropes Ropes mine mine area area and and geologic geologic plans plans and and cross cross sections sections of of Ropes Ropes mine. mine. A-73 �Field Field Trip Trip No. No. 22 Marciuette Mineral District District of of Michicran Michian Marouette Mineral Mining Minincr History History and andGeolociy Geolocrv by Burton Boyum Burton H. Boyum Mining Mining Department, Department, Retired Retired Cleveland-Cliffs, Cleveland-Cliffs, Inc. Inc. and and Robert Robert C. C. Reed Reed Michigan Michigan Geological Geological Survey Survey May, May, 1988 1988 �MARQUETTE MARQUETTE MINERAL MINERAL DISTRICT DISTRICT OF OF MICHIGAN MICHIGAN MINING HISTORY HISTORY AND AND GEOLOGY GEOLOGY MINING Introduction Introduction Welcome to to the the Marquette Marquette Mineral Mineral District District situated situated in in Welcome Marquette County County and and the the eastcentral eastcentral part part of of Baraga Baraga County County in in the the Marquette Upper Peninsula Peninsula of of Michigan Michigan (Figure (FigureA)! A)! This This district district was was the the Upper first of of the the iron iron "ranges" "ranges" of of the the Lake Lake Superior Superior region region to to be be first developed mid-1800ts,and and hosts hosts the the only only iron iron mines mines still developed in in the the mid-1800's, still active in in the the Upper Upper Peninsula, Peninsula, the active the Empire Empire and and Tilden TildenMines. Mines. The The Marquette Marquette Mineral Mineral District District also also contains contains the the only only operating operating gold gold mine in in the the U.S. U.S. portion mine portion of of the the Lake Lake Superior Superior region, region, the the Ropes Ropes Mine, and and has has known knowndeposits depositsof of copper. copper. Mine, The The dominant dominant geologic geologic feature feature of of the the district district is is the the Marquette Marquette trough which which contains contains rocks rocks of of the the Marquette Marquette Range Range Supergroup, Supergroup,an trough an Early Proterozoic Proterozoic sequence sequence of of mostly mostly sedimentary sedimentary and and lesser lesser Early volcanic volcanic rocks rocks deposited deposited unconformably unconformably on on Archean Archean greenstones greenstones and and gneisses of of the the Superior SuperiorCraton. Craton. The The Marquette Marquette Range Range Supergroup Supergroup gneisses consists of of four four groups groups (Cannon (Cannon and and Gair, Gair, 1970), 1970), from from oldest oldest to to consists youngest, the the Chocolay, Chocolay, Menominee, Menominee, Baraga, Baraga, and and Paint Paint River River Groups. Groups. youngest, The three three oldest oldest are are preserved preserved in in the the Marquette Marquette trough, trough, wereas wereas the the The Paint River River Group Group is is found found only only in in the the Iron Iron River-Crystal River-Crystal Falls Falls Paint District to to the the southwest.The southwest.The rocks rocks of of the the Supergroup Supergroup record record aa District progressive progressive change change intectonic intectonicconditions conditionsfrom from aa stable stable craton craton (Chocolay (Chocolay Group) Group) through through aa sedimentary sedimentary basin basin with with mild mild tectonism tectonism (Menominee Group) Group) to to aa highly highly active active tectonic tectonic basin basin (Baraga (BaragaGroup) Group) (Menominee as the the long—stable long-stable Superior Superior Craton Craton was was reactivated reactivated at at the the onset onset of of as the Penokean Penokean Orogeny. Orogeny. The The time time of of deposition deposition of of the the Supergroup Supergroup is is the still poorly poorly constrained, constrained, but but deposition deposition probably probably commenced commenced about about still 2.1 2.1 b.y. b.y. and and was was terminated terminated with with the the Penokean Penokean Orogeny Orogeny about about 1.85 1.85 b.y. (Morey, (Morey,1983). 1983). Keweenawan Keweenawan dikes dikes cut cut rocks rocks of of the theSupergroup, Supergroup, b.y. and the the Jacobsville Jacobsville sandstone, sandstone, of of probable probable Keweenawan Keweenawan age, age, and and and lower lower Paleozoic Paleozoic sedimentary sedimentary rocks rocks unconformably unconformably overlie overlie units units of of the Supergroup locally. the Supergroup locally. Pleistocene Pleistocene sand, sand, gravel, gravel, silt, silt, till, till, and and clay clay were were deposited deposited over over the the district district about about 10,000 10,000 years years ago ago during during retreat retreat of of the the last last Outwash deposits deposits of of silt, silt, sand, sand, and and gravel gravel preserved preserved glaciers. Outwash glaciers. Quaternary Quaternary trees, trees, mostly mostly spruce, spruce, in in the the Tilden Tilden Mine Mine Gribben Gribben Basin Basin Buried Forest Forest near nearPalmer. Palmer. The The remains remains of of more more than than 100 100 trees trees are are Buried preserved with with their their roots rootsin in place. place. Carbon Carbon 14 14 dates dates on on material material preserved from from these these trees, trees, which which have have as as many many as as 150 150 growth growth rings, rings, range range This indicates indicates the the recession recession of of the the y.B.P. This from 9545 9545 to to 10,230 10,230y.B.P. from Valders (Great (GreatLakean) Lakean) glacier glacier(Hughes, (Hughes,1979). 1979). Figure Figure BB shows shows aa Valders cross section section of of the the Gribben Gribben Basin Basin forest. forest. cross Economic Considerations Considerations Economic The The principal principal mineralization mineralization of of the the Marquette Marquette Mineral Mineral District District Total has has been been iron, iron, with with some some manganiferous manganiferousiron ironore. ore. Total shipments shipments of of iron iron ore ore through throughDecnither, December, 1987 1987 were were 590,776,442 590,776,442long longtons. tons. The The the Empire and the Tilden, two two active active iron iron mines mines of of the the district, district, the Empire and the Tilden, each each mine mine taconite taconite type type ore ore in in open open pit pit operations, operations, and and through through the the produce a high grade produce a high grade use of concentrators and pellet plants, use of concentrators and pellet plants, product. Shipping Shipping ports ports for for the the taconite taconite pellets pellets are are Marquette Marquette and and product. Escanaba. Escanaba. B-2 �General Geology ofMichfgan o f Michigan's's Upper Upper Peninsula. Figure A B—3 Figure A �NMU C.rt a r lLob. Ltb. 1978- J.M. 1 SLF SLF Figure B section of of Gribben Gribben Basin Basin Buried Buried Forest. Forest, Paltner Palmer % showing showing cross. cross,section The Reoessiøn of the Valders Glacial Ice, dtring time of Marquette-Munising MoZ'ai Ca,ra 9,925 years B P. 5. •' • • • ... . •* sit S....' •tt• St.. S..b SS ••,••• ' 5 S * S • *' : •.'..: : : S • S • •:. : • S _• - •.. :: •:•e, : %*•t4: •It 55. 55 *5 • • • ,.* • • It.tSi*.s. . . • :. - • •. . • ....t_O.r.. • • • S . . SAN0 . • . • . . ....... -: . • . , ' • •'.' ..0._,.5*,_..t.5, .'etS•5 •• •s''0 •5.....;,., * •.%•. •1• •S • • ''. •'•S .•. s. .. • •*h..5. ' • • •iUNDERLYING • •5 . _...s •Ss.•t St :......,..,5 • IS • Si S v •• • ; ........ .55,. .••t......•. • •••• • •• •,• • • ••1• •. ,•...•• •. ••••t 5 %• • . • • • • • • •S5•• • S. ••••• •••S•••S••S• SO • • I 5 • f.:. — ._..0.s •• •5 • Ste •__• . • _ • •• • • • •e . • • : • • •a • . •• : • . ..• •.e • •.• — ." • s__S.... • it •• • •.. • •.... ••• •• 0.•..• ,•°.° •• • I•,e •5tS5 ,.• S • •_t _.S ••, . • ..-_*•.•• Prepared by John D.Jughes, Northern Michigan University,, 1979 r'±gure B .5 . ORGANIC LAYER._L:. — e—. . • •. .... • • • — • . .. �The The greater greater part part of of the thedistrict's districttsiron ironore orehas hascome comefrom fromthe the Negaunee Iron—Formation Iron-Formationof ofthe theMenominee MenomineeGroup. Group. The The Negaunee, Negaunee! one one Negaunee worldlhas hasaamaximum maximum of the the thickest thickestiron-formations iron-formationsof of the the world, of stratigraphicthickness thickness of of over over1,300 11300meters meters (3,500 (31500feet) feet)in in stratigraphic Negaunee and and Ishpeming. Ishpeming. Some Some iron iron ore ore was was produced produced also also from fromironironNegaunee formation, formationlof of unknown unknown stratigraphic stratigraphiccorrelation correlationto to the theNegaunee Negaunee Iron-Formationlin in the the samller samller Gwinn Gwinn District District to to the the south, southland and Iron-Formation, from the the Bijiki Bijiki Iron-Formation Iron-Formationof ofthe theBaraga BaragaGroup. Group. from Today, Todayltaconite taconiteisisthe theonly onlyore oretype typebeing beingmined.. mined. (The (Theterm term taconiteoriginated originatedin inMinnesota, Minnesota,on onthe theMesabi Mesabi Range, Rangelafter afterState State taconite Geologist N.H. N.H. Winchell Winchell proposed, proposedlin in1884, 1884#that thatthe theiron-formation iron-formation Geologist was of of"Taconic ttTaconic Agett. ) However, Howeverlin in the the past, pastlthe the major ma2or iron ironores ores was Age".) were direct direct shipping shippingor ornatural naturalores oresof of two twomain main varieties. varieties. One were Onewas was ttsofttt ore composed composed of of soft, soft, friable, friablelearthy earthy or or semi—plastic semi-plastic "soft" ore ore hematitelmartite martiteand andgoethite. goethite. The The other other was was "hard" Ithardt8 orecomposed composed hematite, is of dense, denselcompact compactspecular specularhematite hematiteand andmagnetite. magnetite. "Ore" IfOrett is of defined defined as as aa mineral mineral or or minerals minerals from from which which aa metal metal or ormetals metalscan can be mined mined at at aa profit. profit. be natural ores ores were were found found in in three three distinct distinct structural structural The natural The settings. The The soft soft ores ores were were found found in in synclines synclinesand and in infault fault settings. structures structures at at the the base base of of the the Negaunee Negaunee Iron—Formation, Iron-Formationland and in in fault fault structures structures on on the the intrusive intrusive sills sills in in the the upper upper portion portion of of the the Negaunee Iron—Formation. Iron-Formation. The The hard hard ores ores were were found found generally generally at at the the Negaunee Quantitatively, the total top of the Negaunee Iron-Formation. Quantitativelyl the total top of the Negaunee Iron-Formation. footwall long footwall soft soft ores ores shipped shipped from from the the district district was was 186,607,540 1861607f540 long tons, long tonslthe the total total sill sill soft soft ores ores shipped shipped was was 54,092,030 5410921030 longtons, tonsf and the the total total hard hard ores ores was was 60,350,944 6O135OI944 long tons. tons. Maximum Maximum thickness thickness and long of of the the footwall footwall soft soft ore ore was was 80 80 meters meters (260 (260feet) feet) normal normal to to the the bedding; (100feet) feet) bedding; maximum maximum thickness thickness of of the the hard hard ore ore was was 30 30 meters meters (100 (see (see cross cross sections, sectionslFigures FiguresCCand andD). D). The The Marquette Marquette Range Range is is the the only only iron iron range range in in the the Lake Lake Superior Superior Region Region to to have have extensive extensive deposits deposits of of both both hard hard and and soft soft iron ores. ores. The The spatial spatial distribution distribution of of these these two two ore ore types types along along iron the the range range appears appears to to correlate correlate with with the the grade grade of of metamorphism metamorphism of of the host host rocks. rocks. The The soft soft ores ores are are found found mostly mostly in in the the chlorite chlorite the grade grade rocks rocks in in the the Negaunee Negaunee and and Ishpeming Ishpeming area, area, and and the the hard hard ores ores mostly mostly in in higher higher grade grade rocks rocks (ie. (ie.biotite, biotitelgarnet, garnetlstaurolite, staurolitefto to sillimanite sillimanite grade) grade) of of the the Republic Republic metamorphic metamorphic node node (James, (Jamesf1955; 1955; see Figure Figure E). E) see Two Two principal principal hypotheses hypotheses have have been been advanced advanced for for the the formation formation of hypothesis of the the direct direct shipping, shipping! natural natural ores; ores; the the "cold-water" ttcold-watertt hypothesis (VanHise (VanHise and and Bayley, Bayleyl 1897), 1897)f and and the the hydrothermal hydrothermal hypothesis hypothesis (Grunerl1930). 1930). Today, Todayl most most company company geologists geologists favor favor aa (Gruner, hydrothermal hydrothermal origin origin for for both both the the soft soft and and hard hard iron iron ores. ores. ~htoricalSummary summa& Historical The The extensive extensive copper copper deposits deposits of of the the Keweenawan Keweenawan Peninsula Peninsula were were worked over 5,000 worked by by the the ancients ancient;-over if000 years years ago ago and and were were known known to to the the European European explorers, explorerslmissionaries missionariesand and fur furtraders. traders. The The iron iron deposits deposits were were not not known known to to the the Europeans, Europeansf although although some some were were known known to to the the native native Americans Americans who who were were very very superstitious superstitious about about them. them. The The Marquette Marquette Range Range was was the the first first of of the the region's regiontsiron iron ranges ranges The discovery was made by government to be be discovered. discovered. The discovery was made by government surveyors surveyors to The survey survey subdividing subdividing the the land land into into townships townships of of 36 36 square squaremiles. miles. The inventor of of party, partyf under under Deputy Deputy Land Land Surveyor, Surveyorl William William Austin Austin Burt, Burtf inventor . (See (See Figure F i g u r e E-1) E-1) B- 5 �MARQUETTE IRON IRON MARQUETTE 1 GENERALIZED RANGE — - MICHIGAN MICHIGAN RANGE LONGITUDINAL FIGURE SECTION 4 — - N—S N - S CROSS CROSS SECTION SECTION ONE MILE ONE M I L E EAST E A S T OF OF WEST WEST LINE LINE OF OF R.26W R.26W GENERALIZED FIGURE FIGURE LOOKING WEST REv,5c, lq7c #9 D D c �__ MAP MAP SHOWING SHOWING NODES NODES AND AND ZONES ZONES OF OF PENOKEAN REGIONAL REGIONALMETAMORPHISM METAMORPHISM PENOKEAN EXPLANATION EXPLANATION I...] Blotite Blothe zone zone Chloritezone zone ChIert• StauroUte zone Garnet Gornet zone zone Silllmanlte zone zone Sillimanite KEWEENAWAN KEWEENAWAN Marquette ROCKS ROCKS Grovelond Groveland Mine Mim I0 10 I 1 a * . 00 tO II I 10 Figure EE Figure 20 MILES 20 KILOMETERS Modifiedfrom fromJames James (1955) (1955)and and Cannon Cannon (1973) (1973) Modified FLORENCE �G . Matthews, Matthews, Sr., Sr., Frank G. Memorial Fund **HISTORICAL NOTES ** NUMBER ONE * * HISTORICAL NOTES NUMBER ONE ******* The Historical Notes are are prepared prepared to honor the Historical Notes the memory m e m o y of oj Frank G. G. Matthews, Matthews, Sr., Sr., enthusiastic enthusiastichistorian historianand andcollector coilectorof oflore loreof ofearly early iron iron mining mining and and charcoal charcoaliron iron making making of of Michigan's Michigan's Upper UpperPeninsula. Peninsula. ******* FRANK G. G.MATTHEWS. MAmHEWS, SR. SR. FRANK BURT'S SOLAR COMPASS COMPASS used that number 9428X 9428Xfor for his his invention. It was first used year by by him himand and by by his hisson sonAlvin, Alvin,also alsoaasurveyor. surveyor.Here Here year was was his his original originaldevice device attached attached to tothe thestandard standard field field compass of of the the day. day. The Solar Solar Compass Compass of William William Austin Austin Burt Burtrevolurevolutionized tionized the the early early land land surveying surveying and land subdivision by providing providing aa true true north-south north-south direction. direction. Prior Prior to to this this invention, invention, the the surveyor surveyor was was completely completely dependent dependent upon the magnetic magnetic compass, compass, which which could could be beunreunreliable liable due due to to the the local local magnetic magneticcharacter characterof of the the earth earth in the the area area being beingsurveyed. surveyed. in William William Austin AustinBurt BurtofofMt. Mt.Vernon, Vernon,Michigan, Michigan,had had been been appointed appointed aa Deputy Deputy Land Land Surveyor Surveyor for for the the Federal 1834he he surveyed surveyed an an Federal Government Government inin1833. 1833.In In1834 area north of of Milwaukee Milwaukee ininWisconsin WisconsinTerritory. Territory. The The area had local local magnetic attraction attractioncausing causinggreat great diffidifficulty in in surveying surveying for for Burt Burtand andother othersurveyors. surveyors. In In 1835 he he worked worked on a model of his his solar solar compass. compass. then then variation referred to as aa "variation referred to "variation apparatus" apparatus" or or "variation compass." compass." Variation Variation referred referred to to the the amount amount of of differdifference in in degrees degrees between between true true north north and andmagnetic magnetic north. 26, 1836 1836 he received received patent patent north. On On February February 26, THE SUN DIAL DIAL To understand understand how how Burt's Burt's Solar SolarCompass Compass works, works, itit is helpful helpful to to think think of ofthe thesun sundial, dial,which whichmost mostpeople people is is an an ancient ancient device device and and has has have seen. The The sun sun dial dial is many forms. But But the the simple simple garden garden variety variety has has aa dial dial with the the hours hours marked marked on itit and and an an arm arm (called (called aa with "gnomon," from from the theGreek Greekmeaning meaning one one who who knows knows or or indicates) indicates) that that casts casts aashadow shadow read read on on the the hour hour the sun sun dial dial has hasbeen beencorrectly correctlymade madeand and circle. If the circle. correctly oriented, oriented, the the time. time. At At correctly the shadow shadow will will tell the noon, noon, the sun is in in aa true true north-south north-south line line called called the the "meridian." "meridian." one had had aa portable portable instrument instrument and and knew knew the the So, if one time, time, it could could be be oriented oriented to to indicate indicatethe themeridian meridian (provided the sun is is shining shiningor or at at least leasthazy hazy enough enough to to create shadows). This was the heart of Burt's Burt's genius. genius. Burt's Original Solar Attached to a Compass 3-8 Figure E— �the Solar Solar Compass, Compasston on September September 19, 19! 1844, 1844! was was running running the the township township the line line between between Range Range 26 26 West West and and 27 27 West West south south of of Teal Teal Lake Lake in in what what is now now the the City City of of Negaunee. Negaunee. They They noted noted that that their their magnetic magnetic is compass compass pointed pointed south south in in this this area. area. Burt Burt directed directed his his party party to to look and look around around and and they they found found "spathose ltspathose and magnetic magnetic ores ores abunding". abundingl1. However, HoweverI news news of of this this discovery discovery was was overshadowed overshadowed by by the the rush rush for for copper copper in in the the Keweenaw. Keweenaw. In In fact, fact! the the first first iron iron mining mining company company to to operate operate in in the the region, region, the the Jackson Jackson Mining Mining Company, Companyf organized organized on on July July 23, 23! 1845 1845 in in Jackson, Jackson! Michigan, Michigsnl went went to to the the Upper Upper Peninsula Peninsula looking looking for for cooper cooper and and other other base base metals, metals! and and was was persuaded persuaded to to look look for for iron iron by by aa half-breed, half-breed! Louis Louis Nolan. Nolan. Although Although Nolan Nolan could could not not find Gesick" find the the exposures exposures of of iron iron ore, ore! the the local local chief chief "Marji tlMarji Gesickt1 finally finally led led them them to to the the east east shore shore of of Teal Teal Lake, Lake! in in what what is is now now Negaunee. This This location location was was federal federal permit permit Number Number 158, 158! and and was was Negaunee. secured secured by by the the Jackson Jackson Mining Mining Company Company as as Permit Permit Number Number 593, 593! Section Section 1, lt Township Township 47 47 North, North! Range Range 27 27 West, West! on on October October4, 4! 1845. 1845. Their Their intent made intent was was not not to to ship ship iron iron ore, ore! but but to to ship ship iron iron "blooms" llbloomsll made from (Spanish) from charcoal charcoal forges forges of of the the "Catalan" tlCatalanll (Spanish) style style like like those those used time! and and used used in in Europe Europe used in in New New York York and and New New England England at at that that time, for over over 2,000 2t000years. years. They They built built aa townsite townsite on on the the Carp Carp River, River! for along along with with aa dam dam and and the the Forge. Forge. The The first first iron iron blooms blooms were were made made on on February was February 10, lol 1848, 1848! and and "mining" tlminingtl was by by gathering gathering high high grade grade lumps lumps of of ore ore found found on on the the surface surface at at the the Jackson Jackson Mine. Mine. It It was was tough tough going going for for them them and and for for the the other other charcoal charcoal iron iron operations operations that that followed followed them. them. It It soon soon became became apparent apparent to to the the managements managements of of the the mining mining companies, companiest that that the the future future of of the the iron iron industry industry lay lay in in shipping shipping iron iron ore ore rather rather than than the the charcoal charcoal iron iron blooms. blooms. However, However! the the iron iron bloom bloom industry industry limped limped along along in in the the Upper Upper Peninsula Peninsula until until 1898; 1898; over over 1.8 1.8 million million long long tons tons of of processed processed iron iron had had been been shipped shipped from from the the Upper Upper Peninsula. Peninsula. The July! 1849. 1849. The The first first The port port of of Marquette Marquette was was founded founded in in July, iron iron ore ore shipped, shipped! on on July July 7, 7! 1852, 18521 consisted consisted of of six six barrels. barrels. The The opening opening of of the the Sault Sault St. St. Marie Marie locks locks in in June, June! 1855 1855 was was aa great great boon boon to to both both the the infant infant iron iron and and infant infant copper copper mining mining ventures. ventures. Allof the the first first mines mines were were open open pit pit operations operations and were were in All- of in hard iron iron ores. ores. The The hard hard ores ores cropped cropped out out on on hilltops hilltops and and also also hard contained contained enough enough magnetite magnetite to to deflect deflect the the magnetic magnetic compasses compasses where where way! followed followed by by the the Cleveland Cleveland concealed. The The Jackson Jackson Mine Mine led led the the way, concealed. Mines Mines at at the the east east side side of of Ishpeming Ishpeming (Jasper (Jasper Knob), Knob)! the the Humboldt, Humboldtl Republic, Mines on on the the main main Marquette Republicl Champion Champion and and Michigannue Michigame Mines trough, trough! and and the the Isabella Isabella Mine Mine on on the the Cascade Cascade Range. Range. The The first first underground underground mines mines opened opened in in 1868 1868 as as the the miners miners followed followed the the iron iron ore ore in in depth. depth. The The soft soft ores ores in in Negaunee Negaunee were were found found first first at at the the Negaunee Negaunee Mine Mine in in 1873. 1873. The The soft soft iron iron ores ores did did not not crop crop out out because because they they were were easily easily eroded eroded and and were were covered covered by by However! some some soft soft ores ores came came up up varying amounts amounts of of glacial glacial drift. drift. However, varying to ledge ledge surface. surface. to Crude Crude geophysics geophysics by by magnetic magnetic compass compass and and the the dip-needle dip-needle helped helped The diamond diamond drill drill was was developed developed in in locating locating the the iron iron ore ore bodies. bodies. The in in 1876 1876 and and first first employed employed on on the the Marquette Marquette Range Range in in1879. 1879. B- 9 �Mining Mining towns townssprang sprangup uparound aroundthe themines minesin inwhat whatwere weretermed termed fllocations~.Many Many towns townswere were developed developedby by the themining miningcompanies, companies, "locations". with with homes homes and and "boarding—houses" wboarding-houses"subsidized subsidizedby by the thecompanies companiesto to attractemployees. employees. There There was was aa parallelism parallelism between between the thecopper copper attract mining mining companies companiesand and their theirpaternalistic paternalisticefforts effortsto toobtain obtain employees and and retain retainthem, them,and andthe theiron ironmining miningcompanies. companies. Foremost Foremost employees among the the copper copper companies companies was was Calumet Calumet and and Hecla Hecla Consolidated Consolidated among Copper Copper Company Company while while the the foremost foremost iron iron company company was was the the Cleveland Cleveland Iron Iron Mining Mining Company Company (from (from1891 1891 it it was was The The Cleveland-Cliffs Cleveland-CliffsIron Iron Company). C.& C . & H. H. built built the the first firs: hospital hospital in in Calumet Calumet before before the the Company). company paid paid its itsfirst firstdividend. dividend. Cliffs Cliffs also also pioneered pioneered company company company houses,hospitals, hospitals,and andvisiting visitingnurses. nurses. They They had had the the first first houses, pension pension plan plan in in the the Lake Lake Superior SuperiorRegion, Region, the the first firstsafety safety department,and and employed employed thefirst firstcompany companygeologists. geologists. department, the ~ihincrMethods ~ethods Mining On the the Marquette Marquette Range, Range, by by the the 1880's 1880fsalmost almost all all production production On came from from underground undergroundmines. mines. In 1n the the hard hard ore ore mines mines the theprincipal principal came method method was was open openstoping stoping(a (astope stopeis isaa Cornish Cornishword word for foraaroom) room)by by the "room "room and and pillar" pillarwmethod. method. Very Very little little timber timber was was employed employed for for the sloping, ground support. support. In In the the soft soft ore ore mines mines there therewas wassublevel sublevelstoping, ground sublevel sublevel caving, caving,square squareset setmining, mining,and andtop topslicing. slicing. Much Much later, later, the the concept concept of of block block caving caving was was introduced introduced and and used used extensively. extensively. Much Much timber timber was was used used for for ground ground support support in in the the soft soft ore ore mines mines and and One wag said "the best forests of Michigan in the copper mines. "the best forests of Michigan One wag said in the copper mines. are underground." underground. If are The The choice choice of of the the mining mining method, method, and and the the use use of of wood wood or or steel steel supports supports related related directly directly to to the thegeologic geologicconditions. conditions. The The hard hard ores ores were were "competent" NcompetentNand and would would support support an an open open span, span,while while the the soft ores ores did did not not have have that that strength. strength. Other Other factors factors such such as as soft jointing, jointing, ground ground water, water, and and depth depth from from the the surface surface all all entered entered into into both both safety safety considerations considerations and and contamination contamination of of leaner leanermaterial material affecting the the ore ore grade. grade. affecting B-lU �Metallurgical Beneficiation Metallurqical Beneficiation For two two generations, generations, the the Marquette Marquette Range Range iron iron ore ore that that was was For mined and and shipped, shipped, or or used used in in the the charcoal charcoal iron iron industry, industry, was was rich, rich, natural, direct-shipping natural, direct-shipping materials. materials. Both the company the mining company officials and officials and government government geologists geologists recognized recognized that that the the iron— ironformations formations contained contained rich rich bands bands of of iron iron minerals. minerals. The question question was, how how to to separate separate these these bands from the waste or gangue was, materials, materials, essentially essentially the the chert chert or or siliceous siliceous bands. bands. "wellM from from the the Latin) Latin) is is the the process process Beneficiation (to make "well" Beneficiation (to or processes processes used to or to separate separate the the valuable valuable material material from from the the gangue gangue and generally generally consists consists of of several several steps. steps. First First is is to to crush crush and and "liberatew the the valuable valuable grind the the feed feed material material fine fine enough enough to to "liberate" materials, making making them them essentially essentially free free of of the the gangue. gangue. The The next next materials, step step is is to to collect collect and and separate separate the the two two materials materials into into aa "concentrate" of the valuable material from worthless material, wconcentrateN from the the worthless material, the latter the latter called called the the "tails" "tailsw or or "tailings". "tailingsw. The "feedw or or crude crude The "feed" material "headsw. material is is called called the the "heads". This This beneficiation beneficiation process process (or (or processes) processes) is is termed termed "concentrationw. There are are three three principal principal means means of of concentration: concentration: "concentration". There gravity, magnetic, The gravity, magnetic, and and chemical/physical. ~hemical/~hysical~ The gravity gravity process process utilizes the utilizes the differences differences in in specific specific gravity gravity of of the the ore ore minerals minerals in in contrast to This might be contrast to the the gangue. gangue. This be done done with with jigs, jigs, tables, tables, heavy heavy media, media, or or siphonsizers, siphonsizers, to to name name aa few. few. Magnetic Magnetic separation separation applies principally applies principally to to magnetite. magnetite. Chemical/physical seperation separation utilizes utilizes principally principally flotation, flotation, but but could could include include electrostatic electrostatic separation. separation. Flotation Flotation uses uses the the surface surface response response of of various various reagents reagents to to various various minerals. minerals. It possible, in "floatw the the ore ore minerals, minerals, or or It is is possible, in some some instances, instances, to to "float" to float float the the gangue gangue minerals. minerals. It It is is also also possible, possible, in in some some instances, use a instances, to to use a differential differential float float to to separate separate various various ore ore minerals minerals from from one one another. another. Neaaunee Concentrating Concentratinq Works Works Negaunee The The first first commercial commercial concentrating concentrating plant plant on on the the Marquette Marquette Range built on on the the lands lands of of Range was was the the Negaunee Negaunee Concentrating Concentrating Works Works built It used the jaspilite from the North Jackson the Jackson Mine. the Jackson Mine. Jackson Mine, Mine, paying paying aa royalty royalty of of 45 45 cents cents aa ton. ton. The The company, company, organized organized 1881, built a plant 183 feet wide and in 1881, feet long, long, 116 116 feet feet wide and 113 113 feet feet It had a high (nine (nine stories), stories), on on aa rock rock ridge ridge towards towards Teal Teal Lake. Lake. It a 600 horsepower horsepower boiler, 600 boiler, aa boiler boiler house, house, and and an an engine engine house. house. It It In its "CornishN rolls, rolls, and and rotary rotary jigs. jigs. In its first first used aa jaw jaw crusher, crusher, "Cornish" year of year of operation, operation, 1882, 1882, the the plant plant produced produced and and shipped shipped 1,177 1,177 tons tons Production increased of of concentrates. concentrates. Production increased to to 10,394 10,394 tons tons in in 1883. 1883. The The plant plant did did not not operate operate in in 1884 1884 and and 1885, 1885, and and it it closed closed in in 1886, 1886, years ahead years ahead of of its its time. time. Edison's EdisonlsMill, Mill, Humboldt Humboldt The second The second concentrating concentrating plant plant was was built built by by Thomas Thomas A. A. Edison. Edison. He He had patented patented his his electromagnetic electromagnetic separator separator in in 1880 1880 (U.S. (U.S. Patent Patent Number Number 228,329 228,329 on on June June 1, 1, 1880 1880 (see (see Figure Figure F)), F)), after after his his research research Edison looked in in 1879. 1879. Edison looked around around the the iron iron districts districts of of the the United United States States for for an an area area with with magnetic iron iron ores ores and and heard heard of of the the Sampson Sampson Mine (also known known as as the the Edwards Edwards or Mine at at Humnbolt Humbolt (also or the the Argyle Argyle Mines). Mines). He worked with with Walter Walter S. Mallory to to construct construct the the Concentrating Concentrating Plant using magnetic ores and lean ores mined by the Plant using magnetic ores and lean ores mined the Sampson Sampson Edisontsseparator separator was was different different from from the the separators separators of of personnel. Edison's personnel. B-li �(NoModel.) ~ode'l.) (No T.A. A .EDISON. EDISON. T. K a g n e t i c Ore-Separator. Ore-Separator. Magnetic Patented P a t e n t e dJune J u n e 1,1, 1880. 1880. No. 228,329. 228.329. No. y.2. =— — - t: L awn S..r a. B—12 Figure FigureFF �the time timein inthat thatit ithad hadno nomoving movingparts. parts. It It consisted consisted of of aa feed feed the hopper, aa gate, gate,the theunipolar unipolarnon-contact non-contactelectromagnet, electromagnet,aa hopper, partition, partition,and and bins bins for forthe themagnetic magnetic concentrate concentrateand andfor forthe thewast wast material. material. The 1889as asthe theEdison Edison The plant plant was was built built in in 1888 1888and and operated operatedin in1889 Iron Concentrating ConcentratingCompany. Company. It It had had aa Gates Gates jaw jaw crusher, crusher,two two 16 16by by Iron 30 30 Cornish Cornish rolls, rolls,and and screens screenssizing sizing the the feed feed to to20 20mesh, mesh,aagrain grain size for forliberation. liberation. The The iron iron concentrate concentrate analyzed analyzed 62 62to to68 68 size percentiron. iron. The The start—up start-up had had the the usual usual problems problemssuch suchas as percent breakdowns breakdowns of ofthe theprimary primarycrusher crusherand and learning learningthat that20 20mesh meshwas wasnot not fineenough enoughfor forliberation. liberation. The The intermediate intermediateproduct product Edison Edison called called fine nmugwumpw. The The plant plant burned burned in inDecember, December,1890 1890and andwas wasnot notrebuilt. rebuilt. "mugwump". He He said said "Well, "Well, its its all all gone, gone, but but we we had had aa hell hell of of aa good good time time spending it" itN(his (hisinvestment)! investment) ! spending The The third third mill mill to to open open was was that that of of the the Republic RepublicReduction Reduction Company in in1888 1888and and1889; 1889;it itwas wassold soldinin1891. 1891. The Company The Michigamme Michigamme Mine Mine used aa Swedish Swedish"Wenstroin" "Wenstrom" electromagnetic electromagnetic separator separatorstarting startingin in used 1889. Although Although early early results results were were encouraging, encouraging,the theplant plant closed closedin in 1889. 1892. 1892. Minnesota Concentrating ~oncentratina Efforts Minnesota Efforts After After these these early early efforts efforts at at concentration concentrationin in Michigan, Michigan, the the scene shifted shiftedto toMinnesota. Minnesota. In In 1902, 1902, the the first first concentrating concentrating plant plant scene was was built built at at the the west west end end of of the theMesabi Mesabi Range Rangeand and used used the theBiwabik Biwabik Iron-Formationfor forore. ore. Various Various plants plants followed, followed, using using gravity gravity Iron—Formation Professor Edward Edward W. W. Davis, Davis, of of the the vwash-oresw Professor methods on on the the "wash—ores" methods Minnesota Minnesota Mines Mines Experiment Experiment Station, Station,pursued pursued aa vigorous vigorousresearch research program program on on the the magnetic magnetic concentration concentrationof of the themagnetic magnetic portion portionof of the Biwabik Biwabik Iron-Formation, Iron-Formation,starting startingin in1914. 1914. The The Reserve Reserve Mining Mining the Company Company was was organized organized to to mine mine the the magnetic magnetic iron—formation iron-formationand and to to use Davis' Davistideas ideasfor forconcentration. concentration. The The plant plant operated operated in in the the use 19201s,but but closed closed due due to to two two principal principal problems: problems: (1) (1)the the 1920's, difficulty difficulty of of drilling drilling blast blast holes, holes, and and (2) (2)the the high high cost cost of of concentration concentration while while competing competing with with low low cost, cost, open open pit pit mined mined natural natural . . ores. ores. The The idea idea was was revived revived in in the the 1940 1940 by by Professor Professor Davis, Davis,who who had had continued to to work work on on the theproblem. problem. The The Reserve Reserve Mining Mining Company Company was was continued reorganized reorganized and and their theirfirst firstplant plantconuuenced commenced operations operations after afterWorld World I1 on on the the "taconite" '%aconitet'iron-formation. iron-formation. Shortly Shortly after, after, the the fine fine War II War grained grained concentrate concentrate was was agglomerated agglomerated or or pelletized pelletized at at Reserve Reserve Mining. Mining. Michicran Low Low Grade Grade Ores Ores Michigan During During World World War War II, 11, Cleveland Cleveland Cliffs Cliffs investigated investigated various various low low grade grade iron—formations iron-formations that that could could be be amenable amenable to to commercial commercial concentration. The The research research was was directed directed into into two two areas: areas: (1) (1) the the concentration. Bijiki Bijiki Iron—Formation Iron-Formation west west of of Michigamme, Michigamme, and and (2) (2) the the hard hard ore ore jaspilite jaspilite iron-formation iron-formationat at the theold old hard hard ore oremines. mines. The tested well of Michiganune Michigamme tested well in in terms terms of of heavy heavy The Ohio Ohio Mine Mine west west of The opening opening of of two two open open pits pits and and the the media concentration. concentration. The media construction construction of of aa concentrator concentrator started started in in 1951. 1951. The The first first concentrates concentrates were were produced produced in in May, May, 1952. 1952. The The plant plant operated operated until until September, long tons tons of of September, 1960 1960 producing producing aa total total of of 747,729 747,729 long concentrate. This This is is not not significant significant by by today's today's standards, standards,but but it it concentrate. marked marked aa dramatic dramatic shift shift from from underground underground mining mining to to the the new new era era of of open pit pit mining mining and and concentration. concentration. open B-13 �- The The jaspilite, jaspilite, or or "jasper" "jasperN as as Cliffs Cliffs called called it, it, was was being being investigated at at the the Humboldt Humboldt and and Republic Republic Mines. Mines. The investigated The mode mode of of concentration was was to to float float the the specular specular hematite hematite and and magnetite magnetite in in concentration fatty acids. acids. The The Humboldt Humboldt plant plant was was built built in in 1952 1952 as as aa joint joint fatty venture of of Ford Ford Motor Motor Co. Co. and and Cliffs, Cliffs, the the same same year year the the Ohio Ohio Mine Mine venture opened. The The first first concentrates concentrates were were produced produced in in 1954, 1954, but but no no form form opened. of agglomeration agglomerationwas was used. used. of Work Work had had gone gone ahead ahead at at the the Republic Republic Mine Mine and and its its first first concentrates concentrates ere wereproduced producedin in1956, 1956,using using the the same same flow flow sheet sheet as as the Humboldt Humboldt Mine. Mine. The The Republic Republic Mine Mine concentrates concentrates were were shipped, shipped, the starting starting also also in in 1956, 1956, to to Eagle Eagle Mills, Mills, east east of of Negaunee, Negaunee, to to aa This plant had its Straight Grate Plant to be pelletized. Straight Grate Plant to be pelletized. This plant had its share share of of problems, and and Cliffs Cliffs looked looked to to aa different differentprocess. process. problems, Cliffs Cliffs worked worked with with Allis-Chalmers Allis-Chalmers Manufacturing Manufacturing Co. Co. of of Milwaukee Milwaukee to to adapt adapt the the Grate-Kiln Grate-Kiln process, process, used used in in making making cement, cement, to produce produce iron iron concentrates. concentrates. This This was was aa first first in in the the world-wide world-wide to iron ore ore technology. technology. This Humbolt This process process was wasfirst firstapplied appliedatatthe theHuiubolt iron Mine with with two two identical identical "lines" "lineswin in1960. 1960. AA second second plant plant was was Mine started at at the the Republic Republic Mine Mine in in 1962. 1962. started The The Empire Empire Mine, Mine, south south of of Negaunee Negaunee and and west west of of Palmer, Palmer, was was aa magnetite rich rich iron-formation. iron-formation. Test Test work work included included the the development development magnetite of autogenous autogenous grinding grinding (self (self grinding) grinding) mills mills and and aa combination combination of magnetic separation separation and and gravity gravity methods. methods. Later, Later, flotation flotation was was magnetic added as as the the final final step. step. The The concentrates concentrates were were pelletized pelletized by by the the added The first concentrates and pellets were ACL Grate-Kiln system. The first concentrates and pellets were ACL Grate—Kiln system. produced in in December, December, 1963. 1963. produced The The Pioneer Pioneer Pellet Pellet Plant Plant was was started started in in 1964 1964 to to pelletize pelletize Mather Mine Mine underground underground ores. ores. This This improvement improvement in in product, product, Mather appealed appealed to to the the steel steel plants plants and and resulted resulted in in keeping keeping this this last last underground mine mine operating operating until until 1979. 1979. underground The Tilden Tilden Mine Mine had had been been an an open open pit pit operation operation producing producing aa The special special grade grade of of iron—formation iron-formation called called siliceous siliceous ore ore for for use use in in the the open-hearth furnace. furnace. Years Years had had been been spent spent on on metallurgical metallurgical open—hearth "break through" through" occurred occurred in in April, April, 1967 1967 from from aa research. But But aa "break research. joint joint research—development research-development venture venture of of Cliffs Cliffs and and the the U.S. U.S. Bureau Bureau of of The mode of concentration developed Mines at Minneapolis. The mode of concentration developed was was Mines at Minneapolis. "selective flotationH to to recover recover the the non—magnetic non-magnetic "selective flocculation flocculation flotation" The plant and pit were built in hematite and goethite. The plant and pit were built in1972-1974. 1972-1974. hematite and goethite. The first first pellets pellets were were produced produced in in December, December,1974. The 1974. The The initial initial pit pit and and plant plant at at the the Tilden Tilden Mine Mine was was sized sized at at 4.0 4.0 million million long long tons tons of of pellets pellets per per year, year, and and was was known known as as Tilden Tilden I. I. Provision Provision had had been been made made in in the the design design for for doubling doubling the the capacity capacity to to 8.0 8.0 million million tons tons per per year, year, or or even even to to 12.0 12.0 million milliontons tonsper peryear. year. The I1 and and it it commenced commenced The decision decision was was made made to to build build Tilden Tilden II operations in in 1979. 1979. operations The Empire Empire Mine Mine had had had had aa similar similargrowth. growth. Empire The Empire II started started in in 1963, 1963, Empire Empire II I1 in in 1966, 1966, Empire Empire III I11 in in 1974, 1974, and and Empire Empire IV IV in in 1980. 1980. This This brought brought the the annual annual capacity capacity of of each each plant plant to to 8.0 8.0 million million tons tons ftstandbytf per year. year. The The Republic Republic Mine Mine pit pit and and plant plant have have been been on on aa "standby" per basis since since1983. 1983. basis Pellet Pellet shipments shipments for for1987 1987were: were: 7,417,703 long long tons tons Empire Empire Mine Mine 7,417,703 Ti1n Mine 4,458,620long longtons tons Tilc'en Mine4,458,620 B— 14 �In the Tilden In 1987 1987 the Tilden Mine faced faced economic economic necessities necessities and and quality quality product review, review, and and concluded concluded that that aa new new open open pit pit source source of of magnetic ore magnetic ore needed needed to to be be developed developed to to replace replace the the present present open open pit pit mining of mining of hematite hematite and and goethite goethite material. material. A source source of of magnetic magnetic material was material was known known on on the the Cliffs Cliffs Drive, Drive, and and necessary necessary permits permits are are being sought. being sought. The Gogebic Gogebic Range, Range, the The the last last iron iron range range found found in in the the Upper Upper Peninsula, Peninsula, was was the the first first closed, closed, followed followed by by the the Menominee Menominee Range, Range, the Marquette Marquette Range Range active leaving today only the active in in the the Upper Upper Peninsula. Thus, the Marquette Range is Peninsula. Thus, the Marquette is still still alive alive and and continuing, 144 continuing, 144 years years after after its its discovery. discovery. 3-15 �Institute Institute of of Lake Lake Superior Superior Geology Geoloay FIELD FIELD TRIP TRIP No. No. 22 Marquette Marquette Mineral Mineral District District of of Michigan Michigan with with emphasis emphasis on on MINING HISTORY HISTORY and and GEOLOGY GEOLOGY led led by Burton Burton Boyumu Boyum Robert Robert C. C. Reed Reed and and Win. Kangas Wm. Kangas May, May, 1988 1988 The The KEY KEY MAP, MAP, Figure Figure 1, 1, provided provided through through the the courtesy courtesy of of Cleveland-Cliffs, Cleveland-Cliffs, Inc. Inc. B- 16 �H I— Witch LOh. \. CS 4 "I' lop.. DHfL.â. Key Map SiII Soft Ore STATE OF MICHIGAN No. 2 — May, 1988 FootwaII Soft Ore .MAP LOCATION to Field Trip Hord Ore Marquette Iron Range Figure I Sold Nit.. 0 SCALE 2 IN MILLS 1 3 Lok# S&.•fs•r �••1 AcJ<ermanlith.3?9.BtOadWay NY. VIEW VIEW NEAR NEAR CARP CARTRIVER, RIVER.LAKE LAKE SUPERIOR. SUPERIOR B-18 Figure Figure 22 �I k r / B-19 Figure Figure 33 �STOP 11 (Fig. (Fig. 22 and and 3)-3)-- MARQUETTE MARQUETTE HARBOR HARBOR STOP The The port port city city of of Marquette Marquette was was established established July July 10, 10, 1849, 1849, as as Worcester, the the name name of of the the home home city city of of Mr. Mr. Waterman Waterman A. A. Fisher, Fisher, aa Worcester, Figure textile mill mill owner owner of of Worcester, Worcester, Massachusetts. Massachusetts. Figure 22 shows shows aa textile scene of of the the harbor harbor in in 1851, 1851, taken taken from from Foster Foster and and Whitney Whitney (1851). (1851). scene Figure Figure 33 shows shows the the charcoal charcoal bloomery bloomery of of the the Marquette Marquette Iron Iron Company Company and aa part part of of the the community community in in 1852, 1852, as as seen seen from from Ripley's RipleytsRock. Rock. and This This is is the the oldest oldest known known photograph photograph of of Marquette, Marquette, as as the the name name was was changed in in 1851. 1851. changed Mr. Fisher Fisher was was the the principal principal financer financer of of the the Marquette Marquette Iron Iron Mr. Company, which which was was promoted promoted by by Mr. Mr. Robert Robert Graveraet. Graveraet. Although Although the the Company, company had had no no mines, mines, it it built built aa charcoal charcoal iron company iron bloomery bloomery on on the the shore of of Lake Lake Superior, Superior, using using ore ore from shore from the the Jackson JacksonMine. Mine. Previously, in in 1847, 1847, the the Jackson Jackson Mining Mining Company Company had had constructed constructed aa Previously, building in in this this area area for for both both aa habitation habitation and and aa storehouse. storehouse. The building The eastern backers backers of of the the Marquette Marquette Iron Iron Company Company soon soon lost lost interest interest in in eastern the venture venture and and they they sold sold out out to to the the Cleveland Cleveland Iron Iron Mining Mining Company Company the in 1853. 1853. The The plant plant was was destroyed destroyed by by fire fire in in 1853 1853 and and was was not not in rebuilt rebuilt because because the the Cleveland Cleveland Iron Iron Co. Co. was was putting putting its its emphasis emphasis on on shipping shipping ore ore promoted promoted by by the the start start of of construction construction of of the the Sault Sault Ste. Marie Marie (SOO) (SOO) Locks Locks Agitation Agitation had had gone gone on on for for years years to to build build Ste. locks at at the the SOO, SOO, because because all all passengers passengers and locks freight had to portage and freight had to portage around the the rapids rapids each each way. way. On On August August 26, 26, 1852, 1852, U.S. U.S. President President around Millard Fillmore Fillmore signed signed aa bill bill authorizing authorizing the the construction construction of of Millard locks and and aa canal. canal. locks The The first first water water was was let let into into the the system system on on April April 19, 19, 1855, 1855, but but vessel to to lock there were were leaks leaks to to be be reparied. reparied. The The first. first vessel lock through through there was on wIllinoisn,going going "upbound", ttupboundtt, on June June 18th. 18th. The The was the the steamer steamer "Illinois", brigantine "Columbia" flColumbiaHcarried carried the the first first cargo cargo of of iron iron ore, ore, brigantine in amounting to to 132 132 tons, tons, "downbound" ttdownboundtt in August, August, 1855. 1855. Thus, Thus, amounting Marquette became became the the first first iron iron ore ore port port in in the the Great Great Lakes. Lakes. AA Marquette total total of of 1447 1447 tons tons of of iron iron ore ore was was shipped shipped from from Marquette Marquette Harbor Harbor in in that first first year, year, all all by by the the Cleveland Cleveland Iron Iron Mining Mining Company. Company. that The The Cleveland Cleveland Iron Iron Company Company built built its its first first ore ore dock dock in in 1855. 1855. The The Lake Lake Superior Superior Iron Iron Company, Company, Samuel Samuel P. P. Ely, Ely, Agent, Agent, built built their their ore dock dock next next to to them them in in 1857, 1857, but but used used aa radically radically different different ore The Lake Superior Iron Co. dock was 25 feet above design. The Lake Superior Iron Co. dock was 25 feet above the the design. "pocketsNto to hold hold the the ore ore and and chutes chutes to to drop drop the the ore ore water and and had had "pockets" water onto onto the the deck deck or or into into the the hold hold of of vessels. vessels. This This was was the the first first ore ore dock with with pockets pockets built built in in the the world! world! dock . . STOPS 22 (Fig. (Fig. 4)--KONA DOLOMITE DOLOMITE and and COPPER COPPER MINERALIZATION MINERALIZATION STOPS This This is is the the middle middle member member of of the the Chocolay Chocolay Group. Group. It It is is crystalline essentially essentially aa fine fine to to medium medium grained, grained, pink pink to to gray, gray, crystalline siliceous siliceous dolomite dolomite with with some some interlaminated interlaminated argillaceous argillaceous and and Hematite staining staining locally locally gives gives the the rock rock aa arenaceouaphases. phases. Hematite arenaceou pinkish to to reddish reddish hue. hue. Locally, Locally, there there are are large large domal domal algal algal pinkish structures in in the the Kona. Kona. One One classic classic locality locality alongside alongside U.S. U.S. structures Highway 6, T47N, T47N, R24W, R24W, has has been been visited visited by by countless countless Highway 41, 41, in in Section Section 6, geologists; we have have chosen chosen this this series series of of exposures exposures to to geologists; however, however, we show the the algal algal structures. structures. show B-20 �JS JS • JACOBSVILLE JACOBSVILLE SANDSTONE SANDSTONE _UflCOflfOrmity — .Unconformity. SS SS •= SIAMO SIAMO SLATE SLATE Loke ' I MARQUETTE MARQUETTE SYNCLINORIUN SYNCLINORIUM AQ AQ • AJI8IK AJIBIK QUARTZITE QUARTZITE WS WS • WEWE WEWE SCHIST SCHIST KO K O •= KONA KONA DOLOMITE DOLOMITE MQ MQ Superior = MESNARD MESNARD QUARTZITE QUARTZITE EL E L • =ENCHANTMENT ENCHANTMENT LAKE L A K E FM. FM. _Unconformity_ AJnconformity. CCG= COMPEAU COMPEAU CREEK CREEK ONEISS GNEISS CCGa MS MONASCHIST SCHIST M S •* MONA STRATIGRAPHICCONTACT CONTACT --—. STRATIGRAPHIC - - - 44_, Js __-__— '.-' —, lCD —. FAULT CONTACT FAULT CONTACT — . -'. — — — j4tc—:— — FIGURE 44 FIGURE G E N E R A L GEOLOGY G E O L O G Y OF OF GENERAL E A S T E R N PORTION P O R T I O N OF O F THE THE EASTERN MARQUETTE M A R Q U E T T E SYNCLINORIUM SYNCLINORIUM STOP 2 0 t 2 k- After Gair Gatr and and Thadan, Taylor,p972 1972 After Thad.n, 1968, 968. Toylor �Copper Mineralization: Mineralization: A.R. A.R. Renfro Renfro wrote wroteininEconomic EconomicGeolociy, Geoloqv, Copper (1974): "Recently "Recently discovered sedimentary sedimentary and geochemical geochemical processes processes of coastal coastal Sabkhas Sabkhas provide provide the the foundation foundation for for aa hypothesis hypothesis that that of successfully successfully explains explains the the genesis genesis of of these these (copper) (copper) deposits". depositstt. "Coastal sabkhas sabkhas are are evaporite evaporite flats flats that that form form along along the the subaerial subaerial "Coastal landward margins margins of of regressive regressive seas. seas. Because Because of of their their unique unique landward position, coastal coastal sab]thas sabkhas are subsurface flow flow of of position, are nourished nourished by subsurface landward-migrating, Fh-high pH pH sea sea water water and and by by seawardseawardlandward-migrating, low low Eh-high migrating, migrating, high high Eli-low Eh-low pH terrestrial terrestrial water. water. Commonly Commonly they they are are bordered bordered on on the the seaward seaward side side by by intertidal intertidal mudflats mudflats nad nad lagoons lagoons that are are carpeted carpeted by by leather-like leather-like mats mats of of sediment-binding, sediment-binding, bluebluethat green green algae. algae. Fetid Fetid ooze ooze consisting consisting of of interbedded interbedded decaying decaying algae algae and and detrital detrital sediment sediment occurs occurs immediately immediately beneath beneath the the living living algal algal "Coastal sabkhas sabkhas and and their their related related evaporite evaporite facies facies prograde prograde mat." "Coastal seaward seaward across across adjacent adjacent algal-mat algal-mat facies. facies. Upon Upon banal, barial,the the algalalgalmat mat facies facies becomes becomes saturated saturated with with hydrogen hydrogen sulfide sulfide generated generated by by anaerobic bacteria. bacteria. Concurrently, Concurrently, the the trailing, trailing, landward landward edges edges of of anaerobic elastics of of coastal sabkhas sabkhas are are buried buried by by prograding prograding ternigenous terrigenous clastics coastal the desert. desert. As As sabkhas sabkhas migrate migrate basinward, basinward, terrestrial—formation terrestrial-formation the water water eventually eventually must must pass pass upward upward through through the the buried, buried, strongly strongly reducing reducing algal—mat algal-mat in in order order to to reach reach the the surface surface of of evaporation." evaporation.If "Terrestrial-formation wTerrestrial-formationwater water initially initially has has low low pH pH and and high high Eh, Eh, and and thus thus can can mobilize mobilize and and transport transport trace trace amounts amounts of of such such elements elements as as copper, copper, silver, silver, lead, lead, and and zinc. zinc. As As terrestrial—formation terrestrial-formation water water passes passes through through the the hydrogen hydrogen sulfide-charged sulfide-charged algal-mat, algal-mat, its its load load of of solute solute metals metals is is reduced reduced and and precipitated precipitated interstitially interstitially as as sulfides." sulf ides." The ides in in the the Kona Kona dolomite dolomite are bornite, bornite, chalcopyrite, The suif sulfides chalcopyrite, Estimates suggest suggest aa potential potential of of 250 250 million million tons tons of of and pyrite. pyrite. Estimates and mineable material. material. This This potential potential was was not not recognized recognized until until about about mineable 1896. Early Early prospectors prospectors in in the the area area included included Julian JulianCase, Case,J.M. J.M. 1896. Wilkinson, and and Andrew Andrew Pings. Pings. Interest Interest in in the the Longyear, James James Wilkinson, Longyear, sulfide mineralization in sulfide mineralization in the the Kona Kona died died out out by 1898, 1898, but but was was renewed renewed in in the the 1970's, 1970fs,with with drilling drilling and and mapping mapping by by several several groups. groups. Mineralization Mineralization is is not not readily readily seen seen in in place, place, but but diamond diamond drill drill core core and and hand hand specimens specimens will will be be shown. shown. 5)--MORGAN STOP STOP 33 (Fig. (Fig. 5) --MORGAN FURNACE FURNACE As As noted noted in in the the Introduction, Introduction, many many of of the the early early developers developers of of the the Marquette Marquette Iron Iron Range Range had had the the concept concept of of shipping shipping the the iron iron as as blooms blooms rather rather than than as as ore. ore. As As is is typical, typical, commercial commercial development development The Iron Iron sprang were developed. developed. The sprang up up along along the the railroads, railroads, as as they they were Mountain Mountain Railroad Railroad was was incorporated incorporated February February 22, 22, 1855 1855 and and commenced commenced operations operations in in 1857. 1857. It It was reincorporated reincorporated February February 6, 6, 1857, 1857, as as the the Marquette and later later as as the the Marquette, Marquette, Marquette and and Ontonogan Ontonogan Railroad, Railroad, and Houghton Houghton and and Ontonogan Ontonogan Railroad Railroad (M.H.& (M.H.& 0.), O.), followed followed by by the the Duluth, Duluth, South South Shore Shore and and Atlantic Atlantic Railroad Railroad (D.S.S.& (D.S.S.& A.); A.); it it is is now now known known as as the the Soo Soo Line Line Railroad. Railroad. AA Mr. Mr. Schweitzer Schweitzer started started aa grist grist mill mill along along the the line line some some eight eight miles west west of of Marquette Marquette in in aa favorable favorable location location adjacent adjacent to to the the Little Little Carp Carp River River (later (later renamed renamed Morgan Morgan Creek). Creek). Mr. Mr. Cornelius Cornelius Donkersley, Donkersley, active active in in the the railroad, railroad, felt felt this this was was aa good good site site for for aa The Ely family of Rochester, New York, wealthy charcoal charcoal furnace. furnace. The family Rochester, York, wealthy flour flour milling people, people, had taken taken an an interest interest in in the the Marquette Marquette Range Range B- 22 �Morgan in 1$83. MorganFurnace. Furnace.Built Built in 1S63. Figurn 5 B-23 Figure Figure 55 �in the the early early 1850's. 1850's. They They encouraged encouraged Donkersley Donkersley and and financed financed the the in development. The The good good friend friend and and legal legal counsel counsel for for the the family family was was development. Lewis Henry Henry Morgan. Morgan. From From the the beginning, beginning, Morgan Morgan had had advised advisedthem, them, Lewis and he he also also invested invested in in the the development. development. Starting Starting in in1856, 1856, and Donkersley had had cleared cleared the the land land and and built built houses houses for for his his workers. workers. Donkersley The Morgan Morgan Iron Iron Company Company was was incorporated incorporated July July 1, 1, 1863, The 1863, and and had had an an initial capitalization capitalization of of $50,000, $50,000, made initial made up up of of 2,000 2,000 shares shares at at $25 $25 each. The The Ely Ely family family joined joined Morgan Morgan in in this this venture. venture. Annual Annual each. production for for the the company company was was (in (intons): tons): production 1863 337 1868 4023 4023 1873 6324 6324 1873 1868 337 1863 1864 4023 4023 1869-out of of blast blast 1874 1874 5973 5973 1869—out 1864 1875 1865 3489 3489 1870 5952 5952 1875 5377 5377 1870 1865 1876 1866 3749 3749 1871 4755 4755 1876 3278 3278 1871 1866 663 1877 1867 5057 5057 1872 4356 4356 1877 663 1872 1867 Total production production of of 57,573 57,573 tons tons Total Lewis Lewis H. H. Morgan Morgan is is noteworthy noteworthy not not only only for for his his role role with with the the railroads and and with with the the furnace furnacecompany, company,but but also alsoas asaanaturalist. naturalist. railroads He spent spent aa number number of of summers summers on on the the Marquette Marquette Range Range observing observing the the He beaver. His His treatise, treatise, "The "The American American Beaver", Beaveru,was was remarkable, remarkable, and and beaver. established him him as as an an authority authority whose whose works works are arestill stillrespected. respected. established STOP 4--MICHIGAN 4--MICHIGAN IRON IRON INDUSTRY INDUSTRY MUSEUM MUSEUM STOP This is This is the the newest newest of of the the State State of of Michigan Michigan historical historical museums museums outgrowth of of aa community community effort effort dating dating back back to to 1973. 1973. AA and is is the the outgrowth and Michigan Michigan non-profit non-profit corporation, corporation, the the Carp Carp River River Forge Forge Bi-Centennial Bi-Centennial Park, organized organized an an effort effort to to honor honor the the Carp Carp River RiverForge. Forge. It Park, It raised raised In time, it joined money and and purchased purchased land land for forthis thispurpose. purpose. In time, it joined money forces with with the the Bureau Bureau of of History, History,Michigan Michigan Department Departmentof ofState, State, forces and had had the the cooperation cooperation of of The The Cleveland-Cliffs Cleveland-Cliffs Iron Iron Company. Company. The and The result became became this this Museum. Museum. Ground Ground breaking breaking was was in in July July 1986 1986 and and result dedication of of the the museum museum took took place place on on May May 16, 16,1987. 1987. dedication A. Tour Tour of of Museum Museum and and Rest Rest Stop. Stop. A. B. Convene Convene in in Frank Frank G. G. Matthews, Matthews, Sr. Sr. Memorial Memorial Museum Museum B. Remarks Remarks by by Tom Tom Friggens, Friggens, Director, Director, followed followed by by aa brief brief audial-visual program. program. audial—visual C. Solar Solar compass compass demonstration demonstration (rain (rainor or shine). shine). C. The The Historical Historical Introduction Introduction has has already already commented commented on on William William Austin Burt Burt and and his his solar solarcompass. compass. Attached NotesAttached is is Historical Historical NotesAustin Number One, One, which which provides provides more more detail. detail. Also Also demonstrated demonstrated is is aa sun sun Number dial dial compass, compass, probably probably more more used used by by field field geologists geologists than than the the Solar Solar Compass. Compass. STOP 55 (Fig. (Fig.6)--NEGAtJNEE 6)--NEGAUNEE HIGHWAY HIGHWAY CUT CUT STOP This This series series of of road road cut cut exposures exposures along along U.S. U.S. Highway Highway 41 41 contains, over a short distance, the Mesnard Quartzite, contains, over a short distance, the Mesnard Quartzite, basal basal to to the Ajibik Quartzite, Quartzite, basal basal to to the the Menominee Menominee the Chocolay Chocolay Group; Group; the the Ajibik Group; Group; and and the the Siamo Siamo Formation, Formation, the the middle middle member member of of the the Menominee Menominee To the northwest, along the north side of the hill is To the northwest, along the north side of the hill is aa Group. Group. thin (one (one meter) meter) basal basal conglomerate. conglomerate. The The Kona Kona Dolomite Dolomite pinches pinches out out thin just to to the the east east of of these these exposures. exposures. just The The Mesnard Mesnard Formation Formation is is aa thick, thick,vitreous vitreous quartzite, quartzite, Numerous generally generally light light gray, gray, but but sometimes sometimeswith with shades shadesof ofpink. pink. Numerous veins and ripple ripple marks marks and and veins of of quartz quartz and and hematite hematite cut cut the the bedding, bedding, and This is is the the only only member member of of the the crossbedding are are also also present. present. This crossbedding D - �B-25 Figure 6 85 J% - - .- .;'S• --. ... -— 4 q — •.: ., C' ... . faA- — —-... 3 67 :f iç 6 50 - mn p95' I I I 0 — - — - I 8 ks I38' 'Lii1 r • ;) ... NPC ms 80 .- -. %_' ml 1 — A / SS —: - / -' — ' _4.4;-/99 j I Q - 2 -/ . '. - o - - -. flO N 45 ..- .s -4— ,,. 1 mm __ • COJNTY i3 ( 13M FIGURE 6 — -. J%8¼ . :< APR PORT •1I MING : .— bi . .. 83_4zrn 'jr- I ,'-----z - 8 —' kd 87_( md 6re' , ms 4 /, 6O) / Mi1 507 — ) * /f1 - — / 80X- e1;— '. 9 ç"8O8ft4 _ ? e sJ1'; ' '- J/ /4O8, . :.. —.-..- k -. r7L 25 - ' ______ �Chocolay Group Group to tobe be found foundthis thisfar farwest. west. Perhaps Perhaps the the other other Chocolay members were were eroded eroded here here before before deposition depositionof ofthe theMenominee MenomineeGroup, Group, members or they they were were not not deposited deposited this this far far west west from from their their principal principal area area or of deposition. deposition. of The Ajibik Formation Formationis is found The Ajibik found in in the the next next series seriesof of outcrops outcrops to the thesouth. south. It It is is massive massive quartzite quartzite with with minor minor amounts amountsof of to argillaceousand and conglomeratic conglomeraticmaterial. material. In In appearance, appearance,the the Ajibik Ajibik argillaceous resemblesthe the Mesnard Mesnard Quartzite. Quartzite. Present Present in in the the quartzite quartzite is is aa resembles distinctive concentric concentric staining staining similar similar to to Liesegang Liesegang rings. rings. Also distinctive Also present locally, locally,are aredistinctive distinctivegreenish greenishgranules. granules. present The Siamo SiamoFormation Formationconsists consistsof of dark dark gray gray to to light lightgray gray The argillite,slate, slate,graywacke graywackeand andquartzite. quartzite. Slaty Slaty cleavage cleavageis is argillite, common to to conspicuous. conspicuous. Locally, Locally, there there are are carbonate carbonate rich rich layers layers common and beds beds of ofconglomerate. conglomerate. Also clasticdikes dikescomposed composed Also present present are are clastic and of material material similar similarto tothe thegraywacke graywackebeds. beds. The of The contact contactof of the the Siamo Formation Formation with with the the Negaunee Negaunee Iron Iron Formation Formation is isnot not exposed exposed Siamo here, but but it it lies liesjust just south south of of the the Negaunee Negaunee Branch Branch Bank. Bank. here, Also of of interest interestis isthe the Miners' Miners1Park Parkwith with the thepyramidal pyramidal Also monument located located on on the the west west side side of of U.S. U.S. Highway Highway 41. 41. The The monument monument monument was erected erected originally originally by by the the Jackson Jackson Iron Iron Mining Mining Company Companyin in1905 1905 was before the the company company was was sold sold to, to, and and assimilated assimilatedinto, into,the the before Cleveland-CliffsIron IronCompany. Company. Because Because the the monument monument was was erected erected Cleveland—Cliffs "Cornish Town", Townw,now now an an area area of of potential potential subsidence subsidence from from first in in "Cornish first the Shaft, the deep deep underground underground mining mining of of the the Mather Mather Mine Mine "B" l@Btt Shaft,it it was was taken apart, apart, each each stone stone marked, marked, moved, moved, and and reassembled reassembled on on the the taken present site siteby by Cleveland—Cliffs, Cleveland-Cliffs,at atits itsexpense. expense. present STOP 6--BURT 6--BURTSURVEY SURVEYMARKER MARKER (NE (NECORNER, CORNER,SECT.1, SECT.1,T47N, T47N,R27W) R27W) STOP This This brief brief stop stop is is adjacent adjacent to to the the Don Don Tresedder Tresedder Insurance Insurance Agency, 109 109 U.S. U.S. 41 41 W. W. at at the the northeast northeast corner corner of of the the section sectionwhere where Agency, William William Austin Austin Burt Burt commenced commenced his his survey survey of of the the Town Town Line Line between between Ranges 26 26 and and 27. 27. On On the the morning morning of of September September 19, 19, 1844, 1844,he he and and his his Ranges party party went went south south and and discovered discovered the the first first iron iron ore ore of of the the Marquette Marquette Range. The The marker marker was was erected erected by by the the Marquette Marquette County County Historical Historical Range. Michigan's Sesquicentennial. Sesquicentennial. Society in in 1987 1987 as as part part of of Michigan's Society STOP STOP 77 (Fig. (Fig. 7)--RAILWAY 7)-RAILWAY STREET STREET UNOXIDIZED UNOXIDIZED IRON-FORMATION IRON-FORMATION This This series series of of railroad railroad cuts cuts is is ideal ideal to to examine examine the the unoxidized, unoxidized, primary, primary, cherty, cherty, iron iron carbonate carbonate iron—formation. iron-formation. Structurally, Structurally, it it is is located located in in the the faulted faulted section section that that passed passed It is is on on the the north north through through the the Negaunee Negaunee Mine Mine Number Number Three ThreeShaft. Shaft. It dipping limb limb of of the the Athens Athens Enginehouse EnginehouseAnticline. Anticline. dipping Although Although this this section section is is unoxidized unoxidized except except for for recent recent alteration, Several alteration, it it lies lies just just above above aa high high grade grade iron irondeposit. deposit. Several thin intrusivescan can be be seen seenin in this thisexposure. exposure. thin sill—like sill-like intrusives Worthy Worthy of of note note is is the the westward westward plunging plunging zone zone of of gypsum; gypsum; the the Figure 77 shows shows the the structure structure gypsum gypsum was was formed formed after after the the iron iron ore. ore. Figure of of the the zone zone in in plan, plan, together together with with an an east-west east-west longitudinal longitudinal section, looking looking north. north. The The ore-enrichment ore-enrichment extended extended down down the the section, syncline through the the Tracy Tracy Mine, Mine, the the Lucky Lucky syncline from from the the Regent Regent Group, Group, through The Lucky Lucky Star Star Star Star and and Athens Athens Mines, Mines, to to the the Bunker Bunker Hill Hill Mine. Mine. The "Orebody" and ItOrebodytt and the the first first three three levels levels of of the the Athens Athens Mine Mine were were never never mined mined because because of of their their high high sulfur sulfur(gypsum) (gypsum)content. content. The The enrichment enrichment under under the the railway railway street street was was also also high high in insulfur. sulfur. This This B-26 �FIGURE FIGURE 77 PLAN MAP MAPAND ANDCROSS CROSS SECTION SECTION -- STOP STOP 77 PLAN PLAN PLAN MAP MAP -\ '' '. Unoxidized Iron - Formajion - LONGITUDINAL LONGITUDINAL CROSS CROSS SECTION SECTION- LOOKING LOOKINGNORTH NORTH Lucky Lucky Star StarMine Mine Athens Mine Mine Athens k. - Iron- Format/on Formation Iron High Sulfer BOre" $iamO for a B-27 D-II'c Figure Figure 77 �condition condition existed existed also also in in the the upper upper levels levels of of the the Mather Mather Mine. Mine. The The post-ore post-ore interstitial interstitial fillings fillings of of gypsum, gypsumf calcite, calcitefand and sometimes sometimes dickite dickite and(or) and(or) halides halides have have been been found found on on the the Gogebic Gogebic Range, Rangefat at Elyf Minnesota, Minnesotafand and at at the the the Zenith Zenith Mine Mine in in the the Ely Ely trough trough at at Ely, the Steep Rock Rock Mine Mine at at Atikokan, AtikokanfOntario. Ontario. The The latter latter mine mine also also had had Steep some arsenic arsenic minerals. minerals. some STOP STOP 8--JACKSON 8--JAC?<SONGROVE: GROVE: PASTY PASTY LUNCH LUNCH AND AND REST REST STOP STOP The Pasty, Pastyf as as aa meal, mealf is The is aa Cornish Cornish traditional traditional miner's minerfslunch. lunch. It was was developed developed as as aa "package" ffpackageff that the the miner miner could could take take underunderIt that ground and and even even reheat reheat with with aa candle candleunder underhis hisshovel! shovel! It ground It continues continues to to be be aa favorite favorite around around the the world world wherever wherever the the Cornishmen Cornishmen have gone. gone. have STOP 8--SOUTH 8--SOUTH JACKSON JACKSON MINE: MINE: MAGANESE MAGANESE MINERALS MINERALS STOP The The South South Jackson Jackson Mine Mine Pit Pit is is in in aa completely completely different different geologic geologic setting setting from from that that of of the the North North Jackson Jackson Mine. Mine. The The latter latter mine was was in in high high grade grade hard hard ore. ore. The The South South Jackson Jackson Mine Mine was was in in mine intermediate oref like like that that intermediate (iron (ironcontent) content) grade, gradefsoft softore. ore. This This ore, of of the the Lucy Lucy Mine Mine to to the the east, eastf was was high high in in manganese, manganesef principally principally as as The ores ores from from these these mines mines were were the the only only manganite and and pyrolusite. pyrolusite. The manganite There ones ones on on the the Marquette Marquette Range Range to to be be high high in in manganese manganese There were were exotic exotic manganese manganese minerals minerals found found at at the the Champion Champion Mine, Minef such such as as manganiferous manganiferous garnets, garnetsfbut but The The Champion Champion Mine Mine was was in in aa different different geologic geologic setting, settingf both both structually structually and and in in terms terms of of metamorphic metamorphic . grade. grade. . I STOP 10--JASPER 10--JASPER KNOB. KNOB, ISHPEMING ISHPEMING STOP This This is is aa wonderful wonderful exposure exposure of of Jaspilite Jas~ilite(the (the miners' minersfhard hard ore jasper). jasper). Note Note the the complex complex folding folding in in the the jaspilite jaspilite and and the the ore To the the south south and and west west were were irregular irregular replacement replacement by by the the hematite. hematite. To lenses of of high high grade grade hard hard ore. ore. lenses To Inclinef To the the north north are are the the hard hard ore ore open open pits pits of ofthe theIncline, Sawmill, SawmillfSchoolhouse Schoolhouse and and Little LittleMountain MountainMines. Mines. The The first first mining mining The hard hard here here was was in in 1848 1848 by by the the Cleveland Cleveland Iron Iron Mining Mining Company. Company. The ore, oref which which continued continued along along the the pitch pitch of of the the synclinal synclinal axis axis that that passes under passes under the the City City of of Ishpeming, Ishpemingfwas was followed followed underground underground in in the the Cliffs Shaft ShaftMine. Mine. Cliffs The iron—formation The iron-formation characteristically characteristically has has alternating alternating thin thin -or black black beds beds and and lenses lenses of of steel-gray, steel-grayfdark-blue-gray, dark-blue-grayfdark-gray, dark-grayfor specular specular hematite hematite and and bright-red bright-red hematitic, hematiticf fine—grained, fine-grainedfcherty cherty quartzite. Beds Beds commonly commonly range range in in thickness thickness from from aa fraction fraction of of aa quartzite. millimeter centimeters, and and fine fine internal internal laminations laminations millimeter to to about about 22 centimeters, can be be seen seen in in the the thicker thicker layers. layers. Specularite Specularite plates plates are are strongly strongly can oriented oriented parallel parallel to to bedding bedding in in the the hematitic hematiticlayers. layers. Excellent Excellent colored colored illustrations illustrationsof of this this have have been been published publishedin inU.S. U.S. Geological 28. Geological Survey Survey Monograph Monograph 28. Folds Folds having having drag drag folds folds on on their their limbs limbs and and themselves themselves being being drag drag folds folds on on the the limb3 limbs of of aa still still larger larger fold fold are are strikingly strikingly shown shown in most most exposures. exposures. Fold Fold axes axes are are horizontal horizontal to to gently gently plunging. plunging. in In In cross cross section section the the south south limbs limbs of of individual individual anticlinal anticlinal drag drag indicating that that the the folds folds commonly commonly are are longer longer than than the the north north limbs, limbsf indicating major major synclinal synclinalaxis axispasses passessouth southof ofJasper JasperKnob. Knob. - B-28 �Small breccia breccia zones zones occur occur in in the the iron—formation iron-formation at at this this Small locality. Along Along them, themt the the comparatively comparatively brittle brittle reddish reddish cherty cherty locality. (jasper) layers layers in in particular, particulart have have been been fragmented. fragmented. Fractures Fractures (jasper) have been been healed healed mainly mainly by by crystalline crystalline hematite. hematite. Some have Some of of the the , breccia zones breccia zones may may correspond correspond in in orientation orientation to to axial axial plane plane cleavage. cleavage. Two Two principal principal theories theories have have been been advanced advanced for for the the origin origin of of jaspilitic iron—formation iron-formation at atJasper JasperKnob. Knob. One the jaspilitic the One theory theory advocates advocates oxidation of of aa siderite-chert siderite-chert iron-formation oxidation iron-formation during during the the postpostNegaunee erosional erosional interval interval and and its its recrystallization recrystallization to to Negaunee specularite—quartz specularite-quartz during during the the Early Early Precambrian Precambrian Penokean Penokean orogeny orogeny and metamorphism. metamorphism. This This theory theory would would account account for for the the patches patches of of and jaspilite in in carbonate—facies carbonate-facies iron—formation iron-formation which which are are present present near near jaspilite ast for for example, exampletin in the the Cliffs Cliffs Shaft Shaft contacts between between the the two two rocks rocks as, contacts Mine about about 1/2 112 mile mile northwest northwestof ofhere. here. The The second second theory theory advocates advocates Mine primary origin origin for for the the iron iron oxide, oxidef either either as as depositional depositional aa primary diagenetic modification modification of of hematite or or as as magnetite magnetite derived derived by by diagenetic hematite depositional oxides. oxides. The The rock rock here here resembles resembles megascopically, megas~opically~ depositional particularly particularly in in the the very very even even bedding, bedding! magnetite-rich magnetite-rich facies facies of of iron-formation rather rather than than hematitic hematitic facies, fadesf that that is is iron—formation characteristically characteristically irregular irregular bedded bedded and and oolitic. oolitic. STOP 11--CLIFFS 11--CLIFFS SHAFT SHAFT MINE, MINE, ISHPEMING ISHPEMING STOP The and Shafts The distinctive distinctive obelisk obelisk style style headframes headframes of of "A" ffAff and "B" ftBft Shafts were 191gf replacing replacing the the original original wooden wooden headframes headframes were built built in in 1919, erected when when the the shafts shaftswere were sunk sunkin in1873. 1873. The The shaft shaft sections sections show show erected Their tgoarff. Their ultimate ultimate depth depth was was 1250 1250 feet feet that both both shafts shafts cut cut "oar". that shaft from surface. surface. "C" ftCtf shaft was was sunk sunk in in 1954 1954 to to replace replace the the two two from smaller smaller shafts shafts for for more more efficient efficient hoisting hoisting of of the the ore. ore. The The Koepe Koepe hoisting hoisting system system used used in in this this shaft shaft was was the the first first such such installation installation Ifendlessrope" ropetfsystem system in the the Western Western Hemisphere. Hemisphere. It It features features an an "endless in with the the hoist hoist in in the the top top of of the the headframe. headframe. with The Minet closed closed in in December, Decembert1967, 1967#had had the the The Cliffs Cliffs Shaft Shaft Mine, longest longest production production life life of of any any mine mine in in the the Lake Lake Superior Superior region region (1848-1967). It It produced produced 28,960,406 28,96Of4O6long long tons tons of of high high grade grade hard hard (1848—1967). ore. Its Its greatest greatest year year of of production production was was 1942 1942 when when 747,564 747!564 tons tons of of ore. and ore were were shipped. shipped. The The "room ffroom and pillar" pillartfworkings workings present present under under the the ore town town of of Ishpeming, Ishpemingtextend extend to to 1250 1250 feet feet below below the the collar collar of of the the shafts in in the the deepest deepest (15th) (15th)level. level. shafts STOP STOP 12--SOUTH 12--SOUTH PINE PINE STREET, STREET, ISHPEMING ISHPEMING As As noted noted in in the the Introduction, Introductionfthere there are are two two structural structural locations locations for for the the soft soft iron iron ore. ore. The The ores ores in in Negaunee Negaunee and and along along the the north north rim rim in in Ishpeming Ishpeming and and the the North North Lake Lake District District are are all all on on The second second location location the footwall footwall of of the the Negaunee Negaunee Iron IronFormation. Formation. The the The mines mines here here is is in in fault fault structures structures on on the the big big intrusive intrusivesills. sills. The were were the the Lake, Laket Lake Lake Angeline, Angelinet Section Section 16, lGf Holmes, Holmest and and Salisbury Salisbury Lake Angeline Angeline is is aa natural natural expression expression of of the the basin basin in in which which Mines. Lake Mines. The lake lake was was the Lake Lake and and Lake Lake Angeline Angeline deposits depositswere were found. found. The the pumped pumped out out in in 1890 1890 to to permit permit mining mining the the soft soft ore ore on on the the lake lake bottom. These These ores ores were were very very high high grade, gradet and and had had extensive extensive bottom. botryoidal botryoidal and and mammilary mammilary hematite hematite and and goethite goethite with with numerous numerous vugs. vugs. The Minet at at the the west west end end of of Lake Lake Angeline, Angelinelhad had both both The Section Section 16 16 Mine, B- 29 �hard ore ore (above) (above)and and soft soft ore ore (below) (below)in in direct direct contact contact with with one one hard another. another. These mines mines were were the the first first on on the the Marquette Marquette Range Range to to use use These electricity electricity for for electric electric for for underground underground locomotives, locomotivestlights, lightst slusherstand and pumps. pumps. It It was was here here also also that that Cliffs Cliffs voluntarily voluntarily slushers, introduced the the eight eight hour hour work work shift shiftin in1892. 1892. introduced STOP 13--HUMBOLDT 13--HUMBOLDT MINE: MINE: EDISON EDISON HISTORICAL HISTORICAL MARKER MARKER STOP This stop stop is is at at the the historical historical marker marker erected erected by by the the Marquette Marquette This County Historical Historical Society Society in in 1987 1987 for for the the Sesquicentennial Sesquicentennialof of County Michigan. Michigan. This This series series of of hard hard ore ore mines mines operated operated from from 1865 1865 to to 1892 1892 and and from 1908 1908 to to 1917, 1917t producing from producing 1,368,546 1t368t546tons tons of of hard hard ore ore from from both both open pit pit and and underground undergroundoperations. operations. The The Humboldt Humboldt Mine Mine was was open Michiganlsfirst firsttaconite taconite type type open open pit, pittconcentrator Michigan's concentratorand and pellet pellet plant operation. operation. It It was was in in production production from from 1954 1954 to to 1970, 1970tshipping shipping plant 9t433t305 long tons tonsof of concentrates concentratesand andpellets. pellets. 9,433,305 long STOP 12 12 (Fig. (Fig. 8)--REPUBLIC 8)--REPUBLIC MINE MINE OPEN OPEN PIT PIT STOP The The Republic Republic Mine Mine was was opened opened in in 1870 1870 as as aa series seriesof of hard hard ore ore open pits, pitst but but followed followed the the near near vertical vertical dipping dipping beds beds of of the the open Negaunee Iron Iron Formation Formationinto intounderground undergroundoperations. operations. The The Pascoe Pascoe Negaunee 4t000feet feet deep deep (2,910 (2t910feet feet shaft was was an an inclined inclined shaft shaft some some 4,000 shaft vertically) gradethard hard hematite hematite and and magnetite magnetite ore ore to to vertically) with with high high grade, depthtin in aa host hostof ofjaspilite. jaspilite. From From 1872 1872 to to 1926, 1926tthe the that depth, that Republic long Republic Mine Mine shipped shipped 8,563,170 8t563t170 long tons tons of of hard hard ore. ore. It It began began as as taconite type type operation operation in in 1956, 1956tbut but closed closed in in 1983 1983 and and is is on on aa taconite llstand-byll basis. "stand—by" basis. The the The Republic Republic pit pit is is distinctive distinctive for for its its "high *'highwall", wallllt the contact of of the the upper upper portion portion of of the the iron-formation iron-formation with with the the contact metadiabasesill. sill. The The contact contact of of the the Negaunee Negaunee Iron Iron Formation Formation and and metadiabase the overlying overlying Goodrich Goodrich Quartzite Quartzite was was marked marked by by an an extensive extensive the jaspilite. This conglomerate made made up up of of jaspilite. This conglomerate conglomerate was was higher higher in in conglomerate titanium than than the the underlying underlyingNegaunee NegauneeIron IronFormation. Formation. titanium developedtmining mining the the iron—formation iron-formationfrom from As the the open open pit pit was was developed, As footwall to to the the conglomerate conglomerate and and Goodrich Goodrich Quartzite Quartzite the metadiabase metadiabase footwall the hangingwall, hangingwall, numerous numerous underground underground workings workings were were encountered. encountered. These These openings openings were were filled filled with with broken brokencrude crudeore oreso sothe thedrills, drillsttrucks, trucks, and shovels shovels could could work work with with safety. safety. and STOP 15--HIGHWAY 15--HIGHWAY M-95 M-95 ROAD ROAD CUTS: CUTS: MICHIGAMME MICHIGAMME FORMATION FORMATION STOP Tightly Tightly folded folded schist schist of of the the lower lower slate slate member member of of the the Michigamme Michigame Formation Formation is is exposed exposed in in aa roadcut roadcut on on the the east east side sideof of The rock rock here here highway highway M—95 M-95 near near the the axis axisof ofthe theRepublic Republicsyncline. syncline. The is is iron—rich iron-rich metasediment, metasedimentt now now consisting consisting of of biotite—garnetbiotite-garnetamphibole amphibole schist schist that that contains contains aa few few inch-thick inch-thick layers layers of of impure impure Although the the rocks rocks are are in in the the sillimanite sillimanitezone zoneof of quartzite. Although quartzite. metamorphism, metamorphismt sillimanite sillimanite is is not not present present here here because because of of the the lack lack foldsthaving having Minor folds, of appropriate appropriate aluminous aluminoussource sourcematerials. materials. Minor of amplitudes amplitudes much much greater greater than than wavelengths wavelengths and and greatly greatly attenuated attenuated limbs, limbstare are common common and and reflect reflect the the geometry geometry of of the the major major syncline syncline whose whose preserved preserved keel keel is is deeper deeper than than it it is is wide wide at at this this point point and and noncylindbecomes deeper deeper to to the the northwest. northwest. Folding Folding is is markedly markedly noncylind— becomes rical at at outcrop outcrop scale; scale; domains domains of of homogeneous homogeneous strain strain are are commonly commonly rical B- 30 �FIGURE FIGURE 88 GEOLOGY GEOLOGY OF OF THE THEREPUBLIC REPUBLIC MINE MINE AREA AREA a-. 530 000 ,000 , 36 3t s. / ./ / - B-31 _s Fiqure E'iqure g8 / �only aa few few square squarefeet. feet. Most Most minor minor folds folds plunge plunge northwest northwest in in only accordance accordance with with the the regional regional synclinal synclinal axis, axist but but plunges plunges vary vary from from about 15° 15O SE SE to to 600 60 tq NW. about (1to to33 inches) inches) outcroptaa thin thin (1 Near the the north north end end of of the the outcrop, Near quartzite bed bed is is repeated repeated many many times timesby by ninor minor folds. folds. Axes quartzite Axes of of adjacent adjacent folds folds only only aa few few inches inches apart apart have have plunges plunges that that diverge diverge by by This 6 0 ' . This noncylindrical noncylindrical geometry geometry may may be be aa result result of of an an as much much as as 600. as earlier earlier fold fold set set in in the the sedimentary sedimentary rocks rocks that that formed formed prior prior to, tot and and was was strongly strongly overprinted overprinted by, byt the the folding folding which which formed formed the the Republic Republic . sync1 sync 1 ine me. STOP 16 16 (Fig. (Fig. 9)--GREENWOOD 9)--GREENWOOD RESERVOIR RESERVOIR STOP The The Greenwood Greenwood Reservoir Reservoir is is aa prominent prominent new new land land feature feature created created in in 1973 1973 by by the the Tilden Tilden Mining Mining Company Company to to provide provide aa constant constant source source of of water water for for the the concentrating concentratingplant plantrequirements. requirements. The The water water surface surface approximates approximates1,400 lt4O0acres. acres. The The Reservoir Reservoir area area is is open open to to the the public public for for fishing, fishingtboating, boatingt hiking, hikingtand and other other recreational recreational activities. The The agreement agreement with with the the Michigan Michigan Department Department of of Natural Natural activities. Resources thatt at at all all times, timest the the discharge discharge downstream downstream to to Resources provides provides that, the the Middle Middle Branch Branch of of the the Escanaba Escanaba River River will will be be at at least least three three times times the the minimum minimum low low flow flow observed observed by by stream stream gauging gauging over over many many multipart An interesting interesting feature feature of of the the system system is is the the multiport years. An years. discharge discharge system system in in which which any any combination combination of of four four vertically vertically arranged arranged ports ports may may be be utilized utilized to to mix mix waters waters of of varying varying temperatures and and oxygen oxygen content. content. temperatures The The two two principal principal granitic granitic units units forming forming the the Archean Archean Southern Southern 8A (Fig.9) (Fig.9) Compeau Compeau Creek Creek Complex will will be be seen seen here. here. Near Near point point BA Complex Gneiss is is exposed exposed in in aa large large roadcut. roadcut. The The Compeau Compeau Creek Creek Gneiss Gneiss is is Gneiss generally generally mediummedium- to to coarse-grained coarse-grained and and mostly mostly granodiorite granodiorite or or tonalite. It It is is characteristically characteristically both both compositionally compositionally and and tonalite. structurally Heret it it varies varies from from structurally heterogeneous heterogeneous at at outcrop outcropscale. scale. Here, massive massive rocks rocks with with faint faint banding banding or or schleiren schleiren expressed expressed by by variations variations in in percentage percentage of of mafic mafic minerals, minerals, mostly mostly biotite, biotite, to to Clots of of biotite biotite are are common common and and in in rather well well foliated foliated gneiss. gneiss. Clots rather Relict garnet garnet cores cores can can be be places are are aligned aligned in in the the foliation. foliation. Relict places found in in some some clots. clots. Toward Toward the the northeast northeast end end of of the the road road cut, cuttthe the found Compeau Compeau Creek Creek Gneiss Gneiss is is cut cut by by aa nearly nearly vertical vertical dike dike of of Early Early Proterozoic metadiabase. metadiabase. Proterozoic of We hope hope that that you you have have found found this this "sampler" ltsamplerll of This ends ends our our trip. trip. We This the the Marquette Marquette Mineral Mineral District Districtof of interest. interest. B-32 �559 ''f__5_ ) -Wbcg - 30 _j54O Xnic FIGURE 9 A PORTION OF THE GREENWO( 7 MINUTE QUADRANGLE SHOWING THE LOCATION OF STOP 17 Figure 9 �FIELD FIELD TRIP TRIP 33 A STRUCTURAL STRUCTURAL TRAVERSE TRAVERSE ACROSS A PART PART OF TUE THE PENOKEAN PENOKEAN OROGEN ILLUSTRATING ILLUSTRATING EARLY IN NORTHERN NORTHERN MICHIGAN: MICHIGAN: EARLY PROTEROZOIC PROTEROZOIC OVERTHRUSTING OVERTHRUSTING IN TEXT AND FIELD FIELD GUIDE GUIDE TEXT by JOHN KLASNER, Department JOHN S. S . KLASNER, Department of of Geology, Geology, Western Western Illinois Illinois University and U. S. Geological Survey, Macomb, IL IL 61455 61455 University and U. S. Geological Survey,Macornb, PAUL PAUL K. K. SIMS, SIMS, U. S. Geological Geological Survey, Survey, Box Box 25046, 25046, Denver Denver Federal Federal Center, 905, Denver, Denver, CO CO 80225 80225 Center, MS 905, Geological Department of Geology and GREGG, WILLIAM J. GREGG, Department of Geology Geological J. MI Engineering, Michigan Technological University, University, Houghton, Houghton, MI 49931 49931 CHRISTINA CHRISTINA GALLUP, GALLUP, Department Department of of Geological Geological and and Planetary Planetary Science, Science, California CA 91125. 91125. California Institute Institute of of Technology, Technology, Pasedena, Pasedena, CA C-i �INTRODUCTION INTRODUCTION The Early Early Proterozoic Proterozoic Penokean Penokean orogen orogen is is one one of of several several The major orogenic orogenic belts belts in in the the North North American American craton craton that that developed developed major between about about 1.95 1.95 and and 1.85 1.85 Ga Ga (Hoffman, (Hoffman, 1988). 1988). Rocks Rocks of of the the between orogen are are exposed exposed in in Michigan, Michigan, Wisconsin, Wisconsin, and and Minnesota Minnesota (Fig. (Fig. orogen 1) and and extend extend eastward eastward into into the the Lake Lake Huron Huron area area (Sims, (Sims, et et al. al. 1) 1981), and and westward westward in in the the subsurface subsurface into into Iowa Iowa and and Nebraska Nebraska 1981), (Sims and and Peterman, Peterman, 1986). 1986). The The southern southern boundary boundary is is not not exposed exposed (Sims inasmuch as as it it is is overlapped overlapped by by Phanerozoic Phanerozoic platform platform sedimentary sedimentary inasmuch rocks. The The Penokean Penokean orogen orogen is is intruded intruded by by 1.76 1.76 Ga Ga anorogenic anorogenic rocks. rhyolite granite granite which which is is exposed exposed in in Wisconsin. Wisconsin. rhyolite The Penokean Penokean orogen orogen consists consists of of aa northern northern assemblage assemblage of of The sedimentary and and bimodal bimodal volcanic volcanic rocks rocks of of the the Marquette Marquette Range Range sedimentary Supergroup in in Michigan Michigan (Cannon (Cannon and and Gair, Supergroup Gair, 1970) 1970) and and equivalants equivalants in in Minnesota, Minnesota, the the Animikie Animikie Group Group and and Mills Mills Lacs Lacs Group Group deposited deposited on on aa continental Archean Archean margin margin and and aa southern southern terrane terrane' composed composed continental mainly of of Early Early Proterozoic Proterozoic caic-alkaline calc-alkaline plutonic plutonic rocks rocks termed termed mainly The the Wisconsin Wisconsin magrnatic magmatic terrane terrane (Sims, (Sims, 1987 1987 and and in in press). press). The the Minnesota, in recognized magmatic arc terrane has not been recognized in Minnesota, has not been terrane arc magmatic although it it may may occur occur in in the the subsurface subsurface in in southeastern southeastern Minnesota. Minnesota. although The Niagara fault fault zone zone is is aa brOadly broadly arcurate arcurate convex convex Niagara The as much as 10 km northward systems systems of of faults faults and and shears, shears, as much as 10 km wide, wide, northward that separates separates the the continental continental margin margin assemblage assemblage and and Wisconsin Wisconsin that It magmatic terrane terrane (Fig. (Fig. 2). 2). It contains contains flattened flattened , steeply steeply maginatic dipping rocks rocks that that have have prominent prominentstretch stretchlirieations lineations parallel parallel to to dipping , dip dip (Ueng (Ueng and and others, others, 1984; 1984; Sedlock Sedlock and and Larue, Larue, 1985; 1985; and and Sims Sims and and others, 1985), 1985), and and it it is is interpreted interpreted by by the the above above authors authors to to be be others, In the surface surface expression expression of of aa 1850 1850 My My old old suture suture zone. zone. In the northeastern Wisconsin Wisconsin all all of of the the components components of of an an ophiolite ophiolite northeastern assemblage, although although dismembered, dismembered, occur occur near near the the suture suture zone zone assemblage, 1987a). (Schulz,1987a). (Schulz, Following the the initial initial suggestion suggestion of of Van Van Schmus Schmus (1976), (1976), Following several authors authors (Cambray, (Cambray, 1978; 1978; Larue Larue and and Sloss, Sloss, 1980; 1980; Greenburg Greenburg several and Brown, Brown, 1983; 1983; Anderson Anderson and and Black, Black, 1983; 1983; Schulz, Schulz, 1983, 1983,1984; 198-2; and Schulz and and others, others, 1984; 1984; LaBerge LaBerge and and others, others, 1984; 1984; Sims Sims and and Schulz 1984; Klasner Klasner and and others, others, 1985; 1985; Sims Sims and and others, others, 1985; 1985; Peterman , 1984; Peterman Klasner and and Attoh, Attoh, 1986; 1986; Schulz, Schulz, 1987a, 1987a, b; b; and and Sims Sims and and others, others, Klasner tectonic proposed a plate-tectonic scenario for the 1987) have proposed a plate-tectonic scenario for the tectonic have 1987) evolution of of the the Penokean Penokean foldbelt foldbelt in in northern northern Michigan Michigan and and evolution Wisconsin. Although Although they they differ differ in in detail, detail, these these authors authors suggest suggest Wisconsin. that evolution evolution of of the the orogeri orogen began began with with rifting rifting accompanied accompanied by by that and Marquette the troughs (such as formation of basins and troughs (such as the Marquette and basins and formation of the Archean Archean Republic troughs) troughs) along along the the passive passive margin margin of of the Republic followed was This in northern Michigan. by Superior craton craton in northern Michigan. This was followed by Superior with south, the crust to subduction of of oceanic oceanic crust to the south, with ultimate ultimate subduction collision of of arc-related arc-related volcanic volcanic and and plutonic plutonic rocks rocks with with the the collision Archean continental continental margin. margin. Archean , consequence consequence of of the the accretion accretion of of arc-related arc-related crust crust to to of rocks the Superior Superior craton, craton, widespread widespread deformation deformation of rocks of of the the the continental margin margin as as well well as as of of the the magmatic magmatic arc arc is is to to be be continental As As aa C— 2 �EXPLANATION EXPLANATION n Ma and and younger) younger) PHANEROZOIC (600 (600 Ma PHANEROZOIC Sedimentary Sedimentary strata strata MIDDLE MIDDLE PROTEROZOIC PROTEROZOIC (900—1600 (900-1600 Ma) Ma) Mafic Mafic igneous igneous and and sedimentary sedimentary rocks rocks of of Midcontinent Midcontinent rift rift system system (1000—1200 (1000-1200 Ma) Ma) Anorogenic Anorogenic anorthosite anorthosite and and rapakivi rapakivi granite granite (1480—1500 (1480-1500 Ma) Ma) EARLY EARLY PROTEROZOIC PROTEROZOIC (1600—2500 (1600-2500 Ma) Ma) n Granitoid Granitoid rocks rocks (1760—1800 (1760-1800 Ma) Ma) Volcanic Volcanic and and graaitoid granitoid rocks rocks of of Wisconsin Wisconsin magmacic magmatic terrane terrane (1815-1890 Ma) Ma) (1815—1890 -1 Marquette Range Range Super— SuperStratified Stratified rocks rocks of of Animikie Animikie basin; basin; Marquette - ground ground and andAnimikie Animikieand andMil].e Mille Lacs Lacs Groups Groups ARCHEAN A R C W A N (2500 (2500 Ma Ma and and older) older) A Greenstone—granite Greenstone-granite terrane terrane (2600—2750 (2600-2750 Ma) Ma) A n Gneiss Gneiss terrane terrane(2600—3550 (2600-3550Ma) Ma) A Extra-Superior gneiss gneiss and and schist schist (2500—3000 (2500-3000 Ma) ~ a ) Extra—Superior -.--- Great Lakes Lakes tectonic tectonic zone; zone; dots, dots, buried buried trace trace C-4 �480 48° 440 FIGURE 1. 1. Generalized Generalized geologic cjeologic map map of of the the Lake Lake Superior S u ~ ? r j . ~ > region rregion FIGURE units of of the thePeriokean Penoksan orogen o r o p n and and adjacent adjacent areas. aress. showifiq rock rock units showing Xodified from from Morey Morey and znd others others (1982). (1982). Modified C- 5 �FIGURE 2. Map of the eastern part of the Lake Superior region showing e:tent of the Early Proterozoic contlnental-margLn assemblage and Wisconsin rnagrnatic terrane of the Pnokean oroen. Archean rocks are patternd. Stippled area snows location of traverse in this field guidee. IM = iOfl Mountain; M = Marquette. C-6 �expected. In this this guidebook, gui6ebookf we we examine examine evidence evidence from from northern northern In expected. Michigan showing showing that that there there was was extensive extensive overthrusting overthrusting on on the the Michigan continental margin margin during during the the accretionary accretionary event. event. We We examine examine the the continental for overthrusting overthrusting along along aa north-south north-south structural structural evidence for evidence traverse (Fig. (Fig. 2) 2) extending extending from from Falls Falls River River southward southward across across the the traverse and Michigame basin, basinf Arnasa Amasa uplift, and Feich Felch trough-Calumet trough-Calunet trough trough uplift, Michigamrne resion to to .the Niagara fault fault zone zone which which lies lies along along the the the Niagara region fi?ichiqan/~$isconsin border. Michigan/Wisconsin border. This guidebook guidebook is is mainly mainly the the outgrowth outgrowth of of field field work work and and This related related synthesis synthesis done done during during 1986 1986and and 1987. 1987. Critical Critical areas areas for for examination were were selected selected from from several several excellent exc2llent published published examination geological maps maps and and papers papers in in the the south south (principally (principally James James and and geological 1968; Bayley and others, 1966; James and others, othersf 1961; James and othersf 1968; Bayley and othersf 1965; 1961; others, by This Duttonf 1971). 1971). This was was followed, followedf where where appropriate, appropriatef by Dutton, detailed structural structural studies studies in in the the north, northf mainly mainly done done by by Kiasner Klasner detailed previously and Gallup. Gallup. In this this part part of of the the area area previously mapped mapped by by In and and Cannon and Kiasner (see for example mainly W. F. Cannon and Klasner (see for example Cannon and mainly W. F. Cannon Kiasner, Klasnerf 1972; 1972; Kiasner, Klasnerf 1972; 1972; Cannon, Cannonf 1973; 1973; Kiasner, Klasnerf 1978), 1978), field field of addition involved refinement and the work principally principally involved refinement and the addition of new new work detailed observations. observations. Gregg's Greggls work work has has been been in in the the Baraga Baraga detailed basinf primarily primarily northeast northeast of of the the area area covered covered in in this this report. report. basin, 1987 and Sikkalaf 1987 and Sikkala Sikkala and and Detailed studies studies at at Falls Falls River River ( Sikkala, Detailed Greggf 1987), 1987)f however, howeverf mark mark the the northern northern end end of of the the traverse traverse in iil Gregg, the area area of of this this report. report. the , ( GENERAL GEOLOGY GEOLOGY GENERAL of the the Marquette Marquette Range Range Supergroup Supergroup Stratigraphic units units of Stratigraphic (Cannon and and Gair, Gairf 1970) 1970) are are listed listed in in Table Table 1. 1. The The Marquette Marquette (Cannon Range unconformably Range Supergroup Supergroup consists consists of of three three groups groupswhich whichlie lieunconforrnably abovef or or in in fault fault contact contact with, withf underlying underlying Archean Archean greenstone— greenstoneabove, granite or or gneiss. gneiss. The The rocks rocks occupy occupy broad broad open open basins, basinsf such such as as granite fault-bounded troughs troughs the Michigamme Michigamme basin basin or or relatively relativelynarrow, narrowf fault—bounded the such as as the the Marquette Marquette and and Republic Republic troughs troughs (Fig. (Fig. 3). 3). An An such apparently thick thick sequence sequence of of metavolcanic metavolcanic rocks, rocksf the the Hemlock Xeinlock apparently Formztion (see (see Cannon Cannon and and Klasner, Klasnerf 1975 1975 and and Foose, Foasef 1980) 1980) lies lies Formation along the the west west side side of of the the Amasa Amasa uplift. uplift. As As discussed discussed below below , we we along tentatively tentatively interpret interpret this this apparently apparently large large thickness thickness of of volcanic volcanic rocks as as resulting, resultingf at at least least in in part, part, from from tectonic tectonic stacking stacking rocks It should be the Early Protrozoic overthrusting event. during the Early Prot.~rozoic overthrusting event, It should be during noted noted that that the the Michigamme Michigamme Formation Formation is is informally informally divided divided into into an an Member Formation upper and and lower lower slate slate member member by by the the Bijiki Bijiki Iron Iron Formation Nember upper (see Table Table 1). 1). The The lower lower slate slate member member is is the the dominant dominant lithology. lithology. (see evidence for overthrusting is found Much of of the the evidence for overthrusting is found in in the the upper upper Much slate member member (dominantly (dominantly graywacke graywacke ) member member of of the the Michigamrne Michigamme slate Formation. Formation. , ) Archean Archean rocks rocks of of northern norkhern Michigan PTichigan and and Wisconsin Wisconsin have have been divided divided by by Sims Sims (1980) (1980)into into aa granite-greenstone granite-greenstone terrane terrane been (2600 -- 2700 2703 Ma) Ma) on on the the north north and and aa gneiss gneiss terrane terrane (2600 (26CO -- 3550 3550 (2600 Ma) on on the the south. south. The The boundary boundary between between these these two two terranes terranes has has Ma) been In the the study stuZy area, areaf it it been named named the the Great Great Lakes Lakes tectonic tectonic zone. zone. In is oriented oriented eastward eastward and and lies lies roughly roughly along along the the Marquette Narquette trough trough is (Fig. 3). 3). The The Penokean Penokean foldbelt foldbelt is is localized localized along along the the GLTZ, GLTZ, (Fig. The The C- 7 �___________ ____________ ___________________ . .TABLE TABLE II Michigamme Michiqamme Basin Basin paint Paint Felch-Calumet Felch-Calumet trough trough Iron Iron River River syneline svncline Fortune Fortune Lakes Lakes Slate Slate Stambaugh Stambauqh Formation Formatior Hiawatha Hiawatha Graywacke Gravwacke Riverton Riverton Iron— 1ro& Formation F o m a tion Dunn Dunn Creek Creek Slate Slate River River Group Group Saraga Baraqa __________________ Badwater Badwater Greenstone Greenstone Bedwater Bedwater Greenstone Greenstone ichigamme ichiqanme Formatjo, Formatit flichigamme Nichiqannne Slate Slate Michigamme M i c h i g a m Slate Slate 3ijik. ijiki Iron— IronAinasa Amasa Formation Formation Hemlock Formation Hemlock Formation Formation FormationMember Member :larksburg larksburg Volcanics VolcanicsMember Member ;reenwood reenwoodIron— IronFormation FormationMember Hear oodrich ite oodrichQuartz Quartzite ' Group Group - LOCAL UNCONFORMITy UNCONFORMIT' LOCAL — UNCONFORMITY UNCONFORMITY OR DISCONFORMITY — - I4enominee Menomine{ Group Group Marquette Marquette EARLY PROTEROZOIC PROTEROZOIC EARLY Range Range Negaunee Neqaunee Iron— IronFormation Formation Siamo Siamo Slate** Slate** ,. Ajibik Ajibik Quartzite Quartzite Vulcan Vulcan IronIronFormation Formation Felch Felch Formation Formation Supergroup supergroup - — UNCONFORMITY UNCONFORMITY Chocolay Chocolay Not present Not -present Saunders Saunders Formation Formation Grou Group p - ARCHEAB ARCHEAN - Granite ranite — Gneiss Gneiss Randville Randville Dolomite Dolomite Sturgeon iturgeon Quartzite Quartzite Fern 'ern Creek Creek Formation Formation - —- UNCONFORMITY UNCONFORMITY — — UNCONFORMITY— UNCONFORMITY UNCONFORMITY UNCONFORMITY Gneiss Gneiss greenstone reenstone * Upper Upper slate slate member of the the Michigamme Michiqamme Forma.ion F0rma:ion lies above above the the Bijiki Bijiki lies Member and and the the lower lower slate slate member member of of the theMichiganune Michiqame lies lies below below it. it. Member ** Possibly Possibly present present in in the the subsurface subsurfaceof ofthe theMichigalume Michiqamme basin. basin. * ** C-B — - Iron Formation Formation Iron — - �Fkld trip stops \ Thrust fault & Geologic contact Fault of unknown dip block h u- upthrown 1 Strike ond dip direction of foliation Intrusive rocks P= Peavy metamorphic node &= I 8 3 4 Mo gronlte ;J:;erento i ted Point River Group 0 Undifferentiated Barago Group rocks. Includes undifferentiated Bodwater ond Hemlock volconic units Undifferentiated Menominee ond Chocoloy Group rocks @ J z Undifferentiated qronitoid gneiss ond Dickinson Group metoconglomero 0 a a 5 0 0 5 0 Miles I 0 Kilometem FIGURE 3. Geologic map of the study area showing major structural and location of structural location of field stops: features, c-c' is part of the 8); 3—B' Fig. 6) and profiles A—A' (Fig. 9) which lies along a line connecting A composite profile (Fig. Features discussed in the text include A4 = ±-rnasa uplift, to C'. Canyon Fa)ls, CT = BB = Baraga basin, BL = 3ush Lake Fault, CF Calumet trough, DD =Dunbar dome, FR = Falls River location, FT = Feich trough, MB = Michigamme basin, MT = Marquette troi;gh, NC = flO(i, northern complex, TM = Taylor Mine, P = Peavy metamorphiclocain Creek. RT =RepubliC trough. AA is ti and PC = Plunjbaqo of the the granitic granitic intrusion intrusion dated dated at at 1824 1824 Ma Ma (Z.E. (z.E. Peterman, Peterman, perspersof onal onal communication). communication). From From Cannon Cannon (1983) (1983) and and Dutton Dutton and and Linebaugh Linebauqh (1967) (1967). C-9 - - �. deformation which appears appears to to have have played played aa role role in in the the style style of of deformation which North of of the the GLT7J, GLTZr Early Proterozoic Prt7tsroz~ic of Early Early Proterozoic Proterozoic stata. stata. North of strata are are only only gently gently deformed, deformedr whereas whereas south south of of it it Early Zarly strata The traverse traverse described described Proterozoic Proterozoic strata strata are are intensely intensely deformed. deformed. The intensely in in this this guidebook guidebook lies lies mostly mostly south southof ofthe theGLTZ, GLTZ,in in the the intensely Here, Early deformed part part of of the the Penokean Penokean foldbelt. foldbelt. Herer Early Proterozoic Proterozoic deformed strata overlie overlie block block faulted faulted Archean Archean rocks rocks (Cannon (Cannon and and Klasner, Klasner, strata 1972 and and Cannon, Cannonr1973). 1973). 1972 At least least four four regional regional metamorphic metamorphic aureoles aureoles (James, (Jamesl 1955) 1955) At Attoh were formed formed during during the the Penokean Penokean orogenic orogenic event event (Fig. (Fig. 4). 4). Attoh were and Vander Vander Muelen Muelen (1984) (1984)and and Kiasner Klasner and and Attoh Attoh (1986) (1986)argue argue that that and thickening, crustal by were caused tke metamorphic metamorphic aureoles aureoles were caused by crustal thickeningr the possibly due due to to tectonic tectonic stacking stacking associated associated with with overthrustirig overthrustirq possibly during the the Penokean Penokean accretionary accretionary event. event. during c chlorite C chlorite biotite bb biotite 9 garnet ggarnet S - 40 km 40 km s Staurolite Paleozojc Paleozoic Rocks Rocks Peavy Node Node Watersmeet Node Florence Node Node Florence -' F1232E 4. 4. Location Location of of metamorphic netamorphic aureoles aureoles in in northern northsrn Michian bfichiqsn FItrn2 (after James, Samesl1955). 1955). (after Structzral studies stusies (Cannon (Cannon and and Kiasner, Klasner? 1972; 1972; Klasner, Klssnsr, Structural and Klasner, 1978) have shown Early 1972; Cannon, Cannon? 1973; 1973; and Klasnerr 1978) have s h ~ i ~that that n Early 1972; subjected to at least Proterozoic ?rotsrozoic rocks rocks in in northern northern Michigan Michiqan were wers subject& to ~t lsast ( F l ) ws K Z S thin thin thrse periods peri~As of of deformation. defornatici-i. The The first first event event (Fl) three strata resulted in shortening of Early Proterozo1c skinned znd resulted in shortening of Early ProtsrazoiL? strata and skinned widespread widespread west-northwest-trending w e s t - n t ~ r t h ~ c t ? s t - t r ~ f i d' i ~ g and development development of of az and c-10 C10 �block str~ctural fabric(Fig. (Fiq.3). 3 ) . The The second second event evsnt (F2) (F2)involved inv~lve5 block structural fabric structural formation of Archean basement rocks and uplift of Archean basement rocks and formztion of structural of uplift features infoicling features such such as as the theMarquette Karquetteand andRepublic Republictroughs troiighsand an2 infolding of Early Early Proterozoic Proterozoic strata strata into intothe thetroughs. troughs. Larue Larue and and Sloss Sloss of (1980) have have shown shown that that the the troughs troughs actually actually started started to to form form (1980) earlyf during during deposition deposition of of the the sediments, sediinents, and anZ before before Fl Fl early, deformation. Kiasner Klasner (1972, (1972, 1978) 1978) noted notsd aa third, third, late late stage, stags, deformation. brittle deformational deformational event event (F3) (F3) in in the the northern northern part part of of the the brittle Michigamme Michigamme basin basin and and suggested suggested that that it it could could have have been been caused caused by by late block block uplift uplift of of Archean Archean basement. basement. Petrofabric Petrofakric studies studies late (Klasnerf 1972, 1972f 1978) 1978) showed showed that that regional regional metamorphism metamorphisin in in this this (Kiasner, part of of northern northern Michigan Michigan peaked peaked after after Fl Fl deformation, deformation, about about the the part tine of of F2 E'2 deformation. deformation. time Uplift Basin Basin Uplift + 47 Trends Trends of of first first order order structures structures ---- Trends Trends of of second second order structures Paleozoic Rocks 0 0 20 20 miles miles L FIGURE 5. 5 . General General trends trends of of first first and and second second order or6er structures structures in iz FIGURE narthern Michigan Michigan (from (fromCannon, Cannon, 1973). 1973). northern Cancon (1973) (1973) divided Zivided the the regional regional structures structures in in northern northern Cannon ichigan Xichiganinto into"firsts' "first"and and "second'1 "secon~"order order features fsatures (Fig. ( F i q . 5). 5 ) . First First af orientations arier,tations and a n 6 are .3rs ordsr structures structxres have hs-~e aa wide wide range r m q e of order of and block uplift uplift s n ddoming Samincj(Sims (Sins and znd others, others, 1$84a) :-S84a) (2f relste6 to to block related order st.ractu2s structures have ths Archean Archsan crust. S2cond ordsr have a z regular rsqilai-westx?stthe crust. Second of and are related to the Fl shortening trend Early northwest trenz an6 are relstd ta the Fl shortsning of Early northwest C-li �Proterozoic Proterozoic strata. strata. PREVIOUS EVIDENCE EVIEENCE FOR FOR THRUSTING THRUSTING OF OF EARLY EARLY PROTEROZOIC PROTEROZOIC ROCKS ROCKS PREVIOUS The The dichotomy dichotomy in in style style of of deformation deformation between bstween Early Early Proterozoic Proterozoic rocks rocks and and underlying underlying Archean Archean rocks rocks led led Cannon Cannon and and Klasner (1972), (1972) Kiasner Klasner (1972), (1972) Cannon Cannon (1973), (1973) and and Kiasner Klasner (1978) (1978) Kiasner to to suggest suggest that that aa decollement decollement exists exists between between them. them. They They suggested that the shortening of suggested that the shortening of Early Early Proterozoic Proterozoic strata strata relative Archean rocks rocks was was caused caused by by gravity gravity relative to to underlying underlying Archean sliding off slizing off an an ancestral ancestral Penokean Penokean mountain mountain range range in in the the south. south. They They (in (in particular particular Kiasner, Klasnerf 1972, 1972, 1978) 1978) suggested suggested that that Fl Fl deformation deformation occurred, occurredf in in part, partf while while the the sediments sediments were were unconsolidated; unconsolidated; however, howeverf this this postulate postulate is is no no longer longer tenable, tenabler and and it it appears appears that that the the Fl Fl deformational deformational event event involved involved solid solid rocks. rocks. \ Recently, Recently, Hoist Holst (1982, !1982r 1984) 1984) identified identified Early Early Proterozoic Proterozoic structures Similarly, structures in in eastern eastern Minnesota. Minnesota. Similarlyf Maharidge ?.laharidge (1986) (1986) proposed proposed that that the the Felch Felch trough trough area area of of northern northern Michigan ?!ichicjan (Fig. (Fig. 2) 2) represents represents aa crystalline-core crystallice-core nappe nappe feature. feature. He He based basez this this interpretation interpretation on on reexamination reexamination of of sedimentary sedimentary rock rock outcrops outcr~ps in in the the Feich Felcb.trough trough area, areaf previously previously mapped mapped by by James Janes and znd others others (1961), (196llf and and on on microstructural microstructural analysis analysis of of hand hand specimens specimens from from the the region. region. Later, Later, Sims Sims and and others others (1987) (1987)tentatively tentatively suggested sucjgested that that the the Felch Felch trough trough area area may may represent represent the the core core of of aa northnorthverging verging nappe nappe thrust thrust structure, structuref but but this this interpretation interpretation remains remains equivocal; equivocal; and, andf as as discussed discussed below, belowr although although we we cannot cannot rule rule out out the the presence presence of of aa nappe, nappet we we think think that that Felch Felch trough trough area area may may be be part Structural part of of aa south-verging south-vergingbackthrust. backthrust. Structural studies studies underway underway in in this this region rsgion should should permit permit resolution resolution of of this this problem problem in in the the near future. near future. nappe nappe On On the the other other hand, handf Sikkala Sikkala (1987) (1987) and and Sikkala Sikkala and and Gregg Gregg have identified (1987) (1987) have identified recumbent recumbent folds folds and and aa probable probable nappe nappe structure structure in in slate slate and and graywacke graywackeof of the theMichigamrne Michigame Formation Formation at at Falls Falls River River near near L'anse. Ltanse. Similarly, Similarlyf Van Van Roosendaal Roosendaal (1985) (1985) mapped mapped large l a ~ g e scale scale westwest- northwest northwest trending trending thrust thrust systems systems in in slates slates and and graywackes graywackes of of the the Baraga Baraga basin basin (Fig. (Fig. 3) 3) northeast northeast of of Falls Falls River. River. Evidence Evidence for for Early Early Proterozoic Proterozoic overthrusting overthrusting has has recently recently been been found found by by Xlasner Klasner and and others others (1988, (l98Bf in in press) press) in in several several places About Xichigan. About 120 120 km km west west of of the the traverse traverse places in in northern northern Michigan. shown shown in in Figures Figures 22 and and 3, 3 f Early Early Proterozoic Proteroz~icslate slate and and graywacke graywacke of of the the Tyler Tyler Formation Formation (Baraga (BaragaGroup) Group) near near Ironwood, Ironw006~Michigan Xichigan and an6 metavolcanic metavolcanic rocks rocks of of the the Emperor Emperor volcanic volcanic complex camplex at at nearby nsarby Wolf Xolf Mountain eastXountain have have aa penetrative penetrative foliation foliation that that strikes strikes roughly rou~hly 2astwest west and, and, when when corrected corrected for for rotation rotati~ndue due to to deformation deforriiationin in the the the the ca ca 1.1 1.1 Ga Ga Midcontinent MidcontinentRift, Riftf dips dips gently gently south. soath. This This suggests suggests that that these these rocks rocks may may have have been been involved involved in in az thrust, thrustt or or thrustthrust- nappe nappe event event similar similar to to that that mapped mapped about about 100 100 km km west west in in Minnesota Ninnesota by by Holst Holst (1984) (1984)and and at at Falls Falls River River by by Sikkala Sikkala 1987 1987 and and Sikkala (1987). Sikkala and and Gregg Gre~g (1987). Klasner Klasner and and others others (in (inpress) press) also also C-12 �presented evidence to show show that Archean crust is locally involved in the overthrust overthrust event. event. hole about about six six kilometers kilometers east east A drill hole of Canyon Falls in in the the northern northern complex complex (Fig. 3) penetrzted of Canyon (Fig. penetrated 3) underlying sheared gneiss and underlying sheared slate slate and and quartzite, quartzitef all of which which have low dipping foliation. The slate have low dipping foliation. The slate and and quarzite quarzite are are interpreted interpreted to to be be Early Early Proterozoic Proterozoic in in age. age. Similar Similar carbonaceous carbonaceous Taylor Mine and quartzite slate occurs at Taylor quartzite at at nearby nearby Canyon Canyon Falls. Falls. These These relationships suggest that that Archean gneiss gneiss was was thrust thrust over over relationships suggest the the Early Early Proterozoic Proterozoic slate. slate. Earlier nearer to Earlier studies studies in in both both Michigan Michigan and and Wisconsin, Wisconsin, nearer to zonef support support the the idea idea of of overthrusting overthrusting on on the the the Niagara fault fault zone, continental margin. Bayley and James and others continental margin. and others others (1966), (1966)f James others foliations (1961)f and Bayley (1959) (1959) mapped local local subhorizontal subhorizontal foliations (1961), Michigamme Formation, the Michigamme in the Formationf especially especially in in the the region region between in stops Fault. Ueng stops 99 and and 13 13 (Fig. (Fig. 3) just north of the Niagara Niagara Fault. Ueng and others (1984) (1984) attributed this this foliation foliation to to vertical vertical uplift uplift of of Archean However, we attribute attribute the Archean basement. basement. Howeverf we the subhorizontal subhorizontal foliation foliation to thrust thrust faulting, faultingf as as discussed discussed in in some some detail detail below. below. the continent-arc Finally, thrusting resulting Finallyf thrusting resulting from from the continent-arc fault. has also affected rocks collision rocks south south of the the Niagara Niagarz fault. collision has Sims and others From From geologic geologic mapping mapping and and geochemical geochemical evidence, evidence, Sins others (in (in press) have concluded that chemically chemically dissimilar dissimilar rocks rocks in in the the juxtaposed by Dunbar area (Sims (Sins and others, othersf 1985) 1985) have have been juxtaposed Dunbar area thrust faulting faultinq and and related related deformation; deformation; and this interpretation interpretation accords accords with an earlier earlier interpretation interpretation of Klasner and Osterfeld Osterfeld dome modelling that the Dunbar is from gravity from gravity modelling that the Dunbar dome is (1984) (1984) the a consequence of thrusting along allochthonous, either as allochthonousf either as consequence thrusting along the south—dipping Niagara fault south-dipping fault or a subsidiary subsidiary fault. fault. OVERTHRUSTING ALONG THE EVIDENCE FOR OVERTHRUSTING THE STRUCTURAL STRUCTUXAL TRAVERSE TRAVEXSE Geologic mapping detailed structural Geologic napping and detailed structural observations observations at at demonstrate several field localities localities in in the the study study area area demonstrate several selected field moderate-scale thrust thrust faults faults and small to the existence of small to moderate-scale the existence of locally related recumbent recumbent folds. folds. These These features features are are particularly particularly well well exposed at Little Mountain (field (field stop 2) near the northern foliation and and related related the traverse, traversef and subhorizontal subhorizontal foliation end of the end overturned overturned to recumbent recumbent folds folds are are present present at at several several localities, localitiesf especially, as especiallyf as mentioned mentioned above, abovef at Falls River (field (field stop stop 1), lIf 12, and in the broad area area encompassed encompassed by by stops stops 9, g f lZf and 13 13 (see (see and thrusts aad and these observationsf observations, larger—scale thrusts From these From lar9er-scale below) below). possibly can possibly nappes nappes can be inferred inferred where where permissive permissive structural structural features observed in mzpped features are observed in the the rocks rocks and/or where where previously previously mapped faults are better better interpreted interpreted as as thrusts. thrusts. . Proterozoic deformation in To illustrate illustrate the style of Early Pr~terozoic in in northern Michiganf we have compiled compiled the the geologic geologic map ma? shown shown in northern Michigan, sections Figure 3 and Figure and. have constructed c~nstructedtwo two interpretive interpretive cross cross sections 3 on Figure and The thrust system depicted (Figs. 6, (Figs. 6: and 8). The systen depicted on Fiqure 33 8). displays an overall northward sense Zisplays an overall northward sense of of structural structural vergence. ver9er~ce. C-13 �A Folio Criol 2 Lulls MOOOIOIA Cr1811 PlombogO 3 Conon Foils s. HEAN BASEMENT N16E I 4 I 6 III II I I .101. . P.. I. $• 6 7 1 '1 '11 II &. t)ii 11 7I JLt Fold 008$ S 'U.. IA A' SLCTIOO OlIN S. of the profile between stops are shown by arrows at top of figure. S1,ocm,,oc. 00,0,60 iTc toc.Iofl000 IN 0010 CoOls 100(06 IlflCII005 1.00106 (So) 0111$ OTIflh500PIIIC Smucamot 00IIOTOTI005 Ill I $hl.Sl80 b.ddhlq Foliolioul S So BiddIng Note field stop localities. Structural profile A--At. FIGURE 6. stereoplots Lower hemisphere location. for See Figure 3 foliation (Si), ard fold illiitrate orientation of bedding (SO), Directions of each segment axs (black dots) along the traverse. 2. Toylor Mill. '5. LI 2- I �The style style of of deformation deformation in in the the Michigarnme Kichigamme basin basin is is The Structural (Fig. 6). A—A' illustrate6 on on section ssction A-A' (Fig. 6 ) . Structural data 6ata in in illustrated primarily the the upper u 2 p r slate slate member member of of the the Michigainme Xichigznine Formation Forination primarily along along this this profile profile suggests suggests that that the the Early Early Proterozoic Proteroz~icrocks rocks were were of ~ r i 6eform~d as as part p~rt of an an irnbricate iribricate thrust thrust system. systan. As As shown shown on deformed not Figure 6, 6, there there does d~es not seem ssem to to be be much much involvement involvement of of the the Figure Archean rocks rocks in in the the thrusting. thrusting. Structural Structural relationships relationships at at Archean Plumb.go Creek, and Canyon Falls (Fig. Taylor Mine, Ninef Plumb?-goCreekf and Canyon Falls (Fig. 3), 3If however, however, Taylor was some some involvement involverent of of the the basement b~sernsntin in the the indicate that that there there was indicate lies quartzite flat-lying Falls Canyon thrusting. At Canyon Falls flzt-lying quartzite lies At thrusting. on Archean Archean basement basement and and has has only only minor minor evidence evisence of of uriconformably on unconformably km to to Yet at at Taylor Taylor Mine, :4ine, about about 55 km Early Proterozoic Proterozoic deformation. deformation. Yet Early the north, northf Early Early Proterozoic Proterozoic slates slates are are overturned overturned toward towarc? the the the and have have steep steep south south dipping dipping foliation foliation as as shown shown in in Figure Ficpre north and north penetratively At Plumbago Creek, 1.6 km south of Taylor Mine, 7. At Plumbago Creekf 1.6 km south of Taylor Xinet penstratively 7. deformed deforned Early Esrly Proterozoic Proterozoic phyllite phyllite has has aa south-dipping south-dipping foliation foliation data, These structural projects beneath Archean gneiss. which projects beneath Archean gneiss. Thess structural datz, which when plotted plotted on on the the elevation elevation profile, profile, as as shown shown on on Figure Figure 6, 6, when indicate that that there thsre was was some sone involvement involvement of of basement bassinent rocks rocks in in indicate Because 2ecause of of Early Proterozoic Proterozoic overthrusting ovsrthr~stinqin in this this region. rsgion. Early difficult will difficult access, zccessf outcrops outcrops at at Plumbago ? L i ~ m b ~Creek Creek g~ will not not he he visited. vtsited. Taylor Mine Mine? is is an an alternate alternate stop. stop. Taylor SOUTH SOUTH Field stop stop area area Field KORTH NORTH 200 feet o i • SCLE :j N\ I Keweenawan Keweenawan diabase dike diabase ---- -- - dike -..- Folded Folded sandy sandy N Cherty iron iron Cherty formation fortnatiofl 't laver layer Slack Black slate slate with with Si Sl foliation foliation Orientation Orientation of cleavage cleavage of -Y Core core hole hole showing ~howinq core core dips dips Struck~ral cross cross section section in in the the Taylor 76i~e s r s a Structural Ta-lasnd 's t y- l earea r Jj1fl on Fig. 3) showing Sl fcliatici~ c,f on Fia 3) dezornation. DiamonS drill-hole data are frmi Ford ~ o t o r C ~ m p any deformat ion D iamond dri11ho1e data a re f ram Fod tar ( A f h r Klssrxr, 1 9 7 2 1 . FIGTJRE FIGURE 7. 7. (location (locaLlon - 23 2a . C- 15 �_____________ The main main feature feature illustrated illustrated on on section sectionB-B' B - B t (Fig. (Fig. 8) 8 ) is Ts The that the the large large apparent a2parent thickness thickness of of Hemlock Hemlock volcanic volcanic rocks rocks (see (se that 1980) along along the the west west side si6e of of the the Amasa A m s a uplift uplift may, msyr in in Fooser 1980) Foose, partr be be accounted accomted for for by by tectonic tectonic stacking. stackinq. Structural Structural data dsta at st part, alternate field field stops stops 7a 7a and and 7h 7b lend lend support support for for the the idea idea of of alternate At stop 7a mafic volcar..c tectonic thickening of the Hemlock. At stop 7a mafic volcariic Hemlock. tectonic thickening of the rocks are are intensely intsnsely deformed defornsd and and have have aa prominent prominent foliation foliation that that rocks Stretch 3. Figure on shown 3. Stretch is oriented nortkdestward, as shown on Figure as northwestward, oriented is lineations on on the the foliation foliation surfaces surfaces plunge plunge steeply steeply toward toward the the lineations slet west. At At station station 7b 7b axes axes of of small small drag drag folds folds in in siliceous siliceoas slat.? west. plunqe gently gently northwestward northwestward and and their their Z-shape 2-shape symmetry s-pmetryindicates indicates plunge northeastward sense sense of of vergence. vergence. Thinly Thinly layered layere6 tuff tuff at at aa northeastward oriented is a1Qrnate 8 has a penetrative foliation that is orisnted 8 has a penetrative foliation that altrnate stop N55 W, L?, 60 60 SW, S7J, and and other other outcrops outcrops in in the the region region have have similarly similarly N55 oriented foliations. foliations. Taken Taken together, together, these these and and other other outcrops outcrops on on oriented the west west side side of of the the Amasa Amasa uplift uplift indicate indicate that that tectonic tectonic stacking stackiii~ the could have have significantly significantly thickened thickened the the Hemlock Hemlock volcanic volcanic pile. pile. could is not resolved The nature nature of of the the stacking, stacking, however, however, is not resolved at at this this The B-8' (Fig. (Fig. 8) 8 ) suggests suggests that that it it is is an an imbricate imbricate time. Profile Profile B-B' time. may represent thrust fan. fan. Alternately, Alternatsly?the the Arnasa Amzsa uplift zay represent aa domed Zoined thrust Either style of deformation would account fr the far ths Zuplex system. Either style of defornation w o ~ l Z zccocnt duplex system. apparent. the and rocks volcanic s ~ ? z r e~*. thick szction of Hemlock volcanic rocks sn2. the Hemlock of section thick structural discordance discordance between between the the Michigamme NichigxixneFormation Foriaationand an3 the the structural (1980). :Iemlock volcanic volcanic pile pile as as pointed pointed out out by by Foose Foose (1980). Hemlock ....N2OE B J\ 2000 2000 --e 0 I'= xx xxx xxx 0 I000 1000 x 0o O- IIH.m1o L flZ— Rocks Rocks ofof - Baraga Bamga Group Group '—— Badwater Bodwatet Miiigamme Michigomme I L ARCHEAN ARCHEAN Randvilla Rondvlile 0and Rocks ofof Menominee ~enominea Rocks 00 rOUOS Chocolay OCOI ØY GGroups 00 a * Drag Drag Fold FOI~ SmIles 5 miles y 55kilometers kilometers Basemeift Basement Gneiss Gneiss \ Fault FOUI~ Structural profile B—B'. Note drag fold from stop 7. Rou;hly 20 times vertical exageration. See Figure 3 for location. FIGURE 8. C-16 �In particular, particularr either either system system would would explain explain the the structural structural In discordance between between the the Hemlock Hemlock and and the the magnetically magnetically mapped mapped iron iron discordance fornation that that lies lies just just above above the the contact contact in in the the Michigamrne Michigamme formation Formation. We We interpret interpret the the Michigamme Michigamme Formation Formation to to be be separated separated Formation. from the the Hemlock Hemlock Formation Formation by by aa thrust thrustfault. fault. The The configuration configuration from of the the magnetically magnetically mapped mapped iron iron formation formation mimics m.imics the th2 of Inasmuch configuration of of the the thrust thrust fault. fault. Inasmuch as as the the western western edge edge configuration of the the Hemlock Hemlock volcanic volcanic pile pile is is covered, coveredr this this fault fault is is inferred inferred of and was was not not observed observed in in the the field. field. and The The rocks rocks that that lie lie in in the the region region between between the the Bush 8ush Lake Lake fault fault north-verging the 3) are part of 3) are part of the north-verging and the Niagara fault (Fig. Niagara fault (Fig. and the thrust system system described described above, above, but but the the exact exact nature nature of of the the thrust Maharidge's (1986) thrusting in this region remains problematic. Maharidge's (1986) thrusting in this region remains problematic. interpretation interpretation that that the the Feich Felch trough trough is is part part of of aa nappe nappe structure structure also, it cannot be discounted at has not been proven, butr alsor it cannot be discounted at this this has not been proven, but, Early and Archean show that both time. Our recent recent studies studies show that both Archean and Early Our time. Proterozoic rocks rocks possess possess aa prominent prominent low-dipping low-dipping foliation foliation that that Proterozoic is superimposed superimposed upon upon aa steeply-dipping steeply-dipping foliation foliation in in the the Archean Archean is rocks (see (see field field stops stops 10 10 and and 11). 11). Also, Alsor in in this this region region there there is is rocks firm evidence evidence for for southwest southwest verging vercjing thrusting thrusting in in rocks rocks of of both both firm the Feich Felch and and Calumet Calumet troughs. troughs. We We tentatively tentatively interpret interpret the the the south-verging structure structure as as being beincj formed formed due due to to south—directed south-Zirectsd south-verging backthrusting caused by by ramping ramping of of the the north-verging north-verging thrust thrust caused backthrusting faults. Best evidence evidence for for this this southward southward vergence vergence is is found found at at Best faults. stops 9, g r 11, llr 12, 12r and and 13. 13. We We will will visit visit stops stops 9, g r 11, llfand and 12 12 but but stops we will will most most likely likely not not visit visit stop stop 13, 13ran an alternate alternate stop, stopr because becauss we of difficult difficult access. access. of composite section section (Fig. (Fig. 9) 9 ) along along the the length length of of the the AA composite structural traverse traverse summarizes summarizes our our current, currentr and and as as yet, yetr structural tentativer interpretation interpretation of of the the style style of of deformation deformation that that tentative, This interpretation is consistent occured in northern Kichigan. This interpretation is consistent in northern Michigan. occured with aa fore1.nd forelan6 thrust thrust system system as as depicted Zepicted in in the the model zodel of of an an with The idealized orogen by Hatcher and Williams (1986). idealized orogen by Hatcher and Williams (1986). The idealized idealized orogen consists consists of of aa foreland foreland overthrust overthrust belt, beltr an an overthrust overthrust orogen metamorphic core complex that may include ophiolites metamorphic core complex that may include ophiolites and and thrusted thrusted crystalline basement basercient rocks, rocksr and and an an accreted accreted plutonic/volcanic plutonic/volcanic crystalline terrane. Part Part A-A' A-A' of of the the composite composite section section marks marks the the foreland foreland terrane. tectonism thin-skinned overthrust belt belt which which involves involves thin-skinned tectonisn with with overthrust relatively of basement basement rocks rocks in in the the thrusting thrusting relatively little little involvement involvement of (note these these comments comments apply apply to to the the area area close close to to this this traverse, traverse, (note Early and the the amount anount of of basement basement involvement involvenent in in Early Proterozoic Proterozoic and overthr~sting may may change change along along the the strike strike of of the the Penokean Penokesn overthrusting orogen). Telescoped Telescoped and and foreshortened foreshortened Early Early Proterozoic Proterozoic strata strata orogen). are ars separated separated from from basement basement rocks rocks along along aa basal basal detachment detachment fault. fault. (1987) Nd isotope isotope studies studies by by Barovich Barovich and and others, others, (1937) indicate indicats that that Nd the southern southern half half of of this this terrane terrane was was derived derived from from the the Wisconsin Wisconsin the magmatic terrane terrane to to the the south, southr thus thus supporting supp~rtiricj the the idea idea of of magmatic northward tectonic tectonic transport transport of of at at least least aa part part the the Michigamme Michigamme northward Formationr and and explaining explaining the the presence presence of of deep deep water xater turhidite turbidite Formation, deposits on on the the continental continental margin. margin. deposits which Section B-B' B-B' marks marks the the Amasa Amasa uplift uplift area, arear which is is Section defamation between thick-skinned basement-involved transitional between thick-skinned basement-invalved defamation transitional �N S MARGINAL MARGINAL BASEMENT BASEMENT ARCH ARCH A AA I Michlgamme Basin Basin Michigomme Foreland Thrust Thrust Foreland I 'S Baraga Baraga Group Group Rocks x X . — — XX - Felch Felch - Calumet Calumet Imbricate Imbricate Thrust Thrust Belt Belt ——— ——— GL I Uplift Uplift Amaso Amasa — — X X x' ARCHEAN Hemlock Hemlock ~ e n o m inee nee Menomi VolcafliCS volcanics Chocolav && Chocolav Group Group ' -.- —GL X \- & 0 a 10 Ground Ground level level - Bush Bush Lake Lake Fault Fault - NF -- i.l10 Miles a Fault Fault - GL GL 81 BL o Wisconsin Wisconsin Accreted Accreted Magmatic Magmatic Arc Arc XXX XXX Accreted Accreted Volcanic Volcanic Plutonic && Plutonic Rocks Rocks Rocks ~ocks i' a' B' c LIB Niag4ra Niagara Fault Fault Km Composite st.ructuralprof profile C o m p o s i t e st.ruct.ura~1 i 1 e 1ong lt3ng line 1ineconnecting connecting to C' C ' (in c,n Figure? 3 . See See text tsxt for for discussion. dj.scussion. Figure 3. to FIGIJRE 9. 9. FIGUflE <: A X �to the the south south near near the thecontinental continentalmargin, marginf and and the the thin-skinned thin-skinned to tectonism tectonism of of the the foreland foreland thrust thrust belt belt to to the the north. north. Tentatively, Tentatively, we consider consider the the Amasa Amasa uplift uplift as as having having behaved behaved as as aa stable stableblock block we consisting of of an an Archean Archean core core and and aa large large volcanic volcanic pile pile over over consisting which less less competent competentrocks rocksof of the thecontinental continentalmargin marginwere werethrust. thrust. which The thrust thrust system system refracted refracted upward upward from from the theArchean Archeanbasement basement on on The the south south so so that that it it is is largly largly confined confined to to supracrustal supracrustal Early Early the Proterozoic strata strata north north of ofthe theuplift. uplift. Proterozoic Part Part C-C' C-C' on on Figure Figure 99 marks marks the the crystalline crystalline metamorphic metamorphic core core complex sytem sytem of of Hatcher Hatcher and and Williams Williams(1986). (1986). It It consists consistsof of an an complex imbricate, piggy piggy back-type back-type of of crystalline crystalline thrust thrust sheet sheetwhich which is is imbricate, bounded on on the the south south by by the the Niagara Niagara fault faultzone zoneand and on on the the north north bounded by the the Bush Bush Lake Lake Fault Fault(Fig. (Fig. 3). 3). The The Bush Bush Lake Lake Fault Fault appears appears to to by system. It have been a key feature in evolution of the thrust system. It been a key feature in evolution of the thrust have trend which between structures on the north marks a boundary between structures on the north which trend boundary marks a northwest northwest and and those those on on the the south south which which trend trend east-west east-west (see (see Fig. Fig. and 1984 (Attoh and Vander Muelen, isograds 3). Metamorphic isograds (Attoh and Vander Muelenr 1984 and Metamorphic 3). is south side the that indicate Klasner and Attoh, 1986) indicate that the south side is Klasner and Attoh, 1986) which along fault to be a major upthrown. We We interpret interpret it it to be a major fsult along which upthrown. crystalline rocks rocks of of the the continental continental margin margin were were thrust thrust upward upward crystalline and over over the the Amasa Amasa uplift. uplift. and Rocks of of the the Wisconsin Wisconsin magmatic magmatic terrane, terrane, south south of of the the Rocks Niagara Niagara fault fault zone, zone, have have been been accreted accreted to to the the continental continentalmargin. margin. macjmatic Nd Nd isotope isotope data data indicate indicate that that the the volcanic volcanic rocks rocks of of the the magmatic terrane represent represent new new Early Early Proterozoic Proterozoic crustal crustal material material terrane (Barovichand and others, others, 1987). 1987). Klasner Klasner and and Osterfeld Osterfeld (1984) (1984) and and (Barovich Sims and and others others (1984b, (1904b, 1985) 1985) suggested suggested that that the the magmatic magmatic rocks rocks Sims of northeast northeast Wisconsin Wisconsin are, aref in in part, partf allochthonous. allochthonous. Klasner Klasner and and of others (1985, (1985, page page 284) 284) and and Klasner Klasner and and Attoh Attoh (1986) (1986) inferred inferred others that the the actual actual edge edge of of the the continental continental margin margin is is cryptic, cryptic, and and that p~ssibly buried buried beneath beneath the the allochthonous allochthonous magmatic magmatic terrane terrane in in possibly terrane is northern Wisconsin. Wisconsin. The The Wisconsin Wisconsin magrnatic magmatic terrane is equivalent equivalent northern to to the the accreted accreted volcanic/plutonic volcanic/plutonic terrane terrane of of Hatcher Hatcher and and Williams William Schulz crust. oceanic contain slivers of (1986)r which can contain slivsrs of oceanic crust. Schulz which can (1986), northeast in assemblage an ophiolite (1987b) has identified an ophiolite assemblage in northeast identified has (1987b) Xisconsin. wisconsin. The geology geology of of the the Early Early Proterozoic Proterozoic continental continental margin margin The consistent is Michigan younqer assemblage of of northern northern Michigan is consistent with with younger assemblage Atlantic-type (passive) (passive) margins margins (Nelson (Nelsonand and others, others, 1982) 1982) as as Atlantic-type represented in in the the Ouachitas, Ouachitas, New New England England Appalachians, Appalachiansr Tibetan Tibetan represented They have Hiinalayas, and and Oman Oman Mountains. Nountains. They have in in common common an an inboard, inboard, Himalayas, allochthonous foreland foreland thrust thrust belt, belt, and and an an outboard outboard imbricate imbricate allochthonous thrust thrust system system involving involving crystalline crystalline basement basement rocks. rocks. AGE AGE OF OF THRUSTING THRUSTIEG AA minimum minimum age age for for the the overthrusting overthrusting is is 1824 1824 ±+ 2.6 2.6 Ma, Ma, which which granite pluton is aa U—Pb U-Pb zircon zircon intercept intercept age age on on an an undeformed undeformed-granite pluton is that intrudes intrudes Badwater Badwater Greenstone Greenstone at at locality locality AA on on Figure Figure 55 (Z. (Z. that E. Peterman, Peterman, written written communication, communication, 1987). 1987). AA possible possible maximun imximum E. 17 Ma; Ma; two two splits splits of of apatite apatite from from iron iron formation formation age is is 1929 1929 ++ 17 age uriderlying the tEe Michigamme Hichigainme Formation Formation in in the the Earaga Earaga basin basin yield yield underlying �lead-lead 17 Ma lead-lead ages ages of of 1929 1929 ±+ 17 Ma CR. (R. E. E. Zartman, Zartman, written written communication, communication, 1987). 1987). The het thrusting thrusting occured occured within within the the interval interval 1930 1930 to to 1824 1824 Ma. Ma. Data from from northeastern northeastern Wisconsin, Wisconsin, within within the the Data Wisconsin Wisconsin magmatic magmatic terrane, terrane, is is consistent consistent with these these constraints constraints and further further refine refine the the age age limits. limits. dome, deformed In the Dunbar Dunbar dome, granitoid granitoid rocks rocks have have U-Pb U-Pb zircon zircon ages ages of of ca ca 1860 1860 Ma, Ma, whereas whereas an an undeformed, post-tectonic granite granite has has an an age age of of 1835 1835 ±+ 66 Ma (Sims (Sins undeformed, and and others, others, 1985). 1985). These data data suggest suggest collision collision along along the the These Niagara fault fault zone zone occured occured about about 1850 1850 Ma. Ma. Probably Probably the the thrusting thrusting Niagara in in the the continental continental margin margin assemblage assemblage occurred occurred approximately approximately contemporaneous with or or slightly slightly later later than than collision. collision. contemporaneous FIELD FIELD STOPS STOPS AND AND ROAD ROAD LOG LOG The The structural structural traverse traverse across across northern northern Michigan Michigan starts starts in in L'Anse, L'Anse, Michigan and and ends ends near near Florence Florence , Wisconsin. Wisconsin. Eighteen Eighteen stops stops are are shown shown on on Figure Figure 33 but, but, because because of limited limited time time and and difficult difficult access access to to several several of the the localities, localities, only only eight eight to to ten ten of them Localities them will will be be visited. visited. Localities 2b, 2b, 7a, 7a, and and 7b, 7b, will will not not be be visited visited and and localities localities 2a, 2a, 8, 8, and 13 13 are are alternate alternate stops, stops, which which , will be be visited visited only only if if time time permits. permits. Road Road logs logs are are not not given given for for the the alternate alternate stops, stops, but but their their location location is is given given by by section, section, township, township, and and range. range. ROAD LOG Follow Follow highway U. S. S. 41 41 west west from from Marquette Marquette to to L'Anse. L'Anse. ROAD LOG Proceed Proceed west west through through L'Anse L'Anse to to bridge bridge over over Falls Falls River River on on U. U. S. S. 41. Park 41. Park in in the the pulloff pulloff area area on on the the north north side side of of the the highway highway between between the the RR RR tracks tracks and and the the bridge. bridge. Numerous STOP STOP 1-FALLS 1-FALLS RIVER. RIVER. Numerous outcrops outcrops are are present present along along Falls Falls River Structures River on on both both sides sides of of the the highway. highway. Structures consist consist of of northward—verging, small-scale1 folds with northward-verging, small-scale, recumbent recumbent folds with subhorizontal subhorizontal axial-plane axial-plane foliation foliation indicating indicating nappe—thrust nappe-thrust style style of deformation deformation in in this this area. area. ROAD ROAD LOG. LOG. From From the the parking parking lot lot area area for for stop stop 1, 1, follow follow U. U. S. S. 41 41 east east for for 2.6 2.6 miles. miles. Turn Turn west west on on Golf Golf Course Course Road Road and and drive drive 1.75 1.75 miles Follow miles to to the the cul-de-sac cul-de-sac at at the the end end of of the the road. road. Follow footpath footpath to It to Little Little Mountain. Mountain. It is is about about a 15 15 minute minute walk walk to to the the too to? of of the the mountain; mountain; be sure sure to to follow follow left left forks forks of of the the main, main, well well worn worn path. Path path. Path extends extends around around the the southwest southwest corner corner of of the the mountain mountain where where it it turns turns sharply sharply toward toward the the east east up up the the south south flank flank of of the the mountain. Follow mountain. Follow path path to to the the highest highest point point on on the the mountain. mountain. From From this this vantage vantage you you can can see see the the Keweenaw Keweenaw Peninsula Peninsula of of the the Midcontinent Midcontinent Rift Rift System System to to the the north-northwest north-northwest and and the the Archean Archean terrane terrane of of the the northern northern complex complex (Fig. (Fig. 3) 3) to to the the east-southeast. east-southeast. The of the the The low low lying lying area area to to the the south south is is underlain underlain by by rocks rocks of Michigamrne Michigamme basin. basin. Outcrops STOP STOP 2-LITTLE 2-LITTLE MOUNTAIN. MOUNTAIN. Outcrops at at the the highest highest point point on on Little Little Mountain Mountain consist consist of of an an unfoliated unfoliated (ca (ca 1.1 1.1 Ga) Ga) Keweenawan Keweenawan diabase diabase Grading dike dike and and graded graded beds beds of of metagraywacke. metagraywacke. Grading is is expr2ssed expressed by by presence presence of of foliation foliation in in the the finer finer grained grained bed bed tops. tops. The The beds beds face face toward toward the north north and and dip dip steeply steeply south, south, indicating indicating that that they they are are overturned overturned toward toward the the north. north. �4., LITTLE MOUNTAIN, MOUNTAIN. BARAGA BARAGA COUNTY, COUNTY, Mt. MI. LITTLE corner of FIGURE 10 10. Field Field sketch sketch mao map of of the the northeast northeast corner of FIGURE for thrust faulting. Mountain Mountain showing showing evidence evidence for thrust faulting. Little Littls sketch map, map, shows shows the the nature nature of of structural .?t~ii~tar5l Figure 10, 10, aa sketch Figure Here, kcre, deformation deformation near near the the northeast northeast corner corner of Little Little Mourt1n. Mountsin. overturned graded beds of inetagraywacke strike east--west sixilar overturned graded beds of netagr&ywacke strike east--west similar and dip dip steeply steeply south, south, as as does does Si 31 foliation. foliation. In In several several places places and bedding has has aa convoluted convoluted appearance, appearance, indicative indicative of of irtene intense bedding zones deformation. Deformed zones of of concretions concretions crudely crudely define define Deformed deformation. bedding. The long long axes axes of of the the concretions ~oncretio~isplunge plunge steeply steeply The bedding. southwest, indicating indicating extension extension in in this this direction. direction. old Fold ages axes southwest, easternrsz the On a bench at clung& gently aently towardthe toward the west. west. O n a bench at the easternrms:. plunge W.. oriented edge of of the thft mountain mountain similar similar graded graded beds beds are are oriented N(0 NEC*X: edge I T C- 21 �5 7 570NW, Looking and ~ are are ~ upright. upright. ~ Looking west west from from the the bench, bench, the the and intensely intensely deformed deformed beds beds of of an an overlying overlying thrust thrust can can be be seen seen in in the the Tectonic three-meter-high cliff. cliff. Tectonic striations striations can can be be found found on on the the three-meter-high underside of narrow narrow overhangs overhangs on on the the cliff cliff face face aa few few meters meters to to underside The the north north and and west. west. The striations, striations, along along with with northward northward the overturning of of bedding bedding indicate indicate that that the the hanging hanging wall wall of of the the overturning The thrust moved moved northeastward. northeastward. The total total thickness thickness of of the the thrust thrust thrust fault fault zone zone at this locality is aameter meter or or less. less. The The thrust thrust fault fault About can be traced traced down down the the east east flank flank of of Little Little Mountain. Mountain. About 100 100 can meters south south and and two two benches benches down down the the flank flank of of the the mountain mountain aa meters glacially-gouged, glacially-gouged, upright upright bed bed of of metagraywacke metagraywacke which which lies lies beneath beneath It the fault fault observed observed above above is is well well exposed. exposed. It too too has has deformed deformed the concretions concretions whose whose long long axes axes plunge plunge southwest. southwest. The The main main point point at at this this stop stop is is that that Little Little Mountain Mountain probably probably an an erosional erosional remnant remnant of of an an allochthonous allochthonous sheet sheet of of rocks rocks that that has been been thrust thrust northeastward northeastward as as part part of of an an imbricate imbricate thrust thrust has Further system. Further studies studies at at Little Little Mountain Mountain are are needed needed to to fully fully system. document the nature and style of deformation here. document the nature and style of deformation here. is is ROAD LOG LOG Return Return to to the the vehicle vehicle by by walking walking north north and and west west around around ROAD the north north side side of of Little Little Mountain Mountain to to the the intersection intersection of of the the the Turn path. Turn right right (east) (east) on on the the path and and return return to to Golf Golf Course Course path. Follow Road. Follow the the road road eastward eastward to to the the intersection intersection of of Golf Golf Road. Course Course Road Road and and and and U. U. 5. S. 41. 41. Turn Turn right richt (south) (south)on on U. U. S. S. 41. 41. Located ALTERNATE ALTERNATE STOP STOP 2a-TAYLOR 2a-TAYLOR MINE. MINE. Located in in the the NW NW 1/4 1/4 sec. sec. 9, 9, T49N, T49N, R33W, R33W, graphitic graphitic slate slate and and ironiron- formation formation of of the the Michigamme Michigamme Formation near near the the mine mine have have been been folded folded about about aa penetrative penetrative Formation axial-plane south-dipping, axial-plane foliation foliation (see (see Fig. Fig. 7). 7). Keels Keels of of south-dipping, rootless folds folds in in the the graphitic graphitic slate slate indicate indicate that that bedding bedding has has rootless been transposed transposed parallel parallel to to foliation, foliation, and and that that the the beds beds are are been overturned to the the north. north. An An unfoliated unfoliated Keweenawan Keweenawan diabase diabase dike dike overturned Style slate. the ironcuts the graphitic graphitic slate. Style of of folding folding in in the the iron— cuts formation can can be be seen seen in in aa roadcut roadcut about about 30 30 meters meters north north of of the the formation dike. dike. Similar steeply steeply south-dipping south-dipping foliation foliation occurs occurs in in Early Early Similar Proterozoic phyllite about about 22 km km to to the the south south at at Plumbago Plumbago Creek Creek Proterozoic (2b, Fig. 3). 3). The The phyllite phyllite is is exposed exposed in in aa creek creek bed bed at at the the base base (2b, by Archean underlain facing slope that is steep north of a steep north facing slope that is underlain by Archean a of gneiss. Thus, Thus, it it appears appears that that the the foliation foliation in in the the phyllite phyllite dips dips gneiss. beneath the gneiss, suggesting that the gneiss is thrust beneath the gneiss, suggesting that the gneiss is thrust over over the the phyllite. phyllite. ROAD LOG. LOG. From the the intersection intersection of Golf Golf Course Course Road Road and and U. U. S. S. 41 41 ROAD Between drive drive 7.6 7.6 mile mile south south on on U. U. S. S. 41 to Canyon Canyon Falls Falls Park. Park. Between Alberta U. S. S. 41 41 and and Canyon Canyon Falls Falls Park Park the the highway highway passes passes over over Alberta on on U. which is (Fig. 3) the northern northern complex complex (Fig. 3) which is an an the west west end end of the the Follow uplifted block block of of Archean Archean basement basement rock. rock. Follow the the nature nature path path from the parking parking lot lot at at Canyon Canyon Falls Falls Park Park westward westward for for about about 10 10 from the minutes minutes along along Sturgeon Sturgeon River River to to the the Falls. Falls. Proceed Proceed to to the the northnorthNo south oriented cliff cliff face face in in back back of of the the fence. fence. No need need to to walk walk up the the steps steps in in the the cliff cliff face face for the critical critical information information at at up this this stop stop is is visible visible in in the the cliff cliff face. face. �STOP 3-CANYON 3-CANYON FALLS. FALLS. At this this stop stop subhorizontal subhorizontal Early Early At STOP ripples prominent interference Proterozoic quartzite contains prominent interference ripples quartzite contains Proterozoic that appear appear to to be be unaffected unaffected by by Early Early Proterozoic Proterozoic deformation. deformation. •that Close examination examinationof of the thecliff cliffface, face, however, however, reveals reveals that that thin thin Close pelitic layers layers intercalated intercalated between between the the uartzite quartzitebeds bedshave have aa pelitic 27SW. SW. Also, Also, tectonic tectonic penetrative foliation foliation oriented oriented N85°W, N 8 9 W, 27 penetrative 20 striations on on the the quartzite quartzite beds beds are are oriented oriented '2 toward toward NlO°E. N10 E. striations Clearly the the quartzite quartzite has has been been transported transported some some unknown unknown distance distance Clearly northeastward (based (based on on the the north north sense senseof of vergence vergence found found in in northeastward less the by taken up was previous outcrops). Deformation was taken up by the less Deformation outcrops). previous shaly layers; layers;the the more more competent competent quartzite quartzite beds beds appear appear competent shaly competent to have have undergone undergone little, little, or or no, no, internal internal deformation, deformation, but but to detailed petrofabric petrofabric studies studies are are needed needed to to confirm confirmthis. this. detailed As shown shown on on Figure Figure6, 6, the the flat-lying flat-lying quartzite quartzite at at Canyon Canyon As Falls must must lie lie beneath beneath one one or or more more thrust thrust faults faults that that intensely intensely Falls deformed Early Early Proterozoic Proterozoic strata strata at at Taylor Taylor Mine Mine and and Plumbago Plumbaao deformed Creek. Also, Also, elevation elevationdata, data, together together with with structural structural data data at at Creek. these three three localities localitiesnecessitate necessitatelocal local involvement involvementof of Archean Archean these basement rocks rocks in in the the overthrusting. overthrusting. basement Return to to Canyon Canyon Falls FallsPark Parkparking parkinglot. lot. Drive Drive south south on on ROAD LOG LOG Return ROAD U. S. U. S. 41 for 3.0 miles to the intersection with highway U. S. 41 for 3.0 miles to the intersection with highway S. U. 141/28. Turn right right (west) (west)on on highway highway 141/28 141/28 and and follow follow it it for for Turn 141/28. 4.1 miles. miles. Turn south southon on U. U. S. S. 141 141 and and drive drive 4.1 4.1 miles miles to to atop Turn 4.1 4. 4. Numerous outcrops outcrops of of the the upper upper slate slats member member of of the the Numerous 141 south of Covington. S. U. S. 141 south of Covington. Michiganune Formation occur along Formation occur along U. Michigamxne field We have have selected selectedaa few fewof of the the more more informative informative outcrops outcropsas as field We 5 , 6, 6,and and 77on on Figure Figure6). 6). stops (4, (4,5, stops STOP 4-U. 4-U. S. S. highway highway 141. 141. Located Located on on the the east east side side of of the the STOP stop consists of thick beds of graywacke that this stop consists of thick beds of graywacke that are highway, this are highway, graded and and have have flame flame structures structures at at some some bed bed contacts. contacts. graded across (SO)is is Penetrative foliation0refracts foliationrefrac~s across bedding. bedding. Bedding Bedding (SO) Penetrative SW. SW, and cleavage H, 20° 20 SW, cleavage (Si) (Sl)N75°W, N~!?W, 4cf 4CfSH. generally oriented oriented N62 N62 W, generally Lineations formed formed by by the the intersection intersection of of cleavage cleavage and and bedding bedding Lineations Numerous Numerous concretions concretions form form strain strain plunge 140 14 toward toward S83°W. S83 W. plunge ellipses with with the the axes axes of of maximum maximum elongation elongation that that plunge plunge ellipses generally 540 54O toward toward S36°E. ~36¡~ generally At this this outcrop outcrop bedding bedding (SO) (SO)dips dips only only moderately moderately toward toward the the At as bedding marked variations in the orientation of in the orientation of bedding as south, but marked variations but south, one as outcrops can be seen in other well as cleavage (Sl) can be seen in other outcrops as one cleavage (Si) as well U. S. S. highway highway 141. 141. Ne We mainly mainly used used these these proceeds south southalong alongU. proceeds variations in in structure structure to to locate locate the the position position of of thrust thrust faults faults variations shown on on Figure Figure6. 6. shown ROAD LOG. LOG. ROAD Proceed Proceed south south on on U. U. S. S. 141 141for for2.4 2.4 miles. miles. 5-U. S. S. 141. 141. AA long long outcrop outcrop of of thick-bedded thick-bedded graywacke graywacke is is STOP 5-U. STOP beds Graded present on on the the west west side side of of the the highway. highway. Graded beds strike. strike. present and are are nearly nearly vertical; vertical; foliation foliztion is is subparallel sabparallel rouqhly N67oW, N67oM, and roughly C- 23 �•to to bedding. bedding. At At the the north north end end of of the the outcrop outcrop bedding beddin5 is is overturned overturned toward toward the the north. north. ROAD LOG ROAD LOG clearly clearly Proceed south south on on U. U. S. S. 141 141 for for 3.4 3.4 miles. miles. Proceed STOP STOP 6-TRACY 6-TRACY CREEK. CREEK. Examine outcrops outcrops on on both both sides sides of of the the Examine highway highway which which consist consist of of graded graded graywacke graywacke beds. beds. Folds Folds in in be-Jding be3ding (SO) have have axes axes that that plunge plunge gently gently toward toward the the 0northwest. northwest. (SO) Refracted, N86 E, E, 85CSE. 8 9 SE. Refracted, penetrative penetrative Si Sl foliation foliation is is oriented oriented N86 Concretions tend tend to to lie lie in in the the bedding bedding plane. plane. Some concretions, concretions, Concretions Some however, however, have have been been partly transposed transposed so so that that their their long long axes axes are are partly partly parallel parallel to to bedding and and partly partly parallel parallel to to foliation. foliation. Many Many have have been been deformed deformed so so that that their their long long axes axes are are completely completely parallel to This parallel to foliation. foliation. This outcrop outcrop shows shows the the style style of of deformation deformation in in the the slates slates and and metagraywackes metagraywackes of of the the Michigarnne Michigamne Formation. S. 141 141 traverse traverse Formation. Some Some outcrops outcrops on on this this part part of of the the U. S. have 6. A completely completely have two two foliations foliations as as shown shown on on Figure Figure 6. A different, different, north north dipping dipping foliation foliation will will be be seen seen at at the the next next stop. stop. ROAD ROAD LOG. LOG. Proceed south south on on U. U. S. S. 141 141 for for 1.0 1.0 mile. mile. Proceed STOP 7-U. S. S. 141. 141. Most features features in in this this long long outcrop outcrop of of black black STOP 7-U. Most slate slats and and metagraywacke metagraywacke on on the the east east side side of of the the highway highway indicate indicate aa. southward southward sense sense of of thrusting, thrusting, completely completely opposite opposite to t.o that that observed Figure sketch observed at at all all previous previous stops. stops. Figure 11 11 is is aa sketch illustrating illustrating the the types types of of features features observed observed along along the the length length of of the and 9. 9. At point p i n t 55 the outcrop. outcrop. Most significant significant are are points points 55 and Most At small small drag drag folds folds indicate indicate aa southward southward sense sense of of vergence. veqencs. This This southward southward sense sense ofo f -vergence vergence is is confirmed confirmed by by several several other other features features in in this this outcrop outcrop and and indicates indicates backthrusting backthrusting at at this this location. meter-wide zone zone of of siginoidal sigmoidal quartz veins at point point 99 location. AA meter-wide veins at is is one one of of the the more more striking striking features features in in this this outcrop. outcrop. The The sigrnoidal sigrrioidal shape shape of of the the quartz quartz veins veins suggests suggests down-to-the--north down-to-the-north normal normal faulting, faulting, opposite opposite the the sense sense of of movement movement observed observed at at point point 5. The 5. The structure structure at at point point 99 may may be be aa late late feature feature related related to to post-thrusting post-thrusting uplift upliftof ofthe theAniasa Amasa dome. dome. Such Such uplift uplift would would cause cause rotation rotation of of pre-existing pre-existing features, features, but but the the amount amount of of rotation rotation is is not not known. known. We We interpret interpret the the backthrusting backthrusting at at this this locality locality to to be be caused caused abrupt abrupt change change in in dip dip of of the the thrust thrust sytem sytem as as it it ramps ramps off off the the north north edge edge of of the the Amasa Amasa uplift uplift (see (seeFig. Fi9. 6). 6). by by an an ROAD ROAD LOG. LOG. Proceed south south on on U. U. S. S. 141 141 for for aa distance distance of of 23 23 miles miles Proceed S. 141 141 with with U. U. S. S. highway highway 22 at at the the west west end end to the the junction junction of of U. S. to of of Crystal Crystal Falls, Falls, Michigan. Michigan. On On this this segment seqmit of of the the traverse, traverse, the the highway highway passes passes over overthe thewest westflank flankofofthe thaAinasa Amasa uplift. Turn left (east) U. S. S. 141/2 141/2 and and follow follow it it to to the the center center of of Crystal Crystal (east) on on U. Falls, Falls, where where the the highway highway intersects intersects MM 69. 69. This is is at at the the This intersection intersection of of Superior Superior and and Fifth Fifth street, street, near near the the U. 3. S. S . Post Post Office To proceed proceed to alternate alternate stop stos 8, turn Office in in Crystal Crystal Falls. To Falls. to turn - 8, east to stop stop 99 proceed proceed south southon n U. east on on MM 69. 69. To To continue continue on to TJ. . S. uplift. Turn left 2/141. 2/14l. C-24 �STOP STOP 77 C a — C • • •• N g! 4 —U 0 ...- NORTH NORTH : '8 • V o 0 a a •U 2U •6 C V 0 V 0 0 V I-I-I 00 I 10 10 meters meters FIGURE 11. 11. Sketch Sketch of FIGURE 7, east east side side of of roa road, of roadcut roadcut at at stop stop 7, showing location location and and attitude showing attitude of of some some key key structural structural features. features. This ALTERNATE STOP STOP 8-OLD 3-OLD M69. M69. This stop stop is is located located in in the the NW MW 1/4, 1/4, ALTERNATE 20, T43N, R31W, about 500 meters east of the bridge over sec. 20, T43N, about 500 meters east of the bridge over the the sec. Micigamme0River K i ~ ~ i g a m m e R i v on eon r Old Old MM 69. 69. Here Here thinly thinly layered layered tuff, tuff, oriented oriented N20 W, 50 50 Sw, SW, has has aa penetrative penetrative Si Sl foliation foliation oriented oriented NG5CW, N S ~ W , N2j W, This 79 79 SW. SW. This northwest—trending northwest-trending foliation foliation is is characte;istic characteristic of of the the structural structural fabric fabric in in the the region region (west (west side side of of the the Amasa Amass uplift), 3. uplift), as as shown shown on on Figure Figure 3. Falls, To ROAD LOG. LOG. To reach reach stop stop 99 from from the the center center of of Crystal Crystal Falls, ROAD proceed S. 2/141 2/141 for for roughly roughly 66 miles, miles, to to the the road road on on proceed south south on on U. U. S. the the east east to to Horse Horse Race Race Rapids Rapids and and Iron Iron County County Airport. Airport. Turn Turn left left (east) (east) and and follow follow this this road road for for 3.5 3.5 miles miles to to parking parkinq area area at at Horse Race Race Rapids. Rapids. Follow Follow path down down slope slope to to plentiful plentiful outcrops oiitcr~ps Horse along alone the the river. river. This This outcrop outcrop area area is is south south of of gush 3usl-1 At A t this this locality locality graded graded beds beds (SO) (SO) of of face face south, south, and and form forn aa system systsm of of folds axial—plane foliation (1). folds that have a subhorizontal axial-plane (.^1). Fcld Fcld foliation Si Sl foliation has has been been axes in in SO SO plunge plunce gently gently westward. westward. axes refolded n ~ - i r lcoaxial ycoaxialwitli with refolded in in some some places places on on fold fold axes axes that thatare arenearly Syntectonic the fid foldaxes axes in in SO. SO. Syntectonic quartz quartz veins veins occur occur in in the the axes axes STOP STOP 9-HORSE RACE RACE RAPIDS. RAPIDS. Lake Lake Fault Fault (see ( s e e Fig. Fig. 3). 3). graywacke qraywacke stratigraphically stratigraphically C-25 �of of We some folds. folds. We interpret interpret this this outcrop outcrop to to be be part part of of the the some south-verging backthrust backthrust system, system, the the same same as as that that found found in in the the south—verging Feich trough area (see 3). Felch Trough—Caluinet Trough-Calumet trough (see Fig. Fig. 3). Return ROAD LOG. LOG. Return to to the the intersection intersection of of the the Horse Horse Race Race Rapids Rapids ROAD Turn highway road with with U. U. S. S. highway 2/141. 2/141. Turn left left onto onto U. U. S. S. 2/141 2/141 and and road Turn proceed proceed east east for for 18.9 18.9 miles miles tc to the the intersection intersection with with MM 95. 95. Turn 95 and follow follow 10.2 10.2 miles miles to to the the intersection intersection left (north) (north) on M 95 left with with County County Road Road 569 569 which which goes goes eastward eastward to to Feich, Felch..MI. MI. Follow Follow CO CO 569 569 east east through through Feich Felch for for 14.9 14.9 miles miles to to stop stop 10 10 (about (about 1.5 1.5 miles miles west west of of the the village village of of Foster Foster City). City). Mile Map of east 12. east end of Felch Felch trough trough (adapted (adapted from from James Jaws FIGURE 12. FIGURE and others, others, 1961) 1961) showing showing locations locations of of stops s t q s 10 10 and and 11. 11. Small Small and lower hemisphere stereoplots show show orientation low-dippin5 nl hemisphere stereoplots orientation of low-dippinç Shoj steep foliation; large large lower lower hemisphere stereoplot shows s t a e p (Sa) (Sa) foliation; foliation in in Archean Archean gneiss. gneiss. Black Black dots dots in in the the stereoplcts stereoplcts show show foliation orientation by the intersectio' intersecticn oof 3a an>-"! and r^-1. orientation of lineatior formed by f 3.3 Black Black dots dots outside outside the the stereoplots stereoplots show show location location of of outcrops. outcrops. 1 C- 26 �STOP 10:_CO STOP 10LCO 569. 569. Granitoid gneiss on the north side of the road distinct foliations. has The has two two distinct foliations. The steeper steeper foliation,0 foliation, herein herein is an Archean fabric fabric that strikes strikes about about N85 called Sat W , and called Sa, N85W, dips nearly subnearly vertical (see (see large large stereoplot stereoplot on on Fig. Fig. 12). 12). A subhorizontal foliation foliation (Si), (Sl), expressed by0aligned byaligned zones zones and and clots clots of biotite, biotite, is oriented about about Nb N10 W, W, 25 25Nfl. NE. Gneissic foliation foliation Gneissic and fold axes axes in in gneissic gneissic foliation foliation in in Archeari Archean rocks rocks throughout and throughout the Felch trough trough region are steep. the Felch region are The nearly nearly flat lying steep. The flat lying penetrative Si foliation is found throughout penetrative Sl foliation throughout the the Feich Felch trough trough area, area, as shown shown on on Figure Figure 12, 12, but but because because the the Archean Archean fabric fabric (Sa) (Sa) is generally more prominent, it it is is difficult difficult to to recognize recognize Si Sl (for (for example, example, climb climb to the large large outcrop outcrop area in in back of of the the roadcut roadcut Si on this The and look for Sl this nearly nearly horizontal horizontal surface). surface). The small small stereoplots 12 shows shows that that the the Si Sl foliation foliation is is irregular irregular stereoplots on Figure 12 Si also exists in Early in in orientation. orientation. The next stop stop shows shows that Sl Proterozoic rocks. Proterozoic rocks. ROAD LOG. LOG. Turn around at stop 10 and proceed west on CO 569 for miles to the intersection Proceed 6.7 miles 69. Proceed south south 6.7 intersection with Old Old M 69. (left) (left) on M69 for only 0.25 miles miles to to the the bridge. bridge. STOP 11-OLD 11—OLD M 69. Figure i3A isaa geologic showing aa STOP 69. Figure 13A is geologic map showing to south of roughly sequence north to south of roughly vertically bedded sequence from from north Randville Dolomite sandwiched between Sturgeon Quartzite and Randville Dolomite sandwiched between Sturgeon Quartzite Archean gneiss Archean gneiss blocks. blocks. The fact fact that the the stratigraphically stratigraphically older older dolomite indicates quartzite quartzite lies north of the dolomite indicates that that the the section section faces southward. faces southward. Also, bedding in the dolomite on the north side side the river of river dips dips steeply steeply north north suggesting suggesting slight slight overturn overturn of of of the south. bedding the south. bedding toward toward the The dolomite dolomite has has a subhorizontal subhorizontal foliation (Si) foliation (Sl) that is is axial axial planar planar to to small small folds folds in in it. it. the Archean Archean gneiss There are There are two distinct foliations foliations in in the gneiss The south of the the river. river. The steep steep dipping Archean Archean foliation foliation (Sa) (Sa) is is the crosscut by by low-dipping Early Proterozoic Proterozoic foliation foliation (Sl), the crosscut (SI), foliation as found Randville same subhorizontal is in the same subhorizontal foliation as is found in the Randville have note that the dolomite does not a steep Dolomite, but note that dolomite does not have a steep Dolomite, foliation. foliation. in Our interpretation interpretation of the Our the structure structure at at stop stop 11 11 is is shown shown in We suggest cross section section A-A' (Fig. (Fig. 13a). 13a). suggest that that the the Archean Archean cross gneiss has been thrust above the Sturgeon Quartzite and Ra-ndville Randville thrust'above Sturseon Quartzita Dolomite, Dolomite, which which are are exposed as aa window window in in the the Archean thrust thrust indicates southward sheet. Southward facing stratigraphy sheet. Southward facing stratigraphy indicates southward vergence The the Sl Si vergence in in the thrust thrust system. system. The thrusting thrusting created created the subhorizontal foliation in both Early Proterozoic subhorizontal foliation Proterozoic and and Archean Archean rocks, rocks, but the the steep steep Sa Sa fabric fabric occurs occurs only only in in the the Archean Archean gneiss. gneiss. Figure Figure 13D 13B shows shows the the thrust thrust system system in in aa broader broader perspective, perspective, and provides provides additional additional key key evidence evidence for for southward southward vergence vergence in in the Felch the Felch trough trough area. area. Although the the exact exact configuration configuration of of the thr fold which thrust faults faults is not known thrust known at at this this time, time, the drag drag fold which cross shown on occurs in in Sturgeon Sturgeon Quartzite, Quartzite, as as diagrarnatically diagramatically shown on cross The section B-B', unequivocally indicate section B -B', indicate southward southward vergence. vergence. mu lac west of the profile at the drag fold actually occurs about a mile west see it same same structural structural position position along along the the fault. fault. We We will not not see it �______ B B XX XX X X X X X X XXX X X X XXX XXX .m45?. • XXX XX X X X Xn XU X X •V .• X - x x x x x I- ä 2000 felt 30cm 500meters meters 500 00 'I I 0.6 cm XX X Cover 1000 I 0 0 0 feet feet 00 XXX X X - Sondstone x 1!' )C XX )( XX red ounger x x x XXX x x x xXX) x x X XXX o X X x X X X Cover A A XXX X XXX XXA A- I 300 300meters meters 00 Drag folds AA /North North 9 B 7,A 7, A' / •1 d m Strike Strike and and Younger sandstone sandstone Younger > 'a Randviile Dolomite Dolomite Randville vulcan Iron Iron Fm. Fm. Vulcan V I Strik, Strike and and dip dip of af bedding bedding Sense sense ofof vergence vergence pP' Thrust / Thrust fault fault Sturgeon Ouartzlte Quartzite Sturgeon Ix dip dip ofof foliation foliation Archean gneiss gneiss Archean Outcrop Outcrop 4 Fault Fault and and sense ofof movement movement sense FIGERE 13. 13. Geologic Geologic maps maps in in area area of stop 11 (adapted from James FIGURE Map and others, others, 1961). 1961). Map AA and and geologic qeologic cross Gross section seciion shows shoiis the thc and and gneiss Archean structural relationship relationship between between Archean gneiss and Tarly Ezrly structural :.:as Z and xu? Prctsrozoic Sturgeon Sturgeon Quartzite Quartzits and Xandville Dolomite. Map Prcterozoic andville Dolomit€. of location (note cross section is of a larger area structural cross section is of a largsr area (note l~cction of structural These maps show that low-dipping fnliation map A and drag fald). These maps show that low-dig~inq fzliation map A and drag fold). ~herezs occurs in in both both Archean Archeari and and Early Early Proterozoic Proterozoicrocks, rocks: whereas (Sl) occurs (Si) Archean ( Z s )occurs occurs only only in in the the Archean gnei.;s. gneiss. the steeper steeper foliation foliation (ca) the T h s maps nass and an2 cross cross sections sections also also present prssent evidence evidencefor for soi.:thward s~1:thmrZ The Sse text text for for further furtherdiscussion. fiiscussion. structuralvergence. vergeiice. See structural C- 28 �because of of difficult difficult access access to to the the outcrops. outcrops. because In summary, summary, several key points can be be made made from from this this stop: stop: In points can 1) Sa fabric is found only only in in Archean Archean rocks rocks (and (and not not in Sa fabric 1) in Early Proterozoic rocks)f thereby proving proving an Archean Archean age age for for Sa. Protérozoic thereby rocks), Sa. 2)Sub-horizontal Sl fabric is founG and Early Si 2)Sub-horizontal found in both Archean and it is is not not older Proterozoic rocks, thereby that it Proterozoic rocks, thereby proving that older than than Proterozoic age. age. 3) Thrust vergence is is toward the the south south in in Early Proterozoic the the Felch Felch trough trough area. area. ROAD ROAD LOG. LOG. Turn around and return return to to intersection intsrsection of of Old Old 69 69 and and CO CO 569 (a (a distance distance of of 0.25 0.25 miles). miles). Turn Turn left le2t (west) (west) on on 569 569 and and follow it follow it for 8.2 miles miles to to intersection intersection with with MM 95. 95. Turn left Turn left 5.4 miles miles to to Steele (south) on on M 95 and follow follow it it for for 5.4 (south) Steele Road (Swanson Road Road on on right). right). left on on Steele Steele Road Road and and follow follow it it (Swanson Turn left to "THE STEELE FARM" to "THE STEELE end of of road. road. After checking with FARM" at end After checking with residentsf go through through gate gate to to field field on on the the east. east. Outcrops Outcrops are are in in residents, go the southern the southern part the field about about 400 east of of the the part of of the 400 m east farmhouse. farmhouse. This outcrop STOP 12-STEELE 12-STEELE FARM. FARM. outcrop of Michigamme Michigamme Formation Formation is is in in the Calumet Calurnet Trough (Fig. the Trough (Fig. 3). Here graded gradsd beds (SO) of Here beds of 3). (SO) .rnetagraywacke, metagray~acke~ now quartz—sericite-biotite quartz-sericite-biotite schist, schist! have a have a prominent that refracts prominent subhorizontal subhorizontal foliation foliation (SJ.) tha& across ref racts across (Si) bedding. Si is oriented axial bedding. Sl is oriented roughly roughly N90 N90 E, E, 25 25 SE, SE, and is is axial folds in to the metagraywacke metagraywacke that plunge gently planar to folds in the that plunge gently northwest. northwest. Bedding strikes strikes roughly roughly east east and dips dips steeply steeply south. south. metagraywacke indicate indicate Graded beds and flame flame structures structures in in the the metagraywacke that stratigraphic stratigraphic facing that facing is is toward toward the the south. south. Both SO and and Si Sl have been have been refolded with a steeper steeper foliation foliation (S2) (S2) that that strikes strikes N40°E. approximately ~ surfaces approximately 4 0 ~ Also, Alsof ~ . crinkle crinkle folds folds on on the the Si Sl surfaces indicate indicate post-Fl post-Fl folding. folding. summary, this outcrop indicates In summary, indicates that that there there is is aa prominent prominent subhorizontal foliation foliation in the Calurnet strata in subhorizontal Michigamme strata Calumet in Michigarnme in the bedding trough. Sedimentary structures indicate that faces trough. Sedimentary structures indicate that bedding faces This toward toward the the south. south. This implies implies that that SO SO has has been been rotated rotated toward the south that the the Calumet trough is is a south—verging the south and and that Calumet trough a south-verging structure. structure. Return ZOAD LOG. LOG. Return to to MM 95 95 and and turn turn left left (south). (south). The turn t u m to to ROAD alternate stop stop 13 13 is is 1.0 1.0 mile south south of of Steele Steele Road Road on on MM 95 9 5 at at the the intersection 14 95 95 with with Sportsman Sportsman Club Club Road. Road. Turn left left (east) (east) intersection of M on Sportsman S~ortsnanClub Club Road. Road. This a large outcrop area area of of ALTERNATE STOP the ALTEFUJATE STOP 13. 13. This is is a lsrcje outcrop the Michigamme Formation in the Calumet trough Michigaame trough located locatsd in in the the E1/2, E1/2, sec The sec 21, 21f T41N, T41?Jf R28W R28X at at a sharp sharp bend in in the the Sturgeon Sturgeon River. Riwr. The rocks here are now are metagraywacke, metagra~wacke~ now schist schist and and phyllite. phyllits. They have have subhorizontal a sub?iorizontal foliation foliation (Si) (Sl) which which is is axial axial planar p l a n ~ rto to numerous numerous a drag folds Sil draq folds in bedding beddin9 (SO), (SO)f which which indicate indicate south south vergence. vergsnce. S foliation forms a gently undulating surface surface which, which, in in places, placzsf has has been fol6ed folded with with an an S2 S2axial axialplane planethat thatstrikes strikes northwest i andnd is northvest steeply dipping. dipping. steeply Like the the strata strata at at stop stop 12, 12f this outcrop outcrop also also shows that the Calumet trough trough is is a south south verging verging structure. structure. �To reach stop 14 from the intersection of Steele Road ROAD LOG. and M 95, proceed south on M 95 for a distance of 4.8 miles to Turn right and proceed west S. 2/141. the intersection with U. 2/141 for approximately 11 miles to the center of the on U. S. town of Florence, Wisconsin. Turn left (south) on County Road N the center of Florence and proceed south for 3.3 miles to the in Turn right on CO D and go 1.3 intersection with County Road D. Follow this "Site 34". miles west to a gravel road labelled road for 3.4 miles to the Pine River dam. From the parking lot fence near the dam walk onto the dam embankment to a chain link Turn that blocks access to the discharge flume from the darn. fence left and walk down the embankment next to the chain link for about 400 feet (130) meters to outcrops along the river. STOP 14-PINE RIVER FLOWAGE. This outcrop lies within the Niagara foliated fault zone. The rocks here consist of strongly been Primary layering has chloritic-garnetiferous schist. Dextral drag folds in the transposed parallel to Si foliation. which are transposed layering have steeply plunging axes, xes parallel to mineral lineations on the foliation surfaces of gaximum elongation in deformed concretions plunge 60 toward s80 W, parallel to the mineral lineation. completely deformation shown in this outcrop is The previous outcrops. A different from that seen in the lacking as is any evidence for a foliation is subhorizontal Rather, these highly strained southward structural vergence. rocks have an Si foliation that dips steeply south, as do the As defined by Ueng and others elongation (stretching) axes. this stop lies within the Florence-Niagara terrane, (1984), steeply which is characterized by a west-northwest—trending, south-dipping foliation that contains a prominent south—plunging Similarly oriented structures occur in stretch lineation. volcanic rocks of the Wisconsin magmatic terrane on the south margin of the Niagara fault zone, a few miles south of the Pine River dam (Sims and others, 1985). The structural fabric in this region reflects overthrusting of the Wisconsin magmatic terrane from the southeast onto the continental margin. ACKNOWLEDGEMENTS F. Cannon, benefited from conversations with W. L. LaBerge, B. W. Ojakangas, Z. E. Peterman, and K. J. Schulz G. It also benefited from critical who toured with us in the area. Z. IL Peterman provided the Foose and T. Off ield. reviews by N. Dale Beaver drafted the geochronological data on the granite. illustrations. This guide 0-30 �REFERENCES REFERENCES R., and Black, Black, R. R. A., A., 1983, 1983, Early Early Proterozoic Proterozoic Anderson, R. R. fl., and Anderson, development development of of the the southern southernArchean Archean boundary boundary of of the the Superior Superior province province in in the the Lake Lake Superior Superior region region (abs.): (abs.): Geological GeologicalScoScciety iety of of America America Abstracts Abstractswith with Programs, Programs,v.15, v.15, p.515. p.515. K., and Vander Vander Muelen, Muelen, M. M. 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E., Dutton, geology geology of of the the Menominee Menominee iron-bearing iron-bearing district district and and vicinity, vicinity, U. S. S. Geological Geological Survey Survey Map Map 1-466, 1-466, Michigan and and Wisconsin: U. Michigan 1:125,000 scale. scale. 1:125,000 P., 1980, 1980, Geologic Geologic map map of of the the Ned Ned Lake Lake quadrangle, quadrangle, M. P., S. Geological Geological Survey Survey Iron and Baraga Counties, Counties, Michigan: U. S. Iron Miscellaneous Miscellaneous Investigatiosn Investigatiosn Map Map 1-1284, 1-1284, 1:62,500 1:62,500 scale. scale. Foose, Foose, A., Greenburg, Greenburg, J. J. K., K., and and Brown, Brown, B. B. A., 1983, 1983, Lower Lower Proterozoic Proterozoic volcanic southern Lake Lake Superior Superior volcanic rocks rocks and and their their setting setting in in the the southern district: Memoir 160, 160, pp.67-84. pp.67-84. district: Geological Geological Society Society of of America America Memoir Williams, R. R. D. D. and Williams, I?. I., I., 1986, 1986, Mechanical model model for for Hatcher, R. Hatcher, single single thrust thrust sheets, sheets, Part Part I: I: Taxonomy Taxonomy of of crystalline crystalline thrust thrust sheets sheets and their their relationship relationship to to the the mechanical mechanical behavior behavior of of orogenic belts: Geological Geological Society Society of of America America Bulletin, Bulletin, v.97, v.97, orogenic pp.975-985. pp.975—985. I 1 Holst, T. T. B., B., 1982, 1982, Evidence Evidence for for multiple multiple deformation deformation during during the the Holst, Penokean Penokean orogeny orogeny in in the the Middle Middle Precambrian Precambrian Thompson Thompson Formation, Formation, Minnesota: Minnesota: Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences, v.19, v.19, pp.2O43pp.20432047. 2047. T. B., T. B., 1984, 1984, Evidence Evidence for for nappe nappe development development during during the the Early Early Proterozoic Proterozoic Penokean Penokean orogeny, orogeny, Minnesota: Minnesota: Geology, Geology, v.12, v.12, pp. 135—138. 135-138. Holst, Hoist, - Hoffman, P. P. Hoffman, United United plates plates of of America, America, Birth Birth of of aa Protoassembly and growth of Proterozoic craton: Early craton: Early Proterozoic assembly and growth of ProtoAnnual Review Laurentia: Review of of Earth Earth and and Planetary Planetary Sciences, Sciences, Laurentia: 16, in in press. press. v. 16, F., F., 1988, 1988, regional regional metamorphism metamorphism in in the the Precambrian Precambrian of of northern northern Michigan: Michigan: Geological Geological Society Society of of AmeAmerica Bulletin, Bulletin, V.66, V.66, pp.1455—1488. pp.1455-1488. rica James, James, H. H. L., L., 1955, 1955, Zones Zones of of James, H. H. James, 1961, 1961, L., Clark, Clark, L. D., Lamey, Lamey, C. A., and and Pettijohn, Pettijohn, F. F. J., J., Geology of central central Dickinson Dickinson County, County, Michigan: Michigan: U. U. S. S. Geology Geological Geological Survey Survey Professional Professional Paper Paper 310, 310, l76p. 176p. L., Dutton, H. Dutton, C. E., Pettijohn, Pettijohn, F. F. J., J., and and Weir, Weir, K. K. L., L., H. 1968, 1968, Geology and ore deposits of the the Iron Iron River-Crystal River-Crystal Falls Falls U. S. S. Geological Geological Survey Survey district, Iron Iron County, County, Michigan: Michigan: U. district, Professional Paper Paper 570, 570, 134 134 p. p. Professional James, James, �Klasner, Klasner, J. J. S., S., 1972, 1972, Style Style and sequence sequence of of deformation deformation and and metamorphism due associated metamorphism due to to the the Penokean Penokean Orogeny Orogeny in in the the western Marquette Range, DissertaRange, northern Michigan: Ph. D. Dissertation, Michigan Michigan Technological MI, 132 132 p. p. tion, Technological University, University, Houghton, Houghton, MI, 1978, Penokean Klasner, associated Klasner, J. S., 1978, Penokean deformation deformation and and associated J. S., metamorphism metamorphism in in the the western western Marquette Marquette Range, Range, northern northern MichiMichi-. . gan: Geological Society Society of America Bulletin, Bulletin, v.89, v.89, pp.711-722. pp.711-722. S., and Attoh, K., 1986, Klasner, J. S., 1986, Tectonic Tectonic implications implications from from Klasner, J. metamorphic metamorphic and and gravity gravity data data at at Peavy Peavy and and Republic Republic metamormetamorphic nodes, nodes, northern northern Michigan Michigan (abs.): (abs.): Geological Geological Society Society of of America America Abstracts Abstracts with with Programs, Programs, v.18, v.18, no. 6, 6, p. p. 658. 658. Klasner, Klasner, J. S., and and Osterfeld, Osterfeld, D., D., 1984, 1984, Gravity Gravity models models of of gneiss gneiss domes and a granitic granitic pluton in in northeastern northeastern Wisconsin Wisconsin (abs.): (abs.): 30th Annual Institute Institute on on Lake Lake Superior Superior Geology, Geology, Wausau, Wausau, WI, WI, p.24. Klasner, Klasner, R., and Jones, S., J. S., King, King, E. R., Jones, w. J., 1985, 1985, Geologic Geologic J. interpretation of gravity and magnetic interpretation magnetic data data for for northern northern Wisconsin, W. J. Hinze (ed.), Michigan and and Wisconsin, in W. (ed.). The Utility Utility anomaly maps: of gravity and magnetic Exploration magnetic anomaly maps: Society of Exploration Geophysicists, Geophysicists, pp.267—286. pp.267-286. Ojakangas, R. W., Klasner, J. S., Ojakangas, Klasner, W., Schulz, Schulz, K. J., J., and and LaBerge, LaBerge, G. G. L, L, 1988, 1988, Widespread evidence for overthrusting in Early Geological Proterozoic (abs.): Proterozoic rocks rocks in in northern northern Michigan Michigan (abs.): Geological Association of Canada and Mineralogical Association of Canada Programs Programs with with Abstracts, Abstracts, 1988 Annual Meeting, Meeting, in in press. press. LaBerge, G. L., Schulz, LaBerge, Schulz, K. J., and and Myers, Myers, P. P. E., E., 1984, 1984, The The plate plate 30th tectonic tectonic history history of of north-central north-central Wisconsin Wisconsin (abs.): (abs.): 30th Annual Institute Institute on on Lake Lake Superior Superior Geology, Geology, Wausau, Wausau, WI, WI, pp. pp. 25—27. 25-27. D.K., and Sloss, Sloss, L.L., L.L., 1980, 1980, Early Proterozoic sedimentary Larue, D.K., basins basins of the the Lake Lake Superior Superior region: region: Geological Geological Society Society of of America Bulletin, Bulletin, v.91, part 1, 1, pp.450-452, part 2, 2, pp.18361874. 1874. Maharidge, A. D., 1986, Maharidge, 1986, The The structural structural and tectonic history of a portion of the Felch Trough, the Felch Trough, central central Dickinson Dickinson County, County, MichiMichiUniversity, Bowling Green Master of Science Thesis, gan: gan: Master of Science Thesis, Green University, Bowling Green, Bowling Green, OH, OH, 67 67 p. p. B., B., Sims, Sims, P. P. K., Cannon, Cannon, W. F. F. Mudrey, Mudrey, M. M. G. G. Jr., Jr., and and Morey, G. Morey, G. map of the Lake Superior Geologic Southwick, Southwick, D. D. L., L . , 1982, 1982, Geologic map the Lake Superior region: Minnesota, Minnesota, Wisconsin, Wisconsin, and and northern northern Michigan: Michigan: Minnesota Minnesota scale. Geological Geological Survey Survey State State Map Map series series S—13, S-13, 1:1,000,000 1:1,000,000 scale. �Nelson, Nelson, K. K. D., Lillie, Lillie, R. J., J., deVoogd, deVoogd, B., B., Brewer, Brewer, J. J. A., A . , Oliver, Oliver, Brown, L., J. E., L., 1982, 1982, COCORP E., Kaufman, Kaufman, S., and Brown, COCORP seismic seismic reflection in the the Ouachita Ouachita Mountains Mountains of western western reflection profiling in Arkansas: Geometry Geometry and and geologic geologic interpretation: interpretation: Tectonics: Tectonics: v.1, pp. pp. 413—430. 413-430. Geochemistry of Schulz, K. rocks of Schulz, K. J., J., 1983, 1983, Geochemistry of volcanic volcanic rocks of northeastern Wisconsin (abs): northeastern (abs): 29th 29th Annual Institute Institute on on Lake Lake Superior Geology, Superior Geology, Houghton, Houghton, MI, MI, pp.39-40. pp.39-40. Volcanic rocks Schulz, K. K. J., Schulz, J., 1984, 1984, Vol.canic rocks of of northeastern northeastern Wisconsin. Wisconsin. Field Trip 1: Guide to to geology geology of the the Early Early Proterozoic Proterozoic rocks rocks in northeastern northeastern Wisconsin: 30th 30th Annual Institute Institute on on Lake Lake SuSuperior Geology, Geology, Wausau, Wausau, WI, WI, pp.51-93. pp.51-93. Schulz, J., 1987a, 1987a, An Early Proterozoic Proterozoic ophiolite ophiolite in in the the Schulz, K. J., Association of Penokean Penokean orogen orogen (abs.): (abs.): Geological Geological Association of Canada Canada Abstracts with Abstracts with Programs, Programs, v.12, v.12, p.87. p.87. K. K. J., J., 1987b, 1987b, Early Proterozoic evolution evolution of aa rifted rifted continental margin in the Lake Superior Lake Superior region region (abs.): (abs.): GeoGeological Society of America Abstracts with Programs, Programs, v.19, Schulz, Schulz, p.243. p.243. Schulz, Schulz, K. K. J., LaBerge, LaBerge, G. L., Sims, Sims, P. P. K., K., Peterman, Peterman, Z. 2 . E., E . , and and Kiasner, Klasner, J. S., 1984, 1984, The The volcanic-plutonic volcanic-plutonic terrane terrane of of nornorthern thern Wisconsin: implications implications for for Early Early Proterozoic Proterozoic tectonism, tectonisin, Lake of Canada Canada Lake Superior Superior region region (abs.): (abs.): Geological Geological Association Association of Abstracts with with Programs, Programs, v.9, v.9, p.103. p.103. R. L., and Larue, Larue, D. K., 1985, 1985, Fold Fold axes axes oblique oblique to to the the regional plunge and Proterozoic Proterozoic terrane terrane accretion accretion in in southern southern Lake Lake Superior Superior region: region: Precambrian Precambrian Research, Research, v.30, v.30, pp.249-262. pp.249-262. Sedlock, Sedlock, K. M., 1987, Sikkala, Sikkala, K. M., 1987, A structural structural analysis analysis of of Proterozoic Proterozoic rnetasediments, northern Falls Falls River, River, Baraga County, metasediments, northern County, Michigan: Michigan; University, Technological University, Master of of Science Science Thesis, Thesis, Michigan Michigan Technological Houghton, Houghton, MI, MI, 103 103 p. p. Sikkala, K. M., M., and Gregg, Sikkala, Gregg, W, J., J., 1987, 1987, A structural structural analysis analysis of of Proterozoic metasediments, metasediments, northern Proterozoic northern Falls Falls River, River, Baraga Baraga County, County, Michigan Michigan (abs.): (abs.): 33 33 Annual Institute Institute on on Lake Lake Superior Superior Geology, Geology, v. 33, 33, part 1, 1, pp. 65—66. 65-66. Sims, P. K., K., 1980, Sims, 1980, Boundary between Archean greenstone greenstone and and gneiss gneiss terranes terraries in in northern Wisconsin Wisconsin and and Michigan: Michigan: Geological Geoloqical SocSociety of America America Special Soecial Paper Paper 182, 182, pp.113-123. pp.113-123. Proterozoic 1987, P. K., K., 1987, Metallogeny Metallogeny of of Archean Archean and and Proterozoic P. terranes -- AA brief overview: overview: U. U. S. S. terranes in in the the Great Great Lakes Lakes region region -U. S. Geological Geological Survey Survey Bulletin Bulletin 1964, 1964, pp. pp. 56-74. 56-74. Sims, Sims, �Sims, Sims, P. P. K., K., Card, Card, K. K. D., D., and and Lumbers, Lumbers,S.S.13., B . , 1981, 1981, Evolution Evolution of of Early Proterozoic Proterozoic basins basins in in the the Great Great Lakes Lakes region, region, in in Early F. H. H. A. A. Campbell Campbell (ed.), (ed.), Proterozoic Proterozoic basins basins of of Canada: Canada: GeolGeolF. Geological Geological Survey Survey of of Canada Canada Special Special Paper Paper 81-10, 81-10, pp. pp. 379379397. 397. P. P. K., K., and and Peterman, Peterman, Z. Z. E., E., 1984, 1984, A partisan partisan review review of of the the Proterozoic geology geology of of Wisconsin Wisconsin and and adjacent adjacent Michigan Michigan Early Early Proterozoic (abs.): 30th 30th Annual Annual Institute Institute on on Lake Lake Superior Superior Geology, Geology, (abs.): Wausau, Wisconsin, pp. 73-76. Wausau, Wisconsin, pp. 73-76. Sims, Sims, and and Peterman, Peterman, Z. Z. E., E., 1986, 1986, The The Early Early Proterozoic Proterozoic major buried structure Central -- AA major buried structure in in northnorthCentral Plains Plains orogen orogen —— central central United United States: States: Geology, Geology, v. v. 14, 14, pp. pp. 488-491. 488-491. Sims, P. P. Sims, K., K., Sims, K., Peterrnan, Peterman, Z. E., Prinz, Prinz, W. W. C., C., and and Benedict, Bened-ict,F. I?. C., C., Sims, P. P. K., 1984a, Geology, Geology, geochemistry, geochemistry, and and age age of of Archean Archean and and Early Early 1984a, Proterozoic Proterozoic rocks rocks in in the the Marenisco-Watersmeet Marenisco-Watersmeet area, area, northern northern Michigan: Michigan: U. U. S. S. Geological Geological Survey Survey Professional Professional Paper Paper 1292—A, 1292-A, pp. Al-PAl. A1-A41. pp. Peterman P. K.., K.., Peterman Z. Z. E., E., and and Schulz, Schulz, K. K. J., J., 1985, 1985, The The P. Early implications Dunbar gneiss-granitoid gneiss-granitoid dome; dome; implications for for Early Dunbar Proterozoic Proterozoic tectonic tectonic evolution evolution of of northern northern Wisconsin: Wisconsin: GeoloGeological gical Society Society of of America America Bulletin, Bulletin, v.96, v.96, pp.1101-1112. pp.llO1-1112. Sims, Sims, P. P. K., K., Peterman, Peterman, Z. Z. E., E., Kiasner, Klasner, J. J. S., S., Cannon, Cannon, W. VJ. F., F., and and Schulz, Schulz, K. K. J., J., 1987, 1987, Nappe Nappe development development and and thrust thrust faulting faulting in the the upper upper Michigan Michigan segment segment of of the the Early Early Proterozoic Proterozoic in (abs.): Geological Geological Society Society of of America America AbsAbsPenokean orogen orogen (abs.): Penokean tracts with with Programs, Programs, v.19, v.19, p. p. 246. 246. tracts Sims, Sims, K., E., 1984b, 1984b, Guide Guide to to K., Schulz, Schulz, K. K. J., J., and and Peterrnan, Peternan, Z. Z. E., in northeasten rocks Proterozoic the Early Geology of of the Early Proterozoic rocks in northeasten Geology Wisconsin: Wisconsin: Field Field Trip Trip 1, 1, 30th 30th Annual Institute Institute on on Lake Lake Superior Superior Geology, pp.1-50. pp.1-50. Geology, Sims, P. P. Sims, W. P. P. K., Schulz, Schulz, K. K. J., J., Peterman, Peterman, Z. Z. E., E., and and Van Van Schmus, SC~MIIS, W. R., in in press, press, Wisconsin Wisconsin magmatic magmatic terrane, terrane, Lake Lake Superior Superior region, region, in in J. C. C. Reed Reed Jr. Jr. and and others others (eds.), (eds.),Precambrian-conterrninous Precambrian-conterminous Uniited States: States: Geological Geological Society Society of of America, America, The The geology geology of of Uniited North North America, America, v. v. C-2. C-2. Sims, Sims, Ueng, W. W. L., L., Larue, Larue, D. D. K., Sedlock, Sedlock, R. L., L., and and Kasper, Kasper, D. D. A., A., Ueng, 1984, 1984, Early Early Proterozoic Proterozoic tectonostratigraphic tectonostratigraphic terranes terranes of of the the southern southern Lake Lake Superior Superior region: region: Field Field Trip Trip Guide Guide with with summary, sun-iinary, Field Field Trip Trip 2. 2. 30th 30th Annual Annual Institute Institute on on Lake Lake Superior Superior Geology, Geology, 23p. 23p. Van Roosendaal, Roosendaal, D. D. J., 1985, 1985, An An analysis analysis of of rock rock structures structures and and strain strain in in cleaved cleaved pelitic pelitic rocks, rocks, East East Branch Branch of of the the Huron Huron River, River, Baraga Baraga County, County, Michigan: Michigan: Master Master of of Science Science Thesis, Thesis, Michigan Houghton, MI, MI, 82 82 p. p. Michigan Technological Technological University, University, Houghton, �I I Van Van Schmus, Schmus, W. W. R., R . , 1976, 1976, Early Early and and Middle Middle Proterozoic Proterozoic history history of of the the Great Great Lakes Lakes Area, Area, North North America: America: Philosophical Philosophical Transactions Transactions of of the the Royal Royal Society Society of of London, London, A280, A280, pp.605-628. pp.605-628. � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1988 Description An account of the resource Institute on Lake Superior Geology. Marquette, Michigan. May 12-13, 1988. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1988 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/2e727a9fa1fcd2d0abc22690e75dbf6d.pdf a1564fefb4944bae6ad3d41031638cc2 PDF Text Text INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY PROCEEDINGS MAY M A Y 1989 1989 VOLUME 35 VOLUME 35 i Part 1. 1. Abstracts Abstracts 35th 35th Annual Annual Meeting Meeting May 3-6, 3-6, 1989 1989 held at Duluth, Minnesota 55812 Duluth, Minnesota 55812 �Organizing Committee, 35th Annual Annual Meeting, Meeting, ILSG ILSG (1989) (1989) Richard W. W. Ojakangas, Ojakangas, Dept. Dept. of of Geology, Richard Geology, University of Minnesota, Minnesota, Duluth, Duluth, MN MN 55812 55812 John C. Green, Dept. of of Geology, University of Minnesota-Duluth, Duluth, MN MN 55812 Green, Dept. Geology, University Minnesota-Duluth, Duluth, 55812 Timothy B. Hoist, Holst, University University of of Minnesota-Duluth, Minnesota-Duluth, Duluth, Duluth, MN MN 55812 55812 Timothy B. Program Chair Chair and and Abstract Abstract Editor: Editor: John Program John C. C. Green Green Guidebook Editor: Timothy Guidebook Editor: Timothy B. B. Hoist Hoist Volume 35 Parts 1 1 and Volume 35 consists consists of Parts and 2: 2: 1: Abstracts 1: 2: Field Trip Guidebooks Guidebooks Published and Distributed by Published and by Institute on Lake Lake Superior Superior Geology Geology J. Kaiiiokoski, J. Kalliokoski, Secretary/Treasurer SecretaryITreasurer Dept. of Geological Geological Engineering, Engineering, Geology Geology and and Geophysics Geophysics Dept. University Michigan Technological University Houghton, Houghton, Michigan 49931 49931 ISSN 1042-9964 1042-9964 ISSN �35th 3 5 t hANNUAL ANNUAL INSTITUTE INSTITUTEON ONLAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY Proceedings P r o c e e d i n g s and and Abstracts Abstracts D u l u t h , Minnesota Minnesota Duluth, May and 5, 1989 1989 May 44 and Organized O r g a n i z e d by by Richard Ojakangas,UUniversity R i c h a r d WW. . Ojakangas, n i v e r s i t y of o f Minnesota, Minnesota, Duluth Duluth John C. Green, Green, UUniversity n i v e r s i t y of o f Minnesota, Minnesota, Duluth Duluth John C. Timothy Timothy B.B. HHoist, o i s t , University U n i v e r s i t y of o fMinnesota, Minnesota, Duluth Duluth Program Chairmanand and EEditor: Program Chairman ditor: Volume Volume 35. 35. John John C. C . Green Green Part P a r t 11Program Program and and Abstracts Abstracts Part P a r t 22 Field F i e l dTrip T r i Guidebooks p Guidebooks COVER COVER A n t i c l i n ein iThomson n ThomsonFormation F o r m a t i o nataThomson t Thomson Anticline dam dam nnear e a r Thomson, Thomson, Minnesota. M i n n e s o t a . View View from from e a s t bank bank oof f S t . Louis L o u i s River, R i v e r , looking looking east St. west. Wendell Wendell Wilson W i l s o n 5/30/1968 5/30/1968 �PURCHASE O OF AND ABSTRACTS ABSTRACTS AND AND FIELD PURCHASE F PROCEEDINGS PROCEEDINGS AND FIELDGUIDEBOOKS GUIDEBOOKS The andAAbstract andt the The PProceedings r o c e e d i n g s and b s t r a c t and h e FField i e l d Guidebooks Guidebooks ffor o r the t h e 35th 3 5 t hAnnual Annual Institute I n s t i t u t eononLake LakeSuperior S u p e r i o Geology r Geology may may be be purchased purchased bby y ccontacting: ontacting: John C. C. Green Green John Department of Geology Department of Geology University U n i v e r s i t y of o f Minnesota, Minnesota, Duluth Duluth Duluth, D u l u t h , Minnesota Minnesota 55812 55812 PROCEEDINGS VOLUME 35. PART PART 11 ------------------ $5.00 PROCEEDINGS AND AND ABSTRACTS, ABSTRACTS, VOLUME GUIDEBOOKS, VOLUME VOLUME 35, PART 22 ............................ $5.00 FIELD GUIDEBOOKS, 35, PART Issues I s s u e s of o f Proceedings Proceedings and and Abstracts A b s t r a c t s and and Field F i e l dGuidebooks Guidebooks from f r o m previous previous meetings maybe bepurchased purchasedbybyc contacting meetings may o n t a c t i n g tthe h e Secretary-Treasurer: Secretary-Treasurer: Joe KKalliokoski Joe al l i o k o s k i Department and GGeological Department ooff Geology Geology and e o l o g i c a l Engineering Engineering Michigan Technological University M i c h i gan Techno1 ogi cal U niversity Houghton, Houghton, Michigan M i c h i g a n 49931 49931 �TABLE OF OF CONTENTS CONTENTS Institutes I n s t i t u t e sononLake LakeSuperior S u p e r i o rGeology Geology to t o 1989 1989 Constitution Lake C o n s t i t u t i o n of o f the t h eInstitute I n s t i t u ton e on LakeSuperior S u p e r i o rGeology Geology By-Laws ont hthe By-Laws on e IInstitute n s t i t u t eon onLake LakeSuperior S u p e r i o rGeology Geology Goldich G o l d i c h Medal Medal Guidelines Guidelines Student S t u d e n t Travel T r a v e l Award Award i i ii ii iii iii ivv i v Boardooff Directors Board Directors vvii LLocal o c a l Committee Committee vvii Best B e s t Student S t u d e n t Paper Paper Committee Committee vvii Goldich Go1 d i ch Medal Medal Committee Committee vvii Goldich G o l d i c h Medal Medal Recipient Recipient vii Banquet Banquet Speaker Speaker vvii ii Acknowledgements vii vii Report R e p o r t oof f tthe h e Chairs C h a i r s ooff the t h e 34th 3 4 t h Annual Annual I Institute nstitute Calender C a l e n d e r of o f Events Events Poster P o s t e r Papers Papers Abstracts Abstracts viii v i ii x xxvi vi xXviii v i ii �INSTITUTES INSTITUTESON ONLAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY INSTITUTE NUMBER INSTITUTENUMBER DATE DATE PLACE PLACE 1 1955 1955 1956 1956 1957 1957 1958 1958 1959 1959 1960 1960 1961 1961 1962 1962 1963 1963 1964 1964 1965 1965 1966 1966 1967 1967 1968 1968 1969 1969 1970 1970 1971 1971 1972 1972 1973 1973 1974 1974 1975 1975 1976 1976 1977 1977 1978 1978 1979 1979 1980 1980 1981 1981 1982 1982 1983 1983 1984 1984 1985 1985 1986 1986 1987 1987 1988 1988 1989 1989 Minneapolis, M i n n e a p o l i s , MN MN Houghton, MI MI 1 22 33 44 55 66 7 7 88 99 10 10 11 11 12 12 13 13 14 14 15 15 16 16 17 17 18 18 19 19 20 20 21 21 22 22 23 23 24 24 25 25 26 26 27 27 28 28 29 29 30 30 31 31 32 32 33 33 34 34 35 35 East E a s t Lansing, L a n s i n g , MI MI Duluth, D u l u t h ,MN MN Minneapolis, M i n n e a p o l i s ,MN MN Madison, Madison, WI WI Port P o r t Arthur, A r t h u r , Ont. Ont.(Thunder ( T h u n d e rBay) Bay) Houghton, MI Houghton, MI Duluth, D u l u t h , MN MN Ishpeming, MI Ishpeming, MI St. S t . Paul, P a u l ,MN MN Sault MI S a u l t Ste. S t e . Marie, M a r i e , MI East E a s t Lansing, L a n s i n g , MI MI Superior, S u p e r i o r , WI MI Oshkosh, WI WI Thunder Thunder Bay, Bay, Ont. Ont. Duluth, MN D u l u t h ,MN Houghton, MI MI Madison, Madison, WI MI Sault S a u l t Ste. S t e . Marie, M a r i e , Ont. Ont. Marquette, MI M a r q u e t t e , MI St. S t . Paul, Paul MN , MN Thunder Thunder Bay, Bay, Ont. Ont. Milwaukee, WI Milwaukee, WI Duluth, D u l u t h ,MN MN Eau Claire, Eau C l a i r e , WI MI East E a s t Lansing, L a n s i n g , MI MI International I n t e r n a t i o n a l Falls, F a l l s MN , MN Houghton, MI Houghton, MI Wausau, Wausau, WI MI Kenora, Kenora, Ont. Ont. Wisconsin Wisconsin Rapids, R a p i d s , WI W I Wawa, Wawa, Ont. Ont. Marquette, M a r q u e t t e , MI MI Duluth, D u l u t h ,MN MN �___________________________ CONSTITUTION OF CONSTITUTION OF INSTITUTE INSTITUTEON ONLAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY Article Article II Name Name Thename name The o f of t hthe e o rorganization g a n i z a t i o n s hshall a l l b be e t hthe e " I"Institute nstitute Article A r t i c l e VI VI on Lake Superior on Lake S u p e r i o r Geology." Geo 1 o g y . " Article A r t i c l e II I1 Objectives Objectives Theoobjectives The b j e c t i v e s oof f tthis h i s organization o r g a n i z a t i o n are: are: A. 0B.. C. Article III A r t i c l e 111 To pprovide wherebyg geologists To r o v i d e aa means means whereby e o l o g i s t s iin n the the Great G r e a t Lakes L a k e s region r e g i o nmay may exchange exchange ideas i d e a s and and scientific s c i e n t i f i c data. data. To ppromote To r o m o t e bbetter e t t e r uunderstanding n d e r s t a n d i n g oof f tthe h e geology g e o l o g y ooff the t h e Lake Lake Superior S u p e r i o r region. region. To pplan andcconduct To l a n and o n d u c t g egeological o l o g i c a l f i field e l d ttrips. rips. Article A r t i c l e VII VII Directors D irectors The bboard The o a r d oof f ddirectors i r e c t o r s shall s h a l l consist c o n s i s tofo the f t h Chairman, e Chairman, Secretary-Treasurer, andt hthe S e c r e t a r y - T r e a s u r e r , and e l last a s t three t h r e e past p a s t ChairChairmen;bbut t h e board b o a r d should s h o u l d aatt any any ttime i m e cconsist o n s i s t of of men; u t iiff the lless e s s than t h a n five f i v epersons, p e r s o n s , by b y reason r e a s o n of o f unwillingness unwillingness oorr inability i n a b i l i t yofoany f anyofothe f t habove e abovepersons p e r s o n s to t o serve serve as directors, as d i r e c t o r s , the t h evacancies v a c a n c i e s on onthe t h eboard b o a r dmay may be be filled as ttoo bring f i l l e dbyb ythe t h eannual annual meeting m e e t i n g so so as b r i n g the the membershipo of membership f tthe h e bboard o a r d uup p ttoo five f i v emembers. members. Officers icers Off - The The oofficers f f i c e r s of o f this t h i s organization o r g a n i z a t i o n shall s h a l l be b e aa Chairman i r m a n and and aa Secretary-Treasurer. Secretary-Treasurer. Cha A. Status S tatus Noppart No a r t ooff the t h e income income oof f tthe h e organization o r g a n i z a t i o n sshall h a l l inure inure tto o the t h e benefit b e n e f i t ofo fany a n ymember member oor r iindividual. n d i v i d u a l . IIn n the the eevent v e n t oof f dissolution d i s s o l u t i o n the t h e assets a s s e t s of o f the t h e organization organization sshall h a l l be b e ddistributed i s t r i b u t e d to to (some (some t atax x ffree r e e oorganization). rganization). ((To T o aavoid v o i d Federal F e d e r a l and and State S t a t e income income ttaxes, a x e s , the the oorganization r g a n i z a t i o n should s h o u l d be b e not n o t only o n l y " sscientific c i e n t i f i c " oorr "educational " e d u c a t i o n a l " bbut u t aalso l s o "'non-profit.') non-profit.") B. Minn. M i n n . Stat. S t a t . Anno. Anno. 290.01, 2 9 0 . 0 1 , subd. subd. 44 ' 290.05(9) 290.05(9) 1954 1954 Internal I n t e r n a lRevenue Revenue Code Code s. s . 5501(c)(3) 01(c)(3) Article A r t i c l e IV IV Article A r t i c l e VV Membership Membership The membership o n s i s t of of The membership o f oft hthe e o rorganization g a n i z a t i o n sshall h a l 1 cconsist Any ggeologist interested e o l o g i s t interested tthe h e board b o a r d oof f ddirectors. i r e c t o r s . Any in sshall h a l l be b e permitted p e r m i t t e d to t o attend a t t e n d and and pparticipate a r t i c i p a t e in and vote at the annual meetings. and v o t e a t t h e a n n u a l m e e t i n g s . Meetings Meetings The The oorganization r g a n i z a t i o n shall s h a l l meet meet once once aa yyear, e a r , preferably preferably The pplace during d u r i n g the t h e month m o n t h oof f AApril. p r i l . The l a c e and and eexact x a c t date date of o f each each meeting m e e t i n g wwill i l l be b edesignated d e s i g n a t e d by b y the t h e board b o a r d of of directors. directors. Article VIII A r t i c l e VIII The Chairman Chairmans shall The h a l l bbe e eelected l e c t e d each each year y e a r by by the t h e board b o a r d oof f directors, d i r e c t o r s , who who shall s h a l l give g i v edue due cconsideration o n s i d e r a t i o n to t o the t h e wishes w i s h e s of o f any any group group that t h a t may may be be promoting p r o m o t i n g the t h e next n e x t annual annual m e e t i n g . His H i s term t e r m of o f office o f f i c easasChairman Chairman meeting. will w i l l terminate t e r m i n a t e at a t the t h e close c l o s e of o fthe t h eannual annual meeting which m e e t i n g oover ver w h i c h hhe e ppresides r e s i d e s or o r when when his his successor s u c c e s s o r sshall h a l l have h a v e been been appointed. a p p o i n t e d . He He will w i l l then t h e n serve s e r v e for f o r aaperiod p e r i o d of o f three t h r e eyears years as a as a member member o foft hthe e bboard o a r d oof f ddirectors. irectors. The SSecretary-Treasurer The e c r e t a r y - T r e a s u r e r sshall h a l l be b e elected e l e c t e d at at His the t h e annual a n n u a l meeting. meeting. H i s tterm e r m oof f ooffice ffice shall s h a l l be b e two two years y e a r s oor r until u n t i l his h i ssuccessor successor shall s h a l l have have been been appointed. appointed. Amendments Amendments This majority b eamended amended bby y aa m ajority T h i s constitution c o n s t i t u t i o nmay may be who aare r e personally personally vvote o t e of o f those t h o s e persons p e r s o n s who i n , and and voting v o t i n g at a tany any ppresent r e s e n t aat, t , participating p a r t i c i p a t i n g in, organization. meeting aannual nnual m e e t i n g oof f tthe h e organization. �BY-LAWS I.I. Duties D u t i e s of o f the t h e Officers O f f i c e r sand and Directors Directors A. ItI tshall s h a l be l bethe t h eduty d u t yofothe f t h Chairman e Chairman to: to: 1. 1. 2. 2. Preside P r e s i d e at a t the t h eannual annual meeting. meeting. Appoint A p p o i n t all a l lcommittees committees needed needed f for o r tthe h e organization o r g a n i z a t i o n of o f the t h eannual annual meeting. meeting. 3. 3. B. ItI tshall s h a l be l bethe t h eduty d u t of y othe f t hSecretary—Treasurer e S e c r e t a r y - T r e a s u r e r to: to: 1. 1. 2. 2. 3. C. Assume Assume c ocomplete m p l e t e r e responsibility s p o n s i b i l i t y ffor o r the t h e organization o r g a n i z a t i o n and and financing financing of o f the t h eannual annual meeting m e e t i n g over o v e r which w h i c h he he presides. presides. Keep Keep aaccurate c c u r a t e aattendance t t e n d a n c e r erecords c o r d s oof f aall l l annual annual meetings. meetings. Keep of all correspondence Keep aaccurate c c u r a t e rrecords e c o r d s of a l lmeetings m e e t i n g sof, o f and , and correspondence between, between, tthe h e bboard o a r d oof f ddirectors. irectors. Hold H o l d all a l l funds f u n d s that t h a tmay may accure a c c u r e as as profits p r o f i t sfrom fromannual annual meetings m e e t i n g s or or field f i e l dtrips t r i p and s andtot make o make these t h e s e funds f u n d s available a v a i l a b l e for f o r the t h e organization organization and and ooperation p e r a t i o n of o f future f u t u r emeetings m e e t i n g s as as required. required. It I tshall s h a l lbe bethe t h e duty d u t y of o f the t h e board b o a r d of o f directors d i r e c t o r s to t o plan p l a n locations l o c a t i o n s of of annual meetings andt otoaadvise ont hthe andf ifinancing annual m e e t i n g s and d v i s e on e oorganization r g a n i z a t i o n and n a n c i n g oof f all all meetings. meetings. II. 11. Dues and and Expenses Expenses Dues 1. 1. 2. 2. There There shall s h a l l be beno noregular r e g u l amembership r membership dues. dues. Registration R e g i s t r a t i o n fees f e e s for f o rthe t h eannual annualmeetings m e e t i n g s shall s h a l lbe bedetermined d e t e r m i n e d by b y the the Chairman Chairman i nin cconsultation o n s u l t a t i o n wwith i t h tthe h e board b o a r d ooff directors. d i r e c t o r s . It I t is i sstrongly strongly recommended be kkept recommended t hthat a t t hthese e s e be e p t aatt aa minimum minimum tto o encourage encourage attendance a t t e n d a n c e of of graduate g r a d u a t e students. students. III. 111. R u l e s of o f Order Order Rules The The rrules u l e s contained c o n t a i n e d iin n Robert's R o b e r t ' s Rules R u l e s oof f Order Order sshall h a l l govern govern tthis his organization o r g a n i z a t i o n in i n all a l lcases cases to t owhich w h i c h they t h e y are a r e applicable. applicable. IV. IV. Amendments Amendments These maybebeamended amended These bby—laws y - l a w s may b y by a maamajority j o r i t y v ovote t e oof f those t h o s e persons persons who who are are personally annual p e r s o n a l l y present p r e s e n t aat, t , participating p a r t i c i p a t i n gin, i nand , andvoting v o t i n at g aany t any annualmeeting meeting of modifications o f the t h e organization; o r g a n i z a t i o n ; provided p r o v i d e d tthat h a t such such m o d i f i c a t i o n s sshall h a l l nnot o t cconflict onflict with presently w i t h the t h e constitution c o n s t i t u t i oas n as p r e s e n tadopted l y a d o p t eor d osubsequently r s u b s e q u e n t lamended. y amended. 111 �Award Guidelines Award G uidelines SAM SAM GOLDICH GOLDICH MEDAL MEDAL Preamble The The IInstitute n s t i t u t eononLake LakeSuperior S u p e r i oGeology r Geologywas was born b o r non onoro around r around1955, 1955,asasdocumented documented by by the t h e fact f a c t that t h a tthe t h e27th 2 7 t hannual annual meeting m e e t i n g wwill i l l be be held h e l d ini n1981. 1981. The The IInstitutes nstitutes a r e exemplary e x e m p l a r y i in n ttheir h e i r continuing c o n t i n u i n g objectives o b j e c t i v e s of of dealing d e a l i n g with w i t hthose t h o s e aspects a s p e c t s of of are g e o l o g y tthat h a t are a r e related r e l a t e dgeographically g e o g r a p h i c a l l y to t oLake Lake Superior; S u p e r i o r ; ofo fencouraging e n c o u r a g i n g the the geology discussion andssponsoring d i s c u s s i o n oor r ssubjects u b j e c t s and p o n s o r i n g f i efield l d t trips r i p s which w h i c h wwill i l l bring b r i n g together together geologists and i industry; g e o l o g i s t s from f r o m the t h eacademia, academia, government government ssurveys, u r v e y s , and n d u s t r y ; and and of of maintaining an eexceedingly informal m a i n t a i n i n g an xceedingly in f o r m a l bbut u t hhighly i g h l y effective e f f e c t i v e mode mode ooff operation. operation. During membership D u r i n g tthe h e ccourse o u r s e oof f i its t s existence e x i s t e n c e tthe h e membership o f of t h ethe I n Institute s t i t u t e ( t(that h a t iis, s, those whoi nindicate t h o s e ggeologists e o l o g i s t s who d i c a t e anani ninterest t e r e s t i in n tthe h e oobjectives b j e c t i v e s oof f the t h e I.L.S.G. I.L.S.G. by by attending) aware a t t e n d i n g ) has has become become aware o f of t h the e f afact c t t hthat a t ccertain e r t a i n of o f their t h e i colleagues r c o l l e a g u e shave have made p particularly a r t i c u l a r l y noteworthy n o t e w o r t h y and and m e r i t o r i o u s contributions c o n t r i b u t i o n s to t othe t h eimprovement improvement of of made meritorious understanding Superior" and i its u n d e r s t a n d i n g oof f "Lake "Lake S u p e r i o r " geology g e o l o g y and t s mineral m i n e r a l deposits. deposits. The awardwas wasmade made I.L.S.G. tto The eexemplary x e m p l a r y award byby I.L.S.G. o Sam Sam GGoldich o l d i c h iin n 1979 1979 ffor o r his h i smany many contributions 50 years. years. c o n t r i b u t i o n s to t othe t h egeology g e o l o g y of o fthe t h eregion r e g i o nextending e x t e n d i n gover o v e rabout about 50 Award Guidelines Award G uidelines medals shall be awarded awarded Board 1 ) The The medal h a l l be a nannually n u a l l y b yby t h the e Board of of D iDirectors, r e c t o r s , I .I.L.S.G., L . S . G . , to to 1) a geologist namei sIsa associated substantial g e o l o g i s t whose whose name s s o c i a t e d w iwith t h a as u b s t a n t i a l ssustained u s t a i n e d i ninterest t e r e s t in, in, or o r aa major m a j o r contribution c o n t r i b u t i o n to, t o ,the t h egeology g e o l o g y ofo fthe t h eLake LakeSuperior S u p e r i o r region. region. Boardoof Directors, 2) 2 ) The The Board f D i r e c t o r s , I.L.S.G. I.L.S.G. shall s h a appoint l l a p p o i nthe t t hNominating e N o m i n a t i nCommittee. g Committee. Their T h e i r annual annual nominee nominee wwill i l l be be voted v o t e d on on at a tthe t h eannual annualbusiness b u s i n e s s meeting. m e e t i n g . The The initial w i l be l beofothree f t h r e members, e members, one one tto o serve s e r v e for f o r three t h r e e years, y e a r s , one one i n i t i a appointment l a p p o i n t m e n t will for with f o r two, two, and and one one for f o rone oneyear, y e a r ,the t h emember member w i t h the t h e briefest b r i e f e s incumbency t incumbency to t o be be chairman. chairman. After A f t e r the t h e first f i r syear t y e a the r t h eBoard Board of of Directors D i r e c t o r s shall s h a l lappoint a p p o i n t at a teach each spring member s p r i n g meeting m e e t i n g one one new new member whowho w i lwill l s eserve r v e f ofor r tthree h r e e years. y e a r s . In I n the t h e third t h i r d year year this Committeemembership membership t h i smember member sshall h a l l be be the t h echairman. chairman. The The Committee s hshould o u l d r ereflect f l e c t the the main main ffields i e l d s of o f interest i n t e r e sand t andgeographic g e o g r a p h i c distribution d i s t r i b u t i o nofofI.L.S.G. I.L.S.G.membership. membership. 3 ) The The G o l d i c h Medal o m i n a t i n g Committee s h shall a l l s eselect l e c t t hthe e m e d a l i s t and ill 3) Goldich Medal NNominating Committee medalist and wwill make Boardo of make i its t s recommendation recommendation t otot hthe e Board f DDirectors i r e c t o r s by by November November 1,1,o of f tthat h a t year. year. 4) Directors w i l accept l a c c e p tthe t h enominee nominee of of the t h eCommittee, Committee, 4 ) The The BBoard o a r d oof f D i r e c t o r s normally n o r m a l l y will will one medal w i l linform i n f o r mthe t h emedalist m e d a l i simmediately, t i m m e d i a t e l y ,and andwill w i have l l have one medalengraved engraved appropriately a p p r o p r i a t e l y for f o rpresentation p r e s e n t a t i o nata the t t h May e Maymeeting. meeting. ItI tisi srecommended recommended t hthat a t tthe h e Institute I n s t i t u t eset s e aside t a s i d eannually a n n u a l l yfrom fromwhatever whatever sources, suchf ufunds i l l be be rrequired e q u i r e d tto o support s u p p o r t tthe h e ccontinuing o n t i n u i n g ccosts o s t s oof f this this sources, such n d s asasw will 5) 5) award. April A p r i 14,4,1981 1981 J. J. Kalliokoski, K a l 1 i o k o s k iChairman , Chai rman Bill B i l Cannon l Cannon Fred F r e d Kehlenbeck Kehlenbeck Glenn Glenn Morey Morey Greg Greg Mursky Mursky iv �STUDENT STUDENT TRAVEL TRAVEL AWARD AWARD The 1986 1986Board Boardo of The f DDirectors i r e c t o r s established e s t a b l i s h e d the t h e ILSG ILSG Student S t u d e n t Travel T r a v e l Award Award to to The awards awards wwill i l l be bemade made ssupport u p p o r t sstudent t u d e n t pparticipation a r t i c i p a t i o n aatt the t h e annual annual IInstitutes. n s t i t u t e s . The accruedi ninterest fund sset up ffor This ffrom r o m tthe h e accrued t e r e s t ffrom r o m aa sspecial p e c i a l fund e t up o r this t h i s purpose. purpose. T his awardi is some award s iintended n t e n d e d t oto hhelp e l p ddefray e f r a y some o f oft hthe e d idirect r e c t t rtravel a v e l ccosts o s t s tto o the the institute i n s t i t u t eand and includes i n c l u d e s aa waiver w a i v e r of o f registration r e g i s t r a t i o nfees, f e e sbut , b uexcludes t e x c l u d e sexpenses expenses for for numberand ands isize meals, andf i field meals, l lodging, o d g i n g , and e l d t trip r i p registration. r e g i s t r a t i o n . The The number z e wwill i l l be be annual Chairman Chairmani nincconsultation with ddetermined e t e r m i n e d bby y tthe h e annual onsultation w i t h the t h e Secretary S e c r e t a r y Treasurer Treasurer and wwill i l l be beannounced announced aatt the t h e annual annual banquet. banquet, and The considered The ffollowing o l l o w i n g general g e n e r a l ccriteria r i t e r i awill w i be l l be c o n s i d e r e dbyb ythe t h annual e annualChairman, Chairman, who who i is s responsible r e s p o n s i b l e ffor o r the t h e selection: selection: have aactive 11)) The The aapplicants p p l i c a n t s must must have c t i v e resident r e s i d e n t (undergraduate ( u n d e r g r a d u a t e oorr ggraduate) r a d u a t e ) s student t u d e n t s tstatus a t u s a tatt hthe e t itime m e o of f t hthe e i institute, nstitute, ccertified e r t i f i e dbybythe t h edepartment d e p a r t m e n t head. head. whoa rare oneeither an ooral 22) ) Students S t u d e n t s who e t hthe e s senior e n i o r aauthor u t h o r on i t h e r an r a l or or poster i l l be be given g i v e n favored f a v o r e d consideration. consideration. p o s t e r paper paper wwill 33)) IItt isi sdesirable d e s i r a b l e for f o rtwo two or o r more more sstudents t u d e n t s t otoj jointly ointly request r e q u e s t ttravel r a v e l assistance. assistance. 44)) IIn n general, g e n e r a l , ppriority r i o r i t y will w i l lbe begiven g i v e n to t o those t h o s e in i n the the IInstitute n s t i t u t eregion r e g i o nwho who are a r e farthest f a r t h e s taway. away. 5) be made madei ninwwriting, 5 ) Each Each ttravel r a v e l award award rrequest e q u e s t sshall h a l l be r i t i n g , to t o the the annual Chairman,wwith an eexplanation annual Chairman, i t h an x p l a n a t i o n of o f need, need, possible possible author a u t h o r sstatus t a t u s oor r oother t h e r ssignificant i g n i f i c a n t details. details. V �BOARD BOARD OF DIRECTORS DIRECTORS 1989 1989 R.W. Ojakangas Ojakangas( w(with J.C. Green andT.B. T.B. Hoist), R.W. i t h J.C. Green and H o i s t ) , Department Department of o f Geology, Geology, University U n i v e r s i t y of of Minnesota, Minnesota, Duluth, D u l u t h ,Duluth, D u l u t hMinnesota , Minnesota55812 55812 1988 1988 J.S. K l a s n e r (with ( w i t hJ.D. J.D.Hughes Hughes and and K.J. K.J. Schulz), S c h u l z ) ,Department Department of o fGeology, Geology, J.S. Klasner Western l i n o i s University, U n i v e r s i t y ,Macomb, Macomb, IIllinois l l i n o i s61455 61455 WesternI lIllinois 1987 1987 R.P. Sage E.D. FFrey), Ministry R.P. Sage ( (with w i t h E.D. r e y ) , Ontario O n t a r i o Geological G e o l o g i c a l Survey, Survey, M i n i s t r y of o f Northern Northern Development andMines, Mines,7777GGrenville Development and r e n v i l l e Street, S t r e e t , Toronto, T o r o n t o ,Ontario O n t a r iM7A o M7A1W4 1W4 1986 1986 J.K. Greenburg Geological andNNatural History J.K. Greenburg ((with w i t h B.A. B.A. Brown), Brown), Wisconsin Wisconsin G e o l o g i c a l and atural H istory Survey, Survey, 3817 3817 Mineral M i n e r a l Point P o i n tRoad, Road, Madison, Madison, Wisconsin Wisconsin53705 53705 Secretary-Treasurer Secretary-Treasurer J. Kalliokoski, J. K a l l i o k o s k i ,Department Department ofo fGeology Geology and and Geological G e o l o g i c a l Engineering, Engineering, Michigan M i c h i g a n TTechnological e c h n o l o g i c a l University, U n i v e r s i t y ,Houghton, Houghton, Michigan M i c h i g a n 49931 49931 LOCAL COMMITTEE LOCAL COMMITTEE R.W. R.W. Ojakangas: Ojakangas: General Chairman General Chairman J.C. J.C. Green: Green: ProgramChairman; Chairman;Program Programand andA bAbstracts Program s t r a c t s eeditor ditor T.B. Hoist: T.B. Hoist: Field andf i efield F i e l d Trip T r i p Chairman; Chairman; FField i e l d ttrip r i p arrangements arrangements and l d t trip rip guidebookeeditor guidebook ditor BEST STUDENT BEST STUDENT PAPER PAPER COMMITTEE COMMITTEE J.S. J.S. Kiasner: Klasner: WesternI lIllinois Western l i n o i s University, U n i v e r s i t y , Macomb, Macomb, I lIllinois linois Ray Anderson: Ray Anderson: Iowa GGeological Survey, Iowa Iowa e o l o g i c a l Survey, Iowa CCity, i t y , Iowa Iowa Keith K e i t h Laskowski: Laskowski: Newmont Newmont E xExploration, p l o r a t i o n , LLtd., t d . , Duluth, D u l u t h , Minnesota Minnesota GOLDICH MEDAL MEDAL COMMITTEE COMMITTEE JJ.J. . J . Brummer: Brummer: Brummer Brummer C Consulting, o n s u l t i n g , TToronto, o r o n t o , Ontario Ontario M.G. Mudrey, JJr.: M.G. Mudrey, r . : Wisconsin Wisconsin Geologic G e o l o g i c and and Natural N a t u r a l History H i s t o r ySurvey, Survey, Madison, Madison, Wisconsin R.W. Ojakangas: R.W. University U n i v e r s i t y of of Minnesota-Duluth, M i n n e s o t a - D u l u t h , Duluth, D u l u t h , Minnesota Minnesota vi �GOLDICH GOLDICH MEDAL MEDAL RECIPIENT RECIPIENT Jorrna Jorma KKalliokoski, a l l i o k o s k i , Michigan M i c h i g a n Technological T e c h n o l o g i c a l University U n i v e r s i t y (Professor ( P r o f e s s o rEmeritus). Emeritus). Medal by M.G. M.G. Mudrey, Mudrey,JJr., Medal awarded awarded by r . , Wisconsin Wisconsin Geological G e o l o g i c a l and andNatural Natural H i s t o r ySurvey Survey History BANQUET BANQUETSPEAKER SPEAKER S.F. S.F. Sawkins, Sawkins, University U n i v e r s i t y of o fMinnesota, Minnesota, Twin Twin Cities, C i t i e s , 'Ore "Ore genesis genesis models models for for volcano-plutonic v o l c a n o - p l u t o n i c arc a r csystems: systems: an anagnostic a g n o s t i cview viewofo the f t h conventional e c o n v e n t i o n awisdom l wisdom" ACKNOWLEDGMENTS ACKNOWLEDGMENTS Several p e o p l e and and oorganizations r g a n i z a t i o n s aassisted s s i s t e d iinn preparation p r e p a r a t i o n of o fthe t h e35th 3 5 t hAnnual Annual Several people Without their help the many tasks in preparing this meeting could ILSG. W i t h o u t t h e i r h e l p t h e many t a s k s i n p r e p a r i n g t h i s m e e t i n g c o u l d not not ILSG. have been been done. done. The The three t h r e e of o f us us(R.W. ( R . W . Ojakangas, Ojakangas, J.C. J.C. Green, Green, and and T.B. T.B. Holst) Hoist) have would would llike i k e to t othank thank the t h e following f o l l o w i n gpeople people and and organizations o r g a n i z a t i o n s ffor o r their t h e i r help. help. Mary Nash, EExecutive Geology,UUniversity Mary Nash, x e c u t i v e SSecretary, e c r e t a r y , Department Department oof f Geology, n i v e r s i t y of of Minnesota-Duluth, Minnesota-Duluth, for f o r handling h a n d l i n g finances f i n a n c e s and and other o t h e r aspects. aspects. Joan Secretary, Geology, UUniversity Joan Hendershot, Hendershot, SSenior enior S e c r e t a r y , Department Department ofof Geology, n i v e r s i t y of of Minnesota—Duluth, Minnesota-Duluth, f for o r various v a r i o u s tasks. tasks. Avis A v i s Hedin, Hedin, Principal P r i n c i p a lSecretary, S e c r e t a r y ,College C o l l e g e ofofScience Science and and Engineering, E n g i n e e r i n g , University University of o f Minnesota-Duluth, M i n n e s o t a - D u l u t h , ffor o r typing typing. Linda L i n d a Solcich, S o l c i c h . Radisson Radisson Hotel, H o t e l , Duluth, D u l u t h , for f o rmeeting m e e t i n gsite s i t earrangements. arrangements. John Klasner, Departmento fofGeology, Geology, Western 11 1Illinois i n o i s UUniversity, n i v e r s i t y , for f o r mailing mai 1i n g John K l a s n e r , Department Western l is t sand andadvice. advice. lists Graduate University Graduate sstudents t u d e n t s aat t U n i v e r s i t y of o f Minnesota-Duluth, M i n n e s o t a - D u l u t h , for f o r performing p e r f o r m i n g tasks, tasks, including i n c l u d i n g mailing m a i l i n gbrochures brochures and and projection. projection. Numerous company personnel Numerous company personnel f o r for c ocooperation o p e r a t i o n on on f i efield l d t trips. rips. University r aassistance s s i s t a n c e wwith i t h transportation. transportation. U n i v e r s i t y of o fMinnesota—Duluth, Minnesota-Duluth, f ofor Everyone else. else. Everyone vii �34TH ANNUAL ANNUAL INSTITUTE INSTITUTEON ONLAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY Marquette, Michigan, Marquette, M i c h i g a n , 1988 1988 The annual mmeeting The 334th 4 t h annual e e t i n g oof f tthe h e Institute I n s t i t u t eononLake LakeSuperior S u p e r i o rGeology Geology was was held held May10-14, 10-14, 1988, 1988, iinn Marquette, ffrom r o m May Marquette, Michigan. M i c h i g a n . The e e t i n g was o - h o s t e d by by The m meeting was cco-hosted Northern M ichigan U n i v e r s i t y , the t h eU.S. U.S. Geological G e o l o g i c a lSurvey-Branch Survey-Branch of o f Eastern Eastern Northern Michigan University, Mineral andWestern Western M i n e r a l Resources, Resources, and I l lIllinois i n o i s University. U n i v e r s i t y . The The many s k s i ninvolved v o l v e d iinn manyt atasks t h e planning, p l a n n i n g , preparation, p r e p a r a t i o n ,and andconducting c o n d u c t i n g of of the t h emeeting m e e t i n gwere were shared shared by by the the the John KKlasner servedasasggeneral chairman; Klaus Klaus SSchulz cco-hosts. o-hosts. John l a s n e r ooff WIU W I U served e n e r a l chairman; c h u l z oof f the the USGS banquet NMU took took USGS a r arranged r a n g e d f ofor r t hthe e ffield i e l d trips t r i p and s and banquetspeaker; speaker;John JohnHughes Hughes ofo fNMU ccare a r e of of local l o c a larrangements. arrangements. T e c h n i c a l ssessions e s s i o n s and h e banquet banquet were e l d aatt the the Technical and tthe werehheld RamadaI nInn on May May 12 12 and Ramada n on and 13. 13. AA ttotal o t a l of o f 245 245 persons persons registered r e g i s t e r e d for f o r the t h e meeting. meeting. T h i r t y - s e v e n oral o r a l presentations p r e s e n t a t i o n s were were scheduled, scheduled, but b u t two two had had to t o be be cancelled cancelled Thirty-seven becauset hthe were unable unable tto Nineteen because e ppresenters r e s e n t e r s were o attend. attend. N i n e t e e n poster p o s t e r papers papers were were andt hthree ppresented r e s e n t e d and r e e d different i f f e r e n t field f i e l d trips t r i p were s wereconducted. conducted. Newdevelopments developmentsf rfrom New o m s seismic e i s m i c sstudies t u d i e s in i n Lake Lake Superior S u p e r i o rbyb ythe t h GLIMPLE e GLIMPLE program n f o r m a t i o nfrom f r o ma aDOSECC DOSECC workshop h e Keweenawan Keweenawan R Rift ift m e r i t e d aa program and and iinformation workshopon on tthe merited sspecial p e c i a l full f u l day l daysession s e s s i o nononMay May12, 12, on onthe t h e"Geology "Geology ofo fthe t h eKeweenawan Keweenawan RRift." ift.'' Also, A l s o , half h a l fday daysessions s e s s i o n son onMay May 13, 13, were were devoted devoted to t o the t h e"Geology "Geology and and Mineral Mineral Deposits Rocks"and and"Geology "GeologyofofEEarly Rocks..." D e p o s i t s ooff Archean Archean Rocks" a r l y PProterozoic r o t e r o z o i c Rocks Poster paperscovered covereda av avariety respectively. respectively. P o s t e r papers r i e t y oof f ttopics. opics. ...I1 two-dayt trip AA ttotal o t a l of o f 151 1 5 1 persons persons e nenrolled r o l l e d f ofor r f ifield e l d ttrips. rips. A A two-day r i p on on the the "Archean Geologyand andMMineralization Belt" A r c h e a n Geology i n e r a l i z a t i o n ooff the t h e Marquette M a r q u e t t e Greenstone Greenstone B e l t " conducted conducted bby y 1. T . Bornhorst B o r n h o r s t of o fMichigan M i c h i g a n Technological T e c h n o l o g i c a l University U n i v e r s i t yand andR.A. R . A . Brozdowski Brozdowski and and G.W. SScott The ppre-meeting G.W. c o t t of o f Callahan C a l l a h a nMining M i n i n gCompany Company pproved r o v e d vvery e r y popular. p o p u l a r . The re-meeting version people v e r s i o n oof f this t h i s trip t r i pfilled f i l l ewith d w iSO t h 50 p e o p l eand and the t h e leaders l e a d e r s kindly k i n d l y agreed agreed to to conduct Twenty-nine conduct iitt for f o r2828persons personsafter a f t ethe r t hmeeting e m e e t i n gononMay May14 14and and 15. 15. Twenty-nine persons bybB. Boyum, persons pparticipated a r t i c i p a t e d in i naaspecial s p e c i a trip l t r conducted i p conducted y B. Boyum,R.R .Reed, Reed, and and William on "The "TheMMarquette W i l l i a m Kangas Kangas on a r q u e t t e M Mineral i n e r a l D District, i s t r i c t , Mining M i n i n g History H i s t o r yand andGeology." Geology." " A Structural S t r u c t u r a l Traverse T r a v e r s e Across Across aa P a r t of of A l s o , 44 44 persons persons eenrolled n r o l l e d i in n aa ttrip r i p on on "A Also, Part the OrogenI l lIllustrating t h e Penokean Penokean Orogen u s t r a t i n g Overthrusting O v e r t h r u s t i n g ini nNorthern N o r t h e r nMichigan" M i c h i g a n "conducted conducted C. Gallup wasaa cco-author by by J. Klasner, K l a s n e r , P. P.Sims, Sims, and andWilliam W i l l i a mGregg. Gregg. C. G a l l u p was o - a u t h o r oof f tthis his trip t r i p but b u t could c o u l d not n o t attend. attend. Don Davidson Davidson of AA ttotal o t a l ofo 163 f 163people peopleattended a t t e n d e dthe t h eannual annualILSG ILSGbanquet. banquet. Don of Northern N o r t h e r n IIllinois l l i n o i sUniversity U n i v e r s i t presented y p r e s e n t e dthe t h eGoldich G o l d i c h Medal Medal to t o Walter W a l t e r White W h i t e of o f the the USGS manyy years USGS f ofor r hhis i s many e a r s oof f sstudy t u d y of of and and excellent e x c e l l e n tcontributions c o n t r i b u t i o nto s Keweenawan t o Keweenawan P.F. Hoffman g e o l o g y . P.F. Hoffman ooff the t h e Geological G e o l o g i c a l Survey Survey of o fCanada Canada regaled r e g a l e d the t h e banquet banquet geology. audience anooverview early audience wwith i t h an v e r v i e w o foft hthe e t etectonic c t o n i c eevolution v o l u t i o n oof f Laurentia L a u r e n t i a dduring uring e arly and middle Proterozoic and m iddle P r o t e r o z o i c time. time. Inasmuch ILSG encourages t student Inasmuch asast hthe e ILSG t r itries e s t to o encourage u d e n t p aparticipation, r t i c i p a t i o n , both b o t h in in attendance a t t e n d a n c e aat t tthe h e Institute I n s t i t u t eand and presentation p r e s e n t a t i o n of o f papers, papers, we we provided p r o v i d e d ffinancial inancial assistance Waiver ooff a s s i s t a n c e to t o several s e v e r a lstudents s t u d e n t sand andgave gave two two best b e s tpaper paperawards. awards. Waiver rregistration e g i s t r a t i o nfee f e ewas was given g i v e n to t o 17 17 students s t u d e n t s who who aapplied, p p l i e d , and and 13 13 ooff the t h e 17 17 students students were aalso from aa sspecial were l s o ggiven i v e n ssmall m a l l ($20-$4O) ($20-$40) t rtravel a v e l aassistance s s i s t a n c e from p e c i a l fund f u n d set s e t aside aside awardoof $150was wasp rpresented ffor o r this t h i spurpose. purpose. An An award f $150 e s e n t e d t otoBBernhardt e r n h a r d t SSaini-Eidukat a i n i - E i d u k a t of of the Geophysics,UUniversity t h e Department Department ooff Geology Geology and and Geophysics, n i v e r s i t y of o f Minnesota-Minneapolis Minnesota-Minneapolis a $150 a $150award awardwas was given g i v e n to t oPeter P e t e rJongwaard Jongwaard of of ffor o r the t h e best b e s toral o r apresentation l p r e s e n t a t i oand n and tthe h e University U n i v e r s i t y of o fMinnesota-Duluth M i n n e s o t a - D u l u t h ffor o r the t h e best b e s t poster p o s t e r paper. paper. The ILSG ILSGBoard Boardoof Directors The f D i r e c t o r s luncheon luncheon meeting m e e t i n g was was held h e l d at a tthe t h eRamada Ramada Inn I n n on on was attended a t t e n d e d by b y C. C . Blackburn, Blackburn, B. 0 . Brown, Brown, J. Greenburg, Greenburg, J. J. Hughes, Hughes, J. J. May May 13. IIttwas Kalliokoski, M.M. Kehlenbeck, Kehlenbeck, J. J. Klasner, K l a s n e r , R. R. Ojakangas, Ojakangas, R. R . Sage, Sage, and and K. K . Schulz. Schulz. K a l l i o k o s k i , M.M. The ffollowing The o l l o w i n g items i t e m s of o fbusiness b u s i n e s swere were discussed: discussed: viii �- - Review Review ooff minutes m i n u t e s from f r o m 33rd 3 3 r d ILSG. ILSG. No No changes. changes. -- - Treasurer's T r e a s u r e r ' s report r e p o r t by by J. J. Kalliokoski, K a l l i o k o s k i Treasurer , T r e a s u r e rofofthe t h eAmerican American Account, Account, the the -balance b a l a n c e iin n the t h e general g e n e r a l account a c c o u n t as as of o f April A p r i l2,2,1987 1987was was $3,065.21. $3,065.21. The Goldich had aa bbalance M.M. Kehlenbeck, Kehlenbeck, Treasurer M.M. Treasurer G o l d i c h Medal Medal Funds Funds had a l a n c e of $1,153.92. $1,153.92. Account, rreported 1988. ooff the t h e Canadian Canadian Account, eported a a balance b a l a n c e of $9,664.88 $9,664.88 as as of o f May May 12, 12, 1988. - - R.W. i n dindicated i c a t e d t h that a t t hthe e UUniversity n i v e r s i t y oof f Minnesota, u l u t h w will i l l host host R.kJ.Ojakangas Ojakangas Minnesota,DDuluth -— tthe h e 35th 3 5 t h ILSG. ILSG. He He wwill i l l serve s e r v e as aschairman. chairman. - - J. K l a s n e r reported r e p o r t e d tthat h a t mailing m a i l i n g lists l i s t sare are o u t - o f - d a t eand andthere t h e r eare a r names e names J. Klasner out-of-date -whoa rare ooff many many p people e o p l e onon t h ethe l i slist t who e nono l o nlonger g e r a f faffiliated i l i a t e d wwith i t h t hthe e I Institute. nstitute. J. Kalliokoski J. K a l l i o k o s k i volunteered v o l u n t e e r e d t to o uupdate p d a t e t hthis i s l ilist s t and and fforward o r w a r d i it t to t o the the Minnesota Surveywhere wherei tit iiss kept. kept. M i n n e s o t a GGeological e o l o g i c a l Survey --—- M.G. r . of o f the t h e Wisconsin W i s c o n s i n Geological G e o l o g i c a l and and Natural N a t u r a l History H i s t o r y Survey Survey has has M.G. Mudrey, Mudrey,OJr. aagreed g r e e d tto o serve s e r v e on on the t h eGoldich G o l d i c hMedal MedalCommittee. Committee. He He rreplaces e p l a c e s K.D. K.D. Card Cardwho who finished f i n i s h e d his h i sterm t e r mon onthe t h ecommittee. committee. The 334th would nnot been ppossible The 4 t h ILSG ILSG would o t have have been o s s i b l e without w i t h o u t the t h ehelp h e l pof omany f manymembers. members. IIn n particular, p a r t i c u l a r ,the t h esuccess success of o fthe t h emeeting m e e t i n g is i slargely l a r g e l ydue duetot othe t h numerous e numerous high high Numerous members qquality u a l i t y papers papers presented p r e s e n t e d both b o t h orally o r a l l yand and as as poster p o s t e r papers. papers. Numerous members kkindly i n d l y agreed a g r e e d to t oserve s e r v eas asSession S e s s i o n Chairs, C h a i r s , Student S t u d e n tPaper Paper Judges, Judges, Goldich Goldich Committee Members,F Field Actually Committee Members, i e l d TTrip r i p Leaders Leaders and and Board Board ooff Directors D i r e c t o r sMembers. Members. A ctually tthe h e Institute I n s t i t u t eisi a s continuum, a continuum,with w i t heach eachmeeting m e e t i n g built b u i l tupon upon the t h e work work of o f previous previous organizers o r g a n i z e r s and and tthe h e willingness w i l l i n g n e s s of o fmembers members tto o serve s e r v e as as hosts h o s t s and and oorganizers r g a n i z e r s of of future f u t u r e meetings. meetings. We We t hthank a n k a lall l ffor o r their t h e i r help h e l p with w i t h this t h i syear's y e a r ' smeeting. meeting. Respectfully R e s p e c t f u l l y submitted, submitted, J. Hughes Hughes J. Klasner Klasner K. Schulz Co-hosts CO-hosts 34th 3 4 t h ILSG ILSG ix �CALENDAR OF OF EVENTS EVENTS AND PROGRAM PROGRAM WEDNESDAY, MAY MAY 33 FIELD TRIPS TRIPS 1, 22 FIELD departs from from Radisson, 8:00 8:00 a.m. a.m. Field Field Trip Trip 11 (North (North Shore Shore rhyolites, rhyolites, Minnesota) Minnesota) departs Radisson, upper upper level. Green. Will return return in in evening; evening; dinner (Dutch) (Dutch) en route. route. level. Leader: Leader: J.C. Green. 8:00 a.m. Field Field Trip Trip 22 (Penokean (Penokean structural structural terranes terranes in in East-Central East-Central Minnesota) Minnesota) departs departs 8:00 Radisson, level. Leader: T.B. T.B. HoIst. Hoist. Will return return in time time for for dinner dinner in in Radisson, lower level. Duluth. Duluth. 6:00 p.m. to to 9:00 9:00 p.m. p.m. Registration, Registration, Radisson Radisson Hotel, Hotel, Duluth Duluth 7:00 p.m. p.m. to to 10:00 10:OO p.m. p.m. Welcome Welcome get-together get-together and and cash cash bar, bar, Radisson Radisson Hotel. Hotel. x �TECHNICAL PROGRAM PROGRAM THURSDAY, THURSDAY. MAY 44 Morning 8:00 a.m. Welcome and and introduction introduction 8:00 a.m. Midcontinent Rift Session Session Chairs: A.B. Dickas and J.D. Miller, Miller, Jr. Jr. 8:10: James D. Miller, Miller, Jr. Jr. James Geology of the the Beaver Beaver Northeastern Minnesota Minnesota 8:30: Eric A. Jerde Jerde North Shore Hypabyssat rocks of the North Hypabyssal rocks Shore of Lake Superior: evidence for for polybaric Lake Bay Complex, fractionation in the Midcontinent Midcontinent Rift Rift 8:50: 850: Mark J. Severson Severson "Stratigraphy" 'Stratigraphy" and and general general geology of aa Intrusion, portion of the Partridge Partridge River River Intrusion, Duluth Complex, Minnesota Minnesota 9:10: Karl E. Seifert Seifert Pluton: two intrusions intrusions The Mineral Lake Lake Pluton: rather than a layered complex? rather layered complex? 9:30: Mudrey, Jr. Jr. Michael G. Mudrey, Albert B. 6 . Dickas Dickas Fundamental unit unit differentiation differentiation of of the Fundamental middle Proterozoic Proterozoic Midcontinent Midcontinent Rift Rift System, System, North America America 9:50: Coffee Break Break 10:30: McGinnis Lyle D. McGinnis Faulting in Possible in aa Possible Late-Stage Thrust Faulting Keweenawan-Age Keweenawan-Age Accommodation Zone Zone beneath Lake Superior Superior 10:50: J. Kalliokoski Kalliokoski Jacobsville Sandstone and Tectonic Tectonic Activity Activity 11:10: G. Wilson Campbell Craddock clastic dikes dikes as as Keweenawan Keweenawan Mafic and clastic in indicators Huron paleostress in the Huron Mountains, Michigan Michigan 11:30: Thomas Suszek Petrography Petrography *By title only: Susanne 'By Susanne Th. Th. Schmidt Schmidt John C. C. Green Green 11:50: 1 1:SO: and Sedimentation of the Middle Proterozoic Proterozoic (Keweenawan) (Keweenawan) Nonesuch Nonesuch Formation, Formation, Western Western Lake Lake Superior Superior Region, Region, Midcontinent Rift Zone Midcontinent Zone Metamorphic zonation in the the North North Shore Shore Volcanic Group, Group, Minnesota Minnesota Lunch Break Break xi �THURSDAY, MAY 4 THURSDAY, Afternoon Afternoon 1:30 to 2:30: Poster Poster session, session, Viking Viking Room Room Oral Session, Session, Mostly Mostly Economic Economic and and Quaternary Quaternary Chairs: Penelope Morton and Chairs: and David David Groves Groves 2:30: John S. S. Mothersill Mothersill James Fraser Fraser The paleomagnetic paleomagnetic record of Late Late Glacial Glacial and Post Post Glacial Glacial sediments sediments of of Lake Lake Superior Superior 2:50: Gary N. Meyer Gary Meyer Northern Glacial Glacial geology of of Northern mineral exploration exploration applications applications 3:10: E.R. Koopman, E.R. Koopman, B. Dube B. J.M. Franklin J.M. Franklin K.H. Poulsen Poulsen M.R. M.R. Patterson Patterson Deformation of of the Lyon Deformation Lyon Lake Lake massive massive suiphide sulphide deposit, Wabigoon Wabigoon subprovince, subprovince, Northwestern Ontario, Canada Canada 3:30: Coffee Break Break 3:50: Robert J. Horton Horton Robert Minnesota: Minnesota: The mining and and geologic history history of the the The Islet mine, and aa conceptual conceptual ore Silver Islet mine, and ore genesis model for the genesis the deposit deposit 4:10: Mark L. Nebel Nebel and polygenesis Metamorphism Metamorphism and polygenesis of ore ore deposits: an an example from from the the Madem Madem Lakkos PB-ZN-AG-AU deposit, deposit, Greece Greece 4:30: Mark Smyk the West Geology of the West Dead Dead Horse Horse Creek Creek rare metal metal occurrences, diatreme-hosted diatreme-hosted rare Schreiber-Hemlo district, Ontario Ontario 4:50: End of Session Session * * * * * * * * * * * * 5:00-7:00 5:OO-7:00 Cash Cash bar bar 7:00: 7:OO: Banquet Banquet Kalliokoski, Michigan Presentation of Goldich medal medal to to J. Kalliokoski, Michigan Technological Technological Presentation of the Goldich University, University, by M. M. G. G. Mudrey, Mudrey, Jr. Jr. Frederich J. (Sam) Frederich J. (Sam) Sawkins, Sawkins, University University of of Minnesota, Minnesota, Twin Twin Cities Cities "Ore genesis genesis models models for for volcano-plutonic volcano-plutonic arc arc systems: systems: An An agnostic agnostic view of of "Ore the conventional conventional wisdom" wisdom" xii xii Speaker: �FRIDAY, MAY 5 FRIDAY, Morning Morning Mostly Proterozoic Proterozoic R. W. W. Ojakangas Ojakangas Chairs: Val W. Chandler Chandler and A. 8:00: 8100: Gene L. L. LaBerge LaBerge structure and Tectonic Tectonic implications implications of the structure and stratigraphy of quartzites in in Central Central and and Southern Wisconsin Wisconsin 8:20: Bruce A. Brown Brown Significance argillites, and and Significance of conglomerates, conglomerates, argillites, in the Baraboo and dirty sandstones in and of Southeastern quartzites Southeastern Waterloo Wisconsin 8:40: Jeffrey K. K. Greenberg Greenberg Encore: The Proterozoic Proterozoic Baraboo Baraboo interval interval -- Encore: composition composition data et al. al. 9:00: 9:OO: Chan Lung S. Chan Paul E. Myers Myers Paleomagnetic studies of of Wausau Syenite Paleomagnetic studies Syenite Complex and Wissota Complex Wissota Dam Mafic Mafic Dike Dike 9:20: 9:20: Tern Terri Patton Patton M.K. Sood M.K. Sood B. Biddulph Biddulph Petrogenetic evolution of the Proterozoic Petrogenetic evolution Proterozoic Wausau igneous complex, complex, Wisconsin Wisconsin 9:40: 9140: Coffee Break Break 10:10: 1O:lO: Theresa M. Bodus Bodus William F. F. Kean Kean Preliminary paleomagnetic paleomagnetic survey survey of the Preliminary metasediments and metasediments and metavolcanics metavolcanics of of the Niagara Fault Niagara Fault system system in in Florence County, County, Wisconsin 10:30: M. Bodus Bodus Theresa M. Keith A. Sverdrup Sverdrup Preliminary magnetic survey of the Preliminary magnetic the Niagara Niagara in Florence, Forest, fault system system in Florence, Forest, and and Marinette counties, Wisconsin Wisconsin 10:50: 10150: Dennis J. Bebel Bebel A ground A ground resistivity technique for locating locating buried Precambrian fracture aquifers aquifers in in buried Precambrian basement, Central Central Wisconsin Wisconsin 11:10: 11:lO: Timothy Holst Timothy B. HoIst in Minnesota The The Penokean Penokean orogeny orogeny in Minnesota and and A comparison Michigan: A comparison of the upper Michigan: structural geology geology of of the structural the Michigamme Michigamme and and Thomson Formations Formations 111:30: 1:3O: Lunch Break Break Xlii xiii �FRIDAY, MAY MAY 55 Afternoon Afternoon 1:30 to 2:30: 1130 2130: Poster Session, Viking Room Room Oral Session, Session, Mostly Mostly Archean Archean M.A. Jirsa Jirsa and Steven A. Hauck Chairs: Chairs: M.A. Hauck 2130: 2:30: David L. L. Southwick Southwick Bryan Schaap Schaap Val W. Chandler Chandler Multiple Archean Archean terranes in SW Multiple SW MinnesotaMinnesotathe old gray gneiss she ain't what gneiss ain't what she she used used to be be 2:50: 2150: Stephen J. J, Schaefer Schaefer A comparison comparison of two two Archean Archean ultramafic pyroclastic rock units, Northwestern pyroclastic Northwestern Ontario Ontario 3:10: 3110: James L. L. Welsh Welsh Archean rocks Strike-slip faulting rocks in in the the Strike-slip faulting in in Archean Virginia Horn Horn area, area, N.E. N.E. Minnesota: implications implications for the origin origin of the Virginia Horn structure structure 3:30: 3130: Coffee Break Break 3150: 3:50: Mark A. Jirsa Jirsa Stratigraphic and and structural structural evolution evolution of of the Stratigraphic the Northmetavolcanic belt, NorthNorthern Itasca Northern ltasca metavolcanic Central Minnesota Minnesota 4:10: 4:lO: Roger Kuhns Kuhns an indication of as an tectonic environment environmentfor for the the central of tectonic central part of Belt, Greenstone Belt, the Hemlo-Heron Hemlo-Heron Bay Bay Greenstone Ontario Ontario 4130 4:30 William F. F. Read Read possibly two, One, possibly two, impact craters under under One, DePere, Wisconsin, DePere, Wisconsin, discovered discovered via water Basalt geochemistry Basalt well logs logs and and drill drill cuttings cuttings End of Session Session 4:50 4150 * ** * * * ** * * xiv * * ** �SATURDAY, MAY 6 SATURDAY? FIELD TRIPS 3,4 3,4 7:00 a.m. 7100 a.m. Field Field Trip Trip 33(Mellen (MellenComplex, ComplexlWisconsin) Wisconsin) Departs Departs from from liadisson Radisson upper upper level. level. Leaders: Karl Seifert, James Olmsted, Olmstedl Ken Klewin. Klewin. (Vans will return return to Duluth). Duluth). structural settings, settings, (Archean gold gold occurrences Field Field Trip 4 (Archean occurrences and and their structural J. Welsh, Minnesota) departs from Radisson, Leaders: J. D. England, England, D. D. Minnesota) departs Radissonl upper upper level. level. Leaders: Welsh, D. Groves? Levy? P. Hudleston, Hudlestonl D. Southwick, Southwickl R. Bauer?W. Ulland. Ulland. (Vans will return return to to Groves, E. E. Levy, R. Bauer, Duluth). Duluth). 8:00 8100 a.m. xv �POSTER PAPERS PAPERS Authors are requested to be on hand Authors are requested to hand at at their their posters posters during during the the special special poster poster Friday, and sessions sessions from from 1:30 1:30 to 2:30 2:30 Thursday Thursday and and Friday, and other other times times when when convenient. convenient. 1. of the I . Adams, Adamsf D.C., D.C., and and Young, Young, C.T., C.T., Magnetotelluric Magnetotelluric investigation investigation of the contact contact in northeastern northeastern between the Duluth between the Duluth Complex Complex and and the the Animikie Animikie Basin Basin in Minnesota. Minnesota. 2. Belden, 2. Beldenl J., Anderson, Anderson* G., Geland and Watkins, Watkins* I., I.* Zircons Zircons of the the St. St. Cloud Cloud Red Red and and Reformatory Reformatory Granites. Granites. 3. Block, Block, D.P., D.P., and andCavaleri, Cavaleri,M.E., M.E.,Petrogenesis Petrogenesis and andgeochemistry geochemistry ofofrhyoUtes rhyolites from the Chengwatana Chengwatana Volcanic Volcanic Group, Group, Mid-Continent Mid-Continent Rift Rift System. System. 4. Buchheit, Buchheit, R.L., R.L.?Malmquist, Malmquistl K.L., K.L., and and Niebuhr, Niebuhr, J.R., J R 1Glacial Glacialdrift driftgeochemistry geochemistry for strategic strategic minerals, minerals, Lake Lake County, Countyl Minnesota. Minnesota. 5. Cannon, 5. Cannon* W.F., W.Fe1Schulz, Schulz, K.J., K.J., Hinze, Hinze* W.J., W.J., and and Green, Green, A.G., A.G.,Precambrian Precambrian terranes defined by seismic terranes beneath beneath northern northern Lake Lake Michigan Michigan defined seismic and and gravity gravity analysis. analysis. 6. Chandler, Chandler, V.W., V.W., and and Schaap, Schaap, B.D., B.D., New New Bouguer Bouguer gravity gravity anomaly anomaly map map of of Minnesota. Minnesota. 7. 7. Pierre, and and Smith, Dods, S.D., Dods, S.D., Hinze, Hinze, W.J., W.J., Keating, Keating, Pierre? Smith, J.G., J.G., Magnetic Magnetic and and gravity maps of of Lake Lake Huron. Huron. 8. Hinze, W.J., W.J., Ravat, Ravat, D.N., D.N., McGinnis, McGinnis, L.D., L.D., Cannon, Cannon, W.F., W.F., Milkereit, Milkereit, B., B., Sexton, Sexton, J.L., and Wang, Structure J.Le1 Wang, H.F., H.Fa1 Structure of the the Midcontinent Midcontinent Rift Rift System System in in eastern eastern Preliminary results results from from the the 8-sec reflection Lake Superior: Superior: Preliminary reflection seismic data and gravity and and magnetic magnetic anomalies. anomalies. 9. Holm, 9. Holml D.K., D.K., and and Selverstone, Selverstone, J., J., Preliminary Preliminary constraints constraints on on the the P-T P-Tevolution evolution of the Penokean Penokean orogeny: orogeny: east-central Minnesota. Minnesota. 10. Horton, 10. Hortonl R.J., R.Js1and and Smith, Smith, B.D., B.D., Geophysical Geophysical investigations, investigations, International International Falls and Roseau Roseau quadrangles, quadranglesl Minnesota-Ontario. Minnesota-Ontario. of the M.A., Stratigraphic M.A., Stratigraphic and structural structural evolution evolution of the Northern Northern Itasca ltasca metavolcanic belt, north-central north-central Minnesota. Minnesota. 11. I I. Jirsa, Jirsa, 12. Kehlenbeck, M.M., and and Cheadle, Cheadle,S.P.? S.P.,Gravity Gravitysurvey surveyofof aa portion Kehlenbeck, M.M., portion of of the the Quetico and Wawa Wawa subprovinces subprovinces near Thunder Bay, Bay, Ontario. Ontario. xvi �13. 13. Kucks, Kucks, R.P., R.P., Chandler, Chandler, V.W., V.W., Dods, Dads! S.D., S.D., Ervin, Ervin, C.P., C.P., Hood, Hood,P., P.,McConnell, McConnell, anomaly maps K., and Teskey, Teskey! D., D., Potential-field Potential-field anomaly maps of of the Lake Lake K., Superior region. region. Superior 14. 14. MacArthur, MacArthur, J.H., J.H., and and HoIst, Holst, T.B., T.B., Deformation Deformation in the the Archean Archean Knife Knife Lake Lake Group, Group, Ensign Ensign Lake Lake area area of of northeastern Minnesota. Minnesota. northeastern the the eastern eastern Vermilion Vermilion District, District, Characterization Characterization of of the the graphite graphite occurrences occurrences in in the the and western western Penokean Penokean orogen. orogen. southern and 15. McSwiggen, McSwiggen, P.L., P.L., 15. 16. 16. 17. 17. Mudrey, Mudrey, M.G., M.G., McGinnis, McGinnis, L.D., L.D.! Ervin, Ervin, C.P., C.P., Nyquist, Nyquist, J.E., J.E., Dickas, Dickas, A.B., A.B., of the and Sexton, J.L., Structure Morey, Morey! G.B., G.B., Green, Green, A.G., A.G.! and Sexton, J.L., Structure of the Midcontinent Midcontinent Rift Rift System System from from 8-sec 8-sec reflection reflection seismic seismic data data in in Lake Superior. Superior. western Lake Chacko, Chacko, T., T., and and Kuehner, Kuehner, S.M., S.M., Petrographic Petrographic and and near Republic, iron-formation lens of isolated microprobe study study of isolated iron-formation lens near Republic! microprobe Peterson, J.W., Peterson, Michigan: aasearch searchfor forhigh-grade, high-grade,pre-Penokean pre-Penokeanmetamorphism. metamorphism. 18. Reich, Reich, Laura, Laura, Kean, Kean, W., W., and andSverdrup, Sverdrup,K., K.,Preliminary Preliminarygeomagnetic geomagnetic model model the St. St. Croix Croix Horst HorstininPolk PolkCounty, County,Wisconsin. Wisconsin. of the 19. Schulz, Schulz, K.J., K.J., and and Sims, Sims, P.K., P.K., Implications Implications of of igneous igneous rock rock geochemistry geochemistry inin Penokean orogen orogen for metallogeny metallogeny and and tectonic tectonic setting: setting: A A the Penokean synthesis of recent recent data. data. 20. Setterholm, Setterholm, 0., D., and and Hammond, Hammond, R.H., R.H., Manganese Manganese potential potential of the the Cretaceous Cretaceous rocks flanking flanking the the Sioux Sioux Ridge, Ridge, Minnesota Minnesota and and South South Dakota. Dakota. 21. Sims, Simsl P.K., P.K., New New bedrock bedrock geologic geologic map map of of Precambrian Precambrian rocks, rocks, eastern eastern Lake Lake Superior region, region! Wisconsin Wisconsin and and northern northern Michigan. Michigan. 22. Small, in vicinity vicinity of the Small, J.R., J.R., and and Bornhorst, Bornhorst, T.J., T.J., A geological geological investigation investigation in the contact! northern northern block block of the the Marquette Marquette volcanic-plutonic contact, Greenstone Belt, Belt, Michigan. Michigan. 23. 23. Smith, Smith, B.D., B.D., Labson, Labson, V.F., V.F., and and Horton, Horton, R.J., R.J., Airborne Airborne geophysical geophysical surveys surveys Effie-Coon Lake Lake complex, complex, Minnesota. Minnesota. of the Effie-Coon and magnetic data over 24. 24. Sverdrup, Sverdrup, K.A., K.A., and and Kean, Kean, W.F., W.F., Gravity Gravity and magnetic data over the the Fault, S.E. S.E. Wisconsin. Wisconsin. Waukesha Fault, xvii xvii �ABSTRACTS ABSTRACTS �MAGNETOTELLURIC INVESTIGATION MAGNETOTELLIJRIC INVESTIGATION OF OF THE THE CONTACT CONTACT BETWEEN BETWEEN THE IN NORTHEASTERN MINNESOTA MINNESOTA DULUTH COMPLEX AND ANIMIKIE BASIN IN CL, Young, Young, C. C. T. T. (Department (Department of of Geological Geological Adams, Donald C., Engineering, Geology and Geophysics, Geophysics, Michigan Michigan Technological University, University, Houghton Houghton MI, MI, 49931) 49931) Technological Magnetotelluric profiling profiling was was used used to to investigate investigate the the resistivity resistivity contrast contrast of of the the contact contact between between the the Animikie Animikie Basin and Duluth Duluth Complex Complex in in Northeastern Northeastern Minnesota. Minnesota. Data Data at eight eight sites, sites, during during June June and and July July 1988, 1988, were collected at alonq a Northwest Northwest to to Southeast Southeast 37 along 37 km k m line line (Figure (F1qur.e 1) 1) approximately approximately perpendicular perpendicular to to the the contact. contact. Preliminary one one dimensional modeling modeling and and interpretation interpretation of the data indicate indicate that that the the electrical electrical contact contact has has the the shape of a half graben sloping east and stepping to t o a depth of 15 km within the the field field area area (Figure (Figure 2). 2 ) . The The form form of of the the contact between the Duluth Complex and the the Animikie Basin Basin agrees with vith the the half half graben interpretation interpretation of of Weiblen Weiblen and Morey 1980 1980 and approximate depth to to the the contact contact determined by Frederer 1982. 1982. The The Duluth Duluth Complex Complex has has an an apparent apparent resistivity resistivity of of 10,000 10,000 to to 60,000 60,000 ohm ohm meters, meters, while while the the Animikie Basin and 255 255 ohm ohm Basin has has apparent apparent resistivities resistivities of of 33 and meters apparent meters and the the Giants Giants Range Range Granite Granite has has aa apparent resistivity resistivity of of 600 600 to to 3000 3000 ohm ohm meters. meters. The The field field work work was vas supported supported by by aa grant grant from from the the Minnesota geological qeological survey. survey. REFERENCES Frederer, Robert J. (1982): (1982): Gravity And And Magnetic Magnetic Modeling Modeling Of Of Robert J. The Duluth Duluth Complex, Complex, Northeastern Northeastern Minnesota, Minnesota, M.S. M.S. Thesis, Indiana Indiana University, University, 99 99 pages paqes Weiblen, Weiblen, Paul Paul W., W., Morey, Morey, G. G. B. B. (1980): (4980): A Summary Summary Of Of The The Stratigraphy, Petrology, Petrology, And Structure Structure Of Of The Duluth Duluth Complex, American American Journal Journal Of Of Science, Science, v. v. 280-A, 280-A, pp 88— 88133 133 �- • AURORA AURORA 47 47 30' 30' 91130 J45• 92100' 115' • HOYT H O Y T L LAKE AKE 01.0 02.5 02.0 05.0 03.5 N SCALE SCALE 1:384615 11384615 15' — (15' 92(00' 15' 1 130' I 46' FIGURE 11 LOCATION MAP MAP o* C 1.0 2.0 2:5 2.5 STATION S TATION 3 . 0 3.5 4.0 3.0 5.0 5.U 6.0 6 .0 AB ----E z I DC DC \ 10• 10GRG GRG 0 w 20 20- 600 6 0 0 --3000.n.m 3000~m GAG i AB-ANIMIKIE BASIN AB-ANIMIKIE BASIN DC-DULUTH COMPLEX DC-DULUTH COMPLEX GAG-GIANTS GRG-GIANTS RANGE RANGE GRANITE GRANITE SCALE 1:393701 SCALE 1:393701 FIGURE 2 MODEL INTERPRETATION INTERPRETATION 2 �TECHNIQUE FOR AQUIFERS IN A GROUND RESISTIVITY RESISTIVIlY TECHNIQUE FOR LOCATING LOCATING FRACTURE FRACTURE AQUIFERS I N BURIED BURIED PRECAMBRIAN BASEMENT, CENTRAL CENTRAL WISCONSIN Dennis J. J . Bebel, Bebel, Department of of Geology, Northern Illinois I l l i n o i s University, University, DeKaib, DeKalb, IL IL Decreases in Decreases i n aapparent p p a r e n t resistivity r e s i s t i v i t y have been recognized through through comparative measurements of ground ground resistivity r e s i s t i v i t y taken t a k e n above above and and below below the the water table t a b l e located l o c a t e d within w i t h i n buried b u r i e d crystalline c r y s t a l l i n e basement. basement. These decreases decreases have been interpreted i n t e r p r e t e d to t o indicate i n d i c a t e zones zones of of high h i g h fracture f r a c t u r e porosity p o r o s i t y and and therefore water volume allowing t h e r e f o r e increased i n c r e a s e d water a l l o w i n g for f o r greater g r e a t e r electrical electrical cconductivity. o n d u c t i v i t y . The survey method might provide a tool t o o l for f o r locating l o c a t i n g water water well w e l l drilling d r i l l i n g sites s i t e s in i n crystalline c r y s t a l l i n e basement. basement. Vertical A Lee array a r r a y was utilized u t i l i z e d during d u r i n g trial t r i a l surveys. surveys. V e r t i c a l electrical electrical soundings were were conducted at a t points p o i n t s along a l o n g the t h e survey traverses t r a v e r s e s to t o adjust a d j u s t for for surface s u r f a c e and basement topography in i n establishing e s t a b l i s h i n g the t h e depths d e p t h s to t o basement basement and and 18.3 tthe h e water table. t a b l e . Electrode E l e c t r o d e a-spacings a - s p a c i n g s within w i t h i n the t h e range of 4.6 4 . 6 -- 18.3 meters were determined to t o provide p r o v i d e investigation i n v e s t i g a t i o n depths d e p t h s above and and below below the the water table t a b l e along a l o n g the t h e length l e n g t h of of the t h e traverses. t r a v e r s e s . Trial T r i a l surveys s u r v e y s were were conducted near n e a r Dells D e l l s of of Eau Claire C l a i r e Park Park (Marathon (Marathon Co.), C o . ) , WI W I and and at a t Junction Junction City WI. C i t y (Portage ( P o r t a g e Co.), C o . ) , WI. The Dells D e l l s of Eau Claire C l a i r e traverse t r a v e r s e crossed c r o s s e d the t h e contact c o n t a c t between between the t h e Wolf Wolf River R i v e r Granite G r a n i t e and and aa "shear I1shear zone" zone" in i n felsic f e l s i c volcanics. v o l c a n i c s . Exposures of of the the volcanics v o l c a n i c s in i n the t h e Eau Claire C l a i r e River display d i s p l a y an an intense i n t e n s e fracture f r a c t u r e system. system. The The decreased within aapparent p p a r e n t resistivity resistivity d e c r e a s e d below the t h e water table table w i t h i n the t h e volcanics volcanics but b u t not n o t the t h e granite. granite. at The JJunction u n c t i o n City C i t y traverse t r a v e r s e was was at a t aa water water well w e l l site. s i t e . Basement rock rock at this t h i s location l o c a t i o n is i s early e a r l y Proterozoic P r o t e r o z o i c argillite. a r g i l l i t e . An apparent a p p a r e n t resistivity resistivity decrease 9 meters wide) wide) north d e c r e a s e was noted in i n a narrow zone (6 (6 - 9 n o r t h of of the the welisite w e l l s i t e and and on strike s t r i k e with w i t h the t h e local l o c a l basement basement structure. structure. It I t is i s ccurrently u r r e n t l y planned to t o further f u r t h e r test t e s t this t h i s technique t e c h n i q u e during d u r i n g the the Spring, with S p r i n g , 1989 in i n cconjunction onjunction w i t h a Wisconsin Geological and Natural N a t u r a l History History Survey drilling d r i l l i n g program at a t Junction J u n c t i o n City, C i t y , WI. WI. - 3 �ZIRCONS ZIRCONS OF OF THE THE ST ST CLOUD CLOUD RED RED AND REFORMATORY REFORMATORY GREY GREY GRANITES GRANITES J. Belden, Belden, G. G. Anderson, Anderson, and and I. I. Watkins Watkins J. St St Cloud Cloud State State University University St. St. Cloud, Cloud, Mn Mn 56301 56301 Samples Samples of of both both the the Reformatory Reformatory Grey Grey granite granite and and the the St St Cloud Cloud Red Red granites granites of of central central Minnesota Minnesota were were crushed crushed and and sieved. sieved. Using Using methylene methylene iodide, iodide, zircons zircons and and other other heavy heavy minerals minerals were were separated. separated. No No zircons zircons were were found found in in the the material material larger larger than than the the 100 100 ( 149 149 microns) microns) mesh mesh sieve. sieve. Euhedral Euhedral zircons zircons that that passed passed through through the the 100 100 mesh mesh sieve sieve were were picked picked out out of of the the heavies, heavies, mounted on on aa slide slide for for microprobe microprobe analysis analysis with with the the long long axis axis of of the the crystal crystal parallel parallel to to the the surface surface of of the the slide, slide, then then ground ground to to about about one one half half their their thickness. thickness. Micro Micro photographs photographs of of individual individual zircons zircons were were taken taken using using unpolarized unpolarized and and polarized polarized light light as as well well as as with with crossed polars. crossed polars. ( Observations Observations requiring requiring little little or or no no interpretation interpretationare: are: 1. 1. zircon zircon fragments fragments are are inside inside the the euhedral euhedral crystals crystals 2. 2. non—zirconium non-zirconium bearing bearing inclusions inclusions are are inside inside the the euhedral euhedral crystals crystals 3. 3. concentric concentric banding banding is is visible visible in in all all illuminations illuminations in in zircons zircons from from both both granites granites but but is is far far more more consistent consistent in in those those from from the the St St Cloud Cloud Red Red granite granite 4. 4.microprobe microprobe data data shows shows varying varying concentrations concentrations of of zirconium zirconium in in the the crystals crystals but but no no pattern pattern has has yet yet emerged emerged 5. 5. zircons zircons from from both both granites granites are are fractured fractured but but those those from from the the Refomatory Refomatory Grey Grey show show greater greater fracture fracture development development and and subsequent subsequent mineral mineral growth growth along along the the fractures fracturesthan thanthe theSt. St. Cloud Cloud Red Red 6. 6. microprobe microprobe data data of of uranium uranium concentrations concentrations is is unclear unclear at at this this time time but but work work is is continuing. continuing. Observations Observations requiring requiring appreciable appreciable interpretation interpretation with with some some possible possible interpretations interpretationsare: are: 1. apparent apparent overgrowths overgrowths (Sahama, (Sahama,1981) 1981) on on euhedral euhedral crystals crystals 1. occurred occurred so so the the crystal crystal is is no no longer longer euhedral euhedral or orthe thecrystal crystal has has fractured fractured in in aa strange strange way way 2. 2. the the fractures fractures in in the the euhedral euhedral crystals crystals usually usually do donot not follow follow cleavage cleavage planes planes but but always always appear appear dark dark in inany any light. light. The The dark dark color color may may be be due due to to zircon zircon crystallized crystallized at at aa lower lower (Caruba et et al., al., 1985) 1985) or or may may be be due due to to light light not not temperature (Caruba temperature getting getting through through because because of of the the critical critical angle angle of of illumina— illumination tion on on the the fracture. fracture. This This dilemma dilemma will will be be resolved. resolved. 3. 3. concentric concentric banding banding shows shows different different indices indices of of refraction refraction which which may may be be due due to to different different compositions compositions or or different different latlattice (Exarhos,1984). 1984). tice constants constants(Exarhos, 4 �REFERENCES REFERENCES Caruba,P... R., et et al, al, 1985. 1985, An An experimental experimental study study of of hydroxyl hydroxyl Caruba, groups and and water water in in synthetic synthetic and and natural natural zircons: zircons: aa groups model of the metamict state: American Mineralogist, v. model of the metamict state: American Mineralogist, v. 70, D. 1224-1231 70, p. 1224—1231 Exarhos, G.J., G.J., 1984, 1984. Induced Induced swelling swelling in in radiation radiation damaged damaged Exarhos, ZrSi04, Nuclear Instruments and Methods in Physics Re ZrSiO4, Nuclear Instruments and Methods in Physics Re search, Section B, v. 229, p. 538-41 search, Section B. v. 229, p. 538—41 Sahama, T.G., T.G., 1981. 1981, Growth Growth structure structure in in Ceylon Ceylon zircon, zircon,Bul Bul Sahama, v. 104, p. 89-94 letin de Mineralogie, letin de Mineralogie, v. 104, p. 89—94 5 �P E T R O G E N E S I S AND A M D GEOCHEMISTRY G E O C H E M I S T R Y OF O F RHYOLITES R H Y C L I T E S FROM F R O M THE THE PETROGENESIS C H E N G W A T A N A V O L C A N I C G R O U P , M I D C O N T I N E N T R I F T S Y STEM CI-JENGWATANA VOLCANIC GROUP, MID-CONTINENT RIFT SYSTEM D a n i e l R. R . Block B l o c k and and Mark M a r k E. E. Cavaleri, C a v a l e r i , Macalester M a c a l e s t e r College, College, Daniel S a i n t P a u l , M i n n e s o t a , D e p a r t m e n t of G e o l o gy Saint Paul, Minnesota, Department of Geology R h y o l i t e s form form aa significant s i g n i f i c a n t volume v o l u m e but but low l o w (<1%) ( < I ? ) percentage percentage Rhyolites o f t h e M i d c o n t i n e n t R i f t S y s t e m (MRS). D u e p e r h a p s to their their of the Midcontinent Rift System (MRS). Due perhaps to l i m i t e d e x p o s u r e , the r h y o l i t e s of the M R S h a v e not been limited exposure, rhyolites of the the MRS have not been e x t e n s i v e l y studied. s t u d i e d . This T h i s study s t u d y is is based based on o n chemical c h e m i c a l analyses a n a l y s e s of of extensively s a m p l e s taken t a k e n from from two t w o deep d e e p drill d r i l l cores, c o r e s , V66—1 V 6 6 - 1 and and V66—2, V 6 6 - 2 , from from samples V e r m i l l i o n , Minnesota, M i n n e s o t a , about a b o u t forty f o r t y miles m i l e s south s o u t h of of the the Twin Twin Vermillion, Cities. Cities. T h e purpose p u r p o s e of of studying s t u d y i n g these these cores c o r e s is i s two t w o fold. f o l d . First, First, The t h e s e cores c o r e s represent r e p r e s e n t the t h e southernmost s o u t h e r n m o s t sampling s a m p l i n g of of the t h e MRS. M R S , and and these a l s o one o n e of of the t h e few f e w samples s a m p l e s of of Chengwatana C h e n g w a t a n a rhyolites. r h y o l i t e s . The The also g e o c h e m i c a l data d a t a obtained o b t a i n e d during d u r i n g this t h i s study study t h u s forms f o r n s aa geochemical thus s i g n i f i c a n t addition a d d i t i o n to to the t h e data d a t a available a v a i l a b l e on o n the t h e MRS. M R S . Secondly, Secondly, significant r h y o l i t e s from f r o m the t h e MRS M R S has h a s not n o t been been extensively e x t e n s i v e l y studied. s t u d i e d . Within Within rhyolites the last ten years, n u m b e r of of world w o r l d rhyolite-basalt rhyolite-basalt the last ten years, number aa a s s o c i a t i o n s have h a v e been been examined. examined. Data c o l l e c t e d on' o n the the associations Data collected C h e n g w a t a n a rhyolites r h y o l i t e s will w i l l be be compared c o m p a r e d and and contrasted c o n t r a s t e d this this Chengwatana p u b l i s h e d data. data. published C o r e V66-2 V 6 6 - 2 is i s composed c o m p o s e d entirely e n t i r e l y of of rhyolite. r h y o l i t e . Core C o r e V66-1, V 6 6 - 1 , in in Core c o n t r a s t , contains c o n t a i n s only o n l y aa twenty t w e n t y foot foot section s e c t i o n of o f rhyolite r h y o l i t e in in aa contrast, m u c h larger l a r g e r amount a m o u n t of of basalt. b a s a l t . The T h e chemical c h e m i c a l fingerprints f i n g e r p r i n t s of of these these much c o r e s also a l s o differ. differ. R h y o l i t e s from f r o m V66—2 V 6 6 - 2 are a r e high h i g h in i n silica, silica, cores Rhyolites v a r y i n g from f r o m 73 73 to to 81%. 81%. Rhyolites R h y o l i t e s from f r o m V66—1 V66-1 contain c o n t a i n only o n l y about about varying 68% 5102. S i 0 2 . This T h i s suggests s u g g e s t s that t h a t these t h e s e rhyolites r h y o l i t e s of o f V66—1 V 6 6 - 1 could c o u l d have have 68% b e e n c o n t a m i n a t e d by t h e s u r r o u n d i n g .basalts. R h y o l i t e s from been contaminated by the surrounding basalts. Rhyolites from b o t h V 6 6 2 and V66-1 a r e p e r a l u m i n o u s . A 1 2 0 3 c o n c e n t r a t i o n s vary both V66—2 and V66—1 are peraluminous. Al203 concentrations vary f r o m 10 10 to to 14%, 1 4 % , while w h i l e Ca C a varies v a r i e s from from .05 . 0 5 to to 1.90% 1.90% and and Na2O N a 2 0 from from from 0 8 to 2.91%. .08 to 2.91%. Based on o n the t h e orthoclase-albite-quartz o r t h o c l a s e - a l b i t e - q u a r t z phase p h a s e equilibria, e q u i l i b r i a , the the Based r h y o l i t e s o f V 6 6 2 a r e e s t i m a t e d to h a v e f o r m e d in at rhyolites of V66-2 are estimated to have formed at in t e m p e r a t u r e s l e s s t h a n 8 0 0 d e g r e e s c e l s i u s . R h y o l i t e s f r o m V66-1 temperatures less than 800 degrees celsius. Rhyolites from V66-1 h a v e much m u c h higher h i g h e r albite a l b i t e concentrations c o n c e n t r a t i o n s due d u e to to probable p r o b a b l e basaltic basaltic have c o n t a m i n a t i o n . I t i s p o s s i b l e , h o w e v e r t h a t t h i s a l s points contamination. It is possible, however that this alsoo points t o w a r d s a h i g h e r t e m p e r a t u r e of f o r m a t i o n . towards a higher temperature of formation. T r a c e element e l e m e n t analyses a n a l y s e s show s h o w that that the the two t w o cores c o r e s probably p r o b a b l y have have Trace s l i g h t l y d i f f e r e n t p e t r o g e n e t i c h i s t o r i e s . V66-1 h a s m u c h higher slightly different petrogenetic histories. V66—1 has much higher c o n c e n t r a t i o n s of of strontium, s t r o n t i u m , phosphorus, p h o s p h o r u s , and and titanium t i t a n i u m than t h a n V66-2. V66-2. concentrations U n l i k e t h e l o w s i l i c a l e v e l s , these d i f f e r e n c e s c a n n o t be easily Unlike the low silica levels, these differences cannot be easily e x p l a i n e d by s i m p l e a s s i m i l a t i o n of b a s a l t i c m a t e r i a l . explained by simple assimilation of basaltic material. Based on the geochemistry, petrography, and field field Based on the geochemistry, petrography, and r e l a t i o n s h i p s , these t h e s e rhyolites r h y o l i t e s seem s e e m to to be be similar s i m i l a r in i n origin o r i g i n to to relationships, t h o s e studied s t u d i e d elsewhere e l s e w h e r e in i n the t h e MRS M R S and and in i n other o t h e r continental c o n t i n e n t a l rift rift those systems. T h e rhyolite—basalt r h y o l i t e - b a s a l t association a s s o c i a t i o n present p r e s e n t here h e r e and and in in systems. The s i m i l a r units u n i t s is i s commonly c o m m o n l y associated a s s o c i a t e d with w i t h regions r e g i o n s of of thick thick similar e x t e n d i n g crust. crust. Based on o n these t h e s e observations, o b s e r v a t i o n s , the t h e information information extending Based c o l l e c t e d in i n this this study s t u d y can c a n be be combined c o m b i n e d to to propose p r o p o s e aa model m o d e l for for collected t h e origins o r i g i n s of of these t h e s e rhyolites. r h y o l i t e s . The T h e formation f o r m a t i o n of o f the t h e rhyolites rhyolites the b e g i n s by by partial p a r t i a l melting m e l t i n g in i n the t h e upper u p p e r mantle. mantle. T h e magma m a g m a ponds ponds begins The 6 �at at or near n e a r the t h e crust/mantle c r u s t l m a n t l e interface, i n t e r f a c e , where w h e r e it it fractionate f r a c t i o n a t e until until its i t s density d e n s i t y is i s sufficiently s u f f i c i e n t l y low l o w to to allow a l l o w it i t to to rise r i s e to to the the surface. Rhyolites surface. R h y o l i t e s are a r e produced p r o d u c e d by by mafic m a f i c magmas m a g m a s travelling travelling through t h r o u g h narrow n a r r o w crustal c r u s t a l fractures f r a c t u r e s which w h i c h occur o c c u r either e i t h e r along along the the margins m a r g i n s of of the t h e rift r i f t system s y s t e m or o r in in immature i m m a t u r e zones z o n e s of of where w h e r e small small fractures f r a c t u r e s have h a v e not n o t yet y e t aggregated a g g r e g a t e d into i n t o wide w i d e conduits. conduits. Within Within these t h e s e fracture f r a c t u r e zones, z o n e s , the t h e mafic m a f i c magma m a g m a fractionates f r a c t i o n a t e s and and the the remaining r e m a i n i n g material m a t e r i a l becomes b e c o m e s contaminated c o n t a m i n a t e d with w i t h sialic s i a l i c crust crust as a s it it rises r i s e s to t o the t h e surface. surface. 7 �PRELIMINARY SURVEY OF THE METASEDIMENTS PRELIMINARY PALEOMAGNETIC PALEOMAGNETIC SURVEY METASEDIMENTS THE METAVOLCANICS OF OF THE THE NIAGARA NIAGARA FAULT FAULT SYSTEM SYSTEM IN IN FLORENCE FLORENCE COUNTY COUNTY WISCONSIN WISCONSIN AND Theresa M. Bodus Theresa Bodus and William F. Kean, University of Wisconsin Milwaukee, Department Department of of Geosciences, Geosciences, Milwaukee Milwaukee Wisconsin Wisconsin 53201 53201 is Florence County County in in northeastern northeastern Wisconsin Wisconsin is a region region of of a complex geology geology associated associated with the Niagara complex Niagara fault. fault. The rocks rocks Florence County are which flank the the Niagara Niagara Fault Fault system in in Florence are metaconglomerates, metagreywackes, and metavolcanics metaconqlomerates, metavolcanics to to the the north north and gneisses gneisses to to the the south. south. Isotopic Isotopic Nd ages ages of of these rocks rocks give give ages of 1.80—1.88 1.80-1.88 b.y. b.y. (Barovich (Barovich et et al., al., 1989) 1989) Paleomagnetic studies Paleomaqnetic studies were initiated initiated to aid in determining the relationships location of the relationships of of emplacement emplacement and and relative relative location the units on either side side of of the the fault fault system. system. Seven hand samples samples and and using were stepwise A.F. twenty oriented oriented cores cores were analyzed using stepwise demagnetization and thermal demagnetization thermal demagnetization demagnetization to to determine determine magnetic magnetic directions. The characteristics magnetic directions. characteristics and and magnetic The gneiss samples samples exhibited low to 10"-7 10—7 cqs, cgs, and corresponding l0-6 to low intensity, intensity, 10^-6 low magnetic magnetic susceptibilities susceptibilities of of 2.0-20.0 2.0—20.0 xx 10^-6 10-6 cgs. cgs. The rocks rocks had stronger stronger intensities intensities (i.e. (i.e. 10"-5) 10-5) to the the north of of the fault had and correspondingly strong susceptibilities 10—6. susceptibilities 70.0-310.0 70.0-310.0 xx 10^-6. The A. The A. F. demagnetization demagnetization studies indicate predominately single single removal of component magnetization after the the removal of a soft overprint. overprint. Preliminary that all the rocks are reversely indicate that Preliminary results results indicate reversely polarized and magnetic polarized and magnetic direction direction consistent with Irving's Irving's A.P.W.P. for A.P.W.P. for ages ages of of 1.81 to to 1.84 b.y. b.y. for rocks north of the the Niagara Fault. Fault. REFERENCES REFERENCES Barovich, K.M., K.M., P.3. P.J. Patchett, Patchett, Z.E. Z.E. Peterman, Peterman, and and P.K. P.K. Sims, Nd Nd isotopes isotopes and and the origin of 1.9—1.7 1.9-1.7 Ga Penokean Penokean continental continental crust crust of the Lake Lake Superior Superior region: region: G.S.A. G.S.A. Bulletin, v. 101, n. 3. Bulletin, v. 101, n. 3. p.333—338. p.333-338. 8 �PRELIMINARY PRELIMINARY MAGNETIC MAGNETIC SURVEY SURVEY OF OF THE THE NIAGARA NIAGARA FAULT FAULT SYSTEM SYSTEM IN IN FLORENCE, AND MARINETTE MARINETTE COUNTIES, COUNTIES, WISCONSIN WISCONSIN FLORENCE, FOREST, FOREST, AND Theresa M. Bodus Bodus and a n d Keith K e i t h A. A. Sverdrup, S v e r d r u p , University U n i v e r s i t y of o f Wisconsin Wisconsin T h e r e s a M. Milwaukee, Milwaukee, Department D e p a r t m e n t of o f Geosciences, G e o s c i e n c e s , Milwaukee Milwaukee The The Niagara N i a g a r a Fault F a u l t indicated i n d i c a t e d on on the t h e Wisconsin W i s c o n s i n State S t a t e Bedrock Bedrock Map Map extends e x t e n d s from f r o m northwestern n o r t h w e s t e r n Wisconsin W i s c o n s i n across a c r o s s the t h e state s t a t e to to northeastern n o r t h e a s t e r n Wisconsin. Wisconsin. This study concentrates on the the This study concentrates on northeastern n o r t h e a s t e r n portion p o r t i o n of o f the t h e fault f a u l t in i n Florence, F l o r e n c e , Forest, F o r e s t , and and Marinette M a r i n e t t e counties, c o u n t i e s , Wisconsin. Wisconsin. T o t a l field f i e l d magnetic m a g n e t i c data d a t a was was Total obtained 0.1 o b t a i n e d at at 0 . 1 mile mile s p a c i n g using using p r o t o n procession procession spacing aa proton magnetometer profiles m a g n e t o m e t e r in i n two two N-S N-S p r o f i l e s across a c r o s s the t h e Niagara N i a g a r a Fault F a u l t in in Florence 1). T h e s e profiles p r o f i l e s were were positioned p o s i t i o n e d to to F l o r e n c e county c o u n t y (Fig. ( F i g . 1). These c r o s s the t h e Niagara N i a g a r a fault f a u l t and a n d related r e l a t e d faults f a u l t s as a s they t h e y are a r e plotted p l o t t e d on on cross the ( 1 9 8 4 ) . Expected E x p e c t e d locations locations t h e Northeastern N o r t h e a s t e r n Bedrock Bedrock Geology G e o l o g y Map Map (1984). of by the t h e profiles p r o f i l e s are a r e indicated i n d i c a t e d in i n the t h e figure figure o f the t h e faults f a u l t s crossed c r o s s e d by by The b y arrows. arrows. The data d a t a is i s characterized c h a r a c t e r i z e d by b y relatively r e l a t i v e l y low l o w level, level, constant m i l e s south s o u t h of o f the t h e fault f a u l t and and c o n s t a n t values v a l u e s for f o r roughly r o u g h l y twelve t w e l v e miles several s e v e r a l high h i g h amplitude a m p l i t u d e anomalies a n o m a l i e s to t o the t h e north n o r t h suggesting s u g g e s t i n g aa fundamental f u n d a m e n t a l change c h a n g e in i n the t h e geology g e o l o g y between b e t w e e n these t h e s e two two areas. areas. Measurements M e a s u r e m e n t s of of susceptibility s u s c e p t i b i l i t y have h a v e been b e e n made made on o n seventeen seventeen samples s a m p l e s from f r o m five f i v e sites s i t e s in i n the t h e study s t u d y area a r e a to t o assist a s s i s t In i n modeling. modeling. The The values v a l u e s range r a n g e from f r o m 4.0—308.0 4 . 0 - 3 0 8 . 0 xx 10-6 1 0 - 6 cgs. c g s . Preliminary P r e l i m i n a r y modeling modeling of o f the t h e data d a t a has h a s begun, begun, and a n d results r e s u l t s of of the t h e modeling m o d e l i n g will w i l l be be presented. presented. 9 �_____ MAGNETIC PROFILE PROFILE MAGNETIC t af i lb:Hvynu e b:Hvynu a~ file ignetic dataHIGH HIGH isi s608000.0. 608000.0. gnetic data LOU i s 58020.7. ignetic data gnetic data LOW is 58020.7. il lscale l scaledeflection deflectionis i3000.0 s 3000.0gaisas. gammas. Tine Tue 0:16:50 1:27:20 13:16:41 [4:51:29 [5:39:29 Sta Sta Hag Nag _____ __________ ____— 57800. 0 57800.0 60800.0 158350.0 S 4058587.9 Ew '—i 4 FAULT N k 100 58564.8 - 6 NIAGARA FAULT NIAGARA FAULT 4 4- FAULT FAULT 4— 160 58590.8 - - FAULT FAULT L I 195 58440.6 Figure 1. 1. Magnetic survey proflle Figure Magnetic survey profile Florence county. Florence county. 10 along along Highway N Highway N and U in and U in �SIGNIFICANCE OF CONGLOMERATES, CONGLOMERATES, ARGILLITES, SIGNIFICANCE ARGILLITES, AND AND DIRTY SANDSTONES ITES DIRTY SANDSTONES IN IN THE THE BARABOO BARABOO AND WATERLOO WATERLOO QUARTZ QUARTZITES OF WISCONSIN OF SOUTHEASTERN SOUTHEASTERN WISCONSIN Bruce Brown Bruce A. Brown Wisconsin Geological and Natural History Survey 3817 Mineral Point Road Road Madison, Wisconsin 53705 Madison, Wisconsin 53705 studies of Recent studies of suggest that Wisconsin suggest that conglomerate, and that conglomerate, quartzites of to other quartzites of the the Baraboo Baraboo and and Waterloo Waterloo quartzites quartzites of of southeastern southeastern both contxiin abundant abundant beds of of poorly poorly sorted sorted pebble pebble both contain both are anomalously anomalously rich in clay clay matrix matrix when when compared compared the the "Baraboo "Baraboo interval." interval." A of the the Baraboo Baraboo quartzite quartzite by Henry Henry (1975) (1975) identified identified aa lower lower unit, unit, A study of to 200 mm thick, thick, composed 60 to 60 composed of of predominantly lenticular lenticular pebbly pebbly beds beds up up to to 0.6 0.6 mm thick. Milky quartz quartz pebbles pebbles dominate, dominate, with with lesser lesser amounts amounts of of chert, chert, hematitic hematitic thick. chert, siltstone, single single grain grain and polycrystatline polycrystalline clear clear quartz, quartz, and and chert, siltstone, quartzite. quartzite. No clearly clearly identifiable identifiable rhyolite rhyolite pebbles pebbles were were reported reported by by Henry, Henry, silicious pebbles although he suggested that some fine—grained fine-grained silicious pebbles and and scattered scattered exnbayed quartz grains grains might might be volcanic embayed quartz volcanic materials. materials. Pebble Pebble beds beds become become less less abundant upwards, upwards, and and sandy sandy beds beds contain contain up up to to 10 10 to to20% 20 clay matrix abundant (pyrophyllite and kaolinite). (pyrophyllite The Waterloo Quartzite The Waterloo Quartzite shows shows aa similar similar fining—upward fining-upward tendency, t.endency,with with pebble conglomerates conglomerates and matrix rich (sericite) lenticular pebble (sericite) sandstone sandstone common common in in the lower m) lower part of of the the section. section. Pebble Pebble conglomerates conglomeratesare arethicker thicker(up (uptoto2 2in) and more abundant at Waterloo, Waterloo, but pebble pebble lithologies lithologies are are similar. similar. The lithologic lithologic sequence sequence at Waterloo and Baraboo Baraboo are are nearly nearly identical, identical, and and may be directly directly correlatable. correlatable. Roth fine fine upwards from from pebble pebble conglomerates conglomerates to to sandstone. sandstone. Drilling records suggest suggest aa slate slate unit unit overlying overlying Waterloo Waterloo to to the the Drilling records east, correspond to to the the Seely Seely slate slate at at Baraboo. Baraboo. Ferruginous, Ferruginous, tast, which may correspond silicious silicious slate slate drilled drilled in in aa well at Watertown Watertown may he be equivalent equivalent to to Freedom Freedom Formation. well in Monona, Monona, on the east side of Madison, Madison, encountered Formation. A well encountered pebble pebble to the lower part of the section section at Baraboo Baraboo and and Waterloo. conglomerate similar t-o This rock contains types, including including possible possible volcanic volcanic contains more varied pebble types, material. material. Primary Primary sedimentary sedimentary structures structures in in the the Baraboo Baraboo and and Waterloo Waterloo Quartzites Quartzites suggest distal alluvial alluvial to fluvial depositional depositional environment environment (Henry, (Henry, to braided fluvial 1975). 1975). Consistent Consistent southward southward paleocurrents paleocurrents reported reported by by Dott Dott and and Daiziel Dalziel (1972) (1972) indicate indicate fluvial fluvial transport transport to to the the south. south. Pebble Pebble conglomerate conglomerate lenses lenses are are suggestive suggestive of of bars bars or or possibly possibly sheetfiow sheetflow deposits. deposits. Thin argillite argillite beds beds may overbank deposits. deposits. represent overbank scarcity of of rhyolite rhyolite pebbles pebbles is The scarcity is puzzling puzzling if if the the source source terrane terrane for for the the quartzites was the the 1760 1760 ma. granite granite rhyolite rhyolite terrane terrane to to the the north. north. AA possible possible quartzites explanation is is that the the rhyolite rhyolite was was eroded eroded under under severe severe weathering weathering conditions, conditions, explanation contributing contributing only only the the quartz quartz and and the the kaolinite kaolinite clays clays now now seen seen in in the the matrix. matrix. rhyolite debris may have degraded during Alternatively, rhyolite during diagenesis diagenesis to to form form the the 11 Doc. BAB0463 Doc. BAB0463 �ubiquitous matrix. ubiquit.ous matrix. Abundant metamorphic quartz and the the hematitic hematitic cherts cherts suggest that other other sediment sediment sources sources contributed contributed as as well. well. The Quartzite suggest The Barron Quartzite (Rozacky, 1987) and the Sioux quartzite (Ojakangas (Ojakangas and Weber, 1984) apparently (Rozacky, Weher, 1984) contain significantly significantly less less pebble conglomerate conglomerate and less less matrix, matrix, probably probably 'erranes and and transport transporth:istory. history. reflecting very different different source source terranes reflecting very Samples Samples from from deep deep wells wells and and unpublished geophysical geophysical data data suggest suggest that that the the quartzites of Baraboo and Waterloo are continuous over an extensive extensive area area of of southeastern Wisconsin. southeastern Wisconsin. References References Dott, Dott, R.H., Jr. and Daiziel, Dalziel, I.W.D., I.W.D., 1972, 1972, Age and correlation correlation of of the the Precambrian Baraboo Geology, vol. of Wisconsin: Wisconsin: Journal Journalof' of Geology, vol. 80, 80, Precambrian Baraboo Quartzite Quartzite of p. 552—568. 552-568. 1975, Sedimentology Sedimentology and Stratigraphy of the Henry, D.M., 1975, the Baraboo Baraboo Quartzite Quartzite of of South—Central Wisconsin: South-Central Wisconsin: M.S. M.S. Thesis, Thesis, University University of of Wisconsin—Madison, Wisconsin-Madison, 90 p. 90 p. Rozacky, Sedimentation of The Petrology and Sedimentation of the the Lower Lower Proterozoic Proterozoic Rozacky, W.V., 1987, 1987, The Barron Quartzite, Quartzite, Northwestern Northwestern Wisconsin: Wisconsin: M.S. Thesis, Thesis, University University of of Minnesota—Duluth, 94 94p. p. Minnesota-Duluth, Ojakangas, Ojakangas, R.W. and and Weber, Weber, R.E., 1984, 1984, Petrography Petrography and and Paleo:urrents Paleocurrents of of the the Lower Proterozoic Proterozoic Sioux Sioux Quartzite, Quartzite, Minnesota Minnesota and and South South Dakota, Dakota,in in D.L. D.L. Southwick, of the the Sioux Sioux Southwick, ed., Shorter Shorter contributions contributions to to the the geology geology of Geological Survey, Survey, Report of Quartzite, Minnesota Geological of Investigations Investigations 32, 32, 1—15. p. 1-15. p. 12 Doc. BAB0463 Doc. BAB0463 �GLACIAL DRIFT DRIFT GEOCHEMISTRY GEOCHEMISTRY FOR FOR STRATEGIC STRATEGIC MINERALS, MINERALS, LAKE LAKE COUNTY, COUNTY, MINNESOTA MINNESOTA DNA DNR Project Project #262 #262 Funded by Minnesota Minnesota Future Future Resources Resources Commission Commission R.L. R.L. Buchheit, K.L. K.L. Malmquist, Malmquist, and J.R. J.R. Niebuhr Niebuhr Minnesota Department of Natural Natural Resources Resources Division of of Minerals, MN 55746 Minerals, Ribbing, Hibbing, MN 55746 ABSTRACT ABSTRACT This T h i s mineral m i n e r a l diversification d i v e r s i f i c a t i o n InvestIgation i n v e s t i g a t i o n is i s funded funded by by the t h e Minnesota Minnesota Legislature L e g i s l a t u r e for f o r the t h e July J u l y 1, 1 , 1987 1987 through t h r o u g h June June 30, 30, 1989 1989 biennium. biennium. It I t is is aa p i l o t study s t u d y of o f regional r e g i o n a l geochemical geochemical survey s u r v e y methods methods for f o r Identification I d e n t i f i c a t i o n of of pilot non—ferrous, n o n - f e r r o u s , strategic s t r a t e g i c minerals m i n e r a l s in i n vegetation, v e g e t a t i o n , soils s o i l s and and surface, s u r f a c e , and and g l a c i a l deposits. d e p o s i t s . Analytical A n a l y t i c a l results r e s u l t s can c a n indicate i n d i c a t e the t h e presence p r e s e n c e of o f metallic metallic glacial mineral m i n e r a l deposits d e p o s i t s in i n bedrock b e d r o c k or o r outline o u t l i n e geochemically g e o c h e m i c a l l y anomalous locations locations suitable f o l l o w u p studies s t u d i e s or o r mineral m i n e r a l exploration. exploration. s u i t a b l e for f o r detailed d e t a i l e d followup The project p r o - j e c t area a r e a includes i n c l u d e s T.59—61N., T.59-61N., R.7—IIW., R.7-llW., in i n Lake Lake County, County, excluding e x c l u d i n g lands l a n d s Lying l y i n g within w i t h i n the t h e RWCA. BWCA. This T h i s 400 square s q u a r e mile m i l e area a r e a is is underlain u n d e r l a i n by by the t h e Duluth Dulutli Complex Complex and and North North Shore S h o r e Volcanics V o l c a n i c s which which may may host host potentially p o t e n t i a l l y economic economic quantities q u a n t i t i e s of of platinum, p l a t i n u m , PCE's, PGE's, chrome, cobalt, cobalt, titanium, is minimal with w i t h surface surface t i t a n i u m , base b a s e metals, m e t a l s , gold g o l d and and silver. s i l v e r . Outcrop O u t c r o p is cover c o v e r being b e i n g varying v a r y i n g thicknesses t h i c k n e s s e s of o f glacial g l a c i a l deposits d e p o s i t s of o f the t h e Rainy Rainy and and Superior S u p e r i o r lobes. lobes. Approximately A p p r o x i m a t e l y 1200 1200 locations, l o c a t i o n s , statistically s t a t i s t i c a l l y distributed d i s t r i b u t e d according a c c o r d i n g to to existing e x i s t i n g road r o a d access, a c c e s s , are a r e being b e i n g sampled sampled during d u r i n g the t h e 1988 1988 field f i e l d season. season. Samples 1/4-mile Intervals i n t e r v a l s with w i t h overburden o v e r b u r d e n samples samples Samples are a r e normally n o r m a l l y obtained o b t a i n e d at a t 1/4—mile being d e p t h of o f 55 feet. feet. b e i n g obtained o b t a i n e d from from 4—inch 4-inch diameter d i a m e t e r holes h o l e s augered a u g e r e d to t o aa depth Sampled media Include i n c l u d e glacial g l a c i a l overburden, o v e r b u r d e n , humus, humus, AA and and BB soil s o i l horizons horizons and of available a v a i l a b l e species s p e c i e s Including i n c l u d i n g alder, a l d e r , balsam balsam fir, f i r , Jack j a c k pine, pine, and vegetation v e g e t a t i o n of and w h i t e spruce. s p r u c e . The heavy mineral m i n e r a l concentrate c o n c e n t r a t e and —2 -2 micron micron and black b l a c k and and white (clay) ( c l a y ) fraction f r a c t i o n are a r e assayed a s s a y e d from from the t h e glacial g l a c i a l overburden o v e r b u r d e n samples. samples. Ni, Ni, Samples an art!being b e i n g analyzed a n a l y z e d for f o r Pt, P t , Pd, Pd, Cr, Cr. Au, Au, Ag, Ag, Co, Co, 1, Y, T102, TiO,, Cu, Cu, Pb, Zn, Zn, RI, Rl, Sb, S b , Se, S e , Te, Te, As, A s , MgO, MgO, Fe203. Fe203. Results R e s u l t s of o f this t h i s investigation i n v e s t i g a t i o n are a r e available a v a i l a b l e to t o the t h e public p u b l i c on open o p e n file file with w i t h the t h e Minnesota M i n n e s o t a Department Department of o f Natural N a t u r a l Resources, R e s o u r c e s , Division D i v i s i o n of o f Minerals, Minerals, summary report r e p o r t will w i l l be b e Issued i s s u e d by by DNR—Minerals DNR-Minerals in i n Hibbing, H i b b i n g , Minnesota. Minnesota. AA summary after a f t e r July J u l y 1, 1 , 1989. 1989. 13 �Precambrian Precambrian TTerranes e r r a n e s beneath beneath Northern N o r t h e r n Lake Lake Michigan Michigan D e f i n e d by by Seismic Seismic and and Gravity G r a v i t y Analysis Analysis Defined William W i l l i a m F. F. Cannon, Cannon, Klaus K l a u s J. J. Schulz, Schulz, U.S. U.S. Geological G e o l o g i c a Survey l SurveyReston, Reston, VA, VA, 22092; William 22092; W i l l i a m J. J. Hinze, Hinze, Purdue Purdue University, U n i v e r s i t y , West West Lafayette, L a f a y e t t e , IN, IN,47907; 47907; and and Alan G. Green, Green, Geological G e o l o g i c a l Survey Survey ofo fCanada, Canada, Ottawa, Ottawa, Ontario, O n t a r i o ,K1A K I A0Y3 OY3 A l a n G. A seismic s e i s m i c reflection r e f l e c t i o n profile p r o f i l along e alona g line a 1 i nabout e about 290 l o n gfrom f r o mnear near A 290 kmkmlong the Mackinac t h e Straits S t r a i t sofof Mackinactot onear n e aManitowoc, r Manitowoc, Wisconsin, Wisconsin, was was ccollected o l l e c t e d during d u r i n g the the 1986 experimenti in 1986 GLIMPCE GLIMPCE s eseismic i s m i c experiment n nnorthern o r t h e r n and and western western Lake Lake Michigan. Michigan. Data Data were ont the were recorded r e c o r d e d ffor o r 20 20 seconds seconds t oto pprovide r o v i d e iinformation n f o r m a t i o n on h e ffull u l l thickness thickness of the crust and the uppermost mantle. o f t h e c r u s t and t h e uppermost mantle. The The line l i n ecrosses c r o s s e sseveral s e v e r a lPrecambrian Precambrian terranes t e r r a n e s that t h a tare a r eexposed exposed and and well well studied about 100 km to the west in northern Michigan and Wisconsin. s t u d i e d about 100 km t o t h e west i n n o r t h e r n M i c h i g a n and Wisconsin. These These terranes be pprojected t e r r a n e s can c a n be r o j e c t e d oonto n t o t hthe e sseismic e i s m i c l iline n e ((Figure F i g u r e 11) ) wwith i t h tthe h e aid a i d of of regional r e g i o n a l gravity g r a v i t and y andmagnetic magneticmaps. maps. A A gravity g r a v i t ymodel model along a1 ong the t h e seismic seismic profile interpretation. p r o f i l efurther f u r t h e constrains r c o n s t r a i n sthe t h egeologic g e o l o g i c interpretation. At A t the t h e north n o r t h end end of o f the t h e line, l i n e , the t h ewestern w e s t e r n half h a l f of of the t h eMidcontinent M i d c o n t i n e n t Rift Rift basin b a s i n is i sshown shown by by strong s t r o n g continuous c o n t i n u o u s rreflectors e f l e c t o r s from from basalt b a s a l t flows. flows. Reflectors Ref1 e c t o r s can GaGaini basement can be be traced t r a c e d to t oabout about20 20km km depth. depth. The The rift r i f formed t formedata 1.1 t 1.1 n basement rocks Very high h i g h densities d e n s i t i e s inferred inferred b e l i e v e dtot obebemostly m o s t l yArchean Archeangneisses. gneisses. Very r o c k s believed for f o rthe t h elower 1owercrust c r u s suggest t suggest abundant abundant rrift—related i f t - r e 1 a t e d mafic m a f i c intrusive i n t r u s i v e rocks. rocks. The gneissesappear appearonon The Archean Archean gneisses t h the e s eseismic i s m i c r erecord c o r d asasr i richly c h l y rreflective eflective material by aa mu1 multitude m a t e r i a1 dominated domi n a t e d by t i t u d e oof f short, s h o r t , subhorizontal s u b h o r i z o n t a l reflections. r e f 1 e c t ions. AA dense andsstrongly much dense and t r o n g l y rreflective e f l e c t i v e lower l o w e r crustal c r u s t a llayer, l a y e ras , as much as as 20 20 km km tthick, hick, isi sprobably p r o b a b l y granulitic g r a n u l i t i cgneiss. gneiss. The The Moho, Moho, ggenerally e n e r a l l y llocated o c a t e d aatt the t h e rather rather sharp froms tstrongly sharp change change from r o n g l y r reflective e f l e c t i v e lower l o w e r crust c r u s t to t o acoustically a c o u s t i c a l l ytransparent transparent mantle, mantle, dips d i p s gently g e n t l ynorthward n o r t h w a r d toward t o w a r d the t h e Midcontinent M i d c o n t i n e n t RRift, i f t , probably p r o b a b l y as as aa result reaches a depth about 5555kmkmbeneath g , and reaches a d e p tof h of about beneath the the r e s u l tofo flexural f f l e x u r loading, a l l o a d i nand rrIi fft.t . F a r t h e r south, south, the t h e Niagara N i a g a r a fault f a u l t can can be be projected p r o j e c t e d onto o n t o tthe h e profile p r o f i l efrom from Farther the wherei tit is t h e faultss f a u l t ' sexposure exposure ini nnorthern n o r t h e r nMichigan M i c h i g a n and and Wisconsin, Wisconsin, where i s aa steeply s t hsuture e s u t u rbetween e betweenthe t h eArchean Archean s t e e p l y dipping d i p p i n gfault f a u lzone t zonethat t h arepresents t r e p r e s e n tthe craton c r a t o n on on the t h e north n o r t hand and an an Early E a r l y Proterozoic P r o t e r o z o i c volcanic v o l c a n i c arc, a r c ,the t h eWisconsin Wisconsin magmatic No reflections r e f l e c t i o n s can can be be directly d i r e c t l yascribed a s c r i b e d to t othe t h eNiagara Niagara magmatic terrane. t e r r a n e . No fault, location r e f l e c t i v echaracter character f a u l t ,but b uits t i tgeneral s general l o c a t i ois n marked i s markedbybya achange change in i n reflective of of the t h e crust. c r u s t . The The arc a r c terrane t e r r a n e has has abundant abundant ssubhorizontal u b h o r i z o n t a l reflections reflections throughout t h r o u g h o u t the t h e crust, c r u s t , with w i t hthe t h eexception e x c e p t i o nofo fa afew fewnearly n e a r l ytransparent t r a n s p a r e n tareas areas that t h a t we we interpret i n t e r p r e t as as granitic g r a n i t i c intrusive i n t r u s i v erocks. rocks. Gravity G r a v i t y analysis a n a l y s i s indicates indicates that p r o b a b l ya acombination combination t h a tthe t h eterrane t e r r a n eis idominated s dominatedby bylow l o wdensity d e n s i t yrocks, rocks,probably of An intensely intensely o f caic—alkaline c a l c - a l k a l i n e volcanics v o l c a n i c s and and related r e l a t e d granitoid g r a n i t o i drocks. rocks. An reflective r e f l e c t i v elayer l a y eabout r about6 6km km thick t h i c kata the t t h base e baseofo the f t h earc a r terrane c t e r r a n eappears appears to wei ninterpret TheMoho Moho t ohave have unusually u n u s u a l l y hhigh i g h ddensity, e n s i t y , and and we t e r p r e t iitt as as granulite. g r a n u l i t e . The isi sananessentially 40 40 kmkm deep deepbeneath beneath the t h e arc a r c terrane. terrane. e s s e n t i a l l flat y f l surface a t s u r f a about c e about The The southern s o u t h e r n t third h i r d of o f the t h e line l i n econtains c o n t a i n s an an intensely i n t e n s e l y reflective r e f l e c t i v elower lower crustal c r u s t a llayer l a y eabove r above aalargely l a r g e l ytransparent t r a n s p a r e n tmantle. mantle. The The reflective r e f l e c t i v e crust c r u s t isi s tentatively gneisses t e n t a t i v e l yidentified i d e n t i f i as e d Archean as Archean gneissesaccreted a c c r e t e dtot the o t hsouthern e s o u t h e r nmargin margin of o fthe t h earc a r terrane c t e r r a nduring e d u r i nthe g t hPenokean e Penokeanorogeny orogeny about about 1,850 1,850 mil m i llion l i o nyears years ago. ago. Approximately A p p r o x i m a t e l y t hthe e l olower w e r h half a l f oof f tthe h e ccrust r u s t is i s especially e s p e c i a l l y reflective reflective and and has has high h i g h density. d e n s i t y . As As with w i t h the t h e Archean Archean ccrust r u s t tto o the t h e north, n o r t h , we we interpret interpret this t h i sas aslower l o w e r crustal c r u s t a l granulitic g r a n u l i t i cgneiss. gneiss. The The Moho Moho ddips i p s gently g e n t l ynorthward northward beneath beneath this t h i s terrane t e r r a n eand and appears appears to t o have have an an abrupt a b r u p t ooffset f f s e t near near the t h e contact contact with T h i sunusual unusual Moho Moho offset o f f s e tmay may be bea a w i t hthe t h eWisconsin WisconsinMagmatic Ma m a t i c terrane. t e r r a n e . This vestige v e s t i g eofofdeeply d e e p l ysubducted sub u c t e d crust. crust. 2 14 �01 IS I0• U •50- N UQAL 01 - — - --- — - - - — --Z are equal for velocity of 6 km/s. -Archan —- Ns,th.In A,ch.an T.u.n. baIfloIb ) --- akaIajcaana,.jo.d;.:- — ( Garhc ' ——— I — p00 T.rrans — $outh.,n A,ch.an —0 -15 10 0 I' 0 II rl000 $ NT SHOT Agch- Q_—- - - --- -- ---T -—— WIc.nIn M.gm.tlc T.rr.n. 0 cz u u c m u Em-.? a s aJ a m c aJ a a u > A n c L . a aJ m w c.- m u m aJ a = a h0 c UIN c a 0%- & 2 3 w c .F -02 x u a- aJ m > c a u V - L C E - m a +- w u I v c c w a a 02 z -In - u L m A 0 *- "P .? k.7 0 m c . - & E m 3 L Figure 1. Schematic interpretation of line drawing of GLIMPCE line H in northern Lake Michigan and inferred subsurface terranes interpreted from seismic and gravity analysis. Dashed thrust faults are schematic and consistent with tectonic models for on—land geology west of the line. MRS = Midcontinent rift system. M = Moho. Shot spacing is 62.5 m. Horizontal and vertical scales — 0 I.00 ,- L a J 7 . lk ? u L aJ O K u L . . a?.- m c m m aJ u a u o a �Paleomagnetic Paleomagnetic Studies Studies of of Wausau Wausau Syenite Syenite Complex Complex and and Wissota Wissota Dam Dam Mafic Mafic Dike Dike Lung Lung S. S. Chan Chan and and Paul Paul E. E . Myers Myers Department Department of of Geology, Geology, University University of of Wisconsin-Eau Wisconsin-EauClaire Claire Eau Eau Claire, Claire, WI WI 54701 54701 Remanent Remanent magnetism magnetism of of the the Wausau Wausau syenite syenite complex complex in in Marathon Marathon County, Councy, Wisconsin, Wisconsin, shows shows aa westerly westerly declination declination and and yields yields aa virtual virtual geomagnetic geomagnetic pole pole similar similar to to the the 1.1 1.1 Ga Ga paleomagnetic paleomagnetic pole pole of of the the North North American American craton craton [Zich [Zich et et al., al., 1986] 19861. In In addition, addition, the the paleomagnetic paleomagnetic data data reveal reveal multiple multiple magnetic magnetic components. components. The The magnetization magnetization history of of the the Wausau Wausau syenite syenite can can be be worked worked out out by by comparing comparing the the magnetic magnetic results results with with paleomagnetic paleornagne tic directions directions from from mafic mafic dike dike swarms swarms in in the the Southern Southern Superior Superior Province Province and and aa mafic mafic dike dike at at Wissota Wissota Dam Dam in in Chippewa ChippewaFalls, Falls,Wisconsin. Wisconsin. . The The Wausau Wausau syenite syenite complex complex of of Central Central Wisconsin Wisconsin represents representsa apost-Penokean, post-Penokean, anorogenic anorogenic intrusion intrusion which which is is probably probably coeval coeval with with the the Wolf Wolf River River granite granite [LaBerge [LaBerge and and Myers, Myers, 1984). 19841. The The granite granite and and syenite syenite were were intruded intruded by by aa swarm swarm of of east-northeast east-northeast striking striking mafic mafic dikes. dikes. Rubidium-strontium Rubidium-strontium measurements measurements of of two CaGa [Van Schrnus two samples samples from from Wausau Wausauyielded yieldeda aminimum minimumage ageofof1.52 1.52 [Van Schmusetetal., al., 1975]. 19751. Since Since the the Proterozoic Proterozoic polar polar wander wander curve curve for for North North America America Craton Craton contains contains aa gap gap between between 1.60 1.GO Ga Ga and <lnd1.45 1.45Ga, Ga, aa paleomagnetic paleoinagnetic study study of of the the Wausau Wausau syenite syenite may may help help to to fill fill the the gap gap in in the the polar polar wander wander path. path. 00 The The Wausau Wausau syenite syenite was was sampled sampled at at four four locations locations and and demagnetized demagnetized by by both both alternating alternating field field and and thermal thermal techniques. techniques. Kirschvink's Kirschvink's [1980) [I9801 procedure procedure for for vecroral vectoral analysis analysis of of paleomagnetic paleomagnetic data data was was used used to to extract extract linear linear segments segments from from the the results results of of measurements. measurements. AA linear 1inear segment segment is is defined defined here here as as aa set setof ofthree three or or more more consecutive consecutive points points in in aa demagnetization demagnetization curve curve that that show show less less than than 10° lo0 angular angular deviation deviation about about their their mean meandirection. direction. Each Each linear linear segment segment is is considered considered as as aa magnetic magnetic component. component. In In Fig. Fig. 1,1 , the the magnetic magnetic components components of of all all samples samples are are plotted plotted and and contoured contoured on on an an equal-area equal-areaprojection. projection. 270 180 180 Fig. Fig. 1 Contoured Contoured distribution distribution of of magnetic magnetic components components in in Wausau Wausau syenitesamples samplesatat1 1per per1%1%area. area. syenite 1 We We define define aa magnetic magnetic component component cluster cluster as as aa direction direction that that contains contains three three or or more more components components per per 1% 1% of of stereonet stereonet area. area. Magnetic Magnetic components components from from the the Wausau Wausau syenite syenitecomplex complexform formthree threemagnetic magnetic component componentclusters clusters(Fig. (Fig.1), I), the the most most prominent grominent of of which which (A) ( A ) shows showsaadirection directionof ofD—266°, D-266', 1—14° 1-14' and and aa vgp vgp at at lat—2 lat-2 , long—l72°W. 1 0 n ~ - 1 7 2 ~ ~A.A second second cluster cluster (B) (B) has hasa adirection directionofofD—347°, D-347O, 1—57° 1-57' and This magnetic component component cluster clusterprobably probably and aa vgp vgp at atlat—77°, lat-77O,long—147°E. 1 0 n ~ - = 1 4 7 ~This ~ . magnetic represents represents aa present-field present-fieldoverprint overprint because because of of the thehigh highvgp vgplatitude. latitude. AA third third magnetic magnetic component component cluster cluster (C) (C) shows shows aa direction directionD—62°, D-62'. 1-83' and and 1—83° gives gives aa vgp vgpatatlat—50° lat-50' and andlong—71°W. long-71°w This This vgp vgp lies lies on oncourse course with with the the , 16 �the middle Proterozoic Proterozoic polar America extension of the polar wander wander path path of the North America and probably probably represents represents the primary component acquired acquired at at the the time time of of Craton and intrusion. intrusion. The The magnetic magnetic component component A was likely acquired acquired during during the rhe was likely Keweenawan Keweenawan magmatic magmatic event. event. Ilmenite in the syenite is probably an an oxidation oxidation of of aa titanomagnetite. titanomagnetite. Previous paleomagnetic in the the paleomagnetic studies studies of of mafic mafic dikes in Southern Superior Superior Province Province have have also also yielded yielded virtual virtual geomagnetic geomagnetic poles poles that that Southern lie within the the polar polar wander wander path path (Logan (Logan Loop) Loop) for North North America America during during Keweenawan times times 1.2-1.0 1.2-1.0Ga Ga [Green [Green et et al. al., 1987]. 19871. Keweenawan , The 50 50 mm mafic mafic dike dike below below Wissota Wissota Dam in in Chippewa Chippewa Falls Falls represents represents aa shallow shallow intrusion intrusion into into foliated foliated trondjemite trondjemite of of late-middle late-middleProteroProterozoic Although zoic age. age. Although the the dike dike is is symmetrically symmetrically zoned zoned with with regard regard to to composition and grain size, composition and grain size, numerous inclusions inclusions of of very very coarse coarse plagioclase plagioclase (An55) ( ~ n ~and ~ )norite norite are are confined to to aa 2-rn 2-m zone along along the the north north wall. wall. The The 34-rn 34-m core of the the dike dike consists consists of of ilmenite-bearing ilmenite-bearing clinopyroxene-olivine clinopyroxene-olivine gabbro. gabbro. Grain Grain size size diminishes diminishes outward outward to to aa highly highly altered aphanicic clinopyroxene altered aphanitic clinopyroxene basalt. From basalt. From the the center outward outward the dike dike is is symmetrically symmetrically altered, altered, first first to to epidote epidote replacements replacements of of plagioclase, plagioclase, then then to to chloritechloriteepidote epidote replacements replacements of of pyroxene pyroxene accompanied by conversion of accompanied by conversion of olivine olivine to to talc talc and and serpentine. serpentine. Biotite, Biotite, possibly possibly as as aa replacement replacement of of chlorite, chlorite, appears appears about about 66 meters meters from The from each each contact. contact. The ironirontitanium titanium mineral mineral along along the the dike dike margin margin is is aa titanornagnetite titanomagnetite highly highly altered altered to to hematite. hematite. 0 90 1 80 Fig. 2 2 Nrm directions directions in in Wissota Dam Dam Fig. mafic dike dike and and alpha-95 alpha-95 confidence confidence circles circles (triangles (triangles : sites sites 11 and and 2, 2, circles: circles: site site 3, 3 , squares squares : site site 4). [A). : : core samples samples were were collected collected at four four distances distances from from the the northern northern Oriented core dike dike margin: margin: 10 10 cm, cm, lm, lm, 7m, 7m, and and 25m. 25m. The The samples samples were were demagnetized demagnetized with with alternating alternating field field technique technique and and linear segments segments were determined determined by vectoral vectoral analysis. analysis. As shown shown in in Fig. Fig. 2, 2 , the the remanent remanent magnetism directions of of the the center We center sites sites differ differ significantly significantly from from that that of of the the marginal marginal sites. sites. We interpret interpret such such different different directions directions as as aa result result of different different magnetic magnetic mineralogy. mineralogy. The The differentiation differentiation of of the dike rock may signify signify difference difference in in crystallization temperature, temperature, with with inagnetite magnetite formed along the the dike dike crystallization formed earlier along margin, margin, and and the the ilmenite ilmenite of of the the core core crystallized crystallized later later at at lower lower temperature. The temperature. The nrm nrm of of the the finer-grained finer-grained marginal marginal rocks, rocks, therefore, therefore, may may represent represent an an early early acquisition acquisition at at the the time time of of intrusion. intrusion. Considering the the remanent remanent magnetism of the marginal zone zone of the the dike dike an an early early Considering acquisitionl the the two two marginal marginal sites sites yield yield aa vgp vgp at at lat—-2.2°, lat--2.2O, long—163.87°E. acquisition, long-163.87O~. As As shown shown in in Fig. Fig. 3, 3 the vgp falls falls near the the polar polar wander wander path path at at 1.0 1 .O Ga. Ga. AA comparison of of the the vgp vgp coordinates coordinates with previous results obtained from from dike dike 17 �swarms in in the the Southern Southern Superior Superior Province Province suggests suggests aa relatively relatively younger younger swarms intrusion age age of of the the dike dike at at Wissota Wissota Dam. Dam. intrusion Our preliminary preliminary inferences inferences from from the the Our paleomagnetic studies studies of of the the Wausau Wausau paleomagnetic syenite and and the the mafic mafic dike dike at at syenite Wissota Dam may be summarized as Wissota Dam may be summarized as follows : first , the three magnetic follows: first, the three magnetic components present present in in the the Wausau Wausau components syenite represent (1) a primary syenite represent (1) a primary component acquired acquired at at the the time time of of component intrusion, (2) a present field intrusion, present (2) a field overprint, and and (3) aa remagremagoverprint, (3) netization during during the the Keweenawan Keweenawan netization magmatic event. Secondly, the magmatic event. Secondly, the remanent magnetism directions in remanent magnetism directions in the mafic dike near Wissota Dam the mafic dike near Wissota Dam reflect different magnetic reflect different magnetic mineralogy of the dike rocks. mineralogy of the dike rocks. Thirdly, the mafic dike could have Thirdly, the mafic dike could have been emplaced later than he mafic been emplaced later than the mafic dike swarms swarms in in dike Superior Province. Superior Province. the the 0 Nh I _--_--J Fig. 33 Comparison Comparison of of vgps vgps of of Wausau Wausau Fig. syenite (S) (S) and and Wissota Wissota Dam Dam mafic mafic syenite dike (D) with Southern Superior dike (D) with Southern Superior paleomagnetic data data summarized summarized by by paleomagnetic Green et al. [1987]. Green et al. [1987). Southern Southern References cited cited References Green, J.C., J . C. , T.J. T.J . Bornhorst, Bornhors t , et e t al., a1 . , Keweenawan Keweenawan dikes dikes of of the the Lake Lake Superior Superior Green, region: evidence of evolution of the middle Proterozoic midcontinent rift region: evidence of evolution of the middle Proterozoic midcontinent rift of North America, in H . C . Halls and W.F. Fahrig (eds): Mafic Dyke Swarms, of North America, in H.C. Halls and W.F. Fahrig (eds): Mafic Dyke Swarms, 289-316, Geol. Geol. Asso. Asso. Can. Can. Spec. Spec. Paper Paper 34, 34, 1987. 1987. 289-316, Kirschvink, J.L., J.L., The The least-squares least-squares line line and and plane plane and and the the analysis analysis of of Kirschvink, paleomagnetic data, Geophys. Jour. R. Astr. SOC., 62, 699-718, 1980. paleomagnetic data, Geophys. Jour. R. Astr. Soc., 62, 699-718, 1980. LaBerge, G.L., G.L., and and P.E. P.E. Myers, Myers, Two Two early early Proterozoic Proterozoic successions successions in in LaBerge, central Wisconsin and their tectonic significance, Geol. SOC. Amer. central Wisconsin and their tectonic significance, Geol. Soc. Amer. Bull., 95, 95, 246-253, 246-253,1984. 1984. Bull. , Van Schmus, Schmus, W.R., W.R., L.G. L.G. Medaris, Medaris, and and P.O. P.O. Banks, Banks, Geology Geology and and age age of of the the Van Wolf River River Batholjth, Batholith, Wisconsin, Wisconsin, Geol. Geol. Soc. SOC. Amer. Amer. Bull., Bull., 86, 86, 907-914, 907-914, Wolf 1975. 1975. Zich, C., C., L.S. L.S. Chan, Chan, and and P.E. P.E. Myers, Myers, Preliminary Preliminary paleomagnetic paleomagnetic results results Zich, from the the Wausau Wausau syenite syenite complex, complex, Central Central Wisconsin, Wisconsin, EOS EOS Trans., Trans., 67, 67, from 266, 1986. 1986. 266, 18 �NEW NEM BOUGUER BOUGUER GRAVITY GRAVITY ANOMALY ANOMALY MAP MAP OF OF MINNESOTA MINNESOTA Val W. W. Chandler Chandler and a ~ Bryan d Bryac D. D. Schaap, S c h a a p I Minnesota Geological G e o l o g i c a l Survey, Survey, 2642 MN 2642 University U n i v e r s i t y Avenue, Avenue, St. S t . Paul, P a u l I MN 55114—1057 551 14-1057 The Minnesota i s preparing p r e p a r i n g aa new new Bouguer Bouguer gravity gravity Minnesota Geological G e o l o g i c a l Survey Survey is anomaly 1 : SOO,OOO) , marking marking the t h e completion c o m p l e t i o n of o f aa anomaly map map of o f Minnesota Minnesota (scale ( s c a l e 1:500,000), state—wide s t a t e - w i d e gravity g r a v i t y surveying s u r v e y i n q program program that t h a t began began over o v e r 20 20 years y e a r s ago a g o with w i t h the the goal to acquire a c q u i r e data d a t a at a t aa spacing s p a c i n g of of 1.6 1.6 to t o 3.2 3.2 km. km. This T h i s program program was was iniinig o a l to tiated t i a t e d by by P.K. P.K. Sims, Sims, former former director d i r e c t a r of o f the t h e MGS, MGS, and and the t h e first f i r s t surveying surveying was conducted between 1965-1969 under supervision of R.J. w a s conducted between 1965-1 969 u n d e r s u p e r v i s i o n o f R. J. Ikola. Ikola I n the the In following f o l l o w i n g years y e a r s surveying s u r v e y i n g continued c o n t i n u e d under under supervision s u p e r v i s i o n of o f G.E. G. B. Morey, Morey, G.A. G. A. Durfee, D u r f e e , L.D. L.D. McGinnis, McGinnis, C.P. C.P. Ervin, E r v i n , R.J. R. J. Horton, Horton, and and V.W. V.W. Chandler. C h a n d l e r . The The data were published as a series of 1:250,000—scale sheets d a t a were p u b l i s h e d a s a series of 1 : 2 5 0 1 0 0 0 - s c a l e s h e e t s between between 1968 1968 and and 11987. 987. A A few few oolder l d e r data d a t a sets s e t swere were incorporated i n c o r p o r a t e d that t h a twere were determined d e t e r m i n e d to to be be suitably s u i t a b l y accurate. a c c u r a t e . Over Over tthe h e llast a s t several s e v e r a l years y e a r s additional a d d i t i o n a lcoverage c o v e r a g e has has been b e e n acquired a c q u i r e d within w i t h i n several s e v e r a l of of the t h e published p u b l i s h e d sheets, s h e e t s , and and the t h e gravity g r a v i t y datadatabase, b a s e , which which had had numerous numerous eerrors r r o r s and and ommissions, ommissionsI hhas a s bbeen e e n ccarefully a r e f u l l y edited edited and 860 ggravity and corrected. c o r r e c t e d . The m e ffinal i n a l version v e r s i o n contains c o n t a i n s 55, 55,860 r a v i t y sstations, tationsI e q u a t i n g to to an an average a v e r a q e station s t a t i o n spacing s p a c i n g of of about a b o u t 2.4 2.4 km km state s t a t e wide. wide. The The equating edited e d i t e d data d a t a were were reduced reduced using u s i n g aa density d e n s i t y of o f 2.67 2.67 grams grams per p e r cubic c u b i ccentimeter centimeter and gravity 1967 1 . and the t h e 1967 1967 g r a v i t y formula f o r m u l a (International ( I n t e r n a t i o n a lAssociation A s s o c i a t i o nof o fGeodesy, Geodesy I 1967). . The news state mapi sis ccontoured The new t a t e map o n t o u r e d a at t aa 11-milligal - m i l l i g a l interval i n t e r v a l and and is i sbased based on on gridded gridded data m i ~ i m u mcurvature. c u r v a t u r e . This This d a t a generated g e n e r a t e d at a t aa 1.5-km 1.5-km interval i n t e r v a l using u s i n g minimum map map will w i l l be be aa major major improvement improvement over o v e r the the previously p r e v i o u s l y published p u b l i s h e d state s t a t e map map (Craddock and others, o t h e r s , 1970), 19701, which was primarily p r i m a r i l y based based on on stations s t a t i o n s spaced spaced (Craddock 10 1 0 - m i l l i g a l contour c o n t o u r interval. i n t e r v a l . The The gridded g r i d d e d data d a t a can can 1 0 km km apart a p a r t and and used used aa lO—milligal also a l s o be be used used in l n aa wide wide variety v a r i e t y of of computer computer enhancement enhancement options, o p t i o n s , including including second second vertical v e r t i c a l derivative. derivative. The The high h i g h resolution r e s o l u t i o n of o f the t h e new new state s t a t e map map presents p r e s e n t s aa greatly g r e a t l y improved improved perspective p e r s p e c t i v e on Archean Archean and and Proterozoic P r o t e r o z o i c structures. s t r u c t u r e s . In I n the t h eArchean Archean greenstone-granite g r e e n s t o n e - g r a n i t e terrane t e r r a n eof o fnorthern n o r t h e r nMinnesota, M i n n e s o t a I northeast—striking n o r t h e a s t - s t r i k i n g gravity gravity highs m i l l i g a l s I delineate d e l i n e a t e the the h i g h s and and lows, lows, which which differ d i f f e r in i n amplitude a m p l i t u d e by by 30—60 30-60 milligals, metavolcanic Second vertical v e r t i c a l derivative derivative m e t a v o l c a n i c and and granitic g r a n i t i c belts, b e l t s , respectively. respectively Second enhancement i s extremely e x t r e m e l y useful u s e f u l for f o r picking p i c k i n g contacts, c o n t a c t s I which which enhancement of o f these t h e s e data d a h is are a r e commonly commonly traced t r a c e d by by the t h e zero z e r o contour, c o n t o u r , and and for f o r recognizing r e c o g n i z i n g subunits subunits within w i t h i n the t h e granitic g r a n i t i cand andmetavolcanic m e t a v o l c a n i c belts. b e l t s . In I n the t h e Archean Archean gneiss g n e i s s terrane terrane of gravity o f southwestern s o u t h w e s t e r n Minnesota, Minnesoh, g r a v i t y highs h i g h s and and lows lows delineate d e l i n e a t e mafic m a f i c and and felsic twotwonorthwest—striking to f e l s i cunits, u n i t srespectively, , r e s p e c t i v e l yand , and n o r t h w e s t - s t r i k i n g lineaments l i n e a m e n t s appear a p p e a r to r e f l e c t major f a u l t z o n e s t h a t d i v i d e t h e t e r r a n e i n t o t h r e e d i s t i n c t blocks. b l o c k s . Over Over the t h e Early E a r l y Proterozoic P r o t e r o z o i c Penokean Penokean f ofold-and-thrust l d - a n d - t h r u s t bbelt e l t iin n easteastcentral c e n t r a l Minnesota, Minnesota, an a n arcuate a r c u a t e belt b e l tof o fgravity g r a v i t yanomalies a n o m a l i e s extends e x t e n d s through through southwestern s o u t h w e s t e r n Carlton C a r l t o n County, County, central c e n t r a l Crow Crow Wing Wing County, County, and and into i n t o northnorthcentral c e n t r a l Stearns S t e a r n s County; County; iit t is i s believed b e l i e v e d to t o trace tracethe t h eSerpent S e r p e n t Lake Lake structural structural discontinuity d i s c o n t i n u i t yof o fSouthwick Southwick and and others o t h e r s (1988). ( 1 988 1 S o u t h e a s t of o f this t h i smajor major Southeast structural s t r u c t u r a lfront, f r o n t ,a asomewhat somewhat iirregular r r e g u l a r distribution d i s t r i b u t i o n of o f gravity g r a v i t yhighs h i g h s and and lows magmatic terrane t e r r a n ecomposed composed of o f Penokean Penokean iintrusions n t r u s i o n s of of lows characterizes c h a r a c t e r i z e sa amagmatic varying v a r y i n g compositions composi t i o n s and and gneissic g n e i s s i c rocks r o c k s •. In I n the t h e Middle Middle Proterozoic Proterozoic M i d c o n t i n e n t rrift i f t system, s y s t e m , the t h e gravity g r a v i t ydata d a mdelineate d e l i n e a t ethe t hDouglas e Douglasand andPine Pine Midcontinent faults thenorthwestern n o r t h w e s t e r n margin margin oof f the t h e St. S t . Croix C r o i x horst h o r s tand anddefine define f a u l t salong a l o n gthe several Complex. ts s e v e r a lunits u n i t swithin w i t h i the n t hDuluth e Duluth Complex. Thus Thus tthe h e new new sstate t a t e map map and and iits . reflect major fault zones that divide the terrane into three distinct . 19 �digital d i g i t a l data d a t a base b a s e should s h o u l d be b e extremely e x t r e m e l y useful u s e f u l for f o r geologic g e o l o g i c studies s t u d i e s and and mineral m i n e r a l exploration e x p l o r a t i o n for f o r many many years y e a r s into into the t h e future. future. The The gravity g r a v i t y surveying s u r v e y i n g program program has h a s been b e e n funded funded by by the +he Minnesota Minnesota Iron Iron Range Range Resources R e s o u r c e s and and Rehabilitation R e h a b i l i t a t i o n Board, Board, the t h e Minnesota M i n n e s o t a Department D e p a r t m e n t of of Natural the Minnesota Future F u t u r e Resources R e s o u r c e s Commission Commission (formerly ( f o r m e r l y the N a t u r a l Resources, R e s o u r c e s , the t h e Minnesota Legislative L e g i s l a t i v e Commission Commission on on Minnesota Minnesota Resources), R e s o u r c e s ) , and and the t h e U.S. U.S. Geological Geological Survey. being Minnesota b e i n gfunded fundedby bythe the Minnesota S u r v e y . Publication P u b l i c a t i o n of o f the t h estate s t a t map e mapisi s Future F u t u r eResources R e s o u r c e sCommission. Commission. References R e f e r e n c e s Cited: Cited : Craddock, C r a d d o c k , C., C., Mooney, Mooney, H.M., H.M. ,and and Kolehmainen Kolehmainen V., V., 1970, 1970, gravity g r a v i t y map map of o f Minnesota Minnesota and and northwestern n o r t h w e s t e r n Wisconsin: Wisconsin: S i m p l e Bouguer Bouguer Simple M i n n e s o t a Geological Geological Minnesota Survey S u r v e y Miscellaneous M i s c e l l a n e o u s Map Map M—10, M-10, scale s c a l e 1:1,000,000. 1: 1 , 0 0 0 , 0 0 0 . International I n t e r n a t i o n a l Association A s s o c i a t i o n of o f Geodessy, G e o d e s s y , 1967, 1967, Geodetic G e o d e t i c reference r e f e r e n c esystem, system, 1967: 1 967: International I n t e r n a t i o n a l Association A s s o c i a t i o n of o f Geodesy Geodesy Special S p e c i a l Publication P u b l i c a t i o n 3, 3 , 115 1 1 5 p. p. Southwick, P.L., 1988, S o u t h w i c k , D.L., D.L., Morey, Morey, G.B., G.B., and and McSwiggeri, McSwiggen, P.L., 1 9 8 8 , Geologic G e o l o g i c map map (scale ( s c a l e 1:250,000) 1 : 2 5 0 , 0 0 0 ) of of the t h e Penokean Penokean orogen, o r o g e n , central c e n t r a l Minnesota, M i n n e s o t a , and and accomaccompanying 37, p a n y i n g text: t e x t : Minnesota Minnesota Geological G e o l o g i c a l Survey S u r v e y Report R e p o r t of o f Investigations I n v e s t i g a t i o n s37, 25 2 5 p. p. 20 �MAPS OF THE THE LAKE HURON REGION MAGNETIC AND GRAVITY ANOMALY MAPS S. Dwiht J. Hinze2, Hinze2, Pierre Pierre Keating1, Keating 1, DwiahtDads1, ~ods', William William J. and James James G. G. Smith3 smith3 1Geological Survey '~eolo~ical Survey of of Canada, Canada, 1 1 Observatory Observatory Cr., Cr., Ottawa, Ottawa, Ont. Ont. Canada K1AOY3 KlAOY3 2Dept. 2 ~ e p t . of Geological Sciences, Sciences, Purdue Purdue Univ., Univ. , West West Lafayette, Lafayette, IN 47907 47907 3Nobil '~obil Oil Oil Corp., Corp., 4045 4045 N.W. N. W. 64th 64th St., St., Suite Suite 200, 200, Oklahoma Oklahoma City, City, OK 73116 73116 A 1:1 1:l million million scale scale aerornagnetic aeromagnetic compilation of Lake Lake Huron Huron and surrounding areas areas integrates integrates new new surveys surveys over over Lake Lake Huron, Huron, Georgian Georgian Bay, Bay, and and land land areas areas east east of of the the lake lake with with older older aeromagnetic coverage coverage in in Michigan Michigan and and Ontario. Ontario. Existing gravity gravity data data were were compiled compiled at at the the same same scale. scale. A variety variety of derived maps maps have have been been prepared prepared from from these these data data sets sets to to emphasize emphasize particular particular attributes attributes of of the the anomaly anomaly fields fields and and facilitate facilitate the the geologic geologic interpretation interpretation of of the the potential potential field field data. data. In concert with other geophysical geophysical data data and and geologic geologic information from the Lake Lake Huron Huron environs, environs, these these maps map8 are are useful useful in delineating basement structural/petrologic .structural/petrologic provinces provinces of of the lake. lake. Noteworthy Noteworthy is i6 the the magnetic magnetic high high of of the the Grenville Grenville Front Front the tectonic tectonic zone zone that that aids aids in in refining refiningthe theposition positionofofthe the(3renville Grenville Front beneath beneath the the Michigan Michigan Basin. Basin. 21 �THE BARABOOINTERVAL INTERVAL --ENCORE: THE PROTEROZOIC PROTEROZOIC BARABOO ENCORE: COMPOSITION DATA EllAL ET AL COMPOSITION DATA Jeffrey K. Greenbera (Dept. of Geoloav. Wheaton Colleqe. Wheaton IL. 60187) CR. Van surely be to witness C.R. Van Hise Hise would would surely be pleased pleased to witne~ts the the sustained sustained Intrigue intrigue concerning the the Baraboo quartzite and metasedimentary concerning Baraboo quartzite and other other possibly possiblycorrelative correlative metasedlmentary limited by by re\atively relatively few units in Inthe thesouthern southernLake Lake Superior Superior region. region. Although Although limited few to employ everytype typeofof analysis analysis in deciphering scattered outcrops, outcrops, we continue continue to employ every deciphering the the It history ofofthe the'Baraboo 'Baraboointerval.TM Interval.' Ithas hasrecently recentlybeen beensuggested suggested (LaBerge (LaBerge and and Klasner 1988) 1988) that that two quartzitic rocks two different differentsequences sequences of ofBaraboo—type Baraboo-type quartzitic rocks can be be Klasner distinguished (old idea revisited) and that the older sequence represents some type (old idea revisited) and that the older sequence represents s m e type 1850 and thrust thrust southward of clastic clastlcwedge wedgeeroded erodedfrom franArchean Archean basement basement and southward during during Ca. ca. 1850 interpretations depend Ma. arc-continent coll collision Ma. arc-continent ision inincentral centralWisconsin. Wisconsin. These These interpretations depend on on stratigraphic and and structural relationships. relations hips^ indirect stratigraphic Until sufficient age thethe metasedimentary sufficient agedata databecome become available, available*the theorigin originofof metasedlmentary and chemical rocks rocks is is best best indicated indicated by by their theirmodal modal and chemical composition. composition. Compositional Compositional criteria criteria are are nnoww primary factors factors in in the the determination of manatic magmatic origins, origins, The interpretation interpretation of ascertaining both both source source material and and tectonic tectonicenvironment. environment. The of relatively compositional data for for metasedimentary canposltional metasedlmentary rocks can likewise likewi3e be a relatively unambiguousdeterminant determinantof of provenance provenanceand anddepositional depositional environment. environment. unambiguous Tectonic-sedimentation interpretations interpretations of Tectonic-sedimentation of the theBaraboo Baraboo interval interval(see (seeGreenberg Greenberg reassessedthrough throughthe the lntegratlon integration of and Brown 1984) were Brown 1904) were reassessed of chemical chemical analyses analyses from frm over outcrop areas areaswith with other other available data. over twenty twenty outcrop data. The three three major major depositional The deposltlonal (1984) include: clastic hypotheses hypotheses from from Greenberg Greenberg and and Brown B r w n (1984) Include: AA) ) a a near-continuous near-continuous clastlc shelf transgression; transgression: B) B) multiple multlplesequences sequences separated separated by by major major unconformities, unconformltIe~,and and C) epicratoriic environment, basin and fault-bound basins. C) complex complex epicratonic envlronment. basin and range-type range-type fault-bound basins. The The last of ofthese thesewas was previously prevlwsly preferred, preferred,with withthe theconcurrence concurrence ofofSouthwick Southwick and and others others (1986) concerningthe theorigin origin of the interval Sioux in Minnesota. (1906) concerning the Baraboo Baraboo interval Sioux quartzite quartzite In Hinne3ota. Modal/chemicalcharacteristics characteristicsindicate Indicate that that the Baraboo interval rocks rocks are are of Modal/chemica~ Baraboo interval constitution of variable variable provenance. provenance. The typical typical modal constitution of the coarser coarser lithologies lithologles The bespeaks of of variable to mature bespeaks mature weathering weathering and and erosion erosion and and predominantly predminantly felsic felslc igneous Major and and trace trace element contents indicate Igneous or or reworked reworked sedimentary sedimentary sources. sources. Major element contents geparate exposures exposures bear theirown own restricted source areas. For that separate bear evidence evidenceof of their source areas. example, K20, Nb,Nb, andand Zr versus Si% Si02 plots display little of example, X20,HgO, MgO, Zr versus plots display little or or no no clustering clustering of samples, regardless of of grain samples* regardless grain size sllicacontent. content. Rare Rare earth earth abundances abundance3 of ofmany many size or silica arenltic and pelitic peliticsamples samples closely mirror the REE patterns arenitic and the REE patterns of nearby felsic plutons and and extrusives extrusivesofof both Penokeanand andpost-Penokean post-Penokean 1760 1760 Ma. Ha. age. age. Archean plutons both Penokean Archean or mafic are generally absent. mafic terrane terranecomponents components are absent. Eroded ErodedArchean Archeanrocks rocksofofcentral central or northern Wisconsin are are an an unlikely source of the Baraboo Barabm interval interval source for most of sediments. In all sediments. In all instances Instance3 the of data data on on tectonic tectonicdiscriminant discriminantdiagrams diagrams the plots of (such as Tb2 (such Ti02- Fe203+MgO - Fe203+Mg0 and and K20/Na20 i a, 1903; -Th-Co, Tay 1 or K20/Na20-- Fe203+H@, Fe203+MgO,Bhat Bhatia, 1983;Hf Hf-Th-Co, Taylor and McLennan, HcLennan, 1985; 1905; SiO2/Al20 SiO$A120 - -K2O/Na20, K20/Na20* Roser Roser and and Korech, Korsch, 1907) conform3 wl th 1987) conforms with cratonic, passive passive margin, margin, or r ftenvironments. environments. There or rift is no There 1s no Indication lndicatlon of of orogenic orogenic associations(wbduction, (subduction,collision, collision, etc.). etc.). associations ? 22 �Ps As a test of hypotheses, the the composition composition of of Baraboo Baraboo interval interval exposures exposures further further (1984). The (above) of Greenberg supports supports model model CC (above) Greenberg and and Brown Brown (1984). The possibility possiblllty of of multiple multiple sequences (model (model B) sequences B) in ln combination with model model C is is also also compatible compatible with with the the data. data. However, most compelling imp1 ication of of Baraboo interval Interval study study continues continues to to be be Hwever* the most compel l ing implication that the sedimentary mamatic association association represents the the product product of of anorogenic anorogenic that sedimentary -- manatic Such case with many other Proterozoic processes. Such is is also the the case Proterozoic associations associations processes. (Athabasca - Thelon, melon, Gowler, (Athabasca Gowler* Jotnian, Jotnian, Roratma, Roraima,Haninamat). Hamamat). The The most reasonable reasonable age age for most Baraboo interval Similar though for most interval deposition depositlon remains near near 1760 1760 Ma. Ma. though less less evident episodes of of sedlmentation sedimentation could could also also be associated evident episodes associated with earlier earlier or or later later post-orogenicmagnatism manatin in in Wisconsin. Wisconsin. The Jotnian Jotnlan ciastics clastlcs of of Scandanavia Scandanavla were were post-orogenlc in multiple multiple generations separated In deposited in in time by pulses pulses of of felsic felsic to to bimodal bimodal anorogenic magnatim magnatism (Lundqvist Without extensive and accurate (Lundqvist 1979). 1979). Wlthout accurate isotopic Isotopic age exposures might appear all been contemporaneous. data, the Jotnian exposure3 appear to have all contemporaneous. - Tectonin Tectonlsn responsible responsible for for deformation deformation of of the the Baraboo Baraboo interval Interval outcrops outcrops is 1s not Some southward Some southward thrusting is is aa reasonable reasonable interpretation, interpretation, but but it would would likely influences, not It likely have been in in response to to anorogenic anorogenlc (tensional?) (tensional?) influences, not easily comprehended. comprehended. . orogenic. orogen 1c References References Bhatia, M.R., 1983, Plate tectonics Bhatla, M.R.? tectonics and geochemical composition composition of of sandstones: v. 91, 91* p. p. 611-627. 611-627. sandstones: Journal of Geology, Geology* v. Greenberg, J.K. J.K. and and Brown, Brown, B.A., B.A, 1984. Cratonic sedlmentation sedimentation during the 1984. Cratonlc Proterozoic: anorogenic connection In Proterozoic: an anorogenlc In Wisconsin Wlsconsln and and the the upper upper midwest: midwe&: Journal of Geology, Geology, v.92, v.92, p. p. 159-171. 159-171. LaBerge, G.L. G.L. and Klasner, Kiasner, J.S.. J.S., 1988, 1988, The Baraboo Quartzite: a new look lo& at an old problem: (abs.) 34th Institute problem: (abs.1 Institute on Lake Superior superior Geology, Geologyp Marquette, Marquette? MI, M I * p. p. 62-64. 62-64. Lundqvist, 19?9* The The Precambrian Precambrian of of Sweden: Sweden: Lundqvlst, T., 1979, Sveriges Geolgiska Sverlges Geolglska Undersokning, Undersokning* 87p. 87p. Roser, R.J., 1987, Roser* B.P. B.P. and Korsch, R.J., 198?* Determination of tectonic tectonic setting setting of of sandstone—mudstone suites using Si02 sandstone-mudstone suites S102 content and K20/Na20 K20/Na20 ratio: ratio: Journal of of Geology, v.95. Geology* v.95. 1986* Fluvial origin of the lower lower S o u t h ~ l c kD.L.* ~ Morey, G.B. Southwick, D.L., G.B. and Mossier* Mossier, J.H.* J.H., 1986, Proterozoic Quartzite* southwestern southwestern MN: MN: Geological Society of America Proterozoic Sioux SIOUX Quartzite, Bulletin, Bulletin* v.97, v.97* p. 1432-1441. 1432-1441. Taylor, S.R. S.R. and McLennan, S.M., S.M., 1985, 1985* The The Continental Crust: Crust: Evolution: Evolution: Oxford, Oxford, Blackwell, Blackwell, 312 312 p. p. 23 Its Composition and �Structure Structure of the Midcontinent Rift Rift System in Eastern Lake Superior: Preliminary heliminary Results Results from from 8-sec 8-sec Reflection Reflection Seismic Seismic Data Data and and Gravity Gravity and and Magnetic Magnetic Anomalies Anomalies Hinze and andD.N. D.N. Ravat Ravat(Dept. (Dept.of of Earth Earthand andAtmospheric AtmosphericSciences, Sciences,Purdue PurdueUniversity, University, WJJ Hinze W West 47907;317-494-5982) 3 17-494-5982) West Lafayette, Lafayette, IN 47907; McGimis(Engineering (Engineering Geosciences, Geoscience~~ Argonne National National Lab, Lab, 9700 9700 South South Cass Cass L DD McGinnis Argonne Avenue, Avenue*Argonne, Argonne*IL IL 60439; 60439;312-972-8722) 312-972-8722) W WFF Cannon Cannon (USGS, (USGS, Mail Mail Stop Stop 954, 954, Reston, VA 22092; 22092;703-648-6345) 703-648-6345) B B Milkereit Mikereit (Geol. (Geol. Survey Surveyof of Canada, Canada,11Observatory ObservatoryCrescent, Crescent*Ottawa, Ottawa,Ontario, Ontario,Canada Canada K1A KIA 0Y3; OY3: 613-995-5490) 613-995-5490) JJ L L Sexton Sexton (Dept. of Geology, ~ e o l o &Southern * Southern Illinois Illinois University, Carbondale, IL IL 62901; 62901;618618453-3351) 453-335 - - - - - 1) H H FF Wang Wang (Dept. $ePt. of of Geology Geologyand and Geophysics, Geophysics,Univ. Univ. of of Wisconsin, Wisconsin,Madison, Madison*WI WI 53706; 53706; 608-262-5932) 608-262-5932) Seismic Seismic reflection, reflection, gravity, gravity, and and magnetic magnetic anomaly anomaly data data confirm confirm GLIMPCE GLIMPCE interpretations interpretations of the the structural structural style style of of the theMidcontinent MidcontinentRift RiftSystem Systeminineastern easternLake Lake Superior. Superior. InIncontrast contrasttotointerpretations interpretationsmade madeprior priortotoseismic seismicreflection reflectionstudies, studies,eastern eastern Lake Superior Superior is shown shown to to be beunderlain underlain by by a arelatively relativelysymmetric symmetric folded folded graben graben Lake consisting of a thick consisting of thick (>15 (>I5 km) km) btsal b m l layer layerof of mafic mafic volcanic volcanicrocks rocksoverlain overlain by by clastic clastic km sedimentary rocks sedimentary rocks reaching reachingthicknesses thicknessesofofthe theorder orderofof7.5 7.5km. km. A A seismic seismic line line=20 20 km from from the the southern southern shoreline shorelineof of the the lake lakeshows showsthat thatthe thegraben grabencontinues continuesfrom fromthe thecenter center of of the the lake lake into intothe theeastern easternNorthern NorthernPeninsula Peninsulaof ofMichigan Michiganwith withonly onlyminor minorattenuation. attenuation. The The western western margin margin of the the graben graben occurs occurs in the the vicinity of of Grand Grand Island. No Noevidence evidenceof of volcanic volcanic rocks are seen west west of the the graben graben near the southern southern shoreline. shoreline. AA broad broad arch arch with with a relief relief of 3=3km kmoccurs occursoff offDeer DeerPark, Park,MI MI atat =47°N, 47ON, 85°45'W. 85'45'W. The Theaxis axisof of the the graben graben is is interpreted interpretedto to lie lietotothe thewest westofofthe thearch archininthe thevicinity vicinityofofAu AuSable SablePoint, Point*MI. MI. Thick (= km) Keweenawan east of of Keweenawan sedimentary sedimentary rocks rocks overlying volcanic rocks occur east Thick ( 77 1cm) the thearch archassociated associatedwith withaagravity gravityminimum minimumatatthe theend endof ofthe theseismic seismicline. line. Seismic Seismic reflection reflection data dataare areobtained obtainedunder underlicense licensefrom fromGrant GrantNorpac Norpacand andstudies studiesare are supported supportedin in part part by by the theU.S. U.S. Dept. Dept.ofofEnergy, Energy*Office OfficeofofEnergy EnergyResearch Researchunder undercontract contract W-31-109-Eng-38. W-3 1-109-Eng-38. 24 �Preliminary Preliminaw constraints constraintson on the the P-T P-T evolution evolution of of the the Penokean Penokeanorogeny oroaenxeast-central east-centralMinnesota. Minnesota. D.K. D.K. HoIm Holm and and J. Selverstone, Selverstone, Dept. of Earth Earth and and Planetary PlanetarySciences, Sciences,Harvard HarvardUniversity, Universrty,Cambridge, Cambridge,MA, MA, 02 138. 02138. New petrologic Newand andimproved improved petrologictechniques techniques have haveincreased increasedour our understanding understanding of of regional regionalmetamorphism metamorphism during constraints to be made models. Detailed during collision collisionand and allow allow important constraints made on plate tectonic models. Detailed petrologic petrologic studies successful in terrane to studies of of orogenic orogenicbelts beltshave have been successful in using using the metamorphic signature of a terrane to evaluate evaluate the the tectonic tectonic development developmentof of aa region regionand and to to quantify quantifythe thepressure-temperature pressure-temperatureevolution evolutionduring duringorogeny. orogeny. Such Such a study study is is here here applied to rocks rocks which have have been been multiply multiply deformed and metamorphosed metamorphosed during during the Penokean Penokean orogeny. This Thistechnique technique is is particularly paflicularlyuseful usefulinineast-central east-centralMinnesota Minnesotawhere whereconventional conventional geologic very geologic mapping mappingIs is highly highly limited limited by v e v poor poor exposure. exposure. The The Penokean Penokeanorogeny orogeny was was aa major major early early Proterozoic Proterozoic(1875-1825 (18751825Ma) Ma)tectonic tectonicevent eventin inthe theGreat GreatLakes Lakes region. region. Holm Holmand andothers others(1988) (1988)have have proposed proposed aa plate-tectonic plate-tectonicmodel modelfor for the the Panokean Penokean orogeny orogeny based based on of metamorphism metamorphism and and structural structural geology. geology. Their model incorporates incorporates on strain strain analysis, conditions of continental continentalrifting rifting followed followed by by footwall footwall deformation deformation associated associatedwith with oblique oblique continental continental convergence convergence (A-type of the the footwall footwall onto the hangingwall during uplift associated associated with (A-type subduction) subduction) and imbrication of continued continued convergence. Early EarlyProterozoic Proterozoicsupracrustal supracrustalrocks rocks(Denham (Denhamand and Thomson ThomsonFormations) Formations)have have been been multiply multiply deformed deformed and and highly metamorphosed metamorphosed during during the the Penokean Penokean orogeny, with metamorphic metamorphic grade grade increasing increasing from from north north to south. Petrographic Petrographicanalysis analysisof ofthese theserocks rocksindicates indicatesprogressive progressive metamorphism metamorphismduring during an an early early phase of deformation deformationthat thatproduced producedsynkinematic synkinematic (rotated) (rotated)garnet garnet porphyroblasts schistosity. The porphyroblastsand and aa wall-developed welldeveloped schistosity. Thethermal thermalpeak peakof of metamorphism, metamorphism, however, however, occurred occurred after aa later indicated by staurolite later phase phase of of deformation, as indicated staurolite porphyroblasts porphyroblastsoverprinting overprinting both both the the primary primav schistosity schistosQ and and aa younger younger crenulation crewlation cleavage. cleavage. We We have have collected collectedsamples samples across across an an approximately approximately15 15km kmNE-SW NE-SWtransect transect in in garnet garnetand andstaurolite staurolitegrade grade rocks Thomon Formation. Formation. Temperature Temperatureand andpressure pressureestimates estimates of of final final equilibration equilibrationwere were obtained obtained rocks of of the the Thomson using using the the thermobarometric thermobarometrictechniques techniques (on (onrim rimanalyses) analyses)of ofFerry Ferryand andSpear Spear(1978) (1978)and andGhent Ghentand andStout Stout (1981) modified by Hodges and and Crowley Crowley (1%). (1985). The northern most samples of of garnet garnet grade rocks (1981) as modified (Moose temperatures of 440-500° C. Farther (Moose Lake Farther south south in in garnet garnet grade grade rocks rocks h k e area) area) give final equilibration temperatures 440-500ÂC. final final equilibration equilibrationtemperatures temperatures of 470-520° 470-520 C and and a a pressure pressure of around around 6 kb are obtained. Staurolite Staurolitegrade grade Thomson Thomon Formation Formationsamples samples (just (just north north of the Denham DenhamFormation) Formation)give give final equilibration equilibrationtemperatures temperaturesof of 520-590° C and and aa pressure pressureof of around around77 kb. kb. 52G590ÂC Staurolite staurolite+garnet+plagioclase+ Staurolitegrade grade Thomson T h o m n Formation Formation contains contains the the assemblage awmblage staurolite+garnet+plagioclase+ chlorite+muscovite+biotite+quartz. chlorite+muscovite+biotite+quartz.Garnet Garnetshows showsaasystematic systematiccompositional compositionalzoning zoningof of increasing increasing spessartine spessartine and and grossular g r o w l a r content content and decreasing decreasingalmandine almandinecontent contentfrom from rim rimto to core. core. Inclusion-rich surrounded by haloes haloes of inclusion-free two stages of Inclusion-rich(quartz) (quartz) garnet cores surrounded inclusion-free garnet suggest two 25 �contact with garnet growth. Microprobe Microprobeanalyses analyses of piagioctase plagioclase in in contact with garnet indicates indicates two coexisting coexisting plagioclase compositions An attempt attempt was made to plagioclase compositions (albite, (albite,XAnO-O.O5 X ~ ~ = 0 - 0 . 0and 5 oligoclase, XAn"O.23-O.28). X~~'O.23-0.28). An model changes in P and T T using using the the Gibbs Gibbs method method on ongarnet garnet rim rim and and core core analyses. analyses. Assuming oligoclase with garnet garnet and using using almandine and and grossular grossular as as monitors, Gibbs as the plagioclase plagioclase phase in equilibrium with method modelling on two different garnets suggests no change in temperature temperature and an increase in pressure of 1.5-2.0 kb during during garnet garnet growth. growth. This result is 1S2.0 kb is consistent with the model of Holm Holm and others In which which early early formed formed structures structures and and progressive progressive metamorphism metamorphism are considered considered related footwall (1988) in relatedto to footwall deformation southward-directed subduction. subduction. AAsimilar deformation during during southwarddirected similarisothermal isothermalcompression compressionpath pathwas wasobtained obtained by Crawford Crawford and Mark Spear and and Selverstone Selverstone (1983) (1983) on on samples samplesfrom fromthe the lower lower plate plate of a thrust thrust Mark (1982) and Spear modelling predicts predicts a large large change in anorthite anorthite nappe. Our Our results results are are problematic problematic however as the modelling composition (+0.30) composition (+0.30) that is not not observed observed in our samples. Two stage (Xalm,spess) in in the inclusion-rich inclusion-richand and inclusion-free inclusion-free stage modelling modellingusing using compositional compositionalchanges changes(Xaim,spess) staurolite as a phase only for the areas of garnet and and including including staurolite the second stage stage of garnet garnet growth growth again againgives gives no temperature change and only a slight decrease in pressure during garnet growth (60 (60 bars). This Thisresult, result, if real, suggests rapid rapid growth of garnet and high rates of strain. Rapid Rapidgrowth growthrates ratesreported reportedininthe theliterature literature range range from from 0.6-1.5 0.6-1.5 mm/Ma mmIMa (Christensen (Christensen and others, others. 1988; 1988; Staude Staude and and Selverstone, Selverstone, 1988). 1988). Using Usingthese these growth growth rates, rates, the the amount amount of rotation rotationrecorded recordedby by the the garnet garnetduring duringits itsgrowth growthImplies impliesaaminimum minimumshear shear strain strain rate rate of 37.1O14 3-7.10-14Is1s(not (notconsidering consideringbulk bulk strain strainin inthe the matrix). matrix). Assuming Assumingaaslower sloweraverage averagegrowth growthrate rate 0.1 m mm/Ma minimumshear shearstrain strainrate rateofof1.4.1~14 1.4.10- Is. of 0.1 M a gives aa minimum are preliminary preliminary and much further work is We emphasize that the results presented here are Is needed needed to to quantify pressures, pressures, temperatures, strain rates, etc. associated associated with with the the deformational deformationalhistory historyof ofthis thisarea. area. these results indicate indicate that, that, with with further further work, work, such such constraints constraints can can be be obtained obtained and and will will greatly greatly However, these understanding of crustal deformation deformation as well as improve enhance our understanding improve our knowledge knowledge of plate-tectonic plate-tectonic processes processes back back into into the the Precambrian Precambrianera. era. F research has been supported supported by by a Sigma XI grant-in-aid of research research to to Daniel K. K. Holm Hoim and and by by NSF This research Sigma Xi NSF EAR8648145 to to Jane Jane Selverstone. Selverstone. grant EAR86-58145 RaferercBS Christensen, J.N., J.L., DePaolo, D.J., J.N., Rosenfeld, Rosenfeld, J.L.. D.J., 1988, 1988, Eos, 69, p. 508. Crawford, M.L, M.L. and and Mark, Mark, LE., LE., 1982, 1982, Canadian CanadianMineralogist, Mineralogist,20, 20,p.p.333-347. 333-347. J.M., and Spear, Spear, F.S., F.S., 1978, 1978, American American Mineralogist, 64, p. p. 966-985. Ferry, J.M., Mineralogist, 64, Ghent, E., and and Stout, Stout, M., M.. 1981, 1981, Contributions Contributionsto toMineralogy Mineralogyand andPetrology, Petrology,76, 76, p. p. 92-97. 92-97. Hodges, K.V., and Crowley, Crowley, P.D. K.V., and P.D. 1985, American American Mineralogist, Mineralogist, 70, 70, p. p. 702-709. 702-709. Holm, D.K., 1988, Geological Geological Society of America Bulletin, 100, p. p. 1811-1818. 1811-1818. D.K., HoIst, Hoist. T.B., T.B.. and Ellis, M., M., 1988, F.S., and and Selverstone, Selverstone,J., J., 1983, 1983, Contributions to Mineralogy 83, p.p.348-357. 348-357. Spear, F.S., Mineralogy and Petrology, Petrology, 83, Staude, J-M., J-M., and and Selverstone, Selverstone,J.,J.,1988, 1988,Geological GeologicalSociety Societyof ofAmerica America Ab. Ab. w. w. Prog., Prog., 20, 20, p. Staude. p. A332. A332. 26 �THE PENOKEAN PENOKEAN OROGENY OROGENY IN IN MINNESOTA MINNESOTA AND UPPER UPPER MICHIGAN: MICHIGAN: THE A COMPARISON COMPARISON OF OF THE THESTRUCTURAL STRUCTURAL GEOLOGY GEOLOGY OF OF THE THEMICHIGAMME MICHIGAMME AND THOMSON FORMATIONS FORMATIONS Timothy B. B. Hoist Hoist Department Department of of Geology, Geology, University University of Minnesota Duluth Duluth Duluth, Minnesota 55812 Minnesota 55812 An An examination examination of mesoscopic mesoscopic structures structures and and microstructures microstructures and and aa preliminary strain analysis Formation along along aa transect from preliminary strain analysis in in the theMichigamme Michigamme Formation from Covington to Iron Michigan,reveal revealaa striking striking similarity to the Covington to Iron Mountain, Mountain, Michigan, similarity to the structural structural geology geology of of the the Thomson Thomson Formation Formation in in east-central east-centralMinnesota. Minnesota. In In Minnesota there are are two different structural structural terranes, terranes, as as there are Minnesota there two distinctly distinctly different are along this transect transect in inMichigan. Michigan. along In the northern northern terrane terrane in inMinnesota, Minnesota, the dominant structural features features are aa single set of of open open to to close, close, upright, upright, sub-horizontal, sub-horizontal, east-west east-west trending trending folds, folds, with with a single, foliationthat thatisis axial axial'planar planar to to the single, well-developed well-developed foliation the folds. folds. Where fold fold axial surfaces are are not not dipping vertically, the the vergence vergence isis to to the north, axial surfaces dipping vertically, north, with with axial axial axes are sub-horizontal surfaces dipping dipping steeply south. south. Fold Fold axes sub-horizontal except except where where folds folds die out 60° The The foliation is aa out rapidly rapidly along along strike, strike,where where axes axes may may plunge plunge up up to to600. continuous slaty cleavage cleavage in fine-grained fine-grained units and aa disjunctive disjunctive spaced spaced cleavage cleavage the coarse-grained coarse-grainedgraywacke graywacke beds. beds. At At several several places kink bands bands deform deform this this in the foliation, indicating aa small foliation, indicating small amount amount of of late late sub-vertical sub-vertical shortening. shortening. Deformed Deformed concretions, mud mud chips, and a thin thin conglomerate conglomerate unit allow allow the determination determination of of finite strain strain in in the the northern northern terrane. terrane. finite Strain shapes plot plot in Strain ellipsoid ellipsoid shapes in the the flattening field ratios averaging field (0<k<1) X:Y:Z ratios averaging approximately approximately 7:4:1. 7:4:1. Z Z is is (O<k<l)with X:Y:Z The horizontal and and oriented north-south. north-south. The east-west, east-west, vertical foliation approximates the XY plane of the strain XY plane strainellipsoid. ellipsoid. In Michigan, in the Michigan, in the area area from from Covington Covington south south to tothe theBaraga BaragaCounty-Iron County-Iron County line (a (a distance of about County line distance of about 15 15 km) km) structures structures similar similar to to the the northern northern terrane in in Minnesota Minnesota are found. found. AAsingle single foliation foliation is is found, found, again again aa continuous continuous slaty cleavage in the fine-grained units and a disjunctive in the cleavage in fine-grained units disjunctive space space cleavage cleavage in coarse-grained graywackebeds. beds. The attitude coarse-grained graywacke attitude of of the thecleavage cleavagechanges changessomewhat somewhat from north to south from north south along along the the transect, transect, and and is isaxial axial planar planar to, to,and andshows shows normal normal bedding-cleavage vergence relationships relationships (between (between slate slate and greywacke bedding-cleavage vergence greywacke beds) beds) to to folds are are upright upright in in the southern some folds that that exist. some mesoscopic mesoscopic folds exist. These These folds southern part part of of the transect, transect, but but axial axial surfaces surfaces dip dip as as gently gently as as 40 40to to50° 50Âsouth southatatCovington, Covington, Where showing showing northward northward vergence. vergence. Where fold fold axes axes can can be be found, found, they are are sub-horizontal, and bedding-cleavage bedding-cleavage intersections along along the transect transect are sub-horizontal, kink bands bands also also exist exist here, here, and sub-horizontal. Late-stage Late-stage kink and are are also also gently gently sub-horizontal. concretionsand andmud mudchips chipsexist existinin these these rocks, Deformed concretions rocks, and and aa dipping. Deformed preliminary analysis reveals revealsflattening flatteningstrains strainssimilar similartoto those those in the preliminary analysis the northern northern terrane in in Minnesota. Minnesota. 27 �In the southern In southern terrane terrane in inMinnesota, Minnesota, two two main main periods periods of of folding folding have been identified. Early phase (Fj Early phase (F,) folds folds are are isodlinal isoclinal and and recumbent, recumbent, with with east-west east-west F folds as much folds as much as a meter meter or or so so in inamplitude amplitude and and trending fold fold axes. axes. Minor Minor F, wavelength have been been observed, observed, but but nappe-scale nappe-scale structures structures of of this phase wavelength have phase have have been been interpreted interpreted based based on onseveral severallines linesofofreasoning reasoningincluding includingbedding-cleavage bedding-cleavage vergence relationships relationships and facing directions of folds. An vergence of F3 F, folds. An early early foliation, foliation, axial axial planar ttoo these folds, is found found throughout throughout the the southern southern terrane. terrane. As planar folds, is As the the folds folds are are isoclinal and and hinge hinge regions regions of of folds folds are are rare, this isoclinal this foliation foliation is is nearly nearly always always sub-parallel to to bedding. bedding. A found in in the southern sub-parallel A second second phase phase of of folding folding (F2) (FJ isis found southern terrane in Minnesota. style, attitude, attitude, and geometry to terrane Minnesota. These These folds folds are of similar similar style, geometry to the only found in in the the northern terrane. spaced crenulation crenulation cleavage cleavage is the only folds folds found terrane. AAspaced widespreadin in the the southern southern terrane, terrane, in an attitude widespread attitude which which is axial axial planar to to the the F2 F, folds. folds. A A strong strong lineation lineation exists, parallel parallel to the the intersection intersection of of the the two two foliations. foliations. Strain analyses in the southern terrane in Minnesota from deformed conglomerate clasts and and mud mud chips chips indicate indicate that that very conglomerate clasts very large large flattening flattening strains strains accompanied the development of the early accompanied the development of early folds folds and and foliation. foliation. In the the Thomson Thomson Formation Formation in Minnesota, Minnesota, metamorphic metamorphic grade increases progressively progressively from from north to south. The structural geology The geology of of rocks exposed exposed in Michigan Michigan aatt Horse Horse Race Race Rapids Rapids just south just south of of Crystal Crystal Falls, Falls, and at a t Steele Steele Farm Farm and and along along the Sturgeon Sturgeon River River just is quite quite similar similar to the structural north of Iron Mountain, Mountain, is structural geology geology of rocks in the the southern terrane and distinctly distinctly different different from fromthe the rocks rocks of southern terrane in Minnesota, Minnesota, and of the northen terrane in the area northen terrane in Michigan, Michigan, in area just just south southofofCovington. Covington. In In this this The early southern terrane in southern in Michigan Michigan two phases phases of of folding folding are also also found. found. The early phase phase is again again isoclinal isoclinal and and recumbent, recumbent, and and there thereisisa awell-developed well-developed foliation foliation axial planar to to the the folds. foldhinges hinges are arequite quiterare rareso sothis thisfoliation foliation isisusually usually axial planar folds. FF,fold F2 folds open, upright, and found to be sub-parallel sub-parallel to bedding. Fa folds are open, crenulation cleavage cleavageisis found found in in some some places, A spaced spaced crenulation places, in an an sub-horizontal. A is found that isis attitude which which is axial axial planar planar to to the theF'2 Fafolds. folds. A A lineation lineation is found that parallel parallel tto o the intersection intersection of of the the two two foliations, foliations, and and the the metamorphic metamorphic grade grade of of No the rocks rocks in the the southern southern terrane terrane is is higher higher than than in in the the northern northern terrane. terrane. N o strain analysis analysis has been been done in the the southern southern terrane terraneininMichigan. Michigan. The region region of the the boundary between the the northern northern and and southern is not of boundary between southern terrane in Michigan Michigan is as well as is the the northern well exposed exposed as the boundary boundary region region between between the northern and and southern southern It is in that the terranes in in Minnesota. Minnesota. It in this this region region in in Minnesota Minnesota that the best best evidence evidence for nappe-scale structure is found. Based on the similarities for nappe-scale structure found. Based on similarities in structural structural geology in both both northern northern and and southern southern terranes terranes in in the rocks geology in rocks in in Minnesota Minnesota and and Michigan, is suggested that the early in the southern Michigan, itit is suggested that early phase phase of of deformation deformation in southern terrane in Michigan did involve involveaa great great deal deal of of strain, and the terrane Michigan did the development development of of large-scale features features probably probably including including fold fold and and thrust thrust nappes. large-scale nappes. 28 �The Mining and and Geologic History H i s t o r y of of the t h e Silver S i l v e r Islet I s l e t Mine, Mine, and and aa Conceptual Conceptual Ore Genesis Model for Ore f o r the t h e Deposit. Deposit. By Robert Robert J. J. Horton Horton Silver miles s llocated o c a t e d 20 m i l e s east e a s t of of Thunder Bay, Bay, about 3/4 3/4 of of aa mile mile S i l v e r Islet I s l e t iis s i l v e r vein v e i n discovered d i s c o v e r e d on on the the ooff f f the t h e Sibley S i b l e y Peninsula Peninsula in i n Lake Lake Superior. S u p e r i o r . A silver island million i s l a n d produced produced an eestimated stimated 3 m i l l i o n ounces of of silver s i l v e r during d u r i n g a 16 16 year year period p e r i o d from from 1868 1868 to t o 1884. 1884. The island, i s l a n d , roughly 10 10 feet f e e t high high and and 80 80 feet f e e t in in i s located l o c a t e d aatt tthe h e intersection i n t e r s e c t i o n of of a steeply s t e e p l y dipping d i p p i n g gabbroic g a b b r o i c dike, dike, ddiameter, i a m e t e r , is h o s t e d in i n flat f l a t lying l y i n g sediments, sediments, and a fault f a u l t zone zone that t h a t strikes s t r i k e s perpendicular p e r p e n d i c u l a r to to hosted the t h e dike. dike. The silver s i l v e r ore o r e occurs o c c u r s only o n l y in i n the t h e portion p o r t i o n of of the t h e vein v e i n confined confined within ore w i t h i n the t h e dike; d i k e ; the the o r e abruptly a b r u p t l y stops s t o p s where the t h e vein v e i n intersects i n t e r s e c t s the the sediments. Following i s aa b r i e f summary of of the t h e mining and and geologic g e o l o g i c history history Following is brief and a ore o r e genesis g e n e s i s model model for f o r the t h e Silver S i l v e r Islet I s l e t deposit. deposit. MINING M I N I N G HISTORY prospector Joseph Woods patented IIn n 1845, 1845, p r o s p e c t o r Joseph p a t e n t e d 6400 6400 acres a c r e s along a l o n g the t h e Sibley Sibley Peninsula which he sold to the Montreal Mining Company the following P e n i n s u l a which he s o l d t o t h e Montreal t h e f o l l o w i n g year. year. In The "Woods "Woods Patent" Patent" lay l a y idle i d l e for f o r over o v e r 20 20 years. years. I n 1868, 1868, in i n an attempt a t t e m p t to to mining aactivity Ontario, iincrease n c r e a s e mining c t i v i t y iin n O n t a r i o , the t h e Crown levied l e v i e d a two two cent c e n t per per acre a c r e tax tax on mining This iinspired mining lands. lands. This n s p i r e d the t h e Montreal Mining Company Company to t o evaluate e v a l u a t e their their holdings, On July J u l y 10, 10, 1868, 1868, while w h i l e conducting conducting aa h o l d i n g s , including i n c l u d i n g the t h e Woods Patent. Patent. sshoreline h o r e l i n e survey, survey, an eexploration x p l o r a t i o n party p a r t y lead l e a d by by Thomas Thomas MacFarlane landed landed on on what is and d discovered i s now Silver S i l v e r Islet I s l e t and i s c o v e r e d the t h e silver s i l v e r bearing b e a r i n g vein. vein. Five days what The ore later, l a t e r , 1,336 1,336 pounds pounds of of ore o r e was was shipped shipped to t o Montreal. Montreal. o r e assayed assayed at a t 2,087 2,087 Montreal Mining Company ounces of silver s i l v e r per per ton. ton. The Montreal Company worked Silver S i l v e r Islet Islet until u n t i l mid 1870, 1870, producing producing 27,124 27,124 pounds of of ore o r e assayed assayed at a t $25,043.06. $25,043.06. In August of August of 1870 1870 the t h e company sold s o l d all a l l its i t s north n o r t h shore s h o r e holdings h o l d i n g s for f o r $225,000. $225,000. The major obstacle o b s t a c l e facing f a c i n g the t h e newly formed formed Silver S i l v e r Islet I s l e t Mining Mining Company Company The entire was flooding f l o o d i n g and and storm storm damage. damage. e n t i r e mine was was below below lake l a k e level l e v e l and and increasingly i n c r e a s i n g l y larger l a r g e r pumps were required r e q u i r e d when new new leaks l e a k s were were encountered encountered as a s the the workings expanded. expanded. The mine was also a l s o vulnerable v u l n e r a b l e to t o violent v i o l e n t southerly s o u t h e r l y storms storms In which generated g e n e r a t e d waves large l a r g e enough to t o wash completely completely over over the t h e island. island. I n an an attempt mine from storm damage, a t t e m p t to t o protect p r o t e c t the t h e mine damage, aa cofferdam cofferdam was was constructed constructed In around the t h e shaft s h a f t and a wooden breakwall b r e a k w a l l around around the t h e island. island. I n December, 1874, 1874, a violent 350 feet f e e t of of the t h e islands' i s l a n d s ' protective protective v i o l e n t southeasterly s o u t h e a s t e r l y storm swept away 350 breakwall, b r e a k w a l l , composed composed of of 20,000 20,000 feet f e e t of of timber, t i m b e r , 7.5 7.5 tons t o n s of of bolts, b o l t s , and and 5,000 5,000 of rock; and d destroyed of the ttons o n s of rock; and e s t r o y e d some of t h e mines above ground structures. s t r u c t u r e s . An expanded breakwall breakwall was rebuilt, r e b u i l t , to t o act a c t as a s aa buffer b u f f e r against a g a i n s t the t h e waves, waves, that that mine operated iincreased n c r e a s e d the t h e size s i z e of of the t h e original o r i g i n a l island i s l a n d 30 30 fold. fold. The mine operated continuously c o n t i n u o u s l y from from 1870 1870 to t o 1884 1884 except e x c e p t for f o r periods p e r i o d s devoted devoted to t o exploration exploration drilling shipment of of coal c o a l failed f a i l e d to t o arrive arrive d r i l l i n g and and repair r e p a i r of of storm storm damage. damage. A shipment 1884, when during d u r i n g the t h e fall f a l l of of 1883, 1883, causing c a u s i n g the t h e mine to t o flood f l o o d on on January J a n u a r y 20, 20, 1884, Att this A t h i s point p o i n t the t h e mine had reached reached aa tthe h e pumps stopped for f o r lack l a c k of of fuel. fuel. depth and produced an ttotal otal d e p t h of of 1,230 1,230 ffeet, e e t , and a n estimated e s t i m a t e d 3,044,000 3,044,000 ounces ounces of of silver s i l v e r worth $3,500,000. $3,500,000. 29 �GEOLOGIC GEOLOGIC SETTING SETTING The The geology geology of of the t h e region r e g i o n consists c o n s i s t s of of an an Archean Archean basement basement unconformably unconforraably overlain i s part p a r t of of the t h e Wawa— Wawao v e r l a i n by by Proterozoic P r o t e r o z o i c sediments. s e d i m e n t s . The The Archean Archean basement basement is Shebandowan Shebandowan subprovince, s u b p r o v i n c e , composed composed of of mafic m a f i c and and felsic f e l s i c volcanogenic v o l c a n o g e n i c rocks, rocks, minor minor sedimentary s e d i m e n t a r y units, u n i t s , and and felsic f e l s i c and and mafic m a f i c plutonic p l u t o n i c rocks; r o c k s ; with w i t h aa greenschist g r e e n s c h i s t metamorphic metamorphic grade. g r a d e . Jinconformably Unconformably ooverlying v e r l y i n g this t h i s intensly i n t e n s l y deformed deformed greenstone g r e e n s t o n e belt b e l t are a r e the t h e relatively r e l a t i v e l y flat—lying f l a t - l y i n g Proterozoic P r o t e r o z o i c sediments s e d i m e n t s of of the the Gunflint G u n f l i n t and and Rove Rove Formations. Formations. The The Cunflint G u n f l i n t Formation Formation consists c o n s i s t s of of an an iron—rich iron-rich assemblage assemblage of of stratified s t r a t i f i e d sediments. s e d i m e n t s . The The Rove Rove Formation F o r m a t i o n is i s an a n extensive extensive sedimentary s e d i m e n t a r y deposit d e p o s i t composed composed of of black b l a c k pyritic p y r i t i c shale, s h a l e , argillite, a r g i l l i t e , and and graywacke. i s disconformably disconformably graywacke. The The Rove Rove Formation, F o r m a t i o n , up up to t o 1200 1200 feet f e e t thick, t h i c k , is overlain o v e r l a i n by by the t h e Sibley S i b l e y Group Group redbed redbed sedimentary s e d i m e n t a r y sequence. sequence. These These rocks rocks have have been been intruded i n t r u d e d by by diabase d i a b a s e and and gabbro gabbro dikes. dikes. In I n the t h e vicinity v i c i n i t y of of southeasterly s o u t h e a s t e r l y dip. d i p . The The trending t r e n d i n g dike d i k e swarm. swarm. AA the t h e dikes d i k e s and and sediments sediments Silver S i l v e r Islet, I s l e t , the t h e Rove Rove formation f o r m a t i o n has h a s aa shallow shallow sediments s e d i m e n t s are a r e intruded i n t r u d e d by by aa steeply s t e e p l y dipping, d i p p i n g , northeast northeast series s e r i e s of of parallel, p a r a l l e l . faults, f a u l t s , striking s t r i k i n g northwesterly, n o r t h w e s t e r l y , cut cut and and show show 300 300 feet f e e t of of vertical v e r t i c a l displacement. displacement. The N. 500 50' E., E., dips d i p s 75 75 degrees d e g r e e s to t o the the The Silver S i l v e r Islet I s l e t dike d i k e strikes s t r i k e s N. southeast, s o u t h e a s t , and and is is 350 350 feet f e e t wide wide at a t the t h e surface, s u r f a c e , thinning t h i n n i n g to t o 250 250 feet f e e t at a t aa depth d e p t h of of 560 560 feet. f e e t . The The gabbro gabbro dike d i k e has h a s aa metamorphosed metamorphosed contact c o n t a c t with w i t h the t h e host host sediments, is impregnated impregnated with w i t h graphite graphite s e d i m e n t s , has h a s assimilated a s s i m i l a t e d blocks b l o c k s of of shale, s h a l e , and and is and and pyrite. p y r i t e . The The dike d i k e has h a s aa considerable c o n s i d e r a b l e length, l e n g t h , extending e x t e n d i n g at a t least l e a s t 1600 1600 feet feet to t o the t h e northeast n o r t h e a s t and and 1200 1200 feet f e e t southwest s o u t h w e s t of of the t h e island. i s l a n d . Along Along strike, s t r i k e , the the dike d i k e is i s thought thought to t o outcrop o u t c r o p on on other o t h e r islands i s l a n d s over o v e r aa distance d i s t a n c eofof 6060miles. m i l e s . The The Silver S i l v e r Islet I s l e t vein v e i n varies v a r i e s in i n width w i d t h from from aa few few inches i n c h e s to t o 50 50 feet, f e e t , strikes s t r i k e s N. N. 350 35' W. W. and and dips d i p s 85 8 5 degrees d e g r e e s to t o the t h e southeast. s o u t h e a s t . The The vein v e i n has h a s aa strike s t r i k e length l e n g t h of of at at least is composed composed of of calcite, c a l c i t e , harite, barite, l e a s t 1800 1800 feet. f e e t . In I n the t h e sediments, s e d i m e n t s , the t h e vein v e i n is fluorite, f l u o r i t e , and and quartz; q u a r t z ; however, however, within w i t h i n the t h e confines c o n f i n e s of of the t h e dike d i k ethe t h e veins' veins' composition c o m p o s i t i o n is is aa fine f i n e grained, g r a i n e d , homogeneous homogeneous pink p i n k dolomite d o l o m i t ewith w i t h minor minorquartz. quartz. The i s generally g e n e r a l l y thicker t h i c k e r in i n the t h e dike d i k e than t h a n in i n the t h e sediments. sediments. The vein v e i n is The The vein v e i n contains c o n t a i n s both b o t h primary primary and and secondary s e c o n d a r y ore, o r e , which which always always occur o c c u r in in the t h e presence p r e s e n c e of of graphite. g r a p h i t e . About About 90 90 percent p e r c e n t of of the t h e ore o r e is i s primary, p r i m a r y , and and found found throughout is throughout the t h e mine n i n e in i n varying v a r y i n g degrees d e g r e e s of of richness. r i c h n e s s . The The primary primary ore o r e is composed composed of of silver, s i l v e r , argenite, a r g e n i t e , niccolite, n i c c o l i t e , galena, g a l e n a , sphalerite, s p h a l e r i t e , marcasite, marcasite, cobaltite, c o b a l t i t e , smaltite, s m a l t i t e , domeykite, d o m e y k i t e , chalcopyrite, c h a l c o p y r i t e , and and tetrahedrite t e t r a h e d r i t e in i n aa pink pink dolomite d o l o m i t e gangue. gangue. These These ore o r e minerals m i n e r a l s occur o c c u r as a s disseminated d i s s e m i n a t e d grains, g r a i n s , intergrown intergrown aggragrte a g g r a g r t eclusters, c l u s t e r s , and anddendritic d e n d r i t i cforms, forms, and and range r a n g eini n size s i z e from from microscopic microscopic to t o 33 mm mm. The The secondary s e c o n d a r y ore o r e occurs o c c u r s in i n groups g r o u p s of of pockets p o c k e t s irregularly irregularly distributed d i s t r i b u t e d throughout t h r o u g h o u t the t h e vein v e i n system. system. Deposited D e p o s i t e d as a s replacement r e p l a c e m e n t bodies, bodies, cavity v u g s , linings, l i n i n g s , and and veins, v e i n s , these t h e s e secondary s e c o n d a r y ores o r e s occur o c c u r at a t the the c a v i t y fillings, f i l l i n g s , vugs, surface is always always ini nclose close s u r f a c e to t o aa depth d e p t h of of 560 560feet. f e e t . The The secondary s e c o n d a r y ore o r e is proximity p r o x i m i t y to t o primary p r i m a r y ore. o r e . Secondary Secondary ore o r e minerals m i n e r a l s include i n c l u d e quartz, q u a r t z , calcite, calcite, barite, marcasite, b a r i t e , m a r c a s i t e , erhthrite, e r h t h r i t e , and and annabergite. a n n a b e r g i t e . Natie N a t i esilver s i l v e roccurs o c c u r sasa swires, wires, leaves, l e a v e s , and and nuggets, n u g g e t s , commonly commonly in i n clusters c l u s t e r s up up to t o 33 cm cm During the t h e operation operation During of of the t h e mine, mine, two two massive m a s s i v e secondary s e c o n d a r y deposits d e p o s i t s of of native n a t i v e silver s i l v e r were were discovered. winze d i s c o v e r e d . The The first f i r s t "Bonanza" "Bonanza" contained c o n t a i n e d721,632 721,632ounces ouncesofofsilver. s i l v e r . AA winze through t h r o u g h the t h e second second bonanza bonanza showed showed native n a t i v e silver s i l v e r on on four f o u r walls w a l l s for f o r aa length l e n g t h of of 60 60 feet. f e e t . The The following f o l l o w i n g scenario s c e n a r i o is i s aa conceptual c o n c e p t u a l model model for f o r the t h e Silver S i l v e r Islet Islet deposit. deposit 3. 3. . . 30 �ORE GENESIS GENESIS MODEL MODEL ORE The Archean Archean basement basement is i s aa source s o u r c e of of metamorphosed, metamorphosed, metal—rich, metal-rich, The v o l c a n e o g e n i c rocks. r o c k s . During During the t h e Archean—Proterozoic A r c h e a n - P r o t e r o z o i c unconformity u n c o n f o r m i t y (the (the volcaneogenic Eparchean Eparchean interval) i n t e r v a l ) the t h e Archean Archean rocks r o c k s were were exposed exposed to t o an a n extremely e x t r e m e l y long l o n g period period o f intense i n t e n s e physical p h y s i c a l erosion e r o s i o n and and unique unique chemical c h e m i c a l and and climatic c l i m a t i c environments, environments, of which produced produced aa deeply d e e p l y weathered weathered surface. s u r f a c e . This T h i s regional r e g i o n a l weathering w e a t h e r i n g profile profile which contained a variety of elements, derived from metal—rich Archean r o c k s , that that c o n t a i n e d a v a r i e t y o f e l e m e n t s , d e r i v e d from m e t a l - r i c h Archean rocks, were sorted, s o r t e d , fractionated, f r a c t i o n a t e d , and and concentrated c o n c e n t r a t e d by by laterization l a t e r i z a t i o n and and supergene supergene were p r o c e s s e s . With With the t h e onset o n s e t of of Proterozoic P r o t e r o z o i c sedimentation, s e d i m e n t a t i o n , the t h e weathering weathering processes. p r o f i l e was was buried b u r i e d and and preserved p r e s e r v e d in i n aa developing d e v e l o p i n gbasin. b a s i n . The The depth d e p t h of of burial burial profile If a sufficient geothermal gradient was i n c r e a s e d a s t h e b a s i n evolved. I f a s u f f i c i e n t g e o t h e r m a l g r a d i e n t was increased as the basin evolved. e s t a b l i s h e d , deep d e e p circulating c i r c u l a t i n g basinal b a s i n a l brines b r i n e s may may have have further f u r t h e r concentrate concentrate established, elements o r redistributed r e d i s t r i b u t e d them them to t o other other e l e m e n t s within w i t h i n the t h e buried b u r i e d lateritic l a t e r i t i c zone, zone, or h o r i z o n s . horizons. The intrusion i n t r u s i o n of of the t h e gabbro gabbro dikes d i k e s assisted a s s i s t e d in i n the t h e ore o r e genesis g e n e s i s in i n several several The The The dikes d i k e s contributed c o n t r i b u t e d to t o aa higher h i g h e r heat h e a t flow f l o w and and provided p r o v i d e d aa possible possible s o u r c e for f o r additional a d d i t i o n a l metals m e t a l s and and fluids. f l u i d s . The The dikes d i k e s also a l s o partitioned p a r t i t i o n e d the the source sedimentary s e d i m e n t a r y pile p i l e and and the t h e underlying u n d e r l y i n g basement basement rocks r o c k s into i n t o restricted r e s t r i c t e d circulating circulating c e l l s . Most Most importantly, i m p o r t a n t l y , after a f t e r solidification s o l i d i f i c a t i o n and and subsequent s u b s e q u e n t faulting, f a u l t i n g , the the cells. dike d i k e provided p r o v i d e d aa conduit c o n d u i t and and host h o s t rock rock for f o r ascending a s c e n d i n g ore—bearing o r e - b e a r i n g fluids. fluids. Hydrothermal Hydrothermal fluids f l u i d s obtained o b t a i n e d metals m e t a l s from from the t h e lateritic l a t e r i t i c horizon h o r i z o n located l o c a t e d within within the t h e restricted r e s t r i c t e d circulating c i r c u l a t i n g cells c e l l s adjacent a d j a c e n t to t o the t h e Silver S i l v e rIslet I s l e tdike. d i k e . Heat Heat was was provided p r o v i d e d by by the t h e geothermal g e o t h e r m a l gradient, g r a d i e n t , supplimented s u p p l i m e n t e d by by the t h e Keweenawan Keweenawan rifting rifting and associated a s s o c i a t e d intrusive i n t r u s i v e events. e v e n t s . The The fault, f a u l t , produced produced during d u r i n g later l a t e r stages s t a g e s of of and t h e rifting r i f t i n g event, e v e n t , provided p r o v i d e d a aconduit. c o n d u i t . Primary the P r i m a r y ore o r e was was deposited d e p o s i t e d over o v e r aa relatively The r e l a t i v e l y short s h o r t period p e r i o d of of time, t i m e , in i n aa graphite g r a p h i t e rich r i c h portion p o r t i o n of of the t h e dike. d i k e . The primary p r i m a r y ore o r e was was precipitated p r e c i p i t a t e d by by reductions r e d u c t i o n s in i n temperature, t e m p e r a t u r e , pressure, p r e s s u r e , and and r e d u c i n g conditions c o n d i t i o n s confined c o n f i n e d within w i t h i n the t h e dike. d i k e . Secondary S e c o n d a r y ore o r e deposits d e p o s i t s formed formed reducing o v e r aa relatively r e l a t i v e l y long l o n g period p e r i o d of of time, t i m e , possibly p o s s i b l y as a sepitherrnal e p i t h e r m a l or o r mesothermal mesothermal over systems i t as a s cavity cavity systems leached l e a c h e d silver s i l v e r out o u t of of the t h e primary primary deposit d e p o s i t and and redeposited r e d e p o s i t e d it ways. ways. fillings. fillings. 31 �GEOPHYSICAL INVESTIGATIONS, INVESTIGATIONS, INTERNATIONAL INTERNATIONAL FALLS FALLS AND ROSEAU QUADRANGLES, QUADRANGLES, MINNESOTA—ONTARIO MINNESOTA-ONTARIO By BY Horton, and Bruce D. Robert JJ. . Horton, Do Smith Smith Regional aeromagnetic gravity data have aeromagnetic and gravity have been been compiled compiled for for the the International Falls and and Roseau two degree quadrangles by the U.S. U.S. Geological Survey (USGS) in cooperation with the Minnesota Geological Survey (MGS) (MGS) and the Geological Survey Survey of Canada Canada (CGS). (CGS). This compilation was done as part of the Conterminous United States Mineral Assessment Program (CUSMAP) (CUSMAP) for for the the two two quadrangles located along the the U.S.—Canadian U.S.-Canadian border. border. Bedrock Bedrock in in the the area area is is largely buried by largely by Quaternary Quaternary glacial glacial deposits. deposits. Therefore, Therefore, maps maps of of the the bedrock bedrock based primarily on interpretation interpretation of regional geology are based regional aeromagnetic and mapping sparse gravity data supplemented by napping sparse outcrops and lithologic lithologic logging logging of of a limited limited number number of of drill drill holes. holes. Maps of gravity gravity and and magnetic magnetic anomalies anomalies are are presented here along with various maps illustrating computer computer processed processed enhanced maps produced produced to aid geologic interpretation interpretation of the the study study area. area. Data compilation compilation for preparation of aeromagnetic aeromagnetic maps includes includes existing existing data from supplements new data collected The from MCS MGS and CGS which supplements collected by the the USGS. USGS. The new airborne survey 114 mile at at an an elevation elevation survey was flown with a line line spacing spacing of of 1/4 of 300 300 feet feet with with aa high—precision high-precision proton proton sensor. sensor. A variety of navigation navigation systems including radar transponder, LORAN, and photo—recovery photo-recovery were used in in project in order to overcome problems in flight the USCS USGS project flight line location location over over largely featureless largely featureless terrain. terrain. The new new USGS USGS data data were were processed processed along along with with the the map other aeromagnetic data to produce an IGRF—corrected IGRF-corrected total magnetic field field map of quadrangles. quadrangles. Complete Bouguer anomaly gravity maps were also also prepared as as part part of of the the CUSMAP study using new data collected for the project combined with U.S. U.S. Department Department of Defense Defense gravity gravity data data base. base. The new new data were collected collected in in cooperation cooperation with the Minnesota Department of Natural Resources—Division Resources-Division of of on—going gravity Minerals and in cooperation with on-going gravity surveys surveys being done done by by the the MGS. Detailed profiles were made made by the USGS USGS to better define important important The geologic features features interpreted from preliminary preliminary gravity anomaly anomaly maps. maps. The total data set was then processed to produce terrain—corrected terrain-corrected Bouguer Bouguer anomaly anomaly maps maps of of the the two two quadrangles. quadrangles. The compiled aeromagnetic data was processed to to compensate compensate for for inclination and declination of induced magnetic fields fields which offset offset boundaries boundaries of causative causative sources sources from from magnetic magnetic highs. highs. The reduction—to—the—pole reduction-to-the-pole program program magnetic highs highs associated associated with with dipolar magnetic lows to be more shifts the magnetic coincident coincident with with the the source. source. Judicial use of this this enhanced map with with the the original geological interpretation original magnetic map facilitates geological interpretation of the the geophysical geophysical data. Gravity Gravity and magnetic data was further further processed processed to to produce produce color color shaded shaded (CSR), horizontal horizontal derivative, derivative, and and edge edge enhanced enhanced maps. maps. The CSR CSR and and relief (CSR), horizontal horizontal derivative maps emphasize subtle subtle linear linear features features and and level level changes changes in anomaly anomaly intensity. intensity. For example, example, the CRS CRS map of the the reduced reduced aeromagnetic aeromagnetic data data dramatically dramatically emphasizes linear anomalies anomalies due due to to northwest northwest striking striking diabase dikes. dikes. Edge enhanced reduced magnetic and gravity maps emphasize emphasize possible boundaries between geologic units with contrasting contrasting densities densities and/or and/or susceptibilities. susceptibilities. 32 �Interpretation Interpretation of detailed profiles of ground gravity and magnetic surveys through computer modeling of possible bedrock contacts suggests suggests size, size, shape, attitude, shape, attitude, and and physical physical properties properties of of causative causative bodies. bodies. Geophysical Geophysical interpretation interpretation of these maps can be integrated integrated with interpretation interpretation of of geological geological data data to to yield yield an an effective effective mineral mineral resource resource assessment assessment of of the the study study area. area. For CUSMAP studies studies described here, here, regional regional and and site site specific specific electrical electrical geophysical methods geophysical methods were were used. used. Application of electrical electrical geophysical geophysical methods methods is well known known in in the the glacial covered terrain terrain of the the Canadian Canadian Shield Shield and and is is routinely routinely used used by by mineral mineral exploration exploration companies companies in in Minnesota. Minnesota. Current Current implementation implementation of these airborne airborne and ground electrical electrical methods are are too too costly costly to apply over complete 10 lo xx 20 '2 quadrangle. quadrangle. The purpose of this presentation over aa complete presentation is to demonstrate demonstrate some some cost—effective cost-effective applications applications of new new airborne airborne and and selected ground electrical electrical methods in in regional regional mineral mineral resource resource assessment assessment Digital terrain data was processed to enhance trends trends to to aid aid in in programs. interpretation interpretation of of other other geophysical geophysical and and geologic geologic data. data. Interpretation of airborne EM anomalies anomalies and trends which might be be due due to to Interpretation conductive till is facilitated by comparison with trends conductive trends shown shown in in a colored colored shaded shaded relief relief map map of of topography. topography. This map is is also also useful in in showing showing trends trends of of both the East—west trends in the the exposed exposed bedrock bedrock and and glacial glacial deposits. deposits. East-west the central part of the International International Falls Falls Quadrangle Quadrangle result result from from glacial glacial erosion erosion deposition of thick lacustrine sediments and deposition sediments by the the ancient Lake Lake Agassiz. Ground electrical surveys surveys were made in in selected selected parts of the the study study area area supplement interpretation to supplement interpretation of bedrock features features and to to estimate estimate the the thickness thickness of glacial glacial till. till. Frequency and time domain sounding methods were used to to of Measurements of signals estimate till estimate till thickness. thickness. Measurements signals from from natural natural electrical electrical fields (such (such as as generated from from thunderstorms) thunderstorms) using using Audio—magnetotellurics Audio-magnetotellurics (ANT) and and telluric profiling methods added further constraints on overburden (AMT) overburden thickness thickness and and bedrock bedrock conductors. conductors. 33 �Hypabyssal rocks of the North Shore of of Lake Lake Superior: Superior: evidence evidence for for polybaric fractionation fractionation in in the the Midcontinent Midcontinent Rift Rift Eric A. Jerde, Institute Instituteof of Geophysics Geophysicsand and Planetaiy Planetary Physics, Physics, UCLA, UCLA,Los Los Angeles, Angeles, CA CA 90024 90024 The hypabyssal rocks of the North Shore of Lake Superior are found as diabase sills and dikes, and are present present both singly and in groups groups aall ll along the shore shore from from Duluth Duluth to the Canadian Border. Other Otherclusters clusters of of dikes dikes are also present around Lake Superior (1). The The most noteworthy noteworthy swarms swarms on on the the North Shore Shore occur occur near the Border, Border, and and as as aa major major map map unit unit in in the the region of Beaver Bay (e.g. 2). 2). These Theserocks rocksgenerally generallyhave haveolivine olivinetholeiitic tholeiiticcompositions, compositions, although exist. The rocks of the although other, more evolved compositions exist. Themajority majority of of the thehypabyssal hypabyssal rocks North North Shore Shore post-date postdate the the extensive extensive magmatism magmatism responsible responsible for for the the lavas, lavas,and andthus thusprovide providethe the opportunity opportunity to to study study magmatic magmaticproducts productsproduced producedlate latein inthe theevolution evolutionof ofthe theMidcontinent MidcontinentRift. Rift. Even though these dikes dikes and and sills sills appear appear very very similar similar to to one oneanother anotherininmajor majorelement element chemistry (most are aie high-Al), a striking chemistry (most striking range of compositions compositions is apparent apparent in the the trace trace elements. the range from —10 rare-earthelements elements(REE), (REE), thelight lightREE REE range from -10 toto—100 -100 times elements. Among Amongthe therare-earth chondrites, and and the theheavy heavyREE REErange rangefrom from—3 -3 to to —20 -20 times chondrites chondrites (Fig. (Fig.1). 1). Positive Positive europium europium anomalies anomalies are are present in in the most primitive rocks and and are are absent absent to to slightly slightly negative negative in the the more more evolved. Such Suchabundance abundance variations variations of an an order order of of magnitude magnitude suggest suggest that aa significant rocks. sigruf~cantamount amount of fractionation fractionation was was involved involved in in the 1önnation formation of of these these rocks. p I. g Figure 1. Diagram of chondrite-normalized REE data showing variation among the diabases of the North Shore of Lake Superior. a'I p LA Ca M Sm Eu Th Yb Lu Analysis Analysis is is ongoing, ongoing,but but there there appear appear to to be be no nomajor majorregional regionalpatterns patternsininthe thechemical chemical variations variationsalong along the North Shore. Of Ofthe the"evolved" "evolved"material, material, the the greatest greatestamount amount isisfound foundnear near Duluth, in places all all along along the shore. Since Sincethe thehypabyssal hypabyssalrocks rocksof ofthe theNorth North Duluth, but but is is present in Shore final stage stage of of the the rifting rifting process, process, the the apparent apparentrandom random distribution distribution of of Shore represent the fmal compositions compositionsalong along the the shore shoreisis consistent consistent with with aa well well developed developedplumbing plumbingsystem systemallowing allowing magmas magmasto to be be tapped tappedfrom fromcommon commonchambers chambersand and emplaced emplacedat atwidely widelyspaced spacedlocations. locations. Fractionation Fractionationat at multiple multiplelevels levelsin incontinental continentalcrustal crustalregimes regimesisisbecoming becomingmore moreand andmore more recognized recognized as as an an important importantprocess process in in the the generation generationof of magmas magmasseen seeninincontinental continentalsettings settings 34 �(e.g. 3-5). 3-5). In In these these models, models, aamagnesian magnesian melt melt isis produced produced from fromthe themantle, mantle,and andisiscollected collected (underplated) at the base of the crust. Such Suchaa magma magmawould wouldcrystallize crystallizeolivme, olivine,then then olivine olivine and and plagioclase, and eventually become saturated in clinopyroxene as well. Such Suchan anevolution evolution plagioclase, this same samehigh-Al high41 magma magma would produce a high-A1 high-Al magma as discussed discussed by by Klewin Kiewin (5). (5). IfIf this were then emplaced at a higher level level in in the the crust, crust, clinopyroxene clinopyroxene would would not not be be aa stable stable phase phase due to the shrinkage 6,7),and andonly only olivine olivine shrinkage of the the pyroxene pyroxene field field with with lowering lowering pressure pressure (e.g. (e.g. 6,7), and plagioclase would crystallize until until the magma magma was was once once again again saturated saturatedwith with respect respect to to clinopyroxene. clinopyroxene. The Thesuite suiteofofdiabases diabasesfrom fromLake LakeSuperior Superiorprovides providesexcellent excellentevidence evidencefor forjust just such such aa polybaric polybaric fractionation. fractionation. Since Since the primary difference difference between between the the two two fractionation fractionation schemes schemes is is the the presence presence or or crystallizing phase, diagrams such as MgO vs CaO CaO(Fig. (Fig. 2) 2) absence of clinopyroxene as a crystallizing absence work work quite quite well well in in displaying displayingthe the difference differencesince sinceone one quantity quantity(in (inthis thiscase caseMgO) MgO)isisnot not solely solely dependent and the other dependent on clinopyroxene clinopyroxene crystallization, crystallization, and other (CaO) (CaO) isisdependent dependent on on clinopyroxene. clinopyroxene.For Forfractionation fractionationinvolving involvingolivine olivineand andplagioclase, plagioclase,the theconcentration concentrationof ofMgO MgO would expected to to drop drop due due to toincorporation incorporationin in olivine, olivine,but butCaO CaOwould wouldremain re&ainrelatively relatively would be expected unchanged. Whenclinopyroxene clinopyroxenebegins beginsciystallization crystallizationCaO CaOwill willdrop, drop,leading leadingto to aa cross-trend cross-trend unchanged. When on on the the diagram diagram(Fig. (Fig. 2b). 2b). 12 11 I0 . i C 8 7 6 5 3 4 5 6 7 8 9 10 U 12 3 4 5 6 7 8 9 10 11 12 MgO(%) MgO(%) M g 0 (%) M g 0 (%) Figure 2. MgO vs CaO variation Figure 2. MgO vs CaO variationdiagrams diagramsfor forthe thehypabyssal hypabyssalrocks rocksofofthe theNorth NorthShore Shorefrom fromthis this study. " bshows showssuggested suggestedfractionation fractionationpaths. paths. study. Diagram Diagram"b" In Inthe thediagrams diagramsof ofFig. Fig.2,2,most mostsamples samplesare areon onthe theroughly roughlyconstant constantCaO CaOpath, path,indicating indicating that that olivine olivine and and plagioclase plagioclase fractionation fraitionation was a dominant dominant mode. However, However,some somecross-trends cross-trends are These are areconsistent consistent with withaahigh-Al high-A1magma magma("A") ("A")fractionating fractionatingolivine, olivine, arepresent. present. These plagioclase, "B"at some level in the crust. Continued Continuedevolution evolution plagioclase,and and clinopyroxene clinopyroxeneto to produce produce "B" could couldproduce producethe the even evenmore moreevolved evolvedmaterial materialfound foundin inthe the chilled chilledmargins marginsof of the the Lester LesterRiver River and "E").IfIfthe themagma magmaof ofcomposition composition"A" "A"were wereemplaced emplacedat at aa andEndion Endion Sills Sills of of Duluth Duluth (point (point "E"). higher higherlevel, level,the thepyroxene pyroxenestability stabilityfield fieldwould wouldbe besuppressed, suppressed,and andfractionation fractionationofofolivine olivineand and 35 �plagioclase would further down down in MgO, MgO, to to where where clinopyroxene clinopyroxene would plagioclase would take take itit further would be be a phase, i.e. at point "C". would then then lead lead to to a progression of crystallizing phase, "C". Crystallization would compositions toward toward that that of of 'ID. "D". The compositions The presence presence of of still still other other compositions compositions out to very very low low MgO values with CaO CaO —10% -10% isissuggestive crust. suggestiveof of fractionation fractionation at at still still higher higher levels levels in the crust. Three levels of fractionation has been suggested suggested for the lavas lavas of of the the North North Shore ShoreVolcanic Volcanic Group (NSVG) (5). In Inaddition, addition, there there are are several several samples samplesthat that contain contain very high amounts amounts of Whileno nogenuine genuinepicrites picrites have have been been described described for for the North Shore, these samples samples are MgO. While is possible possible that that more magnesian than the parents postulated for much of the rift rift magmatism. magmatism. ItIt is these samples samples represent material brought up from the very base of the crust when the rift was the most developed, and represent material that was evolving toward the high-A1 high-Al "parent" from Thesehigh-MgO high-MgOrocks rocks are are somewhat somewhatsimilar similarto to other, more primitive (picritic?) some other, (picritic?) magma. magma. These the high-MgO material material found found near the the base of the the extrusives exttusiveson on Mamainse Mamainse Point, Point, Ontario Ontario(8). (8). surprising to note that samples samples near near points points "B" "B" & & With regard to trace elements, it is not surprising 'D" variation diagrams, also have have the the "D" showing evidence evidence of of the most fractionation on the variation REE abundances abundances (50-100 (50-100 times times chondrites). chondrites). Even highest REE Even the samples that represent represent crystallization crystallization in the the absence absence of pyroxene pyroxene show show aa general general trend trend from from lower lower REE REE abundance abundance to to higher as the composition goes from high MgO to lower (i.e. (i.e. right right to to left left in in Fig. Fig. 2). 2). Another Another point concerns called a "pareit", "parent",namely namely at at point "A". " A . These Theseare arevery very concernsthe thesamples samplesthat that may be called similar in major element chemistry to the primitive olivine olivine tholeiites tholeiites of the NSVG (9), ( 9 , one one of which was used as a parent in modelling presented by Klewin However, the the incompatible incompatible KIewin (5). However, two or more in the primitive diabases relative to the trace elements are enriched by a factor of ~o of the the NSVG. NSVG. This primitive olivine tholeiites of Thismay may perhaps perhaps be be due due to to replenishment replenishment of of the the fractionating subcrustal subcrustal chambers, chambers, akin akin to to the process fractionating process described described by by O'Hara O'Hara (10), (lo), and consistent with the younger hypabyssal rocks tapping a later magma than the NSVG lavas. References (1) Green, al. (1988) (1988) in Mafic Maficdyke dykeswarms, swarms,Geological Geological Association Association of Canada Canada Green,J.C. J.C. et ct al. Special 289-302. Special Paper Paper 34, 34,289-302. (2) Miller, tripguidebook guidebookfor forselected selectedareas areasin inprecambrian precambriangeology geology of of Miller,J.D. J.D. (1987) (1987)in in Field Fieldtrip northeastern Minnesota, Minnesota Minnesota Geological Geological Survey SurveyGuidebook GuidebookSeries Series#17,43-70. #17,43-70. J. Petrol., (3) Cox, Cox, K.G. K G . (1980) (1980) 3. Petrol., 21, 21, 629-650. 629-650. (4) Weiblen, Weiblen,P.W. P.W. and and Miller, Miller, J.D. (1987) (1987) in Workshop Workshopon on the the growth growth of of continental continental crust, crust, 88-02, 162-164. LPI Technical Report 88-02,162164. (5) Kiewin, J. Geology, Klewin, K.W. K.W. (1989) (1989) J. Geology, 97, 97, 65-76. 65-76. al. (1979) (1979) Contrib. Contrib, Mineral. Mineral. Petrol., Petrol., 70, 70,111-126. 111-126. (6) Walker Walkeret et al. (7) Stolper, Stolper,E. E. (1980) (1980)Contrib. Contrib. Mineral. Mineral. Petrol., Petrol., 74, 74,13-27. 13-27. (8) Berg, Berg,J.H. J.H. and and Kiewin, Klewin, K.W. K.W.(1988) (1988)Geology, Geology, 16, 16,1003-1006. 1003-1006. (9) 3l2p. (9) Brannon, Brannon,J.C. J.C. (1984) (1984) Ph.D. Ph.D.Dissertation, Dissertation,Washington Washington University, St. Louis, 312p. (10) O'Hara, M.J. (1977) Nature, 266, 266, 503-507. 503-507. 36 �STRATIGRAPHIC AND STRUCTURAL EVOLUTION OF THE THE NORTHERN ITASCA METAVOLCANIC METAVOLCANIC STRATIGRAPHIC BELT, BELT, NORTH-CENTRAL NORTH-CENTRAL MINNESOTA MINNESOTA Mark i r s a , Minnesota Minnesota Geological G e o l o g i c a l Survey, S u r v e y , 2642 2642 University U n i v e r s i t y Avenue, Avenue, St. St. Mark A.A. JJirsa, Paul, MN 55114—1057 P a u l , MN 551 14-1057 Geologic i s providing p r o v i d i n g new new insight insight G e o l o g i c mapping in i n northeastern n o r t h e a s t e r n Itasca I t a s c a County is of the Archean, largely the Archean, l a r g e l y supracrustal s u p r a c r u s t a l complex known as a s the the iinto n t o the makeup of northern n o r t h e r n Itasca I t a s c a metavolcanic m e t a v o l c a n i c belt b e l t (NIMB). (NIMB). The NNIMB I M B is i s the w e s t e r n equivalent equivalent western of o f the the Wawa Wawa Subprovince Subprovince of of the t h e Superior S u p e r i o r Province. Province. IIt t iis s bounded on on the the east, east, west, w e s t , and and south s o u t h by by granitic g r a n i t i c rocks. rocks. the north, n o r t h , splays s p l a y s of the t h e Vermilion Vermilion To the the NIMB NIMB from m metasedimentary of the v Vermilion ffault a u l t zone separate s e p a r a t e the e t a s e d i m e n t a r y rocks r o c k s of ermilion Granitic i s generally g e n e r a l l y less less G r a n i t i c Complex Complex (Quetico ( Q u e t i c o equivalent). e q u i v a l e n t ) . Although exposure e x p o s u r e is percent, drilling, tthan han 5 p e r c e n t , ccores o r e s from eexploration x p l o r a t i o n and scientific scientific d r i l l i n g , together t o g e t h e r with with new aeromagnetic a e r o m a q n e t i c data (Bracken (Bracken and Godson, 1988), 19881, fill f i l l data d a t a gaps g a p s between between E-M data d a t a by by the the U.S. U.S. ooutcrop u t c r o p areas. a r e a s . Detailed D e t a i l e d modeling of o f magnetic m a g n e t i c and and E-M Geological G e o l o g i c a l Survey is i s providing p r o v i d i n g valuable v a l u a b l e information i n f o r m a t i o n to to aid a i d geologic g e o l o g i c interpreinterpreEffie—Coon Lake Lake aarea ttation a t i o n in i n the Effie-Coon r e a (western ( w e s t e r n third t h i r d of of map area) a r e a ) where exposure exposure is with i s minimal. A ccooperative o o p e r a t i v e sstudy tudy w i t h the Minnesota Natural N a t u r a l Resources Resources Research R e s e a r c h Institute I n s t i t u t e is i s underway to to define d e f i n e geochemical geochemical characteristics c h a r a c t e r i s t i c s of of the the A data NIMB. N IMB. d a t a base b a s e of of several s e v e r a l hundred hundred analyses a n a l y s e s is i s on file. file. Although the the stratigraphy s t r a t i g r a p h y is i s complicated c o m p l i c a t e d by by folding f o l d i n g and and ffaulting, a u l t i n g , rock rock units to the u n i t s are a r e generally g e n e r a l l y younger younger to t h e north n o r t h within w i t h i n the t h e mapped aarea. r e a . The supracrustal n aapparent p p a r e n t sstratigraphic t r a t i g r a p h i c oorder rder s u p r a c r u s t a l uunits n i t s (Fig. ( F i g . 11)) iin occur ((oldest—youngest) o l d e s t - y o u n g e s t ) and are a r e as follows: f o l l o w s : Units U n i t s 1, 1 , 2, 2, and 3 o c c u r on on two two limbs limbs of o f aa large l a r g e fold f o l d surrounding s u r r o u n d i n g the t h e Wasson Wasson Lake Lake pluton. pluton. The stratigraphic stratigraphic sequence s e q u e n c e differs d i f f e r s somewhat somewhat between between these these two two limbs. limbs. On the the southeast s o u t h e a s t limb, limb, unit broadly and iirregularly s b r o a d l y and r r e g u l a r l y ttransitional r a n s i t i o n a l upward upward from tholeiitic tholeiitic u n i t 11 iis a l c - a l k a l i c vvolcanic o l c a n i c and volcaniclastic v o l c a n i c l a s t i c rocks r o c k s and vvolcanic o l c a n i c rocks r o c k s to ccalc-alkalic Mafic, discontinuous d i s c o n t i n u o u s iron-formation. iron-formation. M a f i c , tholeiitic t h o l e i i t i c volcanics v o l c a n i c s interdigitate interdigitate with Unit limb. U n i t 2 conformably overlies o v e r l i e s unit unit w i t h iron—rich i r o n - r i c h strata s t r a t a on on the t h e north n o r t h limb. of aa monotonous monotonous ssequence massive 1 and consists c o n s i s t s of e q u e n c e of of pillowed p i l l o w e d and m a s s i v e metabasalt metabasalt This sills. T h i s sequence s e q u e n c e contains c o n t a i n s evidence e v i d e n c e of of upward— upwardfflows l o w s and hypabyssal h y p a b y s s a l sills. Unit (Jirsa, 1988). 1988). U n i t 3 contains c o n t a i n s dacitic d a c i t i c to t o andesitic andesitic sshoaling h o a l i n g deposition d e p o s i t i o n (Jirsa, It I t is locally l o c a l l y interbedded i n t e r b e d d e d with w i t h units units 1 vvolcanic o l c a n i c and derived d e r i v e d clastic c l a s t i c rocks. rocks. Unit of aa second m major and 2. 2. U n i t 4 is i s the bbase a s e of a j o r volcanic v o l c a n i c cycle c y c l e and consists c o n s i s t s of of high—iron h i g h - i r o n tholeiitic t h o l e i i t i c metabasalt m e t a b a s a l t flows f l o w s and and sills s i l l s that t h a t are a r e locally l o c a l l y magnetic. magnetic. Unit mafic and and uultramafic U n i t 5 contains c o n t a i n s mafic l t r a m a f i c sills, s i l l s , collectively c o l l e c t i v e l y known as a s the t h e Deer Lake Complex, Complex, that t h a t intrude i n t r u d e bboth o t h aa small s m a l l area a r e a of of compositionally c o m p o s i t i o n a l l y similar similar flows f l o w s and the predominantly predominantly ddacitic a c i t i c volcanic v o l c a n i c and clastic c l a s t i c rocks r o c k s of of unit u n i t 6. 6. The The contact c o n t a c t between between units u n i t s 44 and and 66 extends e x t e n d s more more than t h a n 50 50 kin, km, bbut u t iits t s nature nature iis s enigmatic. e n i g m a t i c . Unit U n i t 7 is i s aa ppoorly o o r l y eexposed, x p o s e d , south-topping, s o u t h - t o p p i n g , metabasalt metabasalt ssequence. equence. The inferred plutonic d i v i d e d into i n t o four f o u r main main i n f e r r e d tectonic t e c t o n i c and p l u t o n i c history h i s t o r y can can be divided eelements l e m e n t s listed l i s t e d chronologically c h r o n o l o g i c a l l y below: below: D1 predominantly 11.. Dl deformation d e f o r m a t i o n involved involved p r e d o m i n a n t l y north—south n o r t h - s o u t h compression c o m p r e s s i o n with w i t h local local perturbations i s adjacent adjacent p e r t u r b a t i o n s related r e l a t e d to t o diapiric d i a p i r i c rise r i s e of o f plutons. p l u t o n s . One such s u c h area a r e a is to was the Wasson Lake pluton p l u t o n which w a s emplaced into i n t o border b o r d e r rocks r o c k s causing causing t o the folding the second s e c o n d deformation. deformation. f o l d i n g and and migmatization m i g m a t i z a t i o n prior p r i o r to t o the The same style 2. i s a northwest-oriented n o r t h w e s t - o r i e n t e d transpressional t r a n s p r e s s i o n a l deformation. deformation. style 2. D2 is of t h e east e a s t in i n the Vermilion V e r m i l i o n District D i s t r i c t (Hudleston ( H u d l e s t o n and and o f deformation d e f o r m a t i o n 60 km to the D2 was was a rregional e g i o n a l transpressional t r a n s p r e s s i o n a l event, e v e n t , affecting affecting oothers, t h e r s , 1988) iimplies m p l i e s tthat h a t D2 a large l a r g e area a r e a of of the the Archean Archean crust. crust. 1 1 37 �Northeast-trending, N o r t h e a s t - t r e n d i n g , dominantly d o m i n a n t l y sinistral s i n i s t r a l faulting f a u l t i n g and and syn— syn- to t o postposttectonic t e c t o n i c emplacement of of variably v a r i a b l y magnetic, magnetic, syenitic s y e n i t i c to t o monzonitic m o n z o n i t i c intrusions intrusions (Bello Lake, Coon Lake and Linden ( B e l l o Lake, Linden plutons). plutons). 4. 4. Ubiquitous, Ubiquitous, northwest—trending, n o r t h w e s t - t r e n d i n g , mostly m o s t l y dextral d e x t r a l faulting. f a u l t i n g . Many Many of of these these faults f a u l t s appear appear to t o be splays s p l a y s or o r to t o be be otherwise o t h e r w i s e related r e l a t e d to t o the the Vermilion Vermilion fault these faults f a u l t s are a r e more more north— northf a u l t zone. zone. The The latest l a t e s t and and most most brittle b r i t t l e of of these northwest-trending n o r t h w e s t - t r e n d i n g and and many many are a r e now now occupied occupied by by Proterozoic P r o t e r o z o i c diabasic d i a b a s i c dikes. dikes. Some a n a l y t i c a l support s u p p o r t was was provided p r o v i d e d by by the the Minnesota Minnesota Some field f i e l d and and analytical Department the Department of of Natural N a t u r a l Resources. Resources. Scientific S c i e n t i f i c drilling d r i l l i n g was was supported s u p p o r t e d by by the Minnesota Minnesota Legislature L e g i s l a t u r e under u n d e r the the Minerals M i n e r a l s Diversification D i v e r s i f i c a t i o n Program. Program. Geophysical Geophysical data d a t a were were provided p r o v i d e d in i n part p a r t by by the the CUSMAP CUSMAP program program of of the t h e U.S. U.S. Geological G e o l o g i c a l Survey. Survey. 3. 3. References: References: Bracken, 1988, R.H., 1988, Aeromagnetic Aeromagnetic map map of of the the northwestern northwestern Bracken, R.E., R.E., and Godson, Godson, R.H., part p a r t of of the t h e Hibbing Hibbing 1° l o xx 2° 2' quadrangle, q u a d r a n g l e , Minnesota: Minnesota: U.S. U.S. Geological Geological Survey Survey Open—File Open-File Report R e p o r t 88—8, 88-8, scale s c a l e 1:62,500. 1:62,500. Hudleston, Hudleston, P.J., P.J., Schultz-Ela, S c h u l t z - E l a , D., D., and and Southwick, Southwick, D.L., D.L., 1988 1988 Transpression T r a n s p r e s s i o n in in an a n Archean Archean greenstone g r e e n s t o n e belt, b e l t , northern n o r t h e r n Minnesota: Minnesota: Canadian Canadian Journal J o u r n a l of of Earth p. 1060—1068. 1060-1068. E a r t h Sciences, S c i e n c e s , v. v. 25, 25, p. Jirsa, 1988, G Geologic J i r s a , M.A.,, M.A., 1988, e o l o g i c map of of the t h e Sherry S h e r r y Lake Lake quadrangle, q u a d r a n g l e , Itasca I t a s c a County, County, Minnesota: ~ i n n e s o t a : Minnesota Minnesota Geological G e o l o g i c a l Survey Survey Miscellaneous M i s c e l l a n e o u s Map Map M—64, M-64, scale scale 1:24,000. 1 :24,000. , Figure F i g u r e 1.1. Schematic Schematic pre— pre- or o r early e a r l y faulting f a u l t i n g reconstruction r e c o n s t r u c t i o n of of the the northern northern Itasca I t a s c a metavolcanic m e t a v o l c a n i c belt. b e l t . Supracrustal S u p r a c r u s t a l units u n i t s 1—7 1-7 are a r e described d e s c r i b e d in i n text. text. Small Small arrows arrows indicate i n d i c a t e direction d i r e c t i o n of of stratigraphic s t r a t i g r a p h i c topping. t o p p i n g . Black Black units u n i t s are are iron-formation—bearing. Vertically V e r t i c a l l y ruled r u l e d units u n i t s are iron-formation-bearing. are ultramafic u l t r a m a f i c and and mafic mafic T o n a l i t i c to t o granitic granitic sills s i l l s of of the the Deer D e e r Lake Lake Complex Complex or o r associated a s s o c i a t e d with with it. it. Tonalitic intrusions to be be early e a r l y (pre-D2) (pre-D2) are a r e the the Wasson Wasson Lake Lake pluton p l u t o n (W), (W), i n t r u s i o n s inferred i n f e r r e d to Effie Late, E f f i e pluton p l u t o n (E), ( E l , and and G. G. L a t e , potassic p o t a s s i c or o r alkalic a l k a l i c intrusions i n t r u s i o n s are a r e the the Bello Bello Lake Lake (B), ( B ) , Coon Coon Lake Lake (C), ( C ) , Linden Linden (L), ( L ) , and and Side s i d e Lake Lake (S) ( S ) plutons. p l u t o n s . Little L i t t l e is is known known of of the t h e other o t h e r intrusions i n t r u s i o n s labelled l a b e l l e d g. g. 38 �Tectonic Activity Jacobsville Sandstone Jacobsville Sandstone and Tectonic Kalliokoski J. Kalliokoski Professor Professor Emeritus Emeritus Michigan Technological Technological University University Houghton, 49931 Houghton, MI MI 49931 Between Keweenaw Bay and Ironwood Ironwood the Jacobsville Jacobsville Sandstone Sandstone (Jss) (Jss) occupies occupies aa portion of a rift flank flank basin along the south south side side of of the the Midcontinent Midcontinent Rift Rift and provides a record for late-tectonic late—tectonic activity System (MRS) and activity along the the MRS (Kalliokoski, 1989). 1989). The sandstone rests on the Powder Powder Mills Group of lavas lavas (Kalliokoski, (PMG; (PMG; about 20,000 20,000' thick). thick). The lavas show a weathered surface surface at three three localities. A thick localities. thick lava lava plateau probably existed existed south south and and east east (Hubbard, (Hubbard, 1975), above the reversely reversely polarized PMG 1975), above PMG dikes dikes (Cannon, (Cannon, 1986). 1986). East of Lake Lake Gogebic the PMG dips 1O—150N 10-15O~under the Jacobsville (Fritts, (Fritts, 1969), l969), with with 5,000 of original 5,000' original thickness thickness remaining remaining at the the outcrop. outcrop. West of Lake Gogebic Gogebic these sequences dip 60—90°N unconformable under 60-90O~and lie unconformable under the the Jss Jss (Hubbard, (Hubbard, 1975). Here the the PMG PMG and and its its basement basement underwent underwent aa rotation rotation to to the the north, north, 1975). accompanied and followed followed by by erosion. erosion. A cryptic fault fault through through Lake Lake Gogebic Gogebic (Klasner and and Jones, 1979) may may have accommodated this rotation rotation and defined margin of a tectonic the east margin tectonic highland. highland. About 15,000 15,000' of PMG PMG had been been eroded by Jacobsville Jacobsville time. time. Only a few hundred feet feet of stratigraphic stratigraphic section section can can be be constructed constructed from from the the gently dipping Jss along Keweenaw Keweenaw Bay, Bay, but more complete complete sections sections are are in in TT—6 available drill cores cores and logs logs (Fig. (Fig. 1). 1). TT-6 (2845) (2845') bottoms bottoms in in coarse, coarse, quartz—rich conglomerate. quartz-rich conglomerate. The core is of pebbly and very coarse—grained coarse-grained AE—1 sandstone, with 1% conglomerate (pebbles (pebbles up sandstone, 1% shale shale and and 97. 9% conglomerate up to to 4t)• 4"). AE-1 (2298) (2298') bottoms bottoms in in saprolite—covered saprolite-covered basalt. basalt. The core core lithologies lithologies are much RL—1 (3620') (3620) bottoms finer grained than than in in TT—6. TT-6. RL-1 bottoms in in sandstone. sandstone. In In his his M.S. M.S. thesis Bowers (1989) divides the core into four units with with boundaries boundaries near 400, 1700 400, 1700 and 2500 2500 feet. feet. The uppermost unit resembles resembles the the classic classic red red Jss Jss but the others others do do not. not. These lower units show thin beds of white sandstone, sandstone, red siltstone, and minor grit, with the three units differing red siltstone, differing in in texture texture and and relative lithologic RL—1 shows a fining lithologic abundances. abundances. RL-1 fining upward sequence sequence expressed by by the upward increase in shale and siltstone Taken expressed siltstone (Fig. (Fig. 1). 1). Taken together, together, the three logs show show a fining from west to east. The sections sections satisfy an alluvial alluvial fan fan model model (Kalliokoski, (Kalliokoski, 1982). 1982). The westward westward coarsening suggests that the area southwest southwest of of Lake Lake Gogebic Gogebic became elevated in early Jacobsville time, and that tectonic tectonic forces forces maintained a northeast draining basin during the deposition deposition of of more more than than 3,000 feet of sediment. sediment. There is other evidence as well for for possible possible tectonic activity during Jacobsville Jacobsville deposition: deposition: 11. . A flexural flexural model for for aa subsiding subsiding MRS basin, basin, such such as as that that suggested suggested by by Peterman and erosion to to the and Sims (1988) requires for the Jss, uplift and erosion south of a hinge and subsidence subsidence to to the the north. north. This would explain explain the the Goodman Bulge (Peterman preservation of paleosols paleosols under under the the Jss. Jss. The Goodman (Peterman and have undergone undergone coeval coeval uplift. uplift. Sims, 1988) might have 39 �2. some clasts 2 . In I n the t h e Bete B e t e Crise G r i s e Bay Bay aarea r e a some c l a s t s in i n the t h e Jss Jss are a r e remarkably r e m a r k a b l y similar similar to t o lithologies l i t h o l o g i e s in i n the t h e PLy, PLV, suggesting s u g g e s t i n g that t h a t there t h e r e had had been been sufficient s u f f i c i e n t uplift uplift along a l o n g the t h e Keweenaw Keweenaw reverse r e v e r s e fault f a u l t to t o remove remove the t h e Oronto O r o n t o cover c o v e r and and expose e x p o s e the the PLV PLV (Brojanigo, ( B r o j a n i g o , 1984). 1984). The The position p o s i t i o n of of the t h e paleosol p a l e o s o l localities l o c a l i t i e s suggests s u g g e s t s that t h a t the t h e hinge h i n g e line l i n e between between areas a r e a s of of deposition d e p o s i t i o n and and erosion e r o s i o n must have h a v e been b e e n many many miles m i l e s south s o u t h of o f the the current c u r r e n t southern s o u t h e r n limit l i m i t of of the t h e Jss. Jss. The The flexure f l e x u r e could c o u l d have h a v e arisen a r i s e n from from southerly s o u t h e r l y thrusting t h r u s t i n g along a l o n g the t h e Keweenaw Keweenaw fault f a u l t or o r from from the t h e cooling c o o l i n g of o f the t h e MRS MRS crust. crust. References Re f e r en ce s Bowers, Bowers, Mark, Mark, 1989, 1989, Vertical V e r t i c a l petrologic p e t r o l o g i c changes c h a n g e s of o f Jacobsville J a c o b s v i l l e Sandstone Sandstone at a t Rice R i c e Lake Lake Hole Hole Number Number 1:1: Unpublished U n p u b l i s h e d M.S. M.S. thesis, t h e s i s , Michigan Michigan Technological T e c h n o l o g i c a l University. University. - Kalliokoski, J . , 1988, 1988, Jacobsville J a c o b s v i l l e Sandstone S a n d s t o n e — an a n up—date: up-date: K a l l i o k o s k i , J., Basin B a s i n Geological G e o l o g i c a l Society S o c i e t y Field F i e l d Guide, G u i d e , in i n press. press. Michigan Michigan Peterman, P e t e r m a n , Z., Z . , and and Sims, S i n s , P.K., P.K., 1988, 1988, The The Goodman Goodman Swell: S w e l l : aa lithospheric lithospheric flexure f l e x u r e caused c a u s e d by b y crustal c r u s t a l loading l o a d i n g along a l o n g the t h e Midcontinent M i d c o n t i n e n t Rift R i f t System: System: Tectonics, T e c t o n i c s , v. v . 7, 7 , p. p. 1077—1090. 1077-1090. Others, O t h e r s , from from the t h e author author. — PM-' LP 9 Amas.. 40 lp 20m' �CriHt CD H 0 OCJ)-1• . O'U) t)C) IOQ Logs of holes in the Jacobsville Sandstone. TT-6 ( S W ~Sec. 33, T48N, R43W); AE-1 (Wi Cor. S e c . 36, T48N, R40W); RL-1 (Sec. 14, T55N, R32W) U. 0 CD .0- 0 C) S'-" CD C)- z CD 0• C U1rt tJi — 0 H '- U) I t1 &) '.• CD 0 0 cJ cJJ 0 0 0 0 0 r'-) I I I I 0 pb 9- cg iL/VC -a m a) 0) 0 .0- (•) • CD U) cn' I rr H CD 0'. , ZC) U) CD 03 . H Figure 1 C -n — RL-1 % shale 100 �Gravity Wawa G r a v i t y survey survey of o f aaportion p o r t i o of n othe f t hQuetico e Q u e t i and c o and Wawasubprovinces subprovinces near near Thunder Bay, Bay, O Ontario. Thunder ntario. M. Departmentofof Geology, M. M. M. Kehlenbeck, Kehlenbeck, Department Geology, Lakehead Lakehead UUniversity, n i v e r s i t y , Thunder Thunder Bay, Bay, P. Cheadle, Geology,UUniversity Ontario O n t a r i o and and S. S. P. Cheadle, Department Department o of f Geology, n i v e r s i t y ooff Calgary, Calgary, Calgary, Calgary, Alberta. A1 b e r t a . with IIn n this t h i s study, study, 350 350 new new gravity g r a v i t y stations s t a t i o n sare a r ecombined combined w i t h 50 50 previously previously surveyedsstations mapo fofa apportion surveyed t a t i o n s iinn aa detailed d e t a i l e dBouguer Bouguer anomaly anomaly map o r t i o n ooff the the Quetico Wawasubprovinces subprovincesn onorth andwest westoof ThunderBay, Bay, OOntario. Q u e t i c o and and Wawa r t h and f Thunder ntario. In I n general, general, high h i g h gravity g r a v i t yvalues values characterize c h a r a c t e r i z e the t h esouthern s o u t h e r n and and southwestern southwestern ppart a r t of o f the t h earea areawhere where metavolcanic metavolcanic rocks r o c k s of o fthe t h eWawa Wawa Muchofof tthe h e Quetico Q u e t i c o subprovince subprovince forms forms aa broad broad subprovince dominate. dominate. Much gravitational g r a v i t a t i o n a l low l o w reflecting r e f l e c t i n gextensive e x t e n s i v eexposures exposures ooff gneisses, gneisses, schists, s c h i s t s , and and gravity migmatites. Conversely, Conversely, wwell e l l defined defined g r a v i t y lows lows are a r e associated a s s o c i a t e d with with several several ggranitic r a n i t i c intrusive i n t r u s i v ebodies. bodies. Modelso of subsurfacec oconfiguration Models f subsurface n f i g u r a t i o n oof f tthe h e ddensity e n s i t y contrasts contrasts representative major showa at rtrough-like r e p r e s e n t a t i v e oof f m a j o r rrock o c k uunits n i t s show o u g h - l i k e sstructure t r u c t u r e ffor o r the the metavolcanic T h i s ttrough-like r o u g h - l i k e structure s t r u c t u r e is is metavolcanic rocks r o c k s of o fthe t h eWawa Wawa subprovince. subprovince. This flanked by aa domical domicalf efeature f l a n k e d by a t u r e i in n tthe h e ggranitoid r a n i t o i d rocks r o c k s to t o the t h e south. south. North North ooff the t h e metavolcanic m e t a v o l c a n i c rocks, rocks, a asuccession succession ofo low-grade f low-gradegreywackes greywackes with and and sslates l a t e s occupy occupy aa bbasinal a s i n a l sstructure. t r u c t u r e . This T h i s sstructure t r u c t u r e together together w i t h tthat h a t of of the andggranitoids form tthe t h e metavolcanic metavolcanic rrocks o c k s and r a n i t o i d s form h e subsurface s u b s u r f a c e cconfiguration o n f i g u r a t i o n of of the subprovincei nint this t h e Wawa Wawa subprovince h i s area. area. The gneisses, gneisses, sschists, of the The c h i s t s , and and migmatites m i g m a t i t e s of t h e Quetico Q u e t i c osubprovince subprovince form f o r m aa thick which uunderlies t h i c k southward southward dipping d i p p i n gwedge—shaped wedge-shaped s t structure r u c t u r e which n d e r l i e s the the This iss s wedge-shaped wedge-shaped s tstructure ructure i sstructures t r u c t u r e s ofo fthe t h eWawa Wawa subprovince. subprovi nce. Thi by aa model modelu unit uunderlain n d e r l a i n by n i t ooff greater g r e a t e r density d e n s i t y representative r e p r e s e n t a t i v e of o f mafic mafic gneisses and and aamphibolites. The denser denser substratum substratum iiss modeled with gneisses m p h i b o l i t e s . The modeled w ith dislocations Lakef afaults. d i s l o c a t i o n s corresponding c o r r e s p o n d i n g to t othe t h eQuetico Q u e t i c oand and Hawkeye Hawkeye Lake ults. The The ccross r o s s sectional s e c t i o n a l and andthree t h r e edimensional dimensionalmodels modelssuggest suggesta acombined combined processo of and1alateral t e r a l aaccretion c c r e t i o n ffor o r the t h e crustal crustal process f vvertical e r t i c a l tectonism t e c t o n i sm and eevolution v o l u t i o n ooff this t h i s part p a r tofo the f t h eSuperior S u p e r i o rProvince. Province. 42 �Deformation of of the the Lyon Lyon Lake Lake Massive Massive Suiphide Sulphide Deposit, Deposit, Deformation Wabigoon Subprovince, Subprovince, northwestern northwestern Ontari&-, Ontario1, Canada. Canada. Wabigoon E.R. Koopman2, Koopman2, B. B. Dubé3, Dubk3, J.M. J.M. Franklin2, Franklin2, K.H. K.H. Poulsen2, Poulsen2, and and E.R. M.R. Patterson4. Patterson4. M.R. The Lyon Lyon Lake Lake deposit deposit is is aa typical typical Zn-Cu-Pb-Ag Zn-Cu-Pb-Ag The volcanogenic massive massive suiphide sulphide deposit deposit located located in in the the volcanogenic Sturgeon Lake Lake area area of of the the Wabigoon Wabigoon volcano-sedimentary volcano-sedimentary Sturgeon Subprovince of of the the Archean Archean Superior Superior Province Province of of the the Canadian Canadian Subprovince Shield. The stratiform stratiform deposit deposit is is hosted hosted by by aa quartz quartz Shield. The crystal rich rich fragmental fragmental rhyolite rhyolite and and its its hanging hanging wall wall is is the the crystal basal maf mafic member of of the the overlying overlying volcanic volcanic cycle. cycle. The The basal ic member footwall to to the the ore ore horizon horizon consists consists of of an an upper upper rhyolitic rhyolitic footwall unit composed composed of of interbedded interbedded ash ash and and lapilli lapilli tuff, tuff, unit immediately underlain by aa lower lower rhyolitic rhyolitic unit unit of of coarsely coarsely immediately underlain by fragmental rock. rock. Underlying Underlying the the rhyolite, rhyolite, aa fining fining upward upward fragmental sequence of of sedimentary sedimentary rocks rocks comprised comprised of of greywacke, greywacke, sequence quartzose siltstone, siltstone, graphitic graphitic shale, shale, massive massive po-py po-py bands, bands, quartzose and capped capped by by an an extensive extensive iron-carbonate iron-carbonate and/or and/or iron iron oxide oxide and Banded Iron Iron Formation(BIF). Formation(BIF1. The occurrence occurrence of of aa BIF BIF Banded The underlying the the massive massive suiphide sulphide horizon horizon indicates indicates that that low low underlying temperature hydrothermal hydrothermal venting venting occurred occurred prior prior to to suiphide sulphide temperature deposition. Massive Massive suiphides sulphides form form several several stacked stacked or or en en deposition. echelon lenses, lenses, and and comprise comprise discontinuous discontinuous and and contorted contorted echelon bands of of coarse coarse grained grained sphalerite sphalerite and and pyrite. pyrite. All bands All stratigraphic units, units, as as well well as as dykes, dykes, and and ore ore are are stratigraphic folded(Fig. 1). 1). The The dominant dominant structural structural feature feature controlling controlling folded(Fig. ore distribution distribution is is aa major major open open fold fold characterized characterized by by aa ore east-southeast(Fig. 1). hinge line line trending trending east-southeast(Fig. 1). Hinge Hinge lines lines of of hinge mesoscopic folds, folds, foliation, foliation, and and striations striations measured measured on on mesoscopic bedding, foliation, foliation, and and fault fault planes planes are are all all subparallel subparallel to to bedding, the hinge hinge line line of of the the major major fold fold and and indicate indicate aa direction direction of of the stretching parallel parallel to to the the fold fold axis. axis. Observed Observed faults faults have have stretching limited control control on on ore ore distribution, distribution, because because there there is is no no limited significant stratigraphic stratigraphic or or ore ore displacement displacement related related to to significant them. However, However, faulting faulting is is consistent consistent with with the the style style of of them. folding. The The contact contact between between the the hanging hanging wall wall mafic mafic unit unit folding. footwall rhyolite rhyolite is is characterized characterized by by aa high high strain strain and footwall and zone, possibly possibly aa fault. fault. Mineral Mineral lineations lineations and and striations striations zone, on foliation foliation planes planes are are subparallel subparallel to to the the mesoscopic mesoscopic folds, folds, on and suggest suggest that that this this high high strain strain zone zone may may be be related related to to and folding. structural contour contour map map of of the the hanging hanging wallwallfolding. AA structural footwall contact indicates that the dip dip of of this this contact contact is is footwall contact indicates that the shallowing in in an an eastward eastward direction direction reflecting reflecting the the plunge plunge shallowing effect of of the the major major open openfold. fold. The The deformation deformation at at Lyon Lyon Lake Lake effect has resulted resulted in in the the re-orientation re-orientation of of portions portions of of orebodies orebodies has into attitudes attitudes that that are are much much shallower shallower than than the the steep steep into regional dip. dip. Structural analysis analysis has has assisted assisted in in the the regional Structural increased effectiveness effectiveness of of devoloping devoloping and mining mining these these increased and flatter orebodies. orebodies. flatter ' 2 ' Contribution to tothe theCanada-Ontario Canada-Ontario MineralDevelopment DevelopmentAgreement Agreement 1985-1990. 1985-1990. Contribution MineraJ. Geological Survey Survey of ofCanada. Canada. Geological Sciences de de la la terre, terre, Université Universitg du du Québec Quebec a Chicoutimi. Chicoutimi. Sciences Noranda Mines, Lyon Lake Ignace, Ontario. Ontario. Noranda Mines, Lyon Lake Division, Division, Ignace, 43 �COMPOSITE SECTION 525'LEVEL - 1800'LEVEL ELEVATION IN FEET tunIc, 0400 COMPOSITE SECTION 525 LEVEL - 1800 LEVEL SECTION 12.200E - SECTION t2,200E 600 LEVEL , 000 , SURFACE MOLE SL-23"4 \ . ,/ . 227 .' / SURFACE HOLE SL 2 3 - 1 4 - 3 2 . •00, '-so, so- is 4330 LEVEL t52 LOT NO £t00I,IiI**ll 0W. 1300 LEVEL L — -- J IIotNIA,! 10011 I,, lIl0•PAP3ltlL 0*ClT,c 110*1 .3,0. 0000 LOOIACI \' 1*10410 LlIllOiOOlC 011*1*01 '"A • 190 .00 Flour* 1. CO~po8itec r o u sKlion (12.200E) ol trià Sub Creek Zone. Inset: liometnc projection ol tho deposit the piunne of the mapi llexure North indicates Mm* Isometric Nonh whicn IS 40. ol east Flgur. 1. snowinq Composite cross section (12.200E) 01 th. Subarrow Creek Zone. Inset: projicilon hi ol projection 01 arrow Section 12.200E). true norm (Note is a fleour.. deposil snowing the Section plunge oft3.500E the mayor North indIcates Mini North which is 40 east of true north. (Note: Section t3,500E is S projection of Section t2.200E). ~ u b k ,B., Koopman, E.R., Franklin, J.M., Poulsen, K.H., and Dubé, B., Koopman, ER., Franklin, J.M., Poulsen, K.H., and Patterson, M.R. Patterson, M.R. 1989: Preliminary study of the stratigraphic and structural 1989: Preliminary study of massive the stratigraphic and structural controls of the Lyon Lake sulphide deposit, Wabigoon controls of the Lyon Lake massive suiphide deposit, Wabigoon Subprovince, northwestern Ontario; in Current Research, Part Subprovince, northwestern Ontario; in Current Research, Part C, Geological Survey of Canada, Paper 89-1C, p. 275-284. C, Geological Survey of Canada, Paper 89-iC, p. 275-284. Franklin, J.M., Gibb, W., Poulsen, K.H., and Severin, P. Franklin, J.M., Gibb, W., Poulsen, K.H., and Severin, 1977: Archean metallogeny and stratigraphy of theP. South 1977: Archean metallogeny and stratigraphy of the South Sturgeon Lake area; Mattabi field trip: 23rd annual meeting Sturgeon Lake area; field trip: 23rd75p. annual meeting of the Institute of Mattabi Lake Superior Geology, of the Institute of Lake Superior Geology, 75p. Harvey, J.D. and Hinzer, J.B. Harvey, J.D. andofHinzer, J.B.Lake ore deposits, Noranda Mines 1981: Geology the Lyon 1981: Geology of the Lyon LakeOntario; ore deposits, Noranda Mines Limited, Sturgeon Lake area, Canadian Institute of Limited, Sturgeon Lake area, Ontario; Canadian Institute of Mining and Metallurgy Bulletin, v. 74, no. 833, p.77-84. Mining and Metallurgy Bulletin, v. 74, no. 833, p.77-84. 44q, �POTENTIAL-FIELD ANOMALY ANOMALY NAPS HAPS OF OF THE THE LAKE LAKE SUPERIOR SUPERIOR REGION REGION POTEMTIAL-FIELD Robert Robert P. P. Kucks1, ~ucks', Val Val Chandler2, Chandler 2, S. S. Dwight Dwight Dods3, Dods3, C. C.Patrick Patrick Ervin4, Ervin 4, Peter Hood3, Hood 3, Ken Ken McConnell3, McConnell 3, and and Dennis Dennis Teskey3 Teskey 3 Geological Survey, Survey,Box Box25046, 25046,MS MS 964, 964,Denver, Denver,CO CO80225 80225 Geological 2Ninnesota ~ i n n e s o t aGeological Geological Survey, Survey, 2642 2642 University University Ave., Ave., St. St. Paul, Paul, MN MN 55114 55114 3Geological 3 ~ e o l o g i c a lSurvey Survey of of Canada, Canada, 1 1 Observatory Observatory Cr., Cr., Ottawa, Ottawa, Ont. Ont. 1U. -'-U. S. S. Canada Canada KIAOY3 KlAOY3 4Dept. of ^ept. of Geology, Geology, Northern Northern Illinois Illinois Univ., Univ., DeKalb, DeKalb, IL IL 60115 60115 New New color color magnetic magnetic and and gravity gravity anomaly anomaly maps maps compiled compiled for for GLIMPCE of the GLIMPCE contribute contribute to to the the understanding understanding of the tectonic tectonic development development of of the the Lake Lake Superior Superior region. region. Although Although the the magnetic magnetic data data were were obtained obtained from from aeromagnetic aeromaqnetic surveys surveys of of variable variable specifications, specifications, a consistent consistent data data set set was was prepared prepared by by adjustment adjustment relative relative to to a a common common reference reference field field and and by by analytical analytical continuation continuation of o f all ail data data to to aa datum datum 305 305 mm above above surface. surface. The The availability availability of the the digital digital data data sets sets allows allows application application of of aa variety variety of o f filtering filtering techniques. techniques. Analysis Analysis by by filtering filtering involves involves conversion conversion of o f the the data data into into a a form form that that enhances enhances particular particular anomaly anomaly characteristics, characteristics, such such as a s wavelength wavelength or or trend. trend. Resulting Resulting filtered filtered maps maps include include (1) (1) first first vertical vertical derivative derivative to to sharpen sharpen anomalies anomalies of of shallow shallow origin origin and and small small areal areal extent, extent, (2) (2) horizontal horizontal gradient gradient to to delimit delimit lithologic lithologic or or structural structural boundaries, boundaries, and and (3) ( 3 ) color color shaded shaded relief relief to to enhance enhance particular particular anomaly anomaly trends. trends. The The filtered filtered anomaly anomaly maps maps permit permit aa refined refined interpretation interpretation of of the the geology geology of of the the Lake Lake Superior Superior region. region. 45 �Basalt Basalt geochemistry geochemistry as an an indication indication of tectonic tectonic environment environment part of the Hemlo-Heron Bay Greenstone for the the central central part of the Hemlo-Heron Bay Greenstone Belt, Belt, Ontario. Ontario. Minneapolis, MN MN 55406 Roger Roger J. Kuhns, Kuhns, BHP-Utah BHP-Utah International, International, Minneapolis, 55406 The The Hemlo-Heron Hemlo-Heron Bay Bay greenstone greenstone belt belt is is part part of of the theeast-trending, east-trending, Schreiber-White River River section section of of the Wawa Wawa Subprovince Subprovince within within the the The Hemlo area is located Superior Province of Ontario (Muir, 1986). in Superior Province Ontario (Muir, 1986). The Hemlo area is located in the central central part part of of the the belt belt(Lat. (Lat.48°41.6'N, 48¡41.6'N Long. Long. 85°57.3'W). 85'57.3'W). HernIa Hemlo U-Pb U-Pb dates dates yield yield a 2,772 2,772 ma ma age age for for metavolcanics metavolcanics and and 2,718 2,718 to to 2,684 2,684 ma maages ages for granitoids granitoids intruding intruding the the supracrustal supracrustal rocks rocks (Corfu (Corfu and and Muir, Muir,1986). 1986). Lithologic Lithologic sequences sequences in in the the Hemlo Hemlo area area consist consist of thin thin flows flows and and tuffs tuffs to to thick thick piles piles of of pillowed pillowed and andmassive massivebasaltic basalticmetavolcanics, metavolcanics, and and rhyolitic metavolcanics (Kuhns, 1988). to aa lesser degree intermediate to lesser degree intermediate to metavolcanics (Kuhns, 1988). These These metavolcanics metavolcanics are are intertayered interlayered with with thick thick sequences sequences of of metametaargillite argillite and and metagreywacke metagreywacke which which represent represent turbiditic turbiditic accumulations. accumulations. An Al versus versusFe' Fe'(Fe' (Fe'==FFeTol/FeTol+MgO) An Al e ~ ~ t ~ l / F e ~ ~ t ~variation lvariation + M g O diagram )diagram for for Archean mafic rocks Archean mafic rocks (Naldrett (Naldrett and and Goodwin, Goodwin, 1977) 1977) applied applied to to the the HernIa Hemlo area area mafic mafic rocks rocks indicate indicate aa dominance dominance of of basalt, basalt, and andlesser lessermagnesiummagnesiumMajor Major element element data data (not (notshown) shown) affinity. indicate these basaltic rocks are of tholeiitic indicate these basaltic rocks are of tholeiitic affinity. and and ferrobasalt ferrobasalt compositions compositions (Fig. (Fig. 1A). 1A). Numerous petroNumerous trace trace element element variation diagrams diagrams illustrating illustrating petrogenetic genetic trends trends and and tectonic tectonic environments environments have have been been constructed constructed from from modern and Phanerozoic basaltic suites (i.e. Pearce and Cann, 1973; BVSP, modern Phanerozoic basaltic suites (i.e. Pearce and Cann, 1973; BVSP, 1981). 1981). The The application application of these these diagrams diagrams to to Archean Archean rocks rocks is arguable, arguable, but but their their purpose purpose is is two-fold: two-fold: (1) (1) the the identification identification of petrogenetic petrogenetic sequences, and (2) the identification of possible tectonic environments. sequences, and the identification of possible tectonic environments. The bridge the the MORB MORB and and IAT fields on Hemlo metabasalts metabasalts bridge on Ti Ti versus versus The Hemlo Cr and and Ti/Cr Ti/Cr versus versus Ni Ni diagrams diagrams (Figs. (Figs. 18, 16, C). C). The The data also also exhibit exhibit aa gross trend from from high high Ni Ni and Cr) to to high gross trend and low low Ti/Cr TiICr (high (high Cr) high Ti Ti and and low low Ni Ni and and Cr concentrations, concentrations, indicative indicative of fractionation trends trends from magnesianmagnesianbasalts basalts --> --> basalts basalts --> ferro-basalts. ferro-basalts. This This apparent apparent fractionation fractionation trend trend agrees with the agrees with the distribution distribution of data data on on Figure Figure 1A. 1A. Volcanic Volcanic cycles cycles have have A plot of Nb versus not been resolved due to folding complications. been resolved due to folding complications. plot of Nb versus Zr Zr shows shows a positive positive correlation correlation also also suggesting suggesting aa fractionation fractionation trend trend in in the the basalts (Fig. The D). The data data plot plot within within the the "Type "Type I"I" basalt basalt field fieldofofmodern modern (Fig. 11D). MORB's basalts erupt erupt along along topographically topographically normal normal MORB's (BVSP, (BVSP, 1981). 1981). Type Type I basalts segments of mid-ocean segments of mid-ocean ridge ridge complexes, complexes, although although similar similar signatures signatures can can also also be be obtained obtained from from island island arc arctholeiitic tholeiitic basalts. basalts. Rare for the 2) indicate indicate at at Rare earth earth element element patterns patterns for the metabasalts metabasalts (Fig. (Fig. 2) least two principal principal groups groups of basalts basalts (Fe-types (Fe-types and a n d Mg-rich Mg-rich to to normalnormalleast two types), which support the trace element data above. Ferrobasalts yield ) , which support the trace element data above. Ferrobasalts yield types I 46 �flat and are are typified by ow flat REE REE patterns patterns and typified by low SmN/YbN S ~ N I Y and ~and N CeN/SmN CeN/SrnN ratios, ratios, and and high E, F). characteristics high SmN S r n ~and YbN Y ~ concentrations Nconcentrations (Figs. (Figs. 11 E, F). These characteristics are (BVSP, are similar similar to to ferrobasalts ferrobasalts from from the the Blake Blake River Rivergroup, group,Ontario Ontario(BVSP, Flat REE patterns and total REE abundances of the ferrobasalts 1981). 1981). Flat REE patterns and total REE abundances of the ferrobasalts are are compatible with some ocean compatible with some island island arc arc basalts, basalts, and and Phanerozoic Phanerozoic Type Type I ocean floor basalts. are not present basalts. Since Type Type IIII basalts basalts are present (Fig. (Fig. 1D) I D ) island island arc arc affinities are favored affinities are favored for the the Hemlo Hemlo area area basalts. basalts. The second second basalt basalt group group exhibits LREE enrichment, and has higher SmN/YbN and CeN/SmN ratios exhibits LREE enrichment, has higher S ~ N I Y ~and N C e ~ l s m Nratios and and SmN S m N concentrations, concentrations, and and lower lower YbN Y ~ concentrations Nconcentrations than than the the ferrobasalts ferrobasalts E, F). The second second group group also also yields yields slightly slightly higher higherMg Mgconcentrations, concentrations, (Fig. 11 E, (Fig. but the the REE REE patterns patterns are are typical typical ofofAl-basalts Al-basalts ininother otherArchean Archeansequences sequences (e.g. Blake River River Group). Group). The LREE LREE enrichment enrichment is similar to to some some IAT's. IAT's. In summary, there are summary, there are two two principal principal groups groups of basalts basalts in in the theHemlo Hemlo area. The first group is comprised of ferro-basalts, which exhibit flat area. The group is comprised of ferro-basalts, which exhibit flat REE REE patterns, low Sm/Yb patterns, low Sm/Yb and and Ce/Sm Ce/Srn ratios, ratios, and and are are similar similar totoPhanerozoic Phanerozoic island island arc arc tholeiitic tholeiitic basalts. basalts. These These rocks rocks are are not notLREE LREEdepleted, depleted,therefore therefore they do not not specifically specifically match match Type Type I mid-ocean ridge ridge basalts. basalts. The second they second less well well defined, defined, but but isis comprised comprised of of Mg-rich Mg-rich to tonormal normalbasalts, basalts, group isis less which which are are LREE LREE enriched, enriched, have have high high Sm/Yb SmIYb and and Ce/Sm CeISm ratios, ratios, and and are are terranes and and may similar Al-basalts in in other other Archean Archean terranes may have have IAT IAT affiniaffinisimilar to to Al-basalts type of island Some type island arc arc setting setting is therefore therefore favored favored for at at least least the the ties. ties. Some central central portion portion of of the the Hemlo-Heron Hemlo-Heron Bay Bay greeristone greenstone belt. belt. This conclusion conclusion is is in in part part supported supported by the the presence presence of of intermediate intermediate to to felsic felsic pyroclastics pyroclastics and and turbidite turbidite basins, basins, although although more more regional regional studies studies need need to to be becompleted. completed. I I References References Basaltic Basaltic Volcanism Volcanism Study Study Project, Project, 1981, 1981, Basaltic Basaltic Volcanism Volcanism on the the Terrestrial Terrestrial Planets: Planets: Pergamon Press, Inc., Inc., N.Y., Pergamon Press, N.Y., p. p. 5-29. 5-29. F., and and Muir, Muir, T.L., T.L., 1986, 1986,Preliminary Preliminary U-Pb U-Pb ages ages from fromthe theHemlo Hemloarea, area,northwestern northwestern Corfu, F., Corfu, Ontario [abs]: Geol. Assoc. Assoc. Canada Canada and and Mi Min. Assoc. Canada, 1986, 1986, Progr. Progr. with with Abstr., Abstr., p.p.59. 59. Kuhns, Kuhns, R.J., R.J., 1988, 1988, The The Golden Golden Giant Giant Deposit, Deposit. Hemlo, Hemlo, Ontario: Ontario: Geologic and and geochemical geochemical relationships relationships between between mineralization, mineralization, alteration, alteration, metamorphism, metamorphism, magmatism magmatism and and tectonism: tectonism: Univ. Univ. Minnesota, Minnesota, Minneapolis, MN, Unpub. Unpub. Ph.D. Ph.D. Thesis, 458 p. p. Muir, Muir, T.L., T.L., 1986, 1986, Geology Geology of the the Hemlo Hemlo area, area, District District of of Thunder Thunder Bay: Bay: Ontario Ontario Geological Geological Survey, Survey, Report Report 217, 217, 65p. 65p. Naldrett, 1977, Volcanic Volcanic rocks rocks of the the Blake BlakeRiver RiverGroup, Group, Abitibi Abitibi Naldrett, A.J., A.J., and and Goodwin, Goodwin, A.M., A.M., 1977, greenstone belt, Ontario, Ontario, and and their Jour. Earth Sci., greenstone belt, their sulfur sulfur content: content: Canadian Canadian Jour. Sci., v. 14, 14, p. p. 539539550. 550. Pearce, J.A., and Cann, Pearce, J.A., Cann, J.R., J.R., 1973, 1973, Tectonic Tectonic setting setting of of basic basic volcanic volcanic rocks rocksdetermined determined using using Sci. Letters, v. 19, trace element element analyses: analyses: Earth Planetary Planetary Sci. Letters, v. 19, p. p. 290-300. 290-300. 47 . �____________________________ 6 24 105 1 (mid-ocean Ridge B a s a l t ) 20 lo4 16 5 .c E i= I-. 8 4 0 1 03 io Fe- bamlt3 0 (Island A r c T h o l e i i t e ) (Is1nd Arc , Tholeilte) . ,....., . . . ,,..., . 102 io2 , Io" 100 20 20 18 18' 1 o1 102 , , ,, 103 lo4 cr Cr D < 16 io2 14 12 12 I- U - z lO 8 101 6 4, 2 100 0 100 0 Hi ppm 4'- 100 Zr 3F I 200 300 FO ferrobasilt GROUP 2 3 MB z z E 0, z 2 0, 2 -S U GROUP 1 U GROUPI = ferrobisIt [BA = b a s a l t I'I'I''' FB FB IBA = basalt 0 I 2 3 4 5 MB GROUP I I- l.a 0 1 '"" leA = basalt Mq—bsaIt LMB 0 GROUP 1 z GROUP 2 6 7 1MB = Mq—basIt 0 8 20 30 40 SmH /YbN 50 Mg 60 70 80 90 100 Mg Figure 1.1. Major, Major, trace, t r a c e , and and rare rare earth element variation diaFigure earth element variation diagrams f o r Hem10 area rnetabasal t s (see t e x t f o r discussion). grams for Hemlo area metabasalts (see text for discussion). • Fe—b3a1t3 a Mq—/normel bee1t3 C C U U C Le Ce Pr Nd Figure2.2 . Figure Sm Eu Gd Dy Ho Er Yb Lu Rare earth element patterns f o r Hem10 Rare earth element patterns for Hemlo area rnetabasal t s (see t e x t f o r discussion). area metabasalts (see text for discussion). 48 48 �TECTONIC TECTONIC IMPLICATIONS IMPLICATIONSOF OF THE THESTRUCTURE STRUCTUREAND AND STRATIGRAPHY STRATIGRAPHY OF OF QUARTZITES QUARTZITES IN IN CENTRAL CENTRAL AND AND SOUTHERN SOUTHERN WISCONSIN. WISCONSIN. Gene L. L, LaBerge, LaBerae, Geology Geology Department, Department, University Universityof of Wisconsin-Oshkosh, Wisconsin-Oshkosh, Oshkosh, Oshkosh, Wisconsin, Wisconsin, and and U.S. U.S. Geological Geological Survey, Survey, and John John S. S. Klasner, Klasner, Geology Geology Macomb, Illinois Illinois and and U.S. U.S. Geological Geological Department, Western Illinois University, Macomb, Survey. Survey. ' Structural and stratigraphic relationships of quartzite quartzite in central central and and southern Wisconsin provide constraints on the nature of the 1,850 1,850 Ma Penokean orogen and the 1,790 The Eau EauPleine Pleine 1?790Ma Central plains Orogen. The fault zone in central Wisconsin represents the boundary between rocks of in of the the Wisconsin Wisconsin magmatic terrane on the north north and and aa complex complex of of Archean Archean and and Proterozoic Proterozoic rocks rocks to the south, south, and and appears appears to to be beaasuture suturezone zone(LaBerge, (LaBerge? Schulz and Myers, Myers?1984, LaBerge, 1986). Isolated Isolated exposures exposures of of Early Early occur near, and south of the Eau fault zone and Proterozoic quartzite occur Eau Pleine fault areas. Dott farther south in the Baraboo and Waterloo areas. Dott (1983) (1983) suggested suggested that that the quartzite quartzite and associated slate, dolomite and iron formation in the Baraboo Baraboo Syncline represents a sequence of sedimentary rocks that developed on aa continental margin. margin. We concur and passive continental and suggest suggest that the sedimentary rocks rocks formed formed on on the the passive passive margin margin of an an Archean Archean craton, craton, remnants remnants of of which which are are Wisconsin. LaBerge exposed in central Wisconsin. LaBerge and andKlasner Klasner (1986, (1986, 1988, 1988, in prep) prep) have have of these these quartzites to to interpreted structural and stratigraphic relationships of fold/thrust system suggest a major south-verging fold/thrust system that pre-dates pre-dates the 1,760 1,760 Ma igneous event in southern Wisconsin, and appears, instead, to be related related to aa collisional event during during the the 1,850 1,850 Ma Ma Penokean PenokeanOrogeny. Orogeny. This interpretation suggests that an Archean continental block with on its margin? margin, was accreted as associated Early Proterozoic platform sediments on an exotic terrane against the southern margin of the Wisconsin magmatic terrane. The Theplatform platformsedimentary sedimentary sequence sequence was thrust southward onto the the accreted Archean block, suggesting suggesting that Archean Archean basement basement extended southward southward from from the the Eau Eau Pleine Pleine fault fault zone at at least least to to the the Baraboo Barabooarea. area. Nd/Sm Nd/Sm isotopic isotopicevidence evidence from from the the 1,450 1,450 Ma Ma pluton pluton near near the the WisconsinWisconsinthat Archean crust did not contribute to that Illinois border indicates that that magma magma (Nelson and DePaolo, 1985). This suggests that Archean Archean crust was not present DePaolo, 1985). area. Therefore, in that area. Therefore, Archean crust evidently evidently does not extend as far south as the Illinois border. The Thenorthern northernmargin marginof of the theCentral Central Plains Plains orogen orogen is is projected through 1986), however, however, the the projected through southern southern Wisconsin Wisconsin (Sims, (Sims, Peterman, Peterman, 1986), nature of the boundary boundary between between the Central Plains orogen and the Penokean orogen is is unclear. unclear. If the boundary was the result of northward northward subduction subduction (Doff, 1983), an Andean margin on the Penokean would have developed. (Dott, 19831, on the Penokean would have developed. Southward subduction near a continental continental margin should produce produce major major northnorthNeither is is evident evident in southern Wisconsin. North-verging verging structures. Neither Wisconsin. North-verging features. The structures are localized, localizedl brittle (shallow) (shallow) features. The nature nature of of PenokeanPenokeanCentral Plains juncture juncture in in this this area area is is speculative. speculative. However, However, the lack of of evidence evidence suggest that that rocks of the for an Andean margin or northward vergence may suggest Central Plains orogen were emplaced by by strike-slIp strike-slip movement in this region. region. 49 �REFERENCES REFERENCES CITED CITED Doff, Dott, R. H., H., Jr., 1983, 1983, "The ''The Proterozoic red quartzite enigma in the north-central north-central United States--resolved by by a plate ccollision?" Society ~ l l i s i o n ?Geological Geological ~~ Society of of 129-141. America Memoir 160 (Medaris, L. F., Ed.) pp 129-141. LaBerge, G. L., L., 1986, 1986, "The Proterozoic Geology of the the Lake Lake Superior Superior Region," Region," LaBerge, G. L., and and Mode, Mode, W. W. N., N,, Guidebook, Guidebook, 50th 50thTn-State Tri-StateGeological Geological Field Conference, Vol. 1, 1, papers. papers. G. L., L., and Kiasner, LaBerge, G. Klasner, J. S., 1986, 1986, "Evidence for a major major south-directed south-directed Early Proterozoic Proterozoic thrust thrust sheet in south central Wisconsin, "Abstract, American Annual Meeting, San San Antonio, Antonio, TX. TX. Geological Society of American LaBerge, G. L., L., and Klasner, Ktasner, J. J. S., S., 1988, 1988,"The "TheBaraboo BarabooQuartzite: Quartzite: A new look at LaBerge, G. an old problem." problem." Abstract, Abstract,34th 34th Annual Annual Institute Institute on on Lake Lake Superior Superior Geology, Marquette, Marquette, Ml, MI,pp. pp.62-64. 62-64. LaBerge, G. G. L., Klasner, J. S. and Myers, E., in in review, review, "New "Newobservations observations on on Myers, P. P. E., the age and structure of Proterozoic Quartzites in Wisconsin," U.S. and structure of Proterozoic Quartzites in Wisconsin," U.S. Geological Survey Bulletin. Bulletin. G. L., L., Schulz, K. J., and Myers, Myers, P. P. E., E., 1984, 1984, "Early "Early Proterozoic Proterozoic Plate Plate LaBerge, G. Tectonics: Evidence Geological Evidencefrom fromnorth-central north-centralWisconsin," W i ~ c o n s i nAbstract, Abstract, ,~~ Geological Society of America, America, Annual Annual Meeting, Meeting, Rena, Reno, NV. NV. continental crust crust Nelson, 6. B. K., K., and DePaolo, D. J., J., 1985, "Rapid production production of continental 1.7 to 1.9 b. y ago: Nd I .7 to 1.9 b. Ndisotopic isotopic evidence evidence from the the basement basement of the North American Mid-continent," Geological Society Society of of America Bulletin, v. v. 9GI 96, pp 746-754. 746-754. Sims, P. P. K., K., Peterman, Z. Z. E., E., 1986, 1986, "Early "Early Proterozoic Proterozoic Central Central Plains Plains Orogen: Orogen: A Sims, A 14, major buried structure in in the north north central central United United States," States," Geology G e o l o ~ v. vv. 14, pp 488-491. 488-491. pp 50 �Possible Late-Stage Thrust Thrust Faulting Faulting in in aaKeweenawan-Age Keweenawan-Age Accommodation Zone Beneath Lake Superior Lake Superior L D McGinnis* (Engineering Geosciences, Argonne National McGinnis* (Engineering National Laboratory, Argonne, Argonne,IL IL60439; 60439;312-972-8722) 312-972-8722) H F Wang Wang (Dept. of of Geology Geology & & Geophysics, Geophysics, U. U. of of Wisconsin, Wisconsin, Madison, WI W I 53706; 608-262-5932) 608-262-5932) J LL Sexton Sexton (Dept. (Dept. of of Geology, Geology, Southern Southern Illinois Illinois U., U., Carbondale, Carbondale, IL 62901; 62901; 618-453—7374) 618-453-7374) JJ Nyquist Nyquist (Health (Health Physics, Physics, Oak Oak Ridge Ridge National National Laboratory, Laboratory, Oak Oak Ridge, TN T N 37830; 37830; 615-574-4646) 615-574-4646) M G Mudrey Mudrey (Geological (Geological & MG & Natural History History Survey, Survey,Madison, Madison,WI Wl 53705; 608-263-5495) 608-263-5495) GB Morey (Minnesota (Minnesota Geol. Survey, St. Paul, B Morey Paul, MN M N 551144; 551144; 612612627-4780) 627-4780) B Milkereit (Geological (Geological Survey Survey of of Canada, Canada, Ottawa, Ottawa, Ontario B Milkereit Ontario K1A 0E8; 613-995-5490) KIA OE8; W Hinze (Dept. (Dept. of of Earth & W J3 Hinze & Atmos. Sciences, Purdue Purdue U., U., West West Lafayette, IN47907; 47907;317-494-5982) 317-494-5982) Lafayette,IN A Green (Geological Survey of of Canada, Ottawa, Ottawa, Ontario OntarioK1A KIA 0E8; OE8; 613-995-5490) C PP Ervin Ervin (Dept. of Geology, Geology, Northern Northern Illinois Illinois U, U., DeKaib, DeKalb,IL IL 60115; 60115; 815—753-1942) 815-753-1942) A B Dickas (Dept. of Geosciences, Geosciences, U. U. of of Wisconsin, Wisconsin, Superior, Superior, WI 54880; 54880;715—394—8311) 715-394-8311) W Reston, VA W FF Cannon (USGS, Reston, VA 22092; 22092; 703-959-6345) 703-959-6345) A A research team team coordinated coordinated by by Argonne Argonne National National Laboratory Laboratory (ANL), underaa grant grant from from the Department (ANL), under Department of of Energy's Energy's Office Office of Basic has entered entered into Basic Energy Energy Sciences Sciences (DOE/OBES), (DOE/OBES), has into an an agreement agreement with with Grant Grant Norpac, Norpac, Inc. Inc. (GNI) (GNI) to license license deep deep seismic reflection, gravity, gravity, and data in seismic reflection, and magnetic magnetic data in the the Great Great Lakes. Data were were licensed licensed to toassist assistDOE/OBES DOEIOBES in the evaluaevalua- tion of the the hydrocarbon hydrocarbon potential potential of of basins basins of Proterozoic Proterozoic age age in North North America. America. The initial initial acquisition acquisition includes includes 1,042 1,042 line line kilometers kilometers of eight eight second second data datainin Lake LakeSuperior. Superior. Data were were collected 1 2 0 groups groups of of collected using using aa tuned tuned array array of of airguns airguns and and 120 25 meter intervals along a receivers receivers spaced spaced at a t 25 meter intervals along a 3.0 3.0 km km streamer. The The60 60fold folddata datahave havebeen beenprocessed processed and and migrated migrated by GNI. Gravity and magnetic magnetic data data were were also also recorded recorded along along by GNI. most of the profiles. profiles. 52 �to strike strike of of the Profiles are oriented oriented parallel parallel and and perpendicular perpendicular to Mideontinent Rift, tying tying together Midcontinent Rift, together profiles profiles collected collected by by the the GLIMPCEconsortium consortium in in 1986. GLIMPCE 1986. A A 342.8 342.8 km k m profile profile (LS-08) (LS-08) from Duluth to 22 2 2 km krn east of of Isle Isle Royale Royale parallels parallels the axis axis of the the Duluth to rift. An An accommodation accommodation zone of the the profile, profile, zoneinin the the center center of associated with a gravity associated with gravity low, low, separates separates axially axially adjacent adjacent basins, basins, and is is composed composed of aa massive massive block block of of Archean Archean Gneiss. Gneiss. Modest thrusting thrusting and and ramping ramping up up to to the west Modest west isissuggested suggested on on the east flank Thrusting must must have occurred the flank of of the the block. block. Thrusting occurred after volcanism Bayfield and and after volcanism but but before before deposition deposition of of the the Bayfield Oronto Sandstones which Oronto Sandstones which unconformably unconformablycover cover the the truncated crest of of the theblock block and andthe theeroded erodedsuberops subcrops of ofvolcanic volcanic flows. flows. If If thrusting thrusting has has occurred occurred in in this this environment, environment, the the proximity proximity of the Grenville Grenville convergence convergence in space and time might might be be aa cause. cause. post-rift thrust thrust or or reverse reverse faulting faulting occurred occurred parallel parallel to to If post-rift strike, as well as across the strike of the rift as already strike, well across the strike of the rift as already reported, with reported, with thrusts t k u s t s generated generated by by stress stress fields fields emanating emanating then the from aa converging from converging plate plate margin, margin, then the rift may may have have become a secondary become secondary tectonic feature, feature,quenched quenched by by the prevailprevailThe unusually great vertical ing tectonics tectonics of of the the Grenville. Grenville. The unusually great ing extent of extent of the the rift riftbasin basinand anditsitsbillion-year billion-year preservation preservation is is probably a consequence consequence of of its its lateral immobilization immobilization aat t aa probably rather early early stage stage of of its itsdevelopment. development. *Work supported by by the the U.S. Department of Energy, Office of *Work supported U.S. Department 1-1 09-Eng-38. Energy Research, Research, under underContract ContractW-3 W-31-109-Eng-38. 53 �CHARACTERIZATION CHARACTERIZATION OF O F GRAPHITE GRAPHITE OCCURRENCES OCCURRENCES IN I N THE THE SOUTHERN SOUTHERN AND AND WESTERN WESTERN PENOKEAN OROGEN PENOKEAN OROGEN McSwiggen, McSwiggen, Peter P e t e r L., L . , Minnesota Minnesota Geological G e o l o g i c a l Survey, S u r v e y , 2642 2642 University University Avenue, Avenue, St. S t . Paul, P a u l , Minnesota Minnesota 55114—1057 551 14-1 057 E l e c t r o m a g n e t i c (E-M) (E-M) surveys, s u r v e y s , geologic g e o l o g i c mapping mapping and and bedrock b e d r o c k drilling drilling Electromagnetic have h a v e shown shown that t h a t the t h e rocks r o c k s of of the t h e southern s o u t h e r n and and western w e s t e r n Penokean Penokean orogen o r o g e n concontain t a i n an a n abundance abundance of o f highly h i g h l y graphitic g r a p h i t i c metasedimentary m e t a s e d i m e n t a r y units u n i t s (McSwiggen, (McSwiggen, 1987; 1987; Southwick Southwick and and others, o t h e r s , 1988). 1 9 8 8 ) . Many Many of o f these t h e s e units u n i t s have have been b e e n drilled drilled t h e m , but but b e c a u s e of of the t h e very v e r y pronounced pronounced E—M E-M anomalies a n o m a l i e s associated a s s o c i a t e d with w i t h them, because very the rocks, r o c k s , particularly p a r t i c u l a r l y with with v e r y little l i t t l e detailed d e t a i l e d work work has h a s been been done done on on the regard r e g a r d to t o the t h e graphite. g r a p h i t e . The The purpose p u r p o s e of o f this this investigation i n v e s t i g a t i o n is is to t o characcharact e r i z e the t h e concentrations c o n c e n t r a t i o n s and and abundance of o f the the graphite, g r a p h i t e , nature n a t u r e and and conconterize the origin o r i g i n of o f the t h e graphite, g r a p h i t e , and and the the c e n t r a t i o n s of o f secondary s e c o n d a r y minerals, m i n e r a l s , the centrations formation f o r m a t i o n of of the the graphite—bearing g r a p h i t e - b e a r i n g units. units. The i t s crystallinity, c r y s t a l l i n i t y , the t h e amount amount of o f precious precious The amounts amounts of of graphite g r a p h i t e and and its a n d base b a s e metals, m e t a l s , and and the t h e sediment s e d i m e n t source s o u r c e of o f the t h e host h o s t rocks r o c k s are a r e all all and exceedingly e x c e e d i n g l y variable. v a r i a b l e . The The graphitic g r a p h i t i c units u n i t s range r a n g e from from less l e s s than t h a n 1 percent percent carbon c a r b o n to t o more more than t h a n 40 40 percent. p e r c e n t . The The crystallinity c r y s t a l l i n i t y of of the the graphite g r a p h i t e reflects reflects the the Emily Emily district d i s t r i c t the the t h e metamorphic metamorphic grade g r a d e of of the t h e locality. l o c a l i t y . North N o r t h of of the carbon c a r b o n occurs o c c u r s as a s amorphous amorphous material m a t e r i a l lacking l a c k i n g any a n y crystallization c r y s t a l l i z a t i o n structure. structure. In Moose Lake—Glen Lake-Glen Township Township structural s t r u c t u r a l panel p a n e l of of I n contrast, c o n t r a s t , samples samples from from the t h e Moose to highly h i g h l y crystalline crystalline S o u t h w i c k and and others o t h e r s (1988) ( 1 9 8 8 ) contain c o n t a i n moderately m o d e r a t e l y th Southwick graphite. graphite. The s l a t e to to The host h o s t rocks r o c k s of of the t h e graphite g r a p h i t e range r a n g e in i n composition c o m p o s i t i o n from from slate chert. the least l e a s t amount amount of of clastic clastic c h e r t . The The richest r i c h e s t carbon c a r b o n samples s a m p l e s contain c o n t a i n the sediments; the primary p r i m a r y nonnons e d i m e n t s ; this t h i s suggests s u g g e s t s that t h a t chemical c h e m i c a l sedimentation s e d i m e n t a t i o n was was the organic these samples. samples. o r g a n i c source s o u r c e of of sediment s e d i m e n t in i n these The The carbon-rich c a r b o n - r i c h samples samples also a l s o typically t y p i c a l l y contain c o n t a i n anomalous anomalous values v a l u e s of o f base base metals m e t a l s (Cu (Cu as a s much much as a s 2900 2900 ppm) ppm) and a n d precious p r e c i o u s metals m e t a l s (Au (Au as a s much much as a s 350 350 ppb ppb and ppm). Preliminary p r e l i m i n a r y results r e s u l t s show show that t h a t only o n l y half h a l f the the gold gold a n d Ag Ag as a s much much as a s 66 ppm). in i n the the sample sample is i s separated s e p a r a t e d with w i t h the t h e sulfide s u l f i d e fraction. f r a c t i o n . This T h i s suggests s u g g e s t s that that half h a l f the the gold g o l d may may be be adsorbed a d s o r b e d to t o the t h e graphite. g r a p h i t e . This T h i s relationship r e l a t i o n s h i p seems seems to to hold the rock. rock. h o l d regardless r e g a r d l e s s of of the t h e total t o t a l gold g o l d or o r sulfur s u l f u r content c o n t e n t of of the 1 References: References : McSwiggen, McSwiggen, P.L., P.L., 1987, 1987, Geology Geology and and Geophysics G e o p h y s i c s of o f the t h e Denham-Mahtowa Denham-Mahtowa area, area, east—central e a s t - c e n t r a l Minnesota: Minnesota: Minnesota Minnesota Geological G e o l o g i c a l Survey S u r v e y Miscellaneous M i s c e l l a n e o u s Map Map Series, 1 :48,000. S e r i e s , M—63, M-63, scale s c a l e 1:48,000. Southwick, S o u t h w i c k , D.L., D.L., Morey, Morey, G.B. G.B. and and McSwiggen, McSwiggen, P.L., P.L., 1988, 1988, Geologic G e o l o g i c map map (scale the Penokean Penokean orogen, o r o g e n , central c e n t r a l and and eastern e a s t e r nMinnesota, Minnesota, ( s c a l e 1:250,000) 1 : 2 5 0 , 0 0 0 ) of o f the and a n d accompanying accompanying text: t e x t : Minnesota Minnesota Geological G e o l o g i c a l Survey S u r v e y Report R e p o r t of of Investigations I n v e s t i g a t i o n s 37, 3 7 , 25 25 p. p. Funding Funding Source: S o u r c e : Minnesota Minnesota Geological G e o l o g i c a l Survey S u r v e y and and Mineral Mineral Diversification D i v e r s i f i c a t i o n Program. Program. 54 �GLACIAL GEOLOGY GEOLOGY OF OF NORTHERN NORTHERN MINNESOTA: MINNESOTA: MINERAL EXPLORATION APPLICATIONS APPLICPTIONS Meyer, N., Minnesota M i n n e s o t a Geological G e o l o g i c a l Survey, S u r v e y , 2642 2642 University U n i v e r s i t y Ave., Ave., St. St. Meyer, Gary N., Paul, P a u l , MN 55114 55114 Glacial major G l a c i a l ice i c e from two m a j o r accumulation a c c u m u l a t i o n centers c e n t e r s advanced repeatedly r e p e a t e d l y across across northern the Pleistocene. P l e i s t o c e n e . The Labradorean L a b r a d o r e a n center center n o r t h e r n Minnesota Minnesota throughout t h r o u g h o u t the northeast, o r t h e a s t , and the t h e Keewatin ccenter e n t e r ice from the the ccontributed o n t r i b u t e d iice c e from the n northwest. the g geologic of movements is more more northwest. IIn n ggeneral e n e r a l the e o l o g i c rrecord ecord o f these iice c e movements complete, and ttherefore drift more complex, complex, south west r i f t stratigraphy s t r a t i g r a p h y more s o u t h and w est c o m p l e t e , and h e r e f o r e the d of o f the t h e major bedrock outcrop o u t c r o p area a r e a of o f northeastern n o r t h e a s t e r n Minnesota. Minnesota. The mostly m o s t l y thin t h i n mantle m a n t l e of o f glacial g l a c i a l sediment s e d i m e n t across a c r o s s northern n o r t h e r n St. S t . Louis, Louis, Lake, and Cook Cook C Counties was laid Wisconsinan) l a s t (late (late W i s c o n s i n a n ) ice ice Lake, o u n t i e s was l a i d down by the last Labradorean It a b r a d o r e a n Rainy R a i n y lobe. lobe. I t consists c o n s i s t s primarily p r i m a r i l y of o f locally locally aadvance d v a n c e of o f the L derived, the east e a s t Proterozoic, p r o t e r o z o i c , bedrock. bedrock. The d e r i v e d , disintegrated d i s i n t e g r a t e d Archean, and and to t o the North outcrop of however, was overridden by N o r t h Shore Shore o u t c r o p aarea rea o f the three t h r e e counties, c o u n t i e s , however, o v e r r i d d e n by Labradorean out Superior basin, Superior uperior b a s i n , the S u p e r i o r lobe, l o b e , which L a b r a d o r e a n iice c e moving o u t of o f the S down ddistinctive from ddisintegrated llaid a i d down i s t i n c t i v e rreddish e d d i s h ssediment e d i m e n t dderived e r i v e d from isintegrated Keweenawan bedrock. bedrock. Late Rainy L a t e Wisconsinan R a i n y lobe l o b e drift d r i f t also a l s o overlies o v e r l i e s bedrock b e d r o c k across across northeastern County, northern the Woods Woods County, County, n o r t h e a s t e r n IItasca t a s c a County, n o r t h e r n and and eastern e a s t e r n Lake Lake of o f the but o f Koochiching Koochiching County County (Martin ( M a r t i n and and others, others, and all all b u t the t h e ssouthwestern o u t h w e s t e r n part of 1988; M Martin and oothers, i s buried b u r i e d there t h e r e by by drift d r i f t of o f the the 1988; a r t i n and t h e r s , in i n progress), p r o g r e s s ) , but b u t is Sediment Keewatin Koochiching lobe. lobe. S e d i m e n t deposited d e p o s i t e d by by the the Koochiching Koochiching lobe, lobe, of northern Minnesota w west of Louis i s tthe h e ssurficial u r f i c i a l ddrift rift o f n o r t h e r n Minnesota est o f St. St. L ouis which is County, County, is i s characteristically c h a r a c t e r i s t i c a l l y finer f i n e rin i ntexture t e x t u r ethan t h a nthat t h a tofo fthe theRainy Rainy lobe, lobe, Cretaceous and Ppaleozoic bbeing e i n g dderived e r i v e d cchiefly h i e f l y from from C r e t a c e o u s sshale h a l e and a l e o z o i c ccarbonate a r b o n a t e ffar a r tto o the drift, t h e west w e s t and and northwest. northwest. Koochiching lobe lobe d r i f t , therefore, t h e r e f o r e , is i s aa poor poor sampling mediumf ofor s a m p l i n g medium r ggeochemical e o c h e m i c a l eexploration. xploration. bedrock The remainder r e m a i n d e r of o f the the b e d r o c k ssurface u r f a c e oof f northern n o r t h e r n Minnesota Minnesota iis s overlain overlain byy aa complex complex ppile of interbedded b i l e of i n t e r b e d d e d glacial g l a c i a l sediment s e d i m e n t of of both b o t h Labradorean L a b r a d o r e a n and and Consequently, Keewatin provenance. provenance. C o n s e q u e n t l y , only o n l y the t h e lower l o w e r drift d r i f t of o f both b o t h ssources ources includes The position i n c l u d e s significant s i g n i f i c a n t amounts amounts of o f detritus d e t r i t u s from from local l o c a l bedrock. bedrock. position of derived d i s t a n c e of of transport t r a n s p o r t are a r e determined d e t e r m i n e d pri— prio f locally locally d e r i v e d cclasts l a s t s and the distance manly m a r i l y by by local l o c a l bedrock b e d r o c k topography t o p o g r a p h y and and basal b a s a l ice i c e velocity. velocity. IIn n general, general, toward ttopographic and ssubglacial u b g l a c i a l ttransport r a n s p o r t ccarries a r r i e s eentrained n t r a i n e d ddebris e b r i s toward o p o g r a p h i c lows, lows, and transport distances through lows are longer than across intervening highs t r a n s p o r t d i s t a n c e s t h r o u g h lows a r e l o n g e r t h a n a c r o s s i n t e r v e n i n g h i g h s Evidently had a l o b e had a relatively r e l a t i v e l y high high ((Clark, C l a r k , 1987). 1987). E v i d e n t l y the Koochiching lobe and ttransported whereas tthe ssliding l i d i n g vvelocity e l o c i t y and r a n s p o r t e d bbasal a s a l ddebris e b r i s llong o n g ddistances, i s t a n c e s , whereas he Rainy lobe l o b e had had a a relatively r e l a t i v e l y low low sliding s l i d i n g velocity v e l o c i t y and a n d transported t r a n s p o r t e d newly newly debris only eentrained ntrained d ebris o n l y short s h o r t distances. distances. be ddetermined e t e r m i n e d iin n bbedrock e d r o c k ooutcrop u t c r o p aareas r e a s from from IIce—flow c e - f l o w ddirections i r e c t i o n s ccan a n be Elsewhere glacial g l a c i a l striation s t r i a t i o n measurements. measurements. E l s e w h e r e drumlins d r u m l i n s and a n d end e n d moraines m o r a i n e s are are qeomorphic good ice—flow i c e - f l o w indicators. indicators. IIn n aareas r e a s where basal b a s a l drift d r i f t predates p r e d a t e s geomorphic ffeatures, e a t u r e s , cclast l a s t lithologic l i t h o l o g i c provenance p r o v e n a n c e implies i m p l i e s general g e n e r a l ice ice flow f l o w direction. direction. Partial s t u d y was provided p r o v i d e d by the Department D e p a r t m e n t of of P a r t i a l support s u p p o r t for f o r this study Natural the Mineral M i n e r a l Diversification Diversification N a t u r a l Resources R e s o u r c e s Mineral M i n e r a l Division D i v i s i o n through t h r o u g h the Fund, Fund, and by the t h e Minnesota Future F u t u r e Resources R e s o u r c e s Commission. Commission. References R e f e r e n c e s Cited Cited Clark, till composition: composition: C l a r k , P.C., P.U., 1987, subglacial S u b g l a c i a l sediment s e d i m e n t dispersal d i s p e r s a l and a n d till Geology, v. JJournal o u r n a l of o f Geology, v. 95, 9 5 , no. no. 4, 4 , p. p. 527—541. 527-541. Martin, T.L., C Chandler, and G.N., LLawler, a w l e r , T.L., h a n d l e r , V.W., V.W., a n d Malmquist, Malmquist, M a r t i n , D.P., D.P., Meyer, Meyer, G.N.,, K.L., 1988, Regional K.L., 1988, R e g i o n a l survey s u r v e y of o f buried b u r i e d glacial g l a c i a l drift d r i f t geochemistry g e o c h e m i s t r y over over Minnesota Archean terrane t e r r a n e in i n northern n o r t h e r n Minnesota: Minnesota: M i n n e s o t a Department D e p a r t m e n t of o f Natural Natural Resources, Division Part R esources, D i v i s i o n of o f Minerals M i n e r a l s Report R e p o r t 252, 252, P a r t I, I , 74 7 4 p., p., Part P a r t II, 11, 386 p. P 55 �GEOLOGY NORTHEASTERN MINNESOTA GEOLOGY OF OF THE THEBEAVER BEAVER BAY COMPLEX, COMPLEX, NORTHEASTERN MINNESOTA James James D. D. Miller, Miller. Jr., Jr.. Minnesota Minnesota Geological Geological Survey, Survey. 2642 University Ave., Ave.. St. St. Paul, Paul, Minnesota Minnesota 55108. 55108. The Beaver Beaver Bay Bay Complex Complex (Grout (Groutand and Schwartz, Schwartz, 1939; 1939; Gehman, Gehman, 1957) 1957)isisaasupersuite supersuiteof ofhypabyssal hypabyssal The to plutonic plutonic gabbroic gabbroic to to granitic granitic intrusions intrusionswhich which were were emplaced in the the upper upper portion portion of of the theKeweenawan Keweenawan to North North Shore Shore Volcanic Volcanic Group Group (NSVG; (NSVG; Green, Green, 1972) 1972) during during the thedevelopment developmentof ofthe theMidcontinent Midcontinentrift rift system. The Thecomplex complexisisbest bestexposed exposedalong alongthe theLake LakeSuperior Superiorcoast coastnear nearthe thetowns townsofofBeaver BeaverBay, Bay,Silver Silver system. lakeshore,the theBeaver BeaverBay Baycomplex Complexextends extendsapproximately approximately30 30km km Bay and and Finland, Finland, Minnesota. Minnesota. From Fromthe thelakeshore, Bay to the the north-northeast north-northeast where it becomes becomes covered by Although ititisisstratigraphically stratigraphicallyand and to by thick thick glacial till. till. Although petrologically distinct from most rocks rocks that that comprise comprise the the deeper deeper intrusions intrusions of of the theDuluth DuluthComplex, Complex, petrologically aeromagneticand and gravity gravityanomalies anomaliesover overthe thecovered covered area areaindicate indicateaahigh highratio ratioofofintrusions intrusionstotovolcanic volcanichost host aeromagnetic rocks rocks and and thereby thereby suggests suggeststhat thatthe the Beaver Beaver Bay Bay Complex Complex is is gradational gradationalinto into the the Duluth DuluthComplex. Complex. Geologic mapping mapping at at aa 1:24,000 1:24,000scale scaleencompassing encompassing about about four four 7.5'quadrangles 7S'quadrangles(Silver (SilverBay Bay w/ w/ Split Split Geologic Rock Point Point NE, NE, IlIgen Illgen City, City, Finland Finland and and Doyle Doyle Lake) Lake) was was initiated initiated 44 years yearsago agoby bythe theMinnesota Minnesota Rock Geological Surveys COGEOMAP program. program. We Geological Survey in conjunction with the U.S. U.S. Geological Geological Survey's We report report here here on on the the major majorresult resultof ofthis thisongoing ongoingproject, project,which which has haselucidated elucidatedmuch muchofofthe thevolcanic, volcanic,intrusive intrusiveand and structural structuralhistory historyof of this thispart partof ofthe theKeweenawan Keweenawansection. section. The The volcanic volcanic rocks rocks that thathost hostthe theBeaver Beaver Bay BayComplex Complex are aredominantly dominantlyflows flowsofoftholeiitic tholciiticbasalt basalttoto basaltic basaltic andesite, andesite, but but also also include include arkosic arkosic interfiow interflow units and several thick (100 (5100m) m)rhyolite rhyoliteflows flows(Miller (Miller lakewarddip dipof ofmost mostNSVG NSVGunits unitsisis and others, others,in in press; press; Miller, Miller, 1988; 1988;Green, Green, 1972). 1972). The Thetypical typicalshallow shallowlakeward and disrupted disrupted in in this this area area due due to to block block faulting faultingduring and after intrusion of the Beaver Beaver Bay Bay Complex. Steep Steep fault NEtotoNNE, NNE,parallel paralleltotothe theaxis axisofofthe therift, rift,and andless lesscommonly commonlyWNW. WNW. fault(and (anddike) dike)trends trendsare aredominantly dominantlyNE All All NE-trending NE-trending faults faultsdeveloped developedcoeval coeval with with intrusion intrusion of of diabase diabase (now (nowdikes) dikes)display displaydowndrop downdropof ofthe the lakeside lakesideblock block consistent consistentwith withthe therift riftbasin basindecping deepingtotothe theSE. SE. five major major events. events. Each Each Current mapping mapping indicates indicates that that the the Beaver Beaver Bay Complex was emplaced in five Current event eventproduced produced aaunique uniquesuite suiteof ofrock rocktypes typesthat thatreflect reflectdifferent differentparent parentmagmas magmasand andmodes modesofofemplacement. emplacement. In In order order of of decreasing decreasingage, age,these theseintrusive intrusivesuites suitesare arethe theLax LaxLake Lakegabbro, gabbro,the theFinland Finlandgranite, granite,the theSonju Sonju Lake Lakelayered layeredintrusion, intrusion,the theBeaver BeaverRiver River diabase, diabase, and and the the Silver Silver Bay Bay intrusions. intrusions.The TheBeaver BeaverBay BayComplex Complex also alsoincludes includesseveral severalminor minordiabase diabaseintrusions intrusionswhose whose genetic genetic relationship relationshipwith with the themajor majorsuites suitesisisunclear. unclear. Subophitic Subophiticolivine olivine gabbro, gabbro,oxide-rich oxide-rich gabbro, gabbro, granophyric granophyric gabbro, gabbro, and mafic mafic granodiorite granodioriteof the the Lax Lax Lake Lakegabbro gabbro(Fig. (Fig.1)1)are arethe theoldest oldestintrusive intrusiverocks rocks in in the the area. area. The Theshape shapeofofthe theintrusion intrusionisisdifficult difficult to to discern discern because because the the rocks rocks lack lackinternal internalstructure structureand and have have been been cut cutby by younger youngerintrusions intrusions(Beaver (BeaverRiver River diabase diabaseand and Finland Finlandgranite) granite)and and faults. faults.The Thegranophyric granophyriccharacter characterand andextensive extensivehydrothermal hydrothermalalteration alterationof of most mostLax Lax Lake Lakegabbro gabbrorocks rocksprobably probably isisthe the result result of of their their early early emplacement emplacementinto intowater-rich water-rich volcanics. volcanics. In of the Lax Lake gabbro suite is the Finland In sharp sharp intrusive intrusive contact contact with the north north margin margin of Finland granite granite(Fig. (Fig.1), 1).a ahomogeneous homogeneousmass massofofpink pinktotoorange, orange,granophyric, granophyric,leucocratic, leucocratic,pyroxene pyroxenegranite. granite. Although Althoughthe thegranite granitecontains containsabundant abundantmiarolitic miaroliticcavities cavitiesindicative indicativeof ofaavapor vaporphase, phase,the thepredominance predominanceofof Fe-rich Fe-rich pyroxene pyroxeneover overhornblcnde hornblendesuggests suggeststhat that the the parent parent magma magma was was water-poor. water-poor. Bordering Borderingthe the Finland Finlandgranite graniteon on the thenorth north and and (as (asimplied implied by by aeromagnetics) aeromagnetics)west west isisaadifferentiated differentiated layered termed the theSonju Sonju Lake intrusion layered sequence sequence of mafic cumulates termed intrusion(Fig. (Fig.1;1;Stevenson, Stevenson,1974). 1974). This This intrusionisisthe the most mostcompletely completelydifferentiated differentiatedbody body known known in in the the Keweenawan Keweenawansection section(Weiblen, (Weiblen,1982). 1982).ItIt intrusion grades gradesfrom fromaabasal basalpicrite/dunite picriteldunitetotoananupper upperapatitic apatiticferrodiorite. ferrodiorite. In Inthe thenorthern northernpart partofofthe thearea, area,the the roughly (15-25') to the the south. south. The Thelaminated laminatedupper upperferrodiorite ferrodioriteisis roughly 1000-rn-thick 1000-m-thick sequence sequence dips dips gently gently (15-25°) overlain overlainby byaamassive massivegranophyric granophyricquartz quartzmonzodiorite monzodioriteto togranodiorite granodioritewith withprismatic prismaticpyroxene pyroxeneand andolivine. olivine. This Thismonzo/granodiorite monzolgranodioritegrades grades into intothe the Finland Finland granite granite suggesting suggesting that that ititrepresents representsmelting meltingand andpartial partial assimilation assimilation of of the thegranite granitewhich whichformed formedthe theroof roofofofthe theintrusion. intrusion. The Theeast eastend endofofthe theSonju SonjuLake Lake intrusion intrusion isisabruptly abruptlytruncated truncatedby by aahigh-angle high-anglefault faultwhich which juxtaposes juxtaposes the the layered layeredsequence sequenceand andBeaver BeaverRiver River diabase. diabase.Field Fieldrelationships relationshipsbetween betweenSonju SonjuLake Lakerocks rocksand andBeaver BeaverRiver Riverdiabase diabaseare areunclear unclearand andallow allowthe the possibility possibilitythat thatthe theunits unitsare arecoeval coevalororthat thatthe thediabase diabaseisisyounger. younger. Dikes Dikesand and sills sillsof ofophitic ophiticolivine olivinediabase, diabase, termed termed Beaver River Riverdiabase, diabase,are arethethemost mostpervasive pervasive intrusions intrusions in in the theBeaver BeaverBay BayComplex Complex(Fig. (Fig.1). 1). Steep Steepdikes dikes feed feedthick thick ((< 100 subhorizontal sheets 100 m)m) subhorizontal sheets which whichform formprominent prominentflat-topped flat-toppedhills. hills. The Thediabase diabaseintrusions intrusionsare areunique uniqueininthat thatthey theycontain containabundant abundant inclusions of of anorthosite anorthositeand and less lessabundant abundantgranite, granite, some some as as much much as as100 100rnmacross, across,which whichtend tendtotobebe inclusions concentrated concentrated in in the thelower lowerparts partsofofsheets. sheets.Typically, Typically,the theanorthosites anorthositesare aremassive, massive,coarse-grained, coarse-grained,and and consist consistalmost almostentirely entirelyofoftabular tabularcalcic calcicplagioclase plagioclase(An (An54-80; 54-80;Morrison Morrisonand andothers, others,1983) 1983)with withminor minor olivine, olivine,hypersthene, hypersthene,augite, augite, and and Fe-oxide. Fe-oxide. Some Someinclusions inclusionsare aretectonized tectonizedand anda afew fewdisplay displaymodal modal 56 �layering. The Thegranite graniteinclusions, inclusions, being medium-grained and micrographic and containing Fe-pyroxene and of Finland Finland granite. miarolitic cavities, are probably xenoliths of The Silver Bay intrusions, intrusions,the theyoungest youngest intrusive intrusive unit unit in in the the area, area, occur occur as as many many concentrically concentrically bodies and as irregularly irregularly shaped shapedmasses masseswithin withinor or adjacent adjacentto to Beaver BeaverRiver Riverdiabase diabase(Fig. (Fig. 1). 1). This zoned bodies spatial relationship suggests that the Silver Bay magmas were emplaced through the same same conduits conduits as the the Beaver River diabase. Moreover, Moreover, the the abundance abundance of of Beaver Beaver River River diabase diabaseinclusions, inclusions,which which are are especially especially centered south south of of Silver Silver Bay, Bay, and and the lack tack of of any chill at the margins of the Silver common in the intrusion centered Bay intrusions intrusions indicate that the ferrodioritic magmas were intruded soon after the diabase diabase had crystallized. crystallized. Zoned Silver Bay intrusions grade abruptly abruptly from from a margin of coarse-grained, van-textured Zoned intrusions grade vari-textured granophyric olivine ferrodiorite ferrodiorite to an interior of medium-grained, laminated, laminated, locally locally layered layered olivine olivine ferrogabbro/diorite. ferrogabbroldiorite. Several irregularly shaped intrusions are composed of mediummedium- to to coarse-grained, coarse-grained,granophyric granophyric olivine olivine dionte, similar diorite, similar to ferrodionte ferrodiorite in the margins of the zoned intrusions. These Thesebodies bodies may may represent represent deeper deeper parts of intrusions which fed into zoned masses above. Some Someintrusions intrusionsalso alsocontain containsignificant significantamounts amounts of mafic granodiorite granodiorite to quartz monzodiorite which have resulted from local melting melting of felsic felsic volcanics volcanics and and immiscibility of the ferrogabbro deeper Finland granite, or perhaps from liquid immiscibility ferrogabbro magmas. Petrogenetic models models of of the relationships between between the various intrusive bodies which compose the Beaver Bay Complex and between these rocks rocks and and the underlying Duluth Complex must await more detailed Field relationships and a minor investigations of their their geochemistry. geochemistry, Field relationships and minor amount amount of geochemical geochemical data, however, permit some preliminary preliminary conclusions. conclusions. The The parental parental magma magma to to the the Lax Lake gabbro was probably moderately evolved basalt which which was driven to more felsic compositions compositions by assimilation of nearby waterbearing volcanics. The Thewholly wholly granitic granitic composition composition and extensive extensive volume of the Finland granite strongly anatectic origin. origin. Further suggests a crustal anatcctic Further geochemical geochemicalstudies studies should should test test whether whether this this shallow shallow intrusion intrusion could have fed any of the rhyolitc rhyolite flows flows in in the the area. area. Although of Although the the lithologies lithologies and modes of occurrence of River, and and Silver Silver Bay Bay intrusions are distinct, it is possible that these rocks the Sonju Lake, Beaver Beaver River, rocks are are comagmatic. Preliminary Preliminary geochemical geochemical data data and the the close closespatial spatialand and temporal temporal association associationof of Beaver Beaver River River rocks of of the the younger younger Silver Silver Bay Bay intrusions suggest that that the the parent parent magmas of of the diabase and ferrodioritic rocks latter may have been derived from from further fractionation of Beaver River magma in deeper chambers. The The Lake intrusion intrusion may may have have been beenone one such such chamber. chamber. Though the field relationships arc are obscure, the the Sonju Lakc diabasic troctolite troctolite in the basal zone of the Sonju Lake intrusion suggests occurrence of anorthosite-bearing diabasic the possibility possibility that the Sonju Lake body resulted from intrusion of of Beaver Beaver River River magma magma into intoaa chamber chamberof of sufficiently large size that crystal fractionation fractionation could occur. occur. It also follows that the Silver Silver Bay Bay magmas magmas upper ferrodioritic ferrodioritic differentiate differentiate of of the the Sonju Sonju Lake Lake body. body. More could have been tapped from the upper More geochemical geochemical data are are currently currently being acquired to evaluate evaluate this this model. Gehman, H.M., H.M., Jr., 1957, 1957, The petrology of the the Beaver Beaver Bay Bay Complex, Complex, Lake Lake County, County,Minnesota: Minnesota: Ph.D. Ph.D. Dissertation, University of Minnesota, 92 p. Dissertation, Green, J.C., J.C., 1972, Group, in Sims, 1972, North North Shore Volcanic Volcanic Group, Sims, P.K. P.K. and and Morey, Morey, G.B., G.B., eds., eds.. Geology Geology of volume: Minnesota Geological Geological Survey, Minnesota: A centennial volume: Survey, p. 294-332. G.M., 1939, 1939, The The geology geology of of anorthosites of of the Minnesota of Lake Grout, F.F., F.F., and Schwartz, G.M., Minnesota coast of Superior: Minnesota Geological Survey Bulletin 28, 119 Superior 119 p. Miller, J.D., J.D., Jr., 1988, 1988, Geologic Geologic map of the the Silver Silver Bay Bay and andSplit SplitRock RockPoint PointNE NEquadrangles, quadrangles,Lake Lake Minnesota: Minnesota Minnesota Geological Survey County, Minnesota: Survey Miscellaneous Miscellaneous Map Map M-65. Miller, J.D., Jr., Green, J.C., J.C., and Boerboom, TJ., TJ., in in press, press.Geologic Geologicmap mapof ofthe theIllgen IllgenCity Cityquadrangle, quadrangle. Geological Survey Lake County, Minnesota: Minnesota Geological Survey Miscellaneous Miscellaneous Map, Map, M-66. M-66. D.A., Ashwal, Ashwal, L.D., L.D., Phinney, Phinney, W.C., W.C., Shih, C-Y., C-Y., and Wooden, J.L., 1983, Morrison, D.A., 1983, Pre-Keweenawan Pre-Keweenawan anorthosite inclusions inclusions in in the Keweenawan anorthosite Keweenawan Beaver Bay Bay and and Duluth Duluth Complexes, Complexes, northeastern northeastern Minnesota: Geological Society of of America America Bulletin, v. 94, p. 206. Stevenson, R.J., RJ., 1974, Stevenson, 1974, A A mafic mafic layered layered intrusion intrusion of of Keweenawan Keweenawan age near Finland, Finland, Lake Lake County, County, Minnesota. 160 p. Minnesota. M.S. M.S. thesis, University of Minnesota, Minneapolis, Minneapolis, 160 P.W., 1982, Keweenawanintrusive intrusiveigneous igneousrocks. rocks.ininWold, Wold,RRiJ & Hinze, W.J., W.J., eds,. eds, Geology Weiblen, P.W., 1982, Keweenawan Geology and tectonics tectonics of the Lake Superior Basin: Basin: Geological Society of America Memoir 156, 156, p. 57-82. 57 �91° 5 ç 4 * 4 * '4. .:. 4 4*4*4* * * 4*44444444 4 47°25 •.. • * * • 4 * • 4 4 . * 4 4 ++*+•**+****+,* .44 4 •**+* • t_. _* * * *%• *.s,. • •.•**,****,t.• 4 * .4•. I ,,•,•.•,••+t•• •t • • • —C. 4... + III ''I II 4, •I•1 7 47°2O C) iver Bay x Silver 8y intrusions 5ever River dlbse E prismotic grcnodiorite (J upper g8bbro 0 C L w > C aver Bay \, lower troctolite Flnlnd granite Sonju Leke in t ru Si On Lx Lake gbbro aD 47° 15- Mlscelløneous gobbroic Intrusions North Shore Volcanic Group A 4 2__ 00 I 4 2 Miles 2MiIes 22Kilometers Kilometers FIGURE1.1.Generalized Generalizedgeology geologyofofthe theBeaver BeaverBay Bay FIGURE Complex, Complex,northeastern northeasternMinnesota. Minnesota. IÑÑIà 58 58 �THE PALEOMAGNETIC PALEOMAGNETIC RECORD RECORD OF OF LATE LATE GLACIAL GLACIAL AND AND POST POST GLACIAL GLACIAL THE SEDIMENTS OF LAKE SUPERIOR SEDIMENTS OF LAKE SUPERIOR John S. S. Mothersill Mothersill and and James James Fraser, Fraser, Royal Royal Roads Roads Military Military John vos IBO College, Victoria, British Columbia, College, Victoria, British Columbia, VOS 130 The Late Late Quaternary Quaternary sedimentary sedimentary sequence sequence consists consists The 9900 years ago of glacial till which was deposited about of glacial till which was deposited about 9900 years ago during the last glacial advance into the Lake Superior during the last glacial advance into the Lake Superior Basin. In In the the Canadian Canadian portion portion of of Lake Lake Superior Superior the the till till Basin. deposits are unconformably overlain by a thin sequence of deposits are unconformably overlain by a thin sequence of bedded sands and silts which are conformably overlain by bedded sands and silts which are conformably overlain by thick sequence sequence of of varved varved sediments sediments which which in in turn turn are are aa thick overlain by postglacial silty clays. Paleodeclination overlain by postglacial silty clays. Paleodeclination logs can can be be used used to to correlate correlate and and and paleoinclination paleoinclination logs and indirectly date cores of this sedimentary sequence that indirectly date cores of this sedimentary sequence that have been taken from the major basins of the Canadian have been taken from the major basins of the Canadian portion of of Lake Lake Superior. Superior. In In addition addition the the paleomagnetic paleomagnetic portion data obtained from six cores has been stacked to form form data obtained from six cores has been stacked to 'type' paleodeclination and paleoinclination logs for Lake Lake 'type' paleodeclination and paleoinclination logs for Superior. These 'type' logs can be correlated with the Superior. These 'type' logs can be correlated with the t y p e ' logs logs obtained obtained for for both both Lakes Lakes Huron Huron and andErie. Erie. 'type' it is is concluded concluded that that rhythmic rhythmic sedimentation sedimentation ceased ceased It 9200 years BP in the southeastern lake proper prior to prior to 9200 years BP in the southeastern lake proper and at at about about 8700 8700 years years BP BP in in the the southeastern southeastern bay bay areas. areas. and 8200 However rhythmic sedimentation continued until about However rhythmic sedimentation continued until about 8200 years BP in the northern part of Lake Superior and until years BP in the northern part of Lake Superior and until about 8000 8000 years years EP BP in in the the Nipigon Nipigon Bay Bay area. area. about 59 �FUNDAMENTALUNIT UNIT DIFFERENTIATION OF THE FUNDAMENTAL THE MIDDLE MIDDLE PROTENOZOIC PROTEROZOIC MIDCONTINENT MIDCONTINENT RRIFT I F T SYSTEM, SYSTEM,NORTH NORTH AMERICA M.G. Mudrey, 3817 Mudrey, .Jr., Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, 3817 Mineral Point Road, Madison, 53705, and Madison, WT WI 53705, A.B. Dickas, Superior, WI WI 54880 54880 A.B. Dickas, University of Wisconsin-Superior, Wisconsin—Superior, Superior, ABSTRACT Analysis of Analysis of geophysical geophysical data data within within the the Lake Lake Superior Superior basin basin of of the t.he Middle Proterozoic Midcontinent Midcontinent Rift Rift system system in in central central North North America America sugsug series of of opposed, opposed, sub-regional sub—regional half-grabens, half—grabens, displaying gests a series displaying igneous igneous sedimentary inf ill packages packages separated separated by accommodation accommodation structures. and sedimentary infill structures. We interpret first—order rift interpret. five first-order rift segments segments (zones) (zones) identified identified by by major major interruption of of gravity gravity and and magnetic magnetic patterns, seismic seismic expression, expression, and interruption terrane composition separated by four four first—order first-order accommodation accommodation strucstructures. Clockwise tures. Clockwise from from the the southwestern southwestern end end of of the the rift, rift, these these segments segments rowa, Superior, Superior, Mackinaw, Mackinaw, and are named named the the Kansas, Kansas, Iowa, and Maumee Maumee zones zones (fig. (fig. Second—order rift segments segments (fundamental 1fl.) . Second-order (fundamental rift rift units) units) are are separated separated Superior zone zone four by second-order accommodation structures. structures. Within Within t.he the Superior four second—order accommodation such such segments are now recognized recognized and and named named the the Chisago, Chisago, Brule, Brule, Ontonagon, and Manitou units Ontonagon, units (fig. (fig. 2). 2). This This model for for the the Midcontinent Midcontinent Rift Rift isisbased basedononthe themod'ern modern East East tn plan plan view the fundamental African Rift Rift (Rosendahl, (Rosendahl,1987). 1987). In fundamental unit unit in in the Gregory Rift is is a parallelogram parallelogram with with lengths lengths on on the the order order of of50 50t.o to 190 km), km), and and widths widths from from20 20to to40 40kmkm(maximum (maximum7070kin). km). 70 km (maximum (maximum 190 cross— to 44 with with an an average average of of 3. 3. In crossLength to width ratios ratios vary vary from from 22 to triangular, defining defining aa half— halfsection the fundamental unit is commonly triangular, Because of graben. graben. of this this haif—graben half-graben geometry, geometry, the the width width of of any any one one rift rift function of halfunit is a function of its its degree degree of of uplift uplift.and and erosion. erosion. When When the thehalf-developed, it graben is initially developed, it is is bordered on its its deep deep side side by by aa curvilinear, normal, normal, listric major curvilinear, listric fault fault system, system, and and on on the the shallow shallow side side by a monocline, or series of normal, normal, small small displacement displacement step step faults. faults. The fundamental unit is bound on its complex structures structures striking striking its ends ends by complex obliquely to the rift axis, axis, and include include interbasinal interbasinal highs, highs, ridges, ridges, and and regions Igneous and sedimentation regions of of uplifted uplifted basement. basement. Igneous sedimentation wedges wedges of of alteralternating isopach patterns distinguish distinguish juxtaposed These iso— juxtaposed rift rift units. These isopach patterns differ by being symmetric symmetric parallel, parallel, but alternating alternating asymasymmetric metric perpendicular, perpendicular, to to the the trend trend of of the the rift rift axis. axis. The least mature of the Midcontinent Rift the Midcontinent Rift System System zones zones appears appears to to be Maumee zone be the the Maumee and and Mackinaw Mackinaw zones zones (table (table 1). 1). The Maumee zone displays displays aa symmetrical, unfaulted, unfaulted, extensional basin associated associated with with a symmetrical, a simple simple gravgravsignature (Brown ity signature (Brown and and others, others, 1982). 1982). The The Mackinaw Mackinaw zone zone is is similar, similar, boundaries of of this this zone zone are are associated associated with differing only in that that t.he the boundaries normal faults, faults, none none of which which can be traced to the listric normal the Moho disconsemi—mature Kansas Kansas zone tinuity (Behrendt (Behrendt and and others, others, 1988). 1988). The semi-mature zone conconsists asymmetric basin plunging sists of an asymmetric plunging to to the the west west and and bounded bounded by by normal normal 1988; Serpa Serpa and and others, others, 1984). 1984). The Iowa Iowa faults (Berendsen (Berendsen and others, others, 1988; zone is identified primarily primarily by zone by strong strong gravity—pattern gravity-pattern changes. changes. An east— eastwest seismic seismic line line in in central central Iowa Iowa is is inconclusive inconclusiveregarding regardingbasin basinsynune— symmetry; and appears as a central horst associated associated and bounded bounded by by reactireacti(Chandler faults, one one of which which can be traced to a depth depth of of 20 20 km km (Chandler vated faults, and others, 1989). The The horst horst may be be aa consequence consequence of of two two opposed opposed funda— fundaothers, 1989). 60 �suggest compression, compression, and may reflect mental units. units. These faults suggest. reflect a Mackinaw, and Kansas greater maturity maturity than than the the Mauinee, Maumee, Mackinaw, Kansas zones. zones. The is the the most mature mature in in the the Midcontinent Midcontinent Rift Rift The Superior Superior zone zone is System (McSwiggen (McSwiggen and and others, 1987), and is recognized by disrupted gravity trends, km, a central central horst bounded bounded by by gravity trends, crustal crustal separation separationofof5050kin, reverse faults, faults, and and gabbroic gabbroic intrusions. intrusions. If the fundamental fundamental rift unit unit reverse concept concept: is a necessary necessary constituent constituent of of modern modern and and ancient ancient rift rift evolution, evolution, then such fundamental units should be recognizable recognizable in the Lake Lake Superior Superior basin. Four Four such such units units can can be identified, identified, average average 150 150 km kin in in length length by basin. 60 60 km in in width, width, for for aa length/width length/width ratio ratio of of 2.5. 2.5. Structural Structural sub—division sub-division of of the the Superior Superior zone zone may may apply apply elsewhere elsewhere along the trend, trend, however the increased increased depth depth of of burial burl-a1of of the the rock units units both directions directions away from the Lake Superior area and the limited disdis— in both such detailed tribution of geophysical data along the rift do not permit such second—order second-order differentiation. differentiation. References Cited References Behrendt, Behrendt, J.C., J.C., Green, Green, A.G., A . G . , Cannon, Cannon, W.F., W.F., Hutchinson, Hutchinson, D.R., D.R., Lee, Lee, M.W., M.W., Milkereit, B., C., 1988, 1988, Crustal Crustal Milkereit, B., Agena, Arfena, W.F., and Spencer, Spencer, C., structure GLIMPCE structure of of the the Midcontinent Midcontinent Rift Rift System: System: Results Results from from GLIMPCE deep deep seismic seismic reflectin reflectin profiles: profiles: Geology, Geology,v. v. 16, 16, P. p. 81—85. 81-85. Berendsen, P., Berendsen, P., Borcherding, Borcherding, R.M., R.M., Doveton, Doveton, J., J., Gerhard, Gerhard,L., L.,Newell, Newell, K.D., 1988, Texaco #1, K.D., Steeples, Steeples,B., D., and andWatney, Watney,W.L.,, W.L., 1988, Texaco Poersch Poersch *1, Washington Washington Dounty, Dounty, Kansas: Kansas: Preliminary Preliminary geologic geologic report report of of the the pre—Phanerozoic pre-Phanerozoic rocks: rocks: Kansas Kansas Geological Geological Survey Survey Open—file Open-file Report Report 88—22, 116 p. 88-22, 116 p. Brown, L., Oliver, Oliver, J., J., Kaufman, Kaufman, S., S., and and Steiner, Steiner, D., D., 1982, Brown, L., Jensen, Jensen, L., 1982, Rift structrures structrures heneqath beneqath the the Michigan Michigan Basin Basin and and COCORP COCORP profiling: profiling: Geology, V. Geology, V. 10, 10, p. 645—649. 645-649. Chandler, Chandler, V.W., McSwiggen, McSwiggen, P.L., P.L., Morey, Morey, G.B., G.B., Hinze, Hinze, W.F., W.F., and and AnderAnderson, R.R., son, R.R., 1989, 1989, Interpretation Interpretation of of seismic seismic reflection, reflection, gravity, gravity, and and magnetic magnetic data data across across Middle Middle Proterozoic Proterozoic Midcontinent Midcontinent Rift Rift System, System, Northwestern Northwestern Wisconsin, Wisconsin, eastern eastern Minnesota, Minnesota,and and central centralIowa: Iowa: 73, p. American Association of of Petroleum Petroleum Geologists Geologists Bulletin, Bulletin, v. 73, 261—275. 261-275. P.L., Morey, Morey, G.B., G.B., and and Chandler, Chandler, V.W., V.W., 1987, 1987, New New model model of of McSwiggen, P.L., McSwiggen, the Midcontinent Mjdcontjnent Rift the Rift in in eastern eastern Minnesota Minnesota and and western western Wisconsin: Wisconsin: Tectonics, v. 6, p. p. 677—685. 677-685. Tectonics, v. 6, Rosendahl, B.R., B.R., 1987, 1987, Architecture Architecture of of continental continental rifts rifts with with special special Rosendahi, reference to to East Africa: Annual Review Review Earth Earth and and Planetary Planetary reference Science, v. Science, v. 15, 445-503. 15, p. 445—503. L., Setzer, Setzer, P., R., Farmer, Fanner, H., Brown, Brown, L., L., Oliver, Oliver, J., J., Kaufman, Kaufman, S., S., Serpa, L., Serpa, and and Sharp, Sharp, J., J., 1984, 1984, Structrure the southern southern Keweenawan Keweenawan Rift Rift Structrure of of the COCORP surveys surveys across across the the midcontinent midcontinent geophysical geophysical anomaly anomaly in in from COCORP from northeastern Kansas: Kansas: Tectonics, Tectonics, v. v. 3, 367-384. northeastern 3, p. p. 367—384. 61 �terminology of of the the Midcontinent Table 1. 1. Zone and unit differentiation terminology Rift System and associated associated geologic geologic features. features. MAUMEE MAUImE Zone : •• (Thiel Fault) 1st Order Order Accommodation Structure Accommod; In Structure rn (Thiel Fau Sag baala basin on COCORP COCORP seismic stlamlc lines llnu McClure #I4Sparks S p r h well well stratigraphy. atnUgnphy McClun #14 p 1st Order 1st Order Accommodation Accommodntion Structure structure Gravity 'dogleg', Montcalm Montalm Co., Ca.,Michigan Mlchl~n Seismic Corp. aetsmtc Flrat atlamk lInterpretation n~lallaa First Sclamlc 1VEACKINAVV MACKINAW Zone ! 1st Order Order 1st Accommodation Structure Structure SUPERIOR SUPENOR Zone 1st Order 1St Order Accommodation Structure IOWA IOWA Zone 1st Order 1st Accommodation Accommodatlon Structure structure GLIMPCE line F extension uniting McClure #1 Beaver Island test Amoco St. Amour #1.29 test and seismology Coalescing oC MRS structure ~ l w c l or n MRS ~ atrwtum previously identifled l l ~ i e Fault l DIWIOVSJY Identifled Thiol Fault bye*k on GUMPCE lIne 0 Major change I. MRS strike Interrupted gravity and magnetic patterns ' / UI' yn7) F*ult Uflit Unit It structure Ideatuued IOWA central IdeaUfled wabal horse hmt m etun Presenceof .( extension teultiag a m a h and eonipewssioa ~ ~ l fanlthg o a Pmenm Amoeo # I Xacbeld t u f and at~WJppby Amoco SI Riacheld teat atratigraphy well control Regional amtd ReciomI Order 2nd Order -. ACC0StL Structure Strueton Broken grsvity and magnetic trends Granite tsrrane, southeastern Nebraska Local well control Soulh.Central Magnetic Uneament lines Extension fh1Umg uniting on Mendon a COCORP COCORP siesinic alamnk lhu AInflWtek central Aaymmatrk c a a graben l m l ~ ~ and mtlgmpby, stretigysphy Texaco #1 Tuna #I Noel Nod Poerach Potneb teat and ONTONA3NTONAGON SON Unit BRULE BRULE CEISAGO XmAo - S isopsc polarity on GUMPtE liii. A Altered Gravity Trend N Isopacb GUMPCE C Duluth Complex Intrusion Remanent Magnetic Reversals N Outcrop Thickening Terminated Gravity Trend Transverse flsssmeai Ridge .rcliena Phelt trend Vertical Outcrop 0ipe filmiest Organic Patruloglea isopech Bear Creek Cores S Isopech Petty.Rsy Seismic S alaomer Fenit Field Evidence Coastrictad Gravity Trend : w isopech Petty-Ray Seismic Unit — IKANSAS WSAS Zone Zone. 2nd Order Ordk Accorn. AcuJln. Structure stmctnm Order 2nd Onlw .. Accom. A Structure sbnctllm STRUCTURAL STRUCI'URAL DETAIL DETAIL Interrupted grsvfty InItm~pted p d Q aud and magnetic mgnetk patterns ptWnIS icutheast Minnesota Grauitk Gnnltk intrusions, l n t r u d o q soathast Mlanemta System Bell* P h l m (bawfom?) Fault System Beji. B O ~ I O I and * V,1t1 p v l Qcontrol, mbd,Blabley B h b l q Co., Mien. - MANITOU I5ANmou Unit, Unit . r 1st Order Accommodation Structure Accommodation Stmcture (BeUe Plaine Fault) mow (Belle Plaine Iao J- DECREASING RIFT MATURITY N — Gravity Hi$b Gravity Low uctom . Accommodadon m . i t c c & h Figure 1. Location of of accomodation accomodation Figure 1. principal structures and andnames names of principal structures om I. • rift rift zones zones. Figure 2. 2. Details of Figure of the the Superior Superior showing the Zone shwing the location, names and polarity of fundamental fundamental rift rift 62 units. units. �STRUCTURE OF THE ST'RUCTURE OF W MIDCONTINENT MIDCONTINENT RIFT RIFTSYSTEM SYSTEM FROM 8—SECREFLECTION REFLECTION SEISMIC SEISMIC DATA FROM 8-SEC DATA IN I NWESTERN WESTERN LAKE LAKE SUPERIOR SIJF'ERIOR M.G. Mudrey, Mudrey, JJr., Geological M.G. r . , Wisconsin G e o l o g i c a l and Natural N a t u r a l History H i s t o r y Survey, Survey, 3817 3817 Mineral M i n e r a l Point P o i n t Road, Road, Madison, WI W I 53705, 53705, L.D. McGinnis, McGinnis, E Engineering Geosciences, L.D. ngineering G e o s c i e n c e s , Argonne Argonne National N a t i o n a l Laboratory, Iaboratory, Argonne, Argonne, IL IL 60439, 60439, C. C. Patrick P a t r i c k Ervin, E r v i n , Department of o f Geology, Geology, Northern Northern Illinois I l l i n o i s University, University, DeKaib, IL DeKalb, IL 60115 Nyquist, Health and S Safety Research Division, JJ.E. .E. N yquist, H e a l t h and afety R esearch D i v i s i o n , Oak Ridge National National Laboratory, P.O. Box 2008, L a b o r a t o r y , P.O. 2008, Oak Oak Ridge, Ridge, TN TN 37830 37830 A.B. Dickas, Dickas, D Division A.B. i v i s i o n of o f Sciences S c i e n c e s and and Mathematics, Mathematics, Ijniversity I J n i v e r s i t y oof f Wisconsin—Superior, S Superior, WII 54880 Wisconsin-Superior, uperior, W G.E. Morey, Morey, Minnesota Minnesota G Geological G.B. e o l o g i c a l Survey, S u r v e y , St. S t . Paul, P a u l , MN 55114 A.G. Green, G Geological Survey Canada, Building A.G. Green, eological S u r v e y of o f Canada, B u i l d i n g 7 Observatory Observatory Crescent, K l A 0Y3 OY3 C r e s c e n t , Ottawa, Ottawa, Ontario O n t a r i o K1A J.L J . L Sexton, S e x t o n , Department of o f Geology, Geology, Southern S o u t h e r n Illinois I l l i n o i s University, IJniversity, Carbondale, IL Carbondale, I L 62901 62901 ABSTRACT Structural major S t r u c t u r a l sstyle t y l e and m a j o r features f e a t u r e s of of the t h e Midcontinent M i d c o n t i n e n t Rift R i f t SysSyswestern Lake S Superior ttem e m (MRS) in in w e s t e r n Lake u p e r i o r interpreted i n t e r p r e t e d from sparse s p a r s e seismic s e ~ s m i cdata data have been been cconfirmed by GLIMPCE have o n f i r m e d tby ~ yrecently r e c e n t l y made available a v a i l a b l e proprietary proprietary 60—fold, 8-sec 8—sec CDP CDP seismic rreflection 60-fold, e f l e c t i o n data d a t a and gravity g r a v i t y and magnetic magnetic anomaly data d a t a (see ( s e e McGinnis and a n d others, o t h e r s , this t h i s volume). volume). Two new reflection west r e f l e c t i o n pprofiles r o f i l e s eeast a s t aand nd w e s t of o f GLIMPCE line l i n e C disclose d i s c l o s e aa deep deep asymmetrical ccentral however, the asymmetrical e n t r a l ggraben; r a b e n ; however, t h e new lines l i n e s ddefine e f i n e a southward thickening volcanic t h i c k e n i n g ssedimentary— edimentary- v o l c a n i c wedge in i n contrast c o n t r a s t to t o line l i n e C, C, complexities iin between m major ssuggesting u g g e s t i n g complexities n sstructural t r u c t u r a l bblocks l o c k s between a j o r MRS rift rift a relief r o a d aarch r c h nnear e a r 447° 7 O 20' 20' N., N . , 90° 900 W with with a r e l i e fofo fmany many zones. A bbroad kkilometers i l o m e t e r s on the t h e long, l o n g , nnortheast o r t h e a s t trending t r e n d i n g reflection r e f l e c t i o n line l i n e in i n the t h e west west Lake SSuperior is ooverlain with sslight arm oof f Lake u p e r i o r is v e r l a i n wit.11 l i g h t aangular n g u l a r unconformity u n c o n f o r m i t y by Middle Proterozoic s t r a t a , suggesting s u g g e s t i n g that t h a t the t h e western w e s t e r n arm arn P r o t e r o z o i c ssedimentary e d i m e n t a r y strata, Superior oof f Lake S u p e r i o r may infact i n f a c t include i n c l u d e at a t least l e a s t two two rift r i f t subzones. s u b z o n e s . AA broad ssyncline Bayfield Peninsula broad y n c l i n e nnortheast o r t h e a s t oof f B ayfield P e n i n s u l a is bounded on the t h e south south by a fault. f a u l t . Whether this t h i s is a continuation c o n t i n u a t i o n of o f the t h e Douglas Isie-Royale Isle-Royale Fault F a u l t System System is is not n o t clear. clear. This work w was T h i s work a s ssupported u p p o r t e d by the t h e U.S. U.S. Department of o f Energy, Office Office ooff Energy Research, R e s e a r c h , under u n d e r Contract C o n t r a c t W—31—l09—ENG--38. W-31-109-ENG-38. 63 �METAMORPHISM AND POLYGENESIS POLYGENESISOF ORE DEPOSITS: ANEXAMPLE EXAMPLE METAMORPHISM DEPOSITS: AN FROM FROM THE MADEM MADEM LAKKOS LAKKOS PB-ZN-AG-AU PB-ZN-AG-AUDEPOSIT, DEPOSIT, GREECE GREECE Mark L. Nebel L. Nebel Dept. of Geology, 80401 Geology, Colorado Colorado School School of Mines, Mines, Golden, Golden, CO CO 80401 Economic Economic geologists geologists frequently frequently encounter encounter difficulties difficulties in in applying applying simple, single-event single-event genetic models to complex complex ore ore deposits. deposits. This This simple, genetic models has invariably invariably led led to opposing opposing camps camps of of geologic geologic thought thought which which stubbornly argue that that specific stubbornly argue specific ore deposits, deposits, and even even entire entire classes classes of ore ore deposits, deposits, are are either either 'syngenetic' 'syngenetic' or or 'epigenetic', 'epigenetic', etc., etc., and and that that these formed by by a single these deposits deposits formed single process process during during aa single single geologic geologic event. event. This This type type of of thinking thinking ignores ignores the the fact fact that that ore ore deposits, deposits, like like all other other rocks, rocks, have have long longand andcomplex complex histories. histories. They are are subject subject to to regional and local metamorphic regional and local metamorphic and/or andlor deformational deformational events, events, magmatic intrusion, and magmatic intrusion, and the the effects effects of of interaction interaction with with circulating circulating fluids fluids of of extremely extremely variable variable chemistry. chemistry. These processes processes can can These profoundly change the the morphology and composition of any profoundly change morphology and composition of any rock rock type, type, including including those those containing containing economic economic minerals. minerals. The The recognition recognition of of multiple or events multiple processes processes or events leading leading to the the formation formation ofofeconomic economic mineral deposits, i.e. i.e. the concept can lead concept of 'polygenesis', 'polygenesi~'~ can lead to to aamuch much mineral deposits, better better understanding understanding of not not only only complex complex and andpoorly-understood poorly-understood ore ore deposits, but also those that 'appear' to be simple. deposits, also those that 'appear' to be simple. The The problems problems and and seeming seeming contradictions contradictions encountered encountered in applying applying single-event single-event genetic genetic models models can often often be be avoided. avoided. The The Madem Madem Lakkos Lakkos deposit deposit in in northern northern Greece Greece serves serves as as an an excellent Madem Lakkos Lakkos excellent example example of aa polygenetic polygenetic ore ore deposit. deposit. The The Madem ores ores are are hosted hosted in in marble marble of ofthe theMesozoic(?) Mesozoic(?) Kerdylia Kerdylia Formation, Formation, aa high-grade high-grade metamorphic metamorphic complex complex composed composed of of migmatitic migmatitic biotite biotite gneiss gneiss interlayered interlayered with with marble, marble, hornblende hornblende gneiss, gneiss, and andamphibolite. amphibolite. The Kerdylia Formation is The Kerdylia Formation is intruded intruded by variety of of synsyn- and and postpostby a variety tectonic felsic intrusions intrusions of of Tertiary Tertiary age. age. LongLongtectonic intermediate intermediate to to felsic believed believed to have have formed formed as as an anepigenetic epigenetic replacement replacement body body related related to to Tertiary Tertiary magmatism, magmatism, recent recent research research has has recognized recognized the thepresence presence of Madem Lakkos Lakkos of three three different different and and distinct distinct ore ore types types inin the the Madem deposit deposit that that require require aa much much longer longer and and more more complex complex genetic genetic history. history. Based Madem Based on on ore ore mineralogy, mineralogy, textures, textures, and and geochemistry, geochemistry, the theMadem Lakkos ores can be be characterized characterized as either either 1) 1) Massive Massive Sulfide Sulfide Ore, Ore, 2) 2) Lakkos Replacement Ore, or 3) Skarn Ore types. Replacement Ore, 3) Skarn Ore types. Massive Massive pyrite-sphaleritepyrite-sphaleritegalena galena ore ore exhibits exhibits abundant abundant and and well-developed well-developed metamorphic metamorphic textures textures that that indicate indicate the the ore ore has has been been metamorphosed metamorphosed to at at least least 600°C 6OO0C (amphibolite (amphibolite grade), grade), together together with with its its marble marble and and gneiss gneiss host host rocks. These textures include rocks. These textures include foliated/lineated foliatedtlineated galena galena and and 64 �I sphalerite, slip and deformation twinning in galena and sphalerite, and granoblastic annealing/recrystallization features in galena, sphalerite, and pyrite with the development of 1200 triple-point junctions. In spite of its metamorphism, the ore preserves a generally stratiform nature, a stratigraphic association with other chemical sediments, primary compositional layering, and metal zonation that are consistent with formation as a carbonate-hosted, syndepositional massive sulfide deposit. Replacement ore consists of complex veins and manto-type impregnations in altered marble composed of pyrite, sphalerite, galena, tennantite, chalcopyrite, arsenopyrite, seligmannite, boulangerite, and minor amounts of a wide variety of additional sulfosalt minerals in a quartz-sericite-manganiferous carbonate gangue. Replacement ore cross-cuts and has reacted with the massive sulfide ore, and does not exhibit evidence of metamorphism. Euhedral zoned crystals with mineral and fluid inclusions, open space fillings, and complex textural relationships are characteristic of this ore type, and suggest replacement of marble by reaction with hydrothermal solutions. Replacement ore is enriched in As, Cu, Bi, Sb, Mn, Sn, and Te with respect to the massive sulfide ore, and was deposited from near-neutral pH solutions at temperatures ranging from 200 to 400°C. Preliminary lead isotope data indicate that massive sulfide and replacement ores have a common homogeneous lead source. Skarn ore contains pyrite, chalcopyrite, minor amounts of other sulfide and sulfosalt minerals, and scheelite in a calc-silicate gangue assemblage of garnet, diopside, calcite, quartz, epidote, and minor chlorite and magnetite. Textures similar to those found in the replacement-type ore and an absence of metamorphic features are characteristic of the skarn ore. Fluid inclusions indicate a magmatic source and high temperature, low pressure deposition for the skarn ore. Skarn ores do not exhibit a clear spatial relationship to foliated aplitic igneous rocks in the mine, and appear to represent a distal skarn, related to co-regional intrusions but formed by hydrothermal replacement of marble at some distance from the source magma. A multi-stage genetic model is proposed for the Madem Lakkos Synsedimentary massive sulfide ore was deposited as a stratiform body within a sequence of Mesozoic(?) shallow water platform carbonate, clastic/volcaniclastic, and evaporitic sediments. This ore and its host rocks were metamorphosed to upper amphibolite grade during Tertiary age regional metamorphism. Post-tectonic intrusion of the Stratoni granodiorite into the deposit. 65 �metamorphosed Kerdylia Kerdylia Formation Formation generated generated heat heat and magmatic metamorphosed magmatic skarn mineralization fluids that produced produced skarn mineralization and and aa continuing convective system that that mixed meteoric waters, convective hydrothermal hydrothermal system mixed with with meteoric waters, extensively altered altered the the marble, and formed ores in extensively marble, and formed the replacement replacement ores in part by part by reaction reaction with with and and remobilization remobilization of the the massive massive sulfide sulfide ore ore and in part and part by by addition addition of ofconstituents. constituents. The Madem deposit exhibits exhibits aa distinctive variety of of ore Madem Lakkos Lakkos deposit distinctive variety ore The types whose features cannot cannot be be explained by aa single types whose combined combined features explained by single The genetic process. genetic process. The mineralization mineralization cannot cannot be characterized characterized as as simply 'syngenetic' or 'epigenetic'. It must considered It must be be considered 'polygenetic', formed by by aa series 'polygenetic', formed series ofofgeologic geologicevents eventssuperimposed superimposed over is likely over an an extended extended period period of of time. time. ItIt is likely that that other other complex, complex, enigmatic, enigmatic, and geologically geologically controversial controversial ore deposits deposits have have formed formed in similarly similarly complex in complex ways. ways. 66 �PETROGENETIC EVOLUTION EVOLUTION OF OF THE THE PROTEROZOIC PROTEROZOIC WAUSAIJ WAUSAU IGNEOUS IGNEOUS COMPLEX, COMPLEX, WISCONSIN WISCONSIN PETROGENETIC T. PATTON, M.K. SOD, B. BIDDULPH, Department of Earth Sciences M.K. SOOD, B. BIDDULPU, Department of Earth Sciences T. PATTON, Northeastern I l l i n o i s University, Chicago, IL I L 60625 60625 Northeastern Illinois University, Chicago, The The 1,520 1,520 m.y. m.y. old old Wausau Wausau Igneous igneous complex complex is is located located in i n Marathon Marathon county, county, north north central Wiscon$in. Wisconln. It les west of the Wolf River batholith and covers an It \ies west of the Wolf River batholith and covers an area area of of roughly roughly 300 300 km km (112 (112 ml m i ). 1. Ilt is is composed composed of of two two plutons, plutons, which which are are somewhat somewhat elongated elongated to t o the the northeast. northeast. The The Stettin S t e t t i n pluton, pluton, which which lies l i e s to t o the the northeast northeast of of the the larger Wausau Wausau pluton, pluton, is is elliptical e l l i p t i c a l and and contains contains aa core core of of nepheline nepheline and and pyroxene pyroxene larger syenite by syenitic syenltic rings. rings. The The subcircular subcircular Wausau Wausau pluton pluton extends extends from from syenite surrounded surrounded by north north of of Wausau, Wausau, southward southward to t o west west of of Mosinee, Mosinee, and and is separated separated into i n t o northern northern and and southern by the the Rib RibRiver Riverlineatnent. lineament. The The northern northern segment segment consists consists of of southern segments segments by Wausau granite, which forms Wausau syenites syenites that t h a t grade grade into i n t o quartz quartz syenite syenite and and the t h e Ninernile Ninemile granite, forms the the largest largest unit u n i t of of the the complex. complex. The Stettin pluton is a petrographically petrographically zoned intrusion characterized by S t e t t i n pluton tabular syenite iin zone, amphibole syenite iin and n the wall zone, n the intermediate zone, zone, and pyroxene zone, which show considerable pyroxene and and nepheline nepheline syenites iin n the core zone, considerable textural textural variations. variations. Perthitic alkali a l k a l i feldspar (50—90%), (50-9011, nepheline nepheline (7—25%), (7-25%), bluish—green bluish-green it sodic (5—114%),aegerine-augite aegerine—augite pyroxene pyroxene (14—10%), constitute the sodic amphibo].es amphiboles (5-14g), (4-1011, constitute the major major minerals minerals in i n the the Stettin S t e t t i n rocks. rocks. Zircon, Zircon, apatite, a p a t i t e , fluorite, f l u o r i t e , calcite, c a l c i t e , magnetite, magnetite, fayalite, f a y a l i t e , biotite, biotite, and and quartz quartz occur occur as a s minor minor minerals. minerals. The also shows shows petrographical petrographical zoning with The Wausau Wausau p].uton pluton also w i t h aa wall wall zone zone of of pyroxene—amphibole with pyroxene-amphibole Wausau syenite w i t h mechanically mixed xenoliths of quartzite quartzite and and Xenoliths and and maf mafic Ic schlieren schlieren s c h i s t in i n aa discontinuous discontinuous but but circular circular configuration. configuration. Xenoliths schist and and clots c l o t s are are more more frequent frequent in i n the t h e intermediate intermediate quartz quartz syenite syenite zone. zone. Sodic Sodic plagioclase perthite (60-8011 (60—80%) and quartz (5—12%) plagioclase and and rnicrocline microcline perthite (5-121) constitute constitute the the major aegerine, ffayalite, magnetite, and carbonate form major minerals minerals and and barkevi.kite, barkevikite, aegerine, a y a l i t e , magnetite, form largely of porphyritic, porphyritic, The Ninemile granite consists largely the the minor minor minerals. minerals. The medium—coarse medium-coarse grained, amphibole—biotite amphibole-biotite granite and a core core of biotite—muscovite biotite-muscovite granite (62-651). granite which which possesses possesses miarolitic miarolitic cavitites. cavitites. Perthitic P e r t h i t i c alkali a l k a l i feldspar feldspar (62—65%), plagioclase (5—7%), (5-7%), and and quartz quartz (21—29%) (21-291) form form the the principal minerals minerals with with minor minor plagioclase is an an important important accessory. accessory. Fluorite Is amounts amounts of of sodic sodic amphiboles amphiboles and and biotite. biotite. Fluorite Electron of the principal phases indicate that Electron microprobe studies of t h a t the the Wausau Igneous of anorogenic, Igneous complex complex has has mineral chemistry chemistry characteristic characteristic of anorogenic, alkalic a l k a l i c (felsic) (f e l s i c ) intrusions, intrusions, as a s sunnarized summarized in i n Table Table 1. 1. Chemically, Chemically, the Wausau rocks show overall alkalic to t o subalkalic affinities affinities (Table (Table 2.) 2.) Syenitization Stettin, Syenitizatlon of of volcanics volcanlcs aatt S t e t t i n , miarolitic cavities c a v i t i e s in i n the the Ninemile Ninemile a s well well granite, granite, the the medium medium to t o coarse coarse grained texture texture of of the the rocks rocks of of the the complex, complex, as as of ffluorite volatile—bearing minerals, a s the the appreciable appreciable amounts amounts of l u o r i t e and other volatile-bearing minerals, suggest suggest the presence of of an active magmatic ffluid l u i d phase during the crystallization and emplacement history history of of the the complex. complex. The The Al A 1 content content of of the the amphiboles amphiboles and and the the emplacement relatively sharp contact relations w with wall rock rock aare i t h the wall r e aalso l s o indicative of of epizonal. emplacement, aat depths of of approximately approximately 10—15 km. t depths 10-15 km. epizonal emplacement, The igneous complex was most likely The magma magma tthat h a t formed the.Wausau igneous l i k e l y generated generated in i n aa crusta]. extension—thermal doming doming environment environment through through ppartial melting of of tthe crustal extension-thermal a r t i a l melting h e Penokean ic crust. crust. The The initial i n i t i a l stages stages may may have have involved involved dehydration dehydrationmelting meltingofofthe themaf mafic portions imparting tthe undersaturated characteristics represented at h e ssilica i l i c a undersaturated a t Stettin. Stettin. The The pervasive pervasive thermal thermal doming doming may have caused progressive progressive "softening" "softening" of of the the upper, upper, less thus changing changing tthe h e magma composition tto o silica s i l i c a oversaturation, oversaturation, as as l e s s mafic, mafic, crust; crust; thus T h i s process process may may have have been been aided aided by by the the represented represented by by the the Ninemile Ninemile granite. granite. This The apparent apparent petrographic petrographic and and chemical chemical limited limited assimilation assimilation of of xenocrystic xenocrystic quartz. quartz. The differences observed observed in i n the the Wausau rocks aare r e reflections reflections of the progressive progressive change change differences of the 67 �i n the the source source rock rock and and the the degree degree of of partial p a r t i a l melting, melting, arid and less l e s s the the result result of of in magmatic differentiation. differentiation. magmatia The Wausau Wausau igneous igneous complex complex represents represents aa magmatic magmatic event, event, related related to to The of the the early early Proterozoic, Proterozoic, with with no no apparent apparent the incomplete incomplete continental continentalrifting r i f t i n gof' the l i n k to t o the the Wolf Wolf River River batholith. batholith: petrogenetic link petrogenetic Table 1.1. Table Mineral chemistry chemistry of of the the Wausau Wausau Igneous Igneous Complex. Complex. Mineral ....................................................................... Mineral Mineral Amphiboles Axnphiboles Fe/Fe+Mg Fe/Fe+Mg Compositional Phases Phases Compositional (Figure 1A) 1A) (Figure Stettin Stettin Wausau Wausau Ninemile Ninemile 0.59-0.98 0.59—0.98 0.76-1 .OO 0.76—1.00 0.91-0.99 0.91—0.99 Ferroedenitic to t o ferro— ferroFerroedenitic hastingsitic hornblende, hornblende, hastingsitic some riebeckite, riebeckite, arfved— arfvedsome sonite, arid and ferrorichterite sonite, ferrorichterite Biotites Biotites (Figure 1B) 1B) (Figure Stettin Stettin Wausau Wausau N i nemile Ninemile 0.93-0.97 0.93—0.97 0.70-0.97 0.70—0.97 0.90-0.99 0.90—0.99 Annitic biotite biotite Annitic Pyroxenes Pyroxenes Stettin Stettin Wausau Wausau 0.68-0.89 0.68—0.89 0.69-1 .OO 0.69—1.00 Aegerine (acmite)—augite (acmitel-augite Aegerine Plagioclase Plagioclase Feldspars Feldspars Stettin Stettin Wausau Wausau — Ninemile Ninemile Alkali Alkali Stettin Stettin Wausau Wausau Ninemile Ninemile Feldspars Feldspars (x-ray data) data) (x—ray -- ---Table 2. 2. Table - Albite-oligoclase Albite—oligoclase An0—An21 An0-An21 An0—An12 12 Or.—Or Microcline perthites perthites Microcline 0r39—0r611 0r52—0r63 --- -------------- Chemistry of of the the Wausau Wausau Igneous Igneous Complex Complex rocks. rocks. Chemistry wt. %1 Wt. Stettin Stettth Wausau Wausau Ninemile Ninemile Si02 Si02 Na20+K20 Na20+K20 511.10—66.10 67.50—76.93 C l , FF Cl, 100—1650 0.01—0.35 62.86—66.39 11.20—12.59 16.51—18.21 88—346 0.01—0.22 Chemistry: Chemistry: Alkalic-peralkalic Alkalic—peralkalic Metaluminous Metaluxn.thous Nepheline Nepheline Normative Normative Quartz Quartz Normative Normative 10.20—13.80 A1203 A].203 Zr (ppm) ( P P Zr . ~ 13.211—21.02 68 9.116—11.01 12.52—15.55 140-1500 0.06—0.111 Peraluminous— Metaluminous Quartz Quartz Normative Normative �PARAGASITE PARAGASITE HASTINSSITE HAST!NSTE ANNITE SIOEROPHYLLITE ANNITE SIDE ROPHY LI ITt WOLF R I V E BATHOLITH R BATHOLITH •8 WOLF RIVER 0 N I N E M I L E GRANITE o NINEMILE A WAUSAU COMPLEX COMPLEX WAUSAU 0 S T E T TCOMPLEX I N COMPLEX 0 STETTIN O) + If, a) Ua) U- • • ••s UOLF RIVER BATHOLITH • WOLF RIVER BATHOLITI4 N I N E R I L E GRANITE NINEMILE i o0 - A (A) 00 0.5 0.5 EDENITE VAUSAUCOMPLEX COMPLEX AUS&U S T E T I N COMPLEX 00 STETTIN COMPLEX Fe/Fe+Mg F'e/Fe+Mg 1 FERROEDENITE FERROEDEIflTE 1 pnLI.OGOplTE PHLOGOPITE (B) 1.5 1.5 R L ATOMS RTOMS AL F i g u r e 1. 1. (A) (A) Compositions Compositions ofofamphiboles amphibolesfrom fromthe t hWausau e Wausau Complex Complex in i n terms t e r m s of of Figure A 1 (VI). (B) Compositions o f b i o t i t e s from t h e Fe/Fe+Mg and Fe/Fe+Mg and Al (VI). (B) Compositions of biotites from the Wausau Complex i nint eterms r m s oof f total t o t a lAlAand 1 and Fe/Fe+Mg. Wausau Complex Fe/Fe+Mg. REFERENCES CITED CITED REFERENCES Sood, M.K., P.E. Meyers, Meyers, and e r l i n , 1980. 1980. Petrology, P e t r o l o g y , geochemistry geochemistry Sood, M.K., P.E. and L.A. L.A. BBerlin, and c o n t a c t r e l a t i o n s of t h e Wausau and S t e t t i n s y e n i t e plutons, and contact relations of the Wau5au and Stettin syenite plutons, c e n t r a l Wisconsin, 2 6 t h Ann. I n s t . Lake S u p e r i o r Geol., F i e l d Trip Trip 3, central Wisconsin, 26th Ann. Inst. Lake Superior Geol., Field 3, Univ. o f Wisconsin, Eau C l a i r e , 59 p. Univ. of Wisconsin, Eau Claire, 59 p. 69 2 EASTONITE EASTONITE �___________________________ PETROGRAPHIC AND MICROPROBE STIJDY STUDY OF OF ISOLATED ISOLATED IRON-FORMATION IRON-FORMATIONLENS LENS PETROGRAPHIC MICHIGAN: A SEARCH FOR HIGH-GRADE, HIGH-GRADE, PRE-PENOKEAN PRE-PENOKEAN NEAR REPUBLIC, MICHIGAN: METAMORPHISM METAMORPHISM J.W. Peterson, T. Chacko, S.M. Kuehner, Kuehner, Department Department of of the Geophysical Geophysical Sciences, Sciences, University University of of Chicago, 312-702-8137 IL60637, 60637,3 12-702-8137 Chicago, Chicago, Chicago, IL Though virtually virtually all all the iron-formation in the Republic Quadrangle Quadrangle of Marquette Marquette County, County, Though Michigan, is of Precambrian X age (Van Schmus and Woolsey, 1975), some isolated lenses of W age age Bell Bell Creek Creek Gneiss Gneiss(Cannon (Cannon iron-formation occur occur within the the mafic units of the Precambrian Precambrian W iron-formation 1973). One Oneof ofthese theselenses lensesoutcrops outcropsapproximately approximately one one mile mile southwest southwestof ofthe the and Simmons, 1973). village of Republic, Michigan, in the the southeast southeast comer corner of of section section 12, 12,T.46N., T.46N.,R.30W. R.30W. Samples from from this outcrop outcrop were were examined examined using using petrographic petrographic and and electron electron microprobe microprobe techniques techniquestoto determine whether whether the the mineralogy mineralogy reveals evidence for an earlier, earlier, higher grade of metamorphism metamorphism determine than that that experienced experienced by by the theNegaunee NegauneeIron Iron Formation Formation—1.9 -1.9 b.y. and Woolsey, Woolsey, than b.y. ago (Van Schmus Schmus and figure and and includes includes zones of the the following following The unit unit isis banded banded on on the the scale scale illustrated illustrated in the figure 1975). The assemblages: ferro-tschermakitichornblende hornblende÷+quartz quartz++ magnetite, magnetite, Fe-rich Fe-rich assemblages: ferro-hornblende ferro-hornblende++ ferro-tschermakitic cummingtonite anthophyllite++ quartz quartz ++ magnetite, magnetite, garnet garnet ++ Fe-rich Fe-rich cummingtonite curnrningtonite±k cumrningtonite±kanthophyllite anthophyllite anthophyllite++ quartz quartz ++ magnetite magnetite ++ ferro-tschermakitic ferro-tschennakitic hornblende, hornblende, Fe-rich Fe-rich cummingtonite cummingtonite ±k anthophyllite anthophyllite++ biotite biotite ++ quartz quartz ++ magnetite magnetite ±k ferro-tschermakitic hornblende, garnet garnet ++ Fe-rich Fe-rich cummingtonite anthophyllite++ quartz quartz++ magnetite, magnetite, Fe-rich Fe-rich cummingtonite cummingtonite±kanthophyllite anthophyllite++ cummingtonite±kanthophyllite biotite biotite ++quartz quartz ++ magnetite, magnetite, and and garnet garnet ++ Fe-rich Fe-rich cummingtonite cumrningtonite±k anthophyllite anthophyllite ++ biotite biotite ++ quartz. quartz. A present and and associated with with the the magnetite. magnetite. Garnet A complex complex mixture mixture of Fe-S phases is also present Garnet and and as those those of of the the highest highest grade grade of of the the Negaunee NegauneeIron Iron amphibole compositions compositions are are virtually virtually the same as amphibole Formation (Haase, (Haase,1982) 1982)and andbiotite-garnet biotite-garnetpairs pairs yield yieldpaleotemperatures paleotemperaturesofof—535°C, -535OC, compared compared to to Formation —550°C forNegaunee NegauneeIron IronFormation Formationrocks rocksininthe thesame samevicinity vicinity(Haase, (Haase,1982). 1982). Though the -550° for higher-grade higher-grade mineral, mineral, orthopyroxene, orthopyroxene, has been reported in in some some of of these these isolated isolated lenses lenses(Cannon (Cannon and 1973),our our preliminary preliminary results suggest that there is no mineralogical mineralogical evidence evidencein in this this and Simmons, Simmons, 1973), locality for for an earlier earlier metamorphism more intense than that experienced by the Negaunee Iron locality Formation. Formation. 11 I II E ferro-hornblende lerro-hornblende +terro-tschermakitic +ferro-tschermakitlc hornbtende hornblende +quartz .magnette Fe-cummingtonile janthophyltite +guartz +rnagnetit. U L garnet +F..Cummingtonite tanthophyflite +quartz +magneute +ferro.tschermakllic hotnbiande Fe-cumminglonite tanthophyilite +biotite .quartz +magnetite jprrp-tschermpicitic hprnblei'Ce garnet +Fe-cummingtonite tanthophyllite +guarlz +magnetite Fe-cummingtonsta ianthooiiyilite +biotit. ..guartz +magnetite garnet +Fe-cumrningtonite tanthop9yIIite +biotite +quartz References ReferencesCited Cited Cannon, Cannon, W.F. W.F. and and Simmons, Simmons,G.C., G f . .1973, 1973,Geology of part pan of of the the Southern SouthernComplex, Complcx,Marquette MarquetteDistrict, District,Michigan: Michigan: Journal Journalof ofResearch, Research,U.S. U.S.Geological Geological Survey, Survey, v. v. 1, 1,n. n.2,2,165-172. 165-172. Haase, Haase, C.S., C.S.,1982, 1982,Metamorphic Mctamorphicpetrology petrology of the the Negaunee Negaunee Iron Iron Formation, Formation,Marquette MarquetteDistrict, District,northern northernMichigan: Michigan: mineralogy, equilibria: Economic 60-81.1. mineralogy,metamorphic metamorphic reactions, reactions, and phase equilibria: EconomicGeology, Geology,v. v. 77, 77.60-8 Van Van Schmus, Schmus,W.R. W.R. and and Woolsey, Woolsey, L.L., L.L., 1975, 1975, Rb-Sr Rb-Sr geochronology geochronology of of the the Republic Republic area, area,Marquette MarquctteCounty, County, Michigan: 1723-1733. Michigan:Canadian CanadianJournal JournalofofEarth EarthSciences, Scicnccs,v.v.12, 12,1723-1733. 70 �ONE, POSSIBLY POSSIBLY TWO, TWO, IMPACT IMPACT CRATERS CRATERS UNDER UNDER DePERE, DePERE, WISCONSIN, WISCONSIN, DISCOVERED DISCOVERED VIA VIA WATER WATER WELL WELL ONE, LOGS AND AND DRILL DRILL CUTTINGS CUTTINGS LOGS William F. F. Read, Read, Dept. Dept. of Geology, Geology, Lawrence Lawrence Univ., Univ., Appleton, Appleton, Wis., Wis., 54912 54912 William - Water—well Water-well drillers drillers in in Wisconsin Wisconsin are are required required to to send send descriptions descriptions of of rock rock units units penetrated penetrated by by their their drills drills to to the the Wisconsin WisconsinGeological Geologicaland andNatural NaturalHistory HistorySurvey. Survey. If If the the well is is to be a "high—capacity" "high-capacity" producer, producer, they they are are required required also also to to send send in in drill drill chips chips collected collected at at 5—foot 5-foot intervals. intervals. From From the the chips chips Survey Survey personnel personnel prepare prepare detailed logs loqs of of the the drill drill holes. holes. These These records, records, which which have have been been accumulating accumulating since since detailed about about 1900, 1900, are are an an extremely extremely valuable valuable source source of of information information on on subsurface subsurface geology. geology. My My interest interest in in impact impact craters craters began began years years ago ago when when II started started work work on on the the Glover Glover Bluff . Bluff structure structure(1) (1). This is is now now "officially" "officially" accepted accepted as as being being of of impact impact origin origin This ( 2 .) . The The Rock Rock Elm Elm structure structure may may also also be be (probably (probably is, is, in in my my opinion) opinion) of of impact impact origin origin (2) ( 3 ) (4). (4). Both Both structures structures appear appear to to be be of of Lower Lower to to Middle Middle Ordovician Ordovician age. age. (3) There There are are plenty plenty of of Lower Lower and and Middle Middle Ordovician Ordovician sedimentary sedimentary rocks rocks in in eastern eastern Wisconsin. Several Several quarries quarries near near Lawrence Lawrence University University were were begun begun in in upper upper Middle Middle Wisconsin. Ordovician Ordovician dolomites dolomites of the the Sinnipee Sinnipee Group Group (5) (5) and and got got down down into into Lower Lower Ordovician Ordovician Prairie Prairie du du Chien Chien dolomite dolomite as as development development progressed. progressed. Lower Lower Middle Middle Ordovician Ordovician strata, strata, mainly mainly the the St. St. Peter Peter sandstone, sandstone, are are commonly commonly thin thin in in this this area area and and may may be be missing missing altogether. In In two two of of these these quarries quarries the the St. St. Peter Peter appears appears only only as as lenses lenses aa few few altogether. meters meters thick. thick. Near Near the the bottoms bottoms of of some some lenses lenses there there are are potato—size potato-size objects objects which which superficially superficially look very much like like chert chert nodules nodules but are quite quite different different in in details details of ( 6 ) . In In external form form and and internal internal composition. composition. II interpret interpret them them as as impact impact bombs bombs (6). external northern Illinois Illinois II found found similar similar objects objects associated associated with with small small spherules spherules that that bear bear aa northern close close resemblance resemblance to to silicified silicified ooids. ooids. But But these these too too are are different different internally internally from from ordinary ordinary ooids. ooids. Some Some appear appear to to have have crystallized crystallized from from glass glass in in aa manner manner similar similar to to that that of of lunar lunar glass spherules spherules and the the "microtektites" "microtektites" found found in in modern modern sea—floor sea-floor sediments. sediments. II interpret interpret them them as as impact impact spherules spherules(7). ( 7 ) . The The Illinois Illinois spherules spherules have have so so far far been been found found only in loose loose chunks chunks of of rock rock but but there there is is good good reason reason to to believe believe that that these these chunks chunks came from near near the the base of the the St. Peter sandstone. sandstone. came from base of St. Peter Since Since these these initial initial discoveries discoveries II have have found found similar similar impact impact bombs(?) bombs(?) and/or and/or impact impact spherules(?) spherules!?) of about about the the same same age age at at aa number number of of other other locations locations in in Wisconsin Wisconsin and and in in Arkansas, Arkansas, Pennsylvania, Pennsylvania, and and Newfoundland. Newfoundland. These These widespread widespread impact impact ejecta(?) ejects(?), plus plus the the known known Lower to Middle Ordovician Ordovician craters craters or or crater crater substructures, substructures, suggest suggest that that Planet Planet Earth may have been hit hit by by an an unusually unusually large large number number df of asteroids asteroids or or comets during during this this time time interval. interval. comets It It occurred to me that the actual abundance abundance of craters craters of of Lower Lower to to Middle Middle Ordovician age might be much greater greater than than the the number number of of known known craters craters now now regarded regarded as as Ordovician age And that that it it might might pay pay to to look look for for buried buried ones ones via via being of of this this age age would would indicate. indicate. And being buried crater crater formed formed near near the the close close logs of, of, and and drill cuttings cuttings from, from, water water wells. wells. AA buried logs of of Lower Lower Ordovician Ordovician time time should should be be filled filled with with an an unusual unusual thickness thickness of of Middle Middle Ordovician Ordovician sediment——in s e d i m e n t ~ i nWisconsin, Wisconsin, St. St. Peter Peter sandstone. sandstone. Conversely, Conversely, the the Lower Lower Ordovician , having Ordovician (Prairie (Prairiedu du Chien Chiendolomite dolomiteininWisconsin) Wisconsin), having been been excavated excavated during durinq crater crater formation, formation, should should be be thin thin or or absent. absent. Unfortunately, Unfortunately, this this criterion criterion alone alone is is an insufficient insufficient guide for buried-crater since the the Prairie Prairie du du Chien, Chien, during durinq aa an buried—crater hunters since brief interval emergence, suffered interval of emergence, suffered considerable considerable erosion erosion by surface surface and subsurface and subsurface water, Chien is is likely likely to to be be found found water, so so that that thick thick St. St. Peter Peter overlying overlying thin thin Prairie Prairie du du Chien impact craters almost almost anywhere. anywhere. An An additional additional criterion criterion must must be be applied: applied: impact craters are are excavations excavations of limited, limited, normally circular, circular, extent; extent; excavations excavations produced produced by by erosion erosion So the the buried—crater buried-crater hunter hunter are likely likely to to be be more more extensive extensive and and irregular irregular in in shape. shape. So are must must look look for for thick thick St. Peter Peter over over thin thin Prairie Prairie du du Chien Chien in in an an area area which which is is at at least least limited limited even if its its shape shape cannot cannot be be determined determined from from the the information informationsupplied suppliedby by well well Even this this criterion criterion leaves leaves open open the the possibility possibility that that the the filled filled "hole" "hole" loqs. Even logs. indicated by a definitely definitely limited limited area area of of thick thick St. St. Peter Peter over over thin thinPrairie Prairiedu du Chien Chien indicated This is is always always an an alternative alternative unless unless the the bottom bottom of of the the simply be be aa sinkhole. sinkhole. This may simply thick thick St. St. Peter Peter goes goes well well below below the the lowest lowest level level reached reached by by holes holeslikely likelyto tohave havebeen been i.e., down into into Cambrian Cambrian sandstone sandstone or the the Precambrian Precambrian generated by by solution: solution: i.e., generated basement. basement. Proof that a buried hole of any kind was produced by impact impact would have to come Impact cratering cratering of of any any magnitude magnitude is is from from rock rock samples samples provided provided by by drill drill cuttings. cuttings. Impact Evidence of of accompanied by aa good good deal deal of of melting melting and and shocking shocking of of the the target targetrocks. rocks. Evidence accompanied one one or or both of these activities activities would have have to to be found found in in drill drill cuttings cuttings before before of anyone would believe that that a buried hole, hole, regardless regardless of extent extent or or depth depth of anyone penetration, penetration, might actually actually be be an an impact impact crater. crater. 71 �Fortunately, Fortunately, Mai and and Dott Dott (8) (8) have have recently recently published published maps maps showing showing (a) (a) variations in the thickness thickness of the the St. St. Peter Peter in in eastern eastern and and southern southern Wisconsin, Wisconsin, and and (b) (b) the the stratigraphic stratigraphic age age of of the the rock rock which which directly directly underlies underlies it. it. The The maps maps are are based on a study of nearly 900 900 "high "high capacity" capacity" wells wells logged logged by by the the State State Survey Survey from from drill drill cuttings. cuttings. From these these maps anyone anyone can can easily pick likely likely locations locations for for buried buried impact impact craters craters using using the the criteria criteria outlined outlined above. above. For For starters, starters, I picked picked the the DePere DePere area, area, one of a number number of areas areas where where the the maps maps show show that that the the St. St. Peter Peter is is unusually unusually thick thick in in a limited limited area and and that that its its bottom bottom cuts cuts well down down into into the the Cambrian. Cambrian. Also Also there there is is good "control" "control" in in that that the the area area contains contains quite quite aa few few high high capacity capacity wells. wells. It It was aa lucky lucky choice. choice. Thin Thin sections sections were prepared prepared from from drill drill chips chips provided provided by by the the State State Survey and, and, sure sure enough, enough, impact impact melt melt (glass, (glass, unaltered unaltered or or partly partly crystallized) crystallized) was found found in in aa number number of of chips chips that that came came from from near near the the bottom bottom of of the the St. mm in in St. Peter. Peter. Some Some features features noted noted in in these these small small samples samples (averaging (averaging about about 55 mm diameter) diameter) are: are: 1. 1. The The melt glass glass is is commonly commonly red, red, often often quite quite aa dark dark red. red. This This is is aa helpful helpful feature feature to to go go by by in in selecting selecting chips chips for for sectioning. sectioning. 2. 2. Individual quartz sand grains, grains, grain qrain fragments, fragments, and bits bits of of sandstone sandstone are are commonly lamellae were were found found in in the the quartz quartz but but commonly present. present. No convincing convincing shock shock lamellae occasional occasional grains grains and and grain grain fragments fragments have have been been converted converted to to diaplectic diaplectic glass. glass. In fragments fragments of sandstone sandstone individual grains may have have been been tightly tightly squeezed together together and some some melting may have occurred occurred at at grain qrain contacts. contacts. 3. In some cases the melt has crystallized completely completely to to aa mixture mixture of of large large 3. In anhedral anhedral crystals crystals of of carbonate carbonate mixed mixed with with aggregates aggregates of of smaller smaller anhedral anhedral quartz quartz crystals. crystals. Drill chips chips consisting of this this kind kind of of material material are are white. white. 4. section, abundant abundant euhedral rhombs rhombs of carbonate carbonate are are present present in in aa 4. In one section, matrix of of red red glass. glass. They They appear appear to to be be miniature miniature phenocrysts. phenocrysts. are 5. granular aggregates aggregates of green, green, or rarely rarely colorless, colorless, epidote epidoteare 5. Rounded granular fairly fairly common common in in red red melt melt glass glass containing containing quartz quartz sand sand grains. grains. In two, rather than than just just one, one, crater crater may may be be that two, In regard to the possibility that present and 66 in Figure 1 almost certainly wells 4, 4, 55 and certainly went went through through the the under DePere: DePere: wells present under bottom bottom of of aa single single crater. crater. The maximum possible size size of this this crater crater is is limited limited to to the the northwest, northwest, northeast, northeast, and and southeast southeast by Survey—logged Survey-logged wells wells Nos. Nos. 7, 7, 3, 3, 22 and and 8. 8. To To the the southwest southwest its its maximum size size is is limited limited by aa cluster cluster of of wells wells for for which which only only drillers drillers' logs logs are are available. available. In In the the middle of this this cluster cluster is is another another Survey—logged Survey-logged well, well, No. 12, 12, where thick thick St. Peter Peter sandstone sandstone rests rests directly directly on on Cambrian Cambrian as as in in wells wells 4, and 6. 6. This This well definitely definitely passes passes through through aa crater crater since since cuttings cuttings from from it it 4, 55 and contain contain an an abundance abundance of of melt. melt. There There may may be be aa separate separate crater crater here. here. If If well 4 , 55 and and 66 the the well 12 12 is Is in In the the same same crater crater as as wells wells 4, driller's driller's log log for well No. 19 19 must must be be regarded regarded as as inaccurate. inaccurate. Or Or at at least least misleading: misleading: the the "lime "lime rock" rock" the the driller driller reported reported under under only only 99 meters meters of of sandstone sandstone could could be be aa slide slide block. block. References: References: (1) (1) Read, Read, W. W. F., F., 1984: 1984: The The circular circular structure structure at at Glover Glover Bluff: Bluff: what what Grieve, R. and and where where it it is is (abs.). (abs.). Meteoritics, Meteoritics,V. v. 22, 22, p. p. 487. 487. (2) ( 2 ) Grieve, R. A. A . F., F., 1987: 1987: Terrestrial Terrestrial impact impact structures. structures. Episodes, Episodes, v. v. 10, 10, p. p. 86. 86. (3) (3) Cordua, Cordua, W. W. S., S., 1985: 1985: Rock Rock Elm Elm structure, structure, Pierce Pierce County, County, Wisconsin: Wisconsin: aa possible possible cryptoexplosion cryptoexplosion structure. structure. Geology, v . 13, 13, p. p. 372—374. 372-374. (4) (4) Read, Read, W. F.,; F.,; Cordua, Cordua, W. W. S., S., 1985: 1985: Comment Comment and and Geology, v. Reply Reply on on Rock Rock Elm Elm structure, structure, Pierce Pierce County, County, Wisconsin: Wisconsin: aa possible possible cryptoexplosion cryptoexplosion Ostrom, M. structure. (5) Ostrom, M. E., E . , 1967: 1967: Paleozoic Paleozoic structure. Geology, Geology, v. v. 13, 13, p. p. 891—892. 891-892. (5) stratigraphic stratigraphic nomenclature nomenclature for for Wisconsin. Wisconsin. Wis. Wis. Geol. Geol. and and Nat. Nat. Mist. Hist. Survey, Survey, Inf. Inf. Circ. 8. 8. (6) (6) Read, Read, W. W. F., F., 1985: 1985: Impact Impact bombs in in Middle Middle Ordovician Ordovician marine marine sediments sediments Circ. of southeastern southeastern Wisconsin. Wisconsin. Abstracts Abstracts of Papers Papers for for 16th 16th Lunar Lunar and and Planetary Planetary Science Science Conference, F., 1986: 1986: Possible Possible impact impact spherules spherules from from near near Conference, p. p. 687—688. 687-688. (7) (7) Read, Read, W. W. F., the the base base of of the the Middle Middle Ordovician Ordovician in in northern northern Illinois. Illinois. Meteoritics, Meteoritics, V. v. 21, 21, p. 251— 251262. 262. (8) (8) Mai, Mai, H., H., and and Dott, Dott, R. R. H., H., Jr., Jr., 1985: 1985: AA subsurface subsurface study study of of the the St. St. Peter Peter sandstone Hist.Survey, Survey,Inf. Inf. sandstone in in southern southern and and eastern eastern Wisconsin. Wisconsin. Wis. Wis. Geol. Geol. and and Nat. Nat. Hist. Circ. Circ. 47. 47. 72 �___________ A S H WA B E NO N 0 / / . 33 / ao / • 0 042 AL I. 0 U E Z •0 0 I. .2 ) 38 F 4.. .-... 47 .2. .-.. ,. 32 -' 65 // , 8 0 27 PE RC 57 I mu. .- I km Wells Fiq. Wells in in TT 23 23 N, N, RR 20 20 E which which pass pass through throuqh the the St. St. Peter Peter sandstone. sandstone. North North 1. Fig. 1. boundaries of the and east boundaries the township are hypothetical hypothetical since since this this area area is is occupied occupied by by old French French land land grants. grants. Empty circles: circles: wells for for which which only only drillers' drillers' logs loqs are are Blacked—in circles: Circles available. Blacked-in circles: wells logged loqqed by by the the State State Survey. Survey. Circles available. surrounded surrounded by by squares: squares: wells in which impact impact melt melt has has been been found. found. Upper figure figure Lower figure: adjacent adjacent to to well: well: well number number (arbitrary). (arbitrary). Lower figure: thickness thickness of of St. St. Peter Peter in in Large circle: maximum possible diameter of crater meters. Larqe circle: maximum crater penetrated penetrated by by wells wells 4, 4 # 55,# meters. lo for for well well 19 19 is is reliable. reliable. 66 if driller's lou I i. gO.fld ,,,,I.CS (IIItSn.d) t.uub.c. sI.,mp. ,n...h f.IIe,, I.IlOt I— 2. ?bove: Above: Cross Cross section section from well 1 to well 22 with with data data from from intervening intervening wells wells Fiq. 2. Fig. projected 5 , 6, b 1 44 projected onto onto it. it. Vertical exaggeration exaweration xlO. ~ 1 0 . Dash Dash marks marks adjacent adjacent to to wells wells 5, indicate levels levels at which which impact impact melt has has been been found. found. Presence fallout Presence of fallout hypothetical: drill chips chips from wells 1,7,2 1,7,2 have not not yet yet been been examined. examined. Below: Below: same hypothetical: same cross cross section section with with no no vertical vertical exaqgeration. exaqqeration. 73 �PRELIMINARYGEOMAGNETIC GEOMAGNETICMODEL MODEL OF OF THE TI-E ST. ST- CROIX CROIX HORST HORST PRELIMINARY IN POLK PO= COUNTY, COUNTYf WISCONSIN WISCONSIN IN FEICH, Laura, Laura, KEAN, KEAN, William William and and SVERDRUP, SVERDRUP, Keith Keith REICH, Department of Geosciences Department of Geosciences University of of Wisconsin Wisconsin University Milwaukeef Wisconsin 53211 Milwaukee, Wisconsin 532].]. Total field field Land Land magnetic magnetic data data was was collected collected in in Polk Polk Total Countyf northwestern Wisconsin, during June and July, l98gf County, northwestern Wisconsin, during June and July, 1989, in order to model the eastern portion of the St. Croix Horst in order to model the eastern portion of the St. Croix Horst and related volcanicsThe St. Croix Horst, a mayor and related volcanics. The St. Croix Horst, a major structural feature of the the Midcontinent Midcontinent Rift Rift System, System, outcrops outcrops feature of structural in Polk Polk County County and and trends trends northeast northeast to to Bayfield Bayfield County, Countyf in Wisconsin. Wisconsin. The study study consisted consisted of of four four survey s u n e y lines lines totalling totalling 60 60 The (Fig. 1). 1). Three Three lines lines traversed traversed west west to to east, east, miles (Fig. miles approximately normal normal to to the the horst. horst. The The fourth fourth line line approximately traversed south south to to north, north, subparal].el subparallel to to the the horst horst axis. axis. traversed Data was was collected collected at at 0.1 0.1 mile mile intervals. intemals. In In general, general, field field Data a p ~for ~for values are are consistent consistent with with available available aeromagnetic aeromagnetic m values maps the area. area- AA magnetic magnetic relief relief of of 3066 3066 gammas gammas was was found found in in the the the 61576 gammas gammas near near the the horst horst area with with aa maximum maximum value value of of 61576 area axis and and aa minimum minimum value value of of 58510 58510 gammas gammas in in the the southeast southeast axis shows the the data data contoured contoured part of of the the study study area. area. Figure Figure 22 shows part with aa contour contour interval interval of of 500 500 gammas. gammas. Magnetic Magnetic with susceptibilitiesf sampled sampled from from outcrops, outcropsf range range from from 0.009 0-009 to to susceptibilities, of 0.004 0.004 cgs. cgs. Values Values for for 0.0003 cgs cgs with with an an average average value value of 0.0003 total magnetic magnetic field field intensity, intensityf declination declination and and inclination inclination total and 73.5 73.5 , used for for modeling modeling are are 58640 58640 gammas, gammas, 33 EE and used respectively. respectively. Preliminary modeling modeling of of the the magnetic magnetic field field data data yields yields Preliminary two models: models: 1) 1) aa rootless rootless system system where where volcanics volcanics are are 55 miles miles two mile thick thick susceptibilities are are high high and and 2) 2) aa 77 mile thick and and susceptibilities thick volcanic sequence sequence with with low low susceptibilities susceptibilities underlain underlain by by aa volcanic deep central central ultramafic ultramafic root root extending extending to to 12 12 miles. miles- Both Both deep half-graben structures structures on on the the eastern eastern flank flank of of models have have half-graben models the horst. horst the SELECTED REFERENCES FOR FURTHER READING Chandler, V., V., 1983, 1983f Correlation Correlation of of Chandler, magnetic anomalies anomalies in in magnetic east-central Minnesota and northwestern Wisconsin: east-central Minnesota and northwestern Wisconsin: on magnitude magnitude and and direction direction of of Keweenawan Keweenawan constraints on Constraints rifting: Geology, v. 11, p. 174-176. rifting: Geology, v. 11, p. 174—176. G - and and Chandler, Chandler, V., V., 1987, 1987f New New Mcswiggenf G., G., Morey, Morey, G. McSwiggen, model of the Midcontinent Rift in eastern Minnesota model of the Midcontinent Rift in eastern Minnesota and western western Wisconsin: Wisconsin: Tectonics, Tectonics, v. v. 6, 6, no. no. 6, Gf and p. 677-685. p. 677—685. Wold, R. R e and and Hinze, Hinzef W., W., 1982, 1982, Geology Geology and and tectonics tectonics of of the the Wold, Lake Superior region: Memoir Geological Society of Lake Superior region: Memoir Geological Society of 280 p. p. America, 156, 15Gf 280 America, 74 �STUDY AREA AREA POLK C O U N T Y t i - LINE2 St. Crolx Fall8 gs LINE 1 9 2 3 0' 9 2 16 SSCALE C A L E 1:250,000 1:250,000 10 MILES 0 I 0 A' A * F'ig. 1. . 5 10 SURVEY LINE LINE BASE STATION STATION Location of study study arez are Location map of and survey survey lines. lines. 75 I 15 KILOMETERS �MAGNETIC ANOMALY ANOMALY MAP MAP MAGNETIC SCALE SCALE 0o 10 MILES MILES 10 5 0 0 IF 0 I6 5 .1_i 10 I 10 16 KILOMETERS I 15 KILOMETERS .'...I a 58500 59000 59600 60000 80500+ GAMMAS POLK COUNTY COIUNTY POLK Fig. 2. 2. Fig. Magnetic anomaly anomaly map map for for Magnetic the study area. the study area. 76 �COMPARISON OF OF TWO TWO ARCHEAN ARCE?EXN ULTRAMAFIC AA COMPARISON ULTR.AMAFICPYROCLASTIC PYROCLASTIC ROCK ROCK UNITS! UNITS, NoRTmsONTARIO NORTHWESTERN ONTARIO Stephen J. J. Stephen D u l u t hl Duluth, S c h a e f e r ! Department Department of o f Geology, Geologyl University U n i v e r s i t y of o f MinnesotaMinnesotaSchaefer, D u l u t h l MN 55812 Duluth, MM 55812 h apart a p a r t on on Two ultramafic u l t r a m a f i c pyroclastic p y r o c l a s t i c rock r o c k units u n i t s occur o c c u r 100 100 km Two o p p o s i t e s i d e s o f t h e Q u e t i c o f a u l t a l o n g t h e s o u t h e r n margin of t h opposite sides of the Quetico fault along the southern margin of thee Wabigoon Subprovince S u b p r o v i n c e of o f the t h e Superior S u p e r i o r Province. Province. D e t a i l e d mapping, mapping! Wabigoon Detailed p e t r o g r a p h y l and and chemical c h e m i c a l analysis analysis h a v e shown shown that t h a t these t h e s e units u n i t s may may petrography, have b e correlated, c o r r e l a t e d ! as a s has h a s been been suggested s u g g e s t e d by by Howard Howard Poulsen P o u l s e n (pers. ( p e r s . comm., corn. be 1 9 8 8 ) . The The two two units u n i t s are: are: 1988). 1) 1) The Dismal Dismal Ashrock Ashrock which which is i s located l o c a t e d 44 km km north n o r t h of o f Atikokan Atikokan and and The i s p a r t o f t h e S t e e p Rock Group (Wilkes a n d N i s b e t ! 1 9 8 8 ) . T his is part of the Steep Rock Group (Wilkes and Nisbet, 1988). This u n i t is 100 t o 400 m t h i c k and 1 0 km i n l e n g t h w i t h e x c e l l e nt unit is 100 to 400 m thick and 10 km in length with excellent e x p o s u r e i n t h e f o r m e r S t e e p Rock i r o n mine. exposure in the former Steep Rock iron mine. 2) 2) The Grassy G r a s s y Portage P o r t a g e Bay BayUltraxnafic U l t r a m a f i c Pyroclastic P y r o c l a s t i c Rock Rock Unit U n i t (GUP) (GUP) The which occurs o c c u r s 100 100 km k m to t o the t h e west, w e s t l along a l o n g the t h e eastern e a s t e r n side s i d e of o f the the which R i c e Bay Bay dome, dome! in i n an an arcuate a r c u a t e fold f o l d interference i n t e r f e r e n c e pattern p a t t e r n 10 10 km km Rice l o n g . It I t has h a s aa maximum maximumthickness t h i c k n e s sofo f800 800in. m. long. Both units u n i t s are a r e delineated d e l i n e a t e d into i n t o sub-units s u b - u n i t s based b a s e d on on physical physical Both i s d i v i d e d into into v o l c a n o l o g i c a l p a r a m e t e r s . The Dismal Ashrock volcanological parameters. The Dismal Ashrock is divided l a p i l l i tuff, t u f f ! volcanic v o l c a n i c breccia b r e c c i a and and pillowed p i l l o w e d flow. flow. The GUP is lapilli The GUP is d i v i d e d i n t o l a p i l l i t u f f and v o l c a n i c b r e c c i a . The l a p i l li divided into lapilli tuff and volcanic breccia. The lapilli f r a g m e n t s a t e a c h l o c a l e r a n g e from s c o r i a c e o u s t o n o n v e s i c u l a r and fragments at each locale range from scoriaceous to non-vesicular and a r e magnetic. magnetic. Two unusual u n u s u a l fragment fragment types types were w e r e recognized r e c o g n i z e d at a t each each are Two 1. composite c o m p o s i t e lapilli l a p i l l i (lapilli-sized ( l a p i l l i - s i z e d fragments f r a g m e n t s consisting consisting l o c a t i o n : 1. location: of multiple m u l t i p l e lapilli l a p i l l i fragments f r a g m e n t s in in a a rind r i n d of o f quenched quenched lava) l a v a ) and and 2. of 2. c o r e d lapilli l a p i l l i (lapilli ( l a p i l l i ffragments r a g m e n t s wwith i t h aa llithic i t h i c ccore o r e and and a a rim r i m of of cored quenched lava) l a v a ) . Spinifex S p i n i f e x and and skeletal s k e l e t a l crystals c r y s t a l s in i n these t h e s e rims r i m s at a t the the quenched S t e e p Rock Rock locality l o c a l i t y document document their t h e i r magmatic magmatic origin o r i g i n as a s opposed opposed to to Steep f o m a t i o n b y a s h a c c r e t i o n . A c c i d e n t a l f r a g m e n t s of c a r b o n a t e and formation by ash accretion. Accidental fragments of carbonate and t o n a l i t e are a r e found found within w i t h i n the t h e Dismal Dismal Ashrock Ashrock and and one one accidental accidental tonalite c a r b o n a t e f r a g m e n t i s found i n t h e GUP. carbonate fragment is found in the GUP. The chemical c h e m i c a l composition c o m p o s i t i o n of of these t h e s e two two units u n i t s shows shows aa good good The c o r r e l a t i o n . Rock samples from t h e l a p i l l i t u f f s and j u v e nile correlation. Rock samples from the lapilli tuffs and juvenile f r a g m e n t s cut c u t from from rock r o c k samples samples are a r e ultramafic; u l t r a m a f i c ; their t h e i r Si02 S i 0 2content content fragments r a n g e s from from 40-46 40-46 wt.% w t . % and and their t h e i r MgO MgO content c o n t e n t ranges r a n g e s from from 16-25 16-25 wt.% wt. % ranges c a l c u l a t e d on on aa volatile v o l a t i l e free f r e e basis. b a s i s . These These samples s a m p l e s plot p l o t within w i t h i n the the calculated k o m a t i i t e field f i e l d on aa Jensen J e n s e n AFM A F M diagram. diagram. However! t h e y a r e much komatiite However, they are much h i g h e r in i n total t o t a l Fe Fe and and Ti02 Ti02 than t h a n those t h o s e on on aa normal normal komatiite k o m a t i i t e trend. trend. higher These d a t a i n d i c a t e t h a t t h e Dismal Ashrock and t h e GUP are are These data indicate that the Dismal Ashrock and the CUP c o r r e l a t i v e . S h e a r zones a t t h e t o p o f t h e Dismal a s h r o c k and on correlative. Shear zones at the top of the Dismal ashrock and on b o t h s i d e s o f t h e G U P i n d i c a t e t h a t a n e a r l y p e r i o d o f d e f o r m a t i o n both sides of the GUP indicate that an early period of deformation, l w i t h some some thrusting, t h r u s t i n g ! may may have have occurred o c c u r r e d before b e f o r e late l a t e movement movement on on the the with Quetico fault. fault. T h i s would would have have resulted r e s u l t e d in i n the t h e splitting s p l i t t i n g of o f an an Quetico This original u l t r a m a f i c ppyroclastic y r o c l a s t i c uunit n i t iinto n t o tthe he u p p e r CUP GUP and and lower lower original ultramafic upper Dismal Ashrock. Ashrock. Dismal Reference Reference . Wilkes! M. M. Wilkes, E. and Nisbet, N i s b e t l E. E . G., G.! E., and Rock Group! n o r t h w e s t O n t a r i o: Rock Group, northwest Ontario: Archean S t r o m a t o l i t e s : Canadian Archean Stromatolites: Canadian p . 370—391. 370-391. p. 77 77 1987, Stratigraphy S t r a t i g r a p h y of o f the t h e Steep Steep 1987, a m a j o r Archean unconformity and a major Archean unconformity and J o u r n a l of E a r t h S c i e n c e s ! v . 2 s1 Journal of Earth Sciences, v.25, �METAMORPHICZONATION ZONATIONIN IN THE ?lETAMORPHIC THE NORTH NORTH SHORE S H O E VOLCANIC GROUP, GROUPtMINNESOTA MINNESOTA ** * Susanne Th. Th. Schmidt and John John C. Green Susanne Schaidt and Green * ** *Mineralogisch_PetrographischesInstitut, Institut, INF *Nineralogisch-Petrographisches INF 236, 236,D6900 D6900 Heidelberg, Heidelberg,West West CaQZ2Qry C ~uiany **Departuient of of Geology, University ofofMinnesota, MN **Department Geologyt University Minnesota,Duluth, Duluth, MI455812 55812 In the (NSVG) aa the southern limb limb of the the North Shore Shore Volcanic VolcanicGroup Group (NSVG) zonation of alteration alteration minerals flows zonation of minerals in in the the basaltic basaltic lava lava f l o w between between Duluth Duluth minerals iinf n f iilll lformer former vesicles ve~icles and Tofte is is observed (Fig. 1). 1). Alteration observed (Fig. Alteration minerals and Tofte alceratiuu ai1tL&@i and fractures and aJ.so repLace replace carry early ormeO fO~~eCI alceraclux~ U ~ I C L U ulLd a~ d ~ icsu3 LSA~COUS and fractures and aLs0 minerals. main features features of as follows: canbebesummarized sumnarlzed as followa: The main of this thiszoning zoningcan minerals, The from a lower 1) Metamorphic facies ranging to Metamorphic facies ranging from lower actinolite—epidote—chiorite actinollte-epidote-chlorite to thomsonite—scolecite--smectite facie8 fades are observed. The an upper upper thomsonite-scolecite-smectite observed* The are an ,--$ ----~4 ~ - 4 *FA A 4 a t + n c ~ v lehad i from top to bottom: bottom: assoclcticnz ra d±tinguishe4 from rilineral top to Cuilwi L U L A U W ~ ~IILALC, a aavLAwb*u...,*-..-..e---.. thomsonite-.scolecite—smectite, heulandite—stilbite—smectite, thom~onite-scolecite-smectite, heulandite-stllbite-smectite, laumontite—prehnite—chlorite—(pumpellyite), laumontite—chiorite, laumontite-chlorite, lauontite-prehnite-chlorite-(pumpellyite) , epidote—actinolite—chiorite. epidote—chlorite—(pumpellyite), epidote-actinolite-chlorite. epidote-chlorite-(pmpellyite), * i . --a? m-m -.- This facies facies succession is consistent with aa trend to This succession is consietent with tohigher highertemperature temperature burial mineral dcpth. asse!ublapb w.LLIi WLL I i li i I I L A eaaing b urid d cpth Eilner&l assen1bidgt 2) clear trend trend is the area area of of the village village 2) The The clear is disturbed disturbed by by aa recurrence recurrence in in the the Little Marais. South of Little Marais of of Little Marais. South of Little Marais the heulandite—stilbite—smectite zone, the upper of the heulandite-stilbite-smectlte zone, typical typical of of the upper parts parts of the occurs apparently sequence, sequence, occurs apparently stratigraphically stratigraphically below below flows flows of of the the laumontite—chiorite zone. zone. B1u.k tectonics can B l u ~ ktectoni~s can explain explain this t h i 3 rocurrence. rccurrence. laumontite-chlorite flows is Albitization of basaltic flows alteration feature. Albitization of the the basaltic isaamain main alteration feature,The The within the the stratigraphic stratigraphic position position within the albitization front is is dependent dependent on on the albitization front the uppermost uppermost part NSVG. Ca-rich Ca—rich plagioclase of KSVG, of the part of of the the sequence eequence is is not not JlPh 2rtpr hhiir-ial tops. w Qltcrcd, vc in th f£1o.r in the l o w topsi t h gr-apnr i ~ r i a l depth d e ~ t halbitization albitizatlon eltcrcdt even flows of In some becomes increasingly pervasive. pervasive. In some flows of the laumontite—chiorite laumontlte-chlorite becomes increasingly completealbitization albitization is is observed. and higher metamorphic facies complete metamorphic facies observed. Further, Further, and flow 18 is dependent onthe the permeability permeability of of the albitizattori front the the albitization front in in each each flow dependent on the flow tops bottomsofofstratigraphically stratigraphically lower flows rock-. the flow tops and and bottoms flows rock-,Whereas Whereas the almost complece compiete alteration, he Iiu.iJ.v U ~ ~ V C C ~ U W L ~ A ~ C L - I O I - S remain remain show alceraLlon, the show almost flow interiors interiors are only altered altered in in aa few, unaltered. unaltered. Massive ~bssiveflow are only few, mainly mainly thin thin the sequence, stratigraphically lowermost flows lowermost part part of of the sequence, i.e., i,eepin in flows in in the stratigraphically laumontite—chiorite up flows up to to flows displaying displaying metamorphic metamorphic grade grade from from lauuontite-chlorite facies. epidote—actinolite—chiorite epidote-actinolite-chlorite facies. Eluw ici.r c!aracterlzea D the zonation zonation cnaracteruea oirerent m3.neLdl addition to In addition to the ~y dirrerenc rnuvstti In assemblages, a compositional the new formed albite replacing a~senblages~ a compositional zonation of of the new formed albite replacing is Ca-rich plagioclase isobserved observed within withinthe the NSVG but also also within single single NSVG Ca—rich plagioclase clear flows. The albite displays a clear flows. The composition composition of of the the new new formed albite displays a metamorphic zonation. zonation. In In neral, generalpiti tcan can be safd t - h ~ t . in upper part metamorphic saii th,t in the upper part of albite shows the sequence sequence albite shows compositions compositlons far faraway away from that of of ideal ideal albite. from that albite. the sequence, i.e., in In lower parts parts of of the sequence, i,e., in flows with higher higher metamorphic metamorphic In lower between 95 95 and and 100 100 % mol Ab Ab approaching approaching facies, albitecomposition composition lies liesbetween fades, albite Z mci that of Composition that of ideal idealalbite. albite. Compositionof ofthe thenew new formed formadalbite albite also displays displays aa 78 �zonation Albite in in flow flow tops tops and and bottoms bottoms of of flows flows zonation within within the the flow flow itself. itself. Albite of cloaer to to stoichiometric stoichiometric composition composition of all all metamorphic metamorphic facies facies lies lies always always cloaer tnan tnan aJ.Dlte albite nInmore moreinner, Inner,i.ess Less intensively lnE@nSlVely alterea alcerea parts p a n s of he respeccive respecclve o the flow. f low. The The metamorphic metamorphic zonation zonation is is furthermore furthermore recognized recognized in in the the composition composition of mflc of the the new new formed formed phyllosilicate phyllosilicate*infilling infillingamygdules amygdulea and and replacing replacing mafic minerahi, minerals, the the stable stable isotopic Isotopic ratios ratios of of alteration alteration minerals, minerals, and and the the nomogentzation 199). flulo inclusions lncluslons (SCHMIDT, (SGHPIIDT, 1989). nomogenlzanon temperatures temperatures or rluia SCHMIDT, SCHMIDT,S.Th. S.Th. (1989) (1989) Alteration Alteration under under conditions conditions of of burial burial metamorphism metamorphiam in in the the North Jorth Shore Shore Volcanic Volcanic Group, Group, Minnesota Mlnnesota — Mineralogical Mineralo~ical and and geochemical in geochemicalzonation. zonation, Heidelberger Hsidelberger Geowissenschaftliche ~eowissen.schaftlicheAbhandlungen, ~bhandiun~en, In press press. - Q 00 ='7 SCH 1000 1000 m LM JC SR :000 3 0 0 m CD TlI 000 3000 Ill KR 4000 400 m 50uu 5000 m 6000 m FR a quadrangle LW 7000 7000 0 dU00 m Fig. Fig, 11Metamorphic Metamorphic zonation zonation within within the the North North Shore Shore Volcanic Volcanic Group. Group. Sampling Sampling positions the flowa flow8 are are indicated indicated in inthe the small small sketch sketch to tothe the positionswithin within the Thiç T h i s fiQure f i m r e is is based based on on 280 280 thin thin sections. sections. 25 258Debve—Scherrer Debve-Scherrer and and 40 40diffractogram diffractogramanalyses analyses and and microprobe microprobe analysis. analysis. The Theletters letters to tothe the left e.g., D: D: Duluth, Duluth, T:T: leftside side indicate indicate the the topographic topographic quddrangle, quadrangle, e.g., Tofte. Tofte. Exact Exact location locationof of flows flowsare aregiven givenininSCHMIDT SCHMIDT(1989). (1989). right.. right. 79 �- licationsofofIgneous IgneousRock Rock Geochemistry Geochemistry in in the thePenokean Penokean Orogen Orogen for Implications for Imp Metallogeny and Tectonic Tectonic Setting: Metallogeny and AA Synthesis of of Recent Recent Data Data Reston,VA, VA,22092 22092 and and P.K. P.K. Sims, Sims, Schulz,U.S. U.S. Geological GeologicalSurvey, Survey,Reston, K.J. Schulz, U.S. Geological U.S. Geological Survey, Survey,Denver, Denver,CO, CO, 80225 80225 Recentgeochemical geochemicalstudies studiesofof igneous igneousrocks rocksinin the the Early Recent Proterozoic Penokean orogenofof the the Lake Superior Penokean orogen Lake Superi or region provide provide important constraints on the tectonic tectonic evolution evolutionofofthe theorogen orogen and and help help important constraints on to establish establish aa basis basis for forpredictive predictivemetallogeny. metallogeny. The The epicratonic epicratonic Marquette which is isnorth zone in in Marquette Range RangeSupergroup, Supergroup, which northofofthe the Niagara Niagarafault fault zone upper Michigan,includes includesa abimodal bimodal tholeiltic basalt basalt and andlesser lesser rhyolite rhyolite upper Michigan, tholeiitic suitehaving having chemical chemical characteristics characteristics(major (majorand and trace traceelements elements volcanic suite including typical of within-plate, magma REEts) typical within-plate,rift-related rift-related magma types. types. The including REE's) compositional characteristics of the compositional characteristics the volcanic volcanic rocks rocks and and results from from recent studies of of the the sedimentary sedimentary rocks continental recent rocks support supportaarifted rifted continental margin history history for thethe Penokean margin forthe thenorthern northernportion portionof of Penokeanorogen. orogen. The major iron thethe Marquette Range major ironformations formationsofof Marquette RangeSupergroup Supergroup probably probably were were deposited duringthe theperiod periodofof rifting rifting before deposited during before actual actual crustal crustal separation, separation, although some iron formations formations also may havebeen beendeposited depositedduring duringlater later although some iron may have evolution of evolution of aa fore-deep fore-deep basin. basin. The Wisconsinmagmatic magmatic terranesoccur occursouth southofofthe theNiagara Niagarafault fault The Wisconsin terranes northern terrane, terrane,consists consists of zone. The northern terrane, the thePembine-Wausau Pembine-Wausau terrane, of zone. The widespread island-arc tholeiitic tholeiitic and sequences widespread island-arc andcaic-alkaline calc-alkaline sequences that thatrange range from to 1880 Maininage ageand andananareally areallymore morerestricted restricted calc-alkaline caic-alkaline from 1860 1860 to 1880 Ma suitethat thatformed formedbetween betweenabout about1835 1835and and1845 1845Ma. Ma. Ophiolitic ultramafic suite ultramafic and basaltic rocks, and basaltic rocks, which which include serpentinite, serpentinite,layered layered totomassive massive gabbro, are found found along along the Niagara fault gabbro, sheeted sheeteddikes, dikes, and andboninite, boninite, are the Niagara fault zone and show showthat that the the fault fault zone zone and zone marks marks the the suture suture between between the Superior Superior craton and terrane. Collision along craton and the thePembine-Wausau Pembine-Wausau terrane. along the the suture suture probably occurred period ofofsouthward southward subduction subduction at about about probably occurred following aa period 1860 Ma. Ma. A terrane, the Marshfield terrane, terrane,contains containsremnants remnants of of A southern southern terrane, the Marshfield mafic to felsic range mafic felsicvolcanic volcanicand andplutonic plutonicrocks rocksthat that rangefrom fromabout about1860 1860 to to 1890 1890 Ma Ma in inage ageand and an anArchean Archean gneiss gneissbasement. basement. This terrane This probably was thethe Pembine-Wausau was accreted accreted to tothe thesouthern southernmargin marginof of Pembine-Wausau following aa period terrane at at about about 1840 1840 Ma Ma following period of ofnorthward northward subduction. subduction. The Eau PI Pleine ei ne shear shear zone zone in in southern southern Marathon Marathon County, County, Wisconsin, Wi sconsi n, The Eau appears to to mark appears mark the suture suture zone zone between between the terranes. terranes. Base-metalmassive massivesulfide sulfide deposits deposits are present Base-metal present in inthe thePembinePembineWausau terraneand andappear appear restrictedtoto aa bimodal, bimodal, calc-alkaline caic-alkaline Wausau terrane to to bebe restricted volcanic suite that volcanic that isiscompositionafly compositional1y distinct distinctfrom from other other volcanic volcanic Thesecompositiona11y compositionallydistinctive distinctive highhighunits within within the the terrane. terrane. These Al20.sulfide-hosting A1 20 - and and light-REE-enriched, 1 ight-REE-enriched, massive massive su1 fide-hosting volcanic volcanic rocks rocks distinctivecomposition composition maytave fi'aveformed formed a within-arcrift. rift. Their distinctive may in in a within-arc enhances theuse useofof lithogeochemistry lithogeochemistry for for massive sulfide exploration enhances the massive sulfide within the within theWisconsin Wisconsin magmatic magmatic terranes. 80 �Late to (about1835 1835Ma) Ma)and andyounger youngeranorogenic anorogenic (1760 (1760 topostorogenic postorogenic(about granitic of rhyol rhyolite graniticintrusions intrusionsand and lesser lesseramounts amounts of i te Ma and 1470-1500 Ma and 1470-1500Ma) Ma) are locally orogen,particularly particularly in locallyabundant abundant within within the thePenokean Penokean orogen, in the the southern Pembine-Wausau terrane and southern portion portion ofofthe the Pembine-Wausau terrane and throughout the Marshfield terrane. rocksrange rangefrom from alkalic terrane. These These rocks ca1calc-alkaline c-a1ka1 i ne totoa1 ka1 ic in in character. mineralization is character. Minor molybdenum molybdenum mineralization isassociated associatedwith withsome some intrusions, have intrusions,and andother otherintrusions intrusions haveanomalous anomalous Sn, Sn,Ta, Ta,Nb, Nb,U, U, and and Th. Th. In particular, Maa1alkali-feldspar in particular,a arecently recentlydiscovered discovered 1733 1733 Ma ka1 i -feldspar granite in the northern thethe Southern Complex northern portion portionofof Southern Complexsouth southofofHumboldt, Humboldt, Michigan, is compositionally similar to rare-metal-rich Michigan, is compositional1y similar rare-metal-rich granites granites of of Nigeria and Sn-W potentialforfor and the the Arabian Arabian Shield Shield and and suggests suggests aa potential Sn-W(Ta-Nb) (Ta-Nb) mineralization mineralizationininupper upperMichigan. Michigan. 81 �THE THE MINERAL HINERAL LAKE LAKE PLUTON: PLUTON: TWO INTRUSIONS INTRUSIONS RATHER RATHER THAN THAN A LAYERED LAYERED COMPLEX? COMPLEX? KARL K A R L E. E. SEIFERT D e p a r t m e n t of o f Geological G e c ~ l c ~ g i c aand al n d Atmospheric A t m o s p h e r i c Sciences, Sciences, Department IA 50011 State t a t e University, U n i v e r s i t y , Ames, A m e s , IA 50011 IIowa owa S I NTRODUCT I ON INTRODUCTION Mellen, The T h e Mineral M i n e r a l Lake L a k e pluton p l u t o n is i s lc'cated l c ~ c a t e d nnear ear M e l l e n , Wisconsin, W i s c o n s i n v on #on the t h e Mellen ss':uuthern ~ : ~ u t h e r nmargin m a r g i n':tf o f Keweenawan kceweendwan eexpcts'.tres x p o s u r e s a s as p apart r t o foft hthe e Me1 l e n CComplex cmplex The (Aldrich, < A 1 d r i c h v 1929; 1 3 2 3 ; Leighton, L e i g h t o n , 1954). 13541. T h e Mineral M i n e r a l Lake L a k e and a n d smaller s m a l l e r Rearing Rearing Pond plutcin, n t r u s i v e ssheets h e e t s of o f aanorthuDsitic n ~ ~ r t h ~ z ~cs igabbrc' gtaib. b r o p l ~ . ~ t t : ~ np,plus l u s aadditi':nal d d i t i n n a l iintrusive Complex aand n d granite, g r a n i t e , form f o r m the t h e western w e s t e r n part p a r t of o f the t h e Mel M e l len len C o m p l e x and a n d are are sseparated e p a r a t e d from f r o m the t h e eastern e a s t e r n part p a r t cf ctf the t h e cu:mplex c~:~mplex bby y the t h e 1.0 1.0 - 11.2 . 2 Ga Ga The Mellen M e l l e n granite. granite. T h e Mineral M i n e r a l Lake L a k e pluton p l u t c ~ nhas h a s been b e e n described d e s c r i b e d as as aa ste9ply mafic s t e e p l y nnorthward ~ : ~ r t h w a r dddipping i p p i n g 44.5 . 5 kkm—thick m-thick m a f i c l1ayerd a y e r e d complex c ~ = ~ m p l intruded eixn t r u d e d as a s a 5ingle s i n g l e magma with w i t h an a n anorthositic a n o r t h o s i t i c gabbrci g a b b r o bbulk u l k composition cc~mpc~sition (Olmsted, From ( O l m s t e d , 1969). 19631. F r c ~ m the t h e base b a s e up u p the t h e plut'Dn p l u t o n cu:'nsists c c t n s i s t s oof f rroughly o u g h l y 1% 1% ultramafic u l t r a m a f i c rocks, r c ~ c k s , 10% 1 9 % anorthositic a n c ~ r t h c ~ s i c'livine t iocl i v i n e gabbrc;, g a b b r ~ l ,73% 73X gabbr':ic gabbrc~ic ancirthosite ferrt:idicsrite a n c t r t h c t s i t e and a n d ancirthosite, a n c ~ r t h c ~ s i tand ea,n d16% 16% f e r r o d i o r i t e (mcunzcqabbrc' < m c ~ n z ~ : ~ g a b bgrgrading cr ~ ading upward quart: mon:odiorite) 1369:). The The o n z o d i c t r i t e l and a n d granite g r a n i t e (Olmsted, ( O l m s t e d , 1969). u p w a r d to to q uartz m pluton also been p l u t o n has has a l s t ~b e e n interpreted i n t e r p r e t e d as a s forming f o r m i n g from f r o m several s e v e r a l magmas magmas (Ktmatar, 11972) 3 7 2 1 bbased a s e d oon n the t h e occasional C I C c a s i c i n a l occurrence CIC c u r r e n c e of n f poorly pcmr l y developed developed (Komatar, thin t h i n rhythmic r h y t h m i c layering l a y e r i n g in i n the t h e anorthcsitic a n o r t h c ~ ~ i gabbrci t igca b b r o intrusion. intrusion. IItt is is h e r e interpreted i n t e r p r e t e d to t o consist c c ~ n s i s of t13f two t w o separate s e p a r a t e intrusions; i n t r u s i o n s ; aa lc'wer lower here aanc'rthc'sitic n c ~ r t h c ~ s i t igcagabbrci b b r a i n tintrusion r u s i ~ z t na nand d a nanu upper p p e r ggranitic r a n i t i c iintrusion. ntrusion. Major d e t e r m i n e d on o n samples s a m p l e s collected collected M a j o r and a n d trace t r a c e elements e l e m e n t s were determined ffrom r m bctth n t r u s i c ~ n sin i n the t h e Mineral M i n e r a l Lake L a k e pluton. pl uton. B a s a l inclusions i n c 1 u s i o n s and and both iintrusions Basal adjacent a l s u sampled s a m p l e d to t o determine d e t e r m i n e their t h e i r compositions cc~mpc~sitic~ns a d . j a c e n t oolder l d e r rrocks a c k s were also a s sciurces s c ~ u r c e socf f ppossible ~ ~ s s i b lcontamination. c eo n t a m i n a t i c ~ n . Three T h r e e plagiciclase p l a g i c ~ c l a s esseparates e p a r a t e s and and as one orthopyro"ene one o r t h c ~ p y r o x e n esseparate e p a r a t e were analyzed a n a l y z e d from f r ~ mthe t h e coarsely c o a r s e l y crystalline crystalline anorthc'sitic Major oxides a b b r c ~intrusion. intrusion. Ma.jor o x i d e s were determined d e t e r m i n e d largely largely a n o r t h o s i t i c ggabbro by X X-ray by - r a y ffluorescence l u o r e s c e n c e (XRF) (XRF1 and a n d trace t r a c e elements e l e m e n t s were were determined d e t e r m i n e d by by instrumental Some trace trace i n s t r u m e n t a l nneutron e u t r o n activation a c t i v a t i o n analysis a n a l y s i s (INAA) CINAAI and a n d XRF. XRF. Some element e l e m e n t and a n d isotope i s c ~ t o p edata d a t a have h a v e been b e e n reported r e p o r t e d previously p r e v i o u s l y (Seifert ( S e i f e r t et et al., a l . , l1985). ?85>. The Anorthositic Gabbro Intrusion Intrusion The T h e anorthc'sitic a n o r t h c ~ s i t i c ggabbrc' a b b r o i nintrusion t r u s i o n cconsists o n s i s t s oof f ttwo w o zones z o n e s with with a a The thin margin t h i n basal b a s a l chilled chilled m a r g i n adjacent a d j a c e n t to t o older o l d e r underlying u n d e r l y i n g country c o u n t r y rocks. rocks. The T h e basal b a s a l chill c h i l l zzone o n e ggrades r a d e s upward u p w a r d into i n t o the t h e aanorthositic n o r t h o s i t i c olivine nlivine g a b b r o zone z o n e which w h i c h in i n turn t u r n grades g r a d e s upward u p w a r d into i n t o the t h e gabbroic g a b b r o i c ancirthosite anorthosite gabbro zone. zc~ne. T he g a b b r o i c aanorthosite n o r t h o s i t e zone z o n e volumetically v ~ ~ l w n e t i cl ayl dominates d o m i n a t e s the the The gabbroic intrusion Lake pluton. p l u t o n . The T h e thin t h i n chill c h i l l zone z o n e and and i n t r u s i o n and a n d the t h e entire e n t i r e Mineral M i n e r a l Lake the t h e upper u p p e r part p a r t oof f the t h e thick t h i c k gabbroic g a b b r o i c anorthosite a n o r t h o s i t e zone z o n e contain c o n t a i n basalt basalt inclusions. Three inclusions. T h r e e plagioclase p l a g i o c l a s e separates s e p a r a t e s and a n d one o n e orthopyroxene orthopyroxene sseparate e p a r a t e were aanalyzed n a l y z e d from f r o m this t h i s coarsely c o a r s e l y crystalline c r y s t a l l i n e intrusion. intrusion. 82 �The Granitic Intrusion Intrusion The qranitic T he g r a n i t i c intrusion i n t r u s i o n consists c o n s i s t s cf o f a llower o w e r rnc'nzodic'rite m o n z o d i o r i t e zzone o n e aand nd The upper with a gradati':na1 g r a d a t i o n a l contact. contact. T h e lower lower zone, z o n e , iin n aann u p p e r ggranite r a n i t e zone zone w ith a ccintact the uunderlying c o n t a c t wwith i t h the n d e r l y i n g aanc'rthcsitic n o r t h o s i t i c gabbri:i g a b b r o i nintrusion, t r u s i o n , is is best best described as a a mon:oqabbr':' m o n z o g a b b r o ggrading r a d i n g uupward p w a r d i into n t o quartz q u a r t z mc'nzodicrite. monzodiorite. d e s c r i b e d as The s t h the e o voverall e r a l l c characteristics h a r a c t e r i s t i c s oof f granite, g r a n i t e , although althctuqh T h e uupper p p e r z zone o n e h ahas This probably tthe h e texture t e x t u r e bbecomes e c o m e s ggranciphyric r a n o p h y r i c l locally. ocally. T h i s intrusion i n t r u s i o n is probably llater a t e r than t h a n the t h e anorthositic a n o r t h o s i t i c gabbr':' g a b b r o intrusion i n t r u s i o nand a n d isi snearly n e a r l cc'nformable y conformable The with margin w i t h the t h e upper upper m a r g i n o fcf t that h a t iintrusion. ntrusion. T h e uupper p p e r ggranite r a n i t e zone zone varies v a r i e s from f r o m ccarse c o a r s e ggrained r a i n e d ggranular r a n u l a r tto o granophyric g r a n o p h y r i c iin n texture t e x t u r e and a n d is is ccharacterized h a r a c t e r i z e d by by the t h e dominance d o m i n a n c e of o f K—spar K - s p a r aand n d qquart: u a r t z cuver o v e r pplagioclase. laqioclase. mc'nzc'diorite The T h e granite g r a n i t e and a n d the t h e K-spar-rich K - s p a r - r i c h upper u p p e r part p a r t of o f the the quartz quartz m onzodiorite "red layer are r e both b o t h red r e d and a n d together t o g e t h e r they t h e y constitute c o n s t i t u t e the t h e " r e d rock" r o c k " portion portion layer a cf t h e Mineral M i n e r a l Lake L a k e pluton. pinton. o f the t h e granitic g r a n i t i c intrusion i n t r u s i o n and the SUMMARY The T h e ggranitic r a n i t i c iintrusion n t r u s i o n is probably p r o b a b l y later l a t e r than t h a n the t h e n':rthcsitic anorthositic gabbrc q a b b r o iintrusion n t r u s i o n and a n d was emplaced e m p l a c e d between b e t w e e nthe t h anorth':'sitic e a n o r t h o s i t i cgabbr':u q a b b r o and and overlying The w o iintrusions ntrusions o v e r l y i n g rocks. rocks. T h e genetic g e n e t i c relationship r e l a t i o n s h i p between b e t w e e n the t h e ttwi:' Whereas was iiss not n o tknown. known. W h e r e a s t hthe e a ancirthcisitic n o r t h o s i t i c gabbri: gabbro w a s iintruded n t r u d e d as as a a crystal c r y s t a l mush aand n d shows s h o w s little l i t t l e eevidence v i d e n c e for f o r differentiation, d i f f e r e n t i a t i o n , the the magma eexhibits ggranitic r a n i t i c magma x h i b i t s the t h e chemical c h e m i c a l and a n d mineralogical m i n e r a l o g i c a l trends t r e n d s expected expected of of d i f f e r e n t i a t i o n . The w o iintrusions n t r u s i o n s ooff aan':rthositic n o r t h o s i t i cgabbro g a b b r ~and la n d T h e ppresence r e s e n c e of ttwo g r a n i t i c ccompositions o m p o s i t i o n s in i n the t h e Mineral M i n e r a lLake L a k plutcin e p l u t o nalsu:' a l s o eexplains x p l a i n s the the granitic gabbrci aadditional d d i t i o n a l sheets s h e e t s oof f anorthositic anorthositic g a b b r o a and n d ggranite r a n i t e tto o tthe h e nnorthwest orthwest cf o f the t h e pluton. pluton. differentiation. REFE RENCES REFERENCES Aldrich, Aldrich, H. H. R. R . ,, 1929, 1 9 2 9 , The T h e geology g e o l o g y of o f the t h e Gogebic G o g e b i c iiron r o n range r a n g e of of Wisconsin: Wisconsin Natural Wisconsin: W i s c o n s i n GGeological eological N a t u r a l History H i s t o r y Survey Survey v. 71, v. 71, 2 7 9 pp. 279 pp. Bulletin, B ulletin, Komatar, F. D., 1972, Komatar, F. D., 1372, Geology G e o l o g y of o f the t h eAnimikian A n i m i k i a nmetasedimentary m e t a s e d i m e n t a r y rocks, rocks, Mellen L a k e gabbro g a b b r o west w e s t of o f Mellen, M e l l e n , Wisconsin Wisconsin M e l l e n granite, g r a n i t e , and a n d Mineral M i n e r a l Lake (M.S. (M.S. tthesis): h e s i s ) : University U n i v e r s i t y ofo fWisconsin, W i s c o n s i n , 75pp. 75pp. Leighton, Leighton, gabbrcu-granophyre W., 194, M. W M. ., 1 9 5 4 , Petrogenesis P e t r o g e n e s i s of of a g a b b r o - g r a n o p h y r e ccomplex o m p l e x in in northern America Bulletin, v. n o r t h e r n Wisconsin: W i s c o n s i n : Geological G e o l o g i c a l Society S o c i e t y of of A merica B u l l e t i n , v. 65, p. 01-442. 6, p. 4401-442. Olmsted, F., O l m s t e d , J. F . , 1969, 1969, Petrology P e t r o l o g y of o f the t h e Mineral M i n e r a l Lake L a k e intrusion, intrusion, 3. northwestern n o r t h w e s t e r n Wisconsin: W i s c o n s i n : in i n Y. Y . W. W. IIsachsen s a c h s e n (editor), ( e d i t o r ) , Origin O r i g i n of of Anorthosite A n o r t h o s i t e aand n d Related R e l a t e d Rocks, R o c k s , New York Y o r k State S t a t e Museum Museum and a n d Science Science Service Memoir 18, 1 8 , p. p. 1149-161. 49-161. S e r v i c e Memoir Seifert, E . , Peterman, P e t e r m a n , Z. n d Windcum, Windom, K. K. E., E . , 198, 1 9 8 5 , Mineral M i n e r a l Lake Lake S e i f e r t , K. K. E., Z. E. E. a and layered NW W Wisconsin: i s c o n s i n : Geological G e o l o g i c a l Society S o c i e t y of o f America America l a y e r e d intrusion, i n t r u s i o n , NW Abstracts v. 17, 17, p. 712" A b s t r a c t s with w i t h Programs, P r o g r a m s , v. p. 712. 83 �MANGANESE POTENTIAL P O T E N T I A L OF O F THE THE CRETACEOUS CRETACEOUS ROCKS ROCKS FLANKING F L A N K I N G THE THE MANGANESE S I O U X RIDGE, R I D G E , MINNESOTA MINNESOTA AND SOUTH DAKOTA DAKOTA SIOUX Dale R. R . Setterholm, Setterholm, Minnesota Minnesota Geological Geological Survey,2642 Survey,2642 Dale S t . Paul, MN 55114, and Richard H. U n i v e r s i t y Avenue, University Avenue, St. Paul, MN 55114, and Richard H. Hamrnond, South Dakota Geological Survey, Science Center, Hammond, South Dakota Geological Survey, Science Center, S D 57069 57069 U n i v e r s i t y of of South South Dakota, Dakota, Vermillion, Vermillion, SD University Cretaceous strata s t r a t a in i n southwestern southwestern Minnesota Minnesota and and eastern eastern Cretaceous South Dakota Dakota have have lithologic, l i t h o l o g i c , geochemical, geochemical, and and depositional depositional South a t t r i b u t e s similar s i m i l a r to t o those t h o s e that t h a t host h o s t economic economic deposits d e p o s i t s of of attributes manganese at a t several s e v e r a l localities l o c a l i t i e s around a r o u n d the t h e world. world. manganese I n v e s t i g a t i o n s are a r e under under way way to t o determine determine if i f the t h e conditions conditions Investigations d e s c r i b e d in i n several s e v e r a l depositional d e p o s i t i o n a l models models (Cannon (Cannon and and Force, Force, described 1 9 8 3 ; Frakes F r a k e s and and Bolton, Bolton, 1984; 1 9 8 4 ; Force Force and and Cannon, Cannon, 1988 1 9 8 8 ), ), 1983; which have have been been proposed proposed to t o explain e x p l a i n these t h e s e ores, o r e s , existed e x i s t e d in in which Minnesota and and South South Dakota, Dakota, and and if i f so, so, whether whether any any anomalous anomalous Minnesota manganese concentrations c o n c e n t r a t i o n s are a r e present. present. manganese The models models propose propose that t h a t aa dilute d i l u t e ore-forming ore-forming solution solution The i n anoxic p o r t i o n s of s t r a t i f i e d s e a s where iron can develop can develop in anoxic portions of stratified seas where iron i s removed a s p y r i t e , and where manganese c o n c e n t r a t e s to is removed as pyrite, and where manganese concentrates to i n normal s e a w a t e r . When v a l u e s up t o 500 times t h o s e common values up to 500 times those common in normal seawater. When i s transported t r a n s p o r t e d to t o an an oxygenated oxygenated t h i s manganese-rich manganese-rich solution s o l u t i o n is this environment, such a s a l o n g t h e margins of a d e positional environment, such as along the margins of a depositional b a s i n , t h e d i s s o l v e d manganese p r e c i p i t a t e s e i t h e r as a s an an basin, the dissolved manganese precipitates either oxide o r carbonate mineral s p e c i e s . P h y s i c a l p r o c e s s e s near oxide or carbonate mineral species. Physical processes near s h o r e may may concentrate c o n c e n t r a t e the t h e manganese-rich manganese-rich material m a t e r i a l to t o yet yet shore h i g h e r g r a d e s . higher grades. In southwestern southwestern Minnesota and in i n adjoining a d j o i n i n g parts p a r t s of of In Minnesota and South Dakota, Upper Cretaceous s t r a t a were d e p o s i t e d a l o n South Dakota, Upper Cretaceous strata were deposited alongg t h e eastern e a s t e r n edge edge of of the t h e Western Western Interior I n t e r i o r Seaway Seaway on on aa gently gently the s l o p i n g s u r f a c e f l a n k e d by t h e Sioux Ridge, a q u a rtzite sloping surface flanked by the Sioux Ridge, a quartzite highland which a t times formed e i t h e r a peninsula o r a group highland which at times formed either a peninsula or a group of i s l a n d s . Rocks of t h e Dakota Formation, Graneros S hale, of islands. Rocks of the Dakota Formation, Graneros Shale, C a r l i l e S h a l e , Niobrara Formation, and Greenhorn Limestone, Greenhorn Limestone, Carlile Shale, Niobrara Formation, and P i e r r e Shale d e f i n e a s h e l f f a c i e s t h a t p a s s e s i n t o nearshore Pierre Shale define a shelf fades that passes into nearshore f a c i e s , such such as a s the t h e Split S p l i t Rock Rock Creek Creek Formation Formation along a l o n g the the facies, S i o u x Ridge p a l e o c o a s t , a n d a r e g i o n a l l y c o n s i s t e nt Sioux Ridge paleocoast, and a regionally consistent llithostratigraphic i t h o s t r a t i g r a p h i c succession s u c c e s s i o n of shallow marine and c o a s t al of shallow marine and coastal c l a s t i c , t h sediments i n Minnesota. Although d e c i d e d l y more sediments in Minnesota. Although decidedly more clastic, thee Minnesota rocks rocks correlate c o r r e l a t e well w e l l with with parts p a r t s of of the t h e established established Minnesota Upper Cretaceous s h e l f sequence i n South Dakota. Upper Cretaceous shelf sequence in South Dakota. Two key key components components of of the t h e manganese manganese depositional d e p o s i t i o n a l models models Two i n t h e s t u d y a r e a . High-manganese/low-iron have been observed have been observed in the study area. High-manganese/low—iron a n o m a l i e s , although a l t h o u g h subeconomic, subeconomic, have have been been observed o b s e r v e d at at anomalies, s e v e r a l places p l a c e s in i n rocks r o c k s deposited d e p o s i t e d on on an an open open shelf shelf several envoronment. These These anomalies anomalies demonstrate demonstrate that t h a t ore—producing ore-producing envoronment. i n t h e seaway, seaway, s o l u t i o n s may have been p e r i o d i c a l l y p r e s e n t solutions may have been periodically present in the and t h a t a t t i m e s , t h e y flowed o n t o t h e e a s t e r n shelf. and that at times, they flowed onto the eastern shelf. Secondly, s t r a t a r e f l e c t i n g c y c l i c o x i c a n o x i c c o n d itions Secondly, strata reflecting cyclic oxic-anoxic conditions have been observed i n both t h e n e a r s h o r e f a c i e s and t h e shelf have been observed in both the nearshore facies and the shelf f a c i e s . This T h i s implies i m p l i e s that t h a t anoxic a n o x i c flowpaths flowpaths existed e x i s t e d between between fades. anoxic parts p a r t s of of the t h e basin, b a s i n , where where manganese—rich manganese-rich solutions s o l u t i o n s had had anoxic 84 �formed, and a n d nearshore n e a r s h o r e sites s i t e s where where oxic o x i c conditions c o n d i t i o n s favorable favorable formed, f o r ore o r e formation f o r m a t i o n existed. existed. for T h i s work work was was cofunded c o f u n d e d by b y the t h e Minnesota M i n n e s o t a Geological G e o l o g i c a l Survey, Survey, This tthe h e South S o u t h Dakota D a k o t a Geological G e o l o g i c a l Survey, S u r v e y , and a n d the t h e Midcontinent Midcontinent U.S. S t r a t e g i c and a n d Critical C r i t i c a l Minerals M i n e r a l s Program Program of o f the t h e U.S. Strategic G e o l o g i c a l Survey. Survey. Geological References: References: E . R . , 1983, 1983, Potential P o t e n t i a l for f o r high-grade high-grade Cannon, W.F., W.F., and a n d Force, F o r c e , E.R., Cannon, s h a l l o w - m a r i n e manganese manganese deposits d e p o s i t s in i n North N o r t h America, America, in in shallow—marine Shanks, W.C., W . C . , ed: e d : Cameron Cameron volume volume on on unconventional u n c o n v e n t i o n a l mineral mineral Shanks, d e p o s i t s : American American Institute I n s t i t u t e of o f Mining, Mining, Metallurgical, M e t a l l u r g i c a l , and and deposits: P e t r o l e u m Engineers, E n g i n e e r s , New New York, York, p. p . 175-189. 175-189. Petroleum F r a k e s , L.A., L . A . , and a n d Bolton, B o l t o n , B.R., B . R . , 1984, 1984, Origin O r i g i n of o f manganese manganese Frakes, g i a n t s : sea s e a level l e v e l change change and a n d anoxic—oxic a n o x i c - o x i c history: h i s t o r y : Geology, Geology, giants: v . 1 2 , p. p . 83—86. 83-86. v.12, E . R . , and a n d Cannon, Cannon, W.F., W.F., 1988, 1988, Depositional D e p o s i t i o n a l model model for for F o r c e , E.R., Force, s h a l l o w m a r i n e manganese d e p o s i t s a r o u n d b l a c k s h a l e b a s ins: shallow-marine manganese deposits around black shale basins: Economic Geology, v . 83, p . 93-117. Economic Geology, v.83, p. 93—117. 85 �t'STRATIGRAPHY" AND OF AA PORTION STRATIGRAPHY" AND GENERAL GENERAL GEOLOGY GEOLOGY OF PORTION OF OF THE THE PARTRIDGE RIVER RIVER INTRUSION, PARTRIDGE INTRUSION,DULUTH DULUTH COMPLEX, COMPLEX, MINNESOTA. MINNESOTA. MARK SEVERSON MARK JJ.. SEVERSON ResearchInstitute, Institute, Natural Resources Resources Research 3151 Miller Miller Trunk 3151 TrunkHwy., Hwy., Duluth, Duluth,MN MN 55811 55811 Reloggingofofover over75 75drill drill holes holes (—90,000 ft.) located Relogging (-90,000 ft.) along the the located along northern (footwall) (footwall) contact northern contact of of the thePartridge Partridge River River Intrusion Intrusion(T.58-59N., (T.58-59N., R.13-14W.) feet Series R.13-14W.)has hasindicated indicatedthat thatthe thebasal basal3000 3000 feetofofthe theTroctolitic Troctolitic Series Rockscan canbebesubdivided subdividedinto into at at least least seven major igneous units on Rocks seven major igneous units on the the basis basis of Most of of the units of rock rock type. type. Most unitsare arecontinuous continuous over over an an indicated indicatedeleven eleven mile strike-length extending (NE SW) strike-length extending (NEto to SW)from fromthe theDunka DunkaRoad Road Cu-Ni Cu-Ni deposit deposit Creek Cu-Ni Cu-Ni deposit. deposit. Some to the theWyman Wyman Creek appear to to Someofofthese these igneous igneous units units appear represent single single cool cooling units in ultrarepresent ing units in that thatthey theyare are floored flooredby byaabedded bedded ultramafic whereas, other contain abundant internal members mafic member; member; whereas, other units units contain abundant internal members reflecting reflectingcontinuous continuousmagma magma replenishment. replenishment. Contacts between between each the each of of the units from sharp units range range from sharp to gradational, gradational, and and pinch-and-swell pinch-and-swell thickness thickness variations all1 seven units. The There1 relative variationsare arecommon common toto a1 seven units. ative spatial regularity regularity of that the of these these units units suggest suggest that the Partridge Partridge River River Intrusion Intrusion(PRI) (PRI)was was intruded intruded as several exhibit dips as several subhorizontal subhorizontal sheets sheets that now now exhibit dipsofofapproximately approximately20 20 degrees Lake Superior Superior (SE). However,some some theunits unitsa1 also exhibit degrees towards Lake (SE). However, ofofthe so exhibit downcutting re1 ationships and and 1lateral ateral"facies" "facies" changesindicating indicatinga acomplex complex downcutting relationships changes intrusive history. history. From thebase baseup, up,these theseunits unitsare arecharacterized characterizedbyby(Figure (Figure I): 1): Unit II From the sulfide-bearing augitetroctolite troctolite with minor minorpicrite picrite to peridotite sulfide-bearing augite peridotite layers; layers; troctolite and augite augite troctol troctolite abundantpicrite picrite to Unit I1 II -- troctolite Unit ite with with abundant to peridotite layers sulfide-bearing zones; zones;Unit Unit I11 III - mottled mottled layers and/or and/or minor minor sulfide-bearing textured anorthositic troctolite textured anorthosi tic troctol i te exhibiting exhibiting aa highly highly irregular olivine 01 ivine distribution; Unit with base and IV - -augite augitetroctolite troctolite witha apicritic picritic base andgrading grading distribution; Unit IV upwardsinto; into; Unit VV - coarse-grained anorthositictroctolite; troctolite; Unit upwards coarse-grained anorthositic Unit VI VI -augite troctolite troctolite to base; augite to anorthositic anorthositic troctolite troctolitewith withaapicritic picritic base;and and Unit Unit peridotite/picrite base. VII Field VII - augite augite troctolite troctol itewith witha awell-bedded well -bedded peridotite/picrite base. Field mapping suggests thatanan eighthunit unit(VIII) (VIII) and possibly additional units mapping suggests that eighth and possibly units are above Unit Unit consists of of troctolite to are present present above Unit VII. Unit VIII VIII consists troctolite to anorthositic witha awell-bedded we1 1 -bedded peridotite peridoti tebase. base. Anorthositic Anorthosi tic anorthositic troctolite troctol i tewith Series rocks are are present SEportion portion of the Series rocks present in the the extreme extreme SE the study study area. area. Intrusive into pegrnatitic Intrusive intoUnits UnitsI Ithrough throughVII VIIare arelate-stage late-stage pegmatiticoxide-bearing oxide-bearing ultramafic samplesfor for whole ul tramafic bodies. bodies. Geochemical Geochemical samples whole rock, rock, trace trace element, element, base metals, analyses have precious and base metals, and rare earth earth element element analyses have been been precious and eachof of these these units units to: 1.) determine collected from from each determinebackground background elemental elemental values for for each 2.) determine if any determine if any values each of the the major major units unitsand and their theirmembers; members; 2.) vertical and variation isispresent vertical and lateral lateralgeochemical geochemical variation present and and to towhat what extent; extent; and 3.) determine and 3.) determine ififany anylithogeochemical lithogeochemical signature signatureassociated associated with witheach each of the the major major units is ispresent. present. Establishment internal"stratigraphy" "stratigraphy"(within (withinaasea seaofoftroctol troctolitic Establ ishment ofofananinternal itic rocks) of an excellent excellent opportunity to of the thePR! PRI has has provided provided an to study study the thenature nature present both thethe basement of any any structural structuraldiscontinuities discontinuities presentwithin within both basement and and the the rocks. Cross-sections illustrating illustrating the internal overlying intrusive rocks. Cross-sections the internal overlying intrusive "stratigraphy" ininseveral areas that in both thethe Dunka "stratigraphy" severaldrilled drilled areasindicate indicate that in both DunkaRoad Road numerous NE-trending NE-trending normal and Wet1 egs areas, areas, numerous normal faults parallel para1 lel to the the and Wetlegs This supports Midcontinent Rift Rift are ha1 f-grabenmodel model of of Midcontinent are present. present. This supports the haif-graben Weiblen and andMorey Morey(1980) (1980)which whichenvisions envisionsaastep-and-riser step-and-riser geometry Weiblen geometry at the the 86 �Also within the the base of the dueto to extensional extensional tectonics. base of the Duluth Duluth Complex Complex due tectonics. Also faulthas hasbeen beenidentified identified Wetlegs area, a NE-trending NE-trending pre-Keweenawan(?) pre-Keweenawan(?) fault Wetlegs area, is in direct along which which an an inferred window window of Biwabik Biwabik Iron-formation Iron-formation is direct along Three oxide-bearing oxide-bearinglate-stage late-stage ultramafic ultramafic bodies contact with with the thePRI. PRI. Three bodies are are genetically along this thiszone zonewhich which suggests suggests that they they may may be be genetically also located located along related re1 ated to toareas areaswhere where massive massive iiron-formation ron-formation assimilation assimi 1 ation has has occurred. occurred. discontinuities were theWyman Wyman Creek Creek area, area, no no major major structural structural discontinuities were Within the located in either or Troctolitic Troctolitic Series located eitherthe thebasement basement or Series rocks. rocks. However, However, aa downcutting relationship of of Unit VV into into Units III1and is indicated Wyman and II is indicatedatat Wyman downcutting relationship Creek. Creek. During the course courseof of collecting collecting field geochemical During field geochemicalsamples, samples, aa mile mile long 1 ong zone of of modally laminated oxide-bearing gabbro was was located located zone laminated and and cross-bedded oxide-bearing in previously been beencalled called the the Colvin Colvin Creek CreekHornfels. Hornfels. Mineralogical in what what has has previously Mineralogical and field field relations actually be and relationssuggest suggestthat thatthe theColvin ColvinCreek Creekbody body may may actually be an an intrusive unit magmatic unitthat thatexhibits exhibits magmatic density density current current features. features. Field that the the Colvin Creekbody bodyisissimilar similar to the relationships also suggest suggest that Colvin Creek the Powerline Gabbro Gabbrowhich whichisisexposed exposedwithin withinabout aboutone onemile mileto to the the northeast. northeast. Powerline REFERENCES REFERENCES Weiblen, P.W., Morey, G.B., G.B., 1980, the stratigraphy, stratigraphy, P.W., and and Morey, 1980, A A summary summary ofofthe Weiblen, petrology and AmericanJournal Journal of of and structure structureofofthe theDuluth DuluthComplex: Complex: American Science, v. 280, p. 88-133. Science, 280, p. 88-133. Funding: Minerals Funding: Minerals Coordinating CoordinatingCommittee Committee Minerals Diversification Plan Mineral s Diversification Pl an 87 �________________________ P A R T R I D G E RRIVER I V E R IINTRLJIN NTRUSION PARIRIDEE U 11 PIIL(S MILES \'YMN W Y M A N CREEK CREEK I WETLEG WETLEGS DUNKA RUAD ROAD DUNKA VII VII VII Peridotit V /or Vi VI —2 Iv V V Iv IV ,,Iv \ / ii —/ it / — - —— I FOOT\..'ALL FODTWALL FIGURE FIGURE 111 FOOT VALL FODTW ALL III II? -7-I - 7 —7—7—2—?— ?- I FOOTVALL Strike-length correlation n a j o r igneous igneous units within the the Strke-I.eng-th corr'e1aton oof'f major units wthn basal 33000 0 0 0 f Ft. t . oof' f tthe h e Partridge P a r t r i d g e River R i v e r Intrusion, Intrusion, k,osat UNtTi UNITS1 II = = utfIde—beoring Sulflde-bearlng aougte u ~ i t ekroctolite, t r o c t o l i t e , III1 == tr'octo(t2 t r o c t o l l t e w'th wlth picrite picriteLayers l a y e r s etc.. etc., III I11 == 'Mottied 'Mottled' onor-thasitic anorthositic troctollte. I VIV = =a auite u ~ i t etroctolite, anorthositic -tr-octoti-te. troctotrte. VV == anorthositic troctoijte troctolite, VI VI = = northost-ttc anorthositic ttroct. r o c t , to t o augIt augltetrocioti-te t r o c t o k t e , VII V I I == augite auglte iroctoilte, troctollte, sharp sharp con-tc-t contact -— - —gracla-tionat -gradational con-tact contact — 88 No scoe scaleimplied. Inplled. No �PRECAMBRIAN ROCKS, NEW BEDROCK BEDROCK GEOLOGIC GEOLOGIC MAP MAP OF PRECAMBRIAN ROCKS, REGION, WISCONSIN AND NORTHERN SUPERIOR REGION, EASTERN LAKE LAKE SUPERIOR NORTHERN MICHIGAN P. K. Sims, Sims, U.S. U.S. Geological Geological Survey, Survey, Denver, Denver, CO CO 80225 80225 A new new geologic geologic map map of of Precambrian Precambrian rocks rocks in in Wisconsin Wisconsin and and northern northern Michigan (scale (scale 1:500,000) 1:500,000) has has been been compiled compiled in in cooperation cooperation with with the the Wisconsin Wisconsin Geological and Natural History Geological History Survey Survey from from published published maps maps and and available available unpublished data. unpublished data. The map has has 108 108 lithologic lithologic units. units. eastern Lake Superior The eastern Superior region region consists consists of of 66 major major Precambrian Precambrian domains that record lithotectonic domains record about 2,500 2,500 m.y. of of geologic geologic time. time. From From oldest to youngest, youngest, these these are are (1) (1) Archean Archean gneiss gneiss terrane terrane of of northern northern Michigan Michigan Archean greenstone-granite Wisconsin (2500-3650 and adjacent Wisconsin (2500-3650Ma), Ma), (2) Archean greenstone-graniteterrane terrane Michigan and adjacent Wisconsin (2700-2600 of northern Michigan adjacent Wisconsin (2700-2600 Ma), Ma), (3) a paired margin assemblage assemblage (Marquette continental margin (Marquette Range Supergroup) Supergroup) and and island-arc island-arc complexes (Wisconsin complexes (Wisconsin magmatic terranes), terranes), separated separated by the the Niagara Niagara fault fault zone, zone, of the early Proterozoic Penokean Penokean orogen, orogen, (4) (4) central central Wisconsin Wisconsin anorogenic anorogenic granite-rhyolite (ca. granite-rhyolite (ca. 1760 1760 Ma) terrane, terrane, (5) (5) 1.47 1.47 Ga Ga Wolf Wolf River River rapakivi rapakivi granite-anorthosite batholith, and granite-anorthosite batholith, and (6) (6) igneous igneous and and sedimentary sedimentary rocks rocks of of the the Ca. 1100 ca. 1100 Ma (Keweenawan) (Keweenawan) Midcontinent Midcontinent rift rift system. system. The Archean gneiss The Archean gneiss and and greenstone-granite greenstone-graniteterranes terranes compose compose the the basement basement of Proterozoic passive the boundary boundary of the Early Proterozoic passive continental continental margin margin assemblage; assemblage; the between the two between two basement basement terranes terranes is is the the Great Great Lakes Lakes tectonic tectoniczone, zone,aapresunied presumed paleosuture. paleosuture. magmatic terranes The Wisconsin magmatic terranes consist consist of of at at least least two two island-arc island-arc northern (Pembine-Wausau) The northern (Pembine-Wausau)terrane terrane is is dominantly dominantly composed composed of of calc-alkaline volcanic rocks deposited deposited in tholeiitic and calc-alkaline in the the interval interval 18601860but contains contains a more restricted 1880 Ma, but restricted succession succession of of calc-alkaline calc-alkalinevolcanic volcanic deposited about rocks deposited about 1835-1845 1835-1845 Ma. Ma. Granitoid Granitoid rocks rocks ranging ranging in in age age from from about about 1870 Ma to 1760 1760 Ma intrude intrude the the volcanic volcanic rocks. rocks. This This terrane terrane was was accreted accreted to to the continental continental margin margin about about 1860 1860 Ma. Ma. The southern southern (Marshfield) (Marshfield) terrane terrane contains remnants of mafic to to felsic felsic volcanic rocks rocks about about 1860 1860 Ma Ma that that were were Archean gneissic gneissic basement, deposited on Archean basement, foliated foliated tonalite tonalite to to granite granite bodies bodies about 1890 Ma, and younger ranging in age from about 1890 Ma to to 1870 1870 Ma, younger undated undated granite granite plutons. plutons. Following Following amalgamation amalgamation of of the the two two arc arc terranes terranes at at about about 1840 1840 Ma, Ma, intraplate magmatism magmatism (1835 alkali(1835 Ma) produced anorogenic anorogenic and and rhyolite rhyolite alkalifeldspar granite that feldspar that straddled straddled the the internal internal suture. suture. complexes. complexes. The 1760-Ma-anorogenic 1760-Ma-anorogenicsilicic-alkalic silicic-alkalic rocks rocks of of central central Wisconsin Wisconsin were were emplaced about 100 culmination of of the the Penokean Penokean orogeny. orogeny. Deep Deep 100 m.y. after culmination seated granitoid rocks intruded within the Pembine-Wausau Pembine-Wausauarc arc terrane terrane rocks were intruded within the approximately contemporaneously contemporaneously with the anorogenic magmatism to the the anorogenic magmatism to the south. south. 89 �The Wolf Wolf River River batholith batholith (1470 (1470 Ma) Ma) constitutes constitutes the the third third successive successive The It is is one one of of the the older older episode of of anorogenic anorogenic magmatism magmatism in inthe theregion. region. It episode intrusions of the 1.4 to 1.5 Ga transcontinental anorogenic province of North North intrusions of the 1.4 to 1.5 Ga transcontinental anorogenic province of America. America. The youngest youngest tectono-magmatic tectono-magmatic activity activity in in the the region region resulted resulted in in The tholeiitic volcanism, layered mafic intrusions, and associated red bed tholeiitic volcanism, layered mafic intrusions, and associated red bed sedimentation within within the the Midcontinent Midcontinent rift rift system system about about 1100 1100Ma. Ma. sedimentation 90 �A Geological Investigation inIn Vicinity Vicinity of of the A Geological Investigation the Volcanic-Plutonic Volcanic-Plutonic Contact, Contact, Northern Block Block of of the Marquette Northern Marquette Greenstone Greenstone Belt, Belt, Michigan. Michigan. J.R. J.R. SMALL, SMALL, and T.J. T.J. BORNHORST BORNHORST (Department (DepartmentofofGeological GeologicalEngineering, Engineering, Geology, Geology, and Geophysics, Michigan Michigan Technological Technological University, University, Houghton, Houghton, MI 49931) 49931) 14 km2 of the During 1988, 1988, 14 the northwesternmost northwesternmost portion portion of of the the Marquette Marquette Greenstone Belt, of the the city Greenstone Belt, located located approximately approximstely 20 miles northwest northwest of city of Marquette, were mapped aatt aa scale geology of Marquette, were geologically geologically mapped scale of of1:9000. 1:9000. The geology this area differs from studies to to the the south this from the the previous previous detailed detailed geologic geologic studies south and east in that east that itit includes includes the the contact contact between between the the volcanic volcanic and and the the bounding bounding The average grade of of metamorphism in the the Penny plutonic rocks. rocks. The average grade metamorphism in Penny Lake Lake area area is of the Archean units units within within the the is higher higher than to to the the south. south. The The structure structure of the Archean indicate at at least area is is complex. complex. Foliations Foliations indicate least two two periods periods of of deformation, deformation, and and the of a pyroclastic unit and aa gabbroic the orientation orientation of pyroclastic unit gabbroic sill sill indicate indicate the the continuation of of aa kilometer scale fold fold which continuation kilometer scale which was was first recognized recognized to the the south south by Johnson Mineralization inin the the Penny Penny Lake area area appears appears by Johnson et et al a1(ILSG (ILSG 1987). 1987). Mineralization to be be sporadic. sporadic. The Archean section in in the the Penny Archean volcanic volcanic section Penny Lake Lake area area is is composed composed of the the Volcanicsofof Silver Silver Mine Mine Lakes Lakes and and is is lithologically similar toto areas areas to to the Volcanics lithologically similar the south south and east, east, such such as as Johnson Johnson et et ala1(ILSG (ILSG1987). 1987). The volcanic volcanic rocks rocks are are composed of pillowed basalts with with minor composed of pillowed basalts minor interbedded interbedded iron iron formation formation and and pyroclastic-sedimentary units. The volcanic section is is intruded pyroclastic-sedimentary volcanic section intruded by by Archean Archean gabbro sill-like sill-like bodies and rhyolite gabbro bodies and rhyolite dikes. dikes. d Archean plutonic Penny Lake Lake area area has has been been divided divided The The Archean plutonic section sectioninin the the Penny into into four different different types. types. The oldest oldest two two have have been been subdivided subdivided into into aa gneiss gneiss unit based on a distinct gneissic fabric and a massive unit which correlates unit based a distinct gneissic and a massive unit which correlates with of Rocking with the Granodiorite Granodiorite of Rocking Chair Lakes Lakes of Johnson Johnson et et ala1(ILSG, (ILSG, 1987). 1987). Both the the gneiss gneiss and and massive massive units quartz monzonite monzonite to to granodiorite granodiorite in in Both units are quartz between these these two two units units is is uncertain; in a composition. The age relationship relationship between uncertain; in broad sense, sense, they they may may represent represent a single, single, extended extended plutonic plutonic event. event. The broad contact between these the volcanics volcanics is is gradational, gradational, zenoliths zenoliths of basalt basalt contact between these units units and and the exist near of the intrusions, exist near the the margins margins of intrusions, and and dike like like bodies bodies of the the granitoid granitoid intrude the the basalts. basalts. The The third type type of of granitoid granitoid intrusion intrusion is is granitic granitic in in compositionand and dike dike like like in form. composition form. These dikes are common common in the the These granite granite dikes Penny Lake Area, Area, and and vary vary in in thickness from under Penny Lake thickness from under .5 .5 meter meter to to over over 10 10 meters. They They cut cut both and are cut both the the gneiss gneiss and and the the massive massive granodiorite, granodiorite, and cut by quartz quartz veins. veins. The dikes have have sharp sharp contacts contacts with with the the volcanics volcanics and and are are variably variably deformed. deformed. The The fourth type type of of granitoid granitoid intrusion intrusion are are four, four, stock-like stock-like bodies of of diorite. stocks are are roughly circular in cross bodies diorite. These These stocks roughly circular cross section, section, and have have maximum diameter few hundred hundred meters. a maximum diameter of of a few meters. The volcanics volcanics are highly highly foliated margins of diorite, but the the contact contact between between the the two two units units foliated near near the the margins of the the diorite, is sharp. sharp. Their massive and the Their massive and unfoliated unfoliated textures textures suggest suggestthey they are are late late in the plutonic history. granite dikes dikes nor nor quartz plutonic history. Neither Neither granite quartz veins veins cut the the diorite diorite stocks, stocks, further suggesting suggesting a late late timing. timing. 91 �Metamorphic grade varies varies within within the the volcanic of the Metamorphic grade volcanic section section of the Penny Penny Lake Lake area, depending depending on on distance distance from from the thelarge largequartz quartzmonzonite-granodiorite monzonite-granodiorite intrusives. facies were were determined determined by by textures textures in in the intrusives. The metamorphic metamorphic facies the field field as well Facies changes changes were were well as as by by limited limited thin thinsection sectionobservations. observations. Facies determined by using using the the change change in calcium determined petrologically, petrologically, by calcium content of of plagioclase, the type plagioclase, the type and color color of of amphiboles, amphiboles, and and the the existence existence of of pyroxenes. pyroxenes. In general, general, the the metamorphic metamorphic grade grade increases increases gradually gradually from south to to north, north, except except for aa portion portion of of the thevolcanic volcanic section section along along the the eastern eastern boundary boundary where where the the grade grade increases increases abruptly abruptly from from greenschist greenschist to to amphibolite amphibolite across across aa north-south north-south trending trending fault. fault. Zones Zones of relatively relatively intense intense alteration alteration and andassociated associated anomalous anomalous precious precious metal are restricted metal mineralization mineralization are restricted to to small small areas areas near near faults. faults. Alteration Alteration in in these areas is most these mineralized mineralized areas most often characterized characterized by by quartz, quartz, carbonate, carbonate, and and sericite. sericite. Sulfides, Sulfides, including including pyrite, chalcopyrite, chalcopyrite, and and sphalerite, sphalerite, are arecommonly commonly found found in in the thealtered alteredrocks rocksasassmall, small,disseminated disseminated grains. grains. Specular Specular hematite hematite isis often often found found associated associated with with granite granite dikes dikes located located within within altered altered zones. zones. Twenty-two from throughout Twenty-two samples samples from throughout the area area were were assayed assayed for for gold. gold. Eight Eight samples anomalousvalues valuesofof greater greater than than ten samples contained contained anomalous ten parts parts per per billion, billion, with with aa maximum maximum assay assay value value of of 274 274 ppb. ppb. This project project was was funded funded by by the theMichigan MichiganGeological Geological Survey Survey and and Michigan Michigan Technological Technological University. University. 92 �AIRBORNE GEOPHYSICAL SURVEYS SURVEYSOF OFTHE THE EFFIE-COON AIRBORNE GEOPHYSICAL EFFIE-COON LAKE LAKE COMPLEX, COMPLEX. MINNESOTA MINNESOTA BY BY Bruce D. Smith, Smith, Victor F. Labson, Labson, Robert Robert J. J. Horton Horton by A program program to improve airborne airborne geophysical geophysical data acquisition and Interpretation interpretation has been implemented by Branch of of Geophysics. Geophysics. The The Effie-Coon Effie-CoonLake Lakearea areaisisone oneofoffour four areas areas chosen chosen to to test test new the USGS USGS Branch geophysical methods methodsto to map geologic for burled geophysical geologic features features favorable favorable for buried mineral mineral deposits. deposits. Airborne Airborne geophysical applications are particularly Important important since glacial and Quatemary Quaternary sediments cover 95% of results from from two new the bedrock bedrock In in the the area. area. This This presentation presentation describes describes preliminary preliminary results new airborne airborne EM EM systems systems and from new new total total field field magnetic magnetic data data processing. processing. The Effie-Coon Lake study study area, area, located located in In north-central Minnesota, Minnesota, is is a 2.7 billion The Effie-Coon Lake billion year year (Ga) (Ga) Precambrian terrain consisting consisting of the Effie Precambrian terrain Effie granitic intrusive complex and and the the Coon CoonLake Lakezoned zonedIntrusive intrusive metavolcanics. The zoned Intrusive, intrusive, thought from from limited limited outcrops outcrops surrounded by metasediments metasediments and and metavolcanics. drilling, to be and shallow shallow drilling, be mainly mainly quartz quartz monzonlte monzonite Is is defined defined mostly mostly from fromaeromagnetic aeromagnetic data. data. AANWNWSE trending 2.1 2.1 Ga mafic mafic dike dike system, system, Interpreted interpreted from from aeromagnetic aeromagnetic maps, maps, Intrudes intrudesthe themetamorphic metamorphic sequences and intrusive Intrusive complexes. complexes. Several Severaldifferent differenttypes typesof of mineral mineral deposits deposits could be present sequences and present in in the the area area including base base metals, metals, gold, gold, and andplatinum platinumgroup groupelement element(PGE) (PGE)deposits. deposits.Advanced Advancedairborne airborne geophysical geophysical methods methods are needed needed to to identify identifysubtle subtle geologic geologic features features favorable favorable for for buried buriedmineral mineraldeposits. deposits. tools for regional (EM) systems could be effective tools regional and and detailed three The two new electromagnetic (EM) properties provide dimensional mapping of electrical electrical resistivity. In general general mapping mapping of electrical dimensional mapping resistivity. In electrical properties provide complementary Information to to aeromagnetic and radiometric radlometric surveys. surveys. The The two two EM systems map shallow shallow and deep system, termed VLF for Very deep resistivity resistivity variations. variations. The shallow shallow penetrating penetrating system, Very Low Low Frequency, Frequency, measures EM EM fields fields generated generated by distant stations at about measures distant Naval Naval communication communication stations about 25,000 25.000 Hz. Hz. Unlike Unlike VLF instrumentation, instrumentation,the the components components measured measuredby bythe the USGS USGS system system are are used used to to compute commercial VLF apparent resistivity resistivity maps. maps. The The deeper deeper penetrating system developed developed by by the Branch apparent penetrating system Branch of of Geophysics Geophysics measures the effect effect of of magnetic fields generated 60,180, 180, and and300 300Hz. Hz. measures the generated by power lines at 60, Apparent resistivities resistlvities computed computed from the VLF data average 300 to Apparent to 400 400 ohm-meters ohm-meters with with some some areas as high as 1000 to 2000 2000 ohm-rn ohm-m and as low as 10's 10's of of ohm-meters. ohm-meters. High High resistivitles resistivities are a guide guide to locating locating shallow shallow or or exposed exposed resistive resistive bedrock bedrock which which is is helpful helpful In in geological geological mapping. mapping. Narrow Narrowresistivity resistivity 93 �highs not not associated associated with bedrock bedrock trends trends are are in in part part due due to to glacial glacial features such such as as eskars eskars which contain highs (>a0 ohm-m) which which may mayhelp help gravels. The Effie complex is characterized by high high apparent resistMtles resistivities (>400 gravels. ohm-rn) to the the define defineboundaries boundaries of of the the intrusive intrusive which which are are not not clearly clearly defined defined by bythe thegravity gravityorormagnetic magneticdata. data. to Areas of low low resistivities resistivities can be attributed attributed to either either thick glacial glacial till or or conductive conductiveshallow shallow bedrock bedrock (for (for Areas example example graphite graphiteIninmetasediments). metasediments). The airborne airborne EM EM instrument instrument which which measures measures magnetic magnetic fields power lines lines has has aa The fields generated generated by power depth of of penetration penetration is is approximately approximately ten times that of of the the VLF VLF system system and and has has aadeeper deeperdepth depthofof depth penetration than most commercial commercial systems. systems. Thus the system system is is much muchmore moresensitive sensitivetotovariations variationsInin penetration bedrock resistivity resistivity than the the VLF VLF system. system. The The measurements measurements are enhance mapping mapping of bedrock are processed processed to enhance conductivebedrock bedrockfeatures features which which may may be beburied buried at at depths depths of of hundreds hundredsof of meters. meters. Important Importantconductive conductive conductive bedrock bedrock features features In in the study study area area are are mainly mainly graphitic graphitic units units In in the the metasediments. metasediments. The The distribution distribution of of these units units isisuseful usefulininunderstanding understandingbedrock bedrockstratigraphy stratigraphy and and structure. structure. In Inaddition, addition,some someconductive conductive these anomalies anomalies could couldIndicate indicatemassive massivemetallic metallicmineralization. mineralization. The VLF VLF and and power power line lineEM The EMmethods methodsdo donot notrequire requireananairborne airbornetransmitter, transmitter,which whichgreatly greatly reduces reduces the the complexity, complexity, weight, weight, and and cost costofofthe thesystems. systems.Successful Successfuldevelopment developmentand andapplication applicationof of methods methods described described In this study study Is is aa critical criticalstep stepinindevelopment development of of electrical electricalmethods methods that that can canbe be routinely used used to to complement complement other other airborne airborne geophysical geophysical data data such such as asmagnetic magneticand andradlometric radiometric routinely measurements. measurements. The The airborne airborne survey survey also alsoIncludes includes standard standard total total field field magnetic magneticdata datawhich whichcombined combinedwith witholder older (1984) USGS USGS data effective flight spacing of 1/8 1/8 mile. mile.AAnumber numberofofdifferent differentstandard standard (1984) data yields yields an effective flight line spacing enhancement enhancement methods used on the the magnetic magnetic data data include: include: a)color a)color shaded shaded relief, relief, b)trend b)trendfiltering, filtering, and and c)boundaryestimatIon. estimation. In Inaddition additionaarelatively relativelynew newmethod methodofofenhancement enhancementusing usingaaterracing terracingoperator operator c)boundary has has been been applied applied to to the thedata. data.This Thisoperator operatorproduces producesmaps mapswith withboundaries boundariesshowing showingterrains terrains with with different differentestimated estimatedrelative relativesusceptibilities. susceptibilities. All InterpretatIon Allofofthe thegeological geologicaland andgeophysical geophysicaldata dataare arebeing beingused usedInInananintegrated Integrated interpretationofofthe the bedrockgeology. geology.Digital Digitalterrain, terrain,shown shownas ascolor colorshaded shadedrelief, relief,Isisbeing beingused usedtotoanalyze analyzepossible possiblesurface surface bedrock expressionsof of bedrock bedrockgeology. geology.Final Finalintegrated integratedInterpretation interpretationmakes makesuse useofofaaGeographic GeographicInformation Information expressions System System(GIS). (GIs). 94 �GEOLOGY OF O F THE THEWEST WESTDEAD D E A DHORSE HORSECREEK CREEKDIATREME-HOSTED DIATREME-HOSTED GEOLOGY R A R E METAL METAL OCCURRENCES, OCCURRENCES, SCHREIBER-HEMLO SCHREIBER-HEMLO DISTRICT, DISTRICT, ONTARIO ONTARIO RARE ** Smyk, Smyk, M.C.,Ontario Ontario Ministry Ministry of of Northern Northern Development ~ c w l o p m e nand and t Mines, Mines, Thunder Thunder M.C., DL., Geology, University of Western Ontario, London, Bay, Kingston, Bay, Kingston, D.L., Geology, University of Western Ontario, London, and Taylor, Taylor,R.P., R.P.,Earth EarthSciences, Sciences,Carleton Carleton University, University, Ottawa. Ottawa. and The Dead Dead Horse Horse Creek Creek complex complex consists consists of of five fiveseparate separatediatremes diatremes located located The immediately west west of of the theMiddle MiddleProterozoic ProterozoicCoidwell Coldwell alkaline alkaline complex complex (Sage, (Sage, immediately 1982). The West Dead Horse Subcomplex diatreme occurs in strongly foliated 1982). The West Dead Horse Subcomplex diatreme occurs in strongly foliated andmetavolcanic metavolcanicrocks, rocks,isisapproximately approximately80 80 by by 40 40mm Archean metasedimentary metasedimentary and Archean in size, size, and and contains contains three three main, main, highly highly radioactive, radioactive, mineralized mineralized zones: zones: (1) (1) in (2) eastern eastern extension, extension, and and (3) (3) western western pits. pits. The T h e eastern eastern pits pits and and eastern pits, pits, (2) eastern eastern extension extension are are situated situated in in the the main main diatreme diatreme which which isis composed composed eastern predominantly of monolithic breccia with hematized clasts set in a carbonatepredominantly of monolithic breccia with hematized clasts set in a carbonaterich matrix matrix that thatalso alsocontains containsriebeckite. riebeckite. The Thewestern western pits pits are are situated situated west west of of rich 130° oblique the main diatreme on a narrow, mineralized structure striking a t the main diatreme on a narrow, mineralized structure striking at 130°, oblique hosted in in aa silicified, silicified, to the the host-rock host-rock foliation. foliation. Here Here mineralization mineralization isis hosted to hematized, carbonate-rich carbonate-rich rock. rock. Although Although the the metal metal associations associations and and hematized, Th, U) U) mineralogy of of the the three threezones zones are a r e broadly broadly similar similar (enriched (enriched in in Zr, Zr, REE, REE, Th, mineralogy significant local variations exist, particularly in the nature and distribution of significant local variations exist, particularly in the nature and distribution of the REE-bearing minerals: the western pits are characterized by high values of the REE-bearing minerals: the western pits are characterized by high values of Be (up (up to to 0.62 0.62 wt.96), wt.%), Sc to 250 250 ppm), ppm), Zr Zr (up (up to to11.6 11.6 wt.%), wt.%), REE REE (up (up to to1250 1250 Be Sc (up (up to pprn), T h (up to 0.52 wt.%) and U (up to 0.31 wt.%). In contrast samples from ppm), Th (up to 0.52 wt.%) and U (up to 0.31 wt.%). In contrast samples from the eastern eastern pits pits and and eastern eastern extension extension contain contain lesser, lesser, but but nevertheless nevertheless the significant abundances of Be (up to 240 ppm), Sc (up to 85 ppm), Zr (uptoto2.8 2.8 significant abundances of Be (up to 240 ppm), Sc (up to 85 ppm), Zr (up wt.%). Th Th (up (uptoto0.15 0.15 wt.%), wt.%), and andUU(up (uptoto0.08 0.08wt.%); wt.%);subequal subequal amounts amounts of of REE REE wt.%), 1220 ppm); and are enriched in P205 (up to 2.46 wt.%) and Y (up to 235 (up to (up to 1220 ppm); and are enriched in P205 (up to 2.46 wt.%) and Y (up to 235 ppm). In In addition additiontotozircon zircon(often (oftenhydrated), hydrated),complex complexCa-Zr-bearing Ca-Zr-bearing silicates silicates ppm). and thorite, phenacite occurs in the western pits, and monazite and xenotime and thorite, phenacite occurs in the western pits, and monazite and xenotimc REE are found foundininthe theeastern easternpits pitsand andeastern easternextension. extension.Chondrite-normalized Chondrite-normalized REE are distributions emphasize the variability of the REE-mineralogy (western pits, distributions emphasize the variability of the REE-niincralogy (western pits, 0.09; eastern eastern pits, pits,LREE..enriched, LREE-enriched, La/LeN L 8 / h N—= 9.1 9.1 to to HREE-enriched, La/LuF HREE-enriched, La/Lu — 0.09; - 17.6). None of the themineralized mineralized samples samples have have aamarked markednegative negativeeuropium europium 17.6). None of anomaly. which which suggests suggests that that the themineralizing mineralizingfluid.s fluids were were nxittj,cd. oxidised. anomaly, 95 �MULTIPLE ARCHEAN TERRANESI IN MULTIPLE ARCHEAN TERRANES N SW SW MINNESOTA MINNESOTA -- THE OLD GRAY OLD GRAY GNEISS SHE SHE AIN'T AIN'TWHAT WHAT SHE SHE USED USED ¶10 TO BE BE D.L. SOUTHWICK, Minnesota Geological University D.L. SOUTHWICK, G e o l o g i c a l Survey, S u r v e y , 2642 2642 U n i v e r s i t y Avenue, Avenue, St. BRYAN Department of Geology and 55114, BRYAN SCHAAP, SCHAAP, Department and Geophysics, Geophysics, S t . Paul, P a u lMN , MN55114, University U n i v e r s i t y of of Minnesota, Minnesota, Minneapolis, M i n n e a p o l i s , MN MN 55414, 55414, and and V.W. V.W. CHANDLER, CHANDLER, Minnesota Geological G e o l o g i c a l Survey. Survey. Major aeromagnetic less a e r o m a g n e t i c and and gravity g r a v i t y lineaments l i n e a m e n t s that t h a t trend t r e n d more more or o r less parallel p a r a l l e l to t o the the Great G r e a t Lakes Lakes Tectonic T e c t o n i c Zone Zone (GLTZ) (GLTZ) subdivide s u b d i v i d e the t h e Archean Archean ggneiss n e i s s terrane t e r r a n e of of southwestern s o u t h w e s t e r n Minnesota into i n t o three t h r e e blocks b l o c k s that t h a t have distinctive d i s t i n c t i v e geophysical g e o p h y s i c a l characteristics. c h a r a c t e r i s t i c s . The block—bounding block-bounding lineaments l i n e a m e n t s are are of north-dipping n o r t h - d i p p i n g zones z o n e s of o f planar p l a n a r structures; s t r u c t u r e s ; therefore therefore tthe h e surface s u r f a c e traces of they t h e y are a r e approximately a p p r o x i m a t e l y parallel p a r a l l e l to t o the the GLTZ in i n three t h r e e dimensions, d i m e n s i o n s , not n o t just just iin n map map view. view. The northernmost n o r t h e r n m o s t block block boundary, boundary, about a b o u t 40 40 km south s o u t h of o f the t h e GLTZ, has has It I t separates s e p a r a t e s the t h e Benson Benson bbeen e e n named the t h e Appleton geophysical g e o p h y s i c a l lineament. lineament. b l o c k on the t h e north n o r t h from from the t h e Montevideo Montevideo block b l o c k on on the south s o u t h and, and, on the the block bbasis a s i s of of sparse s p a r s e drilling, d r i l l i n g , appears a p p e a r s to t o be be aa zone zone of of ductile d u c t i l e shear s h e a r and and faulting f a u l t i n g that t h a t has h a s been been invaded invaded locally, l o c a l l y , and and synkinematically, s y n k i n e m a t i c a l l y , by by sheets s h e e t s of of muscovite m u s c o v i t e leucogranite. l e u c o g r a n i t e . As A s judged judged from from geophysical g e o p h y s i c a l anomaly anomaly patterns p a t t e r n s and and drilling d r i l l i n g data, d a t a , the t h e Benson Benson block block consists c o n s i s t s dominantly d o m i n a n t l y of of granitic g r a n i t i c to t o tonali— tonalitic intrusions into gneissic wall rocks. plutons t i c i n t r u s i o n s i n t o g n e i s s i c w a l l r o c k s . The p l u t o n s range r a n g e from strongly strongly synkinematic as whole whole may may be be aa granitoid granitoid s y n k i n e m a t i c to t o post—kinematic, p o s t - k i n e m a t i c , and and the t h e block b l o c k as intrusive i n t r u s i v e complex complex analogous a n a l o g o u s in i n style s t y l e to t o the the Winnipeg Winnipeg River R i v e r belt b e l t in i n the the Superior S u p e r i o r Province P r o v i n c e of of Manitoba Manitoba and and Ontario. O n t a r i o . The Montevideo block, b l o c k , in in contrast, c o n t r a s t , appears a p p e a r s to t o be be primarily p r i m a r i l y gneissic g n e i s s i c rocks r o c k s comparable comparable to t o those those exposed in i n the t h e Minnesota Minnesota River R i v e r Valley V a l l e y between between Montevideo Montevideo and and Granite G r a n i t e Falls. Falls. M a age a g e component component and and granulite—facies g r a n u l i t e - f a c i e s metamorphism metamorphism that t h a t characcharacThe 3,600 3 , 6 0 0 Ma tterize e r i z e the t h e Montevideo Gneiss G n e i s s have thus t h u s far f a r not n o t been been documented documented in i n the the Benson b block. lock. About45 45kmkmf afarther the lineament l i n e a m e n t that t h a tseparates s e p a r a t e sthe t h eMontevideo Montevideo About r t h e r ssouth, o u t h , the block the Morton block ppasses and ccrosses b l o c k from from the Morton block a s s e s tthrough h r o u g h RRenville e n v i l l e and r o s s e s the the River Sacred Minnesota R i v e r in i n a zone of of no outcrop o u t c r o p between Granite G r a n i t e Falls F a l l s and S acred A zone of A of faulting f a u l t i n g in i n this vicinity v i c i n i t y has h a s long l o n g been postulated p o s t u l a t e d on the basis b a s i s of o f earlier e a r l i e r geophysical g e o p h y s i c a l surveys s u r v e y s and and exposed exposed small s m a l l shear s h e a r zones zones just just t h a t the t h e fault f a u l t zone is i s larger larger nnorth o r t h of of the t h e outcrop o u t c r o p gap. gap. Our data d a t a suggest s u g g e s t that and that previously p r e v i o u s l y thought, t h o u g h t , and and imply imply that t h a t the t h e Morton Morton a n d more fundamental f u n d a m e n t a l that Gneiss G n e i s s and Montevideo Montevideo Gneiss G n e i s s could c o u l d well w e l l be be separate s e p a r a t e and and distinct d i s t i n c t elements elements of o f the t h e Middle Middle Archean Archean crust c r u s t that t h a t have have been b e e njuxtaposed j u x t a p o s e dtectoriically. tectonically. Heart. Heart. All A l l three three blocks b l o c k s of of the t h e Archean Archean gneiss g n e i s s terrane t e r r a n e are a r e truncated t r u n c a t e d geophysi— geophysic a l l y on on the the east e a s t by by anomaly anomaly patterns p a t t e r n s characteristic c h a r a c t e r i s t i c of o f Penokean Penokean plutons plutons cally and, to l e s s e r extent, e x t e n t , of o f folded f o l d e d supracrustal s u p r a c r u s t a l rocks. rocks. S i m i l a r but b u t less less and, t o a lesser Similar diagnostic d i a g n o s t i c patterns p a t t e r n s flank f l a n k the t h e Morton Morton block b l o c k on on the the south s o u t h and and west, west, ssuggesting u g g e s t i n g that t h a t the the Archean gneiss g n e i s s terrane t e r r a n e may be be enveloped enveloped by Early Early Proterozoic magmatic belts. belts. sScientific c i e n t i f i c drilling d r i l l i n g to t o test t e s t these t h e s e interpretainterpretaP r o t e r o z o i c magmatic tions i s underway underway and and will w i l l continue. continue. t i o n s is T h i s work work was was funded funded in i n part p a r t by by the the Minnesota Minnesota Future F u t u r e Resources Resources Commission. Commission. This 96 �Petrography and Sedimentation of The Petrography The Middle Middle Proterozoic Proterozoic (Keweenawan) Nonesuch Nonesuch Formation Western Lake Superior (Keweenawan) Formation Western Superior Region Midcontinent Region Midcontinent Rift Zone Thomas Minnesota-Duluth, Duluth, Thomas J. J. Suszek Suszek (Dept. (Dept. of Geology, University of of Minnesota-Duluth, Duluth, Minnesota 55812) 55812) New information New information from from drill drill hole logs, logs, detailed detailed sedimentological sedimentological descriptions descriptions and petrographic petrographic analysis analysis of Middle Middle Keweenawan Keweenawan Nonesuch Nonesuch Formation Formation in in select Bear Creek drill cores from and Douglas Counties Wisconsin, and Bear Creek drill from Bayfield Bayfield and Douglas Counties Wisconsin, and examination of outcrops in Upper Michigan Michigan provide provide in northwest northwest Wisconsin Wisconsin and and Upper evidence for for source source rocks and environment 1). evidence environment of deposition deposition (Fig. (Fig. 1). These data suggest that Lower Lower Keweenawan Keweenawan volcanic units were were the the major major These data suggest volcanic units contributors the Nonesuch Nonesuch Formation Formation in in northwest northwest Wisconsin, Wisconsin, while while contributors ofof detritus detritus to the Middle volcanics were only Sediment from Early Middle Keweenawan Keweenawan volcanics only minor minor contributors. contributors. Sediment Early Proterozoic and Archean Proterozoic and Archean crystalline crystalline rocks, rocks, although although minor, minor, increase increase ininabundance abundance upsection as older source rocks upsection as rocks were were unroofed. unroofed. Sedimentary structures and stratigraphic stratigraphic relationships relationships suggest suggest that that deltaic Sedimentary structures and processes, sheet floods, floods, turbidity processes, sheet turbidity currents currents and suspension suspension settling settling were were the the primary primary mechanismsofof deposition deposition in in aa lake with mechanisms with constant constant and and perhaps perhaps rapid rapid fluctuations fluctuations in water water levels brought on by by changes changes in in tectonism tectonism and/or and/or climate. climate. The gradational contacts of the Nonesuch Formation The gradational contacts of the Nonesuch Formation with with the the underlying underlying Copper Harbor Harbor Conglomerate Conglomerate and overlying overlying Freda Freda Sandstone, Sandstone, along along with with outcrop outcrop Copper and drill facies facies data, data, suggest suggest deposition deposition of of the the Nonesuch Nonesuch on on aaprograding progradingalluvial alluvial complex in the Midcontinent Midcontinent Rift Rift Zone. Zone. fan complex Examinationofof the the genetic facies, combined combined with with Examination genetic relationship relationship of Nonesuch Nonesuch facies, percentages of the different textural textural elements within each each facies type, and and petrographicdata, data, suggest suggest that that deposition deposition was was generally generally from from the the south petrographic south into the rift rift zone. zone. Deposition occurred in aa basin basin that that was waspartially partiallyrestricted, restricted, Deposition appears appears to to have occurred or perhaps or perhaps completely completely isolated from from areas areas containing containing Nonesuch Nonesuch Formation Formation farther farther east Wisconsin and Upper Upper Michigan. Michigan. east in Wisconsin 97 �Bear Creek Drill Holes Figure1.1. General Generallocation locationof ofoutcrop outcropand anddrill drillhole holestudy study areas. Figure areas. 98 �GRAVITY AND MAGNETIC DATA OVER THE GRAVITY AND MAGNETIC DATA OVER THE WAUKESHA FAULT, S.E. WISCONSIN WAUKESHA FAULT, S.E. WISCONSIN by Keith A. Sverdrup Keith A. Sverdrup F. Kean William William F.Geosciences Kean Department of Department of Geosciences University of Wisconsin-Milwaukee University of Wisconsin—Milwaukee Milwaukee, WI 53201 Milwaukee, WI 53201 In the past few years gravity and magnetic data has been In theover pastthe fewWaukesha years gravity andthe magnetic data has been of collected fault in southeastern corner collected over the Waukesha fault in the southeastern corner ofa thestate. state. The fault can be observed where it passes through the The fault can be observed where it passes through a At this point it appears as a vertical fault quarry inWaukesha. Waukesha. quarry At this appears at as between a vertical 30 fault with ain displacement that haspoint been it estimated with a displacement that has been estimated between 30 feet. (~ikulic and Mikulic, 1977) and 100 (Foley at et al., 1953) (Mikulic and Mikulic, 1977) and 100 (Foley 1953) of feet. The displacement at depth is thought to beetonal., the order 1500 The displacement at depth is thought to be on the order of 1500 feet(Thwajtes, (Thwaites,1957). 1957). feet ~nitially,1500 square miles of gravity data were collected on 1500to square miles of gravity were on a Initially, one mile grid investigate the lineardata extent of collected the fault. aThe oneresultant mile gridgravity to investigate the linear extent of the fault. signature is characterized by a zone The resultant gravity signature is characterized by a zone N40E roughly three miles wide of tightly spaced trending trending N4OE roughly threeextends miles wide tightly spaced for of approximately 6 0 miles from contours. This signature contours. This signature extends for approximately miles from the Lake Michigan shoreline near Port Washington to 60 the southwest the Lake Waukesha Michigan and shoreline near Port Washington- Illinois to the southwest through on towards the Wisconsin border. through and onnorthwest towards the Wisconsin ~ r a v i t Waukesha yvalues on the side of the fault are as border. much as Gravity values on the northwest side of the fault are as much as 19 mgals higher than those to the southeast. 19 mgals than those thefault southeast. Ourhigher initial models ofto the based on the gravity data Our initial models of the fault based on the gravity it as a high angle growth fault downthrown to the data viewed viewed it as a high angle growth fault downthrown to the southeast. The displacement was as little as 40 feet in the southeast. The displacement was as to little as 40 thein the ~iagarandolomite near the surface as much asfeet 2000in feet Niagaran dolomite near the surface to as much as 2000 feet ~recambrian basement. In order to model the large gravityin the Precambrian basement. In order model theto large gravity contrast across the fault it wastonecessary include a high contrast across the fault it was necessary to include a high density mafic material at depth. density mafic material The gravity data at wasdepth. later supplemented by roughly 630 The gravity data was latertaken supplemented roughly 630 square miles of magnetic data on a one by mile grid coincident square miles of magnetic data taken on a one mile grid coincident withgravity gravitystations. stations. Magnetic readings varied between with readings There variedis between no clear linear approximately 57,400 andMagnetic 59,000 gammas. approximately 57,400 and 59,000 gammas. There is no clear Instead there are alinear number feature evident in the magnetic data. feature evident in the magnetic data. Instead there are a number of roughly circular magnetic highs as much as 1300 gammas above of circular highs as much as 1300 gammas These above androughly lows as much asmagnetic 300 gammas below background levels. and lows as much as 300 gammas below background levels. These featuresdo do not not show showany any clear clearindication indicationof ofthe the presence of a features presence fault, rather they suggest individual intrusive bodies ofof a fault, rather they suggest individual intrusive bodies of relatively high susceptibility material and have been modelled as relatively susceptibility material and been modelled Withhigh this supporting information we have are modifying our as such. such. With this supporting information we are modifying our gravity model to incorporate a limited vertical fault consistent gravity model to incorporate a limited vertical fault at consistent intrusives depth. with previous views and individual mafic with previous views and individual mafic intrusives Illinois at depth. 99 �References References Foley, F.C., FC., Walton, Walton, W.C., W.C., and and Drescher, Drescher, W.J., W.J., 1953, 1953, Ground water conditions conditions in in the the Milwaukee—Waukesha Milwaukee-Waukesha area, area, Wisconsin: Wisconsin: Wisconsin p. Wisconsin Geological Geological Survey Survey water water supply supply paper paper 1229, 1229, p. 3—23. 3-23. Mikulic, J.L., 1977, Mikulic, D.G., and Mikulic, J.L., 1977, History of geologic geologic work in the the Sjlurjan Silurian and Devonian Devonian of of southeastern southeastern Wisconsin: Wisconsin: annual Tri-State Tn-State field Guidebook for the 41st annual field conference, conference, p. A19-A27. A19-A27. Thwaites, Thwaites, F.T., F.T., 1957, 1957, Buried Precambrian Precambrian of of Wisconsin: Wisconsin Wisconsin Geological and Geological and Natural History History Survey Survey map. map. 100 �STRIKE-SLIP FAULTING FAULTING IN IN ARCHEAN ARCHEAN ROCKS ROCKS IN IN THE THE VIRGINIA VIRGINIA HORN HORN STRIKE-SLIP AREA, N.E. N.E. MINNESOTA: MINNESOTA: IMPLICATIONS IMPLICATIONS FOR FOR THE THE ORIGIN ORIGIN OF OF THE THE AREA, VIRGINIA HORN STRUCTURE VIRGINIA HORN STRUCTURE JAMES JAMES L. L. WELSH WELSH Department Department of of Geology Geology Gustavus Gustavus Adoiphus Adolphus College College St. St. Peter, Peter, MN MN 56082 56082 Field Field mapping mapping in in Archean Archean metavolcanic metavolcanic and and metasedimentary metasedimentary rocks rocks in in the the Virginia-Eveleth-Gilbert Virginia-Eveleth-Gilbert area area of of northeastern northeastern Minnesota Minnesota has has revealed revealed the the presence presence of of aa significant significant strike— strikeslip slip fault fault system, system, here here called called the the Pike Pike River River System. System. In In this this area area the the fault fault system system is is composed composed of of two two major major northeasterly northeasterly trending trending faults faults connected connected by by aa series series of of more more northerly northerly trending trending en en echelon echelon strands. strands. The The configuration configuration suggests suggests aa strike strike slip slip duplex. duplex. Movement Movement history history along along this this system system appears appears to to have have been been Although offset offset marker marker units units have have not not been been Although identified, map map patterns patterns suggest suggest that that early early and and possibly possibly the the identified, most most significant significant movement movement was was sinistral. sinistral. Kinematic Kinematic indicators, indicators, however, however, indicate indicate that that (latest?) (latest?) movement movement was was dextral. dextral. In In addition addition high high angle angle slickensides slickensides associated associated with with the the duplex duplex strands strands require require aa vertical vertical component componentof ofmovement. movement. complex. complex. The The Pike Pike River River System System trends trends along along the the axis axis of of the the Virginia Virginia Horn Horn (the (the gentle gentle anticline-syncline anticline-syncline structure structure present present in in the the unconformable unconformable superjacent superjacent Proterozoic Proterozoic rocks, rocks, so so prominently 2-shaped map map pattern pattern of of the the prominently outlined outlined by by the the Z-shaped Biwabik Biwabik Iron Iron Formation), Formation), and and most most certainly certainly exerted exerted aa controlling controlling influence influence on on its its formation, formation, although although the the Proterozoic rocks themselves have not been Proterozoic rocks themselves have not been cut cut by by these these faults. faults. It It is is here here suggested suggested that that late late dextral dextral transpressional transpressional movement movement in in the the basement basement rocks, rocks, possibly possibly aa result of the Penokean collision to the south, created result of the Penokean collision to the south, created aa compressional compressional stress stress within within the the reactivated reactivated Pike Pike River River duplex duplex structure, causing localized uplift of the basement structure, causing localized uplift of the basementrocks. rocks. The The Virginia Virginia Horn Horn structure structure is is thus thus interpreted interpreted to to be be aa drape drape structure over the uplifted basement rocks. structure over the uplifted basement rocks. 101 �Mafic and Clastic Clastic Dikes Dikes as as Keweenawan Keweenawan Paleostress Paleostress Indicators in in the the Huron Huron Mountains, Mountains, Michigan Michigan G. Wilson Wilson and andC. C. Craddock G. Department Department of Geology and and Geophysics Geophysics Wisconsin-Madison University of Wisconsin-Madison Madison, 53706 Wl53706 Madison, WI The Huron Mountains Mountains of northwest northwest Marquette Marquette County, Michigan, Michigan, contain the pre-rift basement rocks closest to the northern northern apex apex of of the the Midcontinent MidcontinentRift RiftSystem System (MRS) and thus are aa strategic paleostresses associated associated with with the the strategic place place to to study study paleostresses formation of the rift. rift. This area is is located located astride astride the the Trans-Superior Trans-Superior Tectonic Tectonic Zone Zone (TSTZ) (Fig. 1), I ) , which bisects the arc formed by the two arms of the the rift rift (Klasner (Klasner et et al, al, 1982). This This zone zone lies lies parallel parallel to to the the direction direction along which major crustal separation is inferred to have taken place place across across the the rift. rift. The study area in in the the Huron HuronMountains Mountains was mapped at a scale of 1:6000 1:6000 so that the rocks rocks and structures could be mapped mapped detail. The and plotted in detail. Thebasement basement rocks rocks of of the the Huron Huron Mountains Mountains consist consist mainly mainly of of The Upper Archean Archean granodiorite granodiorite gneiss gneiss and and amphibolite. amphibolite. The Upper Keweenawan Keweenawan (?) (?) Jacobsville Sandstone overlies the Archean Archean rocks rocks nonconformably. nonconformably. Structures in the Huron Mountains Mountains that reveal northern MRS kinematic kinematic patterns patterns include 1) mafic dike swarms and basement rock joints, joints, which record a prepre- to syn-rift extensional cycle, and and 2) 2) aligned extensional cycle, aligned clastic clastic dikes dikes and joint joint sets sets in in the theJacobsville Jacobsville in the the Huron Huron Sandstone that suggest aa post-rift compressional cycle. cycle. Mafic dikes in as much as 60 m wide have subophitic to to diabasic diabasic textures textures and consist of of Mountains as plagioclase plagioclase and clinopyroxene clinopyroxene with subordinate subordinate amounts amounts of of opaque opaqueminerals. minerals. Dominant mafic mafic dike dike trends trends are are N-S and and E-W, E-W, perpendicular perpendicular and and parallel parallel to to the the rift Dominant axis, respectively respectively (Fig. (Fig. 2). 2). Similar trends for mafic dikes in in western western upper upper Michigan Michigan were described by Baxter Perpendicular dike dike trends are Baxter and and Bornhorst Bornhorst (1988). (1988). Perpendicular are unusual in in a rift ordinarily leads leads to to a single unusual rift environment; environment; crustal crustal extension extension ordinarily single set set subparallel to the the rift Thus, the the perpendicular dike pattern subparallel to rift axis. axis. Thus, perpendicular dike pattern is is presently presently somewhat enigmatic. enigmatic. vertical clastic clastic dikes with a consistently Seven vertical consistently NNE trend (Fig. (Fig. 3) 3) have havebeen been found within the the Jacobsville Jacobsville Sandstone Sandstone of of the the Huron Huron Mountains. Mountains. These aligned aligned clastic dikes are are as much clastic dikes much as 20 cm cm in in width, width, more more than 100 100 m m in in length length (they (they disappear beneath beneath Lake Lake Superior), Superior),and andseparated separatedby by as as much disappear much as as 22 km. km. Cathodoluminescence microscopy microscopyand and petrographic petrographic analysis analysis indicates indicates that the Cathodoluminescence the clastic dike dike rock is aa quartz arenite with with well-rounded well-rounded grains, grains, both both texturally texturally and and clastic quartz arenite compositionally more more mature mature than than the the wall compositionally wall rock, rock, the the Jacobsville Jacobsville Sandstone Sandstone -primarily a feldspathic sandstone with conglomerate, conglomerate, siltstone, and and shale shale members. members. Since Since the Jacobsville Jacobsville Sandstone Sandstone rests rests nonconformably nonconformably on on crystalline crystalline basement basement rocks, it is unlikely that that the clastic dikes were were injected injected from from below. below. An An alternative alternative is is rocks, that the dikes that dikes are are of of the the neptunian neptunian model model -- those those that that fill fill fissures fissuresfrom from above. above. Outcrops of Jacobsville are found found as much as 150 Outcrops of Jacobsville Sandstone Sandstone are 150 m m topographically topographically than outcrops that that display the clastic dikes. An higher than Anexplanation explanationmust, must,therefore, therefore, account for a stress account for stress state state that that permits permits the the opening opening of of extension extension fractures fractures at aa minimum depth depth of of 150 m minimum m in inthe theJacobsville Jacobsville bedrock, bedrock, the the inferred inferredminimum minimum 102 �pre-erosional thickness of the Jacobsville Sandstone Sandstone in in the Huron Huron Mountains. Mountains. reflection profiles profiles AA and F suggest the presence of of reverse faults in GLIMPCE reflection that may be an extension of the rift-related rocks offshore from the Huron Mountains that Keweenaw Fault. Keweenaw Fault. The NNE trend of the clastic dikes, dikes, parallei parallei to the TSTZ, TSTZ, places places them in in an an orientation orientation parallel parallel to to the theprobable probabledirection directionofofmaximum maximumcompression compression expected for the apex expected apex of of the the MRS MRS during during its itscompressional compressionalstage stage of of development development (Fig. 1). 1). The trend of the clastic dikes nearly nearly bisects bisects the acute angle between two major joints in the Jacobsville major sets of vertical joints Jacobsville Sandstone. Sandstone. These These joints appear appear to represent a conjugate shear system, and the clastic dikes would thus correspond to the extension position; aa third dikes. Therefore, extension fracture position; third set set of of joints parallels parallels the dikes. Therefore, the the aligned clastic clastic dikes formed parallel parallel to to a aligned dikes may may have have filled extension extension fractures fractures formed compression associated compression associated with the compressional compressional stage stage of of the the MRS. MRS. The compositional compositional and textural maturity of the clastic dike rock in comparison comparison to the Jacobsville wall rock rock suggests that the dikes the Jacobsville Sandstone Sandstone wall suggests that dikes are are composed composed of of sandstone similar to that found in the Munising Munising Formation Formation (Upper Cambrian), a rock unit that overlies unit overlies the the Jacobsville Jacobsville Sandstone Sandstone in slight slight angular angular unconformity unconformity in in outcrops 60 km to the southeast of the study study area. area. If the dike rock is indeed indeed from from the the Munising Formation, then the clastic dikes provide provide a paleostress paleostress indicator, suggest aa timing for some some of of the the compressional compressional event, and and give give reason reason to extend extend the the known known pre-erosional pre-erosional limit of the Munising Munising Formation Formation in in upper upper Michigan. Michigan. 00 50 SO I - 100 100 200 1 I 300 KILOMETERS KILOMETERS of the the TransTransFig. 11 - Location map and orientation of 1982). Superior Tectonic Zone (after Kiasner Klasner et et al, al, 1982). 103 �N N w N=7 - Circi. 43% Clastic Dike Dike Trends Trends Fig. 3 -- Clastic Fig. 2 - Mafic Mafic Dike Dike Trends Trends FIg. Research in the Huron Research Huron Mountains Mountains is partially partially supported supported by by the the Geological Geological Society of of America, and the University Society America, the Michigan Michigan Geological Geological Survey, Survey, and University of of Wisconsin-Madison. Wisconsin-Madison. REFERENCES REFERENCES Baxter, D. A., A., and Bornhorst, T. T. J., J., 1988, 1988, Multiple Multiple discrete discrete mafic intrusions of Archean to Keweenawan Keweenawan age, age, western western upper upper peninsula, peninsula, Michigan: Michigan: Abstract. Inst. on on Lake Lake Superior Superior Geology, Geology, Marquette, Marquette, Michigan, Michigan, p. p. 6-8. 6-8. 34th Annual Inst. Klasner, J. S., Cannon, W. F., F., and and Van Schmus, Schmus, W. R., R., 1982, 1982, The The pre-Keweenawan pre-Keweenawan tectonic history history of of southern southern Canadian Canadian Sheild Sheild and and its its influence influence on formation of the Midcontinent Rift, in in Wold, Wold, R. R. J., J., and and Hinze, Hinze, W. W. J., J., eds., eds., Geology andTectonics of the Lake Lake Superior Superior Basin: Basin: Geol. Geol. Soc. Soc. of of America America Memoir Memoir 156, 156, p. p. 27-46. 27-46. 104 � https://digitalcollections.lakeheadu.ca/files/original/9af34eabd15297edf1bc1cc9977276ea.pdf a17260d67672289910f93f628575c1be PDF Text Text ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY INSTITUTE ON PROCEEDINGS VOLUME 35 VOLUME 35 1989 MAY 1989 2.Field FieldTrip TripGuidebook Guidebook Part 2. Trip 1. 1. North Shore Rhyolites, Rhyolites, Minnesota Minnesota Trip 2. Penokean Penokean Structural Structural Terranes Terranes in East-Central East-Central Minnesota Minnesota Trip 3. 3. Mellen Complex, Wisconsin Wisconsin Trip 4. 4. Archean ArcheanGold Gold Occurrences Occurrences and and Their Their Structural Structural Settings Settings 35th 35th Annual Annual Meeting Meeting May 3-6, 1989 1989 held at at Duluth, 55812 Duluth. Minnesota Minnesota 55812 �Organizing Committee, Committee, 35th 35th Annual Annual Meeting, Meeting, ILSG ILSG(1989) (1989) Richard W. Dept. of Geology, University W. Ojakangas, Ojakangas, Dept. University of of Minnesota, Minnesota, Duluth, Duluth,MN MN55812 55812 John C. C. Green, Green, Dept. Dept. of Geology, Geology, University of Minnesota-Duluth, Minnesota-Duluth, Duluth, MN 55812 55812 Timothy B. B. Hoist, Hoist, University University of of Minnesota-Duluth, Minnesota-Duluth, Duluth, Duluth, MN MN 55812 55812 Program Chair and and Abstract Abstract Editor: Editor: John Program Chair John C. C. Green Green Guidebook Editor: Timothy B. Hoist Hoist Guidebook Editor: Timothy B. Volume 35 35 consists of Parts Parts 11 and Volume and 2: 2: 1: 1: Abstracts Abstracts 2: 2: Field Trip Guidebooks Guidebooks Published and Distributed Distributed by by Institute Institute on on Lake Lake Superior Superior Geology Geology J. Kalliokoski, Kalliokoski, Secretary/Treasurer SecretaryITreasurer Dept. of Geological Geological Engineering, Engineering, Geology Geology and Geophysics Geophysics Michigan Technological University University Houghton, Michigan Michigan 49931 49931 ISSN 1042-9964 1042-9964 �FIELD TRIP TRIP GUIDEBOOK GUIDEBOOK THIRTY-FIFTH ANNUAL MEETING MEETING INSTITUTE ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY 3-6, 1989 1989 MAY 3-6, DULUTH, MINNESOTA MINNESOTA Trip 1: North Shore 1: North Shore Rhyolites, Rhyolites, Minnesota Minnesota Leader: Leader: J. C. C. Green Green University of Minnesota University of Minnesota Duluth Duluth Duluth, Minnesota Minnesota 55812 55812 Trip 2: 2: Penokean Structural Terranes in East-Central East-Central Minnesota Minnesota Leader: Leader: T. B. B. Hoist Hoist University of of Minnesota Minnesota Duluth Duluth Duluth, Minnesota 55812 Minnesota 55812 Trip 3: 3: MeIlen Mellen Complex, Wisconsin Wisconsin Leaders: Leaders: K. W. W. Klewin, Klewin, Northern NorthernIllinois IllinoisUniversity, University,DeKaIb, DeKalb,Illinois Illinois6011 601 15 K. 5 J. F. F. Olmsted, Olmsted, SUNY, SUNY, Plattsburgh, Pittsburgh, New New York York 12901 12901 K.E. K.E. Seifert, Seifert, Iowa Iowa State State University, University, Ames, Ames, Iowa Iowa50011 5001 1 TrIp Trip 4: 4: Archean Gold Occurrences Occurrences and Their Structural Structural Settings Settings Part Part A A (Virginia (Virginia Horn) Horn) Leaders: Leaders: Welsh, Gustavus Gustavus Adolphus Adolphus College, College, St. St. Peter, Peter, Minnesota Minnesota 56082 56082 J. Welsh, England, Rhude Rhude and and Fryberger, Fryberger, Inc. Inc. Hibbing, Hibbing, Minnesota Minnesota 55746 55746 D. England, D. Groves, Groves, Newmont Newmont Exploration, Exploration, Ltd., Ltd., Duluth, Duluth, Minnesota Minnesota 55811 5581 1 Levy, University University of of Minnesota Minnesota Duluth, Duluth, Duluth, Duluth, Minnesota Minnesota 55812 55812 E. Levy, Part B B (Western (Western and and Central Central Vermilion Vermilion District) District) Leaders: Leaders: Hudleston, University University of of Minnesota, Minnesota, Minneapolis, Minneapolis, Minnesota Minnesota 55455 55455 P. J. Hudleston, L. Southwick, Southwick, Minnesota Minnesota Geological Geological Survey, Survey, Saint Saint Paul, Paul, Minnesota Minnesota 55114 551 14 D. L. R. L. L. Bauer, Bauer, University University of of Missouri, Missouri, Columbia Columbia Missouri Missouri 65211 6521 1 Ulland, American American Shield Shield Corporation, Corporation, Duluth, Duluth, Minnesota Minnesota 55802 55802 W. Ulland, Cover: Cover: Anticline in in the the early early Proterozoic Proterozoic Thomson Thomson Formation Formation at at Thomson Dam, view from the east east bank bank of the the St. St. Louis Louis River, River, Thomson just just south south of of the thehighway highway bridge, bridge, looking looking west. west. Drawing Drawing by by Wendell Wendell Wilson. Wilson. �TABLE TABLE OF OFCONTENTS CONTENTS FIELD FIELD TRIP TRIP11 Large Large rhyolites rhyolites ofofthe theKeweenawan KeweenawanNorth NorthShore ShoreVolcanic VolcanicGroup Group J.C. J.C. Green Green.................................................................................... A1- -A15 A15 Al FIELD FIELD TRIP TRIP 22 Penokean Penokean structural structural terranes terranesinineast-central east-centralMinnesota Minnesota T.B. T.B. Hoist Hoist..................................................................................... 61- B17 B17 Bi - FIELD FIELD TRIP TRIP 33 Rock Rock Types Types and and relationships relationshipsofofthe theMellen MellenIgneous IgneousComplex Complex K.W. K.W. Kiewin, Klewin, J.F. J.F. Olmsted, Olmsted, and andK.E. K.E. Seifert Seifert...........................Cl C15 C1- -C15 FIELD FIELD TRIP TRIP44 Archean rocks rocksofofthe theVirginia Virginia General geology and and structure structure of of Archean General Horn HornArea, Area, Northeastern NortheasternMinnesota Minnesota J.L. J.L. Welsh, Welsh, D.L. D.L. England, England,D.A. D.A. Groves, Groves,and and E. E. Levy Levy.......................................................................................... D l3 D l- -D13 Dl Ii Archean Archean gold gold occurrences occurrences and and their their structural structural settings: settings: western western and and central central Vermilion Vermilion district district D.L. D.L. Southwick, Southwick,P.J. P.J. Hudleston, Hudleston,R.L. R.L. Bauer, Bauer,and and - W. W. Ulland Ulland......................................................................................D14 D l 4- D24 D24 •11 �, FIELD FIELD TRIP TRIP#1 #1 LARGE LARGE RHYOLITES RHYOLITES OF THE THE KEWEENAWAN KEWEENAWAN NORTH NORTH SHORE SHORE VOLCANIC VOLCANIC GROUP GROUP Leader: Leader: John John C. C. Green Green Geology Geology Department, Department, University University of of Minnesota, Minnesota,Duluth Duluth INTRODUCTION INTRODUCTION I ) , one of of the the products products of of the the great great The North North Shore Shore Volcanic Volcanic Group (NSVG, (NSVG, Fig. Fig. 1), The Midcontinent Rift of of North Midcontinent Rift North America America (Wold (Wold and and Hinze, Hinze, 1982; 1982; Green, Green, 1983; 1983; Van Van Schmus Schmus and and Hinze, Hinze, 1985), 1985), contains contains aa wide wide variety variety ofofcompositions compositionsofofplateau plateaulavas lavas(BVSP, (BVSP, 1981; Green, 1982a). These range from the predominant olivine tholeiites through These range from the predominant olivine tholeiites through 1981; Green, 1982a). transitional basalts, basalts, basaltic andesites, andesites, andesites andesites and and ferroandesites ferroandesites to to icelandites icelandites and and transitional rhyolites rhyolites (Fig. (Fig. 2). 2). Felsic Felsic rocks rocks (icelandites (icelandites and and rhyolites) rhyolites) are are unusually unusually abundant abundant compared compared to other other Keweenawan Keweenawan plateaus plateaus (e. (e. g. g. Portage PortageLake LakeVolcanics, Volcanics,Mamainse Mamainse Point Point Volcanics, Volcanics, Osler Osier Group, Group, Michipicoten Michipicoten Island, Island, etc.) etc.) and and younger younger plateau plateauprovinces provinces world-wide; they constitute about about 10% of the world-wide; they the southwest southwest limb limb (the (thesection section from fromDuluth Duluthto to Tofte) 25% of of the thenortheast northeastlimb limb(Lutsen (Lutsento toGrand GrandPortage), Portage),as asmeasured measuredby by Tofte) and and about about 25% stratigraphic 2). stratigraphic thickness along the lakeshore lakeshore (Tables (Tables 11 && 2). Airfall Airfall ash and and pumice pumice make make up up aa very very small small percentage percentage of of these these felsic felsic units, units, but but their rarity their rarity is is probably probably exaggerated exaggerated somewhat somewhat by by their their relative relativesusceptibility susceptibility to to erosion erosion and and thus thus their their lack lackofofexposure. exposure. Small Small lava lava flows flows make make up up aa small small portion portion of ofthe thefelsic felsic rocks, rocks, but but the the great great bulk bulk consist consist of of thick thick units, units, several several of of which which can canbe betraced tracedfor forlong long distances. distances. ItIt is is well well understood understood that that magma magmaviscosity viscosity depends depends principally principally on ontemperature temperature and and composition; felsic magmas composition; felsic magmas are predictably predictably many many orders orders of of magnitude magnitude more moreviscous viscous than than basaltic basaltic magmas magmas at at equivalent equivalent stages stages of of crystallization. crystallization. The The most mostcommon common perception for rhyolites perception and expectation expectation for rhyolites is that they they will will erupt erupt as as either eitherdomes domes or orthick, thick, short flows, or as short (high (high aspect-ratio) aspect-ratio) flows, as ash ash or or pumice pumice falls falls or orpyroclastic pyroclasticflows, flows,ininwhich which the the viscous viscous fluid fluid has has been been blown blown apart apart by by its its rapidly rapidly vesiculating vesiculating and andexpanding expanding volatiles. volatiles. Submarine Submarine and and thinner thinner subaerial subaerial ignimbrites ignimbrites are are typically typicallyunwelded, unwelded,whereas whereas thicker thicker subaerial subaerial units have a central central welded welded zone zone (e. (e. g. g. Ross Ross and andSmith, Smith,1961; 1961;Fisher Fisher and 1984; Cas Cas and andWright, Wright,1987). 1987). and Schmincke, Schmincke, 1984; Table Table 33 (from (fromHenry Henryand andothers, others,1988) 1988)summarizes summarizesthe thecharacteristics characteristics typical typical of of pyroclastic pyroclastic flows flows as as contrasted contrasted with with lava lava flows flows and and remobilized remobilized ash ash flows flows (rheoignimbrites). (rheoignimbrites). A-i �Fig.1.1. Generalized Generalized geologic geologic map map of of western western Lake LakeSuperior Superior area, area, showing showing the the North North Fig. Shore Volcanic Volcanic Group Group (NSVG) (NSVG) and and field field trip tripstops. stops. Shore FF A " M Fig.2.2. Alkalies-Iron-Silica Alkalies-Iron-Silica diagram the NSVG NSVG showing showing fields fields ofof rhyolites rhyolites(RHY), (RHY), Fig. diagram for for the icelandites (ICE), andesites (AND), ferroandesites (FA), transitional basalts icelandites (ICE), andesites (AND), ferroandesites (FA), transitional basalts (TB), olivine olivine tholeiites tholeiites(OT), (OT),and andaugite-porphyritic augite-porphyritictransitional transitional basalts basalts(PTB). (PTB). (TB), A-2 A-2 �Table Generalized volcanic Table 1. Generalized volcanic stratigraphy stratigraphy of the southwest southwest limb limb (Duluth Tofte), of the (Duluth to to Tofte), NSVG. From Green, Green, 1979. 1979. # Approx. Approx. (m) tthickness h i c k n e s s (as) Top 1200 >90 >170 >90 >200 1000 315 550 1500 1350 1100 785 3370 70 88720 720 Lithostratigraphic L i t h o s t r a t i q r a p h i c unit unit Lithic L i t h i c character character Middle Keweenawan Keweenawan amygdaloidal Schroeder basalts basalts a a y q d a l o i d a l ophitic o p h i t i c olivine o l i v i n e tholeiites tholeiitem Manitou trachybasalt red—brown granular Manitou t r a c h y b a s a l t flow red-brown q r a n u l a r trachybasalt t r a c h y b a s a l t to to basalt basalt of the (more of t h e Schroeder basalta) basalts) Balmore Bay llava. mostly Belmore avas m o s t l y quartz q u a r t z tholeiita., t h o l e i i t e m , other o t h e r basalts basalt8 Palisade pink, P a l i s a d e rhyolite r h y o l i t e flow flow ggray r a y to to p i n k , porphyritic p o r p h y r i t i c rhyolite rhyolite Baptism River lava. mixed lavas. lavas l a v a s , mostly mostly basalta, b a s a l t s , one f e l s i t e Beaver Bay Bay iintrusive Beaver n t r u s i v ecomplex complex Gooseberry River River bbasalta mixed one ffelsite asalts mixed bbasalta, a s a l t s , one elsite Gooseberry L a f a y e t t e Bluff. B l u f f , Silver S i l v e r Creek Creek C l i f f intrusions intrusions Lafayette Cliff TwoHarbors Harbor,f i fina—grained 'm.laphyre.,"some someq uquartz Two n e - g r a i n e d b a sbasalt. a l t s "melaphyres," a r t z t htholeiite. oleiites Larsasonto pophtic Larsmont h i t i c basaits basalts amyqdaloidal o p h i t i c o l i v i n e t h o l e i i t s Stony S t o n y Point-Knife Ia I s lland a n d diabas. d i a b a s e intrusion intrusion mixed basalta, Sucker River basalt. basalts b a m a l t s , mostly mostly ophitic ophitic mixedbbasalts and aandesites, somef efelaite. Lakewood basalt. basalts mixed a s a l t s and n d e s i t e s , some laitem Lester River diabase Lester R iver d iabase sill Lakeside Lakeaide lavas lavas mixed basalts, b a s a l t s , andasites, andemitem, falaites felmites Endion Endion diabas. diabame m i l l Leif Ericgon Loif Ericson Park Park lavaa lava* mixed bbasalta. a s a l t s , andesites andesites Duluth Complex Complex Lower Keweenawan Keweenawan Ely's basalt. E l y ' s Peak Peak bamalts p o r p h y r i t i c , d i a b a s i c , and o p h i t i c b a a a l t s Total Total Base one felsite asygdaloidal ophitic olivine thol.iita sill gill porphyritic, diabasic. and ophitic basalt. quartz q u a r t z sandstone sandstone Nopeming Sandstone Sandstone Nopeminq Anqular unconformit '5iddle Precambrian slate and graywack. Thomson Formation Table 2. Generalized Generalized volcanic Table 2. volcanic stratigraphy stratigraphy of the northeast northeast limb limb (Lutsen (Lutsen to Grand to Grand Portage), NSVG. NSVG. From Portage), From Green, Green, 1979. 1979. Approx. thickness Approx. thickness (m) (m) llthostratl9raphic L i t h o s t r a t i g r a p h i c unit unit Lithic L i t h k character character Middle MiddleKeweenawan Keweenawan Top TOP Lutsen basal basalts Lutsen ts Olivine O l i v i n e basalts, basalts, oolivine l i v i n e tholelites tholeiites 50 Terrace Point Point basalt b a s a l t flow flow Thomsonite-bearingophi ophitic basalt Thomsontte-bearing tic b asalt 95 GoodHarbor Harbor b8ay Good y aandasites ndtsites Brown, pporphyritic o r 0 h y r i t i C andesite, andesite. trachyandesite trachyandesite 310 310 110 110 Breakwatertrachybasalt trachybasaltflow flowo or Breakwater r ssill ill Brown. coliannar, granular granular trachybasalt Brown, col&ar. 155 155 GrandMarais Maraisf efelsites Grand lsites Pink, red, Pink, red, gray gray pporphyritic o r p h y r i t i c rrhyolite h y o l i t e and and ffelsite elsite 185 185 550 Croftville C r o f t v i l l ebasalts basaltsand andandesites andesites Devil Track Track ffelsites Oevil e l s i tes RedCCliff Red l i f f basalts basalts Kimball Creek Creekf efelsites Kimball lsites Marr Marr Island lavas lavas 310 310 Naniboujox Naniboujou basalts basal t s Granular-diabasic basalts Granular-diabdsic basalts Brule Brule River River rrhyolites h y o l 1tes Pink tto gray pporphyritic Pink o gray o r p h y r i t i c rrhyolite hyolite 310 310 120-275 120-275 400 400 1070 1070 Various fine-grained fine-grained basalts and Various and bbasaltic a s a l t i c andesites andesites Aphyric and andpporphyritic Aphyric o r p h y r i t i c rrhyolite h y o l i t e flows flows Amygdaloida.oophitic olivine Afliygda1oida1, phitic o l i v i n e basalts basalts Pink tto tan, porphyritic Pink o tan, p o r p h y r i t i c felsites, f e l s i t e s , icelandites icelandites Mixed tholelitic Mixed t h o l e i i t i c basalt, basalt, andesites, andesltes, felsites felsites Hovland diabase diabase complex complex Lower Lower Keweenawan Keweenawan 1225((est.) 1225 est.) Mixed porphyritic basalt, basalt, trachybasalt, andesite. rrhyolite trachybasalt, andesne, hyolite Mixed porphyritic Hoviand H0vldnd lavas lavas Reservation River diabase Reservation diabase complex complex (Middle (MiddleKeweenawan) Keueenawan) 610 610 80 80 1380 1380 722UTotal Total flows 772'6 Base RedRock Rockr hrhyolite flow Red y o l i t e flow Red,pporphyritic Red, o r p h y r i t i c rrhyolite hyolite DerondaBay Bayandesite andesite flow flow Deronda Gray-brown, Gray-brown, aphyric andesite andesl t e Grand Portage basal basalts Grand Portage ts Mixed Mixed t tholeiltic h o l e i i t i c basalts; basalts; porphyritic p o r p h y r i t i cbasalts b a s a l t s locally l o c a l l yata base t base Disconformity Cross-bedded quartz sandstone Puckwunge Formation Disconformity Middle Precambrian Shal. and graywacke Rove Formation A- 3 �TABLE 3. CHARACTERISTICS CHARACTERISTICS COMMONLY USED USED TO TO DISCRIMINATE DISCRIMINATE RHYOLITE LAVAS FROM FROM IGNIMBRITES IGNIMBRITES (FROM HENRY ET AL., 1988) 1988) Common in conventional conventional ignimbrites ignimbrites rhyolite Common in Common in rhyolite rheoignimbrites rheoignimbrites lavas lavas and in in Fiamme Fiamme Flow banding banding Ramp structures Eutaxitic texture texture structures Elongated vesicles fragments vesicles Abundant lithic fragments Autobreccias Nonwelded tops, tops, bottoms, sides Autobreccias Vitrophyres at or near tops Gradual thinning thinning at at edges of units Vitrophyres at tops units Lengths generally Wide areal extent of individual c20 km.* km.* generally much <20 individual units units High aspect ratio* Low aspect ratio ratio Glass shards in thin thin section section Broken pheno's, different sizes Gas elutriation pipes pipes *Unlike lava flows, may have have dimensions similar to to those rheoignimbrites may dimensions similar those of of *Unlike rhyolite rhyolite lava flows, rheoignirnbrites other ignimbrites ignimbrites Recently, many many rhyolites rhyolites have Recently, have been been described described which which show show anomalous anomalous behavior behavior These may according according to these these models. models. These may cover cover wide wide areas areas with with low low aspect aspect ratios, ratios, indicating high mobility, mobility, yet yet do do not show some some of of the the common common features features of of ash-flow ash-flow tuffs. tuffs. For some, appears to to have have been a factor For some, high alkali content content (peralkalinity) (peralkalinity) appears factor ininlowering lowering the viscosity viscosity (e. g. Price Price and and others, others, 1986). 1986). For For others, others, aa high high eruptive eruptive temperature temperature and and high rate rate of of effusion effusion appear appear to to have have been been important important contributors; contributors; an increase increase of 100 100 degrees degrees C. will lower lower the the viscosity viscosity about about an an order order ofofmagnitude magnitude (Ekren (Ekren and andothers, others, 1984; relatively low low SiO2 SiO, content content seems seems to be be 1984; Bonnichsen Bonnichsen and Kauffman, Kauffman, 1987). 1987). A relatively A survey of widespread lavas and lava-like units common to many many high-mobility high-mobilityflows. flows. survey of widespread lavas and lava-like units in southwest Idaho and trans-Pecos Texas (Bonnichsen (Bonnichsen and Kauffman, Kauffman, 1987 1987 and and Henry Henry and others, SiO2contents contentsininthe the range range 68 68 to 74%, others, 1988) 1988) shows shows volatile-free volatile-free SiO, 74%, whereas whereas rheoignimbritesinin the the same same areas areas have values of of 72 72 to 77%. rheoignimbrites have S1O2 Si02 values 77%. Many ash ash flows, flows, froth particles, reconsolidate during during and and after made of hot, hot, relatively relatively low-viscosity low-viscosity froth particles, reconsolidate after made of emplacementtoto form form aa devolatilized, "reconstitutedlava" lava"that that can can flow flow en emplacement devolatilized, "reconstituted en masse masse (a (a This flowage, and any subsequent crystallization or devitrification, can rheoignimbrite). rheoignimbrite). flowage, and any subsequent crystallization or devitrification, can Thus the distinction the end result obliterate primary pyroclastic obliterate pyroclastic textures. textures. Thus distinction between between the result of of can become effusive eruption an explosive eruption eruption and and an an effusive eruption can become greatly greatly diminished. diminished. Bonnichsen and Kauffman Kauffman (1987) (1987) and and Bonnichsen and others Bonnichsen and Bonnichsen and others (1988) (1988) have have suggested suggested by which which they they may be recognized, some criteria by recognized, but they and others, notably notably Henry Henry is still still low-aspect-ratio units whose whose origin origin is (1988), have described described widespread, widespread, low-aspect-ratio et al. al. (1988), unclear. unclear. The felsic units units in the the NSVG NSVG show show evidence evidence of of aa wide wide variety variety ofoferuptive eruptive and and The felsic emplacement styles, including large, emplacement large, problematical, problematical,low-aspect-ratio low-aspect-ratioflows. flows. This field trip units throughout throughout the the NSVG section will examine examine several several units section and the physical physical evidence evidence for It is designed their mode mode of of emplacement. emplacement. It designed as aa long long one-day one-day trip, trip, starting starting at atDuluth Duluth Descriptions of of field trip and nearly reaching reaching Grand Portage Portage before before returning returning to to Duluth. Duluth. Descriptions stops of the North stops in other other lithologies lithologies of North Shore Shore (mainly (mainly the the plateau plateau basalts) basalts) can can be be found found in Green, Green, 1979 1979 and 1987, 1987, and and aa discussion discussion of of the the physical physical volcanology volcanology of of the the NSVG NSVG appears geologic map map is also :250,000) geologic also available available (Green, (Green, appears in Green, Green, 1989. 1989. A A regional regional (1 (1:250,000) 1 982b). 1982b). Chemical analyses analyses of of these these felsite felsite units units are are presented in in Table Table 4. 4. A-4 �able Table 4.Chemical 4.Chemical analyses analyses of of felsic felsic volcanic volcanic units units at field field trip trip . stops, recalculated recalculated volatile-free volatile-free A Si02 Si0, Ti02 TiO, A1203 Fe203 -203 FeO FeO MnO Mno MgO MgO CaO CaO Na20 Na20 1(20 K20 P205 p.0. Zr02 ZrO, B C E D F G H J I 75.11 75.41 68.30 75.46 74.85 73.08 69.92 63.81 62.07 72.54 .28 .22 .70 .24 .40 .40 .53 1.11 .99 .25 12.45 11.99 12.76 11.10 11.62 11.76 12.52 12.24 15.09 12.02 1.58 .84 1.61 1.66 8.34 2.79 2.51 .92 3.13 4.09 1.25 3.04 5.79 2.95 3.33 .74 1.63 2.06 6.00 3.64 .03 .06 .32 .01 .07 .30 .09 .27 5.59 2.13 5.92 1.95 2.69 5.68 .02 .03 .01 .06 .08 .12 3.28 .05 .30 .51 .04 .60 .88 .04 .54 .51 .10 .51 .51 1.96 5.72 2.22 5.09 3.54 5.50 .04 .06 .04 — .08 .12 .18 .88 .05 .21 .71 3.43 5.37 1.43 2.26 4.12 4.23 3.67 3.77 4.04 3.86 4.15 .09 .28 .52 .05 — — — A. Stop Creek rhyolite rhyolite (ave. (ave. of of two two analyses). analyses). Stop 1: 1: Tischer Creek B. Stop 2: 42nd Ave E. ignixnbrite (D-87). Stop 2: 42nd Ave E. ignimbrite (D-87). C. Stop Stop 2: 2: icelandite icelandite flow flow beneath beneath BB (0-91). (D-91). D. Stop Palisade rhyolite rhyolite (F-201). (F-201). Stop 3: 3: Palisade E. Stop Stop 5: 5: Silver Silver Beaver Beaver felsite felsite (F-278). (F-278). F. Stop Stop 6: 6: Devil Devil Track Track rhyolite rhyolite (ave. (ave. of of three). three). G. Stop 7: Kimball Creek rhyolite (ave. of Stop 7: Kimball Creek rhyolite (ave. of five). five). H. Stop Stop 8: Rangeline icelandite icelandite (MI-2). (MI-2). 8: Rangeline I. Stop Deronda Bay Bay andesite/icelandite andesite/icelandite (MC-3b). (MC-3b). Stop 9: 9: Deronda J. Stop Rock rhyolite rhyolite (MC-7). (MC-7). Stop 9: 9: Red Rock FIELD FIELD TRIP TRIP STOPS STOPS STOP STOP 1.1. Tischer Tischer Creek Creek at atSuperior SuperiorStreet, Street,Duluth. Duluth. Here the stream stream has has eroded eroded aagorge gorge through through the the small-jointed small-jointed Tischer Tischer Creek Creek Here rhyolite, rhyolite, which is is approximately approximately 300 300 m mthick. thick. This This unit unitcontains containsmany manythin, thin, discontinuous color color bands bands or or laminae laminaethat thatresemble resemblewell-flattened well-flattenedfiamme, fiamme, discontinuous and moderately moderately abundant, abundant, small small xenoliths; xenoliths; both both suggest suggest an anignimbrite ignimbriterather rather and than than aa lava. lava. ItIt also also shows shows occasional occasional open, open, quartz-lined quartz-lined ororquartz-filled quartz-filled tension tension fractures fractures that that must must have have formed formed after after welding. welding. Devitrification Devitrification has has destroyed whatever microscopic microscopic shard or pumice pumice textures were were once once present. present. destroyed The Iaminae laminae (fiamme?) (fiamme?) are generally parallel base of the the unit, unit, but but The are generally paralleltoto the the base locally locally show show folding, folding, indicating indicating flow flow after after deposition deposition and and welding. welding. This This flow flow isis thus probably probablya a"High-temperatureTM "High-temperaturew type according to to Bonnichsen Bonnichsen et et al. al. thus type according (1988). (1988). The The base base of of this thisunit unitisisintruded intruded(and (andprobably probably melted) melted) by by the thethick thick Endion Endion diabase diabase sill. sill. A-5 �STOP STOP 2. 2. Lake Superior Superior shore at at foot foot of of 42nd 42nd Avenue Avenue East, East,Duluth. Duluth. At At this this locality locality isisthe thecontact contact between between two two felsite felsite units, units, an anicelandite icelandite overlain overlain by aa rhyolite the trail reaches rhyolite (Fig. (Fig. 3). 3). Where Where the reaches the shore shore there there are are abundant abundant exposures of the the lower exposures of lower part of aa thick thick (about (about 60 60 m) m) rhyolitic rhyolitic ignimbrite, ignimbrite, full full of small small (1-4 (1-4 cm) cm) slabs slabs and and chips chips ofofwhat whatwere wereprobably probablypumice, pumice, in in aa fine-grained, fine-grained, devitrified devitrified matrix matrix now devoid devoid of of recognizable recognizable shards. shards. Alteration Alteration at to contemporaneous contemporaneous at different different stages, stages, probably probably including including that due due to degassing degassing and later later burial burial metamorphism, metamorphisml has has created created distinct distinct color colorcontrasts contrasts between the the fragments fragments and andmatrix. matrix. Several xenoliths xenoliths are present, present, including including a few blobs blobs (bombs) (bombs) of of chilled chilled mafic mafic lava. lava. The The pumice pumice fragments fragments are not not obviously flattened parallel paralleltoto the the base base of obviously flattened of the the flow, flowl even even though though this this is aa fairly thick that it was thick unit. unit. This indicates indicates that was probably probably erupted erupted at at aarelatively relatively low low temperature et aI.3 al.'s Type Type L) and did temperature (Bonnichsen (Bonnichsen et did not not weld weld ororeven evencompact compact very very much much except except at at the the very very base. base. A very very similar similar texture texture is found found at at the the base base of of the the large, large,Tertiary Tertiary caldera-filling caldera-filling Gomez Gomez Tuff Tuff ofoftrans-Pecos trans-Pecos Texas Texas (Price (Price et et al., ah, 1986). 1986). the impassable impassable cliff cliff up the shore shore to to the the northeast northeast this this rock rock isisdirectly directly In the overlain by another rhyolite with a distinctly different structure. overlain by another rhyolite with a distinctly different structure. Above Above aa narrow narrow transition transition zone zone of of aafew fewcentimeters, centimeters, itit contains contains thin, thin,discontinuous discontinuous color color bands bands and and lamellae, lamellae, rather rather like the the Tischer Tischer Creek Creek unit, unit, but with with aa strong strong lineation lineation of of small small wrinkles wrinkles and and open open fold fold axes. axes. These features features suggest ash flow, resulting suggest aa high-temperature high-temperature ash resulting in in thorough thorough welding welding and and bulk bulk flow, flowl after after emplacement, emplacement, in the direction direction of of the the lineations lineations -- aarheoignimbrite rheoignimbrite of of Bonnichsen Bonnichsen et et aL's aL1sType Type H. H. In the the other other direction direction (SW) (SW) along beach, the basal 22 or or 33 meters meters of of In along the the beach, the basal the the main main unwelded unwelded ash ash flow flow isis not not exposed, ex~osed,but but several several loose loose blocks blocks of of laminated laminated rock, rock, found found only only inin this this vicinity, vkinity,. appear appear to to be be the the strongly strongly compacted compacted and welded welded basal basal portion portion of of this this unit. unit. - roiiLCI...z— J • t- —— uQ(óec pt-topt(i (D-87) - :.. , 4to.' \tcCA(&r .çe& top ociâ, %eøtD (D-qI) Fig. Fig. 3.3. Diagrammatic columnarsection sectionatat field field trip trip Stop Stop 2, 2, lakeshore Diagrammatic columnar lakeshore at foot foot of of 42nd 42nd Ave Ave East, East, Duluth. Duluth. A-6 �Just beyond It beyond this zone is is the the top top of of aa130-rn 130-mthick thickporphyritic porphyritic icelandite. icelandite. It to frothy and the the top meter is highly highly vesicular vesicular to frothy but not pumiceous, pumiceous, and meter or or two two are are penetrated arkosic sandstone sandstone dikes dikes that filled filled in open open cracks cracks in the the flow flow penetrated by by arkosic top before top before eruption eruption of of the the overlying overlying ignimbrite. ignimbrite. The The vesicles vesicles (now (now largely largely calcite are stretched to varying calcite amygdules) amygdules) are stretched to varying degrees, degrees, and large large flowage flowage folds folds are evident. This vesicularity dies out to the southwest as the rock becomes evident. This vesicularity dies out southwest as the rock becomes massive and massive and granular. granular. There is is little brecciation. These textures textures and and brecciation. These structures indicate indicate that this unit unit was was a large large and and fairly fairly hot hot and and rapidly rapidly emplaced lava flow. None of these units None of units can can be be traced traced inland inland for for more more than than aafew fewkilometers kilometers because of glacial ic intrusions. because glacial drift drift cover cover and and intersection intersection by bylarge largemat mafic intrusions. For more details Duluth units units see see Motamedi, Motamedi, 1984. 1984. details on on these these Duluth STOP 3. 3. Palisade Palisade Head, Headl Lake Lake County County (Figs (Figs 4,5). 4?5). This scenic This scenic promontory promontory is made made of of a 90+ 90+ m mthick thickmassive, massive, porphyritic The same rhyolite. The rhyolite. same unit unit forms forms the the prominent prominent Shovel Shovel Point Point to to the the northeast northeast (stratigraphically lower flows (stratigraphically lower flows are are exposed exposed in in the Baptism Baptism River River basin basin in in between), and itit can between)> and can be be traced traced from from East East Beaver Beaver Bay Bay (to (to the the southwest) southwest) at at See also least least 23 km km along along strike strike to to the the northeast. northeast. See also Miller, Miller, 1987 1987 and and 1988 1988 a!.?1987 1987 for for detailed detailed local local geology. geology. and Miller et al., Throughout most of of its Throughout most its extent extent the the Palisade Palisade rhyolite rhyolite closely closely resembles resembles this this exposure with no exposure at Palisade Palisade Head: massive, massive, with no evidence evidence of of pyroclastic pyroclastic texture, texture, Under the only only rare rare xenoliths, xenoliths, and and with with only rare rare broken broken phenocrysts. phenocrysts. Under the microscope after microscope it shows fine-grained, fine-grained, poikilitic quartz pseudomorphic after tridymite, implying implying crystallization crystallizationwell well above above 870 870 degrees degrees CC.. At At the base, basel the the tridymitel only exposure the southwest end of exposure (in (in the southwest end of this this hill) hill) shows shows flow flow laminations, laminations, locally much folded scale, in meters. locally much folded on a small small scale, in the the lowest 11 to 3 meters. At the Elsewhere, larger larger folds folds in laminations Elsewhere, laminations occur occur farther above above the the base. base. At the vesicular (amygdaloidal) the only is vesicular top, the only exposure exposure is (amygdaloidal) but but not not pumiceous pumiceous or or These characteristics suggestan an origin origin as as aa large, brecciated. These characteristics suggest large, unusually unusually mobile, hot However, one one outcrop outcrop in in the interior mobile, hot lava lava flow. flow. However, interior shows shows small, small, discontinuous bands or or streaks streaks that that suggest suggest relict relict fiamme, fiamme? and another another (next (next discontinuous bands stop) contains abundant discontinuous streaks suggesting strongly flattened stop) contains abundant discontinuous streaks suggesting strongly flattened fiamme. fiamme. The Theunit unitmay maybe beaahigh-temperature high-temperaturerhebignimbrite. rheoignimbrite. - - - - - - - - - - - - - - - - py or o r .,reccto.. breccia +op + o ~ U M ~ &WtrLttOI'%S fLdQc rir1esVL (F.wf) qntL o.ttc iior.$ bsLt ou.' Fig. 4. 4. Diagrammatic columnar columnar section sectionofof Palisade Palisade rhyolite, rhyolite,field fieldtrip trip Stops Stops 33 and 4. Diagrammatic A-7 �Fig. Fig. 5.5. View View to to the the southwest southwest of of Palisade Palisade Head Head from from the the top top of of Shovel Shovel Point Point(both (both made Lower cliffs cliffs in in middle middle distance distance at at made of of columnar-jointed columnar-jointed Palisade Palisaderhyolite). rhyolite). Lower right right (at (at Baptism Baptism River River mouth) mouth) are are made made of of the the Silver Silver Beaver Beaver felsite felsite (Stop (Stop5), 5), stratigraphically stratigraphically beneath beneath the thePalisade Palisaderhyolite. rhyolite. STOP STOP 4. 4. Road Road cuts cuts ininPalisade Palisaderhyolite, rhyolite,Minn. Minn.Highway Highway1,1,Illgen lllgenCity. City. Here part part of of the the upper upperportion portion of of this thisunit unitisisexposed, exposed,showing showing inincontrast contrasttoto Here typical typical outcrops, outcrops, aa breccia breccia made made of of diversely diversely oriented oriented blocks. blocks. Each Each block block isis itself flow-laminated. itself flow-laminated. The The laminations laminations appear appear discontinuous discontinuous and and may may be be strongly strongly flattened flattened fiamme. fiamme. Clearly Clearly the the breccia breccia was was formed formed after after cooling cooling across the the ductile-brittle ductile-brittle transition, transition, during during late-stage late-stage movement movement of of the theflow. flow. across STOP STOP5.5. Silver-Beaver 6). Silver-Beaver felsite felsite at at the the Baptism BaptismRiver River(Fig. (Fig.6). (Park (Park at at Rest RestArea AreaatatTettegouche TettegoucheState StatePark Parkheadquarters). headquarters). ,— ) — dbjO.f 51 ,bvded, -gcca. .4 —— - oaded (ç. 27 ) ç.•-' -— = -- ? t6ed {- breccu, Fig. Fig.6.6. Diagrammatic Diagrammatic section section of of Silver SilverBeaver Beaverfelsite, felsite,Stops Stops5a 5aand and5b, 5b,Baptism Baptism River. River A-8 A-8 �A. A. Walk Walk across across Baptism Baptism River River on foot foot bridge, bridge?then left left through through woods woods on on an an unofficial unofficial trail to to aahigh highoutcrop outcrop overlooking overlooking the the river rivermouth mouthatatthe thelakeshore. lakeshore. Here Here is is fairly fairly typical, typicall banded, banded, fine-grained, fine-grained, weakly weakly porphyritic porphyritic to to aphyric aphyric felsite, felsite?dipping dipping steeply steeply to the the east east toward toward the the lake. lake. Across Across the river river the the unit unit is along the the top top of the shore is aatuff-breccia tuff-breccia at atwater water level. level. Follow Follow along shore cliff cliff to to the the south south to to the the first firstbeach-cove. beach-cove. Here Here the basal basal portion portion is is exposed, exposed, overlying overlying aa pale, zone that may pale?chalky-clayey chalky-clayey zone may be be either either altered altered airfall airfall ash ash or or fault fault gouge. gouge. The to 5 m The basal basal 33 to m isis an an irregularly irregularly fractured, fractured? unwelded unwelded tuff-breccia tuff-breccia or or lapilli-tuff lapilli-tuff containing containing fragments fragments of of various various once-glassy once-glassy felsite felsite textural textural types types which which include include pumice, pumice?spherulites, spherulitesl perlitic perlitic cracks, cracks?etc., etc.?considerably considerably altered altered to to kaolinite This kaolinite and and quartz. quartz. This zone zone isis overlain overlain by by what what appears appears to to be be agglutinate, containing faint faint blobby blobby areas areas (Fig. (Fig. 7) 7) and and grading grading up up into into more more agglutinate? containing typical, typicall weakly weakly flow-banded, flow-banded?uniform, uniform?finely finely crystalline crystalline felsite. felsite. Across very discordant, steeply steeplySE-dipping SE-dipping Across the the beach beach to to the thewest westisisa a very discordant? contact contact where where aa laminated laminated basaltic basaltic andesite andesite overlies overlies the the rubbly, rubbly,sand-matrix sand-matrix top top of of another another flow. flow. AA fault fault separates separates these these rocks rocks from from the the felsite. felsite. Return Return to to highway. highway. Fig. Deformed agglutinate agglutinate (?) (?) blobs blobs inin lower lower part part of of the the Silver Silver Beaver Beaver felsite, felsite? Fig.7.7. Deformed lakeshore southwest southwest of of Williams Williams Creek, Creek?Silver Silver Bay Bayarea. area. lakeshore B. After After crossing crossing back back to to the the north north side side of of the theriver, river?go go west west across across the the B. highway and and up up the the trail trail (via (viastairs) stairs) along along the the top top ofof the thebank banktoto aa long longflight flight highway of of wooden wooden steps steps leading leading down down to to the the river riveragain. again. The The outcrops outcrops here here are are near near the the stratigraphic stratigraphic middle middle of of the the Silver Silver Beaver Beaver felsite. felsite. Faulting Faulting has has dropped itit down down relative relative to to its itsexposures exposures at at the the river rivermouth, mouth, but but itit still still dips dips dropped east. east. The The uniform, uniform?typically typically planar planarlamination lamination isis characteristic, characteristic?as as isis the the fine-grained thin section section fine-grained (rather (rather than thandense-aphanitic), dense-aphanitic), aphyric aphyric texture. texture. InIn thin quartz quartz pseudomorphs pseudomorphs after after tridymite tridymite are are abundant, abundant?and andsmall small (1-3 (1-3 mm) mm) spherulites are not uncommon. spherulites are not uncommon. A-9 �, Go downstream the water downstream (if the water level level is is low low enough), enough)?working working toward toward the the top top of the of the unit. unit. A few few meters meters from from the the top top the the flow flow starts starts totoacquire acquire small, small, irregular vesicles, then then becomes becomes broken broken up up in a flow-top irregular vesiclesl flow-top breccia breccia with with lineated lineated vesicles and and ashy This is overlain vesicles ashy gray gray material material between between the the blocks. blocks. This overlain by aa laminated, red tuff tuff only only aa few laminated, red few cm thick, thick, which which lenses lenses in and out. out. These These felsic felsic rocks by aa thin, large rocks are are then then overlain by thinl amygdaloidal basalt basalt flow with with large plagioclase phenocrystsconcentrated concentratedatatthe the base; base; its its top top is intruded by by aa plagioclase phenocrysts is intruded thin black diabase diabase sill. sill. The to have have begun The Silver Silver Beaver Beaver felsite felsite is is interpreted interpreted to begun with with eruption eruption of of glassy ash ash and pumice glassy pumice at aa moderate moderate or or slow slow rate, ratel producing producing an an unwelded unwelded base, base, but then then changed changed to to agglutinate agglutinate as as hotter hotter or or less lessvolatile-rich volatile-richmaterial material became available. available. The The bulk bulk of of the the unit unit was wasproduced produced as aseither eitheragglutinate agglutinate and flowed as aa unit after or a hot hot ash flow that coalesced and (Type V) V) settling/accumulation - perhaps perhaps aa Very High High Temperature (Type settling1accumulation It subsequently in subsequently crystallized rheoignimbrite of Bonnichsen It crystallized in rheoignimbrite of Bonnichsen et et al., al., 1988. 1988. place to tridymite tridymite and and feldspar. feldspar. Climb back up to the trail and and walk walk out out to to the the highway. highway. As the the trip trip progresses progresses up up the the shore shore we we pass passupwards upwards stratigraphically stratigraphically to the exposed the exposed top in in the the Tofte-Lutsen Tofte-Lutsen area area in in southwestern southwestern Cook Cook County. County. An unknown thickness of of lavas lavas was was erupted on top of unknown thickness erupted on of this this sequence sequence and and now now underlies the lake underlies the lake or was was eroded eroded off off before before the the Portage Portage Lake Lake Volcanics Volcanics or or Upper Keweenawan Keweenawansandstones sandstoneswere werelaid laiddown downon on top top of of the Upper the NSVG NSVG here. here. Beyond Lutsen Lutsen we we start descending Here the strata Beyond descending in the the "northeast "northeast limb". limb". Here strata lakeshorel and and dip dipsouth-southeast south-southeast to to south south strike more more easterly easterly than than the the lakeshore, strike (Fig. 8). 8). Grand Marais sits largely largely on on another another large, largel small-jointed small-jointed rhyolite rhyolite complex complex Grand Marais which has been been more more easily easily eroded eroded (to form the the harbor) harbor) than than the the overlying overlying which has "Breakwater trachybasalt". trachybasalt". This thick transitional transitional basalt basalt unit unit that that makes makes This is aa thick the "island" and breakwater breakwater and a cuesta cuesta to to the the west. west. Fig. 8. 8. Generalized geologic geologic map map of of the northeastern northeastern tip of Minnesota showing Generalized Minnesota showing the major major units units of of the the NSVG. NSVG. (from (from Green, Green, continuity along continuity along strike strike of of some some of of the 1979). 1979). A- 10 A-10 �STOP 6. 6. Devil Devil Track Track rhyolite, rhyolite, Highway Highway 61 61 opposite opposite Five Rock east east of of Grand Grand Five Mile Mile Rock Marais. Marais. - This exposure, exposure, at at an an abandoned abandoned wave-cut wave-cut cliff cliff of of the the 5000-year 5000-year old old Nipissing Nipissing stage stage of of Lake Lake Superior, Superior, is is fairly fairly typical typical of of this thislarge largerhyolite. rhyolite. This unit unit can can be be traced for for about about 40 km km to to the the west, west, and and isisabout about 250 250 m m thick. thick. Neither its its traced top or or base baseisisexposed, exposed,and andallalloutcrops outcropsshow showthis thisweakly weaklyflow-laminated, flow-laminated, fine-grained, fine-grained, aphyric to very very weakly weakly porphyritic porphyritic character, character, rather similar to the the Silver Beaver Beaver felsite. felsite. Thin sections sections here here also also show show quartz quartz paramorphs paramorphs after after primary tridymite. tridymite. Tom Tom Fitz Fitz (1988) (1988) has has found found that that the the grain grain size size ofofthese these tridymite toward the the center tridymite plates plates increases increases toward center of of the the unit, unit, implying implying that that itit crystallized as a simple crystallized as simple cooling cooling unit unit (Fig. (Fig. 9). 9). No No significant significant breccia breccia facies facies has been been found. found. The The wide wide extent, extent, lack lack of of breccia breccia or or other other viscous viscous flow flow features features other than than rare rare lineations, lineations, aphyric aphyric texture, texture, and and crystallinity crystallinity suggest suggest that that this this was was aavery veryhot hotpyroclastic pyroclasticflow flowthat thatcompletely completelyconsolidated, consolidated, after after emplacement, to pool ofofdevolatilized devolatilized rhyolite rhyolite magma magma that that crystallized crystallized inin emplacement, to a pool place. place. Assuming that its overall shape was was aa segment of aa sphere Assuming that overall original original shape segment of sphere (it (it appears to pinch appears to pinch out out at at the the western western end end but but is is thick thick through through much much of of the the rest), rest), and and that that its its center center was was at at the the present present lakeshore lakeshore (half (half now now underlies underlies the the lake), lake), itit would would have have had hadan anoriginal originalvolume volumeofofabout about600 600km3. km3. STOP STOP 7. 7. Kimball Creek Felsite, Felsite, Lake Lake Superior Superior shore north north of of Red Red Cliff. Cliff. Here we are are near near the the top top ofofanother anothervery very large large(366 (366mmthick) thick)rhyolite. rhyolite. The The point point at at Red Red Cliff Cliff to to the the south south isisheld heldup upbybya asequence sequenceofofoverlying overlyingolivine olivine tholeiite tholeiite basalts. basalts. This This rhyolite rhyolite isisweakly weakly plagioclase-phyric, plagioclase-phyric, but but otherwise otherwise the the bulk bulk of of this this flow flowisisfine-grained, fine-grained,crystalline, crystalline, and and massive, massive, rather rather like like the theDevil Devil Track Track rhyolite. rhyolite. This This unit unit also also shows shows aa network network of of tridymite tridymite paramorphs paramorphs in inthe the groundmass (Fig. 10), groundmass (Fig. lo), whose whose length length is greatest greatest near near the center center of of the the flow flow (Fig. as a simple (Fig. 9), 9), again again indicating indicating primary primary crystallization crystallization as simple cooling cooling unit. unit. Here (and elsewhere) near the top, however, Here (and elsewhere) near the top, however, itit isis aphanitic aphanitic and and contains contains discontinuous color bands bands and discontinuous color and lamellae lamellae that that are are probably probably flattened flattened and and deformed deformed pumice pumice fiamme. fiamme. These structures structures are are preserved preserved here near the the top top because because of of the the rapid rapid cooling cooling after after welding, welding, preventing preventing the the primary primary crystallization which obliterated crystallization which obliterated them them in in the theinterior. interior. Unfortunately Unfortunately the top top several several meters meters are not not exposed, exposed, as as isis typical typical ofof these theselarge largerhyolites. rhyolites. One One possible possible inference inference is that that the the top topmay maycontain containeasily easilyweathered weatheredand anderoded, eroded, unwelded unwelded pumice pumice and and ash. ash. The base base isis not not exposed exposed either, either, but but aa few few meters meters above, above, the the unit unitshows showsflow-folding flow-folding ofofthin, thin,discontinuous discontinuous streaks streaks and and lamellae lamellae (fiamme?) (fiamme?) (Fitz, (Fitz,1988). 1988). This This unit unit isis thought thought to to have have the the same same origin origin as as the the Devil DevilTrack Trackrhyolite: rhyolite:aahigh-temperature high-temperaturerheoignimbrite. rheoignimbrite. For more more details details on on these these two twolarge largerheoignimbrites rheoignimbrites see see Fitz Fitz(1988). (1988). For STOP STOP 8.8. Rangeline Rangeline icelandite, icelandite,11 1/2 112 mi. mi. EE of ofKadunce KadunceCreek Creek (River). (River). These These road road cuts cuts show show fairly fairly typical typical textures textures and and structures structures of of aa large large (40 (40 m) m) icelandite icelandite lava lava flow. flow. Toward Toward the eastern end end is is the the massive massive lower lower part, part, the eastern to fine-grained and porphyritic; aphanitic to fine-grained and porphyritic; round round amygdules amygdules gradually gradually increase increase aphanitic toward the west. toward the west. Neither Neither top nor nor base base are are exposed, exposed, but but another another icelandite icelandite aa few few miles miles to to the the northeast northeast shows shows strongly strongly stretched stretched amygdules amygdules inin an an aphanitic upper upper crust. crust. Phenocrysts Phenocrysts are areofofplagioclase, plagioclase,ferroaugite, ferroaugite,Fe-olivine, Fe-olivine, aphanitic and and magnetite. magnetite. A-il �£9 0.1 00 I- 100 100 200 300 200 300 V.,tiCal V u t k l dislanc. (inane* abov. above baa. b a r of unit (m). Sotto. Bottom L..gth 01 quwtz Cty$ta*. VS. 350 350 Top SI:.tlgv.plvc P0S.I0fl I' th• Kanbal COsdit rflyodt•. Anhedral quartz q u a r t z masses m a s s e s gradational g r a d a t i o n a l to t ogroups groups Anhedral fused plates plates in inoptical o p t i c a lcontinuity. continuity. oo ffused . 41 0.15 • 4o• 0.0! L.nqth io 30 Sotto. oo Vtic dI.t.nc. aba.. baa. 0* *t (ml 0* tZ ay.t. vS. sbaIlg.pNc posltlo.v hI (hs 0svI T,.ck otipalt.. \ \\%\ i C r o u p s of of plates plates in in optical optical continuity, continuity, Groups some w i t h slight sliqht ra1iatin ra4iatinqnattern. yttern. s o m e with FIG. F I G . 99 F I G . 10 10 FIG. Fig. 9.9. Variation Variation in in lengths lengths of of tridymite tridymite paramorphs paramorphs with height height in the the Devil Devil Track Track and and Kimball Kimball Creek Creek rhyolites rhyolites(from (fromFitz, Fitz,1988). 1988). Fig. 10. Tabular Tabular habits habits of of quartz quartz paramorphs paramorphs after after tridymite tridymite in in the thegoundmass goundmass of ofthe the Fig. 10. Fig. Kimball KimballCreek Creek felsite felsite(from (fromFitz, Fitz,1988). 1988). �STOP STOP 9. 9. Red Red Rock Rock Point Point rhyolite rhyolite atatDeronda DerondaBay, Bay,Grand GrandPortage PortageIndian IndianReservation Reservation (Fig. (Fig. 11). 11). - At At this this locality locality aathick thick(80 (80m) m)andesiteficelandite andesitehcelandite flow flow (MC-3b, (MC-3b, Table Table 3) 3) is is overlain by a large large (>140 (>I40 m) m)rhyolite rhyolite unit unit (MC-7b), (MC-7b), but but the the actual actualcontact contact isis overlain somewhere somewhere under the the beach. beach. The The beach beach shingle shingle contains contains pieces pieces of of both, both, including vesicular vesicular andesite andesite with with pseudomorphs pseudomorphs of of cristobalite cristobalite balls balls in in the the including stretched stretched vesicles. vesicles. The The top top of• o fthe the rhyolite rhyolite is is cut cut out outbybythe theReservation Reservation River diabase diabase intrusion, intrusion, which also ako cuts cuts itit off off to to the the west west so sothat thatitsitslateral lateral River extent is unknown as well. extent is unknown as well. Reseruho, Rwer D3ig VeS3tVe , erptc. (MC 7) çto. tcctsi as (Mc- ) Fig. 11. 11. Diagrammatic Diagrammaticsection section of of the theRed RedRock Rockrhyolite rhyolite at at Stop Stop9,9,Deronda DerondaBay. Bay. Fig. On On the the way way toward toward the the main main cliff cliff outcrop outcrop on on the the south south side side of ofthe thebay, bay, there there are areinstructive instructivelow, low,wet wetoutcrops outcropsand andshallow shallowunderwater underwater"exposures", "exposures", accessible accessible under under favorable favorable lake lake conditions, conditions, of of the the following following gently gently south-dipping sequence, from bottom south-dipping sequence, from bottom toto top: top: a)a) porphyritic porphyritic andesite andesite or or icelandite, icelandite, probably probably part part of of the theMC-3 MC-3complex, complex,overlain overlain -- and andprobably probablybaked baked by by -- b) b)aathin thinbasaltic basalticsill; sill;this thisisisoverlain overlainby, by,and andhas hasbaked bakedsomewhat, somewhat, c) c) aa thin layer layer of of pumice-Iapilli pumice-lapilli tuft; tuff; this this is is overlain overlain by by d) d) aagrayish grayishash ashbed bed2-4 2-4 thin cm cm thick; thick; then then e)e) aa rhyolitic rhyolitic flow-breccia flow-breccia (mostly (mostly underwater) underwater) made made ofof variously-oriented variously-oriented blocks blocks containing containing stretched stretched vesicles. vesicles. Unfortunately Unfortunately boulders boulders cover cover the interval, interval, only only aa few few meters meters thick, thick, between between this this and and the the cliff cliff outcrop outcropahead. ahead. This This isis all all made madeofofred-orange, red-orange,porphyritic porphyriticrhyolite rhyolitethat that does does not not easily easily give give up up clues clues as astoto its its mode modeofofemplacement. emplacement. In Insome some areas areas near near the the base base ititappears appears totobe bea abreccia breccia(simply (simplymore moreofofthe thebasal basal autobreccia autobreccia of aalarge largelava lavaflow?). flow?). In Inothers, others, faint faintsuggestions suggestionsofofpumice pumice chips chips and and spherulites spherulites suggest suggest that that perhaps perhaps this this isis the the basal basalunwelded unwelded pumice pumice zone zone of aa big bigash ashflow, flow, overlain overlain inin the the cliff cliff by by the the devitrified, devitrified, laminated, laminated, welded weldedzone. zone. Because Because of of the the clear clearunderlying underlying breccia brecciaand andthe the lack prefer the the former former model, model, although althoughthis thisflow flowdoes does lack ofofobvious obviousfiamme, fiamme, I I prefer contain containsome somebroken brokenphenocrysts. phenocrysts. The The pumice-lapilli pumice-lapilli tuft tuff and andash ashtuft tuffbeds beds were wereair-falls air-fallswhich whichimmediately immediatelypreceded precededthe therhyolite rhyoliteeruption. eruption. Return Return to to Duluth Duluthvia viaGrand GrandMarais. Marais. A-. 13 �_____ REFERENCES REFERENCES Bonnichsen,Bill Bill and and Kauffman, Kauffman, D. D. F., F., 1987, Bonnichsen, 1987, Physical Physical features features of rhyolite rhyolite lava flows flows in in the Snake River province, southwestern southwesternldaho: Idaho:&i Fink, Fink, J. J. H., H.* the River Plain Plain volcanic volcanic province, editor, The emplacement of silicic editor, emplacement of silicic domes domes and and lava lava flows: flows: Geological Geological Society Society of America Special Special Paper Paper 212, 212* p. p. 119-145. 119-145. Bonnichsen, Bill, Bill, Leeman, Leeman, W. W. P., P., Jenks, Bonnichsen, Jenks, M. D., D., and and Honjo, Honjo, Norio, Norio*1988, 1988,Geologic Geologic field field trip guide guide to to the the central centraland andwestern western Snake SnakeRiver RiverPlain, Plain,Idaho, ldaho,emphasizing emphasizing the silicic rocks: rocks: in in Link, Link, P. P. K. K. and and Hackett, Hackett, W. W. R., R., editors, editors, Guidebook Guidebook to the the geology centrgand and southern southern Idaho: ldaho: Idaho ldaho Geological Geological Survey Survey Bulletin Bulletin 27, 27, geology of central 247-281. p. 247-281. BVSP (Basaltic (Basaltic Volcanism Volcanism Study Study Project), BVSP Project), 1981, 1981, Basaltic Volcanism Volcanism on the the Terrestrial Terrestrial Planets, Pergamon Press, New York, 1286 1286 p. p. Cas, R. R. A. A. F. Cas, F. and and Wright, Wright, J. J. V., V., 1987, 1987,Volcanic VolcanicSuccessions, Successions, Modern Modern and and Ancient: Ancient: Allen Allen and Unwin, Unwin, London, London, 528 528 p. p. Ekren, E. B., Ekren, E. B., Mcintyre, Mclntyre, D. D. H., H., and andBennett, Bennett,E. E.H., H.,1984, 1984,High-temperature, High-temperature,large-volume, large-volume, southwestern Idaho: lava-like ash-flow U. S. lava-like ash-flow tufts tuffs without calderas calderas in in southwestern ldaho: U. S. Geological Survey Professional Professional Paper 1272, 76 p. p. Fisher, R. V. 1984, Pyroclastic V. and andSchmincke, Schmincke, H.-U., H.-U., 1984, Pyroclastic Rocks, Rocks, Springer-Verlag, Springer-Verlag, New New Fisher, R. York, 472 p. York, p. Fitz, T. J., 1988, 1988, Large Large felsic felsic flows flows ininthe theKeweenawan Keweenawan North North Shore Shore Volcanic Volcanic Group Group in in thesis, University University of Cook County, Cook County, Minnesota: Minnesota: unpub. unpub. M. M. S. thesis, of Minnesota, Minnesota, Duluth, 180 180 p. p. Green, Green, J. J. C., C., 1979, 1979, Field Field trip tripguidebook guidebook for forthe theKeweenawan Keweenawan(Upper (UpperPrecambrian) Precambrian) Geological Survey North North Shore Shore Volcanic Volcanic Group, Group, Minnesota: Minnesota: Minnesota Minnesota Geological Survey Guidebook Series, Series, No. 11, 11, 22 22 p. p. 1982a, Geology Geology of of Keweenawan Keweenawanextrusive extrusiverocks, rocks, , Wold, , 1982a, Wold, R. R. J. J. and and Hinze, Hinze, W. W. editors, Geology J., editors, Geology and Tectonice Tectonice of the the Lake LakeSuperior Superior Basin: Basin:Geological Geological America Memoir Memoir 156, 156, p. p. 47-56. 47-56. Society of America 1982b, 1982b, Two Harbors Harbors Sheet, Sheet, Geologic Geologic Map Map of of Minnesota: Minnesota:Minnesota Minnesota Geological Geological Survey. Survey. 1983, Geologic Geologic and and geochemical evidence for for the the nature 1983, geochemical evidence nature and and development development of of the middle middle Proterozoic Proterozoic(Keweenawan) (Keweenawan) Midcontinent Midcontinent Rift Rift of of North North America: America: 94* p. p. 413-437. 413-437. Tectonophysics, v. 94, 1987, Plateau basalts of of the North Shore Shore Volcanic Volcanic Group: Group:& jj , 1987, Plateau basalts the Keweenawan Keweenawan North Biggs, D. Field Guide 3, Geological Biggs, D. L., editor, editor, Centennial Centennial Field Guide Vol. Vol. 3, Geological Society Society of of America, p. 59-62. 59-62. , 1989, Physical Physical volcanology volcanology of of mid-Proterozoic mid-Proterozoic plateau plateau lavas: lavas: the the Keweenawan Keweenawan North Shore America North Shore Volcanic Volcanic Group, Group, Minnesota: Geological Geological Society Society of America Bulletin, v. 101, 101, in in press. press. Bulletin, Self, Stephen, C. D., Price, J. G., G., Rubin, Rubin, J. J. N., N., Parker, Parker, D. D. F., F., Wolff, Wolff* J. J. A., Self, Stephen, Henry, Price, J. Henry, C. lavalike silicic Richard, and Widespread, lavalike silicic Franklin, and Barker* D. S., 1988, Widespread, Franklin, Richard, Barker, D. volcanic rocks of p. 509-512. 509-512. of Trans-Pecos Trans-Pecos Texas: Geology, Geology, v. 16, 16, p. Miller, J. J. D., D., Jr., Jr., 1987, 1987,Geology Geology of of the theKeweenawan Keweenawan (Upper (Upper Precambrian) Precambrian) Beaver Beaver Bay Bay Miller* Complex Complex in the vicinity vicinity of of the the Silver Silver Bay, Bay, Minnesota, Minnesota, hi Balaban, Balaban, N., N., editor, editor, in Precambrian Precambrian geology areas in Field Trip selected areas Field Trip Guidebook for selected geology of Minn. Geol. Survey Guidebook Series No. 17. northeastern Minnesota: Minnesota: Minn. 17. Geologic map map of of the , 1988, 1988, Geologic the Silver Silver Bay Bay and and Split Split Rock RockPoint PointNE NEquadrangles, quadrangles, Lake County, Minnesota: Minnesota: Minn. Minn. Geological Geological Survey Survey Miscellaneous Miscellaneous Map Series Series M-65. M-65. 9- A-14 �Miller, 1987, Road D., Jr., Weiblen, P. W. C., 1987! ~ i l l e rJ. ~ Da1 Weiblen? P. W. and and Green, Green* J. C.? Road log log and and stop stop descriptions for the the Beaver Beaver Bay Bay Complexl Complex, i Balaban, N.?editor, editor* Field Field Trip Trip Balabanl N., descriptions for northeastern in Precambrian Precambrian geology Guidebook for geology of northeastern Guidebook for selected selected areas areas in Minn. Geol. Geol. Survey Survey Guidebook Series No. 17. Minnesota: Minnesota: Minn. 17. Motamedi, Shoaullah, 1984, The Keweenawan lavas in the City of Duluth: Motamedil Shoaullahl 1984?The Keweenawan lavas in the City Duluth: unpub. unpub. M. M. S. S. thesis, thesis* Univ. Univ. of of Minnesota-Duluth, Minnesota-Duluth*140 p. p. Price, J. J. G., G., Henry, C. D., Pricel Henry, C. D.l Parker, Parker* D. D. F., FSl and and Barker, Barker* D. D. S., S.?1986, 1986?Igneous Igneous geology geology of Trans-Pecos Texas: Texas: Field Field trip trip guide Trans-Pecos guide and and research research articles: articles: Guidebook Guidebook 23, 23* Geology, Austin* Austin, 360 p. Bureau of Economic Geologyl Ross, C. C. S. and L.?1961, 19611Ash-flow Ash-flow tufts: tuffs: their their origin, origin*geologic geologic relations relations and and Rossl and Smith, Smith, R. R. L., identification: U. S. Geological p. Geological Survey Professional Professional Paper 366, 366! 81 81 p. Van Schmus, W. A. Van Schmus? W. R. and and Hinze, Hinze, W. W. J., J.l The TheMidcontinent MidcontinentRift RiftSystem: System:Annual AnnualReviews Reviews of Earth v. 13, 13, p. p. 345-383. 345-383. Earth and and Planetary Planetary Science, Science?v. editors, Geology Geology and and Tectonics of the Wold, R. J. and Hinze, Hinze, W. W. J., J., 1982, 1982* editors, Tectonics of the Lake Lake Woldl R. J. and Superior Basin: Geological Society of of America Memoir 156, p. Superior Geological Society 15e1280 280 p. A- 15 �- PENOKEAN STRUCTURAL TERRANES TERRANES IN EAST-CENTRAL MINNESOTA A one-day one-day field trip trip associated associated with the the Thirty-Fifth Annual Meeting of the the Institute on Lake Lake Superior Superior Geology Geology May 3-6, 3-6*1989 1989 By Timothy B. Hoist Holst Department of Geology Geology University of Minnesota Minnesota Duluth Duluth Duluth, Minnesota Duluth1 Minnesota 55812 introduction Introduction I 1 I The orogeny, which which occurred near the the close of The Penokean Penokean orogenyl occurred near of early earlyProterozoic Proterozoic time time (1875-1825 Ma., Van Schmus, (1 875-1825 Ma.* Schmus* 1976, 1976, 1980, 1980, 1981) 1981) involved involved deformation deformation and andmetamorphism metamorphism in Minnesota, Minnesota, Wisconsin, Wisconsin, upper upper Michigan* Michigan, and and the of rocks rocks in the Superior, Superiorl Southern, Southern, and and 1980; Cannon, Grenville provinces Grenville provinces in Canada Canada (HoIst, (Holstl 1982; 1982; Maass Maass and and others, others* 1980; Cannon, 1973; 1973; Brocoum the Penokean Minnesota was Brocoum and Dalziel, Dalziel* 1974). 1974). Until Until recently, recently* the Penokean orogeny orogeny in in Minnesota was usually interpreted as intracratonic (Morey and and Sims, usually interpreted as intracratonic (Morey Sims, 1976; 1976; Sims, Sims* 1976; 1976; Sims Sims and andothers, others, 1980) emphasis on the the role roleofofbasement basementrock rockinvolving involvingverticai "verticalremobilIzation" remobilization" 1980) with with an emphasis in this in (Morey, (Morey, 1979). 1979). Of fundamental fundamental importance importance in this interpretation interpretation is is the boundary, boundary* in west-central Minnesota, Minnesota, between between an an ancient part 3550 west-central ancient (in (in part 3550 Ma.) Ma.) gneissic gneissic terrane terrane and and aa younger (Ca. younger (ca. 2700 2700 Ma.) Ma.) granite-greenstone granite-greenstone terrane terrane (Fig. (Fig. 1). I). Morey Morey and Sims Sims (1976) (1976) suggested that this this boundary boundary is part of suggested that of aa major major Precambrian Precambrian crustal feature more more than than 1200 1200 km long long which which they they called called the the Great Great Lakes Lakes tectonic tectonic zone zone (Sims (Sims and andothers, others*1980). 1980). They They noted noted that that rocks rocks which which overlie overlie the thegranite-greenstone granite-greenstone terrane terrane (Animikie (Animikie Group) Group) are are less less deformed and and metamorphosed than those those which which overlie overlie the the Great Great Lakes Lakes tectonic tectonic zone zone and deformed metamorphosed than Because of of this gneissic terrane. terrane. Because this these these authors authors suggested suggested that that this this early earlyPrecambrian Precambrian . limited intracontinental tectonic movement intracontinental tectonic boundav acted locus for limited movement and and rising rising boundary acted as as aa locus geothermal gradients (Morey, (Morey, 1979). 1979). Recent investigations in Recent structural structural investigations in the early Proterozoic Proterozoic Thomson Thomson Formation Formation in in east-central Minnesota (Hoist* (Hoist, 1982, 1982, 1984c) 1984c) reveal reveal evidence evidence for multiple multiple deformation deformation and and east-central Minnesota document the existence One document existence of of northward-directed northward-directed nappes nappes during the the Penokean Penokeanorogeny. orogeny. One of the would be gravity the possible possible models models of of nappe nappe emplacement emplacement in Minnesota Minnesota would gravity gliding gliding off off aa rising diapir diapir following the suggestions of Morey (1979) and and Sims rising following the suggestions of Morey (1979) Sims and and others others (1980) (1980) for for intracratonic deformation. deformation. However, However* the high high strains strains associated associated with with nappe nappeemplacement emplacement (Hoist, 1985a) 1985a) do do not not support support this this idea idea (see (see the the values values of of strain strain above above aa rising (Holstl rising diapir diapir in Dixon, 1975). 1975). Such strains strains are more more consistent consistent with aa plate plate tectonic tectonic model model(Hoist, (Holst,1985a, 1985a1 1985b). of nappes has also recently been reported reported further further to to the east 1985b). The presence presence of recently been east in in the the al., 1988) 1988) and Penokean orogenic orogenic belt belt (Sims 1987; Klasner, Penokean (Sims and and others, others, 1987; Klasner* at at al.l and Penokean Penokean volcanic rocks have have been been shown shown to to be volcanic rocks be of of island island arc arc affinity affinity (Schulz (Schulz and and others, others, 1984) 1984) resulting in plate tectonic syntheses for several several areas of of the the Penokean Penokean orogenic orogenic belt. belt. The growing body of of structural structural and and petrologic petrologic evidence evidence from from Wisconsin Wisconsin (LaBerge (LaBergeand and 1978) is is others, 1984; 1984; Sims others* Sims and and others, others, 1985) 1985) and and upper upper Michigan Michigan (Cambray, (Cambray, 1977, 1977# 1978) consistent with the Minnesota for for aa convergent consistent with the structural structural evidence evidence in in east-central east-central Minnesota convergent plate plate Recent models of of the 984a, 1984b). 1 984b). boundary model boundary model (HoIst, (Holstl 11984a, Recent models the Penokean Penokean orogeny orogeny in in Minnesota involve aa convergent convergent plate plate margin margin with with subduction subductionofof aa passive or the Minnesota involve passive margin, margin* or close of of aa back-arc back-arc basin basin (Hoim, (Holm,HoIst, Holst, and and Ellis, Ellis, 1988; 1988;Southwick, Southwick, Morey, Morey*and andMcSwiggen, McSwiggen, 1988). 1988). B-i �•VP Middi. Prot&ozoc k" IQneous and k!IJI ssdlm.ntsry rocks I'I Early Prot.rozolc ntrusivs rocks r.a 1 Early Protsrozoc v1 i supracruatals 1 with Iron formation F::::::1 Archean Qranste— greenstoA. terran '1 Arch•an gn.is&c lOOkm Figure Figure 1:1: Generalized geologic map map of of the Generalized geologic the Precambrian Precambrian geology geology of of Minnesota Minnesota (after (after Sims Sims and and others, others, 1980; 1980; Morey Morey and andothers, others, 1982). 1982). GLTZ GLTZ is is the the Great GreatLakes Lakes Tectonic TectonicZone. Zone. Geologic Geoloaic Setting Settinq The can be divided The Precambrian Precambrian rocks of of east-central east-central Minnesota Minnesota can divided into into four four distinct distinct terranes 1) terranes (Fig. (Fig. 1): 1): 1) Archean Archean rocks; rocks; 2) 2) early early Proterozoic Proterozoic stratified stratified rocks; rocks; 3) 3) early early Proterozoic 4) middle middle Proterozoic Proterozoic (Keweenawan) (Keweenawan) sedimentary sedimentary and and Proterozoic plutonic plutonic rocks; rocks; and and 4) volcanic volcanic rocks rocks (Morey, (Morey, 1978). 1978). A A stratigraphic stratigraphic column column for foreast-central east-central Minnesota Minnesota and and detailed descriptions descriptions of different rock rock types types have have been been presented presented by byMorey Morey(1978, (1978, detailed of the different 1979), 1979), although although recent work suggests suggests a rethinking rethinking of some some of of the thecorrelations correlations(Morey (Moreyand and Southwick, Southwick, 1984; 1984; Southwick Southwick and and Morey, Morey, 1988; 1988; Southwick, Southwick, Morey Morey and and McSwiggen, McSwiggen, 1988). 1988). The The Archean Archean terrane terrane consists consists of of aa northern northern granite-greenstone granite-greenstone belt belt terrane terrane (ca. (ca. 2700 2700 Ma.), Ma.), aa southern southern highly highlydeformed deformedgneissic gneissic terrane terrane (in (in part part >3550 >3550 Ma.), Ma.), and and aacentral central sheared, schistose schistose segment the Great Great Lakes Lakes tectonic tectonic zone zone sheared, segment (Morey, (Morey, 1978) 1978) also also known known as the (Sims (Sims and and others, others, 1980). 1980). Along Along this this zone, zone, granitic granitic plutons plutons (2600 (2600 Ma., Ma,, Sims Sims and and others, others, 1980) 1980) acted as aaweld weldbetween betweenthe thenorthern northernand andsouthern southernsegments segmentsforming forming aarelatively relatively stable Archean(Morey, (Morey, 1978). 1978). stable craton craton by by the the end endofofthe theArchean Sedimentation into a large Sedimentation into large basin basin on on this this craton, craton, the the Animikie Animikie basin, basin, began began at at about about 2100 Ma. (Van Schmus, 1976). 2100 Ma. (Van Schmus, 1976). Depositional Depositional patterns reflect reflect contrasting contrastingtectonic tectonicconditions conditions in in the the northern northernand andsouthern southernsegments segments of of the the Animikie Animikie basin. basin. AA relatively relativelythin thinsuccession succession (2-3 (2-3 km) km) ofofpredominantly predominantly sedimentary sedimentary rocks rocks (labeled (labeled the the Animikie Animikie Group, Group, Keighin Keighin and and others, others, 1972) 1972) was deposited deposited north north of the the northern northern front front of of the the Great GreatLakes Lakestectonic tectonic zone, zone, whereas whereas aa much muchthicker thicker and andmore moreheterogeneous heterogeneous succession succession (>6 (>6km) km)ofofsedimentary sedimentaryand and B-2 �vhcanic rocks (Animikie (Animikie and Mule Mille Lacs Groups, Groups, Morey, Morey, 1978) 1978) was was deposited deposited south this volcanic south of this front front (Morey, (Morey, 1983; 1983; Morey Morey and andSouthwick, Southwick, 1984). 1984). Apparently, Apparently, subsidence subsidence was was relatively relatively greater in the the southern southern part part of ofthe thebasin, basin,particularly particularly over over the the Great Great Lakes Lakestectonic tectonic zone zone greater and and the the gneissic gneissic terrane. terrane. Ojakangas Ojakangas (1983) extent of of the the Animikie Animikie basin basin (1983) has inferred the extent on on the the basis basisofofsedimentological sedimentologicaland andtithological lithologicalsimilarities similarities ininMinnesota, Minnesota, Wisconsin, Wisconsin, and and Michigan. Michigan. Because Because rocks rocks of of the the Midcontinent Midcontinent Rift Rift system system (middle (middle Proterozoic Proterozoic igneous igneous and and sedimentary sedimentary rocks, rocks, Fig. Fig. 1)1) separate separate the the Animikie Animikie basin basin into into two two physically physically isolated isolated segments, the strata strata in in the thenorthwestern northwestern segment segment are are assigned assigned to to the theAnimikie Animikieand andMule Mille segments, Lacs Groups Groups whereas whereas those those ininthe thesoutheastern southeastern segment segment are are assigned assigned to to the theMarquette Marquette Lacs Range Range Supergroup. Supergroup. Correlations Correlations have made among among the the Lower LowerProterozoic Proterozoicbedded bedded have been made rocks rocks in in Minnesota, Minnesota,Michigan Michiganand andWisconsin Wisconsin(Morey, (Morey,1983). 1983). All stops stops on on this thisfield fieldtrip triphave havebeen beenmapped mappedhistorically historically as as part part ofofthe theThomson Thomson All Formation. The Thesouthern southernexposures exposureshave haverecently recentlybeen beenassigned assignedto toother, other,as asyet yetunnamed unnamed Formation. units of of early earlyProterozoic Proterozoic metasediments metasediments and metavolcanics, metavolcanics, which older than than the the units which are are older Thomson Formation Formation (Southwick (Southwick and and Morey, Morey, 1988; 1988;Southwick, Southwick,Morey Moreyand andMcSwiggen, McSwiggen,1988). 1988). Thomson Descriptive Descriptive Structural Structural Geology Geoloqy Exposures of of early earlyProterozoic Proterozoic metasediments metasediments and and metavoicanics metavolcanics historically historically called called Exposures greywacke, the Thomson Thomson Formation Formation consist consist of of aathick thicksequence sequenceofofinterbedded interbeddedslate, slate,slaty slatygreywacke, the metagreywacke metagreywacke with with some someintercalated intercalatedvolcanics. volcanics. The The southern southern two-thirds two-thirds of of this thisregion, region, here here designated designated the the southern southern structural structural terrane, terrane, has has aapervasive, pervasive,nearly nearlybedding-parallel bedding-parallel foliation foliation(S1). (SJ. ItIt ranges ranges from from aa slaty slaty cleavage cleavage in in the the north northto to aaschistosity schistosity in in the the south south near near the the Denham DenhamFormation Formation(Hoist, (Holst,1982). 1982). Strain Strain analysis analysis (Hoist, (Holst, 11985a) established 985a) has firmly established the the tectonic tectonic nature natureofofthis thisbedding.paraIlel bedding-parallelfoliation. foliation. Also Also present present in inthe thesouthern southernstructural structural terrane terrane are are isoclinal isoclinal recumbent recumbent folds folds in scales scales ranging ranging from from cms cms to to kms kms(nappes), (nappes), with with east-west east-west fold fold axes axes(F1). (F,). Both Both the the northern northern and and southern southern structural structural terranes terranes have have been been folded folded into into gentle gentle to toopen openupright uprightfolds. folds. Fold Fold axial axial surfaces surfaces strike strike east-west east-west and and fold fold axes axes have In the the southern southernstructural structural terrane terrane have horizontal horizontal to to gentle gentle plunges plunges either either east east or orwest. west. In these well-developed these upright upright folds folds(F2) (F2)refold refoldthe theearlier earlierisoclinal isoclinalrecumbent recumbentfolds folds(F1). (F,). AAwell-developed cleavage, cleavage, vertical or or dipping dipping steeply steeply to to the the south south (axial-planar (axial-planar to the the upright upright folds) folds) is is present present in in both boththe thenorthern northernand andsouthern southernstructural structuralterranes. terranes. In In the the northern northernstructural structural terrane terrane this this cleavage In the the cleavage is is aawell welldeveloped developedcontinuous continuous slaty slatycleavage cleavage ininthe thefiner-grained finer-grainedunits. units. In units units with with graded graded bedding, bedding, and and ininthe theunits unitswith withinterlaminated interlaminatedfine fine and andcoarse coarselayers, layers,the the continuous continuous cleavage cleavage grades grades into into aadisjunctive disjunctivespaced spacedcleavage cleavage(terminology (terminology ofofPowell, Powell, 1979). The spacing spacing of ofthe thecleavage cleavagedomains domainsranges rangesfrom fromcontinuous continuous up uptoto 11 cm cm ininsome some 1979). The of Cleavage domains domains of the themost mostcoarse-grained coarse-grained units, units, but but itit isis rarely rarely over over aa few fewmm. mm. Cleavage constitute constitute from 25% 25Y0 of of the the rock rock (in (inthe the thick thick graywacke graywacke units) units) to to 100% 10O0/~(in (in the the slates slates with with aa continuous continuous cleavage). cleavage). Domain Domain shapes shapes range range from from rough rough to to smooth smooth (smooth (smoothshapes shapes predominate) Within the the microlithons, microlithons, a weak weak fabric, fabric, at at predominate) with with some someanastomosing anastomosingshapes. shapes. Within least, least, isisdeveloped developed everywhere, everywhere,and andcommonly commonlythe thefabric fabricisisstrong strongtotocomplete complete(terminology (terminology of In the the southern southern structural structural terrane terrane the the steep steep foliation foliation isis aawell-developed well-developed of Powell, Powell,1979). 1979). In crenulation crenulation cleavage cleavage (S2). (SJ. This This S2 S2 cleavage cleavage can can be be discrete discrete but but isis most most commonly commonly transitional transitional to to zonal, zonal, or orentirely entirelyzonai zonal(Gray, (Gray,1977; 1977;Powell, Powell,1979). 1979). Spacing Spacing of ofthe thecleavage cleavage domains domains isisvariable. variable. For For the the most mostpart partthe thespaced spacedcrenulation crenulationcleavage cleavagestrikes strikeseast-west east-west and and dips dips steeply steeplyto tothe thesouth southororisisvertical, vertical,and andaxial-planar axial-planartotothe theF2F2folds. folds. Around Around some some microfolds, may fan, microfolds, however, however, the the spaced spaced crenulation crenulation cleavage cleavage may fan, or or be be atataaconstant constantangle angle (up (up to to 40°) 40') totothe theaxial axialplane planeon onone onelimb, limb,and andaxial axialplanar planaron onthe theother otherlimb. limb. The The intersection S1and and S2 S2defines defines aa well welldeveloped developedlineation lineationininthe therock, rock,trending trendingeast-west east-west intersection of of S1 with withsubhorizontal subhorizontalplunges. plunges. Detailed Detailed mapping mapping has has allowed allowed aa boundary boundaryto to be bedrawn drawnbetween between the single main Penokean deformation single main Penokean deformation inin the the north north(the (thenorthern northernstructural structural the area areaofofa a terrane), twotwo Penokean-aged deformations terrane), and and the thearea areaofof Penokean-aged deformations inin the the south south (the (thesouthern southern structural structural terrane). terrane). This This boundary boundary was was interpreted interpreted by Holst (1984c) (1984~)as aa nappe nappe front front by Hoist because because of of the theabrupt abruptnature natureofofthe thechange changeacross acrossthis thisterrane terraneboundary, boundary,and andbecause becausethe the refraction refraction pattern pattern in in the the early earlyfoliation foliation just just south southofofthis thisboundary boundarysuggests suggeststhat thataanappe nappe B-3 �/ front must be be located located in in the the immediate immediate vicinity vicinity to to the the north. north. Underlying the what has hashistorically historically been been called called the theThomson Thomson Underlying the southern southern part part of what Formation is the Formation the early early Proterozoic Proterozoic Denham Denham Formation. Formation. This This has now now been been broken broken into into upper and lower lower members members by by Southwick, Southwick, Morey Morey and and McSwiggen, McSwiggen. (1988). (1988). The rocks rocks of of this this formation have been multiply multiply deformed deformed and metamorphosed inin aa fashion fashion similar similar to the the formation have been and metamorphosed overlying rocks rocks (Holm, (Hoim, 1986a, 1986a, 1986b) 1986b) and and are are here considered part of the overlying considered part the same same nappe nappe terrane. The Denham Denham Formation Formation is is aasequence sequenceofofprimarily primarilyquartz-rich quartz-richmetasedimentary metasedimentary rocks (metaarkose, quartzite, mica schist, and rocks (metaarkose, quartzite, and garnet-staurolite garnet-staurolite schist) schist) with minor minor amounts amounts of marble of marble and and volcanic volcanic rocks. rocks. It has has been been postulated postulated to be be stratigraphically stratigraphically equivalent equivalent to the Chocolay Group of the the Marquette Marquette Range Range Supergroup Supergroup in Michigan Michigan (Larue, (Larue, 1981; 1981; Morey, Morey, 1983). A nearly 1983). Bedding strikes east-west east-west and and dips dipsdominantly dominantlysteeply. steeply. A nearly bedding-parallel bedding-parallel foliation is present present everywhere everywhere in in the the Denham DenhamFormation. Formation. The foliation foliation is refracted refracted at at aa higher higher angle angle to bedding bedding in in the the more morecompetent competent arkosic arkosic and and quartzitic quartzitic units. units. The foliation foliation and bedding and bedding have been been folded folded with with the thedevelopment, development, locally, locally, of of aacrenulation crenulation cleavage. cleavage. Orientations folds vary vary from from horizontal horizontal to vertical and and strike strike Orientationsofof axial axial surfaces surfaces to to these these folds to vertical east-west. east-west. The The Denham Denham Formation Formation also also contains contains aavery verywell-developed, well-developed, nearly horizontal, horizontal, east-west east-west mineral and and crenulation crenulation lineation. lineation. Chocolate-tablet veins Chocolate-tabletboudinage boudinageof of quartz veins bedding throughout throughout the the area. area. occurs parallel to bedding The basement to to this terrane is Archean (2700 (2700 Ma.) Ma.) McGrath McGrath Gneiss Gneiss which which The basement this terrane is the the Archean contains a poorly contains poorly to to well-developed well-developed foliation foliation and a number number of cross-cutting cross-cutting shear zones. zones. ItIt is aa coarse-grained, coarse-grained, pinkish-gray, pinkish-gray, biotite biotite gneiss gneiss containing containing megacrysts megacrysts of of microcline. microcline. Some Some of the megacrysts megacrysts are are rounded, rounded, giving giving the the appearance appearance of augen, augen, but many many are are euhedral euhedraland and oriented to the foliation oriented obliquely obliquely to foliation while still still others others have have aa sigmoidal sigmoidal shape shape and and are arealigned aligned the foliation. foliation. Sense in the Sense of of shear shear from from the thesigmoidal sigmoidalporphyroclasts porphyroclasts (after (after Simpson Simpson and and Schmid, 1983) 1983) indicate indicate that that the the foliation foliation developed developed in aa dominantly dominantly dextral dextral shear shear regime. regime. Schmid, in dip from The foliation foliation is commonly commonly well well developed, developed, strikes strikes east-west, east-west, and varies varies in from to vertical. vertical. A nearly nearly horizontal horizontal east-west east-west mineral mineral lineation horizontal to lineation ranging ranging from from crude to locally well well developed developed is is also present. present. The McGrath McGrath Gneiss Gneiss is locally folded folded and and is is locally is locally strike generally cross-cut shear zones cross-cut by nearly nearly vertical, vertical, commonly commonly anastomosing anastomosing shear zones that that strike generally east-west. east-west. In the the northern northern structural structural terrane terrane there are are some some late-stage late-stage features features including including kink kink bands which deform deform the the steep steep cleavage cleavage ininthe theThomson ThomsonFormation. Formation. The orientation of of bands The orientation these but poles poles to to over these kink kink bands bands is is quite quite variable, variable, but over 100 100 kink kink bands bands define define aa single single The gentle dip of the gentle dip the kink maximum on an maximum an equal-area equal-area projection projection (Clark, (Clark, 1985). 1985). The kink bands bands indicates a sub-vertical finite finite compression during their their formation, formation, estimated estimated to to be about 5% 5% indicates compression during by Clark Clark (1985). (1985). Conditions Of Deformation Deformation Petrographic analysis analysis indicates indicates that that the the basement Petrographic basement and cover rocks rocks have have undergone undergone similar conditions conditions of of deformation deformation related related to to the thePenokean Penokeanorogeny. orogeny. In In all rocks rocks analyzed, analyzed, the predominant appear to to be normal predominant deformational deforrnational processes appear normal crystal-plastic crystal-plastic type, type, involving involving In both and cover dynamic recovery recovery and andrecrystallization. recrystallization. In both basement basement and cover rocks, rocks, quartz quartz has has lattice has produced undulatory undergone ductile deformation. Bending of the crystal undergone ductile deformation. Bending of the crystal lattice has produced undulatory Recovery and and recrystallization are indicated extinction and, locally, locally, deformation deformation bands. bands. Recovery indicated by by the development of of subgrains and strain strain free free new grains grains in and along the margins of quartz subgrains and quartz have occurred aggregates. aggregates. Both brittle brittle and and ductile ductile deformation deformation processes processes have occurred in the the feldspar feldspar deformation is is indicated in the coarser feldspar grains. Brittle deformation feldspar by fractures along which new new grains have Simultaneous ductile ductile deformation deformationofof the the finer finer grained grained feldspars is have recrystallized. recrystallized. Simultaneous indicated by undulatory recovery, and and recrystallization commonlyresulting resultinginin aa undulatory extinction, extinction, recovery, recrystallization commonly indicated granoblastic polygonal strain free free in both polygonal texture. texture. Mica grains grains are relatively relatively strain both basement basement and and cover rocks, rocks, probably probably because because ofofrecrystallization. recrystallization. The The textures textures described described here here indicate indicate dominantly dominantly ductile deformation deformation under moderate moderate to high high temperature temperature and and moderate moderate pressure pressure conditions. conditions. B-4 �Metamorphism Metamorohism Metamorphism the early Metamorphism ofof the early Proterozoic Proterozoic sedimentary sedimentary rocks in in this region region increases increases from from north to south south (Keighin (Keighin and and others, others, 1972). 1972). At the type type locality locality near near Thomson Thomson in the the northern terrane, the the Thomson northern terrane, Thomson Formation Formation is is metamorphosed metamorphosed to lower lower greenschist greenschist fades facies Within (chlorite the Thomson (chlorite zone). zone). Within the Thomson Formation Formation there there is is a progressive progressive increase in increase in metamorphic grade lower amphibolite amphibolite facies (garnet zone) the south south(Morey, (Morey,1979). 1979). metamorphic grade to to lower facies (garnet zone) in the Farther south, south, the the Denham has been been metamorphosed to the the staurolite zone of Farther Denham Formation Formation has metamorphosed to staurolite zone the fades (indicated the amphibolite amphibolite facies (indicated by the the presence presence of of aacoarse-grained coarse-grainedschist schist containing containing quartz÷muscovite+biotite÷garnet÷staurolite). Morey (1983) (1983) has has mapped quartz+muscovite+biotite+garnet+staurolite). Morey mapped the the biotite, biotite, garnet, garnet, and staurolite for early staurolite isograds isograds for early Proterozoic Proterozoic stratifed stratifed rocks rocks in in Minnesota, Minnesota, illustrating illustrating this this progressive the similarity similarity of of the the progressiveincrease increaseinin metamorphic metamorphicgrade gradefrom fromnorth northtoto south south and the trend of metamorphic 7). metamorphic isograds and structural features features (see Morey, 1983, 1983, fig. fig. 7). Petrographic analysis reveals reveals further further information about the timing Petrographic analysis information about timing of of metamorphism metamorphism metamorphismduring duringthe the early early phase phase of deformation and deformation. deformation. Progressive Progressive metamorphism deformation in the the Denham Formationreached reachedthe the garnet garnet zone zone of of the the amphibolite facies as as indicated by the Denham Formation amphibolite facies indicated by presence of syntectonic presence syntectonic garnet garnet porphyroblasts. porphyroblasts. The The peak peak ofofmetamorphism, metamorphism,however, however, occurred during during or or after after the later deformation occurred deformation as indicated indicated by staurolite staurolite overgrowing overgrowing both the schistosity and the crenulation crenulation cleavage. cleavage. Microprobe analysis of garnet Microprobe analysis of garnet shows shows only only slight slight compositional compositional variation variation and and no no 1 986a). Rocks systematic zonation (HoIm, (Holm, 1986a). Rocks of the the southern southern structural structural terrane terrane have have recently recently been studied been studied by Holm Holm and andSelverstone Selverstone (1989). (1989). Using thermobarometric thermobarometric techniques techniques they they final equilibration increasing southward. find temperature and and pressure estimates of final find temperature pressure estimates equilibration increasing southward. Staurolite grade samples samples from from just just north Staurolite grade north of of the theDenham DenhamFormation Formationyield yieldfinal finalequilibration equilibration temperatures of 520-590° 520-590°Cand and aa pressure pressure of of about about 77 kb (depth of about 25 temperatures of 25 km). km). Petrologic and Geochemical Constraints Petroloqic Constraints Penokean aae age volcanic volcanic rocks rocks further furtherto to the the east east have Penokean have been shown shown to to be be of of Island island Horan, Hansen, and arc affinity Schulz affinity (Schulz, ( ~ c h u l z1983; 1983; , Schulz and and others, others, 1984). 1984). Horan, and Spencer Spencer (1987) (1987) suggest that that the the early intrusive rocks rocks in in central were formed at aa suggest early Proterozoic Proterozoic intrusive central Minnesota Minnesota were formed at convergent plate margin, margin, based on isotopic They suggest that convergent plate isotopic and and trace trace element element analysis. analysis. They may have have been been part part of an a gabbro gabbro near Mora, Mora, Minnesota Minnesota may an early early Proterozoic Proterozoic ocean ocean crust, crust, and thus part of Recent geochemical geochemical and isotopic and thus may may represent represent part of aa suture suture zone. zone. Recent isotopic work work reported by by Southwick, Morey, and McSwiggen reported Southwick, Morey, McSwiggen (1988) (1988) shows shows that island island arc arc constituents constituents are not aa major are major portion portion of of the the rocks rocks that that now now make make up upthe thetold-and-thrust fold-and-thrust belt belt of of the the that most of the Penokean Penokean Orogen Orogen in Minnesota. Minnesota. They They also also report report that most of the basaltic basaltic rocks rocks of the the region have a continental (within plate) affinity, indicating indicating that continental crust played played aa role role in determining their their composition. composition. Tectonic Modelling Modellinq HoIm, Hoist HoIst and and Ellis Ellis (1988), using the constraints constraints of structural structural geology, geology, finite finite strain strain Holm. determinations, deformation deformationconditions conditions indicated indicated by by microstructures microstructures and and textures, determinations, textures, and the the results estimates, developed developed a tectonic model results of thermobarometry thermobarometry estimates, model consisting consisting of of southward southward directed oblique subduction along along the Great directed oblique subduction Great Lakes Lakes tectonic tectonic zone. zone. According According to this this model model intense deformation deformation occurred occurred in in the tootwall footwall of the the major major thrust, thrust, which which marked markedthe theboundary boundary (continental) subduction. downgoing and and overriding during A-type between downgoing overriding plates during A-type (continental) subduction. between Sedimentary rocks deposited deposited on on the footwall Sedimentary rocks footwall during during loading loading caused caused by bythrusting thrustingeventually eventually became incorporated into the the deformation deformation zone. zone. Early formed structures structures related related to to footwall footwall deformation are a dominantly deformation are dominantly well-developed foliation foliation in the the gneiss gneiss and andisoclinal, isoclinal,recumbent recumbent Progressive folds folds with with aabedding-sub-parallel bedding-sub-parallelfoliation foliation in the the southern southern structural structural terrane. terrane. Progressive metamorphism during subduction reached reached the the garnet metamorphism during subduction garnet zone zone of the amphibolite amphibolite facies. Various deformation inversions inversions show show that that this early phase Various deformation phase of of deformation deformation involved involved extreme extreme and large flattening (with ZZ vertical) vertical) and large amounts amounts of finite extensional extensional stain in in both both the the flattening (with north-south and east-west east-west directions. directions. B- 5 �, Footwall accretion onto onto the the hanging hanging wall wall Footwafl deformation deformation was was followed by imbrication and accretion during associated with with continued continued compression compression and and isostatic isostatic rebound. rebound. Later during uplift associated Later formed formed structures associated associated with with imbrication imbrication and and deformation deformation within within the the hanging wall consist structures hanging wall consist of of folding development of McGrath Gneiss and open to folding of of the the foliation and development of shear shear zones zones in the McGrath close, upright to overturned overturned folds folds in cover rocks rocks of of both both the thesouthern southern and andnorthern northern close, upright in the the cover structural terranes. The peak peak metamorphic metamorphic event event (represented (represented by staurolite) staurolite) occurred occurred after after the temperatures of the later deformation at at temperatures of around around 520-590° 520-590°Cand and aa pressure pressureofof 77 kb (depth of of about 25 km). about km). Increasing Increasing temperature temperature associated associated with decreasing decreasing pressure pressure (uplift) (uplift) is is explained relaxation caused caused by by crustal crustal thickening thickening and anderosion. erosion. explained by conductive relaxation Southwick, McSwiggen (1988), that several several types types of of plate plate Southwick, Morey, Morey, and and McSwiggen (1988), while while noting noting that margin collisional model for for the the margin collisional models models are are possible, possible, favor favor a collapsing back-arc basin as a model They argue Penokean Penokean orogeny. orogeny. They argue that the lithostratigraphic lithostratigraphic associations the early early associations of the Proterozoic Proterozoic supracrustal rocks rocks in in Minnesota, Minnesota, and geochemical characteristics characteristics of the the and the geochemical volcanic more compatible compatible with back-arc setting setting than than than than with with an anarc-trench arc-trench volcanic rocks rocks are are more with a back-arc environment. environment. GUIDE TO FIELD FIELD TRIP STOPS STOPS The location of the field field trip trip stops stops is is shown shown on on Figure Figure 2. 2. The field trip begins begins at at the the Radisson Duluth Radisson Duluth Hotel Hotel at Superior Superior Street Street and and 5th 5th Avenue Avenue West West inindowntown downtown Duluth, Duluth, Minnesota. Head southwest southwest on Superior Superior Street Street and in in two two blocks blocksjoin join Interstate InterstateHighway Highway 35 going After 14.6 14.6 miles miles on on 1-35, 1-35, take take exit exit 242, 242, turning turning south south (left) (left) on on Canton Carlton going south. south. After County In 2.9 County 1. 1. In 2.9 miles, miles, the the road road crosses crosses aa spillway, spillway, turns turns west, west, and and after after 0.6 0.6 miles, miles, Turn right (north) 210, which which then then turns reaches aa 1 reaches T junction. junction. Turn (north) on Minnesota Minnesota Highway Highway 210, turns left (west) in less (west) less than than 0.1 0.1 mile. mile. In 0.2 miles, miles, Minnesota Minnesota Highway Highway 210 crosses crosses the St. St. Louis Louis River. Pull Pull off off and park just the bridge, River. just before before reaching reaching the bridge, or cross it and and park park in in the the parking parking area on the south side of of the the road. road. STOP STOP 11 THOMSON DAM DAM This is the type This type locality locality of of the theThomson Thomson Formation, Formation, which which here here consists consists of slates slates and and metagraywackes. A metagraywackes. A variety variety of of sedimentary sedimentary structures structures may may be be seen, seen, including including ripple ripple marks, marks, load casts, casts, convolute bedding, bedding, cross cross bedding, bedding, graded graded bedding, bedding, and andsole solemarks. marks. Folds with wavelengths from from cm cm to km They are upright wavelengths km are are present present (Figure (Figure 3). 3). They upright to to steeply steeply inclined inclined to to the south south and have subhorizontal fold axes axes that that trend trend east-west. east-west. Where the subhorizontal fold Where folds folds die die out out along along Two such steeply trend, axes axes may may plunge plunge east east or west trend, west as as much much as as 60°. 60'. Two steeply plunging plunging folds folds may be be seen the foliation may seen in this this area. area. A single single axial-planar axial-planar foliation foliation is is present; present; the foliation ranges ranges from a continuous from continuous slaty cleavage cleavage in in the the fine-grained fine-grained units units to to aadisjunctive disjunctivespaced spacedcleavage cleavage in the the more Abundant carbonate in more coarse coarse graywacke graywacke beds. beds. Abundant carbonate concretions concretions and and weathered weathered concretion voids voids can can be seen flattened concretion flattened in the plane plane of of the the cleavage. cleavage. Strain determinations determinations in this region mud chips, chips, and a thin region using using deformed deformed concretions, concretions, mud thin conglomerate conglomerate bed to the the north of of the reservoir reservoir reveal strain strain ratios ratios of about about X:Y:Z X:Y:Z == 7:4:1, 7:4:1, with with XXvertical, vertical,ZZhorizontal horizontal and north-south north-south (perpendicular (perpendicular to foliation) foliation) and YY horizontal horizontaland andeast-west. east-west. Quartz veins, veins, from a few mm to more than a meter in width are present. Some exhibit ptygmatic folding. from mm to more than a meter in width are present. Some exhibit ptygmatic folding. Basalt dikes of of presumed ageare are also also present, present, as as are Basalt dikes presumed Keweenawan Keweenawan age are kink kink bands bands and and several sets sets of joints. several joints. The The kink kink bands bands dip gently gently and and display display aa single single maximum maximum on on an an 0' to the equal-area projection about 2 equal-area projectionwith withan an average averagestrike strikeofof about about N70E N7OEand andaa dip dip of of about 20° Many of the south. Many the kink kinkbands bandsintersect, intersect, but but the theangle angleofofintersection intersectionvaries variesrandomly randomly between 0 and exists within the kink and 30°. 30'. No cross-cutting pattern exists kink bands bands (Clark, (Clark, 1985). 1985). B-6 �I 4645' Middle Prolerozotc 4Tdd. Protorozoic Igneous Rocks Igneous Rock. Middle Prolerozofc Mddl. Proterozotc Sediments q/s o r Loka 5.dim.nt. Thornson Formotion Thomson Northam Formation Tçrran North.rn T.rran. Thomson Formgton Southern Tsrron Unnomid UnTt of Metassd.t,Iitovolcoriic, Unnomed Politic Schist Unnamed Pelitic Schst Denham formation Denhom Formation Upper Member Upper Member Denham Formollon Denham Formation Lower Member Member Lower McGrath Gn.Tss Figure 2:2: Figure Geologic map map of of the the area area of of the the field field trip trip (after (after Southwick, Southwick, Morey, Morey, and and Geologic McSwiggen, 1988). showing locations of field trip stops. McSwiggen, 1988), showing locations of field trip stops. A Figure 3: 3: Anticline Anticline at at Thomson Thomson Dam, Dam, view view from from the the east east bank bank of of the the St. St.Louis LouisRiver, River, just just Figure south of the highway bridge, looking west. Drawing by by Wendell Wendell Wilson. Wilson. south of the highway bridge, looking west. Drawing B- 7 �Proceed west west on on Minnesota Highway Highway 210 210 for for about about 0.8 mile Driving Directions: Directions: Proceed mile to to the the town town of Canton. Turn right right (north) (north) at at the the stop Carlton. Turn stop sign on on to to Old Old Highway Highway 61. 61. Proceed for one one either the convenience convenience store on the the right rightside side block and park in either store parking parking lot, lot, or or the the large lot on of the road. road. Walk Walknorth north to to first first road roadcut cut outcrop outcrop on on west west side side of of road. road. STOP STOP 2 CARLTON CARLTON ROAD ROAD CUT CUT lnterbedded slates slates and and graywackes graywackes of of the Thomson Formation here dip to Interbedded to the the south. south. is present. is present, flattened in the A subvertical subvertical cleavage cleavage is present. A deformed deformed load load cast cast is flattened in cleavage plane. Numerousdeformed deformedconcretions concretionswith withquite quiteaarange range in in size size are are present plane. Numerous present in The north-south vertical vertical joint joint face face is XZ both slate and and graywacke graywacke beds. beds. The is the the approximate approximate XZ plane of the strain strain ellipsoid ellipsoid in the the northern northern structural structural terrane of the the Thomson Thomson Formation. Formation. Driving Directions: south one block and turn Directions: Reurn south turn right right (west) (west) on on Minnesota Minnesota Highway Highway 210. 210. Proceed about 3 miles Proceed about miles to to the theoverpass overpassintersection intersectionwith with Interstate Interstate Highway Highway 35. 35. Proceed Proceed under the freeway freeway and turn turn left left on onentrance entranceramp ramptoto1-35 1-35South. South. Proceed for approximately approximately 26 miles miles and and take take exit exit 209, 209,Sturgeon Sturgeon Lake. Lake. Turn Turn right right and proceed proceed into into the the town town of of 26 Sturgeon Lake to to the the ITjunction. Sturgeon Lake junction. Turn Turn left on on Highway Highway 61 and and proceed proceed to the the first first right right turn, the abandoned abandoned railroad railroadtrack trackand and then then turns turns left left to to the center turn, which which crosses crosses the center of of town. town. turn right with a bar and a bank In one block turn right (at the intersection with bank on on the the corners) corners) and and follow follow The road winds winds past an old school County 46 out of Pine County of Sturgeon Sturgeon Lake. Lake. The school and and heads heads west west for about a mile, sharply to to the mile, then then bends bends sharply the right and heads north north for a half half mile, mile, and and then then 3.2 miles bends sharply left left and and runs bends sharply runs due due west west for for aa number number of of miles. miles. About About 3.2 miles out out of of Sturgeon Lake (or (or 1.7 1.7 miles west of of the second Sturgeon Lake miles west second sharp sharp bend in the the road) road) there there is is aabridge bridge Park and and proceed to to road cuts on the west side of over the Kettle Kettle River. River. Park of the the river. river. STOP STOP 3 KETTLE KETTLERIVER RIVER ROAD ROAD CUT CUT This bridge was constructed constructed inin the the mid mid 1980s (the old bridge is This bridge was is in aa farmer's farmer's field field just to the the northeast) northeast) and and aa new new road roadcut cutexposes exposesmetasedimentary metasedimentary rocks rocks on on both both the the north north sides of the the road. road. The rocks rocks here here have have been been mapped mapped historically historically as as Thomson Thomson and south sides Formation, but are are part part of the Formation, but the "unnamed "unnamed pelitic pelitic schist" schist" unit unit (Pps) (Pps) of of Southwick, Southwick, Morey Morey and and They are are part of McSwiggen McSwiggen (1988). (1988). They of the the southern southern structural structural terrane terrane of the the rocks rocks deformed deformed during the Penokean orogeny in in east-central Minnesota, and and are are part part of the Penokean orogeny east-central Minnesota, the Moose Moose Lake Lake -Glen Township panal of Southwick, Glen Township structural structural panal Southwick, Morey Morey and and McSwiggen McSwiggen (1988). (1988). The rocks rocks The early here are of here of garnet garnet metamorphic metamorphic grade, grade, and and two two foliations foliations are are observable. observable. The early foliation is subparallel subparallel to bedding, bedding, and and the the later latercrenulation crenulation cleavage cleavage isissubvertical subvertical and and Recent trends east-west. east-west. AA lineation trends lineation exists, exists, parallel parallel to to the the intersection intersection of of the the two twofoliations. foliations. Recent thermobarometricwork work on on samples samples from from this outcrop thermobarometric outcrop (HoIm (Holm and and Selverstone, Selverstone, 1989) 1989) yielded yielded temperature estimates estimates of of 470-520° 470-520°C and and a pressure of around around 66 kb. kb. final equilibration temperature Continue west west on on Pine County County 46 46 for about 2.8 miles. miles. Turn left (south) (south) about 2.8 Driving Directions: Directions: Continue Turn left (east) on another this road south another dirt dirt road. road. Follow this south for 1.5 1.5 miles. miles. Turn on a dirt dirt road. road. Follow mile, the "mainTM roadturns turnstoto the the right right (south), After 1 mile, "main" dirtdirtroad (south), but continue continue straight straight ahead ahead In .3 or .4 .4 mile mile there there isis aarailroad railroadcrossing. crossing. Park near, but but (east) on the the "two-track" "two-track" lane. lane. In not on the the railroad railroad tracks, tracks, and and walk walk along along the the tracks tracks to to the thenortheast. northeast. There There is aa long long railroad cut about .3 .3 mile mile northeast northeast of of the theroad/railroad road/railroadintersection. intersection. 1 8-8 �/ STOP 4 DENHAM DENHAMCEMETERY CEMETERY RAILROAD RAILROAD CUT Rocks exposed another similar the southwest southwest Rocks exposed along along this this cut and another similar cut cut one-half one-halt mile to the have historically historically been called called the the southernmost southernmost exposures exposures of Thomson Thomson Formation. Formation. As the As at the these rocks rocks have have recently recently been been designated designated part of an an unnamed unnamed peletic peletic schist schist unit unit last stop these (Pps), part of the the Moose Moose Lake Lake --Glen GlenTownship Township structural structural panal panal by by Southwick, Southwick, Morey, Morey, and and (Pps), McSwiggen (1988). (1988). A McSwiggen A number number of of F2 F2folds folds are are exposed exposed in this cut. cut. Fold axial surfaces surfaces are are vertical and axes are are subhorizontal. subhorizontal. The S, and east-west. east-west. Fold axes Sl foliation foliation which is is subparallel subparallel to S2 crenulation cleavage (axial-planar to most easily easily seen seen bedding and the S2 cleavage (axial-planar to the the F2 folds) folds) are most in the the more more fine-grained fine-grained schistose schistose units. units. Some Some of of the the metagraywacke metagrayacke units units are are nearly nearly quartzites quartzites here. here. Again Again there is is aaeast-west east-westsubhorizontai subhorizontal lineation. lineation. There There are are quite quite aa number of of early early quartz quartz veins veins which which exhibit exhibit boudinage. boudinage. The rocks number rocks here here are are staurolite staurolite grade grade and garnets Holst and and garnets are are visible visible in in many many samples. samples. Based Based on petrographic petrographic study, Holm, Hoist study, Hoim, Ellis (1988) that the the garnets with the the early early foliation during a Ellis (1988) suggested suggested that garnets were were synkinematic synkinematic with foliation during thermal peak peak of of metamorphism metamorphism occurred occurred after after progressive metamorphic metamorphic event, event, and and that the thermal the later phase of of deformation, deformation, as as indicated indicatedby by staurolite staurolite porphyroblasts porphyroblasts which which overprint overprint both both foliations. the Thermobarometric analysis the S1 S, and and S2 S2 foliations. analysis of samples samples from from this exposure exposure the assemblage assemblagestaurolite÷garnet÷plagioclase÷chlorite+ staurolite+garnet+plagioclase+chlorite+ muscovite+biotite+quartz muscovite+biotite+quartz containing the have yielded temperaturesofof 520-590° 520-590°Cand andpressures pressuresofof about about 7 kb have yielded final final equilibration equilibration temperatures kb (Holm and Selverstone, Selverstone, 1989). 1989). Driving Directions: Return over over the the same Directions: Return same route route to the the town town of of Sturgeon Sturgeon Lake. Lake. After crossing the abandoned left (northeast) crossing abandoned railroad railroad grade grade in in the middle of town turn turn left on the middle of town (northeast) on Highway 61. Follow Highway Highway 61 61 northeast for about 5.2 61. Follow 5.2 miles. miles. Turn left left at at the the intersection intersection and follow Highway one-half mile mile turn turn left left (west) at the stop Highway 61 into into Moose Moose Lake. Lake. In about about one-half stop light one-quarter mile mile up up the the hill to the light in the the center center of town town and and follow follow Highway Highway 27 about about one-quarter the railroad crossing. Park in in the the lot at the on the crossing. Park the old old train train station station on the west side of of the the road, road, and and the south along the the tracks the south side side of of the the railroad railroadtracks. tracks. Walk Walk along tracks to to the the northeast northeast to to some some railroad cut cut exposures. exposures. STOP 5 MOOSE MOOSELAKE LAKE RAILROAD RAILROAD CUT CUT These of metasedimentary rocksare arealso also part part of of the These exposures exposures of metasedimentary rocks the unnamed unnamed pelitic pelitic schist unit (Pps) of the schist the Moose Moose Lake Lake -- Glen GlenTownship Township structural structural panal of of Southwick, Southwick, Morey, Morey, and McSwiggen McSwiggen (1988), and have have historically historically been been mapped mapped as as Thomson Thomson Formation. Formation. In the the last and itit may last decade decade this this cut has has become become distinctly distinctly more more overgrown, overgrown, and may be be necessary necessary to to displace some features here. see some structural features displace some vegetation vegetation to to see some of the the structural here. The Sl S1 bedding-parallel foliationisis well well developed developed in in the the rocks rocks along along this this cut. bedding-parallel foliation cut. Early quartz quartz veins veins show boudinage features documenting documenting finite finite entensional entensionalstrain strainwithin withinthe the plane plane of of the early boudinage features S1 foliation. These These features features can can be seen S, foliation. seen on on outcrop outcrop faces faces in in several several orientations orientations showing showing that that the extension extension within within the plane plane of of this this foliation foliation occurred occurred in in all directions. directions. A mineral mineral lineation defined defined by by muscovite muscovite streaks streaks can can be be seen seen on on the the north north side side of of the tracks tracks at at one one of of folds of of various the first exposures exposures as you walk walk in in along along the the tracks. tracks. Several Several F2 folds various scales scales are are present. At least least one one of of these these folds folds has has an an axial axial plane plane which which dips dips about about 60° 60' to to the the south, south, and the S2 cleavage is is axial planar to the S2 crenulation crenulation cleavage the fold. fold. In some some exposures exposures along along this this cut there are are two two sets sets of ofcrenulation crenulationcleavages, cleavages, both both of of which which are are vertical. vertical. A (presumed) (presumed) Keweenawan basalt basalt dike, dike, vertical and trending approximately N8OEisis exposed exposed in in this cut. approximately N8OE Driving Directions: Continue west west on Highway for 4.0 4.0 miles. miles. Turn right (north) Directions: Continue Highway 27 for (north) off off the the road permission at at the house, road into the the farm farm driveway driveway and and park. park. After After asking asking permission house, walk walk north north from the house, just east house, just east of a line line of of trees trees along along the the edge edge of the the farmer's farmer's field field to to the the banks banks of Glaisby Glaisby Brook. Brook. B-9 �STOP 66(ALTERNATE (ALTERNATE STOP) STOP) GLAISBY GLAISBYBROOK BROOK STOP Rocks of of these theseexposures exposuresalong along Glaisby Glaisby Brook Brookhave havealso alsobeen been mapped historically Rocks mapped historically as Thomson Formation. They are are part part of of aaunnamed unnamed unit unit of of metasedimentary metasedimentary and and as Thomson Formation. They metavolcanic rocks rocks (Pgvi) (Pgvi) ofofSouthwick, Southwick,Morey, Morey,and andMcSwiggen McSwiggen(1988), (1988), but are still part of metavolcanic but are still part of their Moose MooseLake Lake -- Glen GlenTownship Townshipstructural structuralpanal. panal. Although Although the the exposure exposure isisovergrown overgrown their andlichen-covered, lichen-covered, itit isis possible possible to to see seean anisoclinal isoclinalrecumbent recumbentfold fold inin this outcrop, with and this outcrop, with several minor minor folds folds ofofnormal normalvergence vergencerelationship relationship (Figure (Figure4). 4). This This isisthe thelargest largestexample example several of an anF, Fl fold foldfound foundtotodate dateininthis thisregion. region. of Sketch of of F, Fl fold foldatatthe theGlaisby GlaisbyBrook Brookoutcrop outcropabout about 44miles miles west west ofofMoose Moose Figure 4:4: Sketch Figure Lake. Lake. DrivingDirections: Directions: Return Return to to the the town town ofofMoose MooseLake Lakefollowing following Highway Highway 27 27back back to the Driving to the east for for just just over over 44miles. miles. Turn Turn left left(northeast) (northeast) at at the the stop stoplight, light,and andfollow followHighway Highway61 61 to east to the northeast northeast (you (you need need to to turn turn left leftoff offthe the"maine "mainnroad road that that goes goes totothe thefreeway). freeway). Follow Follow the Highway 61 61 to to the thenortheast northeast passing passing through through the the town town of of Barnum Barnum inin just just over over 44miles. miles. Highway Continue for another 6 miles on Highway 61 to the village of Mahtowa. Turn left Continue for another 6 miles on Highway 61 to the village of Mahtowa. Turn left (northwest) on Carlton County 4 at Mahtowa. The road turns north after 0.6 miles, and (northwest) on Canton County 4 at Mahtowa. The road turns north after 0.6 miles, and then west west after afteranother another0.9 0.9miles. miles. Just Just after after the the turn turn to to the thewest, west, turn turnright right(north) (north)onto onto then Carlton County 7 toward Park Lake. Follow Carlton County 7 for 1.7 miles and Park. Carlton County 7 toward Park Lake. Follow Canton County 7 for 1.7 miles and Park. Proceed west west and and slightly slightly south south into into the the woods woods toto aa series seriesofoflinear lineareast-west east-westoutcrop outcrop Proceed ridges. ridges. 8-10 �, STOP 7 PARK PARKLAKE LAKE Rocks Rocks at this this locality locality are are part partofofthe theThomson ThomsonFormation, Formationl and and contain contain two two distinct distinct foliations. foliations. This This region region has has been beenmapped mappedas asPvt2 Pv&by bySouthwick, Southwick,Morey, Morey, and andMcswiggen Mcswiggen (1988): Thomson Formation Formation with with two twofoliations. foliations. The The dominant dominant foliation foliation here is aa cleavage cleavage (1988): Thomson that is is parallel parallel to tobedding bedding(S1). (Sl). The The bedding bedding (S0) (So)and and cleavage cleavage(S1) (St) have have been folded into (FJ that that trend trend east-west. east-west. A crenulation crenulation into open, open, upright uprightsubhorizontal subhorizontal folds folds (F2) cleavage cleavage (S2) (S2) is axial axial planar planar to to these these folds. folds. In In this this area area the thecrenulation crenulation cleavage cleavage (S2) (SJ is is present present in most most outcrops outcrops except except for for some some of of the thegraywacke graywacke units. units. The bedding-parallel bedding-parallel foliation for aa very foliation (S1) (S,) is present everywhere everywhere except except for very few fewcoarse coarsegraywacke graywackebeds. beds. At At the the extreme extreme southwest southwest part part of of this this exposure exposure south south of of Park Park Lake, Lakel small small scale scale isoclinal, isoclinal, recumbent folds (F1) recumbent folds (Fl) are present, present, to to which which the thebeddingbedding-parallel parallelfoliation foliation isis axial planar planar (Figure S,foliation foliation is is at at high high angles angles to to bedding bedding only only in in the the (rare) (rare)hinges hinges of of these these (Figure 5). 5). The S, F, Someofofthe theF1Flfolds foldshave havebeen beenrefolded refoldedby byF2 F2folds folds resulting resulting in in aa Ramsay Ramsay type type 33 F, folds. folds. Some interference interference pattern. pattern. N S 1lcm Figure shown by the silt Sketch of of aa small small fold fold at at stop stop 7, 7, Park ParkLake. Lake. Bedding Bedding (S0) (So) shown silt bed bed Figure 5: 5: Sketch is is folded folded into intoan anisoclinal isoclinalrecumbent recumbentfold fold(F1) (Fl) with withaxial axialplanar planarslaty slatycleavage cleavage(S1) (Sl)parallel parallel with with bedding bedding on the the limbs limbs of ofthe thefold. fold. Bedding Bedding and the S, S1foliation foliation are are folded folded by by later later upright of type interference patterns patterns (Ramsay, (Ramsay, 1967) 1967) and and upright folds (F2) (F2) with the the development development of type 33 interference aa vertical verticalcrenulation crenulationcleavage cleavage(S2). (SJ. Driving Driving Directions: Directions: Return Return south south by the the same same route route (Carlton (Carlton County County 7 and 4) to to the the village village of of Mahtowa. Mahtowa. Turn Turn left left(northeast) (northeast) on on Highway Highway61. 61. Proceed Proceed northeast northeast on Highway Highway 61, 61, passing passing through through the village village of of Atkinson, Atkinsonl and and proceed proceed under under the the freeway freeway bridge bridge 8.1 8.1 miles miles past At the the intersection intersection which which is is 1.05 1.05 miles rniles past pastthe thefreeway freeway bridge, bridge, turn turnright right past Mahtowa. Mahtowa. At (south) (south) and and proceed proceed 0.7 0.7 miles miles south south on on Gillogly Gillogly Road Road to to an an outcrop outcrop on on the the left left(east) (east)side side of of the the road, roadl at at the the top topof of aahill. hill. B-il �STOP 8 GILLOGLY GILLOGLY ROAD ROAD At earlier for two At earlier stops stops on this field field trip trip we we have have seen seen evidence evidence for two periods periods of of folding folding and foliation development in the southern structural terrane, and and one one main period of folding development in structural terranel folding and foliation in (1984) argued argued that that the the early early period of folding in the the northern northern terrane. terrane. Hoist Holst (1984) folding in in the southern The evidence southern terrane terrane also also involved involved the the emplacement emplacement of of nappes. nappes. The evidence he cited for for northward-directed nappes southern terrane terrane included included lithologic lithologic differences differencesbetween between northward-directed nappes in in the southern the (also see the two two terranes terranes (also see Morey Morey and andSouthwick, Southwick, 1984, and Southwick, Southwick, Morey Morey and and 1984, and Mcswiggen, 1988), 1988), and and the pervasive nature of the S1 foliation in the area Mcswiggen, Sl foliation area of of its itsoccurrence. occurrence. Facing area of of the the southern southern Facing directions directions of of F2 folds folds (Figure (Figure 6) 6) also also indicate indicate that that aa very very large area terrane The refraction pattern of of the the St terrane is on the upper upper limb of an an F, F, fold. fold. The refraction pattern Sl foliation foliation pattern pattern in the region region of of this this outcrop outcrop also also suggests suggests the the existence existence ot of northward-directed northward-directednappes nappes in in the the southern terrane, as as explained explained below. below. Several graded beds beds in the Thomson can be be seen at this Several graded Thomson Formation Formation can this locality localitystriking striking east-west and dipping to the the north. north. In the finer finer grained grained tops tops of of these these beds, beds,aacleavage cleavage(S1) (St) can be be observed. observed. ItIt is very very gently gently folded, folded, with with horizontal horizontal axes axes trending trending east-west. east-west. Iflithe the cleavage is traced toward the bottom of a bed, toward the bedl itit isis seen seen to to change change its its orientation orientation markedly, markedlyl and it becomes dipping moderately moderatelytoto the the south south in in the bottom and becomes a spaced spaced cleavage, cleavage, dipping bottom part part of of A crenulation cleavage (SJ, (S2),vertical verticalororvery verysteeply steeplydipping dippingtoto the the south, south, can can be the bed. bed. A crenulation cleavage seen in the upper of the beds. Mud seen upper portion of Mudchips chipsthat that are are flattened flattened in in the the early early S, Slfoliation foliation are present. present. A line line drawing drawing of of these these relationships relationships is is shown shown in in Figure Figure 7.7. To interpret interpret the the pattern of this outcrop, of S0 after the early pattern outcrop, itit is useful useful to to determine determine the the orientation orientation of So and S1 Sl after early phase of deformation, phase deformation, but prior prior to to the thelater laterphase phaseofofdeformation, deformation, which whichproduced producedF2 F2folds, folds, crenulation cleavagel cleavage, and and (very importantly for our puposes the S2 crenulation importantly for puposes here) deformed deformed the the early early S1 cleavage, cleavage, changing changing the geometry This can be S, geometry of of bedding/cleavage beddinglcleavage vergence vergence patterns. patterns. This be done, least to to aafairly fairly good goodapproximation approximation because both the done, at at least becausewe we have have strain strain data data for for both southern and and northern 1985a). Results Results of strain strain southern northern structural structural terranes terranes in the the region region (Hoist, (Holst, 1985a). determinations in in the the southern give the resulted from determinations southern terrane terrane give the finite finite strain strain which resulted from the the strain of the first superposition second deformation superposition of the the strain of the the second deformation upon upon the strain present in the northern deformation. As the only only deformational deformational structures structures present northern terrane are are those those of the the second second deformation, deformation, the the strain strain measured measured there there represents represents the the strain strain associated associated with with strain measured the second By removing that strain removing that strain from from the the finite finite strain measured in the the second deformation. deformation. By south, with the first south, we can can approximate approximate the strain strain associated associated with first deformation deformation in the the southern southern This is illustrated terrane terrane (Hoist, (Holst, 1985a; 1985a; Hoim, Holm, HoIst, Holst, and and Ellis, Ellis, 1988). 1988). This illustrated in Figure Figure 8. 8. By By outcrop we we can reconstruct the removing removing the the second second deformation deformation strain strain from from this this outcrop can reconstruct bedding(S0) /cteavage(S1)geometry geometryprior prior to to the is bedding(So) /cleavage(S,) the second second deformation. deformation. The technique technique is illustrated in Figure to alternating coarse 9. The graded graded sequence sequence is generalized generalized to coarse and fine fine Figure 9. layers, (in the the finest finest and coarsest parts of layers, with the attitude attitude of bedding bedding and and the the S1 Sl cleavage cleavage (in the beds) as Removal of of the the strain associated associated with the the as seen seen now now in in outcrop outcrop (Figure (Figure 9A). 9A). Removal geometrical relationships second deformation allows aa reconstruction deformation allows reconstruction of the the geometrical relationships of these these features features prior prior to to the thesecond seconddeformation deformation (Figure (Figure 9B). 98). The resulting resulting bedding/cleavage beddinglcleavage vergence pattern (cleavage (cleavage refraction refraction pattern) pattern) isis that that to to be expected vergence pattern expected on the the upper upper limb limb and and near the hinge hinge of of aalarge-scale large-scaleisoclinal, isoclinal, recumbent recumbent fold fold (Figure (Figure 10). 10). In the entire entire region region of the the the the southern southern terrane terrane to the the south, south, the the S1 S, cleavage cleavage is seen seen to to be besubparallel subparallel to the the bedding. Significantly that is not true here, and in the outcrop 1 km to the north, along the north, along an an bedding. Significantly that is not true here, and in the outcrop abandoned railroad near near Highway 61, the cleavage/bedding vergencepattern pattern isis the the same abandoned railroad Highway 61, cleavagebedding vergence same as seen this outcrop, there are no seen in in this outcrop, although although there no graded graded beds beds there. there. Further, Further, these two two outcrops are very outcrops are very close close to to the theboundary boundarybetween between the thenorthern northernand andsouthern southernstructural structural terranes. B-12 �Figure6:6: Illustration Illustrationofof facing facing direction directionofofF2 F2folds folds(after (afterBorradaile, Borradaile,1976). 1976). Dashed line is Figure Dashed line is axial plane ofof F1F, fold. fold. Foliation Foliation shown showndiagrammatically diagrammatically isis S2 S2 axial axialplanar planar crenulation axial plane crenulation cleavage. Small Smallarrows arrows indicate indicate stratigraphic stratigraphic tops, topsl large largearrows arrowsindicate indicatefacing facingdirections directions of cleavage. of F2folds. folds. F2 "so Si I Line drawing drawing ofofgeometrical geometricalrelations relationsofofbedding beddin; (S0), (So), early foliation (SJ1 and Figure 7:7: Line Figure early foliation (S1), and crenulation (SJ at Gillogly Road outcrop (Stop 8). Hammer handle isis40 40cm cleavage cmlong. long. crenulation cleavage (S2) at Gillogly Road outcrop (Stop 8). Hammer handle B-13 �N X:Y:Z t5 1:02 Northern A r m NorIh. Aria pj 'II Second Oatormallon Strain S.cond Dito,maion Str.àn Soulharn A r c SOuIh.rn Aria Total Strain (both d~fOrm~llOnal Tolal Strain (both diformailons) NZl0 YZ:t2:1: N X:YZ:4.2t0.3 Lxi 23.1t I, t Modal K Modal I Iod.i H Inlurad Strain of FIfl DaforiMllon Inh.r.d Strain 01 FIrst Oslorinatlon Figure8:8: Representative block diagrams of the state of finite strain in the northern and Figure Representative block diagrams ofinferred the state of finite strain in the northern southern structural terranes, terranes, and andthe thestrain straininferred to have been associated with theand first southern structural to have been associated with the first deformation. deformation. Figure 9:9: Bedding Bedding and and cleavage cleavage atatthe theGillogly GilloglyRoad Road outcrop (Stop 8) (generalized to Figure outcrop 8) (generalized alternating coarse and fine layers instead of graded beds) showing(Stop the present geometry to (A) alternating coarse and fine layers instead of graded beds) showing the present geometry (A) and geometry after removal of the strain associated with the second phase of seformation and geometry after removal of the strain associated with the second phase of seformation (6). (B). Figure 10: 10: Figure Position on onearly earlylarge-scale large-scale isoclinal recumbent fold (nappe) of cleavage Position isoclinal recumbent fold (nappe) of cleavage refraction pattern shown in Figure 9B. refraction pattern shown in Figure 9B. 8-14 �________ _______ Driving Directions: Directions: Return Highway 61 and and turn turn right right Return north north on on Gillogly Gillogly Road Road 0.7 0.7 miles miles to Highway (northeast) on Highway Highway 61. 61. Proceed for for 11 mile to aa road road cut cut with with outcrops outcrops on both both side side of of the road. STOP STOP 9 HIGHWAY HIGHWAY 61 61 ROAD ROAD CUT CUT The structural features features seen the Thomson Thomson Formation Formation are are those those seen in these exposures of the seen at the the type type locality, locality, Thomson Thomson Dam Dam (Stop (Stop 1). 1). Several upright, subhorizontal subhorizontal folds trend east-west. to the south. east-west. An An axial axial planar planar cleavage cleavage is is present, present, vertical or very steeply steeply dipping dipping to Abundant mud chips chips are are flattened flattenedinin the the plane plane of of the the cleavage. cleavage. AA faint Abundant mud faint vertical vertical lineation lineation Is is also present. present. The mud mud chips chips have have been been used used for for finite finite strain strain estimates. estimates. Some examples examples of cleavage cleavage refraction refraction are are present, present, and and they theyshow shownormal normalbedding/cleavage beddinglcleavage vergence vergence of relationships relationships to the upright upright folds. folds. No evidence has locality for the the early early No evidence has been been found found at this locality foliation foliation and recumbent recumbent folding folding seen seen in the the southern southern structural structural terrane. terrane. At point the the At this point terranes seems to be be rather rather sharp. sharp. boundary between the two structural terranes Proceed northeast northeast along along Highway Highway 61 61 for 1 .9 miles miles to to an Driving Directions: Directions: Proceed for 1.9 an intersection intersection with Minnesota Minnesota Highway Highway 210. 210. Turn Turn left (west) on Highway Highway 210 210 and and proceed proceed for for 0.1 0.1 miles miles and and turn turn right right on on the theentrance entrance ramp ramp totothe thefreeway, freeway,1-35 1-35North. North. Return Return to Duluth on on to Duluth Interstate Interstate 35. 35. REFERENCES REFERENCES CITED CITED , I I I I I I Borradaile, G.,J., 1976, facing" (Shakleton's (Shakleton's rule) rule) and and the Paleozoic Borradaile, G.,J., 1976, "Structural "Structural facing" Paleozoic rocks rocks of of the the Malaguide Complex Complex near near Velez Velez Rubio, Rubio, SE Spain: Spain: Koninklijk Nederlandse Akademie Akademie ser. B, v. v. 79, 79, p. p. 330-336 330-336 van Wetenschappen, Wetenschappen, ser. Brocoum, Brocoum, S. J., J., and and Dalziel, Dalziel, 1.I. W. D., D., 1974, 1974, The Sudbury Sudbury Basin, Basin, the the southern southern province, province, the Grenville Front, and and the the Penokean Penokean orogeny: orogeny: Geological Society of America America Bulletin, Bulletin, v. 85, V. 85, p. p. 1571-1580. 1571-1580. Cambray, F. F. W., Michigan: Michigan Basin Cambray, W., 1977, 1977, Field Field guide guide to to the the Marquette Marquette district, district, Michigan: Basin Geological Society Annual Meeting, Meeting, 62 p. p. as aa model , 1978, 1978, Plate Plate Tectonics Tectonics as model for the environment environment of deposition deposition and and deformation of the Early Proterozoic of northern northern Michigan: deformation of the Early Proterozoic (Precambrian (Precambrian X) X) of Michigan: Abstracts with Programs, v. 10, Geological Society of America America Abstracts 10, p. p. 376. 376. Cannon, W. W. F., Young, G. G. M., Cannon, F., 1973, 1973, The The Penokean Penokean orogeny orogeny in in northern northern Michigan, Michigan, Young, M., ed., Association of of Canada Huronian stratigraphy and and sedimentation: sedimentation: Geological Association Canada Special Special Paper, v. 12, 12, p. p. 211-249. 21 1-249. Clark, R.G., Clark, R.G., 1985, 1985, The The structural structural geology geology of the the Thomson Thomson Formation; Formation; Cloquet Cloquet and and Esko Esko quadrangles, east-central Minnesota: Minnesota: unpublished MS thesis, University quadrangles, east-central University of Minnesota Minnesota Duluth, Duluth, Minnesota Minnesota 114 p. diapiric Dixon, strain and progressive progressive deformation deformation in in models models of diapiric Dixon, J. M., 1975, 1975, Finite Finite strain Tectonophysics, v. v. 28, p. 89-124. structures: Tectonophysics, 89-124. Gray, D.R., of crenulation cleavages: cleavages: Journal Journal of of Geology, v. Gray, D.R., 1977, 1977, Morphologic Morphologic classification classification of p. 229-235. 229-235. 85, p. HoIm, D. 0. K., of the Holm, K., 1986a, 1986a, AAstructural structuralinvestigation investigation and and tectonic tectonic interpretation interpretation of the Penokean Penokean orogeny: University of Minnesota Minnesota Duluth, Duluth, 114 114 orogeny: east-central Minnesota, Minnesota, [M.S. [M.S. Thesis]: Thesis]: University a., p. P. , 1986b, 1986b, An account account of of multiphase multiphase deformation deformation during during the the Penokean Penokean orogeny: orogeny: evidence overlying Early Early evidence from from analysis analysis of the the Archean Archean McGrath McGrath Gneiss Gneiss and and overlying in east-central Proterozoic metasedimentary Minnesota: Institute Proterozoic rnetasedimentary rocks rocks in east-central Minnesota: Institute on Lake Lake Superior Geology Geology Abstracts, Abstracts, v. v. 32, 32, p. p. 32-33. 32-33. B-15 �________ _______ ________ Holstl T.B.* Ellis* M., M., 1988, 1988*Oblique Oblique subduction, subduction, footwall footwall deformation, deformation, and HoIm, D.K, D.K, Hoist, T.B., and Ellis, imbrication: imbrication: A model for the Penokean Penokean orogeny orogeny in in east-central A model east-central Minnesota: Minnesota: Geological Society of Bulletinl v. v. 100, 1001P. p. 1811-1818. 1811-1818. of America Bulletin, Holm, D.K., O.K., and and Selverstonel Selverstone,J.* J., 1989# 1989, Preliminary Preliminary constraints constraintson onthe the P-T P-T evolution evolution of of the Penokean orogeny: orogeny: east-central Minnesota: Minnesota: Institute lnstitute on Lake Superior Superior Geology Geology on Lake Abstracts Proceedings, v. Abstracts and Proceedings, v. 35 (this volume). B.*1982, 1982, Evidence Evidence for for multiple multiple deformation deformation during during the Penokean Penokean orogeny orogeny in in the the Hoist, T. T. B., Middle Precambrian Precambrian Thomson Thomson Formation, Formation*Minnesota: Minnesota: Canadian Earth Middle Canadian Journal Journal of Earth Sciencesl v. 19, p. p. 2043-2047. 2043-2047. Sciences, v. 19, 1984a, Penokean tectonics: constraints from the structural geology in 1984al in east-central east-central Minnesota: Institute on on Lake Lake Superior Superior Geology Geology Abstracts* Abstracts, v.v. 30, 30, p. 19. Minnesota: lnstitute 19. 1984b, Proterozoic Penokean orogeny as aa convergent convergent plate plateboundary: boundary: 1984b, The The Early Proterozoic gI p. p. 75. 75. Geological Association Association of of Canada Program with with Abstracts, Abstracts, v. v. 9, , 1 9984c, 8 4 ~Evidence ~ for development during the the early early Proterozoic ProterozoicPenokean Penokean Evidence for nappe nappe development orogeny, Minnesota: Geology, orogenyl Minnesota: Geology, v. 12, 12*p. p. 135-138. 135-138. 1985a, of a large for origin 1985a, Implications Implications of large flattening flattening strain strain for origin of of aabedding-parallel bedding-parallel foliation in the Early foliation in Proterozoic Thomson Thomson Formation, Formation* Minnesota: Journal of Early Proterozoic Minnesota: Journal Structural Geology, Geology, v. 7, 7*p. p. 375-383. 375-383, 1985b, Strain Strain within within early 1985bl early Proterozoic Proterozoic nappes nappes in the the Penokean Penokean orogenic orogenic belt, belt, Minnesota: Geological Geological Society Society of of America America Abstracts Abstracts with with Programs, Programs, v. v. 17, 17*p. p. 293. 293. Minnesota: Horan, G.N., and Spencer, Horan, M.F., M.F., Hanson, Hanson, G.N., Spencer, K.J., K.J., 1987, 1987, Pb Pb and and Nd Nd isotope isotope and andtrace traceelement element constraints on the the origin constraints on origin of basic basic rocks rocks ininan anearly earlyProterozoic Proterozoicigneous igneous complex, complex, Minnesota: Precambrian Minnesota: Precambrian Research, v. 37, p. p. 323-342. 323-342. Keighin, C. W., W., Morey, G. B., S. S., Minnesota@i Sims, ELl and Goldich, Goldich* S. S., 1972, 1972, East-central East-central Minnesota Sims, P. P. Keighin, C. Morey* G. K., and Morey, G. B., of Minnesota: K., Morey, G. B., eds., Geology Geology of Minnesota: AA centennial centennial volume: volume: Minnesota Minnesota Geological Survey, p. p. 240-255. 240-255. Kiasner, Klasner* J.S., J.S., Ojakangas, Ojakangas* R.W., R.W.* Schulz, Schulz, K.J., K.J., and and LaBerge, LaBerge, G.L., G.L., 1988, 1988, Evidence Evidence for for development Proterozoic overthrust-nappe development ofof an early early Proterozoic overthrust-nappe system system in in the Penokean Penokean Orogen Institute on on Lake Orogen of of northern northern Michigan: Michigan: Institute Lake Superior Superior Geology Geology Abstracts Abstracts and and Proceedings, v. v. 34* 34, p. 56-57. Proceedingsl 56-57. Schulz, K. J., and E., 1984, The plate LaBerge, LaBerge, G. G. L., SchuIzl K. J., and Myers, Myers, P. P. E.* 1984, The plate tectonic tectonic history history of of on Lake v. 30, north-central Wisconsin: Wisconsin: Institute lnstitute on Lake Superior Superior Geology Geology Abstracts, Abstracts, v. 30, p. p. 25-27. 25-27. K., 1981, Larue, D. D. K.# 1981, The The Chocolay Chocolay Group, Groupl Lake Lake Superior Superior region, region,USA: USA:sedimentologic sedimentologic evidence for deposition evidence deposition in in basinal basinal and platform platform settings settings on on an anearly earlyProterozoic Proterozoic craton: craton: Geological Geological Society Society of of America America Bulletin Bulletin Part Part I,I, v. 92, p.p.417-435. 417-435. v. 92, Maass, R. A. S., S.* Medaris, Medaris, L. G., G., Jr., Jr., and and Van VanSchmus, Schmus, W. W. R., R.*1980, 1980,Penokean Penokeandeformation deformation in in Maass* central Wisconsin, Wisconsinl fr Morey, Morey, G. B., B.* and and Hanson, Hanson, G. G. N., N.#Selected Selected studies studies of of Archean Archean gneisses and lower lower Proterozoic Proterozoic rocks, rocks, southern southern Canadian Canadian Shield: Shield: Geological Geological Society Society of America Special Paper 182, of 182. p. 147-157. 147-157. Morey, and Middle nomenclature for Morey, G.B., 1978* Lower and Middle Precambrian Precambrian stratigraphic stratigraphic nomenclature 1978, Lower Survey Report Report of of investigations east-central east-central Minnesota: Minnesota: Minnesota Geological Survey Investigations 21, 52 P a p. 1979, Field trip guidebook , 1979* guidebook for the Precambrain Precambrain geology geology of east-central east-central Minnesota: Minnesota: Geological Surveyl Survey, Guidebook Guidebook Series Series No. No. 12* 12, 28 p. Minnesota Geological , 1983, 1983, Lower Proterozoic stratified rocks and the the Penokean Penokean orogeny orogeny in in east-central east-central Minnesota: Minnesota: Geological Geological Society Society of of America America Memoir Memoir 160, 160, p. p. 97-112. 97-112. Morey, G. G. B., K., 1976, 1976*Boundary Boundary between between two two Precambrian Precambrian W terranes terranes in in Morey, B.* and and Sims, Sims* P. P. K., Minnesota and its Geological Society Society of of America its geologic geologic significance: significance: Geological America Bulletin, Bulletin, v. 87, p. 141-152. 87# 141-152. Morey, G. B., Morey, G. BSl Sims, Sims, P. K., K., Cannon, Cannon* W. W, F., F., Mudrey, Mudrey, M. G., G,, Jr., Jr., and and Southwick, Southwickl 0. 0.L., L., 1982, 1982* Geologic map map of the Geologic the Lake LakeSuperior Superior Region, Region*Minnesota, Minnesota, Wisconsin, Wisconsin, and and Northern Northern Michigan: Minnesota Minnesota Geological Geological Survey Survey State State Map Map Series Series S-13. S-13. B-16 �________ ________• Morey, G. Moreyl G. B., Ba1 and Southwick, Southwick, D. D. K., 1984, 1984, Early Proterozoic geology geology of of east-central east-central Early Proterozoic Minnesota -- a review Institute on on Lake Superior Geology review and and reappraisal: reappraisal: lnstitute Geology Abstracts, Abstractsl v. 30, V. 301p. p. 35-36. 35-36. Ojakangasl R. 19831 Tidal deposits in the Early Early Proterozoic Proterozoic basin Lake Superior Superior Ojakangas, R. Ws1 W., 1983, Tidal deposits basin in the Lake region -- The region Palms and andPokegama PokegamaFormations: Formations: evidence for for subtidal-shelf The Palms evidence subtidal-sheif deposition of Superior-type deposition Superior-type banded banded iron iron formations: formations: Geological Geological Society Society of of America America Memoir 160, p. 49-66. 49-66. Powell, C. C. McA., Powelll McA.* 1979, 197g1A A morphological morphological classification classification of rock cleavage: cleavage: Tectonophysics, v. v. p. 21-34. 21-34. 58, P. Ramsayl G., 1967, 1967#Folding Foldina and Fracturing Fracturina of Rocks: Rocks: McGraw York, 568 p. Ramsay, J. J. G., McGraw Hill, Hill, New York, Schulz, Schulz, K.J., K.JsI 1983, 1983* Geochemistry Geochemistry of the the volcanic volcanic rocks rocks of of northeastern northeastern Wisconsin: Wisconsin: Institute lnstitute v. 29, on Lake Lake Superior Superior Geology Abstracts and Proceedings, Proceedingsl v. 2g1p.39. Schulz, LaBergel G. L., Sims, Simsl P. P. K., Ks1Peterman, Petermanl Z. E., and and Klasner, Klasnerl J. J. S., Ss1 1984*The The Schulz, K. K. Js1 J., LaBerge, G. L., Z. E., 1984, volcanic-plutonic terrane terrane of northern volcanic-plutonic northern Wisconsin: Wisconsin: implications implications for early early Proterozoic Proterozoic tectonism, Lake Superior Geological Association Association of of Canada Program tectonism, Superior region: region: Geological Program with with Abstracts, v. 9, Abstractsl v. g1p. 103. 103. Simpson, M., 1983, 1983* An evaluation evaluation of criteria to deduce the sense sense of of Simpson, C., C., and and Schmid, Schmid, S. S. M., of criteria to deduce movement in sheared Geological Society Society America Bulletin, v. 94# 94, p. movement in sheared rocks: rocks: Geological America Bulletinl p. 1281-1288. 1281 -1288. Sims, P. Simsl P. Ke1 Precambrian tectonics mineral deposits, deposits, Lake Lake Superior Superior region: region: K., 1976, 1976, Precambrian tectonics and and mineral Geology, v. v. 71, Economic Geology, 71 p. p. 1092-1118. 1092-1118. Sims, K., Card, 0., Morey, 1980, The Simsl P. P. K., Card, K. K. Dm1 Morey, G. G.B., B., and andPeterman, Peterman, Z. Z. E., 1980, The Great Great Lakes Lakes in central majorcrustal crustalstructure structure in central North North America: America: Geological tectonic zone zone - AA major tectonic Geological Society of of America Bulletin, Bulletin, Pt. Pt. 1, v. 91, Society 91, p. p. 690-698. 690-698. Sims, 1985, K., Peterman, Petermanl Z. E., Eland and Schulz, Schulzl K. K. J., Ja1 19851The TheDunbar DunbarGneiss-granitoid Gneiss-granitoid dome: dome: Sims, P. K., Proterozoic tectonic northern Wisconsin: Implications tectonic evolution evolution of northern Implications for early Proterozoic Geological Society Society of of America Bulletin, v. 96, p. 1101-1112. Geological Bulletin, v. 1101-1112. E., Klasner, Sims, W. F., 1987, Sims, P. P. K., Ks1Peterman, PetermansZ. Z. Es1 Klasnerl J. J. S., S., Cannon, Cannon, W. F., and and Schulz, Schulz, K. K. J., 1987, Nappe development upper Michigan Michigan segment early Nappe development and and thrust thrust faulting faulting in in the the upper segment of of the early Geological Society Proterozoic Penokean Penokean orogen: orogen: Geological Society of America America Abstracts Abstracts with Proterozoic Programs, v. 19, Programs, v. l g l p. 246. 246. Southwick, Southwickl D.L., D.Ls1and Morey, Morey, G.B., G.B., 1988, 1988, Tectonic Tectonic imbrication imbrication and and foredeep foredeep development development inin the Penokean Institute on Lake Penokean Orogen, Orogen, east-central east-central Minnesota: Minnesota: lnstitute Lake Superior Superior Geology, Geologyl v. 34, V. 34#p. p. 106-107. 106-107. Southwick, D.L., D.L., Morey, Morey, G. B., Southwickl B., and and McSwiggen, McSwiggen, P.L., P.L11988, 1988, Geologic Geologic map map (scale (scale1:250,000) 1:250,000) of of the the Penokean Penokean Orogen, Orogen, central central and and eastern eastern Minnesota, Minnesota, and and accompanying accompanying text: text: Minnesota Geological Geological Surveyl Survey, Report Report of Investigations 37, Saint Paul, Minnesota Investigations 37, Paul, Minnesota, Minnesotal 25 25 P p. Van Schmus, W. R., history of of the Great Van Schmusl W. R.# 1976, 1976, Early Early and and Middle Middle Proterozoic Proterozoic history Great Lakes Lakes area, area, Transactionsofof the the Royal Royal Society Society of London, North America: America: Philosophical Philosophical Transactions London* v. v. 280, 2801 p. 605-628. 605-628. 19801 Chronology Chronology of igneous rocks rocks associated associated with the Penokean 1980, of igneous with the Penokean orogeny orogeny in in Wisconsin: Wisconsin: Geological Geological Society Society of of America America Special Special Paper Paper 182, 18Z1p. p. 159-168. 159-168. , 1981, 1981 Possible interpretations interpretations of of the the Penokean Penokean orogeny: orogeny: International Proterozoic Proterozoic Wisconsinl Madison, Madison, Abstracts Abstracts Volume, p. p. 44. 44. Symposium, University of Wisconsin, B-17 �-- AND RELATIONSHIPS RELATIONSHIPS OF THE THE MELLEN MELLEN IGNEOUS IGNEOUS COMPLEX COMPLEX ROCK TYPES AND A One One Day DayField FieldTrip Triptotothe theKeweenawan Keweenawanofofthe theMellen, Mellen,Wisconsin WisconsinArea Area A Trip Leaders Leaders Kenneth Kenneth W. W. Klewin; Klewin; Northern Northern Illinois Illinois University; University; Dekalb, Dekalb, IL IL James F. F. Olmsted; Olmsted; SUNY; SUNY; Plattsburgh, Plattsburgh, NY NY Karl E. E. Seifert; Seifert; Iowa Iowa State State University; University; Ames, Ames, IA IA Introduction Introduction purpose of of this this trip tripisistotoprovide providean anopportunity opportunitytotoexamine examinethe therock-types, rock-types,igneous igneous The purpose features features and and relationships relationships of ofthe theMellen MellenComplex. Complex. We will will examine examine exposures exposures that that provide provide opportunities to compare compare this this with with other other layered layered intrusions intrusions and and make make judgements judgements on on conditions conditions opportunities and processes processes of formation. formation. Critical exposures are often inaccessible inaccessible for brief visits but but there there are many that we think think you you will will find find interesting interesting and provide for lively lively discussion. discussion. AA few few important but less accessible accessible are included if time time and and locations we we consider important are noted and will be included conditions permit. permit, Geology of the the Mellen Mellen Area Area General General The Mellen Mellen Complex Complex includes includes several several layered layered basic basic and andrelated relatedintrusions intrusions emplaced emplaced near near The the the base base of of the the Keweenawan Keweenawan volcanic volcanic pile. pile. So So far far as ashas hasbeen beendetermined determined the the volcanics volcanics in inthe the Mellen area are are Lower Lower Keweenawan Keweenawan nearly nearly conformably conformably overlying the older Proterozoic Proterozoic units of of Mellen the the Gogebic Gogebic Iron Iron Range. Range. The The lower lower contact contact of the the complex complex is is slightly slightly discordant discordant cutting to to lower lower stratigraphic levels westward, westward, beveling bevelingacross acrossthe theentire entireProterozoic ProterozoictotoArchean Archeangneisses. gneisses. All All of of the the Proterozoic Proterozoic units units have have been been tilted tilted toward toward the the northwest northwest into into the the Lake LakeSuperior Superior syncline syncline resulting in in northeast northeast strikes strikes and and steep steep northwest northwest dips. dips. Faulting Faulting has has accompanied accompanied this this tilting tilting but itit isis difficult difficulttotodemonstrate demonstrate ininthe thefield. field. Paleomagnetic 966) show show normal normal polarity polarity for the intrusive et.a1.(1966) intrusive rocks rocks Paleornagnetic studies of of Books, Books, et.aL(1 of of the the Complex Complex indicating indicating Middle Middle Keweenawan Keweenawan age age for for acquisition acquisition of of its itsmagnetism. magnetism. Green(1982) Green(l982) places the the Mellen Mellen Gabbro Gabbro equivalent equivalent to to the the Duluth Duluth Complex Complex but but itit could could be beslightly slightly older. older. Halls Halls and and Pesonen(1982) Pesonen(l982) indicate indicate rocks rocks of the the Duluth DuluthComplex Complex are are found foundinincontact contactwith with volcanics volcanics of normal normal polarity polarity while while the the Mellen Mellenappears appears to tointrude intrudeonly onlyreversed reversedvolcanics. volcanics. We We only only know know that that the the intrusives intrusives acquired acquired their their its its magnetic magnetic polarity polarity during during the normal normal period and and they they do do not not cut cutUpper UpperKeweenawan Keweenawansedimentary sedimentary units. units. Intrusive Intrusive Units Units The The Mellen MellenComplex Complex includes includestwo two layered layeredgabbroic gabbroic intrusions intrusions the the Potato Potato River RiverIntrusion lntrusion (PRI) (PRI) (Klewin (Klewin 1987 1987 & & in inreview) review) on on the theeast eastand andthe theMineral MineralLake LakeIntrusion Intrusion(MLI) (MLI)(Olmsted, (Olmsted, 1969; Seifert, in prep.) to the 1969; Seifert, the west. west. These Theseare areseparated separatedby bythe theMellen MellenGranite Granite(MG) (MG)which which intruded intruded the the gabbro. gabbro. Contacts Contacts between between intrusives intrusives of the the Complex Complex are are sharp, sharp, often often with with well well developed developed breccias but chilling chilling isis only only observed observed where where pre-intrusive pre-intrusive rocks rocks are are involved. involved. Several Several smaller smaller intrusives intrusives include include the the Rearing RearingPond Pond(RP) (RP)intrusion intrusion (Olmsted, (Olmsted, 1979) 1979) and and aa number number of of smaller smaller gabbro gabbro and and granophyre granophyre sills sills at at the thewest westend endofofthe thecomplex complex(Leighton, (Leighton,1954) 1954) The The two two larger largerintrusions intrusions have havethe thesize sizeand andcharacter character ofoflayered layeredintrusions intrusions throughout throughout the the world. world. The ThePRI PRIisisabout about3.5 3.5km. km.wide wideand andextends extends along along strike strike for over 30 km. The TheMLI MLIisis about about 5 km. km. thick thick and and about about1515km kmalong alongstrike strikebut butmay mayhave havebeen beenfaulted faultedoff offon onthe thewest westend end indicating greater. The indicating it's true length length was was somewhat somewhat greater. The RP RP is is aa small small intrusion intrusion of ofelliptical elliptical plan plan with km.. ItIt appears appears intruded intruded into the the upper upper part part of of the the MLI MLI but but with dimensions dimensions about 22 by by 44 km.. mapping mapping does not not indicate indicate timing. timing. AAsmaller smallermore moresill-like sill-likeunit unitofofsimilar similarpetrographic petrographiccharacter character (the (the Picritic Picritic Zone, Zone, Figure Figure 1)has 1)hasintruded intruded near near the the base base of of the thePRI. PRI. Northwest Northwest of of the the MLI MLI are are several that intrude intrude Lower LowerKeweenawan Keweenawanvolcanics volcanics or or other other several large large gabbro gabbro and andgranophyre granophyresills sills that c-i �intwsions but to intrusions to the the west west are are also alsoemplaced emplacedinto intoolder olderProterozoic Proterozoic units(Leighton units(Leight0n 1954). 1954). Leighton Leighton (1954) argued on the basis basis of of differences differences between between dip dip of of igneous igneouslamination laminationand andmodal modal Pesonen (1982) (1982) note that the the layering that tilting took place place during during intrusion. intrusion. Halls & Pesonen pole positions positions of of the Complex lie on paleomagnetic pole on the the APW APW curve curve without without structural structuralcorrection correction This permits tilting prior prior to to or during indicating tilting prior to acquisition acquisition of polarity. polarity. This permits tilting during intrusion intrusion but but is not not conclusive. conclusive. Petrology Petrology PRI Mellen Complex Complex may be classified into three The PRI The Mellen three distinct distinct types types of of intrusives. intrusives. The and MLI are from olivine olivine rich to anorthositic are coarse coarse grained grained feldspathic feldspathic gabbros that range from anorthositic and olivine olivine are are largely largely cumulus cumulus while while pyroxenes more compositions (Tables 1 & 2). 2). Plagioclase and layering is is rare but lamination as postcumulus postcumulus oikocrysts. oikocrysts. Rhythmic layering lamination is is well well commonly occur as developed roughly parallel to the regional regional structure structure (Leighton, (Leighton, 1954; 1954; Olmsted, 1969; 1969; Klewin, Klewin, 1987). The PicriticZone Zoneofofthe thePRI PRIare aremore moremafic maficpicritic picritic intrusions intrusions that that 1987). The RP RP and andthe thePicritic represent pulses represent pulses of of unique unique magma. magma. The TheRP RPininparticular particularisissomewhat somewhat more more primitive primitive than than the the others having much higher Mg#'s and more more calcic calcic plagioclase plagioclase in addition to higher higher mafic mafic mineral mineral third intrusive intrusive type is is the the Mellen Mellen Granite. Granite. content. The third Cryptic zoning is observed in the larger that some some in situ. larger intrusions intrusions indicating that fractionation occurred occurred (Olmsted,1969; (Olmsted,1969;1979; 1979;Klewin,1984). Klewin,1984).These These (PRI (PRI & & MLI) are zoned from from fractionation gabbro compositions compositions through throughferrodiorites ferrodioritestotogranitic graniticrocks. rocks. There is gabbroic or anorthositic gabbro is some evidence that excessive amounts of granophyre from addition of crustal granophyre resulted from crustal minimum minimum melt material (Seifert, in in prep). prep). granophyre often often forms forms the uppermost Two distinct granites granites occur occur at at Mellen. Mellen. Brick red granophyre uppermost It is also found intrusive the layered layered intrusions intrusions (Olmsted, (Olmsted, 1969, 1969, Klewin Klewin 1987). 1987). It intrusive into into units of the (Leighton,l954). Granophyres Granophyres gabbros or metavolcanics in the western part of the the complex complex (Leighton,1954). display spectacular simplectite simplectite textures textures in which quartz quark occurs intergrown with alkali feldspar feldspar in in micrographic, radiating radiating fringe fringe and and vermicular vermicular patterns patterns (Leighton, (Leighton,1954). 1954). Where these granitic units are thickened the above granular with with only minor above textures textures give way to to hypidiomorphic hypidiomorphic granular minor the western western part part of the area intergrowth features. This is well displayed at a granite boss in the area called St.Peters StPeters Dome Dome (sic.) (sic.) In contrast contrast with with the the granophyre granophyre is is the the Mellen Mellen Granite. Granite. This This medium medium to coarse coarse porphyritic porphyritic both the the PRI on the granite is one one of of the the younger younger intrusives intrusives of of the the complex.. complex.. It has intruded both the east and and MLI to the west. east west. On Onthe thesouth southitithas hasintruded intrudedboth bothKeweenawan Keweenawan volcanics volcanics and siltstones of of the the underlying Tyler formation. formation. The nature siltstones underlying Tyler nature of the the upper upper contact contact is not not well well known known as exposure is poor. poor. At this time only only preliminary preliminary analytical analytical work has has been been accomplished accomplished on on this intrusive so its its chemical chemical nature nature poorly poorly known known Descriptions of of the Intrusions Intrusions Potato River Intrusion Intrusion General General (Fig. 1) and will be the The PRI PRI forms the eastern eastern half of the the MeIlen Mellen Complex Complex (Fig. the subject subject of of general, the the PRI is poorly the first part of the the the trip. In general, poorly exposed, exposed, being mostly covered by unconsolidated Pleistocene Pleistocene sediment sediment and and heavy heavy forest forest and and many many of of the exposures exposures are are deeply deeply Relief in the area is weathered. Relief is generally generally less less than than 150m 150m with with the the highest highest hills hills underlain underlain by by lower Keweenawari volcanics. The resistant lower Keweenawan volcanics. The best best exposures exposures of intrusive intrusive rocks are are scattered scattered glacially scoured scoured outcrops outcrops and and along along drainages. drainages. The overall length length of of the PRI is 33 glacially 33 km.. km.. It is is divided approximately approximately in in half half by by a fault along the Tyler Forks River River into into a narrow and a much divided much wider segment. segment. The wider The width width of of the the intrusion intrusion ranges ranges from from about 1 km. to 4.5 km. km. averaging averaging 3.6 east of the Tyler Tyler Forks Forks River River where where the trip trip is is focused. focused. Basal and roof contacts of the PRI PRI are are roughly roughly concordant concordant with the enclosing enclosing volcanics volcanics While the PRI is largely by volcanics volcanics it cuts into the the regional regional structure. structure. While largely enclosed enclosed by and with the xenoliths of of metabasite have been underlying Proterozoic units near its western western end. end. Rare xenoliths been found near the base base of of the the intrusion. intrusion. C- 2 �Pm == PProterozojc roterozoic Pm m e t a s e d i m e n t a r y rocks rocks metasedimentary Keweenawan Ks == Keweenawan s e d i m e n t a r y rocks rocks sedimentary Kv == Keweenawan Keweenawan Ky volcanic rocks Ar = Archean rocks Ks Ar Upper Zone POTATO RIVER R I V E R INTRUSION INTRUSION POTATO Main Zone I\ / \ / / — '5, 5'.' 'S 5' Picritic Zone ,_ 'S f / 'S '5 S 5' MINERAL LAKE INTRUSION 5'- 15 REARING POND INTRUSION Ar MELLEN GRANITE GRANITE MELLEN Figure F i g u r e 11 - . -- . -. . - ..- �Exposures of plagioclase-rich plagioclase-rich rocks commonly exhibit lamination lamination of of the the plagioclase plagioclaselaths. laths. Tabet and Mangham Mangham (1978) (1978) reported an an average average orientation orientation of of N64oE, N64oE, 84oNW. 84oNW. Occurrences abet and Occurrences of rhythmic layering layering with with average orientation N57oE, N57oE, 64oNW 64oNW are restricted to the Picritic Picritic Zone Zone near near the middle of the PRI. Contacts the middle of Contactsbetween betweengabbroic gabbroicrocks rocksare aretypically typicallygradational. gradational. The PRI has been been divided divided into into several several zones zones based based on on lithology lithology (Fig.1; (Fig.l; Kiewin, Klewin, in in review). review). Lowermost Lowermost is is aa poorly poorly exposed exposed Border Border Zone of highly highly altered altered olivine olivine gabbro cut by rare contemporaneous contemporaneous or or later later dikes. dikes. Where Where exposed, exposed, the the Border Border Zone Zone isisirregular irregular ininthickness, thickness, ranging up to to 2 m. Most ranging up Mostofofthe theintrusion intrusionisisassigned assignedto tothe theMain MainZone Zoneofofmedium mediumgrained grained rocks rocks ranging from from olivine gabbro (at leucogabbro and andquartz quartzgabbro gabbrototoferrogabbro ferrogabbro (at the the base base ),),leucogabbro (toward the the top). top). The Present locally locally at the top The average average thickness thickness of the main main zone is 3300 3300 m. m. Present of the intrusion intrusion is an Upper Upper Zone Zone of of intrusive intrusive granite and granophyre. granophyre. On Onthe thebasis basisof oftrace trace element geochemistry (Klewin, (Klewin, in review) the granophyric element geochemistry granophyric rocks appear genetically genetically related to the Zone rocks but coarser grained Main Zone grained granitic granitic dikes dikes and and irregularly irregularly shaped shaped granitic granitic intrusions intrusions dikes?) near near the the top top of of the intrusion west west of of the Tyler Forks (large dikes?) Forks River are not. The Thethickness thickness Finally, midway midway into into the the Main Zone Zone is the of the Upper Upper Zone ranges ranges from from zero zero locally locally to to 120 120m. m. Finally, distinctive intrusive Picritic Picritic Zone Zone consisting consisting of of picrite picrite and and troctolite. troctolite. The The thickness thickness of of the the Picritic Picritic distinctive intrusive Zone is is estimated estimated to to be be 175 to 200 m. The Zone TheMain MainZone Zoneisisfurther furtherdivided divided into into Main Main Zones Zones I,I, IIII Zone I occurs below the Picritic Zone, is 850 m and Ill. Ill. Main Zone Picritic Zone, m thick thick and and consists consists of olivine olivine gabbro and and olivine olivine leucogabbro. leucogabbro. Main gabbro Main Zone Zone Il, 11, above above the the Picritic Picritic Zone, Zone, is is 1650 1650 m m thick thick and and consists of of olivine gabbro, olivine leucogabbro, gabbro and quartz-bearing leucogabbro. leucogabbro. The consists leucogabbro, gabbro The arrival of of cumulus cumulus augite occurs near the top of Main arrival Main Zone Zone II. II. The boundary boundary between between Main Main Zones IIIl & Ill Fe-Ti oxides. oxides. Main Ill is marked by the arrival arrival of cumulus Fe-Ti Main Zone Zone Ill 111consists consists of of quartz quartz Zones gabbro, quartz quartz leucogabbro leucogabbroand and ferrogabbro. ferrogabbro. Average Average thickness thickness isis 800 800 m. m. The The arrival arrival of of gabbro, cumulus apatite apatite occurs occurs in Main Zone Ill. cumulus Ill. Petrography and and Mineral Petrography Mineral Chemistry Potato River River Intrusion Intrusion is is composed composed of olivine olivine gabbro gabbro and and olivine olivine bearing bearing Most of the Potato leucogabbro. leucogabbro. Primary mineralogy is plagioclase, plagioclase, olivine, clinopyroxene, clinopyroxene, orthopyroxene, orthopyroxene, Fe-Ti Fe-Ti oxides and apatite. apatite. Major cumulus minerals minerals are plagioclase plagioclase and and olivine. olivine. Plagioclase typically typically forms normally zoned lath-shaped lath-shaped to to blocky blocky grains. grains. Olivine is subhedral to anhedral anhedral and unzoned. Clinopyroxene unzoned. Clinopyroxene is is anhedral anhedral and and forms forms oikocrysts oikocrysts where it is is intercumulus intercumulus and is is often often moderately zoned. zoned. Orthopyroxene Ilmenite moderately Orthopyroxene is less less common common and occurs as as inverted inverted pigeonite. pigeonite. llmenite titanomagnetite occur occur as as small oikocrysts or interstitial patches or as and titanomagnetite as skeletal skeletal cumulus cumulus grains grains in the ferrogabbros. ferrogabbros. Apatite typically occurs as tiny included included grains but is is larger larger and and cumulus cumulus in in of quartz the ferrogabbros. ferrogabbros. Quartz gabbro is is marked marked by by intercumulus intercumulus micrographic micrographic intergrowths intergrowths of and alkali feldspar. feldspar. Late stage gabbro also also contains contains Ca-amphibole, Ca-amphibole, and and rarely rarely fayatitic fayalitic olivine olivine and pigeonite. pigeonite. the Picritic Zone, plagioclase composition ranges from from An71 Excepting the An71 to An36; olivine Fo63 to Fo31 Fo31 and augite Wo44En44Fs12 Wo44En44Fsl2 to Wo43En32Fs25. Fo63 to Wo43En32Fs25. Even Even in in the thegranophyric granophyric rocks rocks the the augite never never becomes ferroaugite ferroaugite attesting to to the modest degree of iron augite iron enrichment enrichment in in the the intrusion. intrusion. Main Zone rocks are are mostly mostly orthoortho- and and mesocumulates, mesocumulates, with with aa notable notable lack lackof ofadcumulus adcumulus growth of plagioclase or olivine. troctolites, however however are are found in the Picritic olivine. Adcumulate Adcumulate troctolites, Picritic Zone. The granophyric rocks exhibit spectacular spectacular radiating sheaves of intergrown intergrown quartz and alkali alkali feldspar. Modal feldspar. Modal layering layering is is rare rare but butoccurs occurs ininthe the Picritic PicriticZone Zone and andplanar planarlamination lamination of of plagioclase is common in the gabbros. plagioclase gabbros. The Theuniversal universaloccurrence occurrence of of the the latter latterand and almost almost total total lack of the former throughout the complex is an an interesting interesting point point that that bears bears on on processes processes and and conditions during during emplacement. emplacement. Contacts conditions Contacts between between different different gabbroic gabbroic rocks rocks are are gradational gradational supporting the the single magma supporting magma pulse pulse hypothesis hypothesis (excepting (excepting the the Picritic PicriticZone). Zone). with both As judged by textural textural and and structural structural relations relations the parent magma magma was saturated with olivine and and plagioclase. plagioclase. Subsequent olivine Subsequent arrivals arrivals as cumulus minerals were: augite augite (after (after 72% 72% solidified), Fe-Ti Fe-Ti oxides oxides (after (after 750h 75% solidified) solidified) and and apatite apatite (after (after 78% 78% solidified). solidified). The solidified), The cumulus cumulus minerals seem to to come come in gradually this may be more apparent than than real due due to the very minerals seem gradually but this poor exposure. exposure. C-4 �References References on the the Potato Potato River RiverIntrusion Intrusion Klewin, K.W., K.W., 1987, 1987, The The petrology petrology and andgeochemistry geochemistry of of the thePotato PotatoRiver RiverIntrusion, Intrusion,northern northern Kiewin, Wisconsin. Unpublished Ph.D. Ph.D. thesis, thesis, Northern Northern Illinois Illinois University, University, DeKaIb, DeKalb, IL, IL, 357 357 p.p. Wisconsin. Klewin, Klewin, K.W., K.W., in review, review, The The petrology petrology of of the the Proterozoic Proterozoic Potato Potato River Riverlayered layeredintrusion, intrusion, northern northern Wisconsin. Wisconsin. Jour. Jour. of of Petrology. Petrology. Mangham, J.R., J.R., 1975, 1975, The The structure structure and andpetrology petrology of ofthe theeastern easternMellen Mellenintrusive intrusivecomplex, complex,Iron Iron Mangham, County, County, Wisconsin. Wisconsin. M.S. M.S. thesis, thesis, University University of of Wisconsin, Wisconsin, Madison, Madison, 134 134 p. p. Tabet, Tabet, D.E., D.E., 1974, 1974, Structure Structure and and petrology petrology of of the the Mellen Mellen igneous igneous intrusive intrusive complex complex near near Mellen, Mellen, Wisconsin. Wisconsin. M.S. M.S. thesis, thesis, University University of of Wisconsin, Wisconsin, Madison, Madison, 81 81 p. p. Tabet, Tabet, D.E. D.E. and and Mangham, Mangham, J.R., J.R., 1978, 1978, The The geology geology of of the theeastern easternMellen Mellenintrusive intrusivecomplex, complex, Wisconsin. -19. Wisconsin. Geoscience Geoscience Wisconsin, Wisconsin,v.v.3,3,.p.1 .p.1-19. Mineral Mineral Lake LakeIntrusion Intrusion General General As noted noted above above the the Mellen Mellen Complex Complex is is divided divided near near its its midpoint midpoint by by the theMellen Mellengranite. granite. As West West of of the the MG MGare arethe theMineral MineralLake Lakeand andRearing RearingPond Pondintrusions intrusions(Olmsted, (Olmsted,1969, 1969,1979) 1979)along along with with several several smaller smaller sills sills that that make make up upthe thewestern westernpart partofofthe thecomplex.(Leighton complex.(Leighton1954). 1954). Exposure here is probably probably somewhat somewhat better than the east. east. Many Manysimilarities similaritiesand and Exposure than that found to the several important important differences between the the complex. complex. Some Someofof several differences may may be found between the two two halves of the these these will will be be considered considered here. here. Like PRI the theMineral MineralLake LakeIntrusion Intrusionisishyperfeldspathic hyperfeldspathicwith withcumulus cumulusplagioctase plagioclase and and Like the the PRI divine. olivine. AAubiquitous ubiquitousfeature featureisisthe thealignment alignmentofofplagioclase plagioclaselaths lathswhile whilemodal modalororrhythmic rhythmic layering layering is is uncommon. uncommon. The Thelower lowerthird thirdofofthe theMLI MLIhas hasbeen beentermed termedanorthositic anorthositicolivine olivinegabbro gabbro and and represents represents that portion in which which both both olivine olivine and and plagioclase plagioclase are are cumulus. cumulus. Above Aboveabout about 1500 m m above above the the base base olivine olivine becomes becomes less lesscommon common and andthe therock rockgrades gradestotogabbroic gabbroic 1500 anorthosite. anorthosite. This This unit, unit,over over 2000 2000mmthick thickisiscomposed composedof ofover over80% 80%plagioclase plagioclase with with minor minor pyroxene pyroxene and and Fe-Ti Fe-Tioxides. oxides. In In many many exposures exposures the the rock rock isistrue trueanorthosite anorthositeand andthe thelamination lamination almost almost perfect. perfect. In In glacially glacially polished polishedexposures exposureswhere where clinopyroxene clinopyroxene oikocrysts oikocrysts are areabundant abundantthe the rock rock has has aadecided decidedspotted spottedappearance. appearance. Near the the top top of ofthe theintrusion intrusionthe thefeldspathic feldspathic rocks rocks give give way waytotoferrodiorite ferrodioritewhich whichininturn turn Near grades grades upward upward through through granodioritic granodioritic to to granitic granitic or orgranophyric granophyricunits. units. In Inthe thewestern westernpart partofofthe the one complex are are found found several several areas areas of ofabundant abundant granophyre granophyre to to the thepoint pointappearing appearingexcessive excessiveififone complex accepts the the hypothesis hypothesis that that their their origin origin isisentirely entirelythrough throughfractionation fractionation of ofaagabbroic gabbroicparent. parent. accepts These These granophyres granophyres are are often often intrusive intrusive into intoenclosing enclosinggabbros gabbrosoften oftenforming formingspectacular spectacularbreccias. breccias. ItIt isisunfortunate unfortunate that that none none of ofthese these isiseasily easilyaccessible accessible for for your yourinspection. inspection. Recent Recentisotope isotopeand and trace trace element element studies studies on on the the MLI MLIsuggest suggestthat thatthis thisevolved evolvedfelsic felsicsection sectionincludes includesaacrustal crustal component and was was emplaced emplaced and and differentiated differentiated as as aa separate separate conformable conformable intrusion intrusion at at the the top top component of 985; Seifert, of the theanorthositic anorthositicunit unit(Seifert (Seifertet.al.,1 et.a1.,1985; Seifert,ininpreparation). preparation). The The upper upper contact contact of ofthe theMLI MLIisiswith withthe theoverlying overlyingRearing RearingPond Pondintrusion intrusionas aswell wellasas what what are are presumed presumed to to be beLower LowerKeweenawan Keweenawanvolcanics, volcanics, now now strongly strongly recrystallized recrystallized by by contact contact metamorphism. metamorphism. Because Because of ofpoor poorexposure exposureitithas hasnot notbeen beenpossible possibletotoobserve observecontact contactrelations relations between between the MLI MLI and and the the RP RPintrusion intrusion so sorelative relativeage age isisinindoubt. doubt. ItIt isis suspected suspected that that like likethe the case Picritic Zone Zone of of the the PRI PRIthe thecloseness closeness of of timing timing prevented prevented any any chilling. chilling. The Thebasal basal case of of the the Picritic contacts of of the the MLI MLIwith withunderlying underlyingvolcanics volcanics and andhornfels hornfelsare areequally equallypoorly poorlyexposed exposedand andwhat what contacts isisexposed exposedisisoften oftencomplicated. complicated. Considerable Considerable reduction reduction of grain grain size size isisobserved observedatatthe thebase base but but composition composition of of these these rocks rocks disallow disallow their theiruse useas asparent parentmagma. magma. Petrography Petrographyand and Mineral MineralChemistry Chemistry Modal Modal analyses analyses of of representative representative rocks rocks are are found found ininTable Table1.1. At At first firstnote notethe therocks rocks labeled "Chill "Chill Zone" Zone" appear appear ordinary ordinarycandidates candidatesbut butchemistry chemistryindicates indicatesthey theyare aresomewhat somewhat labeled evolved. Likewise their their mineral mineral compositions compositions are are evolved evolved in in comparison comparison to to the therocks rocks evolved. Likewise Overlying the the basal basal rocks rocks isis an andivine olivinerich richzone(MG-4) zone(MG-4)that thatisisprobably probablynot not immediately immediately above. above. Overlying C-5 �__________ cottinuous continuous although although better better exposure exposure might might refute refute this. this. This mafic mafic rich zone zone grades grades upward upward over over 1000 -1500 m with with olivine olivine decreasing decreasing and and plagioclase plagioclaseincreasing. increasing. In this portion portion of of the the intrusion intrusion plagioclase lamination is not not well well developed. developed. Pyroxene and Fe-Ti oxides are are both both intercumulus intercumulus the base a very coarse "pegmatitic" "pegmatitic' unit is this level. level. At about about 1500 m above the throughout this encountered that that appears appears to to be roughly parallel with the base. encountered base. It is is in in this this region region only only where where modal layering layering has has been been observed. observed. While it is this horizon horizon isiscontinuous continuous itithas has modal is not not known known ifif this been mapped over aa distance distanceof of about aboutthree threekm.. km.. This mapped over This is is about about the the level level where where olivine olivine becomes rare rare and and the the rocks above above are are rich in plagioclase becomes plagioclase and are laminated. laminated. Olivine, now Fe-rich reappears as a cumulus phase phase in in the the ferrodiorite ferrodioritewhere where plagioclase, plagioclase, pyroxene, oxides oxides and and apatite apatite are are cumulus. cumulus. The pyroxene, The very very Fe-,Ti-,P-rich Fe-,Ti-,P-rich nature nature of of this this requires requires that that fractionation played played aa substantial substantial role role in their development although in addition fractionation addition contamination contamination by crustal material cannot be ruled ruled out. out. Upwards, intercumulus granophyre becomes becomes important important replace olivine olivine and and pyroxene pyroxene as common phases and modal apatite while amphiboles replace apatite decreases. At decreases. At one onelevel levellarge largeeuhedral euhedral zircons zircons are areabundant. abundant. the basal basal chill zone, zone, plagioclase averages about An60, An60, ranging to rims Excepting the rims of of An20 An20 normal zoning zoning about about An10 AnlO is is common common but but less so in the in the the most most felsic felsic units. units. Moderate Moderate normal the more feldspathic feldspathic adcumulates adcumulates Plagioclase Plagioclase in the basal basal Chill Chill Zone Zone is is more morestrongly strongly zoned zoned but but value of of An42. An42. This This corresponds corresponds with with the the whole whole rock rock chemistry. chemistry. Olivine ranges ranges has an average average value from Fo65 near the base to Fo25 in the ferrodiorites. ferrodiorites. The TheChill ChillZone Zoneolivines olivineshave haveintermediate intermediate Clinopyroxene values values are are Wo42En39Fsl9 Wo42En39Fsl9 to to Wo35En25Fs4O Wo35En25Fs40 in the the ferrodiorite ferrodiorite values. Clinopyroxene demonstrating somewhat somewhat more Fe-enrichment than in the the FRI. PRI. Rearing Pond Pond Intrusion Intrusion The Rearing Rearing Pond Intrusion is unique unique in in several several respects, respects, although although itit somewhat somewhat PRI. It is emplaced emplaced at the top of the the MLI MLI and and with with the the resembles the the Picritic Zone Zone of of the PRI. exception of of its extreme western end end where where it intrudes metavolcanics exception extreme western metavolcanics itit is enclosed entirely by other intrusive intrusive rocks. rocks. Like the Picritic Zone it is is composed composed of of olivine olivine rich rich rocks rocksand andexhibits exhibits some modal modal layering. layering. Textures and mineralogy were studied by Olmsted, Olmsted, 1979, 1979, but but much muchwork work remains to to understand its chemistry. chemistry. Based understand its Based on mineralogy mineralogy it too is is differentiated differentiated but not not to to the the degree of of the MLI. Olmsted degree Olmsted1979, 1979, proposed proposed an an elongated elongated funnel funnel shape for the the intrusion intrusion and and on on suggested that that it has experienced the tilting typical of the the basis of orientation orientation of layering suggested the region. region. Near its outer outer perimeter perimeter is is found found aa peridotite peridotitelayer layercomposed composed largely largely ofofcumulus cumulusolivine olivine clinopyroxeneand andplagioclase. plagioclase. The uppermost rocks are gabbro and quartz with intercumulus clinopyroxene gabbro lying above a large large central central troctolitic troctolitic unit. unit. Abundant Abundant olivine in the RP RP averages averages about about Fo80 Fo80 and andisisrather ratherstrongly stronglyserpentinized. serpentinized. The very high high Mg#'s Mg#'s of the the rock rock analyses analyses are are in inline linewith withthis thisprimative primativecomposition. composition. Plagioclase composition compositionranges rangesfrom fromAn85 An85 in in lowermost lowermost rocks rocks to to An50 An50 in the Plagioclase the gabbro. gabbro. Pyroxenes are equally primative with compositions CPX En49Wo46Fs5 En49Wo46Fs5 and OPX OPX ranging rangingfrom from En80 in the troctolite troctolite and peridotite to En68 En68 in in gabbro. gabbro. we will make one stop that While extensive study intrusion we that While time time will not permit extensive study of this intrusion will provide provide an an opportunity opportunity to examine examine two two of of the thethree threemajor majorrocktypes. rocktypes. to the Mineral Lake References to Lake and and Rearing Rearing Pond PondIntrusions. Intrusions. Leighton, M.W., M.W., 1954, Petrogenesis of of a gabbro-granophyre Leighton, gabbro-granophyre complex in in northern, northern, Wisconsin. Wisconsin. BulI.GeoLSoc.America, v.65, p.401-442. Bull.Geol.Soc.America, v.65, Olmsted, J.F., J.F., 1969, 1969, Petrology of the Mineral Mineral Lake Lake Intrusion, Intrusion, northwestern northwestern Wisconsin. Wisconsin. in in Y.W.lsachsen, Origin of Anorthosite and Related Y.W.Isachsen, Related Rocks, Rocks, p.149-162, p.149-162, N.Y.State N.Y.State Mus. Mus. and and Sd. Sci. Serv. Sew. Memoir. Memoir. 1979, Crystallization Crystallization history history and textures of the 1979, the Rearing RearingPond Pondgabbro, gabbro,northwestern northwestern Wisconsin. Am.Mineral., Am.Mineral., v.64, v.64, p844-855. p844-855. Seifert, K.E., Windom,K.E., 1985, Mineral Seifert, K.E., Peterman,Z.E. Peterman,Z.E, and Windom,K.E., Mineral Lake Lake layered layered intrusion, intrusion, NWWisconsin. Geol. Soc. Soc. America Abs. with Prog.,17, NWWisconsin. Geol. Prog.,17, p.712. p.712. of the Mineral , in prep., prep., Geochemistry Geochemistry of Mineral Lake Lake pluton, pluton, NW NW Wisconsin. Wisconsin. C-6 �Field Field Trip TripStop StopDescriptions Descriptions Potato Potato River RiverIntrusion Intrusion All All of of the the stops stopsare are on on county county forest forest land, land, the the roads roads are arequite quite good good there there should shouldbe beno no difficulty difficulty with access. access. Watch Watch for forticks ticks ininthe thespring, spring,logging loggingtrucks trucksininthe thesummer, summer,deer deerhunters hunters in in the the fall fall and and snowmobiles snowmobiles in the winter. winter. The The locations locations are are shown shown in in Fig. Fig. 22 which which shows shows aa portion Theintrusion intrusionessentially essentiallyparallels parallelsWI WlHwy.77 Hwy.77 portion of of the the Saxon Saxon 7.5' 7.5' quadrangle quadrangle map. map. The between between Mellen Mellen and Hurley. Hurley. The The trip tripbegins beginsat atthe theintersection intersectionof of highways highways 77 77 and and122 122inin Upson, Upson, WI. Wl. STOP Hwy. 122 122north northofofUpson. Upson. Picritic PicriticZone Zonerocks. rocks. along Hwy. STOP11 along Proceed Proceed north north from Upson Upson on Hwy. Hwy. 122 122 over over the the range range of of hills hillsthat thatmarks marksthe the Keweenawan, Powdermill Powdermill Group When the the road roadstraightens straightens to to aanortherly northerlyheading heading(-4.5 (-4.5 Keweenawan, Group lavas. lavas. When mi. Upson)look look for foraagravel gravelroad roadto tothe theright right(E). mi. NNof of Upson) (E). Turn Turn onto onto the the gravel gravelroad roadand andpark parkafter after about South of of the the road roadisisaasmall smalloutcrop outcropofofmassive massivetroctolite troctolite(Tables (Tables1&2) 1&2)ofofthe the about 50 50m. m. South Picritic Picritic Zone. Zone. On Onthe thesouth southside sideofofthe theoutcrop outcropthe thebasal basalcontact contact of of the the Picritic PicriticZone Zone with with altered Zone can be seen. altered pegmatitic pegmatitic gabbro gabbro of the Main Zone seen. The Thetroctolite troctoliteisismassive massiveand andhas has adcumulate adcumulatetexture. texture. Plagioclase Plagioclase grains in in this this rock rockare areequant equantininshape shapeopposed opposedtotolath-shaped lath-shaped as Olivine isis anhedral anhedraland andappears appearstotohave haveundergone undergoneconsiderable considerable as ininthe theother othertroctolites. troctolites. Olivine Withcareful carefulstudy study you you can can observe observe small small grains grains of of Cr-rich Cr-rich spinel spinel in in the the adcumulus adcumulus growth. With troctolite troctolite (>7 (>7 wt.% wt.% Cr203; Cr203; whole whole rock rock Cr Cr up uptoto500 500ppm). ppm).InInterms termsofoftexture texture(massive, (massive, Fo67), and and Cr-spinel; Cr-spinel; this this outcrop outcrop isis adcumulate), mineral mineral composition composition (the most primitive, An70, Fo67), adcumulate), unique unique ininthe thePotato PotatoRiver RiverIntrusion. Intrusion. ItIt may may represent represent an an addition additionof of mafic maficmagma magmaunrelated unrelatedtoto the PicriticZone. Zone. the rest restofofthe thePicritic Return to to Hwy.122 Hwy.122 and proceed N about 200 m m to to aa second second gravel gravel road, road, this this time time to to the the Return left left(W), (W), and anddrive driveabout about200 200mmWWand andpark. park. Directly Directly south south isisanother anotheroutcrop outcropofofPicritic PicriticZone Zone rock. Here again again the the base base of of the the Picritic PicriticZone Zonewith withunderlying underlyingMain MainZone Zonepegmatitic pegmatiticrock rockcan can rock. Here be ThePicritic PicriticZone Zonerock rockininthis thisexposure exposureisisananolivine olivinerich richpicrite picritecontaining containing up up to to 50 50 be seen. seen. The modal modal % %olivine. olivine. The Thetexture textureisismassive massivetotolayered layeredwith withfaint faintrhythmic rhythmiclayering layeringvisible visibleininplaces. places. Large Largeoikocrysts oikocrystsof ofclinopyroxene clinopyroxeneenclose enclose olivine olivineand andplagioclase. plagioclase. Cr-spinel Cr-spinelisislacking lackingand and whole whole rock rock Cr Cr content content is is in in the the range range of of 150-200 150-200 ppm. ppm. Nickel Nickelcontent contentisisalso alsolow lowfor forsuch such olivine olivine rich richrocks rocks in inthe the range range of of 700-750 700-750 ppm. ppm. Inasmuch Inasmuchas asthe theAn Anand andFo Focontents contentsare arenot not high highrelative relativeto to the therest restofofthe theintrusion, intrusion,this thisoutcrop outcropmay mayrepresent representaazone zoneofofaccumulation accumulationofof mafic maficminerals. minerals. STOP Alongthe thePotato PotatoRiver. River. Top TopofofMain MainZone ZoneII.II. STOP 22 Along Continue west west on on the the gravel gravel road road about about three three miles miles where where the the road road ends ends at at aa Continue turn-around. turn-around. Just Just to to the the west west isis the the Potato Potato River River and and aa small small waterfall. waterfall. The Therock rockhere hereisis quartz-bearing quartz-bearingleucogabbro leucogabbro (Tables (Tables 11&&2). 2). In Inaasmall smalloutcrop outcropjust justup upfrom fromthe theriver riverthe the distinctive distinctivereddish reddishcolor colorofofweathered weatheredinterstitial interstitialAlk-Feldspar Alk-Feldsparcan canbebeseen. seen. This Thisrock rockisis composed composedofofplagioclase, plagioclase,clinopyroxene, clinopyroxene, Fe-Ti Fe-Tioxides oxidesand andinterstitial interstitialpatches patchesofofmicrographically micrographically intergrown intergrown quartz quartz and and alkali-feldspar. alkali-feldspar. The Thefeldspar feldsparcontains containssome some iron ironwhich whichproduces producesthe thered red color colorwhen whenaltered. altered. The Theoutcrop outcropininthe theriver riverprovides providesan anexcellent excellentexample exampleofoflamination laminationofof plagioclase plagioclasegrains. grains. The Theoutcrop outcropisiscut cutbybyaphanitic aphaniticbasaltic basalticdikes. dikes. Further Furthernorth northalong alongthe theriver river the theintrusive intrusivenature natureofofthe theUpper UpperZone Zonerocks rockscan canbe beseen. seen. STOP Alonggravel gravelroad roadwest west of of Upson. Upson. Main MainZone ZoneI.I. STOP 33 Along Retrace Retracethe the route routeto toUpson Upsonvia viaHwy Hwy122. 122.Turn Turnright right(W) (W)on onHwy.77, Hwy.77,proceed proceedabout about3 3 miles milesand andturn turnright right(N) (N)on ona agravel gravelroad, road,proceed proceed— 2,5 2,5 miles milesand andpark parkalong alongroad. road. Several Several low Theyare areolivine olivinegabbros gabbros(Tables (Tables11&& lowoutcrops outcropsalong alongthe theroad roadare aretypical typicalofofMain MainZone ZoneI. 1. They - C-7 �C) Figure 2 �Table 11 Modes Modes Table SAMPLE SAMPLE ROCKTY PE ROCKTYPE P LAG. PLAG. MINERAL LAKE MINERAL LAKE INTRUSION INTRUSION Chill 6'6-5-65" -5-65" Chi11Zone Zone Ave.M656-8 Ave.MG56-8 Chill ChillZone Zone MO-4 MG- 4 Olivine Gabbro OlivineGabbro MO-6 MG-6 Gabbro Gabbro MG—9 MG-9 Gab. Anorthosite Gab.Anorthosite ""11-9" 1 1-9" Gab. Gab.Anorthosite Anorthosite "3-10" "310" Gab.Anorthosi te Gab.Anorthosite "25-42" 42" Ferrodior ite "25Ferrodiorite MG-16 Q. Monzodio r ite MG16 Q.Mon2odiorlte MO-i? MG17 Q.Monzodiori te Q.Monzodiorite MG- 18 MG18 Granophyre Granophyre MO-19 MG19 Granophyre GranopI'i're 51.2 55.5 55.5 20.0 20.0 40.0 40.0 80.0 80.0 79.5 79.5 78.0 78.0 61.5 61.5 40.0 40.0 30.0 30.0 OL CPX 20.2 3.6 2.5 40.0 *325 9.3 2.9 14.3 OPX 10.8 *38.0 *59.0 *18.0 *127 OXIDE OXIDE 5.4 5.0 HLBD. HLBD. BlOT. BIOT. AP AP 3.8 4.5 4.0 TR TR K-SPAR K-SPAR QZ QZ OTHER OTHER 1.0 1.0 1.0 2.0 5.1 *11.9 TR *8.0 1.4 1.7 1.7 0.7 6.2 2.0 9.2 0.4 1,3 1.8 30.0 5.0 10.0 13.0 3.0 30.0 49.0 20.0 48.0 30.0 #68.0 2.0 10.0 5.0 5.0 TR 1.0 4.0 0.4 3.0 TR TR 2.9 12.0 2.0 (-1 I * POTATO POTATO RIVER RIVER INTRUSION INTRUSION 84-40D Troctollte Troctolite 83-28C Picrlte Picrite 84-43B Q. Leucogabbro Leucogabbro 84-71A Granophyre Granophyre 84.49A OlivlneOabbro Olivine Oabbro 84-516 LayeredTroctoli Layered Troctoli 84-53D OlivineGabbro Olivine Gabbro 84-54C Quartz Gabbro QuartzGabbro 76.0 76.0 25.0 25.0 66.0 66.0 65.0 65.0 65.0 65.0 52.0 52.0 64.0 64,0 50.0 50.0 20.0 55.0 3.0 15.0 1.0 2.0 3.0 3.0 2.0 5.0 2.0 1.0 1.0 25.0 5.0 15.0 45.0 18.0 15.0 1.0 15.0 TR 3.0 5.0 40.0 REARING POND INTRUSION INTRUSION W-39 W- 163 W-163 W—74 W-74 W-6 W-164 01 Oabbro Oabbro Troctolite Troctollte Peridotite Peridotite Gabbro Gabbro Gabbro Gabbro 54.6 52.8 52.8 24.3 24.3 55.6 55.6 52.7 52.7 13.8 25.6 39.7 72.4 0.5 5.1 0.2 13.2 25.5 5.4 2.2 2.2 15.7 7.6 *Iflcludes undistinguished CPX && OPX OPX undistinguished *IncludesCPX # Largely Largelyaltered alteredgranophyric granophyric material material Page 1 0.6 0.6 0.6 1.1 0.3 4.3 14.6 0.1 TR 1.0 3.2 0.4 TR �Table 22 Analyses Analyses Table Mineral Mineral Lake Lake Intrusion Intrusion MO 55,56 MO - 4 MG - 9 116 MO55,56 MG-4 MG-9 MG-1425-42 MG-16MG-17MG-18 MG-19 - 14 25-42 MO - 16 MG - 17MG - 18 MG - 19 58 Ave. 58 Ave. S102 47.70 48.30 43.56 56.40 60.00 Si02 47.70 44.30 50.40 74.40 75.60 1102 2.57 1.86 1.23 0.87 3.31 1.75 Ti02 2.57 1.67 0.26 0.16 A1203 15.40 9.66 24.10 22.60 13.61 15.20 14.20 A1203 1 5.40 12.80 12.40 Oxides Oxides 14.60 0.21 6.62 8.76 2.75 0.38 0.44 FeUt Feot MnO Mno MgO Mgo CeO CaO Na20 Na20 K20 K20 P205 P 205 LOl LO I ? C TOTAL TOTAL ND 20.70 0.28 14.30 6.05 1.98 0.42 0.20 ND 5.65 0.08 2.06 10.90 4.30 0.76 0.39 ND 8.42 0.10 5.42 20.60 12.50 0.31 0.18 9.46 0.13 2.31 1.91 10.40 3.86 0.10 3.66 9.35 2.62 0.42 5.33 3.39 0.33 1.67 0.54 5.27 4.15 2.28 0.60 ND ND 2.11 ND ND 2.29 0.04 0.18 0.62 3.90 5.47 0.04 Mellen Rearing Rearing Pond Pond Mellen Granite Granite Meann=4 RP Mag Mag 87-1 1 p Mean n=4 RP 69.26 0.45 13.88 4.00 0.07 0.40 1.92 0.04 0.08 0.38 4.07 5.35 0.03 ND ND 1.45 44.47 1.18 18.86 37.22 0.32 4.30 7.84 16.41 0.11 0.27 29.19 2.85 0.13 0.09 10.90 10.13 3.47 1.89 5.61 0.05 0.36 0.12 1.04 ND ND 0.01 99.43 99.75 99.87 100.40 99.11 99.71 99.67 100.00 100.03 99.68 95.86 90.79 45 55 39 53 24 25 26 13 7 15 71 76 0.96 2.36 0.44 3.34 3.54 2.48 16.74 0.85 0.92 2.34 4.49 30.69 44,21 3.08 0.00 6.12 0.00 6.70 0.78 3.67 3.35 6.34 2.50 22.30 24.28 0.00 0.00 9.79 1.18 1.31 0.07 0.30 0.27 0.02 1.53 0.09 0.37 0.50 32.44 29.84 2.84 0.00 29.48 0.00 3.63 0.00 0.11 2.02 3.33 12.47 28.70 20.04 0.00 7.62 2.48 21.46 0.00 1.32 2.91 2.34 0.67 0.58 Mg# C/PW Norms Ap Mt Ii 4.91 Ity 2.25 23.35 28.65 0.00 0.00 10.05 16.50 01 10.40 Or Ab An NE a Di 16.22 0.00 0.00 10.27 8.40 38.14 1.99 1.65 0.59 28.80 43.90 2.05 0.00 4.41 0.00 15.90 13.29 13.83 3.18 13.49 35.17 13.41 0.00 10.45 7.56 13.17 0.00 0.31 32.06 32.20 1.13 0.00 30.04 0.52 2.55 0.00 0.65 0.87 33.56 29.73 5.80 0.00 21.32 11055 ,56,58AVE, ChiliZone, OL Gabbro, STOP 14,MG—9. STOP7;7;MGMG14,MG-9,(3ab.Anorthosite, Gab.Anorthosite,STOPS STOPS99&&10 10 M655,56,58AVE, ChillZone,MO-4, MO-4,Ol.Gabbro, 25—42 MG 7, Q. Monzogbbro, STOP 25-42 Ferrodlorlte, Ferrodiorlte, MO— 16, 16,1 17,Q. Monzogabbro, STOP11 11 - - MO— MO 18, 18, 19,Oranophyre, 19, Oranophyre,STOPD STOP D RPMAG, Troctollte; 87— STOP 2 RPMAO, Troctolite; 87- 1liP1PPeridotite, Peridotite, STOP1 12 Page Page1 1 1.00 6.20 0.00 2.21 16.65 43.65 0.00 0.00 6.34 2.18 24.58 1.21 11.96 0.00 0.00 2.82 9.48 70.06 �Toble Table 2 Analyses Analyses PotatoRRiver Potato i v e r Intrusion PRI Bulk Compositions P R I Estimated Bulk Compositions 84-40D 83-28C 84-40D 83-28C 84-43B 84-43B84-71A 84-71A84—49A 84-49A 84-S1B 84-51 B 84-53D 84-53D 84-54C 84-54C , <-) I S102 si 02 1102 Ti02 A1203 Fe203 Fe203 FeO FeO MnO Mno MgO Mgo CeO CaO Na20 Na20 K20 K20 P205 P205 LOt LOI TOTAL TOTAL 46.06 40.91 51.10 0.41 0.99 6.06 3.76 23.32 0.33 19.67 4.80 0.86 0.16 0.06 1.63 19.62 1.94 20.20 2.27 7.92 0.12 9.16 10.26 2.29 0.23 0.01 ND 5.72 0.12 3.58 11.73 3.07 13.76 5.23 5.28 0.16 1.07 0.51 3.20 3.90 3.18 0.17 0.11 ND ND 61.98 0.77 ND 47.98 1.12 19.59 1.78 8.12 0.12 6.57 11.17 2.61 0.44 0.12 44.35 0.23 14.36 2.56 14.56 0.21 14.70 6.75 2.05 0.20 0.02 ND ND 48.56 1.62 19.48 2.89 7.88 0.13 5.40 9.49 2.92 0.54 0.17 49.31 3.49 15.65 3.36 9.28 0.17 4.22 10.47 2.74 0.61 0.29 ND ND MZ M Z IIIII I PZ MZ M Z IIII 48.64 0.97 47.46 0.75 50.88 50.74 1.25 18.70 1.58 17.91 1.90 10.31 20.62 2.03 6.36 0.12 3.01 14.87 MZ MZ I I 9.10 0.13 7.86 2.66 0.32 0.07 0.15 9.50 9.23 2.50 0.38 0.03 ND ND 10.13 4.51 10.77 3.06 0.47 0.13 ND 4.98 9.78 0.21 3.11 9.01 2.86 1.16 0.76 99.59 100.16 100.12 100.20 100.92 99.19 98.64 99.62 99.99 99.08 66 61 50 18 59 65 52 42 61 62 54 0.0 3.3 0.8 0.1 0.4 2.8 0.3 2.5 0.3 - 0.1 2.6 3.1 2.1 0.9 7.2 3.0 26.0 38.3 0.0 2.4 2.6 1.2 1.8 1.9 1.4 1.4 1.5 19.1 33.6 22.1 17.4 10.8 14.1 40.4 0.0 0.0 29.4 0.0 0.0 0.7 4.9 6.6 3.6 23.2 28.6 0.0 3.7 0.2 2.3 1.9 3.7 0.4 0.4 4.2 0.1 6.4 0.3 2.9 2.4 2.8 25.9 41.1 0.0 0.6 9.4 14.8 0.0 62.27 1.71 12.89 4.31 5.68 0.19 2.01 3.73 3.55 3.65 0.44 ND ND 98.93 UZ 100.49 100.43 d Mg# Mg* 31 31 C/PW Norms Ap Mt Ii Or Ab An NE Q Dl Fly 01 19.4 44.2 0.0 0.0 5.4 3.7 20.8 12.1 0.0 0.0 0.0 4.0 11.6 3.2 12.2 15.4 7.8 14.1 5.4 4.1 49.9 0.0 0.0 12.5 40.5 9.1 3.1 3.2 24.7 38.5 0.0 0.0 6.2 15.8 3.2 22.5 38.1 17.6 10.6 0.0 0.0 9.5 9.8 0.0 14.0 2.8 2.3 21.2 36.5 0.0 0.0 7.4 7.1 21.5 1.8 1.0 7.2 5.7 6.9 24.2 24.3 0.0 7.0 6.3 3.3 21.6 30.0 8.5 0.0 12.8 10.6 5.9 6.5 0.0 0.0 84—40D Massive MassiveTroctolite, Troctolite, 83-28C Picrite, STOP 84-400 STOP 11;; 83—43B, 83-43B, Q.Leucogabbro, Q.Leucogabbro, 84—7 8 4 - 7 1A, lA, Orenophyre, Oranophyre,STOP STOP 2 84—49A, O1.Oabbro, STOP 3; 84-51 B, Layered Troctolite, STOP 4; 84-53D, O1.Gabbro, STOP 5; 84-54C, 84-49A, Ol.Gabbro, STOP 3; 84-5 16, Layered Troctolite, STOP 4; 84-53D, Ol.Oabbro, STOP 5; 84-54C,Q.Gabbro, Q.Gabbro,STOP STOP 66 EstimatedBulk BulkCompositions: Compositions:MZ MZI,I,Main Zone1;I;PZ, Picritic Zone; MZ 11, II,Main II; Estimated Main Zone PZ, Picritic Zone; MZ MainZone Zone 11; MZ 1 1 ,Main Ma1nZone Zone ill; III;UZ, UZ,Upper UpperZone Zone MZ 1lit, Page 2 17.5 �2) composed of cumulus cumulus plagioclase plagioclase (An64-62) (An64-62) and and olivine olivine (Fo62-57) (Fo62-57)along alongwith withintercumulus intercumulus clinopyroxene and Fe-Ti clinopyroxene Fe-Ti oxides. oxides. Rhythmiclayering layeringininthe thePicritic PicriticZone. Zone. Along gravel gravel road road west west of of Upson. Upson. Rhythmic SSTOP T O P 44 Along Continue about about one mile N along Continue along the the gravel gravel road road to to an anovergrown overgrown logging logging road road to to the the There is active logging in the area and roads spring spring up from from year year to year. year. To Todistinguish distinguish correct one road to to the the right right directly directly opposite opposite this this one one as as there there are are in in the correct one there there should not be a road other places. places. Park on the overgrown 00 m). overgrown road and walk W up up aaslight slighthill hilltotothe thetop top(50-1 (50-100 m). At the top of of the hill turn right (N) into 100-200 m, m, Here Here is is aa low lowoutcrop outcrop of of layered layered into the woods woods 100-200 troctolite of Picritic Zone. Zone. The troctolite of the the upper upper part of the Picritic Thedistinctive distinctivefeature featureof of this thisrock rockisisrhythmic rhythmic rich layers layers alternate alternate on the the scale scale modal layering. Plagioclase (An67.5) (An67.5) rich and olivine (Fo63.5) rich of centimeters. grains are laminated in centimeters. Lath-shaped plagioclase grains in the the leucocratic leucocraticlayers. layers. Here the plagioclase magnesian respectively than in in the the adjacent adjacent Main Main plagioclase and and olivine olivine are more calcic and magnesian Zone rocks but less so so than than in inthe themassive massivetroctotites. troctolites. This part of the the Picritic Picritic Zone Zone is is the the only only of the intrusion that exhibits rhythmic layering. layering. What part of exhibits rhythmic What do you you make make of of that? that? left. left. STOP 55 Along Main Zone Zone IIII rocks. rocks. Upson. Main STOP Along gravel gravel road W of Upson. Continue along along gravel gravel road road about about 1.5 1.5miles. miles. As the road Continue road turns turns left left to to round round aa hill hill stop stop when you you are are heading heading W W and and park. park. The when The hill hill isisunderlain underlain by by olivine olivine gabbro gabbro of of the the Main Main Zone Zone III1 (Tables 1 & 2). 2). This is is cut cut by by aatypical typicalKeweenawan Keweenawan high high Ti-P Ti-P dike. dike. This is about about the the highest highest occurrence of of olivine gabbro in the occurrence the intrusion. intrusion. Plagioclase here strongly laminated, laminated, its its here is not strongly composition is olivine composition composition is about about Fo55. Fo55. composition is about An60 and olivine STOP Zone lii STOP 66 Along Along gravel gravel road road rest rest of of Upson. Upson. Main Main Zone Ill rocks. rocks. Continue Continue on the gravel gravel road road for for about about 11 mile until there is another another hilt hill just just to the the left. left. If you reach reach a small lake on the the right right you you have have gone gone too too far. far. This hill hill is is composed composed of of quartz quartz diabase dike. bearing gabbro bearing gabbroofof the the Main Main Zone Zone Ill Ill (Tables (Tables 11 && 2) 2) also also cut cut by by a diabase dike. The The rock rock here here is composed composed of of cumulus plagioclase, clinopyroxene clinopyroxene and and Fe-Ti oxides with interstitial quartz and alkali feldspar. feldspar. This is the the lower lower part part of of the the Main MainZone Zone Ill; Ill;after afterthe theappearance appearanceofofcumulus cumulus oxides, oxides, but before cumulus cumulus apatite. apatite. Return to to Hwy.77, Hwy.77, turn turn right (W) (W) toward toward Mellen Mellen which which is is about about 13 miles. miles. On Return Onreaching reaching Mellen proceed proceed N N on Hwy.13 through Mellen through town town about about 11 mile. mile. Turn right Hwy 169 169 to to Gurney Gurney right on Hwy following the Falls State State Park Park where we will will eat eat lunch. lunch. following the signs signs to Copper Falls STOP A walk the the short short distance distance along along the the trails trails to to and andjust just beyond beyond You are encouraged to walk Brownstone Falls Falls where where the the contact between the volcanics (reversed polarity) and the upper Brownstone upper Keweenawan may be seen. Continuing along along the the path beyond the Brownstone seen. Continuing Brownstone Falls Falls you are are proceeding up up section section through through the Copper Harbor Conglomerate, proceeding Conglomerate, the Nonsuch Formation and into the the lower lower part part of of the the Freda Sandstone. Sandstone. As into As you you will will see see the the units units are are vertical vertical here here with with strike uppermost volcanics at the Brownstone Brownstone Falls are rhyolite rhyolite flows overlying strike about about N60E. N6OE. The uppermost basalt. One here is is a fault. basalt. One of of us usat atleast least(JFO) (JFO)thinks thinks the the MidMid-Upper Upper Keweenawan Keweenawan contact contact here fault. What's yours? yours? Mellen Granite Granite Brief optional stops along the road in in both both cases cases to to observe observe the the porphyritic porphyritic granite. C-I 2 �___p33/ / ' ,- t4 • ;:•: i•4 'Ja_? •. -N --. :::: I .; -= - _, - _.•j. I i JQ -ttT ':i' • •'t -- S — - • . 6 — • LaM j — I ON - 5 - %O $437 rL• - --- I • . — - ••- ---- •.. • - • 7 - ——— - --- - -, •- -•••, •• •-•— • —••-—•••••.- -i. S -:—---.:;.,' .— - - • . A14 — • • , - ——-- -. — -. — . '3O - -. T -•—--• 4-_-- ,- Figure 33 Figure • — •.— .- - — — --. —-—-' C-13 :- p—I - - N iL- .4 —. —-- T' , ;'J'=!> - E-. r--- ° •... •.. _/_4j . Liks •4•••• •J•' .• - - -— — - - -, '- t2 iJ--:—_ 1 —- - 1136 L - -' ' $114 - 15 - f-'j . - AS $133 - — "— •— ,coaj 20 -:1 \S — -- -:-- I - • E 7 I - -'-—-- I ENG I • .•. ; —;--'-- -: i- — t< Z --. - -' -- 1 -: -.--- -- -R — - - - / OQ -/ /--:.. —=-— OTJ JT •• .— - :.. :- . - - —. I - p::- Ii - . - -: — - T. - _- — -, ', - • I.. N\ 1 -L _ :, • .1\_j'\ \ —.4 Nort -,: •. ---'-,----- •.-• 1z2!a .Grw.ipll P.--. -. - - •- •' .-x- 23. - c '7' 402_ I 2 I •••(' A . ) 42 776 .r i _: i1 • 1 r1" I °:— -•t 7 I/ / 8tPjsch i• I.. - (I -• -: M -- 29 - �Brecciaalong alongthe theW W side side of of Hwy Hwy 13 about 1 mile N of STOP B B Intrusive Intrusive Breccia of Mellen. Mellen. \ of gabbro enclosed in coarse Blocks of coarse grained grained granite. granite. Note how itit is is possible possibleto to mentally mentally many of of the the gabbro gabbro fragments fragments back back together. together. Also the granite. granite. 'fit many Also note lack of chilling of the Proceed N on Hwy Hwy 13 13 about about 11 mile and turn left onto County County Hwy C. Continue W W about about 3 miles where road turns right (N), continue N 1/2 112 mile. mile. Turn left on gravel road road proceed proceed W about 1/2 112 mile to top top of of rise. rise. STOP C C Massive Mellen Granite cut by by dikes. dikes. outcrops of of granite granite on on both both sides sides of of road. This is Stop at top of hill where where you see outcrops road. This private land so please respect respect the the owners owners fence. fence. Walk Walk south south of of the the road roadto toexamine examinetextures textures and dike occurrences. occurrences. Continue along road, road,first firstW W one one mile mile then then SS one one mile mile to to a T in the Continue along the road. road. Turn Turn right right (W) (W) proceed W W 112 1/2 mile mile to to a 4-corners. proceed 4-corners. Turn Turn left left(S) (S)(This (Thisbecomes becomesNational NationalForest Forest Road Road188 188 .).) continuing for for about about22 miles milesto to aa gravel gravel road road left left to to English English Lake. Lake. Please continuing Please be be respectful respectful here as into the the English English Lake Lake road, road, the natives natives are are sometimes sometimes unfriendly. unfriendly. Turn left (roughly (roughly S) into about 114 1/4 mile mile to to an unimproved but but passable passable road to the right. proceeding about right. Look for a sign sign stating the the name E. Ceres. Proceed carefully carefufly about about 114 1/4 mile looking for for a fork stating fork to to the the right. right. There is an inconspicuous 2-wire power power line line overhead overhead that that follows follows this this fork of the There inconspicuous 2-wire the road. road. ItIf you you to the the top of the arrive at a cottage on the lake arrive lake you have have gone too too far. far. Return to the hill. hill. Park Park in in the the fork far enough enough so others can pass to the the cottage. cottage. STOP 7. 7. Basal contact of the the Mineral Mineral Lake Lake intrusion. intrusion. Walk along under the power power line (200 m) to the under the the third third power power pole pole that that isis planted planted in inthe the outcrop. The for many many drill core holes in in the the outcrop. The hilt hill drops drops rapidly rapidly here into a small small valley. Look for rock. here is fine grained gabbro rock. Most of the rock exposed here gabbro but the rock on the the SE SE corner corner of of the outcrop is for this contact and look is hornfels. hornfels. Look for look for for inclusions inclusions of of hornfels hornfels within within the the fine fine grained gabbro. gabbro. The The texture texture of of the the gabbro gabbro here here at at the thecontact contact isisintergranular intergranular with with very very (Ol.-Fo40, Cpx. elongate Cpx. Wo40 Wo40 (An42-45). (6-5-65 && MG 55 etc. etc. Tables 1 & 2). 2). (01.-Fo40, elongate plagioclase plagioclase (An42-45). Fs26) Note Note that that back along along the the power line away from the En34 Fs26) the contact contact the the rock rock gradually gradually becomes more coarse and and the the texture texture subophitic. subophitic. Proceeding southwesterly through the the woods woods across a small valley valley to the top of the the next next hill hill where where there there are are aanumber number of ofoutcrops outcropsofofbasal basal olivine rich rich gabbro gabbro (MG-4). (MG-4). Return via the power power line. line. STOP 88 Layered Zone. Olivine Gabbro and "Pegmatitic" and Layered Zone. Return to to FR FR 188. FR187. 188. Turn Turn left, left, W, W, proceed proceed about about 2.5 2.5 miles miles to to intersection intersection with with FR187. Turn right, continue westerly about about 112 1/2 mile mile to to a driveway driveway left left into the home of Harold continue westerly Harold Smith, Smith, proceed about 1/2 Park near near the the house house and and seek seek permission. permission. Walk Walk down to 112 mile mile to to the the house. house. Park the beach and and left left to to the south south end end of of the beach and into the trees to the first the first outcrop. outcrop. This is is 600 m above the base Return to to the car and an olivine gabbro about 600 base of of the the intrusion. intrusion. Return and back back along the the road about about 318 3/8 mile mile to to the the base base of of a steep rise in the road. along road. Small outcrop on W W side side of the road gabbro. This unit miles road of of very very coarse coarse "pegmatitic" "pegmatitic" gabbro. unit has has been been mapped mapped over two miles along the north side of Mineral Mineral Lake Lake and beyond beyond and and represents represents an an important important horizon horizon in in the the intrusion. intrusion. If the water water in the lake is very low low we may may cross cross the the river river where where itit exits exits the the lake lake to to that occurs just just above the pegmatite. examine modal layering that pegmatite. Olivine continues as a minor minor above this this level but but is no longer abundant. phase above abundant. The The rock rockisisexceptionally exceptionally feldspathic feldspathic above. above. c-i 4 �\ Briefly: Spotted Anorthositic Gabbro STOP 9 Briefly: Gabbro Return to to FR 187, (Just 187, turn left (W) about 1/2 112 mile to aa large large outcrop outcrop on on the the right. right. (Just this exposure look for for low low blasted outcrops outcrops on on either either side of the road before this exposure look road which which are are good good Poikilitic Anorthositic Anorthositic Gabbro Gabbro (MG-14, (MG-i 4, 11-9). 11-9). An places to collect collect this this rocktype.) rocktype.) Poikilitic An excellent excellent 01. Fo65, Fo65, Opx Opx En66, En66,Cpx CpxWo42,En39,Fs19. Wo42,En39,Fs19. example showing a common texture. texture. Plag. Plag. An60, 01. 10 Briefly Briefly Laminated Gabbroic Anorthosite Anorthosite STOP 10 Continue Won on FR187 FR187 about about 1.5 1.5 miles miles then then north north at at "Pine "Pine Stump Stump Corner" Corner" and and then then Continue W the Lake "3" Campgrounds, Campgrounds,turn turn right right NE NE on on FR FR 189 go go 5/8 about one mile mile past the 518 mile stop at at what was was once once a small gravel gravel pit pit on on the the left left side side of of the road, now quite overgrown. Large what quite overgrown. Large polished outcrop outcrop of of anorthositic anorthositic rock rock in in back back wall wall of the pit (MG-9 Cpx (MG-9 ).). Plag. An60, Cpx Wo37,En29,Fs34. STOP STOP 1ii1 Ferrodiorite, Monzogabbro etc. (Transition (TransitionZone) Zone) Continue along along FR FR 189 189 Cross Continue Cross Brunsweiler Brunsweiler River at 2 miles, miles, continue continue about 3/4 314 mile mile beyond the the river to where turns to to an E E direction. direction. Walk straight straight S into into the the woods woods about about where the road turns 150 m where an an irregular irregular EW EW ridge ridge exposes exposes black black rust rust stained stained Ferrodiorite Ferrodiorite(25-42; (25-42; Plag. Plag, An45, An45, 01. Fo24, Opx. Opx. En37, Cpx.Wo38 En24 Fs38 Fs38 )) note cumulate and 0 1. Fo24, Cpx.Wo38 En24 and laminated laminated texture and and Retrace your your path path back back crossing crossing the the road to the north conspicuously finer grain grain size. size. Retrace north side side working your way north along the west side of the the hill. hill. Several outcrops here show gradually gradually (MG-16, 17). 17). increasing reddish felsic content content (MG-16, STOP 12 Rearing STOP RearingPond PondIntrusion Intrusion go back back over over the the Brunsweiler River past past aa gravel gravel pit pit on right and turn Turn around and go Brunsweiler River right on woods beyond. Continue woods road a few meters beyond. Continue northerly northerly about about 1/2 112 mile, mile, turn turn left left continue continue another 11 1/ 2 mile mile or less, less, then then left left again, again, and left left again again in in about about 1/4 114 mile. mile. (If you encounter encounter a another After the last OOm to a brook bridge over a brook brook go go back.) back.) After last turn turn proceed proceedcautiously cautiouslyabout about1 100m brook where the the road ends. where ends. An Anoutcrop outcrop on on your your left leftisisperidotite peridotite(W-74, (W-74,similar similar to to 87-i 87-111P)of the lower lower part of the Rearing intrusion. Walk along what remains the road (a path by now) Rearing Pond Pond intrusion. remains of the now) cross the jumping rocks, rocks, and and pick pick up up the the remains remainsofof the the road road on on the the other other side. side. AA few the brook jumping few meters meters beyond the the brook brook search search to to the the right right of of the the path for the the remains remains of aa picnic picnic grounds grounds (a (a couple couple large cliff cliff like like outcrops outcrops beyond. beyond. We of fire places is all all that's that's left) left) and several several large We will will work work our our way way around to the left and and circle the hill studying the rocks and their textures and features as we proceed remains of aa State State trout trout hatchery hatchery that that was was proceed (RPMag, (RPMag, 87-liT 87-1I Tand andW-163) W-163) . This is the remains abandoned at the beginning of of WWII. WWll. Good abandoned at GoodArchaeology Archaeology here. here. . STOP D D Granophyre Time Time Permitting Permitting Return to to FR 189, turn right and return to FR 187. 187. Proceed Proceed N on FR FR 187, 187, 1.5 1.5 miles milesto to the inflection inflection point pointofofan an"S" "S"turn turn(Large (LargeOutcrop Outcropononright) right)park park leftWWside sideofofroad. road. A few few the ononleft this point proceed on a meters SW into the woods is an an outcrop outcrop ot of aa granitic granitic rock. rock. From this of 290 about 300 meters, eventually up up a fairly tiring hill. heading of meters, eventually hill. Good exposures of Granophyre here. here. (MG-18, 19) 19) STOP E E Alternate Granophyre exposure. exposure. Morgan Alternate Granophyre Morgan Falls. Falls. From the the intersection intersectionofof FR FR 187 187 && 198 198 go go N 1/2 1/2 mile, mile, turn turn left left on on FR FR 193 193following following the the From Park in in the the lot provided and and walk walk the trail to the signs to Morgan Morgan Falls. Falls. Park the falls. falls. This is a spectacular foot high waterfall waterfall over over the the brick brick red granophyre. granophyre. Contact spectacular 100 foot Contact of of granophyre granophyre and and gabbro can can be seen west gabbro west of the falls along the upper part of the the ridge. ridge. C-15 �GENERAL GENERAL GEOLOGY GEOLOGY AND AND STRUCTURE STRUCTURE OF OF ARCHEAN ARCHEAM ROCKS ROCKS OF OF THE THE VIRGINIA VIRGINIA HORN AREA, NORTHEASTERN NORTHEASTERN MINNESOTA MINNESOTA HORN AREA, J.L. Welsh, Welsh, D.L. D.L. England, England, D.A. D.A. Groves, Groves, E. E. Levy Levy J.L. IIntroduction nt roduct ion The "Virginia "Virginia Horn" Horn" refers refers to to the the prominent prominent Z-shaped 2-shaped outcrop outcrop The pattern pattern of of Animikie Animikie Group Group rocks rocks present present in in the the Virginia-Eveleth Virginia-Eveleth area I ) , and and reflects reflects the the broad broad area of of the the Mesabi Mesabi Range Range (Fig. (Fig. 1), northeasterly trending trending anticline anticline and and syncline syncline into into which which these these northeasterly rocks have been folded. rocks have been folded. These These Proterozoic Proterozoic rocks rocks unconformably unconformably overlie Archean Archean basement basement rocks, rocks, which which are are exposed exposed north north of of the the overlie Mesabi Mesabi Range Range along along the the Laurentian Laurentian Divide. Divide. Supracrustal Supracrustal metavolcanic metavolcanic and and rnetasedimentary metasedimentary rocks and assorted assorted small small intrusive intrusive bodies bodies of of the the basement basement complex complex occur occur along along aa narrow narrow strip strip which which extends extends from from Mountain Mountain Iron Iron on on the the west west to to the the Aurora Aurora vicinity vicinity on on the the east, east, and and which which are are bordered bordered by by the the Giants Giants Range Range Complex Complex on on the the north. north. These These rocks rocks are are particularly particularly well well exposed exposed in in the the anticlinal anticlinal axis axis of of the the Virginia Virginia Horn, Horn, and and have have been been the the recent recent focus focus of of gold gold exploration. exploration. Previous Previous Work Work Until Until recently, recently, Archean Archean rocks rocks in in the the Virginia Virginia Horn Horn area area have have received received little little attention, attention, and and little little has has been been published published on on these these rocks. rocks. Brief Brief descriptions descriptions of of Archean Archean rocks rocks in in the the area area were were first provided by Leith (1903) as a result of his investigations first provided by Leith (1903) as a result of his investigations into into the the geology geology of of the theMesabi MesabiDistrict. District. J.W. J.W. Gruner Gruner also also investigated investigated the the Archean Archean rocks rocks during during his his studies studies of of the the Mesabi Mesabi District, District, and and reported reported an an occurrence occurrence of of visible visible gold gold in in aa felsic felsic porphyry porphyry body body (Grout, (Grout,1937) 1937). Sutton Sutton (1963) (1963) developed developed aa more more detailed detailed geological geological map map of of the the area, area, based based largely largely on on Gruner's Grunerls work, work, and and provided provided petrographic petrographic descriptions descriptions for for some some metasedimentary metasedimentary rocks rocks and and the thefelsic felsicporphyry porphyrybodies. bodies. . The The metavolcanic metavolcanic and and metasedimentary metasedimentary rocks rocks in in the the Virginia Virginia Horn Horn area area have have in in the the past past been been correlated correlated with with the the Ely Ely Greenstone Greenstone and and the the Knife Knife Lake Lake Series, Series, respectively, respectively, of of the the Vermilion District (e.g. Grout et al., 1951). Vermilion District ( e . g . Grout et al., 1951). As As these these rocks rocks are are physically physically separated separated from from the the Vermilion Vermilion District District by by the the Giants Giants Range Range Complex Complex and and were were correlated correlated only only because because of of lithologic lithologic similarity, similarity, designations designations of of Ely Ely Greenstone Greenstone and and Knife Knife Lake Lake Series Series for for rocks rocks in in the the Virginia Virginia Horn Horn should should no no longer longerbe beused. used. D- 1 �Regional map map of h e ffield i e l dtrip t r i area p a r eshowing a showingthe thegeologic g e o l o g i framework c framework and and the the F i g u r e 1.1. Regional Figure of tthe is a major unconformity s e p a r a t i n g g e n t l y d i p p ing The d o t t e d c o n t a c t major roads. roads. The major dotted contact is a major unconformity separating gently dipping P r o t e r o z o i c strata s t r a t a of of the t h e Animikie Animikie Group Group (on (onthe t h e south) s o u t h ) from from deformed deformed Archean Archean Proterozoic rocks. The Animikie Animikie Group, Group, consisting c o n s i s t i n g of of the t h e Pokegama Pokegama Quartzite Q u a r t z i t e and and Biwabik Biwabik rocks. The Iron-Formation ( open c i r c l e s 1 and t h e V i r g i n i a Formation ( d i a g o n a l r u l e ) is is Iron—Formation (open circles) and the Virginia Formation (diagonal rule), invaded by gabbroic rocks of Keweenawan age (1000 Ma) i n t h e s o u t h e a s t c o r n e r of invaded by gabbroic rocks of Keweenawan age (1000 Ma) in the southeast corner of t h e map map area. area. The The field f i e l d trip t r i p stops s t o p s are a r e all a l l within w i t h i n Archean Archean terrane. terrane. the , D- 2 �Lithologic U n i t s Lithologic Units Supracrustal metavolcanic and metasedimentary rocks comprise Supracrustal metavolcanic and area. metasedirnentary rocks the bulk of Archean rocks of the Also included incomprise this the bulk of Archean rocks of the area. Also included in this sequence are a number of small felsic intrusive bodies, the most sequence are a number of small felsic intrusive bodies, the most important of these being a dacite(?) porphyry body, which is the important of these being a dacite(?) porphyry body, which is the target of current mineral exploration. target of current mineral exploration. Metavolcanic rocks of the region occur in two separate Metavolcanic of the region occur in two separate areas, the north rocks and northwest, and the southeast (Fig. 2); and areas, the north and northwest, and the southeast (Fig. 2); and are separated by a central band of metasedimentary rocks. are separated by a central band of metasedimentary rocks. Significant portions of the contacts between the major Significant portions the contacts between and the probably major metasedimentary and of metavolcanic sequences, all metasedimentary and metavolcanic sequences, and probably all contacts between these sequences, are faults. The northern contacts between these sequences, are faults. metavolcanic sequence is also in fault contact The withnorthern the Giants metavolcanic sequence is also in fault contact with Giants north of Range Complex between the Pike River and Highway 5 3 the Range Complex between the Pike River and Highway 53 north of Virginia. Virginia. Metavolcanic Rocks 1etavo1canjc Rocks Metavolcanic rocks consist primarily of grayish green to consist primarily of grayish green to to medium-grained, massive to locally pillowed dark Metavolcanjc green, fine-rocks dark green, fine- to medium-grained, massive to locally pillowed or brecciated flows. While chemical analyses of these rocks have or brecciated flows. While chemical analyses of these rocks have yet to be obtained, the rocks appear to be predominantly of yet to be obtained, the rocks appear to be predominantly of intermediate composition. Dacitic(?) fragmental rocks are intermediate composition. Dacitic(?) fragmental rocks are interlayered with the flows in the southernmost part of the area interlayered with the flows in the southernmost part of the area and northofofBiwabik. Biwabik. Coarser grained, probably intrusive and north Coarserrocks grained, intrusive metadioritic or metagabbroic also probably occur within this metadioritic or metagabbroic rocks also occur within this sequence, as do finer grained mafic dikes. sequence, as do finer grained mafic dikes. Foliation in the metavolcanic rocks is generally not well Foliation in the metavolcanic rocks is generally not well assemblages of chloritedeveloped. Typical greenschist facies developed. Typical greenschist facies assemblages of chlorite— albite+actinolite+epidote are present. Secondary minerals albite+actinolite+epidote are present. Secondary minerals include calcite? and sericite. include calcite' and sericite. Metasedimentarv Rocks Metasedjmentary Rocks Metasedimentary rocks of the area are subdivided into three Metasedimentary of the unit areaof are subdivided three fault-bounded units:rocks a northern moderately to into highly fault-bounded units: a northern unit of moderately to highly altered, relatively quartzose metagraywackes, a central altered, relatively quartzose metagraywackes, a central conglomeratic unit, and a southern unit of metagraywackes. conglomeratic unit, and a southern unit of metagraywackes. Southern metaqrawackes. This unit comprises the bulk of Southern metagraywackes. This unit comprises the bulk of the metasedimentary rocks of the region. Numerous outcrops occur the metasedimentary rocks of the region. Numerous outcrops occur 1 3 5 . These rocks consist predominantly of south of Hwy. south of Hwy. 135. These rocks consist predominantly of Quartz in these rocks interbedded graywackes and slates. interbedded graywackes and slates. these rocks normalized to exclude . When in averages 5 - 1 0 % rarely exceeding 1 5 %Quartz averages 5-10%, rarely exceeding 15%. When normalized to exclude with matrix, all rocks contain greater than 5 0 % lithic fragments, matrix, all rocks contain greater than 50% lithic fragments, with D- 3 �felsic to felsic-intermediate clasts predominating. Intermediate felsic to felsic-intermediate clasts predominating. Intermediate to mafic clasts, though not abundant, are normally present. to mafic clasts, though not abundant, are normally present. Detrital hornblende occurs in graywackes at one locality. Minor Detrital hornblende in graywackes at oneto locality. amounts of sericiteoccurs are ubiquitous. Moderate abundant Minor amounts of sericite are ubiquitous. Moderate to abundant sericite and carbonate are locally present, especially in more sericite and carbonate are locally present, especially in more highly strainedzones. zones. highly strained These sandstones are turbidites, with Bouma A, AB, ABC, and These sandstones are turbidites, with Bouma AB, ABC, and are rare,A,though some Coarse clasts E divisions discernable. E divisions discernable. Coarse clasts are rare, though some pebbly units do occur. pebbly units do occur. Altered metaqravwackes. Outcrops of this unit are not as Altered metacTraywackes. of this unit are consist not as of These rocks abundant as the graywackes to Outcrops the south. abundant as the graywackes to the south. These rocks consist of moderately to highly altered, felsic volcanic-rich metagraywacke. moderately to highly altered, felsic volcanic-rich metagraywacke. In contrast to the southern metagraywackes, these rocks contain In contrast to the southern metagraywackes, these rocks contain 10-25% quartz and generally do not contain clasts of intermediate 10-25% quartz and generally do not contain clasts of intermediate to mafic composition. composition. Secondary sericite and carbonate are to mafic Secondary 60% of the are rock. abundant, in some places comprisesericite as much and as carbonate abundant, in some places comprise as much as 60% of the rock. It is likely that this alteration is related to the quartz It is likely that this alteration is related to the quartz feldspar porphyry bodies that have intruded this sequence. feldspar porphyry bodies that have intruded this sequence. Beds tend to be thick, with a fair development of grading. tend to be thick, with a fair development (after Walker, WhereBeds discernable, Bouma A, AB, and ABC divisions of grading. Where discernable, Bouma A, AB, and ABC divisions (after Walker, 1984) predominate. 1984) predominate. This unit is typically a dark green, ConqlomeraticUnit. Unit. Conglomeratic This unit It is is typically a dark green, heterogeneous, conglomerate. a composite unit, comprised heterogeneous, conglomerate. it is a composite unit, comprisedThe of various subunits based on differences in clast lithology. of various subunits based on differences in clast lithology. The subunits are typically heterolithic, though one distinctive subunits are typically heterolithic, though one distinctive monolithic unit and units of pyroclastic affinity occur within monolithic unit and units of pyroclastic affinity occur within along strike, thissequence. sequence. The subunits are difficult to trace this The subunits are difficult to trace along strike, and at at least least two two of ofthese thesesubunits subunits are in fault contact with each and are in fault contact with each other. other. Clasts are normally rounded and of volcanic origin, but Clasts are normally rounded types, and of generally volcanic origin, butto consist of various compositional of felsic consist of various compositional, types, generally of felsic to intermediate affinity. Particularly interesting are clasts of intermediate affinity. Particularly interesting are are clasts These hornblende clasts not of euhedral brown hornblende. hornblende. euhedral brown These hornblende clasts are not rounded and suggest a crystal tuff origin. One distinctive rounded and suggest a crystal tuff origin. One distinctive subunit is monolithic, with angular to subangular andesitic subunit is monolithic, with angular to subangular andesitic It too clasts, and was probably deposited as a debris flow. clasts, and was probably deposited as a debris flow. It too With the exception of the contains clasts of brown hornblende. contains clasts of brown hornblende. With the exception of the monolithic unit, the conglomerates are typically clast-supported. monolithic unit, the conglomerates are typically clast-'supported. The matrix matrix of of the the conglomerates conglomeratesis isgenerally generally chloritic; quartz is The chloritic; quartz is rare in in the thematrix. matrix. rare 0-4 �Origin Oriqin of of the the Metasedimentary Metasedimentary Rocks Rocks The conglomerates conglomerates are are interpreted interpreted to to be be upper upper fan fan channel channel The deposits, deposits, deposted deposted by by mass mass flow flow mechanisms. mechanisms. The The graywackes graywackes are are interpreted interpreted to to be proximal proximal to to mid-fan mid-fan deposits, deposits, deposited deposited by by turbidity turbidity currents. currents. The The two two graywacke graywacke units units are are also also compositionally different, and and neither compositions compositions are are compositionally compatible with with those those of of the the conglomeratic conglomeratic unit. unit. Nor Nor are are they they compatible compositionally compatible compatible with with the the adjacent adjacent metavolcanic metavolcanic units. units. compositionally These relationships relationships support support the the notion that all all three three sedimentary sedimentary These units units are are in in fault fault juxtaposition, juxtaposition, being being parts parts of of different different submarine submarine fans. fans. The The fans fans were were located located on on the the flanks flanks of of volcanic volcanic edifices, edifices, for for all all the the detritus detritus is is volcanogenic. volcanogenic. Felsic Intrusjveg AA series series of of quartz-feldspar quartz-feldspar (probably (probably dacite) dacite) porphyry porphyry bodies the altered altered metagraywackes metagraywackes along along aa narrow narrow belt belt bodies intrude intrude the trending trending approximately N8OE, N80E, and and also also appear appear to to intrude intrude the the southernmost southernmost exposures exposures of of metavolcanic metavolcanic rocks rocks along along the the contact contact with with the the altered altered graywackes. graywackes. These These bodies bodies are are recognizable recognizable for for the the most part by by their their conspicuous conspicuous ovoidal ovoidal quartz quartz phenocrysts. phenocrysts. Although Although not not present present in in all all rocks, rocks, these these phenocrysts phenocrysts typically typically vary vary in in amount amount from from 2-5% 2-5% and and range range in in size size from from .5. 5 cm cmto to22cm. cm. Plagioclase 20-30% of of the the rock, rock, range range in in Plagioclase phenocrysts phenocrysts comprise comprise 20-30% size size from from 22 mm to to 1.5 1.5 cm, cm, and and are are nearly nearly pure pure albite albite in in composition composition (Sutton, (Sutton,1963) 1963). The The phenocrysts phenocrysts are are set set in in an an aphanitic, aphanitic, white white to to greenish-gray greenish-gray matrix matrix of of quartz quartzand andfeldspar. feldspar. Secondary Secondary sericite sericite and and carbonate carbonate (siderite (siderite or or ankerite) ankerite) are are abundant, giving the rock its white to greenish color. abundant, giving the rock its white to greenish color. Finely Finely disseminated disseminated sulfides sulfides are are associated associated with with quartz-carbonate quartz-carbonate veins veins and and vary vary greatly greatly in in amount amount from from one one location location to toanother. another. Common Common sulfides sulfides are are pyrite pyrite and and arsenopyrite, arsenopyrite, with with rare rare sphalerite sphalerite and and chalcophyrite. chalcophyrite. . At At least least one one non-porphyritic non-porphyritic phase phase (it (it is is microporphyritic microporphyritic in in thin thin section) section) cuts cuts the the main main porphyry porphyry body. body. Numerous, Numerous, generally generally aphanitic, aphanitic, felsic felsic dikes dikes also also cut cut the the southern southern group group of of graywackes. A few of these intrusives contain quartz graywackes. A few of these intrusives contain quartz phenocrysts, phenocrysts, but but most most do do not. not. In In thin thin section section these these dikes dikes Contain contain 30—50% 30-50% plagioclase plagioclase microphenocrysts microphenocrysts in in aa fine fine felsic felsic matrix. matrix. Structure Structure Upon Upon first first examination, examination, these these rocks rocks appear appear to to be be relatively relatively undeformed; beds typically strike N60-70E. undeformed; beds typically strike -N60-70E. However, However, it it has has been been determined determined that that these these rocks rocks have have been been subjected subjected to to at at least least three three D- 5 �periods of of folding, folding, and have been cut cut by a significant significant northeasterly northeasterly trending trending fault/shear fault/shear system system (Welsh, (Welsh,1988) 1988). Folding Foldinq F1 have not not been been recognized in the field, F, folds have field, but but are are identified identified by by reversals reversals in in structural structural facing. facing. F2 F, folds are are tight tight to to isoclinal, isoclinal, trend northeasterly, and and are are steeply steeply plunging. plunging. While aa few are visible in outcrop, most are F, folds are are identified identified few F2 by reversals reversals in in stratigraphic stratigraphic facing. facing. Cleavage Cleavage (S2) (S,) trends are trends are consistently axial planes planes of of the the F2 F, folds. folds. Minor Minor consistently parallel parallel to to the the axial folds with gentle south-plunging axes have been recognized recognized in in three F3. three localities, localities, and and are are tentatively tentatively designated designatedasasF3. Faulting Faultinq These These rocks rocks have been cut by aa complex complex northeast northeast trending trending fault/shear system system which roughly coincides coincides with with the the axis axis of of the the fault/shear Virginia In 2). In the the northern northern part part of of the the area area most most Virginia Horn Horn (Fig. (Fig. 2) . displacement displacement appears appears to to have have been been taken taken up up along along the the Pike Pike River River Fault (Welsh, (Welsh,1988) 1988). Outcroppings Outcroppings adjacent adjacent to to the the fault fault exhibit exhibit Fault the the effects effects of of considerable considerable ductile ductile shear. shear. In the southern southern part part of of the the area, area, aa number number of of subparallel, subparallel, probably probably en en echelon, echelon, fault fault strands strands Cut cut throughmetasedimentary through,metasedimentary rocks rocks and and appear appear to to link link with with the the Pike Pike River River Fault. Fault. The The contact contact between between the the metasedimentary metasedimentary rocks rocks to to the the southeast is rocks and and rnetavolcanic metavolcanic rocks is also also aa fault. fault. Here Here north-topping north-topping metavolcanic metavolcanic rocks rocks are are juxtaposed juxtaposed against against south—topping south-topping metasedimentary metasedimentary rocks. rocks. These These en en echelon echelon faults faults are are interpreted interpreted as as being part of a strike-slip strike-slip duplex duplex (after (after Woodhouse, 1986). Woodhouse, 1986). . Strain Strain in in these rocks rocks is is concentrated concentrated into into narrow narrow zones zones of of ductile ductile shear shear associated associated with with these these faults. faults. Clasts Clasts along along the the margins margins of of the the conglomerate conglomerate are are distinctly distinctly flattened flattened in in the the plane plane of of foliation. foliation. Clasts Clasts internal internal to to the the body body are are generally generally not not as as flattened, flattened, but appear appear to be elongated elongated in in the the vertical vertical direction. direction. Movement Movement along along this this system system was was probably probably complex. complex. Although Although offset offset market market units units have have not not been been identified, identified, map map patterns patterns suggest N40suggest sinistral sinistral drag, drag, as as beds beds are are typically typically rotated rotated to to aa N4050E 50E strike strike in in the the vicinity vicinity of of the the Pike Pike River River Fault. Fault. En En echelon echelon quartz—filled quartz-filled tension tension fractures fractures in in the the dacite dacite porphyry porphyry also also support support aa sinistral sinistral sense sense of of shear. shear. Other Other kinematic kinematic indicators, indicators, however, however, such such as as minor minor Z-folds, 2-folds, and and asymmetric asymmetric pressure pressure shadows shadows on sense of ofshear shearwas was on porphyroclasts porphyroclasts suggest suggest that that the the (latest?) (latest?) sense dextral. dextral. In In addition, addition, high angle angle slickensides slickensides are are associated associated with with the the en en echelon echelon strands strands of of the the duplex duplex and and indicate indicate vertical vertical movement movement at at some some time time in in the the structural structural history history of of the the area. area. D-6 �p — 4 p £ 4 4. 4 S 4 4 4P, 4 4 4 4 4. 4. 4 4 ' +' 4 4 4. 4. 4 4 4 4. + + 4 4 4 4 4 + 4 4 .s 4 4 4 4 4. 4 4 + 4 4 4 4 4 4 9 4 4. 4 4 4 4 4 9 4 4 4 9 4 4. + 4 4 4 4 4 4 4 4 4 4. 4 4 4 4 4 + + + + + + 4 4 4 + + 4 9 4 4 4. 9 4 4 4 4 4 4 4 ' + 4 4 4. + 4. 4 4. 4 + + 4. •\• $$ 4 4 + + 4 4 4 4 + .4 4 9 4. 4 4 + + 4. + + 4. 9 4 4 + + + 4 4 4 4 4 4 $ + 44 4 9 4 4 4 4 4(4 r—r—,—,— 4 4 4 4 4 4 4/4'•\ c..4 44 444 44 44 # ' 4 4. 4 + 4 4 ,/ + 4 4 — 4 4. + 4 ''— • 4 — a)1!d / // / S 1Y3 J '' B I W B I N lm fWllCN. WITH UNX RL YING P W X W F C RHAIM Ul I W )It8,I6 PCI PILWO4 34fl AL,J VY3Cd jYj IA IOIO3 LYP i -— LYIc .'OW t I 1V4 ~ r m u l l v I Ijwi jV1 WVd5013J-ZjbyrC S3I$&MdtO QWV IVtNI jIIW 3AvCv LVIV I,,jtO3 E±1 ltvHy'oO1vjw I 1'-EI I Figure 2. ein6,j EEIJ v&vjp, LTJ IfJ KTAVCLCANlC5 N4l & r A - I N I R U S I W S S3IPiVtAYjyI N S3AISrg1NI-VJV Generalized geologic mapjoofoq the VirginiaWOH Hornearn area showing pezileieueo oi6ojoe6 dew elu!6.nfl 6ulMoqs the Pike.ieAi RiverIfled FaultwesA System. eqi 8J -a L �Economic Geology Geology Economic The dacite dacite porphyry porphyry body body is is aa current current target target for for gold gold The exploration in the area. Gold was first reported in this unit by by exploration in the area. Gold was first reported in this unit Gruner in 1924 (GroutI l937lI and is associated with the quartzGruner in 1924 (Grout, 1937), and is associated with the quartzcarbonate veins veins and and shear shear zones zones within within the the body. body. carbonate Sericite-carbonate alteration alteration has has also also been been identified identified with with Sericite—carbonate the faultlshear zones of Pike River System (WelshI 1988). the fault/shear zones of Pike River System (Welsh, 1988) Although silicification silicification and and sulfidation suliidation along along the the shear shear zones zones Although appears minimal where rocks are exposedI these zones merit appears minimal where rocks are exposed, these zones merit further investigation. investigation. further References Grout, F. I?. F., E d I1937, 1937, Petrographic Petrographic study study of of gold gold prospects prospects of of Grout, Minnesota: Econ. Ge01.~ vol. 32# pp. 56-68. Minnesota: Econ. Geol., vol. 32, pp. 56-68. Grout I F.F., E'. I?. I Gruner, Gruner, J.W., J.W. I Schwartz, Schwartz, G.M., G.M. I and and Thiel, ThielI G.A., G.A. I 1951, 1951 I Grout, Precambrian stratigraphy of Minnesota: Geol. Soc. Am. Bul1.I Precambrian stratigraphy of Minnesota: Geol. Soc. Am. Bull., v. 62, 6ZI pp. pp. 1017—78 1017-78 v. LeithI C. K. I 1903# The Mesabi iron-bearing iron-bearing district district of of Leith, C. K., 1903, The Minnesota: U.S.Geol. U.S.Geo1. Surv. Surv. Monograph, MonographI vol. vol. 43. 43. Minnesota: SuttonI T. T. C., C., 1963, 1963# Geology Geology of of the the Virginia Virginia Horn Horn area: area: M.S. M.S. Sutton, thesisI University of Minnesota, Minneapolis. thesis, University of Minnesota, Minneapolis. WalkerI R.G., R.GeI1984, 19841 Turbidites Turbidites and and associated associated coarse coarse clastic clastic Walker, deposits: in Facies ModelsI R.G. Walker e d a I Geoscience deposits: in Facies Models, R.G. Walker ed., Geoscience Canada Reprint Reprint Series Series 1, l I pp. pp. 171-188. 171-188. Canada WelshI J. J. L., L. 1988, 1988/ Preliminary Preliminary Structural Structural Analysis Analysis of of Archean Archean Welsh, rocks in in the Virginia Horn area, northeastern Minnesota rocks the Virginia Horn area, northeastern Minnesota (abs): 34th 34th Ann. Inst .on Lake Lake Superior Superior Geology, GeologyI v. v. 34, 3dI (abs): Ann. Inst.on part 1, l I pp. pp. 119—120. 119-120. part WoodhouseI N. H e I1986, 198GI Strike-slip Strike-slip duplexes: duplexes: Journal Journal of of Woodhouse, N. H., Structural GeologyI V. EI no. pp. 725-735. Structural Geology, V. 8, no. 7, pp. 725—735. 0-8 �6-0 AAO-1 PJ qse sewer woj pedpy eeie WOH e!U!6J!A Lfl o Aöoioe6 ueeqoiv eq 6UIMOqS devj S)130?J 3INVD1OAVI3VI [A4 3)DYMAVV13p [—Y 3IVJ3V4O1ONO3v13r [-.iY 3NDYMAVIOVj3r4 O3èl3flY [v C AèAHdJOd dSJ—Zb AAA 6468* / AAAAAAA / AAAAAAAA1 / A A A A A A A A A A A A A A A A A A A A A 8 AAAAAAAAAAAAe' AA6AAAAAAAAAA/f AAAAAAAAAAAAA,' /,/ AAAAAAAAAAAAAA, AAAAAAAAAAAAAA/ / AAAAAAAAAAAAAAA,' AAAAAAAAAAAAAAA, / / AAAAAAAAAAAAAAAA/ AAAAAAAAAAAAAAA,/ ,.' I AAAAAAAAAAAAAAA,/ ,1 AAAAAAAAAAAAAAA'/ , 'AAAAAAAAAAAAAAA,/' / / / / AAAAAAAAAAAAAAA//,/ I AAAAAAAAAAAAA& /, / / AAAAAAA4AA / . / / I I A A A A A A A A A_. A A A A A A AAAAA? ', AAAAA, / AAAAF, . ' AAAA_# ri AAAb - / /, / — / D—JY O9i' ,' A A A A £ -p"j ,AAAAAAAAAAAAb A A A A A A A A A A A A AA / - ,48A A A A A A / .iA A AAA AA AA AA AA AA AA AA AA AA AA AA AA AA AA AAAAA AA A A A ..dAAAAAAAAAAAAAA8AAAAAAAA, — -/ A A A A A A A A A A A A A A A A A A A A A A A A .'AAAAAAAAAAAAAAAAAA AAAAAAAAA / •C ejn6i �Road Log Log Road From Duluth, Duluthf travel travel north north along along U.S. U.S. 53 53 to to Eveleth. Eveleth. Pass Pass From 53 through Eveleth, Eveleth, and and turn turn right right at at the the intersection intersection of of U.S. U.S. 53 through and Minn. 135! and proceed toward Gilbert for 1.5 miles, turning and Minn. 135, and proceed toward Gilbert for 1.5 miles, turning left at at dirt dirt road road (with (withgate) gate). Stop Stop at at gate. gate. left . STOP 1. 1. Entrance Entrance to to Viking Viking Explosive Explosive property. property. STOP At this this locality locality At the contact between the southern graywacke-slates and the the contact between the southern graywacke-slates and the conglomeratic unit unit can can be be observed. observed. Rhythmically Rhythmically bedded bedded conglomeratic turbiditic graywackes graywackes are are exposed exposed on on the the east east side side of of the the access access turbiditic road. Though tops are difficult to discern here, tops are north. road. Though tops are difficult to discern here, tops are north. Careful examination of the outcrop reveals that the sediment Careful examination of the outcrop reveals that the sediment layers are are disrupted disrupted along along faults faults at at low low angles angles to to bedding. bedding. layers Small scale isoclinal folds are also present. Small scale isoclinal folds are also present. sericitized graywackes graywackes also also Rhyhmically bedded, beddedf more more highly highly sericitized Rhyhmically occur on the west side of the access road north of the gate, but occur on the west side of the access road north of the gate, but A prominent 'Zf kink fold is also displayed with tops reversed. with tops reversed. A prominent 'Z' kink fold is also displayed in these these metasediment,s. metasediments. in Outcrops on on the the west west side side of of the the access access road road occupying occupying the the Outcrops higher ground, and exposed along the highway are in the higher ground, and exposed along the highway are in the conglomeratic unit. unit. Here Here the the conglomerate conglomerate is is heterolithic, heterolithic, coriglomeratic consisting of various felsic volcanic clasts in chloritic consisting of various felsic volcanic clasts in aa chloritic matrix. Evidence of grading occurs in outcrops on the south south side side matrix. Evidence of grading occurs in outcrops on the of the the highway, highway, and and indicate indicate south south tops. tops. of The contact contact between between the the graywackes graywackes and and the the conglomerate conglomerate is is aa The phyllonite, and and is is exposed exposed along along the the west west edge edge of of the the access access phyllonite, road. Clasts Clasts in in the the conglomerate conglomerate along along the the contact contact are are flattened flattened road. # Z f folds in the the as a result of the strain. Minor asymmetrical as a result of the strain. Minor asymmetrical 'Z' folds in phyllonite can can be be sernen seen in Z-style phyllonite in thin thin sectionf section, as as are are small small Z—style secondary cleavage, cleavage, probably probably the the result result of of pressure pressure kinks. AA secondary kinks. solution is is also also developed developed in in the the phyllonite. phyllonite. solution The phyllonite phyllonite is is interpreted interpreted to to represent represent aa strand strand of of the the The Pike River River shear shear zone, zonef and and appears appears to to run run along along much much (and (and perhaps perhaps Pike along the the length) length) of of the the contact contact between between the the graywackes graywackes and and the the along conglomerate.The contact between the conglomerate and the altered conglornerate.The contact between the conglomerate and the altered graywackes is is also also highly highly strained strained and and altered, alteredf and and probably probably graywackes " 2 " structures structures associated associated represents another another shear shear zone. zone. The The "Z" represents with these shear zones indicate dextral shear. with these shear zones indicate dextral shear. 0-10 �Proceed back back along along Hwy. Hwy. 135 135 toward toward Virginia Virginia for for about about 1/4 114 mile mile Proceed and turn turn right right secondary secondary road. road. Follow Follow this this road road for for and approximately one mile, and turn right on dirt road to landfill. landfill. approximately one mile, and turn right on dirt road to DM&IR Railroad Tracks and park. Walk east for Proceed to Proceed to DM&IR Railroad Tracks and park. Walk east for approximately 1/4 114 mile, mile, until until first first outcrops outcrops are are reached. reached. approximately STOP 2. 2. STOP At this this locality locality two two feldspar feldspar porphyry porphyry "dikes", "dikes", At generally lacking lacking quartz quartz phenocrysts, phenocrysts, are are interfingered interfingered with with generally and porphyry porphyry are are extensively extensively graywackes. Both Both the the metasediments metasediments and graywackes. altered with with sericite sericite and and iron iron carbonate. carbonate. The The porphyry porphyry contains contains altered abundant quartz-iron carbonate veins and abundant disseminated abundant quartz-iron carbonate veins and abundant disseminated J.W. Gruner Gruner reported reported visible visible gold gold at at this this locality locality (see (see pyrite. J.W. pyrite. 1937). Groutf Grout, 1937) Continue eastward eastward along along the the railroad railroad tracks tracks for for approximately approximately 1/3 113 Continue mile to the next set of outcroppings. mile to the next set of outcroppings. STOP 3. 3. STOP ~etagraywackks ofthe thealtered altered graywacke graywacke unit. unit. Metagraywacks of These graywacke-slates graywacke-slates are are more more thickly thickly bedded bedded than than the the These rhythmically bedded bedded turbidites turbidites of of Stop Stop 1. 1. The The rocks rocks are are rhythmically deformedf and show good bedding-cleavage relationships. The high high deformed, and show good bedding-cleavage relationships. The angle between bedding and cleavage suggests that these outcrops angle between bedding and cleavage suggests that these outcrops occur in in the the nose nose of of aa fold, fold, and and top top relationships relationships from from other other occur graywacke outcrops in the area support this interpretation. graywacke outcrops in the area support this interpretation. Cleavages are are gently gently folded, folded, possibly possibly the the result result of of intrusion intrusion of of Cleavages the dacite dacite porphyry. porphyry. The The contact contact with with the the porphyry porphyry occurs occurs the of the south exposure, and is approximately 50 feet south approximately 50 feet south of the south exposure, and is relatively sharp. relatively sharp. From these these outcrops outcrops walk walk south south to to the the outcrops outcrops near near the the abandoned abandoned From buildings which are in sight. buildings which are in sight. STOP 4. 4. STOP Rhude and and Fryberger Fryberger prospect. prospect. Rhude Numerous outcrops outcrops of of quartz-feldspar quartz-feldspar porphyry porphyry have have been been stripped stripped Numerous at this location. In general the QFP consists of quartz at this location. In general the QFP consists of quartz phenocrysts (.5-2 (-5-2cm/2-5%) cm/2-5%) and and plagioclase plagioclase phenocrysts phenocrysts (2 ( 2 mm—1.5 mm-1.5 phenocrysts cm/25-30%) set set in in aa greenish greenish aphanitic aphanitic groundmass groundmassof ofquartz, quartz, cm/25-30%) feldspar, and sericite. Fine-grained disseminated pyrite and feldspar, and sericite. Fine-grained disseminated pyrite and arsenopyrite occur occur in in variable variable amounts amounts throughout throughout the thearea, areaf arsenopyrite particularly in association with quartz-carbonate veins. particularly in association with quartz-carbonate veins. D-11 �phase of of the the intrusion intrusion is is present present at at The non-porphyritic phase this this location. location. It can be seen cross-cutting the the main porphyritic body on an east-southeasterly east-southeasterly trend. trend. Located Located under under the the power power line line to the west is is aa rotated, rotated, rafted rafted sedimentary sedimentary inclusion inclusion within within QFP. QFP. (As (As you take note note of of the the you survey the outcrops take quartz-carbonate veins, and and how how fracturing fracturing attitudes of the quartz-carbonate affects affects these these veins, veins, and and their their relationship relationship to to foliation. foliation. From From these outcrops outcrops proceed proceed east east along along the the railroad railroad tracks tracks for for approximately 1/3 mile mile (about (about 100 100 yards yards before before the the large large railroad railroad approximately 1/3 cut), cut), to to the the outcrop outcrop on on the the south south side side of of the the tracks. tracks, STOP STOP 5. 5. Newmont Newmont Prospect Prospect This historical occurrence occurrence first first received received attention attention at at the the turn turn This of of the the century. century. C. C. K. Leith's Leithts (1903) (1903) exemplary exemplary study study of of the the geology geology of the Mesabi Range Range described described the the older older volcanic volcanic and and sedimentary rocks rocks of of the the Virginia Virginia Horn Horn area. area. He He noted noted the the presence presence of of "porphyritic "porphyritic granite" granite" with with secondary secondary sericite, sericite, chlorite at this this locality. locality. In In 1924, 1924, Dr. Dr. John John Gruner Gruner chlorite and and quartz quartz at led led a field party through through the the Virginia Horn Horn area area and and collected collected several gold-bearing gold-bearing samples samples from from "rhyolite "rhyolite porphyry". porphyry". Petrographic Petrographic descriptions descriptions of of these these samples samples were were published published by by F. F. F. F. Grout (1937), (1937), and and he he noted noted grains grains of of gold gold in in several several samples. samples. On On the the south south side side of of the the railroad railroad grade grade approximately approximately 1/4 1/4 mile mile east east of of the the old old Hercules Hercules powder powder plant, plant, outcrops outcrops of ofquartz, quartz, feldspar feldspar porphyry flank flank aa stream stream channel channel within within aa narrow narrow topographic topographic low. low. AA flat, flat, glaciated glaciated outcrop outcrop on on the the east east side side of of the stream exhibits several quartz and quartz—carbonate vein sets the stream exhibits several quartz and quartz-carbonate vein sets within within variably sericitized sericitized and and silicified silicified QFP. QFP. At At this this location, location, aa prominent, prominent, steeply-dipping steeply-dipping vein vein set set strikes strikes approximately approximately N—S. N-S. Adjacent Adjacent walirock wallrock contains contains very very fine-grained, fine-grained, disseminated disseminated pyrite pyrite and and arsenopyrite arsenopyrite within within aa gray-green gray-green aphanitic groundmass. The N-S veins occupy en aphanitic groundmass. The N-S veins occupy en echelon echelon tension tension fractures fractures which which flank flank narrow narrow shear shear zones zones striking striking N4OE. N40E. The The attitude attitude of of the the tension tension veins veins to to the the shear shear planes planes indicates indicates aa left-lateral QFP left-lateral sense sense of of shear. shear. Other Other vein vein sets sets within within the the QFP include include 1) 1) foliation-parallel foliation-parallel quartz-carbonate quartz-carbonate veins veins within within shears, shears, and 2) 2) subhorizontal subhorizontal quartz-carbonate quartz-carbonate veins veins occupying occupying conjugate conjugate fractures. fractures. Gold Gold mineralization mineralization is is associated associated with with several several vein vein sets. sets. D-12 �Continue east to large railroad cut. Continue east to large railroad cut. STOP 6. Conglomeratatic unit. STOP 6. Conglomeratatic unit. The most extensive exposures of the coarse volcaniclastic most exposures ofthe theunit coarse Here canvolcaniclastic be divided into unitThe occur atextensive this locality. unit occur at this locality. Here by the cana be divided into monolithic unit two subunits which are separated a unit fault, two subunits which are separated by a fault, a monolithic and a heterolithic unit. The northwestern 250 feet of the unit and a heteroljthjc unit. by The northwestern 250 feet of the railroad cut is marked a remarkably monolithic, generally railroad cut is marked by a remarkably monolithic, generally The clasts are quite irregular in matrix supported conglomerate. matrix supported conglomerate. The clasts are quite irregular both size and shape, are angular to subrounded, and unsorted. in both size and are angular to subrounded, and matrix unsorted. Clasts are ofshape, porphyritc hornblende andesite. The is Clasts are of porphyritc Thisisunit is The matrix chloritic, and contains hornblende hornblende andesite. crystal clasts. chioritic, and hornblende clasts. This unit is interpreted tocontains have been depositedcrystal by debris flow, probably interpreted to have been deposited by debris flow, probably subaqueous lahars. subaqueous lahars. In the southeastern half of the cut, the rocks are marked by In the southeastern of the cut, the rocks arethe marked by distinct morphologic andhalf lithologic differences from north. distinct morphologic and lithologic from the north. The remainder of the conglomeratic differences unit is generally like these The remainder the conglomeratic is generally likeare these rocks at the of southeast~part of theunit railroad cut. They rocks at the southeastipart the supported, railroad cut. and often have normal They are generally heterolithic and of clast generally heterolithic and clast often very have little normal The matrix and contains and inverse to normal grading. supported, and inverse normal contains grading. euhedral The matrix contains very clasts? little quartz, buttolocally brown hornblende quartz, but locally contains euhedral clasts? These conglomerates are thought to bebrown upperhornblende fan channel deposits. These conglomerates are thought to be upper fan channel deposits. Upon returning to vehicles drive to Gilbert. Upon returning to vehicles drive to Gilbert. right and proceed uphill toward school. right and proceed uphill toward school. From town, turn From town, turn STOP 6. (optional) Outcops behind Gilbert High School athletic STOP 6. (optional) field. field. Outcops behind Gilbert High School athletic These outcrops contain the best exposures of pillowed These outcrops the best of pillowed Theexposures pillows strike roughly eastmetavolcanic rocks contain in the area. metavolcanic rocks in the area. The of pillows strike with roughly west (note the northeasterly trend the contact the eastwest (note the northeasterly trend of the contact with the metasedimentary rocks to the west), and top north. (The metasedimentary to the and top north. metasedimentaryrocks sequence to west), the west generally tops (The southeast metasedimentary sequence to the west tops are southeast at generally this locality truncated along the contact). The pillows along the contact) The pillows at this locality are truncated by massive volcanics along a N25E trend. Whether this contact by massive volcanics alongcontact a N25E or trend. represents an intrusive shear Whether has not this been contact determined. represents an intrusive contact or shear has not been determined. However, foliation along this contact, minor quartz veining, and However, along this contact, quartz veining, apparentfoliation drag of the pillows into the minor contact suggest right and apparent drag of the pillows into the lateral shear. Confusing the matter contact are the suggest presenceright of pillows lateral shear. Confusing the matter are the presence of pillows on the far northwest corner of the outcrop area. . on the far northwest corner of the outcrop area. 0-13 �FIELD TRIP 4, 4, PART PART BB AND THEIR THEIR STRUCTURAL STRUCTURAL SETTINGS: WESTERN AND CENTRAL ARCHEAN ARCHEAN GOLD GOLD OCCURRENCES OCCURRENCES AND VERMILION DISTRICT VERMILION DISTRICT Hudleston, R.L. R.L. Bauer, Bauer, W. W. Ulland Ulland Leaders: P.J. Hudleston, Leaders: D.L. D.L. Southwick, Southwick, P.J. INTRODUCTION INTRODUCTION Several S e v e r a l rrecent ecent p u b l i c a t i o n s have i g h l i g h t e d the t h e important i m p o r t a n t role r o l e played played publications have h highlighted by the llater a t e r sstages t a g e s of transpressional b y ductile d u c t i l e shear s h e a r zones zones and and faults f a u l t s in i n the of transpressional the western Vermilion district d i s t r i c t of of northeastern n o r t h e a s t e r n Minnesota Minnesota ttectonism e c t o n i s m in i n the (Sims, 1976; Bauer, Bauer, 1985; Hudleston and o others, (Sims, 1976; 1985; Hudleston t h e r s , 1987, 1987, 1988). 1988). These papers papers also a l s o provide p r o v i d e useful u s e f u l summaries summaries of of the t h e regional r e g i o n a l structural s t r u c t u r a l geology, geology, and and we we f o r background and and further f u r t h e r references r e f e r e n c e s on on rrefer e f e r interested i n t e r e s t e d readers r e a d e r s to them for tthe h e deformational d e f o r m a t i o n a l history h i s t o r y of of the t h e area. area. Various lines t h a t the the deformation deformation responsible r e s p o n s i b l e for for l i n e s of of evidence evidence indicate i n d i c a t e that the second second to to tthe h e regional r e g i o n a l ENE cleavage c l e a v a g e in i n the t h e Vermilion district d i s t r i c t was was the affect a f f e c t the the area, a r e a , or o r D2. D2. The regional r e g i o n a l cleavage c l e a v a g e therefore t h e r e f o r e is i s labelled l a b e l l e d S2 S2 and and it is i s rrelated e l a t e d are a r e F2 F2 sstructures. tructures. tthe h e folds f o l d s to t o which it Finite F i n i t e strain s t r a i n studies studies ( H u d l e s t o n , 1976; Schultz—Ela, Schultz-Ela, 1988) and sense—of—shear sense-of-shear observations o b s e r v a t i o n s imply imply (Hudleston, that t h a t D2 was aa transpression t r a n s p r e s s i o n that t h a t involved i n v o l v e d regional r e g i o n a l north-south north-south flattening, flattening, ssteeply t e e p l y to t o moderately pluiging pludging extension, e x t e n s i o n , and and dextral d e x t r a l shear. s h e a r . The most important to form form in i n the later l a t e r stages s t a g e s of of D2 Dz were were zones zones of of i m p o r t a n t structures s t r u c t u r e s to iintense n t e n s e ductile d u c t i l e or o r brittle—ductile b r i t t l e - d u c t i l e shear s h e a r such s u c h as a s the t h e Mud Mud Creek Creek shear s h e a r zone zone and the the shear s h e a r zones zones near near Shagawa Shaqawa Lake. Lake. More brittle b r i t t l e dextral d e x t r a l faults, f a u l t s , such and iits may be be s still manif a u l t and t s ssubsidary u b s i d a r y bbreaks, r e a k s , may t i l l llater a t e r maniaass the Vermilion fault festations f e s t a t i o n s of of the t h e same same transpressional t r a n s p r e s s i o n a l regime. regime. Structural S t r u c t u r a l studies s t u d i e s in i n gold-mining gold-mining districts d i s t r i c t s in i n the t h e Superior S u p e r i o r Province P r o v i n c e of of Canada Canada have have demonstrated demonstrated that t h a t shear s h e a r zones zones were were instrumental i n s t r u m e n t a l and and perhaps perhaps the localization l o c a l i z a t i o n of of gold ores o r e s (Colvine ( C o l v i n e and and others, o t h e r s , 1988, 1988, and and ccritical r i t i c a l in i n the rreferences e f e r e n c e s therein). t h e r e i n ) . The cclear l e a r sspatial p a t i a l association a s s o c i a t i o n between between shear s h e a r zones zones and and of g greenstone—belt tthe h e most important i m p o r t a n t classes c l a s s e s of r e e n s t o n e - b e l t vein v e i n deposits d e p o s i t s of of gold g o l d has has prompted much much interest i n t e r e s t in i n shear s h e a r zones as a s exploration e x p l o r a t i o n targets. t a r g e t s . For this this rreason e a s o n eexploration x p l o r a t i o n geologists g e o l o g i s t s have have been been working in i n the the shear s h e a r zones zones of of the the and tthey have found found sshear phenomena Vermilion district d i s t r i c t for f o r several s e v e r a l yyears, e a r s , and h e y have h e a r phenomena and even some some major shear s h e a r zones zones that that were were not n o t recognized recognized in i n published published mapping by by geological g e o l o g i c a l surveys. surveys. I Because of the widespread widespread academic and and applied a p p l i e d interest i n t e r e s t in i n shear—zone shear-zone of the phenomena, outstanding phenomena, we w e here h e r e describe d e s c r i b e five five o u t s t a n d i n g and easily e a s i l y accessible a c c e s s i b l e sshear hear zone outcrops o u t c r o p s in i n the t h e Vermilion district d i s t r i c t where the t h e features f e a t u r e s of of the t h e rocks rocks can can b e readily r e a d i l y observed observed and and debated. debated. be ROAD LOG LOG AND AND STOP STOP DESCRIPTIONS DESCRIPTIONS ROAD I ~ I The llog beginsaatt tthe The o g begins h e iintersection n t e r s e c t i o n of of St. S t . Louis Louis County route r o u t e 408 408 (Mud (Mud Creek Road) Road) and and sstate Creek t a t e highway highway 1-169 1-169 aapproximately p p r o x i m a t e l y 11.5 11.5 miles m i l e s eeast a s t of Soudan Soudan (Fig. ( F i g . 1 and 2 ). 2). 1 0.0 0.0 Intersection Intersection of Proceed north n o r t h on on of county route r o u t e 408 408 and highway 1—169. 1-169. and hilly h i l l y and and carries c a r r i e s aa 408 and drive d r i v e cautiously; c a u t i o u s l y ; road is crooked and surprising s u r p r i s i n g volume volume of of traffic. traffic. D-14 D-14 �3.7 a r k vehicles v e h i c l e s on accessible accessible h i g h ground and disembark; disembark; walk walk 3.7 Mud Mud Creek; Creek; ppark high to t o outcrops. outcrops. s t o p 1. 1. s h e a r zone; zone; outcrops o u t c r o p s near n e a r the the crossing c r o s s i n g of of Mud ~ u d Stop The Mud Creek shear Creek Road over o v e r Mud Mud Creek: Creek: SE1/4SE1/4 SE1/4SE1/4 ssec. e c . 5, 5, T. T. 62 62 N., N., R. R. 14 14 W. W. S e v e r a l small s m a l l outcrops o u t c r o p s in i n the t h e valley v a l l e y of of Mud Mud Creek Creek illustrate i l l u s t r a t e various various Several ssmall-scale m a l l - s c a l e structures s t r u c t u r e s characteristic c h a r a c t e r i s t i c of of rocks r o c k s that that have have undergone undergone intense intense D2. sshear h e a r strain, s t r a i n , all a l l attributed a t t r i b u t e d to t o D2. The best b e s t exposures are a r e in i n scrub s c r u b just j u s t north n o r t h of of the the creek c r e e k and and within within of the the road road on on the t h e east e a s t side. s i d e . The best aabout b o u t 100 100 m of b e s t example example of of local l o c a l S2' S21 and F2 Fy developed in i n aa lens l e n s of of otherwise o t h e r w i s e uniform S2 S2 is i s here h e r e (see ( s e e Fig. Fig. 3). 3). IIn n g e n e r a l S2 iis s subparallel s u b p a r a l l e l to t o the t h e margins of of the Mud Creek Creek shear s h e a r zone zone (N. (N. general 700 Locally, 70 E.). E.). L o c a l l y , it i t has has been been perturbed p e r t u r b e d and rotated r o t a t e d clockwise c l o c k w i s e about a b o u t 40°, 40° tto o form folds folds w i t h a secondary crenulation c r e n u l a t i o n cleavage c l e a v a g e (S21) ( S 2 @ developed )developed with the axial a x i a l plane. plane. Both cleavages c l e a v a g e s can c a n be traced t r a c e d from from within w i t h i n the the p a r a l l e l to t o the parallel perturbed S2, iin p e r t u r b e d zone outward to t o merge iinto n t o aa ssingle i n g l e pplanar l a n a r ffabric, a b r i c , S2, n tthe he surrounding be s u r r o u n d i n g rock. rock. Good examples of of en echelon tension t e n s i o n veins v e i n s can can also a l s o be found in i n nearby outcrops. outcrops. bend iin i s aa t h e outside o u t s i d e of of the t h e first f i r s t bend n tthe h e road north n o r t h of of the t h e creek c r e e k is On the rroadcut o a d c u t in i n a pinkish p i n k i s h quartz q u a r t z sericite s e r i c i t e schist, s c h i s t , a rock rock produced produced by by intense intense Nice shear shear. s h e a r . Nice s h e a r bands (or ( o r C' C ' planes; p l a n e s ; see s e e Fig. Fig. 4) 4 ) are a r e developed developed in i n this this s rendered friable f r i a b l e by the t h e closely c l o s e l y spaced spaced and and intersecting i n t e r s e c t i n g SS rrock, o c k , which iis and C' C 1 planes. planes. number of A number of features f e a t u r e s of of these t h e s e outcrops o u t c r o p s provide p r o v i d e indicators i n d i c a t o r s of of sense s e n s e of of C' sshear, h e a r , and these t h e s e are a r e consistently c o n s i s t e n t l y dextral. d e x t r a l . They include i n c l u d e shear s h e a r bands bands (or ( o r C' planes); development of of 82' Sf where p l a n e s ) ; local l o c a l development where S2 S5 has h a s been been perturbed p e r t u r b e d and and rotated rotated clockwise; assoc l o c k w i s e ; and formation f o r m a t i o n of of Z folds f o l d s in i n 8S2 3 ffoliation o l i a t i o n (most (most commonly in i n assowith well cciation iation w i t h SSf) $ ) and and in i n quartz q u a r t z veins. veins. Although w e l l developed in i n highly highly Mud Creek, ssimilar be found found through through ssheared h e a r e d rocks rocks such aas s aatt M ud Creek, i m i l a r ffeatures e a t u r e s ccan a n be much of the t h e Vermilion district, d i s t r i c t , increasing i n c r e a s i n g iin n the iintensity n t e n s i t y of of development development f a u l t is i s approached. approached. aass the Vermilion fault The Mud north f l a n k e d on the n o r t h by pillowed p i l l o w e d greenstone greenstone Mud Creek shear s h e a r zone is flanked member of of the E Ely s moderately deformed deformed except e x c e p t in in h a t iis ((upper u p p e r member l y Greenstone) tthat narrow shear zones, and on the south by assorted felsic tuff, tuff-breccia, s h e a r z o n e s , and on t h e s o u t h assorted f e l s i c t u f f , tuff-breccia, block b l o c k breccia, b r e c c i a , and the the reworked reworked sedimentary eequivalents q u i v a l e n t s of of these these of the Vermilion Formation). ((tuffaceous t u f f a c e o u s member of t h e Lake Vermilion Formation). Sims and Southwick (1980, 1985) iinterpreted highly material (1980, n t e r p r e t e d the the h i g h l y schistose schistose m a t e r i a l within w i t h i n the t h e shear shear zone to t o have been derived d e r i v e d chiefly c h i e f l y from from fine—grained f i n e - g r a i n e d felsic f e l s i c to t o intermediate intermediate It the Lake Vermilion sequence. sequence. I t iis s now recognized recognized that that ttuff u f f belonging belonging to t o the sshear h e a r zones of of this this magnitude commonly commonly contain c o n t a i n the the sheared s h e a r e d equivalent e q u i v a l e n t of of many different more o orr less common "fault "fault d i f f e r e n t rock types, t y p e s , all a l l reduced reduced tto o aa more rock" composed chiefly rock" c h i e f l y of of quartz, q u a r t z , sericite, s e r i c i t e , and and chlorite. chlorite. The phyllonitic phyllonitic Mud zone aare the ""fault rocks" aalong f a u l t rocks" long rrocks o c k s of of the the M ud Creek shear s h e a r zone r e ssimilar i m i l a r tto o the 1983, tthe h e Rainy Lake—Seine Lake-Seine River R i v e r fault f a u l t zone zone in i n southern s o u t h e r n Ontario O n t a r i o (Poulsen, ( P o u l s e n , 1983, and tto 1986) and o tthose h o s e aassociated s s o c i a t e d with many other o t h e r strike—slip s t r i k e - s l i p fault f a u l t zones zones the Mud Creek x t e n t of of the eelsewhere l s e w h e r e in i n the Superior S u p e r i o r Province. Province. The westward eextent sshear h e a r zone beneath Lake Vermilion Vermilion has not n o t been been established. established. D-15 �3.7 3.7 R e t u r n tto o vehicles; v e h i c l e s ; continue c o n t i n u e northwest n o r t h w e s t on Mud Creek C r e e k road road Return u s t y outcrop o u t c r o p of of q u a r t z vein v e i n and eenclosing n c l o s i n g quartz—sericite— quartz-sericite5.0 5.0 LOW, Low, rrusty quartz c h l o r i t e schist s c h i s t at a t edge e d g e of of road road on on east e a s t (right) ( r i g h t ) side. side. P a r k vehicles v e h i c l e s on on chlorite Park s h o u l d e r where room room permits; p e r m i t s ; walk to t o roadside r o a d s i d e outcrop. outcrop. shoulder 2A. Several S e v e r a l outcrops o u t c r o p s of of sheared, s h e a r e d , locally l o c a l l y altered a l t e r e d and a n d veined v e i n e d meta— metaSTOP 2A. basalt b a s a l t near n e a r Mud Creek C r e e k Road Road at a t the the southern s o u t h e r n boundary of of Superior Superior ., R. R. 14 1 4 W. W. N a t i o n a l Forest: F o r e s t : SE SE 1/4 1/4 SE SE 1/4 1/4 sec. National sec. 31, 31, T. T. 63 63 N N., Many of of the the small—scale s m a l l - s c a l e manifestations m a n i f e s t a t i o n s of of intense i n t e n s e dexra]. d e x r a l shear s h e a r that that were seen s e e n at a t the the previous p r e v i o u s stop s t o p are a r e seen s e e n to t o somewhat somewhat better b e t t e r advantage a d v a n t a g e in in is located located tthese h e s e exposures. e x p o s u r e s . The most interesting i n t e r e s t i n g and informative i n f o r m a t i v e outcrop o u t c r o p is aabout b o u t 500 500 ft. f t . into i n t o the the woods woods east e a s t of of the the road r o a d (follow ( f o l l o w well w e l l beaten b e a t e n path), path), quartz-sericite-chlorite schist s c h i s t displays d i s p l a y s excellent e x c e l l e n t C' C1 where phyllonitic p h y l l o n i t i c quartz—sericite—chlorite shear and S2' s h e a r bands bands and y ' crenulations. c r e n u l a t i o n s . Brown q u a r t z c a r b o n a t e a l t e r a t i o n Brown quartz—carbonate alteration zones, z o n e s , disseminated d i s s e m i n a t e d pyrite, p y r i t e , and and narrow, narrow, tectonized t e c t o n i z e d quartz q u a r t z veins v e i n s indicate indicate hydrothermal this shear s h e a r zone segment. segment. Grab samples samples of of fformer ormer h y d r o t h e r m a l activity a c t i v i t y in i n this the the occurrence o c c u r r e n c e has has t h e altered a l t e r e d rock r o c k reportedly r e p o r t e d l y yield y i e l d high h i g h gold g o l d assays, a s s a y s , but b u t the nnot o t been explored e x p l o r e d further f u r t h e r because b e c a u s e of of proximity p r o x i m i t y to t o protected p r o t e c t e d lands l a n d s of of the the Boundary Waters Canoe Canoe Area. Area. w e s t on on Mud Mud Creek C r e e k road road R e t u r n to t o vehicles; v e h i c l e s ; Continue C o n t i n u e north n o r t h and west Return following m i l e aa fault f a u l t 'scarp' ' s c a r p ' (ridge ( r i d g e of o f higher h i g h e r grade g r a d e rocks rocks f o l l o w i n g for f o r about a b o u t a mile N. of o f the the Vermilion V e r m i l i o n fault f a u l t and the the road) r o a d ) westward. westward. iimmediately m m e d i a t e l y N. 5.0 5.0 - 6.2 Park - ffairly of rroad with a i r l y sstraight t r a i g h t stretch s t r e t c h of oad w i t h ridge r i d g e immediately i m m e d i a t e l y to to 6.2 the t h e north. north. The ooutcrop is about STOP 2B. The u t c r o p is a b o u t 500 500 fft. t . from the road r o a d on the the logged logged STOP 2B. the road: road: NW 1/4 1/4 SE 3 N., R. 14 14 W. W. rridge i d g e rrunning u n n i n gWSW WSW from the SE 1/4 1/4 sec. sec. 36, 36, T. T. 663 N., R. The Rice R i c e Creek gold g o l d prospect p r o s p e c t is i s located l o c a t e d in i n a zone zone of o f highly h i g h l y deformed deformed and the Vermilion Vermilion deformation d e f o r m a t i o n zone. zone. The VDZ VDZ is is a n d altered a l t e r e d rock r o c k here h e r e called c a l l e d the bounded on on the the north n o r t h by by the the Vermilion V e r m i l i o n fault f a u l t and and on on the thesouth s o u t hby bythe theMud Mud creek f e a t u r e s widespread carbonate c a r b o n a t e and a n d aericite sericite c r e e k sshear h e a r zone. zone. The VDZ features alteration a l t e r a t i o n as a s well w e l l as a s several s e v e r a l gold g o l d showings. showings. Gold is i s usually u s u a l l y associated associated with mica and and tourmaline. tourmaline. w i t h ankerite a n k e r i t e and a n d pyrite p y r i t e and and occasionally o c c a s i o n a l l y with w i t h green g r e e n mica R i c e Creek showing showing is is located l o c a t e d approximately a p p r o x i m a t e l y 1,000 1 , 0 0 0 feet f e e t south s o u t h of of the the The Rice Vermilion V e r m i l i o n fault f a u l t at a t the the south s o u t h contact c o n t a c t of of aa chert c h e r t iron i r o n formation. f o r m a t i o n . Rocks with with were eelevated l e v a t e d gold g o l d values v a l u e s together t o g e t h e r with w i t h sericite-green s e r i c i t e - g r e e n mica—carbonate m i c a - c a r b o n a t e rocks r o c k s were found on a small s m a l l dump dump created c r e a t e d by by early e a r l y explorers e x p l o r e r s for f o r iron i r o n ore. o r e . The outcrop outcrop ssource o u r c e of of this this material m a t e r i a l can c a n also a l s o be be seen. seen. Gold up to 2 ppm is i s associated a s s o c i a t e d with w i t h pyrite p y r i t e and ankerite a n k e r i t e in i n aa dark d a r k brecbrecThis is in i n contact c o n t a c t with w i t h sheared s h e a r e d sericite s e r i c i t e carbonate carbonate cciated i a t e d chert. chert. T h i s chert c h e r t is Subsequent has g o l d values v a l u e s exist e x i s t at a t the the rrocks. ocks. S u b s e q u e n t ddrilling rilling h a s found that t h a t similar gold nnorth o r t h contact c o n t a c t of of the the iron i r o n formation f o r m a t i o n and and in i n shears s h e a r s in i n the the iron i r o n formation f o r m a t i o n as as well between the the w e l l as a s in i n shears s h e a r s in i n a chiorite—sericite—carbonate chlorite-sericite-carbonate sschist c h i s t lying l y i n g between north n o r t h contact c o n t a c t of of the the iron i r o n formation f o r m a t i o n and and the the Vermilion v e r m i l i o n fault. fault. 6.2 Return to vehicles; drive 6.2 Return to v e h i c l e s ; turn t u r n around and d r i v e south s o u t h on Mud Creek Creek Road Road back b a c k to t o highway highway 1-169. 1-169. D-16 �12.4 unction with 1—169; 1-169; turn t u r n left l e f t (east) ( e a s t ) toward toward Ely. Ely. 12.4 Junction 21.0 County route r o u t e 88 88 enters e n t e r s highway highway from from 21.0 abandoned railroad grade, and turn right r a i l r o a d grade, turn r i g h t from vehicles to abandoned abandoned v e h i c l e s and and walk east e a s t to l e f t (north). ( n o r t h ) . Turn left, l e f t , cross cross left onto dirt track. Disembark o n t o d i r t t r a c k . Disembark quarry. quarry. zone; qquarry and nnatural exposures iin the 3. Longstorff Longstorff Bay shear s h e a r zone; u a r r y and a t u r a l exposures n the STOP 3. SEI/4 sec. SE1/4 s e c . 36, 36, T. T. 63 6 3 N., N., R. R. 13 1 3 W., W., west west of of Ely. Ely. Major shear s h e a r zones form aa b i f u r c a t i n g , wishbone-shaped r a c e tthat hat bifurcating, wishbone-shaped ttrace 5 ) . These zones zones rroughly o u g h l y corresponds c o r r e s p o n d s to t o the t h e outline o u t l i n e of of Shagawa Shagawa Lake Lake (Fig. (Fig. 5). are are collectively c o l l e c t i v e l y referred r e f e r r e d to t o here h e r e as a s the the Shagawa Shagawa Lake Lake shear s h e a r zones. zones. The this shear s h e a r zone system aare r e iinformally n f o r m a l l y rreferred e f e r r e d tto o by tthree h r e e arms of of this by the the rrespective e s p e c t i v e bays bays of of Shagawa Shagawa Lake that that they t h e y transect: t r a n s e c t : The Olson Bay shear shear zone and the the L o n q s t o r f f Bay shear s h e a r zone in i n western Longstorff western Shagawa Shagawa Lake Lake and and the the Spaulding S p a u l d i n g Bay Bay shear s h e a r zone zone in i n eastern e a s t e r n Shagawa Shagawa Lake. Lake. The Olson Bay and and Spaulding of the Shagawa Lake Lake ffault, which S p a u l d i n g Bay shear s h e a r zones follow f o l l o w the trace t r a c e of t h e Shagawa a u l t , which iis s inferred i n f e r r e d to t o be be aa tectonically t e c t o n i c a l l y long—lived l o n g - l i v e d structural s t r u c t u r a l feature. feature. T h i s This family such aas Mud f a m i l y of of shear s h e a r zones is i s eequivalent q u i v a l e n t to t o the t h e D2 sstructures, t r u c t u r e s , such s tthe h e Mud Creek Creek and and Tower—Soudan Tower-Soudan shear s h e a r zones zones of of the t h e western western Vermilion Vermilion district. district. of tthe b e s t exposed exposed of h e tthree, h r e e , deforms The Longstorff L o n g s t o r f f Bay Bay shear s h e a r zone, zone, the best felsic tuff, agglomerate, and graywacke of the Knife Lake Group and aa f e l s i c t u f f , agglomerate, of t h e Knife Lake Group and lamprophyre sill along the contact between the Knife Lake Group and the the s i l l along contact t h e Knife Lake Group and Newton Lake Lake Formation Formation (this ( t h i s stop). s t o p ) . Lens—shaped Lens-shaped islands i s l a n d s of of unsheared, unsheared, mildly The zone m i l d l y deformed deformed lamprophyre lamprophyre occur o c c u r locally l o c a l l y within w i t h i n the t h e shear s h e a r zone. zone. terminates to the the west west against a g a i n s t the the Wolf Wolf Lake Lake fault. fault. t e r m i n a t e s to of the w a s found across a c r o s s any of the Shagawa Lake Although no continuous outcrop o u t c r o p was Longstorff Bay Bay zone zone may be be aas s zzones, o n e s , indirect i n d i r e c t evidence suggests s u g g e s t s that the Longstorff wide as 600 m and and the t h e Spaulding Spaulding Bay zone zone (next ( n e x t stop) s t o p ) may be as wide as a s 1.2 1.2 a s 600 The absence of km. o r r e l a t e d aacross c r o s s the of physical p h y s i c a l markers that t h a t could be ccorrelated exposureofof the the zones, zones, hhas zzones, o n e s , together t o g e t h e r with w i t h the the incomplete incomplete exposure a s inhibited inhibited estimates theamount amount of of shear s h e a r displacement. displacement. e s t i m a t e s of of the . Locality L o c a l i t y 3a: 3a: Sheared Sheared lamprophyre lamprophyre in in quarry q u a r r y pit. pit. Intense s t r o n g mylonite foliation f o l i a t i o n aalong l o n g the I n t e n s e shearing s h e a r i n g has produced a strong ssouthern o u t h e r n margin of of the t h e lamprophyre lamprophyre sill s i l l exposed exposed in i n this t h i s quarry. q u a r r y . Former pyroxene and and hornblende hornblende megacrysts, meqacrysts, now now dark-green dark-green spots s p o t s of of actinolite actinolite ± + occur of this chlorite, o c c u r iin n the t h e less lessdeformed deformed lamprophyre lamprophyre t otot the h e nnorth o r t h of this expoeKpchlorite, The sspots highly to ssure, u r e . The p o t s aare re h i g h l y fflattened l a t t e n e d in i n the t h e foliation f o l i a t i o n and have aa weak weak to shapeiis of the the hhigh moderate llinear i n e a r aspect. a s p e c t . Their T h e i r shape s aa typical t y p i c a l product p r o d u c t of i g h fflatlattening Small—scale t e n i n g sstrains t r a i n s displayed d i s p l a y e d within w i t h i n the the Shagawa Shagawa Lake Lake shear s h e a r zones. zones. Small-scale outcrop sshear h e a r bands and actinolite a c t i n o l i t e foliation f o l i a t i o n fish f i s h from this o u t c r o p aarea r e a iindicate ndicate a dextral observed o only d e x t r a l sense s e n s e of shear; s h e a r ; however, however, these t h e s e features f e a t u r e s were observed n l y iin n ccut ut outcrop. Small hand samples and are a r e not n o t readily r e a d i l y distinguished d i s t i n g u i s h e d in i n outcrop. (centimeter ( c e n t i m e t e r scale) s c a l e ) symmetric crenulations c r e n u l a t i o n s and and chevron chevron folds f o l d s deform deform the the foliation believed thelater later stages f o l i a t i o n locally l o c a l l y and and aare re b e l i e v e d tto o have have formed formed dduring u r i n g the stages off shearing. bandsi ninterpreted be younger younger ffeatures e a t u r e s uunrelated n r e l a t e d to to o s h e a r i n g . Kink Kink bands t e r p r e t e d tto o be the of tthe t h e development development of h e shear s h e a r zones zones are a r e well w e l l developed developed llocally. ocally. Locality L o c a l i t y 3b: Sheared ttuff Sheared u f f of of the t h eKnife K n i f eLake LakeGroup. Group. D-17 �n a r r o w dirt d i r t road r o a d southeast s o u t h e a s t of o f the the quarry q u a r r y and and the the abandoned abandoned railroad railroad A narrow ggrade r a d e leads l e a d s to t o art a n abandoned section s e c t i o n of o f highway. highway. A small ooutcrop u t c r o p oof f h ighly highly the ssheared h e a r e d Knife K n i f e Lake tuff t u f f that t h a t contains c o n t a i n s numerous numerous kink k i n k bands bands crops c r o p s along a l o n g the n o r t h side s i d e of o f the the abandoned abandoned highway t o to the s t ofofthe i r t road r o a d intersecintersecnorth highway thee aeast theddirt tion. tion. 21.0 21 .O 25.1 25.1 Return retrace route R e t u r n t to o vvehicles; e h i c l e s ; retrace r o u t e to t o 11 and e n t to o lleft eft and 169 169and andt hthen ((east) e a s t )back back through t h r o u g h Ely. Ely. Minnesota rroute u r n s south s o u t h toward toward Illgen I l l g e n CIty; C i t y ; ccontinue o n t i n u e east e a s t on on Minnesota o u t e 11 tturns highway 169 toward Winton. Winton. 26.1 26.1 County route r o u t e 88 8 8 (signs ( s i g n s for f o r Echo Trail) T r a i l ) enters e n t e r s from from left l e f t (north); (north); turn t u r n left l e f t onto o n t o route r o u t e 88. 88. 28.1 28.1 Prominent p r o m i n e n t roadcuts r o a d c u t s on either e i t h e r side s i d e of of road; r o a d ; park p a r k on on shoulder s h o u l d e r and and disembark. disembark. STOP 4. STOP 4. Spaulding S p a u l d i n q Bay shear s h e a r zone exposed exposed in i n cuts c u t s along a l o n g County County route route 888, 8 , NW1/4 NW1/4 sec. sec. 23, 23, T. T. 63 6 3 N., N., R. R. 12 1 2 W. W. S p a u l d i n q Bay Bay shear s h e a r zone zone occurs o c c u r s primarily p r i m a r i l y in i n the the Knife K n i f e Lake Lake Group, Group, The Spaulding it affects a f f e c t s adjacent a d j a c e n t variolitic v a r i o l i t i c pillow p i l l o w basalts b a s a l t s of of the the Newton Newton Lake Lake aalthough l t h o u g h it Formation the north n o r t h and andunits u n i t sofofthe theEly E l yGreertstorie G r e e n s t o n e to t o the t h e south. s o u t h . This This F o r m a t i o n to t o the shear Lake, farther s h e a r zone zone presumably extends e x t e n d s toward toward Fall F a l l Lake, f a r t h e r tto o tthe h e eeast, a s t , bbut ut has tthis his h a s not n o t been verified v e r i f i e d by publicly p u b l i c l y available a v a i l a b l e mapping. mapping. Locality L o c a l i t y 4a: 4a: Sheared tuff the Knife K n i f e Lake Lake Group. Group. t u f f of of the Highly the Knife K n i f e Lake Lake Group Group near n e a r its i t s conconH i g h l y sheared s h e a r e d tuffaceous t u f f a c e o u s rocks r o c k s of o f the with the Newton Lake Formation Formation are are exposed exposed here. h e r e . The rocks r o c k s contain contain ttact act w i t h the llocal o c a l concentrations c o n c e n t r a t i o n s of of sulfide s u l f i d e mineralization m i n e r a l i z a t i o n and and abundant abundant kink k i n k bands. bands. - Locality L o c a l i t y 4b: 4b: Sheared S h e a r e d Newton Lake Lake basalt. basalt. Variolitic V a r i o l i t i c pillow p i l l o w basalt b a s a l t and and more massive m a s s i v e flows f l o w s of of the the Newton Newton Lake Lake Formation c u t by by discontinuous d i s c o n t i n u o u s shear s h e a r zones z o n e s at a t this this outcrop. o u t c r o p . Strain Strain F o r m a t i o n are cut analyses a n a l y s e s using u s i n g varioles v a r i o l a s from from this this unit u n i t indicate i n d i c a t e high h i g h flattening f l a t t e n i n g strains strains (k=0.06 and 0.10) 0.10) w with plunging (k=0.06 ith X p l u n g i n g moderately m o d e r a t e l y to to the the southwest. s o u t h w e s t . Weak shear shear bands of the the vverthe order o r d e r of o f 5 cm cm are a r e visible v i s i b l e on some of erb a n d s with w i t h spacings s p a c i n g s on on the ttical i c a l outcrop o u t c r o p faces f a c e s at a t aa high h i g h angle a n g l e to t o the the shear s h e a r zones. zones. This Return i s the the end end of of Field F i e l d Trip T r i p 4. 4. R e t u r n to t o vehicles, v e h i c l e s , turn t u r n around, a r o u n d , and T h i s is retrace route r o u t e to t o Ely. Ely. REFERENCES REFERENCES Bauer, R.L., and younger younger uupright R0L.t 1985, 1985, Correlation C o r r e l a t i o n oof f eearly a r l y recumbent recumbent and pright Bauer, folding f o l d i n g across a c r o s s the the boundary boundary between between an a n Archean Archean gneiss g n e i s s belt b e l t and and greenstone g r e e n s t o n e terrane, t e r r a n e , northeastern n o r t h e a s t e r n Minnesota: Minnesota: Geology, v. v. 1 3, p. p. 13, 6 57-660. 57—660. Colvine, Heather, K.B., Marmont, Marmont, S., S., SSmith, P.M., and and C o l v i n e , A.C., A.C., Fyon, Fyon, JJ.A., .A., H e a t h e r , K.B., m i t h , P.M., Ontario Troop, D.G., 1988, Troop, D.G., 1988, Archean Archean lode l o d e gold g o l d deposits d e p o s i t s in i n Ontario: Ontario: O ntario Geological Paper 136 p. p. G e o l o g i c a l Survey S u r v e y Misecl].aneous Miscellaneous P a p e r 139, 139, 136 D- 18 �Green, K.H., 1982, Geologic Green, J.C., J.C., arid and SSchulz, c h u l z , K.H., G e o l o g i c map map of o f the the Ely E l y quadrangle, quadrangle, St. S t . Louis Louis and and Lake Lake Counties, C o u n t i e s , Minnesota: Minnesota: Minnesota Minnesota Geological G e o l o g i c a l Survey Survey Miscellaneous scale 1:24,000. 1:24,000. M i s c e l l a n e o u s Map Map Series S e r i e s M—50, M-50, scale the H u d l e s t o n , P.J., P.J., 1976, Early E a r l y deformational d e f o r m a t i o n a l history h i s t o r y of o f Archean Archean rocks r o c k s in i n the Hudleston, 1976, Vermilion V e r m i l i o n district, d i s t r i c t , northeastern n o r t h e a s t e r n Minnesota: Minnesota: Canadian Canadian Journal J o u r n a l of of Earth Earth Sciences, S c i e n c e s , v. v. 13, 1 3 , P. p. 579—592. 579-592. D.D., and H u d l e s t o n , P.J., P.J., Bauer, Bauer, R.L., R.L., Southwick, Southwick, D.L., D.L., Schultz—Ej.a, S c h u l t z - E l a , D.D., Hudleston, and Bidwell, the boundary boundary between between Archean Archean B i d w e l l , M.E., M.E., 1987, 1987, Structural S t r u c t u r a l geology g e o l o g y of o f the t e r r a n e s of of low—grade low-grade and and high-grade high-grade rocks, r o c k s , northern n o r t h e r n Minnesota, Minnesota, in in terranes Balaban, Balaban, N.H., N.H., ed., ed., Field F i e l d trip t r i p guidebook guidebook for f o r selected s e l e c t e d areas a r e a s in in Precambrian geology g e o l o g y of of northeastern n o r t h e a s t e r n Minnesota: Minnesota: Minnesota Precambrian Minnesota Geological Geological Survey S u r v e y Guidebook Guidebook Series S e r i e s no. no. 17, 1 7 , p. p. 1-42. 1-42. - Hudleston, and H u d l e s t o n , P.J., P.J., Schultz-Ela, S c h u l t z - E l a , D.D., D.D., and Southwick, Southwick, D.L., D.L., 1988, 1988, Transpreession ~ r a n s p r e e s s i o nin i n an a n Archean Archean greenstone g r e e n s t o n e belt, b e l t , northern n o r t h e r n Minnesota: Minnesota: Canadian Canadian Journal J o u r n a l of o f Earth E a r t h Sciences, S c i e n c e s , v. v. 25, 25, p. p. 1060—1068. 1060-1068. J., 1987, 1987, Kinematics K i n e m a t i c s of of compressional c o m p r e s s i o n a l and a n d extensional e x t e n s i o n a l ductile ductile M a l a v i e i l l e , J., Malavieille, shearing deformation in a metamorphic core complex of the northern s h e a r i n g d e f o r m a t i o n i n a metamorphic c o r e complex of the n o r t h e r n Basin v. 9, 9 , p. p. 541-554. 541-554. B a s i n and and Range: Range: Journal J o u r n a l of of Structural S t r u c t u r a l Geology, Geology, v. Poulsen, 1983, P o u l s e n , K.H., K.H., 1983, Structural S t r u c t u r a l setting s e t t i n g of of vein—type v e i n - t y p e gold g o l d mineralization m i n e r a l i z a t i o n in in the area: Implication I m p l i c a t i o n for f o r the the Wabigoon Wabigoon t h e Mine Mine Centre—Fort C e n t r e - F o r t Frances F r a n c e s area: Subprovince, S u b p r o v i n c e , in i n Colvine, C o l v i n e , A.C., A.C., ed., ed., The The geology g e o l o g y of of gold g o l d in i n Ontario: Ontario: Ontario p. 174—180. 174-1 80. O n t a r i o Geological ~ e o l o g i c aSurvey lS u r v e y Miscellaneous M i s c e l l a n e o u s Paper P a p e r 110, 1 1 0 , p. 1986, An example example of o f an a n Archean Archean subprovince subprovince 1986, Rainy Rainy Lake Lake Wrench Wrench Zone: Zone: An boundary in i n northwestern n o r t h w e s t e r n Ontario O n t a r i o (extended [ e x t e n d e d abs.], a b s . ] , in i n deWit, d e w i t , M.J., M.J., and and boundary Ashwal, the tectonic t e c t o n i c evolution e v o l u t i o n of of greenstone greenstone Ashwal, L.D., L.D., eds., e d s . , Workshop Workshop on on the belts: b e l t s : LPI LPI Technical T e c h n i c a l Report R e p o r t 86-10; 86-10; Houston, Houston, Lunar Lunar and and Planetary Planetary Institute, p. 177—179. 177-1 79. I n s t i t u t e , p. Schultz-Ela, D.D., 1988, 1988, Application A p p l i c a t i o n of o f aa three—dimensional t h r e e - d i m e n s i o n a l finite—element finite-element S c h u l t z - E l a , D.D., method method to t o strain s t r a i n field f i e l d analyses: a n a l y s e s : Journal J o u r n a l of o f Structural S t r u c t u r a lGeology, Geology, v. v. 10, 10, / 263—272. 263-272. Sims, the Sims, P.K., P.K., 1976, 1976, Early E a r l y Precambrian P r e c a m b r i a n tectonic—igneous t e c t o n i c - i g n e o u s evolution e v o l u t i o n in i n the Vermilion V e r m i l i o n district, d i s t r i c t , northeastern n o r t h e a s t e r n Minnesota: Minnesota: Geological G e o l o g i c a l Society S o c i e t y of of America ~ m e r i c aBulletin, B u l l e t i n , v. v. 87, 8 7 , p. p. 379—389. 379-389. Sims, Sims, P.K., P.K., and and Mudrey, Mudrey, M.G., M.G., Jr., Jr., 1978, 1978, Geologic G e o l o g i c map mapof o f the theShagawa ShagawaLake Lake quadrangle, q u a d r a n g l e , St. S t . Louis L o u i s County, County, Minnesota: Minnesota: U.S. U.S. Geological G e o l o g i c a l Survey Survey Geologic scale 1:24,000. 1:24,000. G e o l o g i c Quadrangle Quadrangle Map Map GQ—1423, GQ-1423, scale Sims, Sims, P.K., P.K., and and Southwick, S o u t h w i c k , D.L., D.L., 1980, 1980, Geologic G e o l o g i c map map of o f the the Soudan Soudan quadrangle, q u a d r a n g l e , St. S t . Louis L o u i s County, County, Minnesota: Minnesota: U.S. U.S. Geological G e o l o g i c a l Survey Survey Geologic scale 1:24,000. 1:24,000. G e o l o g i c Quadrangle Quadrangle Map Map GQ—1540, GQ-1540, scale 1985, 1985, Geologic G e o l o g i c map map of o f Archean Archean rocks, r o c k s , western w e s t e r n Vermilion V e r m i l i o n district, district, northern n o r t h e r n Minnesota: Minnesota: U.S. U.S. Geological G e o l o g i c a l Survey S u r v e y Miscellaneous Miscellaneous Investigations I n v e s t i g a t i o n s Series S e r i e s Map Map 1—1527, 1-1527, scale scale 1:48,000. 1:48,000. D-19 �Regional map map of of the t h e field f i e l d trip t r i p area a r e a showing showing the t h e geologic g e o l o g i c framework framework and and the the F i g u r e 1.1. Regional Figure The d o t t e d c o n t a c t is a major unconformity s e p a r a t i n g g e n t l y d i p p ing major roads. major roads. The dotted contact is a major unconformity separating gently dipping P r o t e r o z o i c strata s t r a t a of o f the t h e Animikie Animikie Group Group (on ( o n the t h e south) s o u t h ) from from deformed deformed Archean Archean Proterozoic rocks. The Animikie Group, c o n s i s t i n g o f t h e Pokegama Q u a r t z i t e and Biwabik rocks. The Animikie Group, consisting of the Pokegama Quartzite and Biwabik iron- orm mat ion (open (open circles) c i r c l e s ) and and the t h e Virginia V i r g i n i a Formation Formation (diagonal ( d i a g o n a l rule), r u l e ) , is is Iron—Formation invaded by gabbroic r o c k s o f Keweenawan a g e ( 1 0 0 0 Ma) i n t h e s o u t h e a s t c o r n e r of invaded by gabbroic rocks of Keweenawan age (1000 Ma) in the southeast corner of t h e map map area. a r e a . The The field f i e l d trip t r i p stops s t o p s are a r e all a l l within w i t h i n Archean Archean terrane. terrane. the D-20 �920 30 92° 15 92°OO I. GRA N ITI cC vc.....' V V Figure 2. 2. Geologic Geologic sketch map of the field trip area Figure sketch of the field trip area showing approximate stopmap locations. Modified from showing approximate stop locations. Modified from ( 1 9 8 2 ) and Sims and Southwick Green and Schulz Green and Schulz (1982) and Sims and Southwjck ( 1 9 8 5 ) . Map explanation is on the facing page. (1985). Map explanation is on the facing page. D-21 94 �EXPLANATION FOR FIGURE FIGURE 22 Pdc Duluth Complex; Complex; v various [y] a r i o u s ggabbroic a b b r o i c rocks rocks Middle Proterozoic Proterozoic 1100 Ma) Ma) ( c a . 1100 (ca. INTRUSIVE CONTACT CONTACT 1 Pv 1 VVirginia i r g i n i a Formation; Formation; turbidite turbidite ) : Ppb] Pokegama Quartzite Q u a r t z i t e (tidal ( t i d a l deposits) deposits 1 overlain o v e r l a i n by by Biwabik Biwabik Iron—Formation Iron-Formation - MAJOR UNCONFORMITY UNCONFORMITY ElGiants E vgo ] Early E a r l y Proterozoic Proterozoic 2000 Ma) Ma) ( c a . 2000 (ca - G i a n t s Range batholith; b a t h o l i t h ; granitoid g r a n i t o i d rocks rocks x Vermilion Granitic V ermilion G r a n i t i c Complex, Complex, granitoid g r a n i t o i d rocks, rocks, pparagneiss, a r a g n e i s s , migmatite migmatite INTRUSIVE CONTACT INTRUSIW OR FAULT CONTACT Newton Lake Formation; Formation; tholeiitic t h o l e i i t i c and komatiitic k o m a t i i t i c metabasalt; m e t a b a s a l t ; numerous numerous sills sills FJ K n i f e Lake Group; s e d i m e n t a r y r o c k s o f mixed v o l c a n i c provenance Knife Lake Group; sedimentary rocks of mixed volcanic provenance K iyl V j Eu J I Lake Vermilion Formation; vvolcanic—derived Lake V e r m i l i o n Formation; olcanic-derived sedimentary s e d i m e n t a r y rocks, r o c k s , mainly of of dacitic dacitic pprovenance rovenance Greenstone, upper member; member; cchiefly Ely E ly G r e e n s t o n e , upper hiefly ttholeiitic h o l e i i t i c metabasalt metabasalt Ely E l y Greenstone, G r e e n s t o n e , Soudan Soudan Iron—formation Iron-formation jJEsJ lilil Member; ccherty Member; h e r t y iron—formation i r o n - f o r m a t i o n iinterbedded nterbedded w i t h felsic f e l s i c to t o mafic m a f i c volcanic v o l c a n i c rocks rocks with El Ely Greenstone, member; cchiefly hiefly E ly G r e e n s t o n e , lower lower member; caic—alkaline c a l c - a l k a l i n e metabasalt metabasalt [TI M e t a b a s a l t(unnamed); (unnamed 1 ; probably p r o b a b l y Ely E ~ Y m1 Metabasalt equivalent equivalent ml kti amphibo— Tonalite T o n a l i t e ggneiss, n e i s s , pparagneiss, a r a g n e i s s , amphibollite; i t e ; stratigraphic s t r a t i g r a p h i c pposition o s i t i o n uuncertain ncertain D-22 Late L a t e Archean Ma) ((ca. c a . 2700 Ma) �P Crenulat~on Crenulation Cleavage S2. S2. Cleavage A \ (a) - SingleCleavage Cleavage Single S2 S0 s2=' so Schematic illustration i l l u s t r a t i o n of of the t h e developnent d e v e l o p n e n t of o f F2' F2' folds f o l d s and and S2' S2' Schematic cleavage during a simple deformation that also produced the foliation c l e a v a g e d u r i n g a s i m p l e deformation t h a t a l s o produced t h e f o l i a t i o n CS2) ( s 2 ) being b e i n g folded. folded. Figure F i g u r e 3. 3. C' C t surfaces s u r f a c e s or or shear s h e a rbands. bands. These These develop d e v e l o p in i n rock rock that t h a t has h a s preprev i o u s l y acquired a c q u i r e d aa strong s t r o n g planar p l a n a r foliation f o l i a t i o n due due to t o very v e r y high h i g h shear shear viously strain. C' surfaces s u r f a c e s are a r e new new ssurfaces u r f a c e s of s l i p that t h a tcross c r o s sthe t h emain main s t r a i n . The The C' of slip Figure F i g u r e 4. 4. i s in i nthe t h esame same sense s e n s e as a s the the f o l i a t i o nata moderate t moderate angles; a n g l e s ; slip s l i pon onthem them is foliation overall o v e r a l l sense s e n s e of of shear s h e a r in i nthe t h eshear s h e a rzone. zone. Modified Modified from from Malavieille Malavieille (1987). (1987). D- 23 �N) . modified from Sims and Mudrey (1978) and Green and Schulz (1982). Generalized geologic map of the Shagawa Lake Figure 5. 3-h Geology area showing locations of stops 9 1° 46' � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1989 Description An account of the resource Institute on Lake Superior Geology. Duluth, Minnesota. May 3-6, 1989. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1989 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/e2f7c9cbcfb728f1e2e916113451605b.pdf 56f92e003fa0fe43bd37cefa8c703ef2 PDF Text Text INSTITUTE GEOLOGY NSTITUTE ON ON LAKE LAK SUPERIOR GEOLOGY PROCEEDINGS PROCEEDINGS 36th 36th Annual Annual Meeting Meeting May 1990 May 9-12, 9-12,1990 held held at at Thunder Thunder Bay, Bay, Ontario Ontario H. L. JAMES VOLUME VOLUME 36 VOLUME May 1990 1990 Part Abstracts Part 1. 1. Abstracts �U Organizing OrganizingCommittee, Committee, 36th 36thAnnual AnnualMeeting, Meeting,ILSG ILSG(1990) (1990) I The The Organizing Organizing Committee Committee comprises comprises the the following members members of of the the Department Department of of Geology Geology Lakehead Lakehead University University Thunder 5E1 Thunder Bay, Bay, Ontario Ontario P7B P7B5E1 General Chairman: Manfred General Chairman: ManfredM. M. Kehlenbeck Kehlenbeck Program Editor: Philip W. Fralick Fralick Program Chair and Abstract Editor: PhilipW. Field Field Trip Guidebook Guidebook Editor: Graham GrahamJ. J. Borradaile Borradaile Volume Volume 36 consists consists of of Part Part 1: 1: Abstracts Abstracts Part 2: Part 2: Field Field Trip Trip Guidebook Guidebook Reference Reference to material material in in Proceedings Proceedings Volume should follow follow the the example example below: below: Brown, Bruce Significance of of Conglomerates in the Baraboo quartzite of A., 1989, 1989, Significance Bruce A., southeastern southeastern Wisconsin Wisconsin [abst.J; [abst.]; Institute Institute on Lake Lake Superior Superior Geology Geology Proceedings, 35th v. 35, 35, 35th Annual Meeting, Meeting, Duluth, Duluth, MN, MN, 1989; 1989; Houghton, Houghton, MI, MI, v. part 1, p. 11-12. partl,p.11-12. Published Published and Distributed Distributed by by Institute Institute on on Lake Lake Superior Superior Geology Geology J. Kalliokoski, Kalliokoski, Secretary/Treasurer Secretary/Treasurer Dept. of Geological Geological Engineering, Engineering, Geology and and Geophysics Geophysics Michigan Michigan Technological Technological University University Houghton, Michigan Michigan 49931 49931 ISSN ISSN 1042-9964 1042-9964 1 1 �U Dedication The pioneer pioneer research by by Harold Harold L. James formed formed the widely foundation which widely accepted foundation which geologists. His contributions and ideas stimulated the work work of many geologists. ideas have have become become so so intricately intricately inteiwoven in many many of the interwoven in the later laterstudies studies that thattheir theirsignificance significance and and individuality individuality are are often often obscured. obscured. Born a Canadian 1912,Hal Halgraduated graduatedfrom from the theState StateCollege CollegeofofWashington Washingtonin in Canadianinin1912, During World War 1II1 he mapped asbestos, talc talc and and zinc World War mapped chromite, chromite, manganese, manganese, asbestos, zinc in in 1938. During 1938. Montana Montana for for the theUS. U.S.Geological GeologicalSurvey, Survey,and andafter afterreceiving receiving his his PhD PhDfrom from Princeton PrincetonUniversity University 1945 continued continued with with the the US. U.S.Geological GeologicalSurvey Survey with withbrief brief interruptions interruptionsatatNorthwestern Northwestern in 1945 Universityand and the the University UniversityofofMinnesota, Minnesota. After After the the War his research research interests interests focused focused on on the University in the Lake Superior mated iron-formations in Superior region. region. His His appointment appointment as asChief ChiefGeologist Geologistcu/in culminated hhis i s 50-year long career with the Survey. Survey. He He isis now now retired retired and andlives livesin inBellingham, Bellingham,Washington. Waslzin~qton. Ajier retirement retirement from from the the Survey, he served served as as chairman of the oil the IGUS IGUS Subcommission Subcoi?~~?~i.s.sio/z 011 Ajter Survey, he Precambrian Stratigraphy. Stratigraphy. The concepts and time time lines linesassociated associated with withWXYZ WXYZ Precambrian terminology which which he heput put forward forward for for consideration consideration are are still still actively activelyused usedto todefine definePrecumbriun Precambrian terminology time and and stratigraphy. stratigraphy. I-us principal work work for for many years years involved .s f l I (11, His principal involved meticulous mapping and and microscopic microscopicstwlv of iron deposits in Michigan. Michigan. His pulled from from the rock conclusions that today provide provide His keen keen eye eye pulled provocative geological evolution of this this region. region. His recognition recognition of of differences differences provocative insight insight into the geological in tile of iron-formations due to original sedimentation as the mineralogy of as opposed opposed to todifference difference in in response response to later metamorphism metamorp1zism led led to to the therecognition recognition of of different different depositional basins basins for the the various ore types and regional regional metamorphic metamorphiczoning zoning patterns. patterns. The Thefacies fadesoriginally originallydefined definedJromil fro/I 1 iron-ft)rmnation studiesnow noware aremajor major tools tools in unravelling iron-formation studies unravelling Early Early Proterozoic Proterozoic terrane. terrane. The The recognition of of regional regionalzonal zonal metamorphic metamorphic patterns patterns led led to to concepts concepts of of older olderArchean Archean remobilized basement and and stable stableProterozoic Proterozoiccratons cratonsthat thatcharacterize characterizeworking workingmodels modelsfor for early early Proterozoic Proterozoic continental continental margins. margins. as President President ui in He was was extremely extremely active in the the Society Society of Economic Economic Geologists, Geologists,serving serving as 1970. 1970. He was was awarded awarded the the Penrose Penrose Medal Medal from from the the Society Society in 1976 1976 in in recognition recognition of o f his hi.\ coin prehensivestudy studyofofPrecambrian Precambrian rock rock of of the the Lake Lake Superior region and for establishing comprehensive establi.shi/~gthe tho origin and histomy iron deposits associated with origin history ofof iron with them. them. great pleasure pleasure that the It is with great the Institute Institute on on Lake LakeSuperior SuperiorGeology Geology recognizes recognizes Harold volume to him. L. James' life-time life-time contribution contribution by by dedicating this volume M. G. G. Mudrey, Mudrey, Jr. Jr. �I I I 36th 36th ANNUAL ANNUAL INSTITUTE INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY Proceedings and Abstracts Abstracts Thunder Thunder Bay, Bay, Ontario Ontario May 10 10 and and 11, 11,1990 1990 Organized by by M. M M.Kehienbeck, Kehlenbeck,Lake/zead Lakehead University, University,Thunder ThunderBay Bay G. G. J. Borradaile, Borradaile, Lakehead Lakehead University, University,Thunder Thunder Bay Bay P. W W Fralick, Fralick,Lake/tead LakeheadUniversity, University,Thunder Thunder Bay Bay VoLuMl 36. PART 1 PART 2 PROGRAM AND ABsTRAcTs FIELD TRIP GuIDEBooK �I I I TABLE OF CONTENTS CONTENTS Institutes on on Lake Lake Superior Superior Geology Geology to to 1990 1990 . . . . . . . . . . . . . . . . . . i Constitution of the Institute on Constitution of on Lake Lake Superior Superior Geology Geology . . . . . . . . . . . ii11 By-Laws of the Institute on By-Laws of on Lake Lake Superior SuperiorGeology Geology . . . . . . . . . . . . . 111 iii Goldich Medal Guidelines Guidelines ................................ .. ... iv iv Student Travel Travel Award Award . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vv Board of Directors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi Local Local Committee Committee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi vi Student Paper Award Award Committee Committee . . . . . . . . . . . . . . . . . . . . . . . . . . . vi vi ............................... vi vi Goldich Medal Medal Recipient Recipient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii vi i Banquet Speaker Speaker .. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii vii ..................................... vii vi i Goldich Goldich Medal Medal Committee Committee . Acknowledgements Acknowledgements . . . . . ... Report of of the the Chairs Chairs of of the the 35th 35th Annual Annual Institute Institute . . . . . . . . . . . . . . . viii VIII Calendar of of Events Events Poster Papers Papers Abstracts Abstracts ..................................... . . . xx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii xvii ............................................ xix xix �U 1 INSTITUTES INSTITUTES ON ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY INSTITUTE NUMBER NUMBER 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 DATE 1955 1955 1956 1956 1957 1957 1958 1958 1959 1959 1960 1960 1961 1961 1962 1962 1963 1963 1964 1964 1965 1965 1966 1966 1967 1967 1968 1968 1969 1969 1970 1970 1971 1971 1972 1972 1973 1973 1974 1974 1975 1975 1976 1976 1977 1977 1978 1978 1979 1979 1980 1980 1981 1981 1982 1982 1983 1983 1984 1984 1985 1985 1986 1986 1987 1987 1988 1988 1989 1989 1990 1990 PLACE PLACE Minneapolis, MN MN Houghton, MI MI East Lansing, Lansing, MI MI Duluth, MN MN Minneapolis, MN MN Madison, Madison, WI WI Port Arthur, Arthur, Ont. Ont. (Thunder (Thunder Bay) Bay) Houghton, Houghton, MI MI Duluth, Duluth, MN MN Ishpeming, Ishpeming, MI MI St. Paul, Paul, MN MN Sault Ste. Ste. Marie, Marie, WI WI East East Lansing, Lansing, MI MI Superior, WI WI Oshkosh, WI WI Thunder Bay, Bay, Ont. Ont. Duluth, MN Duluth, MN 1-loughton, Houghton, MI MI Madison, Madison, WI WI Sault Sault Ste. Ste. Marie, Marie, Ont. Ont. Marquette, Marquette, MI MI St. St. Paul, Paul, MN MN Thunder Thunder Bay, Bay, Ont. Ont. Milwaukee, Milwaukee, WI WI Duluth, Duluth, MN MN Eau Eau Claire, Claire, WI WI East East Lansing, Lansing, Ml MI International Falls, International Falls, MN MN Houghton, Houghton, MI MI Wausau, Wausau, WI WI Kenora, Kenora, Ont. Ont. Wisconsin Wisconsin Rapids, Rapids, WI WI Wawa, Wawa, Ont. Ont. Marquette, Marquette, MI MI Duluth, Duluth, MN MN Thunder Thunder Bay, Bay, Ont. Ont. �___________ CONSTITUTION CONSTITUTfON OF INSTITUTE INSTITUTE ON LAKE SUPERIOR GEOLOGY Article I Name shall be be the the "Institute 'Institute on Lake Superior Superior Geology". Geology. The name of the organization shall Article II I1 Objectives Obiectives The objectives objectives of this organization organization are: are: A. To Toprovide providea ameans meanswhereby wherebygeologists geologists in in the the Great Great Lakes Lakes region region may may exchange exchange ideas and scientific data. B. To Topromote promotebetter betterunderstanding understandingofofthe thegeology geologyof of the theLake LakeSuperior Superior region. region. C. To Toplan planand andconduct conductgeological gcologiealfield field trips. trips. Article III I11 Status Status No part of of the the income income of of the organization organization shall shall inure inure to to the the benefit benefit of of any any member member or or individual. individual. In the the event event of of dissolution dissolution the assets assets of of the the organization organization shall shall be be distributed distributed to to (some tax free organization). organization). (To avoid Federal and State State income income taxes, taxes, the organization organization should he be not not only only 'scientific" "scientific" or "educational', "educational", but also also 'non-profit".) "non-profit".) Minn. Stat. Anno. Anno. 290.01, 290.01, subd. 4 Minn. Stat. Stat. Anno. Anno.290.05(9) 290.05(9) Internal Rcvcnue Revenue Code s. 1954 lnternd s. 501(c)(3) SOl(c)(3) Article IV Membership members hi^ of the organization shall consist consistofofthe the board board of of directors. directors. Any The membership membership of organization shall Any geologist geologist interested shall be permitted to attend attend and and participate participate in in and and vote vote at at the theannual annualmeetings. meetings. Article V Meetings Meetings during the the month month of of April. April. The The organization shall meet once a year, preferably during The place place and and exact date of each meeting by the board of directors. meeting will be desginated dcsginated by directors. VI Article VI Directors The board of of directors directors shall shall consist consist of the Chairman, Chairman, Secretary-Treasurer, Secretary-Treasurer, and the last last three three past Chairman; but ifif the board board should should at at any any time time consist consist of of fewer than five five persons, by reaon of unwillingness or or inability of of any any of of the the above persons to serve serve as as directors, directors,the thevacancies vacancieson on the board may may be filled filled by the annual meeting so as to bring the membership of the board up up to five five members. Article VII Arficlc Vll Ofliccrs Officcrs The officers of this organization shall be be a Chairman and Secretary-Treasurer. Secretary-Treasurer. A. The TheChairman Chairmanshall shallbe beelected electedeach eachyear yearby bythe theboard boardofofdirectors, directors,who whoshall shallgive give due due of any group group that may be promoting the next consideration to the wishes of next annual annual meeting. meeting. His term of of office as Chairman will terminate at the the close close of of the the annual annual meeting meetingover overwhich which successor shall shallhave havebeen beenappointed. appointed. He will he presides presides or when when his his successor will then serve for a period of three years as a member member of of the the board board of of directors. directors. Secretary-Treasurer shall shallbe be elected elected atat the the annual annual meeting. meeting. His term B. The Secretary-Treasurer term of of office office shall be two two years years or or until until his his successor successor shall have been appointed. Article VIII Amendments This constitution may be be amended constitution may amended by by a majority majority vote of of those those persons persons who who are arepersonally personally present at, participating in, and voting at any annual meeting of the organization. organization. *. 11 11 �U BY-LAWS BY-LAWS I. Dutiesofofthe theOfficers Officersand andDirectors Directors Duties A. ItItshall shallbe bethe theduty dutyofofthe theAnnual AnnualChairman Chairmanto: to: A. 1.1. 2.2. 3.3. Preside atatthe theannual annualmeeting. meeting. Preside Appoint all committees Appoint all committeesneeded neededfor forthe theorganization organizationofofthe thearmual annualmeeting. meeting. Assume Assume complete completeresponsibility responsibility for for the theorganization organizationand andfinancing financingofofthe the annualmeeting meetingover overwhich whichhe hepresides. presides. annual B. ItItshall shallbe bethe theduty dutyofofthe theSecretary-Treasurer Secretary-Treasurerto: to: B. 1.1. 2.2. 3.3. Keep Keepaccurate accurateattendance attendancerecords recordsofofall allannual annualmeetings. meetings. Keep accurate records of all meetings of, and correspondence Keep accurate records of all meetings of, and correspondencebetween, between, theboard boardofofdirectors. directors. the Hold Hold all allfunds fundsthat thatmay mayaccrue accrueas asprofits profitsfrom fromannual annualmeetings meetingsor orfield field trips trips and and to tomake make these these funds funds available available for the organization organization and operation operation of future futuremeetings meetingsas asrequired. required. of C. ItItshall shallbe bethe theduty dutyof ofthe theboard boardofofdirectors directorstotoplan planlocations locationsofofannual annualmeetings meetings C. and and to toadvise adviseon onthe theorganization organizationand andfinancing financingof ofall allmeetings. meetings. 11. II. Duties and andExpenses Exvenses Duties 1.1. 2.2. 111. III. Thereshall shallbe beno noregular regularmembership membershipdues. dues. There Registration Registration fees fees for for the the annual annual meetings meetings shall shall be determined determined by by the the Chairman Chairman in consultation consultation with with the the board boardofofdirectors. directors. ItIt isisstrongly strongly recommended recommended that that in these these be be kept keptatataaminimum minimumtotoencourage encourageattendance attendanceof ofgraduate graduatestudents. students. Rules of ofOrder Order Rules The Therules rulescontained contained in inRobert's Robert's Rules RulesofofOrder Ordershall shallgovern governthis thisorganization organizationininall all cases to to which which they they are areapplicable. applicable. cases IV. 1V. Amendments Amendments These may be be amended These by-laws by-laws may amended by by a majority majority vote vote of of those those persons persons who who are are personally personally present present at, participating participating in, and voting voting at any any annual annual meeting meeting of of the the organization; organization;provided providedthat thatsuch suchmodifications modificationsshall shallnot not conflict conflict with the the constitution constitution as presently presently adopted adopted or orsubsequently subsequentlyamended. amended. as Ill �U AwardGuidelines Guidelines Award SAMGOLDICH GOLDICHMEDAL MEDAL SAM Preamble Preamble The TheInstitute Instituteon onLake h k eSuperior SuperiorGeology Geologywas wasborn bornon onororaround around1955, 1955,asasdocumented documentedbyby the thefact factthat thatthe the27th 27thannual annualmeeting meetingwill will be beheld heldinin1981. 1981.The TheInstitutes Institutesare areexemplary exemplary inin their theircontinuing continuing objectives objectives of of dealing dealing with with those those aspects aspects of of geology geology that are are related related geographically geographicallytotoLake LakeSuperior; Superior;ofofencouraging encouragingthe thediscussion discussionofofsubjects subjectsand andsponsoring sponsori~~g field field trips tripswhich whichwill will bring bringtogether togethergeologists geologistsfrom fromacademia, academia,government governmentsurveys, surveys,and and industry; industry;and andof ofmaintaining maintainingan anexceedingly exceedinglyinformal informalbut buthighly highlyeffective effectivemode modeof of operation. operation. During Duringthe thecourse courseofofits itsexistence existencethe themembership membershipof ofthe theInstitute Institute(that (thatis,is,those thosegeologists geologists who who indicate indicate an aninterest interestininthe theobjectives objectivesofofthe theI.L.S.G. I.L.S.G. by byattending) attending)has hasbecome becomeaware aware of their colleagues have made particularly of the thefact factthat thatcertain certainof of their colleagues have made particularlynoteworthy noteworthyand and meritorious geology meritoriouscontributions contributionstotothe theimprovement improvementofofunderstanding understandingofof"Lake "LakeSuperior" Superior1' geology andits itsmineral mineraldeposits. deposits. and The The exemplary exemplary award award was was made made by by I.L.S.G. I.L.S.G. to Sam Sam Goldich Goldich in in 1979 1979 for for his hismany many contributions 50years. years. contributions to tothe thegeology geology of of the theregion regionextending extendingover overabout about50 Award Guidelines Guidelines Award 1) 1) The Themedal medalshall shallbebeawarded awardedannually annuallyby bythe theI.L.S.G. I.L.S.G.Board BoardofofDirectors Directorstotoa ageologist geologist whose whosename nameisisassociated associatedwith with aa substantial substantial sustained sustainedinterest interestin, in,or oraamajor majorcontribution contribution to,the thegeology geologyof ofthe theLake LakeSuperior Superiorregion. region. to, 2) 2)The TheBoard BoardofofDirectors, Directors,I.L.S.G. I.L.S.G.shall shall appoint appoint the the Nominating Nominating Committee. The Theinitial initial appointment appointment will will be of of three three members, members, one one to to serve serve for for three three years, years, one one for for two, two, and and onefor forone oneyear, year,the themember memberwith withthe thebriefest briefest incumbency incumbency to be chairman. chairman. After Afterthe the one first year the Board of Directors shall appoint at each spring meeting one new member first year the Board of Directors shall appoint at each spring meeting one new member who will will serve serve for for three threeyears. years. In Inthe thethrid thridyear yearthis thismember membershall shallbe bethe thechairman. chairman. who The TheCommittee Committeemembership membership should should reflect reflect the themain mainfields fieldsofofinterest interestand andgeographic geographic distribution ofofI.L.S.G. I.L.S.G.membership. membership. distribution 3) By By November November 1,1, the the Goldich Goldich Medal Medal Nominating Nominating Committee Committee shall shall make make its its 3) recommendation recommendation to to the the Chairman Chairmanof of the theBoard BoardofofDirectors Directorswho whowill will then then inform inform the the Board of of the thenominee. nominee. Board 4) 4) The TheBoard BoardofofDirectors Directorsnormally normallywill willaccept acceptthe thenominee nomineeofofthe theCommittee, Committee,will willinform inform the the medalist medalist immediately, immediately, and will will have have one onemedal medalengraved engravedappropriately appropriately for for presentation presentation at atthe thenext nextmeeting meetingof of the theInstitute. Institute. 5) ItIt isis recommended recommended that that the theInstitute Instituteset setaside asideannually annuallyfrom fromwhatever whateversources, sources,such such 5) funds funds as as will will be required required to tosupport supportthe thecontinuing continuingcosts costsof of this thisaward. award. April 1981 April4,4,1981 J.J.Kalliokoski, Kalliokoski,Chairman Chairman Bill Bill Cannon Cannon Fred Fred Kehlenbeck Kehlenbeck Glenn Glenn Morey Morey Greg GregMursky Mursky iv �U I I STUDENT STUDENT TRAVEL TRAVEL AWARD AWARD 98OBoard BoardofofDirectors Directorsestaldished establishedthe the1.L.S.G. I.L.S.G.Student Student1'r:ivcI TravelAward Award l to ' Flic I l c II080 o Ssiipjurl ~II)I)OI Institutes. The Lund student at the annual Institutes. s t ~ ~ d cparticipation ~it The awards awards will will be made from fro111a special I.LIIKI up for this purpose. up purpose. This This award award is is intended intended to to help help defray defray some some of of the the direct direct travel travel costs costs to the Institute Institute and and includes includes aa waiver waiver of of registration registration fees, fees, but but excludes excludes expenses expenses for lodging,and andfield fieldtrip tripregistration. registration. The number of awards and value are determined meals, lodging, detern~ined by the the annual Chairman in consultation with the Secretary-Treasurer by Secretary-Treasurer and and will will be announced announced at the annual annual banquet. banquet. set set The following general criteria criteria will will be be considered by the annual The following general considered by annual Chairman, Chairman, who who isis responsible for the selection: responsible selection: active resident resident (undergraduate (undergraduate or or graduate) graduate) student 1) The Theapplicants applicants must must have active status at the the time time of of the the Institute, Institute, certified certified by by the department department head. head. 2) Students Students who who are the the senior senior author on either an oral or or poster poster paper will will be given favored consideration. consideration. 3) It is is desirable desirable for for two two or or more more students students totojointly jointly request requesttravel travelassistance. assistance. priority will will be be given given to to those those in in the Institute 4) IIn n general, general, priority Institute region region who who are arc farthest Farthest away. away. 55)) Each travel award request shall be made in in writing, to the annual Chairman, Chairman, with an explanation of need, possible author status or or other other significant significant details. details. Successful Meeting. Successfulapplicants applicantswill willreceive receivetheir theirawards awardsatatthe the time time of of registration registration for the Meeting. V �I BOARD BOARD OF OFDIRECTORS DIRECTORS 1990 M. M. M. M. Kehienbeck Kehlenbeck 1990 Department P7B5E1 5E1 Department of of Geology, Geology, Lakehead Lakehead University, University, Thunder Bay, Ontario P7B 1989 1989 R. R.W. W.Ojakangas Ojakangas (with (with J. C. Green Green and and T. T. B. B. Hoist) Holst) Department Departmentof ofGeology, Geology,University University of Minnesota, Duluth, Duluth, Duluth, Minnesota Minnesota 55812 558 12 1988 J.S. J.S. Kiasner Klasner (with (with J. J. D. D. Hughes Hughes and andK. K.J.J.Schulz) Schulz) 1988 Department DepartmentofofGeology, Geology,Western WesternIllinois IllinoisUniversity, University,Macomb, Macomb,Illinois Illinois61455 61455 R. P. P. Sage Sage (with (with E. E. D. D.Frey) Frey) 1987 R. 1987 Ontario OntarioGeological Geological Survey, Survey, Ministry Ministry of of Northern Northern Development Developmentand andMines, Mines, 77 77 Grenville Grenville Street, Toronto, Ontario M7A M7A1W4 lW4 Secretary-Treasurer Secretary-Treasurer Kalliokoski J.J. Kalliokoski Department Department of of Geology Geologyand andGeological GeologicalEngineering, Engineering,Michigan MichiganTechnological Technological University, University, Houghton, Houghton, Michigan Michigan49931 4993 1 LOCAL LOCAL COMMI11EE COMMIlTEE M. M. M. Kehienbeck Kehlenbeck M. General General Chairman Chairman P. W. W. Fralick Fralick P. Program and Abstract Abstract Editor Editor G. J. J. Borradaile Borradaile G. Trip Guidebook Guidebook Editor Editor Field Trip STUDENT COMMITFEE 1990 STUDENT PAPER AWARD AWARD COMMI'ITEE 1990 J. S. S. Kiasner, Klasner, Chairman Chairman J. Western Illinois Illinois University, University, Macomb, Macomb, Illinois Illinois W. Kangas Kangas W. Cleveland Cleveland Cliffs Cliffs Iron Co., Co., Ishpeming, Ishpeming, MI MI Southwick D. Southwick Minnesota Minnesota Geological Geological Survey, Survey, St. St. Paul, Paul, MN MN GOLDICH MEDAL MEDAL COMMITFEE COMMI'ITEE 1989-90 1989-90 J. J. Brummer, Brummer, Chairman Brummer BrummerConsulting, Consulting, Toronto, Toronto, Ontario Ontario G. Mudrey, Mudrey, Jr. Jr. M. G. Wisconsin Geologic and Natural Natural History HistorySurvey, Survey,Madison, Madison,WI WI W. Cambray Cambray F. W. Dept. of of Geological Geological Sciences, Sciences, Michigan Michigan State StateUniversity, University, East Lansing, Lansing, MI MI vi �GOLDICHMEDAL MEDALRECIPIENT RECIPIENT1990 1990 GOLDICH Dr. Dr. Ken Ken D. D. Card, Card,Lithosphere Lithosphere and and Canadian CanadianShield ShieldDivision, Division, Geological GeologicalSurvey Survey of of Canada, Canada, 588 Booth Booth Street, Street, Ottawa, Ottawa, Ontario Ontario K1A KIA0E4. OE4. 588 Medal Medal awarded awarded by by M. M. M. M.Kehienheck, Kehlenbeck, Lakehead Lakehead University, University, Thunder Thunder Bay, Bay, Ontario. Ontario. BANQUET SPEAKER SPEAKER BANOUET At At press presstime timewe weare areunable unabletotoconfirm confirmour ourbanquet banquetspeaker speakerdue duetotocircumstances circumstancesbeyond beyond ourcontrol. control. our ACKNOWLEDGMENTS ACKNOWLEDGMENTS We We three three(M. (M.M. M.Kehienbeck, Kehlenbeck,G. G.J.J.Borradaile, Borradaile,and andP.P.W. W.Fralick) Fralick)gratefully gratefullyrecognize recognizethe the unselfish unselfish contributions contributionsof oftime timeand andenergy, energy,by bymany manyindividuals, individuals, without without which which this this meeting meeting could not not have have taken taken place. place. could We We especially especially thank our our Department Department Secretary, Secretary, Sandra Sandra Millar, Millar, for for her hersecretarial secretarialskills skills and and efficiency efficiency in compiling compiling the mailing mailing lists, brochures, Institute Institute volumes, volumes, and and attending attendingtoto many other othertasks. tasks. many The ' h e drafting drafting of of illustrations illustrations for for the theGuidebook, Guidebook,as aswell well as asassistance assistanceduring during the thetechnical technical sessions provided by by Sam Sam Spivak Spivakand and Reino Reino Viitala. Viitala. Two of our our sessions and field trips, trips, was ably provided Two of graduate graduate students, students, Barbara BarbaraSeemayer Seemayer and andDave DaveNicol, Nicol, handled handled the themailing mailingofofbrochures, brochures, helped helped on on the the field field trips trips and and did did many many other other jobs. jobs. The Theassistance assistanceofofBob BobCornell Cornelland andJim Jim Podd Podd of of Lakehead Lakehead University, University, David David Thomson Thomson (Airlane (Airlane Hotel) Hotel) and andnumerous numerouscompany company personnel isis appreciated. appreciated. personnel 'rhanks for for aa job job well well done done also also go go to: to: Thanks Joe -- Joe Brummer, Cambray (Goldich Brummer, Mike Mudrey Mudrey and Bill Cambray (Goldich Medal Medal Committee) Committee) -- Steve Kissin, Kissin, Maurice Maurice Lavigne Lavigneand andJohn John Scott Scott (Field Richard Sutcliffe, Sutcliffe, Steve (Field Trip Trip leaders) leaders) Richard -- and Bill Bill Kangas Kangas (Student John Kiasner, Klasner, Dave Southwick Southwick and (Student Paper PaperAward Award Committee) Committee) John -- To all all those those brave brave souls souls who who conduct conduct the the technical technical sessions sessions and keep keep the theprogram program To time. on time. Special moments Special thanks to Joe Joe Kalliokoski Kalliokoski for his his support support and and sage sage advice advice during during critical critical moments in the the planning planningprocess. process. in Since Since no list list of of this this type type isis ever ever complete, complete, we we thank thankeveryone everyoneelse elsewho whocontributed. contributed. vii vii �35th 35th ANNUAL ANNUAL INSTITUTE ON LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY Duluth, Minnesota Minnesota 1989 1989 Duluth, The The 35th 35th annual annual meeting meeting of of the the Institute Instituteon onLake LakeSuperior SuperiorGeology Geologywas was held held from from May May 3-6, 1989, 1989, in Duluth, Minnesota. The Themeeting meetingwas was hosted hosted by by the theUniversity University of of Minnesota, Minnesota, 3-6, as General Chairman, John C. Green Duluth. Richard Richard W. W. Ojakangas Ojakangas served served as Chairman, John Green served served as as Duluth. Program and Abstract Editor, and and Timothy B. Hoist Holst served served as Field Field Trip Trip Program Chairman Chairman and Abstract Editor, Timothy B. Chairman and and Guidebook Guidebook Editor. Editor. Several Several other UMD UMD faculty faculty members members and and graduate graduate Chairman and the the banquet were held students assisted assisted ininvarious variousways. ways. Technical Technical sessions sessions and held at at the the students Radisson & 5. 5. A A total total of of 202 202 persons registered for for Radisson Hotel on on Thursday Thursday and Friday, May May 44 & the the meeting. meeting. Thirty Thirtypapers papers were were presented presented orally orally and and 24 24 were presented as posters. Two Two field field trips trips were were held held on onWednesday Wednesday May May 33 and and two two were were held held on onSaturday SaturdayMay May 6.6. Paper follows: "Midcontinent Papersessions sessions were were organized organized into into four four one-half one-half day day sessions, sessions, as follows: Rift'; Rift";'Mostly "MostlyEconomic Economicand andQuaternary," Quaternary,''"Mostly "MostlyProterozoic" Proterozoic"and and"Mostly "MostlyArchean". Archean". A A total total of of 124 124 persons registered for for field trips. Field Field trip trip1,1,led ledby by John JohnC. C.Green, Green,was was ledby byTimothy TimothyB. B. Minnesota (30 (30 persons). persons). Field Fieldtrip trip2,2,led to the the North North Shore Shore Rhyolites Rhyolites jf Minnesota to (24 persons). persons). East-Central Minnesota Minnesota(24 Holst was was a visit to Penokean Structural Terranes .f East-Central Holst Field Field trip trip 3, 3, led led by by Karl Karl Seifert, Seifert, James James Olmstead, Olmstead, and and Ken Ken Kiewin Klewin was to the the Mellon Mellon Com~lex.Wisconsin Wisconsin (23 (23 persons). persons). Field Field trip trip 4, 4, entitled entitled Archean Archean Gold GoldOccurrences Occurrences & Complex. their their Structural Structural Settings. Settings. Minnesota, Minnesota, had hadeight eightleaders, leaders,asasfollows: follows: J. J. Welsh, Welsh, D. D.England, England, D. D. Groves, Groves, E. E. Levy, k v y , P. P. Hudleston, Hudleston, D. D. Southwick, Southwick, R. Bauer, Bauer, W. W. Ulland Ulland (47 (47persons). persons). A A total total of of 159 159 people attended attended the the annual annual ILSG ILSG banquet. banquet. Mike MikeMudrey, Mudrey,Jr. Jr.presented presented the KalliokoskiofofMichigan MichiganTechnological Technological University University for for his his many many the Goldich Goldich Medal MedaltotoJ.J.Kalliokoski contributions contributions to to teaching teaching and and research research on onthe theLake LakeSuperior Superiorregion, region,asaswell wellasasfor forhis hislong long The banquet speaker was Frederick J. "Sam" Sawkins of the J. "Samo' Sawkins of the service to the Institute. The banquet speaker was Frederick service to the Institute. University of Minnesota, Twin Cities, who spoke on "Ore genesis models for University Minnesota, Twin Cities, who on "Ore genesis models for volcanoplutonic arc Hisagnostic agnosticviews views arc system: system: An Anagnostic agnosticview viewof ofthe theconventional conventionalwisdom." wisdom." His stimulated stimulated discussions discussions for the remainder remainder of of the themeeting. meeting. In T U G assisted assisted seven seven In continued continued support support of of student student participation participation in in the the meeting, meeting, the the ILSG Six UMD UMD students students with with small small transportation transportation stipends stipends and and waiver waiver of of registration registration fees. fees. Six students students were were given given waivers waivers of registration registration and banquet banquet fees fees for for their theirvalued valuedassistance assistance before Anaward awardofof$150 $150was was presented presented to to Torn Tom before and and during during the the meeting meeting and and field field trips. trips. An Suszek of Minnesota, Minnesota, Duluth, Duluth, for for the best best oral student presentation, Suszek of the University University of presentation, and and $150 award award was was presented presented to to Daniel Daniel Hoim Holm of of Harvard Harvard University University for the the best best poster poster aa $150 paper. John John Kiasner, Klasner, Ray Ray Anderson, Anderson, and and Keith Keith Laskowski Laskowski served served on on the the Best BestStudent Student paper. Paper Committee. Committee. Paper An ILSG ILSG Board Board of of Directors Directors Luncheon Luncheon Meeting Meetingwas was held held on onMay May4.4. It An It was was attended attended J. Greenburg, Greenburg, T. T. Hoist, Holst,J.J.Hughes, Hughes,J.J.Kalliokosi, Kalliokosi,M. M.Kehienbeck, Kehlenbeck, by B. Brown, J. C. Green, by Green, J. J.J. Kiasner, Klasner, R. R.Ojakangas, Ojakangas, R. R.Sage, Sage,S. S.Sawkins, Sawkins, and and K. K. Schulz. Schulz. The Thefollowing followingitems itemswere were discussed: discussed: ... viii Vlll �U from the ILSG (1)$500 $500 from ILSG Treasury Treasury in in the U.S. U.S. and and $500 $500 from from the the ILSG ILSG treasury treasury inin (1) Canada will will be made made available available for for travel travel support support for for students students presenting presenting papers. papers. (2) (2) John Hughes Hughes read read aa letter letterfrom fromBurt BurtBoyum Boyum regarding regarding the the making making of of aa video video on on the the Mining History of of the Marauette Marquette Range. Mining Historv Range. (This (Thiswas wasthe thetitle titleof of aafield fieldtrip tripatatthe the34th 34thILSG ILSG at Marquette Marquette in in1988). 1988). ILSG ILSGwill will support support the the idea ideaand andurges urgesthat thatacknowledgment acknowledgmentof of Burt Burt Boyum and Bob Reed be be included included in in the thevideo. video. Boyum (3) R. (3) Voted to to ask ask Bill Bill Cambray to serve on the Goldich Goldich Medal Medal Committee, Committee, replacing replacing R. W. Ojakangas whose term has has expired. expired. (4) was received. received. The balance in the General (4) The Treasurer's report report by by J. J. Kalliokoski Kalliokoski was General account as as of of April April 30, 30, 1989 1989 was $5,593.03. $5,593.03. The The Goldich Goldich Medal Medal Fund Fundcontained contained$352.15. $352.15. M. Kehlenbeck, Kehienbeck, Treasurer of the Canadian Canadian account, account, reported reported aabalance balanceofof$10,299.90 $10,299.90 as as of of April 30, 30,1989. 1989. April We We wish wish to thank thank all all those those who who helped helped totomake makethis thisa asuccessful successfulILSG ILSG meeting, meeting, including all the speakers, the poster-presenters, including all poster-presenters, the field field trip trip leaders, leaders, the thesession sessionchairs, chairs, the the Student Student Paper Paper Judges, Judges,the the Goldich GoldichMedal MedalCommittee, Committee,the theBanquet BanquetSpeaker, Speaker,Mary MaryNash Nash (UMD who handled (UMD Geology Geology Department Department Executive Executive Secretary) Secretary) who handled the the finances, finances, Joan Joan Hendershot Hendershot (UMD (UMD Geology Geology Department Department Senior SeniorSecretary) Secretary) who who did did nmuch m u c h ofofnecessary necessary arrangements, numerousstudent student assistants, assistants,the the guiding guidingBoard Board ofof Directors, and J.J. arrangements, numerous Directors, and Kalliokoski, Kalliokoski, the Secretary-Treasurer Secretary-Treasurer of of ILSG. ILSG. Finally, Finally, the advice advice and and sympathy sympathy of the the organizers of previous meetings has been been most most helpful. helpful. Respectfully Respectfully submitted, submitted, R. W. W. Ojakangas Ojakangas J. C. C. Green Green T. B. Hoist x �CALENDAR OF OFEVENTS EVENTSAND ANDPROGRAM PROGRAM CALENDAR WEDNESDAY. WEDNESDAY. MAY9 MAY 9 Field Field Trips Trips 1, 1, 2, 2, and and 44 Field Field trips trips depart at 88 am. am.from porn the therear rearparking parking lot lot of of the the Airlane Airlane Motor Motor HoteL Hotel. Lunch Lunchisisprovided. provided. TRTPNO. TRIP NO. I I** Sutcliffe (leader) (leader) -- Mafic Mafic intrusions, intrusions, PGE PGE Sutcliffe mineralization and granitoid rocks of the Lac des Tiles mineralization and granitoid rocks of the Lac des Illes area. area. R. R. VANS VANS TRIP NO. NO.2* 2* TRIP G. G. Borradaile Borradaile (leader) (leader) -- Geology Geology of of the the Shebandowan Shebandowan and and Quetico QueticoArchean ArcheanSubprovinces. Subprovinces. VANS VANS FOR FOR PEOPLE PEOPLEWHO WHO ARE ARE GOING GOING ON ON A A POST-MEETING POST-MEETING TRIP TRIP T N P NO. NO. 4* #* TRIP M. Lavigne Lmigne and and J.J. Scott Scott (leaders) (leaders) -- Base Base metal metal mineralization mineralization in in the the Shebandowan Shebandowan Greenstone GreenstoneBelt. Belt. BUS BUS FOR ARE ALSO GOING ON TRIP I1 FOR PEOPLE PEOPLEWHO WHO ARE All All trips trips terminate terminate at at the theAirlane Airlane Motor Motor Hotel. Hotel. 4 p.m. p.m. -- 88 p.m. p.m. and Check-in Check-in for for Pre-registrants Pre-registrants Registration and p.m. -- 10 10 p.m. p.m. 7 p.m. Welcome Welcome Get-together and Poster Poster Displays Displays Cash Bar Bar * These These field trips trips have have been been duplicated duplicated (i.e. (i.e. pre-meeting pre-meeting and andpost-meeting). post-meeting). * x �THURSDAY. THURSDAY.MAY MAY1010 TECHNICALPROGRAM PROGRAM TECHNICAL I MORNING MORNING SESSION SESSION CHAIRS: CHAIRS: Vat ValW. W.Chandler Chandlerand andDonald DonaldM. M.Davidson. Davidson, Jr. Jr. 7.55 7.55 1.1. WELCOME WELCOME 8:OO Jablinski, Jablinski,J.D.* J.D.* 8:00 Holst,T.B. T.B. Hoist, Cuthill,J.J. Cuthill, Oliver,D.C. D.C. Oliver, Pankka, Pankka,H.S.* H.S.* Bornhorst,T.J. T.J. Bornhorst, 2.2. 8:20 8:20 3.3. $140 Hayes, Hayes,M.J.* M.J.* 8:40 Structural Structuralanalysis analysisof of Archean Archeanmetasedimentary metasedimentaryrocks rocksinin Jardine, the vicinity vicinity of of the the Mineral Mineral Hill HillGold Goldmine, mine,Jardine, the Montana. Montana. Finnish FinnishProterozoic Proterozoicgold goldoccurrences occurrencesand andimplications implicationsfor for the theLake LakeSuperior SuperiorRegion. Region. Geology Geology of of Wright Wright County County using using well well log logdata. data. Nelson,C.L. C.L. Nelson, 4.4. 900 9:00 Venzke, E.A.* Venzke,E.A.* The The geology geology of of the the Greenwood Greenwood Lake Lake area area l)uluth Ihli~th Complex, Complex, Lake Lake County, County, Northwestern NorthwesternMinnesota. Minnesota. 5.5. The The role roleofofvolatiles volatiles in in the theformation formationofofthe thePlatinum Platinum Group Group Element Elementdeposits depositsin inthe theMiddle MiddleProterozoic Proterozoicand and the theTriassic TriassicNoril'sk-Talnakh Noril'sk-Talnakh Intrusions. Intrusions. 9120 9:20 Weiblen, Weiblen,P.P. Sabelin,T.T. Sabelin, Saini-Eidukat,B.B. Saini-Eidukat, Iwasaki,I.I. Iwasaki, 9:4O 9:40 COFFEE COFFEEBREAK BREAKand andPOSTER POSTERSESSION SESSION CHAIRS: CHAIRS: Ted Ted J.J. Bornhorst Bornhorst and andJohn JohnGreen Green 6.6. 1O:OO 10:00 10120 7.7 . 10:20 * Student Student * Ojakangas, Ojakangas,R.W. R.W. Marmo, J.S. Marmo, J.S. Heiskanen,K.!. K.I. Heiskanen, Lower Lower Proterozoic Proterozoic glaciogenic glaciogenic deposits: deposits: A A North North America-Baltic America-Baltic Connection? Connection? Wilkin, Wilkin, R.T.* R.T.* Mavrogenes, Mavrogenes, J.A.* J.A. * Bornhorst, T.J. T.J. Bornhorst, Archean Archean granitoids granitoids of of northern northern Marquette MarquetteCounty, Co~~nty, Michigan. Michigan. xi �U 8. 8. 10:40 10:40 Juneau, PJ. P.J. petrology of iron silicate-rich silicate-rich bodies in the the Origin and petrology Biwabik iron formation, Minnesota. Minnesota. 9. 9. 11:00 1 1:OO Jerde, Jerde, E.A.* E.A.* Reverse zonation the Lester Lester River River Sill, Sill, Duluth, Dulitth, Reverse zonation in in the Minnesota, and evidence evidence for for polybaric polybaric fractionation. fractionation. 10. 10. 11:20 11120 Aubut, A. A. Geology of the Shebandowan Shebandowan Mine. Mine. 11:40 11~40 LUNCH LUNCH BREAK BREAK Tour Lab., Tour of ofRock Rock Mechanics MecLab.,Lalcehead L,akehead University U~ersity Sign-up Sign-up at atRegictration R w a t z o n Desk 1:00 1100 POSTER SESSION SESSION WITH AUTHORS PRESENT AFFERNOON AFTERNOON SESSION SESSION CHAIRS: Ed Frey Frey and and Tim Tim Hoist Holst CHAIRS: Ed 11. 11. 1:30 1130 Kean, Kean, W.F. W.F. Schneiker, Schneiker, R. R. Paleomagnetism of of Baraboo Baraboointerval intervalrocks rocksininWisconsin. Wisconsin. Paleomagnetism 12. 12. 1:50 150 Chandler, Chandler, V.W. V.W. Morey, G.B. Morey, G.B. The The paleomagnetism paleornagnetism of the the early earlyProterozoic Proterozoic Sioux Sioux 13. 1-3. 2:10 2110 Bodus, Bodus, T.M.* T.M.* Kean, Kean, W.F. W.F. Magnetic Magnetic survey of the Niagara Niagara fault fault system system in in northeastern northeastern Wisconsin Wisconsin and and northwestern northwestern Upper Upper Peninsula Peninsula Michigan. Michigan. 2:30 2130 Lagowski, Lagowski,J•* J.* Geology Geology and economic economic potential potential of of northern northernMichigan Michigan graphite. graphite. 14. 14. Johnson, Johnson, A. A. Gere, Gere,M. M. 15. 15. * quartzite. quartzite. 2:50 250 Cannon, Cannon, W.F. W.F. Peterman, Peterman, Z.E. Z.E. Sims, Sims, P.K. P.K. 3:10 3:lO COFFEE COFFEE BREAK BREAK and andPOSTER POSTERSESSION SESSION * Student Student Structural and and isotopic isotopic evidence evidence for for middle middle Proterozoic Proterozoic Structural thrust thrust faulting fmlting of of Archean Archean and and early earlyProterozoic Proterozoicrocks rocks near near the theGogebic GogebicRange, Range,Michigan Michigan and andWisconsin. Wisconsin. xii xii �U I CHAIRS: CHAIRS: Peter Hudleston Hudleston and John Kiasner Klasner Read, Read, W.F.* W.F.* New evidence evidence that that Limestone Limestone Mt., Mt., Michigan Michigan isis part part of New of a large impact impact structure. structure. 17. 17. 350 3:50 Saini-Eidukat, Saini-Eidukat, B.* B.* Review of of analytical analytical methods methods for for the the determination of Review platinum group elements. 18. 4:10 18. 4:lO Victory, D.* D.* Watkins, I.I. The 7'he mineral relief relief of of surfaces surfaces produced produced by by sanding sandingwith with disaggregation, and percussion, thermal disaggregation, quartz percussion, weathering. weathering. 16. 16. 3:30 3130 Tour of Rock Mechanies Mechania Lab., M.Lakehead , Lakehead University Univenity Sign-up at Registration Registrution Desk Dak 6:30 630 CASH BAR 7:30 7:30 BANQUET BANQUET % Presentation of the Goldich Goldich Medal to K.D. K.D. Card, Geological Survey of of Canada, by by M. M. M. M. Kehienbeck. Kehlenbeck. % Dedication of I.L.S.G. volume 36 36 to H. L. I.L.S.G. volume L, James, James, by by M. M. G. G.Mudrey, Mudrey,Jr. Jr. % will do everything Speaker: The Organizing S~eaker: Organizing Committee Committee will everything possible possible to to provide suitable suitable entertainment. entertainment. We We are arepresently presently unable unable to to confirm confirm our our speaker. speaker. Student xiii �U Ii FRIDAY, MAY MAY 11 TECHNICAL PROGRAM MORNING SESSION CHAIRS: Gene G. Mudrev. Mudrey. Jr. Jr. CHAIRS: Gene LaBerge LaBerge and Michael Michael G. 19. 19. 8:00 8:OO Matty, D.J. Stahl, S.D. S.D. Heft, A. A. Huysken, K. K. Petrologic Penoke :in Petrologic and and geochemical geochemical evolution evolution of of the Penokean Peavy Pond Complex, Iron Iron County, County,Michigan. Michigan. 20. 20. 8:20 8:20 Miller, J.D. Schaap, B.D. Chandler, V.W. V.W. The Sonju Lake Intrusion Intrusion and and associated associated Keweenawan Keweenawan rocks: rocks: Geochemical Geochemical and geophysical geophysical evidence evidence of petrogenetic relationships. relationships. 2 1.1. 8:40 8140 Green, J. minerals and and the the P-T trajectory of Tridymite, other Si02minerals Keweenawan lavas, Minnesota. Minnesota. 22. 22. 9:00 9:00 Paces, J.B. Taylor, L.A. L.A. Petrography, mineral chemistry, chemistry, and geothermobarometry ofof mafic mafic granulite geothermobarometry granulite and and eclogite eclogi te nodules from upper Michigan Michigan Kimberlites. Kimberlites. 23. 23. 9:20 920 Koehler, S.R.* S.R.* Geological setting Bush Lake IAIX Geological setting and geochemistry of of the Bush granite in relation to rare-element pegmatites, Florence County, Wisconsin. Wisconsin. 9:40 940 COFFEE BREAK and POSTER POSTER SESSION SESSION CHAIRS: CHAIRS: Zell Zell Peterman Peterman and and Howard Howard Poulsen Poulsen 24. 10:00 10:OO Kalliokoski, J. J. Michigan: A Geology of of Presque Presque Isle Point, Marquette, Michigan: second look. look. 25. 10:20 25. 10120 Jirsa, M.A. M.A. Southwick, D.L. Boerboom, T.J. T.J. f a 1 1ti ng in The significance of of regional-scale left-lateral faulting development of the Vermillion Greenstone Belt development of Belt in in Minnesota. Minnesota. 10:40 26. 26. 10140 ** Student Nachatilo, S.A.* S.A.* Bauer, R.L. R.L. deformat ion Constraints on Archean versus Proterozoic deformation in Archean Archean rocks rocks of of the the Negaunee Negaunee Area, Area, Upper in Michigan. Michigan. xiv �I 27. 11:OO 1 i :00 27. Borradaile, G. G. Particulate flow and the deformation of rock: Field and and experimental results. 28. 11:20 11:20 28. Gregg, W.J. Transposition structures Transposition structuresin in deformed deformed rock, rock, with examples from the Appalachians Appalachians and upper upper Michigan. Michigan. 11:40 LIJNC1I BREAK Tour of Lab., Lakehead of Rock Mechanics Lab., L.ukehead University U~erdy Sign-up Sign-up at at Regictration Registration Desk SESSION WITH AUTHORS PRESENT 1:00 POSTER SESSION 1100 AFTERNOON SESSION SESSION CHAIRS: William Cannon Cannon and and David David Southwick Southwick CHAIRS: William 29. 1:30 1130 Mudrey, M.G. M.G. Dickas, Dickas, A.B. A.B. McGinnis, L.D. Cannon, W.F. W.F. Tectonic ramifications ramifications of of GNIIArgonne GNI/Argonne kdke Lake Superior Tectonic S~lperior Seismic data. data. 30. 30. 11:50 50 Roscoe, S.M. Roscoe,S.M. The reappearance of of the the Huronian Huronian ininWyoming. Wyoming. 331.1. 2:10 2:lO Davis, D.W. problem reconsidered: The Seine-Coutchiching Seine-Coutchiching problem reconsidered: U-Ph U-1% geochronological data concerning the source source and and timing ti~iii~ig Archean sedimentation of Archean sedimentation in in the western western Superior S~iperior Province. Province. Sims, P.K. P.K. The Great Great Lakes Lakes Tectonic Zone -- a major north-verging north-verging late Archean Archean collision collision zone. zone. 32. 2:30 32. 2130 2:50 250 PRESENTATION OF STUDENT PAPER AWARDS PRESENTATION AWARDS 3:00 3100 COFFEE BREAK BREAK 3:30 3130 Watkins, I.I. Shurr, G.W. G.W. Anderson, G.G. G.G. Faults associated with with the Penokean accretion accretion of of allochthonous Minnesota. allochthonous terranes terranes in central Minnesota. 34.3:50 34. 3 5 0 LaBerge, G. G. Kiasner, J. Klasner, Was the Penokean orogeny a hi-polar Was bi-polar event? event? 35. 35. Turek, A. A. Sage, R.P. van Schmus, W.R. of the Michipicoten Advances in geochronology of Michipicoten greenstone belt. 33. 33. 4:10 4110 TAKE-DOWN PPOSTER TAm-DOWN O S E R PAPERS xv �U SATURDAY, MAY 12 12 Field Trips 1, 2, 2, 33 and 4 Field All jield field trips trips depart depart at 8 a.m. All am. from from tile rear parking the parking lot of of the the Afriane Airlane Motor Hotel. Lunch provided. Lunchisisprovided. TRIP T R I PNO. N O .1* l* Sutcliffe (leader) -- Mafic Sutcliffe Mafic intrusions, intrusions, PGE mineralization and llles mineralization and granitoid granitoid rocks rocks of of the Lac des Illes area. area. R. VANS FOR PEOPLE PEOPLE WHO HAVE HAVE GONE ON TRIP NO. 44 TRIP T R I P NO. NO, 2* 2* of the Shebandowan G. Borradaile Borradaile (leader) -- Geology of Shebandowan and Quetico Archean Archean Subprovinces. Subprovinces. VANS TRIP NO. 33 Kissin (leader) -- Granitoid related mineral S. Kissin mineral deposits in the western Lake Superior Superior region. region. BUS B US TRIP T R I P NO. NO. 4* 4* M. (leaders) -- Base metal M. Lavigne Lavigne and and J. Scott Scott (leaders) mineralization Shebandowan Greenstone Belt. mineralization in the Shebandowan BUS FOR PEOPLE PEOPLE WHO ARE ARE NOT GOING ON TRIP 11 terminate at at the theAfriane Airlane Motor MotorHoteL Hotel. All trips terminate ** have been duplicated, (i.e. Indicates trips which which have (i.e. pre-meeting and and post-meeting). post-meeting). xvi mi �U POSTER PAPERS Authors are requested Authors requested to be be present present at at their theirposters postersduring during the thescheduled scheduled times times from 1:00 to 1:30 on Thursday Thursday and and Friday, Friday, and and at other times 1:OO to 1130 on times when when convenient. convenient. from I. Bauer, R.L. and Tabor, J.R. 1. Syntectonic, intermediate-pressure intermediate-pressure regional regional metamorphism metamorphism along along the northern Syntectonic, northern margin of the Quetico Quetico Belt in in northeastern Minnesota: Minnesota: Contrasts margin of Contrasts with with adjacent adjacent boundary areas. 2. Bennett, G., Born, P. and Hatfield, 2. Hatfield, K. K. dolostone unit unit near near Sault Ste. Marie, Ontario A recently discovered discovered dolostone DahI, D.A. and Cartwright, 3. Dahl, 3. Cartwright, D.F. Carbonate in till till units units of of Lake Lake of of the theWoods Woods County, County, Minnesota. Minnesota. 4. Davidson, D.M., Jr. Magnetic susceptibility anisotropy anisotropy and and strain, Thomson formation (Proterozoic), (Proterozoic), Minnesota. Minnesota. 5. 5. Feeney, J.* J." and Kean, Feeney, Kean, W.F. W.F. Paleomagnetism of Keweenawan age basalts of the Chengwatana volcanic group in the St. St. Croix Croix Falls Falls and and Fredrick-Miltown Fredrick-Miltownarea areaof ofPolk PolkCounty, County,Wisconsin. Wisconsin. 6. 6. Geerts, S.D.* S.D.* Geology and mineralization mineralization in in the Dunka Road copper-nickel copper-nickel mineral deposit, deposit, Geology and St. Louis County, County, Minnesota. Minnesota. 7. Jiran, Jiran, J. J. 7. State of Minnesota Minnesota drill drill core core library. library. 8. 8. Johnson, R.C.* R.C.* Structure of the northern Marq~~ette Structure of northern block block of the the Ishpeming Ishpeming Greenstone Belt, Marquette County, Michigan. Michigan. 9. 9. Mancuso, J., J., Stephen, J•* J.* and Kangas, Kangas, W. W. Stratigraphy of the the Negaunee Stratigraphy of Negaunee Iron Iron Formation, Formation, eastern eastern Marquette Marquette Range, Range, Michigan. Michigan. 10. Milkereit, B. et al. 10. al. Crustal structure of northeastern Lake h k e Superior Superior from from GLIMPCE GLIMPCE reflection reflection and and refraction data. ** Student xvii �U 11. Mohn, P.A.* 11. P.A.* and Gregg, Gregg, W.J. W.J. Mesoscopic evidence for B, B1 deformation deformation in lower Proterozoic supracrustal supracrustal rocks rocks near Rockford, Rockford. South Dakota. 12. Morton, R.L., Hudak, G.J., Walker, 12. Walker, J.S. J.S. and Franklin, J.M. volcanology and and hydrothermal hydrothermal alteration alteration associated The physical volcanology associatedwith with the themassive massive sulphide deposits of the South Sturgeon Lake area, northwestern Ontario. sulphide deposits of Ontario. 13. Mudrey, M.G., Dickas, A.B., McGinnis, L.D. L.D. and Cannon, W.F. 13. A.B., McGinnis, W.F. ramifications of of GNIIArgonne GNI/Argonne Lake Tectonic ramifications Lake Superior Superior seismic seismic data. data. 14. O'Brien, M. M. Exploration and mining activity in northwestern northwestern Ontario. Exploration activity in 15. Palmquist, Palmquist, J.C. Archean Mineral Archean and Penokean Penokean strains strains in the the Northern Northern Complex, Complex, Marquette Marquette Mineral District, District, Michigan. Michigan. 16. Saja, D.* and Gregg, Gregg, W.J. W.J. Structural studies in the Huron Huron Bay Bay parautochthon, parautochthon, Upper Upper Michigan. Michigan. 17. Severson, Severson, M.J.* and Hauk, Hauk, S.A. S.A. Geochemistry of of unmineralized unmineralized rocks rocks in in the the Partridge Partridge River Intrusion, Duluth Dulnth Geochemistry Complex. Complex. 18. Shurr, Shurr, G., G., Watkins, Watkins, I., I., Victory, Victory, D.* D.* and and Tozer, Tozer, M.* M.* Geological significance significanceofoflinear linear features features visible visible on on Landsat in westwestGeological Landsat images images in central Minnesota. Minnesota. 19. Smith, Smith, M. M. Bioturbation in the Jacobsville sandstone, sandstone, Lake Lake Linden Linden location - what are the Bioturbation the implications? implications? 20. Thompson, Thompson, M.E., M.E., Ervin, Ervin, C.P., C.P., Mudrey, Mudrey, M.G. M.G. and andBrown, Brown, B.A. B.A. Tectonic ramifications ramifications of of GNIIArgonne GNI/Argonne Lake Superior Tectonic Superior seismic seismic data. data. Informal Informal displays displays by: by: a. Jirsa, M.A., Boerboom, T. and Southwick, a. Southwick, D. B. Ontario h. b. Zayachivsky, Zayachivsky, B. OntarioGeological GeologicalSurvey. Survey. ** Student xviii xviii �U 1 I ABSTRACTS ABSTRACTS xix �U Geology Geoloqv of the the Shebandowan Shebandowan Mine Mine Alan Aubut, Aubut, Inco Inco Exploration Exploration and and Technical Technical Services, Services, Inc., Inc., Thunder Bay, Thunder Bay, Ontario ontario P7C P7C 4Yl 4Y1 owned by Shebandowan Shebandowan Mine, Mine, owned by Inco Limited Limited and and operated operated MacIsaac MacIsaac Explorations, Explorations, is is the the only producing Nickel Copper mine It is northwestern Ontario. Ontario. It is located located 75 km km west—northwest west-northwest Thunder Thunder Bay. Bay. The The by by in of of The geology geology of of the mine mine property property consists consists of mafic of Keewatin Keewatin mafic volcanics and ultramafics ultramafics unconformably unconformably overlain by by Timiskaming Timiskaming type volcanics volcanics and and sediments. sediments. All are intruded intruded by granitic granitic rocks rocks type of the Shebandowan Shebandowan Lake The Crayfish Crayfish Creek Lake Stock. Stock. The Creek Fault Fault is is a major transcurrent fault that crosses the property, just south of the the Shebandowan mine. Shebandowan mine. The suiphide sulphide mineralization at Shebandowan Shebandowan consists consists primarily primarily of of stringer, breccia hosted by sheared stringer, breccia and massive massive sulphides sulphides hosted sheared and and The faulted peridotite. sulphides are faulted peridotite. The main sulphides are pyrrhotite, pyrrhotite, chalcopyrite and and pentlandite. pentlandite. The suiphides sulphides show evidence evidence of of remobilization due remobilization due to to dynamic dynamic metamorphism. metamorphism. Other provide evidence evidence that they Other ultramafics ultramafics in in the immediate immediate area provide komatiite flows are komatiite flows rather rather than than sills sills as as previously previously believed. believed. The The Shebandowan nickel-copper deposit has many physical physical similarities similarities to the the Redross Redross deposit deposit in in Australia, Australia, aa dynamically dynamically metamorphosed metamorphosed nickel-copper sulphide is nickel-copper sulphide deposit deposit hosted hosted by by aa komatiite komatiite flow. flow. It It is postulated that that the the Shebandowan Shebandowan Ni-Cu Ni-Cu mine mine is is also also the the product product of of komatiite hosted sulphide a deformed and remobilized komatiite sulphide deposit. deposit. �I SYNTECTONIC, INTERMEDIATE-PRESSURE REGIONAL METAMORPHISM ALONG THE NORTHERN MARGIN OF THE QUETICO BELT IN NORTHEASTERN MINNESOTA: CONTRASTS WITH ADJACENT BOUNDARY AREAS * I Robert L. Bauer, Department of Geological Sciences, University of Missouri, Columbia, Missouri, 65211 John R. Tabor, Department of Geology, University of Tennessee, Knoxville, Tennessee, 37996 Metamorphism in the schist and migmatite along the northern margin of the Quetico belt is typically post to late tectonic and shows high lateral thermal gradients adjacent to high-level plutons of the region (Percival, Pine and Mackasey (1978), for instance, described a 4 km transition 1989). from the chlorite zone progressively through the biotite, garnet, andalusite, garnet-sillimanite, garnet-cordierite-sillimanite, and migmatite zones in the country rocks north of the Sturgeon Lake batholith (assemblages 1-15 in Fig. Similar low-pressure zonal sequences and high geothermal gradients over 1). distances of less than 6 km have been reported from several localities in the central Quetico belt (Pine and Mackasey, 1978; Sawyer, 1983) and from the area east of Lake Nipigon (Percival, 1983; Pine and Mackasey, 1978). In contrast to these studies, our work along the northern margin of the belt, southeast of International Falls and west of the Sturgeon Lake batholith (SLB), indicates that the schist and migmatite of this area have undergone syntectonic, intermediate-pressure metamorphism that apparently predates the lower pressure, posttectonic metamorphism along the belt margin to the east. The metamorphism in our study area displays a Barrovian zonal series, ranging from the kyanite-staurolite zone to the cordienite - K-feldspar zone (Table 1; The thermal event peaked during the second of assemblages I-VI in Fig. 1). three periods of folding that deform the schist and migmatite of the area Fibrolite tufts from the sillimanite-staurolite zone through (Bauer, 1988). the sillimanite - K-feldspar zone are aligned parallel to an S2 foliation and Cordierite are folded by F3 folds and an S3 crenulation foliation. porphyroblasts locally contain F2-folded inclusion trails of sillimanite and are elongated parallel to a strong L3 lineation that was accentuated by the nearly coaxial nature of the F2 and F3 regional fold systems. Randomly oriented blocky crystals of retrograde muscovite locally replace K-feldspar and sillimanite and may contain inclusion trails of F3The retrograde muscovite and the common partial folded sillimanite. replacement of garnet by biotite + sillimanite suggest a decompression cooling path for the rocks during and following F3 folding. Although porphyroblast growth in the areas of steep thermal gradient north of the SLB is typically post D1 and D2, Kehlenbeck (1976) found evidence for a polymetamorphic history with both syntectonic and posttectonic porphyroblast growth in the rocks north of the SLB north of Thunder Bay. He suggested that either contact or low-pressure regional metamorphism was overprinted on pre-existing regionally metamorphosed rocks in this area. We believe that the syntectonic metamorphism we see in the schist west of the Sturgeon Lake batholith may be correlated with the syntectonic event described by Kehlenbeck (1976). 2 �U REFERENCES REFERENCES CITED CITED B a u c r , R.L. K . L . , 1988, 1988, Bauer, Multiple M u l t i p l e folding f o l d i n g and a n d regional r e g i o n a l fo'd f o l d patterns p a t t e r n s in i n the t h e northern northern Vermilion V e r m i l i o n Granitic G r a n i t i c Complex, Complex, N.E. N.E. Minnesota: M i n n e s o t a : Institute I n s t i t u t e on on Lake Lake Superior Superior Geology, G e o l o g y , Proceedings P r o c e e d i n g s and and Abstracts, A b s t r a c t s , V. V. 34, 3 4 , p.3. p.3. K e h l e n b e c k , M.M. M.M., 1 9 8 6 , Nature N a t u r e of o f the t h e Quetico Q u e t i c o - Wabigoon Wabigoon boundary boundary in i n the t h e de de Kehlenbeck, , 1986, Canadian Journal Courcey-Smiley Lakes area, northwestern Ontario. C o u r c e y - S m i l e y Lakes a r e a , n o r t h w e s t e r n O n t a r i o . Canadian J o u r n a l of of Earth E a r t h Sciences, S c i e n c e s , v. v . 13, 1 3 , p. p . 737-748. 737-748. Pine, P i r i e , J.A. J . A . and a n dMackasey, Mackasey, W.O., W . O . , 1978, 1 9 7 8 , Preliminary P r e l i m i n a r y examination e x a m i n a t i o n of o f regional regional metamorphism in i n parts p a r t s of o f the t h e Quetico Q u e t i c o metasedimentary m e t a s e d i m e n t a r y belt, b e l t , Superior Superior Province, P r o v i n c e , Ontario. O n t a r i o . In J~J Metamorphism Metamorphism in i n the t h e Canadian Canadian shield. s h i e l d . (edited ( e d i t e d by) by) J.A. J . A . Fraser F r a s e r and a n d W.W. W . W . Heywood, Heywood, Geological G e o l o g i c a l Survey S u r v e y of o f Canada, Canada, Paper, P a p e r , 78-10, 78-10, p . 37-48. 37-48. p. Percival, P e r c i v a l , J.A. J.A, . , 1983, 1 9 8 3 , Preliminary P r e l i m i n a r y results r e s u l t s of o f geological g e o l o g i c a l synthesis s y n t h e s i s in i n the the western w e s t e r n Superior S u p e r i o r Province. P r o v i n c e . In Current C u r r e n t Research, R e s e a r c h , part p a r t A. A. Geological Geological Survey S u r v e y of o f Canada, Canada, Paper, P a p e r , 83-la, 8 3 - l a , p. p . 125-131. 125-131. Percival, P e r c i v a l , J.A., J . A . , 1989, 1 9 8 9 , AA regional r e g i o n a l perspective p e r s p e c t i v e of o f the t h e Quetico Q u e t i c o metasedimentary metasedimentary belt, b e l t , Superior S u p e r i o r Province, P r o v i n c e , Canada. Canada. Canadian C a n a d i a n Journal J o u r n a l of o f Earth E a r t h Sciences, S c i e n c e s , v. v. 2 6 , p. p . 677-693. 677-693. 26, Sawyer, , 1983, Sawyer, E.W. E.W., 1 9 8 3 , The structural s t r u c t u r a l history h i s t o r y of o f aa part p a r t of o f the t h e Archean Quetico Quetico metasedimentary m e t a s e d i m e n t a r y belt, b e l t , Superior S u p e r i o r Province, P r o v i n c e , Canada. Canada. Precambrian P r e c a m b r i a n Research, Research, v. 22, p. 445-473. , - Co C) L. C,) (I) C) 0 Temperature (° (O C) cl Fig. 1 Petrogenetic Petrogeneticgrid grid showing showingthe thestability stabilityfields fieldsofof mineral mineral assemblages assemblagesin in pelitic, pel~tic, migmatitic.and and granitic granitic rocks rocks migmatitic. medium and and high high grades grades (from (from Percival, Perctval, 1989). 1989). The Thesmall smallnumbers numberscorrespond correspondtotomineral mineralassembalges assembalgesinin the the at medium in the the vicinity vicini!yof of the the Sturgeon Sturgeon Lake Lake batholith. batholith. The Thelarge largenumbers numbersindicate indicatebathozones bathozones2,2,3, and metamorphic zones zones in metamorphic 3, and of Charmichael, Charmichael,(1978). (1978). The TheRoman Romannumerals numeralsindicate indicatethe themetamorphic metamorphiczones zonesininour ourstudy studyarea areawest westofof the the 4 of batholith. Sturgeon Lake batholith. Fig. 1 3 I �U I Table Table 1. 1. Metamorphic Metamorphic zones, associated associated mineral mineral assemblages assemblages and and reactions reactions Zone Zone Mineral Assemblage Mineral Assemblage Zone Reaction Reaction Zone ky-st.gt-mu-bi-pl-qz-il ky-st-gt-mu-bi-PI-qz-il I ky=sill ky = sill sill-st-gt-mu-bi-pl-qz-il sill-st-gt-mu-bi-PI-qz-il Il st+mu+qz st + mu + qz =sill-s-gt÷bi+H20 = sill + gt + bi + H 2 0 Ill sill-mu-gt-bi-pl-qz-il sill-mu-gt-bi-PI-qz-il IV ksp-mu-sill-gt-bi-pl-qz-il ksp-mu-sill-gt-bi-PI-qz-il mu + qz qz == sill sill + + ksp ksp + H H20 mu + + p1 PI+ 20 ksp-sill-gt-bi-pl-qz-il ksp-sill-gt-bi-PI-qz-il V sill + bi + qz = ccd gtl + ksp + H H20 +qz d+g 20 cd-ksp-gt-sill-bi-pl-qz-il cd-ksp-gt-sill-bi-PI-qz-il VI Mineral Mineral Abbreviations Abbreviations bi bi cd cd gt gt - biotite biotite cordierite cordierite -- garnet garnet - il ksp ksp ky ky ilmenite -- ilmenite - k-feldspar k-feldspar - -- kyanite kyanite mu muscovite mu - muscovite 4 pl -qz -sill sill -St st -p1 plagioclase plagioclase quartz quartz sillimanite sillimanite staurolite staurolite I �U I A RECENTLY DISCOVERED D I SCOVERED DOLOSTONE UNIT UNIT MARIE, ONTARIO. NEAR SAULT SAULT STE. STE. MARIEl ONTARIO. Bennett, B e n n e t t I Ministry M i n i s t r y of o f Northern N o r t h e r n Development Development and and Mines Mines Sault Ontario; S a u l t Ste. S t e . Marie, Mariel O n t a r i o ; P. Born, Bornl Ministry M i n i s t r y of of Northern Northern Lake Superior Development and and Mines, Mines) Toronto; K. K. Hatfield, H a t f i e l d ) Lake Superior Marie, Michigan State S t a t e University, U n i v e r s i t y l Sault S a u l t Ste. S t e . Marie) G. G. unrecognized Born Born ((1987) 1987) rreported eported a previously previously u nrecognized occurrence o c c u r r e n c e of of dolostone d o l o s t o n e in i n Fenwick Fenwick Township, Township) approximately approximately Marie, Ontario. 27 2 7 km km northwest n o r t h w e s t of of Sault S a u l t Ste. S t e . Marie) Ontario. exposed, but The The area a r e a is i s not n o t well w e l l exposed) b u t detailed d e t a i l e d mapping mapping indicates i n d i c a t e s that t h a t the t h e dolostone d o l o s t o n e and and associated a s s o c i a t e d rocks r o c k s probably probably east-west form aan n e a s t - w e s t trending t r e n d i n g fault f a u l t block, b l o c k ) bounded on the t h e south south t h e Lorrain L o r r a i n Formation of of the t h e Huronian Supergroup Supergroup and by by the of the The total Archean rocks r o c k s on the t h e north. north. t o t a l thickness t h i c k n e s s of the exposed dolostone d o l o s t o n e unit u n i t is i s at a t least l e a s t 30 30 meters. m e t e r s . The lowermost one third t h i r d of of the t h e dolostone d o l o s t o n e sequence sequence consists c o n s i s t s mainly of of very very pink dolostone ffine-grained, i n e - g r a i n e d l ppale ale p i n k to t o reddish r e d d i s h pink pink d o l o s t o n e and and Individual dolostone iintercalated n t e r c a l a t e d grey g r e y to t o pink p i n k metachert. metachert. Individual d olostone beds a r e from a few m i l l i m e t e r s t o a t l e a s t a m e t e r t h i c k . beds have have a similar The metachert m e t a c h e r t beds s i m i l a r thickness t h i c k n e s s range r a n g e but b u t form form lless e s s than t h a n 25 25 percent p e r c e n t of of the t h e visible v i s i b l e section. section. beds are from a few millimeters to at least a meter thick. Pale dolostone P a l e grey, g r e y ) clastic clastic d o l o s t o n e iis s most most abundant abundant type t y p e in in This tthe h e upper u p p e r part p a r t of of the t h e carbonate c a r b o n a t e unit. unit. T h i s ccalcarenite alcarenite consists of consists o f variable v a r i a b l e proportions p r o p o r t i o n s of of angular a n g u l a r to t o subrounded subrounded ssand-sized a n d - s i z e d clasts c l a s t s of of fine-grained f i n e - g r a i n e d dolostone d o l o s t o n e and and subrounded subrounded tto o well-rounded w e l l - r o u n d e d quartz q u a r t z grains. g r a i n s . Well Well developed d e v e l o p e d ooliths o o l i t h s aare re llocally o c a l l y present. p r e s e n t . The clastic c l a s t i c dolostone d o l o s t o n e generally g e n e r a l l y forms forms thick thick beds separated by tthin beds s e p a r a t e d by h i n beds beds of of fine f i n e grained g r a i n e d dolostone d o l o s t o n e or or Coarse, a cchert. hert. C o a r s e l pink p i n k coloured coloured b a r i t e l o c a l l y occurs as few few llensoid e n s o i d masses masses up t o 50 50 cm cm across. across. up to barite locally occurs as No were observed No cclearly l e a r l y identifiable i d e n t i f i a b l e stromatolites s t r o m a t o l i t e s were o b s e r v e d in in the dolostone wavey, the d o l o s t o n e of Fenwick Fenwick Township Towns h i p but b u t irregular, i r r e g u l a r ) wavey) laminae mats, are l a m i n a e of brownish c h e r t ) ssuggestive u g g e s t i v e of of algal a l g a l mats) are locally l o c a l l y present. present. of brownish chert, The clastic dolostone is directly overlain by deep red The c l a s t i c d o l o s t o n e i s d i r e c t l y o v e r l a i n by d e e p r e d and red r e d to t o pink p i n k laminated l a m i n a t e d siltstone. s i l t s t o n e . The contact contact between is a b r u p t and and b e t w e e n the t h e red r e d beds beds a n d the t h e dolostone d o l o s t o n e is and abrupt concordant. concordant. The d o l o s t o n e unit u n i t directly d i r e c t l y overlies o v e r l i e s highly highly The dolostone ffractured r a c t u r e d and sheared, s h e a r e d ) locally l o c a l l y laminated, laminatedl g r e e n and maroon maroon green ssiltstone i l t s t o n e and and argillite. a r g i l l i t e . AA few few beds beds of of recrystallized r e c r y s t a l l i z e d chert, chertl at a t least l e a s t 20 20 cm thick thick and one one dolostone d o l o s t o n e bed bed of o f similar similar and sandstone, sandstone) �U I t h i c k n e s s ) was was observed o b s e r v e d within w i t h i n the t h e siltstone. siltstone. thickness, The The presence p r e s e n c e of of red r e d beds beds above above and and below below the t h e dolostone dolostone u n i t ) and a n d the t h e degree d e g r e e of o f metamorphism metamorphism and a n d deformation deformation unit, indicates i n d i c a t e s that t h a t the t h e dolostone d o l o s t o n e is i s post—Quirke p o s t - Q u i r k e Lake Lake Group Group ( H u r o n i a n ) and and pre-Keewenawan. pre-Keewenawan. (Huronian) The only o n l y known known dolostone d o l o s t o n e in i n the t h e general g e n e r a l area a r e a within within the t h e above above constraints c o n s t r a i n t s is i s found found in i n the t h e Gordon Gordon Lake Lake Formation Formation of o f the t h e Huronian Huronian Supergroup(Hofmann Supergroup(Hofmann et e t al. a l . 1983). 1983). A A variety variety of o f sedimentary s e d i m e n t a r y features f e a t u r e s indicate i n d i c a t e the t h e Gordon Gordon Lake Lake Formation Formation was deposited d e p o s i t e d in i n aa shallow, s h a l l o w I active a c t i v e water w a t e r environment environment such s u c h as as nodules aa tital t i t a l flat(Wood, f l a t ( W o o d , 1973, 1973) p. p . 991). 1 ) . The recognition r e c o g n i t i o n of of nodules of o f gypsum gypsum and a n d anhydrite a n h y d r i t e in i n the t h e Gordon Gordon Lake Lake Formation Formation indicates i n d i c a t e s local l o c a l evaporitic e v a p o r i t i c conditions c o n d i t i o n s (Wood, (Wood) 1973, 1973/ p. p. 85). 85). the The The presence p r e s e n c e of o f ooliths o o l i t h s and a n d sulphate s u l p h a t e (barite) ( b a r i t e ) in in the similar indicates a Fenwick Township dolostone d o l o s t o n e of of Fenwick Township i n d i c a t e s a similar depositional environment tto proposed for d e p o s i t i o n a l environment o tthat h a t proposed f o r the t h e Gordon Gordon Lake Lake Formation. Formation. T h e r e has h a s been b e e n aa long l o n g standing s t a n d i n g debate d e b a t e as a s to to There of stratigraphic s t r a t i g r a p h i c equivalence e q u i v a l e n c e of of the t h e Huronian Huronian rocks rocks o f Ontario Ontario and a n d the t h e Middle M i d d l e Precambrian P r e c a m b r i a n rocks r o c k s of o f the t h e Lake Lake Superior Superior r e g i o n . The The lithological l i t h o l o g i c a l and and stratigraphic s t r a t i g r a p h i c similarities s i m i l a r i t i e s of of region. the t h e Chocolay Chocolay Group Group (and ( a n d equivalent e q u i v a l e n t groups groups further f u r t h e r west) w e s t ) and and have the t h e Cobalt C o b a l t Group Group of of the t h e Huronian Huronian of of Ontario Ontario have been been Young pointed p o i n t e d out o u t by by Church Church and and Young Young (1970), (1970)) ( 1983) 1983) and and Cannon (1975). ( 1 9 7 5 ) . However, However) this t h i s time-stratigraphic t i m e - s t r a t i g r a p h i c correlation correlation Cannon has not n o t been been widely w i d e l y accepted a c c e p t e d (e.g. ( e . g. Morey Morey 1973, 1973# P. p. 242-244, 242-244) and Card Card 1978, 1978) p. p. 24) 2 4 ) since s i n c e radiometric r a d i o m e t r i c dating d a t i n g of o f rocks, rocks) considered c o n s i d e r e d to t o underlie u n d e r l i e the t h e Chocolay Chocolay group, group) provide p r o v i d e evidence evidence that t h a t the t h e Chocolay C h o c o l a y Group Group is i s younger y o u n g e r than t h a n the t h e Huronian Huronian Supergroup Supergroup of of Ontario. Ontario. ( The dolostone d o l o s t o n e of o f Fenwick F e n w i c k Township T o w n s h i p very v e r y closely closely The and stratigraphically lithologically r e s e m b l e s ) both both l i t h o l o g i c a l l y s t r a t i g r a p h i c a l l y the the resembles, Kona Dolomite Dolomite and and equivalent e q u i v a l e n t units u n i t s of of the t h e Marquette M a r q u e t t e Range Range Supergroup. Supergroup. REFERENCES REFERENCES CITED CITED Born) P. P. Born, 1987: of 1987: Geology o f the t h e Havilland-Goulais H a v i l l a n d - G o u l a i s Bay Area, Areal District D i s t r i c t of of 11 Algoma; Ontario O n t a r i o Geological G e o l o g i c a l Survey, Survey) O.F.R. 0. F. R. 5602, 5602/ ll4p., 114p. 11 Algoma; 12 photos, and 3 maps in back pocket. 7 tables, figures, figures) t a b l e s ) 1 2 photosI 3 maps i n back p o c k e t . W. F. F. Cannon) W. Cannon, 1975: 1975: Basal B a s a l Conglomerates Conglomerates Marquette Marquette and a n d Weathere.d Weathere.d Zones Zones in i n the the Range Supergroup, Supergroupl Northern N o r t h e r n Peninsula P e n i n s u l a of of 6 �U Michigan Michigan AgeI -- Age, uranium potential, potential, uranium indications i n d i c a t i o n s of of atmospheric a t m o s p h e r i c oxygen, oxygen) and and Z1-Z17, Z1-Z171 in i n Genesis Genesis of of Uranium— Uranium- and and Quartz-Pebble Gold-Bearing Precambrian Precambrian Q u a r t z - P e b b l e Conglomerates, Conglomeratesl Gold-Bearing Paper BB) G e o l o g i c a l Survey Survey Professional Professional P a p e r 1161 1161 -- AA -- BB, Geological States e d i t e d by by Frank Frank C. C. Armstrong, Armstrong) United United S t a t e s Government Government edited P r i n t i n g Office, O f f i c e l Washington. Washington. Printing p. p. K. D. D. Card) K. Card, 1978: Geology Geology of of the t h e Sudbury-Manitoulin Sudbury-Manitoulin Area, Areal Districts D i s t r i c t s of of 1978: Sudbury and and Manitoulin; M a n i t o u l i n ; Ontario O n t a r i o Geological G e o l o g i c a l Survey Survey Report Report Sudbury 166) 238p. Accompanied Accompanied by by Map Map 2360, 2360) scale s c a l e 11 inch i n c h to t o 22 238p. 166, (1: 126,720), miles ( 1 : 126) 7 2 0 ) ) and and 44 charts. charts. miles Church) W. W. R., R. and Young, Young) G. G. M. M. and Church, 1970: D i s c u s s i o n of t h e p r o g r e s s report r e p o r t of of the the 1970: Committee on Huronian Provi n c i a1 Committee on Huronian sstratigraphy: tratigraphy: Provincial Sciences, J o u r n a l of E a r t h S c i e n c e s I v. v. 7, 7 ) p. p. 912-918. 912-918. Discussion of the progress Journal of Earth FederalFederal- Canadian Canadian and H. J. P e a r s o n ) D. D. A. B., B. and Wilson, Wilson) B. B. H. H. H. J., Pearson, 1 9 8 0 : S t r o m a t o l i t e s a n d f e n e s t r a l f a bric i n early and 1980: Huronian Proterozoic H u r o n i a n Supergroup, S u p e r g r o u p I Ontario: O n t a r i o : Canadian Canadian 1 7 ) p. p. 1351-1357. 1351-1357. J o u r n a l of of Earth Earth S c i e n c e s ) v. v. 17, Sciences, Journal Hofmann) Hofmann, Stromatolites Proterozoic fenestral fabric in early Morey) G. G. B. B. Morey, 1973: 1973: Stratigraphic S t r a t i g r a p h i c framework framework of of middle middle Precambrian P r e c a m b r i a n rocks r o c k s in in Huronian ed., G. M., M. ed. Huronian stratigraphy s t r a t i g r a p h y and and Minnesota) in i n Young, Young, G. Minnesota, Huronian G. M. M. , ed., ed. Huronian s e d i m e n t a t i o n ) Minnesota, Minnesota) in i n Young, Young) G. sedimentation, s t r a t i g r a p h y and and sedimentation, s e d i m e n t a t i o n ) G e o l o g i c a l A s s ~ c i a t i o n of stratigraphy Canada S p e c i a l Paper Paper 12, 12) p. p. 211-249. 21 1-249. Canada Special Geological Association of Woodl J. J. Wood, 1973: 1973: Stratigraphy S t r a t i g r a p h y and and depositional d e p o s i t i o n a l environments e n v i r o n m e n t s of o f upper upper Huronian Huronian rocks r o c k s of of the t h e Rawhide Rawhide Lake-Flack Lake-Flack Lake Lake area, a r e a ) Ontario, Ontario) and strati Huronian G , M., M. ed. I Huronian s t r a t i ggraphy raphy and in Young) ed., G. in Young, sedimentation: G e o logi o g ical c a l Association A s s o c i a t i o n of o f Canada Canada Special Special Geol sedimentation: p a p e r 12, 12) p. p. 73-95. 73-95. paper Young) G. G. M. M. Young, 1983: Tectono—sedimentary T e c t o n o - s e d i m e n t a r y history h i s t o r y of of early e a r l y Proterozoic P r o t e r o z o i c rocks rocks 1983: 15-32; the northern Great Lakes region, G r e a t L a k e s r e g i o n , p. p. 1 5 - 3 2 ; in in o f t h e n o r t h e r n of Society Geological S o c i e t y of of America America Memoir Memoir 160, 160, Edited E d i t e d by by L.G. L. G. Geological Medaris) Jr. Jr. Medaris, 7 �Magnetic Survey Survey of of the the Niagara Niagara Fault Fault System System Magnetic in Northeastern Wisconsin and Northwestern in Northeastern Wisconsin and Northwestern Upper Peninsula Peninsula Michigan Michigan Upper T. M. M. Bodus Bodus and and W, W. F. F. Kean Kean T. University of Wisconsin Milwaukee University of Wisconsin Milwaukee The Niagara Niagara fault fault system system has has been been identified identified based based on on The magnetic data. One of the first ground magnetic surveys of the the magnetic data. One of the first ground magnetic surveys of Niagara fault system was conducted on a four square mile area Niagara fault system was conducted on a four square mile area 1958-59 using using vertical vertical near Keyes Keyes Lake Lake by by Weir Weir and and Solberg Solberg in in 1958-59 near intensity magnetometers. Since that time, several aeromagnetic intensity magnetometers. Since that time, several aeroinagnetic surveys have have been been flown flown across across the the area area in in an an attempt attempt to to further further surveys define the the extent extent and and trend trend of of the thesystem. system. This This ground ground magnetic magnetic define paleomagneticstudy studyof of study was was undertaken undertaken in in combination combination with with aa paleomagnetic study the area in order to fully detail the trend of the system and to the area in order to fully detail the trend of the system and to unravel the the tectonic tectonic history history of of the thearea. area. unravel Two hundred thirty seven miles of field field magnetic magnetic data data were were Two hundred thirty seven miles of collected using two EG&G proton procession magnetometers. One collected using two EG&G proton procession magnetometers. One magnetometer was used as a continually recording base station. magnetometer was used as a continually recording base station. The second second magnetometer magnetometer was was used used to to collect collect readings readingsat at .1 .1 mile mile The spacings. The The survey survey area area was was confined confined to to Florence, Florence, Marinette, Marinette, spacings. Dickinson, and and Nenominee Menominee counties counties Wisconsin Wisconsin and and Michigan Michigan (Fig. (Fig. Dickinson, The data was modeled on a computer. The model parameters of 1). The data was modeled on a computer. 1). The model parameters of susceptibility, remnant component intensity, and direction were susceptibility, remnant component intensity, and direction were determined from from laboratory laboratory and and paleomagnetic paleomagnetic analysis analysisof of samples samples determined obtained in the field along survey lines. In areas where obtained in the field along survey lines. In areas where outcrops were were not not available available along along survey survey lines, lines, similar similar units units outcrops from other other outcrops outcrops within within the the study studyarea areawere wereused. used. Model Model from parameters of of length length of of lithologic lithologic or or lithodemic lithodemicunit, unit,depth depthof of parameters unit, and strike half-length were obtained from maps. Because unit, and strike half-length were obtained from maps. Because the maps maps are are based based on on outcrops, outcrops, and and outcrops outcrops are are sparse, sparse,the the the length, depth and strike half-length of the units were adjusted length, depth and strike half-length of the units were adjusted as needed. needed. as indicate that that the the Niagara Niagara Fault Fault The ground ground magnetic magnetic results results indicate The does not trend the way it is represented on the Wisconsin does not trend the way it is represented on the Wisconsin 1984). The The data data points points Northeast sheet sheet map map (Greenberg (Greenbergand and Brown, Brown, 1984). Northeast were upward upward continued continued to to 500 500 feet feet and and the the individual individualanomalies anomalies were produced by by the the faults faults merged merged with with the the regional regional magnetics magnetics and and produced The peaks of these highs did not produced small elliptical highs. produced small elliptical highs. The peaks of these highs did not necessarily coincide with the location of the anomalies produced necessarily coincide with the location of the anomalies produced by the the faults. faults. The The new new trend trend of of the the faults faults are are based based on on the the by individual fault faultanomalies. anomalies. Modeling Modeling results results produced produced only only aa few few individual tectonic settings settings for for the the area. area. tectonic 8 �U I I Figure magnetic F i g u r e 1. 1. M a p iindicating n d i c a t i n g ffield i e l d m a g n e t i c survey s u r v e y lines. l i n e s . Map Brown, Modified t l o i i i f i e i i from f r o m Greenberg G r e e n b e r g aand nd B r o w n , 1984; 1 9 8 4 ; and a n d Champion Champion linLernational n ~ e r n a ~ i o n aCorporation, C lo r p o r a t i o n , 1986. 1986. �U PARTICULATEFLOW FLOWAND AND THE THEDEFORMATION DEFORMATIONOF OFROCK: ROCK:FIELD FIELD PARTICULATE ANDEXPERIMENTAL EXPERIMENTALRESULTS AND G.J.J.Borradaile Borradaile G. Geology GeologyDepartment, Department,Lakehead LakeheadUniversity University ThunderBay, Bay,Ontario Ontario Canada CanadaP7B P7B5E1 5E1 Thunder Field Fieldevidence evidencefrom fromlow-grade low-grademetasedimentary metasedimentaryrocks rocksand andfrom fromtectonically tectonically deformed deformedsediments sedimentsoften oftenshows showsaadiscrepancy discrepancybetween betweenstrains strainsdetermined determinedon onlarge large and andsmall smallscales. scales. Large Largescale scalestrains strains(hand-specimen (hand-specimentotomany manykilometres) kilometres)are areoften often higher higherthan thanthe thestrains strainsofofsmall smallsedimentary sedimentarystructures structuresororindividual individualclastic clasticgrains. grains. When grain-scale strain is removed mathematically from a large structure, it When grain-scale strain is removed mathematically from a large structure, itisis imperfectly imperfectly"de-strained' "de-strained"because becauseconsiderable considerablelarge largescale scaledistortion distortionmay mayremain. remain. ItItisispostulated postulatedthat thatmuch muchof ofthis thismissing missingstrain strainisistaken takenup upby byinterparticle interparticle motion motionwhich whichremains remainselusive elusive to to petrographic petrographicexamination. examination. Thus Thusclastic clasticgrains grainsonly only record recordpart partofofthe thestrain strainhistory historywhile whilemuch muchstrain strainisistaken takenup upby byintergranular intergranular displacements. displacements.This Thisinvolves involvesdisplacements displacementson onmultigranular multigranularboundaries boundariesand, and,being being flow. more moreencompassing encompassingthan thangrain-boundary grain-boundarysliding, sliding,ititisistermed termed'particulate "particulate flow". Recent Recenthigh highpressure pressureexperimental experimental work work has hasconfirmed confirmedthat thatparticulate particulateflow flowisis enhanced enhancedby byhigh highpre-fluid pre-fluidpressures. pressures. These Thesesupport supportsome someofofthe theload loadso sothat thatthe the intergranular intergranularcontact contactstresses stressesare arereduced reduced("effective ("effectivestresses") stresses")and andslippage slippagewithin withinthe the rock mass is eased. These experiments also confirm that grain deformation is rock mass is eased. These experiments also confirm that grain deformation is reduced reducedby bythis thisprocess process(e.g. (e.g.twinning twinninginincalcite calciteisisless lesssevere) severe) and andfluid fluidpressure pressure oscillates oscillatesas as groups groupsofofgrains grainsslide slidepast pastone oneanother anotherproducing producingephemeral ephemeralvolume volume changes changes within within the the specimen. specimen. AAfurther furtherconsequence consequenceof ofthe theexperiments experimentsisis that that the the bulk bulk strain strainexceeds exceedsthe the grain-scale grain-scale strain strain as as the the field field evidence evidence shows. This Thiseffect effectisis greater at at high highpore porefluid fluidpressures. pressures. greater REFERENCES REFERENCES Borradaile, G.J., G.J., 1981. 1981. Particulate Particulateflow flow and andthe the formation formationof of rock rockcleavage. cleavage. Borradaile, Tectonophysics,72: 72:305-321. 305-321. Tectonophysics, Borradaile, McArthur, J., J., 1990. 1990. Experimental Experimentalcalcite calciteaggregates aggregatesininaasynthetic synthetic Borradaile, G.J. G.J. and and McArthur, weaker matrix matrix by by coaxial coaxial and and non-coaxial non-coaxialdeformation. deformation. J.J.Structural StructuralGeology, Geology,InIn weaker Press. Press. 10 �U STRUCTURAL AND ISOTOPIC ISOTOPIC EVIDENCE STRUCTURAL AND EVIDENCE FOR FOR MIDDLE MIDDLE PROTEROZOIC PROTEROZOIC THRUST THRUST FAULTING FAULTING OF ARCHEAN ARCHEAN AND EARLY PROTEROZOIC PROTEROZOIC ROCKS OF AND EARLY ROCKS NEAR NEARTHE THE GOGEBIC GOGEBIC RANGE, RANGE, MICHIGAN AND AND WISCONSIN WISCONSIN William W i l l i a m F.F.Cannon, Cannon, US US Geological G e o l o g i c a l Survey, Survey, Reston, Reston, VA VA Zell Geological CO Z e l l E. E. Peterman, Peterman, US US G e o l o g i c a l Survey, Survey, Denver, Denver,CO Paul Paul K. K. Sims, Sims, US US Geological G e o l o g i c a l Survey, S u r v e y , Denver, Denver,CO CO Faults F a u l t s with w i t h substantial s u b s t a n t i a l reverse r e v e r s edisplacement d i s p l a c e m e n t in i n the t h eMidcontinent Midcontinent R i f t ,such suchasasthe t hKeweenaw e Keweenaw and and Lake Lake Owen Owen FFaults a u l t s ((Figure F i g u r e 1), I ) , have havebeen been Rift, well w e l l documented. documented. They They ooffset f f s e tmost mostunits u n i t of s othe f t Keweenawan h e KeweenawanSupergroup Supergroup but b u t appear a p p e a r tto o be be truncated t r u n c a t e d by by the t h e youngest y o u n g e s t uunits n i t s in i n places, p l a c e s , thereby thereby d a t i n g the t h e fault f a u l tmotion m o t i o n approximately a p p r o x i m a t e l y iin n the t h e interval i n t e r v a l1.1-1.0 dating 1 . 1 - 1 . 0Ga, Ga. An An additional a d d i t i o n a l fault f a u l t or o r set s e t of o ffaults, f a u l t s herein , h e r e i ncalled c a l l e dthe t h eMarenisco M a r e n i s c o Fault, F a u l t , is is a previously p r e v i o u s l yunrecognized u n r e c o g n i z e dcompanion companiontot the o t hKeweenaw e Keweenawand andLake LakeOwens Owens Faults and EEarly Proterozoic F a u l t s and and offsets o f f s e t s Archean Archean and arly P r o t e r o z o i c rrocks o c k s across a c r o s s aa bbelt e l t as as much as 30 30 km kmwwide much as i d e ssouth o u t h ooff the t h e Keweenaw Keweenaw FFault a u l t nnear e a r the t h e Gogebic Gogebic Iron Iron Range. The The eexistence x i s t e n c e of o f Keweenawan Keweenawan o or r yyounger o u n g e r d deformation e f o r m a t i o n i in n some some ooff the the Archean and a r l y PProterozoic r o t e r o z o i c r orocks c k s i in n tthis h i s belt b e l tisi well s w e documented. l l documented. Archean andEEarly Keweenawan and E aEarly r l y PProterozoic r o t e r o z o i c rocks r o c k s along a l o n g the t h eGogebic GogebicRange Range form f o r m an an Keweenawan and u n c o n f o r m a b l e b ubut t s t structurally r u c t u r a l l y cconcordant o n c o r d a n t u nunit i t t hthat a t i is s ttilted i l t e dnorthward northward unconformable along with along w i t h at a t least l e a s some t some of o fthe t h eArchean Archean basement, basement, but b u t the t h e kinematics k i n e m a t i c s and and regional remained r e g i o n a l extent e x t e n t of o f this t h i stilting t i l t i have n g have r e m a i n e dobscure. obscure. We haveused usedt hthe andEEarly We have e oorientation r i e n t a t i o n ofo Keweenawan f Keweenawan and a r l y Proterozoic Proterozoic diabase d i a b a s e ddikes i k e s as as structural s t r u c t u r a lmarkers m a r k e r s to t oaddress a d d r e s s these t h e s e questions. q u e s t i o n s . The The analysis a n a l y s i s isi sbased basedon on the t h eassumption a s s u m p t i o n that t h a tthe t h edikes d i k e were s wereemplaced emplaced nearly nearly vertically v e r t i c a l l yand andthat t h a tthe t h eEarly E a r l Proterozoic y P r o t e r o z o i cdikes d i k e swere were not n o tappreciably appreciably deformed e 1 a t i o n s support s u p p o r t both both d e f o r m e d prior p r i o rtot Keweenawan o Keweenawan time. t i m e . Regional R e g i o n a l rrelations assumptions. u t c r o p s , mostly m o s t l y Archean Archean rocks, rocks, a s s u m p t i o n s . We We have c a t e d aabout b o u t 45 havel olocated 45 ooutcrops, where weccould measure where we o u l d measure o r orientations i e n t a t i o n s o of f ddiabase i a b a s e d dikes i k e s ((see s e e f figure i g u r e 1). 1). Most componento fofddip Most ddikes i k e s have have a a southward s o u t h w a r d component i p iindicating n d i c a t i n gnorthward northward tectonic t e c t o n i c rotation r o t a t i o since n s i n cemplacement. e emplacement. In I n some some ooff the t h e southernmost southernmost outcrops o u t c r o p s tthe h e dikes d i k e s remain r e m a i n nnearly e a r l y vertical v e r t i c a l and and thereby t h e r e b y provide p r o v i d e aa southern southern limit l i m i ttot othe t h erotated r o t a t e darea. a r e a . In I n Michigan, M i c h i g a n , the t h e dikes d i k e sform f o r man anorthogonal orthogonal system andi itt is i spossible p o s s i b l etot odetermine d e t e r m i n e aaunique u n i q u e direction d i r e c t i o nand andamount amount of of s y s t e m and rotation r o t a t i o n that t h a t transposed t r a n s p o s e d bboth o t h ssets e t s ffrom r o m vvertical e r t i c a l to t o their t h e i rpresent present orientation. Figure amountandand shows t hthe e amount d i rdirection e c t i o n o of f r rotation o t a t i o n for for orientation. F i g u r e 1 shows four Ther rotation f o u r areas a r e a s where where tthey h e y aare r e bbest e s t cconstrained. o n s t r a i n e d . The o t a t i o n is i s not n o t uniform uniform and 25 ttoo 60 u g g e s t i n g e ieither t h e r mmultiple u l t i p l e fault f a u l t blocks blocks and vvaries a r i e s from f r o m 25 60 degrees d e g r e e s ssuggesting or o r broad b r o a d folding. folding. 1 Rb-Sr agesoof Rb-Sr ages f bbiotite i o t i t efrom f r o mArchean Archean and and Early E a r l y Proterozoic P r o t e r o z o i c rocks rocks (see 1) help h e l p to t oresolve r e s o l v ethe t h emechanism mechanism ooff deformation d e f o r m a t i o n and and indicate indicate ( s e e Figure F i g u r e 1) that accompanied b y by u puplift l i f t oof f tthe h e ttilted i l t e d blocks. blocks. t h a t northward n o r t h w a r d ttilting i 1 t i n gwas was accompanied Biotite B i o t i t eages ages within w i t h i n the t h e area a r e a containing c o n t a i n i n g rotated r o t a t e d dikes d i k e s are a r e close c l o s e to t o the the ages whereas ages ooff Keweenewan Keweenewan e vevents, e n t s , whereas o l older d e r b biotite i o t i t e ages ages occur o c c u r where where the the dikes maintain dikes m a i n t a i n t their h e i r vertical v e r t i c a l orientation. o r i e n t a t i o n . The The bblocking l o c k i n g temperature t e m p e r a t u r e for for the between 250and and300 300degrees d e g r e e s C, C, t h e Rb-Sr Rb-Sr biotite b i o t i t esystem s y s t e misi thought s t h o u g hto t tbe o be between250 varying v a r y i n g sslightly l i g h t l y as as aa function f u n c t i o n of o f cooling c o o l i n g rate. r a t e . When When r orocks c k s aare r e uuplifted plifted and from f r o m depths d e p t h s where where the t h eambient a m b i e n ttemperature t e m p e r a t u r eexceeds exceeds250-300 250-300degrees d e g r e e sand cooled c o o l e d rrapidly, a p i d l y , the t h e biotite b i o t i t eages ages aproximate a p r o x i m a t e t hthe e t itime m e oof f uuplift. plift. 11 We We �U interpret the the biotite biotiteages ages(1.0-1.1 (1.0-1.1 Ga) Ga) in inthe thezone zone of of rotation rotationas as interpret recording such such uplift upliftand andcooling coolingduring duringlate late Keweenawan thrust thrust recording Keweenawan Older biotite biotiteages ages outside outside of of this thiszone zone record record an an earlier earlier faulting. faulting. Older cool ing event event probably probably associated 1 ization following foll owingthe the cooling associatedwith withstabi stabilization Penokean Penokean orogeny. orogeny. Figure ourinterpretation interpretation of of the structural Figure 2 shows shows our structural and and isotopic isotopic at the the onset onset of faulting data. Figure data. Figure 2a 2a portrays portrays the geometry geometry at faultingand and during Sandstone. relationships during deposition deposition ofofthe theJacobsville Jacobsville Sandstone. Fanning Fanning relationships within sequence of of Keweenawan withinthe thethick thick sequence Keweenawan basalts, basalts,and andunconformable unconformable relationships indicate that that rotation rotation toward therift rift relationships of the the Jascobsville Jascobsville indicate toward the of Oronto of15-30 15-30degrees degrees occurred occurred during volcanism volcanism and and deposition of ofthe theOronto Group. Weinterpret interpret this this as Group. We as flexing flexing ininresponse response to to crustal crustalthinning thinningand and emplacement theload loadof of volcanic volcanic and sedimentaryrocks. rocks.At At this this time emplacement ofofthe and sedimentary time the for biotite biotite was Rb-Sr blocking blocking temperature temperature for was aa nearly nearly the isotherm isotherm of of the the Rb-Sr listric horizontal horizontal surface. surface.Figure Figure2b. 2b.shows showsthe thepresent presentgeometry. geometry. The The listric nature of 30 degrees degreesof of additional ofthe theMarensico Marensico Fault Faulthas has caused caused about about 30 northward rotation of Early Proterozoic northward rotation ofArchean Archean and and Early Proterozoic rocks as as well as as the the Keweenawan sequence. Southward thrustingononthe theorder order of of 10 Keweenawan sequence. Southward thrusting 10 km km is is sufficient thethe present sufficienttotoaccount accountfor for presentgeometry. geometry. North of ofthe theMarenisco Marenisco Fault and Fault the theblocking blockingisotherm isotherm has has been been rotated, rotated, uplifted, up1 ifted, andexposed exposedby by erosion. of Figure 2b biotite biotite ages record the the uplift uplift erosion. Within Within area area aa of Figure 2b ages record event. In In areas areas bb and and c,c,rocks rocksnow now atatthe thesurface surfaceremained remainedabove above the the event. blocking andbiotite biotite ages agesstill still reflect blocking isotherm isotherm and reflectolder olderevents. events. In summary, isotopicand andstructural structuraldata dataindicate indicate that that thrust summary, isotopic thrust faults faults related related to toreverse reverse faults faultswithin withinthe theMidcontinent Midcontinent Rift Rift extend extend for for tens outsideofof the therift. rift. Part tens of kilometers kilometers outside Part of ofthe theMarenisco Marenisco Fault Faulthas has been mapped previously,but butwas wasinterpreted interpreted to to be be of of Archean Archean or Early Early been mapped previously, Proterozoic Proterozoic age. age. Structural Structural analysis analysisofofolder olderrocks rockselsewhere elsewhere near near the the Midcontinent Rift should accountfor for the the possi possibility Midcontinent Rift should account bil i ty of ofMiddle Middle Proterozic on Archean Archeanor or Early Proterozoic Proterozic deformation deformation superimposed superimposed on Proterozoic structures. structures. References References Prinz, 1981, Geologic map thethe Gogebic Range-Watersmeet Prinz,William WilliamC.,C., 1981, Geologic mapof of Gogebic Range-Watersmeet area, area,Gogebic Gogebic and and Ontonagon Ontonagon Counties, Michigan: Michigan: U.S. U.S. Geological Geological Survey Miscellaneous Investigations Investigations Map Survey Miscellaneous Map 1-1365, 1-1365, scale scale 1:125,000. 1:125,000. Z. E., E., Zartman, Zartman,R. R. E., E . , and and Sims, Sims, P. P. K., 1980, 1980, Tonalitic Tonalitic Peterman, Z. gneisses northern Michigan, gneisses of early earlyArchean Archean age age from from northern Michigan, in inSelected Selected studies studies ofofArchean Archean and and Lower Lower Proterozoic Proterozoic gneisses, gneisses,G.B. G.B.Morey Morey and and G. N. N. Hanson Hanson (eds.): (eds.): Geological Geological Society Society of ofAmerica America Special Special Paper Paper G. 182, p. p. 125-134. 125-134. Peterman, Z. Z. E.E. and and Sims, P. P. K., K.,1988, 1988,The TheGoodman Goodman swell: swell: a a lithospheric lithospheric flexure by crustal crustal loading Rift flexure caused caused by loading along along the Midcontinent Midcontinent Rift 7, System, Tectonics, v. p. 1077-1090. 1077-1090. System, Tectonics, v. 7, p. Sims, P. K., K., (in (in press), press), Geologic Geologicmap map of ofPrecambrian Precambrian rocks rocks ininWisconsin Wisconsin Sims, P. and and northern Michigan: Michigan: U.S. Geological Geological Survey Survey Miscellaneous Miscellaneous Investigations Investigations Map, Map, scale scale 1: 1:500,000. 500,000. 12 �U ye O EXPLANATION i-S—-S-S—I Osonto Gsos.p 000gIoOl.S.Sasnal.. nasd.IOn* t/t.n.Sta,an basalt 110*. MaSqss•It• Ranga 000.Sgsossp L/J A c m a n and P r o r r o i o i cCS crystaltin. A rtCflOafl and Early Early POt.,yao,c ySISOIn. recta* Soc/s — Lht*st tao/I; dash.d .IS.S. ConC.al.d by Jacob.,slla Sandston. — -.2? Fa•II Slid, and dsp of •ad.m.nta,y and nolcanIc 50cc. a!' SlId, and dsp of dike AeW \\ Sttdt Of OnfIlnal 41k. 000a9a dO.cl,an and amo.ani Of (01.5.00 Of 4*.. __a. *1(3 Loc.I.oo and Rb-S. ago of biohi. aa,npl. :•.: ...•.. . .f / . : • , 1 -1L 1 • c ?1 MW—*s•'--,APb I\" t13 — Q85 T ,/ / * y //5/0/' i— " // /// 7/ -/ / / //7' _—— / 0 S — / 2_... — -—aye 5- 9t30 — I /', S I — —— i — I —. — -S -i_/ KIEOMETERS S - —— 1 — ) / S —— *1594 — S — - Mi C — — — — - — I / / / - I_ — -S / —— 55 I Figure 1. mapofof ppart Figure 1. Geologic Geologic map a r t of of northern northernMichigan Michigan and and Wisconsin Wisconsin Geology iiss modified showing newly newly defined defined Keweenawan showing Keweenawan t h thrust r u s t f faults. a u l t s . Geology modified from compilations compilations by by Prinz Prinz (1981) andSims Sims( i(in from (1981) and n ppress). r e s s ) . Biotite B i o t i t eages ages include i ncl ude some some previously reported reported ages ages (Peterman (Peterman and and others, o t h e r s , 1980; 1980; Petermanand andoothers, Peterman t h e r s , 1988). 1988). Figure 2. 2 . Schematic e p r e s e n t a t i o n ofofdevelopment developmentofof Keweenawan Schematic rrepresentation Keweenawan sstructures t r u c t u r e s near near the t h e Gogebic Gogebic Iron Range. PPatterns a t t e r n s aas s in Figure 1. 1. Iron Range. in Figure A.-Structure of Midcontinent MidcontinentRRift andpprior A . - S t r u c t u r e aafter f t e r opening opening of i f t and r i o r to t o onset o n s e t of thrust t h r u s t faulting. faulting. B.-Present t r u c t u r e aafter f t e r southward southward tthrusting h r u s t i n g and and rrotation o t a t i o n of of upper upper B. -Presentsstructure p l a t e above above l ilistric s t r i c thrust t h r u s t surface. surface. plate 13 \ - — \_) = — — N I 'S * ''° ' I — S S ._ —S - ° ___ I -S s - • 0 / —— — - I, �U THE PALEOMAGNETISM PALEOMAGNETISM OF EARLY PROTEROZOIC SIOUX SIOUX OF THE EARLY SOUTHWESTERN MINNESOTA MINNESOTA QUARTZITE, SOUTHWESTERN Val W., and G.B. Morey, Minnesota Geological Geological Survey, Survey, 2642 2642 University University CHANDLER, Va! Avenue, St. Paul, MN 55114-1057 55 114-1057 Paleomagnetic studies were conducted on the Early Proterozoic Sioux Quartzite of southwestern Minnesota, a sequence of hematite- and silica-cemented quartz arenites that were deposited by fluvial processes in several elongate depobasins bounded by northwesttrending faults. AAtotal totalof of 158 158samples samplesof of quartz quartz arenitic areniticmaterial material were were collected collected from from 17 17 sites scattered across four four basins (Cottonwood (Cottonwood County County ,, New Ulm, North Pipestone, and South Pipestone). As judged from alternating-field (AF) and thermal demagnetization studies, the magnetization is dominantly single-component, and as judged from high coercivities and blocking temperatures, the magnetic carrier is hematite. A definitive definitive fold fold test test is is difficult difficult to hematite. A perform, perform, because cross cross beds beds obscure obscure gently gently dipping dipping master master bedding bedding features. features. Nonetheless, most of the magnetization seems seems to have occurred before before aa period period of of regionalregionalformed the the basins. Measured scale tilting that formed Measuredpaleomagnetic paleomagneticdirections directions at at both both site site and and basin levels show good clustering, and the average directions directions obtained obtained from from each each of of the four basins are not significantly different different at at the the 95% 95% confidence confidencelevel. level. After the effects of regional tilting tilting were were removed, the the paleomagnetic paleomagnetic directions from the four four basins yield a 10lOW.and and16°N. 16ON.(k=65, (k=65,a95—11°). a95=l lo). combined paleopole paleopole located locatedatat101°W. After AF demagnetization, clasts from a basal conglomerate in the New Ulm basin show a paleomagnetic bias in the direction of that observed in the overlying quartzite, implying post-depositional magnetization. Furthermore, Furthermore, hematite, the primary magnetic carrier in the Sioux, occurs as a diagenetic mineral with a long paragenetic history 1986; Vander Horck, 1984) 1984) and, in the case of the North Pipestone (Southwick and others, 1986; basin, also as veinlets that formed during a strain event (Morey, 1984) that may have been related to regional tilting. On the Early Proterozoic Proterozoic apparent apparent polar polar wander wander curve curve of of Irving Irving (1979) (1979) the theSioux Sioux paleopole paleopole lies lies along along the the 1700-1650 1700-1650m.y. m.y. segment, segment, which which corresponds corresponds in in part part with with the the time time orogen of of Sims and and Peterman Peterman (1986) (1986)of of 1800-1630 1800-1630m.y. m.y. The Sioux of the Central Plains orogen km north of rocks clearly clearly involved involved with the outcrops are located only some 200-300 krn Central Plains orogen (Fig. 1), I), and Southwick and others (1986) (1986) have tentatively suggested that the northwest-trending faults that bound the individual Sioux basins were Conversely,the theSioux SiouxQuartzite Quartzitecould could have have been been deposited depositedatatsome some related to the orogen. Conversely, time well before the orogen and subsequently modified by tectonic processes associated associated with the orogen. In In the the first first situation situation the the paleomagnetic pole position would reflect diagenetic processes that may have closely followed sedimentation, whereas in the second, it would reflect a period of secondary overprinting that would have involved wholesale wholesale recrystallization of hematite. There There isis no no obvious obvious evidence evidence that the hematite in the Sioux, except for that in veinlets, has been been recrystallized. recrystallized. We therefore suggest that it is more related to diagenetic diagenetic processes. processes. likely that the magnetization we observe is primarily related Although considerable uncertainties still exist, our results are consistent with the conclusions of Morey and Van Schmus Schmus (1980), who suggested that the so-called so-called "Bamboo "Baraboo interval quartzites at the Lake Superior region" were deposited during the interval 176017601630 m.y. References References Cited Irving, E., 1979, 1979, Paleopoles and paleolatitudes of North America and speculations speculations about about displaced terrains: Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences, v. v. 16, 16,p. p. 669-694. 669-694. Morey, G.B., 1984, 1984, Sedimentology Sedimentology of the Sioux Quartzite in the Fulda basin, Pipestone County, southwestern Minnesota, in Southwick, D.L., ed., Shorter Shorter contributions contributions to to 14 �_________I I thegeology geologyof ofthe theSioux SiouxQuartzite Quartzite(early (earlyProterozoic), Proterozoic),southwestern southwesternMinnesota: Minnesota: the MinnesotaGeological GeologicalSurvey SurveyReport Reportof of Investigations Investigations32, 32,P.p.59-74. 59-74. Minnesota W.R., 1988, 1988,Correlation Correlationof of Precambrian Precambrianrocks rocks of of the the Morey,G.B., G.B., and andVan VanSchmus, Schmus,W.R., Morey, Lake Superior region, United States: U.S. Geological Survey Professional Paper Lake Superior region, United States: U.S. Geological Survey Professional Paper 1241-F.31 31 1241-F, p.D. Sims. P.K., and Peterman,Z.E., Z.E., 1986, 1986,Early EarlyProterozoic ProterozoicCentral CentralPlains Plainsorogen: orogen: AAmajor major Sims, P.K., and Peterman, buried structure structurein in the the north-central north-centralUnited United States: States: Geology, Geology,v.v.14, 14,p.p.488-491. 488-491. buried D.L., Morey, Morey, G.B., G.B., and andMossier, Mossier,J.FI., J.H., 1986, 1986, Fluvial Fluvial origin origin of of the the lower lower Southwick, D.L., Southwick, Proterozoic Sioux Quartzite, southwestern Minnesota: Geological Society of America Proterozoic Sioux Quartzite, southwestern Minnesota: Geological Society of America 97,p.p.1432-1441. 1432-1441. Bulletin,v.v.97, Bulletin, Vander Horck, M.P., 1984, Diagenesis in in the the Sioux Sioux Quartzite: Quartzite: Unpub. Unpub. M.S. M.S. thesis: thesis: Vander Horck, M.P., 1984, Diagenesis University of Minnesota, Minneapolis, 101 p. University of Minnesota, Minneapolis, 101 p. 7 00 100 Mi 00 Mi. %---+-+ 00 100Km. Km. 100 Figure1.1.Generalized Generalizedgeologic geologicmap mapofofthe thecentral centralplains plainsregion region Figure (fromSouthwick Southwickand andothers, others,1986). 1986). (from 15 I I �CARBONATE IN IN TILL TILL UNITS UNITS OF OF LAKE LAKE OF OF THE THE WOODS WOODS COUNTY, COUNTY,MINNESOTA MINNESOTA CARBONATE D.A. Dahi Dahl and and D.F. D.F. Cartwright Cartwright D.A. Minnesota Department Department of of Natural Natural Resources Resources Minnesota MN 55746 55746 Division of of Minerals, Minerals, Hibbing, Hibbing, MN Division ABSTRACT ABSTRACT Within Lake Lake of the theWoods Woods County, and matrix matrix Within County, carbonate carbonate content content and solubility are are being being used, used, among among other other quantitative quantitative methods, methods, to to solubility characterize the the glacial glacial drift drift that that overlies overlies Archean Archean bedrock. bedrock. characterize Bedrock in in this this northwestern northwestern Minnesota Minnesota county county is is distributed distributed Bedrock as aa belt belt of of Archean Archean supracrustal supracrustal rocks rocks bounded bounded on on the the north north and and as east by by granitic granitic intrusives intrusives and and bounded bounded on on the the south south by by faulted faulted east contactwith with gneisses gneissesof ofthe theQuetico Queticoineta—sedimentary meta-sedimentary subprovince. subprovince. contact The supracrustal supracrustal sequence sequence is is masked masked by by sedimentary sedimentary cover cover The 300feet. feet. (overburden) which which ranges ranges in in thickness thickness from from 60 60to to 300 (overburden) As part part of of aa project project to to encourage encourage exploration exploration in in areas areas of of As deeper (asis is the the case case in in Lake Lake of of the the Woods Woodscounty), county), deeper glacial glacial drift drift (as MnDNR is is conducting conducting an an overburden overburden drilling drilling project project to to characterize characterize MnDNR the the regolith regolith (glacial (glacialdrift drift and and saprolite) saprolite) of of the the area area in in terms terms of of its feasibility feasibility for for use use as as an an exploration explorationmedium. medium. its Three packages packages of of glacial glacial drift drift have have been been recognized recognized beneath beneath Three the surficial surficial Koochiching Koochiching lobe lobe sediments sediments during during descriptive descriptive logging logging the of core core taken taken from from twenty twenty rotasonic rotasonic drill drill holes holes drilled drilled in in twenty twenty of townshipsduring duringthe thefall fallof of 1989. 1989. Matrix Matrix solubility solubility and and carbonate carbonate townships pebble content content of of till till units units within within the the drift drift packages packages are are being being pebble used along along with with textural textural analysis analysis and and trace trace metal metal measurements measurementsto to used develop aa framework framework by by which which the the sub-Koochiching sub-Koochiching drift drift may may be be develop quickly and and accurately accurately differentiated differentiated during during exploration explorationdrilling. drilling. quickly One hundred hundred and and forty forty samples samples of of the the -63um -63um (silt-clay) (silt-clay) One component of of sub—Koochiching sub-Koochiching tills were were leached leached in in 4N 4N HC1 HC1 to to component dissolve any any carbonate carbonate in in the the samples. samples. Weights Weights of of insoluble insoluble dissolve residue were were measured measured and and Ca, Ca, Mg, Mg, and and Fe Fe in in the the soluble soluble portion portion residue Matrix analyzed by by atomic atomic absorption absorption spectroscopy. spectroscopy. Matrix were analyzed were into three fall percent and solubilities range from 3 to 54 percent and fall into three 54 3 to solubilities range from These sub-populations compare well to distinct sub-populations. These sub-populations compare well to distinct sub—populations. subdivisions recognized recognized qualitatively qualitatively during during descriptive descriptive logging. logging. subdivisions Pebble counts counts of of the the coarse coarse (5-15mm) (5-15mm) component component of of the the till till samples samples Pebble also reflect reflect these these distinctions. distinctions. also Characteristic recognition recognition of of the the range, range, median, median, and and Characteristic variability of of the the carbonate carbonatecontent content and and matrix matrix solubility solubilityof ofthe the variability for framework a sub-Koochiching drift packages will provide a framework for provide packages will sub-Koochiching drift recognizing till till units units and and for for resolving resolving intra-till intra-till compositional compositional recognizing variations such such as as contamination contamination by by underlying underlying drift drift units units and and variations incorporation of of siderite/carbonate siderite/carbonate from from underlying underlying saprolite. saprolite. incorporation 16 �U MAGNETIC SUSCEPTIBILITY MAGNETIC SUSCEPTIBILITY ANISOTROPY ANISOTROPY AND STRAIN, STRAIN, THOMSON THOMSON FORMATION FORMATION (PROTEROZOIC), (PROTEROZOIC), MINNESOTA Donald M. M. Davidson, Donald Davidson, Jr. Jr. Department Department of of Geology Geology Northern Northern Illinois Illinois University University DeKalb, IL DeKalb, IL 60115 60115 Four have been Four samples samples of of the the Proterozoic Proterozoic Thomson Thomson Formation Formation have been analyzed analyzed using using a a Sapphire Sapphire Instrument Instrument Model SI-2 SI-2 magnetic susceptibility susceptibility bridge. bridge. Oriented Oriented bulk samples samples were collected collected from from aa fold fold exposed exposed north north of of Carlton, Carlton, Minnesota, well within Minnesota, within the the "northern "northern area" area" interpreted interpreted by Holst Holst (1984) (1984) to to have undergone undergone but but one one phase phase of of Penokian Penokian deformation. deformation. The The purpose purpose of of the the study study was to to evaluate evaluate the the suitability suitability of of susceptibility susceptibility anisotropy anisotropy as as aa measure of of deformation deformation magnitude and and orientation orientation using using these these samples. samples. Natural Strain Natural Strain Data: Data: Hoist (1985) Holst (1985) has presented strain strain data for for the area area based based on on measurements of measurements of deformed deformed concretions concretions and and mudchips. mudchips. Similar Similar data data collected collected by me only only for for "whole"concretions "whole"concretionsare are also also presented. presented. Holst (ID-100) Hoist (nlO0) 1 1 2 2 3 3 1.55 1.39 1.62 Average Average 1.52 4.70 1.52 4.70 Davidson Davidson STA STA 1/4 1/4 STA 22 STA STA 33 STA STA 55 STA STA 88 STA Average Average n n (34) (34) (15) (15) (30) (30) (10) (10) (14) (14) b a Y Y Z Z 3.92 5.84 4.35 X 4.77 4.77 4.70 4.70 4.91 4.91 6.27 6.27 4.20 4.20 2.38 2.38 2.30 2.30 2.83 2.83 3.19 3.19 2.36 2.36 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 4.97 4.97 2.61 2.61 1.00 1.91 1.00 1.91 2.61 2.61 a a 2.00 2.00 2.04 2.04 1.74 1.74 1.97 1.97 1.78 1.78 b b 2.38 2.38 2.30 2.30 2.83 2.83 3.19 3.19 2.36 2.36 l2 23 k K 0.44 0.33 0.48 1.37 1.76 1.47 0.19 0.08 0.19 0.32 0.19 0.33 .42 42 1.53 0.15 0.28 E1-2 =l-=2 .69 .69 .71 .71 .55 .55 .68 .68 .57 .57 2-3 k K .87 .86 .73 .80 .40 .44 .57 .80 .86 .53 .58 .75 .64 .64 .95 .59 .71 .83 1.04 1.16 n=number n=number of of measurements measurements area, the X is vertical and Z is N-S N-S and horizontal; horizontal; hence In this area, concretions concretions are are flattened flattened within within aa well-developed well-developed vertical vertical cleavage. cleavage. 17 �__________ U Magnetic Susceptibility Magnetic Susceptibility Anistropy: Anistropy: Right cylinders cylinders were were cut cut from from the the oriented oriented samples samples and Right and 24 24 orientation orientation measurements were measurements were made made on on each. each. Results to date date are: are: Results to MAX MAX EV(X105) E V(X~O-~) INT INT MIN SD SD (X1-°5) (XI0- 5) EV (MIN) (MIN) R95 DEC R95 DEC INC INC CORE CORE ORIENTATION ORIENTATION DEC DEC INC INC Graywacke 1 Graywacke 1 Slate Slate 1.67 1.67 3.80 3.80 1.62 1.62 3.69 3.69 1.5 1.5 3.40 3.40 1.3 1.3 2.5 2.5 2.6 2.6 6.4 6.4 351 351 351 351 3 3 1 1 303 303 303 303 79 79 18 18 Graywacke 3 Graywacke 3 Slate Slate 3.66 3.66 2.62 2.62 3.43 3.43 2.59 2.59 3.03 3.03 2.49 2.49 3.54 3.54 2.61 2.61 2.7 2.7 4.0 4.0 350 350 291 291 5 5 7 7 18 18 26 26 18 18 19 19 Interpretation Interpretation My natural natural strain strain data, data, although although similar similar to the the values derived derived by Hoist Holst (1985), consistently consistently show strain values, values, hence hence show higher X/Y and lower Y/Z strain (1985), my limited number of larger k k values. values. I attribute the differences to my larger measurements measurements and and to to concretion concretion behavior relative relative to measurements measurements from from 2d 2d sections and sections and deformed deformed mud mud chips. chips. The magnetic anisotophy data are inconsistent, inconsistent, although although the the orientations orientations of of EV EV are are quite quite close close to to similar similar values values for for natural natural strains. strains. believed to contribute contribute to (e.g. near horizontal cores) are believed Sampling problems (e.g. variations. Comparisons the variations. Comparisons of of strain strain and susceptibility susceptibility magnitude magnitude appear appear premature given limited data as as well as the fact fact that that these these rocks rocks are are given the the limited weakly strained strained and may have udergone udergone pressure solution solution effects effects (Borradaile, (Borradaile, 1988). References References Borradaile, G.J., G.J., 1988, petrofabrics and strain: Borradaile, 1988, Magnetic susceptibility, susceptibility, petrofabrics strain: Tectonophysics, 156, Tectonophysics, 156, 1-20. 1-20. Hoist, T.B. , 1984, Holst, T.B., 1984, Evidence for nappe development during the Early Geology 12, Proterozoic Penokian Proterozoic Penokian Orogeny, Orogeny, Minnesota: Minnesota: Geology 12, 135-138. 135-138. 1985, Implications , 1985, Implications of a large large flattening flattening strain strain for for the the origin bedding-parallel foliation Thomson of a bedding-parallel foliation in in the Early Proterozoic Proterozoic Thomson Formation, Minnesota: Formation, Minnesota: Jour. Jour. Structural Structural Geoi. Geol. 7, 7, 375-383. 375-383. 18 �U T H E SEINE-COUTCHICHING PROBLEM RECONSIDERED: U-PB U-PB THE CONCERNING TTHE SOURCE AND AND TIMING TIMING O OF GEOCHRONOLOGICAL DATA CONCERNING H E SOURCE F ARCHEAN SEDIMENTATION IN T THE H E WESTERN SUPERIOR SUPERIOR PROVINCE PROVINCE D.W. DAVIS, DAVIS, Jack Satterly Geochronology Geochronology Laboratory, Royal Ontario Ontario Museum, D.W. Museum, 100 100 Queen's Park, Toronto, Ontario, Ontario, M5S M5S 2C6 Clastic sediments in the Superior Superior Province Province mostly mostly fall fall into into two two categories: categories: an an alluvial alluvial fan-fluvial facies faciesassociation associationof ofsandstone sandstone and and conglomerate conglomerate and a resedimented facies fan-fluvial facies association of of marine marine turbidite (Ojakangas 1985). Rocks Rocks of of the the resedimented facies association association form form the the major major proportion proportion of Archean sediments and make up most of the association supracrustal component of of entire entire subprovinces subprovinces such as the English River, Quetico and Alluvial sediments sediments are relatively relatively minor minor in in volume volume and and are generally exposed along Pontiac. Alluvial within greenstone belts or at the faults either within the boundaries boundaries between between subprovinces. subprovinces. The relationship between these sediment sediment types has been a focus focus for debate in in Archean geology for over a century, beginning with the work of A.C. Lawson (1887, century, beginning (1887, 1913) sediments (Seine (Seine Group) Group) are much in the Rainy Lake area. Lawson Lawson argued that alluvial sediments younger than turhidites turbidites in the area area (Coutchiching (Coutchiching Group). Others Others have have since since argued that that they represent a transition from continental to marine depositional environments. Field they transition from continental marine depositional relationships between these facies facies associations associations are are generally generally complex. complex. Transitional sedimentary facies are rare rare and and ininsome somecases casesturbiditic turbiditic sediments sedimentsoverlie overliealluvial alluvial which is is the the opposite of of what what would would be he expected expected from from a sediments, a relationship which prograding alluvial alluvial fan. It is now possible possible to measure concordant, precise ages on single detrital zircon grains and these studies studies afford afford new new insight into the relationship between sedimentary sedimentary facies facies and their role in in the the tectonic tectonic development development of of the the Superior SuperiorProvince. Province. The Theclassic classic SeineSeineCoutchiching problem problem has been resolved Coutchiching resolved in the Rainy Lake area. Detrital Detrital zircons zircons in in the the Coutchiching of 3059-2704 Ma Coutchiching sediments sediments have have an age range of Ma (Davis (Davis et et al. 1989, errors errors are generally ±Â 2-3 Group was was deformed deformed and and metamorphosed as part 2-3 Ma). The Coutchiching Coutchiching Group of Rice Bay, Bay, and intruded by post-tectonic plutons of a dome structure at Rice plutons such such as as the the Bear  2 Ma. Detrital zircon grains Pass stock at 2693 ± grains in in the the Seine Seine Group Group have a uniform age of of 2693 late in in the the geologic geologic history of the 2693 Ma. Ma. Therefore, Therefore, both sedimentary groups are quite late area but but the the Seine Seine Group Grouppost-dates post-datesdeposition depositionof of the theCoutchiching Coutchiching Group Group and and may may have have derived from from erosion erosionof ofan anactive activevolcanic volcanicedifice edifice overlying overlying the the rising rising Rice Rice Bay Bay dome. dome. been derived The voluminous voluminous Quetico Quetico turbidites turbidites to to the the south have have a detrital zircon age range of 3009-2698 Ma, 3009-2698 Ma,and and were were intruded intruded by by the the late late tectonic tectonic Blalock Blalock Pluton Pluton at at 2688 2688  ± 44 Ma (Davis et al. submitted). Deposition of of the Seine Group may, therefore, have been penecontemporaneous with with parts parts of of the theQuetico Queticosediments. sediments. This This isis supported supportedby byfield field penecontemporaneous evidence in the Geraldton area where Devaney and Williams (1989) have demonstrated in area where Devaney Williams (1989) have demonstrated a transition alluvial and Quetico transition between alluvial and marine marine sediments sediments at at the northern boundary of the Quetico Subprovince. Detrital zircons zircons in both the the Quetico Queticoand andCoutchiching Coutchiching sediments sediments have have aa distinctive distinctive Detrital 19 �pattern in in which which many many of age pattern of the grains grains cluster cluster near near the young young end end of of the the age range, and are similar in age to late-tectonic plutons in the adjacent adjacent Wabigoon Wabigoon Subprovince. Subprovince. The The other grains grains are are generally generally older than than arc-type arc-type volcanism volcanism in adjacent greenstone greenstone belts, belts, but but similar in age to rocks found within metaplutonic terrains in in the the Wabigoon Wabigoon Subprovince Subprovince Winnipeg River Suhprovince. Subprovince. There is also petrographic evidence that that significant significant and the Winnipeg amounts of of felsic felsic volcanic of the the turbidites. turbidites. These These amounts volcanic material material contributed to the provenance of data indicate indicate that thatQuetico-type Quetico-type sediments sedimentsmay may have have been been deposited depositedlargely largelyfrom from erosion erosionof of data active volcanos and older sialic sialic crust during a late orogenic orogenic event. event. The relationship relationship between between sedimentation sedimentation and anddeformation deformationisisclearly clearly evident evident in in the the Manitou Lake area, area, at atthe thesouthern southernmargin marginof of the theKakagi Savant Lake Lake volcanic volcanic Kakagi Lake Lake -- Savant belt. Alluvial sediments are overlain by by marine marine turbidites turhidites (Manitou Lake Group, Group, Teal Teal and and Walker 1977), which are, in turn, structurally overlain by volcanic rocks (Boyer Lake 1977), are, in turn, structurally overlain by Lake Group). Group). Detrital Detritalzircons zirconsininthe theturbiditic turbiditicsediments sedimentsshow showan anage agerange range3039-2706 3039-2706Ma. Ma. Sediments near the base base are areintercalated intercalatedwith with rhyolites rhyolites with an age of <2699 ~ 2 6 9 ±9 33 Ma. The The overlying Boyer Boyer Lake Lake group has an older age age of of 2722 2722 ±Â 5 Ma and was therefore structurally emplaced over over the the sediments, sediments,possibly possibly by thrusting. The entire entire sequence sequencewas was rotated rotated into into aa vertical vertical position position and and intruded intrudedby by the thepost-tectonic post-tectonic Taylor Taylor Lake Lakestock stockatat2696 2696 ± 22 Ma. Therefore, Therefore, sedimentation, sedimentation, probable probable thrusting, thrusting, regional regional folding folding and and late late magmatism occurred within a time span of, at most, 3 ±Â 44 Ma and were likely likely part of of aa single tectonic event. Also, the presence of of out-of-sequence out-of-sequence relationships relationships within within the the supracrustal pile pile suggests suggests that the turhidites turbidites may may have have been structurally structurally superposed superposed on on the the lower alluvial alluvial sediments. sediments. Almost Almost identical identical relationships are found found within the supracrustal sequence sequence in in the the Sioux Lookout Lookout area, on the northern northern boundary boundary of of the Kakagi Kakagi Lake - Savant Savant Lake Lake volcanic volcanic belt (Davis (Davis et al. al. 1988). 1988). This This sequence sequence isis structurally structurally overlain by the Warclub Group, Group, aa belt of turbidites which extends westward westward along along part part of of the boundary between the Subprovinces. The of turbidite turbidite Wabigoon and Winnipeg River Subprovinces. The detrital zircon zircon age pattern of in the Dryden area area indicates indicates that that much much of of the the sediment sediment was was probably derived from the Winnipeg Winnipeg River Subprovince. Subprovince. Deposition Deposition is is dated dated at at about about2714 2714-- 2706 2706 Ma based on on the the age age of of an an intercalated intercalated rhyolite rhyolite and and age age constraints constraints from elastic clastic material and emplacement of Dryberry batholith. batholith. This This time time span span correlates correlates with with deformation, deformation, late late plutonism plutonism and and of the the Dryberry gold mineralization at at the the northern northernboundary boundaryofofthe theWabigoon WabigoonSubprovince, Subprovince,asaswell wellasaswith with metamorphism metamorphism in in the theWinnipeg WinnipegRiver RiverSubprovince, Subprovince, and andtectonic tectonicactivity activity between between the thetwo two subprovinces (Davis (Davis and and Smith, Smith, submitted). submitted). clastic sediments onset of of collisional collisional In summary, deposition of elastic sediments appears appears to mark the onset orogeny. Time constraints on this process from north to south across across the the western western Superior Superior orogeny. Province are are the thefollowing: following: 2714-2706 2714-2706 Ma in the northern northern Wabigoon WabigoonSubprovince, Subprovince,26992699Province 2696 2696 Ma in the the central centralWabigoon, Wabigoon,2698-2688 2698-2688 Ma in in the the Quetico QueticoSubprovince, Subprovince,and and268926892684 Ma in the Shebandowan Shebandowan Subprovince Subprovince (Corfu (Corfu and and Stott Stott1986). 1986).This This process process was was 2684 apparently diachronous diachronous across across the Superior Superior Province Province and may have apparently have been due to progressive progressive southward accretion accretion of of arc arc and and micro-continental micro-continental fragments. fragments. 20 �U-Pb ages ages for for late late magmatism magmatism and and regional regional deformation deformation Corfu, F., and Stott, G.M. 1986. U-Pb in the Shebandowan Belt, Belt, Superior Superior Province, Province, Canada. Canada. Can. Can. Jour. Jour. Earth EarthSci., Sci.,v.v. 23, 23, p. p. 1075-1082. 1075-1082. Davis, D.W., D.W., Pezzutto, Pezzutto, F., F., and and Ojakangas, Ojakangas, R.W. R.W.The The age age and and provenance provenance of of Davis, metasedimentary rocks rocks in the Quetico Quetico Subprovince, Subprovince,Ontario, Ontario, from fromsingle singlezircon zircon analyses: implications implications for forArchean Archean sedimentation sedimentation and and tectonics tectonics in in the the Superior analyses: Province, submitted to Earth Planet. Province. Planet. Sci. Sci. Lett. Davis, D.W., D.W., Poulsen, K.H., New insights insights into into Archean Archean crustal K.H., and Kamo, Kamo, S.L. 1989. New in the the Rainy Rainy Lake Lake area, Superior Province, development from geochronology geochronology in Canada. Jour. Canada. Jour. Geol., Geol.,v.v. 97, 97,p. p. 379-398. 379-398. Davis, D.W., D.W., and Smith, P.M. P.M. Archean Archean gold mineralization in the Wabigoon Subprovince, a in the the Lake of the product of crustal accretion: evidence from U-Pb geochronology in Woods area, Superior Superior Province, Canada. submitted to Jour. Jour. Geol. Geol. Davis, D.W., D.W., Sutcliffe, R.H., R.H., and Trowell, N.F. N.F. 1988. Geochronological Geochronological constraints on the of a late Archean greenstone belt, Wabigoon tectonic evolution of Wabigoon Subprovince, northwest Ontario, Canada. Precamb. Res., v. 39, p. 171-191. Ontario, Canada. Precamb. Res., v. 39, p. 171-191. Devaney, J.R., and Williams, H.R. 1989. Evolution Evolution of of an an Archean subprovince boundary: a sedimentological and structural study of part of of the the Wabigoon Wabigoon -- Quetico Quetico boundary in northern Ontario. Can. Jour. Earth Sci., v. 26, p. 1013-1026. Ontario. Can. Jour. Earth Sci., v. 26, p. 1013-1026. Lawson, A.C. AC. 1887, 1887, Geology of the Rainy Lake region, with remarks on on the the classification classification of of the crystalline crystalline rocks west of Lake Lake Superior. Superior.Am. Am.Jour. Jour.Sci., Sci.,v.v.33, 33,p. p. 473-480. 473-480. Lawson, A.C. A.C. 1913, The The Archean geology of of Rainy Lake re-studied. Can. Can. Geol. Geol.Survey Survey Mem. 111 p. Mem. 40, 40,111 p. Ojakangas, R.W. 1985. Review Review of of Archean Archean clastic clastic sedimentation, sedimentation, Canadian Shield: major felsic volcanic contributions to to turbidite turbidite and andalluvial alluvialfan-fluvial fan-fluvialfacies faciesassociations. associations.in in Ayres, L.D. et al., eds., Evolution of Archean supracrustal sequences, sequences, Geol. Geol.Assoc. Assoc. Canada Canada Spec. Spec.Paper Paper28, 28,p.p.23-47. 23-47. of the the Archean Archean Teal, P.R., and Walker, R.G. 1977. 1977. Stratigraphy and sedimentology of Manitou Group, Group, northwestern northwestern Ontario. Ontario. Geol. Geol. Survey Survey Canada, Paper 77-lA, 77-1A,p. p. 181181184. 184. 21 �U PALEOMAGNETISM OF OF KEWEENAWAN KEWEENAWAN AGE AGE BASALTS BASALTS OF OF THE THE CHENGWATANA CHENGWATANA PALEOMAGNETISM VOLCANIC GROUP GROUP IN IN THE THE ST. ST. CROIX CROIX FALLS FALLS AND AND FREDRICK-MILTOWN FREDRICK-MILTOWN VOLCANIC AREA OF OF POLK POLK COUNTY, COUNTY, WISCONSIN WISCONSIN AREA John Feeney Feeney John and and William William F. F. Kean Kean Departmentof ofGeoscierices Geosciences Department University of of Wisconsin-Milwaukee Wisconsin-Milwaukee University Milwaukee, Wisconsin Wisconsin 53201 53201 Milwaukee, Extensive Extensive paleomagnetic paleomagnetic studies studies have have been been made made in in the the Precambrian Precambrian Keweenawan Keweenawan rocks rocks near near the the shores shores of of Lake Lake Superior. Superior. Over Over 60 60 individual individual paleomagnetic paleomagnetic poles poles have have been been obtained from from these these rocks rocks (Halls (Hallsand and Pesonen, Pesonen,1982). 1982). obtained Exposures Exposures of of Keweenawan Keweenawan age age basalts basalts in in Polk Polk County County (northwestern (northwestern Wisconsin) Wisconsin) give give an an opportunity opportunity to to study study Lake Lake Superior Keweenawan Keweenawan rocks rocks in Superior in their their southernmost southernmost exposure. exposure. 130 130 oriented oriented cores cores from from 18 18 sites sites in in the the St.Croix St.Croix Falls Falls and Fredrick-Miltownarea area of of Polk Polk County, County, Wisconsin Wisconsin were were and Fredrick-Miltown collected and and measured measured for for magnetic magnetic characteristics. characteristics. A.F. A.F. collected demagnetization demagnetization and and remanence remanence acquisition acquisition studies studies indicate indicate that that the the remnant remnant magnetization magnetization is is carried carried by magnetite magnetite and and in some some exposures, exposures,hematite. hematite. Most Most samples samples showed showed aa single single in component component of of magnetization magnetization with with Fisher Fisher average average magnetic magnetic directions directions split split into into two two groups; groups; aa normally normally magnetized, magnetized, or or north 1). north seeking seeking direction direction and and aa "reverse" "reverse" direction direction (Table (Table1). The The normal normal group group gave gave aa magnetic magnetic direction direction and and pole pole position position close to to the the mean mean values values for for the the middle middle Keweenawan Keweenawan Portage Portage close Lake Lake Volcanic Volcanic Group Group given given in in Halls Halls and and Pesonen, Pesonen, 1982, 1982, when when corrected corrected for for geologic geologic dip dip using using lava lava flow flow tops. tops. The The reverse reverse group group showed showed aa large large (60 (60degrees degrees in in declination) declination) asymmetry, asymmetry, possibly possibly caused caused by by magnetic magnetic overprinting overprinting from from adjacent normal normal magnetized magnetized basalt basalt flows. flows. adjacent Susceptibility Susceptibility measurements measurements showed showed aa great great deal deal of of variation variation on on aa within within site site and and aa between between site sitebasis. basis. Mean Mean susceptibility susceptibility from from all all sites sites was was 2892 2892 xx i06 1 0 ^ c.g.s. c.g.s. units, units, and standard standard deviation deviation was was 2686 2686 xx 10-6 l o 6 c.g.s. c.g.s. units. units. The The and i06 c.g.s. units low value value for for aa site site was was 31 31 xx l o 6 c . g . 5 . units and and the the high high low l o 6 c.g.s. c . g . s . units. units. was 9592 9592 xx i06 was 22 �U I TABLE TABLE 11 PALEOMAGNETIC PARAMETERS FOR KEWEENAWAN AGE BASALTS OF POLK PALEOMAGNETIC PARAMETERS WISCONSIN* COUNTY. COUNTY, WISCONSIN* ........................................................... DIRECTION DIRECTION INC. DEC. INC. DEC . K A95 A95 LAT.. LAT V.G.P. V.G.P. LONG. LONG. POL POL 47 .2 288.lk 175.0 17.7 66.4 114.8 -61.0 15.2 29.7 N 85.1 S 183.0 E 316.0 E N R ** 34.9 288.6 1332 2.5 26.5 N 181.2 E N parameter; A95 radius of Symbols; K precision parameter; A95 -- radius of Symbols: K -- precision virtual geographic confidence; confidence; V.G.P. V.G.P. -- virtual geographic pole pole position; position; POL POL magnetization; RR -normal, north seeking polarity; polarity; NN -- normal, seeking magnetization; reverse, reverse, south south seeking seeking magnetization. magnetization. * * Corrected Corrected for geologic dip based on on a flow-top flow-top average average 45.427N, measurement of measurement of NN 23W, 23W, 21W. 21W. Mean Mean site site latitude latitude == 45.427N, longitude = 92.611W. longitude = 92.611W. mean value. **Portage **portage Lake Lake- Volcanic Group Group mean value. REFERENCE REFERENCE Halls, Halls, H.C., H.C., and and Pesonen, Pesonen, L.J., L.J., 1982, 1982, Paleomagnetism Paleomagnetism of Keweenawan Keweenawan rocks: rocks: Geological Geological Society Society of America America Memoir Memoir 156, 173-200. 156, pp. pp. 173-200. 23 �U I GEOLOGY GEOLOGY AND MINERALIZATION IN THE DUNKA ROAD COPPER-NICKEL MINERAL MINERAL DEPOSIT DEPOSIT COPPER-NICKEL COUNTY, MINNESOTA MINNESOTA ST. LOUIS COUNTY, Stephen Geerts Stephen D. Geerts Resources Research Research Institute, Institute, Natural Resources University of of Minnesota, Minnesota, Duluth Duluth The The Dunka Dunka Road Cu-Ni Cu-Ni deposit located within within the deposit is is located the Partridge River Partridge River Intrusion Intrusion (T. (T. 60 60 W., P. R. 13 W.) is part part W.) which is of the Duluth b.y. of the Duluth Complex, Complex, and is approximately is approximately 1.1 1.1 b.y. (Keweenawan) (Keweenawan) in in age age (Figure (Figure 1). 1). Relogging of 46 46 drill drill holes holes at at the Road Cu-Ni Cu-Ni deposit four major major the Dunka Dunka Road deposit identified identified four lithologic units and several internal internal ultramafic ultramafic subunits subunits that lithologic can be be correlated correlated over over two two miles. miles. ultramafic subunits subunits The ultramafic (layers of picrite to peridotite), peridotite), exhibit exhibit relative relative uniform uniform thicknesses and are are present thicknesses and present at the the same same relative relative position position within the within the major major lithologic lithologic units. units. The The major lithologic lithologic units units are the same same as as delineated delineated by by Severson Severson and and Hauck Hauck (1990), (1990), and and upward from upward from the the basal basal contact contact are: are: Unit Unit I, I, a fine— fine- to to coarse— coarsetroctolite (450 grained sulfide-bearing sulfide-bearing troctolite troctolite to pyroxene troctolite (450 ft. thick) with associated ultramafic layers 1(a), I(a), 1(b), I(b), and and Unit I(c); Unit II, 11, a mediummedium- to to coarse-grained coarse-grained troctolite troctolite to to 1(c); pyroxene troctolite troctolite (200 (200 ft. ft. thick) with aa basal basal ultramafic ultramafic Unit 111, III, aa fine-grained, layer 11(a); I1 (a); Unit fine-grained, mottled textured mottled textured troctolitic anorthosite to to anorthositic anorthositic troctolite troctolite (150 (150 ft. ft. thick) with one one minor minor ultramafic ultramafic layer layer 111(a); III(a); and and Unit Unit IV, IV, aa coarse—grained troctolite/pyroxene troctolite to anorthositic coarse-grained troctolite with associated associated ultramafic ultramafic layers layers IV(a) IV(a) and and IV(b) IV(b) (Figure 2). (Figure 2) . Most sulfide sulfide mineralization mineralization occurs occurs within within Unit Unit I. I. Within Within the sulfide Unit I sulfide mineralization mineralization is both both widespread widespread but but Unit I variable 5 % ) , continuity and and variable in in modal modal percentage percentage (rare to 5%), thickness (few thickness (few inches inches to to tens tens of of feet). feet). Sulfide Sulfide mineralization mineralization is generally related with proximity to: to: hornfels hornfels inclusions, inclusions, basal contact with the footwall footwall Virginia Formation, and some of the the internal internal ultramafic ultramafic layers layers within within Unit Unit I. I. Primary Primary sulfide mineralization mineralization includes includes pyrrhotite, pyrrhotite, chalcopyrite chalcopyrite and and pentlandite. pentlandite. Minor amounts amounts of of cubanite, cubanite, bornite, bornite, talnakhite talnakhite been identified and niackinawite/valleriite mackinawite/valleriite have have also also been identified in and in preliminary petrographic observations. preliminary petrographic observations. Precious metal metal Precious mineralization (Pd+Pt+Au) subtle fracturing fracturing mineralization (Pd+Pt+Au) is is associated associated with subtle and alteration alteration of of the the host host rocks. rocks. The alteration alteration assemblage assemblage is chlorite, chlorite, bleached bleached plagioclase, plagioclase, serpentine and and uralite. uralite. Secondary Secondary sulfide sulfide mineralization mineralization occurring occurring as as trace trace amounts amounts of bornite, bornite, is is present present in in these these fractured fractured and and altered altered zones. zones. values range range from from 100 to >2400 Pd+Pt values >2400 ppb over over 10 10 foot foot intervals. intervals. These intervals intervals can can occur occur independently independently as as 10 10 to to as zones, or part of a larger correlatable correlatable 50 foot zones, or as part of a larger foot 50 investigated occurrence/horizon. Two Two mineralized mineralized subareas subareas were investigated 24 �U within the 1) an area which the Dunka Dunka Road Road deposit deposit and and are: are: 1) which is is perforal to aa highly perforal highly anomalous anomalous Pd Pd occurrence occurrence (reported by Morton and 1987; 1989) 1989) herein termed the and Hauck, Hauckl 1987; the usouthwest llsouthwest area", and 2) the the Itnortheast "northeast areatt area" which which contains contains several several drill drill area1l1 holes that that have have near—surface 1% Cu. There are holes near-surface intercepts intercepts of of >> 1% Cu. There are four somewhat large mineralized occurrences occurrences within within the the study study area that area that carry carry >300 >300 ppb ppb combined combined total total Pt+Pd+Au. Pt+Pd+Au. These These mineralized stratigraphically controlled mineralized zones zones appear appear to to be stratigraphically controlled by by Unit I. Three of the ultramafic subunits I. the four ultramafic subunits within within Unit Three of four correlatable zones are found within within the southwest area, correlatable areal and range from range from 40 40 to to 130 130 feet feet thick. thick. High Pd values within these these zones thick with values values of of 800 800 to to 1650 1650 zones range range from from 10 10 to to 20 20 feet feet thick ppb Pd. Pd. In the northeast northeast area, areal the fourth fourth mineralized mineralized zone zone ppb appears continuously I. This This zone zone ranges ranges from from continuously throughout throughout Unit Unit I. appears 120 120 to to 300 300 feet feet thick. thick. High Pd values within this zone zone range range from 10 to 40 40 feet feet thick thick with with values values of of 800 800 to to 1500 1500 ppb ppb Pd. Pd. 30 foot intersections > l ppm ppm Pd+Pt+Au Pd+Pt+Au occur occur Many 5 to intersections of Many 5 to 30 of >1 throughout throughout the the mineral mineral deposit. deposit. References: References: Morton, P., P S Iand and Hauck, Hauckl S. S. A., A - 1987, 19871 PGE, PGEl Au and Ag contents contents of of Mortonl Cu—Ni sulfides found at the base of Cu-Ni of the the Duluth Duluth Complex, Complexl Minnesota: northeastern Minnesota: Natural Resources Research northeastern Natural Resources Research Institute, Institute, Technical Technical Report Report NRRI/GMIN-TR-87-04, NRRI/GMIN-TR-87-041 85 85 pp. pp. Norton, P., and Hauck, F. Hauckl S. S. A., A. 1989, 198g1 Precious metals in in the the Mortonl copper-nickel deposits copper-nickel deposits of of the the Duluth Duluth Complex: Complex: Minn. Minn. Geol. Geol. Survey, pp. 47-48. 47-48. Survey, Inf. Inf. Circ. Circ. 30, 30, pp. Severson, Hauck, SS. A., 1990 1990, Geologyl Geology, geochemistryl geochemistry, J. and Hauckl . A. Severson! M. J., and stratigraphy stratigraphy of of a portion portion of of the the Partridge Partridge River River Intrusion, northeastern Minnesota: Natural Intrusionl Minnesota: Natural Resources Resources Research Institute, Report, NRRIIGMIN-TR-89-lll NRRI/GMIN-TR-89-ll, Research Institutel Technical Technical Reportl Duluth, Minnesota, Duluthl Minnesotal 240 240 pp. pp. CENEFAHZED GIHEOUS LEGEND LEGEND STGATIGPAPHC QLUMN PP II ppHr R TRIAGE RIVER Cl—NI_DRpoCp_____ SVUb> DM10) DUNKA ROAD — OP VIrtEDD — EL ID [Co •YIIAN CREEK - CECTION 17 — 17 L[VIUCAR — 1K LONCUODE - - - 1 LTNT !V Ur-i!T IS UNIT H GO [DIE> 1RVTI_DEAOjO 1PS1S_ CC lION AS K1UD P 11)01 1110) SN 21? UNI I SE VA> INIA FORMATION LUIVvAR!F U ID KM 25 IRON—FOFLL>TIOH I �U TRIDYMITE, OTHER S102 MINERALS AND AND THE PIT TRIDYMITEl S102 MINERALS P / l TRAJECTORY TRAJECTORY OF KEWEENAWAN KEWEENAWAN LAVAS, iAVASl MINNESOTA MINNESOTA Duluth, MN C.Green, Green!Geology GeologyDepartment, Department! University University of of Minnesota, Minnesota! Duluth, Quhth, Duluth, MN John C. 55812 5Ml2 have Four beta and Four Si02 SiQ2 minerals minerals (cristobalite, (cristobalite, tridymite, tridymite, beta and alpha alpha quartz) quartz) have at the North crystallized at one crystallized at one stage stage or or another another in in rhyolites rhyolites of North Shore Shore Volcanic Volcanic Group. Group. Whereas cristobalite is known known only only from from occasional, occasional, hemispherical hemispherical quartz quartz paramorphs paramorphs inin vesicles (metastable, pneumatolytic), and and perhaps perhaps in in spherulitesl spherulites, tridymite tridymite was was the silica (metastable! pneumatolytic), silica is indicated mineral mineral stable stable during during flow flow and andcrystallization crystallization of most most rhyolites. rhyolites. This This is indicated particularly by the the near particularly by near ubiquity ubiquity of of flow flow structure structure formed formed by by quartz quartz paramorphs paramorphs after after (Many of the lavas had previously started to crystallize beta quartz platy tridymite. tridymite. (Many of lavas had previously started to crystallize beta quartz now present now present as phenocrysts phenocrysts -- at higher higher P P in in deeper deeper chambers chambers within within the the crust.) crust.) Aphyric Aphyric rhyolites ponded and also crystallized tridymite (+ feldspar) at the surface, rhyolites ponded and crystallized tridymite (+ feldspar) surfacel without without flow flow structure. 870 degrees degrees C, Cllate-crystallizing late-crystallizingdomains domains crystallized crystallized betabetastructure. On cooling past past 870 573 degrees, the beta quartz (+ tsp) fsp) to to the thesolidus. solidus. Below Below 573 degrees, the beta quartz quartz inverted inverted to to alpha alpha quartz in probably deposited deposited in and some some hydrothermal/pneumatolytic hydrothermal1pneumatolytic quartz quartz was was probably quartz, and re-warming depth and and re-warming burial to Upon openings. Upon later later burial to several several kilometers' kilometers' depth (hydrothermallburial "metamorphism"),the the metastable metastabletridymite tridymite plates plates inverted inverted to alpha (hydrothermalhurial "metarnorphi~rn'~), alpha porphyritic rhyolites, rhyolites,this this nucleated nucleatedon on the the quartz quartz phenocrysts to give give aa In porphyritic quartz. quartz. In phenocrysts to remarkable poiki litic ("snowflake") poikilitic (!'snowflake1') texture. texture. The widespread crystallizationofof tridymite tridymite is is unusual, though noted in The widespread primary primary crystallization unusual, though in around the the world, certain rhyolites rhyolites around world, and and implies implies anomalously anomalously high high temperatures temperatures of of certain eruption. eruption. T°C 0 400 ROO 1200 1200 2 B Kb High Quartz Low Quartz A 26 1600 1600 I I �Transpostion Transpostion structures structures in in deformed deformed rock, rock, with with examples examples from from the the Appalachians Appalachians and and Upper Upper Michigan Michigan William Mi 1 1 iam (Dept. J. Gregg Weqq (Dept. of of Geological Geological Engineering, Engineering, J. Michigan PI1 49931) 49931) Michigan Technological University, University, Houghton, Houghton, MI The term 'transposition' 'transposition9 has h a s come c o m e into into wide wide usage usage in in published descriptions descriptions of of deformed rocks. Unfortunately there t h e r e has h a s been little little consistency consistency in in its i t s application, and and the t h e term has h a s been inappropriately inappropriately applied applied to t o aa wide wide variety variety of structures, structures9 including including slaty slaty cleavage cleavage (Burger (Burger 1982), 1982), crenulation 1961) and schistosity crenulation cleavage cleavage (Rickard tRickard 19611 (Whitten 1966), in in situations where these (Whitten 1966) t h e s e foliations foliations either either render a pre—existing pre-existing foliation f 01 iation obscure, obscurev or when they form domain boundaries boundaries between between rotated rotated segments segments of of an an earlier earlier foliation. foliation. This T h i s broad broad usage usage of of the t h e term to t o indicate indicate any any sort of realignment realignment of o+ aa layering layering has h a s resulted resulted in in much confusion, confusion, and many many rocks r o c k s that that are a r e truly truly transposed transposed have have remained This T h i s confusion confusion remained unrecognized unrecognized as a 5such suchto t othis t h i sday.. day. stems s t e m s largely 1 argel y from from aa mistranslation mi stranslation of of Sanders Sanders (1911) (191 1) work by Knopf in which which illustrations i 1 lustrations of of transposition Knopf (1931) (1931 1 in with crenulation were were perhaps perhaps inadvertently inadvertent1 y switched with crenul ation . cleavage. c 1eavage As 6s Sander pointed out, out, transposition transposition (Umfaltung) (Umfaltung) is is aa mechanical mechanical process that that produces lenticular lenticular elements elements from aa previous previous layering. layering. The T h e elements elements are a r e produced produced by by isoclinal isoclinal folding of of competent layers, followed by boudinage of layers, of the the layers alonq the t h e fold axial axial surface surface in in aa direction direction normal normal layers along to t o the t h e fold axes. axes. A new new foliation foliation need need not not be b e present present in in the t h e transposed transposed layer layer itself itsel+ and and as a s Sander Sander stated stated "the "the only original are original S S layers layers are a r e still still present, present, but but are only misoriented misoriented by by small small particulate particulate displacements". displacements11- Sander Sander never never used used the t h e misnomer misnomer "Umfaltungsclivage" "Um+altungscl ivage" as a s quoted quoted by others others (Knopf (Knopf 1931, 1 9 3 1 9 p. p. 16), and was w a s careful careful to t o point point out out that "cases "cases of true t r u e cleavage cleavage can can be be defined defined when when aa new new S S cuts c u t s an an older older one" one" whereas whereas in in transposition transposition the t h e early early S S surface "is but not not however however cut by a new "is indeed indeed transposed transposed but new . S.'. Sns Studies Studies of of transposed transposed layering layering from from the t h e Northern Northern Appalachians and Upper Michigan Michigan show s h o w that that transposition transposition usually usual1 y develops develops only on1 y in in rocks r o c k s that that have have aa mechanical mechanical anisotropy in Although in the t h e internal internal layering. Although an a n entire entire rock rock unit unit is is sometimes sometimes described described as a s transposed, transposed, it it is is actually only the t h e compentent compentent layers layers within within the t h e unit unit that that show around the s h o w this t h i s type t y p e of of deformation. deformation- The T h e matrix the competent b e characterized characterized by a high high cornpeten< layers layers may may instead instead be strain as. schistosity schistosi t y or o r pinstripe pinstripe layering. layeringstrain foliation foliation such s u c h as Transposed Transposed layering layering usually usually is is recognized recognized by the the presence presence of features f e a t u r e s such such as a s rootless rootless isoclinal isoclinal fold fold hooks hooks and lensoid lensoid remnants remnants of af fold -Fald limbs limbs (Williams (Williams 1967). These These structures structures may may represent represent the t h e dismembered portions portions of of bedding, bedding, although although thick thick secondary secondary layers layers may also also be be transposed. transposi t i on of transposed. The T h e transposition af quartz quartz veins vei n s in in pelitic pel i ti c rocks r o c k s is is extremely common, common, resulting resulting in in white white quartz quartz lenses lenses and and in in quartz—rich quartz-rich rod rod structures structures that that parallel parallel the t h e axes a x e s of of 27 �U DEVELOPMENT OF TRANSPOSED LAYERING tectonic 'pebbles" a I lensoid remnants of fold limbs (in matrix) isolated fold hooks augen (In gneiss) rods (from veins) GREGG- 1990 1 "Whorl" structures "Whorl" s t r u c t u r e s in i n transposed t r a n s p o s e d "Springfield " S p r i n g f i e l d Conglomerate" C~nglomerate~~ from C Central Vermont. Specimen, e n t r a l Vermont. Specimen, from from type t y p e locality, l o c a l i t y , is i s aa cchloritized, h l o r i t i z e d , sulfide—rich s u l f i d e - r i c h mafic mafie rock. rock. Some types 'button' of es a+ 'button' earlier iisoclinal soclinal ffolds.. aldsearlier observed in phyllites l l ite5 may a1 SO structure 1972) may also s t r u c t u r e (Roper (Roper 1972) obser\f represent interfolial segments.. Archean rocks represent inter-+01 ia1 transposed trans m k s * IIn n Rrchean rocks transposition @ for -For the t h e development development t r a n s p o s i t i o n is i s frequently + r e q u e n t l y responsible of augen example iin of auqen structure. s t r u c t u r e 3 ff aor r exa n tthe h e Watersmeet gneisses Green in i n Upper Michigan and in i n numerous nu us examples examples from +ram the the Green Mountains h e &dircmdacksMountains and and tthe Adirondacks the the 28 - �U When flattening Uhen + l a t t e n i n g strains s t r a i n s are a r e extremely extremely high, high, isoclinal isoclinal hooks may may be be ddifficult observe, and tthe f+o old l d hooks i f f i c u l t tto o observe, h e rock rock may may off a pseudo—conglomerate (Ramsay take t a k e on the t h e appearance o a pseudo-conglomerate (Ramsay 1956). AA number o off cases e exist transposed in 1955). x i s t where transposed rocks rocks in high zones been significant have rregionally egionally significant h i g h strain strain zones have been misidentified m i s i d e n t i f i e d as as sedimentary sedimentary units, units, ffor or example tthe he Conglomerate and Paleozoic Hill Springfield Paleozoic Dry Hill Conglomerate and Springfield Dry Conclomerate units u n i t s in i n south—central s o u t h - c e n t r a l Vermont. Vermont. severely transposed rrocks may IIn n s e v e r e l y transpos@d ocks iisolated s o l a t e d fold f o l d hooks hooks may form whorl—structures off in w h o r l - s t r u c t u r e s that t h a t show evidence o rrotations otations i n These structures foliation. indicate tthe h e plane p l a n e of of foliationThese structures i n d i c a t e high high seems vorticity seems tto o be be llittle i t t l e v o r t i c i t y in i n transposed transposed zones zones which structures evidenced in i n less l e s s transposed transposed fabrics.. f a b r i c s . The whorl structures delamination eventually severe and internal d elamination and internal eventually s uf f e r suffer disruption d i s r u p t i o n as as strain s t r a i n progresses. progresses- REFERENCES R EFERENCES Solution Burger, R. and bedding Burger, R. H. S o l u t i o n cleavage cleavage and bedding H.,, 1982, Borradaile, transposition": 6. and J. , t r a n s p o 5 i t i o n " : in i nBayly, Bayly, B. B-M.M.,, Borradaile, G. J., and Atlas of Deformational and C. McA., eds., Powell, C. McA., eds., f3tlas of Deformational and Metamorphic p. 330—331. 330-331. Metamcrphic Rock Fabrics, F a b r i c s , Springer S p r i n q e r Verlag, Verlag, p. Retrogressive Knopf,, E. metamorphism Knopf B. , 1931, R etrogressive metamorphism B., phyllonitization: p h y l l o n i t i z a t i o n : Amer. fimer. jour. JOUP.Sci., Sci., v.21, v.21, p. p. 1—27. 1-27. and and Ramsay, 3. Ramsay, J. 6, G, 1956, 1956, The The supposed 5upposed Moinan Moinan basal basal conglomerate conglomerate at a t Glen S t r a t h f a r r a r , Inverness—shire: Inverness-shire: Geol. Mag. ,, v. Glen Strathfarrar, Geol Mag. v. 93, p. 32-40p. 32—40. . Rickard, M. M. 3.., J., 1961, 19~51, A note n o t e on on cleavages cleavages rock: Geol. v.98, p. rock: Mag., p - 324—332. 324-332. Geol. Mag.., v.98, iin n c renulated crenulated Roper, P. P. 3., J. , 1972, 1972, Structural S t r u c t u r a l significance s i g n i f i c a n c e of o f "button" " b u t t o n " and and Roper, " f i s h scale" scale'' texture t e x t u r e in i n phyllonitic p h y l l o n i t i c schist s c h i s t of of t h e Brevard Brevard "fish the Soc. Amer. Amer. B ull. , Zone, South Carolina: Carolina: Geol. f h o l Soc. Zone, Northwestern Northwestern South Bull., v. p. 853—860. 853-860. v. 83, 83, p. . %,. 1911, Uber Zusammenhange Zusammenhanqe zwischen Teilbewegung Sander, B,. Sander, 1911, Gefuge in i n Gesteinen: Gesteinen: Tscher.. Tscher- flIn. P e t r . Mitt., Mitt., v. 38, und Gefuge Mm. Petr. v. p. 281-317. p. 281—317. E. H. H. T., Structural Whitten, E. Whitten, T., 1966, Structural Rocks, Chicago, Rand McNally, 663 p. p. Chicago, Rand McNally, 663 Rocks, Geology W i l l i a m s , P. P. F - , 1967, tructural h a l y s i s of of Williams, F.,, 1967, SStructural Analysis Broken Hill area of New South Wales: H i l l area of South Wales: Jour. New Broken Jour. A u s t r a l i a , v. v. 14, p. p. 317-332.. 317-332. Australia, 29 o off Folded Folded tthe he L ittle Little Geol. Soc. �U GEOLOGY OF WRIGHT GEOIiOGY WRIGHT COUNTY COUNTY USING LOG DATA DATA USING WELL WEll LOG by Mark J. Hayes and Dr. Charles L. Nelson Department University Department of of Earth Sciences, Sciences, St. Cloud State State University Wright County County well well logs logs were were used to to map bedrock types, types, bedrock elevaelevations, tions, possible possible faults, faults, including including aa previously previouslyuninapped unmapped major major fault fault trending trending southwest-northeast through Wright Wright County County and and a a possible possible explanation for the southwest-northeast positioning of of the the Mississippi Mississippi River River Channel. Channel. Glacial sediments sediments were also also mapped using well logs to give a more precise placement of the St. Croix mapped, Moraine, and a repositioning of the mapped path of the Grantsburg Grantshurg Sublobe Subiobe of Moraine, the the Des Dcs Moines Moines ice ice sheet. sheet. well logs were were used out Three thousand Minnesota Department of Health well of 5000 available available for for Wright Wright County. County. The remaining remaining 2000 2000 logs logs of a total total of of 5000 reasons including incomplete or inaccurate locawere rejected for various reasons localocation (Towntion tion and and strata strata files. files. Each log log had the the following following format: format: location ship—Range—Section),, strata, bedrock ship-~an~e-~ection) strata, and and strata strata thickness. thickness. Sediments Sediments and bedrock types were cataloged into standardized formations, e.g. sandy—clay formations, e.g. sandy-clay and clay— clayStandardization was necessary beboth classified sand were both classified as as clay—sand. clay-sand. Standardization Strata color was also cause percent composition composition of of strata strata was was rarely rarely given. given. Strata color was also light—green, green, green, and and dark dark green green were were standardized so that, for example, light-green, all all classed classed as as green. green. own- It should be noted that well well drillers are not geologists; geologists; however, however, they do know gravel, etc., know the differences between sand and shale, shale, clay and gravel, etc., and differences differences in in color. color. Township—range locations locations were were transformed into rectilinear rectilinear coordinates Township-range coordinates three—dimensional characterisZ-attribute. For numerical data with three-dimensional characteriswith aa Z—attribute. "SURFER" (Golden olden Graphics Graphics tics map file wasgenerated generated using program a map file was using thethe program "SURFER'T tics a file was The file was then thenconverted converted into intoa aGeographic Geographic Information Information Software, Inc.).) . The Software, Inc. System attribute file compatible with "EPPL—I" "EPPL-7"(a(aGIS GISprogram program developed developed by by System attribute file compatible with Management Information the Land Management Information Center, Center, Minnesota Minnesota State State Planning Planning Agency). ~~enc~). the Non—numerical attribute data was mapped using a Thiessen Polygon Polygon Method Non-numerical attribute Department, St. Cloud developed developed by by Dr. Dr. Charles L. Nelson, Earth Sciences Department, State State University. University. Bedrock maps show from just east of the city of Cokato show a curved trend from to to southwest southwest of of Monticello. Monticello. Along this fault are several several series series of of lakes lakes and other Disother topographic topographic features features which which seem seem to to indicate indicate bedrock bedrock control. control. Displacement along along the the fault fault is is unknown. unknown. Bedrock Bedrock elevations elevations are are highest highest in in north—northwestern margin the north-northwestern margin of of the the county. county. An irregular irregular bedrock bedrock ridge ridge extends to to the the east—southeast. east-southeast. The The ridge ridge is is breeched breeched by by several several swales. swales. On the southern southern margin of of the the ridge ridge are are several several semi—enclosed semi-enclosed depressions. depressions. A wide wide low—relief low-relief buried buried valley valley trends trends south south from from the the center center of of the the county. county. level Wright County is covered by At an an elevation of 900 900 feet feet above sea level sediments with with an isolated sandstone deposit near near the MissisMissisunconsolidated sediments 850 feet feet isolated isolated pockets of of sippi sippi River River near near the the village village of of Otsego. Otsego. At 850 30 �U sandstone sandstone and red red granites granites occur occur along along the the river. river. Patches Patches of of shale shale cover cover unconsolidated sediments both unconsolidated sediments and and sandstone sandstone in in aa northwest northwest to to southeastern southeastern trend. unconsolidated sediments trend. Beneath unconsolidated sediments in in the the northwestern northwestern corner corner at at 800 800 feet feet an an area area of of about about 10 10 square square miles miles of of sandstone sandstone exists. exists. A nearly nearly equal equal area area of of sandstone sandstone also also exists exists on on the the far far eastern eastern side side of of the the county. county. AA larger 7 5 0 foot foot larger region region of of shales shales occur occur in in the the center center of of the the county. county. At the the 150 elevation 800 foot foot level level shales. shales. Cretaceous Cretaceous shales shales elevation sandstone sandstone underlies underlies the the 800 covers covers the the southwestern southwestern quarter. quarter. An An arcuate arcuate band band of of sandstones sandstones cuts cuts through through the T O O feet feet above above sea sea level level grey grey granite granite the eastern eastern part part of of the the county. county. At At 100 appears appears in in the the west west central central part part of of the the county. county. Along Along the the river river red red granites granites are are interspersed interspersed with with sandstones sandstones and and shales. shales. Shales Shales covcr cover the the central central secsection tion with with sandstones sandstones and and unconsolidated unconsolidated sediments sediments occurring occurring in in the the southeast. southeast. A five five mile mile wide wide band of of sandstone sandstone surrounding surrounding red granites granites parallels the river river at at 650 650 feet. feet. The The southeast southeast quarter quarter is is also also sandstone. sandstone. Shales Shales and and unconsolidated unconsolidated sediments sediments separate separate the the two two sandstone sandstone bodies. bodies. Granites Granites occupy occupy the the western western one—third one-third of of the the county. county. There north— There are are four four bedrock valleys, valleys, trending south—southwest south-southwest to northnortheast northeast near near the the cities cities of of Annandale, Annandale, Clearwater, Clearwater, Silver Silver Creek, Creek, and Monticello. cello. The The Mississippi Mississippi River appears appears to to be constrained constrained at at present by a series series of small small buried red red granite granite bedrock bedrock highs highs on on the the south south side side of of the the river. river. The The river river was possibly possibly kept kept to to the north north of of the bedrock highs by Grantsburg Sublobe meltwater and sediments, sediments, flowing flowing through through the aforemenaforemenGrantsburg Sublobe tioned glacial tioned valleys. valleys. The The Clearwater channel channel is is apparent apparent even in in the glacial sediments sediments at at the the surface. surface. It It is is the the widest widest of of the the bedrock bedrock channels channels with with aa maximum maximum width width of of one one and and aa half half miles. miles. Several Several narrower narrower and and shorter shorter but but deeper deeper channels channels extend extend northward northward to to the the Mississippi Mississippi River, River, past past the the towns towns of of Maple Maple Lake, Lake, Silver Silver Creek Creek and and Hasty. Hasty. Several Several long long surface surface channels channels eroded into into glacial glacial sediments sediments trend northward ward through through morainic morainic hills. hills. Some Some of of these these channels channels are are superimposed superimposed above above buried buried bedrock bedrock channels. channels. One One channel channel may may be be aa glacial glacial tunnel tunnel valley. valley. The The slope slope of of the the floor floor is is not consistent, consistent, a drainage drainage divide divide exists exists midway along along the the valley, valley, there there are are also also several several enclosed enclosed depressions. depressions. Water Water flowing flowing through through aa glacial glacial tunnel tunnel is is capable capable of of undulating undulating up up and and down down slopes. slopes. The surface surface of of the the northern northern half half of of Wright County County is is St. St. Croix The ~ r o i xend end moThe hills hills are are composed composed of of thick thick deposits deposits of of very very red red clay. clay. They They The trend trend from from the the northwest northwest to to the the southeast. southeast. Deposition Deposition thickness thickness can can exceed exceed 200 200 feet. feet. The The end moraine moraine is is located located on on the the southern southern flank flank of of the the bedrock high. preexisting glahigh. The The central central part of of the the county county consists consists of of reworked reworked preexisting cial cial sediments sediments and and Des Des Moines Moines Lobe Lobe tills. tills. An An eight eight mile mile long long esker esker meanders meanders across across Des Des Moines Moines ground ground moraine moraine in in the the east—central east-central part part of of the the county county from from Pelican Pelican Lake Lake southward southward to to the the Crow Crow River River valley. valley. Des Des Moines Moines tills tills cover cover the the southern southern portion portion of of the the county. county. There There is is little little or or no no correlation correlation between between the the deposition deposition of of Des Des Moines Moines tills tills and and bedrock bedrock topography. topography. There There is is some some correlation correlation between between Des Des Moines Moines outwash outwash and and bedrock bedrock topography. topography. raine. raine. From high high resolution resolution mapping of of bedrock bedrock elevations elevations and and detailed detailed analysis analysis From of Moraine, the path of the Grantsburg of glacial glacial sediments sediments of of the St. Croix End Moraine, Sublobe Sublobe of of the Des Des Moines ice sheet sheet is farther farther to the east than mapped by earlier earlier investigators. investigators. 31 �STRUCTURAL ANALYSIS ANALYSIS OF ARCHEAN ARC TASEDIMENTARY STRUCTURAL METASEDIMENTARY ROCKS IN VICINITY OF THE MINERAL HILL GOLD ROCKS IN THE VICINITY GOLD MINE, MINE, MONTANA JARDINE, MONTANA Joseph D. D. Jabiinski Jablinski and and Timothy Timothy B. B. Hoist Hoist Joseph Department of Geology, University University of of Minnesota, Minnesota, Duluth Duluth Department of Geology, Duluth, Minnesota Minnesota 55812 55812 John John Cuthill American American Copper Copper and and Nickel Nickel Company, Company, Inc. Inc. 4860 Robb Robb St., St., Wheat Wheat Ridge, Ridge, Colorado Colorado 80033 80033 David David C. C. Oliver Oliver Mineral Mineral Hill Mine Mine P. 0. 0.Box Box 92 92 Gardiner, Montana Montana 59030 59030 Jardine Jardine is is located located along along the the western western margin margin of the the Beartooth Beartooth Mountains Mountains in in Placer Placer gold gold was was discovered discovered in in the the Jardine Jardine region in in southwestern southwestern Montana. Montana. 1866, and by Precambrian lode gold 1880Ts, Precambrian iron iron formation-hosted formation-hosted lode gold was was 1866, and by the the mid mid1880's, being the Jardine being mined mined on on Mineral Mineral Hill. Hill. In In 1984, 1984, the Jardine Joint Joint Venture Venture was was formed formed between between American American Copper Copper and and Nickel Nickel Company Company (ACNC) (ACNC) and and Homestake Homestake Mining Mining Company, Company, with with ACNC ACNC acting acting as as the operating operating partner. partner. Renewed surface surface and and Renewed underground exploration by by ACNC underground exploration ACNC has shown shown Mineral Mineral Hill Hill to have have a probable probable ore reserve reserve of 1.0 1.0 million million tons tons at aa grade grade of of 0.3 0.3 ounces ounces of of gold gold per perton. ton. The The bedrock geology geology of the the Jardine Jardine area area consists consists predominantly of Archean Archean metasedimentary metasedimentary rocks rocks which which were were intruded intruded by by granitic granitic stocks stocks and and minor minor mafic mafic dikes dikes and and sills. sills. Greywacke Greywacke and and mudstone mudstone sequences, sequences, which which were were deposited deposited by by turbidity turbidity currents, currents, have have been been regionally regionally metamorphosed metamorphosed to to quartz-biotite schist schist and and biotite schist, schist, respectively. respectively. The original original thickness thickness of of the the sedimentary sedimentary pile pile is is unknown, unknown, and and a diamond diamond drill drill hole hole on on Mineral Mineral Hill, Hill, which to aa depth which was was drilled drilled to depth of of over over 2000 2000 ft., ft., failed failed to intercept intercept the the basement basement to to these The thickness these sediments. sediments. thickness of of the the sedimentary sedimentary pile pile has has probably probably been been exaggerated exaggerated by by tectonic tectonic thickening thickening during during isoclinal, isoclinal, recumbent folding. The The monotonous nature of monotonous nature of this this thick thick pile of metasedimentary metasedimentary rocks rocks is is interrupted interrupted by by aa silicate silicate facies facies iron iron formation formation which which acts acts as the the only onlystratigraphic stratigraphic marker marker horizon ItIt is horizon in in the Jardine Jardine region. region. is this this iron iron formation formation and and proximal proximal schists schists which which host host the the gold gold mineralization. Calculations Calculations from from microprobe microprobe analyses analyses of coexisting coexisting biotite biotite and and staurolite staurolite in in an an aluminum aluminum silicate-rich silicate-rich sample, sample, show show that that peak peak metamorphism metamorphism occurred occurred at 2.9 kb at a pressure pressure and and temperature temperature of of approximately approximately 2.9 kb and and 560° 560' C,C,respectively. respectively. Evidence Evidence for for three three generations generations of of Precambrian folding folding has has been been recognized recognized in in the the Archean Archean metasedimentary metasedimentary rocks rocks of the the Jardine Jardine region. region. During (Fi), isoclinal, isoclinal, recumbent recumbent folds folds were were formed. formed. During the the earliest earliest fold fold phase phase (F1), A A foliation foliation plane, plane, S1. Si, defined defined by by the the growth growth and and preferred preferred orientation orientation of of was created micaceous minerals, during the F1 fold event and is observable micaceous minerals, was created during the Fl fold event and is observable throughout throughout all all rock rock types types in in the the region. region. The The orientation orientation of this this schistosity schistosity isis along texturallyalong or o r nearly nearly parallel to to the the original original compositionallycompositionally- and and texturallydefined defined bedding bedding planes. planes. Si S l surfaces surfaces were were subsequently subsequently crenulated during during the the second and F3 F3 fold fold axial axial surfaces surfaces are are upright upright second (F2) (F2) and and third third (F3) (F3)fold foldevents. events. F2 and and and at at a high high angle angle to to F1 F I fold fold axial axial surfaces surfaces and and to to each each other. other. 32 8 2 and and S3 S3 S2 �U cleavages of of S1. foliations are axial planar planar crenulation crenulation cleavages S l . This zonal zonal crenulation crenulation axial planar by the cleavage (Marshak cleavage (Marshak and and Mitra, Mitra, 1988) 1988) is defined defined by the axial planar alignment alignment of of microfold hinges (symmetric (symmetric zonal crenulation cleavage) and/or domains of reoriented reoriented micas micas (asymmetric (asymmetric zonal zonal crenulation crenulation cleavage) cleavage) and and is is not the result of micaceous of recrystallization of micaceous minerals in the microfold hinges. Linear structures found predominantly structures are are found predominantly in biotite schist because of its rheology and and the the nature nature of ofthe thedeformations. deformations. L2 L2 and and L3 L3 lineations are are the intersection S1i foliation of of S2 S2 and and S3 8 3 axial planar planar crenulation crenulation cleavage surfaces surfaces in the S surface. surface. F2 F2 fold fold axes axes were were the the only only minor minor fold fold lineations lineations which which were were directly directly measurable from from outcrop. The The dominant dominant fold interference pattern created by fold superposition is is a The interference of F2 1, dome Ramsay (1962), Type Ramsay Type 1, dome and and basin basin pattern. pattern. The interference of F2 and and F3 F3 history diagram The structural (see folds are responsible for this pattern. structural diagram folding (Figure below) involves early isoclinal, isoclinal, recumbent recumbent F1 F l folding (Figure IA), lA), with with later refolding by F2 refolding by F2 folds, folds, with with F2 F2 axial axial surfaces surfaces at at aa high high angle angle to to F1 F l axial surfaces surfaces to F1 (Figure F3 fold (Figure IB). 1B). F3 fold axial axial surfaces surfaces are are at at high high angles angles to F l and and F2 F2 fold fold axial axial folds. surfaces IC) and refold both sets of earlier folds. surfaces (Figure 1C) A firm understanding of this fold form is understanding is important for future future regional exploration, the highest since since it has has been been shown shown that that the highest grade grade of of gold gold mineralization mineralization occurs occurs in the the domes of the folded iron formation (John Cuthill, personal communication, 1989). communication, 1989). F, S S A C B FIGURE 1 References References and Mitra, Marshak, S., and Mitra, G., 1988, 1988, Basic Basic methods methods of of structural structural geology: Jersey, Prentice-Hall, Inc., 445 Jersey, Prentice-Hall, Inc., 445 p. p. New Ramsay, J. J. G., 1962, Interference patterns patterns produced produced by by the superposition of 1962, Interference folds of similar folds similar type: type: Journal 1. Journal of Geology, Geology, v. 70, 70,P.P.466-48 466-481. 33 �REVERSE ZONATION ZONATION IN LESTER RIVER RIVER SILL, SILL,DULUTH, DULUTH, REVERSE IN THE LESTER MINNESOTA, AND AND EVIDENCE EVIDENCE FOR FOR POLYBARIC POLYBARIC FRACTIONATION FRACTIONATION Eric Eric A. A. Jerde Jerde Department of Earth and Space Sciences, University of Department of California, California, Los Los Angeles, Angeles, CA CA 90024 The Lester Lester River River Sill Sill intrudes, intrudes, and and is is roughly roughly concordant concordant with, with, the the extrusive extrusive flows flows that that constitute the the North North Shore Shore Volcanic VolcanicGroup Group(NSVG) (NSVG)ofofKeweenawan KeweenawanAge Age(1(l.lGa). .lGa). The sill sill is one of three large sills sills found found in in the the city city of of Duluth, Duluth, Minnesota, Minnesota, the the others others being being the the Endion Endion and and Northland Northland sills, first studied by (1). Since Sincethen, then,the the425 425m mthick thickEndion EndionSill Sillhas hasbeen been the themost most intensely studied 3, 4), and the smaller (5). studied (2, (2,3,4), smaller Northland Northland Sill Sill has has also also been been investigated investigated (5). The most extensive extensive outcrop outcrop of of the the Lester Lester River River Sill Sill occurs occurs in in Duluth, Duluth, along along the the shore shore of of Lake Lake Superior, Superior, beginning beginning just north north of of the the Lester Lester River River and and continuing continuing approximately approximately1.8 1.8 km km in in KitchiKitchiGammi Garnrni Park. ItItcan canbe befollowed followedinland inlandalong alongaastrike strikeof of approximately approximately N18°E N18OE as as aa well defined ridge ridge extending extendingover over25 25km. km.The Thesill silldips dips—20° -20' to tothe thesoutheast, southeast,indicating indicatingaathickness thicknessofof—280 -280 m. m. Outcrop Outcrop along along the shore shore is is excellent, excellent, and and nearly nearly continuous, continuous, providing aa good good cross-section. cross-section. Chemical Chemical analysis analysis of of 36 36 samples samples from from the the sill sillwas wasundertaken undertakenutilizing utilizinginstrumental instrumentalneutron neutron activation analysis (INAA) and electron microprobe analysis of fused glass beads, yielding data for activation analysis (INAA) and electron microprobe analysis of fused glass beads, yielding datafor 34 34 elements. elements. This Thisparticular particularsill sillexhibits exhibitsaa"reverse" "reverse"zonation, zonation,with withthe themost mostprimitive primitivediabase diabase(i.e. (i.e. diabase mg [molar [molarMgO/(MgO+FeO)] MgO/(MgO+FeO)] and and the the lowest lowest abundance abundance of incompatible diabase with with the the highest highest mg elements and S SiO2) occurring in the central regions. The lower half (140 O2) (140 m m stratigraphically) stratigraphically) isis medium-grained, medium-grained, intergranular intergranular diabase. The The upper upper portion portion of of the the sill sill is is more more varied. Most Mostof ofititisis an ophitic diabase, with individual pyroxene pyroxene grains grains up up to to 1 cm cm across. across. Near Near the the top top of of the the sill, sill, stringers of red material become more abundant until, at the topmost part, the rock is a granophyre. stringers material become more abundant until, at the topmost part, the rock is a granophyre. In In general, general, crystallization crystallization from from the the margins margins in in large large sills sills results results in in the the most most evolved evolvedmaterial material being located in the medial portion. portion. An In An example example is is the Palisades Sill of New Jersey (e.g. 6). In the Palisades Sill, the silica content ranges from about 52% at the margins to 60% in the most silica content ranges from about 52% at the margins to 60% in the most evolved rocks, and the incompatible trace elements elements show show great great enrichment enrichment (Fig (Fig la). la). Although Although the the thickness thickness of the the Lester Lester River River Sill Sill is is less less than than that that of of the the Palisades PalisadesSill, Sill,itit isislarge largeenough enoughto toexpect expect extensive fractionation in a slowly cooling environment. The chemical trends across the sill extensive fractionation The chemical trends across the sill (Fig. (Fig. ib) lb) are are opposite opposite in in sense sense to those those trends observed observed in in the the "normal" "normal" Palisades Palisades Sill, with with the themost most 300 I.... 400 a. 250 . 300 a a 200 200 150 5 100 Lester River Palisades k • I) Sm Sm (ppm) 5° (pnn) .ll• 3 6 9 12 5 0 5 10 IS 20 25 Figure Figure 1. Samarium Samariumvariations variations across across the Palisades and and Lester River Sills. Sills, 34 30 35 40 I �U River Sill. Although primitive material in the medial portions of the Lester River Although this this facies facies represents represents the primitive primitive part part of of the the Lester Lester River River Sill, Sill, itit is is considerably considerablymore moreevolved evolved(mg (mg~O.45) 0 . 4 5 than ) the primitive olivine tholeiites tholeiltes of of the theNSVG NSVG(mg (mg20.65; O.65; [7]), [7]), or or even even the the majority majority of diabases diabases from from the the the North North Shore Shore(mg (mg~O.55). rest of the 0.55). "reverse" zoning profile seen in the Lester River Sill makes it unique among The among the the hypabyssal hypabyssal The rocks of the North North Shore. Indeed, sills in in general. general. In Antarctica, the Indeed, such profiles are rare among sills Lake Vanda Sill Sill and and Emmanuel Sheet show show similar similar trends trends (8), although these are not as Lake Vanda Emmanuel Sheet although these as Sill. In In the the Antarctic Antarctic bodies, few of the elemental concentrations pronounced as in the Lester River Sill. vary by as much as a factor of 2 across across the sifis sills (even in the incompatible incompatible elements), elements), whereas whereas in the Lester River Sill the variations 3. variations are are up to factors factors of 3. A likely process that could have produced the pattern seen seen in the Lester Lester River River Sill Sill is is some some form form of multiple intrusion. Multiple intrusion is the preferred model for the emplacement of the 425 m 4). thick Endion Sifi Sill to the south south of the the Lester Lester River River Sill Sill (3, (3,4). The Lester River Sill Sill is located between an an andesite andesite and andaa rhyolite rhyoliteof of the the NSVG. NSVG. The Lester River located between melting point of the rhyolite, temperatures of the intruding material would have been well above the melting and it is apparent from the presence of stringers and blebs of felsic material the upper portions portions of of stringers felsic material in the the sill, that extensive assimilation assimilation of of the therhyolite rhyolitetook tookplace placethere. there. In In the the profile profile of of Fig. Fig. lb, ib, this assimilation is reflected in the chemical chemical trend at the top, which describes a mixing line between the primitive diabase and the rhyolitic host rock. In the inland areas of the Lester River Sill, Sill, where rhyolite was not in contact with the diabase, diabase, there is no "red "red rock" zone, and no discernible discernible mixing mixing features. features. It is presumed that the most primitive diabase diabase of the sill was intruded first, first, since it is this material that contains the blebs and stringers of felsic rock indicating assimilation. contains stringers indicating assimilation. Further intrusion intrusion of more evolved evolved magmas magmas below below those those already alreadypresent present could couldproduce producethe theprofile profileobserved. observed. Mass-balance calculations Mass-balance calculations were undertaken in an attempt to model the generation generation of the primitive diabase in the Lester River Sill. A parent of mean primitive olivine tholeiite diabase A parent of mean primitive olivine tholeiitecomposition composition from from the the NSVG (7) was chosen for mass-balance calculations. From From this this parental parental composition, composition, successive successive increments of of fractionating assemblages were were subtracted subtracted (each (each increment increment consisted consisted of 11 wt% increments fractionating assemblages ± cpx, which form the majority of 01 + + plag k of early early solids solids solids). These These assemblages assemblages consisted of ol produced during during the crystallization crystallization of of basaltic basaltic magmas. magmas. Mineral produced Mineral compositions compositions are are calculated calculated separately separately for for each each increment. increment. In order to successfully successfully obtain compositions compositions similar similar to the more primitive primitive diabase diabase in in the the Lester Lester River Sill, the modelling indicated that the first stage of the fractionation must consist of the 33ol + phase (3A) assemblage + plag plag ++ cpx, cpx, followed followed by a stage stage of of ol 01++ plag, and a third stage stage with with 33 phase (34)) assemblage 01 phases again (Fig. 2). The implication implication of the calculations calculations is is that that at at least least two two (and (and possibly possibly more) more) separate magma chambers at differing crustal levels are required to produce the first Lester River Sill magma from the primitive olivine tholeiite. This Thisresults resultsfrom fromthe thestrong strongeffect effectof of pressure pressureon on the clinopyroxene stability field for basaltic basaltic liquids, liquids, which which shrinks shrinks with with decreasing decreasing pressure. pressure. Therefore, a magma which crystallizes crystallizes ol ++ plag ++ cpx cpx at depth and then rises to a higher, lower could be expected expected to to crystallize crystallize only only ol 01++ plag for a time at the new pressure position in the crust could location At some later time, cpx would location due to this shrinkage shrinkage of the the cpx cpx stability stability field. field. At would then then reappear as a crystallizing crystallizing phase. Magma Magmarising rising to to aa still still higher higher level level would would again again result in only ol 01 + plag crystallizing. Polybaric Polybaricfractionation fractionationsuch such as as this this has has been been used used to explain explain trends trends observed observed + in continental 9), and and has has also also been been proposed proposed for for the the origin origin of of the the compositions compositions continental flood basalts (e.g. (e.g. 9), 35 �U seen in in some someof of the theLake LakeSuperior Superiorvolcanics volcanics(10). (10). seen Additional evidence evidence for for polybaric polybaric fractionation fractionation can can be befound foundusing usingaapseudo-liquidus pseudo-liquidusphase phase Additional thisdiagram, diagram,the theprimitive primitiveolivine olivinetholeiites tholeiitesof ofthe theNSVG NSVG plot plotininaaregion region diagram (Fig. (Fig. 3). 3). InInthis diagram consistent consistent with with aamagma magmathat thatisismultiply multiplysaturated saturatedatatan anelevated elevatedpressure pressure(—10 (-10 kb). The Themost most evolved material material of of the the Lester Lester River River Sifi Sill is is seen seen to to be be consistent consistent with with multiple multiple saturation saturation at at aa evolved is intermediate, suggesting pressure considerably lower (i.e. -1 am). The primitive part of the sill pressure considerably lower (i.e. —1 atm). primitive the sill is intermediate, suggesting region between between the the two two (roughly (roughly 33kb?). kb?). aa region 22 21 21 ^ n 0'4 4 20 20 I I Silica L - o 34 0 A 18' 18 16 16 - 0( 0-0 22 l 3 3 '• lI 44 " • " ' • l 55 66 ' - t I' l. ' I . • I 7 7 8 8 9 9 • Medial Lester River Sill -A 34 3* ' 15 15 + MedIal Lester River SiR o Lester LesterR. R.center center Oe1 - o0Primitive PrimitiveOlivine OlivineThokitie Tholeiiic + Basal Lmtez River Basal 1mstcr RiverSIR Sill A Parent Parent A 1919 17 17 J Calculations Calculations 0o 1 PI'lagiuclase Ia gi oc I ase 100 Clinopyroxene in 0 pv () xcii e MgO M e 0 (%) (%) Figure Figure3.3. Pseudo-liqwdus Pseudo-liquidusphase phasediagram diagramfor forthe the Lester Lester R. R. Sill Sill and andpsimitive primitive ol. 01. tholeiites. tholeiites. Figure2. 2. Mass-balance Mass-balanceresults results for forthe the Lester Lester River River Figure Sill.Each Eachstage stageisis—25% -25% crystallization. crystallization. Sill. Intuitively, Intuitively, itit is not hard to imagine several magma chambers forming at different different levels levels in in aa rifting rifting environment environment where where fracturing fracturing is pervasive. Evidence Evidenceexists existsfor foraahigh high level levelchamber chamberbelow below the the Krafla Krafla volcanic volcanic center center in in Iceland, Iceland,deduced deduced from from studies studiesof of caldera caldera inflation inflation rates rates (11, (11,12). 12).This This chamber chamber is is presumed presumed to to be be an an upper upper crustal crustal chamber chamber filled filled from from another another one below, below, leading to to inflation and uplift of of the the caldera caldera floor. floor. After After aa period period of of time, time, the the magma magma isis injected injected into into the the surrounding surrounding area, forming numerous dikes. This Thisprocess processisisanalogous analogousto to that that suggested suggestedabove above for for the additionalevidence evidencethat that lateral lateral transport transport of of magma magma the formation formation of of the the Lester Lester River River Sifi. Sill. There Thereisisadditional along km) occurs occurs in in Iceland Iceland (13). IfIf aasimilar along the the rift rift over over moderately moderatelylarge largedistances distances(—70 (-70 km) similarprocess process occurred Midcontinent Rift, Rift, itit may may begin begin to to explain explain the the striking strikingsimilarity similarityof of compositions compositions occurred in the Midcontinent observed observed among among the the other other hypabyssal hypabyssalrocks rocksfound foundall allalong alongthe thenorth northshore shoreofofLake LakeSuperior. Superior. References References Sandberg, A.E. A.E. (1940) (1940) Geol. Soc. Soc. America America Bull Bull.,., 551,1,1135-1172. (1) Schwartz, G.M. and Sandberg, 1135-1172. (1) W.G. (1960) (1960) J. (2) Ernst, W.G. J.Petrol., Petrol., 1, 1, 286-303. 286-303. (2) (3) Oestrike, Oestrike, R.W., Jr., Jr., (1983) (1983) Unpub. Unpub. M.S. M.S. thesis, thesis,Univ. Univ. of of illinois, Illinois, Urbana-Champain, Urbana-Champain,lztlp. 141p. (3) (4) Gardner, Gardner, J.E. J.E. (1987) (1987) Unpub. Unpub.M.A. M.A.thesis, thesis,Washington Washington University, University, St. Louis, 359 359 p. p. (4) 7, 325-326. (5) Seifert, Seifert, K.E. K.E. (1985) (1985) Geol, Geol.Soc. Soc.America America Abstracts Abstracts with with Prog., Prog., 117, 325-326. (5) D.N. (1987) (1987) J. Petrol., Petrol., 28, 28,835-865. 835-865. (6) Shirley, D.N. (6) (7) Brannon, Brannon, J.C. J.C. (1984) (1984) Unpub. Unpub.Ph.D. Ph.D.dissertation, dissertation,Washington Washington University, University, St. Louis, 312 3 12 p. p. (7) Acta, 30, (8) Gunn, Gum, B.M. (1966) Geochim. Geochim. Cosmochim. Cosmochim. Acta, 3 0,88 881-920. 1-920. (8) (9) Cox, K.G. (1980) J. J.Petrol., Petrol., 221,1,629-650. 629-650. (9) K.W.(1989) (1989) JJ.. Geol., Geol., 97, (10) Kiewin, Klewin, K.W. 97,65-76. 65-76. (10) Bjomsson, A., A., and and Sigurdsson, Sigurdsson,S. S.(1980) (1980) J. J. Geophysics, (1 1) Johnsen, G.V., G.V, Bjomsson, Geophysics, 47, 4 7,132-140. 132-140. (11) (12) Sigurdsson, Sigurdsson, H. H. (1987) (1987)in in Mafic Maficdyke dykeswarms: swarms: Geol. Geol. Assoc. Assoc. Canada Canada Spec. Spec. Paper Paper 34, 34,55-64. 55-64. (12) H., and and Sparks, Sparks,R.S.J. R.S.J.(1978) (1978) Nature, Nature, 274, (13) Sigurdsson, Sigurdsson, H., 274, 126-130. 126-130. (13) 36 - ---- �U OF SSTATE TATE O F MINNESOTA MINNESOTA DRILL CORE LIBRARY LIBRARY Jacqueline Jiran Jacqueline Minnesota Department Department of of Natural Resources Minnesota Resources Division of Minerals Minerals ABSTRACT The of Minnesota Drill Core Core Library Library is is located located in in the city of Hibbing, T h e State of Minnesota Drill Hibbing, aa 90 90 8:00am a m to to 4:30 4:30 pm daily; Minerals minute drive northwest of Duluth. Duluth. The T h elibrary libraryhours hoursare a r e8:00 Division staff are Division a r e available available during during this thistime timeto todiscuss discuss Division Division projects projects or or subjects subjects related related to Minnesota's Minnesota's mineral mineral potential. Geologists to examine examine aand/or to Geologists are a r e welcome welcome to n d / o r sample sample drill drill core; reservations arc a r c encouraged. encouraged. Drill core corc and cuttings resulting resulting from from iron, iron, base base and and precious precious metal metal exploration exploration in in Minnesota currently stored stored in in two two buildings. buildings. In In anticipation of Minnesota aare r e currently of further f u r t h e r drill drillcore corc acquisitions, aa third building acquisitions, building with with aa capacity capacity of of 630,000 630,000 feet was was constructed. With With the the additional storage, the Drill Core Core Library capacity capacity has has been been expanded expanded to to over over 22 million million feet. Currently, the total total amount amount of of drill drillcore corcand andcuttings cuttingsavailable availableexceeds exceeds 1.5 1.5 million feet, and additional drill drill holes holes are a r e added added monthly. monthly. Also Also as as aa result result of of the the new new expansion, expansion, the the library library 166 linear linear feet. examination table table space space has has increased increased from from 55 55 to 166 feet. Minnesota counties, counties, including including all all of of the Drill Core is available from f r o m 57 57 of the 87 Minnesota counties iinn the Canadian Canadian Shield Shield Terrane of of northern northern Minnesota. Minnesota. These These cores cores arc a r c collected collected through the state's exploratory boring to submit submit their drill through boring law, law, which requires companies companies to core the state aatt the the termination termination of of their state or private private lease. core tto o the lease. An index for f o r the the Drill Drill Core Core Library is available in both printed and and computerized computerized formats and a n d is is sorted by geographic location, as aare r e the corresponding paper files. Other related information available available at a t the the Division Division of of Minerals Minerals office includes: includes: lithologic logs logs ffor lithologic o r many of the the drill drillholes, holes, geochemical geochemical analyses and assays, assays, geophysical studies, and a n d an a n excellent excellent thin thin section section and and polished polished thin thinsection section collection collection (microscopes (microscopes can be be reserved reserved if needed). needed). For ffurther For u r t h e r information information or o rreservations, reservations, contact: contact: Mineral Resources Geologist DNR D N R -- Minerals Division P.O. Box 567 567 Hibbing, MN MN 55746 55746 Phone: (218) (21 8) 262-6767 262-6767 37 �U THESIGNIFICANCE SIGNIFICANCEOF OFREGIONALSCALE REGIONAL-SCALELEFT-LATERAL LEFT-LATERALFAULTING FAULTINGIN INDEVELOPMENT DEVELOPMENTOF OF THE THEVERMILION VERMILIONGREENSTONE GREENSTONEBELT BELTIN INMINNESOTA MINNESOTA THE Boerboom Mark A. A. Jirsa, Jirsa, D.L. D.L.Southwick, Southwick, and andTerrence Terrence J.J.Boerboom Mark Minnesota Minnesota Geological Geological Survey Survey 2642 2642 University University Avenue Avenue St. St. Paul, Paul, MN MN 55114-1057 55114-1057 Northeast-trending longitudinal faults faults were were recognized Northeast-trending longitudinal recognized by the earliest earliest mappers mappers in in the the Vermilion Vermilion greenstone greenstone belt (VGB), (VGB), but until until recently recently their their role role in in the thetectonic tectonic evolution evolution of the the belt belt was was unclear. unclear. Even Evenininthe thebest-exposed best-exposedareas areas of ofnortheastern northeastern Minnesota, Minnesota, longitudinal longitudinal faults faults are are rarely rarely exposed exposed and and their their presence presence was wasinferred inferredmainly mainly from from linear linear topographic topographic depressions depressions across across which which stratigraphic stratigraphic correlations correlations are are tenuous tenuous or 1970s, detailed detailed study study ininthe the or metamorphic metamorphic grades grades are areincompatible. incompatible. In In the the early early 1970s, central central Vermilion Vermilion district district showed showed that that early left-lateral left-lateral faults faults were offset offset by by The right-lateral right-lateral event event appeared appeared northwestnorthwest- to to west-trending west-trending right-lateral right-lateralstructures. structures. The to be the more significant of the two; it accorded well with major right-lateral to be the more significant of the two; it accorded well with major right-lateralfaulting faulting elsewhere elsewhere in in the the Superior Superior Province Province and and was was consistent consistent with with the the overall overall regime regime of ofdextral dextral transpression transpression that that dominated dominated the the tectonic tectonic development development of of the theregion. region. Observations Observations and and inferences inferences from from recent recent mapping mapping in in the the western western and andcentral centralVGB VGB are are the the basis basis for for revised revised thinking thinking about about the the scale, scale, separation separation sense, sense, and and timing timing of of longitudinal faulting. faulting. Many Many of the the early early strike-parallel strike-parallel faults faults are are regional-scale regional-scale longitudinal sinistral sinistral structures structures that that were were fragmented fragmented by by later, later, mostly mostly right-lateral right-lateral fault fault zones zones oriented oriented oblique oblique to their their strike. strike. We Weinfer infersinistral sinistraldisplacement displacement sense sense on on major major longitudinal longitudinal faults from from the the map map geometry geometry of of secondary secondary faults faults and and shear shear zones, zones, which which splay strikesplay from from the the main main structures structures and and offset offset marker marker units. units. Patterns Patterns of of sinistral sinistral strikeslip slip duplexes duplexes and and imbricate imbricate fault fault splays splays both bothindicate indicate dominantly dominantly extensional extensional kinematics. kinematics. Because Because marker marker units units are are rare rare and and displacements displacements on on trunk trunk faults faults may may have havebeen beenvery very great, great, we we also also have have used used the the regional regional distribution distribution of of five five generalized generalized rock rock packages packages to to demonstrate demonstrate offsets. This Thismega-stratigraphic mega-stratigraphic approach approach has has led led us us to to recognize recognize aa fundamental within the the VGB (labelled LLSD on Fig. 1) 1) that that divides divides aa fundamental stratotectonic stratotectonic break within northern one. Although northern terrane from from a southern southern one. Although the the significance significance of of this this break break remains remains to to be be determined, determined, it clearly clearly is is an an early early feature feature that that has has been been disrupted disrupted by by sinistral sinistral fault fault displacements. Left-lateral Left-lateral faulting faulting occurred occurred after after peak peakmetamorphism metamorphismbecause because displacements. metamorphic metamorphic isograds isograds are are displaced displaced at at fault faultboundaries. boundaries. Post-kinematic, alkalic plutons plutons that spatially associated associated with with some some longitudinal longitudinal faults faults are are locally locally inferred inferred to to have have that are are spacially been been emplaced emplaced in in extensional extensional rhombochasms rhombochasms within within sinistral sinistral strike-slip strike-slip duplexes. duplexes. Although unproven, unproven, itit is is probable probable that that some some of of the the sinistral sinistral faults occupy parts of of the the Although earlier earlier structures, structures, including including the the medial medial stratotectonic stratotectonic break break within within the the VGB VGB supracrustal supracrustal sequence. sequence. The fault systems The presence presence of of kinematically kinematically complex longitudinal fault systems in the VGB VGB is is consistent consistent with with recent recent interpretations interpretations of greenstone greenstone belts belts as as the the remnants remnants of of accreted accreted arc-trench systems. systems. Phanerozoic Phanerozoic accretion of arc-trench arc-trench systems systems produces produces linear linear arc-trench blocks blocks of of diverse diverse rock rock suites suites that thatare areseparated separatedand andinternally internallysegmented segmentedby bythrust thrustand and wrench faults. faults. Having recognized some aspects of this deformational deformational style style in inthe the VGB, VGB,we we wrench now can speculate speculate about the broader broader paleotectonic paleotectonic and stratigraphic stratigraphic evolution evolution of the belt destraining" major by "destraining" major fault fault displacements. displacements. by 38 �I Support for mapping and geophysical data were provided by Mineral Diversification Program Program of the the Minnesota Minnesota Legislature Legislature administered administered (1) ( 1) by the Minerals Minerals Coordinating Coordinating Committee. Committee. Legislative Commission on Minnesota Resources (2) (2) CUSMAP CUSMAP Program Program of the U.S. U.S. Geological GeologicalSurvey Survey (3) (3) RLUTONIC P L U T O N I C ROCKS ROCKS late and postkinematic, ulkalic [,-+-,*late - and post - kinematic, alkalic plutons plutons <, a 1, , " * * ,, VERMILION O" ,!a s'e~~,~~j 3, a * ">,,)%,, *w !, ' Vermilion Granitic Vermilion Granitic Complex Complex Eg Giants Giants Range Range batholith batholith -LLSD F. U LTS FAULTS LLSD BRF BRF LLF LLF BL F BLF HF HF VF VF 4 Stratigrophic top direction Leech Lake structural Leech Lake structural disconformity disconformity Bear Bear River River fault fault Lost Lost Lake Lake fault fault Burntside Burntside Lake Lake fault fault Haley Holey fault Vermilion Vermilion fault fault 10 KM — b. SUPRACRUSTAL ROCKS undifferentiated ocks and and sills sills LIII mafic to ultromafic volcanic rocks northern ferrane southern te rrone terrone F7j IJ]JJJII I felsic felsic volcanic volcanic and and volcaniclastic volcaniclastic rocks rocks and and iron — format ion iron - formation mofic to felsic felsic volcanic and iron-formation rnafic to volcanic rocks rocks and iron f for motion / eke structural structural disconformity diconIorm,ty Leecih Lake -Leech graywacke ttuff groywacke, u f f and and slate slate volcanic and volcanic and clastic clastic rocks rocks and and iron iron-formation -formation geologic map map (a) of part of the Figure 1. 1. Simplified Simplified geologic the Vermilion Vermilion greenstone greenstone belt; and and reconstruction (b) (b) to before reconstruction before major major strike-slip strike-slipdisplacement. displacement. 39 I I �U Structure of the northern northern block of of the the Ishpeming Ishpeming greenstone greenstone belt, belt, Structure Marquette County, County, Michigan Michigan I R.C. Johnson, Johnson, Department Department of of Geological Geological Engineering, Engineering, Geology, and Geophysics, R.C. Michigan Michigan Technological Technological University, University,Houghton, Houghton,Michigan, Michigan,49931 4993 1 The The northern northern block block of the Ishpeming Ishperning greenstone greenstone belt is dominated by tholeiitic tholeiitic pillowed basalt sedimentary rocks basalt flows flows with minor minor massive flows and subordinate subordinate pyroclastic and sedimentary 2 covers 150 150km2 krn in in north-central north-central Marquette County, Michigan. There There are are at at least least two two and covers major Archean deformational events: (1) deforrnational events: (1) recumbent recumbent folding folding about east-west axes (Di) (Dl) and and (2) east-west axes (1)2). (2) upright folding folding about east-west (D2). These deformational events resulted in folds with amplitudes amplitudesand and wavelengths wavelengths measured in kilometers kilometers and a Z-shaped Z-shaped pattern of the the distribution distributionof of stratigraphic stratigraphic units. units. Gneissic Gneissicgranitoids granitoidsthat thatbound boundthe theblock blockwere wereintruded intruded during D1 basalt to to amphibolite amphibolite grade. grade. Granodiorite Dl and metamorphosed the surrounding basalt Granodiorite stocks stocks and and quartz quartz and and quartz-feldspar quartz-feldspar porphyritic porphyritic rhyolite rhyolite dikes intrude the basalt in in and and adjacent adjacent to shear shear zones. These Thesefelsic felsicintrusions intrusionsare areinterpreted interpretedas aspart part of of the thesame samemagmatic magmatic event event and and both both were wereprobably probablyemplaced emplacedduring duringD2. D2. T. 501 Explanation Explanation Iron-formation — Trajectory of S1 foliatron 1. 49 I Synform Synforrn showing showing trac, tractof of axial axial plane of plunge plure ofofaxis plane and direction of axis -- Antiform Antdorm showing showingtrace trace of of axial axialplane plane and anddirection directionof of plunge plunpof ofaxis axis —— Fault FauB T. 48 I Figure 1. 1. Sketch Sketch map map showing showingS1 Si foliation foliation trajectory, trajectory, F1 Fl and F2 folds, outcrop pattern Figure of the RCL-the iron-formation iron-formation unit, unit, and major fault in the eastern end of the northern block. RCL -Rocking Chair Chair Lakes. Lakes. -Rocking The youngest youngest folds folds (F2) (F2) control the overall Z-shaped Z-shaped pattern of stratigraphic stratigraphicunits. units. Since are rare, rare, F2 F2 folds are best defined by the folding folding Since sedimentary sedimentaryand and volcaniclastic volcaniclastic rocks rocks are of Si thesoutheast southeastthere thereare aretwo twosmaller smallerfolds folds that that may be be controlled controlled by by the the Sl (fig. (fig. 1). 1).InInthe bounding bounding gneissic granitoids. At Atthe thenorthwest northwestend endof ofthe thebelt, belt, L1 Ll lineations lineationsplunge plunge 40 �I moderately to the southeast and Sl Si is is deformed deformed by by an upright, tight to isoclinal southeastverging to to the the southwest. Further plunging F2 synform verging Further to the east, along the same fold, fold, L1 Ll plunges shallowly to the east and Sl forms an upright, open, shallow easterly plunging F2 synform; while whilebedding bedding (So) (So) forms forms an an open open synformal synforrnal anticline anticline plunging shallowly shallowly to the plunge direction direction indicated in in fig. fig. 1 is is for for folded folded SS1 foliation). This west (note that the fold plunge 1 foliation). contradictoiy fold geometry is produced by folding So S0 and and Si Si surfaces which are apparent contradictory the plunge plunge of of folded folded bedding bedding is is less less than not parallel. L1 Ll in this area is nearly flat lying; the 100 to the the west, west, and and the the plunge plunge of of folded Sl S1 is is less less than than 100 100totothe theeast. east. The contrary 10Âto plunge of fold surfaces may be exacerbated by scissors scissors motion along shear zones. The oldest folds (Fi) can be observed observed folds (F1) northeast and southeast of Rocking Chair I), where the outcrop pattern Lakes (fig. 1), of a pyroclastic pyroclastic unit and gabbro gabbro sills sills define F1 Fl folds. The The southern southern F1 Fl fold is a synformal anticline and the northern synfonnal northern F1 Fl fold is an antiformal syncline. Both Both folds folds are tight to isoclinal, upright, upright, and plunge plunge southeast. in moderately to the southeast. In the the vicinity of the fold hinges, bedding is Si, Si normal to Si, Slisisaxial axialplanar, planar,and andL1 Ll plunges moderately moderately to to the the southeast. southeast. Further to to the the east, east, L1 LI and and F1 Fl folds folds plunge plunge shallowly to the east. east. a) The development of folds in the northern block is shown 2. shown schematically schematically in in figure figure2. recumbent, tight During D1, Dl, large-scale recumbent, developed (fig. to isoclinal F1 Fl folds were developed (fig. 2a). Subsequently, Subsequently,during duringD2, D 2 F1 FI folds folds were refolded forming forming isoclinal isoclinal to to open, open, upright F2 folds (fig. 2b) accompanied 2c). This by shearing shearing(fig. (fig. 2c). c) Figure 2. Figure 2. Schematic cross-section of the northern block showing showing fold fold development and relationships of bedding bedding and and Si foliation, foliation. a) a) Early Early Dl, b) open open recumbent folding folding during during D1, east-west axes D2, folding about east-west axes during during D2, and c) late-stage shearing associated associated with 1)2. E>2. Bar and ball symbol symbol indicate indicate local local stratigraphic stratigraphic tops. deformational sequence maintained the deforrnational So-Si angular relationship relationship relative So-S observed (i.e. S1 S 1 typically dips more 4' I I �U steeplytotothe thenorth norththan thanSo), So),which whichisisconsistent consistentwith withthe theexposed exposedlower lowerlimb limbofofthe theF1Fl steeply recumbent recumbentfold fold(fig. (fig.2c). 2c).AAsimilar similarsequence sequenceofofdeformational deformationalevents eventsisisalso alsoobserved observedinin northernMinnesota Minnesota(Bauer, (Bauer,1985; 1985;Huddleston Huddlestonetetal., al.,1988). 1988). northern This Thisproject projectwas waspartially partiallyfunded fundedby byaagrant grantfrom fromthe theMichigan MichiganGeological GeologicalSurvey Surveyand and the Geological theCOGEOMAP COGEOMAPprogram programofofthe theU.S. U.S. GeologicalSurvey. Survey. References References Bauer, Bauer,Robert RobertL., L.,1985, 1985,Correlation Correlationofofearly earlyrecumbent recumbentand andyounger youngerupright uprightfolding foldingacross across the Archeangneiss gneissbelt beltand andgreenstone greenstoneterrane, terrane,northeastern northeastern theboundary boundarybetween betweenan anArchean Minnesota: Geology, Geology,v.v.13, 13,p.p.657-660. 657-660. Minnesota: P.J.,Schultz-Ela, Schultz-Ela,D., D.,and andSouthwick, Southwick,D.L., D.L.,1988, 1988,Transpression Transpressionininanan Huddleston,P.J., Huddleston, Archean EarthSci. Sci.25, 25,p.p.1060-1068. 1060-1068. Archean greenstone greenstonebelt, belt, northern, northern,Minnesota: Minnesota: Can. Can.J.J.Earth 42 �U ORIGIN ORIGIN AND PETROLOGY OF OF IRON SILICATE-RICH SILICATE-RICH BODIES BODIES IN IN THE THE BIWABIK IRON FORMATION, MINNESOTA MINNESOTA Peter Peter J. Juneau, Juneau, Franklin Franklin Company/E. CompanyIE. I.I. Du Du Pont Pont de de Nemours Ncmours and and Co., Inc., Inc., Wilmington, Wilmington, DE DE Two of taconite taconite containing containing large large amounts amounts Two distinct distinct 'bodiest 'bodies' of of of iron iron silicates silicates and and minor minor amounts amounts of of magnetite magnetite occur occur near near Keewatin, Minnesota. Minnesota. Data Data obtained obtained during during thin-section thin-section and and X-ray X-ray studies lead to the studies lead the conclusion conclusion that that the the bodies bodies are are remnants remnants of of "original" iron formation which did not develop magnetite during original" iron formation which did not develop magnetite during lithification and metamorphism. metamorphism. The bodies occur occurinin the the upper upper 20 20 to to 70 feet The silicate silicate bodies feet (6 (6 to to 21 21 m) m) of of the theLower LowerCherty Cherty member member of of the theBiwabik Biwabik Iron IronFormation. Formation. The The north north body body is 2200 2200 feet feet (671 (671 m) m) long, long, 480 480 feet feet (146 (146 m) m) wide, The south south body body is is located located 800 800 wide, and and 40 feet feet (12.2 (12.2 m) m) thick. thick. The to 1000 feet (244 to 305 m) south of the north body and has 1000 feet (244 305 m) south of the north body and has aa minimum length of of 2300 2300 feet m), is is 1050 1050 feet feet (320 (320 m) m) wide, wide, minimum length feet (701 (701 m), and and 40 feet feet (12.2 (12.2 m) m) thick. thick. Both Both bodies bodies are located located in the the same same stratrigraphic stratrigraphic horizon. horizon. Taconite the silicate Taconite comprising comprising the silicate bodies bodies is grouped grouped into into three -- silicate silicate taconite, taconite, transitional transitional silicate silicate three (3) (3) phases phases -taconite, -- based based on on the the amounts amounts of of taconite, and and silicate-rich silicate-rich taconite taconite -iron silicates silicates and and magnetite magnetite present. present. Silicate Silicate taconite taconite is is highest in iron 40 to 50 highest in iron silicates silicates (generally (generally 40 50 percent, percent, may may be be up up to 90 90 percent) percent) and and lowest lowest in in magnetite magnetite (2 (2 to to 44percent) percent) while while silicate-rich taconite isis highest in magnetite (15 to 20 silicate-rich taconite highest in magnetite (15 20 percent) percent) and and lowest lowest in in iron iron silicates silicates (15 (15 to to 20 20percent). percent). Silicate-rich taconite taconite and and transitional transitional silicate silicate taconite taconite can can be beeconomically economically processed processed but silicate silicate taconite taconite cannot. cannot. The The boundary boundary between between the the silicate silicate bodies bodies and and surrounding surrounding magnetite taconiteisis gradational gradationaland andoccurs occursininaa 66 to 10 magnetite taconite 10 foot foot (1.8 to between the transitional to 3.0 3.0 m) m) zone. zone. The boundary boundary between the transitional zone zone and surrounding surrounding magnetite magnetite taconite taconite is placed placed where where the the first first distinct distinct greenish greenish tinge tinge is is seen seen in in the the magnetite magnetite taconite; taconite; the the exact exact location location of of the the boundary boundary between between the the transitional transitional zone zone and and the silicate silicate taconite taconite isisuncertain. uncertain. 43 �U change in in texture texture and and mineralogy mineralogy is is seen seen ininthe the AA change transition from from silicate silicatetaconite taconitetotomagnetite magnetitetaconite. taconite. In In silicate silicate transition taconite, taconite, the the iron iron silicate silicategranules granules are areusually usuallyunaltered unaltered totopartially partially altered altered and and consist consistdominantly dominantly ofofminnesotaite minnesotaite (primary?), (primary?), with with lesser amounts amounts ofofgreenalite greenalite(primary) (primary)and/or and/orcolorless colorlessminnesotaite minnesotaite lesser small amounts of magnetite occur along granule needles (secondary); small amounts of magnetite occur along granule needles (secondary); In the thetransitional transitional zone, zone,silicate silicategranules granules are aremore morealtered altered outlines. In outlines. of as as distance distance from from the thesilicate silicatebody bodyincreases increases and andthe theamount amount of original iron iron silicates silicatesand andsecondary secondaryminnesotaite minnesotaite needles needles decreases decreases original In magnetite magnetite taconite, taconite, while the theamount amountofofmagnetite magnetiteincreases. increases. In while granules granules consist consist dominantly dominantly of chert chert with with minor minor amounts amounts of of iron iron silicates silicates (minnesotaite, (minnesotaite, stilpnomelane, stilpnomelane, and and possible possible chlorite) chlorite) and and Grains and aggregates of magnetite occur along carbonates. Grains and aggregates of magnetite occur along carbonates. Magnetite and and minnesotaite minnesotaite needles needles are are thought thought granule outlines. outlines. Magnetite granule Because little magnetite to develop developduring duringlow lowgrade grademetamorphism. metamorphism. Because little magnetite to isis found found within within the the silicate silicate bodies, bodies, the the silicate silicate bodies bodies are are considered considered remnant remnant areas areas of of iron ironformation formation which which resisted resisted alteration into into magnetite magnetite taconite. taconite. alteration Carbonaceous Carbonaceous material, material, permeability, permeability, heat heat flow, flow, and and change change in in bulk bulk chemistry chemistry may may have have acted acted as asfactors factorsinindetermining determining development of the development of the silicate silicate bodies bodies within within the the iron ironformation. formation. Of these, a change in magnesium content is thought Of these, a change in magnesium content thought to to be be the the A higher higher magnesium magnesium content content stabilizes stabilizes iron iron dominant factor. factor. A dominant silicates silicates relative relative to to magnetite magnetite and and minnesotaite minnesotaite relative relative toto As a result, magnesium-rich areas in aasilicate-rich As a result, magnesium-rich areas in silicate-rich greenalite. greenalite. iron iron formation formation would would be be better better able able totowithstand withstand higher higher temperatures temperatures before before altering altering to to magnetite magnetite taconite taconite than than would would an area area with with a alesser lessercontent contentofofmagnesium. magnesium. The The source source of of the the an magnesium may either magnesium may either have have been been primary, primary, possibly possibly aa more more magnesium-rich sediment, or secondary, magnesium-rich sediment, secondary, with with enrichment enrichment during during diagenesis or or low-grade low-grade metamorphism. metamorphism. diagenesis 44 �U Geology of Preeque Isle Point, Marquette, Michigan a Second Look J. J. Kailiokoski, Kalliokoski, Professor Professor Emeritus Emeritus MTU, MTU, Houghton, Houghton, Michigan. Michigan. series of AA longer longer series of events events is is recorder recorder by by outcrops outcrops along along the the lie contact. Archean Jacobsville contact than than previously previously reported reported Archean —- Jacobevi p-obable lower lower Proterozoic Proterozoic c,Kaili~kuekl, 1975; Lewan 1975). A probable 1975; unconformity extends extends across across aabasement baseiaeiit of of'Arohean Ar~heaiiserpent serpeiitiii.l.te, unconformity mite, ,cçrnit.e, diabaee The serpentinite is aand iid diabaee. The serperitinite is covered by a a chloritic chloritic j^ranitt?, paleosol the granite paleosml and arid the graniteby by an analuminous aluminous one. one. The The next next event event was was ,u ar t quartz—carbonate alteration, as white veins 1—20mm thick along -I .-arbonate alteration, as white veins l - 2 0 m thick along aridasas f ine-,~rali'ied the shear shear polygons polygons in in serpentinite. serpentiiiite, the and fine—grained iii serpentmnit.e serpentiiiite and (:fig.2>. 2). :).iupreeiiatloriein and qranodiorit.e granodiorite (fig. Textu1-.all-jand and compositionally co~ipaeitional ly the altered rocks r o c k %rCse4ble Feew~bie the altered Texturally !. -calmer "Palmer neiss", ananenigmatic, Gneissit, enigmatic alteration alterationproduct product described described by by fromthe thegegaunee Negaunee iron—forti Gair Gair and Simmons Simmons (1969) (1969) from iron-foi-~t $014 footwall. footwall. At the the point point the the early early alterations alterations in in serpentinite serpentinite are are cut cut by by locally locally abundant, abundant, predominantly vertical, slightly branching branching veins veins of of red, red, fmne—grained, fine-grained, banded, banded, colloforin colloform quartz (jasper), with no fluid fluid Inclusions inclusions or or walirock wallrock alteration alteration (fig. (fig. 3), 3 ) . This This. triple paragenesis is is known known from from Archean Archean basement basement rocks rocks below below an an iron--formation iron--formationalso at and and near near Huron Huron River River (Kalliokoski (Kalliokoski and and Lynatt, Lynott, 1986), 1986). Klliokoki, -7 5-1 triple Its and stratigraphicstratigraphic proximity proximity to toiron—formation iron-formation Its geographic geographic and that the the quartz—carbonate quartz-carbonate alteration is is a wide—spread wide-spread subaqueous subaqueous accompaniment accompaniment iron—formation iron-formation deposition deposition which, which, in in this this instance, instance, affected affected basement basement rocks rocks exposed exposed along along the the footwall footwall unconformity unconf ormity (Kailiokoski (Kalliokoski and and Lynott, Lynott, 1986>. 1 9 8 6 ) . I would would like to suggest further further that that the the jasper jasper veins veins represent represent hydrothermal hydrothermal feeders feeders which which transported iron iron into into the the overlying overlying early early Proterozoic Proterozoic sea. sea. suggests suggests I events were uplift, uplift, erosion of the presumed Lower The succeeding events Proterozoic cover, cover, and the development of a 10—50 10-50 cm cm blanket of of Proterozolc regolith re,%olith 3eiuviumi which overlay an an. active active soil soil layer layer on on the the eluvium:' which Archean Archean basement basement (fig. "fig. 4). 4 ) . The The eluviun eluvium is is an an unsorted, unsorted, matrix—supported matrix-supported breccia. breccia. It It consists consists of of angular, angular, elongate elongate clasts to 10 derived from the red, red, white, 10 x x 25 25 cm) cm) derived from the white, and and grey grey clasts (up (up to veinlets veinlets in in the the serpentinite, serpentinite, in in a fine fine grained grained matrix. matrix. There There are are also also clasts clasts of of quartz—carbonate quartz-carbonatealtered alteredserpentini'te. serpentinite. Locally the the clasts clasts are are imbricated, imbricated, indicative indicative of of down-slope down-slope solifluctiori. solif luction. During During deposition deposition of of the the Jacobsville Jacobsville Sandstone Sandstone the the eluvial eluvial A s proof of this, this, on the west and blanket was unconsolidated. As of the the point point are are 2-60 2-60 cm cm xx 2-50 2-50 mm beds beds of of breccia breccia sides of north sides 15 interl inger with, that t ~ a tunderl underlie, ~ntei-linger w i t h , and/or and or obi o b liqusly i q u e l ~truncate truncate sandstone is identical identical in in composition composition to to the the sandstone beds. beds. This This breccia breccia is eluvium (1-10 mm), nun), most most fragile fragile vein vein segments segments eluvium but but the the thinnest thinnest (1—10 • 45 I �were broken during during transportation. transportation. The The breccia breccia beds beds formed formed from from mudflows mudflows off the serpentinite serpentinite palco—bill, paleo-hill, coeval coeval with with Jacobaville sedimentation 5 a, a, c). c). Jacobsville sedimentation (fig. (fig. 5 I The thin Jacobsville section section CO-4 (O— m) of in) consists ~~ii~is of t ssheets s h e e t s of ~i sandstone, sandstone, silty silty shale, shale, minor fine—grained fine-grained conglomerate, conslomerate, and and breccia exposed exposed in in small small scarps scarps and and broad, broad, flat flat outcrops outcrops(fig. (fig. 6 5 , Trough Troughbeds, beds,foresets, foresets,current current lineations lineations and and rare rare shale shale O. rip—ups rip-ups are predominant features. features. Current Current directions directions indicate indicat.e that the and that that that. the sandstones sandstones transgressed transgressed across across the the basement, basement, and the serpentinite serpentinite formed formed a a topographic topographic high high similar similar to to what what we we see to—day, to-day. The The sandstone sandstonecontains, contains abundant abundant feldspar feldspar and and quartz, quart;, cee ~ i & t i TitOi , k~ and and pebble pebble beds beds contain contain clasts clastsof offeldspar, feldspar,p ~ pointin gr,ÈtiKi 1~ provenance, -pFcivenance. Some Some of of the the quart.z quarts pebble= highly ginitic. pebbles &ow show a highly polished surface, surface, suggestive suggestive of of wind wind action action at at the the source. source, After Jacobeville Jac-okevllle deposition deposition the eluvial blanket and and breccia breccia silica. The weathered zone zone along along the the top top beds were cemented by silica. compacted and the vertical jasper jasper veins veins of the basement became compacted 7 ) . To—day To-day this this zone zone crossing it it were were vertically vertically shortened shortened (fig. (fig. 7). crossing le well into Into its. Its third and erosion. erosion. is third cycle cycle of of weathering weathering and References available fro author :•:• 46 n �U } Figure 6. 6 . Geologic Geologic Figure Map of Of pr--e q u e Isle, iup Preeque Iele a, s , aerpentinite; serpentinite; q-c, quartz—carb. quartz-carb. q—c, alteration; alterat ion; G, G , granite granite; Gw, Gw, weathered granite: granite; weathered D, D , diabase; diabase; Ja, JE, J ac-ubsvi1 ie sandstone: sar~detor~e ; •Jcobsville 1 , 2 , 3 , 4 , location location of of 1,2,2,4, rose rose diagrams. diagrams. rose diagrams: diagrams: On rose n, n , no. no. of cross—bed cross-bed N I / 1. / 2 readings; readings; dashes, trend trend of of dashes, current current lineations; lineations; arrows,trend trough arrows, trend of trough axes, top top viewS view. axes, $ 47 I �U Paleomagnetism of of Baraboo Baraboo Interval Interval Rocks Rocks in in Wisconsin Wisconsin Paleomagnetism William F. F. Kean KeanDepartment Departmentof ofGeosciences GeosciencesUniversity Universityof of William Wisconsin-Milwaukee,P.O. P.O. Box Box 413 413 Milwaukee, Milwaukee, WI WI 53201 53201and and Robert Robert Wisconsin-Milwaukee, Schneiker,Hydrosearch, Hydrosearch,Milwaukee Milwaukee Schneiker, — The Proterozioc ProteroziocBaraboo Baraboo interval intervalis isaa sequence sequenceof ofquartz—rich quartz-rich The metasedimentary metasedimentary rocks rocks of of the the upper upper midwest midwest which which include includethe the Baraboo, Barron. Barren. McCaslin McCaslin and and Waterloo Waterloo quartzites quartzitesof ofWisconsin, Wisconsin, Baraboo, along with with the the Sioux Sioux Quartzites Quartzitesof of Minnesota, Minnesota,South SouthDakota Dakotaand and along Iowa. These These quartzites quartzitesare are associated associatedby by the thesimilarity similarityof of Iowa. their their appearance, appearance,although although there there is is no no firm firm evidence evidenceof oftheir their being time timesynchronous. synchronous. In In Wisconsin, Wisconsin, there there are are also also associated associated being igneous igneous rocks rocks which which include include granites, granites, rhyolites rhyolites and and diorites. diorites. We We have have continued continued paleomagnetic paleomagnetic studies studiesof of this thissequence sequencein in Wisconsin to to better better define define the the time time relationships relationshipsbetween betweenthe the Wisconsin metasediments and and the the igneous igneousrocks. rocks. We We have have recently recently inetasediments concentrated concentrated on on the the outcrops outcrops at at Hamilton Hamilton Mounds Mounds and and Baxter Baxter Hollow. Hollow. Hamilton Mounds Mounds is is an an inlier inlier of of Baraboo Baraboo type type quartzite quartzite Hamilton with aa distinct distinct intruded m.y. with intruded by by aa granite granite dated dated at at 1760 1760 m.y. The granite granite provided provided alteration alteration zone zone adjacent adjacentto tothe thegranite. granite. The no no useful useful paleomagnetic paleomagnetic date date because because the the remanent remanent magnetism magnetism is is too soft. soft. Alternating Alternating field field (A.F.) (A.F.) demagnetization demagnetization removed removed the the too remanence remanence by by 100 100 millitesla millitesla and and the the magnetic magnetic directions directions were were The magnetic magnetic characteristics characteristicsof of the the altered altered very scattered. scattered. The very zone zone indicate indicate the the magnetism magnetism is is due due to tofine finegrain grainmagnetite, magnetite, probably probably resulting resulting from from the the reduction reduction of of hematite hematite in in the the A.F. and and thermal thermal quartzites at at the the time time of of intrusion. intrusion. A.F. quartzites demagnetization demagnetization studies studies show show only only one one component component of of The magnetism magnetism in in the the quartzite quartzite at at Hamilton Hamilton Mound Mound magnetization. The magnetization. is typical typical of of the the Baraboo Baraboo type type quartzites quartzitesin inWisconsin. Wisconsin. The The is remanence remanence is is carried carried by by hematite, hematite, and and appears appears to to be be diagenetic diagenetic in origin. origin. in At Baxter Baxter Hollow Hollow aa granite granite is is exposed exposed below below the thequartzite. quartzite. AA At sheared sheared or or mixed mixed zone zone below below the the quartzite quartzite appears appears to to be be part part of of the granite granite with with assimilated assimilatedquartzite. quartzite. The The contact contact between between the quartzite zone is is not not exposed exposedbut butquartz quartzite is quartz ite and and sheared sheared zone ite is located within within two two meters meters of of the the sheared shearedzone. zone. The The granite granite has has located not been been dated dated but but it it has has been been interpreted interpreted as as being being both both younger younger not and older older than than the the quartzite. quartzite. The The quartzite quartzite and and granite granite at at and Baxter Hollow were previously analyzed by Mercer (1984) Baxter Hollow were previously analyzed by Mercer (1984)and and Kean Kean Mercer (1986). (1986). The The granite granite is is typically typically soft soft magnetically magnetically and and && Mercer of little little use use for for paleomagnetic paleomagnetic studies. studies. The The quartzites quartzites of of this this of area area provide provide good good data, data, with with the the remanence remanence carried carried by by hematite. hematite. In this this report report we we present present data data from from the thesheared shearedzone. zone. The The In sheared or or mixed mixed zone zone is is magnetically magnetically more more complex complex than than the the sheared counterpart counterpart at at Hamilton Hamilton Mounds, Mounds, but but there there is is aa primary primary remanent remanent component carried carried by by magnetite. magnetite. component The The magnetic magnetic directions directions and and pole pole positions positions for for these these sites sites are provided provided in in table table I. I. are 48 I'll �I Table Table II Formation oma at ion No. of ot Mean Mean Samples Samples Hamilton Hamilton Mounds Mounds 10 10 Mean Mean KaDDa Kappa A l ~ h a95 95 Alpha V.G.P. V.G.P. 43.9 332.5 332.5 6.8 19.9 19.9 61 N 150 150 EE 61 77 53.9 174.0 174.0 10.9 19.2 19.2 11 SS 84 84 WW 11 Baxter 10 10 Baxter Hollow Hollow Sheared Sheared Zone Zone 86.3 303.5 303.5 9.3 9.3 16.7 16.7 48 N 98 98 WW 48 Baraboo Baraboo 59.1 199.3 199.3 19.9 15.4 15.4 14 SS 89 89 WW 14 Dec Dec Quartz ite Quartzite Hamilton Hamilton Mound Mound Mixed Mixed Zone Zone 30 30 Quartz ite Quartzite Conclusions Conclusions When When the the pole pole positions positions obtained obtained in in this this and and other other studies studies are are compared compared to to Irvings Irvings (1976) (1976) polarwander polarwander pater pater for for the the time time range 1650-2200in.y. m.y. We We make make the the following following conclusions: conclusions: range 1650-2200 1. 1. The The Baraboo Baraboo Quartzite Quartzite pole pole (structure (structure corrected) corrected) is is very very similar similar to to the the Hamilton Hamilton Mound Mound mixed mixed zone zone and and is is placed placed at 1800 m.y. m.y. based based on on the the location location on on the the at approximately approximately 1800 polar polar wander wander path. path. This This suggests suggests that that the the Baraboo Baraboo Quartzite Quartzite is is at at least least 1760 1760 years years old old and and probably probably older. older. 2. 2. The Baxter Baxter Hollow Hollow sheared sheared zone zone pole pole position position would would place place The its 1650 m.y. m.y. if if one one accepts accepts its its position position on on the the its age age at at 1650 polar polar wander wander path. path. If If the the pole pole position position is is corrected corrected with with the the same same structure structure corrections corrections used used on on the the quartzite quartzite at at this this site, site, it it comes comes near near the the structure structure corrected corrected quartzite quartzite pole. pole. Either Either result result would would imply imply that that the the intrusive intrusive activity activity is is younger younger than than the the quartzite, quartzite, and and possibly possibly as as young young as as 1650 1650 in.y., may., but could could be be as as old old as as 1760 1760 m.y. m.y. 3. 3. The results results from from Hamilton Hamilton Mounds Mounds also also imply imply that that the the The folding 1760 folding of of the the quartzite quartzite at at this this site site is is at at least least 1760 m.y. m.y. old. old. 49 �I I References Irving, E., Irvingf E m f 1978, 1978# Paleopoles Paleopoles and and paleolatitudes paleolatitudes of of North North Aiuerica America and speculations speculations about displaced displaced terrains; terrains; Can. Can. I. I. Earth Earth Sci. Sci. Vol. V O ~ .16, 16# Pp.669—694 Pp.669-694 j Keanf W.F. W.F. and and D. D. Mercer, Mercerf1986, 1986#Paleornagnetisin Paleomagnetism of Kean, of the the Baraboo south Central Central Wisconsin Wisconsin Geosciences Geosciences Wisconsin, Wisconsinl Vol. Vol. Quartzite of south 46-53 10, Pp. 46—53 Mercer, D., Mercerf D e f 1984, 1984# Paleomagnetism Paleomagnetism of of the the Baraboo Baraboo Quartzite: Quartzite: University of Wisconsin—Milwaukee, Wisconsin-Milwaukeef M.S. M.S. thesis, thesisf P. P. 294 294 I I I I I I I I I I I I 50 i �U I GEOLOGICAL GEOLOGICAL SETflNG SElTING AND AND GEOCHEMISTRY GEOCHEMISTRY OF THE THE BUSH BUSH LAKE LAKEGRANITE GRANITE IN IN MENT PEGMATITES, PEGMATITES, FLORENCE FLORENCE COUNTY, COUNTY, RELATION TO RARE-ELEMENT WISCONSIN KOEHLER, Steven R., Dept. of Plant Plantand andEarth EarthScience, Science,University UniversityofofWisconsin Wisconsin- River uwer Falls, tails, River wver Falls, taus, WI Nl54022. 54022. Rare-element Rare-element pegmatites in Florence Florence County, County, Wisconsin Wisconsin have have intruded intruded low lowtotomoderate moderate pressure, fades rocks of metasedimentarylmetavolcanic facies of the theQuinnesec Quinnesec pressure, Abukuma-type Abukuma-type metasedimentary/metavolcanic Formation. Numerous Numerous lines lines of of evidence evidence indicate indicate the the early early Proterozoic Proterozoic age age Bush Bush Lake Lake Formation. Granite Granite is is the thesource sourcefor forthese thesepegmatites. pegmatites. Field Field mapping mapping reveals reveals aa distinct distinct pegmatite pegmatite aureole aureole in in the the Quinnesec QuinnesecFormation Formationnorthwest/north/northeast northwest/north/northeast of of the the Bush BushLake LakeGranite. Granite. Greenberg et a!., a/., (1983) (1983) interpret interpret the the southern southern Penokean Penokean volcanic volcanic belt as as aa complex complex Greenberg et arc environment. environment. Late Late tectonic tectonic intrusion intrusion of the the Bush Bush Lake Lake Granite Granite as as aasecond-order second-order arc diapir diapir occurred occurred after afterpeak peakregional regionalmetamorphism metamorphism(Sims (Simseteta!., a/.,1985). 1985). According According to to Cerny et a!., a/., (1988), (1988), the the tectonic tectonic environment environment and and timing timing of ofgranitic graniticintrusion intrusioncompare compare Cerny et favorably favorably with with documented documented fertile fertilegranite/pegmatite granitelpegmatiteassociations. associations. Compositionally the Bush Compositionally the Bush Lake Lake Granite Granite isis aaperaluminous, peraluminous, megacrystic, megacrystic, biotite biotite Upward gradations from biotite granite into pegmatitic granite. Upward gradations from biotite granite into pegmatitic leucogranite leucogranite and and granite. potassic potassic pegmatite pegmatite are common. common. Pegmatitic Pegmatiticfacies facieswithin withinthe thegranite granitecontain containaccessory accessory Mn-rich garnet, garnet, tourmaline, tourmaline, beryl, beryl, and andmuscovite. muscovite. Bulk Bulk compositions compositions are are silicic, silicic, NaNaMn-rich rich rich (2.84-3.61 (2.84-3.61 wt. wt. % % Na20), NazO), but butare arepoor poorininFe, Fe,Mg, Mg,and andCa Ca(0.29-1.27 (0.29-1.27 wt. wt. % %CaO). CaO). Cs (4.7-13.6 (4.7-13.6 ppm), ppm), Ga Ga (7-51 (7-51 ppm), ppm), and and YY Li Li (17-89 (17-89 ppm), ppm), Rb Rb (235-403 (235-403 ppm), ppm), Cs (7-49 (7-49 ppm) ppm) are are enriched, enriched, while while Ba Ba (34-95 (34-95 ppm) ppm) and and Sr Sr (21-89 (21-89 ppm) ppm)are aredepleted depleted relative to to barren barren granites. granites. High High fractionation fractionation is suggested suggested by by low low Rb/Sr RblSr(17.5-1.9), (17.5-1.9), relative Ba/Rb BalRb (2.9-0.17), (2.9-0.17), Mg/Li MglLi (50.5-4.5), (50.5-4.5), and and K/(Cs Kl(Cs xx 100) 100) (100-17) (100-17) ratios. ratios. Bush Bush Lake Lake Granite Granite K/Rb K/Rb ratios ratios are are low low (172-91), (172-91), but but decrease decrease outward outward to 7.79 7.79 in in albitized, albitized, Li-rich Li-rich pegmatites pegmatites (Koehler, (Koehler, 1989). 1989). REFERENCES REFERENCESC1ED CITED Cerny, Cerny, P. P. and and Meintzer, Meintzer, R.E., R.E., 1988, 1988,Fertile Fertilegranites granites ininthe theArchean Archean and andProterozoic Proterozoic fields of of rare-element rare-elementpegmatites: pegmatites:crustal crustalenvironment, environment, geochemistry, geochemistry,and and petrogenetic relationships, relationships, in in Taylor, Taylor,R.P. R.P.and andStrong, Strong, D.F., D.F., eds., eds., Recent Recent advances advances in in the the geology geology of of granite-related granite-relatedmineral mineraldeposits, deposits,The TheCanadian Canadian Institute Institute of Mining Mining and and Metallurgy, Metallurgy, sp. pub. pub. 39, 39, p. p. 170-206. 170-206. Greenberg, Greenberg, J.K. J.K. and and Brown, Brown, B.A., B.A., 1983, 1983, Lower Lower Proterozoic Proterozoic volcanic rocks rocks and and their their in Medaris, Medaris, L.G., L.G., Jr., Jr., ed., ed., Early Early setting in in the the southern southern Lake Lake Superior Superior district, district, in setting Proterozoic Proterozoic geology geology of of the the Great Great Lakes Lakes region, region, Geol. Geol. Soc. SOC.Am. Am. Memoir Memoir160, 160,p.p. 67-84. 67-84. learing province province in inFlorence FlorenceCounty, County, Wisconsin Wisconsin Koehler, Koehler, S.R., S.R., 1989, 1989, A possible Ta-bearing [abs.]: with Programs v. 21, #4, p. )grams ,, v. p. 39. 39. [abs.]: GSA Abstract / Sims, P.K., P.K., Peterman, Peterman, Z.E., Z.E., and and Schulz, Schulz, K.J., K.J., 1985, 1985,The TheDunbar DunbarGneiss-granitoid Gneiss-granitoid dome: dome: Implications Implications for early early Proterozoic Proterozoic tectonic tectonic evolution evolution of of northern northern Wisconsin: Wisconsin: Geol. Soc. v. 96, 96, p.p.1101-1112. 1101-1112. SOC.Am Am Bull., Bull., v. 51 I �U If WAS THE WAS THE PENOKEAN PENOKEAN OROGENY A BI-POLAR EVENT? Gene L. LaBerge, LaBercfeI Geology Geology Department, DepartmentI University of Wisconsin Wisconsin University of Geological Survey, SurveyI and and OshkoshI OshkoshI WI WI 54901, 54901, and and U. S. Geological Oshkosh, Oshkosh, John SS. Klasner, KlasnerI Geology Geology Department, Department, Western Illinois University, UniversityI John Western Illinois Macomb, IL IL 61455, 614551 and and U. S. S. Geological Geological Survey. Survey. Macomb, Thnvn is i c ! now nnw widespread ~.7iAnen~nsA 3 ~ ~ n n m n n th t = t the +hn Penokean D ~ - - l r n % - orogeny There agreement that Y was the tk result of plate tectonic activity. Most authors suggestt was that cevolution of the orogen in Michigan and Minnesota began with th a rift rifting phase accompanied by formation of basins and troughs along the passive margin of the Archean Superior craton, and wass accompankeu or rocks rOCKS of or the Marquette Range Range accompanied ~y by ueposirion deposition of Supergroup in Michigan and equivalent equivalent Animikie Group rocks in in Supergroup in Group rocks Minnesota Minnesota (Schulz (Schulz and and others, othersI in in press). press). However, HoweverI Hoffman Hoffman (1987) (1987) Southwick and others and Southwick others (1988) (1988) have recently recently suggested suggested that that the the iron-bearing sequences formed in foreland basins basins during accretion. Ironaccretion. Nd isotope isotope studies studies on the Biwabik and Negaunee Negaunee Iron— formations 52 Ma formations suggest deposition of these rocks about 2100 2 ± 52 (Gerlach othersI 1988) 1988). Rifting was followed followed by southward southward (Gerlach and others, subduction of oceanic oceanic crust crust to to form form the arc-related volcanic volcanic and and subduction the arc—related plutonic rocks rocks of of the the Wisconsin Wisconsin magmatic magmatic terranes. terranes. These These were were subsequently subsequently accreted to to the the continental continental margin on on the the north north 1989; LaBerge LaBerge and and between 1900 1900 and 1830 1830 Ma (Sims (Sims and othersl others, 1989; othersI 1984; Larue Larue and and Sloss, SlossI 1980; 1980; Cambray, CanbrayI 1978). 1978). Accretion others, 1984; Accretion rocks to to the the continental continental margin of of the the Superior Superior of the magmatic rocks craton about 11860 Ma (Sims (Sims and others, others! 1989) 1989) resulted resulted in in craton about 1,860 (Attoh and and Klasner, KlasnerI thrusting of rocks rocks onto onto the the craton craton (Attoh northward thrusting 1989; others! 1988a, 1988at 1988b; 1988b; Hoist, HolstI 1982, 1982! 1984). 1984). 1989; Klasner Kiasner and others, ----A- RecentlyI LaBerge LaBerge and and others others (in (in press), press)! LaBerge LaBerge and and Kiasner Klasner Recently, (1989, 1988, 1988, 1986) and and LaBerge LaBerge (1986) proposed proposed that that a a similar (1989! sequence of events occurred in sequer in central central and southern southern Wisconsin Wisconsin during the Penokean L orogeny. durin? orogeny. Widely scattered scattered areas areas of of quartz lly (at (at Baraboo) slate, slate, dolomite dolomite and and ironironquartzite, and locally formationI formation, are interpreted to be remnants of a once-extensive once—extensive passive passive margin margin succession. succession. Archean rocks rocks of of unknown unknown extent extent are are locally exposed in in central central Wisconsin and are are believed to to be be the the locally basement on which these sedimentary rocks accumulated. Stri 2lding and and Structures in the quartz ites indicate south-directed folding thrusting of the sedimentary rocks (LaBerge and others, in thr~ in press; press; Cam1 lean rocks. rocks. Cambray, 1987; LaBerge and Kiasner, 1986) onto the Archean This interpretation This interpretatlon is is supported supported by geophysical geophyslcal evidence evidence presented by Cannon Cannon and and others others (1989). (1989). We suggest suggest that that the the 1,750 11750 meter thick thick sedimentary sedimentary succession succession combined combined with with the the widespread widespread meter evidence evidence for for south-verging south-verging folding folding and thrusting thrusting argues argues for for collision collision of of a a substantial substantial mass of of rocks rocks — perhaps perhaps of micro continent size size - with with the the Proterozoic Proterozoic island island arc arc complex, complexI which which continent is now the the Wisconsin Wisconsin magmatic magmatic terranes. terranes. Sims Sims and and others others (1989) (1989) conclude that that this conclude this collision collision occurred occurred about about 1,840 11840Ma. Ma. - - In Wisconsin In the magmatic terrane terrane of north-central Wisconsin (specifically Marathon County) structures (specifically Marathon County) structures are are upright upright - subsubvertical to (LaBerge and MyersI 19841 1987) and have to vertical -- (LaBerge Myers, 1984, - 52 1 �no no consistent consistent sense sense of of structural structural vergence. vergence. The The magmatic magmatic terrane terrane in in the the Dunbar Dunbar area area of of northeast northeast Wisconsin Wisconsin has has aa strong strong northerly northerly sense 1985). Attoh Attoh and and Klasner Klasner sense of of vergence vergence (Sims (Simsand and others, others,1985). (1989) have suggested (1989) have suggested that that the the magmatic magmatic rocks rocks in in the the Dunbar Dunbar area area are are para—allochthonous, para-allochthonousf having having been been thrust thrust northward northward onto onto the the buried continental continental margin. margin. Dismembered Dismembered ophiolite ophiolite (Schulz, (Schulzf1987) 1987) buried in in nort1east northeast Wisconsin Wisconsin likely likely represents represents aa remnant remnant of of oceanic oceanic crust that that was was thrust thrust onto onto the the continental continental margin. margin. crust Taken Taken together, together, from from southern southern Wisconsin Wisconsin to to northern northern Michigan Michigan (Fig. 1), the the Penokean Penokean orogen orogen consists consists of: of: aa deformed deformed remnant remnant of of (Fig. Archean Archean basement basement overlain overlain by by Early Early Proterozoic Proterozoic platform platform sediments sediments deformed deformed by by south—verging south-verging structures; structures; aa region region of of accreted accreted island island arc arc volcanic volcanic rocks rocks with with upright upright structures; structures; aa region region of of island island arc and plutonic plutonic rocks rocks with with north—verging arc inagmatic magmatic and north-verging structures; structures; and and an an Early Early Proterozoic Proterozoic continental continental margin margin with with platform platform sediments sediments and and prominent prominent north—verging north-verging structures. structures. The platform sediments sediments and and rifted rifted continental continental margins margins The platform Formation of of an an ocean ocean basin basin is is the rifting rifting phase. phase. Formation represent the represent documented documented by ophiolite. The The island—arc island-arc volcanic volc:anic by the the presence presence of of ophiolite. rocks plutonic rocks rocks represent represent the the closing closing phase phase of of the the rocks and and plutonic closure resulted resulted in in accretion accretion of of magmatic magmatic rocks rocksI to ocean. Final F'inalclosure to ocean. ---2--l--- & L a v.... .n1-:--,.A \,; ",*.+,, the margins along the continental contirieri~a~ NMLLJLIIZ. ~ L U I N the L I I ~Eau uxu Pleine ~ A C A U C and ~ A I U Niagara LvAawaLa sutures = ~~dres respectively. Prominent promihent southsout.h(Fig. 1) 1) in in the the south south and and north nc&th respectively. (Fig. verging the continental continental margin margin in in central centra11 verging structures structures formed formed on or1 the Wisconsin structures on on the the continental continental margin. mar-gin. Wisconsin and and north—verging north-verging structures --- of -a2 .Ip--We Penokean We contend contend that that interpretations interpretatiu~ls UL the LIE reIluAeaI1 orogeny U L U L J ~ I I ~ as a = north— 11drthdirected directed only only do do not not accurately accurately represent represent the the event—-the event--the evidence evidence indicates that that it it was was bi-polar. bi-polar. . indicates ---L--i LL- ..- -- I-,-...- North Niagara Niagara South South Fault Fault E a u Pleine Pleine Eau Fault Fault SOU t h - v e r g i ng South—verging North—vrr(M ~ o r t h - v c r r1~ i f ~ q Upri ght struc turcs structures structures struc turcs structures structures x X v ARCI1EAN ------- X x A ARCHEAN x South-central S o u t h - c e n t r a l Wisconsin Wisconsin x x , - % - F a i X Northern N o r t h e r n Michigan Mich~gdn WI W i sscons c o n s in in magma m a g ~ n a tic t i c terra t e r r anes ncs Figure F i g u r e 1. 1. Sketch S k e t c h sshowing h o w i n g mmajor a j o r f features e a t u r e s in i n aa north-south f t h Penokean e P e n o k e a n orogen. orogen. n o r t h - s o u t h transect t r a n s e c tofo the 53 I 1 �I References Cited K, and Klasner, J. S., 1989, Tectonic Attoh, K., Tectonic implications implicationsofofmetamorphism metamorphismand andgravity gravityfield fieldininthe thePenokean Penokeanomgen orogenofofnorthern northern Michigan: Tectonics, Tectonics,v.v.8,8,p.p.911-933. 911-933. . 78, Plate Early Proterozoic Protedc Cambray, F. F. W., W., 19' 1978, Plate tectonics tectonicsas asaa model model for for the environment environment of of deposition deposition and deformation deformation of Early (Precambrian)ofofnorthern northernMichigan. Michigan.Geol. Qj. Soc. Amer., Abstracts with programs, No. 10, (Precambrian) 10, P. p. 376. 376. Cambray, F. W., explained as as aa result result of of superimposition superimposition of of simple simpleshear shear on on aa W., 1987, 1987, The The Baraboo b r a b o oSyncline: Syncline: the shape and refoldmg refolding explained pre-existing fold:Abstract, Abstract, Q. Soc. of Amer., Abstracts with programs, programs, p. p. 192. 192. preexisting fold: Geol. ç. Cannon, W. W. F., Schulz, K. J., J., Hinze, Hinze, W. W.J., J., and and Green, Green, A. A. G., G., 1989, Precambrianterranes terranes beneath beneath northern Lake Michigan defined defined by by Schulz, K 1989, Precambrian seismic and gravity analysis; analysis; Institute Institute on Lake Superior Geology, v. 35, Part 1, 1, Abstracts, p. 14, 14, 15, 15, Duluth, MN. MN. Geology, v. Gerlach, and Carlson, Carlson, R R. W., W., I1988, Ndisotopes isotopesin in Proterozoic Proterozoic iron-formatmns: iron-formations: Evidence S , Nd Evidence for for mixed-age mixed-age Gcrlach, D. C., C., Shirey, Shirey, S. 13., B., and provenance and depositional Geophvs. Union Trans., EOS, v. 69. depositional variability variabili% Abstract, Abstract, Am. Geovhvs. !21 Hoffman, P. F., 1987, 1987, hEarly r l y Proterozoic Foredeeps, Foredeep, Foredeep magmatism, magmatism, and Superior-type Superior-typ iron-formations iron-formations of of the theCanadian CanadianShield, Shield, Pp. in Proterozoic lithospheric evolution, edited by A. Kroner, Kroner, American American Geophysical Geophysical Union, Geodynamics Series, No. No. 17, pp. 85-98. Hoist, Evidence for for multiple multiple deformation deformation during during the the Penokean Penokean orogeny orogeny in in the the Middle Precambrian Precambrian Thomson Thomson Formation, Formation, B., 1982, 1982, Evidence Holst, T. B., Minnesota: Canadian Journaloff &rth Sciences: Minnesota: Canadian Journal Sciences: v. 19, 19, p. p. 2043-2047. 2043-2047. 1984,Evidence Holst, T. B., 1984, Hoist, Evidence for for nappe nappe development development during during the the Early Early Proterozoic Proterozoic Penokean Penokean omgeny, orogeny, Minnesota: Minnesota: Geology, v. 12, p. p. Geolon, v. 135-138. 135-138. Kiasner, J. J. S., S., Ojakangas, R R W., W., Schulz, Schulz, K. K. J., and LaBerge, LaBerge, G. G. L., L.,1988, 1988, Widespread evidence for Early b r l y Proterozoic Proterozoic overthrusting overthrusting in in Klasner, the Penokean Penokeanorogen orogenofofnorthern northern Michigan, Abstract, Michigan, Abstract, Geol.Geol. Assoc.. of Canada Caflada and Mi Min. Assoc. of Can., Programs Programs with with abstracts, v. v. 13, 13, p. p. A67. A67. a., Iàasiler, J. S., Sims, P. K, K., Gregg, W. W. J., J., and Gallup, C., l1988b, structural traverse traverse across acrossaa part part of the Penokean S b , AAstructural Penokean orogen, orogen, hasner, Schulz, K. K J., (ed.) v. v. 2, 2, Field Field Trip TripGuidebooks Guidebooks34th 34th illustrating Early Proterozoic overthrusting werthmsting in in northern northern Michigan; Michigan; in Schulz, Annual Institute on Lake Superior Geology, Geology, Marquette, Marquette, Michigan, Michigan,p. p. C1-C36. Cl-C36. 0. L., Lal3erge, G. G. L L., The Protemoic Proterozoic geology of the Lake LaBerge, ., 1986, 1986, The Lake Superior Superiorregion: region: in & LaBerge, G. L., Attig, Attig, J. J. W., W., and and Mode, Mode, W. W. N., N., Field Conference, Conference,Wausau, Wausau, Wisconsin, Wisconsin, p. 1-29. 1-29. Guidebook, Tri-State Geological Geological Field G. L., and Klasner, Evidencefor foraa major major south-directed south-directedEarly EarlyProtemoic Proterozoicthmst thrust sheet sheet in south central Wasner, J. S., S., 1986, 1986, Evidence LaBerge, G. Wisconsin: Abstract, Soc.of ofAmer., Annual AnnualMeeting, Meeting,San SanAntonio, Antonio,Texas. Texas. Wisconsin: Abstract, Geol. Geol.Soc. m., LaBerge, G. 0. L., J. S., S., 1988, 1988,The ThebBaraboo Quartzite: aa new new look lookatatan an old old problem: problem: Abstract, 34th Annual Annual Institute Institute on on L., and Klasner, J. r a b o o Quartzite: Abstract, 34th LaBerge, Lake Superior Superior Geology, Geoloa, Marquette, Marquette,Michigan, Michigan,p.p. 62-64. 62-64. - LaBerge, G. L., and Klasner, J. S., 1989, Tectonicimplications implicationsofofthe thestmcture structureand andstratigraphy stratigraphyofofquartzites quartzites in in central central and and southern LaDerge, 1989, Tectonic Wisconsin: Wisconsin: Abstract, Abstract, 35th 35th Annual Annual Institute Institute on on Lake Superior Geology, Duluth, Minnesota, Minnesota, p. p. 49-50. 49-50. w, LaBerge, G. L., L., Klasner, Kiasner, J. J. S., S., and and Myers, Myers, P. P. E., E., in press, New New observations observationson on the the age and structure of Proterozoic Protemoic quartzites quartzites in in Lakrge, in Sims, Sims, P. P. K, K., and and (ed.), (ed.), contributions contributionsto to the the Precambrian Precambrian gxology geologyofofthe theLake LakeSuperior Superiorregion: region: U. S. Geol. Wisconsin: Wisconsin: & Sur. Sur. Bull. Bull. 1904-B. 1904-B. %, pp. 246-253. M6-253. LaBerge and Myers, Myers, 1984, 1984, Two Early &rly Proterozoic Proterozoic successions successions in central Wisconsin, Wisconsin, GSA Bulletin, Bulletin, v. 95, LaBerge, Schulz, Schulz, and and Myers, Myers, 1984, 1984,The The plate plate tectonic tectonic history history of of central Wisconsin, Wisconsin,Abstract, Abstract, 30th 30th Annual Annual Institute Institute on Lake Superior Sumxior Geology, Wausau, WI Geolo!zy3 Wl Schulz, K. K. J., J., and and Sims, P. P. K, K., and Morey, 0. G.B., B.,ininpress, press,Tectonic Tectonicsynthesis, synthesis, Penokean Penokeanorogen, orogen,and andassociated associatedepicratonic epicratonicrocks: rock Geol. Soc. Soc. of America America DNAG DNAG volume, volume, C-2, C-2, Precambrian, Precambrian,conterminous conterminousU.S. US. -- - Schulz, 1987,An Anearly earlyProterozoic Proterozoicophiolite ophioliteininthe thePenokean Penokeanorogen: orogen: Abstract, Geol. h o c . of Schulz, 1987, p. 87. 87. m. abstracts with programs, programs, v. v. 12, 12, Sims, P. P. K., W. R, R., Schulz, K K. J., J., and and Peterman, Z. Tectonostratigraphic evolution of the Early K, Van Schmus, W. 2 E., E., 1989, 1989, Tectonostratigraphic &rly Protemzoic Proterozoic Wisconsin magmatic magmaticterranes terranesofofthe the Penokean Penokeanorogen: orogen: Canadian Canadian Journal Journal of of Earth Sciences, Wisconsin Sciences, Sims, Peterman, Peterman, and Schulz, I1988, The Dunbar Dunbar gneiss-granitoid dome; dome; implications implicationsfor for &rly Early Proterozoic Proterozoic tectonic tectonic evolution evolution of of Sims, S , The northeastern Wisconsin:Geol. Qj. Soc. of A s r , Bulletin, northeastern Wisconsin: Bulletin, v. %, %, p. p.1101-1112. 1101-1112. the Penokean Pcnokean orogen, orogen, central and Southwick, D. D. L L, Southwick, .,Morey, Morey,G. G.B., B., and andMcSwiggen, McSwiggen, P., P., 1988, 1988, Geological map (scale: 1:250,000) l:ZO,O@l) ofofthe eastern Minnesota, Minnesota, and and accompanying accompanying text, Minn. Geol. Survey, Suwey, Report of Investigations Inwtigations RI-37. RI-37. 54 �U GEOLOGY AND ECONOMIC POTENTIAL OF NORTHERN MICHIGAN GRAPHITE Jason J. J. Lagowski', ~ a g o w s k iAllan Allan ~ ~ M. M. Johnson2, ~ o h n s o nMilton Milton ~~ ere^ Jason Gere3 1 2 Departmnt Mineral Econanics, Ecmanics, Michigan MichiganTechnoLogicaL Technological Department of of MineraL University, Houghton, 4W31 University, Houghton, MI MI49931 Director, Director,MineraL MineralTechnoLogy/BiotechnoLogy Technology/BiotechnologyResearch Research Group Grcup Department of Mining TechnoLogicaL Department of Mining Engineering, Engineering,Michigan Michigan Technological University, University,Houghton, Houghton,MI MI49931 49931 Region II (Upper Region Peninsula) GeoLogist, GeologisttMichigan MichiganGeoLogicaL Geological (Upper PeninsuLa) Survey Division, Division, Department Survey Department of of NaturaL Natural Resources, Rescurces, Marquette, Marquettet MI MI 49855 49855 1ecent Recent cooperative cooperative research research by Michigan Technological Technological University (MTU) Survey (MGS) University (MTU) and and the the Michigan. ~ichigan~Geological e o l o ~ i c aSurvey l (MGS) was was undertaken to to determine determine the the quantity, quantityl quality quality and and distribution distribution of of the the carbon—rich carbon-rich graphitic graphitic slate slate resource resource present present in in northern northern Michigan. The ultimate ultimate goal goal of of this this research research was was to to provide provide Michigan. The mineralogical, chemical mineralogicall chemical and geophysical geophysical data data that that will will aid aid in in commercial development development of identifying uses that will lead to commercial of this this vast and, andl as—yet, as-yetl untapped untapped resource. resource. The graphite graphite is is present present in in the the early early Proterozoic Proterozoic Lower Lower Slate Slate Michigamme Formation Member of the Michigame Formation in in the the Baraga Baraga Group Group sediments. sediments. investigations (Hwang (Hwanga. . ., 1986) suggest that Earlier investigations 1986) suggest that 33 graphite—bearing slate, billion tons of graphite-bearing slatel grading grading 20—25% 20-25% carbon, carbonl exist at mineable depths depths in in a 30-mile 30-mile long long belt in in Baraga Baraga and and Marquette Compositionally, the Marquette counties counties (Fig. (Fig. 1). 1). Compositionallyl the slate slate consists consists predominately of of fine fine silica silica (43-53%), (43-53%I1 carbon carbon (2-47%), (2-47%)# iron iron oxide oxide (10—14%) and and alumina alumina (7-11%). (7—11%). The The slate slate contains contains relatively low (10-14%) concentrations of the alkaline alkaline earth concentrations earth metal oxides oxides CaO CaO (0.4-0.7%) (0.4-0.7%) and MgO (1—3%). (1-3%). Similarly, Similarlyl concentrations concentrations of of the the alkali alkali metal metal oxides oxides K20 K20 (2—3%) (2-3%) and particularly particularly Na20 Na20 (<0.12%) (<0.12%) were were quite quite low. low. This This composition composition is is consistent consistent with with deposition deposition under under reducing reducing anaerobic anaerobic conditions conditions with with minor minor or or no no clastic clastic input. input. , 1986) This and and earlier earlier studies studies (Hwang (Hwang&. . aJe1 1986)(Kramer (Kramer g&. et. al., or 1987) have determined that the graphite is is of the the "amorphous" llamorphousll or cryptocrystalline cryptocrystalline variety. variety. Typical Typical grain grain size, sizel as as determined determined by by electron electron microscope, microscopel ranged ranged from from 11 to to 33 microns. microns. Carbon analyses analyses 90 samples samples collected collected from from drill drill core core at at the the MGS MGS core core repository repository of 90 Marquette, MIl MI, yielded in Marquettel yielded aa range range of of 22 to to 47% 47% carbon. carbon. There There appeared appeared to to be be no no correlation correlation between between graphite graphite (carbon) (carbon) concentration concentration and and metamorphic metamorphic grade. grade. In drill cores cores with high high sample densityl density, there appeared to be a cyclical cyclical increasing sample increasing and and decreasing decreasing of of carbon carbon content content with with depth. depth. This suggest aa This could suggest cyclical cyclical depositional depositional pattern. Thus, Thusl graphite graphite content content might might be be function of stratigraphic stratigraphic positionl position, though more research research is is required to support support this this interpretation. interpretation. 55 �I: I 1 The reducing conditions underthewhich the slate carbon-rich slate was The reducing conditions under which carbon-rich was depositedf makes makes it it an an ideal ideal utrapti fftraplf for of trace trace and and deposited, for a a variety variety of rare rare earth earth elements. elements. Trace element analysis for 54 54 elements elements Trace element analysis for showed the presence of aa very very large large number number of of rare rare earth, earthf presence of alkaline, base metal and the the precious precious metalsl gold and and silver. silver. alkaline, metals, gold Vanadium'is abundant of of the the trace trace elements elements with with aa range range Vanadium is the most abundant of 1300-2000 1300-2000 ppm. ppm. Vanadium content content is is positively positively correlated correlated to to of carbon content. Althoughf there is is a fairly fairly wide wide divergence divergence in in carbon content. Although, there the absolute trace elements, elementsf the the absolute concentration concentration of the the various various trace ratios between trace elements are uniform for for composite composite ratios trace elements are amazingly amazingly uniform samples taken over aa 30-mile 30-mile zone zone (Fig. (Fig. 1) (Lagowski and and Johnson, Johnsonf samples taken over 1) (Lagowski 1989). Based on this observation, a similar similar chemical chemical environment environment 1989). this observation, of deposition deposition is is inferred. inferred. Alsof overprinting has has not not Also, metamorphic metamorphic overprinting these geochemical altered these geochemical relationships. relationships. I The The geology geology of of the the graphitic graphitic Lower Lower Slate Slate Member Member is is structurally events related related structurally complex due to multiple deiormational deformational events to the the 1850 1850 Ma Penokean Penokean Orogeny (Kiasner, (Klasnerl 1978) 1978) and and later later 1100 1100 Ma Ma to Keweenawan rifting. Keweenawan rifting. Extensive glacial glacial overburden overburden makes makes conventional outcrop conventional outcrop mapping mapping virtually virtually impossible. impossible. Fortunatelyf Fortunately, the the graphitic graphitic strata strata are are highly conductive conductive and and can can be be detected detected by by electrical geophysical electrical geophysical methods. methods. In order to determine determine which which geophysical technique technique or or combination combination of of techniques techniques would would provide provide geophysical the most accurate accurate data data for for future future exploration, explorationl aa multi—component multi-component the geophysical was conducted geophysical survey survey was conducted over over an an area area of of known known geology. geology. The results results of of this this investigation investigation indicate indicate that that the the best best The methods are horizontal loop electromagnetics electromagnetics and electrical methods and very in low frequency electromagnetics electromagnetics using the EM16Rf EM16R, used in combination. combination. The The use use of of geophysics geophysics in in conjunction conjunction with with drilling drilling suitable means means of of defining defining graphite-rich graphite-rich strata. strata. is the only suitable Utilization studies Michigan Tech Utilization studies conducted at at Michigan Tech show show several several promising uses for Upper Upper Michigan Michigangraphite graphite (Johnson (Johnson&. . aJ.f1989). promising al.,l989). One potential "as Ifas is" isffuse for for this this material is is as as aa high high quality quality shale substitute substitute in in the the manufacture The shale manufacture of portland cement. The abundant graphite-rich graphite—rich rock abundant rock may also also be considered considered as as an an unrecognized and and untapped untapped fuel fuel resource. resource. Compared Compared on on an an equal equal volume volume basis basis with with coal, coalf rock rock grading grading 30% 30% graphite graphite is is estimated estimated to to be roughly equivalent the heating value of of low low grade grade (60% (60% equivalent to the carbon) coal. coal. If the graphite material can be beneficiated from from carbon) the 15 15 to 25% carbon range to 80+%, this this material also be be an an carbon range material would also ideal metallurgical metallurgical reductant for the Pelletech Process of making self-fluxing self-fluxing iron iron ore ore pellets. pellets. I ri 56 �Figure1.1. Geologic Geologic map map of of western western Upper Upper Peninsula, Michigan Figure Peninsula, Michigan showing graphite-rich slate and geochemical sample showing graphite—rich slate and geochemical sample locations. locations. REFERERENCES CITED CITED REFERERENCES Huang, J.Y.,Carlsm,D.H., Johnson,A.M., a d VarAktine,J. (I%), l4wang,J.Y.,Car(s,D.H.,Johnson,A.p4, and VanLstine,J. (1986), @lPreliminary Investigatim Graphite Reswrces in Michigana@, 'Pretiminary Investigatia, ofof Graphite Resources in Mithigan", 115th Armat Mtg.,ME A I M , New Orleans, LA LA Preprint. Preprint. 115th Arr*aL Mtg.,SME AIME, lieu Orteans, Johnson, A.M., D.H., and and Cho, Cho, P.(1989),"Utitizatlixi P.(1989),Wti lizatimofof Johnson, A.M., Carlsm, CarLs, D.H., U p p - Michigan Michigan Graphite Graphite Resources', Resourcesa@, Geological Survey Survey Divisim, Upper GeoLogicaL Division, -89, O p n File Report, Michigan DNR Michigan OUR Open FiLe Report. •89, Klasner, J.S. (19Th),"Penokean (19?8),"Penokean Deformation D e f o m t ionand &-d Associated Ktasner,J.S. Associated Metamrphism in the Western Marquette Racge, NorthernMichigan", Michigan1@, Metansrphism in the Western Marquette Range, Northern V.89, pages 711-Z2. Geological Society Scciety of of America & m i c a BuLletin, Eulletin, V.89, GeoLogical pages 711-722. Krmr,R.S.,HuangJ.Y., a d Jthrm,A.M.(1987),'A Jchnsm,A.M.(1987),"A MineraLogicaL Mineralogicaland ad. Kraner,R.S.,Hwangj.Y., and Chemical Study Study of ofthe theGraphitic GraphiticLower LowerState SlateNeither, M-r, MichigChnicaL Michigarn Formation, Marquette Marcpette and a d Baraga Earaga Cou,ties, Comties, Nichigan",Geotogicat Michiganl@,Geological Formation, @en File R e p r t -87. Survey Division, Michigan DNR Survey Division, Michigan OUR cen FiLe Report -87. Lagouski,J. And A d Johnson,A.M.(1989),"Geotogic Johnson,A.M.(1989),@@Ge010gic Investigatim of Lagowski,J. Investigation of Graphite-Rich Strata in the M i c h i g m F o m t i m 0 a r a g a a Graphite-Rich Strata in the Michigatine Formation--Baraga andd Marqmtte Cou,ties, Comties, Michigan',Geotogica( Michiganoa,Ceo1ogicalSurvey Survey Division, Divisim,Michigan Michigan Marquette x r ~file Report -89. DNR Q OUR Open FiLe Report -89. 57 �STRATIGRAPHY OF OF THE THE NEGAUNEE NEGAUNEE IRON IRON FORMATION, FORMATION, STRATIGRAPHY EASTERN RANGE, MICHIGAN MICHIGAN EASTERN MARQUETTE MARQUETTE RANGE, JOE MANCIJSO, MANCUSO, JEFF STEPHEN STEPHEN BOWLING GREEN STATE STATE UNIV., UNIV., BOWLING BOWLINGGREEN, GREEN,OHIO OHIO43403 43403 BOWLING GREEN BILL KANGAS KANGAS ISHPEMING, MICHIGAN MICHIGAN 49849 CLEVELAND CLiFFS CLIFFS IRON IRON CO., ISHPEMING, CLEVELAND Introduction Introduction The stratigraphic stratigraphic subdivisions subdivisions of the Negaunee iron formation in the Empire Mine area (Secs. I9 19&&20) 20)differ differsubstantially substantiallyfrom fromthe theiron ironformation formationininthe theCD CDI Pit I Pitarea area(Sec. (Sec.18I) and and to to the the north in Sec. 5, 5, 6, 7 & 8. The TheEmpire EmpireMine Minearea, area, which which comprises mmprises over over 3000' 3000' of of continuous continuousiron iron formation above above the Siamo Siamo Formation, Formation, is is informally informally subdivided subdividedinto into 55 units units based basedon onmineralogy, mineralogy, texture, and and metallurgy. metallurgy. The TheEmpire EmpirePit Pitisisconfined confinedtotothe thesilicate, siiicate,carbonate, carbonate,and andcIastic clasticUnits units interval(1000' (1000'toto2100') 2100')above abovethe theSam0 Siamocontact. contact. The iron formation which occupy occupy an an 1100' 1100' interval formation in inthe the thick between between the the Siamo Siamo Formation Formation and the CD II Pit area area and and to the north north is is less less than than 1600' 1600' thick Summit Mountain is subdivided into 77 informal informal units. units. The Mountainsill. sill. It is The CD CD II Pit Pit is is located located in in the coarse coarse magnetite magnetite unit unit (unit (unit III) Ill) which which occupies occupies aa300' 300' interval intervalfrom from780' 780'to to1080' 1080' above above the Siamo Siamo Formation. Formation. 0 0 0 A 1 Iron formation with clastic interbeds 0 0 0 0 CD 0 Upper unditterentiated undifferentiated iron iron formation formalion 1 Summit Moujitain Sii b Ull JtiQ..HQEiZfl fIIt!.LIQIIc Magnetite-chert-carbonate Magnetite-cl\ert-carhnate iron formation C Cf 0 Magnetite Maqnetite iron iron formation forniation with with coarse silicates silicates ::-:-:-:-: Tracy Sill IC., rn n Carbonate Horizon . 121 Lj Magnetite iron formation with ligtii bands light green bands ( wavy beds with granules granules)) y Dir.grey grybIack, boddod1II. Dk black, thin 1Ii1nbedded F \ Magnetite-carbonate-silicate. Magnetite.carbonate-s~licatechert iron iron formation formation 5'e \ \ \ 1L \ \ Silicate Horizon ' t, \ \ 1 bl b o m CD . r ,? Interbedded coarse ctastic clastic sediment & iron iron tormation formation t4onmi5neiiie carb chort-silicaig IF. Coarse magnetite iron formation ll Lower undifferentiated iron formation 1I Magnetite-chert-silicate. Magnetite-chert~silicatecarbonate iron iron formation formation Magnetite-chertxarbonate Magnetite-chert-carbonate iron tormation formation chip)) ((poker poker chip Interbedded slate slate &8 Interbedded iron iron formation formation 3 w Siamo Slam0 Formation Format~ori 1 Siamo Formation Siarrio Formation CD II PIT PIT AREA CD A m < EMPIRE MINE EMPIRE MINE AREA AREA > > 3000' 3000' 58 I I I I I I 1600' 1600- I I I I I �U Coarse Coarse Clastic Clastic Interbeds Interbeds The Empire mine section includes a 400' zone of iron formation and interbedded interbedded coarse coarse clastic sediments (greywackes (greywackes or arkoses) arkoses) immediately immediately above above the the Siamo Siamo Formation Formationand andaa250250300' zone zone of of coarse coarse clastic clastic sediments sediments and and iron iron formation formation in in the the clastic clastic horizon horizon which which occupies occupies the the 300 interval from approximately to2000' 2000'above abovethe theSiamo Siamo Formation. Formation. The iron formation approximately 1700' 1700' to formation in in the the CD II Pit ara and and north north contains contains no no coarse coarse clastic clastic sediments. sediments. Riebeckite Zone Zone of iron formation containing blue riebeckite is In the Empire Mine a distinct marker zone of feetofofthe thecarbonate carbonateunit. unit. No riebeckite was seen in the CD II Pit area. area. found in the upper 150 150 feet Diabase Diabase Sills Sills thick) and In the CD CD I1 Pit area the Tracy Sill (250' (250'thick) and the Summit Summit Mountain MountainSill Sill (500' (500' thick) thick) ironformation. formation. No metadiabase sills sills intrude intrude the the 3000' 3000' of of iron intrude into the lower 1600' 1600' ofofiron formation in the Empire Empire Mine Mine area. area. Structure and and Oxidation Oxidation The Empire E. and dips 30-45 NW. ItIt is is offset offset by by aa Empire Mine sequence strikes NS to N . 40 E. number displacement. Very Very little oxidation oxidation is associated with number of WNW faults with less than 100' 100' ofofdisplacement. pit area area strikes strikes NS NSand anddips dips30-35 30-35 W. W. ItIt is is cut by EW EW and the faults. The The iron iron formation formation in the CD I pit apparent. North NW faults with less less than than aa few few hundred hundredfeet feet displacement. displacement. Very little oxidation is apparent. North of the CD I1 Pit in W. and dips 20-50 SW. in sections 5, 6, 7, and 8 the iron formation strikes N. 35-40 W. Numerous Numerous major major EW EW and and NW NW faults faults with with displacements displacementsof of over over1000' 1000' transect the iron iron formation. formation. The iron formation is completely completely oxidized oxidized to hematite hematite and and limonite limonite and, and, in in places, places, leached leached of of silica. silica. Correlation Correlation Similarities between the Empire Empire and CD CD II sections sections are few but but include include the the following: following: very similar similar in in mineralogy, mineralogy, texture, texture, and and metallurgy The carbonate unit in the Empire Mine is very I. to the coarse magnetite thickness and magnetite unit (Unit Ill) Ill) of the CD I1 Pit area; however, they differ in thickness position above the Siamo Siamo Formation. Formation. with magnetite rich granules occur in Zones up to 50' thick of wavy-bedded iron formation with 2. 2. above the the coarse coarse magnetite magnetite unit in unit VI approximately approximatelyIOU' 100' above in the the CD CD II Pit area. Stratigraphically Stratigraphicallythis this corresponds closely to the position position of of the the clastic clastic horizon horizon which which occurs occurs just just above above the the carbonate carbonate unit at the Empire Empire Mine. Mine. Several thin lenses lenses (less (less than 2") composed composed of sand sand sized sized quartz quartz grains grains and and 3. 3. stilpnomelane stilpnomelane occur occur in in the the upper upper undifferentiated undifferentiatedunit unit at at the the Empire EmpireMine Mineand andin inunit unitVI VIininthe theCD CDI I Pit area. area. Conclusions Conclusions south, The Empire Empire mine section section and and the CD IIPit Pit section section appear appear to meet meet abruptly abruptly at at 14600' 14600' south, between 18 and and between DDH DDH holes holes 47 47 and and50 50approximately approximately1200' 1200' north north of of the the boundary boundarybetween betweensecs. sees.18 19. 19. The contact cannot be considered considered aa simple simple fault because because the the relationship relationshipis is not not marked markedby by thickness. Contact Contact displacement or oxidation but by an abrupt change in stratigraphy and thickness. relationships relationships indicate indicate either either a complex fault with great displacement such as the Palmer fault, or an Archean fault zone which was active during deposition of the iron formation and reactivated during the Penokean Penokean Orogeny. Orogeny. 59 �I Petrologic and Evolution ofthe Petrologic and GeochemicalEvolution of the Penokean Penokean Peavy Pond Pond Complex Michigan County,M3chigan Peavy Complex,Iron h n County, David J. Stephen D. D. Stahl, Stahl, Adam Heft, and Kristin Huysken J. Matty, Stephen Department of of Geology, Geology, Central Central Michigan MichiganUniversity, University,Mt. Mt.Pleasant, Pleasant, MI MI 48859 The Peavy Peavy Pond Pond Complex Complex (PPC) is a metamorphosed, composite composite pluton of of Penokean Penokean age age intrudescomplexly complexly deformed, deformed, biotite biotite to to (1.85 Ga, Van Van Schmus, personal communication) that intrudes sillimanite grade grade pelitic pelitic to to quartzose quartzoseshales shalesand andgraywackes graywackesofofthe theProterozoic ProterozoicMichigamme Michigamme lavas of of the theProterozoic Proterozoic Hemlock Hemlock Formation Formation (HF). (HF). Formation (MF) and basic pyroclastics and lavas Rocks of the the PPC are characterized Rocks of characterized by by the thelithologic lithologicsuccession succession gabbro-diorite-tonalitegabbro-diorite-tonalitegranodiorite-granite. Gabbro granodiorite-granite. Gabbro and diorite diorite are are most most abundant abundant and andare arecommonly commonly associated with HF wallrocks wallrocks in the southern southern portion portion of of the the complex. complex. The The more more silicic silicic tonalites, tonalites, granodiorites granodiorites and and granites are granites are restricted restrictedto tooutcroppings outcroppings principally principally in the the northwestern northwestern portion portion of of the the complex complex in close proximity proximity to rocks rocks of of the the MF; these rocks often contain xenoliths xenoliths of of MF and and develop develop locally locally into migmatites. The PPC and surrounding surroundingarea areawere weremapped mapped in inexcellent excellentdetail detailby by Bayley Bayley (1959) (1959) and Dutton (1968). Bayley fractional Bayley interpreted interpreted the themafic maficrocks rocks of of the the PPC PPC to to be products of of fractional of aa parental basaltic magma crystallization of magma and and considered considered the more silicic phases of of the complex parental magma. magma. complex to to have have been been derived derived from from variable variable assimilation assimilation of of the the MF MF by by this this parental Bayley's of Bayley's interpretations interpretations were based largely largely on on field field and and petrographic petrographic data; data; due due to to the lack of uninterrupted outcrops, uninterrupted outcrops,however, however, other otherexplanations explanationsfor forthe thedevelopment developmentof ofthe thecomplex complex must mustbe be considered. These of each each phase phase of of the the PPC PPC as as a separate considered. These include include development development of separate magma, magma, variable variable mixing melting of of walirocks, wallrocks, or some combination combination of processes mixing of of magmas, magmas, partial melting of any any of of these these processes with the the fractionation-assimilation fractionation-assimilation process process originally originally suggested suggested by by Bayley. Bayley. tectonic significance significance in intrudesrocks rocks considered considered to The PPC has potential tectonic in that that it intrudes represent aa passive passive margin margin sequence sequence (Larue, (Larue, 1983; 1983; Ueng et al., 1988), 1988), a rifted passive margin assemblage (Cambray, 1978), 19781, a forearc or backarc basin (Van (Van Schmus, Schmus, 1976), 1976), or aa foredeep foredeep (Hoffman, 1988; 1988;Barovich Barovichetetal., al.,1989). 1989). Recent Recent studies studies of of the the HF HF volcanics volcanicsand and the the associated associated (Hoffman, Kiernan Sills (KS; which lie about 44 km Sills (KS; km to to the thenorth northofofthe thePPC) PPC)indicate indicateMORB-like MORB-likegeochemical geochemical characteristics of While these data suggest of these rocks; While suggest aa MOR-like MOR-like rift-related origin origin for these these interpreted to for the the HF and KS (Ueng et al., units, they also also could be interpreted to reflect reflect a back-arc origin for 1988;Wee, Wee,1989). 1989). Data Data derived from from analyses of of the the nearby Badwater (Greenstone) 1988; (Greenstone) Formation indicates an origin origin closely closely related to that thatof of the the HF HFand andthe theKS KÂfor forthese theselavas lavas(Cudzillo, (Cudzillo,1978; 1978;Wee, Wee, 1989). 1989). The goals of our our study were to determine the the processes by which the PPC evolved and to gain insights into insights into the the tectonic tectonic evolution evolution of of this area area through through geochemical geochemical studies studiesof of the the PPC. PPC. . . . . Variations within Major PPC. m i o r Element Vanwithm the PPC the major major oxides oxidesvs. vs.XFeO/(ZFeO+MgO) FeO/(FeO+Mg0) for Plots the for our our PPC PPC data data relative to that that of of the MF, the HF, the the KS, KS, the the Badwater Badwater Fm. Fm.and andthe theNorthern NorthernWisconsin WisconsinArc ArcComplex Complex clearly clearly distinguish distinguish mafic phases phases of of the the PPC PPC from fromother otherunits units largely largelyon onthe thebasis basisofofthe thehigher higherMgO MgOand andlower lowerXFeO FeO ma% concentrations of of the the PPC PPC rocks. rocks. With With increasing increasing differentiation, the mafic PPC phases show show relatively strong depletions depletions in in FeO, FeO, MnO, MnO, and and MgO MgO and corresponding corresponding enrichments enrichments in in A1203, A1203, Na20, K20, K20, and and to to some some extent in Ti02. These Thesetrends trendssuggest suggestfractionation fractionation of of ferromagnesian ferromagnesian plagioclase. Attempts to apply apply Pearce Pearce Element Element Ratio Ratio Diagrams Diagrams to to test test mineral phases instead of plagioclase. this hypothesis failed as there there are areno no truly trulyconserved conserved major major or or trace trace elements elements in in the thePPC PPCrocks; rocks; this is is true truefor for silicic silicic phases phases of of the the PPC PPC as as well. well. The Themore moresilicic silicicphases phases of of the the complex complex tend to to converge towards the compositions of of the the MF rocks rocks indicating indicating possible possible interaction interaction of the MF in the converge towards the evolution of the the PPC as suggested by Bayley (1958). (1958). Generally higher concentrations of evolution of of 1(20, K20, Si02, Si02, and to some extent Na20 Na20 in be interpreted interpreted as in the the silicic silicic PPC phases relative to to the the MF MF could be as resulting from assimilation processes. processes. The The elevated elevated concentrations concentrations of of these these elements, elements, however, however, 60 I �U melting processes processes involving involving minimum melts of of quartz, quartz, could also be explained by partial melting potassium feldspar and and sodic sodic plagioclase plagioclase in the the MF MF rocks. rocks. . . . . PPC Trace Element Elmmt Variations V m d m n s within the PPC Mafic rocks rocks of of the the PPC PPC are are distinguishable from other mafic rocks of of the the region on the Mafic basis of trace element abundances as well as by major major element element concentrations. concentrations. For For example, example, concentrations of Sc and Co are generally lower and concentrations of Ni, Ni, Ta, Ba and Sr STare are generally higher in the the PPC PPC rocks rocks than than in in the theHF, HF,KS KS metagabbros, metagabbros, or or Badwater Badwater Fm. Fm. trends are are clearly clearly visible visible for the transition metal metal elements elements Sc, Sc, Cr, Crl Co, Co, and Ni in Fractionation trends mafic PPC PPC rocks, rocks, suggesting suggesting removal removal of ofphases phases that that preferentially incorporate these elements, mafic elements, perhaps chromite, chromite, olivine, olivine, pyroxene, pyroxene, or some some combination combination thereof. some field field evidence evidence in thereof. There is some the form 80% Hb) for pyroxene fractionation (ca. 80% form of of cumulate-like cumulate-like hornblende-rich hornblende-rich rocks rocks (ca. pyroxene); this trace (metamorphic hornblende hornblende after pyroxene); this is is the the favored favored starting starting point for future future trace element modelling. would increase increase the the relative modelling. Fractionation Fractionation of of oxides, oxides, olivine olivine or pyroxene pyroxene would concentrations of Ba and Rb in more more differentiated differentiated rocks rocks of of the the complex, complex, consistent with observed observed trends. The Theincrease increaseof of Sr Srconcentration concentration with with increasing increasing differentiation supports the assumption of fractionation, since since this this process process would wouldresult result in in aa systematic decrease in Sr of little plagioclase plagioclase fractionation, with increasing fractionation. Limited Limited plagioclase plagioclase fractionation is also supported by REE data data which which are characterized characterized by by relatively relatively flat, flat,LREE-enriched, LREE-enriched, profiles profiles and development development of of only small positive positive and negative negative Eu Eu anomalies. anomalies. Trace element concentrations concentrations of of PPC PPC silicic silicic rocks rocks also also converge converge towards the thecompositions compositions of MF MF rocks, rocks, supporting supporting the the hypothesis of of MF MFinvolvement involvementininthe the evolution evolutionofofthese theserocks. rocks. This This is of discussed further furtherbelow. below. 3Snidergrams mdermm To test the that silicic rocks are are related by assimilation or the validity validity of the hypothesis that silicic PPC rocks partial melting partial meltingof of MF MF rocks, rocks, we we constructed constructed spidergrams spidergrams(modified (modified from from Thompson, Thompson, 1981) 1981) normalized average MF. MF. normalized to average Among other things* things, the spidergrams indicate that rocks of the the H HF Among other F are depleted in LILE MF. The and enriched in HFSE relative to MF. The PPC PPC diorites and gabbros appear similar in most are the higher concentrations of Sr and the lower respects to the HF H F rocks; rocks; major exceptions exceptions are of Th, Th, P, P, Y, Y, and and Yb Ybininthe the PPC PPC rocks. rocks. The lower Tb concentrations concentrations in in particular lower Th concentrations of are noteworthy in that that these thesevalues valuesmay mayreflect reflectdifferences differences in the the relative relative source source regions regions andlor andor paths of ascent paths of the PPC and the the HF. HF. The PPC tonalites, granodiorites and granites granites cluster cluster around around the the average average MF MF composition. There is only a small composition. small overall variation from from unity (and thus from from average average MF) MF) for gabbroic parental parental 1)large-scale large-scale contamination contamination of gabbroic the PPC tonalites. This Thiscould couldresult resultfrom from1) maginas MF or or 2) 2) almost almost complete complete melting melting of of MF MF to to form form magmas by assimilation assimilation of of extensive extensive amounts amountsof of MF the tonalites; the observed major majorelement elementdata. data. The the latter latterhypothesis hypothesis is is broadly broadly consistent with observed elevated concentrations of of the the LILE LILE and and LREE, LREE, as as well wellas asZr Zrand andHf, Hf,ininthe the PPC PPC granites granites and elevated granodiorites relative to average MF MF suggest suggest that that partial melting processes processes rather rather than assimilation processes processes were were dominantly dominantly responsible responsible for the the production production of of these these rocks; rocks; this thisisis consistent with interpretations interpretationsregarding regardingthe themajor majorelement elementcompositions compositionsof of these theserocks. rocks. D .~ s c.r . . Tectonic Discrimination Tectonic We have so far applied We applied only only a few few of the many available available methods methods of of geochemical geochemical discrimination discrimination diagrams to the PPC PPC rocks to learn more about the tectonic tectonic setting setting of of their origin. origin. AFM diagrams diagrams indicate indicate aa distinct calc-alkaline trend for for all all rocks rocks of ofthe the PPC. PPC. When plotted AFM calc-alkaline trend plotted alone, however, however, the the mafic mafic PPC PPC rocks rockscan canbe beinterpreted interpreted to reflect indistinctly either a calccalcalkaline (arc-derived) trend trend or a tholeiitic trend. Inasmuch tholeiitic (MORB-like) (MORB-like) trend. Inasmuch as the the MF MF rocks rocks are are characterized characterized by a distinct distinct caic-alkaline calc-alkaline trend, trend*reflecting reflecting their their derivation derivation from from the theWisconsin Wisconsin arc to the south to the the north and east Archean calc-alkaline plutonics to east (see (see Barovich Barovich et south and andfrom from the the Archeari al., it is conceivable conceivablethat that the calc-alkaline calc-alkaline trend trend of of the the entire PPC suite largely reflects the a]., 1989), 1989), it apparent genetic apparent genetic association of ofthe themore more silicic silicic phases phases of of the the PPC PPC with with the thecalc-alkaline calc-alkaline MF. MF. 61 �I Plots Plots of of Ca0miO2 CaO/Ti02 vs. vs. Ti02 Ti02 and of A1203mi02 A1203/Ti02vs. vs.Ti02 Ti02 (Sun (Sun and and Nesbitt, Nesbitt, 1978) suggest relatively undepleted mantle source that which the derivation of the PPC from aa relatively source similar to that which MORB. The more silicic silicic rocks rocks of ofthe the PPC PPCtrend trend into into the depleted mantle/arc produces MORB. mantlelarc field in the the A1203mi02 of the the CaOPFiO2 CaOmiO2 vs. A12O31TiO2vs.vs.Ti02 Ti02plot, plot,yet yetfall fallbeyond beyondthe the depleted depleted mantlelarc mantle/arc field of vs. Ti02 Ti02 plot. In plot. In both both cases, cases, however, however, there there is is aa strong strongrelationship relationshipbetween between silicic silicic PPC rocks and those of that once the MF that once again again suggests suggests aa genetic genetic nexus. nexus. A MORB-like MORB-like afinity affinity of ofthe the mafic mafic PPC PPC rocks rocks is is also indicated by Zr/Y vs. Zr plots (Pearce Z r N vs. Tb/Yb plots, plots, however however some some PPC PPC gabbros gabbros could could be be interpreted interpreted and Norry, 1979) 1979) as as well well as as Ta/Yb TaNb vs. ThRb be arc-related on the basis of vs. Zr Zr diagram. diagram. In to be of the ZrIY ZrN vs. In both diagrams, diagrams, silicic silicic phases of of the PPC plot with with rocks rocks of of the the MF. MI?. There exists exists at a t this thistime timeno no unambiguous unambiguous explanation explanation for for the the tectonic tectonic setting setting of of the the PPC. PPC. While iitt seems clear that While thatthe theoriginal originalgabbroic gabbroicmagma magma was wasMORB-like, MORB-like, and probably probably originated originated rift or a back-arc back-arc setting, we we are are unable to distinguish between between these in either a MOR-like MOR-like rift that suggests environments aatt this this time. time. To Tocomplicate complicate matters matters further, further,there thereisissome some evidence evidence that suggests that certain arc. We certain PPC PPC gabbros gabbros may may have originated within a volcanic volcanic arc. We cannot cannot unilaterally unilaterally the northern Wisconsin arc to the PPC, but reject these data data due due to to the the relatively relatively close close proximity of the we believe believe that that the we the arc-like arc-like characteristics characteristicsof of these thesegabbros gabbros could could be explained explained by by assimilation assimilation of of MF. The calc.-alkaline arc-like character character of of the more silicic phases of PPC could also reflect MF. calc-alkaline arc-like reflect an an origin within a volcanic arc environment, however, however, there there appears to be substantial substantialgeochemical, geochemical, origin petrologic, and and petrographic petrographic evidence evidence to to support support the the hypothesis that that these petrologic, these rocks rocks were were derived derived largely from or through assimilation largely from assimilation of of the the calc-alkaline calc-alkaline MF. MF. References Barovich, K.M.,Patchett, Patchett, P.J., Peterman, Z.E., Nd isotopes isotopes and and the origin of Barovich, K.M., Z.E., and Sims, P.K., P.K, 1989, Nd of the 1.9-1.7 1.9-1.7 Ga Penokean continental continental crust crust of of the the Lake Lake Superior Superiorregion: region: Geological Geological Society Society of of 333-338. America Bulletin, Bulletin, v. v. 101, 101,p. p. 333-338. Bayley, R., R., 1959, Geology Geologyofofthe the Lake Lake Mary Mary quadrangle, quadrangle, Iron County, Michigan: U.S. U S .Geological Geological Survey Suwey Bulletin, Bulletin, v. v. 1077, 1077,112 112 p. Cambray, F.W., F.W., 1978, Plate tectonics as aa model model for the environment environment of of deposition and and deformation of of the Early Early Proterozoic Proterozoic (Precambrian (Precambrian X) X) of northern Michigan: Michigan: Geological Geological deformation Society of of America America Abstracts Abstracts with Programs, Programs,v. v. 10, 10,no. no. 7, 7,p. p. 376. 376. Cudzillo, T.F., 1978, Geochemistry of Early Proterozoic Cudzillo, T.F., Geochemistry of Proterozoic igneous rocks, northeastern northeasternWisconsin Wisconsin and upper KS, University Universityof of Kansas, Kansas, 202 202 p. p. upper Michigan: Michigan: Ph.D. Ph.D.thesis, thesis,Lawrence, Lawrence, KS, Dutton, C., of the the Florence Florence area, Wisconsin and Michigan: C., 1968, 1968, Geology Geology of Michigan: U.S. U.S.Geological Geological Survey Survey Professional Paper 54 p. Paper 633, 633,54 p. Hoffman, P.F., P.F., 1988, 1988,Animikie AnimikieGroup: Group: A A Penokean Penokeanforedeep?: foredeep?: Annual Annual Institute Institute of Hoffman, of Lake Superior Geology Proceedings and Abstracts, 40-41. Geology Proceedings Abstracts, v. v. 34, 34, pt. pt. 1,1,p. p. 40-41. Larue, D.K, of the the Lake Superior region: region: Tectonostratigraphic D.K, 1983, 1983, Early Early Proterozoic Proterozoic tectonics of Tectonostratigraphic terranes zone: terranesnear nearthe thepurported purportedsuture suture zone:Geological GeologicalSociety SocietyofofAmerica AmericaMemoir Memoir 160, 160, p. p. 33-47. 33-47. Pearce, JJ.A., Petrogenetic implications implications of ofTi, Ti,Sr, Sr, YYand and Nb Nb variations variations in Pearce, . A , and Norry, M.J., 1979, 1979, Petrogenetic volcanic rocks: Contributions volcanic rocks: Contributionsto toMineralogy Mineralogy and andPetrology, Petrology, v. v. 69, 69, p. p. 33-47. 33-47. regularities and Sun, S.S., S.S., and and Nesbitt, Nesbitt, R.W., R.W., 1978, 1978, Geochemical Geochemical regularities and genetic genetic significance significance of of ophiolitic basalts: Geology, Geology,v. v. 6, 6, p. p. 689-693. 689-693. Ueng, W.C., W.C., Fox, Fox, T.P., T.P., Larue, D.K., J.T., 1988, D.K., and Wilband, J.T., 1988, Geochemistry Geochemistry and petrogenesis of of volcanicrocks rocksand andthe theKiernan Kiernan Sills, Sills, southern southern Lake Lake the Early Proterozoic Proterozoic Hemlock Hemlock volcanic region: Canadian Superior region: CanadianJournal JournalofofEarth EarthScience, Science,v.v.25, 25,p. p. 528-546. 528-546. Van Schmus, W.R., Early and Middle Proterozoic Proterozoichistory history of ofthe the Great Great Lake area, area, North W.R., 1976, Early North America: Philosophical Philosophical Transactions TransactionsofofRoyal RoyalSociety Societyof of London, London, Series SeriesA, A, v. v. 280, 280, p. p. 605605628. 628. Wee, S.M., S.M., 1989, 1989, Geochemical Geochemicalinvestigation investigationofofEarly Early Proterozoic Proterozoicigneous igneousrock rockinin northern northern Wee, Michigan and and the northeast U.S.A.: Ph.D. Ph.D. thesis, East MI, Michigan northeast portion portion of of Wisconsin, Wisconsin, U.S.A.: East Lansing, Lansing, Ml, Michigan State State University, Michigan University, 185 185p. p. 62 �I Crustul structure of northeastern Lake Superior from GLIMPCE reflection and refraction data I Milkereit1, P. Morel-à-l'Huissier1, Morel-5-l'Hiiissierl, A.G. I - c c I ~M.D. ~M.D. , Thomas1 B. Milkeroit1, A.G. G Green', Thomas1 A. Tr&u2, M.W. M.W. Lee3 L G C ~and a n d W.F. W.F. Agena3 ~ g e n a ~ A. Tehii2, 1 Geological Geological SSurvey of CCanada, Ottawa, ~ w v e yof anada, O t t a w a , Canada, C a n a d a , K1A K I A 0Y3 OY3 2O Oregon State regon S t a t e University, U i ~ i v e r s i t yCorvallis, ,Corvallis, Oregon O y c g o n 97331 97331 U.S. U.S. Geological Survey, Denver, D c n v e r , Colorado C o l o r a d o 80225 80225 rrlle deep 'l'lle deep structure of of the the Midcontinent hIidcontincnt Rift Rift beneath beneath Lake Lake Superior Superior was was imaged imaged in in detail during during tile tlie GLIMPCE GLIMI'CE reflection reflection survey survey of of tile tlie Great Great Lakes. Lakes. Reflection Reflection profiles profiles across across the rift revealed graben [Behrendt et al., 1988; Cannon et et al., tlie revealed a deep deep asymmetric asymnxtric central central graben [Belirendt et 1988; Cannon al,, 1989; Green Green et al., 1989] whose existence existence and and magnitude magnitude was was not not documented documented before. before. The The 19891 wllose geometry of of tlie the central graben changes along the the axis axis of of the the Midconti~ient~ Midcontinent Rift geometry changes significantly significantly along System and sedimentary rocks, in in places places greater greater than 30 30 km km System and aa sequence sequence of volcanic volcanic and sedimentary rocks, thick, fills fills the graben. graben. Here Herewe wepresent presentadditional additionalGLIMPCE GLIAIPCEseismic seisnlic reflection reflection sections, sections, refraction and stacking velocity velocity analyses, and potential field field data data from from outside tile the main main rift rift basin basin beneath northeastern nortlieastern Lake Lake Superior. Superior. Figure 1. F i g u r e 1. GLIMPCE reflection reflection profiles profiles(A, (A,B, B,FF and and G) C) and GLIMPCE and OBS OBS recording recording site s h e on on shaded relief relief magnetic anomaly anomaly map. map. 0 63 km nHEf 50 -F= �These data data will will shed shed some some light light on on (a) (a)pre-Keweenawan pre-Keweenawan structures structures (aulacogens (aulacogens ?), ?), (b) (b) Keweenawan rocks (based on seismic seismic velocities), areal correlations among Keweenawan velocities), (c) thickness and areal extent of prepre- and post-rift sediments, sediments, and (d) the the correlation correlation between between potential field potential field data data and seismic seismic structures. st,ructures. and one one of of the the ocean ocean Location of of GLIMPCE GLIAIPCE reflection reflection profiles The Location profiles(A, (A,B, B, FF and and G) and bottom seismometers anomaly map map in Figure seismometers (UBS) (OBS) are shown on a shaded relief relief magnetic anomaly 1. At the intersection A and and G we 1. At intersection of profiles profiles A we have obtained obtained a high high quality quality image image of of the upper crust that has some 3-D control. Figure 2 shows a shallow, fault-bounded graben fault,-bounded graben upper that 11% some 3-II control. Figure 2 shows a sl~allow~ preserved beneath [Osler structure preserved beneath early earlyKeweenawan Keweenawan sediments sediments and and volcanics volca~~ics [Osler volcanics volcanics in in structure the interpretation image supports supports a tectonic model of 19891. This This seismic seismic image model of interpretation by by Cannon Cannon et etal., al.?1989]. lower Proterozoic Proterozoic intracratonic intracratonic rifting prior to units and lower to the the advent advent of of Keweenawan Keweenawan volcanic 11nits I suggests rocks (i.e. (i.e. the pre-Ihweenawan rocks suggests that pre-Keweenawan tile Sibley Sibley Group) Group) were were deposited deposited in in aashallow, sl~allow, probably fault-bounded intracratonic probably intracratonic basin. basin. The reflective, reflective? layered layered Lower Lower Keweenawan Keweenawan sequence, found found on on all all profiles profilesinin northeastern northeastern Lake LakeSuperior, Superior,can canbe be used used as as a marker sequence, marker horizon to define volcanic activity activity outside outside the the main horizon define the lateral extent extent of of early early Keweenawan Keweenawan volcanic rift basin. Figure Figure 2. 2. Migrated reflection profiles along lines lines A A and G showing subsurface structure structure I beneath northeastern northeasteru Lake Lake Superior Superior with with (from (from the thetop) top)non-reflective non-reflective post-rift post-rift sediments, sediments, volcanicunit, unit, and an interpreted image Keweenawan volcanic image of of aa Lower Lower Proterozoic reflective Early Keweenawan fault-bounded fault-bounded rift rift (aulacogen). (aulacogen).Generalized Generalizedvelocity-depth velocity-depthprofile profilewas wasdetermined determinedfrom fromOBS OBS recording along line A. wide angle recording I S I • .• •.•:—. I ----0• I Post-rTff I �I wide-angle wavefields wavefleldsrecorded recorded by by OBS OBS [GLIMPCE The T h e wide-angle [GLIMPCE seismic seismic refraction working working group, 1989] seismic recording recordingsystem system have have been been used used to 19891 and the the 120-channel 120-channel reflection reflection seismic to define velocity structure. structure The hasprovided provided useful useful information information define the shallow shallow velocity Thevelocity velocity model model has for structural structural intcrpretations interpretationsofofcomplex complexreflection reflectionsections. sections.Volcanics Volcanicsand andsediments sedimentsofofKeKeweenawan age outcrop outcrop extensively extensivelyinin the the southern southern and and western Lake Superior Superior region. region. On western Lake On weellawan age contrast, iio region. Earlier northeastern Lake Lake Superior Superior region. no post-rift post-rift sediments sediments outcrop outcrop in the northeastern studies that Lake studies [halls [Halls and and West, West, 1971] 19711 presented presented evidence evidence that Lake Superior Superior is underlain underlain by by as as much thick post-rift post-rift sediments. sediments. The TheGLIMPCE GLIMPCE experiment experiment confirms confirms their interintermuch as 3 km thick pretation velocities appropriate appropriate for upper pretation and andsuggests suggests an aneven even wider wider areal areal extension extension of of low low velocities Keweenawan (Bayfield-Jacobsvifleequivalent) equivalent)sandstones sandstonesthan than previously previously thought; thought; it also Keweenawan (Bayfield-Jacobsville also indicates an apparent (glacial drift) drift) in northeastern apparent lack lack of of thick thick unconsolidated unconsolidated sediments sediments (glacial Lake Superior. Findings Lake Superior. Findings of of the the seismic seismic studies studies such such as (a) (a) the the lateral lateralextension extension of of Early Early Keweenawan volcanics, volcanics,(b) (b) the the lateral lateral extension extension of of low low velocity velocitypost-rift post-rift sediments, sediments, and and (c) Kewccnawan along the basin bounding faults and accommodation the position of late late intrusive intrusive complexes complexes along accommodation zones can can be be correlated correlated with with major major t,rends trends and breaks in the gravity and magnetic anomaly zones anomaly patterns. \ References References W.F. Behrendt, J.C., J.C., A.G. A.G. Green, Green, W.F. W.F. Cannon, Cannon,D.R. D.R. Hutchinson, IIutchinson, M.W. M.W. Lee, Lee, B. Milkereit, Milkereit, W.F. Crustal structure structureof of the the Mid-continent Mid-continent Rift Rift system system -- Results from 1988. GLIMPCE deep deep seismic seismic reflection reflection profiles, profiles, Geology, 16, 16, 81 81 -- 85, 85, 1988. Agena, and C. C. Spencer. Spencer. Cannon,W.F., A.G. Green, D.R. ilutchinson, IIutchinson, M.W. M.W. Lee, Lee, B. Milkereit, Milkereit, J.C. Behrendt, Behrendt, II.C. 1I.C. Halls, J.C. Green, Sutcliffe and C. Spencer, Spencer, The The North North AmerAmerGreen, A.B. A.B. Dickas, Dickas, G.B. G.B. Morey, Morey, R. Sutcliffe ican Midcontinent Rift Rift beneath beneathLake LakeSuperior Superiorfrom fromGLIMPCE GLIMPCEseismic seismicreflection reflection profiling, profiling, 8, 305 305 - 332, 332, 1989. 1989. Tectonics, 8, Green, A.G., Milkereit,D.R. DR. liutchinson, Green, A.G., W.F. Cannon, Cannon, 13. B. Milkereit, Hutchinson, A. Davidson, Davidson, J.C. Behrendt, Behrendt, C. Spencer, M.W. Lee, P. Morel-à-l'hluissier and W.F. W.F. Agena, Agena, A A "GLIMPCE" "GLIMPCE" of of the deep Morel-a-1'IIuissier and crust beneath the in: Properties Properties and andProcesses Processes of of the the Earth's Earth's Lower Lower Crust, Crust, crust the Great Great Lakes, Lakes, in: R.F Mereu, Mereu, S. S. Mueller, Mucller, D.M. D.M. Fountain Fountain (Eds.), (Eds.),Geophysical Geophysical Monograph Monograpli Series, Series, 51, 51, 65 65 -- 80, 1989. 1989. GLIMPCE GLIMPCE Seismic Seismic Refraction Refraction Working Working Group, Group,GLIMPCE GLIMPCEseismic seismicexperiments experiments— - long-offset recordings, EOS, 70, 853, 1989. 1989. recordings, 70, 841 841 - 853, Halls, II.C., iI.C., and survey in Lake Lake Superior, Superior, Canadian Journal Journal and G.F. G.F.\Vest, West, A A seismic seismic refraction refraction survey 1971. of Earth Sciences, of Sciences, 8, 610 610 - 630, 630, 1971. 65 �I THE SONJU SONJU LAKE INTRUSION INTRUSION AND ASSOCIATED KEWEENAWAN ROCKS: GEOCHEMICAL AND GEOPHYSICAL GEOPHYSICAL EVIDENCE EVIDENCEOF OFPETROGENETIC PETROGENETICRELATIONSHIPS RELATIONSHIPS GEOCHEMICAL AND Schaap, and Val W. Chandler MILLER, James D., Jr., Brian D. Schaap, Minnesota Geological Geological Survey, Survey,2642 2642 University UniversityAve., Ave., St. St. Paul, Paul,Minn. Minn.55108 55108 Minnesota The The Sonju Sonju Lake Lake intrusion intrusion (SLI) (SLI) is is aa layered layered sequence sequence of mafic mafic cumulates cumulatesthat that is is one one of of the the most most known in in the the Keweenawan Keweenawan section section(Weiblen, (Weiblen, 1982). 1982). It is part of of completely differentiated bodies known the Beaver intrusive supersuite of gabbroic to granitic granitic rocks which were Beaver Bay Complex Complex -- aa multiple intrusive emplaced into emplaced into volcanic volcanic rocks rocks of the the North Shore Shore Volcanic Volcanic Group Group near near Silver SilverBay Bay and and Finland Finland in in northeastern Minnesota (Fig. 1). Preliminary Preliminarygeochemical geochemical data data and and somewhat somewhat equivocal equivocalintrusive intrusive relationships between ferrogabbroic rocks led Miller relationships between the SLI SLI and spatially associated diabasic and ferrogabbroic (1989) (1989) to suggest suggest that all of these intrusive units may be comagmatic and roughly coeval. Also, Also, chemical data be interpreted interpreted to to indicate indicatethat that the the extensive extensivemass massof of granitic graniticto to chemical data of Rogge Rogge (1989) (1989) can can be granodioritic rocks that overlie differentiates of the layered sequence. overlie the SLI SLI are are siliceous siliceous differentiates sequence. However, further mapping However, the results of geochemical and geophysical modelling, together with further and petrographic studies, studies, indicate indicate that the SLI is genetically and temporally distinct from these other units of the Beaver Bay Complex. Complex. The laminated and locally layered, mafic cumulates of the SLI, first described in detail by (15°-25°) Stevenson (1974), occur as a gently (15' -25O) southward-dipping sequence which has a assuming negligible negligible faulting faulting (Figs. (Figs. 1 & & 2). 2). The stratigraphic thickness of about 1100 meters, assuming footwall of the intrusion is composed of a complex mixture of gabbro, granophyre, granophyre, and volcanic hornfels. The homfels. Theuppermost uppermostlaminated laminatedferrodioritic ferrodioritic cumulates cumulates are are overlain by a massive massive granophyric olivine ferrodiorite olivine ferrodiorite that irregularly irregularly grades grades into into a prismatic mafic granodiorite granodiorite over over aa stratigraphic stratigraphic thickness of about 100 100 meters. Farther Farther south south (200-400 (200-400m m upsection?), upsection?), this prismatic prismatic granodiorite granodiorite grades into a leucocratic granophyric granite. The The granodiorite granodiorite and and granite granite are are collectively collectively termed 1). The The eastern eastern margin margin of the SLI SLI is abruptly abruptly truncated by a NNEthe Finland granite (Fig. 1). trending fault that juxtaposes the SLI and olivine gabbroic rocks rocks of of the the Beaver Beaver River River diabase. diabase. The The aeromagnetic aeromagnetic signature signature of the SLI, SLI, which can be traced to the west beneath a cover cover of glacial till, indicates that the intrusion curves to the south, rimming the underside of the Finland granite (Fig. 1). The TheSLI SLIhas hasaahalf-saucer half-saucershape shapewith with aa strike strikelength length of of at at least least 20 20 kilometers. kilometers. The medium-grained ophitic ophitic olivine olivine diabase diabase The Beaver Beaver River River diabase diabase is typically a fine- to medium-grained the Beaver Beaver Bay Bay Complex Complex (Fig. (Fig.1). occurring in dikes and sills throughout the 1). Emplaced into the Beaver River diabase ferrogabbroic rocks Beaver diabase in scattered scattered locations locations are the typically zoned bodies of ferrogabbroic the termed the Silver Bay intrusions. Geochemical Geochemical modelling by Shank (1990) suggested that the Silver Silver Bay intrusions intrusions represent a more fractionated derivative of the original Beaver River diabase magma. Intrusive Intrusiverelationships relationshipsand andaacompositional compositionalhaitus haitusbetween between these theserock rockunits unitsimply, imply, fractionation must have occurred in in aa deeper deeper magma magma chamber. chamber. These however, that this fractionation These conclusions and the general compositional conclusions compositional similarities similarities of the Silver Silver Bay intrusions intrusions and and the the upper upper cumulates of the SLI cumulates SLI led Miller Miller (1989) (1989) to speculate speculate that the SLI represented such such aa chamber, chamber, and if so, that the Beaver River diabase possibly was parental to the layered cumulates of the SLI. Additional mapping mapping along along the eastern margin of the SLI now indicates that the truncation of the intrusion is due largely to the emplacement of a large dike dike of of Beaver River diabase (Fig. 1). Two Two in the the diabase. diabase. Although large inclusions of the SLI have been found in Although aa postmagmatic postmagmatic fault fault also also relative to the steep fault fault that that accomaccomexists between the SLI and the diabase, it is small scale relative km.. modated the diabase. The Thelatter latter had had east east side-down side-downdisplacement of perhaps as much as 1.5 km Further evidence evidence against against the Beaver River diabase or a similar magma composition having been of an estimated estimated parent parent magma for the parental to the SLI is given by the distinct composition of intrusion. AAweighted weightedsum sumof of over over 20 20 whole whole rock analyses analyses through a stratigraphic stratigraphic section of the SLI SLI (Fig. 2) defines defines aa bulk composition composition that that is is overall overall more more evolved evolved than than average averageBeaver BeaverRiver River diabase (Table (Table 1). 1). The Theplausibility plausibility of of this this estimated estimated parent parent composition, composition,which is is very similar similar to that calculated calculated by Stevenson Stevenson (1974), (1974), is is verified verified in two two ways. The most primitive primitive olivine thebase baseof ofthe theintrusion intrusion is is exactly exactly that which should 1) The olivine (Fo79.5) (F079.5) atatthe should initially crystallize from the estimated parent parent magma. magma. Based K ~ ( ~ e of -of ~0.3 0.3 g) Based on an an olivine-liquid olivine-liquid (FeMg) 66 �I (Roeder (Roeder & & Emslie, Emslie, 1970), 1970), the the calculated calculated mg# mg# (Mg/Mgi-Fe) (Mg/Mg+Fe) of of 53.9-55.3 53.9-55.3 should should produce produce cumulus cumulus olivine Fo79.6-8o.5. olivinewith withaacomposition compositionofof Fo79.6-80.5. 2) The crystallization sequence observed in the SLI (Fig. 2), namely 0011 - 01+P1 01+P1-- Oli-P1+Cpx 01+Pl+Cpx -01÷Pl+Cpxi-Feox, Ol+Pl+Cpx+Feox, is identical to that predicted when the estimated parent composition is applied to a low low pressure fractional crystallization model (Neilsen, 1988). In contrast, plagioclase is apparently the first phase to crystallize from a Beaver River diabase composition when its average composition is is applied to the same model. A A liquid liquid line line of descent calculated for the SLI (by (by summing all rocks above a particular particular level) level) also fits that predicted by fractional crystallization crystallization modelling of the the estimated estimated parent parent magma, magma, ifif aa system system open open to to some someperiodic periodic recharge recharge isisassumed. assumed. The The composition composition of of the the granodioritic granodioritic to to granitic rocks which overlie the layered cumulates correspond siliceous differentiate differentiate of of the theSLI SLI correspond very very well well to to that that which which would would be be expected expected for for aa siliceous (Rogge, 1989). 7%(by (byweight) weight) of of olivine olivine Fe-granodiorite, Fe-granodiorite, which which directly directly overlies overlies the 1989). About About 7% layered cumulates, is included in the estimated SLI parent composition (Table 1). However, However,the the amount amount of additional additional granodioritic granodioriticto to granitic granitic material material that that may be be included included in in the the bulk bulk composition composition is is constrained to less than 5% of the total. More More than this will drop the mg# of the bulk composition F079 olivine at the base of the intrusion. composition to to less less than than what what could couldhave havecrystallized crystallized the theFo79 Based Based on on the the relative relative map map areas, areas,the the volume volume of of felsic felsicmaterial materialappears appearsto tobe bemuch muchtoo toogreat greatrelative relative to to the the amount amount of of mafic mafic material materialto tohave have been been derived derivedfrom fromSLI SLIdifferentiation. differentiation. To To test test whether whether this this apparent apparent disproportion disproportion of felsic felsic to to mafic material is is evident evident in the the third dimension, dimension, gravity gravity and and aeromagnetic aeromagnetic data data were were modelled modelled along along aa traverse traverse over overthe the SLI SLIand and Finland Finland granite (Line A, Fig. 1). lIthe km thick thick beneath beneath the the Finland If theSLI SLIisisassumed assumedtotobe beatatleast least11km granite, the magnetic and and gravity gravity models models constrain constrain the the granite granite and and granodioritic granodioriticmaterial material to to extend extend to a depth of at least 1.5 krn at its thickest point, adjacent to the fault/diabase along its SE SE margin 1.5 km (Fig. 1). AAbest bestfit fitof ofthe thegravity gravityand andmagnetic magnetic data data for for such such aa volume volume of of felsic felsic material material is is produced produced with with relative relative proportions proportions of of mafic mafic to to felsic felsic material of about 1:1 1:1 and thereby indicates that the granitic rocks rocks are are not not upper upper differentiates differentiates of of the the SLI. SLI. In conclusion, conclusion, the the SLI SLIisis temporally temporally and and genetically genetically distinct distinct from from other otherbodies bodiescurrently currentlyknown known to comprise the Beaver Bay Complex. ItIt was emplaced beneath beneath a cap cap of the granitic to was emplaced granodioritic rocks of the Finland granite. (Because are compositionally compositionally similar similar (Because these these felsic felsic rocks rocks are to what a siliceous siliceous differentiate differentiate of the SLI SLI would would be, be, the the amount amount of assimilation assimilation is is difficult difficult to to estimate. Perhaps body Perhapsisotopic isotopicdata datamay may reveal reveal the the extent extent of of assimilation.) assimilation.) The Thedifferentiated differentiatedbody which provides the the genetic genetic link link between between the the evolved evolved Silver Silver Bay Bay intrusions intrusions and and the the Beaver Beaver River River diabase diabase isis not not the the older olderSLI SLIand andremains remains unknown. unknown. - ACKNOWLEDGEMENT: ACKNOWLEDGEMENT:Quadrangle-scale Quadrangle-scalegeologic geologicmapping mappingininnortheastern northeasternMinnesota Minnesotahas hasbeen been conducted conducted by by the the Minnesota Minnesota Geological Geological Survey Survey over over the past 5 years with support support from from the the U.S. Geological Geological Survey's Survey's COGEOMAP COGEOMAPprogram. program. Miller, Miller,J.D., J.D., Jr., Jr., 1988, 1988,Geologic Geologicmap map of of the the Silver SilverBay Bay and and Split SplitRock Rock Point Point NE NE quadrangles, quadrangles,Lake Lake County, County,Minnesota: Minnesota:Minnesota MinnesotaGeological GeologicalSurvey SurveyMiscellaneous MiscellaneousMap Map M-65. M-65. Miller, Inst.on onLake Lake Miller, J.D., J.D., Jr., Jr., 1989, 1989,Geology Geology of of the theBeaver Beaver Bay Bay Complex, Complex,northeastern northeasternMinnesota. Minnesota. Inst. Superior SuperiorGeology, Geology,35th, 35th,Duluth, Duluth,Minnesota, Minnesota,p.p.56-58. 56-58. Neilsen, R.L., 1988, 1988,TRACE.FOR: TRACEFOR: A A program for for the calculation calculation of combined major and trace element liquid liquid lines linesof of descent descentfor fornatural naturalmagniatic magmaticsystems: systems: Computers Computers& &Geosciences, Geosciences,v.v.14, 14,p.p.15-35. 15-35. Roeder, Olivine-liquid equilibria: Contributions Contributions to Mineralogy and Roeder, P.L. and and Emslie, Emslie, R.F., 1970, 1970,Olivine-liquid Petrology, Petrology, v. v. 29, 29, p. p. 275-289. 275-289. Rogge, Rogge, M.K., M.K., 1989, 1989,Geochemistry Geochemistryof of the the Sonju Sonju Lake Lake layered layered maflc mafic intrusion: intrusion: Unpub. Unpub. M.S. thesis, Iowa Iowa State State University, University, 92 92 p. p. Shank, Shank,S.G., S.G., 1990, 1990,The Thepetrology petrologyof ofthe theBeaver BeaverBay BayComplex Complexnear nearSilver SilverBay, Bay,northeastern northeasternMinnesota: Minnesota: Unpub. Unpub. M.S. M.S. thesis, thesis,University Universityof ofMinnesota, Minnesota,Minneapolis, Minneapolis,130 130p.p. Stevenson, Stevenson,R.J., R.J., 1974, 1974,A Amafic maficlayered layered intrusion intrusion of of Keweenawan Keweenawanage age near near Finland, Finland, Lake Lake County, County, Minnesota MinnesotaUnpub. Unpub. M.S. M.S. thesis, thesis,University Universityof of Minnesota, Minnesota,Minneapolis, Minneapolis,160 160p.p. Weiblen, inWold, Wold,R.J., R.J., and andHinze, Hinze,W.J., W.J.,eds., eds., Weiblen, P.W., P.W., 1982, 1982,Keweenawan Keweenawan intrusive intrusive igneous igneousrocks, rocks, in Geology Geology and and tectonics tectonicsof of the theLake LakeSuperior SuperiorBasin: Basin: Geol. Geol.Soc. Soc.America AmericaMemoir Memoir156, 156,p.p.57-82. 57-82. 67 �0 .i C) I CD'< SD 3 =3rD _.l CD ° S a D (fl • • q- I0 ;QC)—u)CD 3 CDCD a I Z E COMPLEX BAY BEAVER II CD 0 CD CDCD . D — I o '< OCD.1 CD —. — CD1 o-t—. 0 r1 snInwno Cumulus MineraIqy A6oIeieuM ivaov SNOIIVIUVA MODAL VARIATIONS us ueiej SLI Parent flNOS 3NV1 NOISfl}LLNI 'COFAp - .- .- .- .CFOP PCFO me.- ee;ooioe OUIA!IO TABLE of SL1 aiavJ. 1. •i Compositions i-is suorlisoduloD jo parent magma pu average t?WW and 9g.IAg iOA9 River 1A!I diabase Beaver PCFo CD - O!6fl Si02 ZO!S Ti02 QJj A1203 EOlV FeOt oe C*14 hhQ 81P 47.8 2.06 9O 14.8 8t'I. $C1. 13.4 610 0.19 06L 7.90 56 9.5 2.61 0.55 550 0.30 OCO P066 99.04 cc:a ON L9 NZO CeY4 o K20 SOd P205 TOTAL 1VIOI (Oei9)#6W css (oe6)#w 6C5 E BQ E1 C8P 48.3 II.39 6C• 1.91 16.1 13.2 LIO 0 .f7 1.18 8.11 501. 10.5 2.27 CC0 0.33 0.14 SPO0L 100.45 C1 l.O t9S 6PS PC0 U-eJ S9PIXO S PC0 CD OiU086! Li eedv s!sesose4 J3 01. 00 65 1.91. 1.9 IN Cli 591. 061 81. 6 S LL A JZ 9L1. £01. iH 6 90 E 4 :rne UOSUOf85 'L6I 0860U 6861 3 epJap qndun) (wp S!qj .L APIMS E 0 a 0 0 w 0 0 * 0 N 0 Cumulative Mode aAtenwn3 apo jo the Sonju uoisnziui showing F I G W 2. oiqdi2nn Stratigraphic profile aunou jijoid of nfuo Lake intrusion 2U!MoqS LBPOW SfllflWflO mineralogy, SEAjOIUI modal variations, 'SUOIWUA cumulus 'i(20J!19U1W and compositon UOUSOdWO3 intervals jo the qi intrusion uoisn.nui (Table summed to the bulk pwuins o determine 9uiuuop qi nq composition uowsodwo3 of ojqfl 1,'j OjO4At rock poi analyses averaged o represent SLI iiuoij Parent). Number ris .ioqwnj of Jo whole Oul0A to uosaidai JO LJ3 EA.I1U! is Si noted. pou the composition each interval 9I UOTUSOdLUOO of su 89 191. 1. fl 80 Ui. 51. El P•I. eo 0C WS n3 qj• 91. C$'I OOZ 1.8 C 9• 1.0 50 LI. I.1. I9 IC CI 1.1. 10 p.O c.0 qA ni L E I I — CD — — �I MESOSCOPIC MESOSCOPIC EVIDENCE EVIDENCE FOR FOR B1 Bl DEFORMATION DEFORMATION IN IN LOWER LOWER PROTEROZOIC PROTEROZOIC SUPRACRUSTAL ROCKS NEAR NEAR ROCHFORD, ROCHFORD, SOUTH SOUTH DAKOTA. DAKOTA. SUPRACRUSTAL ROCKS Patrick Patrick Mohn Mohn and and William William J. J. Gregg, Greggl Department Department of of Geological Geological Engineering, Engineeringl Geology, GeologyI and and Geophysics, GeophysicsI Michigan Michigan Technological Technological University, Universityl Houghton, Houghton, MI MI 49931 49931 Introduction Introduction The located in in the the Precambrian Precambrian is located The Rochford Rochford mining mining district district is core 25 miles (40 (40 core of of the the Black Black Hills Hills Uplift, U~lift.approximately a ~ ~ r o x i m a t e l25 v miles kin) west of Rapid City, South Dakota (Figure 1A). Highly deformed lower Proterozoic rocks underlie most of the area and include slate, phyllite, and schist intercalated with metavolcanics, metagabbro, metachert, and various facies of meta—iron formation (Dewitt and others, 1986). Previous work in the area includes several recent )I.S. theses and an extensive mapping effort by the U.S.G.S. in the late 1960's, which culminated with the publication of the first comprehensive geologic map of the district by Richard Bayley in 1972. Structural interpretations thus far have been based primarily on a preferred stratigraphic sequence which was originally proposed by Bayley (1972), based on correlations with a key unit in the Lead district to the north (Ellison Formation at Lead correlated with the Moonshine Gulch Quartzite at Rochford) and also on two available age dates of intercalated volcaniclastic units within the two areas. The present study involved detailed structural/lithologic mapping of an area about 2 miles southwest of the town of Rochford, located in Pennington County, South Dakota. Our objective was to delineate the nature of major structural features within the map area. To accomplish this task, the cornerstone of our field technique involved using fold overprinting relationships to classify and map mesoscopic fabric elements. In addition, detailed lithologic mapping was carried out utilizing a distinctive biotite—garnet phyllite unit as a structural marker horizon. Descriptive structural geoloc!v Style is defined defined by by the the macroscopic macroscopic outcrop outcrop pattern pattern Style group group B. Bl is of of the the biotite-garnet biotite-garnet phyllite phyllite unit unit and and by by mesoscopic mesoscopicB1 Bl folds folds observed observed at at three three key key localities localities within within the the field field area. B l folds folds observed observed in in outcrop outcrop and and also also on on the the area. B1 macroscopic macroscopic scale scale are are tight tight to to isoclinal. isoclinal. Structural Structural analysis analysis of of B1 B l folds folds on on aa mesoscopic mesoscopic scale scaleis isimpossible, impossiblel since since very very few few first first generation generation fabric fabric elements elements were were preserved presemed in in the thefield fieldarea. area. However, Howeverl based based on on the the predominant predominant southeasterly southeasterly plunge plunge of of L2 L2 bedding-cleavage bedding-cleavage intersection intersection lineations, lineationsl the the first first system system of of folds foldsmay may have have trended trended east-west, east-west, with with steeply steeply south-dipping south-dipping axial axial surfaces. surfaces. 69 1 �___ I I Style group group B2 B2 folds foldsrefold refoldolder olderB.1 Bl structures or bedding bedding Style structures or ( S o ) and and are are observable observable on on both both the the macroscopic macroscopic and and (S0) mesoscopic scales. B2 folds are open to tight, with mesoscopic scales. B2 folds are open to tight, with aa pervasive axial plane foliation (S2) (S2) defined defined by by parallel parallel pervasive axial plane foliation preferred-orientation of mica particles. S2 foliation The preferred-orientation of mica particles. The S2 foliation strikes northwest and dips steeply to the northeast and is strikes northwest and dips steeply to the northeast and is the dominant structural fabric throughout the Rochford the dominant structural fabric throughout the Rochford Both B2 B2 fold fold axes axes and and L2 L2 cleavage-bedding cleavage-bedding district. Both district. intersection lineations plunge to the southeast. intersection lineations plunge to the southeast. Third generation generation (B3) (B3)structures structures are are present present throughout throughout the the Third field area and consist of moderately to strongly developed field area and consist of moderately to strongly developed S2cleavage cleavagesurfaces. surfaces. Elements Elements associated associated crenulationson on S2 crenulations with style group B3 are the S3 crenulation cleavage and the the with style group B3 are the S3 crenulation cleavage and S3 planes strike to the L3 crenulation lineation. L3 crenulation lineation. S3 planes strike to the L3 wrinkle wrinkle northeast and and dip dip to to the the south, south, whereas whereas the the L3 northeast \'4K \\ \ IWEX MAP INDEX MAP SOUTH DAKOTA BLACK n u s SOUTh DAKOTA BLACK HILLS I PHANEROZOIC ROCKS LAINCI COUNTY ROGNPORO STUDY AREA RAPID CITY • PRECAMBRIAN CORE KEYSTONE :: PINUSNSTON COUNTY CUSTIN COUNTY CUSTER o I m I P. MOHN 3190 1A Figure 1 Figure 1. lB 1 Index map map of of the the South South Dakota Dakota Black BlackHills HillsCiA), (lA), Index and a sketch of fold overprinting relationships and a sketch of fold overprinting relationships (IB)as as observed observed on on the the back back of of aa mine mine adit adit C1B) located in the southern part of the field area. located in the southern part of the field area. Heavy stippled pattern shows a Bl isoclinally Heavy stippled pattern shows a B isoclinally by B2, B2,with with the the folded chert chert bed bed refolded refolded by folded The I11 interference pattern. resulting type resulting type III interference pattern. The sketch is a pen and ink tracing of a sketch is a pen and ink tracing of a photograph. photograph. 70 I �I lineation lineation plunges to to the the southeast, southeast, roughly parallel to to L2 L2 lineations. lineations. With the the exception exception of local local reversals reversals of of the the plunge direction direction of of L21B3 LZtB3deformation deformation had little little effect effect on on plunge the the orientation orientation of of major major structures structures within within the the map map area. area. Conclusions Conclusions The The results results of of our our detailed detailed work work show, showt at least least within within the the confines confines of of the the map area, area, that that there there is is aa reversal reversal of of the the stratigraphic stratigraphic rock rock sequence sequence proposed proposed by Bayley Bayley (1972) (1972) for for the the area area on on the the western western edge edge of of the the Rochford Rochford anticlinorium, anticlinorium, where where the the present present study study was was undertaken. undertaken. Secondly, Secondlyt distinctive distinctive first first generation generation (B1) (Bl)folds folds were were observed observed both both on scalet which which on the the mesoscopic mesoscopic scale scale and and on on the the macroscopic scale, is defined by the outcrop pattern of the biotite-garnet phyllite I11 interference interference patterns patterns phyllite marker marker horizon. horizon. Type Type III were were produced produced as as aa result result of of overprinting overprinting by aa later later fold fold generation generation (B2) (B2) which which was was non—coaxial non-coaxial to to the the first— firstgeneration generation B1 Bl folds folds (Figure (Figure lB). 1B). AA third third phase of of folding folding is well—developed is evident evident based on the the presence of a locally locally well-developed crenulation crenulation cleavage cleavage (S3). (S3). This This crenulation crenulation cleavage cleavage overprints B2 mesostructures mesostructures in in the the study study area. area. overprints B2 To To the the best best of of our our knowledge, knowledge, the the delineation delineation of of first first generation generation (B1) (Bl)structures structures and and the the distinctive distinctive structural structural overprinting in the the map area area are are the the overprinting relationships relationships observed observed in first in the the Rochford Rochford district. district. first such such examples examples documented documented in The The structural structural relationships relationships we we propose propose for for the the map map area area are are in in general general agreement agreement with with those those proposed proposed by Redden Redden and and French French (1989) (1989) for for the the central central Black Black Hills Hills near near Mystic, Mystict thereby thereby indicating indicating that that similar similar techniques techniques of of structural/lithologic structural/lithologic mapping mapping may be be successfully successfully applied applied to to other other areas areas in in the the Precambrian Precambrian terrane terrane of of the the Black Black Hills. Hills. References References Bayley, Bayleyt R.W., R.Wat 1972 1972 AA preliminary preliminary report report on on the the geology geology and and gold gold deposits deposits of of the the Rochford Rochford district, district, Black Black Hills, Hills, South South Dakota: Dakota: U.S.G.S. U.S.G.S. Bull. Bull. 1332-A. 1332-A. E., J.A. J.A. Redden, Reddent A.B. A.B. Wilson Wilson and and David David Buscher, Buscher, 1986 1986 Dewitt, E., Dewitt, Mineral resource resource potential potential and and geology geology of of the the Black Black Hills Hills Mineral National National Forest, Forest, South South Dakota Dakota and and Wyoming: Wyoming: U.S.G.S. U.S.G.S. Bull. Bull. 1580. 1580. Redden, Redden, J.A. J.A. and and G.M. G.M. French, French, 1989 1989 Geologic Geologic setting setting and and potential exploration exploration guides guides for for gold gold deposits, depositst Black Black potential Hills, Hills, South South Dakota: Dakota: in in United United States States Gold Gold Terranes. Terranes, Part Part U.S.G.S. I, U.S.G.S. Bull. 1857-B; D.R. Shawet R.P. Ashley, and Bull. 1857-B; D.R. Shawe, R.P. Ashley, and L.M.H. L.M.H. Carter, Carter, eds. eds. , 71 �I THE PHYSICAL PHYSICAL VOLCANOLOGY VOLCANOLOGY AND AND HYDROTHERMAL HYDROTHERMAL ALTERATION ALTERATION THE ASSOCIATED WITH WITH THE THE MASSIVE MASSIVE SULPHIDE SULPHIDE DEPOSITS DEPOSITS OF OF THE THE ASSOCIATED SOUTH STURGEON STURGEON LAKE LAKE AREA, AREAf NORTHWESTERN NORTHWESTERN ONTARIO ONTARIO SOUTH R. L. L. Morton1, or ton' G. G. J. J. Hudak1, ~udak' J. J. S. S. Walker1, wa1kerTfand and J. J. M. M. Franklin2 ~ranklin' R. The south south Sturgeon Sturgeon Lake Lake area area of of northwestern northwestern Ontario Ontario is is The underlain underlain by by aa well well preserved preserved Archean Archean submarine submarine caldera caldera which which is is approximately30 30Km Kmin instrike strikelength. length. Within Within the the caldera caldera five fiveash ash approximately flow flow tuff tuff units units have have been been recognized, recognizedfand and these these range range from from 100 100 to to more than than 1200 1200meters meters in instratigraphic stratigraphicthickness. thickness. The The ash ash flow flow more units units vary vary from from massive massive and and pumice-rich pumice-rich to tobedded. bedded. Commonly, Commonlyf quartz crystal-Ipumice—rich pumice-rich basal basal units units are are overlain overlain and and separated separated quartz crystal—, by well well bedded bedded ash ashunits. units. The The five five known known massive massive sulphide sulphide deposits deposits by (Mattabi, (MattabifF-Group, F-Groupl Sturgeon Sturgeon Lake, Lakel Lyon Lyon Lake, Lakel and and Creek Creek Zone) Zone) occur occur within within the the caldera caldera and and are are hosted hosted by by the the ash ash flow flow tuff tuff deposits. deposits. Associated Associated with with the the ash ash flow flow tuffs tuffs are are coarse coarse heterolithic heterolithic breccias breccias which which contain contain clasts clasts that that are are composed composed dominantly dominantly of of precaldera lithologies. lithologies. The The breccias breccias underlie, underliel and and locally, locallyf are are precaldera The breccias breccias vary vary from from 100 100 interlayeredwith, withfthe theash ashflow flowtuffs. tuffs. The interlayered to more more than than 750 750 meters meters in in thickness. thickness. Clasts Clasts in in the the breccia breccia vary vary to from from lapilli-sized lapilli-sizedto tolarge largeblocks blocksat at least least 100 100 meters meters in in diameter. diameter. The The five five ash ash flow flow units units indicate indicate five five separate separate periods periods of of explosive, silicic volcanism volcanism accompanied accompanied by by caldera caldera collapse; collapse; the the explosivelsilicic breccias breccias represent representmesobreccia mesobreccia deposits deposits formed formed from from material material which which slumped slumped into into the the caldera caldera during during and and after after each each caldera caldera collapse collapse episode occurred. occurred. episode Ore Ore forming forming hydrothermal hydrothermal activity activity was was associated associatedwith with at at least least four of of these these eruptive eruptiveepisodes. episodes. Early, Earlyf regional regional carbonatization carbonatization four of of the the rocks rocks is is cross-cut cross-cut by by alteration alteration assemblages assemblages containing: containing: a) a) iron carbonate carbonate ±2 iron iron chlorite; chlorite; b) b) chloritoid chloritoid ±& iron iron carbonate carbonate iron and/or iron iron chlorite; chlorite; c) c) aluminum aluminum silicates silicates (pyrophyllite, (pyrophyllitef and/or andalusite and/or and/or kyanite) kyanite) ++ chloritoid; chloritoid; and and d) d) aluminum aluminum andalusite, silicates. Aluminum Aluminum silicate silicate alteration alteration zones zones are are dominantly dominantly silicates. confined confined to to the the synvolcanic synvolcanic faults faults that that acted acted as as conduits conduits for for the the metallifer~us~ ore-forming hydrothermal hydrothermal fluids. fluids. These These zones zones lead lead metalliferous, ore-forming up massive suiphide turn, surrounded surrounded up to to the the massive sulphide deposits, depositsl which which are, aref in in turn1 by zones of of aluminum aluminum silicatel silicate, aluminum aluminum silicate semiconformable zones silicate ++ by seiniconforinable chloritoidf and and chloritoid chloritoid alteration. alteration. chioritoid, I Department, University University Economic Volcanology Volcanology Research Research Lab, Labf Geology Geology Departmentf Economic Duluthf Duluthf MN 55812 of Minnesota Duluth, MN 55812 Duluth, of Minnesota - * 2 Geological Geological Survey Survey of of Canada, Canadaf Minerals Minerals Resources Resources Division, Division, 601 601 Booth St., St., Ottawa, Ottawaf Ontario Ontario K1A-0E8 KIA-OE8 Booth I I 1 72 I �U GNI/ARGONNE LAKE LAKE SUPERIOR SUPERIOR SEISMIC SEISMIC DATA DATA TECTONIC RAMIFICATIONS OF GNI/ARGONNE M.G. Mudrey, Mudrey, Jr., Jr., Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey, Survey,3817 3817 Mineral Mineral M.G. Point Road, Road, Madison, Madison, WI 53705 Point 53705 A.B. Dickas, Dickas, Division Division of of Sciences Sciences and and Mathematics, Mathematics, University University of of WisconsinWisconsinA.B. Superior, Superior, Superior, Superior, WI 54880 54880 L.D. Reclamation Engineering Engineering and and Geosciences, Geosciences, Argonne Argonne National National L.D. McGinnis, McGinnis, Reclamation Laboratory, Argonne, Argonne, IL Laboratory, IL 60439 60439 U.S. Geological Geological Survey, Survey, W.F. Cannon, Cannon, Eastern Eastern Mineral Mineral Resources Resources M.S. M.S. 954, 954,U.S. W.F. National National Center, Center, Reston, Reston, VA VA 22092 22092 ABSTRACT Geologic analysis of of Grant-Norpac Grant-NorpacInc. Inc. (GNI)/Argonne (GNI)/Argonne reflection reflection seismic seismic Geologic analysis lines in in western Lake Superior Superior requires requires revision revision of of Middle Middle Proterozoic Proterozoic KeweenaKeweenalines western Lake wan wan stratigraphy, stratigraphy, tectonics tectonics and and basin basin evolution. evolution. The The seismic seismic diagrams diagrams were were prepreviously presented presented as as aa poster poster session session at at the the Duluth Duluth 1989 1989 ILSG ILSG Annual Annual meeting. meeting. viously The Isle Isle Royale Royale Fault Fault is is not not continuous continuous with with the the Douglas Douglas Fault. Fault. No No ververtical or high-angle reverse fault fault with displacement displacement more more than than 0.2 0.2 seconds seconds of of high-angle reverse two-way travel two-way travel time, time, roughly roughly equivalent equivalentto to500 500in, m, is is seen seen to to cross cross Grant-NorGrant-Norpac/Argonne Line-08. Line-08. If If there there is is aa fault, fault, it it does does not not express express itself itself as as highhighangle, angle, but but it it could could be be aa thrust thrust fault, fault, and and as as such such is is not not evident evident in in the the seismic data. seismic data. The The Bayfield Bayfield Group Group rests rests with with strong, strong, regional regional angular angular unconformity unconformity on on the the Oronto Oronto Group, Group, which which has has lost lost up up to to one-half one-halfits its thickness thickness as as aa result result of of eroerosion prior to sion to deposition deposition of of the the Bayfield Bayfield Group. Group. Western Lake Western Lake Superior Superior consists consists of of two two distinct distinct basins basins separated separated by by an an ArArchean-cored ridge western volcanic/sedimenvolcanic/sedimenchean-cored ridge (the (the locus locus of of GLIMPCE GLIMPCE Line-C). Line-c). The western herein named the tary basin is is herein the Claude Claude Jean Jean Allouez Allouez Basin Basin (informally (informally referred referred to as the Allouez Basin); the the eastern eastern basin, basin, the the Jacques Jacques Marquette Marquette Basin Basin (infor(inforBasin); and the intervening ridge, ridge, the mally referred referred to to as the Marquette Basin); Walter White Walter White Ridge Ridge (informally (informally referred referred to to as as the the White White Ridge). Ridge). Each Each basin basin conconsists of multiple volcanic successions successions overlain overlain by aa transgressive transgressive Oronto Oronto sesebasins, and quence which filled filled the the two two basins, and ultimately ultimately covered covered the the White White Ridge., Ridge., Seismic The The Oronto Oronto in in turn turn is is unconformably unconformably overlain overlain by by the the Bayfield Bayfield Group. Group. Seismic cross lines cross lines define define stratigraphic stratigraphic relations. relations. Seismic Seismic form form lines lines in in the the Portage Portage Lake Volcanic Group Group suggests suggests abundant abundant intra-formation intra-formation sedimentary sedimentary units, units, and and supports continuity supports continuity of of the the Greenstone Greenstone Flow Flow from from Isle Isle Royale Royale to to the the Keweenaw Keweenaw Peninsula. Peninsula. It may be possible to define the the lateral lateral extent extent of of the the Oak Oak Bluff Bluff Formation (formerly Formation (formerly the the unnamed unnamed formation formation of of Johnson Johnson and and White, White, 1969). 1969). These relationships These relationships strongly strongly support support aa fundamental, fundamental, rift-unit rift-unitframework framework of of The isolated basins separated isolated basins separated by by syndepositional syndepositional accommodation accommodation structures. structures. The Walter White Ridge Ridge is is the the first first direct direct evidence evidence of of accommodation accommodation structures structures being associated associated with with the the Midcontinent Midcontinent Rift Rift System. System. This work work was Department of of Energy, Energy, Office Office of of Energy Energy supported by by the the 'U.S. U.S. Department This was supported Research, under Research, under Contract Contract W-3l-109-ENG-38. W-31-109-ENG-38. 73 �I Ii ^ I Reference cited: cited: Reference I Johnson,R..F., R.F., and W.S., 1969, 1969, Preliminary Preliminary report on the bedrock geology Johnson, and White, White, W.S., report on the bedrock geology and copper deposits of the Matchwood quadrangle, Ontonagon County, and copper deposits of the Matchwood quadrangle, Ontonagon County, Michigan: U.S. Geological Survey open-file report, 31 p. Michigan: U.S. Geological Survey open-file report, 31 p. ^I 100 0 t_____1 kilometers kilometers Locationof of seismic seismic profiles profiles and and Isle Isle Royale Royale and and Douglas Douglas Faults Faults Location u C) M rIm-. I 2 SW SW Allouez Basin Basin Allouez ;3 0 Walter Walter White White I Ridge Ridge 0 Lfl -1- z z 0 00 I I Marquette Basin Basin Marquette B 0 A A A 00 50 50 IÑÑÑà Archean? B-Bayfield,0—Oronto 0-Oronto B—Bayfield, V,A Keweenawan VolcanicRock Rock V,AKeweenawan Volcanic 7' 1' kilometers kilometers GNA-08(prepared (preparedby by A. A. Dickas Dickasand and M. M. Mudrey, Mudrey,1989) 1989) Interpretationof of CNA-08 Interpretation 74 NE I I I I I I I I I I I I I I I �Constraints on Archean Archean versus versus Proterozoic Proterozoic deformation deformation in in Constraints Archean Archean Rocks of the the Negaunee Negaunee area, area, Upper Upper Michigan Michigan Scott A. Scott A. Nachatilo Nachatilo and and Robert Robert 1.L.Bauer, Bauer,Department Department of of Geological Sciences, Geological Sciences, University University of Missouri, Missouri, Columbia, Columbia, Missouri Missouri 65211 6521 1 The Negaunee Negaunee area area of Michigan's Michigan's upper upper Peninsula Peninsula contains contains deformed Archean Archean greenstones and and metasedimentsof of the the Northern metasediments Northern Complex Complex as well well as asProterozoic Proterozoic metasediments metasediments along along the the northern margin margin of of the Marquette northern Marquette syncline and the southeastern southeastern end of the the Dead Dead River RiverBasin. Basin. Although the Proterozoic Although the Proterozoic rocks rocks of the the area area were were obviously obviously deformed deformed during during the the Penokean Penokean Orogeny, the effects Orogeny, the effects of this this event event on on the theadjacent adjacent Archean Archean rocks rocks are are unclear. unclear. The regional regional foliation foliation trends in in both both the the Archean Archean and andProterozoic Proterozoic rocks rocks are aresubparallel subparallel (vertical, (vertical, striking striking Ca. N.700 70° W.), W.), and the principle ca. N. principle axes axes of of finite finite strain strain measured measured ininprevious previous studies studies (Carter, (Carter, 1989 and Westjohn, Westjohn, 1978) are also nearly parallel in the the Archean Archean and and Proterozoic Proterozoic rocks. rocks. We have analyzed deformation fabrics and finite strains (Rf/phi technique) from analyzed deformation fabrics and finite strains technique) from Archean Archean rocks of of the Kitchi rocks Kitchi Schist Schist and and the the Mona Mona Schist Schist in in an an effort effort totoevaluate: evaluate:(1) (1)the thedeformation deformation sequence in the Archean sequence in Archean rocks, rocks, and and (2) (2) the the degree degree totowhich whichProterozoic Proterozoic deformation deformation has has effected the Archean rocks. As As aalocal localstandard standardof ofcomparison, comparison,we we have haveanalyzed analyzedthe the geometry geometryof of Proterozoic folding folding in the Goodrich Proterozoic Goodrich Quarztite Quarztite and lower lower units units of of the theMichigamme Michigamme Formation Formation along the southeastern margin margin of of the the Dead River River Basin. Basin. Our Our analysis analysis indicates indicates that Proterozoic Proterozoic deformation did not effect effect Archean Archean rocks rocks in in aaductile ductilefashion. fashion. The oldest Archean generated an an L to LS Archean deformation generated LS fabric fabric with with aasteeply steeplyplunging plunginglinear linear axis in the Kitchi Kitchi Schist Schist south of the Dead Dead River Basin. The The planar planar aspect aspect of of the the fabric fabricdefines defines aa locally well well developed vertical foliation foliation striking striking N. N. 700 70° W. locally developed vertical W. that that is is prominent prominent in the the clastic clastic units of both units both the the Kitchi Kitchi Schist Schist and andespecially especially the the Mona Mona Schist Schist throughout throughout the the region region (Figure (Figure 1A). Finite IA). Finite strains strains that we believe believe were were generated generated primarily primarily as a result result of of this thisdeformation deformation were in the of the Kitchi were measured measured in the agglomerates agglomerates of Kitchi Schist Schist and and show show slightly slightly prolate prolate strain strain principle ellipsoids ellipsoids with with the the maximum maximum (X), (X), intermediate intermediate (Y), (Y), and and minimum minimum (Z) (2) principle axes axes vertical, E-W, 2A and vertical, E-W, and N-S, N-S, respectively respectively (Figure (Figure 2A and 3). 3). Strain Strain analyses analyses from from the the Kitchi Kitchi Schist and the adjacent and the the dominant dominant N. N. 70° adjacent Mona Schist (Carter, 1989), and 700 W. W. foliation foliation are are consistent N- to to NNE-directed NNE-directed shortening shortening during during this this event. event. Sparse Sparse folds folds with with E-W E-W consistent with with Ntrending trending axial planes planes occur occur in the the Nealy Nealy Creek Creek (NC) (NC) and and sheared sheared rhyolite rhyolite tuff tuff (srt) (srt) members members of the Mona Mona Schist Schist north north of of the the Dead Dead River River Basin Basin where where the the dominant dominant foliation foliation orientation orientation is These folds that plunge roughly E-W. roughly E-W. These folds have have variable variable hinge-line hinge-line orientations orientations that plunge shallowly shallowly to moderately east east and west. Stretching lineations moderately west. Stretching lineations in these these same same rocks rocks show show aa similar similar distribution, also plunging plunging to to both both the the east east and west. west. We distribution, also Webelieve believethat that these theselineations lineations and and the the sparse folds folds may have have been been reoriented reoriented during a second second period of deformation deformation that is is variably variably partitioned into the NC and srt members members of the the Mona Mona Schist. Schist. The second produced aa set of conjugate cleavages that that are locally second deformation produced conjugate crenulation cleavages developed in the highly foliated NC and sri srt members members of the Mona Mona Schist. Schist. Although some of of the crenulations occur in an area mapped as a broad zone of shear, they also occur several crenulations occur in an area mapped as broad zone of shear, they also occur several Crenulations kilometers outside parts of of the the NC NC member member that that are are not not sheared. sheared. Crenulations kilometers outside of of this zone in parts with axial planes planes that that strike strike NNW-SSE NNW-SSE have "S" asymmetry asymmetry while those with axial axial planes planes that that strike roughly E-W E-W have have "Z" "2" asymmetry asymmetry (Figure (Figure 18). 16). The concomitant concomitant generation generation of these these strike roughly orientations requires that that the the greatest greatest principle principle stress stress be be at a low orientations requires low angle angle to to the the earlier earlierfoliation foliation planes and coincident coincident with the the bisector bisector of of the theangle anglebetween betweenthe theconjugate conjugatecleavage cleavageplanes planes consistent with with this (Cosgrove, 1976); 1976); only only aa NW-directed (Cosgrove, NW-directed compression compression is is consistent this geometry. geometry. Strain analyses analyses of of crenulated samples from from the the srt srt member Strain crenulated samples member are also consistent consistent with NW-SE NW-SE 75 �I: I I directed shortening. shortening. In directed In these these samples, samples, the the XV XY principle principle plane plane of of the the finite finitestrain strainellipsoid ellipsoid isis steeply steeply dipping, dipping, NE-striking, NE-striking, and and normal normal to the the direction direction ofofshortening shortening estimated estimated from from crenulation crenulation axial axial planes planes (Figure (Figure 2B). 2B). We Webelieve believethis thissecond seconddeformation deformation isisalso alsoofofArchean Archean age, age, because becauseNW-directed NW-directedcompression compression is is not not observed observed in inthe theProterozoic Proterozoicrocks rocksof ofthe theregion. region. For For instance, instance, regional regional folding folding of of the theProterozoic Proterozoic Goodrich Goodrich Quartzite Quartzite and and the the lower lowerpart partofof This fold orientation the Michigamme Formation is about a N. 700 W. axial plane (Figure 1C). the Michigamme Formation is about a N. 700 W. axial plane (Figure 1C). This fold orientation and the the associated associated axial axial plane planefoliation foliation requires requires aaNN-totoNE-directed NE-directedcompression. compression. Similarly, Similarly, and strain strain analyses analyses from from reduction reduction spots spots ininthe theProterozoic ProterozoicKona KonaFormation Formationwithin within the theMarquette Marquette syncline compression. These 1978) show show no no evidence evidence of NW-directed NW-directed compression. These data data yield yield an an syncline (Westjohn, (Westjohn, 1978) E-W E-W striking striking XV XY principle principle plane plane of of finite finite strain strain (Figure (Figure 2B) 2B)indicative indicative of ofNN-totoNE-directed NE-directed (1978) reports reports sparse sparse late-stage late-stage kink kink bands bands ininthe theProterozoic Proterozoic shortening. Although Although Klasner Klasner (1978) shortening. Michigamme with near W., he he Michigamme Formation Formation with near vertical vertical kink kink planes planes striking striking N. N.200 200E. E.and and N. N. 50° 500 W., attributes blockuplift upliftof ofthe theArchean ~ r c h e abasement. nbasement. attributes these these to to late-stage late-stageblock Kitchi Schlst Schist Kitchi Crenulatlon Crenulation Cleavage Cleavage Fabrics Fabrics N N Compression • :: 8 B. I I I I Proterozoic Fold Fold Geometry Geometry Figure 1. 1. Archean Archean and and Proterozoic Proterozoic fabric fabric data. A. Poles Poles to to foliation foliation data. A. (crosses) (crosses) and and lineation lineation orientations orientations (triangles). 8.Poles Poles to tocrenulation crenulation (triangles). B. S" asymmetry cleavages; (circles), cleavages; "S" asymmetry (circles), Z" *Z"asymmetry asymmetry(triangles). (triangles). Hinges Hinges of of crenulation crenulation cleavage cleavage (crosses). (crosses). C. C. Proterozoic Proterozoic fold fold geometry; geometry; poles poles to to N N bedding bedding (circles), (circles), poles poles to to axial axial (crosses), foliation planar planar foliation (crosses), (Small line intersection intersection l i n eat a t ion ion (small triangles), and and best-fit best-fit Pi-axis Pi-axis orientation orientation from from poles poles to to bedding bedding (large (large triangle). triangle). 11 76 �InInsummary, Proterozoic summary,although althoughthe theregional regionaltrend trendofofthe thedominant dominantArchean Archeanand and Proterozoicfoliations foliations isissubparallel, subparallel, the theorientation orientationofofsecond seconddeformation deformationconjugate conjugatecrenulation crenulationcleavages cleavagesininthe the Archean Archean rocks rocks isisincompatible incompatible with withthe thedeformation deformation features features recognized recognized in inthe theadjacent adjacent Proterozoic second deformation Proterozoicrocks. rocks. These Thesedata datatherefore thereforesuggest suggestthat thatthe thefirst firstand and second deformationfeatures features we weobserve observeininthe theArchean Archeanrocks rocksof ofthis thisarea areawere werenot notimposed imposedby byProterozoic Proterozoicdeformation. deformation. Carter, Carter, P.J. P.J.Jr., Jr.,1989, 1989,Finite Finitestrain strainestimates estimatesfor forArchean ArcheanMona MonaSchist Schistpillows pillowsand andEnchantment EnchantmentLake Lake Formation Unpublished M.S. Formationmetawackes metawackesininthe theeastern easternupper upperpeninsula peninsulaofofMichigan: Michigan: Unpublished MS.Thesis, Thesis, MichiganState StateUniversity, University,East East Lansing Lansing Ml., MI., 97 97p.p. Michigan Cosgrove Cosgrove,J. ,J.W., W., 1976, 1976,The Theformation formationofofcrenulation crenulationcleavage: cleavage:Jour. Jour.Geol. Geol.Soc. Soc.Lond., Lond.,vol. vol.132, 132.p.p. 155-1 78. 155-1 78. Klasner, Klasner,1978, 1978,Penokean Penokeandeformation deformationand andassociated associatedmetamorphism metamorphismininthe thewestern westernMarquette Marquette Range, northern northernMichigan: Michigan: Geol. Geol. Soc. Soc. Amer. Amer. Bull., Bull.,vol. vol.89, 89,p.p.711-722. 711-722. Range, Westjohn, D.B., 1978, 1978,Finite Finitestrain strainininthe thePrecambrian PrecambrianKona KonaFormation, Formation,Marquette MarquetteCounty, County,Michigan: Michigan: Westjohn, D.B., UnpublishedM.S. M.S. thesis, thesis, Michigan MichiganState StateUniv., Univ.,East EastLansing LansingMl., MI.,72 72p.p. Unpublished Principle Principle Axes Axes of of Finite FiniteStrain, Strain, Principle ofFinite FiniteStrain, Strain, Principle Axes Axes of Archean (Crenulated) and Archean (Crenulated) and Kitchiand andMona MonaSchist Schist Kitchi Proterozoic ProterozoicRocks Rocks N N FIgure Figure 22(above). (above). Principle Principle axes axes of of finite finite strain, A. strain, Archean Archean and andProterozoic Proterozoicrocks. rocks. A. X,Y, X,Y, and and ZZaxes axesfrom fromthe theKitchi KitchiSchist Schistare are open open circles, circles, open opensquares, squares, and andtriangles triangles (this X, Y, Y, and and ZZaxes axesfrom fromthe the (thisstudy). study). X, Mona Mona Schist Schist are areshaded shadedcircles, circles,shaded shaded squares, squares, and andcrosses crosses(Carter, (Carter,1989). 1989). B. B.X,X, Y, axesfrom fromthe thecrenulated crenulatedArchean Archean Y, and andZZaxes Mona Mona Schist Schist (srt (srtmember) member)are areopen opencircles, circles, open open squares, squares, and andtriangles triangles(this (thisstudy). study). X,X, Y, Y, and and ZZaxes axesfrom fromthe theProterozoic ProterozoicKona Kona Formation Formation are are shaded shaded circles, circles, shaded shaded squares, squares, and and crosses crosses(Westjohn, (Westjohn, 1978). 1978). Figure Figure 3 3 (left). (left). Log Log Flinn Flinn plot plot of of finite finite strains strains from from the the Kitchi KitchiSchist Schist(triangles) (triangles) (this (this study), study), Mona Mona Schist Schist (crosses) (crosses) (Carter, (Carter, 1989), 1989), srt srt member member of of Mona MonaSchist Schist (circles) (circles) (this (this study), study), and and the theProterozoic Proterozoic Kona Kona Formation Formation(squares)(Westjohn, (squares)(Westjohn,1978). 1978). Log Flinn Flinn plot plot of ofFinite FiniteStrains Strains Log / 0.5, 0.5 0.4 8 +0 0.3 3.. x 0 -J 0.0 0.1 Log(Y/Z) 77 �I MINING ACTIVITY IN IN EXPLORATION AND MINING NORTHWESTERN ONTARIO ONTARIO NORTHWESTERN ............................................................ 0' BRIEN, BRI EN, M. , RESOURCE RESOURCE GEOLOGIST, ONTARI 0 MINISTRY OF OF GEOLOGIST, ONTARIO NORTHERN NORTHERN DEVELOPMENT DEVELOPMENT AND MINES, MINES, THUNDER THUNDER BAY BAY S., S. m i n e r a l sector s e c t o r in i n Ontario O n t a r i o provided 25,962 d i r e c t jobs The mineral provided 25,962 direct jobs and produced produced materials m a t e r i a l s with w i t h a total t o t a l Canadian dollar d o l l a r value v a l u e of of $6,853,756,000 in i n 1988. 1988. This poster p o s t e r displays d i s p l a y s the t h e producing producing mines mines and and advanced advanced mineral mineral exploration e x p l o r a t i o n projects p r o j e c t s in i n the t h e Northwestern Region of the the Province Currently producing gold gold Province of of Ontario. Ontario. C u r r e n t l y there t h e r e are a r e 88 producing mines, 44 base b a s e metal metalmines1 mines, 6 6 stone s t o n e quarries., q u a r r i e s , and and 55 seasonal seasonal amethyst amethyst mines mines iin n tthe h e region r e g i o n employing employing 2152, 2152, 1133, 1133, 26 26 and 36 36 people There p e o p l e respectively. respectively. There are a r e also a l s o 22 22 projects p r o j e c t s in i nadvanced advanced exploration. exploration. In I n 1989, 1989, the t h e region r e g i o n produced produced approximately: approximately: 50,843 kg 50,843 kg (kilograms) ( k i l o g r a m s ) of gold; gold; 125,310 kg kg of silver; silver; 125,310 30,514,973 30, 514, 973 kg of copper; copper; 6,667,808 6, 667,808 kg kg of of nickel; n i c k e l ; 3,794,754 3,794, 754 kg kg of lead; for a a total t o t a l Canadian Canadian l e a d ; and and 112,799,350 112,799,350 kg kg of of zinc z i n c -- for dollar 225, 284, 402.RRepresentative d o l l a r value v a l u e of of $1, $1,225,284,402. e p r e s e n t a t i v e oore r e samples of of Northwestern Northwestern Ontario O n t a r i o are a r e also a l s o on on display. display. A A statistical s t a t i s t i c a l summary summary booklet b o o k l e t that t h a t tabulates t a b u l a t e s regional r e g i o n a l data data such s u c h as a s reserves, r e s e r v e s , grades, grades, location, l o c a t i o n , ownership ownership and and development development i s available a v a i l a b l e free f r e e of of charge c h a r g e in i n both b o t h English E n g l i s h and and French. French. is I I I I I I 78 I �I LOWER PROTEROZOIC PROTEROZOIC GLACIOGENIC GLACIOGENIC DEPOSITS: DEPOSITS: A NORTH BALTICCONNECTION? CONNECTION? NORTH AMERICA AMERICA -- BALTIC Richard W. Ojakangas, Ojakangas, Department Department of Geology, Geology, University University of of Minnesota-Duluth, Minnesota-Duluth, Duluth, Duluth, MN MN 55812, 55812, Jukka Jukka S. S. Marmo, Marmo, Geological Geological Survey Survey of of Finland, Finland, SF-02150 SF-02150 Espoo Espoo 15, 15, Geology, USSR Institute of Geology, FINLAND, I. Heiskanen, Heiskanen, Institute FINLAND, Kim Kim I. USSR Academy Academy of of Sciences, Sciences, Petrozavodsk, USSR. USSR. ABSTRACT Lower glaciogenic deposits deposits of of approximately the same age(?) Lower Proterozoic Proterozoic glaciogenic approximately the age(?) occur occur Baltic (Fennoscandian) in North North America America and and on the at several several localities localities in the Baltic (Fennoscandian) Shield Shield in in Finland Finland and in the the USSR USSR just just east east ofofFinland. Finland. The main main evidence evidence for aa glacial glacial history history is the association association of of fine-grained fine-grained laminated laminated units units containing containing oversized oversized lonestones lonestones (some (some clearly "dropstones"), "dropstones"), with diamictite diamictite (matrix-supported (matrix-supported conglomerate). conglomerate). associationhas has long long been This "diamictite-dropstone This "diamictite-dropstone laminite" laminite" association been known known in in the Huronian Supergroup Supergroup of of Ontario, Ontario, especially especially in the Gowganda Huronian Gowganda Formation Formation (e.g., (e.g., Young, Young, 1981), the slightly slightly older older Ramsey Ramsey Lake Lake and and Bruce BruceFormations. Formations. In the Upper Upper 1981), but but also in the Peninsula of of Michigan, laminite association associationisis present present in three Peninsula Michigan, the diamictite-dropstone diamictite-dropstone laminite units - the the Reany Reany Creek Creek (Puffett, (Puffett, 1969) 1969) and and Enchantment Enchantment lake lake (Gair, (Gair, 1981) 1981) Formations Formations of Range area area and and in in the theFern FernCreek CreekFormation Formation (Pettijohn, (Pettijohn, 1943) 1943) of of of the the Marquette Marquette Range southern Dickinson Dickinson County, to the the south south(Ojakangas, (Ojakangas,1984). 1984). All three Michigan Michigan southern County, 80 km to occurrences are the basal units occurrences are the basal units of the the Lower Lower Proterozoic Proterozoic rock rock column column at those those Similar deposits deposits are are known in southern west of Hudson localities. localities. Similar southern Wyoming, Wyoming, west Hudson Bay, Bay, and and in central central Quebec, Quebec, and and an an Early Early Proterozoic Proterozoic glaciation glaciation covering covering about about 55 million million km2 km2was was suggested by Young Young (1970). (1970). Such deposits deposits were recently discovered discovered in eastern Finland in the the Sariolian Sariolian Group Group the Karelian Karelian Supergroup Supergroup (Marmo (Marmo and andOjakangas, Ojakangas,1984). 1984). The Urkkavaara Urkkavaara Formation, Formation, of the which we have have interpreted interpreted as as glaciomarine, glaciomarine, is subdivided subdivided into into four four informal informal members members as as argillite member, a graded sandstone member, an upper siltstonefollows: a lower lower argillite member, a graded sandstone member, an upper siltstoneThe argillite member, and and aa diamictite diamictite member. argillite member, member. The lower lower three three members members contain contain dropstones, and the upper siltstone-argillite grades upward into the dropstones, and the upper siltstone-argillite grades upward into the diamictite diamictite fades. facies. Subsequently, Marmo (1986) (1986) described described three three additional members that that overlie the Subsequently, Marmo additional members the initial initial sequence as follows: sandstone member, sequence follows: an an upper graded graded sandstone member, aa parallel-bedded parallel-bedded conglomerate member member and and aa massive conglomerate massive conglomerate conglomerate member. member. He interpreted interpreted these these three members to be be comprised comprised of of glaciofluvial glaciofluvial sediments. sediments. The Urkavaara Urkavaara Formation, Formation, three members about 300 300 m thick, is capped about capped by by aa 100 100 m m thick thick meta-regolith meta-regolith that appears appears to have have been been Close Proterozoic weathering. largely intensive Early largely conglomeratic conglomeratic rock rock prior prior to to intensive Early Proterozoic weathering. Close inspection of the same inspection of same stratigraphic stratigraphic horizon horizon in the Sariolian Sariolian Group Group has has resulted resulted in in the the five other in eastern recognition of glaciogenic glaciogenic characteristics characteristics in in five other areas areas in eastern and and central central recognition Finland; some of these localities localities are are separated separated by by 350 350 km. km. Negrutsa and Negrutsa (1981a,b) described 15 diamictite localities localities in Negrutsa Negrutsa (1981a,b) in the described 15 Sariolian Group and its its equivalents, equivalents, many many with with associated associated lonestones, lonestones, in in Karelia, Karelia, USSR; USSR; they proposed they proposed sedimentary-tectonic sedimentary-tectonic and and volcanotectonic volcanotectonic origins. origins. We We visited visited seven seven localities m 1988, and diamictite units are are associated localities m diamictite and lonestone lonestone units associated in the rock rock column column At one locality, at each. each. At locality, aa thick thick sequence sequence of of diamictite diamictite is is overlain overlain by by thinly thinly laminated laminated metasiltstone with dropstones dropstones that that clearly clearly penetrate and deform the laminae metasiltstone with penetrate and laminae (Ojakangas (Ojakangas et al, 1989). 1989). 79 �The presence The presence of glaciogenic glaciogenic lithologies lithologies in widely widely spaced spaced areas areas of of sedimentary sedimentary rocks on the Baltic Baltic Shield Shield allows allows for for correlation, correlation, as as aa glaciation glaciation isisan anuncommon uncommon"mega"megaevent" related to climatic of these these deposits deposits are are indeed indeed climatic change change (Ojakangas, (Ojakangas, 1988). 1988). If all of of of the the same same age, age, the the area area on on the the Baltic Baltic Shield Shield that was affected affected by by this this Early that was Early Proterozoicglaciation glaciationhad hadaa minimum minimumsize sizeofof about about 500 500 km km by 250 Proterozoic 250 km. km. If the other other diamictite (tilloid) occurrences describedby by Negrutsa Negrutsa and and Negrutsa on the diamictite (tilloid) occurrences described Negrutsa on the Kola Kola Peninsula in northwesternmost northwesternmost USSR been unable unable to to Peninsula USSR are are included, included, although although we we have been study those localities to attempt attempt to the area study those localities to verify verify glacial glacial characteristics, characteristics, the area directly directly affected by the the Early glaciationmay maybe be on on the the order affected by Early Proterozoic Proterozoic glaciation order of 200,000 200,000 km, km , suggestive of aa continental-scale continental-scale glaciation. glaciation. The rock rock Units units in which which these these glaciogenic glaciogenic rocks occur in in Finland Finland and and East Eastkarelia karelia are by lava flows are underlain underlain by flows dated dated at about about 2450 2450 m.y. m.y. and are are intruded intruded by by dikes dikes and and The Huronian Supergroup has 2450 2450 m.y. sills dated at about about 2180 2180 to 2160 2160 m.y. m.y. The Supergroup has m.y. lavas lavas at its its base base and and isis intruded intruded by by Nipissing Nipissing dikes dikes and and sills dated dated at about about 2180 2180 to to 2150 2150 m.y. m.y . I is A contemporaneous or penecontemporaneous glaciationseems seemslikely, likely, and and it is A contemporaneous or penecontemporaneous glaciation Baltic Shields possible American and possible that the the North North American and Baltic Shields were in in close close proximity proximity approximately approximately 2300-2200 m.y. ago ago (Ojakangas, (Ojakangas,1988). 1988). 80 I I I I I I I I I I I �________ _________ ________ _______ I References Cited Cited in the Koli-Kaltimo Koli-Kaltimo area, North Karelia, Marmo, J.S., stratigraphy in Marmo, J.S., 1986, 1986, Sariolian Sariolian stratigraphy North Karelia, Eastern Finland, Finland, in V.A. V.A. Sokolov Sokolov and K.l. K.I. Heiskanen, Heiskanen, eds., eds., Early Early Proterozoic Proterozoic of of in Baltic Shield: the Baltic Shield: Proceedings Proceedings of the the Finnish-Soviet Finnish-Soviet Symposium Symposium held held in Petrozavodsk 19-27 August 1985, 1985, p. p. 149-190. 149-190. Marmo, J.S., Marmo, J.S., and and Ojakangas, Ojakangas, R.W., R.W., 1984, 1984, Lower Lower Proterozoic Proterozoic glaciogenic glaciogenic deposits, deposits, eastern Finland: Finland: Geol. Soc. Soc. America America Bull., Bull., v. v. 95, 95, p. p. 1055-1062. 1055-1062. Negrutsa, T.F., T.F., and Negrutsa, V.Z. V.Z. 1981a, Early Proterozoic Lammos tilloids of the Kola Negrutsa, Lammos tilloids Kola M.J. and Harland, Peninsula, U.S.S.R., Hambrey, M.J. Harland, W.B.eds., W.B.eds., Earth's Earth's PrePreU.S.S.R., in Hambrey, Pleistocene glacial glacial record: record: Cambridge 678-680. Pleistocene Cambridge Univ. Univ. Press, Press, p. 678-680. 1981b, Early Early Proterozoic Proterozoic Sarioli Sariolitilloids tilloids in in the the eastern , 1981b, eastern part of the the Hambrey M.J., M.J., and and Harland, W.B., eds., eds., Earth's PreBaltic ~ a l t i cShield, U.S.S.R., U.S.S.R., in Hambrey Harland, W.B., PrePleistocene glacial record, p. p. 683-686. 683-686. Ojakangas, R.W., 1984, Basal Ojakangas, R.W., 1984, Basal Lower Lower Proterozoic Proterozoic glaciogenic glaciogenic formations, formations, Marquette Marquette Range Supergroup, Range Supergroup, Upper Upper Peninsula, Peninsula, Michigan Michigan (Abs.): (Abs.): 30th 30th Institute Institute on lake lake Superior Geology Proceedings, Proceedings, Wausau, WI., WL, p. p. 43. 43. an uncommon as a key , 1988, 1988, Glaciation: Glaciation: an uncommon "mega-event" "mega-event" as key totointracontinental intracontinental and intercontinental correlation of of early Proterozoic basin fill, North intercontinental correlation North American American and and Baltic cratons, cratons, in fr K.L. Baltic K.L. Kleinspehn Kleinspehn and C. Paola, Paola, eds., eds., New New Perspectives Perspectives in Basin Basin Analysis: Analysis: Springer-Verlag, p. 431-444. 431-444. 1989, Lower Marmo, J.S. and Heiskanen, K.l., 1989, , Marmo, Heiskanen, K.I., Lower Proterozoic Proterozoic glaciogenic glaciogenic deposits: deposits: Finland Finland and U.S.S.R., U.S.S.R., Baltic Baltic Craton Craton (Abs.): (Abs.): 28th 28th International International Geologic Geologic Congress Abstracts, Washington, Washington, D.C., D.C., p. 2-542. 2-542. 1943, Basal of Menominee Pettijohn, F.J., 1943, Pettijohn, Basal Huronian Huronian Conglomerates Conglomerates of Menominee and and Calument Calument districts, Michigan: Jour. Jour. Geology, v. 51, 51, p. p. 387-397. 387-397. W.P., 1969, Puffett, W.P., 1969, The Reany Reany Creek Creek Formation, Formation, Marquette Marquette County, County, Michigan: Michigan: Bull Bull U.S. U.S. Geol. Surv. Surv. 1274-F, 1274-F, p. p. F1-F25. F1-F25. Young, Young, G.M., G.M., 1970, 1970, An An extensive extensive early Proterozoic Proterozoic glaciation glaciation in in North North America? America? Palaeogeogr., Palaeoclimat., Palaeoclimat., Palaeoecol., Palaeoecol., v.v. 7, p. 85-101. 85-101. Palaeogeogr., Ontario, Canada: 1981, The , 1981, The early early Proterozoic Proterozoic Gowganda Gowganda Formation, Formation, Ontario, Canada: 6 Hambray, M.J. M.J. and and Harland, Harland, W.B. W.B. (eds.), (eds.), Earth's Earth'sPre-Pleistocene Pre-Pleistocene Glacial Glacial Record. Record. Cambridge Univ. Press, Press, p. p. 807-812. 807-812. 81 ^. �U Mafic Granulite Granulite and Eclogite Nodules Nodules Petrography, Mineral Chemistry, and Geotherinobarometry Geothermobarometryof Mafic from Upper Michigan Kimberlites. James PACES* & Lawrence A. TAYLOR, Department Departmentof ofGeological GeologicalSciences, Sciences,University University of of James B. PACES* Tennessee, Tennessee, Knoxville, Knoxville, TN 37996-1410. 37996-1410. *pfltly at: Branch Branch of Isotope IsotopeGeology, Geology,U.S. U.S. Geological GeologicalSurvey, Survey,MS MS963, 963, *Presentlyat: Denver Federal FederalCenter, Center,Denver, Denver,CO CO80225. 80225. Accidental Accidental xenoliths xenoliths and and xenocrysts xenocrysts contained contained within diatremes within diatremes from the theMichigan Michigan Kimberlite Kirnberlite Province (Cannon (Cannon and Mudry, Province Mudry, 1981; 1981; Jarvis Jarvis and and 1988)represent represent one of the few means of Kalliokoski, 1988) sampling the deep Phanerozoic crust and upper sampling the Phanerozoic crust upper mantle mantle beneath beneath the the southern southernSuperior SuperiorProvince. Province. These materials are vital vital both both for forinvestigating investigating the composition and chemical composition and chemical history history of of the the deep deep lithosphere, and and for testing lithosphere, testing lithospheric lithospheric structural structural geophysical data models derived derived from geophysical data (i.e., GLIMPSE studies). studies). Diatremes Diatremes were were emplaced emplaced during during the Jurassic Jurassic (Jarvis (Jarvisand andKalliokoski, Kalliokoski,1988) 1988) into a geologically complex complex region region along along the the southern southern Superior Province in Upper boundary of the Superior boundary Michigan (Fig. 1). 1). Although Michigan (Fig. Although the the lithosphere lithosphere in in this this during the area formed formed and/or and/or stabilized stabilized during the late late Archean, it was Archean, was likely likely modified modified during during subsequent subsequent tectono-magmatic processes associated associated with with Lower Lower Penokean orogenesis Proterozoic Proterozoic Penokean orogenesis and and Middle This Proterozoic Midcontinent Rifting. This paper Proterozoic presents initial results of aa nodule nodule study study whose whose long range goal is to to better betterunderstand understandthe thepetrological petrological continental and geochemical geochemical structure structure of the continental and lithosphere and its lithosphere its modification through time. Data reported reported here herewere were obtained obtainedfrom from discrete discrete Ellen E MhicontinentRift(1.1 Ga) 7) Penokean passive (Z") Penokean passivemargin margin(1.8-1.9 (1.8-1.9Ga) (S) Penokean maginatic <SS> Penokean magmaticarc are(1.8-1.9 (1.8-1.9Ga) Ga) 0> Archean Archean (2.7.3.2 (2.7-3.2Ga) Ga) Fig. 1: General General Geological Geological Map. ' \? granulite and eclogite eclogite nodules nodules collected collected by William William Jarvis of Jarvis of Jack Jack Murphy, Murphy, Trustee, Trustee, from from trenches trenches excavated in the the Lake Lake Ellen and Site 69 pipes (Fig. excavated in (Fig. 1). Nodules Nodules range range in in size size from 2 to 8 cm in diameter and weigh 20 and and 400 400 g. g. Paleozoic Paleozoic and weigh between between 20 and low-grade low-grade metamorphic metamorphic clasts clasts were were carbonate and largely excluded. excluded. Although the present nodule largely nodule suite suite nodules) and and does does not represent an is limited (—50 (-50 nodules) an unbiased sampling unbiased sampling of of the the lithospheric lithospheric column, column, lithologies described lithologies described here form form a substantial substantial proportion of of the the"deep" "deep"xenolith xenolith population. population. The The Site 69 pipe contains aa variety variety of of mafic mafic amphibolites amphibolites and granulites, granulites, but but no no discrete discrete upper upper mantle mantle and/or ultramafic pipe ultramafic nodules. nodules. In contrast, the Lake Ellen pipe includes includes a variety variety of of eclogites, eclogites, pyroxenites, pyroxenites, garnet garnet peridotites, spinel peridotites, and mantle mantle xenocrysts xenocrysts (McGee (McGee and Hearn, Hearn, 1983) 1983) in addition addition to less less abundant mafic abundant mafic granulites. granulites. Attempts Attempts to to better are under underinvestigation. investigation. quantify xenolith populations are The current results results focus on lower lower crustal crustal granulite granulite eclogite nodules from the the two two pipes. pipes. and eclogite GRANULITES: Granulites nearly GRANULITES: Gramilitesfrom fromboth both pipes pipes nearly all have have mafic mafic compositions compositionscontaining containingplagioclase plagioclase (18-37 vol.%) and (18-37 vol.%) and dlinopyroxene clinopyroxene (19-40%) ( 1 9 4 % ) along along amphibole (0-11% (0-11% in gtgtwith garnet (16-42%)  with garnet (16-42%) ± amphibole rocks, up up to to 37% 37% in in gt-free gt-free rocks). rocks). Minor (1bearing rocks, 2%) ilmenite ilmenite (occasionally (occasionally rutile) is ubiquitous, ubiquitous, while may be be present, but only quartz and orthopyroxene orthopyroxene may only gt ++qtz qtz in minor amounts. AAsingle singlenodule noduleofofplg+ pig+@ with minor cpx represents + cpx represents the the most-"felsic" with minor rut rut+ most-"felsic" granulite observed. observed. Granulites exhibit exhibit nonfoliated, nonfoliated, (0.5-1.5 mm mm diam.), equigranular (0.5-1.5 dim.), granoblastic equigranutar granoblastic textures. Although textures. Although no no obvious obvious fabrics fabrics are are observed observed nodules, some thin sections in individual individual nodules, sections show show nonnonhomogeneous distributions homogeneous distributions of of phases. phases. Mineral compositions within within single single nodules vary only within small limits that local small limits suggesting suggesting that local equilibrium equilibrium was was acheived. Plagioclase in gtgtacheived. Plagioclase isis most most sodic sodic (An25-40) (An25o) in bearing assemblages assemblages and and most mostcatcic calcic(An5o..s5) (Anso-5s) in gtgtfree assemblages assemblages (Fig. 2). 2). Clinopyroxenes Clinopyroxenes contain low Cr203 0 - 2 0 3 (<0.04 (<0.04 wt.%), wt.%), substantial substantial A1203 A1203 and and low wt.%, and and 1-2 1-2 wt.%, wt.%, resp.) Na20 (3-5wt.%, Na20 (3-5 resp.) and and Mg#'s Mg#'s ((Mg/Mg+Fe2) M ~ / M ~ + of Fof~0.71-0.80. 0.71-0.80. - ~ ~ ) Ilmenite Ilmenitecontains contains 1-2 1-2 wt.% gt-bearing rocks 0.2-0.7 wt.% in in wt.% MgO in gt-bearing rocks and 02-0.7 82 I I I I I I I I I I I I I �I A// (1-10%) + rutile rutile (1-2%) (1-2%) with with accessory accessory Clfeldspar (1-10%) Hearn and apatite, silica, silica, and Fe Fe suffide. sulfide. Heam and McGee McGee (1983) (1983) also report kyanitekyanite- and andcorundum-bearing corundum-bearing similar major-phase eclogites with eclogites with similar major-phase compositions. compositions. Edogites exhibit Eclogites exhibit granoblastic-polygonal granoblastic-polygonal textures textures (05-3 thin (0.5-3 mm diam.) diam.) with no obvious obvious fabrics on a thin section scale. section Only minor intragranular intragranular compositional variations variations are present. compositional present. Omphacitic (Fig. 2) 2) have high A1203 Al203 (14.8 wt.%) clinopyroxenes (Fig. and Na20 (7.7 (7.7 wt%), wt%), low low Cr203 Cr203 (<0.07 wt%), and (Fig 2) 2) Mg#'s between between0.72-0.74. 0.72-0.74. Orange garnets (Fig Mg# == 0.39are high in is-on iron (FeOt = = 20.5 wt%, wt%, Mg# - 2 0 3 (<0.05 0.42) 0.42) and, and, like pyroxene, pyroxene, low lowin in 0Cr203 (<0.05 wt%). K-feldspar is is unequally unequally distributed within single thin K-feldspar sections and contains contains high high 1(20 K2O (—16.3 (-16.3 wt%), low low Na20 (<0.5 Na20 ( ~ 0 . wt%), 5wt%), and andappreciable appreciable BaO BaO (0.3-1.1 (0.3-1.1 of wt%). The Thepresence presenceof of small, small, rounded rounded inclusions inclusions of K-feldsparinin pyroxene and garnet K-feldspar pyroxene and garnet with with similar similar compositions indicates indicatesthat that K-feldspar K-feldspar isis a primary compositions phase. Reddish-brown rutile rutile is relatively pure with phase. Reddish-brown only small small amounts amountsof ofFeO, FeO,Al203, Al203,and andZr02 Zr02 (< (<13, 1.5, 0.5, and 0.4 wt.%, in 0.5, wt.%, resp.). resp.). Degree of alteration alteration in eclogites varies widely. reacts most eclogites varies widely. Clinopyroxene Clinopyroxene reacts readily; first around around grain grain boundaries boundaries and then along readily, first internal net-like fabric. internal fractures producing producing a net-like fabric. Omphacitic pyroxenes pyroxenes in in highly highly altered nodules are are completely replaced replaced by milky, augite-rich aggregates. aggregates. Large books of biotite biotite may also also be developed. developed. Ab Plagioclase / An Pyroxenes & Pyroxenes Garnets Circles = Granulites = Fkbgites Mg Fig. 2: Plagioclase, Garnet Chemistry. Plagioclase, Pyroxene and Garnet Chemistry. Orange, almandine-rich alinandine-rich garnet gt-free garnet gt-free rocks. contains 23-27wt.% wt.%FeOt, FeO, 6-9 contains 23-27 6-9 wt.% MgO, MgO, and and 6-7 6-7 wt.% CaO (Fig. wt.% (Fig. 2). 2). Garnets in some some nodules nodules are are qtz. with both both cpx graphically intergrown cpx and and qtz. graphically intergrown with alteration affect affect Varying Varying degrees degrees of of retrograde retrograde alteration garnets beginning beginning with fibrous, fibrous, green-black green-black rims rims progressing to a distinct pseudomorphic replacement by fme, gtfine, plg-sp-chl pig-sp-chi aggregates. aggregates. Amphiboles Amphiboles in gtbearing granulites granulites exhibit a similar similar mottling mottling of of finefmegrained opaques, opaques, and may may represent represent recrystallization recrystallization of keliphytic aggregates. aggregates. Many Many granulites granulitesalso also show show a network serpentine/chlorite alteration alteration along along network of of serpentine/chlorite grain boundaries adjacent to fresh cpx and pig. pig. This This network may extend into grains grains along along cracks where where it sometimes terminates in in patchy patchybrown, brown, mesostasismesostasislike material. material. These These features features are interpreted interpreted as as devitrified and altered decompression decompression melts formed formed during nodule transport transport and and emplacement. emplacement. WHOLE ROCKCOMPOSITIONS: COMPOSmONS:Granulite Granulite whole WHOLE ROCK whole reconstructed from mineral rock compositions compositions reconstructed chemistry chemistry and modal modal proportions yield close approximations to moderately-evolved,high-Al203 high-A1203 to moderately-evolved, 1). (Table 1). basaltic liquids liquids (Table Typical normative normative (Anso-po), 5-15% 5-15% 01, 01, mineralogy includes includes 50-60% 50-60% P1 PI (An5070), 20-35% Di Di++Hy. Hy. The The single single "felsic" 'felsic' nodule yields an 20-35% andesitic composition and contains contains 13% 13%normative normative Qz and and 3% 3%normative normative corundum. corundum. Eclogites yield yield high-Al, basaltic, whole rock compositions similar to to with the exception the mafic mafic granulites granulites with exception of higher higher alkalies. and and Ti02. Ti02. As a result, result, the the two twoanalyzed analyzed eclogites are Ne normative (6-8% Ne) with otherwise comparable PI, 01 01 and Di. comparable normative Fl, ECLOGLTES: Eclogites constitute the largest ECLOGITES: Eclogites constitute largest mantle xenoliths percentage percentage (85%) of upper mantle xenoliths previously reported from the Lake previously reported Lake Ellen Ellen kiinberlite kimberlite The three (McGee and Hearn, 1983). (McGee Hearn, 1983). three sanidine sanidine eclogites included included in in the present present suite suite are aretexturally texturally compositionally similar to to those described and compositionally earlier. Mineral Mineralassemblages assemblagesconsists consistsof of omphacitic omphacitic clinopyroxene(49-58%) (49-58%)++ garnet garnet (26-38%) (26-38%) t+ KKclinopyroxene TABLE 1: 1:Average Average Reconstructed ReconstructedWhole Whole Rock Rock Compositions Compositions for Granulites and Eclogites N Si02 Si02 Ti02 Mafic Granulites Granulites 6 49.18 Mafk Intermed. Gran. 11 55.98 Interned. Gran. Eclogite Eclogite 2 49.49 1.16 1.16 0.88 0.88 1.74 A1203 FeO FeO MnO MnO MgO CaO CaO Na20 K20 16.01 16.01 18.74 18.74 17.28 17.28 12.26 12.26 11.09 11.09 9.48 0.25 0.24 0.15 6.45 3.93 3.93 6.20 10.70 10.70 6.00 9.86 0.24 0.20 1.00 1.00 83 3.12 2.86 4.43 Total Cr203 Cr203 Total 0.02 0.01 0.01 0.04 99.39 99.93 99.93 99.64 99.64 I �I U Ii F Reconstructed Whole Rock A M Fig. 3: 3: AFM Fig. AFh4 Diagram Diagram For For Reconstructed ReconstructedWhole Whole Rocks. Rocks. Preliminary P-T GEOTHERMOBAROMETRY: GEOTHERMOBAROM~Y: Prelimiiary P-T Qtz± t ~ Opx OPX k estimates from unzoned Gt-Cpx-Plg± Gt-Cpx-Plgk Q estimates assemblages in granulites yield temperature temperature ranging ranging from 712-760° 712-760°Cand andpressures pressures from from 9-12 9-12 kb. kb. Results obtained using several different thermobarometers using several diierent thermobarometers show reasonable agreement ( 210°C 10° and ±T1.5 1.5 kb). kb). agreement (± These These results results are are comparable comparable to to P-T P-Tconditions conditions (Bohlen. observed in regional granulite granulite terrains terrains (Bohlen, observed in regional although pressures pressures for for nodules nodules are are higher higher than than 1987) although similar most uplifted uplifted granulite terrains terrains at similar most Estimated pressures correspond temperatures. Estimated corfespond to depths km. Depths Depths to to seismic-Moho seismic-Moho depths of of 30-42 30-42 km. reflectors in in this area have have been measured measured at at 36-42 36-42 km (Behrendt, (Behrendt, in press). Establishing EstablishingP-T P-T conditions conditions for more difficult due the the lack lack of of a for eclogites eclogites isis more difficult due assemblages. reliable geobarometer for gt-cpx assemblages. reliable Eclogite gt-cpx gt-cpx temperatures temperatures range between 980Eclogite between 9801070°C forpressures pressuresofof 15-40 15-40kb. kb. The presence of 1070° for in this thistemperature temperature range requires kyanite-eclogites in requires a of 14 kb kb (McGee (McGee and Hearn, 1983). minimum of 1983). CpxCpxopx composite xenocrysts xenocrysts (McGee (McGee and Hearn, Hearn, 1983) 1983) yield yield P-T estimates estimates of of 840-920°C 840-920° and 12-17 12-17 kb. kb. Although the opx Although the opx pressures pressures are are questionable questionable for for these xenocrysts, the combined combined data data preserve these xenocrysts, the preserve a consistent geotherm geotherm (Fig. (Fig. 4) intermediate consistent intermediate between between rift lconditions conditions (Berg (Berget etal., al., 1989) 1989)and andcold1 cold, shield hot, d (Pollack and Chapman, conditions (Pollack Chapman,1977). 1977). underplating and hjection underplating magmas injection of basaltic basaltic magmas 1987 Griffi (Bohlen, 1987; Griffm and and O'Reilly, O'Reilly, 1987). Eclogites s i m i l a r compositions compositions may may represent represent basaltic basaltic with with similar magmas emplaced below below the the sei..mic-Moho. seismic-Moho. At least thrie ma$ tectono-magmatic tectono-magmatic episodes episodes at —2.7, -2.7, three major —1.85and and -1.10 —1.10Ga Ga could could be responsible -1.85 responsible for for emplacement of nodule protoliths. Seismic seismic reflectors reflectors the Lake Superior region are interpreted throughout the interpreted to have origins associated with Midcontinent Rifting Rifting (Behrendt d., in press). However, nearby (Behrendt et a!., However, nearby tholeiitic volcanics associated with Penokean Penokean passive passive margin assemblages, assemblages, as as well as as Archean Archean metavolcanics,indicate indicate older older potential metavolcanics, potential magmatic magmatic sources. Further sources: Furthergeochemcial, geochemcial,geochronological, geochronological, and isotopic studies studies which which may may help help constrain protolith isotopic petrogenesis are currently in progress. References: Tectonophys 1172, (inpress); press); Berg Referma%: Behrendl 61. Bebrcndt et ef aL, d.,(1990) (1990)Tedonophys 72, (UI Berg et u d. (1989) EPSL 93,98-10% 93, 98-108; Bohlcn Bohlen (1987) .J M Gaol..95,6174g 95, 617-632; Cannon Cannon & (19S9) (1987)3 & Mudiy Mudry(1980) (1980) USGS C CIre 842; (1987) Mantle irc 8 42 GriMn Griffin&&O'Reilly 0 ' (1987)In, lqP.R. P.H.Nixon, N m n ,nil, ed, Mum&Xenollth.t, X e m b h , J3.. Wiley & Sons. (1988) Sous,413.430; 4 1 M W JJarvi m &&Ilalliokoeki KaU~okvsh (198S)Inst InstSLSuper SuperGaol C d34, 34,46-48; W Wflq McGee M cGe & & Ream Heam (1988) (19X3)USGS USCS Open-fin O p i U eRep Rep83-156. 83-156,22p; Z p ; MacGregor MacGmpr (1974) (1574)Am Am MIneral 59.110-11% 59,110-119; Poilack Chapman (1977) Tectoflophys 38,279-296 38,219.296 Mineral P O W& Chapman (1977)Tdonophys T (°C) 500 1000 1500 0 10 -- 20 ,—. 30 40 New Data 50 Initial results indicate CONCLUSIONS: Initid indicate that mafic igneous derived from igneous granulites were were derived from ma& granulites which equilibrated within within the lower protoliths which lower crust crust Noo at depths depths as great grmt as the theseismic-Moho. seismic-Moho. N granulites with metasediinentary metasedimentary affinities affinities have yet yet recognized. These data are are consistent consistent with with been recognized. models of of aa mafic mafk lower lower crust crust derived derived through through models •= MaScot MaficQtGranulite Granulite O 0 Sanidine S ~ e E CEclogite lo$te \.. 1. 3. i. k McGee McGee & & Hearn, Heam,1983 1983 60 A A CPX-OPX Xncryts OX-OPX COInp. &mp. Xncqats 0PXXenocg.at OPXXenocryt A 70 Fig. 4: Calculated CalculatedP-T P-Tconditions conditionsfor forMichigan Michigannodules. nodules. 84 F I I I I �I ARCHEAN AND AND PENOKEAN PENOKEANSTRAINS STRAINS IN IN THE THE NORTHERN NORTHERN COMPLEX, COMPLEX, ARCHEAN MARQUETTE MINERAL DISTRICT, DISTRICT, MICHIGAN MICHIGAN MARQUETTE MINERAL John C. Palmquist, Palmquist, Department Department of of Geology, Geologyl University, Appleton, Appleton, WI Lawrence Universityl Wl 54912 54912 The complexity Archean rocks rocks in the The complexity of dynamothermal dynamothermal metamorphism metamorphism ofof Archean the Marquette by the Marquette District, District, Michigan Michigan was was recognized recognized by the earliest earliest workers workers ; Van Hi?- and n n A I ni+h 4 0 1 4 \ A w n h n n n -fi+n-nw-h:n (Williams, (Williams, 1891 1891; Van Hise Leith, 1911). Two Archean metamorphic events were documented events were documente( by Gair and Thaden (1968) but the problems; associated associated with with sorting out these Archean events from the Penokean1 Modern techniques of quantitative strain1 overprint overprint remain remain with with us. Recent work analysis give promise of these problems. analysis give promise of 01 solving ~ u l ~ ~some aulllw l l y pi wwlvll vvul A chnwinn thn ~lnce cimilaritv of n f strain ctrain ellipsoid nllincnid axes ayoc orientations, nriontatinnc and aqd showing the close similarity in the the Marquette in the rocks to to those magnitudes the Archean Archean rocks those of of rocks rocks in Marquet magnitudes in Supergroup (Carter, 1989, 1989, p. p. 69) that either Supergroup (Carterl 69) suggested suggested that either the the Archean Archean rocks roc1 were undeformed prior to to the were undeformed prior the Penokean, Penokean, and and thus thus record record only only Penokean Penoke: ctrgin nr that thn rnnztcttrnd ctrainc in +he A r ~ h n a n r n ~ k c ara indnc in the Archean are indeed strain, ~ , m ~or l i that lL,luL , the measured , l l u u ~ ~ strains su~ , . , w ~ m w ~rocks m ~ mmmuwzd Archean but the rocks Archean but rocks behaved behaved in in aa brittle brittlefashion fashion during during the thePenokean Penokean argue for for aa third interpretation, namely namely that that this paper paper II argue third interpretation, deformation. In this the Archean the Archean rock rock fabrics fabrics record record both both Archean Archean and and Penokean Penokean strains, strains, in aa complex sequence sequence of events. events. T n . 8 ~ # w.mw..m,vy .,,w wewww w,,.m.,ua,., w. Lllu w..-.,, w,.,y.a..," a .,... w.,.a.......w..w, svwm.w e L m w m t m e . u q w Strain in variolitic pillow pillow lavas lavas of the Mona Mona Schist Schi Strain measurements in horizontal indicate north-south north-south horizont between and Negaunee between Marquette and Negaunee indicate shortening of 27-36% vertical extension extension of 40-60%, 40-6O0Io, and and near near plane plar shortening of 27-36% and and vertical strain (Carter, strain (Carter, 1989). 1989). These These data are are consistent consistent with with those thosedocumented document( n 4 the +hn K ~ n mC n v r n - t i n n - n A quartzites m ~ ~ - v t v i t n en f thn h A n e n ~ r r 4 ~ n r 4A i i h for slates a m w a of ul ulc Kona nulta Formation 1 u ~ ~ and alw ~ q~u a ta u l L ~ e a of ul ~ the uu w Mesnard l~ v l u a~ l l a t u and allu Ajibik + -,ki Formations of the Formations of the Marquette Marquette Supergroup Supergroup (Westjohn, (Westjohn, 1978; 1978; 1986; 1986; 1987). 1987). New strain strain measurements pressurefringes fringesinin aa chlorite chlorite schist schist from New measurements ofof pressure from the lnwer memhnr nf tho Mona Mnna Schict show chnw a a minimum m i n i m ~ ~vertical vnrtical m e ~ t e n s i n nof of lower member of the extension ... Schist .........,-... -...-..-.-.. The pressure fibers grown 1100%. The 100%. pressure fringes fringes are quartz-chlorite quartz-chlorite fibers grown on the the ends en( s These data suggest of hematite porphyroblasts. porphyroblasts. These suggest the the interpretation interpretatk~n c)f rigid hematite that Archean rocks rocks of of varying varying strengths strengths have have responded responded differently, differently, and a1l d t hat Archean pillow lavas thus yield heterogeneous heterogeneous strain strain indicators. indicators. The The variolitic variolitic pillow Iavi3s t hus yield < n w e-lm+nm w..w, ..,w,,.-w, w. .,.w w,*- -w...w. w,,w.. - --.....-a -..:--..:I.. A..-L--..,L----n &LA &-:--fie primarily Archean strains fringes, developed ~IIIII~IIIY NGIIG~II W ~ I I whereas W I ~ I I G I G ~ ~the LIIG pressure ~ I G ~ ~ U IIIIIYG~, I G U G V W U ~ G ~ in more of Archean strain as as well as in more ductile ductile rocks, rocks, record record larger larger amounts amounts of Archean strain as deformation in the an additional additional increment increment of of Penokean Penokean strain. strain. Penokean Penokean deformation the Archean basement is is concentrated in high Archean basement concentrated in high strain strain shear shear zones zones and and within within the more the more ductile ductile lithologies. lithologies. )---..A ~GGUIU record -&-A:-- - - - n n m . - n 85 An.n-l--, �I The division The division of the the Mona Mona Schist Schist into into an an upper upper (Lighthouse (Lighthouse Point) Point) and and lower lower member by Gair member by Gair and and Thaden, Thadenl 1968) 1968) was was based, based, in in part, part, on the the division division between the the banded greenstonesofof the the upper between banded greenstones upper part part and and the the massive massive greenstones of the greenstones of the lower lower part. part. They They recognized, recognizedl however, howeverl the higher higher metamorphic grade grade of of the metamorphic the layered layered amphibolitic amphibolitic schist schist characteristic characteristic of the Lighthouse suggest that that the boundary boundary separating separating the the Lighthouse Point Point member. member. II suggest members of the Mona members of Mona Schist Schist is is tectonic tectonic rather rather than than stratigraphic. stratigraphic. In In addition to to the abrupt grade, the the strain addition abrupt change change in in metamorphic metamorphic grade, strain fabrics fabrics are are different across different across the the boundary. boundary. Mylonitic Mylonitic fabrics fabrics in the the meta-rhyodacites meta-rhyodacites with the Archean strains strains interlayered with the Lighthouse Lighthouse Point Point Member Member suggest suggest Archean interlayered whereas S-C structures flinty quarz whereas S-C structures in associated associated laminated laminated flinty quarz sericite sericite rock rock indicate movementconsistent consistentinin sense sense and and position indicate up-to-the-north up-to-the-north movement position with with a Penokean Penokean zone zone of of displacement displacement to account account for for the thehigher highermetamorphic metamorphic grade in the Lighthouse Point member (upthrown) and lower grade grade the Lighthouse Point member (upthrown) and lower grade in in the the Lower (downthrown) member. member. These same rocks also show interpreteted as as the asymmetrically developedkink kink bands bands which asymmetrically developed which are are interpreteted the Archean basement of the axial Archean basement manifestation manifestation of axial shortening shortening and andcross-folding cross-folding developed in in the Animikie developed Animikie rocks rocks of of the theMarquette Marquettesynclinorium. synclinorium. The The Archean Archean rocks rocks north north of of the theMarquette Marquette synclinorium, synclinorium, the the "northern "northern complex" appear to to show complex" appear show three three strain strain regimes. regimes. To To the the north, northl in in the Compeau Creek Creek gneiss* gneiss, ductile ductile shear Compeau shear zones zones provide provide evidence evidence of of Archean Archean A dextral of diabase reactivation of diabase dikes. dikes. A dextral transpression transpression regime regime seems seems The central sector, mainly the Lighthouse this zone. well-developed well-developed in in zone. The central sector, mainly the Lighthouse has a complex mylonitic fabric fabric locally locally complex strain strain pattern pattern with mylonitic Point Member, Member, has in the amphibolitic layers and in its felsic layers and vertically vertically stretched stretched boudins boudins in amphibolitic in its Some geologists geologists have have speculated speculatedthat that the the lenticular schist. Some lenticular layers layers in this If that is is correct, correctl the unit are are actually actually extremely extremely flattened flattened pillows. Lighthouse Point member is much more flattened as well as of Lighthouse Point member is much more flattened as well of higher higher metamorphic grade grade than than the lower The strain strain fabric fabric of the the lower lower metamorphic lower member. member. The essentially ranging from dominated by vertical member is member is dominated vertical extension ranging from variolitic pillow pillow lavas lavas to to a minimum undeformed to to 60% undeformed 60% in in variolitic minimum of of 100% 100% in in Future work work will will be directed chlorite directed at at further further chlorite schists schists and slaty slaty units. units. Future northern complex partitioning within the documenting documenting the the strain strain partitioning the northern complex and and the Archean attempting to establish establish the relationships relationships between between the Archean and and Penokean deformations. deformations. REFERENCES REFERENCES CITED CITED Carter, Carter, P. J., JWlJr., Jr., 1989, 198g1Finite Finite strain strain estimations estimations for for Archean Archean Mona Mona Schist Schist pillows and early early Proterozoic Proterozoic Enchantment Enchantment Lake Lake Formation Formation Metawackes in the eastern upper peninsula of Michigan: Metawackes in eastern upper peninsula of Michigan: Michigan Michigan State Univ. unpub.M. unpub.M. S. thesis, thesis, 97 97 p. p. 86 �Gair, J. E. and Thaden, Thaden, ft R.E., E.,1968, 1968,The TheGeology Geologyof ofthe theMarquette Marquetteand andSands Sands Quadrangles, Marquette County, County, Michigan: Michigan: U.S. U.S. Geol. Geol. Survey Prof. Quadrangles, Prof. Paper 397, 77 p. p. Van Hise C. R. K., 1911, 1911, The The Geology Geology of of the the Lake Lake Superior Superior R. and and Leith, Leith, C. C. K., Region: U.S. Geol. Survey Mon. Mon. 52, 52, 641 641 p. p. Williams, G. G. H., 1891, Williams, 1891, The The greenstone greenstone schist areas of the the Menominee Menominee and Marquette regions of of Michigan: U.S. Geol. Geol. Survey Survey Bull. Bull. 62, 62, 238 p. Marquette regions Michigan: U.S. p. 87 �U FINNISH PROTEROZOIC PROTEROZOIC GOLD GOLD FINNISH AND IMPLICATIONS FOR THE LAKE AND IMPLICATIONS FOR THE LAKE OCCURRENCES OCCURRENCES SUPERIOR REGION REGION SUPERIOR Heikki S. S. Pankka Pankka and and Theodore Theodore 1. 3. Bornhorst, Bornhorst, Department Departmentof of Heikki Geological Engineering, Geology, and Geophysics, Michigan Geological Engineering, Geology, and Geophysics, Michigan ~echnologicalUniversity, University, Houghton, Houghton, MI MI 49931 49931 (Pankka (Pankkaalso also Technological with the the Geological Geological Survey Survey of of Finland) Finland) with The Proterozoic Proterozoic geology geology of of Finland Finland is is similar similar to to that that of of The the Lake Superior region and is consistent with Proterozoic the Lake Superior region and is consistent with Proterozoic plate reconstructions reconstructions which which suggest suggest that that Finland Finland and and Greenland Greenland plate were connected connected with with North North America. America. Thus, Thus, it it is is appropriate appropriate to to were use the the geologic geologic setting setting of of Proterozoic ~roterozoicgold gold occurrences occurrences in in use In the the ProProFinland as as analogs analogs for for the the Lake Lake Superior Superiorregion. region. In Finland terozoic of Finland there are a significant number (34) of terozoic of Finland there are a significant number (34) of gold occurrrences occurrrences of of economic economic interest, interest, in in the the Lapland Lapland greengreengold in the Lapland granulite terrane of north Finstone belt and stone belt and in the Lapland granulite terrane of north Finland, and in the Svecokarelian complex of south Finland. land, and in the Svecokarelian complex of south Finland. These three three areas areas have have been been interpreted interpreted as as subparallel subparallel rift rift These intracontinental zones. The The Lapland Lapland greenstone greenstone belt belt was was intracontinental zones. whereas the the other other two two developed developed oceanic oceaniccrust. crust. whereas The Lapland Lapland granulite granulite terrane terrane is is composed composed of of graywackes graywackes The granulitization around 2.1 to 2.0 Ga. This This which underwent which underwent granulitization around 2.1 to 2.0 Ga. Archean baseterrane was overthrusted to the southwest onto terrane was overthrusted to the southwest onto Archean basePlacer gold has been ment and the Lapland greenstone belt. ment and the Lapland greenstone belt. Placer gold has been recovered in in small small amounts amounts from from this this terrane terrane since since the the late late recovered 1800's. This This gold gold was was derived derived from from retrogressive retrogressive shear shear zones. zones. 1800's. The Lapland Lapland greenstone greenstone belt belt of of early early Proterozoic Proterozoic age age (2.5 (2.5 The to 2.0 Ga) consists of bimodal volcanics overlain by quartzto 2.0 Ga) consists of bimodal volcanics overlain by quartzin the the lower lower part part and and of of komatiitic komatiitic to to thothorich sediments sediments in rich leiitic volcanics with related volcaniclastics in the upper leiitic volcanics with related volcaniclastics in the upper part. Mafic Mafic intrusions intrusions are are common common at at 2.4 2.4 and and 2.2 2.2 Ga. Ga. These These part. rocks were were deformed deformed at at about about 1.9 1.9 Ga Ga in in aa style style that that resembled resembled rocks clastic foreland fold fold thrust thrust belts. belts. Synorogenic Synorogenic granitoids, granitoids, clastic foreland sediments, and and felsic felsic volcanics volcanics were were followed followed by by postorogenic postorogenic sediments, granites. Gold Gold mineralization mineralization occurs occurs in in quartz—carbonate quartz-carbonate granites. ultramafic and mafic rocks, in in quartzquartzveins hosted by altered veins hosted by altered ultramafic and mafic rocks, carbonate veins associated with felsic dikes and related gracarbonate veins associated with felsic dikes and related gra— and in disseminated sulfides or breccia pipes hosted nitoids, nitoids, and in disseminated sulf ides or breccia pipes hosted albitized quartzites. quartzites. Faults, Faults, shear shear zones, zones, or or folds folds play play aa by albitized by Gold is is epigenetic epigenetic role in in localization localization of of all all occurrences. occurrences. Gold role and emplaced emplaced after after the the peak and peak of of regional regional greenschist greenschist facies fades metamorphism and and deformation. deformation. metamorphism The Svecokarelian Svecokarelian complex complex ranges ranges in in age age from from about about 2.2 2.2 to to The It consists of a thick succession of metamorphosed 1.75 Ga. 1.75 Ga. It consists of a thick succession of metamorphosed platform to to deep-water deep-water turbidites. turbidites. Mafic Mafic igneous igneous rocks rocks are are aa platform small component component of of the the complex. complex. These These rocks rocks were were deformed deformed small between about about 2.0 2.0 to to 1.75 1.75 Ga Ga during during the the Svecokarelian Svecokarelian orogeny. orogeny. between I 88 i �About About three three quarters quarters of of the the complex complex consists consists of of syntectonic syntectonic tonalite tonalite to to granodiorite granodiorite and and associated associated intermediate intermediate to to felsic felsic volcanics. AA major major portion portion of of the the complex complex represents represents juvenile juvenile volcanics. crust. Gold Gold is is hosted hosted by by tonalite tonalite to to quartz quartz diorite diorite stocks stocks crust. and intermediate intermediate volcanics/intrusives. volcanics/intrusives. AA few few occurrences occurrences are are and in supracrustal supracrustal rocks. rocks. Metamorphic Metamorphic grade grade of of the the host host rocks rocks is is in Gold tends tends to to be be associated associated with with either either amphibolite amphibolite facies. facies. Gold Alteration is is characcharaclithological lithological contacts contacts or or shear shear zones. zones. Alteration terized terized by by quartz-sericite-biotite quartz-sericite-biotite and and K-feldspar K-feldspar and and lacks lacks carbonates. Gold Gold was was likely likely emplaced emplaced during during the the late late stages stages carbonates. of of the the orogeny orogeny and and may may be be linked linked with with magmatic magmatic processes. processes. Geologic Geologic environments environments exist exist in in the the Lake Lake Superior Superior region region that that are are very very similar similar to to gold gold bearing bearing ones ones in in Finland. Finland. Thus, Thus, it it is is reasonable reasonable to to suspect suspect that that numerous numerous significant significant gold gold occurrences occurrences exist exist in in early early Proterozoic Proterozoic rocks rocks of of the the Lake Lake SupeSuperior rior region. region. 89 �p I NEW NEW EVIDENCE THAT LIMESTONE MT., MT., MICH MICHIGAN, SRUCT1JRE IGAN, IS PART OF A LARGE IMPACT STRU CTURE M F. Geology Dept., Dept., Lawrence Lawrence Univ., Univ., Appleton, Appleton, WI WI 54912 William F . Read, Geology Rising abruptly to aa height Of Rising of about 100 m m above the low ground which which immediately immediately surrounds it, Limestone it was was Limestone Mt. Mt. is, topographically, topographically, aa rather rather impressive feature. When When it discovered that the "mountain" "mountain" COnSiStS limestone (or (or dolostone), discovered consists mainly of limestone dolostone), whereas all but one the other other high hills in the area are sandstone, sandstone, quarrymen geologists were immediately immediately of the quarrymen and geologists attracted to to it. it. The other projecting mass of limestone limestone in in the area is is Sherman Sherman Hill Hill (see (see attracted Fig. 1), much smaller and lower than "the mountain." Fig. l), smaller lower than " the mountain. " Geologists soon soon found out that the the (unmetamorphosed) and, Geologists (unmetamorphosed) limestone limestone is is full full of of fossils, fossilsi, and, from these, that the age of the the rock rock is is Ordovician. Ordovician. In the "mountain," "mountain," the layers layers are arei not horizontal but warped down in a pronou pronounced displaced by numerous need syncline syncline and displaced numerous small small faults. f etults. e,. ----,-A -----o- ~ - -e The same same is is true true to to aa lesser lesser degree degree of of Sherman J L L ~ L N U X U Hill. "ALL. - 1 . ~ - 1 . & led LCU to w ~ u n i ~ ~ a e r especulation specunation This considerable involves, not only the two two hills, also a good regarding the cause of the deformation, deformation, which involves, hills, but also of deal of the neighboring where this this is is visible. visible. Fig. neighboring sandstone sandstone (Jacobsville) (Jacobsville where Fig. 1 shows shows most of the known known exposures exposures of of Jacobsville Jacobsville which which are are relevant relevant to to this this paper. paper. These exposures low exposures are low and inconspicuous. inconspicuous. Obviously, Obviously, the the limestone limestone is is much more more resistant resistant to to erosion. erosion. Most structural studies have been aimed primarily at "the "the mountain." mountain." In relatively recent relatively recent years, qeophysics geophysics has has played played a a part part in these studies and some geophysicists geophysicists have covered a good territory beyond Limestone Limestone Mt. Mt. and and its its immediate immediate vicinity. vicinity. For example, Campbell, deal of territory CampbelL. in preparing a 1952 prfparinq 1952 M.S. M.S. thesis thesis on on the the "Silver "Silver Mountain Mountain area" area" (1) (1) did ground did a good deal of ground magnetic gravity work work as as far north as (Silver Mt. Mt. is a a prolecting projecting knob magnetic arid and gravity as Limestone Limestone Mt. Mt. (Silver knob of basalt tens tens of of miles miles to to the thesouthwest.) southwst. The The U.S. U.S. Geological Geological Survey Survey published published in in 1965 1965 aa set set of of (quadrangle by quadrangle) quadrangle) aeromagnetic aeromagnetic maps The (quadrangle by maps covering covering the the area area around around Limestone Limestone Mt. Mt. The contours shown magnetic contours shown in in Fig. I 1 were traced traced from from these these maps, maps. complete bibliography Hoehl's Hoehl's massive massive M.S. M.S. thesis thesis (2) ( 2 ) provides a virtually complete bibliography of the the relevant relevant contribution which he missed, literature literature up to to 1981. 1981. The only contribution missed, an important important one one from from my point of view, is the first large tectonic map of the U.S., published in 1944 by the National view, is large U.S., in 1944 the disturbances in otherwise otherwise flat-lying Research Council. Council. Walter Bucher, who regarded many local disturbances flat-lying of "cryptovolcanic" "cryptovolcanic" activity, activity, was on the committee coHmittee that put this sedimentary rock as evidence of map together, and presumably responsible for getting getting Limestone Mt. Mt. on it as an example of this map goodly number of geologists have subsequently reinterpreted these kind of activity. activity. A qoodly these structures as due to structures to the the sudden sudden collision collision of of aa flying flying oversize oversize meteorite, meteorite,planetesimal,. planetesimal, or or result in comet comet with with the the earth's earth's surface. surface. Any such collision is bound to result in an awesome awesome explosion explosion which excavates a crater very much larger than the projectile itself and causes deformation crater larger the pro] ectile itself aiid causes deformation well beyond the Some geologists g<sologists still the boundaries of the the crater crater and below below its its bottom. Some still adhere adhere to to nward effects r fm a i n long after the the idea that this kind of deformation,of deformation,of which which the dow downward remain 2 to crater crater itself itself has has been been eroded eroded away, away, is is due due to to vulcanism. vulcanism. Others, u t i i e ~ s ,unwilling unwilling to take take sides, sides, refer to the structures in question as the result of some unidentified kind of 'cryptoexplosion." "cryptoexplosion." Except for the circle, which I have drawn in rather arbitrarily arbitrarily on the the assumption assumption that that the the by exposures on Limestone Limestone Mt., Mt., Sherman Hill, and sandstone sandstone to the disturbance recorded by southeast southeast is is in in fact fact the the result result of of impact, impact, Fig. Fig. 1 is is mostly mostly factual. factual. I have been been convinced convinced of of this for quite some time but heretofore heretofore have been been uncertain as to where the center of the the structure was likely to be and, consequently as to size of the circle. structure likely to be and, consequently as to size of the circle. was quided guided mainly by by the M-shaped M—shaped series In a first try at locating locating the the center, center, I was series of exposures exposures (Fig. (Fig. 1) between Limestone Limestone Mt. Mt. and and the the village village of of Pelkie. Pelkie. These These are are the the surface surface expression of a slightly more resistant layer in the Jacobsville which here is folded into a pair of north—plunging north-plunging anticlines. anticlines. A number number of people who who have studied studied large, large, well—exposed well-exposed have noticed noticed similar similar anticlines anticlines plunging plunging away away from from what what is generally generally referred referred impact structures have a "central "central uplift." uplift." Central uplifts uplifts are characteristic characteristic of impact structures structures which have a to as a If the direction of plunge were always directly away from the diameter of more more than than 2—3 2-3 km. km. direction of were always directly uplift, Limestone Mt. Mt. structure structure should be somewhere somewhere on a broad line uplift, then the center of the Limestone a somewhat Result: extending southward southward in in the the direction direction of of the the axes axes of of these these two two folds. folds. Result: somewhat have drawn on Fig. smaller smaller circle circle than than the the one one I have Fig. 1, assuming that that the the distances distances from from Limestone Limestone Mt. structure are, for some reason or other, other, about the Mt. and Sherman Sherman Hill to the center of the structure Unfortunately, the plunge is now always directly directly away from a central uplift, as anyone same. unfortunately, same. This can see who examines Plate 3 of Professional Professional Paper 599-H 599—H issued in 1972 by the USGS. USGS. This paper describes a "cryptoexplosion" "cryptoexplosion" structure structure in southwest southwest Texas named after the peak which Sierra Madera. crowns crowns its its central central uplift: uplift: Sierra Madera. seems to me a rhe magnetic high near The near the the center center of of Fig. Flq. 1 now seems a such much more more reliable reliable indicator indicator of of the actual location location of the (assumed) (assumed) uplift which lies at the center of the (assumed) (assumed) impart impact structure named after Limestone Limestone Mt. Mt. One One thing thing all the the magnetics people agree agree on is that that there there is a slightly curving string of of magnetic magnetic highs highs beginning beginning several several tens tens of of miles miles to to the the southwest and petering out rather rather abruptly abruptly aa short short distance distance north north of of Limestone Limestone Mt. Mt. These highs highs are are generally attributed to a a buried buried ridge ridge of of basalt basalt which which makes makes its its last surface surface appearance appearance on on the way to to Limestone Limestone Mt. Mt. in in the the aforementioned aforementioned Silver Silver Mt. Mt. Keweenawan basalt similar similar to, to, and and which forms the the backbone backbone of of the the Keweenaw Keweenaw Peninsula Peninsula is thought presumably an extension of, that which to underlie most sost of the area where where Jacobsville Jacobsville sandstone is now now present present directly directly below below whatever whatever happens, the unconsolidated unconsolidated material material may may lie lie on on top top of of it. it. As it happens, the strong strong magnetic magnetic high high which which II have chosen as indicating indicatinq the the location location of of the the (assumed) (assumed)central central uplift uplift in in the the Limestone LimestoneMt. Mt. structure structure is is several several km km southeast southeast of of the the main main string string of of magnetic maqnetic highs. (3) highs. Meshref Meshref and and Hinze Hinze (3) have explained explained this this as as due due to to aa horizontally—small horizontally-small block, block, bounded bounded on on all all sides sidesby by faults, faults, having been inexplicably inexplicably pushed pushed closer closer to to the the surface surface at at this this particular particular location. location. Many things happen as, and and soon after, after, the,initial theinitial crater Many crater is is excavated. excavated. They They are are so so complex, and and so so variable--dependin variable——depending on on aa number number of of factors~that factors——that to to describe describe them them numerous, so complex, 2) all in an abstract or depict their their effects effects accurately accurately in in aa diagrammatic diagrammatic cross—section cross-section(Fig. (Fig. 2) more or or impossible. The rise of a central uplift in a crater of the size suggested here is more is impossible. less inevitable, inevitable. Considerable Considerable downsliding downslidinq of of larqe larqe and and small small slices slices of of the the original oriqinal steep steep less " - 7 , ".k.- >---L-- . -A,.--- I 90 1 �I crater walls my cross-section cross—section II have Limestone Mt. walls is is also also more more or or less less inevitable. inevitable. In my have shown shown~imestone Mt. as having dropped down below its original level riding single huge slide block. block. ridinq on top of a sinqle Another possibility is that may have dropped down into a rift ("ring grab4n") that developed that. it may ("rinq qrab6n") i.nthe the rock rock surrounding surrounding the in the original original crater as an its its walls, walls, momentarily compressed compressed by the force force of the the explosion, explosion, bounced bounced back back toward, toward, and and even even beyond, beyond, their their original oriqinallocation. location. This might miqht better explain the fact that, in some places on the east. east side of "the mountain," rock layers are bent sharply upward as if draqqed dragged into that position by by downward movement relative to a either case case the diameter diameter of of the proposed disturbed (hidden) little farther farther east. east. In either (hidden) fault a little outer limits remains the area indicated indicated by by the the circle circle on on Fig. Fig. 1 remains the same. same. Its Its outer limits are are Set set by by apparently apparently undisturbed exposures of Jacobsville along the west branch of the the Otter River to the north and below below the the dam dam responsible responsible for for Prickett Prickett Lake Lake to to the the south. south. So much for for theory. theory. Now what about about evidence evidence to to support support it, it, as as promised promised by by the the title title to to situ," and this paper? paper? The evidence evidence is is divisible divisible into into two two categories: categories: (1) and (2) (2) this (1( "in situ," transported. transported. The "in situ" evidence is derived mainly from the isolated exposure of Jacobsville about Examination of Jacobsville about 2.5 2.5 km km due due west west of of the the peak peak of of the the magnetic magnetic high. high. Examination of aa thin thin section of rock here reveals that most of the original pore space between sand grains has been filled in with small angular fragments in what what is now glass, or partly crystallized crystallized glass-glass—— evidently aa fluid fluid mush mush when when squeezed squeezed into into place. place. Also Also the the original original sand sand grains, grains, in in some some cases cases together, implying implying a temporary, temporary, somewhat more or less crushed, have been squashed together, somewhat plastic condition. These two factors combined are probably responsible responsible for the fact that, among local condition. well drillers, the sandstone near the magnetic high has a reputation reputation for "tightness," well "tightness," meaning that it is is reluctant reluctant to to yield yield an an adequate adequate supply supply of of groundwater. groundwater. It may be mentioned mentioned also also that that the bedding visible visible in in this this small small exposure exposure dips dips about about 200 20' west. west. This This is is as as observed observed in in small small blocks pried out from between intersecting joints. We may be dealing here with cross—bedding, from between intersecting joints. be dealing here with cross-bedding, a very common feature feature in in the the Jacobsville. Jacobsville. If it is "true" "true" (overall?) (overall?) bedding, bedding, the the dip dip is is at least consistent Consistent with with the the idea idea of of aa central central uplift uplift to to the the east, east, which which must must have have been been least accompanied by some some outward outward tilting tilting of of adjoining adjoining sediments. sediments. The transported evidence evidence is found in thin mud flows flows apparently apparently derived derived from from retreating much thicker layers of outwash sand. These assumed glacial ice and intercalated between much sand. These assumed cobbles, are to be seen in two mudflows, heavily laden with slightly rounded pebbles and cobbles, sandpits a short distance east of the village of Alston, as shown in Fig. sandpits short distance east of the village of Alston, as shown in Fig. 1. 1. Although the the drumlin—like low hills direction of the last ice advance was from the northeast, indicated by drumlin-like in this area, suggesting that the cobbles and pebbles in the mudflows should have come from well to the north of the area of "tight" surrounding the (proposed) some place well "tight" sand surrounding (proposed) central sandstone show exactly the same uplift, thin sections of a few of the harder ones composed of sandstone the.same sort of metamorphism exhibited by thin sections sections cut cut from the the isolated exposure exposure of bedrock close close to the (assumed) (assumed) central central uplift. iiplift. REFERENCES REFERENCES ---,-.-. ( 1 ) Campbell, -- -..Area, (1) Campbell, R. N. E., E., 1952, 1952, Area, Houghton County, Michigan," unpublished M.S. thesis, Michigan Technological County, Michigan," M.S. thesis, Technological University. (2) Hoehl, . J., Hoehl, EE. J., 1981, 1981, "Geophysical "Geophysical Investigation Investigation of of the the Limestone Limestone Mountain Mountain Area Area of of Baraqa Baraga and and Houghton Counties, Counties, Michigan," M.S. Michigan," unpublished M .S. thesis, thesis, Michigan Technological Technological University. Meshref, W. N. MM., and W. W. J. J. Hinze, Hjnze, I""" 1970, -."Geologic Interpretation of Aeromagnetic Data in in ((3) 3 ) Meshref, . , and keromaqnetic Data Western Upper Peninsula !port of Investigation Investigation 12. 12. Peninsula of Michig; Michigan," Michigan Geological Survey, Report 'Connhv*?lr^a1 T n v o c t i rrati on n f tthe h o ?i lvor M o n ritain --.-_"Geophysical Investigation of Silver Mountain ' 91 �I I AEROMAGNETICS of the LIMESTONE MT. STRUCTURE Contour Interval—SO gammas Large circle—suggested outer limit of elide biocki from Crater wails K—bedrock esposure W . Read 1989 I I I I I I I 1 Fig. 1 1 CtU zz 00 +-I- U', m2 / POST-CRATFRING SLIDE SLOCIS, ETC. = SURFACE SURFACE BEFORE B E F O R E IMPACT IMPACT - I GLACIAL DEPOSITS 1 I Fig. Fig. t 2 Oiagrammatic Diagrammatic cross-section cross-section along along aa line line passing passing through through Limestone Limestone Mt. Mt. and and the the peak peak of of the the magnetic magnetic high hiyh shown shown in in Fiq. rig. 1. 2 92 1 I I I �THE T H E REAPPEARANCE REAPPEARANCE OF OF THE T H EHURONIAN HURONIAN IN IN WYOMING WYOMING Stuart Stuart M. M. Roscoe Roscoe Geological of Canada, 601 Booth St., Ottawa, Canada KJA Geological Survey Survey of Booth St., K I A 0E8 OE8 Positive Positive matches matches of of all all stratigraphic stratigraphic units units through through the thePhantom Phantom Lake strata, Deep Lake Group and lower part of the Libby Group Lake strata, Deep Lake Group and lower part of the Libby Group inin Wyoming Wyoming with with every every unit unit in in the the western western part part of of the the Huronian Huronian Supergroup in Ontario Supergroup in Ontario show show that that the the two twosuccessions successions were were originally originally contiguous. contiguous. Recognition Recognition of this this establishes establishes an animportant importantcontinental continental sundering sundering and and subsequent subsequent reconstruction, reconstruction, and and improves improves insights insights into into environments of deposition of Paleoaphebian environments of deposition of Paleoaphebian (earliest (earliest Proterozoic) Proterozoic) strata strata in in the the southern southern part part of of the theCanadian Canadian Shield Shield and andWyoming Wyoming structural structural province. province. The The Wyoming Wyoming Province, Province, like like the the Minnesota Minnesota River River Valley Valleyterrane, terrane, was was welded welded onto onto the the southern southern margin margin of of the the present present Superior Superior Province Province at at 2.7 2.7 Ga. Ga. Huronian Huronian strata strata were were deposited deposited 2.5-2.4 2.5-2.4 Ga in in an an ensialic repository developed astride ensialic repository developed astride the the boundary boundary between between the the two two future future structural structural provinces. provinces. Deposition Deposition was was controlled controlled by by synsyn - depositional depositional faulting faulting and and warping warping accompanying accompanying uplifts uplifts in in regions regions to to the east, north, and west as well as by superimposed effects of glacial the east, north, and west as well as by superimposed effects of glacial loading loading and and unloading unloading and and sea sealevel levelchanges. changes. Some Some enigmatic enigmatic granite granite bodies were intruded at 2.4 Ga. bodies were intruded at 2.4 Ga. Following Following intrusion intrusion of of Nipissing Nipissing gabbro gabbro sheets sheets atat 2.2 2.2 Ga, Ga, the the continent was fragmented. continent was fragmented. The The Wyoming Wyoming Province Province fragment fragment was was split split off off along along the the Manitoulin-Niagara Manitoulin-Niagara structural structural zone zone and and rotated rotated about about 135° 135' as asindicated indicated by byforesets foresetsand andother otherdirectional directionalfeatures features inin preserved preserved remnants remnants of of the the southeasterly southeasterly part part of of the the Huronian Huronian Supergroup Supergroup inin the the Medicine Medicine Bow Bow and and Sierra Sierra Madre MadreMountains Mountains inin southern Wyoming. southern Wyoming. The The Boxelder Boxelder Creek Creek Formation Formation in in the the Black Black Hills Hills of of South South Dakota Dakota isisanother anotherremnant remnant ofofrafted raftedHuronian Huronian rocks. rocks. Younger Younger Aphebian Aphebian strata strata were were deposited deposited on on margins margins of of the the Archean cratonic cratonic fragments, fragments, first on shelves shelves during during their their post post 2.2 2.2 Ga Ga Archean first on separation separation and and later laterininforedeeps.formed foredeeps.formed during duringocean oceanclosures. closures. They They include the the iron ironformation-bearing formation-bearing Marquette Marquette Range Range Supergroup, Supergroup, the the include fault-bounded upper part part of fault-bounded upper of the the Libby Libby Creek Creek Group, Group, rocks rocks inin the the Hartville Hartville uplift, uplift, and and the theEstes Estesand andRoberts RobertsDraw DrawFormations Formations inin the the Black Black Hills. Hills. Huronian Huronian rocks rocks were were folded foldedand andmetamorphosed metamorphosed along along with with these these younger younger strata strata during during 1.9-1.8 1.9-1.8 Ga Gacollisions collisions with with island island arc arc terranes terranes toto the the south, south, resulting resulting inin the the preservation preservation of of remnants remnants of of both both sets sets ofofstrata strataofofdisparate disparateage ageand andcharacter character on on the thenorth northsides sides of the theNiagara-Manitoulin Niagara-Manitoulin zone zone and and the theCheyenne Cheyennetectonic tectonic zone. zone. of 93 �I Review of of Analytical Analytical Methods Methods for the the Determination Determination of of Review Platinum Platinum Group GroupElements Elements Bernhardt BernhardtSaini-Eidukat Saini-Eidukat Dept. DepLof ofGeology Geologyand andGeophysics, Geophysics,University Universityof ofMinnesota, Minnesota,Minneapolis, Minneapolis,Minnesota Minnesota55455 55455 PGE's (platinum (platinum group group elements: elements: Pt, Pt, Pd, Pd, Rh, Rh, Ru, Ru,Ir, Ir,Os) 0 s )present presentanalytic analyticdifficulties difficulties PGE's due due to to low low natural natural background background levels levels in rocks (Pt and Pd: 10 10 ppb; Ru: 0.1 ppb). The in insolubiity solubilityofofthe thepure puremetals metalsinincommon commonacids acidsand andthe theease easewith withwhich whichRu Ruand andOs 0 soxidize oxidizetoto volatile volatilespecies speciespresent present additional additionaldifficulties difficultieswhich, which, when when ignored, ignored, lead lead to to low low recoveries recoveries of of Os 0 sand andRu Ru(Van (VanLoon, Loon,1984). 1984).Steps Stepswhich whichmust must be beconsidered consideredininany anyPGE PGEanalysis analysis include: include: 1) 1)sample sampledecomposition, decomposition, 2) 2) separation separation of of the the POE's PGE's from from the the products productsof ofthe the sample sample decomposition, decomposition,and and 3) 3) quantitative quantitative determination of concentration. concentration. The The following following survey survey of of analytical analyticaltechniques techniques is is presented presented to to provide provide aa guide guide to to the the current current literature. literature. Sample Sample decomposition decomposition techniques techniques The The major major elements elements in in PGE-bearing PGE-bearing rocks can be readily readily brought brought into into solution solution with with conventional conventionalacid acidtechniques techniquessuch suchasasHF-aqua HF-aquaregia regiadissolution. dissolution.However, However, little littledata data exists exists on on the the solubility solubilityof of major majorplatinum platinum group groupminerals minerals such suchas assulfides sulfidesand andarsenides. arsenides. Reported Reported analyses analyses for Pt Pt and and Pd Pd on onstandard standardreference reference materials materials using using acid aciddigestion digestion usually usually are are low low (Hall (Hall and and Bonham-Carter, Bonham-Carter, 1988), 1988), and and Os 0 s and and Ru Ru are aregenerally generallylost lostas as volatile Chlorination can canbe beused used volatile tetroxides tetroxides unless distillation procedures are employed. Chlorination to to decompose decomposesamples samplesby by passing passingdry drychlorine chlorineover overaamixture mixtureof of the thesample samplewith withNaC1 NaCl and and activated activatedCC (Westland, (Westland,1981; 1981;Dolezal Dolezalet etal., al., 1966). 1966).The Thevolatilized volatilizedmetals metalsare areabsorbed absorbedinin HC1, resulting in soluble can also be HC1, resulting soluble PGE-chlorides. PGE-chlorides. Decomposition Decomposition can be achieved achieved with with oxidizing oxidizing fusions fusionsusing usingNa Naand andKKcarbonate carbonateor orhydroxide, hydroxide, Na202, Na202, borax borax or orboric boric oxide, oxide, Li Li tetraborate tetraborateor or metaborate, metaborate, K K pyrosulfite, pyrosulfite,or or the the alkaline alkalinefluorides fluorides(Johnson (Johnsonand and Maxwell, Maxwell, 1981). 1981).Such Such fusions fusions may may suffer sufferfrom fromslow slow attack attack on onPGE's PGE's (Westland, (Westland,1981), 1981), and and may may also alsoresult resultin inloss lossof ofOs 0 sand andRu. Ru. The reducing fusion fusion (classical (classical lead lead fire fireassay) assay)serves servestwo twofunctions: functions: The reducing decomposition decomposition and and POE PGE separation. separation. The The fusion fusion produces produces aa two two phase, phase, Pb°-slag PbO-slagsystem system in in which which the the PGE's PGE's are are distributed distributedinto into the the Pb°. PbO.Upon Upon oxidation oxidation (cupellation) (cupellation) to remove remove the the Pb, Ir, and Ru occurs. occurs. Pb, the the POE's PGE's are are left left in in aapurified purified metallic metallic state, state, although although loss of Os, Os, Jr. Any number of determination methods can be used on the bead. Detailed accounts Any number of determination methods can be used on the bead. Detailed accountsof of the thePb Pb assay assay method method are given given in in Beamish Beamish and and Van Loon (1977) and Haffty et al. (1977). (1977). To To overcome of the Pb fire assay, similar to matte overcome the limitations limitations of assay, a collection collection method method similar matte smelting wasdeveloped developed (the (the nickel nickel sulfide sulfide fire fireassay; assay;Robert Robertetetal., al.,1971; 1971;1972). 1972). smeltingwas The The sample sample is is decomposed decomposed and and the the POE's PGE's are are distributed distributed into the the sulfide sulfide phase. phase. This This method has proven proven equal equal to to or or better better than collection using Pb. Among the advantages advantages of aa NiS NiS collector collectorare: are: •lower •smaller *smallercharge chargeto to sample sampleratio ratio *lowerfusion fusion temperature temperature •collection *collectionof of all allPGE's PGE's with with no nopretreatment pretreatmentfor forhigh highSS samples samples as as in in the the lead lead method, method, and and •no *nochange change in in charge charge composition composition required for for different samples, samples, except for chromite chrornite ores. The The PGE's PGE's are are separated separatedfrom fromthe theNiS NiSusing usingHC1 HC1 and are are determined determined by by neutron neutron activation activation analysis analysis (NAA) (NAA) (all (all POE's), PGE's), or or are are dissolved dissolved in in aqua aqua regia regia and anddetermined determinedby byemission, emission, absorption absorption or or mass mass spectrometry spectrometry(Pt, (Pt, Pd, Pd, Rh). Rh). Recent Recent advances advancesin in this this method method include includethe the reduction reduction of of collector collectormass mass to to as as little little as as 0.5 0.5 gram gram without affecting affecting element element recovery (Asif (Asif and and Parry, Parry, 1989). 1989). 94 * �I Separation Separation techniques In the Pb fire fire assay assay ,,Ag Ag is is separated separated from from Au, Pt and and Pd by by nitric acid. acid. In In the theNiS NiS fire fire assay, assay, the the PGEs PGE'sare areseparated separatedfrom fromthe thenickel nickelsulfide sulfideby bydissolution dissolutionof ofthe thebutton buttonininHC1; HC1; the the PGE PGE sulfides sulfides are are filtered filtered and and their theirconcentration concentration determined. determined. Any Any POE's PGE's lost lost due duetoto dissolution into HC1 HC1can canbe berecovered recoveredby bycoprecipitation coprecipitation with Te (Shazali et al., al, 1987). 1987). Os 0 s and and Ru Ru can can be beseparated separatedfrom fromcomplex complex solutions solutions and and from from each each other other using using distillation. distillation.The Thetetroxides tetroxidesare arecollected collectedin in reducing reducing or or alkaline alkalinesolutions, solutions, or or in hydrogen hydrogen peroxide (Beamish Loon, 1977; 1977; Walker, Walker, 1988). 1988). Koster Koster & & Schmuckler Schmuckler (1967) (1967) (Bearnish and Van Loon, synthesized synthesized chelating chelating ion ion exchange exchangeresins resinswhich whichstrongly stronglybind bind PGE's PGE's and and Au Au but but not not base base metals. metals. This This method method involves involves acid acid dissolution dissolution of the the sample, sample, binding binding of of aaPOEPGEhydroxy-chloride hydroxy-chloridecomplex complex to to the the resin, and elution (Warshawsky et al., 1980). A variety of determination methods can can be applied. Nadkarni determination methods Nadkarni and Morrison Momson (1974) used an an ion ion exchange exchange resin resin to to separate separatePOE's PGE's from from samples samples already already activated activated with with neutrons; neutrons; the the resin resin with adsorbed Potential loss of adsorbed PGE's was was counted counted to determine determine PGE concentrations. Potential PGE's during dissolution and incomplete elution of PGE's from the resin may may hamper hamper POE extraction methods PGE analysis using resins. Liquid—liquid Liquid-liquid extraction methods are are undergoing intensive research for for both both analytical analytical and and extracfive extractivepurposes purposes (Warshawsky, (Warshawsky, 1983), 1983),but but routine routine laboratory arenot notyet yetcommon. common. laboratorymethods methods for forPOE PGE determination determinationare Determination Determination techniques techniques The The variety variety of of analytical analyticaltechniques techniquesavailable availableto to determine determinePGE's PGE's has hasincreased increasedsince since Crocket Crocket and and Cabri's Cabri's (1981) (1981) review review of of POE PGE analytical analyticalmethods. methods. Graphite Graphite furnace furnace atomic atomic absorption absorption spectrometry spectrometry (GF-AAS), (GF-AAS),inductively inductivelycoupled coupledplasma plasma emission emissionspectrometry spectrometry (ICP-ES), (ICP-ES),and anddirect directcurrent currentplasma plasma emission emission spectrometry spectrometry (DCP-ES) (DCP-ES) are arecurrently currently widely used for for the the determination determination of Pt, Pt, Pd, Pd, and and Rh, Rh, usually usually on on samples samplesfrom from which which PGE's PGE's have have been been separated separated and and concentrated. concentrated. The The trend trend in in determinative determinative techniques techniques isis toward ( N A A) A ) and and inductively inductively coupled coupled plasma-mass plasma-mass toward neutron neutron activation activation analysis analysis (NA spectrometry spectrometry (ICP-MS). (ICP-MS).AAcomparison comparisonof of current currenttechniques techniques can can be be found found in in Hall Hall and and Bonharn-Carter Bonham-Carter(1988). (1988). NAA NAA is is widely widely used used for fordetermination determination of of all allsix sixPGE's PGE'satatlow lowconcentrations concentrations (Hoffman, (Hoffman, et al., al., 1978; 1978;Shazali Shazalietetal., al.,1987). 1987).Decomposition Decomposition and and separation separationsteps stepsare are usually usually employed employedto to increase increasesensitivity sensitivity and and reduce reduce interferences; interferences; these these include includethe the Pb Pb and and NiS NiS fire fire assay assay techniques, techniques, ion ion exchange exchange resins resins and and distillations. distillations.The The sample sample is is bombarded bombarded with with neutrons, neutrons, and and the the intensities intensities and and wavelengths wavelengths of any radioactive daughter daughter elements elements produced producedare aremeasured. measured. Quantitative Quantitativedetermination determinationis is made made by by comparison comparisonwith with standards. standards. Recent in this method of Rh Recent advances advances in method include include the direct direct determination determination of Rh with with no no preconcentration preconcentration using using 38 38MeV MeV alpha alphaparticles particles(Volfinger, (Volfinger,1989). 1989). A A review review of of the the technique technique of of ICP-MS ICP-MScan canbe befound foundininFlouk Houkand andThomson Thomson(1988), (1988), and and its its application application to to PGE PGE determination determination is is described in Date et al. al. (1987) (1987) and and Gregoire Gregoire (1988). (1988). The The decomposed decomposedsample sampleisisintroduced introduced as asaa fluid fluid usually usually via via aa nebulizer nebulizerto toaaplasma plasma are conducted conducted to to aa quadrupole quadrupolemass mass in which which atomization atomizationand andionization ionization occur. occur. The The ions ions are in analyser. analyser. The The technique technique affords affords excellent excellent sensitivity, sensitivity, linear linear dynamic dynamic range range and andmultimultielement capability. capability. Determination Determination of of Pt, Pt, Pd, Pd, and and Rh Rh using using fire fireassay assay preconcentration preconcentrationisis element already aa standard standardtechnique. technique. As As usual, usual,precautions precautionsin in the thedecomposition decompositionstep stepmust mustbe be already 0 s and and Ru. Ru. Techniques Techniques such such as as isotope isotope dilution dilution have have been been taken when when analyzing analyzing for for Os taken developedfor for determination determinationofofPtPtand andOs 0 son onthe theICP-MS ICP-MS(Date (Dateetetal., al.,1987). 1987). developed 95 �I REFERENCES Asif, M and Parry, J.,1989, 1989, Elimination Elimination of of reagent blank problems in the fire-assay pre-concentration Parry, S SJ., pre-concentration of of the platinum group elements and gold with a nickel sulfide bead bead of of less than than one gram mass. mass, Analyst, v.114, V. 114,pp. pp. 1057-1059. 1057-1059. Beamish, F. E. and Van Loon, J.J.C., Bearnish, C., 1977, 1977,Analysis Analysis of ofNoble Noble Metals, Metals,Academic Academic Press, Press, N.Y. N.Y. Crocket, J.H. J.H. and Cabri, LJ., U., 1981, elements, in in Cabri, Cabri, L.J., U., 1981,Analytical Analyticalmethods methods for for the the platinum-group platinum-group elements, ed., Platinum-Group Elements: Geology, Recovery, Can. Can. Inst. Mining Elements: Mineralogy, Mineralogy, Geology, Mining Metall. Metall. Spec. Spec. Pub. 23, pp. 71-82. 71-82. A.R., Davis, A.E. Y.Y., 1987, The potential potential of fire assay and inductively Date, A.R., A.E. and Cheung, Y.Y., inductively coupled plasma source mass spectromeiry spectrometry for the determination determination of platinum group elements in geological geological materials, 112, pp. 1217-1222. 1217-1222. materials, Analyst, v. 112, Dolezal, J., J., Povondra, P., and Dolezal, and Sulcek, Sulcek, Z., Z., 1966, 1966,Decomposition Decomposition Techniques Techniques in in Inorganic Inorganic Analysis, Analysis, American Elsevier Publ. Co., Inc., Inc., N.Y., N.Y., 224 pp. Gregoire, D.C., D.C., 1988, Gregoire, 1988, Determination Determination of platinum, platinum, palladium, palladium, ruthenium, ruthenium, and iridium in in geological geological materials materials by inductively inductivelycoupled coupled plasma plasma mass mass spectrometry spectrometry with with sample sampleintroduction introductionby by electrothermal electrothermal vaporization, J. Anal. Atom. Atom. Spectrom., Spectrom., v. 3, 3, pp. pp. 309-314. 309-314. Haffty, J., Riley, L. B., and Goss, W. D., 1977, 1977, A A manual on fire fire assaying assaying and determination determination of the noble noble metals in geological 1445, 58 58 pp. pp. geological materials, materials, U.S.G.S. U.S.G.S. Bull. Bull. 1445, G.F., 1988, Review of of methods methods to determine gold, platinum 1988, Review platinum and Hall, G.E.M. G.E.M. and Bonham-Carter, Bonham-Carter, G.F., palladium in production production oriented oriented geochemical geochemical laboratories, laboratories,with with application applicationof of aa statistical statisticalprocedure procedureto to bias, J. Geochem. Geochcm. Explor., Explor., v. v. 30, 30, pp. pp. 255-286. 255-286. test for bias, Hoffman, E.L., E.L., Hancock, Hancock, R., R., Naldrett, Naldrett, A.J., A.J., Van Van Loon, Loon,J.C., J.C., Hancock, Hancock,R.G.V. R.G.V.and and Manson, A., Hoffman, A.. 1978, 1978, The determination determination of all the platinum group elements and gold in rocks and ores by neutron activation preconcentration by sample size, size. Anal. Anal. analysis after preconcentration by a nickel sulfide fire assay technique on large sample Chim. Acta, v. 102, 102, pp. pp. 157-176. 157-176. R.S. and Thomson, J.T., J.T., 1988, spectrometry, Mass Spectrom. Rev., Rev., v. 7, Houk, R.S. 1988, Inductively coupled mass spectrometry. 425-461. pp. 425-461. Johnson, W.M. and Maxwell, J.A., 1981, Rock and Mineral Analysis, 2nd John Wiley Wiley and and Sons, Sons, 489 489 Johnson, 2nd ed., ed., John pp., pp., N.Y. N.Y. K0ster.G. Schmuckler, 1967, 1967, Separation Separation of Koster,G. and and G. 0. Schmuckler, of noble noble metals metals from from base base metals metals by by means means of of a new chelating resin, Anal. Chim. Acta, v. 38, 38, pp. 179-184. 179-184. Nadkarni, R.A G.H., 1974, Determination R.A and Morrison, G.H., Determinationof of the the noble noble metals metals in in geological geological materials materials by by neutron activation analysis, Anal. Anal. Chem., Chem., v. v. 46, 46, pp. pp. 232-236. 232-236. Robert, Robert. R. V. V. D., D., van van Wyck, Wyck, E., E., Palmer, Palmer, R., R., 1971, 1971,Concentration Concentration of of the the noble noble metals metals by by aafire-assay fire-assay technique technique using nickel sulfide sulfide as as the the collector, collector, N.I.M. N.I.M. Report Report 1371, 1371, 14 14 pp. pp. 1972,The The development development of of aafire-assay fire-assay Robert, R. V. D., D., van van Wyck, Wyck, E., E., Palmer, Palmer, R., R., and and Steele, Steele,T.W., T.W., 1972, Robdrt, procedure using nickel sulphide as the collector for the noble metals, Journal of the the South South African African Chemical Inst., v. 179-189. v. 25, pp. 179-189. I., Van't Dack, L., and Gijbels, Shazali, I., Gijbels, R., 1987, 1987, Determination Determination of precious metals in ores ores and and rocks rocks by by i e assay and thermal neutron activationigamma-spectrometry activation/gamma-spectrometry after preconcentration by nickel sulphide ffire coprecipitation with tellurium, Anal. Chim. Acta, v. 196, 196, pp. 49-58. J.C., 1984, Accurate Accurate determination of the noble metals I. Sample decomposition decomposition and methods of Van Loon, J.C., separation, Trends Trends in Anal. Chem., v. 3, pp. pp. 272-275. 272-275. v. 3, Volfinger, Volfinger, M., 1989, 1989, Determination Determination of of rhodium rhodium in in geomaterials geomaterialsby by high-energy high-energyalpha-particle alpha-particleactivation, activation,J.J. Radioan. Nucl. Chem., Articles, v. 131, 131, pp. 19-35. 19-35. Walker, RJ., R.J., 1988, 1988,Low-blank Low-blank chemical chemical separation separation of rhenium rhenium and osmium osmium from gram quantities of Walker, from gram of 60, pp. measurement by resonance ionization mass spectrometry, Anal. silicate rock for measurement Anal. Chem., v. 60, 1231-1234. 1231-1234. Warshawsky, A., A., Fieberg, Fieberg, M.M.B., Mihalik, P., P., Murphy, Murphy, T.G. T.G. and Y.B. M.M.B., Mihalik, Y.B. Ras, 1980, 1980, The separation separation of Platinum group metals (PGM) (PGM) in chloride media by isothiourium isothiourium metals, metals, Separation Separation and and Purification Purification Methods, v. 9, pp. 209-265. 209-265. Warshawsky, Warshawsky, A., 1983, 1983, Integrated Integrated ion ion exchange exchange and and liquid-liquid liquid-liquid extraction extraction process process for for the the separation separation of of platinum group metals (POM), (PGM), Separation and and Purification Purification Methods, Methods, v. v. 11,95-130. 11,95-130. Westland, A.D., A.D., 1981, Inorganic platinum-groupelements, elements,in IaCabri, Cabri,L.J., U., ed., Inorganic chemistry of the platinum-group ed., PlatinumPlatinumGroup Elements: Mineralogy, Geology, Recovery, Recovery, Can. Can. Inst. Inst. Mining Mining Metall. Metall. Spec. Spec. Pub. Pub. 23, 23, pp. pp. 5-18. 96 1 �I Structural Structuralstudies studies in inthe the Huron Huron Bay Bay Parautochthon, Parautochthon, Upper Upper Michigan. Michigan. SAJA, (Dept. SAJA, D.B., D.B., and and Gregg, Gregg, W.J. W.J. (Dept. of of Geological Geological Engineering, Engineering, Michigan Michigan Tech. Univ., Houghton, Houghton, Mi. Mi. 49931) 49931) The The Huron Huron Bay Parautochthon, Parautochthon, located located between between the the Huron Huron Mountains Mountains and and Keweenaw Keweenaw Bay Bay in in Baraga Baraga County, County, Upper Upper Michigan, Michigan, is is aa belt bound by the belt of of strained strained Proterozoic Proterozoiciuetasediinents metasediments bound the Jacobsville Jacobsville sandstone sandstone to to the the north north and Archean Archean Gneisses Gneisses to to the the east east and and south south (fig. (fig. 1). 1). This This belt of of deformed deformed metasediments metasediments belongs belongs to to the the Upper Upper Slate Slate Member Member of of the the Michigamme Michigamme Formation. Formation. It consists consists of a thin thin sequence sequence of shelf sediments sediments overlain overlain by aa thick thick sequence sequence of of slates slates and and discontinuous discontinuous psainmitic psanunitic units. Early work in the region region by Klasner (1978) (1978) showed at least least four four generations tectonic lineations generations of foliation foliation and three tectonic lineations exist exist as as aa result result of of the the 1.9 1.9 Ga Ga Penokean Penokean orogeny. orogeny. Recent Recent studies studies by Dyke Dyke (1988), Sikkila (1987), (1987), and Van Roosendaal (1985) (1985) in in the the area area basin have have documented documenteda athrust/fold thrust/fold formerly formerly known known as as the the Baraga Baraga basin belt belt characterized characterized by multiple multiple generations generations of of iinbricate imbricate thrusting associated with northward northward verging verging folds. folds. A prominent prominent change change in in the the structural structural style style and amount of finite strain strain was shown shown by Gregg (1989) to mark the existence of an east-west trending Gr6 nding thrust fault near the village of L'Anse. This large scale th] :ale Figure 1: Generalized geologic map of the Huron Bay Parautochthon. A — Huron River, B - Slate River, C - Silver Falls Anticline, D — Keweenaw Bay, E Falls River, F Mountain Syncline. Little 97 I �I I 1 cm I so I-i 1 cm I I I I I 2: rauics Faults viewed normal Figure L: figure nonnax to 10 the \.ne plane p~-aneof o r cleavage. cxeavage. discontinuity, discontinuity, known known as as the Falls River Thrust, separates separates the the Baraga Belt into into two two previously unrecognized unrecognized structural structural domains, domains, the Huron Bay Parautochthon Parautochthon to the north, and the autochthonous autochthonous the Falls River Slice Slice to to the the south south (fig. (fig. 1). 1). the upper Throughout the Huron Bay Parautochthon, rocks of the slate member display only one one structural structural style style group. group. Generally Generally by Bl B1 folds with with Sl S1 cleavage, this style group is characterized by B1 overprinted by small overprinted small post-kinematic low low angle angle thrust thrust faults. faults. Bl folds display shallow axial plunges to to northwest northwest and and southeast, southeast, and axial planes that that dip to to the the southwest southwest from from 45 45 to to 60 60 degrees. degrees. Fold profiles vary from open to gentle folds with amplitudes amplitudes of less than 2 meters in the north-central north—central and northeast parts of 1), to high amplitude the parautochthon (areas (areas AA and B on fig. fig. 11, S1 tight folds folds along the the south south west west section section (area (area CC of of fig. fig. 1). 1). Sl slaty cleavage continuous mica films cleavage is is defined defined by by anastoinosing, anastornosing, continuous films with bedding-parallel of neomineralized white mica , with fine neomineralized white bedding—parallel fine detrital layer silicates and opaque minerals in the intervening intervening quartzo-feldspathic quartzo-feldspathic microlithons. microlithons. Large chorite-white mica aggregates with (001) (001) traces parallel to bedding occur aggregates occur commonly it a within the microlithons microlithons and and have have strain strain shadows shadows parallel parallel to to SS, feature which which distinguishes Sl S1 from other foliations foliations present in I , 98 i �the allochthonous the allochthonous Falls Falls River River Slice. Slice. The The length length of of the the strain strain shadows shadows increases increases from from east east to west in in the the parautochthon, parautochthon, and and Thrust, with from north to south across the Falls River Thrust, increasing strain. parautochthon increasing strain. In the eastern end of the parautochthon numerous structural domains occur, numerous structural domains occur, marked by small small changes changes in in the the the dip of fold trend of L1 Ll and in in the fold axial axial surfaces surfaces and and slaty slaty cleavage. Thrust faults faults striking striking N58'W dipping 18° 18" to to the the cleavage. N58°W and dipping south the domains domains and drag bedding bedding into south define the into a a near near vertical vertical attitude. Although Although no no second second generation generation fabric fabric elements elements are are attitude. ^ = - l + - are =l^kely post post B1 Bl present in in the area, the the area, the faults most likely structures. structures. Widespread evidence evidence of normal faulting has has been been observed observed in in the parautochthonous both the parautochthonous and and autochthonous autochthonous terrains. terrains. This This evidence in scale from outcrop size evidence of extension, extension, ranges ran' discontinuities to small surfaces a few square discontinuities small slickensided s centimeters centimeters in in area area (fig. (fig. 2). Smaller fault surfaces are curviplanar curviplanar to to nearly nearly cylindrical ~yli..-~.^~in shape. Stereo net analysis ui.ulysis of the the surfaces surfaces shows shows that that the the slickenlines slickenlines are are typically typically parallel to to the the cylindrical cylindrical axis axis which itself itself lies lies in in the the plane plane of Sl cleavage. cleavage. A coating coating of of goethite, goethite, which is is layered layered over over the the of S1 slaty cleavage surfaces, enhances slickensides frequently slickensides and frequently delineates motion as delineates the the plane plane of of motion as it it oscillates oscillates between between the the cylindrical cylindrical fault fault surfaces, surfaces, bedding bedding planes, planes, and and cleavage. cleavage. Further movement along the Further evidence evidence of of movement the preexisting preexisting planes planes of of cleavage is is the the normal normal offset offset along along cleavage cleavage of of aa reduction reduction spot spot cleavage viewed parallel to the the bedding-cleavage bedding-cleavage intersection intersection lineation. lineation. parallel to observed with with Finally, foIds observed Finally, the the existence existence of sigmoidal sigmoidal drag drag folds offset rock deformation. deformation. offset laminar laminar bedding is is evidence evidence of hard rock mn-+ "--- -^.- REFERENCES Dyke, G.A., 1988, Dyke, G.A., 1988, Structure Structure and stratigraphy stratigraphy on on the the Silver Silver River River area, area, Baraga Baraga County, County, Michigan, Michigan, (unpub. (unpub. M.S. M.S. thesis), thesis), Michigan Technological Michigan Technological University, University, Houghton, Houghton, Michigan, Michigan, 87 87 p. p. W.J., 1989, Gregg, W.J., 1989, Effects Effects of large large scale scale overthrusting overthrusting on on fold fold geometry geometry and and finite finite strain strain in in the the Baraga Baraga thrust/fold belt, belt, Upper Michigan: Geol. of Upper of Michigan Michigan Symposium Symposium I. I. Michigan Michigan Department of Natural Resources, Resources, Lansing, Lansing, Michigan, Michigan, p. 14. Department 14. Klasner, J.S., 1978, Penokean Penokean deformation and associated associated Klasner, J.S., 1978, deformation and metamorphism in in the the Western Western Marquette Marquette Range, Range, northern northern Michigan, Geol. Soc. Amer. Bull., v. 89, 89, p. 711—722. 711-722. Michigan, Sikkila, K.M., 1987, Sikkila, K.M., 1987, A structural structural analysis analysis of of Proterozoic Proterozoic metasediments, northern metasediments, northern Falls Falls River, River, Baraga Baraga County, County, Michigan, (unpub. Michigan, (unpub. M.S. M.S. thesis), thesis), Michigan Michigan Technological Technological University, Houghton, Michigan, Michigan, 103 103 p. p. University, Houghton, Van Roosendaal, Roosendaal, D.J., D.J., 1985, 1985, An An analysis analysis of of rock rock structures structures and and Van of the the Huron Huron strain in cleaved politic pelitic rocks, East Branch of River, River, Baraga Baraga county, county, Michigan, Michigan, (unpub. (unpub. M.S. M.S. thesis), thesis), Michigan Technological University, University, Houghton, Houghton, Michigan, Michigan, 82 82 p. p. Michigan Technological 99 I I �U GEOCHEMISTRY GEOCHEMISTRY OF OF UNMINERALIZED UNMINERALIZED ROCKS ROCKS IN IN THE THE PARTRIDGE RIVER RIVER INTRUSION, INTRUSION, DULUTH DULUTH COMPLEX COMPLEX PARTRIDGE Severson and and Steven Steven A. Hauck Hauck Mark J. Severson Mark Natural Natural Resources Resources Research Research Institute, Institute, University of of Minnesota, Minnesota, Duluth Duluth University The Partridge Partridge River River intrusion intrusion(PRI) (PRI) of of the the Duluth Duluth Complex, Complex, The northeastern Minnesota, contains aa wide wide variety variety of of troctolitic, troctolitic, northeastern gabbroic, and and ultramafic ultramafic rock rock types. types. on correlations correlations in in Based on (83 holes) holes) and and reconnaissance reconnaissance mapping, mapping, the the PRI PRI has has been been drill core core (83 drill subdivided subdivided (Figure (Figure 1) 1) into: into: Partridge River River Troctolite Troctolite Series Series Gabbro Complex (PRGC), (PRGC), and and Oxide-bearing Oxide-bearing (PRTS), Partridge River Gabbro Ultratnafic Intrusions (OUI). Ultramafic Intrusions (OUI). The The PRTS PRTS consists consists of of at at least least eight eight igneous units that that are are correlated correlated in in drill drill holes holes over over an an major igneous indicated indicated eleven eleven mile mile strike strike length length extending extending (NE (NE to to SW) SW) from from the the Dunka Cu-Ni deposit deposit to to the the Wyman Wyman Creek Creek Cu-Ni Cu-Ni deposit deposit Dunka Road Road Cu-Ni (Severson, 1988; 1988; Severson Severson and and Hauck, Hauck, 1990). 1990). These These eight eight units units are are (Severson, characterized by by various various troctolitic troctolitic rocks rocks and and are characterized are diagrammatically diagrammatically portrayed Most portrayed in Figure Figure 2. 2. Most of of the the upper upper units units (Ill-VIlI) (III-VIII) represent represent single single cooling cooling units units in in that that they they are are floored floored by by aa bedded bedded ultramafic member (picrite (picrite to dunite); dunite) ; whereas, other units near the exhibit an overall overall heterogeneous heterogeneous nature the footwall footwall (I (I and and II) 11) exhibit nature and and contain abundant abundant internal internal members members reflecting reflecting continuous continuous magma magma replenishment. lateral ftfaciesff "fades" replenishment. Some Some of the the units also exhibit lateral changes changes along along strike strike and and downcutting downcutting relationships relationships indicating indicating aa complex complex intrusive intrusive history. history. The The PRGC PRGC is is situated situated at at the the southeastern southeastern portion portion of of the the investigated investigated area area and consists consists of oxide—bearing oxide-bearing gabbroic gabbroic and and troctolitic troctolitic rocks; rocks; both both locally locally exhibit exhibit excellent excellent modal modal bedding. bedding. Portions Portions of of the the PRGC PRGC were were originally originally interpreted interpreted as as aa hornfelsed hornfelsed basalt basalt (Colvin (Colvin Creek Creek "Gabbro", MGabbroN,and and parts parts of of the the Powerline PowerlineGabbro). Gabbro). However, reconnaissance reconnaissance mapping mapping revealed revealed the the presence presence of of several several However, unusual unusual sedimentary—like sedimentary-like structures that are not not indicative indicative of of typical typical North North Shore Shore Volcanic Volcanic basalts, basalts, and and an an origin origin via via magmatic magmatic density density currents currents is is suggested. suggested. The are later later pegmatitic pegmatitic intrusions intrusions consisting consisting of The OTJIs OUIs are of dunite, dunite, peridotite, peridotite, clinopyroxenite, clinopyroxenite,and and lesser lesser picrite picrite and and melagabbro; melagabbro; all all are massive oxide (>lo%) and and contain contain semi—massive semi-massive to to massive oxide are oxide—bearing oxide-bearing (>10%) horizons. horizons. These These bodies bodies are are intrusive intrusive into into the the PRTS PRTS and and include include the the Longnose, Longnose, Longear, Longear, Section Section 17, 17, Wyman Wyman Creek, Creek, and and Skibo Fe—Ti Fe-Ti prospects. prospects. The portions of all units The unmineralized unmineralized portions units were were sampled sampled (155 (155 in order order to to establish establish background background geochemical geochemical levels levels and and samples) in lithogeochemical signatures units of of lithogeochexnical signatures for for each each of of the the various various rock rock units Whole the the PRI. PRI. Whole rock, rock, rare-earth rare-earth elements, elements, trace trace metals, metals, and and precious precious metal metal analyses analyses were were conducted. conducted. Background Background Pd, Pd, Pt, Pt, and and Au Au values in in the the major major rock rock groups groups average average 10 10 ppb, ppb, 20 20 ppb, ppb, and and 55 ppb ppb values respectively. respectively. However, However, slightly slightly elevated elevated background background values values are are associated I1 (15 (15 ppb, ppb, 24 24 ppb, ppb, and and 99 ppb ppb respectively), respectively), associated with with Unit Unit II and and the the OUI OUI rock rock group group (15 (15 ppb, ppb, 24 24 ppb, ppb, and and 17 17 ppb ppb respectively). respectively). In ides), five (<I%suif sulfides), five In the the course course of of sampling sampling unmineralized unmineralized rock rock(<1% anomalous anomalous samples samples (>200 (>200 ppb ppb combined combined Pd Pd and and Pt) Pt) were were revealed revealed with with maximum of of 910 910 ppb. ppb. The The OUI OUI units units are are the the most most geochemically geochemically aa maximum I 100 1 �unique unique in in that that they they have have elevated elevated background backgroundvalues valuesfor forTi02, Ti02,V, V, Cr, Cr, relative to to the the other other Pb, Te, Te, Au, and and W relative Pb, igneous igneous rocks rocks of of the the Partridge Partridge River River intrusion. intrusion. Geochemical data (whole (whole rock, REE) support the the breakdown of Co, Co, Cu, Cu, Cd, Cd, C, C, Be, Be, Sc, Sc, the various various rock rock units units identified identified within within the the Partridge Partridge River River intrusion. Several intrusion. Several X—Y X-Y plots plots and and spider spider diagrams diagrams have have been been constructed constructed and and show show aa definite definite clustering clustering of of specific specificrock rockunits, units, and major igneous and within within each each of of the the major igneous rock rock units units some some specific specific rock rock types types also also show show clustering clustering (the (the MG-Number MG-Number plot plot depicted depicted in in Figure Figure 3 is one example). example). For is one For instance, instance, Units Units II and and II I1 exhibit exhibit aa markedly markedly different geochemical signature when compared to to the the other other PRTS PRTS units. One interpretation units. interpretation of of this this difference difference is that that magma magma contamination contamination due due to to assimilation assimilation of of footwall footwall material material was was important in The lower in their their genesis. genesis. lower half of of Unit Unit I, I, which which contains the the most most hornfels hornfels inclusions, inclusions, demonstrates demonstrates aa markedly markedly different geochemical geochemical signature signature when compared compared to to the the other other PRTS PRTS units. units. The The basal basal ultramafic ultramafic horizons horizons within within the the PRTS PRTS all all cluster cluster together together and and represent represent the the most most primitive primitive rock rock type type sampled. sampled. All All rock rock units units of of the the PRGC PRGC exhibit exhibit aa different different geochemical geochemical signature, signature, which, in in turn, turn, is is similar similar to to the the geochemical geochemical signature signature for for the the lower half half of of Unit Unit I. I. The The OUT OUT units units exhibit exhibit aa markedly markedly different different lower geochemical geochemical signature signature when when compared compared to to the the PRTS PRTS ultramafic ultramafic horizons horizons and and to to all all the the other other PRI PRI units. units. Severson, Severson, M.J., M. J., 1988, 1988, Geology and and structure structure of of aa portion portion of of the the Partridge Partridge River River intrusion: intrusion: aa progress progress report: report: Technical Technical Report 78 p. p. Report NRRI/GMIN-TR-88-08, NRRI/GMIN-TR-88-08, Duluth, Duluth, Minnesota, Minnesota, 78 Severson, Severson, N.J., M.J., and and Hauck, Hauck, S.A., S.A., 1990, 1990, Geology, Geology, geochemistry, geochemistry, and and stratigraphy of aa portion portion of of the the Partridge Partridge River River Intrusion: Intrusion: Technical Technical Report Report NRRI/GMIN-TR-89-ll, NRRI/GMIN-TR-89-11, Duluth, Duluth, Minnesota, Minnesota, 236p. 236p. LEGEND PRTS - OUTLINES AREA OF PARTRIDGE RIVER TROCTDLITE SERIES PRGC - PARTRIDGE RIVER GABERO COMPLEX Cu-Ni Deposits MINNAMAX DUNKA ROAD WETLEGS WYMAN CREEK - MMAX - DR - WL - WC Fe-Ti De~ouits (Om SECTION 17 LONGCAR --LONGNOSE SECTION 22 SKIED - - - 17 LE LN 22 SK I FIUURE FIGURE 11: GENERAL GENERAL GEOLOGIC GEOLOGICMAP MAP OF Of THE THE PARTRIDGE PARTRIDGE RIVER RIVERINTRUSION INTRUSION 101 �U I I * I PARTRIDGE RIVER INTRUSION INTRUSION PARTRIDGE r UMMJf VYMAN CREEK I 1 WETLEGS I DUNKA ROAD /' SEC. SEC, 17 17 LEINc3EAR LONGEAR LDt'4GNUSE LDNGMDSI \ V / rv Iv - = FQCT'./ALL FOOTWALL FOOTWALL trIke—lenth within tthe Strlke-length correlotion correlation of' of r'iajor naJor igneous IQneous unI-ts unlts within he bQO1 3000 fft. t . of o f the t h e PortrIcge Partridge River River Intruion, Intrusion, basal 3OO II C:SuIfIdt-hearing —no'e out* troctoirte, ii I1= =tractotte wrth augitt irOct~litQ, troctotitn withpcrI-te picrite ICyer'C layers aic. etc. FIGuRE FIGURE 2: £ L*4IT. UNITS' - - - ou9rte troctoirt VV encethosttic q r t e troctolrte, &not-thosltic troctoirte, Vi V I =s anorthoitic anorthosrtic -tract t r o d .tot o aygitetrocto&ite, t r o c t d l t e , VII VII==augi-te ougfte troctoirte. troctolite. trortoltte, ougrte — — —Qracdetlonni contact sharp contact - ~flnadatlonat contact scale mlled. bNogcaie 1n5)!IeS. III Mottid' Cnorthoe-tle toirte, IV Ill —'Mottlrd' inorthosrtrc 'tro troctolrte, IV — 1har contact - PR1RIflGE PARTRIDGE RIVER RIVER INTRUrnw INTRUSION , 26 26 - PM1ftt) Can TPCCTBITIC nas anra nia u.n a 24 1 re7l man incas m—vnE PRIS PRROGITTR-,iCOtc W JUTS C 22 PRIR1I1E RtiR* R'jIRC cnwain • PawR*u,C sAnnea 20 .Rc • cmvi.. nRa, 'mum' • MIWTHOflTTC S*IBTi. ti.rTeurS Or mc mum cOWLtR C., en IL1Rst JwtRLr.,tI VOX ULTKAHW I E 3"f.r.lVl-I IC.,, <WI> 18 KMTH 3È M O - C A i a C Ii- # <WVW -or. Gftm Utt. 16 C PRTS ISt ICuiffARl HLm..tLC WOSC MUWAW H O W C L SaOa <a> 14 12 - UNIT II "*I4 UNIT I Cu -J PICRITC- 10 r.25 B- 6' flu', 4. 2 0B I I I I I I I I 0.2 0,s 0.4 0.4 0.6 0.6 MG MG NUME:R NUMBER rigre Figure3. 3~ MG Nui*er v,vs.A12G3 MG Number A1203 0.8 I I I I I I 102 i �I The -A major north-verging north-verging The Great Great Lakes Lakes tectonic tectoniczonezone--A Late Late Archean Archean collision collision zone zone P.K. P.K. Sims, Sims, U.S. U.S. Geological Geological Survey, Survey, Denver, Denver, CO CO 80225 80225 The The Great Great Lakes Lakes tectonic tectonic zone zone (GLTZ) (GLTZ) is is an an Archean Archean crustal crustal boundary boundary of of subcontiriental length that that separates separates aa Late Late Archean Archean greenstone-granite greenstone-granite terrane subcontinental length terrane (Wawa subprovince subprovince of the Superior province, Canadian Shield) on the north north from Superior province, from It Archean gneiss gneiss terrane terrane on on the the south. south. It is is generally generally Early to to Late Late Archean an Early interpreted interpreted as as aa paleosuture paleosuture that that resulted resulted from from continent-continent continent-continentcollision. collision. The The tectonic tectonic zone zone is is covered covered at at most most places places in in the the Lake Lake Superior Superior region region by by Proterozoic rocks rocks or or Pleistocene Pleistocene glacial glacial deposits, deposits, and and its its position position and and Proterozoic characteristics previously have been determined mainly by geophysical geophysical data. data. been determined mainly by Geologic Geologic mapping mapping in in the the Marquette, Marquette,Michigan Michigan area area (Sims, (Sims,in in press) press) provides provides direct direct observations observations of of the the structure structure for for the the first first time. time. In the the Marquette Marquette area, area, the the GLTZ GLTZ is is aa 2.4-km-wide 2.4-km-wide zone zone of mylonite mylonite In (orthomylonite) that has has been superposed (orthomylonite) that superposed on on predominantly predominantly massive granitoid granitoid rocks Archean greenstone-granite rocks of of the the Archean greenstone-graniteterrane terrane and and on on previously previously deformed deformed rocks rocks of of the the gneiss gneiss terrane. terrane. Foliation Foliation in in the the mylonite mylonite strikes strikes about about N. N. 60° 60' W. and and dips dips steeply steeply southwest, southwest, subparallel subparallel to to the the boundary boundary between between the the two two terranes. terranes . AA pronounced pronounced stretching stretching lineation lineation and and tight tight fold fold hinges hinges plunge plunge about about 45° 45' S. S. 45' E. E. The The attitude attitude of of the the stretching stretching lineation lineation (line (line of of tectonic tectonic transport) transport) 45° together together with with asymmetric asymmetric structures structuresindicative indicativeof of sense sense of of movement movement indicate indicatethat that collision Marquette area resulted in dextral-thrust dextral-thrust shear collision in in the the Marquette area was oblique and resulted along the the boundary, boundary, northwestward northwestward vergence, vergence, and and probable probable overriding overriding of of the the This greenstone-granite greenstone-granite terrane terrane by the the gneiss gneiss terrane. terrane. This implies implies southward southward subduction of of the the greenstone-granite greenstone-graniteterrane. terrane. Transmittal Transmittal of of the the dextral dextral shear shear subduction stress to to the north iiiay stress across across aa large largearea areaof ofthe theSuperior Superiorprovince provincecrust crust the north may have have been responsible responsible for for the the nearly nearly east-west east-west foliation, foliation, upright upright folds, folds, and and northwestnorthwest- to to east-west-trending east-west-trendingdextral dextral faults faults and and shear shear zones zones at at least least as as far far north Quetico fault north as as the the Quetico fault (Qf, (Qf, fig. fig. 1), I), in in southern southern Ontario, Ontario,aa distance distance of of about about 250 250 km. km. As aa whole, whole, the the GLTZ GLTZ is is characterized characterized by by systematic systematic angular angular bends bends that that alternately west-northwestward, as alternately trend trendwest-northwestward, as in in the the Marquette Marquette area, area, and and northeastward northeastward (fig. 1). 1). This This zigzag zigzag pattern pattern probably reflects reflects original original irregularities irregularities in in the the (fig. continental continental margin margin (Superior (Superior province). province). Late Archean Archean convergence convergence along along this this margin variable trajectory margin resulted resulted in in aa variable trajectory of of stress stress northward northward into into the the greenstonegreenstonegranite granite crust crust and and probably probably in in along-strike along-strikediachroneity diachroneityof of orogeny. orogeny. The The major major deformation deformation was caused caused by by oblique oblique compression compression at at promontories, promontories, which which acted acted as as buttresses buttresses against against which which compressive compressive stress stress was was directed directed into into the the crust. crust. In In addition addition to to the the dominant dominant foliation foliation and and upright upright folds, folds, major major brittle-ductile brittle-ductileto to brittle brittle strike-slip strike-slip faults, faults, such such as as the the Vermilion Vermilion fault fault system system (Vf, (Vf, fig. fig. 1) 1) in in northern northern Minnesota Minnesota and and the the Quetico Quetico and and Rainy Rainy Lake-Seine Lake-Seine River River faults faults (RL-SRf, (RL-SRf, resulted from from a more brittle continuum of the fig. 1) 1) in southern southern Ontario, resulted the fig. transpressive transpressive shear shear caused caused by by collision collision along along the the GLTZ. GLTZ. Precise Precise isotopic isotopic ages ages (Davis (Davis and and others, others, 1989) 1989) suggest suggest that that the the collision collision occurred occurred at at about about 2,690 2,690Ma. Ma. References References D.W., Poulsen Poulsen K.H., K.H., and and Kamo, Kamo, S.L., S.L., 1989, 1989, New insights insights into into Archean Archean Davis, D.W., Davis, crustal development development from from geochronology geochronology in in the the Rainy Rainy Lake Lake area, area, Superior Superior Province, Canada: Canada: Journal Journal of of Geology, Geology, v. v. 97, 97, p. p. 379-398. 379-398. Province, Sims, Sims, P.K., P.K., in in press, press, Great Great Lakes Lakes tectonic tectonic zone zone in in Marquette Marquette area, area, Michigan-Michigan-Implications Implications for for Archean Archean tectonics tectonics in in north-central north-centralUnited United States: States: U.S. U.S. Geological Geological Survey Survey Bulletin Bulletin 1904-E. 1904-E. 103 �______ ______ I I 9/ 88° I I 1 I I I I I U Geologic map map of of Precambrian Precambrian rocks, rocks, north-central north-central United United States States Geologic EXPLANATION EXPINAT ION I MIDDLE PROTEROZOIC PROTEROZOIC MIDDLE ',-'Â¥'Â¥ Rocks of of Midcontinent Midcontinent rift rift system system Rocks EARLY PROTEROZOIC PROTEROZOIC EARLY 1-1 [_J '1.L-L I Wisconsin magmatic magmatic terranes terranes (1,860-1,889 (1,860-1,889Ma) Ma) Wisconsin I ARCHEAN ARCH EAN Greenstone-granite terrane terrane (2,680-2,750 (2,680-2,750Ma) Ma) Creenstone-granite Gneiss terrane (2,600-3,600 Ma) Gneiss terrane (2,600-3,600 Ma) Direction oof tectonic tectonic transport transport Direction I I 104 1 I �I Geologic Geologic Significance Significance of of Linear Linear Features Features West-central Minnesota Visible on Landsat Images in West-central George W. Shurr, Ivan Ivan Watkins, Denise Victory, and Mary Tozer Department Department of of Earth Earth Sciences Sciences St. Cloud State State University University St. Cloud, Cloud, MN 56301-4498 56301-4498 The geologic significance of linear features visible on Landsat images can Observations of can be assessed assessed by integration integration with with several several data data sets. sets. Observations of linlinwest-central Minnesota are compared ear features features on four Landsat images in west-central with with aeromagnetic aeromagnetic maps and the the resulting resulting data data set set is is then then compared compared with: 1-published 1-published interpretations interpretations of of faults faults in in Precambrian Precambrian crystalline crystallinerocks, rocks, 2-concentration 2-concentration of of radon radon in in groundwater, groundwater, and and 3-water 3-water well well records. records. It It apappears that linear Landsat, in places correspond linear features features visible on Landsat, correspond with Precambrian crystalline rocks and and that these basement faults fault zones in Precambrian have influenced influenced fluid fluid movement movement and and Mesozoic Mesozoic weathering weathering patterns. patterns. Images Images employed in this study are standard EROS produces at scales scales of and 1:250,000 (paper) and were were provided provided by a 1:1,000,000 (film positives) and grant from Linear features from the the Minnesota Minnesota Geological Geological Survey. Survey. Linear features were mapped on on the multispectral scanner images in bands 2 and 4, compiled on an uncorrected mosaic, and compared 1). Individual Individual linear linear mosaic, compared with with aeromagnetic aeromagnetic maps maps (Fig. (Fig. 1). both bands are virtually virtually all parallel to linear aerofeatures observed on both magnetic magnetic anomalies. anomalies. These linear features are believed to be most signifisignificant and form the basis for the interpretation interpretation of lineament lineament zones zones which are corridors of linear-feature linear-feature concentration concentration separating separating large large areas with differdifferent linear-feature linear-feature orientation. orientation. Lineament zones zones correspond with Precambrian Precambrian convergent margins and with fault zones zones trending oblique to the margins However, it is the geologic (Shurr and Watkins, Watkins, in (Shurr in press). press). However, geologic significance significance of individual individual linear linear features features which which is is assessed assessed in in this this current current study. study. Precambrian crystalline Specific linear features and faults in Precambrian crystalline rocks rocks are shown shown in in Figure Figure 2. 2. In addition to linear linear features features shown shown in in Figure Figure 1, 1, some original data set (viz., bands 2 4) are some linear features from the original 2 or 4) included in in Figure Figure 22 where where they they parallel parallel aa fault. fault. Published Published faults faults or or fault fault zones 1-the Serpent Serpent zones which are are marked marked by by Landsat Landsat linear linear features features include: include: 1-the discontinuities (1-A Lake and Malma structural structural discontinuities (1-A and 1-B, 1-By respectively) (South(southwick and and others, others, 1988); 1988); 2-the 2-the Great Great Lakes Lakes Tectonic Tectonic Zone Zone (Sims (Sims and and others, others, 1980); 3-the 3-the Appleton Appleton geophysical 1980); geophysical lineament lineament (Southwick (~outhwickand and others, others, 1989); 1989); 4-a basement fault near Renville (4-A) others, 1989) and a 4-a (4-A)(Southwick (southwick and others, fault bounding bounding aa Precambrian Precambrian depositional depositional basin basin (4-B) (4-B) (Southwick (Southwick and and Mossler, Mossler, 1984); 5-two paired, parallel faults bounding Precambrian Precambrian basins (5-A 1984); 5-two (5-A and 5-B) (Southwick (Southwick and Mossler, 1984); 1984); and 6-faults 6-faults bounding the Nimrod outlier outlier 6-B, respectively) (Southwick and Long Prairie basin (6-A (6-A and 6-By (Southwick and others, others, 1988). These major fault zones zones correspond with lineament lineament zones zones and indiindi1988). vidual faults within the faults within the zones zones are are marked by specific specific linear linear features. features. or In southwest Minnesota, Minnesota, contour maps maps summarizing radon concentrations concentrations Landsat linear linear features. features. in groundwater show patterns patterns corresponding corresponding with with Landsat groundwater show (J, Fig. 2), 21, an an area area of of high high radon radon activity activity in in groundwater groundwater Jeffers (J, Near Jeffers (Southwick Precambrian (Southwick and Lively, 1984) lies along a fault zone mapped in Precambrian quartzite (Southwick (~outhwickand Mossler, 1984); the radon anomaly and fault zone zone Mossler, 1984); 105 �I Ii I are marked are marked by by aa Landsat Landsat linear linear feature. feature. Near Clarkfield (C, ( c , Fig. Fig. 2), 2), concontours tours of radon radon concentration concentration in in groundwater groundwater (Lively (Lively and and Southwick, Southwick,1981) 1981) generally parallel the northeast trend of a basement fault zone zone which has expression expression on on Landsat. Landsat. Near Benson, Benson, (B, (B, Fig. 2), 21, radon radon concentrations concentrations paralAppleton geophysical which has has clear clear definition definition on lel the Appleton geophysical lineainent lineament which on Landsat. Landsat. In In addition, addition, individual individual radon radon anomalies anomalies in in groundwater groundwater overlie overlie linear linear aeroaeromagnetic magnetic anomalies. anomalies. Radon anomalies anomalies in in soil soil gas gas data data have have recently recently been been rerelated to faults in crystalline crystalline rocks in the southeastern southeastern United States (Gates (Gates and Gunderson, 1989); 1989); these data may provide an analogy for the Minnesota groundwater groundwater anomalies. anomalies. In In any case, case, there there is is aa strong strong suggestion suggestion that that fluids fluids move along along faults faults in in bedrock bedrock which which are are marked marked by by Landsat Landsat linear linear features. features. In central Minnesota, geologic central Minnesota, geologic interpretations interpretations of of water water well well logs logs proprovide another another data data base base which which can can be be integrated integrated with with Landsat Landsat observations. observations. Near St. Cloud (Sc, (SC, Fig. Fig. 1) 1) individual individual linear linear features features mapped mapped at at 1:250,000, 1:250,000, generally parallel contours contours summarizing summarizing the elevation of the crystalline crystalline Linear features bedrock surface surface in in eastern eastern Stearns Stearns county. County. Linear features trending trending northnorthwest and east-west outline bedrock highs and follow the trend of bedrock east-west follow lows. Correlation of Cretaceous stratigraphic units shows that the bedrock lows. The lows have thick weathering weathering residuum residuum and and probably probably are are fault fault traces. traces. The individual linear linear features features are are all all components components of of aa northeast-trending northeast-trending linealineament zone zone which corresponds corresponds with an important fault fault zone zone in in central central Minnesota (Watkins (Watkins and and others, others, 1990). 1990). REFERENCES REFERENCES Gates, Gates, A.E., A.E., and Gunderson, Gunderson, L.C.S., L.C.S., 1989, 1989, Role of ductile ductile shearing shearing in in concenconcenGeology, v. 17, tration of radon radon in in the the Brookneal Brookneal zone, zone, Virginia: Virginia: Geology, 17, p. 391-394. p. 391-394. Lively, Lively, R.S., R.S., and Southwick, Southwick, D.L., D.L., 1981, 1981, Radon Radon activity activity in in groundwaters groundwaters of of Minnesota Geological Geological Survey seven test seven test areas areas in in Minnesota: Minnesota: Minnesota Survey Report of of Investigations 25, 25, 60 60 p. p. Investigations Shurr, G.W., G.W., and Watkins, Watkins, I., in press, Basement blocks, tectonics, tectonics, and fluid Shurr, It Proceedings, through the movement --seeping" through the sedimentary sedimentary cover: cover: Proceedings, --- "seeping" movement Seventh thematic conference Seventh conference on on remote remote sensing sensing for for exploration exploration geology. geology. Sims, P.K., P.K., Card, K.D., K.D., Morey, G.B., G.B., and Peterman, Peterman, Z.E., Z.E., 1980, 1980, The Great Sims, Lakes Lakes tectonic tectonic zone zone -- aa major major crustal crustal structure structure in in central centralNorth NorthAxnerAmerGeological Society ica: ica: Geological Society of of America America Bulletin, Bulletin, Part Part I, I, v. v. 91, 91, p. p. 690-698. 690-698. Southwick, D.L., and Southwick, and Lively, Lively, R.S., R.S., 1984, 1984,Hydrogeochetnical Hydrogeochemical anomalies anomalies associassociated with the basal contact of the Sioux Quartzite along the north margin of in Southwick, Southwick, D.L., D.L., ed., Shorter Shorter of the the Cottonwood County basin, basin, 2 contributions contributions to to the the geology geology of of the the Sioux Sioux Quartzite Quartzite (Early (~arlyProterozoic) Proterozoic) southwestern southwestern Minnesota: Minnesota: Minnesota Geological Geological Survey Survey Report of of InvestiInvestigations gations 32, 32, p. p. 45-58. 45-58. Southwick, D.L., Morey, G.B., G.B., and McSwiggen, McSwiggen, P.L., 1988, Southwick, D.L., 1988, Geological map of the Penokean Penokean Orogen, Orogen, central and eastern Minnesota Minnesota and accompanying Minnesota Geological text: text: Minnesota Geological Survey Survey Report Report of of Investigations Investigations 37, 37, 25 25 p. p. Southwick, D.L., and Mossier, Mossier, J.H., J.H., 1984, Southwick, D.L., 1984, The Sioux Quartzite and subjacent subjacent regolith regolith in in the the Cottonwood Cottonwood County County basin, basin, Minnesota, Minnesota, in in Southwick, Southwick, D.L., D.L., ed., Shorter Shorter contributions to the geology of the Sioux Quartzite (Early (Early Proterozoic) Proterozoic) southwestern southwestern Minnesota: Minnesota: Minnesota Minnesota Geological Geological Survey Survey Report Report of Investigations Investigations 32, 32, p. p. 17-44. 17-44. 106 �Southwick, D.L., Schaapy Schaap, B B., Chandler, V.WSy V.W., l98gy 1989, Multiple Multiple Archean Southwicky D.L.y e yand Chandlery terranes in Minnesota -- the the old gray gneiss gneiss she she ain't ain't what what in southwest southwest Minnesota she she used used to to be: be: Institute on Lake Superior Superior Geology Geology Proceedings, Proceedings, v. v. 96. 35y 35, p. 96. Watkins, I., Shurr, G.W.y C.W., and Anderson, G.G., 199OY 1990, Faults associated with Watkinsy I.> Shurry the Penokean Penokean accretion accretion of of allocthanous allocthanous terranes terranes in in central central Minnesota: Minnesota: Institute Institute on Lake Lake Superior Superior Geology Geology Proceedings, Proceedingsy v. v. 36. 36. FIGURES FIGURES Precambrian faults faults /Precambrian Bands 2 & 4; Uneament Zone Boundary wIthgwphyskal geophysical expmsslon expression ,Eands Bands 22&&44with Bands 2 &4 ,Bands 22 or 4 ,Bands , ' 2 Figure 2 Figure Figure Figure 11 Linear features Linear features visible visible on on Landsat Landsat and 4 images in bands 2 & 4 and are are parallel to to aeromagnetic aeromagnetic patterns patterns west-central Minnesota (Shurr in west-central (Shurr and Watkins, Watkinsy in in press). press). Correspondence Correspondence of of specific specific Landsat Landsat linear features features with published published structural features structural features in in the the PrecamPrecamwest-central Minnesota brian of west-central (Shurr Watkins, in in press). press). (Shurr and Watkinsy Letters refer Letters refer to to localities localities disdiscussed cussed in in the the text. text. 107 �I BIOTURBATION IN I N THE JACOBSVILLE SANDSTONE, LINDEN LOCATION LOCATION — SANDSTONE, LAKE LINDEN WHAT W HAT ARE THE IMPLICATIONS? IMPLICATIONS? Marian M. M. Smith, Smith, Department of o f Geological Engineering, Engineering, Geology and and Geophysics, Geophysics, Marian Michigan Technological Technological University, U n i v e r s i t y , Houghton, Houghton, M MII 49931 49931 B i o t u r b a t i o n may have been overlooked in i n tthe h e JJacobsville a c o b s v i l l e sandstone and Bioturbation t h e world world due due to t o the t h e size s i z e of o f the t h e traces. traces. The The indeed many sandstone around the ichnofauna reported in observed oonly microscopic ichnofauna i n tthis h i s research can be observed n l y aatt tthe h e microscopic injected llevel. e v e l . Petrographic examination o h i n sections made from sandstone injected off tthin with porosity permeability differing w i t h blue dyed epoxy revealed patterns p a t t e r n s in in p o r o s i t y and p ermeability d iffering within somewhat w i t h i n aa few few centimeters. centimeters. Closer examination revealed various patches in i n the t h e thin t h i n section s e c t i o n where where aa pattern p a t t e r n of o f several several grains grains (approximately) (approximately) mm across would be interrupted 1 mtn i n t e r r u p t e d by by aa zone zone of o f mixed mixed grains grains varying varying in i n diameter diameter from mm to mm. t o 11 mm. These mixed grains do n o t appear tto o be from n a t u r a l grain graiq from . I1 mm not natural s t a i n (possibly (possibly hematite). hematite). IIn n some some s e t t l i n g and they are are often o f t e n coated coated with w i t h aa stain settling t h i n sections actual actual paths can be traced ffor o r approximately 1.5 1.5 c m before it it thin cm becomes becomes diffuse. d i f f u s e . In I n other instances instances the t h e areas of o f mixed mixed small small and and large l a r g e grains grains (with ( w i t h dark coatings) coatings) may cover an an area area approximately approximately 1I cm2. cm2. The thin t h i section ~ sectjon these ttracings an angle angle such such tthat arcuate patches patches ((less seems tto o aalso l s o ccut u t these r a c i n g s aatt an h a t arcuate less than 1mm measurements, speculations could 3mm across) across) appear. appear. From these initial i n i t l a 1 measurements, be made tthat approximately I mm h a t an annelid type burrower tthat h a t was approximately mm wide was was resembling glauconite is i s also a l s o found in i n these responsible. A greenish mineral resembling thin with in t h i n sections along w i t h an apparent sedimentary rock fragments (1 ( 1 mm in length) tthat closely length) hat c l o s e l y resembles resembles recent recent annelid annelid fecal f e c a l pellets. pellets. observations can be substantiated substantiated many many o off tthe IIff these initial i n i t i a l observations h e ttheories heories off the of tthe off Michigan w will i l l be o t h e paleogeography paleogeography and ttectonics e c t o n i c s OF h e Upper Peninsula o open for f o r reinterpretation. r e i n t e r p r e t a t i o n . The sands most often o f t e n interpreted i n t e r p r e t e d as as fluvial, fluvial, coming off o f f of o f alluvial a l l u v i a l fans fans would would change. change. IIff these are indeed indeed ichnofauna ichnofauna and and tthe h e greenish mineral is i s glauconite, glauconite, these sands wwill i l l have tto o be interpreted i n t e r o r e t e d as marine or o r at a t least l e a s t nearshore nearshore continental continental shelf. s h e l f . Cross bedded bedded units m i t s would would iindicate n d i c a t e tthe h e latter l a t t e r to t o be be more more likely. likely. o f the t h e ichnofauna ichnofauna raises r a i s e s many questions as to to The postulated presence of tthe h e age o m o n l y referred off these sediments which are most ccommonly r e f e r r e d tto o as pre put orr has tthe Cambrian. Does tthis his p u t tthis h i s unit u n i t into i n t o tthe h e Cambrian o h e Edicara fauna off tthe i n the t h e Proterozoic Proterozoic been been found? found? o h e "Lost Age" Age" in 1 108 �U I I TECTONIC RAMIFICATIONS LAKE SUPERIOR SEISMIC DATA TECTONIC W I F I C A T I O N S OF OF ONI/AB.GONNE GNI/ARGONNE LAXE DATA Michael E. 0eoiogy, Northern Illinois Michael E, Thompson, Thompson, flepartment Depertment of Geology, Il~inols University, De Univer~icy, De Kaib, Kalb, IL I L 60115 60115 C. P Patrick C. a t r h k Ervth, Ervin, Department Department of of Geology, Geology, Northern Northern Illinois Illinoia University, Unlveraity, De Kalb, IL, IL 60115 Dc Kaib, 60115 M.(. Mudrey, Wisconsin C M.G. Mudrey, Jr.., J r - , Wisconsin e o l o g h a l and and Natural. Nakural Himtory 3817 Geological Uistory Survey, 3817 Polnt Road, Road, MadLson, Madison, WI 53705 53705 Mineral Point B.A. Brown1 Brown, Wisconsin W i a c o n s h Geological and and Natural Natural History History survey, Sumey, 3817 3817 Mineral Point Road, Madison, JI 53705 Mlneral WI 53705 ABSTRACT ABSTRACT gravity anomaly anomaly maps have have been been prepared prepared for for the the Detailed bouguer gravity Superior and Northwest Superhr Northwest Wisconsin Wisconsin map map areas. areas. Data collected collected in in previous years were augmented augmented with with additional additional data &ta collected collected during during 1989. 1989. Strong gravity gradients gradient8 define the posittan position of major major Keweenawan Keweenawan !the deep deep gravity gravity low low over over the the Bayfield Bayfield Peninsula Penineula abuts abuts aa faults. The faults. Btrong po~itfve strong positive gravity feature to the southwest 1n in Bayfield Bayfield County County and and define aa major m a j o r Keweenawan Keweenawan cross croaa fault fault or or adjustment adjustment feature. feature. may define moderate gravity The moderate gravity low low in i n southern southern Iron Iron County County corresponds corresponds to to the Archean Arehean Puritan Puritan batholith batholith and and helps helps to t o define define relations relations to to Proterozoic Proterozoic metavolcanic and and metasedimantary metasedimentary rock rock to to the the south. south. !Shie mpported by the U . S , Geological Sumey, This work wag was supported U.S. Survey, COGEOMAP COCEOMAP progam. progkam. 109 �_______________________ I n ggeochronology e o c h r o n o l o g y of o f the t h e Michipicoten M i c h i p i c o t e n greenstone g r e e n s t o n e belt. belt. Advances iin II A . Turek, T u r e k , Department D e p a r t m e n t of o f Geology, G e o l o g y , University U n i v e r s i t y of o f Windsor, W i n d s o r , Windsor, Windsor, A. Ontario. O ntario. N9B 3P4 3P4 R.P. Sage, S a g e I Ontario O n t a r i o Geological G e o l o g i c a l Survey, S u r v e y I 918-77 918-77 Grenville G r e n v i l l e Street, Street, R.P. Toronto, T o r o n t o , Ont. Ont. lB3 M5S 1B3 W.R. W . R . Van Schmus, Schmus, Department D e p a r t m e n t of o f Geology, G e o l o g y , University U n i v e r s i t y of o f Kansas, Kansas, Lawrence, KS 66045 Lawrence, KS 66045 New N e w U—Pb U-Pb zircon z i r c o n ages a g e s for f o r the t h e Wawa area a r e a enlarge e n l a r g e the t h e existing e x i s t i n g data d a t a base b a s e of of i s now well well aages g e s for f o r this t h i s belt. belt. e x i s t e n c e of o f four f o u r volcanic v o l c a n i c cycles c y c l e s is The existence documented. a s s o c i a t i o n of o f volcanism v o l c a n i s m and a n d plutoriism p l u t o n i s m continues c o n t i n u e s to t o be be The association There cconfirmed. onfirmed. T h e r e is i s no difference, d i f f e r e n c e , in i n terms t e r m s of o f ages, a g e s , between b e t w e e n the t h e internal internal and a n d external e x t e r n a l plutons. plutons. The internal internal b e i n g those t h o s e that t h a t are a r e within w i t h i n the the being while the ssupracrustal u p r a c r u s t a l rrocks ocks w h i l e eexternal x t e r n a l aare r e tthose h o s e ssurrounding u r r o u n d i n g aand n d embaying the greenstone g r e e n s t o n e belt. belt. Michipicoten belt was formed by The M ichipicoten b e l t was formed b y several s e v e r a l volcanic v o l c a n i c cycles c y c l e s and a n d plutonic plutonic over of be divided i m e I that t h a t ccan an b e d i v i d e d into i n t o six s i x events events eevents vents o v e r aa pprotracted r o t r a c t e d pperiod eriod o f ttime, The oldest as shown in i n the t h e tabulation t a b u l a t i o n below. below. o l d e s t event e v e n t is i s dated d a t e d by a granite, g r a n i t e , aa porphyry, next of volcanism p o r p h y r y I and a n d aa volcanic v o l c a n i c at a t ca. c a . 2888 2888 Ma. Ma. The n e x t cycle cycle o f v o l c a n i s m and and associated Alden volcanic has a s s o c i a t e d plutonism p l u t o n i s m was was at a t ca. c a . 2743 2 7 4 3 Ma. Ma. The A lden v o l c a n i c tuff tuff h a s been been Ma dated Ma, tthe 2747 ± 1 5 Ma, h e JJubille u b i l l e ffelsic e l s i c vvolcanic o l c a n i c aatt 2747 ? 11 11 M a and a n d the the d a t e d aatt 2746 f± 15 The Goodreau volcanic JJubille u b i l l e porphyry p o r p h y r y at a t 2742 2742 ±? 6 Ma. v o l c a n i c center c e n t e r yields y i e l d s an a n age age Ma. aand belongs of nd b e l o n g s either e i t h e r here h e r e or o r in i n Event E v e n t III I11 at a t ca. c a . 2717 2717 Ma. Ma. o f 2729 ±? 3 Ma. Event has well by vvolcanic plutonic E v e n t IIV V h a s bbeen een w e l l ddefined e f i n e d by o l c a n i c aand nd p l u t o n i c rrocks o c k s aatt ca. c a . 2696 Na. Ma. The age a t 2701 2 7 0 1 ± 8 Ma Ma can c a n be b e assigned a s s i g n e d to to a g e obtained o b t a i n e d for f o r the t h e McCormic Lake tuff t u f f at 13 Ma New tthis h i s event. N e w ages a g e s that t h a t fit f i t into i n t o Event E v e n t VV are: a r e : 2686 2686 ± 1 3 M a for f o r the the event. Dubreuilville at D u b r e u i l v i l l e external e x t e r n a l granite, g r a n i t e , the t h e internal i n t e r n a l granite g r a n i t e at a t Dickenson D i c k e n s o n Lake Lake, at The youngest Ma. aand 2673 ±? 88 Ma. n d the t h e Lund Lake granitic g r a n i t i c stock s t o c k at a t 2663 2663 ±5 6 Ma. Ma. youngest event Ma pertain e v e n t aatt 2615 M i s thought t h o u g h t to to p e r t a i n to t o a tectonic t e c t o n i c event e v e n t in i n the t h e region. region. a is * * The new ages a g e s reported r e p o r t e d here h e r e conform c o n f o r m to t o the t h e established e s t a b l i s h e d pattern p a t t e r n of o f ages a g e s in in Also, they are in good agreement with ages for other nearby the t h e area. area. Also, t h e y are i n agreement w i t h a g e s f o r o t h e r nearby with of which greenstone g r e e n s t o n e bbelts, i t h tthe xception o t h e 2888 Ma Ma event h i c h has n o t been elts, w h e eexception f the event w h a s not been It appears that the Michipicoten belt evolved in identified in them. i d e n t i f i e d i n them. It a p p e a r s t h a t t h e Michipicoten b e l t evolved i n Moreover, ca. Ma. Moreover, it i t seems that t h a t volcanism, v o l c a n i s m , much of of the t h e associated associated c a . 220 220 Ma. sedimentation, s e d i m e n t a t i o n , aand l u t o n i s m I is i s essentially e s s e n t i a l l y synchronous, s y n c h r o n o u s , or o r coeval c o e v a l in i n the the n d pplutonism, Obviously g r e e n s t o n e belt, b e l t I rather r a t h e r than t h a n sequential. sequential. O bviously a eevolution v o l u t i o n of o f a greenstone It ccogenetic o g e n e t i c relation r e l a t i o n between b e t w e e n volcanics v o l c a n i c s and a n d plutonics p l u t o n i c s is i s likely. likely. I t is i s also also granitoid cclear l e a r tthat xternal g r a n i t o i d terraines o f batholithic d i m e n s i o n s formed h a t tthe h e eexternal t e r r a i n e s of b a t h o l i t h i c dimensions formed by m multiple by u l t i p l e intrusions i n t r u s i o n s over o v e r ca. c a . 220 220 Ma. Ma. 110 I �I Z i r c o n Ages Agcs ffor o r the ilic Michipicoten M i c h i p i c o t c n greenstone g r c e n s t o n e belt belt Zircon (Wawa, (Wawa, Gamitagama, Gamitagama, Michibishu). Michibishu). I EVENT EVENT (Ma) (Ma) 2615 VI Ca. V 2668 Ca. EXTERNAL EXTERNAL INTERNAL INTERNAL PLUTONS PLUTONS PLUTONS PLUTONS VOLCAJICS VOLCA!$ICS 2615 2662 2662 2671 2663 2673 2668 2675 2668 2686 2673 2677 2685 IV Iv 2702 2693 ca. ca. 2696 2696 2696 2694 2698 2696 2691 2698 2701 2698 - I11 ca ca III 2717 2717 II II Ca. ca. 2721 2721 2722 2722 2713 2713 2747 2747 2737 2737 2729 2729 2742 2742 2744 2744 2745 2 74 5 2746 2746 2743 2743 2747 2747 ca. I Ca. 2888 2889 2881 2888 Note: Note: - Ages A g e s in i n above a b o v e tabulation t a b u l a t i o n are a r e as a s reported r e p o r t e d here h e r e plus p l u s as a s reported r e p o r t e d and and Compiled c o m p i l e d by: by: Turek T u r e k A., A . , Keller K e l l e r R., R . , Van Van Schmus Schmus W.R., W.R., (1990). ( 1 9 9 0 ) . The T h e age a g e of o f volcanism volcanism and Mishibishu a n d plutonisrn p l u t o n i s m iin n tthe he M i s h i b i s h u ggreenstone r e e n s t o n e belt b e l t near n e a r Wawa, Wawa, Canadian ( i n press). press). Ontario. C a n a d i a n Journal J o u r n a l of o f Earth E a r t h Sciences S c i e n c e s 27, 2 7 , 5 (in Ontario. 111 �I THEGEOLOGYOFTHEGREENWOODLAKEAREA THE GEOLOGY OF THE GREENWOOD LAKE AREA DULUTH COMPLEX, LAKECOUNTY, COUNTY, NORTHEASTERN NORTHEASTERN MINNESOTA MINNESOTA DULUTH COMPLEX, LAKE Edward Edward A. A. Venzke Venzke Department of of Geology, Geology,University University of of Minnesota MinnesotaDuluth Duluth Department Duluth, Duluth, Minnesota Minnesota 55812 558 12 The The dominant dominant feature featurein in the theGreenwood Greenwood Lake Lake area area isis the the Greenwood GreenwoodLake Lake (or (or"Snake") "Snake") Anomaly. Anomaly. This Thispositive positivemagnetic magneticanomaly anomalywithin within the the troctolitic troctolitic series series of of the the southern southernDuluth Duluth Complex was was previously previously described described by by Vadis Vadis and and others others (1981). (1981).Geologic Geologicmapping mappingatat1:24,00() 1:24,000 Complex scale scale during during the the summer summer of 1989 1989 of four four 7.5' 7.5' quadrangles quadrangles (Greenwood (Greenwood Lake Lake West, West,Greenwood Greenwood Lake Lake East, East, Mt. Mt. Weber, Weber, and andWhyte) Whyte)located locatedpreviously previouslyknown known outcrops outcrops (Bonnichsen, (Bonnichsen, 1971) 1971)as as well and geochemical geochemical analyses. analyses. The well as as new new outcrops, outcrops, all all which which were were sampled sampled for petrography and The area area mapped mapped encompasses encompasses rocks rocks of the the anorthositic anorthositic and and troctolitic series, series, granophyric granophyric granite, granite,and and basalts and sediments of the North Shore Volcanic Group. A geologic map has been constructed basalts and sediments Group. A geologic map has been constructed (Figure (Figure 1) 1) based based on onoutcrop outcropmapping mappingand andaeromagnetic aeromagneticquadrangle quadrangle maps. maps. Aeromagnetic Aeromagneticmaps maps were were used used to to delineate delineate units units using using magnetic magnetic trends trends in in areas areaswith withpoor poortotononexistent nonexistentoutcrop outcrop coverage. coverage. The Theinfluence influenceof ofbedrock bedrockon ontopography topography was was also also taken taken into intoaccount. account. The The oldest oldestrocks rocksare arethe theanorthosites, anorthosites,gabbroic gabbroicanorthosites, anorthosites,and andtroctolitic troctoliticanorthosites anorthosites of Toimidrumlin drumlinfield fieldhas has of the the anorthositic anorthositic series. series. One OneNE-SW NE-SWtrending trendinghill hillon on the theedge edgeof ofthe theToimi extensive anorthositic gabbro. gabbro. A extensive outcrops of gabbroic anorthosite and anorthositic A few few isolated isolatedoutcrops outcropsof of troctolitic troctolitic anorthosite anorthositewith with aa distinctive distinctivespotted spotted appearance appearance caused caused by by poikilitic poikilitic olivines olivinesare arealso also present. present. These Theseisolated isolatedoutcrops outcropsmay maybe belarge largexenoliths xenolithsfrom fromaaprevious previousanorthositic anorthositicintrusion intrusion at at depth. depth. Another Anothersmaller smalleranorthositic anorthositicbody body contains contains1.5 1.5 -- 22 cm cm clots clots of of magnetite. magnetite. Intrusive with the the troctolitic troctolitic series. series. Numerous Intrusive into into the anorthosites anorthosites are rocks associated with Numerous outcrops of labradorite-augite-olivine cumulate ferrogabbro (> 10% oxides) were found alongthe the outcrops of labradorite-augite-olivinecumulate ferrogabbro (> 10% oxides) were foundalong shores shores of of Greenwood Greenwood Lake Lake and and along along NE-SW trending ridges to the northwest. The Theferrogabbros ferrogabbros are are all all magnetic magnetic totovarying varyingdegrees, degrees,and andgenerally generallyhave haveweak weaktotostrong strongigneous igneouslamination lamination Petrographic evidence indicates that magnetite was an early phase (foliation). Petrographic evidence indicates that magnetite was an early phase in the the (foliation). crytallization euhedralgrains grainsofoftitaniferous titaniferousmagnetite magnetite are arecommon common as as crystallizationsequence. sequence.Subhedral Subhedraltotoeuhedral inclusions inclusions in olivine, olivine, augite, augite, and andoccasionally occasionally ininplagioclase. plagioclase. Olivine Olivine is is often often seen seenrimming rimming magnetite. The The early early appearance appearance of of oxides oxides indicates indicates that that the the magma magma was was slightly slightlyenriched enriched in in magnetite. oxygen. oxygen. None None of of the the outcrops outcrops identified identified are are believed believed to represent the lithology of the Greenwood Lake Lake Anomaly Anomaly itself, which which can be be seen seen on ontopographic topographic maps maps to to be becompletely completelycovered covered by by swampy terrain Lake. The terrain and Greenwood Greenwood Lake. The only only direct direct evidence evidence of of the the rocks rockscomposing composingthe the anomaly are from two drill holes holes that that intersect intersect the the anomaly. anomaly. DDH S-1 S-i (Vadis (Vadis and and others, others, 1981) 1981) only penetrated 30 30 feet feet into intobedrock bedrock and andintersected intersectedfoliated foliatedoxide oxideand andolivine-bearing olivine-bearinggabbros, gabbros, only a thin thin band band of of oxide oxide augite augite troctolite, troctolite, and two layers layers (6.5' and and 3.3' thick) thick) of of feldspathic feldspathic oxide oxide peridotite. DDH DDHMN MN27015 27015(USX (USXCorporation) Corporation)at at the the south south end end of of Greenwood Greenwood Lake Lake intersected intersected 56' 56' of offoliated, foliated,moderately moderatelymagnetic magnetic anorthositic anorthositic ferrogabbro, ferrogabbro, a 4' 4' band bandofofstrongly stronglymagnetic magnetic oxide troctolite, 405' of offoliated foliatedanorthositic anorthositicferrogabbro ferrogabbro before before grading grading into into troctolite, and then then another another 405' 90' 90' of offerrogabbro ferrogabbrowith withvariable variablefoliation, foliation,finally finallyending endingininoxide-bearing oxide-bearinganorthositic anorthositicgabbros. gabbros. In general, general, the the anomaly anomaly appears appears to to be be composed composed of of layers layers of of aavariety varietyof ofolivine olivineand andoxide-rich oxide-rich troctolitic troctolitic cumulates. cumulates. The Therelationship relationshipbetween between the the exposed exposed foliated foliated ferrogabbro ferrogabbroand and the the adjacent adjacent 112 H 1 �I rocks of the the Greenwood Greenwood Lake Anomaly is not clear. The Theferrogabbros ferrogabbros are are probably probably part of of the the same intrusive body body as the the more more mafic, mafic, magnetic, magnetic, and and strongly strongly foliated foliated troctolitic troctolitic rocks that compose compose anomaly. anomaly. Two large large bodies bodies of of granophyric granophyric granite granite are are intrusive intrusive to to both both anorthositic anorthositic and and troctolitic troctolitic rocks rocks along along the eastern margin of the Greenwood Greenwood Lake Anomaly. In Incontrast contrasttotothe thegabbros, gabbros,the the granophyre granophyre is relatively resistant and forms large hills and ridges, the the best-known best-known example of which which is Mt. Weber. Weber. Felsic Felsicveins veinswere were observed observed in in gabbros gabbros on Greenwood Greenwood Lake, and a large granophyre dike cuts the magnetic basalt to the east. The Thegranophyre granophyre isis bordered bordered to to the theeast eastby by granophyre magnetic magnetic basalts and at at least leastone onesmall smallbasin basincontaining containingaamagnetic, magnetic,bedded, bedded,quartz-bearing quartz-bearing volcanic sandstone. The Thebasalts basaltsadjacent adjacenttotothe thegranophyre granophyreare areall allmassive, massive,but butbasalts basaltsfurther further volcanic south are amygdaloidal arnygdaloidal at at some some locations. locations. south and and away away from from the the felsic felsicintrusions intrusions are Preliminary geochemical geochemical interpretations interpretations and determination determination of oxide oxidecompositions compositionshas has Preliminary begun. begun. The Theresults resultsof ofthis thiswork workwill willalso alsobe bepresented, presented,with with an an evaluation evaluation of of potential potential Platinum Platinum Group Group Element Element mineralization. mineralization. This This project project has has been been funded funded by by the the Minnesota Minnesota Mineral Mineral Diversification Fund, and by the the Mineral Mineral Resources Resources Research Research Center. Center. References References Cited Cited Bonnichsen, B., 1971, Bonnichsen, B., 1971, Outcrop Outcrop map of of southern southern part part ofofDuluth DuluthComplex Complexand andassociated associated Keweenawan rocks, St. Louis Keweenawan rocks, Louis and and Lake Lake Counties, Counties, Minnesota: Minnesota: Minnesota Minnesota Geological Geological Survey Survey Miscellaneous Miscellaneous Map Map Series SeriesM-11, M-1 1,scale scale1:125,000. 1:125,000. Vadis, Vadis, M. M. K., K., Gladen, Gladen, L. L. W., W.,and andMeineke, Meineke,D.D.G., G.,1981, 1981,Geological, Geological,geophysical geophysical and and geochemical surveys of of Lake, Lake, St. Louis and geochemical surveys and Cook Cook counties, counties, Minnesota Minnesota for the the 1980 1980 drilling project: drilling project: Hibbing, Hibbing, Minnesota, Minnesota, Minnesota Minnesota Department Department of Natural Natural Resources, Resources, Division Division of of Minerals, Minerals,Report Report201, 201,13 13p.p. 113 �—I II ______ r) N N or'0—40 + + ::: :: : + + Grenvoc,d Lcke fJODODfl0( DO00ODoo 00 000 0 000 00 jon o 000000000 DO 00 0 00 0 00 00001 0030000000000W 000000000 DODD 0 DODD EDDDOO0LOOOD0OD 0000001 DO 0000 I 000000' 000000 000000 0-0-0- D-0 * HiHH Il\0oDDDoooooo HI ,P?0O00EOD0DODD0OO 111111 N 1+ * + * 4 4- * * 4- + * 4- * -t * * * fl Whyte 0 00 0 00000 L0 0 0000 0 00 0 00 0 0 0 0 0 000 0 00 0000 0 00 000000poooooo 0000000000000000 * 4- 4 * * + + * * * * * * * 4 *1*, * * * * 4 * -f * * * * * * * * 4-**-*+ * **+ • *4 * * * *_* + * * + * — * * *** * * * -* — * - - * * - 0 DOD 4- NjJriI+,'DODCDDQ 0000000000 0000000 000000 000000 000000 0000000 000_00 0300000 *DOG0D0O000DOOOO0OO =—'DIQO00 00 0 4- * * * *4-4-*+* 4- +*•+*** + LO 0 0 0 0 0 0 0 0 0 0 0 0 0 0 [ 0 0 0 C 0 0 0 0 0 00 0 0 0 00 000000000000000000000000 0 U0 0-0 Oil 30-D jDOODOODCODOG 4- 0 0 0-D-0- 0 0 0 0 000 0000 000i0000 0000 '000000000000000 0000 000000000 D DDO00o0o00JC00ooDoOOD0 L0000000000DOD 00000000000000 100 OO00ODODODD00O00O0ODODO00DOO P E00D 0000000000000000_000000000000 0 GP00000000000U000000000000 0000000000 0000000000000 DDDDooDoo IflOD000UD0DJD0DD Jill II IOOD0ODOOOOCOOOI ii iH Hi fl In iii 0DDDOO0COOD00DQ foo4fl( IJkDDO0DDO0OOODOpD iii Hill iji jI Jj\DOODOODDO0DD0D0 ih0DDODO0O00ooooo ii l1h0oDDooooooocoo OCODODDOO0OD lii ii III DODD [130000000000000] O0DO*DOOI 00000000A ODD0o11TTTll C0D0D H111 OOOoI onDoflt Dog liii liii 1S+M +D1 PooMf4a4i C (1J N +4 4- —to >- 0 0- o2, •444 -0 -&i 0 -t - 0 0 0 i 4-, C 4, 40 '4 2 -0 5 . 2 0 Q (4 2 (4- *2 2 (4 - (_:4 4, 2° oE 0 0(4 01 0= mll 1D :1 4- Ii C. 4-- —'S— I-. — _i i I — — — — — — — — — — — — — — — — CO N '0 04 �I I THE MINERAL RELIEF OF SURFACES PRODUCED BY SANDING SANDING WITH QUmTZ QUARTZ THE MINERAL SURFACES PRODUCED PERCUSSION, THERMAL PERCUSSION, THERMAL DISAGGREGATION, DISAGGREGATIONy AND AND WEATHERING WEATHERING by Denise Denise Victory Victory and and Ivan Ivan Watkins Watkins We We have have hypothesized hypothesized that that the the processes which archaeological archaeological stonestonemasons used when working stone stone left surfaces surfaces that could be used to idenprocess used by those Because the minerals in tify the process those stonemasons. stonemasons. Because in a a rock properties such hardness, coefficient rock have different different properties such as cleavage, cleavagey hardness, coefficient thermal expansivity, expansivity, coefficient coefficient of thermal conductivity, absorption absorption of thermal coefficients for coefficients for radiant radiant energy energy (color), (color), and and reactivity reactivity with with water water conconoxygen and taining oxygen and hydrogen hydrogen ion ion we we were were able able to to devise devise several several observaobservational tests that could be be used used to to classify the the stonemasons method method of of tional surface production. hypothesis on a sample Reformatory tested our hypothesis sample of Reformatory surface production. We tested Grey Grey granite granite supplied supplied to to us us by by Cold Cold Spring Spring Granite Granite Company. Company. We produced surfaces by the methods that archaeologists have have suggested for Peruvian Peruvian surfaces 1 the relative relative mineral relief we we observed for each stone works. stone works. In In Table Table 1 surface with the surface is is tabulated tabulated with the process process used used to to produce produce the the surface. surface. The that, if archaeologist The logical logical conclusions from from the table are that, if an archaeologist relief of a surface, archaeolwere educated educated to to look look for for the the mineral relief surface, that archaeolwould be able to determine the process process the ancient stonemasons stonemasons used used ogist would which are to produce the the artifacts artifacts which are found found today. today. There There are are no no processes processes distinguished from all of the we used on on the the grey grey granite granite that that can can not be distinguished from all other processes. other processes. Of course course it it is possible to hypothesize two or more proHowever, if cesses being used by the the stonemasons stonemasons to to produce produce the the surface. surface. However, if hammering or quartz are combined, result is or wedging and sanding sanding with quartz combined, the result same as just with quartz. the same just sanding sanding with quartz. 115 �— L I — .1 I ———————————————— Table Table 11 RELIEF SURFACE SURFACE MINERAL MINEFKG RELIEF PROCESS PROCESS quartz quartz quartz quartz mica mica mica mica vs vs vs vs vs vs vs vs vs vs biotite biotite HAIvIMERING HAMMERING OR hornblende hornblende feldspar feldspar hornblende feldspar feldspar feldspar feldspar vs vs hornblende hornblende There was was no no pattern. p a t t e r n . Any Any mineral mineral could could stand stand above above any any other. o t h e r . The The There cleavage surfaces s u r f a c e s of of all a l l minerals minerals in i n the t h e rock rock were were observed. observed. cleavage WEDGING WEDGING quartz above biotite biotite quartz quartz above hornblende hornblende quartz above feldspar feldspar hornblende above above mica feldspar feldspar above above biotite biotite NO PATTERN PATTERN OBSERVED OBSERVED DISAGREGATION GATION biotite biotite above above quartz hornblende hornblende above above quartz quartz feldspar feldspar above above quartz quartz NO PATTERN PATmN OBSERVED OBSERVED biotite biotite above above feldspar feldspar hornblende above above feldspar feldspar WEATHERING WEATHERING OR ACID SOLUTION SOLUTION quartz above above biotite biotite quartz quartz above above hornblende hornblende quartz quartz above above feldspar feldspar hornblende hornblende above above biotite biotite feldspar feldspar above above biotite biotite feldspar feldspar above above hornblende SANDING SANDING WITH WITH QUARTZ QUARTZ THEmNL THERMAL AWAY!!! THE BIOTITE BIOTITE HAS BEEN BEEN WEATHERED WEATHEREJI AWAY !!! THE �I FAULTS ASSOCIATED WITH FAULTS WITH THE THE PENOKEAN PENOKEAN ACCRETION OF ALLOCTHANOUS ALLOCTHANOUS TERRANES TERRANES IN IN CENTRAL CENTRAL MINNESOTA by by Watkins, George W. Shurr, Ivan Watkinsy Shurry and Carry Garry G. G. Anderson Anderson Department of Department of Earth Earth Sciences Sciences St. Cloud State State University University Cloud, MN 56301-4498 St. Cloud, 56301-4498 The theory of continental allocthanous terranes continental growth by docking of allocthanous has now now been been accepted accepted by by most most geologists. geologists. Plate Plate tectonic tectonic interpretations interpretations for the Penokean Penokean orogen orogen in in the the Lake Lake Superior Superior region region have have slowly slowly been been emergemerging in the literature (Laruey 1983; 1983; LaBerge LaBerge and and Myers, Myers, literature over over the the past past decade decade (Larue, 1984; Minnesota recent 1984; Barovich Barovich and and others, othersy 1988). 1988). In In central Minnesota recent reinterpretareinterpretaSouth( ~ o l s t1984; 1984; ~ Southtions have recognized the the orogen orogen as as aa convergent convergent margin margin (Holst, convergence is wick and and others, othersy 1988; 1988; Holm Holm and and Selverstone, Selverstone, 1990). 1990). Since convergence is rarely perpendicular to to the the continental continental margin, marginy accretion accretion occurs occurs in in aa transtransmargin is reflected in the faults pressive regime and the geometry of the margin are produced. produced. The The northeast northeast trend, trend, parallel parallel to to the the continental continental margin, margin, that are will be primarily low low angle angle faults faults with dominant dominant dip-slip dip-slip and some some strikestrikeslip displacement. margin, i.e. northwesty northwest, should slip displacement. Faults Faults perpendicular to to margin, should be primarily subvertical subvertical with dominant strike-slip strike-slip and some some dip-slip dip-slip displacement. The relative placement. relative importance importance of each fault trend is is determined by the angle angle of of transpression. transpression. The predicted fault fault geometries have been documented in recent mapping in the area of Mille Mille Lacs Lake and have have also been been observed on several data bases bases farther farther south south in in the the St. St. Cloud Cloud area. area. Linear Linear features features visible visible on on satsat1:1,000,000 correspond with with faults mapped mapped by by ellite images at a scale of l:lyOOOyOOO Mule Lacs other investigators (Shurr and and Watkins, Watkinsy in in press). press). Near Mille Lacs northnorthinvestigators (Shurr east-trending structural discontinuities dip southeast and northwest-trendnorthwest-trendeast-trending structural discontinuities ing faults faults are near vertical vertical (Southwick (southwick and and others, othersy 1988). 1988). In In the the St. St. Cloud Cloud area, satellite linear features mark mark the contact between between Archean Archean gneisses areay Proterozoic granitic and Lower Proterozoic granitic rocks. rocks. This contact and other faults faults have expression on magnetic magnetic data 1:250,000 and and 1:24,000. 1:24y000. clear expression data at at scales scales of of 1:250,000 The fractures fractures and faults associated with accreted terranes terranes have magnetic netic lineations lineations produced produced by by water water flux. flux. The water provided oxygen oxygen from from atmosphere and ion the atmosphere ion transport transport to to convert convert the the primary primary magnetic magnetic mineral, mineral, inagnetite, into into hematite hematite which which is magnetite, is nonmagnetic. nonmagnetic. Magnetic anomaly anomaly maps then then necessarily necessarily have have aa lineation lineation parallel parallel to to the the faulting. faulting. Magnetic Magnetic lineation lineation between the Proterozoic granitic rocks is obvious obvious on the Archean gneisses and Proterozoic aeromagnetic aeromagnetic maps at 1:250,000 1:25Oy0O0 and corresponds corresponds to linear features features visible on aeromagnetic maps on satellite satellite images. images. Lenticular patterns on 1:24,000 aeromagnetic are interpreted as possible strike-slip strike-slip faults and can be investigated in in outcrop. outcrop. Outcrop observations observations along the northeast trend near St. Cloud show show south-dipping south-dipping shear surfaces with with fabric that indicates the south block block fault has has aa strike-slip strike-slip component. component. The The gneisses gneisses of of is upthrown and the fault the northern block are in in places places blocky, blocky, broken broken and and coarse-grained, coarse-grained,but but corresponding change change of magnetite to range to mylonite texture with the corresponding hematite in the the recrystallized recrystallized regions. regions. The presence of of northwest northwest faults faults hematite in is confirmed by observations observations in in outcrops, outcropsy cores, coresy and and thin thin sections, sectionsybut but 117 �I interpretation interpretation of of the the complex complex patterns patterns awaits awaits Ii the the completion completion of of detailed detailed mapping mapping which which is is currently currently underway. underway. Thin sections sections made made from from red red granite granite samples samples collected collected near near faults faultsshow: show: Thin faulted k-spar k-spar porphroblasts, porphroblasts, some some with with tails; tails; mica mica fish; fish;no no magnetite, magnetite,but but faulted abundant microabundant hematite; hematite; and and chlorite chlorite and and biotite biotite partly partly filling fillingubiquitous ubiquitousmicrofractures. fractures. The The reasonably reasonably euhedral euhedral zircons zircons present, present, are are all all fractured fractured with with aa very very dark dark zircon zircon overgrowth overgrowth in in the the fractures fractures indicating indicating low-temperature low-temperature shearing (Belden and and others, others, 1989). 1989). shearing and and metamorphism metamorphism (Belden In summary, summary, observations observations spanning spanning aa scale scale range range from from regional regionalsatellite satellite In images images to to thin thin sections, sectionsy verify verify the the existence existence of of faults faults predicted predicted from from the the accretion accretion model. model. Faults Faults trending trending northeast northeast and and northwest northwest have have been been documentdocumented The structural structural grain grain produced produced during during Penokean Penokean accretion accretion ed at at all all scales. scales. The left left zones zones of of weakness weakness for for subsequent subsequent reactivation. reactivation. During During the the Midcontinent Midcontinent rifting rifting event, event, faults faults were were reactivated reactivated and and some some filled filled with with basalt. basalt. The The recognition recognition of of ubiquitous ubiquitous faulting faulting in in central central Minnesota Minnesota should should preclude preclude any any serious serious consideration consideration of of the the area area for for disposal disposal of of radioactive radioactiveor orhazardous hazardous wastes wastes. REFERENCES REFERENCES Barovich, Peteman, Z.E., Z.E., and and Sims, SimsyP.K., P.K., 1989, 1989,Nd Nd isoisoBarovich, K.M., K.M., Patchett, Patchett, P.J., P.J., Peteman, topes and and the the origin origin of of 1.9-1.7 1.9-1.7 Ga Ga Penokean Penokean continental continental crust crustof ofthe theLake Lake topes Superior Superior region: region: Geological Geological Society Society of of America America Bulletin, Bulletinyv. v. 101, 10ly p. p. 333333- — 338. 338. Belden, Belden, J., J., Anderson, Anderson, G., G., and and Watkins, Watkins, I., I., 1989, 1989$ Zircons Zircons of of the the St. St. Cloud Cloud Red Red and and Reformatory Reformatory Gray Gray granites: granites: Institute Institute on on Lake Lake Superior Superior Geology Geology ProProceedings, ceedings$v. v. 35, 35Âp. p. 4-5. 4-5. Hoim, Holm, D.K., D.K., and and Selverstone, SelverstoneyJ., J., 1990, 1990, Rapid Rapid growth growth and and strain strain rates rates inferred inferred from from synkinematic synkinematic garnets, garnetsyPenokean Penokean orogeny, orogenyyMinnesota: Minnesota: Geology, Geology, v. v. 18, 18 p. 166-169. 166-169. p. Holst, Holsty T.B., T.B., 1984, 1984, Evidence Evidence for for nappe nappe development development during during the the Early Early Proterozoic Proterozoic Penokean Penokean orogeny, orogeny,Minnesota: Minnesota: Geology, Geology, v. v. 12, 12,p. p. 135-138. 135-138. LaBerge, LaBergeyG.L., G.L., and and Myers, Myers, P.E., P.E.$ 1984, 1984,Two Two Early Early Proterozoic Proterozoic successions successions in in central central Wisconsin Wisconsin and and their their tectonic tectonicsignificance: significance: Geological Geological Society Society of of America America Bulletin, Bulletin, v. v. 95, 95$p. p. 246-253. 246-253. - Larue, Larue$ D.K., D.K., 1983, 1983, Early Early Proterozoic Proterozoic tectonics tectonics of of the the Lake Lake Superior Superior region region tectonostratigraphic tectonostratigraphic terranes terranes near near the the purported purported collision collisionzone, zone,in 9 Medaris, Medaris, L.C., L.G., Jr., Jr., ed., ed., Early Early Proterozoic Proterozoic geology geology of of the the Great Great Lakes Lakes region: region: Geological Geological Society Societyof of America America Memoir Memoir160, 160,p. p. 33-47. 33-47. I Southwick, D.L., Morey, Morey, C.B., C.R., and and McSwiggen, McSwiggen,P.L., P.L., 1988, 1988,Geological Geologicalmap mapof ofthe the SouthwickyD.L., I'enokean orogen, central Penokean orogrn, ccrit r a l and and eastern eastern Minnesota, Minncsot a, and ~ n accompanying ditccompanyinp,text: rcxt: Minnesota Minnesota Ceological Geological Survey Survey Report Report of of Investigations Investigations 37, 37, 25 25 p. p. Shurr, C.W., and Watkins, I., in press, Basement blocks, tectonics, and fluid movement —— ''seeping'' through the ned i mt ut a ry cover: I' I'OC(Pd I I1M , SCVeO t iheunat Ic conference on remote senu ng for exploration geology. — 118 ii I �I The Element deposits 3Jkz Role Roleof of Volatiles V o l a bin inthe theFormation Formationof ofthe thePlatinum PlatinumGroup GOUD E l e m u sitsininthe thg Middle and M~ddleProterozoic ProterozoicDuluth Duluth Complex Com~lex andthe the Triassic TriassicNoril'sk-Talnakh Nor11 sk-TalnakhIntrusions Intrusion3 I PAUL W.WEIBLEN WEIBLEN(Minnesota (MinnesotaGeological GeologicalSurvey, Survey,Saint SaintPaul, Paul,MN MN55114) 551 14) PAULW. TATIANA SABELIN SABELIN(Mineral (MineralResources ResourcesResearch ResearchCenter, Center,UM, UM,Mpls.,MN Mpls.,MN (55455) (55455) TATIANA BERNHARDTSAINI-EJDUKAT SAINI-EIDUKAT(Dept. (Dept.Geology Geologyand and Geophysics, Geophysics,UM, UM, Mpls., Mpls., MN MN BERNHARDT 55455) 55455) IWAO WAOIWASAKI WASAKI(Mineral (MineralResources Resources Research Research Center, Center, UM, Mpls., MN MN55455) 55455) Over Overthe thepast pastdecade, decade,studies studiesof ofPt-group Pt-groupelement element (PGE) (PGE)deposits depositshave have focused focusedon ontwo two contrasting contrastingfacets facetsof oftheir theirprobable probableorigin origin(Macdonald, (Macdonald,1988). 1988). Much Muchevidence evidencedocuments documents their theiroccurrence occurrencein inmafic maficcumulates cumulatesand andrelates relatestheir theircharacteristics characteristicsto tothe the idiosyncracies idiosyncraciesof of melt-crystal melt-crystalequilibria equilibriaand andphysical physicalprocesses processes of of melt-crystal melt-crystal segregation segregationduring duringformation formation of of mafic maficcumulates cumulates (Campbell (Campbell and and others, others, 1983). 1983). At Atthe thesame sametime timeevidence evidencehas hasbeen been found foundfor forsynsyn-and andpost-magmatic post-magmatic transport transport and and deposition deposition from from aa fluid fluid phase phase which which could could have haveevolved evolvedin in closed closed or or have have been been introduced in open magmatic magmaticsystems systems(Ballhaus (Ballhausand and Stumpfl, Stumpfl,1986; 1986;Boudreau, Boudreau,1988). 1988). The Theevidence evidencedescribed describedbelow belowfor forthe therole roleof ofvolatiles volatilesin in the the origin originof of the the occurrences occurrencesof of PGE's PGE'sininthe theMiddle MiddleProterozoic ProterozoicDuluth Duluth Complex Complex in the the Lake Lake Superior Superior region and andthe the Triassic TriassicNoril'sk-Talnakh Noril'sk-Talnakhintrusions intrusionsininthe theSiberian Siberianplatform platformmay may be be related relatedto tosimilarities similarities inintheir theirtectonic tectonicregimes regimesand andgeologic geologicsettings settings(Weiblen (Weiblenand andMorey, Morey,1980; 198kUrvantseva, Urvantseva, 1971). Both are arerelated relatedtotoextensional extensionaltectonic tectonicregimes regimesinincontinental continentalcrust. crust. Both Both 1971). Both intrusions intrusionsare areassociated associatedwith withrift-related rift-relatedfaults: faults:the theNorilsk-Talnakh Norilsk-Talnakhintrusions intrusionssitsitastride astrideaa N-NE N-NEtrending trendingfault faultzone zoneand andthe theDuluth DuluthComplex Complexisisbounded boundedby byfaults faultswhich whichparallel parallelthe the rift riftboundary. boundary.Drilling Drillingand andgeophysical geophysicaldata dataindicate indicatethat thatthe thefaulting faultingininboth bothintrusions intrusions defines definesaahalf-graben half-grabengeometry geometry probably probably related related to to down-to-basin down-to-basin normal normal faulting faulting in in aa continental continental rift. rift. There Thereisisevidence evidencethat thatthe thefaulting faultingoccurred occurredprior priorto, to,during, during,and andafter after intrusion. intrusion. The Thebasement basementrocks rocksofofthe theNoril'sk-Talnakh Noril'sk-Talnakhintrusions intrusionsare areDevonian Devoniancoal coalbearing bearing shales areLower LowerProterozoic Proterozoic shalesand andlimestones limestonesand andthe thecountry countryrocks rocksfor forthe theDuluth DuluthComplex Complexare meta-argillites meta-argillitesand andiron ironformation. formation. Both Bothbasement basementsequences sequencescontain containabundant abundanthydrous hydrous mineral mineralassemblages assemblagesand andlesser lesseramounts amountscarbonaceous carbonaceousmaterial materialand andiron ironsulfides. sulfides. Given Giventhe thenature natureof of the the host host rocks rocks and andthe thedynamic dynamictectonic tectonic regimes regimes ititisisperhaps perhapsnot not surprising surprisingthat thatboth bothintrusions intrbsionsprovide provideevidence evidenceofofdevolatilization devolatilizationofofcountry counrryrocks rocksand and mixing volatiles with intrusive mixingof of country country rocks rocks and country rock volatiles intrusivemagmas. magmas. Evidence Evidencefor for these thesephenomena phenomenafrom. fromfrom fromthe theCu-Ni Cu-Nideposits depositsininboth bothintrusions intrusionsisisshown shownschematically schematically ininFig. Fig.1.1.Similar Similartextural texturalrelationships relationshipsare arecommon commonin in the the field fieldand anddrill drillcore coredata dataononCuCuNi Nideposits depositsininthe theDuluth DuluthComplex Complex(Foose (Fooseand and Weiblen, 1986). 1986). The Thestable stableisotope isotopestudies studies ofofRipley Ripleyand andhis hisstudents studentsover overthe theyears yearsprovide providethe thegreatest greatestin-depth in-depthelucidation elucidationofofthe the roles rolesof ofcountry countryrock rockvolatiles volatilesininthe theformation formationof ofthe theCu-Ni Cu-Nideposits depositsininthe theDuluth Duluth Complex Complex(Ripley, (Ripley,1986). 1986). Evidence Evidencefor forvolatile volatiletransport transportofofPGE's PGE'shas hasnow nowbeen beenfound foundininthe theDuluth DuluthComplex Complexby by Sabelin Sabelin(Sabelin (Sabelin and and others, others, 1989): 1989): Pt-Fe Pt-Fealloy alloyand andPt-Pd Pt-Pdsulfides sulfidesare are found found ininveins veins cuttingolivine olivineand andchrome-spinel chrome-spinelin in aamafic mafic cumulate cumulate in in the the Duluth Duluth Complex. Complex. Perhaps Perhaps cutting more morestriking strikingisisthe thediscovery discoveryby bySabelin Sabelinof ofPd Pdsulfide sulfidereplacing replacing chalcopyrite. chalcopyrite. Similar Similar relationshipshave havebeen beenalluded alludedtotoininthe theTalnakh Talnakhdeposits depositsby byGenkin Genkinand andEvstigneeva Evstigneeva relationships %)by byDahlberg Dahlberg(pers. (pers. (1986).The Thediscovery discoveryofofaahydrous hydrousiron ironchloride chloridephase phase(14 (14wt. wt.%) (1986). comm.)ininaahighly highlyserpentinized serpentinizedsection sectionofoftroctolite troctoliteinindrill drillcore corelends lendscredence credencetotothe the comm.) concept that thatthese thesereplacement replacement textures textures might might be be products productsofoftransport transportofofPGE's PGE'sasas concept chloride chloridecomplexes. complexes. There Thereisisa apaucity paucityofofexperimental experimentaldata data ononvolatile volatiletransport transportofof 119 �U PGE's. PGE's. However,the the results resultsof of an an experiment experimenton on the the roasting roasting of of Cu-Ni Cu-Ni ores ores in in aa mixture mixture However, of of salt salt and and coke coke fragments fragments (Iwasaki (Iwasaki and and others, others, 1971) 1971)indicated indicated that that segregation segregation of of the the metals could be beachieved achievedwith with salt salt and and coke cokebut but not notwith withcoke cokeor orother otherreductants reductantsalone. alone. metals These These results results suggest suggest that that CI Cl isisrequired required asasaatransporting transportingagent. agent. Perhaps Perhaps similar similar requirements requirementsmust mustbe bemet metfor forPGE's PGE's to tobe be concentrated concentratedin in natural natural ores. ores. PAMIMLY C1YSTAWM $ASALIIC MW © 0 u4€ vI OJIWILUS.I 0' e A B Fig. Fig.1.1. Field Field relations relationsof ofhornfels homfelsinclusions inclusionsand andsulfide sulfidemineralization mineralizationininthe the Duluth Duluth A) Schematic Schematicrepresentation representation of of aapelitic pelitic Noril'sk-Talnakh intrusions. Complex and and the the Noril'sk-Talnakh Complex intrusions. A) homfelsinclusion inclusionininmineralized mineralizedgabbro gabbroininthe thefootwall footwallofofthe theDuluth DuluthComplex. Complex.Modified Modified homfels from fromChurchill Churchill(1978, (1978*p. p. 95). 95). B) B) Inclusion Inclusionininaagabbroic gabbroicNoril'sk Noril'sk intrusion. intrusion.Sulfides Sulfides (4) (4) ingabbroic gabbroicpegmatoid pegmatoid(3) (3)mantling mantlingaaxenolith xenolithof of labradorite labradoriteporphyry porphyry (2) (2)in ingabbro gabbro(1). (1). in From From Urvantseva Urvantseva(1971, (1971, P. p. 239). 239). Both Both occurrences occurrences of of sulfide sulfide can can be beinterpreted interpretedtoto representmigration migrationof ofsulfur sulfurfrom fromthe theinclusions inclusionsand andmetals metalsfrom fromthe theenclosing enclosinggabbroic gabbroic represent magma magmaas asshown shownininA. A. I References References Ballhaus, Ballhaus, C.G. C.G. and andStumpfl, Stumpfl*E.F., E.F.*1986, 1986,Sulfide Sulfideand andplatinum platinum mineralization mineralization in in the the Merensky Reef: Reek Evidence Evidence from fiom hydrous hydrous silicates silicates and and fluid fluidinclusions. inclusions.Contrib. Conmb. Merensky Mineralogy Mineralogy Petrology Petrology 94: 94:193-204. 193-204. Boudreau, Boudreau,A.E., A.E., 1988, 1988,Investigations Investigationsof ofthe theStiliwater StillwaterComplex. Complex. IV. IV.The Therole roleof ofvolatiles volatiles ininthe petrogenesis of the J-M Reef, Minneapolis Adit section. Canadian Minerologist the petrogenesis of the J-M Reef*Minneapolis Adit section. Canadian Mineralogist 26: 26: 193-208. 193-208. Campbell, Campbell, I.H., I.H.*Naldrett, Naldrett*AJ. A.J.and andBarnes, Barnes,S.-J., S.-J., 1983, 1983,AAmodel modelfor forthe theorigin originofofthe thePtPtrich theBushveld Bushveldand andStillwater StillwaterComplexes. Complexes.Journal JournalPetrology Petrology24: 24: richsulfide sulfidehorizons horizons- -the 133-165. 133-165. I Churchill, Churchill,K.C., K.C., 1978, 1978*AAgeochemical geochemicaland andpetrological pemlogical investigation investigationof of the theCu-Ni Cu-Nisulfide sulfide genesis MSthesis, thesis,University Universityof ofMinnesota: Minnesota:101 101p.p. Complex*Minnesota. MiinesomMS genesisininthe theDuluth DuluthComplex, Foose, Foose?M. M.and andWeiblen, Weiblen,P.W., P.W.*1986, 1986,The Thephysical physicaland andpetrologic petrologicsetting settingand andtextural texturaland and compositional compositionalcharacteristics characteristicsofofsulfides sulfidesfrom fromthe theSouth SouthKawishiwi KawishiwiIntrusion, Intrusion,Duluth Di~li~th Complex, Naldrett, in Friedrich, Fricdrich. G.li., G l I . , Genkin, Genkin, Ai), All., Naldrett,A.J., A.J.,Ridge, Ridge, Complex, Minnesota, Minnesota, USA. USA. in J.D., J.D., Sillitoe, Sillitoe?R.H., R.H., and andVokes, Vokes,F.M., F.M.,eds., eds.,Geology Geologyand andmetallogeny metallogenyofofcopper copper deposits, for deposits,Soc. SOC. forGeology GeologyApplied AppliedtotoMineral MineralDeposits, Deposits*Special SpecialPublication PublicationNo. No.4,4, Berlin, Berlin*Springer-Verlag: Springer-Verlag:8-24. 8-24. I 120 �Referencescontinued continued ... References Genkin, T.l., 1986, Associations of platinum-group minerals of the Ge&, A.D. A.D. and and Evstigneeva, Evstipeeva, T.l., Noril'sk 1:1203-1212. Noril'sk copper-nickel copper-nickelsulfide sulfideores, ores, Economic EconomicGeology Geology881: 1203-1212. Goryainov, I.N., 1971, The The genesis of the deposit, in in The The petrology petrology and and Goryainov, I.N., genesis of the Talnakh Talnakh deposit, economic economic geology geology of of the the Talnakh Talnakh and and Noril'sk Noril'sk differentiated differentiatedintrusions, intrusions,Urvantseva, Urvantseva, N.N. N.N. (ed.)182-312. (ed.) 182-312. Iwasaki, I., Takahashi, Takahashi, Y., Y., and and Kahata, Kahata,H., 1971, 1971, Segregation Segregation process for for copper copper and and nickel ores, in Progress Progressin in Extractive Extractive Metallurgy, Metallurgy, 1, 1, Gordon and Breach, NY. Macdonald, Macdonald, S.J., S.J., 1988, 1988, The The platinum group element deposits: classification classification and genesis. genesis. Geoscience GeoscienceCanada Canada14: 14:155-166. 1%- 166. Sabein, Sabelin, T., T., Weiblen, Weiblen, P.W., P.W., and and Saini-Eidukat, Saini-Eidukat, B., B., 1989, 1989, Similarities Similarities in textures textures and associations of platinum group minerals in the the Duluth Duluth Complex, Complex, MN h4N and andthe the mineral associations Noril'sl-Talnakh Geol. Soc. Amer. Amer. Abstr. with with Prog. Prog. 21: 21: Noril'sl-Talnakh intrusions, USSR USSR [abstr.1. [abstr.]. Geol. A262. Urvantseva, N.N. (ed.), (ed.), 1971, 1971, The The petrology petrology and and economic economic geology geology of of the theTalnakh Talnakhand and Urvantseva, N.N. Noril'sk differentiated differentiated intrusions, kLeningrad,3l2. n i n j p d , 3 12. Weiblen, P.W. and G.B., 1980, 1980, A summary summary of the stratigraphy, stratigraphy, petrology and and Morey, Morey, G.B., structure structureof of the the Duluth Duluth Complex. Complex. American American Journal Journal Sci. Sci. 280-A: 280-A: 88-133. 88-133. 121 �U Archean Granitoids Granitoids Of Of Northern Northern Marquette Marquette County, County, Michigan. Michigan. Archean Richard T. T. Wilkin, Wilkinf John John A. A. Mavrogenes, Mavr~genes~ Richard and Theodore Theodore J. J. Bornhorst Bornhorst and Department of of Geological Geological Engineering, Engineeringf Geology, Geologyf and and Department ~eophysics~ Michigan Technological Universityf Houghtonf Geophysics, Michigan Technological University, Houghton, MI 49931 49931 MI Granitoid rocks rocks of of Archean Archean age age crop crop out out in in aa large large Granitoid The Archean Archean rocks rocks The have been been subdivided subdivided into into the the northern northern (granite-greenstone) (granite-greenstone) have and the the southern southern (granite—gneiss) (granite-gneiss)complexes. complexes. These These and complexes are divided by a major crustal structure: the complexes are divided by a major crustal structure: the (Simsf 1980). The granitoid rocks Great Lakes tectonic zone Great Lakes tectonic zone (Sims, 1980). The granitoid rocks of the the northern northern portion portion of of the the southern southern complex complex have have been been of described by by Hoffman Hoffman (1987). (1987). The The granitoid granitoid rocks rocks of of the the described northern complex, complexf which which have have not not been been previously previously described, described, northern are the the focus focus of of this this on—going on-going study. study. are portion of of Marquette Marquette County, County, Michigan. Michigan. portion I In the the northern northern complex, complex, the the contact contact between between the the In granitoids and the Marquette greenstone belt is gradational granitoids and the Marquette greenstone belt is gradational and foliations foliations in in the the volcanics volcanics parallel parallel those those in in the the and The presence presence of of abundant abundant amphibolite amphibolite xenoliths xenoliths granitoids. The granitoids. in the the granitoids granitoids near near the the contact contact and and compositionally compositionally in in the the volcanics volcanics suggest suggest that that the the similar granitoid granitoid dikes dikes in similar granitoids intrude intrude the the volcanics. volcanics. The The emplacement emplacement of of these these granitoids belt bounding plutonic rocks is considered to be belt bounding plutonic rocks is considered to be contemporaneous with with recumbent recumbent folding folding of of the the volcanic volcanic rocks rocks contemporaneous (Johnson and Bornhorst, in press). The granitoids range (Johnson and Bornhorst, in press). The granitoids range tonalite based based from tonalite tonalite to to granite granite and and are are dominantly dominantly tonalite from on the the IUGS IUGS classification classification (Streckeisen, (Streckeisenf1973), 1973)# and and on on the the on Debon and and Le Le Fort Fort (1982). (1982). chemical classification classification scheme scheme of of Debon chemical Tonalites tend tend to to be be foliated foliated whereas whereas granites granites are are generally generally Tonalites Although most most of of these these granitoids granitoids were were emplaced emplaced massive. Although massive. during recumbent recumbent folding, foldingf it it is is possible, possiblef as as discussed discussed below below during that some may be younger. that some may be younger. Stocks and and related related rhyolite rhyolite dikes dikes were were emplaced emplaced within within Stocks the greenstone greenstone belt belt during during aa second second deformational deformational event event the Bornhorstf in in press). press). Modally, Modallyf these these stocks stocks (Johnson and and Bornhorst, (Johnson from diorite diorite to to granite granite and and most most are are granodiorite granodiorite or or range from range monzodiorite. One One pluton pluton described described by by Puffett Puffett(1974) (1974) quartz monzodiorite. quartz includes aa porphyritic porphyritic syenite. syenite. Age Age relationships relationships between between includes individual stocks are often equivocal because of spatial individual stocks are often equivocal because of spatial separation. separation. both the the belt belt bounding bounding and and In the the northern northern complex, complex, both In intra-belt granitoids granitoids generally generally fall fall along along calc-alkalic calc-alkalic intra—belt trends; however, howeverf aa tonalite—trondhjemite tonalite-trondhjemite trend trend is is also also trends; observed in the belt bounding granitoids (Debon and LeFort, Fort, observed in the belt bounding granitoids (Debon and Le 2? I �1982;Barker Barkerand andArth, Arthf1976). 1976). on On the thebasis basis of ofthe themajor major 1982; element tectonic tectonic discrimination discrimination method method of of Maniar Maniar and and Piccoli Piccoli element (1989) the the belt belt bounding bounding granitoids granitoids on (1989) on the the north northand and northeast sides sides of of the the volcanics volcanics and and the the intra—belt intra-belt northeast granitoids represent represent an an island island or or continental continental arc arc granitoids environment. This This is isconsistent consistentwith with the the trace traceelement element environment. discriminationmethod method of of Pearce Pearceet.al. et.al. (1984). (1984). Although Although discrimination these plutonic plutonic rocks rocks were were emplaced emplaced during during major major Archean Archean these deformation probably probably related related to to collision/suturing collision/suturingalong along the the deformation Great Lakes Lakes tectonic tectonic zone, zoneftheir their geochemical geochemical character characteris is Great similarto toan anarc arcenvironment. environment. Thus, ThusIthe the environment environment of of similar emplacementmay may be be transitional transitionalfrom fromarc arcto tocollision. collision. emplacement Granitoids Granitoids which which bound bound the the southwest southwest side sideof of the the greenstone greenstone belt belt in in the the northern northern complex complex classify classify as as collisional collisionalgranites, granitesfon onthe thebasis basisof ofmajor majorelements. elements. This This In the southern In the southern is not not confirmed confirmedby by the thetrace traceelements. elements. is complex, complexfthe the Bell Bell Creek Creek Granite Granite of of Hoffman Hoffman (1987) (1987)has has both both major major and and trace trace element element composition composition most most similar similarto to Perhaps these these granitoids granitoids are are younger younger collisionalgranites. granites. Perhaps collisional than aboveI and and were were emplaced emplaced during during the the than those those discussed discussed above, mature mature phase phase of of suturing suturing along along the the Great Great Lakes Lakes tectonic tectonic This hypothesis hypothesis could could be be tested tested by by radiometric radiometricage age zone. This zone. determinations. Although Although this this is is merely merely aa progress progressreport, reportf determinations. it it is is clear clear that that these these Archean Archean granitoids granitoids are are aa critical critical component component to to understanding understandingthe theArchean Archeanin inMichigan. Michigan. References References Barkerf F. F. and and Arth, ArthI J.G., J.G.f 1976, 1976# Generation Generation of of trondjehmitic trondjehmitic Barker, -tonalitic -tonalitic liquids liquids and and Archean Archean bimodal bimodal trondjehmitictrondjehmiticbasalt suites: suites: Geology, GeologyIv.4, v.4# p. p. 596—616. 596-616. basalt Debon! F, Ff and and Le Le Fort, Fortf P., P e f1982, 1982f AA chemical-mineralogical chemical-mineralogical Debon, classification classification of of common common plutonic plutonic rocks rocks and and assocassocTrans. R. Soc. Edinb., Earth Sciences, 73, R. SOC. Edinb.! Earth SciencesI 73#p. p. iations: Trans. iations: 135-49. 135—49. Hoffman, Hoffmanf M.A., M.Aef1987, 1987# The The geology geology of of the the southern southern complex: complex: geology, geologyf geochemistry, geochemistryIand and mineral mineral chemistry chemistry of of selectselected ed uranium—and uranium-and thorium—rich thorium-rich granites: granites: Ph.D. Ph.D. DisserDissertation, tationf Michigan Michigan Technological Technological University, Universityf Houghton, Houghton! 382 p. p. 382 Johnsonf R.J. R.J. and and Bornhorst, Bornhorst, T.J., T.J.! Archean Archean geology geology of of the the Johnson, northern beltI MarMarnorthern block block of of the the Ishpeming Ishpeming greenstone greenstone belt, quettef County, Countyf MI: MI: U.S. U.S. Geological Geological Survey Survey Bulletin Bulletin quette, 1904fin in press. press. 1904, 123 �1 Maniar, discrimManiar, P.D. P.D. and Piccoli, P.M., P.M., 1989, Tectonic discrimination of granitoids: granitoids: Geological Society of America Bulletin, Bulletin, v. 101, 101, P. p. 635—43. 635-43. J.A., Harris, N.B.W, N.B.W, and Tindle, A.G., A.G., 1984, Pearce, J.A., 1984, Trace Trace element element discrimination diagrams diagrams for for the the tectonic tectonic interpretation of granitic rocks: Journal Journal of of Petrology, Petrology, v. 25, 25, P. p. 956—83. 956-83. I W.P., 1974, Geology of the Negaunee Quadrangle,MarQuadrangle,MarPuffett, W.P., quette County, Michigan: Michigan: U.S. U.S. Geological Geological Survey Survey ProfProfessional Paper p. essional Paper 788, 788, 51 51 p. P.K., 1980, Boundary between Archean greenstone greenstone and Sims, P.K., gneiss terranes terranes in northern Wisconsin and Michigan: Geologic Society of America Special Paper Paper 182, 182, p. 113113124. 124. A.L., 1973, Plutonic rocks: rocks: classification classification and Streckheisen, A.L., and nomenclature recommended by the IUGS IUGS Subdivision Subdivision on on the the nomenclature Systematics Systematics of Igneous Igneous Rocks: Geotimes, v. v. 18, 18, p. 26— 2630. 30. 124 I I I I I I I I I I I I �PURCHASE OF OFPROCEEDINGS PROCEEDINGSAND ANDABSTRACTS ABSTRACTS AND AND FIELD FIELD GUIDEBOOK GUIDEBOOK PURCHASE Copies of of the the Proceedings Proceedings and and Abstracts, Abstracts, Part Part 1, 1, and and the the Field Field Guidebook, Guidebook, Part Part 2, 2, for for the the Copies 36th Annual Annual Institute Institute on on Lake LakeSuperior SuperiorGeology Geology may may be be purchased purchased during duringthe themeeting. meeting. 36th Proceedings and and Abstracts, Abstracts, Volume Volume 36, 36, Part Part 11 Proceedings Field Guidebook, Guidebook, Volume Volume 36, 36, Part Part 22 Field . . . . . . . . . .$5.00 $5.00 Canadian Canadian . . . . . . . . . . . . . . . . . $5.00 $5.00 Canadian Canadian Payable to to Institute Instituteon onLake LakeSuperior SuperiorGeology Geology Payable ****************************************************************************** Issues of of Proceedings Proceedings and Abstracts, Abstracts, Part 1, 1, and Field Field Guidebook, Guidebook, Part Part2, 2, from from this this and and the the Issues three previous previous meetings, meetings, may may be ordered ordered from: from: three JoeKalliokoski KalZbkosJd,SecretaiySecretary-Treasurer Joe Treasurer Department of Geology and GeologicalEngineering Engineering Department of Geology and Geological Universily Michigan Technological Michigan Technological University Houghton, Michigan 49931 49931 Houghton, 906-482-6107 The cost cost for for each eachpart partordered orderedisis$6.00 $6.00U.S. U.S. The Orders will will be be filled filled while while supplies supplieslast. last. Orders ****************************************************************************** All volumes volumes back to to 1955 1955 are are available available for for photocopying photocopying at the the prevailing prevailing rate, rate, All from the theMichigan MichiganTechnological TechnologicalUniversity UniversityLibraty, Library, from through Mr. M. S. Spence, Archivist. through Mr. M. S. Spence, Archivist. Phone 906-487-2505 � https://digitalcollections.lakeheadu.ca/files/original/0777f53be72394c03c31a48988da325f.pdf fc82e698b41221481038bd2022b4b742 PDF Text Text INSTITUTE GEOLOGY INSTITUTE ON ON LAKE LAKE SUPERIOR GEOLOGY PROCEEDINGS PROCEEDINGS . e 36th 36th Annual Annual Meeting Meeting May 1990 May 9-12, 9-12,1990 held at held at Thunder ThunderBay, Bay, Ontario Ontario H.L. JAMES JAMES VOLUME VOLUME VOLUME VOLUME36 36 May 1990 1990 May Part Part2. 2. Field Field Trip Trip Guidebook Guidebook �Organizing Committee, 36th Organizing 36th Annual Annual Meeting, Meeting, ILSG ILSG(1990) (1990) Committee comprises comprises the the following following members of the The Organizing Committee Department of Geology Geology Lakehead University Thunder Bay, Bay, Ontario P7B P7B5E1 5E1 General Chairman: Chairman: Manfred Manfred M. M. Kehienbeck Kehlenbeck Chair and and Abstract Abstract Editor: Editor: Philip PhilipW. W. Fralick Fralick Program Chair Editor: Graham Graham J. Borradaile Boiradaile Field Trip Guidebook Editor: & Volume 36 consists of Part 1: m: Abstracts Abstracts mPart 2 2:: Field F W Trip Guidebook Guktnwk to material in Proceedings Volume should should follow the Reference to the example example below: below: A., 1989, 1989, Significance Significance of of Conglomerates Conglomerates in in the the Baraboo quartzite quartzite of Brown, Bruce A., southeastern Wisconsin Wisconsin [abst.]; Institute on Lake Lake Superior Superior Geology Geology [abst.I; Institute Proceedings, 35th Annual Meeting, Duluth, MN, 1989; Houghton, Ml, 35, 1989; Houghton, MI, v. 35, part part 1, 1, p. p. 11-12. 11-12. Published Published and Distributed Distributed by by Institute on Lake Superior Geology Geology J. Kalliokoski, Secretary/Treasurer Dept. of Geological Geological Engineering, Geology and and Geophysics Geophysics Michigan Technological Technological University Michigan University 49931 Houghton, Michigan Michigan 49931 ISSN 1042-9964 1042-9964 �TABLE OF CONTENTS TABLE OF CONTENTS Introduction duction . ........... ... 1 M. M. J. J. Lavigne, Lavigne, Jr. Jr. FIELD TRIP 1 Mafic PGE mineralization Mafic intrusions, intrusions, PGE mineralization and and granitoid granitoid rocks of the Lac des Illes area. rocks of the Lac des Illes area. R. R. H. H.Sutcliffe Sutcliffe ....................... 11 FIELD TRIP FIELD TRIP22 Geology Geology of of the the Shebandowan Shebandowan and and Quetico QueticoArchean Archean Subprovinces. Subprovinces. U. J. Borradaile . . . 43 . FIELD FIELD TRIP TRIP33 Granitoid-related Granitoid-related mineral mineral deposits deposits in inthe thewestern western Lake Superior region. Lake Superior region. 52 S. A. Kissin FIELD FIELD TRIP TRIP44 Base Base Metal Metal Mineralization Mineralizationin inthe theShebandowan Shebandowan Greenstone GreenstoneBelt. Belt. M. Lavigne Jr., A. J. Aubut & & J. J. F. F.Scott Scott M. J. Lavigne 11 67 �GEOLOGY W THE LAKEIIEAD REGION GEOLOGY OF THE IIAREFIFD REGION by Maurice J - Lavigne Jr. Manriee J. Lavigne Jr. Ontario Ministry of Northern Development and Mines Ontario Ministry of Northern Development and Mines & Thunder Bay Thunder Bay S 1 �c.O —H 'CIt, ((lCD l-' (f) Ft (fl<t H- (1) (DO CD 0.0 flu) P1 H 0.0 C 'It!) N) CD Ni cto) It (DC) —0 r1 O(D H0 l.a. Oct CD Lithatectonic ~ul.$provinces of the Superior Province ( a f t e r Card and C i e a i e l s k i , 1986) 11 H I-I. 'a C II Figure 18 �INTRODUCTION The Lakehead LakeheadRegion Regionisisan anarea area bound houndtoto the the east east by The by LakeSuperior, Superior,to to the the south the international Lake south by by the internationalborder, border, includes includes Lake Nipigon, and extends to the west as far as the town of town of Atikokan. Atikokan. This region region is is underlain underlain by precambrian precambrian rocks of the Canadian Canadian Shield, Shield, in in particular, particular, Archean Archean rocks rocks the Superior Superior Province and Proterozoic Proterozoic rocks the Province and rocks of of the theSouthern Southern Province (Fig (Fig 1). Three subprovinces subprovinces of of the the Superior Province 1). Three Superior Province are are represented; Quetico, and Province represented;Wabigoon, Wabigoon, Quetico, and the the Abitibi—Wawa. The The Southern SouthernProvince Provinceisis subdivided subdivided into into the Abitibi-Wawa. the Nipigon Nipigon Plate Plate and the the Port Port Arthur Homocline, Homocline, the the northern northern fringe fringe of the the Aninikie Aninikie basin basin (enclosed (enclosed nap) nap). Stockwell (1964,1970) (1964,1970) and and Card Card and and Ciesielski Ciesielski (1986) (1986) subdivided the Superior Superior Province Province on the basis of structure structure and lithology. and lithology. In In this thisregion, region,the thesubprovinces subprovinces are are supracrustal-intrusive complexes, the predominance of either either s~ipracrustal-intrusivecomplexes, the predoninance of volcanic or sedimentary rock volcanic rock being a key distinguishing distinguishing characteristic. The Ahitibi—Wawa characteristic. Abitibi-Wawa and the Wabigoon Wabigoon b Suhprovinces are arcuate assemblages Subprovinces assemblages of volcanic rock dominated dominated belts, belts, "greenstone 'greenstone belts', belts", and tonalitic tonalitic to to granodioritic, granodioritic, massive massive to to gneissic gneissic intrusions. intrusions. The Quetico Quetico Subprovince is a linear linear metasedimentary terrane terrane cored by Subprovince granitic intrusions granitic intrusions and and migmatites. migmatites. The subprovince subprovince boundaries are boundaries are broad schist schist zones zones and/or and/or distinct distinct faults, faults, the Seine Seine River—Quetico River-Quetico fault fault couple, couple, which which separate separate the the Quetico from from the the Wabigoon, Wabigoon, being being good examples examples of of both both of of these types these types of of strain. strain. Nipigon Plate Arthur Homocline The Sipigon Plate and the Port nithur Homocline consist consist of flat lying lying sedimentary sedimentary rock rock uncomformibly unconformibly over'ying overlying the the Superior Province. Superior Province. These also include diabase sills sills and dykes, late dykes, late nafic oafic intrusions intrusions and and v,lcanic vzlcanic rocks. rocks 3 :' �ARCHEAN STRATICRAPHY High precision U—Pb zircon geochronology, carried out ,. ,- . at the has resulted resulted in&.draraatic in a dramatic the Royal Royal Ontario Ontario &tuseun, Museura, has <<.r. . of the change in in the the rate rate. of of increased increased understanding understanding,/of the . * archean. archean. Absolute dates dates corbined combined with with structural structural interpretations of well documented lithological distribution distribution interpretations has has resolved resolved the the stratigraphy stratigraphy within within some some greenstone greenstone belts. belts. It has also helped resolve resolve the the relationships relationships between plutonism, volcanism, plutonism, volcanisn, sedimentation, sedimentation, metamorphism, metanorphisra, deformation and deformation and mineralization. mineralization. Many stratigraphic stratigraphic relationships within subprovinces, relationships subprovinces, and in between subprovinces have subprovinces have also also been been resolved. resolved. In the Lakehead Region some some fundamental fundamental distinctions, distinctions, and an2 similarities, similarities can now be he drawn in between the Wabigoon and the Abitibi-Wawa Abitibi-Wawa tonalite-greenstone terranes and and their their relationship the tonalite-greenstone terranes relationship to to-the intervening- paragneiss of interveninq of the theQuetico. Quetico. -paracmeiss Atilcakan, In Atikokan, the the Marrnion Lake Batholith,aatonalite tonalite In larmion Lake Batholith, complex, omplex, has been dated at 3004 3004 ma (Davis (Davis et et al, al, 1988). 1988). This his hatholith batholith is is uncomformibly uncomformibly overlain overlain by the the Steeprock Steeprock Group This roup sedimentary sedinentary rocks rocks and subsequent subsequent volcanic rocks. rocks. This unconformity ncoraformity is is well exposed exposed on on the the east east wall of of the the Roberts Roberts v. pit. Stone et al.(in press) describe the unconformity and the overlying Wagita Formation e overlying Formation as follows; follows; "The "The uncomformity uncoraformity at t the the base of of the the Wagita Formation Formation is is marked by aa transition ransition from from unaltered tonalite tonalite to sericitized sericitized tonalite tonalite and nd a a sericite—carbonate-quartz sericite-carbonate-quartz 'grit', 'grit', which which becomes becomes well well bedded formation added and and clast clast bearing bearing up up section". section". The The ccagita Wagita formation is overlain by the stroriatolitic Mosher Carbonate Formation and altered altered iron iron formation formation (Jolliffe (Jolliffe Ore Zone Zone Formation). This his sedimentary sedimentary sequence sequence is is overlain overlain in in ascending ascending order order by; by; ultranafic pyroclastics, mafic pillow lavas and intermediate to felsic flows, o felsic flows, tuffs tuffs and and breccias. bre overlain by clastic sediments. This sequence is then Felsic tuffs in the Lumby Lake Creenstone Belt,on the 4 - , �I north Lake Batholith, Batholith, have have been been dated dated at orth side side of of the the .Marmjcin Marnion Lake at 950 ma na aria and 2999 aa (Davis Jackson, 1988). 1988). These are 2950 2999 rma (Davis and Jackson, These are considered onsidered to to be be the the stratigraphic stratigraphic equivalents equivalents to the the felsic felsic volcanics older, carbonate olcanics in in the the Steeprock Steeprock nine nine area. area. This older, carbonate sediment bearing, volcariic—sedirnerit:a rysequence sequence has has been diment bearing, volcanic-sedimentary been recognized in many manygreenstone greenstonebelts beltsininthe the northern northern parts parts of cognized in of the he superior superiorprovince province (Thurstori (Thurston and and Chivers, Chivers, 1990). 1990). These These sequences, equences, as well as quartz arenites—iron arenites-iron formation— fornationultrarnafic lava lava sequences sequences recognized recognized in in other other belts, belts, have ultramafic shallow water shallow water sedimentary sedimentary features. features. This is is the the basis basis for for the recognition sequences which the recognition of of early early archeari archean platfot-nal platfornal sequences developed at at about 3000 developed 3000 ma (Wood (Wood et et al, al, 1986). 1986). 1 These These shallow shallow water water guartz—arenite quartz-arenite and and carbonate carbonate I bearing sequences ('2.85 earinq sequences (>2.85 Ga) are generally overlain overlain by mafic—ultramafic afic-ultramafic volcanic volcanic sequences sequences (2.740 (2.740 to 2.700 2.700 Ga) Ga) and and mafic afic to to felsic felsic volcanic cycles cycles (2.775 (2.775 to 2.700 Ga) and comprise what comprise hat is is stratigraphically stratigraphically referred referred to to as as "Keewatin". Keewatin rocks volumetrically dominate Keewatin". rocks volumetrically doninate all all greenstone reenstone belts belts in in the the Superior Superior province. province. The younger younger of of these hese Keewatin Keewatin volcanic sequences sequences are not recognized in the Atikokan area. Atikokan area. They are however, the only recognizable recognizable volcanic sequence sequence older than than 2.700 Ga in the Shebandowan shebandowan greenstone belt of greenstone of the the Abitibi—Nawa Abitibi-Kawa subprovince. subprovince. Thurston Thurston (1986) (1986) interprets interprets two mafic to to felsic felsic volcanic volcanic cycles. cycles. Corfu and Stott Stott (1986) (1986) have generated a date of 2.733 Ga for felsic volcanics volcanics in in the the Middle Middle Shebandowan Shebandowan Lake Lake area. area. Stratigraphic relationships Stratigraphic relationships in this belt have been masked by intense intense deformation. deformation. A common connon thread thread for i.ur both both the the Abitibi-Wawa Abitibi-Wawa and and the the Vabigoon is Wabigoon is that that they they both both contain contain younger younger "Temiskaming""Temiskaming"type greenstone belts in the y p e sequences, sequences, found in many greenstone Canadian Shield. Canadian shield. These volumetrically volunetrically insignificant insignificant sequences sequences consist consist of of alluvial—fluvial alluvial-fluvial sedimentary sedimentary rock, rock, mainly conglomerate and arkose with or without alkalic and shoshinitic volcanic rock (Shegelski, 1980). In the S �Atikokan—?line Centre area, a distinctive conglomerate unit, referred to as as the the Seine Seine Conglomerate, Conglonerate, is is found found along along the the Quetico—Wabigoon uetico-Mabigoon subprovince subprovince boundary. boundary. The The contact contact relationship elationship with with adjoining adjoining Quetico Quetico sediments sediments and and Wahigocn Kabigoon volcanics olcanics is is unclear unclear because because of of poor poor exposure exposure and and shearing. shearing. Poulsen (1984), deduced that the Seine Conglomerates were younger ion ounger on on the the basis basis of of preserved preserved evidence evidenceof of defornat defornati history. istory. This This is is supported supported by by U-Pb C-Pb dates dates of of 2685 2 6 8 5 ma na for for aa clast last in in the the conglomerate conglomerate and and an an age age range range of of 2700 2 7 0 0 tO tG 2795 2795 ma a for for detrital detrital zircons zircons in in the the Quetico Quetico Metasedinents Mstasediments (Danis (Daris ett al, 1990). al, 1 9 9 0 ) . In In the the northern northern Shehandowan Shebandowan greenstone greenstone belt, belt, interdigitated conglomerates "Teniskaming' alkaline volcanics, and sandstones are dated at 2689 ma and the underlying at 2733 ma na (Corfu (Corfu and and Stott, Stott, nderlying "ICeewatin" "Keewatin" volcanic-s volcanics at 1986). 9 8 6 ) . The The contact contact relationship relationship is is obscured obscured by by well well developed eveloped foliation foliation leading leading to to speculation speculation that that the the "Temiskaning" 'Teniskaning" rocks rocks developed developed in in aa fault fault bounded bounded through. through. AA second econd belt belt of of Teniskaming Teniskaroing rocks rocks aa few few miles miles to to the the south south has stratigraphic relationship relationship with as aa clearly clearly discomfort-uable disconforniable stratigraphic with underlying nderlying "Keewatin" "Keewatin" volcanic volcanic rocks. rocks. In In summary, suranary, the the stratigraphy stratigraphy within within the the volcanic— volcanictonalite nalite terrane terrane consist consist of of 33 b.y. b.y. old old tonalite tonalite basement, basement, overlain 'erlain by by aa 33 b.y. b.y. old platfornal platfornal sequence, sequence, 2.74 2 . 7 4 b.y. b.y. subsubalkalic 2.68 b.y. b.y. old old calc—alkalic calc-alkalic volcanics volcanics Ikalic volcanics volcanics and and 2.68 and nd sedimentary sedimentary rocks. rocks. Recent Recent age age dates dates on on detrital detrital zircons zircons from on Quetico Quetico greywacke greywacke range range from from 2700 2700 al, 1990) strongly suggesting a coeval sub—alkalic volcanics. The suggestion to to 2795 2 7 9 5 ma ma (Davis (Daviset et relationship with the by Williams (1987), that at the the Quetico Quetico represents represents an an accretionary accretionary prism prism is is well well accepted. A host to the 3 b.y. tonalite intrusive has yet to bee recognized. recognized. The The last last major major geological geological event event in in the the tonalite— tonalitegreenstone nstone terrane. terrane is represented represented by by the the voluminous voluminous tonalites analites which which intruded intruded from from 2690 2690 to to 2677 2 6 7 7 Ma Ma (Colvine, (Colvine, et et C) �al 1988). granitic Quetico al 1 9 8 8 ) ; TThe. he g r a n i t i c rocks r o o k s in i n tthe he Q u e t i c o intruded i n t r u d e d from from 2670 tO Both of 2670 t 0 2650 Ma Ma (Percival, ( P e r c i v a l , 1989). 1 9 8 9 ) . Both o f these these have widespread ssubprovinces ubprovinces h ave w i d e s p r e a d mmafic a f i c i intrusions n t r u s i o n s which w h i c h aare r e not not well constrained well c o n s t r a i n e d geochronoloyically. CJe0~hr~~n0l9gi~ally. The iisoclinally The s o c l i n a l l y folded, f o l d e d , steeply s t e e p l ydipping d i p p i n g archean a r c h e a n rocks roc off tthe overlain by tthe o h e Superior S u p e r i o r Province, P r o v i n c e , aare re o v e r l a i n by h e shallow shallow off tthe dipping Southern d i p p i n g protei-ozoic p r o t e r o z o i c rocks rocks o he S o u t h e r n Province. Province. The Port Arthur Gunflint Port A r t h u r Honocline i l o m o c l i n e consist c o n s i s t of o f the the G u n f l i n t Formation Formation ((taconite, t a c c n i t e , aalgal l g a l cchert, h e r t , limestone, l i m e s t o n e , and a n d tuffaceous t u f f a c e o u s shale) s h a l e ) and an tthe h e overlying o v e r l y i n g Rove Rove Formation F o r m a t i o n (shale, ( s h a l e , greywacke). greywacke). The age a g e of of poorly but tthese h e s e rocks r o c k s is is p o o r l y constrained constrained b u t is i s cconsidered o n s i d e r e d to t o be be Nipigon older o l d e r than t h a n 1850 1 8 5 0 Ma. Ma. (Morey, ( ? I o r e y , 1983). 1 9 8 3 ) . The X i p i g o n Plate Plate consist c o n s i s t ci o f the t h e Pass P a s s Lake Formation F o r m a t i o n (quartz ( q u a r t z aarenite), r a n i t e ) , the the Passport dolestone, R o s s p o r t Fornation F o r n a t i o n ( " rredbeds" e d b e d s " —- d o l e s t o n e , ssandstone, andstone, ( chart, i l l Formation F o r m a t i o n (nudstone) (mudstone). c h e r t , mudstone) m u d s t o n e ) aand n d tthe h e Kana Kama HFill These T h e s e tthree h r e e formations f o r n a t i o n s comprise c o m p r i s e the t h eSibley S i b l e yGroup G r o u pwhich which uncomfornibly unconiforraibly ooven v e r l iies e s archean a r c h e a n rocks r o c k s and a n d the t h eRove Rove Formation. Formation. These T h e s e sedimentary s e d i m e n t a r y rocks r o c k s are a r eoverlain o v e r l a i nbybythe t hKeweenawan e Keweenawan They hhave volcanic O s i e rGroup. Group. They a v e aalso l s o been been v o l c a n i c rocks r o c k s of o f the t h eOsler intruded by eearly i n t r u d e d by a r l y Keweenawan diabase, d i a b a s e , the t h e dominant d o n i n a ~ lithology tl i t h o l o g y in the Nipigon Plate, and late Reweenawan gabbroic stocks and dykes. METALLOGENY METALLOGEN The Lakehead Region to a wide variety of types i s hhost ost t ~ a k e h e a dR e g i o n is of mineral o f m i n e r a l deposits. deposits. The greenstone—tonalite g r e e n s t o n e - t o n a l i t e terrane terrane volcanogenic with ccontain ontain v o l c a n o g e n i c Cu-Zn Cu-Zn deposits d e p o s i t s aassociated ssociated w i t h felsic felsic volcanic v o l c a n i c rocks, r o c k s , konatiite k o r n a t i i t e (intrusive (intrusive 7 ? extrusive e x t r u s i v e 7) ? ) hosted hosted Ni—Cu deposits, hosted Ni-Cu d e p o s i t s , nafic r n a f i c intrusive intrusive h o s t e d platinum p l a t i n u m metal m e t a l group group deposits, iron deposits, and lode gold deposits. 7 The :' �Quetico Quetico subprovince subprovince contains contains subeconomic sufceconomic rare rare element element deposits group and deposits in in pegmatites pegmatitea and and platinum platinum metal metal group and Cu-Ni Cu-Xi deposits in naf Ic intrusive*. intrusives. Proterozoic. Proterozoic rocks deposits in nafic rocks contain contain numerousveins veins in in sedimentary rocks with with varied varied amounts amounts of af numerous sedimentary rocks silver, zinc, lead, harite and fluorite in; native copper silver, zinc, lead, barite and fluorite in; native copper deposits deposits in in nafic maficvulcanic volcanicrocks; rocks;and andplatinum platinum metal neta groupCu—Ni deposits in CU-xi deposits in mafic i i a f i c intrusives. intrusives. S �REFERENCES REFERENCES Card, rd, lCD. K.D. and and Ciesielski, Ciesielski, A. A. 1986: 86: Subdivisions of of the Province of Subdivisions the Superior Superior Province of the the Canadian Shield. Canadian Shield, Geoscience Geoscience Canada, Canada, 13:5—13. 13:5-13 Colvine, olvine, A.C., A.C., Fyon, Fyon, J.A., J.A., Heather, Heather, N.E., K.B., Marmont, Marnont, S., a., Smith, ith, P.M. P.M. and and Troop, Troop,D.G. D.G. 1988: 988: Archean Archean Ontario Ontario lode lode gold gold deposits deposits in in Ontario. Ontario. Geological Survey, Misc. Geological Survey, Misc. Pap., Pap., 139, 139, 136p 136p Corfu, F. Corfu, F. and and Stott, Stott, G.M. G.H. 1986: U-Pb ages 1986: C-Pb ages for for late late magnatisn magnatisn and and regional regional deformation in Belt, Superior deforiaation in the the Shebandowan Shebandowan Belt, Superior Province, Canada. Canada. Can. Earth Scie., Scie., 23:1075— Province, Can. 3. J. Earth 23:10751082. 1082. Davis, D.W. Davis, D.K. and and Jackson, Jackson, M.C. M.C. Geochronology 1988: 1988: Geochronology of of the the Lumby Lumby Lake Lake Greenstone Greenstone belt: belt: 3 Ga complex within the Wabigoon a a 3 Ga complex within the Wabigoon subprovince, subprovince, northwest northwest Ontario. Ontario. Geol. Geol. Soc. Soc. Am. Am. Bull., Bull., 100(6) :818—824. 100(6):818-824. Davis, D.W., Davis, D.W., Poulsen, Poulsen, N.H. K.H. and and Kamo, Kano, S.L. S.L. New insights 1989: 1989: Kew insights into into Archean Archean crustal crustal development development geochronology in from geochronology in the the Rainy Rainy Lake Lake area, area, Journal of Superior Superior Province, Province, Canada. Canada. Journal of Geology, Geology, 98. 98. Hyde, Hyde, R.S. R.S. Sedimentary facies 1980: 1980: Sedinentary facies in in the Archean Temiskaming Teraiskaning Group, and their Group, their tectonic implications, implications, Abitibi Abitibi greenstone belt, northeastern Ontario, Ontario, Canada. greenstone Precambrian Precanbrian Res., Res., 12:141—160. 12:141-160. Percival, J.A. Percival, J.A. and and Williams, Williams, H.R. H.R. 1989: 1989; The late late Archean Quetico Quetico accretionary accretionary complex, complex, Superior Province, Geology 17:23-25. Province, Canada. Geology 17:23-25. Paulsen, N.H. Poulsen, K.H. Archean tectonics 1984b: 1984b: tectonics and and mineralization mineralization at at Rainy Rainy Lake, Ph.D. Thesis, Thesis, Queens Queens Lake, northwestern northwestern Ontario. Ontario. Ph.D. University, Kingston, University, Kingston, Ont., Ont., 342pp.(unpublished). 342pp.(unpublished). Shegeiski, P.3. Shegelski, R.J. Archean cratonization, 1980: 1980: cratonization, emergence and red bed development, development, Lake Lake Shebandowan Shebandowan area, area, Canada. Precambrian Research, volume 12, Precambrian Research, 12, p.331—347. p.331-347. 9 �S t o c k w e l l , C.H. C.H Stockwell, 1 9 6 4 : F o u r t h report r e p o r t on o n structural s t r u c t u r a l provinces, provinces, orogenies 1964: Fourth nd t i m e - c l a s s i f i c a t i o n o f r o c k s o f t h eorogenies Canadian and of rocks of the Canadian r e ctime-classification ambrian S h i e l d . I n Age d e t e r m i n a t i o n s and Precambrian Shield. 11.determinations G e o l o g i c a l S u rand vey o f e o l o g i c a l s t u d i e s , pIn a r tAge geological Survey of n a d a , P a studies, p e r 6 4 - 1 7 ,part p p . 4II. 4 - 5 4Geological . Canada, Paper 64—17, pp.44—54. 1970: Geology of t h e Canadian S h i e l d , i n t r o d u c t i o n . I n Geology of the Canadian Shield, introduction. In Geology and economic minerals of Canada, part A. Edited by R.J.W. Douglas, Geological Survey of Canada, Economic Geology Report 1, pp.44-54. W i l l i a m s , H.R. H.R. ccillians, 1987c: Structural studies in the Wabigoon and Wood, Wood, 1986: 1986: Quetico subprovinces. Ontario Geological Survey, Open File Report 5668. J., Thurston, P.C., C o r f u , F . a n d D a v i s , D.W. J.,AThurston, P.C., Corfu, r b oand n c i e n t q u a r t z i t e s a n d c aF. n a t eDavis, s i n n D.W. orthw Ancient guartzites and carbonates O n t a r i o ~ e v i d e n c ef o r e a r l y ( A r c hin e a nnorthwestern ) stabi Ontario—-evidence for early (Archean) stability? Geol. Assoc. Can./Mineral Assoc. Can., Progr. with Abstr., 11, p.146. 10 �J9ELD TRIP 1 I I I I I I I I I I �MAFIC INTRUSIONS, MAFIC INTRUSIONS,PLATINUM-GROUP-ELEMENTS PLATINUM-GROUP-ELEMENTS MINERALIZATION MINERALIZATION AND AND DES ILES AREA GRANITOID ROCKS IN THE GRAMITOID THE LAC LAC DES Introductory Introductory Discussion Discussion and Field Field Guide Guide 36th Annual Institute Institute on Lake Lake Superior Superior Geology Geology Thunder Bay, Ontario ' Ontario by R.H. R.H. Sutcliffe Sutcliffe Ontario Geological Survey Survey 77 Grenville Street Street Toronto, Toronto, Ontario Ontario M7A lW4 1W4 11 �INTRODUCTION INTRODUCTION The The Lac Lac des des ties Iles region region provides provides an an opportunity opportunity to to examine a wide range of Late Archean plutonic examine a wide range of Late Archean plutonic rock rock types. types. This This field field trip trip will will emphasize: emphasize: the the role role of of mafic mafic magmatism magmatism in the evolution of this Late Archean plutonic in the evolution of this Late Archean plutonic terrane; terrane; the the relationship and granitoid granitoid plutonism; plutonism; relationshipbetween betweenmafic maficxnag-inas magmas and and and aspects aspects of of platinum—group—elements platinum-group-elements mineralization. mineralization. The The field field trip trip is is based based on on surveys surveys done done in in the the Lac Lac des des lies Iles area area by by the the Ontario Ontario Geological Geological Survey Survey in in 1985 1985 and and 1986. 1986. This This work work included included detailed detailed mapping mapping of of the the Lac Lac des des lies Iles Complex Complex (Sutcliffe (Sutcliffe and and Sweeny, Sweeny, 1986) 1986) and and Tib Tib Gabbro Gabbro (Smith (Smith and and Sutcliffe, Sutcliffe, 1987), 1987), regional regional mapping mapping of of the the granitoid granitoid rocks rocks (Sutcliffe (Sutcliffe and and Smith, Smith, 1988), 1988). and and aa gravity gravity survey survey of the the area area (Gupta (Gupta and and Sutcliffe, Sutcliffe, in in press). press). The The discussion discussio presented presented here here makes makes considerable considerable use use of of excerpts excerpts from from Sutcliffe (1989) and Sutcliffe et al (1989) Sutcliffe (1989) and Sutcliffe (1989) to to which which the the reader reader is is referred referred for for further further details details on on aspects aspects of of the the geochemistry geochemistry of of the the plutonic plutonic rocks. rocks. Previous Previous mapping mapping in in the the area area is is primarily primarily the the reconnaissance reconnaissance mapping mapping and and compilation compilation of al (1974). of Sage Sage et U (1974). OVERVIEW OVERVIEW Mafic racks in the Lac des lies Mafic to to ultramafic ultramafic intrusive in area trending linear zone of area form form part part of of an an east—northeast east-n Late Late Archean Archean mafic mafic piutons plutons which extends over 200 km from Atikokan Atikokan to to Lake Lake Nipigon. Nipigon. This zone parallels the boundary between Subprcvinces (Stockweli et between the the Wabigoon Wabigoon and and Quetico Qu j 1972). 1972). The The rocks rocks examined examined on on this this field field trip trip are are all a11 within within the the Wabigoon WabigoonSubprovince. Subprovince. In In the the immediate immediate region region of of the the field field trip, trip, the the mafic mafic to to ultramafic ultramafic plutons plutons are are intruded intruded into into gneissic gneissic tonalite tonalite host host rocks rocks and and are are distributed distributed in in aa circular circular pattern, pattern, the the diameter diameter of of which which is is approximately approximately 30 30 km tan (Figure (Figure1). 1). These These plutons plutons are are composed composed of of serpentinite, serpentinite, wehrlite, wehrlite, minor minor lherzolite, lherzolite, clinopyroxenite clinopyroxenite and and websterite websterite to to magnesian magnesian gabbronorite gabbronorite and and ferrogabbro ferrogabbro(Sutcliffe (Sutcliffeand and Smith Smith1988). 1988). The The Lac Lac des des Iles Iles Complex Complex (LDIC) (LDIC)is is the the largest largest of of the the mafic ma to to ultramafic ultramafic plutons plutons and and displays displays the the most most complete complete spectrum spectrum of of lithologies. lithologies. The The Tib Tib Gabbro Gabbro is is the the second second largest largest intrusion intrusion and and consists consists of of predominantly predominantly gabbronorite. gabbronorite. The The marginal marginal zones zones of of larger larger intrusions intrusions and an some some of of the the smaller smaller intrusions intrusions consist consist of of hornblendite, hornblendite, and and hornblende hornblende gabbro qabbro to todiorite. diorite. Most Most of of the the mafic mafic to to ultramafic ultramafic intrusions intrusions have have well well preserved preserved igneous igneous mineralogy mineralogy and and are are not not significantly significantlydeformed. deformed. The The form form and and tectonic tectonic setting Ic intrusions, setting of of the themafic-ultramaf mafic-ultramafic intrusions, particularly particularly the LIflC, LDIC, is is similar similar to to mafic mafic intrusions intrusions associated associated with with orogenic orogenic terrains terrains such such as as the the Mesozoic Mesozoic Alaskan Alaskan complexes complexes (Taylor (Taylor1967, 1967, Findlay Findlay 1969). 1969). Preliminary Preliminary U/Pb U/Pb zircon zircon data data indicate indicate that that the the qabbroic gabbroic rocks rocks of of the the Lac Lac des des Iles IlesComplex Comp and and the the Tib Tib Gabbro Gabbro are are 2.69 2.69 Ga Ga (D.W. (D.W. Davis, Davis, Royal Royal Ontario Ontario Museum, Sm/Nd age age of Museum, unpublished unpublished data), data), however, however, an an older older Sm/Nd of 2,738+/—27 2,738+/-27 Ma Ma is is reported reported for for the the ultramafic ultramafic rocks rocksof ofthe the LOIC LDIC by by Brugmann Brugmann and and Naldrett Naldrett(1987). (1987). 12 �A major zone of platinum-group-elements (PGE) (PGE) and Cu—Ni Cu-Ni sulphide occurs in sulphide mineralization, known as the Roby Zone, occurs gabbroic gabbroic rocks rocks of of the the LDIC. LDIC. The property is being developed by Madelaine Mines Limited and this this may become the the first first primary producer of platinum group elements elements (PGE) (PGE) in Canada mineralization in (Northern Miner Miner Press (Northern Press 1988). 1988). The PGE mineralization in the the Roby Zone Zone of the the LDIC is is associated with suiphides sulphides and altered silicates altered silicates in in gabbroic gabbroic rocks. rocks. This mineralization characteristics suggesting the control of both exhibits characteristics magmatic mixing processes (Naldrett (Naldrett and Campbell Campbell 1979; 1979; Todd et al 1982; Sharpe 1985) and volatile dominated processes (Talkington and Watkinson 1 (Talkington Watkinson 1984; 1984; Boudreau Boudreau et al 1986; 1986;Stumpf Stumpfl and Ballhaus Ballhaus 1986). 1986). PGE mineralization also also occurs occurs in in ultramafic rocks of the LDIC and in other intrusions intrusions in the PGE's were area and these occurrences occurrences indicate that PGE's concentrated at several stages in the fractionation concentrated fractionation of the mafic magmas. Two granitoid plutons consisting of hornblende tonalite and biotite biotite tonalite The tonalite intrude intrude older older gneissic gneissic tonalite. tonalite. The gneissic tonalite is dated at approximately 2.77 Ga and the tonalite 2.77 younger hornblende hornblende tonalite U/Pb zircon tonalite at 2.73 2.73 Ga by the U/Pb zircon method (D.W. (D.W. Davis, Davis, unpublished unpublished data). data). The younger younger granitoid plutons contain net—veined mafic dikes contain numerous net-veined the coexistence of mafic mafic and and other textures indicating the felsic magmas. felsic magmas. Although the association association of mafic magmas with late late Archean granitoids granitoids has not been commonly commonly recognized, there are other examples of associated Late Archean mafic and felsic magmatism in the Wabigoon Subprovince Subprovince (e.g. (e.g. Morrison Morrison et al 1986). 1986). Based on field field relationships, relationships, Sutcliffe Sutcliffe (1989) (1989) considered that hornblende tonalite mafic—ultramafic intrusions tonalite and the the mafic-ultramafic intrusions were contemporaneous. The contemporaneous. The geochronology geochronology does does not not support support this this conclusion conclusion and the the mixing textures therefore are probably than that that associated which an an older older phase phase of of mafic mafic inagmatism magmatism than which generated generated the the major major mafic—ultramafic mafic-ultramafic plutons. plutons. Further studies will test studies test this this hypothesis. hypothesis. piutonic rocks In this guide, plutonic rocks are are named using using the the classification of classification of Streckeisen Streckeisen (1976). (1976). a a LAC DES ILES IAC ILES COMPLEX Geo 1 oqy Geoloav Mapping by Pye (1968) (1968) indicated indicated that that the the Lac Lac des des Iles lies Complex (LDIC) Complex (LDIC) has has an an area area of of approximately approximately 30 30 km2. km2. The LDIC (Figure (Figure 2) consists of a predominantly ultramafic sequence centred on Lac des lies and predominantly gabbroic sequences south of the lake (Pye, Watkinson and seauences fPve. 1968; 1968: Watkinson Dunning, description given here is largely based ~ u i n i n ~1979). 1979). , The description on mapping by Sutciiffe Sutcliffe and Sweeny (1986) (1986) and the work of Sutcliffe et al (1989). Sutcliffe (1989). Details of the mineral assemblages assemblages textures for and textures for rock rock types types are are summarized summarized in in Table Table 1. 1. A gravity study study by Gupta Gupta and and Sutcliffe Sutcliffe (in (in press) press) indicates that the LDIC LOIC is is associated with aa 30 30 mgal mgal gravity gravity . - . 13 - �high high and and is is modelled modelled as as aa funnel funnel shaped shaped body body part part of of which which extends to aa depth depth of of 4.5 4.5 km. tan. extends to The The ultramafic ultramafic sequence sequence is is composed composed of of two two coalescing coalescing centers which are defined by the different distributions centers which are defined by the different distributions of of ultramafic ultramafic lithologies lithologies and and by by the the attitudes attitudes of of igneous igneous layering layering (Figure (Figure2). 2). Hornblendite Hornblendite to t o pyroxene pyroxene hornblendite hornblendite and hornblende gabbro occur along the western and hornblende gabbro occur along the western margin margin of of the the LDIC LDIC and, and, with with increasing increasing modal modal pyroxene, pyroxene, grade grade into into pyroxenite. pyroxenite. The The hornblende-rich hornblende-rich lithologies lithologies are are invaded invaded and and brecciated brecciated by by veins veins of of hornblende hornblende diorite diorite to t o quartz quartz diorite. diorite. The The northern northern ultramafic ultramafic center center is is nearly nearly circular circular in in plan with a diameter of approximately 4 km (Figure plan with a diameter of approximately 4 tan (Figure 2) 2) and and consists consists of of several several cycles cycles of of serpentinite serpentinite and and wehrlite, wehrlite, olivine livine clinopyroxenite clinopyroxenite and and clinopyroxenite, clinopyroxenite, and and websterite websterit too gabbronorite. gabbronorite. Lindhardt Lindhardt and and Sues Bues (1987) (1987) have have shown shown that tha these hese cycles cycles are are typically typically 100 100 to t o 500 500 mm thick thick in in plan plan and and individual individual layers layers can can be be traced traced along along strike strike for for up up to t o 1.5 1.5 km. Olivine cumulates are most abundant around the southern tan. olivine cumulates are most abundant around the southern and and eastern eastern perimeter perimeter of of the the center center and and the the rocks rocks become become more pyroxene—rich towards the nothwest. The more pyroxene-rich towards the nothwest. The absence absence of of distinct distinct marker marker horizons horizons and and extent extent of of outcrop outcrop exposure exposure places places significant significant limitations limitations on on the the interpretation interpretation of of the lateral lateral continuity continuity and and thickness thickness of of the the cycles. cycles. Modal Modal layering layering due due to t o variation variation in in proportions proportions of of plagiociase plagioclase and and pyroxenes, pyroxenes, olivine olivine and and clinopyroxene, clinopyroxene, and a orthopyroxene orthopyroxene and and clinopyroxene clinopyroxene is is observed. observed. Generally Generally the the modal modal layers layers are are 11 to t o 20 20 cm cm thick thick and and are are continuous continuous for for meters. meters. Minor Minor disseminated disseminated euhedral euhedral grains grains of of chromite chromite are are enclosed enclosed in in cumulus cumulus olivine olivine and and clinopyroxene clinopyroxene and and are are locally locally concentrated concentrated in in layers layers up up to t o 11 cm cm wide wide in in the the northern northern center. center. Igneous Igneous lamination lamination defined defined by by planar planar alignment alignment of of pyroxenes pyroxenes or or plagioclase plagioclase is is also also observed observed at at several everal localities. localities. Layer Layer attitudes attitudes indicate indicate that that the the northern orthern center center has has an an upright upright funnel—shaped funnel-shaped form. form. Minor Min discordant serpentinite dikes, which iscordant serpentinite dikes, which contain contain angular angular fragments fragments of of pyroxenite pyroxenite intrude intrude the the northern northern ultramafic ultramafic center. The The southern southern ultramafic ultramafic center center is is elliptical elliptical in in plan plan with with an an irregularly irregularly shaped shaped wehrlite wehrlite core core centered centered on on Southeast Southeast Angle Angle Bay Bay of of Lac Lac des des lies. lies. The The wehrlite wehrlite core core is is surrounded surrounded by by websterite websterite which which in in some some areas areas contains contains inclusions inclusions of of wehrlite. wehrlite. Along Along the the eastern eastern margin margin of of the the center center the the websterite websterite grades grades into into gabbronorite. gabbronorite. The The southern southern center center is is predominantly predominantly composed composed of of massive massive rocks rocks and and lacks lacks well well defined defined igneous igneous layering. layering. The The ultramafic ultramafic rocks rocks are are partially partially separated separated from from the the gabbroic abbroic rocks rocks south south of of Lac Lac des des Iles lies by by aa septum septum of of tonalite. onalite. Watkinson Watkinson and and Dunning Dunning (1979) (1979)considered considered that thatthe ultramafics ltramafics were were emplaced emplaced later later than than the the gabbroic gabbroic rocks rocks based ased on on the the presence presence of of gabbroic gabbroic inclusions inclusions in inthe the uitramafics. ultramafics. The The only only clearly clearly defined defined gabbroic gabbroic inclusions inclus observed and observed during during the the current current study study are are troctoiitic t and not readily readily related related to t othe thegabbroic gabbroicsuite. suite. 14 �A 50 m wide, composite dike consisting of olivine A gabbronorite, gabbronorite, olivine websterite to lherzoiite lherzolite with hornblende diorite margins outcrops on the south—west south-west shore of Lac des This des lies lies and and along along the the west west side side of of the the gabbro. gabbro. This dike is olivine—rich olivine-rich (picritic) (picritic) and is potentially a feeder for the southern ultramafic center Gabbroic rocks occur largely in the southern part of the LDIC host to to the the Pd, Pd, Pt the LDIC (Figure (Figure 2) 2) and and are are host Pt mineralization of Based largely on detailed detailed mineralization of the the Roby Roby Zone. Zone. Based studies studies of drill core in in the immediate immediate vicinity of the the Roby Zone, Watkinson and Dunning (1979) (1979) indicated that the the gabbro could ould be divided into into two two major units known as the the Eastern Gabbro abbro (EG) (EG) and and Western Western Gabbro Gabbro (WG). (WG). As defined by Watkinson and Dunning (1979), the atkinson (1979), the WG consists consists of interlayered nterlayered gabbroic, noritic, pyroxenitic, and anorthositic northositic rocks rocks and the the EG consists consists of oxide—rich oxide-rich gabbroic abbroic and and noritic noritic rocks. rocks. This distinction is significant because ecause the the Roby Zone Zone is is interpreted interpreted to to occur along along the the contact ontact of of the the two two units. units. Macdonald (1985), (1985), Sutcliffe and Sweeny weeny (1986), (1986), and Sweeny and Edgar (1987) (1987) suggested suggested that the the relationships relationships between the the units units are complex complex and and that that many of the the layers layers identified identified in in drill core core by Watkinson Watkinson and and Dunning (1979) (1979) are are separate separate intrusive intrusive phases. phases. The gabbroic part of the LDIC consists of a leuco— leucogabbro to anorthositic anorthositic gabbro unit and a unit of predominantly the vicinity vicinity of the Roby predominantly gabbronorite. gabbronorite. In the Zone, these units correspond correspond with the EG and WG respectively, respectively, although although in detail there is not a simple geographic subdivision geographic subdivision (Figure (Figure 3). 3). As defined by Sutcliffe et al (1989), (1989), both the EG and WG contain cumulus plagioclase, oclase, however, however, the the WG contains contains cumulus cumulus orthopyroxene orthopyroxene or alteration This teration products pseudomorphing orthopyroxene. This represents a different different definition of the units than than that of Watkinson Watkinson and and Dunning Dunning (1979), (1979), however, however, because because there there is is an an important geographic geographic connotation connotation to to the the terms tens EG and WG in the Roby Zone, Zone, these these names names have have been been retained. retained. The EG displays igneous igneous lamination lamination and weakly developed wispy modal pervasively altered obscuring the primary layering and is pervasively igneous assemblages. WG typically consists of igneous assemblages. The WG gabbronorite Locally, in gabbronorite to norite and is fresh to altered. Locally, the the vicinity of the the "D 'ID Zone", the the WG contains contains cumulus cumulus olivine. olivine. Within the the WG near the EG/WG EG/WG contact, pegmatitic gabbro, gabbro breccia, gabbronorite, gabbronorite, and clinopyroxenite clinopyroxenite form an arc—shaped arc-shaped zone zone of of variable variable width width (Figure (Figure 3). 3). In this this part of the the WG, pegmatitic gabbro phases occur occur primarily primarily as as inclusions, inclusions, pegmatoidal pegmatoidal segregations segregations and and discordant discordant pegmatite pegmatite dikes. dikes. Pegmatitic phases are rare in the the EG. EG. The WG truncates truncates the igneous lamination and weakly developed developed modal layering layering of of the the EG, EG, indicating indicating that that the the WG WG is younger younger than than the the EG. EG. An intrusion medium—grained hornblende hornblende gabbro gabbro to to intrusion of medium-grained leucogabbro with minor coarse—grained coarse-grained hornblende melagabbro occurs age of the hornblende occurs south south of of the the EG EG and and WG. WG. The aae 15 �gabbro gabbro relative relative to to other other units units of of the the LDIC LDIC has has not not been been determined. determined. Late dikes of microdiorite—gabbro microdiorite-gabbro intrude intrude the the gabbroic gabbroic rocks rocks and locally result result in in intrusion intrusion breccia consisting consisting of of angular angular gabbroic gabbroic and less less common common tonalitic tonalitic fragments fragments in in aa fine—grained fine-grained igneous igneous matrix. matrix. Late Late leucocratic leucocratic tonalitic tonalitic dikes dikes and and veins veins also also cross cross cut cut the the gabbroic gabbroic rocks. rocks. Petrological Petrological and and geochemical geochemical studies studies by by Sutcliffe Sutcliffe et al (1989) indicate that that distinct distinct magma sequences sequences can can be be (1989) indicate recognized on a basis of crystallization crystallization order, differences differences in in cumulus cumulus minerals, minerals, intrusive intrusive relations relations and and geochemical geochemical differences. These sequences are 1) hornblende differences. These sequences are 1) hornblende gabbro, gabbro, 2)gabbro 3) ultramafic. ultramafic. Where Where there there is is 2)gabbro and and gabbronorite gabbronorite and and 3) evidence evidence of intrusive intrusive relations relations the most primitive primitive sequences sequences are are emplaced emplaced late late and and toward toward the the north north end end of of the the complex. complex. In In the the absence absence of of rocks rocks representative representative of of liquids, liquids, parental parental magma magma compositions compositions can can only only be be constrained constrained by by the the compositions compositions of of cumulus cumulus phases. phases. Mineral Mineral chemistry chemistry and and crystallization sequences crystallization sequences indicate indicate that that the the parental parental magmas of of the the gabbroic gabbroic and and ultramafic sequences sequences had tholeiitic tholeiiti basalt basalt parental parental magmas magmas with with high high alumina alumina and and picritic picritic affinities affinities respectively. resvectivelv. - .. . - .>*:..; - . . . . . + . . . . Mineralization Mineralization . . 5. . .. ;teg*'.:;. :p , Exploration Exvloration by bv Texasgulf Texasaulf Canada Limited and Boston Bay Bav Mines 1976 outlined Mines Limited ~imitedin in 1975 1975 and and1976 outlined 20.4 20.4 million million tonnes tonne; of 0.2% Cu ++ Ni Ni of mineralization grading grading 66 ppm Pd and Pt and 0.2% in long Roby Roby Zone Zone along along the the EG/WG EG/WG contact contact in the the 600 600 m long (Northern (Northern Miner Miner Press Press 1976). 1976). Pt/(Pt+Pd) Pt/(Pt+Pd) is is in in the the range range of of 0.1 0.1 (Watkinson (Watkinson and and Dunning Dunning 1979) 1979) to to 0.2 0.2 (Sutcliffe (Sutcliffeet al 1989). 1989). Drill Drill core core sections sections show show that that the the highest highest grade grade mineralization WG immediately immediately adjacent adjacent to to the the mineralization occurs occurs in in the the WG contact with the EQ (Figure 4). contact with the EG (Figure 4). PGE PGE mineralization mineralization in in the the gabbroic gabbroic rocks rocks is is associated associated with with 1) 1) finely finely disseminated disseminated sulphide sulphide mineralization mineralization (1 (1to to 22 modal sulphide) in in altered altered pyroxenite pyroxenite sheets sheets along along the the modal %% sulphide) WG/EG WG/EG contact contact 2) 2) disseminated, disseminated, bleb-like bleb-like and and net-textured net-textured sulphide sulphide mineralization mineralization in in gabbronorite gabbronorite (1 (1 to to 44 modal modal %% sulphide) sulphide) and and 3) 3) coarse coarse interstitial interstitial sulphide sulphide in in pegmatitic peg-matitic gabbro. gabbro. In In addition addition to to mineral mineral assemblages assemblages noted noted in in Table Table 1, rare euhedral apatite is observed in mineralized 1, rare euhedral apatite is observed in mineralized gabbros gabbros in in the the Roby Roby Zone. Zone. AA detailed detailed study study of of drill drill core core from from the the Roby Roby Zone Zonee (Dunning Watkinson and Dunning -(Dunning 1979; 1979; Watkinson Dunning 1979; 1979; Cabri Cabri and and Laflamme Laflamme 1979) 1979) showed showed that that vysotskite vysotskite and and braggite braggite are are the the most most abundant abundant platinum platinum group group minerals minerals (PGM) (PGM) along along with with minor minor isomertieite, isomertieite, merenskyite, merenskyite, kotulskite, kotulskite, sperrylite sperrylite and and moncheite. moncheite. In In addition, addition, electrum electrum and and Pt—Fe Pt-Fe alloys alloys have have been been identified identified by by Sweeny Sweeny (1989). (1989). The The PGE PGE mineralization mineralization is is associated associated with with chalcopyrite, chalcopyrite, pyrrhotite, pyrrhotite, pentlandite pentlandite and and pyrite pyrite interpreted interpreted by by Watkinson Watkinson and and Dunning Dunning (1979) (1979) as as being being slightly slightly metamorphosed metamorphosed equivalents equivalents of of primary primary exsolution exsolution from from monosulphide nionosulphide solid solid solution. solution. Millerite Millerite and and violarite violarite - a 16 �are present in secondary assemblages assemblages (Watkinson (Watkinson and Dunning 1979). PGM in the Roby Zone Zone are most commonly found with postcumulus postcumulus hydrosilicates hydrosilicates near silicate—suiphide silicate-sulphide interfaces interfaces (Talkington and Watkinson 1984). (Talkington Watkinson 1984). In this association, association, the the PGM occur occur both within the the hydrosilicates hydrosilicates and at the the sulphide—silicate interface. sulphide-silicate interface. pGE's also occur in the ultramafic rocks with with sparsely PGE's disseminated disseminated to to net-textured chalcopyrite, pyrrhotite, and pentlandite pentlandite (ci (<1 modal modal %% sulphide). sulphide). This This type type of of mineralization mineralization is is most commonly commonly associated associated with websterite websterite and gabbronoritic gabbronoritic phases of the northern and southern southern ultramafic ultramafic centers. centers. Field and geochemical relations indicate that the EG and WG cumulates cumulates crystallized from a common magma and were subsequently subsequently emplaced as crystal mushes with the more fractionated fractionated and and hydrous hydrous EG EG emplaced emplaced first. first. Lower Lower concentrations concentrations of PGE, Au and S in the EG relative relative to WG suggests the magma prior to suggests that that suiphides sulphides were removed from the to the the crystallization crystallization of the EG cumulates cumulates or that the the parental magma was not saturated saturated in in sulphides sulphides at the time time of cumulate cumulate formation. have localized localized some some sulphide sulphide formation. Magma mixing may have mineralization mineralization along along the the EG/WG EG/WG interface. interface. However, However, because because the the phases phases are are interpreted interpreted to to have have been been emplaced emplaced as as mushes, mushes, there there was probably limited limited opportunity for for sulphides sulphides to to interact interact with with magma. magma. This would suggest suggest aa low low R—factor R-factor and and that this this process may not be the explanation explanation for the high grade grade mineralization. mineralization. Fe—rich Fe-rich pyroxene pyroxene cumulate cumulate sheets sheets intruded intruded into into the the EG EG and WG are are another another possible possible source source of of PGE PGE in in the the Roby Roby Zone. Zone. The close close spatial association of the sheets sheets and mineralization mineralization suggest suggest that that the the pyroxene pyroxene cumulates cumulates are are aa likely source of PGE. As previously noted, the altered likely source of PGE. As previously noted, the altered pyroxene pyroxene cumulate cumulate sheet sheet at at the the EG/WG EG/WG contact contact contains contains particularly particularly high-grade high-grade mineralization. mineralization. Limited Limited sampling sampling of of this this group of rocks rocks suggests suggests that, that, in general, they have higher higher PGE PGE contents contents than than other other samples samples of the ultramafic ultramafic suite. suite. Mixing of magmas which formed the pyroxene cumulates cumulates and the the gabbro gabbro cumulates cumulates may have played a role in causing causing sulphide sulphide saturation saturation in in the the pyroxene pyroxene cumulates. cumulates. The The association association of of PGM PGM with secondary secondary sulphides sulphides and and altered altered silicates silicates lead lead Watkinson and Talkington Talkington (1984) (1984) to to suggest suggest that that fluid fluid processes were active active in in mobilization mobilization and concentration concentration of of PGE PGE in in the the Roby Roby Zone. Zone. The The role role of of fluids fluids in PGE mineralized zones PGE mineralized zones in in the the Bushveld Bushveld and and Stillwater Stillwater Complexes Complexes is is indicated indicated by by the the occurrence occurrence of of pegmatoids, pegmatoids, volatile-rich phases and hortonolite replacement phases and hortonolite replacement pipes pipes (Todd (Todd et al 1982; 1982; Stumpfl Stumpfl and and Balihaus Ballhaus 1986; 1986; Schiffries Schiffries 1982; 1982; Stumpf and Rucklidge Rucklidge 1982). Stumpfl1 and 1982). Fluid-bearing Fluid-bearing phases phases and and fluid fluid inclusions in in both both complexes complexes suggest suggest fluids fluids that that may may be be rich rich inclusions in Cl (Boudreau (Boudreau et al 1986; 1986; Stumpfl Stumpfl and and Balihaus Ballhaus 1986). 1986). Several Several features features of of the the Roby Roby Zone Zone indicate indicate the the importance importance of of aa volatile volatile rich rich magma. magma. These These include: include: the the association association of of PGM PGM with postcumulus postcumulus hydrosilicates hydrosilicates near near 17 �silicate—sulphide silicate-sulphide interfaces; interfaces; the the association association of of PGM PGM with with pegmatitic pegmatitic phases phases and and the the mineralized breccia breccia zones zones cored cored by peginatitic gabbro which which appear appear to to have have been fluid channelpegmatitic gabbro channelways; ways; and and the the highly highly fractionated fractionated Pd/Ir. Pd/Ir. Cl-rich Cl-rich apatite apatite in in mineralized mineralized gabbro gabbro suggest suggest that that the the fluids fluids associated associated with the the mineralizing mineralizing process process were were Cl—rich. Cl-rich. Brugmann Brugmann et al a1 (1989) (1989) have have recently recently proposed proposed aa modification of this hypothesis and suggested modification of this hypothesis and suggested that that the the volatile volatile content content of of the the residual residual magma triggered triggered partial re— remelting melting of of the the gabbro gabbro cumulates cumulates in in a process referred referred to to as as "constitutional "constitutional zone zone refining". refiningn. Occurrences Occurrences of of PGE-bearing PGE-bearing sulphides sulphides in in the the ultramafic ultramafic sequence sequence are are hosted hosted mainly mainly by by websterite websterite at at the the top top of of cyclic cyclic units units and and by by peridotites peridotites at the the base of of overlying overlying units. units. These These occurrences occurrences have have not not been been studied studied in in detail detail but but may represent represent stratifonu stratiform mineralization mineralization related related to to the the interaction interaction of of fractionated fractionated magma magma with with aa new new magma magma pulse pulse in in the the ultramafic ultramafic chamber chamber (Sutcliffe (Sutcliffe and and Sweeny Sweeny 1986; 1986; Brugmann Brugmann and and Naldrett Naldrett 1987). 1987). The The presence presence of of this this mineralization, mineralization, however, however, emphasizes emphasizes that that ?GE's PGE1swere were concentrated concentrated at at several several stages stages in in the the fractionation fractionation of of the the LDIC LDIC magmas. magmas. TIB TIB GABBRO GABBRO Geology Geoloav The The Tib Tib Gabbro Gabbro (Figure (Figure5) 5) is a layered layered intrusion intrusion with with an an area area of of approximately approximately 25 25 km2 located located approximately approximately 15 15 km northwest of the Lac des Iles Complex. The intrusion was northwest of the Lac des Iles Complex. The intrusion was mapped mapped by by Kaye Kaye (1966) (1966) and and Smith Smith and and Sutcliffe Sutcliffe (1987). (1987). The The information summarized here is largely from Smith (in information summarized here is largely from Smith (in press). press). Petrological Petrological and and geochemical geochemical studies studies are are in in progress progress and and most most of of this this summary summary is is based based in in field field observations. observations. The The gabbro gabbro is is emplaced emplaced into into an an older older suite suite of of foliated foliated to to gneissic gneissic biotite biotite tonalite tonalite which outcrops outcrops around around the the eastern, eastern, northern northern and and aouthern aouthern margins margins of of the the intrusion. intrusion. AA younger suite of megacrystic granodiorite and younger suite of megacrystic granodiorite and granite granite intrudes intrudes the the Tib Tib Gabbro Gabbro and and older older gneissic gneissic tonalites. tonalites. The The Tib Tib Gabbro Gabbro is is characterized characterized by by well well preserved preserved primary primary igneous igneous mineralogy mineralogy and and moderately moderately well well developed developed layering. layering. Layer Layer attitudes attitudes indicate indicate that that the the intrusion intrusion is is funnel funnel shaped shaped and and has has been been tilted tilted to to the the northeast. northeast. The The southwest southwest part part of of the the gabbro gabbro therefore therefore represents represents the the base base of survey by Gupta of the the exposed exposed section. section. AA gravity gravity survey Gupta and and Sutcliffe Sutcliffe (in (in press) press) supports supports this this interpretation interpretation and and models models the the 16 16 mgal mgal gravity gravity high high associated associated with with the the intrusion intrusion as as aa tilted tilted basin-shaped basin-shaped body. body. The The intrusion intrusion is is divided divided into into four four zones zones by by Smith Smith and and Sutcliffe Sutcliffe (1987) (1987) which which from from the the southwest southwest to to northeast northeast are are the the Border, Border, Lower, Lower, Middle Middle and and Upper Upper Zones. Zones. The The 50 50 to to 150 150 mm thick thick Border Border Zone Zone is is defined defined on on aa basis basis of of the the abundance abundance of of coarse coarse grained grained to to pegmatoidal pegmatoidal gabbro gabbro which which occurs occurs around around the the northwestern, northwestern, western western and and southern southern margins margins of of the the intrusion. intrusion. The The Lower Lower and and Middle Middle zones zones probably probably represent represent distinct distinct magma magma pulses pulses which which crystallized crystallized from from the the base base upwards. upwards. These These 18 18 �I I I I I I I zones record the crystallization of evolving cumulus assemblages which results in a mappable igneous stratigraphy assemblages stratigraphy with pyroxene pyroxene rich rich cumulates cumulates near the the base and plagioclase— plagioclaseand magnetite-rich magnetite—rich cumulates cumulates near near the the top. top. The Upper Upper Zone Zone consists of consists of amphibole-rich amphibole-rich gabbro gabbro and and is is not not well well layered. layered. wide Lower Lower Zone Zone consists consists of of aa sequence sequence of The 1.5 1.5 kin km wide layered gabbronorite gabbronorite with layers orthopyroxenite and layers of orthopyroxenite melagabbronorite melagabbronorite (pyroxene (pyroxene cumulate) cumulate) near near the the base. base. Above the orthopyroxenite orthopyroxenite the lithologies lithologies become more leucocratic leucocratic anorthosite appears and anorthosite appears as as distinct distinct layers. layers. The The top top of of the the by magnetite-rich magnetite-rich gabbronorite with zone is marked by leucocratic layers. leucocratic layers. The 1.6 1.6 km wide Middle Zone Zone is is predominantly gabbronorite, however, leucocratic predominantly leucocratic units are more abundant Conformable pegmatite abundant than than in in the the Lower Lower Zone. Zone. Conformable pegmatite layers and discordant dikes are common in the upper part of magnetite— the zone. the zone. The top top of the zone is again marked by - magnetite. rich gabbronorite. gabbronorite; The Upper Upper Zone Zone is is characterized characterized by by hornblende—rich, hornblende-rich, massive to to weakly weakly layered layered gabbronorite qabbronorite with with cumulus cumulus apatite. apatite. The layers form a concentric pattern with a shallow shallow inward dip. dip. Leucocratic quartz—bearing quartz-bearing granulite granulite forms forms aa discontinuous septa between the Upper and Middle Zones Zones and the unit is interpreted to be metamorphosed tonalite tonalite but may alternatively be a alternatively a final final product product of of fractionation. fractionation. Layering in the Tib Gabbro is comparable to that developed in developed in the the Mulcahy Mulcahy Gabbro Gabbro (Morrison (Morrison et al 1986). 1986). Planar lamination of feldspars and pyroxene is found throughout the throughout the intrusion. intrusion. Modal layering layering defined by changing compositions compositions of cumulus minerals is best developed the upper upper part part of the the Lower Lower Zone and and occurs occurs in both both in the cyclic and intermittent intermittent layer layer sequences. sequences. Distinctive modal layers include: othopyroxenite othopyroxenite (orthopyroxene (orthopyroxene cumulate) cumulate); websterite (clinopyroxene orthopyroxene cumulate) websterite (clinopyroxene — orthopyroxene cumulate); magnetite—rich anorthosite (plagioclase (plagioclase cumulate) and magnetite-rich cumulate. The modal modal layers are usually tens of centimetres cumulate. in width width and persist for for tens tens of metres metres along along strike. strike. - - e 3 . p Mineralization Mineralization The The Tib Tib Gabbro Gabbro is is the the second second largest of the the mafic des lies Iles area area and and is an an exploratiion intrusions in the lac des target for Intermittent target for PGE PGE and and Cu—Ni Cu-Ni mineralization. mineralization. Intermittent exploration exploration on the intrusion since 1966 has outlined a Cu—Ni sulphide number of areas areas of disseminated Cu-Ni sulphide mineralization in the gabbro, some mineralization some of which contain associated PGE. associated PGE. To To date, the the most significant significant mineralization that has been reported is at the Kuhner Occurrence in the the Border Zone Zone along the south south margin of the intrusion. At this intrusion. this location, location, net textured textured sulphide sulphide mineralization is gabbronorite and mineralization is present in coarse coarse grained gabbronori assay values up to 190 ppb Pt, 390 ppb Pd, 120 ppb Au, 1140 ppm Ni Mi and 710 710 ppm Cu Cu are are reported reported by by Smith Smith (in (in press) press) 19 �GRANITOIDS GRANITOIDS AND AND RELATED RELATED ROCKS ROCKS Tonalite Tonalite Gneissic Gneissic to to strongly strongly foliated biotite tonalite tonalite gneiss gneiss is is the the oldest intrusive intrusive phase ~ h a S ein in the the Lac des lies lies area area and and is is the the host rock rock into into which most of the the younger younger plutons are are emplaced. emplaced. Discordant Discordant intrusive intrusive relations relations between between the the mafic— maficultramafic ultramafic intrusions intrusions and tonalitic tonalitic gneiss gneiss are are locally locally developed developed on on the the margins margins of of intrusions intrusions such such as as the the Tib Tib Gabbro, Gabbro, where where gabbro gabbro apophyses apophyses cross-cut the the fabric fabric of of the the gneiss gneiss and and tonalitic tonalitic gneiss gneiss enclaves enclaves occur occur in in the the gabbro. gabbro. Two Two late late granitoid granitoid plutons plutons occupy occupy the the center center of of the the circular circular structure structure defined defined by by the the mafic mafic intrusions. intrusions. These These plutons plutons also also discordantly discordantly intrude intrude the the tonalitic tonalitic gneiss gneiss and contain contain tonalitic tonalitic gneiss gneiss enclaves. enclaves. The The plutons plutons include include aa hornblende—bearing hornblende-bearing tonalite tonalite with an area of 150 150 km2 and aa younger, younger, foliated foliated to to massive massive biotite biotite tonalite tonalite to to microcline microcline zuegacrystic granodiorite pluton pluton which locally megacrystic granodiorite locally contains contains enclaves enclaves of of the the hornblende-bearing hornblende-bearing tonalite. tonalite. The The hornblende hornblende tonalite tonalite is is intruded intruded by by numerous numerous mafic to to intermediate intermediate dikes dikes and and exhibits exhibits textures textures indicating indicating the the coexistence coexistence of of mafic mafic and and felsic felsic rnagmas magmas (Sutcliffe (Sutcliffe1989). 1989). These These textures textures are are the the focus focus of of the the field field trip trip stops stops in in the the granitoid granitoid rocks. rocks. The The association association of of early early tonalitic tonalitic gneisses gneisses and and later later massive terranes of of the the massive plutons plutons is is common common in in granitoid granitoid terranes western western Superior Superior Province Province (Schwerdtner (Schwerdtner et et al. al. 1979). 1979). Modal Modal analyses analyses of of representative representative tonalites tonalites and and other other samples samples are are shown shown in in figure figure 6. 6. The The tonalite tonalite has has aa medium— mediumto to coarse—grained, coarse-grained, hypidiomorphic hypidiomorphic texture texture and is is massive massive to to weakly weakly foliated. foliated. The The presence presence of of coarse coarse (1 (1 to to 22 cm), cm), blocky blocky to to prismatic prismatic hornblende hornblende is is aa conspicuous conspicuous feature feature of of the the pluton. pluton. The The major major mineral mineral phases phases are: are: 22 to to 44 mm mm subhedral, subhedral, tabular plagioclase of composition tabular plagioclase of composition An28—34 An28-34 (40—58%); (40-58%); anhedral, ; 0.5 anhedral, weakly weakly strained strainedquartz quartz(29—38%) (29-38%); 0.5 to to 22 mm brown—green brown-green pleochroic pleochroic biotite biotite (7—16%) (7-16%) and and subhedral subhedral to to prismatic, prismatic, 22 mm mm to to 22 cm, cm, green green pleochroic pleochroic hornblende hornblende (1(115%). 15%). Accessory Accessory phases phases are are sphene, sphene, apatite apatite and and zircon. zircon. Plagioclase Plagioclase locally locally displays displays weak weak to to moderate moderate oscillatory oscillatory zoning zoning and and minor minor alteration alteration to to sericite sericite and and epidote. epidote. Although Although hornblende hornblende is is locally locally subordinate subordinate to to biotite, biotite, this this lithological litholoqical unit unit is is referred referred to to as as hornblende hornblende tonalite tonalite throughout throughout the the paper paper to to distinguish distinguish it it from from the the younger younger biotite biotite tonalite tonalite in in which which hornblende hornblende is is absent. absent. Mela-tonalite containing containing up up to to 60% 60% hornblende hornblende occurs occurs as as Mela-tonalite irregular irregular patches patches and and intrusive intrusive dike-like dike-like bodies bodies up up to to several several meters meters in in extent extent which which grade grade into into normal normal tonalite. tonalite. Mela-tonaiite Mela-tonalite is is the the major major constituent constituent in in 22 to to 3% 3% of of outcrops outcrops in in the the hornblende hornblende tonalite tonalite pluton. pluton. Hornblende Hornblende in in mela—tonalite mela-tonalite is is typically typically coarse, coarse, occurring occurring as as grains grains up up to to 22 cm cm of of euhedral, euhedral, prismatic prismatic to to skeletal skeletal habit. habit. Textural Textural gradations between between skeletal skeletal hornblende hornblende and and coarse coarse blocky blocky gradations hornblende hornblende are are present. present. The The mela—tonalites mela-tonalites have have complex complex a 20 �internal characterized iharacterized by comb—layering comb-layering and and iternal structures struc colloform colloform structures structures of of mafic mafic material material in in felsic felsic host. host. Skeletal hornblende is best developed in mela-tonalite mela-tonalite adjacent to adjacent to mafic-felsic mafic-felsic interfaces. interfaces. Euhedral skeletal skeletal hornblende grains also occur as wispy schlieren in hornblende tonalite tonalite and in hornblendite units of mafic intrusions. intrusions. The skeletal skeletal grains have hollow hollow cores cores plagioclase. These containing biotite or biotite + + plagioclase. These between amphibole and assemblages probably reflect reaction between trapped liquid. trapped liquid. Large rounded hornblende hornblende aggregates aggregates as as large large as as 22 cm cm in in proto—orbicular texture according diameter locally display a proto-orbicular to the classification of Leveson (1966). (1966). These are present tonalite adjacent to mela-tonalite and mafic dikes. The in tonalite The pale—green pleochroic composite grains have central areas of pale-green hornblende intergrown intergrown with quartz and feldspar producing a sieve texture. sieve texture. Their rims are composed composed of of dark—green dark-green pleochroic grains grains of interlocking interlocking prismatic prismatic hornblende. hornblende. A breccia pipe, approximately 300 m in diameter, is emplaced into the western end of the hornblende-bearing hornblende—bearing tonalite pluton. tonalite pluton. The pipe consists consists of of sub—angular sub-angular hornblende—tonalite fragments hornblende-tonalite fragments and minor hornblendite fragments set in a matrix of fine—grained, fine-grained, comminuted comminuted and and silicified silicified tonalite. tonalite. Tonalite fragments fragments within the the breccia breccia are of the same composition composition and texture as the host rock but contain 2 to 3 cm thick silicified, sericitized and epidotized epidotized rinds. rinds. Mafic dikes dikes and hybrid hvbrid textures textures A wide range of textures indicative indicative of contemporaneous mafic and felsic felsic magmatism is developed associated with the emplacement emplacement of mafic to intermediate dikes in hornblende tonalite. tonalite. The dikes range from parallel-sided intrusions, intrusions, 11 to 2 m wide, with sharp contacts which cross cut foliation foliation disaggregated linear inclusion swarms in in the tonalite, to disaggregated which the the mafic mafic magma magma appears appears to to have have lost lost internal internal contiguity. contiguity. These structures structures are are similar similar to to textures textures indicative of contemporaneous indicative contemporaneous mafic—felsic mafic-felsic magmatism magmatism and and mixing reported reported by Blake Blake (1981), (1981), Marshall Marshall and and Sparks Sparks (1984), (1984). Furman and Spera (1985) (1985) and Hyndman and and Foster Foster (1988). (1988). Mafic dikes are are observed in in approximately 15% 15% of the the outcrops of the the hornblende hornblende tonalite tonalite pluton. The dikes are generally fine—grained, fine-grained, lack chilled margins and are typically back-veined by tonalite which typically back-veined forms wispy nets separating separating rounded rounded centimeter— centimeter- to to decimeter-sized mafic mafic globules. globules. This texture is described as net-veining by Marshall and and Sparks Sparks (1984). (1984). With increased veining the net-textured dikes grade into disaggregated disaggregated dikes dikes in in which which the the mafic mafic to to intermediate intermediate rock forms rounded and elongate elongate bodies bodies which which resemble resemble pillows In pillows of extrusive extrusive rocks rocks in in the the host host tonalite. tonalite. In contrast to other descriptions of similar structures in Tertiary Tertiary intrusives intrusives (Vogel (Vogel 1982; 1982; Brown Brown and and Becker Becker 1986; 1986; 21 �Marshall and Marshall and sparks Sparks 1984), 1984), chilled chilled rinds rinds on on "pillows" npillowsm at at Lac Lac des Iles are generally absent. des Iles are generally absent. Mineralogically the moderately fresh Mineralogically the dikes dikes consist consist of of moderately fresh 0.5 mm laths of plagioclase (andesine An4o_46) and 1 mm 0.5 mm laths of plagioclase (andesine An40-46) and 1 mm grains of prismatic hornblende to pale green fibrous grains of prismatic hornblende to pale green fibrous amphibole, and amphibole, and minor minor biotite, biotite, quartz, quartz, apatite apatite and and opaques. opaques. The mafic to intermediate intermediate dikes locally locally display discontinuous hornblende-rich hornblende—rich reaction reaction rims rims adjacent adjacent to to host host discontinuous In addition, addition, mela-tonalite mela-tonalite to tonalite. tonalite. In to hornblendite hornblendite phases phases are generally are generally associated associated with with zones zones of of dike dike emplacement. emplacement. Magma Mixinq Mixing Maama Field evidence maamas has has evidence suggests suaaests that that mixing mixina between between magmas - --taken place. Geochemical data does not readily constrain the taken place. ~eochemiciidata does not readily constrain the mixing process process due due to of fractionation mixing to complications complications of fractionation of of mafic end mafic end members members and and the the presence presence of of multiple multiple components. components. The most most likely magma chamber the The likely magma chamber configuration configuration during during the emplacment of the late tectonic plutons plutons is that that of a zoned chamber with mafic magma magma underplating underplating felsic magma magma (Figure (Figure This schematic configuration has been supported by 7). This schematic configuration has been supported by 7). gravity studies studies (Gupta (Gupta and and Sutcliffe Sutcliffe in in press). press). An important aspect of the interaction interaction between the mafic and mafic and tonalitic tonalitic magmas magmas at at Lac Lac des des Iles lies is is the the development of hornblende—rich cumulus phases. The skeletal skeletal development hornblende-rich cumulus phases. The texture of these phases suggests they may have formed in a texture may supercooled magma during mixing. supercooled magma during mixing. Field relations and geochemical considerations suggest that the open system magmatic processes at Lac des Iles resulted in a continuum of disequilibrium textures, ranging tonalite magmas to from hybrid tonalite to late late net—veined net-veined mafic mafic and and intermediate dikes. These textures intermediate textures reflect reflect emplacement emplacement and and mixing of basic magma with varying degrees of fractionation fractionation into felsic felsic magma throughout throughout a large large interval interval of of the the cooling cooling history of the felsic magma. Furman and Spera (1985) felsic magma. (1985) have mixing associated with with injection suggested that features of mixing pluton represent a continuum of mafic magma into a Sierran pluton of mixing states states which can can largely largely be be related related to to host host When the host magma has low crystallinity crystallinity. crystallinity. (<30%) convective convective velocities velocities are high and mixing features (<30%) features occur on a a scale scale of of centimeters centimeters or or less. less. At approximately 30—70% 30-70% host crystallinity, crystallinity, mesoscopic mesoscopic schlieren, schlieren, mafic mafic inclusions inclusions and inclusion inclusion swarms swarms are are preserved. preserved. At higher higher crystallinity, outcrop scale scale textures textures such such as as dike dike swarms swarms crystallinity, outcrop and large large inclusion inclusion swarms swarms are are evident. evident. These stages stages correspond correspond to to the the observed observed textures textures at at Lac Lac des des Iles. Iles. Net— Netveined dikes and other conspicuous conspicuous mixing features features at Lac des Iles Iles probably formed at the latest stages of mixing when the efficiency of mixing is reduced but outcrop evidence for the the coexistence coexistence of of two two magmas magmas is is enhanced. enhanced. Breecia Breecia zones zones within the the tonalite tonalite containing fragments of tonalite and mafic mafic rocks rocks with thick thick alteration selvedges selvedges provide evidence explosive degassing of explosive degassing of of the the chamber. chamber. In an evaluation of the situation situation of of aa zoned zoned mafic— maficfelsic chamber, Rice (1985) has shown that mixing (1985) has shown that mixing of of aa 22 �convecting, convecting, density density stratified stratified column column is is possible possible given given large dimensions and a reasonable thermal large dimensions and a reasonable thermal gradient. gradient. An important important aspect aspect of of aa zoned zoned chamber chamber is is the the probability probability of of roll roll over over and and explosive explosive degassing degassing if if the the magmas magmas contain contain volatiles volatiles (Rice (Rice 1985). 1985). Evidence Evidence for for degassing, mixing and and violent emplacement violent emplacement of of mixed mixed chambers chambers has has also also been been documented documented by by Marshall Marshall and and Sparks Sparks (1984). (1984). Density instability of mafic magmas at the instability of magmas the base of of a chamber chamber may be established established by by vesiculation vesiculation of of mafic mafic magma magma and and can can lead lead to to rapid rapid transfer transfer of of mafic mafic magma magma across across aa formerly formerly stable stable mafic/felsic mafic/felsic magma magma interface interface (Eichelberger (Eichelberger 1980; 1980; Rice Rice 1985). 1985). Several Several of of the the associations associations reported reported in in this this study study are are common common to to other other granitoid granitoid terranes terranes in in the the Superior Superior Province Province and and suggest suggest the the model model presented presented here here may may have have wide wide applicability to late granitoids, particularly applicability to late granitoids, particularly those those containing Xenoliths ranging ranging in in composition composition containing hornblende. hornblende. Xenoliths from from hornblendite hornblendite to to microdiorite microdiorite are are aa particularly particularly widespread widespread feature feature in in late late Archean Archean plutons plutons (eg. (eg. Davis Davis and and Edwards, Edwards, 1985). 1985). These These inclusions inclusions have have conventionally conventionally been been interpreted interpreted as as pre—existing pre-existing mafic mafic rocks. rocks. However, However, as as this this and other studies (eg. Didier and other studies (eg. Didier 1987) 1987) have have suggested suggested the the inclusions inclusions may may be be chilled chilled mantle—derived mantle-derived magma. magma. Other Other features features of of contemporaneous contemporaneous mafic mafic and and felsic felsic magmatism magmatism reported reported elsewhere elsewhere include include the the presence presence of of net—veined net-veined dike dike rocks rocks in tonalitic to to granodioritic granodioritic plutons plutons (Davis (Davis and and in tonalitic Edwards Edwards 1985). 1985). Recent Recent precise precise U-Pb U-Pb zircon zircon geochronology geochronology also Archean also indicates indicates aa close close temporal temporal association association of of late late Archean gabbro plutons with granitoid rocks in other parts gabbro plutons with granitoid rocks in other parts of of the the Wabigoon Wabigoon Subprovince Subprovince (Morrison (Morrisonet et al. al. 1985). 1985). These These features features suggest suggest that that mantle—derived mantle-derived mafic mafic magmas magmas are are an an important important aspect asnect of of late late Archean Archean granitoid m-anitoid magmatism. magmatism. 23 �FIELD FIELD TRIP TRIP GUIDE GUIDE The The field field trip trip is is designed aesigned to to be be completed completed in in one One day, aay, including including travel travel from from and and return return to to Thunder Thunder Bay. Bay. The The trip trip includes stops on on includes 11 stop stop on on gneissic gneissic tonalite tonalite host host rock, rock, 33 stops the the Tib Tib Gabbro, Gabbro, 44 stops stops to to examine examine the the granitoids, granitoids, and and one one stop stop at at the the PGE PGE and and Cu-Ni Cu-Ni mineralization mineralization at at the the Roby Roby Zone Zone of of Madelaine Mines Limited. Madelaine Mines Limited. Due to to logging logging and mineral exploration exploration activity activity in in the the field trip area, the road conditions are continually field trip area, the road conditions are continually changing. changing. If If you you are are doing doing this this trip trip on on your your own own you you will will need logging roads roads in in the the area. area. need an an up—to—date up-to-date map map of of logging Proceed Proceed west west from from Thunder Thunder Bay Bay along along highway highway 11/17. 11/17. At At Shabaqua, turn north on highway 17 towards Dryden. Shabaqua, turn north on highway 17 towards Dryden. Turn north on the (also signposted signposted to to the Dog River Road (also Great Lakes Pulp and Paper company Camp 234) Great Lakes Pulp Paper Company 234) which is is approximately approximately 10 10 km km west west of of the the townsite townsite of of Raith Raith and and 11 km west of the the Central Time Time Zone/Eastern Time Time Zone Zone marker. marker. Begin Begin recording recording mileage mileage at at the the start start of of the the Dog River as loaded loaded trucks trucks are are River Road. Road. Drive carefully as using Proceed north on on the the Dog Dog River River Road Road using this this road! road! Proceed for at which which point point there there is a major junction junction for 21 21 1cm, km, at with with aa branch branch road road from from the the east. east. The The first first outcrop outcrop is is the the large large exposure on the southeast side side of branch road approximately approximately 50 50 metres metres from from the the junction. junction. - Stop st00 11 - Gneissic Gneissic tonalite tonalite This This outcrop outcro~has not been studied studied in detail but is is included as a stop to illustrate as stop to illustrate the the host host lithology lithology into into which and granitoid granitoid intrusions intrusions are which the the mafic—ultratnafic mafic-ultramafic and are emplaced. is typical of other other areas areas of gneissic gneissic tonalite tonalite emplaced. As is in northwestern northwestern Ontario, Ontario, the the outcrop outcrop is is complex complex and and several several granitoid granitoid phases phases are are present. present. continue north on the Dog River Road, pass through through camp Continue 234, at 40 km (distance from highway 17) turn 40 (distance from highway 17) turn northeast northeast (right) (right) at the the major major fork. fork. Proceed Proceed northeast northeast for for 6.2 6.2 km and then then turn turn east east along along branch branch road road to to Tib Tib Lake. Lake. Proceed east along road to Tib Lake for 2.7 2.7 km at which point there there is is aa small small track track that that leads leads to to the the north. north. Stop Stop 22 is is on the the west side side of the track track approximately 100 metres metres north north of of the the Tib Tib lake lake Road. Road. - Stop Tib Gabbro Gabbro Border Border Zone Zone Stov 22 — Tib The Border Zone Zone of the the Tib Gabbro Gabbro is is defined based on the the abundant abundant pegmatitic gabbro gabbro that occurs occurs around the the base of the the intrusion. intrusion. This well-exposed outcrop outcrop displays displays the the typical typical textural textural variation variation in in this this zone. zone. Proceeding Proceeding upward from the lowermost exposed part of the the outcrop outcrop textures textures range from coarse—grained coarse-grained and pegmatitic gabbro to medium grained gabbro and gabbronorite with conformable pegmatitic layers. layers. 24 �, Return to to Tib Tib Lake Lake Road Road and and proceed proceed Return 1.2 km. Stop 3 is on the north side 1.2 tan. Stop 3 is on the north side in the bush approximately 10 metres in the bush approximately 10 metres east for another east for another of the road and is of the road and is from the road. from the road. Stop 3 Tib Gabbro Gabbro lavering 1averjg stov 3 — - Tib Layered gabbronorite gabbronorite in in the the upper upper part part of of the the Lower Lower Layered Zone of Zone of the the Tib Tib Gabbro. Gabbro. Well developed intermittent intermittent layering locally locally shows shows modal modal grading grading with with pyroxene-rich pyroxene-rich layering bases and plagioclase—rich tops. tJralitic alteration (green bases and plagioclase-rich tops. Uralitic alteration coloured) occurs along fractures which locally cross cut the fractures primary layering. primary layering. Return Return to to Tib Tib lake lake Road Road and and proceed proceed east east for for another another 0.3 0.3 km. km. Stop 4 is on the south side of the Tib Lake Road, approximately 20 20 metres from from the the road, and is is on the east side of a culvert. the east side of a culvert. - Stop Tib Gabbro Lower Zone Stov 4 4 - Tib Zone This outcrop displays wispy layered gabbronorite near wispy layers consist of the top top of the the Lower Lower Zone. Zone. The wispy plagioclase or pyroxene rich bands in gabbronorite. Thin Thin pyroxenite dikelets of various orientations orientations cut the layering layering and contain contain inclusions inclusions of of host host gabbronorite. gabbronorite. The dikelets are interpretted to be injections injections of cumulate material. AA small hornblende—feldspar Green hornblende-feldspar dikelet dikelet is is also also present. present. Green uralitic alteration alteration of pyroxenes is associated with fractures and is fractures is a late late feature. feature. Return to the Tib lake Road and continue east for for another 3.2 3.2 km, km, past the outlet from Tib Lake, to to a road which runs Turn runs down down the the east east side side of of Tib Tib Lake. Lake. Turn south along this road and proceed for 11 km to to the the junction with another another major logging road which is is referred Take this referred to to here here as as the the "Lac "Lac des des Iles Iles Road". Roadw. Take road to the southwest southwest (in (in the direction of the Dog River Road) for for 6.5 6.5 km, until the junction with the the Take the the Roenicke road Roenicke Lake Lake Road is is reached. reached. Take north for for 1.8 1.8 km and turn west along an unnamed bush road. Proceed along this road, taking the left fork road. after 2.1 km and reaching the outcrop for for stop stop 55 after 5.0 km. 5.0 km. Note: Note: The bush road into this stop is becoming overgrown overgrown and will probably be difficult to to recognize recognize if you are following following this this after after the the spring spring of of 1990. 1990. - Stop Stov 55 - Tonalite Tonalite breccia This distinctive distinctive breccia zone with dimensions of approximately approximately 100 100 by 300 metres cross—cuts cross-cuts the the hornblende hornblende tonalite tonalite east east of of the the Dog Dog River. River. The breccia consists of subrounded subrounded fragments fragments of tonalite with 2 to 33 cm thick thick sericite—epidote-silicif led alteration alteration rinds. The matrix sericite-epidote-silicified consists of altered, fine grained and locally comminuted comminuted tonalite. Rounded irregular mafic clots up to 0.5 0.5 metres long are locally pr<="=on+ present interstitial to +he the tonalite interstitipi <-A 25 . �fragments. Several quartz—feldspar porphyry dikes intrude the breccia. The The breccia breccia is is interpreted interpreted to to be be the the product product of of an an explosive degassing of a magma chamber. explosive degassing of a magma chamber. The The process process is is thought thought to to provide provide further further evidence evidence for for underplating underplating of of granitic granitic magma magma by by mafic mafic magma. magma. Explosive Explosive devolatilization devolatilization is an an expected expected consequence consequence of of the the cooling cooling of of such such aa system system if the the mafic mafic magma magma contains contains volatiles volatiles (Rice (Rice1985). 1985). Return Return to to Roenicke Roenicke Road Road and and then then proceed proceed south south to to the the "Lac "Lac des des Iles lies Road". Roadw. Turn Turn southwest southwest along along the the "Lac "Lac des des Iles Iles Road" RoadM (toward (toward Dog Dog River River Road) Road) and and proceed proceed for for 6.5 6. km km to to the the Garden Garden Road. Road. Turn Turn east east on on the the Garden Garden Road Road and proceed for 1.8 km. Stop 6 is an outcrop and proceed for 1.8 km. Stop 6 ro on the south south side side of of the the road. road. - Stop Stop 66 — Net-veined Net-veined dikes dikes Mafic Mafic dikes dikes are are abundant abundant in in this this area area of of the the tonalite tonalite and and range range from from intrusions intrusions with with sharp sharp contacts contacts to to dikes dikes which which are are extensively extensively veined veined by by tonalite, tonalite, such such as as the the dike dike in in this this outcrop. outcrop. The The back back veining veining texture texture is is known known as as net—veined net-veined since since the the tonalite tonalite forms forms aa wispy wispy net net which which surrounds surrounds rounded rounded centimetre— centimetre- to to decimetre—sized decimetre-sized mafic mafic globules. globules. The The structure indicative of of emplacement emplacement of of the the mafic mafic magma magma structure is is indicative prior consolidationof of the the felsic felsichost. host. prior to to the the consolidation Proceed Proceed for for another another 2.2 2.2 km km east east on on the the Garden Garden Road. Road. Stop 7 is a group of outcrops on either on either side side of of the the road. Stop 7 — Mixing textures In In this this series series of of outcrops, outcrops, mixing mixing of of mafic mafic and and tonalitic tonaliticmaginas magmas has resulted resulted in in aa variety variety of of igneous igneous textures. textures. Net-veined Net-veined and and disaggregated disaggregated mafic mafic dike dike material material is is present present in in the the lower lower part part of of the the outcrop. outcrop. The The disaggregated disaggregated mafic mafic material material could could be be readily readily confused confused with with rounded mafic inclusions. Adjacent to the net rounded mafic inclusions. Adjacent to the net veined veined dike, dike, the the foliation foliation of of the the tonalite tonalite is is destroyed destroyed by by remobilization remobilization of of the the felsic felsicmaterial. material. At At the the top top of of the the outcrop, outcrop, the the hornblende—rich hornblende-rich mela-tonalite mela-tonalite is is interpreted interpreted to to be be aa hybrid hybrid composition composition resulting resulting from from more more complete complete interaction interaction of of the the mafic mafic and and felsic felsicmagmas. magmas. Abundant Abundant skeletal skeletal textures textures in in this this rock rock may may result result from from supercooling supercooling due due to to magma magma mixing. mixing. Turn Turn around around and and proceed proceed west west for for0.7 0.7 km. km. Stop Stop 88 is is an an outcrop on the north side of the road. outcrop on the north side of the road. - - Stop Stop B8 - Hornblendite Hornblendite Hornblendite occurs as outcrop scale pods within the tonalite and are gradational with the mela—tonalite. The hornblendite and mela—tonalite have complex internal structures such as comb—layering and colloform structures. Comb—layering is defined by the alignment of coarse acicular to skeletal hornblende which is oriented perpendicular to 26 �layering. These rocks rocks have have geochemical geochemical characteristics characteristics ering. These which ch suggest suggest that that they they are are cumulates cumulates derived derived from from the the mafic mat dike suite. hornblendites also resemble a suite of suite. The hornblendites rocks which are described in some ks known as as "appinites" I1appinitess1 some Phanerozoic shoshonitic plutonic nerozoic shoshonitic plutonic suites. suites. Return to the "Lac des Ties Road" and turn back to th the Iles Roadn northeast towards Lac des lies. Proceed for 11 km to 11 t northeast towards Lac des Iles. the road the right which provides provides access access to to the the the road on on the right which Nadelaine towards Madelaine Mines Mines property. property. Turn east (right) (right) towards the Madelaine Mines Property, taking a left fork afte after 3.2 At the 3.2 km and another another left left fork fork after after 6.1 6.1 km. km. At Nadelaine Madelaine Mines Mines Property Property there there is is a gate gate and we will be b met by staff from the company. met by staff from the company. Stop 9 — PGE mineralization and geology in the vicinity of the Roby Zone — Madelaine Mines Limited Note: te: Due Due to to the the ongoing ongoing exploration exploration and and development development work work on o thee Roby Zone, which includes extensive stripping and Roby Zone, which includes extensive stripping and blasting, asting, it it is is not not possible possible to to plan plan the the precise precise features features that at can can be examined at this this location prior to arrival at the the site. site. Naps Maps of of the the geology geology of of the the gabbroic gabbroic units units in in the the vicinity of the Roby Zone (Figure 8) show the complex vicinity of the Roby Zone (Figure 8) show the complex relations relations between between intrusive intrusive units. units. Figure Figure 3 shows shows that that the the Roby Roby Zone Zone occurs occurs along along the the contact contact between between uniform EC EG and and the the more more complex complex WG. WG. Sheets and minor discordant dikes of pyroxene The pyroxene cumulate cumulate intrude intrude the the EG EG and and the the EG/WG EG/WG contact. contact. Th sheets websterite in sheets and dikes dikes which are gabbronorite gabbronorite to websterite composition, contain clinopyroxene contain cumulus cumulus orthopyroxene orthopyroxene + + clinopyroxene and intercumulus plagioclase and vary from altered nd intercumulus from altered to to fresh, fresh, even ven where where hosted hosted by by altered altered EG. EG. The highly uralitized pyroxenite oxenite is is termed termed amphibolite amphibolite in in drill drill logs. logs. The altered altered pyroxenite oxenite sheet sheet is is approximately approximately 55 to to 10 10 m m thick thick and and intrudes gabbronorite of rudes the EG but appears appears to grade into gabbronorite the WG and and is is approximately approximately conformable conformable with the the EG/WG contact. Figure Figure 88 is is aa detailed detailed outcrop outcrop map map from from the the "C—Zone". "C-ZO~~~~. This his zone zone is is within within the the WG WG at at the the southern southern end end of of the the Roby Roby Zonee and and illustrates illustrates the the complexity complexity of of the the WG WG unit. unit. The The outcrop crop is is predominantly fresh fresh to to moderately altered altered gabbronorite ronorite of of the the WG WG with with several several units units of of altered altered leucogabbro leucogabbro which form form inclusions inclusions and layers layers within within the the gabbronorite. surfaces gabbronorite. Some of the inclusions inclusions have cuspate surfaces and gradational gradational contacts contacts suggesting suggesting that they were not solid solid at at the the time time of of incorporation. incorporation. Also present within the the gabbronorite abbronorite are are inclusions inclusions of of pegmatitic pegmatitic gabbro, gabbro, altered altered pyroxenite, yroxenite, and and fine—grained, fine-grained, recrystallized, recrystallized, clinopyroxene clinopyroxene amphibolite. The gabbronorite gabbronorite and and leucogabbro leucogabbro are are amphibolite. The discordantly discordantly intruded intruded and and disrupted disrupted by by mineralized mineralized gabbro gabbro pegmatite to 44 mm wide wide mineralized mineralized intrusion intrusion egmatite dikes dikes and and aa 11 to breccia. reccia. The The breccia breccia is is defined defined by an an abundance abundance of of gabbroic gabbroic 27 �inclusions and contains a core of gabbro pegmatite. (Note: Unfortunately this outcrop is now partially destroyed by blasting.) Textures in the WG, such as those shown in Figure 8, suggest that some type of incomplete mixing or contamination of the WG by the EG took place. The presence of rounded inclusions, particularly of EG in WG and complex interfingering of the two gabbro types on a decimeter scale suggests that the EG was not completely solidified when the WG was intruded. Contacts between the two gabbro phases are commonly cuspate, net—veined and disaggregated. These textures are similar to those described in mixing zones between mafic and felsic magmas by Marshall and Sparks (1984) and would be reflected in the chemistry of the rocks only by more detailed sampling than that done in this study. The limited development of modal layering, the presence of cumulate textured dikes of WG intruding EG and the abundance of inclusion—rich outcrops suggests that the cumulates did not form in—situ but were emplaced as crystal mushes. This situation situation contrasts contrasts with with layered layered intrusions intrusions that that crystallized cumulate— crystallized by upward and inward growth of a cumulate liquid Irvineet al 1983). 1983). id interface interface (eg. (eg.Irvine End of trip. Return route to Thunder Bay will be by the recently opened access route to Lac des Iles from highway highway 527. 527. This is is a shorter shorter trip trip than than returning returning via the the Dog Dog River River road. road. Acknowledqments I would like to thank J.M. Sweeny and A.R. Smith for capable assistance mapping the Lac des lies area. J.P. Sheridan is thanked for access to map and sample the Lac des Iles property of Madelaine Mines Limited. D.W. Davis is thanked for permission to use unpublished lished geochonological geochonologic results. K. Gil drafted the figures. s. Published Published with with permission of the Director, Ontario Geological Survey. 28 �REFERENCES REFERENCES Blake, Blake, D.H. D.H. 1981. 1981. Intrusive Intrusive felsic-mafic felsic-mafic net—veined net-veined complexes complexes in in north north Queensland. Queensland. BMR Journal Journal of of Australian and Geophysics, Geophysics, v. v. 6, 6, pp. 95-99. 95-99. Australian Geology Geology and Boudreau, Boudreau, A.E., A.E., Mathez, Mathez, E.A., E.A., and and McCallum, McCallum, 1.5. I.S. 1986. 1986. Halogen Halogen geochemistry geochemistry of of the the Stillwater Stillwater and and Bushveld Bushveld Complexes: Evidence for the transport of Complexes: Evidence for the transport of the the Platinum— Platinum group group elements elements by by Cl-rich Cl-rich fluids. fluids. Journal Journal of of Petrology, Petro v.27, v.27, pp. pp. 967—986. 967-986. Brown, Brown, P.E. P.E. and and Becker, Becker, S.M. S.M. 1986. 1986. 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Stockwell, Stockwell, C.H., C.H., McGlynn, McGlynn, J.C., J.C., Emslie, Emslie, R.F., R.F., Sanford, Sanford, B.V., B.V., Norris, A.W., A.W., Donaldson, J.A., J.A., Fahrig, W.F., W.F., and Morris, Geology ofV the Currie, K.L. Currie. K.L. 1972. 1972. G ~O~OU the Canadian Canadian Shield, Shield. in in Douglas, R.J.W. R.J.w. (editor), (editor), Geology and and Economic Economic Minerals Minerals of Canada. Geological Survey of Canada, Economic Geology Report Geology Report No. No. 1, 1, 838 838 p. p. Streckeisen, A. 1976. 1976. To To each each plutonic plutonic rock rock its its proper proper name. name. Streckeisen, A. Earth-science Earth-Science Reviews, Reviews, v. 12, 12, pp. pp. 1-33. 1-33. Stumpf 1, E.F., E.F., and and Ballhaus, Balihaus, C.G. e.G. 1986. 1986. Stratiform Stratiform platinum platinum Stumpfl, deposits : New data and concepts. Fortschritte der deposits Mineralogie, v. 64, Mineralogie, 64, pp. pp. 205—214. 205-214. E.F., and Rucklidge, J.C. J.C. 1982. 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The The geochemistry, geochemistry, origin origin and and economic economic potential potential of of platinum platinum group group element element bearing bearing rocks rocks of of the the Lac Lac des des lies lies Complex, Complex, northwestern northwestern Ontario. In Geoscience Research Grant Ontario. U Geoscience Research Grant Program, Program, Summary Summary of of Research, Research, 1986-1987. 1986-1987. Ontario Ontario Geological Geological Survey Survey Miscellaneous Miscellaneous Paper Paper 136, 136, pp. pp. 140—152. 140-152. Sweeny, J.M. 1989. The geochemistry Sweeny, J.M. 1989. The geochemistry and and origin origin of of the the Roby Roby Zone, Zone, Lac Lac des des Iles lies Complex. Complex. MSc MSc thesis, thesis, The The University University of of Western Western Ontario, Ontario, London, London, Ontario. Ontario. Talkington, Talkington, R.W., R.W., and and Watkinson, Watkinson, D.H. D.H. 1984. 1984. Trends Trends in in the the Distribution Distribution of of the the Precious Precious Metals Metals in in the the Lac Lac des des Iles lies Complex, Complex, Northwestern Northwestern Ontario. Ontario. Canadian Canadian Mineralogist, Mineralogist, v. v. 22, 22, pp. pp. 125—136. 125-136. Taylor, H.P. Taylor, H.P. 1967. 1967. The The zoned zoned ultramafic ultramafic intrusions intrusions of of southeastern Alaska. Ultramafic and southeastern Alaska. In Ultramafic and related related rocks, rocks, edited edited by by P.J. P.J. Wyllie, Wyllie, 3. J. Wiley Wiley and andSons, Sons, pp. pp. 97—121. 97-121. Todd, Todd, S.G., S.G., Keith, Keith, D.W., D.W., Schissel, Schissel, D.J., D.J., LeRoy, LeRoy, L.L., L.L., Mann, Mann, E.L., E.L., and and Irvine, Irvine, T.N. T.N. 1982. 1982. The The J-M J-M platinum-palladium platinum-palladium reef reef of of the the Stillwater Stillwater complex, complex, Montana Montana : Igneous Igneous Stratigraphy and Petrology. Stratigraphy and Petrology. Economic Economic Geology, Geology, v. v. 77, 77, pp. 1454—1480. pp. 1454-1480. Vogel, Vogel, T.A. T.A. 1982. 1982. Magma Magma mixing mixing in in the the acidic—basic acidic-basic complex complex of of Ardnamurchan: Ardnamurchan: Implications Implications on on the the evolution evolution of of shallow shallow magma magma chambers. chambers. Contributions Contributions to to Mineralogy Mineralogy and and Petrology, Petrology, V. V. 79, 79, pp. pp. 411—423. 411-423. Watkinson, D.H., and Dunning, Watkinson, D.H., and Dunning, G. G. 1979. 1979. Geology Geology and and PlatinumPlatinumgroup Mineralization, Lac des lies Complex, group Mineralization, Lac des Iles Complex, Northwestern Northwestern Ontario. Ontario. Canadian Canadian Mineralogist, Mineralogist, v. v. 17, 17, pp.453—462. pp.453-462. : 32 �List of of Fiaures Figures List Generalized geology of the Lac des lies area. Simplified from mapping by by the the Ontario Ontario Geological Geological Simplified from mapping survey (Sutcliffe and Smith 1988). Location of field Survey (Sutcliffe and Smith 1988). Location of trip stops are shown. trip stops are shown. Figure 2. Geology of the Lac des lies Complex based on mapping by Sutcliffe and Sweeny (1986) with modifications from Lindhardt and Rues (1987). Location of field trip stop is shown. Figure 3. Geological map of the LDIC in the vicinity of the Roby Zone. Location of map is shown on Figure 2. Mineralized zones A to F from Pye (1968). Figure 4. Section through the Roby Zone showing lithologies and total total PGE PGE values values plotted plotted against against length length of of drill drill and hole. Based on diamond drill core logs of Texasgulf hole. Based on diamond drill core logs of Texasgulf Canada Limited. Figure 5. Geological map of the Tib Gabbro. From Smith and Sutcliffe (1987). Location of field trip stops are Figure 1. shown. Figure chemically analyzed samples re 6. 6. Modal analyses of chemically variation in quartz-plagioclase-alkali quartz—plagioclase—alkali feldspar feldspar showing variation and quartz—feldspar—mafic quartz-feldspar-mafic minerals. Figure Schematic cross-section cross—section of of the the crust crust in in the the Lac Lac ure 7. 7. Schematic des Iles area showing possible configuration of zoned lies possible chamber. magma chamber. Figure outcrop map showing details of mineralized mineralized ure 8. 8. Outcrop Located breccia zone zone and pegmatitic gabbro. Located approximately 200 meters meters southeast southeast of of the the Roby Roby Zone in approximately the "C—zone" Phase contacts contacts at at "Aw "A" and and "C-zone" (see (see figure figure 3). 3). Phase "B" are interpreted to be primary igneous 'B" igneous layers. layers. Leucogabbro inclusion at "C" An *tC"has cuspate cuspate surfaces. surfaces. An intrusion breccia zone cross—cuts cross-cuts igneous igneous layering. layering. dikes occur occur in the the core core of of the the Pegmatitic gabbro dikes breccia and also disrupt the layering as at location "D". A channel sample at "E" indicates that the highest values of PGE are associated with the pegmatitic phases. 33 �90°oo' 89030* 49° 15 :TAMNLAxE:s INTRUsIoN: WITH MAGMA MIXING + t + + + + —:--:—..- +••.k•Iomete -. 4+ 49°OO' PROTEROZOIC ! hornblende diorite Early Granitoid Rocks diabase AR CH E A N Late Granitoids k'+T4 biotite tonalite :—_—:—g I— hornblende tonalite Late Mafic to IJltramafic Rocks I mafic maficto tointermediate intermediatedikes dikes ultramaf Ic t gabbro to gabbronorite gabbronorite gabbro to 1 hornblende gabbro, hornblendite T1 tonalltic gneiss Supracrustal Rocks [II 11111 matic metavolcanics t::c:i metasediments -• —— fault fault - PGE PGE occurrence occurrence — contact contact breccia Zone Figure Figure 1. 1. 34 �1 -r Li —L, \j LAG DES ILES alTAao\ "N) strike & dip of layering fault geological contact hornblende gabbro gabbronor its hybrid zone leuco gabbro Gabbroic Rocks Figure 2. hornblendite, hornblende pyroxenite, hornblende diorite clinopyroxenite, welirlite, serpentinite websterite, gabbronorite Ultraroaf Ic & Related Rocks granitoids(unsubdivided) ARCHEAN diabase PROTEROZOIC LI 490 15 ______ ______ ______ —— a �______ I Western Gabbro— Pegmatitic gabbro, gabbro breccia,norite, I -] Pegmatitic gabbro, gabbro breccia, norite, r—- gabbro, gabbronorjte, gabbronorite, clinopyroxene clinopyroxene * + + + + I + + [c:%:::J + ++ ++ + + + + + + I + + U + 4 + 4 t + + + + + + + + + ÷ + "J1 Eastern Gabbro— + + + ++ ++ + + + ÷+ ÷+ 4+ + + + + + t + 4- 4 1 a, L't sj + + t 4 ++ ++ + ++ ++ 4+ ++ + ++ ++ ++ ++ ++ ++ + + + ++ ++ + + ++ +++ ++ + ++ ÷+ ÷+ + + + ++ ++ ++ ++ ++ ++ ++ + + + + + + + + + + + + + + + ROSY + Western Gabbro — Gabbronorite, pyroxenite, gabbro, anorthosite + ZONE Uralitized leuco—gabbro Diabase 0 Approximate location of mineralized - C-, FZONE to surface surface projected to Geological r-ontact rontact road + ÷ + + + ft< 1 + ' ".1 t ... - 0-ZONE + ++ + + + ÷ + + + + + t t 4 4. 4. ÷ + + + + ++ + $ 4 4- + + + + + ++ + + + ++ ++ ++ + + + + + ++ + + + + + + + —'--- Igneous layering (strike and dip) + 4+ + + ÷ + + + ++ Foliation (strike and dip) + 4 4 + 4- + ++ 4 + + ÷ r <'A + + ÷ 200 metres Figure 3. zone �- w E 103 + 75 106 - Section 515 s. 0 20 40 60 80 metres metres 55 0 0 10 10 15 15 20 20 ppm PGE ppm PGE -t .... Eastern Gabbro 0 Gabbro 0Western Gabbro 75 drill 75 drill hole hole number number Altered Altered Pyroxenite + + elevation elevation reference reference Figure 44.. Figure 37 �- ..... _. r.. 70 60 - -. - - - - - -. -• -0 - - V. - ;. - -. - - :1: - • - -s-uii. ::,!. 'I • —I . . • : - : - .. . - : - . . — - - - -. - - . ,l__ - - : 0 - •. . 0.5 'I - . . . . . . . . • . . • . . • • . . . . —a' — - . .•..•......... • F, :: :::MIDDLEZaNE.:::::.::. road LOWER ZONE" .--o :: •: r + + + + -c—r+ + + + + + + + + + P'KUHNER OCCURRENCE + + + .+ + + + + + + + + + + + + + + + + + + + +-+ foliated togneissic gneissic biotite bbttte foliatedto diabase diabase - tonalite — / lithological lithalogical contact contact A RC HE A N ARCHEAN +4 granodiorite grand!a~ite(megacrystic) tmegacrystk> granodiorite, granaciiarite~Hb Hb tonalite tanakite (foliated) (foliated) . . : - #- hornblende+quartz±biotite h&enW auar%-#2bbtite gabbro gabbm magnetite-rich magnetiterichgabbronorite gabbronorite pegmatitic pegmatiticgabbro gabbro quartz quartzgranulite granulite I: - :±j gabbro gabbronorite, m i t e ,norite norite - r' TIB TIB GABBRO GABBRO I-,,.: * * * a tj + mafic metavolcanics PROTEROZOIC PROTEROZOIC 1+ + + I' . • + 1.0 . • . . :87. . . - • -K . -. - --4 - • • - 0 -, * fault fault layering layering (strike (strikeand anddip) dip) foliation foliation (strike (strike and anddip) dip) ultramafic ultremaficcumulates cumulates zone zone contact contact trench trench site site A suiphide sulphide mineralization mineralizationwith with >>SOppb SOppbPOE P6E 00 sulphide subhide mineralization mineralizationwith with >>500ppb SOOppbPOE PGK 38 Figure Figure 5. 5. �QTZ QTZ • HORNBLENDITE HORNBLENDITE + • HORNBLENDE TONALITE HORNBLENDE TONALITE • MAFIC MAFIC TO TO o 0 O o MELA-TONALITE MELA-TONALITE o QUARTZ a QUARTZ FELDSPAR FELDSPAR INTERMEDIATE DIKES DIKES PORPHYRY PORPHYRY • S 0 0 0 055 FELD BIOTITE TONALITE TONALITE 1 S MAFICS Figure 6. Figure 6. PLAG �.1:- C Figure 7. �\ \ ,1 it / / / / channel sample I' Li Itrench / EG — Ieucogabbro WG — gabbronorite gabbroic inclusions pegmatitic gabbro dikes gabbroic intrusion breccia fault 6 0 m Figure 8. 41 �+ opt op pi opt, pi p2 • Rb • net - ap I I - - :- - - phi -phionopite; bto-baotite: act—acttnol its artthr'phyiniate, I nesocurrolate bio, qtz pI. cps. Rb, act, qtz, myt act p1, opt, Rb. p1, opt, Rb, bro pl. qtz, bio p1, Rb, phi cpx. opt, hb. p1, net qtz—quartz. snozoisite • to Rvpxda,onorphtc coarse qrained , lsoqranoiar subophitio .________ - . I F othocunulate, mesocss,su late to hvpidiomorphic nesocuisuiate to orthocunu late mesocunta.Iate 1cm — 6cm 2—4 1w, 2cm, 2—4 cm 2—4 run :—4 mm 2—4 tel ire, — i—S rIS 1—1 nfl 1—3 nfl 1-4 rwt 1-4 no •t'lt-ain liar' hb—hornblende; pi—piaqiociase; ngt—oaynetate: ap—apatite; epidote, olsnozossite chlorite uralite. chlorite sericate epidote. ci anozois Ste add inosite. uraiite, tale anthophviiite, ci inozoisite epidote,ohiorite. as abeve ci epndote. chlorite, to riesi-unhi late - ninorc'art,orcate, - talc flinor ph] opt to ol tosc-rp-rrqt, 'lestut,- adcun:rlate hb Alteration opt to act, nsnor —— cpx, ops. hb, rpn, =.- Tnlercunu 'us Minerals Abbreviations: oi—olivine; ohr—chromite; ops—clinopyroxene; opx—orthops'rosene: —— Rb, - hb pi *cpt+hb*mqt ' ops'opx p1 * pi. p - opt p2 oi Rb, Rb Hornt Tende Gabhro I or's pl •cps*opx . - - opt opt, eRr •oiscps'npt - Pegnst:T ic Gabbro and Gabbronorite Gabbro Maenetite—rioh - Leuccqahbro, Anortr,os+tio Gabbro Gabbronorite Norite —- Hornbiendite, Pyrosene Hornbiendite UI Gabbronorste dike iherrolite , 01 Isc-lsterste- dike — -Rebstei-t.-,Gabbr000ritecps clrnnovroxenite OlCllnorvroierra te, ol ol. ol -cbs serpt-ntrr'ite, wenrirte Cunu us nincrals — 'etronraphy ol Litholoures fron the rae Des Ties Connie,. Rock Tsre Table L Sunnirv of ____ chr, - Or's ci - * + • p1. - ops - + Rb, p1 - - • hb. opt, i pl Rb ap net and qabbro rgt gabbronorite pl • cpx cpy similar to p1 - * pi qtz Rb hb, opt * hb opt pi. pi pl oi cpx - chr. ops 'CPA. opx'cps. pI ol Rio rrcr[se:tuer,v-t. opt cops. pi opt. opi 0] CiceraliIza: �2 FIELD TRIP 2 �1.1.5.0. FIELD TRIP Geology of the Shebandowan & Quetico Archean subprovinces 0. Borradaile Geology Department Lakehead University Thunder Bay, Ontario P7B 5E1 Canada Proterozoic Rocks Proterozoic Rocks 1. 1. KakabekaFFalls. Recessedpost-glacial post—glacialgorge gorgei ninProterozoic Proterozoic shale. shale. Kakabeka a l l s . Recessed Soft sediment deformation in Proterozoic shales — car park exposure. S o f t sediment deformation i n Proterozoic shales - c a r park exposure. 2. 2. Basal con conglomerate of Proterozoic sequence. Basal (Kakabeka Formation). (Kakabeka (Care on Highway!) Archean Rocks Rocks SStructural t r u c t u r a l facing. facing. 33.. Pillow gradedt utuffs. P i l l o w lavas lavas and and graded ffs. (Fig. (Fig. la, l a , bc). be). 4. Fourway School. Younger Younger "Timiskaming-1 "Timiskaming—like" Fourway iken' sequence sequence ooff Archean. Archean. (Fig. 3). 3). ooff downward—structural downward-structural ffacing a c i n g sediments. sediments. (Fig. 5. 12. 11. 6. ' }. Flap Flap i IIntertidal n t e r t i d a lsequence. sequence'. Finnmark exposure. "Timiskaming—like" sediments. Finnmark exposure. "Timiskaming-like" (General structural Fig. 22). ). (General s t r u c t u r a l sstyle t y l e ooff area, area, see see Fig. Quetico gneisses, gneisses, Raith. "phase" deformation. deformation. "phase" D1f afabric. D, bric. Migmatites,d idiktyonitic structure, mmultiMigmatites, k t y o n i t i c structure, ulti. + -4 beltt gneisses. Quetico be1 gneissesi ., ., Shebandowan Mine Mine Road. Shebandowan Road. ! ;y. "." Q,-T" -,. ,. ",- . . ,> Pi c.^".\-~-! , ,. ~. .?'.>: <, .... - , .: ,? .~d t .: < + . ..> . "Timiskaming—like" "Timiskaminci-1 ike" sequence seouence ...,., .. (a) Fragmental Fragmentalr ered igneousrock rock (!?) (U) d igneous (b) conglomerate. Fabrics Fabricsand ands tstrain region (see (see Fig. Fig. 5,6,7);" 5,6,7). r a i n i in n region (c) sslate late - , . Archean rocks rocks ",& Older Keewatin—type Keewati n - t v ~ eArchean (d) ppillow i l l o w lava lava (e) iiron r o n formation formation "A ^-$ -..I -'/; >: , ? z . a ' ', ,?+; ,' ..* .-. 3 4 .E 5 " ,,,: Strain Fig. 1,2)? S t r a i n (see (see Fig. 1,2)? :'.I ,.:4 Â¥ . . .- ~ ;. , ~ . .> 6 :c .;,= Younging? SStructural Younging? tructural 1. SwampCreek CreekP Pillow lavas. Swamp i l l o w lavas. faci ng? facing? 8. Tuffs T u f f s and and ppillow i l l o w lavas. lavas. 9. Increasing metamorphic group) towards Increasing metamorphic grade grade in i nmetasediments metasediments (Kashabowie (Kashabowie group) towards beltt boundary. be1 boundary. 10. ((Structural S t r u c t u r a l facing facing and and folds? folds? Gneissose rocks of the Quetico Belt. 43 seeFig. Fig. 88). ). see �ARCHEAN LITHOLOGIES "TIMISKAMING" METASEDIMENTS 0 IH:.•:1 GREENSTONES I>/-cI GRANITOIDS 1x-'I PARAGNEISS IEI GREYWACKES 7., r..— LAC — - LiIlr- "BELT" LAKE RAITH 7.— '' QUETICO "BELT 9 ---,- ,,C()':/ LA TIMISKAMING METASEDIMENTS c. 2690 my j 0 I0 20 KM MT. McKAY FORMPIt0H L. - �o long ', EIIIII' "cij.p-centre lIne the model the model notural pillow nolurol pillow An idealised lava pillow An idealised natural natural lava pillow before before straining straining and and the the geometric used in in this this paper. paper. geometric model model of of iti t which whichisis used C)T k a- / /__ Fig. F i g . la la up structural tacint U. I (a) Undeformed Undeformed bed with idealised idealised pillow. pillow. The The cusp-t-ntre cusp-to-centre (a) bed with line of of the the pillow pillow gives gives the theyoungingdirection. younging direction,(b) (h) Deformed Deformed bed bedwith with line idealised pillow. pillow. The The cusp-to-ccntre cusp-to-centre line line of of the the pillow pillow now the idealised now tracks tracks the 'stratigraphic thickness' thickness'direction, direction, 1t'. to the -stratigraphic ' . This This may may approximate approximate to the direction, The simple , younging direction direction is is no nolonger longer istructural n i d i i m l facing facine direction. The simole vounoinf ~~~.~~~ -~~~ ~~~~~r perpendicular to of the case, but.bv but, by eroendicular to the the long lonoaxis axisof the pillow nillow in the thegeneral ~eneralcase. definition, it remains perpendicular to bedding. ~ 000 cusp in peor - like pear-like terminations bmhtims crescent - stuoped crescent-shaped pillow pillow Fig. 1b b Fig. tndeformed irdeformed piltow pillow deformot, .. ..[/f,4,//1,~-~4.5/ .....deformation ............... Schematic sequence sequenceofof proeressivcly progressivelydcformed deformed pillows pillows inSchematic ferred from from held Whenthe the linite finite str;nin strain cellipse fen-cd field observations, observations. When l t i n ~ ratio ;ratio reachesaboul4.5 about 4.5the thepillows pillowstk-vclnp develop p~iir.likc pear-like tcrniinations terminations reaches of heterogeneousstrain. strain, and subsequently the ends ends of of aitss a ~ result iresult of :nod suhscqucntly pillow become so pointed pointed thiit that iitt is difficult diftieuls to identify identify the cusp the pillow 45 �sy Sketch of' of aa deformed deformed pillow pillow showing the the selvage sel'age thickthickFIG. PtO. I.1. Sketch ,,S. nesses in the nesses the principal principaldirections direcuons of of strain: wain S . 5..S.S-.The The ratios ratun of d these thicknesses give the ratio ratio of the principal principal strains if the thickness that the be noted noted that of the selvage was originally originally constant. ItIt should should be the not normally in the same are not principal selvage principal selvagethicknesses thicknesses arc ->ame ratio ratioas as the the dimensions: one exception is the unlikcly unlikely event that deformed pilIow's ~illow'silin~'n~iuns: oneexccplion is the cvcm that the original, undelbrmcd Ac original. undefonned pillow pillowwas wasspherical. spherical -. Fig. ic Fig. 1c 46 �N N (B) (A) S moxifflum maxImum Susc.ptibilitin :  Suç~~tibilitià £ inteonediot. A mfrmdiif plunge// inmfctton inlerseclion llmation X: meon fold plunge Irneetion X: i i ~ f l ntold Fl g. /, bed I/ orientation b'Zientation I m. minimun mtftimum 2 Lower-hemisphere equai-azea stereonets showing the mean mean reonets showing n intersection cleavage orientation (great circle) and mean intersectionlineation lineationfor for the eastern eastern Finmark Finmark area (A) the Shebandowan mine area and (B) the (east of Fourway School) (see Fig. I). The principal principalmagnetic magneticsuscepsusceptibility orientations for the slates are also shown. cleavage cleavage ' downward downward structural ,k: ,. . strucfural facing facing Interpretatlo Interpretatic Planof of an an outcrop outcmp surface surfaceon onthe thesouth southside sideofofHig Hig Plan II —17. 17,about about100 100mm west west of of Finmark 11 Finmark Road. Road. Where the the glacial polish Where polish has has been been weathered weathered away away vertical cleavage is pronounced; pronounced; elsewhere the thesedimentary sedimentarydetai deta vertical preserved. Ripple Ripple marks, graded graded bedding, and sand sand intrusions preserved. thatthe thewestward-closing westward-closingfold foldhas hasolder olderrocks rocksininits itscore: core:iti acase t e that anticline. However, However, the east: it it is aa synfonn. synform. '' anticline. the fold foldplunges plunges to to the east: this ht-generation fuss-generation fold fold isis aa downward-facing downward-facingfold fold that that pml pm this inverted flap developedwhen whenfolding folding affected affectedaa locally locally inverted flap of of sedim sedim developed The geometrical shown inin the the sketch sketch atat bo bo The geometrical interpretation interpretation isis shown Younging directions directions are are indicated by by "Y." Y." Younging Fly. 3 47 �F. Stylized regional fold geometry for the Shebandowan gmup deduced from cleavage—bedding and intenection lineation relationships. The fold plunge variation is infened to be quite large, although the principal magnetic susceptibilities of the slates ("max." and "mt.") show relatively little change in orientation within the axialplanar cleavage. Because the susceptibility is due to the grain fabric of the rock, we Suggest that the variation in fold plunge occurred during the development of the folds rather than later. Fig. 6 Geological map of northern part of Shebandowan Lake greenstone structure (SLGS) with horizontal line segment (QT) use for strain estimate of overall shortening. Strain stations (see Table 2 are numbered. lJ clastic meta— [7J sedimentary rocks Fig. fl volcanic rocks (mainly basic) Granitoid rocks Simplified regional geology after Pye and Fenwick (1965) with subprovinces (SW = Shebandowan—Wawa. Q = Quetico. W Wabigoon) after Goodwin (1977). Infonnation on boxed areas is presented in Figs. 2 and 3. 48 �— #9 + + +' + + — — — — —— — RELATIVE STRENGTH OF MINERAL LINEATION A FOLIATION LoR $ — — • — + 4f + + — + +— — + + + — 4 ¼_4. / '-7 + + MINE + + + 4 2 PLUNGING STRAIN FIELDS 5 O + I + I + I I O + + 8OLJNDARY 8ETWEEN OPPOSITELY— —-30 MINERAL LINEATIONS LOCAL FAULTS • SHEBANDOWAN + + + ++ + ,PEEWATAI LAKE +•_.—_ + 55— :÷ +'r+ +' __\LDERCHING . GULL PLUTON'. lt_J___'.J + GNEJSSTERRAIN+_+++1&4++++ •+ + + + + + ii TONALITIC/GRANODIORITIC 0 —— NORTHERN LIGHT — SYN/POST TECTONIC PLUTONS LEG END • + _+ ,- 1"— 7-4" —4• ftJRCHELL LAKE +/ + + ++ ++ +j — ; —;—- 1 — p Fig. 6 7 MI 10KM 25 �-- ... . ... . 0 ~ttf-wa ww) toed (c) (d) F i y. 8 I The The structural structuralfacing facingof of folds. folds. (a) (a)AAgeneral general illustration illustrationof ofthe theconcept conceptof ofstructural structuralfacing facingofoffolds. folds.The Thestructural structu facing remains consistently oriented directions are variable. An outcrop sketch ofofa a small fold racing direction directionremainsconsistently orientedwhile whiteyounging youngingdirectionsare variable.(b) (b)Anoutcropsketch smallF2 F fol which is axial axial planar. (c) (c) Lower Lower hemisphere which demonstrates demonstratesthat thatthe theS2 Si cleavage is hemispherestereographic stereographicrepresentation representationof ofbedding beddi and cleavage and their mutual intersection. ( A schematic profile view of bedding and cleavage. F2 folds face downward since younger youngerbeds beds are are encountered encountereddownward downwardalong alongthe theS2 S;cleavage. c 50 �References References Borradaile, G.J. "Structural facing" G.J. 1976. 1976. "Structural facing" (Shackleton's (Shackleton's rule) r u l e ) and and the the Paleozoic rocks Vdez Rablo, Rabio, SE SE Spain. Spain. rocks of o fthe theMalaguide MalaguideComplex Complex near near Velez Proc. Kon. Proc. Kon. Nederl. Nederl. Akad. Akad. van vanWetens., Wetens., 8 B79, 79,330—336. 330-336. Tectonically deformed as an an iindicator Tectonically deformed ppillow i l l o w llava a v a as n d i c a t o r of of way up up and way and bedding. 469—479. J. Struct. Struct.Geol., Geol.,4, 4, 469-479. Borradaile, Rorradaile, G.J. G.J. 1982. 1982. Borradaile, G.J. G.J. and andSchwerdtner, Schwerdtner, W.M. W.M. 1984. 1984. Horizontal shortening shortening of o fupward upward facing greenstone facing greenstone structures in i nthe thesouthern southernSuperior SuperiorProvince, Province,Canadian Canadian Shield. Can. EarthSci., Sci.,21,21,611—615. 611-615. Can. J. Earth The Shebandowan Group:"Timi Timiskaming G. J. and andBrocon, Brocon, H.G. H.G. 1987. 1987. The Shebandowan Group: skamingBorradaile, G.J. like" 1i k e "Archean Archean rocks rocks in i nNorthwestern Northwestern Ontario. Ontario. Can. J. J. Earth 185-188. Can. Earth Sci., Sci.,24,24,185—188. agesf ofor and regional regional Corfu, F. F. and and Stott, S t o t t , G.M. G.M. 1986. 1986. U—Pb U-Pb ages r llate a t e magmatism magmatism and Corfu, deformation in i nthe theShebandowan Shebandowan bbelt, e l t , Superior Superior Province, Province,Canada. Canada. Can. J1. Jl. Earth 1075—1082. Can. EarthSci., Sci.,23:23: 1075-1082. Application ooff [-S Schwerdtner, W.M., W.M., Bennett, Bennett, P.J. P.J. and and Janes, Janes, T.W. T.W. 1977. 1977. Application L-S Schwerdtner, fabric f a b r i c scheme scheme tto o structural s t r u c t u r a lmapping mapping and and paleostrain analysis. analysis. Can. J. Earth 1021—1032. Can. J. EarthSci., Sci.,14,14, 1021-1032. Strain Schwerdtner, W.M.,SStott, andSSutcliffe, Schwerdtner, W.M., t o t t , G.M. G.M. and u t c l i f f e , R.H. R.H. 1983. 1983. S t r a i n patterns patterns of crescentic crescentic granitoid g r a n i t o i d plutons piutons ini nthe theArchean Archean greenstone greenstone t terrain e r r a i n of of Ontario. J. Struct. 419—430. Struct.Geol., Geol.,5, 5, 419-430. Stott, G.M. and andSchwerdtner, Schwerdtner, W.M. W.M. 1981. 1981. AA sstructural t r u c t u r a l analysis analysis of o f the the central central S t o t t ,G.M. part Shebandowan belt. inetavolcanic-metasedimentary be1 t. p a r t ofo the f the Shebandowan metavolcanic—metasedimentary Ontario Geological Geological Survey, Survey, Open Open FFile i l e Rep. Rep. ## 5349 5349 44 44 p. p. 1 I Gold mineralization Shebandowan Gold m i n e r a l i z a t i o nini the n the Shebandowan beltt and and its i t srelation re1a t i o ntot oregional regionaldeformation deformation patterns. patterns. be1 Ont. Ont. Geol. Geol. Survey, Survey, Misc. Misc.Paper Paper110, 110,181—193. 181-193. Stott, S t o t t , G.M. G.M. and and Schnieders, Schnieders, B.R. B.R. 1983. 1983. 51 �fiELD �Granitoid-related Granitoid-related mineral mineral deposits deposits of of the the western western Lake Lake Superior Superior region. region. Stephen Kissin Stephen A. Kissin Lakehead Lakehead University University Thunder Thunder Bay, Bay, Ontario Ontario P7B P7B5E1 5E1 Canada Canada 52 �Introduction Introduction The locations of surface exposures of granitoid rocks rocks of of the the western western Lake Lake Superior region are illustrated in Figure 1. The Archean granitoids are found in a a Superior region are illustrated in Figure 1. The Archean granitoids are found in western area in the vicinity of Thunder Thunder Bay, which which is separated by Proterozoic Proterozoic from various various plutons lying south of sediments and diabase sills of the Nipigon Plate from Lake Nipigon. The western group is associatd with the Lake Nipigon. The western group is associate) with theShebandowan-Wawa Shebandowan-Wawa greenstone subprovince and and its its boundary boundary with with Quetico Quetico Subprovince Subprovince to to the the north. north. The greenstone subprovince The (6), easterly group of granitoids, with the exception of the Black Black Sturgeon Sturgeon Lake Lake granite granite (6), lies within the Quetico Subprovince. The plutons in Figure 1 are numbered for lies within the Quetico Subprovince. The plutons in Figure 1 are numbered for purposes of identification the following following discussion. discussion. The identification in the The names names of the bodies, bodies, with with aa exceptions, are are those those employed employedby by McCrankad. McCrank.t at. (1981) (1981) in in their compendium. few exceptions, . The Glacier Lake pluton pluton (3) (3)is is aa batholith-sized batholith-sized body consisting consisting of two-mica two-mica leucogranite in the the north north grading grading into into biotite biotite granite graniteto tothe thesouth. south. The rocks rocks show minor penetrative deformation within a kilometer of of their northern contact and and are bounded by aa weakly defined contact aureole in the intruded metasedimentary intruded metasedimentary rocks, rocks, suggesting late tectonic emplacement. emplacement. The rocks are The rocks are moderately moderately to to strongly strongly peraluminous, and although bearing no aluminous minerals other than micas, have the geochemical characteristics (A/(CNK).. 1.1, normative 1.l, normativecorundum, corundum, characteristics of S-type granitoids (A/(CNK)L^. high &O and high initial 87SR/°6Sr). Textural and geochemical patterns suggest <180and high initial "SR/^Sr). geochemical patterns suggest that that has been beentilted tiltedtotothe thenorth northsince since emplacement (Zayachivsky., .eta.,1989). 1989). the pluton has emplacement (Zayachivsky The MNW stock (1), characteristics, appears appears to to be a (I), with with essentially essentially identical characteristics, satellite of of the the Glacier Glacier Lake Lake Pluton. Pluton. The llgour satellite llgour Lake Lake Group Group of of Zayachivsky Zayachivsky (1985) (1985) and and Kissin and Zayachivsky (1985), equivalent to to the Kilgour Lake-Steen Lake metagabbro (1981), is isaa zoned of McCrank McCrankaA. (1981), zoned granitoid granitoid intrusive intrusive with a core of monzogabbro monzogabbro grading outward outward to tonalites tonaliies and and granodiorites. granodiorites. . Also present in the Georgia Lake area are numerous tabular tabular intrusions of leucotonalite to granodiorite of thickness ranging from aa few meters leucotonaliie (trondhjemite) to meters to to aa few tons of meters meters and strike lengths of up up to several several kilometres. The Thepetrogenic petrogenic affinities of these these are are unclear unclear as as is isthe thetiming timingof oftheir theiremplacement. emplacement. In fact, fact, contacts affinities of among the Glacier Lake pluton, the Kilgour Lake group and and the the tabular intrusions intrusions have have not been been observed observed in in the the field. field. exposed to to the south of the Georgia The Glacier Lake pluton is well exposed Georgia Lake Lake area, but but its its eastern eastern margin margin is is unmapped unmappedat at present. present. It is exposed exposed in in the the west west along along Highway 11, 11, but but to the west, between Highway 11 and the Nipigon Nipigon River system, is a region soillwav between betweenthe the Lake Lake reaion of thick thick Pleistocene Pleistocenesediments, sediments, deposited deoositedin in aa spiliway Nipigon basins. Metasedimentary ~ i b i ~ and o n Lake Superior basins. ~etkedimentaryrocks are intruded intruded by granitoids granitoids of variable size and form: form; however, of outcroo outcrop makes Door availability of makes interpretation interoretation of however. poor to thewest, the west, a well-defined intrusion, the the overall geologic geologic picture picture difficult. difficult ' Farther to Church Lake is seen to intrude intrude Archean metasediments metasediments and and Lake quartz quartz monzonite monzonite (4), is "migmatites". "migmatites". The The petrography petrography of of these these rocks rocks is is similar similar to that of of the the Glacier Glacier Lake Lake pluton (Coates, 1972), and it is possible that they are parts of the same batholithicbatholithicsized sized body. body. The Pine Portage intrusion (5) is exposed in a window in Proterozoic Proterozoic rocks rocks at at 53 �Figure 1. * BAY THUNDER: Boy Thunder • Sh,Iabeer Sturgeon L Lake Superior \fiion + Geology of the western Lake Superior region indicating the locations of major granitoid plutons. Numerical codes are discussed in the text. Lake boundaries Province + Subprovince rocks C numbered Dog ) undivided ) Shebandowan Subprovince 25 km N A ear Subprovince (meta sediments + paragneisses LI Quetico Gp. + Nipigon Plate undivided) Southern Province ( Animikie I �composed of two-mica leucogranites the source source of of the the Nipigon NipigonRiver. River. It is composed leucoaranites cut by bv tabular leucotonatites, similar to those in the Georgia Lake area. The leucotonatites,similar The granitoids granitoidsare are closely associated with lithium-bearing pegmatite dikes, cutting metasedimentary closelv lithium-bearina cuttina metasedimentarv rocks rocks - .oeamatite - in rare-element to the east. Geochemical fractionation trends theeast. Geochemical fractionation trends in rare-element and and simple simple pegmatites pegmatites suggest that they are derived by fractionation fractionation of a leucogranite parent. The Black Sturgeon Lake granite (6) is exposed in a window of Archean rocks rocks east of Black Black Sturgeon SturgeonLake. Lake. It is associated with greenstone-like lithologies and may lie in the Wabigoon Wabigoon Subprovince. Subprovince. lies the the Hilma HilmaLake Lakegranite granite(7). (7). The body consists West of the Nipigon Plate lies (Tihor, 1973), 1973), although although textural textural compositional compositional white to pink pink two-mica two-mica leucogranite leucogranite (Tihor, variations of the rock are found, including pegmatitic granite granite and and pegmatite. pegmatite. The The relationship to the Penassen Penassen Lakes stock of Scott Scott (1985), (1985), equivalent to the the Wailer Waller Lake Lake granite of of M McCrank.a!. c C r a n k M(1981), . (1981),isisunclear unclearowing owing to to aa lack lack of of mapping. mapping. The The two two bodies are shown as contiguous by McCrank.eta!., McCrankad., although although the the different different names names were applied to to the separate bodies suggested suggested in in Figure Figure 1. 1. This differentiation of the two supported by bodies is supported by the the rather rather different different petrography petrography of the the Penassen Penassen Lakes Lakes stock, which isismostly mostlycoarse-grained coarse-grainedporphyritic porphyriticgranite granite to to quartz quartz monzonite monzonite with with local local hornblende syenite and syenite phases. syenite and syenite phases. The Mackenzie MacKenzie granite granite (9), (9), equivalent to the Waylan Lake granite of McCrank a aL (1981), has a complex outcrop metavoicanics and at. (1981), has a complex outcrop pattern intruding Archean metavolcanics Group (Gunflint metasediments, lying unconformably below Animike Group (Gunflint and and Rove Rove Formations) sediments and intruded intruded by by Keweenawan Keweenawan diabase diabase sills and and dikes. dikes. According biotite granite. granite. The (1979), it is a medium-to-coarse-grained biotite According to Rogers Rogers (1979), Mackenzie granite is MacKenzie is possibly possibly equivalent equivalent to to the the Kivikoski Kivikoski granite granite (10), (lo), equivalent equivalent to to the the Mcintyre granite of McCrank .. (1981), of the the Mclntyre McCrankad. (1981),as asgranite graniteisisknown knownto tounderlie underliemuch much of city of Thunder Bay as basement to to the the Animike Animike Group. Group. The Gorham granite of McCrank.Qta!. (1981) is included on Figure 1 as part of the McKenzie McCrankad. McKenzie granite (M.M. kehienbeck, pers. Kehlenbeck, pers. comm., comm., 1990). 1990). The Trout Lake granite (11), (1I), Barnum Barnum Lake Lake quartz quartz monzonite monzonite (12) (12) and andWhiteliiy Whitelily similar plutons plutons of of circular to to elliptical outcrop outcrop pattern Lake granite (13) are three similar pattern aligned west to east near the Shebandowan-Quetico Subprovince Subprovince boundary. boundary. The aliened The rocks are characteristically hornblende and biotite-bearing, porphyritic quartz rocks out monzonites. Kehlenbeck Kehlenbeck(1977) f1977) pointed ~ointed outtheir their late latesyntectonic svntectonicemplacement, em~lacement.as as aureoles in indicated by well defined defined contact &nta&aureoles in the the intruded intrudedArchean Archean metasedimentary metasedimentary and metavolcanic metavolcanic rocks. rocks. Mineral Deposits Pegmatites Peamatites The most most spectacular spectacular granitoid-related aranitoid-relatedmineral mineral deposits deoosits of of the the area area are arerarerarepegmatites Georgia element ~ e ~ m a t i t einsthe ~ e o r ~Lake i a area and a small smail but similar pegmatite pegmatite field in in Portage area (Pve. (Pye,. 1965). 1965). These the Pine Portaae These have have been been studied more more recently recently by bv , Zayachivsky (1985) Archibald (1987), and and these these and and other results are reported reported by (7985) and ~rchibald Kissin & Zayachivsky Zayachivsky (1985), (1985), Kissin Kissinetal. d.(1986) (1986) and and Kissin Kissin and Archibald (1988). The The . .. 55 �rare-element pegmatites pegmatitesof ofthe theGeorgia GeorgiaLake Lakearea areaare areshown shownininFigure Figure2.2. The The pegmatites may be subdivided into three groups, a northern group whose members pegmatites may be subdivided into three groups, a northern group whose members show little difference in relative fractionation fractionation of of trace trace element element and and central central and and southern southern group degrees of of fractionation fractionation from from east east to to west. west. group whose whose members members show show increasing increasing degrees Barren pegmatites pegmatites lie lieto to the the east east of of the the central centraland and southern southerngroup group but but are are not not shown in Figure Figure 2. in 2. Most of of the the pegmatites are unzoned unzoned and and contain contain phenocrystic phenocrystic spodumene; spodumene; Most pegmatites are however, the more highly fractionated pegmatites of the central and southern group however, the more highly fractionated pegmatites of the central and southern group show weak to well developed developed zoning and and may may contain, as as well as as spodumene, spodumene, tantalite-columbite group minerals, beryl, cassiterite or staringite and various Li Li tantalite-columbite group minerals, beryl, cassiterite or staringite and various phosphate minerals. minerals. The MNW pegmatite contains spodumene-quartz-intergrowth The MNW (SOUl) (SQUI) and is a potential potential source of of ceramic ceramic grade grade spodumene. spodumene. An entirely separate separate group group of pegmatites occurs within the Quetico Subprovince Subprovince (1978) described described uraniferous, uraniferous, white white albiteto the west of of the the Nipigon NipigonPlate. Plate. Franklin (1978) muscovite-biotite-quartz peamatites pegmatites containing containing 60-100 60-100ppm ppm U. U. The pegmatites have have muscovite-biotite-quartz .peamatites been found to contain uraninite, and all such pegmatites containing accessory apatite contain uianinite, and containing apatite' found to be uraniferous. These trending have been found These pegmatites oeamatites occur occur in in an an east-west east-west trendina. within the the Quetico Quetico Subprovince. Subprovince. sTheir origin is is obscure, obscure, as as they they appear appearto to be be zone within heir origin unrelated to to anatectic mobilizate mobilizate pods pods in in high-grade high-grade metamorphic metamorphic rocks rocks nor nor to to pink syenitic peamatites pegmatites apparently apparently co-magmatic co-magmaticwith withgranitic graniticintrusions intrusionsininthe thearea. area. The The svenitic Hilma Likegranite, Lake granite, however,was however, was mentioned mentioned as as having having an ananomalous anomalous uranium uranium content content thma with respect to other rocks of the area (Franklin, (Franklin, 1978). 1978). - Molybdenum A sub-economic sub-economic molydenite occurrence occurrence is is located located at at Anderson Anderson Lake, Lake, at at the the western margin of the Hilma Lake ggranite. Molydenite occurs as coarse aggregrates in quartz veins and within pink pink pegmatitic pegmat granite. It is unclear as to whether the mineralization process processwas was pegmatit pegmatitic or hydrothermal. The quartz veins lack however, hydrothermal alteration characteristic of veincharacteristics of pegmatites; howeve deposits is also lacking. The average grade of the or porphyry-style porphyry-style molybdenite deposi occurrence is reportedly 2.85% Mo; however, the apparent small size of the reserves is reportedly responsible for a lack lack of of exploitation. exploitation. Non-magmatic deposits, hosted in gra granite Non-magmatic Uranium Superior region region were were summarized summarized by by Uranium occurrences in the western Lake Superior (1978). Those related to granitoid rocks include uraniferous pegmatites in in the the Franklin (1978). Quetico Subprovince and vein-type occurrences occurrences in in granitic granitic basement basement or or cutting cuffing Sibley Group sediments. The The vein-type vein-type occurrences occurrences are not not of direct direct hydrothermal hydrothermal derivation from granitic granitic magmas, but but may may be be related related to uraniferous uraniferous pegmatites pegmatites and and uranium-rich uranium-rich granites as protore. protore. (1) in in The uraniferous uraniferous pegmatites are prominent prominent in in the Greenwich Greenwich Lake Lake area area (U (U(1) 4), and and exploratory exploratory work work has indicated indicated that thatthey they occur occur about about 40 40 km km to to the west west Figure 4), 56 �:/;: m::. NAMA CREEK )••• 7. :NoRTH NAMA CREEK1 SOUTI 5 Postogoni 2 ¶I. . • :• . . • \\\. •• : fr':. NEWK IRK : :'?s .;'9gjz1SALO. : :..Xy SOUTHWESTr fI + • • • a • . . .t.÷_,.Spl + 1÷ + +11- +iI+ e- +1 + de Fault Fault _.___— Contact Contact km I 1,1111111 I10 km 0 0 I Figure F i g u r e 2. 2. 1÷ + + LEGEND LEGEND Metasedin,ent Metasediment I ++I Granifoid Gran~toid 1 1+ + Rare element element pegmatite oeamatite - Nipigon Nipigon diabase diabase I 1 !ANS0NL•.j.j_r+ + t O ~ P ~ 8 8 9 ~ 1 The GeorgiaLake LakePegmatite Pegniatite The Georgia F i eField l d i l lillustrating u s t r a t i n g tthe h e granitoid granitoid rocks rocks and and rare-element rare-element pegmatites. pegmatites. Named pegmatite bodies Named pegmatite bodies were were studied by by Zayachivsky Zayachivsky (1985). (1985). 57 �along Highway Highway 527. As within aa .&aq Asdescribed describedpreviously, previously,these thesepegmatites pegmatitesare arecontained containedwithin relatively narrow narrow east-west east-west trending trending zone. zone. The small pods and :relatively small size of the pegmatite pegmatitepods and lenses and their low low uranium uranium content content preclude preclude the possibility of economic economic deposits. deposits. lenses :mN The vein-type occurrences occurrences (Figure 4) at at Greenwich Greenwich Lake Late (U(1)) and and Innes fines Lake take (U(2)) have been been described described by by Franklin (1S78) (1978) and and Yule Yule (1978). (1979). Both [U(2y> Both occurrences occurrencesare are sub-economic but were the source of considerable excitement in the late %%Â¥& 1970's. Both sub-economicbutwarethesourceofconsiderableexcitement;hthe occurrences are are localized localized in in brecciated occurrences brecdatedshear shear zones zones cutting cuttingall all Archean Arehean lithologies. ÈaiGitoes Lake occurrence occurs in in well defined veins with with quartz and and pyrtte pyrite The Greenwich ;Lake gangue and minor pitchblende yielding grab sample grades of 0.5 to 2.0% U. and minor pitchblende yielding grab sample grades of 0.5 to Hydrothermal ateralion alteration of wall rock is distinct, Hydrothermal is d isfinct,and and the the vein veto contains containsaltered Sibley Group fragments indicating its Proterozoic Proterozoic age. age. The Innes Innes Lake occurrence has no recognisable uranium minerals, although the shear zone recognisable uranium although the shear zoneis is much enriched in apatite, which is thought to to be the carrier of uranium. Hydrothermal be (he carrier uranium. Hydrothermalalteration alterationincluding .jndutfi chloritization, sericitizatton sericitizationand and hetnattization hematitizationisisdistinctive distinctiveabout aboutthe the.&ear shearzones. zones. 'The chloritization, The shear zone zone yielded yieldedvalues valuesas ashigh highas as633 633ppm ppmU308. U.4. (1978) also also described described minor minor uranium occurrences (up (up to 540 Franklin (1978) 540 ppm ppm U) U)in in the Enterprise Mine, one of aa group group of of vein-type vein-type deposits deposits known knownas asthe thelead-zinc-barite tead-zinc-bante veins. These veins. These are arediscussed discussedmore morefully fully in inthe thenext next section; section;however, however, both bothFranklin Franklin (1978) and and Yule Yule (1979) (1979) believed believed that that the the Greenwich Greenwich Lake Lake and and Innes lnnes Lake occurrences occurrences (1978) were formed by by the the same same process processthat that formed formedthe thesulfide-rich sulfide-richlead-zinc-barite lead-zinc-bariteveins. veins. Briefly, the the hypothesis favored is circulation of basinal brines through uranium-enriched circulation basinal brines through uranium-enriched and anomalous anomalous granitic granitic rocks. rocks. The source rocks, the uraniferous pegmatites and The brines brines circulated through faults marginal to the Sibley Group depositional basin and rose and and cooled in response to hydraulic gradients. cooled in response to hydraulic gradients. Lead-zinc-barite The lead-zinc-barite veins veins (Figure (Figure3) 3)are are near nearthe the margins margins of of the the present present outcrop outcrop of the Sibley Group or its inferred former former outcrop. outcrop. The Theveins veins were were studied studied in in detail detail by by who found them to Franklin & Mitchell (1977), who to contain contain galena, galena, sphalerite sphalerite and andbarite, barite, with minor chalcopyrite and marcasite in in quartz quartz and and calcite calcite gangue. gangue. The The veins occur occur in three settings: (A) (A) fractures fractures within within the the Sibley Sibley Group, (B) (B) fractures fracturesat at the theSibleySibleybasement unconformity and (C) fractures fractures within granitic basement. Franklin Franklin&&Mitchell Mitchell believed that the deposits formed by mixing of bacterially reduced H25 with metal-rich deposits formed by mixing of bacterially reduced H2Swith metal-rich derived by occurred in brines derived by leaching leaching of of the theSibley Sibley basinal basinalfill. fill. Deposition occurred in structural structural traps at or near near the the basin basin margin. The Thebasinal basinalcharacter character of of the the brines brineswas was confirmed confirmed in recent recent fluid inclusion studies by Haynes (1988). inclusion studies by Haynes (1988). The differentiation of structural settings by Franklin & Mitchell suggests that type (C) may 1C) mav be a portion oortion of of aa continuum continuumof of deposits depositsextending extendinato to the theuraniferous uraniferous occurrences at Greenwich Lake and lnnes~ake. Innes Lake. The The lead-zinc-barite lead-zinc-bariteveins represent occurrences whereas the the uranium occurrences are a sulfide-rich but uranium-poor end-member, whereas sulfide-poor but uranium-rich. The Thedifferential differential factor seems seems to to have have been been the the relative relative amount of interaction amount interaction with with basinal basinal fill (base metal metal source) or or granitic granitic basement basement (uranium source). 58 �PROTEROZOIC PROTEROZOIC ARCHEAN ARCHEAN Diabase k1 Diabase II...... Sibley SibleyGroup Group I I Anirnikie AnimikieGroup Group L1 A Pb-Zn—Barite Pb-Zn-Barite Granitic Granitic Rocks Rocks Metasedimenfary Metasedirnentary Gneissic Gneissic Rocks Rocks Metavolcanic Metavo'canic Rocks Rocks •ÂAmethyst Amethyst deposit deposit deposit deposit Figure Dorionarea areaillustrating illustrating the Figure 3. 3. The The Dorion the locations locations of of major major amethyst amethyst deposits deposits and and lead-zinclead-zincbarite star is barite veins. veins. The The star is the the location location of ofthe theThunder ThunderBay Bay Amethyst Amethyst Mine. Mine. 59 �Amethyst The The largest largest deposits deposits of of amethyst amethystin in North NorthAmerica America are are located locatedin inthe theThunder Thunder Bay Bay area area (Figure (Figure 3). Amethyst Amethyst isisthe theprovincial provincialgemstone gemstone of of Ontario Ontario and andisisaa significant the region. Nearly Nearlyall allthe the important important significant generator of economic activity in the deposits occur in a 10 km-long, east-west trending near the margin deposits occur in a 10 km-long, east-west trending near the marginofofthe theSibley Sibley Group outcrop and with Hilma Lake granite as the basement. A few other Group outcrop and with Hilma Lake A few otherscattered scattered occurrences occurrences are are spatially spatially related related to the the Sibley Sibley Group Group outcrop outcrop and andare areinvariably invariablyhosted hosted in in granite. granite. The The amethyst amethyst deposits deposits consist consist mostly mostlyof of quartz quartzincluding includingmuch muchofofthe thevariety variety amethyst with minor calcite, barite and sulfides such as pyrite, chalcopyrite and with minor calcite, barite and sulfides such as pyrite, chalcopyriteand bornite. The Thesimilar similargeologic geologicselling settingofofthese thesedeposits depositstotothat thatofofthe thelead-zinc-barite lead-zinc-barite veins suggests that they are cogenetic. cogenetic. Fluid Fluidinclusion inclusionstudies studies by by McArthur McArthur(1988), (1988), reported Kissin(1988), (I=),indicate indicate that that most most amethyst amethyst formed formednear nearthe the reportedin in McArthur McArthur &81Kissin surface at temperatures ranging ranging from from 60 60 to to 90 90 C. C. The deposits appear to be lowdeposits be lowtemperature temperature derivatives derivatives of lead-zinc-barite lead-zinc-bariteveins, poor poor in in sulfides sulfides and andricher richerininquartz. quartz. A crucial crucial factor factor appears appears to to have have been beenpassage passageof of the the quartz-depositing quartz-depositingsolutions solutions through granite. A through aa uranium uranium enriched host rock, e.g. e.g. the Hilma Lake granite. A source source of of silica silica (from (from sericitization sericitization of feldspar) and radioactivity are probable requirements for the the formation formation of amethyst. The Theformation formation of of the the electronic electronic colour colour center in in quartz quartz producing the blue of amethyst has been attributed to the coupled electronic producing the blue of amethyst has been coupled electronic transition: Fe3(substitutional)-+ Fe'(substitutional) + e Fe3(interstitial) + e-Fe2(interstitial) The Fe4*(substitutional) (substitutional) ++ Fe2 Fez*(interstitial) (interstitial) defect defect (Cohen (Cohen&&Hassan, Hassan, The associated associated Fe4 1974) is evidently unstable at high temperatures, as older generations as older generations ofof amethyst amethyst high were observed bebleached bleachedby byinflux influx of of holler hotterfluids. fluids. observed to to be REFERENCES REFERENCES Archibald, Archibald, D.L. D.L 1987: Granitoids Granitoiasand anaPegmatites Pegmatitesof of the thePine PinePortage PortageArea, Area, Northwestern NonnwesiernOntario; Ontario; Unpublished B.Sc. Thesis, Lakehead Unviersity, Thunder Bay, 89 p. Unpublished Lakehead 89 p. Coates, Coates, M.E. M.E. 1972: Geology Geology of of the the Black Black Sturgeon Sturgeon River River area, District District of Thunder Bay; Ontario Ontario Department of Mines Mines and and Northern NorthernAffiars, Affiars, Geological Geological Report Report 98, 98, 41 41 p. p. Cohen, A.J., A.J., and andHassan, Hassan,F. F. 1974: Ferrous Ferrous and and Ferric Ferric Ions Ionsin inSynthetic Synthetic a-Quartz a-Quartz and and Natural Natural Amethyst; American American Mineralogist, Volume Mineralogist, Volume 59, 59, p. p. 719-728. 719-728. 60 �Franklin, J.M. Franklin, J.M. 1978: Uranium in the the Nipigon Nipigon Area, Area, Thunder Thunder Bay Bay District, District, Ontario; Ontario; 1978: Uranium Mineralization Mineralization in Current Research, Part A, Geological Survey of Canada Paper 78-lA, p. 275275Current Research, Part A, Geological Survey of Canada Paper 78-1A, p. 282. 282. Franklin, J.M., J.M., and and Mitchell, Franklin, Mitchell, R.H. R.H. 1977: Lead-zinc-barite Veins of of the the Dorion Dorion Area, Area, Thunder Thunder Bay Bay District, District, Ontario; Ontario; 1977: Lead-zinc-barite Veins Canadian Journal of Earth Sciences, Volume 14, p. 1963-1979. Canadian Journal of Earth Sciences, Volume 14, p. 1963-1979. Haynes, F.M. Haynes, F.M. 1988: Fluid-inclusion in Archean Archean Basement, Basement, Thunder Thunder Bay Bay Fluid-inclusion Evidence of Basinal Brines in Pb-Zn-Ba District, District, Ontario, Ontario, Canada; Canada; Canadian Canadian Journal Journal of of Earth Pb-Zn-Ba Earth Sciences, Sciences, Volume 25, Volume 25, p. p. 1884-1894. 1884-1894. Kissin, S.A., S.A.,and andArchibald, Archibald, D.L. DL. Kissin, 1988: Genesis of Pegmatites in the Quetico Gneiss Belt of of Northwestern Ontario 1988: Pegmatites and Associated Granitoids of the Pine Portage Area; Area; Grant Grant 225, 225, p. p. 44Pegmatites and Associated Granitoids of the Pine Portage 13 Geoscience Research 13jn Geoscience Research Grant Program, Program, Summary Summary of of Research Research1987-1988, 1987-1988, edited by V.G. V.G. Milne, Ontario Ontario Geological Geological Survey, Miscellaneous Miscellaneous Paper 140, 251 p. P- Kissin, S.A.. S.A., and and Zayachivsky, Kissin. Zavachivskv. B. 6. 1985: Genesis Northwestern Ontario 1985: ~enesisof Pegmatites ~ k ~ m a t i t in e sthe Quetico Gneiss Belt of Northwestern Pegmatitesand andAssociated AssociatedGranitoids Granitoidsof ofthe the Georgia Georgia Lake Lake Rare-Element Pegmatites Pegmatite Field; Grant 225, p. 186-199 in Geoscience Research Grant Program, Pegmatite Field; Grant 225, p. Jn Geoscience Research Grant Program, Summary of Research 1984-1985, edited by V.G. Milne, Ontario Geological Research 1984-1985, edited by - V.G. Survey, Miscellaneous 246 p. ~iscellaneousPaper 127, 127,246 Kissin, S.A, S.A., Zayachivsky, Zayachivsky, B B., and Branscornbe, Branscombe, L.A. Kissin, ., and LA. of Northwestern Northwestern Ontario 1986: Genesis of Pegmatites in the Quetico Gneiss Belt of 'Barren' Pegmatites, Granitoids, "Barren" Pegmatites, and and Metasediments, Metasediments, with Additional Data on Rare-Element Pegmatites, Pegmatites,from from the the Georgia Georgia Lake Lake Pegmatite Pegmatite Field; Field; Grant Grant 225, 225, p. p. in Geoscience Research Grant Grant Program, Program, Summary of Research 198565-78 jn edited by by V.G. V.G. Milne, Ontario Geological Survey, Survey, Miscellaneous Paper 1986, edited 130, 235 p. 130,235 McArthur, J1 J. McAfthur, 1988: Fluid Fluid Inclusion Inclusion and and Stable Isotopic Isotopic Studies on Amethyst, Thunder Bay Amethyst Mine, Thunder Thunder Bay District, Ontario; Unpublished Unpublished B.Sc. Mine, B.Sc. Thesis, Lakehead Lakehead University, Thunder Bay, 108 108 p. McArthur, J., McArthur, J., and andKissin, Kissin, S.A. S.A. 1988: Stable Isotope, to the the 1988: Isotope, Fluid Fluid Inclusion, and Mineralogical Studies Relating to of Amethyst, Amethyst, Thunder Thunder Bay Bay Amethyst Amethyst Mine, Mine, Ontario, Ontario, Canada; Canada; p. p. A40 A40in hi Genesis of of America, America, October October 31-November 31-November 3, 3, Denver, Denver, Abstracts Abstracts with with Geological Society of Programs, Volume 20, 423 p. J.D., G.F. D.,Misuira, J .D., and and Brown, Brown, P.A. P.A. McCrank, G.F.D., 1981: Plutonic Rocks in Ontario; Geological 80-23, 171 p. p. 1981: Plutonic Rocks in Geological Survey of Canada, Paper 80-23, 61 �Pye, Pye, E.G E.G 1965: 1965: Georgia Georgia Lake Lake Area; Area; Ontario Ontario Department Department of of Mines, Mines, Geological Geological Report Report 31, 31,113 113 p. p. Scott Scoff, J. J. 1985: MacGregor Township, District District of of Thunder ThunderBay; Bay;p.p.67-70jn 67-70 j Summary MacGregor Township, Summary of of Field Field Work and Other Activities 1985, Ontario Geological Survey, edited by J. Wood, Wood, Work and Other Activities 1985,Ontario Geological Survey, edited by J. O.L. O.L. White, White, RB. R.B. Barlow, Barlow,and andA.C. A.C. Colvine, Colvine, Ontario OntarioGeological GeologicalSurvey, Survey, Miscellaneous Paper 351 p. 126,351 p. Miscellaneous Paper 126, Yule, GM. Yul e, G.R. 1979: 1979: Investigations Investigations of of the the Good Good Morning Morning Lake Lake Radioactive Radioactive Fault Fault Breccia: Breccia: Innes Innes Lake Lake Area, Dorion Township, Northwestern Ontario; Unpublished B.Sc. Thesis, Area, Dorion Township, Northwestern Ontario; Unpublished B.Sc. Thesis, Lakehead University, Thunder Bay, 93 p. p. Lakehead University, Thunder Bay, 93 Zayachivsky, B. B. Zavachivskv. 1985: Granitoids 1985: ~ r a n i o i d and sand Rare-Element Rare-Element Pegmatites Pegmatites of the Georgia Georgia Lake Lake Area, Area, Northwestern Ontario; Unpublished M.Sc. Thesis, Lakehead University, Northwestern Ontario:- Unoublished M.Sc. Thesis. Lakehead Universitv. Thunder Thunder . Bay, 234 p. Bay, 234 p. - Zayac/iivsky, 8.. 8., Kissin, and Branscombe, Kissin. S.A., S.A. and Branscornbe. L.A. LA. Zavachivskv. 1989: The Granitoid 1989: ~ h Georgia e ~ e &Lake Lake ~ i aPegmatite pegmatite Field, Field, Northwestern ~orthwesternOntario, Ontario, Part Part II. 11. Granitoid Rocks and their Relationship to Rare-Element Rare-Element Peamatites: Pegmatites;o. p.A20 A20in jj Geological Relationshio to Geoloaical Association of Canada and Mineralogical Association of Canada, May 15-17, Association of Canada and~ineralogical~ssociationof Canada, May15-17, Montreal, Joint Annual Meeting, Program with Abstracts, Volume Volume 14, 14, 135 135p. p. 62 �- Quetico Subprovince ( meto sediments paragneisses ) + Shebondowon Subprovince ( undivided ) Plutonic rocks Province 0 Figure 4. Figure 4. + Subprovince boundories stop locations Geology Superior region region showing numbered Geology oof f the t h e western western Lake Lake Superior showing numbered f i efield l d t rtrip i p stops. U ( 2 ) indicate i n d i c a t ethe t h elocations l o c a t i o nof s othe f t hGreenwich e GreenwichLake Lakeand and Innes Lake Lake U ( 1 )and and U(2) U(l) �*. FIELD TRIP LOG This field trip will attempt to illustrate as many of the features as as possible possible in in one one day. Unfortunately, some of the most interesting ones are the most inaccessible. inaccessible. The The trip route is illustrated in Figure 4, together with a simplified geological map. Stop 1: Southeast Southeast margin margin of of the the Mackenzie MacKenzi granite (Lakeshore Drive near Silver Harbour Drive near Silver Harbour Road). Road). In this location location the intrusive intrusive contact of the the Mackenzie MacKenziegranite granite with with Archean Archean can be seen. seen. The metavolcanic can The metavolcanics metavokxnics are are amphibolitic amphiboliiic near near the contact reflecting their contact metamorphism metamorphism to hornblende hornblende hornfels hornfels facies, fades, according according to Rogers (1979). South of Lakeshore Drive the granite is in fault contact to Rogers (1979). South of Lakeshore Drive the granite is in fault contact with with the Proterozoic Formation. A outcrop occurs Proterozoic Gunflint Formation. A small small Gunflint outcrop occurs on on the the north west of of the the granite granite co contact. The granite is jointed north side of Lakeshore Drive, west quartz-calcite vein is and in places places the joints have been been mineralized. AAsmall s amounts of base metal visible here, but other veins contain pyrite and small a sulfides. Small Smallveins veins of of amethyst amethyst also also occur occur ininthe thearea. are A short distance to the west and south toward Silver Harbour are a series of silver mines, which operated in the late 19th Century. From north to south these are the 3A, Beck or Silver Harbour and Algoma Mines. The shafts have been capped or sealed and most dump material has been removed in recent years. Little can be seen of these. These deposits were formed in Keweenawan times (Franklin 1986) and are unrelated to granitic rocks of the area. Stop 2: Main phase, Mackenzie granite (Highway 11-17 near Mackenzie River bridge). The massive and leucocratic character of the granite can be be seen seen here. (1979), the the color color index index is is always always5 s 5, making a making the granite g According to Rogers (1979), leucogranite. The The only only primary primarymafic mafic mineral mineral is is biotite biotite and and the the only only accessories accessories noted noted are traces of sphene and apatite. No Nomineral mineraloccurrences occurrencesare areassociated associated with this pluton pluton apart apart from from some some small small but but commercial commercial amethyst-bearing amethyst-bearingveins veins east of the the Mackenzie MacKenzieRiver. River. 64 �Stop S t o 3: ~ 3: Anderson occurrence (East Loon Road Anderson Lake Lake Molybdenum Molybdenum occurrence (East Loon Road from Highway 11-17. Continue 1.8 km to north Highway Continue 1.8 km to north side side of of Loon Loon Lake. Turn Turnright rightimmediately immediately past past bridge bridge over over small small stream. stream. Continue Continue about about 200 m m to Hydro Hydro transmission lines and clearing. clearing. Park Parkand and continue continue north north on on road road by by foot for about about 3 3 km km to to Anderson AndersonLake.) Lake.) The molybdenite occurrence described described in the introductory text was diamond drilled to the chaotic scene drilled and and blasted blasted at surface in the 1960's, giving rise to here. Good Goodspecimens specimensofofcoarse-grained coarse-grainedmolybdenite molybdeniteand andpegmatitic pegmatiticgranite granite host host rock rock may may be becollected. collected. Stop S t o 4: ~ 4: Thunder Bay Bay Amethyst Mine (back-track on on East East Loon Loon Road to junction with road road to to Thunder Thunder Bay Bay Amethyst Amethyst Mine. Mine. Turn right right and and continue continue for approximately 10 km to the Mine.) Mine.) Note: This m: Thisisisaacommercial commercialoperation operationentered entered by by - permission owner. There permission of the owner. There is to be be no no hammering hammerina nor collecting kollecting in in the the pit. pit. Collecting may be done done in in the the designated dump area, but material collected here is not to designated dump be broken by hammering. be broken by hammering. The The amethyst-bearing amethyst-bearing vein system occupies an an east-west east-west striking, near near vertical fault fault zone. The Thefault fault isisparallel parallel to to the the trend trend of occurrence occurrence of of other other amethyst amethyst deposits deposits in in the area area (Figure (Figure 3) and may form a major margin margin to the the Sibley Group depositional basin. The fault is offset by steps of a few meters by a Group The fault is series of northerly faults. The northerly striking en-echelon faults. The easterly easterly and and westerly limits of the the fault fault have have not notbeen beendetermined. determined. The The amethyst amethyst reaches reaches its its most most spectacular spectacular development development in in large large vugs vugs where where crustiform cm long long and and 10 10to to 15 15 crustiform aggregates aggregates contain contain crystals of quartz 30 to 40 cm cm cm in in diameter. diameter. The Thecrystals crystalsdisplay display growth growth zoning, zoning, which which is is consistent consistent throughout throughout the the deposit. deposit. The Theveins veinscontain containlittle little apart apart from from quartz, quartz, although although minute sulfide crystals occur in some growth zones. The Thealtered alteredgranite granite countryrock countryrock contains contains occasional occasionalaccumulations accumulations of pyrite, chalcopyrite, chalcopyrite, bornite bornite and other minor sulfides. The vein system is surrounded by a well-defined, and other minor sulfides. The vein system is surrounded by a well-defined, sericitized, sericitized, hydrothermal hydrothermalalteration alterationzone. zone. The The vuggy vuggy character character of of the the vein vein indicates indicates that it must have formed near the surface. surface. However, However,even evenmore moreconvincing convincingis is the the presence presence of breccia breccia fragments in in the the vein vein consisting consisting of of Sibley Sibley Group lithologies. The The Sibley Sibley Group Group has has been been entirely entirely removed removed from the area by erosion, but its its former presence presence is obvious. On On aa granite granite knob knob north northof of the the vein, vein, aa chloritized chloritized and and hematitic hematitic surface possibly may may represent representaaPrecambrian Precambrianpaleoregolith. paleoregolith. 65 �Stop 5: High-grade central portion of the Quetico Subprovince (Highway 11, east side of Lake Helen). In this this area, area, well well developed developed miamatites migmatites are indicative indicative of of the the highest In hiihest metamorphic grades attained in the Quetico Subprovince. Metamorphic metamorphic grades attained the QueticoSubprovince. ~e-morphicgrades grades decline rapidly rapidly to to the the north, decline north, and and much muchof of the the metasedimentary metasedimentary terrane terrane in inthe the Georgia Lakearea Lake area is is lower lower amphibolite amphibolite to to upper upper greenschist greenschist faci. fades. Georgia Stop 6: McVittie cutting the the Postagoni McViie Pegmatite Pegmatite cutting Postagoni Lake Lake sill silt (turn (turn off off Highway 11 at George Creek and continue from Highway 11 at George Creek and continue from approximately km to to well-defined clear cut cut on approximately 88 krn well-defined clear on west west side side of of road Lake. Park west on on foot foot for for road at at Postagoni Postagoni Lake. Park and and proceed proceedwest 1/2 km 112 kmto to north northside sideof of Dive Dive Lake Laketo to McVittie McViie pegmatite.) pegmatite.) The McVittie is a a north 10m mwide, wide, The McVittie Pegmatite Pegmatite is north striking striking vertical vertical dike dike approximately approximately10 which cuts the east-west striking tonalites of the Postagoni Lake sill. The which cuts the east-west striking tonalites of the Postagoni Lake sill. The pegmatite is is typical typical of of the the north pegmatite north group group pegmatites pegmatiies of of the the Georgia GeorgiaLake Lakearea areain i that that itit is is unzoned unzonedand and contains containsno norare-element-bearing rare-element-bearingminerals minerals other other than than spodumene. The spodumene. Thespodumene spodumeneisistypical typicalphenocrystic phenocrysticspodumene spodumenacontaining containing several percent iron and forming euhedral, prismatic crystals up to several percent iron forming euhedral, prismatic crystals up to 10 10cm cmlong. long. The spodumene appears greenish owing to its iron content and partial The spodumene appears greenish owing to its iron content and partial decomposition to decomposition to chlorite chloriteand andsericite. sericite. REFERENCES REFERENCES Franklin, JJ.M., .M., Kissin, LA., S.A., Smyk, Smyk, M.C., M.C., and andScott, Scott, S.D. S.D. 1986: Silver Deposits Associated with the Proterozoic Rocks of the Thunder Bay District, Ontario; Canadian Journal of Earth Earth Sciences, Volume 23, p. p. 1576-1591. 1576-1591. Rogers, J.A. 1979: The Southeastern Margin of the Mackenzie Granite, Northwestern Ontario; Unpublished B.Sc. Thesis, Lakehead University, Thunder Bay, 68 p. 66 �FIELD TRIP 4 �METAL MINERALIZATION MINERALIZATION BASE METAL IN TTHE HE SHEBANDOWAN GREENSTONE BELT Introductory Discussion and Field Guide 36th Annual. Institute on Lake Superior Geology Thunder Bay, Ontario by Maurice J.Lavigne Jr. Jr. Development and and Mines Mines Ontario Ministry of Northern Development Thunder Bay, Ontario Aubut A.J.Aubut. A. J . Technical Services Services Inc. Inc. Inco Exploration and Technical Thunder Bay, Ontario John Scott Scott rio Ministry Ministry of of Northern Northern Development Development and and Mines Mines Ontario Thunder Bay, Ontario 67 �INTRODUCTION Mineral deposits deposits of of the the Shebandowan Shebandowan greenstone greenstone belt belt bring bring about an an extra extra degree of controversy controversywith withrespect respectto to their their about degree of origins as the origins as the result result of the destruction of prerequisite prerequisite diagnostic textures textures and diagnostic and relationships relationships by by intense intense deformation. This is deformation. is especially true true for for deposits deposits which which as synvolcanic LD2date deformation, ::-idate deformation, such such as synvolcanic mineralization. mineralization. Althoughunintended, unintended, thisfield fieldtrip triphighlights highlightsthe the trial trial Although this nd tribulations toto "pigeon hole" highly and tribulationsofoftrying trying "pigeon hole" highlydeformed deforced mineralization. Three styles r!ineralization. styles of of base base metal metal mineralization mineralization will will be examined during the the cdurse course of this this trip, trip, and and all all are are proposed candidates candidates for for synvolcanic synvolcanic origins. origins. Allan Aubut will be presenting arguments arguments which which favour favour that that the the Shebandowan nickel-copper nickel-copper mine mine is is komatiite konatiite flow flow hosted, hosted, te., Kambalda ie., Kambalda type. type. The other authors authors will bring forth forth arguments that the North Coldstrean Coldstream Mine is is the the stringer stringer zone of a I<uroko type, volcanogenic, volcanogenic, pclymetallic polymetallic sulphide sulphide Kuroko type, zcne deposit and that the Vanguard prospect is is the the exhallative exhallative component component of of such such aa deposit. deposit. 68 �KILOMETERS 5 HWY 11 ó I 5 I 10 15 I 20 u.s.L CANADA r 25 30 SUPERIOR 0 HWY 527 �STOP 1; SHEBANDOWAN MINE INTRODUCTION The The Shebandowan Shebandowan Mine Mine is is aa nickel-copper nickel-copper deposit deposit owned owned by by Inca Inco Limited Linited and is is presently presently being being operated operated by by MacIsaac MacIsaac Explorations. Explorations. It It is is located located in in northwestern northwestern Ontario, Ontario, 75 75 kilometres of Thunder Bay. The mine kilorne*'.reswest—northwest west-northwest of Thunder Bay. nine is is situated south—western of of Lower Shebandowan situatedononthe the south-westernshore shore Lower Shebandowan '~ .~. Lake (Fig. 1). 1). It It has has been in production since since 1972 1972 at a an in semi-continuous sani-contin~iousproduction an average average production production rate rate of of about about 2000 2000 tons tons per per day. day. Presently Presently reserves reserves of of broken broken and and developed developed material material stand stand at at approximately million tons grading approximately .2 2 nillion grading 2.10 2.10 per per cent cent nickel nickel and 0.95 per per cent c-snt copper. copper. Accessory Accessory platinum platinum group group metals metals and 0.95 and and gold gold are are also also recovered. recovered. Concentrate Concentrate produced produced is is shipped shipped by by truck truck to to Sudbury, Sudbury, Ontario, Ontario, for for smelting smelting and and refining. refining. The The Shebandowan Shebandcwan Mine line has has had had aa iony long history history with with nickel— nickelcopper s p p e r suiphide sulphide mineralization '"uneralizaticn being being first first discovered discovered in in 1913 1913 at at what what is is now now Discovery Discovery Point, Point, on on Lake Lake Shebandowan Shebandowan (just (just east east of of stop stop2, 2 , Fig Fig 1). 1). The The International International Nickel Sickel Company of Canada, Canada, now now Inco Inco Limited, L i r u t a d , optioned optioned the the property property Ccmpany of in in 1936. 1936. The The property property was was purchased purchased for for $250,000 $250,000 in in 1937 1937 (Daily (Daily Times Tines Journal, Journal, 1937). 1937). moo Incoexplored exploredthe theproperty property off off and 28 years. years. Between Between 1965 1965 and and 1968 1968 and on on for for the the next next 28 exploration exploration was was intensified intensified with faiththe the collaring collaring of of an an exploration 1966. AA production production decision decision was was exploration shaft shaft in in 1966. announced in 1968 and the first shipment of ooncentrate was was r.tade in 1972. 70 �iç t9i 'Ca C,' Mafic Volcanics Felsic Volcanics Ultramafics Tim iskaning Sediments Timiskaming Volconics Felsic Intrusives I PC KM 2 — General Geology Shebandowan Mine Area General Geology of ASTOCL SHEBANDO WAN LAKE 4 �REGIONAL GEOLOGY The ?ha area area in in the the vicinity vicinity of of the the Shebandowan Shebandowan Mine Mine (Fig. (Fig. 2) 2) is is underlain tholeiitic volcanics volcanics unconforraably unconfornably underlain by by ricewatin Keewatin tholeiitic overlain by Timiskaning Tiniskaming type type sediments sediments and and calc-alkaline cab-alkaline volcanics. volcanics, This This unconformity unconformity is truncation of of is indicated indicated by by aa truncation Keewatin axialsurface surfacetrends, trends,the the dissimilarity dissir.ilarity in Iiriewatin axial in chemistry chemistry (tholeiitic (tholeiitic versus calc—alkaline) calc-alkaline) and and the the presence presence of jasper jasper from from Reewatin Keewatin banded iron iron formation, formation, as as clasts clasts within conglomerates 'ifchin Tiniskaminy Tiniskanin~-) conglomerates (Borradaile (Borradaile and Brown, Brown 1087; Sheyelski, Shegelski, 1930) 1930). 1937; -. MINE MIXE GEOLOGY GEOLOGY the thethe Shebandowan the vicinity vicinityofof ShebandowanMine Mine the thegeology geology cart can be be divided divided into intotwo two domains domains separated separated by by the theCrayfish CrayfishCreek Creek Fault, Fault, a regional reyional dextral dextral transcurrent transcurrent fault. fault. To To the the south south In In of the thz fault fault the the rocks rocks are are predominantly predominantly tholeiitic tholeiitic basalts, basalts, andesites andesites and some some felsic felsic pyroclastios pyroclastics (Figs. (Figs. 22 and and 3). 3). Intercalated Intercalated with these these are are several several peridotite peridotite bodies bodies :. believed to to be komatiite komatiite flows flows (Morton, (lorton, 1982). 1982). These These ultranafics ultranafics are are now now either either serpentinite serpentinite or or talc—carbonate talc-carbonate schist. overlain, in close proximity schist. All All are are uriconfornably unconforiaably overlain, 1n close proximity to to the the fault, fault, by by Timiskaming Timiskaning volcanic volcanic breccia. breccia. .,. -' , To To the the north north of of the the fault fault aa thin thin wedge wedge of of intercalated intercalated nafic mafic volcani.cs and and ultranafics ultramafics is is present present between between the the fault fault and and volcanics 'jranitic granitic rocks Lake Stock. Stock. Within Within this rocks of of the theShebandowan Shebandowan Lake this wedge appear to to be be two distinct volcanic wedge are are what what appear twc distinct volcanic cycles cycles characterized characterized by by intercalated nafic mafic flows flows and and ultramafics. ultramafics. intercalated The northern northern cycle cycle includes includes the the ultramafic ultramafic unit unit that that hosts hosts The the the Shebandowan Shebandowan nickel nickel copper copper deposit deposit while while the the southern southern cycle ultramafic unit unit that cycle includes includes an an ultranafic that hosts hosts chronite chronite mineralization mineralization (Figs. (Figs. 3 3 and and 4). 4 ) . The The relationship relationshipbetween betwe the nafic mafic-vobcanics volconics and and the the ultramafics ultranafics is isunclear unclear due due to to widespread deformation with the theCrayfish Crayf widespread deformation associated associated with Creek Fault deformation nation zone. zone. -, 'b �xx xxx x xxxxxx xx xxx x xx xxx xx -- x x x x x x x —4 F'elsic Intrusives . Timiskaming Timiskaming l!1 8;::- n'#.8;: 1-:sl, Volcanics Volcanics Ultramafics 1000 Level Plan .,.".. .... ". ."."". Volcanics ....., Mafic Votcanics Metres Figure Figure 3: 3: Mine Shebandowan Mine 1000' Level Plan —- Shebandowan 1000' �N ;IN INN' Felsic I x NI IN IN'. Intrusives 4N N N 'C iN> 1N x :::::::t:;:sN N LC1 Timiskaming N I'Tr11 Volcanics 1NNNNNN YZZt NN N N N Ultramafics :;;;:::1NN)CNN Mafic "jN 'C :ij 9 lcanics L,C N NN N N (N N N N NN N NN N JN I Ni-Cu I Suiphides N N N IN NNx 7W N 1N1 • Chromite Mineralization "''r'"L f"jN I 1"" (N N .'JN JN N 2 Ci N 'C IN N N NN N FN N JNL N :::;:;;;;:i NN "IN N 4."jN N N IN' 1' N 0 I' N N Nx I'CI /NJ 1I N r Nj -'iixN N N 48::':;:;ix jf N 'C • N N x N 'C N ':JxL:;;;:::1 hS"''*'# ..tNNNC' M""' J /NJ ::1N C j Nf r 50 Metres £NNNNN, 2NNTS%N * 25 r fy NN £;:;;I N :::IN a N :::::.J 'Ci 'C I N N jN .'—;;;;:;::'J N tt IN 25000 E Section hebandowan Figure 4: 25000E Section Shebandowan Mine 74 Mine �STRECTUPAL STRUCTURALGEOLOGY GEOLOG The The main main structural structural feature feature of of the the Shebandowan Shebandowan Mine Mine is is the the Crayfish Crayfish Creek Creek Fault. Fault. This This major major dextral dextral transcurrent transcurrent fault fault dips dips steeply steeply to to the the south. south. Though Though aa distinct distinct fault fault breccia breccia a wide zone zone zone up to to several several metres metres thick thick is is present present a wide zone of of deformation deformation characterized characterized by by extensive extensive shearing shearing is is present. present. To th fault To the the south south of the fault much much of of the the deformation deformation is is hosted hosted by by the the Timiskaning Timiskaning volcanic volcanic breccia breccia resulting resulting in in aa highly highly possessing foliated f a t e d quartz quartz sericite sericiteschist schist possessingremnant remnant breccia breccia ,. , fragments ~. ~ , . fragments and and relict relict hornblende-phyric hornblende-phyric texture. texture. ~ ",*.::<,: . . ... ., . North North of of the the fault fault shearing shearing is is' not not as as pervasive, pervasive, likely likely due due to to the the more more incompetent incompetent nature nature of of the the ultramafic—mafic ultramafic-mafic contacts contacts and and the the ultramafics ultranafics themselves. themselves. This This resulted resulted in in deformation deformation being being focused focused into into numerous numerous narrow narrow shear shear zones, zones, commonly commonly concentrated concentrated along along contacts contacts with with dextral dextral transposition transposition of of slices. slices. This This tectonic tectonic reworking reworking has has had had aa major major effect effect on on the the nickel—copper nickel-copper mineralization mineralization Producing producing significant significant sulphide sulphide movement. The The sulphide sulphide zones zones show show .. numerous nunerouy signs signs of this this remobilization remobilization such such as: as: disseminated disseminated zones zones occurring occurring above, above, below below and and in in blocks blocks within withinmassive riassivn suTphide zones; as between semi— sulphide zones; as sharp sharpcontacts contacts betweenmassive massiveorcr semimassive riassive ore ore and and disseminated disseminated sulphide sulphide bearing bearing ultranafic; ultranafic; the presence of pentiandite banding within the massive sulphides. sulphides. ~- and and the presence of pentlandite banding within the massive ~ .~, .!: .".~ Another Another factor factor that has has greatly greatly added added to to the the complexity complexity of of deposit is the presence of numerous apophyses of the the the deposit is the presence of numerous apophyses of the Shebandowan Shebandowan Lake Lake Stock. Stock. These These frequently frequently follow follow along along contacts, contacts, shears shears and sulphide sulphide zones zones as as well as as crcss—cuttiny cross-cutting these these features. features. This This has made interpretation interpretation of of stratigraphy stratigraphy in in the the mine environment environment very v e r y difficult difficult as as well as as producing producing dilution dilution problems problems in in the the ore. ore. 75 �MINERALI ZATIOX 'Â¥1iSERALIZATIO A) A) Sickel-Copper Xickel-Copper The Mine hosts threemain main typesofofore: ore: stringer stringer The Shebandowan Shebandowan Mine hosts three types suiphides, breccia sulphides, brecciasulphides sulphidesand andmassive nassive suiphides. sulphides.Though Though disseminated suiphides are are present economic disseminated sulphides present they they are arenot notofof economic rnortance q ~ortance. The st'ilnger suiphides are confined to nineralized Th? Â¥itcinge sulphides are confined to caineralized shear shear zcnes. Sulphides Suiphides present include chalcopyrite, zones. chalcopyrite, pyrite and ninor ninor pyrrhotite pyrrhotite and and pentlandite. pentlandi'te. Breccia suiphides sulphides consist consist of of fragments fragments of of ultramafic, ultramafic, volcanic volcanic and and granite g,raniteset set in in aa matrix matrix of of pyrrhotite, pyrrhotite, chalcopyrite and pentlandite. Frequently Frequently chalcopyrite chalcopyrite coats coats many of of the the inclusions inclusions within within the the breccia breccia suiphide. sulphide. Chalcopyrite is also commonly concentrated along the the margins margins of ,sf the tha breccia breccia zones. zones. Massive Massive sulphide sulphide is is composed composed of of pyrrhotite, pyrrhotite, chalcopyritze chalcopyrite and and entIandite. pentlandite. The The latter latter is is usually usually present present as as discontinuous discontinuous layers that are generally generally parallel parallel to to the the ore ore zone zone contacts. contacts. These These layers layers also also wrap wrap around around large large inclusions. inclusions.:.. .:. . ' s..,. The average copper to copper-nickel ratio ratio is is 0.36 0.36 with it it being being higher, higher, or or more copper copper rich, rich, in in the the western western portions portions of the nine mine and lower, lower, or more nickel rich, rich, in in the the eastern eastern portions portions of of the the mine. This This variation variation in in copper-nickel copper-nickel ratio ratio corresponds to to the higher proportion of the the more chalcopyrite rich breccia sulphide sulphide in in the the western part of of the the ore ore body. bodv. 76 �B) Chromite Chromite Uneconomic chromite mineralization is is also present in in the the Shebandowan Mine Mihe environment. This chromite is is hosted by ultramafics within the second volcanic cycle, close close to to the the Crayfish Creek Fault. Chromite is present as finely finely disseminated grains in all the ultramafics disseninated ultraraafics in in the the area area (Morton, (Morton, 1982). 1922). The second nafic volcanic—ultramafic volcanic-ultramafic cycle cycle hosts chronitite chromitite ' . (chronite rock) as massive to strongly (chronite strongly contorted contorted bands bands . . millimetres to varying from from a few millilietres to several several metres metres in in thickness. On either side of this nain main zone thickness. zone chromite is is found as brecciated chromitite chromitite and and chromitiferous chromitiferous peridotite. Chrornitite mineralization has has been been traced . .,, peridotite. chromitite mineralization discontinuously along strike for a distance of about 33 kilonetres. kilometres. Chromium trioxide trioxj.de assays have been reported as high as as 44 44 per cent but are typically much lower. lower. Minor platinum platinum group group metals cietals are associated with the the chromite. chrrmite. The The chrome—iron chrome-iron ratio varies from from 1.2 To 1.8 1.8 although although it it rarely rarely exceeds exceeds 1.6. 1.6. GENESIS OF THE NICKEL-COPPER ORE SICKEL-C The ore body has been subjected subjected to to intense intense structural structural deformation which has resulted in the remobilization defor~ation remobilization of nickel—copper nickel-copper sulphides. Primary textures have been obscured obscured if not erased. Regardless, Regardless, away from the Crayfish Creek Fault Deformation Zone there is evidence that many if if not all of of these these ultramafics ultramafics are are komatiites. komatiites. konatiite a komatiite is defined simply sinply as being an an ultranafic ultranafic volcanic rock with 18 18";or or greater greater MgO >I90(Arndt (Arndtand and Brooks, Brooks, 1980). These high magnesian raagnesian flows flows have have aa number number of of physical physical . 77 �characteristics characteristics which can can he be used used to to identify identify then. then. AA conclusive conclusive feature feature of komatiite komatiite flows flows is is the the presence presence of of aa relatively relatively thin thin layer layer with with spinifex spinifex texture. texture. According According to to Arndt Arndt et et ai. a:. (1979) (1979) most ultramafic flows flows are are not not spinifex spinifex textured textured but but massive massive with with polyhedral polyhedral jointing. jointing. These These Polyhedra polyhedra are are coarse coarse in in the the centre centre of of the the flow flow and and become become finer finer as as the the contacts contacts are are approached. approached. It It is is this this polyhedral polyhedral jointing that is common commcn in many of the ultramafic ultranafic bodies bodies at at S1banJowan. Sh.=banJowii. Another Another common common feature feature at at Shebandowan Shebandowan is is the the presence presence of of chemical c5umical sediments, sediments, as as both both handed banded cherty cherty iron iron formation formation and and chert, immediately c'l':~rt, innediately overlying overlying the the ultramafics ultramafics (Morton, (Morton, 1982). 1982). This This feature feature implies inplies that that when when the the sediments sediments were were deposited deposited the the ultramafics ultranafic,~must have have been been present present as as flows flows on on the the ocean ocean floor. floor. The The Shebandowan Shebandowan Mine Mine ore ore body body shows shows aa lot lot of of physical physical similarities similarities with the the komatiite konatiite hosted hosted Redross Redross deposit, deposit, in in the Kambaida region region of of Australia. The The Bedross Redross deposit deposit is is the Eanbalda located located 58 33 kilometres kilometres south qouth of of Falgoorlie. Kalgoorlie. It It has has been been affected affected by by regional regional dynamic dynamic metamorphism metanorphism with with faulting faulting and and shearing, shearing, primarily primarily along along the the footwall fcctwali contact contact between between the the sulphide sulphide bearing bearing komatiite komatiite flow flow and and nafic mafic volcanics volcanics (Barrett (Barrett et et al, al, 1977). 1977). The The sulphides sulphides have have undergone undergone major major remobilization remobilization along along the the footwall footwall contact contact and and shear shear zones. zones. AA major major ore ore type type consists consists of of brecciated brecciated wall wall rocks rocks cemented cenented by by sulphides. sulphides. Contacts Contacts between between massive nassive or or semi—massive semi-massive ore ore and and disseminated disseminated ore ore are are commonly conxcnly very very sharp sharp with with none none of of the the intervening intervening matrix matrix ore ore associated associated with with other other Ranbalda Kambalda deposits deposits (ibid.). (ibid.). The The ore ore zones zones at at Redross Redross possess possess structures structures and and textures textures remobilization of of both both disseminated disserainatad and and more more produced by by renobili:ation produced massive nassive mineralization mineralization (ibid.). (ibid.). 78 �Shehandowan Mine .\L the the Shebandowan At Mine the the same sane chaeacteristics characteristics exist exist an affinity affinity of of sulphide mineralization for including an including sulphide mineralization for one one side of of the It is therefore suggested side the ultramafic ultraraafic body. body. It is therefore suggested that that the h e Shebandowan nickel-copper deposit is is the product of of dynamic netamorphisn metamorphism of a sulphide bearing komatiite konatiite flaw flow with with remobilization remobilization and and subsequent subsequent redeposition redeposition of of the the sulphides in sulphides in low low strain strain areas. areas. FIELD TRIP FIELD TRIP STOPS STOPS 5 1; Shebandowan Mine Headframe, Headframe, Fig. Fig. 5 STOP 1; At this stop stop we will examine strongly strongly deformed Timiskaming Timiskaming cab—alkaline volcani& calc-alkaline volcanic breccia breccia as as well well as as the the ultranafic ultranafic unit hosting the Shebandowan Shebandowan nickel—copper nickel-copper deposit. deposit. The Main structural feature at the Shebandowan Mine is is the the Creek Fault. South of the fault Tiniskanirg Tiniskaning Crayfish Creak volcanics have been strongly deformed deforned and are now now quartz— quartzsericite 5ericite schist with possessing relic textures. North of of the the deornation has fault fault deformation has not not been been as as focused into narrow narrow shear shear zones separating lenses of serpentinized peridotite. This This deformation has resulted in the remobilization remobilization of the the Ni-Cu Xi-Cu sulphides and subsequent deposition in in lower lower strain strain areas areas within the the host host ultranafic. ultramafic. STOP 1A. STOP 1A. This outcrop outcrop consists of strongly strongly deformed deforned hornblende hornblende phyric phyric Tiniskaming type volcanic breccia. Note the the highly highly foliated foliated Fault, nature reflecting its proximity to the Crayfish Creek Fault, approximately 100 100 metres to the the north. Though Though strongly stronaly foliated note the many similarities with the undeformed Tiniskaming long the Tiniskaming volcanic volcanic breccias breccias seen seen to to the the east east ealong the road leading to Shehandowan road leading tothe the Shebandowan Mine. Mine. 79 �Co C Mat Ic Volcanics Felsic Volcanics Iiitrarnafics Figure 5: Timiskaming Volcanics Felsic Intrusives Ta Metres tOO Stop 200 Shebandowon Mine Ore mat ics hosting Shebondowiru jC Lake Stock intruding Ultra- Ia) Apophyses of Shebandowon Production Shaft Stop 1 - Shebandowan Mine 0 Lake She bando wan �STOP 13. STOP IB. This consists of This outcrop, outcrop, beside beside the the #2 ? 2 Shaft Shaft headfrarne, headframe, consists of serpentinized peridctite peridotite with numerous narrow zones zones of talc— talc- carbonate schist that form torn an anastomosing anastonosing network. network. It It is is this unit that is host to the nickel-copper sulphides. sulphides. Note Note on or. the north side of the outcrop a feldspar feldspar porphyry dyke, dyke, of the LakeStock, Stock, cutting cubuing across across anapcphysis an apophysis of theShebandowan Shebandowan Lake the 2eridotite. the peridotite. STOP Fig. 66 2, Fig. STOP 2, w-nw,,fofStop Stop11is is aa narrow unit of Approximate1y 3 km w-nw Approximately narrow unit of serpentinized serpentinized peridotite hosting Ni-Cu Xi-Cu suiphides sulphides hosted hosted by by banded mafic volcanics. These rock rock units units are are exposed exposed in in aa small trench on the side of a hill, hill, approximately 75 75 metres met.res north of the Crayfish Creek Fault. Points Points of interest interest at at this outcrop are: the banding within the t-he nafEc mafic volcanics, volcanics, ultramafic and the breccia sulphides. The the thin wedge of ultranafic latter consist cf of numerous nafic to ultranafic volcanic fragments cemented by pyrrhotite, chaicopyrite chalcopyrite and pentlandite. This suiphide pentlandit?. sulphide zone zone averages 1.88% 1.88% Ni Xi and and 1.61% 1.61% Cu. Note Mote the porphyry dyke, an apophysis apophysis of the the Shebandowan Shebandowan Lake Stock, Stock, intruding intruding the the sulphides. sulphides. STOP STOP 3, 3, Fig. Fig. 77 4.5 Km tv—sw of the the Shebandowan Shebandowan mine mine headfrane headfrane is a typical w-sw of exposure of of ultranafic ultranafic rock, rock, common common in in the the area, area, exposure interdigitated with felsic volcanic fragmentals, fragnentals, nafic volcanics and With the and and and intruded intruded by by aa felsic felsic dyke. dyke. Kith the exception of of portions portions of of the the ultrarnafic ultramafic rock and the dyke, dyke, exception the entire outcrop is is strongly strongly foliated foliated to to schistose. schistose. Well developed developed mineral aggregate lineations lineations and and clast clast elongations elongations are are vertical. vertical. Stratigraphic tops are to the south, south, as �N-) o 1.88% Ni 5 Figure 6: Metres 2.5 1.61 %Cu Stop 2 — Trench IflOOE Stop 2 Maf Ic Volcanics Shebandowan Mine '-C, Ultramafics Breccia Suiphides Felsic Intrusives Trench 15200E — Shebandowan Mine c x lxxx x Fx �Figure 7: Stop 3 - meters (approximate) Otto Lake Rd. xtize -. - 1 tuft, agrnerate Strongly sheared PYROCLASTIC Lap [.:.YC:1Oc1ASTC itzaN PORPHYRY '7J1 QUARTZ-FELDSPAR to potysutwed UJRAMAFC �interpreted i a t e r ~ r e t from dfron the t h e occurrence o c c u r r e n c 3 oof f black black chert c h e r t fragments f r a g n e n t s in in the metresoof t!>e lower l o w e r few few metres f t the h e Efelsic e l s i c fragmental f r a ~ n e n t a laatt site s i t eA?A on on Fig. 7. These clast are interpreted to have been derived from an underlying chert bed, exposed at site on Fig. 7. The margins of the ultrarnafics are schistose, and more often than not, covered. The relationship with the enclosing felsic volcanic rocks is therefore unclear. The ondeformed ::ndeformed interior i n t e r i o r of o f the t h e ultranafic u l t r a m f i c is is fine f i n e grain, g r a i n , and am3 has has polyhedral p:-;iybedral jointing. j o i n t i n 5 . .It I t can c a n be b e argued a r g u e d that that these t h e s e two two textural t e x t u r a l observations o i i s e r v a t i o n s support s u p p o r t an a n extrusive e x t r u s i v e origin o r i g i n for f o r this this unit, u a i t , although a l t h o u g h they t h e y could could common c m m o n juxtapcsit4on j u x t a p c s i t ; a n with with be b e considered c o n s i d e r e d equivocal, e q u i v o c a l . the The chemical a l s o lends l e n d s some some c h e m i c a l sediments s e d i n e n t s also support s u p p o r t to t o an a n extrusive e x t r u s i v e origin. o r i g i n . Definitive D e f i n ~ t i v eflow f l o w features feature8 such a s spinnifex s p i n n i f e h and a n d flow f l o w top t o p breccia breccia have h a v e not n o t been been 5uch as observed o b s e r v e d in i n th th,eultranafic u l t r a m a f i c rocks r ~ c k in si n this t h i 3 area. a r e a . The The positive positive identification i d e n t i f i c a t i o n of flow rocks r o c k s in in the t h e area area would would o f ultramafic u l t r a m a f i c flow support % u p p o r t the t h e contention c o n t e n t ~ o nthat t h a t the t h e Shehandowan Shebandcwan Mine X i n e is i s aa Rambalda I < x ~ b a l d atype t y p e nickel n i c k e l deposit d e p o s i t since s i n c e the t h e host h o s t rock r u c k at at the t h e nine nine has textures destoyed by shearing. 2s had h a d its i t s primary pr STOP 4; .'orth Ccldstream Mine, Burchell Lake INTRODUCTION 2liTRODECTIOX Copper C o p p e r mineralization m i n e r a l i z a t i o n was was discovered d i s c o v e r e d on on the t h e north n o r t h side s i d e of of Burchell B u r c h e l l Lake Lake in i n 1872. 1 8 7 2 . Copper C o p p e r was was produced p r o d u c e d in i n 1903, 1 9 0 3 , 1906, 1906, 1916—17, t o t a l of o f 102 1 0 2 000 000 000 000 1916-17, 1957—58 1957-58 and a n d 1960—67 1960-67 for f a r aa total pounds. pcunds. Most Most of o f this t h i s production p r o d u c t i c m occurred a c c u r r e d fran f r o m 1960 1 9 6 0 to t o 1967 1967 when %"he>the t h : e mine n i n e was w a s operated o p e r a t e d by by Noranda Xoranda at a t aa capacity c a p a c i t y of o f 1000 I000 tons w a s producing p r o d u c i n g 14 14 000 000 000 000 pounds 'aunds of o f copper capper t a n s per p e r day d a y and a n d was annually. m i l 1 produced p r o d u c e d concentrate c m c e n t r a t e containing c o n t a i n i n g 26¾ 26% a n n u a l l y . The The mill copper, c o p p e r , 2.65 2 - 6 5 o.p.t. c - p - t . silver silver and a n d 0.09 0 . 0 9 o.p.t. c.$.t.. gold. g o l d * The The ore ope contained c a n t a i n e d 2¾ ?%,copper, c o p p e r , 0.012 0.012 o.p.t 0 . p . t gold g o l d and 0.22 0 . 2 2 o.p,t. ~~.p.t, silver. silver. The closed as the result of depleted The mined n reserves. 84 �REGIONAL GEOLOGY The ?he North Xorth Coldstream Coldstream Mine Nine is is located located in in the the western western portion portion of :>f the t . 1 ~Shebandowan Shebandowan greenstone greenstone belt. belt. Stratigraphic Stratigraphic and and structural structural trends trends are are northeasterly. northeasterly. Outcrops Outcrops have have well well developed developed foliation fgliation and and are are often often schistose. sc!~istose. According According to to Stott Stott and and Schwerdtner, Scl-.werdtner. 1981, 1981, deformation deforxation in in this this area area was as dominated dcminated by by sinistral sinistral shear. shear. The The nine nine is is on on the the souanwestern linh s~>uci~western i i ~ of b of an an anticline anticline with witn an an axial axial plane plane striking striI<ing northeast northeast (Fig. (Fig. 2) 8 ) . The ?ha? anticline 2nticl ine is is cored c<>redwith with felsic felsic volcanics volcanics which which are are overlain overlain by by nafic nafic volcanics. volcanics. At .At aa regional regional scale, sca.le,the the mine mine is is at at-this this contact, contact, with wit-hfeisic felsic volcanics volcanics as as stratigraphic stratigraphic footwall footwall and and mafic mafic volcanics volcanics as as hangingwall. hangingwall. Along Along its its entire entire length, length, this this mafic—felsic mafic-felsic volcanic olcanic contact contact is is aa 11 km km wide wide schist schistzone. zone. At At the the ninesite, inesite, this this contact contact was was intruded intruded by by aa gabbroic gabbroic stock stock which hich is is the the immediate immediate footwali £ootwal to to the the nine. nine. Foliation Foliation orientation minesite shows shows aa departure departure from from the the rientation at at the the minesite regional regional orientation, orientation, in in that that it it consist consist of of an an enclave enclave of of east ast trending trending foliation, foliation, with with dextral dextral kinematic kinenatic indicators. indicators. Wether ether or :>r not not this this foliation faliation orientation orientati~nis is independent independent of of elsic plutons, plutons, both both to to the the north north and and south south of of the the nine mine is is feisic as Of yet undetermined. MINE GEOLOGY Copper C ~ p p e mineralization rmineralizationat atthe theNorth SorthColdstream Coldstream>line >line consist consist of lenses with with aa high high density density network network of of chalcopyrite chalcopyrite and and >f lenses pyrite yrite veinlets veinlets (stringers). (stringers). Some Sone massive massive and and disseminated disseminated ineralization also also exist. exist. As As seen seen on on the the 500 5 0 0 foot footlevel level mineralization plan (Fig. (Fig.9), 9), cross-section cross-section geometry geometry of of these these lenses lenses is is plan ariable, with with maximum maximum horizontal horizontal dimensions dimensions of of 200 200 by by 200 200 variable, feet. eet. The The greatest greatest dimension dimension of of these these ore ore lenses lenses (plunge) ($lunge) is is oriented oriented at at 50 50 degrees degrees to to the theeast. east. Giblin, Giblin, (1964) (1964) reported reported three three types types of I>Âcoarse caarse grain graic veins veins which which crosscut crosscut the the orebodies. crebodies. The The most nost common conmon type type of cf vein vein consist r2onsist of of 85 �Figure 8: Geology Western Shebandowan Volcanic Belt 86 �quartz, carbonate, pyrite and chalcopyrite. Carbonate veinlets constitute the second commonest type. Relatively rare are veins rare a re v e i n s cconsisting o n s i s t i n g of o f quartz, q u a r t z , carbonate, c a r b o n a t e , barite, barite, purple fluorite, dark brown sphalerite and chalcopyrite. The by 400 h e ore o r e is i s hosted h o s t e d by by a a massive m a s s i v e siliceous s i l i c e o u s lenses, l e n s e s , 1000 1 0 0 Q by 400 feet, e e t , cconsisting c n s i s t i n g aalmost l m o s k entirely e n t i r e l y of s f aphanitic a p h a n i t i c quartz q u a r t z and and historically i s t o r i c a l l y has h a s been b e e n referred r e f e r r e d to t o as as chert, c h e r t , with w i t h or o r without igithout Locally, ;anetc .' -. ccnnctatcns. ,-.,*---tations. L o c a l l y , fabric f a b r i c is i s discernable Fiiscerz65l2 .&.. nega.scopically, n q ~ s c o p i ~ s l l yaand n, d ggenerally e n e r a l l y in i n these t h e s e ccases a s e s tthe h e siliceous siliceous .~.,8..." rock The r o c k is i s white. white. The most m o s t common common colour, c o l o u r , and a n d always alwa>rs in i n close close association A subtle a s s o c i a t i o ~with w i t h the t h e ore, o r e , is i s brownish b r o w n i s h mauve. mauve. A subtle variant ~ y a r i a n tto t o this t h i s last l a s t colour c o l o u r is i s buff, b u f f , and a n d appears a p p e a r s to t o be be restricted r e s t r i c t e d to t o the t h e south s o u t h central c e n t r a l portion p o r t i o n of o f the t h e mineralized mineralized complex, c o m p l e x , in i n close c l o s e proximity p r o x i m i t y to a non—siliceous buff alteration o f mafic m a f i c rock. rock. a l t e r a t i o n of The The dominant d o m i n a n t lithology l i t h o l o g y surrounding s u r r o u n d i n g the t h e siliceous s i l i c e o u s rock r o c k is i s aa chlorite c h l o r i t e schist, s c h i s t , then t h e n sericitic s e r i c i t i c schist. s c h i s t . The northern n o r t h e r n band band of r;E chlocitic c h l o r i t i c schist s c h i s t separates s e p a r a t e s the t h e ore o r e complex complex from f r o m aa yabbroic a b b r o i c stock. s t o c k . At , A t the t h e eastern e a s t e r n end end of g f the t h e complex c o n p l e s aa lens l e n s of of sericitic s e r i c i t i c schist s c h i s t separates s e p a r a t e s this t h i s chlorite c h l c r i t e schist s c h i s t from f r o m the t h * ore ore ccmplex. c c m ~ : l e s . At . A t the t h e western w e s t e r n end, e n d , the t h e chlorite c h l o r i t e schist s c h i s t contains contains abundant All a b u n d a n t bluish b l u i s h quartz q u a r t z segrecjations s e g r e g a t i o n s and a n d magnetite. magnetite. A ll contacts the complexa nand c o n t a c t s between between t h e oore r e complex d t h the e s esericitic r i c i t i c sschist chist are a r e sharp, s h a r p , and a n d the t h e smaller siliceous s i l i c e o u s pods p o d s are a r e boudin b o u d i n like l i k e in in that The t h a t the t h e sericitic s e r i c i t i c foliation f o l i a t i o n wraps w r a p s around a r o u n d them. them. The southern s o u t h e r n contact c o n t a c t has h a s been b e e n described d e s c r i b e d by by Scott, S c o t t , (1963) ( 1 9 5 3 ) as as sharp, s h a r p , although a l t h o u g h as a s described d e s c r i b e d above, a b o v e , there t h e r e appears a p p e a r s to t o be b e aa transition t r a n s i t i o n locally l o c a l l y from f r o m buff b u f f siliceous s i l i c e o u s to t o buff b u f f alteration, alteration, in i n less less strained s t r a i n e d rock. r o c k . The sharp s h a r p contacts c o n t a c t s are a r e most n o s t likely likely the t h e products p r o d u c t s of o f shear s h e a r juxtaposition j u x t a p o s i t i o n and a n d the t h e destruction d e s t r u c t i o n of of gradational g r a d a t i o n d l contacts. c o n t a c t s . The gradational g r a d a t i o n a l contact c o n t a c t between b e t t s e e n the the gabhro s a b b r o stock s t o c k and a n d tthe h e cchlorite h l o r i t e schist s c h i s t indicate i n d i c a t eaagabhroic gabbroic protolith protolith at a t this t h i s location l o c z t i g n for f c r the t h e schist. schist. G i b l i n (1964), (1964), Giblin noticed n c t i c e d an a n increasing i n c r e a s i n g amount amount of o f bluish b l u i s h quartz q u a r t z in i n this this 87 �Figure 9: Geology 500' Level North Coldstream Mine �chlorite siliceous rock. rook. This nay may be chlorite schist schisttcwards towards the the siliceous This be interpreted the gabbro. cjabhro. interpreted as as increasing increasing silicification of the protolith for for the chlorite schist schist at margin protolith the chlorite at the the southern margin The of the ore nay be mafic volcanic, although a gabbroic gabbro the ore complex may protolitn. is also also possible. possible. protolit3 is The protolith rotolith for for the the sericitic sencitic schist schist nay nay be felsic felsic volcanic preserved, questionable, volcanic as as indicated indicated by by poorly poorly preserved, questionable, frajrientai As intense intense alteration alteration is frdyciental texture. texture. As is probable, probable, the the protolith protolith to to the t.he sericite sericiteschist schistcould could also also be be nafic nafic volcanic volcanic or or intrusive. intrusive. GENESIS GENESIS OF THE NORTH COLOSTREAM COLDSTREAM MINE Several fundanntal fundamental questions questions must must be be answered answered in in order order to to contemplate theNorth NorthCol'Jstrearn Coldstream Mine. Mine. What contemplate the the origin originofofthe is the siliceous host? host? -chert —chert or or silicification; silicification What is is the or felsic the host host rock? rock? —mafic -mafir: or felsicvolcanic volcanic—or -or gabbro gabbro: The nasive of the the siliceous nassive nature nature of siliceous zone, zone, the the lack lack of of sedimentary features, and andother other sedinentary sedimentarylitholcgies, lithologies, its its sedimentary features, absence onstrike, strike, and contacts all all support absence on and the the gradational gradational contacts support silicification. Silicification Silicification of this this intensity intensity is is only only known ld deposits (of known to to occur occur in inhydrothermal hydrothermal jo gold (of all all ages) ages), silicification. and and in in the theKeiko Keikozone zoneof ofsome someHuroko Kuroko type t.ype volcanoyenic volcan::?yenic massive massive sulphide salphide deposits. deposits. The former can be negated negated as as aa gold content content at at the the North Coldstream Coldstream of of 450 450 ppb ppb is is much much too too low, Siliôification in low, and is is typical typical of of the the latter. latter. Silicification in gold gold systems systems tends tends to to be be "late", "late", ie ie post post tectonic, tectonic, is is of of the the highest ore ore grades grades and and is is superimposed superimposed on on fabrics. fabrics. Silicification Silicification at at this this site site predates predates deformation deformation as as evidenced evidenced by by siliceous siliceous boudins boudins and and inherited inherited fabric. fabric. A volcanogenic volcanogenic origin origiri is is also also supported supported by by the t.he "stringer" "stringer" style style of of the the ore, ore, the the piped piped shaped shaped host host silicification silicification and and to t some some extent, extent, the the sequence sequence of of alteration. alteration. It therefore therefore appears appears that thatthe theNorth NorthColdstream Coldstrean Mine is is the the stringer stringer zone zone of cf avoloanocjenic a volcanogenic massLve xassive sulphide sulphide deposit. deposit. 89 �At one location iocation there there isisevidence It one evidence that thatthe thegabbro gabbromay nay be be a hust lust rock. rock. If Ifone one considers considers the theapparent apparent increasing increasing sLiciEicatLon or the gabbro gahhro to indicate its its presence presence durin'j durin 1 . LC ificat ion of Lh. nneralizng event, 5.:Âmineralizing event,then thenthe thenineralizing mineralizingevent eventmust nust be be However,the thelack lackofof fabric fabric within rost volcanic. post volcanic. However, within the the yabbro at the end of the gabbro the east east end the mineralized complex complex indicates indicates gabbro is that the t'r't.-i is.post tectonic, tectonic, and therefore therefore post that . -...,, ,.Â¥ Thioy under the .c;:!raIrac12n. L :.. ~ : n . T ~ k i . ~this this -j under consideration, consiaaraticn, the chtoritic chloritic schist along the margin of o the gabbro gabbro may be releted to emplacement and and the blue quartz generated during related feldspar destruction and chioritization. Ghloritization. . .1- complex appears This mineralized ccoplex mafic rwfic volcanic volcanic contact. contact. This is regional scale, reyional scale, but difficult difficult to to to be located located at at aa felsic— felsiccertainly true true at at a a demonstrate decionstrate at at mine mine scale. scale. FIELD TRIP STOPS FTELD STOPS STOP 4ct; STOP 4a; This is an an outcrop of altered hornblende This hornblende gabbro gabbro on on the the Despite northern margin of the the mineralized mineralized complex. complex. Despite epidote-chiorite alteration and multiple shear epidote-chlorite shear sets, sets, igneous igneous textures and mineralogy are textures are preserved. preserved. This gabbroic gabbroic stock stock composition and texture has variable conposition texture and this this location location we find f i ~ da a medium nediun grain, grain, equigranular eguigranulargabhro gabbroand anda aperdmatitic pegmatitic hornblende is fibrous phase. In thin section the hornblende fibrous and secondary. secondary. I I I STOP STOP 4b; 4b; Group of outcrop's outcrops on on south south side side of of road, road, only only 25 2 feet Group feet from from stop 4.3. 4a. These outcrop% outcrops have have rare, rare, ghost ghost like, like, relic relic igneous igneous textures textures which indicate indicate that that the the protolith protolith is is gabbro. gabbro. The The yabbro chloritized at the -.^t-,-hhas been sheared and increasingly increasingly chloritized the 90 I I �Thechlorite chlorite is expense of epidote. expense of epidote. The 1.5 pervasive pervasive and and also also Blue quartz seyregations and occurs occurs as as segregation. se3regation. Blue quartz se::;recjations and Leucoxene and nagnetite are irregularly raagnetite are irregularly distributed. distributed. Leucoxene and grains, nagnetite as sub—millimetre magnetite a r e dispersed dispersed as sub-millinetre grains, nagnetite nagnet-it.eare also also Some cm occurs ra in in length. length. Some occurs as as acicular acicular crystals crystals up up to to 35 e layers layers in in the the chlorite chlorite schist schist are are in in fact, fact, fibrous fibrous thethe magnetite—leucoxene hornblende, hornblende, which which are are later laterthan than maqnetite-leucoxene more random alteration, and alteration, and have hava a a ncre random orientation orientation than than . . . chlorite, post l o r i t e , indicating iric-iic~itir'.q post tectonic tectonic growth. grcwth. The distribution distribution of The of quartz quartz as as irregular irregular blebs, hlebs, and and the the volume volume of of this this quartz quartz could could be be produced produced in in situ situ during during shearing and chlorite chlorite alterati-on, alteration, as as opposed opposed to shearing and to . .> : silicification silicification from from an an external external source. source. chlorite schist schist zone zone are are Those quartz rich rich portion of the the ch1orit.e . termed "quartz "quartz complex" complex" in in mine mine terminology. terminology. , ~ J , - , . :',, ' STOP STOP 4c; 4c; This white siliceous zone zone is is the transition transition from from the the quartz quartz It complex to the more massive brownish mauve rock. It nauve host rock. consist of of strained strainedquartz quartzand and101Osericxte consist "; sericiteand and leuooxene. leucoxene. STOP 4d: 4d; STOP It's This brownish mauve siliceous rock This rock is is the the ore ore host. host. it's white siliceous unit is that only dissimilarities with the white mosaic of fine, it unstrained, and as such is an even grain riosaic fine, equant quartz equant. quartz crystals. crystals. STOP STOP 4e; 4e; A ft third variety of the silicification is is buff coloured and with the brownish mauve only aa subtle subtle difference exist iiith snatially related to aa buff buff variety is spatially variety. This This variety variety. relate3 to alteration zone along the south central portion of the mineralized nip,eralized complex. complex. This buff alteration is the . -. ' . �sericit of aa felsic a r i c i t Lzatlcn i z a t i c n sf f e l s i crock r o c k bearing b e a r i n g quarts q u a r t s eyes, eyes, L5sLhiV i s s i b l y f flsic a l s i c volcanic. v o l c a n i c . Thec The c odour l o u r oof f tthe h e ssilicification ilicification na . ,.iv reflect r c i f l e c the t t h composition e c o n p o s i t i c n of o f the the protolith. protolith. STOP TOP 4f; 4f; This h i s is i s an a outcrop of The h e rock r o c k is i s massive, cassive, the buff alteration described in 4e. fine f i n e grain, g r a i n , and a n d textureless. featureless. STOP 4g; An An ooutcrop u t c r o p oof f oore r e iin n ssharp h a r p ccontact o n t a c t wwith i t h aa ssericite e r i c i t e schist. Â¥ichi'-it At A t the t h e top t o p of o f the theoutcrop, o u t c r o p , fragmental f r a g m e n t a l textures t e x t u r e sof o fequivocal equivocal origins rigins and a n d aa siliceous s i l i c e o u s boudin b o u d i n wrapped w r a p p e d in i n sericitic s e r i c i t i c schist. schist. STOP 4h . This buff outcrop is included in the sericite schist unit its because b e c a u s e of o f i t s felsic f e l s i c appearance, a p p e a r a n c e , although a l t h o u g h it it. ray m a y contain contain more A t this t h i s location l o c a t i o n aa fragmental fragmental n o r e chlorite c h l o r i t e than t h a n s e r i c i t e . At sericite. helm terpreted texture. texture mar equivocal STOP as volcanic, hut is ccnsidered an 4i; large ridge at the east issgabbro. g a b b r o . The The lack la.ck oof f fabric f a b r i c indicates i n d i c a t e s that t h a t ititwas wasnot not This e n d of o f the t h emineralized m i n e r a l i z e dcomplex comp h i s l a r g e r i d g e a t t h e e a s t end affected f f e c t a dby by the t h edeformation d e f o r m a t i o n that t h a tproduced p r o d u c e d the t h eadjacent adjacen schist n u s t therefore t h e r e f o r ebe b eyounger y o u n g e r and a n d crosscut c r o s s c u t the t h e ore s c h i s tand a n dmust complex. It cannot therefore be the host rock. 92 ~ �Vanguard Prospec INTRODCCTTON The Vanguard Prospect is situated south of the junction between Highway 802X and Highway 11 at Kashabowie, Ontario (Fig. 8 ) . A private bush road trends south of this intersection and accesses the showine; area. The prospect is situaced on Mining Locations K 5 6 and 271. The property is private land and permission frcra the owners is required to visit the prospect. The property is currently under option to Minnova Inc. GEOLOGY The prospect area is underlain by sheared volcanic r the Shebandowan Greenstone Belt. Anorthositic gabbro suite rocks intrude the volcanic sequence. The mineralized zone strikes 0 6 0 degrees and dips steeply to the south. The zone has been traced intermittently along strike for 1 3 1 0 m ( 4 3 0 0 ft.). The prospect consists of two mineralized sections about 7 0 0 m apart and have been designated the West and East stop we will be examining the east zone. The Vanguard East Occurrence forms part of a large outcrop knoll on the east side of the bush road approximately 8 0 0 metres south of Highway 11. The occurrence is very well . exposed by stripping and trenching. At the Vanguard East location, a massive sulphide lens containing sphalerite, chalcopyrite, pyrite and pyrrhotite is hosted by a variolitic to massive mafic volcanics; bedded silicic tuff caps a portion of the mineralized zone and has been interpreted by Minnova to be "exhalite". Alteration associated with the deposit includes silicification and iron ��The rocks are chloritized. With reference to Fig. 10, the sulphide ninsralization is ZJ, this zone yielded 2 . 4 7 % Cu, 6 . 9 2 % 40.6 grams per ton Ag, and 1.39 grams per ton Au across an apparent width of 4 ~eters. The sulphide ore is finely banded and in the sample -xanined, consisted of approximately 25'6 sphaierite, 7 0 % pyrite, and the balance silica, rock fragments, and other gangue minerals. Chalcopyrite also occurs in the suphide The two other major rock units exposed near the main trench ara a silicified variolitic mafic volcanic and a chocolate brown (weathered surface) carbonate-rich rock. An alteration zone consisting of massive to bedded silica/carbonate with disseminated iron sulphides is situated west of the south end of the main t.rench. The contact area between this zone and the varioliti:: nafic volcanic to the west is marked by quartz (veins?). Sheared but otherwise hell preserved volcanic features such i s varioles can be examined throughout the large flat stri-pped area north of the sulphide lines. Most of the faulting trends approximately 270 degrees with apparent dextral offsets. The intense deformation of the rocks of the showing area is perhaps explained by the proximity of the Crayfish Creek Fault. This fault presumably underlies the low ground to the' east of the stripped area. �. . .. Reef a r a n c e s .:rndt, X. Â¥WiO and Brooks, C. K c r a a t i i t e a ; G e o l o g y , Vol.8, - " '\r-,'Jt, V., 1979: p p 135-156. - " - A F r a n c i s , D. a n d H y n e s , A . J . The F i e l d C h a r a c t e r i s t i c s a n d P e t r o l o g y o f A r c h e a n and p r o t e r o z o i c K o m a t i i t e s ; Can. yol17, B a c r e t t , P.M., Mineralogist, " , ;?p : 4 7 - 1 6 3 . B i n n s , H.A., G r o v e s , 9.1.. Marston, R.J. and McQueen, K.G. 1977: S t r u c t u r a l H i s t o r y and Metamorphic M o d i f i c a t i o n of Archean Volcanic-type Nickel D e p o s i t s , Y i l g a r n B l o c k , W e s t e r n A u s t r a l i a ; Economic G e o l o g y , ~ 0 1 . 7 2 , pp 1195-1223. ~ o r r a d a i l e ,G. 19B7: a n d Brown, H. The Shebandowan G r o u p : " T i r a i s k a m i n g - L i k e " Archean Rocks i n S o r t h w e s t a r n O n t a r i o ; CJES, V o l . 2 4 , pp 185-188. The D a i l y T i m e s J o u r n a l 1937: I n t . X i c k e l Buys Shebandowan O r e ; p u b l i s h e d i n Fort William, Ontario. G i b l i n , P.E. 1964; B u r c h e l l L a k e Area; O n t a r i o D e p a r t m e n t o f M i n e s , G e o l o g i c a l R e p o r t 1 9 , 39p. N o r t o n , P. 1982: Archean V o l c a n i c S t r a t i g r a p h y , P e t r o l o g y a n d CLcraistry of Mafic and L ' l t r a m a f i c Rocks, Chromite a n d t h e Shebandowan Xi-Cu Mine. Shebandowan, N o r t h n e s t e r n O n t a r i o ; U n p u b l i s h e d PhO T h e s i s , Carlton L'niversity. �.. Pye, E . G . and Fenwick, 3 . G . 1964: Atikokan-Lakehead Sheet, Geological Compilation S e r i e s ; O n t . D e p t . o f M i n e s , >!ap 2 0 6 5 , S c a l e 1:253,440. S c o t t , S.3. 1963: R e p o r t on t h e N o r t h C o l d s t r e a m Mine L t d . i dz~::kl LS:::~ : S h e g e l s k i , R.2. 1980: A r c h e a n C r a t o n i z a t i c r n , Emergence a n d Red Bed Dfivelopraent, L a k e Shebandowan A r e a , C a n a d a ; Precambrian Research, Vol.12, pp 331-347. S t o t t , G.M. 1981: A S t r u c t u r a l A n a l y s i s of t h e C e n t r a l P a r t o f t h e Shebandowan Metavolcanic-Metasedimentary Belt.; Ontario 44p.l G e o l o g i c a l S u r v e y , Open F i l e R e p o r t 3349, �PURCHASE OF PROCEEDINGS AND ABSTRACTS AND FIELD GUIDEBOOK Copies of the Proceedings and Abstracts, Part 1, and the Field Guidebook, Part 2, for the 36th Annual Institute on Lake Superior Geology may be purchased during the meeting. . . . . . . . . . . $5.00 Canadian . . . . . . . . . . . . . . . . . $5.00 Canadian Proceedings and Abstracts, Volume 36, Part 1 Field Guidebook, Volume 36, Part 2 Payable to Institute on Lake Superior Geology Issues of Proceedings and Abstracts, Part 1, and Field Guidebook, Part 2, from this and the three previous meetings, may be ordered from: Joe KaSEokoski, .Secretary-Treasurer Department of Geology and Geological Engineering Michigan Technological University Houghtan, Michigan 49931 The cost for each part ordered is $6.00 U.S. Orders will be filled while supplies last. .............................................................................. All volumes back to 1955 are available for photocopying at the prevailing rate, from the Michigan Technological University Library, through Mr. M. S. Spence, Archivist. Phone 906-487-2505 .............................................................................. � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1990 Description An account of the resource Institute on Lake Superior Geology. Thunder Bay, Ontario. May 9-12, 1990. 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